Abstract: In light of the slab quality problems in the production of Q235B steel, the chemicophysics properties of the mold powder were analyzed; and then combining the quality of slabs, the microstructures of slag films were roundly studied. The results showed that, the melting temperature, viscosity of this flux was lower than the theoretical value of fluxes casting for peritectic steel, and the microstructures were different between reasonable films and unqualified films. The mineralogical phase of reasonable films for Q235B steel slab casting, of which crystal rate could reach 90 %～95 %, include akermanite, cuspidine and wollastonite. The outstanding characteristic of unqualified films with longitudinal cracks accidents was that crystal rate could be only 65 %～70 %. As to unqualified films with sticking breakout accidents, the biggest difference comparing with reasonable films was the mass formation of cuspidine, while crystal rate could anomaly reach 95 % or more. Combining the parameters of casting technics and chemical components of the mold powder casting for Q235B steel, the causes of abnormal film structures and quality defects of slab surface were finally given.

Key words: mold powder, chemicophysics properties, slag films, microstructure, Q235B steel