Masters Theses

Keywords and Phrases

EDS; Foundry; Inclusions; SEM; Steel

Abstract

"The effects of sample area and automated SEM/EDS feature analysis parameters (step size, magnification and threshold) on nonmetallic inclusion characterization results has been investigated and optimized. A post-processing program was developed to automatically determine average inclusion chemistry, total element concentrations within inclusions, and for generating joint ternary diagrams with size visualization for representing nonmetallic inclusion populations. Using these tools the evolution of nonmetallic inclusions was examined for 4320 steel at a participating industrial steel foundry. The steel was sampled throughout electric arc furnace melting through ladle refining to the final casting where an in-mold sampling procedure was developed to procure numerous test samples representative of final heavy section castings in effort to further understand the effect of different metallurgical factors on impact toughness for slow solidification rate high strength cast steel. Nonmetallic inclusion nucleation, growth, and flotation were monitored through liquid steel processing by size-classified area fraction. The use of zirconium as an addition for nitrogen/oxygen removal was found to lead to a large number of ZrO2 inclusions, which resulted in insufficient flotation due to the higher density of zirconia and, less effective calcium treatment. No ZrN formation was observed owing to the high FeO acid slag practice used. Argon stirring was found to mitigate the flotation problems associated with the zirconium addition and significantly contribute to the removal of large size (>5µm) inclusions. In-mold heavy section samples were tested at -40⁰C and 25⁰C to examine how different microstructural features such as nonmetallic inclusions, porosity, and hardness influence the impact energy of the steel for brittle and ductile fracture modes. SEM fractography was used to characterize failures modes: brittle, ductile, and quasi-ductile at energies ranging from 14-40 ft-lbs. For brittle fracture, hardness had an adverse influence on impact energy absorbed, while increasing the average area fraction and diameter of nonmetallic inclusions led to improved toughness. The opposite trends were observed for ductile fracture in specimens tested at room temperature, where area fraction of nonmetallic inclusions and porosity were detrimental to the impact energy absorbed"--Abstract, page iv.

Advisor(s)

Richards, Von

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

Sponsor(s)

Kent D. Peaslee Steel Manufacturing Research Center

Research Center/Lab(s)

Peaslee Steel Manufacturing Research Center

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2016

Journal article titles appearing in thesis/dissertation

  • Improved methodology for automated SEM/EDS non-metallic inclusion analysis of mini-mill and foundry steels
  • Evolution of non-metallic inclusions in foundry steel casting processes
  • Factors affecting impact toughness of cast heavy section 4320 steel CT

Pagination

xi, 82 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2016 Marc Leonard Harris, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Subject Headings

Steel -- InclusionsContinuous casting -- Mathematical modelsSteel -- MetallurgySteel foundries

Thesis Number

T 10957

Electronic OCLC #

958293657

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Included in

Metallurgy Commons

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