To provide a rotary, having both breaking resistance and wear resistance to cope with a material to be cut and cutting conditions in a wide range.
A microdrill contains a cemented carbide formed of a hard phase mainly composed of tungsten carbide and a bonded phase mainly composed of cobalt. The microdrill includes: a central part 10 extending along the central axis; and an outer peripheral part 20 covering the central part 10 and provided with an outer peripheral blade 4. The outer peripheral part 20 has an outer peripheral surface 5, and the radius x of the central part satisfies the relationship expressed by 0.05 R≤x≤0.9 R when the radius of the outer peripheral surface 5 is taken as R. The central part 10 contains cobalt of A mass % at the proportion of occupying the whole of the central part 10, and the outer peripheral part 20 contains cobalt of B mass % at the proportion of occupying the whole of the outer peripheral part 20. A and B satisfy the relationship expressed by 0.5 ≤B/A<1.
OMORI NAOYA
Toshio Morita
Yoshihei Nakamura
Yutaka Horii
Hisato Noda
Masayuki Sakai