Garcia-Gonzalez, Jose Enrique
(2005)
Fundamental Study on the Austenite Formation and Decomposition of low-Si, Al added Nb-Mo TRIP steels.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
TRIP (Transformation Induced Plasticity) steels are under development for automotive applications that require high strength and high formability. Conventional TRIP steels consist of a multiphase microstructure consisting of a ferrite matrix with a dispersion of bainite and metastable retained austenite. The high ductility exhibited by these steels results from the transformation of the metastable retained austenite to martensite during straining. In conventional TRIP steel processing, the multiphase microstructure is obtained by controlled cooling from the austenite+ferrite region to an isothermal holding (bainitic)temperature. During this holding, bainite forms and carbon is rejected out into the austenite, which stabilizes the austenite to room temperature.In this research project, a fundamental study in a low-Si, Mo-Nb added cold rolled TRIP with and without Al additions was conducted, where the austenite formation in the two-phase region and the characteristics of the decomposition of intercritically annealed austenite were analyzed. The systematic study of the recrystallization of ferrite during intercritical annealing was also of primary importance. Similarly, this study intended to obtain a fundamental knowledge of the decomposition behavior of intercritically annealed austenite by controlled cooling rates. Of special interest was to study the effect of the initial hot band microstructure and intercritically annealed austenite on the formation of bainite during the isothermal holding temperature as well as the formation of epitaxial ferrite during cooling from the intercritical annealing temperature to the isothermal holding temperature. Furthermore, the influence of the starting hot band microstructure and processing parameters during TRIP steel processing on the type, amount, and composition of retained austenite and its stability were evaluated. During this research study, techniques such as OM, SEM, EBSD, TEM, XRD and Magnetometry analysis were used to fully characterize the corresponding microstructures.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
21 June 2005 |
| Date Type: |
Completion |
| Defense Date: |
15 April 2005 |
| Approval Date: |
21 June 2005 |
| Submission Date: |
3 April 2005 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Materials Science and Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
austenite decomposition; bainite; EBSD; epitaxial ferrite; IQ analysis; retained austenite; TRIP steel |
| Other ID: |
http://etd.library.pitt.edu/ETD/available/etd-04032005-165518/, etd-04032005-165518 |
| Date Deposited: |
10 Nov 2011 19:33 |
| Last Modified: |
15 Nov 2016 13:38 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/6715 |
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