Abstract: A welded joint formed by performing projection welding on a high-strength coated steel sheet and a nut, includes a content of solid solution Mn in a first region in a surface layer of the steel sheet on an outermost periphery of a weld is 40% or less of a content of solid solution Mn in a second region in a central region in a thickness direction of the steel sheet on the outermost periphery of the weld, and a content of solid solution Mn in a third region in the surface layer of the steel sheet on an innermost periphery of the weld is 40% or less of a content of solid solution Mn in a fourth region in the central region in the thickness direction of the steel sheet on the innermost periphery of the weld.

Abstract: Provided is an alloyed galvanized steel sheet with excellent resistance to cracking in resistance welding at a welded portion, even if crystal orientations of an Fe-based electroplating layer and a cold-rolled steel sheet are integrated at a high ratio at the interface between the Fe-based electroplating layer and the cold-rolled steel sheet. The alloyed galvanized steel sheet has a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % to 3.0 mass %; an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet with a coating weight per surface exceeding 20.0 g/m2, and an alloyed galvanized layer formed on the Fe-based electroplating layer, where crystal orientations of the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet are integrated at a ratio of more than 50% at the interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet.

Abstract: A resistance spot welded member and a resistance spot welding method. The resistance spot welded member includes a resistance spot weld formed by resistance-spot-welding a plurality of steel sheets including at least one high strength coated steel sheet. The high strength coated steel sheet has a specific chemical composition. The at least one high strength coated steel sheet includes a coated layer, a base metal, and an Fe-based electroplated base layer interposed between the coated layer and the base metal. The amount of solute Si and the amount of solute Mn in a region on a steel sheet surface in the vicinity of the edge of the corona of the resistance spot weld are 35% or less of the amount of solute Si and 35% or less of the amount of solute Mn, respectively, at a position ¼ of the sheet thickness.

Abstract: A steel sheet having a tensile strength (TS) of 1180 MPa or more, high LME resistance, and good weld fatigue properties. The steel sheet has a specific chemical composition and a specific steel microstructure. Crystal grains containing an oxide of Si and/or Mn in a region within 4.9 ?m in a thickness direction from a surface of the steel sheet have an average grain size in the range of 3 to 10 ?m, the lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m in the thickness direction from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy a specified formula.

Abstract: A base steel sheet containing Si in an amount of 0.50 to 3.00 mass % is subjected to an Fe-based electroplating treatment using an Fe-based electroplating solution containing Fe ions and transition metal ions other than the Fe ions to form an Fe-based electroplated layer, and then to an annealing treatment. In the Fe-based electroplating solution, a content of the Fe ions is 1.0 mass % or more and a content of the transition metal ions is 10 to 1000 mass ppm. A coating amount of the Fe-based electroplated layer per one surface of the base steel sheet is 1.0 g/m2 or more. Thus, a steel sheet having high strength and excellent resistance to resistance-weld cracking of a welded portion is obtained.

Abstract: There is provided a raw material cold-rolled steel sheet with Fe-based coating film excellent in primary rust prevention property or plating appearance. The raw material cold-rolled steel sheet with Fe-based coating film comprises: a base steel sheet having a chemical composition containing C of 0.80 mass % or less, Si of 0.10 mass % or more and 3.00 mass % or less, Mn of 1.50 mass % or more and 3.50 mass % or less, P of 0.100 masse or less; S of 0.0300 mass % or less, Al of 0.100 mass % or less, with a remaining part consisting of Fe and inevitable impurities; and a P-adhered Fe-based coating film containing an Fe-based coating film disposed on at least one surface of the base steel sheet and a P-containing substance adhered to a surface of the Fe-based coating film, and an adhesion amount of the P-containing substance in terms of P is 0.2 mg/m2 or more.

Abstract: To provide a galvanized steel sheet having high strength, specifically, a tensile strength of 1,150 MPa or more, and excellent resistance spot weldability, a base steel sheet has a defined chemical composition, an amount of diffusible hydrogen in the base steel sheet is 0.20 mass ppm or less, and surface roughness Ra of the galvanized steel sheet is 0.6 ?m or less.

Abstract: Disclosed is an Fe-based electroplated steel sheet including: a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less; and an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet with a coating weight per surface of 5.0 g/m2 or more, in which in an intensity profile measured by glow discharge optical emission spectrometry, a peak of emission intensity at wavelengths indicating Si is detected within a range from a surface of the Fe-based electroplating layer to more than 0.2 ?m in a thickness direction and not more than a thickness of the Fe-based electroplating layer, and an average value of C concentration in a region ranging from 10 ?m to 20 ?m in the thickness direction from the surface of the Fe-based electroplating layer is 0.10 mass % or less.

Abstract: To provide an Fe-based electroplated steel sheet that not only has excellent chemical convertibility or excellent coating appearance when subjected to hot-dip galvanizing, but also has excellent resistance to cracking in resistance welding. Disclosed is an Fe-based plated steel sheet including: a cold-rolled steel sheet having a chemical composition containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less; and an Fe-based electroplating layer formed on one or both surfaces of the cold-rolled steel sheet with a coating weight per surface of 1.0 g/m2 or more, in which a thickness of an internal oxidation layer is 2.00 ?m or less, and an average value of C concentration in a range of 10 ?m to 20 ?m in a thickness direction from the surface of the Fe-based electroplating layer is 0.10 mass % or less.

Abstract: Disclosed is a galvannealed steel sheet including: a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less; an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet; and a galvannealed layer formed on the Fe-based electroplating layer, in which in an intensity profile measured by glow discharge optical emission spectrometry, ISi,Fe/ISi,bulk is 0.30 or more, and an average value of C concentration in a region ranging from 10 ?m to 20 ?m in the thickness direction from the interface between the galvannealed layer and the Fe-based electroplating layer towards the Fe-based electroplating layer is 0.10 mass % or less.

