| 摘要 |
PURPOSE:To give an embossed shape easily by controlling a martensite transformation quantity by varying the cooling temp. in the longitudinal direction in case of cooling a steel pipe from the austenitizing temp. CONSTITUTION:A steel pipe 1 is passed continuously through an induction heater 4, etc. and cooling water jet device 5, etc. In this case, the unevenness is periodically formed in the length direction of the steel pipe 1 by varying the cooling water quantity of the cooling water jet device 5 periodically for the part becoming >=austenitizing temp. by coming out of the induction heater 4. Namely, the outer diameter La1 and inner diameter Lb1 of the part 2 which is rapidly cooled after being heated >=austenitizing temp. become larger respectively than the outer diameter La2 and inner diameter Lb2 of the slowly cooled part 3 and the embossed shape is formed in the length direction of the steel pipe 1. This method may be applied easily for the dissimilar pipe of angular pipe, etc. as well.
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