Thermodynamics of phosphorus in carbon-saturated manganese-based alloys

The interaction coefficient of phosphorus with silicon in a Mn-Si-C_sat alloy has been measured at 1573 K, equilibrating CaC₂, C, and Ca₃P₂ in a quartz capsule to keep the phosphorus partial pressure as high as 33.7 Pa. The activity coefficient of phosphorus in the melts increases with increasing silicon content, and the interaction parameter between silicon and phosphorus in the melts at carbon saturation ε^Si_P, C_sat was found to be 10.4. The activity of phosphorus in a carbon-saturated Fe-Mn alloy was also determined at temperatures of 1573 to 1673 K using a chemical equilibration technique between BaO-BaF₂ fluxes and Fe-Mn-C_sat with manganese mass contents ranging from 0 to 85.3 %. A slight decrease in the activity coefficient of phosphorus in Fe-Mn-C_sat alloys was observed with increasing manganese content, as a reflection of a stronger interaction between manganese and phosphorus than that between iron and phosphorus. The value for e^Mn_P,Csat was found to be -0.0029 between 1573 and 1673 K.