WO2020039696A1 - 高強度鋼板及びその製造方法 - Google Patents
高強度鋼板及びその製造方法 Download PDFInfo
- Publication number
- WO2020039696A1 WO2020039696A1 PCT/JP2019/022848 JP2019022848W WO2020039696A1 WO 2020039696 A1 WO2020039696 A1 WO 2020039696A1 JP 2019022848 W JP2019022848 W JP 2019022848W WO 2020039696 A1 WO2020039696 A1 WO 2020039696A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- less
- steel sheet
- content
- strength
- area ratio
- Prior art date
Links
Images
Classifications
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following hot rolling
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—Final recrystallisation annealing
-
- 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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- 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
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
Definitions
- the present invention relates to a high-strength steel sheet suitable for cold press forming used through a cold press forming step in automobiles, home appliances, and the like, and a method for producing the same.
- Patent Literature 1 proposes a method of improving the bending property by defining the distribution form of inclusions in the surface layer from the surface of the steel sheet to a depth of (sheet thickness ⁇ 0.1).
- Patent Document 2 proposes a method in which a soft portion having a hardness of 80% or less of the central portion of the steel plate is formed in the surface layer of the steel plate to improve the bendability. Further, it is described that the surface soft portion has a structure that does not contain ferrite as much as possible, so that significant deterioration in fatigue characteristics can be suppressed.
- Patent Document 1 can suppress a visible level of coarse cracks originating from inclusions, but cannot sufficiently suppress fine cracks of 1 mm or less formed in the extremely surface layer region of the steel sheet.
- the present invention has been made in order to solve the above problems, and an object of the present invention is to provide a high-strength steel sheet having excellent bending properties and fatigue properties and having a tensile strength of 1320 MPa or more, and a method for producing the same.
- “high strength” means that the tensile strength (TS) is 1320 MPa or more.
- the present inventors have conducted intensive studies to solve the above-mentioned problems.
- the component composition is adjusted to a specific range, and the area ratio of ferrite in a region from the surface to 10 ⁇ m is adjusted to a specific range.
- the present invention provides the following.
- Hv High strength steel sheet.
- Hv is the Vickers hardness at a position of 15 ⁇ m from the surface in the thickness direction
- ⁇ represents the tensile strength (MPa).
- the component composition is, in mass%, Mo: 0.005% to 0.3%, Cr: 0.01% to 1.0%, Nb: 0.001% to 0.10. %, Ti: 0.001% to 0.10%, B: 0.0002% to 0.0050%, Sb: 0.001% to 0.1%, Ca: 0.0002% to 0 0.0040% or less, V: 0.003% to 0.45%, Cu: 0.005% to 0.50%, Ni: 0.005% to 0.50% and Sn: 0.002%
- the high-strength steel sheet according to [1] containing at least one kind of at least 0.1% or less.
- a cold-rolled steel sheet having the component composition described in [1] or [2] is maintained at an annealing temperature of 840 ° C or more for 180 seconds or more at a dew point of ⁇ 35 ° C or less in a temperature range of 750 ° C or more. Then, at a cooling start temperature of 740 ° C. or more, a continuous annealing step of cooling a temperature range from the cooling start temperature to 150 ° C. at an average cooling rate of 100 ° C./s or more, and after the continuous annealing step, if necessary, A method for producing a high-strength steel sheet, comprising: re-heating and maintaining the steel sheet in a temperature range of 150 to 260 ° C. for 30 to 1500 seconds.
- % of the content of the component means “% by mass”.
- a region from the surface of the steel sheet to 10 ⁇ m in the thickness direction is simply referred to as a surface layer region.
- C 0.13% or more and less than 0.40% C is necessary for improving the hardenability and obtaining a steel structure in which the total area ratio of martensite or bainite at a 1/4 thickness position is 95% or more. It is. Further, C is necessary from the viewpoint of increasing the strength of martensite or bainite and ensuring TS ⁇ 1320 MPa. When the content of C is less than 0.13%, a predetermined strength cannot be obtained. Therefore, the C content is set to 0.13% or more. From the viewpoint of obtaining TS ⁇ 1470 MPa, the C content is preferably set to 0.15% or more. C content is more preferably 0.17% or more. When the C content is 0.40% or more, it becomes difficult to obtain good weldability and delayed fracture resistance. Therefore, the C content is set to less than 0.40%. The C content is preferably at most 0.35%, more preferably at most 0.32%.
- Si 0.01% or more and 1.0% or less
- Si is a strengthening element by solid solution strengthening, and suppresses generation of film-like carbide when tempered in a temperature range of 200 ° C. or more, and improves bendability. It is contained from the viewpoint. From the viewpoint of obtaining the above effects, the Si content is set to 0.01% or more. The Si content is preferably at least 0.10%, more preferably at least 0.20%. On the other hand, if the content of Si is too large, the amount of segregation increases and the bendability deteriorates. On the other hand, when the Si content is too large, the rolling load in hot rolling and cold rolling is significantly increased. Therefore, the Si content is 1.0% or less. The Si content is preferably 0.8% or less, more preferably 0.6% or less.
- Mn 1.7% or less (0% is not included) Mn contributes to an effect of increasing the total area ratio of martensite and bainite through an increase in hardenability and an improvement in strength through solid solution strengthening. Further, S in the steel is fixed as MnS, and Mn is contained in order to reduce hot brittleness.
- the lower limit of the Mn content is not particularly defined, it is preferable to contain Mn in an amount of 0.2% or more in order to stably obtain a predetermined total area ratio of martensite and bainite industrially.
- the Mn content is more preferably at least 0.5%, even more preferably at least 0.7%.
- the Mn content is set to 1.7% or less from the viewpoint of welding stability.
- the Mn content is preferably at most 1.6%, more preferably at most 1.5%.
- P 0.030% or less
- P is an element that strengthens steel, but when its content is large, spot weldability is significantly deteriorated. Therefore, the P content is set to 0.030% or less. From the viewpoint of sufficiently suppressing the deterioration of spot weldability, the P content is preferably set to 0.010% or less.
- the lower limit of the P content is not specified, the lower limit that can be practically used industrially at present is about 0.002%, and the P content is often substantially higher.
- S 0.010% or less S has a significant effect on bendability and fatigue properties through the formation of MnS and the like. For this reason, it is desirable to reduce the S content.
