Theses and Dissertations

ORCID

https://orcid.org/0000-0002-3296-183X

Issuing Body

Mississippi State University

Advisor

El Kadiri, Haitham

Committee Member

Rhee, Hongjoo

Committee Member

Mujahid, Shiraz

Committee Member

McClelland, Zackery B.

Date of Degree

8-9-2022

Document Type

Graduate Thesis - Open Access

Major

Mechanical Engineering

Degree Name

Master of Science (M.S.)

College

James Worth Bagley College of Engineering

Department

Department of Mechanical Engineering

Abstract

Intercritically annealed medium manganese steels are a promising third-generation advanced high-strength steel candidate, relying on large fractions of Mn-enriched retained austenite for excellent strength-ductility combinations. The present study proposes a novel cyclic intercritical annealing to promote nucleation and efficient stabilization of austenite in a medium Mn microstructure. Design of the heat treatment is driven by the hypothesis that the distribution of ductile austenite is key in mitigating the strain incompatibility that accelerates failure in these steels. Development and preliminary testing of the heat treatment are first detailed and compared with literature results for equivalent isothermal annealing. The effects of cyclic annealing parameters on the amount and stability of retained austenite are also explored through diffraction methods and mechanical testing. Finally, steps are taken towards quantifying austenite formation during the cyclic treatment, and recommendations are made for adapting the designed heat treatment to thicker gauges.

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