JPS5855111B2 - High hardness sintered body for tools and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Cubic boron nitride (hereinafter abbreviated as CBN) is a substance 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 metal Co or the like are also used in some cutting applications.

When this sintered body of CBN bonded with metal is used as a cutting tool, there are disadvantages such as a decrease in wear resistance due to the softening of the bonded metal phase at high temperatures, and damage to the tool because the work material metal is easily welded. There is.

The present invention relates to a new CBN sintered body suitable for tool applications such as cutting tools, which uses a hard metal compound as a binder phase with high strength and excellent heat resistance, rather than a sintered body bonded with such metals. It is.

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, but
For this purpose, as described in Japanese Patent Publication No. 39-8948, it is necessary to perform sintering at an extremely high pressure and high temperature of about 70 Kb or more and 1900° C. or more.

Current ultra-high pressure and high temperature equipment can generate such high pressure and high temperature conditions, but if the equipment is scaled up on an industrial scale, the number of service life of the high pressure and high temperature generation part will be 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 titanium nitride (TiN) as a bonding material for CBN.
Alternatively, by using a compound mainly containing zirconium nitride (ZrN) and At, and finding more appropriate manufacturing conditions, we can create a product with a CBN content of more than 80% by volume, which has unprecedented wear resistance and toughness. A sintered body with high hardness could be obtained.

Further, similar studies were 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.

A sintered body using CBN as a hard wear-resistant component will be described in detail below, but the same can be said when using a wurtzite type or a mixture of CBN and wurtzite type boron nitride.

An object of the present invention is to obtain a highly hard sintered body for tools with a high CBN content.

This allows us to take full advantage of the characteristics of CBH and, for example,
It can be applied to tool materials for cutting highly hard materials such as C cemented carbide, wire drawing dies, etc.

As described above, a sintered body made only of CBN has drawbacks such as difficulty in manufacturing and insufficient strength of the sintered body itself.

For this reason, it is possible to improve these drawbacks by adding a suitable binder to CBN.

One of the known methods is a method using a metal bonding material, and an example is a commercially available sintered body of CBN bonded with metal Co or the like.

Also, CBH contains compounds other than metals, such as At203 and B4.
Attempts have also been made to mix C and the like and sinter the mixture.

The former method is a liquid phase sintering under high pressure, in which sintering is carried out at a temperature at which a metal bonding material such as Co is melted.

In the latter case, the binder is not dissolved but sintered in a solid state.

The inventors previously discovered that using carbides, nitrides, borides, and silicides of metals from groups 4a, 5a, and 6a of the periodic table as binders, these binder compounds form a continuous binder phase in the structure of the sintered body. Eggplant C
Invented a sintered body for high hardness tools containing 40 to 80% by volume of BN, and filed a patent application in 1977-7781.
1).

In this case as well, sintering is performed in a solid state, but because the binder content is relatively high, the pressure and temperature conditions required to obtain a dense sintered body are required compared to sintering only CBN. eased.

The inventors further investigated products with a higher content of CBH.

If the content of CBN exceeds 80% by volume, even if the CBN and the compound powder of metals from groups 4a, 5a, and 6a of the periodic table are sufficiently uniformly mixed and sintered under ultra-high pressure and high temperature, high A strong sintered body was not obtained.

When examining the fracture surface of this sintered body, it was found that between CBN particles and CB
It is often destroyed between N and binder compound particles, and C
It is considered that the bonding strength between the BN particles or between the CBN and the binder crystal particles is low.

When the content of CBH is large, the sinterability deteriorates as described above, and a high-strength sintered body cannot be obtained.

In order to improve this, we conducted a further wide range of experiments and found that when a powder containing more than a certain amount of At is used as a binder for TiNx or ZrNx whose X value is below a certain value, the content of CBH increases. It has been found that a high-strength sintered body can be obtained even when the amount exceeds 80%.

TiNx or ZrNx is, for example, as shown in FIG.
A phase having a NaC4 type structure exists in a wide composition range of Ti--N and ZrN.

When the value of
It was also confirmed that the sinterability was further improved when an At compound was added to the binder than when only TiNx or ZrNx was used as the binder.

The preferable range of the value of X of TiNx and ZrNx used as the binder raw material is 0.9 or less.

Further, when At is present in the binder in an amount of 5% or more as an At element, a high-strength sintered body can be obtained.

The CBN content in the sintered body was set to 85% by volume, and sintered bodies were prototyped by varying the value of X of TiNx as a binder raw material and the amount of added A7, and the performance as a cutting tool was evaluated. Particularly high strength and excellent tool performance were achieved when the value of X was 05 to 09 and the amount of At added was 5 to 3 by weight in the binder.
It was in the range of 0%.

In the sintered body of the present invention, high-pressure phase boron nitride is present in a volume percentage of more than 80% and less than 95% in the sintered body.

