JPS5938168B2 - Method for producing hard solid solution containing molybdenum - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of composite carbides intended for use in cemented carbide, particularly in which WC in the alloy is replaced by MoC.

Conventionally, the raw material for cemented carbide has been mainly composed of WC powder, which has also been supplemented with T 1 y T at Nbt Mo, H
High melting point metal carbides or carbonitrides such as fV and Cr are added depending on the required characteristics of the alloy, and iron group metals are mainly used as the bonding metal.

However, tungsten is a relatively expensive metal;
Since it can only be found in very small quantities on earth,
It is considered as a so-called "strategic" material, and the degree to which it is used can be said to have political value.

Another carbide that can replace WC with another refractory metal carbide is molybdenum monocarbide.

Only this carbide is a simple hexagonal type having the same crystal structure as WC, and its mechanical properties are thought to be close to WC.

However, the existence of molybdenum monocarbide alone has been questioned to this day, and attempts have been made to stabilize MoC by forming a solid solution with tungsten carbide.

This method was first reported by W. D. Awihl in 1950, but at that time, no industrial value was found for this solid solution and not much study was conducted.

Recently, with the rise in W price, again (Mox
Research on the use of solid solutions of Wy)C(X+Y=1) is becoming more active.

However, it is very interesting to know why little research has been done on it, and no active attempts have been made to use it.

The conventional method for producing solid solutions of Mo and C-WC is to produce WC, Mo and C powders or Wp M .

A commonly used method is to add cobalt to C powder, form a mixed powder, fill it in a carbon container, and react at a temperature of 1000 to 2000°C.

(W? Dawihl: Zp anog chem26
2 (1950) 212) At this time, the role of cobalt is said to be to assist in the formation of carbides and to promote solid solution of Mo and C in WC.

Certainly C. It appears that a solid solution of (MoW)C cannot be obtained without the presence of .

In general, in the method for producing composite carbides, in most cases, a uniform solid solution can be obtained by heating using a diffusion aid such as carbides or Co.

However, in a solid solution composition containing 70% or more of MoC, a uniform solid solution cannot be obtained simply by interdiffusion by high-temperature heating.

This is because MoC is unstable at high temperatures, but (MOW)C
This is because it is decomposed into solid solutions such as □-x and (MoW)3C2, so a WC type solid solution of (Mo-W)C cannot be obtained by simply cooling it.

As a stabilization method, the Mo2
After diffusing C and WC, there is a method of holding it at a low temperature for a long time.

[JP-A-51-146306 (4)] It takes a considerable amount of diffusion time and recrystallization time to release more (MopW)C from (MoW)CI Xp (MoW)3c2 at a low temperature while keeping the temperature low.

If such a process is to be carried out industrially, it must be heated in a furnace for a long time in order to obtain a complete carbide.

This results in low productivity per furnace, which requires a large number of furnaces.

On the other hand, if it were to be carried out in a continuous furnace, a long heating furnace would be required, which would make mass production difficult from an industrial perspective.

The feature of the present invention is that after heating at a temperature within the stability region of (MO2W)C1-X, the manufacturing method is heated for a long time after the temperature is lowered to a temperature at which monocarbide of (Mo,W)C is stable [Patent application The reason lies in the discovery of a manufacturing method that is more industrial and of higher quality than Sho 51-146306).

An object of the present invention is to produce -monocarbide by heating at a temperature at which the monocarbide of (Mo,W)C is stable and by heating for a short time.

The first feature of the present invention is that 0.3% of the starting material before carbide production
It consists of an alloy powder consisting of a solid solution of (MO, W) consisting of ~20μ and carbon.

The second feature is that it is heated at a temperature in the stable temperature range of monocoverite or higher, which is selected from the temperature range of 1100 to 2100'C, depending on the mixing ratio of Mo and W. The third feature is , Applying strain to the carbide by mechanical treatment such as crushing, compression, and mixing of the carbide heated in the above temperature range.

The fourth feature is that the strained carbide is re-carburized within the stable temperature range of monocarbide.

The effects of the present invention will be explained below.

The characteristics of the alloy powder are tungsten ammonium salt and
By mixing the ammonium salt of molybdenum in a solution state, W
After obtaining a finely mixed oxide powder by eutectoiding loose salts of and Mo, or co-precipitating both WO3 and MoO3 with HNO3 and H(l), this is reduced to form a mixture of Mo and W. An alloy powder is obtained.

Mix carbon powder with this alloy powder,
The purpose is to carbonize at a temperature of °C.

The carbonization temperature at this time may be determined by the particle size of the alloy powder, but a carbide formation temperature of 1100°C or higher is sufficient.

