The generation of micro-cracks by EDM of cemented carbides has been often discussed as an important problem. However, a clear explanation has not been made regarding the effect of the surface defects containing micro-cracks on material strength. In this study, the surface defects of cemented carbides were examined experimentally and its influence on the transverse rupture strength (TRS) was clarified. Moreover, the temperature dependence of the TRS was studied and the fracture stress distribution was obtained from the statistical analysis. The results are as follows:
(1) The surface damage of cemented carbides by EDM mainly consists of micro-cracks and deep micro-craters.
(2) The TRS is shown by a curve with both minimum and maximum value as the discharge energy increases.
(3) At higher temperature above 600°C, the defects such as micro-cracks and deep micro-craters indicate the structure insensitive property on the TRS. And the scatter of the TRS can be explained by using Weibull's equation.