Mechanical and Microstructural Characteristics of Gas Tungsten Arc Welded Similar and Dissimilar Joints of SS-316 L and Hastelloy C276

Hastelloy C-276 nickel alloy is widely preferred for nuclear power plant applications where steam generators operate at 600 degrees C. However, stainless steels are still used for tubes in steam gas reformers which necessitates welds between dissimilar materials. In this study, hastelloy C-276 and SS 316 L alloys were joined using GTAW process. The welding parameters of GTAW were optimized to minimize the defects in samples of similar (SS 316 L-SS 316 L, HAS C-276-HAS C-276), and dissimilar (HAS C-276-SS 316 L) joints. SEM/EDS results confirm the presence of columnar dendritic and cellular structure in fusion zone for dissimilar weldments (HAS C-276-SS 316 L). EDS results also revealed the presence of larger amount of Mo, W and lower amount of Ni in the subgrain boundary as compared to the subgrain body. Compared to the similar (HAS C-276- Has C-276) and dissimilar (HAS C-276-SS 316 L) welded joints FZs, the enrichment of Mo is lesser in SS 316 L-SS 316 L similar welded joints. Higher UTS was obtained for dissimilar (HAS C-276-SS 316 L) GTAW joints 780 MPa compared to the similar welded joints of SS316 (552 MPa) and HAS C-276 (740 MPa). The average microhardness for the dissimilar SS 316 L and HAS C-276 is 220 Hv, which is higher compared to the similar welded joints, SS 316 L and HAS C-276, i.e., 190 Hv and 210 Hv, respectively. This study shows that GTAW process is suitable to fabricate sound weld joints of similar (SS 316 L- SS 316 L, HAS C-276-HAS C-276), and dissimilar (HAS C-276-SS 316 L) alloys which are useful for the nuclear power plant boilers.