ROLLING-CONTACT FATIGUE AND SLIDING WEAR PERFORMANCE OF FERRITIC NITROCARBURIZED M-50 STEEL

The rolling contact fatigue and sliding wear performance of two types of ferritic nitrocarburizing techniques (gaseous and fluidized bed) were evaluated on AISI M-50 steel. These processes produced a thin compound layer over a nitrogen-rich diffusion zone. It was observed that compound layer thicknesses less than 1-mu-m increased the rolling contact fatigue (RCF) L10 life up to a factor of six over the untreated M-50 steel. Compound layers greater than 2-mu-m had a tendency to flake off the substrate near the spalled region, producing lower L10 lives than the baseline M-50 steel. Sliding wear tests on ferritic nitrocarburized M-50 showed that the compound layer exhibited slightly larger friction coefficients than the nitrogen-rich diffusion zone, although this layer had slightly greater resistance to catastrophic wear at higher contact stresses.