To provide a manufacturing method of a steel tube by an induction heating method capable manufacturing the steel tube of excellent seam quality and having excellent surface skin with excellent productivity.
After a steel strip 1 is continuously formed by a forming roll group 3 to manufacture an open tube 7, the open tube 7 is preheated by a tubular body preheating equipment 13, and edge heating in which heating is achieved by the induction heating to the temperature range ≥1300°C and under the melting point is performed to each edge part of the open tube 7 using an induction heating coil for edge heating, and the tubes are butted to each other by a squeeze roll for pressure welding. Preheating is performed at the temperature ≤800°C. Edge heating and pressure welding are preferably performed in the atmosphere where the oxygen concentration is lower than that in the atmosphere, or in the atmosphere where the dew point is ≤-10°C. The time when the welded part is kept at the temperature of ≥1300°C after the pressure welding is preferably ≥0.03sec, or not less than the time to be determined by the oxygen concentration in the atmosphere.
HASHIMOTO YUJI
ITAYA MOTOAKI
YORIFUJI AKIRA
ONISHI TOSHIO
TANAKA NOBUKI
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