阅读说明：本技术 烧结体以及包含该烧结体的切削工具 (Sintered body and cutting tool comprising same ) 是由 冈村克己 石井显人 久木野晓 于 2018-07-26 设计创作，主要内容包括：本申请提供了一种烧结体,该烧结体包含3体积％至80体积％的立方氮化硼颗粒和结合剂,其中结合剂包含：选自由至少一种化合物及其固溶体组成的组中的至少一者,所述至少一种化合物包含至少一种第一元素和至少一种第二元素,第一元素选自由元素周期表中的第4族元素、第5族元素和第6族元素、Al和Si组成的组,第二元素选自由C、N、O和B组成的组；以及选自由Li、Ca、Na、Sr、Ba和Be组成的组中的至少一种金属元素。结合剂包含总计0.001质量％至0.5质量％的金属元素以及0.1质量％至10.0质量％的氧。(The present application provides a sintered body comprising 3 to 80 vol% cubic boron nitride particles and a binder, wherein the binder comprises: at least one selected from the group consisting of at least one compound comprising at least one first element selected from the group consisting of group 4 elements, group 5 elements and group 6 elements in the periodic table of the elements, Al and Si, and at least one second element selected from the group consisting of C, N, O and B; and at least one metal element selected from the group consisting of Li, Ca, Na, Sr, Ba and Be. The binder contains a total of 0.001 to 0.5 mass% of metal elements and 0.1 to 10.0 mass% of oxygen.)

1. A sintered body having 3 to 80 vol% cubic boron nitride particles and a binder,

The binding agent comprises: one or more selected from the group consisting of one or more compounds consisting of one or more first elements selected from the group consisting of group 4 elements, group 5 elements and group 6 elements in the periodic table, Al and Si, and one or more second elements selected from the group consisting of C, N, O and B, and solid solutions of these compounds; and one or more metal elements selected from the group consisting of Li, Ca, Na, Sr, Ba and Be,

The content of the one or more metal elements in the binder is 0.001 mass% or more and 0.5 mass% or less in total,

The oxygen content in the binder is 0.1 mass% to 10.0 mass%.

2. The sintered body according to claim 1, wherein the binder contains one or both of the Li and the Ca in an amount of 0.001% by mass or more and 0.1% by mass or less in total, and the content of the oxygen in the binder is 0.5% by mass or more and 5.0% by mass or less.

3. The sintered body according to claim 1 or 2, wherein the binder contains a nitride of one or both of Ti and Zr, one or both of Li and Ca, the oxygen, and carbon, the binder contains one or both of Li and Ca in a total amount of 0.001 mass% or more and 0.01 mass% or less, and contains 0.001 mass% or more and 0.5 mass% or less of the carbon.

4. A cutting tool comprising the sintered body according to any one of claims 1 to 3.

Technical Field

The present disclosure relates to a sintered body having cubic boron nitride particles and a binder, and a cutting tool including the sintered body. The present application claims priority based on japanese patent application No.2017-209056 filed on 2017, 10, 30. The entire contents described in this japanese patent application are incorporated herein by reference.

Background

In machining of iron-based difficult-to-cut materials, particularly high hardness quenched steels, it is becoming more and more common to perform finish machining by cutting using a tool that utilizes a sintered cubic boron nitride (hereinafter also referred to as "cBN") compact. In recent years, when a cBN sintered body is used for high efficiency machining, the requirements for the cBN sintered body have become more and more stringent, and further, it has been required to extend the tool life.

Japanese patent laid-open No.2005-187260 (patent document 1) and WO 2006/112156 (patent document 2) disclose that trace amounts of elements such as alkali metals, alkaline earth metals, carbon, etc. are contained in cBN particles to increase the bonding force between cBN particles, thereby extending the tool life when processing difficult-to-cut materials.

WO 2008/093577 (patent document 3) discloses that a trace amount of a transition metal element or the like is blended with a binder to improve the wear resistance and chipping resistance of a cBN sintered body when processing a difficult-to-cut material.

