Understanding the materials performance of additive manufactured stainless steel components in high temperature water

Austenitic stainless steels and Ni base alloys are extensively used in the primary circuit internals of pressurized water reactors (PWR) due to their high corrosion resistance properties. However, it is also well known that materials processing can have a strong impact on the susceptibility to stress corrosion cracking (SCC) of these materials when exposed in high temperature aqueous environment water coolant under active loading. Historically, components have been manufactured via conventional manufacturing routes, such as forging and welding; however, there is the desire to produce near net shape components via additive manufacturing thanks to the reduce machining costs, more agile manufacturing, and shorter lead times. However, there is currently insufficient knowledge on the impact of the metallurgical quality of the material produced by such processes on the materials performance. It is critical, therefore, to have a fundamental understanding of the relationship between manufacturing via modern near-to-net-shape manufacturing technologies, such as laser powder bed fusion, so that potential degradation caused by changes to current manufacturing practices can be judged. This, in turn, requires a scientifically-based understanding of the various underlying mechanisms influencing/controlling the environmental degradation and their linking to the end effects.
SCC is one of the most insidious forms of materials degradation and its initiation behaviour in as manufactured components are major technical challenges. Although the SCC performance of stainless steels, Ni-base alloys in light water reactors environments has been studied extensively, the SCC data are not available for components produced using near-net-shape technologies. The overall aim of this project is to characterise the microstructure of additively manufactured (AM) stainless steels produced via laser powder bed fusion, and compare the mechanical properties (tensile strength, fracture toughness) and susceptibility to environmentally assisted cracking (EAC) of material in the three conditions of interest: forged, AM and heat treated. The secondary aim is to develop an understanding of the processing-microstructure-mechanical property relationships at work, and hence suggest process alterations to optimise material performance.