Evaluation of Temperature and S Concentration Effect on Interfacial Tension between Molten Microalloyed Steel and Alumina
In order to lower the amount of oxygen in steel during the steelmaking process, deoxidation is carried out by using deoxidizer. Alumina inclusions are formed in molten steel when Aluminum is used as a deoxidizer. These inclusions are generally removed in the refining process, but unremoved inclusions would be left in the steel, resulting in defects in the steel product. Therefore, it is essential to remove the inclusion during the refining or the continuous casting process. Zeze and Mukai  suggested a semi-empirical model to determine the capture/wash away behavior of inclusions and bubbles at the solid-liquid interface during solidification. In this study, the interfacial tension between microalloyed steel and alumina was experimentally determined to predict the behavior of alumina inclusions at the solid-liquid interface. In the present work, the surface tension of microalloyed steel was measured using the constrained drop method. The temperature was controlled within the range of 1823 – 1873 K and the concentration of S 11 – 94 ppm. It was found that the surface tension increased with increasing the temperature and decreased with increasing sulfur content. The contact angle between microalloyed steel and alumina was measured using the sessile drop method. Moreover, it was noted that the contact angle decreased with increasing temperature in most experiments. The interfacial tension between molten microalloyed steel and alumina was evaluated using Young’s equation. The surface tension of alumina was taken from the literature. The interfacial tension decreased with increasing temperature in most cases. However, the interfacial tension increased with increasing temperature at 92 ppm of Sulphur. The wash-away velocity of pushing/engulfment of alumina inclusions at the solid-liquid interface of microalloyed steel was predicted using the derived interfacial tensions in the present study. It was concluded that the inclusions pushing from the solidification interface are more likely to occur as the sulfur concentration decreases when the sulfur concentration is lower than 64 ppm.