ArcelorMittal S.A.
High strength steel and manufacturing method

Abstract:

A cold-rolled and annealed steel sheet is provided, the chemical composition of which comprises, the contents being expressed by weight percent: 0.10.ltoreq.C.ltoreq.0.13% 2.4.ltoreq.Mn.ltoreq.2.8% 0.30.ltoreq.Si.ltoreq.0.55% 0.30.ltoreq.Cr.ltoreq.0.56% 0.020.ltoreq.Ti.ltoreq.0.050% 0.0020.ltoreq.B.ltoreq.0.0040% 0.005.ltoreq.Al.ltoreq.0.050% Mo.ltoreq.0.010% Nb.ltoreq.0.040% 0.002.ltoreq.N.ltoreq.0.008% S.ltoreq.0.005% P.ltoreq.0.020%, the remainder consisting of iron and unavoidable impurities resulting from the smelting, the steel sheet having a microstructure consisting of, in surface proportion, martensite and/or lower bainite, said martensite comprising fresh martensite and/or self-tempered martensite, the sum of the surface proportions of martensite and lower bainite being comprised between 60 to 95%, 4 to 35% of low carbide containing bainite, 0 to 5% of ferrite, and less than 5% of retained austenite in island form.