JPH08143987A - Production of sintered hard alloy containing plate crystal wc - Google Patents

Abstract

PURPOSE: To improve hardness, toughness, and plastic deformability by incorporating a fixed amount or more of plate crystal tungsten carbide into a sintered hard alloy. CONSTITUTION: Carbon and/or graphite is blended with a W alloy powder containing 2-30wt.% of Co and/or Ni, or further, Co, Ni, Cr, W, W2 C, WC, or W and one or more kinds among compound carbides consisting of Co, Ni, and carbon are added to the blended powder. The resulting powder mixture is mixed, compacted, and then heated in vacuum or in a nonoxidizing gas atmosphere and sintered, by which the sintered hard alloy having a composition consisting of 3-40vol.% of binding phase composed essentially of Co and/or Ni and the balance tungsten carbide can be obtained. Further, plate crystal tungsten carbide comprises >=10vol.% of the tungsten carbide in this alloy. It is preferable that, at the time of sintering the alloy, the process is constituted of two stages consisting of a stage for forming compound carbides and a stage for crystallizing plate crystal WC of 2-10μm grain size from the compound carbides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cemented carbide in which a large amount of plate-shaped tungsten carbide (hereinafter, referred to as plate-shaped WC) is contained in tungsten carbide. , Drills, end mills, cutters and cutting tools used for these, cutting tools such as insert tips, brazing tips, solid tips, plastic working tools such as drawing dies, ironing dies, forging dies, punching dies, slitters, etc. Abrasion resistant tools typified by shearing tools, bits used for road construction, civil engineering, tunnel construction, civil engineering mining tools typified by drilling tools,
Plates suitable as mechanical seals, sliding materials typified by bearings, decorative / corrosion-resistant materials typified by clock frames, fishing tackles, tie pins, nozzles, and various structural materials used for mechanical parts and parts for the chemical industry. The present invention relates to a method for producing a WC-containing cemented carbide.

[0002]

2. Description of the Related Art Cemented carbide contains tungsten carbide or a hard phase composed of tungsten carbide and a cubic compound as C.
It is a sintered alloy that is bonded with a binder phase containing o and / or Ni as a main component and has excellent properties, and thus is widely used for various purposes. This cemented carbide is
The characteristics can be adjusted mainly by the grain size of tungsten carbide, the content of the binder phase, and the content of the cubic system compound. However, in general, the properties of cemented carbide are such that strength, toughness, and fracture resistance decrease with increasing hardness and wear resistance, and conversely, hardness and wear resistance increase with increasing strength, toughness, and fracture resistance. There is a problem of showing an antinomy tendency of decreasing.

In order to solve this problem, as one proposed from one direction, attention has been paid to the anisotropy of mechanical properties due to the crystal plane of tungsten carbide, specifically, for example, of tungsten carbide. Since the (001) crystal plane has the highest hardness and the (100) crystal plane exhibits the highest elastic modulus, the (001) crystal plane having a high hardness or the tungsten carbide-containing cemented carbide obtained by growing a certain crystal plane or There is one related to the manufacturing method.

Representative examples of prior art relating to plate-shaped WC-containing cemented carbides include Japanese Patent Publication No. 47-23049, Japanese Patent Publication No. 47-23050, and Japanese Patent Laid-Open No. 57-34008.
Japanese Patent Application Laid-Open No. 2-47239, Japanese Patent Application Laid-Open No. 2-51
408, JP-A-2-138434, JP-A-2-274827 and JP-A-5-339659.
There is a gazette.

