METHOD OF PRODUCING HIGH-STRENGTH SHEET STEEL, CHARACTERIZED BY IMPROVED DUCTILITY AND MOLDABILITY, AND OBTAINED SHEET STEEL Russian patent published in 2020 - IPC C21D8/02 C21D9/46 C22C38/58 C23C2/06 

FIELD: metallurgy.

SUBSTANCE: to increase mechanical properties of sheet steel, method of producing sheet steel includes following successive stages: obtaining cold-rolled sheet steel, wherein chemical composition of steel includes, wt %: 0.15 % ≤ C ≤ 0.23 %; 2.0 % ≤ Mn ≤ 2.8 %; 1.0 % ≤ Si ≤ 2.1 %; 0.02 % ≤ Al ≤ 1.0 %; wherein 1.7 % ≤ Si + Al ≤ 2.1 %; 0 ≤ Nb ≤ 0.035 %; 0 ≤ Mo ≤ 0.3 %; 0 ≤ Cr ≤ 0.4 %; wherein the residue is Fe and unavoidable impurities, annealing the sheet steel at the annealing temperature T_A so as to obtain a structure, containing at least 65 % of austenite and up to 35 % of intercritical ferrite, hardening of sheet at cooling rate of at least 20 °C/s, from temperature of at least 600 °C, up to quenching temperature QT, concluded within Ms −170 °C to Ms −80 °C, sheet heating to distribution temperature of PT in range from 350 °C to 450 °C and preservation of sheet at given temperature during distribution time Pt, concluded within 80 to 440 seconds, immediate cooling of sheet to room temperature, wherein sheet steel has a final microstructure, consisting in surface proportions of: from 40 % to 70 % of tempered martensite, from 7 % to 15 % of residual austenite, from 15 % to 35 % of ferrite, at most 5 % of fresh martensite, at most 15 % of bainite.

EFFECT: proposed method of producing high-strength sheet steel characterized by improved ductility and moldability, and produced sheet steel.

30 cl, 3 tbl, 1 dwg