ROLLING-CONTACT FATIGUE OF SURFACE-DENSIFIED FLN2-4405

摘要

Powder metallurgy (P/M) processing is capable of producing dimensionally accurate components that have replaced many high-strength wrought counterparts, Advances in both powder production and P/M part manufacturing technologies now facilitate part densities > 7.4 g/cm~3 with single-press/single-sinter processing. This high sintered density promotes uniformity of density throughout the part, minimizing low-density zones, which are often the region of highest loading in gearing applications. Despite the many successes of P/M, the property requirements of automatic transmission pinion gears exceed the current capabilities of materials fabricated by conventional P/M processing. Presently, these gears are produced from low-alloy wrought steel wire that is hot shaped, machined, gear-cut, carburized, and hard-finished. The performance requirements of these gears dictate a high resistance to rolling-contact fatigue (RCF) in order to guarantee long-life powertrain reliability. A recent comprehensive study performed by the Center for Powder Metal Technology (CPMT) demonstrated that the RCF behavior of P/M components is a function of surface density and heat-treat condition. Once near-full density is achieved on the surface, RCF life proved to be equivalent to that of wrought steel. This study did not investigate the depth of densification or carburizing variables on RCF response. Additionally, the surfaced-densified samples utilized in the CPMT study were double-pressed and double-sintered (DP/DS) to core densities approaching 7.5 g/cm~3. Such processing is impractical in the manufacture of helical gearing. Ensuing work by Slattery et al.