Abstract Combining DSC/TG–QMS analysis and dilatometry experiments at constant heating rates, the sintering behaviors of the Ti(C,N)‐based cermets with carbon additives were studied. It is found that the additives of diamond or graphite could promote the interactions among raw powders during solid‐state sintering. The outgassing behavior and endothermic effect were enhanced, thereby resulting in the increasing densification activation energy. The negative activation energy during the liquid phase sintering indicates that the dissolution–precipitation process occurs easily and provides a rapid densification path. The dissolution–precipitation process for cermets with .6‐wt% graphite or .6‐wt% diamond additive became more efficient than for cermets without additional carbon additive. The white‐core/gray‐rim grains were clustered together in the cermets with .6‐wt% graphite additive, whereas they were distributed evenly in the cermets with .6‐wt% diamond additive. Moreover, the average sizes of ceramic grains in the cermets without additional carbon additive, and with .6‐wt% graphite or .6‐wt% diamond additives, were .453, and .517, or .525 μm, respectively.