JPS6220149B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is a cubic crystal material suitable for use as the cutting edge of cutting tools used for cutting high-hardness steels that require high hardness, excellent wear resistance, and toughness, as well as Ni-based or Co-based superalloys. The present invention relates to a method for producing a boron carbonitride sintered body. In recent years, when cutting materials such as high-hardness steel and Ni-based or Co-based superalloys, sintered bodies made of cubic boron nitride (hereinafter referred to as c-BN), which is a highly hard substance in addition to diamond, have been used. Although it is used as a cutting tool cutting edge, c-BN
has a problem that its hardness is lower than that of diamond, and therefore it tends to wear out easily under severe conditions. On the other hand, although a sintered body made of diamond is harder than c-BN, when it is used as a cutting tool tip for cutting high-hardness steels such as those mentioned above, or Ni-based or Co-based superalloys, Since these work materials are mainly made of iron group metals, they are currently unusable due to extremely large wear. Therefore, the present inventors conducted research to eliminate the drawbacks of the sintered body made of c-BN and to find a sintered material that can sufficiently withstand wear even under severe cutting conditions. Boron carbonitride (hereinafter c-
It was concluded that a sintered body consisting of B (denoted as C, N)) is a useful material that satisfies these conditions. In other words, since the above c-B(C,N) is made of boron nitride (BN) having a tetrahedral structure and carbon dissolved in solid solution, c-BN can maintain the chemical stability of c-BN. They recognized that it has the property of being harder than other materials. Currently, c-B(C,N) powder is used as an abrasive, and it is manufactured by a method such as that described in Japanese Patent Application Laid-Open No. 101000/1982, but these methods c-B manufactured by
Even if a cutting tool cutting edge is manufactured using (C,N) powder as a raw material powder, it has been impossible to obtain one with satisfactory cutting characteristics. The method for synthesizing c-B(C,N) powder described in JP-A-53-101000 is to synthesize hexagonal or amorphous boron carbonitride compound from group 8 of the periodic table. Co, Ni, or Fe, which are metals,
In the presence of a solvent consisting of a mixture or alloy with Al, phase transformation is carried out under conditions of a pressure of 50 kilobar or more and a temperature of 1300°C or more. The present inventors believe that the cause of the poor sinterability of c-B(C,N) powder obtained by the above-mentioned known method is due to the components and physical properties of the powder itself obtained by such method. The c-B(C,N) sintered body has excellent cutting performance from two points of view: the sintering conditions for obtaining the sintered body have not yet been elucidated. As a result of further research to obtain this, we obtained the findings shown below. That is, (a) c- synthesized under conditions without using a solvent metal, as proposed by the present inventors in another patent application.
B(C,N) powder has less impurities other than C, N, and B;
-B(C,N) powder is a raw material powder for producing a good sintered body. (b) As the raw material powder for the sintered body, c-B(C,N) powder, which is fine grained and has poor crystallinity, is desirable from the viewpoint of sinterability. (c) Fine-grained c-B(C,N) powder with poor crystallinity can be easily produced by synthesis without using a solvent metal. (d) When a mixed powder containing c-B(C,N) powder and a portion of hexagonal boron carbonitride (hereinafter referred to as h-B(C,N)) powder is used as the raw material powder, sintering The body tends to become dense. (e) C formed during pressurization and temperature rise for sintering
If the bridge portion between B(C,N) particles is sintered as is, the constriction at the bridge portion will not grow and the shape will be brittle;
When sintering with a small amount of h-B(C,N) present on the (C,N) particle surface, sintering is promoted at the bridge part and the constriction is eliminated.
c-B(C,N) particles become firmly bonded to each other. Therefore, this invention was made based on the findings shown in (a) to (e) above, and includes: c-B(C,N) powder: 70% by volume or more, h-B(C,N) Powder: A mixed powder consisting of the remaining c-B (C,
N) 80% by volume or more of the powder is fine powder with a particle size of 3 μm or less, and on the other hand, the average particle size of the h-B(C,N) powder is the average particle size of the c-B(C,N) powder. , and more than 50% by volume has a particle size of 1μ.
A green compact of mixed powder, which is a fine powder of less than m, is heated to 1800℃.
At the following temperature and under a pressure of 50 kilobar or more, and temperature T (℃) and pressure P (kilobar)
After sintering under stable conditions of h-B(C,N) satisfying the relationship T-10P>800, at a temperature of 1300°C or higher and under a pressure of 100 kilobar or lower, and T - By sintering under stable conditions of c-B (C, N) that satisfies 10P≦800, it has excellent hardness and wear resistance.
