Carburizing steels 23KhN2M, 22KhNM, and 20KhGNM are studied with the aim to determine the critical quenching rates corresponding to formation of layers with martensite and half-martensite structures for the method of end quenching. Approximation of experimental data is used for deriving regression equations describing the dependence of the critical quenching rate on the chemical composition of the steels.