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
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.