- the S content must be at least 0.010% or less in order to reduce the adverse effects caused by inclusions.
- the lower limit of the S content is not specified, the lower limit which can be industrially implemented at present is about 0.0002%, and the S content is often substantially higher.
- Al 0.20% or less (excluding 0%) Al is contained to perform sufficient deoxidation and reduce inclusions in the steel.
- the lower limit of the Al content is not particularly specified, it is preferable that the Al content is 0.01% or more in order to stably perform deoxidation.
- the content of Al is set to 0.20% or less.
- N 0.010% or less
- N is an element that forms nitrides such as TiN, (Nb, Ti) (C, N) and AlN and carbonitride-based inclusions in steel, and bends through the formation of these. Deterioration of fatigue and fatigue properties. Therefore, the N content needs to be at least 0.010% or less. Although the lower limit of the N content is not specified, the lower limit practically practicable at present is about 0.0006%, and the N content is often substantially higher.
- the component composition of the steel sheet of the present invention may include at least one of the following optional elements.
- Nb 0.001% or more and 0.10% or less Nb contributes to high strength through refinement of the internal structure of martensite or bainite.
- the Nb content is set to 0.001% or more. Preferably it is 0.005% or more, more preferably 0.008% or more.
- the content of Nb is set to 0.10% or less.
- the Nb content is preferably 0.08% or less, more preferably 0.06% or less.
- Ti 0.001% or more and 0.10% or less Ti contributes to high strength through refinement of the internal structure of martensite or bainite. From the viewpoint of obtaining this effect, the Ti content is set to 0.001% or more. Preferably it is 0.005% or more, more preferably 0.008% or more. However, when the Ti content is excessive, a large amount of inclusions such as TiN and TiC are generated, and the bendability is deteriorated. In order to reduce such adverse effects, the Ti content is set to 0.10% or less. The Ti content is preferably 0.06% or less, more preferably 0.03% or less.
- B 0.0002% or more and 0.0050% or less
- B is an element that improves the hardenability of steel, and has an advantage of generating martensite or bainite with a predetermined area ratio even with a small Mn content.
- the B content is set to 0.0002% or more. Preferably it is 0.0005% or more, more preferably 0.0010% or more.
- the B content is set to 0.0050% or less.
- the B content is preferably 0.0040% or less, more preferably 0.0030% or less.
- Cu not less than 0.005% and not more than 0.50% Cu improves the corrosion resistance in the use environment of an automobile.
- Cu is an element that is mixed in when scrap is used as a raw material. By allowing the mixing of Cu, recycled materials can be used as raw materials, and manufacturing costs can be reduced.
- the Cu content is 0.005% or more from the above viewpoint.
- the Cu content is preferably at least 0.010%, more preferably at least 0.050%. However, if the content is too large, it causes surface defects, so the Cu content is set to 0.50% or less.
- the Cu content is preferably at most 0.40%, more preferably at most 0.30%.
- Ni 0.005% or more and 0.50% or less
- Ni is also an element having an effect of improving corrosion resistance.
- Ni has an effect of reducing surface defects that are likely to occur when Cu is contained.
- the Ni content is set to 0.005% or more.
- the Ni content is preferably at least 0.008%, more preferably at least 0.010%.
- the Ni content is set to 0.50% or less.
- the Ni content is preferably 0.20% or less, more preferably 0.15% or less.
- Cr 0.01% or more and 1.0% or less Cr can be added to obtain the effect of improving the hardenability of steel.
- the Cr content is set to 0.01% or more. Preferably it is 0.03% or more, more preferably 0.05% or more. If the Cr content exceeds 1.0%, the rate of solid solution of cementite during annealing is delayed, and the unbindered cementite is left to deteriorate the bendability. Further, the pitting corrosion resistance is also deteriorated. Further, the chemical conversion property also deteriorates. Therefore, the Cr content is set to 1.0% or less.
- Mo 0.005% or more and 0.3% or less Mo can be added for the purpose of improving the hardenability of steel and obtaining the effect of increasing the strength by refining martensite. To obtain these effects, the Mo content is set to 0.005% or more.
- the Mo content is preferably 0.010% or more, more preferably 0.040% or more. However, when Mo is contained at more than 0.3%, the chemical conversion property deteriorates. Therefore, the Mo content is set to 0.3% or less.
- the Mo content is preferably 0.2% or less, more preferably 0.1% or less.
- V 0.003% or more and 0.45% or less
- V is an effect of improving the hardenability of steel, an effect of generating fine carbides containing V serving as hydrogen trap sites, and a delay resistance due to miniaturization of martensite. It can be added for the purpose of obtaining the effect of improving the breaking characteristics.
- the V content is made 0.003% or more. Preferably it is 0.005% or more, more preferably 0.010% or more. However, when V is contained at more than 0.45%, castability is significantly deteriorated. Therefore, the V content is set to 0.45% or less.
- the V content is preferably at most 0.30%, more preferably at most 0.20%.
- Ca 0.0002% or more and 0.0040% or less Ca fixes S as CaS and improves the bendability.
- the Ca content is set to 0.0002% or more. Preferably it is 0.0003% or more, more preferably 0.0004% or more.
- the Ca content is set to 0.0040% or less.
- the Ca content is preferably 0.0036% or less, more preferably 0.0032% or less.
- Sb 0.001% or more and 0.1% or less Sb suppresses oxidation and nitridation in the surface layer region of the steel sheet, thereby suppressing a decrease in the content of C and B in the surface layer region. By suppressing the reduction of C and B, the formation of ferrite in the surface layer region is suppressed, thereby contributing to higher strength and improved fatigue characteristics. From the viewpoint of obtaining this effect, the Sb content is set to 0.001% or more. The Sb content is preferably at least 0.002%, more preferably at least 0.005%. However, when the Sb content exceeds 0.1%, the castability deteriorates, and Sb segregates at the old ⁇ grain boundary to deteriorate the bendability. Therefore, the Sb content is set to 0.1% or less. The Sb content is preferably 0.04% or less.
