For many highly stressed engineering applications like bearings and gears, contaminated steel parts can lead to devastating outcomes such as an emergency shutdown or the end of a mission. Ensuring that these critical components are as homogeneous as possible and free from porosity and other flaws is vital to performance, yet conventional steelmaking processes have multiple pathways of entry for unwanted contamination.
The conventional process typically begins with uncleaned, dirty scrap steel. Subsequent processing steps involve ceramic-lined crucibles, ceramic-lined piping, and brick-lined furnaces and crucibles, any one of which can introduce further contamination. Although modern steelmakers use various purification steps to remove impurities, some particle inclusions inevitably make their way into the final product.
Innovators at NASA's Glenn Research Center have devised a method for creating ultra-pure steel alloys that are free from ceramic particle contamination. These ultra-high-quality steels can be used to make bearings, gears, or any other machine components. The innovative method starts with only elementally pure (at least 99.99% pure) ingredients and ceramic-free melting processes followed by ceramic-free atomization and powder metallurgy techniques.
First, the elementally pure steel constituents are melted inside a water-cooled, copper crucible “plasma hearth furnace” vacuum chamber. The melted steel is then solidified inside the copper crucible to form an absolutely pure ingot. This ingot is then atomized into pure powder using an electrode induction gas atomizer. The resulting powder is placed into a clean steel can that is hot-isostatic-pressed into a pure, finegrained ingot of steel. At no point in the process does the steel or its ingredients come into contact with any non-metal or ceramic materials. Furthermore, the steel is never exposed to air or oxygen at high temperatures (which could lead to oxide inclusions).
Glenn's process for creating steel alloys has proven to be nearly perfect, with the potential for significantly better performance than conventional steels, especially in high-stress-cycle applications like rolling element bearings.