On the crystal structure of Cr₂N precipitates in high-nitrogen austenitic stainless steel

The crystal structure of Cr₂N precipitates in high-nitrogen austenitic stainless steel was investigated by transmission electron microscopy (TEM). Based on the analyses of selected area diffraction (SAD) patterns, the crystal structure of Cr₂N was confirmed to be trigonal (P1m) and was characterized by three sets of superlattice reflections: (001), (0) and (1). These could be explained in terms of the [epsilon]-type occupational ordering of nitrogen. The static concentration waves (SCWs) method was applied to describe the ordered superstructure of Cr₂N. The occupation probability function (OPF) for describing the distribution of N atoms in the Cr₂N superstructure was derived based on the superlattice reflections obtained in the SAD patterns and could be expressed as: . The crystallographic models for [epsilon]-type ordering, mainly suggested in the Fe–N system, were discussed in comparison to the present model.