Reference list

Patent document

Patent document 1: japanese patent laid-open No.2005-187260

Patent document 2: WO 2006/112156

Patent document 3: WO 2008/093577

Disclosure of Invention

A sintered body according to an aspect of the present disclosure is a sintered body having 3 vol% or more and 80 vol% or less of cubic boron nitride particles and a binder,

The binding agent comprises: one or more selected from the group consisting of one or more compounds consisting of one or more first elements selected from the group consisting of group 4 elements, group 5 elements and group 6 elements in the periodic table, Al and Si, and one or more second elements selected from the group consisting of C, N, O and B; and one or more metal elements selected from the group consisting of Li, Ca, Na, Sr, Ba and Be,

The content of at least one metal element in the binder is 0.001-0.5 mass% in total,

The oxygen content in the binder is 0.1 mass% to 10.0 mass%.

A cutting tool according to one aspect of the present disclosure is a cutting tool including the above sintered body.

Detailed Description

[ problem to be solved by the present disclosure ]

However, even with the techniques of patent documents 1 to 3, it is not possible to satisfy both the stringent requirements applied to recent efficient machining and the requirement for excellent tool life, and thus better performance is required.

Accordingly, it is an object to provide a sintered body exhibiting excellent tool life when applied to a cutting tool and even used for efficient machining of high hardness quenched steel, and a cutting tool comprising the sintered body.

[ advantageous effects of the present disclosure ]

According to the above aspect, a sintered body can be provided which exhibits excellent tool life when applied to a cutting tool and even to high-efficiency machining of high-hardness quenched steel.

[ description of the embodiments ]

First, embodiments of the present disclosure will be enumerated and described in detail.

(1) A sintered body according to an aspect of the present disclosure is a sintered body having 3 vol% or more and 80 vol% or less of cubic boron nitride particles and a binder. The binding agent comprises: one or more selected from the group consisting of one or more compounds consisting of one or more first elements selected from the group consisting of group 4 elements, group 5 elements and group 6 elements in the periodic table, Al and Si, and one or more second elements selected from the group consisting of C, N, O and B; and one or more metal elements selected from the group consisting of Li, Ca, Na, Sr, Ba and Be. The content of one or more metal elements in the binder is 0.001 mass% or more and 0.5 mass% or less in total. The oxygen content in the binder is 0.1 mass% to 10.0 mass%.

when the sintered body of the present embodiment is applied to a cutting tool and used for efficient machining of high hardness quenched steel, the sintered body exhibits excellent tool life. The sintered body of the present embodiment exhibits excellent tool life not only in efficient working of high hardness quenched steel, but also in efficient working of difficult-to-cut materials such as iron-based heat-resistant alloys, nickel-based heat-resistant alloys, titanium alloys, and the like.

(2) The binder preferably contains one or both of Li and Ca in an amount of 0.001 to 0.1 mass% in total, and the oxygen content in the binder is preferably 0.5 to 5.0 mass%. This provides a further extended tool life.

(3) The binder preferably contains a nitride of one or both of Ti and Zr, one or both of Li and Ca, oxygen, and carbon, and contains one or both of Li and Ca in an amount of 0.001 mass% to 0.01 mass% in total, and carbon in an amount of 0.001 mass% to 0.5 mass%. This provides a further extended tool life.

(4) A cutting tool according to one aspect of the present disclosure is a cutting tool comprising the sintered body described in the above clauses (1) to (3). The cutting tool of the present embodiment exhibits excellent tool life in efficient machining of high hardness quenched steel.

[ detailed description of the embodiments ]

Specific examples of sintered bodies according to embodiments of the present disclosure will now be described below.

