ArcelorMittal S.A.
TEMPERED AND COATED STEEL SHEET HAVING EXCELLENT FORMABILITY AND A METHOD OF MANUFACTURING THE SAME

Abstract:

A tempered and coated steel sheet having a composition containing the following elements, expressed in percentage by weight: 0.17%.ltoreq.carbon.ltoreq.0.25%, 1.8%.ltoreq.manganese.ltoreq.2.3%, 0.5%.ltoreq.silicon.ltoreq.2.0%, 0.03%.ltoreq.aluminum.ltoreq.1.2%, sulphur.ltoreq.0.03%, phosphorus.ltoreq.0.03%, the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet containing in area fraction, 4 to 20% residual austenite, 0 to 15% of ferrite, 40 to 85% tempered bainite and a minimum of 5% of tempered martensite, wherein the cumulated amounts of tempered martensite and residual austenite is between 10 and 30%. The composition may also contain one or more of the following elements: chromium.ltoreq.0.4%, molybdenum.ltoreq.0.3%, niobium.ltoreq.0.04%, titanium.ltoreq.0.1%. Manufacturing methods and use of tempered and coated steel sheet for making vehicle parts are also described.