Measurement and Thermodynamics of Carbon Solubilities of Molten Si-Fe, Si-Ni and Si-Fe-Cr Alloys at 2073 K

A study has been carried out to evaluate the equilibrium phase relations of molten Si Fe, Si-Ni, and Si-Fe-Cr alloys saturated with either silicon carbide (SiC) or graphite. The measured carbon solubilities at 2073 K were 0.19-6.6 mol% for Si-(24.1-70.1) mol%Fe, 0.061-5.2 mol% for Si-(30.0-85.0) mol%Ni, and 1.1-3.9 mol% for Si-(50-x) mol%Fe - x mol%Cr (x=10.4-40.1) alloys, respectively. Quasi-chemical model, which assumes carbon atoms to be introduced into interstitial sites of Si-Fe, Si-Ni, and Si-Fe-Cr solvents and obstruct the bonding between solvent atoms, was adopted to evaluate the activity coefficient of carbon in each alloy, and its estimation reproduced fairly well the tendency of measured carbon solublities. On the other hand, estimation using the sub-regular solution model often overestimated the carbon solubilities. It was thus found that the carbon behaviors in silicon-transition metal alloys can be well described by using the quasi-chemical model.