JPH1121119A - Production of compound carbide and cemented carbide using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a WC type compound carbide consisting of chromium-containing fine primary crystals by regulating the average grain size by the Fischer method (Fsss method) to a specific value or above, also regulating the half-width of the 211 face of the WC crystal by X-ray diffraction and the grain size by the Fsss method so that they satisfy a specific relation, and specifying the shrinkage factor at the time of manufacture of a cemented carbide. SOLUTION: As a raw material powder, 5 to 7 wt.% of W powder and C powder, having 1.0 to 7.0 μm average grain size, and 0.2 to 2.5 wt.%, as an additive quantity expressed in terms of metallic chromium based on the amount of carbide, of any of chromium carbide, metallic chromium, chromium oxide, and chromium-containing inorganic and organic compounds are blended. The resultant powder mixture is carbonized at 1200 to 1700 deg.C in a steam current, in an inert atmosphere of nitrogen, argon, etc., or in vacuum. By the above procedure, a chromium diffused phase is formed in the WC grain. Further, when the half-width of the 211 face (JCPDS card 25-1047, d=0.9020) and the grain size by the Fischer method are represented by Y and X, respectively, Y>0.61-0.33 log (X) is satisfied. Moreover, the shrinkage factor is regulated to 16.7 to <20%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to powder metallurgy having fine primary crystal grains as a raw material of a WC-Co-based cemented carbide having high hardness and high strength and having a low shrinkage rate during sintering of cemented carbide. The present invention relates to a WC-based composite carbide powder for use and a method for producing a cemented carbide using the same.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Unexamined Patent Publication No.
JP-A-5-147916 (hereinafter referred to as prior art 1 and prior art 2 respectively) discloses that WC powder having an average particle size of 0.5 μm or less is used as a raw material, and as a grain growth inhibitor. V is 0.1 to 2% by weight, Cr is 0.1 to 2% by weight, Ta is 0.2 to 3% by weight, and Co or Ni is 5%.
WC having a composition of WC phase of 0.8 μm or less, with a composition consisting of WC and unavoidable impurities,
-Co-based cemented carbide is disclosed. This WC-Co based cemented carbide is used for cutting tools such as end mills, reamers, and various types of shearing blades.

[0003] In a WC-Co-based cemented carbide, the apparent density decreases as the particle size of the WC powder becomes finer, and the shrinkage rate generated during sintering of the cemented carbide increases. WC-C of 0.8μm or less WC phase
The shrinkage ratio of the o-based cemented carbide is 20% or more, which makes it difficult to accurately adjust the dimensions of the cemented carbide, and has the disadvantage of causing defects such as pores.

[0004]

In recent years, there has been a strong demand for automation of the cutting and cutting processes described above, and tools used for these processes tend to be used under severe conditions. WC powder of 1 μm or less is used as a raw material for these tools. Many of these WC powders are carbonized at a low temperature of 1300 ° C. or less, and are unstable and easily grow grains. Are affected by the particle size distribution of the W powder, so that coarse particles are likely to be mixed, and these are defects that reduce the strength of the cemented carbide.

Further, these materials do not satisfy the demand for high dimensional accuracy due to high shrinkage.

Further, in order to produce WC powder of 1 μm or less used for fine-grain cemented carbide, W powder of 1 μm or less is required, which is more expensive than coarse W powder of 1 μm or more. Therefore, the cost of the fine WC powder was high, and the fine cemented carbide was not satisfactory in terms of price.

[0007]

Means for Solving the Problems Therefore, the present inventors have proposed:
Research was conducted to produce a WC-Co based cemented carbide having a uniform structure. As the raw material powder, W powder having an average particle size of 1.0 to 7.0 μm, 5 to 7% by weight of C powder, and 0.2 to 2.5% by weight of carbide are added as metal chromium. Any of inorganic or organic compounds containing chromium carbide or metallic chromium or chromium oxide or chromium is mixed with these metal powders, carbon powders, oxide powders, inorganic or organic compound powders, mixed, and then mixed. This mixed powder is carbonized at 1200 to 1700 ° C. in a hydrogen stream, in an inert atmosphere such as nitrogen or argon, or in a vacuum, and a chromium diffusion phase is formed on the WC particles to thereby form a WC crystal 211 by X-ray diffraction. Assuming that the half width of the surface (JCPDS card 25-1047, d = 0.920) is Y and the particle size by the Fisher (Fsss) method is X, Y> 0.61-0.33 log A cemented carbide having a high hardness and high strength WC phase microstructure of 1 μm or less and a shrinkage of 16.7 to 20% can be obtained from the WC-based composite carbide powder characterized by being (X). .

