| 摘要 |
A seamless steel pipe for line pipe having a high strength and good toughness and corrosion resistance even though having a thick wall has a chemical composition comprising, in mass percent, C: 0.02 - 0.08%, Si: at most 0.5%, Mn: 1.5 - 3.0%, Al: 0.001 - 0.10%, Mo: greater than 0.4% to 1.2%, N: 0.002 - 0.015%, Ca: 0.0002 - 0.007%, and a remainder of Fe and impurities, wherein the contents of the impurities are at most 0.03% for P, at most 0.005% for S, at most 0.005% for O and less than 0.0005% for B and wherein the value of Pcm calculated by the following Equation (1) is at least 0.185 and at most 0.250. The steel pipe has a microstructure which primarily comprises bainite and which has a length of cementite of at most 20 micrometers: Pcm = C + Si / 30 + ( [ Mn ] + Cr + Cu ) / 20 + [ Mo ] / 15 + V / 10 + 5 B
wherein [C], [Si], [Mn], [Cr], [Cu], [Mo], [V] and [B] are numbers respectively indicating the content in mass percent of C, Si, Mn, Cr, Cu, Mo, V and B. |
