Mold Flux Research Articles

Effect of Al2O3 Inclusions or Mold Flux Particles on Their Surrounding Microstructures of Sliver Defects on the Surface of Automobile Exposed Panel

The Al2O3 inclusions and mold flux particles are the initial causes of the sliver defects on the surface of automobile exposed panels. During the rolling process, the smashed Al2O3 inclusions or mold flux particles will hinder the growth of recrystallized grains. Compared with mold flux particles, the smashed Al2O3 inclusions have a smaller size, a denser distribution, and a larger number density, so the smashed Al2O3 inclusions have a stronger ability to hinder grain boundary migration. Therefore, the average grain size is small in the following sequence: Al2O3 defect zone with Al2O3 inclusions (Al2O3 DZ with Al2O3), mold flux defect zone with mold flux particles (MFDZ with MFP), mold flux defect zone without mold flux particles (MFDZ without MFP), Al2O3 defect zone without Al2O3 inclusions (Al2O3 DZ without Al2O3), and non-defect zone (NDZ). The influence of particles on the grain orientation of the defect zones results in the microtexture of Al2O3 DZ without Al2O3 is {111}<313>, which is close to the {111}<101> microtextures of NDZ and MFDZ without MFP, while the {001}<114> microtexture on Al2O3 DZ with Al2O3 and the {313}<111> microtexture on MFDZ with MFP are quite different from that of NDZ. Due to differences in the inclusions, orientation, and microtexture of the defect zones and NDZ, dark-gray or bright white sliver defects on the surface of the automobile exposed panel are eventually formed.

Effect of TiO2 on viscosity and structure for CaO-SiO2-Al2O3-based mold flux

The viscosity of CaO-SiO2-Al2O3-MgO-Na2O-CaF2-(TiO2) was measured by the rotating column method, and the viscosity, break temperature and viscous flow activation energy of the slag were analyzed based on the results. The effect of TiO2 content on the structure of the slag was studied by Raman spectroscopy. The results show that with the increase of TiO2 content in CaO-SiO2-Al2O3-based mold flux, the viscosity of mold flux increases, the break temperature increases from 1418 K to 1535 K, and the viscous flow activation energy changes little. At high temperature, TiO2 can depolymerize the [Si-O] and enter into the network structure as [Ti-O], which increases the frictional resistance to the viscous flow of the mold flux. At the same time, the crystallization temperature and viscosity of the slag is increased.

Estimation of Changes in Content and Characteristics of Mold Flux during Continuous Casting

Estimation of changes in the composition and physical properties of mold flux during continuous casting was investigated for control of slab surface quality. In this study, 0.7 mass% Al steel and normal Al-killed steel were cast with three kinds of mold flux having Al2O3 contents of 1.3 to 6.0 mass% and different basicities. The results can be summarized as follows:(1) The Al2O3 content of these mold fluxes increased to 30 mass% during continuous casting. The composition change of the mold flux can be reproduced by the Equilibrium Effective Reaction Zone Model (EERZM) by fitting parameters, referring to the casting results.(2) The analysis by EERZM revealed that the viscosity of the mold flux and the throughput of the molten steel affect the rate of increase of the Al2O3 content in the mold flux.(3) The change of the physical properties of the mold flux was estimated based on the changes in the flux composition. The change of the crystallization temperature and main crystal can be estimated by FactSage.(4) Mold flux viscosity can be estimated by revising the modified Iida’s equation, which considers the effect of Al2O3 as an amphoteric oxide.

Influence of Fluorine and CaO/Al2O3 Ratio on the Wetting Behavior Between CaO–Al2O3‐Based Mold Flux and Steel Substrate

In article 2200598, Lejun Zhou and co-workers study the influence of typical components of CaO-Al2O3-based mold flux on the wetting behavior of the flux on the steel substrate. They find the influence mechanism based on analysis of the changes in melt structure and contact angle of flux/steel at the interface.

