Thermodynamic Study Of Al And Ti Deoxidation Equilibrium In High Temperature Molten Steel

Aluminum and Titanium are the main deoxidizers in the steelmaking process. Al2O3in big size is the main cause for reducing the purity of steel and causing nozzle clogging during continuous casting process. However, Al-and Ti-compounds in tiny size can be the nuclanuts for the innergranular ferrite (IGF), which is helpful for the increase of the ductility and intensity of steel. Therefore, it is necessary to study the Al-0equilibrium in molten steel to make sure the factors influencing the formation of Al2O3in order to control the size and amounts of Al2O3. Meanwhile, there are more than one kind of titanium-oxides, it is also necessary to find the co-existing conditions for the titanium-oxides in order to choose the needed one.In this paper, Fe-Al-O and Fe-Ti-O system are deeply studied with thermodynamic calculation and high-temperature Al-0reaction experiments in molten steel. It is found that,A. Fe-AI-O systemâ‘ Al2O3forms in priority in Fe-Al-O system at1873K.â‘¡The knee point at aluminum content [Al]=0.3%on soluble Al-O curve in molten steel is explained. When [Al]<0.3%, the oxygen content [O] deduces with the increase of aluminum; While [Al]>0.3%, the oxygen content increases gradually.â‘¢When [Al]<0.01%, all of the results with the parameters proposed by various researchers are in good agreement including the results with software Thermo-calc When [Al]>0.01%, Itoh’s parameters which include the first-and second-order parameters and the cross-product items are recommended for considering the thermodynamic equilibrium relationships more complicatedly in Fe-Al-O system.â‘£The high-temperature Al-0reaction experiments are performed.in the temperature range of1873K-1923K. The measured data are in good agreement with the calculated Al-0curve with Itoh parameters. The minimum error is0.01%[O] between calculated and measured data at [Al]=2.61%, and the maximal error is0.018%[O] where [Al]=1.38%.B. Fe-Ti-O systemâ‘ Ti-O compounds form in priority in Fe-Ti-O system at1873K. With the increase of titanium content, the titanium oxides form following the sequence of TiO2â†'Ti3O5â†'Ti2O3â†'TiO.â‘¡According to the transformation reaction of Ti3O5and Ti2O3, following the relations of excess free energy in Fe-Ti binary system, the co-existing point of Ti3O5and Ti2O3is at [Ti]=0.36%.â‘¢The parameters proposed by Pak are recommended for Fe-Ti-O system, which includes the first-and second-order interaction parameters and cross-product terms.