Effect of chemical composition on microstructure evolution, mechanical properties and solidification cracking sensitivity in dissimilar welding of Incoloy 825 and AISI 321 stainless steel was investigated in this research. Samples of mentioned parent metals were prepared with the design of butt joint and each of them was GTA welded with Inconel 625, Incoloy 65, and ER347 filler metals. Optical Microscope, Scanning Electron Microscope, Energy Dispersive X-ray analysis and X-ray Diffraction method were used to investigate different areas including base metals microstructure, weld zone, and heat affected zone. Tensile strength, impact toughness and micro-hardness of the weldments were tested. Weld metals had predominantly austenitic structure and segregation of Mo and Nb to inter-dendritic spaces and solidification grain boundaries led to secondary phase precipitation in Incoloy and Inconel welds. Tensile test results showed that Inconel 625 weld had the highest strength and ruptures occurred in stainless steel base metals. All weldments showed the ductile mode of fracture. The lowest hardness value belongs to ER347 weld comparing to other samples. Varestraint weldability tests were done to evaluate the welded sample’s resistivity of solidification cracking. Thus, innumerous standard samples were fitted up and welded, and then GTA was applied to remelt the weld metal while the samples are under bending strains of 0.25, 1, 2 and 4 percents. Cracked solidified weld pools were extracted by Plasma Cutting Process for further investigations with Optical Microscope, and combined Scanning Electron Microscope with Energy dispersive X-ray method. Inconel 625 welds had the most hot crack resistivity, while continuous network of low-melting phases precipitated along ER347 welds grain boundaries caused a high crack sensitivity comparing to other welds. Dilatometery test also was done over samples of dissimilar base metals and undiluted filler metals to . Results demonstrated that among three fillers, Inconel 625 could be effective as a bridge to join two dissimilar parent metals in terms of thermal expansion coefficient. Key words; Incoloy 825, dissimilar welding, weldability, Varestraint, dilatometery
