Case hardening is a thermochemical surface hardening process which, through carburisation and subsequent hardening, produces a high-strength, wear- and fatigue-resistant surface layer with a tough core, and is therefore used in particular for highly stressed notched gear shafts and bearing seats.
In integral design concepts according to DIN 743 or FKM, the effective components of case hardening are reduced to a process-specific hardening influence (Kv), whereby the complexity of the process and the local stress are neglected and the prediction of long-term strength is subject to increased uncertainty, particularly in the case of notch and surface layer-dominated stresses.
In contrast, the differentiated approach of FKM (Section 5.5) and the FVA-guideline allow for the separate consideration of essential strength-relevant influencing factors such as hardness/strength gradients, surface layer-induced residual stresses and local stress states.
The aim of the ongoing research work is to systematically differentiate and quantify these partial effects of case hardening with regard to their contribution to long-term strength in order to increase the predictive accuracy of strength design.