硼对无氟保护渣熔渣微观结构的影响

 在钢铁行业产能过剩和节能减排的背景下,积极寻找保护渣中氟的替代物,开发新型无氟保护渣已成为实现绿色高效化连铸生产的重要途径。硼作为氟的理想替代物以其经济成本和助熔效果的优势,成为无氟保护渣技术新的研究热点,并被认为具有最广泛的应用前景。为探究含硼无氟保护渣的熔化结晶机理,从熔体微观结构变化的角度阐明含硼无氟渣黏度性能变化的内因,以期实现其工业化应用,选用高炉渣、石灰石、石英砂、纯碱和硼砂作为主要原料制备含硼无氟保护渣,结合拉曼光谱技术和Scigress分子动力学模拟对无氟保护渣熔渣的键长、配位数和结构单元等微观结构进行了系统研究。结果表明,随着硼砂质量分数从4%增加到16%,熔渣中硼氧骨干的结构发生较大变化,B—O的平均配位数从3.028增加到3.096,Si—B的平均配位数从0.229增加到0.898,[BO₃]三面体转变为[BO₄]四面体,B—O的平均键长保持1.375 nm不变;熔渣中桥氧数量增加,结构单元由简单的岛状结构、环状结构向着复杂的层状结构和架状结构转变,形成了复杂的硼硅酸盐结构,使熔渣聚合度升高,导致原子基团和离子的迁移阻力被加强,不利于晶体的成核和生长,抑制了保护渣的结晶,从而使熔渣黏度进一步降低。综合来看,含硼无氟渣系中硼砂质量分数为7%～16%时,熔渣聚合度较高,网络结构较复杂,黏度稳定性较好。

Effect of boron on microstructure of fluorine-free mold fluxes

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.