Corrosion testing of Hastelloy N in molten fluoride salt was performed in purified molten 2 7 LiF-BeF 2 (66-34mol%) (FLiBe) salt at 700°C for 1000 hours, in pure nickel and graphite capsules. In the nickel capsule tests, the nearsurface region of the alloy exhibited an about 200 nm porous structure, an approximately 3.5 µm chromium depleted region, and MoSi 2 precipitates. In the tests performed in graphite capsules, the alloy samples gained weight due to the formation of a variety of Cr 3 C 2 , Cr 7 C 3 , Mo 2 C and Cr 23 C 6 , carbide phases on the surface and in the subsurface regions of the alloy. A Cr depleted region was observed in the near-surface region where Mo thermally diffused toward either surface or grain boundary, which induced an approximately 1.4 µm Ni 3 Fe alloy layer in this region. The carbide containing layer extended to about 7 µm underneath the Ni 3 Fe layer. The presence of graphite dramatically changes the mechanisms of corrosion attack in the Hastelloy N in molten FLiBe salt. Evaluated by in terms of the depth of attack, graphite clearly accelerates the corrosion, but the results appear to indicate that the formation of Cr 23 C 6 phase might stabilize the Cr and mitigate its dissolution in molten FLiBe salt. Moreover, a thermal diffusion controlled corrosion model that was fundamentally derived from Fick's second law was applied to predict the corrosion attack depth of 17.2 µm/year for the Hastelloy N in molten FLiBe in the pure nickel capsule at 700°C.