COLD-ROLLED AND DOUBLE ANNEALED STEEL SHEET Russian patent published in 2023 - IPC C21D1/26 C21D6/00 C21D8/02 C21D9/46 C22C38/04 C22C38/06 C22C38/12 C22C38/14 

FIELD: metallurgy.

SUBSTANCE: invention relates namely to high-strength steel sheets with good weldability characteristics. Cold-rolled and double-annealed steel sheet made of steel having the following composition, wt.%: C 0.03 – 0.18, Mn 6.0 – 11.0, 0.2 ≤Al < 3, 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: Si ≤ 1.20, Nb ≤ 0.050, Ti ≤ 0.050, Cr ≤ 0.5, V ≤ 0.2, iron and inevitable impurities formed during smelting - the rest. The sheet has a microstructure containing, in surface fractions: from 0 to 45% ferrite, from 20 to 50% retained austenite, from 5 to 80% annealed martensite, from 0 to 5% fresh martensite, carbide density below 4×10⁶/mm². In this case, the ratio ([C]_A² x [Mn]_A) / (C% ² x Mn%) is satisfied, ranging from 4.5 to 11.0, where [C]_A and [Mn]_A are the carbon content and manganese in austenite, expressed in mass percent, C% and Mn% - nominal values of the C and Mn content in steel, wt.%. A weld of resistance spot welding of two steel parts made from cold-rolled and double-annealed steel sheet of the specified composition is characterized by the value α, which is at least 30 daN/mm², whereα - ratio of tensile strength, which is the force applied to destroy the weld point obtained by welding two parts, to the product of the diameter of the weld point and the thickness of the base of the seam.

EFFECT: sheets have high yield strength and tensile strength, and are also easy to form.

11 cl, 6 tbl, 3 ex