JPS6218622B2 - - Google Patents

Description

[Detailed description of the invention]

Because W is a scarce resource and is a strategic material, its price has increased significantly in recent years. The main component is W.
So-called WC-based cemented carbide has no choice but to become increasingly expensive, and there is even a risk that it will become unusable due to resource depletion in the future. To deal with this, we define WC as (Mo,W)C
There are attempts to replace it with
(Unexamined Japanese Patent Publication No. 51-146306) It is not practical as it requires a long heat treatment. Therefore, the inventors conducted extensive research on these issues and noticed the following points. The first point is to include N in (W, Mo)C,
When (W, Mo) (C, N) z is used, a stable hexagonal WC type raw material can be obtained without long-term heat treatment. The second point was found to be more stable by adding O to (W, Mo) (C, N) z to make (W, Mo) (C, N, O) z. The third point is (W, Mo) (C, N) z or (W, Mo) (C, N, O) z plus Cr (W,
Mo, Cr) (C, N)z or (W, Mo, Cr)
It has also been found that (C,N,O)z provides a lightweight and inexpensive raw material. The fourth point is that when producing these raw material powders, a mixture of oxides and/or metals and/or carbides and/or carbon is heated at a temperature of 700°C or higher and at a nitrogen partial pressure during part of the carbonization process. It was also found that a stable powder could be obtained if the powder was placed under a pressure of 300 Torr or higher. The fifth point is that when the above metal powders are used and bonded mainly with iron group metals, an alloy with high toughness can be obtained if two or more types of simple hexagonal WC type hard phases with different compositions are present in the resulting alloy. It was also found that this occurs. Furthermore, one or more MC types or less
It was also found that when an M ₂ C type phase exists and the M ₂ C phase is uniformly dispersed, high hardness and high toughness are exhibited. The above five points form the basis of the present invention, and as in the case of ordinary cemented carbide, a part of the MO type phase consists of a, Va, and a group metals and nonmetallic elements.
Naturally, this happens all the time when elements added to ordinary cemented carbide such as Ag, Si, B, Cu, Al, etc. are present in the iron-metal bonding metal when they are substituted by a type solid solution. The effects of the present invention are not hindered even when hard phase forming elements are dissolved in solid solution. The limited scope of the invention will be described below. In the system where a simple hexagonal phase containing Mo and W and/or M ₂ C type coexist, which is the most important of the present invention, for the final alloy sintered with the bonding metal, the following value A = (Nitrogen atomic %/ It was found that a range of (Mo+W) atomic %) x (1-W atomic %/(Mo+W) atomic %) 0.005A0.5 is suitable. The lower limit is the range below which the positive effect of nitrogen does not appear, and the upper limit is because if the nitrogen content increases beyond this, sintering becomes difficult and performance deteriorates. Among these, the most suitable range is 0.01A0.4. Next, regarding the effect of oxygen, regarding the following value B, the following range is suitable: B = (oxygen atomic % / (Mo + W) atomic % × (1-W atomic % / (Mo + W) atomic %) 0.005≦B≦0.05 The lower limit is the range below which the positive effect of oxygen does not appear, and the upper limit is the range below which if the oxygen content increases, it will become difficult to sinter and the performance will deteriorate. The range is 0.01≦B≦0.04.The atomic ratio of W and Mo is 5/95~
Preferably 90/10. This is because if it is less than 5/95, it is unstable, and if it exceeds 90/10, the advantages of substitution (lighter weight, lower cost) will not occur. The amount of Cr that can replace W and Mo is expressed as an atomic ratio (W
+Mo) is 0.5 or less. If it exceeds this range, the corrosion resistance will improve, but the alloy will become brittle. It is known that it is advantageous to form a B1 type solid solution in addition to the simple hexagonal phase mainly for cutting tools. The constituent elements are Ti,
These are Zr, Hf, V, Nb, Ta, Cr, Mo, W, so-called a, Va, group a transition metals, and nonmetallic components of C, N, and O. The amount of B1 type solid solution is preferably changed depending on the cutting application, but substitution is performed up to 45% by volume. In this case, the appropriate amount of substitution is in the range of 1 to 45% by volume. If it exceeds 45% by volume, the original Mo and W
This is undesirable because the properties of the solid solution, such as impact resistance and high temperature properties, will be impaired. In this case, a part of the amount of nitrogen is occluded by the B1 type solid solution, but the definition of A is A = (Nitrogen atomic % / AAA group metal atomic %) (1 - W atomic % / AAA group metal atomic %) As a result of various experiments with different changes, experimentally 0.005A
It was found that a range of 0.5 is suitable. Among these, the optimum range is 0.01A0.4. Also, regarding the amount of oxygen, a part of it is occluded by the B1 type solid solution, but the definition of B is as follows: B = (oxygen atom%/AAA group metal atom%) (1-W atom%/AAA group metal atom%) As a result of various experiments with different values, it was experimentally found that 0.005≦B≦0.05 is still a suitable range. Among these, the optimal range is 0.01≦B≦0.04. In addition, as the binding metal, iron group metal is used as the bonding metal in the composition.
This is because if the content is less than 3%, which is required to contain 50% by weight, it will be too brittle, and if it is more than 50%, it will be too soft to use. In addition, the simple hexagonal compound mentioned above may decompose during alloy preparation, and in this case, an M ₂ C type compound is generated. In this case, if the amount of this compound does not exceed 10% by volume, it is necessary to incorporate Fe into the bonding metal. This makes it possible to make the compound spherical, thereby maintaining its toughness. Next, regarding the raw material preparation method, the usual
In H ₂ hydrogen atmosphere, in the case of carbonization with (Mo, W) powder + carbon, reduction with oxide powder + carbon, carbonization all at once, or a combination of these, exposure to high temperatures is required to promote carbonization. However, since (Mo, W) C decomposes into (Mo, W) ₂ C at high temperatures, long-term heating at low temperatures is required. However, if this is carried out in an elemental atmosphere, these heatings are unnecessary and it is extremely convenient. As for the nitrogen atmosphere, we investigated the decomposition nitrogen pressure of (Mo, W) (C, N) and found that it differs depending on the temperature, but it is 300 Torr above 700℃ where carbonitriding reaction occurs.
It was found that more external pressure was required. The coexistence of hydrogen is not necessarily harmful, but in order not to interfere with the nitriding reaction, the amount of hydrogen should be less than twice the volume of nitrogen, preferably less than the same amount, and ammonia decomposition gas should be used. Nitrogen enrichment may be necessary in some cases. Furthermore, in order to create a raw material containing oxygen, it is necessary for CO and CO ₂ to coexist in the atmosphere. In this case, the amount of hydrogen is not subject to the above restrictions, but the amount of hydrogen in the total atmosphere is
It is not preferable to exceed 50%. Furthermore, in order to prevent denitrification and deoxidation during alloy sintering, it is effective to heat and sinter the alloy in a nitrogen or carbon oxide atmosphere. Examples will be described below. Example 1 2μ of Mo ₂ C, 2μ of WC powder and carbon powder, and a trace amount of Co as a diffusion aid were added, and the composition of the final carbonitride was (Mo _0.8 , W _0.2 ) (C _0.95 , N _0.0
5 ) The nitrogen partial pressure of the mixture is _1.0 .
The reaction was carried out at 1800°C for 30 minutes in a flow of nitrogen and hydrogen at 0.5 atm. In the X-ray diffraction results, the Mo ₂ C peak completely disappeared, and all showed a WC type simple hexagonal type crystal form. Co powder was added to this powder to make the final alloy composition (Mo _0.8 , W _0.2 )(C,N) 10% by weight Co. The mixed powder was stamped, shaped into a predetermined shape, and then sintered. This sintering condition is up to 1000℃
It was heated under a vacuum of 10 ^-2 Torr and heated from 1000°C to 1400°C under a reduced pressure of 10 Torr in a carbon monoxide atmosphere. At the same time, an alloy was prepared in which nitrogen was not used in the carbide manufacturing process and carbon monoxide was not used in the sintering process, and compared with the method of the present invention. The results are shown in Table 1.

