The distribution of C and N atoms on the octahedral interstitial sites of the face-centered-cubic austenite phase in Fe–C and Fe–N alloys, especially in austenitic stainless steels, was considered. The results of Mössbauer experiments were presented here in order to advance the understanding of this interstitial occupation. Therefore, laser carburized and laser nitrided austenitic stainless steel was investigated by means of X-ray diffraction and Mössbauer spectroscopy. Three sub-spectra in terms of different Fe sites were resolved in the Mössbauer spectra for these Fe–C and Fe–N austenites. The isomer shifts, the quadrupole splittings and in particular the sub-spectra fractions depended on the type of the introduced atom and undergo changes when increasing the C or N content. This was considered in connection with the existing ordering models for interstitial atoms. No clear evidence could be found for a perfect random occupation, nor for a perfect ordered occupation of the interstitials. Nevertheless, there seems to a tendency for a weak attractive interaction for N interstitials, and for a stronger repulsive force for the C interstitials in laser nitrided/carburized austenitic stainless steel.

Interstitial Ordering of Nitrogen and Carbon in Laser Nitrided and Laser Carburized Austenitic Stainless Steel. H.Binczycka, M.Kahle, S.Cusenza, E.Carpene, P.Schaaf: Journal of Physics - Condensed Matter, 2006, 18[47], 10561-70