Effect of simultaneous addition of CaO–Al2O3 flux and CaSi on the modification of inclusions in aluminium-killed steel

This paper investigates the effect of CaO-Al 2 O 3 flux, used in conjunction with CaSi, on the formation of inclusions in aluminium-killed steel. 50 kg scale experiments were carried out in an air induction furnace. The amounts of CaSi (1.25-2.5 kg/t) and fluxes (CaO:Al 2 O 3 from 40:60 to 60:40) were varied in different experimental heats. The volume fraction and size of inclusion were determined through quantitative metallography. The change in the composition of inclusions was qualitatively studied through elemental x-ray analysis by EPMA. The size of inclusions in general was found to be larger in the case of the simultaneous addition of CaSi with flux, compared to that obtained through CaSi alone. Larger inclusions lead to easier flotation resulting in lesser volume fraction. The inclusion content was lowest with flux containing 40% CaO and 60% Al 2 O 3 . Better globularisation of alumina inclusion was observed in the case of the simultaneous addition of flux with CaSi, compared to situations where CaSi alone is added. The present investigation has therefore identified the specific amount and composition of flux necessary for restricting the inclusion content as well as improving its globularisation.