Viscosity effect of titanium pickup by mould fluxes for stainless steel

Abstract

Mould flux samples from an operating continuous caster showed a steady state increase in titanium oxide content of 3-4% for a titanium stabilised ferritic stainless steel and about 6% for a titanium stabilised austenitic stainless steel. Owing to the reduction of silica the flux basicity increased from 0 . 8 to 0 . 9, and from 0 . 95 to 1 . 2, for the ferritic and austenitic steels, respectively. Similar changes in composition were found for mould shims, which had been recovered from the mould after casting the ferritic steel. The increased titanium oxide content caused a decrease in the flux viscosity, for the original basicity. However, when the flux basicity was increased from 0 . 95 to 1 . 2, the apparent viscosity of the mould flux of the austenitic steel increased markedly, for 10% TiO 2 and temperatures of 1250uC and below. Precipitation of perovskite was found to be responsible for the higher apparent viscosity.

Viscosity Measurements of Some Mould Flux Slags

“…[3][4][5][6][7][8] The viscosity values reported in these references are in most cases considerably higher than those found in the present study. This diversity is attributed to the differences in the chemical compositions.…”

“…Several experimental studies have earlier been carried out in order to determine viscosity data for mould flux slags, [3][4][5][6][7][8][9][10][11][12] both industrial ones as well as synthetic slags with compositions close to industrial mould fluxes. Almost all mould powders contain CaF 2 as it lowers the viscosity and melting point of the fluxes.…”

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.…”

“…[1][2][3] During the casting of titanium-stabilized stainless steel, titanium in the steel have a tendency to reacting with silica in mould fluxes to generate TiO 2 into mould fluxes, and mould powder can inevitably pick up Ti-bearing compounds inclusions floating up from steel, which leads to increase of the concentration of TiO 2 in mould flux. 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.…”

“…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.…”