STABILITY FIELD OF AUSTENITE AND MARTENSITIC-TRANSFORMATION IN THE SYSTEM FE-CR-MN-N

The phase equilibria between ferrite and austenite as well as between austenite and the hexagonal epsilon nitride ''Cr2N'' were calculated f or different compositions of Fe-Cr-Mn-N alloys. Corresponding phase di agrams show, that single-phase austenite can be obtained by heat treat ment only above about 1200 and below about 1600 K. The difference Delt a G(m) of the Gibbs energies of ferrite and austenite causes martensit ic transformation, when the critical driving force Delta G(Ms) is surp assed. Applying recently published thermodynamic data the correspondin g martensite start temperatures of alloys containing different mass co ntents of chromium and manganese were estimated. They were drawn into [%N]-T-phase diagrams, From the diagrams the conditions can be red whe re martensite can be formed by quenching single-phase austenite.