Abstract: Provided is a steel sheet with excellent resistance to cracking in resistance welding at a welded portion, even if the crystal orientations of an Fe-based electroplating layer and a Si-containing cold-rolled steel sheet are integrated at a high ratio at the interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet. Provided is an Fe-based electroplated steel sheet having a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less; and an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet with a coating weight per surface of more than 20.0 g/m2, where the crystal orientations of the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet are integrated at a ratio of more than 50% at the interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet.

Abstract: Provided is an alloyed galvanized steel sheet with excellent resistance to cracking in resistance welding at a welded portion, even if crystal orientations of an Fe-based electroplating layer and a cold-rolled steel sheet are integrated at a high ratio at the interface between the Fe-based electroplating layer and the cold-rolled steel sheet. The alloyed galvanized steel sheet has a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % to 3.0 mass %; an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet with a coating weight per surface exceeding 20.0 g/m2, and an alloyed galvanized layer formed on the Fe-based electroplating layer, where crystal orientations of the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet are integrated at a ratio of more than 50% at the interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet.

Abstract: Provided is a galvanized steel sheet with excellent resistance to cracking in resistance welding at a welded portion, even if crystal orientations of an Fe-based electroplating layer and a cold-rolled steel sheet are integrated at a high ratio at the interface between the Fe-based electroplating layer and the cold-rolled steel sheet. The galvanized steel sheet has a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % to 3.0 mass %; an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet with a coating weight per surface of more than 20.0 g/m2, and a galvanized layer formed on the Fe-based electroplating layer, where crystal orientations of the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet are integrated at a ratio of more than 50 % at the interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet.

Abstract: To provide a steel sheet with excellent resistance to cracking in resistance welding at a welded portion. Disclosed is a galvanized steel sheet including: a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less; an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet with a coating weight per surface of 5.0 g/m2 or more; and a galvanized layer formed on the Fe-based electroplating layer, in which in an intensity profile measured by glow discharge optical emission spectrometry, ISi,Fe/ISi,bulk is 0.50 or more, and an average value of C concentration in a region ranging from 10 ?m to 20 ?m from an interface between the galvanized layer and the Fe-based electroplating layer towards the Fe-based electroplating layer is 0.10 mass % or less.

Abstract: A steel sheet having a tensile strength (TS) of 780 MPa or more and less than 1180 MPa, high LME resistance, and good weld fatigue properties. The steel sheet has a specific chemical composition and a specific steel microstructure. Crystal grains containing an oxide of Si and/or Mn in a region within 4.9 ?m in a thickness direction from a surface of the steel sheet have an average grain size in the range of 3 to 10 ?m, the lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m in the thickness direction from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy a specified formula.

Abstract: A steel sheet with a tensile strength (TS) of 1180 MPa or more, a member, and a method for producing them. In a region of the steel sheet within 4.9 ?m in the thickness direction, a region with a Si concentration not more than one-third of the Si concentration in the chemical composition of the steel sheet and with a Mn concentration not more than one-third of the Mn concentration in the chemical composition of the steel sheet has a thickness of 1.0 ?m or more. The lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m in the thickness direction from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy the following formula (1): LSi+LMn?(TSi+TMn)/4??(1).

Abstract: A steel sheet with a tensile strength (TS) of 780 MPa or more and less than 1180 MPa, a member, and a method for producing them. In a region of the steel sheet within 4.9 ?m in the thickness direction, a region with a Si concentration not more than one-third of the Si concentration in the chemical composition of the steel sheet and with a Mn concentration not more than one-third of the Mn concentration in the chemical composition of the steel sheet has a thickness of 1.0 ?m or more. The lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy the following formula (1): LSi+LMn?(TSi+TMn)/4??(1).

Abstract: A steel sheet having a tensile strength (TS) of 1180 MPa or more, high LME resistance, and good weld fatigue properties. The steel sheet has a specific chemical composition and a specific steel microstructure. Crystal grains containing an oxide of Si and/or Mn in a region within 4.9 ?m in a thickness direction from a surface of the steel sheet have an average grain size in the range of 3 to 10 ?m, the lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m in the thickness direction from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy a specified formula.

Abstract: To obtain a high-strength hot-dip galvanized steel sheet having excellent surface appearance even in the case where a steel strip containing Mn at a predetermined ratio or more to Si is subjected to hot-dip galvanizing treatment, a method of producing a hot-dip galvanized steel sheet using a continuous hot-dip galvanizing apparatus comprises: subjecting a steel strip to annealing, by conveying it in an annealing furnace; and subjecting the steel strip discharged from a cooling zone to hot-dip galvanizing using a hot-dip galvanizing line, to obtain a hot-dip galvanized steel sheet. The steel strip has a chemical composition containing, in mass %, Mn: 1.7% or more and 3.5% or less and Si: 0.2% or more and 1.05% or less and satisfying [Si]/[Mn]?0.30. The chemical composition, a dew point of an atmosphere in the soaking zone, and a delivery temperature of the heating zone satisfy Formula (1).

Abstract: There is provided a high-strength galvanized steel sheet and a relatively low-strength galvanized steel sheet that undergoes complex forming, a galvanized steel sheet that exhibits consistently excellent press formability and that generates no hazardous fumes during welding as well as a manufacturing method therefor. The galvanized steel sheet has an oxide layer on the surface, where the oxide layer has an average thickness of 20 nm or more, and the oxide layer contains 30 mg/m2 or more of Zn, 1.0 mg/m2 or more of S, and 50 mg/m2 or more and 1,000 mg/m2 or less of polyethylene particles having an average particle size of 5.0 ?m or less.