Nooning, Jr., Robert Gerard
(2003)
EFFECT OF STABILIZING ELEMENTS ON THE PRECIPITATION BEHAVIOR AND PHASE STABILITY OF TYPE 409 FERRITIC STAINLESS STEELS.
Master's Thesis, University of Pittsburgh.
(Unpublished)
Abstract
Type 409 ferritic stainless steels have gained widespread use in the automotive industry in exhaust systems. Largely responsible for the acceptance of these steels is the stabilization with titanium and/or niobium which prevents sensitization due to the formation of chromium carbides. While both forms of stabilization (titanium or titanium plus niobium) have been demonstrated to be effective at preventing sensitization, the physical metallurgy of these alloying elements in these steels has not been studied. It is therefore the aim of this research to study the precipitation behavior and the formation of austenite in these steels in the temperature ranges typical of hot rolling and annealing.Two steels were studied in this research, a single stabilized titanium only Type 409, and a dual stabilized titanium plus niobium Type 409. First, thermodynamic models were used to predict the temperatures where carbides are expected to be stable in the two steels. Next, the initial as-received transfer bars of the two steels were characterized. A detailed analysis of the precipitates was conducted to characterize the size, composition, structure, and orientation relationship of the carbides. Subsequently, the steels were reheated in order to observe both the dissolution of the carbides and the formation of austenite in the temperature range of 700 to 1300 °C. The austenite formation was studied using EBSD in the SEM to characterize the grain boundaries between the ferrite grains, and also to characterize the interfaces between the ferrite and the martensite (quenched austenite). Finally, continuous cooling deformation testing was used to determine the precipitation start temperatures of the steels.The main findings of this research were that the (Ti,Nb)C precipitates in the dual stabilized steel were stable to much higher temperatures than the TiC precipitates in the single stabilized steel. During continuous cooling, the dual stabilized steel precipitated carbides at 1210 °C, while the single stabilized steel did not precipitate carbides until 840 °C. These results are discussed in the thesis and their possible effect on the final microstructure and mechanical properties are inferred.
Share
| Citation/Export: |
|
| Social Networking: |
|
Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
| Creators | Email | Pitt Username | ORCID  |
|---|
| Nooning, Jr., Robert Gerard | rgnst@pitt.edu | RGNST | |
|
| ETD Committee: |
|
| Date: |
6 January 2003 |
| Date Type: |
Completion |
| Defense Date: |
16 December 2002 |
| Approval Date: |
6 January 2003 |
| Submission Date: |
16 December 2002 |
| 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: |
MSMSE - Master of Science in Materials Science and Engineering |
| Thesis Type: |
Master's Thesis |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
CCP; continuous cooling deformation; precipitation behavior; EBSD; ferritic stainless steels |
| Other ID: |
http://etd.library.pitt.edu:80/ETD/available/etd-12162002-233833/, etd-12162002-233833 |
| Date Deposited: |
10 Nov 2011 20:11 |
| Last Modified: |
15 Nov 2016 13:54 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/10384 |
Metrics
Monthly Views for the past 3 years
Plum Analytics
Actions (login required)
 |
View Item |
![[feed]](/images/feed-icon-32x32.png){kind=icon}