Inclusion Removal Research Articles

How to electromagnetically stir in the slab continuous casting mould

Fluid flow plays a significantly important role in the continuous casting process which has a great influence on the steel quality. Electromagnetic stirring (EMS) has become a fairly established technology to control the flow behaviour within the mould. However, there still exist two important questions need to be answered, that is, what kind of flow pattern is the best one to achieve the high steel quality under EMS, and how to determine the optimal EMS parameters. Therefore, in order to clarify these questions, a methodology based on numerical simulation in an actual slab continuous casting mould has been developed to select an optimal EMS current, and three evaluation criteria are proposed in this paper, including: (1) a free surface rational criterion, (2) a uniformity criterion of the flow velocity distribution, (3) an inclusion removal criterion. By synthetically considering these evaluation criteria, the optimal EMS current is determined under different operating parameters. Meanwhile, this methodology can also be applied to optimize other operating conditions of continuous casting. Tables 1, Figs 8, Refs 13.

Insights into the influence of oxide inclusions on corrosion performance of additive manufactured magnesium alloys

The corrosion performance of binder jet additive samples is compared with cast samples through potentiodynamic polarization in Na2SO4 solution. Higher zinc levels in the magnesium matrix and the presence of MgO within the microstructure of the binder jet printed alloy contribute to increases in the anodic and cathodic kinetics, respectively. It is proposed that electron inhomogeneity at the Mg/MgO interface in the binder jet printed alloy is the source of the catalytic activity of the hydrogen evolution reaction. The removal of MgO inclusions suppressed the cathodic reaction relative to the large increase in kinetics seen in similarly treated cast samples.

Exploration of the Relationship between the Electromagnetic Field and the Hydrodynamic Phenomenon in a Channel Type Induction Heating Tundish Using a Validated Model

It is essential to understand the relationship between the electromagnetic field and the transport process in a channel type induction heating tundish precisely to improve the quality of the slab. A validated mathematical model was established to investigate the magnetic field characteristics, flow, temperature distribution and the movement of inclusions. In comparison with prior researches, we obtained the effective active zone of the magnetic field by analysing the dimensionless parameters Ha, N and Re. It should contain the channels and the nearby walls connected with the channels. Besides, the electromagnetic force is distributed asymmetrically near the channel outlets, and it is significantly larger within the upper zones of the channel outlets. This leads to the downward flow of the main stream in the distributing chamber, and it also changes the trajectories of the inclusions. When the induction heating is applied, about 75% of the inclusions entering the distribution chamber, regardless of the particle size, will be adsorbed by the tundish covering flux, and about 90% of them will float to the free surface within 120 s. The electromagnetic force can sharply promote the removal of small inclusions (diameter less than 60 µm). The induction heater should not be used intermittently during the casting process because 40%–80% of the inclusions may enter the mold directly during the period of power at 0 kW.

Low-oxygen Ti3AlC2 MAX powder deoxidized by Ca reductant: Comparison of contact and noncontact deoxidation mechanism

This study investigates the decrease in oxygen concentration caused by the removal of α-Al2O3 inclusions in Ti3AlC2 MAX powder. The Ti3AlC2 MAX powder was deoxidized in the solid-state using calcium (Ca) as the reductant under contact and noncontact conditions. The oxygen concentration was decreased by removing the α-Al2O3 inclusions in Ti3AlC2 MAX powder through Ca contact and non-contact deoxidation. In the α-Al2O3 reduction reaction, Al diffusion and excess Ca interactions led to the formation of a Ti2AlC phase, which was suppressed by reducing amount of Ca used. Oxygen reduction without any phase change was possible through contact deoxidation at 750 °C for 5 h. The oxygen concentration of deoxidized MAX powder was 9,450 ppm. In the case of noncontact deoxidation, the Ti2AlC phase was suppressed by reducing the amount of Ca used to 0.5 g. The oxygen concentration of the deoxidized MAX powder was 3,400 ppm.

