JPH05230588A - Hard alloy - Google Patents

Abstract

PURPOSE:To produce a hard alloy where hardness is improved and deterioration in toughness is prevented by incorporating CoxWyCz into a sintered compact of a hard alloy containing specific percentages of WC of specific grain size, Co, and group IVa, Va, and VIa metals. CONSTITUTION:CoxWyCz (where the symbols X, Y, and Z represent atomic ratios) is incorporated into a sintered compact of a hard alloy having a composition consisting of, by weight, >=80% of WC of <=2mu average grain size, >=0.2% Co, and the balance one or >=2 kinds among the metals, carbides, nitrides, and carbonitrides of the group IVa, Va, and VIa metals of the periodic table. The intermetallic compound CoxWyCz so far known is Co3W9C4, Co3W3C1, Co6W6C1, Co2W4C1. Further, 2.0-7.0wt.% of Mo and/or Mo2C and 0.2-0.6wt.% of VC and/or CrC can be added, if necessary. By this method, the hard alloy where hardness is improved and deterioration in toughness is prevented can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high pressure water jet nozzle,
The present invention relates to a hard alloy having excellent cutting characteristics, such as high hardness, high wear resistance, high corrosion resistance, and high rigidity, which is used for tools such as cutting, sliding, and drawing dies.

[0002]

2. Description of the Related Art In order to obtain a hard alloy with high hardness, high wear resistance, high corrosion resistance, and high rigidity, which has excellent cutting characteristics for tools such as high-pressure water jet nozzles, cutting, sliding, and wire drawing dies, Therefore, it is considered that silicon carbide, silicon nitride, and improved ceramics such as boron carbide are used. These ceramics are obtained by molding raw material powder into a shape close to the final shape and then sintering. On the other hand, hard alloys for tools with good wear resistance and excellent cutting characteristics are IVa, Va, VI
It is well known that it is obtained from a hard phase composed of a carbide or nitride of a group a metal element and a bonded phase of an iron group metal.
In particular, WC-Co based cemented carbide is most useful in the field of cutting tools and wear resistant tools because it has the best mechanical properties.
This WC-Co based cemented carbide is composed of WC powder (hard phase) and C
It is obtained by pressing a powder obtained by drying and granulating a mixed powder of o powder (bonding phase) and sintering the powder.

However, since ceramics have higher hardness but lower toughness, it is quite difficult to apply them to a field that receives an impact. Further, it is said that the hardness of a cemented carbide composed of hard phases of carbides and nitrides of IVa, Va, and VIa group metal elements and a binding phase of iron group metals has a limit. This is because when the amount of binder phase is reduced in an attempt to improve hardness, the toughness of the alloy decreases, and when the amount of binder phase in the alloy is less than 2% by weight, the binder phase is uniform on the surface of the WC particles, which is a hard phase. This is because it is very difficult to disperse it in the steel, and the toughness is remarkably deteriorated. Therefore, the binder phase made of Co or the like cannot be made less than 2% by weight in a normal cemented carbide.

Here, in Japanese Patent Application No. 3-250437 previously filed by the applicant of the present invention, even if a predetermined amount of Mo ₂ C and VC are added to the WC-Co mixture and the Co amount is reduced, WC is reduced. -By preventing the wettability of Co from being impaired, and further selecting the WC grain size and adjusting the HIP conditions to the optimum value for the material of this binder phase amount, W containing a small amount of binder phase is obtained.
It was capable of hard alloy consisting of _{C-Mo 2 C-VC-} Co.

[0005]

[SUMMARY OF THE INVENTION However, even the above hard alloy, the composition of _{WC-Mo 2 C-VC-} Co 4
As long as Co is present as a metal in the alloy and functions as a normal binder phase, the hardness and toughness have the same limits as before. Further, since there are large differences in properties such as Young's modulus and hardness between the hard phase and the binder phase, a large stress is present at the interface, impairing the toughness of the alloy.

The present invention has been made in view of the above conventional problems, and provides a hard alloy capable of improving the hardness of an alloy more than before with a small amount of binder phase and preventing the toughness of the alloy from decreasing. The purpose is to do.

[0007]

The present invention provides a material having particularly high hardness and high toughness and wear resistance among tools such as high-pressure water jet nozzles, cutting, sliding, and drawing dies. The purpose is. Since the toughness is insufficient, ceramics were first excluded from the scope of study, and studies were conducted to achieve the above-mentioned object by improving the composition of the cemented carbide.

