عنوان اختراع: ورق فولاد نورد سرد آنیل شده و روشی برای ساخت آن"Cold rolled and annealed steel sheet and method of manufacturing the"

خلاصه اختراع

Cold rolled and annealed steel sheet and method of manufacturing the same Abstract The invention deals with a cold-rolled and heat-treated steel sheet, made of a steel having a composition comprising, by weight percent:: C : 0.03 - 0.25 % Mn : 3.5 - 8 % Si : 0.1 – 2.0 % Al : 0.03 – 2.0 % Ti ≤ 0.080 % Nb ≤ 0.080 % V ≤ 0.2 % V + Ti + Nb > 0.01% S ≤ 0.010 % P ≤ 0.020 % N ≤ 0.008 % and comprising optionally one or more of the following elements, in weight percentage: Mo : 0.1 - 0.5 % Cr : 0.01 - 1 % B : 0.0005 - 0.004 % the remainder of the composition being iron and unavoidable impurities resulting from the smelting, said cold-rolled steel sheet having a microstructure consisting of, in surface fraction: - between 10% and 30% of retained austenite, said retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of such Martensite Austenite islands having a size above 0.5 µm, - at most 10% of fresh martensite and - recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. It also deals with a manufacturing method thereof.