In particular, it is characterized in that it produces a dense sintered body consisting essentially of c-B (C, N), which is suitable for use as a cutting tool edge. In addition, the appropriate pressurization time under stable conditions for h-B(C,N) above is 10 minutes or more and less than 2 hours, and c
- It is preferable that the pressurization time under stable conditions of B(C,N) be 10 minutes or more. Next, in the method for producing a c-B(C,N) sintered body of the present invention, c-B(C,N) powder and h-B
The reason why the mixing ratio with the (C,N) powder, the particle size of each powder, and the range of temperature and pressure during sintering were limited as described above will be explained. (a) Particle size and mixing ratio of raw material powder The smaller the particle size of the raw material powder, the easier sintering progresses, and the cleavage strength of individual crystal grains in the manufactured sintered body is high, resulting in a sintered body with high toughness. Although a solid is obtained, the particle size of the c-B(C,N) powder is 3 μm.
If it exceeds this, coarse particles tend to form bridges (a phenomenon in which powders are not compressed uniformly or are not sintered uniformly), creating large gaps, and the relative pressure within these spaces increases. The particle size should not exceed 3 μm, since uniform sintering will be difficult to proceed due to the low particle size. However, c-B (C,
N) If more than 80% by volume of powder is mixed, even if the remaining c-B(C,N) powder with coarse particles exceeding 3 μm is included, the above-mentioned bridge will not be formed, resulting in a uniform product. As sintering begins to take place,
It is necessary to blend c-B(C,N) powder with a particle size of 3 μm or less in an amount of 80% or more by volume. In addition, c-B (C, N) powder and h-B (C,
The relationship between the c-B(C,N) particles and the N) powder is that the c-B(C,N) particles have a continuous skeleton structure (a framework structure formed by the particles having contact parts), and the h-B(C,N) particles are in the micro gaps between them. , N) powder is preferably in a state that the h-B(C,
N) Powder is converted to c-B(C,N) while c-
It acts in the direction of promoting sintering at the contact area between c-B(C,N) particles by eliminating the constriction at the contact area between B(C,N) particles, and as a result, a strong c-B
(C,N) particle bonds can be obtained. Furthermore, the reason why the blending amount of c-B(C,N) powder is set to be 70% by volume or more is that if the blending amount of c-B(C,N) powder is less than 70% by volume, h-B
If the amount of (C,N) powder blended is too large, h-
B(C,N) powder tends to take a continuous structure, and if sintering is performed in this state, not only will the volume change become large, but also unconverted h-B will be contained in the sintered body.
This is based on the reason that (C,N) remains and the strong particle bond between the c-B(C,N) particles is damaged. In addition, the average particle size of h-B(C,N) powder is c-
If the particle size is larger than the average particle size of the B(C,N) powder, the h-B(C,N) powder tends to localize in the mixed powder, and even after sintering, unconverted h-B(C,N) powder remains in the sintered body. -B(C,N) tends to remain, so
The average particle size of h-B(C,N) powder is c-B(C,
N) Must not be larger than the average particle size of the powder. Furthermore, when more than 50% by volume of h-B(C,N) powder has a particle size larger than 1 μm, h
- There is no large shape and dimensional difference between B(C,N) powder and c-B(C,N) powder,
Since the frequency of skeleton formation between c-B(C,N) particles decreases and it becomes impossible to secure strong particle bonds, h-B(C,
N) At least 50% by volume of the powder must be fine powder with a particle size of 1 μm or less. (b) Temperature and pressure during pressure sintering For sintering, the raw material mixed powder is first
(C,N) under stable conditions and c-B(C,
By placing the c-B(C,N) particles under conditions that are not too far from the stability conditions of -B(C,N) When sintered under stable conditions, c
- A strong bond between B(C,N) particles can be obtained. However, during the first stage of pressure sintering, if the pressure is less than 50 kbar and the temperature is less than 1300°C, almost no phase transformation occurs near the surface of the c-B(C,N) particles; If the pressure exceeds 100 kbar or the temperature exceeds 1800°C, sintering will progress too quickly and will tend to progress locally, resulting in some parts of the sintering remaining even after sintering is complete. Temperature and pressure ranges excluding the above-mentioned disadvantageous temperature and pressure ranges, as h-B(C,N) may remain or grain growth may increase, making the structure more likely to become non-uniform. must be done. However, the range of temperature-pressure conditions excluding the above-mentioned disadvantageous temperature and pressure ranges includes an additional h
-B (C, N) includes an unstable region, so the temperature-pressure condition range must exclude this region.
