Isaacs, Jack L. (2020) Modelling the diffusion of aluminium and manganese solutes and oxygen for low-density dual phase steel oxidation in short annealing conditions. PhD thesis, University of Warwick.

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Abstract

The incentivisation of low density steel research is rooted in the reduction of greenhouse gases by lowering vehicle weight and increasing fuel efficiency whilst retaining the properties of conventional automotive high strength steels. Fe-Al-Mn-C steels are a promising class of monolithic low density steels that offer a combination of outstanding mechanical properties, weight reduction, high strength, and good oxidation resistance at elevated temperatures, amongst others. The incorporation of aluminium into these steels means that oxidation is prevalent at elevated temperatures both internally and externally. The dual phase steels in the Fe-Al-Mn-C category are of concern for the lack of knowledge surrounding the internal oxidation behaviour. This project focusses on the ferrite-austenite dual phase steels, which exhibit different diffusion speeds along with the different aluminium and manganese concentrations. This project was aimed at the investigation of the effects that adjacent ferrite and austenite grains have on the internal oxidation behaviour in short annealing conditions. The research involved the annealing of four low density steels of varying ferritic and austenitic crystal phases with grain sizes up to 20µm, at 850°C in different Ar + H2O atmospheres to assess the effects of the dual phase nature of the steel on the oxidation at different surface oxygen concentrations. A computational model was built using COMSOL Multiphysics to compare and interrogate the results further. The results of the experiments did not present a significant difference in oxidation behaviour due to the dual phase nature; however, the simulation results show a slight difference in the oxidation of adjacent ferrite-austenite grains. The effect is obscured in the experimental results by the dominance of the aluminium grain-boundary flux component on the oxidation behaviour which transports the vast majority of the oxidising solute from deeper within the sample to the internal oxidation zone. Suggested further research is on the characterisation of when the dual phase nature of the steel has a large enough effect on the oxidation behaviour to become significant in terms of grain sizes. The knowledge generated by this project is this understanding of the internal oxidation behaviour of low density dual phase Fe-Al-Mn-C steels during short industrial annealing conditions with grain sizes up to 20µm. Specifically the affirmation of the roles of the effective diffusivity, oxygen and metal solute flux, and the roles the grain boundary and grains play in the internal oxidation behaviour of low density Fe-Al-Mn-C with high aluminium and manganese under short industrial annealing conditions

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TL Motor vehicles. Aeronautics. Astronautics T Technology > TN Mining engineering. Metallurgy
Library of Congress Subject Headings (LCSH):	Automobiles -- Materials, Steel, Automobile, Steel-aluminum alloys, Steel -- Metallurgy, Steel, High strength, Oxidation
Official Date:	June 2020
Dates:	Date Event June 2020 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Warwick Manufacturing Group
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Auinger, Michael
Sponsors:	Tata Steel
Format of File:	pdf
Extent:	308 leaves : illustrations (some colour)
Language:	eng

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