The Precipitation of Cr₂N in 17%Cr Steels

The precipitation of Cr2N in a 17%Cr ferritic stainless steel has been studiedby thin-foilelectron microscopy and electron diffraction. Trace analysishas shownthat the acicular precipitates have a (113)αgrowth direction, and this has been found to correspond to the minimum mismatch of interatomic distances along crystallographic directions which are parallel in matrix and precipitate. The usefulness of the interatomic distance, rather than the interplanar spacing criterion, is discussed with reference to other M2X-type phases. The occurrence of a hexagonal superlattice in Cr2N has been confirmed,and this is discussedin terms of the lattice strains and interatomic forces associated with the interstitial atoms.