Abstract
The authors present a series of complementary test methods which were developed and used to investigate reactions between high aluminium steel and silica rich inclusions. Non-metallic inclusions (NMIs) cause many defects in the final steel product, therefore the ability to track their size, morphology and composition and correlate this with fundamental reaction kinetics provides important knowledge to support the production of clean quality steel products. Novel steel grades such as TRIP, TWIP and low-density steels have high aluminium contents; aluminium is a readily oxidisable species presenting the potential for instability and excessive reaction with commonly used mould powders that contain silica. A novel combination of techniques including HT-CLSM (High-Temperature Confocal Laser Scanning Microscope), XCT (X-ray computed tomography) and SEM/EDS (scanning electron microscopy/electron dispersive spectroscopy) have been used to study the interaction of entrained mould powder inclusions with steel at high temperatures simulating industrial conditions. This report presents a discussion on the development of techniques and samples to achieve representative and repeatable results that can provide information on the complex chemical and physical interaction phenomena with confidence. Each experimental technique had its own learning points and consequent results. Outcomes presented include possible confirmation of the chemical reaction rate controlling step being aluminium mass transfer; heterogeneous local environmental conditions including fluidity and chemical composition; and occurrence of spontaneous emulsification where the mould powder inclusion breaks apart into a cloud of smaller fragments.
Highlights
Non-metallic inclusions cause various defects in steel such as slag spots and line defects (Zhang et al, 2002)
Indirect methods are widely adopted in industry to determine the number of inclusions and consist of determining the chemical composition of the slag as well as the conditions of the refractory and composition of the liquid steel giving information of how much of the alloying elements have reacted with the slag
The main goal of this paper is to explore the development of a method to study the interaction between steel and an inclusion and the floatation rates of the inclusions in the liquid steel, which are influenced by the composition and size of the inclusions
Summary
Non-metallic inclusions cause various defects in steel such as slag spots and line defects (Zhang et al, 2002). An oscilloscope is used to compare the signals emitted to indicate the quality of the sample This non-destructive test method can be used to detect inclusions larger than 20 μm in solidified steel samples (Zhang and Thomas, 2003). The main goal of this paper is to explore the development of a method to study the interaction between steel and an inclusion and the floatation rates of the inclusions in the liquid steel, which are influenced by the composition (density) and size of the inclusions These factors are affected by the exchange of material across the inclusion-steel interface driven by the system’s starting chemical potential. 0.0006 0.0006 impurities such as graphite or soot are burnt away during the 600oC preheat and not dissolved in the slag
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