Further, if necessary, Ta, V, Mo, Nb, and the like for suppressing the grain growth occurring during the sintering of the cemented carbide.
One or more oxides or carbide powders of Zr are added in an amount of 0.2 to 3.5%, and the remainder is composed of WC and unavoidable impurities. It has high hardness and high strength 1μm or less WC phase microstructure from WC-based composite carbide powder which formed fine primary WC crystal particles by diffusing chromium,
A cemented carbide having a shrinkage of 16.7% or more and less than 20% is obtained.

Therefore, in producing a fine-grained cemented carbide as in the prior art, a finer WC powder having a particle size of 1 μm or less by the Fsss method is not used, and a uniform grain size, a low shrinkage rate and a low dimensional accuracy are used. It has become possible to produce cemented carbide with excellent performance.

Next, the reason why the manufacturing conditions in the present invention are limited as described above will be described.

First, the average particle size of the raw material W powder will be described. If the average particle size of the raw material W powder is less than 1.0 μm, it is too fine, the diffusion of chromium into the W particles becomes non-uniform, and abnormal growth due to coalescence of the W particles is likely to occur. When the thickness exceeds 7 μm, chromium does not diffuse to the center of the W particles, and the cemented carbide becomes a non-uniform braid.
The average particle size was adjusted to 1.0 to 7.0 μm.

Next, the amount of chromium added will be described.
The larger the amount of chromium added, the easier it is to form fine primary WC particles. However, if the amount of chromium is too large, it exceeds the solid solution limit in the binder phase and the third phase, which causes a decrease in strength, precipitates, so that it is 2.5% by weight or less. And When the addition amount of chromium is small, the generation of fine primary WC particles becomes insufficient, so the content was set to 0.2% by weight (preferably 0.4% by weight or more).

Next, the addition amounts of Ta, V, Mo, Nb, and Zr will be described. Ta, V, Mo, Nb. If the addition amount of Zr is less than 0.2%, the effect of suppressing grain growth during sintering of the cemented carbide cannot be expected and the effect of refining the WC phase cannot be expected. Conversely, if the content is too large, the content exceeds the solid solution limit in the binder phase or the WC phase, and a third phase that causes a decrease in strength is precipitated, so that the content is set to 3.5% by weight or less.

Next, the half width (half width) by X-ray diffraction will be described. 2 of WC crystal by X-ray diffraction of WC powder
11 (JCPDS card 25-1047, d = 0.
9020) is Y, and the particle size by the Fsss method is X, Y <0.61-0.33 log
In the case of (X), the value of the half value width with respect to the particle size of the Fsss method is small, so that it becomes impossible to produce a cemented carbide having a fine and uniform particle size.

Therefore, the 211 face of the WC crystal (JCPDS card 25-1047, d =
0.9020) is defined as Y, and when the particle size by the Fsss method is defined as X, the value of Y is defined as Y> 0.61-0.33 l.
og (X).

Finally, the shrinkage ratio will be described. According to the conventional general method, the shrinkage ratio of the cemented carbide from the WC powder having an average particle size of 0.8 μm or less is 20% or more.
If the dimensional variation of the sintered body becomes large and the shrinkage is reduced by pressing at a high pressure, cracks occur in the green compact or the life of the press die becomes extremely short. Therefore, the content is set to 16.7% or more and less than 20% at which the above-mentioned problem is solved in a practical range of 0.5 to 2 ton / cm ² pressing pressure.

[0017]

Embodiments of the present invention will be described below.

First, an example of the production of a WC-based composite carbide powder for powder metallurgy, in which fine primary WC crystal particles of the present invention are formed, will be described.

W powder as a raw material powder shown in Table 1 below,
C powder, metallic chromium or fermented chromium or an inorganic or organic compound containing chromium, Ta, V, Mo, Nb, Z
The oxide, metal or carbide powder of r was blended in the composition shown in Table 1 below, mixed for 30 minutes with a Henschel mixer, and carbonized under the conditions shown in Table 1 below. WC
The properties of the powders are shown in Table 2 below, and one WC powder
An excess or deficiency of W powder or C powder is wet-mixed with an attritor for 10 hours so that the 0 wt% Co powder and the sintered alloy have a sound carbon content, and the dried powder mixture is dried.
Press molding at a pressure of 5 to ² ton / cm ² , sintering the molded body in vacuum at 1400 ° C. for 1 hour,
The HIP material was subjected to a HIP treatment at 1000 atm, and the particle size of the WC phase of the HIP material (structure observation with a scanning electron microscope (SEM)), bending strength, hardness, shrinkage, and dimensional variation were determined.
The results are shown in Table 2 below. The shrinkage was determined by the following equation (1).

