Study of fusion boundary microstructure and local mismatch of SA508/alloy 52 dissimilar metal weld with buttering

•Double-sided buttered A52 dissimilar metal weld (DMW)•First of a kind in Europe and representative of real nuclear component•The fusion boundaries (FBs) of SA508/Alloy 52 buttering were investigated•Crystal structure, microstructure, elemental diffusion and hardness were correlated•The FB types affect the local strength mismatch and brittle fracture crack path A SA508/Alloy 52 dissimilar metal weld (DMW) mock-up with double-sided Alloy 52 butterings, which is fully representative of Ringhals pressurizer surge nozzle DMW repair solution, was studied. The microstructure, crystal structure, elemental diffusion, carbide formation and macro-, micro- and nano-hardness of the SA508/nickel-base Alloy 52 buttering fusion boundary (FB) were investigated. Three types of FBs were analyzed, i.e., narrow FB (∼80–85% of whole FB), tempered martensitic transition region (∼15%) and wide partially mixed zone (∼1–2%). The different FB types were induced by the local heat flow and respective elementary diffusion, which significantly influence the local hardness mismatch across the DMW interface and the local brittle fracture behavior.