Author

Matthew Cagle

Advisor

Rhee, Hongjoo

Committee Member

El Kadiri, Haitham

Committee Member

Hammi, Youssef

Committee Member

Mandal, Kamalesh

Date of Degree

8-1-2020

Original embargo terms

Complete embargo for 6 months||Complete embargo for 6 months||5/15/2021

Document Type

Dissertation - Open Access

Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Department of Mechanical Engineering

Abstract

This dissertation demonstrates that substantial ductility improvement is possible for low-manganese transformation induced plasticity steel compositions through the quenching and partitioning heat treatment approach using a Gleeble thermo-mechanical simulator. Two investigated compositions had unique microstructures and mechanical behavior from an identical applied quenching and partitioning process. Electron backscattered diffraction analyses indicate that Comp-2 and Comp-5 both contained retained austenite which resulted in enhanced ductility. The face-centered cubic phase (austenite) more efficiently mitigates strain incompatibilities when located at martensitic grain boundaries known for hot spots and damage initiation. This location effect leads to enhanced ductility and improved toughness in a lean, transformation induced plasticity steel. However, the increase in ductility in Comp-2 and Comp-5 is limited; the partitioning of carbon cannot stabilize austenite to reach strength/ductility targets set by the Department of Energy. Comp-2 and Comp-5 lack sufficient manganese to stabilize austenite to a higher degree. Chem-2A will be explored to determine if the partitioning stage can stabilize austenite closer to the martensite finish temperature. Periodic intercritical annealing will be applied to Chem-1A to see if mechanical properties can be increased further than current research values. Ultimately, through literature, Manganese is proven to be a more effective austenite stabilizer than carbon, and with tailored heat-treatment, the DOE targets can be reached.

URI

https://hdl.handle.net/11668/18415

Sponsorship

Engineering Research and Development Center

Comments

Retained austenite||Manganese||Carbon||Quenching||Partitioning

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