Abstract: Finite element numerical simulation method was adopted to study the effects of power frequency, current density and induction coil moving speed on surface temperature field of the workpiece during induction hardening for the Cr12MoV die steel. According to Maxwell's equations and non-stationary thermal conductivity differential equations, a moving dual-loop induction coil model coupled with electromagnetic field and temperature field was established, by which the temperature field on surface of the workpiece was calculated. And the simulation results were verified by induction hardening experiments. The results show that the temperature rising curve at the center of the workpiece surface is a bimodal curve. The rate and amplitude of temperature rising increase with the increase of power frequency and current density, while decrease with the increase of induction coil moving speed. Through the hardness analysis in the thickness direction of the workpiece after hardening, it is found that the depth of the high-temperature region obtained by simulation calculation is roughly consistent with the depth of the hardened layer. The temperature rising curve measured in experiments basically matches the numerical simulation results, with a maximum error of about 7%, which shows that the process parameters for practical application can be optimized by numerical simulation method, realizing the precise control of depth of hardened layer and hardness of the workpiece after hardening.

Key words: Cr12MoV die steel, induction hardening, electromagnetic thermal coupling model, dual-loop coil, numerical simulation, temperature field