Thermodynamics of Molten Fe-Cr-C_satd. Alloy

Abstract

The activity of chromium in molten Fe-Cr-C_satd. alloy has been measured at temperatures ranging from 1548 to 1773 K by a chemical equilibrium technique. There is little temperature dependence of the activiy of chronium in the region of low chromium contents by weight, and the activity coefficient of chromium decreases as the chromium content increases.
The activity coefficient of chromium in silver, which was needed for the foregoing measurement, was predetermined.
By thermodynamic discussion in combination with the carbon solubility in molten iron-chromium alloys, the expression for the activity coefficient of chromium in Fe-Cr-C_satd. alloy has been obtained as a function of chromium content and temperature as follows.

ln_γCr(s)= -2.52+_T³⁸⁸⁰ +(8.31-_T²³³⁰⁰)X_Cr+(-4.21+_T¹⁴⁹⁰⁰)X_Cr² (1623 to 1773K)

The standard Gibbs energy of mixing of Fe-Cr-C_satd. alloy was also estimated using the Gibbs-Duhem relationship, indicating that chromium and manganese behave similarly in terms of affinity for carbon and iron in molten carbon-saturated iron.