Magnetohydrodynamic Phenomena, Fluid Control and Computational Modeling in the Continuous Casting of Billet and Bloom

Abstract

Magnetohydrodynamic flow phenomena with electromagnetic stirring were studied in billet casting. Solidification microstructure and oscillation marks were also investigated. EMS with 310 A current was proven to increase central equiaxed zone from 10-15% in unstirred billet to over 45% in stirred billet for steel grade 40CrMo4. Dendritic microstructures at the billet corners were found to deflect downwards due to the sustained upward flow along the mould corners. Rhomboidity was observed to relate to the unsteady flow in the mould during changes of casting speed and EMS intensities. Computational modeling was performed and validated with the results obtained from the casting experiments. Through modeling, a declining phenomenon of the injected stream from the SEN was observed towards the back wall under certain stirring intensities. This would influence thermal distribution of the strand shell and casting qualities, thus requiring correct matching of the vertical shear flow field with the horizontal rotation flow in order to obtain a favorable flow field. In addition, vortexes were found on the free surface around the SEN tube, which were influential to the cleanliness of steel melt. Modeling was also performed for a bloom caster with various SEN designs in the context of cleanliness. It was found that ported SENs showed obvious advantage on inclusion removal over the straight bore SEN. Reducing casting speed is actually an effective way to improve cleanliness. Casting trials with 65 bloom casting heats verified the modeling results and remarkable improvement in cleanliness was observed by using a 2-port SEN.

Numerical Simulation on Multiple Physical Fields Behaviors in Billet Continuous Casting with Different Stirrer Positions

“…Figure 9 quantitatively describes the removal ratio of inclusions. It is noted that the highest point of steel/slag interface appears at the corner of mold, and its lowest point is adjacent to the submerged entry nozzle, which is in line with the results of Wang et al [16] This phenomenon is attributed to the flow pattern of upper circulation flow. [8] In this Figure, when the stirrer center position is moved from Y ¼ 515to Y ¼ 815 mm, the removal ratio of inclusions with size of 5 μm increases from 43.9% to 63.6%, and that of 60 μm increases from 52.5% to 76.0%.…”

“…[8,10,16] Governing equations c) In this study, the electromagnetic phenomenon is assumed to be a magneto quasi-static problem, and the time averaged electromagnetic force is applied.…”

“…Geng et al [11] conducted a 3D numerical simulation in a round billet continuous casting with M-EMS. Some researchers [16][17][18][19] also pointed out that M-EMS could aggravate the mold-level fluctuation, thus increasing the probability of slag entrapment. The studies by Li et al, Ren et al, and Trindade et al [12][13][14][15] proved that the M-EMS promoted the superheat dissipation of molten steel, and the increasing current intensity could further reduce the temperature of molten steel.…”

Numerical Study on the Capture of Large Inclusion in Slab Continuous Casting with the Effect of In-mold Electromagnetic Stirring

“…41) The steel samples under the same process parameters used in the present work have been taken in a steel plant. The composition of the non-aqueous electrolyte is 99% ethanol and FeCl 3 . Figure 14 shows the device used in this method.…”

“…[3][4][5] Stirring the molten steel in the specific region of the mold is generally used to change the flow pattern. Besides, the flow pattern affects the inclusion capture and the molten steel's solidification in the mold.…”