T92/HR3C异种钢接头的蠕变损伤演化

Damage evolution of T92/HR3C dissimilar steel welded joints during creep

对T92/HR3C异种钢焊接接头进行温度为650℃、应力为90 MPa的系列蠕变中断试验,利用光学显微镜、扫描电子显微镜对经过不同蠕变寿命分数试样的显微组织和蠕变孔洞损伤进行了观察与定量,并测试了接头蠕变断裂后的硬度分布.结果表明,T92/HR3C异种钢接头断裂在T92侧细晶粒热影响区(FGHAZ),断裂方式为IV型开裂,接头镍基焊缝和HR3C侧未见孔洞损伤.接头T92侧FGHAZ的蠕变损伤过程可划分为3个阶段,在蠕变初期(<40%t_(f),t_(f)为断裂寿命),FGHAZ的孔洞数量很少;在蠕变中期(60%t_(f)~80%t_(f)),蠕变损伤快速积累,孔洞数量急剧增加,并出现少量微裂纹;在蠕变寿命的后期(>80%t_(f)),大量微裂纹形成并扩展形成宏观裂纹.接头中T92侧FGHAZ的硬度最低,蠕变性能劣化最严重,加上在高温蠕变过程中存在Laves相粒子的析出和长大,促进了蠕变孔洞损伤的形成.

A series of creep interrupt tests were carried out on the T92/HR3C dissimilar steel welded joint(DSWJ)at a temperature of 650℃and a stress of 90 MPa.The microstructure and creep void damage of specimens with different creep life fractions were observed by OM and SEM and then quantified using image process software.The hardness distribution of the joint after creep was measured.The results show that the weakest area is the fine grain heat-affected zone(FGHAZ)of T92 side in the DSWJ,and the fracture mode is type IV cracking.No creep void damage was found in the Nibased weld metal and HR3C side of the joint.The creep damage process in the T92-side FGHAZ of DSWJs can be divided into three stages.In the initial creep stage(<40%t_(f),t_(f) is the fracture life),the number of cavities was very small.In the middle period of creep(60%t_(f)-80%t_(f)),creep damage accumulated rapidly,the number of cavities increased sharply,and a few microcracks appeared.In the late stage of creep(>80%t_(f)),a large number of microcracks formed and expanded to form macrocracks.The hardness of T92 side FGHAZ is the lowest in the DSWJ,the creep properties deteriorate seriously,and the second phase particles,especially the Laves phase precipitate and grow up,all of which promote the formation of creep cavity damage and eventually type IV fracture occurs.