The present work shows the microstructural and mechanical results obtained in joints WC-Co / steel 90MnCrV8 (high strength steel). The joints were carried out using diffusion welding processes and soft interlayers Cu-Ni. The binary Cu-Ni alloys were obtained by electrochemical deposition techniques. The microstructural and mechanical changes provoked in the steel, due to heat treatments, were studied in order to know plastic deformation during the joints. The diffusion welds were obtained in an Edwards vacuum furnace (10(-3) - 10(-4) Pa), three welding temperatures were used, (825 degrees C, 850 degrees C and 875 degrees C) and 30, 45 and 60 minutes, as welding times. The constant pressure was 5 MPa. The welding interface microstructure was studied by scanning electron microscopy (SEM-EDX). In order to determine the mechanical behaviour of all joints were carried out shear tests. The optimum results were obtained at 850 degrees C / 45 min and 850 degrees C / 60 min. Nevertheless, the diffusion welding conditions allowed attaining high quality welding interfaces in all joints of WC-Co / 90MnCrV8.