he technology of the HIP diffusion bonding of YG 15C cemented carbide to 45# carbon steel has been studied. The effects of bonding temperature. pressure time.interlayer and its thickness. residual thermal stress on bonding strength have been researched. The results show that: In the HIP diffusion bonding of YG 15C to 45# carbon steel, the bonding strength depends on bonding temperature strongly and is controlled by the residual thermal stress d ne to the therm al expansion mismatch after honding. By using N i asinterlayer, the effect of residual thermal stress on bonding can be diminished effectively sothat the bonding strength can be improved apparently.