JPS6039137A - Manufacture of tungsten carbide-base sintered hard alloy - Google Patents

Abstract

PURPOSE:To make WC particles fine and to obtain a WC-base sintered hard alloy with high strength and toughness by forming WC and Co by decomposition when a powdery mixture of a powdery Co-W-C compound with carbon powder is sintered. CONSTITUTION:A powdery Co-W compound and/or a powdery Co-W-C compound is blended with carbon powder to prepare a powdery starting material. The starting material may be mixed with powder of one or more kinds of components selected among the carbides and nitrides of the IVa, Va and VIa group transition metals and solid solns. each consisting of two or more kinds of said compounds. The powdery mixture is compacted and sitnered at about 1,350 deg.C. Said Co-W compound is decomposed during the sintering to form WC and Co. By regulating the sintering conditions, the average particle size of WC particles is reduced to <= about 0.8mum, and a WC-base sintered hard alloy with high strength and toughness is obtd. The alloy has a structure contg. uniformly and finely dispersed WC and Co.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides fine tungsten carbide (hereinafter referred to as WC) particles forming a dispersed phase having an average particle size of about 0.0 g Itm or less and having high strength and toughness.
This relates to a method for producing C cemented carbide.

In general, W consists of WC particles that form a dispersed phase as a main component, which are bonded with Co that is a bonded phase forming component.
CC cemented carbide or, in addition, carbides and nitrides of transition metals of groups 4a, 5a and 6a of the periodic table as dispersed phase forming components, and solid solutions of two or more of these (hereinafter collectively referred to as WCC cemented carbide containing one or more types of metal carbon/nitride in a ratio of usually 0.1 to 20% (weight @ %, the same hereinafter), cutting tools and They are used as wear tools and impact-resistant tools, and play an important role in industry.

Among these WCC super-zero alloys, fine-grained ones with an average WC grain size of 111 m or less are suitable for cutting tools with relatively low cutting speeds such as end mills, drills, and slitter knives, and cold wear-resistant tools. However, due to the recent demand for improved productivity, W has been made into finer particles and has higher strength and toughness.
There is a growing demand for CC cemented carbide.

In general, this type of WCC cemented carbide has fine WC particles,
Usually, the raw material powder is a mixed powder consisting of fine WC powder and Co powder, or one type or 2 F++ of metal carbon/nitride that has the effect of suppressing grain growth.
It is manufactured by sintering using a powder metallurgy method using a mixed powder containing the above powders. However, some of the commercially available WC powders have an average particle size of about 0.5 μm, which is the finest, but this WC powder is easily oxidized, making it difficult to handle, and it also has poor quality stability. However, there is also a problem that when finer WC powder is used, cavities are likely to form in the sintered body, resulting in a decrease in strength. In addition, in this type of WCC cemented carbide, the crack propagation resistance at the interface between the dispersed phase and the binder phase is relatively high, but the crack propagation resistance at the interface between the dispersed phases is low; For example, when used as a cutting tool, there is a problem that the cutting speed is slow, so the workpiece material is welded, and when the material is peeled off, fracture occurs at the interface between the dispersed phases, resulting in a decrease in toughness.

