Microstructure investigation on the fusion zone of steel/nickel-alloy dissimilar weld joint for nozzle buttering in nuclear power industry

Abstract Microstructure of the fusion zone steel/nickel-alloy dissimilar metal welds (DMWs) for nozzle buttering was investigated by optical microscopy (OM), scanning electron (SEM), energy-dispersive spectroscopy (EDS), and back-scattered (EBSD). The results showed that joint complete, without welding defects. structures included beach structure along boundary, peninsula connected with island in weld. distribution these three types near boundary uneven. formed because insufficient mixing solidification molten liquid base material filler metal, width ranging between 0 150 μm. were undercooling insufficiently mixed entered weld convection scouring pool. composition depended on degree a dilution ratio 40 60%. beach, peninsula, decreased turn. With an increase ratio, initial temperature corresponding increased significantly. When exceeded 94.5%, phase transformed from face-centered cubic γ-austenite into body-centered ferrite, solidified form ferrites boundary. austenite grain orientations at side are dispersed 75% large (> 15°) misorientation frequency overall texture orientation distributes dispersedly deviating < 100 > direction.