A deoxidation thermodynamic model for 304 stainless steel considering multiple-components coupled reactions

Abstract

A thermodynamic model for predicting the equilibrium oxygens of 304 stainless steel was developed based on the theory of slag–steel equilibrium, the law of mass conservation, and the ion and molecule coexistence theory. In the developed model, the Fe–Cr–Mn–Si–Al–S–O–melts reaction system and CaO–MgO–CaF₂–FeO–MnO–Al₂O₃–SiO₂–Cr₂O₃ slags were considered. The oxygen contents calculated by the model are in good agreement with experimental results and reference data. The equilibrium oxygen contents in 304 stainless steel mainly decrease with increasing binary basicity ($w_{{({\text{CaO}})}} /w_{{({\text{SiO}}_{2} )}}$, where w_(i) is the mass percentage of component i) and decreasing temperature. Controlling binary basicity at 2.0 while maintaining temperatures lower than 1823 K will keep the oxygen contents in the 304 stainless steel lower than 15 × 10^–6. The equilibrium oxygen contents may also be decreased with increasing content of MgO in slags, which is more significant at lower binary basicity. Besides, a small amount of FeO, MnO, and Al₂O₃ (about 0–2.5 wt.%) in slags has little effect on equilibrium oxygen contents. Furthermore, it is found that the [C]–[O] reaction may occur during refining process but will not significantly affect the equilibrium oxygen contents.

Appendix

See Tables 9 and 10.

Table 9 Expression of structural units as ion couples or molecules, their mole numbers, and related mass action concentrations expressions of in CaO–MgO–CaF₂–FeO–MnO–Al₂O₃–SiO₂–Cr₂O₃–S slags

Table 10 Chemical reaction formulas of forming complex molecules, their standard molar Gibbs free energy changes and expression of mass action concentrations in CaO–MgO–CaF₂–FeO–MnO–Al₂O₃–SiO₂–Cr₂O₃–S slags at metallurgical temperature