JP2802587B2 - Manufacturing method of plate-shaped WC-containing cemented carbide - Google Patents

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 plate-like WC-containing cemented carbide for producing a cemented carbide having plate-like WC crystals, and more particularly, to a method for producing a plate-like WC in a cemented carbide. Cutting tools such as bites, drills, and end mills, drawing dies, and ironing dies that have excellent hardness, toughness, wear resistance, fracture resistance, plastic deformation resistance, and heat crack resistance by forming crystals. , Composition processing tools such as forging dies, punching dies,
Wear-resistant tools typified by shearing tools such as slitters, sliding materials typified by mechanical seals and bearings,
This is a method for producing plate-like WC-containing cemented carbide, which is the optimal method for producing corrosion-resistant and decorative materials such as watch parts, tie-pins, fishing tackle parts, and structural materials such as various precision machine parts. is there.

[0002]

2. Description of the Related Art In general, a cemented carbide comprising a hard phase of a metal compound and a binder phase of a metal has been put to practical use in a variety of applications. In this conventional cemented carbide, when the hardness is increased and the wear resistance is improved, a decrease in toughness and a decrease in fracture resistance occur,
Conversely, there is a problem that when the toughness and the fracture resistance are increased, the hardness and the wear resistance are reduced, which is a trade-off tendency. Many proposals have been made to solve this problem.

As one direction of these proposals, attention has been paid to the anisotropy of mechanical properties due to the crystal plane of WC. Specifically, for example, the (001) plane of the WC crystal has the highest hardness and (100) ) Since the plane direction shows the highest elastic modulus, it is preferentially grown in the (100) plane direction, and (001)
Plate-shaped WC represented by triangular or hexagonal shape with developed surface
And a method of manufacturing the same.

[0004] Representative examples of prior art relating to plate-like WC include Japanese Patent Publication No. 47-23049 and Japanese Patent Publication No. 47-2.
JP-A-3050, JP-A-57-34008, JP-A-2-47239, JP-A-2-51408, JP-A-2-138434, JP-A-2-274
827 and JP-A-5-339659.

[0005]

Among prior arts relating to a plate-like WC, Japanese Patent Publication No. 47-23049 and Japanese Patent Publication No. Sho 4
Japanese Patent Application Laid-Open No. 7-23050 discloses a plate using, as a starting material, a composition comprising a colloidal tungsten carbide powder formed of a porous aggregate for growing a plate-like WC and a powder of Fe, Ni, Co or an alloy thereof. A method for producing a cemented carbide containing WC is described. The starting materials of the compositions described in these two publications are difficult to prepare colloidal tungsten carbide powder, and when using this to produce cemented carbide, a plate-like WC crystal during heat sintering is used. There is a problem that the production ratio is small, it is difficult to control the particle size and content thereof, and the whole manufacturing process is complicated and expensive.

JP-A-57-34008 discloses that a small amount of a Fe group metal salt is added to a strongly pulverized mixed powder of W and C, and then heated and carbonized to change the (001) plane into a twin plane. It describes a method for producing twin tungsten carbide joined as a. The powder obtained by the method described in the publication has a low content ratio of twin tungsten carbide, and is difficult to separate.When a cemented carbide is produced using this powder as a starting material, There is a problem that the twin tungsten carbide content is further reduced and the effect is extremely weakened.

Further, JP-A-2-47239 and JP-A-2-138434 disclose that a solid solution of (W, Ti, Ta) C containing tungsten carbide in a supersaturated state is used as a starting material to form a sheet during heat sintering. It describes a method for producing cemented carbide by crystallizing WC. And, regarding the starting material of the solid solution composition containing tungsten carbide in supersaturation described in both these publications,
It is described in detail in JP-A-2-51408.
When a cemented carbide is produced using a solid solution composition containing tungsten carbide in supersaturation described in these three publications, the rate of formation of plate-like WC during sintering is small, and the composition components are restricted. There is a problem that it can be applied only to the cemented carbide that has been used.

[0008] Japanese Patent Application Laid-Open No. 2-274827 discloses that a composition powder obtained by oxidizing and reducing a used cemented carbide and then carbonizing the same is used as a starting material. A powder for producing an anisotropic cemented carbide alloy compact in which fine tungsten carbide in the starting material is grain-grown into plate-like WC crystals is described. In the composition powder described in the publication, the production process for producing this powder is complicated and expensive, and when producing a cemented carbide using this powder, the generation ratio of plate-like WC crystals is low. There is a problem that it is difficult to control the particle size.

