Macrosegregation Improvement by Swirling Flow Nozzle for Bloom Continuous Castings
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TRODUCTION
MACROSEGREGATION, especially the centerline macrosegregation, has been one of the major internal defects for the continuous casting (CC) process, which is the main reason leading to inhomogeneity of the final product’s mechanical properties due to the persistence of heavily segregated regions during the subsequent hot working. Other researchers have attempted many techniques to solve this problem,[1,2] such as low temperature casting,[3] electromagnetic stirring (EMS),[4–8] soft reduction,[9,10] intensive cooling[2,11] at the final solidification stage, etc. For the bloom casting processes, the technologies of low temperature casting and EMS, which help enhance nucleation and lower temperature gradient at the solidification front, are frequently used, fundamental, and effective ways to improve the as-cast macrosegregation in casting production.[3,12,13] To achieve low temperature casting, the most immediate way is to lower the pouring temperature from the ladle shroud, which will lead to a bad condition for inclusion flotation removal from molten steel in tundish and possible nozzle clogging. To avoid the negative effects, the technologies of tundish induction heating[14,15] and plasma heating[16,17] were proposed to obtain a lower and constant casting temperature by compensating the heat loss of molten steel in the tundish during sequence casting. Ayata[18] designed a submerged
HAIBO SUN, Ph.D. Candidate, and JIAQUAN ZHANG, Professor, are with the Department of Metallurgical Engineering and State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian District, Beijing 100083, P.R. China. Contact e-mail: [email protected] Manuscript submitted July 1, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
entry nozzle (SEN) with an air cooling system and EMS at the upper part of nozzle to reduce the teeming temperature of steels. However, the operation space at the CC working platform is limited to the additional installation of the EMS apparatus, which greatly restricts the development and adoption of the above two technological measures. Therefore, at present, the EMS technology, including in-mold stirring (M-EMS), in-strand stirring (S-EMS), and final stirring (F-EMS) located near the final solidification zone of the strand, is being popularly used in steel mills to indirectly obtain low superheat molten steel in the liquid pool by generating horizontal or vertical swirling flow in the specified region of the strand. However, the additional equipment investment of the EMS should be included together with the following huge maintenance cost for daily production. Moreover, the effect of EMS is frequently unsteady due to the various casting situations, and a negative effect such as white band segregation can also be observed if there are improper stirring parameters or locations.[7,19–21] To solve the above-mentioned difficulties and improve the superheat dissipation in the mold region, in this investigation, a quadfurcated swirling flow nozzle (SFN) has been designed
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