| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a welded steel pipe having excellent crushing strength, which can be produced in high productivity at a low cost without deteriorating its circularity and deformability, and has excellent brittle crack propagation arresting performance, and to provide a method for producing the same. <P>SOLUTION: The steel pipe is obtained by subjecting a thick steel plate having a composition comprising specified amounts of C, Si, Mn, P, S, Al, Nb, Ti and N, and further comprising one or more kinds selected from Cu, Ni, Cr, Mo and V to bending into a pipe shape and welding the butted parts so as to be a steel pipe, and thereafter expending the steel pipe, wherein the total of the volume fractions of a ferrite phase and a bainite phase in the steel pipe is≥80%, the average hardness difference of the two phases is 50 to 150, the volume fraction of an insular martensite phase included in the balance is≤2%, and the gathering degree of the (100) plane in the rolling face at the central position of the pipe thickness obtained by X-ray diffraction is≥1.5. <P>COPYRIGHT: (C)2010,JPO&INPIT</p> |