In the present specification, when a compound or the like is represented by a chemical formula without specifying any particular atomic ratio, it includes any conventionally known atomic ratio, and is not necessarily limited to those falling within a stoichiometric range. For example, for "TiCN", the ratio of the number of atoms constituting TiCN is not limited to Ti: C: N ═ 1:0.5:0.5, but includes any conventionally known atomic ratio. Further, in the present specification, the expression of the form "a to B" represents the upper and lower limits of the range (i.e., a above B and below), and when there is no unit after a and only a unit after B, the units of a and B are the same.

[ sintered body ]

The sintered body according to the present embodiment is a sintered body including 3 vol% or more and 80 vol% or less of cubic boron nitride particles (hereinafter also referred to as "cBN particles") and a binder (the sintered body will hereinafter also be referred to as "cBN sintered body"). The sintered body according to the present embodiment may contain other components as long as the sintered body contains two components of cBN and the binder, and may contain inevitable impurities generated due to the raw materials used, the production conditions, and the like.

(cubic boron nitride particles)

The sintered body contains 3 to 80 vol% of cubic boron nitride particles. The cBN particles have high hardness, high strength and high toughness, and function as a skeleton in the sintered body and function to maintain the strength of a material that can withstand cutting of high hardness quenched steel.

When the content of the cBN particles is less than 3 vol%, the material strength capable of withstanding cutting of high hardness quenched steel cannot be maintained. On the other hand, when the content of the cBN particles exceeds 80% by volume, the binder content is relatively decreased, resulting in a decrease in wear resistance. In order to extend the tool life, the content of the cBN particles is preferably 20 vol% or more and 75 vol% or less, and more preferably 45 vol% or more and 65 vol% or less.

The content (% by volume) of the cBN particles in the sintered body can be confirmed by observing the structure of the sintered body using an energy dispersive X-ray analyzer (EDX) equipped with a Scanning Electron Microscope (SEM), performing elemental analysis on the sintered body, and the like.

specifically, the content (% by volume) of cBN particles can be determined by: first, cutting is performed at a desired position of the sintered body to prepare a sample including a cross section. The cross section of the sintered body can be prepared using a focused ion beam apparatus, a cross section polishing apparatus, or the like. Subsequently, the cross section of the cBN sintered body was observed with an SEM at a magnification of 2000 times to obtain a back scattered electron image. In the back-scattered electron image, the region where cBN grains were present was a black region, and the region where the binder was present was a gray region or a white region.

Subsequently, the backscattered electron image is binarized using image analysis software (for example, "WinROOF" by Mitani Corporation), and the respective area ratios are calculated from the binarized image. The content (% by volume) of cBN can be obtained by regarding the calculated area ratio as a value expressed in% by volume. Thus, the volume percentage of the binder can be obtained simultaneously.

The content (% by volume) of cBN particles in the sintered body was the same as the content of cBN powder in the whole raw material powder (hereinafter also referred to as "final powder product"). Therefore, by controlling the content of the cBN powder in the final powder product at the time of manufacturing the sintered body, the content of the cBN particles in the sintered body can be adjusted to fall within a desired range.

Cubic boron nitride (cBN) exists in the sintered body as cBN particles. The average particle diameter (D50) of the cBN particles is not particularly limited and may be, for example, 0.1 μm to 10.0 μm. In general, the smaller the average grain size, the higher the hardness of the cBN sintered body tends to be, and the smaller the variation in grain size, the more uniform the properties of the cBN sintered body tend to be. For example, the average particle diameter of the cBN particles is preferably 0.5 to 4.0. mu.m.

D50 for the cBN particles was determined by: first, according to the above-described method of determining the content of cBN particles, a sample containing a cross section of the base material was prepared, and a back-scattered electron image was obtained. Subsequently, the equivalent circle diameter of each black area in the backscattered electron image is calculated using image analysis software. It is preferable to calculate the equivalent circle diameters of cBN particles of 100 or more by observing 5 or more fields.

