The effects of applied magnetic fields on the α/γ phase boundary in the Fe–Si system

Abstract

The CALPHAD (calculations of phase diagrams) method is used to examine the effects of applied magnetic fields on the α/γ phase boundary in the Fe–Si system in the paramagnetic state. The reported susceptibility data for pure Fe is first re-evaluated. The contributions to the total Gibbs energy of the ferrite (α) and austenite (γ) from the external fields are calculated based on the Curie–Weiss law and the re-evaluated susceptibility data. The Fe–Si phase diagram on the Fe-rich side as a function of applied field is calculated using the Thermo-Calc™ package. With increasing field strength, the γ loop shrinks monotonically; that is, the α/γ-Fe transition temperature increases while that for γ/δ-Fe transition decreases, albeit more slowly. Finally, in conformance with the existing CALPHAD databank, Redlich–Kister polynomials are proposed to account for the compositional and temperature dependence of the contribution to the total Gibbs energy from the applied field in the paramagnetic state in the range over which the Curie–Weiss law is obeyed.