Therefore, from the above-mentioned viewpoint, the present inventors conducted research to obtain a WCC cemented carbide having high strength and high toughness by making the WC particles into fine particles. As long as powder is used, the average particle size of the WC particles in the resulting WCC cemented carbide will be approximately 0, even if metal carbon/nitride powder, which has the effect of suppressing grain growth, is blended.
．． The limit is 8 μm, and it is impossible to make the particles finer than this. Also, as long as Co powder is used as the raw material powder, it has ductility and cannot be completely crushed during mixing, resulting in coarse 00 particles. Since it is impossible to avoid contact between WC powders when mixing WC powder and Co powder, interfacial destruction in the sintered body can be completely prevented. 1. Co3W+ as raw material powder
Co-W compounds such as co7w6, Co3W3C
When using powders of Co-W-C compounds such as , C06W6 C, Co, ,'w4C, Co3%C4, these compound powders have brittle characteristics peculiar to intermetallic compounds, so they cannot be easily pulverized. When carbon powder is mixed with this and the green compact is sintered, these compounds easily decompose to form WC and CO, so the sintering conditions must be adjusted accordingly. , if grain growth is prevented after WC formation, the WC particles not only have a very fine structure with an average particle size of about 0.8 μm or less, but also the adhesion between the WC particles is extremely small, and the binder phase is Since it is formed by precipitated Co like WC particles, a WCC cemented carbide with almost no coarse Co particles that cause cavities can be obtained, and the resulting WCC cemented carbide has high strength and high toughness. We obtained this knowledge.

This invention was made based on the above knowledge, and when manufacturing WCC cemented carbide by powder metallurgy, C0-W compound powder and Co
-One or more of the W-C compound powders,
A mixed powder made by blending carbon powder in the amount necessary to combine with W in these compounds to form a spine, taking into account the amount of decarburization and carburization during sintering, or a mixed powder containing WC particles in addition to this. For the purpose of suppressing grain growth and improving the wear resistance, heat resistance, and corrosion resistance of the alloy, one or more powders of metal carbons and nitrides are added, preferably from 0.1 to
A mixed powder containing 20% is used, and the mixed powder is sintered as a green compact, preferably at a temperature of 1350°C or less, and during this sintering, the above-mentioned compounds are decomposed to form WC and Co. By producing WC grains, the average grain size of the WC grains is about 0.8 μm or less, and a WCC cemented carbide having high strength and toughness is produced.

Note that the CO-W compound powder and Co-W-C compound powder used in the method of the present invention are, for example, Co-W-based compound powder and Co-W-C based compound powder.
Powder and W powder, or Co powder, W powder, carbon source powder such as WC and W2C, or cobalt oxide powder, tungsten oxide powder, and carbon powder are blended into a predetermined composition, and in a non-oxidizing atmosphere, 800-13
WCC cemented carbide can be manufactured by heating to a predetermined temperature within the range of 00°C, and the WCC cemented carbide composition to be manufactured can be prepared using raw material powders such as (:o, ,
If W powder is used, the Co content in the alloy after sintering is 47
%, similarly co, W3C is 23%, C02W4
Since it is 13% for C and 9% for Co3W and C1, a predetermined composition can be obtained by appropriately combining these raw material powders. If the WCC cemented carbide is subjected to hot isostatic pressure treatment after sintering to remove the few remaining cavities, the properties can be further improved.

Next, the method of the present invention will be specifically explained using examples.

Example 1 For the purpose of preparing a CO-W compound, average particle size: 1.3
/1 m Co powder and the same 1.0 μm W powder were prepared,
These powders were blended at a ratio of Co powder: 27% and W powder = 73%, and after dry mixing, the mixture was kept at a temperature of 900°C for 3 hours in a hydrogen stream of 1 atm to form a Co-W compound powder. was manufactured. This C.

The -W-based compound powder was found to have a single composition of Co7w6 by X-ray diffraction. Next, 4.6% carbon black was blended into this Co-W-based compound powder,
A mixed powder is obtained by mixing 24 hours a day in a ball mill, and after drying, it is press-molded into a green compact, and this green compact is sintered in a vacuum at a temperature of 1280'C for 2 hours. Method 1 of the present invention was carried out. This wc-based cemented carbide obtained by method 1 of the present invention, containing 26% Co, w
It had a structure in which c and Co were neatly dispersed, and the average grain size of the cwc particles was extremely fine, 0.3 μm, and no abnormally grown WC particles or bores were observed.

