The thick meat high tension hot rolling steel sheet and its production method of being superior in low temperature tenacity

摘要

PPROBLEM TO BE SOLVED: To provide a method for producing a thick and high tension hot-rolled steel plate which is suitable as a raw metal for high strength electroseamed steel pipe having X65-class or higher, and excellent in low temperature toughness. PSOLUTION: To a steel raw material containing, by mass, 0.02-0.25% C, 0.3-2.3% Mn, 0.03-0.25% Nb, 0.001-0.10% Ti so as to satisfy (Ti+Nb/2)/C4, hot-rolling composed of rough-rolling and finish-rolling, is applied, and after completing the finish-rolling, a first process which performs accelerated cooling till becoming ≤500°C at ≥30°C/s surface cooling speed, a second process which performs air-cooling within 10s after the first process, and successively, a third process which acceleratively cools till becoming in the temperature range of 350°C to 600°C of the center of the plate, are applied in order, and this cooled steel plate is wound at the winding temperature of 350°C to 600°C. PCOPYRIGHT: (C)2010,JPO&INPIT