Provided is a high-strength cold-rolled steel sheet having excellent ductility and stretch-flangeability as well as weldability in a range in which a tensile strength is 980 MPa or higher and a 0.2% yield strength is less than 700 MPa (preferably 500 MPa or higher). In the high-strength cold-rolled steel sheet of the present invention, the chemical composition is adjusted as appropriate, and the area ratio of below-mentioned metal structures at a position of sheet thickness in the steel sheet satisfies following requirements: tempered martensite: 10 area % to less than 30 area %, bainite: more than 70 area %, total of tempered martensite and bainite: 90 area % or more, ferrite: 0 area % to 5 area %, and retained austenite: 0 area % to 4 area %. The high-strength cold-rolled steel sheet has excellent ductility, stretch-flangeability, and weldability, and has a tensile strength of 980 MPa or higher and a 0.2% yield strength of less than 700 MPa.

A steel sheet for a hot stamping member contains, as a chemical composition, 0.10 mass % to 0.35 mass % of C; 0.01 mass % to 1.0 mass % of Si; 0.3 mass % to 2.3 mass % of Mn; 0.01 mass % to 0.5 mass % of Al; limited to 0.03 mass % or less of P; limited to 0.02 mass % or less of S; limited to 0.1 mass % or less of N; and a balance consisting of Fe and unavoidable impurities, in which a standard deviation of diameters of iron carbides which are contained in a region from a surface to a thickness position of the steel sheet is less than or equal to 0.8 m.

Provided is a method for producing a galvanized steel sheet that includes an oxide layer forming step of bringing a galvanized steel sheet into contact with an acidic solution containing sulfate ions, then holding the galvanized steel sheet in contact for 1 to 60 seconds, and then washing the galvanized steel sheet with water; and a neutralization treatment step of holding a surface of an oxide layer, which has been formed in the oxide layer forming step, in contact with an alkaline aqueous solution for 0.5 seconds or longer, and then performing washing with water and drying. The alkaline aqueous solution contains 0.1 g/L or more of carbonate ions.

A plated steel material including a plated layer and a base steel material. In a cross section perpendicular to a surface of the plated steel material, a length L of a boundary line between the plated layer and the base steel material satisfies (LL.sub.0)/L.sub.01002.0 (%), wherein L.sub.0 is a linear distance between ends of the boundary line in an observation region, and L is a length of the boundary line between the ends. The plated layer includes a first region where an Fe concentration is less than 5.0 mass %, a second region where an Fe concentration is 5.0 mass % or more and less than 30.0 mass %, and a third region where an Fe concentration is 30.0 mass % or more and 80.0 mass % or less, the first region including an Al-containing phase at an area fraction of 5% or more.

A plated steel material including a plated layer and a base steel material. In a cross section perpendicular to a surface of the plated steel material, a length L of a boundary line between the plated layer and the base steel material satisfies (L-L.sub.0)/L.sub.0 1002.0 (%), wherein L.sub.0 is a linear distance between ends of the boundary line in an observation region, and L is a length of the boundary line between the ends. The plated layer includes a first region where an Fe concentration is less than 5.0 mass %, a second region where an Fe concentration is 5.0 mass % or more and less than 30.0 mass %, and a third region where an Fe concentration is 30.0 mass % or more and 80.0 mass % or less, the first region including an Al-containing phase at an area fraction of 0% and less than 5%.

To more reliably suppress LME and blowhole formation while maintaining excellent corrosion resistance. A plated steel sheet according to the present invention, includes: a steel sheet as a base material; a plating layer located on at least part of a surface of the steel sheet; and an oxide layer located on a surface of the plating layer, where a chemical composition of the plating layer is made up of prescribed components, and Zn and impurities as the balance, and when a position at a depth of 5 nm from an uppermost surface of the oxide layer is observed by X-ray photoelectron spectroscopy (XPS), a value of an intensity ratio ([AlO]+[MgO])/[ZnO]) calculated from intensity of peaks respectively attributed to an AlO bond, an MgO bond, and a ZnO bond is 5.0 or more.

A tailored welded blank produced from at least two blank parts, where at least one is a press-hardenable manganese-boron steel and at least one has a coating of aluminum or an aluminum-based alloy. The parts are welded by laser-beam welding or hybrid laser/gas-metal-arc welding, while retaining the coating, using shielding gas and a filler wire having in % by weight: C: 0.41 to 0.9; Si: 0.4 to 4; Mn: 0.4 to 3; optionally Cr: 0 to 10; and with optional alloying of one or more of: Mo: 0.01 to 1.0; B: 0.0008 to 0.0040; Ti: 2.5B<=Ti<=5B; V: 0.01 to 0.4; Nb: 0.01 to 0.2; W: 0.01 to 0.2; the remainder Fe and unavoidable impurities. The high proportion of C and Cr or additionally or alternatively of Mo, V, Nb and/or W enables hardening by carbide formation in a weld-seam region after welding.

A method of manufacturing steel strip including the steps of: casting molten steel into slabs; reheating the slabs at 1150 C. or more for 1 hour or more; hot rolling the steel into a strip, preferably with an average F1 slab entry temperature above 1000 C.; coiling the hot rolled steel strip; batch annealing the steel strip: at an intercritical temperature (i.e. between Ac1 and Ac3), preferably below 700 C.; in non-oxidising and non-nitrogenated atmosphere; total annealing time at least 5 hours, preferably at least 10 hours to get Mn enrichment in austenite such that Mn content is at least 1.25 times bulk Mn content of the steel and C enrichment such that C content is at least 1.2 times bulk C content of the steel;
cooling the steel after batch annealing in air, forced air or water quench.

A plated steel material including a plated layer and a base steel material. In a cross section perpendicular to a surface of the plated steel material, a length L of a boundary line between the plated layer and the base steel material satisfies (LL.sub.0)/L.sub.01002.0 (%), wherein L.sub.0 is a linear distance between ends of the boundary line in an observation region, and L is a length of the boundary line between the ends. The plated layer includes a first region where an Fe concentration is less than 5.0 mass %, a second region where an Fe concentration is 5.0 mass % or more and less than 30.0 mass %, and a third region where an Fe concentration is 30.0 mass % or more and 80.0 mass % or less, the first region including an Al-containing phase at an area fraction of 5% or more.

A plated steel material including a plated layer and a base steel material. In a cross section perpendicular to a surface of the plated steel material, a length L of a boundary line between the plated layer and the base steel material satisfies (LL.sub.0)/L.sub.01002.0 (%), wherein L.sub.0 is a linear distance between ends of the boundary line in an observation region, and L is a length of the boundary line between the ends. The plated layer includes a first region where an Fe concentration is less than 5.0 mass %, a second region where an Fe concentration is 5.0 mass % or more and less than 30.0 mass %, and a third region where an Fe concentration is 30.0 mass % or more and 80.0 mass % or less, the first region including an Al-containing phase at an area fraction of 0% and less than 5%.