Inclusion Removal Research Articles

The effects of Soluble Gas Floatation Technology on the flow field of ladle and inclusion removal in RH refine process

The effects of soluble gas flotation technology (SGFT) on the flow field of the ladle and the inclusion removal effect during RH refining process were studied by RH water model. The nucleation mechanisms and trajectories of the bubbles precipitated in RH water model and the prototype were also analyzed. The results show that when SGFT is used in RH water model, bubbles can be nucleated in the low pressure area near the blowholes; a large amount of fine bubbles moved into the ladle from the downleg, and bubbles which are smaller than 200 μm account for more than 80%; the precipitated bubbles will affect the flow field of RH water model resulting in increases of diffusion rate by 6.6%–11.6% and decreases of mixing time by 8–14s when the gas flow rates are 3–5 m3/h, respectively. However, bubbles can be nucleated in the upleg, downleg and vacuum chamber in prototype. The trajectories of bubbles in the RH water model and prototype are similar and the mechanisms of inclusion removal are similar. The removal rates of particles are 67.1%, 74.34% and 86.18% when the gas flow rates are 3, 4 and 5 m3/h, respectively.

Novel concept of fine inclusion removal using carbonate powder injection through the ladle shroud

ABSTRACTTundish is the last refractory vessel in the steelmaking process. The fluid phenomena in tundish have a strong effect on the separation of non-metallic inclusions. In this paper, a new inclusion removal approach using powder injection through the shroud has been proposed and the devices have been set up. The plant trials have been carried out and the ruling factors have been analysed. The results indicate that this novel technique is beneficial to separate the small non-metallic inclusion removal from the molten steel. Compared with conventional inclusion removal technology, the number of the oxide inclusions can be decreased to a lower level and the inclusion becomes finer.

Evaluating slag–metal deoxidation equilibrium in secondary steelmaking

Steel–slag reactions are important in steelmaking, in special in secondary steelmaking. Currently, desulfurization, deoxidation and inclusion removal are mostly performed during ladle refining. The extent to which these reactions proceed is governed by the initial state of the material reaching the ladle, the additions made to the ladle and by undesired interactions such as reoxidation and steel-refractory reactions. In this work, the extent to which equilibrium is approached for the different deoxidation reactions is Al-killed and Si–Mn deoxidized steel is evaluated using thermodynamics. These results are compared to measurements performed in industrial ladle furnaces. The comparisons make possible evaluating the efficiency of the deoxidation process. The results indicate that reoxidation by air caused by agitation probably play a key role on the ability to approach equilibrium, reaching low oxygen content in steel. It is also concluded that relatively long treatments with controlled agitation are needed to achieve steel–slag equilibrium.

Vacuum Electromagnetic Levitation Melting of Ti–Al Based Alloy Prepared by Aluminothermic Reduction of Acid Soluble Ti Bearing Slag

A Ti-Al based alloy was prepared by aluminothermic reduction of acid soluble titanium slag followed by electromagnetic levitation refining. It was observed from the XRD and microstructure analysis that the alloy after refining was mainly composed of TiAl2 phase, with Mn and Fe dissolving into Al lattice, Ti5Si3, TiAl, and other metallic compounds. With increase of the vacuum degree or refining time, the phase of the alloy changed from an Al-rich compound to a Ti-rich phase due to Al loss by evaporation. The kinetics of Al evaporation demonstrated that the rate determining step of Al evaporation was controlled by the mass transfer in the liquid metal phase. The oxygen removal showed increasing tendency with increase of vacuum degree and refining time. The removal rate of oxygen after refining at 1858 K, 400 Pa for 25 min was over 40% and the final percentage of oxygen in the alloy was 0.59 wt%. Vickers hardness of the alloy showed increasing tendency with increase of vacuum degree and refining time, while its bending strength showed decreasing tendency. These results are mainly attributed to the comprehensive effect of oxide inclusions removal and phase transition in the refining process.