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

(Equation 1)

For the purpose of comparison, WC powder according to the conventional method was mixed with W powder, C powder or chromium oxide powder in the composition shown in Table 1 and mixed for 30 minutes with a Henschel mixer. The carbonization was carried out under the conditions described above. The properties are shown in Table 2 below. Each WC powder was wet-mixed with 10 wt% Co powder and insufficient C powder for 10 hours using an attritor so that the sintered alloy had a sound carbon content. Then, the dried mixed powder is press-molded at a pressure of 0.5 to 2.0 ton / cm ² , and
After sintering at 00 ° C for 1 hour,
HIP processing was performed at 1000 atm. Table 2 shows the characteristics of the HIP material.

From the above results, the WC-based composite carbide of the present invention allows the WC particles to diffuse Cr, V, Ta, Mo, Nb, and Zr, and has fine primary WC crystal grains. The 211 plane of the WC crystal (J
CPDS card 25-1047, d = 0.920)
Where Y is the half-value width of Y and X is the particle size determined by the Fsss method, the characteristic is that Y> 0.61-0.33 log (X), the shrinkage of the fine WC crystal is low, and the dimensional variation is small. The conventional methods 1 to 4 do not have fine primary WC crystal particles, whereas
The half-value width of the 211 plane of the WC crystal by X-ray diffraction is small,
Y <0.61-0.33 log (X).

Therefore, when the composite carbide of the conventional method is used, the grain size of the WC phase in the cemented carbide is large, the hardness is low, the shrinkage is large, and the dimensional variation is large.

On the other hand, as described above, according to the embodiment of the present invention, the composite carbide is formed on the 211 face of the WC crystal (JCPDS card 25-1) by X-ray diffraction of WC powder.
047, d = 0.9020), the half-width is Y, and Fss
When the particle size by the s method is X, Y> 0.61-0.
By having the characteristic of 33 log (X), it is possible to provide a high-hardness, high-strength, fine-grain cemented carbide having a low shrinkage ratio of fine WC crystals and a small dimensional variation.

[0027]

As described above, according to the present invention, according to the present invention, the composite carbide has 211 faces of a WC crystal obtained by X-ray diffraction of WC powder (JCPDS card 25-1047, d =
When the half width of 0.9020) is Y and the particle size by the Fsss method is X, Y> 0.61-0.33 log
By providing the feature (X), a high-hardness and high-strength fine-grained cemented carbide having a low shrinkage rate of fine WC crystals and a small dimensional variation, a composite carbide as a raw material powder thereof, and a method for producing the same are provided. can do.

Claims (6)

[Claims] 1. A WC-based composite carbide composed of tungsten carbide composed of fine primary crystals containing chromium in the range of 0.2 to 2.5% by weight, having an average particle diameter determined by a Fischer (Fsss) method. At 1 μm or more, 211 face of WC crystal by X-ray diffraction (JCPDS card 25-
1047, d: 0.9020), the half-width of Y, Fsss
When the particle size by the method is X, Y> 0.61-0.33
A composite carbide characterized by satisfying a relational expression of log (X) and having a shrinkage ratio of 16.7% or more and less than 20% when a cemented carbide is manufactured. 2. The composite carbide according to claim 1, wherein T
a, V, Mo, Nb, Zr.
A composite carbide comprising 2 to 3.5% by weight. 3. W powder having an average particle size of 1.0 to 7.0 μm, C of 5 to 7% by weight, and 0.2 to 2.5% of chromium element.
% Of chromium carbide, metallic chromium, chromium oxide, an inorganic compound or an organic compound, and carbonized at 1200 to 1700 ° C. in an inert atmosphere such as hydrogen, nitrogen, argon or a vacuum. Production method. 4. A process for producing a cemented carbide, comprising mixing, pressing and sintering Co powder with the composite charcoal compound according to claim 1 to obtain a cemented carbide having a shrinkage of 16.7% or more and less than 20%. Method. 5. W powder having an average particle size of 1.0 to 7.0 μm,
5-7% by weight of C and 0.2-2.5% by weight of chromium element
Chromium carbide, metallic chromium, chromium oxide, inorganic compounds or organic compounds, Ta. V, Mo, Nb, Zr at least one oxide, metal or carbide of 0.2 to 3.5
% By weight and carbonized at 1200 to 1700 ° C. in an inert atmosphere of hydrogen, nitrogen, argon or the like or in a vacuum. 6. A method for producing a cemented carbide, comprising mixing, pressing and sintering the composite carbide according to claim 2 and Co powder to obtain a cemented carbide having a shrinkage of 16.7 to less than 20%. Method.