Thermodynamic behaviours of manganese and phosphorus between CaO-MgOsat-SiO2-Al2O3-FetO-MnO-P2O5 ladle slag and liquid iron

The thermodynamic equilibria of manganese and phosphorus between liquid iro n and CaO-MgOsat-SiO2-FetO-MnO-P2O5-Al2O3 (0-33%) ladle slag have been inve stigated at 1873 K from the viewpoint of Mn and P yields for the production of high-strength steels. The equilibrium distribution ratios of Mn and P w ere found to increase with increasing FetO content; however, these ratios v ary with basicity, but they do this the other way round. The addition of al umina into slag at a fixed basicity and FetO content decreases both the equ ilibrium manganese and phosphorus distributions. The equilibrium distributi on ratios were discussed in terms of the variation of activity coefficients of FetO, MnO and PO2,5, according to the slag basicity and Al2O3 content. The quantitative contributions of basicity and (%FetO + %MnO) on L-Mn and L -P were empirically determined and their usefulness was discussed with the aid of plant data: I-Mn = -45.2 (%CaO+%MgO)/(%SiO2+%Al2O3+%P2O5) + 6.2(%FetO+%MnO)-2.96, L-p = 97.0 (%CaO+%MgO)/(%SiO2+%Al2O3+%P2O5) + 1.23(%FetO+%MnO) - 115.9. To improve Mn and P yields in the practical RH operation, it is strongly re commended that Fe-Mn and Fe-P alloys be added after Al deoxidation treatmen t inducing relatively high Al2O3 in Slag and maintaining low FetO content. in addition, a ladle slag composition for the targeted Mn and P contents in liquid iron was substantially estimated using the empirical relationships.