Influence of CaF2 and Li2O on the Viscous Behavior of Calcium Silicate Melts Containing 12 wt pct Na2O

Abstract

Understanding the viscous behavior of silica-based molten fluxes is essential in maintaining the reliability of steel casting operations and in preventing breakouts. In particular, high concentrations of aluminum in recently developed transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) steels tend to promote reduction of silica in the mold fluxes that result in the formation of alumina, which in turn increases the viscosity. To counteract this effect, significant amounts of fluidizers such as CaF 2 and Li 2 O are required to ensure that mold fluxes have acceptable lubrication and heat transfer characteristics. The viscous behavior of the slag system based on CaO-SiO 2 -12 wt pct Na 2 O with various concentrations of CaF 2 and Li 2 O has been studied using the rotating spindle method to understand the effects on the viscosity with these additives. CaF 2 additions up to 8 wt pct were effective in decreasing the viscosity by breaking the network structure of molten fluxes, but CaF 2 concentrations above this level had a negligible effect on viscosity. Li 2 O additions up to 2 wt pct were also effective in decreasing the viscosity, but the effect was comparatively negligible above 2 wt pct. Using Fourier transform infrared (FTIR) analysis of as-quenched slag samples, it was concluded that the viscosity was controlled more effectively by changing the larger complex silicate structures of rings and chains than by changing the amounts of simpler dimers and monomers.

Viscous Flow and Crystallization Behaviors of P-bearing Steelmaking Slags with Varying Fluorine Content

“…3 that the viscosity decreased significantly with the initial CaF 2 addition with 3 wt.%, while the decrease became less pronounced at higher CaF 2 addition. Similar results were obtained by Park et al 14) In addition, the detailed relation between viscosity and slag structure will be discussed in Section IV.…”

“…Shahbazian 17) examined the effect of CaF 2 on the viscosity of CaO-FeO-SiO 2 -CaF 2 system in the temperature range of 1 435-1 749 K and obtained the similar variation trend. As many researchers have pointed out, 14,15,18) the decrease of viscosity with CaF 2 addition may suggest that the CaF 2 plays the role of network modifier in silicate slags to break the silicate network. It was also noteworthy in Fig.…”

“…The viscosity decreased, as expected, with increasing CaF 2 content, consistently to the trends observed by previous works. Park et al 14,15) investigated the viscosities of CaO-SiO 2 -Na 2 O-CaF 2 and CaOSiO 2 -MgO-CaF 2 slags and observed that the viscosity for slags with different basicities (0.8, 1.0 and 1.3) decreased with a small addition of CaF 2 . Ko et al 16) found that the viscosity of CaO-SiO 2 − 10 wt.% MnO-CaF 2 slag continuously decreased by CaF 2 addition.…”

“…One possible reason is that fluorine ions are quite effective at depolymerizing silicate networks. [14][15][16] The reaction can be illustrated schematically through Fig. 12(a) that the F − ions can behave similar to the free oxygen and depolymerize the complex silicate structure to simple units, which, in turn, leads to the decrease of degree of polymerization (DOP) and later the decrease of viscosity.…”

Assessment of CaO^|^ndash;Al2O3 Based Mold Flux System for High Aluminum TRIP Casting

“…Considerable efforts have been carried out to suppress the abrupt change of mold flux properties such as viscosity during high alloy steel casting by optimizing the ratio of CaO/ SiO2, 2,3) Al2O3/SiO2 4,5) or the amount of fluidizers [6][7][8] for the conventional lime-silica based oxide system. However, it is difficult to design an optimal composition of mold fluxes for high Al grade steel due to constantly changing (usually increasing) viscosity with the progress of Eq.…”