TECHNICAL FIELD

The present disclosure relates to a cemented carbide and a cutting tool including the cemented carbide. The present application claims a priority based on Japanese Patent Application No. 2020-072993 filed on Apr. 15, 2020, the entire content of which is incorporated herein by reference.

BACKGROUND ART

As hard materials including titanium (Ti), a cemented carbide, a cermet, and the like have been known. These hard materials are excellent in wear resistance and have been therefore used suitably for cutting tools, wear-resistant tools, and the like. For example, WO 2011/136197 (Patent Literature 1) discloses a cermet including: a first hard phase composed of a composite carbonitride including Ti; a second hard phase composed of tungsten carbide (WC); and a binder phase mainly composed of one or both of cobalt (Co) and nickel (Ni). Further, WO 2017/191744 (Patent Literature 2) discloses a cemented carbide including: a first hard phase mainly composed of WC; and a second hard phase mainly composed of a composite carbonitride including Ti and W.

CITATION LIST
Patent Literature

PTL 1: WO 2011/136197

PTL 2: WO 2017/191744

SUMMARY OF INVENTION

A cemented carbide of the present disclosure includes first hard phase grains, second hard phase grains, third hard phase grains, and a metal binder phase, wherein

each of the first hard phase grains includes tungsten carbide,

each of the second hard phase grains has a core portion in a form of a grain and a peripheral portion that coats at least a portion of the core portion,

the core portion is composed of a first composite carbonitride represented by Ti_1-X-ZNb_XM_ZC_1-YN_Y,

the peripheral portion is composed of a second composite carbonitride, the second composite carbonitride being a carbonitride that has a composition different from a composition of the core portion and that at least includes titanium, niobium, and tungsten,

the M represents at least one element selected from a group consisting of vanadium, chromium, and molybdenum,

the X is more than or equal to 0.1 and less than or equal to 0.2,

the Y is more than or equal to 0.3 and less than or equal to 0.6,

the Z is more than or equal to 0 and less than or equal to 0.02,

each of the third hard phase grains is composed of the first composite carbonitride,

the metal binder phase includes an iron group element,

the cemented carbide has a total of 70 unit regions,

the total of 70 unit regions are provided by continuously arranging 7 unit regions in a longitudinal direction and 10 unit regions in a lateral direction in an electron microscope image obtained by imaging an arbitrary cross section of the cemented carbide at a magnification of 1500×, each of the unit regions being constituted of a square having each side of 8 μm,

the number of unit regions each having a percentage of less than 0.43% or more than 2.43% is less than or equal to 10 among the total of 70 unit regions,

the percentage is a percentage of the total number of the number of the second hard phase grains and the number of the third hard phase grains in each unit region with respect to the total number of the number of the second hard phase grains and the number of the third hard phase grains in the total of 70 unit regions,

the number of the second hard phase grains in the unit region is the number of second hard phase grains having core portions each having a grain size of more than or equal to 0.2 μm and less than or equal to 3 μm in the unit region,

the number of the third hard phase grains in the unit region is the number of third hard phase grains each having a grain size of more than or equal to 0.5 μm and less than or equal to 2.5 μm in the unit region, and

in a total of 10 unit regions existing in a fourth row of the total of 70 unit regions in the longitudinal direction in the cemented carbide, a percentage of the number of the third hard phase grains each having a grain size of more than or equal to 0.5 μm and less than or equal to 2.5 μm with respect to the total number of the number of the second hard phase grains having the core portions each having a grain size of more than or equal to 0.2 μm and less than or equal to 3 μm and the number of the third hard phase grains each having a grain size of more than or equal to 0.5 μm and less than or equal to 2.5 μm is more than or equal to 5% and less than or equal to 15%.

A cutting tool of the present disclosure is a cutting tool including the above-described cemented carbide.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view schematically showing one cross section of a cemented carbide according to the present embodiment.

FIG. 2 is a diagram showing the number of second hard phase grains having core portions each having a grain size of more than or equal to 0.2 μm and less than or equal to 3 μm (upper side) and the number of third hard phase grains each having a grain size of more than or equal to 0.5 μm and less than or equal to 2.5 μm (lower side) in each unit region provided in an electron microscope image.

FIG. 3 is an explanatory diagram showing, in a percentage, the total number of the second hard phase grains and the third hard phase grains in each unit region with respect to the total number of the second hard phase grains and the third hard phase grains in a total of 70 unit regions provided in the electron microscope image.

FIG. 4 is a partial cross sectional view showing an exemplary configuration of a cutting tool according to the present embodiment.

DETAILED DESCRIPTION
Problems to Be Solved By the Present Disclosure

In the hard material of Patent Literature 1, the composite carbonitride has a core represented by (Ti_1-x-yL_xMo_y)(C_1-zN_z). In this chemical formula, L is at least one element selected from a group consisting of Zr, Hf, Nb, and Ta, x is more than or equal to 0.01 and less than or equal to 0.5, y is more than or equal to 0.03 and less than or equal to 0.05, and z is more than or equal to 0.05 and less than or equal to 0.75. Therefore, in the composite carbonitride, an atomic ratio of Mo in all the metallic elements (Ti, L, and Mo) is more than or equal to 0.03. However, Mo serves to deteriorate a reaction resistance (hereinafter, also referred to as “welding resistance”) of the carbonitride against steel. Hence, a small content of Mo is preferable.

Patent Literature 2 discloses that the second hard phase mainly composed of the composite carbonitride including Ti and W is dispersed uniformly in the whole of the cemented carbide by decreasing a distance (σ²) between the respective centers of gravity of two grains closest to each other, thereby improving breakage resistance. However, Patent Literature 2 does not state the reaction resistance of the cemented carbide against steel. Thus, no hard material having an excellent reaction resistance against steel has been obtained yet. Development of such a hard material has been desired.

In view of the above-described actual circumstance, the present disclosure has an object to provide: a cemented carbide having an excellent breakage resistance and an excellent reaction resistance against steel; and a cutting tool including the cemented carbide.

Advantageous Effect of the Present Disclosure

According to the present disclosure, there can be provided: a cemented carbide having an excellent breakage resistance and an excellent reaction resistance against steel; and a cutting tool including the cemented carbide.

DESCRIPTION OF EMBODIMENTS

First, embodiments of the present disclosure are listed and described.

(1) A cemented carbide of the present disclosure includes first hard phase grains, second hard phase grains, third hard phase grains, and a metal binder phase, wherein