Corrosion cracking of carbon and low-alloy steels in alkaline solutions occurs at temperatures above 323~ is distinguished by a clearly expressed relationship to polarization potential, and is controlled by the presence and concentration of oxidizers [1-4 eta!.]; i,e., the tendency of steels toward corrosion cracking is related to the occurrence of specific electrochemical processes, the description of which is possible on the basis of the thermodynamic characteristics of the metal--medium system. There is information on the thermodynamic stability of iron in water at pH values from 0 to 15 and temperatures up to 573~ [I, 2]. It is assumed [i] that the appearance of caustic cracking of steels is related to the formation of HFeO=ions. The approach to treatment of localized forms of corrosion from positions of the thermodynamics of electrochemical reactions has been used for certain Me--H~O systems (Fe, Ni, Co, Cu) under conditions of the service of atomic electric power plant equipment and also for materials experiencing the action of geothermal solutions [3, 4]. The basis of such an approach for describing and predicting corrosion processes in an Me--H=O system is calculation of the thermodynamic stability of the chemical element and its compounds at a certain temperature in the working range of pH and ~. The method of constructing equilibrium diagrams (Pourbaix diagrams [5]) has been improved both by the author himself [5, 6] and by other investigators [1-4]. However, the wide use of such a method of studying corrosion processes has been impeded by a number of circumstances, including the absence of original thermodynamic values for a number of ions, compounds, and elements;'the absence of a proven method of calculating the diagrams of multicomponent systems, solutions and alloys which are complex in composition, in which the elements are in different phases; the absence of proven means of taking into consideration the influence of water vapor and the partial pressures of hydrogen and oxygen; and in part the difficulty of calculations, although at present four or five algorithms have been developed for conducting operations on the computer [7]. Nevertheless, even at the present level of investigations with the use of thermodynamic calculations of the stability of metals in Me--HsO systems it is possible to obtain valuable information both for interpretation of the mechanism of many corrosion processes and for the purpose of predicting the corrosion resistance of a metal and, as a prospect, of an alloy under specific service conditions taking into consideration the operating life of the equipment.