WO2023218576A1 - Galvanized steel sheet, member, and methods for producing these - Google Patents

Galvanized steel sheet, member, and methods for producing these Download PDF

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Publication number
WO2023218576A1
WO2023218576A1 PCT/JP2022/019991 JP2022019991W WO2023218576A1 WO 2023218576 A1 WO2023218576 A1 WO 2023218576A1 JP 2022019991 W JP2022019991 W JP 2022019991W WO 2023218576 A1 WO2023218576 A1 WO 2023218576A1
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steel sheet
galvanized steel
bending
area ratio
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PCT/JP2022/019991
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French (fr)
Japanese (ja)
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由康 川崎
悠佑 和田
秀和 南
達也 中垣内
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Ｊｆｅスチール株式会社
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Priority to PCT/JP2022/019991 priority Critical patent/WO2023218576A1/en
Priority to PCT/JP2023/006924 priority patent/WO2023218730A1/en
Priority to JP2023565496A priority patent/JPWO2023218730A1/ja
Publication of WO2023218576A1 publication Critical patent/WO2023218576A1/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc

Definitions

  • the present invention relates to galvanized steel sheets, members made from the galvanized steel sheets, and methods of manufacturing them.
  • high-strength steel plates are used for the main structural members and reinforcing members (hereinafter also referred to as automobile frame structural members) that are assembled into the frame of the car cabin.
  • the number of applications of high-strength steel plates of 780 MPa or higher is increasing.
  • high-strength steel plates used for automobile frame structural members and the like are required to have high member strength when press-formed.
  • YR yield ratio
  • YS yield stress
  • TS yield stress
  • impact absorption energy the impact absorption energy at the time of a car collision increases.
  • a crash box has a bent portion. Therefore, from the viewpoint of press formability, it is preferable to use a steel plate having high bendability for such parts.
  • steel sheets used as materials for automobile parts are often galvanized. Therefore, it is desired to develop a hot-dip galvanized steel sheet that not only has high strength but also has excellent press formability and impact resistance.
  • Patent Document 1 as a steel plate that is a material for such automobile parts, C is 0.04 to 0.22%, Si is 1.0% or less, and Mn is 3.0%. % or less, P is 0.05% or less, S is 0.01% or less, Al is 0.01-0.1%, and N is 0.001-0.005%, with the balance being Fe and unavoidable impurities. It is composed of a ferrite phase as a main phase and a martensite phase as a second phase, and the maximum grain size of the martensite phase is 2 ⁇ m or less and its area ratio is 5% or more.
  • a high-strength steel plate with excellent stretch flangeability and collision resistance characteristics is disclosed.
  • Patent Document 2 describes a cold-rolled steel sheet whose surface layer has been polished to a thickness of 0.1 ⁇ m or more and which is pre-plated with Ni at 0.2 g/m2 or more and 2.0 g/m2 or less .
  • Containing two or more types of martensite [3] of three types of martensite [1], [2], and [3], 1% or more of bainite, and 0 to 10% of pearlite, and containing the three types of martensite [1], [2], and [3] are volume fractions, respectively: martensite [1]: 0% or more, 50% or less, martensite [2]: 0% or more, less than 20%, martensite [3] : 1% or more and 30% or less, and has a hot-dip galvanized layer containing less than 7% Fe, with the remainder consisting of Zn, Al and inevitable impurities, and has a tensile strength TS (MPa), Plating adhesion characterized by having a total elongation rate EL (%) and a hole expansion rate ⁇ (%) of TS x EL of 18000 MPa % or more, TS x ⁇ of 35000 MPa % or more, and a tensile strength of 980 MP
  • High-strength hot-dip galvanized steel sheet with excellent formability (martensite [1]: C concentration (CM1) is less than 0.8%, hardness Hv1 is Hv1/(-982.1 ⁇ CM1 2 +1676 ⁇ CM1+189) ⁇ 0.60, martensite [2]: C concentration (CM2) is 0.8% or more, hardness Hv2 is Hv2/(-982.1 ⁇ CM2 2 +1676 ⁇ CM2+189) ⁇ 0.60, martensite [3]: It is disclosed that the C concentration (CM3) is 0.8% or more and the hardness Hv3 is Hv3/(-982.1 ⁇ CM3 2 +1676 ⁇ CM3+189) ⁇ 0.80.
  • Patent Document 3 in mass %, C: 0.15% or more and 0.25% or less, Si: 0.50% or more and 2.5% or less, Mn: 2.3% or more and 4.0% or less. , P: 0.100% or less, S: 0.02% or less, Al: 0.01% or more and 2.5% or less, with the balance consisting of Fe and unavoidable impurities.
  • Martensite phase 30% or more and 73% or less, ferrite phase: 25% or more and 68% or less, retained austenite phase: 2% or more and 20% or less, other phases: 10% or less (including 0%), and The other phases include martensitic phase: 3% or less (including 0%), bainitic ferrite phase: less than 5% (including 0%), and the average grain size of the tempered martensitic phase is 8 ⁇ m.
  • Patent Document 4 discloses an alloyed hot-dip galvanized steel sheet having an alloyed hot-dip galvanized layer on the surface of the steel sheet, in which the steel sheet has a carbon content of 0.03% or more and 0.35% or less in mass %. , Si: 0.005% or more and 2.0% or less, Mn: 1.0% or more and 4.0% or less, P: 0.0004% or more and 0.1% or less, S: 0.02% or less, sol. It has a chemical composition consisting of Al: 0.0002% or more and 2.0% or less, N: 0.01% or less, and the balance is Fe and impurities, and is stretched in the rolling direction at a depth of 50 ⁇ m from the surface of the steel plate.
  • the average spacing in the direction perpendicular to the rolling direction of the enriched regions where Mn and/or Si are concentrated is 1000 ⁇ m or less, and the number density of cracks with a depth of 3 ⁇ m or more and 10 ⁇ m or less on the surface of the steel sheet is 3 pieces/mm or more and 1000 pieces/mm or less, and contains bainite: 60% or more, retained austenite: 1% or more, martensite: 1% or more, and ferrite: 2% or more and less than 20%, and
  • the alloyed hot-dip galvanized steel sheet has a steel structure in which the average distance between the ultrahard phases, which is the average value of the closest distance between martensite and retained austenite, is 20 ⁇ m or less, and the alloyed hot-dip galvanized steel sheet has a tensile strength (TS) of 780 MPa or more.
  • TS tensile strength
  • TS tensile strength
  • the yield stress YS (hereinafter sometimes simply referred to as YS) and the yield ratio YR (hereinafter simply referred to as YR) are ) is effective.
  • YS and YR of a steel sheet are increased, press formability, particularly properties such as ductility, hole expandability, and bendability are generally reduced.
  • the steel sheets disclosed in Patent Documents 1 to 4 also have a TS of 780 MPa or more, high YS and YR, excellent press formability (ductility, hole expandability, and bendability), and impact resistance. It cannot be said that it has rupture properties (bending rupture properties and axial crush properties).
  • the present invention was developed in view of the above-mentioned current situation, and has a tensile strength TS of 780 MPa or more, a high yield stress YS, a high yield ratio YR, and excellent press formability (ductility, hole expandability).
  • the object of the present invention is to provide a galvanized steel sheet having good properties (bending properties and bending properties) and fracture resistance upon collision (bending fracture properties and axial crushing properties), and a method for manufacturing the same.
  • Another object of the present invention is to provide a member made of the above-mentioned galvanized steel sheet and a method for manufacturing the same.
  • the galvanized steel sheet here refers to a hot-dip galvanized steel sheet (hereinafter also referred to as GI) or an alloyed hot-dip galvanized steel sheet (hereinafter also referred to as GA).
  • GI hot-dip galvanized steel sheet
  • GA alloyed hot-dip galvanized steel sheet
  • the tensile strength TS is measured by a tensile test based on JIS Z 2241.
  • high yield stress YS and yield ratio YR means that YS measured in a tensile test based on JIS Z 2241 is one of the following (A) or (B) depending on the TS measured in the tensile test. Indicates that the formula is satisfied.
  • B When 980MPa ⁇ TS, 600MPa ⁇ YS and 0.61 ⁇ YR
  • excellent hole expansion property refers to a critical hole expansion rate ( ⁇ ) of 30% or more measured in a hole expansion test based on JIS Z 2256.
  • R (limit bending radius)/t (plate thickness) measured in a V-bending test based on JIS Z 2248 is expressed by the following formula (A) or (B) depending on the TS. It refers to satisfying the following.
  • excellent axial crushing properties means that the critical spacer thickness (ST) in the U-bending + close-contact bending test satisfies the following formula (A) or (B) depending on the TS.
  • ST critical spacer thickness
  • having excellent axial crushing characteristics means that the stroke at maximum load (SFmax) measured in the V-bending + orthogonal VDA bending test satisfies the following formula (A) or (B) depending on the TS. Point.
  • SFmax stroke at maximum load measured in the V-bending + orthogonal VDA bending test
  • having excellent bending rupture properties means that the critical spacer thickness (ST) in the above U-bending + close-contact bending test satisfies the above formula (A) or (B) depending on the TS, and It means that the stroke at maximum load (SFmax) measured in the bending + orthogonal VDA bending test satisfies the above formula (A) or (B) depending on the TS.
  • the above El (ductility), ⁇ (stretch flangeability), and R/t (bendability) are characteristics that indicate the ease of forming a steel plate during press forming (the degree of freedom in forming for press forming without cracking). It is.
  • the U-bending + close bending test is a test that simulates the deformation and fracture behavior of the vertical wall part in a collision test, and the critical spacer thickness (ST) measured in the U-bending + close bending test is It is an index showing the resistance to cracking (impact resistance properties for absorbing impact energy without breaking) of steel plates and components of automobile bodies.
  • V-bending + orthogonal VDA bending test is a test that simulates the deformation and fracture behavior of the bending ridge line part in a collision test, and the stroke (SFmax) at the maximum load measured in the V-bending + orthogonal VDA bending test is the energy This is an index showing the resistance of the absorbent member to cracking.
  • the present inventors have made extensive studies and have obtained the following knowledge.
  • the area ratio of tempered martensite is controlled to 10.0% or more, the island-like hard second phase (martensite + retained austenite) in contact with the ferrite grain boundaries is reduced, and the area ratio within the ferrite grains is reduced.
  • the ratio of the isolated fine island-like hard second phase (martensite + retained austenite)
  • the The critical spacer thickness (ST) measured in a U-bending + close bending test that simulates the deformation and fracture behavior of vertical walls in a crash test, which is an indicator of the impact resistance properties of steel plates and components of a car body
  • SFmax stroke at maximum load
  • a galvanized steel sheet comprising a base steel plate and a galvanized layer formed on the base steel plate, the base steel plate comprising: In mass%, C: 0.030% or more and 0.250% or less, Si: 0.01% or more and 0.75% or less, Mn: 2.00% or more and less than 3.50%, P: 0.001% or more and 0.100% or less, S: 0.0200% or less, Al: 0.010% or more and 2.000% or less, N: 0.0100% or less, , with the remainder consisting of Fe and unavoidable impurities;
  • Ferrite area ratio 20.0% or more and 80.0% or less
  • Fresh martensite area ratio 15.0% or less
  • Area ratio of retained austenite 3.0% or less
  • the component composition further includes, in mass%, Nb: 0.200% or less, Ti: 0.200% or less, V: 0.200% or less, B: 0.0100% or less, Cr: 1.000% or less, Ni: 1.000% or less, Mo: 1.000% or less, Sb: 0.200% or less, Sn: 0.200% or less, Cu: 1.000% or less, Ta: 0.100% or less, W: 0.500% or less, Mg: 0.0200% or less, Zn: 0.0200% or less, Co: 0.0200% or less, Zr: 0.1000% or less, Ca: 0.0200% or less, Se: 0.0200% or less, Te: 0.0200% or less, Ge: 0.0200% or less, As: 0.0500% or less, Sr: 0.0200% or less, Cs: 0.0200% or less, Hf: 0.0200% or less, Pb: 0.0200% or less,
  • the surface layer has a soft surface layer whose Vickers hardness is 85% or less with respect to the Vickers hardness at the 1/4 position of the plate thickness, Nano hardness of 300 points or more in a 50 ⁇ m x 50 ⁇ m area of the plate surface at 1/4 position and 1/2 depth in the plate thickness direction of the surface soft layer from the surface of the base steel plate, respectively.
  • the proportion of measurements where the nano-hardness of the plate surface at 1/4 of the depth in the thickness direction of the soft surface layer from the surface of the base steel sheet is 7.0 GPa or more is 1/4 of the depth in the thickness direction of the soft surface layer.
  • the standard deviation ⁇ of the nano-hardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface is 1.8 GPa or less
  • the standard deviation ⁇ of the nano-hardness of the plate surface at a position 1/2 the thickness direction depth of the surface soft layer from the base steel plate surface is 2.2 GPa or less.
  • a galvanizing step is performed on the steel sheet to obtain a galvanized steel sheet; Applying a tension of 2.0 kgf/mm 2 or more to the galvanized steel sheet in a temperature range of 300 ° C. or higher and 450 ° C. or lower, Thereafter, the galvanized steel sheet is passed through 5 passes or more while being in contact with a roll having a diameter of 500 mm or more and 1500 mm or less for 1/4 rotation of the roll per pass, Then, a second cooling step of cooling to a cooling stop temperature of 250° C. or less; a reheating step of reheating the galvanized steel sheet to a temperature range of not less than the cooling stop temperature and not more than 440° C.
  • a method for producing a galvanized steel sheet comprising a cold rolling step of cold rolling a steel sheet at a rolling reduction of 20% or more and 80% or less to obtain a cold rolled steel sheet.
  • the method for producing a galvanized steel sheet according to [10] above wherein the annealing in the annealing step is performed in an atmosphere with a dew point of -30°C or higher.
  • a method for manufacturing a member comprising the step of subjecting the galvanized steel sheet according to [1] or [2] to at least one of forming and bonding to produce a member.
  • a method for producing a member including the step of subjecting the galvanized steel sheet according to [3] above to at least one of forming and bonding to produce a member.
  • a method for manufacturing a member comprising the step of subjecting the galvanized steel sheet according to [4] above to at least one of forming and bonding to produce a member.
  • a method for producing a member comprising the step of subjecting the galvanized steel sheet according to [5] above to at least one of forming and bonding to produce a member.
  • the tensile strength TS is 780 MPa or more, high yield stress YS and yield ratio YR, excellent press formability (ductility, hole expandability, and bendability), and rupture resistance at the time of collision.
  • a galvanized steel sheet having the following properties (bending fracture properties and axial crush properties) is obtained.
  • the members made of the galvanized steel sheet of the present invention have high strength and excellent press formability and impact resistance, so they are extremely advantageously applicable to automobile frame members and impact energy absorbing members. can do.
  • FIG. 13 This is an example of a SEM image of the present invention (Invention Example No. 13 of Examples).
  • (a) is a diagram for explaining the U-bending process (primary bending process) in the U-bending + close-contact bending test of the example.
  • (b) is a diagram for explaining the close bending process (secondary bending process) in the U-bending + close bending test of the example.
  • (a) is a diagram for explaining the V-bending process (primary bending process) in the V-bending + orthogonal VDA bending test of the example.
  • (b) is a diagram for explaining the orthogonal VDA bending process (secondary bending process) in the V-bending + orthogonal VDA bending test of the example.
  • (a) is a front view of a test member manufactured for carrying out an axial crush test of an example, in which a hat-shaped member and a steel plate are spot-welded.
  • (b) is a perspective view of the test member shown in FIG. 1(d).
  • (c) is a schematic diagram for explaining the axial crush test of the example.
  • the galvanized steel sheet of the present invention is a galvanized steel sheet comprising a base steel sheet and a galvanized layer formed on the surface of the base steel sheet, wherein the base steel sheet has a C: 0.030 in mass%.
  • the area ratio of ferrite is 20.0% or more and 80.0% or less
  • the area ratio of fresh martensite is 15.0% or less
  • the area ratio of retained austenite is 3.0% or less.
  • the area ratio of tempered bainite is 10.0% or less, the area ratio of tempered martensite is 10.0% to 70.0%, and island-like fresh martensite and island-like residual It has a steel structure in which the average grain size of austenite is 2.0 ⁇ m or less, the amount of diffusible hydrogen contained in the base steel sheet is 0.50 mass ppm or less, and the tensile strength is 780 MPa or more.
  • compositions First, the composition of the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention will be described. Note that the units in the component compositions are all “mass %”, but hereinafter, unless otherwise specified, they will simply be expressed as "%".
  • C 0.030% or more and 0.250% or less C is an effective element for producing an appropriate amount of tempered martensite, bainite, tempered bainite, etc., and ensuring a TS of 780 MPa or more, high YS, and high YR. It is.
  • the C content is less than 0.030%, the area ratio of ferrite increases and it becomes difficult to make the TS 780 MPa or more. It also causes a decrease in YS and YR.
  • the C content exceeds 0.250%, the area ratio of fresh martensite increases, TS becomes excessively high, and El decreases.
  • the C content is set to 0.030% or more and 0.250% or less.
  • the C content is preferably 0.050% or more. Further, the C content is preferably 0.130% or less.
  • Si 0.01% or more and 0.75% or less Si promotes ferrite transformation during annealing and during the cooling process after annealing. That is, Si is an element that affects the area ratio of ferrite. Here, if the Si content is less than 0.01%, the area ratio of ferrite decreases and ductility decreases.
  • the Si content is set to 0.01% or more and 0.75% or less.
  • the Si content is preferably 0.10% or more. Further, the Si content is preferably 0.70% or less.
  • Mn 2.00% or more and less than 3.50%
  • Mn is an element that adjusts the area ratio of tempered martensite, bainite, and further tempered bainite.
  • the Mn content is less than 2.00%, the area ratio of ferrite increases and it becomes difficult to make the TS 780 MPa or more. It also causes a decrease in YS and YR.
  • the Mn content is 3.50% or more, the martensite transformation start temperature Ms (hereinafter also simply referred to as the Ms point or Ms) decreases, and the martensite generated in the first cooling step decreases.
  • the Mn content is set to 2.00% or more and less than 3.50%.
  • the Mn content is preferably 2.20% or more. Further, the Mn content is preferably 3.00% or less.
  • P 0.001% or more and 0.100% or less
  • P is an element that has a solid solution strengthening effect and increases the TS and YS of the steel sheet.
  • the P content is set to 0.001% or more.
  • P segregates at prior austenite grain boundaries and embrittles the grain boundaries. Therefore, during the V-bending test, voids are generated and cracks grow along the prior austenite grain boundaries, making it impossible to obtain the desired R/t.
  • the P content is set to 0.001% or more and 0.100% or less.
  • the P content is preferably 0.030% or less.
  • S 0.0200% or less S exists as a sulfide in steel.
  • the S content exceeds 0.0200%, voids are generated and cracks propagate starting from the sulfides during the V-bending test, making it impossible to obtain the desired R/t.
  • the S content is set to 0.0200% or less.
  • the S content is preferably 0.0080% or less. Note that although the lower limit of the S content is not particularly specified, it is preferable that the S content is 0.0001% or more due to constraints on production technology.
  • Al 0.010% or more and 2.000% or less
  • Al promotes ferrite transformation during annealing and during the cooling process after annealing. That is, Al is an element that affects the area ratio of ferrite.
  • the Al content is set to 0.010% or more and 2.000% or less.
  • Al content is preferably 0.015% or more. Further, the Al content is preferably 1.000% or less.
  • N 0.0100% or less N exists as a nitride in steel.
  • the N content exceeds 0.0100%, voids are generated and cracks propagate starting from the nitride during the V-bending test, making it impossible to obtain the desired R/t.
  • the N content is set to 0.0100% or less.
  • the N content is preferably 0.0050% or less. Note that, although the lower limit of the N content is not particularly specified, it is preferable that the N content is 0.0005% or more due to constraints on production technology.
  • the basic component composition of the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention has been explained above, but the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention contains the above-mentioned basic components and other than the above-mentioned basic components.
  • the remainder has a composition containing Fe (iron) and unavoidable impurities.
  • the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention contains the above-mentioned basic components, with the remainder consisting of Fe and inevitable impurities.
  • the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention may contain at least one selected from the following optional components.
  • the effects of the present invention can be obtained for the optional components shown below as long as they are contained in amounts below the upper limit shown below, so no lower limit is set in particular.
  • the following arbitrary elements are contained below the preferable lower limit value mentioned later, the said elements shall be contained as an unavoidable impurity.
  • Nb 0.200% or less
  • Ti 0.200% or less
  • V 0.200% or less
  • B 0.0100% or less
  • Cr 1.000% or less
  • Ni 1.000% or less
  • Mo 1.000% or less
  • Sb 0.200% or less
  • Sn 0.200% or less
  • Cu 1.000% or less
  • Ta 0.100% or less
  • W 0.500% or less
  • Mg 0.200% or less
  • Nb 0.200% or less Nb increases TS, YS, and YR by forming fine carbides, nitrides, or carbonitrides during hot rolling or annealing.
  • the Nb content is 0.001% or more.
  • the Nb content is more preferably 0.005% or more.
  • the Nb content exceeds 0.200%, large amounts of coarse precipitates and inclusions may be generated. In such cases, coarse precipitates and inclusions become starting points for voids and cracks during hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests, so that the desired ⁇ , R/t, ST and SFmax may not be obtained. Therefore, when Nb is contained, the Nb content is preferably 0.200% or less.
  • the Nb content is more preferably 0.060% or less.
  • Ti 0.200% or less Like Nb, Ti increases TS, YS, and YR by forming fine carbides, nitrides, or carbonitrides during hot rolling or annealing. In order to obtain such an effect, it is preferable that the Ti content is 0.001% or more. The Ti content is more preferably 0.005% or more. On the other hand, if the Ti content exceeds 0.200%, a large amount of coarse precipitates and inclusions may be formed.
  • the Ti content is preferably 0.200% or less.
  • the Ti content is more preferably 0.060% or less.
  • V 0.200% or less Like Nb and Ti, V increases TS and YS by forming fine carbides, nitrides, or carbonitrides during hot rolling or annealing. In order to obtain such an effect, it is preferable that the V content is 0.001% or more. The V content is more preferably 0.005% or more. The V content is more preferably 0.010% or more, and even more preferably 0.030% or more. On the other hand, when the V content exceeds 0.200%, large amounts of coarse precipitates and inclusions may be generated.
  • V content is preferably 0.200% or less.
  • the V content is more preferably 0.060% or less.
  • B 0.0100% or less
  • B is an element that improves hardenability by segregating at austenite grain boundaries. Further, B is an element that controls the generation and grain growth of ferrite during cooling after annealing. In order to obtain such an effect, it is preferable that the B content is 0.0001% or more. The B content is more preferably 0.0002% or more. The B content is more preferably 0.0005% or more, and even more preferably 0.0007% or more. On the other hand, if the B content exceeds 0.0100%, cracks may occur inside the steel sheet during hot rolling.
  • the internal crack becomes the starting point of the crack, so the desired ⁇ , R/t, ST and SFmax can be obtained. may not be possible. Therefore, when B is included, the B content is preferably 0.0100% or less. The B content is more preferably 0.0050% or less.
  • the Cr content is preferably 0.0005% or more. Further, the Cr content is more preferably 0.010% or more. Cr is more preferably 0.030% or more, and even more preferably 0.050% or more. On the other hand, if the Cr content exceeds 1.000%, the area ratio of fresh martensite increases, hole expandability and V-bending test bendability decrease, and the desired ⁇ and R/t may not be obtained. There is. Therefore, when Cr is contained, the Cr content is preferably 1.000% or less. Further, the Cr content is more preferably 0.800% or less, still more preferably 0.700% or less.
  • Ni 1.000% or less
  • Ni is an element that improves hardenability, and the addition of Ni produces a large amount of tempered martensite, thereby increasing TS, YS, and YR.
  • the Ni content be 0.005% or more.
  • the Ni content is more preferably 0.020% or more.
  • the Ni content is more preferably 0.040% or more, and even more preferably 0.060% or more.
  • the Ni content exceeds 1.000%, the area ratio of fresh martensite increases, hole expandability and V-bending test bendability decrease, and the desired ⁇ and R/t may not be obtained. There is. Therefore, when Ni is contained, the Ni content is preferably 1.000% or less.
  • the Ni content is more preferably 0.800% or less.
  • the Ni content is more preferably 0.600% or less, and even more preferably 0.400% or less.
  • Mo 1.000% or less
  • Mo is an element that improves hardenability, and the addition of Mo generates a large amount of tempered martensite, thereby increasing TS, YS, and YR.
  • the Mo content is 0.010% or more.
  • Mo content is more preferably 0.030% or more.
  • the Mo content exceeds 1.000%, the area ratio of fresh martensite increases, hole expandability and V-bending test bendability decrease, and the desired ⁇ and R/t may not be obtained. There is. Therefore, when Mo is contained, the Mo content is preferably 1.000% or less.
  • the Mo content is more preferably 0.500% or less, still more preferably 0.450% or less, and even more preferably 0.400% or less.
  • the Mo content is more preferably 0.350% or less, and even more preferably 0.300% or less.
  • Sb 0.200% or less
  • Sb is an effective element for suppressing the diffusion of C near the surface of the steel sheet during annealing and controlling the formation of a soft layer near the surface of the steel sheet. If the soft layer increases excessively near the surface of the steel sheet, it may be difficult to increase the TS to 780 MPa or more. Furthermore, there is a possibility that YS will be lowered. Therefore, it is preferable that the Sb content is 0.002% or more. The Sb content is more preferably 0.005% or more. On the other hand, when the Sb content exceeds 0.200%, a soft layer is not formed near the surface of the steel sheet, which may lead to a decrease in ⁇ , R/t, ST, and SFmax. Therefore, when Sb is contained, the Sb content is preferably 0.200% or less. The Sb content is more preferably 0.020% or less.
  • Sn 0.200% or less
  • Sn is an effective element for suppressing the diffusion of C near the surface of the steel sheet during annealing and controlling the formation of a soft layer near the surface of the steel sheet. If the soft layer increases excessively near the surface of the steel sheet, it may be difficult to increase the TS to 780 MPa or more. Furthermore, there is a possibility that YS will be lowered. Therefore, it is preferable that the Sn content is 0.002% or more. The Sn content is more preferably 0.005% or more. On the other hand, if the Sn content exceeds 0.200%, a soft layer will not be formed near the surface of the steel sheet, which may cause a decrease in ⁇ , R/t, ST, and SFmax. Therefore, when Sn is contained, the Sn content is preferably 0.200% or less. The Sn content is more preferably 0.020% or less.
  • Cu 1.000% or less
  • Cu is an element that improves hardenability, so adding Cu generates a large amount of tempered martensite, increasing TS, YS, and YR.
  • the Cu content is 0.005% or more.
  • the Cu content is more preferably 0.008% or more, and even more preferably 0.010% or more.
  • the Cu content is more preferably 0.020% or more.
  • the area ratio of fresh martensite may increase excessively. Further, a large amount of coarse precipitates and inclusions may be generated.
  • the Cu content is preferably 1.000% or less.
  • the Cu content is more preferably 0.200% or less.
  • Ta 0.100% or less Like Ti, Nb, and V, Ta increases TS, YS, and YR by forming fine carbides, nitrides, or carbonitrides during hot rolling and annealing. let In addition, Ta is partially dissolved in Nb carbides and Nb carbonitrides to form composite precipitates such as (Nb, Ta) (C, N). This suppresses coarsening of precipitates and stabilizes precipitation strengthening. This further improves TS and YS. In order to obtain such an effect, the Ta content is preferably 0.001% or more. The Ta content is more preferably 0.002% or more, and even more preferably 0.004% or more.
  • the Ta content is preferably 0.100% or less.
  • the Ta content is more preferably 0.090% or less, and even more preferably 0.080% or less.
  • W 0.500% or less
  • W is an element that improves hardenability, and the addition of W generates a large amount of tempered martensite, thereby increasing TS, YS, and YR.
  • the W content is 0.001% or more.
  • the W content is more preferably 0.030% or more.
  • the W content exceeds 0.500%, the area ratio of fresh martensite increases, hole expandability and V-bending test bendability decrease, and the desired ⁇ and R/t may not be obtained. There is. Therefore, when W is contained, the W content is preferably 0.500% or less.
  • the W content is more preferably 0.450% or less, still more preferably 0.400% or less. It is even more preferable that the W content is 0.300% or less.
  • Mg 0.0200% or less
  • Mg is an effective element for spheroidizing the shape of inclusions such as sulfides and oxides and improving the hole expandability and bendability of the steel sheet.
  • the Mg content is 0.0001% or more.
  • the Mg content is more preferably 0.0005% or more, and even more preferably 0.0010% or more.
  • the Mg content exceeds 0.0200%, large amounts of coarse precipitates and inclusions may be formed. In such cases, excessively coarse precipitates and inclusions become starting points for voids and cracks during the hole expansion test, V-bending test, U-bending + close-contact bending test, and V-bending + orthogonal VDA bending test.
  • the Mg content is preferably 0.0200% or less.
  • the Mg content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • Zn 0.0200% or less
  • Zn is an effective element for spheroidizing the shape of inclusions and improving the hole expandability and bendability of the steel sheet.
  • the Zn content is preferably 0.0010% or more.
  • the Zn content is more preferably 0.0020% or more, and even more preferably 0.0030% or more.
  • the Zn content exceeds 0.0200%, large amounts of coarse precipitates and inclusions may be formed.
  • the Zn content is preferably 0.0200% or less.
  • the Zn content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • Co 0.0200% or less
  • Co is an effective element for spheroidizing the shape of inclusions and improving the hole expandability and bendability of the steel sheet.
  • the Co content is preferably 0.0010% or more.
  • the Co content is more preferably 0.0020% or more, and even more preferably 0.0030% or more.
  • the Co content exceeds 0.0200%, a large amount of coarse precipitates and inclusions may be formed. In such cases, excessively coarse precipitates and inclusions become starting points for voids and cracks during hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests. ⁇ , R/t, ST and SFmax may not be obtained. Therefore, when Co is contained, the Co content is preferably 0.0200% or less.
  • the Co content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • Zr 0.1000% or less
  • Zr is an effective element for making the shape of inclusions spherical and improving the hole expandability and bendability of the steel sheet.
  • the Zr content is preferably 0.0010% or more.
  • the Zr content exceeds 0.1000%, excessively coarse precipitates and inclusions may be detected in hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests.
  • the desired ⁇ , R/t, ST and SFmax may not be obtained because it becomes a starting point for voids and cracks. Therefore, when Zr is contained, the Zr content is preferably 0.1000% or less.
  • the Zr content is more preferably 0.0300% or less, and even more preferably 0.0100% or less.
  • Ca 0.0200% or less Ca exists as inclusions in steel.
  • the Ca content is preferably 0.0200% or less.
  • the Ca content is preferably 0.0020% or less.
  • the Ca content is more preferably 0.0019% or less, and even more preferably 0.0018% or less.
  • the lower limit of the Ca content is not particularly limited, but the Ca content is preferably 0.0005% or more.
  • the Ca content is more preferably 0.0010% or more.
  • Se 0.0200% or less, Te: 0.0200% or less, Ge: 0.0200% or less, As: 0.0500% or less, Sr: 0.0200% or less, Cs: 0.0200% or less, Hf: 0.0200% or less, Pb: 0.0200% or less, Bi: 0.0200% or less, and REM: 0.0200% or less Se, Te, Ge, As, Sr, Cs, Hf, Pb, Bi, and REM are all is also an effective element for improving the hole expandability and bendability of steel sheets. In order to obtain such an effect, it is preferable that the content of Se, Te, Ge, As, Sr, Cs, Hf, Pb, Bi, and REM is each 0.0001% or more.
  • the content of Bi and REM is preferably 0.0200% or less, and the content of As is preferably 0.0500% or less.
  • the Se content is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • the Se content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • the Te content is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • the Te content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • the Ge content is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • the Ge content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • As content it is more preferred that it is 0.0010% or more, and it is still more preferred that it is 0.0015% or more.
  • As content it is more preferred that it is 0.0400% or less, and it is still more preferred that it is 0.0300% or less.
  • the Sr content is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • the Sr content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • the Cs content is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • the Cs content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • the Hf content is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • the Hf content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • the Pb content is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • the Pb content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • the Bi content is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • Bi is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • REM is more preferably 0.0005% or more, and even more preferably 0.0008% or more.
  • REM is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
  • Area ratio of ferrite 20.0% or more and 80.0% or less
  • Soft ferrite is a phase that improves ductility. It is also a necessary phase to generate isolated island-like fresh martensite and isolated island-like retained austenite within grains, and to suppress the connection of voids and the propagation of cracks.
  • the area ratio of ferrite is set to 20.0% or more.
  • the area ratio of ferrite increases excessively, it becomes difficult to increase the TS to 780 MPa or more. It also causes a decrease in YS and YR. Therefore, the area ratio of ferrite is set to 80.0% or less. Further, the area ratio of ferrite is preferably 30.0% or more.
  • Fresh martensite area ratio 15.0% or less (including 0.0%)
  • the area ratio of fresh martensite is set to 15.0% or less.
  • the area ratio of fresh martensite is preferably 10.0% or less. Note that the lower limit of the area ratio of fresh martensite is not particularly limited, and may be 0.0%.
  • the fresh martensite referred to here is martensite that is still quenched (not tempered).
  • the fresh martensite referred to herein also includes (isolated) island-like fresh martensite within ferrite grains, which will be described later.
  • Area ratio of retained austenite 3.0% or less (including 0.0%)
  • the area ratio of retained austenite is set to 3.0% or less.
  • the area ratio of retained austenite is preferably 2.5% or less, more preferably 2.0% or less.
  • the lower limit of the area ratio of retained austenite is not particularly limited, but is preferably 0.1% or more, more preferably 0.2% or more.
  • the retained austenite referred to herein also includes (isolated) island-like retained austenite within ferrite grains, which will be described later.
  • a tension of 2.0 kgf/mm 2 or more is applied in a temperature range of 300°C or more and 450°C or less, and then the steel plate is heated to a diameter of 500 mm or more and 1500 mm or less per pass.
  • untransformed austenite undergoes deformation-induced transformation to become fresh martensite, and in the subsequent reheating process, the fresh martensite is tempered.
  • the area ratio of fresh martensite to 15.0% or less and the volume ratio of retained austenite to 3.0% or less, it is possible to secure the desired area ratio of tempered martensite. Become.
  • the value obtained by dividing the sum of the area ratios of island-like fresh martensite and island-like retained austenite in the ferrite grains by the sum of the area ratio of fresh martensite and retained austenite in the entire steel sheet 0.65 or more , as shown in Figure 1, isolated island-like fresh martensite (M') and isolated island-like retained austenite (RA') within ferrite (F) grains are tempered martensite (TM) existing at ferrite grain boundaries. It is finer than the hard second phase (fresh martensite (M) + retained austenite (RA)), and although it can serve as a void generation site, it is a structure that is unlikely to be involved in void connection or crack propagation.
  • the value obtained by dividing the total area ratio of isolated island-like fresh martensite and isolated island-like retained austenite in the ferrite grain by the sum of the area ratio of fresh martensite and retained austenite ((M'+RA' )/(M+RA)) shall be 0.65 or more. Further, the value obtained by dividing the sum of the area ratios of isolated island-like fresh martensite and isolated island-like retained austenite in the ferrite grain by the sum of the area ratio of fresh martensite and retained austenite is preferably 0. It is 70 or more.
  • the upper limit of the value obtained by dividing the sum of the area ratios of isolated island-like fresh martensite and isolated island-like retained austenite in the ferrite grain by the sum of the area ratio of fresh martensite and the volume ratio of retained austenite is not particularly limited, but This value is preferably 0.94 or less, more preferably 0.92 or less.
  • Area ratio of bainite and tempered bainite 10.0% or less (including 0.0%) If the area ratio of the tempered bainite produced in the first cooling process and the bainite produced in the reheating process is tempered, the desired area ratio of tempered martensite cannot be obtained, and the TS of 780 MPa or more It will be difficult to secure. Therefore, the area ratio (B+BT) of bainite and tempered bainite is 10.0% or less. Further, the area ratio of bainite and tempered bainite is preferably 8.0% or less. The area ratio of bainite and tempered bainite may be 0.0% or less.
  • tempered martensite Area ratio of tempered martensite: 10.0% or more and 70.0% or less
  • the hard second phase fresh martensite + retained austenite
  • tempered martensite is produced by applying a tension of 2.0 kgf/mm2 or more in a temperature range of 300°C to 450°C during the second cooling step in the manufacturing method described later, and then applying a tension of 2.0 kgf/mm2 or more to the galvanized steel sheet in one pass.
  • the untransformed austenite undergoes deformation-induced transformation to become fresh martensite by contacting a roll with a per-diameter of 500 mm or more and 1500 mm or less for 1/4 rotation of the roll and passing the roll for 5 or more passes.
  • This structure is obtained by tempering the sites and exists mostly at ferrite grain boundaries.
  • the above-mentioned tempered martensite has a structure necessary to obtain desired ⁇ , R/t, ST and SFmax. Therefore, the area ratio of tempered martensite is set to 10.0% or more.
  • the area ratio of tempered martensite is preferably 20.0% or more.
  • the area ratio of tempered martensite is 70.0% or less.
  • the area ratio of tempered martensite is preferably 60.0% or less.
  • Average crystal grain size of island-like fresh martensite and island-like retained austenite within ferrite grains 2.0 ⁇ m or less
  • the average crystal grain size of island-like fresh martensite and island-like retained austenite (M'+RA') within the ferrite grains is set to 2.0 ⁇ m or less.
  • the average crystal grain size of the island-like fresh martensite and the island-like retained austenite within the ferrite grains is preferably 1.0 ⁇ m or less.
  • the average crystal grain size of the island-like fresh martensite and the island-like retained austenite in the ferrite grains is preferably 0.1 ⁇ m or more, more preferably 0.2 ⁇ m or more.
  • the area ratio of the remaining structures other than those mentioned above is preferably 10.0% or less.
  • the area ratio of the remaining tissue is more preferably 5.0% or less. Further, the area ratio of the remaining tissue may be 0.0%.
  • the residual structure is not particularly limited, and examples thereof include carbides such as pearlite and cementite.
  • the type of residual tissue can be confirmed, for example, by observation using a scanning electron microscope (SEM).
  • the area ratio of ferrite, bainite, tempered bainite, tempered martensite, and hard second phase is measured as follows at the 1/4 thickness position of the base steel plate. That is, the sample is cut out so that the plate thickness cross section (L cross section) parallel to the rolling direction of the steel plate serves as the observation surface. Next, the observation surface of the sample is polished with diamond paste, and then final polished with alumina. Next, the observation surface of the sample was exposed to 3 vol. % nital to reveal the tissue. Next, the observation position is set at 1/4 of the thickness of the steel plate, and 5 fields of view are observed using an SEM at a magnification of 3000 times.
  • the area of each constituent structure (ferrite, bainite, tempered bainite, tempered martensite, and hard second phase (fresh martensite + retained austenite)) was measured using Adobe Photoshop from Adobe Systems. The area ratio divided by is calculated for five fields of view, and these values are averaged to determine the area ratio of each tissue.
  • Ferrite A black region with a block-like shape. In addition, it contains almost no carbide. Furthermore, isolated island-like fresh martensite and isolated island-like retained austenite within the ferrite grains are not included in the area ratio of ferrite.
  • Bainite and tempered bainite A black to dark gray area, with a lumpy or irregular shape. It also contains a relatively small amount of carbide.
  • Tempered martensite A gray area with an amorphous shape. It also contains a relatively large number of carbides. Hard second phase (retained austenite + fresh martensite): This is a white to light gray region with an amorphous shape. Also, it does not contain carbide. Carbide: A white region with a dotted or linear shape. It is included in bainite, tempered bainite, and tempered martensite. Remnant structure: Examples include the above-mentioned pearlite and cementite, and their forms are known.
  • the total area of isolated island-like fresh martensite and isolated island-like retained austenite within ferrite grains can be calculated as follows: The average area is determined by dividing by the number of island-like retained austenites, and the 1/2 power is taken as the average crystal grain size.
  • the area ratio of retained austenite is measured as follows. That is, the base steel plate is mechanically ground in the thickness direction (depth direction) to a position of 1/4 of the plate thickness, and then chemically polished with oxalic acid to form an observation surface. Then, the observation surface is observed by X-ray diffraction. MoK ⁇ rays were used for the incident X-rays, and the diffraction intensity of the (200), (211) and (220) planes of BCC iron was compared with the (200), (220) and (311) planes of FCC iron (austenite). The ratio of the diffraction intensities of each surface is determined, and the volume fraction of retained austenite is calculated from the ratio of the diffraction intensities of each surface. Then, assuming that the retained austenite is three-dimensionally homogeneous, the volume fraction of the retained austenite is defined as the area fraction of the retained austenite.
  • the area ratio of fresh martensite is determined by subtracting the area ratio of retained austenite from the area ratio of the hard second phase determined as described above.
  • [Area ratio of fresh martensite (%)] [Area ratio of hard second phase (%)] - [Area ratio of retained austenite (%)]
  • Amount of diffusible hydrogen (in steel) contained in the base steel sheet 0.50 mass ppm or less
  • the amount of diffusible hydrogen in the steel sheet exceeds 0.50 mass ppm, the desired ⁇ , R/t, ST and SFmax I can't get it.
  • the amount of diffusible hydrogen in the steel sheet is preferably 0.25 mass ppm or less.
  • the lower limit of the amount of diffusible hydrogen in the steel sheet is not particularly specified, it is preferable that the amount of diffusible hydrogen in the steel sheet is 0.01 mass ppm or more due to constraints on production technology.
  • the base steel plate on which the amount of diffusible hydrogen is measured may be a high-strength steel plate before plating, or a base steel plate that is a high-strength galvanized steel plate after galvanizing and before processing.
  • it may be a base steel plate of a steel plate that has been subjected to processes such as punching and stretch flange forming after galvanizing, or it may be a base part of a product manufactured by welding the processed steel plate. I don't mind.
  • the method for measuring the amount of diffusible hydrogen in a steel sheet is as follows. A test piece with a length of 30 mm and a width of 5 mm is taken, and the hot-dip galvanized layer or the alloyed hot-dip galvanized layer is alkali-removed. Thereafter, the amount of hydrogen released from the test piece is measured by temperature programmed desorption analysis. Specifically, after continuously heating from room temperature (-5 to 55°C) to 300°C at a heating rate of 200°C/h, the test piece was cooled to room temperature, and the cumulative hydrogen released from the test piece from room temperature to 210°C was measured. The amount is measured and taken as the amount of diffusible hydrogen in the steel sheet.
  • the room temperature should be within the range of local temperature changes over a one-year period, taking into account production in various countries around the world. Generally, the temperature is preferably in the range of 10 to 50°C.
  • the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention preferably has a soft surface layer on the surface of the base steel sheet.
  • the soft surface layer contributes to suppressing the propagation of bending cracks during press molding and car body collisions, further improving the bending fracture resistance.
  • the surface soft layer means a decarburized layer, and is a surface layer region having a Vickers hardness of 85% or less of the Vickers hardness of the cross section at the 1/4 thickness position.
  • the surface soft layer is formed in an area of 200 ⁇ m or less in the thickness direction from the surface of the base steel sheet.
  • the lower limit of the thickness of the surface soft layer is not particularly determined, it is preferably 8 ⁇ m or more, and more preferably more than 17 ⁇ m. Vickers hardness is measured based on JIS Z 2244-1 (2020) with a load of 10 gf.
  • the proportion of measurements where the nanohardness of the plate surface at 1/4 of the depth in the thickness direction of the surface soft layer from the surface of the base steel sheet was 7.0 GPa or more was the same as the thickness of the surface soft layer.
  • the ratio of the number of measurements where the nanohardness of the plate surface at 1/4 of the depth in the thickness direction of the soft layer is 7.0 GPa or more is relative to the total number of measurements at 1/4 of the depth in the thickness direction of the surface soft layer. is preferably 0.10 or less.
  • the ratio of nanohardness of 7.0 GPa or more is 0.10 or less, it means that the ratio of hard structures (martensite, etc.), inclusions, etc. is small; It becomes possible to further suppress the generation and connection of voids during press molding and collision, as well as the propagation of cracks, resulting in excellent R/t and SFmax.
  • the standard deviation ⁇ of the nano-hardness of the plate surface at a position 1/4 of the depth in the thickness direction of the surface soft layer from the steel plate surface is 1.8 GPa or less, and The standard deviation ⁇ of the nanohardness of the plate surface at the 1/2 position is 2.2 GPa or less.
  • the standard deviation ⁇ of the nano-hardness of the plate surface at 1/4 of the depth in the thickness direction of the soft layer is 1.8 GPa or less, and furthermore, the standard deviation ⁇ of the nanohardness of the plate surface at 1/4 of the depth in the thickness direction of the surface soft layer from the steel plate surface is 1/2 of the depth in the thickness direction of the surface soft layer.
  • the standard deviation ⁇ of the nanohardness of the plate surface is 2.2 GPa or less.
