Affiliation:
1. Leibniz-Institut für Werkstofforientierte Technologien—IWT 1 , Badgasteiner Str. 3, 28359Bremen, DE
2. Laboratory for Machine Tools, Production Engineering (WZL) of RWTH Aachen University 2 , Steinbachstraße 19, 52074Aachen, DE
Abstract
Increasing power density and rotational speed raise major challenges for transmission development, especially in the field of aerospace technology and electromobility. Both the increase in energy input and the decrease in capability of heat dissipation lead to an increase in the operating temperature of high-performance transmissions. As a result of this increase in operating temperature, the microstructures of conventional bearings and gears are exposed to tempering, which can reduce the load capacity of these components. Especially for gear applications, a complex load capacity profile is needed, since the gears have to resist high contact pressure on the tooth flank and high bending stress in the tooth root. Considering the increase in operating temperatures, it is only permissible to manufacture the gears in high-performance transmissions from heat-resistant and high-performance materials. It is mandatory to achieve the necessary high-performance by heat treatment of gears. Today high-performance gears are typically case-hardened to achieve the best performance in service. Due to the metastable characteristics of martensite, the microstructure of a gear can degrade during service if the operating temperature meets or exceeds the former tempering temperature. This degradation leads to reduced hardness and a decrease in performance. To achieve a more stable state of microstructure prior to service, new heat treatments and alternative steel grades are continuously being developed. The aim of this paper is to investigate the strength of gears made out of the recently developed Hybrid 55 material (EN X20NiCrAlMoV6-5-2-1) and to compare the performance of these gears with commonly employed gears that are made out of EN20MnCr5 material. Initially various carburizing and nitriding treatment variants were used for heat treatment of the gears, and then the gears were tested for tooth root strength at 180°C in a newly developed test rig.
Publisher
ASTM International100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959