Search Results (48)

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. Full article

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. Full article

As the third generation of thin slab continuous casting and rolling technology, endless strip production (ESP) has been widely used in the steelmaking industry. The key equipment in this process, the funnel-type mold, is prone to accidents such as slag entrainment, surface cracks and steel leakage under high casting speed conditions. To reduce the incidence of the above accidents, the numerical model of flow, heat transfer and solidification in the funnel-type mold is established by using the k-ε model, enthalpy–porosity method and magnetohydrodynamics (MHD), and the influence mechanism of the mold cavity and submerged entry nozzle (SEN) on the molten steel is studied, providing a new solution for optimizing the ESP process. The results show that compared with the type-I mold, the influence of the geometric disturbance of the top cavity on the flow state of the middle and lower body is localized, while the type-II funnel mold increases the thickness of the solidified shell at the outlet of mold; the marked enhancement in solidified shell thickness and uniformity at the mold exit achieved through the type-II SEN due to the distribution of temperature and velocity are more reasonable, reducing the risk of surface cracks and steel leakage. Full article

Based on a physical water model with a scaling factor of 0.5 and a coupled flow–heat transfer–solidification numerical model, this study investigates the influence of the submerged entry nozzle (SEN) depth on the mold surface behavior, slag entrapment, internal flow field, temperature distribution, and initial solidification behavior in slab casting. The results indicate that when the SEN depth is too shallow (80 mm), the slag layer on the narrow face is thin, leading to slag entrapment. Within a certain range of SEN depths (less than 170 mm), increasing the SEN depth reduces the impact on the mold walls, shortening the “plateau period” of stagnated growth on the narrow face shell. This allows the upper recirculation flow to develop more fully, resulting in an increase in the surface flow velocity and an expansion in the high-temperature region near the meniscus, which promotes uniform slag melting but also heightens the risk of slag entrainment due to shear stress at the liquid surface (with 110 mm being the most stable condition). As the SEN depth continues to increase, the surface flow velocity gradually decreases, and the maximum fluctuation in the liquid surface diminishes, while the full development of the upper recirculation zone leads to a higher and more uniform meniscus temperature. This suggests that in practical production, it is advisable to avoid this critical SEN depth. Instead, the immersion depth should be controlled at a slightly shallower position (around 110 mm) or a deeper position (around 190 mm). Full article

To achieve uniform cooling and effective homogenization control in ultra-large beam-blank molds necessitates the optimization of submerged-entry-nozzle (SEN) structures. This study employed computational fluid dynamic (CFD) modeling to investigate the impact of two-port and three-port SEN configurations on fluid flow characteristics, free-surface velocities, temperature fields, and solidification behaviors. Subsequently, integrating numerical simulations with the non-dominated sorting genetic algorithm II (NSGA-II) and metallurgical quality-control expertise facilitated the multi-objective optimization of a three-port SEN structure suitable for beam-blank molds. The optimized parameters enabled the three-port SEN to deliver molten steel to the meniscus at an appropriate velocity while mitigating harmful effects such as SEN port backflow, excessive surface temperature differences, and shell thickness reduction due to fluid flow. The results indicated that the three-port SEN enhanced the molten-steel flow pattern and mitigated localized shell thinning compared with the two-port SEN. Additionally, the optimized design (op2) of the three-port SEN exhibited reduced boundary layer separation and superior fluid dynamics performance over the initial three-port SEN configuration. Full article

Submerged entry nozzle (SEN) clogging will affect the production efficiency and product quality in the continuous casting process. In this work, the transient SEN clogging model is developed by coupling the porous media model defined by the user-defined function (UDF) and the discrete phase model (DPM). The effects of the transient SEN clogging process on the flow field, the distribution of argon gas bubbles and the fluctuation of the interface between steel and slag in the concave bottom SEN in the continuous casting slab mold with a cross-section of 1500 mm × 230 mm are studied by coupling transient SEN clogging model, DPM and volume of fluid (VOF) model. The results show that the actual morphology and thicknesses of SEN clogging are in good agreement with the numerical simulation results. The measurement result of the surface velocity is consistent with the numerical simulation result. With increasing the simulation time, the degree of SEN clogging increases. The flow velocities of molten steel flowing from the outlet of the side hole increase, because the flow space is occupied with the clogging inclusions, which leads to the increased number of argon gas bubbles near the narrow wall. The steel–slag interface fluctuation near the narrow walls also increases, resulting in the increased risk of slag entrapment. Full article

