Molten Steel Flow Research Articles

Mathematical modeling of the effect of SEN outport shape on the bubble size distribution in a wide slab caster mold

Herein, the effects of outport shapes of the submerged entry nozzle (SEN) on the size distribution of argon bubbles were studied in a wide slab caster mold by the mathematical modeling. The Eulerian–Eulerian model coupled with Multiple-Size-Group (MUSIG) approach were used to solve equations of the two phase flow and polydispersed bubbly flow in the mold, respectively. The effect of the SEN outport angle and shape on the distribution of the molten steel flow, argon gas volume fraction, and argon bubble size were investigated. The outport shapes of the SEN included large rectangular, small rectangular, square, trapezoid, and runway. Results showed that the speed of molten steel increased within the range of 260 mm from the SEN, and decreased within the range of 550 mm from the narrow face with the outport angle of SEN increased from 20° to 45°. The bubble diameter was 5.7 mm at 255 mm distance from the SEN along the mold width at different outport angles. The average speed of molten steel at the outport of SEN decreased from 0.91 to 0.72 m/s with the outport shape changed from small rectangular to runway, trapezoid, square and large rectangular. The average diameter of bubbles was approximate 5.2 mm at the outport for the five types of nozzles, and increased from 3.2 to 3.45 mm inside the mold with the outport shape changed from the runway to square, trapezoid, large rectangular and small rectangular, indicating the rate of bubble breakup was larger with the runway and square SEN casting.

Influence of Electromagnetic Field on Stirring Energy in Selected Metallurgical Equipment

This article analyzes the turbulence dissipation rate in liquid steel in selected metallurgical equipment (i.e., electric arc furnace, ladle furnace, and tundish) based on advanced computational fluid dynamics simulations. The approach enables evaluation of the efficiency of electromagnetic stirrer (EMS) devices based on the molten steel flow behavior in comparison with the standard mixing process. Particular attention is put on the determination of the effectiveness of novel EMS with the horizontal stirring device, which supports the mixing process of molten steel. For that, the concept of the new formula to evaluate the stirring energy is presented and compared with the literature results to prove the correctness of the developed method.

Simulation and Experimental Study of Fluid Flow and Solidification Behavior in Thin Slabs Continuous Casting Process under Secondary Electromagnetic Stirring

During the thin slab continuous casting process of silicon steel, electromagnetic stirring (EMS) can control the flow, heat transfer, and solidification of molten steel through electromagnetic force. Herein, a 3D mathematical model coupling the fluid flow, heat transfer, solidification, and the electromagnetic field is built. The effects of varied current intensities on the flow, heat transfer, and solidification of molten steel in the thin slab under secondary EMS are explored based on applying the electromagnetic brake in the mold region. In the findings, it is demonstrated that increasing the current intensity increases the flow rate and vorticity of the molten steel in the second cooling zone, eliminating the superheating phenomenon and improving the uniformity of the molten steel's temperature distribution. Meanwhile, based on the nucleation and growth parameters determined from thermal simulation experiments, the cellular automation finite‐element model is used to simulate the microstructure evolution during the solidification of thin slab. In the results, it is shown that the stirring energy increases when the current intensity increases, potentially promoting equiaxed crystal growth and grain refinement. Compared to the production sample, a reasonable qualitative agreement is achieved for the grain morphology, equiaxed crystal ratio, and columnar to equiaxed transition.

Simulation Study on the Influence of Different Molten Steel Temperatures on Inclusion Distribution under Dual-Channel Induction-Heating Conditions.

