Reaction mechanism between carbon and CaO–SiO2–Al2O3–Na2O slag system during continuous casting process

The reaction behavior between the carbon and mold fluxes during the heating process is vital for a successful continuous casting process and the high billet quality. A detailed investigation combined with thermogravimetry-mass spectrometry (TG-MS), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and transmission electron microscopy (TEM) techniques was carried out to systematically investigate the transformation mechanistic of the macro physicochemical properties, melting behavior, viscosity, crystallization, and heat transfer performance caused by the reaction behavior. The results showed that the mold flux underwent carbonate decomposition (973–1223 K), solid reaction (1273–1573 K), and melting process (1473–1673 K) during the continuous casting process. The carbon-bearing mold flux exhibited an endothermic peak at approximately 1673 K, corresponding to a weight loss ratio of approximately 14.5% on the TG curve, confirming that carbon could react with the middle mineral phases Ca2SiO4, Ca2Al2SiO7, and Na6Ca3Si6O18 to form SiC, increasing the breaking temperature by approximately 293 K. SEM and TEM results indicated that the melting behavior was restrained by the carbon itself and the newly formed components. Besides, the addition of carbon increased the degree of polymerization of molten slag, the thickness of slag film and the proportion of small crystals in slag film, further leading to an increase in crystallization and heat transfer performances. The reaction mechanism between carbon and slag and the subsequent effects on melting point, viscosity, crystallization ratio and heat flux density were clearly understood, which is meaningful for the carbon blending process of the mold flux.