| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a welded steel pipe of a low-yield-ratio and HIC resistance, exhibiting excellent weld toughness after SR (stress relief annealing), and a method of producing the same. <P>SOLUTION: The welded steel pipe of a low-yield-ratio and HIC resistance, exhibiting excellent weld toughness after SR, includes a base material comprising Al, Ti and Ca, and further comprising at least one element selected from Cu, Ni, Cr, Mo, Nb and V, and is characterized in that Ceq is at least 0.28, PHIC is 1.00 or lower, ACR is from 1.0 to 4.0. The metal structure of the base material present in the central part in the thickness direction of the pipe includes polygonal ferrite and pseudo polygonal ferrite having a mean particle diameter of 10 to 40 μm and a mean aspect ratio of not higher than 2.0 in an amount of from 80 to 95 volume%, and a second hard phase in an amount of from 5 to 20 volume%. The weld metal part of the welded steel pipe is made of a similar metal to the base material, and Pcm is at least 0.12, and PSR is not higher than 0.025. <P>COPYRIGHT: (C)2013,JPO&INPIT |
