Radiation hardness of 6H silicon carbide (SiC) p+n diode particle detectors has been studied. The charge collection efficiency (CCE) of the detectors decreases with the increased fluence of electrons with energies of 0.2 MeV and higher. Defect X2 with an activation energy of 0.5 eV was found in all detectors which showed the decreased CCE. The decreased CCE was restored to the initial value by thermal annealing of defect X2. It is concluded that defect X2 is responsible for the decreased CCE of 6H-SiC p+n diode particle detectors.