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The numerical methods based on the unsteady Reynolds-averaged Navier–Stokes (URANS) equations are robust tools to model the turbulent flow for the industrial processes. They allow an acceptable grid resolution along with reasonable calculation time. Herein, the URANS approach is validated against a water model experiment for the special single port submerged entry nozzle (SEN) design used in the thin slab casting (TSC) process. A 1-to-2 under-scaled water model was constructed, including the SEN, mold, and strand Plexiglas segments. Paddle-type sensors were instrumented to measure the submeniscus velocity supported by videorecording of the dye injections to provide both qualitative and quantitative verification of the SEN flow simulations. Two advanced URANS-type models (realizable k–ε and shear stress transport k–ω) were applied to calculate velocity pattern on meshes with various resolutions. An oscillating single jet flow was detected in the experiment, which the URANS simulations initially struggled to reflect. The dimensionless analysis of the mesh properties and corresponding adjustment of the boundary layers inside the SEN allowed to resolve the flow pattern. The performed fast Fourier transform (FFT) verified a good numerical prediction of the flow frequency spectrum. The corresponding simulation strategy is proposed for the industrial CC process using the URANS approach. [ABSTRACT FROM AUTHOR]

The surging demand for large high-quality rotor shafts or similar steel components in heavy industries (energy sector) poses new challenges to steelmakers. Based on the experience of conventional ingot and continuous casting, several new process concepts have been proposed, e.g., vertical continuous casting (VCC), semi-continuous casting (SCC), and segment casting (SC), but none of them are optimally put in operation. The main problems include the control of the as-cast structure and macrosegregation. Electromagnetic stirring (EMS) is necessary to obtain the center equiaxed zone, but EMS-induced multiphase flow can cause severe macrosegregation and uneven distribution of the as-cast structure between equiaxed and columnar. In this study, an advanced mixed columnar-equiaxed solidification model was used to investigate the formation of the as-cast structure and macrosegregation in an example of SCC with a large format (diameter 1 m). The main role of EMS is to create crystal fragments by fragmentation, which is regarded in this work as the only origin of equiaxed grains. The created equiaxed grains are brought by the EMS-induced (primary and secondary) flow and gravity-induced sedimentation to the central/lower part of the casting. The main goal of this study was to understand the solidification principle of SCC. In addition, a numerical parameter study by varying the EMS parameters was also performed to demonstrate the model capability towards the process optimization of SCC. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

Continuous casting (CC) is nowadays the world‐leading technology for steel production. The thin slab casting (TSC) is featured by a slab shape close to the final products and a high casting speed. The quality of the thin slabs strongly depends on the uniformity of the turbulent flow and the superheat distribution, defining the solid shell growth against a funnel‐shaped mold. In most studies, it is commonly assumed that the submerged entry nozzle (SEN) is properly arranged, and the melt inflow is symmetric. However, the misalignment or clogging of the nozzle can lead to an asymmetric flow pattern. Herein, the asymmetry is imposed via a partial SEN clogging: a) a local porous zone inside the nozzle reflects the presence of the clog material; b) the resistance of the clog is varied from low to high values. The solidification during TSC is modeled, including the effects of the turbulent flow. The variation of the flow pattern and the solidified shell thickness are studied for different permeability values of the SEN clogging. These effects are considered with and without the applied electromagnetic brake (EMBr) using an in‐house magnetohydrodynamics (MHD) and solidification solver developed within the open‐source package OpenFOAM. [ABSTRACT FROM AUTHOR]

A two‐phase solidification model coupling mold electromagnetic stirring (M‐EMS) is used to investigate the initial solidification in the mold region of billet continuous casting. One novelty of this numerical study is to quantify how the M‐EMS induces primary and secondary flows, interacting with the jet flows coming from the submerged entry nozzle, and how those flows further influence the dissipation of superheat and the initial solidification. The role of the M‐EMS in speeding up the superheat dissipation in the mold region, known from previous studies and casting practices, is quantitatively verified. Additionally, some new knowledge regarding the M‐EMS is found. The total heat transfer rate from the strand surface to the water‐cooled copper mold is not affected by the M‐EMS; with the M‐EMS, the superheat effect on the solid growth can only be detected in the out‐of‐the‐mold region, while the shell growth inside the mold region is quite independent of the superheat; a strong M‐EMS tends to accelerate the growth of the solid shell in the mold region, but delays its growth in the secondary cooling zones. The aforementioned new findings may only be valid for the case of the current billet casting, to be confirmed for other casting formats/parameters. [ABSTRACT FROM AUTHOR]

