The development of residual stress in an induction hardened small spur gear is numerically simulated. A full scale 3D simulation is utilized to obtain the results, providing the possibility to evaluate the complete distribution of residual stress in the hardened component. Electromagnetic and thermal solutions under induction heating conditions are obtained with Cedrat Flux 3D, whereas EDF Code Aster software is used for thermal simulation during the quenching stage, phase transformation, and stress-strain simulations. The simulated induction heating isotherms and distribution of residual stress are compared with experimental investigations done by Larregain et al. and Savaria et al.

A robust method is proposed for the measurement of surface temperature fields during induction heating. It is based on the original coupling of temperature indicating lacquers and a high-speed camera system. Image analysis tools have been implemented to automatically extract the temporal evolution of isotherms. This method was applied to the fast induction treatment of a 4340 steel spur gear, allowing the full history of surface isotherms to be accurately documented for a sequential heating, i.e., a medium frequency pre-heating followed by a high frequency final heating. Three isotherms, 704°C, 816°C, and 927°C, were acquired every 0.3 ms with a spatial resolution of 0.04 mm per pixel. The information provided by the method is described and discussed. Finally, the transformation temperature Ac1 is linked to the temperature on specific locations of the gear tooth.