Thermodynamic aspects of steel reoxidation behavior by the ladle slag system of CaO-MgO-SiO2-Al2O3-FetO-MnO-P2O5

The reoxidation behavior of steels by slag in the secondary steelmaking process was addressed by investigating the thermodynamic equilibria between the liquid iron containing Mn and P and CaO-MgO-SiO2-Al2O3-P2O5-MnO-FetO ladle slag at 1873 K. The activity coefficient of FetO shows a maximum value in the vicinity of the basicity ((X-CaO + X-MgO + X-MnO)/(X-SiO2 + X-Al2O3 + X-P2O5)) = 2.5 at the specific mole fraction range of FetO, while that of MnO seems to increase gradually with increasing the basicity. However, the values of gamma(FetO) and gamma(MnO) showed minima with respect to P2O5 content of slag. In addition, the values of gamma(FetO) and gamma(MnO) increased as (pct CaO)/(pct Al2O3) ratio increased at given SiO2, MgO, and P2O5 contents. The conversion equations between the FetO and MnO activities and their calculated activities via regular solution model were derived by the correlation between the measured and calculated activities over the limited ranges of FetO and MnO contents. The regular solution model was used to estimate the oxygen potential in the slag. For MgO saturated slags, a(FetO(l)) = 0.864a(FeO(R.S.)), a(Mno(l)) 6.38a(MnO(R.S)). For Al2O3 saturated slags, a(FetO(l)) =2.086(aFeO(R.S.)), a(MnO(l)), = 14.39a(MnO(R.S.)).