ArcelorMittal S.A.
High formability steel sheet for the manufacture of lightweight structural parts and manufacturing process

Abstract:

A steel sheet has a composition comprising, by weight: 0.010%.ltoreq.C.ltoreq.0.080%, 0.06%.ltoreq.Mn.ltoreq.3%, Si.ltoreq.1.5%, 0.005%.ltoreq.Al.ltoreq.1.5%, S.ltoreq.0.030%, P.ltoreq.0.040%, Ti and B such that: 3.2%.ltoreq.Ti.ltoreq.7.5% and (0.45.times.Ti)-1.35.ltoreq.B.ltoreq.(0.45.times.Ti)-0.43, optionally Ni.ltoreq.1%, Mo.ltoreq.1%, Cr.ltoreq.3%, Nb.ltoreq.0.1%, V.ltoreq.0.1%, the remainder being iron and unavoidable impurities resulting from the smelting. The steel sheet has a structure consisting of ferrite, at most 10% of austenite, and precipitates comprising eutectic precipitates of TiB.sub.2, the volume fraction of TiB.sub.2 precipitates with respect to the whole structure being of at least 9%, the proportion of TiB.sub.2 precipitates having a surface area lower than 8 .mu.m.sup.2 being of at least 96%.