The transverse-rupture strength affected by carbon contents of the WC-Co alloys was investigated in the temperature range from 600 to 900°C in relation to fracture sources. The WC-(620)%Co high and low carbon two phase alloys with carbide grain size of 1.2 p. were used as specimens. The stress increasing rate was kept at 1 kg/mm2/sec.
The high temperature strength of the low carbon alloy was confirmed to be substantially superior to the high carbon alloy. However, actually, this relation due to the carbon content was not always observed over a wide range of temperatures up to 900°C, because in conventional alloys structural defects were apt to be fracture sources with decreasing temperature and Co content: That is, the above relation was usually held at temperatures higher than the specified one which was determined according to Co contents and defect dimensions. In this case, a specific fracture source (R-region) always appeared and was smaller in the low carbon alloy. Discussions concerning the influence of stress increasing rate on the strength have been made.