1178.    GERASIMOV, Y.  [Activities of Components of Austenite.]  Acta Physicochim, U.S.S.R., vol. 18, 1943, pp. 275-299; Chem. Abs., vol. 38, 1944, p. 5717.

        Thermodynamic method is given for the calculation of the activities and free energies of a binary solution from the gas-solution equilibrium constants.  The activities of the components Fe-C and Fe-Fe₃C at 800°-1,100° are calculated on the basis of the equilibrium constants between austenite and CO₂+CO.  The values of K_g at 800°, 850°, and 900° K are, respectively, 268.8 N₂, 510 N₂ and 962 N₂, where N₂ is the mole fraction of C in austenite.  Since this means that the activity coefficient is practically unity, austenite can be considered a regular solution of a regular modification of carbide Fe₃Cr in γ-ferrite at 800°-1,100°.  The free energy of formation of cementite is small and positive.  The integral heats of solution of carbide and the solubilities of a “regular” carbide modification in Fe are given as:  Fe₃C(β) in Fe(γ), 10,243 cal.; Fe₃C(β) in a saturated solution, 5,000-7,000 cal.  This latter modification is found to be less stable than cementite.  The results indicate that the data of Bramley and Lord (see abs. 330) are probably vitiated by some sort of systematic error.