Formation Conditions of Mg2TiO4 and MgAl2O4 in Ti-Mg-Al Complex Deoxidation of Molten Iron

It is important to study the complex deoxidation equilibrium of molten iron in Ti-Mg-Al system from the view point of inclusion control. The equilibrium experiments between molten iron and TiOx-MgO-Al2O3 slag and the thermodynamic calculation on the complex deoxidation are conducted at 1973 K in the present study. The liquid phase region of TiOx-MgO-Al2O3 system in equilibrium with molten iron is clarified at 1973 K. The equilibrium compounds which are coexisted with the slag on the liquidus curve in the system are identified to be Mg2TiO4, and MgAl2O4. The equilibrium relation between the deoxidation products (Mg2TiO4 or MgAl2O4) and the composition of solute elements in steel is investigated, and the conditions that Mg2TiO4 forms instead of MgAl2O4 nor Al2O3 are examined in the complex deoxidation of Ti-Mg-Al system. When the aluminum content of molten iron is under 4 mass ppm, Mg2TiO4 forms over the wide concentration range. The concentration range of MgAl2O4 formation widens as the aluminum content of molten iron increases. It is necessary to increase Mg content and to decrease Al content in order to form Mg2TiO4 in the Ti-Mg-Al complex deoxidation of molten iron in the range Ti<0.01 mass%. However, it is difficult in the range of Ti>0.01 mass% to form Mg2TiO4.