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

For the design of cyclically loaded components, influence of defects, i.e., non-metallic inclusions, and thus, defect tolerance of material have to be considered. Preliminary work on bearing steel 100Cr6 has shown, that the cyclic hardening potential and associated defect tolerance increase with higher contents of retained austenite, whereby deformation-induced austenite-α’-martensite-transformations have beneficial effect on defect tolerance [1]. However, phase transformations also lead to dimensional deviations, which are inacceptable for common applications.
In this work, modified 100Cr6 with variable contents of Si (0.6 and 1.5 wt.-%) or Al (1.5 wt.-%) were differently heat treated to realize bainitic microstructure and relatively high contents of retained austenite with defined stability, which depends on chemical composition and heat treatment condition. For each condition cyclic indentation tests (CITs) were performed to determine the respective cyclic hardening potential, which correlates with defect tolerance. By comparing the cyclic hardening potential obtained in CITs at ambient as well as elevated temperatures of 100°C, the austenite stability and thus, influence of phase transformation on defect tolerance was examined. It was shown that more pronounced increase of cyclic hardening potential at elevated temperature indicates more stable austenitic phase. To validate the defect tolerance as well as the austenite stability indicated by CITs, fatigue tests were performed at materials in selected heat treatment conditions, which are assumed to exhibit a pronounced defect tolerance as well as high austenite stability. The evolution of phase distribution during cyclic loading was analysed with X-Ray diffraction in interrupted fatigue tests.
The present results show that a higher content of retained austenite increases the cyclic hardening potential of a material, which depends on the stability of the austenitic phase and can be determined efficiently by using CITs.
[1] Kramer et al.: Int. J. Fat. (63), 2014.