METHOD OF PRODUCING SHEET STEEL, CHARACTERIZED BY IMPROVED STRENGTH, DUCTILITY AND FORMABILITY Russian patent published in 2020 - IPC C21D8/02 C21D9/46 C21D1/26 C23C2/00 C22C38/00 

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy. To increase yield point and ultimate tensile strength, method of producing sheet steel with microstructure consists of the following components: from 20 % to 50 % of intercritical ferrite, from 10 % to 20 % of residual austenite, from 25 % to 45 % of tempered martensite, from 10 % to 20 % of fresh martensite and bainite and from 30 % to 60 % of total amount of tempered martensite and bainite, includes production of cold-rolled sheet steel containing chemical composition, wt. %: 0.18 ≤ C ≤ 0.25, 0.9 ≤ Si ≤ 1.8, 0.02 ≤ Al ≤1.0, wherein 1.00 ≤ Si + Al ≤ 2.35, 1.5 ≤ Mn ≤ 2.5, 0.010 ≤ Nb ≤ 0.035, 0.10 ≤ Cr ≤ 0.40, Fe and unavoidable impurities are the rest, annealing of sheet steel at annealing temperature T_A during annealing time t_A with provision of structure containing 50 % to 80 % austenite and 20 % to 50 % ferrite, quenching of sheet at cooling rate from 20 °C/s to 50 °C/s to quenching temperature QT from Ms - 50 °C to Ms - 5 °C, sheet heating to distribution temperature of RT from 375 °C to 450 °C and holding the sheet at the distribution temperature of the PT during the Pt distribution time of at least 50 s, and cooling the sheet to room temperature.

EFFECT: high yield point and ultimate tensile strength.

21 cl, 8 tbl