EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The growing requirements in the power density of gears, driven by the wind industry, enhance the need for further development of the methods for assessing the risk of material failure. Broadly applied, the case-hardening process provides beneficial compressive residual stresses and hardness to the gear’s tooth surface. However, the subsequent tensile residual stresses introduced in the material’s depth have been identified as a key factor, increasing the exposure to fracture mechanisms such as Tooth Flank Fracture (TFF). The experimental determination of residual stresses in depths exceeding a few hundreds of micrometers represents a challenge for most of the usual measurement methods, among which many require the destruction of the component. In contrast, a simulation model for the case-hardening heat-treatment enables to investigate the influence of geometrical and process-related parameters on the residual stresses in the gear’s volume, thus providing essential insights into the material’s failure risks. A Finite-Element (FE) heat-treatment model is built based on extensive dilatometric and metallographic investigations on the steel 18CrNiMo7-6, which considers complex interactions of the steel’s behavior such as those related to carbon diffusion, phase transformations, transformation plasticity and tempering effects. Using the developed FE-model on varying process conditions brings out correlations between the process parameters and the resulting residual stress state and provides guidance towards increasing the gear’s lifetime through the optimized heat-treatment.