Effect of abnormal surface layer on tooth surface strength increase of gas carburized gears

摘要

Gas carburizing has been widely applied to power transmission gears in mass production. Gas carburized gears have so called abnormal surface layers on their surfaces that are generated during the carburizing process. Although the influence of the abnormal surface layer on the bending strength of the gear tooth has already been reported (Lyu et al., 1994), that on the tooth surface strength has not been clarified. The authors have carried out experiments to study the influence of the layer on the tooth surface strength. As a result of the experiments, it was found that the layer on the tooth surface has an effect to increase the tooth surface strength and that the effect of the layer greatly depends on its characteristics. By examining the layer microscopically five characteristics were given, and their suitable conditions that increase the tooth surface strength were discussed. Furthermore, experiments were carried out to examine whether the tooth surface strength of Cr-Mo alloy steel (JIS SCM42OH) can be increased by improving the characteristics of the abnormal surface layer. A trial material was prepared by modifying the chemical composition of the Cr-Mo alloy steel. From the experiments with the gears made of the modified Cr-Mo alloy steel, it is demonstrated that the tooth surface strength of the gas carburized gears can be increased by improving the characteristics of the layer.