WO2022107580A1 - Plated steel sheet for spot welding use, joining member, automotive member, and method for manufacturing joining member - Google Patents

Plated steel sheet for spot welding use, joining member, automotive member, and method for manufacturing joining member Download PDF

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Publication number
WO2022107580A1
WO2022107580A1 PCT/JP2021/040169 JP2021040169W WO2022107580A1 WO 2022107580 A1 WO2022107580 A1 WO 2022107580A1 JP 2021040169 W JP2021040169 W JP 2021040169W WO 2022107580 A1 WO2022107580 A1 WO 2022107580A1
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steel sheet
spot welding
plating layer
plated steel
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PCT/JP2021/040169
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French (fr)
Japanese (ja)
Inventor
千智 吉永
登代充 中村
真二 児玉
卓哉 光延
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日本製鉄株式会社
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Publication of WO2022107580A1 publication Critical patent/WO2022107580A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/10—Spot welding; Stitch welding
    • B23K11/11—Spot welding
    • 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
    • C22C18/00—Alloys based on zinc
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • 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
    • C22C38/60—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
    • C23C2/04—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
    • 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

Definitions

  • the present disclosure relates to a plated steel sheet for spot welding, a joining member, an automobile member, and a method for manufacturing the joining member.
  • LME cracking When multiple metal plates are stacked and spot welded, cracking (LME cracking) may occur due to liquid metal embrittlement (LME: Liquid Metal Embrittlement).
  • Liquid metal embrittlement is the embrittlement of a solid metal that originally exhibits ductility when a tensile stress is applied to the solid metal in contact with the liquid metal, and is typically steel (solid metal) and zinc (liquid metal). ).
  • LME cracking is likely to occur when spot welding is performed using a high-strength steel plate having a high alloy concentration and a tensile strength of 780 MPa or more.
  • Patent Document 1 As a method for manufacturing an alloyed hot-dip galvanized steel sheet that suppresses the occurrence of LME cracks due to spot welding, A method for manufacturing alloyed hot-dip galvanized steel sheets including the following continuous steps. A.
  • a method including an alloying heat treatment for forming an alloyed hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet manufactured by this method are disclosed.
  • the chemical composition of the base metal is mass%, C: 0.17 to 0.40%, Si: 0.10 to 2.50%, Mn: 1.00 to 10.00%, P: 0.001 to 0.03%, S: 0.0001 to 0.02%, Al: 0.001 to 2.50%, N: 0.0001 to 0.010%, O: 0.0001 to 0.010%, Ti: 0 to 0.10%, Nb: 0 to 0.10%, V: 0 to 0.10%, B: 0 to 0.010%, Cr: 0 to 2.00%, Ni: 0 to 2.00%, Cu: 0 to 2.00%, Mo: 0 to 2.00%, Ca: 0 to 0.50%, Mg: 0 to 0.50%, REM: 0 to 0.50%, Remaining: Fe and impurities, It has an internal oxide layer in which at least a part of the crystal grain boundaries is coated with an oxide from the surface of the base metal to a depth of 5.0 ⁇ m or more, and A steel sheet having a grain boundary coverage of 60% or
  • Patent Document 1 Japanese Patent Application Laid-Open No. 2020-52141
  • Patent Document 2 International Publication No. 2019/116531
  • a cold-rolled steel sheet may be used as a mating material or internal oxidation may occur.
  • spot welding is performed using a plate without a layer, zinc is present on the mating surface with the mating material, so LME cracking is likely to occur.
  • the occurrence of LME cracking is suppressed when a plated steel sheet having high tensile strength is spot welded, and even if a cold-rolled steel sheet is used as the mating material or a plate without an internal oxide layer is used, the LME cracking in the mating material is suppressed. It is an object of the present invention to provide a plated steel sheet for spot welding, a joining member using the same, a member for an automobile, and a method for manufacturing the joining member.
  • the gist of this disclosure to achieve the above objectives is as follows. ⁇ 1> By mass%, C: 0.05 to 0.70%, Si: 3.50% or less, Mn: 8.00% or less, P: 0.020% or less, S: 0.050% or less, Al: 3.000% or less, and N: 0.010% or less, including Optionally, Ti: 0.300% or less, Nb: 0.300% or less, V: 0.30% or less, Cr: 5.0% or less, Mo: 2.00% or less, Cu: 2.00% or less, Ni: 10.0% or less, B: 0.020% or less, Ca: 0.003% or less, REM: 0.05% or less, Includes one or more selected from the group consisting of Mg: 0.05% or less and Zr: 0.05% or less.
  • the balance has a steel composition consisting of Fe and impurities.
  • a plating layer of 2.0% by mass or more, Including The tensile strength is 780 MPa or more. Plated steel sheet for spot welding.
  • ⁇ 2> The plated steel sheet for spot welding according to ⁇ 1>, wherein a plating layer containing Ni and a plating layer containing Zn are formed as the plating layer from the base steel sheet side.
  • ⁇ 3> The plated steel sheet for spot welding according to ⁇ 1>, wherein a plating layer containing Zn and a plating layer containing Ni are formed as the plating layer from the base steel sheet side.
  • ⁇ 4> The spot welding according to ⁇ 1>, wherein a plating layer containing Ni, a plating layer containing Zn, and a plating layer containing Ni are formed as the plating layer from the base steel plate side. Plated steel plate.
  • ⁇ 5> The plated steel sheet for spot welding according to any one of ⁇ 1> to ⁇ 4>, wherein at least one of the plating layers is a plating layer containing Zn and Ni.
  • ⁇ 6> The plated steel sheet for spot welding according to any one of ⁇ 1> to ⁇ 5>, which is a non-alloyed plated steel sheet.
  • the steel composition is, in mass%, instead of a part of the Fe.
  • Ti 0.001% or more and 0.300% or less
  • Nb any one of ⁇ 1> to ⁇ 6> including one or more selected from the group consisting of 0.001% or more and 0.300% or less
  • V 0.001% or more and 0.30% or less.
  • the steel composition is, in mass%, instead of a part of the Fe.
  • the spot welding according to any one of ⁇ 1> to ⁇ 7> which comprises one or two types of Cr: 0.001% or more and 5.0% or less and Mo: 0.001% or more and 2.00% or less.
  • the steel composition is, in mass%, instead of a part of the Fe.
  • the spot welding according to any one of ⁇ 1> to ⁇ 8> which comprises one or two types of Cu: 0.001% or more and 2.00% or less and Ni: 0.001% or more and 10.0% or less.
  • the steel composition is, in mass%, instead of a part of the Fe.
  • B The plated steel sheet for spot welding according to any one of ⁇ 1> to ⁇ 9>, which contains 0.001% or more and 0.020% or less.
  • the steel composition is, in mass%, instead of a part of the Fe.
  • Ca 0.0005% or more and 0.003% or less
  • REM 0.001% or more and 0.05% or less
  • the plated steel sheet for spot welding described in one.
  • a method for manufacturing a joining member including.
  • the thickness of the internal oxide layer having the steel composition according to any one of ⁇ 1> to ⁇ 11> and having at least a part of the crystal grain boundary coated with the oxide is deep from the surface.
  • a plating layer containing Zn is formed on one side or both sides of a base steel sheet having a thickness of less than 5.0 ⁇ m, and two or more sheets including a spot welding plated steel sheet having a tensile strength of 780 MP or more are laminated.
  • the process of making a plate and The foil containing Ni and having a Ni content of 2.0% by mass or more in the plating layer and the entire foil in the region where the foil is arranged is the foil of the plated steel sheet for spot welding.
  • a method for manufacturing a joining member including.
  • the occurrence of LME cracks is suppressed when a plated steel sheet having high tensile strength is spot welded, and even if a cold-rolled steel sheet is used as the mating material or a plate having no internal oxide layer is used, the mating material has Provided are a plated steel sheet for spot welding in which the occurrence of LME cracks is suppressed, a joining member using the same, an automobile member, and a method for manufacturing the joining member.
  • the "%" indication of the content of each element means “mass%”.
  • the numerical range represented by using “-” means a range including the numerical values before and after “-” as the lower limit value and the upper limit value unless otherwise specified.
  • the numerical range when "greater than” or “less than” is added to the numerical values before and after “to” means a range in which these numerical values are not included as the lower limit value or the upper limit value.
  • the upper limit of the numerical range described in one step may be replaced with the upper limit value of the numerical range described in another step.
  • the lower limit may be replaced with the lower limit of the numerical range described in other steps.
  • the upper limit value or the lower limit value of a certain stepwise numerical range may be replaced with the value shown in the embodiment.
  • the term "process” is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.
  • Patent Document 1 discloses an alloyed hot-dip zinc-plated steel sheet that has been Ni-plated, Zn-plated, and then alloyed and heat-treated.
  • LME resistance during spot welding was disclosed. It was found that the characteristics are more influenced by the Ni concentration in the entire plating layer than the formation order of Ni plating and Zn plating and the alloying heat treatment. It is thought that by adding Ni to the galvanized layer, the melting point of the plating changes (the melting point rises due to the addition of Ni), which changes the ease with which zinc penetrates into the steel grain boundaries and suppresses the occurrence of LME cracks. Be done.
  • Ni plating 0, 3, or 10 g / m 2 and Zn plating 50 g / m 2 are applied and the plating layers are uniformly mixed
  • the Ni concentration is 0, 5.7, 16.7 mass.
  • Can be converted to% It can be seen that at these concentrations, the temperature at which all liquids are formed and the temperature at which the liquid phase is generated increase in the former as the Ni concentration increases, and in the latter, the Ni concentration increases particularly at around 16.7% by mass. ..
  • the effect of suppressing LME cracking can be obtained by changing the Ni concentration in the temperature characteristics of the plating.
  • Patent Document 2 discloses an alloyed hot-dip galvanized steel sheet having an internal oxide layer up to a depth of 5.0 ⁇ m or more from the surface of the base steel sheet, Ni-plated, Zn-plated, and further alloyed and heat-treated. Has been done. Since the Zn-plated steel sheet having an internal oxide layer is less likely to cause LME cracking during spot welding than the Zn-plated steel sheet having no internal oxide layer on the surface of the base steel sheet, the present inventors have 2.0. In the case of a Zn-plated steel sheet on which a Zn-based plated layer containing Ni by mass% or more is formed, it is considered advantageous to form an internal oxide layer on the surface layer of the base steel sheet.
  • a steel sheet having high tensile strength and prone to LME cracking during spot welding has an internal oxide layer of 5.0 ⁇ m or more in the surface layer portion of the base steel sheet.
  • a Zn-plated steel sheet containing Zn and Ni as at least a part of the plating layer and having a Ni content of 2.0% by mass or more in the entire plating layer is used, so that a Zn-plated steel sheet containing no Ni is used. It has been found that LME cracking is effectively suppressed during spot welding as compared with the case. Further, in this case, the internal oxide layer may obtain a higher effect of suppressing LME cracking.
  • the Ni content of the entire plating layer is less than 2.0% by mass regardless of the presence or absence of the internal oxide layer. In some cases, no effect of suppressing LME cracking was found. On the other hand, when the Ni content of the entire plating layer is 2.0% by mass or more, LME cracking is effective for the steel sheet and the mating material regardless of the presence or absence of the internal oxide layer on the surface of the base steel sheet. It was found that it was suppressed.
  • the internal oxide layer may be formed in a steel sheet manufacturing process, for example, in a hot rolling or annealing process.
  • the spot-welded plated steel sheet according to the present disclosure (may be simply referred to as “plated steel sheet” in the present disclosure) is in mass%.
  • a base steel sheet having a steel composition in which the balance is composed of Fe and impurities, and the thickness of the internal oxide layer in which at least a part of the grain boundaries is covered with an oxide is less than 5.0 ⁇ m from the surface.
  • the steel composition of the base steel sheet in the plated steel sheet for spot welding is C: 0.05 to 0.70%, Si: 3.50% or less, Mn: 8.00% or less, P: 0.020% or less, S: 0. It is 050% or less, Al: 3.000% or less, and N: 0.010% or less, and the balance is composed of Fe and impurities.
  • the plated steel sheet for spot welding has a mass% as an optional element instead of a part of Fe in the steel composition of the base steel sheet.
  • C 0.05 to 0.70%
  • C is an element that enhances the hardenability of steel and contributes to the improvement of strength. If the C content is less than 0.05%, high tensile strength cannot be obtained, so the lower limit is set to 0.05%.
  • the lower limit of the C content may be 0.10% or 0.15%.
  • joint strength the joint strength at the time of spot welding
  • the upper limit is set to 0.70%.
  • the upper limit of the C content may be 0.65% or 0.55%. In order to secure a good balance between strength and workability, the C content is preferably 0.15 to 0.55%.
  • Si 3.50% or less Si is an element that enhances the strength of steel by solid solution strengthening and structure strengthening.
  • the upper limit of the Si content may be 2.50% or 2.00%.
  • the lower limit of the Si content is not particularly limited and is more than 0%, but is preferably 0.10% or more from the viewpoint of increasing the tensile strength. From the viewpoint of ensuring a good balance between strength and workability, the Si content is more preferably 0.50 to 2.00%.
  • Mn 8.00% or less Mn is an element that enhances the strength of steel.
  • the lower limit of the Mn content is not particularly limited and is more than 0%, but is preferably 0.50% or more from the viewpoint of increasing the tensile strength. From the viewpoint of ensuring a good balance between strength and workability, the Mn content is preferably 1.00 to 4.80%. More preferably, it is 1.50 to 3.50%.
  • P 0.020% or less P is an impurity and is an element that causes embrittlement. If the P content exceeds 0.020%, it is difficult to obtain the required joint strength, so the upper limit is set to 0.020%.
  • S 0.050% or less
  • S is an impurity and an element that causes embrittlement, like P. Further, S is an element that forms coarse MnS in the steel, which lowers the workability of the steel and also lowers the joint strength. If the S content exceeds 0.050%, it is difficult to obtain the required joint strength, and the workability of the steel is lowered. Therefore, the upper limit is set to 0.050%.
  • Al 3.000% or less
  • Al is an element that has a deoxidizing action, and is an element that stabilizes ferrite and suppresses the precipitation of cementite.
  • Al is contained for deoxidation and control of steel structure, but Al is easily oxidized, and when the Al content exceeds 3.000%, inclusions increase, the workability decreases, and the joint strength also increases. Since it will decrease, the upper limit will be 3.000%. In terms of ensuring workability, the preferable upper limit is 1.200%.
  • the lower limit of the Al content is not particularly limited and is more than 0%, but the preferable lower limit of the Al content is 0.001% for deoxidation and control of the steel structure.
  • N 0.010% or less N is an element that enhances the strength of the base steel sheet, but is an element that forms coarse nitrides in the steel and deteriorates the formability of the steel. If the N content exceeds 0.010%, the formability of the steel is significantly deteriorated and the joint strength is significantly reduced. Therefore, the upper limit is set to 0.010%. The lower limit of the N content is more than 0%.
  • Fe and impurities The balance is Fe and impurities.
  • Impurities refer to components contained in raw materials such as ore and scrap, or components mixed in the manufacturing process, which are not intentionally contained in the base steel sheet.
  • the base steel sheet in the present disclosure may contain an element (arbitrary element) other than the above instead of a part of Fe.
  • the optional elements that can be contained in the base steel sheet in the present disclosure will be described below. The following optional elements may not be contained, that is, the content may be 0%, and if they are contained, the lower limit may be more than 0%.
  • the mass% is used.
  • Ti 0.300% or less, It may contain one or more selected from the group consisting of Nb: 0.300% or less and V: 0.30% or less.
  • Ti 0.300% or less
  • the lower limit of the Ti content is not particularly limited, but it is preferably 0.001% or more in order to obtain the content effect. More preferably, it is 0.01% or more. However, if Ti is contained in excess, the manufacturability is lowered and not only cracks occur during processing but also the joint strength is lowered. Therefore, when Ti is contained, the upper limit is 0.300%, preferably 0.200. % Or less.
  • Nb 0.300% or less
  • Nb is an element that forms fine carbonitrides and suppresses the coarsening of crystal grains.
  • the lower limit of the Nb content is not particularly limited, but it is preferably 0.001% or more in order to obtain the content effect. More preferably, it is 0.010% or more.
  • the upper limit is 0.300%, preferably 0.200% or less. be.
  • V 0.30% or less
  • V is an element that forms fine carbonitrides and suppresses the coarsening of crystal grains.
  • V is contained, it is preferably contained in an amount of 0.001% or more in order to obtain a content effect. More preferably, it is 0.03% or more.
  • the upper limit is preferably 0.30%, more preferably 0.25% or less. ..
  • the base steel sheet in the present disclosure has a mass% of Cr: 5.0% or less instead of a part of Fe.
  • Mo 1 or 2 types of 2.00% or less may be contained.
  • Cr and Mo are elements that contribute to the improvement of steel strength. When Cr or Mo is contained, it is preferably contained in an amount of 0.001% or more in order to obtain a content effect. More preferably, it is 0.05% or more.
  • the upper limit of the Cr content is 5.0%, preferably 3.0% or less
  • the upper limit of the Mo content is 2.00%, preferably 1.00%.
  • the base steel sheet in the present disclosure has Cu: 2.00% or less and Ni in mass% instead of a part of Fe in order to improve the strength of the steel. 1 or 2 types of 10.0% or less may be contained.
  • Cu and Ni are elements that contribute to the improvement of steel strength. When Cu or Ni is contained, it is preferable to contain 0.001% or more in total in order to obtain the content effect. More preferably, it is 0.10% or more. However, if the Cu content exceeds 2.00% or the Ni content exceeds 10.0%, not only may problems occur during pickling and hot working, but also the joint strength may decrease. Sometimes. Therefore, the upper limit of the Cu content is 2.00%, preferably 1.50% or less, and the upper limit of the Ni content is 10.0%, preferably 7.0% or less.
  • the base steel sheet in the present disclosure is divided into% by mass instead of a part of Fe.
  • Ca 0.003% or less, REM 0.05% or less, It may contain one or more selected from the group consisting of Mg: 0.05% or less and Zr: 0.05% or less.
  • Ca, REM (rare earth metal), Mg, and Zr are elements that contribute to the improvement of formability by refining oxides after deoxidation and sulfides existing in hot-rolled steel sheets.
  • the Ca content exceeds 0.003%, the REM content exceeds 0.05%, or the Mg or Zr content exceeds 0.05%, the workability of the steel deteriorates. do. Therefore, it is preferable that the upper limit of the Ca content is 0.003%, the upper limit of the REM content is 0.05%, and the upper limit of each content of Mg and Zr is 0.05%.
  • Ca is 0.0005% or more
  • REM is 0.001% or more
  • Mg is 0.001% or more in order to obtain the content effect.
  • Zr is preferably 0.001% or more.
  • REM is a general term for a total of 17 elements of Sc, Y, and lanthanoids, and the content of REM refers to the total content of one or more elements of REM. Further, REM is generally contained in mischmetal. Therefore, for example, REM may be contained in the form of misch metal so that the REM content is within the above range.
  • the base steel sheet in the present disclosure may contain B: 0.020% or less in mass% instead of a part of Fe.
  • B is an element that segregates at the grain boundaries to increase the grain boundary strength. When B is contained, it is preferably 0.0001% or more, more preferably 0.0008% or more, in order to obtain the content effect. On the other hand, if B is excessively contained, not only the toughness is impaired and the manufacturing becomes difficult, but also the strength of the joint is lowered. Therefore, the upper limit of the B content is 0.020%, preferably 0.010% or less.
  • the thickness of the internal oxide layer on the surface layer is less than 5.0 ⁇ m.
  • the internal oxide layer means a layer in which at least a part of the grain boundaries is covered with an oxide.
  • the thickness of the internal oxide layer of less than 5.0 ⁇ m includes the case where the thickness is 0 ⁇ m, that is, the internal oxide layer is not formed.
  • the presence or absence of the internal oxide layer on the surface layer of the base steel sheet and the measurement of the thickness can be performed by observing the cross section in the thickness direction by SEM observation. A specific observation method will be described in Examples.
  • the thickness of the base steel sheet in the present disclosure is not particularly limited and can be selected according to the application after spot welding.
  • the thickness of the base steel sheet is, for example, 1.0 to 3.5 mm, but is not limited to this range.
