Nb and V are used in steels as micro-alloying elements. So far Nb and V is not used in heat treatable steels as micro-alloying element. Therefor the aim of the work was to determine the influence of micro-alloying elements on the properties of a classic heat treatable steel after quenching and tempering. For that two types of the treatable steel 42CrMo4 were produced. One type was micro-alloyed with Nb and the other one with Nb+V. For comparison the 42CrMo4-steel without micro-alloying elements was investigated. The heat-treatment was simulated by a dilatometer with different heating rates, austenitising temperatures and tempering temperatures. For determination of the different conditions the hardness was measured. The results revealed that tempering between 600°C and 690°C leads to a plateau in hardness at the micro-alloyed steels. By using TEM and atom probe it was shown that the plateau results from clusters of niobium and vanadium, which are generated during the tempering at dislocations. Tensile tests were accomplished in addition to the measurements of hardness and showed an increase in strength as proposed by hardness tests. Furthermore, two TTT-curves were recorded to determine the difference in the behaviour of transformation by micro-alloying. Due to the micro-alloying elements the formation of ferrite, bainite and pearlite occurs later and at lower temperatures.