Development of nano-structure China low-activation martensitic steel for fusion reactors

Herein, we report a new castable nanostructured alloy (CNA), which was first melted in a vacuum induction furnace to introduce micron- and submicron-sized inclusions, strengthened by the multiscale secondary phases for fusion reactors. The large micron-scale inclusions are removed, whereas submicron-scale inclusions were retained during an electroslag remelting process. The ingot was subjected to heat treatment at 1050 °C for 0.5 h followed by heating at 650 °C for 1.5 h to obtain tempered martensite along with the nanosized (Ti, W) carbides. The improvement in the mechanical properties of the sample treated at 750 °C was attributed to the removal of blocky Y-rich inclusions along with the strengthening of the submicron-sized Y2O3 oxides. The performance of the sample treated at 650 °C was explained by the precipitation of the fine (Ti, W) carbides.

Flow Field, Temperature Field, and Inclusion Removal in a New Induction Heating Tundish with Bent Channels

In order to study the flow field, temperature field, and inclusion removal in a new induction heating tundish with bent channels, a three-dimensional (3D) transient mathematical model is established. The effects of both the channel radius and heating power on the multi-physical field and inclusion removal in the bent channels’ induction heating tundish are investigated. The results show that the tundish with the channel radius of 3 m shows better flow characteristics than those with the channel radii of 4 m and 2 m. With the increase of channel length, the heating efficiency increases at first, and then decreases, while the radius of 3 m is the best one for heating efficiency. After all the inclusions are placed into the tundish, the radii of 3 m and 2 m show good efficiency regarding inclusion removal, while it is poor when the radius is 4 m. Therefore, 3 m is the optimal radius of the channel in this work. Under the optimal channel radius, the heating power of 800 kW seems better than those of 600 kW and 1000 kW on flow characteristics control in the tundish. The temperature in the receiving chamber rises gradually and distributes quite uniformly with the increasing heating power, and the removal rate of inclusions increases with the increasing heating power.

Flow Interaction in Continuous Casting Tundish Due to Bubble Curtain Operation

Tundish argon bubbling has been studied in literature regarding homogenization and non‐metallic inclusion removal. Argon bubbling not only alters the flow within the tundish, which might aid the natural flotation of inclusions, argon bubbles also can directly capture inclusions, when bubbles and inclusions collide. The ascending bubbles from the line sparger induce a recirculating flow within the tundish. This recirculating flow interacts with the incoming liquid jet, emanating from the ladle shroud. For a sufficiently strong recirculating flow, the incoming liquid jet is deflected in a similar manner as a jet in cross‐flow. For this paper, computational fluid dynamics (CFD) simulations have been carried out with OpenFOAM to reproduce experiments, studying the jet deflection in a 1:3 water model due to gas bubbling. In the course of the CFD simulations, several modeling approaches are tested. A significantly large jet deflection might adversely affect the internal flow patterns of the tundish, as the liquid jet might hit a present turbulence inhibitor off‐center or miss it entirely. Tundish jet deflection constitutes an adverse effect of gas bubbling in a tundish leading to an off‐design, internal flow, which has not been studied so far, to the best of the authors’ knowledge.

Numerical study on the removal and distribution of non-metallic inclusions in electroslag remelting process

A transient model coupling the magnetohydrodynamic flow and heat transfer is developed to predict the removal and distribution of non-metallic inclusions in electroslag remelting process. The interaction between the melt and non-metallic inclusions was described by two-way coupled Euler-Lagrange method. Both original inclusions from electrode and newly precipitated ones with solidification were considered. The effect of current on the inclusion behaviour was also studied. The model was validated by experiments. The overall removal ratio of original inclusions 2–20 µm in diameter increases from 80.47% to 94.75%. The inclusions with 30 µm even is completely removed. A proper increase of current is conductive to the removal efficiency. In the mushy zone the drag force and buoyancy force play a major role in the entrapment and distribution of newly precipitated inclusions. The inclusion amount increases along radius, but slightly decreases when ranging from 0.9 to 1.0 radius in the solidified ingot. The buoyancy force is great enough for almost all of the 20 µm inclusions to escape from the mushy zone. The absorption ratio of inclusions into slag decreases from 50.5% to 28.7% when the current increases from 3100 A to 3700 A due to the increase of solidification rate.

