ArcelorMittal S.A.
Process for manufacturing cold-rolled and annealed steel sheet with a very high strength, and sheet thus produced

Abstract:

The present invention provides a cold-rolled and annealed steel sheet with a strength greater than 1200 MPa, the composition of which includes, the contents being expressed by weight: 0.10%.ltoreq.C.ltoreq.0.25%, 1%.ltoreq.Mn.ltoreq.3%, A.gtoreq.0.010%, Si.ltoreq.2.990%, S.ltoreq.0.015%, P.ltoreq.0.1%, N.ltoreq.0.008%, it being understood that 1%.ltoreq.Si+Al.ltoreq.3%, it being understood that Cr+3Mo.gtoreq.0.3%, Ti in an amount such that Ti/N.gtoreq.4 and Ti.ltoreq.0.040%. A balance of the composition includes iron and inevitable impurities resulting from the smelting. The microstructure of the steel includes 15 to 90% bainite, the remainder includes martensite and residual austenite.