In Situ Observation of Aggregation of Calcium Aluminate Inclusions at Steel/Ar Interface

In the current study, the aggregation of CaO-Al₂O₃ inclusions with different CaO contents at the steel/Ar interface was in situ observed using the confocal laser scanning microscope. The critical acceleration distance and attractive force during the inclusion aggregation process were measured and calculated, and effects of inclusion composition and radius on the aggregation of inclusions were analyzed. When the CaO content in CaO-Al₂O₃ inclusions in 16Mn steels increased from 3 to 51 pct, inclusions gradually changed from solid to liquid. Solid and partial liquid inclusions aggregated to form large clusters with a maximum diameter of 446.2 μm. When the CaO content in inclusions increased from 3 to 26 pct, the critical acceleration distance between inclusion pairs decreased from 104.9 to 62.1 μm, and the attractive force between inclusion pairs decreased from 1.0 × 10⁻¹⁶ N~1.0 × 10⁻¹³ N to 1.0 × 10⁻¹⁸ N~1.0 × 10⁻¹⁵ N. As the host inclusion radius increased from 5~15 to 25~35 μm, the critical acceleration distance increased from 104.9 to 166.6 μm. For liquid inclusions, when the CaO content in inclusions increased from 38 to 51 pct, the critical deceleration distance increased from 59.7 to 93.6 μm, and the repulsive force increased from 1.0 × 10⁻¹⁷ N~5.0 × 10⁻¹⁵ N to 1.0 × 10⁻¹⁷ N~1.0 × 10⁻¹³ N. The liquid inclusion overcame the repulsive force and aggregated, when the host inclusion radius was larger than 10 μm, and the initial velocity of the guest inclusion was faster than 150 μm/s. The calculated attractive force between inclusions was larger than the theoretical value calculated by Kralchevsky-Paunov model.