Effects of SrO and Basicity on Structure and Thermal Properties of Fluorine‐Free Mold Fluxes for High‐Titanium Steels
Zijing Ni, Zhuo Chen, Jiajing Zhang, Yiman Chen, Weitong DuABSTRACT
To overcome the property degradation of traditional CaO‐SiO 2 fluxes reacting with titanium for the casting of high‐titanium steel, this study introduces an eco‐friendly, fluorine‐free flux using SrO to replace CaO partially. This modification regulates the microscopic network structure of the slag melt and thereby affects its fluidity and heat‐transfer behavior. A multi‐component fluorine‐free mold flux system, CaO–SrO–SiO 2 –TiO 2 –Al 2 O 3 –B 2 O 3 –Na 2 O–MgO, was developed and its microstructural evolution and regulatory effects on macroscopic properties (viscosity and thermal conductivity) were analyzed using molecular dynamics (MD) simulations and Raman spectroscopy. The results indicate that with increasing SrO content at a constant CaO/SiO 2 ratio, the melt structure undergoes initial depolymerization followed by repolymerization, reaching its lowest degree of polymerization and minimum bridging oxygen proportion at 3.6 wt% SrO. Furthermore, variations in basicity significantly impact the network, as the CaO/SiO 2 ratio decreases from 1.08 to 0.84, the degree of network polymerization increases due to a higher proportion of SiO 2 . However, for low basicity, the amphoteric oxide Al 2 O 3 shifts from acting as a network former to a network modifier due to insufficient charge compensation from Ca 2+ , which subsequently decreases the degree of polymerization. Macroscopically, the viscosity of the slag is positively correlated with the degree of polymerization. The introduction of SrO effectively reduces the system's viscosity and flow resistance by depolymerizing the silicate network. Additionally, calculations using the reverse non‐equilibrium MD method reveal that thermal conductivity exhibits non‐monotonic fluctuations with increasing SrO content. It reaches a local minimum at 1.8 wt% due to reduced structural polymerization, and peaks at 5.4 wt% owing to the formation of stable coordination structures. Finally, as the CaO/SiO 2 ratio decreases, thermal conductivity shows a non‐monotonic response to decreasing C/S, increasing from 1.08 to 0.84 and then decreasing to 0.77.