In Situ Observation of the Agglomeration of MgO-Al2O3 Inclusions on the Surface of a Molten GCr15-Bearing Steel

In the current study, thermodynamic calculations and laboratory experiments were conducted to investigate the evolution of MgO-Al2O3 inclusions in a GCr15-bearing steel with varied Mg contents. Inclusions were transformed from Al2O3 to MgO-Al2O3 to MgO in the steel with the increase of Mg content from 3.9 to 61.0 ppm. The agglomeration of MgO-Al2O3 inclusions was in situ observed using the confocal scanning laser microscopy. With the increase of the MgO content in MgO-Al2O3 inclusions, the collision tendency of MgO-Al2O3 complex inclusions became weaker. The agglomeration attraction force of MgO-Al2O3 inclusions was calculated using Newton's second law, which was obviously related to the distance between inclusions and the type of inclusions. With the decrease of the distance between inclusions, the attractive force between Al2O3 inclusions increased from 1.0 x 10(-15) to 1.0 x 10(-13) N, while it was 1.0 x 10(-16) to 1.0 x 10(-14) N for MgO-Al2O3 complex inclusions and 1.0 x 10(-17) to 1.0 x 10(-15) N for pure MgO inclusions, respectively. 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 increase of the height difference. Based on the calculation of the simplified Kralchevsky-Paunov model and experimental results, the capillary attraction between inclusion pairs was Al2O3 > MgO-Al2O3 > MgO.

Automated summary

In this study, thermodynamic calculations and laboratory experiments were conducted to investigate the evolution of MgO-Al2O3 inclusions in a GCr15-bearing steel. It was found that the inclusions transformed from Al2O3 to MgO-Al2O3 to MgO with the increase of Mg content. The agglomeration of MgO-Al2O3 inclusions was observed, and the attraction force between inclusions was calculated.