  • the standard deviation ⁇ of the nano-hardness of the plate surface at a position 1/4 of the depth in the thickness direction of the surface soft layer from the steel plate surface is 1.8 GPa or less, and If the standard deviation ⁇ of the nanohardness of the plate surface at the 1/2 position is 2.2 GPa or less, it means that the difference in microstructure hardness in the micro region is small, and it is difficult to prevent the formation and connection of voids during press forming and collision. It becomes possible to further suppress the propagation of cracks, and excellent R/t and SFmax can be obtained.
  • a preferable range of the standard deviation ⁇ of the nanohardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface is preferably 1.7 GPa or less.
  • a more preferable range of the standard deviation ⁇ of the nano-hardness of the plate surface at 1/2 the thickness direction depth of the surface soft layer from the base steel plate surface is 2.1 GPa or less.
  • the nanohardness of the plate surface at the 1/4 position and 1/2 position of the depth in the thickness direction is the hardness measured by the following method.
  • Nanohardness is measured using Hysitron's tribo-950 with a Berkovich-shaped diamond indenter under the conditions of load: 500 ⁇ N, measurement area: 50 ⁇ m ⁇ 50 ⁇ m, and dot spacing: 2 ⁇ m. Further, mechanical polishing is performed to 1/2 the depth in the thickness direction of the surface soft layer, buff polishing with diamond and alumina, and further colloidal silica polishing. Then, the nanohardness is measured using Hysitron's tribo-950 with a Berkovich-shaped diamond indenter under the conditions of load: 500 ⁇ N, measurement area: 50 ⁇ m ⁇ 50 ⁇ m, and dot spacing: 2 ⁇ m.
  • the galvanized steel sheet according to an embodiment of the present invention has a metal plating layer (first plating layer, pre-plating layer) (in addition, a metal plating layer (first plating layer) on one or both surfaces of the base steel sheet. ) preferably has a hot-dip galvanized layer (excluding the galvanized layer of the alloyed hot-dip galvanized layer).
  • the metal plating layer is preferably a metal electroplating layer, and below, the metal electroplating layer will be explained as an example.
  • the metal electroplating layer on the outermost layer contributes to suppressing the occurrence of bending cracks during press forming and when a vehicle body collides, so that the bending rupture resistance is further improved.
  • the thickness of the soft layer can be increased, and the axial crushing properties can be made very excellent.
  • the present invention by having a metal plating layer, it is possible to obtain the same axial crushing characteristics as when the soft layer thickness is large even if the soft layer thickness is small and the dew point is ⁇ 20° C. or lower.
  • the metal species of the metal electroplating layer include Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Rt, Any of Au, Hg, Ti, Pb, and Bi may be used, but Fe is more preferable.
  • a Fe-based electroplated layer will be explained as an example.
  • the amount of the Fe-based electroplated layer deposited is more than 0 g/m 2 , preferably 2.0 g/m 2 or more.
  • the upper limit of the amount of the Fe-based electroplated layer per side is not particularly limited, but from the viewpoint of cost, it is preferable that the amount of the Fe-based electroplated layer applied per side is 60 g/m 2 or less.
  • the amount of the Fe-based electroplated layer deposited is preferably 50 g/m 2 or less, more preferably 40 g/m 2 or less, and even more preferably 30 g/m 2 or less.
  • the adhesion amount of the Fe-based electroplating layer is measured as follows. A sample with a size of 10 x 15 mm is taken from a Fe-based electroplated steel plate and embedded in resin to form a cross-sectional embedded sample. Three arbitrary points on the same cross section were observed using a scanning electron microscope (SEM) at an accelerating voltage of 15 kV and a magnification of 2,000 to 10,000 times depending on the thickness of the Fe-based plating layer. By multiplying the average value by the specific gravity of iron, it is converted into the amount of adhesion per one side of the Fe-based plating layer.
  • SEM scanning electron microscope
  • Fe-based electroplating layers include Fe-B alloy, Fe-C alloy, Fe-P alloy, Fe-N alloy, Fe-O alloy, Fe-Ni alloy, Fe-Mn alloy, Fe- An alloy plating layer such as Mo alloy or Fe-W alloy can be used.
  • the composition of the Fe-based electroplated layer is not particularly limited, but 1 selected from the group consisting of B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co.
  • the composition contains two or more elements in a total of 10% by mass or less, with the remainder consisting of Fe and unavoidable impurities.
  • the C content is preferably 0.08% by mass or less.
  • the tensile strength of the galvanized steel sheet according to one embodiment of the present invention is 780 MPa or more.
  • the yield stress (YS), yield ratio (YR), total elongation (El), critical hole expansion ratio ( ⁇ ), and critical spacer in the U-bending + close-contact bending test of the zinc-based plated steel sheet according to an embodiment of the present invention The reference values for the thickness (ST) and the stroke at maximum load (SFmax) in the V-bending + orthogonal VDA bending test, and the presence or absence of fracture (appearance cracking) in the axial crushing test are as described above.
  • tensile strength (TS), yield stress (YS), yield ratio (YR), and total elongation (El) are measured by a tensile test based on JIS Z 2241, which will be described later in Examples.
  • the critical hole expansion rate ( ⁇ ) is measured by a hole expansion test based on JIS Z 2256, which will be described later in Examples.
  • the critical spacer thickness (ST) is measured by the U-bending + close-contact bending test described later in Examples.
  • the stroke (SFmax) at maximum load in the V-bending + orthogonal VDA bending test is measured by the V-bending + orthogonal VDA bending test described later in the Examples.
  • the presence or absence of fracture (appearance cracking) in the axial crushing test is determined by the axial crushing test described later in Examples.
  • Galvanized layer (second plating layer)
  • a galvanized steel sheet according to an embodiment of the present invention has a galvanized layer formed on a base steel sheet (on the surface of the base steel sheet or on the surface of the metal plating layer if a metal plating layer is formed), and The plating layer may be provided only on one surface of the base steel plate, or may be provided on both surfaces. That is, the steel sheet of the present invention has a base steel plate, and a second plating layer (a galvanized layer, an aluminum plating layer, etc.) may be formed on the base steel plate.
  • a metal plating layer (a first plating layer (excluding the second plating layer of the galvanized layer)) and a second plating layer (a zinc plating layer, an aluminum plating layer, etc.) may be formed in this order on the base steel sheet.
  • the galvanized layer here refers to a plating layer containing Zn as a main component (Zn content is 50.0% or more), and includes, for example, a hot-dip galvanized layer and an alloyed hot-dip galvanized layer.
  • the hot-dip galvanized layer is preferably composed of, for example, Zn, 20.0% by mass or less of Fe, and 0.001% by mass or more and 1.0% by mass or less of Al.
  • the hot-dip galvanized layer may optionally include one selected from the group consisting of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and REM.
  • the total content of a species or two or more elements may be 0.0% by mass or more and 3.5% by mass or less.
  • the Fe content of the hot-dip galvanized layer is more preferably less than 7.0% by mass. Note that the remainder other than the above elements are unavoidable impurities.
  • the alloyed hot-dip galvanized layer is preferably composed of, for example, 20% by mass or less of Fe and 0.001% by mass or more and 1.0% by mass or less of Al. Additionally, the alloyed hot-dip galvanized layer may optionally be selected from the group consisting of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and REM. One or more types of elements may be contained in a total amount of 0% by mass or more and 3.5% by mass or less.
  • the Fe content of the alloyed hot-dip galvanized layer is more preferably 7.0% by mass or more, and still more preferably 8.0% by mass or more. Further, the Fe content of the alloyed hot-dip galvanized layer is more preferably 15.0% by mass or less, still more preferably 12.0% by mass or less. Note that the remainder other than the above elements are unavoidable impurities.
  • the amount of plating deposited on one side of the galvanized layer is not particularly limited, but is preferably 20 g/m 2 or more and 80 g/m 2 or less.
  • the plating adhesion amount of the galvanized layer is measured as follows. That is, a treatment solution is prepared by adding 0.6 g of a corrosion inhibitor for Fe (Ivit 700BK (registered trademark) manufactured by Asahi Chemical Co., Ltd.) to 1 L of a 10% by mass hydrochloric acid aqueous solution. Next, a galvanized steel sheet serving as a test material is immersed in the treatment liquid to dissolve the galvanized layer. Then, by measuring the amount of mass loss of the test material before and after melting, and dividing that value by the surface area of the base steel sheet (the surface area of the part covered with plating), the amount of plating coating (g/m 2 ) is calculated.
  • a corrosion inhibitor for Fe Ivit 700BK (registered trademark) manufactured by Asahi Chemical Co., Ltd.
  • the thickness of the galvanized steel sheet according to an embodiment of the present invention is not particularly limited, but is preferably 0.5 mm or more. Further, the thickness of the galvanized steel sheet is preferably 3.5 mm or less.
  • the method for producing a galvanized steel sheet of the present invention includes a hot rolling process in which a steel slab having the above-mentioned composition is hot-rolled at a finish rolling temperature of 820°C or higher to obtain a hot-rolled steel sheet; A temperature raising step in which the steel plate after the hot rolling step is heated in a temperature range of 350°C or more and 600°C or less at an average heating rate of 7°C/sec or more, an annealing temperature: 750°C or more and 900°C or less, Annealing time: Annealing under the conditions of 20 seconds or more, and after the annealing step, the average cooling rate from (annealing temperature -30°C) to 650°C is 7°C/second or more, and from 650°C to 500°C.
  • a tension of 2.0 kgf/mm 2 or more is applied to the steel sheet in a temperature range of 300°C or higher and 450°C or lower, and then the galvanized steel sheet is rolled by 1/4 of a roll with a diameter of 500 mm or more and 1500 mm or less per pass.
  • a second cooling step is performed in which the galvanized steel sheet is passed through 5 passes or more while being in contact with the surrounding area, and then cooled from room temperature to a cooling stop temperature of 250°C or less.
  • the method of melting the steel material is not particularly limited, and any known melting method such as a converter or an electric furnace is suitable.
  • the steel slab (slab) is preferably manufactured by a continuous casting method, but it is also possible to manufacture it by an ingot method, a thin slab casting method, or the like.
  • the steel slab is charged into a heating furnace as a hot piece without being cooled to room temperature, or it is slightly heat-retained. Energy-saving processes such as direct rolling and direct rolling, which involve rolling immediately after rolling, can also be applied without problems.
  • the slab heating temperature is preferably 1100° C. or higher from the viewpoint of dissolving carbides and reducing rolling load. Further, in order to prevent an increase in scale loss, the slab heating temperature is preferably 1300° C. or lower. Note that the slab heating temperature is the temperature of the slab surface. In addition, slabs are roughly rolled into sheet bars under normal conditions, but if the heating temperature is lower, from the perspective of preventing trouble during hot rolling, a bar heater etc. is used to roll the slabs into sheets before finishing rolling. Preferably, the bar is heated.
  • Finish rolling temperature 820°C or higher Finish rolling increases the rolling load and the reduction rate in the non-recrystallized state of austenite, which develops an abnormal structure that is elongated in the rolling direction, resulting in poor ductility and holes in the final material. Decreases spreadability and bendability. For this reason, the finish rolling temperature is set to 820°C or higher.
  • the finish rolling temperature is preferably 830°C or higher, more preferably 850°C or higher. Further, the finish rolling temperature is preferably 1080°C or lower, more preferably 1050°C or lower.
  • the coiling temperature after hot rolling is not particularly limited, but it is necessary to consider the case where the ductility, hole expandability, and bendability of the final material are reduced. For this reason, the coiling temperature after hot rolling is preferably 300°C or higher. Further, the coiling temperature after hot rolling is preferably 700°C or less.
  • the rough rolled plates may be joined together during hot rolling and finish rolling may be performed continuously. Alternatively, the rough rolled plate may be wound up once. Further, in order to reduce the rolling load during hot rolling, part or all of the finish rolling may be performed as lubricated rolling. Performing lubricated rolling is also effective from the viewpoint of uniformity of the shape of the steel sheet and uniformity of material quality. Note that the friction coefficient during lubricated rolling is preferably in the range of 0.10 or more and 0.25 or less.
  • pickling process The hot rolled steel sheet produced as described above may be pickled. Since pickling can remove oxides on the surface of the steel sheet, it can be carried out to ensure good chemical conversion treatment properties and plating quality in the final high-strength steel sheet. Further, the pickling may be carried out once or may be carried out in multiple steps.
  • the hot-rolled pickled plate or hot-rolled steel plate obtained as described above is subjected to cold rolling, if necessary.
  • the pickled plate may be cold rolled after hot rolling, or cold rolling may be performed after heat treatment. Further, optionally, the cold rolled steel sheet obtained after cold rolling may be pickled.
  • Cold rolling is performed, for example, by multi-pass rolling that requires two or more passes, such as tandem multi-stand rolling or reverse rolling.
  • cold rolling reduction rate 20% or more and 80% or less
  • the cold rolling reduction rate (cumulative reduction rate) is not particularly limited, but should be 20% or more and 80% or less. It is preferable. If the rolling reduction ratio in cold rolling is less than 20%, the steel structure tends to become coarse and non-uniform in the annealing process, and there is a risk that the TS and bendability of the final product will deteriorate. On the other hand, if the rolling reduction ratio in cold rolling exceeds 80%, the steel sheet tends to be defective in shape, and the amount of zinc plating deposited may become uneven.
  • Metal plating (metal electroplating, first plating) process
  • metal plating is applied to one or both sides of the steel plate after the hot rolling process (or after the cold rolling process if cold rolling is performed) and before the temperature raising process.
  • the method may include a first plating step of forming a plating layer (first plating layer).
  • first plating layer the surface of the hot-rolled steel sheet or cold-rolled steel sheet obtained as described above may be subjected to a metal electroplating treatment to obtain a pre-annealed metal electroplated steel sheet in which a pre-annealed metal electroplating layer is formed on at least one side.
  • the metal plating mentioned here excludes zinc plating (secondary plating).
  • the metal electroplating method is not particularly limited, but as described above, it is preferable that the metal electroplating layer is formed on the base steel sheet, so it is preferable to perform the metal electroplating process.
  • a sulfuric acid bath, a hydrochloric acid bath, or a mixture of both can be used in the Fe-based electroplating bath.
  • the amount of deposited metal electroplating layer before annealing can be adjusted by adjusting the current application time and the like.
  • pre-annealed metal electroplated steel sheet means that the metal electroplated layer has not undergone an annealing process, and refers to a hot rolled steel sheet before metal electroplating, a pickled sheet after hot rolling, or a cold rolled steel sheet that has been annealed in advance. This does not exclude such aspects.
  • the metal species of the electroplating layer include Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Any of Rt, Au, Hg, Ti, Pb, and Bi may be used, but Fe is more preferable, so a method for producing Fe-based electroplating will be described below.
  • the Fe ion content in the Fe-based electroplating bath before the start of current application is preferably 0.5 mol/L or more as Fe 2+ . If the Fe ion content in the Fe-based electroplating bath is 0.5 mol/L or more as Fe 2+ , a sufficient amount of Fe deposition can be obtained. Further, in order to obtain a sufficient amount of Fe deposited, it is preferable that the Fe ion content in the Fe-based electroplating bath before the start of current application is 2.0 mol/L or less.
  • the Fe-based electroplating bath contains Fe ions and at least one selected from the group consisting of B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co. It can contain one type of element.
  • the total content of these elements in the Fe-based electroplating bath is preferably such that the total content of these elements in the Fe-based electroplated layer before annealing is 10% by mass or less.
  • the metal element may be contained as a metal ion, and the non-metal element may be contained as a part of boric acid, phosphoric acid, nitric acid, organic acid, or the like.
  • the iron sulfate plating solution may contain a conductivity aid such as sodium sulfate or potassium sulfate, a chelating agent, or a pH buffer.
  • the temperature of the Fe-based electroplating solution is preferably 30° C. or higher, and preferably 85° C. or lower, in view of constant temperature retention.
  • the pH of the Fe-based electroplating bath is not particularly specified, it is preferably 1.0 or higher from the viewpoint of preventing a decrease in current efficiency due to hydrogen generation, and considering the electrical conductivity of the Fe-based electroplating bath, .0 or less is preferable.
  • the current density is preferably 10 A/dm 2 or more from the viewpoint of productivity, and preferably 150 A/dm 2 or less from the viewpoint of facilitating control of the amount of Fe-based electroplated layer deposited.
  • the plate passing speed is preferably 5 mpm or more from the viewpoint of productivity, and preferably 150 mpm or less from the viewpoint of stably controlling the amount of adhesion.
  • degreasing treatment and water washing can be performed to clean the steel sheet surface, and furthermore, pickling treatment and water washing can be performed to activate the steel sheet surface.
  • pickling treatment can be performed to activate the steel sheet surface.
  • Fe-based electroplating treatment is performed.
  • the method of degreasing and washing with water is not particularly limited, and ordinary methods can be used.
  • various acids such as sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof can be used. Among these, sulfuric acid, hydrochloric acid, or a mixture thereof is preferred.
  • the acid concentration is not particularly defined, it is preferably about 1 to 20 mass% in consideration of the ability to remove an oxide film and the prevention of rough skin (surface defects) due to overacid washing.
  • the pickling treatment liquid may contain an antifoaming agent, a pickling accelerator, a pickling inhibitor, and the like.
  • metal plating after the hot rolling process (if cold rolling is performed, after the cold rolling process, and/or if metal plating to form a metal plating layer (first plating layer) is performed, includes a temperature raising step of raising the temperature of the steel plate in a temperature range of 350° C. or higher and 600° C. or lower at an average heating rate of 7° C./sec or higher.
  • Average heating rate in the temperature range of 350°C to 600°C: 7°C/second or more by increasing the average heating rate in the temperature range of 350°C to 600°C, isolated fine particles within the ferrite grains By increasing the ratio of the island-like hard second phase (martensite + retained austenite), improvements in ⁇ , R/t, ST, and SFmax can be realized. Therefore, the average heating rate in the temperature range from 350°C to 600°C is 7°C/s or more. It is preferably 9°C/s or more.
  • the upper limit is not particularly limited, but the average heating rate in the temperature range from 350°C to 600°C is preferably 100°C/s or less, more preferably 90°C/s or less.
  • the average heating rate (°C/s) is calculated from (heating end temperature (°C) - heating start temperature (°C))/heating time (s).
  • One embodiment of the present invention includes an annealing step after the temperature raising step, in which annealing is performed at an annealing temperature of 750° C. or more and 900° C. or less and an annealing time of 20 seconds or more.
  • Annealing temperature 750°C or more and 900°C or less
  • the annealing temperature is set to 750°C or more and 900°C or less.
  • the annealing temperature is preferably 880°C or lower. Note that the annealing temperature is the highest temperature reached in the annealing step.
  • Annealing time 20 seconds or more
  • the annealing time is set to 20 seconds or more.
  • the annealing time is preferably 30 seconds or more, more preferably 50 seconds or more.
  • the upper limit of the annealing time is not particularly limited, the annealing time is preferably 900 seconds or less, more preferably 800 seconds or less.
  • the annealing time is the holding time in a temperature range of (annealing temperature -40° C.) or higher and lower than the annealing temperature. That is, in addition to the holding time at the annealing temperature, the annealing time also includes the residence time in the temperature range from (annealing temperature -40°C) to below the annealing temperature during heating and cooling before and after reaching the annealing temperature.
  • the number of times of annealing may be two or more times, but from the viewpoint of energy efficiency, one time is preferable.
  • Dew point of annealing process atmosphere ⁇ 30° C. or higher
  • the dew point of the annealing step atmosphere is ⁇ 30° C. or higher.
  • the dew point of the annealing atmosphere in the annealing step is more preferably -25°C or higher, even more preferably -15°C or higher, and most preferably -5°C or higher.
  • the annealing atmosphere in the annealing process should be set.
  • the dew point is preferably 30°C or lower.
  • the average cooling rate from (annealing temperature -30°C) to 650°C is 7°C/second or more, and the average cooling rate from 650°C to 500°C is 14°C/second or less. It includes a first cooling step of cooling.
  • Average cooling rate from (annealing temperature -30°C) to 650°C: 7°C/sec or more when cooling quickly in a high temperature range of 650°C or higher, fine austenite is left behind at the ferrite grain boundaries, resulting in the final The ratio of isolated fine island-like hard second phases (martensite + retained austenite) within ferrite grains increases. Therefore, the average cooling rate from (annealing temperature -30°C) to 650°C is 7°C/sec or more.
  • the average cooling rate from (annealing temperature -30°C) to 650°C is preferably 9°C/sec or more.
  • the average cooling rate from (annealing temperature -30°C) to 650°C is preferably 80°C/second or less, more preferably 60°C/second or less.
  • the average cooling rate (°C/s) is calculated from (annealing temperature (°C) - 30 (°C) - 650 (°C))/cooling time (s).
  • Average cooling rate from 650°C to 500°C 14°C/sec or less
  • fine austenite at the ferrite grain boundaries coalesce between adjacent ferrites with similar orientations. After that, it becomes one ferrite grain, and is left behind as a fine island-like austenite isolated within the ferrite grain, and finally the ratio of isolated fine island-like hard second phase (martensite + retained austenite) within the ferrite grain increases. Therefore, the average cooling rate from 650°C to 500°C is 14°C/second or less, preferably 12°C/second or less.
  • the average cooling rate from 650°C to 500°C is preferably 1°C/second or more, more preferably 2°C/second or more.
  • the average cooling rate (°C/s) is calculated from (650 (°C) - 500 (°C))/cooling time (s).
  • the steel sheet is galvanized to obtain a galvanized steel sheet.
  • the galvanizing treatment include hot-dip galvanizing and alloyed galvanizing.
  • hot-dip galvanizing it is preferable to immerse the steel sheet in a galvanizing bath at a temperature of 440° C. or higher and 500° C. or lower, and then adjust the coating amount by gas wiping or the like.
  • the hot-dip galvanizing bath is not particularly limited as long as it has the composition of the galvanized layer described above. It is preferable to use a plating bath having a composition comprising: and unavoidable impurities.
  • alloyed galvanizing treatment after hot-dip galvanizing treatment as described above, it is preferable to heat the hot-dip galvanized steel sheet to an alloying temperature of 450°C or more and 600°C or less to perform alloying treatment. . If the alloying temperature is less than 450° C., the Zn--Fe alloying speed will be slow and alloying may become difficult. On the other hand, when the alloying temperature exceeds 600°C, untransformed austenite transforms into pearlite, making it difficult to make the TS 780 MPa or higher. Note that the alloying temperature is more preferably 500°C or higher, and still more preferably 510°C or higher. Further, the alloying temperature is more preferably 570°C or lower.
  • the coating weight of the hot-dip galvanized steel sheet (GI) and the alloyed hot-dip galvanized steel sheet (GA) be 20 to 80 g/m 2 per side. Note that the amount of plating deposited can be adjusted by gas wiping or the like.
  • a tension of 2.0 kgf/mm2 or more is applied to the galvanized steel sheet in a temperature range of 300°C or higher and 450°C or lower, and the galvanized steel sheet is heated to a diameter of 500 mm or more per pass.
  • a second cooling step is included in which the material is passed through 5 passes or more while being brought into contact with a roll of 1500 mm or less for 1/4 rotation of the roll, and then cooled to a cooling stop temperature (second cooling stop temperature) of 250° C. or less.
  • a tension of 2.0 kgf/mm 2 or more is applied to the galvanized steel sheet at least once as described above.
  • most of the austenite becomes martensite through deformation (stress/strain)-induced transformation, and then undergoes tempering in the reheating process, which reduces the area ratio of fresh martensite in the final structure.
  • a suitable amount can be secured.
  • the amount of austenite immediately after the second cooling step can be reduced, and the volume fraction of retained austenite in the final structure can be reduced.
  • desired ⁇ , R/t, ST and SFmax are obtained.
  • the load cell must be placed parallel to the tension direction.
  • the load cell is preferably arranged at a position 200 mm from both ends of the roll.
  • the length of the roll used is preferably 1500 to 2500 mm.
  • this tension is preferably 2.2 kgf/mm 2 or more, more preferably 2.4 kgf/mm 2 or more.
  • the number of passes is preferably 15.0 kgf/mm 2 or less, more preferably 10.0 kgf/mm 2 or less.
  • the galvanized steel sheet is passed through a roll having a diameter of 500 mm or more and 1500 mm or less while being in contact with the roll for 1/4 rotation per pass: 5 passes or more
  • the galvanized steel sheet is passed through a roll having a diameter of 500 mm or more and 1500 mm or less.
  • Second cooling stop temperature 250°C or less
  • the cooling conditions for the second cooling step are not particularly limited, and may be according to a conventional method.
  • the cooling method for example, gas jet cooling, mist cooling, roll cooling, water cooling, air cooling, etc. can be applied.
  • an appropriate amount of austenite transforms into martensite and is then tempered in the reheating process, which reduces the area ratio of fresh martensite in the final structure.
  • an appropriate amount of tempered martensite can be secured.
  • the amount of austenite immediately after the second cooling step can be reduced, and the volume fraction of retained austenite in the final structure can be reduced. As a result, desired ⁇ , R/t, ST and SFmax are obtained.
  • the lower limit is not particularly limited, but it is preferably room temperature (-5°C or higher and 55°C or lower).
  • the average cooling rate is preferably, for example, 1° C./second or more and 50° C./second or less.
  • the galvanized steel sheet is reheated to a temperature range of above the cooling stop temperature (second cooling stop temperature) and below 440° C. and held for 20 seconds or more.
  • Reheating temperature Temperature range above the above cooling stop temperature (second cooling stop temperature) and below 440°C Reheating holding time: 20 seconds or more
  • reheating to above the cooling stop temperature (second cooling stop temperature) By holding the temperature for 20 seconds or more, diffusible hydrogen in the steel is released. Furthermore, the area ratio of fresh martensite in the final structure can be reduced, and an appropriate amount of tempered martensite can be secured. Further, the amount of austenite immediately after the second cooling step can be reduced, and the volume fraction of retained austenite in the final structure can be reduced. As a result, desired ⁇ , R/t, ST and SFmax are obtained.
  • the temperature is reheated to a temperature range from the second cooling stop temperature to 440° C. and held for 20 seconds or more.
  • the galvanized steel sheet obtained as described above may be further subjected to temper rolling. If the reduction ratio in temper rolling exceeds 2.00%, the yield stress will increase, and there is a risk that the dimensional accuracy when forming the galvanized steel sheet into a member will decrease. Therefore, the reduction ratio in temper rolling is preferably 2.00% or less.
  • the lower limit of the rolling reduction in skin pass rolling is not particularly limited, but from the viewpoint of productivity, it is preferably 0.05% or more.
  • skin pass rolling may be performed on a device that is continuous with the annealing device for performing each process mentioned above (online), or on a device that is discontinuous with the annealing device for performing each process (offline). You may go. Further, the number of times of temper rolling may be one, or two or more times. Note that rolling with a leveler or the like may be used as long as it can provide an elongation rate equivalent to that of temper rolling.
  • Conditions for other manufacturing methods are not particularly limited, but from the viewpoint of productivity, a series of treatments such as annealing, hot-dip galvanizing, and alloying treatment of galvanizing are performed on a CGL (Continuous Galvanizing Line), which is a hot-dip galvanizing line. It is preferable to carry out the process using Line). After hot-dip galvanizing, wiping can be performed to adjust the coating weight. Note that the conditions for plating and the like other than the above-mentioned conditions can be based on a conventional method for hot-dip galvanizing.
  • a member according to an embodiment of the present invention is a member made of (made of) the above-mentioned galvanized steel plate.
  • the material is a galvanized steel plate that is subjected to at least one of forming and joining processes to produce a member.
  • the above-mentioned galvanized steel sheet has a TS of 780 MPa or more, high YS and YR, excellent press formability (ductility, hole expandability, and bendability), and rupture resistance at the time of collision (bending fracture properties and axial crush properties). Therefore, the member according to one embodiment of the present invention has high strength and excellent impact resistance. Therefore, a member according to an embodiment of the present invention is particularly suitable for application as an impact energy absorbing member used in the automotive field.
  • a method for producing a member according to an embodiment of the present invention includes subjecting the above galvanized steel sheet (for example, a galvanized steel sheet produced by the above method for producing a galvanized steel sheet) to at least one of forming processing and joining processing. It has a process of making it into a member.
  • the molding method is not particularly limited, and for example, a general processing method such as press working can be used.
  • the joining method is not particularly limited, and for example, common welding such as spot welding, laser welding, arc welding, riveting joining, caulking joining, etc. can be used.
  • the molding conditions and bonding conditions are not particularly limited, and conventional methods may be followed.
  • a galvanized steel sheet comprising a base steel plate and a galvanized layer formed on the base steel plate, the base steel plate comprising: In mass%, C: 0.030% or more and 0.250% or less, Si: 0.01% or more and 0.75% or less, Mn: 2.00% or more and less than 3.50%, P: 0.001% or more and 0.100% or less, S: 0.0200% or less, Al: 0.010% or more and 2.000% or less, N: 0.0100% or less, , with the remainder consisting of Fe and unavoidable impurities;
  • Ferrite area ratio 20.0% or more and 80.0% or less
  • Fresh martensite area ratio 15.0% or less
  • Area ratio of retained austenite 3.0% or less
  • the component composition further includes, in mass%, Nb: 0.200% or less, Ti: 0.200% or less, V: 0.200% or less, B: 0.0100% or less, Cr: 1.000% or less, Ni: 1.000% or less, Mo: 1.000% or less, Sb: 0.200% or less, Sn: 0.200% or less, Cu: 1.000% or less, Ta: 0.100% or less, W: 0.500% or less, Mg: 0.0200% or less, Zn: 0.0200% or less, Co: 0.0200% or less, Zr: 0.1000% or less, Ca: 0.0200% or less, Se: 0.0200% or less, Te: 0.0200% or less, Ge: 0.0200% or less, As: 0.0500% or less, Sr: 0.0200% or less, Cs: 0.0200% or less, Hf: 0.0200% or less, Pb: 0.0200% or less,
  • the nanohardness of the plate surface at 1/4 of the depth in the thickness direction of the surface soft layer from the surface of the base steel sheet is 7.0 GPa or more is the total number of measurements at 1/4 of the depth in the thickness direction of the surface soft layer. 0.10 or less for the number
  • the standard deviation ⁇ of the nano-hardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface is 1.8 GPa or less
  • any one of [1] to [3] above, wherein the standard deviation ⁇ of nano-hardness of the plate surface at a position 1/2 the thickness direction depth of the surface soft layer from the base steel plate surface is 2.2 GPa or less.
  • Galvanized steel sheet described in Crab [5] The galvanized steel sheet according to any one of [1] to [4] above, which has a metal plating layer formed between the base steel sheet and the galvanized layer on one or both sides of the galvanized steel sheet. . [6] The galvanized steel sheet according to any one of [1] to [5], wherein the galvanized layer is a hot-dip galvanized layer or an alloyed hot-dip galvanized layer. [7] A member using the galvanized steel sheet according to any one of [1] to [6] above.
  • a galvanizing step is performed on the steel sheet to obtain a galvanized steel sheet; Applying a tension of 2.0 kgf/mm 2 or more to the galvanized steel sheet in a temperature range of 300 ° C. or higher and 450 ° C. or lower, Thereafter, the galvanized steel sheet is passed through 5 passes or more while being in contact with a roll having a diameter of 500 mm or more and 1500 mm or less for 1/4 rotation of the roll per pass, Then, a second cooling step of cooling to a cooling stop temperature of 250° C. or less; a reheating step of reheating the galvanized steel sheet to a temperature range from the cooling stop temperature to 440° C.
  • a method for manufacturing a galvanized steel sheet comprising a cold rolling step of cold rolling a previous steel sheet at a rolling reduction of 20% or more and 80% or less to obtain a cold rolled steel sheet.
  • the galvanized steel sheet according to [8] or [9] which includes a metal plating step of applying metal plating to form a metal plating layer on one or both sides of the galvanized steel sheet before the annealing step. manufacturing method.
  • a method for producing a member comprising the step of subjecting the galvanized steel sheet according to any one of [1] to [6] to at least one of forming and bonding to produce a member.
  • a steel material having the component composition shown in Table 1 (the remainder being Fe and unavoidable impurities) was melted in a converter and made into a steel slab using a continuous casting method.
  • Table 1 indicates the content at the inevitable impurity level.
  • the obtained steel slab was heated to 1200°C, and after heating, the steel slab was subjected to rough rolling and hot rolling to obtain a hot rolled steel plate. Then, the obtained hot rolled steel sheet No. 1 ⁇ No. 57 and no. 60 ⁇ No. No. 83 was pickled and cold rolled to obtain a cold rolled steel sheet having the thickness shown in Table 3. Moreover, No. of the obtained hot-rolled steel sheet. 57 ⁇ No. 59 and no. 84 ⁇ No. No. 91 was pickled to obtain a hot rolled steel plate (white skin) having the thickness shown in Table 3.
  • the obtained cold-rolled steel sheet or hot-rolled steel sheet (white skin) is subjected to treatments in a temperature raising step, an annealing step, a first cooling step, a plating step, a second cooling step, and a reheating step under the conditions shown in Table 2. Also, under the conditions shown in Table 4, a temperature raising process, a first plating process (metal plating process), an annealing process, a first cooling process, a second plating process (zinc plating process), a second cooling process and a re- A galvanized steel sheet was obtained by processing in a heating process.
  • a temperature raising process a first plating process (metal plating process), an annealing process, a first cooling process, a second plating process (zinc plating process), a second cooling process and a re- A galvanized steel sheet was obtained by processing in a heating process.
  • hot-dip galvanizing treatment or alloyed galvanizing treatment was performed to obtain a hot-dip galvanized steel sheet (hereinafter also referred to as GI) or an alloyed hot-dip galvanized steel sheet (hereinafter also referred to as GA).
  • GI hot-dip galvanized steel sheet
  • GA alloyed hot-dip galvanized steel sheet
  • Table 2 the types of plating processes are also indicated as "GI” and "GA”.
  • the alloying temperature is indicated as - because no alloying treatment is performed in the case of GI steel sheets.
  • the zinc plating bath temperature was 470° C. in both GI and GA production.
  • the amount of zinc plating deposited was 45 to 72 g/m 2 per side when manufacturing GI, and 45 g/m 2 per side when manufacturing GA.
  • the composition of the galvanized layer of the finally obtained hot-dip galvanized steel sheet contains, in GI, Fe: 0.1 to 1.0 mass%, Al: 0.2 to 0.33 mass%, The remainder was Zn and unavoidable impurities.
  • GA contained Fe: 8.0 to 12.0% by mass, Al: 0.1 to 0.23% by mass, and the remainder was Zn and inevitable impurities. Further, all galvanized layers were formed on both sides of the base steel sheet.
  • the method for measuring the surface soft layer is as follows. After smoothing the thickness section (L section) parallel to the rolling direction of the steel plate by wet polishing, using a Vickers hardness tester, the thickness was measured 100 ⁇ m from a position 1 ⁇ m in the thickness direction from the steel plate surface under a load of 10 gf. Measurements were made at 1 ⁇ m intervals up to the position. Thereafter, measurements were taken at intervals of 20 ⁇ m up to the center of the plate thickness. The area where the hardness has decreased to 85% or less compared to the hardness at 1/4 of the plate thickness is defined as a soft layer (surface soft layer), and the thickness of this area in the plate thickness direction is defined as the thickness of the soft layer. .
  • yield stress (YS), yield ratio (YR), total elongation (El), critical hole expansion rate ( ⁇ ), R/t in V-bending test, critical spacer thickness in U-bending + close contact bending test ( ST), the stroke at maximum load (SFmax) measured in the V-bending + orthogonal VDA bending test, and the presence or absence of fracture (appearance cracking) in the axial crushing test were evaluated.
  • ⁇ YS ⁇ (Passed) (A) If 780MPa ⁇ TS ⁇ 980MPa, 500MPa ⁇ YS (B) If 980MPa ⁇ TS, 600MPa ⁇ YS ⁇ (fail): (A) If 780MPa ⁇ TS ⁇ 980MPa, 500MPa>YS (B) If 980MPa ⁇ TS, 600MPa>YS
  • ⁇ YR ⁇ (Passed) (A) When 780MPa ⁇ TS ⁇ 980MPa, 0.64 ⁇ YR (B) If 980MPa ⁇ TS, 0.61 ⁇ YR ⁇ (fail): (A) If 780MPa ⁇ TS ⁇ 980MPa, 0.64>YR (B) If 980MPa ⁇ TS, 0.61>YR
  • ⁇ R/t ⁇ (Passed) (A) When 780MPa ⁇ TS ⁇ 980MPa, 2.0 ⁇ R/t (B) If 980MPa ⁇ TS, 2.5 ⁇ R/t ⁇ (fail): (A) When 780MPa ⁇ TS ⁇ 980MPa, 2.0 ⁇ R/t (B) When 980MPa ⁇ TS, 2.5 ⁇ R/t
  • Tensile test The tensile test was conducted in accordance with JIS Z 2241. That is, a JIS No. 5 test piece was taken from the obtained galvanized steel sheet so that the longitudinal direction was perpendicular to the rolling direction of the base steel sheet. Using the sampled test piece, a tensile test was conducted at a crosshead speed of 10 mm/min, and TS, YS, YR, and El were measured. The results are shown in Tables 3 and 5.
  • ⁇ is an index for evaluating stretch flangeability.
  • the results are shown in Tables 3 and 5.
  • ⁇ (%) ⁇ (D f - D 0 )/D 0 ⁇ 100 here, D f : Diameter of hole in test piece at the time of crack occurrence (mm) D 0 : Diameter of hole in initial test piece (mm) It is.
  • V bending test The V (90°) bending test was conducted in accordance with JIS Z 2248. A 100 mm x 35 mm test piece was taken from the obtained galvanized steel plate by shearing and end face grinding. Here, the 100 mm side is parallel to the width (C) direction.
  • Bending radius R Changes at 0.5mm pitch
  • Test method Die support, punch press molding load: 10 tons
  • Test speed 30mm/min Holding time: 5s
  • Bending direction Evaluation was performed three times in the direction perpendicular to rolling (C), and R/t was calculated by dividing the minimum bending radius (limit bending radius) R at which no cracks appeared in each case by the plate thickness t.
  • U-bending + close-contact bending test was conducted as follows. A 60 mm x 30 mm test piece was taken from the obtained galvanized steel sheet by shearing and end face grinding. Here, the 60 mm side is parallel to the width (C) direction. A test piece was prepared by performing U bending (primary bending) in the width (C) direction with the rolling (L) direction as the axis at a radius of curvature/plate thickness of 4.2. In the U-bending process (primary bending process), as shown in FIG. 2(a), a punch B1 was pushed into a steel plate placed on a roll A1 to obtain a test piece T1. Next, as shown in FIG.
  • test piece T1 placed on the lower mold A2 was subjected to close bending (secondary bending) by crushing it with the upper mold B2.
  • D1 indicates the width (C) direction
  • D2 indicates the rolling (L) direction. Note that a spacer S, which will be described later, was inserted between the test pieces.
  • the U-bending conditions in the U-bending + close contact bending test are as follows.
  • Test method Roll support, punch pushing Punch tip R: 5.0mm Clearance between roll and punch: plate thickness + 0.1mm Stroke speed: 10mm/min Bending direction: rolling perpendicular (C) direction
  • the conditions for close bending in the U-bending + close bending test are as follows.
  • Spacer thickness Changes at 0.5mm pitch
  • Test method Die support, punch press molding load: 10 tons
  • V-bending + orthogonal VDA bending test is performed as follows.
  • a 60 mm x 65 mm test piece was taken from the obtained galvanized steel plate by shearing and end face grinding. Here, the 60 mm side is parallel to the rolling (L) direction.
  • a test piece was prepared by performing a 90° bending process (primary bending process) in the rolling (L) direction with the width (C) direction as the axis at a radius of curvature/plate thickness of 4.2. In the 90° bending process (primary bending process), as shown in FIG.
  • a punch B3 was pushed into a steel plate placed on a die A3 having a V-groove to obtain a test piece T1.
  • the punch B4 is pushed into the test piece T1 placed on the support roll A4 so that the bending direction is perpendicular to the rolling direction (secondary bending). bending process).
  • D1 indicates the width (C) direction
  • D2 indicates the rolling (L) direction.
  • V-bending conditions in the V-bending + orthogonal VDA bending test are as follows. Test method: die support, punch press molding load: 10 tons Test speed: 30mm/min Holding time: 5s Bending direction: rolling (L) direction
  • VDA bending conditions in the V-bending + orthogonal VDA bending test are as follows. Test method: Roll support, punch pushing Roll diameter: ⁇ 30mm Punch tip R: 0.4mm Distance between rolls: (plate thickness x 2) + 0.5mm Stroke speed: 20mm/min Test piece size: 60mm x 60mm Bending direction: rolling right angle (C) direction
  • SFmax is an index for evaluating the fracture resistance at the time of a collision (the fracture resistance of a bending ridgeline portion in an axial crush test). The results are shown in Tables 3 and 5.
  • Axial crush test A 150 mm x 100 mm test piece was taken from the obtained galvanized steel sheet by shearing. Here, the 150 mm side is parallel to the rolling (L) direction. Using a mold with a punch shoulder radius of 5.0 mm and a die shoulder radius of 5.0 mm, the molding process (bending process) was performed to a depth of 40 mm. A hat-shaped member 10 shown in b) was produced. Further, a steel plate used as a material for the hat-shaped member was separately cut into a size of 80 mm x 100 mm. Next, the cut steel plate 20 and the hat-shaped member 10 were spot welded to produce a test member 30 as shown in FIGS. 4(a) and 4(b). FIG.
  • FIG. 4A is a front view of a test member 30 produced by spot welding the hat-shaped member 10 and the steel plate 20.
  • FIG. 4(b) is a perspective view of the test member 30.
  • the spot welds 40 were positioned so that the distance between the end of the steel plate and the weld was 10 mm, and the distance between the welds was 20 mm.
  • the test member 30 was joined to the base plate 50 by TIG welding to prepare a sample for an axial crush test.
  • the impactor 60 was made to collide with the produced sample for the axial crush test at a constant velocity of 10 mm/min, and the sample for the axial crush test was crushed by 70 mm.
  • the crushing direction D3 was parallel to the longitudinal direction of the test member 30. The results are shown in Tables 3 and 5.
  • the ground surface is the inside of the bend (valley side)
  • the ground surface is was set as the outside of the bend (peak side)
  • the ground surface was set as the inside of the bend (valley side) during the subsequent VDA bending test.
  • the U-bending + close bending test V-bending + orthogonal VDA bending test, and axial crushing test of galvanized steel sheets with a thickness of less than 1.2, the effects of the sheet thickness were small, so the tests were conducted without grinding.
  • ⁇ Nano hardness measurement> In order to obtain excellent bendability during press forming and excellent bending rupture properties during collision, it is necessary to place the base material at a position of 1/4 of the depth in the thickness direction and 1/2 of the depth in the thickness direction of the surface soft layer from the surface layer of the substrate.
  • nanohardness was measured at 300 or more points in a 50 ⁇ m x 50 ⁇ m area of the plate surface at each position, the nanohardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface was It is more preferable that the number of measurements of 7.0 GPa or more is 0.10 or less with respect to the total number of measurements at 1/4 position of the depth in the plate thickness direction.
  • the ratio of nanohardness of 7.0 GPa or more is 0.10 or less, it means that the ratio of hard structures (such as martensite) and inclusions is small. It becomes possible to further suppress the generation and connection of voids and the propagation of cracks during press molding and collisions, and excellent R/t and SFmax can be obtained.
  • the members obtained by forming or joining the steel sheets of the present invention example have tensile strength (TS), yield stress (YS), yield ratio (YR), Elongation (El), critical hole expansion rate ( ⁇ ), R/t in V-bending test, critical spacer thickness (ST) in U-bending + close bending test, and measured in V-bending + orthogonal VDA bending test
  • TS tensile strength
  • Yield stress Yield stress
  • YiR yield ratio
  • El Elongation
  • ⁇ critical hole expansion rate
  • ST critical spacer thickness
  • All of the strokes (SFmax) at the maximum load applied have the excellent characteristics characterized by the present invention, and there is no breakage (appearance cracking) in the axial crush test, and the excellent characteristics characterized by the present invention. I understand.
  • TS 780 MPa or more, high YS and YR, excellent press formability (ductility, hole expandability, and bendability), and rupture resistance properties at the time of collision (bending rupture properties and axial)
  • ductility, hole expandability, and bendability excellent press formability
  • rupture resistance properties at the time of collision bending rupture properties and axial

Abstract

The following are achieved: a TS of at least 780 MPa, a high YS and a high YR, an excellent press formability (ductility, hole expandability, and bendability), and excellent fracture resistance characteristics in impact (bending fracture characteristics and axial crushing characteristics).　The base steel sheet has a prescribed component composition, and the steel structure of the base steel sheet at a location 1/4 of the sheet thickness has prescribed ranges for ferrite, fresh martensite, retained austenite, bainite, tempered bainite, and tempered martensite. The value provided by dividing the sum of the area ratios of the isolated retained austenite islands and the isolated fresh martensite islands in the ferrite grains, by the sum of the area ratio of the fresh martensite and the volume ratio of the retained austenite, is at least 0.65. In addition, the average crystal grain diameter of the isolated retained austenite islands and the isolated fresh martensite islands in the ferrite grains is not more than 2.0 µm, and the amount of diffusible hydrogen contained in the base steel sheet is not more than 0.50 mass-ppm.

