Prediction and Analysis on Formation of Internal Cracks in Continuously Cast Slabs by Mathematical Models.

Abstract

The formation of internal cracks in continuously cast slabs is mainly attributed to the strain status and microsegregation near the solidifying front of the slabs. Based on this understanding, the effects of the strain status at solidifying front and the chemical composition of liquid steel on the internal cracks were studied using a strain analysis model and a microsegregation model developed in the present study. The tensile strains at the solidifying front caused by bulging, unbending, and misalignment of supporting rolls in a fourpoint-unbending bow caster were calculated. The roll gap in the caster was measured for the calculation of the strains caused by the misalignment of the supporting rolls. The calculated strain status near the solidifying front was used to predict the internal cracks. Critical strains based on some experimental data were adopted as the crack criteria. Sulfur prints of the slab transverse sections were used to verify the model predictions. The enrichment of chemical compositions in the interdendritic liquid and its effect on the freezing temperature of the liquid were studied with the microsegregation model, in which the transition of ferritic/austenitic solidification and the precipitation of MnS were taken into account. S and P were revealed to strongly accumulate at the columnar grain boundaries, and the segregation of P increases significantly when C content increases from 0.1 % to 0.2 %. With the accumulation of P and S in the interdendritic liquid, the freezing temperature of the liquid decreases obviously, thus the internal crack tendency is greatly increased.KEY WORDS: continuously cast slab; internal cracks; strain analysis; microsegregation; mathematical models.lidifying front and the steel composition on the formation of internal cracks were studied using an empirical equation based strain analysis model and a microsegregation model developed in the present study. The tensile strains at the solidifying front caused by bulging, straightening, and misalignment of supporting rolls in a four-point-unbending bow caster were calculated. The roll gap was measured for the calculation of the strains caused by the misalignment of supporting rolls. The calculated tensile strains were used to predict the formation of the internal cracks. The sulfur prints of the slab transverse sections were used to verify the model predictions. On the other hand, the accumulation of impurity elements, mainly S and P, in the interdendritic liquid and its effect on the freezing temperature of the liquid were studied using a microsegregation model, in which the transition of ferritic/austenitic solidification and the precipitation of MnS were taken into account. Mathematical Models Strain Analysis ModelThe strain analysis model for the continuously cast slab is based on a heat transfer model, which was developed to calculate the variations of surface temperature and solidified shell thickness of the slab in the casting direction. According to the characteristics of heat transfer and solidification of the...

Modeling Solidification Phenomena in the Continuous Casting of Carbon Steels

“…3 line 1 depicts the bulging strain along the caster with the aforementioned formulation. Left-hand-side (LHS) axis is used to present the bulging strain which is also presented by dashed line 2 with the means of another formulation (Han et al, 2001) which is presented by the following equations:…”

“…In this way, the secondary dendrite arm spacing can be sufficiently computed with respect to carbon content and local cooling rates. In another study (Han et al, 2001), the formation of internal cracks in continuously cast slabs was mathematically analyzed with the implementation of a strain analysis model together with a microsegregation model. The equation of heat transfer was also numerically solved along the caster.…”

“…Any caster misalignment of value M can be computed according to (34), as described in the works of (Han et al, 2001) and (Zhu et al, 2003):…”

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