Thermo-mechanical model of steel shell behavior in continuous slab casting
Moitra, Avijit
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Permalink
https://hdl.handle.net/2142/19269
Description
Title
Thermo-mechanical model of steel shell behavior in continuous slab casting
Author(s)
Moitra, Avijit
Issue Date
1993
Doctoral Committee Chair(s)
Thomas, Brian G.
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Engineering, Metallurgy
Engineering, Materials Science
Language
eng
Abstract
The behavior of the solidifying shell in the early stages of solidification has an important influence on the final quality of continuously-cast steel slabs. In order to understand the thermal and mechanical behavior of the shell, a two-dimensional transient stepwise-coupled finite-element model has been developed. The model simulates a transverse section of the slab as it moves down through the mold and below and incorporates the effects of heat conduction, solidification, shrinkage, non-uniform superheat dissipation due to turbulent fluid flow, thermal distortion of the mold and the visco-plastic mechanical behavior of the steel. Coupling between the thermal and the mechanical portions of the model are based on the mutual dependence of heat transfer across the interface between the shell and the mold and the size of the gap. The effects of mold distortion and taper on the gap size are also included. The effect of fluid flow has been incorporated via a heat flux imposed at the solid-liquid interface, which is obtained from a separate fluid flow model. The high temperature creep and plasticity of the steel is incorporated through a unified constitutive law defining the inelastic strain rates as a function of temperature, composition, accumulated plastic strain and the stress state. The model has been successfully verified with analytical solutions and measurements of temperature and shell thickness on an operating caster. Non-uniform dissipation of superheat caused by asymmetrical fluid flow has been found to have a critical influence on shell growth in the mold, in places where the interfacial gap size is significant. Model results suggest that a simple linear taper necessary to compensate for the slab shrinkage is not sufficient for low carbon steels because of the non-linear shrinkage associated with the $\delta$-$\gamma$ phase transformation. Model simulations extending below the mold suggest that bulging of the shell between rollers is responsible for the formation of off-corner depressions when the off-corner region of the shell leaving the mold is relatively thinner than other places. The model developed in this work is an effective tool and can be judiciously used to understand the formation mechanisms of various defects in continuous slab casting.
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