Production method for seamless steel pipe used in line pipe, and seamless steel pipe used in line pipe

摘要

Disclosed is a production method for seamless steel pipes used in line pipes, whereby the toughness of seamless steel pipes used in line pipes can be improved. A round billet having a chemical composition that includes, in mass%, 0.02 to 0.15% C, no more than 0.5% Si, and 0.5 to 2.5% Mn, with the remainder comprising Fe and impurities, is heated (S1). Rotary piercing is performed on the heated round billet to produce a blank tube (S2). The blank tube is rolled and the diameter thereof is fixed, thereby producing a seamless steel pipe (S3). The seamless steel pipe is cooled with water, and water cooling is halted when the temperature of the seamless steel pipe reaches 450°C or lower (S5). The cooled seamless steel pipe is quenched (S6). The quenched seamless steel pipe is tempered (S7).