[Table] Except for the WC type, the alloys of the present invention have only a binder phase, and no other phases are precipitated, and the reaction rate is extremely high. It can be seen that the reaction rate of conventional alloys is poor. The alloy of the present invention is lightweight, and test results show that it has excellent impact resistance and high temperature hardness, making it suitable for all types of tool applications and wear-resistant applications. Example 2 An alloy was prepared according to Example 1 by adding 2μ of Mo ₂ C, 1μ of WC, 1μ of Cr ₃ C ₃ powder, carbon powder, and Fe as a diffusion aid. The composition converted into the hard phase was (Mo _0.8 W _0.15 Cr _0.05 ) (C _0.93 N _0.06 O _0.01 ), and the binder phase had a Co/Ni ratio of 1:1 and was 9.5 wt%. (Contains a small amount of Fe) When analyzed by X-ray diffraction, this alloy was found to contain only a WC-type simple hexagonal phase and an FCCγ phase that do not contain free carbon or complex compounds. When this alloy was soaked in artificial sweat, it was found that the amount of corrosion was small as shown in Table 2, and it was found to have superior corrosion resistance compared to the WC-Co alloy. In addition, since it is lightweight, it has been found to be convenient for use in decorative items such as watch parts, anti-corrosion applications, and non-magnetic alloys.

