New High Performance Gear Steels for Rotorcraft Transmission Applications (Ferrium® C61™ and Ferrium C64™)

Abstract

QuesTek Innovations LLC will present an overview of its Ferrium® C61™ and Ferrium C64™ high-performance gear steels. QuesTek designed, developed and implemented these two new steels using its Materials by Design® technology, an “Integrated Computational Materials Engineering” (ICME)-type approach. Both steels are commercially available (Ferrium C61 falls under Aerospace Materials Specification [AMS] number 6517 and Ferrium C64 falls under AMS 6509) and both can significantly reduce rotorcraft weight and manufacturing costs while increasing operational robustness (including gear steel oil-out/high temperature survivability). Ferrium C61 and C64 are new high strength, secondary hardening gear steels that offer different levels of case hardness. These highly-processable steels exhibit excellent hardenability, and were explicitly designed to leverage the advantages of high-temperature vacuum carburization. Ferrium C61 (AMS 6517) exhibits both excellent surface fatigue and core properties (225 ksi yield strength, 240 ksi ultimate tensile strength, 130 ksi•?in fracture toughness), and is a good candidate for integral gear/shaft applications where maximum torque transfer with minimum weight is tantamount. Ferrium C64 (AMS 6509) exhibits excellent surface hardness (62+ HRC after vacuum carburization), with the potential for significantly better surface fatigue performance as compared to incumbent gear steels such as AISI 9310 (AMS 6265) and Pyrowear® Alloy 53 (AMS 6308). The final tempering temperatures of both C61 and C64 (482–510°C) are 200–300°C higher than most incumbent gear steels, providing excellent scoring resistance and superior thermal stability in high-temperature environments and “oil-out” emergency conditions. Rotorcraft applications underway include an evaluation of C64 by Bell Helicopter under the U.S. Army Future Advanced Rotorcraft Drive Systems (FARDS) program, and of C61 for the forward rotorshaft of Boeing’s CH-47 Chinook under a U.S. Army Small Business Innovation Research (SBIR) Phase II project.