Influence of heat treatment on microstructure and mechanical properties of pulsed Nd: YAG laser welded dissimilar sheets of Hastelloy C-276 and Monel 400

The study involved using a pulsed Nd:YAG laser welded Hastelloy C-276-Monel 400 dissimilar sheet by the process parameters viz. a pulse energy of 10 J, pulse repetition rate of 20 Hz and pulse duration of 0.006 s under spot weld mode. The objective was to investigate the effects of various post weld heat treatment (PWHT) conditions on the welded sheets. Microscopic analysis showed that the fusion zone and interfaces between the two metals contained smaller dendritic grains containing chromium-rich carbides and nickel-rich oxides. Both the Hastelloy C-276 and Monel 400 interfaces exhibited these traits. The PWHT of the quenched weld (water cooling) produced higher mechanical strength, while the annealed weld (furnace cooling) resulted in lower strength. Tensile failures were observed in the fusion zone for quenched and normalized welds, and in the base alloy of Hastelloy C-276 side for annealed weld under ductile fracture mode. XRD analysis showed the presence of more secondary phases and intermetallic compounds in the fusion zone and Hastelloy C-276 side in the annealed weld. The corrosion study indicated that the fusion zone and Monel 400 side had better corrosion resistance, followed by the Hastelloy C-276 side.