JPH0798964B2 - Cubic boron nitride cemented carbide composite sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a CBN cemented carbide composite in which a sintered layer of cubic boron nitride (hereinafter referred to as CBN) and a cemented carbide layer mainly composed of tungsten carbide (WC) are joined. The present invention relates to a sintered body, and more specifically to a CBN cemented carbide composite sintered body using a specific alloy as a binder metal of the cemented carbide layer.

Conventional technology CB, which is a super-hard material, for cutting various materials, drilling tools, etc.
Demand for N sintered compacts has increased rapidly in recent years. Most of the sintered bodies are directly bonded to a WC-Co type cemented carbide as a substrate, and the cemented carbide is used by being held by a tool shank by brazing or the like.

Problems to be Solved by the Invention The thermal expansion coefficient α (room temperature to 800 ° C., the same applies hereinafter) of a CBN sintered body is generally (4 to 6) × 10 ⁻⁶ (1 / ° C.). Meanwhile, normal
The cemented carbide used in the CBN cemented carbide composite sintered body is a WC-Co system, in which Co is 8 to 14% by weight (% represents% by weight unless otherwise specified), and α is (6 to 8) × 10 ^-6 (1 / ° C). If Co is decreased, α can be 6 × 10 ⁻⁶ (1 / ° C.) or less, but the strength required as a substrate cannot be obtained.

The above difference in the coefficient of thermal expansion between the CBN sintered body and the cemented carbide substrate is a big problem. The elastic modulus of CBN sintered body is about 5 × 10 ⁴ (Kg / m
m ² ), considering that the softening of the cemented carbide virtually stops at 1000 ° C or less, the stress generated between them at 1000 ° C or less is
The value is 50 to 100 kg / mm ² , which is comparable to the bending strength of the sintered body.

These residual stresses warp and peel when the material is thinned by scraping the cemented carbide, brazing cracks when brazing to the tool shank, and cemented carbide-CBN that is strongly demanded as a material for drilling-CBN -The conventional cemented carbide sandwich structure causes horizontal cracks in the CBN layer.

In order to solve these problems, a composite having a substrate other than cemented carbide has been proposed (Japanese Patent Laid-Open No. 61-26574).

However, WC-based cemented carbide has excellent properties such as high rigidity, strength and hardness, and silver brazing is possible.

An object of the present invention is to provide a composite in which a CBN sintered layer and a cemented carbide layer are joined, and the thermal expansion coefficient of the CBN sintered body is reduced as much as possible without lowering the above-mentioned characteristics of the cemented carbide. By adjusting the coefficient and maintaining high strength, peeling of the composite, generation of cracks, etc. can be prevented.

Means for Solving the Problems As a result of various studies on the binder metal of the cemented carbide mainly composed of WC, the present inventor has made α of the cemented carbide low and Fe-having a specific composition as a metal having high strength. The inventors of the present invention have found that the alloy is a Ni-Co alloy and have completed the present invention.

That is, the present invention comprises 90 to 96% of WC-based carbides and 4 to 10% of Fe-based alloys, and the Fe-based alloys include Ni of 20 to 50% and Co2 to 2%.
This is a CBN cemented carbide composite sintered body in which a cemented carbide layer with 0% balance Fe and a sintered layer of CBN are joined.

Carbide of cemented carbide used as the substrate is usually WC, but 50
A material in which TaC, TiC or the like is substituted within% can be used in the same manner.

In the case of Fe-Ni alloy, when Ni is 30-40%, α of cemented carbide is small from room temperature to 200 ℃, but α at high temperature is normal WC-Co.
It becomes close to the system. By adding Co to this, α can be kept small even in a high temperature region. To obtain this effect, Co must be at least 2%, and even if it is too much, α becomes large, so an upper limit of 20% is appropriate. Ni when Co is in this range
Is around 30%, the α of cemented carbide is the smallest, but CBN
Since the coefficient of thermal expansion of the sintered body has a wide range and is used according to this, an alloy having Ni in the range of 20 to 50% is suitable. Outside this range, the effect of reducing α is poor, and conversely, defects appear in terms of corrosion resistance and heat resistance.

CBN content is 60 ~ 90 due to the variety of work materials.
%, And various binders such as metals and various ceramics are used, and accordingly α has a width in the range of (4 to 6) × 10 ⁻⁶ .

In the present invention, α of the cemented carbide using the binder metal is (4.6 to 6.0) × 10 ⁻⁶ (1 / ° C.), and is selected from among them according to the α of the CBN sintered body. For example, α is 4.8 × 10
Fe-29% Ni-17% Co is suitable for the system of WC-6% Fe alloy as an example of the composition which becomes ^-6 (1 / ° C). And in cemented carbide
Α is 6.0 × 10 ^-6 (1 / ° C) by increasing the Fe content or increasing or decreasing the Ni content in the Fe alloy from the above value.
Can be changed.

As for the ratio of carbide mainly composed of WC and Fe-Ni-Co alloy, if the latter is less than 4%, the strength required as a substrate cannot be maintained,
On the other hand, if it exceeds 10%, α of the cemented carbide becomes larger than 6 even if the Fe alloy of the present invention is used, so 90 to 96% of the carbide, 4 of the alloy
~ 10% is suitable.

As the CBN sintered body in the present invention, a CBN powder obtained by adding a metal such as Al, Ni, Co or Mn, or various ceramics and sintering the CBN powder is used. Its thickness is often 0.5-1.5 mm.

