“…Besides the experimental research works above, mathematical models have also been developed to study the viscosity of F-free mold flux. 17,18) In the respect of crystallization of F-free mold flux, Choi et al, 19) have investigated the influence of basicity on the crystallization behavior, and the results showed that the basicity tends to enhance the crystallization of the F-free glass mold flux. Fox et al,20) chose the combination of B 2 O 3 and Na 2 O as alternative substitutes for CaF 2 in billet fluxes and found that the crystallinity decreased with the increase of B 2 O 3 .…”
Viscosity and crystallization are essential properties to characterize the lubrication and heat transfer performances of mold flux. Therefore, in this paper, the viscosity and crystallization behaviors of conventional F-containing commercial mold flux and newly designed F-free mold fluxes were investigated by using rotating cylinder method and Single/Double Hot Thermocouple Technique (SHTT/DHTT). Results shows that the viscosities of designed F-free mold fluxes are close to the F-containing mold flux; and the crystallization temperatures of F-free mold fluxes increases with the increase of basicity and Na 2 O/Li 2 O content; while it decreases with the increase of cooling rate and the addition of B 2 O 3 . The final steady state structure of F-free mold fluxes during the DHTT tests shows it is composed of a major crystalline and a thin liquid layer (5.42-7.2%) without glass phase. The results of XRD indicate that the main crystalline phases formed in designed F-free mold fluxes were calcium borosilicate (Ca 11
“…Besides the experimental research works above, mathematical models have also been developed to study the viscosity of F-free mold flux. 17,18) In the respect of crystallization of F-free mold flux, Choi et al, 19) have investigated the influence of basicity on the crystallization behavior, and the results showed that the basicity tends to enhance the crystallization of the F-free glass mold flux. Fox et al,20) chose the combination of B 2 O 3 and Na 2 O as alternative substitutes for CaF 2 in billet fluxes and found that the crystallinity decreased with the increase of B 2 O 3 .…”
Viscosity and crystallization are essential properties to characterize the lubrication and heat transfer performances of mold flux. Therefore, in this paper, the viscosity and crystallization behaviors of conventional F-containing commercial mold flux and newly designed F-free mold fluxes were investigated by using rotating cylinder method and Single/Double Hot Thermocouple Technique (SHTT/DHTT). Results shows that the viscosities of designed F-free mold fluxes are close to the F-containing mold flux; and the crystallization temperatures of F-free mold fluxes increases with the increase of basicity and Na 2 O/Li 2 O content; while it decreases with the increase of cooling rate and the addition of B 2 O 3 . The final steady state structure of F-free mold fluxes during the DHTT tests shows it is composed of a major crystalline and a thin liquid layer (5.42-7.2%) without glass phase. The results of XRD indicate that the main crystalline phases formed in designed F-free mold fluxes were calcium borosilicate (Ca 11
“…As a result, it would deteriorate both the casting operation and the surface quality of cast slabs, and cause many problems such as increased crack frequency, non-uniform heat transfer across the mould flux, reduced lubrication and so on. [2][3][4] In order to solve the problem on chemical composition change of mould fluxes and develop optimal mould flux to meet the requirements of the high aluminum steel casting, previous researchers have proposed the nonreactive CaOAl 2 O 3 based mould flux to substitute for conventional limesilica-based mould fluxes. 2,[5][6][7][8][9][10][11] Blazek et al 7) developed lime-alumina-based mould flux for casting high aluminum TRIP steel.…”
Crystallization behaviors of new developed CaO-Al2O3 based mould fluxes with TiO2 addition for casting of high-Al steels were investigated by using DTA techniques combined with SEM-EDS and XRD analysis. XRD and SEM analyzed on the crystallized samples showed that the sequence of crystal precipitation for TiO2-free mould flux during cooling was MgO, and followed by Ca12Al14O33 during cooling. The sequence of crystal formation for TiO2-bearing mould fluxes during cooling is CaTiO3 to MgO, and then Ca12Al14O33. Continuous cooling transformation diagrams (CCT) were constructed for analysis of the crystallization behaviors. The Undercooling values for onset crystallization of various crystals were calculated by using liquidus temperature obtained by heating DTA and crystallization temperature of various crystals. The crystallization temperatures of CaO-Al2O3 based mould fluxes increased with increasing TiO2 content. The undercooling values for onset crystallization of CaTiO3 decreased with increasing TiO2 content, which indicating that the crystallization of CaTiO3 was enhanced with increasing TiO2 content. The undercooling values for onset crystallizations of Ca12Al14O33 and MgO only changed slightly with increasing TiO2. This indicated that crystallizations of Ca12Al14O33 and MgO crystals were only slightly influenced by TiO2 addition. The overall crystallization of mould fluxes was enhanced with increasing TiO2 content.
“…3,6,8,[10][11][12][13][14] Lubrication and heat-transfer behavior which control performances of mould fluxes between copper mould and steel shell are very sensitive to the viscosity and crystallization characteristics. [1][2][3][4][5][6][7][8][9] The crystallization of mould fluxes reduces the horizontal heat transfer by two effects: (1) radiation thermal conductivity could be decreased by crystallites which scatter the radiation; 12) (2) interfacial resistance between mould and solidified slag can be increased with formation of more air gaps accompanying crystallization due to the fact that the density of the crystalline phase is greater than that of the glass. 8) Accordingly, it is essential to carry out investigations on the crystallization behaviour of slags.…”
Section: Introductionmentioning
confidence: 99%
“…[1][2][3][4] Some reports have shown that B2O3 and/or TiO2 may become most promising substitute for fluorides in traditional mould fluxes. [1][2][3][4][5][6][7] According to some previous studies, 1,3,6,7) the existence of TiO2 in mould fluxes can easily lead to the formation of some crystals (e.g. CaTiO3 or CaTiSiO5) with high melting point, which is potential to replace the cuspidine generated by fluorine in mould fluxes and ensure the crystallization ability of slag to achieve good heat transfer performance.…”
Section: Introductionmentioning
confidence: 99%
“…Besides, B2O3, as an effective fluxing agent to lower the melting point of mould flux, has been taken into consideration for being added to mould fluxes to adjust the viscosity or melting properties of slag. 2,4,5) Accordingly, it is important to investigate the properties of slag containing B2O3 and/or TiO2 for the development of optimal fluorine free mould fluxes.…”
Crystallization characteristics of the CaO-SiO2-TiO2-10%B2O3 glassy slag at w(CaO)/w(SiO2)=1 have been studied by Differential Thermal Analysis (DTA) and Matusita-Sakka method. Crystallization products have been distinguished by employing X-ray diffraction (XRD) and Scanning Electron Microscopy equipped with Energy Dispersive Spectroscopy (SEM-EDS). As the TiO2 content is within 10-18%, the crystal phase precipitated is mainly CaSiO3, and the effective activation energies for crystal growth increase with the increase of TiO2 content. Crystallization mechanism for CaSiO3 shifted from surface crystallization to onedimensional growth with increase of TiO2. As the TiO2 content in slag further increases to 22% and 26%, CaTiSiO5 becomes the predominant crystal phase precipitated, and the effective activation energies for crystal growth decrease with the increase of TiO2 content. Crystallization mechanism for CaTiSiO5 is mainly surface crystallization. Therefore, with the increase of TiO2 content, the crystallization ability of the CaO-SiO2-TiO2-10%B2O3 glass system decreases initially and then increases.
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