Development of a Low Silica Calcium Aluminate Based Mould Flux for Casting High Al/Mn Steels

The third generation of AHHS is a new type of advanced high-strength steel that has improved ductility and can be used in a variety of applications in automobiles. Because of its high Al (0.5–2 wt.%) % and Mn (5–7 wt.%) contents, Al and Mn easily react with the oxides such as SiO2 present in the conventional calcium silicate mold flux which affects the lubrication and crystallization ability provided by the slag film resulting in casting defects such as Break Out Prediction (BOP) alarms, Transverse and Longitudinal depressions. In this study, a calcium aluminate-based alternative mold flux containing different fluxing agents (Na2O, B2O3, SiO2, and CaF2) has been developed. Using a differential scanning calorimeter (DSC/DTA) at three different heating rates, 10 K/min, 15 K/min, and 20 K/min, the onset and peak temperatures of crystallization for the composition having w(CaO)/w(Al2O3) = 1 were determined. The melt structure of the vitreous calcium aluminate-based mold flux was also examined using Raman spectroscopy, and it was shown to have several [AlO4] structural units with [BO3] pyroborate units. The deconvolution results of Raman spectra reveal the degree of polymerization (DOP) of the aluminosilicate network present in calcium aluminate-based mold flux. Utilizing structural data such as the area fraction of various structural units found in the melt structure allowed us to examine the tendency of these fluxes to crystallize.