METHOD FOR PRODUCING ULTRA HIGH STRENGTH COATED OR NON-COATED STEEL SHEET AND OBTAINED SHEET Russian patent published in 2018 - IPC C21D8/02 C22C38/00 C23C2/06 C21D9/46 

FIELD: metallurgy.

SUBSTANCE: improve the strength-ductility balance and formability, a cold-rolled steel sheet having a tensile strength ≥ 1470 MPa and total elongation of TE ≥ 19 % is obtained, the method comprising steps of annealing at an annealing temperature AT ≥ As₃ an untreated steel sheet, the chemical composition of which comprises, wt. %: 0.34 ≤ C ≤ 0.40, 1.50 ≤ Mn ≤ 2.30, 1.50 ≤ Si ≤ 2.40, 0 < Cr ≤ 0.5, 0 < Mo ≤ 0.3, 0.01 ≤ Al ≤ 0.07, the balance being Fe and unavoidable impurities, and quenching the annealed steel sheet by cooling it to quenching temperature QT < Ms transformation temperature and between 150 °C and 250 °C, and performing partitioning treatment by reheating the quenched steel sheet to a partitioning temperature PT between 350 °C and 420 °C and holding the steel sheet at this temperature for a partitioning time between 15 seconds and 120 seconds.

EFFECT: improving the strength-ductility balance and improving formability.

5 cl, 3 tbl