JPS6242989B2 - - Google Patents

Description

[Detailed description of the invention]

Cubic boron nitride (hereinafter abbreviated as CBN) is a material with the second highest hardness after diamond, and is synthesized under ultra-high pressure and high temperature. Currently, it is already being used as abrasive grains for grinding, and sintered bodies made of CBN bonded with Co, etc. are also used in some cutting applications. When this CBN sintered body was used as a cutting tool, it had the disadvantage that the cutting edge of the tool would break at an early stage, especially when there was interrupted cutting. The present invention relates to a new CBN sintered body that overcomes these drawbacks and has high toughness and excellent wear resistance. As mentioned above, CBN is a material that has high hardness and excellent heat resistance and wear resistance. Various attempts have been made to sinter only this CBN; for example, as described in Japanese Patent Publication No. 39-8948,
It is approximately 70kb or more and needs to be sintered at ultra-high pressure and high temperatures of over 1900℃. Current ultra-high-pressure, high-temperature equipment can generate such high-pressure, high-temperature conditions, but if the equipment is scaled up on an industrial scale, the number of lifetimes of the high-pressure, high-temperature generating section is limited, making it impractical.
Furthermore, although a sintered body made only of CBN has high hardness, it has poor toughness when used as a tool. The inventors used Ti, Zr, which are transition metals of groups a, a, and a of the periodic table, as binders for CBN.
A compound containing Cu or Cu and an iron group metal in a mixture or mutual solid solution of one or more of Hf, V, Nb, Ta, Cr, Mo, and W or a compound containing Al is used, and By finding appropriate manufacturing conditions, we were able to obtain a highly hard sintered body with a CBN content of 20 to 90% by volume, which has unprecedented wear resistance and toughness. A similar study was also conducted on wurtzite boron nitride, which is another form of high-pressure phase boron nitride, and results similar to those obtained using CBN were obtained. Details will be given below regarding a sintered body using CBN as a hard wear-resistant component, but the same can be said when using a wurtzite type or a mixture of CBN and wurtzite type boron nitride. As mentioned above, a sintered body made only of CBN has drawbacks such as difficulty in manufacturing and insufficient strength of the sintered body itself. Therefore, it is possible to improve these defects by adding an appropriate binder to CBN. One of the known methods is to use a metal bonding material, and an example is a commercially available sintered body of CBN bonded with metal Co or the like. A sintered body using this Co as a binder has low toughness as described above. To investigate the cause of this, Co
The composition of the CBN sintered body of the binder was investigated using X-rays. As a result, in addition to CBN, a large amount of Co boride was detected in the sintered body, but no metallic Co was observed, indicating that the binding material of this CBN sintered body was Co boride. Usually, these borides are hard but very brittle substances;
It is presumed that such a sintered body has low toughness. The present inventors investigated a binder phase with toughness, created various sintered bodies, and examined their toughness.
As a result, Ti, Zr, Hf, which are group a, a, and a transition metals of the periodic table, were used as binders for CBN.
We have discovered that a sintered body with excellent toughness and wear resistance can be produced by using V, Nb, Ta, Cr, Mo, or W, an Al compound, Cu or Cu, and Ni or/and Co, which is an iron group metal. The reason why the sintered body of the present invention has high toughness is presumed to be as follows. That is, the sintered body of the present invention has
As a result of line diffraction, in the bonded phase, periodic table a,
There was a portion where transition metals of groups A and A existed in a metallic state and a small amount of transition metal boride. If the adhesive strength between CBN and the binder is high, cracks that occur will propagate within the grains of CBN and the binder phase, but since the transition metals in the binder phase have high toughness, cracks will not occur in the sintered body. However, it is thought that this metal inhibited the propagation of cracks, preventing them from growing and resulting in high toughness. When we actually applied an indentation to the sintered body using a Bitkers indenter and observed the propagation of cracks, we found that the propagation of cracks was very small and that most of the cracks were stopped by the transition metal in the binder phase. Furthermore, there were no cracks along the bonding interface between the CBN particles and the binder. As described above, the bonding strength between CBN and the binder is increased,
