JPH0559481A - Sintered hard alloy having high hardness - Google Patents

Abstract

PURPOSE:To improve the machinability, wear resistance and corrosion resistance of a sintered hard alloy by specifying Co, Mo, Mo2C, VC and WC and forming it of a hard phase consisting essentially of WC and contg. Mo, VC or the like and a bonding phase consisting essentially of Co. CONSTITUTION:This sintered hard alloy having high hardness is formed of a hard phase consisting essentially of WC having <=2mum grain size and contg. Mo or Mo2C and VC and a bonding phase consisting essentially of Co. Then, the alloy compsn. after sintering is constituted of, by weight, 0.2 to 1% Co, 2 to 7% Mo or Mo2C, 0.2 to 0.6% VC and the balance WC. Thus, the amounts of Cr and V to be added at the time of manufacturing the conventional WC powder are reduced, and the amounts of oxides such as Cr2O3 and V2O3 are reduced, by which the wettability of WC-Co improves. The obtd. above hard alloy has >=14.8g/cm<2> density, 2300kg/mm<2> Vickers hardness and 3 fracture toughness value.

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 cemented carbide having a high hardness, a high wear resistance, a high corrosion resistance, and a high rigidity, which is excellent in cutting characteristics for tools such as cutting, sliding, and drawing dies.

[0002]

2. Description of the Related Art Conventionally, a hard alloy for tools having good wear resistance and excellent cutting characteristics is composed of a hard phase composed of carbides and nitrides of IVa, Va and VIa group metal elements and a binder phase of iron group metal. It is well known that it has been obtained. Especially WC
Since the Co-based cemented carbide has the best mechanical properties, it is useful in the field of cutting tools and wear resistant tools. This WC-
The Co-based cemented carbide is obtained by drying / granulating → pressing → sintering a mixed powder of WC powder (hard phase) and Co powder (binding phase), which improves hardness and strength of the alloy. In order to improve wear resistance and the like, it is necessary to make WC particles in the alloy into fine particles. In this case, a method is adopted in which the WC powder used as a raw material is made into a fine powder. But fine WC
If a powder is used, the hard phase will undergo grain growth under liquid phase sintering. In order to prevent this, in the past, when producing WC powder, C
By adding r, V, etc., the grain growth is suppressed.

[0003]

However, when Cr and V are added to suppress the grain growth of WC as in the above-mentioned conventional example, the stability of Cr ₂ O ₃ , V ₂ O _5, etc. in WC is improved. A large amount of oxide is included, and the amount thereof is, for example, 0.3 to 0.8% in the WC raw material powder. The presence of this stable oxide hinders the wettability with a small amount of the binding metal, and prevents the densification of the alloy. As a result, there are some limits in terms of hardness and strength, making it impossible to manufacture by ordinary powder metallurgy,
Further, there is a drawback that the strength becomes low when the high pressure and high temperature method or the melting method is used.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is intended to reduce the amount of oxides in WC powder before sintering to improve the wettability of WC-Co. It is an object of the present invention to provide a high-density, high-strength cemented carbide capable of achieving the above.

[0005]

Means for Solving the Problems The inventors of the present invention, after earnest research, did not add Cr, V, etc. during the production of WC powder, and added Co, Mo or Mo ₂ C, and VC to the obtained WC powder. By mixing at a predetermined content to form a raw material powder, the amount of stable oxide can be reduced, the wettability of WC-Co is improved, and the hardness is excellent in high hardness, wear resistance, corrosion resistance, and high rigidity. The inventors have found that an alloy can be obtained, and completed the present invention.

That is, the present invention provides a WC having a particle size of 2 μm or less.
And a hard phase containing Mo or Mo ₂ C and VC, and a binder phase containing Co as a main component, and the alloy composition after sintering is 0.2 to 1.0 wt% Co. , 2.0-
7.0 wt% Mo or Mo ₂ C, 0.2 to 0.6 wt%
It is a high-hardness cemented carbide characterized by having VC and the rest being WC.

[0007]

The present invention, as described above, has WC, Co and Mo.
Alternatively, Mo ₂ C and VC are used as raw material powders. WC, which is the main hard phase, does not contain Cr, V, etc.
A WC powder having a particle size of 2 μm or less obtained by mixing 687 wt /% C powder with 3.87 wt /% W powder and carbonizing in a carbonization furnace in a non-oxidizing atmosphere is used.

Co as a binding metal is incorporated in a low proportion of 0.4% by weight. Since CR, V, etc. are not added to the WC powder, the amount of stable oxide is reduced, and thus the wettability of WC-Co is not hindered even if the amount of Co is reduced.

By the way, when the amount of Co is reduced, in addition to WC (α phase) -γ (Co phase containing W) in the alloy, W ₃ C
o ₃ C (ζ phase) intermetallic compounds and free carbon (Free
Carbon) is more likely to appear. When this appears,
This causes the hardness and strength of the alloy to decrease. In order to prevent this, in the present invention, Mo or Mo ₂ C is added in a proportion of 5.5% by weight.

On the other hand, since Cr, V, etc. are not added during the production of the WC powder, stable oxides can be prevented from being generated,
Grain growth of the hard phase (WC) is facilitated under liquid phase sintering. In order to prevent this, the present invention uses 0.4% by weight of VC.
Blend. Grain growth can be suppressed by this VC, and densification of the alloy is achieved.