Within this composition range 4, in a sufficiently dense sintered body, the higher the CBN content, the higher the hardness of the sintered body.

If it exceeds 95%, a decrease in the toughness required for the sintered body as a tool is observed.

Further, if the content is less than 80%, the binder phase of the sintered body forms a continuous phase in the structure, resulting in a decrease in hardness.

Let us consider why the sinterability of high-pressure phase boron nitride is improved when the binder according to the present invention is used.

Taking TiNx as an example, the hardness of a sintered body containing only TiNx at room temperature is maximum when the value of X is about 0.7.

However, at high temperatures, the lower the value of X, the greater the degree of decrease in hardness.

When CBN and TiNx are mixed and sintered under ultra-high pressure and high temperature, CBN crystals are difficult to deform, but TiNx particles can be easily deformed.

For the reasons mentioned above, in this case, TiNx with a high concentration of nitrogen atoms and a low value of X is easily deformed, and easily penetrates between CBN crystal grains, resulting in densification.

However, this alone does not provide sufficient bonding strength between CBN particles.

For example, in liquid phase sintering of W C-Co cemented carbide, if hard particles are dissolved in a binder phase and reprecipitated, a product with high bonding strength between the binder phase and hard particles or between the hard particles can be obtained. .

In the sintered body of the present invention, it has been found that a phenomenon similar to this occurs when an AA compound is present in the binder.

When an At compound is added to TiNx as a binder,
As the amount increases, sinterability improves, and a sintered body with high hardness can be obtained even when sintered at a low temperature.

When the sintered body is ground with a diamond grindstone and further lapping is observed, no CBN particles are observed to fall off when the amount of added At is 5% or more by weight in the binder.

Furthermore, when observing the fracture surface of the sintered body, most of the CBN particles were intragranularly fractured.

Fe, Co. It is already known that an alloy of N1 and At can serve as a solvent during CBN synthesis.

In the present invention, alloys of such iron group metals and At, or At
It is not intended to be used alone as a binding material.

In the present invention, At is the main component of the binder, TiNx, Zr.
It is present in the powder before sintering in the form of an intermetallic compound of Ti or Zr and At produced by the reaction with Nx, or a compound such as T i 2AtN, A7N, or AtN.

Such At compounds have a high melting point, and in the sintered body of the present invention, they are highly reactive with CBN particles even if they do not form a liquid phase during sintering, and react with them in a solid phase to form bonds between CBN particles. It is also believed that a strong bonding state can be obtained between the CBN and the binder particles.

Compounds produced by the reaction between At and TiNx and ZrNx, which are the main components of the binder, include excessive Ti in TiNx or ZrNx, or intermetallic compounds between Zr and Al.

This includes the amount of calories added in A7, the value of X (i.e. excess Ti,
Compounds with various composition ratios may exist depending on the Zr ratio) and sintering conditions.

Figures 3 and 4 show the phase diagrams of kt-T i and kt-Z r, respectively, and the intermetallic compounds present are AtTi3.
AtTi2. AtTi, A4Ti.

A/! , 23Tig, A43Ti, AtZr3.
A7Zr2. At3Zr5.

At2 Z r 3 , At3 Z r4 , At
Zr, Al-3Zr2, A72Zr.

A4Zr etc.

In addition, Ti2AtN, Zr2A, which further contains nitrogen,
tN may also exist.

Further, T IB 2 and ktN are generated by the reaction between boron nitride and these intermetallic compounds during sintering.

These are TiN present in the binder of the sintered body of the present invention,
It is a heat-resistant compound other than ZrN.

According to experiments, in the sintered body of the present invention, the compound particles of the binder are made finer due to the reaction between TiNx, ZrNx, which are the main components of the binder, and these At compounds during sintering. Confirmed.

The sintered body of the present invention has high strength because the binder is composed of fine crystals of 1 μm or less.

Various methods can be considered for adding At.

The simplest method is to add Kt as pure A7 to the mixed powder with CBN before sintering, but it is difficult to obtain At fine powder of 1μ or less, and coarse particles will result in an uneven structure of the sintered body. easy.

Excess Ti in the most preferred binders TiNx and ZrNx
, Zr and metal A7 are reacted in advance, and Ti −
A7, forming an intermetallic compound of Zr-Al,
This method uses pulverization.

1 In this case, the bonding materials T iNx , Z rNx and A7
An extremely fine binder powder of 1 μm or less, consisting of an intermetallic compound, can be easily obtained.

In addition, Ti-A7 is synthesized by reacting metal Ti or Zr with metal A7 in advance. Zr l'-1 intermetallic compounds (e.g. AtAt3. T + kl, T +2A/1
．． .

Easily pulverized powders such as ZrA73, ZrAA, etc.) may also be used.

