Impact of Buttering on Microstructure and Mechanical Behavior of IN718-ASS304L Dissimilar Joint

This study investigates the metallurgical and mechanical properties of gas tungsten arc welded dissimilar joints between Inconel 718 (IN718) and austenitic stainless steel 304L (ASS304L), incorporating an ERNiCr-3 buttering layer and two different filler materials, ERNiCrCoMo-1 and ERNiCr-3. The application of the buttering layer aims to improve metallurgical compatibility between the dissimilar weld metals. An ERNiCr-3 buttering layer approximately 6 to 7 mm thick was deposited onto the ASS304L plates, followed by dissimilar welding using two different filler wires: ERNiCrCoMo-1 (IN617) and ERNiCr-3. Microstructural analysis using optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy indicates the formation of different dendritic solidification patterns (cellular, columnar, and equiaxed patterns) within the buttering zone and weld metals. The ERNiCr-3 buttering zone and weld metal exhibited Nb/Ti-rich precipitates, while the ERNiCrCoMo-1 welds showed a higher density of Mo/Cr-rich carbide phases. The buttering interface with ASS304L displayed minimal unmixed zones and a smooth elemental transition, effectively mitigating carbon migration. The fusion interfaces exhibited epitaxial grain growth, and no significant defects such as hot cracking or porosity were observed, as confirmed by X-ray radiography. Mechanical evaluations demonstrated that the ERNiCrCoMo-1 weld achieves a higher mean hardness (249 HV0.5) than the ERNiCr-3 weld (231 HV0.5), attributed to the solid strengthening effect of Mo-rich phases. Tensile testing indicates a fracture within the ERNiCr-3 buttering zone, with ultimate tensile strength of 620 MPa (ERNiCrCoMo-1) and 613 MPa (ERNiCr-3), both meeting ASME standards. Charpy impact toughness testing further confirmed the improved performance, with the weld center toughness values measured at 92 J (ERNiCrCoMo-1) and 151 J (ERNiCr-3), significantly higher than comparable non-buttered joints reported in literature. The buttering zone also achieved toughness values above 70 J, meeting the minimum standards for elevated temperature conditions. The findings conclusively demonstrate that the application of a Ni-based buttering layer substantially enhances the metallurgical compatibility, hardness profile, tensile strength, and impact toughness of IN718-ASS304L dissimilar welds.