  • the plated steel sheet for spot welding according to the present disclosure has one or more plated layers formed on one side or both sides of the base steel sheet having the above steel composition, and Zn and Ni are used as at least a part of the plated layers. It is contained, and the Ni content in the entire plating layer is 2.0% by mass or more.
  • the plating layer in the plated steel sheet for spot welding according to the present disclosure contains Zn and Ni as at least a part of the plating layer, and the Ni content in the entire plating layer is 2.0% by mass or more.
  • the layer structure of is not particularly limited.
  • the plating layer is one layer, it is a Zn—Ni-containing plating layer containing Zn and Ni and having a Ni content of 2.0% by mass or more.
  • the Zn—Ni-containing plating layer may contain a metal element other than Zn and Ni.
  • the number of plating layers is two or more, at least one layer is a Zn-containing plating layer containing Zn, and at least one layer is a Ni-containing plating layer containing Ni, and the Ni content in the entire two or more plating layers. Is 2.0% by mass or more.
  • the Ni-containing plating layer may contain a metal element other than Ni, and may be, for example, a Zn—Ni-containing plating layer containing Ni and Zn. The same applies to the Zn-containing plating layer. Examples of the two or more plating layers include, but are not limited to, the following combinations.
  • the Zn content in the entire plating layer is not particularly limited, but from the viewpoint of exerting a high anticorrosion effect, the Zn content in the entire plating layer is preferably 30% by mass or more, preferably 50% by mass or more. More preferred.
  • the upper limit of the Zn content in the entire plating layer is 98% by mass.
  • the Ni content in the entire plating layer is preferably 5% by mass or more, more preferably 10% by mass or more, from the viewpoint of more effectively suppressing the occurrence of LME cracks during spot welding. ..
  • the Ni content in the entire plating layer is preferably 70% by mass or less, preferably 50% by mass or less. Is more preferable. It is preferable that 2.0% by mass ⁇ Ni content ⁇ Zn content in the entire plating layer.
  • the layer structure of the plated steel sheet for spot welding for example, the following layer structure can be mentioned from the base steel sheet side.
  • Base material steel plate / Zn-Ni-containing plating layer (2) Base material steel plate / Ni-containing plating layer / Zn-containing plating layer (3) Base material steel plate / Zn-containing plating layer / Ni-containing plating layer (4) Base material Steel plate / Ni-containing plating layer / Zn-containing plating layer / Ni-containing plating layer (5) Base steel plate / Ni-containing plating layer / Zn-Ni-containing plating layer
  • the plated steel plate for spot welding according to the present disclosure is limited to the above layer structure.
  • the effect of LME resistance during spot welding (suppressing the occurrence of LME cracking) (2), (4), and (5) are preferable from the viewpoint that the effect) may be enhanced, and when the steel plate (counterpart material) to be combined at the time of spot welding is a cold-rolled steel plate without plating, the mating material is used. From the viewpoint of preventing LME cracking, (3) and (4) are preferable.
  • the plating amount of each plating layer is not particularly limited, and can be selected according to the application after spot welding, the required performance, and the like.
  • the plating amount of the entire plating layer on each surface of the steel sheet is preferably 3 mg / m 2 or more, and is 800 g / m 2 or less from the viewpoint of suppressing the occurrence of defects such as blow holes during welding. preferable. Further, from the viewpoint of exerting the anticorrosion effect which is the purpose of plating, it is preferable that the amount of Zn plated is the largest. If the entire plating layer is a single Zn-Ni-containing plating layer, it is preferable to increase the Zn content rather than the Ni content.
  • the Zn-containing plating layer is plated. It is preferable to use the main plating having the largest amount.
  • the Zn-containing plating layer may be referred to as "main plating”, the plating formed before the main plating may be referred to as “pre-plating”, and the plating layer formed after the main plating may be referred to as "post-plating”.
  • each plating layer (method of forming the plating layer) is not particularly limited, but hot-dip plating or electroplating is preferable.
  • Each plating layer contains one or both of Ni and Zn, but may also contain other metallic elements. Examples of other metal elements that can be contained in the plating layer include Al, Mg, and Fe. Further, even if some of the two or more plating layers do not contain Zn or Ni, the other plating layers contain Zn and Ni and do not contain Zn and Ni.
  • the Ni content of the entire plating layer including the plating layer may be 2.0% by mass or more.
  • the plated steel sheet for spot welding according to the present disclosure may be subjected to alloying heat treatment. If the alloying heat treatment of the plating layer is applied, it is possible to prevent the zinc plating from adhering to the tool during processing.
  • the usual method can be applied to the alloying heat treatment. For example, after forming a Zn-containing plating layer, it is heated to form an alloyed hot-dip galvanized steel sheet, and further, a Ni-containing plating layer is formed so that the Ni content of the entire plating layer is 2.0% by mass or more. May be good.
  • the alloying heat treatment after forming the plating layer increases the number of manufacturing processes and causes an increase in manufacturing cost.
  • the alloying heat treatment may promote tempering of the base steel sheet, making it difficult to obtain high tensile strength.
  • LME resistance characteristics in order to suppress the occurrence of LME cracks during spot welding (LME resistance characteristics), it is desirable that the concentration of Ni is higher at the portion of the plating layer in contact with the base steel plate. Therefore, it is easier to exhibit higher LME resistance characteristics when Ni is not diffused by the alloying heat treatment. Therefore, it is also preferable to use a spot welded galvanized steel sheet (non-alloyed galvanized steel sheet for spot welding) that is not subjected to alloying heat treatment.
  • the plating layer in the present disclosure may be formed on one side of the base steel plate or may be formed on both sides.
  • the zinc plating on the welded portion melts and LME cracks are likely to occur, but the surface on the side where the electrodes contact (outer surface of the zinc-plated steel plate).
  • the zinc plating melts and LME cracking occurs. Therefore, in the case of a spot-welded plated steel sheet in which zinc-plated layers are formed on both sides of the base steel sheet, it is preferable that the Ni content of the entire plated layer on each surface is 2.0% by mass or more.
  • the plated steel sheet for spot welding according to the present disclosure has a tensile strength of 780 MPa or more.
  • a joint member spot welded joint
  • the joint strength joint strength
  • the tensile strength of the spot-welded plated steel sheet according to the present disclosure is preferably 980 MPa or more, more preferably 1180 MPa or more, and further preferably 1470 MPa or more.
  • the tensile strength of the spot-welded plated steel sheet according to the present disclosure is a value obtained by preparing a tensile test piece of JIS No. 5 and performing a tensile test in accordance with JIS Z2241: 2011, and measuring the tensile strength.
  • the method for manufacturing a plated steel sheet for spot welding according to the present disclosure is not particularly limited.
  • the base steel sheet before forming the plating layer may be either a hot-rolled steel sheet or a cold-rolled steel sheet as long as it has the above-mentioned steel composition.
  • the steel structure is also not particularly limited. However, regardless of whether a hot-rolled steel sheet or a cold-rolled steel sheet is used, a steel sheet having an internal oxide layer thickness of less than 5.0 ⁇ m in the surface layer portion is used.
  • the tensile strength of the spot-welded plated steel sheet after forming the plating layer is 780 MPa or more
  • the tensile strength of the base steel sheet before forming the plated layer is also preferably 780 MPa or more.
  • the base steel sheet before forming the plating layer can be manufactured, for example, by the following method.
  • steel adjusted to the above-mentioned steel composition is melted in a converter to form a slab by a continuous casting method, and the slab is kept at a high temperature or cooled to room temperature and then inserted into a heating furnace for 1100-1300. It is heated in a temperature range of ° C., and then finish rolling is performed in a temperature range of 800 to 950 ° C. It is water-cooled from the finish rolling temperature to 500 to 650 ° C., and then air-cooled. Then, cold rolling is performed to obtain a steel sheet having a desired thickness.
  • heat treatment is performed.
  • the heat treatment is performed by heating at 10 to 100 ° C./sec from 750 to 850 ° C., and then performing heat treatment such as cooling and reheating.
  • a base steel sheet having a tensile strength of 780 MPa or more and a thickness of the internal oxide layer in the surface layer portion of less than 5.0 ⁇ m can be produced.
  • Zn and Ni are contained as at least a part of the plating layer on one side or both sides of the base steel sheet having the above steel composition and the thickness of the internal oxide layer is less than 5 ⁇ m, and the Ni content in the entire plating layer is 2.
  • a plating layer having one layer or two or more layers having a weight of 0.0% by mass or more is formed.
  • Each plating layer can be formed by hot-dip plating or electroplating, and after forming the plating layer, alloying heat treatment may be performed if necessary.
  • the plating step can be performed by either a continuous plating facility having a non-oxidizing furnace or a continuous plating facility not having a non-oxidizing furnace. Further, a film of an inorganic compound or an organic compound may be formed on the surface of the plating layer.
  • the method for manufacturing a joining member according to the first embodiment of the present disclosure includes a step of forming a plate assembly in which two or more plate materials including the above-mentioned spot welding plated steel plate according to the present disclosure are laminated. A process in which the plate assembly is sandwiched between a pair of electrodes in the plate thickness direction and energized while pressurizing to perform spot welding. It is a manufacturing method of a joining member including.
  • FIG. 2 schematically shows an example of a joint portion (nugget) formed when spot welding is performed on a plate set in which two plated steel plates are stacked.
  • the electrodes 2A and 2B are pressed against each other so as to sandwich the plate assembly in which the plated steel plates 1A and 1B for spot welding are overlapped in the plate thickness direction, and electricity is supplied between the electrodes 2A and 2B. I do.
  • a nugget 13 and a heat-affected zone (so-called HAZ) 14 are formed in the energized portion between the plated steel plate 1A and the plated steel plate 1B, and both steel plates are welded to form a joining member.
  • HAZ heat-affected zone
  • At least one of the two or more plate materials constituting the plate assembly may be a plated steel plate for spot welding according to the present disclosure.
  • the two or more plate materials constituting the plate assembly are all the plated steel plates for spot welding according to the present disclosure, but the plating for spot welding according to the present disclosure. It may be a plate assembly of a steel plate and another steel plate, for example, a cold-welded steel plate without a plating layer, or a plate assembly with a metal plate other than the steel plate such as an aluminum plate.
  • the conditions for spot welding (current value, energization time, etc.) are not particularly limited, and ordinary conditions can be applied.
  • the joining member according to the present disclosure is particularly suitable for an automobile member.
  • the type of automobile member is not particularly limited.
  • the method for producing a welded member according to the second embodiment of the present disclosure has the above-mentioned steel composition, and the thickness of the internal oxide layer in which at least a part of the crystal grain boundary is covered with an oxide is deep from the surface.
  • a Zn-containing plated layer is formed on one side or both sides of a base steel sheet having a tensile strength of less than 5.0 ⁇ m, and a plate set in which two or more sheets including a plated steel sheet for spot welding having a tensile strength of 780 MP or more are laminated.
  • the process of The foil containing Ni and having a Ni content of 2.0% by mass or more in the plating layer and the entire foil in the region where the foil is arranged is the foil of the plated steel sheet for spot welding.
  • a Ni-containing foil is used instead of the Ni-containing plating layer in the above-mentioned spot welding plated steel sheet according to the present disclosure. 2.
  • the Ni-containing foil is placed on the surface of the spot-welded plated steel plate on which the Zn-containing plating layer is formed, and the total Ni content of the Zn-containing plating layer and the Ni-containing foil is determined in the region where the Ni-containing foil is placed.
  • the Zn-containing plating layer contains metal elements other than Zn.
  • the Ni-containing foil may contain a metal element other than Ni.
  • the spot welding conditions are not particularly limited in the method for manufacturing the joint member according to the second embodiment, and ordinary conditions can be applied.
  • spot welding is performed using a plated steel sheet for spot welding in which Zn-containing plated layers are provided on both sides of the base steel sheet, not only the inner surface (the side where the joint is formed) but also the outer surface of the galvanized steel sheet is formed.
  • the Zn-containing plating layer on the side surface may also melt and LME cracking may occur. Therefore, spot welding is performed by arranging Ni-containing foils between the two overlapping plated steel sheets (inner surface of the plated steel sheet) and between the electrode and the plated steel sheet for spot welding (outer surface of the plated steel sheet). Is preferable.
  • the plated steel sheet for spot welding according to the present disclosure will be described more specifically by way of examples.
  • the plated steel sheet for spot welding according to the present disclosure is not limited to these examples.
  • Underlined values in each table mean outside the scope of this disclosure.
  • Example 1 [Manufacturing of test materials] Ingots made by melting and casting materials with the chemical components shown in Table 1 in a laboratory are hot-rolled (heating temperature 1250 ° C, rolling temperature (finish rolling temperature) 900 ° C, then water-cooled to 500 ° C, and then air-cooled). After that, a steel plate (base steel plate) having a thickness of 1.40 mm was manufactured by cold rolling.
  • test materials A to D Both sides of the manufactured base steel sheet were plated as shown in Table 2 below to prepare test materials A to D.
  • the test material B was subjected to hot-dip Zn plating on the base steel sheet, heated to 530 ° C. as an alloying heat treatment, held for 1 minute, and then air-cooled. After the alloying heat treatment, Ni electroplating was performed.
  • the test material D is a non-plated material of steel grade C.
  • test material base steel sheet
  • base steel sheet is subjected to wet polishing on a cross section perpendicular to the plate thickness, and further buffed using diamond particles having an average diameter of 1 ⁇ m to prepare a cross-section sample. Obtained. SEM observation was performed on this cross-sectional sample.
  • the SEM used for the measurement is JSM-7001F manufactured by JEOL Ltd.
  • the internal oxide present on the surface layer of the test material is confirmed by the backscattered electron image at a magnification of about 3000 times, and the region where the internal oxide exists from the surface of the test material is defined as the internal oxide layer.
  • the area of the internal oxide layer was measured in a visual field having a width of at least 30 ⁇ m or more, and the average distance from the surface was calculated by dividing by the area, which was defined as the thickness of the internal oxide layer. As a result, no internal oxide layer was formed on the surface of any of the test materials.
  • test material B and the test material D were overlapped and welded under the above conditions. The test material D was placed on the lower plate where LME cracking was likely to occur.
  • FIG. 3 shows an example of the cross-sectional observation result of the test material A after spot welding.
  • the cracks generated inside and outside the pressure contact portion were marked with an ellipse, and the length of each crack was measured.
  • FIG. 4 shows a graph in which the welding current value is plotted on the horizontal axis and the crack length is plotted on the vertical axis for each Ni plating amount. If multiple cracks occurred, the total length was used. From FIG. 4, Ni electroplating was performed compared to the sample in which spot welding was performed using a test material (Ni electroplating: 0 g / m 3 ) in which Ni electroplating was not performed as pre-plating before Zn electroplating. In the sample subjected to spot welding using the test material, the occurrence of LME cracks is suppressed, and the larger the amount of Ni plating, the smaller the LME crack length tends to be.
  • Ni electroplating Ni electroplating: 0 g / m 3
  • the LME crack length was also measured for the samples subjected to spot welding using each of the test materials B and the test materials C.
  • the relationship between the welding current value and the LME crack length for each Ni plating amount is shown in FIGS. 5, 6 and 7, respectively.
  • the Ni plating amount was converted from the Ni content in the Zn—Ni plating layer.
  • Example 2> Manufacturing of plated steel sheets for spot welding
  • Ingots made by melting and casting materials having the chemical components shown in Table 3 (the rest is Fe and impurities) are hot-rolled (heating temperature 1250 ° C, rolling temperature (finish rolling temperature) 900 ° C, and then 500 ° C. After water cooling and then air cooling), a cold-rolled steel sheet (base steel sheet) having a thickness of 1.40 mm was manufactured by cold rolling.
  • the manufactured base steel sheet (excluding a part) was plated as shown in Table 4 below to manufacture a plated steel sheet for spot welding.
  • Ni plating instead of Ni plating as "post-plating" on zinc plating, it was decided to place Ni foil at the position where spot welding is to be performed and perform spot welding.
  • Ni plating as pre-plating and Ni plating as post-plating were not performed on each base metal plate, and the same was applied except that the Ni-containing zinc-based plating as the main plating was changed to zinc-based plating.
  • a plated steel plate for spot welding was manufactured.
  • a tensile test piece of JIS No. 5 was prepared for the obtained galvanized steel sheet for spot welding, and a tensile test was conducted in accordance with JIS Z 2241: 2011, and the tensile strength was measured.
  • the obtained test material (base steel sheet) is subjected to wet polishing on a cross section perpendicular to the plate thickness, and further buffed using diamond particles having an average diameter of 1 ⁇ m to prepare a cross-section sample. Obtained. SEM observation was performed on this cross-sectional sample.
  • the SEM used for the measurement is JSM-7001F manufactured by JEOL Ltd.
  • the internal oxide present on the surface layer of the test material is confirmed by the backscattered electron image at a magnification of about 3000 times, and the region where the internal oxide exists from the surface of the test material is defined as the internal oxide layer. Further, the area of the internal oxide layer was measured in a visual field having a width of at least 30 ⁇ m or more, and the average distance from the surface was calculated by dividing by the area, which was defined as the thickness of the internal oxide layer.
  • spot welding Using the manufactured plated steel sheet for spot welding, spot welding was performed under the same conditions as in Example 1 to manufacture a joint member. For a plated steel sheet for spot welding in which a plated layer was formed only on one side of the base steel sheet, spot welding was performed with the side where the joint portion (nugget) was formed by spot welding as the plating layer to manufacture a joint member. Further, the manufactured plated steel sheet for spot welding and a cold-rolled steel sheet of 980 MPa class were superposed, and spot welding was performed under the same conditions as in Example 1 to manufacture a joint member.
  • a steel sheet prepared by plating a zinc-based plating containing no Ni in the same amount and a cold-rolled steel sheet of 980 MPa class were superposed and spot welded to manufacture a bonded member.
  • the plating amount was adjusted to the amount excluding Ni for each plating.
  • the Ni content in the plating is 5.3% and the total amount of plating is 79.3 g / m 2 , so the plating amount excluding Ni is 75.1 g / m 2 .
  • the plating components other than Ni were the same.
  • Ni foil is placed on the side where the joint is formed by spot welding and spot welding is performed to form the joint member.
  • spot welding is performed to form the joint member.
  • a joint member was manufactured by spot welding without arranging Ni foil.
  • the tensile strength of the plated steel sheet for spot welding was measured by the above-mentioned tensile test, and it was judged that the tensile strength of the plated steel sheet for spot welding was insufficient if the tensile strength was less than 780 MPa. It can be seen that when the spot-welded plated steel sheet according to the present disclosure is used, the occurrence of LME cracks is suppressed as compared with the spot-welded plated steel sheet to be compared. Furthermore, it can be seen that the occurrence of LME cracks in the mating material is also suppressed.