Impurity elimination in tundishes is an essential metallurgical function in continuous casting. If inclusions in a tundish cannot be effectively removed, their presence will have a serious impact on the quality of the bloom. As a result, this research investigates the locations of inclusion particles in a six-strand induction-heating tundish in depth, combining the flow, temperature, and inclusion trajectories of molten steel under electromagnetic fields. The results show that a pinch effect occurred in the induction-heating tundish, and a rotating magnetic field formed in the channel, with a maximum value of 0.158 T. The electromagnetic force was directed toward the center of the axis, and its numerical distribution corresponds to the magnetic flux density distribution, with a maximum value of 2.11 × 105 N/m3. The inclusion particles' movement speed accelerated as the molten steel's temperature rose, and their distribution in the channel was identical to the rotating flow field distribution. When the steel's temperature rose from 1750 K to 1850 K, the removal percentage of inclusion particles in the discharge chamber rose by 9.20%, the removal rate at the outlet decreased from 8.00% to 3.00%, and the adhesion percentage of inclusion particles in the channel decreased from 48.40% to 44.40%.

Physical and Numerical Simulation Study on Structure Optimization of the Inner Wall of Submerged Entry Nozzle for Continuous Casting of Molten Steel

The submerged entry nozzle (SEN) plays an important role in the continuous casting production process. It is a cast refractory pipe fitting installed in the lower part of the tundish and inserted below the molten steel level of the mold. It not only affects the speed of molten steel flow, but is also prone to nodules and affects production. In the present work, the flow behavior of molten steel in a traditional nozzle and that in a new type of nozzle whose inner wall was distributed with arrays of hemispherical crowns were studied by means of both physical simulation (using a water model) and numerical simulation (using ANSYS CFX) based on the prototype of a production continuous casting slab mold. Both experimental and numerical simulation results show that, compared with the traditional nozzle, the impact depth generated by the new-type nozzle in the mold is reduced by 21.06–26.03 cm, the impact angle is reduced by 14–17 degrees, and swirl flow was generated inside the new-type nozzle, which not only improves the flow characteristics inside the submerged entry nozzle and changes the dead zone size in the submerged entry nozzle, but also improves the velocity distribution at the outlet of the nozzle and minimizes the possibility of nodulation. In addition, in contrast to the traditional nozzle that generates flat body-shaped jets of molten steel flow, the new-type nozzle produces baseball glove-shaped jets that penetrate shallower into the molten steel bath in the mold, which significantly reduces the outlet velocity and is conducive to the floating of inclusions.

Evaluation of Molten Steel Flow Behaviors in a Multistrand Tundish via Numerical Simulation and Grey Relational Analysis with a New Dimensionless Operator

Optimizing the tundish structure can effectively improve billet or solid product quality. The correlation between the structural parameters of the baffle and the flow characteristics of molten steel in a tundish is a prerequisite for tundish structural optimization. In this study, molten steel flow behaviors are stimulated in a five‐strand tundish using computational fluid dynamics. The behaviors are characterized by the dead‐zone ratio of the entire tundish and the flow consistency of five strands at the outlets. Further, the influences of different structural parameters on the characteristics are analyzed, and the degree of influence is evaluated using grey relational analysis (GRA). Four traditional nondimensionalization operators are used for GRA. However, the results obtained from different operators are inconsistent. Therefore, a benchmark deviation dimensionless operator is proposed to improve the accuracy of GRA. The improved grey correlation degrees are consistent with the results obtained through numerical simulation. The rank of the grey correlation degree indicates that the diameter and inclination angle of Orifice B, which is at the lower position of the baffle, are highly correlated with the dead‐zone ratio. The inclination angles should have a larger correlation degree for flow consistency than the orifice diameter.

