Mechanical Integrity of Inconel 617-AISI 304H Steel-Welded Joints Fabricated by Pulsed GTAW

Abstract This study presents a comprehensive evaluation of the mechanical properties and microstructural evolution of a multi-pass dissimilar welded joint (DWJ) fabricated between Inconel 617 (IN617) and austenitic stainless steel AISI 304H using the Pulsed Gas Tungsten Arc Welding (PGTAW) process. Nickel-based filler metals ERNiCr-3 and ERNiCrCoMo-1 were employed for fabricating the DWJ, owing to their superior metallurgical compatibility and proven ability to mitigate weldability issues during welding of Ni- and Fe-based alloys. The weld metal (WM) exhibited a heterogeneous microstructure comprising columnar, cellular, and equiaxed dendrites, along with carbide precipitation and elemental segregation, as observed by optical microscopy and field-emission scanning electron microscopy. Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed that the ERNiCrCoMo-1 weld, with its finer austenitic dendritic structure, contained Mo 6 C and M 23 C 6 precipitates enriched in Mo and Cr, whereas NbC and TiC precipitates dominated the ERNiCr-3 weld. Microstructural analysis of the WM/AISI 304H interface revealed a filler-deficient zone featuring unmixed zones, islands, and peninsulas, while the IN617/WM interface showed a distinct partially melted zone (PMZ) with negligible unmixed zones, especially in the ERNiCrCoMo-1 filler. The electron backscatter diffraction (EBSD) analysis confirms a substantial change in the microstructural orientation of the WM, heat-affected zone (HAZ), and across the weld interface. The inverse pole figure (IPF) maps confirm that the weld exhibits better-oriented grains as compared to the weld interfaces. Grain boundary (GB) maps show a higher fraction of high-angle grain boundary (HAGBs) in the ERNiCrCoMo-1 weld in comparison to ERNiCr-3, which confirms smaller grains and higher strength of ERNiCrCoMo-1 weld. Room-temperature tensile testing indicated that the cross-weld specimens exhibited tensile strength marginally lower than that of Inconel 617 but exceeded that of the AISI 304H base metal for both filler metals and it was 676 ± 4 and 678 ± 3 MPa for ERNiCrCoMo-1 weld and ERNiCr-3 weld, respectively. Under elevated temperature conditions, the ERNiCrCoMo-1 weld maintained tensile strength (370 MPa at 650 °C and 299 at 700 °C) substantially lower than Inconel 617 and significantly higher than AISI 304H, whereas the ERNiCr-3 weld showed tensile strength (308 MPa at 650 °C and 240 at 700 °C) comparable to AISI 304H, indicating acceptable high-temperature performance, particularly for the ERNiCrCoMo-1 weld. Microhardness results revealed superior hardness in the ERNiCrCoMo-1 weld (249 ± 6 HV) compared to ERNiCr-3 (238 ± 6 HV), with both exhibiting a declining trend from IN617 towards AISI 304H base metal. Charpy impact testing showed that the ERNiCr-3 weld exhibited a higher impact toughness of 136 ± 5 J compared to 123 ± 3 J for the ERNiCrCoMo-1 weld. Nevertheless, both filler metal welds satisfied the minimum impact energy requirement of 47 J as stipulated by ASME standards, confirming their adequacy for structural applications. Based on comprehensive microstructural and mechanical evaluations, the ERNiCrCoMo-1 filler metal demonstrated the best balance of performance and reliability compared to ERNiCr-3 when employed for dissimilar welding of IN617 and AISI 304H base metals using the Pulsed GTAW process.