COLD-ROLLED ANNEALED STEEL SHEET AND METHOD OF ITS MANUFACTURE Russian patent published in 2023 - IPC C21D1/18 C21D1/22 C21D6/00 C21D8/02 C21D9/46 C22C38/04 C22C38/06 C22C38/12 

FIELD: metallurgy.

SUBSTANCE: invention relates to high-strength steel sheets with good weldability characteristics. Cold-rolled and annealed steel sheet made of steel having the following composition, 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, and optionally one or more of the following: Si ≤ 1.20, Ti ≤ 0.050, Nb ≤ 0.050, Cr ≤ 0.5, V ≤ 0.2, while the rest of the composition consists of iron and inevitable impurities formed during smelting. The sheet has a microstructure that includes, in surface fractions: from 25 to 55% retained austenite, from 5 to 50% ferrite, from 5 to 70% precipitated martensite, from 0 to 5% fresh martensite, while the content of carbon [C]_A and manganese [Mn]_A in austenite, expressed in wt.%, is such that the ratio ([C]_A² x [Mn]_A) / (C%² x Mn%) is from 3.0 to 8.0, where C% and Mn% represent the nominal values of carbon and manganese in wt.% and the heterogeneous distribution of manganese with areas below and above the nominal value of manganese. A weld produced by resistance spot welding of two parts made from the specified cold-rolled and annealed steel sheet has the meaning α, constituting at least 30 daN/mm², where α represents the ratio of tensile strength to the product of the diameter of the weld spot and the thickness of the base.

EFFECT: cold rolled and annealed steel sheet has high mechanical properties.

11 cl, 2 dwg, 7 tbl, 4 ex