Wälzfestigkeit von Sinterstählen unter konstanter Hertz'scher Pressung mit überlagerter Reibung
Rolling contact fatigue of sintered steels under Hertzian pressure and sliding
In most investigations the rolling contact fatigue properties of sintered steels are determined without superposition of an additional sliding which is present on the flanks of gears during operation. In such investigations an improvement of the fatigue strength is principally related to an increase in density. However, the realistic and most severe condition between sliding gear teeth in contact is a sliding of minus 24 percent (relative velocity between two sliding surfaces). The rolling contact fatigue tests with sliding were performed with the mixed alloys Fe plus 1.5 percent Cu, carbonitrided, Fe plus 1.5 percent Cu plus 0.5 percent C, as-sintered as well as quenched and tempered, in the densities of 6.8, 7.1 and 7.4 g/ccm, and the diffusion alloyed powder Fe minus 4.0 percent Niminus 1.5 percent Cu minus 0.5 percent Mo, as-sintered, carbonitrided, case hardened, plasmanitrided (densities 7.1 and 7.4 g/ccm) and additionally mixed with 0.5 percent C (densities 7.0 and 7.2 g/ccm). T he tribological environment was the gear-box oil SAE 80 at 80 deg. C. With superposition of sliding an optimum rolling fatigue strength at about 7.2 g/ccm is observed for the investigated PMsteels in the as-sintered as well as differently heat-treated states in the density range of 6.8 to 7.4 g/ccm. This is due to effects based on open and closed porosity in interaction with tribological environment.