For steel investigation and development, exact knowledge about the microstructural state is inevitable. The information obtained from 2-dimensional images alone is often not capable of properly reflecting the real 3-dimensional microstructure properties like carbide phase distribution, homogeneity and retained austenite amount after heat treatment. In order to obtain reliable information for meaningful models, simulations and correlations it is necessary to accompany standard metallography with 3-dimensional data, which unfortunately are very difficult to access. Two general ways are available for obtain a 3D microstructure, X-Ray computed tomography and serial sectioning optical microscopy methods. In this article, serial sectioning method was used to gain retained austenite amount and carbide distribution information in AISI D3 cold work tool steel. Using this procedure, 3D microstructural information was extracted from AISI D3 steel grade and a virtual 3D-model of the spatial phase distribution and retained austenite amount were generated and compared with X-Ray diffraction information.