JPS6335591B2 - - Google Patents

Description

[Detailed description of the invention]

This invention has excellent wear resistance, high toughness, and true density, and is particularly useful for cutting high-hardness steels that require these properties, as well as carburized and hardened steels that have a steep hardness gradient on the surface. Cubic boron nitride (CBN) exhibits excellent cutting performance when used as
The present invention relates to a method for producing ultra-high pressure sintered materials (denoted by ). Previously, the same applicant filed a patent application No. 53-100932 (Japanese Unexamined Patent Publication No. 55-31517) on carbides of metals of groups 4a, 5a, and 6a of the periodic table;
High melting point compound consisting of nitride, carbonitride, carbonate, or carbonitride: 5-50% Aluminum oxide (hereinafter referred to as Al ₂ O ₃ ): 10-50%
70%, CBN and unavoidable impurities: 25-85% (the above is volume %, the following % is volume %), and is especially used as a cutting tool for cutting high hardness steel and Ni-based heat-resistant alloys. We have filed a patent application for a CBN-based ultra-high pressure sintered material that exhibits excellent cutting performance when It is true that the CBN-based ultra-high pressure sintered material of the above-mentioned prior invention shows excellent cutting performance when cutting under normal conditions, but for the purpose of improving productivity, for example, it is difficult to make deep cuts into high-hardness steel or In cases where a relatively excessive cutting force (especially thrust force) is applied to the cutting tool, such as occurs during high-feed cutting, or when higher heat resistance is required, and when the surface of the workpiece is hard. When cutting carburized and hardened steel, etc., which has a steep gradient, the desired stable cutting performance was not achieved due to insufficient strength and toughness, and the cutting performance was not necessarily highly reliable. Therefore, the present inventors proposed CBN of the above-mentioned prior invention.
Focusing on ultra-high pressure sintered materials, we conducted research to give them high strength and toughness, and as a result, we developed CBN with an average particle size of 10 μm or less as a raw material powder.
Powder, ultrafine titanium carbide of 0.2 μm or less (hereinafter referred to as
TiC) powder, titanium nitride powder (hereinafter referred to as TiN) of 1 μm or less, ultrafine particles of 0.2 μm or less
Prepare Al ₂ O ₃ powder and Ti ₂ AlN powder of 1 μm or less, and mix these raw powders with CBN: 20 to 80%, TiC, or TiC + TiN (however, in terms of volume ratio,
TiN/(TiC+TiN)=0.05-0.5): 5-50%, Al ₂ O ₃ : 10-70%, Ti ₂ AlN: 5-20%, and after mixing this blended powder. , it is formed into a green compact by press molding, and then this green compact is pre-sintered under the conditions of a vacuum of 10 ^-2 torr or less, a temperature of 1200 to 1400°C, and a holding time of 5 to 60 minutes. When applied, during this preliminary sintering,
Ti ₂ AlN acts as a sintering aid, and the TiN decomposed from this reacts with ultrafine TiC to form highly active ultrafine titanium carbonitride (hereinafter referred to as TiCN). The result is that the ultrafine Al ₂ O ₃ , which mainly has a γ structure and a part of it has a δ structure, undergoes a crystal transformation into an α structure and becomes extremely activated through a densification process due to particle rearrangement. The pre-sintered body is a high-density, high-strength tertiary body in which the activated ultrafine TiCN particles and α-Al ₂ O ₃ are tightly intertwined and strongly bonded, and have extremely few microvoids. As the original skeleton structure is formed, the heat resistance properties of the sintered material are further improved.Subsequently, this preliminary sintered body is subjected to ultra-high pressure equipment to maintain stable temperature-pressure conditions for CBN. In other words, if ultra-high pressure sintering is performed under the conditions of temperature: 1200-1500℃, pressure: 40-70KB, and holding time: 5-60 minutes, true density sintering with excellent wear resistance, high strength, and high toughness can be achieved. They obtained the knowledge that it became possible to obtain a binding material. This invention was made based on the above knowledge, and the reason why the manufacturing conditions were limited as described above will be explained below. A. Average particle size of raw material powder (1) CBN powder If the average particle size of CBN powder exceeds 10 μm,
Due to the decrease in specific surface area, CBN
phase and activated ultrafine TiCN and ultrafine particles
The throwing power between the binder phase, which is a skeleton structure formed by strong bonding with Al ₂ O ₃ , is insufficient, and as a result, sufficient interfacial strength cannot be obtained, and CBN particles may fall off during cutting. The average particle size of the CBN powder was set to 10 μm or less because damage such as chipping is likely to occur. (2) Ultra-fine TiC powder As mentioned above, ultra-fine TiC reacts with the sintering aid Ti ₂ AlN during pre-sintering to form activated ultra-fine particles with superior heat resistance properties.