In other words, in the graph shown in Figure 1 with pressure P on the vertical axis and temperature T on the horizontal axis, at 50 kilobar,
The line connecting the 1300°C point and the 1800°C point at 100 kilobar is on the higher temperature and lower pressure side, that is, in the temperature and pressure range where T-10P>800, that is, the diagonal line in Figure 1 is applied. The sintering conditions within the above range must be maintained during the first stage pressure sintering. In addition, during the second stage pressure sintering, if the pressure is less than 50 kilobar and the temperature is less than 1300℃, h-
Almost no phase transformation of B(C,N) to c-B(C,N) occurs; on the other hand, when the pressure exceeds 100 kbar and the temperature exceeds 1800°C, grain growth increases and the structure deteriorates. tend to be unevenly distributed. In this case as well, even if the temperature and pressure are within the range excluding the above disadvantageous range, c-B(C,
N) must not deviate from the stable range, so the second
The shaded area in the figure, i.e. 1300
It is necessary to maintain sintering conditions within the range of temperature above .degree. C. and pressure below 100 kilobar, and further satisfying the condition of T-10P≦800. Next, the present invention will be specifically explained using examples and comparing with comparative examples. As raw material powders, c-B (C, N) powder and h- powder each having a particle size distribution shown in Table 1 were used.
B (C, N) powder is prepared, and both raw material powders are blended in the proportions shown in Table 1. After mixing, a green compact is formed from this mixed powder under normal compression conditions, and then these Sintered bodies 1 and 2 of the present invention and comparative sintered bodies 1 to 1 were obtained by performing first and second stage sintering of the green compacts under the same pressure sintering conditions shown in Table 1. 8 were produced respectively. The comparative sintered bodies 1 to 8 were manufactured under conditions shown in Table 1 under which the conditions marked with * were outside the scope of the present invention.

[Table] Comparative sintered bodies 1 to 8 obtained as a result are all easily scratched and scratched by commercially available c-BN sintered bodies, and have significantly inferior wear resistance. It was hot. Furthermore, trace amounts of hexagonal boron carbonitride were detected in comparative sintered bodies 1 to 3, and considerably large amounts of hexagonal boron carbonitride were detected in comparative sintered bodies 4 to 8. On the other hand, the sintered bodies 1 and 2 of the present invention each substantially consist of c-B (C, N) single phase,
Even when rubbed with a commercially available c-BN sintered body, there was no scratch at all. Next, a cutting edge was cut out from the sintered bodies 1 and 2 of the present invention, brazed onto a tungsten carbide-based cemented carbide alloy, and ground, thereby using the sintered body of the present invention as a cutting edge. Cutting tools (hereinafter referred to as cutting tools of the present invention) 1 and 2 were manufactured. The above-mentioned cutting tools 1 and 2 of the present invention and commercially available c-BN
When cutting Haynes Alloy Stellite No. 6, a Co-based superalloy, using a conventional cutting tool manufactured from a sintered body under the same conditions, the conventional cutting tool reached the end of its life after machining 400 pieces. On the other hand, cutting tool 1 of the present invention reached its lifespan after 2000 pieces, and cutting tool 2 of the present invention reached its life after 2500 pieces. As described above, according to the present invention, a sintered body having high hardness and excellent wear resistance and toughness can be manufactured, and this sintered body can be made of high hardness steel, Ni-based or Co When used as the cutting edge of a cutting tool for cutting base superalloys, etc., it exhibits extremely excellent cutting characteristics, which brings about industrially useful effects.

[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. A mixed powder consisting of: 1. cubic boron carbonitride powder: 70% by volume or more; hexagonal boron carbonitride powder: the remainder; and 80% by volume or more of the cubic boron carbonitride powder. is a fine powder with a particle size of 3 μm or less, and on the other hand, the average particle size of the hexagonal boron carbonitride powder is smaller than the average particle size of the cubic boron carbonitride powder, and moreover, more than 50% by volume of the hexagonal boron carbonitride powder is particles. A green compact of mixed powder, which is a fine powder with a diameter of 1 μm or less, is prepared at a temperature (T) of 1800°C or less, a pressure (P) of 50 kilobar or more, and the temperature T (°C) and pressure P (kilobar) are After the first stage pressure sintering under the condition that the relationship T-10P>800 is satisfied, the temperature (T) is 1300℃ or more, the pressure (P) is 100 kilobar or less, and the temperature T (°C) and pressure P (kilobar), which is characterized in that the second stage pressure sintering is performed under conditions that satisfy T-10≦800, and is made essentially only of cubic boron carbonitride. A method for manufacturing sintered bodies for cutting tool edges.