Subsequently, the equivalent circle diameters are arranged from the minimum value to the maximum value to obtain a cumulative distribution. The particle diameter at which the cumulative distribution reached a cumulative area of 50% was D50. It should be noted that the equivalent circle diameter refers to the diameter of a circle having the same area as the area of the cBN particles measured.

(Binder)

The binding agent comprises: one or more selected from the group consisting of one or more compounds selected from the group consisting of group 4 elements in the periodic table (Ti (titanium), Zr (zirconium), Hf (hafnium), etc.), group 5 elements in the periodic table (V (vanadium), Nb (niobium), Ta (tantalum), etc.), group 6 elements in the periodic table (Cr (chromium), Mo (molybdenum), W (tungsten), etc.), Al (aluminum), and Si (silicon), and solid solutions of these compounds (hereinafter also referred to as "binder materials"), and one or more second elements selected from the group consisting of C (carbon), N (nitrogen), O (oxygen), and B (boron); and one or more metal elements selected from the group consisting of Li (lithium), Ca (calcium), Na (sodium), Sr (strontium), Ba (barium), and Be (beryllium).

The binder plays a role in making the cBN particles, which are difficult to sinter material, sinterable at industrial levels of pressure and temperature. In addition, the binder is less reactive with iron than cBN. Therefore, when the sintered body contains a binder and is used for cutting high-hardness quenched steel, chemical wear and thermal wear of the sintered body are suppressed. Further, the sintered body containing the binder is enhanced in wear resistance in high-efficiency working of high-hardness quenched steel.

Specific examples of the first element selected from the group consisting of group 4 elements, group 5 elements and group 6 elements in the periodic table, Al and Si, and one or more second elements selected from the group consisting of C, N, O and B will be described hereinafter.

The compound (i.e., carbide) composed of the first element and C (the second element) may be, for example, titanium carbide (TiC), zirconium carbide (ZrC), hafnium carbide (HfC), Vanadium Carbide (VC), niobium carbide (NbC), tantalum carbide (TaC), chromium carbide (Cr), or the like₃C₂) Molybdenum carbide (MoC), tungsten carbide (WC), aluminum carbide (Al)₄C₃) And silicon carbide (SiC).

The compound (i.e., nitride) composed of the first element and N (the second element) may be, for example, titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), Vanadium Nitride (VN), niobium nitride (NbN), tantalum nitride (TaN), chromium nitride (Cr), or the like₂N), molybdenum nitride (MoN), tungsten nitride (WN), aluminum nitride (AlN), silicon nitride (Si)₃N₄) Titanium zirconium nitride (TiZrN), titanium hafnium nitride (TiHfN), titanium vanadium nitride (TiVN), titanium niobium nitride (TiNbN), titanium tantalum nitride (TiTaN), titanium chromium nitride (TiCrN), titanium molybdenum nitride (TiMoN), titanium tungsten nitride (TiWN), zirconium hafnium nitride (zhfn), zirconium vanadium nitride (ZrVN), zirconium niobium nitride (ZrNbN), zirconium tantalum nitride (ZrTaN), zirconium chromium nitride (ZrCrN), zirconium molybdenum nitride (ZrMoN), zirconium tungsten nitride (ZrWN), hafnium vanadium nitride (HfVN), hafnium niobium nitride (HfNbN), hafnium tantalum nitride (HfTaN), hafnium chromium nitride (HfCrN), hafnium molybdenum nitride (HfMoN), hafnium tungsten nitride (hftungsten), vanadium niobium nitride (VNbN), vanadium tantalum nitride (VTaN), vanadium chromium nitride (VCrN), vanadium molybdenum nitride (VMoN), vanadium tungsten nitride (vm VWN), tantalum nitride (NbTaN), chromium nitride (nbrn), tantalum nitride (tawn), tantalum nitride (TaCrN), tantalum nitride (tawnn), tantalum nitride (trnn), NitridingTantalum tungsten (TaWN), chromium molybdenum nitride (CrMoN), chromium tungsten nitride (CrWN), and molybdenum tungsten nitride (MoWN).

