Critical assessment of the welded joint between SS-316 and Inconel 718

Dissimilar welding of Inconel 718 and SS-316 was carried out using TIG welding with SS304 filler, followed by post-weld heat treatment (PWHT) at 900 °C, 950 °C, and 1000 °C under air cooling (normalizing) and furnace cooling (annealing). Microstructural analysis revealed a defect-free fusion zone with dendritic solidification, along with unmixed zones and Nb-rich Laves phases concentrated in the Inconel heat-affected zone (HAZ). The maximum hardness measured on the Inconel side reached 418 HV, while the fusion zone exhibited an average hardness of 184 HV, and the SS-316 side showed ~ 163 HV, confirming a progressive hardness increase from SS toward Inconel. Tensile testing showed that all samples fractured in the SS-316 parent metal, establishing that the welds possessed higher strength than both base metals. The average tensile strength of the as-welded joints was ~ 600 MPa, which decreased to ~ 573 MPa after PWHT at ≥ 950 °C due to Laves phase coarsening and microstructural changes. Annealed samples at 950 °C and 1000 °C exhibited the highest ductility with a maximum strain of 0.32 mm. The results confirm that TIG welding produced a sound dissimilar joint and that PWHT significantly influenced microstructure, hardness, and tensile performance, with moderate-temperature annealing improving hardness without severely compromising strength.