White Etching Areas im Wälzlagerstahl 100Cr6
Zusammenfassung der Projektergebnisse
WEAs/WECs were produced on 100Cr6 steel samples by using ZF-type modified Rolling Contact Fatigue (RCF) test rig. A systematic variation of the dominant operating parameters was conducted, to identify conditions in which early failures by WEAs / WECs are expected. Detailed microstructural characterizations were performed on pristine and tested samples. These include the acquisition of SEM BSE and SE panoramic and detail images as well as EBSD measurements. In tested samples, the repeatable generation of WEA under the chosen testing conditions was proven by the microstructural investigations. The microstructural investigations of the pristine sample provided several input parameters for the simulations, e.g. interaction between carbides and steel matrix, carbide size, distances between carbides, and carbide shape. The interaction between the (Fe,Cr)3C carbides and the steel matrix was investigated by SEM BSE and SE imaging. Moreover, information about the carbide size, the distances between carbides, and the carbide shape were derived from SEM EBSD measurements. The microstructural investigations of the tested samples showed several examples of sheared carbides. These are thought to be a potential initiation point of WEAs. Therefore, shearing of carbides was included into the simulations. The influence of carbide inclusions during the formation of WEAs was studied using multi-scale modelling. For single elliptical carbides, the parameters like the carbide stiffness, size, orientation angles, distribution and the depth of carbides directly affect the location of high stress concentrations. However, no plastic deformation was detected irrespective the parameters when single carbides were considered. When multiple carbides were considered, all the above parameters were observed to be interlinked and to play a critical role in the formation of high local stress concentrations. This makes the prediction of the location of WEAs extremely difficult. Moreover, it explains the randomness or wide range of WEAs formation depths. A possible critical case scenario model was built on which the strain accumulation by ratcheting in the vicinity of carbide was captured using a combined non-linear isotropic/kinematic hardening model. This model predicts that the strain values can reach around 15% after 60000 cycles, which shows the significance of carbide particles during formation of WEAs. Finally, carbide shearing under adiabatic and non-adiabatic conditions was introduced into the critical model. As a result of this effect, the matrix is subjected to strain increase of ~9000 % and ~7000 %, respectively. This model can predict severe local plastic deformation as well as the temperatures that could occur in adiabatic conditions which can be related to WEA formation mechanisms. It shows that the carbides can act as nucleating point during formation of WEAs. It also supports hypothesis 2, namely that WEAs form first, followed by crack formation.
Projektbezogene Publikationen (Auswahl)
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"A study on the initiation processes of white etching cracks (WECs) in AISI 52100 bearing steel”, Wear
J. Spille, J. Wranik, S. Barteldes, J. Mayer, A. Schwedt, M. Zürcher, T. Lutz, L. Wang, W. Holweger
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"A Study on Early Stages of White Etching Crack Formation under Full Lubrication Conditions”, Lubricants
W. Holweger, A. Schwedt, V. Rumpf, J. Mayer, C. Bohnert, J. Wranik, J. Spille and L. Wang
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"Simulation of the Fatigue Crack Initiation in SAE 52100 Martensitic Hardened Bearing Steel during Rolling Contact”, Lubricants
K. J. Dogahe, V. Guski, M. Mlikota, S. Schmauder, W. Holweger, J. Spille, J. Mayer, A. Schwedt, B. Görlach, J. Wranik