Then, a study was made to extremely reduce the amount of the binder phase of the cemented carbide. Basically, WC, which has excellent properties in toughness, strength, and hardness, is used as the central component of the hard phase, so WC is 80% by weight or more in the hard sintered body. If it is less than 80% by weight, it is impossible to obtain a hard alloy having desired hardness, toughness and wear resistance.

In the technical field related to conventional cemented carbides, those having a binder phase content of less than about 5% by weight are practically used because they are unmanufacturable or have low toughness even when hardness increases. I didn't.

The inventors have made intensive studies on the above causes, and have begun to study the amount of Co, which is considered to function as a binder phase, to be 2% by weight or less. Since the amount of binder phase is small, it is necessary that the components in the hard alloy have good wettability with each other. In that sense, it was considered to add Mo or Mo ₂ C. It has not been confirmed in what form these additive components exist in the hard sintered body. However, since Mo ₂ C is a relatively stable compound, Mo ₂ C
Is likely to be.

It has been found that the hard alloy thus obtained has improved strength as a sintered body as compared with an alloy not added. However, when it is less than 2.0% by weight, its effect is small, and it is 7.0% by weight.
It was found that the hardness was lowered when it exceeded. It is considered that these additives were effective in improving the wettability of WC and the binder phase.

However, with the above composition, the density of the hard alloy was not stable, and therefore the characteristics of the hard alloy became unstable. Preliminary experiments were conducted to clarify the cause. Preliminary experiments have shown that there is a close relationship between the grain size of WC and the density of the sintered body. Furthermore, when this effect was examined in detail, the results shown in FIG. 1 were obtained. That is, by setting the average grain size of WC in the hard alloy to be 2 μm or less, a hard sintered body having a high density can be obtained. When the average particle size of WC is about 1.0 μm, the density reaches almost 100%.

What is important here is to keep the grain size of WC in the sintered body at 2 μm or less, but generally, the grain size of WC varies depending on the sintering conditions. The higher the sintering temperature and the longer the sintering time, the larger the WC grain size. Naturally, the particle size and particle size distribution of WC in the raw material powder also affect the particle size of WC in the sintered body.

Therefore, the particle size of WC in the sintered body is extremely unstable, and in order to achieve the object of the present invention, how to control the particle size of WC in the sintered body is one important factor. It turned out to be an element.

In cemented carbide that has been put to practical use, V
C and CrC are well known as a grain growth inhibitor for WC. However, even in the case of a cemented carbide having a small amount of binder phase as in the present invention, it is unclear whether the conventional common sense can be applied as it is.

That is, it is considered that in the conventional cemented carbide, Co is dissolved in the sintered body, WC is dissolved therein, and re-precipitation is performed. In this process, CrC and VC are W
The particle growth of C is suppressed. As in the present invention, when the binder phase Co is 2 wt% or less, it is not known what the sintering mechanism is.

Although it is unclear what results will be obtained, the inventors investigated the effect of various amounts of VC and CrC anyway. As a result, 0.2 to 0.
It was found that adding 6% by weight of VC or CrC was very effective. If it is less than 0.2% by weight, the effect is not obtained, and if it exceeds 0.6% by weight, the sinterability is extremely deteriorated.

Although it is a very small amount of binder phase, in order to obtain a hard alloy having a higher hardness, the amount of binder phase is 0.2-.
1.0 wt% Co is preferred. However, since the amount of the binder phase is small, not a few defects remain in the hard sintered body. In order to crush alloy defects in the process,
HIP treatment is effective, but the effect of HIP does not appear unless the alloy before HIP is in a state close to normal. In order to obtain a normal alloy after HIP, it is necessary that the density be 98% or more at least before HIP. This is probably because if the density is too low, the cavities in the alloy seem to be connected to the surface to some extent, and the HIP pressure reaches the inside of the cavities and cannot be collapsed.

In addition, addition of carbides, nitrides, and carbonitrides of Group IVa, Va, and VIa metals of the periodic table has the same effect as that of the present invention. When carbon in the hard sintered body is insufficient, W ₂ C is generated, but it does not have a particularly bad influence.

The hard alloy thus obtained is shown in FIG.
As shown in FIG. 4, the hardness is high, the fracture toughness is practically high enough, and the wear resistance is also excellent.

Among the hard alloys mentioned above, the inventors have examined X-ray diffraction analysis for a hard alloy having particularly excellent wear resistance. One example is shown in FIG. What has been clarified here is that the unexpected peaks of Co ₂ W ₄ C and W ₂ C are seen together with the peak of WC. The hard alloy of the present invention is normally liquid phase sintered as described above. Therefore, when WC once dissolves in the liquid phase of Co and is re-precipitated, the precipitates differ depending on whether the amount of C is insufficient or excessive. From such a viewpoint, various sintered bodies were produced and the phases in the hard sintered body were confirmed.

