Cemented carbide and cutting tool using same

A cemented carbide in which a hard phase containing WC the most is bound by a binder phase containing Co the most,

• said binder phase being substantially constituted of Co, or Co and Ni, a total content of Co and Ni being not less than 4.5 mass % and not more than 15 mass % with respect to the total mass of the cemented carbide,
• the WC grains in the cemented carbide having an average diameter of not less than 0.4 μm, and not more than 4 μm,
• when the average diameter of the WC grains in the cemented carbide is represented by x (μm), the cemented carbide having a thermal diffusivity X (cm2/sec) satisfying X>0.055x+0.238, and
• in a cross section of the cemented carbide, the average number of sharp edges per WC grain being not more than 0.25, said average number of sharp edges per WC grain being determined by dividing the number of sharp edges each having a curvature radius of 100 nm or smaller among the edges of the WC grains by the average number of WC grains.