Researchers say the ability to 3D print marine grade, low-carbon stainless steel (316L) could have widespread implications for industries such as aerospace, automotive, and oil and gas. (Photo by Kate Hunts/LLNL)Researchers say the ability to 3D print marine grade, low-carbon stainless steel (316L) could have widespread implications for industries such as aerospace, automotive, and oil and gas. (Photo by Kate Hunts/LLNL)The material that oil pipelines, welding, kitchen utensils, chemical equipment, medical implants, engine parts and nuclear waste storage have in common is marine grade stainless steel. It can withstand corrosive environments and delivers high ductility – the capacity to bend under stress without deformation or breakage.

Efforts to strengthen this steel usually undermine ductile properties, prompting a group of U.S. researchers to test 3D printing technology in pursuit of both traits. The result: 316L steel with the desired combination of high-strength and high-ductility properties.

"We were able to 3D print real components in the lab with 316L stainless steel, and the material's performance was actually better than those made with the traditional approach. That's really a big jump. It makes additive manufacturing very attractive and fills a major gap," said U.S. Lawrence Livermore National Laboratory (LLNL) materials scientist Morris Wang.

A major challenge entailed managing the porosity caused during the laser melting (or fusion) of metal powders that can cause parts to degrade and fracture easily. Researchers addressed this through a density optimization process involving experiments and computer modeling, along with manipulation of the materials' underlying microstructure.

"This microstructure we developed breaks the traditional strength-ductility tradeoff barrier," Wang said. "For steel, you want to make it stronger, but you lose ductility essentially; you can't have both. But with 3D printing, we're able to move this boundary beyond the current tradeoff."

Thin plates of stainless steel 316L were printed, using two different laser powder bed fusion systems, for mechanical testing. The laser melting technique inherently resulted in hierarchical cell-like structures that could be tuned to alter the mechanical properties.

"The key was doing all the characterization and looking at the properties we were getting," said LLNL scientist Alex Hamza. "When you additively manufacture 316L it creates an interesting grain structure, sort of like a stained-glass window. The grains are not very small, but the cellular structures and other defects inside the grains that are commonly seen in welding seem to be controlling the properties.”

The eventual goal, he said, is to use high-performance computing to validate and predict future performance of stainless steel, using models to control the underlying microstructure and discover how to make high-performance steels. A similar strategy will also be applied to other lighter weight alloys that are brittle and prone to cracking.

Researchers from Ames National Laboratory, Georgia Tech University and Oregon State University also collaborated on this research.

To contact the author of this article, email shimmelstein@globalspec.com