Transformation induced plasticity (TRIP) steels are a class of steels with exceptional formability properties, due mainly to the presence of meta-stable retained austenite which transforms to martensite under loading, locally hardening the steel. The volume fraction and mechanical stability of the retained austenite play an important role in producing the high formabilities of TRIP steels. In this thesis, two separate morphologies of retained austenite, equiaxed versus lamellar, have been produced through thermo-mechanical processing of a single common TRIP steel chemistry. The sheet formability characteristics of these two microstructures were examined, with varying volume fractions of retained austenite, through uniaxial tensile and in-plane plane-strain (IPPS) testing.
It was found that higher levels of retained austenite produced better formability properties for both microstructures and strain paths. In uniaxial tension it was seen that the the lamellar microstructure attained higher strains at maximum load, and exhibited more sustained instantaneous n values than the equiaxed structure, despite having a lower volume fraction of retained austenite.
IPPS testing was performed using an optical measurement of local strain and a comparative forming limit based on differences in strain rate between a developing neck and the surrounding material. It was found that the lamellar microstructure performed better than the equiaxed microstructure for this strain path, achieving higher strains before reaching the comparative forming limit. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2010-01-25 16:36:07.598
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OKQ.1974/5402 |
| Date | 27 January 2010 |
| Creators | Lawrence, Benjamin |
| Contributors | Queen's University (Kingston, Ont.). Theses (Queen's University (Kingston, Ont.)) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | 8104314 bytes, application/pdf |
| Rights | This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner. |
| Relation | Canadian theses |
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