No abstract

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.

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.

The drawback of LES model is the long calculation time. Therefore, for general purpose to estimate the dynamic behavior of NMI in ICF both k-ω SST and LES are recommended. For the precise calculation of the motion of NMI smaller than 10 µm only LES model is appropriate. IntroductionUnderstanding the turbulent flow and other transport phenomena, like dissolution of alloying elements and removal of non-metallic inclusions in induction crucible furnace (ICF) is one of the important subjects in steel metallurgy. The flow pattern in the melt is mainly governed Lorentz force. The interaction between the induced electrical current and magnetic field results in Lorentz force acting on the bulk melt in the direction towards the center of crucible. Typically two or more eddies with turbulent pulsations between them might form [1]. This phenomenon has been subject of various researches [2][3][4][5].Jardy et al.[6] carried out experimental and theoretical study to characterize the hydrodynamic behavior and the transport of dissolved elements in the molten steel in vacuum induction furnace. 2D simulation using k-ε turbulence model, with a standard set of constants, showed adequate results [7,8]. Nevertheless, in spite of the k-ε results demonstrating highest values of turbulent kinetic energy in the eddy centers and the lowest between the eddies, the experimental results showed that the maximum of the turbulent energy is between the vortices of the averaged flow and close to the wall of the crucible [5,9]. Umbrashko et al. [5] simulated turbulent flow in an induction furnace for a low melting temperature metal and compared averaged with non-averaged Navier Stokes models. Their study revealed that the low-frequency velocity oscillations play the major role in the convective heat and mass transfer when flow structure contains two or more large vortexes of the mean flow. Therefore, they concluded that the Large Eddy Simulation (LES) model is more reliable in the melt agitation in the induction furnace.

A transient numerical model was proposed and validated by the current authors for nozzle clogging (Barati et al. in Powder Technol 329:181-98, 2018). The model can reproduce the experiment in pilot scale satisfactorily. In the present article, the main objective is to validate the model for application in industry process continuous casting of steel, referring to the model accuracy and calculation efficiency. The results have shown that for the complex geometry of submerged entry nozzle (SEN), where it is difficult to create hexahedron mesh in the entire domain, a mixed mesh type is recommended, i.e., the wedge mesh for regions adjacent to SEN walls and the tetrahedron mesh for inner regions. Another challenge to the calculation of real SEN clogging is the huge number of particles involved in the industry process. An artificial factor, the N-factor, has to be introduced to reduce the calculation cost. A dimensionless number (a) is defined to limit the N-factor and ensure the modeling accuracy. Simulation of a test case has indicated that by an appropriate N-factor (1000, corresponding to a = 6 9 10 À5), the calculation time would be reduced significantly to a reasonable time.