JP2003183760A - Tungsten carbide-based hard metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultra-fine particulate hard metal having a high toughness and an extremely small WC particle size, by solving the problem associated with the addition of Ta to ultra-fine particulate hard metals, which, as in the case of combining V and Ta, results in decreased toughness. <P>SOLUTION: The tungsten carbide-based hard metal comprises 2-30% Co and/or Ni, 0.1-2.0% V, 0.1-2.0% Cr, 0.01%≤Ta<0.4% and the balance being tungsten carbide and unavoidable impurities. Here, the average particle size of tungsten carbide is ≤0.6 μm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cemented carbide, and more particularly to a so-called ultrafine cemented carbide having tungsten carbide particles having an average particle size of 0.6 μm or less.

[0002]

2. Description of the Related Art Ultrafine cemented carbide containing WC particles having an average particle diameter of 1 .mu.m or less is widely used for end mills, drills for printed circuit boards, various shear blades, etc. because of its high hardness and toughness. In recent years, along with the tendency of fine processing, the demand for ultrafine grained alloys having smaller and smaller average grain sizes has been increasing. Therefore, conventionally known V, Ta, C
Metals such as r, or compounds of those metals (carbides,
(Nitrides, carbonitrides, etc.) have been used alone as grain growth inhibitors for WC, but two or more species have been added aiming at an average grain size of 0.6 μm or less. For example, Japanese Patent Publication No. 62-56224 (Patent No. 1)
No. 5,399,991) discloses a device in which two kinds of V and Cr are added and the third phase does not appear in the alloy so as not to deteriorate the toughness. Also, the patent number 300
According to Japanese Patent Publication No. 8532, the addition of V and Cr together and the presence of the composite carbide containing V and W as the third phase at the grain boundary between the metal binder phase and WC can improve the transverse rupture strength. It is disclosed. Japanese Patent No. 3010859 is also a patent for the composite addition of V and Cr, but it does not precipitate Cr carbide and (W, V) C, but it is a composite carbide of Cr and V, more accurately (Cr, V ) It is disclosed that only ₂ C is dispersed in the matrix to improve both hardness and toughness.

Further, in the case of adding three kinds of composites, Japanese Patent Publication No.
Japanese Patent No. 56493 (Patent No. 1467291) discloses addition of three kinds of V, Cr and Mo. Also, Japanese Patent Publication No. 62-56494 (Patent No. 1487)
479), V and Cr, and Ta of 0.5 to 8.0% by weight.
It is disclosed that a finer cemented carbide can be obtained by adding three kinds of C or (Ta, Nb) C. In this case TaC
Alternatively, it is said that if the precipitation phase of the solid solution carbide phase mainly composed of (Ta, Nb) C is not more than a certain amount, the toughness is not deteriorated. Japanese Patent Publication No. 03-46538 discloses the addition of three kinds of V, Cr and 0.4 to 0.5% TaNbC. Japanese Patent No. 3206375 also discloses an ultrafine grained alloy having a WC grain size of 0.7 to 1.0 μm by the combined addition of V, Cr and 0.05 to 2.5% TaC.

[0004]

