Viscosity and Viscosity Estimate Model of Fluoride-free and Titanium-Bearing Mold Fluxes

The relationship between the binary basicity (CaO/SiO2),TiO2,Na2O,Li2O,MgO,MnO,B2O3 and viscosity for fluoride-free and titanium-bearing mold fluxes were systematically researched. The rotating cylinder method was employed in the experiment to measure the viscosity of the slag. The results indicate that Li2O, B2O3 and Na2O play major roles in decreasing viscosity, especially Li2O, which is the most effective flux, while MgO and MnO exert little influence on viscosity. Meanwhile, it can be concluded that with increasing TiO2 content, the viscosity of fluoride-free and titanium-bearing mold fluxes increases at first but then falls when the amount of TiO2 is greater than 6.0%. Based on large amounts of experimental statistics of the viscosity of fluoride-free and titanium-bearing mold fluxes, an available model in literature for predicting the mold-slag viscosity was modified. This modified model can be used to predict the viscosity of fluoride-free and titanium-bearing mold fluxes. In fact, the predicted values approximate the observed values with a ±10.6% average deviation. Compared with the classical models,the average deviation is higher and it was found that the modified model can be used to estimate the viscosity of fluoride-free and titanium-bearing mold fluxes.     

Viscosity of Fluoride‐Free Mold Fluxes Containing B2O3 and TiO2

Viscosities of B₂O₃ and TiO₂‐bearing fluoride‐free mold fluxes have been measured by the rotating cylinder method in this work. Effects of different B₂O₃, TiO₂ content, and basicities on the viscosity characteristics have been examined. Viscosity of fluoride‐free mold fluxes containing B₂O₃ and TiO₂ was found to decrease with the increase of B₂O₃, TiO₂ content, and basicity. The values of apparent activation energy for viscous flow of slags decrease with additions of B₂O₃ and TiO₂ and the increase of basicity. Two parameters A and B in Riboud model were re‐evaluated based on the present experimental data, and the modified Riboud model was used to estimate the viscosity of fluoride‐free slag system investigated in present work. The viscosity values obtained by the experimental measurement were in good agreement with those calculated by the modified Riboud model.     

Effects of Transition Metal Oxides on Thermal Conductivity of Mould Fluxes

The thermal conductivity of the mould fluxes containing transition metal oxides was measured by hotline method at different temperatures. The relationship between the thermal conductivity of mold fluxes and the contents of transition metal oxides was discussed. The synthetic slags were composed of 30.0% — 35.4% CaO, 34.7% — 38.6% SiO₂, 6% Al₂O₃, 9% Na₂O, 14.4% CaF₂, 0–4% Cr₂O₃ and 0–8% MnO in mass percent. The results indicated that Cr₂O₃ and MnO had a negative effect on thermal conductivity of mold fluxes. The thermal conductivity of mold fluxes was about 0.25 — 0.55 W/(m K) when the temperature reached 1300 °C, and it increased sharply to about 1.32–1.99 W/(m K) when the temperature reduced from 1300 to 1000 °C. The thermal conductivity of mold fluxes containing Cr₂O₃ and MnO was 10%—25% lower than those of original fluxes. The decrease in thermal conductivity was attributed to the change of molecular structure of mold fluxes. In addition, the poor integrity and regulation of polycrystal structure, complexity of crystal structure, and effects of impurities in the boundary and lattice distortion leaded to the reduction in the thermal conductivity. Na₂CrO₄, Mn₂SiO₄ and other minor phases were also found in the samples containing Cr₂O₃ and MnO, respectively.     

Effect of MgO on Crystallization and Heat Transfer of Fluoride-Free Mold Fluxes

The effect of MgO on crystallization and heat transfer of fluoride-free mold fluxes was studied using single/double-hot thermocouple technique (SHTT/DHTT) and infrared emitter technique (IET), respectively. SHTT experiments demonstrated that the increase of MgO concentration promoted the crystallization tendency of mold fluxes. XRD analysis showed that the dominant phases changed from CaSiO₃ to CaSiO₃/Ca₂MgSi₂O₇/Ca₁₁Si₄B₂O₂₂, and to Ca₂MgSi₂O₇ as the MgO content was increased. The heat flux across mold flux disks was reduced from 671 to 615 kW/m² in IET experiments when MgO concentration was increased from 0.9 to 4.9 mass pct.     

