METHOD FOR PRODUCTION OF HIGH-STRENGTH SHEET STEEL WITH APPLIED COATING, CHARACTERIZED BY IMPROVED DUCTILITY AND MOLDABILITY, AND PRODUCED SHEET STEEL WITH APPLIED COATING Russian patent published in 2020 - IPC C21D8/02 C23C2/06 C22C38/00 C21D9/46 B23K11/11 

FIELD: metallurgy.

SUBSTANCE: for production of coated steel sheet characterized by ultimate tensile strength TS of at least 1100 MPa, total relative elongation of TE, in accordance with ISO 6892-1 component making at least 12 %, wherein product of TS×TE ultimate tensile strength and total elongation is at least 14200 MPa–%, and the HER orifice expansion ratio, according to ISO 16630:2009 standard making at least 25 %, the following successive steps are carried out: obtaining a cold-rolled sheet steel containing the following, wt %: 0.15 ≤ C ≤ 0.23; 2.0 ≤ Mn ≤ 2.7; wherein C + Mn/10 ≥ 0.420; 0 ≤ Cr ≤ 0.40; wherein Mn + Cr ≥ 2.25; 0.2 ≤ Si ≤ 1.6; 0.02 % ≤ Al ≤ 1.2; wherein 1.0 ≤ Si + Al ≤ 2.2; 0 ≤ Nb ≤ 0.035; 0 ≤ Mo ≤ 0.1; Fe and unavoidable impurities—balance, sheet steel is annealed at annealing temperature T_A to obtain a structure containing at least 65 % of austenite and not more than 35 % of intercritical ferrite, tempering the sheet from temperature of at least 600 °C, at cooling rate in range from 20 °C/s to 50 °C/s, up to quenching temperature QT in range from 200 °C to 270 °C, sheet heating to PT temperature, lying within 400 °C to 480 °C, and holding at PT temperature for time Pt, lying within range of 50 s to 250 s, application on coating sheet by immersion into melt at temperature of less than 515 °C, coated sheet is cooled to room temperature, wherein sheet steel has a microstructure consisting of surface proportions of: from 3 % to 15 % of residual austenite of at least 30 % of tempered martensite, at most 5 % of fresh martensite, at most 35 % of bainite, wherein sum of surface fractions of tempered martensite, fresh martensite and bainite is in range from 55 % to 92 %, and from 5 % to 35 % of ferrite.

EFFECT: proposed is a method of producing high-strength sheet steel with applied coating, characterized by improved ductility and moldability, and produced sheet steel with applied coating.

33 cl, 4 tbl, 1 dwg