PRODUCTION METHOD FOR SEAMLESS STEEL PIPE USED IN LINE PIPE, AND SEAMLESS STEEL PIPE USED IN LINE PIPE

摘要

There is provided a method for manufacturing a seamless steel pipe for line pipe, capable of improving the toughness of the seamless steel pipe for line pipe. A round billet having a chemical composition, by mass percent, of C: 0.02 to 0.15%, Si: at most 0.5%, and Mn: 0.5 to 2.5%, the balance being Fe and impurities, is heated (S1). The heated round billet is piercing-rolled to produce a hollow shell (S2). The hollow shell is elongated and rolled and sized to produce a seamless steel pipe (S3). The seamless steel pipe is water cooled, and the water cooling is stopped when the temperature of the seamless steel pipe reaches at most 450°C (S5). The water-cooled seamless steel pipe is quenched (S6), and the quenched seamless steel pipe is tempered (S7).