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Abstract

Provided is a plated steel sheet for spot welding use, which comprises: a base steel sheet which has a steel composition containing, in % by mass, 0.05 to 0.70% of C, 3.50% or less of Si, 8.00% or less of Mn, 0.020% or less of P, 0.050% or less of S, 3.000% or less of Al, and 0.010% or less of N, and also containing an arbitrarily selected element, with the remainder comprising Fe and impurities, in which the thickness of an inner oxide layer corresponds to a depth of less than 5.0 μm from the surface thereof; and a plating layer which is formed on one surface or both surfaces of the base steel sheet, and is composed of one or more layers, in which Zn and Ni are contained as at least a portion of the plating layer and the Ni content in the whole of the plating layer is 2.0% by mass or more. The plated steel sheet has tensile strength of 780 MPa or more. Also provided are a joining member, an automotive member, and a method for manufacturing a joining member, in each of which the plated steel sheet is used. A Ni-containing foil may be applied in place of the Ni-containing plating layer.

Description

スポット溶接用めっき鋼板、接合部材、及び自動車用部材、並びに接合部材の製造方法A method for manufacturing plated steel sheets for spot welding, joining members, automobile members, and joining members.
　本開示は、スポット溶接用めっき鋼板、接合部材、及び自動車用部材、並びに接合部材の製造方法に関する。 The present disclosure relates to a plated steel sheet for spot welding, a joining member, an automobile member, and a method for manufacturing the joining member.
　複数枚の金属板を重ねてスポット溶接する場合、液体金属脆化（ＬＭＥ：Ｌｉｑｕｉｄ　Ｍｅｔａｌ　Ｅｍｂｒｉｔｔｌｅｍｅｎｔ）による割れ（ＬＭＥ割れ）が生じる場合がある。液体金属脆化とは、固体金属に液体金属が接触した状態で引張り応力を付与すると本来延性を示す固体金属が脆化することであり、代表的には鋼（固体金属）と亜鉛（液体金属）との間で生じる。特に合金濃度が高く、引張強さが７８０ＭＰａ以上となる高強度鋼板を用いてスポット溶接を行った場合にＬＭＥ割れが発生し易い。 When multiple metal plates are stacked and spot welded, cracking (LME cracking) may occur due to liquid metal embrittlement (LME: Liquid Metal Embrittlement). Liquid metal embrittlement is the embrittlement of a solid metal that originally exhibits ductility when a tensile stress is applied to the solid metal in contact with the liquid metal, and is typically steel (solid metal) and zinc (liquid metal). ). In particular, LME cracking is likely to occur when spot welding is performed using a high-strength steel plate having a high alloy concentration and a tensile strength of 780 MPa or more.
　例えば、スポット溶接によるＬＭＥ割れの発生を抑制する合金化溶融亜鉛めっき鋼板の製造方法として、特許文献１では、
　以下の連続工程を含む合金化溶融亜鉛めっき鋼板の製造のための方法であって、
　Ａ．ニッケルから成る第１被覆物を使用し、及び１５０～６５０ｎｍの厚みを有する鋼板の被覆であり、前記鋼板は、重量パーセントで以下の組成：
　０．１０＜Ｃ＜０．４０％、
　１．５＜Ｍｎ＜３．０％、
　０．７＜Ｓｉ＜３．０％、
　０．０５＜Ａｌ＜１．０％、
　０．７５＜（Ｓｉ＋Ａｌ）＜３．０％、
　及び単に任意の主成分で、
　Ｎｂ≦０．５％、
　Ｂ≦０．０１０％、
　Ｃｒ≦１．０％、
　Ｍｏ≦０．５０％、
　Ｎｉ≦１．０％、
　Ｔｉ≦０．５％などの１つ以上の成分と、
　鉄及び精錬によって生じる不可避不純物で構成されている残りの組成と、を有する、鋼板の被覆と、
　Ｂ．６００～１２００℃の温度で焼鈍された前記被覆鋼板の焼鈍と、
　Ｃ．亜鉛系第２被覆物による工程Ｂ）で得られる前記鋼板の被覆と、
　Ｄ．合金化溶融亜鉛めっき鋼板を形成するための合金化熱処理と、を含む方法、並びに、この方法により製造される合金化溶融亜鉛めっき鋼板が開示されている。 For example, in Patent Document 1, as a method for manufacturing an alloyed hot-dip galvanized steel sheet that suppresses the occurrence of LME cracks due to spot welding,
A method for manufacturing alloyed hot-dip galvanized steel sheets including the following continuous steps.
A. A first coating made of nickel and a coating of a steel sheet having a thickness of 150-650 nm, wherein the steel sheet has the following composition by weight percent:
0.10 <C <0.40%,
1.5 <Mn <3.0%,
0.7 <Si <3.0%,
0.05 <Al <1.0%,
0.75 <(Si + Al) <3.0%,
And simply with any principal component,
Nb ≤ 0.5%,
B ≤ 0.010%,
Cr ≤ 1.0%,
Mo ≤ 0.50%,
Ni ≤ 1.0%,
With one or more components such as Ti ≤ 0.5%,
With a coating of steel sheet, with the remaining composition, which is composed of iron and unavoidable impurities produced by refining.
B. Annealing of the coated steel sheet annealed at a temperature of 600 to 1200 ° C.
C. The coating of the steel sheet obtained in step B) with the zinc-based second coating and
D. A method including an alloying heat treatment for forming an alloyed hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet manufactured by this method are disclosed.
　特許文献２では、
　母材の化学組成が、質量％で、
　Ｃ：０．１７～０．４０％、
　Ｓｉ：０．１０～２．５０％、
　Ｍｎ：１．００～１０．００％、
　Ｐ：０．００１～０．０３％、
　Ｓ：０．０００１～０．０２％、
　Ａｌ：０．００１～２．５０％、
　Ｎ：０．０００１～０．０１０％、
　Ｏ：０．０００１～０．０１０％、
　Ｔｉ：０～０．１０％、
　Ｎｂ：０～０．１０％、
　Ｖ：０～０．１０％、
　Ｂ：０～０．０１０％、
　Ｃｒ：０～２．００％、
　Ｎｉ：０～２．００％、
　Ｃｕ：０～２．００％、
　Ｍｏ：０～２．００％、
　Ｃａ：０～０．５０％、
　Ｍｇ：０～０．５０％、
　ＲＥＭ：０～０．５０％、
　残部：Ｆｅおよび不純物であり、
　前記母材の表面から５．０μｍ以上の深さまで、結晶粒界の少なくとも一部が酸化物に
被覆された内部酸化層を有し、かつ、
　前記母材の表面から５．０μｍの深さまでの領域において、前記酸化物の粒界被覆率が
６０％以上である鋼板が開示されている。 In Patent Document 2,
The chemical composition of the base metal is mass%,
C: 0.17 to 0.40%,
Si: 0.10 to 2.50%,
Mn: 1.00 to 10.00%,
P: 0.001 to 0.03%,
S: 0.0001 to 0.02%,
Al: 0.001 to 2.50%,
N: 0.0001 to 0.010%,
O: 0.0001 to 0.010%,
Ti: 0 to 0.10%,
Nb: 0 to 0.10%,
V: 0 to 0.10%,
B: 0 to 0.010%,
Cr: 0 to 2.00%,
Ni: 0 to 2.00%,
Cu: 0 to 2.00%,
Mo: 0 to 2.00%,
Ca: 0 to 0.50%,
Mg: 0 to 0.50%,
REM: 0 to 0.50%,
Remaining: Fe and impurities,
It has an internal oxide layer in which at least a part of the crystal grain boundaries is coated with an oxide from the surface of the base metal to a depth of 5.0 μm or more, and
A steel sheet having a grain boundary coverage of 60% or more in the region from the surface of the base metal to a depth of 5.0 μm is disclosed.
　　特許文献１：特表２０２０－５２１０４１号公報
　　特許文献２：国際公開第２０１９／１１６５３１号 Patent Document 1: Japanese Patent Application Laid-Open No. 2020-52141 Patent Document 2: International Publication No. 2019/116531
　特許文献１に開示されているような合金化溶融亜鉛めっき鋼板又は特許文献２に開示されているような内部酸化層を有する鋼板を用いても、相手材として冷延鋼板を用いたり、内部酸化層が無い板を用いてスポット溶接を行うと相手材との合わせ面においては亜鉛が存在するためＬＭＥ割れが生じ易い。
　本開示は、引張強さが高いめっき鋼板をスポット溶接したときにＬＭＥ割れの発生が抑制され、相手材として冷延鋼板を用いたり、内部酸化層が無い板を用いても相手材におけるＬＭＥ割れの発生が抑制されるスポット溶接用めっき鋼板、それを用いた接合部材、及び自動車用部材、並びに接合部材の製造方法を提供することを目的とする。 Even if an alloyed hot-dip galvanized steel sheet as disclosed in Patent Document 1 or a steel sheet having an internal oxide layer as disclosed in Patent Document 2 is used, a cold-rolled steel sheet may be used as a mating material or internal oxidation may occur. When spot welding is performed using a plate without a layer, zinc is present on the mating surface with the mating material, so LME cracking is likely to occur.
In the present disclosure, the occurrence of LME cracking is suppressed when a plated steel sheet having high tensile strength is spot welded, and even if a cold-rolled steel sheet is used as the mating material or a plate without an internal oxide layer is used, the LME cracking in the mating material is suppressed. It is an object of the present invention to provide a plated steel sheet for spot welding, a joining member using the same, a member for an automobile, and a method for manufacturing the joining member.
　上記目的を達成するための本開示の要旨は次の通りである。
＜１＞　質量％で、
　Ｃ：０．０５～０．７０％、
　Ｓｉ：３．５０％以下、
　Ｍｎ：８．００％以下、
　Ｐ：０．０２０％以下、
　Ｓ：０．０５０％以下、
　Ａｌ：３．０００％以下、及び
　Ｎ：０．０１０％以下
を含み、
　任意選択的に、
　Ｔｉ：０．３００％以下、
　Ｎｂ：０．３００％以下、
　Ｖ：０．３０％以下、
　Ｃｒ：５．０％以下、
　Ｍｏ：２．００％以下、
　Ｃｕ：２．００％以下、
　Ｎｉ：１０．０％以下、
　Ｂ：０．０２０％以下、
　Ｃａ：０．００３％以下、
　ＲＥＭ：０．０５％以下、
　Ｍｇ：０．０５％以下、及び
　Ｚｒ：０．０５％以下
からなる群より選ばれる１種又は２種以上を含み、
　残部がＦｅ及び不純物からなる鋼組成を有し、
　結晶粒界の少なくとも一部が酸化物に被覆されている内部酸化層の厚みが、表面から深さ５．０μｍ未満である母材鋼板と、
　前記母材鋼板の片面又は両面に形成されている１層又は２層以上のめっき層であって、前記めっき層の少なくとも一部としてＺｎ及びＮｉを含み、かつ前記めっき層全体でのＮｉ含有量が２．０質量％以上であるめっき層と、
を含み、
　引張強さが７８０ＭＰａ以上である、
　スポット溶接用めっき鋼板。
＜２＞　前記めっき層として、前記母材鋼板側から、Ｎｉを含むめっき層と、Ｚｎを含むめっき層とが形成されている、＜１＞に記載のスポット溶接用めっき鋼板。
＜３＞　前記めっき層として、前記母材鋼板側から、Ｚｎを含むめっき層と、Ｎｉを含むめっき層とが形成されている、＜１＞に記載のスポット溶接用めっき鋼板。
＜４＞　前記めっき層として、前記母材鋼板側から、Ｎｉを含むめっき層と、Ｚｎを含むめっき層と、Ｎｉを含むめっき層とが形成されている、＜１＞に記載のスポット溶接用めっき鋼板。
＜５＞　前記めっき層の少なくとも１層が、Ｚｎ及びＮｉを含むめっき層である、＜１＞～＜４＞のいずれか１つに記載のスポット溶接用めっき鋼板。
＜６＞　非合金化めっき鋼板である、＜１＞～＜５＞のいずれか１つに記載のスポット溶接用めっき鋼板。
＜７＞　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
　Ｔｉ：０．００１％以上０．３００％以下、
　Ｎｂ：０．００１％以上０．３００％以下、及び
　Ｖ：０．００１％以上０．３０％以下
　からなる群より選ばれる１種又は２種以上を含む＜１＞～＜６＞のいずれか１つに記載のスポット溶接用めっき鋼板。
＜８＞　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
　Ｃｒ：０．００１％以上５．０％以下及びＭｏ：０．００１％以上２．００％以下の１種又は２種を含む＜１＞～＜７＞のいずれか１つに記載のスポット溶接用めっき鋼板。
＜９＞　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
　Ｃｕ：０．００１％以上２．００％以下及びＮｉ：０．００１％以上１０．０％以下の１種又は２種を含む＜１＞～＜８＞のいずれか１つに記載のスポット溶接用めっき鋼板。
＜１０＞　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
　Ｂ：０．００１％以上０．０２０％以下を含む＜１＞～＜９＞のいずれか１つに記載のスポット溶接用めっき鋼板。
＜１１＞　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
　Ｃａ：０．０００５％以上０．００３％以下、
　ＲＥＭ：０．００１％以上０．０５％以下、
　Ｍｇ：０．００１％以上０．０５％以下、及び
　Ｚｒ：０．００１％以上０．０５％以下
からなる群より選ばれる１種又は２種以上を含む＜１＞～＜１０＞のいずれか１つに記載のスポット溶接用めっき鋼板。
＜１２＞　＜１＞～＜１１＞のいずれか１つに記載のスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組がスポット溶接された接合構造を有する接合部材。
＜１３＞　＜１２＞に記載の接合部材を含む自動車用部材。
＜１４＞　＜１＞～＜１１＞のいずれか１つに記載のスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組とする工程と、
　前記板組を一対の電極で板厚方向に挟み込んで加圧しながら通電してスポット溶接を行う工程と、
　を含む接合部材の製造方法。
＜１５＞　＜１＞～＜１１＞のいずれか１つに記載の前記鋼組成を有し、結晶粒界の少なくとも一部が酸化物に被覆されている内部酸化層の厚みが、表面から深さ５．０μｍ未満である母材鋼板の片面又は両面にＺｎを含むめっき層が形成されており、引張強さが７８０ＭＰ以上であるスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組とする工程と、
　Ｎｉを含む箔であって、前記箔が配置された領域において前記めっき層及び前記箔の全体でのＮｉ含有量が２．０質量％以上となる前記箔を、前記スポット溶接用めっき鋼板の前記めっき層が形成されている面に配置する工程と、
　前記箔が配置された領域において前記板組を一対の電極で板厚方向に挟み込んで加圧しながら通電してスポット溶接を行う工程と、
　を含む接合部材の製造方法。 The gist of this disclosure to achieve the above objectives is as follows.
<1> By mass%,
C: 0.05 to 0.70%,
Si: 3.50% or less,
Mn: 8.00% or less,
P: 0.020% or less,
S: 0.050% or less,
Al: 3.000% or less, and N: 0.010% or less, including
Optionally,
Ti: 0.300% or less,
Nb: 0.300% or less,
V: 0.30% or less,
Cr: 5.0% or less,
Mo: 2.00% or less,
Cu: 2.00% or less,
Ni: 10.0% or less,
B: 0.020% or less,
Ca: 0.003% or less,
REM: 0.05% or less,
Includes one or more selected from the group consisting of Mg: 0.05% or less and Zr: 0.05% or less.
The balance has a steel composition consisting of Fe and impurities.
A base steel sheet in which the thickness of the internal oxide layer in which at least a part of the grain boundaries is covered with an oxide is less than 5.0 μm from the surface, and
One or more plating layers formed on one side or both sides of the base steel sheet, which contains Zn and Ni as at least a part of the plating layer, and the Ni content in the entire plating layer. With a plating layer of 2.0% by mass or more,
Including
The tensile strength is 780 MPa or more.
Plated steel sheet for spot welding.
<2> The plated steel sheet for spot welding according to <1>, wherein a plating layer containing Ni and a plating layer containing Zn are formed as the plating layer from the base steel sheet side.
<3> The plated steel sheet for spot welding according to <1>, wherein a plating layer containing Zn and a plating layer containing Ni are formed as the plating layer from the base steel sheet side.
<4> The spot welding according to <1>, wherein a plating layer containing Ni, a plating layer containing Zn, and a plating layer containing Ni are formed as the plating layer from the base steel plate side. Plated steel plate.
<5> The plated steel sheet for spot welding according to any one of <1> to <4>, wherein at least one of the plating layers is a plating layer containing Zn and Ni.
<6> The plated steel sheet for spot welding according to any one of <1> to <5>, which is a non-alloyed plated steel sheet.
<7> The steel composition is, in mass%, instead of a part of the Fe.
Ti: 0.001% or more and 0.300% or less,
Nb: any one of <1> to <6> including one or more selected from the group consisting of 0.001% or more and 0.300% or less, and V: 0.001% or more and 0.30% or less. The plated steel sheet for spot welding described in one.
<8> The steel composition is, in mass%, instead of a part of the Fe.
The spot welding according to any one of <1> to <7>, which comprises one or two types of Cr: 0.001% or more and 5.0% or less and Mo: 0.001% or more and 2.00% or less. For plated steel sheets.
<9> The steel composition is, in mass%, instead of a part of the Fe.
The spot welding according to any one of <1> to <8>, which comprises one or two types of Cu: 0.001% or more and 2.00% or less and Ni: 0.001% or more and 10.0% or less. For plated steel sheets.
<10> The steel composition is, in mass%, instead of a part of the Fe.
B: The plated steel sheet for spot welding according to any one of <1> to <9>, which contains 0.001% or more and 0.020% or less.
<11> The steel composition is, in mass%, instead of a part of the Fe.
Ca: 0.0005% or more and 0.003% or less,
REM: 0.001% or more and 0.05% or less,
Any one of <1> to <10> containing one or more selected from the group consisting of Mg: 0.001% or more and 0.05% or less, and Zr: 0.001% or more and 0.05% or less. The plated steel sheet for spot welding described in one.
<12> A joining member having a joint structure in which a plate assembly in which two or more plate materials including the plated steel plate for spot welding according to any one of <1> to <11> is superposed is spot welded.
<13> An automobile member including the joining member according to <12>.
<14> A step of stacking two or more plate materials including the spot welding plated steel plate according to any one of <1> to <11> to form a plate assembly.
A process in which the plate assembly is sandwiched between a pair of electrodes in the plate thickness direction and energized while pressurizing to perform spot welding.
A method for manufacturing a joining member including.
<15> The thickness of the internal oxide layer having the steel composition according to any one of <1> to <11> and having at least a part of the crystal grain boundary coated with the oxide is deep from the surface. A plating layer containing Zn is formed on one side or both sides of a base steel sheet having a thickness of less than 5.0 μm, and two or more sheets including a spot welding plated steel sheet having a tensile strength of 780 MP or more are laminated. The process of making a plate and
The foil containing Ni and having a Ni content of 2.0% by mass or more in the plating layer and the entire foil in the region where the foil is arranged is the foil of the plated steel sheet for spot welding. The process of arranging on the surface where the plating layer is formed and
In the region where the foil is arranged, the plate assembly is sandwiched between a pair of electrodes in the plate thickness direction and energized while pressurizing to perform spot welding.
A method for manufacturing a joining member including.
　本開示によれば、引張強さが高いめっき鋼板をスポット溶接したときにＬＭＥ割れの発生が抑制され、相手材として冷延鋼板を用いたり、内部酸化層が無い板を用いても相手材におけるＬＭＥ割れの発生が抑制されるスポット溶接用めっき鋼板、それを用いた接合部材、及び自動車用部材、並びに接合部材の製造方法が提供される。 According to the present disclosure, the occurrence of LME cracks is suppressed when a plated steel sheet having high tensile strength is spot welded, and even if a cold-rolled steel sheet is used as the mating material or a plate having no internal oxide layer is used, the mating material has Provided are a plated steel sheet for spot welding in which the occurrence of LME cracks is suppressed, a joining member using the same, an automobile member, and a method for manufacturing the joining member.
Ｎｉ付与による亜鉛の液相線および固相線の変化を示すＺｎ－Ｎｉの二元系状態図である。It is a binary system state diagram of Zn—Ni which shows the change of the liquid phase line and solid phase line of zinc by the addition of Ni. ２枚の鋼板を重ね合わせた板組に対して抵抗スポット溶接を行った場合に形成される接合部の一例を概略的に示す図である。It is a figure which shows typically an example of the joint part formed in the case of performing resistance spot welding to the plate assembly which overlapped two steel plates. 実施例における供試材Ａを用いたスポット溶接後の断面観察結果の例を示す図である。It is a figure which shows the example of the cross-section observation result after spot welding using the test material A in an Example. 図３に示すスポット溶接後の断面観察結果について、横軸に溶接電流値、縦軸に割れ長さを示す図である。About the cross-sectional observation result after spot welding shown in FIG. 3, the horizontal axis shows the welding current value, and the vertical axis shows the crack length. 実施例における供試材Ｂを用いたスポット溶接後の断面観察結果について、横軸に溶接電流値、縦軸に割れ長さを示す図である。It is a figure which shows the welding current value on the horizontal axis, and the crack length on a vertical axis about the cross-sectional observation result after spot welding using the test material B in an Example. 実施例における供試材Ｃを用いたスポット溶接後の断面観察結果について、横軸に溶接電流値、縦軸に割れ長さを示す図である。It is a figure which shows the welding current value on the horizontal axis, and the crack length on a vertical axis about the cross-sectional observation result after spot welding using the test material C in an Example. 実施例における供試材Ｂと供試材Ｄを重ねた板組のスポット溶接後の断面観察結果について、横軸に溶接電流値、縦軸に割れ長さを示す図である。It is a figure which shows the welding current value on the horizontal axis, and the crack length on a vertical axis about the cross-sectional observation result after spot welding of the plate assembly which overlapped the test material B and the test material D in an Example.
　本開示の一例である実施形態について説明する。
　本開示において、各元素の含有量の「％」表示は「質量％」を意味する。また、本開示において、「～」を用いて表される数値範囲は、特に断りの無い限り、「～」の前後に記載される数値を下限値及び上限値として含む範囲を意味する。また、「～」の前後に記載される数値に「超」又は「未満」が付されている場合の数値範囲は、これら数値を下限値又は上限値として含まない範囲を意味する。
　本開示に段階的に記載されている数値範囲において、ある段階的な数値範囲の上限値は、他の段階的な記載の数値範囲の上限値に置き換えてもよく、ある段階的な数値範囲の下限値は、他の段階的な記載の数値範囲の下限値に置き換えてもよい。また、ある段階的な数値範囲の上限値又は下限値は、実施例に示されている値に置き換えてもよい。
　また、「工程」との用語は、独立した工程だけではなく、他の工程と明確に区別できない場合であってもその工程の所期の目的が達成されれば、本用語に含まれる。 An embodiment which is an example of the present disclosure will be described.
