METHOD OF MANUFACTURING HIGH-STRENGTH STEEL SHEET WITH IMPROVED STRENGTH, PLASTICITY AND FORMABILITY Russian patent published in 2019 - IPC C21D9/46 C21D8/02 C21D1/20 C22C38/38 

FIELD: metallurgy.

SUBSTANCE: method of producing a high-strength steel sheet having YS yield strength of at least 850 MPa, TS tensile strength of at least 1180 MPa, a full elongation of at least 14 % and a distribution coefficient of the HER hole of at least 30 %. Composition of the steel contains in wt. %: 0.15≤C≤0.25; 1.2≤Si≤1.8; 2≤Mn≤2.4; 0.1≤Cr≤0.25; Nb≤0.05; Ti≤0.05; Al≤0.50 and the rest being Fe and inevitable impurities. This sheet is annealed at TA annealing temperature above Ac₃, but below 1000 °C for a time longer than 30 s by cooling it to QT quenching temperature between 275 °C and 325 °C with cooling rate, sufficient to obtain, immediately after annealing, a structure consisting of austenite and at least 50 % of martensite, the content of austenite is such that the final structure contains 3–15 % of residual austenite and 85–97 % of the sum of martensite and bainite without ferrite, is heated to the RT redistribution temperature of 420–470 °C, incubated at this temperature for a time of 50–150 s and cooled to room temperature.

EFFECT: resulting steel sheet has improved ductility and improved formability.

14 cl, 1 dwg, 1 tbl