ArcelorMittal S.A.
Galvannealed steel sheet

Abstract:

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%.ltoreq.C.ltoreq.0.45%, 1.50%.ltoreq.Mn.ltoreq.2.30%, 1.50%.ltoreq.Si.ltoreq.2.40%, 0%<Cr.ltoreq.0.7%, 0%.ltoreq.Mo.ltoreq.0.3%, 0.10%.ltoreq.Al.ltoreq.0.7%, optionally 0%.ltoreq.Nb.ltoreq.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.degree. C. and 250.degree. C., reheated to a partitioning temperature between 350.degree. C. and 450.degree. C., maintained at the partitioning temperature for at least 80 s, then coated by galvannealing, with an alloying temperature between 470.degree. C. and 520.degree. C. A steel sheet is also provided.