Effect of TiO₂ Addition on Crystallization Characteristics of CaO-Al₂O₃-based Mould Fluxes for High Al Steel Casting

Abstract

Crystallization behaviors of new developed CaO-Al2O3 based mould fluxes with TiO2 addition for casting of high-Al steels were investigated by using DTA techniques combined with SEM-EDS and XRD analysis. XRD and SEM analyzed on the crystallized samples showed that the sequence of crystal precipitation for TiO2-free mould flux during cooling was MgO, and followed by Ca12Al14O33 during cooling. The sequence of crystal formation for TiO2-bearing mould fluxes during cooling is CaTiO3 to MgO, and then Ca12Al14O33. Continuous cooling transformation diagrams (CCT) were constructed for analysis of the crystallization behaviors. The Undercooling values for onset crystallization of various crystals were calculated by using liquidus temperature obtained by heating DTA and crystallization temperature of various crystals. The crystallization temperatures of CaO-Al2O3 based mould fluxes increased with increasing TiO2 content. The undercooling values for onset crystallization of CaTiO3 decreased with increasing TiO2 content, which indicating that the crystallization of CaTiO3 was enhanced with increasing TiO2 content. The undercooling values for onset crystallizations of Ca12Al14O33 and MgO only changed slightly with increasing TiO2. This indicated that crystallizations of Ca12Al14O33 and MgO crystals were only slightly influenced by TiO2 addition. The overall crystallization of mould fluxes was enhanced with increasing TiO2 content.

Effect of CaF2 substitution with TiO2 on the crystallization characteristics of low-fluoride slag for electroslag remelting

“…As shown in Figure 4(b), the precipitation temperature of the second crystalline phase CaTiO 3 in slag A is much lower than those in slag B and slag C. And increasing TiO 2 content from 8.6 wt% to 13.0 wt% has no obvious effect on the precipitation temperature of CaTiO 3 . This result is consistent with the finding reported by others [25]. The slag with a higher crystallization temperature easily forms a thick slag skin and unstable heat flux across the slag skin.…”

“…Therefore, TiO 2 addition increasing activity values of some main components (CaO, Al 2 O 3 , and CaF 2 ) during Ca 12 Al 14 O 32 F 2 formation was the main factor in the enhancement of slag crystallization ability with increasing TiO 2 content. This is similar to the role of Li 2 O on the crystallization behavior of CaO-SiO 2based mold flux [25], but different from the effect of TiO 2 on the crystallization behavior of CaO-Al 2 O 3 -based mold flux when the crystallization behavior of slag is controlled by element diffusion [28]. The morphology of CaTiO 3 crystal changed from needle-like to blocky with increasing TiO 2 content.…”

Simulation for Mass Transfer Kinetics at Slag-Steel Interface during High Al Steel Continuous Casting

“…Non-reactive slag is a type of CaO-Al 2 O 3 system slag with low or no (SiO 2 ), which could inhibit the reaction and has the potential to solve the problem fundamentally. 13,14) However, its properties are obviously different from those of the conventional slag, which leads to new problems such as strong crystallization performance, large slag ring, etc., affecting the continuous casting process and causing the defects of the slab. 15,16) Although metallurgical researchers have been committed to studying all aspects of the properties of the new type of slag to avoiding reaction from the perspective of thermo-dynamics, there are still many problems to be solved and wide application of the new type of slag still cannot be achieved.…”

Review of Mold Fluxes for Continuous Casting of High‐Alloy (Al, Mn, Ti) Steels

“…The fluorine plays a dominant role in inhibiting crystallization in the low‐temperature zone . The crystallization temperatures and crystallization of CaTiO 3 were enhanced by increasing TiO 2 content from 0 to 10 wt% in CaO‐Al 2 O 3 ‐based mold fluxes, which is unfavorable for lubrication. Therefore, this again suggested that TiO 2 may not be a suitable component in CaO‐Al 2 O 3 ‐based mold fluxes.…”