Rolling bearings are essential mechanical components that enable low-friction operation between sliding elements and are therefore indispensable for numerous applications. They are particularly widespread in high-end mechanical engineering. A failure of rolling bearings can lead to significant economic consequences, including costs for repair, replacement, and consequential damage. A good example of this is the complex repair processes of offshore wind turbines. Among the many causes of failure - arising from complex loading conditions and various factors during assembly and operation - are phenomena such as spalling, micropitting, and corrosion pitting. For this reason, considerable efforts have been and are being made to improve the reliability of rolling bearings. Improvements in steel cleanliness and lubricant quality, among others, have contributed to optimally designing rolling bearings for specific applications and significantly extending their service life. However, over the past 20 years, premature failures of rolling bearings have repeatedly occurred due to so-called White Etching Cracks (WEC), the causes of which are not among the usual ones. These involve groups and networks of cracks accompanied by a white-etching, altered microstructure at the crack flanks, referred to as White Etching Area (WEA). Similar microstructural changes are also observed in the vicinity of non-metallic inclusions during uniaxial fatigue after very high numbers of load cycles (VHCF). In this case, fine granular areas (FGA) are formed. WEA/WEC and FGA have so far mostly been observed separately, and models of possible formation mechanisms have been developed independently of each other. The aim of this research project is to investigate whether similar microstructural changes occur during the formation of WEA/WEC and FGA - in rolling bearing operation and under very high cycle fatigue - and whether they can be attributed to a common mechanism. This subproject focuses on analyzing the stress states and the influence of hydrogen on fine grain formation.