阅读说明：本技术 硬质合金、包含该硬质合金的切削工具以及硬质合金的制造方法 (Cemented carbide, cutting tool comprising same, and method for producing cemented carbide ) 是由 深江恒佑 城户保树 渡边真实 今村晋也 于 2019-08-08 设计创作，主要内容包括：一种硬质合金,包含第二硬质相颗粒,该第二硬质相颗粒各自包含含有Ti和Nb的碳氮化物,其中各第二硬质相颗粒包括芯部,芯部由以Ti_(1-X-Z)Nb_XM_ZC_(1-Y)N_Y表示的复合碳氮化物构成,M表示选自由V、Cr和Mo组成的组中的至少一种杂质元素,X表示范围为0.1以上0.2以下的数值,Y表示范围为0.3以上至0.6以下的数值,Z表示范围为0以上至0.02以下的数值,并且在以1500倍的放大倍率将硬质合金的任意截面成像而获得的电子显微镜图像中,在通过沿纵向方向连续布置7个各自由各边为8μm的正方形构成的单位区域并且沿横向方向连续布置10个单位区域从而设置总共70个单位区域的情况下,当通过计数各单位区域中芯部的数量来计算总共70个单位区域中的芯部的总数,并且计算各单位区域中的芯部的数量相对于上述总数的百分比时,其中该百分比小于0.43％或大于2.43％的单位区域的数量为10个以下。(A cemented carbide comprising secondary hard phase particles each comprising a carbonitride comprising Ti and Nb, wherein each secondary hard phase particle comprises a core comprised of Ti 1‑X‑Z Nb X M Z C 1‑Y N Y M represents at least one impurity element selected from the group consisting of V, Cr and Mo, X represents a numerical value ranging from 0.1 to 0.2, Y represents a numerical value ranging from 0.3 to 0.6, and Z represents a numerical value ranging from 0 to 0.02, and in an electron microscope image obtained by imaging an arbitrary cross section of the cemented carbide at a magnification of 1500 times, in a composite carbonitride composition represented by (A), 7 single units each consisting of a square having sides of 8 μ M are arranged continuously in the longitudinal directionIn the case of bit regions and 10 unit regions arranged consecutively in the lateral direction to provide a total of 70 unit regions, when the total number of cores in the total 70 unit regions is calculated by counting the number of cores in each unit region, and the percentage of the number of cores in each unit region with respect to the total number is calculated, the number of unit regions in which the percentage is less than 0.43% or more than 2.43% is 10 or less.)

1. A cemented carbide comprising: first hard phase particles each comprising WC; second hard phase particles each comprising a carbonitride containing Ti and Nb; and a metallic binder phase comprising an iron group element, wherein

Each of the secondary hard phase particles includes a core portion in the form of particles and an outer peripheral portion covering at least a part of the core portion,

the core is composed of Ti_1-X-ZNb_XM_ZC_1-YN_YThe composition of the compound carbonitride shown is,

the M is at least one impurity element selected from the group consisting of V, Cr and Mo,

wherein X is 0.1 to 0.2,

y is 0.3 to 0.6 inclusive,

wherein Z is 0 to 0.02 inclusive,

the composition of the outer peripheral portion is different from that of the core portion, and

in an electron microscope image of an arbitrary cross section of the cemented carbide taken at a magnification of 1500 times, in the case where a total of 70 unit regions are provided by successively arranging 7 unit regions each composed of a square having sides of 8 μm in a longitudinal direction and 10 unit regions in a transverse direction, when a total number of the core portions in the total of 70 unit regions is calculated by counting the number of the core portions in each of the unit regions, and a percentage of the number of the core portions in each of the unit regions with respect to the total number of the core portions is calculated, the number of the unit regions in which the percentage is less than 0.43% or more than 2.43% is 10 or less.

2. The cemented carbide according to claim 1, wherein a grain diameter of each of the core portions whose number has been counted in each of the unit regions is 0.2 μm or more and 3 μm or less.

3. The cemented carbide of claim 1 or claim 2, wherein the outer peripheral portion is a carbonitride comprising Ti, Nb, and W.

4. The cemented carbide according to any one of claims 1 to 3, wherein the core has a particle diameter of 0.2 μm or more and 2 μm or less at a cumulative value of 50% in a particle diameter distribution on an area basis.

5. The cemented carbide according to any one of claims 1 to 4, wherein a volume ratio of the core in the cemented carbide is 2 vol% or more and 10 vol% or less.

6. A cutting tool comprising the cemented carbide of any one of claims 1 to 5.

7. The cutting tool of claim 6, comprising: a base material composed of the cemented carbide; and a coating film for coating the base material.

8. A method of manufacturing a cemented carbide, the method comprising:

obtaining a catalyst formed from Ti_1-X-ZNb_XM_ZC_1-YN_YA powder of the indicated compound carbonitride;

mixing the powder of composite carbonitride, WC powder and iron group element powder by using a ball mill for 9 hours to 15 hours to obtain a powder mixture;

obtaining a shaped body by pressure-forming the powder mixture; and

obtaining a sintered body by sintering the formed body, wherein

The M is at least one impurity element selected from the group consisting of V, Cr and Mo,

wherein X is 0.1 to 0.2,

y is 0.3 to 0.6 inclusive,

z is 0 to 0.02 inclusive, and

the powder obtained from the composite carbonitride comprises

Obtaining a third powder by mixing a first powder comprising Ti and Nb and a second powder comprising at least graphite,

granulating the third powder to obtain granules,

obtaining a powder precursor composed of the composite carbonitride by heat-treating the granules at 1800 ℃ or higher in an atmosphere containing nitrogen, and

obtaining a powder of the composite carbonitride by pulverizing the powder precursor.

Technical Field

The present disclosure relates to cemented carbide, a cutting tool including the same, and a method of manufacturing the same. The present application claims priority based on japanese patent application No.2018-189083, filed on day 4/10/2018, the entire contents of which are incorporated herein by reference.

Background

As a hard material containing titanium (Ti), cemented carbide, cermet, and the like are known. These hard materials are excellent in wear resistance and thus are suitable for cutting tools, wear-resistant tools, and the like. For example, WO2011/136197 (patent document 1) discloses a cermet including: a first hard phase composed of a composite carbonitride containing 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, WO2017/191744 (patent document 2) discloses a cemented carbide including: a first hard phase mainly composed of WC; and a secondary hard phase mainly composed of a composite carbonitride containing Ti and W.

Reference list

Patent document

Patent document 1: WO2011/136197

Patent document 2: WO2017/191744

Disclosure of Invention

A cemented carbide according to an embodiment of the present disclosure includes: first hard phase particles each comprising WC; second hard phase particles each comprising a carbonitride containing Ti and Nb; and a metal binder phase containing an iron group element, wherein each of the secondary hard phase particles includes a core in the form of a particle and an outer peripheral portion covering at least a part of the core, the core being composed of Ti_1-X-ZNb_XM_ZC_1-YN_YM is at least one impurity element selected from the group consisting of V, Cr and Mo, X is 0.1 to 0.2, Y is 0.3 to 0.6, Z is 0 to 0.02, the composition of the outer peripheral portion is different from the composition of the core portion, and in an electron microscope image of an arbitrary cross section of the cemented carbide taken at a magnification of 1500 times, in the case where a total of 70 unit regions are provided by successively arranging 7 unit regions each composed of a square having sides of 8 μm in the longitudinal direction and 10 unit regions in the transverse direction, when the total number of cores in the total 70 unit regions is calculated by counting the number of cores in each unit region, and the percentage of the number of cores in each unit region with respect to the total number of cores is calculated, wherein the number of unit areas having a percentage of less than 0.43% or greater than 2.43% is 10 or less.

A cutting tool according to one embodiment of the present disclosure includes the cemented carbide described above.

A method of manufacturing cemented carbide according to an embodiment of the present disclosure includes: obtaining a catalyst formed from Ti_1-X-ZNb_XM_ZC_1-YN_YA powder of the indicated compound carbonitride; mixing a composite carbonitride powder, a WC powder, and an iron group element powder for 9 hours to 15 hours using a ball mill to obtain a powder mixture; obtaining a shaped body by pressure-forming the powder mixture; and obtaining a sintered body by sintering the formed body, wherein M is at least one impurity element selected from the group consisting of V, Cr and Mo, and X is 0.1 or more0.2 or less, Y is 0.3 or more and 0.6 or less, and Z is 0 or more and 0.02 or less, and the powder for obtaining composite carbonitride includes obtaining a third powder by mixing a first powder containing Ti and Nb and a second powder containing at least graphite, obtaining a granulated body by granulating the third powder, obtaining a powder precursor composed of composite carbonitride by heat-treating the granulated body at 1800 ℃ or more in an atmosphere containing nitrogen, and obtaining a powder for composite carbonitride by pulverizing the powder precursor.

Drawings

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

Fig. 2A is a diagram showing a photograph showing an electron microscope image of one cross section of cemented carbide according to sample 12.

Fig. 2B is an explanatory diagram showing the number of cores in each unit region set in the electron microscope image shown in fig. 2A.

