Doctoral Dissertations

Abstract

"Lightweight duplex steels with combinations of either bainite, acicular ferrite, and austenite or martensite and austenite were investigated as third generation advanced high strength steels targeted for automotive applications. Large additions of manganese (>13 wt%) and carbon (<0.2wt%) were employed to stabilize the austenite phase. Silicon additions between 1 and 2 wt% were added to suppress cementite formation. Strength and ductility were increased while density was decreased with aluminum additions between 2.4 and 5.5 wt% to the steel. This research addressed the dependence of alloying on microstructures and mechanical behavior for high manganese and aluminum duplex steels that were cast and subsequently hot rolled.

Duplex steels with different volume fractions of primary δ -ferrite were used to study the crystallography of austenite formed during the peritectic reaction. Solute profiles across the peritectic interface showed aluminum segregated near the interface which promoted bainitic ferrite formation. Thermal treatments were used to manipulate the concentration and type of oxides and the ferrite plate density was found to correlate with inclusions of low misfit in steels with austenite grain size of 16.5 µm.

A steel with bainite and acicular ferrite produced an ultimate tensile strength of 970 MPa and elongation of 40%. The mechanical properties depended on the strengths and size of the microstructural constituents. Work hardening behavior was examined in a steel exhibiting multiple martensitic transformation induced plasticity (γ -austenite→(ε-martensite->α-martensite). A strain hardening exponent as high as 1.4 was observed with ultimate tensile strength and elongation as high as 1,165 MPa and 34%"--Abstract, page iv.

Advisor(s)

Van Aken, David C.

Committee Member(s)

Richards, Von
Medvedeva, Julia E.
Peaslee, Kent D., 1956-2013
OKeefe, Matt

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Metallurgical Engineering

Sponsor(s)

National Science Foundation (U.S.)
United States. Department of Energy

Publisher

Missouri University of Science and Technology

Publication Date

2012

Journal article titles appearing in thesis/dissertation

  • On the crystallography of peritectic austenite and the role of primary ferrite in high manganese and aluminum steel
  • Nucleating acicular ferrite with galaxite (Al₂O₃MnO) and manganese oxide (MnO₂) in FeMnAlC steels
  • Working hardening behavior in a steel with multiple TRIP mechanisms

Pagination

xiv, 134 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2012 Meghan Colleen McGrath, All rights reserved.

Document Type

Dissertation - Restricted Access

File Type

text

Language

English

Library of Congress Subject Headings

Steel, High strength -- Mechanical properties
Steel -- Hardenability
Steel, Automobile -- Mechanical properties

Thesis Number

T 10144

Print OCLC #

861226255

Electronic OCLC #

908857437

Link to Catalog Record

Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.

http://laurel.lso.missouri.edu:80/record=b10118172~S5

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