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...

Purpose-To present a numerical model of squeeze casting process. Design/methodology/approach-The modelling consists of two parts, namely, the mould filling and the subsequent thermal stress analysis during and after solidification. Mould filling is described by the Navier-Stokes equations discretized using the Galerkin finite element method. The free surface is followed using a front tracking procedure. A thermal stress analysis is carried out, assuming that a coupling exists between the thermal problem and the mechanical one. The mechanical problem is described as an elasto-visco-plastic formulation in an updated Lagrangian frame. A microstructural solidification model is also incorporated for the mould filling and thermal stress analysis. The thermal problem is solved using enthalpy method. Findings-During the mould-filling process a quasi-static arbitrary Lagrangian-Eulerian (ALE) approach and a microstructural solidification model were found to be applicable. For the case of the thermal stress analysis the influence of gap closure, effect of initial stresses (geometric nonlinearity), large voids and good performance of a microstructural model have been demonstrated. Research limitations/implications-The model can also be applied to the simulation of indirect castings. The final goal of the model is the ability to simulate the forming of the material after mould filling and during the solidification of the material. This is possible to achieve by applying arbitrary contact surfaces due to the sliding movement of the cast versus the punch and die. Practical implications-The presented model can be used in engineering practice, as it incorporates selected second-order effects which may influence the performance of the cast. Originality/value-During the mould-filling procedure a quasi-static ALE approach has been applied to SQC processes and found to be generally applicable. A microstructural solidification model was applied which has been used for the thermal stress analysis only. During the thermal stress analysis the influence of gap closure and initial stresses (geometric nonlinearity) has been demonstrated.

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