COLD-ROLLED, ANNEALED AND REDISTRIBUTED STEEL SHEET AND METHOD FOR ITS MANUFACTURE Russian patent published in 2024 - IPC C21D1/18 C21D1/22 C21D8/02 C21D9/46 C22C38/02 C22C38/04 C22C38/06 C22C38/12 C22C38/14 C22C38/18 

FIELD: metallurgy.

SUBSTANCE: high-strength steel sheets with high weldability can be used in the automotive industry. Cold rolled, annealed and carbon redistributed steel sheet made of steel having a composition containing, in wt.%: C 0.05–0.18, Mn 6.0–11.0 ≤Al < 0,05, Mo 0.5–0.0005, B 0.005–0.010, S ≤ 0.020, P ≤ 0.008, 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, V≤ 0.2, iron and inevitable impurities formed during smelting - the rest. The sheet has a microstructure that includes, in surface fractions: from 0 to 30% ferrite, which, if present, has a grain size of less than 1.0 µm, from 8 to 40% of retained austenite, with the proportion of austenite islands larger than 0.5 µm equal to 5% or less, 30 to 92% redistributed martensite, 0 to 3% fresh martensite, carbon [C]_A and manganese [Mn]_A content of austenite, expressed as percent by weight, such that the ratio ([C]_A²× [Mn]_A) / (C%²×Mn%) is less than 18.0, with C% and Mn% being the nominal values of carbon and manganese content in wt%. The resistance spot weld of two steel parts is made of cold-rolled, annealed and carbon redistributed steel sheet, 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.

EFFECT: sheet is characterized by high values of mechanical properties, weldability and resistance to liquid metal embrittlement.

13 cl, 3 dwg, 7 tbl, 2 ex