Effect of boron on microstructure of fluorine-free mold fluxes
YAN Xiao-peng1, LIU Lei2, HAN Xiu-li2, WANG Yin-hui2, ZHANG Di2
1. College of Metallurgy and Energy, North China University of Science and Technology, Tangshan 063210, Hebei, China; 2. College of Mining Engineering, North China University of Science and Technology, Tangshan 063210, Hebei, China
Abstract:Nowdays, under the background of steel overcapacity and energy conservation in the steel industry, actively looking for substitutes to fluorine in mold fluxes and developing new fluorine-free mold fluxes have become an important way to achieve green and efficient continuous casting production. As an ideal substitute for fluorine, boron has become a new research focus of fluorine-free mold fluxes technology due to its economic cost and fluxing effect, and it is considered to have the broadest application prospects. In order to explore the melting and crystallization mechanism of boron-containing and fluorine-free mold fluxes, and to clarify the internal cause for the change of viscosity properties of boron-containing and fluorine-free mold fluxes from the perspective of the change of melt microstructure, blast furnace slag, limestone, quartz sand, soda ash and borax was used as the main raw material to prepare boron-containing and fluorine-free mold fluxes, in order to realize its industrial application. Combined with Raman spectroscopy and Scigress molecular dynamics simulation, the microstructure such as bond length, coordination number and structural unit of fluorine-free mold fluxes were analyze. The results show that as the borax content increases from 4% to 16%, the structure of boron-oxygen backbone in the slag has undergone major changes, the average coordination number of B—O increases from 3.028 to 3.096, and the average coordination number of Si—B increases from 0.229 to 0.898, moreover, the [BO3] trihedron transforms into [BO4] tetrahedron, and the average bond length of B—O remains unchanged at 1.375 nm. The number of bridging oxygen in the slag increases, and the structural unit changes from a simple island-like structure and a ring-like structure to a complex one. The layered structure and the framework structure are transformed, forming a complex borosilicate structure, which increases the DOP of slag, as a result, atomic groups and the migration resistance of ions is strengthened. This is not conducive to the nucleation and growth of crystals, and inhibits the crystallization of mold fluxes, thereby reducing the viscosity of mold fluxes further. On the whole, when the borax content in the boron-containing fluorine-free slag system is 7%-16%, the slag polymerization degree is higher, the network structure is more complex, and the viscosity stability is better.
闫晓鹏, 刘磊, 韩秀丽, 王印会, 张玓. 硼对无氟保护渣熔渣微观结构的影响[J]. 钢铁, 2022, 57(5): 72-80.
YAN Xiao-peng, LIU Lei, HAN Xiu-li, WANG Yin-hui, ZHANG Di. Effect of boron on microstructure of fluorine-free mold fluxes[J]. Iron and Steel, 2022, 57(5): 72-80.
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