Since the WC particles undergo grain growth during sintering, the particle size of the WC particles in the alloy is larger than that before sintering. Therefore, research on a method for suppressing the grain growth of WC by adding a grain growth inhibitor has been advanced, and it is known that V is the most effective and Cr, Ta, and Mo are also effective. If it is desired to have an average grain size of 0.6 μm or less, and preferably 0.5 μm or less, a large amount of grain growth suppressing material, especially V, may be added, but if a large amount of V is added, the toughness of the alloy is rapidly lowered. . For this reason, attempts have been made to reduce the amount of V added and to supplement the resulting decrease in grain growth suppressing effect with Cr or Ta, that is, to add a grain growth suppressing material in combination. However, the inventors of the present invention, including the above-mentioned prior art, have studied earnestly, and in the combination of V and Cr, a third phase other than the binder phase and the WC phase is precipitated during cooling after sintering,
It has become clear that it reduces toughness. Therefore, if the addition amount is reduced to such an extent that the third phase does not precipitate, the grain growth suppressing effect becomes weak. With the combination of V and Ta, the appearance of the third phase becomes easier and the toughness is severely reduced. Therefore, in order to obtain a high toughness cemented carbide with an average grain size of 0.6 μm or less, and preferably 0.5 μm, V, Cr, and Ta are required.
There is no choice but to rely on the addition of 3 kinds of. However, as a result of additional testing of the above-mentioned prior art, it was found that addition of Ta is a major obstacle to reduction in toughness, as in the combination of V and Ta.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted various studies from the viewpoint of why the addition of V, Cr, and Ta can evaluate the grain growth suppressing effect but cause a significant decrease in toughness. It was observed that a distinct phase distinct from the binder phase and the WC phase, and possibly other phases, were spread throughout the alloy. This different phase and the one that is likely to be present (hereinafter referred to as the appearance phase) increases with the amount of Ta added, and with the same amount of Ta, the lower the carbon alloy is, the less it is, and the cooling rate from the completion of sintering to the liquid phase disappearance temperature is fast. It has been found that the amount decreases, and in some cases it does not appear. Moreover, it became clear that the toughness evaluated by the transverse rupture strength value drastically decreased with the increase of this appearance phase. Therefore, Ta (T
In the case of the compound a, a strict investigation was conducted on the appropriate amount of Ta). When it exceeds 0.4%, the appearance phase becomes excessive, and sufficient toughness is obtained in the range of V addition amount of 0.1 to 2.0. It became clear that could not be maintained. If you write further, V
Is 0.1 to 2.0% and Cr is 0.1 to 2.0%, no matter how the alloy carbon amount is adjusted,
Even if the cooling rate is increased in the practical range, the desired upper limit of the appearance phase is exceeded, and a sufficiently tough alloy having an average grain size of WC of 0.6 μm or less cannot be obtained.

That is, the first invention of the present application is one or two of Co and Ni: 2 to 30%, V: 0.1 to
2.0%, Cr: 0.1 to 2.0%, Ta: 0.01%
A tungsten carbide-based cemented carbide having a composition of 0.4% or more and less than 0.4%, and a balance of tungsten carbide and unavoidable impurities, wherein the average grain size of tungsten carbide is 0.6 μm or less. And the second invention is
One or two of Co and Ni: 2 to 30%, V:
0.1-2.0%, Cr: 0.1-2.0%, TaC:
0.01% or more and less than 0.4%, the remainder: a composition having a composition of tungsten carbide and unavoidable impurities, and a binder phase mainly composed of Co and / or Ni, and an average particle size of 0. Tungsten carbide of 6 μm or less, Cr, T
A cemented carbide characterized by having a structure of three phases or three phases or more with a compound mainly composed of one or more kinds of metal elements selected from a, V and W.

In the present invention, V (V component in the case of V compound) is 0.1 to 2.0%. If it is less than 0.1%, a sufficient grain growth suppressing effect cannot be obtained, which is contrary to the gist of the present invention. If it exceeds 0.2%, sufficient toughness cannot be obtained, and the transverse rupture strength falls below the practical range. Here, the practical range of the transverse rupture strength is set to 3000 MPa or more, but even if it is less than that, it can be used depending on the application, and is not strictly defined. Cr (in the case of a Cr compound, the Cr content) is 0.1 to
2.0%. If it is less than 0.1%, a sufficient grain growth suppressing effect cannot be obtained, which is contrary to the gist of the present invention. If it exceeds 0.2%, sufficient toughness cannot be obtained, and the transverse rupture strength falls below the practical range. Ta (Ta content in the case of Ta compound) is specified to be 0.01% or more and less than 0.4%. If it is less than 0.01%, a sufficient synergistic effect of suppressing the grain growth of V + Cr + Ta cannot be obtained, which is contrary to the gist of the present invention. 0.4%
With the above, sufficient toughness cannot be obtained and the transverse rupture strength falls below the practical range. Co and / or Ni is in the range of 2 to 30%. If it is less than 2%, sufficient toughness cannot be obtained. If it exceeds 30%, the hardness, which is one of the essential properties of the cemented carbide, is markedly reduced, which is not practical except for some applications.

The microstructure of the cemented carbide of the present invention is basically composed of two phases, a metal phase and a WC phase, but other phases may appear depending on manufacturing conditions. Moreover, the appearance phase is observed depending on the condition in one case or in plural cases. The appearance phase is mainly composed of one or more metals of Cr, Ta, and V and C, and sometimes Co and W as its constituent elements. The appearance phase has various constituent elements and composition ratios which vary depending on the production conditions, and therefore does not strictly define the chemical composition. As a result of intensive investigations by the present inventors,
If the appearance phase is increased above a certain amount, the toughness is significantly reduced. Therefore, another feature of the present invention is that the amount of the appearance phase is limited by defining the amount of Ta, and as a result, the toughness WC has an average grain size of 0.6 μm or less, preferably 0.4 μm or less. This is where ultra-fine grained alloys are obtained. Hereinafter, the present invention will be described in detail with reference to Examples.

