Search

Mold flux, which plays an important role in continuous casting, occurs when liquid slag on top of the molten steel infiltrates the gap between the shell and mold. During this process, a liquid slag film forms on the shell side, whereas a solid slag film forms on the mold side. The behavior of the slag film between the shell and mold has a significant effect on the sequence casting and quality of the slab surface. To investigate the in-mold behavior and heat transfer of slag film, researchers have simulated the formation of slag film in the laboratory. Measurements and theoretical calculations have been performed to study the heat transfer of slag film. In this paper, the experimental methods used to simulate the formation of slag film were described and the research related to heat transfer in slag film was summarized, including the interfacial thermal resistance, the thermal conductivity of the mold flux, radiative heat transfer, and optical properties of the slag film. The issues related to the formation and heat transfer of slag film were also identified, that require further investigation. The results of recent studies indicate that the hot thermocouple technique could be applied to observe the formation of slag film, and the copper-finger dig test could be used to obtain samples for investigations related to the microstructure of solid slag film. The interfacial heat resistance is reported to be between 0.0002 and 0.002 m2·K·W-1. The thermal conductivity of mold flux at 800℃ ranges from 1.0-2.0 m2·K·W-1, and increases with increased temperature. Crystals in the solid slag film not only increase the interfacial heat resistance, but also decrease the radiative heat flux by reducing the reflectivity of slag film. Furthermore, due to the resulting change in optical properties, the addition of transition metal oxides and fine particles dispersed in slag film may also influence the radiative heat transfer through slag film.

Solidification of micro-alloyed steels under different cooling processes was simulated by confocal laser scanning micros-copy (CLSM), and the change of the sample surface was in-situ observed. The correlation between the change of the sample surface and the precipitation of secondary phases was discussed. It is found that some small reliefs appear on the sample surface during liquid steel solidification. The appearing temperature and the distribution of reliefs are consistent with the results of the theoretical calculation of secondary phase precipitation and the characterization of transmission electron microscopy (TEM). The precipitation of secondary phases can be indirectly characterized by in-situ observations of surface reliefs, which will be helpful to analyze the effect of secondary phases on the evolution of the matrix.

In order to eliminate the hazard effects of the leaching of fluorine in mold fluxes,this paper introduces a mold flux with high Al2O3 content. The effects of Al2O3 content on the concentration of F- ions and the pH value of leaching water were investigated,and the dependence of Al2O3 on the structure of mold fluxes was analyzed by X-ray photoelectron spectroscopy(XPS). When the mass fraction of Al2O3 is 4%,the concentration of F- ions in leaching water is about 22.8 to 35.4 mg·L-1,and the pH range is between 4.0 and 9.5. The F- concentration and the pH range initially reduces and then slightly rises again as the Al2O3 content increases from 4% to 34%. The XPS spectra show that the Al-F bond forms in the mold flux when the Al2O3 content increases. This can restrain the dissolution of fluorine in water. Controlling the content of Al2O3 between 16% and 34%,the F- concentration in leaching water is about 4.0 to 10.0 mg·L-1,and the pH range is between 6.5 and 7.5. This is helpful to reduce the hazard effects of the leaching of fluorine in mold fluxes.