Fig. 2C is an explanatory diagram showing the percentage of the number of cores in each unit region with respect to the total number of cores in the total 70 unit regions set in the electron microscope image shown in fig. 2A.

Fig. 3A is a diagram showing a photograph showing an electron microscope image of a section of cemented carbide according to the test sample 114.

Fig. 3B is an explanatory diagram showing the number of cores in each unit region set in the electron microscope image shown in fig. 3A.

Fig. 3C is an explanatory diagram showing the percentage of the number of cores in each unit region with respect to the total number of cores in the total 70 unit regions set in the electron microscope image shown in fig. 3A.

Fig. 4 is a partial sectional view showing an exemplary structure of a cutting tool according to the present embodiment.

Detailed Description

[ problem to be solved by the present disclosure ]

In the hard material of patent document 1, composite carbonitrideHas a structure of (Ti)_1-x-yL_xMo_y)(C_1-zN_z) The core shown. In the chemical formula, L is at least one element selected from the group consisting of Zr, Hf, Nb, and Ta, x is 0.01 to 0.5, y is 0.03 to 0.05, and z is 0.05 to 0.75. Therefore, in the composite carbonitride, the atomic ratio of Mo in all the metal elements (Ti, L, and Mo) is 0.03 or more. However, Mo deteriorates the steel reactivity resistance (hereinafter, also referred to as "weld resistance") of carbonitride. Therefore, the content of Mo is preferably low.

Patent document 2 discloses that the fracture resistance is improved by reducing the distance (σ 2) between the centers of gravity of each of two particles that are closest to each other, thereby uniformly dispersing a secondary hard phase mainly composed of a composite carbonitride containing Ti and W in the entire cemented carbide. However, patent document 2 does not describe the steel reactivity resistance of cemented carbide. Therefore, a hard material having excellent steel reactivity has not been obtained. The development of such hard materials is required.

In view of the above-described circumstances, an object of the present disclosure is to provide a cemented carbide having excellent steel reactivity resistance, a cutting tool including the cemented carbide, and a method of manufacturing the cemented carbide.

[ advantageous effects of the present disclosure ]

According to the present disclosure, a cemented carbide having excellent steel reactivity resistance, a cutting tool including the cemented carbide, and a method of manufacturing the cemented carbide can be provided.

[ description of the embodiments ]

The present inventors have developed cemented carbides containing carbonitride containing Ti and Nb (hereinafter, also referred to as "TiNbMCN") as a new raw material. It was found that the cemented carbide has more excellent steel reactivity resistance than the conventional Ti-based compound due to the inclusion of TiNbMCN. Further, it was found that both steel reactivity resistance and mechanical strength can be ensured by appropriately controlling the composition of Nb and N in TiNbMCN.

However, TiNbMCN tends to agglomerate in cemented carbides. It was found that if the grain size of TiNbMCN is made small to prevent aggregation, Ti and Nb in TiNbMCN tend to be solid-dissolved in WC crystals in the sintering step for manufacturing cemented carbide. Based on this finding, it is conceived that cemented carbide having higher steel reactivity resistance is obtained by dispersing TiNbMCN in cemented carbide in a well-balanced manner while avoiding solid dissolution of TiNbMCN in WC crystals. In this way, the present inventors have obtained the present disclosure.

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

[1]A cemented carbide according to an embodiment of the present disclosure includes: first hard phase particles each comprising WC; second hard phase particles each comprising a carbonitride containing Ti and Nb; and a metal binder phase containing an iron group element, wherein each of the secondary hard phase particles includes a core in the form of a particle and an outer peripheral portion covering at least a part of the core, the core being composed of Ti_1-X-ZNb_XM_ZC_1-YN_YM is at least one impurity element selected from the group consisting of V, Cr and Mo, X is 0.1 to 0.2, Y is 0.3 to 0.6, Z is 0 to 0.02, the composition of the outer peripheral portion is different from the composition of the core portion, and in an electron microscope image of an arbitrary section of cemented carbide taken at a magnification of 1500 times, in the case where a total of 70 unit regions are provided by successively arranging 7 unit regions each composed of a square having sides of 8 μm in the longitudinal direction and 10 unit regions in the transverse direction, when the total number of cores in the total 70 unit regions is calculated by counting the number of cores in each unit region, and the percentage of the number of cores in each unit region with respect to the total number of cores is calculated, wherein the number of unit areas having a percentage of less than 0.43% or greater than 2.43% is 10 or less. Cemented carbides having such characteristics may have excellent steel reactivity resistance.

[2] Preferably, the particle diameter of each core part whose number has been counted in each unit region is 0.2 μm or more and 3 μm or less. Therefore, the core having such a particle diameter that the core is not solid-dissolved in the WC crystal and is not easily aggregated can be dispersed in the cemented carbide in a well-balanced manner, thus obtaining excellent steel reactivity resistance.

[3] Preferably, the outer peripheral portion is a carbonitride comprising Ti, Nb, and W. Therefore, more excellent steel reactivity resistance can be obtained.

[4] Preferably, the particle diameter of the core portion in the particle diameter distribution based on the area is 0.2 μm or more and 2 μm or less at a cumulative value of 50%. Thus, excellent steel reactivity resistance can be obtained with good yield.

[5] Preferably, the volume ratio of the core portion in the cemented carbide is 2 vol% or more and 10 vol% or less. Thus, excellent steel reactivity resistance can be obtained with good yield.

[6] A cutting tool according to one embodiment of the present disclosure includes the cemented carbide described above. Such a cutting tool may have not only excellent mechanical strength inherent in cemented carbide but also excellent steel reactivity resistance.

[7] Preferably, the cutting tool includes: a base material composed of cemented carbide; and a coating film for coating the substrate. Such a cutting tool may have not only excellent mechanical strength inherent in cemented carbide but also excellent steel reactivity resistance.

[8]A method of manufacturing a cemented carbide according to an embodiment of the present disclosure includes: obtaining a catalyst formed from Ti_{1-X- Z}Nb_XM_ZC_1-YN_YA powder of the indicated compound carbonitride; mixing a composite carbonitride powder, a WC powder, and an iron group element powder for 9 hours to 15 hours using a ball mill to obtain a powder mixture; obtaining a shaped body by pressure-forming the powder mixture; and obtaining a sintered body by sintering the formed body, wherein M is at least one impurity element selected from the group consisting of V, Cr and Mo, X is 0.1 or more and 0.2 or less, Y is 0.3 or more and 0.6 or less, and Z is 0 or more and 0.02 or less, and obtaining a powder of a composite carbonitride includes obtaining a third powder by mixing a first powder including Ti and Nb and a second powder including at least graphite, obtaining a granulated body by granulating the third powder, and obtaining a powder composed of a composite carbonitride by heat-treating the granulated body at 1800 ℃ or more in an atmosphere including nitrogen gasAnd pulverizing the powder precursor to obtain a powder of composite carbonitride. According to this method of manufacturing cemented carbide, cemented carbide having excellent steel reactivity resistance can be manufactured.

[ details of embodiments of the present disclosure ]

Although an embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described in detail below, the present embodiment is not limited thereto. In the following description, reference will be made to the accompanying drawings.

Here, in the present specification, the expression "a to B" represents a range from a lower limit to an upper limit (i.e., a to B). When no unit is specified for a and only a unit is specified for B, the unit of a is the same as that of B. Further, when compounds and the like are represented by chemical formulas in the present specification and the atomic ratio is not particularly limited, it is assumed that all conventionally known atomic ratios are included. The atomic ratio is not necessarily limited to only one atomic ratio in the stoichiometric range. For example, when "TiAlN" is described, the atomic ratio in TiAlN is not limited to Ti: Al: N ═ 0.5:0.5:1, and includes all conventionally known atomic ratios. The same applies to compounds other than "TiAlN". In the present embodiment, the metallic element and the nonmetallic element do not necessarily constitute stoichiometric compositions. Examples of the metal element include titanium (Ti), aluminum (Al), silicon (Si), tantalum (Ta), chromium (Cr), niobium (Nb), and tungsten (W). Examples of the nonmetallic elements include nitrogen (N), oxygen (O), and carbon (C). In the present specification, the term "mechanical strength" refers to mechanical strength including various characteristics of cemented carbide such as wear resistance, fracture resistance, bending strength, and the like.

< cemented carbide >

As shown in fig. 1, the cemented carbide according to the present embodiment includes: first hard phase particles 1 each containing WC; second hard phase particles 2 each containing carbonitride containing Ti and Nb; and a metal binder phase 3 containing an iron group element. Each of the secondary hard phase particles 2 includes a particle-form core portion 21 and an outer peripheral portion 22 that covers at least a part of the core portion 21. The core 21 is made of Ti_1-X-ZNb_XM_ZC_1-YN_YA compound carbonitride represented by the formula, M isAt least one impurity element selected from the group consisting of V, Cr and Mo, X is 0.1 to 0.2, Y is 0.3 to 0.6, and Z is 0 to 0.02. The composition of the outer peripheral portion 22 is different from that of the core portion 21.

