X80埋弧焊热影响区的微观组织与局部软化行为分析

Analysis of microstructure and local softening of heataffected zone of submerged-arc welded X80 joint

以X80高等级管线钢埋弧焊接头作为研究对象,利用小尺寸拉伸样配合数字图像相关技术(DIC)对其热影响区的局部软化现象和失效行为做了表征,研究接头热影响区的强度退化和组织演变之间的关系.应用数字图像相关技术的拉伸应变云图表明,单道焊热影响区内的一次细晶区(FGHAZ)及两道焊交叠热影响区内的二次细晶亚区(UAFZHAZ和ICFGHAZ)均发生了明显的软化现象.微观组织表征结果表明,微区内部位错缠结、位错墙等亚结构消失导致的位错强化效果的下降和M/A组元形态及数量变化导致的析出强化效果的减弱是软化发生的主要原因;在两道焊交叠热影响区,二次细晶亚区的局部软化可以被周围的其它区域有效缓和,对接头的安全服役威胁较小,相比之下,一次细晶区的强度退化更值得关注.

X80 pipeline steel was welded by submerged arc welding process.The local softening phenomenon and failure behavior of heat-affected zone(HAZ)of the welding joint were characterized by digital image correlation(DIC)tensile tests using mini-sized flat specimens.The relationship between strength degradation and microstructural evolution was discussed carefully.The DIC results show that the primary fine-grain heat-affected zone(FGHAZ)and the secondary heataffected zone(UAFZHAZ and ICFGHAZ)are both the softening areas in HAZ of joint.The microstructural characterization shows that the softening is mainly attributed to the dislocation strengthening weakening resulting from the decreasing of dislocation tangles and dislocation walls and the precipitation strengthening weakening due to the changes in form and quantity of M/A.But,the softening of secondary heat affected zone can be effectively alleviated by other surrounding regions which is favorable to joint.On the contrary,the strength degradation of the primary heat affected zone has a greater threat to the service safety of welded joints.