Modeling of Dendritic Evolution of Continuously Cast Steel Billet with Cellular Automaton
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FAMOUS for its high levels of automation and metal yield, continuous casting has become the main approach for industrial steel solidification.[1] However, under influences of the solidification characteristics of steel and processing parameters of continuous casting, steel strands suffer seriously from solidification defects, such as inner cracking and central segregation,[2,3] which inevitably reduce the rolling yield and the performance of steel products. In order to address these restrictive factors for the manufacture of high-quality steel, metallurgists have proposed a series of techniques such as soft reduction (SR) and electromagnetic stirring (EMS).[4,5] However, the optimal technical parameters are usually determined in steel plants by trial and error,
WEILING WANG, CHENG JI, SEN LUO, and MIAOYONG ZHU are with the School of Metallurgy, Northeastern University, Shenyang, 110819, China. Contact e-mail: [email protected] Manuscript submitted April 12 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
and exhibit low stability as the process fluctuates,[4] because the quantitative relationship between the continuous casting process and the solidification defects is still unclear. Although the macroscale solidification behavior of steel strands has been substantially investigated, the establishment of the dendritic growth, from the microscopic to mesoscopic scales, as the key link between the continuous casting process and the solidification defects, is far from complete. During the solidification of steel, the solute tends to be enriched in the interdendritic liquid, defined as microsegregation.[6] Microsegregation can cause variations in the X-ray absorptivity between the dendrite and interdendritic regions.[7] Therefore, approaches such as dendrite corrosion[8] and electron probe microanalysis[7] were employed to investigate the dendritic structure of steel strands, including the preferential growth orientation, dendrite arm spacing, and the ratio of interior equiaxed dendrite. Accordingly, the relationships between the dendritic structure of the steel strand and the casting conditions such as EMS, cooling intensity, superheat, and casting speed have been preliminarily determined. However, these investigations focus only on
the dendrite structure after the complete solidification, and cannot clarify the dendritic evolution. With X-ray synchrotron radiation, Yasuda et al.[9–11] achieved in situ observations of dendritic growth in Fe-based alloy and steel. Subsequently, they measured the growth velocities of columnar dendrites of steels and revealed the effect of the peritectic reaction on the dendritic growth. However, this method is restricted to millimeter-scale samples. Zhong et al.[12] developed a thermal simulation apparatus to simulate the solidification of continuously cast steel and obtained the transient solidification structure through quenching. The measured solidification parameters such as the shell thickness and the location of the columnar-to-equiaxed transition (CET) zone were very close to simulation re
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