In addition, JP-A-5-339659 discloses that a WC of 0.5 μm or less, a cubic compound of 3 to 40% by weight, a Co and / or Ni of 1 to 25% by weight are used.
Using a starting material consisting of a mixed powder consisting of
A method for producing a cemented carbide having a plate-like WC crystal by sintering is described above. The starting material described in the publication is fine by long-time mixing and pulverization, and because it is a powder containing tungsten carbide with a high strain amount,
There is a problem that the amount of impurities increases, the manufacturing process time increases, and when using this to produce a cemented carbide, the generation rate of plate-like WC crystals is small, and it is difficult to control the particle size. .

[0010] The present invention has solved the above-mentioned problems, and specifically has a feature that a plate-like WC crystal can be easily formed at the time of sintering in producing a cemented carbide. By using the starting material, it is possible to easily control the content of the plate-like WC crystal and the particle size thereof, and obtain a cemented carbide having excellent hardness, wear resistance, and high toughness and fracture resistance. A method of producing a plate-like WC-containing cemented carbide that exhibits a synergistic effect due to high hardness, high toughness, and high strength that cannot be considered with cemented carbides obtained by conventional methods and has a long life. It is the purpose.

[0011]

Means for Solving the Problems For many years, the present inventors have studied the strength and strength of a cemented carbide without reducing its hardness and wear resistance.
While studies were being conducted to improve toughness and fracture resistance, it was found that a cemented carbide containing a plate-like WC crystal would tend to achieve its purpose. In order to obtain this cemented carbide, The selection of starting materials to be used, in particular, the adjustment of the content of the carbon source and the particle size thereof for producing plate-like WC, and the generation of a composite carbide composed of W, C and Co in the sintering step, The present inventors have found that plate-like WC crystals can be easily and largely produced in a cemented carbide in the present invention, and have completed the present invention.

That is, the method for producing the plate-like WC-containing cemented carbide according to the present invention comprises Co, Ni, Cr and a Co precursor substance,
i-precursor material, at least one binder phase-forming powder of the Cr precursor material, carbon and / or a carbon source of the carbon precursor material, and the balance being W or a combination of W and tungsten carbide. A mixing step of mixing the starting materials to obtain a mixed powder, a forming step of forming the mixed powder to form a powder compact, and applying the powder compact in a vacuum or in a gas atmosphere. Heat sintering and the main components are Co and N
a sintering step of forming a cemented carbide with 2 to 30% by weight of at least one binder phase of i and Cr and the remaining tungsten carbide, wherein the heating during the sintering step is performed. A sintering process that includes a first step of generating a composite carbide composed of W and carbon and at least one of Co, Ni, and Cr, and a second step of generating a plate-like WC from the composite carbide. It is a characteristic manufacturing method.

The starting material in the production method of the present invention is specifically, for example, Co, Ni, C
r, Co-Ni alloy, Ni-Cr alloy, Co-Cr alloy, Co-Ni-Cr alloy, and CoO, Co ₂ O _3,
Co ₃ O ₄ , Co ₂ C, Co (C ₅ H ₇ O ₂ ) Co precursor, NiO, Ni precursor of Ni ₃ C, Cr ₂ O ₃ , C
r ₃ C ₂ , Cr precursor of Cr ₇ C ₃ , and carbon sources include carbon, graphite, thermal carbon, resin as a carbon precursor, petroleum pitch, charcoal, coke, and W or W as the rest. W ₂ C, a combination of W and WC, and a combination of W, W ₂ C, and WC can be given.

When the carbon source among these starting materials is a mixture of coarse powder and fine powder, the fine carbon source reacts with one or more of W and Co, Ni, Cr. Preferentially, to form a composite carbide composed of W and C and at least one of Co, Ni, and Cr, and thereafter, the composite carbide reacts with the coarse-grained carbon source to form a plate-like WC crystal. This is preferred because it facilitates the formation of a binder phase. This carbon source has an average particle size of 1 to 20 μm, preferably an average particle size of 1 to 20 μm.
A coarse powder of 10 μm graphite and an average particle diameter of 0.5 μm
It is preferable to combine the following fine powders made of carbon, and particularly preferable when the ratio of the average particle diameter of the coarse powder to the average particle diameter of the fine powder is 5 or more. This carbon source uses a carbon source having the same particle diameter, and in a mixing step of the next step, pulverizes a predetermined amount of the carbon source into fine powder, and selectively uses the remaining predetermined amount of the carbon source as coarse powder. be able to.

