Effect of CaF2 substitution with TiO2 on the crystallization characteristics of low-fluoride slag for electroslag remelting

Abstract

The effect of CaF 2 substitution with TiO 2 on the crystallization characteristics of low-fluoride slag was studied using differential scanning calorimetry (DSC) combined with XRD 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 TiO 2 content. Increasing TiO 2 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 TiO 2 contents during continuous cooling. The crystalline phases were Ca 12 Al 14 O 32 F 2 , CaTiO 3 , MgO, and CaF 2. The first and second crystallization phase were Ca 12 Al 14 O 32 F 2 and CaTiO 3 , respectively. The dominant crystalline phase was faceted Ca 12 Al 14 O 32 F 2 crystals. The morphology of CaTiO 3 crystal changed from needle-like to blocky with increasing TiO 2 content. The MgO crystal was with little blocky morphology, and the needlelike CaF 2 distributed among CaTiO 3 crystal. The precipitated amount of both MgO and CaF 2 was very small. The effective activation energy for Ca 12 Al 14 O 32 F 2 formation decreased with increasing TiO 2 content in the slag, indicating that TiO 2 enhanced the crystallization tendency of the slag.

Effect of TiO2 on fluoride evaporation from CaF2–CaO–Al2O3–MgO–Li2O–(TiO2) slag

“…This alters the slag composition and affects critical metallurgical properties of slag during the practical ESR process. Furthermore, the fluoride emission of fluorinecontaining gaseous species, such as HF, AlF 3 , CaF 2 or AlOF, would cause severe environmental degradation and health problems [3][4][5][6][7].…”

Fluoride Evaporation and Melting Characteristics of CaF2–CaO–Al2O3–MgO–Li2O–(TiO2) Slag for Electroslag Remelting

“…The main technique for developing lowfluoride slags is to control the CaO/Al 2 O 3 mass ratio and substitute a small amount of MgO or Li 2 O for CaF 2 to improve the physicochemical properties of ESR slags. [11][12][13][14] Adding a small amount of Li 2 O has been observed to significantly reduce slag viscosity, which is beneficial for as-cast ingot molding during ESR refining. [15] Based on this principle, CaF 2 -CaO-Al 2 O 3 -MgO-Li 2 O slag was designed for ESR processing.…”

Crystallization characteristics of B2O3 and TiO2-bearing glassy fluoride-free mold fluxes

“…And the implementation of the above mentioned functions is bound up with the existence of fluorides in traditional mold fluxes, which plays significant roles in adjusting physio-chemical properties of the mold fluxes. However, the fluorides can lead to erosion to continuous caster, pollution of environment, acidification of the cooling water, human health hazard, and a series of other harmful influences [6,[12][13][14][15][16]. Thus, there is a pressing need for fluoride-free mold fluxes, and the investigation on it has become a research area of interest.…”