For the submerged entry nozzle (SEN) samples obtained during continuous casting of Ti-IF steels with different Ti contents, the characteristics of the SEN deposits were systematically studied using X-ray fluorescence, X-ray diffraction, and scanning electron microscope with energy-dispersive spectroscopy (SEM-EDS). The cleanliness of various Ti-IF steel slabs was analyzed using automatic scanning microscope, SEM-EDS, and oxygen/nitrogen analyzer. The experimental results show that the nozzle deposits for the Ti-IF steel with high Ti content can be divided into three layers. However, for the Ti-IF steel with low Ti content, it consists only of two layers. As the Ti content in the Ti-IF steel increases, the Ti element in the nozzle deposits aggregating significantly, and the cleanliness of Ti-IF steel slabs worsens gradually, and the possibility and severity of the nozzle clogging also increase accordingly. Therefore, two different clogging mechanisms for Ti-IF steels with various Ti contents were obtained in this paper.

Clogging mechanism of Al2O3–SiO2–C submerged entry nozzle during continuous casting of Al-killed steel

Slag entrainment within the mold is a significant cause of surface defects in continuously cast slabs. As a key component for controlling molten steel flow, the structure of the submerged entry nozzle directly influences the flow field characteristics and slag entrainment behavior within the mold. This paper employs a 1:4-scale water-oil physical model combined with numerical simulation to investigate the effects of elliptical and circular submerged entry nozzles on slag entrainment behavior in a wide slab mold under different casting speeds and immersion depths. High-speed cameras were used to visualize meniscus fluctuations and oil droplet entrainment processes. An alternating control variable method was employed to quantitatively delineate a slag-free "safe zone" and a "slag entrainment zone" where oil droplets fall, determining the critical casting speed and critical immersion depth under different operating conditions. The results show that, given the nozzle immersion depth and slag viscosity, the maximum permissible casting speed range without slag entrainment can be obtained, providing a reference for industrial production parameter control. The root mean square (RMS) of surface fluctuations was introduced to characterize the activity of the meniscus flow. It was found that the RMS value decreases with increasing nozzle immersion depth and increases with increasing casting speed, showing a good correlation with the frequency of slag entrainment. Numerical simulation results show that compared with elliptical nozzles, circular nozzles form a more symmetrical flow field structure in the upper recirculation zone, with a left-right vortex center deviation of less than 5%, resulting in higher flow stability near the meniscus and thus reducing the risk of slag entrainment.

To increase the casting speed of φ150 mm round billets, a 3D mathematical model is established to investigate the effects of casting speed, mold parameters, and electromagnetic stirring (M‐EMS) on molten steel flow and heat transfer. The results indicate that higher casting speeds deepen the impingement zone and enlarge the high‐temperature region, leading to thinner shells and higher surface temperatures. When casting speed rises from 2.2 to 2.6 m min −1 , mold level fluctuation amplitude increases from 0.652 to 2.013 mm, and surface flow velocity rises from 0.0247 to 0.0293 m s −1 . Using a submerged entry nozzle (SEN) with a 25 mm diameter shifts the high‐temperature zone upward, accelerates superheat dissipation, and enhances heat transfer to the mold wall. The velocity distribution of molten steel near the solidification front correlates positively with shell growth in the M‐EMS zone. Both shell uniformity and remelting index decrease with increasing current intensity of M‐EMS. Industrial trials on 20# steel show that center porosity and segregation are controlled at grade 0.5 or below. When the superheat exceeds 25 °C, the proportion of billets with center shrinkage cavities below grade 0.5 decreases from 84.62% to 65%, while the occurrence of core defects increases significantly.

