Review of Mold Fluxes for Continuous Casting of High‐Alloy (Al, Mn, Ti) Steels

Abstract

During continuous casting of high‐alloy (Al, Mn, Ti) steels, the operational issues and quality problems caused by interfacial reaction or peritectic features need to be solved by applying suitable mold fluxes. Intensive efforts have been made to optimize properties, and hereby, several types of mold fluxes, including mold fluxes with high basicity and high glassy property (dual‐high mold fluxes), mold fluxes with strong oxidizing components to protect SiO2 from reduction, mold fluxes with high SiO2 content to decrease the viscosity and basicity, mold fluxes with low SiO2 content for the purpose of attenuated reactivity, and molten mold fluxes to increase consumption, have been developed. Significant efforts have been made to study the theoretical basis and practical application of these mold fluxes. To summarize, the most potential solution of mold fluxes for high‐alloy (Al, Mn, Ti) steel continuous casting is to further optimize the nonreactive mold fluxes systematically to achieve a coordinated control of lubrication and heat transfer.

Effect of Substituting CaO with BaO and CaO/Al2O3 Ratio on the Viscosity of CaO–BaO–Al2O3–CaF2–Li2O Mold Flux System

“…This perfectly accords with next-generation steel for automobiles, the development of which is continuously devoted to pursuing safety and energy conservation and environmental protection [1,2]. However, the high aluminum content, is an unprecedented challenge to the production of high Mn-high Al steel using continuous casting, and the key to the solution for this is to select a proper mold flux [3]. It is well known that high Al content in molten steel will react with the traditional CaO-SiO 2 -based mold flux, leading to a sharp reduction of SiO 2 and an increase of Al 2 O 3 in molten slags, as shown in Equation (1), which will convert the original CaO-SiO 2 -based mold flux into CaO-Al 2 O 3 -based mold flux [4,5].…”

Review on the High-Temperature Thermophysical Properties of Continuous Casting Mold Fluxes for Highly Alloyed Steels

“…With increased global urbanization, demand for renewable energy, lower energy dissipation during energy conversion, and fuel-efficient transportation, the steel industry has seen substantial growth for highly alloyed steels that can contain substantially higher Al, Mn, and Ti contents than typical carbon steels. [1][2][3][4][5][6] These new grades of steel seek to satisfy requirements for higher strength and formability with greater weight reductions, higher corrosion resistance at elevated temperatures, and higher relative magnetic permeability, resulting in lower hysteresis loss. [7][8][9] To be cost effective in producing these highly desired steels, continuous casting is necessary, and mold fluxes play an essential role in ensuring the external and internal product quality.…”

“…However, similar to the actual steelmaking slag reactions in refining, the reactions forming complex oxides have yet to be fully understood, which can fundamentally alter the thermodynamic driving forces that govern the kinetics of the reactions and the thermophysical properties of the mold flux. 1,27,29) For high-Mn or high-Ti steels, the content of MnO or TiO 2 in the mold flux increases, and the corresponding SiO 2 content decreases. For high-Al steels, there is a rapid and significant amount of Al 2 O 3 formation and subsequent SiO 2 reduction observed, which reach a steady-state within a relatively short residence time.…”

“…Further deterioration conditions in the mold, including low mold flux consumption and heavily sintered layers, may also cause a breakout prevention alarm and the interruption of the continuous casting process. 1) These are caused by the fact that the slag crystallization behavior and heat transfer uniformity cannot meet the current steel grade. Furthermore, regardless of the grade of steel, it is necessary to ensure good lubricity of the mold flux in the continuous casting process.…”

Development of Non-reactive F-Free Mold Fluxes for High Aluminum Steels: Non-isothermal Crystallization Kinetics for Devitrification

“…To deal with this question, a possibility is to remove SiO 2 from mold flux, which would result in ''non-reactive'' mold fluxes, i.e., the reaction could not happen. [4][5][6] Another industry demand related to mold fluxes is the need for eliminating fluorine from their composition. Volatile and water-soluble fluorine compounds are formed when using traditional CaO-SiO 2 -CaF 2 -based mold fluxes, causing corrosion of casting facilities and environmental pollution.…”