Gong, Yu
(2016)
The Mechanical Properties and Microstructures of Vanadium Bearing High Strength Dual Phase Steels Processed with Continuous Galvanizing Line Simulations.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
For galvanized or galvannealed steels to be commercially successful, they must exhibit several attributes: (i) easy and inexpensive processing in the hot mill, cold mill and on the coating line, (ii) high strength with good formability and spot weldability, and (iii) good corrosion resistance. At the beginning of this thesis, compositions with a common base but containing various additions of V or Nb with or without high N were designed and subjected to Gleeble simulations of different galvanizing(GI), galvannealing(GA) and supercooling processing. The results revealed the phase balance was strongly influenced by the different microalloying additions, while the strengths of each phase were somewhat less affected. Our research revealed that the amount of austenite formed during intercritical annealing can be strongly influenced by the annealing temperature and the pre-annealing conditions of the hot band (coiling temperature) and cold band (% cold reduction). In the late part of this thesis, the base composition was a low carbon steel which would exhibit good spot weldability. To this steel were added two levels of Cr and Mo for strengthening the ferrite and increasing the hardenability of intercritically formed austenite. Also, these steels were produced with and without the addition of vanadium in an effort to further increase the strength. Since earlier studies revealed a relationship between the nature of the starting cold rolled microstructure and the response to CGL processing, the variables of hot band coiling temperature and level of cold reduction prior to annealing were also studied. Finally, in an effort to increase strength and ductility of both the final sheet (general formability) and the sheared edges of cold punched holes (local formability), a new thermal path was developed that replaced the conventional GI ferrite-martensite microstructure with a new ferrite-martensite-tempered martensite and retained austenite microstructure. The new microstructure exhibited a somewhat lower strength but much high general and local formabilities. In this thesis, both the physical and mechanical metallurgy of these steels and processes will be discussed. This research has shown that simple compositions and processes can result in DP steels with so-called Generation III properties.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
| Title | Member | Email Address | Pitt Username | ORCID |
|---|
| Committee Chair | DeArdo, Anthony J. | deardo@pitt.edu | DEARDO | | | Committee Member | To, Albert Chi Fu | | | | | Committee Member | Mao, Scott X. | | | | | Committee Member | Barnard, John A. | | | | | Committee Member | Nettleship, Ian | | | | | Committee Member | Haezebrouck, Dennis | | | | | Committee Member | Vallejo, Luis E. | | | |
|
| Date: |
26 January 2016 |
| Date Type: |
Publication |
| Defense Date: |
30 October 2015 |
| Approval Date: |
26 January 2016 |
| Submission Date: |
23 November 2015 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
291 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Mechanical Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Dual Phase Steels, Vanadium, Galvanizing line simulations, High Strength, Sheared edge formability |
| Date Deposited: |
26 Jan 2016 14:55 |
| Last Modified: |
15 Nov 2016 14:30 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/26358 |
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