Phosphorus Partition between Fe-Cr-C Melts and BaO-BaF₂ Fluxes and the Activity of BaO

Abstract

The phosphorus partition between BaO-BaF₂ fluxes and Fe-Cr-C_satd. alloys was measured at temperatures ranging from 1 175°C to 1 300°C under a CO atmosphere.
The phosphorus partition ratio increases with increasing BaO content in the fluxes and decreases with increasing chromium content in Fe-Cr-C_satd. alloys. The BaO-BaF₂ system was found to have a large phosphate capacity ranging from 10²⁶ to 10^28.5 at 1300°C, which is much larger than that for the CaO-CaF₂ system. The enthalpy change for the dephosphorization reaction by BaO bearing fluxes was determined to be-528 kJ/mol. The chromium partition ratio increases with an increase in BaO content especially in the higher BaO content range. The possibility of the removal of phosphorus from Fe-16% Cr-C alloys without much oxidation loss of chromium by using 50% BaO-50% BaF₂ flux was demonstrated.
Furthermore, the activity of BaO for the BaO-BaF₂ system was determined at 1 200°C and 1 300°C and the activity of BaF₂ was calculated by using the Gibbs-Duhem relationship. The phase diagram for the BaO-BaF₂ system was also discussed.