Behavior of Alumina Inclusions Just after Deoxidation

Abstract

Many efforts have been made to remove nonmetallic inclusions from molten steel, however, the required level of steel cleanness from steel users has become stricter year by year. Not only the way of removing the inclusions but also the way of keeping the inclusion size small are considered effective countermeasures for meeting the users' demand. Hence, it is important to investigate control factors governing the size distribution of inclusions in steel. From the viewpoint described above, the initial size distribution of alumina inclusions just after deoxidation reaction in steel has been studied by using a new sampling method with varying aluminum and oxygen contents in laboratory scale experiment. Two kilograms of steel was melted in a Tammann furnace at 1 873 K under an Ar gas atmosphere, then the carbon and oxygen concentrations were adjusted. The sampling method that enables to take a steel sample just after the addition of aluminum was used. The size distribution of alumina inclusions in steel samples was measured by using an electron probe micro analyzer with LaB₆ filament of an electron beam gun and with newly developed software for particle analysis. The result showed that the size distribution of alumina inclusions was affected by oxygen content in the steel, and that the growth of the inclusions during 1 s after the deoxidation was considered to be controlled by the oxygen diffusion.