COLD-ROLLED ANNEALED STEEL SHEET AND METHOD OF ITS MANUFACTURE Russian patent published in 2023 - IPC C21D8/02 C21D6/00 C21D9/46 C22C38/12 C22C38/06 C22C38/04 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 6.0–11.0, Al 0.2–3, Mo 0.05–0.5, 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 steel sheet has a microstructure containing, in surface fractions, from 25 to 55% retained austenite, from 45 to 75% ferrite, from 0 to 5% fresh martensite. The content of carbon [C]_A and manganese [Mn]_A in austenite, expressed in wt.%, is such that the ratio ([C]_A×[Mn]²_A)/(C%×Mn%) is from 19.0 to 41.0 wt%, wherein C% and Mn% are the nominal values of the carbon and manganese content of the steel sheet in wt%. The density of carbides in the microstructure is less than 3×10⁶/mm² and heterogeneous re-release 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 profile curve of -30 or more.

EFFECT: sheet has a high level of mechanical properties.

9 cl, 2 dwg, 7 tbl