X70管线钢焊接热影响区韧性的研究

TOUGHNESS OF WELDING HEAT AFFECTED ZONE OF X70 PIPELINE STEEL

采用热模拟技术再现了X70管线钢焊接热影响区的组织,研究了热循环的改变对热影响区低温冲击韧性的影响及其断口特征.重点探讨了过热区的韧性对焊后冷速改变的敏感性.试验结果表明.随着峰值温度的提高.冲击韧性明显下降.断口形貌由韧窝状过渡到解理断裂.峰温950℃时.冲击韧性远远高于母材;峰温在1150℃和1350℃时,冲击韧性低于母材.加热到1350℃后,改变冷却速度.低温冲击韧性将发生显著变化.t_(8/5)为20s时.冲击韧性最佳.

By means of thermal cycle simulation technique, the paper deals with the changes of toughness with welding thermal cycle at low temperature of welding heat affected zone (HAZ). The toughness sensitivity of superheated zone to the variation of post cooling rate is discussed. The results show that its impact toughness reduced greatly after cyclic heating from high peak temperatures. The impact fracture morphology of pipeline X70 changes from dimple rupture to cleavage fracture. When peak temperature of thermal cycle is 950℃, the impact toughness is the highest. However, these values are low after cyclic heating to 1150℃ and 1350℃ peak temperatures. At the peak temperature of 1350℃, the toughness is very sensitive to the variation of post cooling rate. There is an optimum value of impact toughness while the retention time equals 20 seconds at high-temperature.