Microstructure and Mechanical Properties of Dissimilar Welded Joint of SP2215/T92

Dissimilar welded joints (DWJs) of SP2215 and T92 tubes were prepared by manual-gas tungsten arc welding (M-GTAW) and ERNiCr-3 filler. The microstructure, mechanical properties and tensile fracture mechanism of DWJ before and after heat treatment were studied. The results show that the weld metal (WM) is solidified into columnar dendrites with complete austenite structure, and Nb element is segregated between dendrites to form Nb-rich secondary phase particles. The post-welded heat treatment (PWHT) has no significant effect on the microstructure of weld seam. Island or peninsula macro-segregation is formed at both T92/WM and SP2215/WM interfaces, and the carbon migration occurs to a certain extent across the T92/WM interface. However, the phenomenon that the carbon migrates across the SP2215/WM interface is not obvious, and PWHT has no significant effect on macro-segregation and carbon migration. The hardness of the coarse grain heat affected zone (CGHAZ) at T92 side is the highest, followed by that of the fine grain heat affected zone (FGHAZ), whereas the inter-critical heat affected zone (ICHAZ) has the lowest hardness. PWHT reduces the hardness of CGHAZ and FGHAZ significantly and modifies the microstructure and mechanical properties of T92 HAZ. delta ferrite is formed near the fusion line in the T92 side, which is the area of DWJ with the lowest hardness. PWHT has no significant effect on the hardness of delta ferrite. Both the as-welded and heat-treated DWJs are fractured at the weld seam in a ductile manner at room temperature, whereas they are fractured at the T92 side in a ductile manner at 650 degrees C.