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Title: TMPC-property relationship of strong steels
Author: Rahnama, Alireza
ISNI:       0000 0004 5354 8600
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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A method based on the kinetics of crystal growth has been developed and applied to the computation of three-dimensional microstructure in austenite-matensite steels. The model takes into account the phenomenological theory of martensite crystallography which can predict the shape and orientations of martensite precisely. The interaction energy based on the plastic work model is taken into account to compute the variant selection in an austenitic stainless steel and formation of martensite under externally applied stress. This method is programmed in C++ and visualized with an in-house software AcaVisual. This model is able to deal with every circumstance where the shape deformation due to martensitic transformation is defined, provided that detailed crystallographic data is available. To further investigate the processing-microstructure-property relationship in strong steel, a low carbon steel has been selected to study its microstructure and property evolution under various processing conditions. It is found that the interlamellar spacing increases as the number of pulses increases. The addition of energy change due to electropulsing to the interfacial energy is thought to be responsible for the increase in the spacing. It is noted that after a critical number of applied pulses, the interlamellar spacing remains invariant to the further electropulsing. Mechanical properties are examined as functions of the number of pulses and interlamellar spacing. It is shown that softening occurs after 1000 times of current pulses which is attributed to the spheroidisation of the lamellar structure. The present work also reports the experimental observation of electropulse-induced microstructural evolution in a ferritic-pearlitic steel at ambient temperature. Electropulsing treatment leads to the formation of new cementite plates aligned with the current direction. These effects are attributed to the reduction of the system free energy. It was thought that the enhancement of carbon diffusivity, the generation of vacancies, and the reduction of electrical resistance under electropulsing are factors that cannot be neglected.
Supervisor: Qin, Rongshan S. Sponsor: POSCO (Firm ; Korea)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available