Removal of fluid inclusions from vein quartz by stepwise chlorination roasting and mechanism study

Abstract This study mainly investigates the effect of the bottom-blowing regime of the ladle on the mixing time of the molten pool and the removal of inclusions, providing a process optimization scheme for the development of high-quality clean steel materials. In this study, a hydraulic model was first established at a 1:4 scale, and water modeling experiments were conducted. Based on the water modeling experiments, the optimal positions of the two bottom-blowing plugs were determined to be at 0.7R and 0.4R (R is the radius of the ladle bottom), with a relative angle of 90° between the two plugs. Further CFD (Computational Fluid Dynamics) simulation experiments were conducted, combined with the results of the water modeling experiments, to determine that under a total bottom-blowing argon flow of 800 L/min, when the flow rate of the plug at 0.7R is 600 L/min and at 0.4R is 200 L/min, the shortest mixing time of 36 seconds can be achieved, forming a more uniform flow field and an extended circulation zone. Under the optimized bottom-blowing regime, the removal rate of alumina inclusions in the molten steel increased from 82.8% (original scheme) to 97.5%.

Removal and distribution of non-metallic inclusions in electroslag fusion welding process

Optimization of inclusion removal in spring steel with Rb2O-containing refining slag

Tundish with channel‐type induction heating is a popular operation for clean steel production. The relationship between the electromagnetic force proximal to the channel wall and the included angle closely resembles a sinusoidal function. Due to a unique physical structure where the receiving chamber is separated from the discharging chamber, three combined models are applied in receiving chamber, channel, and the discharging chamber, respectively. After induction heating, the plug volume fraction rises 1.89 times in the receiving chamber, the well‐mixed volume fraction increases by 5.28 times in the channel, the well‐mixed volume fraction increases by 25.46% in the discharging chamber. Furthermore, the inclusion mass/population conservation model, which involves electromagnetic force effect is applied to predict inclusion behavior in this study. The receiving chamber and discharging chamber are the main areas for inclusion removal.

In this study, the metallic Y, CaF2, and sponge Ti were employed to regulate the composition and achieve the deoxidation of the SHS-TiAl alloy, respectively. The results indicate that the metallic Y could effectively reduce the oxygen concentration of the SHS-TiAl alloys, which could all be controlled below 0.06 wt.%. The alloying control of SHS-TiAl could be further realized by adding sponge Ti with the achievement of a typical α + γ phase microstructure. Additionally, the CaF2 could adsorb the Y2O3 products, which were formed during the deoxidation reaction. However, due to the relatively high initial oxygen content in the SHS-TiAl alloy, the generated Y2O3 could not be fully removed, leading to the partial inclusions remaining in the alloy matrix. Also, the residual Y would react with Al in the alloy to form YAl2 inclusions.

Herein, the effect of annular argon bubbling (AAB) process on tracer diffusion and inclusion removal behaviors in a tundish was studied by water model experiments, and the influence of slag layer on the variation in results was compared as well with the aid of numerical simulation. The results show that the AAB process can significantly change the flow field structure in the pouring region, inhibit the short‐circuit flow, and increase the volume fraction of mixed flow in the tundish. The presence of slag layer can significantly slow down the diffusion rate and alter local flow behavior of the tracer underneath the slag layer; the interfacial velocity decreases from 0.031 m s −1 without oil layer to 0.007 m s −1 with oil layer when the AAB process is not adopted. When the experimental condition without argon bubbling ( q = 0 L min −1 ) and slag layer is changed to that with argon bubbling ( q = 4 L min −1 ) and slag layer, the tracer peaking time extends from 154.45 to 424.95 s, the volume fraction of piston flow increases from 18.27% to 37.26%, and the average removal rate of small sized inclusions (20–60 μm) is lifted from 64.05% to 77.10%, which was well verified in industrial tests.