Description

亜鉛めっき鋼板、部材およびそれらの製造方法Galvanized steel sheets, members and their manufacturing methods
　本発明は、亜鉛めっき鋼板、該亜鉛めっき鋼板を素材とする部材およびそれらの製造方法に関する。 The present invention relates to galvanized steel sheets, members made from the galvanized steel sheets, and methods of manufacturing them.
　自動車車体に使用される鋼板の薄肉軽量化での燃費向上によるＣＯ２排出量の削減と、衝突安全性向上の両立を目的に、自動車用鋼板の高強度化が進められている。また、新たな法規制の導入も相次いでいる。そのため、車体強度の増加を目的として、自動車キャビンの骨格に組み付ける主要な構造部材や補強部材（以下、自動車の骨格構造部材などともいう）に対する高強度鋼板、とくに、引張強さ（以下、単にＴＳともいう）で７８０ＭＰａ以上の高強度鋼板の適用事例が増加している。また、自動車の骨格構造部材などに用いられる高強度鋼板には、プレス成形した際に、高い部材強度を有することが要求される。部品強度の上昇については、例えば、鋼板の降伏応力（以下、単にＹＳともいう）をＴＳで除した値の降伏比（以下、単にＹＲともいう）を高めることが有効である。これにより、自動車衝突時の衝撃吸収エネルギー（以下、単に衝撃吸収エネルギーともいう）が上昇する。さらに、自動車の骨格構造部材などのうち、例えば、クラッシュボックスなどは、曲げ加工部を有する。そのため、このような部品には、プレス成形性の観点から、高い曲げ性を有する鋼板を適用することが好ましい。また、車体防錆性能の観点から、自動車部材の素材となる鋼板には、亜鉛めっきが施されることが多い。そのため、高い強度を有することに加え、プレス成形性と耐衝撃特性に優れた溶融亜鉛めっき鋼板の開発が望まれている。 2. Description of the Related Art Progress is being made in increasing the strength of steel plates for automobiles, with the aim of reducing CO2 emissions by improving fuel efficiency by making the steel plates used in automobile bodies thinner and lighter, and improving collision safety. Additionally, new laws and regulations are being introduced one after another. Therefore, for the purpose of increasing the strength of the car body, high-strength steel plates are used for the main structural members and reinforcing members (hereinafter also referred to as automobile frame structural members) that are assembled into the frame of the car cabin. The number of applications of high-strength steel plates of 780 MPa or higher is increasing. Furthermore, high-strength steel plates used for automobile frame structural members and the like are required to have high member strength when press-formed. In order to increase the strength of parts, it is effective, for example, to increase the yield ratio (hereinafter also simply referred to as YR), which is the value obtained by dividing the yield stress (hereinafter also simply referred to as YS) of the steel plate by TS. As a result, the impact absorption energy (hereinafter also simply referred to as impact absorption energy) at the time of a car collision increases. Further, among automobile frame structural members, for example, a crash box has a bent portion. Therefore, from the viewpoint of press formability, it is preferable to use a steel plate having high bendability for such parts. In addition, from the viewpoint of anticorrosion performance of the car body, steel sheets used as materials for automobile parts are often galvanized. Therefore, it is desired to develop a hot-dip galvanized steel sheet that not only has high strength but also has excellent press formability and impact resistance.
　このような自動車部材の素材となる鋼板として、例えば、特許文献１には、質量％で表して、Ｃを０．０４～０．２２％、Ｓｉを１．０％以下、Ｍｎを３．０％以下、Ｐを０．０５％以下、Ｓを０．０１％以下、Ａｌを０．０１～０．１％及びＮを０．００１～０．００５％含有し、残部Ｆｅ及び不可避的不純物からなる成分組成を有するとともに、主相であるフェライト相と、第二相であるマルテンサイト相から構成され、かつマルテンサイト相の最大粒径が２μｍ以下で、その面積率が５％以上であることを特徴とする伸びフランジ性と耐衝突特性に優れた高強度鋼板が開示されている。 For example, in Patent Document 1, as a steel plate that is a material for such automobile parts, C is 0.04 to 0.22%, Si is 1.0% or less, and Mn is 3.0%. % or less, P is 0.05% or less, S is 0.01% or less, Al is 0.01-0.1%, and N is 0.001-0.005%, with the balance being Fe and unavoidable impurities. It is composed of a ferrite phase as a main phase and a martensite phase as a second phase, and the maximum grain size of the martensite phase is 2 μm or less and its area ratio is 5% or more. A high-strength steel plate with excellent stretch flangeability and collision resistance characteristics is disclosed.
　また、特許文献２には、表面層を厚さ０．１μｍ以上研削除去された冷延鋼板上にＮｉを０．２ｇ／ｍ２以上２．０ｇ／ｍ２以下プレめっきされた冷延鋼板の表面に溶融亜鉛めっき層を有する溶融亜鉛めっき鋼板であって、質量％で、Ｃ：０．０５％以上、０．４％以下、Ｓｉ：０．０１％以上、３．０％以下、Ｍｎ：０．１％以上、３．０％以下、Ｐ：０．０４％以下、Ｓ：０．０５％以下、Ｎ：０．０１％以下、Ａｌ：０．０１％以上、２．０％以下、Ｓｉ＋Ａｌ＞０．５％、を含有し、残部Ｆｅ及び不可避的不純物からなり、ミクロ組織が、体積分率で主相としてフェライトを４０％以上含有し、残留オーステナイトを８％以上、下記に規定する３種類のマルテンサイト［１］［２］［３］のマルテンサイト［３］を含む２種以上と１％以上のベイナイト及び０～１０％のパーライトを含有し、且つ、前記３種類のマルテンサイト［１］［２］［３］がそれぞれ、体積分率で、マルテンサイト［１］：０％以上、５０％以下、マルテンサイト［２］：０％以上、２０％未満、マルテンサイト［３］：１％以上、３０％以下、である鋼板の表面に、Ｆｅを７％未満含有し、残部がＺｎ、Ａｌおよび不可避的不純物からなる溶融亜鉛めっき層を有し、引張強度ＴＳ（ＭＰａ）、全伸び率ＥＬ（％）、穴拡げ率λ（％）としてＴＳ×ＥＬが１８０００ＭＰａ・％以上、ＴＳ×λが３５０００ＭＰａ・％以上であり、引張強度９８０ＭＰａ以上有することを特徴とするめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板（マルテンサイト［１］：Ｃ濃度（ＣＭ１）が０．８％未満で、硬さＨｖ１が、Ｈｖ１／（－９８２．１×ＣＭ１２＋１６７６×ＣＭ１＋１８９）≦０．６０、マルテンサイト［２］：Ｃ濃度（ＣＭ２）が０．８％以上で、硬さＨｖ２が、Ｈｖ２／（－９８２．１×ＣＭ２２＋１６７６×ＣＭ２＋１８９）≦０．６０、マルテンサイト［３］：Ｃ濃度（ＣＭ３）が０．８％以上で、硬さＨｖ３が、Ｈｖ３／（－９８２．１×ＣＭ３２＋１６７６×ＣＭ３＋１８９）≧０．８０が開示されている。 Furthermore, Patent Document 2 describes a cold-rolled steel sheet whose surface layer has been polished to a thickness of 0.1 μm or more and which is pre-plated with Ni at 0.2 g/m2 or more and 2.0 g/m2 or less . A hot-dip galvanized steel sheet having a hot-dip galvanized layer on the surface, in mass %, C: 0.05% or more and 0.4% or less, Si: 0.01% or more and 3.0% or less, Mn: 0.1% or more, 3.0% or less, P: 0.04% or less, S: 0.05% or less, N: 0.01% or less, Al: 0.01% or more, 2.0% or less, Contains Si + Al > 0.5%, the remainder consists of Fe and unavoidable impurities, the microstructure contains 40% or more of ferrite as the main phase in volume fraction, and 8% or more of retained austenite, as specified below. Containing two or more types of martensite [3] of three types of martensite [1], [2], and [3], 1% or more of bainite, and 0 to 10% of pearlite, and containing the three types of martensite [1], [2], and [3] are volume fractions, respectively: martensite [1]: 0% or more, 50% or less, martensite [2]: 0% or more, less than 20%, martensite [3] : 1% or more and 30% or less, and has a hot-dip galvanized layer containing less than 7% Fe, with the remainder consisting of Zn, Al and inevitable impurities, and has a tensile strength TS (MPa), Plating adhesion characterized by having a total elongation rate EL (%) and a hole expansion rate λ (%) of TS x EL of 18000 MPa % or more, TS x λ of 35000 MPa % or more, and a tensile strength of 980 MPa or more. High-strength hot-dip galvanized steel sheet with excellent formability (martensite [1]: C concentration (CM1) is less than 0.8%, hardness Hv1 is Hv1/(-982.1×CM1 2 +1676×CM1+189) ≦0.60, martensite [2]: C concentration (CM2) is 0.8% or more, hardness Hv2 is Hv2/(-982.1×CM2 2 +1676×CM2+189)≦0.60, martensite [3]: It is disclosed that the C concentration (CM3) is 0.8% or more and the hardness Hv3 is Hv3/(-982.1×CM3 2 +1676×CM3+189)≧0.80.
　また、特許文献３には、質量％で、Ｃ：０．１５％以上０．２５％以下、Ｓｉ：０．５０％以上２．５％以下、Ｍｎ：２．３％以上４．０％以下、Ｐ：０．１００％以下、Ｓ：０．０２％以下、Ａｌ：０．０１％以上２．５％以下、残部がＦｅおよび不可避的不純物からなる成分組成を有し、面積率で、焼戻しマルテンサイト相：３０％以上７３％以下、フェライト相：２５％以上６８％以下、残留オーステナイト相：２％以上２０％以下、他の相：１０％以下（０％を含む）であり、かつ、該他の相としてマルテンサイト相：３％以下（０％を含む）、ベイニティックフェライト相：５％未満（０％を含む）を有し、前記焼戻しマルテンサイト相の平均結晶粒径が８μｍ以下、前記残留オーステナイト相中のＣ量が０．７質量％未満である鋼板組織を有する高強度溶融亜鉛めっき鋼板が開示されている。 Furthermore, in Patent Document 3, in mass %, C: 0.15% or more and 0.25% or less, Si: 0.50% or more and 2.5% or less, Mn: 2.3% or more and 4.0% or less. , P: 0.100% or less, S: 0.02% or less, Al: 0.01% or more and 2.5% or less, with the balance consisting of Fe and unavoidable impurities. Martensite phase: 30% or more and 73% or less, ferrite phase: 25% or more and 68% or less, retained austenite phase: 2% or more and 20% or less, other phases: 10% or less (including 0%), and The other phases include martensitic phase: 3% or less (including 0%), bainitic ferrite phase: less than 5% (including 0%), and the average grain size of the tempered martensitic phase is 8 μm. The following discloses a high-strength hot-dip galvanized steel sheet having a steel sheet structure in which the amount of C in the retained austenite phase is less than 0.7% by mass.
　また、特許文献４には、鋼板の表面に合金化溶融亜鉛めっき層を備える合金化溶融亜鉛めっき鋼板であって、前記鋼板は、質量％で、Ｃ：０.０３％以上０.３５％以下、Ｓｉ：０.００５％以上２.０％以下、Ｍｎ：１.０％以上４.０％以下、Ｐ：０.０００４％以上０.１％以下、Ｓ：０.０２％以下、ｓｏｌ．Ａｌ：０.０００２％以上２.０％以下、Ｎ：０.０１％以下、残部Ｆｅおよび不純物からなる化学組成を有し、鋼板の表面から５０μｍの深さの位置における、圧延方向に展伸したＭｎおよび/またはＳｉが濃化した濃化部の圧延直角方向の平均間隔である濃化部平均間隔が１０００μｍ以下であり、鋼板の表面における深さ３μｍ以上１０μｍ以下のクラックの数密度が３個／ｍｍ以上１０００個／ｍｍ以下であり、面積％で、ベイナイト：６０％以上、残留オーステナイト：１％以上、マルテンサイト：１％以上、およびフェライト：２％以上２０％未満を含有するとともに、マルテンサイトおよび残留オーステナイトの最近接距離の平均値である超硬質相平均間隔が２０μｍ以下である鋼組織を有し、前記合金化溶融亜鉛めっき鋼板は、引張強さ（ＴＳ）が７８０ＭＰａ以上である機械特性を有することを特徴とする、合金化溶融亜鉛めっき鋼板が開示されている。 Further, Patent Document 4 discloses an alloyed hot-dip galvanized steel sheet having an alloyed hot-dip galvanized layer on the surface of the steel sheet, in which the steel sheet has a carbon content of 0.03% or more and 0.35% or less in mass %. , Si: 0.005% or more and 2.0% or less, Mn: 1.0% or more and 4.0% or less, P: 0.0004% or more and 0.1% or less, S: 0.02% or less, sol. It has a chemical composition consisting of Al: 0.0002% or more and 2.0% or less, N: 0.01% or less, and the balance is Fe and impurities, and is stretched in the rolling direction at a depth of 50 μm from the surface of the steel plate. The average spacing in the direction perpendicular to the rolling direction of the enriched regions where Mn and/or Si are concentrated is 1000 μm or less, and the number density of cracks with a depth of 3 μm or more and 10 μm or less on the surface of the steel sheet is 3 pieces/mm or more and 1000 pieces/mm or less, and contains bainite: 60% or more, retained austenite: 1% or more, martensite: 1% or more, and ferrite: 2% or more and less than 20%, and The alloyed hot-dip galvanized steel sheet has a steel structure in which the average distance between the ultrahard phases, which is the average value of the closest distance between martensite and retained austenite, is 20 μm or less, and the alloyed hot-dip galvanized steel sheet has a tensile strength (TS) of 780 MPa or more. An alloyed hot-dip galvanized steel sheet is disclosed that is characterized by mechanical properties.
特許第３８８７２３５号公報Patent No. 3887235 特許第５９５３６９３号公報Patent No. 5953693 特許第６０５２４７２号公報Patent No. 6052472 特許第５６９９７６４号公報Patent No. 5699764
　ところで、センターピラーに代表される自動車の骨格部材では、引張強度ＴＳ（以下単にＴＳとだけ記すこともある。）が５９０ＭＰａを超える鋼板の適用が進んでいるが、フロントサイドメンバーやリアサイドメンバーに代表される自動車の衝撃エネルギー吸収部材は、ＴＳが５９０ＭＰａ級の鋼板の適用に留まっているのが現状である。 Incidentally, steel plates with a tensile strength TS (hereinafter simply referred to as TS) exceeding 590 MPa are increasingly being used in automobile frame members such as center pillars, but this is typical for front side members and rear side members. Currently, impact energy absorbing members for automobiles are limited to steel plates with a TS of 590 MPa.
　すなわち、衝突時の吸収エネルギー（以下、衝撃吸収エネルギーともいう。）を高めるには、降伏応力ＹＳ（以下単にＹＳとだけ記すこともある。）および降伏比ＹＲ（以下単にＹＲとだけ記すこともある。）の向上が有効である。しかしながら、鋼板のＹＳおよびＹＲを高めると、一般的に、プレス成形性、特には、延性や穴広げ性、曲げ性といった特性が低下する。そのため、このようなＴＳおよびＹＳを高めた鋼板を前記した自動車の衝撃エネルギー吸収部材への適用を想定すると、単にプレス成形が難しくなるのみならず、衝突試験を模擬した軸圧壊試験で当該部材が割れてしまう、換言すれば、ＹＳの値から想定されるほどには実際の衝撃吸収エネルギーが高くならない。そのため、前記の衝撃エネルギー吸収部材は、ＴＳが５９０ＭＰａ級の鋼板の適用に留まっているのが現状である。 In other words, in order to increase the absorbed energy at the time of a collision (hereinafter also referred to as shock absorption energy), the yield stress YS (hereinafter sometimes simply referred to as YS) and the yield ratio YR (hereinafter simply referred to as YR) are ) is effective. However, when the YS and YR of a steel sheet are increased, press formability, particularly properties such as ductility, hole expandability, and bendability are generally reduced. Therefore, if we assume that a steel plate with high TS and YS is to be applied to the above-mentioned impact energy absorbing member of an automobile, it will not only be difficult to press-form, but also the member will be difficult to perform in an axial crush test simulating a crash test. In other words, the actual impact absorption energy is not as high as expected from the value of YS. Therefore, the current situation is that steel plates with a TS of 590 MPa are used as the above-mentioned impact energy absorbing members.
　実際、特許文献１～４に開示される鋼板も、ＴＳが７８０ＭＰａ以上であり、かつ、高いＹＳおよびＹＲと、優れたプレス成形性（延性、穴広げ性および曲げ性）と、衝突時の耐破断特性（曲げ破断特性および軸圧壊特性）を有するものとは言えない。 In fact, the steel sheets disclosed in Patent Documents 1 to 4 also have a TS of 780 MPa or more, high YS and YR, excellent press formability (ductility, hole expandability, and bendability), and impact resistance. It cannot be said that it has rupture properties (bending rupture properties and axial crush properties).
　本発明は、前記の現状に鑑み開発されたものであって、引張強度ＴＳが７８０ＭＰａ以上であり、かつ、高い降伏応力ＹＳおよび高い降伏比ＹＲと、優れたプレス成形性（延性、穴広げ性および曲げ性）と、衝突時の耐破断特性（曲げ破断特性および軸圧壊特性）を有する亜鉛めっき鋼板およびその製造方法を提供することを目的とする。
　また、本発明は、前記の亜鉛めっき鋼板を素材とする部材およびその製造方法を提供することを目的とする。 The present invention was developed in view of the above-mentioned current situation, and has a tensile strength TS of 780 MPa or more, a high yield stress YS, a high yield ratio YR, and excellent press formability (ductility, hole expandability). The object of the present invention is to provide a galvanized steel sheet having good properties (bending properties and bending properties) and fracture resistance upon collision (bending fracture properties and axial crushing properties), and a method for manufacturing the same.
Another object of the present invention is to provide a member made of the above-mentioned galvanized steel sheet and a method for manufacturing the same.
　なお、ここでいう亜鉛めっき鋼板とは、溶融亜鉛めっき鋼板（以下、ＧＩともいう）または合金化溶融亜鉛めっき鋼板（以下、ＧＡともいう）である。 Note that the galvanized steel sheet here refers to a hot-dip galvanized steel sheet (hereinafter also referred to as GI) or an alloyed hot-dip galvanized steel sheet (hereinafter also referred to as GA).
　また、ここで、引張強度ＴＳは、ＪＩＳ　Ｚ　２２４１に準拠する引張試験で測定される。
　また、降伏応力ＹＳおよび降伏比ＹＲが高いとは、ＪＩＳ　Ｚ　２２４１に準拠する引張試験で測定されるＹＳが、当該引張試験で測定されるＴＳに応じて、以下の（Ａ）または（Ｂ）式を満足することを指す。
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、５００ＭＰａ≦ＹＳ、且つ０．６４≦ＹＲ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、６００ＭＰａ≦ＹＳ、且つ０．６１≦ＹＲ Moreover, here, the tensile strength TS is measured by a tensile test based on JIS Z 2241.
In addition, high yield stress YS and yield ratio YR means that YS measured in a tensile test based on JIS Z 2241 is one of the following (A) or (B) depending on the TS measured in the tensile test. Indicates that the formula is satisfied.
(A) When 780MPa≦TS<980MPa, 500MPa≦YS and 0.64≦YR
(B) When 980MPa≦TS, 600MPa≦YS and 0.61≦YR
　また、延性に優れるとは、ＪＩＳ　Ｚ　２２４１に準拠する引張試験で測定される全伸び（Ｅｌ）が、当該引張試験で測定されるＴＳに応じて、以下の（Ａ）または（Ｂ）式を満足することを指す。
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、１９．０％≦Ｅｌ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、１５．０％≦Ｅｌ Furthermore, excellent ductility means that the total elongation (El) measured in a tensile test according to JIS Z 2241 is expressed by the following formula (A) or (B) depending on the TS measured in the tensile test. Refers to being satisfied.
(A) When 780MPa≦TS<980MPa, 19.0%≦El
(B) When 980MPa≦TS, 15.0%≦El
　また、穴広げ性に優れるとは、ＪＩＳ　Ｚ　２２５６に準拠する穴広げ試験で測定される限界穴広げ率（λ）が３０％以上であることを指す。 In addition, "excellent hole expansion property" refers to a critical hole expansion rate (λ) of 30% or more measured in a hole expansion test based on JIS Z 2256.
　また、曲げ性に優れるとは、ＪＩＳ　Ｚ　２２４８に準拠するＶ曲げ試験で測定されるＲ（限界曲げ半径）／ｔ（板厚）がＴＳに応じて、以下の（Ａ）または（Ｂ）式を満足することを指す。
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２．０≧Ｒ／ｔ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、２．５≧Ｒ／ｔであることを指す。 In addition, excellent bendability means that R (limit bending radius)/t (plate thickness) measured in a V-bending test based on JIS Z 2248 is expressed by the following formula (A) or (B) depending on the TS. It refers to satisfying the following.
(A) When 780MPa≦TS<980MPa, 2.0≧R/t
(B) When 980 MPa≦TS, it means that 2.5≧R/t.
　また、軸圧壊特性に優れるとは、Ｕ曲げ＋密着曲げ曲げ試験での限界スペーサー厚さ（ＳＴ）がＴＳに応じて、以下の（Ａ）または（Ｂ）式を満足することを指す。
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２．５ｍｍ≧ＳＴ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、４．０ｍｍ≧ＳＴ Furthermore, "excellent axial crushing properties" means that the critical spacer thickness (ST) in the U-bending + close-contact bending test satisfies the following formula (A) or (B) depending on the TS.
(A) When 780MPa≦TS<980MPa, 2.5mm≧ST
(B) When 980MPa≦TS, 4.0mm≧ST
　さらに、軸圧壊特性に優れるとは、Ｖ曲げ＋直交ＶＤＡ曲げ試験で測定される荷重最大時のストローク（ＳＦｍａｘ）がＴＳに応じて、以下の（Ａ）または（Ｂ）式を満足することを指す。
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２８．０ｍｍ≦ＳＦｍａｘ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、２６．５ｍｍ≦ＳＦｍａｘ Furthermore, having excellent axial crushing characteristics means that the stroke at maximum load (SFmax) measured in the V-bending + orthogonal VDA bending test satisfies the following formula (A) or (B) depending on the TS. Point.
(A) When 780MPa≦TS<980MPa, 28.0mm≦SFmax
(B) When 980MPa≦TS, 26.5mm≦SFmax
　さらに、軸圧壊特性に優れるとは、軸圧壊試験後に破断（外観割れ）が、図４（ｂ）の下部２箇所の曲げ稜線部のＲ＝５.０ｍｍ、２００ｍｍの範囲内で１箇所以下であることを指す。 Furthermore, having excellent axial crushing properties means that after the axial crushing test, there is no more than one fracture (appearance crack) within the range of R = 5.0 mm and 200 mm at the lower two bending ridges in Figure 4(b). refers to something.
　また、曲げ破断特性に優れるとは、上記のＵ曲げ＋密着曲げ曲げ試験での限界スペーサー厚さ（ＳＴ）がＴＳに応じて、上記の（Ａ）または（Ｂ）式を満足すると共に、Ｖ曲げ＋直交ＶＤＡ曲げ試験で測定される荷重最大時のストローク（ＳＦｍａｘ）がＴＳに応じて、上記の（Ａ）または（Ｂ）式を満足することを指す。 Also, having excellent bending rupture properties means that the critical spacer thickness (ST) in the above U-bending + close-contact bending test satisfies the above formula (A) or (B) depending on the TS, and It means that the stroke at maximum load (SFmax) measured in the bending + orthogonal VDA bending test satisfies the above formula (A) or (B) depending on the TS.
　上記のＥｌ（延性）、λ（伸びフランジ性）およびＲ／ｔ（曲げ性）はプレス成形時の鋼板の成形のしやすさ（割れずにプレス成形するための成形の自由度）を示す特性である。一方、Ｕ曲げ＋密着曲げ試験は衝突試験での縦壁部の変形および破断挙動を模擬した試験であり、Ｕ曲げ＋密着曲げ試験で測定される限界スペーサー厚さ（ＳＴ）は、衝突時の自動車車体の鋼板および部材の割れにくさ（破断せずに衝撃エネルギーを吸収するための耐衝撃特性）を示す指標である。
また、Ｖ曲げ＋直交ＶＤＡ曲げ試験は衝突試験での曲げ稜線部の変形および破断挙動を模擬した試験であり、Ｖ曲げ＋直交ＶＤＡ曲げ試験で測定される荷重最大時のストローク（ＳＦｍａｘ）はエネルギー吸収部材の割れにくさを示す指標である。 The above El (ductility), λ (stretch flangeability), and R/t (bendability) are characteristics that indicate the ease of forming a steel plate during press forming (the degree of freedom in forming for press forming without cracking). It is. On the other hand, the U-bending + close bending test is a test that simulates the deformation and fracture behavior of the vertical wall part in a collision test, and the critical spacer thickness (ST) measured in the U-bending + close bending test is It is an index showing the resistance to cracking (impact resistance properties for absorbing impact energy without breaking) of steel plates and components of automobile bodies.
In addition, the V-bending + orthogonal VDA bending test is a test that simulates the deformation and fracture behavior of the bending ridge line part in a collision test, and the stroke (SFmax) at the maximum load measured in the V-bending + orthogonal VDA bending test is the energy This is an index showing the resistance of the absorbent member to cracking.
　本発明者らは、上記した課題を達成するために、鋭意検討を重ねた結果、以下の知見を得た。
（１）所定の成分で、焼戻しマルテンサイトの面積率を１０．０％以上に制御し、フェライト粒界に接する島状硬質第二相（マルテンサイト＋残留オーステナイト）を低減し、フェライト粒内の孤立した微細な島状硬質第二相（マルテンサイト＋残留オーステナイト）の比率を増やすことで、７８０ＭＰａ以上のＴＳの確保が実現できる。
（２）所定の成分で、焼戻しマルテンサイトの面積率を１０．０％以上に制御し、フェライト粒界に接する島状硬質第二相（マルテンサイト＋残留オーステナイト）を低減することで、高いＹＳおよびＹＲの確保が実現できる。
（３）所定の成分で、フェライトの面積率を２０．０％以上に制御することで、（プレス成形性の一つのモードである張出し成形性と相関のある）延性の向上が実現できる。
（４）所定の成分で、フレッシュマルテンサイトの面積率を１５．０％以下、残留オーステナイトの面積率を３．０％以下、焼戻しマルテンサイトの面積率を１０．０％以上に制御し、フェライト粒内の孤立した微細な島状硬質第二相（マルテンサイト＋残留オーステナイト）の比率を増やすことで、プレス成形性の一つのモードである伸びフランジ性と相関のある穴広げ性の向上が実現できる。
（５）所定の成分で、フレッシュマルテンサイトの面積率を１５．０％以下、残留オーステナイトの面積率を３．０％以下、焼戻しマルテンサイトの面積率を１０．０％以上に制御し、フェライト粒内の孤立した微細な島状硬質第二相（マルテンサイト＋残留オーステナイト）の比率を増やすことで、プレス成形性の一つのモードである曲げ性の向上が実現できる。
（６）Ｓｉ：０．７５％以下および所定の成分で、残留オーステナイトの面積率を３．０％以下に制御することで、打ち抜き加工およびプレス成形などの一次加工時に生じる残留オーステナイトの加工誘起変態によって生成した硬いフレッシュマルテンサイトの生成を抑制し、その後の試験でボイドの生成および亀裂の進展を抑止することが可能である。さらに、焼戻しマルテンサイトの面積率を１０．０％以上に制御し、フェライト粒内の孤立した微細な島状硬質第二相（マルテンサイト＋残留オーステナイト）の比率を増やすことで、衝突時の自動車車体の鋼板および部材の耐衝撃特性の指標である、衝突試験での縦壁部の変形および破断挙動を模擬したＵ曲げ＋密着曲げ試験で測定される限界スペーサー厚さ（ＳＴ）、衝突試験での曲げ稜線部の変形および破断挙動を模擬したＶ曲げ＋直交ＶＤＡ曲げ試験で測定される荷重最大時のストローク（ＳＦｍａｘ）の向上が実現できる。 In order to achieve the above-described problems, the present inventors have made extensive studies and have obtained the following knowledge.
(1) With the specified ingredients, the area ratio of tempered martensite is controlled to 10.0% or more, the island-like hard second phase (martensite + retained austenite) in contact with the ferrite grain boundaries is reduced, and the area ratio within the ferrite grains is reduced. By increasing the ratio of the isolated fine island-like hard second phase (martensite + retained austenite), it is possible to secure a TS of 780 MPa or more.
(2) By controlling the area ratio of tempered martensite to 10.0% or more with the specified ingredients and reducing the island-like hard second phase (martensite + retained austenite) in contact with the ferrite grain boundaries, high YS and YR can be secured.
(3) By controlling the area ratio of ferrite to 20.0% or more using a predetermined component, it is possible to improve ductility (correlated with stretch formability, which is one mode of press formability).
(4) With predetermined components, control the area ratio of fresh martensite to 15.0% or less, the area ratio of retained austenite to 3.0% or less, and the area ratio of tempered martensite to 10.0% or more, and By increasing the ratio of isolated fine island-like hard second phases (martensite + retained austenite) within the grains, it is possible to improve hole expandability, which is correlated with stretch flangeability, which is one mode of press formability. can.
(5) With predetermined ingredients, control the area ratio of fresh martensite to 15.0% or less, the area ratio of retained austenite to 3.0% or less, and the area ratio of tempered martensite to 10.0% or more, and By increasing the ratio of isolated fine island-like hard second phases (martensite + retained austenite) within the grains, bendability, which is one mode of press formability, can be improved.
(6) By controlling the area ratio of retained austenite to 3.0% or less with Si: 0.75% or less and a predetermined component, processing-induced transformation of retained austenite that occurs during primary processing such as punching and press forming It is possible to suppress the generation of hard fresh martensite generated by the process, and to suppress the generation of voids and the propagation of cracks in subsequent tests. Furthermore, by controlling the area ratio of tempered martensite to 10.0% or more and increasing the ratio of the isolated fine island-like hard second phase (martensite + retained austenite) within the ferrite grains, the The critical spacer thickness (ST) measured in a U-bending + close bending test that simulates the deformation and fracture behavior of vertical walls in a crash test, which is an indicator of the impact resistance properties of steel plates and components of a car body, It is possible to improve the stroke at maximum load (SFmax) measured by a V-bending + orthogonal VDA bending test that simulates the deformation and fracture behavior of the bending ridge line.
　本開示は、上記知見に基づいてなされたものである。すなわち、本開示の要旨構成は以下のとおりである。
［１］素地鋼板と、該素地鋼板の上に形成された亜鉛めっき層と、を備える、亜鉛めっき鋼板であって、前記素地鋼板は、
質量％で、
Ｃ：０．０３０％以上０．２５０％以下、
Ｓｉ：０．０１％以上０．７５％以下、
Ｍｎ：２．００％以上３．５０％未満、
Ｐ：０．００１％以上０．１００％以下、
Ｓ：０．０２００％以下、
Ａｌ：０．０１０％以上２．０００％以下、
Ｎ：０．０１００％以下、
を含有し、残部がＦｅおよび不可避的不純物からなる成分組成と、
前記素地鋼板の板厚１／４位置の組織として、
フェライトの面積率：２０．０％以上８０．０％以下であり、
フレッシュマルテンサイトの面積率：１５．０％以下であり、
残留オーステナイトの面積率：３．０％以下であり、
　フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの面積率の合計を、鋼板全体のフレッシュマルテンサイトの面積率と残留オーステナイトの面積率の合計で除した値：０．６５以上であり、
ベイナイトおよび焼戻しベイナイトの面積率：１０．０％以下であり、
焼戻しマルテンサイトの面積率：１０．０％以上７０．０％以下であり、
さらに、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの平均結晶粒径が２．０μｍ以下である鋼組織と、
を有し、
前記素地鋼板に含まれる拡散性水素量が０．５０質量ｐｐｍ以下であり、引張強さが７８０ＭＰａ以上である、亜鉛めっき鋼板。
［２］前記成分組成は、さらに、質量％で、
　　Ｎｂ：０．２００％以下、
　　Ｔｉ：０．２００％以下、
　　Ｖ：０．２００％以下、
　　Ｂ：０．０１００％以下、
　　Ｃｒ：１．０００％以下、
　　Ｎｉ：１．０００％以下、
　　Ｍｏ：１．０００％以下、
　　Ｓｂ：０．２００％以下、
　　Ｓｎ：０．２００％以下、
　　Ｃｕ：１．０００％以下、
　　Ｔａ：０．１００％以下、
　　Ｗ：０．５００％以下、
　　Ｍｇ：０．０２００％以下、
　　Ｚｎ：０．０２００％以下、
　　Ｃｏ：０．０２００％以下、
　　Ｚｒ：０．１０００％以下、
　　Ｃａ：０．０２００％以下、
　　Ｓｅ：０．０２００％以下、
　　Ｔｅ：０．０２００％以下、
　　Ｇｅ：０．０２００％以下、
　　Ａｓ：０．０５００％以下、
　　Ｓｒ：０．０２００％以下、
　　Ｃｓ：０．０２００％以下、
　　Ｈｆ：０．０２００％以下、
　　Ｐｂ：０．０２００％以下、
　　Ｂｉ：０．０２００％以下および
　　ＲＥＭ：０．０２００％以下
のうちから選ばれる少なくとも１種の元素を含有する、前記［１］に記載の亜鉛めっき鋼板。
［３］前記素地鋼板は、素地鋼板表面から板厚方向に２００μｍ以下の領域を表層とした際、
前記表層に、板厚１／４位置のビッカース硬さに対して、ビッカース硬さが８５％以下である表層軟質層を有し、
　前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置および板厚方向深さの１／２位置の夫々における板面の５０μｍ×５０μｍの領域において、３００点以上のナノ硬度を測定したとき、
前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度が７．０ＧＰａ以上の測定数割合が、前記表層軟質層の板厚方向深さの１／４位置の全測定数に対して０．１０以下であり、
さらに、前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度の標準偏差σが１．８ＧＰａ以下であり、
さらに、前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／２位置の板面のナノ硬度の標準偏差σが２．２ＧＰａ以下である、前記［１］または［２］に記載の亜鉛めっき鋼板。
［４］前記亜鉛めっき鋼板の片面または両面において、前記素地鋼板と前記亜鉛めっき層の間に形成された金属めっき層を有する、前記［１］または［２］に記載の亜鉛めっき鋼板。
［５］前記亜鉛めっき鋼板の片面または両面において、前記素地鋼板と前記亜鉛めっき層の間に形成された金属めっき層を有する、前記［３］に記載の亜鉛めっき鋼板。
［６］前記［１］または［２］に記載の亜鉛めっき鋼板を用いてなる、部材。
［７］前記［３］に記載の亜鉛めっき鋼板を用いてなる、部材。
［８］前記［４］に記載の亜鉛めっき鋼板を用いてなる、部材。
［９］前記［５］に記載の亜鉛めっき鋼板を用いてなる、部材。
［１０］前記［１］または［２］に記載の成分組成を有する鋼スラブに、
仕上げ圧延温度：８２０℃以上の条件で熱間圧延を施し、熱延鋼板を得る、熱間圧延工程と、
該熱間圧延工程後の鋼板に対して、３５０℃以上６００℃以下の温度域を平均加熱速度７℃／秒以上の条件で昇温する昇温工程と、
焼鈍温度：７５０℃以上９００℃以下、焼鈍時間：２０秒以上の条件で焼鈍する、焼鈍工程と、
前記焼鈍工程後、（前記焼鈍温度－３０℃）から６５０℃までの平均冷却速度を７℃／秒以上とし、６５０℃から５００℃までの平均冷却速度を１４℃／秒以下とする条件で冷却する第一冷却工程と、
前記第一冷却工程後、鋼板に亜鉛めっき処理を施し、亜鉛めっき鋼板を得る、亜鉛めっき工程と、
前記亜鉛めっき鋼板に対して、３００℃以上４５０℃以下の温度域で２．０ｋｇｆ／ｍｍ２以上の張力を付与し、
その後、前記亜鉛めっき鋼板を、１パス当たり直径５００ｍｍ以上１５００ｍｍ以下のロールにロール１／４周分接触させながら、５パス以上通過させ、
ついで、２５０℃以下の冷却停止温度まで冷却する、第二冷却工程と、
前記亜鉛めっき鋼板を、前記冷却停止温度以上４４０℃以下の温度域まで再加熱して２０秒以上保持する、再加熱工程と、を含み、あるいはさらに
前記熱延工程後、かつ前記昇温工程前の鋼板に、圧下率が２０％以上８０％以下である冷間圧延を施し、冷延鋼板を得る、冷間圧延工程を含む、亜鉛めっき鋼板の製造方法。
［１１］前記焼鈍工程における焼鈍を、露点：－３０℃以上の雰囲気下で行う、前記［１０］に記載の亜鉛めっき鋼板の製造方法。
［１２］前記焼鈍工程の前に、前記亜鉛めっき鋼板の片面または両面において、金属めっきを施し金属めっき層を形成する金属めっき工程を含む、前記［１０］に記載の亜鉛めっき鋼板の製造方法。
［１３］前記焼鈍工程の前に、前記亜鉛めっき鋼板の片面または両面において、金属めっきを施す工程を含む、前記［１１］に記載の亜鉛めっき鋼板の製造方法。
［１４］前記［１］または［２］に記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。
［１５］前記［３］に記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。
［１６］前記［４］に記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。
［１７］前記［５］に記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。 The present disclosure has been made based on the above findings. That is, the gist of the present disclosure is as follows.
[1] A galvanized steel sheet comprising a base steel plate and a galvanized layer formed on the base steel plate, the base steel plate comprising:
In mass%,
C: 0.030% or more and 0.250% or less,
Si: 0.01% or more and 0.75% or less,
Mn: 2.00% or more and less than 3.50%,
P: 0.001% or more and 0.100% or less,
S: 0.0200% or less,
Al: 0.010% or more and 2.000% or less,
N: 0.0100% or less,
, with the remainder consisting of Fe and unavoidable impurities;
As the structure at the 1/4 plate thickness position of the base steel plate,
Ferrite area ratio: 20.0% or more and 80.0% or less,
Fresh martensite area ratio: 15.0% or less,
Area ratio of retained austenite: 3.0% or less,
The value obtained by dividing the total area ratio of island-like fresh martensite and island-like retained austenite in the ferrite grains by the sum of the area ratio of fresh martensite and retained austenite in the entire steel sheet: 0.65 or more,
Area ratio of bainite and tempered bainite: 10.0% or less,
Area ratio of tempered martensite: 10.0% or more and 70.0% or less,
Furthermore, a steel structure in which the average crystal grain size of island-like fresh martensite and island-like retained austenite in the ferrite grains is 2.0 μm or less,
has
A galvanized steel sheet, wherein the amount of diffusible hydrogen contained in the base steel sheet is 0.50 mass ppm or less, and the tensile strength is 780 MPa or more.
[2] The component composition further includes, in mass%,
Nb: 0.200% or less,
Ti: 0.200% or less,
V: 0.200% or less,
B: 0.0100% or less,
Cr: 1.000% or less,
Ni: 1.000% or less,
Mo: 1.000% or less,
Sb: 0.200% or less,
Sn: 0.200% or less,
Cu: 1.000% or less,
Ta: 0.100% or less,
W: 0.500% or less,
Mg: 0.0200% or less,
Zn: 0.0200% or less,
Co: 0.0200% or less,
Zr: 0.1000% or less,
Ca: 0.0200% or less,
Se: 0.0200% or less,
Te: 0.0200% or less,
Ge: 0.0200% or less,
As: 0.0500% or less,
Sr: 0.0200% or less,
Cs: 0.0200% or less,
Hf: 0.0200% or less,
Pb: 0.0200% or less,
The galvanized steel sheet according to [1] above, containing at least one element selected from Bi: 0.0200% or less and REM: 0.0200% or less.
[3] When the base steel plate has an area of 200 μm or less in the thickness direction from the surface of the base steel plate as the surface layer,
The surface layer has a soft surface layer whose Vickers hardness is 85% or less with respect to the Vickers hardness at the 1/4 position of the plate thickness,
Nano hardness of 300 points or more in a 50 μm x 50 μm area of the plate surface at 1/4 position and 1/2 depth in the plate thickness direction of the surface soft layer from the surface of the base steel plate, respectively. When measuring,
The proportion of measurements where the nano-hardness of the plate surface at 1/4 of the depth in the thickness direction of the soft surface layer from the surface of the base steel sheet is 7.0 GPa or more is 1/4 of the depth in the thickness direction of the soft surface layer. 0.10 or less for the total number of measurements at 4 positions,
Furthermore, the standard deviation σ of the nano-hardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface is 1.8 GPa or less,
Further, according to [1] or [2] above, the standard deviation σ of the nano-hardness of the plate surface at a position 1/2 the thickness direction depth of the surface soft layer from the base steel plate surface is 2.2 GPa or less. galvanized steel sheet.
[4] The galvanized steel sheet according to [1] or [2], which has a metal plating layer formed between the base steel sheet and the galvanized layer on one or both sides of the galvanized steel sheet.
[5] The galvanized steel sheet according to [3] above, which has a metal plating layer formed between the base steel sheet and the galvanized layer on one or both sides of the galvanized steel sheet.
[6] A member using the galvanized steel sheet according to [1] or [2] above.
[7] A member using the galvanized steel sheet according to [3] above.
[8] A member made of the galvanized steel sheet according to [4] above.
[9] A member using the galvanized steel sheet according to [5] above.
[10] A steel slab having the composition described in [1] or [2] above,
A hot rolling process in which hot rolling is performed at a finish rolling temperature of 820°C or higher to obtain a hot rolled steel plate;
A heating step of raising the temperature of the steel plate after the hot rolling step in a temperature range of 350° C. or higher and 600° C. or lower at an average heating rate of 7° C./sec or higher;
An annealing step of annealing at an annealing temperature of 750°C or more and 900°C or less and an annealing time of 20 seconds or more;
After the annealing step, cooling under conditions such that the average cooling rate from (the annealing temperature -30°C) to 650°C is 7°C/second or more, and the average cooling rate from 650°C to 500°C is 14°C/second or less. a first cooling step,
After the first cooling step, a galvanizing step is performed on the steel sheet to obtain a galvanized steel sheet;
Applying a tension of 2.0 kgf/mm 2 or more to the galvanized steel sheet in a temperature range of 300 ° C. or higher and 450 ° C. or lower,
Thereafter, the galvanized steel sheet is passed through 5 passes or more while being in contact with a roll having a diameter of 500 mm or more and 1500 mm or less for 1/4 rotation of the roll per pass,
Then, a second cooling step of cooling to a cooling stop temperature of 250° C. or less;
a reheating step of reheating the galvanized steel sheet to a temperature range of not less than the cooling stop temperature and not more than 440° C. and holding it for 20 seconds or more, or further after the hot rolling step and before the temperature raising step. A method for producing a galvanized steel sheet, comprising a cold rolling step of cold rolling a steel sheet at a rolling reduction of 20% or more and 80% or less to obtain a cold rolled steel sheet.
[11] The method for producing a galvanized steel sheet according to [10] above, wherein the annealing in the annealing step is performed in an atmosphere with a dew point of -30°C or higher.
[12] The method for producing a galvanized steel sheet according to [10] above, including a metal plating step of applying metal plating to form a metal plating layer on one or both sides of the galvanized steel sheet before the annealing step.
[13] The method for manufacturing a galvanized steel sheet according to [11], which includes a step of applying metal plating to one or both sides of the galvanized steel sheet before the annealing step.
[14] A method for manufacturing a member, comprising the step of subjecting the galvanized steel sheet according to [1] or [2] to at least one of forming and bonding to produce a member.
[15] A method for producing a member, including the step of subjecting the galvanized steel sheet according to [3] above to at least one of forming and bonding to produce a member.
[16] A method for manufacturing a member, comprising the step of subjecting the galvanized steel sheet according to [4] above to at least one of forming and bonding to produce a member.
[17] A method for producing a member, comprising the step of subjecting the galvanized steel sheet according to [5] above to at least one of forming and bonding to produce a member.
　本発明によれば、引張強度ＴＳが７８０ＭＰａ以上であり、かつ、高い降伏応力ＹＳおよび降伏比ＹＲと、優れたプレス成形性（延性、穴広げ性および曲げ性）と、衝突時の耐破断特性（曲げ破断特性および軸圧壊特性）を有する亜鉛めっき鋼板が得られる。
　また、本発明の亜鉛めっき鋼板を素材とする部材は、高強度であり、かつ、優れたプレス成形性と耐衝撃特性を有するため、自動車の骨格部材および衝撃エネルギー吸収部材などに極めて有利に適用することができる。 According to the present invention, the tensile strength TS is 780 MPa or more, high yield stress YS and yield ratio YR, excellent press formability (ductility, hole expandability, and bendability), and rupture resistance at the time of collision. A galvanized steel sheet having the following properties (bending fracture properties and axial crush properties) is obtained.
