The microstructures and hot deformation behaviors of the Co-29Cr-6Mo (CCM) alloy and the same alloy with C and N addition (CCMCN) were compared and analyzed systematically. The results indicated that the gamma phase of this alloy could be stabilized effectively by the slight addition of the elements C and N; however, M(Cr,Mo)(23)C-6 precipitates were observed in the CCMCN alloy according to the results of the X-ray diffraction (XRD) pattern and electron probe micro analyzer (EPMA). The grain sizes of these two alloys after dynamic recrystallization (DRX) are influenced to a certain degree by the balance between athermal martensitic transformation during cooling in the CCM alloy and the existence of carbide in the CCMCN alloy, respectively. Athermal martensitic transformation during the cooling process significantly enhanced the grain refinement process in the CCM alloy at lower strain levels; while carbide helped to further refine grain size in the CCMCN alloy more significantly at high strain levels. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.