| Through the microscopic observation of slab surface layer and the variation test of mold powder and Ar gas flow rate purged into submerged entry nozzle, the formation mechanism of pin hole in the surface layer of slab was verified. By changing casting variables, such as casting width, immersion depth, pouring angle of submerged entry nozzle and strand withdrawal speed, the effect of stream velocity on pin hole formation was investigated. Ar gas is the main source of pin hole, which is formed due to entrappment of Ar gas by solidifying meniscus hook. When the stream velocity in meniscus increases or exothermic mold powder is used, pin hole formation is reduced due to hotter meniscus, which retards the hook formation. |
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