Patent ID: 9175360
Filing Date: 2015-11-03
Classification: C21D,C22C,F16L

Abstract:
1. A method for manufacturing a seamless steel pipe for line pipe, comprising the steps of: heating a round billet having a chemical composition comprising, by mass percent, C: 0.02 to 0.15%, Si: at most 0.5%, Mn: 0.5 to 2.5%, and Cu: 0.05 to 1.5% the balance being Fe and impurities; producing a hollow shell by piercing-rolling the heated round billet; producing a seamless steel pipe by elongation rolling and sizing the hollow shell; water cooling the seamless steel pipe at a cooling rate of at least 10° C./sec and stopping water cooling when the temperature of the seamless steel pipe reaches lower than 400° C. to cause bainitic transformation; heating and soaking the water-cooled seamless steel pipe to cause reverse transformation from a bainite to an austenitic structure; water cooling the heated and soaked seamless steel pipe; and tempering the heated, soaked, and water-cooled seamless steel pipe.