Effect of AlN on properties of non-reactive CaO-Al2O3-based mold flux for high-Al steel

Effect of AlN on properties of non-reactive CaO-Al2O3-based mold flux for high-Al steel

Crystallization of Slag Films of CaO-Al2O3-BaO-CaF2-Li2O-Based Mold Fluxes for High-Aluminum Steels' Continuous Casting.

In this study, solidified films of CaO-Al2O3-BaO-CaF2-Li2O-based mold fluxes with different contents of Al2O3 addition were acquired by immersing an improved water-cooled copper probe in bulk molten slags. This probe can obtain films with representative structures. Different slag temperatures and probe immersion times were employed to investigate the crystallization process. The crystals in the solidified films were identified using X-ray diffraction, the morphologies of the crystals were observed using optical microscopy and scanning electron microscopy, and the kinetic conditions, especially the activation energy of devitrified crystallization in glassy slags, were calculated and discussed based on the differential scanning calorimetry. The results indicated that after adding extra Al2O3, the growing speed and thickness of the solidified films increased, and more time was required for the film thickness to reach a steady state. In addition, fine spinel (MgAl2O4) precipitated in the films at the early stage of solidification after adding 10 wt% of extra Al2O3. Together with LiAlO2, spinel (MgAl2O4) acted as nuclei for the precipitation of BaAl2O4. The apparent activation energy of initial devitrified crystallization decreased from 314.16 KJ/mol (original slag) to 297.32 KJ/mol (5 wt% Al2O3 added) and 269.46 KJ/mol (10 wt% Al2O3 added). The crystallization ratio of the films also increased after adding extra Al2O3.

Heat Conduction through Different Slag Layers in Mold. Thermal Conductivity Measurement of Commercial Mold Fluxes

The thermal conductivity of two commercial mold fluxes has been investigated using the transient hot-wire method in the temperature range of 298 K to 1573 K. Experiments were conducted on granules, sintered granules, molten fluxes and glassy samples under ambient atmosphere. Characteristic temperatures of the mold fluxes were investigated using a hot stage microscope. Results are discussed in the context of the characteristic temperatures, the particle size of granules, the bulk density and the structure of the mold fluxes. The temperature dependence of the thermal conductivity for granules of mold fluxes is positive in the temperature range of 298 to 873 K (λ = 0.058 + 1.245 × 10−4 T). The further temperature increase causes the rapid increase of the thermal conductivity above the temperature, at which the granules start to sinter Tdeformation. The thermal conductivity of the glassy sample is around two times lower than the thermal conductivity of the devitrified sample. The effect of the glass transition temperature on the thermal conductivity was shown. The thermal conductivity rapidly increases above the glass transition temperature in the glass transition region as the temperature rises and decreases above the softening temperature Tsoftening. The further temperature increase caused the crystallization of the sample. The crystallization of the sample was observed at T ≈ Tg + 100 K. Moreover, results show the dependence of the thermal conductivity of molten mold fluxes on the basicity (CaO/SiO2) at 1573 K.

Evaluation of Surface Tension of CaO–SiO2–Al2O3‐Based Mold Flux Containing Ce2O3

The calculation model based on the surface tension of CaO–SiO2–Al2O3‐based mold flux containing Ce2O3 is studied using the modified Butler equation, and the surface tension of mold flux is measured by the sessile drop method. The experimental results show that the calculated surface tension based on the model agrees well with the experimental values, and the absolute value of the error is less than 3.23%. With the content of Ce2O3 in the mold flux increasing from 0% to 20%, the surface tension of the mold flux increases from 0.380 to 0.405 N m−1. The O2− dissociated from Ce2O3 makes the radius of the silicon–oxygen tetrahedral anion decrease, and the ion‐to‐ion interaction force in the melt increase. Therefore, the surface tension of the melt increases with the increase of Ce2O3 content in the mold flux. However, the amount of dissociated O2− is limited, so the effect of Ce2O3 on the surface tension of the mold flux is limited.

