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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...

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a b s t r a c tDue to the extensive applications in the automotive and aerospace industries of Al-7Si-Mg casting alloys, an understanding of their dendrite microstructural formation in three dimensions is of great importance in order to control the desirable microstructure, so as to modify the performance of castings. For this reason, a three-dimensional cellular automaton model (3-D CA) allowing for the prediction of dendrite growth of ternary alloys is presented. The growth kinetics of the solid/liquid (S/L) interface is calculated based on the solutal equilibrium approach. This proposed model introduces a modified decentered octahedron algorithm for neighborhood tracking, in order to eliminate the effects of mesh dependency on dendrite growth. The thermodynamic and kinetic data needed in the simulations are obtained through coupling with the Pandat software package in combination with thermodynamic/kinetic/equilibrium phase diagram calculation databases. The solute interactions between alloying elements are considered in the model. The model was first used to simulate the Al-7Si dendrite, followed by a validation using theoretical predictions. The influence of Mg content on the dendrite growth dynamics and dendrite morphologies was investigated. Also, the model was applied to Al-7Si-0.5Mg dendrite simulation both with and without a consideration of solute interactions between the Si and Mg alloying elements and the effects on dendrite growth process was analyzed using the simulation results. This model was finally used in order to simulate the dendrite growth in different crystallographic orientations in an Al-7Si-0.36Mg ternary alloy during polycrystalline solidification, resulting in a predicted secondary dendrite arm spacing (SDAS) and dendrite volume fraction data that show a reasonable agreement with experimental results. The single dendrite and polycrystalline growth simulations effectively demonstrate the capability of this model in predicting the three-dimensional dendrite microstructure of ternary alloys. Ó 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

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A full scale water modeling experiment has been conducted to address the relationship between the instability of fluid flow and level fluctuation in the continuous thin slab casting mould with the particle image visualization. The results show that the internal fluid flow and level fluctuation are unsteady and periodical. The probabilities of fluctuated meniscus and moving circumfluence center position seem Possion distributions with the highest frequency near the average position. The circumfluence and meniscus profile are asymmetrical, and the phase difference of wave height and circumfluence center in the two sides of mould centerline is half period. The average meniscus profile, the highest and lowest meniscus positions are generally symmetry about the mould centerline, and the circumfluence center swings with a similar trace. The wave height mainly depends on the circumfluence center position along the mould height. The wave height has an inverse relation with the circumfluence center depth, and the wave height decreases with descending circumfluence.

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