Another form of A7 compound is A7N. T 12AtN
, Z r2 AtN or the like may be added in the form of a nitrogen-containing compound.

The binder component of the sintered body of the present invention is TiNx.

In addition to ZrNx, nitrides, carbides, carbonitrides, borides, etc. of metals from groups 4a, 5a, and 6a of the periodic table may be partially added thereto.

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 decrease, and especially when used as a cutting tool, a finer crystal grain will give a better machined surface.

Another feature of the present invention is that the particle size of the binder phase consists of extremely fine crystal grains of 1 μm or less.

As a result, although the sintered body has a high content of CBN, it has a structure in which the binder phase is uniformly dispersed between the CBN particles, and a high-strength sintered body can be obtained.

In manufacturing the sintered body, we use ultra-high temperature equipment used for diamond synthesis, at a pressure of 20 Kb or more and a temperature of 900°C.
That's all for now.

Particularly preferable sintering pressure and temperature conditions are 30 Kb to 70 Kb.
Kb, and the temperature is 1100°C to 1500°C.

The upper limits of these pressure and temperature conditions are all within the range of practical operating conditions for industrial scale ultra-high pressure, high temperature equipment.

Further, the pressure and temperature conditions must be within the stable range of high-pressure phase type boron nitride shown in FIG.

Hereinafter, a more specific explanation will be given with reference to Examples.

Example 1 A mixed powder consisting of 90% by volume CBN particles having an average particle size of 3 μm and binder powder was prepared.

The binder powder was prepared by mixing T I No. 82 powder and A7 powder at a weight percentage of 80% and 20%, respectively, and heating it in a vacuum furnace at 1000°C for 30 minutes and then pulverizing it to an average particle size of 0.
It is made into a fine powder of 3 μm.

When this binder powder was examined by X-ray diffraction, it was found that TiN
In addition to T 12AtN , T 1A73 , T i
Compounds such as At generated by the reaction between TiN and At were detected, but metallic At was not detected.

This occurred in opposition to the addition of A7 in excess of Ti relative to N in T iN6 B 2 .

A mixed powder of CBN and a binder was pressurized to a pressure of 50 kb using a molded layer girdle type ultra-high pressure and high temperature device, then heated to a temperature of 1250° C. and held for 20 minutes.

The taken out sintered body was ground using a diamond grindstone and further polished using diamond paste.

When observed under an optical microscope, it was found to be a dense sintered body with no pores.

The hardness was measured using a Vickers hardness tester at a load of 5 klI, and the result showed a value of 4,800.

A chip for cutting was created using this sintered body.

The work material is WC-1 with a Vickers hardness of approximately 1,200.
A plastic working punch made of 5% Co cemented carbide was selected, cutting speed 18 m/min, depth of cut 0.2 mm, feed rate 0.1 rr.
Cutting was performed for 20 minutes at rm/revolution.

For comparison, a test was conducted under the same conditions using a chip made of a commercially available sintered body in which approximately 90% CBN by volume was bonded with a metal containing CO as the main component.

When we observed the wear of the tip after cutting, we found that the maximum flank wear width of the sintered body of the present invention was 0.12 wrn, whereas that of the commercially available sintered body made of CBN bonded with a metal mainly composed of Co. was 0.23 mm.

When the sintered body of the present invention was examined by X-ray diffraction, CBN was found.
, trace amounts of TiB2 and AtN were detected in addition to the TiN diffraction peak.

This is considered to be caused by decomposition of the T 1-kl-based intermetallic compound and T I 2 ktN in the binder powder before sintering as they react with CBN.

Example 2 The binder powder shown in Table 1 was prepared.

TiNx powders with different nitrogen contents are produced by heating fine powder of titanium metal in a pure nitrogen stream to nitride it, and controlling the amount of bound nitrogen by changing the heating temperature.

The binder powder having the composition shown in Table 1 was heat treated and pulverized in the same manner as in Example 1.

This binder powder and CBN powder having an average particle size of 3 μm were mixed to prepare a mixed powder having the composition shown in Table 2.

In the same manner as in Example 1, a pressure of 50
kb, kept at a temperature of 1150°C for 20 minutes (condition 1)
, and held at a pressure of 50 kb and a temperature of 1400° C. for 20 minutes (condition 2). Two types of sintered bodies were created.

The measurement results of each hardness are shown in Table 2.

Comparing the sintered bodies of A, B, and C, when the CBN content is 80% by volume, the Vickers hardness is 3.500 or less, and 97%.
%, the hardness decreases.

In this case, the binder content in the sintered body is insufficient, and a completely dense sintered body cannot be obtained under such pressure and temperature conditions.

Comparing E and F with different At contents in the binder, within this range, the higher the A7 content, the higher the hardness, and a sintered body with high hardness was obtained at a low temperature.

