Abstract

Casting powders or mold fluxes, as they are more commonly known, are used in the continuous casting of steel to prevent the steel shell from sticking to the copper mold. The powders first melt and create a pool of liquid flux above the liquid steel in the mold, and then the liquid mold fluxes penetrate into the gap between water-cooled copper mold and steel shell, where crystallization of solid phases takes place as the temperatures gradually drop. It is important to understand the crystallization behavior of these mold fluxes used in the continuous casting of steel because the crystalline phase fraction in the slag films plays a crucial role in determining the horizontal heat flux during the casting process. In this work, the existing literature on the crystallization kinetics of conventional and fluoride-free mold fluxes used in the continuous casting of steel has been reviewed. The review has been divided into two main sections viz. the isothermal crystallization kinetics and non-isothermal crystallization kinetics. Under each of these sections, three of the most widely used techniques for studying the crystallization kinetics have been included viz. thermoanalytical techniques such as differential scanning calorimetry/differential thermal analysis (DSC/DTA), the single and double hot thermocouple technique (SHTT and DHTT), and the confocal scanning laser microscopy (CSLM). For each of these techniques, the available literature related to the crystallization kinetics of mold fluxes has been summarized thereby encompassing a wide range of investigations comprising of both conventional and fluoride-free fluxes. Summaries have been included after each section with critical comments and insights by the authors. Finally, the relative merits and demerits of these methods vis-à-vis their application in studying the crystallization kinetics of mold fluxes have been discussed.

Highlights

  • IN the continuous casting process of steel, molten steel is poured from the ladle through a submerged entry nozzle (SEN) into the tundish, which maintains a constant head for molten steel to flow into the continuous casting mold.[1]

  • Zhang et al.[57] investigated the isothermal crystallization kinetics of CaO-SiO2-Al2O3-CaF2-based mold fluxes used in the continuous casting of transformation induced plasticity (TRIP) steels under isothermal conditions using a confocal scanning laser microscopy (CSLM)

  • As a concluding remark, the relative merits and demerits of these methods have been summarized. The thermoanalytical techniques such as differential scanning calorimetry/differential thermal analysis (DSC/DTA) are the most commonly used methods used in the study of crystallization kinetics in glass-forming liquids

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Summary

INTRODUCTION

IN the continuous casting process of steel, molten steel is poured from the ladle through a submerged entry nozzle (SEN) into the tundish, which maintains a constant head for molten steel to flow into the continuous casting mold.[1]. The use of these new fluxes minimizes the amount of Al2O3 formed as a result of the reaction between Al in steel and SiO2 in the mold slag.[1] with the use of these new CaO-Al2O3based fluxes, there is a significant change in the composition of the crystalline phases and in a recent study, Zhou et al.[20] reported that the precipitated phases change from cuspidine (Ca4Si2O7F2) to nepheline (NaAlSiO4) and CaF2, and into gehlenite (Ca2Al2SiO7) as the alumina content increases from ~ 7 to 40 wt pct The impact of these newer crystalline phases on the overall crystallization process is not fully understood and is an area of active research. For the sake of brevity, the general principles involved in the analyses of isothermal and non-isothermal reaction kinetics are not discussed here and interested readers are referred to some of the relevant articles on these topics.[21,22,23,24,25,26] This article only focusses on the studies relevant to mold flux crystallization and is broadly divided into two sections—viz. the isothermal crystallization kinetics and non-isothermal crystallization kinetics

ISOTHERMAL CRYSTALLIZATION KINETICS OF MOLD FLUXES
Thermoanalytical Techniques
NON-ISOTHERMAL CRYSTALLIZATION KINETICS OF MOLD FLUXES
Tp will yield activation
CONCLUDING REMARKS
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