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

Abstract:

A cold rolled and heat treated steel sheet having a composition with the following elements, expressed in percentage by weight: 0.10%.ltoreq.Carbon.ltoreq.0.5%,1%.ltoreq.Manganese.ltoreq.3.4%, 0.5%.ltoreq.Silicon.ltoreq.2.5%, 0.03%.ltoreq.Aluminum.ltoreq.1.5%, 0%.ltoreq.Sulfur.ltoreq.0.003% 0.002%.ltoreq.Phosphorus.ltoreq.0.02%, 0%.ltoreq.Nitrogen.ltoreq.0.01% and can contain one or more of the following optional elements 0.05%.ltoreq.Chromium.ltoreq.1%, 0.001%.ltoreq.Molybdenum.ltoreq.0. 5%, 0.001%.ltoreq.Niobium.ltoreq.0.1%, 0.001%.ltoreq.Titanium.ltoreq.0.1%, 0.01%.ltoreq.Copper.ltoreq.2%, 0.01%.ltoreq.Nickel.ltoreq.3%, 0.0001%.ltoreq.Calcium.ltoreq.0.005%, 0%.ltoreq.Vanadium.ltoreq.0.1%, 0%.ltoreq.Boron.ltoreq.0.003%, 0%.ltoreq.Cerium.ltoreq.0.1%, 0%.ltoreq.Magnesium.ltoreq.0.010%, 0%.ltoreq.Zirconium.ltoreq.0.010% the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet having in area fraction, 10 to 30% Residual Austenite, 10 to 40% Bainite, 5% to 50% Annealed Martensite, 1% to 20% Quenched Martensite and less than 30% Tempered Martensite, wherein the cumulated amounts of Bainite and Residual Austenite is more than or equal to 25%.