- Sn 0.002% or more and 0.1% or less Sn suppresses oxidation and nitridation in the surface layer region of the steel sheet, thereby suppressing a decrease in the content of C and B in the surface layer region. By suppressing the reduction of C and B, the formation of ferrite in the surface layer region is suppressed, thereby contributing to higher strength and improved fatigue characteristics. From the viewpoint of obtaining this effect, the Sn content is set to 0.002% or more. The Sn content is preferably 0.005% or more. However, when the Sn content exceeds 0.1%, the castability deteriorates, and the Sn segregates at the prior austenite grain boundary to deteriorate the bendability. Therefore, the Sn content is set to 0.1% or less. The Sn content is preferably 0.04% or less.
- the balance other than the above is Fe and inevitable impurities.
- the above-mentioned optional elements are contained below the lower limit, the above-mentioned optional elements are included as inevitable impurities.
- the total area ratio of martensite and bainite at a plate thickness 1/4 position is 95% or more and 100% or less.
- the steel structure In order to achieve a high strength of TS ⁇ 1320 MPa, the steel structure must be martensite and bainite at a plate thickness 1/4 position. Is 95% or more.
- the total area ratio is preferably 97% or more, and more preferably 98% or more. The remaining part included when the total area ratio is other than 100% is retained austenite and the like. Retained austenite remains in the cooling step of the annealing step and can have an area ratio of up to 5%.
- the area ratio of ferrite in the region (surface layer region) from the steel plate surface to the plate thickness direction up to 10 ⁇ m is 10% or more and 40% or less. % To 40% ferrite. To obtain this effect, the area ratio of ferrite needs to be 10% or more.
- the area ratio of ferrite is preferably at least 13%, more preferably at least 16%.
- the area ratio of the ferrite is set to 40% or less.
- the area ratio of ferrite is preferably 35% or less, more preferably 30% or less.
- the area ratio of ferrite in the surface layer region is set to 10% or more and 40% or less.
- the dew point and the annealing temperature in continuous annealing is important to control the dew point and the annealing temperature in continuous annealing to be described later. The area ratio is measured by the method described in Examples.
- the area ratio of ferrite in the region (surface layer region) from the steel sheet surface to the thickness direction of 10 ⁇ m (surface layer region) is adjusted to 10% or more and 40% or less, the remaining structure other than the ferrite in the region becomes any structure. It may be.
- the remainder other than ferrite includes martensite, bainite, retained austenite, and the like.
- the Vickers hardness at a position of 15 ⁇ m in the thickness direction from the surface of the steel sheet satisfies the following equation (1).
- Hv is the Vickers hardness at a position of 15 ⁇ m in the thickness direction from the surface of the steel sheet
- ⁇ indicates the tensile strength (MPa).
- the Vickers hardness and tensile strength are measured by the methods described in Examples.
- the hardness is controlled according to the strength of the steel sheet itself as defined in the equation (1), excellent fatigue characteristics can be obtained.
- the slab obtained by continuous casting is used as a steel material, subjected to hot rolling, after finishing rolling, cooled and wound into a coil, then pickled, cold-rolled, and then continuously rolled. Anneal and overage to produce high strength steel sheet.
- conditions up to cold rolling may be general conditions.
- conditions employed in the continuous annealing step and the overaging treatment step will be described.
- the temperature is the surface temperature of the steel sheet.
- the cold-rolled steel sheet having the above-mentioned composition is held at an annealing temperature of 840 ° C. or more for 180 seconds or more under a condition that a dew point in a temperature range of 750 ° C. or more is ⁇ 35 ° C. or less.
- a temperature range from the cooling start temperature to 150 ° C. is cooled at an average cooling rate of 100 ° C./s or more.
- the annealing temperature is lower than 840 ° C., austenite (transformation to martensite or bainite after quenching) required for securing predetermined strength is not generated during annealing, and a tensile strength of 1320 MPa or more is obtained even after quenching after annealing. May not be possible. Therefore, the annealing temperature is 840 ° C. or higher. From the viewpoint of stably securing the equilibrium area ratio of austenite of 40% or more, the annealing temperature is preferably set to 850 ° C. or more.
- de-C and B are generated in the vicinity of the surface layer of the steel sheet, and in order to secure austenite stably and maintain the above Hv at a certain level or more, 840 ° C. or higher is essential.
- the upper limit of the annealing temperature is not particularly limited, but is preferably 900 ° C. or less because there is a possibility that the austenite grain size becomes coarse and the toughness is deteriorated.
- the holding time of the annealing temperature is set to 180 seconds or more.
- the upper limit of the holding time in annealing is not particularly limited, but is preferably 600 seconds or less because there is a possibility that the austenite grain size becomes coarse and the toughness is deteriorated.
- the temperature range from the cooling start temperature to 150 ° C. is an average cooling rate of 100 ° C./s or more. Need to be cooled. If the cooling start temperature is lower than this or the average cooling rate is lower than this, ferrite and residual austenite are excessively formed, which causes a decrease in strength and deterioration of fatigue properties.
- the upper limit of the average cooling rate in the temperature range from the cooling start temperature to 150 ° C. is not particularly limited, but even if it exceeds 1500 ° C./s, the effect is saturated.
- the cooling start temperature is not particularly defined, the lower limit of the annealing temperature is 840 ° C. or lower because the lower limit of the annealing temperature is 840 ° C.
- the average cooling rate from 150 ° C. to the cooling stop temperature is not particularly limited.
- the dew point in the temperature range of 750 ° C. or more is controlled to ⁇ 35 ° C. or less. If the dew point is higher than this, ferrite is excessively generated in the surface layer of the steel sheet, and the hardness decreases.
- the lower limit of the dew point is not particularly defined, it is preferable to set the lower limit to ⁇ 60 ° C. from the viewpoint of manufacturing cost.
- the overaging treatment step is a step in which, after the continuous annealing step, reheating is performed as necessary, and the temperature is kept in a temperature range of 150 to 260 ° C. for 30 to 1500 seconds.
- Carbide distributed inside martensite or bainite is a carbide generated during holding in a low temperature range after quenching, and it is necessary to appropriately control the bendability and TS ⁇ 1320 MPa in order to secure the bending property.
- it is necessary to reheat from a temperature of 150 ° C. or less to a temperature range of 150 to 260 ° C. if necessary, and to maintain the temperature range for 30 to 1500 seconds.