The compound (i.e., oxide) composed of the first element and O (the second element) may be, for example, titanium oxide (TiO)₂) Zirconium oxide (ZrO)₂) Hafnium oxide (HfO)₂) Vanadium oxide (V)₂O₅) Niobium oxide (Nb)₂O₅) Tantalum oxide (Ta)₂O₅) Chromium oxide (Cr)₂O₃) Molybdenum oxide (MoO)₃) Tungsten oxide (WO)₃) Alumina (Al)₂O₃) And silicon oxide (SiO)₂)。

The compound (i.e., boride) composed of the first element and B (the second element) may be, for example, titanium boride (TiB)₂) Zirconium boride (ZrB)₂) Hafnium boride (HfB)₂) Vanadium Boride (VB)₂) Niobium boride (NbB)₂) Tantalum boride (TaB)₂) Chromium boride (CrB )₂) Molybdenum boride (MoB), tungsten boride (WB), aluminum boride (AlB)₁₂) And silicon boride (SIB)₄)。

The compound (i.e., carbonitride) composed of the first element, C (second element), and N (second element) may be, for example, titanium carbonitride (TiCN), zirconium carbonitride (ZrCN), hafnium carbonitride (HfCN), titanium zirconium carbonitride (TiZrCN), titanium niobium carbonitride (TiNbCN), and titanium hafnium carbonitride (TiHfCN).

the compound (i.e., oxynitride) composed of the first element, O (second element), and N (second element) may be, for example, titanium oxynitride (TiON), zirconium oxynitride (ZrON), hafnium oxynitride (HfON), Vanadium Oxynitride (VON), niobium oxynitride (NbON), tantalum oxynitride (TaON), chromium oxynitride (CrON), molybdenum oxynitride (MoON), tungsten oxynitride (WON), and aluminum oxynitride (AlON).

The solid solution of the above-mentioned compounds means a state in which two or more of these compounds are dissolved in each other's crystal structure, and means an interstitial solid solution or a substitutional solid solution.

When the above-mentioned compound is not limited to any particular atomic ratio, it is assumed that the compound includes any conventionally known atomic ratio, and is not necessarily limited to those falling within the stoichiometric range. For example, for "TiN"The ratio of the number of atoms constituting TiN is not limited to Ti: N ═ 1:1, but includes any conventionally known atomic ratio (for example, TiN and Ti)₃N₄)。

The above compounds may have any known crystal structure. The above-mentioned compound may be one compound or a combination of two or more compounds.

The binder contains at least one metal element selected from the group consisting of Li, Ca, Na, Sr, Ba and Be in a total amount of 0.001 to 0.5 mass%. By containing these metal elements in the above amounts in the binder, the tool life at the time of high-efficiency working of high-hardness quenched steel is significantly improved.

The present inventors have conducted efficient machining of high hardness quenched steel using a cutting tool using a conventional cBN sintered body, and have studied in detail the cutting edge at the time when the tool reaches the end of its life. The results confirmed that the binder had undergone selective slight breakage and abrasion. Further, the starting point of the damage was examined by a transmission electron microscope, and as a result, it was found that cracks were generated starting from the inside of the primary particles of the binder. The primary particle of the binder is presumed to be a single crystal, and the starting point of the crack is a lattice defect of the single crystal. Thus, the inventors have hypothesized that: if the lattice defects are replaced with appropriate elements, the chipping resistance and wear resistance of the binder can be significantly improved. As a result of attempting various additive elements, the present inventors found that by making the binder contain a predetermined amount of one or more metal elements selected from the group consisting of Li, Ca, Na, Sr, Ba, and Be, chipping can Be suppressed and a significantly extended tool life can Be achieved.

