In situ observation of collision and aggregation behavior of inclusions at steel-argon interface by high-temperature confocal laser scanning microscope

This study employed a confocal laser scanning microscope (CLSM) to investigate collision and aggregation behavior of MgO-Al 2 O 3 , MgO, and CaO-Al 2 O 3 -MgO inclusions at the steel-argon interface. The experimental results indicated that at the steel-argon interface, both MgO-Al 2 O 3 and MgO inclusion pairs could aggregate to form irregular block-like structures or clusters. In contrast, CaO-Al 2 O 3 -MgO inclusion pairs exhibited mutual repulsion in addition to aggregation, ultimately existing predominantly in a spherical form. Following collision, the average size of inclusion increased by 0.49–0.77 μm. Based on experimentally back-calculated interaction forces, the attractive forces between MgO-Al 2 O 3 inclusion pairs (ranging from (8.00 ± 3.91) × 10 –18 to (1.97 ± 0.05) × 10 –16 N) were greater than those between MgO inclusion pairs ((3.11 ± 1.53) × 10 –18 to (3.71 ± 0.15) × 10 –16 N). Conversely, repulsive forces were observed between CaO-Al 2 O 3 -MgO inclusion pairs (ranging from (3.39 ± 0.47) × 10 –17 to (6.63 ± 0.13) × 10 –15 N). All these interaction forces intensified with decreasing distance between the inclusions. Theoretical analysis of collision mechanisms suggests that, in the CLSM bath under no-stirring conditions, the collision behavior of inclusions is co-dominated by Stokes collisions and Brownian collisions. Regarding the aggregation mechanism, as two inclusions approach each other prior to contact, capillary force governs the aggregation process and determines whether the inclusions exhibit mutual attraction or repulsion. When non-wetted solid inclusions come into contact and form a stable cavity bridge, the cavity bridge force becomes significantly higher than the capillary force and van der Waals force, establishing it as the dominant driving force for inclusion aggregation. The magnitude of this force increases with increasing inclusion radius and contact angle with the molten steel.