Numerical Simulation of a Novel Submerged Entry Nozzle for High-Speed Continuous Casting Slabs

Manual process control of the continuous casting (CC) process is difficult due to the big number of influencing factors. During continuous casting, manual top-freezing controls must be carried out. Every manual performed mould control can affect the strand quality and even increase the risk of failure. Therefore, regular top-freezing controls are performed after a certain casting duration. However, top-freezing events between the regular controls cannot be detected and are a major risk for plant safety. In the RFCS (Research Fund for Coal and Steel) project RealTimeCastSupport, the aim of the research was the digitalisation and optimised control of continuous casting machines. A real-time support system was developed to predict quality-relevant top-freezing events and thus achieve improved control. This was reached by offline material tracking, synchronisation of data streams and statistical analysis by application of Big Data technologies, the development of a digital twin and the exploitation of various CC data and surface inspection to predict reliability of steel production. Results The following results were achieved: Identification of defect promoting scenarios by correlation of statistical results and surface defect detection.Realisation of an offline 3D digital twin of the mould with two different casting sizes, different geometries, and a varying immersion depth of the submerged entry nozzle (SEN), considering heat transfer, inert gas feeding, and solidification for parameter studies to identify the most influential factors in top-freezing as a defect promoting scenario. Input variables from the continuous casters were evaluated by CFD simulations and afterwards used to develop and train an online support system which was connected to the existing database in the plant. The system will be finetuned offline to internal specifications. This will further allow an optimized system with increased recall and precision parameter. The application of a real-time support system enables the prediction of top-freezing events during the whole casting process. Subsequently, this significantly increases the plant safety and offers to carry out top-freezing inspections in a more targeted manner in the future. This publication is part of a series of papers in the frame of the dissemination project METACAST.

A 1:3 scaled water model experimental system was established based on the similarity principle. High-speed cameras and particle image velocimetry were employed to capture bubble images, and ImageJ was used for image processing to extract bubble trajectories, size distribution, and gas volume fraction. The motion behavior of multi-sized bubbles in the continuous casting mold was systematically investigated. The experimental results indicate that the casting speed, flow rate, mold size, and slag layer all have significant effects on the movement and distribution patterns of multi-sized bubble-like flows within the mold. First, small bubbles exhibit a distinct fan-shaped flow pattern, whereas large bubbles remain confined near the submerged entry nozzle, rising almost vertically. Both casting speed and gas flow rate influence the strength of the upper recirculating flow, which in turn affects the spatial distribution and movement behavior of bubbles. Moreover, the width of the mold influences bubble trajectories by altering the jet impingement area. As the mold width increases from 1050 to 1750 mm, the trajectories of small bubbles gradually evolve into a fan-shaped flow. Consequently, fewer bubbles follow the downward flow into the deeper region of the mold, and the gas volume fraction decreases from 6.52% to 4.26%. In addition, due to its inherent viscous resistance and surface tension, the slag significantly suppresses the gas–liquid two-phase flow. As the slag thickness increases from 0 to 2 cm, the rising velocity of bubbles decreases, and the overall gas volume fraction drops from 5.29% to 2.62%.

Herein, a coupled three‐dimensional large eddy simulation model and volume of fluid model is established to systematically investigate the effect of the argon injection through single‐channel and multi‐channel stopper rods, casting speed, and argon flow rate on the molten steel flow, spatial distribution of bubbles, and jet characteristics of a bifurcated submerged entry nozzle (SEN). The comparison with the water model shows that the current model can accurately predict the bubble distribution in the SEN. The multi‐channel argon blowing makes the argon distribution more uniform and generates bubbles with smaller diameters and larger quantities. The average diameter of bubbles is 16.72 mm in the single‐channel blowing, while the average diameter of bubbles is 12.03 mm in the multi‐channel blowing. The dispersion degree of argon bubbles increases with the increase of casting speed. The jet speed and backflow speed increase with the increase of the casting speed, while the jet vertical angle and the proportion of the backflow zone decrease gradually. With the increase of the argon flow rate, the fluctuation of the backflow speed at the outport will also increase. The injection of argon has a significant impact on the jet characteristics at the outport.

Abstract In this study, effects of interface contact, adhesion, and reaction behavior between clogging and molten steel under different electric field conditions are studied using the most common aluminum‐killed steel clogging as research object. Results show that wettability between Al2O3 and molten steel is poor. However, formation of solidified steel and rough surface structure in aluminum‐killed steel clogging significantly influence wettability, which enhances formation and growth of clogging. Meanwhile, interfacial contact, wetting, and reaction behavior are controlled by electric field. Positive electric field enhances interfacial contact, reaction, and wettability, which exacerbate formation and growth of clogging on submerged entry nozzle (SEN). Conversely, negative electric field suppresses clogging growth, preserving SEN structure and ensuring stable continuous casting operations.

