JPS6228111B2 - - Google Patents

Description

[Detailed description of the invention]

This invention has high hardness as well as excellent wear resistance and toughness, and is particularly useful as a cutting tool edge used for cutting high-hardness steel, Ni-based or Co-based super alloys, etc., which require these properties.
The present invention also relates to a method for producing a cubic boron carbonitride-based sintered material suitable for use as wear-resistant tools such as dies and nozzles. In recent years, sintered materials whose main component is cubic boron nitride (hereinafter referred to as c-BN), which has a high hardness comparable to diamond, have been used for cutting materials such as high-speed steel and Ni-based or Co-based superalloys. is used as the cutting edge of cutting tools, but the c-
BN-based sintered materials have lower hardness than diamond, so when used under harsh conditions, they are prone to wear and chipping due to lack of toughness. ing. This c-
The causes of the lack of toughness in BN-based sintered materials are residual strain due to an excessively large difference in coefficient of thermal expansion between c-BN particles and additive particles, and a decrease in sinterability due to significant concentration changes between different types of particles. This is thought to be due to a decrease in particle interface strength. On the other hand, although diamond is harder than c-BN-based sintered material, when it is used as a cutting tool edge to cut high-hardness steel, Ni-based or Co-based superalloy, for example, Currently, the workpiece material of this method is mainly composed of iron group metals, which causes extremely large wear and cannot be used for practical use. Therefore, from the above-mentioned viewpoints, the present inventors have developed a material that has both excellent wear resistance and toughness, and that can be used as a cutting tool tip for cutting high-speed steel, Ni-based or Co-based super alloys, etc. In order to obtain a material that exhibits excellent performance when used as wear-resistant tools such as dies and nozzles, we developed c-BN, which is made of boron nitride (BN) with a tetrahedral structure and carbon dissolved in it. As a result of research focusing on cubic boron carbonitride (hereinafter referred to as c-B (CN)), which has higher hardness than c-BN while maintaining chemical stability, we found that (a) conventional , c-B(CN) powder is used as an abrasive, for example, by the method described in JP-A-53-101000, that is, hexagonal or amorphous boron carbonitride compound is cyclically polished. Co, Ni, or Fe, which are metals in Group 8 of the Table of Laws,
It is manufactured by a method of phase transformation in the presence of a mixture with Al or a solvent consisting of an alloy thereof at a pressure of 50 Kb (kilobar) or higher and a temperature of 1300°C or higher, but these conventional methods c-B for abrasives manufactured by
Even if (CN) powder is used as a raw material powder to manufacture cutting tool edges, wear-resistant tools, etc., the sinterability is extremely poor, so if it is put into practical use, it will not exhibit satisfactory performance. (b) However, when c-B(CN) powder is synthesized under conditions without using a solvent metal as in the conventional method, the resulting c-B(CN)
The powder has relatively high purity without contamination with the solvent metal, etc., and the c-B(CN) powder containing few impurities has extremely good sinterability. (c) The c-B(CN) powder should have fine particles and poor crystallinity and exhibit good sinterability. (d) Fine-grained c-B(CN) powder with poor crystallinity is
Easily synthesized under conditions that do not use solvent metals. (e) The dense c-B(CN)-based sintered material
(CN) powder mixed with boron (hereinafter referred to as B) powder and hexagonal boron carbonitride (hereinafter referred to as h-B(CN)) as a raw material powder. What you can get from it. (f) c- formed during pressurization and temperature rise during sintering
If the bridge parts between B(CN) particles are sintered as they are, the constrictions at the bridge parts will remain in a state without growth, so only a brittle sintered material will be obtained, but c-B(CN) particles When sintering is performed with h-C (BN) particles and B particles present in contact with each other on the surface, the c-B
c-B(CN) because sintering at the bridge between particles is promoted and the constriction is eliminated.
Bonds between particles become significantly stronger. that's all
The findings shown in (a) to (f) were obtained. This invention was made based on the above knowledge, and in terms of volume %, B powder: 0.1 to 2%, h-B(CN) powder: 1 to 30%, c-B(CN) powder: the remainder. , and the c-B
80% or more of the (CN) powder is fine with a particle size of 3 μm or less, while the average particle size of the h-B(CN) powder is smaller than the average particle size of the c-B(CN) powder, Moreover, a green compact is formed from a mixed powder of which 50% or more is composed of fine powder with a particle size of 1 μm or less under normal conditions, and then the green compact is heated at a temperature (T ₁ ) of 1800°C or less and a pressure of (P ₁ ): 50Kb or more, the relationship between temperature (T ₁ ) and pressure (P ₁ ) is T ₁ −10P ₁
After the first stage pressure sintering under conditions satisfying >800 _, the temperature (T ₂ ) and _the pressure By performing the second stage pressure sintering under conditions where the relationship (P ₂ ) satisfies T ₂ −10P ₂ ≦800, B: 0.1 to 2%, c-B(CN) and unavoidable Impurities: The remainder has a composition of c-, which exhibits outstanding performance when used in the manufacture of tools, etc.
This method is characterized by producing a B(CN)-based sintered material. In addition, when manufacturing the c-B(CN)-based sintered material of this invention, the holding time under the above heating and pressurizing conditions is determined based on the stability of the c-B(CN) powder and h-B(CN) powder. 10 minutes to 2 hours is appropriate to ensure that. Next, the reason why the manufacturing conditions and component composition of the c-B(CN)-based sintered material of the present invention are limited as described above will be explained. A. Manufacturing conditions (a) Amounts of B powder and h-B(CN) powder In the green compact according to the present invention, c-
The B (CN) powder forms a continuous skeleton structure (a framework structure formed by the powders having contact parts), and the B powder and h
-B(CN) powder is preferably mixed with the powder, so that during sintering, B powder adheres to the surfaces of c-B(CN) powder and h-B(CN) powder. By removing oxygen in the form of boron oxide, the surface is activated and sinterability is promoted, and both of the above-mentioned B
A mutual substitution reaction occurs with the B component in the (CN) powder to improve the bonding strength between the powders. On the other hand, the h-B(CN) powder is converted to c-B(CN) while c-B( The c-B(CN) particles are strongly bonded by eliminating the constriction at the contact area between the c-B(CN) particles and promoting sintering at the contact area between the c-B(CN) particles. This makes it possible to obtain a c-B(CN)-based sintered material. However, B powder (preferably average particle size 3μ)
