Ferrium® C64®


Ferrium C64 (AMS 6509) is a new high strength, high surface hardness, good fracture toughness carburizable steel that also has high temperature resistance and hardenability. C64 steel is a higher performance upgrade from 9310, X53 (AMS 6308), EN36A, EN36B, EN36C and 8620. It can achieve a surface hardness of 62-64 Rockwell C (HRC) via vacuum carburization.

C64 steel is double vacuum melted (i.e., vacuum induction melted and then vacuum arc remelted or "VIM/VAR") for high purity, leading to much greater fatigue strength.

Improved C64 Steel Properties versus Incumbent Materials

The following table shows that for example C64 steel has equivalent toughness to 9310, but a a greater surface hardness (up to ~63 HRC) and a yield strength that is ~45 ksi greater:

Additional information can be found in the C64 Datasheet or on Carpenter's Ferrium C64 page.


One leading application for C64 steel is as an upgrade from X53 (AMS 6308) steel in demanding Bell Helicopter and Sikorsky transmission gear boxes. Under an Army-funded Future Advanced Rotorcraft Drive System (FARDS) program, Bell and Sikorsky are evaluating and qualifying C64 steel to displace Alloy X53 (AMS 6308). Benefits include greater temperature resistance, pitting resistance and corrosion resistance.

Under an Army-funded SBIR Phase I program, QuesTek is evaluating and demonstrating C64 steel for the Additive Manufacturing (AM) of aerospace gears and fatigue-driven applications.

Other applications can include racing transmission gears, gears with integral bearing races, integrally-geared driveshafts, bearings, actuators, and other power transmission components where durability, compactness, weight savings, high temperature resistance or high surface fatigue resistance is valued. C64 steel can offer increased performance and reliability of wind turbine transmission gear boxes, thus reducing maintenance costs and downtime, and increasing reliability.

If you need even greater strength and fracture toughness in a carburizing-grade steel, see Ferrium C61.


Benefits of using C64 steel vs. alloys such as 9310/EN36, X53 (AMS 6308), or 8620 for power transmission applications can include:

  • Smaller, lighter-weight gears (including gears with integral bearing races), or greater throughput or durability, including improving existing gears by replacing current materials with C64 steel. Gears and gearboxes using C64 steel can often handle approximately 15% higher loads than comparable designs using traditional materials, or be reduced in size and weight by comparable amounts, due in part to C64 steel's excellent surface contact fatigue resistance and bending fatigue resistance. Conventional gear steels such as 9310 or 8620 cannot typically achieve 62-64 Rockwell “C” Hardness case hardness with a fatigue-resistant microstructure. The combination of high surface hardness and excellent gear fatigue properties also makes C64 steel an attractive new option for gears that incorporate integral bearing races (e.g. planetary gears in epicyclical transmissions).
  • Smaller, lighter-weight driveshafts, or greater throughput or durability, including improving existing driveshafts by replacing current materials with C64 steel. Integrally-geared driveshafts using C64 steel can often handle approximately 20-25% higher loads than comparable driveshafts using traditional materials, or be reduced in size and weight by comparable amounts. C64 steel’s core UTS of 229 ksi is a ~31% increase vs. 9310, for example.
  • Reduced manufacturing times and costs, with increased flexibility and control. C64 steel was designed to resist grain growth even at high temperatures, have high hardenability, and use vacuum carburizing with a direct low pressure gas quench, to thus: maintain good properties in large, thick-sectioned components (even with vacuum carburizing); reduce final machining/finishing costs by eliminating intergranular oxide formation and reducing quench distortion; eliminate the time, expense, equipment and non-uniformity of the traditional after-carburizing oil quench “hardening” step; and permit “dial-in” control of carburized case hardness profiles. AGMA technical paper 11FTM27 provides a detailed comparison of costs and time (see below).
  • Superior high temperature operability and survivability such as in oil-out emergency conditions or high-temperature environments. The 925°F tempering temperature of C64 steel is 400-600°F higher than most incumbent alloys, yielding superior thermal stability and allowing gearboxes to run hotter (thus reducing cooling system weight, size, drag, etc.).
  • Greater corrosion resistance. Under a Navy-funded project, QuesTek has shown C64 steel's corrosion resistance to be greater than that of both 9310 and Pyrowear 53.

Forging, Machining, Heat Treatment and Finishing Processes

C64 steel was designed for high-temperature carburizing. This allows solution heat treatment to be combined with the carburizing treatment and C64 steel is therefore quenched directly from the carburizing temperature. After quenching to room temperature, C64 steel is subjected to cryogenic treatment to assure a complete martensitic transformation. C64 steel is typically tempered at 925°F (496°C) and has excellent thermal resistance approaching this temperature.

For detailed information about forging, machining, heat treating and finishing processes of C64 steel, please refer to our Manufacturing and Thermal Processing of C64 Steel document.

C64 Steel Availability and Pricing

Carpenter Technology produces and typically keeps an inventory of C64 steel in round bar form of the following sizes, usually with immediate shipment and no minimum order: 1.25", 2.75", 4", 5.25" and 6.75" OD. Some large commercial aerospace companies are using 10" and 14" and these sizes may also be available from inventory.

Other sizes will be added in time, and they can produce custom diameters, round corner square and octagon, although longer lead times and minimum orders in the range of 800 lbs are likely.

For pricing, inventory availability and lead time please contact Carpenter Latrobe facility by phone (800-241-8527) or e-mail at service@cartech.com. You may also contact the Reading facility by phone (800-572-2800 or 800-245-5030) or e-mail at sales@cartech.com

Technical Assistance

If you have a specific application engineering or technical question that is not answered by the processing document above, then feel free to Contact Us.

Design and Development Background

We computationally designed and developed C64 steel under STTR Phase I and Phase II projects, in direct response to solicitation N05-T006 by the U.S. Navy Naval Air Systems Command (NAVAIR) for improved performance, power density and manufacturability of rotorcraft transmissions when compared to using incumbent carburized gear steels.

In 2012 SAE International issued AMS 6509 to cover C64 steel.

In 2011 we co-authored an AGMA technical paper that analyzed total gear manufacturing costs and compared Ferrium C61 and C64 to baseline alloys (see below).

In 2011 we announced a subcontract award from Bell Helicopter to jointly evaluate the application of C64 steel for helicopter gears, as part of the $30 million Technology Investment Agreement awarded to Bell by the U.S. Army Aviation Applied Technology Directorate to develop state-of-the-art drive system technology under the Army’s Future Advanced Rotorcraft Drive System (FARDS) program (see below). During this subcontract, QuesTek will work with Bell to further develop the thermal processing and finishing processes of C64 steel to optimize the combination of strength and hardness in the gear case and core.

Relevant files


Material Data Sheets


Press Releases