Further, for example, as shown in fig. 2A to 2C, in the cemented carbide according to the present embodiment, in the case where a total of 70 unit regions are provided by successively arranging 7 unit regions each composed of a square having sides of 8 μm in the longitudinal direction and 10 unit regions in the transverse direction in an electron microscope image of an arbitrary section of the cemented carbide taken at a magnification of 1500 times, when the total number of core portions in the total 70 unit regions is calculated by counting the number of core portions in each unit region and the percentage of the number of core portions in each unit region with respect to the total number of core portions is calculated, the number of unit regions in which the percentage is less than 0.43% or more than 2.43% is 10 or less. Cemented carbides having such characteristics may have excellent steel reactivity resistance.

< first hard phase particles >

Each of the first hard phase particles 1 contains WC. Preferably, the first hard phase particles 1 are mainly composed of WC (tungsten carbide). In addition to WC, the first hard phase particles 1 may comprise: unavoidable elements introduced during the manufacturing process of WC; a small amount of impurity elements; and so on. In order to exhibit the effect of the present disclosure, the content of WC in the first hard phase particles 1 is preferably 99 mass% or more, and more preferably substantially 100 mass%. Examples of elements that may be contained in the first hard phase particles 1 include molybdenum (Mo), chromium (Cr), and the like, in addition to W and C.

In the cemented carbide, the content of the first hard phase particles 1 is preferably 65% by volume to 95% by volume. When the content of the first hard phase particles 1 in the cemented carbide is less than 65% by volume, sufficient mechanical strength tends not to be obtained. When the content of the first hard phase particles 1 in the cemented carbide is more than 95 vol%, sufficient toughness tends not to be obtained. The preferred content of the first hard phase particles 1 in the cemented carbide is 75 to 85 vol%.

The content (% by volume) of the first hard phase particles 1 can be calculated using the following measurement method. Specifically, the cemented carbide is subjected to CP (section polisher) processing using an argon ion beam or the like, thereby obtaining a specimen having a smooth section. An image of a cross section of the sample was photographed at 5000 times using a field emission scanning electron microscope (FE-SEM; trade name: "JSM-7000F", supplied by JEOL) to obtain an electron microscope image (SEM-BSE image) of the cross section of the sample. Further, the outer contour of the first hard phase particles 1 in the electron microscope image is specified.

Next, the total sum (total area) of the areas of all the first hard phase particles 1 in the electron microscope image was calculated based on binarization processing using image analysis software (trade name: "Mac-View", supplied by MOUNTECH). Finally, the total area can be regarded as the content (volume%) of the first hard phase particles 1 in the cemented carbide by assuming that the total area is continuous in the depth direction of the cross section. In particular, the content (volume%) of the first hard phase particles 1 is preferably calculated as an average value of the total area of the first hard phase particles 1 calculated in five electron microscope images (five fields), in which the presence of overlapping image-captured portions in the cross section of the specimen is avoided while preparing the five electron microscope images.

< second hard phase particles >

The secondary hard phase particles 2 contain carbonitride containing Ti and Nb. Each of the secondary hard phase particles 2 includes a particle-form core portion 21 and an outer peripheral portion 22 that covers at least a part of the core portion 21. The core 21 is made of Ti_1-X-ZNb_XM_ZC_1-YN_YThe compound carbonitride represented by (1), wherein M is at least one impurity element selected from the group consisting of V, Cr and Mo, X is 0.1 to 0.2, Y is 0.3 to 0.6, and Z is 0 to 0.02. The composition of the outer peripheral portion 22 is different from that of the core portion 21. In particular, the outer peripheral portion 22 is preferably a carbonitride containing Ti, Nb, and W. When the atomic ratio of the compositions (Ti, Nb, C, and N) of the particle-form core portions 21 in each of the second hard phase particles 2 falls within the above range, the cemented carbide may have excellent steel reactivity resistance. Will be described hereinafter as being represented by M and selected from the group consisting of V, Cr and MoAt least one impurity element of the group consisting of.

In the cemented carbide, the content of the secondary hard phase particles 2 is preferably 2 to 15 vol%. When the content of the secondary hard phase particles 2 in the cemented carbide is less than 2 vol%, sufficient steel reactivity resistance tends not to be obtained. When the content of the secondary hard phase particles 2 in the cemented carbide is more than 15 vol%, sufficient mechanical strength tends not to be obtained. The preferred content of the secondary hard phase particles 2 in the cemented carbide is 5 to 10 vol%.

The content (% by volume) of the second hard phase particles 2 can be calculated by the same method as the method for measuring the content of the first hard phase particles 1.

(core part)

The core 21 is made of Ti_1-X-ZNb_XM_ZC_1-YN_YThe indicated complex carbonitride. X is 0.1 to 0.2, Y is 0.3 to 0.6, and Z is 0 to 0.02. That is, in the core 21, Ti is a main component, and Nb is a sub-component. M is at least one impurity element selected from the group consisting of V, Cr and Mo. The atomic ratio (1-X-Z) of Ti is 0.8 to 0.9 in order to keep the addition amount of the subcomponents below the solid solution limit and to sufficiently exhibit the effects of Ti and Nb as the added metal elements. In order to obtain excellent steel reactivity, Y, which represents the atomic ratio of nitrogen (N) in the composite carbonitride, is 0.3 to 0.6. The composition of the core portion 21 should not be particularly limited as long as the effects of the present disclosure are exhibited, the atomic ratios (X, Y, Z) fall within the above ranges, and the composition of the core portion 21 is different from the composition of the outer peripheral portion 22. Examples of the composition of the core 21 include Ti_0.85Nb_0.15C_0.5N_0.5、Ti_0.8Nb_0.2C_0.45N_0.55And the like.

Herein, Ti is used_1-X-ZNb_XM_ZC_1-YN_YIn the composite carbonitride of the core portion 21 shown, X is preferably 0.12 to 0.18. Further, X is more preferably 0.14 to 0.16. Y is preferably 0.4 to 0.55. Thus, excellent steel reactivity resistance is obtained, while in terms of, for example, wear resistance and resistancePreferable characteristics can be obtained in terms of mechanical strength such as fracture property.

With respect to the core 21 contained in the second hard phase particles 2 appearing in the electron microscope image having the cross section of the cemented carbide, the composition and atomic ratio of the composite carbonitride contained in the core 21 can be determined by analyzing it using an energy dispersive X-ray spectrometer (EDX) in a field emission scanning electron microscope (FE-SEM) or using an Electron Probe Microanalyzer (EPMA). The composition of WC in the first hard phase particles 1 and the composition of an iron group element in the following metal binder phase 3 can also be determined by analyzing both the first hard phase particles 1 and the metal binder phase 3 appearing in the above electron microscope image using the same measurement method.

(degree of dispersion of core part)

In the cemented carbide according to the present embodiment, in the electron microscope image of an arbitrary section of the cemented carbide taken at a magnification of 1500 times, in the case where a total of 70 unit regions R are provided by successively arranging 7 unit regions R each composed of a square having sides of 8 μm in the longitudinal direction and 10 unit regions R in the transverse direction, when the total number of core portions in the total 70 unit regions R is calculated by counting the number of R core portions in each unit region, and the percentage of the number of core portions in each unit region R with respect to the total number of core portions is calculated, the number of unit regions R of which percentage is less than 0.43% or more than 2.43% is 10 or less.

As described above, the present inventors have made the present invention by avoiding Ti as a core_1-X-ZNb_XM_ZC_1-YN_YWhile being dissolved in WC crystal, Ti is dissolved_1-X-ZNb_XM_ZC_1-YN_YAre dispersed in the cemented carbide in a well-balanced manner, resulting in a cemented carbide with higher resistance to steel reactivity. Specifically, in an electron microscope image in which any section of cemented carbide is taken, a total of 70 unit regions each having a predetermined size are set, the number of cores in each unit region is counted, and the percentage of the number of cores in each unit region is calculated.Further, the number of unit regions in which the number of cores represented by the percentage falls outside the specific range (0.43% to 2.43%) is calculated.

As a result, it was found that when the number of unit regions in which the number of cores falls outside the specific range is 10 or less, the cores are evaluated as being uniformly dispersed in the cemented carbide in a well-balanced manner, with the result that the cemented carbide has excellent steel reactivity resistance. Further, it has also been found that when the number of such unit regions is 11 or more, it tends to be difficult for cemented carbide to have the required excellent steel reactivity resistance. Here, in the present specification, the term "dispersion degree of cores" may be used, depending on whether "dispersion degree of cores" in cemented carbide is high or low, thereby indicating whether or not the cores are uniformly dispersed in the cemented carbide in a balanced manner.

Referring to fig. 2A to 2C, a method of evaluating whether the degree of dispersion of the core portion in the present embodiment is high or low (hereinafter, also referred to as "dispersion degree measuring method") is described below. Fig. 2A to 2C are each a diagram corresponding to a cemented carbide produced as a test piece 12 in the example described below.

First, a smooth cross section of the cemented carbide was prepared by CP-processing the cemented carbide using an argon ion beam. An image of the cross section was taken at 1500 times using a field emission scanning electron microscope (FE-SEM; trade name: "JSM-7000F", supplied by JEOL), thereby obtaining an electron microscope image (SEM-BSE image) shown in FIG. 2A.

