Argonne Scientists Investigate 3D-Printed Steels for Use in Next-Generation Nuclear Reactors

LEMONT, Ill.--(BUSINESS WIRE)--Stainless steel has long been a workhorse material for the nuclear industry. It fortifies walls and forms crucial components throughout nuclear reactors, where it withstands decades of extreme heat, pressure and irradiation.

Industry needs a deeper understanding of 3D-printed steels before these materials can be trusted in nuclear reactor environments.

In two recent studies, researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory used X-ray diffraction and electron microscopy to investigate steels made with an additive manufacturing process called laser powder bed fusion (LPBF).

During LPBF, a laser melts precise designs into a metal powder one layer at a time to construct a solid, 3D metal object. The rapid heating and cooling caused by the laser creates unique features in the microstructures of steel.

During heat treatment, a material begins to heal through a process called recovery, where high temperatures allow atoms to shift and repair dislocations. This can lead to recrystallization, where new, strain-free grains replace the original structure altogether. But keeping some dislocations can be beneficial; they promote the precipitation of particles that, in the right quantities, can further improve a material’s performance.

In one of the studies, Argonne’s researchers focused on LPBF-printed samples of 316H, a well-known structural material in its wrought form.

The researchers took the detailed structural data they obtained at Argonne’s Center for Nanoscale Materials (CNM) and Advance Photon Source (APS)—two DOE Office of Science user facilities at the laboratory—and related the data to mechanical properties, including strength under tension and resistance to creep. A major consideration for the nuclear industry, creep is the slow deformation of a material under a constant mechanical load.

The other study focused on A709, a newer, more advanced stainless steel designed for high-temperature environments like those inside sodium fast reactors. In this experimental first, researchers investigated LPBF-printed samples of A709.

They also studied the strengths of the heat-treated samples under tension. At both room temperature and 1022 F (550 C) — a temperature relevant to sodium fast reactors — the printed A709 displayed higher tensile strengths than wrought A709. This was likely because the printed samples began with more dislocations, which also promoted the formation of more precipitates during heat treatment.

“Our research is providing practical recommendations for how to treat these alloys,” said Xuan Zhang, materials scientist at Argonne and co-author on both studies. ​“But I believe our biggest contribution is a greater fundamental understanding of printed steels.”