Another method for producing alloy powder of Mo and W is to obtain a solid solution by heating and diffusing a mixed powder of metal powder at high temperature, but this method requires pulverization, which is troublesome.

However, if the powder used is finer, the heating temperature can be lowered, making it possible.

In the diffusion of Mo in W, the sizes of particles that can be diffused at the heating temperature have the relationships shown in Table 1 below.

That is, when using metal Mo powder and W powder as starting materials 1
The heating time is 2000 for fine powder of about 0.5μ.
It becomes a solid solution at temperatures below ℃.

However, since powders with a diameter of 1 μm or more require heating temperatures of 2000° C. or more, it is difficult to make alloy powders from metal powders.

However, when mixed from a solution state or in an oxide state, the particle size becomes very small and a solid solution can be formed at a low temperature, so an alloy powder can be easily produced at a low temperature.

In an aqueous solution of ammonium salt in which molybdenum and tungsten coexist, the amount of tungsten and molybdenum that precipitates changes depending on the concentration of free hydrochloric acid in the aqueous solution. For example, we have discovered that molybdenum and tungsten can be finely and uniformly precipitated in a predetermined ratio.

The alloy powder obtained by the method of the present invention is reacted with carbon.
If heated at a temperature of 100°C or higher, complete (MoW)
C powder is obtained.

However, when obtaining coarse-grained (MoW)C powder where monocarbide is not stable at 210,000 or more, (MoW)
If the reduction temperature of 03 is increased and the carbonization temperature is further increased, 6
Carbide of μ size can also be obtained.

Furthermore, it has been found that the following method is effective in bringing the amount of bonded carbon in the carbide obtained by the above method close to the stoichiometric composition of the (Mo, W)C monocarbide.

That is, the present inventors investigated various methods for industrially stable production of (MO2W)C, and as a result, discovered a very efficient method.

That is, at high temperatures, due to the diffusion reaction of Mo and W (Mo, W
) is reacted at the stable temperature of monocarbide or at a temperature above it, and then quickly cooled to room temperature to form primary carbide in the high temperature unreacted state. In this case, carbon is A few coefficients remain in the powder layer.

This primary carbide is crushed into a slightly finer powder by a mechanical pulverizer, and then heated again for a short time at the stable temperature of (Mo, W)C to convert it into (Mo, W)C powder, which is a complete monocarbide. I discovered that.

If this mechanical pulverization is troublesome, use a continuous furnace to speed up the quenching rate.The rapid contraction during cooling will cause distortion in the reactants, so heating again will accelerate the solid solution reaction in the same way. In some cases.

Industrially, this method can process large quantities by combining continuous furnaces, and if a simple impact device is installed in the middle of the process,
A stable carbide can always be obtained.

If there are still non-uniform parts in the primary reactant, stable carbide cannot be obtained no matter how much the heating conditions are changed.

In the method of the present invention, if a pulverizer such as a ball mill is used, the uniformity of the reactants will increase, and the reactants will react well by secondary heating.

In the present invention, the same effect is obtained not only when the carbide is stabilized but also when the carbide contains nitrogen or a small amount of oxygen.

Although the molybdenum and tungsten composite compound has been described above, the effects of the present invention will not change even if it coexists with a BI type solid solution consisting of rva, Vay group VIa metals and non-metallic components.

In addition to replacing carbon with nitrogen or oxygen, it is also effective to replace carbon with B in order to stabilize carbides.

Example I 54 g of Mo powder and 46 g of W powder were dissolved in 28% ammonia water.

This ammonium salt was gradually neutralized with hydrochloric acid, and a mixed hydroxide of tungsten and molybdenum was coprecipitated when the free hydrochloric acid concentration was 4N.

This was dried to create an oxide of molybdenum and tungsten, and when the mixture of molybdenum and tungsten was examined using an electron microscope, it was found that the mixture was uniform and fine.

This oxide was sintered at 800°C in air.

This mixed powder was charged into a Ni boat, the boat was covered with a lid, and mx was carried out at 1000°C in an H2 stream, resulting in a 4μ alloy powder.

Add 9% of carbon powder to this (Mo8.7Wo, 3) alloy powder.
．． The mixture was mixed in a ball mill for 36 hours under a zero weight topper.

The mixed powder (Mo).

, 7 Wo, 3) The reaction was carried out at a temperature range in which C monocarbide is stable, that is, at 1700° C. in a hydrogen stream for 1 hour.

The carbide was cooled once and ground in a ball mill for 1 hour, and then carbonized again at a temperature at which the monocarbide of the carbide is stable, that is, 1400 ° C. in a hydrogen stream.The characteristics of the obtained carbide were investigated. As shown in Table 2, the amount of bonded carbon was sufficiently close to the theoretical value, and all were WC type monocarbide.