[0005]

Among the prior art relating to plate-shaped WC-containing cemented carbide, Japanese Patent Publication No. 47-23049 and Japanese Patent Publication No. 47-23050 disclose 0.1.
A hard metal containing WC having a maximum size of ˜50 μm and having a maximum size of at least 3 times the minimum size, colloidal tungsten carbide powder consisting of porous agglomerates and a Fe group metal or It describes a method for producing a cemented carbide containing plate-like crystals WC by using a mixed powder of powders of these alloys. This cemented carbide contains plate crystals WC, and it is very difficult to suppress the average particle size of the entire tungsten carbide to 1.0 μm or less, or the content of plate crystals WC is small. However, there is a problem that the effect of improving various properties of the cemented carbide represented by hardness, wear resistance, strength, toughness, and fracture resistance is weak, and particularly all of these properties cannot be improved. On the other hand, in the manufacturing method, it is difficult to adjust the colloidal tungsten carbide powder to be used, and when a cemented carbide is produced using this, the grain growth action of fine colloidal tungsten carbide that occurs during heat sintering is Since this is the method used, there is a problem that it is very difficult to control the particle size of the plate crystal WC.

Further, Japanese Patent Application Laid-Open No. 57-34008 describes a method for producing twinned tungsten carbide grown on a (001) crystal plane and bonded at the (001) plane. The twinned tungsten carbide described in the publication is difficult to produce and has a low production rate, so even if a cemented carbide is produced using this, it is the same as the cemented carbide described in the above publication. However, there is a problem that the effect is weak.

Further, JP-A-2-47239, JP-A-2-51408 and JP-A-2-13843.
Japanese Patent Publication No. 4 describes a cemented carbide containing tungsten carbide having a (0001) crystal plane grown thereon, or a composition for obtaining the cemented carbide. The cemented carbides or the cemented carbides obtained from the compositions thereof described in these three publications have a low content of tungsten carbide having a (001) crystal plane, and the average grain size of the entire tungsten carbide. Is very difficult to adjust to 1.0 μm or less, and as a result, similar to the cemented carbide described in the above publication, there is a problem that its effect is weak.

Next, JP-A-2-274827 describes a method for producing an anisotropic cemented carbide using a powder obtained by oxidizing a used cemented carbide, reducing it, and then carbonizing it. Has been done. Since the method described in the publication is a method utilizing the grain growth action of the tungsten carbide powder generated by reduction and carbonization, it is difficult to control the grain size of tungsten carbide, particularly plate-like crystals WC, There is a problem that it is very difficult to make the average particle diameter of the whole tungsten carbide 1 μm or less.

In addition, in JP-A-5-339659, a mixed powder consisting of WC of 0.5 μm or less, a cubic compound of 3 to 40% by weight, and Co and / Ni of 1 to 25% by weight is disclosed. A method for producing a plate-shaped crystal WC-containing cemented carbide by mixing and pulverizing for a long time and sintering at 1450 ° C. or higher is described. The method described in the publication is to obtain a powder containing fine and high strain amount tungsten carbide by long-time mixing and pulverization, so that the amount of impurities is large, the manufacturing process is long, and Plate W in Used Cemented Carbide
It is difficult to control the particle size and content of C, the plate-like WC content is small, and the effect is weak.

The present invention solves the above-mentioned problems. Specifically, in producing a cemented carbide,
Control of the content of plate-like crystals WC and control of the particle size thereof are performed by using a starting material having a characteristic capable of easily crystallizing plate-like crystals WC, particularly coarse-grained plate-like crystals WC during sintering. Easy, high hardness, excellent wear resistance, high toughness, fracture resistance,
It is a method that can obtain a cemented carbide with excellent impact resistance and plastic deformation resistance, and has the synergistic effect of high hardness, high toughness, and high strength impact resistance that cannot be expected with conventional cemented carbide. It is an object of the present invention to provide a method for producing a plate-shaped WC-containing cemented carbide that exhibits a long life.

[0011]

The present inventors have, for many years, been able to improve the strength, the wear resistance, and the strength of cemented carbide without sacrificing strength and strength.
When conducting a study to improve toughness and fracture resistance, it was found that the purpose tends to be achieved when a cemented carbide containing plate-like crystals WC is used, and that when coarse-grained plate-like crystals WC are used, It was found that the above-mentioned excellent properties can be obtained, and in order to obtain this cemented carbide, it can be easily achieved by using a powder in which carbon and / or graphite is added to a W alloy powder of Co and W. As a result, the present invention has been completed.

