Critical evaluation and thermodynamic optimization of Fe–Cu, Cu–C, Fe–C binary systems and Fe–Cu–C ternary system

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Development of an efficient process for recycling ferrous scrap containing Cu requires reliable thermodynamic knowledge of Fe–Cu based alloy system. It is shown that there still remain discrepancies in existing databases from known experimental data. In order to provide an accurate prediction tool for the process development, a CALPHAD type thermodynamic modeling for the Fe–Cu–C system is presented with re-optimization of its binary sub-systems, Fe–Cu, Cu–C, and Fe–C. Liquid phase was modeled using the Modified Quasichemical Model in the pair approximation which generally gives better results in systems exhibiting positive deviation from ideality (such as in Fe–Cu). Solid solutions such as fcc and bcc were described using Compound Energy Formalism. A supplement experimental work was carried out in order to provide more accurate solid/liquid equilibria in Fe–Cu binary system. The obtained model parameters along with the model equations were shown to reproduce significantly better correspondence to the experimental data, such as the phase equilibria, activity of component in the Fe–Cu–C system, liquidus projections etc., within experimental uncertainty. High temperature stabilization of bcc phase in Fe–C binary system in previous thermodynamic modeling was revisited, and was resolved in the present study.