Phase Transformation in a High Flux Magnetic Field

A pure Fe and a binary iron carbon alloy were examined using neutron diffraction in a high flux magnetic field to characterize the influence of the field on the equilibrium allotropic phase transformation. Previous literature indicated the transformation of a common steel alloy from ferrite to austenite increased by 3°C per tesla applied. This work found that this common alloy was not typical for all commercial steels, however the change was found to be consistent across hypoeutectoid carbon levels. A change in the normal hysteresis between heating and cooling was measured, as the magnetic field favored the ferromagnetic phase. The measured temperature change was related to the corresponding change in Gibbs free energy and its reduction of the stable critical nucleus size, which predicts finer grain sizes and lath spacings when steel is subjected to a field during a phase transition. This allows the Hall-Petch relationship to explain the enhanced physical properties seen using this technique.