[en] Full text: The microstructure of two high speed steels (nom. Composition wt %: 1.6 C, 4.8 Cr, 2.0 Mo, 5.0 V, 10.5 W und 8.0 Co) with different processing procedure (powder metallurgical - vacuum casting) have been examined using 3-dimensional atom probe technique. By time-of-flight depth profiling analysis and using of lateral position sensitive recording precipitate phases of MC and M₂C (M = Mo, Fe, Cr, V, W) have been analyzed and tomographic images of the specimen volume have been reconstructed by computer modelling from the achieved data. Usually a cylindrical volume of 10 to 15 nm in diameter and up to 50 nm in depth has been probed. Precipitations as found shown to be needle shaped or like platelets with a thickness of a few atomic layers. In the mass spectra most of the species which can be assigned to the precipitates are of MC type, while the leading constituent in this MC is Mo. Besides Mo very few W can be found. M₂C complex ions have been observed in the precipitate phases only in small amounts. Co shows to be evenly distributed in the matrix. While these observations stand for powder metallurgical as well as for conventional processed steel samples it can be seen that the precipitates are generally smaller and more evenly distributed in the matrix of the powder metallurgical processed steel. It can be shown that atom probe technique provides unique features for analyzing structural phenomena on a close to atomic scale. Important nanostructural parameters like size, shape distribution in volume and chemical composition of fine dispersed precipitation can be directly evaluated from 3D reconstructed data. (author)