METHOD OF PRODUCING HIGH-STRENGTH STEEL SHEET WITH COATING, HAVING IMPROVED STRENGTH AND DUCTILITY, AND OBTAINED SHEET Russian patent published in 2019 - IPC C21D9/46 C22C38/02 C22C38/04 C22C38/06 C22C38/12 C21D1/19 C23C2/06 C23C2/40 B32B15/01 

FIELD: iron metallurgy.

SUBSTANCE: invention relates to a method of producing high-strength steel sheet with coating, having yield point YS of at least 800 MPa, tensile strength TS of at least 1180 MPa, total elongation of at least 14 % and HER hole distribution coefficient of at least 30 %. Steel contains, wt. %: 0.13 % ≤ C ≤ 0.22 %, 1.2 % ≤ Si ≤ 1.8 %, 1.8 % ≤ Mn ≤ 2.2 %, 0.10 % ≤ Mo ≤ 0.20 %, Nb ≤ 0.05 %, Al ≤ 0.5 %, Ti < 0.05 %, the rest being Fe and unavoidable impurities. Sheet is annealed at temperature TA exceeding Ac₃, but below 1000 °C, for a period of time of 30–300 s, then quenched by cooling at temperature QT from 325 °C to 375 °C, at a cooling rate sufficient to obtain a structure consisting of austenite and at least 60 % martensite, wherein content of austenite is such that final structure can contain from 3 % to 15 % residual austenite and from 85 % to 97 % sum of martensite and bainite, without ferrite, wherein cooling rate exceeds 30 °C/s, then sheet is held at quenching temperature QT during holding time from 2 s to 8 s, after which sheet is heated to temperature redistribution of PT from 430 °C to 480 °C and held at this temperature for a time of redistribution of Pt from 10 s to 90 s, then hot coating is applied by immersion with subsequent cooling to room temperature.

EFFECT: present invention relates to a method for producing a high strength coated steel sheet having improved strength, ductility and formability and to the sheets obtained with the method.

13 cl, 1 dwg, 2 tbl, 10 ex