In addition, the members made of the galvanized steel sheet of the present invention have high strength and excellent press formability and impact resistance, so they are extremely advantageously applicable to automobile frame members and impact energy absorbing members. can do.
本発明のＳＥＭ像の一例である（実施例の本発明例Ｎｏ．１３）。This is an example of a SEM image of the present invention (Invention Example No. 13 of Examples). （ａ）は実施例のＵ曲げ＋密着曲げ試験における、Ｕ曲げ加工（一次曲げ加工）を説明するための図である。（ｂ）は実施例のＵ曲げ＋密着曲げ試験における、密着曲げ加工（二次曲げ加工）を説明するための図である。(a) is a diagram for explaining the U-bending process (primary bending process) in the U-bending + close-contact bending test of the example. (b) is a diagram for explaining the close bending process (secondary bending process) in the U-bending + close bending test of the example. （ａ）は実施例のＶ曲げ＋直交ＶＤＡ曲げ試験における、Ｖ曲げ加工（一次曲げ加工）を説明するための図である。（ｂ）は実施例のＶ曲げ＋直交ＶＤＡ曲げ試験における、直交ＶＤＡ曲げ加工（二次曲げ加工）を説明するための図である。(a) is a diagram for explaining the V-bending process (primary bending process) in the V-bending + orthogonal VDA bending test of the example. (b) is a diagram for explaining the orthogonal VDA bending process (secondary bending process) in the V-bending + orthogonal VDA bending test of the example. （ａ）は実施例の軸圧壊試験をするために製造した、ハット型部材と、鋼板とをスポット溶接した試験用部材の正面図である。（ｂ）は図１（ｄ）に示す試験用部材の斜視図である。（ｃ）は実施例の軸圧壊試験を説明するための概略図である。(a) is a front view of a test member manufactured for carrying out an axial crush test of an example, in which a hat-shaped member and a steel plate are spot-welded. (b) is a perspective view of the test member shown in FIG. 1(d). (c) is a schematic diagram for explaining the axial crush test of the example.
　本発明を、以下の実施形態に基づき説明する。 The present invention will be explained based on the following embodiments.
［１．亜鉛めっき鋼板］
　本発明の亜鉛めっき鋼板は、素地鋼板と、該素地鋼板の表面上に形成された亜鉛めっき層と、を備える、亜鉛めっき鋼板であって、素地鋼板は、質量％で、Ｃ：０．０３０％以上０．２５０％以下、Ｓｉ：０．０１％以上０．７５％以下、Ｍｎ：２．００％以上３．５０％未満、Ｐ：０．００１％以上０．１００％以下、Ｓ：０．０２００％以下、Ａｌ：０．０１０％以上２．０００％以下、Ｎ：０．０１００％以下、を含有し、残部がＦｅおよび不可避的不純物からなる成分組成と、素地鋼板の板厚１／４位置の組織として、フェライトの面積率：２０．０％以上８０．０％以下であり、フレッシュマルテンサイトの面積率：１５．０％以下であり、残留オーステナイトの面積率：３．０％以下であり、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの面積率の合計をフレッシュマルテンサイトの面積率と残留オーステナイトの面積率の合計で除した値：０．６５以上であり、ベイナイトおよび焼戻しベイナイトの面積率：１０．０％以下であり、焼戻しマルテンサイトの面積率：１０．０％以上７０．０％以下であり、さらに、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの平均結晶粒径が２．０μｍ以下である鋼組織と、を有し、素地鋼板に含まれる拡散性水素量が０．５０質量ｐｐｍ以下であり、引張強さが７８０ＭＰａ以上である。 [1. Galvanized steel sheet]
The galvanized steel sheet of the present invention is a galvanized steel sheet comprising a base steel sheet and a galvanized layer formed on the surface of the base steel sheet, wherein the base steel sheet has a C: 0.030 in mass%. % or more and 0.250% or less, Si: 0.01% or more and 0.75% or less, Mn: 2.00% or more and less than 3.50%, P: 0.001% or more and 0.100% or less, S: 0 .0200% or less, Al: 0.010% or more and 2.000% or less, N: 0.0100% or less, with the balance consisting of Fe and unavoidable impurities, and the thickness of the base steel plate 1/ As the structure of the 4-position, the area ratio of ferrite is 20.0% or more and 80.0% or less, the area ratio of fresh martensite is 15.0% or less, and the area ratio of retained austenite is 3.0% or less. and the value obtained by dividing the total area ratio of island-like fresh martensite and island-like retained austenite in the ferrite grain by the sum of the area ratio of fresh martensite and retained austenite: 0.65 or more, and bainite The area ratio of tempered bainite is 10.0% or less, the area ratio of tempered martensite is 10.0% to 70.0%, and island-like fresh martensite and island-like residual It has a steel structure in which the average grain size of austenite is 2.0 μm or less, the amount of diffusible hydrogen contained in the base steel sheet is 0.50 mass ppm or less, and the tensile strength is 780 MPa or more.
　成分組成
　まず、本発明の一実施形態に従う亜鉛めっき鋼板の素地鋼板の成分組成について説明する。なお、成分組成における単位はいずれも「質量％」であるが、以下、特に断らない限り、単に「％」で示す。 Composition First, the composition of the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention will be described. Note that the units in the component compositions are all "mass %", but hereinafter, unless otherwise specified, they will simply be expressed as "%".
　Ｃ：０．０３０％以上０．２５０％以下
　Ｃは、焼戻しマルテンサイトやベイナイトおよび焼戻しベイナイトなどを適正量生成させて、７８０ＭＰａ以上のＴＳと、高いＹＳおよび高いＹＲを確保するために有効な元素である。ここで、Ｃ含有量が０．０３０％未満では、フェライトの面積率が増加して、ＴＳを７８０ＭＰａ以上とすることが困難になる。また、ＹＳおよびＹＲの低下も招く。一方、Ｃ含有量が０．２５０％を超えると、フレッシュマルテンサイトの面積率が増加し、ＴＳが過度に高くなり、Ｅｌが低下する。また、フレッシュマルテンサイトの面積率が増加し、Ｖ曲げ試験の曲げ性が低下し、所望のＲ／ｔ（プレス成形性）が得られない。さらに、残留オーステナイトの面積率が増加し、穴広げ試験で鋼板に打抜き加工を受けた時、Ｕ曲げ＋密着曲げ試験でＵ曲げ加工を受けた時、またはＶ曲げ＋直交ＶＤＡ試験でＶ曲げ加工を受けた時、残留オーステナイトの加工誘起変態によって生成した硬いフレッシュマルテンサイトが生成され、その後の試験でボイドの生成および亀裂の進展が生じ、所望のλ（プレス成形性）、ＳＴ（衝突時の耐破断特性）およびＳＦｍａｘ（衝突時の耐破断特性）が得られない。したがって、Ｃ含有量は、０．０３０％以上０．２５０％以下とする。Ｃ含有量は、好ましくは０．０５０％以上である。また、Ｃ含有量は、好ましくは０．１３０％以下である。 C: 0.030% or more and 0.250% or less C is an effective element for producing an appropriate amount of tempered martensite, bainite, tempered bainite, etc., and ensuring a TS of 780 MPa or more, high YS, and high YR. It is. Here, if the C content is less than 0.030%, the area ratio of ferrite increases and it becomes difficult to make the TS 780 MPa or more. It also causes a decrease in YS and YR. On the other hand, when the C content exceeds 0.250%, the area ratio of fresh martensite increases, TS becomes excessively high, and El decreases. Furthermore, the area ratio of fresh martensite increases, the bendability in the V-bending test decreases, and the desired R/t (press formability) cannot be obtained. Furthermore, the area ratio of retained austenite increases when the steel plate undergoes punching in the hole expansion test, U-bending in the U-bending + close bending test, or V-bending in the V-bending + orthogonal VDA test. During the test, hard fresh martensite is generated due to deformation-induced transformation of retained austenite, and in subsequent tests, voids are formed and cracks propagate, resulting in desired λ (press formability) and ST (at impact). fracture resistance) and SFmax (fracture resistance at the time of collision) cannot be obtained. Therefore, the C content is set to 0.030% or more and 0.250% or less. The C content is preferably 0.050% or more. Further, the C content is preferably 0.130% or less.
　Ｓｉ：０．０１％以上０．７５％以下
　Ｓｉは、焼鈍中および焼鈍後の冷却過程におけるフェライト変態を促進させる。すなわち、Ｓｉは、フェライトの面積率に影響する元素である。ここで、Ｓｉ含有量が０．０１％未満では、フェライトの面積率が減少し、延性が低下する。一方、Ｓｉ含有量が０．７５％超では、残留オーステナイトの体積率が増加し、穴広げ試験で鋼板に打抜き加工を受けた時、Ｕ曲げ＋密着曲げ試験でＵ曲げ加工を受けた時、および、Ｖ曲げ＋直交ＶＤＡ試験でＶ曲げ加工を受けた時、残留オーステナイトの加工誘起変態によって生成した硬いフレッシュマルテンサイトが生成され、その後の試験でボイドの生成および亀裂の進展が生じ、所望のλ、ＳＴおよびＳＦｍａｘが得られない。したがって、Ｓｉ含有量は、０．０１％以上０．７５％以下とする。Ｓｉ含有量は、好ましくは０．１０％以上である。また、Ｓｉ含有量は、好ましくは０．７０％以下である。 Si: 0.01% or more and 0.75% or less Si promotes ferrite transformation during annealing and during the cooling process after annealing. That is, Si is an element that affects the area ratio of ferrite. Here, if the Si content is less than 0.01%, the area ratio of ferrite decreases and ductility decreases. On the other hand, when the Si content exceeds 0.75%, the volume fraction of retained austenite increases, and when the steel plate is subjected to punching in the hole expansion test or U-bending in the U-bending + close bending test, When subjected to V-bending processing in the V-bending + orthogonal VDA test, hard fresh martensite is generated due to deformation-induced transformation of retained austenite, and in the subsequent test, void formation and crack propagation occur, resulting in the desired λ, ST and SFmax are not available. Therefore, the Si content is set to 0.01% or more and 0.75% or less. The Si content is preferably 0.10% or more. Further, the Si content is preferably 0.70% or less.
　Ｍｎ：２．００％以上３．５０％未満
　Ｍｎは、焼戻しマルテンサイト、ベイナイト、さらに焼戻しベイナイトなどの面積率を調整する元素である。ここで、Ｍｎ含有量が２．００％未満では、フェライトの面積率が増加して、ＴＳを７８０ＭＰａ以上とすることが困難になる。また、ＹＳおよびＹＲの低下も招く。一方、Ｍｎ含有量が３．５０％以上となると、マルテンサイト変態開始温度Ｍｓ（以下単に、Ｍｓ点又はＭｓともいう。）が低下し、第一冷却工程で生成するマルテンサイトが減少する。その結果、第二冷却工程で生成するフレッシュマルテンサイトが増加し、その後の再加熱工程で前記フレッシュマルテンサイトが十分に焼戻されず、フレッシュマルテンサイトの面積率が増加し、Ｖ曲げ試験の曲げ性が低下し、所望のＲ／ｔが得られない。したがって、Ｍｎ含有量は、２．００％以上３．５０％未満とする。Ｍｎ含有量は、好ましくは、２．２０％以上である。また、Ｍｎ含有量は、好ましくは３．００％以下である。 Mn: 2.00% or more and less than 3.50% Mn is an element that adjusts the area ratio of tempered martensite, bainite, and further tempered bainite. Here, if the Mn content is less than 2.00%, the area ratio of ferrite increases and it becomes difficult to make the TS 780 MPa or more. It also causes a decrease in YS and YR. On the other hand, when the Mn content is 3.50% or more, the martensite transformation start temperature Ms (hereinafter also simply referred to as the Ms point or Ms) decreases, and the martensite generated in the first cooling step decreases. As a result, the amount of fresh martensite generated in the second cooling process increases, and the fresh martensite is not sufficiently tempered in the subsequent reheating process, resulting in an increase in the area ratio of fresh martensite and the bending property of the V-bending test. decreases, and the desired R/t cannot be obtained. Therefore, the Mn content is set to 2.00% or more and less than 3.50%. The Mn content is preferably 2.20% or more. Further, the Mn content is preferably 3.00% or less.
　Ｐ：０．００１％以上０．１００％以下
　Ｐは、固溶強化の作用を有し、鋼板のＴＳおよびＹＳを上昇させる元素である。このような効果を得るため、Ｐ含有量を０．００１％以上にする。一方、Ｐ含有量が０．１００％を超えると、Ｐが旧オーステナイト粒界に偏析して粒界を脆化させる。そのため、Ｖ曲げ試験時、旧オーステナイト粒界に沿ってボイドの生成および亀裂の進展が生じ、所望のＲ／ｔが得られない。また、穴広げ試験で鋼板に打抜き加工を受けた時、Ｕ曲げ＋密着曲げ試験でＵ曲げ加工を受けた時、またはＶ曲げ＋直交ＶＤＡ試験でＶ曲げ加工を受けた時、旧オーステナイト粒界に沿ってボイドの生成および亀裂の進展が生じ、所望のλ、ＳＴおよびＳＦｍａｘが得られない。したがって、Ｐ含有量は、０．００１％以上０．１００％以下とする。Ｐ含有量は、好ましくは０．０３０％以下である。 P: 0.001% or more and 0.100% or less P is an element that has a solid solution strengthening effect and increases the TS and YS of the steel sheet. In order to obtain such an effect, the P content is set to 0.001% or more. On the other hand, when the P content exceeds 0.100%, P segregates at prior austenite grain boundaries and embrittles the grain boundaries. Therefore, during the V-bending test, voids are generated and cracks grow along the prior austenite grain boundaries, making it impossible to obtain the desired R/t. In addition, when a steel plate is punched in a hole expansion test, when it is subjected to U bending in a U bending + close bending test, or when it is subjected to V bending in a V bending + orthogonal VDA test, prior austenite grain boundaries Void generation and crack propagation occur along the curve, making it impossible to obtain the desired λ, ST, and SFmax. Therefore, the P content is set to 0.001% or more and 0.100% or less. The P content is preferably 0.030% or less.
　Ｓ：０．０２００％以下
　Ｓは、鋼中で硫化物として存在する。とくに、Ｓ含有量が０．０２００％を超えるとＶ曲げ試験時、前記硫化物を起点にボイドの生成および亀裂の進展が生じ、所望のＲ／ｔが得られない。また、穴広げ試験で鋼板に打抜き加工を受けた時、Ｕ曲げ＋密着曲げ試験でＵ曲げ加工を受けた時、またはＶ曲げ＋直交ＶＤＡ試験でＶ曲げ加工を受けた時、前記硫化物を起点にボイドの生成および亀裂の進展が生じ、所望のλ、ＳＴおよびＳＦｍａｘが得られない。したがって、Ｓ含有量は０．０２００％以下とする。Ｓ含有量は、好ましくは０．００８０％以下である。なお、Ｓ含有量の下限は特に規定しないが、生産技術上の制約から、Ｓ含有量は０．０００１％以上とすることが好ましい。 S: 0.0200% or less S exists as a sulfide in steel. In particular, when the S content exceeds 0.0200%, voids are generated and cracks propagate starting from the sulfides during the V-bending test, making it impossible to obtain the desired R/t. In addition, when a steel plate is punched in a hole expansion test, when it is subjected to a U-bending process in a U-bending + close bending test, or when it is subjected to a V-bending process in a V-bending + orthogonal VDA test, the sulfides are Void generation and crack growth occur at the starting point, making it impossible to obtain the desired λ, ST, and SFmax. Therefore, the S content is set to 0.0200% or less. The S content is preferably 0.0080% or less. Note that although the lower limit of the S content is not particularly specified, it is preferable that the S content is 0.0001% or more due to constraints on production technology.
　Ａｌ：０．０１０％以上２．０００％以下
　Ａｌは、焼鈍中および焼鈍後の冷却過程におけるフェライト変態を促進させる。すなわち、Ａｌは、フェライトの面積率に影響する元素である。ここで、Ａｌ含有量が０．０１０％未満では、フェライトの面積率が減少し、延性が低下する。一方、Ａｌ含有量が２．０００％を超えると、フェライトの面積率が過度に増加して、ＴＳを７８０ＭＰａ以上とすることが困難になる。また、ＹＳおよびＹＲの低下も招く。したがって、Ａｌ含有量は、０．０１０％以上２．０００％以下とする。Ａｌ含有量は、好ましくは、０．０１５％以上である。また、Ａｌ含有量は、好ましくは１．０００％以下である。 Al: 0.010% or more and 2.000% or less Al promotes ferrite transformation during annealing and during the cooling process after annealing. That is, Al is an element that affects the area ratio of ferrite. Here, if the Al content is less than 0.010%, the area ratio of ferrite decreases and ductility decreases. On the other hand, when the Al content exceeds 2.000%, the area ratio of ferrite increases excessively, making it difficult to make the TS 780 MPa or more. It also causes a decrease in YS and YR. Therefore, the Al content is set to 0.010% or more and 2.000% or less. Al content is preferably 0.015% or more. Further, the Al content is preferably 1.000% or less.
　Ｎ：０．０１００％以下
　Ｎは、鋼中で窒化物として存在する。特に、Ｎ含有量が０．０１００％を超えるとＶ曲げ試験時、前記窒化物を起点にボイドの生成および亀裂の進展が生じ、所望のＲ／ｔが得られない。また、穴広げ試験で鋼板に打抜き加工を受けた時、Ｕ曲げ＋密着曲げ試験でＵ曲げ加工を受けた時、またはＶ曲げ＋直交ＶＤＡ試験でＶ曲げ加工を受けた時、上記窒化物を起点にボイドの生成および亀裂の進展が生じ、所望のλ、ＳＴおよびＳＦｍａｘが得られない。したがって、Ｎ含有量は０．０１００％以下とする。また、Ｎ含有量は、好ましくは０．００５０％以下である。なお、Ｎ含有量の下限は特に規定しないが、生産技術上の制約から、Ｎ含有量は０．０００５％以上が好ましい。 N: 0.0100% or less N exists as a nitride in steel. In particular, if the N content exceeds 0.0100%, voids are generated and cracks propagate starting from the nitride during the V-bending test, making it impossible to obtain the desired R/t. In addition, when the steel plate was punched in the hole expansion test, when it was subjected to U bending in the U bending + close bending test, or when it was subjected to V bending in the V bending + orthogonal VDA test, the above nitrides were Voids are generated and cracks grow at the starting point, making it impossible to obtain the desired λ, ST, and SFmax. Therefore, the N content is set to 0.0100% or less. Further, the N content is preferably 0.0050% or less. Note that, although the lower limit of the N content is not particularly specified, it is preferable that the N content is 0.0005% or more due to constraints on production technology.
　以上、本発明の一実施形態に従う亜鉛めっき鋼板の素地鋼板の基本成分組成について説明したが、本発明の一実施形態に従う亜鉛めっき鋼板の素地鋼板は、上記基本成分を含有し、上記基本成分以外の残部はＦｅ（鉄）および不可避的不純物を含む成分組成を有する。ここで、本発明の一実施形態に従う亜鉛めっき鋼板の素地鋼板は、上記基本成分を含有し、残部はＦｅおよび不可避的不純物からなる成分組成を有することが好ましい。 The basic component composition of the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention has been explained above, but the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention contains the above-mentioned basic components and other than the above-mentioned basic components. The remainder has a composition containing Fe (iron) and unavoidable impurities. Here, it is preferable that the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention contains the above-mentioned basic components, with the remainder consisting of Fe and inevitable impurities.
　本発明の一実施形態に従う亜鉛めっき鋼板の素地鋼板には、上記基本成分に加え、以下に示す任意成分のうちから選択される少なくとも一種を含有させてもよい。なお、以下に示す任意成分は、以下で示す上限量以下で含有していれば、本発明の効果が得られるため、下限は特に設けない。なお、下記の任意元素を後述する好適な下限値未満で含む場合、当該元素は不可避的不純物として含まれるものとする。 In addition to the above basic components, the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention may contain at least one selected from the following optional components. Note that the effects of the present invention can be obtained for the optional components shown below as long as they are contained in amounts below the upper limit shown below, so no lower limit is set in particular. In addition, when the following arbitrary elements are contained below the preferable lower limit value mentioned later, the said elements shall be contained as an unavoidable impurity.
　Ｎｂ：０．２００％以下、Ｔｉ：０．２００％以下、Ｖ：０．２００％以下、Ｂ：０．０１００％以下、Ｃｒ：１．０００％以下、Ｎｉ：１．０００％以下、Ｍｏ：１．０００％以下、Ｓｂ：０．２００％以下、Ｓｎ：０．２００％以下、Ｃｕ：１．０００％以下、Ｔａ：０．１００％以下、Ｗ：０．５００％以下、Ｍｇ：０．０２００％以下、Ｚｎ：０．０２００％以下、Ｃｏ：０．０２００％以下、Ｚｒ：０．１０００％以下、Ｃａ：０．０２００％以下、Ｓｅ：０．０２００％以下、Ｔｅ：０．０２００％以下、Ｇｅ：０．０２００％以下、Ａｓ：０．０５００％以下、Ｓｒ：０．０２００％以下、Ｃｓ：０．０２００％以下、Ｈｆ：０．０２００％以下、Ｐｂ：０．０２００％以下、Ｂｉ：０．０２００％以下およびＲＥＭ：０．０２００％以下のうちから選ばれる少なくとも１種 Nb: 0.200% or less, Ti: 0.200% or less, V: 0.200% or less, B: 0.0100% or less, Cr: 1.000% or less, Ni: 1.000% or less, Mo: 1.000% or less, Sb: 0.200% or less, Sn: 0.200% or less, Cu: 1.000% or less, Ta: 0.100% or less, W: 0.500% or less, Mg: 0. 0200% or less, Zn: 0.0200% or less, Co: 0.0200% or less, Zr: 0.1000% or less, Ca: 0.0200% or less, Se: 0.0200% or less, Te: 0.0200% Below, Ge: 0.0200% or less, As: 0.0500% or less, Sr: 0.0200% or less, Cs: 0.0200% or less, Hf: 0.0200% or less, Pb: 0.0200% or less, At least one type selected from Bi: 0.0200% or less and REM: 0.0200% or less
　Ｎｂ：０．２００％以下
　Ｎｂは、熱間圧延時や焼鈍時に、微細な炭化物、窒化物または炭窒化物を形成することによって、ＴＳ、ＹＳおよびＹＲを上昇させる。このような効果を得るためには、Ｎｂ含有量を０．００１％以上とすることが好ましい。Ｎｂ含有量は、より好ましくは０．００５％以上である。一方、Ｎｂ含有量が０．２００％超えると、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験およびＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘ得られない場合がある。したがって、Ｎｂを含有させる場合、Ｎｂ含有量は０．２００％以下が好ましい。Ｎｂ含有量は、より好ましくは０．０６０％以下である。 Nb: 0.200% or less Nb increases TS, YS, and YR by forming fine carbides, nitrides, or carbonitrides during hot rolling or annealing. In order to obtain such an effect, it is preferable that the Nb content is 0.001% or more. The Nb content is more preferably 0.005% or more. On the other hand, if the Nb content exceeds 0.200%, large amounts of coarse precipitates and inclusions may be generated. In such cases, coarse precipitates and inclusions become starting points for voids and cracks during hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests, so that the desired λ , R/t, ST and SFmax may not be obtained. Therefore, when Nb is contained, the Nb content is preferably 0.200% or less. The Nb content is more preferably 0.060% or less.
　Ｔｉ：０．２００％以下
　Ｔｉは、Ｎｂと同様、熱間圧延時や焼鈍時に、微細な炭化物、窒化物または炭窒化物を形成することによって、ＴＳ、ＹＳおよびＹＲを上昇させる。このような効果を得るためには、Ｔｉ含有量を０．００１％以上とすることが好ましい。Ｔｉ含有量は、より好ましくは０．００５％以上である。一方、Ｔｉ含有量が０．２００％超えると、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験およびＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、したがって、Ｔｉを含有させる場合、Ｔｉ含有量は０．２００％以下が好ましい。Ｔｉ含有量は、より好ましくは０．０６０％以下である。 Ti: 0.200% or less Like Nb, Ti increases TS, YS, and YR by forming fine carbides, nitrides, or carbonitrides during hot rolling or annealing. In order to obtain such an effect, it is preferable that the Ti content is 0.001% or more. The Ti content is more preferably 0.005% or more. On the other hand, if the Ti content exceeds 0.200%, a large amount of coarse precipitates and inclusions may be formed. In such cases, coarse precipitates and inclusions become starting points for voids and cracks during hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests, so that the desired λ , R/t, ST and SFmax may not be obtained. Therefore, when Ti is contained, the Ti content is preferably 0.200% or less. The Ti content is more preferably 0.060% or less.
　Ｖ：０．２００％以下
　Ｖは、ＮｂやＴｉと同様、熱間圧延時や焼鈍時に、微細な炭化物、窒化物または炭窒化物を形成することによって、ＴＳおよびＹＳを上昇させる。このような効果を得るためには、Ｖ含有量を０．００１％以上とすることが好ましい。Ｖ含有量は、より好ましくは０．００５％以上である。Ｖ含有量は、０．０１０％以上であることがさらに好ましく、０．０３０％以上であることがさらにより好ましい。一方、Ｖ含有量が０．２００％超えると、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験およびＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ/ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｖを含有させる場合、Ｖ含有量は０．２００％以下が好ましい。Ｖ含有量は、より好ましくは０．０６０％以下である。 V: 0.200% or less Like Nb and Ti, V increases TS and YS by forming fine carbides, nitrides, or carbonitrides during hot rolling or annealing. In order to obtain such an effect, it is preferable that the V content is 0.001% or more. The V content is more preferably 0.005% or more. The V content is more preferably 0.010% or more, and even more preferably 0.030% or more. On the other hand, when the V content exceeds 0.200%, large amounts of coarse precipitates and inclusions may be generated. In such cases, coarse precipitates and inclusions become starting points for voids and cracks during hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests, so that the desired λ , R/t, ST and SFmax may not be obtained. Therefore, when V is contained, the V content is preferably 0.200% or less. The V content is more preferably 0.060% or less.
　Ｂ：０．０１００％以下
　Ｂは、オーステナイト粒界に偏析することにより、焼入れ性を高める元素である。また、Ｂは、焼鈍後の冷却時に、フェライトの生成および粒成長を制御する元素である。このような効果を得るためには、Ｂ含有量を０．０００１％以上にすることが好ましい。Ｂ含有量は、より好ましくは０．０００２％以上である。
　Ｂ含有量は、０．０００５％以上であることがさらに好ましく、０．０００７％以上であることがさらにより好ましい。
一方、Ｂ含有量が０．０１００％を超えると、熱間圧延時に鋼板内部に割れが生じるおそれがある。また、穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験またはＶ曲げ＋直交ＶＤＡ曲げ試験時に、前記内部割れが亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｂを含有させる場合、Ｂ含有量は０．０１００％以下とすることが好ましい。Ｂ含有量は、より好ましくは０．００５０％以下である。 B: 0.0100% or less B is an element that improves hardenability by segregating at austenite grain boundaries. Further, B is an element that controls the generation and grain growth of ferrite during cooling after annealing. In order to obtain such an effect, it is preferable that the B content is 0.0001% or more. The B content is more preferably 0.0002% or more.
The B content is more preferably 0.0005% or more, and even more preferably 0.0007% or more.
On the other hand, if the B content exceeds 0.0100%, cracks may occur inside the steel sheet during hot rolling. In addition, during the hole expansion test, V-bending test, U-bending + close bending test, or V-bending + orthogonal VDA bending test, the internal crack becomes the starting point of the crack, so the desired λ, R/t, ST and SFmax can be obtained. may not be possible. Therefore, when B is included, the B content is preferably 0.0100% or less. The B content is more preferably 0.0050% or less.
　Ｃｒ：１．０００％以下
　Ｃｒは、焼入れ性を高める元素であるため、Ｃｒの添加により焼戻しマルテンサイトが適正量生成するため、ＴＳ、ＹＳおよびＹＲを上昇させる。このような効果を得るためには、Ｃｒ含有量は０．０００５％以上にすることが好ましい。また、Ｃｒ含有量は、より好ましくは０．０１０％以上である。
　Ｃｒは、０．０３０％以上であることがさらに好ましく、０．０５０％以上であることがさらにより好ましい。
一方、Ｃｒ含有量が１．０００％を超えると、フレッシュマルテンサイトの面積率が増加し、穴広げ性やＶ曲げ試験の曲げ性が低下し、所望のλおよびＲ／ｔが得られない場合がある。したがって、Ｃｒを含有させる場合、Ｃｒ含有量は１．０００％以下にすることが好ましい。また、Ｃｒ含有量は、より好ましくは０．８００％以下、さらに好ましくは０．７００％以下である。 Cr: 1.000% or less Since Cr is an element that improves hardenability, addition of Cr generates an appropriate amount of tempered martensite, thereby increasing TS, YS, and YR. In order to obtain such effects, the Cr content is preferably 0.0005% or more. Further, the Cr content is more preferably 0.010% or more.
Cr is more preferably 0.030% or more, and even more preferably 0.050% or more.
On the other hand, if the Cr content exceeds 1.000%, the area ratio of fresh martensite increases, hole expandability and V-bending test bendability decrease, and the desired λ and R/t may not be obtained. There is. Therefore, when Cr is contained, the Cr content is preferably 1.000% or less. Further, the Cr content is more preferably 0.800% or less, still more preferably 0.700% or less.
　Ｎｉ：１．０００％以下
　Ｎｉは、焼入れ性を高める元素であるため、Ｎｉの添加により焼戻しマルテンサイトが多量に生成するため、ＴＳ、ＹＳおよびＹＲを上昇させる。このような効果を得るためには、Ｎｉ含有量を０．００５％以上にすることが好ましい。Ｎｉ含有量は、より好ましくは、０．０２０％以上である。Ｎｉ含有量は、０．０４０％以上であることがさらに好ましく、０．０６０％以上であることがさらにより好ましい。
一方、Ｎｉ含有量が１．０００％を超えると、フレッシュマルテンサイトの面積率が増加し、穴広げ性やＶ曲げ試験の曲げ性が低下し、所望のλおよびＲ／ｔが得られない場合がある。したがって、Ｎｉを含有させる場合、Ｎｉ含有量は１．０００％以下とすることが好ましい。Ｎｉ含有量は、より好ましくは０．８００％以下である。
Ｎｉ含有量は、０．６００％以下であることがさらに好ましく、０．４００％以下であることがさらにより好ましい。 Ni: 1.000% or less Ni is an element that improves hardenability, and the addition of Ni produces a large amount of tempered martensite, thereby increasing TS, YS, and YR. In order to obtain such an effect, it is preferable that the Ni content be 0.005% or more. The Ni content is more preferably 0.020% or more. The Ni content is more preferably 0.040% or more, and even more preferably 0.060% or more.
On the other hand, if the Ni content exceeds 1.000%, the area ratio of fresh martensite increases, hole expandability and V-bending test bendability decrease, and the desired λ and R/t may not be obtained. There is. Therefore, when Ni is contained, the Ni content is preferably 1.000% or less. The Ni content is more preferably 0.800% or less.
The Ni content is more preferably 0.600% or less, and even more preferably 0.400% or less.
　Ｍｏ：１．０００％以下
　Ｍｏは、焼入れ性を高める元素であるため、Ｍｏの添加により焼戻しマルテンサイトが多量に生成するため、ＴＳ、ＹＳおよびＹＲを上昇させる。このような効果を得るためには、Ｍｏ含有量を０．０１０％以上にすることが好ましい。Ｍｏ含有量は、より好ましくは、０．０３０％以上である。一方、Ｍｏ含有量が１．０００％を超えると、フレッシュマルテンサイトの面積率が増加し、穴広げ性やＶ曲げ試験の曲げ性が低下し、所望のλおよびＲ／ｔが得られない場合がある。したがって、Ｍｏを含有させる場合、Ｍｏ含有量は１．０００％以下にすることが好ましい。Ｍｏ含有量は、より好ましくは０．５００％以下であり、さらに好ましくは０．４５０％以下であり、さらにより好ましくは０．４００％以下である。Ｍｏ含有量は、０．３５０％以下であることがより好ましく、０．３００％以下であることがさらにより好ましい。 Mo: 1.000% or less Mo is an element that improves hardenability, and the addition of Mo generates a large amount of tempered martensite, thereby increasing TS, YS, and YR. In order to obtain such an effect, it is preferable that the Mo content is 0.010% or more. Mo content is more preferably 0.030% or more. On the other hand, if the Mo content exceeds 1.000%, the area ratio of fresh martensite increases, hole expandability and V-bending test bendability decrease, and the desired λ and R/t may not be obtained. There is. Therefore, when Mo is contained, the Mo content is preferably 1.000% or less. The Mo content is more preferably 0.500% or less, still more preferably 0.450% or less, and even more preferably 0.400% or less. The Mo content is more preferably 0.350% or less, and even more preferably 0.300% or less.
　Ｓｂ：０．２００％以下
　Ｓｂは、焼鈍中の鋼板表面近傍でのＣの拡散を抑制し、鋼板表面近傍における軟質層の形成を制御するために有効な元素である。鋼板表面近傍に軟質層が過度に増加すると、ＴＳを７８０ＭＰａ以上とすることが困難な場合がある。また、ＹＳの低下を招く可能性もある。そのため、Ｓｂ含有量を０．００２％以上とすることが好ましい。Ｓｂ含有量は、より好ましくは０．００５％以上である。一方、Ｓｂ含有量が０．２００％を超えると、鋼板表面近傍に軟質層が形成されず、λ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘの低下を招くおそれがある。したがって、Ｓｂを含有させる場合、Ｓｂ含有量は０．２００％以下にすることが好ましい。Ｓｂ含有量は、より好ましくは０．０２０％以下である。 Sb: 0.200% or less Sb is an effective element for suppressing the diffusion of C near the surface of the steel sheet during annealing and controlling the formation of a soft layer near the surface of the steel sheet. If the soft layer increases excessively near the surface of the steel sheet, it may be difficult to increase the TS to 780 MPa or more. Furthermore, there is a possibility that YS will be lowered. Therefore, it is preferable that the Sb content is 0.002% or more. The Sb content is more preferably 0.005% or more. On the other hand, when the Sb content exceeds 0.200%, a soft layer is not formed near the surface of the steel sheet, which may lead to a decrease in λ, R/t, ST, and SFmax. Therefore, when Sb is contained, the Sb content is preferably 0.200% or less. The Sb content is more preferably 0.020% or less.
　Ｓｎ：０．２００％以下
　Ｓｎは、Ｓｂと同様、焼鈍中の鋼板表面近傍でのＣの拡散を抑制し、鋼板表面近傍における軟質層の形成を制御するために有効な元素である。鋼板表面近傍に軟質層が過度に増加すると、ＴＳを７８０ＭＰａ以上とすることが困難な場合がある。また、ＹＳの低下を招く可能性もある。そのため、Ｓｎ含有量を０．００２％以上とすることが好ましい。Ｓｎ含有量は、より好ましくは０．００５％以上である。一方、Ｓｎ含有量が０．２００％を超えると、鋼板表面近傍に軟質層が形成されず、λ、Ｒ/ｔ、ＳＴおよびＳＦｍａｘの低下を招くおそれがある。したがって、Ｓｎを含有させる場合、Ｓｎ含有量は０．２００％以下にすることが好ましい。Ｓｎ含有量は、より好ましくは０．０２０％以下である。 Sn: 0.200% or less Like Sb, Sn is an effective element for suppressing the diffusion of C near the surface of the steel sheet during annealing and controlling the formation of a soft layer near the surface of the steel sheet. If the soft layer increases excessively near the surface of the steel sheet, it may be difficult to increase the TS to 780 MPa or more. Furthermore, there is a possibility that YS will be lowered. Therefore, it is preferable that the Sn content is 0.002% or more. The Sn content is more preferably 0.005% or more. On the other hand, if the Sn content exceeds 0.200%, a soft layer will not be formed near the surface of the steel sheet, which may cause a decrease in λ, R/t, ST, and SFmax. Therefore, when Sn is contained, the Sn content is preferably 0.200% or less. The Sn content is more preferably 0.020% or less.
　Ｃｕ：１．０００％以下
　Ｃｕは、焼入れ性を高める元素であるため、Ｃｕの添加により焼戻しマルテンサイトが多量に生成するため、ＴＳ、ＹＳおよびＹＲを上昇させる。このような効果を得るためには、Ｃｕ含有量を０．００５％以上にすることが好ましい。Ｃｕ含有量は、０．００８％以上であることがさらに好ましく、０．０１０％以上であることがさらにより好ましい。Ｃｕ含有量は、より好ましくは０．０２０％以上である。
一方、Ｃｕ含有量が１．０００％を超えると、フレッシュマルテンサイトの面積率が過度に増加する場合がある。また、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、過度に生成したフレッシュマルテンサイトと粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験およびＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｃｕを含有させる場合、Ｃｕ含有量は１．０００％以下とすることが好ましい。Ｃｕの含有量は、より好ましくは０．２００％以下である。 Cu: 1.000% or less Cu is an element that improves hardenability, so adding Cu generates a large amount of tempered martensite, increasing TS, YS, and YR. In order to obtain such an effect, it is preferable that the Cu content is 0.005% or more. The Cu content is more preferably 0.008% or more, and even more preferably 0.010% or more. The Cu content is more preferably 0.020% or more.
On the other hand, if the Cu content exceeds 1.000%, the area ratio of fresh martensite may increase excessively. Further, a large amount of coarse precipitates and inclusions may be generated. In such cases, excessively generated fresh martensite and coarse precipitates and inclusions can cause voids and cracks during hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests. Since this is the starting point, the desired λ, R/t, ST and SFmax may not be obtained. Therefore, when Cu is contained, the Cu content is preferably 1.000% or less. The Cu content is more preferably 0.200% or less.
　Ｔａ：０．１００％以下
　Ｔａは、Ｔｉ、ＮｂおよびＶと同様に、熱間圧延時や焼鈍時に、微細な炭化物、窒化物または炭窒化物を形成することによって、ＴＳ、ＹＳおよびＹＲを上昇させる。加えて、Ｔａは、Ｎｂ炭化物やＮｂ炭窒化物に一部固溶し、（Ｎｂ，Ｔａ）（Ｃ，Ｎ）のような複合析出物を生成する。これにより、析出物の粗大化を抑制し、析出強化を安定化させる。これにより、ＴＳ、ＹＳをさらに向上させる。このような効果を得るためには、Ｔａ含有量を０．００１％以上とすることが好ましい。Ｔａ含有量は、０．００２％以上であることがさらに好ましく、０．００４％以上であることがさらにより好ましい。一方、Ｔａ含有量が０．１００％を超えると、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、過粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験またはＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｔａを含有させる場合、Ｔａ含有量は０．１００％以下が好ましい。
Ｔａ含有量は、０．０９０％以下であることがさらに好ましく、０．０８０％以下であることがさらにより好ましい。 Ta: 0.100% or less Like Ti, Nb, and V, Ta increases TS, YS, and YR by forming fine carbides, nitrides, or carbonitrides during hot rolling and annealing. let In addition, Ta is partially dissolved in Nb carbides and Nb carbonitrides to form composite precipitates such as (Nb, Ta) (C, N). This suppresses coarsening of precipitates and stabilizes precipitation strengthening. This further improves TS and YS. In order to obtain such an effect, the Ta content is preferably 0.001% or more. The Ta content is more preferably 0.002% or more, and even more preferably 0.004% or more. On the other hand, if the Ta content exceeds 0.100%, large amounts of coarse precipitates and inclusions may be produced. In such cases, excessively coarse precipitates and inclusions become starting points for voids and cracks during the hole expansion test, V-bending test, U-bending + close bending test, or V-bending + orthogonal VDA bending test, so that the desired λ, R/t, ST and SFmax may not be obtained. Therefore, when Ta is contained, the Ta content is preferably 0.100% or less.
The Ta content is more preferably 0.090% or less, and even more preferably 0.080% or less.
　Ｗ：０．５００％以下
　Ｗは、焼入れ性を高める元素であるため、Ｗの添加により焼戻しマルテンサイトが多量に生成するため、ＴＳ、ＹＳおよびＹＲを上昇させる。このような効果を得るためには、Ｗ含有量を０．００１％以上とすることが好ましい。Ｗ含有量は、より好ましくは０．０３０％以上である。一方、Ｗ含有量が０．５００％を超えると、フレッシュマルテンサイトの面積率が増加し、穴広げ性やＶ曲げ試験の曲げ性が低下し、所望のλおよびＲ/ｔが得られない場合がある。したがって、Ｗを含有させる場合、Ｗ含有量は０．５００％以下にすることが好ましい。Ｗ含有量は、より好ましくは０．４５０％以下、さらに好ましくは０．４００％以下である。Ｗ含有量は、０．３００％以下であることがさらにより好ましい。 W: 0.500% or less W is an element that improves hardenability, and the addition of W generates a large amount of tempered martensite, thereby increasing TS, YS, and YR. In order to obtain such an effect, it is preferable that the W content is 0.001% or more. The W content is more preferably 0.030% or more. On the other hand, if the W content exceeds 0.500%, the area ratio of fresh martensite increases, hole expandability and V-bending test bendability decrease, and the desired λ and R/t may not be obtained. There is. Therefore, when W is contained, the W content is preferably 0.500% or less. The W content is more preferably 0.450% or less, still more preferably 0.400% or less. It is even more preferable that the W content is 0.300% or less.
　Ｍｇ：０．０２００％以下
　Ｍｇは、硫化物や酸化物などの介在物の形状を球状化し、鋼板の穴広げ性および曲げ性を向上させるために有効な元素である。このような効果を得るためには、Ｍｇ含有量を０．０００１％以上とすることが好ましい。Ｍｇ含有量は、０．０００５％以上であることがより好ましく、０．００１０％以上であることがさらに好ましい。一方、Ｍｇ含有量が０．０２００％を超えると、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、過粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験、Ｖ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｍｇを含有させる場合、Ｍｇ含有量は０．０２００％以下とすることが好ましい。Ｍｇ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。 Mg: 0.0200% or less Mg is an effective element for spheroidizing the shape of inclusions such as sulfides and oxides and improving the hole expandability and bendability of the steel sheet. In order to obtain such an effect, it is preferable that the Mg content is 0.0001% or more. The Mg content is more preferably 0.0005% or more, and even more preferably 0.0010% or more. On the other hand, if the Mg content exceeds 0.0200%, large amounts of coarse precipitates and inclusions may be formed. In such cases, excessively coarse precipitates and inclusions become starting points for voids and cracks during the hole expansion test, V-bending test, U-bending + close-contact bending test, and V-bending + orthogonal VDA bending test. λ, R/t, ST and SFmax may not be obtained. Therefore, when Mg is contained, the Mg content is preferably 0.0200% or less. The Mg content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
　Ｚｎ：０．０２００％以下
　Ｚｎは、介在物の形状を球状化し、鋼板の穴広げ性および曲げ性を向上させるために有効な元素である。このような効果を得るためには、Ｚｎ含有量は、０．００１０％以上にすることが好ましい。Ｚｎ含有量は、０．００２０％以上であることがより好ましく、０．００３０％以上であることがさらに好ましい。一方、Ｚｎ含有量が０．０２００％を超えると、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、過粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験およびＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｚｎを含有させる場合、Ｚｎ含有量は０．０２００％以下とすることが好ましい。Ｚｎ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。 Zn: 0.0200% or less Zn is an effective element for spheroidizing the shape of inclusions and improving the hole expandability and bendability of the steel sheet. In order to obtain such effects, the Zn content is preferably 0.0010% or more. The Zn content is more preferably 0.0020% or more, and even more preferably 0.0030% or more. On the other hand, if the Zn content exceeds 0.0200%, large amounts of coarse precipitates and inclusions may be formed. In such cases, excessively coarse precipitates and inclusions become starting points for voids and cracks during the hole expansion test, V-bending test, U-bending + close bending test, and V-bending + orthogonal VDA bending test, so that the desired λ, R/t, ST and SFmax may not be obtained. Therefore, when Zn is contained, the Zn content is preferably 0.0200% or less. The Zn content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
　Ｃｏ：０．０２００％以下
　Ｃｏは、Ｚｎと同様、介在物の形状を球状化し、鋼板の穴広げ性および曲げ性を向上させるために有効な元素である。このような効果を得るためには、Ｃｏ含有量は、０．００１０％以上にすることが好ましい。Ｃｏ含有量は、０．００２０％以上であることがより好ましく、０．００３０％以上であることがさらに好ましい。一方、Ｃｏ含有量が０．０２００％を超えると、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、過粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験およびＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｃｏを含有させる場合、Ｃｏ含有量は０．０２００％以下とすることが好ましい。Ｃｏ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。 Co: 0.0200% or less Co, like Zn, is an effective element for spheroidizing the shape of inclusions and improving the hole expandability and bendability of the steel sheet. In order to obtain such an effect, the Co content is preferably 0.0010% or more. The Co content is more preferably 0.0020% or more, and even more preferably 0.0030% or more. On the other hand, if the Co content exceeds 0.0200%, a large amount of coarse precipitates and inclusions may be formed. In such cases, excessively coarse precipitates and inclusions become starting points for voids and cracks during hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests. λ, R/t, ST and SFmax may not be obtained. Therefore, when Co is contained, the Co content is preferably 0.0200% or less. The Co content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
　Ｚｒ：０．１０００％以下
　Ｚｒは、ＺｎおよびＣｏと同様、介在物の形状を球状化し、鋼板の穴広げ性および曲げ性を向上させるために有効な元素である。このような効果を得るためには、Ｚｒ含有量は、０．００１０％以上にすることが好ましい。一方、Ｚｒ含有量が０．１０００％を超えると、このような場合に、過粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験およびＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｚｒを含有させる場合、Ｚｒ含有量は０．１０００％以下とすることが好ましい。
Ｚｒ含有量は、０．０３００％以下であることがより好ましく、０．０１００％以下であることがさらに好ましい。 Zr: 0.1000% or less Zr, like Zn and Co, is an effective element for making the shape of inclusions spherical and improving the hole expandability and bendability of the steel sheet. In order to obtain such an effect, the Zr content is preferably 0.0010% or more. On the other hand, if the Zr content exceeds 0.1000%, excessively coarse precipitates and inclusions may be detected in hole expansion tests, V-bending tests, U-bending + close bending tests, and V-bending + orthogonal VDA bending tests. During the test, the desired λ, R/t, ST and SFmax may not be obtained because it becomes a starting point for voids and cracks. Therefore, when Zr is contained, the Zr content is preferably 0.1000% or less.
