Effect of B2O3 Addition to Slag on the Dynamic Change Behavior of Interfacial Tension between Liquid Iron and Molten Slag

The interfacial tension between liquid steel and molten slag is an important consideration for the continuous casting process because it significantly affects the inclusion of mold flux in liquid steel when the metal/slag interface is disturbed. Specifically, dynamic changes in interfacial tension are observed when liquid iron and molten silicate slag are contacted. This behavior is explained well by a mechanism in which oxygen generated by the decomposition of SiO2 adsorbs at the interface, temporally decreasing interfacial tension, followed by the desorption of this oxygen from the interface to the bulk metal, recovering the interfacial tension. B2O3 has emerged as an alternative to fluorides as a component of mold flux that controls its physicochemical properties, such as liquid viscosity and crystallization behavior. However, its effect on interfacial-tension dynamics is not currently understood. Accordingly, in this study, the dynamic interfacial tension between liquid iron and molten B2O3-bearing slag was investigated by the floating lens method. When B2O3-bearing slag was used, the interfacial tension significantly decreased to a minimum in the initial stage then slowly increased and finally recovered to the value observed when the B2O3-free slag was contacted with liquid iron. The decomposition of both B2O3 and SiO2, providing oxygen to the metal/slag interface, was proposed as a reason for the significant decrease in interfacial tension. Furthermore, it was proposed that the B2O3 decomposition occurs continuously, which causes the slow increase of interfacial tension after the initial stage.