Role of Retained Austenite in Mechanical Response of Additively Manufactured 17-4 PH Stainless Steel
Open Access
- Author:
- Shaffer, Derek
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 20, 2020
- Committee Members:
- Todd Palmer, Thesis Advisor/Co-Advisor
Allison Michelle Beese, Committee Member
Jayme Scot Keist, Committee Member
Amrita Basak, Committee Member
John C Mauro, Program Head/Chair - Keywords:
- Retained Austenite
17-4 PH
Additive Manufacturing
Mechanical Properties - Abstract:
- 17-4 precipitation hardened (PH) martensitic grade stainless steel has been shown to have varying as-deposited chemical compositions depending on starting feedstock compositions. These composition changes can lead to variations in austenite volume fraction and therefore microstructure. Austenite levels can then cause significant changes in mechanical behavior. Material made from nitrogen and argon atomized powders were used to evaluate the effect of composition and aging and mechanical behavior. Material made using argon atomized powder had little to no austenite, leading to a mechanical response with minimal work hardening and a continuous yield behavior, similar to wrought. Samples made with nitrogen atomized powder had increases in strength and ductility as well as exhibiting strain induced austenite-to-martensite phase transformations. Very large ductility from strain induced transformations was defined by discontinuous yielding behavior and increased work hardening while the added nitrogen also improved the ultimate tensile strength. Aging behavior of the material changed with increasing nitrogen content. In the nitrogen atomized samples peak-aging temperatures increased, strain induced phase transformation occurred in all aging cases, and discontinuous yielding in the as-deposited condition changed to continuous yielding in the peak-aged and over-aged conditions. Retained austenite was shown in these ways to be a primary contributor to the mechanical behavior of this material.