Subsurface hooks in continuous casting slabs of low-carbon steel

Hook characteristics in continuous casting slabs of low-carbon steel under different casting conditions were investigated. According to hook morphology, hooks were classified into different types. Distributions of bubbles and inclusions near hooks were analyzed, and the influence of casting parameters on hook depth was discussed. Bikerman's equations and theory of meniscus solidification were used to explain the various hook morphology. Results show that on the basis of morphology hooks can be classified into four types, including whole-leaf type, double-hook type, truncated type and re-solidified type. The percentage of re-solidified type is the highest (46.8%), and the percentages of whole-leaf type, truncated type and double-hook type are respectively 25.3%, 7.6% and 6.3%. Studies demonstrate that the inclusion number near hooks is obviously higher than that in other zone, indicating floating inclusions in the mold can be captured by hooks. Comparing different casting parameters, the use of FC-Mold, the decrease of the submerged depth of the submerged entry nozzle (SEN) and the increase of casting speed can reduce the hook depth. Calculated results of Bikerman's equation and theory of meniscus solidification can explain the formation mechanisms of different hook morphologies.