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Intensive Recrystallization-Controlled Rolling of High-Temperature-Processing Linepipe Steel with Low Niobium Content

Solis Bravo, Gregorio (2020) Intensive Recrystallization-Controlled Rolling of High-Temperature-Processing Linepipe Steel with Low Niobium Content. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The goal of this research was to gain a systematic understanding of the major factors that control the mechanical behavior and the final microstructure of a linepipe steel after High Temperature Processing and Controlled Cooling processing. Based on this in-depth knowledge, an innovative hot deformation process for optimized microstructure, strength and impact toughness using less alloying content was developed.
The science and understanding of the underlying phenomena in High-Temperature Processing (HTP) of a new alloy is the focus of this work. Nb content was considered an important variable, an opportunity for its reduction was hypothesized and proved. HSLA linepipe steel with three different Nb contents (0.09, 0.07 and 0.05wt%) was compared through two different deformation approaches. The conventional approach, having thickness reductions of 75% in roughing and 67% in finishing deformation passes. And the Intensive Recrystallization-Controlled Rolling (IRCR), having 85% reduction in roughing and 46% in finishing. Mechanisms were found, that explain for these alloys the grain coarsening behavior of austenite, the mean flow stress at rolling temperatures, the temperature of non-recrystallization, the precipitation in all stages of the process and the transformations involved from slab-reheating to plate-coiling.
An innovative hot deformation process was introduced, the IRCR process. While this work focused on the science, IRCR was devised as a robust thermomechanical process that can easily be scaled up to industrial proportions. This process achieved improved microstructural control, used less alloying and required less time for product processing. The microstructural control derived in improved mechanical properties and minimized variability through thick linepipe products (15-19mm). The science and engineering involved are presented and discussed in this document.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Solis Bravo, Gregoriogrs52@pitt.edugrs520000-0001-6522-6965
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Thesis AdvisorGarcia, C. Isaaccigarcia@pitt.educigarcia
Wang, Guofengguw8@pitt.eduguw8
Nettleship, Iannettles@pitt.edunettles
Tan, Sushengsut6@pitt.edusut6
Date: 15 January 2020
Defense Date: 10 January 2020
Approval Date: 31 July 2020
Submission Date: 22 January 2020
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 173
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: Recrystallization, complex precipitation, epitaxial precipitation, austenite reconstruction, grain size control, hot rolling, low niobium, Ti-Nb linepipe steel, HSLA steel, high-temperature processing, HTP
Related URLs:
Date Deposited: 31 Jul 2020 17:30
Last Modified: 31 Jul 2020 17:30

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