A Study of Physical Modeling and Mathematical Modeling on Inclusion Behavior in a Planar Flow Casting Process

Flow pattern and inclusion removal in a novel-designed crucible in the planar flow casting process were studied in the present paper. A color dye water experiment was used to show the flow field and validate the mathematical modeling. It was shown that the flow pattern predicted by the Large Eddy Simulation model is maximally consistent with that in the physical modeling. The validated mathematical model was used to predict the flow pattern and inclusion behavior in the crucible with various prototypes using combinations of multiple facilities. The results show that the flow field, by using the stopper, enhances compared to that using none of the facilities, which causes the inclusion removal to become even worse when the stopper is individually used. Furthermore, as the magnetic field is added, the electromagnetic brake weakens the flow field in the magnetic zone. The function of the electromagnetic brake to weaken the flow pattern is most efficient for inclusion removal.

Image Processing Procedure to Evaluate Inclusion Dissolution in a Slag Observed by High-Temperature Confocal Scanning Laser Microscopy

In situ study of the inclusion dissolution behavior in a slag utilizing high-temperature confocal scanning laser microscopy helps to understand the phenomenon of the removal of non-metallic inclusions from liquid steel before the casting process. The current work introduces an image processing procedure to automate and measure the inclusion diameter during its dissolution. Silica and alumina particle dissolution were considered as they appear differently when suspended in the slag (bubble-like transparent and solid-like opaque, respectively). The procedure consists of two parts: (1) morphological isolation and construction of the inclusion, and (2) inclusion diameter calculation. The inclusion diameters could be successfully measured over a series of images and showed good agreement with the manually measured diameters. The image processing procedure has the advantages of significant time saving and standardization compared to manual measurements.

Numerical Study on the Influence of Distributing Chamber Volume on Metallurgical Effects in Two-Strand Induction Heating Tundish

Reducing the volume of distributing chamber by shortening its width is one of the ways to obtain good metallurgical effects for a large two-strand induction heating tundish. A multi-field coupling numerical model was established to figure out the effect of distributing chamber volume on the flow field, temperature field of molten steel, and removal of inclusions. Three tundishes with distributing chamber widths of 1.216 m (tundish A), 0.838 m (tundish B), and 0.606 m (tundish C) were modeled. The results indicated that reducing the width of the distributing chamber from 1.216 m to 0.838 and 0.606 m could improve the fastest heating rate from 0.4 K/min to 0.6 and 0.8 K/min and reduce the energy consumption from 476 kWh to 444 and 434 kWh. The temperature fluctuation of molten steel in the distributing chamber rose with the decrease in distributing chamber volume during the continuous casting process. Besides, tundish B performs the best temperature uniformity. The flow field in the distributing chamber was no longer symmetrical, and a short-circuit flow appeared when the width was reduced to 0.606 m. As a result, the floating ratio and removal ratio of inclusions decreased and the ratio of inclusions flowing into the mold sharply increased in tundish C. When the width was reduced from 1.216 to 0.838 m, the floating ratio of inclusions had little change and the removal ratio increased slightly. The floating efficiency increased with the decrease in the volume of distributing chamber, and the removal efficiency is the highest in tundish B. Taken together, tundish B should be adopted.

Characterization of SiC and Si3N4 inclusions in solar cell Si scraps and their motion at the Si/slag interface

The separation of SiC and Si3N4 inclusions from solar cell Si scraps to the slag phase during slag refining is essential to the recovery and production of high-purity Si. This study characterized the SiC and Si3N4 inclusions in solar cell Si scraps, which formed large clusters with complex shapes. According to the experimental and theoretical investigations, the inclusions with large diameters were found to be conducive to passing through the Si/slag interface and then being retained in the slag phase. The favorable conditions such as positive overall wettability, high operating temperature, low viscosity slag, and prolonged-time can promote the small inclusion removal from molten Si scraps.

