Analysis of Crystallization Behavior of Mold Fluxes Containing TiO2 Using Single Hot Thermocouple Technique

The crystallization behavior of mold fluxes containing 0—8 mass% TiO2 was investigated using the single hot thermocouple technique (SHTT) and X-ray diffraction (XRD) to study the possible effects on the coordination of heat transfer control and strand lubrication for casting crack-sensitive peritectic steels. Time-temperature-transformation (TTT) and continuous-cooling-transformation (CCT) curves were plotted using the data obtained from SHTT to characterize the crystallization of the mold fluxes. The results showed that crystallization of the mold fluxes during isothermal and non isothermal processes was suppressed with TiO2 addition. From the TTT curves, it could be seen that the incubation and growth time of crystallization increased significantly with TiO2 addition. The CCT curves showed that the crystallization temperature initially decreased, and then suddenly increased with increasing the TiO2 content. XRD analysis suggested the presence of cuspidine in the mold fluxes with lower TiO2 content (< 4 mass%), while both perovskite and cuspidine were detected in the mold fluxes when the TiO2 content was increased to 8 mass%). In addition, the growth mechanisms of the crystals changed during the isothermal crystallization process from interface-controlled growth to diffusion-controlled growth with increasing the TiO2 content.