- the holding time it is necessary to control the holding time to 30 to 1500 seconds. If the holding temperature is lower than 150 ° C. or the holding time is shorter than 30 seconds, the carbide distribution density becomes insufficient and the toughness may be deteriorated. On the other hand, if the holding temperature is higher than 260 ° C. or the holding time is longer than 1500 seconds, coarsening of carbides in the grains and at the grain boundaries of the blocks becomes remarkable, and the bendability deteriorates.
- a test steel having the composition shown in Table 1 (the remainder is Fe and unavoidable impurities) was vacuum-melted to form a slab.
- the slab was heated at a temperature of 1200 to 1280 ° C., and then 840 to 950 ° C.
- Hot rolling at a finish rolling temperature of 450 ° C. and a winding temperature of 450 to 650 ° C.
- the resulting hot-rolled steel sheet was pickled to remove the surface scale, and then cold-rolled at a rolling reduction of 40% or more.
- continuous annealing and overaging treatment were performed under the conditions shown in Table 2. Thereafter, temper rolling of 0.1% was performed to obtain a steel sheet.
- Test specimens were collected from the steel sheet obtained as described above, and the steel structure was observed, a tensile test, a Vickers hardness test, a bending test, and a fatigue test were performed. These results are shown in Table 3.
- Observation of the steel structure was carried out by mechanically polishing and nital etching a cross section parallel to the rolling direction.
- Four visual fields were observed with a scanning electron microscope (SEM).
- SEM scanning electron microscope
- the area ratio of each tissue was determined by image analysis of a 2000 times SEM image.
- the area ratio was determined by averaging the area ratios determined for each of the four visual fields.
- martensite, bainite, and retained austenite are shown as a grayish structure in SEM.
- ferrite is a region that exhibits a black contrast in SEM.
- the area ratio of the retained austenite is determined by measuring the sheet surface by a mechanical analysis and chemical polishing to a quarter of the sheet thickness, and then obtaining a volume ratio by an X-ray diffraction method. I asked by considering it. In this measurement, it was calculated from the integrated intensity ratio of the (200) ⁇ , (211) ⁇ , (220) ⁇ , (200) ⁇ , (220) ⁇ , and (311) ⁇ diffraction plane peaks measured by Mo-K ⁇ ray. did.
- the total area ratio of martensite and bainite was determined as the balance of the total area ratio of ferrite and residual austenite when there was no residual structure (eg, pearlite, sulfide, nitride, oxide, etc.). If there is a residual structure, the total area ratio of martensite and bainite was calculated using the total of ferrite, retained austenite, and the residual structure.
- the tensile test was performed by cutting out a JIS No. 5 tensile test piece so that the direction perpendicular to the rolling direction on the steel sheet surface was the longitudinal direction at the position of a quarter of the width of the steel sheet, and the tensile test (JIS Z2241) was performed. Yield strength (YS), tensile strength (TS) and elongation (El) were determined by a tensile test.
- the Vickers hardness test was carried out using a micro hardness tester (HM-200, manufactured by Mitutoyo) at 10 locations at a position of 15 ⁇ m from the surface of the steel sheet under an indenter load of 10 g, and the average value was determined.
- HM-200 micro hardness tester manufactured by Mitutoyo
- the bending test cuts out a strip-shaped test piece of 100 mm in the direction perpendicular to the rolling direction and 35 mm in the rolling direction on the steel sheet surface at a quarter width position of the steel sheet. Performed using. The radius of curvature of the inner angle of the jig tip is changed to find the minimum inner angle of the jig tip where no crack is observed on the surface of the test piece, and the obtained radius (R) is divided by the thickness (t) to limit bending. The radius (R / t) was calculated. The smaller this value, the better the bendability. Cracks were determined using a stereoscopic microscope at a maximum magnification of 20 times, and the length of the cracks was measured. Since it is difficult to distinguish a minute crack smaller than 0.1 mm from surface irregularities by a stereoscopic microscope, a crack larger than 0.1 mm was determined to be a crack.
- Fatigue properties were evaluated by a pulsating tensile fatigue test.
- a test piece 10 having the shape shown in FIG. 1 was cut out with the direction perpendicular to the rolling direction as a longitudinal direction on the steel sheet surface, and subjected to a maximum of 10 million repetitions at a stress ratio of 0.1 and a frequency of 20 Hz.
- the left-right direction with respect to the paper surface corresponds to the rolling direction of the steel sheet, and R80 means that the radius of curvature is 80 mm.
- the tester used was Model: Servop @ lab manufactured by Shimadzu Corporation.
- the maximum applied stress at which no fracture occurred after 10 million cycles was defined as the fatigue strength.
- the endurance ratio was calculated as a value obtained by dividing the fatigue strength by the tensile strength of the material, and was used as an index of the fatigue characteristics.
- the steel sheet of the present invention has a tensile strength of 1320 MPa or more, excellent bendability of R / t of 3.0 or less, and excellent fatigue properties of 0.50 or more in durability ratio.
- the steel sheet of the comparative example does not satisfy at least one of those conditions.
- the present invention it is possible to provide a steel having a tensile strength of 1320 MPa or more excellent in bendability and fatigue properties. By improving such properties, it becomes possible to apply a high-strength steel sheet having a TS of 1320 MPa or more, which has been difficult to perform cold working by bending or the like, to an automobile part, thereby contributing to an improvement in part strength and a reduction in body weight.
