Phosphorus Distribution between Fe-Cr-C Melts and CaO Bearing Fluxes

Abstract

In view that Fe-Cr-C melts should be dephosphorized preferably by CaO bearing fluxes for economical reasons, the lowest phosphorous content attainable in equilibrium by the treatment was estimated by measuring 1) the GIBBS free energy of formation of CaO·Cr₂O₃, which determines the maximum oxygen partial pressure and 2) phosphorous distribution between CaO-SiO₂-CaF₂ fluxes and Fe-Cr-C melts at 1 300°C.
The results are summarized as follows:
1) The Gibbs free energy of formation of CaO·Cr₂O₃ can be expressed by the following equation.
2Cr(s)+ CaO+ 3/2O₂= CaO·Cr₂O₃
ΔG°=-1 350 000 + 344 T±10 000 J/mol
2) For effective dephosphorization of carbon saturated Fe-16%Cr melts the phosphate capacity of the flux must be higher than 10²⁷.
3) The addition of a small amount of Na₂O or BaO to CaO-SiO₂-CaF₂ fluxes saturated doubly with CaO and 3CaO·SiO₂ was observed to increase significantly their dephosphorization capacity.
4) The interaction parameter e_P^Cr was found to be -0.039 at 1 300°C.