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By cold forming metastable austenitic steels below 0 °C, the strength is increased significantly through martensite phase transformation in addition to strain hardening. This deformation-induced effect enables the use of corrosion-resistant materials for highly loaded applications such as bearings under oxidative atmospheres, where the use of conventional corrosion-prone steels is unsuitable. In this context, components made of austenitic steel could enable an economic application through a sustainable manufacturing process. The aim of this study is the modification of the functional surface layer of angular ball bearing rings made of X5CrNi18-10 (AISI 304) through bulk forming to increase their service life. Forming parameters and tool settings are determined numerically to obtain the material flow and prevent tool cracking, since tool steels show a lower resistance to high mechanical loads at process temperatures below 0 °C. After forming, local martensite formation in the surface layer of the angular ball bearing rings is detected through metallographic analyses. The resulting increase in martensite content and dislocations is correlated to the achieved surface hardness and to the simulated true plastic strain. It can be shown that by adapting the forming process, a significant increase in hardness is achieved in the running surface of the angular ball bearing ring.
Keywords: Austenitic steel, cryogenic forming, martensite formation, bearing rings© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.