Partial Molar Volumes from High-Temperature Lattice Parameters of Iron–Carbon Austenites

Abstract

The lattice parameters of a number of iron–carbon alloys have been measured in the austenite field for temperatures up to 1200° C (1473 K). By extrapolation and interpolation of these data the variation with carbon concentration of the lattice parameter of austenite has been determined for a wide range of temperatures, and used to calculate partial molar volumes of iron and carbon in austenite. Both partial molar quantities show little variation with composition but V _c, γ decreases with increasing temperature, while V _Fe, γ increases. The values obtained for the partial molar volume of carbon in austenite are appreciably lower than those cited earlier. It is probable that the differences previously reported between the measured and calculated effect of pressure on the composition of austenite in equilibrium with cementite at 727° C (1000 K), are due primarily to the use in the calculations of too high a value for the partial molar volume of carbon in austenite.