Effect of Water Vapor on Evaporation and Melt Crystallization of Mold Fluxes

ABSTRACT Melt crystallization behavior of both the fluorine-containing and fluorine-free mold fluxes has been investigated using a single hot thermocouple technique (SHTT). By increasing the dew point of atmosphere from 223 K to 285.5 K (−50 °C and 12.5 °C), the primary crystalline phase of fluorine-containing mold flux was changed from cuspidine (Ca 4 Si 2 O 7 F 2 ) to Ca 2 SiO 4 with accelerated nucleation rates. Enhancement of fluorine evaporation due to hydroxyl is attributed to the main reason for the abnormal crystallization behavior of the fluorine-containing mold flux under humid atmosphere, which may bring a sticking-type breakout during the commercial continuous casting process. In contrast, the effect of water vapor on crystallization of fluorine-free mold flux was negligible. This implies that the application of fluorine-free mold fluxes can become a countermeasure to prevent the hydrogen-induced breakout during the continuous casting process under wet atmosphere.