During the continuous casting (CC) of Ti-bearing steel, a steel lump can solidify in the mold (i.e., floater steel) more easily than in the Ti-free steels. This causes severe surface defects or even a breakout. We have examined the mechanisms of floater formation during the CC of 321 stainless steel by analyzing the inclusions in the floater steel and in the 321 steel that was sampled from the mold. Additionally, we calculated the disregistry between the metallic phases and common inclusions. The mineralogy and morphology of the inclusions were examined while using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Thermodynamic calculations on the Ti_xO_y inclusions at different oxygen potentials were performed while using FactSage 7.2. Using this approach, we determined that ferrite nucleates grow on TiN and MgO inclusions following solidification, which then form micro-aggregates as a result of dynamic collisions and alliances. Analysis of the mold slag from the metallurgy stage indicated that altering the basicity and properties of the mold flux systematically might minimize the reaction between the slag and steel, which would achieve a coordinated control over lubrication and heat transfer.

In the present study, laboratory-scale experiments and thermodynamic calculation between the mould slags and the steel were performed to investigate reaction performances of mould slags during continuous casting (CC) of 321 stainless steel. The results show that in the final Slag1 (traditional mould slag), SiO₂ decreased by 3.86 wt-% and TiO₂ increased by 4.85 wt-%, whereas the melting temperature, viscosity and crystallization rate increased noticeably. Perovskite (CaTiO₃) and TiN were precipitated during the steel-slag reaction. Compared to Slag1, both properties and constituents of Slag2 (newly developed) with low SiO₂ changed moderately, despite TiO₂ in the final Slag2 increased by 3.96 wt-%. The precipitation of TiN and the reactivity between steel and slag were evaluated by the thermodynamic method. A comprehensive enthalpy change of steel-slag reaction was estimated to elucidate the formation of frozen steel or clogging based on the experimental results and the thermodynamic calculation.