A quantitative predictive model for the austenite/ferrite phase equilibrium in Fe-C alloys under high magnetic fields with experimental validation

A fundamental understanding of how magnetic fields govern phase stability is crucial for the design and processing of metallic materials. This study develops a thermodynamic model to quantify the non-linear migration of the A₃ phase line in Fe-C alloys under high magnetic fields. The model employs a temperature‑dependent power‑law formulation, incorporating two physical parameters that separately quantify the intensity and functional shape of the field effect. It thereby captures the curvature transition of the A₃ phase line and enables the direct calculation of equilibrium carbon concentration of γ phase along the A₃ phase line and the phase fractions of γ or α phase for arbitrary temperature and magnetic field conditions. Its predictive accuracy was experimentally verified using a eutectoid Fe-0.77 wt% C alloy under a 7 T magnetic field: the calculated proeutectoid ferrite volume fraction agrees well with the experimentally measured value obtained from isothermal transformation experiments.