With the ongoing shift away from fossil energy sources towards more sustainable resources, hydrogen is considered an alternative form of energy storage. However, as most steels show undesired embrittlement when used in a hydrogen atmosphere, accurate knowledge of composition of the microstructure is essential to prevent this problem. The martensitic Cr-steel X30CrMoN15-1, which has been used in rolling bearings and tribologically stressed components due to its high hardness and excellent wear resistance in the past, is a promising candidate for usage in dry-running ball bearings in a hydrogen atmosphere In the course of this master's thesis, two heat treatment conditions of the X30CrMoN15-1 steel, which differ only in their tempering temperature, were examined and compared regarding their micro- and nanostructure. Various diffraction methods such as X-ray diffraction or electron backscatter diffraction were used to characterize the matrix composition, in particular the retained austenite content and any possible precipitates. Scanning electron microscopy and scanning transmission electron microscopy were used to precisely determine the precipitate content and size distribution. Additional atom probe measurements and energy-dispersive X-ray spectroscopy were also used to obtain the chemical composition of the matrix and the precipitates. Both considered states showed very similar microstructure with high fraction of retained austenite, up to 30 %, and significant fraction of precipitates, about 1.5 %, in form of trigonal carbonitrides with typical sizes of few hundreds nanometres. Although both microstructures were very similar in the observed size scales, tempering at higher temperatures led to significantly higher hardness values. In addition, HE-XRD measurements revealed a reduction in the lattice parameters of martensite and austenite from the 350°C state to the 450°C state. Thus, the reason for the increased hardness of the 450°C state is therefore to be assumed in differences of smaller magnitudes such as segregations, cluster formations or early-stage precipitates. A very good correspondence in phase quantification between electron microscopy-based methods and x-ray diffraction-based methods was demonstrated.