ArcelorMittal S.A.
STEEL SHEET HAVING EXCELLENT TOUGHNESS, DUCTILITY AND STRENGTH, AND MANUFACTURING METHOD THEREOF

Abstract:

A cold-rolled and heat treated steel sheet, has a composition comprising 0.1%.ltoreq.C.ltoreq.0.4%, 3.5%.ltoreq.Mn.ltoreq.8.0%, 0.1%.ltoreq.Si.ltoreq.1.5%, Al.ltoreq.3%, Mo.ltoreq.0.5%, Cr.ltoreq.1%, Nb.ltoreq.0.1%, Ti.ltoreq.0.1%, V.ltoreq.0.2%, B.ltoreq.0.004%, 0.002%.ltoreq.N.ltoreq.0.013%, S.ltoreq.0.003%, P.ltoreq.0.015%. The structure consists of, in surface fraction: between 8 and 50% of retained austenite, at most 80% of intercritical ferrite, the ferrite grains, if any, having an average size of at most 1.5 .mu.m, and at most 1% of cementite, the cementite particles having an average size lower than 50 nm, martensite and/or bainite.