| 摘要 |
PURPOSE: To produce a welded steel pipe for oil well capable of executing laser welding at the welding speed equal to ERW method and having >=L80kg grade excellent in SSC resistance of weld zone. CONSTITUTION: In the case where a hoop consisting of the prescribed composition is continuously formed to open pipe like by passing through forming roll groups, both edges are butted by pressing this open pipe by a squeeze roll. The butted part is irradiated with laser beam and butt welded for welded steel tube, by irradiating laser beam and welding under the conditions satisfying the formula, V>=2 (V is welding speed, m/min) and formula, P>=0.4Vt/e<a(> T<-> T<0)> [wherein is 0.0006; P is laser output (kW); (t) is hoop thickness (mm); T is preheating temp. of both edges of hoop ( deg.c); and T is room temp. ( deg.C)]. Then a welded seam part or whole steel tube is heated to AC3 temp. or more, successively is tempered at 600 deg.C to AC1 or less. |