The Zr content is more preferably 0.0300% or less, and even more preferably 0.0100% or less.
　Ｃａ：０．０２００％以下
　Ｃａは、鋼中で介在物として存在する。ここで、Ｃａ含有量が０．０２００％を超えると、粗大な介在物が多量に生成する場合がある。このような場合に、過粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験、Ｖ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｃａを含有させる場合、Ｃａ含有量は０．０２００％以下にすることが好ましい。Ｃａ含有量は、好ましくは０．００２０％以下である。Ｃａ含有量は、０．００１９％以下であることがより好ましく、０．００１８％以下であることがさらに好ましい。なお、Ｃａ含有量の下限は特に限定されるものではないが、Ｃａ含有量は０．０００５％以上が好ましい。また、生産技術上の制約から、Ｃａ含有量は０．００１０％以上がより好ましい。 Ca: 0.0200% or less Ca exists as inclusions in steel. Here, if the Ca content exceeds 0.0200%, a large amount of coarse inclusions may be generated. In such cases, excessively coarse precipitates and inclusions become starting points for voids and cracks during the hole expansion test, V-bending test, U-bending + close-contact bending test, and V-bending + orthogonal VDA bending test. λ, R/t, ST and SFmax may not be obtained. Therefore, when Ca is contained, the Ca content is preferably 0.0200% or less. The Ca content is preferably 0.0020% or less. The Ca content is more preferably 0.0019% or less, and even more preferably 0.0018% or less. Note that the lower limit of the Ca content is not particularly limited, but the Ca content is preferably 0.0005% or more. Furthermore, due to production technology constraints, the Ca content is more preferably 0.0010% or more.
　Ｓｅ：０．０２００％以下、Ｔｅ：０．０２００％以下、Ｇｅ：０．０２００％以下、Ａｓ：０．０５００％以下、Ｓｒ：０．０２００％以下、Ｃｓ：０．０２００％以下、Ｈｆ：０．０２００％以下、Ｐｂ：０．０２００％以下、Ｂｉ：０．０２００％以下およびＲＥＭ：０．０２００％以下
　Ｓｅ、Ｔｅ、Ｇｅ、Ａｓ、Ｓｒ、Ｃｓ、Ｈｆ、Ｐｂ、ＢｉおよびＲＥＭはいずれも、鋼板の穴広げ性および曲げ性を向上させるために有効な元素である。このような効果を得るためには、Ｓｅ、Ｔｅ、Ｇｅ、Ａｓ、Ｓｒ、Ｃｓ、Ｈｆ、Ｐｂ、ＢｉおよびＲＥＭの含有量はそれぞれ０．０００１％以上にすることが好ましい。一方、Ｓｅ、Ｔｅ、Ｇｅ、Ｓｒ、Ｃｓ、Ｈｆ、Ｐｂ、ＢｉおよびＲＥＭの含有量がそれぞれ０．０２００％を超えると、または、Ａｓの含有量がそれぞれ０．０５００％を超えると、粗大な析出物や介在物が多量に生成する場合がある。このような場合に、過粗大な析出物や介在物が穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験またはＶ曲げ＋直交ＶＤＡ曲げ試験時に、ボイドおよび亀裂の起点となるため、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない場合がある。したがって、Ｃｅ、Ｓｅ、Ｔｅ、Ｇｅ、Ａｓ、Ｓｒ、Ｃｓ、Ｈｆ、Ｐｂ、ＢｉおよびＲＥＭのうちの少なくとも１種を含有させる場合、Ｓｅ、Ｔｅ、Ｇｅ、Ａｓ、Ｓｒ、Ｃｓ、Ｈｆ、Ｐｂ、ＢｉおよびＲＥＭの含有量はそれぞれ０．０２００％以下、Ａｓの含有量は０．０５００％以下とすることが好ましい。
　Ｓｅ含有量は、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。Ｓｅ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。
　Ｔｅ含有量は、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。Ｔｅ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。
　Ｇｅ含有量は、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。Ｇｅ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。
　Ａｓ含有量は、０．００１０％以上であることがより好ましく、０．００１５％以上であることがさらに好ましい。Ａｓ含有量は、０．０４００％以下であることがより好ましく、０．０３００％以下であることがさらに好ましい。
　Ｓｒ含有量は、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。Ｓｒ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。
　Ｃｓ含有量は、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。Ｃｓ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。
　Ｈｆ含有量は、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。Ｈｆ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。
　Ｐｂ含有量は、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。Ｐｂ含有量は、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。
　Ｂｉ含有量は、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。Ｂｉは、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。
　ＲＥＭは、０．０００５％以上であることがより好ましく、０．０００８％以上であることがさらに好ましい。ＲＥＭは、０．０１８０％以下であることがより好ましく、０．０１５０％以下であることがさらに好ましい。 Se: 0.0200% or less, Te: 0.0200% or less, Ge: 0.0200% or less, As: 0.0500% or less, Sr: 0.0200% or less, Cs: 0.0200% or less, Hf: 0.0200% or less, Pb: 0.0200% or less, Bi: 0.0200% or less, and REM: 0.0200% or less Se, Te, Ge, As, Sr, Cs, Hf, Pb, Bi, and REM are all is also an effective element for improving the hole expandability and bendability of steel sheets. In order to obtain such an effect, it is preferable that the content of Se, Te, Ge, As, Sr, Cs, Hf, Pb, Bi, and REM is each 0.0001% or more. On the other hand, if the content of Se, Te, Ge, Sr, Cs, Hf, Pb, Bi and REM exceeds 0.0200% each, or if the content of As exceeds 0.0500% each, coarse A large amount of precipitates and inclusions may be generated. In such cases, excessively coarse precipitates and inclusions become starting points for voids and cracks during the hole expansion test, V-bending test, U-bending + close bending test, or V-bending + orthogonal VDA bending test, so that the desired λ, R/t, ST and SFmax may not be obtained. Therefore, when containing at least one of Ce, Se, Te, Ge, As, Sr, Cs, Hf, Pb, Bi and REM, Se, Te, Ge, As, Sr, Cs, Hf, Pb, The content of Bi and REM is preferably 0.0200% or less, and the content of As is preferably 0.0500% or less.
The Se content is more preferably 0.0005% or more, and even more preferably 0.0008% or more. The Se content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
The Te content is more preferably 0.0005% or more, and even more preferably 0.0008% or more. The Te content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
The Ge content is more preferably 0.0005% or more, and even more preferably 0.0008% or more. The Ge content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
As for As content, it is more preferred that it is 0.0010% or more, and it is still more preferred that it is 0.0015% or more. As for As content, it is more preferred that it is 0.0400% or less, and it is still more preferred that it is 0.0300% or less.
The Sr content is more preferably 0.0005% or more, and even more preferably 0.0008% or more. The Sr content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
The Cs content is more preferably 0.0005% or more, and even more preferably 0.0008% or more. The Cs content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
The Hf content is more preferably 0.0005% or more, and even more preferably 0.0008% or more. The Hf content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
The Pb content is more preferably 0.0005% or more, and even more preferably 0.0008% or more. The Pb content is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
The Bi content is more preferably 0.0005% or more, and even more preferably 0.0008% or more. Bi is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
REM is more preferably 0.0005% or more, and even more preferably 0.0008% or more. REM is more preferably 0.0180% or less, and even more preferably 0.0150% or less.
　鋼組織
　つぎに、本発明の一実施形態に従う亜鉛めっき鋼板の素地鋼板の鋼組織について説明する。 Steel Structure Next, the steel structure of the base steel sheet of the galvanized steel sheet according to one embodiment of the present invention will be described.
　フェライトの面積率：２０．０％以上８０．０％以下
　軟質なフェライトは延性を向上させる相である。また、粒内に孤立した島状フレッシュマルテンサイトや孤立した島状残留オーステナイトを生成し、ボイドの連結および亀裂の進展を抑制するために必要な相である。所望の延性と良好なλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘを両立するために、フェライトの面積率は２０．０％以上とする。一方、フェライトの面積率が過度に増加すると、ＴＳを７８０ＭＰａ以上とすることが困難になる。また、ＹＳおよびＹＲの低下も招く。そのため、フェライトの面積率は８０．０％以下とする。また、フェライトの面積率は、好ましくは３０．０％以上である。 Area ratio of ferrite: 20.0% or more and 80.0% or less Soft ferrite is a phase that improves ductility. It is also a necessary phase to generate isolated island-like fresh martensite and isolated island-like retained austenite within grains, and to suppress the connection of voids and the propagation of cracks. In order to achieve both desired ductility and good λ, R/t, ST and SFmax, the area ratio of ferrite is set to 20.0% or more. On the other hand, if the area ratio of ferrite increases excessively, it becomes difficult to increase the TS to 780 MPa or more. It also causes a decrease in YS and YR. Therefore, the area ratio of ferrite is set to 80.0% or less. Further, the area ratio of ferrite is preferably 30.0% or more.
　フレッシュマルテンサイトの面積率：１５．０％以下（０．０％を含む）
　本発明において、フレッシュマルテンサイトの面積率が過度に増加すると、穴広げ試験の穴広げ加工時またはＶ曲げ試験の曲げ加工時、フレッシュマルテンサイトがボイド生成起点となるため、所望のλおよびＲ／ｔが得られない。そのため、フレッシュマルテンサイトの面積率は１５．０％以下とする。また、フレッシュマルテンサイトの面積率は、好ましくは１０．０％以下である。なお、フレッシュマルテンサイトの面積率の下限についてはとくに限定されず、０．０％であってもよい。ここでいうフレッシュマルテンサイトとは、焼入れままの（焼戻しを受けていない）マルテンサイトである。また、ここでいうフレッシュマルテンサイトには、後述のフェライト粒内の（孤立した）島状フレッシュマルテンサイトも含まれる。 Fresh martensite area ratio: 15.0% or less (including 0.0%)
In the present invention, if the area ratio of fresh martensite increases excessively, fresh martensite becomes the starting point for void generation during hole expansion in the hole expansion test or bending in the V-bending test, so that the desired λ and R/ t cannot be obtained. Therefore, the area ratio of fresh martensite is set to 15.0% or less. Further, the area ratio of fresh martensite is preferably 10.0% or less. Note that the lower limit of the area ratio of fresh martensite is not particularly limited, and may be 0.0%. The fresh martensite referred to here is martensite that is still quenched (not tempered). Furthermore, the fresh martensite referred to herein also includes (isolated) island-like fresh martensite within ferrite grains, which will be described later.
　残留オーステナイトの面積率：３．０％以下（０．０％を含む）
　本発明において、残留オーステナイトの面積率が過度に増加すると、穴広げ試験で鋼板に打抜き加工を受けた時、Ｕ曲げ＋密着曲げ試験でＵ曲げ加工を受けた時、またはＶ曲げ＋直交ＶＤＡ試験でＶ曲げ加工を受けた時、残留オーステナイトの加工誘起変態によって生成した硬いフレッシュマルテンサイトが生成され、その後の試験でボイドの生成および亀裂の進展が生じ、所望のλ、ＳＴおよびＳＦｍａｘが得られない。そのため、残留オーステナイトの面積率を３．０％以下とする。残留オーステナイトの面積率は、好ましくは２．５％以下であり、より好ましくは２．０％以下である。残留オーステナイトの面積率の下限は特に限定されないが、好ましくは０．１％以上であり、より好ましくは０．２％以上である。
ここでいう残留オーステナイトには、後述のフェライト粒内の（孤立した）島状残留オーステナイトも含まれる。 Area ratio of retained austenite: 3.0% or less (including 0.0%)
In the present invention, when the area ratio of retained austenite increases excessively, when the steel plate is punched in the hole expansion test, when the steel plate is subjected to U bending in the U-bending + close bending test, or when the steel plate is subjected to U-bending in the V-bending + orthogonal VDA test, When subjected to V-bending, hard fresh martensite is generated due to deformation-induced transformation of retained austenite, and in subsequent tests, voids are formed and cracks grow, and the desired λ, ST, and SFmax are not obtained. do not have. Therefore, the area ratio of retained austenite is set to 3.0% or less. The area ratio of retained austenite is preferably 2.5% or less, more preferably 2.0% or less. The lower limit of the area ratio of retained austenite is not particularly limited, but is preferably 0.1% or more, more preferably 0.2% or more.
The retained austenite referred to herein also includes (isolated) island-like retained austenite within ferrite grains, which will be described later.
　ここで、後述する製造方法における第二冷却工程時に、３００℃以上４５０℃以下の温度域で２．０ｋｇｆ／ｍｍ２以上の張力を付与し、その後、鋼板を、１パス当たり直径５００ｍｍ以上１５００ｍｍ以下のロールにロール１／４周分接触させながら、鋼板を５パス以上通過させることで、未変態オーステナイトが加工誘起変態し、フレッシュマルテンサイトとなり、その後の再加熱工程で前記フレッシュマルテンサイトが焼戻され、最終的にフレッシュマルテンサイトの面積率が１５．０％以下、残留オーステナイトの体積率が３．０％以下になるよう制御することにより、所望の焼戻しマルテンサイトの面積率の確保が可能となる。 Here, during the second cooling step in the manufacturing method described later, a tension of 2.0 kgf/mm 2 or more is applied in a temperature range of 300°C or more and 450°C or less, and then the steel plate is heated to a diameter of 500 mm or more and 1500 mm or less per pass. By passing the steel plate through 5 or more passes while contacting the roll for 1/4 rotation of the roll, untransformed austenite undergoes deformation-induced transformation to become fresh martensite, and in the subsequent reheating process, the fresh martensite is tempered. By controlling the area ratio of fresh martensite to 15.0% or less and the volume ratio of retained austenite to 3.0% or less, it is possible to secure the desired area ratio of tempered martensite. Become.
　フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの面積率の合計を、鋼板全体のフレッシュマルテンサイトの面積率と残留オーステナイトの面積率の合計で除した値：０．６５以上
　本発明において、図１に示すとおり、フェライト（Ｆ）粒内の孤立した島状フレッシュマルテンサイト（Ｍ’）と孤立した島状残留オーステナイト（ＲＡ’）は、フェライト粒界に存在する焼戻しマルテンサイト（ＴＭ）および硬質第二相（フレッシュマルテンサイト（Ｍ）＋残留オーステナイト（ＲＡ））より微細であり、ボイドの生成位置には成りうるが、ボイドの連結や亀裂の進展には関与しにくい組織であり、７８０ＭＰａ以上のＴＳを確保しつつ、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘを得るのに必要な組織である。そのため、フェライト粒内の孤立した島状フレッシュマルテンサイトと孤立した島状残留オーステナイトの面積率の合計をフレッシュマルテンサイトの面積率と残留オーステナイトの面積率の合計で除した値（（Ｍ‘＋ＲＡ’）／（Ｍ＋ＲＡ））を０．６５以上とする。また、フェライト粒内の孤立した島状フレッシュマルテンサイトと孤立した島状残留オーステナイトの面積率の合計をフレッシュマルテンサイトの面積率と残留オーステナイトの面積率の合計で除した値は、好ましくは０．７０以上である。
フェライト粒内の孤立した島状フレッシュマルテンサイトと孤立した島状残留オーステナイトの面積率の合計をフレッシュマルテンサイトの面積率と残留オーステナイトの体積率の合計で除した値の上限は特に限定されないが、この値は０．９４以下とすることが好ましく、０．９２以下とすることがより好ましい。 In the present invention, the value obtained by dividing the sum of the area ratios of island-like fresh martensite and island-like retained austenite in the ferrite grains by the sum of the area ratio of fresh martensite and retained austenite in the entire steel sheet: 0.65 or more , as shown in Figure 1, isolated island-like fresh martensite (M') and isolated island-like retained austenite (RA') within ferrite (F) grains are tempered martensite (TM) existing at ferrite grain boundaries. It is finer than the hard second phase (fresh martensite (M) + retained austenite (RA)), and although it can serve as a void generation site, it is a structure that is unlikely to be involved in void connection or crack propagation. This structure is necessary to obtain the desired λ, R/t, ST and SFmax while ensuring a TS of 780 MPa or more. Therefore, the value obtained by dividing the total area ratio of isolated island-like fresh martensite and isolated island-like retained austenite in the ferrite grain by the sum of the area ratio of fresh martensite and retained austenite ((M'+RA' )/(M+RA)) shall be 0.65 or more. Further, the value obtained by dividing the sum of the area ratios of isolated island-like fresh martensite and isolated island-like retained austenite in the ferrite grain by the sum of the area ratio of fresh martensite and retained austenite is preferably 0. It is 70 or more.
The upper limit of the value obtained by dividing the sum of the area ratios of isolated island-like fresh martensite and isolated island-like retained austenite in the ferrite grain by the sum of the area ratio of fresh martensite and the volume ratio of retained austenite is not particularly limited, but This value is preferably 0.94 or less, more preferably 0.92 or less.
　ベイナイトおよび焼戻しベイナイトの面積率：１０．０％以下（０．０％を含む）
　第一冷却工程で生成するベイナイト、再加熱工程で生成する前記ベイナイトが焼戻しを受けた焼戻しベイナイトの面積率が過度に増加すると、所望の焼戻しマルテンサイトの面積率が得られなくなり、７８０ＭＰａ以上のＴＳを確保が困難となる。そのため、ベイナイトおよび焼戻しベイナイトの面積率（Ｂ＋ＢＴ）は１０．０％以下とする。また、ベイナイトおよび焼戻しベイナイトの面積率は、好ましくは８．０％以下である。ベイナイトおよび焼戻しベイナイトの面積率は、０．０％以下であってもよい。 Area ratio of bainite and tempered bainite: 10.0% or less (including 0.0%)
If the area ratio of the tempered bainite produced in the first cooling process and the bainite produced in the reheating process is tempered, the desired area ratio of tempered martensite cannot be obtained, and the TS of 780 MPa or more It will be difficult to secure. Therefore, the area ratio (B+BT) of bainite and tempered bainite is 10.0% or less. Further, the area ratio of bainite and tempered bainite is preferably 8.0% or less. The area ratio of bainite and tempered bainite may be 0.0% or less.
　焼戻しマルテンサイトの面積率：１０．０％以上７０．０％以下
　フェライト粒界に存在する硬質第二相（フレッシュマルテンサイト＋残留オーステナイト）は、プレス成形時および衝突時にボイドの生成および亀裂の進展を助長する組織である。一方、焼戻しマルテンサイトは、後述する製造方法における第二冷却工程時に、３００℃以上４５０℃以下の温度域で２．０ｋｇｆ／ｍｍ２以上の張力を付与し、その後、亜鉛めっき鋼板を、１パス当たり直径５００ｍｍ以上１５００ｍｍ以下のロールにロール１／４周分接触させながら、５パス以上通過させることで、未変態オーステナイトが加工誘起変態し、フレッシュマルテンサイトとなり、その後の再加熱工程で上記フレッシュマルテンサイトが焼戻されることで得られる、殆どがフェライト粒界に存在する組織である。上記焼戻しマルテンサイトは、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘを得るのに必要な組織である。そのため、焼戻しマルテンサイトの面積率は１０．０％以上とする。焼戻しマルテンサイトの面積率は、好ましくは２０．０％以上である。一方、焼戻しマルテンサイトの面積率は過度に増加した場合、所望のフェライトの面積率が得られず、所望の延性が確保できない。そのため、焼戻しマルテンサイトの面積率は７０．０％以下とする。焼戻しマルテンサイトの面積率は、好ましくは６０．０％以下である。 Area ratio of tempered martensite: 10.0% or more and 70.0% or less The hard second phase (fresh martensite + retained austenite) present at the ferrite grain boundaries causes void formation and crack growth during press forming and collision. It is an organization that promotes On the other hand, tempered martensite is produced by applying a tension of 2.0 kgf/mm2 or more in a temperature range of 300°C to 450°C during the second cooling step in the manufacturing method described later, and then applying a tension of 2.0 kgf/mm2 or more to the galvanized steel sheet in one pass. The untransformed austenite undergoes deformation-induced transformation to become fresh martensite by contacting a roll with a per-diameter of 500 mm or more and 1500 mm or less for 1/4 rotation of the roll and passing the roll for 5 or more passes. This structure is obtained by tempering the sites and exists mostly at ferrite grain boundaries. The above-mentioned tempered martensite has a structure necessary to obtain desired λ, R/t, ST and SFmax. Therefore, the area ratio of tempered martensite is set to 10.0% or more. The area ratio of tempered martensite is preferably 20.0% or more. On the other hand, when the area ratio of tempered martensite increases excessively, the desired area ratio of ferrite cannot be obtained and the desired ductility cannot be ensured. Therefore, the area ratio of tempered martensite is 70.0% or less. The area ratio of tempered martensite is preferably 60.0% or less.
　フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの平均結晶粒径：２．０μｍ以下
　本発明において、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの平均結晶粒径が小さい場合、７８０ＭＰａ以上のＴＳを確保しつつ、よりボイドの生成を抑制でき、より良好なλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘを得ることができる。そのため、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイト（Ｍ’＋ＲＡ’）の平均結晶粒径が２．０μｍ以下とする。なお、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの平均結晶粒径は、好ましくは１．０μｍ以下である。
下限は特に限定されないが、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの平均結晶粒径は、好ましくは０．１μｍ以上であり、より好ましくは０．２μｍ以上である。 Average crystal grain size of island-like fresh martensite and island-like retained austenite within ferrite grains: 2.0 μm or less In the present invention, when the average crystal grain size of island-like fresh martensite and island-like retained austenite within ferrite grains is small , 780 MPa or more, the generation of voids can be further suppressed, and better λ, R/t, ST and SFmax can be obtained. Therefore, the average crystal grain size of island-like fresh martensite and island-like retained austenite (M'+RA') within the ferrite grains is set to 2.0 μm or less. The average crystal grain size of the island-like fresh martensite and the island-like retained austenite within the ferrite grains is preferably 1.0 μm or less.
Although the lower limit is not particularly limited, the average crystal grain size of the island-like fresh martensite and the island-like retained austenite in the ferrite grains is preferably 0.1 μm or more, more preferably 0.2 μm or more.
　なお、前記以外の残部組織の面積率は１０．０％以下とすることが好ましい。残部組織の面積率は、より好ましくは５．０％以下である。また、残部組織の面積率は０．０％であってもよい。 Note that the area ratio of the remaining structures other than those mentioned above is preferably 10.0% or less. The area ratio of the remaining tissue is more preferably 5.0% or less. Further, the area ratio of the remaining tissue may be 0.0%.
　残部組織としては、とくに限定されず、例えば、パーライト、セメンタイトなどの炭化物が挙げられる。なお、残部組織の種類は、例えば、ＳＥＭ（Ｓｃａｎｎｉｎｇ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ；走査電子顕微鏡）による観察で確認することができる。 The residual structure is not particularly limited, and examples thereof include carbides such as pearlite and cementite. The type of residual tissue can be confirmed, for example, by observation using a scanning electron microscope (SEM).
　ここで、フェライト、ベイナイト、焼戻しベイナイト、焼戻しマルテンサイトおよび硬質第二相（フレッシュマルテンサイト＋残留オーステナイト）の面積率は、素地鋼板の板厚１／４位置において、以下のように測定する。
　すなわち、鋼板の圧延方向に平行な板厚断面（Ｌ断面）が観察面となるよう試料を切り出す。ついで、試料の観察面に、ダイヤモンドペーストによる研磨を施し、ついで、アルミナを用いて仕上げ研磨を施す。ついで、試料の観察面を３ｖｏｌ．％ナイタールでエッチングし、組織を現出させる。ついで、鋼板の板厚の１／４位置を観察位置とし、ＳＥＭにより、倍率：３０００倍で５視野観察する。得られた組織画像から、Ａｄｏｂｅ　Ｓｙｓｔｅｍｓ社のＡｄｏｂｅ　Ｐｈｏｔｏｓｈｏｐを用いて、各構成組織（フェライト、ベイナイト、焼戻しベイナイト、焼戻しマルテンサイトおよび硬質第二相（フレッシュマルテンサイト＋残留オーステナイト））の面積を測定面積で除した面積率を５視野分算出し、それらの値を平均して各組織の面積率とする。
フェライト：黒色を呈した領域であり、形態は塊状である。また、炭化物を殆ど内包しない。また、フェライト粒内の孤立した島状フレッシュマルテンサイトと孤立した島状残留オーステナイトは、フェライトの面積率に含まない。
ベイナイトおよび焼戻しベイナイト：黒色から濃い灰色を呈した領域であり、形態は塊状や不定形などである。また、比較的少数の炭化物を内包する。
焼戻しマルテンサイト：灰色を呈した領域であり、形態は不定形である。また、炭化物を比較的多数内包する。
硬質第二相（残留オーステナイト＋フレッシュマルテンサイト）：白色から薄い灰色を呈する領域であり、形態は不定形である。また、炭化物を内包しない。
炭化物：白色を呈する領域であり、形態は点状や線状である。ベイナイト、焼戻しベイナイトおよび焼戻しマルテンサイトに内包される。
残部組織：上述したパーライトやセメンタイトなどが挙げられ、これらの形態等は公知のとおりである。 Here, the area ratio of ferrite, bainite, tempered bainite, tempered martensite, and hard second phase (fresh martensite + retained austenite) is measured as follows at the 1/4 thickness position of the base steel plate.
That is, the sample is cut out so that the plate thickness cross section (L cross section) parallel to the rolling direction of the steel plate serves as the observation surface. Next, the observation surface of the sample is polished with diamond paste, and then final polished with alumina. Next, the observation surface of the sample was exposed to 3 vol. % nital to reveal the tissue. Next, the observation position is set at 1/4 of the thickness of the steel plate, and 5 fields of view are observed using an SEM at a magnification of 3000 times. From the obtained structure image, the area of each constituent structure (ferrite, bainite, tempered bainite, tempered martensite, and hard second phase (fresh martensite + retained austenite)) was measured using Adobe Photoshop from Adobe Systems. The area ratio divided by is calculated for five fields of view, and these values are averaged to determine the area ratio of each tissue.
Ferrite: A black region with a block-like shape. In addition, it contains almost no carbide. Furthermore, isolated island-like fresh martensite and isolated island-like retained austenite within the ferrite grains are not included in the area ratio of ferrite.
Bainite and tempered bainite: A black to dark gray area, with a lumpy or irregular shape. It also contains a relatively small amount of carbide.
Tempered martensite: A gray area with an amorphous shape. It also contains a relatively large number of carbides.
Hard second phase (retained austenite + fresh martensite): This is a white to light gray region with an amorphous shape. Also, it does not contain carbide.
Carbide: A white region with a dotted or linear shape. It is included in bainite, tempered bainite, and tempered martensite.
Remnant structure: Examples include the above-mentioned pearlite and cementite, and their forms are known.
　上記の組織分率測定に用いたＳＥＭ像から、フェライト粒内の孤立した島状フレッシュマルテンサイトと孤立した島状残留オーステナイトの面積の合計を、フェライト粒内の孤立した島状フレッシュマルテンサイトと孤立した島状残留オーステナイトの個数で割って平均面積を求め、その１／２乗を平均結晶粒径とする。 From the SEM image used for the above-mentioned structure fraction measurement, the total area of isolated island-like fresh martensite and isolated island-like retained austenite within ferrite grains can be calculated as follows: The average area is determined by dividing by the number of island-like retained austenites, and the 1/2 power is taken as the average crystal grain size.
　また、残留オーステナイトの面積率は、以下のように測定する。
　すなわち、素地鋼板を板厚方向（深さ方向）に板厚の１／４位置まで機械研削した後、シュウ酸による化学研磨を行い、観察面とする。ついで、観察面を、Ｘ線回折法により観察する。入射Ｘ線にはＭｏＫα線を使用し、ｂｃｃ鉄の（２００）、（２１１）および（２２０）各面の回折強度に対するｆｃｃ鉄（オーステナイト）の（２００）、（２２０）および（３１１）各面の回折強度の比を求め、各面の回折強度の比から、残留オーステナイトの体積率を算出する。そして、残留オーステナイトが三次元的に均質であるとみなして、残留オーステナイトの体積率を、残留オーステナイトの面積率とする。 Moreover, the area ratio of retained austenite is measured as follows.
That is, the base steel plate is mechanically ground in the thickness direction (depth direction) to a position of 1/4 of the plate thickness, and then chemically polished with oxalic acid to form an observation surface. Then, the observation surface is observed by X-ray diffraction. MoKα rays were used for the incident X-rays, and the diffraction intensity of the (200), (211) and (220) planes of BCC iron was compared with the (200), (220) and (311) planes of FCC iron (austenite). The ratio of the diffraction intensities of each surface is determined, and the volume fraction of retained austenite is calculated from the ratio of the diffraction intensities of each surface. Then, assuming that the retained austenite is three-dimensionally homogeneous, the volume fraction of the retained austenite is defined as the area fraction of the retained austenite.
　また、フレッシュマルテンサイトの面積率は、前記のようにして求めた硬質第二相の面積率から、残留オーステナイトの面積率を減じることにより求める。
　［フレッシュマルテンサイトの面積率（％）］＝［硬質第二相の面積率（％）］－［残留オーステナイトの面積率（％）］ Further, the area ratio of fresh martensite is determined by subtracting the area ratio of retained austenite from the area ratio of the hard second phase determined as described above.
[Area ratio of fresh martensite (%)] = [Area ratio of hard second phase (%)] - [Area ratio of retained austenite (%)]
　また、残部組織の面積率は、１００．０％から前記のようにして求めたフェライトの面積率、ベイナイトおよび焼戻しベイナイトの面積率、焼戻しマルテンサイトの面積率、硬質第二相の面積率を減じることにより求める。
　［残部組織の面積率（％）］＝１００．０－［フェライトの面積率（％）］－［ベイナイトおよび焼戻しベイナイトの面積率（％）］－［焼戻しマルテンサイトの面積率（％）］－［硬質第二相の面積率（％）］ In addition, the area ratio of the residual structure is obtained by subtracting the area ratio of ferrite, the area ratio of bainite and tempered bainite, the area ratio of tempered martensite, and the area ratio of the hard second phase obtained as described above from 100.0%. Find by.
[Area ratio of residual structure (%)] = 100.0 - [Area ratio of ferrite (%)] - [Area ratio of bainite and tempered bainite (%)] - [Area ratio of tempered martensite (%)] - [Hard second phase area ratio (%)]
　素地鋼板に含まれる（鋼中の）拡散性水素量：０．５０質量ｐｐｍ以下
　鋼板中の拡散性水素量を０．５０質量ｐｐｍ超の場合、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られない。
なお、鋼板中の拡散性水素量は、好ましくは０．２５質量ｐｐｍ以下とする。また、鋼板中の拡散性水素量の下限は特に規定しないが、生産技術上の制約から、鋼板中の拡散性水素量は０．０１質量ｐｐｍ以上とすることが好ましい。
なお、拡散性水素量を測定する素地鋼板は、めっき処理前の高強度鋼板のほか、亜鉛めっき処理後加工前の高強度亜鉛めっき鋼板の素地鋼板であってもよい。また、亜鉛めっき処理後、打ち抜き加工および伸びフランジ成形等の加工を施された鋼板の素地鋼板であってもよく、さらに加工後の鋼板を溶接して製造された製品の素地部分であってもかまわない。 Amount of diffusible hydrogen (in steel) contained in the base steel sheet: 0.50 mass ppm or less When the amount of diffusible hydrogen in the steel sheet exceeds 0.50 mass ppm, the desired λ, R/t, ST and SFmax I can't get it.
Note that the amount of diffusible hydrogen in the steel sheet is preferably 0.25 mass ppm or less. Further, although the lower limit of the amount of diffusible hydrogen in the steel sheet is not particularly specified, it is preferable that the amount of diffusible hydrogen in the steel sheet is 0.01 mass ppm or more due to constraints on production technology.
The base steel plate on which the amount of diffusible hydrogen is measured may be a high-strength steel plate before plating, or a base steel plate that is a high-strength galvanized steel plate after galvanizing and before processing. In addition, it may be a base steel plate of a steel plate that has been subjected to processes such as punching and stretch flange forming after galvanizing, or it may be a base part of a product manufactured by welding the processed steel plate. I don't mind.
　ここで、鋼板中の拡散性水素量の測定方法は、以下の通りである。長さが３０ｍｍ、幅が５ｍｍの試験片を採取し、溶融亜鉛めっき層または合金化溶融亜鉛めっき層をアルカリ除去する。その後、試験片から放出される水素量を昇温脱離分析法によって測定する。具体的には、室温（－５～５５℃）から３００℃までを昇温速度２００℃／ｈで連続加熱した後、室温まで冷却し、室温から２１０℃までに試験片から放出された積算水素量を測定して、鋼板中の拡散性水素量とする。拡散性水素量の測定は、鋼板の鋼板の製造完了後に行うことが好ましい。
なお、室温は世界各国での生産を踏まえた場合、現地での１年間での気温の変化の範囲内とする。一般的には、１０～５０℃の範囲であることが好ましい。 Here, the method for measuring the amount of diffusible hydrogen in a steel sheet is as follows. A test piece with a length of 30 mm and a width of 5 mm is taken, and the hot-dip galvanized layer or the alloyed hot-dip galvanized layer is alkali-removed. Thereafter, the amount of hydrogen released from the test piece is measured by temperature programmed desorption analysis. Specifically, after continuously heating from room temperature (-5 to 55°C) to 300°C at a heating rate of 200°C/h, the test piece was cooled to room temperature, and the cumulative hydrogen released from the test piece from room temperature to 210°C was measured. The amount is measured and taken as the amount of diffusible hydrogen in the steel sheet. It is preferable to measure the amount of diffusible hydrogen after the production of the steel sheet is completed.
In addition, the room temperature should be within the range of local temperature changes over a one-year period, taking into account production in various countries around the world. Generally, the temperature is preferably in the range of 10 to 50°C.
　表層軟質層
　本発明の一実施形態に伴う亜鉛めっき鋼板の素地鋼板では、素地鋼板表面に表層軟質層を有することが好ましい。プレス成形時および車体衝突時に表層軟質層が曲げ割れ進展の抑制に寄与するため、耐曲げ破断特性がさらに向上する。なお、表層軟質層とは、脱炭層を意味し、板厚１／４位置の断面のビッカース硬さに対して、８５％以下のビッカース硬さの表層領域のことである。
　ここで、表層軟質層は、素地鋼板表面から板厚方向に２００μｍ以下の領域で形成されている。なお、表層軟質層の厚さの下限については、特に定めないが、８μｍ以上が好ましく、１７μｍ超がより好ましい。
　ビッカース硬さは、ＪＩＳ　Ｚ　２２４４－１（２０２０）に基づいて、荷重を１０ｇｆとして測定する。 Soft Surface Layer The base steel sheet of the galvanized steel sheet according to one embodiment of the present invention preferably has a soft surface layer on the surface of the base steel sheet. The soft surface layer contributes to suppressing the propagation of bending cracks during press molding and car body collisions, further improving the bending fracture resistance. Note that the surface soft layer means a decarburized layer, and is a surface layer region having a Vickers hardness of 85% or less of the Vickers hardness of the cross section at the 1/4 thickness position.
Here, the surface soft layer is formed in an area of 200 μm or less in the thickness direction from the surface of the base steel sheet. Although the lower limit of the thickness of the surface soft layer is not particularly determined, it is preferably 8 μm or more, and more preferably more than 17 μm.
Vickers hardness is measured based on JIS Z 2244-1 (2020) with a load of 10 gf.
　ナノ硬度
　素地鋼板表面から表層軟質層の板厚方向深さの１／４位置および板厚方向深さの１／２位置の夫々における板面の５０μｍ×５０μｍの領域において、３００点以上のナノ硬度を測定したとき、素地鋼板表面から表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度が７．０ＧＰａ以上の測定数割合が、表層軟質層の板厚方向深さの１／４位置の全測定数に対して０．１０以下
　本発明において、プレス成形時の優れた曲げ性と衝突時の優れた曲げ破断特性を得るためには、素地鋼板表面から表層軟質層の板厚方向深さの１／４位置及び板厚方向深さの１／２位置の夫々における板面の５０μｍ×５０μｍの領域において、３００点以上のナノ硬度を測定したとき、素地鋼板表面から表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度が７．０ＧＰａ以上の測定数割合が、表層軟質層の板厚方向深さの１／４位置の全測定数に対して０．１０以下であることが好ましい。ナノ硬度が７．０ＧＰａ以上の割合が０．１０以下の場合、硬質な組織（マルテンサイトなど）、介在物などの割合が小さいことを意味し、硬質な組織（マルテンサイトなど）、介在物などのプレス成形時および衝突時のボイドの生成や連結、さらには亀裂の進展をより抑制することが可能となり、優れたＲ／ｔおよびＳＦｍａｘが得られる。 Nanohardness Nanohardness of 300 points or more in an area of 50 μm x 50 μm on the plate surface at 1/4 depth in the thickness direction and 1/2 depth in the thickness direction of the surface soft layer from the surface of the base steel sheet. When measured, the proportion of measurements where the nanohardness of the plate surface at 1/4 of the depth in the thickness direction of the surface soft layer from the surface of the base steel sheet was 7.0 GPa or more was the same as the thickness of the surface soft layer. 0.10 or less for the total number of measurements at the 1/4 position In the present invention, in order to obtain excellent bending properties during press forming and excellent bending rupture properties during collision, it is necessary to When nanohardness was measured at 300 or more points in an area of 50 μm x 50 μm on the plate surface at 1/4 depth in the thickness direction and 1/2 depth in the thickness direction, it was found that The ratio of the number of measurements where the nanohardness of the plate surface at 1/4 of the depth in the thickness direction of the soft layer is 7.0 GPa or more is relative to the total number of measurements at 1/4 of the depth in the thickness direction of the surface soft layer. is preferably 0.10 or less. If the ratio of nanohardness of 7.0 GPa or more is 0.10 or less, it means that the ratio of hard structures (martensite, etc.), inclusions, etc. is small; It becomes possible to further suppress the generation and connection of voids during press molding and collision, as well as the propagation of cracks, resulting in excellent R/t and SFmax.
　鋼板表面から表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度の標準偏差σが１．８ＧＰａ以下であり、さらに、鋼板表面から表層軟質層の板厚方向深さの１／２位置の板面のナノ硬度の標準偏差σが２．２ＧＰａ以下
　本発明において、プレス成形時の優れた曲げ性と衝突時の優れた曲げ破断特性を得るためには、鋼板表面から表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度の標準偏差σが１．８ＧＰａ以下であり、さらに、鋼板表面から表層軟質層の板厚方向深さの１／２位置の板面のナノ硬度の標準偏差σが２．２ＧＰａ以下であることが好ましい。鋼板表面から表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度の標準偏差σが１．８ＧＰａ以下であり、さらに、鋼板表面から表層軟質層の板厚方向深さの１／２位置の板面のナノ硬度の標準偏差σが２．２ＧＰａ以下の場合、ミクロ領域における組織硬度差が小さいことを意味し、プレス成形時および衝突時のボイドの生成や連結、さらには亀裂の進展をより抑制することが可能となり、優れたＲ／ｔおよびＳＦｍａｘが得られる。
また、素地鋼板表面から表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度の標準偏差σの好ましい範囲は、１．７ＧＰａ以下であることが好ましい。素地鋼板表面から表層軟質層の板厚方向深さの１／２位置の板面のナノ硬度の標準偏差σのより好ましい範囲は、２．１ＧＰａ以下である。 The standard deviation σ of the nano-hardness of the plate surface at a position 1/4 of the depth in the thickness direction of the surface soft layer from the steel plate surface is 1.8 GPa or less, and The standard deviation σ of the nanohardness of the plate surface at the 1/2 position is 2.2 GPa or less. In the present invention, in order to obtain excellent bendability during press forming and excellent bending rupture properties during collision, it is necessary to The standard deviation σ of the nano-hardness of the plate surface at 1/4 of the depth in the thickness direction of the soft layer is 1.8 GPa or less, and furthermore, the standard deviation σ of the nanohardness of the plate surface at 1/4 of the depth in the thickness direction of the surface soft layer from the steel plate surface is 1/2 of the depth in the thickness direction of the surface soft layer. It is preferable that the standard deviation σ of the nanohardness of the plate surface is 2.2 GPa or less. The standard deviation σ of the nano-hardness of the plate surface at a position 1/4 of the depth in the thickness direction of the surface soft layer from the steel plate surface is 1.8 GPa or less, and If the standard deviation σ of the nanohardness of the plate surface at the 1/2 position is 2.2 GPa or less, it means that the difference in microstructure hardness in the micro region is small, and it is difficult to prevent the formation and connection of voids during press forming and collision. It becomes possible to further suppress the propagation of cracks, and excellent R/t and SFmax can be obtained.
Further, a preferable range of the standard deviation σ of the nanohardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface is preferably 1.7 GPa or less. A more preferable range of the standard deviation σ of the nano-hardness of the plate surface at 1/2 the thickness direction depth of the surface soft layer from the base steel plate surface is 2.1 GPa or less.
　ここで、板厚方向深さの１／４位置、１／２位置の板面のナノ硬度とは、以下の方法により測定される硬度である。
　まず、めっき層が形成されている場合は、めっき層剥離後、素地鋼板の表面から表層軟質層の板厚方向深さの１／４の位置－５μｍの位置まで機械研磨を実施し、素地鋼板の表面から表層軟質層の板厚方向深さの１／４位置までダイヤモンドおよびアルミナでのバフ研磨を実施し、さらにコロイダルシリカ研磨を実施する。Ｈｙｓｉｔｒｏｎ社のｔｒｉｂｏ－９５０を用い、バーコビッチ形状のダイヤモンド圧子により、荷重：５００μＮ、測定領域：５０μｍ×５０μｍ、打点間隔：２μｍの条件でナノ硬度を測定する。
　また、表層軟質層の板厚方向深さの１／２位置まで機械研磨を実施し、ダイヤモンドおよびアルミナでのバフ研磨を実施、さらにコロイダルシリカ研磨を実施する。そして、Ｈｙｓｉｔｒｏｎ社のｔｒｉｂｏ－９５０を用い、バーコビッチ形状のダイヤモンド圧子により、荷重：５００μＮ、測定領域：５０μｍ×５０μｍ、打点間隔：２μｍの条件でナノ硬度を測定する。 Here, the nanohardness of the plate surface at the 1/4 position and 1/2 position of the depth in the thickness direction is the hardness measured by the following method.
First, if a plating layer is formed, after peeling off the plating layer, mechanical polishing is performed from the surface of the base steel sheet to a position 1/4 of the thickness direction depth of the surface soft layer - 5 μm, and the base steel plate is Buff polishing with diamond and alumina is performed from the surface to 1/4 of the depth in the board thickness direction of the surface soft layer, and further polishing is performed with colloidal silica. Nanohardness is measured using Hysitron's tribo-950 with a Berkovich-shaped diamond indenter under the conditions of load: 500 μN, measurement area: 50 μm×50 μm, and dot spacing: 2 μm.
Further, mechanical polishing is performed to 1/2 the depth in the thickness direction of the surface soft layer, buff polishing with diamond and alumina, and further colloidal silica polishing. Then, the nanohardness is measured using Hysitron's tribo-950 with a Berkovich-shaped diamond indenter under the conditions of load: 500 μN, measurement area: 50 μm×50 μm, and dot spacing: 2 μm.
