Analysis of Solidification Cracking Using the Specific Crack Susceptibility.

Abstract

Using a 2-dimensional finite element, the effects of carbon content, slab width, narrow face taper and casting speed on solidification cracking during continuous casting of slabs were analyzed. The possibility of solidification cracking during continuous casting of slabs was predicted using the "Specific Crack Susceptibility", S S C . The new proposed parameter, S S C , can represent the averaged possibility of solidification cracking of the strand during continuous casting in the mold. The surface crack formed near corner region of strand at the initial stage of solidification, and the internal crack was found in the internal regions of wide center, corner and off-corner at the middle and final stage of solidification. The carbon range sensitive to solidication cracking is between 0.1 wt% C and 0.14 wt% C steels. At the slab widths of 1 900 mm and 2 150 mm, the possibility of solidification cracking increased in the regions of wide center, corner and offcorner in comparison with the slab width of 1 600 mm. With increasing narrow face taper, the possibility of solidification cracking decreased along the region of wide face due to the mechanical compression imposed by the narrow face taper. With increasing casting speed, the possibility of solidification cracking increased in the regions of wide center, corner and off-corner, because the shell thickness is largely decreased due to decrease of dwelling time of strand within the mold. These predictions at various casting conditions were in good agreement with the experimental observations in industry.KEY WORDS: specific crack susceptibility; solidification cracking; carbon content; slab width; narrow face taper; casting speed.dency during continuous casting of steels. They divided the mushy zone into the mass/liquid feeding zone (0.4Ͻf s Ͻ0.9) and the cracking zone (0.9Ͻf s Ͻ0.99). Cracks formed in the mass/liquid feeding zone are refilled with the surrounding liquid, whereas cracks formed in the cracking zone can not be refilled with the liquid, because the dendrite arms are close enough to resist feeding of the surrounding liquid. They proposed the critical solid fraction to resist feeding of 0.9. However, the crack susceptibility coefficient can be increased with increasing carbon content, because the mushy zone increases with increasing carbon content. Many researchers 3,5,15) estimated the possibility of cracking in comparison with the maximum principal stress and transverse stress along the wide and narrow face. And, some investigators 4,16) have used a strain based fracture criterion in the mushy zone, assuming that the material fractures if the total mechanical strain exceeds 0.2% 4) and 1.6%. 16) However, the comparison of the absolute stress and strain values is not enough to investigate the possibility of cracking during continuous casting, because the stress in the solidifying shell changes as a function of temperature and the mushy zone solidifies in almost stress free state, even though the strain occurs in the mushy zone. Kelly et al. 6) and Kim et ...

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