EFFECT OF CaF2 SUBSTITUTION WITH TiO2 ON. THE CRYSTALLIZATION CHARACTERISTICS OF LOW-FLUORIDE SLAG FOR ELECTROSLAG REMELTING

The effect of CaF2 substitution with TiO2 on the crystallization characteristics of low-fluoride slag was studied using differential scanning calorimetry (DSC) combined with MID and SEM-EDS analysis. The effective activation energy for crystallization of the slag was evaluated. The results showed that the liquidus temperature of the slag increased unnoticeably with increasing TiO2 content. Increasing TiO2 addition from 4.3 wt% to 13.0 wt% decreased the undercooling of the slag and enhanced the crystallization ability of the slag. There is no change in the types and precipitation sequence of the crystalline phase in the slag with different TiO2 contents during continuous cooling. The crystalline phases were Ca12Al14O32F2, CaTiO2, MgO, and CaF2. The first and second crystallization phase were Ca12Al14O32F2 and CaTiO3, respectively. The dominant crystalline phase was faceted Ca12Al14O32F2 crystals. The morphology of CaTiO3 crystal changed from needle-like to blocky with increasing TiO2 content. The MgO crystal was with little blocky morphology, and the needlelike CaF2 distributed among CaTiO3 crystal. The precipitated amount of both MgO and CaF2 was very small. The effective activation energy for Ca12Al14O32F2 formation decreased with increasing TiO2 content in the slag, indicating that TiO2 enhanced the crystallization tendency of the slag.