Physical and chemical conditions for longterm functioning of restorations with zirconium-based framework: literature review

The aim of the study is to determine the optimal physico-chemical conditions and factors for the long-term perspective of zirconia-based restorations. Materials and methods Information was searched in English without time limits in the PubMed electronic database, a Google search and literature lists of relevant studies and reviews. Full-text articles from 2003 to 2018 were selected, in which studies of frameworks made of zirconium dioxide, a protocol for changing firing temperatures, and a description of the structure are described. Results. Totally 79 articles were identified. After the selection of articles on the inclusion criteria and removal of duplicate articles, the total number was 5. The review of the literature included studies of 3 types of zirconium: 3Y-TZP, ATZ, 12Ce-TZP. In a number of studies, the authors studied experimentally the influence of the oral environment on the long-term functioning of zirconium, and a number of authors conducted a study on the effect of heating and cooling gradients, as well as mechanical processing of zirconium frameworks. Conclusion. This literature review has shown the optimal physicochemical conditions and factors for the long-term prospects for restorations with a zirconia-based framework, starting from its composition, technical and laboratory stages, and pumping over the oral cavity factors. The combination of these factors can reduce the effect of the transition of zirconium dioxide from the tetragonal to the monoclinic phase, as well as reduce the stress outcomes resulting from the processing of zirconia frameworks and their facing layer.

Thermodynamic Modelling for Design of Synthetic Slag for Inclusion Removal

Enhancement in steel cleanliness is essential for high-performance steels for their high-end applications in structural, automotive, defence and strategic sectors. The non-metallic inclusions play a decisive role in clean steelmaking. The inclusions have to be necessarily minimized or modified by controlling their morphology, composition and size distribution to reduce the detrimental effect of inclusion on the mechanical properties of steel. The present article discusses the results of a thermodynamic study carried out on the various synthetic slags for inclusion removal. It involves computational thermodynamics determining the products of deoxidation, their physical properties and their implication on the quality of steel.

Mechanism of Flotation of Metallic Droplets in Oxide Melts

The flotation of droplets in liquids is a frequent phenomenon. For example, flotation is the basis of the removal of liquid nonmetallic inclusions from steel. However, the mechanism of this phenomenon is still poorly understood. The mechanism of flotation of metallic droplets in a melt is comprehensively studied using gold as an example. The kinetics and stages of formation of a gas bubble–attached gold droplet system and the subsequent gold flotation in a melt are investigated. Once a gas bubble and a droplet are in contact, the gold–gas surface and a wetting perimeter are added to the existing slag–gas and gold–slag surfaces. The time is takes for gold droplets about 3 μm in radius to achieve equilibrium is about 10–4 s. Therefore, the formation of an equilibrium bubble–droplet system is fast and does not retard the general process of collection and coarsening of gold droplets by gas bubbles. The flotation condition for the fine (Au, Pt, Pd) droplet–oxide melt system is analyzed. This condition is met for metallic droplets up to 3500 μm in radius.

Numerical Analysis of Turbulence Inhibitor Toward Inclusion Separation Efficiency in Tundish

There is scientific agreement on tundish performance improvement on incorporating a turbulence inhibitor box or turbostop, but also a dearth of commentary on the principles of its design. Industrial practice often employs incredible detail and customization into these devices, in parts due to this lack of perspective. In the current work, numerical simulation has been carried out to examine the elements of turbostop design, in context of modifying flow to promote inclusion removal in the tundish. Isothermal turbulent single-phase steady-state analysis was carried out to study the residence time distribution in aqueous tundish systems and analyze the effect of turbostop design on it. Significant improvement in bulk flow characteristics was found with the use of tapered walls and such device shapes which adhere closely to local flow symmetry near the shroud. Additional elements such as ridged walls and partial cover were found to have small impact on overall flow characteristics. More generally, the efficiency of turbulence containment is predominantly a function of local flow redirection around the submerged jet, rather than specific to bulk tundish design, which shows nominal sensitivity to local flow behavior in the containment region.

