抄録
The effects of residual compressive stress (σro) due to surface-grinding on the transverse-rupture strength (σm) of WC-Co cemented carbide were studied in detail. Specimens of WC-(10∼30)%Co high carbon two-phase alloys which were free from residual pores of more than about 20μφ were made by vacuum sintering. The sintered specimens were ground by using diamond-wheels with a diamond grain size of about 70 and 150μ (abbreviated as G-specimen), or sufficiently polished so as to remove the surface layer associated with σro (P-specimen).
The results obtained were as follows. (1) The effects of σro were confirmed to exist in this case, differing from the case of conventional alloys. The effects of σro were remarkable in the alloy with lower Co contents, so that the dimension of the defect acting as a fracture source and the distance from the tension surface to the defect increased generally in G-specimen; and the σm of G-specimen was higher than that of P-specimen by about 25 and 15 kg/mm2 in 10 and 20%Co alloys, respectively. (2) These effects of σro were discussed in terms of the dimension of the defect, the resulting stress developed in the specimen when the transverse-rupture stress was applied, the surface strength of the specimen, etc. (3) In addition, the anomalous phenomenon that the external stress acting on the defect at the moment of fracture never increases and attains a definite value, when the dimension of the defect decreases to a value less than about 8μ, was reasonably explained by the influence of residual tensile stress in the resulting stress mentioned above.