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
Description
Hv≧0.294×σ ・・・(1)
ここで、Hvは表面から板厚方向に15μmの位置におけるビッカース硬さであり、σは引張強さ(MPa)を示す。
Cは、焼入れ性を向上させて、板厚1/4位置におけるマルテンサイトもしくはベイナイトの合計面積率が95%以上である鋼組織を得るために必要である。また、Cは、マルテンサイトもしくはベイナイトの強度を上昇させ、TS≧1320MPaを確保する観点から必要である。Cの含有量が0.13%未満では所定の強度を得ることができなくなる。そこで、C含有量は0.13%以上とする。TS≧1470MPaを得る観点からはC含有量は0.15%以上とすることが好ましい。C含有量はより好ましくは0.17%以上である。C含有量が0.40%以上になると良好な溶接性や耐遅れ破壊特性を得ることが難しくなる。そこで、C含有量は0.40%未満とする。C含有量は好ましくは0.35%以下、より好ましくは0.32%以下である。
Siは固溶強化による強化元素として、また、200℃以上の温度域で焼き戻す場合のフィルム状の炭化物の生成を抑制して曲げ性を改善する観点から含有する。上記効果を得る観点からSi含有量を0.01%以上とする。Si含有量は好ましくは0.10%以上、より好ましくは0.20%以上である。一方、Siの含有量が多くなりすぎると、その偏析量が多くなり曲げ性が劣化する。また、Si含有量が多くなりすぎると、熱延、冷延での圧延荷重の著しい増加を招く。そこで、Si含有量は1.0%以下である。Si含有量は好ましくは0.8%以下、より好ましくは0.6%以下である。
Mnは焼入れ性の増加を通じてマルテンサイトおよびベイナイトの合計面積率を増加させる効果や固溶強化により強度向上に寄与する。また、鋼中のSをMnSとして固定し、熱間脆性を軽減するためにMnを含有する。Mn含有量の下限は特に規定しないが、工業的に安定して所定のマルテンサイトおよびベイナイトの合計面積率を確保するためにはMnを0.2%以上含有することが好ましい。Mn含有量はより好ましくは0.5%以上、さらに好ましくは0.7%以上である。一方、Mn含有量は溶接の安定性の観点から1.7%以下とする。Mn含有量は好ましくは1.6%以下、より好ましくは1.5%以下である。
Pは鋼を強化する元素であるが、その含有量が多いとスポット溶接性が著しく劣化する。したがって、P含有量は0.030%以下とする。スポット溶接性劣化を十分に抑える観点から、P含有量は0.010%以下とすることが好ましい。P含有量の下限は規定しないが、現在工業的に実施可能な下限は0.002%程度であり、P含有量は実質的にそれ以上となることが多い。
SはMnS等の形成を通じて曲げ性や疲労特性に大きな影響を及ぼす。このため、S含有量を、低減することが望ましい。介在物による弊害を軽減するためにS含有量は少なくとも0.010%以下とする必要がある。S含有量の下限は規定しないが、現在工業的に実施可能な下限は0.0002%程度であり、S含有量は実質的にそれ以上となることが多い。
Alは十分な脱酸を行い、鋼中介在物を低減するために含有する。Al含有量の下限は特に規定しないが、安定して脱酸を行うためにはAl含有量を0.01%以上とすることが好ましい。一方、Al含有量が0.20%超となると、巻取り時に生成したセメンタイトが焼鈍過程で固溶しにくくなり、曲げ性が劣化する恐れがある。したがって、Alの含有量は0.20%以下とする。
Nは鋼中でTiN、(Nb,Ti)(C,N)、AlN等の窒化物、炭窒化物系の介在物を形成する元素であり、これらの生成を通じて曲げ性や疲労特性を劣化させる。したがって、N含有量は少なくとも0.010%以下とする必要がある。N含有量の下限は規定しないが、現在工業的に実施可能な下限は0.0006%程度であり、N含有量は実質的にそれ以上となることが多い。
Nbはマルテンサイトやベイナイトの内部構造の微細化を通じて高強度化に寄与する。この効果を得る観点からNb含有量は0.001%以上とする。好ましくは0.005%以上、より好ましくは0.008%以上である。しかし、Nbの含有量が過剰になるとNbC等の介在物が多量に生成し曲げ性が劣化する。このような悪影響を軽減するために、Nbの含有量を0.10%以下とする。Nb含有量は好ましくは0.08%以下、より好ましくは0.06%以下である。
Tiはマルテンサイトやベイナイトの内部構造の微細化を通じて高強度化に寄与する。この効果を得る観点からTi含有量を0.001%以上とする。好ましくは0.005%以上、より好ましくは0.008%以上である。しかし、Ti含有量が過剰になるとTiNやTiC等の介在物が多量に生成し曲げ性を劣化させる。このような悪影響を軽減するために、Ti含有量は0.10%以下とする。Ti含有量は好ましくは0.06%以下、より好ましくは0.03%以下である。
Bは鋼の焼入れ性を向上させる元素であり、少ないMn含有量でも所定の面積率のマルテンサイトやベイナイトを生成させる利点を有する。このようなBの効果を得るには、B含有量は0.0002%以上とする。好ましくは0.0005%以上、より好ましくは0.0010%以上である。一方、Bを0.0050%超で含有すると、その効果が飽和するだけでなく、焼鈍時のセメンタイトの固溶速度を遅延させ、未固溶のセメンタイトを残存させることで曲げ性が劣化する。したがって、B含有量は0.0050%以下とする。B含有量は好ましくは0.0040%以下、より好ましくは0.0030%以下である。
Cuは自動車の使用環境での耐食性を向上させる。Cuはスクラップを原料として活用するときに混入する元素であり、Cuの混入を許容することでリサイクル資材を原料資材として活用でき、製造コストを削減することができる。Cu含有量は上記の観点から0.005%以上含有する。Cu含有量は好ましくは0.010%以上、より好ましくは0.050%以上である。しかし、その含有量が多くなりすぎると表面欠陥の原因となるので、Cu含有量は0.50%以下とする。Cu含有量は好ましくは0.40%以下、より好ましくは0.30%以下である。
Niも耐食性を向上させる作用のある元素である。また、NiはCuを含有させる場合に生じやすい表面欠陥を低減する作用がある。上記の効果を得る観点からは、Ni含有量を0.005%以上とする。Ni含有量は好ましくは0.008%以上、より好ましくは0.010%以上である。しかし、Niの含有量が多くなりすぎると加熱炉内でのスケール生成が不均一になり表面欠陥の原因になるとともに、著しいコスト増となる。したがって、Ni含有量は0.50%以下とする。Ni含有量は好ましくは0.20%以下、より好ましくは0.15%以下である。
Crは鋼の焼入れ性を向上させる効果を得るために添加することが出来る。その効果を得るにはCr含有量を0.01%以上とする。好ましくは0.03%以上、より好ましくは0.05%以上である。Cr含有量が1.0%を超えると焼鈍時のセメンタイトの固溶速度を遅延させ、未固溶のセメンタイトを残存させることで曲げ性を劣化させる。また、耐孔食性も劣化させる。さらに化成処理性も劣化させる。したがって、Cr含有量は1.0%以下とする。
Moは、鋼の焼入れ性を向上させる効果、およびマルテンサイトを微細化することによる高強度化の効果を得る目的で添加することが出来る。これらの効果を得るにはMo含有量を0.005%以上とする。Mo含有量は好ましくは0.010%以上、より好ましくは0.040%以上である。しかしながら、Moを0.3%超で含有すると化成処理性が劣化する。したがって、Mo含有量を0.3%以下とする。Mo含有量は好ましくは0.2%以下、より好ましくは0.1%以下である。