Effects of Refining Slag on Transformation and Removal of Inclusions in Type 430 Stainless Steel

Effects of Refining Slag on Transformation and Removal of Inclusions in Type 430 Stainless Steel

Numerical Investigation on Gas Bubbling Assisted Inclusion Transport and Removal in Multistrand Tundish

Numerical Investigation on Gas Bubbling Assisted Inclusion Transport and Removal in Multistrand Tundish

Modeling Inclusion Removal when Using Micro-bubble Swarm in a Full-Scale Tundish with an Impact Pad

Modeling Inclusion Removal when Using Micro-bubble Swarm in a Full-Scale Tundish with an Impact Pad

Non-metallic inclusions in a superalloy during refining through cold crucible levitation melting process

Oxide and nitride inclusions in a Ni-based superalloy during the cold crucible levitation melting (CCLM) process were investigated towards a better understanding for the removal of inclusions from the metal. The number, morphology, size distribution and spatial distribution of inclusions were characterized using an automated scanning electron microscopy with energy-dispersive X-ray spectroscopy. Inclusions in the alloy were efficiently agglomerated and removed by floating during CCLM process. Inclusion clusters as big as 30-400 ?m were observed. Oxide clusters were efficiently floated during pouring process. The removal ratios of oxides were about 21% without pouring and 62% with pouring, respectively. Additionally, CCLM promotes the separation of oxides from nitrides. The effect of CCLM on the removal of nitride inclusions is not such evident compared with oxides. The mechanism of inclusion removal during CCLM was clarified.

First-principles study on yttrium inclusions in micro alloyed steels

The removal and control of inclusions has always been a hot issue in the field of metallurgy, and rare earth modifying is a proven method. However, some rare earth inclusions cannot be accurately judged due to the necessary assumptions for thermodynamic calculations and the lack of certain thermodynamic data. On the other hand, most of the currently reported researches focus on the changes in the morphology of the inclusions, and rarely involve the inherent properties of the inclusions. To address these two deficiencies, this work investigated elaborately the stability, elastic modulus, elastic anisotropy and thermal expansion coefficient of yttrium (Y) inclusions in micro alloyed steels by first-principles calculation. Then, the role of yttrium inclusion in the initial stage of crack initiation was discussed. The results showed that it was practical to judge the possibility of unknown inclusions formation in steel by formation enthalpy. The inclusions were changed from Al2O3 to Y2O3, Y2O2S, YAlO3-Y2Si2O7 composite inclusions with yttrium treatment, which was consistent with the metallographic observations. The bulk modulus (B), shear modulus (G), Young’s modulus (E), and Poisson’s ratio (σ) were calculated in a framework of the Voigte-Reusse-Hill approximation. In light of B/G and σ values, Al2O3 showed apparent brittleness, and the toughness of yttrium inclusions were improved to varying degrees compared to Al2O3 inclusions. Moreover, the order of the degree of elastic anisotropy for these inclusions was Y2Si2O7 > Al2O3 > Y2O3 > Y2O2S > YAlO3. Furthermore, the thermal expansion coefficient of Y2O3, Y2O2S, YAlO3 inclusions at any temperature were greater than that of Al2O3 and were relatively close to that of Fe, whereas, Y2Si2O7 inclusion was much larger than that of Fe. Finally, the difference between yttrium inclusions and iron matrix in the aspect of incompressibility, brittleness, toughness, mechanical anisotropy, and thermal expansion was reduced significantly, thereby improving the consistency of the matrix, this could be used to explain the phenomenon of alleviating stresses concentration and delaying the formation of micro voids.

