During continuous casting,properties of mold flux and mineralogical structures of flux film play important roles in controlling steel quality.The effect of soda ash on the physical properties and crystallization characteristics of mold flux was investigated using process mineralogy,including polarizing microscopy,X-ray diffraction,and electron microprobe,etc.Mold flux was mainly prepared using cement clinker and industrial mineral materials under laboratory conditions,and the mineralogical structures of the flux film were systematically identified and quantitatively analyzed.The results showed that,by increasing the soda ash content from 10mass% to 18mass%,the crystallization temperature,critical cooling rate and crystallization ratio of the flux film decreased,but the crystallization ratio still reached 75% after adding soda ash,and the mineral compositions and microstructures of the flux film changed slightly.When the soda ash content exceeded 14mass%,the critical cooling rate and the crystallization ratio decreased slightly,whereas the mineral content of the flux film changed evidently,with a large amount of cuspidine precipitation and a significant decrease in the wollastonite content until it reached zero,which resulted in deterioration of the lubrication of the flux film. During continuous casting, properties of mold flux and mineralogical structures of flux film play important roles in controlling steel quality. The effect of soda ash on the physical properties and crystallization characteristics of mold flux was investigated using process mineralogy, including polarizing microscopy, X-ray diffraction, and electron microprobe, etc. Metal flux was mainly prepared using cement clinker and industrial mineral materials under laboratory conditions, and the mineralogical structures of the flux film were systematically identified and quantitatively analyzed. The results showed that, by increasing the soda ash content from 10 mass% to 18 mass%, the crystallization temperature, critical cooling rate and crystallization ratio of the flux film decreased, but the crystallization ratio still reached 75% after adding soda ash, and the mineral compositions and microstructures of the flux film changed slightly. the soda ash content exceeded 14 mass%, the critical cooling rate and th e crystallization ratio decreased slightly, while the mineral content of the flux film changed evidently, with a large amount of cuspidine precipitation and a significant decrease in the wollastonite content until it reached zero, which resulted in deterioration of the lubrication of the flux film.