在役15X1M1Φ钢焊接接头早期失效分析及其预防

Analysis and countermeasures for earlier failure of welded joint of 15X1M1Φ steel in service

通过理化检验、裂纹形貌观察,研究了在役15X1M1Φ钢焊接接头裂纹性质及其原因。结果表明,裂纹起源于靠近熔合线的焊缝金属或热影响区粗晶区,可观察到宏观裂纹、微裂纹和空洞3种不同缺陷形貌。根据裂纹产生的位置、过程和形貌特征,可以判断该裂纹为焊接再热裂纹。焊后热处理温度场不合理产生的残余应力,焊接结构导致的强应力集中,支吊架不正常引起的附加应力,服役过程中接头塑性的降低,是导致该裂纹产生的主要原因。优化焊接和焊后热处理工艺以保证接头足够的临界塑性变形能力εc,服役过程中避免和降低应力集中和附加应力以降低接头塑性变形量εp,始终保证εc>εp,以避免具有再热裂纹敏感性的焊接接头服役过程中产生再热裂纹。

Characteristics and forming causes of the cracks in welded joint of 15X1M1Φ steel in service were investigated by mechanical and chemical testing and crack morphology observation.The results show that the cracks initiate from welded metal or coarse grain heat affect zone near fusion line,and there are three kinds of defects which are macrocracks,microcracks and voids observed in the crack region.According to the forming position,process and morphology of the cracks,it is estimated that the cracks are kind of stress relief cracking.The main reasons of the cracking are because of residual stress caused by improper temperature field during post welding heat treatment,strong stress concentration caused by welding structure,additional stress caused by abnormal hangers supports and decreased ductility of welded joint in service.The stress relief crack in welded joint with high sensitivity of stress relief cracking in service can be avoided through optimizing the welding process and postweld heat treatment process to ensure enough critical ductility deformation ability εc and avoiding and reducing stress concentration and additional stress to decrease ductility deformation εP of welded joint which make εcεp consistently.