Critical Evaluation and Thermodynamic Optimization of the Fe-P System

Thermodynamic optimization of the Fe-P system was performed using the CALculation of PHAse Diagrams (CALPHAD) method based on critical evaluation of all available phase equilibria and thermodynamic data. The Gibbs energies of liquid phase and solid solutions were described using the Modified Quasichemical Model and Compound Energy Formalism, respectively. The Fe-P phase diagram, thermodynamic properties of P in liquid Fe and stability of intermediate iron phosphides (Fe₃P, Fe₂P, FeP and FeP₂) in the entire composition range were reoptimized for resolving the discrepancies left in the previously optimized database. Several problems in previous assessments were resolved, and a more accurate and consistent description of the Fe-P system was achieved compared to experimental data. The distribution of P between molten Fe-P alloys and slag at different temperatures was also calculated to present the applicability of the present work to steel dephosphorization calculation.