Physical Properties and Regulating Mechanism of Fluoride-Free and Harmless B2O3 -Containing Mould Flux

There were certain amounts of CaF2, NaF orNa2Oin traditional mould fluxes ai ming to modifythe melting property of mould fluxes[1 -5], whichwould do great harmto the service performance ofmould fluxes . Meanwhile the environment was pol-luted seriously and health of operators was i mpairedheavily .Calciumfluorideledtothe separating out ofhigh melting point substance as spars , which de-stroyed the glass properties of mould fluxes .If flu-oride-containing mould fluxes entered the coolingwater…     

Modeling the Viscosity of Silicate Melts Containing Lead Oxide

Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing lead oxide. The model requires three pairs of adjustable parameters that are fitted to the experimental viscosities in the following systems: pure PbO, PbO-SiO₂, and PbO-Al₂O₃-SiO₂. The viscosity of other ternary and multicomponent silicate melts containing PbO is then predicted by the model without any additional adjustable model parameters. Experimental viscosity data are reviewed for melts formed by PbO with SiO₂, Al₂O₃, CaO, MgO, Na₂O, and K₂O. The deviation of the available experimental data from the viscosities predicted by the model is within experimental error limits.     

Viscosity Estimations of Multi‐Component Slags

A model for viscosity estimation of molten aluminosilicate slag, which was developed in our previous study, was extended to estimate viscosity of multi‐component slag containing alkali oxide and calcium fluoride in this study. The charge compensations of alkali oxides for Al tetrahedral ions are explicitly taken into account in the equations. The effect of calcium fluoride on the viscosity of slag was modeled by considering Ca‐2F species and no network‐breaking effect of CaF₂ were considered. The present model was applied to estimate the viscosity of slags within Al₂O₃‐CaO‐FeO‐MgO‐SiO₂‐CaF₂‐Na₂O‐K₂O system. A good agreement with a mean deviation of ～20% was achieved by comparison between estimated and measured values.     

Optimization of Mold Flux for the Continuous Casting of Cr-Contained Steels

To compensate the negative effect caused by the absorption of chromium oxide inclusions during the casting process of Cr-contained steels, a new mold flux system has been designed and investigated. The melting temperature range of the newly designed mold flux system is from [1124 K to 1395 K (851 °C to 1122 °C)]. The viscosity at 1573 K (1300 °C) and the break temperature increase with the addition of MnO and Cr₂O₃ but decrease with the addition of B₂O₃. The crystalline fraction of mold flux decreases from 81 to 42.1 pct with the addition of MnO and Cr₂O₃, and then further decreases to 25.3 pct with the addition of B₂O₃; however, it improves from 54.4 to 81.5 pct when the basicity increases. Besides, the heat-transfer ability of mold flux is inverse to the crystallization ratio of the slag. The comprehensive study of the properties for the four designed mold fluxes suggests that the mold flux with 1.15 basicity-3.01 pct B₂O₃-1.10 pct MnO-2.10 pct Cr₂O₃ shows the best properties for the continuous casting of Cr-contained steels.     

