The application of both high strength gear steels and shot peening technology has succeeded in strengthening automotive transmission gears. This technology, though, improves mainly the fatigue strength at the tooth root, but not the pitting property at the tooth face. Therefore, demand has moved to the development of new gear steels with good pitting resistance.
In order to improve pitting resistance, the authors studied super carburizing which is characterized by carbide dispersion in the case, especially processed with a plasma carburizing furnace. Firstly, the influence of the carburizing temperature and carburizing period on the carbide morphology was investigated and the optimum carburizing conditions were determined. Secondly, the fatigue strength and pitting resistance was evaluated using carbide dispersed specimens.
Gear fatigue tests and roller pitting tests show that the 0.18%C-0.5%Si-0.3%Mn-2.25%Cr-0.4%Mo steel super carburized by the plasma carburizing furnace and shot peened has a better pitting resistance than gears conventionally gas carburized and shot peened. Furthermore, as revealed by a gear pitting test that simulates real transmission, the combination of the steel and the process shows good pitting durability.