[Table] Example 3 MoO ₃ powder and WO ₃ powder at a Mo:w ratio of 8:2
It was weighed to give the calculated amount. At the same time, carbon was added to remove the oxygen oxide, and 0.2% Fe was added as a catalyst to fix nitrogen during the reaction. The mixture was converted into (NH ₃ +
The reaction was carried out at 1500°C for 1 hour in a gas stream (10Vol%Co). When the compound is examined with X-rays (Mo _0.7 W _0.3 )
A hexagonal type compound of (C _0.93 N _0.06 O _0.01 ) _0.98 was produced. 10% by weight of Co and Ni in this carbonitride (however,
Co/Ni=1) and mixed to produce an alloy according to the method of Example 1. When the properties of the final alloy were investigated, it was found that A=0.2 and B=0.03. Also, the anti-analytical power is
The alloy was extremely strong at 210Kg/mm ² and had excellent impact resistance. Example 4 Co was 10% by weight, Ni was 10% by weight, and the total amount of Mo and W double carbonitride prepared in Example 3 and carbon was
Alloys with various amounts of carbon were prepared, with a carbon content of 80% by weight. The transverse rupture strength of the obtained alloy, the amount of added carbon, and the M ₂ C type crystal structure precipitated in the alloy (Mo,
The amount of W) ₂ (C, N, O) is shown in Table 4 as "M ₂ C precipitation amount".

【table】

[Table] As mentioned above, it has an M ₂ C type crystal structure (Mo,
It can be seen that when 10% by volume or more of W) ₂ (C, N, O) precipitates, the transverse rupture strength decreases significantly.

Claims (1)

[Claims] 1. The crystal structure is simple hexagonal.
Double carbide of Mo and W as hard phase, 3 to 50% by weight
In an alloy bonded by iron group metals, part of the carbon in the hard phase is replaced by nitrogen and oxygen, and the amount of substitution is 0.005≦[nitrogen atomic %/(Mo+W) atomic %] × [1- W atomic%/(Mo+W) atomic%〕≦0.
5 0.005≦[Oxygen atom%/(Mo+W) atom%] × [1-W atom%/(Mo+W) atom%]≦0.
05 A superhard alloy containing Mo. 2. In the alloy according to claim 1,
Mo with a simple hexagonal crystal structure
1. A superhard alloy containing Mo, characterized in that the double carbide of Mo and W having an M ₂ C type crystal structure is contained in the double carbide of Mo and W in an amount of 1 to 10% by volume. 3. The crystal structure is simple and hexagonal.
Double carbide of Mo and W as hard phase, 3 to 50% by weight
In an alloy bonded by iron group metals, part of the carbon in the hard phase is replaced by nitrogen and oxygen, and the amount of substitution is 0.005≦[nitrogen atomic %/(Mo+W) atomic %] × [1- W atomic%/(Mo+W) atomic%〕≦0.
5 0.005≦[Oxygen atom%/(Mo+W) atom%] × [1-W atom%/(Mo+W) atom%]≦0.
05 A superhard alloy containing Mo, characterized in that in the hard phase, Mo and W are substituted with Cr in a range of 1 to 50% (atomic ratio). 4. The crystal structure is simple hexagonal.
Double carbide of Mo and W as hard phase, 3 to 50% by weight
In an alloy bonded by iron group metals, part of the carbon in the hard phase is replaced by nitrogen and oxygen, and the amount of substitution is 0.005≦[nitrogen atomic %/(Mo+W) atomic %] × [1- W atomic%/(Mo+W) atomic%〕≦0.
5 0.005≦[Oxygen atom%/(Mo+W) atom%] × [1-W atom%/(Mo+W) atom%]≦0.
05, in the process of carbonization heat treatment of a mixture of Mo, W, and carbon or a mixture of Mo oxide, W oxide, and carbon at 700℃.
Producing a composite compound raw material of Mo and W produced by heating and holding in an atmosphere containing nitrogen of 300 Torr or more and/or carbon oxide of 1 Torr or more at a temperature above, then adding an iron group metal to this raw material, A method for producing a superhard alloy containing Mo, which comprises mixing and pulverizing, stamping, and sintering at a temperature of 1200°C to 1450°C in a vacuum or reduced pressure nitrogen and/or carbon monoxide atmosphere.