Identification of temperature and hardness distribution during dual frequency induction hardening of gear wheels

Induction surface hardening means the hardening of a thin zone of the material only, while its core remains soft. The paper deals with the modelling of the Consecutive Dual Frequency Induction Hardening (CDFIH) of gear wheels and its validation. For gear wheels with modulus m smaller than 6 mm a contour profile of hardness distribution could be obtained. The investigated gear wheel is heated first by a medium frequency inductor to the temperature approximately equal to the modified lower temperature Ac1m. It means beginning of the austenite transformation. Then the gear wheel is heated by the high frequency inductor to the hardening temperature making it possible to complete the austenite transformation and immediately cooled. In order to design the process it is necessary to identify modified critical temperatures and to obtain expected temperature distribution within the whole tooth.