The pressure and flow rate of an argon line embedded within a stopper rod serve as useful industrial indicators and control factors for mitigating air aspiration into the Submerged Entry Nozzle (SEN) during the continuous casting of steel. This manuscript investigates several challenges associated with interpreting monitored argon line pressures and gas flow rates, including variations in gas pressure during delivery, actual volumes of gas entering the nozzle, argon leakage, and air aspiration. To address these issues, a new one-dimensional (1D) analytical model of compressible argon flow in the stopper rod was developed, incorporating gas dynamics and heat transfer. This concise 1D model was validated using data from a continuous casting simulator (CCS) employing a low-melting-point Bi-Sn alloy (melting point 137 °C). Pilot trials were conducted to replicate various industrial casting scenarios, generating datasets for model validation and demonstration of real-time operation. The 1D model predictions were compared with those from a CFD-based compressible flow model under CCS operating conditions. Following validation, parametric studies were conducted to explore realistic industrial scenarios (e.g., gas flow rate < 5 SLPM, nozzle diameter < 5 mm), including extreme conditions such as air aspiration and choking: a critical nozzle diameter (1.223 mm) corresponds to choked flow, limiting the maximum achievable gas flow rate to 5 SLPM. Additionally, the real-time prediction capabilities of the model were demonstrated using measured argon line pressures and flow rates from CCS trials. The proposed 1D model thus provides a practical tool for accurately interpreting SEN flow conditions from monitored argon pressures and effectively estimating argon bubble injection by clarifying actual gas pressures and flow rates at the stopper injection point.

BackgroundManual process control of the continuous casting (CC) process is difficult due to the big number of influencing factors. During continuous casting, manual top-freezing controls must be carried out. Every manual performed mould control can affect the strand quality and even increase the risk of failure. Therefore, regular top-freezing controls are performed after a certain casting duration. However, top-freezing events between the regular controls cannot be detected and are a major risk for plant safety.MethodsIn the RFCS (Research Fund for Coal and Steel) project RealTimeCastSupport, the aim of the research was the digitalisation and optimised control of continuous casting machines. A real-time support system was developed to predict quality-relevant top-freezing events and thus achieve improved control. This was reached by offline material tracking, synchronisation of data streams and statistical analysis by application of Big Data technologies, the development of a digital twin and the exploitation of various CC data and surface inspection to predict reliability of steel production. Results The following results were achieved:Identification of defect promoting scenarios by correlation of statistical results and surface defect detection.Realisation of an offline 3D digital twin of the mould with two different casting sizes, different geometries, and a varying immersion depth of the submerged entry nozzle (SEN), considering heat transfer, inert gas feeding, and solidification for parameter studies to identify the most influential factors in top-freezing as a defect promoting scenario. Input variables from the continuous casters were evaluated by CFD simulations and afterwards used to develop and train an online support system which was connected to the existing database in the plant. The system will be finetuned offline to internal specifications. This will further allow an optimized system with increased recall and precision parameter.ConclusionsThe application of a real-time support system enables the prediction of top-freezing events during the whole casting process. Subsequently, this significantly increases the plant safety and offers to carry out top-freezing inspections in a more targeted manner in the future. This publication is part of a series of papers in the frame of the dissemination project METACAST.

Effects of Submerged Entry Nozzle Parameters on Fluid Flow, Heat Transfer, and Solidification in High-Speed Continuous Casting Slab Mold