　金属めっき層（第一めっき層）
　さらに、本発明の一実施形態に伴う亜鉛めっき鋼板は、素地鋼板の片面または両面の表面上において、金属めっき層（第一めっき層、プレめっき層）（なお、金属めっき層（第一めっき層）は、溶融亜鉛めっき層、合金化溶融亜鉛めっき層の亜鉛めっき層を除く）を有することが好ましい。金属めっき層は金属電気めっき層とすることが好ましく、以下では、金属電気めっき層を例に説明する。
金属電気めっき層が鋼板表面に形成されることで、プレス成形時および車体衝突時に最表層の前記金属電気めっき層が曲げ割れ発生の抑制に寄与するため、耐曲げ破断特性がさらに向上する。
　本発明では、露点を－２０℃超えとすることで、軟質層の厚みをより大きくすることができ、軸圧壊特性を非常に優れたものとすることが可能になる。この点、本発明では、金属めっき層を有することで、露点を－２０℃以下で、軟質層厚みが小さくても、軟質層厚みが大きい場合と同等の軸圧壊特性を得られる。 Metal plating layer (first plating layer)
Furthermore, the galvanized steel sheet according to an embodiment of the present invention has a metal plating layer (first plating layer, pre-plating layer) (in addition, a metal plating layer (first plating layer) on one or both surfaces of the base steel sheet. ) preferably has a hot-dip galvanized layer (excluding the galvanized layer of the alloyed hot-dip galvanized layer). The metal plating layer is preferably a metal electroplating layer, and below, the metal electroplating layer will be explained as an example.
By forming the metal electroplating layer on the surface of the steel sheet, the metal electroplating layer on the outermost layer contributes to suppressing the occurrence of bending cracks during press forming and when a vehicle body collides, so that the bending rupture resistance is further improved.
In the present invention, by setting the dew point to more than -20°C, the thickness of the soft layer can be increased, and the axial crushing properties can be made very excellent. In this regard, in the present invention, by having a metal plating layer, it is possible to obtain the same axial crushing characteristics as when the soft layer thickness is large even if the soft layer thickness is small and the dew point is −20° C. or lower.
　金属電気めっき層の金属種としては、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｇａ、Ｇｅ、Ａｓ、Ｒｕ、Ｒｈ、Ｐｄ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｏｓ、Ｉｒ、Ｒｔ、Ａｕ、Ｈｇ、Ｔｉ、Ｐｂ、Ｂｉのいずれでもかまわないが、Ｆｅであることがより好ましい。以下では、Ｆｅ系電気めっき層を例に説明する。 The metal species of the metal electroplating layer include Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Rt, Any of Au, Hg, Ti, Pb, and Bi may be used, but Fe is more preferable. In the following, a Fe-based electroplated layer will be explained as an example.
　Ｆｅ系電気めっき層の付着量は、０ｇ／ｍ２超とし、好ましくは２．０ｇ／ｍ２以上とする。Ｆｅ系電気めっき層の片面あたりの付着量の上限は特に限定されないが、コストの観点から、Ｆｅ系電気めっき層の片面あたりの付着量を６０ｇ／ｍ２以下とすることが好ましい。Ｆｅ系電気めっき層の付着量は、好ましくは５０ｇ／ｍ２以下であり、より好ましくは４０ｇ／ｍ２以下であり、さらに好ましくは３０ｇ／ｍ２以下とする。 The amount of the Fe-based electroplated layer deposited is more than 0 g/m 2 , preferably 2.0 g/m 2 or more. The upper limit of the amount of the Fe-based electroplated layer per side is not particularly limited, but from the viewpoint of cost, it is preferable that the amount of the Fe-based electroplated layer applied per side is 60 g/m 2 or less. The amount of the Fe-based electroplated layer deposited is preferably 50 g/m 2 or less, more preferably 40 g/m 2 or less, and even more preferably 30 g/m 2 or less.
　Ｆｅ系電気めっき層の付着量は、以下のとおり測定する。Ｆｅ系電気めっき鋼板から１０×１５ｍｍサイズのサンプルを採取して樹脂に埋め込み、断面埋め込みサンプルとする。同断面の任意の３か所を走査型電子顕微鏡（ＳｃａｎｎｉｎｇＥｌｅｃｔｒｏｎ Ｍｉｃｒｏｓｃｏｐｅ；ＳＥＭ）を用いて加速電圧１５ｋＶで、Ｆｅ系めっき層の厚みに応じて倍率２０００～１００００倍で観察し、３視野の厚みの平均値に鉄の比重を乗じることによって、Ｆｅ系めっき層の片面あたりの付着量に換算する。 The adhesion amount of the Fe-based electroplating layer is measured as follows. A sample with a size of 10 x 15 mm is taken from a Fe-based electroplated steel plate and embedded in resin to form a cross-sectional embedded sample. Three arbitrary points on the same cross section were observed using a scanning electron microscope (SEM) at an accelerating voltage of 15 kV and a magnification of 2,000 to 10,000 times depending on the thickness of the Fe-based plating layer. By multiplying the average value by the specific gravity of iron, it is converted into the amount of adhesion per one side of the Fe-based plating layer.
　Ｆｅ系電気めっき層としては、純Ｆｅの他、Ｆｅ－Ｂ合金、Ｆｅ－Ｃ合金、Ｆｅ－Ｐ合金、Ｆｅ－Ｎ合金、Ｆｅ－Ｏ合金、Ｆｅ－Ｎｉ合金、Ｆｅ－Ｍｎ合金、Ｆｅ－Ｍｏ合金、Ｆｅ－Ｗ合金等の合金めっき層が使用できる。Ｆｅ系電気めっき層の成分組成は特に限定されないが、Ｂ、Ｃ、Ｐ、Ｎ、Ｏ、Ｎｉ、Ｍｎ、Ｍｏ、Ｚｎ、Ｗ、Ｐｂ、Ｓｎ、Ｃｒ、Ｖ及びＣｏからなる群から選ばれる１または２以上の元素を合計で１０質量％以下含み、残部はＦｅ及び不可避的不純物からなる成分組成とすることが好ましい。Ｆｅ以外の元素の量を合計で１０質量％以下とすることで、電解効率の低下を防ぎ、低コストでＦｅ系電気めっき層を形成することができる。Ｆｅ－Ｃ合金の場合、Ｃの含有量は０．０８質量％以下とすることが好ましい。 In addition to pure Fe, Fe-based electroplating layers include Fe-B alloy, Fe-C alloy, Fe-P alloy, Fe-N alloy, Fe-O alloy, Fe-Ni alloy, Fe-Mn alloy, Fe- An alloy plating layer such as Mo alloy or Fe-W alloy can be used. The composition of the Fe-based electroplated layer is not particularly limited, but 1 selected from the group consisting of B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co. Alternatively, it is preferable that the composition contains two or more elements in a total of 10% by mass or less, with the remainder consisting of Fe and unavoidable impurities. By controlling the total amount of elements other than Fe to 10% by mass or less, a decrease in electrolytic efficiency can be prevented and an Fe-based electroplated layer can be formed at low cost. In the case of Fe--C alloy, the C content is preferably 0.08% by mass or less.
　つぎに、本発明の一実施形態に従う亜鉛めっき鋼板の機械特性について、説明する。 Next, the mechanical properties of the galvanized steel sheet according to one embodiment of the present invention will be explained.
　引張強さ（ＴＳ）：７８０ＭＰａ以上
　本発明の一実施形態に従う亜鉛めっき鋼板の引張強さは、７８０ＭＰａ以上である。
　なお、本発明の一実施形態に従う亜鉛系めっき鋼板の降伏応力（ＹＳ）、降伏比（ＹＲ）、全伸び（Ｅｌ）、限界穴広げ率（λ）、Ｕ曲げ＋密着曲げ試験での限界スペーサー厚さ（ＳＴ）およびＶ曲げ＋直交ＶＤＡ曲げ試験での荷重最大時のストローク（ＳＦｍａｘ）の基準値、および軸圧壊試験での破断（外観割れ）の有無については上述したとおりである。 Tensile strength (TS): 780 MPa or more The tensile strength of the galvanized steel sheet according to one embodiment of the present invention is 780 MPa or more.
In addition, the yield stress (YS), yield ratio (YR), total elongation (El), critical hole expansion ratio (λ), and critical spacer in the U-bending + close-contact bending test of the zinc-based plated steel sheet according to an embodiment of the present invention The reference values for the thickness (ST) and the stroke at maximum load (SFmax) in the V-bending + orthogonal VDA bending test, and the presence or absence of fracture (appearance cracking) in the axial crushing test are as described above.
　また、引張強さ（ＴＳ）、降伏応力（ＹＳ）、降伏比（ＹＲ）および全伸び（Ｅｌ）は、実施例において後述するＪＩＳ　Ｚ　２２４１に準拠する引張試験により、測定する。限界穴広げ率（λ）は、実施例において後述するＪＩＳ　Ｚ　２２５６に準拠する穴広げ試験により、測定する。限界スペーサー厚さ（ＳＴ）は、実施例において後述するＵ曲げ＋密着曲げ試験により、測定する。Ｖ曲げ＋直交ＶＤＡ曲げ試験での荷重最大時のストローク（ＳＦｍａｘ）は実施例において後述するＶ曲げ＋直交ＶＤＡ曲げ試験により、測定する。軸圧壊試験での破断（外観割れ）の有無は実施例において後述する軸圧壊試験により、測定する。 In addition, tensile strength (TS), yield stress (YS), yield ratio (YR), and total elongation (El) are measured by a tensile test based on JIS Z 2241, which will be described later in Examples. The critical hole expansion rate (λ) is measured by a hole expansion test based on JIS Z 2256, which will be described later in Examples. The critical spacer thickness (ST) is measured by the U-bending + close-contact bending test described later in Examples. The stroke (SFmax) at maximum load in the V-bending + orthogonal VDA bending test is measured by the V-bending + orthogonal VDA bending test described later in the Examples. The presence or absence of fracture (appearance cracking) in the axial crushing test is determined by the axial crushing test described later in Examples.
　亜鉛めっき層（第二めっき層）
　本発明の一実施形態に従う亜鉛めっき鋼板は、素地鋼板の上（素地鋼板表面上または金属めっき層が形成された場合は金属めっき層表面上）に形成された亜鉛めっき層を有し、この亜鉛めっき層は、素地鋼板の一方の表面の上のみに設けてもよく、両面の上に設けてもよい。
　すなわち、本発明の鋼板は、素地鋼板を有し、該素地鋼板上に第二めっき層（亜鉛めっき層、アルミニウムめっき層等）が形成されていてもよく、また、素地鋼板を有し、該素地鋼板上に金属めっき層（第一めっき層（亜鉛めっき層の第二めっき層を除く））と第二めっき層（亜鉛めっき層、アルミニウムめっき層等）とが順に形成されていてもよい。 Galvanized layer (second plating layer)
A galvanized steel sheet according to an embodiment of the present invention has a galvanized layer formed on a base steel sheet (on the surface of the base steel sheet or on the surface of the metal plating layer if a metal plating layer is formed), and The plating layer may be provided only on one surface of the base steel plate, or may be provided on both surfaces.
That is, the steel sheet of the present invention has a base steel plate, and a second plating layer (a galvanized layer, an aluminum plating layer, etc.) may be formed on the base steel plate. A metal plating layer (a first plating layer (excluding the second plating layer of the galvanized layer)) and a second plating layer (a zinc plating layer, an aluminum plating layer, etc.) may be formed in this order on the base steel sheet.
　なお、ここでいう亜鉛めっき層は、Ｚｎを主成分（Ｚｎ含有量が５０．０％以上）とするめっき層を指し、例えば、溶融亜鉛めっき層や合金化溶融亜鉛めっき層が挙げられる。 Note that the galvanized layer here refers to a plating layer containing Zn as a main component (Zn content is 50.0% or more), and includes, for example, a hot-dip galvanized layer and an alloyed hot-dip galvanized layer.
　ここで、溶融亜鉛めっき層は、例えば、Ｚｎと、２０．０質量％以下のＦｅ、０．００１質量％以上１．０質量％以下のＡｌにより構成することが好適である。また、溶融亜鉛めっき層には、任意に、Ｐｂ、Ｓｂ、Ｓｉ、Ｓｎ、Ｍｇ、Ｍｎ、Ｎｉ、Ｃｒ、Ｃｏ、Ｃａ、Ｃｕ、Ｌｉ、Ｔｉ、Ｂｅ、ＢｉおよびＲＥＭからなる群から選ばれる１種または２種以上の元素を合計で０．０質量％以上３．５質量％以下含有させてもよい。また、溶融亜鉛めっき層のＦｅ含有量は、より好ましくは７．０質量％未満である。なお、上記の元素以外の残部は、不可避的不純物である。 Here, the hot-dip galvanized layer is preferably composed of, for example, Zn, 20.0% by mass or less of Fe, and 0.001% by mass or more and 1.0% by mass or less of Al. Further, the hot-dip galvanized layer may optionally include one selected from the group consisting of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and REM. The total content of a species or two or more elements may be 0.0% by mass or more and 3.5% by mass or less. Further, the Fe content of the hot-dip galvanized layer is more preferably less than 7.0% by mass. Note that the remainder other than the above elements are unavoidable impurities.
　また、合金化溶融亜鉛めっき層は、例えば、２０質量％以下のＦｅ、０．００１質量％以上１．０質量％以下のＡｌにより構成することが好適である。また、合金化溶融亜鉛めっき層には、任意に、Ｐｂ、Ｓｂ、Ｓｉ、Ｓｎ、Ｍｇ、Ｍｎ、Ｎｉ、Ｃｒ、Ｃｏ、Ｃａ、Ｃｕ、Ｌｉ、Ｔｉ、Ｂｅ、ＢｉおよびＲＥＭからなる群から選ばれる１種または２種以上の元素を合計で０質量％以上３．５質量％以下含有させてもよい。合金化溶融亜鉛めっき層のＦｅ含有量は、より好ましくは７．０質量％以上、さらに好ましくは８．０質量％以上である。また、合金化溶融亜鉛めっき層のＦｅ含有量は、より好ましくは１５．０質量％以下、さらに好ましくは１２．０質量％以下である。なお、上記の元素以外の残部は、不可避的不純物である。 Furthermore, the alloyed hot-dip galvanized layer is preferably composed of, for example, 20% by mass or less of Fe and 0.001% by mass or more and 1.0% by mass or less of Al. Additionally, the alloyed hot-dip galvanized layer may optionally be selected from the group consisting of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and REM. One or more types of elements may be contained in a total amount of 0% by mass or more and 3.5% by mass or less. The Fe content of the alloyed hot-dip galvanized layer is more preferably 7.0% by mass or more, and still more preferably 8.0% by mass or more. Further, the Fe content of the alloyed hot-dip galvanized layer is more preferably 15.0% by mass or less, still more preferably 12.0% by mass or less. Note that the remainder other than the above elements are unavoidable impurities.
　加えて、亜鉛めっき層の片面あたりのめっき付着量は、特に限定されるものではないが、２０ｇ／ｍ２以上８０ｇ／ｍ２以下とすることが好ましい。 In addition, the amount of plating deposited on one side of the galvanized layer is not particularly limited, but is preferably 20 g/m 2 or more and 80 g/m 2 or less.
　なお、亜鉛めっき層のめっき付着量は、以下のようにして測定する。
　すなわち、１０質量％塩酸水溶液１Ｌに対し、Ｆｅに対する腐食抑制剤（朝日化学工業（株）製「イビット７００ＢＫ」（登録商標））を０．６ｇ添加した処理液を調整する。ついで、該処理液に、供試材となる亜鉛めっき鋼板を浸漬し、亜鉛めっき層を溶解させる。そして、溶解前後での供試材の質量減少量を測定し、その値を、素地鋼板の表面積（めっきで被覆されていた部分の表面積）で除することにより、めっき付着量（ｇ／ｍ２）を算出する。 In addition, the plating adhesion amount of the galvanized layer is measured as follows.
That is, a treatment solution is prepared by adding 0.6 g of a corrosion inhibitor for Fe (Ivit 700BK (registered trademark) manufactured by Asahi Chemical Co., Ltd.) to 1 L of a 10% by mass hydrochloric acid aqueous solution. Next, a galvanized steel sheet serving as a test material is immersed in the treatment liquid to dissolve the galvanized layer. Then, by measuring the amount of mass loss of the test material before and after melting, and dividing that value by the surface area of the base steel sheet (the surface area of the part covered with plating), the amount of plating coating (g/m 2 ) is calculated.
　なお、本発明の一実施形態に従う亜鉛めっき鋼板の板厚は、特に限定されないが、好ましくは０．５ｍｍ以上である。また、亜鉛めっき鋼板の板厚は、好ましくは３．５ｍｍ以下である。 Note that the thickness of the galvanized steel sheet according to an embodiment of the present invention is not particularly limited, but is preferably 0.5 mm or more. Further, the thickness of the galvanized steel sheet is preferably 3.5 mm or less.
［２．亜鉛めっき鋼板の製造方法］
　つぎに、本発明の一実施形態に従う亜鉛めっき鋼板の製造方法について、説明する。
　本発明の亜鉛めっき鋼板の製造方法は、上述した成分組成を有する鋼スラブに、仕上げ圧延温度：８２０℃以上の条件で熱間圧延を施し、熱延鋼板を得る、熱間圧延工程と、該熱間圧延工程後の鋼板に対して、３５０℃以上６００℃以下の温度域を平均加熱速度７℃／秒以上の条件で昇温する昇温工程と、焼鈍温度：７５０℃以上９００℃以下、焼鈍時間：２０秒以上の条件で焼鈍する、焼鈍工程と、焼鈍工程後、（焼鈍温度－３０℃）から６５０℃までの平均冷却速度を７℃／秒以上とし、６５０℃から５００℃までの平均冷却速度を１４℃／秒以下とする条件で冷却する第一冷却工程と、第一冷却工程後、冷延鋼板に亜鉛めっき処理を施し、亜鉛めっき鋼板を得る、亜鉛めっき工程と、亜鉛めっき鋼板に対して、３００℃以上４５０℃以下の温度域で２．０ｋｇｆ／ｍｍ２以上の張力を付与し、その後、亜鉛めっき鋼板を、１パス当たり直径５００ｍｍ以上１５００ｍｍ以下のロールにロール１／４周分接触させながら、５パス以上通過させ、ついで、室温から２５０℃以下の冷却停止温度まで冷却する、第二冷却工程と、亜鉛めっき鋼板を、冷却停止温度以上４４０℃以下の温度域まで再加熱して２０秒以上保持する、再加熱工程と、を含み、あるいはさらに熱間圧延工程後、かつ昇温工程前の鋼板に、圧下率が２０％以上８０％以下である冷間圧延を施し、冷延鋼板を得る、冷間圧延工程を含む。 [2. Manufacturing method of galvanized steel sheet]
Next, a method for manufacturing a galvanized steel sheet according to an embodiment of the present invention will be described.
The method for producing a galvanized steel sheet of the present invention includes a hot rolling process in which a steel slab having the above-mentioned composition is hot-rolled at a finish rolling temperature of 820°C or higher to obtain a hot-rolled steel sheet; A temperature raising step in which the steel plate after the hot rolling step is heated in a temperature range of 350°C or more and 600°C or less at an average heating rate of 7°C/sec or more, an annealing temperature: 750°C or more and 900°C or less, Annealing time: Annealing under the conditions of 20 seconds or more, and after the annealing step, the average cooling rate from (annealing temperature -30°C) to 650°C is 7°C/second or more, and from 650°C to 500°C. A first cooling step in which the average cooling rate is cooled at 14° C./sec or less, a galvanizing step in which a cold rolled steel sheet is subjected to galvanizing treatment to obtain a galvanized steel sheet after the first cooling step, and a galvanizing step in which a galvanized steel sheet is obtained. A tension of 2.0 kgf/mm 2 or more is applied to the steel sheet in a temperature range of 300°C or higher and 450°C or lower, and then the galvanized steel sheet is rolled by 1/4 of a roll with a diameter of 500 mm or more and 1500 mm or less per pass. A second cooling step is performed in which the galvanized steel sheet is passed through 5 passes or more while being in contact with the surrounding area, and then cooled from room temperature to a cooling stop temperature of 250°C or less. A reheating step of heating and holding for 20 seconds or more, or further cold rolling with a rolling reduction of 20% or more and 80% or less on the steel plate after the hot rolling step and before the temperature raising step. , including a cold rolling process to obtain a cold rolled steel plate.
　本発明において、鋼素材（鋼スラブ）の溶製方法は特に限定されず、転炉や電気炉等、公知の溶製方法いずれもが適合する。また、鋼スラブ（スラブ）は、マクロ偏析を防止するため、連続鋳造法で製造するのが好ましいが、造塊法や薄スラブ鋳造法などにより製造することも可能である。また、鋼スラブを製造した後、一旦室温まで冷却し、その後再度加熱する従来法に加え、室温まで冷却しないで、温片のままで加熱炉に装入する、あるいは、わずかの保熱を行った後に直ちに圧延する直送圧延・直接圧延などの省エネルギープロセスも問題なく適用できる。 In the present invention, the method of melting the steel material (steel slab) is not particularly limited, and any known melting method such as a converter or an electric furnace is suitable. Moreover, in order to prevent macro segregation, the steel slab (slab) is preferably manufactured by a continuous casting method, but it is also possible to manufacture it by an ingot method, a thin slab casting method, or the like. In addition to the conventional method of manufacturing a steel slab, cooling it to room temperature and then heating it again, there are also methods in which the steel slab is charged into a heating furnace as a hot piece without being cooled to room temperature, or it is slightly heat-retained. Energy-saving processes such as direct rolling and direct rolling, which involve rolling immediately after rolling, can also be applied without problems.
　（熱間圧延工程）
　スラブを加熱する場合は、炭化物の溶解や、圧延荷重の低減の観点から、スラブ加熱温度を１１００℃以上とすることが好ましい。また、スケールロスの増大を防止するため、スラブ加熱温度は１３００℃以下とすることが好ましい。なお、スラブ加熱温度はスラブ表面の温度である。また、スラブは通常の条件で粗圧延によりシートバーとされるが、加熱温度を低めにした場合は、熱間圧延時のトラブルを防止する観点から、仕上げ圧延前にバーヒーターなどを用いてシートバーを加熱することが好ましい。 (Hot rolling process)
When heating the slab, the slab heating temperature is preferably 1100° C. or higher from the viewpoint of dissolving carbides and reducing rolling load. Further, in order to prevent an increase in scale loss, the slab heating temperature is preferably 1300° C. or lower. Note that the slab heating temperature is the temperature of the slab surface. In addition, slabs are roughly rolled into sheet bars under normal conditions, but if the heating temperature is lower, from the perspective of preventing trouble during hot rolling, a bar heater etc. is used to roll the slabs into sheets before finishing rolling. Preferably, the bar is heated.
　仕上げ圧延温度：８２０℃以上
　仕上げ圧延は、圧延負荷の増大や、オーステナイトの未再結晶状態での圧下率が高くなり、圧延方向に伸長した異常な組織が発達した結果、最終材の延性、穴広げ性および曲げ性を低下させる。このため、仕上げ圧延温度は８２０℃以上とする。仕上げ圧延温度は、好ましくは８３０℃以上であり、より好ましくは８５０℃以上である。また、仕上げ圧延温度は、好ましくは１０８０℃以下であり、より好ましくは１０５０℃以下である。 Finish rolling temperature: 820°C or higher Finish rolling increases the rolling load and the reduction rate in the non-recrystallized state of austenite, which develops an abnormal structure that is elongated in the rolling direction, resulting in poor ductility and holes in the final material. Decreases spreadability and bendability. For this reason, the finish rolling temperature is set to 820°C or higher. The finish rolling temperature is preferably 830°C or higher, more preferably 850°C or higher. Further, the finish rolling temperature is preferably 1080°C or lower, more preferably 1050°C or lower.
　また、熱間圧延後の巻取温度については、特に限定されないが、最終材の延性、穴広げ性および曲げ性を低下する場合を考慮する必要がある。このため、熱間圧延後の巻取温度は３００℃以上とすることが好ましい。また、熱間圧延後の巻取温度は７００℃以下とすることが好ましい。 Furthermore, the coiling temperature after hot rolling is not particularly limited, but it is necessary to consider the case where the ductility, hole expandability, and bendability of the final material are reduced. For this reason, the coiling temperature after hot rolling is preferably 300°C or higher. Further, the coiling temperature after hot rolling is preferably 700°C or less.
　なお、熱間圧延時に粗圧延板同士を接合して連続的に仕上げ圧延を行ってもよい。また、粗圧延板を一旦巻き取っても構わない。また、熱間圧延時の圧延荷重を低減するために仕上げ圧延の一部または全部を潤滑圧延としてもよい。潤滑圧延を行うことは、鋼板形状の均一化、材質の均一化の観点からも有効である。なお、潤滑圧延時の摩擦係数は、０．１０以上０．２５以下の範囲とすることが好ましい。 Note that the rough rolled plates may be joined together during hot rolling and finish rolling may be performed continuously. Alternatively, the rough rolled plate may be wound up once. Further, in order to reduce the rolling load during hot rolling, part or all of the finish rolling may be performed as lubricated rolling. Performing lubricated rolling is also effective from the viewpoint of uniformity of the shape of the steel sheet and uniformity of material quality. Note that the friction coefficient during lubricated rolling is preferably in the range of 0.10 or more and 0.25 or less.
　（酸洗工程）
　上記のようにして製造した熱延鋼板に、酸洗を行ってよい。酸洗は鋼板表面の酸化物の除去が可能であることから、最終製品の高強度鋼板における良好な化成処理性やめっき品質の確保のために行うことができる。また、酸洗は、一回でも良いし、複数回に分けても良い。 (pickling process)
The hot rolled steel sheet produced as described above may be pickled. Since pickling can remove oxides on the surface of the steel sheet, it can be carried out to ensure good chemical conversion treatment properties and plating quality in the final high-strength steel sheet. Further, the pickling may be carried out once or may be carried out in multiple steps.
　（冷間圧延工程）
　上記のようにして得られた熱延後酸洗処理板または熱延鋼板に、必要に応じて、冷間圧延を施す。冷間圧延を施す場合、熱間圧延後、酸洗処理板のままで冷間圧延を施してもよいし、熱処理を施したのちに冷間圧延を施してもよい。また、任意に、冷間圧延後に得られた冷延鋼板に酸洗を施してもよい。
冷間圧延は、例えば、タンデム式の多スタンド圧延やリバース圧延等の、２パス以上のパス数を要する多パス圧延により行う。 (cold rolling process)
The hot-rolled pickled plate or hot-rolled steel plate obtained as described above is subjected to cold rolling, if necessary. When cold rolling is performed, the pickled plate may be cold rolled after hot rolling, or cold rolling may be performed after heat treatment. Further, optionally, the cold rolled steel sheet obtained after cold rolling may be pickled.
Cold rolling is performed, for example, by multi-pass rolling that requires two or more passes, such as tandem multi-stand rolling or reverse rolling.
　必要に応じて、冷間圧延の圧下率：２０％以上８０％以下
　冷間圧延を施す場合、冷間圧延の圧下率（累積圧下率）は特に限定されないが、２０％以上８０％以下とすることが好ましい。冷間圧延の圧下率が２０％未満では、焼鈍工程において鋼組織の粗大化や不均一化が生じやすくなり、最終製品においてＴＳや曲げ性が低下するおそれがある。一方、冷間圧延の圧下率が８０％を超えると、鋼板の形状不良が生じやすくなり、亜鉛めっきの付着量が不均一になるおそれがある。 If necessary, cold rolling reduction rate: 20% or more and 80% or less When cold rolling is performed, the cold rolling reduction rate (cumulative reduction rate) is not particularly limited, but should be 20% or more and 80% or less. It is preferable. If the rolling reduction ratio in cold rolling is less than 20%, the steel structure tends to become coarse and non-uniform in the annealing process, and there is a risk that the TS and bendability of the final product will deteriorate. On the other hand, if the rolling reduction ratio in cold rolling exceeds 80%, the steel sheet tends to be defective in shape, and the amount of zinc plating deposited may become uneven.
　（金属めっき（金属電気めっき、第一めっき）工程）
　本発明の一実施形態においては、熱間圧延工程後（冷間圧延を施す場合は、冷間圧延工程後）、かつ昇温工程の前の鋼板の片面もしくは両面において、金属めっきを施し、金属めっき層（第一めっき層）を形成する第一めっき工程を含んでいてもよい。
　例えば、上記のようにして得られた熱延鋼板または冷延鋼板の表面に金属電気めっき処理を施して、焼鈍前金属電気めっき層が少なくとも片面に形成された焼鈍前金属電気めっき鋼板としてもよい。なお、ここでいう金属めっきは、亜鉛めっき（第二めっき）を除く。
金属電気めっき処理方法は特に限定されないが、前述したように素地鋼板上に形成させる金属めっき層としては、金属電気めっき層とすることが好ましいため、金属電気めっき処理を施すことが好ましい。
例えば、Ｆｅ系電気めっき浴では硫酸浴、塩酸浴あるいは両者の混合などが適用できる。また、焼鈍前金属電気めっき層の付着量は、通電時間等によって調整することができる。なお、焼鈍前金属電気めっき鋼板とは、金属電気めっき層が焼鈍工程を経ていないことを意味し、金属電気めっき処理前の熱延鋼板、熱延後酸洗処理板または冷延鋼板について予め焼鈍された態様を除外するものではない。 (Metal plating (metal electroplating, first plating) process)
In one embodiment of the present invention, metal plating is applied to one or both sides of the steel plate after the hot rolling process (or after the cold rolling process if cold rolling is performed) and before the temperature raising process. The method may include a first plating step of forming a plating layer (first plating layer).
For example, the surface of the hot-rolled steel sheet or cold-rolled steel sheet obtained as described above may be subjected to a metal electroplating treatment to obtain a pre-annealed metal electroplated steel sheet in which a pre-annealed metal electroplating layer is formed on at least one side. . Note that the metal plating mentioned here excludes zinc plating (secondary plating).
The metal electroplating method is not particularly limited, but as described above, it is preferable that the metal electroplating layer is formed on the base steel sheet, so it is preferable to perform the metal electroplating process.
For example, in the Fe-based electroplating bath, a sulfuric acid bath, a hydrochloric acid bath, or a mixture of both can be used. Furthermore, the amount of deposited metal electroplating layer before annealing can be adjusted by adjusting the current application time and the like. Note that "pre-annealed metal electroplated steel sheet" means that the metal electroplated layer has not undergone an annealing process, and refers to a hot rolled steel sheet before metal electroplating, a pickled sheet after hot rolling, or a cold rolled steel sheet that has been annealed in advance. This does not exclude such aspects.
　ここで、電気めっき層の金属種としては、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｇａ、Ｇｅ、Ａｓ、Ｒｕ、Ｒｈ、Ｐｄ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｏｓ、Ｉｒ、Ｒｔ、Ａｕ、Ｈｇ、Ｔｉ、Ｐｂ、Ｂｉのいずれでもかまわないが、Ｆｅであることがより好ましいため、Ｆｅ系電気めっきの製造方法を以下に述べる。 Here, the metal species of the electroplating layer include Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Any of Rt, Au, Hg, Ti, Pb, and Bi may be used, but Fe is more preferable, so a method for producing Fe-based electroplating will be described below.
　通電開始前のＦｅ系電気めっき浴中のＦｅイオン含有量は、Ｆｅ２＋として０．５ｍｏｌ／Ｌ以上とすることが好ましい。Ｆｅ系電気めっき浴中のＦｅイオン含有量が、Ｆｅ２＋として０．５ｍｏｌ／Ｌ以上であれば、十分なＦｅ付着量を得ることができる。また、十分なＦｅ付着量を得るために、通電開始前のＦｅ系電気めっき浴中のＦｅイオン含有量は、２．０ｍｏｌ／Ｌ以下とすることが好ましい。 The Fe ion content in the Fe-based electroplating bath before the start of current application is preferably 0.5 mol/L or more as Fe 2+ . If the Fe ion content in the Fe-based electroplating bath is 0.5 mol/L or more as Fe 2+ , a sufficient amount of Fe deposition can be obtained. Further, in order to obtain a sufficient amount of Fe deposited, it is preferable that the Fe ion content in the Fe-based electroplating bath before the start of current application is 2.0 mol/L or less.
　また、Ｆｅ系電気めっき浴中にはＦｅイオン、並びにＢ、Ｃ、Ｐ、Ｎ、Ｏ、Ｎｉ、Ｍｎ、Ｍｏ、Ｚｎ、Ｗ、Ｐｂ、Ｓｎ、Ｃｒ、Ｖ及びＣｏからなる群から選ばれる少なくとも一種の元素を含有することができる。Ｆｅ系電気めっき浴中でのこれらの元素の合計含有量は、焼鈍前Ｆｅ系電気めっき層中でこれらの元素の合計含有量が１０質量％以下となるようにすることが好ましい。なお、金属元素は金属イオンとして含有すればよく、非金属元素はホウ酸、リン酸、硝酸、有機酸等の一部として含有することができる。また、硫酸鉄めっき液中には、硫酸ナトリウム、硫酸カリウム等の伝導度補助剤や、キレート剤、ｐＨ緩衝剤が含まれていてもよい。 In addition, the Fe-based electroplating bath contains Fe ions and at least one selected from the group consisting of B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co. It can contain one type of element. The total content of these elements in the Fe-based electroplating bath is preferably such that the total content of these elements in the Fe-based electroplated layer before annealing is 10% by mass or less. Note that the metal element may be contained as a metal ion, and the non-metal element may be contained as a part of boric acid, phosphoric acid, nitric acid, organic acid, or the like. Further, the iron sulfate plating solution may contain a conductivity aid such as sodium sulfate or potassium sulfate, a chelating agent, or a pH buffer.
　Ｆｅ系電気めっき浴のその他の条件についても特に限定しない。Ｆｅ系電気めっき液の温度は、定温保持性を考えると、３０℃以上とすることが好ましく、８５℃以下が好ましい。Ｆｅ系電気めっき浴のｐＨも特に規定しないが、水素発生による電流効率の低下を防ぐ観点から１．０以上とすることが好ましく、また、Ｆｅ系電気めっき浴の電気伝導度を考慮すると、３．０以下が好ましい。電流密度は、生産性の観点から１０Ａ／ｄｍ２以上とすることが好ましく、Ｆｅ系電気めっき層の付着量制御を容易にする観点から１５０Ａ／ｄｍ２以下とすることが好ましい。通板速度は、生産性の観点から５ｍｐｍ以上とすることが好ましく、付着量を安定的に制御する観点から１５０ｍｐｍ以下とすることが好ましい。 Other conditions for the Fe-based electroplating bath are not particularly limited either. The temperature of the Fe-based electroplating solution is preferably 30° C. or higher, and preferably 85° C. or lower, in view of constant temperature retention. Although the pH of the Fe-based electroplating bath is not particularly specified, it is preferably 1.0 or higher from the viewpoint of preventing a decrease in current efficiency due to hydrogen generation, and considering the electrical conductivity of the Fe-based electroplating bath, .0 or less is preferable. The current density is preferably 10 A/dm 2 or more from the viewpoint of productivity, and preferably 150 A/dm 2 or less from the viewpoint of facilitating control of the amount of Fe-based electroplated layer deposited. The plate passing speed is preferably 5 mpm or more from the viewpoint of productivity, and preferably 150 mpm or less from the viewpoint of stably controlling the amount of adhesion.
　なお、Ｆｅ系電気めっき処理を施す前の処理として、鋼板表面を清浄化するための脱脂処理及び水洗、さらには、鋼板表面を活性化するための酸洗処理及び水洗を施すことができる。これらの前処理に引き続いてＦｅ系電気めっき処理を実施する。脱脂処理及び水洗の方法は特に限定されず、通常の方法を用いることができる。酸洗処理においては、硫酸、塩酸、硝酸、及びこれらの混合物等各種の酸が使用できる。中でも、硫酸、塩酸あるいはこれらの混合が好ましい。酸の濃度は特に規定しないが、酸化皮膜の除去能力、及び過酸洗による肌荒れ（表面欠陥）防止等を考慮すると、１～２０ｍａｓｓ％程度が好ましい。また、酸洗処理液には、消泡剤、酸洗促進剤、酸洗抑制剤等を含有してもよい。 Note that as treatments before performing the Fe-based electroplating treatment, degreasing treatment and water washing can be performed to clean the steel sheet surface, and furthermore, pickling treatment and water washing can be performed to activate the steel sheet surface. Following these pre-treatments, Fe-based electroplating treatment is performed. The method of degreasing and washing with water is not particularly limited, and ordinary methods can be used. In the pickling treatment, various acids such as sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof can be used. Among these, sulfuric acid, hydrochloric acid, or a mixture thereof is preferred. Although the acid concentration is not particularly defined, it is preferably about 1 to 20 mass% in consideration of the ability to remove an oxide film and the prevention of rough skin (surface defects) due to overacid washing. Further, the pickling treatment liquid may contain an antifoaming agent, a pickling accelerator, a pickling inhibitor, and the like.
　（昇温工程）
　本発明の一実施形態においては、熱間圧延工程後（冷間圧延を施す場合は、冷間圧延工程後、および／または金属めっき層（第一めっき層）を形成する金属めっきを施す場合は、金属めっき第一めっき工程後）、鋼板を、３５０℃以上６００℃以下の温度域を平均加熱速度７℃／秒以上の条件で昇温する昇温工程を含む。 (Temperature raising process)
In one embodiment of the present invention, after the hot rolling process (if cold rolling is performed, after the cold rolling process, and/or if metal plating to form a metal plating layer (first plating layer) is performed, , metal plating (after the first plating step), includes a temperature raising step of raising the temperature of the steel plate in a temperature range of 350° C. or higher and 600° C. or lower at an average heating rate of 7° C./sec or higher.
　３５０℃以上６００℃以下の温度域における平均加熱速度：７℃／秒以上
　本発明において、３５０℃以上６００℃以下の温度域における平均加熱速度が上昇することで、フェライト粒内の孤立した微細な島状硬質第二相（マルテンサイト＋残留オーステナイト）の比率を増やすことで、λ、Ｒ/ｔ、ＳＴおよびＳＦｍａｘの向上が実現できる。したがって、３５０℃以上６００℃以下の温度域における平均加熱速度は７℃／ｓ以上とする。好ましく９℃／ｓ以上とする。
　上限については、特に限定されないが、３５０℃以上６００℃以下の温度域における平均加熱速度は１００℃／ｓ以下とすることが好ましく、９０℃／ｓ以下とすることがより好ましい。
ここで、平均加熱速度（℃／ｓ）は、（加熱終了温度（℃）－加熱開始温度（℃））／加熱時間（ｓ）より算出される。 Average heating rate in the temperature range of 350°C to 600°C: 7°C/second or more In the present invention, by increasing the average heating rate in the temperature range of 350°C to 600°C, isolated fine particles within the ferrite grains By increasing the ratio of the island-like hard second phase (martensite + retained austenite), improvements in λ, R/t, ST, and SFmax can be realized. Therefore, the average heating rate in the temperature range from 350°C to 600°C is 7°C/s or more. It is preferably 9°C/s or more.
The upper limit is not particularly limited, but the average heating rate in the temperature range from 350°C to 600°C is preferably 100°C/s or less, more preferably 90°C/s or less.
Here, the average heating rate (°C/s) is calculated from (heating end temperature (°C) - heating start temperature (°C))/heating time (s).
　（焼鈍工程）
　本発明の一実施形態においては、昇温工程後、焼鈍温度：７５０℃以上９００℃以下、焼鈍時間：２０秒以上の条件で焼鈍する、焼鈍工程を含む。 (Annealing process)
One embodiment of the present invention includes an annealing step after the temperature raising step, in which annealing is performed at an annealing temperature of 750° C. or more and 900° C. or less and an annealing time of 20 seconds or more.
　焼鈍温度：７５０℃以上９００℃以下
焼鈍温度が７５０℃未満の場合、フェライトとオーステナイトの二相域での加熱中におけるオーステナイトの生成割合が不十分になる。そのため、焼鈍後にフェライトの面積率が過度に増加して、所望のＴＳ、ＹＳおよびＹＲが得られない。一方、焼鈍温度が９００℃を超えると、２０．０％以上のフェライトの面積率が得られず、延性が低下する。したがって、焼鈍温度は７５０℃以上９００℃以下とする。焼鈍温度は、好ましくは８８０℃以下である。なお、焼鈍温度は、焼鈍工程での最高到達温度である。 Annealing temperature: 750°C or more and 900°C or less When the annealing temperature is less than 750°C, the proportion of austenite produced during heating in the two-phase region of ferrite and austenite becomes insufficient. Therefore, the area ratio of ferrite increases excessively after annealing, making it impossible to obtain desired TS, YS, and YR. On the other hand, when the annealing temperature exceeds 900° C., an area ratio of ferrite of 20.0% or more cannot be obtained, and ductility decreases. Therefore, the annealing temperature is set to 750°C or more and 900°C or less. The annealing temperature is preferably 880°C or lower. Note that the annealing temperature is the highest temperature reached in the annealing step.
　焼鈍時間：２０秒以上
　焼鈍時間が２０秒未満になると、フェライトとオーステナイトの二相域での加熱中におけるオーステナイトの生成割合が不十分になる。そのため、焼鈍後にフェライトの面積率が過度に増加して、ＴＳ、ＹＳおよびＹＲが得られない。そのため、焼鈍時間は２０秒以上とする。焼鈍時間は、好ましくは３０秒以上であり、より好ましくは５０秒以上である。なお、焼鈍時間の上限はとくに限定されないが、焼鈍時間は９００秒以下とすることが好ましく、より好ましくは８００秒以下である。
なお、焼鈍時間とは、（焼鈍温度－４０℃）以上焼鈍温度以下の温度域での保持時間である。すなわち、焼鈍時間には、焼鈍温度での保持時間に加え、焼鈍温度に到達する前後の加熱および冷却における（焼鈍温度－４０℃）以上焼鈍温度以下の温度域での滞留時間も含まれる。
なお、焼鈍回数は２回以上でもよいが、エネルギー効率の観点から１回が好ましい。 Annealing time: 20 seconds or more When the annealing time is less than 20 seconds, the proportion of austenite produced during heating in the two-phase region of ferrite and austenite becomes insufficient. Therefore, the area ratio of ferrite increases excessively after annealing, making it impossible to obtain TS, YS, and YR. Therefore, the annealing time is set to 20 seconds or more. The annealing time is preferably 30 seconds or more, more preferably 50 seconds or more. Although the upper limit of the annealing time is not particularly limited, the annealing time is preferably 900 seconds or less, more preferably 800 seconds or less.
Note that the annealing time is the holding time in a temperature range of (annealing temperature -40° C.) or higher and lower than the annealing temperature. That is, in addition to the holding time at the annealing temperature, the annealing time also includes the residence time in the temperature range from (annealing temperature -40°C) to below the annealing temperature during heating and cooling before and after reaching the annealing temperature.
The number of times of annealing may be two or more times, but from the viewpoint of energy efficiency, one time is preferable.
　焼鈍工程の雰囲気（焼鈍雰囲気）の露点：－３０℃以上
　本発明の一実施形態においては、焼鈍工程の雰囲気（焼鈍雰囲気）の露点を－３０℃以上とすることが好ましい。焼鈍工程における焼鈍雰囲気の露点を－３０℃以上にして焼鈍を行うことで、脱炭反応が促進され、表層軟質層をより深く形成できる。焼鈍工程の焼鈍雰囲気の露点は、より好ましくは－２５℃以上、さらにより好ましくは－１５℃以上、最も好ましくは－５℃以上である。焼鈍工程の焼鈍雰囲気の露点の上限は特に定めないが、Ｆｅ系電気めっき層表面の酸化を好適に防ぎ、亜鉛めっき層を設ける際のめっき密着性を良好にするため、焼鈍工程の焼鈍雰囲気の露点は３０℃以下とすることが好ましい。 Dew point of annealing process atmosphere (annealing atmosphere): −30° C. or higher In an embodiment of the present invention, it is preferable that the dew point of the annealing step atmosphere (annealing atmosphere) is −30° C. or higher. By performing annealing with the dew point of the annealing atmosphere at -30° C. or higher in the annealing step, the decarburization reaction is promoted and a deeper soft surface layer can be formed. The dew point of the annealing atmosphere in the annealing step is more preferably -25°C or higher, even more preferably -15°C or higher, and most preferably -5°C or higher. Although there is no particular upper limit for the dew point of the annealing atmosphere in the annealing process, in order to suitably prevent oxidation of the surface of the Fe-based electroplated layer and improve plating adhesion when providing the galvanized layer, the annealing atmosphere in the annealing process should be set. The dew point is preferably 30°C or lower.
　（第一冷却工程）
　本発明では、焼鈍工程後、（焼鈍温度－３０℃）から６５０℃までの平均冷却速度を７℃／秒以上とし、６５０℃から５００℃までの平均冷却速度を１４℃／秒以下とする条件で冷却する第一冷却工程を含む。 (First cooling process)
In the present invention, after the annealing step, the average cooling rate from (annealing temperature -30°C) to 650°C is 7°C/second or more, and the average cooling rate from 650°C to 500°C is 14°C/second or less. It includes a first cooling step of cooling.
