Wettability and Interfacial Phenomena Between Silicon and Sulfur-Bearing Steels and Solid CaO Substrates

The wettability between a Si–S steel with 0.2 wt pct sulfur and 0 3.5 wt pct silicon and a CaO substrate was investigated using a sessile drop method at 1550 °C. The equilibrium contact angle between the Si–S steel and the CaO substrate was 95, 136, 142 and 142 deg when the content of silicon in the steel was 0, 1.4, 2.8, and 3.5 wt pct, respectively. When there was no silicon in the steel, the steel hardly reacted with the CaO substrate. However, when the steel contained > 1 wt pct silicon, a reaction layer composed of CaS and 2CaO·SiO2 was generated at the interface between the molten steel and the substrate. Besides, the thickness of the reaction layer increased from 0 to 36 μm with the silicon content in the steel increasing from 0 to 2.8 wt pct, because the dissolved oxygen was reduced by silicon. However, when the silicon content increased to 3.5 wt pct, the thickness of the reaction layer reversely decreased, which was attributed to the prevention of the sulfur diffusion in the dense solid state reaction layer.