ArcelorMittal S.A.
COLD ROLLED AND HEAT TREATED STEEL SHEET AND A METHOD OF MANUFACTURING THEREOF

Abstract:

A cold rolled and heat treated steel sheet, the steel having a composition with, in weight percentage, 0.18%.ltoreq.carbon.ltoreq.0.24%, 1.5%.ltoreq.manganese.ltoreq.2.5%, 1.2%.ltoreq.silicon.ltoreq.2%, 0.01%.ltoreq.aluminum.ltoreq.0.06%, 0.2%.ltoreq.chromium.ltoreq.0.5%, phosphorus.ltoreq.0.02%, sulfur.ltoreq.0.03%, and optionally one or more of the following elements niobium.ltoreq.0.06%, titanium.ltoreq.0.08%, vanadium.ltoreq.0.1%, calcium.ltoreq.0.005% and the balance including iron and unavoidable impurities, the steel sheet having a microstructure having 0% to 15% of tempered martensite, 10% to 15% of residual austenite and optionally up to 30% of ferrite in area fractions, the balance being made of bainite, bainite content being at least 55% and having an internal oxide layer of 3 microns or less on both surfaces of the steel sheet. A manufacturing method and with use of such grade for making vehicle parts is also provided.