Effect of Sulfur in Slag on Dynamic Change Behavior of Liquid Iron/Molten Slag Interfacial Tension

In continuous casting process of steel, the slag entrapment into liquid steel should be minimized by controlling the interfacial tension between liquid steel and molten slag. However, the liquid iron/molten slag interfacial tension dynamically changes when redox chemical reaction occurs at the iron/slag interface. This dynamic change behavior of the interfacial tension could be explained by assuming excess adsorption of oxygen atoms made by the decomposing reaction of slag components and its desorption at the iron/slag interface. In this study, we investigate the effect of sulfur in slag on the dynamic change of the liquid iron/molten slag interfacial tension, where sulfur initially exists in slag but not in iron. We evaluate apparent contact angle at the gas/molten slag/liquid iron triple interface in the floating lens method, which is determined by the balances among surface tension of iron, surface tension of slag and interfacial tension between iron and slag in both horizontal and vertical directions. When a silicate slag droplet contacted with liquid iron surface, the apparent contact angle rapidly decreased, reached the minimum and then gradually increased to achieve the steady value. The 0.1 mass% sulfur addition in the slag further decreased the contact angle at the minimum. It was indicated that sulfur as well as oxygen in the slag are simultaneously adsorbed at the iron/slag interface to dynamically decrease the interfacial tension.