ArcelorMittal S.A.
COLD ROLLED AND ANNEALED STEEL SHEET, METHOD OF PRODUCTION THEREOF AND USE OF SUCH STEEL TO PRODUCE VEHICLE PARTS

Abstract:

A cold rolled and annealed steel sheet is provided which includes by weight: 0.6<C<1.3%, 15.ltoreq.Mn<35%, 6.0.ltoreq.Al<15%, Si.ltoreq.2.40%, S.ltoreq.0.015%, P.ltoreq.0.1%, N.ltoreq.0.1%, possibly one or more optional elements chosen among Ni, Cr and Cu in an individual amount of up to 3% and possibly one or more elements chosen among B, Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, the microstructure of said sheet comprising at least 0.1% of intragranular kappa carbides, wherein at least 80% of such kappa carbides have an average size below 30 nm, optionally up to 10% of granular ferrite, the remainder being made of austenite, the average grain size and average aspect ratio of the austenite being respectively below 6 .mu.m and comprised between 2 and 10 and the average grain size and average aspect ratio of the ferrite, when present, being respectively below 5 .mu.m and below 3.0, the density of said steel sheet being equal or below 7.2 and its tensile elongation being at least 5.0%. Also provided is a manufacturing method and with use of such grade for making vehicle parts.