On the Alternate Stirring Mode of F-EMS for Bloom Continuous Castings
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RODUCTION
THE compositional inhomogeneity at the macroscopic level of a casting, which is termed macrosegregation, continues to be one of the major and classical internal defects in a continuous casting (CC) process, particularly for heavy sectioned or high carbon steels.[1,2] Such defect[3,4] will result in the heterogeneity of the physical and mechanical properties for the whole casting, and preventing its products to perform as expected in the specific application because of the persistence of heavily segregated regions during subsequent hot rolling or forging process. Thus, in-depth understanding of the control technologies for the observed macrosegregation during the CC process is significant to enhance the internal qualities of steel products. Final electromagnetic stirring (F-EMS)[5] is an effective method[6] of improving the homogeneity of bloom continuous castings, and has been widely applied in steel
HAIBO SUN is with the School of Materials Science and Energy Engineering, Foshan University, Foshan 528000, Guangdong, China. Contact e-mail: [email protected] LIEJUN LI is with the School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, Guangdong, China. DEXIN YE and XUEXING WU are with the Guangdong Shaoguan Iron & Steel Co., Ltd. Baowu Steel Group, Shaoguan 512123, China. Manuscript submitted December 3, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
mills.[5,7] It is obvious that local melt stirring condition generated by the F-EMS significantly affects the componential homogeneity and grain refinement during final solidification stage of casting.[8] In this regard, scientists have been paying close attention toward optimizing the technological parameters of F-EMS for further improving its metallurgical performances.[9,10] It has been shown that the installation position of F-EMS must be first chosen in a careful manner.[11,12] Ayata et al.[13] recommended that the optimal range of the strand center solidification fraction, fs, at the F-EMS installation location center should be 0.1 to 0.2. Oh et al.[14] conducted a series of industrial tests to investigate the macrosegregation behavior at the final solidification stage for bloom and billet castings. The optimal stirring pool thicknesses at the F-EMS center were found to be 70, 54, and 30 mm for blooms of P70, S82, and SU2 steels, and 65 and 55 mm for the S30 and S72 steel billets, respectively. Sun et al.[15] studied the effect of F-EMS position on segregation degree in the as-cast bloom by conducting plant trials and numerical simulation. Their results showed that the optimal solidification ratio at F-EMS center increases with the increasing carbon content. Based on the determined optimal position, the running current and frequency of F-EMS can be subsequently designed according to the criteria involving equipment capacity, skin effect, and the critical condition of white band formation[16–18]. Jiang et al.[19] applied a mixed columnar-equiaxed solidification model to optimize the F-EMS parameters for the
as-cast
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