Properties of Densification by Surface Rolling and Load Bearing Capacity of 1.5Cr-0.2Mo High Density Sintered Steel Rollers and Gears

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Surface rolling experiments and surface durability tests were carried out using powder metallurgy (P/M) gears made of 1.5Cr-0.2Mo single-press single-sinter (1P1S) high density (7.55×10<SUP>3</SUP> kg/m<SUP>3</SUP>) sintered steel. The fundamental densification properties of this P/M material were first examined using P/M rollers. A high precision form rolling machine of two roller-dies transverse type was employed. The porosity became nearly zero from the surface down to a depth of at least 0.5 mm when the amount of decrease in the roller radius was more than 0.15 mm. Next, the gear tooth profile analysis was done by finite element simulation (FE-simulation) to optimize some shape parameters of a modified convex tooth profile of P/M spur gears before rolling. Simulation results agree well with the experimental data and gears with good tooth profile accuracy and a fully densified surface layer of about 0.5 mm in depth on the gear flank could be obtained. The gear running tests were finally conducted using a power re-circulating type gear testing rig with a counter pinion gear made of Ni-Cr-Mo wrought steel. Both P/M gears and counter pinions were case-carburized and finished by grinding under the same conditions. The test results confirmed that high density 1.5Cr-0.2Mo P/M gears had sufficiently high load bearing capacity as an automotive power transmission gear and those surface durability tended to increase by surface rolling.