Behavior of alumina-magnesia complex inclusions and magnesia inclusions on the surface of molten low-carbon steels

It is well known that alumina inclusions on the surface of molten Al-killed steel quickly attract each other to form clusters. On the other hand, alumina-magnesia complex inclusions on the surface of molten low-carbon steel with a high oxygen content have a much weaker tendency to form clusters. In the present work, the reason for the different behaviors of the two types of inclusions was analyzed in detail. A confocal scanning laser microscope was used to carry out the experiment of in-situ observation of the two types of inclusion on the molten pool. The first type of inclusion was 93 mass pct alumina-7 mass pct magnesian, obtained in a Mg-added Al-killed steel. The second type of inclusion was nearly pure magnesia, obtained in a Mg-killed steel. The attractive force between a pair of inclusions, for both cases, was found to be approximately 1O⁻¹⁷ to 10⁻¹⁶ N and one-tenth of that between a pair of alumina inclusions. The various effects of contact angle, surface tension, and oxygen content of the steel melt on the attractive force are discussed in detail from the viewpoint of the capillary force.