To increase the fatigue limit of high-strength steels which typically fail from non-metallic inclusions it is necessary to modify the inclusions and/or the surrounding matrix. The goal must be a higher threshold for crack initiation and/or crack propagation. One possibility to reach this goal is to execute a thermal or thermomechanical treatment (TT and TMT). The present work discusses a series of such treatments that were applied to classical bainitic materials states. The different treatments consisted of shortened isothermal bainitic transformations as well as cyclic loading, either with constant or stepwise increasing load amplitude, which were applied at increased temperature in the range of dynamic strain ageing. The lifetime behaviour of the different material states was determined in bending fatigue tests. In order to describe and compare the different treatments it was necessary to evaluate the stress intensity factors arising at the critical inclusions. The results for cyclic loading yielding a lifetime of 107 cycles turned out to be in good agreement with the predictions using the stress intensity factor developed by Murakami. To consider different numbers of cycles to failure this calculation method was successfully extended and a modified stress intensity factor was defined. The same method was also used to test and evaluate specimens with artificial flaws. These showed the same behaviour as the specimens which failed from natural non-metallic inclusions. © 2010 Published by Elsevier Ltd.
Kerscher, E., & Lang, K. H. (2010). Influence of thermal and thermomechanical treatments on the fatigue limit of a bainitic high-strength bearing steel. In Procedia Engineering (Vol. 2, pp. 1731–1739). https://doi.org/10.1016/j.proeng.2010.03.186