A Model Study on Collision–Coalescence, Transport, and Removal Behavior of Non-metallic Inclusions in a Single-Strand Tundish

A computational fluid dynamics-population balance model-boundary transfer model (CFD-PBM-BTM) coupled model was developed to predict the dynamic change behaviors of inclusions in molten steel. Brownian collision, turbulent collision, and Stokes collision were used to describe the collision–coalescence of inclusions in molten steel. Moreover, three boundary transfer models, namely ideal removal model, Stokes removal model, and Fan-Ahmadi removal model, were adopted to calculate the removal rate of inclusions at the steel/slag interface. The results show that inclusion size and number density distribution predicted by the developed model, with the Flint-Howarth coalescence probability sub-model, Fan-Ahmadi removal sub-model, were in good agreement with the industrial measurements. The deviation of model predictions with 21 inclusion size groups was only around 9 pct from industrial measurements. Turbulent collision was found to significantly affect the collision–coalescence rate of small size inclusions. For inclusions larger than around 10 μm, Stokes collision becomes critical and the Stokes collision rate can reach 1×10^-13 m³/s for the collision between 24.3 and 42.5 μm inclusions. In addition, the inclusion removal ratio in the pouring region was about 50 pct of that in the casting region. This is due to the impinging steel flow effect on inclusion moving. As inclusion diameter increased from 1.1 to 42.2 μm, the removal rate increased from 1.4×10^-4 to 7.7×10⁻⁴ m/s. Furthermore, the inclusion removal rate increased with an increased steel/slag interface roughness. Specifically, the total removal ratio of 1.1, 10.6, 24.3, and 42.2 μm inclusions was 0.1, 3, 14, and 42 pct for the roughness value of 0 mm, respectively. The ratio increased to 7, 10, 21, and 50 pct, respectively, when the roughness value was 1 mm.

Graphical Abstract