TECHNICAL FIELD

The present disclosure relates to a cubic boron nitride sintered material. The present application claims a priority based on Japanese Patent Application No. 2019-133029 filed on Jul. 18, 2019, the entire content of which is incorporated herein by reference.

BACKGROUND ART

A cubic boron nitride sintered material (hereinafter, also referred to as “cBN sintered material”) is a high-hardness material used for cutting tools and the like. The cBN sintered material is normally constituted of cubic boron nitride grains (hereinafter, also referred to as “cBN grains”) and a binder phase. Depending on a content ratio of the cBN grains and a composition of the binder phase, characteristics of the cBN sintered material tend to differ.

Hence, in the field of cutting, different types of cBN sintered materials are applied to cutting tools in accordance with the material of a workpiece, required precision in processing, or the like.

For example, as a cBN sintered material that can be used for intermittent cutting of a high-hardness steel, Japanese Patent Laying-Open No. 2017-030082 (PTL 1) discloses a cubic boron nitride sintered material including cubic boron nitride grains and a TiC phase serving as a binder phase.

CITATION LIST
Patent Literature

PTL 1: Japanese Patent Laying-Open No. 2017-030082

SUMMARY OF INVENTION

A cubic boron nitride sintered material according to the present disclosure is a cubic boron nitride sintered material including: more than or equal to 20 volume % and less than or equal to 80 volume % of cubic boron nitride grains; and more than or equal to 20 volume % and less than or equal to 80 volume % of a binder phase, wherein

the binder phase includes first binder grains and second binder grains,

each of the first binder grains and the second binder grains includes one compound composed of titanium, at least one first metal element selected from a group consisting of zirconium, hafnium, a group 5 element, a group 6 element in a periodic table, and aluminum, and one or both of nitrogen and carbon,

in each of the first binder grains, a ratio of the number of atoms of the first metal element to a total of the number of atoms of the titanium and the number of atoms of the first metal element is more than or equal to 0.01% and less than 10%,

in each of the second binder grains, a ratio of the number of atoms of the first metal element to a total of the number of atoms of the titanium and the number of atoms of the first metal element is more than or equal to 10% and less than or equal to 80%,

in an X-ray diffraction spectrum of the cubic boron nitride sintered material, one or both of the following conditions 1 and 2 are satisfied,

the condition 1 is such a condition that 2θ of a first A peak originated from a (220) plane of the first binder grain falls within a range of more than or equal to 59.9° and less than or equal to 62.3°, 2θ of a second A peak originated from a (220) plane of the second binder grain falls within a range of more than or equal to 56.3° and less than or equal to 65.8°, and peak positions of the first A peak and the second A peak are different from each other, and

the condition 2 is such a condition that 2θ of a first B peak originated from a (222) plane of the first binder grain falls within a range of more than or equal to 75.4° and less than or equal to 78.7°, 2θ of a second B peak originated from a (222) plane of the second binder grain falls within a range of more than or equal to 70.6° and less than or equal to 83.5°, and peak positions of the first B peak and the second B peak are different from each other.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an image showing an exemplary reflected electron image obtained by observing a cBN sintered material according to the present disclosure using a SEM.

FIG. 2 shows an image obtained by loading the reflected electron image of FIG. 1 into image processing software.

FIG. 3 shows an upper image that is the reflected electron image, and shows a lower image that is a concentration cross section graph obtained from the reflected electron image.

FIG. 4 is a diagram for illustrating a method of defining a black region and a binder phase.

FIG. 5 is a diagram for illustrating a boundary between the black region and the binder phase.

FIG. 6 shows an image obtained by performing binarization processing onto the reflected electron image of FIG. 1.

FIG. 7 shows an exemplary X-ray diffraction spectrum of the cubic boron nitride sintered material according to the present disclosure.

FIG. 8 shows an exemplary X-ray diffraction spectrum of the cubic boron nitride sintered material according to the present disclosure.

FIG. 9 shows an exemplary X-ray diffraction spectrum of the cubic boron nitride sintered material according to the present disclosure.

DETAILED DESCRIPTION
Problem to be Solved by the Present Disclosure

A hardened steel having high strength and toughness has been used for gears, shafts, and bearing components of automobiles. In recent years, these components have been required to have mechanical characteristics to endure higher torque. In order to improve the mechanical characteristics of the hardened steel, a high-strength hardened steel has been developed in which hard grains are dispersed in a hardened steel base material, for example.

Since the high-strength hardened steel has a very high hardness, it is very difficult to process the high-strength hardened steel using a tool. In particular, in the case of high-efficiency processing, there has been required a tool having a tool life that is less likely to be decreased due to breakage.

The present disclosure has an object to provide a cubic boron nitride sintered material that can attain a long life of a tool particularly in high-efficiency processing of a high-strength hardened steel when used as a tool material.

Advantageous Effect of the Present Disclosure

The cubic boron nitride sintered material according to the present disclosure can attain a long life of a tool particularly in high-efficiency processing of a high-strength hardened steel when used as a tool material.

DESCRIPTION OF EMBODIMENTS

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

(1) A cubic boron nitride sintered material according to the present disclosure is a cubic boron nitride sintered material including: more than or equal to 20 volume % and less than or equal to 80 volume % of cubic boron nitride grains; and more than or equal to 20 volume % and less than or equal to 80 volume % of a binder phase, wherein