An Experiment on Surface Fluctuation of Ga-In-Sn Alloy with a Permanent Magnet Flow Control Mold

To control well the surface fluctuation of liquid metal in a slab mold, a new type of combined permanent magnets braking system, namely a permanent magnet flow control mold (PMFC-Mold) is proposed by our research group, of which its main feature is that the device can control the flow of molten steel in the mold without additional energy. To observe the fluctuation state of the alloy with the PMFC-Mold, instantaneous surface fluctuations were recorded by a laser level meter and camera. To study the effect of various casting speeds and permanent magnet placement on surface fluctuations, the three measurement points, which were 7, 18, and 36 mm away from the narrow surface of the mold, were selected to record the trend of level fluctuation. Three types of permanent magnet placement were designed by setting the differences between the height center of the permanent magnet and the free surface in the slab mold, which were H1 = 0 mm, H2 = −25 mm, and H3 = −75 mm. The experimental results indicated that with the acceleration of the casting speed, the average height and standard deviation of surface fluctuation at the measurement point increased, but the surface fluctuation pattern remained. When the permanent magnets were arranged at H1 = 0 mm and H2 = −25 mm, the position of the magnetic field was reasonable and the surface fluctuation could be effectively suppressed. In contrast, when the permanent magnets were arranged at H3 = −75 mm, the level fluctuation was intensified.

Analysis of Flow and Fluctuation Characteristics in Coated Slag Using a 2D Model in the Meniscus Region of Mold

Steel is mainly produced through continuous casting; molten steel flows into the mold from the tundish, where it cools and then enters the secondary cooling zone, ultimately solidifying into a billet. During the continuous casting production process, the quality of the casting billet is mainly related to the lubrication state of the coated slag. In the upper part of the mold, the consumption of liquid protective slag directly affects the friction state of the initial solidified billet shell. Therefore, the flow and fluctuation characteristics of coated slag in the meniscus area are very important. There is limited research on the flow and fluctuation characteristics of coated slag in the meniscus area, and little consideration has been given to the shape of the meniscus. In this work, a two-dimensional numerical model for the flow and fluctuation of coated slag in the meniscus region was established, and the transient flow velocity of protective slag and molten steel at each moment of the vibration cycle was obtained, as well as the fluctuation of the slag/steel interface in the meniscus region. The results show that when the surface mold vibrated upwards, the protective slag in the meniscus area flowed clockwise. When the mold moved downwards, the protective slag in the slag pool generated a counterclockwise flow vortex. When the mold was in a positive slip state, the negative pressure formed by the upward flow of the protective slag on the meniscus and the inertia force of steel liquid pushed the meniscus toward the inner wall of the mold. During negative slip, the flow of coated slag generated positive pressure on the slag/steel interface, pushing the meniscus toward the steel liquid, and at the initial moment of negative slip, the steel liquid overflowed into the slag channel. This model could provide a theoretical basis for the flow control of protective slag.

Study on Stirring Effect of Spiral Magnetic Field in Continuous Casting of Round Blooms

Herein, for the continuous casting of round blooms with strand electromagnetic stirring, the effects of rotating magnetic field (RMF) and spiral magnetic field (SMF) on the electromagnetic, fluid flow, heat transfer, solidification, and macrostructure are investigated by numerical simulation and industrial experiments, respectively. The results show that the molten steel flows in a spiral shape along the casting direction with the RMF and SMF. Due to the influence of secondary flow caused by electromagnetic stirring (EMS), and the zone of high velocity of molten steel accounts for 13.7% of the whole stirring range with the RMF. The SMF has a strong stirring effect in the whole range of secondary flow, the zone of high velocity of molten steel accounts for 49.1% of the whole stirring range, and the liquid fraction of the SMF at the liquid core is also lower. The results of the industrial experiments prove that the SMF has a wider stirring depth than the RMF, and the center crack range is significantly reduced.

