Abstract: The evolution of chemical composition，size，proportion，and morphology of the Al-Ti-Mg-O inclusions during the steelmaking process of interstitial free (IF) steel were investigated by means of Auto-SEM. Results showed that after RH deoxidation，the main inclusions were pure Al2O3 inclusions. Then the proportion of Al2O3 in inclusions decreased，while the proportion of inclusions containing titanium and magnesium increased from RH deoxidation to slab. The size of pure Al2O3 inclusions was larger and the size of inclusions containing titanium was smaller. Thermodynamic analysis resulted showed that the inclusions should be stable with Al2O3 at the concentration of molten steel. But the titanium alloying and spontaneous enrichment would make a high titanium concentration environment that was in favor of the TiOx existence. Moreover，more TiOx component could control Al-Ti-Mg-O inclusions with a lower melting temperature.

Key words: interstitial free steel, inclusion evolution, Al-Ti-Mg-O inclusions, inclusion thermodynamics