Investigation on Mold Flux Melting and Consumption During Continuous Casting of Liquid Steel
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INTRODUCTION
MOLD fluxes added during continuous casting of liquid steel form a layer of molten mold flux above the liquid steel. Molten mold flux preserves the initial solidifying steel shell, absorbs nonmetallic inclusions, provides thermal insulation, and prevents the reoxidation of liquid steel during the continuous casting process. Molten mold flux also seeps through the gap between the solidifying steel strand and the mold wall and is consumed in the process. During molten flux infiltration, it serves as a lubricant and controls the heat extraction in the horizontal direction. It is desired to increase the productivity of the continuous casting process by increasing the casting speed for a specific grade of steel. However, it should be ensured that harmonization between the mold powder melting rate and proper lubrication (consumption) is achieved for smooth casting.
ASHOK KAMARAJ and PREMKUMAR MURUGAIYAN are with the CSIR-National Metallurgical Laboratory, Jamshedpur 831007, India. Contact e-mail: [email protected] ANSUMAN DASH is with the Tata Steel Ltd, Jamshedpur 831001, India. SIDDHARTHA MISRA is with the Tata Steel Ltd BSL, Angul 759121, India. Manuscript submitted February 3, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Several investigators proposed empirical correlations[1,2] and experimental methods[2–7] to estimate the melting rate of mold fluxes. The experimental methods to determine the melting rate of mold flux can be categorized into three groups: (1) powder displacement method, (2) slag drip test, and (3) powder melting method. Many researchers[1,2,7–11] investigated the influence of various factors, such as free carbon, carbon morphology, particle size, depth of molten flux, vertical heat flux, carbonate content, powder bulk density, and steel-slag interface turbulence, on the melting rate and proposed empirical equations to estimate the melting rate of a mold powder. It is also reported that the decrease in the melting rate is due to the presence of free carbon content in mold flux.[7,8,10] Bhardwaj et al.[9] concluded that the melting rate of mold fluxes varies inversely to the activation energy of carbon and directly to the amorphous content in the flux. Based on the experimental observation, Go¨rnerup et al.[12] and D’Haeyer et al.[13] concluded that the melting rate of mold fluxes decreases with the increase in mold flux basicity and viscosity, respectively. Kromhout and van der Plas[7] reported that the melting rate of mold powders decreases with the increase in the thickness of slag layer. Similarly, the consumption of mold flux in the continuous casting process is another important process parameter to be monitored to control the quality of cast products. Several investigators[14–23] established mathematical correlation considering the casting parameters to predict the mold flux consumption rate. A few
investigators[24,25] also developed equations considering the density of mold flux along with the casting parameters. Sridhar et al.[8] established a correlation between the melting rate and
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