Cooling Capacity Evolution of Steel Strip during Oscillatory Feeding Process in Slab Continuous Casting

To comprehensively understand the effect of oscillation on cooling capacity of steel strip, a mathematical model is proposed to investigate the distribution of temperature fields in continuous cast slabs, taking into account the oscillatory feeding process. Strip oscillation results in a periodic variation of nearby molten steel flow. It intensifies the turbulence of surrounding molten steel and enhances the interfacial heat transfer. During the feeding process, the morphology of strip undergoes three stages: upheaval, fluctuation, and disappearance. As the strip oscillation frequency increases, the maximum cross‐sectional area of the strip gradually decreases during the upheaval stage, the fluctuation stage gradually disappears, and the strip disappearance speed gradually increases during the disappearance stage. These observations suggest that an increase in the oscillation frequency accelerates the melting of the strip, which is caused by the enhanced heat transfer between the strip and molten steel. This results in a gradual growth of strip's cooling capacity and a decrement in the liquid fraction of molten steel surrounding the strip. In addition, feeding strip is advantageous in preventing the jet from impinging onto narrow surfaces of slab. The blocking effect initially increases and then remains almost unchanged as the strip oscillation frequency increases.

Migration Behavior of Inclusions at the Solidification Front in Oxide Metallurgy.

Distribution of inclusions plays an essential role in inducing intracrystalline ferrite, and the migration behavior of inclusions during solidification has a significant influence on their distribution. The solidification process of DH36 (ASTMA36) steel and the migration behavior of inclusions at the solidification front were observed in situ using high-temperature laser confocal microscopy. The annexation, rejection, and drift behavior of inclusions in the solid-liquid two-phase region were analyzed, providing a theoretical basis for regulating the distribution of inclusions. Analysis of inclusion trajectories showed that the velocity of inclusions decreases significantly as they near the solidification front. Further study of the force on inclusions at the solidification frontier shows three situations: attraction, repulsion, and no influence. Additionally, a pulsed magnetic field was applied during the solidification process. The original dendritic growth mode changed to that of equiaxed crystals. The compelling attraction distance for inclusion particles with a diameter of 6 μm at the solidification interface front increased from 46 μm to 89 μm, i.e., the effective length for the solidification front engulfing inclusions can be increased by controlling the flow of molten steel.

Optimal Control of Inclusions to Prevent “Sand-Hole” Surface Defects in Deep Cold-Drawn Battery Cups for Electrical Vehicles

The present work was conducted to elucidate the influence of inclusionson surface quality of deep cold-drawn battery cups for electrical cars. The obtained results revealed that, to prevent the surface defects of sand-holes in battery cups in deep cold-drawing process, attentions should be paid to steelmaking and casting process for optimal control of inclusions. Because sand-holes were often caused by large Al2O3 clusters and CaO-Al2O3 particles. Most important, a worthy finding was that these inclusions were not safe when they were over 100 μm and bigger than 27 μm, respectively, which was important for process optimization. By reducing (FeO) contents in ladle slag and tundish covering flux to about 5% or lower, together with optimal fluid flow of molten steel in tundish, such large inclusions can be well decreased to prevent the occurrences of sand-holes in battery cups in industrial production.

3D Numerical Modeling of Molten Steel Flow and Inclusion Transports During the Solidification Process of a Large Steel Ingot

3D Numerical Modeling of Molten Steel Flow and Inclusion Transports During the Solidification Process of a Large Steel Ingot

Surrogate-based Shape Optimization of Immersion Nozzle in Continuous Casting

In continuous casting, molten steel is fed from the tundish into the mold through the immersion nozzle. In the immersion nozzle, inclusions mainly composed of alumina present in the molten steel adhere and accumulate, it causes limitation of continuous castings. To prevent the nozzle clogging, Ar gas is blown into the immersion nozzle. However, Ar bubbles flow into the mold along with the molten steel and become trapped in the solidifying shell, causing bubbling defects of the slab. To suppress bubbling defects, it is effective to keep Ar bubbles away from the solidification interface or to use molten steel to wash away Ar bubbles that have adhered to the solidification interface. The molten steel flow in the mold is greatly affected by the shape of the immersion nozzle. In this paper, we consider the optimization of the shape of the immersion nozzle to reduce Ar bubbles trapped in the solidifying shell. A numerical model of molten steel flow and heat transfer solidification in the mold is combined with an optimization method. In the optimization process, Ar bubbles trapped in the solidifying shell are evaluated by a neural network to improve the calculation speed. The application of this method to the search for immersion nozzle shape is also reported, and the effectiveness of the obtained nozzle shape in reducing Ar bubbles is discussed.

