Influence of magnetic fields on alpha/gamma 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 iro n due to interaction with magnetic fields was calculated from Weiss molecul ar field theory. The partial molar free energy of an alloying element was e valuated in the framework of the Weiss theory taking into account the influ ence of the alloying element on the Curie temperature and the magnetic mome nt of iron solid solution. From the derived partial molar free energy of co mponent atoms the ortho- and paraequilibrium alpha/gamma phase boundaries w ere calculated. It is shown that the alpha to gamma transformation temperat ure is raised 1-3 degrees C per one Tesla depending on the alloy compositio n and the intensity of applied fields whereas the gamma to delta transforma tion temperature is lowered similar to 0.4 degrees C per one Tesla. In orde r to cool unalloyed iron to room temperature without transforming to austen ite a magnetic field close to similar to 100 T may be necessary.