Closure of Internal Porosity in Continuous Casting Bloom During Heavy Reduction Process
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porosity (also referred to as internal void) is a kind of internal quality defect in continuous casting steel that results from volume shrinkage and gas entrapment during the solidification of liquid steel. The voids should be eliminated in the subsequent forging or rolling process to avoid their adverse effects on the mechanical properties of the final products (for example, decreasing the yield strength and fatigue life of materials). To study the closure behavior of internal voids in metallic material during hot working processes, many numerical and experimental investigations were carried out by previous researchers. With regard to studies
CHENHUI WU, CHENG JI and MIAOYONG ZHU are with the Key Laboratory for Ecological Metallurgy of Multimetallic Ores (Ministry of Education), Shenyang 110819, P.R. China and also with the School of Metallurgy, Northeastern University, 3-11, Wenhua Road, Shenyang 110816, P.R. China. Contact e-mail: [email protected] Manuscript submitted December 28, 2018.
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during the forging process, Kakimoto et al.[1] studied the closure behavior of internal voids during the compression and extent forging process, and the limit closing evaluation value in extent forging process was quantified. By comparing the experimental and numerical simulation results, Lee et al.[2] noted that a local effective strain ‡ 0.6 should be achieved to completely close an internal void during forging. Park[3] investigated the closure of cylindrical voids during the flat-die forging process and found that the effective strain for closuring voids was dependent on the aspect ratio of the void cross section but independent of the void size. Based on the simulation results, Chen et al.[4] proposed a void aspect ratio evaluation index and established a theoretical model, which was proven to be capable of accurately predicting the void aspect ratio in large forgings during hot working processes. With respect to studies during the rolling process, Chen[5] studied the closure behavior of voids in porous metal sheets under various rolling conditions and provided the critical reduction for completely closing the internal voids. Nakasaki et al.[6] modified the hydrostatic integration to better describe the void closure behavior and successfully applied the modified parameter to support a mill modification for
producing larger bars without voids. Based on the simulated void deformation results under various cold rolling conditions, Chen et al.[7] developed a back-propagation neural network model, which was able to predict the void closure behavior effectively and precisely. Li et al.[8] found that, compared with uniform temperature rolling (UTR), gradient temperature rolling (GTR) could obviously contribute to the closure and bonding of the central cracks in heavy plates. Furthermore, by performing physical rolling and numerical simulation, Li et al.[9] found that a small reduction deformation could effectively minimize the internal porosity and segregation in continuous casting steel before r
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