Three-dimensional stability diagram of Al–Mg–O inclusions in molten steel

Stability diagrams are of great importance for investigating deoxidation equilibrium and controlling inclusions in molten steel. Combined with programming for calculation and drawing, the three-dimensional stability diagrams of MgO, MgO·Al2O3, and Al2O3 in the Fe–Al–Mg–O system were successfully drawn, which can visually explain the meaning of the iso-oxygen contours and the borderlines among different phases. They also offer straight evidence that the borderline method is imperfect. The three-dimensional stability diagrams can visually show more vital details that cannot be illustrated by the iso-oxygen contours. The most significant advantage of three-dimensional stability diagrams is not only judging the most stable phase in the specific component area but also visually showing the transformation trend among the phases from a three-dimensional perspective, especially when the equilibrium surfaces of these phases are relatively close. Besides, an interesting transformation of inclusions in the Fe–Al–Mg–O system was found. When the magnesium content is higher than 0.0065% and the aluminum content is lower than 0.21%, the equilibrium products of aluminum-magnesium composite deoxidation may be transformed from MgO to MgO·Al2O3 and Al2O3 in turn, which can be directly observed from the three-dimensional stability diagram based on the calculations.