Development of fluoride-free mold powders for peritectic steel slab casting

In this paper, titanium-bearing blast furnace slags (CaO-SiO ₂-TiO₂) produced at Panzhihua Iron and Steel Company (P. R. China) is used as the base material to develop fluoride-free (F-free) mold powders to improve the heat transfer between the mold and the strand. Effects of the binary basicity (CaO/SiO₂), TiO₂, Na₂O, Li₂O, MgO, MnO and B₂O₃ on the melting temperature, viscosity and heat flux of F-free mold powders are investigated. The laboratory results indicate that 1) the melting temperature and the viscosity of the F-free powder decrease, as expected, with increasing the content of Li₂O, B₂O₃ and Na₂O respectively, but the lowest viscosity is achieved with 6.0mass% TiO ₂; 2) the heat flux of the F-free slag film with 1.0-6.0 mass% TiO₂ is close to that of a conventional mold slag film with 2.0-10.0 mass% F; 3) the effect of basicity of the F-free powder on the heat flux is the same as the powder bearing fluoride; 4) the heat flux changes significantly with more than 8.0mass% Na₂O and about 4.0mass% MnO, whereas the effects of Li₂O and B₂O₃ in the F-free powder on heat flux are not significant. The suitable range of main components of the F-free powder with TiO₂ is proposed for casting peritectic-grade-steel slabs. The industrial trials of peritectic steel casting, using the proposed F-free flux, reveals a good surface quality of the slab, and well-controlled heat transfer at the continuous casting mold by the F-free powder with the precipitated crystalline phase being perovskite (CaTiO₃) instead of cuspidine In the conventional mold slags that contain fluoride.