Next, as shown in fig. 2B, a total of 70 unit regions R are set by arranging 7 unit regions R in the longitudinal direction and 10 unit regions R in the transverse direction in the electron microscope image. Further, the number of the core portions 21 in each unit region R was counted by performing image analysis using image analysis software (trade name: "Mac-View", supplied by MOUNTECH). Then, the total number of the core portions 21 in the total 70 unit regions R is calculated, and the percentage of the number of the core portions 21 in each unit region R with respect to the total number of the core portions 21 is calculated as shown in fig. 2C.

Since a total of 70 unit regions R are provided by arranging 7 unit regions R in the longitudinal direction and 10 unit regions R in the transverse direction in the electron microscope image, the number of the core portions 21 in each unit region R is expressed as 1.43% (1/70 × 100%) in percentage when the core portions 21 are uniformly dispersed in the cemented carbide in a completely uniform manner. Therefore, when the number (percentage) of the cores 21 counted in the unit region R falls within the range of 0.43% to 2.43% (within ± 1% with respect to 1.43%), it is determined that the number of the cores 21 in the unit region R is balanced. On the other hand, when the number (percentage) of the core portions 21 counted in the unit region R is less than 0.43% or more than 2.43% (more or less than ± 1% with respect to 1.43%), it is determined that the number of the core portions 21 in the unit region R is unbalanced.

Next, based on such a determination, the number of unit regions R in which the number of core portions 21 represented by the above-described percentage is less than 0.43% or greater than 2.43% is calculated. Therefore, the smaller the number of unit regions R in which the number of cores 21 is less than 0.43% or more than 2.43%, the more uniform the dispersion of the cores 21 in the cemented carbide in the electron microscope image can be evaluated in a more balanced manner. In other words, in the cemented carbide in which the number of the unit regions R in which the number of the core portions 21 is less than 0.43% or more than 2.43% is 10 or less (15% or less of the total number of the unit regions R), the dispersion degree of the core portions 21 is high, thereby obtaining excellent steel reaction resistance. In view of the above, by analyzing whether the number of the unit regions R having the above percentage of less than 0.43% or more than 2.43% in the electron microscope image is 10 or less, it is possible to evaluate whether the dispersion degree of the core portions 21 in the cemented carbide is high or low.

In fig. 2C, the number of unit regions R in which the above percentage is less than 0.43% or more than 2.43% is 4 (6% of the total number of unit regions R). Therefore, the cemented carbide (sample 12) in the electron microscope image of fig. 2A can be evaluated as having a high degree of dispersion of the core portions 21. Therefore, it is considered that excellent steel reactivity resistance is obtained.

On the other hand, fig. 3A to 3C are each a diagram corresponding to a cemented carbide manufactured with sample 114 as a comparative example described below. Fig. 3A is a diagram showing a photograph showing an electron microscope image of one cross section of cemented carbide according to the sample 114. Fig. 3B is an explanatory diagram showing the number of cores in each unit region set in the electron microscope image shown in fig. 3A. Fig. 3C is an explanatory diagram showing the percentage of the number of cores in each unit region with respect to the total number of cores in the total 70 unit regions set in the electron microscope image shown in fig. 3A. In fig. 3C, in the cemented carbide of the test piece 114, the number of the unit regions R in which the above percentage is less than 0.43% or more than 2.43% is 12 (17% of the total number of the unit regions R). Therefore, the cemented carbide (sample 114) in the electron microscope image of fig. 3A can be evaluated as having a low dispersion degree of the core portions 21. Therefore, it is considered difficult to obtain the desired steel reactivity resistance.

In the dispersion degree measuring method, the particle diameter of the core portion 21 located in the unit region R counted by image analysis using the image analysis software is preferably 0.2 μm or more and 3 μm or less. In other words, it is preferable to count only the number of the core portions 21 which are located in the unit region R and each of which has a particle diameter of 0.2 μm or more and 3 μm or less. That is, in the dispersion degree measuring method, only the core part 21 (made of Ti) which is not solid-dissolved in WC crystal is counted_1-XNb_XC_1-YN_YThe indicated compound carbonitride). Therefore, the core 21 having such an appropriate particle diameter as to make the core 21 less prone to aggregation and avoid its solid solubility in the WC crystal can be dispersed in the cemented carbide in a well-balanced manner. Such cemented carbide may have more excellent steel reactivity resistance.

Each core portion 21 having a particle size of less than 0.2 μm in the unit region R tends to aggregate in cemented carbide and adversely affects steel reactivity resistance. Each core portion 21 having a particle diameter of more than 3 μm in the unit region R is difficult to finely disperse in the cemented carbide, and therefore such core portion 21 tends to have an adverse effect on the steel-resistance reactivity. It should be noted that a method of determining the particle diameter of each core portion 21 will be described below.

Further, in the above-described dispersibility measuring method, when there are core portions 21 that span adjacent unit regions R, the core portions 21 are counted assuming that the core portions 21 are included in the unit regions R having the smaller number of core portions 21 in the unit regions R that the core portions 21 span. In the dispersion degree measuring method, five electron microscope images (five fields of view) of one cross section of the cemented carbide were prepared while avoiding the presence of overlapping image pickup portions. These five fields of view preferably consist of: a field of view located in a central portion of a cross-section; and four views located at upper and lower sides and right and left sides of the aforementioned one view. In the above-described dispersibility determination method, the number of unit regions R having a percentage of less than 0.43% or more than 2.43% in each of the above-described five fields of view is calculated. Only when the number of such unit regions R in the five fields of view is 10 or less, the cemented carbide in the above electron microscope image is evaluated as having excellent steel reactivity resistance.

(permissible impurity elements in the core)

The core part 21 is made of Ti_1-X-ZNb_XM_ZC_1-YN_YThe indicated complex carbonitride. M is at least one impurity element selected from the group consisting of V, Cr and Mo. Therefore, the core 21 may contain at least one impurity element selected from the group consisting of V, Cr and Mo. In this case, Z is preferably 0 or more and 0.02 or less, that is, the total amount of V, Cr and Mo is preferably less than 2 atomic% with respect to the total amount of Ti, Nb, V, Cr, and Mo. This makes it possible to sufficiently suppress V, Cr and Mo, which are elements that adversely affect the steel-resistance reactivity of cemented carbide.

The composite carbonitride serving as each core portion 21 is a carbonitride composed of Ti as a main component and Nb as an accessory component; however, in a special case, the composite carbonitride may contain the metal element V, Cr and Mo as impurity elements. As for the amount of these impurity elements allowed to be contained in the core 21, the total amount of V, Cr and Mo is preferably less than 2 atomic% with respect to the total amount of Ti, Nb, V, Cr, and Mo. When V, Cr and Mo are contained in a total amount of 2 atomic% or more, these metal elements as impurity elements tend to affect the steel reactivity resistance of the composite carbonitride.

(core D50)

The particle diameter of the core 21 at which the cumulative value in the area-based particle diameter distribution is 50% (hereinafter also referred to as "D50 of the core") is preferably 0.2 μm or more and 2 μm or less. Therefore, excellent steel reactivity resistance can be obtained with good yield.

That is, when the core portions 21 appearing in the electron microscope image for measuring the degree of dispersion of the core portions are measured, the D50 of the core portions 21 is preferably 0.2 μm or more and 2 μm or less. The D50 of the core 21 is more preferably 0.6 μm or more and 1.6 μm or less, and further preferably 0.8 μm or more and 1.4 μm or less. When D50 of the core 21 is less than 0.2 μm, it tends to be difficult to obtain the desired steel resistance. When D50 of the core 21 is larger than 2 μm, it tends to be difficult to obtain sufficient mechanical strength.

The particle diameter of each core portion 21 can be calculated based on the electron microscope image described above to measure the degree of dispersion of the core portions. Specifically, the core portion 21 is specified by subjecting the above electron microscope image to binarization processing using image analysis software for measuring the content of the first hard phase particles. Further, the diameter of a circle equal to the area of the core portion 21 (equivalent circle diameter) is calculated, and the equivalent circle diameter is regarded as the particle diameter of the core portion 21. For D50 of the core 21 (the particle diameter at which the cumulative value in the area-based particle diameter distribution of the core 21 is 50%), the average of the calculated equivalent circle diameters of all the core 21 appearing in the electron microscope image described above can be employed.

(volume ratio of core)

The volume ratio of the core portion 21 in the cemented carbide is preferably 2 vol% or more and 10 vol% or less. Therefore, excellent steel reactivity resistance can be obtained with good yield. The volume ratio of the core portion 21 in the cemented carbide is more preferably 4 vol% or more and 8 vol% or less.

The volume ratio of the core 21 in the cemented carbide can be calculated in the same manner as in the case where the particle diameter of the core 21 is calculated in the process of specifying the core 21 by using the image analysis software. Specifically, after specifying the core 21 using the image analysis software, the area ratio of the core 21 in the electron microscope image is calculated, and it is assumed that the area ratio is continuous in the depth direction of the above cross section, whereby the area ratio can be calculated as the volume ratio of the core 21 in the cemented carbide. As for the volume ratio of the core portion 21 in the cemented carbide, it is preferable to use the average value of the respective volume ratios calculated in five electron microscope images (five fields) prepared in which a cross section of one cemented carbide is photographed.

