Manufacturing method of seamless steel pipe for line pipe and seamless steel pipe for line pipe

摘要

Provided is a method for producing a seamless steel pipe for a line pipe, which can improve the toughness of the seamless steel pipe for a line pipe. A round billet containing, by mass%, C: 0.02 to 0.15%, Si: 0.5% or less, Mn: 0.5 to 2.5%, and the balance of Fe and impurities. Is heated (S1). The heated round billet is pierced and rolled to produce a blank (S2). The raw pipe is drawn and rolled to produce a seamless steel pipe (S3). The seamless steel pipe is cooled with water, and the water cooling is stopped when the temperature of the seamless steel pipe reaches 450 ° C. or less (S5). The water-cooled seamless steel pipe is quenched (S6). The quenched seamless steel pipe is tempered (S7).