On the Formation of Interdendritic Internal Cracks During Dendritic Solidification of Continuously Cast Steel Slabs
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A zero-defects strategy is an important tool to gain insight to avoid the formation of casting defects during complex solidification processes. One of these defects is the interdendritic cracks that form between the dendrites during the dendritic solidification of steel alloys (Figure 1(a)), where these cracks are of prime importance for the control of the properties and quality of the cast product.[1–4] Static steel castings tend to exhibit coarser dendritic structures especially in the center of the ingot with high positive macrosegregation and centerline porosity. Continuously cast steel, which solidified more rapidly than the static ingot, exhibits a finer dendritic structure with less macrosegregation and centerline porosity. Therefore, these castings generally are hot worked extensively during plastic deformation in the hot-rolling processes. This tends to close these interdendritic cracks as shown in Figures 1(b) through (d) and decrease the effective macrosegregation in steel alloys, MOSTAFA OMAR EL-BEALY, Chair Professor, is with the Military Technical College (MTC), Khalifa El-Maamon st., Kobri Alkobaa, Cairo 11566, Egypt; Clausthal Technical University (CTU), Clausthal-Zellerfeld 38678, Germany; Kungliga Tekniska Ho¨gskolan (KTH), Stockholm SE-100 44, Sweden; and Massachusetts Institute of Technology (MIT), Materials Processing Center (MPC), University Materials Council, Cambridge, MA 02139. Contact e-mail: moelbealy@ hotmail.com Manuscript submitted August 24, 2011. Article published online September 5, 2012. 1488—VOLUME 43B, DECEMBER 2012
which results in the attainment of satisfactory mechanical properties.[3–9] All these investigations focused on the effect of decreasing the degree of the plastic deformation process on the reduction and redistribution of casting defects, whereas the width of these defects or interdendritic distance between the dendrites in the continuously cast steel is ignored.[1,6–9] Therefore, the optimum amount of hot reduction that is required to close these cracks or the interdendritic friction welding conditions to reweld them interdendriticly during or directly at the end of metallurgical length[10] and to give satisfactory mechanical, physical, and chemical properties in the final product are still indistinct.[4,11–13] The need to optimize the hot-working conditions to minimize the severity of the continuously cast inner defects has led to a series of investigations in which important relations have been established between typical solidification variables, interdendritric strain, and macrosegregation level to determine the distribution and direction of the interdendritic distance between the dendrites for different parts in the cast products.[4,14] Many previous computational models and experimental works have investigated interdendritic areas during the continuous casting of steel, to include the interdendritic internal cracks of slab casting, beam blanks, and billet casting.[15–17] Recently, El-Bealy and Thomas[6] first proposed a formula to compute the formation and growth of t
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