Provided is a highly corrosion-resistant plated steel sheet having plating adhesion and resistance to liquid metal embrittlement. A highly corrosion-resistant plated steel sheet comprises a base steel sheet and a plated layer, which sequentially comprises an Fe—Al alloy layer and an MgZn.sub.2 layer from an interface with the base steel sheet.

Provided is a high strength steel sheet that has a predetermined chemical composition and is manufactured under optimum conditions, the high strength steel sheet having a steel microstructure including, by area, ferrite: 30% or more and 80% or less, tempered martensite: 3.0% or more and 35% or less, and retained austenite: 8% or more, wherein the quotient of the area fraction of grains of the retained austenite, the grains having an aspect ratio of 2.0 or more and a minor axis length of 1 μm or less, divided by the total area fraction of the retained austenite is 0.3 or more, wherein the quotient of the average Mn content (mass %) in the retained austenite divided by the average Mn content (mass %) in the ferrite is 1.5 or more.

The invention relates to a system and a method for the hot-dip galvanization of motor-vehicle components, preferably for mass-production hot-dip galvanization of a plurality of identical or similar motor-vehicle components, in particular in batches, preferably for batch galvanization, especially preferably for high-precision hot-dip galvanization.

The invention relates to a system and a method for the hot-dip galvanization of motor-vehicle components, preferably for mass-production hot-dip galvanization of a plurality of identical or similar motor-vehicle components, in particular in batches, preferably for batch galvanization, especially preferably for high-precision hot-dip galvanization.

Thick high-strength steel having a high yield ratio and excellent durability, and a method for manufacturing same are provided. The thick high-strength steel having a high yield ratio and excellent durability of the present invention comprises, in percentage by weight, C: 0.05 to 0.15%, Si: 0.01 to 1.0%, Mn: 1.0 to 2.3%, Al: 0.01 to 0.1%, Cr: 0.005 to 1.0%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.07%, Ti 0.005 to 0.11%, Fe and unavoidable impurities.

A coated steel member includes: a steel sheet substrate containing, as a chemical composition, by mass %, C: 0.25% to 0.65%, Si: 0.10% to 1.00%, Mn: 0.30% 1.00%, P: 0.050% or less, S: 0.0100% or less, N: 0.010% or less, Ti: 0.010% to 0.100%, B: 0.0005% to 0.0100%, Nb: 0.02% to 0.10%, Mo: 0.10% to 1.00%, Cu: 0.15% to 1.00%, and Ni: 0.05% to 0.25%; and a coating formed on a surface of the steel sheet substrate and containing Al and Fe. The maximum Cu content in a range from the surface to a depth of 5.0 μm is 150% or more of the Cu content of the steel sheet substrate.

A steel sheet has a predetermined chemical composition, in which a microstructure in a ¼ width portion, a microstructure in a ½ width portion, and a microstructure in a ¾ width portion, include, by area %, ferrite: 80% or more, martensite: 2% or less, and residual austenite: 2% or less, in which a proportion of unrecrystallized ferrite in the ferrite is 5% to 60%, an average grain size of carbonitrides is 6.0 nm to 30.0 nm, and Expressions (2) to (5) are satisfied.

Δ.sub.SF/μ.sub.SF≤0.10  (2)

Δ.sub.dF/μ.sub.dF≤0.20  (3)

Δ.sub.SUF≤20  (4)

Δ.sub.dC/μ.sub.dC≤0.50  (5)

Provided is a high-strength steel sheet having a tensile strength of 780 MPa or higher. The high-strength steel sheet has a low yield ratio and excellent ductility (El) and strain hardening exponent (n) and thus has enhanced processability.

A method for producing a coated steel sheet having a tensile strength TS of at least 1450 MPa and a total elongation TE of at least 17% includes the successive steps of providing a cold rolled steel sheet made of a steel having a chemical composition comprising, in weight %: 0.34%≤C≤0.45%, 1.50%≤Mn≤2.30%, 1.50≤Si≤2.40%, 0%<Cr≤0.7%, 0%≤Mo≤0.3%, 0.10%≤Al≤0.7%, and optionally 0%≤Nb≤0.05%, the remainder being Fe and unavoidable impurities, annealing the cold-rolled steel sheet at an annealing temperature AT higher than the Ac3 transformation point of the steel, quenching the annealed steel sheet by cooling it down to a quenching temperature QT lower than the Ms transformation point of the steel and comprised between 150° C. and 250° C., and reheating the quenched steel sheet to a partitioning temperature PT between 350° C. and 450° C. and maintaining the steel sheet at the partitioning temperature PT for a partitioning time Pt of at least 80 s, and coating the steel sheet by galvannealing, with an alloying temperature GAT comprised between 470° C. and 520° C.

A method for producing a coated steel sheet having a tensile strength TS of at least 1450 MPa and a total elongation TE of at least 17% includes the successive steps of providing a cold rolled steel sheet made of a steel having a chemical composition comprising, in weight %: 0.34%≤C≤0.45%, 1.50%≤Mn≤2.30%, 1.50≤Si≤2.40%, 0%<Cr≤0.7%, 0%≤Mo≤0.3%, 0.10%≤Al≤0.7%, and optionally 0%≤Nb≤0.05%, the remainder being Fe and unavoidable impurities, annealing the cold-rolled steel sheet at an annealing temperature AT higher than the Ac3 transformation point of the steel, quenching the annealed steel sheet by cooling it down to a quenching temperature QT lower than the Ms transformation point of the steel and comprised between 150° C. and 250° C., and reheating the quenched steel sheet to a partitioning temperature PT between 350° C. and 450° C. and maintaining the steel sheet at the partitioning temperature PT for a partitioning time Pt of at least 80 s, and coating the steel sheet by galvannealing, with an alloying temperature GAT comprised between 470° C. and 520° C.