When the binder contains one or more metal elements in a total amount of less than 0.001 mass%, slight breakage or abrasion of the binder cannot be effectively prevented. On the other hand, when the binder contains one or more metal elements in an amount exceeding 0.5 mass% in total, the weak point (i.e., low hardness) of the one or more metal elements becomes conspicuous, and may result in a decrease in hardness of the sintered body. In order to prolong the tool life, the binder preferably contains one or more metal elements in a total amount of 0.002 mass% to 0.1 mass%, more preferably 0.004 mass% to 0.01 mass%.

The binder preferably contains one or both of Li and Ca in a total amount of 0.001 mass% to 0.1 mass%. This provides a further extended tool life. The binder more preferably contains one or both of Li and Ca in a total amount of 0.002 to 0.01 mass%, and still more preferably in a total amount of 0.004 to 0.01 mass%.

The binder preferably contains one or both of Li and Ca in an amount of 0.001 to 0.1 mass% in total, and oxygen in an amount of 0.5 to 5.0 mass%. This provides a further extended tool life. The binder more preferably contains one or both of Li and Ca in a total amount of 0.002 to 0.01 mass%, and more preferably in a total amount of 0.004 to 0.01 mass%. The binder preferably contains oxygen in an amount of 0.5 mass% or more and 5.0 mass% or less, and more preferably 1.0 mass% or more and 3.0 mass% or less.

The binder preferably contains a nitride of one or both of Ti and Zr, one or both of Li and Ca, oxygen, and carbon, and contains one or both of Li and Ca in a total amount of 0.001 mass% to 0.01 mass%, and contains carbon in an amount of 0.001 mass% to 0.5 mass%. This provides a further extended tool life. The binder more preferably contains one or both of Li and Ca in a total amount of 0.002 to 0.007 mass%. More preferably, the binder contains carbon in an amount of 0.01 to 0.20 mass%.

The kind of the metal element contained in the binder and the amount (in mass%) of the metal element contained in the binder are determined by: first, the sintered body was immersed in a fluoronitric acid (an acid mixture composed of concentrated nitric acid (concentration: 60%): distilled water: concentrated hydrofluoric acid (concentration: 47%) mixed together at a volume ratio of 2:2:1, respectively) in a closed container for 48 hours. As a result, the binder is completely dissolved in the fluoronitric acid, and the cBN particles are not dissolved and thus remain in solution. The quantitative detection of the metal elements Li, Ca, Na, Sr, Ba and Be was performed on the solution in which the binder was dissolved by inductively coupled plasma atomic emission spectrometry (ICP-AES), thereby calculating the content of each metal element contained in the binder.

The content (in mass%) of one or more metal elements in the binder can be controlled as follows: in the process of manufacturing the sintered body, powders of the metal elements Li, Ca, Na, Sr, Ba, Be, or powders of nitrides, boronitrides, and the like of these metal elements are added to the raw material powder of the binder in such amounts that the binder contains the required amount (mass%) of one or more metal elements in the sintered body.

The source of Li may be metallic lithium, lithium nitride, lithium boron nitride, lithium calcium boron nitride, and the like in powder form. The source of Ca may be calcium nitride, calcium boron nitride, lithium calcium boron nitride, etc., in powder form. The source of Na may be sodium nitride, sodium boronitride, etc. in powder form. The source of Sr may be strontium nitride, strontium boronitride, etc. in powder form. The source of Ba may be barium nitride, barium boron nitride, etc. in powder form. The source of Be may Be beryllium nitride in powder form, beryllium boron nitride, and the like. The method of adding one or more metal elements is not limited to the above method, and any method may be employed as long as the method can set the content of one or more metal elements in the binder within a desired range.

(carbon)

The binder containing a nitride as a main component preferably contains carbon (C) in an amount of 0.001 mass% to 0.5 mass%. If the carbon content is less than 0.001 mass%, the effect of improving the strength of the sintered body by solid solution of carbon may not be obtained. In contrast, if the carbon content exceeds 0.5 mass%, the carbon cannot maintain its completely solid-dissolved form in the binder material, but exists as free carbon and may reduce the strength of the sintered body. The carbon content in the binder is more preferably 0.01 mass% or more and 0.20 mass% or less.

