Masters Theses

Keywords and Phrases

304 Stainless Steel; Cooling Rates; Laser Power; Phase Transformation; Selective Laser Melting; SLM

Abstract

"This study examines the thermal profile and the ferrite-austenite phase fractions upon heating and cooling of 304- stainless steel powder via Selective Laser Melting (SLM). Experiments were performed to validate the ABAQUS finite element model, while the phase transformation simulation was performed using MatCalc and ThermoCalc. A correlation between the thermo-mechanical changes in ABAQUS and the microstructural changes from MatCalc was obtained by matching their cooling rates. The result indicates that cooling rate has a significant effect on the phase fractions of FCC and BCC formed in 304L stainless steel via the SLM process. The results also indicate that for high cooling rates (typically > 105 K/s and consistent with laser powers ≥ 100W) the proportions of FCC and BCC were comparable, with FCC phase about 55% and BCC about 45% of the solidified matrix. This result was similar to the results predicted by the Scheil Gulliver model suggesting high cooling rates follow a diffusionless transformation process.

For lower cooling rates, the fractions of FCC increased and that of BCC decreased progressively such that the phase fraction of FCC was greater than 91% with a cooling rate of 3400K/s which corresponds to a laser power of 40W. Such relatively low cooling rate around the phase transformation temperature (i.e. 900K to 450K) is an indication of possible diffusional transformation where the BCC (δ) phases transform to an FCC (γ) phase.

A higher FCC grade stainless steel has better corrosion properties and produces less magnetic interference in certain critical applications and was another motivation for this study in addition to establishing a process of altering the phase fractions of metals by a cooling-rate only control in SLM"--Abstract, page iii.

Advisor(s)

Kinzel, Edward C.

Committee Member(s)

Liou, Frank W.
Chandrashekhara, K.

Department(s)

Mechanical and Aerospace Engineering

Degree Name

M.S. in Mechanical Engineering

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2018

Pagination

x, 82 pages

Note about bibliography

Includes bibliographical references (pages 78-81).

Rights

© 2018 Eberechukwu Anthony Okoro, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 11307

Electronic OCLC #

1041858674

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