Characteristics of Surface and Subsurface Defects in The Continuously Cast Slab of IF Steel

by Yen-Hao Su, Kuan-Ju Lin, Fu-An Feng, Wen-Hsien Wang, Wen-Chang Li

Publisher - China Steel Corporation, Kaohsiung, Taiwan

Category - General Novel

Surface or subsurface defects, such as entrapped mold slag, gas bubbles and clusters of inclusions in the continuously cast slab of IF steel are commonly understood to correlate with the causes of sliver, blister or line defect in the downstream cold-rolled coil. Radiographic method was adopted in order to investigate the defect characteristics in slab subsurface area. With over forty heats of slabs examined, it revealed that the ratio of detected defect was inversely proportioned to the casting speed within the normal operation range. The majority of defect type was gas bubble from microscopic observation. Spatial distribution analysis showed two bands with high incidence of defects in the thickness direction of slab. With the help of the water model experiment, together with the numerical simulation, it could be clarified that the defect trapping regions in the mold was corresponding to those with low flow velocity of molten steel. Simulation results also showed that the casting speed or throughput significantly affected the distribution of those stagnation regions, which in turn was believed to influence the spatial distribution of the above-mentioned defects in the slab.

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