Abstract
It is well known that the strength of WC-Co low carbon cemented carbide decreases with precipitation of Co3W, when the alloy is annealed at about 800°C. The present study was undertaken to reveal the reason of the strength decrease, in relation to the structural defects which would act as a fracture source. The WC-10 and 20% Co low carbon two-phase alloys (mean grain size of carbide, about 1.2 μ) were annealed at 800°C for up to 15 hr, and used as specimens. After the transverserupture test had been performed according to the Japanese Industrial Standard, measurements of the sort, dimension and location of the defects were made on the fracture surface.
Results obtained were as follows. (1) It was shown that the sort, dimension distribution and average dimension of the defects as a fracture source didn't vary by the precipitation treatment, that is, neither the development of new defects nor the growth of the pre-xisting defects took place. (2) The strength of the sound matrix (σ0) decreased by the treatment. Thus, it became clear that the strength decrease was resulted from the decrease of σ0 only. (3) However, further investigation is needed to make clear the machanism of the decrease of σ0.
