JPH1150182A - Cemented carbide and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cemented carbide combining impact strength and toughness with rigidity and hardness and to provide its production. SOLUTION: In the cemented carbide where hard phases composed essentially of WC are dispersed in binding phases of Co-containing iron group metal, the crystal structure of Co satisfies inequality 0<=I(Co.hcp)/I(Co.fcc)<=0.1, where I(Co.hcp) is the X-ray diffraction intensity in the (101) plane of Co in the hcp structure and I(Co.fcc) is the X-ray diffraction intensity in the (111) plane of Co in the fcc structure. This cemented carbide can be obtained by sintering a prescribed raw material, temporarily cooling the resultant sintered compact, heating the sintered compact up to a temp. right under the liquid-phase-forming temp., and rapidly cooling it by immersion in a liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cemented carbide capable of improving impact strength and a method for producing the same.

[0002]

2. Description of the Related Art The impact strength and toughness of a cemented carbide are incompatible with the rigidity and hardness, and it is difficult to achieve both.
As a technique for improving this point, those described in Japanese Patent Publication No. 5-20492, Japanese Patent Application Laid-Open No. 58-39764, and Japanese Patent Publication No. 61-4899 are known. These aim at compatibility of toughness and strength mainly by specifying the cooling rate from the sintering temperature.

[0003]

However, none of the above-mentioned technologies is sufficient in terms of both impact strength and toughness and rigidity and hardness. Materials that can cope with plastic deformation due to insufficient hardness have been demanded. Further, rapid cooling from a sintering temperature of about 1400 ° C. results in too large a thermal shock, and there is a strong possibility that cracks occur in the cemented carbide. Furthermore, when quenching from the sintering temperature, there is a problem that HIP processing cannot be performed later to maintain the quenching effect.

Accordingly, the main objects of the present invention are toughness and strength,
In particular, it is an object of the present invention to provide a cemented carbide capable of achieving both impact strength and a method for producing the same.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for forming C in a cemented carbide.
The above object is achieved by controlling the crystal structure and the amount of solid solution of o. That is, the cemented carbide according to the present invention is characterized in that, in a cemented carbide in which a hard phase mainly composed of WC is dispersed in a binder phase of an iron group metal containing Co, the crystal structure of Co satisfies the following formula. I do. 0 ≦ I (Co · hcp) / I (Co · fcc) ≦ 0.1 where I (Co · hcp) is the X-ray diffraction intensity of the (101) plane of Co of the hcp structure, and I (Co · fcc) ) Is (11) of Co of fcc structure.
1) X-ray diffraction intensity on the surface.

Here, a more preferable range of I (Co · hcp) / I (Co · fcc) is 0.01 to 0.05. Further, the lattice constant of Co is preferably 3.570 or more. The amount of the binder phase is preferably about 10 to 30 wt%.

When "I (Co.hcp) / I (Co.fcc)" exceeds 0.1, Co having a fragile hcp structure increases and the toughness is insufficient. Therefore, when such a cemented carbide is used for a forging tool, cracks are likely to occur and the tool life is shortened. Further, when the lattice constant is less than 3.570, it means that the solid solution amount of W in Co is small, and the toughness tends to be insufficient.

[0008] The method for producing a cemented carbide according to the present invention comprises the steps of:
A step of sintering and cooling the hard phase mainly composed of and the binder phase of the iron group metal containing Co, and after this cooling, the sintered body is heated to a temperature just below the appearance of the liquid phase, and immersed in the liquid. Quenching step.

The temperature immediately below the appearance of the liquid phase is 1200 to 1
About 300 ° C. is preferable. The rapid cooling rate is 1000
C./min or more is desirable. The liquid in which the sintered body is immersed during rapid cooling is not particularly limited. For example, water and oil are mentioned. After sintering the hard phase and the binder phase, HIP processing may be performed as necessary.

Generally, a cemented carbide product is manufactured by the following steps. Mixing of raw material powder → press → intermediate sintering → molding → sintering → (H
IP) → Inspection That is, the mixed raw material is pressed to form, for example, a block, and intermediately sintered at about 700 ° C. Then, the intermediate sintered body is formed into a predetermined tool shape and sintered at about 1400 ° C. In order to further reduce voids in the sintered body, HIP (for example, about 1340 ° C.) may be performed after sintering.

In the above-mentioned prior arts, attention is focused on the speed at the time of cooling from the sintering temperature. In the present invention, cooling from the sintering temperature is not particularly defined, and is characterized in that once cooled, heated again and then rapidly cooled.

Such quenching passes through the transformation temperature range of the Co crystal structure (around 413 ° C.) in a very short time, and (1) transforms the fcc structure, which is a stable phase at a high temperature, to the hcp structure. (2) solidifies without dissolving W in solid solution in Co immediately before quenching, during cooling,
It is especially effective.

The quenching is started from a temperature immediately below the liquid phase appearance temperature because a large amount of W can be dissolved in Co and fcc → hcp
This is because the temperature condition is closest to the transformation temperature. 1400
Rapid cooling from a temperature in the vicinity of the sintering temperature of about ℃ causes a large thermal shock and may cause cracking. The specific reheating temperature is about 1200 to 1300 ° C., particularly 1220 to 1280.
C. is preferred.