It is a component that forms TiCN, and in order to complete this reaction, the average particle size must be
It needs to be 0.2 μm or less, preferably 0.05 to 0.1 μm. That is, when the average particle size of ultrafine TiC exceeds 0.2 μm, the above reaction becomes insufficient, unreacted TiC remains, and the material no longer exhibits stable cutting edge strength at high temperatures. Note that as the ultrafine TiC powder, it is preferable to use one produced by chemical vapor deposition. (3) Ultra-fine-grained Al ₂ O ₃ powder As mentioned above, the crystal structure of ultra-fine-grained Al ₂ O ₃ is usually mainly a γ structure, with a part of it consisting of a δ structure, but it transforms into an α crystal structure during pre-sintering. Then, through a densification process due to particle rearrangement, it becomes activated, and this activated ultrafine particle
The activated ultrafine TiCN forms a skeleton structure in which Al ₂ O ₃ and activated ultrafine TiCN form a strong bond, and the ultrafine TiCN is used to produce a high-density, strong pre-sintered body with few microvoids.
However, if the average particle size exceeds 0.2 μm, not only microvoids are likely to be formed, but also the formation of a skeleton structure is insufficient, resulting in a lack of the desired high toughness and high strength. The average grain size should not exceed 0.2 μm, as this will make it difficult to manufacture the pre-sintered body. In addition, it was manufactured from commercially available anhydrous aluminum chloride by a high-temperature hydrolysis method.
The Al ₂ O ₃ powder has an average particle size of 0.2 μm or less,
Moreover, since the crystal structure is mainly composed of γ structure and a part of it is composed of δ structure, it is ideal as a raw material powder. (4) Ti ₂ AlN powder Ti ₂ AlN powder is produced by heating and reacting Ti nitride and Ti-Al intermetallic compound in vacuum or inert gas. As mentioned above, during pre-sintering, it acts as a sintering aid, and between CBN.
It is a raw material powder that is essential for forming the three-dimensional skeleton structure of TiCN-Al ₂ O ₃ , but when its average particle size exceeds 1 μm, the surface area decreases relatively and the above decomposition reaction becomes slow. Therefore, it is difficult to form a high-density skeleton structure by strengthening the bonds between the particles, so the average particle size was set at 1 μm or less. (5) TiN powder When a part of the ultra-fine TiN powder is replaced with TiN powder as necessary to take advantage of the excellent high-temperature stability of TiN itself, the above-mentioned ultra-fine TiCN and ultra-fine Al ₂ O ₃ A structure in which TiN is dispersed or partially dissolved in a skeleton structure in which TiN is strongly combined with TiC is formed, but when the average particle size exceeds 1 μm, it becomes ultrafine TiC.
The average particle size was set at 1 μm or less because not only would the reaction with Ti ₂ AlN be inhibited, but also it would be difficult to form a uniformly intertwined skeleton structure. B. Composition (1) CBN CBN has a hardness second only to diamond (6000 to 7000 Kg/mm ² in terms of Bitkers hardness), is more stable than diamond at high temperatures, and is reactive with iron group metals. Therefore, if the amount of CBN is less than 20%, the desired wear resistance cannot be achieved, while if the amount exceeds 80%, the relative If the amount is too large, the formation of a skeleton structure will be insufficient, resulting in a decrease in toughness and chipping wear during cutting, so the blending amount was set at 20 to 80%. (2) TiC TiC is a sintering aid as mentioned above.
Reacts with Ti ₂ AlN and has better heat resistance,
In addition, activated ultrafine TiCN particles are formed, which constitute a member of the skeleton structure and have the effect of improving the toughness of the sintered material, but if the content is less than 5%, the desired effect is not obtained. On the other hand, if the content exceeds 50%, TiC will remain and it will be difficult to obtain stable high temperature strength, so the content was set at 5 to 50%. In addition, in this case, replacing part of it with TiN will further improve the heat resistance properties, so it may be added as necessary, for example, in cutting applications where high heat generation is involved or thermal shock is applied. If the amount of substitution is less than 5% relative to TiC, the desired property improvement effect cannot be obtained, while if it exceeds 50%, the formation of ultrafine TiCN decreases, resulting in a skeleton structure with strong bonding strength. Therefore, the amount of TiN substituted must be 5 to 50% relative to TiC, that is, TiN/(TiC+TiN) = 