Study HC – HV properties of WC-Co alloys with different microstructures

Measurement of magnetic parameters is a method for express product quality control in processing of WC-Co tool hardmetals. The coercivity value is often used to estimate the WC grain size and the hardness of the hardmetal, whereas the nature of the WC grain size distribution is often disregarded. H C – HV properties of WC-Co hardmetals with different microstructures were studied. For production samples of WC – 10 % Co hardmetals, it is shown that H C does not depend on the width of the WC grain distribution and is a function of the average size d 1.0 . The hardness HV 30, which is affected by the width of the WC grain distribution, is a function of the d 3.2 value. Based on the obtained relations, a H C – HV property map is plotted, taking into account the width of the WC grain size distribution. The map shows that measuring only the coercivity value will introduce uncertainty in the estimated hardness in the 100 – 120 HV range. However, joint measurement of H C and HV makes it possible to estimate the width of the WC grain size distribution in the hardmetal. Based on the analysis of experimental hardmetal samples with a carbon content near the lower boundary of the carbon window and sintered at a relatively low temperature, the formation of an unusual structure was observed featuring the uniformly distributed large cobalt lakes. In such a structure, the size distribution of Co lakes is bimodal and the average size of the lakes is not proportional to the average size of WC grains. Moreover the formation of such a structure does not affect the hardness of the hardmetal, but leads to a significant decrease in the coercivity. The results obtained can be used for industrial inspection of the WC-Co hardmetals properties, as well as in the interpretation of experimental data.