In Situ Observation on Behaviors of CaO-MgO-Al2O3-SiO2 Complex Inclusions at Solid–Liquid Interface of Low-Oxygen Special Steel

Abstract

The movements of CaO-MgO-Al2O3-SiO2 inclusions at solid–liquid (S–L) interface during the solidification of low-oxygen special steel were observed in real time by the confocal laser scanning microscope, in an attempt to explore the possible formation mechanism of the D-type and DS-type inclusions. It was found that S–L interfaces showed strong interaction with the inclusions, especially when the inclusions were captured. Collision and agglomeration between inclusion in liquid steel and inclusion captured by the S–L interface were reproducibly observed, followed by an obvious size growth. During this process, inclusions in liquid steel acted as the guest particles, while the S–L interface capture inclusions acted as the host particles. There were also inclusions first moved toward and then later away from the S–L interfaces. To explain the behaviors of inclusion pairs, the forces acted on inclusions were estimated and discussed. Based on the obtained result, it can be cautiously pointed out that collision and agglomeration of inclusions at S–L interface during the casting of steel are probably important reasons for the frequent existence of D-type and DS-type inclusions during the production of low-oxygen special steel despite the high cleanliness. Therefore, minimization of inclusion size is significant except for the reduction of the inclusion numbers.