Ceramic-metal composites, or cermets, are employed for a wide range of applications, in both bulk material and coating forms. This is largely due to their high wear and corrosion resistance. In the current study, a ‘pack boriding’ diffusion treatment has been applied to TiC-316L cermets, to further harden their surface. Boriding is achieved by heating the cermet samples within a packed powder-bed, containing a boron source, between 950 and 1150 °C, for a period of four hours. The surface transition for these materials is complex. A semi-continuous borided layer can be developed, with transformation of the steel binder to high hardness iron borides (i.e., FeB and Fe₂B). Fine TiB_x nanocrystals are also shown to form on the surface TiC during boriding, while the core of the TiC ‘core-rim’ structure is also preferentially attacked/removed. While the boriding treatment increases the surface roughness, it is also shown to increase both the cermet Vickers hardness and scratch hardness, highlighting the potential benefits of this such diffusion-based surface treatments.