Control of macrosegregation at the steel gradient transition by submerged entry nozzle and mold electromagnetic stirring

Abstract

The limited demand for specialty steel grades, which cannot meet the production quantity of a single-casting sequence in the continuous caster, is addressed through steel grade transition. This study aims to reduce the length of transition blooms generated during the steel grade transition by controlling macrosegregation in the bloom. A three-dimensional numerical simulation of the steel grade transition has been established based on models involving fluid flow, solidification, heat transfer, electromagnetic, and mass transfer. This study takes into account macrosegregation phenomena in the transition bloom that were not considered in previous research. The findings indicate that using a four-port submerged entry nozzle (SEN) and deactivating the mold electromagnetic stirring (M-EMS) can mitigate subcutaneous negative segregation, resulting in shorter transition blooms. The optimal configuration reduces the length of transition blooms by 4.3 m compared to the worst-case scenario. While lowering the casting speed can reduce center segregation, it also extends the mixing time of solute elements in the molten steel. These combined effects lead to a slight increase in the length of the transition bloom, from 10.88 m to 12.41 m. Therefore, for steel grade transition, utilizing a four-port SEN and deactivating the M-EMS can minimize the length of transition blooms, without the need to alter casting speed.