NUMERICAL-ANALYSIS OF PHASE-TRANSFORMATIONS AND RESIDUAL-STRESSES IN STEEL CONE-SHAPED ELEMENTS HARDENED BY INDUCTION AND FLAME METHODS

Numerical model simulations of induction and flame hardening and harde ning after furnace heating are presented in the paper. In the models t he coupling between electromagnetic, thermal field, phase transformati ons field and stress field are considered. The electromagnetic field i s calculated from Maxwell's equations taking into account changes in t he conductivity and permeability of the material during the process. T he thermal field in the conducting materials is calculated on the basi s of Fourier-Kirchhoff equation. The kinetics of diffusion-dependent p hase transformation and martensitic transformations are coupled to the transient heat flow. The fractions of phases created during the phase transformations are calculated by use of TTT-heating diagrams and TTT -cooling diagrams. Thermoplasticity theory with isotropic hardening wa s applied to calculate the internal stresses resulting from phase chan ges as well as temperature variations. The changes in the thermomechan ical parameters of the material, as a function of phase content and th ermal field, were considered in the stress calculations. The numerical calculations have been made for surface-hardened cone-shaped steel ma chine parts. (C) 1998 Elsevier Science Ltd.