N093-166 TITLE: Adjusted Nitrogen Alloyed Stainless Steel with Optimized Thermal Processing for Superior Balanced Performance

TECHNOLOGY AREAS: Air Platform, Materials/Processes

ACQUISITION PROGRAM: Joint Strike Fighter, ACAT I

OBJECTIVE: Develop highly corrosion resistant bearing and gear steels with surface technology for robust wear, scuffing, and rolling contact fatigue resistance.

DESCRIPTION: Corrosion protection of high performance bearing and gear steels without debit of mechanical and tribological properties is critical for sustaining Navy equipment readiness. Due to insufficient corrosion resistance of bill-of-material bearings and gears, the U.S. Navy has developed corrosion inhibited oils for aircraft propulsion systems. These specially formulated oils are utilized to reduce the number of rejected mechanical system parts at overhaul due to corrosion. Oil formulations for corrosion protection limit the ability of these oils for boundary lubrication (tribology) performance. The lubrication performance penalty limits the growth in power density needed for aero propulsion engine and gearbox systems. Advanced bearing steels, like carburized case hardened Pyrowear 675, provide reasonable tribology performance, but only marginal improvement in corrosion protection. A new family of stainless steels: High Nitrogen Martensitic Stainless Steels (HNS) have recently been developed with excellent corrosion resistance. In addition to corrosion resistance, these steels have excellent rolling contact fatigue resistance. However, they lack essential attributes for abrasive and adhesive wear resistance. HNS bearing surfaces also have poor resistance to high speed and high temperature scuffing. This is due to the very alloy formulation that provides corrosion resistance but has not been optimized for balanced mechanical and tribological properties. Rather, current HNS attributes for corrosion resistance appear to be at odds with boundary lubrication. The surface must have sufficient iron or iron oxide content to react with oil additives. Chrome oxides (for corrosion protection) limit the surface reactivity for the formation of boundary lubricating films. In addition, the micro-structure of HNS seems to have limited shear stability to avoid adhesive wear or catastrophic scuffing.

PHASE I: Demonstrate the feasibility of bearing or gear steels with both high corrosion resistance and robust tribology performance.

PHASE II: Develop, test and demonstrate prototype bearing or gear steels. Perform corrosion resistant testing and key tribology performance attribute testing for wear, scuffing and rolling contact fatigue (both surface and subsurface initiated). Cooperation with a bearing company and OEM engine company should be considered. A viable series of test methods should be established to provide production ready technical information. The test methods may include attributes for wear, scuffing and fatigue, as well as their competitive interactions.

PHASE III: Finalize the designed technology and establish commercialization of the material and surface modification technologies. Transition the technology to the fleet.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Direct spin-off of corrosion resistant steels with robust tribology performance is immediately possible in marine equipment, heavy duty construction equipment, automotive and industrial applications where corrosion is important. Efficient and cost-effective production methods are essential for dual use applications.

REFERENCES:
1. H. Spikes. "Tribology Research In The Twenty-First Century." Tribology International, Volume 34, Issue 12, December 2001, Pages 789-799

2. H. Berns, F-J Ebert and H-W Zoch. "The New Low Nitrogen Steel LNS � A Material for Advanced Aircraft Engine and Aerospace Bearing Applications." Bearing Steels: Into the 21st Century, ASTM STP 1327, J.J. Hoo and W.B. Green Eds, American Society for Testing and Materials, 1998.

3. L. Manes, J.M. De Monicault and R. Gras. "Behavior of the Nitrogen Bearing Martensitic Stainless Steel: XD15NW in Cryotechnical Environment." 4th European Mechanics of Materials Conference on Processes, Microstructures and Mechanical Properties, J. Phys, IV France 11 (2001) Pr4-303-Pr4-309; http://cat.inist.fr/?aModele=afficheN&cpsidt=1121925

4. D. Girodin, L. Manes, J-Y. Moraux and J-M. de Monicoult. "Characterization of the XD15N High Nitrogen Martensitic Stainless Steel for Aerospace Bearing." 4th International Conference on Launcher Technology "Space launcher Liquid Propulsion", 3-6 Dec. 2002, Liege (Belgium);
http://www.snr-bearings.com/group/fr/fr-fr/file.cfm/04characterisationofxd15n.pdf?contentID=1155

KEYWORDS: Corrosion resistant steels; Bearings; Gears; Surface treatments; Tribology; Heat treatment

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