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

The non‐reactive CaO–Al 2 O 3 ‐based mold flux system is proposed to avoid the reaction problems during the casting process of advanced high‐strength steels, when conventional CaO–SiO 2 ‐based mold flux system is applied. However, new problems such as low consumption and insufficient lubrication are introduced during the industrials of CaO–Al 2 O 3 ‐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–Al 2 O 3 ‐based mold fluxes are summarized and discussed. The structural roles of Al 2 O 3 , B 2 O 3 , and SiO 2 in CaO–Al 2 O 3 ‐based mold flux system are quite complex because the structural transformation occurs in aluminate network structure, such as [AlO 4 ] 5− and [AlO 5 ] 7− , and borate network structure, such as [BO 3 ] 3− and [BO 4 ] 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 Ba 2+ , and the strong electrostatic attraction between Al 3+ and F − . On the contrary, many Al‐bearing crystal phases with high melting point precipitate in the CaO–Al 2 O 3 ‐based melt, which will improve the crystallization ability of slag and deteriorate its lubrication performance.