Furthermore, by allowing the transition metal to remain in the metal state in the binder, it was possible to produce a sintered body with excellent toughness and wear resistance, and the reason for this will be discussed below. In producing the sintered body of the present invention, the temperature is raised under high pressure. At this time, Cu or Cu and iron group metal M ₁ react with Al and transition metal M ₂ to form a liquid phase with a low melting point, and CBN and penetrate uniformly into the interface of transition metals. M ₂ −Al−Cu or M ₂ − extending into this interface
M ₁ −Al−Cu has good affinity with CBN and transition metals, and a portion of this liquid phase reacts with CBN and transition metals, probably increasing the bonding strength between CBN and transition metals. . In addition, during sintering, the liquid phase containing Cu surrounds CBN and the transition metal, preventing direct contact between CBN and the transition metal, and suppressing the diffusion of boron into the transition metal, so the transition metal remains in a metallic state. This is thought to have made it possible to exist in the bonded phase. In fact, sintered bodies that do not contain Cu, such as CBN, transition metals, and Al, or those to which iron group metals are added, have a large amount of transition metal boride, and are poor in toughness. The content of CBN in the sintered body of the present invention is expressed by volume.
20% or more and 90% or less is good. CBN content is 20%
If it is less than that, the effect of containing CBN cannot be fully exhibited. Furthermore, if the CBN content exceeds 90%, the amount of transition metal becomes too small, making it impossible to obtain a sintered body with high toughness. Next, the Al content is preferably 5% or more and 30% or less. When the Al content is less than 5%, the affinity between the CBN interface and the liquid phase is lost, and the bonding strength between the CBN and the transition metal decreases. Furthermore, if the Al content exceeds 30%, the hardness of the sintered body decreases. Further, the content of Cu or Cu and iron group metals is preferably 1% or more and 50% or less by weight. If the content of Cu or Cu and iron group metal is less than 1%, it will not be possible to sufficiently suppress the generation of transition metal borides in the sintered body, and if it exceeds 50%, the hardness of the sintered body will decrease. This will cause the tool performance to deteriorate. In particular, when using Cr, Mo, and W from group a of the periodic table as transition metals, Cu does not have good affinity with these transition metals.
By containing an iron group metal having good affinity with Cr, Mo, and W, adhesion with these transition metals is improved, and toughness and wear resistance are also improved. The amount of iron group metal contained is preferably equal to or less than the same amount of Cu by weight. If this value is exceeded, a large amount of boride with the iron group metal is generated, resulting in a decrease in toughness and wear resistance. The content of metals in groups a, a, and a of the periodic table is
20-94% by weight is good. When the content is less than 20%, the strength of the binder decreases because the amount of these high-strength metals decreases. On the other hand, when it exceeds 94%, Al, Cu,
This is not preferable because the content of Ni, Co, etc. decreases. Various methods can be considered for adding Al, Cu, or Cu and iron group metals. The simplest method is to add CBN as a metal or in the form of a compound to a mixed powder of CBN and transition metal before sintering. Also, Al, Cu
Alternatively, Cu and iron group metals can be melted and introduced from the outside of the sintered body during sintering. The grain size of the CBN crystal used in the present invention needs to be 10 μm or less in view of the performance of the sintered body as a tool. If the crystal grains are coarse, the strength of the sintered body will be reduced, and especially when used as a cutting tool, the finer the crystal grains, the better the machined surface can be obtained. The sintered body is manufactured using ultra-high pressure and high temperature equipment used for diamond synthesis at a pressure of over 20kb and a temperature of over 900℃. Particularly preferred sintering pressure and temperature conditions are pressure 30kb ~ 70kb and temperature 1100℃ ~
The temperature is 1500℃. The upper limits of these pressure and temperature conditions are both within the range of practical operating conditions for ultra-high pressure and high temperature equipment on an industrial scale. Furthermore, the pressure and temperature conditions are
