The metallurgical deterioration and carbon diffusion caused during welding in the vicinity of the fusion interfaces between dissimilar metals have been investigated in case of gas tungsten arc and shielded metal arc welded SA508Gr.3Cl.1 steel substrate with Ni–Fe alloy and Inconel 182. The study was conducted to investigate the effect of Ni–Fe matrix as buffer layer and SMAW process for buttering deposition on the carbon diffusion and metallurgical changes. Quantitative measurement and validation of carbon/alloying elements distribution in as-welded, thermally aged, and postweld heat-treated conditions were performed in buttering deposits by using optical emission spectrometry and electron probe microanalysis. The extent of carbon diffusion has been estimated using Groube’s diffusion couple and confirmed with microstructure microhardness and X-ray diffraction. Martensite formation has been estimated for its thickness and validated with metallurgical properties. The effect of buffer layer is significant for carbon diffusion and tempering of martensite with thermal aging, PWHT, and multipass deposition. The concentration and activity gradient of carbon has been established due to Ni–Fe matrix as buffer layer and higher dilution for buttering. The obtained results are confirming the control of carbon diffusion and lesser metallurgical deterioration in suggested buttering procedure.

The experimental investigations of two dissimilar metal weld (DMW) joints between SA508Gr.3Cl.1 ferritic steel and SS304LN austenitic stainless steel using Inconel 82/182 (ERNiCr-3/ENiCrFe-3) and Inconel 52/152 (ERNiCrFe-7/ENiCrFe-7) filler metals have been conducted in the present work. The integrity assessment of DMW joints and the mechanical properties variations has made pertaining to ASME Section-III and Section-IX. Mechanical tests comprising bend test, transverse tensile test (TTT), tensile test, Charpy impact test, microhardness measurement have been carried out along with microstructural evolution using the standard test specimens according to respective ASTM standards. Bend tests have shown that interfaces of the SA508–Inconel, Inconel–Inconel, and Inconel–SS304LN are free from any lack of fusion or cracks. TTTs have shown that failures of the specimens are from the SS304LN indicating integrity of the weld joint. Tensile tests confirm that tensile strength of the different regions agreed the required strength as per ASME Section-II. The weld strength mismatch and plastic instability strength (PIS) are found to be important factors during integrity assessment of joints. Based on the comparative investigations, owing to better mechanical properties, Inconel 82/182 filler metals could be an optimum choice over Inconel 52/152 filler metals for present DMW joints required in pressure vessel system of nuclear plants.