Volume 79, Issue 3

Gearboxes of modern drivetrains, e.g., in wind turbines, can be exposed temporarily to low ambient temperatures during their manufacturing or during operation. During manufacturing or assembly, for example, very low temperatures sometimes occur during joining processes due to the cryogenic treatment of the components. In these cases, the temperature depends on the cooling medium used (typically dry ice or liquid nitrogen). Furthermore, depending on the application, gearboxes may be exposed to low ambient temperatures up to -60 °C when used in cold regions. The low temperatures can have an impact on the component properties and thus on the gear load carrying capacity. Therefore, the knowledge of these influences is very important regarding the design and dimensioning of gearboxes. In this publication, further investigations on the load carrying capacity of cryogenic treated gears are presented based on previous research work. The focus is on results on the tooth root and pitting load carrying capacity. The load carrying capacity is analyzed in the context of changes in the component properties as a result of different low temperature treatments, and the dominant influencing factors are identified.

The combination of forming with continuous cooling bainitic steels offers a new path for reaching energy-efficient manufacturing chains. Improved energy efficiency is achievable thanks to the suppression of conventional, energy-intensive heat treatments. In the present paper, different thermomechanical processing strategies, including laboratory and industrial scale forgings, were assessed alongside their impact on the resulting microstructure. Firstly, phase transformation kinetics were assessed in precisely controlled environments via dilatometry coupled to in situ techniques. Secondly, the microstructure, mechanical properties, and forgeability of large-scale forged components were investigated in laboratory and industrial conditions. These investigations were also assisted by finite element method simulation. The comparison between controlled and industrial-scale conditions illustrates pitfalls in the transfer of knowledge to conditions approaching a real manufacturing chain. Nevertheless, alloy and process design is shown to be a key aspect to overcome the discussed challenges, allowing homogeneous bainite microstructures and mechanical properties to be achievable over a flexible range of processing conditions.

Sinter hardening grade steels were prepared using hybrid alloying by combining Cr-Mo and Mo prealloyed powders with fine Mn-Si masteralloy powders. Compacts from both base powders showed the “internal getter” effect, which however was much more pronounced for the Cr-Mo powders because of the markedly high starting oxygen content. Combining the base powders with the masteralloy resulted in the desired sinter hardenability, the Mo prealloyed powder resulting in somewhat better properties because of more complete dissolution of the masteralloy and lower residual oxygen content.