Demystifying the CC Mold at the University of Toronto: The First Full-Scale Mold Water Model in North American Academia

摘要

The.continuous casting (CC) operation is the final stage of the steelmaking process for producing slabs/billets/blooms in modern steel mills. For slabs, they are then rolled and coated to manufacture steel coils for various end-use applications. Slabs and coils slated for automotive applications are often made from ultra-low carbon (ULC) steel grades. These steel grades are particularly susceptible to undesirable defects (e.g. slivers, seams and blisters) on the surface of coils. During the CC operation, most of these surface defects are caused at the steel/slag interface (meniscus) by entrainment of alumina inclusions, slag, and mold powder particles on slabs during the CC operation. The meniscus in the mold is crucial for transient heat transfer, chemical interactions, and onset of solidification, thus understanding the liquid steel flow behavior at the meniscus is essential for improving quality and productivity of cast products. During the continuous casting the liquid steel flow in the mold depends on the operational factors: (a) mold width, (b) casting speed, (c) argon gas flow rate, and (d) physical properties of mold flux/argon gas/SEN refractory material and the SEN design factors: (a) SEN bore design, (b) port size, (c) port angles, (d) bed-depth/shape and (e) SEN submergence depth. During the CC operation, the liquid steel flowing through the SEN creates a negative pressure. To prevent the ingress of the ambient air leading to nitrogen pickup and re-oxidation of the liquid steel, argon is injected into the mold. In addition, argon prevents clogging of the SEN ports. The combination of all these factors determine the liquid steel jet trajectory exiting for example, a typical bifurcated submerged entry nozzle (SEN). The sources of momentum force for liquid steel jet are primarily the casting speed (casting throughput) and the buoyant Ar gas, which determines the point of impact (impingement point).