| 摘要 |
<p>PURPOSE: To stabilize the hardness near an electric resistance welded part and to prevent the crack defect caused by stress concn. CONSTITUTION: In a method for executing heat treatment to a welded part of an electric resistance welded steel tube 1 at a prescribed temp., plural sets of post-annealing devices 2, 3, 4 are arranged as zigzag state by centering a welding wire W, and the welded part is heated to the Ac3 temp. or higher. By this method, fracture of the electric resistance welded steel tube caused by the stress concn. to near the electric resistance welded part can be prevented.</p> |
