Effect of heat input on the microstructures and mechanical properties of gas tungsten arc welded dissimilar joints between Hastelloy C-22 and Nitronic 50 stainless steel

Dissimilar metal welding is increasingly essential in advanced engineering applications such as chemical processing, marine, and nuclear industries, where the combination of high corrosion resistance and mechanical strength is required. However, achieving reliable joints between dissimilar alloys remains challenging due to differences in thermal and metallurgical properties. To address this, the present study investigates the influence of heat input on gas tungsten arc welded dissimilar joints between Hastelloy C-22 and Nitronic 50 stainless steel. Weldments were fabricated using two heat input conditions: low heat input (LHI, 162 J/mm) and high heat input (HHI, 270 J/mm), by varying the welding current (45 A and 75 A) while keeping voltage (15 V) and welding speed (2.5 mm/s) constant. ERNiCrMo-4 filler wire and argon shielding gas were used throughout. SEM confirmed the absence of welding defects, and optical microscopy revealed a mixed dendritic morphology in the LHI weld, while coarser columnar dendrites formed under HHI. EDS analysis showed Mo-rich intermetallic compounds (IMCs) in the interdendritic regions of both welds, with higher accumulation at the weld interface in the HHI condition due to slower cooling. Mechanical testing revealed better performance for the LHI weld, with higher tensile strength (825 MPa vs. 750 MPa), impact toughness (37.17 J vs. 15.21 J), and average hardness (220.7 HV vs. 190.8 HV). The LHI joint fractured in the Nitronic 50 base metal, while the HHI joint failed at the weld interface. These findings suggest that LHI conditions enhance weld quality by refining microstructure and limiting IMC formation.