Mold Flux Research Articles

Investigation of the Dissolution Behavior of AlN in CaO–Al2O3–MgO Refining Slag and CaO–Al2O3–F–Li2O–BaO Mold Flux

Low‐density steels have garnered widespread attention as novel lightweight materials. Owing to its high Mn and Al content, brittle AlN inclusions, detrimental to both steelmaking and steel properties, can precipitate directly from the molten steel. Employing slag absorption effectively removes these floating AlN inclusions from the molten steel. Herein, a series of analytical methods are utilized to investigate the dissolution behavior of AlN in CaO–Al2O3–MgO refining slag and CaO–Al2O3–F–Li2O–BaO mold flux. The results indicate that the initial dissolution temperatures of AlN in the slag and mold flux are 1361 and 1080 °C, respectively. The dissolution in the refining slag is attributed to the high‐temperature self‐decomposition of AlN, producing N2(g). In the mold flux, the dissolution reaction involves both the high‐temperature self‐decomposition of AlN and its reaction with Li2O in mold flux, generating N2(g) and Li(g). No reaction interface is observed at the AlN‐slag/mold flux boundary. As the dissolution mass of AlN in the slag/mold flux increases, the Al2O3 content in the slag/mold flux rises. The main phases in slag transition from Ca9(Al6O18) to Ca12Al14O33 and Ca3Al2O6. In the mold flux, the LiBaF3 phase disappears, and the 11CaO·7Al2O3·CaF2 phase, which can degrade the flux's physicochemical properties, becomes the dominant phase.

Melting, viscosity and structure of lithium-free CaO-SiO2 based melt: Substituting Li2O with Na2O and B2O3

Lithiation-free mold fluxes with excellent performances are urgently needed to be developed, due to the desire for Li2CO3 (Li2O) from the lithium battery industry. So, in this study, the melting, viscosity and structure of the CaO-SiO2 based flux melt, with the aim to replace Li2O by Na2O and B2O3, were investigated. Results show that the melting temperature decreased from 1258.1-1651.9 K to 1245.3–1632.5 K, and the viscosity at 1573 K decreased from 0.310 to 0.098 Pa s, when the ratio of Li2O/(Na2O + B2O3) decreased from 0.38 to 0.00. Meanwhile, the break temperature reduced from 1475.3 to 1451.4 K, and the activation energy of viscous flow also decreased from 181.44 to 55.39 kJ/mol, with the decease of Li2O/(Na2O + B2O3) ratio. Melt structure analyses indicate that the simpler structural units, such as Q0(Si), Q1(Si), [AlO4]5- tetrahedral and B-O- in [BO3] increased, while the more complex structural units, like Q2(Si), Q3(Si), bending vibration of Si-O-Al and boron ring in borate reduced, when Li2O was replaced by Na2O and B2O3. These changes suggest that the DOP of the flux melt was reduced and the melt structure was simplified during the lithiation-free process.

Wetting and Reaction Behavior of TiN and TiO2 with Different Mold Fluxes for High Ti-Bearing Stainless Steel

Wetting and Reaction Behavior of TiN and TiO2 with Different Mold Fluxes for High Ti-Bearing Stainless Steel

Kinetic Study of NaF Gas Formation During Mold Flux Melting Based on Different Fluorides by Experimental and Computational Methods

Low‐basicity fluorine‐containing mold flux, which forms a porous slag film with NaF pores, is expected to solve the contradiction between heat transfer and lubrication in the continuous casting of peritectic steel. Herein, the kinetic mechanism and the influence of NaF gas formation based on the different fluorine raw materials (NaF, CaF2, and Na3AlF6) at 0.9 basicity and 6 wt% fluorine are investigated by the combination of experiments and calculations. The results show that CaF2 is the first to generate NaF gas at 1189 K, followed by Na3AlF6 (1238 K) and NaF (1328 K). NaF raw material produces the most NaF gas with the lowest activation energy in the three raw materials, due to high Na ion kinetic energy, the simple degree of polymerization, and Na‐F1 bonds. Correspondingly, NaF bubbles in the molten slag are the largest based on their aggregation. Na3AlF6 and CaF2 raw materials rank second and third, with F atoms primarily bonded as Al‐Fx and Ca‐Fx and the higher proportion of and structure. Notably, at 0.9 basicity and 6 wt% fluorine, Na3AlF6 as raw material generates a suitable amount of gas, making diffuse and fine NaF bubbles in the molten slag.

