Thermomechanical processing, which is a combination of deformation and heat treatment, is an optimum method to control the microstructural evolution and, accordingly, to generate the desired mechanical properties of materials. TRIP (Transformation-Induced-Plasticity) behavior is a powerful mechanism with which to improve mechanical properties. The basis of TRIP behavior is the retention of austenite with optimum characteristics (volume fraction, stability, size, morphology and composition) at room temperature. The transformation of retained austenite to martensite during deformation can lead to TRIP-enhanced properties. This work deals with the effects of thermomechanical processing parameters on the microstructural characteristics of TRIP steels, primarily from the point of view of the retained austenite condition in Si-Mn and Si-Mn-Nb bearing TRIP steels. Initially, a new test technique based on continuous cooling compression (CCC) testing was developed to find the critical temperatures of thermomechanical processing (TMP). A major finding from the CCC test is the ability to determine the $Ae sb3$ (equilibrium austenite-to-ferrite transformation) temperature. In the CCC test, the $Ae sb3$ appeared to be associated with an increase in the rate of increase in flow stress with decreasing temperature. In order to further evaluate this result, neutron diffractometry at high temperatures was used to monitor any crystallographic changes associated with the metastable region. The results revealed an increase in the rate of contraction of the austenite lattice as the temperature decreases through the metastable state (below $Ae sb3),$ compared with that observed as the temperature decreases through the stable austenite region. Having defined the critical TMP temperatures, the effects of processing parameters on the state of the retained austenite were examined by changing the thermomechanical processing conditions. These effects were more fundamentally considered by tak
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.41798 |
| Date | January 1994 |
| Creators | Zarei Hanzaki, Abbass |
| Contributors | Yue, S. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Mining and Metallurgical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001403118, proquestno: NN94728, Theses scanned by UMI/ProQuest. |
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