Numerical Simulation and Experimental Investigation on Inclusion‐Argon‐Liquid Steel Phenomenon in RH Refining of High‐Manganese and High‐Aluminum Steel

In this paper, factors influencing the inclusion removal in high‐manganese and high‐aluminum steel in RH refining process were studied by numerical simulations, production practice, and metallographic experiments. A mathematical model for inclusion removal was established, and the phenomenon of inclusions mixing in RH up‐leg region was verified due to fluid circulation. Removal efficiency of RH circulation time 120 s is much better than 600 s, and it was the lowest efficiency after 600 s. After 600 s circulation time, it shall not apply in production practice. The mass concentration of inclusions in practical steel was 11.64% probability error than values obtained by numerical simulation, because the numerical simulation did not consider the problem of inclusions adsorbing to the walls of refractory materials and corrosion of refractories. This work lays the foundation for the optimization and upgrading of process technology and establishes big data for full automation of RH out of furnace refining.

Removal of Oxide Inclusions in Aluminium Scrap Casting Process with Sodium based Fluxes

The investigation of Oxide Inclusions removal in aluminium scrap casting process with sodium based fluxes has been carried out. The purpose of this research is to investigate the effect of Na2SO4 and NaCl based fluxes addition onto the fluidity and microstructure of aluminium product. The alloy which is used in this investigation is Al-Si which mixed with metal scrap using gravity casting method. The variation of melting temperature in this investigation are 700°C, 740°C, and 780°C. In this research, material characterization was determined using DSC, EDAX, XRD, and fluidity test. The results show that the number of oxide inclusions decrease as the addition of 0,2% wt. flux, and completly removed after the addition of 0,4% wt. flux. The highest fluidity and tensile strength was obtained after the addition of 0,4% wt. flux. at 740°C.

Effect of reoxidation on inclusions in steel during calcium treatment

In the current study, the effect of reoxidation on inclusions during calcium treatment was studied via adding Fe2O3 into a Al-killed molten steel at 1 min after the addition of calcium. The total oxygen (T.O.) content increased from 10 to 24 ppm just after the reoxidation occurred, while it finally decreased to 14 ppm since inclusions were floated to the top of the steel and absorbed by the formed slag layer. The increased T.O. favored the decomposition of CaS, especially for the heat with high sulfur contents. The vaporization of calcium, which leads to the decrease of calcium content, is the driving force for the evolution of inclusions from CaO-CaS-(Al2O3) to CaO-Al2O3-(CaS) due to the limited degree of reoxidation. The contact angle between inclusions and the molten steel increased with the increase of Al2O3 in calcium alumina, which favored the removal of inclusions. Increased sulfur content decreased the surface tension of molten steel, which led to remove less inclusions since the contact angle between inclusions and the molten steel was decreased. Thus, more inclusions were measured in heats with higher sulfur content.

Numerical model of inclusion separation from liquid metal with consideration of dissolution in slag

The transport of inclusion particles through the liquid metal/molten slag interface and their dissolution in the slag are two key processes of inclusion removal. Based on the latest version of inclusion transport model that takes into account full Reynolds number range and a dissolution kinetics model, a coupled model was developed to simulate the whole process of inclusion removal, from floating in the liquid steel to crossing the interface and further to entering and dissolving in the molten slag. The interaction between the inclusion motion and dissolution was discussed. Even though the inclusion velocity is a key parameter for dissolution, the simulation results show no obvious dissolution during moving state because the process is too short and most of the inclusions dissolve during its static stay in the slag side above the interface. The rate-controlling step of inclusion removal is the transport through the steel–slag interface for the small-size inclusion and static dissolution above the interface for the large-size inclusion, respectively.

