Steel produced by the PM-HIP route has a more homogenous microstructure compared with that obtained in conventionally produced material. This is an important advantage in many applications, and is therefore of interest to predict. The homogeneity of the microstructure is possible due to the rapid solidification of the powder grains in the atomization and the small size of the powder grains. Computational predictions of the variations of composition in powder grains, compacted material and conventionally produced material are compared with microstructure investigations. The microstructure is investigated in SEM with coupled composition analysis by EDS/WDS. The computational predictions are based on a description of the equilibria in the steel, and of the kinetics of segregation on solidification. The effect of alloying elements is discussed, and the effect in a stainless steel and in a tool steel is calculated.