MODELLING OF THERMO-MECHANICAL STRESSES IN TWIN-ROLL STRIP CASTING- PROCESS

Abstract

Near-net-shape casting technology is one of the mast important research areas in the iron and steel industry today. Driving forces for the development of this technology include a reduction in the number of operations needed for conventionally produced strip through hot rolling operations. Thus, there is consequent reduction in investment cost Out of various processes for near-net-shape casting; twin roll strip casting process represents a major area of interest worldwide. A major problem encountered in twin-roll strip casting process is the formation of cracks and other defects in the solidified strip. These defects arise due to thermo-mechanically induced stresses and strains because of temperature gradients and applied loads. Thus, the control of quality in twin roll strip casting can not be achieved without understanding of thereto-mechanical state (temperature and stresses) of strip due to variation in process parameters. In present work, the thermo-mechanical behavior of strip has been simulated using a two dimensional model based on considerations of fluid flow, heat transfer and solidification. The steady state conditions are assumed. The different boundary conditions have been applied in various zones. A well known CFD software (FLUENT) has been chosen for the solution of the governing equations to predict the temperature distribution in the strip. The calculated temperature is used as input to ANSYS software for the analysis of stresses. The effects of variation in casting speed, heat transfer coefficient, melt super heat; strip thickness and grade of steel have been analyzed. It has been shown that the magnitude of thermal stresses in the cast strip decreases as the casting speed increases. The increase in heat transfer coefficient increases the stresses within the solidified strip. And it has been found that the stress distribution within the strip is not a strong function of change of superheat at a higher value of superheat. The increase of strip thickness increases the maximum value of stress at surface of the strip. For different grades of steel with the increasing percentage of carbon, stresses within strip thickness increases. The results presented in this dissertation work show the thenno-mechanical behavior of strip under different operating conditions. iii