The present master thesis was conducted in the framework of the K-project “metal JOINing”. One of the main goals of the project is the development of a filler metal for joining of high strength sheet steel by gas metal arc welding. The realization of welded joints with the same strength level as the base metal is essential for lightweight constructions with challenging requirements of high load carrying capacities, e.g. mobile cranes. This master thesis deals with the determination of the amount of retained austenite (RA) in 13 high strength, martensitic weld metals via electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and magnetic measurements. In direct comparison of the different methods, the magnetic measurement was found to be the most reliable method of RA determination as it has the highest tested volume and no sample preparation is needed. Consequently, there is no risk of strain induced transformation from RA to martensite. Furthermore, the determined RA contents were compared with the mechanical properties. Some of the alloys showed an increase of the 0.2%-yield strength and a decrease of the Charpy impact energy at room temperature with increasing amount of RA determined through magnetic measurements. This is in contradiction to the literature and indicates the presence of embrittling martensite-austenite constituents instead of RA in the weld metal samples.