Research on shear-thinning and surface properties of CaO–SiO₂–CaF₂–Al₂O₃-based mould flux

The main feature of high-efficiency continuous casting production is the increase in casting speed. This leads to an increased risk of slag entrapment in the liquid surface area of the mould and steel leakage due to the bonding of the casting billet. Both traditional mould flux and non-Newtonian fluid mould flux with only shear-thinning properties cannot effectively solve these problems. This study selected a practical high-casting speed thin slab mould flux from a steel plant as the original mould flux. Add 4.6–12.1% Al 2 O 3 and 3.6–4.9% MnO and other additives to prepare a new type of mould flux with both shear thinning characteristics and high surface tension. The shear-thinning properties, interface properties and microstructure of the mould flux were detected and studied using methods such as the rotating cylinder method. The results showed that with the increase of Al 2 O 3 content, the shear-thinning properties of the mould flux first enhanced and then weakened. The strongest effect was observed when the Al 2 O 3 content was 8.7%. The contact angle, surface tension and interface tension of the mould flux were significantly improved and the degree of molecular polymerisation gradually increased. The shear-thinning properties of mould flux are mainly related to the Si–O–Al structure. The interaction force between Al 3+ in the slag and the surface O 2− of the mould flux increases, and the surface tension of the mould flux increases. When the Al 2 O 3 content is more than 10.5%, a large amount of AlO 2− will be repelled to the surface of the mould flux, and the change in surface tension is no longer significant.