| 摘要 |
PURPOSE:To manufacture an electric welded steel pipe having exactly improved toughness at the weld zone by heat-treating the weld zone of an electric welded steel pipe by holding at the Ac3 point -1,000 deg.C for a specified time. CONSTITUTION:The weld zone of an electric welded steel pipe manufactured by high frequency welding is heat-traated by holding at the Ac3 point -1,000 deg.C for 30-120min. When the temp. is <1,000 deg.C, the grains are coarsened to deteriorate the toughness. When the holding time is <30min, the toughness improving effect of the heat treatment is not produced, and the effect is not further improved even when the holding time exceeds 120min. |