Aggregation kernel of globular inclusions in local shear flow: application to aggregation in a gas-stirred ladle

The control of metal cleanliness has always been a concern for metallurgists since inclusions directly influence the mechanical properties of alloys. In most metallurgical routes, a refining treatment of the liquid alloy is performed, in particular with the aim of improving the metal cleanliness that is achieved via a better control of particle contents and particle size. Since the efficiencies of inclusion removal mechanisms increase with inclusion size, the turbulent aggregation process plays a major role in all refining treatments. Interaction between particles such as aggregation is usually modelled through kinetics kernels which may be difficult to estimate. This paper contributes to express turbulent aggregation kernel taking into account the hydrodynamic effects at the inclusion scale. The numerical approach combines three numerical techniques, a Lattice Boltzmann Method to resolve the flow, an immersed boundary method for the particle-fluid interactions and a Lagrangian tracking for the motion of individual particles. Deterministic simulations of spherical particle pair trajectories leading to collision or avoidance allow us to calculate statistical kernels in a shear flow. The results show a strong influence of the short distance hydrodynamic effects on the collision kernel, particularly when the diameter ratio of the two interacting particles is far from unity. An application of this new aggregation kernel is applied to simulate the time evolution of the particle size distribution in a typical steel gas-stirred ladle.

Argon Bubble Coalescence and Breakup in a Steel Ladle with Bottom Plugs

Gas‐stirred ladles are widely used in the steel secondary refining process. In order to produce high‐quality steel, a range of stirring conditions, from hard stirring for mixing to gentle stirring for inclusion removal, is required. In this paper, a full scale unsteady three‐dimensional computational fluid dynamics (CFD) model is developed to simulate the bubble behavior in a steel ladle. A volume of fluid (VOF)‐Lagrangian approach is applied to simulate multiphase flow characteristics. The VOF method is used to track the liquid steel and slag, while the Lagrangian method is used to track the movement of argon bubbles. A water model is used to validate the gas‐stirred ladle model against experimental data. Flow field and bubble breakup and coalescence phenomena inside the ladle is studied in the baseline case, and the effects of initial bubble diameter and gas flow rate during the stirring process have been investigated through parametric study as well.

Effect of Rb<sub>2</sub>O on Inclusion Removal in C96V Saw Wire Steels Using Low-Basicity LF Refining Slag

A novel Rb2O-containing synthetic LF refining slag has been developed in order to produce ultraclean C96V saw wire steel. In addition, the thermodynamic and kinetics mechanism of Rb2O on inclusion removal have been discussed fully. The results indicated that (1) Rb2O additions (≤10.00 wt%) seems to significantly enhance inclusion removal in steel melts. ① The average diameter of nonmetallic inclusions decreased significantly with the Rb2O addition in synthetic LF refining slag increasing. In particular, the diameter of most of inclusions was less than 3.0 × 10−6 m (3.0 µm) when Rb2O addition was 10.00 wt% ② The number of nonmetallic inclusions decreased sharply with the content of Rb2O in synthetic LF refining slag raising. ③ Both of the MnO–SiO2–Al2O3, CaO–SiO2–Al2O3 inclusions system mainly concentrated in the low melting point zone. (2) For the 15.00 wt% Rb2O-containing synthetic LF refining slag, not only the average diameter of inclusion increases slightly with reaction times increasing, but also the number. This is due to the fact that, the effect of Rb2O on the ability of refining slag to absorb inclusions is a double-edged sword: On the one hand, Rb2O addition would promote the thermodynamic conditions of inclusion removal, then, inclusions would enter the slag spontaneously easier. On the other hand, Rb2O addition could also exacerbate the kinetic conditions of inclusion removal by increasing the viscosity of slag at the same time.

Numerical Study of Inclusion Removal in Steel Continuous Casting Mold Considering Interactions Between Bubbles and Inclusions

Numerical Study of Inclusion Removal in Steel Continuous Casting Mold Considering Interactions Between Bubbles and Inclusions