1. School of Metallurgical and Ecological Engineering，University of Science and Technology Beijing，Beijing 100083，China 2. Shougang Research Institute of Technology，Shougang Group Corporation，Beijing 100041,China
Abstract：A distinctive microstructural feature called a “hook” is often observed on the subsurface of low carbon aluminum- killed steel slabs during continuous casting processes. Inclusions and bubbles are easy to be entrapped by the hooks，which makes Al2O3 cluster and “Ar+Al2O3” type inclusions gathered in subsurface layer of the slabs. A large number of samples were obtained from wide face，narrow face，and corner of the slab in this experiment. The characteristics of hooks in different positions of the slab were investigated. The results showed that in the wide face the center of hooks are deeper than others，in the narrow face the hook depth increase when close to the corner of slab，and hooks near the corners of the slab exhibited three- dimensional morphology. Furthermore，a mechanism of hooks entrapping alumina inclusions and argon bubbles was proposed，which suggested that marangoni force in the process of continuous casting plays an important role on the entrapment of alumina inclusions and argon bubbles. By investigating the behavior of inclusions and bubbles in solidification front of hooks，this mechanism explained the process of how hooks entrapping large side inclusions and bubbles well. From the result，the countermeasure of reduction of hooks and inclusions was proposed.
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