Crystallization Characteristics of CaO-Al2O3-Based Mold Flux and Their Effects on In-Mold Performance during High-Aluminum TRIP Steels Continuous Casting

Crystallization behaviors of the newly developed lime-alumina-based mold fluxes for high-aluminum transformation induced plasticity (TRIP) steels casting were experimentally studied, and compared with those of lime-silica-based mold fluxes. The effects of mold flux crystallization characteristics on heat transfer and lubrication performance in casting high-Al TRIP steels were also evaluated. The results show that the crystallization temperatures of lime-alumina-based mold fluxes are much lower than those of lime-silica-based mold fluxes. Increasing B₂O₃ addition suppresses the crystallization of lime-alumina-based mold fluxes, while Na₂O exhibits an opposite effect. In continuous cooling of lime-alumina-based mold fluxes with high B₂O₃ contents and a CaO/Al₂O₃ ratio of 3.3, faceted cuspidine precipitates first, followed by needle-like CaO·B₂O₃ or 9CaO·3B₂O₃·CaF₂. In lime-alumina-based mold flux with low B₂O₃ content (5.4 mass pct) and a CaO/Al₂O₃ ratio of 1.2, the formation of fine CaF₂ takes place first, followed by blocky interconnected CaO·2Al₂O₃ as the dominant crystalline phase, and rod-like 2CaO·B₂O₃ precipitates at lower temperature during continuous cooling of the mold flux. In B₂O₃-free mold flux, blocky interconnected 3CaO·Al₂O₃ precipitates after CaF₂ and 3CaO·2SiO₂ formation, and takes up almost the whole crystalline fraction. The casting trials show that the mold heat transfer rate significantly decreases near the meniscus during the continuous casting using lime-alumina-mold fluxes with higher crystallinity, which brings a great reduction of surface depressions on cast slabs. However, excessive crystallinity of mold flux causes poor lubrication between mold and solidifying steel shell, which induces various defects such as drag marks on cast slab. Among the studied mold fluxes, lime-alumina-based mold fluxes with higher B₂O₃ contents and a CaO/Al₂O₃ ratio of 3.3 show comparatively improved performance.     

Crystallization Behaviors of CaO-SiO2-Al2O3-Na2O-CaF2-(Li2O-B2O3) Mold Fluxes

The effects of basicity (CaO/SiO₂), B₂O₃, and Li₂O addition on the crystallization behaviors of lime-silica-based mold fluxes have been investigated by non-isothermal differential scanning calorimetry (DSC), field emission scanning electron microscopy, X-ray diffraction (XRD), and single hot thermocouple technique. It was found that the crystallization temperature of cuspidine increased with increasing the basicity of mold fluxes. The crystallization of wollastonite was suppressed with increasing the mold flux basicity due to the enhancement of cuspidine crystallization. The addition of B₂O₃ suppresses the crystallization of mold flux. The crystallization temperature of mold flux decreases with Li₂O addition. The size of cuspidine increases, while the number of cuspidine decreases with increasing mold flux basicity. The morphology of cuspidine in mold fluxes with lower basicity is largely dendritic. The dendritic cuspidine in mold fluxes is composed of many fine cuspidine crystals. On the contrary, in mold fluxes with higher basicity, the cuspidine crystals are larger in size with mainly faceted morphology. The crystalline phase evolution was also calculated using a thermodynamic database, and compared with the experimental results determined by DSC and XRD. The results of thermodynamic calculation of crystalline phase formation are in accordance with the results determined by DSC and XRD.     

A Viscosity Estimation Model for Molten Slags in Al2O3‐CaO‐MgO‐SiO2 System

A model for viscosity estimation of molten slags in the Al₂O₂‐CaO‐MgO‐SiO₂ system is presented in this work. The model is an extension to the viscosity estimation model of molten slags in the CaO‐FeO‐MgO‐MnO‐SiO₂ system developed before by the present author. The present model has explicitly taken charge compensation into consideration. It is postulated that Al exists in a structural unit MAl₂O₄ when MO/ Al₂O₃ >1 for the Al₂O₃‐MO‐SiO₂ system (MO=CaO, MgO). MAl₂O₄ has a similar behaviour as SiO₂, i.e. it can form an Al‐O‐Al network and be depolymerised by network modifying oxides (CaO, MgO). The present model is applied in viscosity estimation of some slags within the Al₂O₃‐CaO‐MgO‐SiO₂ system. A mean deviation of less than 25% is achieved for the present model.     

