COLD-ROLLED, ANNEALED STEEL SHEET OR HOT-PRESSED, ANNEALED STEEL PART Russian patent published in 2023 - IPC C21D1/18 C21D1/22 C21D8/02 C21D9/46 C22C38/02 C22C38/04 C22C38/06 C22C38/12 C22C38/14 C22C38/18 

FIELD: metallurgy.

SUBSTANCE: cold-rolled, annealed and tempered steel sheets with good weldability. The cold-rolled, annealed and tempered steel sheet is made of steel having a yield strength YS of 1000 MPa or more and having the composition, wt.%: C 0.03–0.18, Mn 6.0–11.0, Mo 0.05–0.5, B 0.0005–0.005, S ≤ 0.010, P ≤ 0.020, N ≤ 0.008, and optionally including one or more of the following: Al < 3, Si ≤ 1.20, Ti ≤ 0.050, Nb ≤ 0.050, Cr ≤ 0.5 and V ≤ 0.2, iron and inevitable impurities formed during smelting - the rest. The sheet has a microstructure in surface fractions: from 0 to 30% ferrite having a grain size of less than 1.0 μm, from 3 to 30% retained austenite, from 40 to 95% tempered martensite, from 0 to 5% fresh martensite, while the content carbon [C]_A and manganese [Mn _A in austenite, expressed as a mass percentage, such that the ratio ([C]_A²× [Mn]_A)/(C%²× Mn%) is less than 7.80, with C% and Mn% being the nominal values of carbon and manganese content in % wt. A resistance spot weld of two steel parts made of cold-rolled, annealed and tempered steel sheet, and the weld is characterized by the valueα, constituting at least 30 daN/mm², whereα is the ratio of the tensile strength of a weld obtained by welding two parts to the product of the diameter of the weld point and the thickness of the base of the weld.

EFFECT: sheets are characterized by high mechanical properties and high resistance to liquid metal embrittlement.

12 cl, 2 dwg, 7 tbl, 7 ex