In the present disclosure, the "%" indication of the content of each element means "mass%". Further, in the present disclosure, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value unless otherwise specified. In addition, the numerical range when "greater than" or "less than" is added to the numerical values before and after "to" means a range in which these numerical values are not included as the lower limit value or the upper limit value.
In the numerical range described stepwise in the present disclosure, the upper limit of the numerical range described in one step may be replaced with the upper limit value of the numerical range described in another step. The lower limit may be replaced with the lower limit of the numerical range described in other steps. Further, the upper limit value or the lower limit value of a certain stepwise numerical range may be replaced with the value shown in the embodiment.
Further, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.
　特許文献１には、Ｎｉめっき後、Ｚｎめっきを施し、さらに合金化熱処理した合金化溶融亜鉛めっき鋼板が開示されているが、本発明者らが実験を重ねたところ、スポット溶接時の耐ＬＭＥ特性は、ＮｉめっきとＺｎめっきの形成順序や合金化熱処理よりも、めっき層全体でのＮｉ濃度による影響が大きいことを見出した。
　亜鉛めっき層にＮｉを付与することによりめっき融点が変わる（Ｎｉ添加によって融点が上昇する）ことによって亜鉛の鋼粒界への侵入しやすさが変化し、ＬＭＥ割れの発生が抑制されると考えられる。図１は、Ｎｉ付与による亜鉛の液相線および固相線の変化を示すＺｎ－Ｎｉの二元系状態図である。例えば、Ｎｉめっき０、３、又は１０ｇ／ｍ２とＺｎめっき５０ｇ／ｍ２を施し、めっき層が均一に混ざり合ったことを前提とすると、Ｎｉ濃度は０、５．７、１６．７質量％と換算できる。これらの濃度において、すべて液体となる温度と液相が発生する温度は、前者はＮｉ濃度が増加するにつれて上昇し、後者はＮｉ濃度が１６．７質量％付近で特に上昇していることが分かる。このように、めっきの温度特性がＮｉ濃度の変化によってＬＭＥ割れの抑制効果が得られると考えることができる。 Patent Document 1 discloses an alloyed hot-dip zinc-plated steel sheet that has been Ni-plated, Zn-plated, and then alloyed and heat-treated. However, as a result of repeated experiments by the present inventors, LME resistance during spot welding was disclosed. It was found that the characteristics are more influenced by the Ni concentration in the entire plating layer than the formation order of Ni plating and Zn plating and the alloying heat treatment.
It is thought that by adding Ni to the galvanized layer, the melting point of the plating changes (the melting point rises due to the addition of Ni), which changes the ease with which zinc penetrates into the steel grain boundaries and suppresses the occurrence of LME cracks. Be done. FIG. 1 is a dual system state diagram of Zn—Ni showing changes in the liquid phase line and the solid phase line of zinc due to the addition of Ni. For example, assuming that Ni plating 0, 3, or 10 g / m 2 and Zn plating 50 g / m 2 are applied and the plating layers are uniformly mixed, the Ni concentration is 0, 5.7, 16.7 mass. Can be converted to%. It can be seen that at these concentrations, the temperature at which all liquids are formed and the temperature at which the liquid phase is generated increase in the former as the Ni concentration increases, and in the latter, the Ni concentration increases particularly at around 16.7% by mass. .. As described above, it can be considered that the effect of suppressing LME cracking can be obtained by changing the Ni concentration in the temperature characteristics of the plating.
　さらに、本発明者らは、ＮｉとＺｎ系めっきが割れ発生部にてどのように分布しているのかをエネルギー分散型Ｘ線（ＥＤＳ）にてマッピングしたところ、ＺｎとＮｉが存在する位置はほぼ重なりあっており、溶接時に溶融し、混じりあっていたと考えられる。このことは、ＮｉめっきがＺｎめっきに対して上下どちらであっても大きな差異は見られなかったが、板界面でＺｎのカウントが少ない部分でもＮｉのカウント数が高い部分があった。これは、ＺｎとＮｉの融点の差からＺｎのほうが先に溶融し排出が進んだためであると推察される。このようにスポット溶接時の電極による圧接部内においても、Ｎｉはすべて排出されることなくＬＭＥ割れを抑制する効果を発揮したと考えられる。 Furthermore, when the present inventors mapped how Ni and Zn-based plating are distributed in the crack generation portion by energy dispersion type X-ray (EDS), the positions where Zn and Ni exist are located. It is probable that they almost overlapped and melted and mixed at the time of welding. This did not show a large difference between the upper and lower Ni plating with respect to the Zn plating, but there was a part where the Ni count number was high even in the part where the Zn count was small at the plate interface. It is presumed that this is because Zn melted earlier and was discharged from the difference in melting points between Zn and Ni. As described above, it is considered that all Ni was not discharged even in the pressure-welded portion formed by the electrodes during spot welding, and the effect of suppressing LME cracking was exhibited.
　一方、特許文献２には、母材鋼板の表面から５．０μｍ以上の深さまで内部酸化層を有し、Ｎｉめっき後、Ｚｎめっきを施し、さらに合金化熱処理した合金化溶融亜鉛めっき鋼板が開示されている。母材鋼板の表面に内部酸化層を有さないＺｎめっき鋼板よりも内部酸化層を有するＺｎめっき鋼板の方がスポット溶接時のＬＭＥ割れが発生し難いため、本発明者らは、２．０質量％以上のＮｉを含むＺｎ系めっき層を形成したＺｎめっき鋼板の場合も母材鋼板の表層部には内部酸化層を形成した方が有利であると考えた。 On the other hand, Patent Document 2 discloses an alloyed hot-dip galvanized steel sheet having an internal oxide layer up to a depth of 5.0 μm or more from the surface of the base steel sheet, Ni-plated, Zn-plated, and further alloyed and heat-treated. Has been done. Since the Zn-plated steel sheet having an internal oxide layer is less likely to cause LME cracking during spot welding than the Zn-plated steel sheet having no internal oxide layer on the surface of the base steel sheet, the present inventors have 2.0. In the case of a Zn-plated steel sheet on which a Zn-based plated layer containing Ni by mass% or more is formed, it is considered advantageous to form an internal oxide layer on the surface layer of the base steel sheet.
　そして、本発明者らが実験を繰り返したところ、引張強さが高く、スポット溶接時にＬＭＥ割れが発生し易い鋼板であっても、母材鋼板の表層部における内部酸化層を５．０μｍ以上有する鋼板においても、めっき層の少なくとも一部としてＺｎ及びＮｉを含み、めっき層全体でのＮｉ含有量が２．０質量％以上であるめっき鋼板とすることで、Ｎｉを含まないＺｎめっき鋼板を用いる場合に比べ、スポット溶接時にＬＭＥ割れが効果的に抑制されることを見出した。さらにこの場合、内部酸化層によって、より高いＬＭＥ割れ抑制効果が得られる場合もあった。 Then, as a result of repeated experiments by the present inventors, even a steel sheet having high tensile strength and prone to LME cracking during spot welding has an internal oxide layer of 5.0 μm or more in the surface layer portion of the base steel sheet. Also in the steel sheet, a Zn-plated steel sheet containing Zn and Ni as at least a part of the plating layer and having a Ni content of 2.0% by mass or more in the entire plating layer is used, so that a Zn-plated steel sheet containing no Ni is used. It has been found that LME cracking is effectively suppressed during spot welding as compared with the case. Further, in this case, the internal oxide layer may obtain a higher effect of suppressing LME cracking.
　しかしながら、相手材として冷延鋼板を用いたり、内部酸化層が無い板を用いた場合には内部酸化層の有無にかかわらず、めっき層全体でのＮｉ含有量が２．０質量％未満である場合にはＬＭＥ割れを抑制する効果は見出されなかった。
　一方、めっき層全体でのＮｉ含有量が２．０質量％以上である場合には、母材鋼板の表面の内部酸化層の有無にかかわらずその鋼板および相手材に対してもＬＭＥ割れが効果的に抑制されることを見出した。
　内部酸化層は鋼板の製造工程において、例えば熱間圧延や焼鈍工程において生成される場合がある。意図的に５μｍ以上の内部酸化層を付与するためには、それらの工程の雰囲気、温度、通板速度等の緻密な制御が必要となる。ゆえに内部酸化層を付与しかつめっき層の少なくとも一部としてＺｎ及びＮｉを含み、めっき層全体でのＮｉ含有量が２．０質量％以上であるめっき鋼板を両者とも具備することは、その製造性観点より困難であるものと考えられる。よって内部酸化層の厚みが５μｍ未満の鋼板に対してめっき中のＮｉ含有量を２．０質量％以上とすることでＬＭＥ割れ発生抑制効果を得ることが有利である。 However, when a cold-rolled steel sheet is used as the mating material or a plate without an internal oxide layer is used, the Ni content of the entire plating layer is less than 2.0% by mass regardless of the presence or absence of the internal oxide layer. In some cases, no effect of suppressing LME cracking was found.
On the other hand, when the Ni content of the entire plating layer is 2.0% by mass or more, LME cracking is effective for the steel sheet and the mating material regardless of the presence or absence of the internal oxide layer on the surface of the base steel sheet. It was found that it was suppressed.
The internal oxide layer may be formed in a steel sheet manufacturing process, for example, in a hot rolling or annealing process. In order to intentionally add an internal oxide layer of 5 μm or more, it is necessary to precisely control the atmosphere, temperature, plate passing speed, etc. of those processes. Therefore, it is possible to provide both of the plated steel sheets having an internal oxide layer, containing Zn and Ni as at least a part of the plating layer, and having a Ni content of 2.0% by mass or more in the entire plating layer. It is considered to be difficult from a sexual point of view. Therefore, it is advantageous to obtain the effect of suppressing the occurrence of LME cracks by setting the Ni content in plating to 2.0% by mass or more with respect to the steel sheet having an internal oxide layer thickness of less than 5 μm.
［スポット溶接用めっき鋼板］
　本開示に係るスポット溶接用めっき鋼板（本開示において単に「めっき鋼板」と記す場合がある。）は、質量％で、
　Ｃ：０．０５～０．７０％、
　Ｓｉ：３．５０％以下、
　Ｍｎ：８．００％以下、
　Ｐ：０．０２０％以下、
　Ｓ：０．０５０％以下、
　Ａｌ：３．０００％以下、及び
　Ｎ：０．０１０％以下
を含み、
　任意選択的に、
　Ｔｉ：０．３００％以下、
　Ｎｂ：０．３００％以下、
　Ｖ：０．３０％以下、
　Ｃｒ：５．０％以下、
　Ｍｏ：２．００％以下、
　Ｃｕ：２．００％以下、
　Ｎｉ：１０．０％以下、
　Ｂ：０．０２０％以下、
　Ｃａ：０．００３％以下、
　ＲＥＭ：０．０５％以下、
　Ｍｇ：０．０５％以下、及び
　Ｚｒ：０．０５％以下
からなる群より選ばれる１種又は２種以上を含み、
　残部がＦｅ及び不純物からなる鋼組成を有し、結晶粒界の少なくとも一部が酸化物に被覆されている内部酸化層の厚みが、表面から深さ５．０μｍ未満である母材鋼板と、
　前記母材鋼板の片面又は両面に形成されている１層又は２層以上のめっき層であって、前記めっき層の少なくとも一部としてＺｎ及びＮｉを含み、かつ前記めっき層全体でのＮｉ含有量が２．０質量％以上であるめっき層と、
を含み、
　引張強さが７８０ＭＰａ以上である。 [Plated steel sheet for spot welding]
The spot-welded plated steel sheet according to the present disclosure (may be simply referred to as “plated steel sheet” in the present disclosure) is in mass%.
C: 0.05 to 0.70%,
Si: 3.50% or less,
Mn: 8.00% or less,
P: 0.020% or less,
S: 0.050% or less,
Al: 3.000% or less, and N: 0.010% or less, including
Optionally,
Ti: 0.300% or less,
Nb: 0.300% or less,
V: 0.30% or less,
Cr: 5.0% or less,
Mo: 2.00% or less,
Cu: 2.00% or less,
Ni: 10.0% or less,
B: 0.020% or less,
Ca: 0.003% or less,
REM: 0.05% or less,
Includes one or more selected from the group consisting of Mg: 0.05% or less and Zr: 0.05% or less.
A base steel sheet having a steel composition in which the balance is composed of Fe and impurities, and the thickness of the internal oxide layer in which at least a part of the grain boundaries is covered with an oxide is less than 5.0 μm from the surface.
One or more plating layers formed on one side or both sides of the base steel sheet, which contains Zn and Ni as at least a part of the plating layer, and the Ni content in the entire plating layer. With a plating layer of 2.0% by mass or more,
Including
The tensile strength is 780 MPa or more.
＜母材鋼板＞
　本開示に係るスポット溶接用めっき鋼板における母材鋼板、すなわち、めっき層以外の鋼板部分（以下、「本開示における母材鋼板」又は単に「母材」と記す場合がある。）の鋼組成について具体的に説明する。
　本開示における母材鋼板の鋼組成は、Ｃ：０．０５～０．７０％、Ｓｉ：３．５０％以下、Ｍｎ：８．００％以下、Ｐ：０．０２０％以下、Ｓ：０．０５０％以下、Ａｌ：３．０００％以下、及びＮ：０．０１０％以下であり、残部がＦｅ及び不純物からなる。また、本開示に係るスポット溶接用めっき鋼板は、上記母材鋼板の鋼組成におけるＦｅの一部に代えて、任意選択元素として、質量％で、
　Ｔｉ：０．３００％以下、
　Ｎｂ：０．３００％以下、
　Ｖ：０．３０％以下、
　Ｃｒ：５．０％以下、
　Ｍｏ：２．００％以下、
　Ｃｕ：２．００％以下、
　Ｎｉ：１０．０％以下、
　Ｂ：０．０２０％以下、
　Ｃａ：０．００３％以下、
　ＲＥＭ：０．０５％以下、
　Ｍｇ：０．０５％以下、及び
　Ｚｒ：０．０５％以下
からなる群より選ばれる１種又は２種以上を含んでもよい。
　以下、各元素の含有量を限定した理由について説明する。 <Base steel plate>
Regarding the steel composition of the base steel sheet in the plated steel sheet for spot welding according to the present disclosure, that is, the steel plate portion other than the plated layer (hereinafter, may be referred to as "base steel sheet" or simply "base material" in the present disclosure). This will be described in detail.
The steel composition of the base steel sheet in the present disclosure is C: 0.05 to 0.70%, Si: 3.50% or less, Mn: 8.00% or less, P: 0.020% or less, S: 0. It is 050% or less, Al: 3.000% or less, and N: 0.010% or less, and the balance is composed of Fe and impurities. Further, the plated steel sheet for spot welding according to the present disclosure has a mass% as an optional element instead of a part of Fe in the steel composition of the base steel sheet.
Ti: 0.300% or less,
Nb: 0.300% or less,
V: 0.30% or less,
Cr: 5.0% or less,
Mo: 2.00% or less,
Cu: 2.00% or less,
Ni: 10.0% or less,
B: 0.020% or less,
Ca: 0.003% or less,
REM: 0.05% or less,
It may contain one or more selected from the group consisting of Mg: 0.05% or less and Zr: 0.05% or less.
Hereinafter, the reason for limiting the content of each element will be described.
Ｃ：０．０５～０．７０％
　Ｃは、鋼の焼入れ性を高め、強度向上に寄与する元素である。Ｃ含有量が０．０５％未満であると、高い引張強さが得られないので、下限を０．０５％とする。Ｃ含有量の下限は０．１０％でもよく、０．１５％でもよい。
　一方、Ｃ含有量が０．７０％を超えると、強度が向上しすぎて加工性が低下するとともに、スポット溶接したときの継手強度（以下、単に「継手強度」と記す場合がある。）も低下するので、上限を０．７０％とする。Ｃ含有量の上限は０．６５％でもよく、０．５５％でもよい。
　強度と加工性をバランスよく確保するには、Ｃ含有量は０．１５～０．５５％が好ましい。 C: 0.05 to 0.70%
C is an element that enhances the hardenability of steel and contributes to the improvement of strength. If the C content is less than 0.05%, high tensile strength cannot be obtained, so the lower limit is set to 0.05%. The lower limit of the C content may be 0.10% or 0.15%.
On the other hand, when the C content exceeds 0.70%, the strength is excessively improved and the workability is lowered, and the joint strength at the time of spot welding (hereinafter, may be simply referred to as “joint strength”) is also obtained. Since it decreases, the upper limit is set to 0.70%. The upper limit of the C content may be 0.65% or 0.55%.
In order to secure a good balance between strength and workability, the C content is preferably 0.15 to 0.55%.
Ｓｉ：３．５０％以下
　Ｓｉは、固溶強化及び組織強化により、鋼の強度を高める元素である。一方、Ｓｉ含有量が３．５０％を超えると、加工性が低下するとともに継手強度も低下するので、上限を３．５０％とする。Ｓｉ含有量の上限は２．５０％でもよいし、２．００％でもよい。
　Ｓｉ含有量の下限は特に限定されず、０％超であるが、引張強さを高める観点から、０．１０％以上とすることが好ましい。強度と加工性をバランスよく確保する観点から、Ｓｉ含有量は０．５０～２．００％がより好ましい。 Si: 3.50% or less Si is an element that enhances the strength of steel by solid solution strengthening and structure strengthening. On the other hand, if the Si content exceeds 3.50%, the workability is lowered and the joint strength is also lowered, so the upper limit is set to 3.50%. The upper limit of the Si content may be 2.50% or 2.00%.
The lower limit of the Si content is not particularly limited and is more than 0%, but is preferably 0.10% or more from the viewpoint of increasing the tensile strength. From the viewpoint of ensuring a good balance between strength and workability, the Si content is more preferably 0.50 to 2.00%.
Ｍｎ：８．００％以下
　Ｍｎは、鋼の強度を高める元素である。一方、Ｍｎ含有量が８．００％を超えると、加工性が劣化するとともに継手強度も低下するので、上限を８．００％とする。
　Ｍｎ含有量の下限は特に限定されず、０％超であるが、引張強さを高める観点から、０．５０％以上とすることが好ましい。強度と加工性をバランスよく確保する観点から、Ｍｎ含有量は１．００～４．８０％が好ましい。より好ましくは、１．５０～３．５０％である。 Mn: 8.00% or less Mn is an element that enhances the strength of steel. On the other hand, if the Mn content exceeds 8.00%, the workability deteriorates and the joint strength also decreases, so the upper limit is set to 8.00%.
The lower limit of the Mn content is not particularly limited and is more than 0%, but is preferably 0.50% or more from the viewpoint of increasing the tensile strength. From the viewpoint of ensuring a good balance between strength and workability, the Mn content is preferably 1.00 to 4.80%. More preferably, it is 1.50 to 3.50%.
Ｐ：０．０２０％以下
　Ｐは、不純物であり、脆化を起こす元素である。Ｐ含有量が０．０２０％を超えると、所要の継手強度を得ることが難しいので、上限を０．０２０％とする。 P: 0.020% or less P is an impurity and is an element that causes embrittlement. If the P content exceeds 0.020%, it is difficult to obtain the required joint strength, so the upper limit is set to 0.020%.
Ｓ：０．０５０％以下
　Ｓは、Ｐと同様に、不純物であり脆化を起こす元素である。また、Ｓは、鋼中で粗大なＭｎＳを形成し、鋼の加工性を低下させるとともに継手強度も低下させる元素である。Ｓ含有量が０．０５０％を超えると、所要の継手強度を得ることが難しく、また、鋼の加工性が低下するので、上限を０．０５０％とする。 S: 0.050% or less S is an impurity and an element that causes embrittlement, like P. Further, S is an element that forms coarse MnS in the steel, which lowers the workability of the steel and also lowers the joint strength. If the S content exceeds 0.050%, it is difficult to obtain the required joint strength, and the workability of the steel is lowered. Therefore, the upper limit is set to 0.050%.
Ａｌ：３．０００％以下
　Ａｌは、脱酸作用をなす元素であり、また、フェライトを安定化し、セメンタイトの析出を抑制する元素である。Ａｌは、脱酸、及び鋼組織の制御のため含有させるが、Ａｌは酸化し易く、Ａｌ含有量が３．０００％を超えると、介在物が増加して加工性が低下するとともに継手強度も低下するので、上限を３．０００％とする。加工性を確保する点で、好ましい上限は１．２００％である。Ａｌ含有量の下限は特に限定されず、０％超であるが、脱酸、及び鋼組織の制御のため、Ａｌ含有量の好ましい下限値は、０．００１％である。 Al: 3.000% or less Al is an element that has a deoxidizing action, and is an element that stabilizes ferrite and suppresses the precipitation of cementite. Al is contained for deoxidation and control of steel structure, but Al is easily oxidized, and when the Al content exceeds 3.000%, inclusions increase, the workability decreases, and the joint strength also increases. Since it will decrease, the upper limit will be 3.000%. In terms of ensuring workability, the preferable upper limit is 1.200%. The lower limit of the Al content is not particularly limited and is more than 0%, but the preferable lower limit of the Al content is 0.001% for deoxidation and control of the steel structure.
Ｎ：０．０１０％以下
　Ｎは、母材鋼板の強度を高める元素であるが、鋼中で粗大な窒化物を形成し、鋼の成形性を劣化させる作用をなす元素である。Ｎ含有量が０．０１０％を超えると、鋼の成形性の劣化、継手強度の低下が顕著となるので、上限を０．０１０％とする。Ｎ含有量の下限は０％超である。 N: 0.010% or less N is an element that enhances the strength of the base steel sheet, but is an element that forms coarse nitrides in the steel and deteriorates the formability of the steel. If the N content exceeds 0.010%, the formability of the steel is significantly deteriorated and the joint strength is significantly reduced. Therefore, the upper limit is set to 0.010%. The lower limit of the N content is more than 0%.
残部：Ｆｅ及び不純物
　残部は、Ｆｅ及び不純物である。不純物とは、鉱石、スクラップ等の原材料に含まれる成分、又は、製造の過程で混入する成分が例示され、意図的に母材鋼板に含有させたものではない成分を指す。 Remaining: Fe and impurities The balance is Fe and impurities. Impurities refer to components contained in raw materials such as ore and scrap, or components mixed in the manufacturing process, which are not intentionally contained in the base steel sheet.
　本開示における母材鋼板は、Ｆｅの一部に代えて上記以外の元素（任意元素）を含んでもよい。以下に本開示における母材鋼板に含み得る任意元素について説明する。以下の任意元素は含まない、すなわち含有量が０％でもよいし、含む場合の下限値は０％超であってもよい。 The base steel sheet in the present disclosure may contain an element (arbitrary element) other than the above instead of a part of Fe. The optional elements that can be contained in the base steel sheet in the present disclosure will be described below. The following optional elements may not be contained, that is, the content may be 0%, and if they are contained, the lower limit may be more than 0%.