That is, the method for producing a plate-shaped WC-containing cemented carbide according to the present invention comprises: a W alloy powder comprising 2 to 30% by weight of Co and / or Ni and the balance W; and a carbon and / or graphite powder. Or a first compounded powder containing Co, Ni, Cr, W, W ₂ C,
WC, or a second compounded powder obtained by adding at least one kind of a composite carbide composed of W and Co and / or Ni and carbon, after mixing and molding, heating in a vacuum or in a non-oxidizing gas atmosphere A method for producing a cemented carbide, which comprises sintering and a binder phase containing Co and / or Ni as a main component in an amount of 3 to 40% by volume, and the balance being tungsten carbide, wherein 10% of the tungsten carbide in the cemented carbide is used. The method is characterized in that at least vol.% Is plate-shaped tungsten carbide.

When the amount of Co and / or Ni in the W alloy powder in the method for producing a plate-shaped WC-containing cemented carbide of the present invention is less than 2% by weight, the amount of binder phase generated by sintering is 3%.
When the volume% or less, it becomes difficult to sinter and the production ratio of plate-like crystals WC is reduced, so that the strength and hardness are remarkably reduced. Is 40% by volume or more, the hardness, wear resistance, and plastic deformation resistance are significantly reduced. Further, the composition of the alloy powder is such that W in which 1 wt% or less of Co and / or Ni is solid-dissolved, W ₆ Co ₇ , WCo ₃ , WNi ₄ and 20 wt% or more of Co and / or W in solid solution Alternatively, it may be an alloy in which at least one of Ni is uniformly dissolved.
Furthermore, when the cubic compound described below is contained,
For example, W alloy powder such as W—Co—Ti and W—Co—Cr—Ta alloys to which metals of the periodic tables 4a, 5a and 6a are added may be used.

The carbon and / or graphite powder in the method for producing the plate-shaped WC-containing cemented carbide of the present invention is specifically, for example, a carbon precursor substance such as graphite, carbon or petroleum pitch, or thermosetting resin. Powders can also be mentioned. Particularly, the average particle size is 2 to 20 μm
In the case of graphite, the production ratio of plate crystals WC is increased, and a coarse grained and uniform alloy structure is formed, whereby hardness and toughness are greatly improved, which is preferable. Carbon and /
Alternatively, the amount of the graphite powder added may be in a range such that the η phase (Co ₃ W ₃ C) or free carbon does not project in large amounts in the cemented carbide obtained by sintering.

The plate-like crystal WC in the method for producing a plate-like crystal WC-containing cemented carbide according to the present invention is less than 10% by volume with respect to the total amount of WC in the obtained cemented carbide, and has a hardness due to the plate-like crystal WC. Little effect of improving toughness. Further, it is preferable that the ratio of the maximum dimension to the minimum dimension of the plate-like crystals WC in the cross-sectional structure is 3.0 or more, because the toughness is significantly improved. Furthermore, it is preferable that the plate-like crystal WC has an average particle diameter of 2.0 to 10 μm, since the hardness decreases less and the toughness increases.

In the method for producing a plate-shaped WC-containing cemented carbide of the present invention, at least one metal selected from Co, Ni, Cr and W, W and Co and / or N may be used.
It is preferable to add one or more powders selected from a composite carbide consisting of i, a carbide of group 4a, 5a, and 6a metals of the periodic table, a nitride, and at least one compound among these mutual solid solutions. .

Specific examples of the composite carbide include Co ₃ W ₉ C ₄ , Co ₂ W ₄ C, Co ₃ W ₃ C, Co ₆ W ₆ C,
Examples of the compound include Ni ₂ W ₄ C and the like, for example, WC, W
₂ C, TaC, NbC, TiC, (W, Ti) C,
(W, Ti, Ta) C, TiN, ZrN, Ti (C
N), (W, Nb, Zr) CN and the like. Here, both of the composite carbide and W ₂ C have a large effect of increasing the production ratio of plate-like crystals WC and improving hardness and toughness.

