| 摘要 |
PURPOSE:To improve toughness at low temp. in a weld zone, by heating the weld zone of an electric resistance welded tube from the outside surface of the steel tube and by applying rapid cooling from the inside surface of the steel tube directly after the temp. in the central part of the thickness reaches a specific value. CONSTITUTION:The weld zone of a the electric resistance welded tube is heated from the outside surface of the electric resistance welded tube by using an induction heating device. When the temp. in the central part of the thickness of the weld zone reaches >=1,000 deg.C, the weld zone is rapidly cooled without delay from the inside surface of the electric resistance welded tube. By heating the central part of the thickness up to >=1,000 deg.C as mentioned above, an ice- flower-like structure is dissipated in a short time and further a fine microstructure is formed by means of rapid cooling from the inside surface, so that a weld zone having toughness at low temp. equal to that in a base metal part can be obtained.
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