In this study, a laboratory-scale slag–steel reaction experiment was conducted to systematically evaluate the influence of the initial MgO content (3–7 wt.%) in LF refining slag on the cleanliness of GCr15 bearing steel. The assessment was performed from multiple perspectives by comparing the total oxygen content (T[O]) in molten steel, the inclusion area fraction, and the inclusion number density after 30 min of slag–steel interaction. To further elucidate the thermodynamic driving forces and kinetic mechanisms governing inclusion capture by slag, a predictive slag adsorption model was developed using an in-house computational code coupled with FactSage 8.1. Under conditions of slag basicity R (CaO/SiO2) ranging from 4.0 to 8.0, MgO content varying from 0 to 7 wt.%, and a constant Al2O3 content of 32 wt.%, the chemical driving force ΔC (the mass-fraction difference between slag components and inclusions), the slag viscosity η, and the combined parameter ΔC/η were calculated at 1600 °C for three representative inclusion types: Al2O3, MgO·Al2O3, and MgO. In addition, the model was employed to quantitatively characterize the adsorption capacity of slag toward Mg–Al binary inclusions under varying MgO levels. Both experimental observations and model calculations demonstrate that the slag–steel reaction markedly enhances inclusion removal, as evidenced by pronounced decreases in T[O], inclusion number density, and inclusion area fraction after reaction. With increasing MgO content in slag, T[O] and inclusion-related indices exhibit a consistent trend of first decreasing and then increasing, reaching minimum values at an MgO level of 5 wt.%. Further analysis reveals a positive correlation between the apparent inclusion-removal rate constant ko and ΔC/η corresponding to MgO·Al2O3 inclusions. Moreover, the slag’s adsorption capacity toward Mg–Al binary inclusions decreases overall as the MgO fraction in inclusions increases. Notably, when the MgO content in inclusions exceeds 29 wt.%, the adsorption capacity undergoes an abrupt drop, indicating a pronounced cliff-like attenuation behavior.

The novel industrial trial is conducted to investigate the effect of argon injection into the down-leg of the RH degasser on the inclusion removal. The 'cold steel plate dipping' is used to take samples of molten steel and argon bubbles from the RH ladle. The industrial CT detection and electron microscope observation are applied to analyze the bubble characteristics. The results show that the size of bubbles generated by argon injection in the down-leg ranges from 7 to 1430 μm. Among them, the number density of bubbles with a diameter of 60 μm is the largest, reaching 0.1 per mm3. After adopting the down-leg argon injection technology, the average oxygen activity at the end of the RH process decreases by 2.35 ppm, and the surface defects of cold-rolled sheets of all grades are reduced. Based on the theoretical analysis of bubble collision and adhesion to inclusions, the small-sized bubbles have a relatively high capture probability for inclusions smaller than 10 μm. Comprehensively analyzing the experimental results, it is found that the down-leg argon injection technology has an obvious effect on removing inclusions.

This study investigates the effect of Al 2 O 3 content and the CaO/SiO 2 ratio in ladle furnace (LF) refining slag on the cleanliness of GCr15 bearing steel at 1600 °C through laboratory-scale thermal simulation experiments. Additionally, the influence of stirring during refining on the removal of single globular type inclusions by the slag was qualitatively evaluated. Large inclusion particles were nondestructively extracted from steel samples using anhydrous electrolysis. The morphology and chemical composition of these inclusions were analyzed via scanning electron microscopy (SEM). Using FactSage 8.4 software, variations in the low melting-point region of the CaO-Al 2 O 3 -SiO 2 -MgO slag system due to compositional changes were calculated. Results indicate that with a refining slag basicity of 4, the total oxygen content in the steel is minimized, and both the size and number density of group DS inclusions are reduced. Low-basicity slag effectively removes single globular type inclusions but exhibits limited capacity for removing other inclusion types. High-basicity slag has poor Al 2 O 3 removal capability and promotes the formation of numerous calcium-containing composite DS type inclusions. Increasing Al 2 O 3 content to 30% enhances slag fluidity, eliminating the need for CaF 2 addition, thereby reducing ladle lining erosion and environmental pollution. Furthermore, stirring during refining promotes collision and aggregation of fine inclusions, effectively reducing single globular type inclusions in the steel.