Formation mechanism of surface upwarping and black line defects on low carbon hot rolled plate

To improve the surface quality of low-carbon hot-rolled steel plates, the upwarping and black line defects were investigated by means of XRF (X-ray diffractometer), OM (optical microscopy), SEM (scanning electron microscopy) and EBSD (electron back scatter diffraction). The results showed that the micro area compositions under surface upwarping and black line defects were mainly made of secondary oxide particles, steelmaking slag and mould flux respectively. According to the metallographic structure, inclusion compositions and grains texture analysis, it could be concluded that surface defects on hot rolled plates were attributed to the entrapment of ladle slag or mould flux, gas bubbles, micro-cracks of casting slab in the steelmaking process, rolled-in scale and unreasonable sizing press rolling parameters during the rolling process, and the position and formation process of typical surface defects on hot rolled plates were discussed in detail. Finally, it concluded that the slag entrapment and solidification hook should be controlled during continuous casting.

Modeling study of EMBr effects on molten steel flow, heat transfer and solidification in a continuous casting mold

During continuous casting process, the internal molten steel flow pattern of the mold is one of the important factors affecting the quality of slab products. The application of electromagnetic braking (EMBr) technology in the slab caster provides an effective solution to improve the molten steel flow pattern in the mold. In the current research, one of the commonly used EMBr technology is studied, namely the Ruler-EMBr technology. In detail, the effect of magnetic flux density on the behavior of the molten steel jet flow, heat transfer, and solidification in a 1450 mm × 230 mm slab mold is numerically simulated through a Reynolds-averaged Navier-Stokes (RANS) turbulence model together with an enthalpy-porosity approach. The simulation results indicate that the electromagnetic force generated by the Ruler-EMBr can significantly suppress the diffusion of the impinging jet to the narrow face of the mold with the increase of magnetic flux density. By that, the impact of the upward backflow on the meniscus region in the mold is suppressed. Correspondingly, the uniformity of the temperature distribution in the mold is effectively improved. The parametric studies suggest that the optimized magnetic flux density is 0.3 T to ensure the improvement of steel quality with a casting speed of 1.6 m/min. By applying the magnetic flux density of 0.3 T, the Ruler-EMBr has a better capability to reduce the maximum amplitude of the surface velocity by 24.5% and increase the average surface temperature of the molten steel by 0.25% when compared to the case of No-EMBr. With this electromagnetic parameter, the Ruler-EMBr technology can well prevent the mold flux entrapment and promote solidified shell uniform growth along the casting direction.

Real-Time Air Gap and Thickness Measurement of Continuous Caster Mold Flux by Extrinsic Fabry–Perot Interferometer

Real-Time Air Gap and Thickness Measurement of Continuous Caster Mold Flux by Extrinsic Fabry–Perot Interferometer

Combing role of MgO and Al2O3 on viscosity and its correlation to structure of fluorine-free mold fluxes

By using FactSage calculations, Fourier transform infrared spectroscopy (FTIR), rotational viscometers, and X-ray diffraction (XRD), the combined effect of MgO and Al2O3 on fluorine-free mold flux was confirmed. The viscosity of the slag at 1300 oC decreased with 2-10 wt% MgO, and higher Al2O3 increased the overall viscosity. The trend of the experimental results was consistent with the models of Riboud and Iida, while the FactSage calculation values were relatively higher. The viscosity of the slag was more influenced by the Si-O network than by the Al(B)-O structure and the MgO has a dual effect on the slag structure. The viscosity-temperature curves changed from alkaline to acidic slag characteristics when Al2O3 increased from 8 wt% to 12 wt%, and the trend was not uniform with the addition of 2-10 wt% MgO. Both FactSage calculation and XRD patterns showed that increasing MgO content gradually promoted the growth of Ca3MgSi2O8 and Ca11Si4B2O22 crystals, while the addition of Al2O3 inhibited crystal precipitation.