　（焼鈍温度－３０℃）から６５０℃までの平均冷却速度：７℃／秒以上
　本発明において、６５０℃以上の高温域で早く冷却した場合、フェライト粒界に微細なオーステナイトが取り残され、最終的にフェライト粒内の孤立した微細な島状硬質第二相（マルテンサイト＋残留オーステナイト）の比率が増加する。したがって、（焼鈍温度－３０℃）から６５０℃までの平均冷却速度は７℃／秒以上とする。（焼鈍温度－３０℃）から６５０℃までの平均冷却速度は、好ましくは９℃／秒以上である。
（焼鈍温度－３０℃）から６５０℃までの平均冷却速度は、好ましくは８０℃／秒以下であり、より好ましくは６０℃／秒以下である。
ここで、平均冷却速度（℃／ｓ）は、（焼鈍温度（℃）－３０（℃）－６５０（℃））／冷却時間（ｓ）より算出される。 Average cooling rate from (annealing temperature -30°C) to 650°C: 7°C/sec or more In the present invention, when cooling quickly in a high temperature range of 650°C or higher, fine austenite is left behind at the ferrite grain boundaries, resulting in the final The ratio of isolated fine island-like hard second phases (martensite + retained austenite) within ferrite grains increases. Therefore, the average cooling rate from (annealing temperature -30°C) to 650°C is 7°C/sec or more. The average cooling rate from (annealing temperature -30°C) to 650°C is preferably 9°C/sec or more.
The average cooling rate from (annealing temperature -30°C) to 650°C is preferably 80°C/second or less, more preferably 60°C/second or less.
Here, the average cooling rate (°C/s) is calculated from (annealing temperature (°C) - 30 (°C) - 650 (°C))/cooling time (s).
　６５０℃から５００℃までの平均冷却速度：１４℃／秒以下
　本発明において、６５０℃以下の中温域でゆっくり冷却した場合、フェライト粒界の微細オーステナイトが、近い方位を有した隣接するフェライトの合体後、一つのフェライト粒となり、そのフェライト粒内に孤立した微細な島状オーステナイトとして取り残され、最終的にフェライト粒内の孤立した微細な島状硬質第二相（マルテンサイト＋残留オーステナイト）の比率が増加する。したがって、６５０℃から５００℃までの平均冷却速度は、１４℃／秒以下であり、好ましくは１２℃／秒以下である。６５０℃から５００℃までの平均冷却速度は、好ましくは１℃／秒以上であり、より好ましくは２℃／秒以上である。
ここで、平均冷却速度（℃／ｓ）は、（６５０（℃）－５００（℃））／冷却時間（ｓ）より算出される。 Average cooling rate from 650°C to 500°C: 14°C/sec or less In the present invention, when cooling slowly at a medium temperature range of 650°C or less, fine austenite at the ferrite grain boundaries coalesce between adjacent ferrites with similar orientations. After that, it becomes one ferrite grain, and is left behind as a fine island-like austenite isolated within the ferrite grain, and finally the ratio of isolated fine island-like hard second phase (martensite + retained austenite) within the ferrite grain increases. Therefore, the average cooling rate from 650°C to 500°C is 14°C/second or less, preferably 12°C/second or less. The average cooling rate from 650°C to 500°C is preferably 1°C/second or more, more preferably 2°C/second or more.
Here, the average cooling rate (°C/s) is calculated from (650 (°C) - 500 (°C))/cooling time (s).
　（亜鉛めっき工程（第二めっき工程））
　本発明では、第一冷却工程後、鋼板に亜鉛めっき処理を施し、亜鉛めっき鋼板を得る。
　亜鉛めっき処理としては、例えば、溶融亜鉛めっき処理や合金化亜鉛めっき処理が挙げられる。 (Zinc plating process (second plating process))
In the present invention, after the first cooling step, the steel sheet is galvanized to obtain a galvanized steel sheet.
Examples of the galvanizing treatment include hot-dip galvanizing and alloyed galvanizing.
　溶融亜鉛めっき処理の場合、鋼板を４４０℃以上５００℃以下の亜鉛めっき浴中に浸漬させた後、ガスワイピング等によって、めっき付着量を調整することが好ましい。溶融亜鉛めっき浴としては、前記した亜鉛めっき層の組成となれば特に限定されるものではないが、例えば、Ａｌ含有量が０．１０質量％以上０．２３質量％以下であり、残部がＺｎおよび不可避的不純物からなる組成のめっき浴を用いることが好ましい。 In the case of hot-dip galvanizing, it is preferable to immerse the steel sheet in a galvanizing bath at a temperature of 440° C. or higher and 500° C. or lower, and then adjust the coating amount by gas wiping or the like. The hot-dip galvanizing bath is not particularly limited as long as it has the composition of the galvanized layer described above. It is preferable to use a plating bath having a composition comprising: and unavoidable impurities.
　また、合金化亜鉛めっき処理の場合、前記の要領で溶融亜鉛めっき処理を施した後、溶融亜鉛めっき鋼板を４５０℃以上６００℃以下の合金化温度に加熱して合金化処理を施すことが好ましい。
合金化温度が４５０℃未満では、Ｚｎ－Ｆｅ合金化速度が遅くなり、合金化が困難となる場合がある。一方、合金化温度が６００℃を超えると、未変態オーステナイトがパーライトへ変態し、ＴＳを７８０ＭＰａ以上とすることが困難となる。なお、合金化温度は、より好ましくは５００℃以上であり、さらに好ましくは５１０℃以上である。また、合金化温度は、より好ましくは５７０℃以下である。 In addition, in the case of alloyed galvanizing treatment, after hot-dip galvanizing treatment as described above, it is preferable to heat the hot-dip galvanized steel sheet to an alloying temperature of 450°C or more and 600°C or less to perform alloying treatment. .
If the alloying temperature is less than 450° C., the Zn--Fe alloying speed will be slow and alloying may become difficult. On the other hand, when the alloying temperature exceeds 600°C, untransformed austenite transforms into pearlite, making it difficult to make the TS 780 MPa or higher. Note that the alloying temperature is more preferably 500°C or higher, and still more preferably 510°C or higher. Further, the alloying temperature is more preferably 570°C or lower.
　また、溶融亜鉛めっき鋼板（ＧＩ）および合金化溶融亜鉛めっき鋼板（ＧＡ）のめっき付着量はいずれも、片面あたり２０～８０ｇ／ｍ２とすることが好ましい。なお、めっき付着量は、ガスワイピング等により調節することが可能である。 Furthermore, it is preferable that the coating weight of the hot-dip galvanized steel sheet (GI) and the alloyed hot-dip galvanized steel sheet (GA) be 20 to 80 g/m 2 per side. Note that the amount of plating deposited can be adjusted by gas wiping or the like.
　（第二冷却工程）
　本発明では、亜鉛めっき工程後、亜鉛めっき鋼板に対して、３００℃以上４５０℃以下の温度域で２．０ｋｇｆ／ｍｍ２以上の張力を付与し、亜鉛めっき鋼板を、１パス当たり直径５００ｍｍ以上１５００ｍｍ以下のロールにロール１／４周分接触させながら、５パス以上通過させ、ついで、２５０℃以下の冷却停止温度（第二冷却停止温度）まで冷却する第二冷却工程を含む。 (Second cooling process)
In the present invention, after the galvanizing process, a tension of 2.0 kgf/mm2 or more is applied to the galvanized steel sheet in a temperature range of 300°C or higher and 450°C or lower, and the galvanized steel sheet is heated to a diameter of 500 mm or more per pass. A second cooling step is included in which the material is passed through 5 passes or more while being brought into contact with a roll of 1500 mm or less for 1/4 rotation of the roll, and then cooled to a cooling stop temperature (second cooling stop temperature) of 250° C. or less.
　３００℃以上４５０℃以下の温度域で付与する張力：２．０ｋｇｆ／ｍｍ２以上
　本発明において、上記のように亜鉛めっき鋼板に対して２．０ｋｇｆ／ｍｍ２以上の張力を一回以上付与することで、オーステナイトの大半が加工（応力・ひずみ）誘起変態によりマルテンサイトとなり、その後、再加熱工程で焼戻しを受けるため、最終組織のフレッシュマルテンサイトの面積率を低減でき、さらに、焼戻しマルテンサイトを適正量確保できる。また、第二冷却工程直後のオーステナイトの量を低減でき、最終組織の残留オーステナイトの体積率を低減できる。その結果、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られる。
　ここで、張力は、ロール左右のロードセルの荷重（ｋｇｆ）の合計値を、鋼板の断面積（＝板厚（ｍｍ）×板幅（ｍｍ））（ｍｍ２）で割ることで得られる。なお、ロードセルの配置は、張力方向と平行にする必要がある。
ここで、ロードセルの配置位置は、ロール両端部から２００ｍｍ位置とすることが好ましい。また、用いるロールの胴長は、１５００～２５００ｍｍとすることが好ましい。
　また、この張力は、好ましくは２．２ｋｇｆ／ｍｍ２以上であり、より好ましくは２．４ｋｇｆ／ｍｍ２以上である。また、このパス数は、好ましくは１５．０ｋｇｆ／ｍｍ２以下であり、より好ましくは１０．０ｋｇｆ／ｍｍ２以下である。 Tension applied in a temperature range of 300°C to 450°C: 2.0 kgf/mm 2 or more In the present invention, a tension of 2.0 kgf/mm 2 or more is applied to the galvanized steel sheet at least once as described above. As a result, most of the austenite becomes martensite through deformation (stress/strain)-induced transformation, and then undergoes tempering in the reheating process, which reduces the area ratio of fresh martensite in the final structure. A suitable amount can be secured. Further, the amount of austenite immediately after the second cooling step can be reduced, and the volume fraction of retained austenite in the final structure can be reduced. As a result, desired λ, R/t, ST and SFmax are obtained.
Here, the tension is obtained by dividing the total value of the loads (kgf) of the load cells on the left and right sides of the roll by the cross-sectional area of the steel plate (=plate thickness (mm) x plate width (mm)) (mm 2 ). Note that the load cell must be placed parallel to the tension direction.
Here, the load cell is preferably arranged at a position 200 mm from both ends of the roll. Further, the length of the roll used is preferably 1500 to 2500 mm.
Further, this tension is preferably 2.2 kgf/mm 2 or more, more preferably 2.4 kgf/mm 2 or more. Further, the number of passes is preferably 15.0 kgf/mm 2 or less, more preferably 10.0 kgf/mm 2 or less.
　亜鉛めっき鋼板を、１パス当たり直径５００ｍｍ以上１５００ｍｍ以下のロールにロール１／４周分接触させながら、通過させるパス数：５パス以上
　本発明において、亜鉛めっき鋼板を、直径５００ｍｍ以上１５００ｍｍ以下のロールに１パス当たりロール１／４周分接触させながら、めっき鋼板を５パス以上通過させることで、オーステナイトの大半が加工（応力・ひずみ）誘起変態によりマルテンサイトとなり、その後、再加熱工程で焼戻しを受けるため、最終組織のフレッシュマルテンサイトの面積率を低減でき、さらに、焼戻しマルテンサイトを適正量確保できる。また、第二冷却工程直後のオーステナイトの量を低減でき、最終組織の残留オーステナイトの体積率を低減できる。その結果、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られる。 Number of passes in which the galvanized steel sheet is passed through a roll having a diameter of 500 mm or more and 1500 mm or less while being in contact with the roll for 1/4 rotation per pass: 5 passes or more In the present invention, the galvanized steel sheet is passed through a roll having a diameter of 500 mm or more and 1500 mm or less. By passing the plated steel plate through 5 or more passes while contacting the steel plate for 1/4 roll per pass, most of the austenite becomes martensite due to processing (stress/strain) induced transformation, and then is tempered in a reheating process. Therefore, the area ratio of fresh martensite in the final structure can be reduced, and furthermore, an appropriate amount of tempered martensite can be secured. Moreover, the amount of austenite immediately after the second cooling process can be reduced, and the volume fraction of retained austenite in the final structure can be reduced. As a result, desired λ, R/t, ST and SFmax are obtained.
　第二冷却停止温度：２５０℃以下
　第二冷却工程の冷却条件は特定に限定されず、常法に従えばよい。冷却方法としては、例えば、ガスジェット冷却、ミスト冷却、ロール冷却、水冷および空冷などを適用することができる。第二冷却停止温度を２５０℃以下にすることにより、適正量のオーステナイトがマルテンサイトに変態し、その後、再加熱工程で焼戻しを受けるため、最終組織のフレッシュマルテンサイトの面積率を低減でき、さらに、焼戻しマルテンサイトを適正量確保できる。また、第二冷却工程直後のオーステナイトの量を低減でき、最終組織の残留オーステナイトの体積率を低減できる。その結果、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られる。なお、表面の酸化防止の観点から、２００℃以下まで冷却することが好ましい。下限は特に限定されないが、室温（－５℃以上５５℃以下）とすることが好ましい。平均冷却速度は、例えば、１℃／秒以上５０℃／秒以下とすることが好適である。 Second cooling stop temperature: 250°C or less The cooling conditions for the second cooling step are not particularly limited, and may be according to a conventional method. As the cooling method, for example, gas jet cooling, mist cooling, roll cooling, water cooling, air cooling, etc. can be applied. By setting the second cooling stop temperature to 250°C or less, an appropriate amount of austenite transforms into martensite and is then tempered in the reheating process, which reduces the area ratio of fresh martensite in the final structure. , an appropriate amount of tempered martensite can be secured. Further, the amount of austenite immediately after the second cooling step can be reduced, and the volume fraction of retained austenite in the final structure can be reduced. As a result, desired λ, R/t, ST and SFmax are obtained. In addition, from the viewpoint of preventing surface oxidation, it is preferable to cool to 200° C. or lower. The lower limit is not particularly limited, but it is preferably room temperature (-5°C or higher and 55°C or lower). The average cooling rate is preferably, for example, 1° C./second or more and 50° C./second or less.
　（再加熱工程）
　第二冷却工程後、再加熱工程として、亜鉛めっき鋼板を、上記冷却停止温度（第二冷却停止温度）以上４４０℃以下の温度域まで再加熱して２０秒以上保持する。 (Reheating process)
After the second cooling step, as a reheating step, the galvanized steel sheet is reheated to a temperature range of above the cooling stop temperature (second cooling stop temperature) and below 440° C. and held for 20 seconds or more.
　再加熱温度：上記冷却停止温度（第二冷却停止温度）以上４４０℃以下の温度域
　再加熱保持時間：２０秒以上
　本発明において、冷却停止温度（第二冷却停止温度）以上まで再加熱することおよび２０秒以上保持することにより、鋼中の拡散性水素が放出される。また、最終組織のフレッシュマルテンサイトの面積率を低減でき、焼戻しマルテンサイトを適正量確保できる。また、第二冷却工程直後のオーステナイトの量を低減でき、最終組織の残留オーステナイトの体積率を低減できる。その結果、所望のλ、Ｒ／ｔ、ＳＴおよびＳＦｍａｘが得られる。一方、再加熱温度が４４０℃を超える場合、亜鉛めっきが一部溶解し、ロールに付着してしまい、均一に亜鉛めっきされた溶融亜鉛めっき鋼板が得られない。また、再加熱保持時間が２０秒未満の場合、鋼中の拡散性水素が所望量放出されない。
　よって、本発明では、第二冷却停止温度以上４４０℃以下の温度域まで再加熱して、２０秒以上保持する。 Reheating temperature: Temperature range above the above cooling stop temperature (second cooling stop temperature) and below 440°C Reheating holding time: 20 seconds or more In the present invention, reheating to above the cooling stop temperature (second cooling stop temperature) By holding the temperature for 20 seconds or more, diffusible hydrogen in the steel is released. Furthermore, the area ratio of fresh martensite in the final structure can be reduced, and an appropriate amount of tempered martensite can be secured. Further, the amount of austenite immediately after the second cooling step can be reduced, and the volume fraction of retained austenite in the final structure can be reduced. As a result, desired λ, R/t, ST and SFmax are obtained. On the other hand, if the reheating temperature exceeds 440° C., a portion of the zinc plating will melt and adhere to the roll, making it impossible to obtain a uniformly galvanized hot-dip galvanized steel sheet. Moreover, when the reheating holding time is less than 20 seconds, the desired amount of diffusible hydrogen in the steel is not released.
Therefore, in the present invention, the temperature is reheated to a temperature range from the second cooling stop temperature to 440° C. and held for 20 seconds or more.
　また、上記のようにして得た亜鉛めっき鋼板に、さらに、調質圧延を施してもよい。調質圧延の圧下率は２．００％を超えると、降伏応力が上昇し、亜鉛めっき鋼板を部材に成形する際の寸法精度が低下するおそれがある。そのため、調質圧延の圧下率は２．００％以下が好ましい。なお、調質圧延の圧下率の下限は特に限定されるものではないが、生産性の観点から０．０５％以上が好ましい。また、調質圧延は上述した各工程を行うための焼鈍装置と連続した装置上（オンライン）で行ってもよいし、各工程を行うための焼鈍装置とは不連続な装置上（オフライン）で行ってもよい。また、調質圧延の圧延回数は、１回でもよく、２回以上であってもよい。なお、調質圧延と同等の伸長率を付与できれば、レベラー等による圧延であっても構わない。 Additionally, the galvanized steel sheet obtained as described above may be further subjected to temper rolling. If the reduction ratio in temper rolling exceeds 2.00%, the yield stress will increase, and there is a risk that the dimensional accuracy when forming the galvanized steel sheet into a member will decrease. Therefore, the reduction ratio in temper rolling is preferably 2.00% or less. Note that the lower limit of the rolling reduction in skin pass rolling is not particularly limited, but from the viewpoint of productivity, it is preferably 0.05% or more. In addition, skin pass rolling may be performed on a device that is continuous with the annealing device for performing each process mentioned above (online), or on a device that is discontinuous with the annealing device for performing each process (offline). You may go. Further, the number of times of temper rolling may be one, or two or more times. Note that rolling with a leveler or the like may be used as long as it can provide an elongation rate equivalent to that of temper rolling.
　その他の製造方法の条件は、とくに限定しないが、生産性の観点から、上記の焼鈍、溶融亜鉛めっき、亜鉛めっきの合金化処理などの一連の処理は、溶融亜鉛めっきラインであるＣＧＬ（Ｃｏｎｔｉｎｕｏｕｓ　Ｇａｌｖａｎｉｚｉｎｇ　Ｌｉｎｅ）で行うのが好ましい。溶融亜鉛めっき後は、めっきの目付け量を調整するために、ワイピングが可能である。なお、上記した条件以外のめっき等の条件は、溶融亜鉛めっきの常法に依ることができる。 Conditions for other manufacturing methods are not particularly limited, but from the viewpoint of productivity, a series of treatments such as annealing, hot-dip galvanizing, and alloying treatment of galvanizing are performed on a CGL (Continuous Galvanizing Line), which is a hot-dip galvanizing line. It is preferable to carry out the process using Line). After hot-dip galvanizing, wiping can be performed to adjust the coating weight. Note that the conditions for plating and the like other than the above-mentioned conditions can be based on a conventional method for hot-dip galvanizing.
［３．部材］
　つぎに、本発明の一実施形態に従う部材について、説明する。
　本発明の一実施形態に従う部材は、上記の亜鉛めっき鋼板を用いてなる（素材とする）部材である。例えば、素材である亜鉛めっき鋼板に、成形加工または接合加工の少なくとも一方を施して部材とする。
　ここで、上記の亜鉛めっき鋼板は、ＴＳ：７８０ＭＰａ以上であり、かつ、高いＹＳおよびＹＲと、優れたプレス成形性（延性、穴広げ性および曲げ性）と、衝突時の耐破断特性（曲げ破断特性および軸圧壊特性）を有する。そのため、本発明の一実施形態に従う部材は、高強度であり、かつ、耐衝撃特性にも優れている。したがって、本発明の一実施形態に従う部材は、自動車分野で使用される衝撃エネルギー吸収部材に適用して特に好適である。 [3. Element]
Next, a member according to an embodiment of the present invention will be explained.
A member according to an embodiment of the present invention is a member made of (made of) the above-mentioned galvanized steel plate. For example, the material is a galvanized steel plate that is subjected to at least one of forming and joining processes to produce a member.
Here, the above-mentioned galvanized steel sheet has a TS of 780 MPa or more, high YS and YR, excellent press formability (ductility, hole expandability, and bendability), and rupture resistance at the time of collision (bending fracture properties and axial crush properties). Therefore, the member according to one embodiment of the present invention has high strength and excellent impact resistance. Therefore, a member according to an embodiment of the present invention is particularly suitable for application as an impact energy absorbing member used in the automotive field.
　［４．部材の製造方法］
　つぎに、本発明の一実施形態に従う部材の製造方法について、説明する。
　本発明の一実施形態に従う部材の製造方法は、上記の亜鉛めっき鋼板（例えば、上記の亜鉛めっき鋼板の製造方法により製造された亜鉛めっき鋼板）に、成形加工または接合加工の少なくとも一方を施して部材とする、工程を有する。
　ここで、成形加工方法は、特に限定されず、例えば、プレス加工等の一般的な加工方法を用いることができる。また、接合加工方法も、特に限定されず、例えば、スポット溶接、レーザー溶接、アーク溶接等の一般的な溶接や、リベット接合、かしめ接合等を用いることができる。なお、成形条件および接合条件については特に限定されず、常法に従えばよい。 [4. Manufacturing method of parts]
Next, a method for manufacturing a member according to an embodiment of the present invention will be described.
A method for producing a member according to an embodiment of the present invention includes subjecting the above galvanized steel sheet (for example, a galvanized steel sheet produced by the above method for producing a galvanized steel sheet) to at least one of forming processing and joining processing. It has a process of making it into a member.
Here, the molding method is not particularly limited, and for example, a general processing method such as press working can be used. Further, the joining method is not particularly limited, and for example, common welding such as spot welding, laser welding, arc welding, riveting joining, caulking joining, etc. can be used. Note that the molding conditions and bonding conditions are not particularly limited, and conventional methods may be followed.
　以上、説明した本発明の要旨は、以下の通りである。
［１］素地鋼板と、該素地鋼板の上に形成された亜鉛めっき層と、を備える、亜鉛めっき鋼板であって、前記素地鋼板は、
質量％で、
Ｃ：０．０３０％以上０．２５０％以下、
Ｓｉ：０．０１％以上０．７５％以下、
Ｍｎ：２．００％以上３．５０％未満、
Ｐ：０．００１％以上０．１００％以下、
Ｓ：０．０２００％以下、
Ａｌ：０．０１０％以上２．０００％以下、
Ｎ：０．０１００％以下、
を含有し、残部がＦｅおよび不可避的不純物からなる成分組成と、
前記素地鋼板の板厚１／４位置の組織として、
フェライトの面積率：２０．０％以上８０．０％以下であり、
フレッシュマルテンサイトの面積率：１５．０％以下であり、
残留オーステナイトの面積率：３．０％以下であり、
フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの面積率の合計を、鋼板全体のフレッシュマルテンサイトの面積率と残留オーステナイトの面積率の合計で除した値：０．６５以上であり、
ベイナイトおよび焼戻しベイナイトの面積率：１０．０％以下であり、
焼戻しマルテンサイトの面積率：１０．０％以上７０．０％以下であり、
さらに、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの平均結晶粒径が２．０μｍ以下である鋼組織と、
を有し、
前記素地鋼板に含まれる拡散性水素量が０．５０質量ｐｐｍ以下であり、引張強さが７８０ＭＰａ以上である、亜鉛めっき鋼板。
［２］前記成分組成は、さらに、質量％で、
　　Ｎｂ：０．２００％以下、
　　Ｔｉ：０．２００％以下、
　　Ｖ：０．２００％以下、
　　Ｂ：０．０１００％以下、
　　Ｃｒ：１．０００％以下、
　　Ｎｉ：１．０００％以下、
　　Ｍｏ：１．０００％以下、
　　Ｓｂ：０．２００％以下、
　　Ｓｎ：０．２００％以下、
　　Ｃｕ：１．０００％以下、
　　Ｔａ：０．１００％以下、
　　Ｗ：０．５００％以下、
　　Ｍｇ：０．０２００％以下、
　　Ｚｎ：０．０２００％以下、
　　Ｃｏ：０．０２００％以下、
　　Ｚｒ：０．１０００％以下、
　　Ｃａ：０．０２００％以下、
　　Ｓｅ：０．０２００％以下、
　　Ｔｅ：０．０２００％以下、
　　Ｇｅ：０．０２００％以下、
　　Ａｓ：０．０５００％以下、
　　Ｓｒ：０．０２００％以下、
　　Ｃｓ：０．０２００％以下、
　　Ｈｆ：０．０２００％以下、
　　Ｐｂ：０．０２００％以下、
　　Ｂｉ：０．０２００％以下および
　　ＲＥＭ：０．０２００％以下
のうちから選ばれる少なくとも１種の元素を含有する、前記［１］に記載の亜鉛めっき鋼板。
［３］前記素地鋼板は、素地鋼板表面から板厚方向に２００μｍ以下の領域を表層とした際、
前記表層に、板厚１／４位置のビッカース硬さに対して、ビッカース硬さが８５％以下である表層軟質層を有する、前記［１］または［２］に記載の亜鉛めっき鋼板。
［４］前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置および板厚方向深さの１／２位置の夫々における板面の５０μｍ×５０μｍの領域において、３００点以上のナノ硬度を測定したとき、
前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度が７．０ＧＰａ以上の測定数割合が、板厚方向深さの１／４位置の全測定数に対して０．１０以下であり、
さらに、前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度の標準偏差σが１．８ＧＰａ以下であり、
さらに、前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／２位置の板面のナノ硬度の標準偏差σが２．２ＧＰａ以下である、前記［１］～［３］のいずれかに記載の亜鉛めっき鋼板。
［５］前記亜鉛めっき鋼板の片面または両面において、前記素地鋼板と前記亜鉛めっき層の間に形成された金属めっき層を有する、前記［１］～［４］のいずれかに記載の亜鉛めっき鋼板。
［６］前記亜鉛めっき層が、溶融亜鉛めっき層または合金化溶融亜鉛めっき層である、前記［１］～［５］のいずれかに記載の亜鉛めっき鋼板。
［７］前記［１］～［６］のいずれかに記載の亜鉛めっき鋼板を用いてなる、部材。
［８］前記［１］または［２］に記載の成分組成を有する鋼スラブに、
仕上げ圧延温度：８２０℃以上の条件で熱間圧延を施し、熱延鋼板を得る、熱間圧延工程と、
該熱間圧延工程後の鋼板に対して、３５０℃以上６００℃以下の温度域を平均加熱速度７℃／秒以上の条件で昇温する昇温工程と、
焼鈍温度：７５０℃以上９００℃以下、焼鈍時間：２０秒以上の条件で焼鈍する、焼鈍工程と、
前記焼鈍工程後、（前記焼鈍温度－３０℃）から６５０℃までの平均冷却速度を７℃／秒以上とし、６５０℃から５００℃までの平均冷却速度を１４℃／秒以下とする条件で冷却する第一冷却工程と、
前記第一冷却工程後、鋼板に亜鉛めっき処理を施し、亜鉛めっき鋼板を得る、亜鉛めっき工程と、
前記亜鉛めっき鋼板に対して、３００℃以上４５０℃以下の温度域で２．０ｋｇｆ／ｍｍ２以上の張力を付与し、
その後、前記亜鉛めっき鋼板を、１パス当たり直径５００ｍｍ以上１５００ｍｍ以下のロールにロール１／４周分接触させながら、５パス以上通過させ、
ついで、２５０℃以下の冷却停止温度まで冷却する、第二冷却工程と、
前記亜鉛めっき鋼板を、前記冷却停止温度以上４４０℃以下の温度域まで再加熱して２０秒以上保持する、再加熱工程と、を含み、あるいはさらに
前記熱間圧延工程後、かつ前記昇温工程前の鋼板に、圧下率が２０％以上８０％以下である冷間圧延を施し、冷延鋼板を得る、冷間圧延工程を含む、亜鉛めっき鋼板の製造方法。
［９］前記焼鈍工程における焼鈍を、露点：－３０℃以上の雰囲気下で行う、前記［８］に記載の亜鉛めっき鋼板の製造方法。
［１０］前記焼鈍工程の前に、前記亜鉛めっき鋼板の片面もしくは両面において、金属めっきを施し金属めっき層を形成する金属めっき工程を含む、前記［８］または［９］に記載の亜鉛めっき鋼板の製造方法。
［１１］前記亜鉛めっき処理が、溶融亜鉛めっき処理または合金化溶融亜鉛めっき処理である、前記［８］～［１０］のいずれかに記載の亜鉛めっき鋼板の製造方法。
［１２］前記［１］～［６］のいずれかに記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。 The gist of the present invention described above is as follows.
[1] A galvanized steel sheet comprising a base steel plate and a galvanized layer formed on the base steel plate, the base steel plate comprising:
In mass%,
C: 0.030% or more and 0.250% or less,
Si: 0.01% or more and 0.75% or less,
Mn: 2.00% or more and less than 3.50%,
P: 0.001% or more and 0.100% or less,
S: 0.0200% or less,
Al: 0.010% or more and 2.000% or less,
N: 0.0100% or less,
, with the remainder consisting of Fe and unavoidable impurities;
As the structure at the 1/4 plate thickness position of the base steel plate,
Ferrite area ratio: 20.0% or more and 80.0% or less,
Fresh martensite area ratio: 15.0% or less,
Area ratio of retained austenite: 3.0% or less,
The value obtained by dividing the total area ratio of island-like fresh martensite and island-like retained austenite in the ferrite grains by the sum of the area ratio of fresh martensite and retained austenite in the entire steel sheet: 0.65 or more,
Area ratio of bainite and tempered bainite: 10.0% or less,
Area ratio of tempered martensite: 10.0% or more and 70.0% or less,
Furthermore, a steel structure in which the average crystal grain size of island-like fresh martensite and island-like retained austenite in the ferrite grains is 2.0 μm or less,
has
A galvanized steel sheet, wherein the amount of diffusible hydrogen contained in the base steel sheet is 0.50 mass ppm or less, and the tensile strength is 780 MPa or more.
[2] The component composition further includes, in mass%,
Nb: 0.200% or less,
Ti: 0.200% or less,
V: 0.200% or less,
B: 0.0100% or less,
Cr: 1.000% or less,
Ni: 1.000% or less,
Mo: 1.000% or less,
Sb: 0.200% or less,
Sn: 0.200% or less,
Cu: 1.000% or less,
Ta: 0.100% or less,
W: 0.500% or less,
Mg: 0.0200% or less,
Zn: 0.0200% or less,
Co: 0.0200% or less,
Zr: 0.1000% or less,
Ca: 0.0200% or less,
Se: 0.0200% or less,
Te: 0.0200% or less,
Ge: 0.0200% or less,
As: 0.0500% or less,
Sr: 0.0200% or less,
Cs: 0.0200% or less,
Hf: 0.0200% or less,
Pb: 0.0200% or less,
The galvanized steel sheet according to [1] above, containing at least one element selected from Bi: 0.0200% or less and REM: 0.0200% or less.
[3] When the base steel plate has an area of 200 μm or less in the thickness direction from the surface of the base steel plate as the surface layer,
The galvanized steel sheet according to [1] or [2], wherein the surface layer has a soft surface layer whose Vickers hardness is 85% or less of the Vickers hardness at the 1/4 position of the sheet thickness.
[4] 300 points or more in an area of 50 μm x 50 μm on the plate surface at 1/4 position and 1/2 depth in the plate thickness direction of the surface soft layer from the surface of the base steel plate, respectively. When measuring the nanohardness of
The percentage of measurements where the nano-hardness of the plate surface at 1/4 of the depth in the thickness direction of the surface soft layer from the surface of the base steel sheet is 7.0 GPa or more is the total number of measurements at 1/4 of the depth in the thickness direction of the surface soft layer. 0.10 or less for the number,
Furthermore, the standard deviation σ of the nano-hardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface is 1.8 GPa or less,
Furthermore, any one of [1] to [3] above, wherein the standard deviation σ of nano-hardness of the plate surface at a position 1/2 the thickness direction depth of the surface soft layer from the base steel plate surface is 2.2 GPa or less. Galvanized steel sheet described in Crab.
[5] The galvanized steel sheet according to any one of [1] to [4] above, which has a metal plating layer formed between the base steel sheet and the galvanized layer on one or both sides of the galvanized steel sheet. .
[6] The galvanized steel sheet according to any one of [1] to [5], wherein the galvanized layer is a hot-dip galvanized layer or an alloyed hot-dip galvanized layer.
[7] A member using the galvanized steel sheet according to any one of [1] to [6] above.
[8] A steel slab having the composition described in [1] or [2] above,
A hot rolling process in which hot rolling is performed at a finish rolling temperature of 820°C or higher to obtain a hot rolled steel plate;
A heating step of raising the temperature of the steel plate after the hot rolling step in a temperature range of 350° C. or higher and 600° C. or lower at an average heating rate of 7° C./sec or higher;
An annealing step of annealing at an annealing temperature of 750°C or more and 900°C or less and an annealing time of 20 seconds or more;
After the annealing step, cooling under conditions such that the average cooling rate from (the annealing temperature -30°C) to 650°C is 7°C/second or more, and the average cooling rate from 650°C to 500°C is 14°C/second or less. a first cooling step,
After the first cooling step, a galvanizing step is performed on the steel sheet to obtain a galvanized steel sheet;
Applying a tension of 2.0 kgf/mm 2 or more to the galvanized steel sheet in a temperature range of 300 ° C. or higher and 450 ° C. or lower,
Thereafter, the galvanized steel sheet is passed through 5 passes or more while being in contact with a roll having a diameter of 500 mm or more and 1500 mm or less for 1/4 rotation of the roll per pass,
Then, a second cooling step of cooling to a cooling stop temperature of 250° C. or less;
a reheating step of reheating the galvanized steel sheet to a temperature range from the cooling stop temperature to 440° C. and holding it for 20 seconds or more, or further after the hot rolling step and the heating step A method for manufacturing a galvanized steel sheet, comprising a cold rolling step of cold rolling a previous steel sheet at a rolling reduction of 20% or more and 80% or less to obtain a cold rolled steel sheet.
[9] The method for producing a galvanized steel sheet according to [8] above, wherein the annealing in the annealing step is performed in an atmosphere with a dew point of -30°C or higher.
[10] The galvanized steel sheet according to [8] or [9], which includes a metal plating step of applying metal plating to form a metal plating layer on one or both sides of the galvanized steel sheet before the annealing step. manufacturing method.
[11] The method for producing a galvanized steel sheet according to any one of [8] to [10], wherein the galvanizing treatment is a hot-dip galvanizing treatment or an alloyed hot-dip galvanizing treatment.
[12] A method for producing a member, comprising the step of subjecting the galvanized steel sheet according to any one of [1] to [6] to at least one of forming and bonding to produce a member.
　表１に示す成分組成（残部はＦｅ及び不可避的不純物）を有する鋼素材を転炉にて溶製し、連続鋳造法にて鋼スラブとした。表１中、－は不可避的不純物レベルの含有量を示す。 A steel material having the component composition shown in Table 1 (the remainder being Fe and unavoidable impurities) was melted in a converter and made into a steel slab using a continuous casting method. In Table 1, - indicates the content at the inevitable impurity level.
　得られた鋼スラブを１２００℃に加熱し、加熱後、鋼スラブに粗圧延と熱間圧延を施し、熱延鋼板とした。ついで、得られた熱延鋼板のＮｏ．１～Ｎｏ．５７およびＮｏ．６０～Ｎｏ．８３に、酸洗および冷間圧延を施し、表３に示す板厚の冷延鋼板とした。また、得られた熱延鋼板のＮｏ．５７～Ｎｏ．５９およびＮｏ．８４～Ｎｏ．９１に酸洗を施し、表３に示す板厚の熱延鋼板（白皮）とした。
ついで、得られた冷延鋼板または熱延鋼板（白皮）に、表２に示す条件で、昇温工程、焼鈍工程、第一冷却工程、めっき工程、第二冷却工程および再加熱工程における処理を行い、また、表４に示す条件で、昇温工程、第一めっき工程（金属めっき工程）、焼鈍工程、第一冷却工程、第二めっき工程（亜鉛めっき工程）、第二冷却工程および再加熱工程における処理を行い、亜鉛めっき鋼板を得た。 The obtained steel slab was heated to 1200°C, and after heating, the steel slab was subjected to rough rolling and hot rolling to obtain a hot rolled steel plate. Then, the obtained hot rolled steel sheet No. 1~No. 57 and no. 60~No. No. 83 was pickled and cold rolled to obtain a cold rolled steel sheet having the thickness shown in Table 3. Moreover, No. of the obtained hot-rolled steel sheet. 57~No. 59 and no. 84~No. No. 91 was pickled to obtain a hot rolled steel plate (white skin) having the thickness shown in Table 3.
Then, the obtained cold-rolled steel sheet or hot-rolled steel sheet (white skin) is subjected to treatments in a temperature raising step, an annealing step, a first cooling step, a plating step, a second cooling step, and a reheating step under the conditions shown in Table 2. Also, under the conditions shown in Table 4, a temperature raising process, a first plating process (metal plating process), an annealing process, a first cooling process, a second plating process (zinc plating process), a second cooling process and a re- A galvanized steel sheet was obtained by processing in a heating process.
　ここで、亜鉛めっき工程では、溶融亜鉛めっき処理または合金化亜鉛めっき処理を行い、溶融亜鉛めっき鋼板（以下、ＧＩともいう）または合金化溶融亜鉛めっき鋼板（以下、ＧＡともいう）を得た。なお、表２では、めっき工程の種類についても、「ＧＩ」および「ＧＡ」と表示している。表２、表４中、ＧＩ鋼板の場合に合金化処理を行わないため合金化温度を－と示す。 Here, in the galvanizing process, hot-dip galvanizing treatment or alloyed galvanizing treatment was performed to obtain a hot-dip galvanized steel sheet (hereinafter also referred to as GI) or an alloyed hot-dip galvanized steel sheet (hereinafter also referred to as GA). In addition, in Table 2, the types of plating processes are also indicated as "GI" and "GA". In Tables 2 and 4, the alloying temperature is indicated as - because no alloying treatment is performed in the case of GI steel sheets.
　亜鉛めっき浴温は、ＧＩおよびＧＡいずれを製造する場合も、４７０℃とした。
　亜鉛めっき付着量は、ＧＩを製造する場合は、片面あたり４５～７２ｇ／ｍ２とし、ＧＡを製造する場合は、片面あたり４５ｇ／ｍ２とした。
　なお、最終的に得られた溶融亜鉛めっき鋼板の亜鉛めっき層の組成は、ＧＩでは、Ｆｅ：０．１～１．０質量％、Ａｌ：０．２～０．３３質量％を含有し、残部がＺｎおよび不可避的不純物であった。また、ＧＡでは、Ｆｅ：８．０～１２．０質量％、Ａｌ：０．１～０．２３質量％を含有し、残部がＺｎおよび不可避的不純物であった。
　また、亜鉛めっき層はいずれも、素地鋼板の両面に形成した。 The zinc plating bath temperature was 470° C. in both GI and GA production.
The amount of zinc plating deposited was 45 to 72 g/m 2 per side when manufacturing GI, and 45 g/m 2 per side when manufacturing GA.
In addition, the composition of the galvanized layer of the finally obtained hot-dip galvanized steel sheet contains, in GI, Fe: 0.1 to 1.0 mass%, Al: 0.2 to 0.33 mass%, The remainder was Zn and unavoidable impurities. Furthermore, GA contained Fe: 8.0 to 12.0% by mass, Al: 0.1 to 0.23% by mass, and the remainder was Zn and inevitable impurities.
Further, all galvanized layers were formed on both sides of the base steel sheet.
　得られた亜鉛めっき鋼板を用いて、上述した要領により、素地鋼板の鋼組織の同定を行った。測定結果を表３、表５に示す。表３、表５中、Ｆはフェライト、Ｍはマルテンサイト、ＲＡは残留オーステナイト、Ｍ’およびＲＡ’は孤立した島状フレッシュマルテンサイトおよび孤立した島状残留オーステナイト、ＢおよびＢＴはベイナイトおよび焼戻しベイナイト、ＴＭは焼戻しマルテンサイト、Ｐはパーライト、θは炭化物、Ｆ’は未再結晶フェライトである。 Using the obtained galvanized steel sheet, the steel structure of the base steel sheet was identified in the manner described above. The measurement results are shown in Tables 3 and 5. In Tables 3 and 5, F is ferrite, M is martensite, RA is retained austenite, M' and RA' are isolated island-like fresh martensite and isolated island-like retained austenite, B and BT are bainite and tempered bainite. , TM is tempered martensite, P is pearlite, θ is carbide, and F' is unrecrystallized ferrite.
　表層軟質層の測定方法は、以下の通りである。鋼板の圧延方向に平行な板厚断面（Ｌ断面）を湿式研磨により平滑化した後、ビッカース硬度計を用いて、荷重１０ｇｆで、鋼板表面から板厚方向に１μｍの位置より、板厚方向１００μｍの位置まで、１μｍ間隔で測定を行った。その後は板厚中心まで２０μｍ間隔で測定を行った。硬度が板厚１／４位置の硬度に比して８５％以下に減少した領域を軟質層（表層軟質層）と定義し、当該領域の板厚方向の厚さを軟質層の厚さと定義する。 The method for measuring the surface soft layer is as follows. After smoothing the thickness section (L section) parallel to the rolling direction of the steel plate by wet polishing, using a Vickers hardness tester, the thickness was measured 100 μm from a position 1 μm in the thickness direction from the steel plate surface under a load of 10 gf. Measurements were made at 1 μm intervals up to the position. Thereafter, measurements were taken at intervals of 20 μm up to the center of the plate thickness. The area where the hardness has decreased to 85% or less compared to the hardness at 1/4 of the plate thickness is defined as a soft layer (surface soft layer), and the thickness of this area in the plate thickness direction is defined as the thickness of the soft layer. .
　表１～５中下線部は本発明の適正範囲外を示す。
　また、以下の要領により、引張試験、穴広げ試験、Ｖ曲げ試験、Ｕ曲げ＋密着曲げ試験、Ｖ曲げ＋直交ＶＤＡ曲げ試験および軸圧壊試験を行い、以下の基準により、引張強さ（ＴＳ）、降伏応力（ＹＳ）、降伏比（ＹＲ）、全伸び（Ｅｌ）、限界穴広げ率（λ）、Ｖ曲げ試験でのＲ／ｔ、Ｕ曲げ＋密着曲げ曲げ試験での限界スペーサー厚さ（ＳＴ）、Ｖ曲げ＋直交ＶＤＡ曲げ試験で測定される荷重最大時のストローク（ＳＦｍａｘ）、および、軸圧壊試験での破断（外観割れ）有無を評価した。 The underlined portions in Tables 1 to 5 indicate outside the appropriate range of the present invention.
In addition, tensile tests, hole expansion tests, V-bending tests, U-bending + close-contact bending tests, V-bending + orthogonal VDA bending tests, and axial crushing tests were conducted according to the following criteria, and the tensile strength (TS) was determined according to the following criteria. , yield stress (YS), yield ratio (YR), total elongation (El), critical hole expansion rate (λ), R/t in V-bending test, critical spacer thickness in U-bending + close contact bending test ( ST), the stroke at maximum load (SFmax) measured in the V-bending + orthogonal VDA bending test, and the presence or absence of fracture (appearance cracking) in the axial crushing test were evaluated.
