A small part of tool steels form the so-called plastic mould steels, which have to withstand high mechanical stresses and very aggressive conditions. Within this thesis new lower alloyed materials with varying chromium- and molybdenum-contents and different heat treatments were evaluated. These materials were characterized regarding their corrosion behavior and were compared with existing alloys. The experimental part included electrochemical investigations and immersion tests. The aim of this research work was the advancement of cost-effective plastic mould steels by optimization of the material properties and especially of the corrosion resistance by modification of the alloy composition. Moreover the limits of their applicability in respect of pitting resistance in artificial sea water and the mass loss induced by uniform corrosion in diluted acetic acid should be determined. Besides the chemical composition especially the choose of the heat treatment turns out to be a critical parameter of the corrosion resistance. As limit for the application relating to the claimed corrosion resistance, minimum contents of 11.5 wt.-% chromium and 0.2 wt.-% molybdenum for the hardened material condition were determined.