Influence of Low Temperatures on Material Properties and Tooth Root Bending Strength of Case-Hardened Gears

This paper presents the main results of performed investigations and discusses the possible influences of different low temperature treatments on relevant material characteristics in correlation with the obtained tooth root bending strength of case-hardened gears made of materials 18CrNiMo7-6, 20MnCr5 and 15NiCr13. Most of the investigations were performed on gears that were exposed to low temperatures after heat treatment. Additionally, the effect of low temperatures within the heat treatment process was examined. For shot blasted gears, which were treated by low temperatures after heat treatment process, all examined materials showed no decrease of the tooth root bending strength. In contrast, for almost all gears which were cooled down to low temperatures within the heat treatment, a decrease in the tooth root bending strength was observed in unpeened as well as in shot blasted condition. Additional investigations show a correlation of tooth root bending strength and relevant material properties.