Application of crystallization additivity principle in continuous casting mould flux

Application of crystallization additivity principle in continuous casting mould flux

The Study of the Behavior of CaO-SiO2-Al2O3-Na2O-Based Mold Flux in 1,400ºC by a Fiber-Optic Raman Sensor

The Study of the Behavior of CaO-SiO2-Al2O3-Na2O-Based Mold Flux in 1,400ºC by a Fiber-Optic Raman Sensor

Analysis of Longitudinal Cracking and Mold Flux Optimization in High-Speed Continuous Casting of Hyper-Peritectic Steel Thin Slabs

Longitudinal crack defects are a frequent occurrence on the surface of thin slabs during the high-speed continuous casting process. Therefore, this study undertakes a detailed analysis of the solidification characteristics of hyper-peritectic steel thin slabs. By establishing a three-dimensional heat transfer numerical model of the thin slab, the formation mechanism of longitudinal cracks caused by uneven growth of the initial shell is determined. Based on the mechanism of longitudinal crack formation, by adjusting the performance parameters of the mold flux, the contradiction between the heat transfer control and lubrication improvement of the mold flux is fully coordinated, further reducing the incidence of longitudinal cracks on the surface of the casting thin slab. The results show that, using the optimized mold flux, the basicity increases from 1.60 to 1.68, the F- mass fraction increases from 10.67% to 11.22%, the Na2O mass fraction increases from 4.35% to 5.28%, the Li2O mass fraction increases from 0.68% to 0.75%, and the carbon mass fraction reduces from 10.86% to 10.47%. The crystallization performance and rheological properties of the mold flux significantly improve, reducing the heat transfer performance while ensuring the lubrication ability of the molten slag. After optimizing the mold flux, a surface detection system was used to statistically analyze the longitudinal cracks on the surface of the casting thin slab. The proportion of longitudinal cracks (crack length/steel coil length, where each coil produced is about 32 m long) on the surface of the thin slab decreases from 0.056% to 0.031%, and the surface quality of the thin slab significantly improves.

Investigation of the erosion mechanism of fluorine-free mold flux on the submerged entry nozzle under the influence of negative electric field

Fluorine-free mold flux is receiving increasing attention due to the environmental and health problems associated with using fluorinated flux in casting. However, the erosion problem in the submerged entry nozzle is still exists and not solved. Therefore, in this study, the electric field is used to improve the erosion resistance capability of the nozzle. The results show that a thick protective adhesion layer is formed on the surface of the slag-line material under the action of a negative electric field due to an electrochemical reaction. This protective layer further reacts with the CaO/SiO2 content of the fluorine-free slag-line material to generate an interfacial reaction layer composed mainly of Ca2SiO4 and CaZrO3. Due to the presence of Ca2SiO4 in the interfacial reaction layer, a small amount of crystalline transformation occurs during the cooling process. Thus, under the protection of the double protective layer generated by the action of the negative electric field, the slag-line material is not subject to the erosion of the fluorine-free mold flux, and the erosion rate is only 0.37%.

Synergistic reutilization of spent pot lining and water quenched blast furnace slag as mold flux

A treatment method that synergistic reusing spent pot lining (SPL) and blast furnace slag (BFS) as mold flux (a functional material used in steel enterprises) was developed to achieve the harmless treatment of hazardous substances and recycling of valuable resources in spent pot lining. Mold flux made of SPL and BFS shows outstanding metallurgical performance. More importantly, toxic fluoride and cyanide in SPL were effectively harmless-treated utilizing industrial waste heat after making mold flux. The fluorine leaching ratio of amorphous mold flux residual after a leach test for 128 h is 1.08 wt%, which is 1/24 of that of raw SPL. The microstructure characterization proved the addition of BFS enhanced the fluorine immobilization effect by optimizing the network structure of amorphous mold flux residue. Compared to the traditional landfill treatment, the estimated additional economic benefits of processing one ton of SPL with this method are approximately 1924 USD.

Viscosity, Density, Surface Tension, and Crystallization Behavior of Commercial Mold Fluxes

This study investigates the viscosity, density, surface tension, and crystallization behavior of two commercial mold fluxes that are utilized to cast ultralow‐carbon, low‐carbon, and medium‐carbon steel grades, as well as electric steels (high‐B magnetic and grain‐oriented steels). Experiments are performed in the temperature range of 1073–1673 K using the rotating bob method, maximum bubble pressure method, buoyancy method, and single hot thermocouple technique. The phase structure is investigated via scanning electron microscopy and X‐ray powder diffraction. The results indicate that viscosity and density exhibit nonlinear temperature dependence. Increased basicity (CaO/SiO2) results in reduced viscosity and elevates the break temperature of the mold fluxes. Furthermore, the incubation time required for phase formation decreases with increasing basicity. Finally, time–temperature transformation and continuous cooling transformation diagrams are constructed.

