To solve the problem of high longitudinal cracks on the surface of slab during high-speed thin slab continuous casting, in this study, the heat transfer capacity of mould flux was reduced by increasing the basicity, and the influence mechanism was revealed. According to our results, when the basicity increased from 1.60 to 1.80, the crystallization temperature range of the mould flux broadened, the critical cooling rate increased, and the crystallization activation energy decreased; thus, increasing the basicity promoted the crystallization of the mould flux. Simultaneously, increasing the basicity reduced the heat flux density of the slag film, promoted the precipitation of the main mineral phase cuspidine (Ca₄Si₂F₂O₇) in the slag, and reduced the heat transfer performance. FTIR and Raman spectra demonstrated that increasing the basicity reduced the aggregation of molecular clusters in the slag and increased the crystallization rate, which was beneficial to the crystal growth but detrimental to the heat transfer performance.

To solve the problems of slag entrapment risk and frequent bond alarm in the field application of mould flux for high-speed thin slab continuous casting, the idea of ‘non-Newtonian fluid mould flux with shear-thinning property’ is introduced. It was found that with an increase in the Al₂O₃ content, the shear-thinning behaviour of the mould flux first increased and then decreased. The sample with 8.61% Al₂O₃ content had the strongest shear-thinning property and the lowest fluidity index, which reached 0.75. With the addition of Al₂O₃, the degree of polymerization of the mould flux molecules increased, and the relative strength of the Si–O–Al bond increased. It was found that the Al₂O₃ content has a significant influence on the ^IVAl complexes. The XPS results showed that Q³(1Al) was the structural unit most easily affected by shear stress, and the higher the content of Q³(1Al), the stronger the shear-thinning property of the mould flux.