In this paper, the fluid flow, slag entrainment and solidification process in a slab mold were studied using physical modeling and numerical simulation. The effect of two types of submerged entry nozzles (SENs) was also studied. The results showed that the surface velocity for type A SEN was larger than that using type B SEN. For type A SEN, the maximum surface velocity was 0.63 m/s and 0.56 m/s, and it was 0.20 m/s and 0.18 m/s for type B SEN. The larger shear effect on the top surface made the slag at narrow face impacted to the vicinity of 1/4 wide face, while the slag layer at the top surface was relatively stable for type B SEN. Increasing the immersion depth of SEN decreased the surface velocity and slag entrainment. For type A SEN, the thickness of the solidified shell at the narrow face of the mold outlet was thin (12.3 mm) and there was a risk of breakout. For type B SEN, the liquid steel with high temperature would flow to the meniscus and it was beneficial to the melting of the mold flux. The thickness of the solidified shell at the narrow face of the mold outlet was increased. Furthermore, the surface velocity was also increased and it was not recommended for high casting speed. Full article

This work studies how the sliding-gate valve (SGV) modifies the features and the dynamic behavior of the outlet jets for flat-bottom and well-bottom bifurcated submerged entry nozzles (SENs) used in continuous casting machines. Three conditions for the SGV were studied: no obstruction, moderate obstruction, and severe obstruction. The experimental study used a scaled model, employing cold water as the working fluid. A high-frequency analysis of the flow inside the SEN’s bore arriving at the outlet ports was performed by employing the particle image velocimetry (PIV) technique. Low-frequency measurements of the volumetric flow at the exit port were obtained by splitting the exit jet into four quadrants and employing digital flowmeters. It was observed that reducing the SGV clearance increases the turbulence of the flow inside the SEN bore, but the flow displays ordered rather than erratic fluctuations. Flowmeter measurements showed that, regardless of the level of obstruction in the SGV, the outlet jets on flat-bottom and the well-bottom SENs have dynamic behaviors and features with significant differences. This finding is relevant because the flow distribution inside the outlet ports is directly related to the jet’s wideness, affecting the recirculation pattern inside the mold and, therefore, the quality of the finished steel slab. Full article

A three-dimensional model is established to investigate the effect of argon injection mode, argon flow rate and casting speed on the gas–liquid two-phase flow behavior inside a slab continuous casting mold. The Eulerian–Eulerian model is employed to simulate the gas–liquid flow, and the population balance model is applied to describe the bubble breakage and coalescence process in the mold. The numerical simulation results of the bubble size distribution are verified using the water model experiment. The results show that the flow field and bubble distribution are similar between the argon injection at the upper submerged entry nozzle (SEN) and tundish upper nozzle (TUN), while the number density is larger for the argon injection of TUN. The coalescence rate of bubbles and the bubble size inside the mold increase with increasing argon flow rate. When the argon flow rate exceeds 4 L/min, the flow pattern of liquid steel changes from double-roll flow to complex flow, with aggravation of the level fluctuation of the top surface near the SEN. When the casting speed increases, the bubble breakup rate increases and results in a decrease in the size of bubbles inside the mold. At a high casting speed, the flow pattern tends to form double-roll flow, and the liquid level at the narrow face of the top surface increases. Full article

Argon injection is usually applied in the continuous casting mold to prevent submerged entry nozzle (SEN) clogging. However, the stability of the slag–steel interface is affected by the injected gas, even leading to the formation of the slag eye. A computational fluid dynamics–discrete bubble model–volume of fluid (CFD-DBM-VOF) model is established to predict the argon–slag–steel–air four-phase flow in the continuous casting mold. The bubble behavior is treated with the Lagrangian approach considering bubble coalescence and breakup. The movement behavior of the slag–steel interface is analyzed with and without argon blowing, validated with the water model. The results show that the large bubble tends to float up into the slag–steel interface near the SEN with argon injection, resulting in fluctuations in the slag–steel interface near the SEN. The bubble distribution, flow field, fluctuation height of the slag–steel interface and configuration of the slag eye in the mold are analyzed. Furthermore, the effect on the casting speed, gas flow rate and thickness of the slag layer is obtained based on the result. The mathematical prediction results showcase a combination of well-established phenomena and newly generated predictions. Full article