　本開示における母材鋼板は、鋼板組織の粗大化を抑制するため、Ｆｅの一部に代えて、質量％で、
　Ｔｉ：０．３００％以下、
　Ｎｂ：０．３００％以下、及び
　Ｖ：０．３０％以下
からなる群より選ばれる１種又は２種以上を含有してもよい。 In the base steel sheet in the present disclosure, in order to suppress the coarsening of the steel sheet structure, instead of a part of Fe, the mass% is used.
Ti: 0.300% or less,
It may contain one or more selected from the group consisting of Nb: 0.300% or less and V: 0.30% or less.
Ｔｉ：０．３００％以下
　Ｔｉは、析出物を形成し、鋼板組織を細粒とする元素である。Ｔｉ含有量の下限は特に限定されないが、含有効果を得るため、０．００１％以上含有することが好ましい。より好ましくは０．０１％以上である。
　ただし、Ｔｉを過剰に含有すると、製造性が低下し、加工時に割れが生じるだけでなく継手強度の低下も起こすので、Ｔｉを含有する場合、上限は０．３００％とし、好ましくは０．２００％以下である。 Ti: 0.300% or less Ti is an element that forms a precipitate and makes the steel sheet structure into fine particles. The lower limit of the Ti content is not particularly limited, but it is preferably 0.001% or more in order to obtain the content effect. More preferably, it is 0.01% or more.
However, if Ti is contained in excess, the manufacturability is lowered and not only cracks occur during processing but also the joint strength is lowered. Therefore, when Ti is contained, the upper limit is 0.300%, preferably 0.200. % Or less.
Ｎｂ：０．３００％以下
　Ｎｂは、微細な炭窒化物を形成し結晶粒の粗大化を抑制する元素である。Ｎｂ含有量の下限は特に限定されないが、含有効果を得るため、０．００１％以上含有することが好ましい。より好ましくは０．０１０％以上である。
　ただし、Ｎｂを過剰に含有すると、靭性を阻害し製造困難になるだけでなく継手強度の低下を引き起こすため、Ｎｂを含有する場合、上限は０．３００％とし、好ましくは０．２００％以下である。 Nb: 0.300% or less Nb is an element that forms fine carbonitrides and suppresses the coarsening of crystal grains. The lower limit of the Nb content is not particularly limited, but it is preferably 0.001% or more in order to obtain the content effect. More preferably, it is 0.010% or more.
However, if Nb is contained in an excessive amount, not only the toughness is impaired and the manufacturing becomes difficult, but also the joint strength is lowered. Therefore, when Nb is contained, the upper limit is 0.300%, preferably 0.200% or less. be.
Ｖ：０．３０％以下
　Ｖは、微細な炭窒化物を形成し結晶粒の粗大化を抑制する元素である。Ｖを含有する場合、含有効果を得るため、０．００１％以上含有することが好ましい。より好ましくは０．０３％以上である。
　ただし、Ｖを過剰に含有すると、靭性を阻害し製造困難になるだけでなく継手強度の低下を引き起こすため、上限を０．３０％とすることが好ましく、より好ましくは０．２５％以下である。 V: 0.30% or less V is an element that forms fine carbonitrides and suppresses the coarsening of crystal grains. When V is contained, it is preferably contained in an amount of 0.001% or more in order to obtain a content effect. More preferably, it is 0.03% or more.
However, if V is excessively contained, not only the toughness is impaired and the manufacturing becomes difficult, but also the joint strength is lowered. Therefore, the upper limit is preferably 0.30%, more preferably 0.25% or less. ..
Ｃｒ：５．０％以下
Ｍｏ：２．００％以下
　本開示における母材鋼板は、鋼の強度の向上のため、Ｆｅの一部に代えて、質量％で、Ｃｒ：５．０％以下及びＭｏ：２．００％以下の１種又は２種を含有してもよい。
　Ｃｒ及びＭｏは、鋼の強度の向上に寄与する元素である。Ｃｒ又はＭｏを含有する場合、含有効果を得るため、０．００１％以上含有することが好ましい。より好ましくは０．０５％以上である。
　ただし、Ｃｒ含有量が５．０％を超えると、又はＭｏ含有量が２．００％を超えると、酸洗時や熱間加工時に支障が生じることがあるだけでなく、継手強度の低下を招く。そのため、Ｃｒ含有量の上限は５．０％とし、好ましくは３．０％以下であり、Ｍｏ含有量の上限は２．００％とし、好ましくは１．００％である。 Cr: 5.0% or less Mo: 2.00% or less In order to improve the strength of the steel, the base steel sheet in the present disclosure has a mass% of Cr: 5.0% or less instead of a part of Fe. Mo: 1 or 2 types of 2.00% or less may be contained.
Cr and Mo are elements that contribute to the improvement of steel strength. When Cr or Mo is contained, it is preferably contained in an amount of 0.001% or more in order to obtain a content effect. More preferably, it is 0.05% or more.
However, if the Cr content exceeds 5.0% or the Mo content exceeds 2.00%, not only may problems occur during pickling and hot working, but also the joint strength may decrease. Invite. Therefore, the upper limit of the Cr content is 5.0%, preferably 3.0% or less, and the upper limit of the Mo content is 2.00%, preferably 1.00%.
Ｃｕ：２．００％以下
Ｎｉ：１０．０％以下
　本開示における母材鋼板は、鋼の強度向上のため、Ｆｅの一部に代えて、質量％で、Ｃｕ：２．００％以下及びＮｉ：１０．０％以下の１種又は２種を含有してもよい。
　Ｃｕ及びＮｉは、鋼の強度の向上に寄与する元素である。Ｃｕ又はＮｉを含有する場合、含有効果を得るため、合計で０．００１％以上含有することが好ましい。より好ましくは０．１０％以上である。
　ただし、Ｃｕ含有量が２．００％を超えると、又はＮｉ含有量が１０．０％を超えると、酸洗時や熱間加工時に支障が生じることがあるだけでなく継手強度の低下を招くことがある。そのため、Ｃｕ含有量の上限は２．００％とし、好ましくは１．５０％以下であり、Ｎｉ含有量の上限は１０．０％とし、好ましくは７．０％以下である。 Cu: 2.00% or less Ni: 10.0% or less The base steel sheet in the present disclosure has Cu: 2.00% or less and Ni in mass% instead of a part of Fe in order to improve the strength of the steel. 1 or 2 types of 10.0% or less may be contained.
Cu and Ni are elements that contribute to the improvement of steel strength. When Cu or Ni is contained, it is preferable to contain 0.001% or more in total in order to obtain the content effect. More preferably, it is 0.10% or more.
However, if the Cu content exceeds 2.00% or the Ni content exceeds 10.0%, not only may problems occur during pickling and hot working, but also the joint strength may decrease. Sometimes. Therefore, the upper limit of the Cu content is 2.00%, preferably 1.50% or less, and the upper limit of the Ni content is 10.0%, preferably 7.0% or less.
　本開示における母材鋼板は、熱間圧延工程における成形性の向上のため、Ｆｅの一部に代えて、質量％で、
　Ｃａ：０．００３％以下、
　ＲＥＭ０．０５％以下、
　Ｍｇ：０．０５％以下、及び
　Ｚｒ：０．０５％以下からなる群より選ばれる１種又は２種以上を含有してもよい。 In order to improve the formability in the hot rolling process, the base steel sheet in the present disclosure is divided into% by mass instead of a part of Fe.
Ca: 0.003% or less,
REM 0.05% or less,
It may contain one or more selected from the group consisting of Mg: 0.05% or less and Zr: 0.05% or less.
　Ｃａ、ＲＥＭ（ｒａｒｅ　ｅａｒｔｈ　ｍｅｔａｌ）、Ｍｇ、及びＺｒは、脱酸後の酸化物や、熱間圧延鋼板中に存在する硫化物を微細化し、成形性の向上に寄与する元素である。ただし、Ｃａの含有量が０．００３％を超え、ＲＥＭの含有量が０．０５％を超え、又は、Ｍｇ若しくはＺｒの各含有量が０．０５％を超えると、鋼の加工性が低下する。そのため、Ｃａ含有量の上限を０．００３％とし、ＲＥＭ含有量の上限を０．０５％とし、Ｍｇ及びＺｒの各含有量の上限を０．０５％とすることが好ましい。
　Ｃａ、ＲＥＭ、Ｍｇ、及びＺｒのうち少なくとも１種の元素を含有する場合、含有効果を得るため、Ｃａは０．０００５％以上、ＲＥＭは０．００１％以上、Ｍｇは０．００１％以上、Ｚｒは０．００１％以上とすることが好ましい。 Ca, REM (rare earth metal), Mg, and Zr are elements that contribute to the improvement of formability by refining oxides after deoxidation and sulfides existing in hot-rolled steel sheets. However, if the Ca content exceeds 0.003%, the REM content exceeds 0.05%, or the Mg or Zr content exceeds 0.05%, the workability of the steel deteriorates. do. Therefore, it is preferable that the upper limit of the Ca content is 0.003%, the upper limit of the REM content is 0.05%, and the upper limit of each content of Mg and Zr is 0.05%.
When at least one element of Ca, REM, Mg, and Zr is contained, Ca is 0.0005% or more, REM is 0.001% or more, and Mg is 0.001% or more in order to obtain the content effect. Zr is preferably 0.001% or more.
　「ＲＥＭ」とはＳｃ、Ｙ、及びランタノイドの合計１７元素の総称であり、ＲＥＭの含有量はＲＥＭのうちの１種又は２種以上の元素の合計含有量を指す。また、ＲＥＭについては一般的にミッシュメタルに含有される。このため、例えば、ＲＥＭは、ＲＥＭ含有量が上記の範囲となるように、ミッシュメタルの形で含有させてもよい。 "REM" is a general term for a total of 17 elements of Sc, Y, and lanthanoids, and the content of REM refers to the total content of one or more elements of REM. Further, REM is generally contained in mischmetal. Therefore, for example, REM may be contained in the form of misch metal so that the REM content is within the above range.
Ｂ：０．０２０％以下
　本開示における母材鋼板は、Ｆｅの一部に代えて、質量％で、Ｂ：０．０２０％以下を含んでもよい。
　Ｂは、粒界に偏析して粒界強度を高める元素である。Ｂを含有する場合、含有効果を得るため、０．０００１％以上含有することが好ましく、より好ましくは０．０００８％以上である。
　一方、Ｂを過剰に含有すると靭性を阻害し製造困難になるだけでなく継手の強度低下を引き起こすため、Ｂ含有量の上限を０．０２０％とし、好ましくは０．０１０％以下である。 B: 0.020% or less The base steel sheet in the present disclosure may contain B: 0.020% or less in mass% instead of a part of Fe.
B is an element that segregates at the grain boundaries to increase the grain boundary strength. When B is contained, it is preferably 0.0001% or more, more preferably 0.0008% or more, in order to obtain the content effect.
On the other hand, if B is excessively contained, not only the toughness is impaired and the manufacturing becomes difficult, but also the strength of the joint is lowered. Therefore, the upper limit of the B content is 0.020%, preferably 0.010% or less.
　本開示における母材鋼板は、表層における内部酸化層の厚みが５．０μｍ未満である。内部酸化層とは、結晶粒界の少なくとも一部が酸化物に被覆されている層を意味する。内部酸化層の厚みが５．０μｍ未満とは、厚みが０μｍ、すなわち内部酸化層が形成されていない場合も含まれる。
　母材鋼板の表層部における内部酸化層の有無の確認及び厚さの測定は、厚さ方向の断面をＳＥＭ観察によって行うことができる。具体的な観察方法は、実施例において説明する。 In the base steel sheet in the present disclosure, the thickness of the internal oxide layer on the surface layer is less than 5.0 μm. The internal oxide layer means a layer in which at least a part of the grain boundaries is covered with an oxide. The thickness of the internal oxide layer of less than 5.0 μm includes the case where the thickness is 0 μm, that is, the internal oxide layer is not formed.
The presence or absence of the internal oxide layer on the surface layer of the base steel sheet and the measurement of the thickness can be performed by observing the cross section in the thickness direction by SEM observation. A specific observation method will be described in Examples.
　本開示における母材鋼板の厚みは特に限定されず、スポット溶接した後の用途に応じて選択することができる。母材鋼板の板厚は、例えば１．０～３．５ｍｍが挙げられるが、この範囲に限定されるものではない。 The thickness of the base steel sheet in the present disclosure is not particularly limited and can be selected according to the application after spot welding. The thickness of the base steel sheet is, for example, 1.0 to 3.5 mm, but is not limited to this range.
＜めっき層＞
　本開示に係るスポット溶接用めっき鋼板は、上記鋼組成を有する母材鋼板の片面又は両面に１層又は２層以上のめっき層が形成されており、めっき層の少なくとも一部としてＺｎ及びＮｉを含み、かつめっき層全体でのＮｉ含有量が２．０質量％以上である。 <Plating layer>
The plated steel sheet for spot welding according to the present disclosure has one or more plated layers formed on one side or both sides of the base steel sheet having the above steel composition, and Zn and Ni are used as at least a part of the plated layers. It is contained, and the Ni content in the entire plating layer is 2.0% by mass or more.
　本開示に係るスポット溶接用めっき鋼板におけるめっき層は、めっき層の少なくとも一部としてＺｎ及びＮｉを含み、かつ、めっき層全体でのＮｉ含有量が２．０質量％以上であれば、めっき層の層構成は特に限定されない。
　例えば、めっき層が１層であれば、ＺｎとＮｉを含み、Ｎｉ含有量が２．０質量％以上であるＺｎ－Ｎｉ含有めっき層とする。Ｚｎ－Ｎｉ含有めっき層は、Ｚｎ及びＮｉ以外の金属元素を含んでもよい。
　めっき層が２層以上であれば、少なくとも１層がＺｎを含むＺｎ含有めっき層であり、少なくとも１層がＮｉを含むＮｉ含有めっき層であり、２層以上のめっき層全体でのＮｉ含有量が２．０質量％以上である。Ｎｉ含有めっき層はＮｉ以外の金属元素を含んでもよく、例えば、ＮｉとＺｎを含有するＺｎ－Ｎｉ含有めっき層であってもよい。Ｚｎ含有めっき層も同様である。
　２層以上のめっき層として例えば、以下のような組み合わせが挙げられるが、これらの組み合わせに限定されない。
　Ｎｉ含有めっき層とＺｎ含有めっき層との組み合わせ
　Ｎｉ含有めっき層とＺｎ－Ｎｉ含有めっき層との組み合わせ
　Ｚｎ含有めっき層とＺｎ－Ｎｉ含有めっき層との組み合わせ
　Ｎｉ含有めっき層とＺｎ含有めっき層とＺｎ－Ｎｉ含有めっき層との組み合わせ The plating layer in the plated steel sheet for spot welding according to the present disclosure contains Zn and Ni as at least a part of the plating layer, and the Ni content in the entire plating layer is 2.0% by mass or more. The layer structure of is not particularly limited.
For example, if the plating layer is one layer, it is a Zn—Ni-containing plating layer containing Zn and Ni and having a Ni content of 2.0% by mass or more. The Zn—Ni-containing plating layer may contain a metal element other than Zn and Ni.
If the number of plating layers is two or more, at least one layer is a Zn-containing plating layer containing Zn, and at least one layer is a Ni-containing plating layer containing Ni, and the Ni content in the entire two or more plating layers. Is 2.0% by mass or more. The Ni-containing plating layer may contain a metal element other than Ni, and may be, for example, a Zn—Ni-containing plating layer containing Ni and Zn. The same applies to the Zn-containing plating layer.
Examples of the two or more plating layers include, but are not limited to, the following combinations.
Combination of Ni-containing plating layer and Zn-containing plating layer Combination of Ni-containing plating layer and Zn-Ni-containing plating layer Combination of Zn-containing plating layer and Zn-Ni-containing plating layer Ni-containing plating layer and Zn-containing plating layer Combination with Zn-Ni-containing plating layer
　めっき層全体でのＺｎ含有量は特に限定されないが、高い防食作用を発揮させる観点から、めっき層全体でのＺｎ含有量は３０質量％以上であることが好ましく、５０質量％以上であることがさらに好ましい。めっき層全体でのＺｎ含有量の上限は９８質量％である。
　一方、めっき層全体でのＮｉ含有量は、スポット溶接時のＬＭＥ割れの発生をより効果的に抑制する観点から、５質量％以上であることが好ましく、１０質量％以上であることがより好ましい。また、防食作用を考慮してめっき層全体でのＺｎ含有量を上記好ましい範囲とする観点から、めっき層全体でのＮｉ含有量は７０質量％以下であることが好ましく、５０質量％以下であることがより好ましい。めっき層全体では、２．０質量％≦Ｎｉ含有量＜Ｚｎ含有量であることが好ましい。 The Zn content in the entire plating layer is not particularly limited, but from the viewpoint of exerting a high anticorrosion effect, the Zn content in the entire plating layer is preferably 30% by mass or more, preferably 50% by mass or more. More preferred. The upper limit of the Zn content in the entire plating layer is 98% by mass.
On the other hand, the Ni content in the entire plating layer is preferably 5% by mass or more, more preferably 10% by mass or more, from the viewpoint of more effectively suppressing the occurrence of LME cracks during spot welding. .. Further, from the viewpoint of setting the Zn content in the entire plating layer to the above preferable range in consideration of the anticorrosion effect, the Ni content in the entire plating layer is preferably 70% by mass or less, preferably 50% by mass or less. Is more preferable. It is preferable that 2.0% by mass ≤ Ni content <Zn content in the entire plating layer.
　本開示に係るスポット溶接用めっき鋼板の層構成として、母材鋼板側から例えば以下のような層構成が挙げられる。
（１）母材鋼板／Ｚｎ－Ｎｉ含有めっき層
（２）母材鋼板／Ｎｉ含有めっき層／Ｚｎ含有めっき層
（３）母材鋼板／Ｚｎ含有めっき層／Ｎｉ含有めっき層
（４）母材鋼板／Ｎｉ含有めっき層／Ｚｎ含有めっき層／Ｎｉ含有めっき層
（５）母材鋼板／Ｎｉ含有めっき層／Ｚｎ－Ｎｉ含有めっき層
　本開示に係るスポット溶接用めっき鋼板は、上記層構成に限定されるものではないが、上記層構成（１）～（５）のうち、母材鋼板に近い層でＮｉの濃度を高めるとよりスポット溶接時の耐ＬＭＥの効果（ＬＭＥ割れの発生を抑制する効果）が高まる場合があるという観点から（２）、（４）、及び（５）が好ましく、スポット溶接時に組み合わせる鋼板（相手材）が、めっきのない冷延鋼板である場合の相手材でのＬＭＥ割れを防ぐ観点からは（３）及び（４）が好ましい。 As the layer structure of the plated steel sheet for spot welding according to the present disclosure, for example, the following layer structure can be mentioned from the base steel sheet side.
(1) Base material steel plate / Zn-Ni-containing plating layer (2) Base material steel plate / Ni-containing plating layer / Zn-containing plating layer (3) Base material steel plate / Zn-containing plating layer / Ni-containing plating layer (4) Base material Steel plate / Ni-containing plating layer / Zn-containing plating layer / Ni-containing plating layer (5) Base steel plate / Ni-containing plating layer / Zn-Ni-containing plating layer The plated steel plate for spot welding according to the present disclosure is limited to the above layer structure. However, if the Ni concentration is increased in the layer close to the base steel plate among the above layer configurations (1) to (5), the effect of LME resistance during spot welding (suppressing the occurrence of LME cracking) (2), (4), and (5) are preferable from the viewpoint that the effect) may be enhanced, and when the steel plate (counterpart material) to be combined at the time of spot welding is a cold-rolled steel plate without plating, the mating material is used. From the viewpoint of preventing LME cracking, (3) and (4) are preferable.
　各めっき層のめっき量は特に限定されず、スポット溶接後の用途、要求される性能等に応じて選択することができる。鋼板の各面におけるめっき層全体でのめっき量は、３ｍｇ／ｍ２以上であることが好ましく、溶接時のブローホールなどの欠陥の発生を抑制する観点から、８００ｇ／ｍ２以下であることが好ましい。
　また、めっきの目的である防食作用を発揮させる観点から、Ｚｎのめっき量が最も多いことが好ましい。めっき層全体が１層のＺｎ－Ｎｉ含有めっき層であればＮｉ含有量よりもＺｎ含有量を多くすることが好ましく、２層以上のめっき層を形成する場合は、Ｚｎを含むめっき層をめっき量が最も多い主めっきとすることが好ましい。本開示において、Ｚｎ含有めっき層を「主めっき」とし、主めっきの前に形成するめっきを「プレめっき」、主めっきの後に形成するめっき層を「後めっき」と記す場合がある。 The plating amount of each plating layer is not particularly limited, and can be selected according to the application after spot welding, the required performance, and the like. The plating amount of the entire plating layer on each surface of the steel sheet is preferably 3 mg / m 2 or more, and is 800 g / m 2 or less from the viewpoint of suppressing the occurrence of defects such as blow holes during welding. preferable.
Further, from the viewpoint of exerting the anticorrosion effect which is the purpose of plating, it is preferable that the amount of Zn plated is the largest. If the entire plating layer is a single Zn-Ni-containing plating layer, it is preferable to increase the Zn content rather than the Ni content. When forming two or more plating layers, the Zn-containing plating layer is plated. It is preferable to use the main plating having the largest amount. In the present disclosure, the Zn-containing plating layer may be referred to as "main plating", the plating formed before the main plating may be referred to as "pre-plating", and the plating layer formed after the main plating may be referred to as "post-plating".
　各めっき層の種類（めっき層の形成方法）は特に限定されないが、溶融めっき又は電気めっきが好適である。
　各めっき層は、Ｎｉ及びＺｎの一方又は両方を含むが、他の金属元素を含んでもよい。めっき層に含み得る他の金属元素としては、Ａｌ、Ｍｇ、Ｆｅなどが挙げられる。
　また、２層以上のめっき層のうち一部のめっき層にはＺｎもＮｉも含まれていない場合でも、他のめっき層にはＺｎ及びＮｉが含まれており、かつＺｎ及びＮｉを含まないめっき層も含めためっき層全体でのＮｉ含有量が２．０質量％以上であってもよい。 The type of each plating layer (method of forming the plating layer) is not particularly limited, but hot-dip plating or electroplating is preferable.
Each plating layer contains one or both of Ni and Zn, but may also contain other metallic elements. Examples of other metal elements that can be contained in the plating layer include Al, Mg, and Fe.
Further, even if some of the two or more plating layers do not contain Zn or Ni, the other plating layers contain Zn and Ni and do not contain Zn and Ni. The Ni content of the entire plating layer including the plating layer may be 2.0% by mass or more.
