Thermodynamic Reassessment and Phase Diagram Calculations of the Fe–P and Fe–C–P Systems

Abstract

A comprehensive thermodynamic assessment of the Fe–P system was conducted based on experimental phase diagram data and thermodynamic properties. The obtained parameters, combined with previously reported parameters for the Fe–C system, were employed to calculate the Fe–C–P ternary phase diagram. To improve the stability of the Fcc phase, additional parameters for the Fcc phase of the P–C system were introduced. For the liquid phase, association model considering Fe₂P and Fe₂C species was adopted. The Fcc and Bcc phases were described using a two-sublattice model with the (Fe,P)₁(C,Va)_0.25.

The Fe–P binary system was successfully reproduced across the entire composition range, including high phosphorus compounds such as FeP₂ and FeP₄. The calculated results successfully reproduced the experimental data for both the phase diagram and thermodynamic properties. Furthermore, for the Fe–C–P ternary system, a satisfactory reproduction of numerous experimental data was achieved without introducing any ternary interaction parameters. The set of parameters obtained from the present model exhibited better agreement with experimental observations compared to those calculations using the regular solution model in the liquid phase.