2002 Volume 42 Issue 1 Pages 23-32
The equilibrium relation between dissolved Cr and O in liquid high Cr steel has been assessed on the condition of pure solid Cr2O3 saturation in our previous paper. Following this, the present work deals with the equilibrium between Cr and O in liquid iron saturated with FeO·Cr2O3 solid solution and phase equilibria among liquid Fe–Cr alloy and Cr2O3 containing oxides for the full understanding of the thermodynamic behavior of oxygen in liquid Fe–Cr alloy. The free energy of formation of FeO·Cr2O3 and activities of the constituents in FeO·Cr2O3 solid solution have also been measured by the chemical equilibrium technique at 1823 to 1923 K.
The free energy of formation of FeO·Cr2O3 was given by the following equation.Fe(s) + 1/2 O2(g) + Cr2O3(s) = FeO·Cr2O3(s)
ΔG° = –307600 + 66.82T (±6800) (J/mol) (1423 K < T < 1923 K) The activities of FetO(l) and Cr2O3 (s) in FeO·Cr2O3 solid solution exhibit negative deviation from ideality. The oxide phase in equilibrium with liquid Fe–Cr alloy is not Cr2O3 but FeO·Cr2O3 solid solution when Cr content in metal is less than the critical Cr content of approximately 7 mass%. The present experimental results are in good accord with the thermodynamic relation between dissolved Cr and O calculated by the parameters which have been proposed in our previous work, if appropriate correction for Cr2O3 activity is applied.
