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The kinetics of proeutectoid ferrite transformation in Fe-C base alloys in a strong magnetic field (7.5 T) were studied. The transformation kinetics were accelerated at temperatures not only below but also significantly above the Curie temperature. The free energy and equilibrium ferrite/austenite phase boundaries in applied magnetic fields were calculated using the reported experimental magnetic susceptibility and Weiss molecular field theory. The persistence of magnetic field effects above the Curie temperature can be attributed to the rapidly diminishing difference in relative stability between ferrite and austenite toward the Ae 3 temperature of iron.

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We have evaluated controlled decarburization as a method for probing the effect of alloying elements on ferrite growth from austenite. The technique permits the exploration of longer-time ferrite layer growth; it minimizes the effects of interface structure on ferrite growth; and it permits the isolation of the effects of temperature and alloying element concentration on ferrite/austenite interface motion. The study of the decarburization of initially homogeneous Fe-C-Ni alloys was complemented by experiments using specimens with a controlled nickel concentration gradient. Although the decarburization method yields consistent results at longer times, it is found to be less appropriate for the study of initial ferrite growth. Nucleation in the gas/solid interface region, coupled with uncertainties about the precise time of decarburization, leads to large relative errors at the earliest times. For these reasons, the method is considered a valuable complement to studies based on precipitation boundary conditions.