For the design of cyclically loaded components made of 100Cr6, e.g., roller bearing rings, the influence of microstructural defects, i.e., non-metallic inclusions, must be considered. In this context, besides the defect size, also the defect tolerance of the material matrix influences the fatigue life. Preliminary work has shown that the defect tolerance of steel 100Cr6 increases with higher contents of retained austenite, caused by a higher plasticity and the beneficial effect of deformation-induced austenite to α'-martensite transformation. However, excessive phase transformations can lead to dimensional deviations, being inacceptable for common applications. Hence, for an improvement of the fatigue performance, the retained austenite requires a defined volume fraction and mechanical stability.

Consequently, in the presented work two variants of 100Cr6 steel, having an increased content of Al (1.5 wt.-%) and Si (1.5 wt.-%), respectively, were analyzed. The aim of these alloying concepts was a realization of a relatively high content of retained austenite with a sufficient phase stability. Therefore, the materials investigated were bainitized, while the heat treatment parameters were determined based on a parameter analysis, as presented in [1].

To analyze the influence of the volume fraction and the stability of the retained austenite on the fatigue behavior, for each condition Woehler curves were determined in the high cycle (HCF) and very high cycle fatigue (VHCF) regime. In accordance with [2] the √area approach established by Murakami [3] was applied to evaluate the defect tolerance, which was complemented by X-ray diffraction phase analyses to determine the contribution of the phase transformation on the defect tolerance.

These investigations revealed for both steels an increased defect tolerance in relation to the standard condition of 100Cr6. Comparing the two alloys, the Si-alloyed variant shows a lower stability as well as a finer distribution of the retained austenite, resulting in a better defect tolerance and thus, a higher fatigue strength than observed for the Al-alloyed variant.