The properties of steel strongly depend on the alloy composition but also on the steel cleanness. Most efforts to improve final steel quality apply to secondary metallurgical deoxidation processes. This master thesis investigates the impact of the deoxidation process on the non-metallic inclusions and the development of the oxygen content from the ladle furnace to the ingot casting of Breitenfeld Edelstahl AG, to derive a connection between the micro cleanness and macro-inclusions in ingots and in the semi-finished product. The focus is on the influence of aluminum deoxidation. Special attention was paid to CrNiMo case hardening and hardened steels. Both Celox and Total Oxyen Samples were taken to track the development of the oxygen content. So-called cone-samples were used for the examination of the steel cleanness. The steel cleanness of four batches of 18CrNiMo7-6, before and after vacuum treatment and additionally one sample during casting, were characterized by means of SEM/EDS analysis and the development of the non-metallic inclusions was monitored. The findings from the operational tests and the process data as well as a literature study were used to show possible reasons for macro inclusions in the product and to prevent them in the future. In addition, equilibrium calculations were carried out with FactSage and the results of the calculations were compared with the results from the SEM/EDS analysis. The secondary metallurgical process of Breitenfeld Edelstahl AG was assessed positively regarding deoxidation and steel cleanness. In addition, the development of the composition of non-metallic inclusions over the course of the process was successfully displayed and possible solutions for avoiding macro inclusions were offered.