Inclusion Agglomeration on Ultra-Low C Liquid Steel Surface: Roles of Ti in the Steel and the Oxygen Potential

Behavior of inclusions as particles on liquid Ultra-Low C (ULC) steel was investigated both by an in-situ observation and a theoretical analysis. The behavior was examined in view of Ti content in the steel as an alloying component and of oxygen potential exerted on the surface of the steel melt. A confocal scanning laser microscopy with a gold image furnace was used for the observation, and the force exerted between two particles was extracted. It was found that the inclusions showed attraction each other, and agglomerated. When the oxygen potential was low ( P_O_2≃ 10^-22 bar), the presence of Ti ( [% Ti] = 0.0735 ) did not influence on the agglomeration force as well as the acceleration. However, increasing P_O_2 ( ≃ 10^-15 bar) resulted in slight decrease of the acceleration. When Ti content was very low ( [% Ti] =0.0018 ), P_O_2 did not influence the attraction. A post-mortem analysis of the inclusion composition revealed that the inclusions on the Ti-free steel surface were mostly alumina regardless of the P_O_2 employed in the present study, while those on the Ti-added steel were composed of Fe_tO – Al_2O_3 (low P_O_2 ) or Fe_tO – TiO_x (– Al_2O_3 ) (high P_O_2 ). From the analysis using Kralchevski-Paunov model for lateral capillary force between two spherical particles, it is suggested that the formation of Fe_tO -containing oxidation product lowers the contact angle between the inclusion and the liquid steel, thereby lowering the agglomeration force as well as the acceleration. However, the model generally underestimated the agglomeration force. Graphical abstract