FIELD: metallurgy.
SUBSTANCE: invention relates to a method of producing high-strength steel sheet with coating, having improved plasticity and formability, wherein the steel sheet with coating has a YS yield point of at least 800 MPa, a ultimate tensile strength TS of at least 1,180 MPa, a total elongation of at least 14 % and a HER bore distribution coefficient of at least 30 %, by means of thermal treatment and application of coating on sheet made of steel, having the following chemical composition, wt%: 0.13≤C≤0.22, 1.9≤Si≤2.3, 2.4≤Mn≤3, Al≤0.5, Ti≤0.05, Nb≤0.05, the rest is Fe and unavoidable admixtures, thermal treatment and coating include the following stages: sheet annealing at annealing temperature TA higher than Ac3, but below 1,000 °C for 30 to 300 s, quenching the sheet by cooling it to quenching temperature QT between 200 °C and 280 °C with cooling rate sufficient to obtain a structure consisting of austenite and at least 50 % martensite, with an austenite content such that the final structure, i.e. after treatment, coating and cooling to room temperature, can contain from 3 % to 15 % residual austenite and from 85 % to 97 % total martensite and bainite, without ferrite, sheet heating to PT redistribution temperature between 430 °C and 490 °C and sheet holding at this temperature during Pt redistribution time between 10 s and 100 s, this stage is a redistribution stage, hot coating of sheet by dipping and sheet cooling to room temperature. Invention covers also steel sheet coated by said method.
EFFECT: production of high-strength steel sheet with coating, which has improved strength, ductility and formability and improved flanging ability of inner edges.
18 cl, 1 dwg, 1 tbl, 8 ex
