In secondary steelmaking, calcium treatment is practised to modify the solid alumina or spinel
inclusions into liquid or partially liquid calcium aluminates. It has been seen that the dissolved
calcium reacts with sulfur or oxygen present in the steel to form CaS or CaO type of transient
inclusions. Post-calcium treatment these transient inclusions further react with pre-existing alumina
or spinel inclusions and modify them. In addition, direct modification of pre-existing inclusions is also
reported in the literature.
In the present study, laboratory-scale induction furnace-based experiments are carried out to melt
electrolytic iron in an alumina crucible followed by deoxidation with aluminium. The CaS-based
composite material, prepared in-house, is added after the aluminium deoxidation to study the stability
of CaS at the steelmaking temperature. Multiple steel samples were also taken to track the
dissociation of CaS by means of sulfur pick-up in steel. Additionally, inclusion analysis of these steel
samples was also performed to track changes in the chemical composition of inclusions in response
to CaS addition. It has been seen that the CaS dissociates leading to a gradual pick-up of sulfur in
steel. The scanning electron microscope – energy dispersive X-ray spectroscopy (SEM-EDS)
analysis reveals that the alumina crucible and floated alumina inclusions are modified into calcium
aluminates and the extent of modification depends on the contact time of CaS with the two sources
of alumina mentioned earlier. However, the modification of alumina inclusions in the bulk steel did
not occur during these experiments.