The surface of continuously cast steel blooms were observed to exhibit periodic defects typically characterised by gradually deepening oscillation marks, followed immediately by longitudinal striations or 'glaciation marks'. In severe cases, deep depressions were clearly visible within the glaciated region. These defects were investigated through plant trials and both physical and mathematical modelling The defects were found to exhibit a characteristic temperature history; temperature troughs that move down the mold at the casting speed. These defects may be monitored in much the same way as sticker breakouts, thereby allowing existing thermocouple based breakout detection systems to be modified to include a quality alarm. This study has attributed these defects to high-amplitude, low-frequency, mold level fluctuations. A mechanism has been postulated which ascribes the generation of these defects to the interaction of the meniscus with the slag rim at peaks in the mold level cycle. The implementation of a new mold level control system was found to eliminate these defects from the bloom surface and to significantly improve the rolled billet quality.
ASJC Scopus subject areas
- Metals and Alloys