An example of the production of the cemented carbide of the present invention will be described. WC, Co, Mo or Mo ₂ C, VC described above.
The raw material powder consisting of is blended with a commercially available ball mill wet mixer, and the mixture is dried, granulated, press-molded, pre-sintered under predetermined conditions, and then 50 kg at a temperature lower than the liquidus appearance temperature. It is obtained by hot isostatic pressing (HIP) in a high-pressure inert gas at a pressure of at least 1 cm ² / cm ² .

The pre-sintering conditions in the present invention are preferably 1300 ° C. to 1600 ° C. × 1 Hr in a vacuum or a special atmosphere. Sintering by hot isostatic pressing is carried out at 80 kg / in an inert gas atmosphere such as argon. under pressure over cm ² , 13
A temperature of 00 ° C to 1600 ° C x 1 Hr is suitable.

The cemented carbide obtained by the above manufacturing method is
The composition range of the cemented carbide is 0.2 to 1.0 wt% Co,
2.0-7.0 wt% Mo or Mo ₂ C, 0.2-0.6
Weight% VC, balance WC. Here, when the Co content is less than 0.2% by weight, Co does not uniformly wet the surface of the hard phase, and significant segregation occurs. As a result, the alloy-like properties are inferior. On the other hand, when Co exceeds 1.0% by weight, the Co phase wets the surface of the hard phase almost uniformly, but the characteristics of the Co phase appear as an alloy. Further, when the above Mo or Mo ₂ C is less than 2.0% by weight, it reacts with free carbon (FC) in the WC powder used, and Mo
₂ C generation or / and aWC + bC + cMo → a′WC +
The wettability of the Co phase to the hard phase due to the dMo ₂ C + eMo reaction is not promoted, and Co in the alloy segregates. On the other hand, when Mo or Mo ₂ C exceeds 7.0% by weight, M
The effect of the characteristics of o or Mo ₂ C appears as alloy characteristics, and the hardness becomes low. Further, when the above VC is less than 0.2% by weight, the wettability of VC with Co and the hard phase is poorly segregated, the grain growth suppressing effect of WC is reduced, and WC grows. On the other hand, when VC exceeds 0.6% by weight, VC
Of the alloy has a great influence on the alloy characteristics (such as a decrease in alloy hardness), and the toughness of the alloy characteristics is deteriorated due to the formation and precipitation of intermetallic compounds with other elements.

Further, the obtained cemented carbide has a density of 1
4.8g / cm ² or more, Vickers hardness is 2300kg / mm
^{It is 2} or more and the fracture toughness value is 3.0 or more.

Further, the porosity of the cemented carbide is AST.
The M standard is A06 or less, B06 or less or C02 or less. According to this ASTM standard, the nest size is 10 μm for A type
Less than 10 μm, less than 25 μm for type B, and free carbon for type C. A06 is 0.2% (vol.) In a microscopic structure magnified 200 times, and B06 is 1
0.2% (vo
l.) (1300pores / cm ² ).

[0016]

EXAMPLES The present invention will now be described in detail with reference to examples.

The four types of composition shown in Table 1 (composition weight /
%) Were mixed in a ball mill for about 8 hours to prepare raw material powders.

[0018]

[Table 1]

After drying and granulating these raw material powders, 1.0T
/ Cm ² (20 x 20 x 20 mm), press-molded and pre-sintered at 1470 ° C for about 1 hour, and then 1320 ° C at a high pressure of 1000 kg / cm ^{2 in} an argon gas atmosphere.
Hot isostatic pressing sintering (HIP) was performed for a time to obtain a hard alloy.

Table 2 shows the alloy properties after hot isostatic pressing. It can be seen that Example A is superior to Comparative Example B in high density, high hardness, and fracture toughness.

[0021]

[Table 2]

The high-strength cemented carbide according to the present invention is excellent in corrosion resistance, porosity, wear resistance, electric discharge machining, and glossiness, so that it can be used for cutting tools (V _B , K _B) for general works. _T
(Wide wear) and wear resistant tools, as well as in the field of difficult-to-work workpieces such as W-Ni.

[0023]

As described above, according to the present invention, WC having a particle size of 2 μm or less is mainly used, and Mo or Mo ₂
It is composed of a hard phase containing C and VC and a binder phase containing Co as a main component, and the alloy composition after sintering is 0.2 to
1.0 wt% Co, 2.0-7.0 wt% Mo or Mo
₂ C, 0.2 to 0.6 wt% VC, since balance is WC, Cr in WC powder, the V like is not added, it is possible to reduce the amount of stabilizing oxides, addition, Mo or Mo ₂
By adding C and VC, grain growth of the hard phase is suppressed and the wettability of WC-Co is improved. As a result, it is possible to obtain a cemented carbide having excellent cutting characteristics and having high hardness, high wear resistance, high corrosion resistance, and high rigidity as an alloy for tools such as high-pressure water jet nozzles, cutting, sliding, and drawing dies.

Claims (3)

[Claims] 1. Mainly composed of WC having a particle size of 2 μm or less, Mo
Or a hard phase containing Mo ₂ C and VC, and Co
Consisting of a binder phase consisting mainly of, and the alloy composition after sintering is
0.2-1.0 wt% Co, 2.0-7.0 wt% Mo
Or Mo ₂ C, 0.2-0.6 wt% VC, balance WC
High hardness cemented carbide. 2. The density of the obtained hard alloy is 14.8 g /
cm ² or more, Vickers hardness of 2300 kg / mm ² or more,
Further, the fracture toughness value is 3.0 or more, and the high hardness cemented carbide according to claim 1. 3. The high hardness cemented carbide according to claim 1, wherein the porosity of the obtained hard alloy is A06 or less, B06 or less, or C02 or more according to the ASTM standard.