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To evaluate the crystallization behavior of Ti-bearing blast furnace slag-based glass ceramics, SiO2-Al2O3-CaO-MgO-TiO2 systems with various TiO2 were investigated. The crystallization process and mechanical properties were analyzed. The results show that with TiO2 increasing, exothermic peak temperature (Tp) decreases, and the crystallization is promoted by the introduction of TiO2. A small amount of TiO2 (≤4%) addition can significantly promote crystallization, and when TiO2 continues to increase, the crystallization is decreased slightly. The Avrami parameter (n) of all samples is less than 4, indicating that in prepared glass-ceramics, it is hard to achieve three-dimensional crystal growth. The main crystalline phase is akermanite–gehlenite. The addition of TiO2 has no obvious effect on the type of main crystalline phase. The prepared glass-ceramic with 4% TiO2 show good mechanical properties with the hardness values of 542.67 MPa. The recommended content of TiO2 is 4% for preparing glass-ceramics.

The phase and crystal morphology transitions of two typical types of mold fluxes were investigated fundamentally using differential scanning calorimetry (DSC) and confocal scanning laser microscopy (CSLM) techniques. For the traditional CaO–SiO2–CaF2-based mold flux, different cooling rates can change the phases and the crystal morphologies. Faceted cuspidine and CaSiO3 are co-precipitated when the cooling rate is less than 50 °C·min−1. The phases transform from Ca4Si2O7F2 and CaSiO3 to Ca4Si2O7F2 at the cooling rate of 50 °C·min−1. Cuspidine shows four different morphologies: faceted shape, fine stripe, fine stripe dendrite, and flocculent dendrite. The crystalline phases of CaAl2O4 and Ca3B2O6 are co-precipitated in the CaO–Al2O3-based mold flux. Neither the phases nor the crystal morphologies change in the low cooling rate range (5 °C·min−1 to 50 °C·min−1). With decreasing temperature, the morphology of CaAl2O4 firstly becomes dendritic, and then the dendritic quality gradually changes to a large-mesh blocky shape at the cooling rates of 100 °C·min−1, 200 °C·min−1, and 500 °C·min−1. Different cooling rates do not show an obvious impact on the morphology transition of CaAl2O4. The strong crystallization ability and large rate of crystallization affect the control of the heat transfer of the CaO–Al2O3-based mold flux during casting. The big morphology difference between primary crystals of the CaO–SiO2–CaF2-based mold flux and the CaO–Al2O3-based mold flux is probably one of the biggest factors limiting lubrication between the CaO–Al2O3-based mold flux and high-Al steel during casting.