Homogenisation treatments for laser powder bed fusion 316 stainless steel and their effect on primary water stress corrosion cracking

As more is being understood about additive manufacturing, and specifically the Laser Powder Bed Fusion (LPBF) technique, more companies are utilising it and its many advantages (i.e. faster processing time, less material waste, less post-processing machining, etc). Because of this, companies that work with fusion power are evaluating a switch in processing techniques, however within these environments, and for 316 Stainless Steels (316 SS) in particular, it is known that Stress Corrosion Cracking (SCC) is a concern.

It is known that for 316 SS, the current post processing Hot Isostatic Pressing (HIP) treatment does not result in a homogeneous microstructure which has previously been linked to better SCC performance. Possible explanations for the slower recrystallisation are oxide pinning and solute drag, requiring a higher grain boundary energy to induce recrystallisation. Currently the temperature to begin recrystallisation for 316 SS is 1150 °C, a temperature that is not feasible for an industry setting. 
To reduce the post-processing heat treatment needed, varying levels of cold work have been applied to the as-received LPBF 316 SS to improve the recrystallisation kinetics and homogenise the microstructure. From there, the as-received material’s SCC performance will be compared to the homogenised material to understand how the treatment affects the performance. Following this, additional cold work will be applied to the as-received and homogenised material to simulate the cold work that can be induced through welding post-heat treatments, to see if the comparison between SCC performances of the materials changes. This work will provide a novel understanding of how the as-received material performs within this simulated environment and how homogenising the current material will affect the material’s SCC performance. 

Within my first year, I was able to attend and present my first year's research as a poster at the 2025 Environmental Degradation international conference. Being able to attend and share my current work at such an early stage with experts in Pressurized Water Reactors and SCC research was valuable experience, allowing me insight into how to best align my research with what information is currently lacking. 

Sydney Coates

Sydney was involved in a STEM ambassador program, where she was able to practice explaining material science concepts to an audience much less familiar with these subjects. Through this, she not only learned how to break down material science concepts into a more digestible format but also how to create a lesson plan and project to introduce material science in a tangible way that would be interesting to secondary school students. 
As scientific communication impacts how information is shared between scientists and how the general population understands what we are working towards, it is important to continue to hone communication skills in a way to have the best impact on how people understand the current research being done and how it affects them.

Equipment Used (and any access schemes utilised if applicable)

• Cormet autoclave is used for slow strain rate SCC tensile testing
• SEM, TEM, and FIB are being utilised for characterisation
• Autoclave setup for slow strain rate SCC tensile testing

Biography

Sydney Coates received her undergraduate degree in Welding Engineering at Ohio State University. She continued onto her Masters degree in Welding Engineering at Ohio State, where her project, funded by Los Alamos National Labs, focused on characterising laser beam welds’ transition from conduction mode to keyhole mode. From there, she was inspired to continue working in material science research and joined the Advanced Metallics CDT at the University of Manchester to complete her PhD. Sydney’s PhD research focuses on the effects of additive manufacturing and incomplete recrystallization on the materials' SCC performance in a PWR primary water environment.