Numerical Simulation of the Flow Field in an Ultrahigh-Speed Continuous Casting Billet Mold

Ultrahigh-speed continuous casting is a critical element in achieving high-efficiency continuous casting. In the present work, a three-dimensional model of a 160 mm × 160 mm billet ultrahigh-speed continuous casting mold was developed for use in studying the influences of different casting parameters on molten steel flow. The results showed that the flow pattern in the mold was not associated with its casting speeds, submerged entry nozzle (SEN) immersion depths, or inner diameters. Variation in casting speeds significantly affected the liquid level of the steel–slag interface. Its liquid level fluctuation was reasonable at an SEN immersion depth of 80 mm. Its impact depth reached the shallowest point, which was conducive to upward movement within high-velocity and high-temperature regions, and accelerated the floating of non-metallic inclusions. Expanding the inner diameter of the SEN could effectively weaken the initial kinetic energy of the jet. However, it may cause a deeper impact depth and a degree of upward movement in the raceway, which exhibited the shallowest impact depth in the jet and the most reasonable behavior of molten steel at a liquid level for which the inner diameter of the SEN was 40 mm.

CFD modelling of steel desulfurisation in a gas-stirred ladle

ABSTRACT Low sulfur content is crucial in secondary steelmaking to enhance steel quality. The desulfurization rate is influenced by slag-steel interactions, including slag eye size and interfacial mass transfer coefficient. Gas-stirred ladles can impact the interaction through stirring conditions such as argon flow rate and dual plug separation angle. Using a 3D CFD simulation model, the effects of different stirring conditions on the desulfurization rates, molten steel flow, and slag-steel interfacial behaviors were investigated. Results showed that 180° separation angle leads to higher desulfurization efficiency than 90°. A higher argon gas flow rate increases desulfurization rate, and using 20 SCFM (8.92×10-3 Nm3/s) argon flow rate for both plugs resulted in higher desulfurization rate than using 5 SCFM (2.23×10-3 Nm3/s) for one plug and 20 SCFM for the other. The smallest desulfurization efficiency was observed when using 5 SCFM for both plugs.

Effect of Mold Electromagnetic Stirring on Metallurgical Behavior in Ultrahigh Speed Continuous Casting Billet Mold

A three‐dimensional model of fluid flow, heat transfer, solidification, and inclusion motion in billet mold at ultrahigh casting speed under electromagnetic field is developed. The low Reynolds number k–ε model coupled with electromagnetic model and Lagrangian discrete phase model is used to investigate the flow field, temperature field, solidification, and inclusions transport under different current intensities. The results show that mold electromagnetic stirring (M‐EMS) significantly alters the flow pattern of molten steel. The impact depth of the molten steel decreases as the stirring current intensity increases, and the horizontal swirl intensities of the molten steel increase with the stirring current intensity. As the current intensity increases from 500 to 700 A, the impact depth decreases from 0.637 to 0.575 m and the maximum tangential velocity increases from 0.477 to 0.898 m s−1. When the stirring current is intense, the flow of molten steel near the mold exit is reversed, and the molten steel flows asymmetrically and unsteadily. The M‐EMS effectively improves the transverse heat transfer of the molten steel in the mold, contributing to the dissipation of the molten steel superheat and the growth of the solidified shell. In addition, the removal ratio of the inclusions is improved significantly.

