The application of water–air spray cooling in the process of induction surface hardening according to the simultaneous dual-frequency technology represents a hitherto unexploited and equivalent alternative to conventionally employed polymer solutions. The reason for this is that the selection of the optimum parameters is associated with a high experimental outlay and analytical effort for performing the tests and evaluating the results, respectively, and the parameters must be selected for a specific application. In order to reduce this effort, a numerical model was developed to formulate the coupled thermal, microstructural, and mechanical processes during quenching by means of water–air spray cooling of induction heated spur gearwheels made from 42CrMo4 hardening and tempering steel. The model was implemented in the commercial simulation software ANSYS Workbench 13.0 and verified using simulation results for temperature development, hardness distribution, residual stresses, and distortion. A comparison of the simulated and experimental results show that the model introduced here is suitable for predicting the hardening results during quenching using spray cooling subsequent to induction heating.