Abstract
Surface durability tests were carried out using powder metallurgy (P/M) pinions and gears made of 1.5Cr-0.2Mo single-press single-sinter (1P1S) high-density (7.55 × 103 kg/m3) sintered steel. A mating gear was made from standard grade Ni – Cr – Mo wrought steel. The P/M gear specimens were machined from sintered packs and some were surface-rolled. All test gears were case-carburized under the identical condition and finished by grinding. A power re-circulating type gear running testing rig was employed. The gear dimensions and the mating gear material were found to scarcely affect the surface durability of as-sintered P/M gears. When the as-sintered P/M gear was set as the driver, the surface fatigue strength after 1.5 × 107 cycles was approximately 10 % smaller than when this gear was set as the follower. The load bearing capacities of the surface-rolled P/M gears were higher than those of the Ni – Cr – Mo wrought steel pinions regardless of the drive system. The finite element analysis of contact stress shows that the maximum shear stress distributions beneath the gear flank surface during loading can explain an appropriate case-hardening depth, a sufficient densification layer by surface rolling and the surface durability properties obtained in gear running tests.