Vは鋼の焼入れ性を向上させる効果、水素トラップサイトとなるVを含む微細な炭化物を生成させる効果、およびマルテンサイトを微細化することによる耐遅れ破壊特性の改善効果を得る目的で添加することが出来る。その効果を得るにはV含有量を0.003%以上とする。好ましくは0.005%以上、より好ましくは0.010%以上である。しかしながら、Vを0.45%超で含有すると鋳造性が著しく劣化する。したがって、V含有量は0.45%以下とする。V含有量は好ましくは0.30%以下、より好ましくは0.20%以下である。
CaはSをCaSとして固定し、曲げ性を改善する。この効果を得るためにはCa含有量を0.0002%以上とする。好ましくは0.0003%以上、より好ましくは0.0004%以上である。ただし、Caを多量に添加すると表面品質や曲げ性を劣化させるので、Ca含有量は0.0040%以下とする。Ca含有量は好ましくは0.0036%以下、より好ましくは0.0032%以下である。
Sbは鋼板表層域の酸化や窒化を抑制し、それによるCやBの表層域における含有量の低減を抑制する。CやBの低減が抑制されることで表層域のフェライト生成を抑制し、高強度化と疲労特性の改善に寄与する。この効果を得る観点から、Sb含有量は0.001%以上とする。Sb含有量は好ましくは0.002%以上、より好ましくは0.005%以上である。ただし、Sb含有量が0.1%を超えると鋳造性が劣化し、また、旧γ粒界にSbが偏析して曲げ性を劣化させる。このため、Sb含有量は0.1%以下とする。Sb含有量は好ましくは0.04%以下である。
Snは鋼板表層域の酸化や窒化を抑制し、それによるCやBの表層域における含有量の低減を抑制する。CやBの低減が抑制されることで表層域のフェライト生成を抑制し、高強度化と疲労特性の改善に寄与する。この効果を得る観点からSn含有量を0.002%以上とする。Sn含有量は好ましくは0.005%以上である。ただし、Sn含有量が0.1%を超えると鋳造性が劣化し、また、旧オーステナイト粒界にSnが偏析して曲げ性が劣化する。このため、Sn含有量は0.1%以下とする。Sn含有量は好ましくは0.04%以下である。
TS≧1320MPaの高い強度を達成するために、鋼組織は、板厚1/4位置におけるマルテンサイトおよびベイナイトの合計面積率を95%以上とする。合計面積率は好ましくは97%以上であり、より好ましくは98%以上である。なお、合計面積率が100%以外の場合に含まれる残部は残留オーステナイト等である。残留オーステナイトは焼鈍工程の冷却過程で残存するもので面積率5%まで許容できる。以上の組織以外は、微量のフェライト、パーライト、硫化物、窒化物、酸化物等であり、これらは面積率で5%以下である。なお、残部を含まず、マルテンサイトおよびベイナイトの合計面積率が100%でもよい。また、上記面積率は実施例に記載の方法で測定する。
曲げ加工時に生じる1mm以下の微細な亀裂を抑制するため、鋼板の表層域に面積率で10%以上40%以下のフェライトを含有させる。この効果を得るためにはフェライトの面積率は10%以上必要である。フェライトの面積率は好ましくは13%以上、より好ましくは16%以上である。また、面積率40%を超えてフェライトを含有すると疲労特性が劣化する。そこで、上記フェライトの面積率は40%以下とする。フェライトの面積率は好ましくは35%以下、より好ましくは30%以下である。また、後述する(1)式で表される構成から明らかな通り、10μmまでの領域のみを軟質とすることで、曲げ性と疲労特性の両立が図られる。したがって、表層域のフェライトの面積率は10%以上40%以下とする。このように鋼板の表層域にだけ微量のフェライトを形成させるためには、後述する連続焼鈍における露点の制御と焼鈍温度の制御が重要となる。また、上記面積率は実施例に記載の方法で測定する。
Hv≧0.294×σ ・・・(1)
ここで、Hvは鋼板の表面から板厚方向に15μm位置におけるビッカース硬さであり、σは引張強さ(MPa)を示す。上記ビッカース硬さと引張強さは実施例に記載の方法で測定する。
Claims (3)
- 質量%で、
C:0.13%以上0.40%未満、
Si:0.01%以上1.0%以下、
Mn:1.7%以下(0%は含まない)、
P:0.030%以下、
S:0.010%以下、
Al:0.20%以下(0%は含まない)、
N:0.010%以下を含有し、残部はFeおよび不可避的不純物からなる成分組成と、
板厚1/4位置におけるマルテンサイトおよびベイナイトの合計面積率が95%以上100%以下であり、前記合計面積率が100%以外の場合の残部が残留オーステナイトを含み、表面から板厚方向に10μmまでの領域におけるフェライトの面積率が10%以上40%以下である、鋼組織と、を有し、
引張強さが1320MPa以上であり、
表面から板厚方向に15μmの位置におけるビッカース硬さが下記(1)式を満たす高強度鋼板。
Hv≧0.294×σ ・・・(1)
ここで、Hvは表面から板厚方向に15μmの位置におけるビッカース硬さであり、σは引張強さ(MPa)を示す。 - 前記成分組成は、質量%で、さらに
Mo:0.005%以上0.3%以下、
Cr:0.01%以上1.0%以下、
Nb:0.001%以上0.10%以下、
Ti:0.001%以上0.10%以下、
B:0.0002%以上0.0050%以下、
Sb:0.001%以上0.1%以下、
Ca:0.0002%以上0.0040%以下、
V:0.003%以上0.45%以下、
Cu:0.005%以上0.50%以下、
Ni:0.005%以上0.50%以下およびSn:0.002%以上0.1%以下の少なくとも1種を含有する請求項1に記載の高強度鋼板。 - 請求項1または2に記載の成分組成を有する冷延鋼板を、750℃以上の温度域の露点が-35℃以下の条件で、840℃以上の焼鈍温度で180秒以上保持し、740℃以上の冷却開始温度で、該冷却開始温度から150℃までの温度域を100℃/s以上の平均冷却速度で冷却する連続焼鈍工程と、
前記連続焼鈍工程後、必要に応じて再加熱を行い、150~260℃の温度域で30~1500秒保持する過時効処理工程と、を有する高強度鋼板の製造方法。
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2019553996A JP6683297B1 (ja) | 2018-08-22 | 2019-06-10 | 高強度鋼板及びその製造方法 |
US17/269,312 US11898230B2 (en) | 2018-08-22 | 2019-06-10 | High-strength steel sheet and method for manufacturing same |
MX2021001962A MX2021001962A (es) | 2018-08-22 | 2019-06-10 | Lamina de acero de alta resistencia y metodo para la fabricacion de la misma. |
EP19852813.5A EP3825433B1 (en) | 2018-08-22 | 2019-06-10 | High-strength steel sheet and method for manufacturing same |
KR1020217005058A KR102512610B1 (ko) | 2018-08-22 | 2019-06-10 | 고강도 강판 및 그 제조 방법 |
CN201980054800.2A CN112585291B (zh) | 2018-08-22 | 2019-06-10 | 高强度钢板及其制造方法 |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2018-155231 | 2018-08-22 | ||
