Phase diagram in the iron-rich corner of the Fe-Cr-Mo-V-C system below 1000 K

Relevant experimental phase equilibria were used with the THERMOCALC program to refine thermodynamic parameters for the low-temperature region, in the steels with composition 0.4 to 2.5 wt.% Cr, 0 to 1 wt.% Mo, and 0 to 0.5 wt.% V. The refined parameters were used to calculate phase relationships, which were then compared with experimental results. The main interest was focused on the temperature and concentration regions of existence of the chromium-rich carbides M7C3 and M23C6 and Mo-rich carbides M6C and M2C. Results of experiments indicate that M7C3 carbide replaces M23C6 carbide in the temperature region between 773 and 873 K. Similar behavior was also found for molybdenum-rich phases M6C and M2C. Some modifications of existing thermodynamic parameters in the low-temperature region, as well as the establishment of some new parameters, were necessary to obtain reasonable agreement between theoretical and experimental results.