The formation mechanism of black streak defects in hot-rolled steel sheets was investigated to address the influence of the process parameters on the surface quality during the production of 304 stainless steels. Macro-/microstructural characterization revealed that the defect regions contained necessary mold slag components (Ca, Si, Al, Mg, Na, K) which originated from the initial stage of solidification in the mold region of the continuous casting process, indicating obvious slag entrapment during continuous casting. On this basis, a three-dimensional coupled finite-element model for the molten steel flow–thermal characteristics was established to evaluate the effects of typical casting parameters using the determination of the critical slag entrapment velocity as the criterion. Numerical simulations demonstrated that the maximum surface velocity improved from 0.29 m/s to 0.37 m/s with a casting speed increasing from 1.0 m/min to 1.2 m/min, which intensified the meniscus turbulence. However, the increase in the port angle and the depth of the submerged entry nozzle (SEN) effectively reduced the maximum surface velocity to 0.238 m/s and 0.243 m/s, respectively, with a simultaneous improvement in the slag–steel interface temperature. Through MATLAB (version 2023b)-based reverse optimization combined with critical velocity analysis, the optimal mold slag properties were determined to be 2800 kg/m3 for the density, 4.756 × 10−6 m2/s for the kinematic viscosity, and 0.01 N/m for the interfacial tension. This systematic approach provides theoretical guidance for process optimization and slag design enhancement in industrial production.

Interface behavior between the molten steel and submerged entry nozzle controlled by using an external electric field

Study on interfacial reaction between Al2O3-C / ZrO2-C submerged entry nozzle and molten steel with La-Ce alloy

In order to enhance the liquid surface activity in ultra-wide slab mould with a cross-sectional dimension of 2920 mm × 150 mm (with a width-to-thickness ratio of nearly 20), this study established a two-phase flow model for steel and liquid slag, comparing and analysing the effect of submerged entry nozzle (SEN) inclination angle on both the flow field and temperature field within the mould. The primary findings indicated that at a nozzle angle of 15°, the upward reflux was weak, resulting in a liquid surface velocity below 0.23 m/s, slow renewal of molten steel, which were not conducive to the melting of the mould flux. To improve both liquid surface activity and the melting and flow of the mould flux, the nozzle angle was reduced from 15° to 10°. This adjustment allowed the maximum liquid surface flow velocity to reach 0.35 m/s, thereby enhancing liquid surface activity and facilitating greater energy transfer to the liquid surface. The uniform distribution of heat-flux density around the mould further demonstrated that reducing the nozzle angle significantly enhances liquid surface activity. However, when the nozzle angle was further decreased to 5°, strong upward reflux was observed, resulting in the adjacent slag layer being washed away to one-quarter of the mould's width, which increased the risk of slag entrapment and exposure at the corners. Given the large width-to-thickness ratio of the ultra-wide slab mould, the flow jet from the submerged nozzle was prone to early collided with the wide surface during its movement towards the narrow surface. This interaction leaded to a reduction in kinetic energy, weaker upward reflux, lower heat flux near the liquid surface, and larger fluctuations in heat flow distribution along the mould's width. This study illustrates that appropriately reducing the nozzle angle can mitigate these adverse conditions and provides a theoretical foundation for selecting SENs for ultra-wide slab moulds.

To extend the antierosion properties of submerged entry nozzle and enhance the fluidity of fluorine‐free slag, the present study examines the effects of an applied electric field on the wetting behavior between fluorine‐free slag and slag‐line refractories, as well as on the erosion of slag‐line refractories by fluorine‐free slag. The results indicate that the applied electric field alters wettability by influencing the dissolution and the interfacial reaction between the slag‐line refractories surface and the fluorine‐free slag. Under a positive electric field, the dissolution and interfacial reaction between the slag‐line refractories surface and the fluorine‐free slag is enhanced, reducing the apparent contact angle to ≈40° at 20 V. Conversely, under a negative electric field, the dissolution and interfacial reaction are inhibited, resulting in an apparent contact angle of about 54° at 20 V, which is roughly 14° higher than under the positive electric field. Applying an electric field not only protects the slag‐line refractories from erosion (with an erosion rate of just 0.09% under a negative electric field) but also improves the fluidity of the fluorine‐free slag. This improvement is due to the bond‐breaking of the SiOSi structure and the pulsed oscillation effect in the fluorine‐free slag.

