SAE International has issued Aerospace Material Specification 6517 for Ferrium C61, a high-strength, high-toughness, high-temperature-resistant, carburizing-grade steel that was computationally designed by QuesTek Innovations LLC, and is commercially produced and sold by Latrobe Specialty Steel Company of Latrobe, PA, USA. SAE AMS 6517 covers the procurement of bars, forgings and forging stock of C61 as a double-vacuum-melted (i.e., VIM/VAR) aircraft-quality alloy, defining chemistry, thermal processing, minimum properties and other material requirements.
The core of C61 is more than 30 percent stronger and more than 50 percent tougher than conventional premium steels such as AISI 9310 (in typical properties) with a corresponding improvement in axial fatigue resistance, enabling high performance shafting with integral gears. The case can be carburized up to 60-62 Rockwell C hardness and was designed to have higher resistance to bending fatigue than conventional gear steel alloys, resulting in lighter, more durable transmissions and gearbox assemblies. C61 also offers improved resistance to high-temperature service (either during normal operation or emergency "oil-out" conditions) since C61's tempering temperature is 900°F (approximately 600 °F higher than that of 9310).
Processes to carburize C61 are covered by SAE AMS 2759/7. QuesTek designed C61 to have high hardenability so that it can efficiently use modern, clean, low-pressure (i.e., vacuum) carburizing processes with a mild gas quench to produce hardened parts with very low distortion which require less final machining.
Charlie Kuehmann, President and CEO of QuesTek, commented: "The issuance of SAE AMS 6517 represents an important industry milestone for aerospace applications of Ferrium C61, and provides additional information and data for users in racing, defense, energy, industrial and other power transmission industry sectors. We thank SAE's committee and council members for their diligent efforts to issue specifications for new high-performance, engineered materials such as C61."