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Low Temperature Plasma Nitriding of Pyrowear 675
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High performance mechanical systems such as bearing and gears in advanced gas turbine engines are required to operate at ever increasing speeds, temperature, and loads. Advanced high temperature case hardened bearing steel, Pyrowear 675, has been developed for these applications. The basic mechanical properties and desired microstructure have been achieved by conventional carburizing. The corrosion resistance is better than conventional bearing steel M50 but not as good as 440C. A nitriding process for carburized Pyrowear 675 using low temperature plasma was developed to improve corrosion resistance. The microstructure, carbon and nitrogen profile, micro-hardness profile, hot hardness profile, residual stress profile, and retained austenite profile were examined for nitrided samples. The corrosion resistance of nitrided Pyrowear 675 was evaluated using anodic polarization corrosion test. The results show that the introduction of nitrogen through plasma nitiriding process significantly improved corrosion resistance while maintaining required basic mechanical properties and microstructure. The nitiriding process resulted in increased surface hardness, hot hardness, and compressive residual stress. Ball-on-rod RCF tests and sub-scale bearing fatigue tests conducted with plasma nitrided Pyrowear 675 showed poor rolling contract fatigue life compared to carburized Pyrowear 675.
plasma nitriding, corrosion resistance, rolling element bearing
Trivedi, Hitesh K.
UES Inc., Dayton, OH
Ionic Technologies Inc., Greenville, SC