The content of carbon (C) in the binder (in mass%) is determined in the following manner: first, the sintered body was immersed in a fluoronitric acid (an acid mixture composed of concentrated nitric acid (concentration: 60%): distilled water: concentrated hydrofluoric acid (concentration: 47%) mixed together at a volume ratio of 2:2:1, respectively) in a closed container for 48 hours. As a result, the binder is completely dissolved in the fluoronitric acid, and the cBN particles are not dissolved and thus remain in solution. The carbon content was calculated by quantitative determination of carbon by infrared absorption of the solution in which the binder was dissolved.

The content (in mass%) of carbon (C) in the binder may be adjusted as follows so as to fall within a desired range: mixing melamine (C)₃H₆N₆) Polyamide ([ -NH (CH) ]₂)₅CO-]_n) Or the like, is added to a binder powder mixture containing raw material powder of the binder, powder of the metal element, and the like, and the subsequent sintering process is performed under a controlled heat treatment temperature, time, and atmosphere. Furthermore, when the powder mixture of the binder and the cBN powder are mixed together in a cemented carbide ball mill, WC (tungsten carbide) introduced as a contaminant from the ball mill can also be used as a carbon source.

(oxygen)

In the process for producing the sintered body of the present embodiment, oxygen is introduced into the sintered body. For example, during the step of crushing and stirring the raw material powder for a binder, the step of mixing the cBN powder and the raw material powder for a binder, and the storage of the final powder product comprising the cBN powder and the raw material powder for a binder, these powders are exposed to oxygen present in the air, and thus oxygen is introduced into these powders.

The content of oxygen (O) in the binder is 0.1 mass% to 10.0 mass%. Reducing the oxygen content in the binder to less than 0.1 mass% may result in excessively high manufacturing costs. In contrast, if the oxygen content in the binder exceeds 10.0 mass%, the properties of the oxide, i.e., brittleness, become apparent, and the chipping resistance of the sintered body may be impaired. The oxygen content in the binder is preferably 0.5 mass% to 5.0 mass%, more preferably 1.0 mass% to 3.0 mass%.

The content (in mass%) of oxygen (O) in the binder was measured as follows: first, the sintered body was immersed in a fluoronitric acid (an acid mixture composed of concentrated nitric acid (concentration: 60%): distilled water: concentrated hydrofluoric acid (concentration: 47%) mixed together at a volume ratio of 2:2:1, respectively) in a closed container for 48 hours. As a result, the binder is completely dissolved in the fluoronitric acid, and the cBN particles are not dissolved and thus remain in solution. The oxygen content was calculated by quantitative determination of oxygen by infrared absorption on the solution in which the binder was dissolved.

The content (in mass%) of oxygen (O) in the binder can be controlled by controlling the manufacturing conditions in the sintered body manufacturing process, controlling the amount of oxygen in the final powder product including the cBN powder and the raw material powder for the binder, and the like. From the viewpoint of making the sintered body uniform and making the constituent particles fine, it is preferable to control the amount of oxygen by subjecting the final powder product to a reduction treatment.

For example, the reduction treatment is performed by heating the final powder product in a nitrogen atmosphere having a low oxygen partial pressure. The heating temperature is preferably 1500 ℃ to 2000 ℃, more preferably 1800 ℃ to 2000 ℃. By heating to 1800 ℃ or higher, the reduction treatment can be efficiently performed. By setting the heating temperature to 2000 ℃ or lower, particles in the final powder product can be prevented from melting and becoming coarse. Therefore, the final powder product can be prevented from having an average particle diameter after heating thereof larger than that before heating thereof.

