Masters Theses

Keywords and Phrases

Grain refining; High manganese; Toughness

Abstract

"Low density high Mn and Al steels, or FeMnAl steels, show great promise for military vehicles and automotive applications in which high strength and toughness is a requirement. However, these steels are subject to processing challenges including development of oxide and nitride inclusions during melting and casting as well as a large as-cast grain size and heavy interdendritic segregation. This can lead to non-uniform heat treatment response and cracking during subsequent hot rolling. Adding up to 10%Al lowers the density of these steels by as much as 15%, unfortunately, this also results in large amounts of hard and faceted AlN inclusions that are known to reduce toughness. Inclusion engineering techniques in other cast alloys can mitigate the effect of harmful inclusions or decrease grain size, segregation, and microporosity and improve ductility and toughness. Unfortunately, there is limited understanding of inclusion evolution in FeMnAl steels and the inclusion engineering strategies to improve mechanical properties.

The goal of this research is to explore potential nonmetallic inclusions as inoculants to refine the as-cast grain size as well as potential mitigation of detrimental AlN by soft and globular MnS co-precipitation. MnS was effective at coating most of the AlN inclusions. However, this produced a large overall inclusion population that reduced dynamic fracture toughness.

The potential of Ti(C,N), Nb(C,N), and complex Ce-oxides to refine the as-cast grain size was investigated. A decrease in the columnar zone was observed with addition of FeSiMg+FeTi and Ce addition, however, the equiaxed grain size did not decrease. A low N melt practice with Ti additions was effective at eliminating AlN”--Abstract, page iv.

Advisor(s)

Bartlett, Laura

Committee Member(s)

Lekakh, S. N. (Semen Naumovich)
O'Malley, Ronald J.

Department(s)

Materials Science and Engineering

Degree Name

M.S. in Metallurgical Engineering

Comments

The author would like to thank Defense Logistics Agency in cooperation with Steel Founders Society and Army Research Lab for sponsoring this project.

Research Center/Lab(s)

Peaslee Steel Manufacturing Research Center

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2019

Journal article titles appearing in thesis/dissertation

  • Understanding the role of inclusions on the dynamic fracture toughness of high strength lightweight FeMnAl steels
  • Progress in grain refinement of FeMnAl castings. Part 1. Fully austenitic FeMnAlC steel treated by complex TiN bearing master alloy
  • Progress in grain refinement of FeMnAl castings. Part 2. Two-stage inoculation with MgAl₂O₄ and Ti(C,N)

Pagination

xiv, 180 pages

Note about bibliography

Includes bibliographic references.

Rights

© 2019 Rairu Vaz Penna, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 12098

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