Method of producing boron nitride polycrystal, boron nitride polycrystal, cutting tool, wear-resisting tool, and grinding tool

A method of producing a boron nitride polycrystal, the method comprising:

• a first step of obtaining a thermally treated powder by performing a thermal treatment onto a powder of a high pressure phase boron nitride at more than or equal to 1300° C. and less than or equal to 2100° C.;
• and
• a second step of obtaining a boron nitride polycrystal by sintering the thermally treated powder under a condition of 8 to 20 GPa and 1200 to 2300° C.,
• the high pressure phase boron nitride being a cubic boron nitride or a wurtzite type boron nitride, wherein
• the thermally treated powder comprises thermally treated boron nitride, and
• crystal grains of the thermally treated boron nitride have a shape described as a spherical shape or a polygonal shape with rounded corners.