In the cemented carbide obtained by adding one or more powders selected from the metal, the composite carbide and the compound, specifically, as a binder phase containing Co and / or Ni as a main component, Alloys such as Co-W, C-W-Cr, and Ni-Cr-W containing 20% by weight or less of W and Cr can be mentioned. If the amount is less than 3% by volume, sintering becomes difficult. Cavities remain inside and plate crystals WC
When the ratio of crystal formation is reduced, the strength and hardness are significantly reduced. On the other hand, when it exceeds 40% by weight, the hardness and wear resistance are significantly reduced. Further, as the cubic compound, specifically, for example, (W, Ti) C, (W, Ti, Ta)
C, (W, Ti) (C, N) and the like,
When this amount exceeds 50% by weight and increases, the amount of WC including plate-like WC relatively decreases, so that the strength and toughness significantly decrease.

In the method for producing a plate-shaped WC-containing cemented carbide according to the present invention, the first step of forming a composite carbide composed of carbon, W, Co and / or Ni during heating and sintering, and the composite carbide. The second step of producing plate crystals WC from, increases the ratio of plate crystals WC,
It is preferable because it improves hardness and toughness.

[0020]

In the method for producing a plate-shaped WC-containing cemented carbide according to the present invention, Co-containing W alloy powder reacts with carbon powder during heating and sintering to crystallize coarse-grained plate-shaped WC. In addition, the plate-like crystals WC having a coarse grain function to enhance the toughness and plastic deformation resistance of the cemented carbide.

[0021]

EXAMPLES First, the average particle size on the market is 2.3 μm.
m and W of 6.0 (abbreviated as W / M and W / C, respectively),
0.1 μm Co , 1.3 μm Ni powder, 2-4 μm
TiH₂, TaH₂Use powder to obtain the composition shown in Table 1.
Weigh and mix in a ball mill, then in vacuum at 1300 ° C
Heat treatment for 1 hour to obtain W alloy powders A to E
Was. The composition and components identified by X-ray diffraction are also shown in Table 1.
did.

[0022]

[Table 1] Next, the obtained W alloy powders A to E and 6 μm graphite (abbreviated as G), 0.02 μm carbon black (abbreviated as C), 1.2 μm Co, 5.3 μm W,
2.7 μm Cr ₃ C ₂ , 4.5 μm WC, 2.2 μm
TaC, 1.5 μm (W, Ti, Ta) C solid solution (weight ratio WC / TiC / TaC = 50/20/30,
WTT), 3.5 μm Co ₃ W ₃ C powders are weighed to the composition shown in Table 2 and inserted into a stainless steel pot together with an accent solvent and a cemented carbide pole,
After mixing and pulverizing for 48 hours, it was dried to obtain a mixed powder. Then, these mixed powders are filled in a mold to obtain 2 ton / c.
A powder compact of approximately 5.5 × 9.5 × 29 mm is created by pressurizing m ² , and placed on a sheet made of alumina and carbon fibers and heated in a vacuum with an atmospheric pressure of 10 ^-2 Torr. Then, each of the cemented carbides was obtained by the methods 1 to 7 of the present invention and the comparative methods 1 to 5 in which the temperature shown in Table 2 was maintained for 1 hour.

The cemented carbide sample thus obtained was wet-ground with a # 230 diamond grindstone to obtain 4.0 × 8.0 ×.
A 25.0 mm sample was prepared and the transverse rupture strength (JIS method) was measured. Moreover, after lapping one surface of the sample with a diamond pace of 1 μm, Vickers hardness at a load of 196 N and fracture toughness value: K ₁ c (IM method) at 490 N were measured. Furthermore, the lapped surface is photographed with an electron microscope, and the average particle diameter of WC and the ratio of the maximum diameter to the minimum diameter (aspect ratio) of the WC are 3.0.
Volume ratio of plate-like crystals WC above (to the whole WC)
I asked. Table 3 shows the results. The approximate composition is also shown in Table 3.

