Viscosity Of Mold Flux Research Articles

Effect of lepidolite on melting, viscosity and structure of CaO–SiO2 based melt

It will be an economic, environmental-friendly and energy-saving way to utilize lepidolite as a substitution of industrial grade lithium carbonate for preparation of commercial mold flux. Therefore, the melting behavior, viscosity and melt structure of mold fluxes with different lepidolite content were investigated in this study. The results show that the initial melting temperature of the fluxes increases from 1278.4 to 1301.2 K, meanwhile the complete melting temperature increases from 1622.0 to 1674.4 K with the addition of lepidolite from 15.10 to 37.80 wt%. The viscosity of mold fluxes at 1573 K increases from 0.12 to 0.44 Pa s, whereas the break temperature reduces from 1467.7 to 1386.9 K with the increase of lepidolite. The melt structure analyses suggests that the simple structural units, such as Q0, Q1, Q2 and [AlO4]5-- tetrahedral asymmetric stretching reduce; while the complex structural units, like Q3, Q4, [AlO4]5-- tetrahedral symmetric stretching and Al–O–Si bending increase with the addition of lepidolite. These changes suggest that the free oxygen transforms into bridging oxygen and non-bridging oxygen, and the structure of melt becomes more complex when lepidolite is added in the flux.

Effective mechanism of BaO on the structure and fluid behavior of CaO-SiO2-B2O3-based melts

The influence of BaO contents on structure and fluid behavior of fluorine-free CaO-SiO2-B2O3 based melts were examined using molecular dynamic (MD) simulation, rotary viscometer, X-ray diffraction and Fourier transform infrared spectroscopy. The FTIR results matched well with the MD simulation results that with the addition of BaO contents in CaO-SiO2-B2O3 based melts, more cations were provided to balance the negative charge of [BO4]5– tetrahedrons, leading to the structures of Si-O and B-O were more aggregated and the adjacent structural units were more closely connected, which made the structure complex, so the viscosity of mold fluxes at high temperature in the basicity range 1.15–1.25 was intensify. Meanwhile, when BaO replaced CaO under distinctive basic conditions, the viscous activity of fluorine-free mold flux was decreasing generally, showing that as the temperature was decreased, the tendency of slag to converge into complex network structural units was also decreasing, which states the improvement of lubrication capacity of the slag during cooling process.

Effects of Li2O on Structure and Viscosity of CaO-Al2O3-Based Mold Fluxes

Since CaO-Al2O3-based mold fluxes are one of the most important mold flux systems in metallurgic processes, it is important to explore their structure characteristics and viscosity. Molecular dynamics simulation is performed to study the effect of w(CaO)/w(Al2O3) ratio on both the structural and viscosity properties of CaO-Al2O3-based mold fluxes. A systematic analysis of the structure and thermodynamics on CaO-Al2O3-based mold fluxes is carried out, and it is well known that the viscosity of mold fluxes is related to the structure. The results show that the formation of stable structures of Si-O in the mold fluxes was beneficial to reduce the probability of structural interconnection, degree of polymerization, and viscosity of the molten slag. In the cationic structure, the contents of Ca-O-Al and Ca-O-Si are more stable, the interconnection of the Ca-O-Al and Ca-O-Si network weakens, and the viscosity decreases. The tetrahedra [AlO4] and [SiO4] have similar structures, but they exhibit different thermodynamic and physical properties. Viscosity test shows that CaO/Al2O3 = 0.88–2 continuously increased, when the cosolvent content Li2O = 1%–4%, CaO-Al2O3-based mold flux viscosity decreased, the degree of network structure polymerization decreased, and the complex structure depolymerized. Increasing the water content in the cosolvent is beneficial to reduce the viscosity of the crystallizer.

