In order to improve the surface durability of case-carburized gears, the influence of initial surface roughness on fatigue and wear of rolling-sliding contact surface was investigated. First, case-carburized test rollers having three kinds of surface textures were made and roller tests were carried out at various inlet oil temperatures and load conditions. Secondly, the surface fatigue and surface roughness of test rollers were measured with the use of a stereoscopic microscope and a roughness measuring instrument. After the roller tests were carried out, the following results are obtained in the test rollers with initial smooth surface: It is possible to decrease the surface temperature and generating noise during running, the number of pits and the amount of wear. Therefore, in the case-carburized gears under the high load condition, the influence of initial surface roughness on surface fatigue and wear is significantly high.
