Influence of magnetic field on ferrite transformation in a Fe-C-Mn alloy

The kinetics of ferrite transformation in a Fe-0.10mass%C-2.94mass%Mn alloy in a strong magnetic field of 8 T were studied with regard to alloying element-partitioned and partitionless growth. According to the theory of diffusion-controlled growth, the slow Mn diffusion dictates partitioned growth that occurs at a low undercooling, whereas partitionless growth at a larger undercooling is rate-controlled by fast carbon diffusion. The alloy was austenitized and isothermally reacted at temperatures that encompass the two growth modes. The nucleation and growth rates of ferrite increased at all temperatures in the magnetic field, whereas the amount of increase was somewhat greater at lower temperatures. In the region of slow growth, besides its sluggish diffusion Mn possibly destabilizes the ferrite phase due to the influence on the magnetic moment and the Curie temperature of bcc Fe solid solution, and partially offsets the accelerating effect of transformation. The temperature of transition from the slow to the fast growth is predicted to increase, due to the shift in the ferrite/austenite phase boundaries in the presence of magnetic field.