Examination of phase transformations in the system Fe–N–C by means of nitrocarburising reactions and secondary annealing experiments; the α + ∊ two-phase equilibrium

Abstract

Abstract The until now controversially discussed existence of the two-phase equilibrium α-Fe + ∊-Fe3(N, C)1+x in the ternary system Fe – N – C was proven by the investigation (optical microscopy, X-ray diffraction, Electron Backscatter Diffraction) of compound-layer microstructures generated by gaseous nitrocarburising of pure iron and subsequent secondary annealing experiments under static inert-gas atmosphere. The invariant transition reaction γ-Fe4N + Fe3C → α-Fe + ∊-Fe3(N, C)1+x could be shown to proceed at a (single) temperature (at constant pressure of 1 atm) between 833 K and 843 K.