(peripheral part)

The second hard phase particles 2 include an outer peripheral portion 22 covering at least a part of the core portion 21. The outer peripheral portion 22 is formed in a sintering step (fourth step) of sintering cemented carbide described below. In the liquid phase sintering process, the grains of the composite carbonitride and the surrounding WC grains are dissolved and precipitated in solid solution with each other, whereby the outer peripheral portion 22 is formed around the core portion 21, and the composition of the outer peripheral portion 22 is opposite to that of the composite carbonitride (Ti) of the core portion 21_1-X-ZNb_XM_ZC_1-YN_Y) Is rich in W and C. Thus, the outer peripheral portion 22 covers at least a part of the core portion 21, and has a different composition from the core portion 21. In particular, the outer peripheral portion 22 is preferably a carbonitride containing Ti, Nb, and W.

The outer peripheral portion 22 functions as an adhesion layer for improving adhesion strength between the second hard phase particles 2 and the metal binder phase 3. Therefore, a decrease in the interface strength between the second hard phase particles 2 and the metal bonding phase 3 can be suppressed, and the mechanical properties of the cemented carbide can be improved. The outer peripheral portion 22 may cover a part or the whole of the core portion 21, and the thickness of the outer peripheral portion 22 should not be limited as long as the effect of the present disclosure is exhibited. The composition of the outer peripheral portion 22 should not be particularly limited as long as the effects of the present disclosure are exhibited and the composition of the outer peripheral portion 22 is different from that of the core portion 21. Examples of the composition of the outer peripheral portion 22 include Ti_0.82Nb_0.13W_0.05C_0.5N_0.5、Ti_0.78Nb_0.14W_0.08C_0.65N_0.35And the like.

< Metal binding phase >

The metallic bonding phase 3 contains an iron group element. That is, the metallic bonding phase 3 is mainly composed of an iron group element. The metal binder phase 3 may contain, in addition to the iron group element: inevitable elements introduced from the first hard phase particles 1 and the second hard phase particles 2; a small amount of impurity elements; and the like. In order to maintain the metallic bonding phase 3 in a metallic state and avoid the formation of brittle intermediate compounds, the content of the iron group element in the metallic bonding phase 3 is preferably 90 atomic% or more, and more preferably 95 atomic% or more. The upper limit of the content of the iron group element in the metallic bonding phase 3 is 100 atomic%. Here, the iron group elements refer to group 8 elements, group 9 elements, and group 10 elements in the fourth period of the periodic table, i.e., iron (Fe), cobalt (Co), and nickel (Ni). Examples of other elements contained in the metallic bonding phase 3 in addition to the iron group element include titanium (Ti), tungsten (W), and the like.

The metal binder phase 3 is preferably mainly composed of Co. The content of the iron group element other than Co in the metallic bonding phase 3 is preferably less than 1 vol%, and more preferably less than 0.5 vol%.

The content of the metallic binder phase 3 in the cemented carbide is preferably 7 to 15 vol%. When the content of the metallic binder phase 3 in the cemented carbide is less than 7% by volume, sufficient adhesion strength cannot be obtained, and as a result, toughness tends to be reduced. When the content of the metallic binder phase 3 in the cemented carbide is more than 15% by volume, the hardness tends to decrease. A more preferred content of the metallic binder phase 3 in the cemented carbide is 9 to 13 vol%. The content (% by volume) of the metal binder phase 3 can be calculated by the same method as the method for measuring the content of the first hard phase particles 1.

Further, the sum of the contents of each of the first hard phase particles 1, the second hard phase particles 2, and the metal binding phase 3 is preferably 95% by volume or more, more preferably 98% by volume or more, and most preferably 100% by volume. Therefore, excellent steel reactivity resistance can be obtained with good yield.

[ method for producing cemented carbide ]

Although the method of manufacturing the cemented carbide according to the present embodiment should not be particularly limited, the following method is preferably employed. Namely, the method for manufacturing cemented carbide includes: obtaining a catalyst formed from Ti_1-X-ZNb_XM_ZC_1-YN_YThe step of compounding carbonitride powder (first step) shown; mixing the composite carbonitride powder, the WC powder and the iron group element powder for 9 hours or more by using a ball mill to 1 hour or moreA step of obtaining a powder mixture (second step) within 5 hours or less; a step of obtaining a formed body by press-forming the powder mixture (third step); and a step of obtaining a sintered body by sintering the formed body (fourth step). At Ti_1-X-ZNb_XM_ZC_1-YN_YWherein M is at least one impurity element selected from the group consisting of V, Cr and Mo, X is 0.1 to 0.2, Y is 0.3 to 0.6, and Z is 0 to 0.02. According to this manufacturing method, a cemented carbide having excellent steel reactivity resistance can be manufactured.

< first step >

The first step is to obtain a titanium alloy consisting of Ti_1-X-ZNb_XM_ZC_1-YN_YThe indicated procedure for the powder of composite carbonitride. The first step further comprises the following steps. The first step, namely the step of obtaining a powder of composite carbonitride, comprises: a step of obtaining a third powder by mixing a first powder containing Ti and Nb and a second powder containing at least graphite (mixing step); a step of obtaining granules by granulating the third powder (granulation step); a step (heat treatment step) of obtaining a powder precursor composed of composite carbonitride by heat-treating the granules at 1800 ℃ or higher in an atmosphere containing nitrogen gas; and a step (pulverization step) of pulverizing the powder precursor to obtain a powder of composite carbonitride.

(mixing step)

In the mixing step, a third powder is obtained by mixing a first powder containing Ti and Nb and a second powder containing at least graphite.

The first powder includes Ti and Nb. The first powder is preferably an oxide comprising Ti and Nb. When the first powder is an oxide, the primary particle diameter of the composite carbonitride powder obtained by the pulverization step described below can be easily thinned, whereby the particle diameter at which the cumulative value in the area-based particle diameter distribution of the core is 50% (D50 of the core) can be, for example, 0.2 μm to 2 μm. Further, the first powder may contain one or more impurity elements selected from the group consisting of V, Cr and Mo as an impurity element introduced from a manufacturing apparatus or the likeThe ingredients are added. In this case, in the first powder, the total amount of V, Cr and Mo is preferably less than 2 atomic% relative to the total amount of Ti, Nb, V, Cr, and Mo. Specific examples of the first powder include composite oxides such as Ti_0.9Nb_0.1O₂. The first powder may be a powder comprising, for example, TiO₂Or Nb₂O₅Such as oxide powders. Unless the purpose is contrary, the oxidation number of each element, the content of impurity elements, and the like may be changed.

The second powder comprises at least graphite. In the mixing step, a third powder is obtained by mixing the second powder with the first powder. This enables the following reactions to be carried out simultaneously and continuously in the following heat treatment steps: reduction reaction of the above oxides; solid solution reaction due to diffusion of Ti and Nb into each other in the reduced oxide; and carbonitriding reaction of the solid-dissolved Ti and Nb. As a result, composite carbonitride can be obtained efficiently.

As a method of mixing the first powder and the second powder, a conventionally known method may be used. However, in order to obtain a small D50 (particle diameter at a cumulative value of 50% in the particle diameter distribution based on the area) of the third powder, a mixing method using a dry ball mill capable of having a high pulverizing action or a mixing method using a wet ball mill may be suitably used. Further, a mixing method using a rotary blade type fluid mixer capable of having a low pulverization action, or the like may be used. D50 of the third powder was calculated based on the total particles of the third powder appearing in the observation image observed at a magnification of 10000 times by using an SEM (scanning electron microscope). The equivalent circle diameters of all the particles of the third powder appearing in the observation image were calculated using the above-described image analysis software, and the equivalent circle diameter corresponding to the particles having a cumulative value of 50% can be regarded as D50 of the third powder. The mixing ratio of the first powder and the second powder is preferably as follows: when the ratio of the first powder is 1, the ratio of the second powder is 0.3 to 0.4.

(granulation step)

In the granulating step, the granulated body is obtained by granulating the third powder. As the granulation method in the granulation step, a conventionally known granulation method can be used. Examples thereof include a method using a known apparatus such as a spray dryer or an extrusion granulator. In addition, in the granulation, a binder component such as wax, for example, can be suitably used as the binder. The shape and size of the granules should not be particularly limited. For example, the granulated body may be a cylindrical shape having a diameter of 0.5mm to 5mm and a length of 5mm to 20 mm.

(Heat treatment step)

In the heat treatment step, the granulated body is heat-treated at 1800 ℃ or higher in an atmosphere containing nitrogen gas, thereby obtaining a powder precursor composed of composite carbonitride. In the heat treatment step, oxygen in the oxide of the first powder contained in the above-described granulated body reacts with graphite in the second powder under an atmosphere containing nitrogen gas, thereby reducing Ti and Nb in the first powder. In addition, the reduced Ti and Nb diffuse into each other, and thus a solid solution reaction occurs. At the same time, the reduced Ti and Nb undergo a carbonitriding reaction, wherein the reduced Ti and Nb react with nitrogen in the atmosphere and graphite in the second powder. Thereby, Ti is formed as described above_1-X-ZNb_XM_ZC_1-YN_YThe powder precursor composed of the indicated compound carbonitride.

