Transformation mechanism of secondary phase and its effect on intergranular corrosion in laser wire filling welding Ni-based alloy/304 stainless steel

To clarify the transformation mechanism of secondary phase and the mechanism of intergranular corrosion in laser welding Ni-based alloy (Hastelloy C-276)/304 stainless steel with filler wire, the secondary phase was analyzed by electron probe micro-analysis (EPMA) and transmission electron microscopy (TEM). The evaluation of intergranular corrosion resistance of the welded joints was conducted by double-loop electrochemical potentiokinetic reactivation (DL-EPR) method, and at the same time the chemical compositions of the corrosion surface were analyzed by energy-dispersive spectrometry (EDS). The results show that p phase has complete coherence relationship with mu phase, and the coherent relationship is described as [001](p)//[01 (1) over bar0](mu) and [430](p)//[0001](mu). The mu phase is rapidly transformed from p phase, which is the inhomogeneous phase transformation. The transformation of secondary phase will increase the susceptibility to intergranular corrosion. Therefore, the transformation of secondary phase should be avoided in the welding process.