Abstract
Single tooth bending fatigue tests were first carried out using Ni-Mo pre-alloyed sintered steel (46F4H) spur gears with different densities in the range of 7.30~7.54 Mg/m3. The sintered gears specimens were machined from sintered steel packs made from the single-press single-sinter route and some were surface-rolled using CNC form rolling machine. All test gears were case-carburized. The experimental results showed that the surface-rolled sintered gears with a density of 7.40 Mg/m3 or more had sufficiently high bending fatigue strength to replace gears made of typical Cr-Mo case-carburized wrought steel. Then, the stress analysis in the root fillet area of gear teeth was performed using a FEM simulation model considering a void distribution. The peak value of the maximum principal stress in the surface near the most critical stressed point was increased with the increase of porosity for un-surface rolled gears and was decreased as the amount of surface fully densified depth was increased. These simulation results can explain well the experimental results and show the appropriate material initial density and the surface densification level.
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