HIGH-STRENGTH HOT-ROLLED STEEL WITH HIGH IMPACT STRENGTH AND YIELD POINT OF NOT LESS THAN 800 MPA AND METHOD FOR PRODUCTION THEREOF

摘要

FIELD: metallurgy.;SUBSTANCE: invention relates to metallurgy, particularly, to high-strength structural hot-rolled steel. Steel has the following chemical composition, in wt. %: C 0.02–0.05, Si≤0.5, Mn 1.5–2.5, P≤0.015, S≤0.005, Al 0.02–0.10, N≤0.006, Nb 0.01–0.05, Ti 0.01–0.03, 0.03 ≤ Nb + Ti ≤ 0.06, Cr 0.1–0.5, Mo 0.1–0.5, B 0.0005–0.0025, the balance being Fe and unavoidable impurities. Steel is melted in converter or electric furnace, secondary cleaning is carried out in vacuum furnace and casting in form of cast workpiece or ingot. Cast billet or ingot is heated to temperature of 1100–1200 °C and maintained for 1–2 hours. Performing hot rolling at initial rolling temperature equal to 1000–1100 °C, wherein multi-pass rolling is carried out at temperature ≥950 °C with accumulated strain rate ≥50 % to obtain intermediate billet, which is cooled to temperature of 900–950 °C, and last 3–5 rolling passes are performed with accumulated rate of deformation ≥70 %. Performing successive hardening at cooling rate ≥5 °C/s from temperature exceeding ferrite extraction temperature by 800–900 °C, to temperature below formation of martensite Ms or room temperature to obtain fine-grained super-low-carbon rack martensite.;EFFECT: obtaining steel having yield point of not less than 800 MPa, ultimate tensile strength ≥900 MPa, relative elongation ≥13 % and impact energy ≥100 J at temperature of −80 °C.;6 cl, 6 dwg, 3 tbl