In addition to these starting materials, 4 of the periodic table
Addition of at least one metal compound powder among carbides, nitrides, oxides and mutual solid solutions of metals of groups a, 5a, and 6a as a starting material causes periodicity in the resulting plate-like WC-containing cemented carbide. This is preferable because at least one cubic compound in the carbides, nitrides, and mutual solid solutions of metals belonging to groups 4a, 5a, and 6a in the table can be contained. As the metal compound powder, specifically, for example, TiC, ZrC, HfC, V
C, NbC, TaC, Cr ₃ C ₂ , Mo ₂ C, TiN, Z
rN, HfN, VN, NbN, TaN, TiO, TiO
_{2, ZrO 2, HfO 2,} V 2 O 5, V 2 O 3, Nb 2 O 5, C
r ₂ O ₃ , Ti (C, N), Ti (C, O), Ti (N,
O), Ti (C, N, O), (Ti, W) C, (Ti,
Zr) C and (Ti, Ta, W) C. Among the metal compound powders, the case of the oxygen-containing compound powder is preferable because the formation of the composite compound in the first step in the sintering step described later and the formation of the plate-like WC crystal in the second step are promoted. It is.

The cubic compound corresponds to a compound obtained by removing an oxide from the above-mentioned metal compounds.

The mixing step of selecting these starting materials, weighing the starting substances to a predetermined blending composition and then mixing them to form a mixed powder, and the forming step of forming the mixed powder into a powder compact, are the conventional processes. For example, the mixing can be performed by a powder metallurgy method, such as a mixing process using a ball mill, an attritor, or a vibration mill, or a molding process such as centrifugal molding, cast molding, roll molding, die molding, extrusion molding, or injection molding.

The powder compact obtained through these steps is sintered.
In the sintering furnace during the sintering process
The atmosphere is vacuum or nitrogen gas, hydrogen gas, inert gas
The atmosphere consists of representative gas atmospheres.
Must be selected based on the specified starting materials
In the case of air, it can be performed under reduced pressure or increased pressure. Ma
Heat sintering in the sintering step is performed by using W, carbon, Co, N
a composite carbide comprising at least one of i and Cr
One process, specifically, depends on the type and atmosphere of the starting materials.
Before the liquid phase is generated, for example, 800 to 1200 ° C.
At a temperature of at least partially below the stoichiometric value
To form a composite carbide, and then the particle size of the carbon source
Heats up to 1600 ° C, depending on and dispersion state
To form plate-like WC crystals due to the reaction between composite carbide and carbon
And a second process that causes the formation of a bonded phase.
is there. Specific examples of the composite carbide at this time include:
For example, Co_ThreeW₉C_Four, Co_ThreeW_ThreeC , Ni_TwoW_FourC, Co_TwoW_Four
C , (Co, Cr)_ThreeW₉C_Four, (Co, Ni)_ThreeW_ThreeC ,
(Ni, Cr)_TwoW_FourC can be mentioned. Also the first
Heat sintering in the process is particularly performed at 800 to 1200 ° C.
When the heating rate is 10 ° C / min or less, a larger amount of composite carbonized
This is good because it produces things.

The plate-like WC crystal formed in the second step may have a triangular shape as observed at an arbitrary cross section of the cemented carbide, or a needle-like, rod-like, square-like, or hexagonal-like main shape. A plate-like WC having an aspect ratio of 3 to 20, preferably a plate-like WC having an average aspect ratio of 3 to 10, and more preferably a plate-like WC having an average aspect ratio of 3.5 to 7.0. WC is contained, and the plate-like WC comprises 30% by volume or more of the whole tungsten carbide, preferably 50% by volume or more of the whole tungsten carbide. If the plate-like WC is less than 30% by volume with respect to the whole tungsten carbide, the effect of improving hardness, wear resistance, strength, toughness, and fracture resistance is reduced.

