NUCLEAR POWERScientists Investigate 3D-printed Steels for Use in Next-Generation Nuclear Reactors

By Savannah Mitchem

From composition to performance, two recent studies show how additively manufactured steels measure up to their conventionally produced counterparts.

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.

Compared to conventional methods for steelmaking, techniques in additive manufacturing — or 3D-printing — offer a way to produce complex stainless steel parts more efficiently and with greater design flexibility. But additive manufacturing processes can leave behind defects in the microscopic structures of steel parts, impacting their performance.

Before they can be trusted in reactor environments, the nuclear industry needs a deeper understanding of 3D-printed steels and how to control them.

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).

With LPBF, they printed samples of two stainless steel alloys that are of interest to the nuclear industry. One study focused on 316H, an established type of stainless steel for structural components in nuclear reactors. Another study focused on Alloy 709 (A709), a newer alloy designed for advanced reactor applications.

Both studies uncovered important differences between printed steels and their wrought — or conventionally produced — counterparts. They also revealed how printed steels responded to heat treatments typically used for wrought materials.

“Our results will inform the development of tailored heat treatments for additively manufactured steels,” said Argonne materials scientist Srinivas Aditya Mantri, a co-author on both studies. ​“They also provide foundational knowledge of printed steels that will help guide the design of next-generation nuclear reactor components.”

Healing and Fortifying Printed Steels with Heat
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.

For example, printed steels show higher numbers of dislocations — defects where an otherwise consistent pattern in a material’s structure suddenly shifts. Dislocations strengthen steel, but they also increase its internal stress, leaving it more vulnerable to fracture.