Behavior of nonmetallic inclusions in front of the solid-liquid interface in low-carbon steels

The present study is concerned with the interaction phenomena of nonmetalli c inclusions in front of a moving solid-liquid interface. The in situ obser vation was done in a high-temperature experiment by using a laser microscop e. Alumina inclusions in an aluminum-killed steel with low oxygen content e xhibited the well-known clustering behavior. The velocity of the advancing interface first increased while approaching the particle, but became stagna nt during engulfment and increased again after that. Alumina-magnesia compl ex inclusions in a magnesium-added steel with high oxygen content were very finely dispersed in the molten pool. These inclusions escaped from the adv ancing interface during solidification, but gathered again at the retreatin g interface during remelting. The tiny inclusions were thought to behave ju st as tracer particles of a local flow. The velocity of particles was measu red on a video image, and the significant acceleration or deceleration was found near the interface. It was concluded that the flow was induced by the Marangoni effect due to the local difference in temperature and oxygen con tent in front of the interface, particularly in the case of a higher oxygen content. However, the flow was weak in the case of a low oxygen content.