Modeling the Effects of Strand Surface Bulging and Mechanical Softreduction on the Macrosegregation Formation in Steel C
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IN recent years, continuous casting has become the major manufacturing method for semi-finished steel products like slabs, billets, or blooms. Many efforts have been made to avoid macrosegregation formation at the centerline of these products during solidification. Particularly positive centerline macrosegregation leads to problems during the succeeding forming processes and to inhomogeneous mechanical product properties. Hence, reducing this casting defect brings an essential quality improvement. Since macrosegregation cannot be removed from the solidified products, controlling its formation immediately during the casting process is crucial to obtain the required steel quality. Industrial practice has shown that mechanical softreduction (MSR) represents an effective technology to achieve this.[1–7] To operate MSR facilities successfully requires a deep understanding of the macrosegregation formaJOSEF DOMITNER, Ph.D. Student, ABDELLAH KHARICHA, Senior Scientist, and ANDREAS LUDWIG, Professor, are with the Chair of Simulation and Modeling of Metallurgical Processes, University of Leoben, 8700 Leoben, Austria. Contact e-mail: [email protected] MENGHUAI WU, Associate Professor, is with the Chair of Simulation and Modeling of Metallurgical Processes, University of Leoben, and also with the Christian Doppler Laboratory for Advanced Process Simulation of Solidification and Melting, University of Leoben. BERNHARD KAUFMANN, Senior Project Manager R&D, is with the voestalpine Stahl GmbH, 4020 Linz, Austria. JU¨RGEN REITER, Project Manager R&D, is with the voestalpine Stahl Donawitz GmbH & Co KG, 8700 Leoben, Austria. THOMAS SCHADEN, Metallurgist, is with the Siemens VAI Metals Technologies GmbH & Co, 4031 Linz, Austria. Manuscript submitted September 25, 2012. Article published online October 24, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
tion mechanisms inside of the strand. Since experimental plant trials are usually time-consuming and expensive, detailed numerical simulations become increasingly important to understand the phenomenon of macrosegregation formation. Macrosegregation formation is related to relative motion between the solid phase and the melt inside of the cast product. For example, thermal, solutal, or forced convection, shrinkage-induced feeding and solid deformation may cause relative motion between the phases.[8,9] Flemings et al.[10,11] developed analytic expressions to describe the general influence of different solidification variables on the formation of macrosegregation in castings. The analytical predictions were also verified by experiments, which illustrated that the flow of enriched liquid to feed volume shrinkage due to solidification or to thermal contractions can cause macrosegregations.[12] In continuous strand casting, deformation of the solid strand shell was identified to cause the formation of positive centerline segregation.[13–18] Due to the high metallostatic pressure of the liquid melt inside of the strand, the thin shell is bulged between adjacent guiding rolls. With
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