The cemented carbide obtained by the comparative method 1 has
About 2% by volume of pores of 5 μm were present.

[0025]

[Table 2]

[Table 3]

[0026]

The cemented carbide containing the coarse-grained plate-like crystals WC of the present invention has a hardness of 1.0 GPa or more and a fracture as compared with the conventional cemented carbide having the same composition and particle size. Toughness K1
It has a remarkably excellent effect of improving hardness and toughness, in which c is 1.5 MPa · m ^1/2 or more.

Claims (8)

[Claims] 1. A W alloy powder comprising 2 to 30% by weight of Co and / or Ni and the balance W, carbon and / or
Alternatively, a first compound powder composed of graphite powder, or Co, Ni, Cr, W, W ₂ C, W in the first compound powder.
A second compounded powder obtained by adding at least one kind of a composite carbide of C, or W and Co and / or Ni and carbon is heated in a vacuum or in a non-oxidizing gas atmosphere after mixing and molding. Sintered, Co and / or N
A method for producing a cemented carbide in which a binder phase having i as a main component is 3 to 40% by volume and the rest is tungsten carbide,
Plate-like crystal W characterized in that 10% by volume or more of tungsten carbide in the cemented carbide is plate-like crystal tungsten carbide
A method for producing a C-containing cemented carbide. 2. The first compound powder has an average diameter of 2 to 20 μm.
2. The method for producing a plate-shaped WC-containing cemented carbide according to claim 1, which contains m of graphite. 3. A W alloy powder comprising 2 to 30% by weight of Co and / or Ni and the balance W, carbon and / or
Or graphite powder and 4a, 5a, 6 of the periodic table
A third compound powder consisting of a carbide, a nitride of a group a metal and at least one compound powder among these mutual solid solutions, or Co, Ni, Cr, W,
After mixing and molding a fourth compounded powder containing at least one of W ₂ C, WC, or a composite carbide composed of W and Co and / or Ni and carbon, it is mixed in a vacuum or a non-oxidizing gas. 3 to 40% by volume of a binder phase containing Co and / or Ni as a main component, which is sintered by heating in an atmosphere;
Fabrication of a cemented carbide in which 50% by volume or less of a cubic compound consisting of at least one of carbides, nitrides and mutual solid solutions of 4a, 5a and 6a metals in the periodic table and the balance being tungsten carbide The method for producing a plate-shaped WC-containing cemented carbide, characterized in that 10% by volume or more of the tungsten carbide in the cemented carbide is plate-shaped tungsten carbide. 4. The third compounded powder has an average diameter of 2 to 20 μm.
The method for producing a plate-shaped WC-containing cemented carbide according to claim 3, wherein m of graphite is included. 5. The W alloy powder is W ₆ Co ₇ , WC.
O ₃ , WNi ₄ , or W containing 1 wt% or less of Co and / or Ni as a solid solution, or at least one of Co and / or Ni containing 20 wt% or more of W as a solid solution The method for producing the plate-shaped WC-containing cemented carbide according to claim 1, 2, 3, or 4. 6. The plate-shaped WC-containing cemented carbide according to claim 1, 2, 3, 4 or 5, wherein the plate-shaped tungsten carbide has an average particle size of 2.0 to 10 μm. Manufacturing method. 7. The plate-shaped tungsten carbide has a shape in a cross-sectional structure of the cemented carbide and has a ratio of a maximum dimension to a minimum dimension of 3.0 or more.
A method for producing a plate-shaped WC-containing cemented carbide according to 2, 3, 4, 5, or 6. 8. The first heat-sintering produces a composite carbide composed of W and Co and / or Ni and carbon.
Second step of forming a plate-like crystal WC from the composite carbide
Claim 1, 2, characterized in that it includes a process
A method for producing a plate-shaped WC-containing cemented carbide according to 3, 4, 5, 6, or 7.