Electromagnetic stirring (EMS) has been recognized as a mature technique in steel industry to control the as-cast structure of steel continuous casting (CC), and computational magnetohydrodynamic (MHD) methods have been applied to study the EMS efficiency. Most MHD methods de-coupled the calculations of electromagnetic and flow fields or simplifications were made for the flow–electromagnetic interactions. However, the experimental validations of the MHD modeling have been rarely reported or very limited. In this study, we present a benchmark, i.e., a series of laboratory experiments, to evaluate the MHD methods, which have been typically applied for steel CC process. Specifically, a rotating magnetic field (RMF) with variable intensity and frequency is considered. First experiment is performed to measure the distribution of magnetic field without any loaded sample (casting); the second experiment is conducted to measure the RMF-induced torque on a cylindrical sample (different metals/alloys in solid state); the third experiment is (based on a special device) to measure the RMF-induced rotational velocity of the liquid metal (Ga75In25), which is enclosed in a cylindrical crucible. The MHD calculation is performed by coupling ANSYS Maxwell and ANSYS Fluent. The Lorentz force, as calculated by analytical equations, ANSYS Fluent addon MHD module, and external electromagnetic solver, is added as the source term in Navier–Stokes equation. By comparing the simulation results with the benchmark experiments, the calculation accuracy with different coupling methods and modification strategies is evaluated. Based on this, a necessary simplification strategy of the MHD method for CC is established, and application of the simplified MHD method to a CC process is demonstrated. [ABSTRACT FROM AUTHOR]

The clogging of the submerged entry nozzle (SEN) during the continuous casting of steel can be divided into two stages: the "early stage," when the initial layer of the clog covers the SEN refractory surface owing to chemical reactions, and the "late stage," when the clog layer continues to grow because of the deposition of non-metallic inclusions (NMIs). In this paper, a mathematical formulation is proposed for the build-up of the initial oxide. The chemical reaction mechanism is based on the work of Lee and Kang (Lee et al. in ISIJ Int 58:1257–1266, 2018): a reaction among SEN refractory constituents produces CO gas, which can re-oxidize the steel melt and consequently form an oxide layer on the SEN surface. The proposed formulation was further incorporated as a sub-model in a transient clogging model, which was previously developed by the current authors to track the late stage of clogging. The thermodynamics and kinetics of CO production, depending on the local pressure and temperature, must be considered for the sub-model of early-stage clogging. Test simulations based on a section of an actual industrial SEN were conducted, and it was verified that the clogging phenomenon is related to the SEN refractory, the chemical reaction with the steel melt, the local temperature and pressure, and the transport of NMIs by the turbulent melt flow in the SEN. The model was qualitatively validated through laboratory experiments. The uncertainty of some parameters that govern the reaction kinetics and permeability of the oxide layer is discussed. [ABSTRACT FROM AUTHOR]

Metallurgists are embroiled in a debate on the role of solidification in submerged entry nozzle (SEN) clogging during continuous casting of steel: does clogging originate from solidification, or does clogging cause the solidification? This study tries to clarify this debate. An enthalpy‐based mixture continuum model is used to simulate solidification in a clog structure. The 3D structure of the clog is reconstructed using X‐ray tomography images of an as‐clogged piece in an SEN, and is directly used in the numerical model. The flow and solidification in the open pores/channels of the clog structure are then calculated. The modeling results demonstrate that although solidification does occur deep in the clog structure as the melt flow is stopped, a gap remains between the solidification and clog fronts. This gap signifies an open‐channel clog region, and the clog structure in this region needs to be mechanically strong to withstand the impact of the melt flow; otherwise, fragmentation occurs. The study verifies that the solidification cannot occur before clogging if the molten steel has sufficient superheat and the SEN is properly preheated. A SEN made of an isolating refractory material can postpone the clogging, thereby extending its service life. [ABSTRACT FROM AUTHOR]

