A method for producing a coated steel sheet having a tensile strength of at least 1450 MPa and a total elongation of at least 17% is provided. The method includes providing a cold rolled steel sheet having a chemical composition 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%, optionally 0%≤Nb≤0.05%, and a remainder of Fe and unavoidable impurities. The sheet is annealed at an annealing temperature higher than the Ac3 transformation point of the steel, quenched to a quenching temperature lower than the Ms transformation point of the steel and between 150° C. and 250° C., reheated to a partitioning temperature between 350° C. and 450° C., maintained at the partitioning temperature for at least 80 s, then coated by galvannealing, with an alloying temperature between 470° C. and 520° C. A steel sheet is also provided.

A method for producing a coated steel sheet having a tensile strength of at least 1450 MPa and a total elongation of at least 17% is provided. The method includes providing a cold rolled steel sheet having a chemical composition 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%, optionally 0%≤Nb≤0.05%, and a remainder of Fe and unavoidable impurities. The sheet is annealed at an annealing temperature higher than the Ac3 transformation point of the steel, quenched to a quenching temperature lower than the Ms transformation point of the steel and between 150° C. and 250° C., reheated to a partitioning temperature between 350° C. and 450° C., maintained at the partitioning temperature for at least 80 s, then coated by galvannealing, with an alloying temperature between 470° C. and 520° C. A steel sheet is also provided.

Provided is a low-density clad steel sheet having excellent formability and fatigue properties, including a base material; and cladding materials provided on both side surfaces of the base material, wherein the base material is a lightweight steel sheet including, by weight, C: 0.3 to 1.0%, Mn: 4.0 to 16.0%, Al: 4.5 to 9.0%, and a remainder of Fe and inevitable impurities, and each of the cladding materials is martensitic carbon steel including, by weight, C: 0.1 to 0.45%, Mn: 1.0 to 3.0%, and a remainder of Fe and inevitable impurities.

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%C0.45%, 1.50%Mn2.30%, 1.50Si2.40%, 0%<Cr0.7%, 0%Mo0.3%, 0.10%Al0.7%, and optionally 0%Nb0.05%, 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 80s, 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%C0.45%, 1.50%Mn2.30%, 1.50Si2.40%, 0%<Cr0.7%, 0%Mo0.3%, 0.10%Al0.7%, and optionally 0%Nb0.05%, 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 80s, and coating the steel sheet by galvannealing, with an alloying temperature GAT comprised between 470 C. and 520 C.

Provided are a high-strength galvanized hot-rolled steel sheet and a method for manufacturing the steel sheet. A steel sheet has a chemical composition, and a galvanized layer is disposed on the steel sheet. The chemical composition includes, in mass %, C: 0.02% or greater and 0.30% or less, Si: 0.01% or greater and 2.5% or less, Mn: 0.3% or greater and 3.0% or less, P: 0.08% or less, S: 0.02% or less, and Al: 0.001% or greater and 0.20% or less. The galvanized layer has a coating weight per side of 20 to 120 g/m.sup.2. A surface of the steel sheet has a specific surface area ratio, r, of 2.5 or less, and an amount of Si present in the galvanized layer and an amount of Mn present in the galvanized layer respectively satisfy: amount of Sir0.06, and amount of Mnr0.10.

Provided are a high-strength galvanized hot-rolled steel sheet and a method for manufacturing the steel sheet. A steel sheet has a chemical composition, and a galvanized layer is disposed on the steel sheet. The chemical composition includes, in mass %, C: 0.02% or greater and 0.30% or less, Si: 0.01% or greater and 2.5% or less, Mn: 0.3% or greater and 3.0% or less, P: 0.08% or less, S: 0.02% or less, and Al: 0.001% or greater and 0.20% or less. The galvanized layer has a coating weight per side of 20 to 120 g/m.sup.2. A surface of the steel sheet has a specific surface area ratio, r, of 2.5 or less, and an amount of Si present in the galvanized layer and an amount of Mn present in the galvanized layer respectively satisfy: amount of Sir0.06, and amount of Mnr0.10.

In a projection material for mechanical plating, a steel particle is used as a core, and the surrounding surface thereof is coated with a zinc alloy in which the content of Al is more than 5% by mass but equal to or less than 16% by mass, the content of Mg is equal to or more than 5.5% by mass but equal to or less than 15% by mass and the remaining portion is Zn and an impurity, and the content of Fe is equal to or more than 3% by mass but equal to or less than 80% by mass. In this way, the corrosion resistance of a zinc-based coating itself formed in mechanical plating is remarkably enhanced without dependence on protective coating formation treatment such as chromate treatment.

In a projection material for mechanical plating, a steel particle is used as a core, and the surrounding surface thereof is coated with a zinc alloy in which the content of Al is more than 5% by mass but equal to or less than 16% by mass, the content of Mg is equal to or more than 5.5% by mass but equal to or less than 15% by mass and the remaining portion is Zn and an impurity, and the content of Fe is equal to or more than 3% by mass but equal to or less than 80% by mass. In this way, the corrosion resistance of a zinc-based coating itself formed in mechanical plating is remarkably enhanced without dependence on protective coating formation treatment such as chromate treatment.

A steel sheet with a metallic coating is provided. A composition of the metallic coating includes from 2.0 to 24.0% by weight of zinc, from 7.1 to 12.0% by weight of silicon, optionally from 1.1 to 8.0% by weight of magnesium, and optionally additional elements chosen from Pb, Ni, Zr, or Hf. The content by weight of each additional element is less than 0.3%. A balance of the composition is aluminum, unavoidable impurities and residual elements. A ratio Al/Zn is from 4.0 to 6.0.