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

Abstract

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-Fe _t O ladle slag at 1873 K. The activity coefficient of Fe _t O 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 Fe _t O, while that of MnO seems to increase gradually with increasing the basicity. However, the values of $\gamma _{Fe_t O}$ and γ _MnO showed minima with respect to P₂O₅ content of slag. In addition, the values of $\gamma _{Fe_t O}$ and γ _MnO increased as (pct CaO)/(pct Al₂O₃) ratio increased at given SiO₂, MgO, and P₂O₅ contents. The conversion equations between the Fe _t O 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 Fe _t O and MnO contents. The regular solution model was used to estimate the oxygen potential in the slag. For MgO saturated slags, $a_{Fe_t O_{(l)} } = 0.864a_{FeO_{(R.S.)} } ,a_{MnO_{(l)} } = 6.38a_{MnO_{(R.S.)} }$. For Al₂O₃ saturated slags, $a_{Fe_t O_{(l)} } = 2.086a_{FeO_{(R.S.)} } ,a_{MnO_{(l)} } = 14.39a_{MnO_{(R.S.)} }$.