The requirements towards high strength steels in engineering applications are continuously increasing. These requirements do not only address the maximum fatigue strength in itself, but also the scattering of local properties is of increasing importance. Since at the same time the acceptance of failures in industry is decreasing, following the „zero defect strategy“, the reduction of scattering in fatigue life supersedes the importance of its average value. An approach to meet these requirements is the development of microstructures which are more damage tolerant.
At Leibniz IWT this general approach has already a certain tradition. In the presentation three different approaches for through- and case hardening bearing steels, investigated in the context of current research projects, are compared. The first is based on the generation of fine bainitic microstructure in standard bearing alloys, which allows higher plastic deformation at significant strength levels. The second is the development of high strength steel grades with alloying elements stabilizing retained austenite within the heat treatment procedure. As third variant case hardening steels were carbonitrided to stabilize the retained austenite due to the enhanced nitrogen content in the case. The reason for enhancement of the damage tolerance due to an elevated and stabilized retained austenite content is assumed in the locally enhanced plasticity and its possible stress induced transformation into martensite. The effect achieved by the different approaches will be discussed and guided to an outlook.