Here, in the heat treatment step, when the metal powder containing Ti and Nb or the powder containing Ti carbonitride and Nb carbonitride is mixed with the second powder without being mixed with the first powder and the resultant powder mixture is heat-treated under the above conditions, the powder precursor composed of the above complex carbonitride cannot be obtained. This is due to the following reasons: since the carbonitriding reaction rapidly proceeds in the metal powder containing Ti and Nb by the heat treatment, the solid solution reaction due to the interdiffusion of Ti and Nb does not proceed. Another reason for this is as follows: since the powder containing carbonitride of Ti and carbonitride of Nb is chemically stable even in a high temperature region exceeding 2000 ℃, solid solution reaction due to interdiffusion of Ti and Nb does not proceed.

The atmosphere of the heat treatment in the heat treatment step should not be particularly limited as long as the atmosphere containsAnd (4) nitrogen gas. The atmosphere for the heat treatment may be pure N₂Gas, or is N₂Gas and hydrogen (H)₂Gas), argon (Ar gas), helium (He gas), carbon monoxide gas (CO gas), and the like.

The temperature of the heat treatment in the heat treatment step is 1800 ℃ or more, and preferably 2000 ℃ or more, to perform and promote the reduction reaction, the solid solution reaction, and the carbonitriding reaction of the first powder. However, in order to prevent excessive aggregation of the powder precursor obtained by the heat treatment, the temperature of the heat treatment is preferably 2400 ℃ or less.

The heat treatment time in the heat treatment step is preferably adjusted according to D50 of the third powder. For example, when the D50 of the third powder in which the first powder and the second powder are mixed with each other is 0.3 μm to 0.5 μm, the heat treatment time is suitably 15 minutes to 60 minutes. It is preferable that the smaller the value of D50 of the third powder, the shorter the heat treatment time in the heat treatment step, and the larger the value of D50 of the third powder, the longer the heat treatment time in the heat treatment step.

In the heat treatment step, a rotary type continuous heat treatment apparatus such as a rotary kiln is preferably used. The heat treatment apparatus includes an inclined rotary reaction tube. Further, the heat treatment apparatus includes: the heating mechanism is used for heating the rotary reaction tube; a gas inlet for introducing a gas containing nitrogen into the rotating reaction tube; a gas outlet for discharging a gas containing nitrogen from the rotating reaction tube; an introduction port for introducing the granulated body into the rotary reaction tube; a take-out port for taking out the powder precursor from the rotary reaction tube; and so on. Such a heat treatment apparatus is preferable because the apparatus can heat-treat the granulated body under a constant condition, and thus the powder precursor of the composite carbonitride having stable quality can be efficiently and continuously produced.

In the heat treatment step, when the above-described heat treatment apparatus is used, the rotary reaction tube is first heated at 1800 ℃ or higher using a heating mechanism, and a nitrogen atmosphere is obtained in the rotary reaction tube by introducing a nitrogen-containing gas from a gas inlet. The granulated body is continuously supplied from an inlet located at the upper part of the rotary reaction tube, and is moved in the rotary reaction tube by rotating the rotary reaction tube, thereby performing heat treatment on the granulated body. Thus, a powder precursor composed of the composite carbonitride powder can be formed. The powder precursor may be taken out from an outlet located at the lower portion of the rotary reaction tube.

(crushing step)

In the pulverization step, the powder of the above-described composite carbonitride is obtained by pulverizing the powder precursor obtained as described above. As a method for pulverizing the powder precursor, a conventionally known pulverization method can be used. Thereby, Ti can be obtained_{1-X- Z}Nb_XM_ZC_1-YN_YThe indicated composite carbonitride powder. At Ti_1-X-ZNb_XM_ZC_1-YN_YWherein M is at least one impurity element selected from the group consisting of V, Cr and Mo, X is 0.1 to 0.2, Y is 0.3 to 0.6, and Z is 0 to 0.02.

< second step >

The second step is a step of mixing the powder of composite carbonitride, the WC powder, and the iron group element powder by using a ball mill for 9 hours or more and 15 hours or less to obtain a powder mixture. These powders can be obtained by using a conventionally known mixing method using a ball mill. For example, it is preferable to use: a mixing method using a dry ball mill capable of high pulverization; or a mixing method using a wet ball mill. The mixing time using the ball mill is 9 hours to 15 hours. The mixing time using a ball mill is preferably 11 hours to 13 hours. Therefore, in the cemented carbide produced by the sintering step (fourth step) described below, the dispersion degree of the composite carbonitride (core) can be improved.

When the mixing time using a ball mill is less than 9 hours, the mixing may be insufficient, with the result that the degree of dispersion of the composite carbonitride (core) may not be sufficiently increased in the cemented carbide produced by the sintering step (fourth step) described below. When the mixing time is more than 15 hours using a ball mill, the mixing may be excessive, with the result that in the cemented carbide produced by the sintering step (fourth step) described below, desired mechanical strength, particularly desired toughness, may not be obtained.

< third step >

The third step is a step of obtaining a formed body by press-forming the powder mixture. As a method of press-molding the powder mixture, a conventionally known press-molding method can be used. For example, the powder mixture may be set in a metal mold and may be formed into a predetermined shape under a predetermined pressure. Examples of the molding method include a dry press molding method, a cold isostatic press method, an injection molding method, an extrusion molding method, and the like. The pressure during the forming is preferably about 0.5 ton/cm²(about 50MPa) or more and 2.0 ton weight/cm²(about 200MPa) or less. The shape of the shaped body can be determined according to the desired shape of the article. For the shape of the molded body, a less complicated shape is selected.

< fourth step >

The fourth step is a step of obtaining a sintered body by sintering the formed body. A method of sintering the formed body by holding the formed body in a temperature region where a liquid phase is generated for a predetermined time is preferable. The sintering temperature is preferably 1300 ℃ to 1600 ℃. The holding time is preferably 0.5 hour or more and 2 hours or less, and more preferably 1 hour or more and 1.5 hours or less. The atmosphere during sintering is preferably an atmosphere of an inert gas such as nitrogen or argon or a vacuum (about 0.5Pa or less). Therefore, by performing machining as necessary after obtaining the sintered body, a cemented carbide as a final product can be obtained. The cemented carbide obtained by this manufacturing method may have excellent steel reactivity resistance.

Here, the composition and atomic ratio in the powder of composite carbonitride can be determined by conventionally known compositional analysis techniques. For example, inductive plasma emission spectroscopy, high-frequency combustion, or thermal conductivity methods may be used to determine the composition (metals, carbon, nitrogen, etc.) in the powder and their content.

The D50 (particle diameter with a cumulative value of 50% in the area-based particle diameter distribution) of the composite carbonitride powder is preferably controlled to be 0.5 μm or more and 3.5 μm or less in order to facilitate handling and to have excellent steel resistance reactivity when used as a cutting tool described below. The D50 of the composite carbonitride powder can be calculated by the same method as that of measuring D50 of the third powder.

[ cutting tools ]

The cutting tool according to the present embodiment comprises the cemented carbide described above. Since the cutting tool of the present embodiment includes the cemented carbide described above, the cutting tool may have excellent steel reaction resistance in addition to excellent mechanical strength inherent to the cemented carbide.

Here, examples of applications of the cutting tool include a drill, an end mill, a replaceable cutting insert for a drill, a replaceable insert for an end mill, a disposable insert for milling, a disposable insert for turning, a metal saw, a gear cutting tool, a reamer, a tap, a cutting bit, a wear-resistant tool, a friction stir welding tool, and the like.

When the cutting tool is a replaceable cutting insert or the like, the substrate may or may not include a chip breaker. The shape of the cutting edge ridge line, which is a main part of the cut workpiece, includes any of a sharp edge (an edge where the rake face and the flank face intersect with each other), a honed edge (a sharp edge processed into an arc), a negative land (beveling), a combination of the honed edge and the negative land, and the like.

Further, the cutting tool according to the present embodiment includes: a base material made of the cemented carbide; and a coating film for coating the base material. Fig. 4 is a partial sectional view showing an exemplary structure of a cutting tool according to the present embodiment. As shown in fig. 4, the cutting tool 10 includes:

a base material 11 made of cemented carbide; and a coating film 12 which is in contact with the substrate 11 and covers the substrate 11. Since the cutting tool 10 further includes the coating film 12, the cutting tool 10 has more excellent wear resistance and fracture resistance in addition to excellent mechanical strength and excellent steel reactivity inherent in cemented carbide. Here, the coating 12 may cover the entire surface of the base material 11, or may cover only a part thereof (for example, a cutting edge which contributes to the cuttabilityA large area). Further, the composition of the coating film 12 of the coated substrate 11 should not be particularly limited, and a conventionally known coating film 12 may be suitably employed. Examples of the composition of the coating film 12 for coating the substrate 11 include AlTiSiN, AlCrN, TiZrSiN, CrTaN, HfWSiN, CrAlN, TiN, TiBNO, TiCN, TiCNO, TiB₂、TiAlN、TiAlCN、TiAlON、TiAlONC、Al₂O₃And the like.

