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Title: Electrochemical studies of inclusion decomposition in steel
Author: Harris, S. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2002
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The feasibility of removal of sulphur from the surface of a solid steel sample by decomposing sulphide inclusions was investigated, using a direct electrochemical reduction technique in a molten CaCl2 electrolyte operating at an elevated temperature of 1123K. Sulphur removal was investigated with sulphur in two different forms, as iron (II) sulphide (FeS) and as mixed iron-manganese sulphide ((Fe, Mn)S) inclusions. Steel samples were prepared to contain different concentrations of sulphur in these forms. Unelectrolysed samples were verified for morphology using scanning electron microscopy (SEM) and the chemical nature of the inclusions using energy dispersive x-ray (EDX) analysis. These were then compared with steel samples that were subjected to cathodic potentials. Chronoamperometry was conducted with the steel samples used as cathodes, for varying durations with various applied potentials with respect to a carbon anode. Samples were examined after electrolytic treatment using SEM and EDX. The depth to which sulphur depletion had occurred was measured and compared to calculated values for diffusion models. Cyclic voltammetry was performed to characterise reactions occurring at the electrode-electrolyte interfaces in the electrochemical cell and both reduction reactions for the cathode and oxidation (gas evolution) reactions identified for the anode. Sulphur depletion depths of up to 45mm were achieved for steel samples containing 0.3 wt% S as globular FeS inclusions, in agreement with diffusion model-predicted values based on random-walk estimation. Samples with higher sulphur (1 wt.% S as FeS) concentration achieved S depletion depths up to 55 mm. The calculated effective diffusion coefficients were observed to be higher and could be related to the presence of S along the grain boundaries, thus providing faster short-circuit paths for diffusion. In steel samples containing MnS inclusions (along with FeS), sulphur depletion by decomposition of sulphide inclusions were consistently achieved to a depth of 5-15mm, with a secondary effect to 40mm, where the inclusion's morphology was affected.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available