METHOD OF PRODUCING A COATED STEEL SHEET HAVING HIGH STRENGTH, DUCTILITY AND DEFORMABILITY Russian patent published in 2019 - IPC C21D8/02 C21D9/46 C21D1/26 C23C2/00 

FIELD: metallurgy.

SUBSTANCE: to provide yield point > 550 MPa, ultimate tensile strength TS > 980 MPa and increased plasticity and deformability sheet is made from steel containing, wt. %: 0.15 ≤ C ≤ 0.25, 1.2 ≤ Si ≤ 1.8, 2 ≤ Mn ≤ 2.4, 0.1 ≤ Cr ≤ 0.25, Al ≤ 0.5, Fe and rest impurities are heated to temperature between TA1 = Ac₃ - 0.45 * (Ms - QT) and TA2 = 830 °C for at least 30 s and cooled at a rate greater than 30 °C/s to quenching temperature QT 180–300 °C, then sheet is heated to PT redistribution temperature equal to 380–480 °C, with exposure for time Pt of 10–300 s, and cooled to room temperature with a cooling rate of at least 25 °C/s. To produce steel sheet with coating between stages of steel sheet heating to PT redistribution temperature with holding and cooling to room temperature coating is applied by its immersion into melt or coating is applied by electrolytic method after sheet is cooled to room temperature. Steel sheet has structure comprising 5–25 % of intercritical ferrite, at least 50 % of redistributed martensite, more than 10 % of residual austenite, less than 10 % of fresh martensite and bainite, wherein sum of redistributed martensite and bainite is at least 60 %. Sheet is made with or without coating.

EFFECT: disclosed is a method of producing a coated steel sheet having high strength, ductility and deformability.

20 cl, 3 tbl, 1 dwg