Evaluation of Behavior of Continuous Bubbles Rising in a Gallium Alloy under Influence of Horizontal Magnetic Field by Using a High-speed Ultrasonic Tomography

In the continuous casting process, argon gas is injected into the tundish to homogenize the molten steel and remove the undesired inclusion. Furthermore, the molten steel flow is controlled by applying a magnetic field to the mold. The inclusion of argon gas as the molten steel flows into the mold can lead to product defects. Therefore, it is essential to predict the motion of the bubble in liquid metals under influence of the magnetic field, and further investigations are required for the liquid-metal two-phase flows. However, measurement techniques which can be applicable to opaque fluids such as liquid meat are limited. The authors have developed a high-speed ultrasonic tomography for measuring bubbles motion and investigated the behavior of continuously released bubbles motion in gallium alloy under influence of a horizontal magnetic field. The ultrasonic tomography measurements were carried out with 500 frames per second. It was shown that as the magnetic field strength increases, the variation of the bubble passing position in the measurement cross-section becomes smaller. Furthermore, it was confirmed that the distribution changed slightly depending on the direction of the applied magnetic field and that the bubbles tended to distribute in the direction perpendicular to the magnetic field. This trend changes depending on the difference in the gas flow rate. It is thought that the greater the influence of the wake, the more pronounced the anisotropy of the distribution.

Dual optimization of the geometric design and inductor parameters of the induction heating tundish based on numerical simulations

Based on the application of electromagnetism and hydrodynamics in metallurgy, the selection of the number of inductors as well as the direction of inductor current access is investigated for channel-type induction heating (IH) tundish with dual-channel (D-Ch), three-channel (T-Ch) and four-channel (F-Ch) tundish designs. The results show that when a single inductor is used, the Joule heat power (JHP) and electromagnetic force (EMF) are essentially the same within the two channels of the D-Ch tundish, but in the T-Ch tundish and the F-Ch tundish, the JHP and EMF of channel No.1 (Ch1) is much larger than other channels, which is extremely asymmetric. This will further be reflected in the influence on the flow and temperature consistency of the molten steel in the tundish. When a single inductor is used in the T-Ch or F-Ch tundish, the molten steel flow velocity in Ch1 is 4.2 and 7.4 times higher than that in the symmetric channel, respectively, and the temperature difference at the symmetric strand can be as high as 11 K or more. However, the maximum flow velocity of the molten steel in Ch1 and channel No.2 (Ch2) of the D-Ch tundish is 0.21 and 0.19 m⋅s−1, respectively, and the maximum temperature difference at the symmetrical strand is only 2.3 K. For the tundish with double inductors, the influence of the direction of the access current of the inductors should be taken into account. The inductors of a D-Ch tundish can effectively heat the molten steel only by accessing the same direction current. The physical fields in the intermediate and side channels are significantly different when the same or opposite current is accessed to the dual inductors of T-Ch tundish. The temperature rise rate of the molten steel is 36% higher when the dual inductors of the F-Ch tundish are accessed to the opposite current than when they are accessed to the same current. Therefore, a D-Ch design should be used for the channel-type tundish with a single inductor. And for the channel-type tundish with dual inductors, the same direction current should be accessed under the D-Ch design, and the opposite current should be accessed under the F-Ch design.

A New Insight into the Flow and Pressure Behavior of a Stopper Rod Flow Control System

A previously unnoticed anomaly is recently identified in a stopper rod flow control system for the continuous casting of steel by comparing full‐scale water model experiments with plant data. Despite extensive research previously done on the continuous casting fluid flow phenomena, this anomaly and its background physics are not well understood by researchers. Computational fluid dynamics (CFD) modeling of the molten steel flow in the stopper rod system is performed with predictions matching closely with water model data but deviating from plant measurements. It is thus suggested by this comparison that certain aspects of the liquid steel flow and pressure behavior in the stopper rod system cannot be effectively described by traditional modeling techniques due to their embedded limitations. Through water modeling, CFD simulations, plant measurements, and theoretical analysis, the current study for the first time presents a thorough discussion of this observed anomaly, which brings new insights into understanding the complex fluid flow behavior and pressure distributions inside the stopper rod control system during the continuous casting process.