JP2018155231 | 2018-08-22 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2020039696A1 true WO2020039696A1 (ja) | 2020-02-27 |
Family
ID=69592843
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/JP2019/022848 WO2020039696A1 (ja) | 2018-08-22 | 2019-06-10 | 高強度鋼板及びその製造方法 |
Country Status (7)
Country | Link |
---|---|
US (1) | US11898230B2 (ja) |
EP (1) | EP3825433B1 (ja) |
JP (1) | JP6683297B1 (ja) |
KR (1) | KR102512610B1 (ja) |
CN (1) | CN112585291B (ja) |
MX (1) | MX2021001962A (ja) |
WO (1) | WO2020039696A1 (ja) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN112593158A (zh) * | 2020-12-11 | 2021-04-02 | 湖南华菱涟源钢铁有限公司 | 690MPa耐低温超高强耐候钢板及制备方法 |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2020039697A1 (ja) * | 2018-08-22 | 2020-02-27 | Jfeスチール株式会社 | 高強度鋼板及びその製造方法 |
CN113122783A (zh) * | 2021-04-23 | 2021-07-16 | 唐山全丰薄板有限公司 | 一种1300MPa级汽车用超高强度冷轧钢板及其制造方法 |
KR20240090672A (ko) * | 2021-10-29 | 2024-06-21 | 아르셀러미탈 | 냉연 열처리 강판 및 그 제조 방법 |
Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2010215958A (ja) * | 2009-03-16 | 2010-09-30 | Jfe Steel Corp | 曲げ加工性および耐遅れ破壊特性に優れる高強度冷延鋼板およびその製造方法 |
JP4977879B2 (ja) | 2010-02-26 | 2012-07-18 | Jfeスチール株式会社 | 曲げ性に優れた超高強度冷延鋼板 |
JP5466576B2 (ja) | 2010-05-24 | 2014-04-09 | 株式会社神戸製鋼所 | 曲げ加工性に優れた高強度冷延鋼板 |
WO2016152163A1 (ja) * | 2015-03-25 | 2016-09-29 | Jfeスチール株式会社 | 冷延鋼板およびその製造方法 |
WO2016199922A1 (ja) * | 2015-06-11 | 2016-12-15 | 新日鐵住金株式会社 | 合金化溶融亜鉛めっき鋼板およびその製造方法 |
WO2018062381A1 (ja) * | 2016-09-28 | 2018-04-05 | Jfeスチール株式会社 | 鋼板およびその製造方法 |
KR20180074284A (ko) * | 2016-12-23 | 2018-07-03 | 주식회사 포스코 | 항복비가 낮고 균일연신율이 우수한 템퍼드 마르텐사이트 강 및 그 제조방법 |
Family Cites Families (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP5614035B2 (ja) * | 2009-12-25 | 2014-10-29 | Jfeスチール株式会社 | 高強度冷延鋼板の製造方法 |
JP4947176B2 (ja) * | 2010-03-24 | 2012-06-06 | Jfeスチール株式会社 | 超高強度冷延鋼板の製造方法 |
JP6291289B2 (ja) * | 2013-03-06 | 2018-03-14 | 株式会社神戸製鋼所 | 鋼板形状および形状凍結性に優れた高強度冷延鋼板およびその製造方法 |
CN106574340B (zh) * | 2014-08-07 | 2018-04-10 | 杰富意钢铁株式会社 | 高强度钢板及其制造方法、以及高强度镀锌钢板的制造方法 |
DE102014017274A1 (de) * | 2014-11-18 | 2016-05-19 | Salzgitter Flachstahl Gmbh | Höchstfester lufthärtender Mehrphasenstahl mit hervorragenden Verarbeitungseigenschaften und Verfahren zur Herstellung eines Bandes aus diesem Stahl |
CN107250409B (zh) * | 2015-02-17 | 2019-07-05 | 杰富意钢铁株式会社 | 高强度冷轧薄钢板及其制造方法 |
CN107406939B (zh) * | 2015-03-13 | 2018-12-18 | 杰富意钢铁株式会社 | 高强度冷轧钢板及其制造方法 |
KR102162785B1 (ko) * | 2016-03-31 | 2020-10-07 | 제이에프이 스틸 가부시키가이샤 | 박 강판 및 도금 강판, 그리고, 열연 강판의 제조 방법, 냉연 풀 하드 강판의 제조 방법, 박 강판의 제조 방법 및 도금 강판의 제조 방법 |
US10920294B2 (en) | 2016-03-31 | 2021-02-16 | Jfe Steel Corporation | Steel sheet, coated steel sheet, method for producing hot-rolled steel sheet, method for producing full-hard cold-rolled steel sheet, method for producing heat-treated sheet, method for producing steel sheet, and method for producing coated steel sheet |
KR101967959B1 (ko) | 2016-12-19 | 2019-04-10 | 주식회사 포스코 | 굽힘 가공성이 우수한 초고강도 강판 및 이의 제조방법 |
WO2020039697A1 (ja) * | 2018-08-22 | 2020-02-27 | Jfeスチール株式会社 | 高強度鋼板及びその製造方法 |
-
2019
- 2019-06-10 EP EP19852813.5A patent/EP3825433B1/en active Active
- 2019-06-10 MX MX2021001962A patent/MX2021001962A/es unknown
- 2019-06-10 CN CN201980054800.2A patent/CN112585291B/zh active Active
- 2019-06-10 WO PCT/JP2019/022848 patent/WO2020039696A1/ja active Application Filing
- 2019-06-10 KR KR1020217005058A patent/KR102512610B1/ko active IP Right Grant
- 2019-06-10 JP JP2019553996A patent/JP6683297B1/ja active Active