If the amount of (preferably less than m) is less than 0.1%, the desired effect cannot be obtained from the above action,
On the other hand, if the amount exceeds 2%, the effect of the above-mentioned B component becomes too strong, making it impossible to secure the desired properties, so the amount of B powder blended is set at 0.1 to 2%. In addition, the blending amount of h-B (CN) powder is 1%.
Even if it is less than that, the desired effect cannot be obtained from the action brought about by the h-B(CN) powder, and
On the other hand, if it is blended in excess of 30%, the relative h-
The amount of B(CN) powder blended is too large,
The h-B(CN) powder itself tends to take on a continuous structure, and when sintered in this state,
Not only will the volume change become large, but unconverted h-B(CN) will remain and the strong particle bond between the c-B(CN) particles will be impaired, so the blending amount should be increased from 1 to 1. It was set at 30%. (b) Particle size of c-B(CN) powder In general, the smaller the particle size of the raw material powder, the easier sintering will progress, and the cleavage strength of individual crystal grains will be higher in the manufactured sintered material. A sintered material with high toughness can be obtained. Therefore, if the particle size of c-B(CN) powder exceeds 3 μm, bridging occurs between coarse powders (powders are not compressed uniformly, or If the thickness exceeds 3 μm, it is easy to create a large gap space (shelf hanging phenomenon that occurs as a result of not being sintered uniformly), and the pressure within this space is relatively low, making it difficult to proceed with uniform sintering. The particle size shall not be too large.
However, c-B(CN) with a particle size of 3 μm or less
If more than 80% powder is mixed, the remaining 3μ
Even if c-B (CN) powder with coarse grains exceeding m is included, the above-mentioned bridges are not formed, and as a result, uniform sintering is performed. It is necessary to mix 80% or more of B(CN) powder. (c) Particle size of h-B(CN) powder The average particle size of h-B(CN) powder is c-B
If the particle size is larger than the average particle size of the (CN) powder, h-B(CN) powder tends to be localized in the mixed powder, and even after sintering, unconverted h-B(CN) powder remains in the sintered material. ) tends to remain, so the average particle size of the h-B(CN) powder should not be made larger than the average particle size of the c-B(CN) powder. In addition, more than 50% of h-B(CN) powder is 1
When the particle size becomes larger than μm, h
- There is no large shape and dimensional difference between B(CN) powder and c-B(CN) powder, and the frequency of skeleton formation between c-B(CN) particles is reduced, resulting in strong particle bonding. Because it becomes impossible to secure
At least 50% of the h-B(CN) powder must be fine powder with a particle size of 1 μm or less. (d) Temperature and pressure during pressure sintering For sintering, the raw material mixed powder is first
- Under stable conditions of B(CN) powder, and c-
By placing the c-B(CN) powder under conditions that are not too far from the stable conditions, a part of the c-B(CN) powder near the surface undergoes a phase transformation to h-B(CN), and then c- When sintering is performed under stable conditions for B(CN) powder, strong bonding between c-B(CN) particles can be obtained. However, during the first stage pressure sintering, if the pressure is less than 50Kb and the temperature is less than 1300℃, c
- There is almost no phase transformation near the surface of the B(CN) powder.On the other hand, if the pressure exceeds 100Kb or the temperature exceeds 1800℃, sintering progresses too quickly, resulting in localized Sintering progresses easily, and as a result, some h
- Since B(CN) may remain or grain growth may increase, resulting in a non-uniform structure, the temperature-pressure range must be set excluding the above-mentioned disadvantageous temperature and pressure ranges. . However, the above unfavorable temperature −
Since the temperature-pressure range excluding the pressure range further includes the unstable region of h-B(CN), the temperature-pressure range must also exclude this range. In other words, in the graph shown in Figure 1 with pressure P ₁ on the vertical axis and temperature T ₁ on the horizontal axis, a point at pressure: 50 Kb and temperature: 1300°C, and a point at pressure: 100 Kb and temperature: 1800°C. The side with higher temperature and lower pressure than the connecting straight line, that is, the inequality:
Temperature-pressure range that satisfies T ₁ −10P ₁ >800,
In other words, the sintering conditions within the shaded range in FIG. 1 must be observed in the first stage pressure sintering. In addition, during the second stage pressure sintering, the pressure is 50Kb.
If the temperature is less than 1300℃, h-
Almost no phase transformation of B(CN) to c-B(CN) occurs, and on the other hand, when the pressure exceeds 100 Kb and the temperature exceeds 1800°C, grain growth increases and the structure becomes non-uniform. easy to become.
In this case as well, even if the temperature and pressure are within the range excluding the above disadvantageous range, c-B
Since it is important not to deviate from the stability region of (CN), the inequality in the shaded range in Figure 2, that is, the range of temperatures above 1300℃ and pressures below 100Kb: T ₂ −
It is necessary to perform sintering in a temperature-pressure range that satisfies the condition of 10P ₂ ≦800. Next, the present invention will be specifically explained using examples and comparing with comparative examples. As raw material powders, c-B (CN) powder and h-B powder each having a particle size distribution shown in Table 1 were used.
(CN) powder and B powder with an average particle size of 2 μm are prepared, and these raw material powders are blended in the proportions shown in Table 1. After mixing, this mixed powder is compacted under normal compression conditions. The sintered materials 1 to 1 of the present invention are obtained by molding the compacts and then subjecting these green compacts to first and second stage pressure sintering under the same pressure sintering conditions shown in Table 1. 4 and Comparative Sintered Materials 1 to 6 were produced, respectively. The comparative sintered materials 1 to 6 were manufactured under the conditions shown in Table 1, where the conditions marked with an asterisk (*) were outside the scope of the present invention. Comparative sintered materials 1 to 6 obtained as a result were all easily scratched and scratched by commercially available c-BN-based sintered materials, and had significantly inferior wear resistance. Ta. Moreover, comparative sintered materials 1 to 3 contained a small amount of h-, and comparative sintered materials 4 to 6 contained a considerably large amount of h-.

