ArcelorMittal S.A.
Method for producing a ultra high strength coated or not coated steel sheet and obtained sheet

Abstract:

A method for producing a cold rolled steel sheet having a tensile strength .gtoreq.1470 MPa and a total elongation TE.gtoreq.19%, the method comprising the steps of annealing at an annealing temperature AT.gtoreq.Ac3 a non-treated steel sheet whose chemical composition contains in weight %: 0.34%.ltoreq.C.ltoreq.0.40%, 1.50%.ltoreq.Mn.ltoreq.2.30%, 1.50.ltoreq.Si.ltoreq.2.40%, 0<Cr.ltoreq.0.5%, 0<Mo.ltoreq.0.3%, 0.01%.ltoreq.Al.ltoreq.0.07%, the remainder being Fe and unavoidable impurities, quenching the annealed steel sheet by cooling it to a quenching temperature QT<Ms transformation point and between 150.degree. C. and 250.degree. C., and making a partitioning treatment by reheating the quenched steel sheet to a partitioning temperature PT between 350.degree. C. and 420.degree. C. and maintaining the steel sheet at this temperature during a partitioning time Pt between 15 seconds and 120 seconds.