Gas injection through the submerged entry nozzle (SEN) into the continuous casting mold can be an effective approach for preventing SEN clogging and promoting the floatation of the non‐metallic inclusions. However, sometimes the exposed slag eyes due to gas injection appear on the top surface of the liquid slag layer, resulting in heat losses, re‐oxidation, and nitrogen pickup in the molten steel. An Eulerian multiphase‐flow model is developed to predict the argon‐steel‐slag three‐phase flow in a slab continuous casting mold. All the phases are treated based on Eulerian approach. The mathematical model is compared with the industrial observations and the water model experiments. Both of physical and numerical results reproduce the phenomenon of the high gas concentration at the SEN exit port. Most of the argon bubbles stay below the slag layer for quite long time because the slag blocks their floatation. Furthermore, the argon bubbles would gradually gather in a dense plume while escaping through the slag layer. Scattered argon exit spots are found at the top surface of slag layer. Two main locations of the exposed slag eye are found: 1) adjacent to the SEN; 2) at the mold's mid‐section at the position where a concentrated argon plume breaches through the slag layer. The near‐SEN exposed eye occurs under any of considered conditions. The one at the mid‐section is formed when the meniscus convex reaches a critical level, been dependent on the casting conditions.
Large eddy simulation (LES) of transient magnetohydrodynamic (MHD) turbulent flow under a single-ruler electromagnetic brake (EMBr) in a laboratory-scale, continuous-casting mold is presented. The influence of different electrically-conductive boundary conditions on the MHD flow and electromagnetic field was studied, considering two different wall boundary conditions: insulating and conducting. Both the transient and time-averaged horizontal velocities predicted by the LES model agree well with the measurements of the ultrasound Doppler velocimetry (UDV) probes. Q-criterion was used to visualize the characteristics of the three-dimensional turbulent eddy structure in the mold. The turbulent flow can be suppressed by both configurations of the experiment’s wall (electrically-insulated and conducting walls). The shedding of small-scale vortices due to the Kelvin–Helmholtz instability from the shear at the jet boundary was observed. For the electrically-insulated walls, the flow was more unstable and changed with low-frequency oscillations. However, the time interval of the changeover was flexible. For the electrically-conducting walls, the low-frequency oscillations of the jets were well suppressed; a stable double-roll flow pattern was generated. Electrically-conducting walls can dramatically increase the induced current density and electromagnetic force; hence they contribute to stabilizing the MHD turbulent flow.
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/m 2) 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.
The mushy zone and solid shell formed during solidification of a continuous casting are mostly uneven, and this unevenness of shell growth might lead to surface defects or breakout. One known example is the unevenness of shell growth at the impingement point between the jet flow (coming from submerged entry nozzle) and the solidification front. This phenomenon is primarily understood as the local remelting caused by the superheat of the melt, which is continuously brought by the jet flow towards the solidification front. A recent study of the authors [Metall. Mater. Trans. B, 2014, in press] hinted that, in addition to the aforementioned superheat-induced local remelting (1), two other factors also affect the shell growth. They are (2) the advection of latent heat in the semi-solid mushy zone and (3) the enhanced dissipation rate of energy by turbulence in the bulk-mush transition region. This paper is going to perform a detailed numerical analysis to gain an insight into the flow-solidification interaction phenomena. Contributions of each of the above factors to the shell formation are compared.
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