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It is observed that the equations describing induction heating in ferromagnetic materials are rather nonlinear. Although the thermal properties are nonlinear, the greatest nonlinearity arises from the ferromagnetic behavior of the material. A way of circumventing this difficulty while retaining the important magnetization curve is presented. A numerical solution accounting for temperature variations in the saturation magnetization, electrical and thermal conductivities, and specific heat is presented. It is found for case hardening applications that only a narrow near surface region heats to the vicinity of the Curie temperature, and a simple theory describing this region is derived. Just beyond the near surface region a sharp temperature gradient results which is of importance in case hardening. A simple expression for the gradient is developed. These expressions, verified by a complete numerical analysis, aid in the choice of an induction heating excitation system for case hardening applications.