The electromagnetic brake (EMBr) is a well-known and widely applied technology for controlling the melt flow in the continuous casting (CC) of the steel. The effect of a steady (DC) magnetic field (0.31 T) in a CC mold is numerically studied based on the GaInSn experiment. The electrical boundary conditions are varied by considering a perfectly insulating/conductive mold or the presence of a conductive solid shell, which is experimentally modeled by 0.5 mm brass plates. An intense current density (up to 350 kA/m2) is induced by the EMBr magnetic field in the form of loops. The electric current loop tends to close either inside the liquid bulk or through the conductive solid. Based on the character of the induced current loop closures, the turbulent flow is affected as follows: (i) it becomes unstable in the insulated mold, forming 2D self-inducing vortex structures aligned with the magnetic field; (ii) it is strongly damped for the conductive mold; and (iii) it exhibits transitional behavior with the presence of a solid shell. The application of the obtained results for the real CC process is discussed and validated. [ABSTRACT FROM AUTHOR]

In order to demonstrate how CFD can help scientists and engineers to better understand the fundamentals of engineering processes, a number of examples are shown and discussed. The paper covers (i) special aspects of continuous casting of steel including turbulence, motion and entrapment of non-metallic inclusions, and impact of soft reduction; (ii) multiple flow phenomena and multiscale aspects during casting of large ingots including flow-induced columnar-to-equiaxed transition and 3D formation of channel segregation; (iii) multiphase magneto-hydrodynamics during electro-slag remelting; and (iv) melt flow and solidification of thin but large centrifugal castings. [ABSTRACT FROM AUTHOR]

Continuous casting (CC) is one of the most important processes of steel production; it features a high production rate and close to the net shape. The quality improvement of final CC products is an important goal of scientific research. One of the defining issues of this goal is the stability of the casting process. The clogging of submerged entry nozzles (SENs) typically results in asymmetric mold flow, uneven solidification, meniscus fluctuations, and possible slag entrapment. Analyses of retained SENs have evidenced the solidification of entrapped melt inside clog material. The experimental study of these phenomena has significant difficulties that make numerical simulation a perfect investigation tool. In the present study, verified 2D simulations were performed with an advanced multi-material model based on a newly presented single mesh approach for the liquid and solid regions. Implemented as an in-house code using the OpenFOAM finite volume method libraries, it aggregated the liquid melt flow, solidification of the steel, and heat transfer through the refractory SENs, copper mold plates, and the slag layer, including its convection. The introduced novel technique dynamically couples the momentum at the steel/slag interface without complex multi-phase interface tracking. The following scenarios were studied: (i) SEN with proper fiber insulation, (ii) partial damage of SEN insulation, and (iii) complete damage of SEN insulation. A uniform 12 mm clog layer with 45% entrapped liquid steel was additionally considered. The simulations showed that parasitic solidification occurred inside an SEN bore with partially or completely absent insulation. SEN clogging was found to promote the solidification of the entrapped melt; without SEN insulation, it could overgrow the clogged region. The jet flow was shown to be accelerated due to the combined effect of the clogging and parasitic solidification; simultaneously, the superheat transport was impaired inside the mold cavity. [ABSTRACT FROM AUTHOR]

Mold electromagnetic stirring (M-EMS) has been introduced into the continuous casting of steel billets to promote the formation of a central equiaxed zone; however, the formation mechanism of the equiaxed crystals and the effect of M-EMS on crystal transport are not fully understood. Currently, a three-phase volume average model was used to study the solidification in a billet continuous casting (195 mm × 195 mm). The modeling results showed that the main function of M-EMS in this type of billet casting is to promote superheat dissipation in the mold region, leaving the liquid core out of the mold region undercooled. Although both, heterogeneous nucleation and crystal fragmentation, are considered to be the origins of equiaxed crystals, M-EMS appeared to impact crystal fragmentation more effectively. A small portion of equiaxed crystals could be brought by the M-EMS induced swirling flow into the superheated zone (upper mold region) and remelted; most equiaxed crystals settled in the lower undercooled zone, where they continued to grow and form a central equiaxed zone. These simultaneous phenomena represent an important species/energy transport mechanism, influencing the as-cast structure and macrosegregation. Negative segregation occurred in the central equiaxed zone, positive segregation occurred at the border of the columnar zone, and a trail of negative segregation occurred in the subsurface region of the billet. Finally, parameter studies were performed, and it was found that the shielding effect of the copper mold, electrical isolation at the strand-mold interface, and relatively high electrical conductivity of the strand shell affect the M-EMS efficiency. [ABSTRACT FROM AUTHOR]