Influence of magnetic fields on α/γ equilibrium in Fe-C(-X) alloys

The influence of applied magnetic fields on the free energy and equilibrium of ferrite (alpha) and austenite (gamma) in Fe-C and Fe-C-X alloys, where X is an alloying element, was studied. The partial molar free energy of iron due to interaction with magnetic fields was calculated from Weiss molecular field theory. The partial molar free energy of an alloying element was evaluated in the framework of the Weiss theory taking into account the influence of the alloying element on the Curie temperature and the magnetic moment of iron solid solution. From the derived partial molar free energy of component atoms the ortho- and paraequilibrium alpha/gamma phase boundaries were calculated. It is shown that the alpha to gamma transformation temperature is raised 1-3 degrees C per one Tesla depending on the alloy composition and the intensity of applied fields whereas the gamma to delta transformation temperature is lowered similar to 0.4 degrees C per one Tesla. In order to cool unalloyed iron to room temperature without transforming to austenite a magnetic field close to similar to 100 T may be necessary.