In order to predict the behavior of tools is is very important to determine the distribution of temperature during cutting. The difficulty of this problem is the impossibility to lay out the thermocouples at the surfaces placed between the cutting tool and the part to be cut. It is known that the rising of the tempering temperature leads to a gradual decrease of the fineness of the phase mixture and consequently to a decrease in hardness. In this paper is presented a method to determine distribution of temperature during cutting based on the hardness obtained after tempering.