METHOD OF PRODUCING HIGH-STRENGTH SHEET STEEL, CHARACTERIZED BY IMPROVED DUCTILITY AND MOLDABILITY, AND OBTAINED SHEET STEEL

FIELD: metallurgy.SUBSTANCE: to provide ultimate tensile strength of at least 980 MPa, relative elongation of at least 16%, hole expansion factor of more than 20 %, method for production of sheet steel involves the following consecutive stages: obtaining cold-rolled sheet steel containing, in wt %: 0.15 ≤ C ≤ 0.23; 1.4 ≤ Mn ≤ 2.6; 0.6 ≤ Si ≤ 1.5; 0.02 ≤ Al ≤ 1.0; at that 1.0 ≤ Si + Al ≤ 2.0; 0 ≤ Nb ≤ 0.035; 0 ≤ Mo ≤ 0.3; 0 ≤ Cr ≤ 0.3; Fe and unavoidable impurities-the rest, annealing of sheet steel at annealing temperature TA, which is within range from Acto Ac, so as to obtain structure, containing at least 40 % of austenite and at least 40 % intercritical ferrite, tempering sheet from temperature of at least 600 °C, at cooling rate, making at least 20 °S/s, up to quenching temperature QT, concluded within 180 °C to 260 °C, sheet heating up to PT tempering temperature in range from 375 °C to 470 °C and maintaining the sheet at a given tempering temperature of PT for a time Pt in range of 25 s to 440 s, wherein time Pt will be included in range from 100 s to 440 s in case of tempering temperature of PT, ranging from 375 °C to 400 °C, and will be confined within 25 s to 150 s in case of tempering temperature of PT, enclosed within 450 °C to 470 °C, sheet cooling to room temperature, wherein sheet steel has a final microstructure, consisting of parts of area from: at least 11 % of tempered martensite, from 10 % to 20 % of residual austenite, from 40 % to 60 % of ferrite, at most 6 % of fresh martensite, at most 18 % of bainite.EFFECT: proposed method of producing high-strength sheet steel characterized by improved ductility and moldability, and produced sheet steel.35 cl, 5 tbl, 1 dwg Изобретение относится к области металлургии. Для обеспечения предела прочности при растяжении по меньшей мере 980 МПа, относительного удлинения по меньшей мере 16%, коэффициента раздачи отверстия более 20% способ производства листовой стали включает следующие последовательные стадии: получение холоднокатаной листовой стали, содержащей в мас. %: 0,15 ≤ С ≤ 0,23, 1,4 ≤ Mn ≤ 2,6, 0,6 ≤ Si ≤ 1,5, 0,02 ≤ Al ≤ 1,0, при этом 1,0 ≤ Si + Al ≤ 2,0, 0 ≤ Nb ≤ 0,035, 0 ≤ Мо ≤ 0,3, 0 ≤ Cr ≤ 0,3, Fe и неизбежные примеси - остальное, отжиг листовой стали при температуре отжига TА, заключенной в пределах от Асдо Ас, таким образом, чтобы получить структуру, содержащую по меньшей мере 40% аустенита и по меньшей мере 40% межкритического феррита, закалка листа от температуры, составляющей по меньше