Melting and Flowing Behavior of Mold Flux in a Continuous Casting Billet Mold for Ultra-High Speed

High casting speed coincides with the development trend of billet continuous casting, which significantly changes the casting characteristics. A mathematical model of the billet mold, which includes multiphase fluid flow, transient heat transfer, and solidification during ultra-high speed of the casting process was developed. The model is first applied to investigate the flow field of molten steel in the mold, studying the influence of steel flow upon the melting and flowing behavior of mold flux. The temperature and velocity distributions of the flux pool that formed above the molten steel surface are described. A parametric study on the melting temperature and viscosity of mold flux on liquid flux thickness and flow velocity is then carried out. Finally, the model is used to derive the relationship between interfacial tension and level fluctuations. The predictions provide an improved understanding of the melting and flowing behavior of mold flux in the billet mold and give the guidance for the design and optimization of mold flux for ultra-high speed of billet casting.

Viscosity and structure evolution of CaO–SiO2-based mold fluxes with involvement of CaO–Al2O3-based tundish fluxes

In this study, the effect of involvement of CaO–Al2O3–SiO2–MgO tundish flux into CaO–SiO2–Al2O3–Na2O–CaF2 mold flux on viscosity and structure of mold flux was investigated through employing the rotating viscometer and associated structure analysis including high resolution Raman spectroscopy and solid-state 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR). The results showed that the viscosity continuously increases with increasing involvement of tundish flux. The apparent activation energy obtained from the temperature dependence of the viscosity presents an increase from 128.5 kJ/mol to 149.1 kJ/mol with increase of involvement ratio from 0 to 0.75. Semi-quantitative analysis using the deconvoluted Raman spectra and 27Al MAS-NMR spectra revealed an increase in amounts of [AlO4] and Si–O–Al units, but in the meanwhile a decrease in amounts of [AlOnF4-n] and [AlO5] units, this indicates the structure transformation from prevalent silicate structure to complex alumino-silicate structure with increasing involvement ratio. A self-developed structurally-based viscosity model can predict the viscosity of mold flux with varying involvement ratio and presents a smallest deviation of 15.8% compared to those prevalent viscosity models despite of the great transformation of the melt from silicate system to alumino-silicate system.

Effect of Al2O3/(B2O3 + Na2O) Ratio on CaO-Al2O3-Based Mold Fluxes: Melting Property, Viscosity, Heat Transfer, and Structure

CaO-Al2O3-based mold fluxes, which are under development for the continuous casting of high-Al steel, contain fluxing compounds, such as Na2O and B2O3. The reaction between [Al] and the fluxing agents in mold fluxes leads to an increase in Al2O3 and a decrease in B2O3 and Na2O concentrations, changing the properties of mold fluxes. The effect of the Al2O3/(B2O3 + Na2O) ratio on the melting properties, viscosity, heat transfer, and structure of the CaO-Al2O3-based mold fluxes is presented in this work. The increase of the Al2O3/(B2O3 + Na2O) ratio in the fluxes raised the melting temperature and high-temperature viscosity of mold fluxes but decreased the heat transfer rate across the flux disks. It also enhanced the degree of polymerization by promoting the formation of 3-D aluminate structure, which accounted for the change of the viscous behavior.

Effects of CeO2 on Viscosity, Structure, and Crystallization of Mold Fluxes for Casting Rare Earths Alloyed Steels

The CaO-Al2O3-based mold fluxes are proposed for the Ce-bearing heavy rail steel continuous casting because of the low reactivity. Effects of CeO2 on the melting temperature, the viscous property, and the crystallization behavior of the CaO-Al2O3-Li2O-B2O3 mold fluxes were studied using hemisphere melting point method, rotating cylinder method, and X-ray diffraction (XRD) in the present work. The microstructure of the mold fluxes was analyzed by Fourier-transform infrared spectroscopy (FTIR). The results revealed that the addition of CeO2 would increase the melting temperature, but decrease the viscosity at each temperature due to its influence on increasing the depolymerization of the mold fluxes at high temperature. The precipitation of CaO was restrained and CaCeAlO4 generated with increasing CeO2 content since the crystal phases were affected by the microstructure of the melts. The change of the crystalline phases in mold fluxes influences the break temperature and the viscosity of the mold fluxes below the break temperature. These results obtained can provide guidelines for designing new mold fluxes for casting rare earth alloy heavy rail steels.