　本開示に係るスポット溶接用めっき鋼板は、合金化熱処理が施されていてもよい。めっき層の合金化熱処理が施されていれば、加工時に亜鉛めっきが工具に付着することを抑制することができる。合金化熱処理は通常の方法を適用することができる。例えば、Ｚｎ含有めっき層を形成した後、加熱することで合金化溶融亜鉛めっき鋼板とし、さらにめっき層全体でＮｉ含有量が２．０質量％以上となるようにＮｉ含有めっき層を形成してもよい。あるいは、Ｎｉ含有量が２．０質量％以上となるように、Ｚｎ－Ｎｉ含有めっき層を形成した後、又は、Ｎｉ含有めっき層とＺｎ含有めっき層を形成した後、熱処理して合金化してもよい。 The plated steel sheet for spot welding according to the present disclosure may be subjected to alloying heat treatment. If the alloying heat treatment of the plating layer is applied, it is possible to prevent the zinc plating from adhering to the tool during processing. The usual method can be applied to the alloying heat treatment. For example, after forming a Zn-containing plating layer, it is heated to form an alloyed hot-dip galvanized steel sheet, and further, a Ni-containing plating layer is formed so that the Ni content of the entire plating layer is 2.0% by mass or more. May be good. Alternatively, after forming a Zn—Ni-containing plating layer so that the Ni content is 2.0% by mass or more, or after forming a Ni-containing plating layer and a Zn-containing plating layer, heat treatment is performed to alloy them. May be good.
　一方、めっき層を形成した後の合金化熱処理は、製造工程が増え、製造コストの上昇を招く。また、合金化熱処理によって母材鋼板の焼戻しが進んでしまい、高い引張強さを得にくくなる可能性がある。また、スポット溶接時のＬＭＥ割れの発生抑制（耐ＬＭＥ特性）のため、めっき層の母材鋼板と接する部分でＮｉがより高濃度になることが望ましい。そのため、合金化熱処理によるＮｉの拡散をしない方がより高い耐ＬＭＥ特性を発揮し易い。
　そのため、合金化熱処理を行わないスポット溶接用めっき鋼板（スポット溶接用非合金化めっき鋼板）とすることも好ましい。 On the other hand, the alloying heat treatment after forming the plating layer increases the number of manufacturing processes and causes an increase in manufacturing cost. In addition, the alloying heat treatment may promote tempering of the base steel sheet, making it difficult to obtain high tensile strength. Further, in order to suppress the occurrence of LME cracks during spot welding (LME resistance characteristics), it is desirable that the concentration of Ni is higher at the portion of the plating layer in contact with the base steel plate. Therefore, it is easier to exhibit higher LME resistance characteristics when Ni is not diffused by the alloying heat treatment.
Therefore, it is also preferable to use a spot welded galvanized steel sheet (non-alloyed galvanized steel sheet for spot welding) that is not subjected to alloying heat treatment.
　本開示におけるめっき層は、母材鋼板の片面に形成されていてもよいし、両面に形成されていてもよい。例えば亜鉛めっき鋼板を２枚重ねてスポット溶接を行った場合、溶接部側の亜鉛めっきが溶融してＬＭＥ割れが発生し易いが、電極が接触する側の面（亜鉛めっき鋼板の外側面）の亜鉛めっきが溶融してＬＭＥ割れが発生する場合もある。そのため、母材鋼板の両面に亜鉛めっき層を形成したスポット溶接用めっき鋼板とする場合は、それぞれの面においてめっき層全体でのＮｉ含有量が２．０質量％以上であることが好ましい。 The plating layer in the present disclosure may be formed on one side of the base steel plate or may be formed on both sides. For example, when two zinc-plated steel plates are stacked and spot-welded, the zinc plating on the welded portion melts and LME cracks are likely to occur, but the surface on the side where the electrodes contact (outer surface of the zinc-plated steel plate). In some cases, the zinc plating melts and LME cracking occurs. Therefore, in the case of a spot-welded plated steel sheet in which zinc-plated layers are formed on both sides of the base steel sheet, it is preferable that the Ni content of the entire plated layer on each surface is 2.0% by mass or more.
＜引張強さ＞
　本開示に係るスポット溶接用めっき鋼板は、引張強さが７８０ＭＰａ以上である。これにより、本開示に係るスポット溶接用めっき鋼板を用いてスポット溶接によって接合部材（スポット溶接継手）を製造した場合に接合強度（継手強度）が高く、高強度の接合部材を得ることができる。
　本開示に係るスポット溶接用めっき鋼板の引張強さは、好ましくは９８０ＭＰａ以上であり、より好ましくは１１８０ＭＰａ以上であり、さらに好ましくは１４７０ＭＰａ以上である。 <Tensile strength>
The plated steel sheet for spot welding according to the present disclosure has a tensile strength of 780 MPa or more. As a result, when a joint member (spot welded joint) is manufactured by spot welding using the spot-welded plated steel sheet according to the present disclosure, the joint strength (joint strength) is high, and a high-strength joint member can be obtained.
The tensile strength of the spot-welded plated steel sheet according to the present disclosure is preferably 980 MPa or more, more preferably 1180 MPa or more, and further preferably 1470 MPa or more.
　本開示に係るスポット溶接用めっき鋼板の引張強さは、ＪＩＳ５号の引張試験片を作製してＪＩＳ Ｚ ２２４１：２０１１に準拠して引張試験を行い、引張強さを測定した値である。 The tensile strength of the spot-welded plated steel sheet according to the present disclosure is a value obtained by preparing a tensile test piece of JIS No. 5 and performing a tensile test in accordance with JIS Z2241: 2011, and measuring the tensile strength.
［スポット溶接用めっき鋼板の製造方法］
　本開示に係るスポット溶接用めっき鋼板の製造方法は特に限定されない。
　めっき層を形成する前の母材鋼板は、前述した鋼組成を有していれば、熱延鋼板でも冷延鋼板でもよい。鋼組織も特に限定されない。ただし、熱延鋼板又は冷延鋼板のいずれの鋼板を用いる場合でも、表層部における内部酸化層の厚さが５．０μｍ未満である鋼板を用いる。
　また、めっき層を形成した後のスポット溶接用めっき鋼板の引張強さを７８０ＭＰａ以上とする観点から、めっき層を形成する前の母材鋼板の引張強さも７８０ＭＰａ以上であることが好ましい。 [Manufacturing method of plated steel sheet for spot welding]
The method for manufacturing a plated steel sheet for spot welding according to the present disclosure is not particularly limited.
The base steel sheet before forming the plating layer may be either a hot-rolled steel sheet or a cold-rolled steel sheet as long as it has the above-mentioned steel composition. The steel structure is also not particularly limited. However, regardless of whether a hot-rolled steel sheet or a cold-rolled steel sheet is used, a steel sheet having an internal oxide layer thickness of less than 5.0 μm in the surface layer portion is used.
Further, from the viewpoint that the tensile strength of the spot-welded plated steel sheet after forming the plating layer is 780 MPa or more, the tensile strength of the base steel sheet before forming the plated layer is also preferably 780 MPa or more.
　めっき層を形成する前の母材鋼板は、例えば、以下の方法によって製造することができる。
　まず、転炉で上述した鋼組成に調整された鋼を溶製して連続鋳造法によりスラブとし、スラブを高温状態のまま、あるいは、室温まで冷却した後、加熱炉に挿入し、１１００～１３００℃の温度範囲で加熱し、その後、８００～９５０℃の温度範囲で仕上げ圧延を行う。仕上げ圧延温度から５００～６５０℃まで水冷し、その後空冷する。
　次いで、冷間圧延によって所望の厚みを有する鋼板にする。 The base steel sheet before forming the plating layer can be manufactured, for example, by the following method.
First, steel adjusted to the above-mentioned steel composition is melted in a converter to form a slab by a continuous casting method, and the slab is kept at a high temperature or cooled to room temperature and then inserted into a heating furnace for 1100-1300. It is heated in a temperature range of ° C., and then finish rolling is performed in a temperature range of 800 to 950 ° C. It is water-cooled from the finish rolling temperature to 500 to 650 ° C., and then air-cooled.
Then, cold rolling is performed to obtain a steel sheet having a desired thickness.
　冷間圧延後、熱処理を行う。熱処理は７５０～８５０℃まで１０～１００℃／ｓｅｃで加熱し、その後、冷却や再加熱などの熱処理を行う。
　以上の工程を経て、引張強さが７８０ＭＰａ以上であり、表層部における内部酸化層の厚さが５．０μｍ未満である母材鋼板を製造することができる。 After cold rolling, heat treatment is performed. The heat treatment is performed by heating at 10 to 100 ° C./sec from 750 to 850 ° C., and then performing heat treatment such as cooling and reheating.
Through the above steps, a base steel sheet having a tensile strength of 780 MPa or more and a thickness of the internal oxide layer in the surface layer portion of less than 5.0 μm can be produced.
　上記の鋼組成を有し、内部酸化層の厚みが５μｍ未満である母材鋼板の片面又は両面に、めっき層の少なくとも一部としてＺｎ及びＮｉを含み、めっき層全体でのＮｉ含有量が２．０質量％以上となる１層又は２層以上のめっき層を形成する。各めっき層は、溶融めっき又は電気めっきによって形成することができ、めっき層を形成した後、必要に応じて合金化熱処理を行ってもよい。
　めっき工程は、無酸化炉を有する連続式めっき設備でも無酸化炉を有しない連続式めっき設備でもめっき可能である。
　また、めっき層表面に無機系化合物又は有機系化合物の皮膜などを形成してもよい。 Zn and Ni are contained as at least a part of the plating layer on one side or both sides of the base steel sheet having the above steel composition and the thickness of the internal oxide layer is less than 5 μm, and the Ni content in the entire plating layer is 2. A plating layer having one layer or two or more layers having a weight of 0.0% by mass or more is formed. Each plating layer can be formed by hot-dip plating or electroplating, and after forming the plating layer, alloying heat treatment may be performed if necessary.
The plating step can be performed by either a continuous plating facility having a non-oxidizing furnace or a continuous plating facility not having a non-oxidizing furnace.
Further, a film of an inorganic compound or an organic compound may be formed on the surface of the plating layer.
［接合部材の製造方法］
（第１実施形態）
　本開示の第１実施形態に係る接合部材の製造方法は、前述した本開示に係るスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組とする工程と、
　前記板組を一対の電極で板厚方向に挟み込んで加圧しながら通電してスポット溶接を行う工程と、
　を含む接合部材の製造方法である。 [Manufacturing method of joining members]
(First Embodiment)
The method for manufacturing a joining member according to the first embodiment of the present disclosure includes a step of forming a plate assembly in which two or more plate materials including the above-mentioned spot welding plated steel plate according to the present disclosure are laminated.
A process in which the plate assembly is sandwiched between a pair of electrodes in the plate thickness direction and energized while pressurizing to perform spot welding.
It is a manufacturing method of a joining member including.
　図２は、２枚のめっき鋼板を重ねた板組に対してスポット溶接を行った場合に形成される接合部（ナゲット）の一例を概略的に示している。図２に示すように、スポット溶接用めっき鋼板１Ａ，１Ｂを重ね合わせた板組を板厚方向に挟み込むように電極２Ａ、２Ｂを押し当てた状態のまま、電極２Ａと電極２Ｂの間で通電を行う。これによりめっき鋼板１Ａとめっき鋼板１Ｂとの通電部にはナゲット１３及び熱影響部（いわゆるＨＡＺ）１４が形成され、両鋼板が溶接された接合部材となる。 FIG. 2 schematically shows an example of a joint portion (nugget) formed when spot welding is performed on a plate set in which two plated steel plates are stacked. As shown in FIG. 2, the electrodes 2A and 2B are pressed against each other so as to sandwich the plate assembly in which the plated steel plates 1A and 1B for spot welding are overlapped in the plate thickness direction, and electricity is supplied between the electrodes 2A and 2B. I do. As a result, a nugget 13 and a heat-affected zone (so-called HAZ) 14 are formed in the energized portion between the plated steel plate 1A and the plated steel plate 1B, and both steel plates are welded to form a joining member.
　板組を構成する２枚以上の板材は、少なくとも１枚が本開示に係るスポット溶接用めっき鋼板であればよい。スポット溶接時のＬＭＥ割れを抑制する観点から、板組を構成する２枚以上の板材は、いずれも本開示に係るスポット溶接用めっき鋼板であることが好ましいが、本開示に係るスポット溶接用めっき鋼板と他の鋼板、例えばめっき層のない冷延鋼板との板組でもよいし、アルミニウム板などの鋼板以外の金属板との板組であってもよい。
　スポット溶接の条件（電流値、通電時間など）は特に限定されず、通常の条件を適用することができる。 At least one of the two or more plate materials constituting the plate assembly may be a plated steel plate for spot welding according to the present disclosure. From the viewpoint of suppressing LME cracking during spot welding, it is preferable that the two or more plate materials constituting the plate assembly are all the plated steel plates for spot welding according to the present disclosure, but the plating for spot welding according to the present disclosure. It may be a plate assembly of a steel plate and another steel plate, for example, a cold-welded steel plate without a plating layer, or a plate assembly with a metal plate other than the steel plate such as an aluminum plate.
The conditions for spot welding (current value, energization time, etc.) are not particularly limited, and ordinary conditions can be applied.
　本開示に係るスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組としてスポット溶接によって接合することで、防食作用を有し、高強度であり、スポット溶接で形成されたナゲット１３や熱影響部１４におけるＬＭＥ割れが抑制された接合部材を得ることができる。そのため、本開示に係るスポット溶接用めっき鋼板及びそれを用いてスポット溶接を行った接合部材は、例えば、自動車の車体部品や建築物の構造体など、スポット溶接を利用した様々な構造部品の製造に適用することが可能である。本開示に係る接合部材は、特に自動車用部材に好適である。自動車用部材の種類は特に限定されない。 A nugget 13 having anticorrosion action, high strength, and formed by spot welding by joining by spot welding as a plate assembly in which two or more plate materials including a plated steel plate for spot welding according to the present disclosure are laminated. It is possible to obtain a joint member in which LME cracking in the heat-affected zone 14 is suppressed. Therefore, the plated steel sheet for spot welding and the joining member to which spot welding is performed using the plated steel plate for spot welding according to the present disclosure are manufactured of various structural parts using spot welding, for example, vehicle body parts of automobiles and structures of buildings. It is possible to apply to. The joining member according to the present disclosure is particularly suitable for an automobile member. The type of automobile member is not particularly limited.
（第２実施形態）
　本開示の第２実施形態に係る接合部材の製造方法は、前述した鋼組成を有し、結晶粒界の少なくとも一部が酸化物に被覆されている内部酸化層の厚みが、表面から深さ５．０μｍ未満である母材鋼板の片面又は両面にＺｎ含有めっき層が形成されており、引張強さが７８０ＭＰ以上であるスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組とする工程と、
　Ｎｉを含む箔であって、前記箔が配置された領域において前記めっき層及び前記箔の全体でのＮｉ含有量が２．０質量％以上となる前記箔を、前記スポット溶接用めっき鋼板の前記めっき層が形成されている面に配置する工程と、
　前記箔が配置された領域において前記板組を一対の電極で板厚方向に挟み込んで加圧しながら通電してスポット溶接を行う工程と、
　を含む接合部材の製造方法である。 (Second Embodiment)
The method for producing a welded member according to the second embodiment of the present disclosure has the above-mentioned steel composition, and the thickness of the internal oxide layer in which at least a part of the crystal grain boundary is covered with an oxide is deep from the surface. A Zn-containing plated layer is formed on one side or both sides of a base steel sheet having a tensile strength of less than 5.0 μm, and a plate set in which two or more sheets including a plated steel sheet for spot welding having a tensile strength of 780 MP or more are laminated. And the process of
The foil containing Ni and having a Ni content of 2.0% by mass or more in the plating layer and the entire foil in the region where the foil is arranged is the foil of the plated steel sheet for spot welding. The process of arranging on the surface where the plating layer is formed and
In the region where the foil is arranged, the plate assembly is sandwiched between a pair of electrodes in the plate thickness direction and energized while pressurizing to perform spot welding.
It is a manufacturing method of a joining member including.
　すなわち、本開示の第２実施形態に係る接合部材の製造方法は、前述した本開示に係るスポット溶接用めっき鋼板におけるＮｉ含有めっき層の代わりにＮｉ含有箔を用いるものである。Ｎｉ含有箔をスポット溶接用めっき鋼板のＺｎ含有めっき層が形成されている面に配置し、Ｎｉ含有箔を配置した領域においてＺｎ含有めっき層及びＮｉ含有箔の全体でのＮｉ含有量を２．０質量％以上とした状態でスポット溶接を行うことで、ＬＭＥ割れを効果的に抑制することができる。
　Ｎｉ含有箔を配置した領域においてＺｎ含有めっき層及びＮｉ含有箔の全体でのＮｉ含有量が２．０質量％以上であれば、Ｚｎ含有めっき層にはＺｎ以外の金属元素が含まれていてもよいし、Ｎｉ含有箔にはＮｉ以外の金属元素が含まれていてもよい。
　第２実施形態に係る接合部材の製造方法もスポット溶接の条件（電流値、通電時間など）は特に限定されず、通常の条件を適用することができる。 That is, in the method for manufacturing a joining member according to the second embodiment of the present disclosure, a Ni-containing foil is used instead of the Ni-containing plating layer in the above-mentioned spot welding plated steel sheet according to the present disclosure. 2. The Ni-containing foil is placed on the surface of the spot-welded plated steel plate on which the Zn-containing plating layer is formed, and the total Ni content of the Zn-containing plating layer and the Ni-containing foil is determined in the region where the Ni-containing foil is placed. By performing spot welding in a state of 0% by mass or more, LME cracking can be effectively suppressed.
If the total Ni content of the Zn-containing plating layer and the Ni-containing foil is 2.0% by mass or more in the region where the Ni-containing foil is arranged, the Zn-containing plating layer contains metal elements other than Zn. Alternatively, the Ni-containing foil may contain a metal element other than Ni.
The spot welding conditions (current value, energization time, etc.) are not particularly limited in the method for manufacturing the joint member according to the second embodiment, and ordinary conditions can be applied.
　例えば、母材鋼板の両面にＺｎ含有めっき層が設けられたスポット溶接用めっき鋼板を用いてスポット溶接を行うと、亜鉛めっき鋼板の内側面（接合部が形成される側）だけでなく、外側面のＺｎ含有めっき層も溶融してＬＭＥ割れが発生する場合がある。そのため、重なる２枚のめっき鋼板の間（めっき鋼板の内側面）と、電極とスポット溶接用めっき鋼板との間（めっき鋼板の外側面）にそれぞれＮｉ含有箔を配置してスポット溶接を行うことが好ましい。
　一方、母材鋼板の片面にＺｎ含有めっき層が設けられたスポット溶接用めっき鋼板を用い、Ｚｎ含有めっき層が外側となるようにスポット溶接を行う場合は、電極とスポット溶接用めっき鋼板との間（めっき鋼板の外側面）にＮｉ含有箔を配置してスポット溶接を行うことで外側面におけるＬＭＥ割れを抑制することができる。 For example, when spot welding is performed using a plated steel sheet for spot welding in which Zn-containing plated layers are provided on both sides of the base steel sheet, not only the inner surface (the side where the joint is formed) but also the outer surface of the galvanized steel sheet is formed. The Zn-containing plating layer on the side surface may also melt and LME cracking may occur. Therefore, spot welding is performed by arranging Ni-containing foils between the two overlapping plated steel sheets (inner surface of the plated steel sheet) and between the electrode and the plated steel sheet for spot welding (outer surface of the plated steel sheet). Is preferable.
On the other hand, when a spot welding plated steel plate having a Zn-containing plating layer provided on one side of the base steel plate is used and spot welding is performed so that the Zn-containing plating layer is on the outside, the electrode and the spot welding plated steel plate are used. By arranging a Ni-containing foil in the space (outer surface of the plated steel plate) and performing spot welding, LME cracking on the outer surface can be suppressed.
　以下、実施例によって本開示に係るスポット溶接用めっき鋼板をより具体的に説明する。本開示に係るスポット溶接用めっき鋼板はこれらの実施例に限定されるものではない。各表において下線を付した値は、本開示の範囲外であることを意味する。 Hereinafter, the plated steel sheet for spot welding according to the present disclosure will be described more specifically by way of examples. The plated steel sheet for spot welding according to the present disclosure is not limited to these examples. Underlined values in each table mean outside the scope of this disclosure.
＜実施例１＞
［供試材の製造］
　表１に示す化学成分を有する材料を実験室にて溶解して鋳込んだインゴットを熱間圧延（加熱温度１２５０℃、圧延温度（仕上げ圧延温度）９００℃のち５００℃まで水冷却、その後空冷）した後、冷間圧延にて厚さ１．４０ｍｍの鋼板（母材鋼板）を製造した。 <Example 1>
[Manufacturing of test materials]
Ingots made by melting and casting materials with the chemical components shown in Table 1 in a laboratory are hot-rolled (heating temperature 1250 ° C, rolling temperature (finish rolling temperature) 900 ° C, then water-cooled to 500 ° C, and then air-cooled). After that, a steel plate (base steel plate) having a thickness of 1.40 mm was manufactured by cold rolling.
Figure JPOXMLDOC01-appb-T000001
 
