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A Comparison Study of the Transformation Behavior during Uniform Continuous Cooling and Hot Deformation Characteristics of a Wrought and Selective Laser Melting 4340 Steels

WANG, YUANKANG (2021) A Comparison Study of the Transformation Behavior during Uniform Continuous Cooling and Hot Deformation Characteristics of a Wrought and Selective Laser Melting 4340 Steels. Master's Thesis, University of Pittsburgh. (Unpublished)

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This study compares the Austenite Grain Growth Behavior and its Transformation Behavior during the uniform Continuous Cooling of a Selective Laser Melting (SLM) 4340 and conventional Wrought 4340 steels. SLM 4340 steels exhibit inferior mechanical properties then conventional Wrought 4340 steels. Hence, the effect of hot deformation on the final microstructure and mechanical properties of SLM 4340 steel were also investigated in this study. Standard dilatometry testing was used to study the Austenite decomposition behavior at different cooling rates and to develop the CCT diagrams. Hot Compression Testing was performed to investigate the effect of hot deformation on the microstructure of austenite for both systems SLM 4340 and Wrought 4340. Advanced microstructural characterization techniques, Scanning Electron Microscopy (SEM) and Orientation Imaging Microscopy (OIM) were employed to support the CCT diagrams. Electron Backscatter Diffraction (EBSD) and a special EBSD-IQ characterization technique were used to assess the percentage of the microstructural components observed. Three important observations were made: 1) the hardenability of the Wrought 4340 steel was higher than the SLM 4340 steel; 2) the presence of Granular Bainite was observed after slow cooling conditions in both steels. MTEXT, a MatLab program, was used to reconstruct the prior Austenite grains (PAG). The SLM steel exhibited finer Austenite grain size distribution than the Wrought steel in the temperature range studied; and 3) the porosity in SLM 4340 was closed during the hot compression tests improving its mechanical properties. The level of microstructural refinement of austenite after hot deformation was measured by the effective interfacial area per unit volume (Sv) parameter for the SLM 4340 and Wrought 4340 steels.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
WANG, YUANKANGyuw135@pitt.eduyuw1350000-0002-5855-0668
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Thesis AdvisorGarcia, Calixto
Committee MemberNettleship,
Committee MemberTan,
Date: 26 January 2021
Date Type: Publication
Defense Date: 12 November 2020
Approval Date: 26 January 2021
Submission Date: 13 November 2020
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 83
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Materials Science and Engineering
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Dilatometry; Hot Compression; EBSD-IQ; Selective Laser Melting; 4340 Steel; CCT diagram; Transformation Behavior; Austenite Grain Coarsening
Date Deposited: 26 Jan 2021 20:03
Last Modified: 26 Jan 2021 20:03

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