Effect of Slag-Steel Reaction on the Initial Solidification of Molten Steel during Continuous Casting

With the mold simulator technique, the effect of slag-steel reaction on the initial shell solidification as well as the heat transfer and lubrication behavior of the infiltrated mold/shell slag film was studied in this article. The results showed that the Al2O3 content, the CaO/SiO2 ratio, and the viscosity of mold flux were increased with the progress of the slag-steel reaction during casting. The slag-steel reaction has two major effects on the initial shell solidification: one is increasing the mold heat flux and shell thickness by the decrease of slag film thickness. The other is the reduction of mold heat flux by the increase of crystal fraction in slag film. Mold flux with a lower basicity, viscosity, and crystallization temperature would result in a larger liquid slag consumption and the uneven infiltration of slag into the mold and shell gap that eventually leads to the irregular solidification of initial shell with a poor surface quality, such as slag entrapment and depressions as well as glaciation marks. Conversely, mold flux with a higher viscosity, basicity, and crystallization temperature would result in a smaller liquid slag consumption, which would cause the poor mold lubrication, the longitudinal shell surface defects, and drag marks.

Effect of basicity and B2O3 on the viscosity and structure of fluorine-free mold flux

The effect of basicity (weight ratio of CaO/SiO2) and B2O3 on the viscosity and structure of Fluorine-free mold flux for the casting of medium carbon steels was conducted in this article, through the rotating cylinder method combined with the Fourier transform infrared (FTIR) spectroscopy. The results showed that, with the increase of basicity, the viscosity of mold flux was attenuated dramatically, and then kept constant or slight increased in the low temperature region. The reason could be explained as the degree of polymerization (DOP) of the network structure was first reduced significantly with the addition of basicity, and then the further depolymerization is less pronounced with the further increase of basicity. Beside the formation of high melting point substance leads to the slight increase of viscosity. Moreover, it suggested that the viscosity of mold flux is decreased with the addition of B2O3 content, due to the fact that B2O3 is a low melting point oxide which could substantially lower the break temperature of mold flux. The result of FTIR indicated B2O3 acts as network former, and tends to form [BO3]-trihedral and [BO4]-tetrahedral structural units, which would connect with each other to form some simple network structure such as diborate or pentaborate. With the addition of B2O3, the free oxygen ions (O2−) would depolymerize the diborate structural unit, and the depolymerized diborate would link again with free [BO3]-trihedral to form complex pentaborate groups. Moreover, the effect of above addition on the apparent activation energy for viscous flow and break temperature of mold flux also were discussed. The results obtained in this paper provide the detailed study of the structure evolution of Fluorine-free mold flux when B2O3 is added.

Study of the Viscosity of Mold Flux Based on the Vogel–Fulcher–Tammann (VFT) Model

Viscosity is one of the most important properties of mold flux and affects the process of continuous casting significantly. In order to describe the variation of viscosity of mold flux accurately in a wide range of temperature occurring in the casting mold, a non-Arrhenius Vogel–Fulcher–Tammann (VFT) model was adopted in this study. The results showed that the adjusted coefficient of determination (Adj. R 2) of non-Arrhenius VFT Model ranges from 0.92 to 0.96, which suggests this model could be well adapted to predict the relationship between viscosity and temperature of mold flux. The temperature at which viscosity becomes infinite, T VFT, increased with the addition of Cr2O3 and improvement of basicity, while it decreased with the addition of B2O3, as it was determined by both the degree of polymerization of the melt structure and crystallization behavior of the melt. Also, the pseudo-activation energy, E VFT, of Samples 1 to 5 was 60.1 ± 3.6, 94.7 ± 14.9, 101.7 ± 19.0, 38.0 ± 4.8, and 32.4 ± 4.0 kJ/mol, respectively; it increased with the addition of Cr2O3 and B2O3, but deceased with the increase of basicity.

Application of Non-Arrhenius Models to the Viscosity of Mold Flux

The mold flux in continuous casting mold experiences a significant temperature gradient ranging from more than 1773 K (1500 °C) to room temperature, and the viscosity of the mold flux would therefore have a non-Arrhenius temperature dependency in such a wide temperature region. Three non-Arrhenius models, including Vogel–Fulcher–Tammann (VFT), Adam and Gibbs (AG), and Avramov (AV), were conducted to describe the relationship between the viscosity and temperature of mold flux in the temperature gradient existing in the casting mold. It found that the results predicted by the VFT and AG models are closer to the measured ones than those by the AV model and that they are much better than the Arrhenius model in characterizing the variation of viscosity of mold flux vs temperature. In addition, the VFT temperature and AG temperature can be considered to be key benchmarks in characterizing the lubrication ability of mold flux beyond the break temperature and glass transition temperature.