Influence of CaF<Subscript>2</Subscript> and Li<Subscript>2</Subscript>O on the Viscous Behavior of Calcium Silicate Melts Containing 12 wt pct Na<Subscript>2</Subscript>O

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 CaF₂ and Li₂O are required to ensure that mold fluxes have acceptable lubrication and heat transfer characteristics. The viscous behavior of the slag system based on CaO-SiO₂-12 wt pct Na₂O with various concentrations of CaF₂ and Li₂O has been studied using the rotating spindle method to understand the effects on the viscosity with these additives. CaF₂ additions up to 8 wt pct were effective in decreasing the viscosity by breaking the network structure of molten fluxes, but CaF₂ concentrations above this level had a negligible effect on viscosity. Li₂O 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.     

Thermophysical Properties of Continuous Casting Mold Flux for Advanced Steel Developments

The effect of Al₂O₃ on the crystallization and viscosity of calcium-silicate based fluxes with Na₂O and Li₂O additions used for continuous casting mold fluxes have been studied using the confocal laser scanning microscope and the rotating spindle rheometer. Al₂O₃ additions lowered the crystallization temperature of the flux and several crystalline phases for fluxes with high concentrations of SiO₂ forms depending on the cooling rate. High Al₂O₃ containing fluxes formed relatively few crystalline phases and were not highly dependent on the cooling rate. At slow cooling rates of 25 K/min for 10 and 20 wt% Al₂O₃ containing samples, SEM images revealed dendrites formed within the crystalline phases. At faster cooling rates the dendrite formation is inhibited and a spherical morphology could be observed. The substitution of SiO₂ with Al₂O₃ content modified the dominant silicate network into complex alumino-silicates. This increased the viscosity of the melt. FTIR and Raman analysis showed increased amounts of symmetric Al–O⁰ stretching with higher Al₂O₃. With higher CaO/(SiO₂ + Al₂O₃), the symmetric Al–O⁰ stretching and the Si–O–Al seems to decrease.     

Effects of Li2O and Na2O on the Crystallization Behavior of Lime-Alumina-Based Mold Flux for Casting High-Al Steels

With the development of advanced high strength steel (AHSS), a large amount of aluminum was added into steels. The reaction between aluminum in the molten steel and silica based mold flux in the continuous-casting process would tend to cause a series of problems and influence the quality of slabs. To solve the above problems caused by the slag–steel reaction, nonreactive lime-alumina-based mold flux system has been proposed. In this article, the effect of Li₂O and Na₂O on the crystallization behavior of the lime-alumina-silica-based mold flux has been studied by using the single hot thermocouple technology (SHTT) and double hot thermocouple technology (DHTT). The results indicated that Li₂O and Na₂O in the above mold flux system play different roles as they behaved in traditional lime-silica based mold flux, which would tend to inhibit general mold flux crystallization by lowering the initial crystallization temperature and increasing incubation time, especially in the high-temperature region. However, when their content exceeds a critical value, the crystallization process of mold fluxes in low temperature zone would be greatly accelerated by the new phase formation of LiAlO₂ and Na _x Al _y Si _z O₄ crystals, respectively. The crystalline phases precipitated in all samples during the experiments are discussed in the article.     

Effect of Li<Subscript>2</Subscript>O on the Behavior of Melting,Crystallization, and Structure for CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Based Mold Fluxes

The effect of Li₂O content on the behavior of melting, crystallization, and molten structure for CaO-Al₂O₃-based mold fluxes was investigated in this article, through use of single hot thermocouple technology (SHTT), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction (XRD). The SHTT results showed that the melting temperature range of the designed mold fluxes decreases and the crystallization of mold fluxes is inhibited first and then becomes enhanced when the Li₂O content increases from 1 to 6 mass pct. The FTIR and Raman spectroscopy results suggested that Li₂O could release O^2? ions to break the complex Al-O-Al structural unit into Al-O^? structure. Meanwhile, Li₂O could also stabilize the structural unit of Si-O-Al by link aluminate and Q ₀ ^Si structure through providing Li⁺ ions to merge into the network and compensate for the charges between Al³⁺ and Si⁴⁺. Besides, the XRD results indicated that the precipitation of LiAlO₂ in molten slag would enhance the crystallization behavior of mold flux when Li₂O content is over 4.5 mass pct.     

