Effects of Cr3C2 on the microstructure and mechanical properties of the brazed joints between WC–Co and carbon steel

Brazing between WC–Co and carbon steel using multiple layers of Cu and Ni alloys as insert metal was successfully carried out without weld defects. However, as the brazing time was increased, brittle intermediate phases and coarsening of WC grains were produced and deteriorated the joint strength. On the basis of inhibiting WC grain growth by the addition of carbides during sintering, this study focused on the improvement of the joint strength related to microstructural changes caused by various concentrations of Cr3C2 during the brazing. Increased amounts of Cr3C2 were effective to prevent the formation of η phase (Co3W3C) and the coarsening of WC grains, however, in the case of 1.0% Cr3C2 addition, deteriorated the shear strength due to the formation of brittle Cr7C3 in the insert metal layer. The highest shear strength was 370 MPa under the condition of 0.5% Cr3C2 concentration in WC–8%Co, which was higher than that (310 MPa) of a similar joint without Cr3C2 under same brazing condition of 1323 K and 0.6 ks.