Research on the corrosion behavior of low carbon mold flux on submerged nozzle refractory

AbstractIn this paper, the wetting and corrosion behavior between medium and low carbon mold flux and Al2O3‐ZrO2‐C nozzle refractory were studied through a high‐temperature wetting experiment. Combined with microstructure analysis, the corrosion mechanism of low carbon mold flux on nozzle slag line material was clarified. The results show that the wettability of low‐carbon mold flux and Al2O3‐ZrO2‐C nozzle refractory is better, compared with the traditional medium carbon mold flux, the contact angle between low‐carbon mold flux and Al2O3‐ZrO2‐C material is smaller and the mold flux spreads faster on the nozzle surface at the same temperature range. According to the microstructure analysis, the corrosion degree of low‐carbon protective slag on the ZrO2‐C material of the nozzle slag line is serious, and the corrosion depth is large. Due to the influence of carbon content, the wettability between low‐carbon mold flux and ZrO2‐C material of the nozzle slag line is better, which provides favorable kinetic conditions for the dissolution and penetration of low‐carbon mold flux into the nozzle. In addition, compared with medium carbon slag, the carbon concentration difference between low‐carbon mold flux and nozzle material is larger, resulting in greater diffusion driving force of carbon atoms, which affects the wetting, dissolution, and chemical reaction of the interface between the two phases.

Influences of the Braking Effect of Ruler EMBr on Molten Steel Flow and Steel–Slag Interface Fluctuation in a Continuous Casting Mold

Electromagnetic braking (EMBr) technology, as one of the most effective technologies in the continuous casting process, provides an effective tool for improving the internal and external defects of steel products. Specifically, the EMBr technology takes the benefit of the generation of Lorentz force to decrease flow instability, mold powder entrapment, and surface defects, if applied properly. For this purpose, to gain a clear understanding of the effect of EMBr technology on the continuous casting process, a commonly used EMBr technology, namely ruler EMBr technology, is applied in the current work to investigate the dynamic behaviors of molten steel flow and steel–slag interface fluctuation inside a slab mold. Furthermore, to obtain a desirable braking effect of the ruler EMBr technology, operational parameters including the magnetic flux density, submerged entry nozzle (SEN) depth, and magnetic pole location are numerically investigated. The results demonstrate that the braking effect exerted by the ruler EMBr device is favorable for suppressing the impact of upward stream on the steel–slag interface with the magnetic flux density exceeding 0.3 T. For the influence of the SEN depth and magnetic pole location on the effect of ruler EMBr mold, the results show that a steady jet flow pattern can be obtained through the adjustment of a location between the ruler EMBr device and the SEN depth. For instance, when the ruler EMBr device installation position of 225 mm corresponds to the SEN depth of 150 mm, the upward deflection of jet stream is suppressed and a stable interface fluctuation profile is formed. With this adjustment, the possibility of mold flux entrapment is decreased.

Thermophysical Characteristics of Mold Flux Bulk Layer for Continuous Casting of Steel

Thermophysical Characteristics of Mold Flux Bulk Layer for Continuous Casting of Steel

Influence of Fluorine and CaO/Al2O3 Ratio on the Wetting Behavior Between CaO–Al2O3‐Based Mold Flux and Steel Substrate

The wetting behavior of flux melt on the initial solidified shell greatly determines the slag entrapment in the casting product and the sliver defect in the rolled product. Herein, the wetting behavior of CaO–Al2O3‐based mold flux with various fluorine (F) contents and CaO/Al2O3 (C/A) ratio on steel substrate is studied using the sessile drop method. Results show that the contact angle decreases from 71.35° to 59.86° and from 65.96° to 22.73°, meanwhile, the interfacial tension decreases from 1743.02 to 1669.69 mN m−1 and from 1705.40 to 1448.53 mN m−1, with the addition of F and the increase of C/A ratio, respectively. X‐ray photoelectron spectroscopy analysis indicates that the addition of F and increase of C/A ratio lead to positive adsorption () of non‐bridging oxygen (O−) and free oxygen (O2−) at the interface, which is the main reason why the interfacial tension between the mold flux and steel is reduced and the wettability of flux droplet on the steel is enhanced.

