| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a heat treatment method for an electric resistance welded steel tube by which toughness in a weld zone of the electric resistance welded steel tube can be efficiently and stably improved. <P>SOLUTION: Heat treatment is applied to the weld zone of the electric resistance welded tube using a high-frequency induction heating apparatus in which a plurality of stands of the high-frequency induction heating means having induction coils on the outer surface of the tube in its longitudinal direction are arranged in a series. In this case, until the outer surface temperature of the tube weld zone exceeds an Ac<SB>3</SB>transformation point, the tube weld zone is heated so that the outer surface temperature of the tube weld zone at the outlet side of each stand becomes higher than the outer surface temperature of the tube weld zone in the outlet side of a stand one stand before each stand, and after the outer surface temperature of the tube weld zone exceeds the Ac<SB>3</SB>transformation point, in the high-frequency induction heating means of each stand, the frequency is adjusted and the outer surface temperature of the tube weld zone is set to the suitable temperature equal to the Curie point or higher so that the magnetic flux concentrates on the inner surface of the tube weld zone, and the tube weld zone is heated while the outer surface temperature of the tube weld zone is kept at the suitable temperature equal to the Curie point or higher. Thereby, the outer surface and the inner surface can be uniformly heated to the temperature exceeding the Ac<SB>3</SB>transformation point and the toughness in the weld zone is improved. <P>COPYRIGHT: (C)2009,JPO&INPIT</p> |
