Revolution and Control of Fe-Al-(Mg, Ti)-O Oxide Inclusions in IF Steel during 260t BOF-RH-CC Process

The evolution of inclusions that contain Al, Mg, and Ti was studied through industrial-grade experiments. Field emission scanning electron microscopy, energy dispersive spectrometry, inductively coupled plasma atomic emission spectrometry, and FactSage software were used to analyze the evolution mechanisms of inclusions in Al-killed titanium alloyed interstitial free (IF) steel. The research found that the evolution of inclusions during the smelting process of IF steel is results in ‘large sphere-like SiO2-CaO-FeO-MgO-MnO’ and ‘small cluster spherical FeO-MnO’ change to cluster-like Al2O3 and irregular MgO·Al2O3, then change to Al2O3·TiOx and Al2O3, and finally change to Al2O3. It is difficult for Al2O3·TiOx to stably exist in the IF molten steel. It is the key to extend the holding time properly after Ruhrstahl Heraeus (RH) to ensure the removal of Al2O3 inclusion. With the increase of Mg content, the change path of MgAl2O4 inclusion in IF steel is that Al2O3 changes to MgO·Al2O3, and finally changes to MgO. It is difficult to suppress MgO·Al2O3 spinel formation by controlling the oxygen in the steel, but Ca can modify part of the MgO·Al2O3 spinel inclusions during RH refining. In order to ensure the removal of 6–10 μm inclusions, the holding time is suitable for 19–42 min.