Crystallization behavior of CaF2-TiO2 fluxes geared towards high heat input submerged arc welding

Crystallization behaviors of CaF2-TiO2 fluxes with varying TiO2 contents from 10 to 40 wt.% for high heat input submerged arc welding application have been systematically investigated by using single hot thermocouple technique (SHTT), field emission scanning electron microscopy (SEM), and X-ray diffraction (XRD). It is demonstrated that, as a function of the TiO2 content, the crystallization temperature initially decreases (from 10 to 30 wt.%) but increases afterwards (>30 wt.%), while the incubation time follows an opposite trend. It has been confirmed that CaTiO3 and CaF2 are the two dominant precipitated phases. It is further shown that the growth of CaTiO3 crystals follows a three-dimensional pattern while that of CaF2 a two-dimensional one. The effective activation energy is the highest when the TiO2 content is 30 wt.%, indicating the greatest barrier to crystallize and the highest capability to achieve the most desired production of amorphous welding fluxes for high heat input applications.