This thesis deals with the influence of boron on the microstructure of a high nitrogen alloyed austenitic steel (P556), with emphasis on grain refinement. Therefore, melts with varying boron content and different sizes were produced and partly forged. Furthermore, the influences of boron on the deformability and recrystallization behaviour were investigated using a so called “Gleeble”. With the use of light optical microscopy as well as scanning electron microscopy the influence of boron on grain size, cleanliness and precipitation behaviour were investigated. In addition, the mechanical properties and the corrosion behaviour were tested. Finally, the influence on the precipitation behaviour was investigated using time-temperature-precipitation diagrams. The analysis indicated that grain refinement could be observed only on very small scale samples, whereas this phenomenon could not be observed on bigger blocks (15 kg) or on the forged material. The time-temperature-precipitation diagrams lead to the conclusion that the addition of boron triggers the segregation of Cr2N precipitates.