Observations of Crystallization in Mold Slags with Varying Al2O3/SiO2 Ratio

Zhang, Z.T.; Wen, Guangrui; Liao, Junlin; Sridhar, Seetharaman

doi:10.1002/srin.201000058

Cited by 46 publications

(36 citation statements)

References 28 publications

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“…As per the aforementioned discussions, a trend to form high melting point crystals such as Ca 2 Al 2 SiO 7 with increasing alumina content was observed. 28) This might partly explain the increase in crystallization tendency with increasing alumina content. 4) The heat flux was correspondingly decreased with increasing alumina content.…”

Section: Effect Of Alumina Content In Slag Nomentioning

confidence: 99%

Crystallization Behaviors of Slags through a Heat Flux Simulator

et al. 2010

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This paper investigates how the basicity and alumina content in synthetic slags influence the crystallization behavior that takes place in a heat flux simulator for mold slags. The purpose is to elucidate the variation in crystallization behavior for model slags that are expected to be glassy, partly crystalline and fully crystalline in order to correlate the changes in heat flux to the dynamic solid evolution that occurs in the simulator. Three levels of alumina content (3, 15 and 25 wt%) were chosen to investigate the heat transfer behavior through slag film which have different tendency of reaction with molten steel during continuous casting of high aluminum containing Transformation Induced Plasticity (TRIP) steels. A Confocal Scanning Laser Microscopy (CSLM) was used to develop TTT diagrams for the slags. XRD and SEM were also used to analyze the micro-structures of the crystalline phases.The measured heat fluxes through the mold slags tested were found to increase, as the crystallinity of the slag film decreased with decreasing basicity and alumina content. It was found that the crystallization temperature increased, while the incubation time for crystallization decreases with increasing basicity and alumina content. The increase in alumina content induced the precipitation of CaF 2 during cooling process and hence a change in the crystalline phase from Ca 4 Si 2 O 7 F 2 to Ca 2 Al 2 SiO 7 .KEY WORDS: mold slag; TRIP steel; crystallization behavior; heat flux.formance of a mold slag simulator that was developed by Wen 12) by using model mold slags whose crystallization behavior can be predicted. The second purpose was to analyze the heat fluxes with TTT diagrams developed using CSLM method.In recent years, advanced high strength steels (AHSS) have attracted much attention to be used as car bodies due to its excellent combination of high strength and ductility, [13][14][15] which necessitate the development of AHSS steels for continuous production in steel plants. However, there are several problems that need to be overcome and some are related to the high amount of reactive elements in these alloys. 16,17) For example, it is difficult to control the alloy composition during continuously casting of some grades of AHSS, such as TRIP steels, as a result of reactions between the mold slag and the melt, involving the formation of alumina. Critical properties of the mold slag can change during casting as a result of alumina pick-up, 18,19) when casting high aluminum TRIP steel and this could cause surface cracks on the slab or sticker break-outs. It is therefore necessary to study how to suppress the reactions between the mold slag and the melt. One possible method to accomplish this is to increase the alumina content in the mold slag. The details of the incorporation of alumina in slags is however not completely known and depending on this the alumina content in mold slag could result in changes in the key thermophysical properties of mold slag, such as viscosity, crystallization and thermal conductivity. The t...

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Section: Effect Of Alumina Content In Slag Nomentioning

confidence: 99%

Crystallization Behaviors of Slags through a Heat Flux Simulator

et al. 2010

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“…Plant experiments on continuous casting of TRIP steels indicate that a significant change of chemical composition occurred at around 10 to 15 min after the process started and alumina pickup and silica drop seem to pass a critical point. 27) In previous studies, [28][29][30] the variations of viscosity and crystallization behaviors with increasing mAl 2 O 3 /mSiO 2 ratio have been investigated, and the experimental results indicated that these thermophysical properties changed with varying mAl 2 O 3 /mSiO 2 ratio. However, the effect of mAl 2 O 3 / mSiO 2 ratio on the slag structure has not yet been investigated.…”

Section: Introductionmentioning

confidence: 99%

Effect of Al2O3/SiO2 Ratio on the Viscosity and Structure of Slags

et al. 2012

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The present paper investigates how the mass ratio between Al2O3 and SiO2 (mAl 2 O 3 /mSiO 2 ) in slag compositions influences the structure, viscosity and crystallization of the slag melts. The objective is to study the variations in viscosity and structure of slags with increasing mAl 2 O 3 /mSiO 2 ratio. In practice the results of the study are relevant to the significant changes in slag property caused by the changes in chemical composition during continuous casting of steels containing high amounts of dissolved aluminum.The viscosity was found to decrease slightly with increasing mAl 2 O 3 /mSiO 2 ratio up to 0.56. The degree of polymerization for [SiO4]-tetrahedra was found to decrease with increasing mAl 2 O 3 /mSiO 2 ratio based on the Fourier Transformation-Infrared Spectra (FT-IR) and Raman spectra, which could explain the observed decrease in viscosity. AtmAl 2 O 3 /mSiO 2 ratios above 0.56, the viscosity was found to abruptly increase which could be caused by the presence of spinel crystals. The activity coefficient was computed and it was found that the activity coefficient of alumina presents negative deviation when mAl 2 O 3 /mSiO 2 ratio is less than 0.35, while it shows a positive deviation when mAl 2 O 3 /mSiO 2 ratio exceeds 0.35. This phenomenon may be related to the change of the primary phase region correlating to the phase diagram to the slag composition.

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“…21) In the present work, crystallization behaviors of CaO-Al2O3-based mould fluxes with varying TiO2 content were investigated by the differential thermal analysis (DTA). Continuous cooling transformation (CCT) diagrams of mould fluxes were constructed.…”

Section: Introductionmentioning

confidence: 99%

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

Shu

Hou

et al. 2015

ISIJ Int.

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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.

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Observations of Crystallization in Mold Slags with Varying Al₂O₃/SiO₂ Ratio

Cited by 46 publications

References 28 publications

Crystallization Behaviors of Slags through a Heat Flux Simulator

Crystallization Behaviors of Slags through a Heat Flux Simulator

Effect of Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub> Ratio on the Viscosity and Structure of Slags

Effect of TiO<sub>2</sub> Addition on Crystallization Characteristics of CaO-Al<sub>2</sub>O<sub>3</sub>-based Mould Fluxes for High Al Steel Casting

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