JP2001329331A - High hardness and high toughness cemented carbide and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide WC-Co cemented carbide excellent in hardness and toughness even though the kind and adding amount of a particle growth inhibitor are limited. SOLUTION: This cemented carbide has a composition containing, by weight, 4 to 20% Co and Cr and/or a Cr compound of 0.2 to 2% as a metallic content, and the balance WC with the average particle size of <=1 μm with inevitable impurities, and also, in the temperature rising stage for sintering, gas pressure, in the case the gas pressure in the furnace in a part or the whole in which the temperature in the furnace is >=1,500 K is defined as P (MPa), the average particle size of the raw material of WC composing the body to be sintered as (x) (μm), and the Co content as (y) (%), at least satisfying P>=9/(xy) is applied, and then, sintering is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a WC-Co cemented carbide having much higher hardness and toughness than conventional WC-Co cemented carbide.

[0002]

2. Description of the Related Art A WC-Co cemented carbide has a characteristic that if the grain size of WC is reduced, a decrease in toughness can be suppressed even if the hardness is increased. For this reason, WC-Co-based cemented carbides are used for processing tools for IC substrates, etc., utilizing their high hardness and high toughness. However, even in such a WC-Co alloy, WC grain growth in the sintering step is inevitable in the production of the alloy, and as a result, both the hardness and the toughness may be reduced due to coarsening of the grain size. Therefore, VC, TaC, NbC, Ti are used for the purpose of suppressing the grain growth of WC.
It has been common practice to add a small amount of a transition metal carbide such as C or Cr ₃ C ₂ .

[0003]

However, as a result of repeated experiments and studies conducted by the present inventors, it was found that VC, Cr ₃ C ₂ , and TaC were the most effective in suppressing the grain growth of WC.
C has almost no effect of suppressing grain growth. Further, VC increases the hardness but slightly lowers the toughness, and it has been found that Cr ₃ C ₂ is particularly effective in improving the toughness.

[0004] The present invention has been made in view of such circumstances, and is intended to provide a WC-Co cemented carbide having excellent hardness and toughness while limiting the type and amount of the transition metal carbide. It is something to offer.

[0005]

According to the present invention, the gas pressure in the furnace is set to P (MPa), the average particle size of the raw material of WC constituting the sintered body is set to x (μm), and the Co content is set to y ( %), P
A cemented carbide sintered by applying a gas pressure of ≧ 9 / (xy), wherein the cemented carbide is 4% ≦ Co ≦ 20% and contains 0.2% of Cr and / or Cr compound as a metal component. ~ 2%
A high-hardness and high-toughness cemented carbide characterized by the balance consisting of WC having an average particle size of 1 μm or less and unavoidable impurities. The manufacturing method is 4% ≦ Co ≦ 20% (meaning by weight%, the same applies hereinafter), Cr And / or a Cr compound having a metal content of 0.2
WC with an average particle diameter of 1 μm or less, and in the heating process for sintering, the gas pressure in the furnace is increased to P or K when the temperature in the furnace is 1500 K or more. (MPa), assuming that the average particle size of the WC raw material constituting the sintered body is x (μm) and the Co content is y (%), a gas pressure of P ≧ 9 / (xy) is applied. It is a high-hardness and high-toughness cemented carbide characterized by sintering. More preferably, WC is partially replaced with a compound of TaC and / or Ta in the range of 0.1 to 0.2%. It is a high hardness and high toughness cemented carbide.

The present invention contains 4% ≦ Co ≦ 20%, Cr, Ta, V or a compound thereof as a grain growth inhibitor, the balance consisting of WC having an average particle size of 1 μm or less and unavoidable impurities, and sintering. The gist is to pressurize with a gas pressure to promote the effect of suppressing grain growth and to suppress the decrease in toughness by limiting the amount of the grain growth inhibitor added as much as possible. Also, the gas pressure in the furnace is preferably P ≧ 10 /
(Xy).

[0007]

As described above, when the hardness of the alloy is increased, the toughness tends to be reduced, but the present invention is based on Cr and / or Cr.
While increasing the hardness by adding the compound of
Alternatively, the toughness is reduced by the addition of a Cr compound by using the effect of suppressing the grain growth by pressurizing to limit the amount of the addition and prevent the toughness from being reduced.

The reasons for limiting the amount of the added component are as follows.

4% ≦ Co ≦ 20% The toughness of WC with high hardness and insufficient toughness is improved by adding Co. However, if the added amount is less than 4%, a sufficient effect of addition cannot be obtained. If it exceeds 20%, on the contrary, the hardness becomes insufficient.

0.2% <Cr and / or Cr compound ≦ 2% When the addition amount is 0.2% or less, the effect of suppressing grain growth is not improved and the addition effect cannot be obtained. On the other hand, if it exceeds 2%, the toughness becomes insufficient.

0.1% <V and / or compound of V ≦ 2% When the addition amount is 0.1% or less, the effect of suppressing grain growth is not improved and there is no addition effect. On the other hand, if it exceeds 2%, the toughness becomes insufficient.

0.1% <Ta and / or Ta compound <2% When the addition amount is 0.1% or less, the effect of suppressing the grain growth is not improved and the addition effect is insufficient. On the other hand, if it exceeds 2%, the toughness becomes insufficient.

