A Thermodynamic Evaluation of Carbide Solubilities in the Fe–Mo–C,Fe–W–C,and Fe–Mo–W–C Systems at 1000°C

The equilibria involving carbides and ferrite or austenite in the systems Fe–Mo–C, Fe–W–C, and Fe–Mo–W–C have been studied at 1000°e, using carefully selected alloys and well-controlled heat treatments. It seems probable that a constant carbon activity was achievedin all the encapsulated samples,and carbon activitymeasurementswerethus used in the theoretical analysis of the experimental data. The measurements concerned the carbides: cementite, ɛ-carbide, M₆C, M₂C, and MC. The experimental data were analysed in terms of thermodynamic models for the individual phases. Parameter values were evaluated which were then used to synthesize the phase diagrams. Good agreement with the experimental data was obtained and this technique of treating experimental information appears to be useful. In the course of this work the free energies of formation have been evaluated for a number of carbides, metastable as well as stable.