Abstract:Inconel 625 base metal and weld metal were subjected to 75% Na2SO4-25% NaCl mixed molten salt hot corrosion experiments at 750°C. The physical phase, surface morphology, corrosion weight loss rate and corrosion mechanism of corrosion products were studied and analyzed. The results show that the organization of Inconel 625 joints is austenitic equiaxial crystal at the base material and dendrite at the weld. The weight loss curves of both base metal and weld metal follow parabolic laws with weight loss rate constants of 3.43 and 4.18, respectively. The weld metal is less resistant to corrosion compared to the base material due to the precipitation of Nb-rich second phase, and corrosion exhibits "inhomogeneity". Inconel 625 in both states has the same corrosion layer structure, the outer layer of NiO particles and lamellar NiCr2O4, the middle layer of dense Cr2O3 oxide layer, and the inner layer of "honeycomb" Ni2S3 sulfide layer of the three-layer structure. The main corrosion mechanism of Inconel 625 alloy in 75% Na2SO4-25% NaCl mixed salt at 750°C is: "sulfidation-oxidation" corrosion.