Average particle size of WC: 1 μm or less When a WC coarsening inhibitor is added to a WC-Co cemented carbide, the effect of addition depends on the average particle size of WC.
The present invention has an average particle size of 1 μm or less, particularly 0.3 to 0.8 μm.
Is effective in the case of.

P ≧ 9 / (xy) In the present invention, sintering is promoted by gas pressure at a temperature not lower than the liquid phase generation temperature, and the grain refinement and the toughness of the alloy are improved. Naturally, the grain growth becomes more remarkable as the sintering temperature is higher and the holding time is longer. However, the density ratio is almost 100
%, It is desirable that the sintering temperature is high and the holding time is long. Therefore, if the sintering temperature is lowered to suppress grain growth, a density ratio of 100% cannot be achieved, and a good sintered body cannot be obtained. Therefore, when sintering is promoted by gas pressure, a sintered body having a density ratio of 100% is obtained. That is, sintering pressure is equivalent to the effect of suppressing grain growth and promoting sintering. According to the present invention, based on such viewpoints, the effective gas pressure was investigated for various alloys having a limited grain growth inhibitor. As a result, the effective gas pressure P (Mpa) was determined as the average particle diameter x (μm) of the WC raw material powder.
And the Co content y (%) of the alloy, and the relationship is P
≧ 9 / (xy), desirably P ≧ 10 / (xy). In other words, the smaller the Co content, the higher the required pressure, and the smaller the average particle size of the WC raw material powder, the higher the required pressure. This seems strange at first glance. According to conventional sintering theory, the finer the grain, the higher the surface energy, and that energy promotes sintering. However, the promotion of sintering by gas pressure is more sensitive to coarser grains and less sensitive to finer grains. When P ≦ 9 (xy), the effect of pressurization cannot be expected. Hereinafter, examples will be described in comparison with comparative examples.

[0015]

Example 1 A JIS bent piece was press-formed from a test material in which the proportions of the powder materials of the constituent components were mixed in the range shown in Table 1.
After vacuum heating to 1350 ° C., N ₂ gas was introduced at the same temperature, the pressure in the furnace was increased, and the temperature was maintained for 30 minutes, followed by cooling to complete sintering. The porosity, WC average particle size, bending force and hardness were measured using the JIS bending test piece thus obtained.
The values are also shown in Table 1.

[0016]

[Table 1]

As is clear from Table 1, in each of Examples 1 to 16 of the present invention, a dense sintered body can be obtained by adjusting the gas pressure so as to be inversely proportional to the WC particle size and the Co amount. ,
High hardness, high toughness, low porosity, and a density ratio of almost 100%. Examples 1 to 9 of the present invention using Cr, a carbide of Cr as a grain growth inhibitor had high transverse rupture strength of 4000 Mpa or more, and Examples 10 to 16 of the present invention to which a Ta compound was further added.
However, the same bending strength and hardness were obtained.

On the other hand, Comparative Example 17, which is out of the range of the present invention, has the same composition and the same hardness but has the same porosity as the Comparative Example 3 in spite of the small WC average particle diameter, as compared with Example 3 of the present invention. High bending strength is very poor. In comparison with Inventive Example 9 in which the amount of Co and the WC particle size are the same and the hardness is almost the same, Inventive Example 9 has a much higher transverse rupture strength despite the addition of a large amount of Cr. Comparative Examples 18, 19, 20, 21 each have the same composition,
Compared with inventive examples 4, 5, 7, 8 of the same WC particle size,
Although the hardness is almost the same, the porosity is high and the bending strength is very poor.

[0019]

As described in detail above, the cemented carbide of the present invention can provide a WC-Co-based cemented carbide having excellent toughness while maintaining high hardness.

Claims (4)

[Claims] When the gas pressure in the furnace is P (MPa), the average particle diameter of the WC raw material constituting the sintered body is x (μm), and the Co content is y (%), P ≧ 9. / (Xy) is a cemented carbide sintered by applying a gas pressure, wherein the cemented carbide is 4
% ≦ Co ≦ 20%, containing 0.2% to 2% of Cr and / or a Cr compound as a metal component, with the balance being WC having an average particle size of 1 μm or less and unavoidable impurities, and characterized by high hardness and high toughness. Hard alloy. 2. The high-hardness and high-toughness cemented carbide according to claim 1, wherein a part of WC is 0.1 to 0.2% of Ta.
A high hardness and high toughness cemented carbide characterized by being replaced with a compound of C and / or Ta. 3. 4% ≦ Co ≦ 20%, Cr and / or C
The compound contains 0.2 to 2% of an r compound as a metal component, the balance being WC having an average particle size of 1 μm or less and unavoidable impurities, and a furnace temperature of 1500 in a heating process for sintering.
The gas pressure in the furnace is P (MP
a) The average particle diameter of the WC raw material constituting the sintered body is x
(Μm), when the Co content is y (%), P ≧ 9 /
A method for producing a high-hardness and high-toughness cemented carbide characterized by sintering by applying a gas pressure of (xy). 4. The method for producing a high-hardness and high-toughness cemented carbide according to claim 1, wherein the gas pressure P in the furnace is P ≧ 10 / (xy),
A method for producing a high-hardness and high-toughness cemented carbide characterized by sintering by applying a gas pressure of