Crystallization Temperature and Crystallization Ratio of Mold Flux

Moldfluxformsaliquidphaseinfiltratinginto thegapbetweenthemoldandstrand.Thelayerof fluxfilmonthemoldplateisasolidglassylayer,whilethelayerclosesttothestrandremainsliquid andacrystallizationlayerliesbetweenthistwolay ers[1-3].Thecrystallizationtemperatureo…     

Investigation on viscosity of mould fluxes during continuous casting of aluminium containing TRIP steels

Abstract

Transformation induced plasticity steel with a high content of Al (Al-TRIP) is an advanced high strength steel. The reaction between Al and SiO₂ would lead to compositional changes in mould fluxes, which results in a decrease in SiO₂ content and an increase in Al₂O₃ content, and influences the physical properties of the molten fluxes. In the present study, the changes of viscosities of a series of mould fluxes with different additives and addition amounts were examined by a rotating viscometer and the crystals in the D series mould fluxes were analysed by scanning electron microscopy and X-ray diffraction. The results show that (a) the Al₂O₃ in mould fluxes containing Li₂O presents amphoteric characteristic; (b) the viscosity of the fluxes with 8% B₂O₃ decreases with the increase in w(Al₂O₃)/w (SiO₂) ratio, the result shows that the Al₂O₃ presents alkaline; (c) the viscosity of flux containing both 4% Li₂O and 5% B₂O₃ changes a little with the increase in w(Al₂O₃)/w(SiO₂) ratio. When the Al₂O₃ content is 30%, the viscosity is 0·204 Pa s and the break temperature is 1130°C; (d) mould fluxes used for Al-TRIP steel precipitate CaF₂ crystals; (e) base on the Riboud model, a suitable viscosity mathematical model for the mould fluxes with high Al₂O₃ content is established.     

Viscosity of blast furnace type slags

The effect of MgO, TiO₂, or Fe₂O₃ on the viscosity of 40CaO-40SiO₂-20Al₂O₃ (mass pct) slags has been measured by the rotating crucible viscometer. Viscosity of these quaternary slags decreased with an increase in the content of additive oxide. At the same content of additive oxide, the viscosity decreases from MgO, TiO₂ to Fe₂O₃. In addition, the effect of SiO₂ or Al₂O₃ on the viscosity of 26.1CaO-73.9Fe₂O₃ (mass pct) (CF) and 14.9CaO-85.1Fe₂O₃ (mass pct) (CF₂) slags has been measured. Viscosity of calcium ferrite slags increased with increasing SiO₂ or Al₂O₃ content. Al₂O₃ was found to be more effective for increasing the viscosity at the same content of the additive oxide. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Effects of Rare Earth Oxide on Viscosity of Mold Fluxes for Continuous Casting

The effects of RE (rare earth) oxide on viscosity of mold fluxes were investigated with a rotary viscometer. The results show that : (1) The viscositv of mold fluxes is remarkably inereased by RE oxide addition, especially when the mass fraction of RE oxide is more than 10%. (2) By addition of RE oxide, precipitation of the insohlble particles with high melting point from the molten slag with the decreasing of the temperature leads to the inerease of viscosity. Viscosity curve shows that RE oxide is soluble in some extent in mold fluxes. When RE oxide is in a state of supersaturation, the existence of insoluble particles also makes the viscosity of mold fluxes increase. (3) Not only the viscositv of nlold fluxes can be reduced, but also the capacity to dissolve and absorb RE oxide can be increased by Li2O, B2O3 and BaO. However, the contents of Li2O, B2O3, and BaO should be controlled to suitable levels. (4) The solidification temperature of mold fluxes can be increased by the addition of RE oxide, which is unfavorable to heat transfer and luhrication of mold fluxes between steel shell and mold.