The aim of the project was to characterize the fatigue behavior and fatigue-related microstructural changes in metastable, austenitic Cr-Ni steels due to cyclical stress at elevated, operationally relevant temperatures (≤ 300 ° C) up to the very high-cycle fatigue (VHCF) range. It was important to clarify the effects of deformation-induced martensite formation at elevated temperatures on the material’s cyclic deformation behavior and associated length of service life. The fatigue tests were carried out on servo-hydraulic testing machines with test frequencies up to 1 kHz.