Masters Theses

Keywords and Phrases

Austenitic Stainless Steel; Equiaxed Grains; Grain Refinement; Heterogeneous Nucleation; Spinel Oxide; Titanium Nitride

Abstract

"The goal of this research project is to develop an industrially viable melting process that will control the crystallization macrostructure of austenitic grades of cast steels. Titanium nitride (TiN) has proven to be an effective grain refiner of austenite. Theoretical simulation and experimental application has led to the development of a repeatable grain refining melt process for austenitic stainless steel alloys.

Grain refinement of the as-cast structure of Cr-Ni stainless steel alloys solidified with primary FCC, BCC and dual FCC/BCC phases was studied experimentally. Refinement was achieved in both cast ferritic and austenitic grades. Dual solidification of FCC/BCC phases resulted in an unrefined macrostructure. It is proposed that solidification sequence can limit the grain refining capability of heterogeneous nuclei.

Two inoculation-based melt practices were developed to study grain refinement in cast austenitic stainless steels. The first includes in-situ formation of TiN on to Mg-Al spinel oxides, and the second involves master alloy additions containing preformed TiN. The master alloy method extended the equiaxed zone and improved the distribution of TiN in the casting. The in-situ method showed more effective grain size refinement.

The effect of the developed grain refining melt practice on the properties of cast superaustenitic stainless steel (similar to CK3MCuN) was examined. Heat treatment had no effect on the as-cast grain size. The grain refined alloy exhibited a reduction in segregation after heat treatment; an increase in ultimate tensile strength (+11%), yield strength (+13%), ductility (+8%), hardness (+2%), pitting corrosion; a decrease in impact strength and intergranular corrosion rate in comparison to the unmodified, base alloy"--Abstract, page iv.

Advisor(s)

O'Malley, Ronald J.

Committee Member(s)

Lekakh, S. N. (Semen Naumovich)
Bartlett, Laura

Department(s)

Materials Science and Engineering

Degree Name

M.S. in Metallurgical Engineering

Sponsor(s)

Kent D Peaslee Steel Manufacturing Research Center

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2018

Journal article titles appearing in thesis/dissertation

  • Effect of phase solidification sequence in stainless steel on grain refining efficiency
  • Two inoculation methods for refining as-cast grain structure in austenitic 316L steel
  • Effect of grain refining on properties of superaustenitic stainless steel

Pagination

xvi, 153 pages

Note about bibliography

Includes bibliographic references.

Rights

© 2018 Dustin Alan Arvola, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 11369

Electronic OCLC #

1051223071

Included in

Metallurgy Commons

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