・ＴＳ
　〇（合格）：７８０ＭＰａ以上
　×（不合格）：７８０ＭＰａ未満 ・TS
〇(Pass): 780MPa or more ×(Fail): Less than 780MPa
・ＹＳ
　〇（合格）：
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、５００ＭＰａ≦ＹＳ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、６００ＭＰａ≦ＹＳ
　×（不合格）：
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、５００ＭＰａ＞ＹＳ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、６００ＭＰａ＞ＹＳ ・YS
〇(Passed):
(A) If 780MPa≦TS<980MPa, 500MPa≦YS
(B) If 980MPa≦TS, 600MPa≦YS
× (fail):
(A) If 780MPa≦TS<980MPa, 500MPa>YS
(B) If 980MPa≦TS, 600MPa>YS
・ＹＲ
　〇（合格）：
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、０．６４≦ＹＲ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、０．６１≦ＹＲ
　×（不合格）：
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、０．６４＞ＹＲ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、０．６１＞ＹＲ ・YR
〇(Passed):
(A) When 780MPa≦TS<980MPa, 0.64≦YR
(B) If 980MPa≦TS, 0.61≦YR
× (fail):
(A) If 780MPa≦TS<980MPa, 0.64>YR
(B) If 980MPa≦TS, 0.61>YR
・Ｅｌ
　〇（合格）： 
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、１９．０％≦Ｅｌ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、１５．０％≦Ｅｌ
　×（不合格）：
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、１９．０％＞Ｅｌ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、１５．０％＞Ｅｌ ・El
〇(Passed):
(A) When 780MPa≦TS<980MPa, 19.0%≦El
(B) When 980MPa≦TS, 15.0%≦El
× (fail):
(A) When 780MPa≦TS<980MPa, 19.0%>El
(B) When 980MPa≦TS, 15.0%>El
・λ
　〇（合格）：３０％以上
　×（不合格）：３０％未満 ・λ
〇(Pass): 30% or more ×(Fail): Less than 30%
・Ｒ／ｔ
　〇（合格）： 
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２．０≧Ｒ/ｔ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、２．５≧Ｒ/ｔ
　×（不合格）：
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２．０＜Ｒ/ｔ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、２．５＜Ｒ/ｔ ・R/t
〇(Passed):
(A) When 780MPa≦TS<980MPa, 2.0≧R/t
(B) If 980MPa≦TS, 2.5≧R/t
× (fail):
(A) When 780MPa≦TS<980MPa, 2.0<R/t
(B) When 980MPa≦TS, 2.5<R/t
・ＳＴ
〇（合格）
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２．５ｍｍ≧ＳＴ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、４．０ｍｍ≧ＳＴ
×（不合格）：未満
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２．５ｍｍ＜ＳＴ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、４．０ｍｍ＜ＳＴ ・ST
〇(Passed)
(A) When 780MPa≦TS<980MPa, 2.5mm≧ST
(B) When 980MPa≦TS, 4.0mm≧ST
× (Fail): Less than (A) If 780MPa≦TS<980MPa, 2.5mm<ST
(B) When 980MPa≦TS, 4.0mm<ST
・ＳＦｍａｘ
〇（合格）
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２８．０ｍｍ≦ＳＦｍａｘ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、２６．５ｍｍ≦ＳＦｍａｘ
×（不合格）：２６ｍｍ未満
（Ａ）７８０ＭＰａ≦ＴＳ＜９８０ＭＰａの場合、２８．０ｍｍ＞ＳＦｍａｘ
（Ｂ）９８０ＭＰａ≦ＴＳの場合、２６．５ｍｍ＞ＳＦｍａｘ ・SFmax
〇(passed)
(A) When 780MPa≦TS<980MPa, 28.0mm≦SFmax
(B) When 980MPa≦TS, 26.5mm≦SFmax
× (Fail): Less than 26 mm (A) If 780 MPa≦TS<980 MPa, 28.0 mm>SFmax
(B) When 980MPa≦TS, 26.5mm>SFmax
・軸圧壊破断（外観割れ）有無
◎（合格）：軸圧壊試験後のサンプルに外観割れが観察されなかった。
〇（合格）：軸圧壊試験後のサンプルに外観割れが１箇所以下観察された
×（不合格）：軸圧壊試験後のサンプルに外観割れが２箇所以上観察された - Presence or absence of axial crushing fracture (external appearance cracking) ◎ (passed): No external appearance cracking was observed in the sample after the axial crushing test.
〇 (Pass): One or less appearance cracks were observed in the sample after the axial crush test. × (Fail): Two or more appearance cracks were observed in the sample after the axial crush test.
（１）引張試験
　引張試験は、ＪＩＳ　Ｚ　２２４１に準拠して行った。すなわち、得られた亜鉛めっき鋼板から、長手方向が素地鋼板の圧延方向に対して直角となるようにＪＩＳ５号試験片を採取した。採取した試験片を用いて、クロスヘッド速度が１０ｍｍ／ｍｉｎの条件で引張試験を行い、ＴＳ、ＹＳ、ＹＲおよびＥｌを測定した。結果を表３、表５に示す。 (1) Tensile test The tensile test was conducted in accordance with JIS Z 2241. That is, a JIS No. 5 test piece was taken from the obtained galvanized steel sheet so that the longitudinal direction was perpendicular to the rolling direction of the base steel sheet. Using the sampled test piece, a tensile test was conducted at a crosshead speed of 10 mm/min, and TS, YS, YR, and El were measured. The results are shown in Tables 3 and 5.
（２）穴広げ試験
　穴広げ試験は、ＪＩＳ　Ｚ　２２５６に準拠して行った。すなわち、得られた亜鉛めっき鋼板から、１００ｍｍ×１００ｍｍの試験片を剪断加工により採取した。該試験片に、クリアランスを１２．５％として直径１０ｍｍの穴を打ち抜いた。ついで、内径：７５ｍｍのダイスを用いて穴の周囲にしわ押さえ力：９ｔｏｎ（８８．２６ｋＮ）を加え、そのた状態で頂角：６０°の円錐ポンチを穴に押し込み、亀裂発生限界（亀裂発生時）における試験片の穴の直径を測定した。そして、次式により、限界穴広げ率：λ（％）を求めた。なお、λは、伸びフランジ性を評価する指標となるものである。結果を表３、表５に示す。
　λ（％）＝｛（Ｄｆ－Ｄ０）/Ｄ０｝×１００
　ここで、
　Ｄｆ：亀裂発生時の試験片の穴の直径（ｍｍ）
　Ｄ０：初期の試験片の穴の直径（ｍｍ）
である。 (2) Hole expansion test The hole expansion test was conducted in accordance with JIS Z 2256. That is, a 100 mm x 100 mm test piece was taken from the obtained galvanized steel sheet by shearing. A hole with a diameter of 10 mm was punched into the test piece with a clearance of 12.5%. Then, using a die with an inner diameter of 75 mm, a wrinkle pressing force of 9 tons (88.26 kN) was applied around the hole, and in that state, a conical punch with an apex angle of 60° was pushed into the hole to reach the crack generation limit (crack generation limit). The diameter of the hole in the specimen was measured at Then, the critical hole expansion rate: λ (%) was determined using the following formula. Note that λ is an index for evaluating stretch flangeability. The results are shown in Tables 3 and 5.
λ (%) = {(D f - D 0 )/D 0 }×100
here,
D f : Diameter of hole in test piece at the time of crack occurrence (mm)
D 0 : Diameter of hole in initial test piece (mm)
It is.
（３）Ｖ曲げ試験
Ｖ（９０°）曲げ試験は、ＪＩＳ　Ｚ　２２４８に準拠して行った。
得られた亜鉛めっき鋼板から、１００ｍｍ×３５ｍｍの試験片を剪断・端面研削加工により採取した。ここで、１００ｍｍの辺は幅（Ｃ）方向に平行する。
曲げ半径Ｒ：０．５ｍｍピッチで変化
試験方法：ダイ支持、パンチ押し込み
成型荷重：１０ｔｏｎ
試験速度：３０ｍｍ/ｍｉｎ
保持時間：５ｓ
曲げ方向：圧延直角（Ｃ）方向
３回評価を行い、いずれも割れが出ない最小の曲げ半径（限界曲げ半径）Ｒを板厚ｔで除したＲ／ｔを算出した。また、ライカ製実体顕微鏡を用いて、２５倍の倍率で長さが２００μｍ以上のき裂を割れと判断した。なお、ＴＳが７８０ＭＰａ以上９８０ＭＰａ未満では、２．０≧Ｒ／ｔを、ＴＳが９８０ＭＰａ以上では、２．５≧Ｒ／ｔを良好と判断した。 (3) V bending test The V (90°) bending test was conducted in accordance with JIS Z 2248.
A 100 mm x 35 mm test piece was taken from the obtained galvanized steel plate by shearing and end face grinding. Here, the 100 mm side is parallel to the width (C) direction.
Bending radius R: Changes at 0.5mm pitch Test method: Die support, punch press molding load: 10 tons
Test speed: 30mm/min
Holding time: 5s
Bending direction: Evaluation was performed three times in the direction perpendicular to rolling (C), and R/t was calculated by dividing the minimum bending radius (limit bending radius) R at which no cracks appeared in each case by the plate thickness t. Further, using a Leica stereoscopic microscope, cracks with a length of 200 μm or more at 25x magnification were determined to be cracks. In addition, when TS was 780 MPa or more and less than 980 MPa, 2.0≧R/t was judged as good, and when TS was 980 MPa or more, 2.5≧R/t was judged as good.
（４）Ｕ曲げ＋密着曲げ試験
　Ｕ曲げ＋密着曲げ試験は以下のようにして行った。
得られた亜鉛めっき鋼板から、６０ｍｍ×３０ｍｍの試験片を剪断・端面研削加工により採取した。ここで、６０ｍｍの辺は幅（Ｃ）方向に平行する。曲率半径/板厚：４．２で圧延（Ｌ）方向を軸に幅（Ｃ）方向にＵ曲げ加工（一次曲げ加工）を施し、試験片を準備した。Ｕ曲げ加工（一次曲げ加工）では、図２（ａ）に示すように、ロールＡ１の上に載せた鋼板に対して、パンチＢ１を押し込んで試験片Ｔ１を得た。次に、図２（ｂ）に示すように、下金型Ａ２の上に載せた試験片Ｔ１に対して、上金型Ｂ２で押し潰す密着曲げ（二次曲げ加工）を施した。図２（ａ）において、Ｄ１は幅（Ｃ）方向、Ｄ２は圧延（Ｌ）方向を示している。なお、試験片の間には、後述するスペーサーＳを挿入している。 (4) U-bending + close-contact bending test The U-bending + close-contact bending test was conducted as follows.
A 60 mm x 30 mm test piece was taken from the obtained galvanized steel sheet by shearing and end face grinding. Here, the 60 mm side is parallel to the width (C) direction. A test piece was prepared by performing U bending (primary bending) in the width (C) direction with the rolling (L) direction as the axis at a radius of curvature/plate thickness of 4.2. In the U-bending process (primary bending process), as shown in FIG. 2(a), a punch B1 was pushed into a steel plate placed on a roll A1 to obtain a test piece T1. Next, as shown in FIG. 2(b), the test piece T1 placed on the lower mold A2 was subjected to close bending (secondary bending) by crushing it with the upper mold B2. In FIG. 2(a), D1 indicates the width (C) direction, and D2 indicates the rolling (L) direction. Note that a spacer S, which will be described later, was inserted between the test pieces.
　Ｕ曲げ＋密着曲げ試験におけるＵ曲げの条件は、以下のとおりである。
試験方法：ロール支持、パンチ押し込み
パンチ先端Ｒ：５．０ｍｍ
ロールとパンチのクリアランス：板厚＋０．１ｍｍ
ストローク速度：１０ｍｍ／ｍｉｎ
曲げ方向：圧延直角（Ｃ）方向
　Ｕ曲げ＋密着曲げ試験における密着曲げの条件は、以下のとおりである。
スペーサー厚さ：０．５ｍｍピッチで変化
試験方法：ダイ支持、パンチ押し込み
成型荷重：１０ｔｏｎ
試験速度：１０ｍｍ／ｍｉｎ
保持時間：５ｓ
曲げ方向：圧延直角（Ｃ）方向 The U-bending conditions in the U-bending + close contact bending test are as follows.
Test method: Roll support, punch pushing Punch tip R: 5.0mm
Clearance between roll and punch: plate thickness + 0.1mm
Stroke speed: 10mm/min
Bending direction: rolling perpendicular (C) direction The conditions for close bending in the U-bending + close bending test are as follows.
Spacer thickness: Changes at 0.5mm pitch Test method: Die support, punch press molding load: 10 tons
Test speed: 10mm/min
Holding time: 5s
Bending direction: rolling right angle (C) direction
　上記Ｕ曲げ＋密着曲げ試験を３回実施し、３回とも割れが発生しなかったときの限界スペーサー厚さ（ＳＴ）とした。また、ライカ製実体顕微鏡を用いて、２５倍の倍率で長さが２００μｍ以上のき裂を割れと判断した。なお、ＳＴは、衝突時の耐破断特性（軸圧壊試験における縦壁部の耐破断特性）を評価する指標となるものである。結果を表３、表５に示す。 The above U-bending + close-contact bending test was performed three times, and the limit spacer thickness (ST) was determined when no cracking occurred all three times. Furthermore, using a Leica stereomicroscope, cracks with a length of 200 μm or more at 25x magnification were determined to be cracks. Note that ST serves as an index for evaluating the fracture resistance at the time of a collision (the fracture resistance of the vertical wall portion in an axial crush test). The results are shown in Tables 3 and 5.
（５）Ｖ曲げ＋直交ＶＤＡ曲げ試験
　Ｖ曲げ＋直交ＶＤＡ曲げ試験は以下のようにして行う。
　得られた亜鉛めっき鋼板から、６０ｍｍ×６５ｍｍの試験片を剪断・端面研削加工により採取した。ここで、６０ｍｍの辺は圧延（Ｌ）方向に平行する。曲率半径／板厚：４．２で幅（Ｃ）方向を軸に圧延（Ｌ）方向に９０°曲げ加工（一次曲げ加工）を施し、試験片を準備した。９０°曲げ加工（一次曲げ加工）では、図３（ａ）に示すように、Ｖ溝を有するダイＡ３の上に載せた鋼板に対して、パンチＢ３を押し込んで試験片Ｔ１を得た。次に、図３（ｂ）に示すように、支持ロールＡ４の上に載せた試験片Ｔ１に対して、曲げ方向が圧延直角方向となるようにして、パンチＢ４を押し込んで直交曲げ（二次曲げ加工）を施した。図３（ａ）及び図３（ｂ）において、Ｄ１は幅（Ｃ）方向、Ｄ２は圧延（Ｌ）方向を示している。 (5) V-bending + orthogonal VDA bending test The V-bending + orthogonal VDA bending test is performed as follows.
A 60 mm x 65 mm test piece was taken from the obtained galvanized steel plate by shearing and end face grinding. Here, the 60 mm side is parallel to the rolling (L) direction. A test piece was prepared by performing a 90° bending process (primary bending process) in the rolling (L) direction with the width (C) direction as the axis at a radius of curvature/plate thickness of 4.2. In the 90° bending process (primary bending process), as shown in FIG. 3(a), a punch B3 was pushed into a steel plate placed on a die A3 having a V-groove to obtain a test piece T1. Next, as shown in FIG. 3(b), the punch B4 is pushed into the test piece T1 placed on the support roll A4 so that the bending direction is perpendicular to the rolling direction (secondary bending). bending process). In FIGS. 3(a) and 3(b), D1 indicates the width (C) direction, and D2 indicates the rolling (L) direction.
　Ｖ曲げ＋直交ＶＤＡ曲げ試験におけるＶ曲げの条件は、以下のとおりである。
試験方法：ダイ支持、パンチ押し込み
成型荷重：１０ｔｏｎ
試験速度：３０ｍｍ/ｍｉｎ
保持時間：５ｓ
曲げ方向：圧延（Ｌ）方向 The V-bending conditions in the V-bending + orthogonal VDA bending test are as follows.
Test method: die support, punch press molding load: 10 tons
Test speed: 30mm/min
Holding time: 5s
Bending direction: rolling (L) direction
　Ｖ曲げ＋直交ＶＤＡ曲げ試験におけるＶＤＡ曲げの条件は、以下のとおりである。
試験方法：ロール支持、パンチ押し込み
ロール径：φ３０ｍｍ
パンチ先端Ｒ：０．４ｍｍ
ロール間距離：（板厚×２）＋０．５ｍｍ
ストローク速度：２０ｍｍ／ｍｉｎ
試験片サイズ：６０ｍｍ×６０ｍｍ
曲げ方向：圧延直角（Ｃ）方向 The VDA bending conditions in the V-bending + orthogonal VDA bending test are as follows.
Test method: Roll support, punch pushing Roll diameter: φ30mm
Punch tip R: 0.4mm
Distance between rolls: (plate thickness x 2) + 0.5mm
Stroke speed: 20mm/min
Test piece size: 60mm x 60mm
Bending direction: rolling right angle (C) direction
　上記ＶＤＡ曲げを施した際に得られるストローク－荷重曲線において、荷重最大時のストロークを求める。前記Ｖ曲げ＋直交ＶＤＡ曲げ試験を３回実施した際の当該荷重最大時のストロークの平均値をＳＦｍａｘ（ｍｍ）とした。なお、ＳＦｍａｘは、衝突時の耐破断特性（軸圧壊試験における曲げ稜線部の耐破断特性）を評価する指標となるものである。結果を表３、表５に示す。 In the stroke-load curve obtained when performing the above VDA bending, determine the stroke at the maximum load. The average value of the stroke at the maximum load when the V-bending + orthogonal VDA bending test was performed three times was defined as SFmax (mm). Note that SFmax is an index for evaluating the fracture resistance at the time of a collision (the fracture resistance of a bending ridgeline portion in an axial crush test). The results are shown in Tables 3 and 5.
（６）軸圧壊試験
　得られた亜鉛めっき鋼板から、１５０ｍｍ×１００ｍｍの試験片を剪断加工により採取した。ここで、１５０ｍｍの辺は圧延（Ｌ）方向に平行する。パンチ肩半径が５．０ｍｍであり、ダイ肩半径が５．０ｍｍである金型を用いて、深さ４０ｍｍとなるように成形加工（曲げ加工）して、図４（ａ）及び図４（ｂ）に示すハット型部材１０を作製した。また、ハット型部材の素材として用いた鋼板を、８０ｍｍ×１００ｍｍの大きさに別途切り出した。次に、その切り出した後の鋼板２０と、ハット型部材１０とをスポット溶接し、図４（ａ）及び図４（ｂ）に示すような試験用部材３０を作製した。図４（ａ）は、ハット型部材１０と鋼板２０とをスポット溶接して作製した試験用部材３０の正面図である。図４（ｂ）は、試験用部材３０の斜視図である。スポット溶接部４０の位置は、図４（ｂ）に示すように、鋼板の端部と溶接部が１０ｍｍ、溶接部間が２０ｍｍの間隔となるようにした。次に、図４（ｃ）に示すように、試験用部材３０を地板５０とＴＩＧ溶接により接合して軸圧壊試験用サンプルを作製した。次に、作製した軸圧壊試験用サンプルにインパクター６０を衝突速度１０ｍｍ／ｍｉｎで等速衝突させ、軸圧壊試験用のサンプルを７０ｍｍ圧壊した。図４（ｃ）に示すように、圧壊方向Ｄ３は、試験用部材３０の長手方向と平行な方向とした。結果を表３、表５に示す。 (6) Axial crush test A 150 mm x 100 mm test piece was taken from the obtained galvanized steel sheet by shearing. Here, the 150 mm side is parallel to the rolling (L) direction. Using a mold with a punch shoulder radius of 5.0 mm and a die shoulder radius of 5.0 mm, the molding process (bending process) was performed to a depth of 40 mm. A hat-shaped member 10 shown in b) was produced. Further, a steel plate used as a material for the hat-shaped member was separately cut into a size of 80 mm x 100 mm. Next, the cut steel plate 20 and the hat-shaped member 10 were spot welded to produce a test member 30 as shown in FIGS. 4(a) and 4(b). FIG. 4A is a front view of a test member 30 produced by spot welding the hat-shaped member 10 and the steel plate 20. FIG. 4(b) is a perspective view of the test member 30. As shown in FIG. 4B, the spot welds 40 were positioned so that the distance between the end of the steel plate and the weld was 10 mm, and the distance between the welds was 20 mm. Next, as shown in FIG. 4(c), the test member 30 was joined to the base plate 50 by TIG welding to prepare a sample for an axial crush test. Next, the impactor 60 was made to collide with the produced sample for the axial crush test at a constant velocity of 10 mm/min, and the sample for the axial crush test was crushed by 70 mm. As shown in FIG. 4(c), the crushing direction D3 was parallel to the longitudinal direction of the test member 30. The results are shown in Tables 3 and 5.
　板厚１．２ｍｍ超の亜鉛めっき鋼板のＵ曲げ＋密着曲げ試験、Ｖ曲げ＋直交ＶＤＡ曲げ試験および軸圧壊試験では板厚の影響を考慮し、全て板厚１．２ｍｍの鋼板で実施した。板厚１．２ｍｍ超の鋼板は片面研削し、板厚を１．２ｍｍにした。研削加工により鋼板表面の曲げ性が影響されるおそれがあるため、Ｕ曲げ＋密着曲げ曲げ試験では研削面を曲げ内側（谷側）とし、Ｖ曲げ＋直交ＶＤＡ曲げ試験ではＶ曲げ試験時に研削面を曲げ外側（山側）とし、その後のＶＤＡ曲げ試験時に研削面を曲げ内側（谷側）とした。一方、板厚１．２未満の亜鉛めっき鋼板のＵ曲げ＋密着曲げ試験、Ｖ曲げ＋直交ＶＤＡ曲げ試験および軸圧壊試験では、板厚の影響が小さいため、研削処理無しで試験を行った。 U-bending + close bending tests, V-bending + orthogonal VDA bending tests, and axial crushing tests on galvanized steel sheets with a thickness of over 1.2 mm were all conducted on steel sheets with a thickness of 1.2 mm, taking into account the influence of the sheet thickness. Steel plates with a thickness of more than 1.2 mm were ground on one side to a thickness of 1.2 mm. Since the bendability of the steel plate surface may be affected by the grinding process, in the U-bending + close bending bending test, the ground surface is the inside of the bend (valley side), and in the V-bending + orthogonal VDA bending test, the ground surface is was set as the outside of the bend (peak side), and the ground surface was set as the inside of the bend (valley side) during the subsequent VDA bending test. On the other hand, in the U-bending + close bending test, V-bending + orthogonal VDA bending test, and axial crushing test of galvanized steel sheets with a thickness of less than 1.2, the effects of the sheet thickness were small, so the tests were conducted without grinding.
＜ナノ硬度測定＞
　プレス成形時の優れた曲げ性と衝突時の優れた曲げ破断特性を得るためには、素地表層から表層軟質層の板厚方向深さの１／４位置および板厚方向深さの１／２位置の夫々における板面の５０μｍ×５０μｍの領域において、３００点以上のナノ硬度を測定したとき、素地鋼板表面から表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度が７．０ＧＰａ以上の測定数が、板厚方向深さの１／４位置の全測定数に対して０．１０以下であることがより好ましい。ナノ硬度が７．０ＧＰａ以上の割合が０．１０以下の場合、硬質な組織（マルテンサイトなど）、介在物などの割合が小さいことを意味するため、硬質な組織（マルテンサイトなど）、介在物などのプレス成形時および衝突時のボイドの生成・連結および亀裂の進展をより抑制することが可能となり、優れたＲ／ｔおよびＳＦｍａｘが得られる。 <Nano hardness measurement>
In order to obtain excellent bendability during press forming and excellent bending rupture properties during collision, it is necessary to place the base material at a position of 1/4 of the depth in the thickness direction and 1/2 of the depth in the thickness direction of the surface soft layer from the surface layer of the substrate. When nanohardness was measured at 300 or more points in a 50 μm x 50 μm area of the plate surface at each position, the nanohardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface was It is more preferable that the number of measurements of 7.0 GPa or more is 0.10 or less with respect to the total number of measurements at 1/4 position of the depth in the plate thickness direction. If the ratio of nanohardness of 7.0 GPa or more is 0.10 or less, it means that the ratio of hard structures (such as martensite) and inclusions is small. It becomes possible to further suppress the generation and connection of voids and the propagation of cracks during press molding and collisions, and excellent R/t and SFmax can be obtained.
　本実施例では、めっき剥離後、素地鋼板の表面から表層軟質層の板厚方向深さの１／４位置－５μｍまで機械研磨し、素地鋼板の表面から表層軟質層の板厚方向深さの１／４位置までダイヤモンドおよびアルミナでのバフ研磨後、コロイダルシリカ研磨を実施した。Ｈｙｓｉｔｒｏｎ社のｔｒｉｂｏ－９５０を用い、バーコビッチ形状のダイヤモンド圧子により、
　荷重：５００μＮ
　測定領域：５０μｍ×５０μｍ
　打点間隔：２μｍ
の条件で計５１２点のナノ硬度を測定した。 In this example, after the plating was removed, mechanical polishing was performed from the surface of the base steel plate to a depth of 1/4 of the thickness direction depth of the surface soft layer -5 μm, and from the surface of the base steel plate to the thickness direction depth of the surface soft layer. After buffing with diamond and alumina to the 1/4 position, colloidal silica polishing was performed. Using Hysitron's tribo-950, with a Berkovich-shaped diamond indenter,
Load: 500μN
Measurement area: 50μm x 50μm
Dot spacing: 2μm
Nanohardness was measured at a total of 512 points under these conditions.
　次いで、上記表層軟質層の板厚方向深さの１／２位置まで機械研磨、ダイヤモンドおよびアルミナでのバフ研磨およびコロイダルシリカ研磨を実施した。Ｈｙｓｉｔｒｏｎ社のｔｒｉｂｏ－９５０を用い、バーコビッチ形状のダイヤモンド圧子により、
　荷重：５００μＮ
　測定領域：５０μｍ×５０μｍ
　打点間隔：２μｍ
の条件で計５１２点のナノ硬度を測定した。 Next, mechanical polishing, buff polishing with diamond and alumina, and colloidal silica polishing were performed to a depth of 1/2 of the thickness of the surface soft layer. Using Hysitron's tribo-950, with a Berkovich-shaped diamond indenter,
Load: 500μN
Measurement area: 50μm x 50μm
Dot spacing: 2μm
Nanohardness was measured at a total of 512 points under these conditions.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000005
  
Figure JPOXMLDOC01-appb-T000005
  
　表３、表５に示したように、発明例ではいずれも、引張強さ（ＴＳ）、降伏応力（ＹＳ）、降伏比（ＹＲ）、全伸び（Ｅｌ）、限界穴広げ率（λ）、Ｖ曲げ試験でのＲ/ｔ、Ｕ曲げ＋密着曲げ曲げ試験での限界スペーサー厚さ（ＳＴ）、および、Ｖ曲げ＋直交ＶＤＡ曲げ試験で測定される荷重最大時のストローク（ＳＦｍａｘ）の全てが合格であり、軸圧壊試験での破断（外観割れ）はなかった。
　一方、比較例では、引張強さ（ＴＳ）、降伏応力（ＹＳ）、降伏比（ＹＲ）、全伸び（Ｅｌ）、限界穴広げ率（λ）、Ｖ曲げ試験でのＲ/ｔ、Ｕ曲げ＋密着曲げ曲げ試験での限界スペーサー厚さ（ＳＴ）、Ｖ曲げ＋直交ＶＤＡ曲げ試験で測定される荷重最大時のストローク（ＳＦｍａｘ）、および、軸圧壊試験での破断（外観割れ）有無の少なくとも１つが十分ではなかった。
なお、表５において、露点が－３０℃以上－２０℃以下の範囲では、表層の軟質層厚さが１７μｍ以下となり、軸圧壊試験での破断（外観割れ）の判定は「○」であるが、表層の軟質層厚さが１７μｍ以下の場合でも金属めっき層を有する場合は、軸圧壊試験での破断（外観割れ）の判定は「◎」となる。 As shown in Tables 3 and 5, in the invention examples, tensile strength (TS), yield stress (YS), yield ratio (YR), total elongation (El), critical hole expansion rate (λ), R/t in the V-bending test, critical spacer thickness (ST) in the U-bending + close bending test, and stroke at maximum load (SFmax) measured in the V-bending + orthogonal VDA bending test. It passed, and there was no fracture (appearance cracking) in the axial crush test.
On the other hand, in the comparative example, tensile strength (TS), yield stress (YS), yield ratio (YR), total elongation (El), critical hole expansion rate (λ), R/t in V-bending test, and U-bending + Critical spacer thickness (ST) in close bending test, stroke at maximum load (SFmax) measured in V-bending + orthogonal VDA bending test, and presence or absence of fracture (appearance cracking) in axial crushing test. One wasn't enough.
In addition, in Table 5, when the dew point is in the range of -30°C or more and -20°C or less, the soft layer thickness of the surface layer is 17 μm or less, and the judgment of fracture (appearance cracking) in the axial crush test is "○". Even if the soft layer thickness of the surface layer is 17 μm or less, if the metal plating layer is present, the judgment of fracture (appearance cracking) in the axial crush test will be “◎”.
　また、本発明例の鋼板を用いて、成形加工を施して得た部材または接合加工を施して得た部材は、引張強さ（ＴＳ）、降伏応力（ＹＳ）、降伏比（ＹＲ）、全伸び（Ｅｌ）、限界穴広げ率（λ）、Ｖ曲げ試験でのＲ／ｔ、Ｕ曲げ＋密着曲げ曲げ試験での限界スペーサー厚さ（ＳＴ）、および、Ｖ曲げ＋直交ＶＤＡ曲げ試験で測定される荷重最大時のストローク（ＳＦｍａｘ）の全てが本発明で特徴とする優れた特性を有し、軸圧壊試験での破断（外観割れ）はなく、本発明で特徴とする優れた特性を有することがわかった。 In addition, the members obtained by forming or joining the steel sheets of the present invention example have tensile strength (TS), yield stress (YS), yield ratio (YR), Elongation (El), critical hole expansion rate (λ), R/t in V-bending test, critical spacer thickness (ST) in U-bending + close bending test, and measured in V-bending + orthogonal VDA bending test All of the strokes (SFmax) at the maximum load applied have the excellent characteristics characterized by the present invention, and there is no breakage (appearance cracking) in the axial crush test, and the excellent characteristics characterized by the present invention. I understand.
　１０　　ハット型部材
　２０　　亜鉛めっき鋼板
　３０　　試験用部材
　４０　　スポット溶接部
　５０　　地板
　６０　　インパクター
　Ａ１　　ダイ
　Ａ２　　支持ロール
　Ａ３　　ダイ
　Ａ４　　支持ロール
　Ｂ１　　パンチ
　Ｂ２　　パンチ
　Ｂ３　　パンチ
　Ｂ４　　パンチ
　Ｄ１　　幅（Ｃ）方向
　Ｄ２　　圧延（Ｌ）方向
　Ｄ３　　圧壊方向
　Ｓ　　スペーサー
　Ｔ１　　試験片
　Ｔ２　　試験片
　Ｆ　　フェライト
　Ｍ　　マルテンサイト
　ＲＡ　　残留オーステナイト
　Ｍ’　　孤立した島状フレッシュマルテンサイト
　ＲＡ’　　孤立した島状残留オーステナイト
　Ｂ　　ベイナイト
　ＢＴ　　焼戻しベイナイト
　ＴＭ　　焼戻しマルテンサイト 10 Hat-shaped member 20 Galvanized steel plate 30 Test member 40 Spot weld 50 Base plate 60 Impactor A1 Die A2 Support roll A3 Die A4 Support roll B1 Punch B2 Punch B3 Punch B4 Punch D1 Width (C) direction D2 Rolling (L) Direction D3 Crushing direction S Spacer T1 Test piece T2 Test piece F Ferrite M Martensite RA Retained austenite M' Isolated island fresh martensite RA' Isolated island retained austenite B Bainite BT Tempered bainite TM Tempered martensite
　本発明によれば、ＴＳ：７８０ＭＰａ以上であり、かつ、高いＹＳおよびＹＲと、優れたプレス成形性（延性、穴広げ性および曲げ性）と、衝突時の耐破断特性（曲げ破断特性および軸圧壊特性）を有する亜鉛めっき鋼板および部材の製造が可能になる。また、本発明の方法に従って得られた亜鉛めっき鋼板および部材を、例えば、自動車構造部材に適用することによって車体軽量化による燃費向上を図ることができ、産業上の利用価値は極めて大きい。
  According to the present invention, TS: 780 MPa or more, high YS and YR, excellent press formability (ductility, hole expandability, and bendability), and rupture resistance properties at the time of collision (bending rupture properties and axial It becomes possible to manufacture galvanized steel sheets and members with high crushing properties. Further, by applying the galvanized steel sheets and members obtained according to the method of the present invention to, for example, automobile structural members, it is possible to improve fuel efficiency by reducing the weight of the car body, and the industrial value thereof is extremely large.

Claims (17)

  1. 　素地鋼板と、該素地鋼板の上に形成された亜鉛めっき層と、を備える、亜鉛めっき鋼板であって、前記素地鋼板は、
    質量％で、
    Ｃ：０．０３０％以上０．２５０％以下、
    Ｓｉ：０．０１％以上０．７５％以下、
    Ｍｎ：２．００％以上３．５０％未満、
    Ｐ：０．００１％以上０．１００％以下、
    Ｓ：０．０２００％以下、
    Ａｌ：０．０１０％以上２．０００％以下、
    Ｎ：０．０１００％以下、
    を含有し、残部がＦｅおよび不可避的不純物からなる成分組成と、
    前記素地鋼板の板厚１／４位置の組織として、
    フェライトの面積率：２０．０％以上８０．０％以下であり、
    フレッシュマルテンサイトの面積率：１５．０％以下であり、
    残留オーステナイトの面積率：３．０％以下であり、
    　フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの面積率の合計を、鋼板全体のフレッシュマルテンサイトの面積率と残留オーステナイトの面積率の合計で除した値：０．６５以上であり、
    ベイナイトおよび焼戻しベイナイトの面積率：１０．０％以下であり、
    焼戻しマルテンサイトの面積率：１０．０％以上７０．０％以下であり、
    さらに、フェライト粒内の島状フレッシュマルテンサイトと島状残留オーステナイトの平均結晶粒径が２．０μｍ以下である鋼組織と、
    を有し、
    前記素地鋼板に含まれる拡散性水素量が０．５０質量ｐｐｍ以下であり、引張強さが７８０ＭＰａ以上である、亜鉛めっき鋼板。     A galvanized steel sheet comprising a base steel plate and a galvanized layer formed on the base steel plate, the base steel plate comprising:
    In mass%,
    C: 0.030% or more and 0.250% or less,
    Si: 0.01% or more and 0.75% or less,
    Mn: 2.00% or more and less than 3.50%,
    P: 0.001% or more and 0.100% or less,
    S: 0.0200% or less,
    Al: 0.010% or more and 2.000% or less,
    N: 0.0100% or less,
    , with the remainder consisting of Fe and unavoidable impurities;
    As the structure at the 1/4 plate thickness position of the base steel plate,
    Ferrite area ratio: 20.0% or more and 80.0% or less,
    Fresh martensite area ratio: 15.0% or less,
    Area ratio of retained austenite: 3.0% or less,
    The value obtained by dividing the total area ratio of island-like fresh martensite and island-like retained austenite in the ferrite grains by the sum of the area ratio of fresh martensite and retained austenite in the entire steel sheet: 0.65 or more,
    Area ratio of bainite and tempered bainite: 10.0% or less,
    Area ratio of tempered martensite: 10.0% or more and 70.0% or less,
    Furthermore, a steel structure in which the average crystal grain size of island-like fresh martensite and island-like retained austenite in the ferrite grains is 2.0 μm or less,
    has
    A galvanized steel sheet, wherein the amount of diffusible hydrogen contained in the base steel sheet is 0.50 mass ppm or less, and the tensile strength is 780 MPa or more.
  2. 　前記成分組成は、さらに、質量％で、
    　　Ｎｂ：０．２００％以下、
    　　Ｔｉ：０．２００％以下、
    　　Ｖ：０．２００％以下、
    　　Ｂ：０．０１００％以下、
    　　Ｃｒ：１．０００％以下、
    　　Ｎｉ：１．０００％以下、
    　　Ｍｏ：１．０００％以下、
    　　Ｓｂ：０．２００％以下、
    　　Ｓｎ：０．２００％以下、
    　　Ｃｕ：１．０００％以下、
    　　Ｔａ：０．１００％以下、
    　　Ｗ：０．５００％以下、
    　　Ｍｇ：０．０２００％以下、
    　　Ｚｎ：０．０２００％以下、
    　　Ｃｏ：０．０２００％以下、
    　　Ｚｒ：０．１０００％以下、
    　　Ｃａ：０．０２００％以下、
    　　Ｓｅ：０．０２００％以下、
    　　Ｔｅ：０．０２００％以下、
    　　Ｇｅ：０．０２００％以下、
    　　Ａｓ：０．０５００％以下、
    　　Ｓｒ：０．０２００％以下、
    　　Ｃｓ：０．０２００％以下、
    　　Ｈｆ：０．０２００％以下、
    　　Ｐｂ：０．０２００％以下、
    　　Ｂｉ：０．０２００％以下および
    　　ＲＥＭ：０．０２００％以下
    のうちから選ばれる少なくとも１種の元素を含有する、請求項１に記載の亜鉛めっき鋼板。     The component composition further includes, in mass%,
    Nb: 0.200% or less,
    Ti: 0.200% or less,
    V: 0.200% or less,
    B: 0.0100% or less,
    Cr: 1.000% or less,
    Ni: 1.000% or less,
    Mo: 1.000% or less,
    Sb: 0.200% or less,
    Sn: 0.200% or less,
    Cu: 1.000% or less,
    Ta: 0.100% or less,
    W: 0.500% or less,
    Mg: 0.0200% or less,
    Zn: 0.0200% or less,
    Co: 0.0200% or less,
    Zr: 0.1000% or less,
    Ca: 0.0200% or less,
    Se: 0.0200% or less,
    Te: 0.0200% or less,
    Ge: 0.0200% or less,
    As: 0.0500% or less,
    Sr: 0.0200% or less,
    Cs: 0.0200% or less,
    Hf: 0.0200% or less,
    Pb: 0.0200% or less,
    The galvanized steel sheet according to claim 1, containing at least one element selected from Bi: 0.0200% or less and REM: 0.0200% or less.
  3. 　前記素地鋼板は、素地鋼板表面から板厚方向に２００μｍ以下の領域を表層とした際、
    前記表層に、板厚１／４位置のビッカース硬さに対して、ビッカース硬さが８５％以下である表層軟質層を有し、
    　前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置および板厚方向深さの１／２位置の夫々における板面の５０μｍ×５０μｍの領域において、３００点以上のナノ硬度を測定したとき、
    前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度が７．０ＧＰａ以上の測定数割合が、前記表層軟質層の板厚方向深さの１／４位置の全測定数に対して０．１０以下であり、
    さらに、前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／４位置の板面のナノ硬度の標準偏差σが１．８ＧＰａ以下であり、
    さらに、前記素地鋼板表面から前記表層軟質層の板厚方向深さの１／２位置の板面のナノ硬度の標準偏差σが２．２ＧＰａ以下である、請求項１または２に記載の亜鉛めっき鋼板。     When the base steel plate has an area of 200 μm or less in the thickness direction from the surface of the base steel plate as the surface layer,
    The surface layer has a soft surface layer whose Vickers hardness is 85% or less with respect to the Vickers hardness at the 1/4 position of the plate thickness,
    Nano hardness of 300 points or more in a 50 μm x 50 μm area of the plate surface at 1/4 position and 1/2 depth in the plate thickness direction of the surface soft layer from the surface of the base steel plate, respectively. When measuring,
    The proportion of measurements where the nano-hardness of the plate surface at 1/4 of the depth in the thickness direction of the soft surface layer from the surface of the base steel sheet is 7.0 GPa or more is 1/4 of the depth in the thickness direction of the soft surface layer. 0.10 or less for the total number of measurements at 4 positions,
    Furthermore, the standard deviation σ of the nano-hardness of the plate surface at a position 1/4 of the thickness direction depth of the surface soft layer from the base steel plate surface is 1.8 GPa or less,
    Further, the zinc plating according to claim 1 or 2, wherein a standard deviation σ of nanohardness of the plate surface at a position 1/2 the thickness direction depth of the surface soft layer from the base steel plate surface is 2.2 GPa or less. steel plate.
  4. 　前記亜鉛めっき鋼板の片面または両面において、前記素地鋼板と前記亜鉛めっき層の間に形成された金属めっき層を有する、請求項１または２に記載の亜鉛めっき鋼板。 The galvanized steel sheet according to claim 1 or 2, having a metal plating layer formed between the base steel sheet and the galvanized layer on one or both sides of the galvanized steel sheet.
  5. 　前記亜鉛めっき鋼板の片面または両面において、前記素地鋼板と前記亜鉛めっき層の間に形成された金属めっき層を有する、請求項３に記載の亜鉛めっき鋼板。 The galvanized steel sheet according to claim 3, having a metal plating layer formed between the base steel sheet and the galvanized layer on one or both sides of the galvanized steel sheet.
  6. 　請求項１または２に記載の亜鉛めっき鋼板を用いてなる、部材。 A member using the galvanized steel sheet according to claim 1 or 2.
  7. 　請求項３に記載の亜鉛めっき鋼板を用いてなる、部材。 A member made of the galvanized steel sheet according to claim 3.
  8. 　請求項４に記載の亜鉛めっき鋼板を用いてなる、部材。 A member made using the galvanized steel sheet according to claim 4.
  9. 　請求項５に記載の亜鉛めっき鋼板を用いてなる、部材。 A member made using the galvanized steel sheet according to claim 5.
  10. 　請求項１または２に記載の成分組成を有する鋼スラブに、
    仕上げ圧延温度：８２０℃以上の条件で熱間圧延を施し、熱延鋼板を得る、熱間圧延工程と、
    該熱間圧延工程後の鋼板に対して、３５０℃以上６００℃以下の温度域を平均加熱速度７℃／秒以上の条件で昇温する昇温工程と、
    焼鈍温度：７５０℃以上９００℃以下、焼鈍時間：２０秒以上の条件で焼鈍する、焼鈍工程と、
    前記焼鈍工程後、（前記焼鈍温度－３０℃）から６５０℃までの平均冷却速度を７℃／秒以上とし、６５０℃から５００℃までの平均冷却速度を１４℃／秒以下とする条件で冷却する第一冷却工程と、
    前記第一冷却工程後、鋼板に亜鉛めっき処理を施し、亜鉛めっき鋼板を得る、亜鉛めっき工程と、
    前記亜鉛めっき鋼板に対して、３００℃以上４５０℃以下の温度域で２．０ｋｇｆ／ｍｍ２以上の張力を付与し、
    その後、前記亜鉛めっき鋼板を、１パス当たり直径５００ｍｍ以上１５００ｍｍ以下のロールにロール１／４周分接触させながら、５パス以上通過させ、
    ついで、２５０℃以下の冷却停止温度まで冷却する、第二冷却工程と、
    前記亜鉛めっき鋼板を、前記冷却停止温度以上４４０℃以下の温度域まで再加熱して２０秒以上保持する、再加熱工程と、を含み、あるいはさらに
    前記熱間圧延工程後、かつ前記昇温工程前の鋼板に、圧下率が２０％以上８０％以下である冷間圧延を施し、冷延鋼板を得る、冷間圧延工程を含む、亜鉛めっき鋼板の製造方法。     A steel slab having the composition according to claim 1 or 2,
    A hot rolling process in which hot rolling is performed at a finish rolling temperature of 820°C or higher to obtain a hot rolled steel plate;
    A heating step of raising the temperature of the steel plate after the hot rolling step in a temperature range of 350° C. or higher and 600° C. or lower at an average heating rate of 7° C./sec or higher;
    An annealing step of annealing at an annealing temperature of 750°C or more and 900°C or less and an annealing time of 20 seconds or more;
    After the annealing step, cooling under conditions such that the average cooling rate from (the annealing temperature -30°C) to 650°C is 7°C/second or more, and the average cooling rate from 650°C to 500°C is 14°C/second or less. a first cooling step,
    After the first cooling step, a galvanizing step is performed on the steel sheet to obtain a galvanized steel sheet;
    Applying a tension of 2.0 kgf/mm 2 or more to the galvanized steel sheet in a temperature range of 300 ° C. or higher and 450 ° C. or lower,
    Thereafter, the galvanized steel sheet is passed through 5 or more passes while being in contact with a roll having a diameter of 500 mm or more and 1500 mm or less for 1/4 rotation of the roll per pass,
    Then, a second cooling step of cooling to a cooling stop temperature of 250° C. or less;
    a reheating step of reheating the galvanized steel sheet to a temperature range from the cooling stop temperature to 440° C. and holding it for 20 seconds or more, or further after the hot rolling step and the heating step A method for manufacturing a galvanized steel sheet, comprising a cold rolling step of cold rolling a previous steel sheet at a rolling reduction of 20% or more and 80% or less to obtain a cold rolled steel sheet.
  11. 　前記焼鈍工程における焼鈍を、露点：－３０℃以上の雰囲気下で行う、請求項１０に記載の亜鉛めっき鋼板の製造方法。 The method for manufacturing a galvanized steel sheet according to claim 10, wherein the annealing in the annealing step is performed in an atmosphere with a dew point of -30°C or higher.
  12. 　前記焼鈍工程の前に、前記亜鉛めっき鋼板の片面または両面において、金属めっきを施し金属めっき層を形成する金属めっき工程を含む、請求項１０に記載の亜鉛めっき鋼板の製造方法。 The method for manufacturing a galvanized steel sheet according to claim 10, comprising a metal plating step of applying metal plating to form a metal plating layer on one or both sides of the galvanized steel sheet before the annealing step.
  13. 　前記焼鈍工程の前に、前記亜鉛めっき鋼板の片面または両面において、金属めっきを施し金属めっき層を形成する金属めっき工程を含む、請求項１１に記載の亜鉛めっき鋼板の製造方法。 The method for manufacturing a galvanized steel sheet according to claim 11, comprising a metal plating step of applying metal plating to form a metal plating layer on one or both sides of the galvanized steel sheet before the annealing step.
  14. 　請求項１または２に記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。 A method for producing a member, the method comprising the step of subjecting the galvanized steel sheet according to claim 1 or 2 to at least one of forming and bonding to produce a member.
  15. 　請求項３に記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。 A method for producing a member, the method comprising the step of subjecting the galvanized steel sheet according to claim 3 to at least one of forming and bonding to produce a member.
  16. 　請求項４に記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。 A method for producing a member, the method comprising the step of subjecting the galvanized steel sheet according to claim 4 to at least one of forming and bonding to produce a member.
  17. 　請求項５に記載の亜鉛めっき鋼板に、成形加工、接合加工の少なくとも一方を施して部材とする工程を含む、部材の製造方法。
          A method for producing a member, the method comprising the step of subjecting the galvanized steel sheet according to claim 5 to at least one of forming and bonding to produce a member.
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