Rolling Contact Fatigue Properties of Selected PM-Materials for Gear-Box Applications 1999-01-0333
Rolling contact fatigue tests with a sliding of -24% were performed with the mixed alloys Fe+1.5%Cu, carbonitrided, Fe+1.5%Cu + 0.5%C, as-sintered as well as quenched and tempered, diffusion alloyed powder Fe-4.0%Ni-1.5%Cu-0.5%Mo, as-sintered, plasmanitrided, carbonitrided, case hardened and additionally mixed with 0.5%C and prealloyed powders Fe-4.0%Ni-0.5%Mo and Fe-1.5%Mo with addition of Cu and C in different heat treatments. The densities investigated were 6.8, 7.1, 7.4 and 7.8 g/cm3. The tribological environment was the gear-box oil SAE 80 at 80°C. With superposition of sliding the highest rolling contact fatigue strength was achieved with powder forged specimens (density of 7.8 g/cm3). An optimum for the sintered specimens in the range of 6.8 to 7.4 g/cm3 was found at around 7.1 g/cm3 for the most sintered steels independent of the heat treatment. This is due to effects based on open and closed porosity in interaction with the tribological environment. In case of variable loading the fatigue strength under constant loading can be exceeded by factors of 1.42 to 1.76.