抄録
The temperature dependence of Vickers hardness was obtained in the range of -196°C to 250°C for molybdenum (Mo) and -196°C to about 550°C for tungsten (W) by impressions in the central region of the specimens. On the other hand, when one makes impressions in the region near the edge of the specimen the macroscopic cracks were found on the edge side of the impressions under certain conditions. If we assume that the temperature in nearly equal zero on the apparent total length of the cracks is the boundary between the ductile zone and the transition zone, and that the temperature which is nearly constant at the upper point of the brittle zone, the results obtained in this paper can be recognized to be consistent with the ductile-brittle transition based on tensile properties of Mo and W hitherto obtained by other authors by taking account of the difference of the material conditions. By the above definition the ductile zone, the transition zone and the brittle zone are >-39°C, -39°C∼-92°C and <-92°C for Mo, and >394°C, 394°C∼-33°C and <-33°C for W, respectively.
The crack formation modes of Mo were essentially of transgranular type with a few intergranular type in the temperature range investigated here, and that of W was intergranular type above about -100°C and essentially transgranular with a few intergranular type below about -100°C, which was not consistent in detail with the results obtained by Bechtold et al.
