| 摘要 |
<p>[PROBLEMS] To provide a seamless steel pipe for a line pipe which is a thick steel pipe, has high strength and is excellent in toughness; and a method for producing the seamless steel pipe. [MEANS FOR SOLVING PROBLEMS] A thick seamless steel pipe for a line pipe having high strength and good toughness, characterized in that it has a chemical composition that c: 0.03 to 0.08 %, Si: 0.25 % or less, Mn: 0.3 to 2.5 %, Al: 0.001 to 0.10 %, Cr: 0.02 to 1.0 %, Ni: 0.02 to 1.0 %, Mo: 0.02 to1.2 %, Ti: 0.004 to 0.010%, N: 0.002 to 0.008 %, the total of one or more of Ca, Mg and REM: 0.0002 to 0.005 %, V: 0 to 0.08%, Nb: 0 to 0.05 %, Cu: 0 to 1.0 %, and the balance: Fe and impurities, with the proviso that P in the impurities is 0.05 % or less and S in the impurities is 0.005 % or less. The steel pipe may further comprise 0.0003 to 0.01 % of B in addition to the above components. A method for producing the steel pipe is characterized by the cooling rate of a cast steel product, the heating conditions for piercing and the heat treatment conditions after the formation of a pipe.</p> |