The average value of the maximum dimension of the plate-like WC is preferably 0.1 to 3.0 μm, and particularly preferably the average value of the maximum dimension is 1.0 to 2.5 μm.

Specific examples of the binder phase constituting the cemented carbide thus obtained are, for example, Co, Ni, Co—Ni alloy, Co—Cr alloy, Ni—Cr alloy, Co—Ni—C
Examples thereof include an r alloy, a Ni—Mo alloy, a Co—W alloy, and an alloy containing a trace amount of an element constituting a cubic compound described later, mainly Fe as an inevitable impurity, or the like. Of these binder phases, for applications that emphasize corrosion resistance, 2 to 20% by volume based on the total binder phase amount
Cr-containing Ni-Cr alloy, Co-Cr alloy, N
An i-Co-Cr alloy is preferred, and for applications where emphasis is placed on wear resistance, a Co-W alloy containing 0.5 to 5% by volume of W with respect to the total binder phase amount, a Ni-W alloy, Co-Ni
-W alloys are preferred. If the amount of the binder phase is less than 2% by weight based on the whole cemented carbide, sintering becomes difficult and pits are likely to remain inside, resulting in a significant decrease in strength and hardness, and conversely, 30%. When the content is more than the weight%, the amount of tungsten carbide is relatively reduced, and as a result, the hardness and the wear resistance are significantly reduced.

Of course, the weighing, mixing, molding, and sintering steps of the starting materials may be automatically and continuously performed, and it is not necessary to separate the respective steps. The molding step and the sintering step are performed continuously. It is also preferable that the cemented carbide obtained by the production method of the present invention is further subjected to hot isostatic pressure treatment to obtain a denser cemented carbide.

[0023]

According to the production method of the present invention, the adjustment of the starting material and the sintering step mainly promotes the formation of composite carbide, and the composite carbide reacts with the residual carbon source to promote the formation of plate-like WC crystals. Is what it is.

[0024]

Examples: Commercially available W having an average particle size of 1.5 μm, Co having an average particle size of 1.2 μm, and Ni having an average particle size of 0.3 μm.
O, graphite having an average particle size of 7.5 μm (denoted as G in the table), carbon black having an average particle size of 0.02 μm (denoted as C in the table), Cr ₃ C _{2 having} an average particle size of 2.7 μm, and an average particle size 1.2
μm TaC, WC having an average particle size of 1.5 μm, TiO ₂ having an average particle size of 0.03 μm, (W,
Ti, Ta) C solid solution (weight ratio WC / TiC / Ta
C / = 50/20/30, described as WTT in the table), a phenol resin having an average particle size of 5 μm (referred to as FR in the table), and W ₂ C powder having an average particle size of 1.4 μm. Was mixed into a stainless steel pot together with an acetone solvent and a cemented carbide ball, mixed and pulverized for 48 hours, and then dried to obtain a mixed powder. Graphite or carbon in parentheses in the composition column in Table 1 was added after mixing for 48 hours, and further mixed for 5 hours. These mixed powders were filled in a mold, and pressurized at ² t / cm ² to about 5.5 ×
A powder compact of 9.5 × 29 mm is prepared, and the powder compact is placed on a sheet made of alumina and carbon fibers,
The temperature of the furnace was raised in a furnace at an atmosphere pressure of 10 ^-2 Torr at the heating rate described in Table 1 and the sintering temperature shown in Table 1 was maintained for 1 hour. A cemented carbide was obtained. Table 1 also shows the composition of these cemented carbides.

In the above steps, the powder compact is placed in a furnace and maintained at 900 ° C., 1050 ° C., and 1200 ° C., which are intermediate temperatures in the sintering process until sintering, for 10 minutes each. At each of these temperatures, the products of the present invention 1 to 12
And among the comparative products 1 to 9, the present invention products 2, 3, 8, 10,
11 and Comparative Products 2, 4, and 6 were taken out, and these components were subjected to X-ray diffraction and determined by an internal addition method. The results are shown in Table 2.