During the continuous casting process, the submerged entry nozzle (SEN) should be maintained at the geometric center of the mold. However, in actual production, factors such as deformation of the tundish bottom and inaccurate positioning of the traversing car occasionally cause SEN offset. SEN offset can make the molten steel flow field in the mold asymmetric, increasing the risks of slag entrainment on the surface of the casting blank and breakout accidents. To evaluate the influence of different SEN offsets on the mold flow field, this study uses a slab continuous casting mold with a cross-section of 920 mm × 200 mm from a specific factory as the research object. Mathematical simulations were used to investigate the influence of SEN offsets (including width-direction and thickness-direction offsets) on the flow behavior of molten steel in the mold. A physical water model at a 1:1 scale was established for verification. Two parameters, the symmetry index (S) and the bias flow index (N), were introduced to quantitatively evaluate the symmetry of the flow field, and the rationality of the liquid-level fluctuation under this flow field was verified using the F-number (proposed by Japanese experts for mold level fluctuation control) from the index model. The results show the following: when the SEN offset in the thickness direction increases from 0 to 50 mm, the longitudinal symmetry index (Sy) of the molten steel flow field in the mold decreases from 0.969 to 0.704—a reduction of 27.4%; the longitudinal bias flow index (Ny) of molten steel level fluctuation increases from 0.007 to 0.186, representing a 25.6-fold increase, and the F-number rises from 4.297 to 8.482; when the SEN offset in the width direction increases from 0 to 20 mm, the transverse-axis symmetry index (Sx) of the flow field decreases gradually from 0.969 to 0.753 at a 20 mm offset, which is a reduction of approximately 22.29%; the transverse-axis bias flow index (Nx) increases from 0.015 to 0.174 at a 20 mm offset—an increase of 10.6 times; and the F-number increases from 4.297 to 5.548. Considering the comprehensive evaluation of horizontal/vertical symmetry indices, bias flow indices, and F-numbers under the two working conditions, the width-direction SEN offset has the most significant impact on the symmetry of the molten steel flow field.

The failure of the submerged entry nozzle (SEN) during continuous casting of Ti‐bearing ultra‐low carbon steel is studied experimentally based on morphological analysis and related thermodynamic calculations. The types of inclusions in molten steel have been discussed, and the failure mechanism has been studied in detail. The results show that the carbothermic reaction of SiO 2 and graphite and the formation of pores promote the adhesion of Al 2 O 3 inclusions in the inner wall. The clogging can be divided into: dense clogging, solidified steel, and loose clogging. Among them, the initial clogging is caused by the decarburization. Large‐size inclusions fall off from the loose clogging and enter the mold, which deteriorates the slab quality. The inclusions in the slab are mainly composed of TiN‐wrapped Al 2 O 3 , TiN‐bearing Al 2 O 3 , and Al 2 O 3 . With the further increase of the size of Al 2 O 3 , the inclusions in the slab are mainly Al 2 O 3 . To improve the service life of the SEN, suggestions of optimizing the refining process, changing the position of slag‐line erosion, and adopting carbon‐free SEN are given. Additionally, applying electric field may help as well.

In thin slab continuous casting, argon injection is commonly employed to prevent nozzle clogging. However, the bubbles significantly influence the flow field, interface fluctuations, and slag entrainment within the mold. Notably, bubble entrapment at the solidification front may induce quality defects in cast slabs. In this study, a numerical model combining Large Eddy Simulation (LES), Volume of Fluid (VOF), and two-way coupled Discrete Phase Model (DPM) was established, along with a force balance model-based bubble capture criterion, to investigate the internal transient multiphase flow behavior under varying argon injection rates. The results reveal that argon bubbles form vortical structures near the Submerged Entry Nozzle (SEN), constraining flow space in the upper recirculation zone. In the lower recirculation zone, small bubbles generate multiple small vortices through alternating buoyancy and drag forces. While increased argon flow rate elevates absolute bubble entrapment quantity, the relative proportion remains unaffected. Furthermore, argon flow rate substantially impacts interface fluctuation amplitude and slag entrainment. Crucially, the analysis demonstrates that 99% of bubbles and all entrapped slag inclusions are concentrated within 23 and 17 mm below the slab surface, respectively, with argon flow rate exhibiting negligible impact on inclusion entrainment depth. This study enhances understanding of multiphase interaction about molten steel, slag, and argon bubbles, while providing data-driven insights for optimizing trimming strategies in industrial production and a recommended upper limit for argon injection flow rate.