Impact of Atomization and Processing Gas on the Heat Treatment Response of Additively Manufactured 17-4 PH Stainless Steel
Open Access
- Author:
- Meredith, Scott
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 18, 2018
- Committee Members:
- Todd Palmer, Thesis Advisor/Co-Advisor
Allison Michelle Beese, Committee Member
Reginald Felix Hamilton, Committee Member
Jayme Scot Keist, Committee Member - Keywords:
- stainless steel
precipitation hardening (PH)
additive manufacturing (AM)
nitrogen
gas atomization
aging - Abstract:
- Precipitation hardened (PH) grade martensitic stainless steels are commonly used in additive manufacturing (AM) processes. In order to obtain properties similar to their wrought counterparts, post-processing solutionizing and aging heat treatments are required. Depending on the powder feedstock composition, which can be varied by the choice of atomization gas and, to a lesser extent, the processing gas during component fabrication, the post-process heat treatment response can be significantly altered. When the standard heat treatment cycles developed for wrought alloys are applied to as-deposited 17-4 PH grade stainless steel structures fabricated from argon or nitrogen atomized powder feedstocks on different powder bed fusion (PBF) systems, the AM components exhibited a difference response. Argon atomized feedstocks contain approximately 0.01 wt.% nitrogen, possess low levels of retained austenite, and respond as expected to standard solutionizing and aging heat treatment cycles. In contrast, 17-4 PH grade stainless steel structures fabricated using nitrogen atomized feedstocks with higher nitrogen levels (0.06 – 0.14 wt.%) and retained austenite levels (up to 81%) do not respond to standard solutionizing and aging techniques. Peak aging at these high nitrogen levels occurs at a temperature of approximately 680°C, which is significantly higher than the standard peak aging heat treatment at 482°C.