THERMODYNAMIC ANALYSIS AND EVALUATION OF THE FE-CR-MN-N SYSTEM

In the present work, the thermodynamic properties of the Fe-Cr-Mn-N system have been studied using models for Gibbs energy of its various phases after combining recent descriptions of the Fe-Cr-Mn, Fe-Cr-N, Fe-Mn-N, and Cr-Mn-N systems. Close attention is paid to the solubility of N in the Fe-Cr-Mn liquid, face-centered cubic (fcc), and body-centered cubic (bcc) phases and precipitation of the hexagonal close-packed (hcp) nitride (i.e., Cr2N) from fcc at various conditions. In addition, the properties of the Fe-Cr-Mn hcp phase referred to as martensite were assessed by comparing the calculated T0 temperature between fcc and hcp with experimental martensitic transformation temperatures A(s) and M(s). A consistent description of the Fe-Cr-Mn-N system has been obtained, and a number of solubility curves and sections of the Fe-Cr-Mn-N phase diagram calculated using this description are presented, which can provide an important basis for the materials and technology design. From comparisons with experiments, it has been shown that the solubility of N in the Fe-Cr-Mn liquid and fcc phases is well described by the present calculation, including the dependences of the solubility on temperature and pressure. The effects of N on the precipitation of the hcp nitride, on the fcc phase region, and on the formation of the sigma phase are also described very well. Finally, it is pointed that there is need for experiments to examine the effect of Mn on the N solubility in the Fe-Cr delta-ferrite.