| 摘要 |
PROBLEM TO BE SOLVED: To provide a forged steel pipe excellent in workability and capable of stably withstanding strong working by improving an adhesive strength of a forged abutting portion. SOLUTION: The forged steel pipe has a 0.15 mm-or-short-deep line (do) in a forged abutting potion on the outer surface of the forged steel pipe, a 0.25 mm-or-short-deep line (di) in the forged abutting portion on the inner surface of the forged steel pipe, and an occupancy rate (A) of foreign matters in the forged abutting portion defined by a following formula <1> and being in the range of following formulas <2> and <3>. However, A=(L/t)×100 <1> (however, A: the occupancy rate of foreign matters (%) L: a total length in the direction of a thickness of the foreign matter in the forged abutting portion (mm) t: a thickness of the steel pipe (mm)), A≤-33×do+5.0 <2>, A≤-20×di+5.0 <3>. COPYRIGHT: (C)2007,JPO&INPIT
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