To provide a method for manufacturing a hardened steel tube, in which even in case of applying a working method opened in Patent Literature 1, the generation of oxidized scale can be restrained or eliminated.
The steel tube 10 is heated in the hardenable temperature zone with a high frequency induction heating coil 13 set at a first position A separated from the steel tube 10 while feeding the steel tube 10 in the longitudinal direction, and the hardened steel tube 10-1 is manufactured by injecting cooling water onto the steel tube 10 with a cooling device set in a second position B at the down-stream side of the feeding direction of the steel tube 10 from the first position A to harden the steel tube 10. N2 gas is supplied into a space 22 surrounding the heated portion 21 by injecting the N2 gas toward the directing side to the second position B from the first position A onto the heated portion with the high frequency induction heating coil 13 in the steel tube 10.
TOMIZAWA ATSUSHI
FUJIMOTO HIRONORI
NISHIHATA HITOMI
INOUE SABURO
SUMITOMO PIPE & TUBE CO LTD
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