| 摘要 |
PROBLEM TO BE SOLVED: To restrain hardening of a seam part formed by jointing an open pipe edge part in a wide range of a component system. SOLUTION: In this manufacturing method, a belt steel 10 is molded into an open pipe 11 while it is continuously fed, and both opposed edge parts are jointed by welding or solid-phase pressure welding to form a raw pipe 12. Then, the raw pipe is sequentially draw-rolled to form a product pipe 13 of a given size. In this case, immediately after welding or solid-phase pressure welding, a seam part 14 is bead-rolled by a bead rolling device 6 at a rolling temperature of 750-950 deg.C and a pressing ratio of 15% or more.
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