A cutting insert according to one embodiment includes: a rake face; a flank face continuous to the rake face; and a cutting edge constituted of a ridgeline between the rake face and the flank face. A coolant flow path is provided inside the cutting insert. One end portion of the coolant flow path opens in the flank face to form a coolant ejection hole. The flank face is provided with a coolant guide groove extending from the coolant ejection hole toward the cutting edge with a base end portion of the coolant guide groove being connected to the coolant ejection hole and with a front end portion of the coolant guide groove being disposed at a position close to the cutting edge relative to the base end portion.

A cemented carbide including tungsten carbide grains and a binder phase, in which a total content of the tungsten carbide grains and the binder phase in the cemented carbide is no less than 80 vol %, a content of the binder phase in the cemented carbide is no less than 0.1 vol % and no more than 20 vol %, in a histogram showing distribution of orientation differences between adjacent pairs each consisting of two of the tungsten carbide grains adjacent to each other in the cemented carbide, a first peak is present in a class of the orientation differences of no less than 29.5° and less than 30.5°.

A cemented carbide comprises a first hard phase comprising tungsten carbide particles and a binder phase including Co and Cr. In any surface or any cross section of the cemented carbide, a region in which there is a distance X of 5 nm or less between surfaces respectively of tungsten carbide particles adjacent to each other, with the surfaces facing each other along a length L of 100 nm or more, is referred to as a WC/WC interface, and a ratio C(R)/C(C) has an average value of 0.17 or more, where C(R) and C(C) represent peak values of atomic percentages of Cr and Co, respectively, at a WC/WC interface having a distance X of 1 nm or more and 5 nm or less and having therein an atomic percentage of Co higher than an average value of atomic percentages of Co in the tungsten carbide particles+2 at %.

A cemented carbide comprises a first hard phase comprising tungsten carbide particles and a binder phase including Co and Cr. In any surface or any cross section of the cemented carbide, a region in which there is a distance X of 5 nm or less between surfaces respectively of tungsten carbide particles adjacent to each other, with the surfaces facing each other along a length L of 100 nm or more, is referred to as a WC/WC interface, and a ratio C(R)/C(C) has an average value of 0.17 or more, where C(R) and C(C) represent peak values of atomic percentages of Cr and Co, respectively, at a WC/WC interface having a distance X of 1 nm or more and 5 nm or less and having therein an atomic percentage of Co higher than an average value of atomic percentages of Co in the tungsten carbide particles+2 at %.

A cutting insert according to one embodiment includes: a rake face; a flank face continuous to the rake face; and a cutting edge constituted of a ridgeline between the rake face and the flank face. A coolant flow path is provided inside the cutting insert. One end portion of the coolant flow path opens in the flank face to form a coolant ejection hole. The flank face is provided with a coolant guide groove extending from the coolant ejection hole toward the cutting edge with a base end portion of the coolant guide groove being connected to the coolant ejection hole and with a front end portion of the coolant guide groove being disposed at a position close to the cutting edge relative to the base end portion.

The coating film includes a laminated structure including at least one first layer and at least one second layer alternately disposed. The or each first layer has an average thickness of 0.5 to 100.0 nm and has an average composition: (Al.sub.xTi.sub.1-x-y-zMy)B.sub.zN, where M is at least one element selected from the group consisting of Groups 4, 5, and 6 elements, and lanthanide elements in the periodic table, 0.100?x?0.640, 0.001?y?0.100, and 0.060?z?0.400. The or each second layer has an average thickness of 0.5 to 100.0 nm and has an average composition: (AlpCr1-p-q-rMq)BrN, where M is at least one element selected from the group consisting of Groups 4, 5, and 6 elements, and lanthanide elements in the periodic table, 0.650?p?0.900, 0.000?q?0.100, and 0.000?r?0.050.

A cemented carbide including tungsten carbide grains and a binder phase, in which a total content of the tungsten carbide grains and the binder phase in the cemented carbide is no less than 80 vol %, a content of the binder phase in the cemented carbide is no less than 0.1 vol % and no more than 20 vol %, in a histogram showing distribution of orientation differences between adjacent pairs each consisting of two of the tungsten carbide grains adjacent to each other in the cemented carbide, a first peak is present in a class of the orientation differences of no less than 29.5? and less than 30.5?.

A cemented carbide includes a plurality of tungsten carbide particles, and a binder phase including Co. The binder phase further includes Cr. A region in a cross section of the cemented carbide where a distance X between surfaces of the tungsten carbide particles adjacent to each other having an opposing surface length L of 100 nm or more is 5 nm or less is a WC/WC region. A peak value of atomic percentage of Cr obtained by an elemental analysis in a transverse direction from one tungsten carbide particle to the other tungsten carbide particle in the WC/WC region is a Cr value, and a peak value of atomic percentage of Co thus obtained is a Co value. A ratio of the Cr value and the Co value (Cr value/Co value) is a Cr/Co ratio, and the Cr/Co ratio is larger than 1. A cutting tool includes the cemented carbide.

A surface coated cutting tool comprising a substrate and a coating layer on the substrate, the substrate comprising a WC-based cemented carbide comprising a hard phase component of WC grains and a binder phase primarily composed of Co, wherein (a) an interfacial layer is disposed between the substrate and the coating layer; (b) the interfacial layer includes a region A directly above the hard phase component and a region B directly above the binder phase, and the interfacial layer has an average thickness; at the midpoint across the average thickness of the interfacial layer, the W content in the region A ranges from 90 to 99 mass %, while the W content in the region B ranges from 30 to 65 mass %, the C content C.sub.A in the region A satisfies C.sub.A?0.05 mass %, and the C content C.sub.B in the region B satisfies C.sub.A?C.sub.B?0.09 mass %.

Diamond particles with enhanced reactivity are used to sinter polycrystalline diamond (PCD), under high pressure and high temperature conditions. Copper and tin form a solution with transition metal catalyst (cobalt) used to sinter diamond particles. Copper and tin enhance the reactivity of the diamond particles, reduce the coefficient of thermal expansion (CTE) mismatch between cobalt and polycrystalline diamond, and lead to a more homogeneous distribution of catalyst metal in PCD. A cutting element may comprise a substrate and a polycrystalline diamond table bonded to the substrate produced by sintering diamond particles with enhanced reactivity mixed with standard diamond particles and chemical additives. These combined effects (more reactive diamond particles, reduced CTE mismatch, and homogeneous distribution of catalyst metal) lead to better performing tools.