[en] Carbide formation in nickel-base alloys (Alloy 600, and Alloy 690) is evaluated using a thermodynamic model. The Kohler method was adopted for evaluating chromium activity internary Ni-Cr-Fe system. For calculation of carbon activity, an empirical relationship was used, which shows a linear relationship between carbon activity and carbon solubility limit in the given alloy systems. The results show that Cr₂₃C₆ was thermodynamically and kinetically stable for Alloy 690. In case of Alloy 600, there is no significant difference in free energy changes between Cr₂₃C₆ and Cr₇C₃. At low temperature such as 650.deg.C or below, Cr₂₃C₆ needs less carbon contents for carbide formation. However, for heat treatment temperatures higher than 650.deg.C, Cr₇C₃ needs less carbon contents for carbide formation. The accuracy and limits of these calculations are discussed