Effect of TiO_2 Addition on Crystallization Characteristics of CaO-Al_2O_3-based Mould Fluxes for High Al Steel Casting

摘要

Crystallization behaviors of new developed CaO-Al_2O_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_2O_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.