Co thin films were subjected to 50 keV carbon ion implantation.At the dose of 2.5×10~(17)/cm~2,a hexagonal Co-carbide phase was observed for the first time.The lattice con-stants from electron diffraction are a=0.2685 nm and c=0.4335 nm.The phase does not dis-appear until the dose of 9×10~(17)/cm~2.Auger spectra showed that the stoichiometry wasCo_(2-3)C.The behavior of the ferromagnetic carbides along the descending sequence ofNi-Fe-Co by Fermi energy of solids was interpreted.Furthermore,based on the kinetic con-dition of phase transformation and the band theory of solids,a possible explanation about thedifference of the results of ion-metallurgy and thermal metallurgy was proposed. Co-carbide phase was observed for the first time. The lattice con-stants from electron diffraction a = 0.2685 nm and c = 0.4335 nm. The phase does not dis-appear until the dose of 9 × 10 ~ (17) / cm ~ 2.Auger spectra showed that the stoichiometry was Co_ (2-3) C. The behavior of the ferromagnetic carbides along the descending sequence of Ni-Fe-Co by Fermi energy of solids was interpreted. Future plus, based on the kinetic con-dition of phase transformation and the band theory of solids, a possible explanation about the difference of the results of ion- metallurgy and thermal metallurgy was proposed.