Performance of a ferritic/martensitic steel for nuclear reactor applications fabricated using additive manufacturing

Abstract

Ferritic/martensitic (FM) steels are being targeted for use in a range of advanced reactor concepts as cladding and structural components. FM steels for nuclear reactor applications have historically been produced using traditional methods (e.g., casting and forging), but recently, additive manufacturing processes have become of interest for making FM-based components. Here, the laser-blown-powder additive manufacturing process was used to fabricate an FM steel, HT9, followed by microstructural and mechanical performance evaluations to determine the viability of future use of additive manufacturing for FM-based component fabrication. Results showed that the as-built condition formed a layered structure with alternating layers of $\delta$-ferrite and martensite, which resulted in anisotropic engineering and true-stress, true-strain mechanical performance. Post-build normalizing and tempering treatments alerted the prior austenite grain size and precipitate distributions, and drove the mechanical performance to near-isotropic properties that mimic wrought-processed properties. The resulting microstructures in all conditions were rationalized in the context of multi-pass welding and the synergies are discussed.