Figure JPOXMLDOC01-appb-T000001
 
　製造した母材鋼板の両面に下記表２に示すめっきを施して供試材Ａ～Ｄとした。供試材Ｂは、母材鋼板に溶融Ｚｎめっきを施した後、合金化熱処理として５３０℃に加熱して１分間保持したのちに空冷し、その合金化熱処理後にＮｉ電気めっきを行った。また供試材Ｄは鋼種Ｃの非めっき材である。 Both sides of the manufactured base steel sheet were plated as shown in Table 2 below to prepare test materials A to D. The test material B was subjected to hot-dip Zn plating on the base steel sheet, heated to 530 ° C. as an alloying heat treatment, held for 1 minute, and then air-cooled. After the alloying heat treatment, Ni electroplating was performed. The test material D is a non-plated material of steel grade C.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
（内部酸化層の厚み測定）
　得られた供試材（母材鋼板）に対して、板厚に対して垂直な断面に、湿式研磨を施し、さらに、平均径が１μｍのダイヤモンド粒子を用いたバフ研磨を施して断面サンプルを得た。この断面サンプルに対して、ＳＥＭ観察を行った。測定に用いたＳＥＭは、日本電子株式会社（ＪＥＯＬ）製のＪＳＭ－７００１Ｆである。倍率は３０００倍程度として反射電子像で供試材の表層に存在する内部酸化物を確認し、供試材の表面から内部酸化物が存在する領域を内部酸化層とする。さらに少なくとも幅３０μｍ以上の視野において、内部酸化層の面積を測定し、その幅で除すことによって表面からの平均距離を算出し内部酸化層の厚みと定義した。
　その結果、いずれの供試材も表層には内部酸化層が形成されていなかった。 (Measurement of thickness of internal oxide layer)
The obtained test material (base steel sheet) is subjected to wet polishing on a cross section perpendicular to the plate thickness, and further buffed using diamond particles having an average diameter of 1 μm to prepare a cross-section sample. Obtained. SEM observation was performed on this cross-sectional sample. The SEM used for the measurement is JSM-7001F manufactured by JEOL Ltd. The internal oxide present on the surface layer of the test material is confirmed by the backscattered electron image at a magnification of about 3000 times, and the region where the internal oxide exists from the surface of the test material is defined as the internal oxide layer. Further, the area of the internal oxide layer was measured in a visual field having a width of at least 30 μm or more, and the average distance from the surface was calculated by dividing by the area, which was defined as the thickness of the internal oxide layer.
As a result, no internal oxide layer was formed on the surface of any of the test materials.
［スポット溶接］
　これらの供試材に対して、同じ鋼板同士を２枚重ね合わせて、溶接時の試験片を拘束条件として打角３°（下板を２直線支持）および非稼働の下電極と鋼板までの距離を０．３ｍｍとした。この拘束条件によって、鋼板は電極との中心から角度がつき、かつ曲げ変形を受けながら溶接されることとなる。単相交流サーボ加圧の溶接機を使用し、電極は径が１６φで先端が６φで４０ＲのＤＲタイプとした。溶接条件はスクイズ１ｓ、通電時間０．３６ｓ、ホールド（無通電時間）０．０８ｓとして溶接電流は４．５ｋＡから０．５ｋＡピッチで散り（溶融金属の飛散）発生まで溶接した。
　さらに、相手材へのＬＭＥ割れ抑制効果を検証するため、供試材Ｂと供試材Ｄを重ね合わせ、上記の条件にて溶接した。なお、供試材ＤをＬＭＥ割れが発生しやすい下板に配置した。 [Spot welding]
Two of the same steel plates are superposed on these test materials, and the hammering angle is 3 ° (the lower plate is supported by two straight lines) and the lower electrode and the steel plate that are not in operation are up to the steel plate with the test piece at the time of welding as a constraint condition. The distance was set to 0.3 mm. Due to this constraint condition, the steel sheet is angled from the center of the electrode and is welded while undergoing bending deformation. A welding machine with single-phase AC servo pressurization was used, and the electrode was a DR type with a diameter of 16φ, a tip of 6φ, and 40R. Welding conditions were squeeze 1s, energization time 0.36s, hold (non-energization time) 0.08s, and the welding current was scattered at a pitch of 4.5kA to 0.5kA (scattering of molten metal) until welding occurred.
Further, in order to verify the effect of suppressing LME cracking on the mating material, the test material B and the test material D were overlapped and welded under the above conditions. The test material D was placed on the lower plate where LME cracking was likely to occur.
［評価］
（ＬＭＥ割れ）
　以上の条件で得た接合部材のサンプルを断面観察することでＬＭＥ割れ発生状況を確認した。供試材Ａのスポット溶接後の断面観察結果の例を図３に示す。断面写真において圧接部内外で発生した割れには楕円を付し、各割れの長さを測定した。 [evaluation]
(LME cracking)
The state of LME cracking was confirmed by observing the cross section of the sample of the joining member obtained under the above conditions. FIG. 3 shows an example of the cross-sectional observation result of the test material A after spot welding. In the cross-sectional photograph, the cracks generated inside and outside the pressure contact portion were marked with an ellipse, and the length of each crack was measured.
　Ｎｉめっき量ごとに、横軸に溶接電流値、縦軸に割れ長さをとったグラフを図４に示す。割れが複数個発生している場合は、合計長さとした。図４より、Ｚｎ電気めっきの前に、プレめっきとしてＮｉ電気めっきを行わなかった供試材（Ｎｉ電気めっき：０ｇ／ｍ３）を用いてスポット溶接を行ったサンプルに比べ、Ｎｉ電気めっきを行った供試材を用いてスポット溶接を行ったサンプルではＬＭＥ割れ発生が抑制されており、また、Ｎｉのめっき量が多いほどＬＭＥ割れ長さが小さくなる傾向にある。 FIG. 4 shows a graph in which the welding current value is plotted on the horizontal axis and the crack length is plotted on the vertical axis for each Ni plating amount. If multiple cracks occurred, the total length was used. From FIG. 4, Ni electroplating was performed compared to the sample in which spot welding was performed using a test material (Ni electroplating: 0 g / m 3 ) in which Ni electroplating was not performed as pre-plating before Zn electroplating. In the sample subjected to spot welding using the test material, the occurrence of LME cracks is suppressed, and the larger the amount of Ni plating, the smaller the LME crack length tends to be.
　同様に、供試材Ｂ同士、供試材Ｃ同士、および供試材Ｂと供試材Ｄを重ね合わせた場合、それぞれ用いてスポット溶接を行ったサンプルについてもＬＭＥ割れ長さを測定した。Ｎｉのめっき量ごとに、溶接電流値とＬＭＥ割れ長さの関係を、それぞれ図５、図６及び図７に示す。供試材Ｃについては、Ｚｎ－Ｎｉめっき層におけるＮｉ含有量からＮｉめっき量を換算した。 Similarly, when the test materials B and the test materials C and the test materials B and the test material D were overlapped with each other, the LME crack length was also measured for the samples subjected to spot welding using each of the test materials B and the test materials C. The relationship between the welding current value and the LME crack length for each Ni plating amount is shown in FIGS. 5, 6 and 7, respectively. For the test material C, the Ni plating amount was converted from the Ni content in the Zn—Ni plating layer.
　図５及び図６に見られるように、溶融Ｚｎめっき後にＮｉ電気めっきを施した供試材Ｂを用いてスポット溶接を行ったサンプル及びＺｎとＮｉを含む溶融めっきを施した供試材Ｃを用いてスポット溶接を行ったサンプルのいずれにおいても、めっき層全体でのＮｉ含有量が０ｇ／ｍ２の供試材を用いてスポット溶接を行ったサンプルに比べ、ＬＭＥ割れが低減されている。また、供試材Ａと同様、Ｎｉのめっき量が多いほどＬＭＥ割れ長さが小さくなる傾向にある。 As can be seen in FIGS. 5 and 6, a sample obtained by spot welding using the test material B subjected to Ni electroplating after hot-dip Zn plating and a test material C subjected to hot-dip plating containing Zn and Ni are obtained. In all of the samples subjected to spot welding using the sample, LME cracking is reduced as compared with the sample subjected to spot welding using the test material having a Ni content of 0 g / m 2 in the entire plating layer. Further, as in the case of the test material A, the larger the plating amount of Ni, the smaller the LME crack length tends to be.
（相手材に対するＬＭＥ割れ抑制効果検証）
　図７に見られるように、相手材として、めっき材でなく冷延鋼板が配置された場合にも、めっき層全体でのＮｉ含有量が０ｇ／ｍ２の供試材を用いてスポット溶接を行ったサンプルに比べ、ＬＭＥ割れが低減されている。また、供試材Ａと同様、Ｎｉのめっき量が多いほどＬＭＥ割れ長さが小さくなる傾向にある。 (Verification of LME crack suppression effect on mating material)
As can be seen in FIG. 7, even when a cold-rolled steel sheet is arranged as a mating material instead of a plating material, spot welding is performed using a test material having a Ni content of 0 g / m 2 in the entire plating layer. Compared with the sample performed, LME cracking is reduced. Further, as in the case of the test material A, the larger the plating amount of Ni, the smaller the LME crack length tends to be.
＜実施例２＞
（スポット溶接用めっき鋼板の製造）
　表３に示す化学成分（残部はＦｅ及び不純物）を有する材料を実験室にて溶解して鋳込んだインゴットを熱間圧延（加熱温度１２５０℃、圧延温度（仕上げ圧延温度）９００℃のち５００℃まで水冷却、その後空冷）した後、冷間圧延にて厚さ１．４０ｍｍの冷延鋼板（母材鋼板）を製造した。 <Example 2>
(Manufacturing of plated steel sheets for spot welding)
Ingots made by melting and casting materials having the chemical components shown in Table 3 (the rest is Fe and impurities) are hot-rolled (heating temperature 1250 ° C, rolling temperature (finish rolling temperature) 900 ° C, and then 500 ° C. After water cooling and then air cooling), a cold-rolled steel sheet (base steel sheet) having a thickness of 1.40 mm was manufactured by cold rolling.
Figure JPOXMLDOC01-appb-T000003
 