0.05 to 0.5%. (3) As mentioned above, Al ₂ O ₃ Al ₂ O ₃ transforms into an activated α-crystalline structure during pre-sintering, and forms a skeleton structure rich in toughness with activated ultrafine TiCN particles. However, if the amount of CBN is less than 10%, the desired effect cannot be obtained, while if it exceeds 70%, the amount of CBN is relatively too small to achieve the desired effect. Since it would no longer be possible to ensure excellent wear resistance, the blending amount was set at 10 to 70%. (4) Ti ₂ AlN As mentioned above, Ti ₂ AlN acts as a sintering aid during preliminary sintering, reacts with ultrafine TiC to form ultrafine TiCN, and forms a bond between this and ultrafine Al ₂ O ₃ . It is essential for forming a skeleton structure with strong cohesion. Therefore, if the blending amount is less than 5%, the formation of ultrafine TiCN particles is insufficient, and the desired skeleton structure with extremely high toughness cannot be formed. On the other hand, if the blending amount exceeds 20%, TiN and AlN now remain in the sintered material, and these
Since TiN and AlN are stable compounds, they have poor reactivity and act as inhibitors to the formation of a skeleton structure with strong bonding strength.
It was set at 20%. In this case, instead of Ti ₂ AlN, TiN, AlN, TiAl, or TiAl ₃
Even if Ti 2 AlN is used as a sintering aid, the same effects as Ti ₂ AlN cannot be obtained. In other words, in the case of TiN, since it is a stable heat-resistant oxide, the constituent CBN,
It is not possible to create a reaction that binds ultrafine TiC and ultrafine Al ₂ O ₃ . Furthermore, since AlN is also a stable compound with a high vapor pressure, it has poor reactivity and acts as a sintering inhibiting factor during ultra-high pressure sintering after preliminary sintering. Furthermore, TiAl
and _TiAl3 are easily decomposed during pre-sintering, but in this case relatively excess Al is generated,
The above-mentioned AlN is formed. Therefore, metal Al also has a low melting point and generates AlN through a liquid phase reaction. In this way, during pre-sintering, TiAl, which forms AlN, It is undesirable to use TiAl ₃ or metal Al as a sintering aid. C Pre-sintering conditions Pre-sintering may have secondary effects such as deoxidation and cleaning of each component particle, but the main effect is to react ultra-fine TiC and Ti ₂ AlN to form highly active ultra-fine particles. The purpose is to generate TiCN and form a skeleton structure with high bonding strength, which is fine, has few microvoids, and is tightly intertwined with the ultrafine α-Al ₂ O ₃ activated at the same time. These reactions are carried out at a temperature as high as possible within the range that does not completely reverse transform CBN into a hexagonal crystal form, with the degree of vacuum in the atmosphere kept at 10 ^-2 torr or less, preferably 10 ^-4 torr or less. This can be carried out by heating to a temperature at which completely transformed α-Al ₂ O ₃ is obtained, that is, 1200 to 1400° C., and a reaction holding time of 5 to 60 minutes is sufficient. D Ultra-high-pressure sintering conditions Ultra-high-pressure sintering produces fewer microvoids and a higher initial density than those obtained by the preliminary sintering described above.
This is done to make a high-strength pre-sintered body true density, so it is necessary to sinter in a stable pressure and temperature range for CBN, and the pressure-temperature conditions are: pressure: 40 to 70KB,
Temperature: 1,200 to 1,500℃, and sintering time of less than 5 minutes is insufficient for sintering, while sintering time of more than 60 minutes is unnecessary. It was set at ~60 minutes. Next, the method of the present invention will be specifically explained using examples. Example As raw material powder, CBN powder with average particle size: 3 μm,
Ultra-fine TiC powder with a diameter of 0.08 μm formed by ordinary chemical vapor deposition, TiN powder with a diameter of 0.6 μm prepared by mechanical crushing, and ultra-fine grains with a diameter of 0.1 μm manufactured by high-temperature hydrolysis of anhydrous aluminum chloride. Al ₂ O ₃ powder and 0.9 μm Ti ₂ AlN powder prepared by mechanical grinding were prepared, and these raw material powders were blended into the composition shown in Table 1, and mixed in a ball mill. It was press-formed into a disk-shaped green compact with dimensions of diameter: 10 mmφ x thickness: 1 mm at a pressure of 3 ton/cm ² , and then the green compact was pre-sintered under the conditions shown in Table 1. The resulting pre-sintered body is then fused to a tungsten carbide (WC)-based cemented carbide (Co:
The ultra-high-pressure sintered material of the present invention was obtained by charging the ultra-high-pressure equipment with chips made of 12% by weight (WC: the remainder) and performing ultra-high-pressure sintering under the conditions shown in Table 1. 1 to 12 were produced respectively. Also, for comparison purposes, the above pre-sintering

