Cold rolled and heat-treated steel sheet and a method of manufacturing thereof

Abstract

The invention relates to a cold rolled and heat-treated steel sheet having a composition comprising in percentage by weight: C : 0.03 - 0.12 %, Mn : 1.2 - 2.3%, Al : 0.01 - 0.1%, Nb : 0.01% - 0.1%, Ti ≤ 0.12%, P ≤ 0.09 %, S ≤ 0.09 %, N ≤ 0.009% and can contain Si ≤ 2 %, Cr ≤ 0.5 %, Ni ≤ 3%, Ca ≤ 0.005%, Cu ≤ 2%, Mo ≤ 0. 5%, V ≤ 0.1%, B ≤ 0.003%, Ce ≤ 0.1%, Mg ≤ 0.010%, Zr ≤ 0.010%, the remainder being iron and unavoidable impurities caused by processing, the microstructure of said steel sheet comprising in area fraction, 5% to 10% Cementite, 31 to 50% of Recrystallized ferrite wherein the average grain size of recrystallized ferrite is less than or equal to 2.5 microns, 45 to 64% of non-recrystallized ferrite, wherein the cumulated amount of recrystallized ferrite and non-recrystallized ferrite is from 85% to 95% and includes 0.5% to 2% of Carbides of Niobium, the optional cumulated amount of residual austenite and martensite being from 0% to 5%.

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