Understanding the iron adsorption on the surface of particles is important to predict their nucleation activity and find efficient precipitates. Ab initio calculations of adsorption energy for Fe on the (0 0 1)MX surface (M = Ti, V, Nb, Zr, Hf or Ta and X = C or N) were performed to study the initialization of Fe nucleation. We find that the trends in Fe adsorption as dependent on the M and X atoms do not follow the lattice parameter or surface energy of MX, but are closely related to the number of the M and X valence electrons. The strongest binding was predicted for Fe on (0 0 1)NbC, and this carbide should have the high nucleation potential at early stage that is consistent with the observed grain refinement of ferritic and austenitic steels with NbC. In order to establish the alloying effect, we studied the adsorption of 3d atoms (M = Ti, V, Cr, Mn, Co, and Ni) on (0 0 1)NbC and concluded that Cr and Mn may compete with Fe in adsorption. The calculations of Fe adsorption on the NbC surface covered with 3d atoms demonstrated that the initial layer of the Cr or Mn atoms enhances the subsequent Fe adsorption.