Activity of carbon and solubility of carbides in the FCC Fe-Mo-C, Fe-Cr-C, and Fe-V-C alloys.

The activity of carbon in austenitic Fe-Mo-C, Fe-Cr-C, and Fe-V-C alloys has been studied by equilibration with controlled CH-H atmospheres at temperatures in the range 850° to 1200°C. The observations included a number of compositions in the two-phase fields, γ + carbide. Equations are given for the activity coefficient of carbon as a function of temperature and composition in the austenite field and from these the other thermodynamic properties of the solution may be computed as desired. The phase boundaries γ/γ + carbide were determined by breaks in the isoactivity lines. This was supplemented in the case of Fe-Mo-C alloys by metallographic linear analysis of equilibrated samples. The results confirm certain published phase diagrams and discredit others. [ABSTRACT FROM AUTHOR]