The study is devoted to optimizing the composition of flux based on sodium chloride (NaCl) and potassium chloride (KCl) to improve the quality of secondary aluminum alloys obtained from various types of aluminum scrap, including armor scrap, household scrap, industrial chips, and return scrap from own production. The aim of the work is to analyze the effect of a binary eutectic mixture of NaCl-KCl (50 mol% NaCl and 50 mol% KCl) on the chemical composition, microstructure, mechanical and casting properties of alloys, as well as to determine the optimal flux dosage to ensure high quality castings suitable for use in the aviation industry. During the study, different types of aluminum scrap were used, which made it possible to evaluate the effectiveness of the flux in the processing of raw materials with varying levels of contamination. The flux was added in concentrations of 1%, 2%, 3%, 4%, 5%, 10 %, and 15 % of the melt mass after drying at 120 °C to remove moisture. The samples were poured into a metal mold pre-treated with non-stick paint at a temperature of 200 °C. The results showed that the use of NaCl-KCl flux contributes to a significant purification of the melt from non-metallic inclusions, oxides (Al2O3, MgO, SiO2) and gases, in particular hydrogen, which improves the quality of the alloy. The maximum aluminum content (95.13 %) was achieved with 15 % flux, which indicates the effective removal of impurities such as silicon, magnesium, manganese, and zinc. In particular, the silicon content is reduced to 0.54-0.90 % already at a flux content of 1 %, which indicates its high efficiency in removing silicon inclusions. However, excessive fluxing (over 5 %) leads to a decrease in the content of alloying elements, which negatively affects the plasticity of the alloy. Studies of temporary tensile strength showed that the optimal flux concentration range (3-5 %) provides maximum strength up to 235 MPa and fluidity up to 585 mm, which is associated with effective melt cleaning and viscosity reduction. At the same time, an increase in flux concentration to 15 % contributes to a decrease in plasticity (relative elongation decreases from 4.41 % to 1.32 %, narrowing from 4.52 % to 0.85 %) due to a decrease in silicon eutectics and the formation of brittle phases. Microstructural analysis confirmed that at a flux content of 2-4 %, a homogeneous structure with a plastic type of fracture is formed, while at 15 %, brittle intergranular cracking is observed due to excessive slag formation. The fluidity of the alloy increases in the range of 5-10 % flux due to a decrease in viscosity and the removal of inclusions, but excess flux (over 10 %) reduces this indicator due to the formation of thick slag films and local cooling of the melt. An optimal flux content of 3 to 5 % provides a balance between purification, preservation of alloying elements, and high fluidity, making the alloy suitable for precision casting. Thus, NaCl-KCl flux is effective for cleaning secondary aluminum, allowing for increased aluminum content, reduced impurities, and improved mechanical properties. An optimal flux concentration of 3 to 5 % is recommended for industrial use, as it ensures high alloy quality, energy efficiency, and compliance with standards for high-tech applications.

This study employs the Volume of Fluid (VOF) polyphase flow model and the DPM model to numerically simulate the flow dynamics of the plume inside the Argon Oxygen Decarburization (AOD) furnace under different side-blowing flow rate conditions. The focus is on analyzing the slag layer disturbance, slag entrainment behavior, wall shear force distribution, and the evolution of the bubble plume. The results indicate that during the initial phase, bubbles enter the furnace at a high velocity. Once inside the furnace, the kinetic energy of the bubbles is gradually dissipated, transitioning to buoyancy-dominated upward motion, which causes the bubbles to rise and push the slag surface, forming slag eyes. At a flow rate of 35 Nm³/min, the slag layer experiences disturbances, but no slag entrainment is observed. However, when the flow rate increases to 45 Nm³/min, large slag droplets are entrained into the liquid steel, leading to the formation of a clear slag entrainment phenomenon. A suitable side-blowing flow rate, such as 40 Nm³/min, effectively stabilizes the flow field and prevents unstable flow patterns. Under high flow rate conditions, the wall shear force near the nozzle region is significantly increased, and the shear force extends further from the nozzle. This may exacerbate the erosion of the furnace's refractory materials. Overall, the numerical simulation results provide a theoretical basis for optimizing bubble behavior and AOD furnace flow field design.

