Abstract
Because of the regulation related to the global environment, the automotive powertrain system becomes smaller to increase fuel efficiency and to decrease CO2 emission. Meanwhile, the operating condition of the gear components become tough under the higher transmitted load caused by downsizing. It becomes, therefore, more critical for automotive industry to insure the durability of the components as per the trends. In this work, the development of the material for the planetary gear system was performed to improve the durability of the gear in the downsized auto-transmission system. The metallic composition was designed to 1) improve resistance of the gear to softening phenomenon by heat generation during operation 2) insure the superior carburizing properties under the conventional heat treatment condition, and 3) improve the strength and toughness by optimizing Si, Cr, Ni and V. As a result of this development, it was shown that the characteristic L10 for the roller pitting fatigue test was increased by more than 200% and the bending fatigue limit was increased by 15%.
