Finite-element simulation of induction heat treatment

An efficient finite-element procedure has been developed for the analysis of induction heat treatment problems involving nonisothermal phase changes. The finite-element procedure first simulates the magnetic field developed when currents flow through an induction coil by solving Maxwell’s electromagnetic field equations; at the following step, it calculates the temperature distribution in the workpiece due to eddy currents induced by the magnetic field. The final stage of the simulation involves the determination of the distributions of residual stress, hardness, and microstructure in the workpiece. The finite-element analysis includes temperature-dependent material properties, changes in permeability of the workpiece at the Curie temperature, a mixed hardening rule to describe the material constitutive model, and the incorporation of time-temperature-transformation (TTT) diagram. The procedure was applied to the simulation of the induction hardening of 1080 steel bar. Firstly, the magnetic field and temperatures developed in the workpiece during (a) the induction heating of an infinitely long 1080 steel cylinder by a single encircling coil and (b) the induction heating of a semi-infinite half-space by a single coil suspended above it were calculated using the finite-element procedures. These were validated by comparing them with analytical solutions derived for these configurations using a Green’s function method. Finally, to demonstrate the predictive capability and practical applicability of the current finite-element procedure, two examples pertaining to the induction heat treatment of an infinite 1080 steel bar of square cross section and a notched finite 1080 steel cylinder of circular cross section were analyzed to predict the magnetic field, temperature, and residual stress distributions. The current finite-element procedure could be used as a powerful design tool for linking induction heat treating parameters with the mechanical property attributes of the heat treated component.