Investigation on Carbonizing From Mold Flux into Ultra-low-Carbon Steel During Continuous Casting

Investigation on Carbonizing From Mold Flux into Ultra-low-Carbon Steel During Continuous Casting

Effect of Microstructure on the Granule Strength of Hollow Granulated Mold Fluxes for Continuous Casting

During the automatic powder‐feeding process, the hollow granulated mold fluxes are easily broken due to insufficient granule strength, which leads to dust pollution and the deterioration of the properties of mold fluxes during the continuous casting. Herein, a drum‐type granule strength testing device, laser granule size analyzer, and scanning electron microscope are used to analyze the attrition mechanism of three kinds of hollow granulated mold fluxes and the effect of microstructure on the attrition mechanism. The results show that: 1) the result of the drum‐type granule strength test is in good agreement with the practical application effect of mold fluxes; 2) abrasion has dominated the breakage of three kinds of mold fluxes and the dust pollution is caused by the generation of a large number of granules with granule sizes ranging from 20 to 80 μm; 3) the uniform and dense surface film structure on the surface of mold flux effectively inhibits the abrasion and improves the granule strength of mold flux; and 4) the difference in granule size and solubility of different raw materials in the spray granulation process leads to the deposition of Na2CO3, binder, and carbon black on the surface to form the film structure.

Properties and Structure Evolution of CaO–Al2O3–La2O3 Slags with Various Alkali Metal Oxide Contents

To restrain the serious flux–steel reaction, CaO–Al2O3–La2O3‐based mold flux is designed for continuous casting of La‐bearing FeCrAl alloy. The properties and structure of slags with various alkali metal oxide contents are investigated. Results show that with the increase in Na2O or Li2O contents from 0 to 10 wt%, the melting temperature of slags decreased, and the fluxing effect of Li2O is improved. The addition of Na2O within 10 wt% reduces the slag viscosity at the temperature range of 1663–1823 K. While further increasing Na2O content to 15 wt%, the viscous behavior of the slag depends on the balance between the strong charge compensation effect of Na+ and the breaking network effect of O2−. Increasing Li2O contents from 0 to 15 wt% greatly reduces the slag viscosity, which is attributed to the reduction of the fraction of high‐polymerized QAl 4 units from 23.55% to 9.70% and the increase of [AlO6] octahedrons from 0 to 9.02% caused by more O2−. The NBO/Al and NBO fraction is calculated, which is consistent with the viscosity variations. In the melts, the structural roles of Na+, Li+, Ca2+, and La3+ are elucidated. Moreover, the relationship between the variations of crystalline phases and slag structure is discussed.

Effect of Mold Flux Containing Ce2O3 on the Contents of Aluminum, Silicon, and Titanium in Incoloy825 Super Alloy

The effect of mold flux containing Ce2O3 on the contents of aluminum, silicon, and titanium in Incoloy825 super alloy was investigated based on the slag-steel interfacial chemical reaction experiment between mold flux and alloy. Firstly, the activity model of the CaO-SiO2-Al2O3-Na2O-MgO-CaF2-Ce2O3 slag system was established according to the ion and molecule coexistence theory (IMCT), and the calculation results show that with the increase of Ce2O3 content in the mold flux, the activity of Al2O3 decreases significantly and the activity of SiO2 decreases and gradually tends to 0. Secondly, thermodynamic calculations of the slag-steel interfacial chemical reaction revealed that the main chemical reaction in this study system is [Ti] + (SiO2) = [Si] + (TiO2). With the increase of Ce2O3 content in the mold flux, the slag-steel interfacial chemical reaction is weakened and the oxidation of Al and Ti in steel is inhibited. Finally, the results of slag-steel reaction experiment show that the increase rate of Al content increases from 1.03% to 10.31%, the increase rate of Si content decreases from 55.95% to 31.25%, and the oxidation rate of Ti content decreases from 33.27% to 20.00% when Ce2O3 content in the mold flux increases from 0% to 15% and the slag-steel reaction for 40 mins.