Effect of buffer-layered buttering on microstructure and mechanical properties of dissimilar metal weld joints for nuclear plant application

In this study, we present the metallurgical and mechanical investigation of four dissimilar welds between SA508Gr.3Cl.1 and SS304LN. The welding processes for buttering deposition and fill-pass welding were varied with ERNiCr-3/ENiCrFe-3 consumables. The Ni-Fe alloy buffer layer was introduced as intermediate layer in buttering and then the joints (with and without buffer layer in buttering) were fabricated. The effect of Ni-Fe buffer layered buttering and welding processes on the resulting weld joints properties has been addressed. Metallurgical and mechanical properties, fracture toughness were measured and various examinations were carried out for integrity assessment on all the weld joints. Addition of a Ni-Fe buttering layer leads to the development of more favourable properties than observed in welded joints made using the current practice without a buffer layer. Control of carbon migration and its subsequent effect on metallurgical, mechanical properties due to buffer layer has been justified in the study. Conventional procedure of DMW fabrication has been proven to be the least favourable against the new technique suggested. Modification in current integrity assessment procedure would be possible by considering the properties at interfacial regions, introduction of yield strength ratio mismatch and the plastic instability strength in the integrity assessment.