The composite sintered body of the present invention includes not only one having a CBN sintered layer and a cemented carbide layer connected thereto but also one having a sandwich structure in which a cemented carbide layer is joined to the outside of the CBN sintered layer.

The thickness of the cemented carbide layer bonded to the CBN sintered layer is 0.1-2.0 mm
Is suitable.

Since the CBN sintered layer and the cemented carbide layer are pressure bonded under high temperature and high pressure, they are firmly bonded. Further, in the present invention, Mo, W, T is formed between the sintered layer and the cemented carbide layer according to a known method.
It is also possible to interpose a thin metal plate selected from a and Nb.

The thin metal plate has the effect of increasing the bonding strength between the CBN sintered layer and the cemented carbide layer, and also has the effect of relaxing the thermal stress that occurs between the two to some extent. The thickness of the thin metal plate is 50 μm to 200
μm is suitable.

Next, a method for producing the CBN cemented carbide composite sintered body of the present invention will be described.

As the binder metal, powders of Fe, Ni, and Co may be mixed and used within the above composition range, or a preliminarily alloyed powder may be crushed and used. In the former case, it becomes an alloy during sintering of the cemented carbide. These metal mixed powders or alloy powders
It is used as a mixture with carbide powder mainly composed of WC.

CBN is sintered by mixing the powder with additives as described above.

The cemented carbide may be pre-sintered. CBN layer containing cemented carbide or its composition and additives are superposed, using a high pressure device, preferably 1300 ~ 1600 ℃, 40 ~
Sinter in the range of 60 Kb to obtain a CBN cemented carbide composite sintered body.
When a thin metal plate is used, it is placed at the interface between the two and pressure bonded. Α of W, Mo, Ta and Nb is 4 to 7 × 10 ^-6
It is about (1 / ° C), and carbides and nitrides are formed by the action of CBN and WC during sintering, but since α is smaller than that of metals, there is no problem such as peeling due to thermal stress.

Preparation of Cemented Carbide First, a cemented carbide was prepared with the composition shown in Table 1. Fe, Ni and Co used had an average particle size of 2 μm. Each powder was blended according to Table 1, preformed using camphor, dried, and then vacuum-heated at 1350 ° C. for sintering. The characteristics are shown in Table 1.
Shown in.

From Table 1, the thermal expansion coefficient of No. 1 of the present invention is close to that of the comparative example.
No. 3, No. 4, 6, 7, 8, 9, 10 of the present invention and N of Comparative Example
As can be seen by comparing No. 5 of the present invention having the same coefficient of thermal expansion of Nos. 2, 4, 5 and No. 1 of the comparative example, the invention has a high transverse rupture strength.

Example 1 94% WC powder having an average particle size of 5 μm, Ni29%, Co17%, Fe54%
A cemented carbide (No. 2 of the present invention in Table 1) was obtained from Fe alloy 6%. This substrate and a compact of mixed powder of 70% CBN, 20% TiC, and 10% Al were overlaid and compressed at 40 Kb and 1350 ° C, and the obtained composite was 0.8 mm thick for CBN layer, 0.8 mm thick for cemented carbide layer, and total thickness. After preparing 1.6 mm, it was cut into a rectangle of 20 × 3 mm, brazed to a high-speed steel end mill shank, and after polishing, could be used for grooving of SKD11H _R C60 without any problem in processing. The thermal expansion coefficient (room temperature to 800 ° C) of this CBN sintered body is about 4.7.

For comparison, WC-6% Co cemented carbide (Comparative Example No. 1 in Table 1)
A composite sintered body of 1) and a CBN sintered body was prepared, but horizontal delamination occurred in the CBN layer during brazing in the end mill shank preparation.

Example 2 A mixture of 70% CBN, 20% TiC and 10% Al has a thickness of 50 μm on both outer sides.
No. 3 cemented carbide of the present invention (sintered thickness 1.0 mm) of Table 1 was placed on the outside of the Mo plate, and sintered at 40 Kb 1350 ° C. The obtained composite having a sandwich structure was wire-cut into an umbrella shape and brazed so as to be sandwiched between slits provided at the tip of a cemented carbide drill shank to prepare a drill. It was used to drill holes in the FC25 engine block, but it was 100
It was possible to drill holes.

In comparison, when the No. 1 WC-6Co cemented carbide of the comparative example in Table 1 was used, more than half of the cracks were generated at the material manufacturing stage, and there may be apparently no abnormalities. It fractured in the middle of the CBN layer during attachment.

EFFECTS OF THE INVENTION According to the present invention, WC is used within a range that does not impair the excellent properties of WC.
The coefficient of thermal expansion of cemented carbide can be made equal to that of CBN sintered body. As a result, the composite sintered body can be used without causing separation due to thermal stress or the like.

Claims (2)

[Claims] 1. 90 to 96% by weight of a carbide mainly composed of tungsten carbide and 4 to 10% by weight of an iron-based alloy, wherein the iron-based alloy is 20 to 50% by weight of nickel, 2 to 20% by weight of cobalt, and the balance iron. A cubic boron nitride cemented carbide composite sintered body obtained by joining the cemented carbide layer which is the above and a sintered layer of cubic boron nitride. 2. A carbide containing 90 to 96% by weight mainly of tungsten carbide and 4 to 10% by weight of an iron-based alloy, the iron-based alloy being 20 to 50% by weight of nickel, 2 to 20% by weight of cobalt, and the balance iron. A cubic boron nitride cemented carbide composite sintered body obtained by bonding a thin plate selected from molybdenum, tungsten, tantalum, and niobium between the cemented carbide layer and the sintered layer of cubic boron nitride. .