Figure JPOXMLDOC01-appb-T000003
 
　製造した母材鋼板（一部除く）に下記表４に示すめっきを施してスポット溶接用めっき鋼板を製造した。
　一部の母材鋼板については、亜鉛めっき上に「後めっき」としてのＮｉめっきの代わりに、スポット溶接を行う位置にＮｉ箔を配置してスポット溶接を行うこととした。
　また、比較対象として、各母材鋼板に対し、プレめっきとしてのＮｉめっき及び後めっきとしてのＮｉめっきは行わず、主めっきとしてのＮｉ含有亜鉛系めっきを亜鉛系めっきに変更したこと以外は同様にめっきを施したスポット溶接用めっき鋼板を製造した。 The manufactured base steel sheet (excluding a part) was plated as shown in Table 4 below to manufacture a plated steel sheet for spot welding.
For some base steel sheets, instead of Ni plating as "post-plating" on zinc plating, it was decided to place Ni foil at the position where spot welding is to be performed and perform spot welding.
For comparison, Ni plating as pre-plating and Ni plating as post-plating were not performed on each base metal plate, and the same was applied except that the Ni-containing zinc-based plating as the main plating was changed to zinc-based plating. A plated steel plate for spot welding was manufactured.
（引張強さの測定）
　得られたスポット溶接用めっき鋼板に対して、ＪＩＳ５号の引張試験片を作製してＪＩＳ Ｚ ２２４１：２０１１に準拠して引張試験を行い、引張強さを測定した。 (Measurement of tensile strength)
A tensile test piece of JIS No. 5 was prepared for the obtained galvanized steel sheet for spot welding, and a tensile test was conducted in accordance with JIS Z 2241: 2011, and the tensile strength was measured.
（内部酸化層の厚み測定）
　得られた供試材（母材鋼板）に対して、板厚に対して垂直な断面に、湿式研磨を施し、さらに、平均径が１μｍのダイヤモンド粒子を用いたバフ研磨を施して断面サンプルを得た。この断面サンプルに対して、ＳＥＭ観察を行った。測定に用いたＳＥＭは、日本電子株式会社（ＪＥＯＬ）製のＪＳＭ－７００１Ｆである。倍率は３０００倍程度として反射電子像で供試材の表層に存在する内部酸化物を確認し、供試材の表面から内部酸化物が存在する領域を内部酸化層とする。さらに少なくとも幅３０μｍ以上の視野において、内部酸化層の面積を測定し、その幅で除すことによって表面からの平均距離を算出し内部酸化層の厚みと定義した。 (Measurement of thickness of internal oxide layer)
The obtained test material (base steel sheet) is subjected to wet polishing on a cross section perpendicular to the plate thickness, and further buffed using diamond particles having an average diameter of 1 μm to prepare a cross-section sample. Obtained. SEM observation was performed on this cross-sectional sample. The SEM used for the measurement is JSM-7001F manufactured by JEOL Ltd. The internal oxide present on the surface layer of the test material is confirmed by the backscattered electron image at a magnification of about 3000 times, and the region where the internal oxide exists from the surface of the test material is defined as the internal oxide layer. Further, the area of the internal oxide layer was measured in a visual field having a width of at least 30 μm or more, and the average distance from the surface was calculated by dividing by the area, which was defined as the thickness of the internal oxide layer.
（スポット溶接）
　製造したスポット溶接用めっき鋼板を用い、実施例１と同様の条件でスポット溶接を行い、接合部材を製造した。
　母材鋼板の片面のみにめっき層を形成したスポット溶接用めっき鋼板については、スポット溶接によって接合部（ナゲット）が形成される側をめっき層としてスポット溶接を行い、接合部材を製造した。
　さらに、製造したスポット溶接用めっき鋼板と、９８０ＭＰａ級の冷延鋼板を重ね合わせ、実施例１と同様の条件でスポット溶接を行い、接合部材を製造した。
　また、比較対象としてＮｉを含まない亜鉛系めっきをめっき量をそろえて作製した鋼板と９８０ＭＰａ級の冷延鋼板を重ね合わせ、スポット溶接を行って接合部材を製造した。この際、めっき量はそれぞれのめっきのＮｉを除いた量に揃えた。例えば、試験番号１では、めっき中のＮｉ含有量が５．３％、めっきの総量は７９．３ｇ／ｍ２であるため、Ｎｉを除いためっき量は、７５．１ｇ／ｍ２である。なお、Ｎｉ以外のめっき成分は同様とした。 (Spot welding)
Using the manufactured plated steel sheet for spot welding, spot welding was performed under the same conditions as in Example 1 to manufacture a joint member.
For a plated steel sheet for spot welding in which a plated layer was formed only on one side of the base steel sheet, spot welding was performed with the side where the joint portion (nugget) was formed by spot welding as the plating layer to manufacture a joint member.
Further, the manufactured plated steel sheet for spot welding and a cold-rolled steel sheet of 980 MPa class were superposed, and spot welding was performed under the same conditions as in Example 1 to manufacture a joint member.
Further, as a comparison target, a steel sheet prepared by plating a zinc-based plating containing no Ni in the same amount and a cold-rolled steel sheet of 980 MPa class were superposed and spot welded to manufacture a bonded member. At this time, the plating amount was adjusted to the amount excluding Ni for each plating. For example, in Test No. 1, the Ni content in the plating is 5.3% and the total amount of plating is 79.3 g / m 2 , so the plating amount excluding Ni is 75.1 g / m 2 . The plating components other than Ni were the same.
　母材鋼板の片面のみにＮｉ箔を配置してスポット溶接を行うスポット溶接用めっき鋼板については、スポット溶接によって接合部が形成される側にＮｉ箔を配置してスポット溶接を行い、接合部材を製造した。
　また、比較対象として、Ｎｉ箔を配置せずにスポット溶接を行って接合部材を製造した。 For spot-welded plated steel plates in which Ni foil is placed on only one side of the base metal plate and spot welded, Ni foil is placed on the side where the joint is formed by spot welding and spot welding is performed to form the joint member. Manufactured.
Further, as a comparison target, a joint member was manufactured by spot welding without arranging Ni foil.
［評価］
（ＬＭＥ割れ）
　以上の条件で得た接合部材を実施例１と同様にして断面観察し、ＬＭＥ割れ発生状況を確認した。
　比較対象のスポット溶接用めっき鋼板を用いてスポット溶接を行った接合部材におけるＬＭＥ割れ発生状況と対比し、以下の基準によってＬＭＥ割れ発生抑制効果を評価し、結果を表４に示した。
優：　接合部における割れ長さが、比較対象の接合部における割れ長さの６０％未満
良：　接合部における割れ長さが、比較対象の接合部における割れ長さの６０％以上９０％未満
同等：接合部における割れ長さが、比較対象の接合部における割れ長さの９０％以上 [evaluation]
(LME cracking)
The cross-section of the joined member obtained under the above conditions was observed in the same manner as in Example 1, and the state of LME cracking was confirmed.
The effect of suppressing the occurrence of LME cracks was evaluated according to the following criteria in comparison with the state of occurrence of LME cracks in the joint member subjected to spot welding using the galvanized steel sheet for spot welding to be compared, and the results are shown in Table 4.
Excellent: The crack length at the joint is less than 60% of the crack length at the joint to be compared. Good: The crack length at the joint is equivalent to 60% or more and less than 90% of the crack length at the joint to be compared. : The crack length at the joint is 90% or more of the crack length at the joint to be compared.
(相手材へのＬＭＥ割れ抑制効果)
　以上の条件で得た９８０ＭＰａ級の冷延鋼板との板組の接合部材を実施例１と同様にして断面観察し、ＬＭＥ割れ発生状況を確認した。
　比較対象のスポット溶接用めっき鋼板を用いてスポット溶接を行った接合部材におけるＬＭＥ割れ発生状況と対比し、以下の基準によってＬＭＥ割れ発生抑制効果を評価し、結果を表４に示した。
優：　接合部における割れ長さが、比較対象の接合部における割れ長さの６０％未満
良：　接合部における割れ長さが、比較対象の接合部における割れ長さの６０％以上９０％未満
同等：接合部における割れ長さが、比較対象の接合部における割れ長さの９０％以上 (LME crack suppression effect on mating material)
The cross-sectional observation of the joint member of the plate assembly with the 980 MPa class cold-rolled steel sheet obtained under the above conditions was carried out in the same manner as in Example 1, and the state of occurrence of LME cracks was confirmed.
The effect of suppressing the occurrence of LME cracks was evaluated according to the following criteria in comparison with the state of occurrence of LME cracks in the joint member subjected to spot welding using the galvanized steel sheet for spot welding to be compared, and the results are shown in Table 4.
Excellent: The crack length at the joint is less than 60% of the crack length at the joint to be compared. Good: The crack length at the joint is equivalent to 60% or more and less than 90% of the crack length at the joint to be compared. : The crack length at the joint is 90% or more of the crack length at the joint to be compared.
Figure JPOXMLDOC01-appb-T000004
 
Figure JPOXMLDOC01-appb-T000004
 
　鋼板製造中に破断が生じたものなどは製造困難と判断し、めっき層の形成は行わなかった。
　前述した引張試験により、スポット溶接用めっき鋼板の引張強さを測定し、引張強さが７８０ＭＰａを下回るものは強度不足と判断した。
　本開示に係るスポット溶接用めっき鋼板を用いた場合、比較対象のスポット溶接用めっき鋼板に比べてＬＭＥ割れの発生が抑制されていることがわかる。さらに相手材へのＬＭＥ割れの発生も抑制されていることがわかる。 It was judged that it was difficult to manufacture steel sheets that were broken during manufacturing, and no plating layer was formed.
The tensile strength of the plated steel sheet for spot welding was measured by the above-mentioned tensile test, and it was judged that the tensile strength of the plated steel sheet for spot welding was insufficient if the tensile strength was less than 780 MPa.
It can be seen that when the spot-welded plated steel sheet according to the present disclosure is used, the occurrence of LME cracks is suppressed as compared with the spot-welded plated steel sheet to be compared. Furthermore, it can be seen that the occurrence of LME cracks in the mating material is also suppressed.
　２０２０年１１月１７日に出願された日本特許出願２０２０－１９１１０８の開示はその全体が参照により本明細書に取り込まれる。本明細書に記載された全ての文献、特許出願、および技術規格は、個々の文献、特許出願、および技術規格が具体的かつ個々に記された場合と同程度に、本明細書中に参照により取り込まれる。 The entire disclosure of Japanese patent application 2020-191108 filed on 17 November 2020 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are referenced herein to the same extent as if individual documents, patent applications, and technical standards were specifically and individually described. Is taken in by.
１Ａ、１Ｂ　スポット溶接用めっき鋼板
２Ａ、２Ｂ　電極
１３　ナゲット
１４　熱影響部（ＨＡＺ） 1A, 1B Plated steel plate for spot welding 2A, 2B Electrode 13 Nugget 14 Heat-affected zone (HAZ)

Claims (15)

  1. 　質量％で、
    　Ｃ：０．０５～０．７０％、
    　Ｓｉ：３．５０％以下、
    　Ｍｎ：８．００％以下、
    　Ｐ：０．０２０％以下、
    　Ｓ：０．０５０％以下、
    　Ａｌ：３．０００％以下、及び
    　Ｎ：０．０１０％以下
    を含み、
    　任意選択的に、
    　Ｔｉ：０．３００％以下、
    　Ｎｂ：０．３００％以下、
    　Ｖ：０．３０％以下、
    　Ｃｒ：５．０％以下、
    　Ｍｏ：２．００％以下、
    　Ｃｕ：２．００％以下、
    　Ｎｉ：１０．０％以下、
    　Ｂ：０．０２０％以下、
    　Ｃａ：０．００３％以下、
    　ＲＥＭ：０．０５％以下、
    　Ｍｇ：０．０５％以下、及び
    　Ｚｒ：０．０５％以下
    からなる群より選ばれる１種又は２種以上を含み、
    　残部がＦｅ及び不純物からなる鋼組成を有し、
    　結晶粒界の少なくとも一部が酸化物に被覆されている内部酸化層の厚みが、表面から深さ５．０μｍ未満である母材鋼板と、
    　前記母材鋼板の片面又は両面に形成されている１層又は２層以上のめっき層であって、前記めっき層の少なくとも一部としてＺｎ及びＮｉを含み、かつ前記めっき層全体でのＮｉ含有量が２．０質量％以上であるめっき層と、
    を含み、
    　引張強さが７８０ＭＰａ以上である、
    　スポット溶接用めっき鋼板。     By mass%,
    C: 0.05 to 0.70%,
    Si: 3.50% or less,
    Mn: 8.00% or less,
    P: 0.020% or less,
    S: 0.050% or less,
    Al: 3.000% or less, and N: 0.010% or less, including
    Optionally,
    Ti: 0.300% or less,
    Nb: 0.300% or less,
    V: 0.30% or less,
    Cr: 5.0% or less,
    Mo: 2.00% or less,
    Cu: 2.00% or less,
    Ni: 10.0% or less,
    B: 0.020% or less,
    Ca: 0.003% or less,
    REM: 0.05% or less,
    Includes one or more selected from the group consisting of Mg: 0.05% or less and Zr: 0.05% or less.
    The balance has a steel composition consisting of Fe and impurities.
    A base steel sheet in which the thickness of the internal oxide layer in which at least a part of the grain boundaries is covered with an oxide is less than 5.0 μm from the surface, and
    One or more plating layers formed on one side or both sides of the base steel sheet, which contains Zn and Ni as at least a part of the plating layer, and the Ni content in the entire plating layer. With a plating layer of 2.0% by mass or more,
    Including
    The tensile strength is 780 MPa or more.
    Plated steel sheet for spot welding.
  2. 　前記めっき層として、前記母材鋼板側から、Ｎｉを含むめっき層と、Ｚｎを含むめっき層とが形成されている、請求項１に記載のスポット溶接用めっき鋼板。 The plated steel sheet for spot welding according to claim 1, wherein a plating layer containing Ni and a plating layer containing Zn are formed as the plating layer from the base steel sheet side.
  3. 　前記めっき層として、前記母材鋼板側から、Ｚｎを含むめっき層と、Ｎｉを含むめっき層とが形成されている、請求項１に記載のスポット溶接用めっき鋼板。 The plated steel sheet for spot welding according to claim 1, wherein a plating layer containing Zn and a plating layer containing Ni are formed as the plating layer from the base steel sheet side.
  4. 　前記めっき層として、前記母材鋼板側から、Ｎｉを含むめっき層と、Ｚｎを含むめっき層と、Ｎｉを含むめっき層とが形成されている、請求項１に記載のスポット溶接用めっき鋼板。 The plated steel sheet for spot welding according to claim 1, wherein a plating layer containing Ni, a plating layer containing Zn, and a plating layer containing Ni are formed as the plating layer from the base steel sheet side.
  5. 　前記めっき層の少なくとも１層が、Ｚｎ及びＮｉを含むめっき層である、請求項１～請求項４のいずれか１項に記載のスポット溶接用めっき鋼板。 The plated steel sheet for spot welding according to any one of claims 1 to 4, wherein at least one of the plating layers is a plating layer containing Zn and Ni.
  6. 　非合金化めっき鋼板である、請求項１～請求項５のいずれか１項に記載のスポット溶接用めっき鋼板。 The plated steel sheet for spot welding according to any one of claims 1 to 5, which is a non-alloyed plated steel sheet.
  7. 　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
    　Ｔｉ：０．００１％以上０．３００％以下、
    　Ｎｂ：０．００１％以上０．３００％以下、及び
    　Ｖ：０．００１％以上０．３０％以下
    からなる群より選ばれる１種又は２種以上を含む請求項１～請求項６のいずれか１項に記載のスポット溶接用めっき鋼板。     The steel composition is, in mass%, instead of a portion of the Fe.
    Ti: 0.001% or more and 0.300% or less,
    Any one of claims 1 to 6 including one or more selected from the group consisting of Nb: 0.001% or more and 0.300% or less, and V: 0.001% or more and 0.30% or less. The plated steel sheet for spot welding according to item 1.
  8. 　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
    　Ｃｒ：０．００１％以上５．０％以下及びＭｏ：０．００１％以上２．００％以下の１種又は２種を含む請求項１～請求項７のいずれか１項に記載のスポット溶接用めっき鋼板。     The steel composition is, in mass%, instead of a portion of the Fe.
    The spot welding according to any one of claims 1 to 7, which includes one or two types of Cr: 0.001% or more and 5.0% or less and Mo: 0.001% or more and 2.00% or less. For plated steel sheets.
  9. 　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
    　Ｃｕ：０．００１％以上２．００％以下及びＮｉ：０．００１％以上１０．０％以下の１種又は２種を含む請求項１～請求項８のいずれか１項に記載のスポット溶接用めっき鋼板。     The steel composition is, in mass%, instead of a portion of the Fe.
    The spot welding according to any one of claims 1 to 8, which includes one or two types of Cu: 0.001% or more and 2.00% or less and Ni: 0.001% or more and 10.0% or less. For plated steel sheets.
  10. 　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
    　Ｂ：０．００１％以上０．０２０％以下を含む請求項１～請求項９のいずれか１項に記載のスポット溶接用めっき鋼板。     The steel composition is, in mass%, instead of a portion of the Fe.
    B: The plated steel sheet for spot welding according to any one of claims 1 to 9, which comprises 0.001% or more and 0.020% or less.
  11. 　前記鋼組成が、前記Ｆｅの一部に代えて、質量％で、
    　Ｃａ：０．０００５％以上０．００３％以下、
    　ＲＥＭ：０．００１％以上０．０５％以下、
    　Ｍｇ：０．００１％以上０．０５％以下、及び
    　Ｚｒ：０．００１％以上０．０５％以下
    からなる群より選ばれる１種又は２種以上を含む請求項１～請求項１０のいずれか１項に記載のスポット溶接用めっき鋼板。     The steel composition is, in mass%, instead of a portion of the Fe.
    Ca: 0.0005% or more and 0.003% or less,
    REM: 0.001% or more and 0.05% or less,
    Any one of claims 1 to 10 including one or more selected from the group consisting of Mg: 0.001% or more and 0.05% or less, and Zr: 0.001% or more and 0.05% or less. The plated steel sheet for spot welding according to item 1.
  12. 　請求項１～請求項１１のいずれか１項に記載のスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組がスポット溶接された接合構造を有する接合部材。 A joint member having a joint structure in which a plate assembly in which two or more plate materials including the plated steel plate for spot welding according to any one of claims 1 to 11 is superposed is spot welded.
  13. 　請求項１２に記載の接合部材を含む自動車用部材。 A member for an automobile including the joining member according to claim 12.
  14. 　請求項１～請求項１１のいずれか１項に記載のスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組とする工程と、
    　前記板組を一対の電極で板厚方向に挟み込んで加圧しながら通電してスポット溶接を行う工程と、
    　を含む接合部材の製造方法。     A step of forming a plate assembly in which two or more plate materials including the plated steel plate for spot welding according to any one of claims 1 to 11 are laminated.
    A process in which the plate assembly is sandwiched between a pair of electrodes in the plate thickness direction and energized while pressurizing to perform spot welding.
    A method for manufacturing a joining member including.
  15. 　請求項１～請求項１１のいずれか１項に記載の前記鋼組成を有し、結晶粒界の少なくとも一部が酸化物に被覆されている内部酸化層の厚みが、表面から深さ５．０μｍ未満である母材鋼板の片面又は両面にＺｎを含むめっき層が形成されており、引張強さが７８０ＭＰ以上であるスポット溶接用めっき鋼板を含む２枚以上の板材を重ね合わせた板組とする工程と、
    　Ｎｉを含む箔であって、前記箔が配置された領域において前記めっき層及び前記箔の全体でのＮｉ含有量が２．０質量％以上となる前記箔を、前記スポット溶接用めっき鋼板の前記めっき層が形成されている面に配置する工程と、
    　前記箔が配置された領域において前記板組を一対の電極で板厚方向に挟み込んで加圧しながら通電してスポット溶接を行う工程と、
    　を含む接合部材の製造方法。     5. The thickness of the internal oxide layer having the steel composition according to any one of claims 1 to 11 and having at least a part of the grain boundaries coated with oxide is deep from the surface. A plate set in which a plating layer containing Zn is formed on one side or both sides of a base steel plate having a tensile strength of less than 0 μm, and two or more plate materials including a plated steel plate for spot welding having a tensile strength of 780 MP or more are laminated. And the process of
    The foil containing Ni and having a Ni content of 2.0% by mass or more in the plating layer and the entire foil in the region where the foil is arranged is the foil of the plated steel sheet for spot welding. The process of arranging on the surface where the plating layer is formed and
    In the region where the foil is arranged, the plate assembly is sandwiched between a pair of electrodes in the plate thickness direction and energized while pressurizing to perform spot welding.
    A method for manufacturing a joining member including.
PCT/JP2021/040169 2020-11-17 2021-10-29 Plated steel sheet for spot welding use, joining member, automotive member, and method for manufacturing joining member WO2022107580A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160319415A1 (en) * 2013-12-25 2016-11-03 Posco Hot dip galvanized steel sheet having excellent resistance to cracking due to liquid metal embrittlement
WO2019082036A1 (en) * 2017-10-24 2019-05-02 Arcelormittal A method for the manufacture of a coated steel sheet
WO2019082037A1 (en) * 2017-10-24 2019-05-02 Arcelormittal A method for the manufacture of a coated steel sheet, two spot welded metal sheets and use thereof
WO2019116531A1 (en) * 2017-12-15 2019-06-20 日本製鉄株式会社 Steel sheet, hot-dip zinc-coated steel sheet, and alloyed hot-dip zinc-coated steel sheet

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160319415A1 (en) * 2013-12-25 2016-11-03 Posco Hot dip galvanized steel sheet having excellent resistance to cracking due to liquid metal embrittlement
WO2019082036A1 (en) * 2017-10-24 2019-05-02 Arcelormittal A method for the manufacture of a coated steel sheet
WO2019082037A1 (en) * 2017-10-24 2019-05-02 Arcelormittal A method for the manufacture of a coated steel sheet, two spot welded metal sheets and use thereof
WO2019116531A1 (en) * 2017-12-15 2019-06-20 日本製鉄株式会社 Steel sheet, hot-dip zinc-coated steel sheet, and alloyed hot-dip zinc-coated steel sheet

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