The hardening characteristics could be achieved by a proper selection of the grinding conditions. It is necessary to keep the heat flux above the critical limit for the film-boiling and the austenitization within the grinding zone. In this paper, a critical thermal analysis was presented to calculate the critical heat flux, following the methods for predicting thermal damages in creep grinding and high efficient grinding. The appearances of the hardening phenomena were predicted for dry grinding and wet grinding. It also can guide the selection of the grinding conditions. Theoretical analysis was verified by the experiments. Measurements are found to be in good agreement with the theoretical predictions.