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

摘要

Crystallization behaviors of new developed CaO–Al_(2)O_(3) based mould fluxes with TiO_(2) 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 TiO_(2)-free mould flux during cooling was MgO, and followed by Ca_(12)Al_(14)O_(33) during cooling. The sequence of crystal formation for TiO_(2)-bearing mould fluxes during cooling is CaTiO_(3) to MgO, and then Ca_(12)Al_(14)O_(33). 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–Al_(2)O_(3) based mould fluxes increased with increasing TiO_(2) content. The undercooling values for onset crystallization of CaTiO_(3) decreased with increasing TiO_(2) content, which indicating that the crystallization of CaTiO_(3) was enhanced with increasing TiO_(2) content. The undercooling values for onset crystallizations of Ca_(12)Al_(14)O_(33) and MgO only changed slightly with increasing TiO_(2). This indicated that crystallizations of Ca_(12)Al_(14)O_(33) and MgO crystals were only slightly influenced by TiO_(2) addition. The overall crystallization of mould fluxes was enhanced with increasing TiO_(2) content.