- 2019-06-10 US US17/269,312 patent/US11898230B2/en active Active
Patent Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2010215958A (ja) * | 2009-03-16 | 2010-09-30 | Jfe Steel Corp | 曲げ加工性および耐遅れ破壊特性に優れる高強度冷延鋼板およびその製造方法 |
JP4977879B2 (ja) | 2010-02-26 | 2012-07-18 | Jfeスチール株式会社 | 曲げ性に優れた超高強度冷延鋼板 |
JP5466576B2 (ja) | 2010-05-24 | 2014-04-09 | 株式会社神戸製鋼所 | 曲げ加工性に優れた高強度冷延鋼板 |
WO2016152163A1 (ja) * | 2015-03-25 | 2016-09-29 | Jfeスチール株式会社 | 冷延鋼板およびその製造方法 |
WO2016199922A1 (ja) * | 2015-06-11 | 2016-12-15 | 新日鐵住金株式会社 | 合金化溶融亜鉛めっき鋼板およびその製造方法 |
WO2018062381A1 (ja) * | 2016-09-28 | 2018-04-05 | Jfeスチール株式会社 | 鋼板およびその製造方法 |
KR20180074284A (ko) * | 2016-12-23 | 2018-07-03 | 주식회사 포스코 | 항복비가 낮고 균일연신율이 우수한 템퍼드 마르텐사이트 강 및 그 제조방법 |
Non-Patent Citations (1)
Title |
---|
See also references of EP3825433A4 |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN112593158A (zh) * | 2020-12-11 | 2021-04-02 | 湖南华菱涟源钢铁有限公司 | 690MPa耐低温超高强耐候钢板及制备方法 |
CN112593158B (zh) * | 2020-12-11 | 2021-11-30 | 湖南华菱涟源钢铁有限公司 | 690MPa耐低温超高强耐候钢板及制备方法 |
Also Published As
Publication number | Publication date |
---|---|
EP3825433A4 (en) | 2021-05-26 |
KR20210034640A (ko) | 2021-03-30 |
MX2021001962A (es) | 2021-04-28 |
EP3825433B1 (en) | 2023-02-15 |
US11898230B2 (en) | 2024-02-13 |
EP3825433A1 (en) | 2021-05-26 |
CN112585291B (zh) | 2022-05-27 |
CN112585291A (zh) | 2021-03-30 |
KR102512610B1 (ko) | 2023-03-22 |
US20210180163A1 (en) | 2021-06-17 |
JPWO2020039696A1 (ja) | 2020-08-27 |
JP6683297B1 (ja) | 2020-04-15 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
KR102119333B1 (ko) | 고강도 강판 및 그 제조 방법 | |
JP4977879B2 (ja) | 曲げ性に優れた超高強度冷延鋼板 | |
JP4947176B2 (ja) | 超高強度冷延鋼板の製造方法 | |
JP6017341B2 (ja) | 曲げ性に優れた高強度冷延鋼板 | |
KR102507715B1 (ko) | 고강도 강판 및 그의 제조 방법 | |
JP6683297B1 (ja) | 高強度鋼板及びその製造方法 | |
JP2017048412A (ja) | 溶融亜鉛めっき鋼板、合金化溶融亜鉛めっき鋼板、およびそれらの製造方法 | |
JP2007162078A (ja) | 高強度鋼板及びその製造方法 | |
WO2016148037A1 (ja) | 冷間加工性と浸炭熱処理後の靱性に優れる浸炭用鋼板 | |
WO2013180180A1 (ja) | 高強度冷延鋼板およびその製造方法 | |
JP5543814B2 (ja) | 熱処理用鋼板及び鋼部材の製造方法 | |
JP6065121B2 (ja) | 高炭素熱延鋼板およびその製造方法 | |
JP6065120B2 (ja) | 高炭素熱延鋼板およびその製造方法 | |
JP5302840B2 (ja) | 伸びと伸びフランジ性のバランスに優れた高強度冷延鋼板 | |
JP5811725B2 (ja) | 耐面歪性、焼付け硬化性および伸びフランジ性に優れた高張力冷延鋼板およびその製造方法 | |
JP2009215572A (ja) | 降伏応力と伸びと伸びフランジ性に優れた高強度冷延鋼板 | |
JP4696853B2 (ja) | 加工性に優れた高炭素冷延鋼板の製造方法および高炭素冷延鋼板 | |
CN113692456A (zh) | 剪切加工性优异的超高强度钢板及其制造方法 | |
JP6645637B1 (ja) | 高強度鋼板及びその製造方法 | |
JP4471486B2 (ja) | 深絞り性に優れた中・高炭素鋼板 | |
KR20230134146A (ko) | 강판, 부재 및 그들의 제조 방법 | |
WO2015194572A1 (ja) | 衝突特性に優れる超高強度鋼板 | |
JP5076691B2 (ja) | 高強度冷延鋼板の製造方法 | |
JPH11270531A (ja) | 遅れ破壊特性の優れた高強度ボルトおよびその製造方法 | |
JP6575727B1 (ja) | 高延性高強度鋼板及びその製造方法 |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
ENP | Entry into the national phase |
Ref document number: 2019553996 Country of ref document: JP Kind code of ref document: A |
|
121 | Ep: the epo has been informed by wipo that ep was designated in this application |
Ref document number: 19852813 Country of ref document: EP Kind code of ref document: A1 |
|
ENP | Entry into the national phase |
Ref document number: 2019852813 Country of ref document: EP Effective date: 20210217 Ref document number: 20217005058 Country of ref document: KR Kind code of ref document: A |
|
WWE | Wipo information: entry into national phase |
Ref document number: 2101000970 Country of ref document: TH |
|
NENP | Non-entry into the national phase |
Ref country code: DE |