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

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 Ni-based 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.