Motion and removal behavior of inclusions in electrode tip during magnetically controlled electroslag remelting: X-ray microtomography characterization and modeling verification

• Detailed 3D microtomography characterizations of inclusions in electrode tip are performed. • Motion/removal behavior of inclusions in electrode tip are clarified based on experimental results and simulation verification. • The number and size of the inclusions in LMF are decreased due to the applied ASMF. • The mechanism is that the ASMF enhances the kinetic conditions for inclusion migrating to LSI and removal in LMF. Detailed three-dimensional (3D) microtomography characterizations of inclusions in electrode matrix, mushy zone (MZ) and liquid melt film (LMF) were performed to elucidate the motion and removal behavior of inclusions in electrode tip during magnetically controlled electroslag remelting (MC-ESR) process. A transient 2D numerical model was also built to verify the experimental results and proposed mechanisms. The number and size of inclusions exhibited an obvious increasing trend from edge to mid region in LMF, while remained almost the same in electrode matrix and MZ. The inclusions in LMF migrated from edge to mid region of LMF, accompanied with removal process. In addition, the kinetic conditions for inclusion migrating to LMF/slag interface (LSI) were enhanced during MC-ESR process, thereby improving the inclusion removal efficiency in LMF. This work highlights the 3D characterization and motion/removal mechanisms of inclusions in electrode tip, as well as sheds new light on preparing high purity materials.

The effect of different deoxidation processes on the inclusions characteristics in cold drawn tubing steel

ABSTRACT The non-metallic inclusions of cold-drawn tubing steel with different deoxidation processes were carried out in this study. The morphologies, compositions and size distribution of oxide inclusions in two heats were obtained by FE-SEM&EDS. The evolution of inclusion types in SM/AC process and SMA/C process were compared. In addition, it was summarized that the removed inclusion of SM/AC process was relatively more at LF station, while the removed inclusion of SMA/C process was mainly at VD station, which is closely related to the calcium treatment intensity at VD station. Moreover, kinetic model calculations of inclusion behaviour were carried out. Taking molten steel-slag-inclusion-refractory four-phase equilibrium into account, and considering the aggregation, floatation, remove and modification of inclusion. The results can well explain the existence of inclusions in the actual production process and can guide the removal of inclusions in different deoxidation processes and to know the removal limits.

Influence of Slag Viscosity and Composition on the Inclusion Content in Steel

Influence of slag viscosity and composition on the inclusion content in the steel is studied using laboratory experiments and modeling simulations. The steel samples are taken during the experimental process to record the inclusion content change. Afterwards the prepared samples are analyzed using automated scanning electron microscope and energy dispersive spectroscopy (SEM/EDS) method. A simple steel/slag reaction model is constructed based on the effective equilibrium reaction zone (EERZ) method. The inclusion content evolution process is discussed by combining the experimental and calculated results. It is found that the inclusion content evolution in the steel is determined by the inclusion generation and removal.

Effect of Top‐Swirling Turbulence Inhibitor on Multiphase Flow in a Single‐Strand Tundish During Transient Casting

The turbulence and multiphase flows in a single‐strand slab casting tundish during the start‐up operation, steady‐state casting, and the ladle changeover process without a turbulence inhibitor (TI), with an ordinary TI, and with a top‐swirling TI are numerically investigated and compared to assess the metallurgical advantages of a top‐swirling TI. The results show that the designed top‐swirling TI has no negative effect on the turbulence flow of molten steel during steady‐state casting, as the swirling flow may enhance the inclusion removal rate, and erosion of the guide vanes is relatively weak. During start‐up operation, the use of a top‐swirling TI effectively alleviated level fluctuations in the impact zone, which decreased from 38.75 mm at 90 s to 12.5 mm at the start‐up tonnage, then decreased to zero within 180 s. During ladle changeover, the second stage of steel exposure could be eliminated by the top‐swirling TI, while the areas of steel exposure remaine around 1550 and 750 cm2 without a TI and with an ordinary TI after 60 s of refilling time. The top‐swirling TI could effectively improve the turbulence flow of molten steel, avoiding secondary oxidation and slag entrapment, making it suitable for widespread application and popularization.

