超音波探傷法による連鋳スラブ中欠陥分布評価と鋳型内の電磁ブレーキによる偏流低減効果

摘要

In order to clarify the mechanism of suppression of unbalanced flow in the mold under high throughput conditions in continuous casting, the relationsnip 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. 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. 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. 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.%連続鋳造時に凝固シェルに捕捉され，スラブ内に残存した気泡や介在物は，熱間もしくは冷間圧延時の疵発生の原因になる場合がある。近年，高生産性と高品質化の両立が要求されており，高速，高スループット鋳造時の鋳片品質を向上させることが課題となっているが，連続鋳造での高速，高スループット銬造時には，一般的にスラブ品質が悪化する。