Evolution and Influence of Flow Field Affected by Coupled Swirling Flows in Round Billet Mold

Abstract

The quality of round billet is affected by the flow characteristics of molten steel during continuous casting. The application of nozzle swirling flow combined with electromagnetic stirrer (M-EMS) can increase the number of equiaxed crystal and alleviate macrosegregation, which has been demonstrated in our previous industrial test. However, flow field cannot be visually observed in industrial tests. In this paper, for the first time, the evolution of flow field and its influence on the macrosegregation and liquid level fluctuation under the action of coupled swirling flows were studied. Compared with that by using only mold stirring, the flow field was distributed more symmetrically in the upper part of mold and its impact depth decreased from 350 mm to 246 mm when the rotating speed of stirring propeller was 70 r/min. The centerline segregation level was reduced owing to the inward flow weakened by the outward nozzle swirling flow. Additionally, the tangential velocity at 1/2 radius near the surface was decreased from 0.589 m/s to 0.469 m/s, leading to the reduction of liquid level fluctuation. Consequently, both the internal quality and the surface quality can be improved by coupled swirling flows, provided that the rotating intensities of nozzle swirling flow and M-EMS are selected properly in the actual continuous casting production.