Effect of substituting SiO₂with TiO₂on viscosity and crystallisation of mould flux for casting titanium stabilised stainless steel

Abstract

During casting of titanium stabilised stainless steel, a gradual increase in TiO 2 content in the molten mould slag from absorption of TiO 2 inclusions causes changes in properties of the mould flux, such as viscosity, solidification temperature and crystallisation behaviour. To simulate this effect mould fluxes were prepared with SiO 2 being substituted with 5 and 10%TiO 2 and viscosity and crystallisation behaviour studied. Experimental results indicate that the substitution of SiO 2 with TiO 2 leads to suppression of crystallisation of cuspidine and formation of perovskite in glass quenched from mould fluxes. The crystallisation tendency is reduced by the introduction of TiO 2 . The high temperature viscosity of mould fluxes shows a decrease with increasing TiO 2 . At lower temperature, the viscosity of mould fluxes with 10%TiO 2 is greater than that of TiO 2 free slag, which could be attributed to precipitation of solid particles.

Structural Study of Glassy CaO–SiO2–CaF2–TiO2 Slags by Raman Spectroscopy and MAS-NMR

“…Many researchers 4,5) have reported that viscosity of mould fluxes decreases with increased pickup of TiO2 in fluxes during casting. According to the present structural study, degree of polymerization is slightly enhanced with TiO2 increase.…”

“…The Ti-O bonds are expected to be weaker than Si-O bonds. It was also reported 5) that crystallization ability of mould fluxes also decreases with increase of TiO2. The slightly enhanced degree of polymerization could be one reason for decreased crystallization.…”

“…This phenomenon can be illustrated by following equation: 4) Increase of TiO 2 concentration due to above reaction could have strong influence on physicochemical properties of mould slag such as viscosity and crystallization ability, and performance of heat transfer and lubricity, which would bring instability and even problems during operation of casting. 4,5) Physicochemical properties of melts strongly depend on the microstructure and investigation of structure characteristics can be employed to explain the changes of physiochemical properties. [6][7][8] For example, there are correlations between polymerization degree of molten slag and viscosity.…”

Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 2 Specialist Mould Powders

“…However, B 2 O 3 additions frequently result in a decrease in viscosity. 7,[42][43][44] In pure B 2 O 3 the structure is made up of 3-coordinated BO 3 units arranged in the form of 2-dim rings. However, additions of CaO or Na 2 O result (shown in Eqs.…”

“…It is well established that TiO 2 additions result in a decrease in slag viscosity. 11,30,32,39) There are three possible ways TiO 2 can modify the slag structure, namely (i) Ti 4 + is incorporated into the SiO 4 network (ii) Ti acts as a network breaker (by adopting coordination of 5-or 6-) and (iii) by forming TiO 2 -like structures (clusters). 40) There is some dispute which is the dominant mechanism in the geological literature and recent publications are equally inconclusive.…”