As a method for coating a substrate composed of cemented carbide with a coating film, a conventionally known method can be used. Examples thereof include a Physical Vapor Deposition (PVD) method, a Chemical Vapor Deposition (CVD) method, and the like. In particular, as the PVD method, for example, a resistance heating deposition method, an Electron Beam (EB) deposition method, a Molecular Beam Epitaxy (MBE) method, an ion plating method, an ion beam deposition method, a sputtering method, or the like can be used.

(pay)

The above description includes embodiments described further below.

(pay 1)

A cemented carbide comprising: first hard phase particles each comprising WC; second hard phase particles each comprising a carbonitride containing Ti and Nb; and a metallic binder phase comprising an iron group element, wherein

Each of the secondary hard phase particles includes a core portion in the form of particles and an outer peripheral portion covering at least a part of the core portion,

the core is composed of Ti_1-XNb_XC_1-YN_YThe composition of the compound carbonitride shown is,

x is 0.1 to 0.2,

y is 0.3 to 0.6 inclusive,

the composition of the outer peripheral portion is different from that of the core portion, and

in an electron microscope image of an arbitrary cross section of cemented carbide taken at a magnification of 1500 times, in the case where a total of 70 unit regions are provided by successively arranging 7 unit regions each composed of a square having sides of 8 μm in the longitudinal direction and 10 unit regions in the transverse direction, when the total number of core portions in the total 70 unit regions is calculated by counting the number of core portions in each unit region, and the percentage of the number of core portions in each unit region with respect to the total number of core portions is calculated, the number of unit regions in which the percentage is less than 0.43% or more than 2.43% is 10 or less.

(pay 2)

The hard metal according to note 1, wherein the grain size of each core portion, the number of which is counted in each unit region, is 0.2 μm or more and 3 μm or less.

(pay 3)

The cemented carbide according to note 1 or note 2, wherein the outer peripheral portion is a carbonitride containing Ti, Nb, and W.

(pay 4)

The cemented carbide of any one of notes 1 to 3, wherein when the composite carbonitride includes at least one impurity element selected from the group consisting of V, Cr and Mo, the total amount of V, Cr and Mo is less than 2 atomic% relative to the total amount of Ti, Nb, V, Cr, and Mo.

(pay 5)

The hard metal according to any one of notes 1 to 4, wherein a particle diameter of the core portion at a cumulative value of 50% in a particle diameter distribution based on an area is 0.2 μm or more and 2 μm or less.

(pay 6)

The cemented carbide according to any one of notes 1 to 5, wherein a volume ratio of the core portion in the cemented carbide is 2 vol% or more and 10 vol% or less.

(pay 7)

A cutting tool comprising the cemented carbide of any one of notes 1 to 6.

(pay 8)

The cutting tool according to note 7, comprising a base material made of cemented carbide; and a coating film for coating the substrate.

(pay 9)

A method of manufacturing a cemented carbide, the method comprising:

obtaining a catalyst formed from Ti_1-XNb_XC_1-YN_YA powder of the indicated compound carbonitride;

mixing a composite carbonitride powder, a WC powder, and an iron group element powder using a ball mill for 9 hours to 15 hours to obtain a powder mixture;

obtaining a shaped body by pressure-forming the powder mixture; and

obtaining a sintered body by sintering the shaped body, wherein

X is 0.1 to 0.2,

y is 0.3 to 0.6 inclusive, and

the powder obtained from the composite carbonitride comprises

Obtaining a third powder by mixing a first powder comprising Ti and Nb and a second powder comprising at least graphite,

granulating the third powder to obtain granules,

obtaining a powder precursor composed of composite carbonitride by heat-treating the granules at 1800 ℃ or higher in an atmosphere containing nitrogen, and

the powder of composite carbonitride is obtained by pulverizing the powder precursor.

Examples

Although the present disclosure will be described in more detail below with reference to examples, the present disclosure is not limited thereto.

< example 1>

< production of samples 11 to 13 and samples 111 to 114 >

(first step)

As the first powder, TiO was prepared₂Powder (size about 0.5 μm; supplied by Kojundo Chemical Laboratory) and Nb₂O₅Powder (size about 1 μm; supplied by Kojundo Chemical Laboratory). As a second powder, graphite powder (having a size of about 5 μm; supplied by Kojundo Chemical Laboratory) was prepared. These powders were mixed at a certain mixing ratio to obtain the composition of composite carbonitride represented by samples 11 to 13 and samples 113 to 114 and the composition of carbonitride represented by samples 111 and 112 in table 1, respectively, to obtain a third powder (mixing step). Mixing was performed according to the ball milling method.

Next, the third powder was granulated using an extrusion granulator (extrusion hole diameter: 2.5mm) to obtain a cylindrical granulated body having an average diameter of 2.4mm and an average length of about 10mm (granulation step). The average diameter and average length of the mitochondria were measured using a micrometer.

Next, the granulated body was heat-treated at 1800 ℃ in a nitrogen atmosphere using the rotary kiln described above, to obtain a powder precursor composed of composite carbonitride (heat treatment step). The time for the granules to pass through the heating part of the rotary kiln was about 30 minutes.

Finally, the powder precursor was dry-pulverized using a known pulverizer (rolling ball mill using cemented carbide balls of 4.5mm in diameter as a pulverizing medium), thereby obtaining powders of composite carbonitrides of samples 11 to 13 and samples 113 to 114 having the compositions shown in table 1, respectively, and powders of carbonitrides of samples 111 and 112 having the compositions shown in table 1 (pulverizing step). The composition of the composite carbonitride powder and the carbonitride powder was measured using the method described above.

(second step)

A powder mixture was obtained by mixing 10 vol% of each of the above-described composite carbonitride or carbonitride powders, 75 vol% of a commercially available WC powder (trade name: "WC-25", supplied by Japan New Metals), and 15 vol% of a commercially available Co powder (size about 5 μm; supplied by Kojundo Chemical Laboratory) as an iron group element powder. Mixing was carried out by wet ball milling for 10 hours. However, in the case of sample 114, 10 vol% of the composite carbonitride powder, 75 vol% of the above WC powder and 15 vol% of the above Co powder were mixed for 5 hours by a wet ball milling method to obtain a powder mixture.

(third step)

The above powder mixture was granulated by using camphor and ethanol and weighed at 1 ton/cm²Press forming was performed under a pressure of (about 98MPa), thereby obtaining a formed body.

(fourth step)

The formed body was sintered at 1410 ℃ in a vacuum (0.1Pa) atmosphere using a liquid phase sintering method for 1 hour, thereby obtaining a sintered body. Next, a diamond wheel of No. (#)400 (No. (#) indicates the fineness of abrasive grains; the larger the number, the finer the abrasive grains) was used to cut and remove the sintered skin of the sintered body, thereby obtaining cutting tools (each of samples 11 to 13 and samples 111 to 114) having a shape of SNGN120408 and composed of cemented carbide.

The composition of the core portion of the secondary carbonitride phase particles in these cutting tools (cemented carbides) was analyzed by EDX by the above-described method, and the composition was in accordance with the respective compositions of the composite carbonitride and carbonitride powder shown in table 1. By EDX, it was confirmed that the outer peripheral portion had a composition obtained by adding W to the composition of the core portion. By visually observing the electron microscope image, it was confirmed that each outer peripheral portion covered at least a part of the core portion. Further, by EDX, composite carbonitrides and carbonitrides (Ti) in the core portion were also confirmed_1-X-ZNb_XM_ZC_1-YN_Y) Does not contain an impurity element such as V, Cr or Mo as M (i.e., Z ═ 0).

Table 1 shows the compositions of the outer peripheral portions in samples 11 to 13 and samples 111 to 114. Further, with respect to the respective cutting tools (cemented carbides) of samples 11 to 13 and samples 111 to 114, analysis was made with respect to the particle diameter and the degree of dispersion of the core portion (the number of unit regions in which the number of core portions expressed by percentage is less than 0.43% or more than 2.43%) at a cumulative value of 50% in the particle diameter distribution based on the area of the core portion, using the above-described measurement method. The analysis results are shown in Table 1. In each of the cutting tools (cemented carbide) of samples 11 to 13 and samples 111 to 114, the volume ratio of the core portion in the cemented carbide was 10 vol%.

Further, fig. 2A to 2C and fig. 3A to 3C show: electron microscope images (fig. 2A and 3A) for analyzing the degree of dispersion of the core portions in each of the samples 12 and 114; the number of cores in each unit region (fig. 2B and 3B); and the percentage of the number of cores in each unit area (fig. 2C and 3C).

< cutting test >

As the cutting test, a test of steel resistance reactivity was performed on each of the cutting tools of samples 11 to 13 and samples 111 to 114 under the following conditions. The results are shown in Table 1. Here, the cutting tools of samples 11 to 13 correspond to the examples of the present disclosure, the cutting tools of samples 111 to 113 correspond to the comparative examples, and sample 114 corresponds to the reference example.

(test of Steel resistance)

Workpiece: SCM435

Peripheral speed: 150m/min

Feeding: 0.15mm/rev

Cutting depth: 1.5mm

Cutting oil: is free of

In the test of steel reactivity, the cutting time (in minutes) until the flank wear width of the cutting edge of the cutting tool of each sample was 0.2mm or more was measured to evaluate the weld wear. The longer this time, the more excellent the steel reactivity resistance is evaluated.

