Additive manufacturing enables the development of new production processes which allows unrivaled individualization of parts and an acceleration of product development. Therefore, this technology has been improved significantly. Nevertheless, there are still unsolved problems. The thesis describes the additive manufacturing of an alloyed cold-work tool steel. The major task was to find out, if it is possible to build dense constructions via selective laser sintering. In the course of this, also the avoidance of hot cracks which were detected in a preliminary study should be investigated. For this purpose, a process parameter study was carried out and the occurring defects were characterized. It was shown that this process mainly uses liquid phase sintering as fusion mechanism of the powder feedstock. Therefore, there is an increase in porosity, while the formation of hot cracks cannot be excluded. Furthermore, a kinetic law which enables the prediction of porosity depending on the process parameters was successfully applied. In addition, the master thesis considers other fusion mechanisms of powder particles. The appearance of these mechanisms was regulated by the energy density of the laser beam.