COLD-ROLLED ANNEALED STEEL SHEET AND METHOD OF ITS MANUFACTURE Russian patent published in 2023 - IPC C21D8/02 C21D6/00 C21D9/46 C22C38/02 C22C38/04 C22C38/06 C22C38/12 C22C38/14 C22C38/38 C22C38/32 C22C38/28 C22C38/26 C22C38/24 C22C38/22 B23K11/11 

FIELD: metallurgy.

SUBSTANCE: cold-rolled and martensitic steel sheet used in the automotive industry. The sheet is made of steel having a composition comprised of the following (wt.%): C: 0.03–0.18%, Mn: ≤6.0, Al: 0.2 - 3 Mo: {B>(0,05) B<B} 0.0005 – 0.005, S≤ 0.010,P≤ 0.020, N≤ 0.008, optionally at least one element selected from: Si≤ 1.20, Ti≤ 0.050, Nb≤ 0.050, Cr≤ 0.5 and V≤ 0.2, the rest is iron and inevitable impurities formed during smelting. The sheet has a microstructure containing, in surface fractions: from 30% to 55% of retained austenite, from 45% to 70% of ferrite, from 0 to 5% of fresh martensite. The concentrations of carbon [C]_A and manganese [Mn]_A in austenite, expressed in wt.%, satisfy the following condition: [C]_A*[Mn]_A/((0.1+C%²)*(Mn%+2))≥1.10, with C% and Mn% representing the nominal values of carbon and manganese content in wt.%. In the microstructure, heterogeneous re-precipitation of manganese with areas above and below the nominal value of manganese content in the steel sheet is characterized by a deviation of the manganese concentration distribution curve of -30 or more.

EFFECT: sheet has the required combination of mechanical properties.

11 cl, 2 dwg, 7 tbl