The Effect of Secondary Refining Slag for Ultra Low Carbon Aluminum Killed Steel

Abstract

As the demands for high quality clean steel have been increased, the problems originated by an inclusion were emerged. In order to remove the inclusion, the ability of a slag to dissolve the inclusion into the liquid slag should have been needed. It was well known that FetO in liquid slag can improve the ability to dissolve inclusions. However, it behaves as a reoxidizing agents which can supply oxygen into liquid steel. For the efficient usage of FetO, the behavior as a reoxidizing agents should be understood. In the present study, the mechanism of reoxidation between Al in ULCAK liquid steel and FetO in liquid slag based on CaO-Al2O3-MgO-FetO system was investigated. The experiments were carried out under the atmosphere filled with purified argon at 1550 °C. The methodology based on the investigation for the reaction between liquid steel and liquid slag was employed to identify the mechanism of reoxidation. In order to verify what the rate controlling step is, the mass transfer at each of phases were evaluated by calculating the mass transfer coefficients. In order to suggest what the species diffuse most slowly at each phase, the effect of the amount of slag was discussed by the present experimental data. As following the results of the present study, the rate controlling step was elucidated that it could be altered by the compositions of slags with regarding to the change of mass transfer coefficients.