Optimizing Argon Curtain Positioning for Fine Inclusion Removal in Tundish: An EE-IATE-DPM Model-Based Computational Study

Effect of refining slag basicity on transformation and removal of inclusions in Al-killed S-containing steel

A novel model for the removal and capture of inclusions in electroslag remelting process

Modeling inclusion removal mechanisms induced by argon blowing and bubble-inclusion interactions in a thin slab casting mold with EMBr

The cleanliness of aluminium alloys has a decisive effect on their properties and performance. In this work, the melts of several Al-Mg-Si alloys (6xxx series) were refined using rotary flux injection (RFI) of the salt fluxes in the industrial environment. A typical charge consisted of 25 % to 30 % external scrap, 45 % to 50 % internal scrap, and 20 % to 30 % primary aluminium. During injection, the entire melt volume was mixed uniformly. The melt was filtered using a porous ring filtration apparatus. The fraction and type of non-metallic inclusions were determined using light and scanning electron microscopy. The contents of alkali and alkaline-earth metals were determined using optical emission spectroscopy. The reduction of alkali and alkaline earth metals and the fraction of non-metallic inclusions were used to evaluate the process efficiency and the flux selection for the regular production. An analysis of more than 100 industry charges confirmed that the flux selected after the experimental trials, consisting of a mixture of MgCl2, KCl, NaCl and CaF2, was effective in regular production.

Extreme removal of fine inclusions from 304 stainless steel via high-temperature supergravity fields

This water-model study investigates the movement dynamics of non-metallic inclusions at dynamic steel-slag interfaces. Using polypropylene (PP) particles to simulate inclusions, deionized water for molten steel, and silicone oil for slag, the experiments employed static/dynamic similarity principles. Controlled different flow velocities were imposed via a pump. High-speed imaging revealed that particles encountering the water-oil interface experienced deformation resistance, causing downward rebound before secondary ascent and potential penetration. Under static conditions, particles achieved a dimensionless displacement of 0.75 and terminal velocity of 0.09 m/s, stabilizing near the interface after 2 s. Increasing simulated steel flow velocity significantly enhanced particle penetration: dimensionless displacement rose by 18–36% and terminal velocity increased from 0.061 m/s to 0.086 m/s. Flow-induced interfacial oscillations and lateral deflections were observed, contrasting with static rebound behavior. At inlet flow rate of 9.21 L/min, subsurface flow peaked at 80.49 mm/s with a 20.82 mm velocity gradient layer. These findings demonstrate that higher steel flow velocities overcome interfacial resistance, promoting inclusion removal into slag phases.

This study aims to use Computational Fluid Dynamics (CFD) analysis to improve inclusion removal efficiency in tundishes used in the steelmaking industry, with the broader goal of promoting more sustainable steel production and supporting circular economy objectives by producing cleaner steel. Inclusions are non-metallic particles, such as alumina, that enter the tundish with the molten steel and travel through it; if not removed, they can exit through the nozzles and adversely affect the mechanical properties of the final product and process yield. An existing tundish design is modified using three passive techniques, including adding a vertical dam, adding a horizontal baffle, and inclining the side walls, to assess their influence on fluid flow behavior and inclusion removal. Residence time distribution (RTD) analysis is employed to evaluate flow characteristics via key metrics such as dead zone and plug flow volume fractions, as well as plug-to-dead and plug-to-mixed flow ratios. In parallel, a discrete phase model (DPM) analysis is conducted to track inclusion trajectories for particles ranging from 5 to 80 μm. Results show that temperature gradients due to heat losses significantly influence flow patterns via buoyancy-driven circulation, changing RTD characteristics. Among the tested modifications, inclining the side walls proves most effective, achieving average inclusion removal improvements of 8% (Case B1) and 19% (Case B2), albeit with increased heat loss due to greater top surface exposure. Vertical dam and horizontal baffle, despite showing favorable RTD metrics, generally reduce the inclusion removal rate, highlighting a disconnect between RTD-based predictions and DPM-based outcomes. These findings demonstrate the limitations of relying solely on RTD metrics for evaluating tundish performance and suggest that DPM analysis is essential for a more accurate assessment of inclusion removal capability.