Interdendritic Strain and Macrosegregation-Coupled Phenomena for Interdendritic Crack Formation in Direct-Chill Cast She
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DRITIC crack formation during dendritic solidification is a problem that has plagued the ferrous and nonferrous casting industries for last several decades. Although this defect in the case of an equiaxed crystal structure is intermittent and affects less than the susceptible columnar crystal structure, the problem persists and is expensive. Because the slab has surface or subsurface interdendritic cracks in the direct-chill casting process, it must be scrapped where it affects the structure morphology, mechanical properties, and therefore, the stability of hot rolling of sheet ingots. Much effort has been made to understand the mechanism of interdendritic crack formation and several theories have been proposed in the literature.[1–8] Generally, it is believed that interdendritic crack starts to develop in the mushy zone when it is definitely coherent, but continuous films of interdendritic liquid still exit and tensile strain is sufficient.[1–3] Also, most interdendritic crack MOSTAFA OMAR EL-BEALY, Chair Professor of Materials Processing and Technology, is with Companies’ Chair of Swedish Iron Masters Association, S-100 44 Stockholm, Sweden. Contact email: [email protected] Manuscript submitted August 29, 2011. Article published online December 21, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
criteria simply consider the size of the solidification interval, stating that the solidification range is associated with more interdendritic cracking susceptibility than a short range.[4,5] Pellini[3] stated that an interdendritic crack will occur if the material is subjected to high accumulated strain within the so-called vulnerable part of the solidification interval. Campbell,[1] Kinoshita et al.,[6] and Guven and Hunt[7] emphasized the role of tensile stresses in the forming of interdendritic cracks. Clyne and Davies[8] formulated a more refined criteria based on the time spent in different regimes of the solidification interval. They defined a vulnerable region of the solidification interval where thermal strains are induced, the film cannot sustain the stresses, and an interdendritic crack forms. Feurer[9] focused on the pressure of the interdendritic liquid present between the dendrites and argued that an interdendritic crack will nucleate as a pore if the liquid no longer can fill the intergranular openings caused by the solidification shrinkage. Rappaz and co-workers[10,11] extended this approach to take into account the feeding associated with the tensile deformation of the solidified alloy in the direction transversal to the columnar dendritic growth. The reader is referred to Sigworth[12] for a more detailed review on work related to an interdendritic crack. El-Bealy and VOLUME 43B, JUNE 2012—635
Thomas[13] proposed a new criterion to define the distance between the dendrites as a result of the accumulated interdendritic strain generated in the coherent mushy region. Recently, El-Bealy[14] extended and proposed an approach to explain the mechanism of interdendritic crack formation and the effect of interdendritic strain and
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