Numerical Simulation of Solid-Solid Phase Transformations During Induction Hardening Process

A multi-scale multiphysical finite element (FE) analysis is presented in this paper to predict the microstructural evolution during induction hardening processes. An ad-hoc code has been developed in order to calculate the metallurgical phase changes that occur during heating and cooling steps. This routine has been coupled with a FEM code able to solve the coupled electromagnetic and thermal problem that typically describes the induction heating processes. In induction contour hardening of steels, an external layer of the piece is heated up to the austenitization temperature and then it is cooled down to obtain a layer of martensite. In thermo-metallurgical model, material properties depend on the temperature distribution but also on the microstructure since the material is a mixture of different phases. From the solution of the coupled steady-state, at a given frequency, electromagnetic and transient thermal problem, temperature distribution as well as heating and cooling rates are used for the evaluation of the existing metallurgical phases at every time step. The effect of the latent heat of solid-solid phase transformations has been also considered. The numerical results are compared with experimental ones