Abstract: Dealing with the weldability of the steel-bonded hard alloy DT40 and the tool steel Cr12, the effect of interlayer metals near the bonded interface on a vaccum diffusing process and the mechanical properties of the bonded specimens were investigated. The interlayers were made in different Ni-base alloys and added by different methods such as powders, cold rolled foils and brush plating films. The joint was successfully bonded and the tensile strength of the joint was high. The connectivity of the joint was examed by mechanical dectection, metallograph, SEM and EDPX analyses. This paper also discussed the principle of the diffusing welding process adopted the interlayers added by brush plating films.