Development of a Mold Cracking Simulator: The Study of Breakout and Crack Formation in Continuous Casting Mold
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Obviously, a breakout in the process of continuous casting would not only cause the loss of production, but also introduce the severe safety issues. Breakouts are broadly classified into two categories: hanging- or sticking-type breakout[1–3] caused by improper lubrication between mold and strand, and cracking-type breakout caused by longitudinal corner crack and broad face longitudinal cracks in the strand. Intensive research has been conducted for the detection and prevention of breakouts. The method based on mold/strand friction has been proved to be a successful way for the detection of sticking-type breakout, while the detected signals sometimes might be false because the friction is associated with complicated mold flux infiltration in the copper mold during continuous casting. Other breakout prediction systems are based on the recording temperature signals[4] or coupled with mathematical calculation.[5] However, these methods can only detect the risk of breakout, and the variation of heat transfer, responding temperatures, as well as the association with the mold movement is still not clear.
YEXIN ZHANG, Graduate Student, WANLIN WANG, Professor, Director, and HAIHUI ZHANG, Post Doctor, are with the School of Metallurgy and Environment, Central South University, Changsha 410083, China, and also with the National Center for International Research of Clean Metallurgy, Central South University, Changsha 410083, China. Contact e-mail: [email protected] Manuscript submitted April 11, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
Meanwhile, mold flux entrapment, solute segregation, oscillation marks, etc.[6,7] have great influence on the surface quality of the cast products, and the corresponding surface cracks tend to affect the hot ductility of steels and introduce potential breakouts occurred in the casting process.[8,9] Brimacombe[10] reviewed that the formation of most surface cracks is within a high-temperature zone: 1613 K (1340 °C) to the solidus temperature, as the strength and ductility are relatively low in this region, due to the presence of liquid films in the interdendritic regions[11]; they further indicated that transverse cracks may result from excessive friction in the mold. The transverse cracks are usually found along the oscillation marks (OMs), and Weisgerber[12] has investigated the relationship between the crack formation and the different types of oscillation marks; the research suggested that the segregation of solute elements has been found at the bottom of deeper OMs and it would further cause the primary crack at the bottom of the OMs. Besides, coarser austenite grain has been confirmed to reduce the hot ductility of slab and enhance the cracking of slab surface.[13,14] In order to improve the hot ductility of the slab, Kato[15] controlled the cooling temperature during the second cooling zone with the aim to refine the slab surface microstructure. However, most of these studies focus on the slab samples that have been processed through secondary cooling and bending segment. Very few
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