A thermodynamic model for non-stoichiometric cementite; the Fe–C phase diagram

• A new model of the cementite phase in the system Fe–C is developed.
• The new model accounts for the non-stoichiometric character of cementite.
• It is consistent with models from literature, only considering stoichiometric Fe3C.

On the basis of recently published experimental data a new thermodynamic model for the cementite phase was developed, accounting for its non-stoichiometry in equilibrium with α, γ and liquid solution phases. The predictions from the model were discussed in the context of experimental and ab initio data from the literature. Further, the model was compared to existing models for stoichiometric and non-stoichiometric cementite. It was shown that the resulting description is consistent with thermodynamic descriptions of the Fe–C system, excluding the non-stoichiometry of cementite, from the literature. Thus, the new model is suitable as a basis for multi-component systems correctly predicting the constitution of technically applied alloys.