ArcelorMittal S.A.
METHOD FOR PRODUCING A HIGH STRENGTH COATED STEEL SHEET HAVING IMPROVED STRENGTH AND DUCTILITY AND OBTAINED SHEET

Abstract:

A coated steel sheet includes a chemical composition including in weight %: 0.13%.ltoreq.C .ltoreq.0.22%; 1.2%.ltoreq.Si.ltoreq.1.8%; 1.8%.ltoreq.Mn.ltoreq.2.2%; 0.10%.ltoreq.Mo.ltoreq.0.20%; Nb.ltoreq.0.05%; Al.ltoreq.0.5%; Ti.ltoreq.0.05%; and a remainder being Fe and unavoidable impurities. A structure of the steel sheet consists of, by volume fraction, 3% to 15% of residual austenite and 85% to 97% of martensite and bainite. The structure includes at least 65% of martensite and does not including ferrite. At least one face of the coated steel sheet includes a metallic coating. The steel sheet has a yield strength of at least 800 MPa, a tensile strength of at least 1180 MPa, a total elongation of at least 14% and a hole expansion ratio HER of at least 30%.