Evaluation of Defect Distribution in Continuously-Cast Slabs by Using Ultrasonic Scanning System and Effect of Electromagnetic Brake on Decreasing Unbalanced Flow in the Mold

In order to clarify the mechanism of suppression of unbalanced flow in the mold under high throughput conditions in continuous casting, the relationship the distribution of defects entrapped in the solidified shell was measured by ultrasonic defect detection, and the correlation between the defects distribution and the unbalanced flow in the mold when using an electromagnetic brake was investigated. The main results are summarized as follows. (1) By using a new ultrasonic testing system, rapid and accurate measurement could be achieved for the depth of defects with diameters of more than 0.6 mm in the region 2-10 mm from the slab surface. (2) The measured value of the effect of the electromagnetic brake on decreasing molten steel momentum was consistent with the calculated value. Molten steel momentum could be reduced by more than 50% when the Stuart number was more than 3.5. (3) The position of entrapped defects in the solidified shell in the mold was influenced by the throughput condition and the magnetic flux density of the electromagnetic brake.