Numerical study on inclusion collision, coalescence and removal in an extra-thick slab continuous casting mold with M-EMS

Surface flaw detection is one of the main problems of extra-thick slab. In practice, it is considered that the application of mold electromagnetic stirring (M-EMS) is an effective means to reduce the inclusions located at the subsurface of thick slab. The present study conducted numerical studies on the inclusion transports in an extra-thick slab continuous casting mold with the effects of M-EMS. The influences of M-EMS on the inclusion collision, coalescence and removal were revealed. The predicted results indicate that the majority of inclusions entering the mold are smaller than 20 mu m. The application of M-EMS promotes the collision, aggregation, and flotation of these inclusions. When the inclusions entering the mold are larger than 30 mu m, the flotation removal of inclusions significantly increases, and the collision and aggregation among inclusions decreases accordingly. Furthermore, the predicted results show that inclusions larger than 200 mu m in size are unlikely to follow the downward flow into the lower region of the mold, with the primary removal location concentrated near the nozzle. Large-size inclusions have been quantitatively extracted from samples with and without M-EMS using galvanostatic electrolysis method. The results indicate that the inclusions of various sizes in the slab surface layer are reduced when M-EMS is employed. Notably, inclusions sized 50-150 mu m show the most significant reduction, with their mass density decreasing from 38.17 mg/10 kg to 15.11 mg/10 kg. This demonstrates a substantial reduction in large-size inclusions on the slab surface layer following the introduction of M-EMS in the mold.