ArcelorMittal S.A.
COLD ROLLED ANNEALED STEEL SHEET WITH HIGH HOLE EXPANSION RATIO AND MANUFACTURING PROCESS THEREOF

Abstract:

A cold rolled annealed steel sheet having a chemical composition including, in weight %: 0.30%.ltoreq.C.ltoreq.0.50%, 1.00%.ltoreq.Mn.ltoreq.2.50%, 1.00%.ltoreq.Si.ltoreq.2.00%, Al.ltoreq.2.00%, Cr.ltoreq.0.100%, 0.100%.ltoreq.Mo.ltoreq.0. 500%, 0.020%.ltoreq.Nb.ltoreq.0.200%, B.ltoreq.0.0005%, P.ltoreq.0.02%, S.ltoreq.0.005%, N.ltoreq.0.01%, the remainder being Fe and unavoidable impurities, with the percentages in carbon, manganese, chromium, molybdenum and boron are such that the alloy satisfies the following condition: 250% C+120% Mn-200% Cr+200% Mo-10000% B.gtoreq.320, and wherein the microstructure comprises in surface fraction, 35% to 45% of islands of martensite and retained austenite (M-A), the total retained austenite is higher than or equal to 24%, the remainder consisting of bainitic ferrite.