Induction heating is currently considered as an interesting alternative to thermo-chemical diffusion

This article presents a robust method for measuring the surface temperature fields during induction

heating. It is based on the original coupling of temperature indicating lacquers and high-speed camera

system. Image analysis tools have been implemented to automatically extract the temporal evolution of

isotherms. Isotherms from 400 ⁰C to 1038⁰C are described every 0.3 milliseconds with a spatial

resolution between 0.01 mm and 0.05 mm. This method was applied to the induction treatment of a 4340

steel spur gear. It permitted to very accurately describe the full history of surface isotherms for different

heating parameters, i.e., with or without pre-heating, through either simultaneous or sequential high

frequency/medium frequency final heating.

Key Words : induction heating, temperature measurement, 4340 steel gear

processes for surface hardening of aerospace structural gears. This process presents the advantages of

being green, very fast, energetic efficient and its high reproducibility enables a better control of the

hardened layer. To optimize induction heating processes, in terms of induced hardened depths and

residual stresses profiles, it is necessary to assess the thermal history across the gear. In this purpose,

numerous multiphysics modeling tools have been developed in order to simulate these thermal fields.

Nevertheless, little experimental validation is available due to the very high temperature rates, i.e.,

around 4000 °C/s, and high thermal gradients typically encountered during fast induction heating.