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 pro cess was addressed by investigating the thermodynamic equilibria between th e liquid iron containing Mn and P and CaO-MgO-SiO2-Al2O3-P2O5-MnO-FetO ladl e 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 M nO seems to increase gradually with increasing the basicity. However, the v alues of gamma(FetO) and gamma(MnO) showed minima with respect to P2O5 cont ent of slag. In addition, the values of gamma(FetO) and gamma(MnO) increase d as (pct CaO)/(pct Al2O3) ratio increased at given SiO2, MgO, and P2O5 con tents. The conversion equations between the FetO and MnO activities and the ir calculated activities via regular solution model were derived by the cor relation between the measured and calculated activities over the limited ra nges of FetO and MnO contents. The regular solution model was used to estim ate 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.)).