| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To overcome the difficulty of efficiently heating an electric resistance welded steel pipe across its entire wall thickness to a target temperature in a conventional heat-treatment (seam annealing) method of a welded part of the pipe. <P>SOLUTION: A plurality of stands 15, each of which having induction coils 11a and 13a disposed at both inside and outside of the pipe 5, is disposed in a direction in which the pipe is passed, and the welded part is subjected to induction heating from both inside and outside of the pipe. At a stand between a first stand and a stand other than the last stand, the welded part is heated until the inside and outside temperatures of the welded part at the outlet side of the stand exceed an Ac<SB>3</SB>transformation temperature, and at the following stands, the welded part is heated so that the inside and outside temperatures of the welded part are kept at a prescribed temperature higher than the Curie point and that the center of thickness of the welded part reaches a target temperature. <P>COPYRIGHT: (C)2009,JPO&INPIT</p> |
