Observation on Physical Growth of Nonmetallic Inclusion in Liquid Steel During Ladle Treatment

The behaviors of several types of inclusions at a high temperature were examined using a confocal scanning laser microscope (CSLM, 1LM21H/SVF17SP). Although alumina inclusions tended to impact on each other, agglomerate, and grow quickly, no other inclusion type, such as spinel as well as solid and liquid calcium aluminate, was observed to attract each other. The results of confocal microscope study were compared with the industrial investigation. For this purpose, many steel samples were taken at different stages of ladle treatment. The samples were analyzed by scanning and light optical microscopes. Approximately 50,000 inclusions of several types were examined. Only alumina inclusions were attracted to each other and agglomerate. No agglomeration by attractive behavior was observed in the other types of inclusions, including liquid inclusions. Both the industrial data and the in situ observation by CSLM indicate that, although the attraction force and the agglomeration play a significant role in the growth of alumina inclusions, the agglomeration of spinel and calcium aluminate inclusions does not need special consideration in ladle treatment. The agglomeration of liquid calcium aluminate inclusions took place only when they occasionally met as a result of external force, which led to low collision probability. However, the agglomeration of the liquid calcium aluminate inclusions along with alumina particles could be detrimental in the casting process.