Machine Learning Combining High-Temperature Experiments for the Prediction of Wetting Angle of Mold Fluxes

Machine Learning Combining High-Temperature Experiments for the Prediction of Wetting Angle of Mold Fluxes

Simulation of the Effect of Flux Layer Thickness on the Melting Behavior of Mold Fluxes Based on the Copper Bath Method

Simulation of the Effect of Flux Layer Thickness on the Melting Behavior of Mold Fluxes Based on the Copper Bath Method

Effect of thermal fluctuations on mold coating delamination during continuous casting of high-alloy (Mn, Al) steel

During the continuous casting of high-alloy (Mn, Al) steels, mold coating delamination occurs specifically at the narrow face (NF) mold corner immediately below the meniscus, different from where mold surface problems are generally known to occur. Most mechanical analyses have been performed assuming negligible thermal fluctuations and steady state interfacial heat fluxes. However, high-alloy steels exhibit larger thermal fluctuations than general steels during continuous casting, attributable to the reaction between the high-alloy steels and mold flux. Therefore, in this study, thermo-mechanical analyses are performed under both steady and fluctuating interfacial heat fluxes to compare the effects of thermal fluctuations on the continuous casting mold, with the results indicating that monotonic stresses are generated under steady interfacial heat fluxes at the corner of the NF mold, whereas cyclic stresses are induced by thermal fluctuations under fluctuating interfacial heat fluxes. Accordingly, the cyclic stresses at the corner of the NF mold, induced by thermal fluctuations, are determined as the major cause of mold coating delamination. These results can be applied to develop methods to reduce mold coating delamination, prevent the degradation of strand quality, and improve mold life.

Viscosity and melting temperature prediction of mold fluxes based on explainable machine learning and SHapley additive exPlanations

Viscosity and melting temperature are indispensable properties for mold flux design and evaluation, significant investment is required for measurement. In this paper, viscosity and melting temperature predictive model for mold fluxes were established and trained based on 3300 groups of data and four representative machine learning algorithms. The gradient boosting regression tree (GBRT) algorithm-based model performed best prediction with the determination coefficient R2 of 0.969 and 0.900 for viscosity and melting temperature. It also far outperforms the widely used viscosity and melting temperature prediction models, with a least mean deviation of 7.06% and 0.8%. SHapley Additive exPlanations (SHAP) analysis revealed that Al2O3, followed by SiO2 showed the strongest positive correlation with viscosity, Na2O has the greatest negative contribution to melting temperature. Ternary viscosity and melting temperature distribution diagrams were constructed to visualize the prediction results. Insights from this study will highly benefit computer-aided design of mold fluxes with desired properties.

Reaction mechanism between carbon and CaO–SiO2–Al2O3–Na2O slag system during continuous casting process

The reaction behavior between the carbon and mold fluxes during the heating process is vital for a successful continuous casting process and the high billet quality. A detailed investigation combined with thermogravimetry-mass spectrometry (TG-MS), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and transmission electron microscopy (TEM) techniques was carried out to systematically investigate the transformation mechanistic of the macro physicochemical properties, melting behavior, viscosity, crystallization, and heat transfer performance caused by the reaction behavior. The results showed that the mold flux underwent carbonate decomposition (973–1223 K), solid reaction (1273–1573 K), and melting process (1473–1673 K) during the continuous casting process. The carbon-bearing mold flux exhibited an endothermic peak at approximately 1673 K, corresponding to a weight loss ratio of approximately 14.5% on the TG curve, confirming that carbon could react with the middle mineral phases Ca2SiO4, Ca2Al2SiO7, and Na6Ca3Si6O18 to form SiC, increasing the breaking temperature by approximately 293 K. SEM and TEM results indicated that the melting behavior was restrained by the carbon itself and the newly formed components. Besides, the addition of carbon increased the degree of polymerization of molten slag, the thickness of slag film and the proportion of small crystals in slag film, further leading to an increase in crystallization and heat transfer performances. The reaction mechanism between carbon and slag and the subsequent effects on melting point, viscosity, crystallization ratio and heat flux density were clearly understood, which is meaningful for the carbon blending process of the mold flux.