The heating time is not particularly limited as long as it is continued until the oxygen content of the final powder product is 10.0 mass% or less, and may be, for example, 1 hour to 12 hours. The oxygen partial pressure employed in the reduction treatment is preferably 1X 10^-29Low oxygen partial pressure below atm. By heating at such a low oxygen partial pressure, the reduction treatment can be efficiently performed so that the oxygen content is 10.0 mass% or less. In addition, the reduction heat treatment in a hydrogen atmosphere or an ammonium atmosphere is also effective.

[ method for producing sintered body ]

For example, the sintered body of the present embodiment can be produced by the following method:

Raw material powders for a binder, that is, powders of one or more compounds composed of one or more first elements selected from the group consisting of group 4 elements, group 5 elements and group 6 elements in the periodic table, Al and Si, and one or more second elements selected from the group consisting of C, N, O and B, or powders of solid solutions of these compounds, are prepared.

A metal element-containing powder composed of one or more metal elements selected from the group consisting of Li, Ca, Na, Sr, Ba, and Be or nitrides, boron nitrides, and the like of these metal elements is added to a raw material powder for a binder in such an amount that the binder contains one or more metal elements in a total amount of 0.001 mass% or more and 0.5 mass% or less, and mixed in a ball mill to obtain a powder mixture for a binder. At this time, organic substances (such as melamine and polyamide) serving as a carbon source may be added and mixed together.

When the oxygen content in the powder mixture for a binder exceeds 10 mass%, the powder mixture for a binder is heated in a nitrogen atmosphere having a low oxygen partial pressure to perform a reduction treatment. For example, at 1 × 10^-29The reduction treatment performed at an oxygen partial pressure of atm or less, a reduction temperature of 1800 c, and a reduction time of 2 hours can reduce the oxygen content in the powder mixture for a binder to 10 mass% or less. Under the same conditions, the oxygen content can be reduced to 5% by mass or less when the reduction time is 5 hours, and the oxygen content can be reduced to 1% by mass to 3% by mass when the reduction time is 10 hours.

Subsequently, the powder mixture for bonding agent and the cBN powder in a desired volume ratio are prepared and mixed together using a ball mill or a bead mill, thereby obtaining a final powder product. The cBN particles have a polar surface which will be a by-product after sintering. Therefore, the content ratio (in vol%) of cBN particles in the sintered body is reduced by 0% to 2% as compared with the content ratio of cBN powder in the final powder product. Therefore, the content of cBN powder introduced in the final powder product is determined by taking into account the amount of cBN reduced by sintering.

The oxygen content in the binder may also be reduced to adjust it to the target oxygen content by subjecting the above-described final powder product to a treatment similar to the above-described reduction treatment applied to the powder mixture for a binder.

Subsequently, the final powder article is introduced into a sealed capsule made of Mo, and an ultra-high pressure device is used to increase the pressure and temperature, thereby applying a pressure of 5.0GPa to 8.0GPa and a temperature of 1400 ℃ to the final powder article, and the final powder article is maintained at the pressure and temperature for 1 minute to 30 minutes, thereby sintering the final powder article, thereby obtaining a sintered body.

[ cutting tools ]

The cutting tool of the present embodiment is a cutting tool including the sintered body described above. The cutting tool according to the present embodiment is not limited to a cutting tool formed entirely of the above sintered body, and also includes a tool in which only a part (particularly, a cutting edge part (cutting edge) or the like) is composed of a sintered body. For example, the cutting tool according to the present embodiment further includes a tool: wherein only the cutting edge portion in the base body (or the support body) made of cemented carbide or the like is composed of a sintered body. In this case, the cutting edge portion should be literally regarded as a cutting tool. In other words, the sintered body should be referred to as a cutting tool when it occupies only a part of the cutting tool.

The cutting tool according to the present embodiment is not particularly limited in shape and application. For example, there may be included drills, end mills, replacement cutting inserts for drills, replacement cutting inserts for end mills, replacement cutting inserts for milling, replacement cutting inserts for turning, metal saws, gear cutting tools, reamers, taps, cutting inserts for crankshaft milling, and the like.