Influence of chemical composition of mold flux on viscosity and texture of slag film

ABSTRACTThe aim of this study was to examine the influence of the chemical composition of mold flux on viscosity and texture of slag film using a viscosity test instrument and polarizing microscope. The results showed that viscosity of mold flux decreased and the corresponding crystallization ratio rose with increase in basicity, Na2O, and F−. The formation of cuspidine might be promoted, and generation of melilite diminished by basicity and F−. Meanwhile, it is of interest that Na2O promoted the formation of melilite and cuspidine, and inhibited generation of pseudowollastonite and wollastonite. To improve the quality of low carbon steel, Na2O and F− of mold flux need to be reduced. Improvement in the quality of medium steel was noted when basicity and F− were reduced, whereas Na2O needs be elevated.

Effect of basicity and B2O3 on viscosity, melting and crystallization behaviors of low fluorine mold fluxes for casting medium carbon steels

As potential substitutes for fluorides, the influences of basicity and B2O3 content on viscosity, melting and crystallization behaviors of low fluorine mold fluxes for casting medium carbon steels were investigated by using Brookfield viscometer and Single Hot Thermocouple Technique in this study. Results suggested that, the break temperature, crystallization temperature and critical cooling rate of low fluorine mold fluxes were increased with the increase of basicity; while they were decreased with the further addition of B2O3. Meantime, the viscosity and melting temperature range were first attenuated, and then increased greatly with the increase of basicity; however, they would tend to be reduced with the addition of B2O3 content. Also, it was found that the viscosity of mold flux is not only decided by the degree of polymerization of silicate structure, but also greatly affected by its crystallization behavior.

The Mould Flux Viscosity Designing of High Carbon Steel for Thin Slab Continuous Casting

Viscosity is very important for the high carbon steel for thin slab continuous casting, in this research the orthogonal experiment has been carried out, and the results showed that: the effect for the flux viscosity form strong to weak is: R>F>BaO>Na2O>MgO. and in the experiment range, with the R increasing, when the R is between 0.80 and 0.90, the flux viscosity is diminished slowly; but when the R is bigger than 0.90, the flux viscosity is diminished sharply; Na2O,MgO and F- could decrease the flux viscosity; BaO could lower the melting temperature of the flux to decrease the flux viscosity.

Simulation of heat transfer and strain behaviour in bloom casting mould

An optimum casting model was developed to simulate the effect of mould flux on bloom heat transfer and strain behaviour based on a 3D MiLE method, and the influence of casting speed and superheat on bloom heat transfer and lubrication were also investigated. The simulation results showed that solidified shell thickness growth conforms to a Square Root Law, and that the model predicted results are basically in agreement with previous data in the literature, and provide confidence in model. The bloom temperature distribution range in the corner area is smaller than that in the mid-face, and the corner regions form a high cracking risk zone. The hot tearing indicator and effective stress in the corner area are significantly greater than that in the mid-face, so the corner area is the dangerous zone of cracking; The mould flux lubrication in the bloom mid-face is better than for the bloom corner region, due to a higher shell temperature and a fluid slag; The increasing of casting speed can delay air gap formation of the bloom corner area, improving the lubrication conditions, but when the casting speed is changed, it is also necessary for the mould flux viscosity and crystallization temperature be changed also. Increasing the superheat has little influence on the completely solidified distance of liquid flux in the bloom corner area.

Viscosity measurement of mould fluxes using inclined plane test and development of mathematical model

During the current research and development activities at Tata Steel Teesside Technology Centre, UK, the inclined plane test (IPT) is adopted as a quick method to measure the viscosity/fluidity of mould powders being used currently for continuous casting of different steel qualities and section sizes. The usefulness of the IPT method was also validated by comparing the viscosities that were measured by a high temperature viscometer. It has been established that the IPT measured viscosity values are comparable with the mould powder supplier’s data. The IPT ribbon lengths of different powders have been correlated with the viscosities using an Arrhenius type relationship. The ribbon lengths of the solidified fluxes were found to have a good correlation with the molar ratios of the corresponding powders. Hence, the relationship was further tuned to develop a viscosity prediction model using the chemical compositions of the mould fluxes (i.e. the model can be used for a quick assessment of mould flux viscosity based on its chemical composition).

