| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel pipe with isotropic and superior ductility and collision-impact resistance characteristics without requiring a large-scale process modification by combining stretch-rolling and skew-rolling at the rolling temperature from Ac3 transformation point to specific temperature after the material containing C, Si, Mn and Al of specific compositions and having a composition composed of Fe and unavoidable impurities of the remaining portion is made into a material pipe. SOLUTION: The material containing 0.005 to 0.30% C, 0.01 to 3.0% Si, 0.01 to 4.0% Mn, and 0.001 to 0.10% Al in weight is rolled by combining stretch- rolling and skew-rolling at the rolling temperature from Ac3 transformation point to 400 deg.C. It is preferable to add one type or more selected from 1% or less Cu, 2% or less Ni, 2% or less Cr, and 1% or less Mo, and/or one type or more selected from 0.1% or less Nb, 0.3$ or less V, 0.2% or less Ti, and 0.004% or less B, and/or one or two types selected from 0.02% or less REM and 0.01% or less Ca.
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