A method of producing a nitrided cut tap that includes a nitrogen diffusion layer. The method includes (a) a nitriding step for forming the nitrogen diffusion layer in which nitrogen atoms contained in an atmospheric gas are diffused from a surface of a base material of the cut tap under heat, such that the nitrogen diffusion layer has a thickness ranging from 10 ?m to 30 ?m; and (b) a honing step for rounding a cutting edge portion by colliding abrasive particles against a local part of the cutting edge portion of the base material of the cut tap that has been subjected to the nitriding step, such that a difference between a thickness of the nitrogen diffusion layer in the cutting edge portion and a thickness of the nitrogen diffusion layer in flank and rake surfaces sandwiching the cutting edge portion, is not larger than 5 ?m.

A cutting edge of a machining tool and a surface treatment method for the same. A cutting edge of a machining tool and a region in the vicinity of the cutting edge, e.g. a region of at least 1 mm and preferably at least 5 mm from the cutting edge, are defined as a treatment region; and substantially spherical injection granules having a median diameter of 1 to 20 m are injected onto the treatment region with an injection pressure of 0.01 MPa to 0.7 MPa in order for dimples having an equivalent diameter of 1 to 18 m and preferably 1 to 12 m, and a depth at least equal to 0.02 m and at most equal to 1.0 m to be formed such that the projected surface area of the dimples is at least equal to 30% of the surface area of the treatment region.

A cutting edge of a machining tool and a surface treatment method for the same. A cutting edge of a machining tool and a region in the vicinity of the cutting edge, e.g. a region of at least 1 mm and preferably at least 5 mm from the cutting edge, are defined as a treatment region; and substantially spherical injection granules having a median diameter of 1 to 20 m are injected onto the treatment region with an injection pressure of 0.01 MPa to 0.7 MPa in order for dimples having an equivalent diameter of 1 to 18 m and preferably 1 to 12 m, and a depth at least equal to 0.02 m and at most equal to 1.0 m to be formed such that the projected surface area of the dimples is at least equal to 30% of the surface area of the treatment region.

A surface treatment method capable of continuously forming a uniform nanocrystalline structure along the surface of a metal product regardless of whether the metal product is hard or soft. A substantially spherical spray powder that has a median diameter of 1-20 m and a fall velocity in the air of 10 sec/m or more is sprayed onto a metal product at a spray pressure of 0.05-0.5 MPa. Thus, even when the metal product is made of a soft material, it is possible to form a uniform continuous nanocrystalline structure layer in which nanocrystals are micronized to an average crystal grain size of not more than 300 nm, preferably not more than 100 nm, without forming a laminar worked structure, impart a high compression residual stress of from about 180 MPa up to the order of 1200 MPa, and strengthen the surface of the metal product.

A surface-coated cutting tool includes a base material and a coating formed on the base material. The coating includes an -Al.sub.2O.sub.3 layer containing a plurality of -Al.sub.2O.sub.3 crystal grains. The -Al.sub.2O.sub.3 layer includes: a first region made up of an edge ridgeline, a region A of a rake face, and a region B of a flank face; a second region which is a region of the rake face except for the region A and covered with the coating; and a third region which is a region of the flank face except for the region B. The -Al.sub.2O.sub.3 layer satisfies a relation ba>0.5, where a is an average value of a TC(006) in the first region in texture coefficient TC(hkl) and b is an average value of the TC(006) in the second region or the third region in texture coefficient TC(hkl).

A method of treatment of a cutting piece (2) is provided. This method includes a first step in which a cutting surface (5) of this cutting piece (2) is subjected to shots thrown by an ultrasonic shot peening apparatus (10) to become a cutting surface (5) with shot impacts, and a second step in which the cutting surface (5) with shot impacts is grinded over a chosen thickness to become a treated cutting surface (5).

A method of treatment of a cutting piece (2) is provided. This method includes a first step in which a cutting surface (5) of this cutting piece (2) is subjected to shots thrown by an ultrasonic shot peening apparatus (10) to become a cutting surface (5) with shot impacts, and a second step in which the cutting surface (5) with shot impacts is grinded over a chosen thickness to become a treated cutting surface (5).

The present disclosure relates to a method of treating a cutting tool of a cemented carbide or cermet substrate, wherein the cutting tool is subjected to shot peening at a temperature of or above 100 C. The cutting tool typically has a rake face, a flank face and a cutting edge extending therebetween. The shot peening is performed at least on the rake face of the cutting tool. The present disclosure also relates to a cutting tool treated with the method.

Equipment for treating a cutting piece is provides which includes an ultrasonic shot peening apparatus arranged for throwing shots on a cutting surface of the cutting piece so the cutting surface defines a cutting surface with shot impacts; and a grinding device arranged for grinding the cutting surface with shot impacts over a chosen thickness so that the cutting surface with the shot impacts defines a treated cutting surface.

Equipment for treating a cutting piece is provides which includes an ultrasonic shot peening apparatus arranged for throwing shots on a cutting surface of the cutting piece so the cutting surface defines a cutting surface with shot impacts; and a grinding device arranged for grinding the cutting surface with shot impacts over a chosen thickness so that the cutting surface with the shot impacts defines a treated cutting surface.