Effect of CaO/Al₂O₃ratio on viscosity and crystallisation behaviour of mould flux for high Al non-magnetic steel

Abstract

In order to facilitate the development of CaO-Al 2 O 3 based mould flux for casting high aluminium, non-magnetic steel, the effect of CaO/Al 2 O 3 ratios from 0.6 to 3.2 on viscosity and crystallisation characteristics were investigated with the aid of a rotational viscometer, Fourier transform infrared spectroscopy, a single hot thermocouple technique and X-ray diffraction analysis. The results showed that, at temperatures above 1543 K (12708C), the viscosity first decreased and then became stable with increase in the CaO/Al 2 O 3 ratio. At temperatures below 1543 K (12708C), the viscosity again first decreased but then increased, with the CaO/Al 2 O 3 ratio. This viscosity behaviour can be attributed to changes in the network structure characteristics and the precipitation of solid particles within the liquid flux. Increase in the CaO/Al 2 O 3 ratio also first inhibited and then enhanced crystallisation as demonstrated by the changes in initial crystallisation temperatures and incubation times. The X-ray diffraction results confirmed that, at both low and high CaO/Al 2 O 3 ratios, the dominant precipitates were compounds with high melting points. On the other hand, with CaO/Al 2 O 3 ratios in the midrange, the dominant precipitates were compounds with relatively low melting temperatures. It is concluded that mould flux with a CaO/Al 2 O 3 ratio in the range 1.1-1.6 is the most appropriate for casting high aluminium, non-magnetic steels.

Effects of CaO on Reduction of Copper Slag by Biomass Based on Ion and Molecule Coexistence Theory and Thermogravimetric Experiments

“…Thus, the degree of weight loss reflects the reduction degree of iron ore oxides. Reduction degree of copper slag was calculated as follows: 25,26) Δ A t , Δ B t , Δ C t are weight loss of sample A, B and C (as shown in Fig. 8).…”

Review on the High-Temperature Thermophysical Properties of Continuous Casting Mold Fluxes for Highly Alloyed Steels

“…Adapted from published literature. 53,54,57,66,[87][88][89]93) 8 wt% CaF 2 and NaF have similar effects on depolymerizing the slag network, which lowers the viscosity and improves the diffusion kinetics to accelerate the formation of the primary cuspidine phase during cooling. However, the reactions of CaF 2 and NaF with SiO 2 and the volatilization of the fluorides at high temperatures may result in other operational problems at the casters that would need to be considered.…”

Review of Mold Fluxes for Continuous Casting of High‐Alloy (Al, Mn, Ti) Steels

“…As the amphoteric behavior of Al 2 O 3 , a large discrepancy in the effect of Al 2 O 3 on viscosity was found in different slag systems. [39,44,46,[59][60][61][62][63] The results regarding the effect of BaO and MgO content on viscosity and structure of the CaO-Al 2 O 3 -based mold fluxes system suggested that BaO works in a complicated fashion since it has a strong charge compensation effect on the [AlO 4 ] 5tetrahedron, while the addition of MgO tends to decrease the viscosity of the slag melt because the free O 2ions from MgO depolymerize the network structure, which leads to the reduction of melt flow resistance and apparent activation energy. [64,65] Moreover, the viscosity of CaO-Al 2 O 3 -based mold fluxes decreased with the increasing TiO 2 content, and the Raman spectral results revealed that the degree of polymerization is reduced by increasing TiO 2 .…”