Next, products 1 to 12 of the present invention and comparative products 1 to
9 was wet-ground with a # 230 diamond grindstone to prepare a 4.0 × 8.0 × 25.0 mm sample, and the transverse rupture strength (JIS method) was measured. The results are shown in Table 3. After lapping one surface of each sample with a 1 μm diamond paste, Vickers hardness and fracture toughness (IM method) were measured under a load of 20 kgf, and the results are shown in Table 3. Further, a photograph of the structure of the lap-processed surface is taken with an electron microscope, and the average particle diameter of the WC and the ratio of the maximum diameter to the minimum diameter (aspect ratio) of the plate-like WC of 3.0 or more are measured by an image processing apparatus. The volume ratio (the ratio to the total WC) was determined, and the results are shown in Table 3.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

According to the production method of the present invention, it is possible to obtain a cemented carbide having a large content of plate-like WC, and to obtain the plate-like WC thus obtained.
With the same bending strength, hardness and fracture toughness of cemented carbide
Compared with the conventional cemented carbide having the C particle size and the same composition component, (Examples 2 to 7 and Comparative Example 2, Example 8 and Comparative Example 3, Example 9 and Comparative Example 4 , Inventive product 1
0 and Comparative Product 5 and Comparative Product 11 of the present invention and Comparative Product 6), the bending strength is improved by 0.1 to 0.2 GPa, and the hardness is 1.1 to 1.
7 GPa and a fracture toughness value (K ₁ c) of 0.4 to ₁ .
An excellent effect of improving 4 MPa · m ^3/2 is exhibited.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 1/05 C22C 29/08

Claims (6)

(57) [Claims] 1. Co, Ni, Cr and at least one binder phase forming powder of a Co precursor material, a Ni precursor material, and a Cr precursor material, and a carbon source of carbon and / or a carbon precursor material. Using a starting material whose remainder is W or a combination of W and tungsten carbide, mixing the starting material to obtain a mixed powder, and forming the mixed powder into a powder compact. Forming step, and heating and sintering the powder compact in a vacuum or gas atmosphere to form
2 to 30% by weight of at least one binder phase of o, Ni, Cr;
A sintering step of forming a cemented carbide with the remaining tungsten carbide, wherein at the time of the heat sintering during the sintering step, at least one of W, carbon, Co, Ni and Cr A method for producing a plate-like WC-containing cemented carbide, comprising: a first step of producing a composite carbide consisting of: and a second step of producing a plate-like WC from the composite carbide. 2. Co, Ni, Cr and at least one binder phase forming powder of Co precursor material, Ni precursor material, Cr precursor material, carbon and / or carbon precursor material, At least one metal compound powder in carbides, nitrides, oxides and mutual solid solutions of metals belonging to groups 4a, 5a and 6a in the table, and the balance being W or W
A mixing step of mixing the starting materials to form a mixed powder by using a starting material composed of a combination of tungsten and tungsten carbide; a forming step of forming the mixed powder to form a powder compact; The body is heated and sintered in a vacuum or in a gas atmosphere to form at least one binder phase of Co, Ni, or Cr.
-30% by weight, 50% by weight or less of at least one cubic compound in carbides, nitrides and mutual solid solutions of metals belonging to groups 4a, 5a and 6a of the periodic table, and the balance of tungsten carbide A method for producing a cemented carbide comprising a sintering step of forming a hard alloy, wherein, during the heating and sintering during the sintering step, a composite carbide comprising W and carbon and at least one of Co, Ni, and Cr is formed. A method for producing a plate-like WC-containing cemented carbide, comprising: a first step of forming; and a second step of forming a plate-like WC from the composite carbide. 3. The carbon source contained in the starting material comprises graphite having an average particle size of 1 to 20 μm, and graphite having an average particle size of 0.5 μm.
3. The method for producing a plate-like WC-containing cemented carbide according to claim 1 or 2, comprising carbon of m or less. 4. The carbon source contained in the starting material comprises carbon and / or graphite of a coarse powder and carbon and / or graphite of a fine powder, and the coarse source with respect to the average particle size of the fine powder. 3. The method for producing a plate-like WC-containing cemented carbide according to claim 1, wherein the ratio of the average particle diameter of the granular powder is 5 or more. 5. The first step in the sintering step,
5. The process for producing a plate-like WC-containing cemented carbide according to claim 1, wherein the temperature rising rate at 800 to 1200 [deg.] C. is 10 [deg.] C./min or less. 6. The second step in the sintering step,
The method for producing a plate-like WC-containing cemented carbide according to claim 1, 2, 3, 4, or 5, wherein the heating is performed by heating at 1200 to 1600 ° C.