In the prior arts, the cooling from the sintering temperature is rapidly cooled. If the HIP is performed after the cooling, the quenching effect is lost. Therefore, it is difficult to perform the HIP subsequent to the sintering. However, in the present invention, since the steel sheet is reheated and then rapidly cooled, HIP can be performed between sintering and reheating to obtain a denser cemented carbide.

[0015]

Embodiments of the present invention will be described below. Commercial WC powder (average particle size 6.5 μm and 3 μm)
And Co powder (average particle size: 1.2 μm) were blended in the composition shown in Table 1, wet-mixed with an attritor, and then dried to prepare a powder. This powder is pressed at a pressure of 1 t / cm ² ,
Sintered at 1380 ° C. to 1400 ° C. for 60 minutes and then cooled to produce a cemented carbide test piece. Some of these test pieces were further subjected to HIP treatment (1340 ° C., 1 t /
cm ² , Ar gas atmosphere). The test piece cooled by sintering or HIP processing is kept in an electric furnace preheated to 1250 ° C. for 15 minutes, then taken out of the furnace and immediately immersed in water (within 30 seconds), and quenched. Was given. In addition, the thing which did not perform the said rapid cooling process and the thing which performed the conventional gas cooling were made into the comparative example. The gas cooling is performed by introducing nitrogen gas, and the cooling rate is at most 500 ° C./min.

The obtained test piece was subjected to X-ray diffraction to determine the crystal structure of Co (I (Co · hcp) / I (Co · fcc)),
Analysis and measurement of lattice constant, impact strength, hardness and bending force were performed. Table 2 shows the results.

[0017]

[Table 1]

[0018]

[Table 2]

As shown in Table 2, it can be seen that the hardness and the transverse rupture strength of all the examples are equal to those of the comparative example, but the impact strength is remarkably improved. This is due to the C
This is presumably because the crystal structure of o became an fcc structure with rich ductility, and a large amount of W dissolved in Co, resulting in an improvement in lattice constant and strengthening. The cooling rate in each example was 12
Since it took at most about 10 seconds to cool from 50 ° C. to almost room temperature, it is estimated to be about 120 ° C./sec.

On the other hand, the comparative examples are all inferior in impact strength. That is, Comparative Examples 1 to 6 in which the quenching treatment was not performed are all low in both impact strength and lattice constant. Comparative Examples 7 and 8 in which gas cooling was performed by introducing nitrogen gas
Despite cooling at about ° C / min, impact strength comparable to that of the examples was not obtained.

Similar results were obtained when the cooling medium used for rapid cooling was oil instead of water.

(Test Example) Using the powder having the composition A shown in Table 1,
A 29-L137 mm hot forging punch was produced.
The manufacturing conditions were the same as in Example 1, and the pressing pressure was 1 t /
cm ² , sintering temperature: 1380 ° C to 1400 ° C, sintering time:
After 60 minutes, a quenching treatment was performed after the HIP treatment. As a comparison, a punch without quenching treatment was also manufactured. After cutting these punches, work: SCM15, work temperature: 1
100 ° C, cycle time: 75 / min, surface pressure: 6
It was used as a forging tool under the condition of 5 kg / mm ² , and the number of shots up to the life and the observation of the tool surface were measured. The results are shown in Table 3 and FIGS.

[0023]

[Table 3]

The punch made of the cemented carbide of the present invention has a remarkably large number of shots up to its life of 145,000 times, and no thermal cracks are observed on the tool surface as shown in FIG. That is, the tool of the cemented carbide of the present invention is 2 to 10 times more than the conventional tool.
It turns out that it has twice the life. On the other hand, the punch that was not quenched failed 35,000 shots and caused many thermal cracks as shown in FIG.

[0025]

As described above, the cemented carbide of the present invention can achieve both impact strength and hardness, and is expected to be used for forging tools and the like that require high impact strength. Further, the method of the present invention is an optimal method for producing the cemented carbide of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a hitting surface after forging of a punch using the cemented carbide of the present invention.

FIG. 2 is a schematic view showing a hitting surface after forging of a punch using a conventional cemented carbide.

Claims (5)

[Claims] 1. A cemented carbide in which a hard phase mainly composed of WC is dispersed in a binder phase of an iron group metal containing Co, wherein the crystal structure of Co satisfies the following formula: . 0 ≦ I (Co · hcp) / I (Co · fcc) ≦ 0.1 where I (Co · hcp) is the X-ray diffraction intensity of the (101) plane of Co of the hcp structure, and I (Co · hcp) fcc) is (11)
1) X-ray diffraction intensity on the surface. 2. The cemented carbide according to claim 1, wherein the lattice constant of Co is 3.570 or more. 3. a step of sintering and cooling a hard phase mainly composed of WC and a binder phase of an iron group metal containing Co, and after the cooling, heating the sintered body to a temperature immediately below the appearance of a liquid phase;
Dipping in a liquid and quenching it. 4. The temperature immediately below the appearance of the liquid phase is from 1200 to 130.
The method for producing a cemented carbide according to claim 3, wherein the temperature is 0 ° C. 5. The method for producing a cemented carbide according to claim 3, wherein the quenching rate is 1000 ° C./min or more.