Generally, the lower the value of X of the binder material powder TiNx and the higher the At content, the better the sinterability is, and even when sintered at a low temperature, a product with high hardness tends to be obtained.

In addition, when the sintered body G was examined by X-ray diffraction, the binder phase included A-AT 13 and T s 21t in addition to TiN.
N.

T iB 2 and A tN were detected.

Example 3 A binder powder having the composition shown in Table 1 was prepared.

CB with an average particle size of 3μ was heat-treated in the same manner as in Example 1.
N powder and this binder powder were blended and mixed so that the volume percentages were 85% and 15%.

The sintering conditions were the same as in Example 1, and sintering was performed under ultra-high pressure and high temperature.

All of the sintered bodies had a Vickers hardness of 4.000 or more.

Example 4 Using wurtzite boron nitride powder synthesized by the shock wave method with a particle size of 1μ or less, the binder powder used in Example 1 was mixed with wurtzite boron nitride powder 85% by volume and binder powder 15% by volume.
They were mixed in a proportion of % by volume.

Sintering was carried out under the same conditions as in Example 1 using an ultra-high pressure, high temperature device.

The hardness of the sintered body was 5,000 on the Vickers scale.

Example 5 The mixed powder of CBN and binder powder of Example 1 (MO9W
), Co, 9-5 wt% Co-5 wt% Ni-0,
A (Mo W ) C-based metal having a composition of 5 wt% Fe was placed on a disk with a diameter of 10 TML and a thickness of 3 mm,
This was sintered in the same manner as in Example 1 using an ultra-high pressure, high temperature device at a pressure of 45 kb and a temperature of 1200°C.

Thickness of hard sintered body containing 90% by volume of CBN: 1m+n
A composite sintered body was obtained in which the layers were bonded to a cermet disk.

When this composite sintered body was cut and the joint portion of the cross section was observed using an X-ray microanalyzer, it was found that (MoW)C is a bonding metal of the cermet from the Met part to the hard sintered body part. Almost no Ni intrusion was observed.

At the bonding interface, Ti in the hard sintered body is partially dissolved in (MOW)C of the cermet, resulting in (Mo W Ti )C.
It formed a compound of

This sintered body was brazed to one corner of a WCC cemented carbide indexable tip to create a cutting tip.

For comparison, a chip of the same shape was made of a sintered body (Vickers hardness: 3,000) made of At and TiN with a CBN content of 60% by volume and the remainder of the binder phase being 10% by weight.

A chilled roll having a Shore hardness of Hs83 was tested for cutting using these two types of chips.

Cutting speed 50m/min, depth of cut 1mm, feed 0.5mm/
When the flank wear of the 1-hour cutting-resistant chip was measured during rotation, the wear was 0.15 mm for the sintered body containing 90% by volume of CBN of the present invention, whereas the CBN content was 0.15 mm. In the case of the 60% comparative material, the length during wear reached 0.3 m.

[Brief explanation of drawings]

FIG. 1 is a phase diagram of a Ti--N system for explaining the characteristics of the method for manufacturing the sintered body of the present invention. FIG. 2 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. FIG. 3 is a phase diagram of Al--Ti, which is the binder of the sintered body of the present invention, and FIG. 4 is a phase diagram of Zr--At.

Claims (1)

[Claims] 1 Volume % of high-pressure phase type boron nitride with an average particle size of 10μ or less
It contains more than 80% and less than 95% of Ti, and the remaining binder phase is Ti.
Intermetallic compounds of N or ZrN and AA-Ti or At-Zr and also At, high-pressure phase boron nitride, TiN or Z
Consists of a heat-resistant compound formed by reaction with rN,
A high hardness sintered body for tools, characterized in that the content of At in the binder phase exceeds 50% by weight, and most of the crystal grains of the binder phase consist of fine particles of 1 μm or less. 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 10μ or less and a binder with a value of
The following T iNx and ZrNx powders are mixed with At or an alloy or compound powder containing At, and after molding into a powder form or molding, the mixture is heated at a pressure of 20K using an ultra-high pressure/high temperature device.
The content of high-pressure phase boron nitride, which is characterized by being sintered at a temperature of 900° C. or higher, is 8% by volume in the sintered body.
more than 0% and less than 95%, and the remaining bonding phase is TiN or ZrN and kl-Ti, or A/1. - Zr intermetallic compounds and also At, high pressure phase boron nitride, TiN or Z
Consists of a heat-resistant compound formed by reaction with rN,
A method for producing a high hardness sintered body for tools, in which the content of AA in the binder phase exceeds 5% by weight, and most of the crystal grains in the binder phase are fine particles of 1 μm or less. 4. The method for manufacturing a sintered body for a high-hardness tool according to claim 3, characterized in that cubic boron nitride powder is used as the high-pressure phase boron nitride powder.