【table】

[Table] (*mark: Chipping occurs on the nose)
Comparative ultra-high pressure sintered materials 1 to 12 were manufactured under the same conditions except that no sintering was performed. Next, from the ultra-high pressure sintered materials 1 to 12 of the present invention and comparative ultra-high pressure sintered materials 1 to 12 obtained as a result,
After cutting the cutting chip, brazing it to a WC-based cemented carbide holder, and polishing it, workpiece material: SCM-415 carburized and quenched material (surface hardness: H _R C60±1, carburized layer depth: A continuous cutting test was conducted under the following conditions: cutting speed: 120 m/min, depth of cut: 0.3 mm, feed: 0.2 mm/rev, cutting time: 20 min, and the flank wear width of the cutting edge was measured. The results are shown in Table 1. From the results shown in Table 1, the ultra-high pressure sintered materials 1 to 12 of the present invention can be
Both have excellent wear resistance and are capable of subsequent cutting, whereas comparative ultra-high-pressure sintering, in which the green compact is directly ultra-high-pressure sintered without pre-sintering, Binding materials 1 to 12 are all 3 to 15
Within a few minutes, a peeling phenomenon appeared on the rake face of the cutting blade, and in some cases, chipping occurred on the nose, and the service life was reached in a short period of time. As mentioned above, the CBN-based ultra-high pressure sintered material of the present invention has high strength, high toughness, and true density, so it is suitable for deep cutting and high-feed cutting of high-hardness steel, etc., which are subject to relatively excessive cutting resistance. Furthermore, when used as a cutting tool for cutting carburized and hardened steel, which has a steep hardness gradient on the surface, it exhibits excellent wear resistance and stable cutting performance, making it possible to use it for a long time.

Claims (1)

[Claims] 1. Raw material powders include cubic boron nitride powder with an average particle size of 10 μm or less, ultrafine titanium carbide powder with an average particle size of 0.2 μm or less, titanium nitride powder with an average particle size of 1 μm or less, and cubic boron nitride powder with an average particle size of 0.2 μm or less.
ultrafine aluminum oxide powder of less than m, and
It has an average particle size of 1 μm or less, and contains titanium nitride and Ti.
Prepare Ti ₂ AlN powder as a sintering aid produced by reacting -Al with an intermetallic compound. , or titanium carbide and titanium nitride (titanium nitride/(titanium carbide + titanium nitride)
= 0.05 to 0.5, volume ratio): 5 to 50%, aluminum oxide: 10 to 70%, Ti ₂ AlN: 5 to 20%, and after mixing this powder mixture, press molding. This green compact is then pre-sintered in a vacuum of 10 ^-2 torr or less at a temperature of 1200 to 1400°C and a holding time of 5 to 60 minutes. Then, TiN produced by the decomposition of Ti ₂ AlN and ultrafine titanium carbide are reacted to form fine titanium carbonitride with excellent heat resistance, and the ultrafine titanium carbonitride and ultrafine aluminum oxide are strengthened. This pre-sintered body is then heated to a temperature of 1200~
Excellent wear resistance characterized by ultra-high pressure sintering of cubic boron nitride at 1500℃, pressure: 40-70KB, holding time: 5-60 minutes under stable temperature and pressure conditions to achieve true density. and a method for producing a cubic boron nitride-based ultra-high pressure sintered material for cutting tools with high toughness. 2 Average particle size produced by chemical vapor deposition method:
The method for producing a cubic boron nitride-based ultra-high pressure sintered material for cutting tools according to claim 1, characterized in that ultrafine titanium carbide powder having a particle diameter of 0.05 to 0.1 μm is used as the raw material powder. 3 Manufactured by high-temperature hydrolysis of anhydrous aluminum chloride, the average particle size is 0.2 μm or less, and the crystal structure is mainly γ structure, with some δ
2. A method for producing a cubic boron nitride-based ultra-high pressure sintered material for cutting tools according to claim 1, characterized in that an ultra-fine aluminum oxide powder having a structure is used as a raw material powder.