The effect of refining time and calcium addition on the removal of oxygen, nitrogen, and hydrogen from IN713LC during vacuum induction refining

This research was intended to decrease the gas content, namely, oxygen, nitrogen, and hydrogen, in the nickel-based superalloy IN713LC using vacuum induction refining (VIR) and calcium addition. To accomplish this, the molten superalloy was subjected to individual VIR for up to 15 min, as well as a combination of VIR and calcium addition up to 0.03 wt%. Then the removal of oxygen, nitrogen, and hydrogen through the superalloy's constituent carbon and added calcium was investigated. The results showed that with increasing refining time and calcium content, total oxygen and nitrogen levels decreased continuously according to second- and first-order kinetic models, respectively. However, the addition of 0.03 wt% Ca resulted in the lowest concentration of total oxygen, and a refining time of 15 min resulted in the lowest concentration of total nitrogen and hydrogen. The remaining air in the crucible's unfilled crevices was proposed as the reason for the need for calcium addition to achieve greater oxygen removal than the carbon deoxidation process. In addition, the influence of calcium addition on the removal of Al2O3 inclusions as one of the probable mechanisms of total oxygen decrease was discussed using the phase stability diagram of the Al2O3–CaO inclusion system, which was constructed in the current study.

Experimental and Simulation Analysis of Physical Water Model through Tracer Injection under Various Baffles and Turbulence Inhibitor Conditions for Developing the Fluid Flow Parameters and Inclusion Removal Rates in Tundish

Tundish is a critical part involved in the continuous casting process, which ensures the constant flow of liquid metal and with performing different functions. In odd-numbered multistrand tundish, the confirmation consistency of the fluid flow among all the strands is one of major concerns. In this study, five-strand tundish with a set of weirs and a baffle is utilized for investigation concerning fluid flow parameters and inclusion removal analysis. The simulation is carried out in ANSYS FLUENT 19.2 software through the defined numerical model, and the experimental analysis is performed on a scaled physical water model through tracer injection. Four different baffles are designed along with two different types of turbulence inhibiter for the tundish to enhance the fluid flow parameters and inclusion removal rates. The inclusion sizes were varied from 10 to 100 µm with a difference of 20 µm respectively for studying the inclusion removal rate concerning inclusion sizes. From the outcomes obtained like the residence time distribution (RTD) curves and others, it was concluded that the fourth baffle version with the first turbulence inhibiter, which are equipped in tundish version TV8 is the most beneficial tundish version for the enhancement in fluid flow and inclusion removal rates as compared to other tundish versions in this study.

Dissolution Behavior of Different Inclusions in High Al Steel Reacted with Refining Slags

Al2O3, Al2O3·TiN, Al2O3·MgO, and CaO·2Al2O3 are four different types of inclusions in high Al steels. To improve the steel cleanness level, the effective removal of such inclusions during secondary refining is very important, so these inclusions should be removed effectively via inclusion dissolution in the slag. The dissolution behavior of Al2O3, Al2O3·TiN, Al2O3·MgO, and CaO·2Al2O3 in CaO-SiO2-Al2O3-MgO slags, as well as the steel-slag reaction, was investigated using laser scanning confocal microscopy (LSCM) and high-temperature furnace experiments, and thermodynamic calculations for the inclusion in steel were carried out by FactSage 7.1. The results showed that Al2O3·TiN was observed to be completely different from the other oxides. The composite oxides dissolved quickly in the slags, and the dissolution time of the inclusions increased as their melting point increased. SiO2 and B2O3 in the slag were almost completely reacted with [Al] in steel, so the slags without SiO2 showed a positive effect for avoiding the formation of Al2O3 system inclusions and promoting inclusions dissolution as compared with SiO2-rich slags. The steel-slag reaction was also found to influence the inclusion types in steel significantly. Because of the rapid absorption of different inclusions in the slag, it was found that the dissolution time of inclusions mainly depends on the diffusion in the molten slag.