Modeling Magnetically Influenced Phase Transformations in Alloys

We have investigated four models for calculating the contribution of an applied magnetic field to the free energy of Fe and Fe alloys—Weiss Molecular Field Theory (WMFT), Kuz’min, Arrott, and Curie-Weiss. On the basis of these models, the shifts in phase transformation including both ferromagnetic and paramagnetic phases as a function of magnetic field and alloy content can be predicted. The Kuz’min model is easiest to solve and is also best able to predict the trends in experimentally observed shifts in ferrite/austenite phase transformations for Fe-based alloys under an applied magnetic field both below and near the Curie temperature. For phase transformations above the Curie temperature, the predictions using the Curie-Weiss form with WMFT parameters, here extended to alloy systems, are in good agreement with experimental results. Different aspects of the four models have been discussed in detail with a view to developing a reliable methodology to predict shifts in phase diagrams as a function of alloy content.