HIGH-STRENGTH COLD-ROLLED SHEET STEEL AND METHOD OF ITS PRODUCTION Russian patent published in 2015 - IPC C21D8/02 C22C38/00 

FIELD: metallurgy.

SUBSTANCE: steel plate is produced with definite chemical composition and microstructure including in vol %: ferritic phase from 40% to 60%, beinite phase from 10% to 30%, tempered martensite phase from 20% to 40%, and residual austenite phase from 5% to 20%. Complies with the condition when fraction of the tempered martensite phase with main axis length ≤ 5 mcm in relation to total volume fraction of the tempered martensite phase is from 80% to 100%. During the plate production hot rolling, pickling, first annealing at temperature range from 350°C to 650°C, cold rolling, second annealing at temperature range from 820°C to 900°C, third annealing at temperature range from 720°C to 800°C, cooling with rate from 10°C/s to 80°C/s to holding temperature from 300°C to 500°C are performed. Holding time at temperature in the specified range is from 100 s to 1000 s, and fourth annealing at temperature range from 100°C to 300°C is performed.

EFFECT: assurance of good weldability of the steel plate, bending properties, ability of flanging and tensile strength 1180 MPa or over, increased relative elongation.

2 cl, 3 tbl