The invention relates to a drilling tool (50), in particular a dowel hole drill, for the machining of workpieces, in particular workpieces made of wood, plastics, composite materials, comprising a drill shaft (56) with a front surface (60), and to a drill head (58) with at least one cutting edge (66), which is firmly connected, such as soldered, to the drill shaft (56). In order to make available a drilling tool of the type mentioned at the start, which has a broad range of application and is simple to produce, it is provided that the drill head (58) is formed from a composite material with exclusively two layers (38), namely a hard metal layer (36) and an ultra-hard layer (38) which is connected to the hard metal layer (36) and preferably formed from polycrystalline diamond or polycrystalline boron nitride, that the ultra-hard layer (38) is connected directly to the front surface (60) of the drill shaft (56) and that the at least one cutting edge (66) is formed by the ultra-hard layer (38), and a drill bit (62) such as a centering tip is formed by the hard metal layer (36).

A surface-coated cutting tool includes a base material and a coating formed on a surface of the base material. The coating includes a first hard coating layer including crystal grains having a sodium chloride-type crystal structure. The crystal grain has a layered structure in which a first layer composed of nitride or carbonitride of Al.sub.xTi.sub.1-x and a second layer composed of nitride or carbonitride of Al.sub.yTi.sub.1-y are stacked alternately into one or more layers. The first layer each has an atomic ratio x of Al varying in a range of 0.6 or more to less than 1. The second layer each has an atomic ratio y of Al varying in a range of 0.45 or more to less than 0.6. The largest value of difference between the atomic ratio x and the atomic ratio y is 0.05≤x−y≤0.5.

A cutting insert may include a first surface including a corner and a first side, a second surface, a third surface, an inclined surface located between the first surface and the third surface, a first ridgeline located on an intersection of the inclined surface and the first surface, and a second ridgeline located on an intersection of the inclined surface and the third surface. An imaginary straight line passing through a center of the first surface and a center of the second surface may be a central axis. In a cross section which is parallel to the central axis and is orthogonal to the first side, an imaginary straight line connecting the first ridgeline and the second ridge line may be a first straight line, and the inclined surface may include a first inclined surface located more away from the central axis than the first straight line.

A polycrystalline cubic boron nitride comprising 96% by volume or more of cubic boron nitride, wherein the cubic boron nitride has a dislocation density of more than 8×10.sup.15/m.sup.2, the polycrystalline cubic boron nitride comprises a plurality of crystal grains, and the plurality of crystal grains have a median diameter d50 of an equivalent circle diameter of less than 100 nm.

A cutting insert includes a substrate and a cutting-edge insert. The substrate has, in a thickness direction of the substrate, a bottom surface, and a top surface opposite to the bottom surface. The top surface has a polygonal shape composed of a plurality of sides in a plan view as seen along the thickness direction. The top surface is provided with a projection projecting to a side opposite to the bottom surface along the thickness direction. The projection has a through-hole passing through the substrate along the thickness direction. The projection has a side surface contiguous to the top surface. The side surface is composed of a curved line protruding to a side opposite to the through-hole in the plan view as seen along the thickness direction.

A cubic boron nitride sintered material comprises 30% by volume or more and 80% by volume or less of cubic boron nitride grains and 20% by volume or more and 70% by volume or less of a binder phase, the cubic boron nitride grains having a dislocation density of 3×10.sup.17/m.sup.2 or more and 1×10.sup.20/m.sup.2 or less.

A cubic boron nitride sintered material comprises cubic boron nitride particles and a bonding material, wherein the bonding material comprises at least one first metallic element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten; cobalt; and aluminum; the cubic boron nitride sintered material has a first interface region sandwiched between an interface between the cubic boron nitride particles and the bonding material, and a first virtual line passing through a point 10 nm apart from the interface to the bonding material side; and when an element that is present at the highest concentration among the first metallic elements in the first interface region is defined as a first element, an atomic concentration of the first element in the first interface region is higher than an atomic concentration of the first element in the bonding material excluding the first interface region.

Chip discharge during high-feed machining and low-feed machining particularly in a high-depth-of-cut state or the like is improved so as to allow so-called freedom of feed during cutting to be improved. A cutting edge body of a cutting insert includes a front cutting edge formed on one end side in a longitudinal direction, the front cutting edge being a cutting edge formed on an intersecting edge between a peripheral side surface and an upper surface of the cutting edge body having a prismatic shape, a side cutting edge formed on one end side in a lateral direction, a recessed part provided in the upper surface of the cutting edge body to be subsequent to the side cutting edge in the lateral direction, and a wall part having a wavy wall surface formed in a portion of the recessed part and a discrete wall surface formed at a position between the wavy wall surface and the side cutting edge and including a plurality of surfaces which are discrete along the longitudinal direction.

A cutting insert for a cutting tool includes a cutting edge of PCBN or PCD formed in a corner region in a transition between a side surface and a chamfer formed in an upper side of the cutting insert. A chip breaker is formed in the chamfer inside of the cutting edge, extending between a lower chamfer portion and an upper chamfer portion. The chip breaker includes a chip breaker bottom connected to the lower chamfer portion and a chip breaker wall extending from the upper chamfer portion to the chip breaker bottom. An upper transition is formed between the upper chamfer portion and the chip breaker wall. As seen in a top view, the upper transition follows a smoothly curved path including a convex middle portion. As seen in cross-section, perpendicular to the cutting edge, the chip breaker wall and the chip breaker bottom form a smooth concave profile.

The cubic boron nitride sintered material is a cubic boron nitride sintered material comprising: cubic boron nitride particles in an amount of 70 vol % or more and less than 100 vol %, and a bonding material, wherein the bonding material includes an aluminum compound, and includes cobalt as a constituent element; the cubic boron nitride sintered material has a first region in which a space between adjacent cubic boron nitride particles is 0.1 nm or more and 10 nm or less; and when the first region is analyzed by using an energy dispersive X-ray analyzer equipped with a transmission electron microscope, the atom % of aluminum in the first region is 0.1 or more.