Crystallization of Slag Films of CaO-AlO-BaO-CaF-LiO-Based Mold Fluxes for High-Aluminum Steels' Continuous Casting.

In this study, solidified films of CaO-AlO-BaO-CaF-LiO-based mold fluxes with different contents of AlO addition were acquired by immersing an improved water-cooled copper probe in bulk molten slags. This probe can obtain films with representative structures. Different slag temperatures and probe immersion times were employed to investigate the crystallization process. The crystals in the solidified films were identified using X-ray diffraction, the morphologies of the crystals were observed using optical microscopy and scanning electron microscopy, and the kinetic conditions, especially the activation energy of devitrified crystallization in glassy slags, were calculated and discussed based on the differential scanning calorimetry. The results indicated that after adding extra AlO, the growing speed and thickness of the solidified films increased, and more time was required for the film thickness to reach a steady state. In addition, fine spinel (MgAlO) precipitated in the films at the early stage of solidification after adding 10 wt% of extra AlO. Together with LiAlO, spinel (MgAlO) acted as nuclei for the precipitation of BaAlO. The apparent activation energy of initial devitrified crystallization decreased from 314.16 KJ/mol (original slag) to 297.32 KJ/mol (5 wt% AlO added) and 269.46 KJ/mol (10 wt% AlO added). The crystallization ratio of the films also increased after adding extra AlO.