As a result, Co ₃ W ₉ C ₄ and Co ₃ W ₃ C
The surprising fact that various intermetallic compounds, which are supposed to be ₁ , Co ₆ W ₆ C ₁ and Co ₂ W ₄ C ₁ , are present has been found.

Such an intermetallic compound was a compound which should not be contained in a usual hard alloy. Therefore, in order to obtain a sintered body free of these compounds, various compounds are eliminated by controlling various sintering conditions, compounding compositions, etc. The present inventor also conducted various studies to remove these intermetallic compounds, but a hard alloy having good performance has not been developed yet.

[0024]

The intermetallic compound Co _x W _y C _z has a hardness higher than those of WC and Co, and has an action of improving the hardness of the alloy. On the other hand, the toughness thereof is lower than that of the ordinary binder phase Co, It is fragile by itself. Since the intermetallic compound Co _x W _y C _z has a small toughness in a large structure, the toughness of the alloy can be suppressed as much as possible by precipitating it in a minute amount.

The (x, y, z) of Co _x W _y C _z are those known at present (3, 9, 4), (3, 3, 1),
There are (6, 6, 1) and (2, 4, 1), all of which have the above-mentioned effects.

Mo ₂ C or Mo in the alloy reacts with free carbon in the raw WC powder (aWC + bC + cMo ₂ C).
(Or Mo) → a′WC + dMo ₂ C + eMo) to improve the wettability of the hard phase and the binder phase. In addition, the alloy composition has VC
By adding the above, the grain growth of WC in the liquid phase sintering process can be suppressed, and the densification of the alloy can be achieved. Also, if Mo is added in the absence of free carbon,
Part of WC decomposes to form W ₂ C and Mo ₂ C.

In the case of a so-called pseudo binderless cemented carbide in which the Co content in the alloy is less than 1% by weight, the presence of Co _x W _y C _z described above further improves the alloy hardness,
In addition, Co _x W _y C _z has a good wettability with the WC hard phase, and by precipitating this Co _x W _y C _z as a microstructure, it is possible to prevent deterioration of alloy toughness, The alloy can be obtained.

There is an appropriate value for the WC grain size of the raw material. If the grain size is too large, the spacing between grains becomes too large, and the amount of binder phase for forming a normal alloy with no cavities becomes large. In a quasi-binderless cemented carbide with an extremely small amount of binder phase, if the WC particles are large, many voids are generated in the alloy. Therefore, it is desirable that the WC particle size is about 0.5 to 3.0 μm.

On the other hand, HIP treatment is carried out in order to crush the cavities in the sintered body, but if there are many cavities in the alloy before HIP and the density is too low, the cavities are connected to the surface to some extent.
The pressure of the HIP reaches the inside of the nest and it becomes impossible to crush it. Therefore, it is necessary that the density be high to some extent before HIP. Therefore, the obtained sintered body is H
It is desirable that the theoretical density ratio is 98% or more before IP.

[0030]

Embodiments of the present invention will be described below.

(Example 1):

Raw materials were prepared by mixing the blended compositions (% by weight) shown in Table 1 in a ball mill for about 8 hours. The average particle size of the WC used here was 1.5 μm.
After drying and granulating these raw material powders, press molding at 1.0 T / cm ² and pre-sintering at 1470 ° C for about 1 hour, then 1320 ° C at a high pressure of 1000 kg / cm ^{2 in} an argon gas atmosphere. ,
Hot isostatic pressing sintering (HIP) was carried out for 1 hour to obtain a hard alloy.

The properties of these alloys are also shown in Table 1.
Sample Nos. 6 and 7 are comparative examples outside the scope of the present invention.

[0034]

[Table 1]

(Example 2):

W used in the hard alloy of the present invention
C grain size is 0.7μm, 1.0μm, 2μm, 3μm, 4
A so-called pseudo-binderless cemented carbide having a binder phase content of less than 0.8% by weight was produced in the same manner as in Example 1 by using five kinds of WC particle size raw materials having a particle size of μm.

The alloy densities at the respective WC grain sizes of the obtained alloy are shown in FIG. It can be seen that the alloy density changes depending on the WC particles, and the alloy density is most improved in the vicinity of 1.0 μm.

