| 摘要 |
Disclosed is a seamless steel pipe for line pipes which has high strength, good toughness and good corrosion resistance even when it is formed thick. This seamless steel pipe for line pipes has a chemical composition consistin g of, in mass%, 0.02-0.08% of C, not more than 0.5% of Si, 1.5-3.0% of Mn, 0.0 01- 0.10% of Al, more than 0.4% and not more than 1.2% of Mo, 0.002-0.015% of N, 0.0002-0.007% of Ca, and the balance of Fe and impurities. In the impurities , P is not more than 0.03%, S is not more than 0.005%, O is not more than 0.005%, and B is less than 0.0005%. The seamless steel pipe for line pipes i s also characterized in that the value of Pcm calculated by the formula (1) below is not less than 0.185 and not more than 0.250, and the seamless steel pipe has a metal structure mainly composed of bainite wherein the length of cementite is not more than 20 .mu.m. Pcm = [C] + [Si]/30 + ([Mn] + [Cr] + [Cu])/20 + [Mo]/15 + [V]/10 + 5[B] (1) In the formula, [C], [Si], [Mn], [Cr] , [Cu], [Mo], [V] and [B] represent numbers corresponding to respective conten ts of C, Si, Mn, Cr, Cu, Mo, V and B expressed in mass%.
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