Multiphase Simulation on the Collision, Transport, and Removal of Non-metallic Inclusions in the Molten Steel During RH Refining

The initial size distribution of inclusions in the molten steel during the Ruhrstahl-Heraeus (RH) refining was investigated through an industrial trial. A three-dimensional numerical model for the steel-argon multiphase fluid flow and the collision, transport, and removal of inclusions in the steel was established to simulate the evolution of inclusions during the RH refining. The particle-size-grouping (PSG) method was applied to evaluate the collision of inclusions, which divided inclusions into sixteen groups with a volume ratio of 2.5 between adjacent groups. Detected inclusions were mostly Al2O3 in aggregations or clusters. The initial number density of inclusions with diameter less than 1 mu m was closed to 1 x 10(15) #/m(3), while that with diameter greater than 10 mu m was less than 1 x 10(10) #/m(3). The calculated total oxygen content in the steel dropped from 251 to 93 ppm in approximately 10 minutes and was 14 ppm after refining for 1800 seconds which agreed well with measured ones. The removal fraction of inclusions increased with the refining time, while the removal rate showed a decrease. The removal fraction was larger than 90 pct at 1800 seconds, indicating a high efficiency of the RH refining in removing inclusions. After 300 seconds of collision, the number density of small inclusions with diameter less than 2.5 mu m declined apparently from 10(13) to 10(15) #/m(3) to 10(12) #/m(3). The distribution of inclusions and the total oxygen content in the steel was position-dependent. Due to the removal condition at the steel surface in the ladle, the number density of inclusions and the total oxygen in the steel near the steel surface and near the zone between two snorkels in the ladle had a minimum value, while that near the side wall of the ladle showed a relatively higher value. The gradient of the T.O content in the cross section near the free surface of the ladle was relatively large, around 15 ppm on the side and less than 2 ppm in the center.