N and C Interstitial Diffusion and Thermodynamic Interactions in $$\varepsilon $$-Iron Carbonitride

Abstract

The simultaneous diffusion of N and C over the interstitial sites of the Fe-sublattice of $$\varepsilon $$ -iron carbonitride was studied. To this end, gas nitrocarburizing experiments of pure Fe and Fe-C alloys were performed at 853 K (580 °C), leading to two different types of microstructures containing $$\varepsilon $$ (sub)layers. These microstructures were investigated by light microscopy, electron probe microanalysis, and X-ray diffraction in order to evaluate the components of the (N and C) diffusivity matrix. The off-diagonal components of the diffusivity matrix were shown to have significant, non-negligible values. These results provided insight into the thermodynamics of the Fe-N-C system.