[Table] B (CN) was observed. On the other hand, the above-mentioned sintered materials 1 to 4 of the present invention are
All of them consisted of component B in substantially the same amount as the blended amount, c-B(CN), and inevitable impurities, and were completely free of scratches even when rubbed with a commercially available c-BN-based sintered material. . Next, a cutting edge is cut out from the sintered materials 1 and 3 of the present invention, brazed onto a base metal made of tungsten carbide-based carbide material, and ground. Cutting tools A and B used as cutting edges were manufactured. Haynes Alloy Stellite No. 6, a Co-based superalloy, was cut using these cutting tools A and B and a conventional cutting tool manufactured from a commercially available c-BN-based sintered material under the same conditions. However, while the conventional cutting tool reached the end of its life after machining 400 pieces, the cutting tool A and the cutting tool B reached the end of their life after machining 1800 pieces and 2700 pieces, respectively. As described above, according to the present invention, c-B has high hardness and excellent wear resistance and toughness.
(CN)-based sintered material can be produced, and this c-B(CN)-based sintered material can be used as a cutting tool cutting edge for cutting high-speed steel, Ni-based or Co-based superalloy, etc. Furthermore, when used in the manufacture of wear-resistant tools such as dies and nozzles, it provides industrially useful effects such as extremely superior performance.

[Brief explanation of the drawing]

FIGS. 1 and 2 are graphs showing the scope of the present invention with respect to first-stage and second-stage pressure sintering conditions.

Claims (1)

[Scope of Claims] 1 Boron powder: 0.1 to 2% by volume, hexagonal boron carbonitride powder: 1 to 30% by volume, cubic boron carbonitride powder: the remainder; At least 80% by volume of the boron carbonitride powder is fine powder with a particle size of 3 μm or less, while the hexagonal boron carbonitride powder has an average particle size smaller than the average particle size of the cubic boron carbonitride powder, and More than 50% by volume of the particle size is 1.
A green compact is formed from a mixed powder composed of fine powder of μm or less under normal molding conditions, and then the green compact is heated at a temperature (T ₁ ) of 1800°C or less and a pressure (P ₁ ) of 50.
Above kilobar, temperature (T ₁ ) and pressure (P ₁ )
After the first stage pressure sintering under conditions that satisfy the relationship T ₁ −10P ₁ > 800, the temperature (T ₂ ):
1300℃ or more, pressure (P ₂ ): 100 kilobar or less, and the relationship between temperature (T ₂ ) and pressure (P ₂ ) is T ₂
A method for producing a cubic boron carbonitride-based sintered material having toughness and wear resistance, the method comprising performing a second stage pressure sintering under conditions satisfying −10P ₂ ≦800.