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Investigation of the reaction between mould slag inclusions and high aluminium steels in the continuous caster : innovation report
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Raviraj, Akalya (2021) Investigation of the reaction between mould slag inclusions and high aluminium steels in the continuous caster : innovation report. EngD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3763907
Abstract
Mould slag entrainment during the continuous casting process presents a late-stage source of non-metallic inclusions (NMI) with a high likelihood of ending up in the final steel product. The reaction between the entrained slag phase and surrounding liquid steel in the continuous casting mould affects the inclusion morphology and properties. The changes in composition can have adverse effects with the viscosity and heat transfer properties of the mould flux. However, there is a lack of information on the kinetics of the NMI-steel reaction. Using a controlled synthetic inclusion and metal samples, the interaction between inclusion-slag droplets and steel can be investigated to study the reaction and any change in morphology of the inclusion.
Using a correlative approach combining High-Temperature Confocal Scanning Laser Microscopy (HT-CSLM), X-ray Computed Tomography (XCT) and advanced electron microscopy techniques offers the ability to observe the size, shape and composition of an unconstrained reacting inclusion within the steel matrix without dissolving the steel. To investigate this, a low aluminium steel (0.04 wt. %) and a high aluminium steel (1 wt. %) in contact with an inclusion-slag phase with a starting composition aligned to a typical silica-rich mould slag. It was found that the reaction between silica and aluminium across the interface of the two phases provided a driving force for spontaneous emulsification of the inclusion to occur.
Further tests were carried out with an inclusion particle positioned in a dimple on the surface of the steel heated to different temperatures (representing conditions of solid inclusion – solid steel; liquid inclusion – solid steel; and liquid inclusion – semi-solid steel to calculate reaction times that could be present in the continuous caster as the steel slab is cooling.
A mathematical model has also been developed to calculate the kinetics of the reaction by using Gibbs Free energy to calculate the equilibrium constant and the compositions of the components at equilibrium. It has been found that the emulsification of inclusions will have an effect on the floatation rate and potential inclusion removal can be up to 11% longer if spontaneous emulsification were to occur in the continuous caster. Battery cans with inclusions were also investigated and characterised to define a potential pathway for these defects to occur.
The knowledge created has a great impact as inclusions affect all grades of steel, which results in huge losses of yield. Improving any aspect of the yield will have an enormous effect on sustainability due to steel manufacturing being extremely energy intrusive and having a large carbon footprint. The steels used in this study AHSS (Advanced High Strength Steel) including TRIP (Trans- formation Induced Plasticity) steel and DP (Dual Phase) steel are becoming prevalent for their low cost and high strength characteristics.
Item Type: | Thesis (EngD) | ||||
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Subjects: | T Technology > TN Mining engineering. Metallurgy T Technology > TS Manufactures |
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Library of Congress Subject Headings (LCSH): | Slag, Metal castings, Molding (Founding), Steel founding, Steel -- Metallurgy, Aluminium -- Metallurgy, Solid-liquid interfaces, Flux (Metallurgy) | ||||
Official Date: | April 2021 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | EngD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Spooner, Stephen ; Davis, Claire ; Williams, Mark A. ; Seetharaman, Sridhar | ||||
Sponsors: | Engineering and Physical Sciences Research Council ; Tata Iron and Steel Company | ||||
Description: | |||||
Format of File: | |||||
Extent: | xvii, 73 leaves : illustrations | ||||
Language: | eng |
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