ArcelorMittal S.A.
FORGED PART OF BAINITIC STEEL AND A METHOD OF MANUFACTURING THEREOF

Abstract:

A steel for forging mechanical parts including of the following elements, expressed in percentage by weight: 0.15% .ltoreq.C.ltoreq. 0.22%; 1.6% .ltoreq.Mn.ltoreq. 2.2%; 0.6% .ltoreq.Si.ltoreq. 1%; 1% .ltoreq.Cr.ltoreq. 1.5%; 0.01% .ltoreq.Ni.ltoreq. 1%; 0% .ltoreq.S.ltoreq. 0.06%; 0% .ltoreq.P.ltoreq. 0.02%; 0% .ltoreq.N.ltoreq. 0.013%; and having optional elements 0% .ltoreq.Al.ltoreq. 0.06%; 0.03% .ltoreq.Mo.ltoreq. 0.1%; 0% .ltoreq.Cu.ltoreq. 0.5%; 0.01% .ltoreq.Nb.ltoreq. 0.15%; 0.01% .ltoreq.Ti.ltoreq. 0.03%; 0% .ltoreq.V.ltoreq. 0.08%; 0.0015% .ltoreq.B.ltoreq. 0.004%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel having microstructure by area percentage including of cumulative presence of residual austenite and martensite-austenite island between 1% and 20%, the remaining microstructure being bainite having at least 80%, wherein the fraction of grain boundaries of bainite with a misorientation angle of 59.5.degree. are at least 7% and with an optional presence of martensite between 0% and 10%.