On the other hand, for the purpose of comparison, as a raw material powder, average particle size: 0
．． WC powder with a diameter of 55 μm was ground in a ball mill to a diameter of 0.2 μm, and a Co powder with a diameter of 1.3/zm was used.
Conventional method 1 was carried out under the same conditions as method 1 of the present invention described above except that powder was used. Although the WC particles of the WCC cemented carbide manufactured by conventional method 1 have an average particle size of 0.8 μm, there are scattered WC particles that have abnormally grown to several μm, and the dispersion of the WC particles is poor. Bores were observed on the polished surface.

In addition, WCC cemented carbide manufactured by method 1 of the present invention,
In contrast, the material produced by Conventional Method 1 exhibited a low transverse rupture strength of only 300 kg/ma, whereas it exhibited an extremely high transverse rupture strength of 480 kg/ma.

Example 2 First, for the purpose of producing a C0-W-C compound powder, in addition to the same Co powder and W powder used in Example 1,
Using unmilled WC powder, these powders were mixed with Co powder=1
4%, W powder = 64%, WC powder = 22%, dry mixed, heated in vacuum at 1000°C for 2 hours, and the composition formula was determined by X-ray diffraction. 2C0
A Co-W-C compound powder containing a compound exhibiting 2W4C as a main component was produced.

Next, 4.1 was applied to this Co-W-C compound powder.
% of carbon black was mixed in a ball mill for 48 hours, dried to form a mixed powder, and a green compact formed from this mixed powder was sintered in a vacuum at a temperature of 71,290°C for 1 hour. Method 2 of the present invention was carried out by tying. This WCC cemented carbide manufactured by the method 2 of the present invention contains 13% CO, has a structure in which WC and Co are neatly dispersed, and has an average particle size of WC particles of 0.2
The particles were micro-sized, no abnormally grown WC particles or bores were observed, and showed a high transverse rupture strength of 400 kg/+ut.

On the other hand, Conventional Method 2 was conducted under the same conditions as Method 2 of the present invention, except that a mixed powder of Co powder and WC powder was used as the raw material powder. In this case 2, the average particle size of the WC particles is n, 97im, and the abnormally grown W
C particles were scattered, WC and CO were poorly dispersed, and the polished surface had a structure with bores.
It was not possible to produce a WCC cemented carbide having a transverse rupture strength of only g/IB7i.

Example 3 For the purpose of producing the same Co-W-C compound powder, in addition to the same CO powder and W powder used in Example 1,
Prepare W2C powder having an average particle size of 1.5 μm, and combine these powders with CO powder = 9%, W powder: 10%, W2C
Powder = 81% ratio, further KCO powder: 2
4%, W powder = 25%, W2C powder: 51% were also prepared, and these two types of blended powders were mixed 24 hours a day in a ball mill, and after drying,
By heating in vacuum at a temperature of 1000°C for 1 hour, the composition formulas were determined by X-ray diffraction:
A Co-W-C-based compound powder containing compounds representing Co3W9C4 and Co3W3C as main components was produced.

Next, the resulting CO, W, C4 yarn compound powder and CO3W3 Ca compound powder, and carbon black were mixed into a Co3 W9 C4-based compound powder (35%, C).
o, W3C compound powder: 61%, carbon black: 4%, mixed in a ball mill for 48 hours, dried, press-molded into a green compact, this green compact is Method 3 of the present invention was carried out by sintering in vacuum at a temperature of 1280° C. for 1.5 hours. The WCC cemented carbide manufactured by this method 3 of the present invention, CO
: Contains 18%, exhibits an average particle size of WC particles of 0.3 μm, has a fine grain structure in which WC and CO are neatly dispersed, has no abnormally grown WC particles or bores, and has a transverse rupture strength of 420 kg. /mA.

On the other hand, as conventional method 3, average particle size: 1.3 μm
WCC cemented carbide manufactured under the same manufacturing conditions as the method 3 of the present invention, except for using a mixed powder of CO powder of
mm, and its structure is 0.
．． Although exhibiting an average particle size of 8 μm, 11- abnormally grown WC particles are scattered, WC and C.

