Cold-rolled flat steel product and method for the production thereof

Abstract

A cold-rolled flat steel product may have a yield strength Rp0.2 of not more than 320 MPa, a fracture elongation A80 of at least 20% and a microstructure having by percent area 62%-82% ferrite, 10%-30% martensite, 1.5%-8% residual austenite, and a sum total of not more than 10% other microstructure constituents. The flat steel product may comprise a steel alloy containing in percent by weight 0.06%-0.1% C; 0.15%-0.4% Si; 1.5%-2% Mn; 0.2%-0.5% Cr; not more than 0.1% Al; wherein the sum total of C, Si, Mn, and Cr is at least 2.3% and not more than 2.8%; wherein the sum total of Si and Al is not more than 0.4%; not more than 0.03% P; not more than 0.006% S; not more than 0.008% N; unavoidable impurities including not more than 0.0006% B, not more than 0.02% V, and not more than 0.01% each of Nb and Ti, and not more than 0.1% each of Mo, Ni, and Cu; as well as iron. For production of such a flat steel product, a cold-rolled flat steel product may first be produced and then brought to 760-860° C. in a continuous run and kept at that temperature over an annealing period Gt for which, depending on the thickness D of the flat steel product, Gtu≤Gt≤Gto with[s]=3.56*[s/mm]−5.1*[s/mm]+9.8 s[s]=−21.4*[s/mm]+132.8*[s/mm]+47 s.