The metastable m phase layer on ion-nitrided austenitic stainless steels Part 2: crystal structure and observation of its two-directional orientational anisotropy

The single phase formed by ion nitriding austenitic stainless steels for sh ort times and at low temperatures has variously been identified in the lite rature as the S, epsilon' or m phase, but a definitive study has yet to be performed. In this work we confirm the tetragonal structure reported previo usly by ourselves and by Angelini et al. [E. Angelini, A. Burdese, B. DeBen edetti, Metall. Sci. Technol. 6 (2) (1998) 33] ], and we discuss the alloy chemical context of the m-phase in terms of a structure lying between the f ee (Cu type) and bcc (W type) host metal structures. Further, pole figure r esults are presented which show evidence of a pronounced [101] texture norm al to the surface and an unexpected strong (112)-pole in-plane anisotropy. (C) 1999 Elsevier Science S.A. All rights reserved.