Composite sintered material

A composite sintered material comprising:

• a plurality of diamond grains having an average grain size of less than or equal to 2 μm;
• a plurality of cubic boron nitride grains having an average grain size of less than or equal to 1 μm;
• a plurality of aluminum oxide grains having an average grain size of less than or equal to 0.2 μm;
• and a remainder of a binder phase, wherein
• at least parts of adjacent diamond grains are bound to one another,
• the binder phase includes cobalt and a chemical component including at least one element selected from a group consisting of tungsten, titanium, zirconium, hafnium, niobium, tantalum, chromium, aluminum, silicon, and molybdenum, and
• in the binder phase, a content of the cobalt is more than or equal to 50 mass % and less than or equal to 99.5 mass %, and a content of the chemical component is more than or equal to 0.5 mass % and less than or equal to 50 mass %,
• at least a part of the binder phase is at least one of a carbide, a carbonitride, a nitride, an oxide, an oxynitride, and a boride,
• in the composite sintered material, a content of the diamond grains is more than or equal to 50 volume % and less than or equal to 70 volume %, a content of the cubic boron nitride grains is more than or equal to 10 volume % and less than or equal to 30 volume %, a content of the aluminum oxide grains is more than or equal to 2 volume % and less than or equal to 15 volume %, and a content of the cobalt is more than or equal to 5 volume % and less than or equal to 15 volume %,
• in a visual field having a longitudinal side of 18 μm and a lateral side of 23 μm within an arbitrarily specified cross section, twenty straight lines are drawn, comprising ten straight lines in a longitudinal direction and ten straight lines in a lateral direction in a form of a lattice to divide the visual field into eleven equal portions in the longitudinal direction and divide the visual field into eleven equal portions in the lateral direction,
• wherein for each line segment in a number of line segments on the twenty straight lines, a distance between adjacent aluminum oxide grains with a grain size of more than or equal to 0.1 μm located on each line segment is more than or equal to 0.2 μm,
• wherein each line segment in a total number of line segments on the twenty straight lines is connected between corresponding adjacent aluminum oxide grains,
• a ratio of the number of line segments with respect to the total number of line segments is more than or equal to 90%, and
• less than or equal to one aluminum oxide grain having a grain size of more than or equal to 1 μm exists in the visual field having the longitudinal side of 18 μm and the lateral side of 23 μm within the arbitrarily specified cross section.