METHOD FOR PRODUCING LOW YIELD RATIO HIGH TENSILE STRENGTH STEEL SHEET HAVING EXCELLENT GAS CUTTING CRACK RESISTANCE AND HIGH HEAT INPUT WELDED JOINT TOUGHNESS AND REDUCED ACOUSTIC ANISOTROPY

摘要

PROBLEM TO BE SOLVED: To provide an advantageous method for producing a high tensile strength steel sheet having excellent gas cutting crack resistance and high heat input welded joint toughness, also having reduced acoustic anisotropy, further having high plastic deformability, and having tensile strength in the class of 590 MPa.;SOLUTION: A steel stock in which a chemical componential composition is suitably controlled is heated to the temperature range of 950 to 1,300°C, is then rolled at a cumulative draft in the temperature range of an austenite unrecrystallization temperature t(°C) shown by prescribed formula or below so as to be finished at ≥(austenite unrecrystallization temperature t-80°C) to ≤1,100°C, is thereafter directly quenched from a temperature of ≥780°C to ≤300°C at the cooling rate of ≥3°C/s, is successively subjected to reheating quenching in the temperature range of 760 to 840°C, and is subsequently tempered in the temperature range of 450 to 550°C.;COPYRIGHT: (C)2006,JPO&NCIPI