Original Article

Behavior of bubbles near narrow faces of the mold for slab continuous casting: an investigation based on detailed force analysis

¹ Key Laboratory for Ecological Metallurgy of Multimetallic Mineral (Ministry of Education), Northeastern University, Shenyang 110819, Liaoning, PR China
² School of Metallurgy, Northeastern University, Shenyang 110819, PR China

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Received: 3 September 2025
Accepted: 9 December 2025

Abstract

In the vicinity of solidification front adjacent to narrow face of the continuous casting mold, the relatively large gradients of velocity, temperature and concentration play a crucial role in the horizontal motion behavior of local (argon) bubbles, thus determining the quality of the cast slab. Based on force analysis of an individual bubble, it was first identified that the horizontal motion of bubbles at the narrow-face solidification front are mainly affected by the pressure gradient force and the Marangoni forces of temperature concentration, with the pressure gradient force (essentially governed by velocity gradient) being the most prominent one. After that, detailed physical fields as well as liquidus and solidus points of steel were obtained on the basis of numerical modeling and according to the significant difference in velocity gradients the slab mold was divided into three regions along the height direction: the upper recirculation zone, the impact zone, and the lower recirculation zone. Horizontal force analysis of bubbles in each zone was subsequently carried out. The results showed that in the upper and lower recirculation zones, the position where the resultant force of bubbles becomes zero approaches the liquidus point of steel, making it difficult for the narrow-face solidification front to capture the bubbles. In the impact zone, however, the position of zero resultant force is close to the solidus point, indicating that the probability of bubbles being captured by the narrow-face solidification front is enhanced drastically. Further industrial trials found that bubbles are mainly concentrated and captured within a range of 10–12 mm beneath the narrow face of each cast slab examined, which is highly consistent with the predicted range of the predicted solidus point position in the impact zone (i.e., the thickness of the shell is 9–12 mm). The current work provides a theoretical basis for predicting and controlling the distribution of subcutaneous bubbles beneath the narrow face of slab.