Critical Role of IN82 and IN625 Filler/Buttering Combinations on the Integrity of Nuclear‐Grade P91/304L Gas Tungsten Arc Welding Joints

This study evaluates the microstructural and mechanical impacts of three filler/buttering combinations (IN82 and IN625) on dissimilar welded joints between P91 martensitic steel and 304L austenitic stainless steel using gas tungsten arc welding. Microstructural analysis revealed that IN625/IN625 (Joint 1) featured a wide carbon‐depleted zone. IN82/IN625 (Joint 3) produced narrower carbon‐enriched and depleted zones. The presence of Type I and II boundaries is depicted at IN82/IN82 (Joint 2) and Joint 3, but absent in Joint 1. The highest ultimate tensile strength is achieved by Joint 1 (647 ± 5 MPa) and an efficiency of 110%. In comparison, Joint 2 achieved superior ductility (27 ± 3%) and toughness (148 ± 5 J) in the weld metal. In contrast, Joint 3 exhibited the lowest tensile strength (621 ± 6 MPa) and toughness (62 ± 3 J), attributed to Mo and Nb segregation. Hardness profiling indicates peak values in the coarse‐grained heat‐affected zone of 278 HV, 315 HV, and 352 HV for Joints 1, 2, and 3, respectively. Fractography analysis shows ductile dimpling in Joint 2, brittle fracture in Joint 1 due to intermetallics, and a hybrid fracture mode in Joint 3. While all joints met standard requirements, the IN82/IN82 emerges as the most cost‐effective option, which indicates the suitability for long‐term service conditions.