[ Table 1]

< review >

As can be seen from table 1, the cutting tools of examples (samples 11 to 13) had more excellent steel resistance reactivity than that of the cutting tools of comparative examples (samples 111 to 113) and the cutting tool of reference example (sample 114).

< example 2>

< production of samples 21 to 27 and samples 211 to 216 >

(first step)

As the first powder, TiO was prepared₂Powder (size about 0.5 μm; supplied by Kojundo Chemical Laboratory) and Nb₂O₅Powder (size about 1 μm; supplied by Kojundo Chemical Laboratory). As a second powder, graphite powder (having a size of about 5 μm; supplied by Kojundo Chemical Laboratory) was prepared. These powders were mixed at a certain mixing ratio to obtain the compositions of the composite carbonitrides represented by samples 21 to 27 and samples 211 to 216 in table 2, respectively, to obtain a third powder (mixing step). Mixing was performed according to the ball milling method. Here, in sample 215 and sample 216, WO₃Powder (purity 3N; supplied by Kojundo Chemical Laboratory) was added to the first powder to obtain the composition of the composite carbonitride shown in Table 2.

Next, the same granulation step, heat treatment step and pulverization step as in example 1 were performed, thereby obtaining powders of composite carbonitrides having the compositions of samples 21 to 27 and samples 211 to 216 in table 2.

(second step)

A powder mixture was obtained by mixing 5 vol% of the powder of each of the above-described composite carbonitrides, 85 vol% of a commercially available WC powder (trade name: "WC-25", supplied by Japan New Metals), and 10 vol% of a commercially available Co powder (size about 5 μm; supplied by Kojundo Chemical Laboratory) as an iron group element powder. This mixing was carried out according to the wet ball milling method for 10 hours using the same balls and mills as in example 1. However, in the case of samples 213 and 214, 5 vol% of the powder of composite carbonitride, 85 vol% of the above WC powder, and 10 vol% of the above Co powder were mixed by wet ball milling for 3 hours and 5 hours, respectively, to obtain a powder mixture.

(third and fourth steps)

Next, the third step and the fourth step were performed in the same manner as in example 1, thereby obtaining cutting tools each having a shape of SNGN120408 and composed of each cemented carbide (samples 21 to 27 and samples 211 to 216).

The composition of the core portion of the secondary carbonitride particles in these cutting tools (cemented carbides) was analyzed by EDX by the above method, and the composition was in accordance with the composition of the powder of composite carbonitride of table 2. By EDX, it was confirmed that the composition of the outer peripheral portion was obtained by adding W to the composition of the core portion. By visually observing the electron microscope image, it was confirmed that each outer peripheral portion covered at least a part of the core portion. Further, by EDX, composite carbonitride (Ti) in the core portion was also confirmed_1-X-ZNb_XM_ZC_1-YN_Y) Does not contain an impurity element such as V, Cr or Mo as M (i.e., Z ═ 0).

Table 2 shows the compositions of the outer peripheral portions in samples 21 to 27 and samples 211 to 216. Further, with respect to the respective cutting tools (cemented carbide) of samples 21 to 27 and samples 211 to 216, analysis was made with respect to the particle diameter and the degree of dispersion of the core portion (the number of unit regions in which the number of core portions expressed by percentage is less than 0.43% or more than 2.43%) at a cumulative value of 50% in the particle diameter distribution based on the area of the core portion, using the above-described measurement method. The analysis results are shown in Table 2. In each of the cutting tools (cemented carbide) of samples 21 to 27 and samples 211 to 216, the volume ratio of the core portion in the cemented carbide was 5 vol%.

< cutting test >

As a cutting test, a test of steel resistance reactivity was performed on each of the cutting tools of samples 21 to 27 and samples 211 to 216 under the same conditions as in example 1. The results are shown in Table 2. Here, the cutting tools of samples 21 to 27 correspond to the examples of the present disclosure, and the cutting tools of samples 211 to 216 correspond to the comparative examples.

[ Table 2]

< review >

As can be seen from table 2, the cutting tools of examples (samples 21 to 27) had more excellent steel resistance reactivity than that of the cutting tools of comparative examples (samples 211 to 216).

< example 3>

< production of samples 31 to 37 >

As the first powder, TiO was prepared₂Powder (size about 0.5 μm; supplied by Kojundo Chemical Laboratory) and Nb₂O₅Powder (size about 1 μm; supplied by Kojundo Chemical Laboratory). As a second powder, graphite powder (having a size of about 5 μm; supplied by Kojundo Chemical Laboratory) was prepared. Further, for each of samples 31 to 37, when the first powder was prepared, V was set₂O₅Powder (purity 3N; supplied by Kojundo Chemical Laboratory), Cr₂O₃Powder (particle size about 3 μm; supplied by Kojundo Chemical Laboratory) and MoO₃Powder (purity 3N; supplied by Kojundo Chemical Laboratory) was added to the first powder so that a carbonitride complex (Ti)_{1-X- Z}Nb_XM_ZC_1-YN_Y) The composition of (1) contains impurity elements (V, Cr and Mo; these elements are expressed as M) in the composition, so that the total amount (atomic%) of impurity elements with respect to the total amount of Ti, Nb, V, Cr and Mo as shown in table 3 is obtained. The compositions of samples 31 to 37 except for the impurity elements were the same as those of sample 12, and cemented carbide was produced. However, in example 3, the article shape is CNGN 120404.

Further, the cemented carbide of samples 31 to 37 was used as a base material, and the base material was coated with a coating film composed of TiAlN under PVD conditions described below, thereby manufacturing cutting tools of samples 31 to 37.

(PVD conditions)

AlTi target (target composition: Al: Ti ═ 50:50)

Arc current: 100A

Bias voltage: -100V

Chamber pressure: 4.0Pa

Reactive gas (b): nitrogen is present in

Cutting tests (tests of steel resistance reactivity) were performed on the respective cutting tools of samples 31 to 37 under the same conditions as in example 1. The results are shown in Table 3. However, in the test of the steel reactivity resistance of example 3, the cutting time was 5 minutes, and a specimen in which the flank wear width of the cutting edge was less than 0.2mm when 5 minutes elapsed was evaluated as a good product. The time for confirming that the flank wear width of the cutting edge was 0.2mm or more for the cutting edge samples whose flank wear width was confirmed to be 0.2mm or more before and after not reaching 5 minutes is shown in table 3.

[ Table 3]

< review >

As can be seen from table 3, each of the cutting tools of samples 31 to 33 has more excellent steel resistance reactivity than that of the cutting tools of samples 34 to 37, and thus realizes a long life, in which the total amount of V, Cr and Mo is less than 2 atomic% (that is, Z is 0 or more and less than 0.02) relative to the total amount of Ti, Nb, V, Cr and Mo in the composite carbonitride of the core in each of the cutting tools of samples 31 to 33.

< example 4>

< production of samples 41 to 46 >

In the case of each of samples 41 to 46, first, a powder having the same amount of impurity elements (V, Cr and Mo) as sample 31 and the same composition of composite carbonitride as sample 31 was used, and this powder was pulverized in advance by a ball mill method to adjust the particle diameter of the powder, thereby obtaining D50 (particle diameter at a cumulative value of 50% in the particle diameter distribution on an area basis) of the core portion shown in table 4 (first step). Then, by performing the second step, the third step, and the fourth step in the same manner as in example 2, each of the cutting tools of samples 41 to 46 having a shape of SNGN120408 and composed of cemented carbide was manufactured. The same steel reactivity test as in example 1 was conducted for each of these cutting tools. The results are shown in Table 4.

[ Table 4]

< review >

As can be seen from table 4, the cutting tools of each of samples 42 to 45 having D50 of the core portion falling within the range of 0.2 μm to 2 μm had more excellent steel resistance reactivity than that of the cutting tools of samples 41 and 46.

< example 5>

< production of samples 51 to 56 >

For each of samples 51 to 56, a cutting tool composed of cemented carbide was produced in the same manner as sample 12 except that the above-described composite carbonitride powder, WC powder and Co powder in sample 12 were adjusted so that the volume ratio (%) of the core portion in the cemented carbide was as shown in table 5, and then the second step was performed. However, the article shape in example 5 is TNGN 160404. The same steel reactivity test was performed on each of these cutting tools under the same conditions as in example 1. The results are shown in Table 5.

[ Table 5]

< review >

As can be seen from table 5, the respective cutting tools of samples 52 to 55 in which the volume ratio (%) of the core portion in cemented carbide was 2 to 10 vol% had more excellent steel resistance reactivity than that of the cutting tools of samples 51 and 56.

So far, the embodiments and examples of the present disclosure have been explained, but it is originally intended to appropriately combine the constitutions of the embodiments and examples.

The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the embodiments described above, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.

List of reference numerals

1: first hard phase particles; 2: secondary hard phase particles; 10: a cutting tool; 11: a substrate; 12: coating a film; 21: a core; 22: a peripheral portion; 3: a metal binding phase; r: a unit area.