The dispersion of the particles was also poor, and bores were observed on the polished surface.

Example 4 As a raw material powder, the compound powder mainly composed of Co2W, C produced in Example 2, average particle size: 1.3 μm CO
Powder, 0.2 pm WC powder, 1.1 μm VC
Powder, 1.3 μm TjC powder, and carbon black were prepared, and these raw material powders were blended into the composition shown in Table 1, and thereafter, the method 4 of the present invention was carried out under the same conditions as in Example 1. , 5 and conventional methods 4 and 5, respectively.

For the various WCC cemented carbides obtained as a result, we measured and observed the Co content, the dispersion state of WC and Co, the average particle size of WC particles, the bore state based on ASTM standards, and the transverse rupture strength. It is also shown in Table 1.

As shown in Table 1, the same results as in Examples 1 to 3 were obtained in this case, and all of the WCC cemented carbide produced by the method 4.5 of the present invention had a fine grain structure. It is clear that it has high strength and high toughness.

Example 5 As raw material powder, C03WQ C manufactured in Example 3
4-based compound powder and co3W, C-based compound powder, and (Ta, Nb) CN with average particle size: ], 3 μrn
Powder (TaC/NbN = 7/3, heavy duty ratio), 'J
Using a line I/C force M, these powders were
03W, C4 compound powder 33%, C0AW3C compound powder = 58%, (Ta, Nb) CN powder 25%,
Curtain fluff: Method 6 of the present invention was carried out under the same conditions as in Example 2, except that the blending ratio was 4% and the sintering temperature was 1340°C. This unexploded WCC cemented carbide obtained by method 6, CO content: 16%, WC
Average particle size of particles: 0.25 μm, with WC and CO uniformly and finely dispersed, with slightly coarse particles (Ta, Nb)
It had a structure in which CN particles were uniformly dispersed, and no bores were observed. In addition, this alloy has a transverse rupture strength of 1370
kg/-.

On the other hand, as conventional method 6, the above (Ta, Nb)
・WCC cemented carbide and WC particles obtained as a result of carrying out the process under the same conditions as the method 6 of the present invention described above, except that the same WC powder and CO powder used in Example 4 were used in addition to the CN powder. Average particle size: 0.8 ttm, but
To 260! 9/mu It is only an indication, and WC and CO
The dispersion was poor, and there was a mortar of about A-2.

As described above, according to the method of the present invention, at least Co-W compound powder and Co-W compound powder are used as the raw material powder.
-C-based compound powder and carbon powder are used, and W is used during sintering.
Since C and Co are decomposed and produced, the obtained WCC cemented carbide not only becomes fine particles with an average particle size of about 0.8 μm or less, but also WC and C.

To produce WCC cemented carbide that has industrially useful properties such as having a uniform and finely dispersed structure and having almost no bores, so it has high strength and high toughness. This is possible.

Applicant: Mitsubishi Metals Corporation Agent Kazuo Tomita and 1 other person

Claims (2)

[Claims] (1) When producing a tungsten carbide-based cemented carbide by a powder metallurgy method, one or more of Co-W-based compound powder and Co-W-C-based compound powder and carbon powder are used as raw material powders. Using a mixed powder consisting of
During sintering, the above compounds are decomposed to form tungsten carbide and C.
1. A method for producing a tungsten carbide-based cemented carbide having high strength and toughness by finely pulverizing tungsten carbide particles and producing O. (2) When producing a tungsten carbide-based cemented carbide by a powder metallurgy method, one or more of C0-W compound powder and Co-W-C compound powder and carbon powder are used as raw material powders. and carbides and nitrides of transition metals of Groups 4a, 5a and 6a of the Periodic Table, and one or more solid solutions of these two or more. A method for producing a tungsten carbide-based cemented carbide having high strength and toughness, in which tungsten carbide particles are finely divided, and the compound is decomposed during sintering to generate tungsten carbide and CO. .