The present invention relates to a method for the manufacture of a coated steel sheet comprising the following successive steps: A. the coating of the steel sheet with a first coating consisting of nickel and having a thickness between 600 nm and 1400 nm, the steel sheet having the following composition in weight: 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 on a purely optional basis, one or more elements such as Nb≤0.5%, B≤0.010%, Cr≤1.0%, Mo≤0.50%, Ni≤1.0%, Ti≤0.5%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, B. the recrystallization annealing at a temperature between 820 to 1200° C., C. the coating with a second coating based on zinc not comprising nickel.

The entirety or a part of this hot stamped product includes, as a chemical composition, by mass %, C: 0.001% or more and less than 0.080%, Si: 2.50% or less, Mn: 0.01% or more and less than 0.50%, P: 0.200% or less, S: 0.0200% or less, sol.Al: 0.001% to 2.500%, N: 0.0200% or less, Cr: 0.30% or more and less than 2.00%, and a remainder: Fe and impurities, in which a metallographic structure contains, by vol %, ferrite: more than 60.0%, martensite: 0% or more and less than 10.0%, and bainite: 0% or more and less than 20.0%, a tensile strength is less than 700 MPa, and ΔTS, which is a decrease in the tensile strength after a heat treatment at 170° C. for 20 minutes, is 100 MPa or less.

Provided is a plated steel material which can be used for an automobile, a household appliance, a building material, and the like and, more particularly, to a zinc alloy plated steel material having excellent corrosion resistance after being processed and a method for manufacturing the same.

Provided is a plated steel material which can be used for an automobile, a household appliance, a building material, and the like and, more particularly, to a zinc alloy plated steel material having excellent corrosion resistance after being processed and a method for manufacturing the same.

The present disclosure relates to an aluminum alloy-plated steel sheet having excellent workability and corrosion resistance and a method for manufacturing the same, and more particularly, to an aluminum alloy-plated steel sheet preventing microcracks generated during hot forming and has excellent seizure resistance and corrosion resistance, and a method for manufacturing the same.

An exemplary embodiment in the present disclosure provides a hot-dip Zn—Al—Mg-based alloy-plated steel material having excellent corrosion resistance in a processed portion, and a method for manufacturing the same. The steel material includes: an iron substrate; and a hot-dip alloy-plated layer formed on the iron substrate, wherein the hot-dip alloy-plated layer contains, by wt %, more than 8% to 25% of Al, more than 4% to 12% of Mg, and a balance of Zn and inevitable impurities, a fraction of a MgZn2 phase in the hot-dip alloy-plated layer is 10 to 45 area %, cracks are formed inside the MgZn2 phase, and the number of cracks present per 100 μm in a direction perpendicular to a thickness direction of a steel sheet in a field of view in which the cracks are observed based on a cross section in the thickness direction of the steel sheet is 3 to 80.

The present disclosure relates to a high-strength hot-dip galvanized steel sheet having excellent surface quality and electrical resistance spot weldability, and a method for manufacturing the same. A galvanized steel sheet according to an aspect of the present disclosure is a galvanized steel sheet including a base steel sheet and a zinc-based plating layer formed on a surface of the base steel sheet, wherein a ratio (a/b) of a hardness of a surface layer portion (a) to a hardness of an internal portion (b) of the base steel sheet may be less than 0.95.

The present disclosure relates to a high-strength hot-dip galvanized steel sheet having excellent surface quality and electrical resistance spot weldability, and a method for manufacturing the same. A galvanized steel sheet according to an aspect of the present disclosure is a galvanized steel sheet including a base steel sheet and a zinc-based plating layer formed on a surface of the base steel sheet, wherein a ratio (a/b) of a hardness of a surface layer portion (a) to a hardness of an internal portion (b) of the base steel sheet may be less than 0.95.

A steel sheet has a predetermined chemical composition containing, in mass %, C: more than 0.18% and less than 0.30%, Mn: more than 2.50% and 4.00% or less, and other elements. The steel micro-structure at a position at a depth of ¼ of the sheet thickness from the surface in an L cross section of the steel sheet is, in area %, tempered martensite: 25 to 90%, ferrite: 5% or less, retained austenite: 10 to 50%, and bainite: 5% or less. At a position at a depth of ¼ of the sheet thickness from the surface of the L cross section, the proportion of a total area of retained austenite grains having an area of 1 μm.sup.2 or more and having a grain shape circularity of 0.1 or more is less than 50% with respect to the entire area of retained austenite. The steel sheet satisfies the formula C.sub.Mnγ/C.sub.Mnα≥1.2.

A steel sheet has a predetermined chemical composition containing, in mass %, C: more than 0.18% and less than 0.30%, Mn: more than 2.50% and 4.00% or less, and other elements. The steel micro-structure at a position at a depth of ¼ of the sheet thickness from the surface in an L cross section of the steel sheet is, in area %, tempered martensite: 25 to 90%, ferrite: 5% or less, retained austenite: 10 to 50%, and bainite: 5% or less. At a position at a depth of ¼ of the sheet thickness from the surface of the L cross section, the proportion of a total area of retained austenite grains having an area of 1 μm.sup.2 or more and having a grain shape circularity of 0.1 or more is less than 50% with respect to the entire area of retained austenite. The steel sheet satisfies the formula C.sub.Mnγ/C.sub.Mnα≥1.2.