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. Full article

In the current study, the transient flow characteristics on the top surface of a steel slab continuous casting strand were numerically investigated using a large eddy simulation combined with volume of fluid (LES + VOF) model. The validation of numerical simulation was verified via nail board measurement in the industrial continuous casting mold. The effects of casting speed on the top surface level profile and the instantaneous distribution of vortex were discussed. The level variation profile migrated after a period of time, moving from one side of the wide face of the mold to the other. The wave height and transient variation degree of the standing wave increased with an increase in the casting speed. The region near the SEN was more likely to promote the formation of vortices. The vortex generation became easier when the vorticity peaks were concentrated on the outer edge of the low-speed confluence area near the submerged entry nozzle. In addition, the effect of surface velocity on the instantaneous level fluctuation was analyzed. The frequency of level fluctuations was highest at 3~4 mm, and the high-frequency range of velocity fluctuation was 20~60 mm/s at 0.9 m/min casting speed for a 1500 mm × 200 mm caster section. The linear relationship between the level fluctuation and surface velocity magnitude was obtained. The present work aimed at evaluating the dynamic problem of the standing wave at the liquid powder–molten steel interface on the top surface of the mold, which is helpful in optimizing the casting parameters for regular casting practice and improving the quality of the steel slabs. Full article

A kind of composite magnetic field for flow control in slab mold is proposed, in which an electromagnetic stirring (EMS) is carried out near the meniscus and an electromagnetic braking (EMBr) is carried out near the outlet of the submerged entry nozzle (SEN), simultaneously. The yoke for the EMS and the EMBr is made independent from each other, with a ruler type for the EMBr. A three-dimensional model of the magnetic field calculation is established. The simulation results show that the magnetic induction intensity generated with the EMS mainly concentrates in the EMS area. The magnetic induction intensity generated with the EMBr has a large component in the EMS results, which has little effect on the flow of this area. Based on the composite magnetic field calculation results, the three-dimensional numerical simulation of the flow field is carried out, and the flow field obtained is compared to that without the magnetic field but with the EMS and the EMBr only, respectively. The results show that under the composite magnetic field, EMBr and EMS can play their respective roles well under certain conditions, the impact of the jet flow on the narrow face is reduced, and the stirring beneath the meniscus is intensified. Full article

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. Full article

Complex multi-phase phenomena, including turbulent flow, solidification, and magnetohydrodynamics (MHD) forces, occur during the continuous casting (CC) under the applied electromagnetic brake (EMBr). The results of the small-scale experiment of the liquid metal model for continuous casting (mini-LIMMCAST) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), investigating MHD flow with a deep immersion depth of 100 mm, are supplemented by newly presented numerical studies with the shallow position of the submerged entry nozzle (SEN) at 50 mm below the meniscus. Herein, the focus is on the MHD effects at the meniscus level considering (i) a fully insulating domain boundary, (ii) a perfectly conductive mold, or (iii) the presence of the solid shell. The volume-of-fluid (VOF) approach is utilized to model a Galinstan flow, including free surface behavior. A multiphase solver is developed using conservative MHD formulations in the framework of the open-source computational fluid dynamics (CFD) package OpenFOAM^®. The wall-adapting local eddy-viscosity (WALE) subgrid-scale (SGS) model is employed to model the turbulent effects on the free surface flow. We found that, for the deep immersion depth, the meniscus remains calm under the EMBr for the conductive and semi-conductive domain. For the insulated mold disregarding the SEN position, the self-inducing MHD vortices, aligned with the magnetic field, cause strong waving of the meniscus and air bubble entrapment for shallow immersion depth. Secondary MHD structures can form close to the meniscus under specific conditions. The influence of the EMBr and immersion depth on the flow energy characteristics is analyzed using power spectral density (PSD). Full article