Evolution Mechanism of Inclusions during the Reoxidation Process of Titanium-Stabilized AISI 321 Stainless Steel in Continuous Casting Tundish

This study systematically examines reoxidation-induced effects on the formation and evolutionary behavior of inclusions during the transfer process of Ti-stabilized AISI 321 molten stainless steel from the LF-refined ladle to the tundish. Compositional analysis of three heats reveals average oxygen content increases by 0.0020 wt% and nitrogen by 0.0015 wt% during LF-to-tundish transfer. Compared to the inclusions in the molten steel at the end of LF refining, the number of TiN inclusions in the tundish increased significantly while their size decreased significantly. At the same time, the content of Ca and Al in the oxide increased significantly, and there was no obvious heritability in the inclusion characteristics between the two processes. Moreover, the formation mechanisms of complex oxides and TiN inclusions in molten steel were discussed. After the molten steel flows from the ladle into the tundish, oxygen reacts with Ca, Al, Mg, and Ti to form complex oxides. During this process, nitrogen competing with oxygen for Ti (which would otherwise form oxides) leads to TiN inclusion formation, reducing titanium content in complex oxides. Simultaneously, due to the limited total magnesium content in the molten steel, (Ca-Al)rich-Ti-Mg-O complex oxides ultimately form.