High-temperature oxidation mechanism and microstructure evolution of Cr-Mn-Si alloyed steel oxidized by Fe2O3 contained in mold flux

The high-temperature oxidation behavior of Cr-Mn-Si alloyed steel by Fe2O3 contained mold flux in high temperatures, and its effect on microstructure evolution were investigated in detail by TEM, EBSD, CLSM, SEM, and XPS. A novel oxidation mechanism was firstly revealed that the Fe2O3 in mold flux melts during high temperatures plays a role of oxidizing alloyed steels by the released free oxygen ions (O2−) from the transformation of Fe2O3 (Fe3+) to FeO (Fe2+). The formed oxidized dots within the oxide layer changed from SiO2 and MnSiO3 to MnCr2O4 spinel phases by increasing the content of Fe2O3 in the mold flux. Notably, the amorphous SiO2 was discovered in the core region of MnSiO3 phase due to its selective oxidative behavior in high temperatures. This research provides conclusive evidence that the small size MnSiO3 oxides can be acted as a nucleation core for the refinement of austenite grains through in-situ observation.

Effect of fluorine on the viscosity and structure of non-reactive mold fluxes for high-Mn high-Al steel

The impact of varying F content from 4 wt% to 10 wt% on the structure and properties of non-reactive mold slag for high-Mn high-Al steel was investigated in this study. Employing a combination of techniques including a rotary viscometer, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy, the viscosity and structure of mold slag were analyzed. The findings revealed that increasing F content led to a gradual reduction in viscosity, activation energy for viscous flow, and the internal friction within the mold fluxes, consequently enhancing its fluidity. The Al–O–Al structure remained stable throughout the experimental range. The decrease in QAl2 content indicated a continuous depolymerization process, leading to the formation of free [Al2OF6] and [AlO6] structures as F content increased. At the same time, the replaced O2− ions were assimilated by [AlO4] tetrahedron, facilitating the formation [AlO6] octahedron. Consequently, the slag structure was simplified, resulting in a reduction in the degree of polymerization and viscosity.

An in-situ investigation on the microstructure and viscosity characteristic of mold flux during slag-metal reaction process

The slag-metal reaction during the continuous casting of high Al steel changes the molten slag structure from silicon-oxygen to silicon-oxygen-aluminum network structure, greatly affecting the viscosity properties of mold flux. In order to reveal the internal mechanism of the viscosity change during slag-metal reaction, the molecular dynamics simulation was employed to monitor the microstructure evolution characteristics of molten slag under different Al2O3/SiO2. The results showed that Q3Al decrease from 25.48% to 22.26%, Q4Al and Q5Al increase from 68.82% and 1.70% to 71.26% and 2.88%, respectively with an increase of Al2O3/SiO2 from 0.1 to 1.2. The [AlO4]5- tetrahedral structure changed from low coordination to high coordination structure, the degree of polymerization increased, and the viscosity increased. The viscosity calculated by molecular dynamics is in good agreement with the experimental measurement. Finally, A dynamic link model between structural transformation and viscosity was innovatively established.

Capturing the Interaction Between Mold Flux and Different Steel Compositions During Industrial-Scale Continuous Casting Trials

Capturing the Interaction Between Mold Flux and Different Steel Compositions During Industrial-Scale Continuous Casting Trials

Formation of nepheline in the heating process of mould fluxes and its effect on sintering behaviour

This study explores the formation mechanism of nepheline (NaAlSiO4) in the 500–900 °C heating process of mould flux and the influence of Al-containing materials on the nepheline formation using thermogravimetric-differential scanning calorimetry, scanning electron microscope and X-ray diffraction. The results show that the formation behaviour of nepheline depends on the type of Al2O3-containing materials. At 500 °C, flint clay (Al2SiO5) forms nepheline by solid-state reaction with sodium carbonate (Na2CO3). During the solid-state reaction process, F− improves the kinetic conditions by promoting the diffusion of Na+ into the flint clay particle. F- is derived from the tiny NaF formed by the reaction of cryolite (Na3AlF6) with sodium carbonate. Unlike flint clay, bauxite (Al2O3) reacts with liquid phase at 700 °C to form nepheline. Therefore, the low-temperature sintering of mold flux bauxite-containing is weaker than the flux containing cryolite and flint clay. At 500 °C, the sintered rate of bauxite-containing flux is 22.55%, and the sintered rate of flux containing cryolite and flint clay is 39.50%. With the increase in temperature, the sintered rate of bauxite-containing flux increases, which is gradually close to that of flux containing cryolite and flint clay. Until 900 °C, the sintered rate of bauxite-containing flux (63.45%) is the same as that of flux containing cryolite and flint clay (62.15%).