Formation of the anomalous microstructure in the weld metal of Co-based alloy/AISI 410 stainless steel dissimilar welded joint

The Co-based alloy/AISI 410 stainless steel dissimilar welded joint was fabricated by the electron beam welding (EBW) technique. The anomalous microstructure containing the element transition zone (ETZ) and/or core of tail-like zone (CTLZ) is in the weld metal (WM) adjacent to the fusion line. The melting temperature difference between the WM and AISI 410 steel, melt stirring effect and element diffusion can trigger the formation of such anomalous microstructure. In particular, the larger distance of the region in WM away from the fusion line, the smaller CTLZ and larger ETZ occurred. Compared with the fine and ellipsoidal precipitates in the as-welded CTLZ, a large number of chain-type clustered precipitates were detected in the CTLZ and ETZ interface after the aging treatment at 566 °C for 1 000 h. The element diffusion under elevated temperature in WM is regarded as the crucial factor for such anomalous microstructure evolution during the aging treatment.