Thermodynamics of Oxygen in Liquid Fe-Cr Alloy Saturated with FeO Cr2O3 Solid Solution.

Abstract

The equilibrium relation between dissolved Cr and O in liquid high Cr steel has been assessed on the condition of pure solid Cr 2 O 3 saturation in our previous paper. Following this, the present work deals with the equilibrium between Cr and O in liquid iron saturated with FeO.Cr 2 O 3 solid solution and phase equilibria among liquid Fe-Cr alloy and Cr 2 O 3 containing oxides for the full understanding of the thermodynamic behavior of oxygen in liquid Fe-Cr alloy. The free energy of formation of FeO.Cr 2 O 3 and activities of the constituents in FeO.Cr 2 O 3 solid solution have also been measured by the chemical equilibrium technique at 1 823 to 1 923 K. The free energy of formation of FeO.Cr 2 O 3 was given by the following equation. Fe(s)+1/2 O 2 (g)+Cr 2 O 3 (s)=FeO.Cr 2 O 3 (s) ΔG=-307 600+66.82T (±6 800) (J/mol) (1 423 K<T<1 923 K) The activities of Fe t O(l) and Cr 2 O 3 (s) in FeO.Cr 2 O 3 solid solution exhibit negative deviation from ideality. The oxide phase in equilibrium with liquid Fe-Cr alloy is not Cr 2 O 3 but FeO.Cr 2 O 3 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 Cr 2 O 3 activity is applied.