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Nano-Scale Steel Powders Upgrade Additive Manufacturing Parts

Nano-Scale Steel Powders Upgrade Additive Manufacturing Parts

NanoSteel Co., which develops high-performance steel alloys, began producing steel powders for additive manufacturing (AM) last year and now supplies them commercially for freeform laser deposition and laser powder bed fusion processes.

The powders target high-performance requirements, said to include exceptional hardness (>1,000 HV) and high wear resistance and enabling gradient-material design in AM that allows different properties in the same end-part.

The company formulates "nano-structured" steels. This means crystal structures of the steel form in grain and matrix sizes that are smaller than 100 nanometers -- up to three orders of magnitude less than in conventional steels. These nano-structures are said to enhance the mechanical and physical properties of products.

Some of the AM steel powders also contain nano-scale grains and phases. "These nanostructures provide the materials' unique mechanical and physical properties," said Harald Lemke, NanoSteel's vice president and general manager of engineering powders.

In hardness, for example, the above-1,000 HV level achieved by the powders rivals carbides, ceramics, and the hardest heat-treated tool steels, Lemke notes.

Gradient-material design permits the incorporation of two properties in a part. "It could be useful to have a part with a very hard end-surface, so it does not wear, with the remainder of the part being ductile to provide for impact resistance," Lemke said.

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Normally, this would be achieved by case hardening, a heat treatment that hardens the surface without affecting internal structure.

NanoSteel uses gradient design in its Digital Case Hardening process for AM. "The advantages [of the process] are that there is no limitation to the thickness of the very hard surface, no subsequent heat treatment, and there is more flexibility in deploying different alloys and process parameters," Lemke explained.

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The powders are entirely ferrous metal (although there is, of course, carbon) and, for now, are formulated from the company's high-wear-resistance alloys. The powders have a uniform metal matrix comprised of two phases: a hard phase embedded in a ductile phase. The hard phase increases wear resistance of the material, according to Lemke, and the ductile phase adds toughness, so the material absorbs impact without cracking.

"The phases of the metal matrix composite work in concert to provide properties that one phase would not be able to on its own," he said.

The powders come in two particle sizes -- 20-45 micron for laser powder bed fusion, and 45-150 micron for freeform laser deposition. The smaller size reportedly produces parts with finer features. Additional sizes can be supplied.

Lemke said the powders are priced competitively with AM materials.

Pat Toensmeier has more than 30 years of experience writing for business-to-business publications. His main areas of coverage have been defense, design, manufacturing, technology and chemicals, especially plastics and composites. He has reported extensively on developments in these areas from the U.S. and Europe, and covered industry events as well in Brazil and Asia. Toensmeier has held various positions at major publishers such as the McGraw-Hill Companies and Hearst Corporation. A graduate of the University of Missouri, he is a contributing editor for several print and online publications. Toensmeier is based in suburban New Haven, Conn.

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