[0009]

Example: As a raw material powder, WC having an average particle size of 0.6 μm
The powder, about 1 μm of Co, VC, Cr ₃ C ₂ , and TaC raw material powders were blended so as to obtain the final composition shown in Table 1, (VC, Cr3C2, and TaC are V and C, respectively).
After being mixed for 12 hours in an alcohol containing a molding binder with an attritor, the mixture was granulated and dried by spray drying.

[0010]

[Table 1]

The obtained granulated powder was press-molded at a pressure of 100 MPa to obtain a green compact, and the green compact was sintered in a vacuum atmosphere of 10 Pa to obtain a sintered body. Next, each of these sintered bodies was ground to prepare a JIS bending test piece of 4 mm x 8 mm x 24 mm, and the bending strength by 3-point bending was measured at a span of 20 mm, and the Rockwell A scale hardness ( HRA is also measured, and scanning electron microscope (SE
The average grain size of WC was determined by observing the structure in (M). In addition, the fracture surface after measuring the transverse rupture strength was measured with an X-ray micro analyzer (XM
Elemental mapping was performed in A) to investigate the presence or absence of appearance phases.
The results are summarized in Table 1. For sintering, we selected the temperature that seems to be optimal from the study results. Since the amount of the appearance phase decreases when the cooling rate after sintering is fast, the rapid quenching with nitrogen gas was performed in the partial cooling process.

From Table 1, it can be seen from the examples that the combined addition of V, Cr, and Ta makes the synergistic effect remarkable by controlling the respective amounts. In Comparative Example 1, since the Ta addition amount is 0, there is no synergistic effect of mixing the three types, and the transverse rupture strength is 3
It shows a low value of 000 MPa or less. It is speculated that there is an internal appearance phase that has a remarkable toughness-reducing property. Invention Example 2
Nos. 5 to 5 are high toughness alloys with an average grain size of WC of 0.6 μm or less and a bending strength of 3000 MPa or more. In Comparative Example 6, the Ta content exceeds 0.4%, so that the amount of the appearance phase increases and the transverse rupture strength is less than 3000 MPa.

In Comparative Example 7, since the amount of V added was 0, the average grain size of WC was coarsened to 0.65 μm, and the grain suppressing effect was weak. Inventive Examples 8 to 10 have V content within the range of the present invention, that is, within the range of 0.1 to 2.0%, so that both grain growth and reduction in toughness are suppressed, and ultrafine grains have high toughness. It is an alloy of. In Comparative Example 11, the bending strength is 30 because V is excessive.
A sharp decrease in toughness is recognized when it is 00 MPa or less. In Comparative Example 12, since the added amount of Cr is 0, the grain growth suppressing effect is weak. Comparative Example 14 has an excessive amount of Cr and has a grain growth suppressing effect, but has a transverse rupture strength of 3000 MPa or less and low toughness. In Comparative Example 15, Co is too small and sufficient toughness is not obtained. Comparative Example 18 is C
O is excessive and rigidity becomes insufficient, and sufficient bending strength is not obtained. In other examples of the present invention, the average particle size of WC is 0.6.
Achieving a minimum of 0.36 μm and a bending strength of 30
It is maintained at 00 MPa or more.

[0014]

From the above, the cemented carbide of the present invention has a very small WC grain size and high toughness, and is used for various cutting tools, shearing tools, small diameter end mills, printed circuit board drills, etc. Excellent performance when used for.

Claims (2)

[Claims] 1. One or two of Co and Ni: 2 to
30%, V: 0.1-2.0%, Cr: 0.1-2.0
%, Ta: 0.01% or more and less than 0.4%, and the balance: tungsten carbide and inevitable impurities, and the average particle size of tungsten carbide is 0.6 μm or less. And tungsten carbide based cemented carbide. 2. One or two of Co and Ni: 2 to
30%, V: 0.1-2.0%, Cr: 0.1-2.0
%, TaC: 0.01% or more and less than 0.4%,
The rest: a binder phase having a composition of tungsten carbide and unavoidable impurities, and containing Co and / or Ni as a main component, and tungsten carbide having an average particle size of 0.6 μm or less,
A cemented carbide having a three-phase or three-phase structure with a compound mainly containing one or more metal elements selected from Cr, Ta, V and W.