Improvement of Ductile-Brittle Transition Temperature in Reactor Pressure Vessel Steel Fabricated Using Powder Bed Fusion

The application of reactor pressure vessels (RPVs) in small modular pressurized water reactors is gaining traction, driven by the need for advanced manufacturing techniques that support complex geometries and extended lifespans. This study evaluates the tensile and Charpy features of SA508 Gr.3—a commonly used material for nuclear RPVs—produced using powder bed fusion (PBF) additive manufacturing. By varying the hatch distance, the study investigates how thermal properties influence microstructural evolution and mechanical performance. Results showed significant variations in grain morphology, dislocation density, and martensite phase fraction across different hatch distances. Because of the finer grain structure and increased dislocation activity made possible by the formation of dislocation cells during the PBF process, the PBF-fabricated specimens showed a 130% increase in yield strength and an improved ductile-to-brittle transition temperature when compared to samples that were manufactured conventionally. These findings suggest that additive manufacturing holds great potential for advancing the mechanical properties and lifespan of RPV components, marking it as a promising strategy for next-generation nuclear reactor design.