Aluminum is a very common deoxidizer in steel-making processes. The solubility of oxygen in molten iron decreases with increasing aluminum content. For the deoxidation process, the solubility of oxygen in Fe–Al melts decreases with increasing aluminum content. When %Al is increased to 0.34 wt.%, %O decreases to 6.4 ppm, which is the lowest point of the FeAl 2O 4 curve. Then the Al 2O 3 curve appears and replaces the FeAl 2O 4 curve, where the interconnection point of the two curves is the coexistence point of FeAl 2O 4 and Al 2O 3 phases. When %Al is increased to 0.4%, the %O decreases to 6.35 ppm, which is the lowest point of the Al 2O 3 curve. The solubility of oxygen in Fe–Al alloys is about 6.35 ppm with 0.4 wt.% aluminum at 1873 K. Liquid FeO–Al 2O 3, hercynite (FeAl 2O 4), and alumina (Al 2O 3) are three possible products during the deoxidation process. Based on thermodynamic calculation, the value of the interaction coefficient of e o Al was determined as −0.75 at 1873 K. This value is in good agreement with experimental curves in the literature.