A Review of the Melt Structure and Crystallization Behavior of Non‐Reactive Mold Flux for the Casting of Advanced High‐Strength Steels

Abstract

The non‐reactive CaO–Al2O3‐based mold flux system is proposed to avoid the reaction problems during the casting process of advanced high‐strength steels, when conventional CaO–SiO2‐based mold flux system is applied. However, new problems such as low consumption and insufficient lubrication are introduced during the industrials of CaO–Al2O3‐based mold fluxes, which is closely associated with its melt structure and crystallization behavior. Herein, the studies on the melt structure and crystallization property of CaO–Al2O3‐based mold fluxes are summarized and discussed. The structural roles of Al2O3, B2O3, and SiO2 in CaO–Al2O3‐based mold flux system are quite complex because the structural transformation occurs in aluminate network structure, such as [AlO4]5− and [AlO5]7−, and borate network structure, such as [BO3]3− and [BO4]5−, in the system. In addition, it is suggested that the addition of basic metal oxides and fluorides will strengthen the stability of network structure, due to the charge compensation effect of Li+ and Ba2+, and the strong electrostatic attraction between Al3+ and F−. On the contrary, many Al‐bearing crystal phases with high melting point precipitate in the CaO–Al2O3‐based melt, which will improve the crystallization ability of slag and deteriorate its lubrication performance.

Properties and Structure Evolution of CaO–Al2O3–La2O3 Slags with Various Alkali Metal Oxide Contents

“…For Li 2 O, with the increase in the content of Li 2 O from 0 to 10 wt%, the melting temperature of slags decreases sharply to 1514 K, which significantly affects the improvement in the melting characteristics of mold fluxes. However, with the further increase in Li 2 O content to 15 wt%, the melting temperature increases significantly, which may be caused by the formation of high‐melting‐point phases, such as LiAlO 2 (melting point 1973 K [ 18 ] ). Figure 2 presents the comparative analysis with the previous study, [ 19 ] revealing that the effect of Li 2 O on decreasing the melting temperature of CaO–Al 2 O 3 –Ce 2 O 3 slag is stronger than that of CaO–Al 2 O 3 –La 2 O 3 slag, which may be attributed to the larger liquid region of CaO–Al 2 O 3 –Ce 2 O 3 slags.…”

Unveiling Non-isothermal Crystallization of CaO–Al2O3–B2O3–Na2O–Li2O–SiO2 Glass via In Situ X-ray Scattering and Raman Spectroscopy

“…In contrast to the well-documented crystallization characteristics of conventional silicate glasses, − crystallization kinetics of alumino-borosilicate glasses is not well understood. Meanwhile, most of the research on the crystallization of glasses mainly focuses on stoichiometry glasses with only a few components, whereas mold flux glasses contain more than five components to tune the properties and behaviors (viscosity, melting, and crystallization). ,, For example, alkali, mainly Li and Na oxides added into the glasses, provides free oxygen in the glass network and decreases the viscosity. The tendency of crystallization of such glassy fluxes is high, and the crystalline products usually have variations in compositions compared with the glass matrix.…”