In-Situ Observation of Collision and Agglomeration of La₂O₃–La₂S₃ Inclusions on Surface of Molten 304 Stainless Steels

In the current study, thermodynamic calculations and laboratory experiments were conducted to investigate the evolution of inclusions in a 304 stainless steel with varied lanthanum contents. A thermodynamic database of rare earths elements was established. The agglomeration and collision behavior of inclusions in steel with different La contents were in-situ observed by the high-temperature confocal scanning laser microscope (CSLM). As the distance between inclusions decreased, the critical acceleration distance of La₂O₃–La₂S₃–Al₂O₃–SiO₂ inclusions with the La content of 32 ppm was 50 μm, which was larger than the critical distance for La₂O₃–La₂S₃–Al₂O₃ inclusions in steel with 140 ppm La and La₂O₂S inclusion in steel with 230 ppm La. The attraction force range of La₂O₃–La₂S₃–Al₂O₃–SiO₂ complex inclusions was 1.0 × 10⁻¹⁶ to 5.0 × 10⁻¹⁵ N, which was stronger than 1.0 × 10⁻¹⁷ to 5.0 × 10⁻¹⁶ N for La₂O₃–La₂S₃–Al₂O₃ inclusions and 1.0 × 10⁻¹⁸ to 1.0 × 10⁻¹⁶ N for La₂O₃–La₂S₃ inclusions. The increase of La content in steel retarded the agglomeration and collision of inclusions. The height difference of the molten steel around the inclusion pushed two inclusions closer. The impelling effect of the molten steel on inclusions became stronger with the larger height difference.