It is necessary to carry out the process within the stability range of high-pressure phase type boron nitride shown in the figure. When using such an excellent sintered body as a cutting tool, the high hardness sintered body only needs to be used in the part that will become the cutting edge.
Its performance can be fully demonstrated by bonding it to cemented carbide, which has excellent thermal conductivity. This will be explained in more detail below with reference to Examples. Example 1 A mixed powder was prepared consisting of 70% by volume CBN powder with an average particle size of 5 μm and the balance being binder powder. Binding material powders are W, Al, Cu, and Ni, each weighing 80%.
%, 10%, 6%, 4% composition.
The material used was one that was heated at 1000°C for 30 minutes and then ground. this
Mixed powder of CBN and binder was mixed into an outer diameter of 14 mm and an inner diameter of 10 mm.
A cemented carbide having a composition of WC-6% Co (outer diameter 10 mm, height 2.5 mm) was placed in a Mo container (0.4 g). Furthermore, on top of this is a cemented carbide (outer diameter 10 mm, height 2
mm), a Mo stopper was placed, and the entire container was placed in an ultra-high pressure device used for diamond synthesis.
The pressure was increased to 50kb and then heated to a temperature of 1350°C and held for 20 minutes. The removed sintered body was ground using a diamond grindstone until a highly hard sintered body appeared, and further polished using diamond paste. When observed with an optical microscope, it was found to be a dense sintered body with no pores. As a result of investigating the products of this sintered body by X-ray diffraction, it was found that CBN, W,
In addition to AlN and Cu, trace amounts of Ni, AlB ₂ and borides of Ni and W were detected. For comparison, a sintered body with the above composition excluding Cu was also produced under the same conditions and examined by X-ray diffraction. As a result, borides of CBN, W, AlN, AlB ₂ and a large amount of NiW were observed. A cutting chip was made of these two types of sintered body and a commercially available sintered body containing 90% CBN and bonded with a metal mainly composed of Co. has a groove of
Cutting speed 100m/ SKD11 die steel (H _RC 61)
Min, depth of cut 0.3mm, feed 0.5mm/rev Dry test. As a result, the sintered body of the present invention containing Cu could be cut for 20 minutes until the cutting edge broke, whereas the sintered body that did not contain Cu and the commercially available sintered body could both be cut after 5 minutes. The tip of the blade was damaged. Example 2 A mixed powder consisting of 60% by volume CBN powder with an average particle size of 5 μm and binder powder was prepared. The binder powder is a mixture of Mo and Al with a composition of 75% and 25% by weight, respectively. This mixed powder of CBN and binder was placed in a Mo container with an outer diameter of 14 mm and an inner diameter of 10.1 mm, the inside of which was wrapped with Ta foil with a thickness of 50 μm.
Co cemented carbide base metal (outer diameter 10mm, height 3mm)
After that, 0.4g was filled and a Cu-Ni-Co (weight ratio 6:3:1) embossed body having an outer diameter of 10 mm and a thickness of 1 mm was placed thereon. Furthermore, a cemented carbide of WC-10% Co composition (outer diameter 10 mm, height 2 mm) was placed on top of this, and Mo
It had a made-of-white stopper. This container was sintered in the same manner as in Example 1 at a pressure of 55 kb and a temperature of 1400°C. The removed sintered body was ground using a diamond grindstone until a high hardness sintered body appeared. The composition of this sintered body was investigated using an X-ray microanalyzer. Cu,
Co and Ni are uniformly contained in the sintered body, and their content is approximately 3% and approximately 2% by weight in the binder, respectively.
%, about 1%. In addition, when the products in the sintered body were investigated by X-ray diffraction, CBN, Mo, AlN,
Cu and a small amount of Ni, Co and a small amount of _AlB2 and Ni, Co, Mo
bolide was detected. A cutting chip was made of this sintered body and a commercially available sintered body containing 90% CBN by volume and bonded with a metal mainly composed of Co, and after heat treatment to have two V grooves in the cylindrical direction. Cutting 9 types of SNCM steel. The hardness of the work material is H _RC 54, cutting conditions are cutting speed 120m/min, depth of cut 0.2mm, 0.45
mm/rev dry method. As a result, the sintered body of the present invention could be cut in 60 minutes, whereas the commercially available CBN
The tool could only cut for 10 minutes. Example 3 A binder powder having the composition shown in Table 1 was prepared. Binder powders having these compositions were heat treated and pulverized in the same manner as in Example 1.

