| 摘要 |
A microdrill bit is made of a tungsten carbide based cemented carbide which contains a binder phase of 6% by weight to 14% by weight of a cobalt alloy and a hard dispersed phase of balance tungsten carbide. The cobalt alloy contains cobalt, chromium, vanadium and tungsten and has weight ratios so as to satisfy the relationships of 0.04</=(c+d)/(a+b+c+d)</=0.10 and 0.50</=c/(c+d)</=0.95, where a, b, c and d denote weight ratios of tungsten, cobalt, chromium and vanadium, respectively. The drill bit is formed so as to have a Rockwell A scale hardness of 92.0 to 94.0.
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