Transport and Entrapment of Particles in Steel Continuous Casting
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CTS in cast and rolled steel products, such as slivers and blisters, are often caused by captured inclusion clusters, slag, bubbles, and other particles.[1] During continuous casting, jets of molten steel from the submerged entry nozzle (SEN) ports carry bubbles and inclusion particles into the mold cavity from upstream processing, as shown in Figure 1.[2] In addition, droplets of liquid mold slag may become entrained into the flowing steel because of fluid flow problems, via several mechanisms, including meniscus level fluctuations, and excessive velocity across the slag–steel interface.[3] The particles are transported with the flow, along chaotic, circulating trajectories through the mold cavity. Particles reaching the top surface are harmlessly removed into the liquid slag layer, so long as the slag is not saturated and the surface tension forces are not BRIAN G. THOMAS, C.J. Gauthier Professor, and RUI LIU, Graduate Student, are with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign (UIUC), 1206 W. Green Street, Urbana, IL 61801. Contact e-mail: bgthomas@ illinois.edu QUAN YUAN, Formerly Graduate Student, with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign (UIUC), is now with UOP, A Honeywell Company, 25 E Algonquin Rd, Des Plaines, IL 60017. SANA MAHMOOD, Formerly Graduate Student, with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign (UIUC), is now with Caterpillar Inc., 100 NE Adams Street, Peoria, IL, 61629. RAJNEESH CHAUDHARY, Formerly Graduate Student, with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign (UIUC), is now with the ABB Corporate Research Center, Whitefield Road, Bangalore, 560048, Karnataka, India. Manuscript submitted July 30, 2012. Article published online August 6, 2013. 22—VOLUME 45B, FEBRUARY 2014
excessive. Otherwise, the particles are eventually entrapped into the solidifying steel shell. Particles captured near the meniscus lead to surface defects, while particles captured deep in the caster lead to internal defects in the final steel product. Figure 2 shows some typical inclusion particles that can be entrapped from the flowing liquid into the solidifying steel shell to form defects in continuous-cast product. Small, spherical inclusions, especially deoxidation products such as alumina, may collide together over time to form larger clusters, as in Figure 2(a).[4] Large, dendritic inclusions form when the oxygen concentration is very high, such as found during reoxidation, when the molten metal is exposed to air later during processing, as in Figure 2(b).[4] Slag entrainment often produces very large inclusions, which are spherical (Figure 2(c))[5,6] because they are still liquid when the solidifying steel entraps them. Finally, some of the argon bubbles resulting from argon gas injection into the nozzle to prevent clogging may become entrapped. These bubbles are often coated with a detrimental layer o
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