Advanced Bearing and Gear Steel Materials and Thermal Processing

Pitting corrosion limits the lifetime and performance of turbine engine bearings and gears operated in marine environments. A number of alloys and improved treatments have been attempted to increase corrosion resistance while maintaining mechanical performance of the bearings, but few meet the expectations. Some more corrosion resistant treatments such as the low temperature expanded austenite (S-phase) have good corrosion resistance, but lack the case depth to prevent spalling in demanding applications. Others reach mechanical requirements by precipitating hard, wear resistant carbides in the matrix, but this method sacrifices the alloying elements that provide corrosion protection for carbide formation. IBC has developed a duplex chemo-thermal process that utilizes both carbon and nitrogen in the case structure to balance the need for mechanical and corrosion resistance. IBC will employ past experience with and knowledge of heat treatment of tool steels, low pressure vacuum carburizing, and duplex treatment of martensitic stainless steels with computer assisted materials design to develop a new stainless alloy that meets the corrosion and mechanical requirements of bearings and gears used in marine and other corrosive environments. IBC will balance the diffusion of both carbon and nitrogen such that the required case depth and hardness are obtained. The balance of the diffusion species is below the point of saturation in the matrix such that precipitates are controlled.