FIG. 2 compares the hardness of the pseudo-binderless alloys of the examples with the characteristics of a conventional WC-Co alloy with the amount of binder phase varied, where A is the pseudo-binder according to the examples of the present invention. B is a coarse-grained W because it shows the characteristics of the less cemented carbide.
C-Co alloy, C is a medium-grain WC-Co alloy, and D is a curve showing the relationship between the amount of binder phase and the hardness of ultrafine-grain WC-Co alloy.

As is apparent from FIG. 2, the pseudo-binderless alloy of the present invention is on the extension line of the hardness in each binder phase amount of the ultrafine grained material. This is because, in a material having coarse particles of WC, even if the amount of the binder phase is small, the volume of the binder phase filling the gaps of the WC particles is large, and the ratio depending on the characteristics of the binder phase is high. This is because the ultrafine grained material has little dependence on the properties of the binder phase, and it can be seen that the pseudo binderless alloy of the present invention is present on this extension line.

FIG. 3 shows the results of evaluation of wear resistance by CCPA using the alloys of the examples, and the results are shown with respect to the amount of binder phase (where A is a pseudo of 99% density). Binderless alloy, A'is a pseudo binderless alloy with a density of 93%).

As is clear from FIG. 3, the pseudo-binderless alloy of the present invention exhibits wear resistance 10 times to 100 times or more that of ordinary cemented carbide. This is because the wear basically originates from the soft binder phase, so the alloy of this example with extremely low binder phase is extremely wear resistant. However, in the alloy A ′ having a low density, since the WC particles are not sufficiently bonded by the binder phase due to the presence of the cavities, high wear resistance cannot be realized.

FIG. 3 compares the fracture toughness of the pseudo-binderless alloys of the examples obtained by the Vickers method with those of ordinary cemented carbides. The fracture toughness (K _IC ) of an alloy is a value that depends on the thickness of the binder phase and the interface between WC and the binder phase. The alloy of this example with an extremely small amount of binder phase has a lower fracture toughness value than the ordinary alloy, but Co _x W _y C _z
The presence of the element prevents a significant decrease in toughness.

[0043]

As described above, according to the present invention, the hardness of the hard alloy can be further improved, the wettability of the hard phase and the binder phase containing WC as a main component can be improved, and the deterioration of the alloy toughness can be prevented. In particular, when it is applied to a pseudo-binderless alloy in which Co is minute and the toughness is likely to be lowered, it is effective in improving the hardness and preventing the toughness from being lowered.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a WC grain size of a raw material and an alloy density in an example of the present invention.

FIG. 2 is a diagram showing the relationship between the amount of binder phase and hardness shown in order to compare one example of the present invention with a conventional example.

FIG. 3 is a diagram showing the relationship between the amount of binder phase and wear resistance, which is shown in order to compare one embodiment of the present invention with a conventional example.

FIG. 4 is a diagram showing the relationship between the amount of binder phase and fracture toughness, which is shown in order to compare one example of the present invention with a conventional example.

[Fig. 5] X-ray of the hard alloy of Sample No. 3 of Example 1 of the present invention
It is a diffraction diagram analyzed by line diffraction.

[Explanation of symbols]

 A Pseudo binderless alloy (density 99%) A'Pseudo binderless alloy (density 93%) B Coarse grain WC-Co C Medium grain WC-Co D Ultrafine grain WC-Co

Claims (5)

[Claims] 1. A WC having an average particle size of 2 μm or less, 80% by weight or more, 0.2% by weight or more and 2% by weight or less of Co, and the balance being a metal, carbide or nitriding group IVa, Va or VIa metal of the periodic table. A hard alloy containing one or more of a metal oxide and a carbonitride, wherein Co _x W _y C _z (x, y,
z represents an atomic ratio). 2. The method according to claim 1, wherein the IVa of the periodic table is
One or more of Va, VIa group metals, carbides, nitrides, and carbonitrides are 2.0 to 7.0 in the hard alloy.
A hard alloy comprising at least one of Mo and Mo ₂ C in weight%. 3. The hard alloy according to claim 1, wherein one or more of metals, carbides, nitrides and carbonitrides of Group IVa, Va and VIa metals of the periodic table are in a hard alloy. A hard alloy comprising 0.2 to 0.6% by weight of one or more of VC and CrC. 4. The method according to claim 1, wherein one or more kinds of metals, carbides, nitrides and carbonitrides of Group IVa, Va and VIa metals of the periodic table are W ₂ C. A hard alloy characterized by being present. 5. The hard alloy according to claim 1, wherein Co is 0.2% by weight or more and 1% by weight or less in the hard sintered body.