Effect of substituting SiO2 with TiO2 on viscosity and crystallisation of mould flux for casting titanium stabilised stainless steel

During casting of titanium stabilised stainless steel, a gradual increase in TiO2 content in the molten mould slag from absorption of TiO2 inclusions causes changes in properties of the mould flux, such as viscosity, solidification temperature and crystallisation behaviour. To simulate this effect mould fluxes were prepared with SiO2 being substituted with 5 and 10%TiO2 and viscosity and crystallisation behaviour studied. Experimental results indicate that the substitution of SiO2 with TiO2 leads to suppression of crystallisation of cuspidine and formation of perovskite in glass quenched from mould fluxes. The crystallisation tendency is reduced by the introduction of TiO2. The high temperature viscosity of mould fluxes shows a decrease with increasing TiO2. At lower temperature, the viscosity of mould fluxes with 10%TiO2 is greater than that of TiO2 free slag, which could be attributed to precipitation of solid particles.

Influence of Different Oxides on the Viscosity of Fluorine-Free Mold Fluxes

Mold fluxes play an important role in the steel continuous casting process. Mainly, they must prove adequate lubrication between the solidified steel shell and the copper mold. Thus, the knowledge of mold flux viscosity with the temperature is a relevant property for industry applications in order to prevent operation problems and product defects. On the other hand, for environmental reasons, the replacement of fluorine by non-pollutants compounds, is one of the objectives in the design of new compositions for these slags. In this paper, the viscosity is calculated in the range: 1250-1400 ¼C applying two models based on their chemical composition and another one using the differential thermal analysis technique. The results obtained with this model showed a good correlation with respect to other traditional models using the chemical composition of the mold flux to estimate the viscosity. The aim is to observe the effect of different oxides on the viscosity of mold fluxes. One of the mold powders was designed with a chemical composition similar to a commercial one (containing 10 wt% of fluorine), while the others powders were fluorine-free (containing boron and lithium). It should be noted that a fluorine-free powder with a viscosity similar to the powder with fluorine was produced replacing 10 wt% fluorine by 4 wt% Li2O and 6 wt% B2O3.

Study on Slag Entrapment of Molten Steel in Mold with Electromagnetic Stirring Technology

Considering the process conditions of the continuous billet casting, this paper has studied the slag entrapment behavior of molten steel in mold by using of a water model, and analyzed the influence rules of the submerged nozzle immersion depth, the electromagnetic stirring intensity and the mould flux viscosity on the slag entrapment in mold. The results show that the surface velocity in meniscus gradually increases with the stirring intensity increasing and the submerged nozzle immersion depth decreasing. When the submerged nozzle immersion depth is shallower, the mould flux viscosity is lower, and the stirring intensity is high, the interface turbulence of the liquid steel and slag is more severe, slag entrapment may occur in the extreme state. In order to avoid the slag entrapment in the working condition, it is necessary to increase the submerged nozzle immersion depth and decrease stirring intensity mildly.

Control for Surface Faint-Sliver Defects in Cold-Rolled IF Steel Sheet

The samples of cold-rolled sheets, hot-rolled plates and continuously cast slabs have been analyzed with the condition of faint-sliver defects appeared in IF steel of Pangang, and it was shown that faint-sliver defects in cold-rolled steel sheet were mainly caused by micro-cracks in the surface of strands, slag entrapment in mold during casting and inclusions in sub-surface of strand. Faint-sliver defects were controlled effectively with the technical measures, which were decreasing oxidation of ladle slag, controlling the ratio of CaO/Al2O3 in slag, extending circulation time of deoxidization and alloying in RH process, controlling the casting speed and increasing the viscosity of mold fluxes. Therefore, the ratio of downgrade induced by faint-sliver defects reduced from 10.97% to 1.0%.