[Table] This bonded powder and CBN powder having an average particle size of 5 μm were mixed to create a mixed powder having the composition shown in Table 2. Note that G contains more Ni than Cu, H has a smaller amount of Al, and L has no Cu, so G, C, and R are all comparative examples. Note that J, K, L, and M in Table 2 are also comparative examples. In the same manner as in Example 1, WC-6 was placed in a Mo container.
%Co cemented carbide was placed, the finished powder and cemented carbide were placed on top of that, a Mo stopper was placed, and an ultra-high pressure and high temperature device was used to

[Table] Sintering was performed under the conditions shown in Table 2. Cutting chips were made using these sintered bodies, and chips with an outer diameter of 80 mm were made.
The end face of SKD11 (H _RC 61) was sliced.
The cutting conditions are cutting speed 200m/min (rotation speed
430 rpm), depth of cut 0.5 mm, and feed rate 50 mm/min. In addition, the commercially available volume contains 90% CBN,
A cutting chip made of a sintered body bonded with Co-based metal was also created and tested. These results are also the second
Shown in the table. In addition, the cutting speed for SKD11 with an outer diameter of 100 mm
Table 2 also shows the possible cutting time until the tool flank wear width reaches 0.2 mm when dry cutting is performed at 100 m/min, depth of cut 0.2 mm, and feed rate 0.1 mm/rev. Example 4 The binder powder shown in Table 1 and WBN powder with a particle size of 1 μm or less were mixed at a volume ratio of 1:1, and this powder was placed in a Mo container in the same manner as in Example 1. After placing 6% Co cemented carbide, it was filled, then another cemented carbide was placed on top of this, and a Mo stopper was placed.
Using ultra-high pressure and high temperature equipment, the pressure is 50kb and the temperature is 1400℃.
sintered for 15 minutes. Using this sintered body, H _RC 58~
Cutting a round bar with 4 U-shaped grooves on the outer circumference using 60 SNCM435 at a speed of 100 m/min, depth of cut of 0.2 mm, and feed.
Dry cutting was performed at 0.1mm/rev. Commercially available for comparison
A cutting chip made of a sintered body containing 90% CBN by volume and bonded with a metal whose main component is Co was also fabricated and tested. As a result, the sintered body of the present invention did not break even after cutting for 10 minutes, whereas the comparative material did break after cutting for 30 seconds.

[Brief explanation of the drawing]

FIG. 1 is for explaining the manufacturing conditions of the sintered body of the present invention, and shows the thermodynamically stable region on the pressure-temperature phase diagram of high-pressure phase type boron nitride.

Claims (1)

[Scope of Claims] 1 Contains 20 to 90% by volume of high-pressure phase type boron nitride with an average particle size of 10 μm or less, and the remaining binder phase is a transition metal of Groups A, A, and A of the Periodic Table.
A mixture or mutual solid solution of one or more of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, or a mutual solid solution thereof, is contained in the binder phase in an amount of 20 to 94% by weight, and a compound of Al is contained in the binder phase. Al content is 5-30% by weight
and further contains 1 to 50% by weight of Cu, or 1 to 50% by weight of Cu and Ni or/and Co, in which the content of Cu is higher. Body. 2. The high-hardness sintered body for tools according to claim 1, wherein the high-pressure phase boron nitride is cubic boron nitride. 3 High-pressure phase type boron nitride powder with an average particle size of 10 μm or less by volume of 20 to 90% and periodic table a, a,
Group a transition metals Ti, Zr, Hf, V, Nb,
A mixed powder or mutual solid solution powder of one or more of Ta, Cr, Mo, and W powders is added in the binder phase.
20-94% by weight of Al or a compound powder containing Al in the binder phase, and 1-50% by weight of Cu, or 1-50% of Cu and Ni or/and Co in the binder phase. High hardness for tools, which is characterized in that it is mixed with a higher Cu content by weight and is then molded into a powder or molded form and then sintered using an ultra-high pressure device at a pressure of 20 kb or more and a temperature of 900°C or more. A method for producing a sintered body. 4. Claim 3, characterized in that cubic boron nitride is used as the high-pressure phase boron nitride powder.
A method for manufacturing a high-hardness sintered body for tools as described in . 5 20 to 90% by volume of high-pressure phase boron nitride powder with an average particle size of 10 μm or less and items a, a,
Group a transition metals Ti, Zr, Hf, V, Nb,
A mixed powder or mutual solid solution powder of one or more of Ta, Cr, Mo, and W powders is added to the binder phase for 200 min.
~94% by weight and Al or a compound powder containing Al are mixed in a binder phase at 5% to 30% by weight, and after molding into powder or molding, sintering is performed using an ultra-high pressure device at a pressure of 20 kb or higher and a temperature of 900°C or higher. 1 to 50% by weight of Cu in the binder phase, or 1 to 50% by weight of Cu and Ni or/and Co from the outside at the same time as sintering.
5. The method for manufacturing a high-hardness sintered body for a tool according to claim 3 or 4, wherein a larger amount of .