Thermal Distortion of Solidifying Shell near Meniscus in Continuous Casting of Steel

A two-dimensional, transient, finite-element model has been developed to simulate temperature, shape, and stress development in the steel shell, during the initial stages of solidification in the mold. The model is applied to predict the distorted shape of a vertical section through the shell, during a sudden fluctuation in liquid level at the meniscus. The calculation includes the effects of temperature-dependent properties, thermal shrinkage, phase transformations, and creep, using an elastic-viscoplastic constitutive equation for low carbon steel. The model features a robust, efficient algorithm to integrate the highly temperatureand stress-dependent constitutive equation for the inelastic-creep strain rate. The results show that thermal stress causes the exposed portion of the thin shell to bend towards the liquid, when there is a sudden drop in liquid level. In addition, the axial temperature gradient creates high transverse stresses. The subsequent rise in liquid level increases the bending. These results illustrate an important mechanism contributing to the formation of transverse surface depressions and short longitudinal surface cracks associated with liquid level fluctuations.