Example 2 Using the manufacturing method shown in Example 1 (M Oo,, sa WC,
15) An attempt was made to make a prototype of solid solution carbide of C.

As in Example 1, (M OO, 85WO, □,
) was prepared as a prototype, and the alloy powder was thoroughly mixed with 9.8% by weight of carbon powder and 2 parts of Co powder.

Insert the graphite boat containing the mixed powder into a vacuum furnace and heat it for 16 minutes.
The temperature was raised to 00° C. over about 3 hours, heated at the maximum temperature for 1 hour, and then cooled to room temperature over 10 hours.

Table 3 shows the results of examining the carbon content of the powder.

As expected, the amount of bonded carbon was small, and the reaction rate was only 74.2%.

In this X-ray diffraction result, As expected, a large amount of the peak of (Mo 2 , W) 2C remained.

MoC monocarbide is not formed in conventional composite carbide manufacturing methods.

Next, this powder was phase-pulverized using Chaucracy, and then placed in a Tammann furnace heated at 1250° C. in a hydrogen stream, and heated for about 40 minutes.

Table 4 shows the results of investigating the characteristics of this carbide.

In the X-ray results, the (Mo, W)2C peak almost disappeared, and all the crystals were of the WC type.

It has been found that any primary carbide can be converted to monocarbide using the method of the present invention.

Example 3 According to the method of Example 1, alloy powder of (Moo, Wo, 1) was obtained.

2,700 g of the alloy powder, 310 g of carbon, and 33 g of Co powder were ground in a ball mill for 15 hours to give strain, and then reacted in a hydrogen stream at 1,200° C. for 30 minutes.

The obtained primary carbide was pulverized in a ball mill for 10 hours, and then heated again at 1250° C. for 30 minutes in a hydrogen stream.

The obtained carbide was as shown in Table 5.

When the obtained carbide was examined by X-ray, it was found to be only WC type monocarbide.

Example 4 (M o ) obtained in Example 1.

, 7W6.3) Carbide of C (bonded carbon/theoretical carbon is 9
9.8%), added 2% by weight each of TiCNbC and TaC, mixed in a ball mill for 3 hours, and then mixed in a hydrogen stream for 1% by weight.
A heating reaction was carried out at 800°C for 1 hour.

After cooling the carbide once and pulverizing it in a ball mill for 1 hour,
Carbonized at 1400°C.

When the properties of the carbide were investigated, it was found that the bonded carbon content was close to the theoretical value, and all of the carbides were WC type monocarbide.

Example 5 The (MOo, 7%a) alloy powder obtained in Example 1 containing 9% by weight of carbon powder (referred to as A powder) and B4C
A mixed powder of powder and carbon powder (weight ratio 2:8) of 11% by weight (referred to as B powder) was mixed in a ball mill for 36 hours, and then reacted at 1700° C. for 1 hour in a hydrogen stream.

The compound was cooled once and ground in a ball mill for 1 hour.
Powder A was reacted at 00° C. in a mixed gas flow of hydrogen and nitrogen and in a mixed gas flow of hydrogen and carbon dioxide (mixing ratio 9:1).

Powder B was also reacted in a hydrogen stream.

When these compounds were investigated, the results shown in Table 6 were obtained.

Example 6 356 g of WO and 382 g of MoO, each having a particle size of 1 to 2 μm, and 461 g of H2WO and 392 g of H2MoO were mixed in a mixed ball mill for 120 hours.

The mixture was dried and sintered at 800°C in air.

Further reduction was performed at 1000° C. in a H2 stream, and a 3μ (Mo 0.7W0.3) alloy powder was obtained.

This (M o □, 7 W □, 3) alloy powder was loaded with 9 weights of carbon powder, mixed in a ball mill for 36 hours, and then mixed in a ball mill for 20 hours.
After carbonizing at 00℃ for 1 hour and grinding at room temperature, 1400℃
Carbonized in a hydrogen stream.

The amount of bonded carbon in the carbide is 99.6% of the theoretical carbon amount, 99
．． It was 8%.

Claims (1)

[Scope of Claims] 1. A compound of molybdenum and tungsten in the production of a solid solution consisting of one or more hard phases having a simple hexagonal crystal structure, which is a composite carbide or carbonitride of molybdenum and tungsten. While the solution is still in powder form, the resulting mixture is reduced by thorough stirring, and an appropriate amount of carbon is added to the alloy powder to form an alloy powder, which is a solid solution of molybdenum and tungsten. The mixture is reacted to form a primary carbide in a temperature range of 2100°C, and after processing to add strain to the primary carbide, the temperature is heated again from 1100°C to 1800°C.
A method for producing a hard solid solution containing molybdenum, the method comprising heating at a temperature of . 2. The method for producing a hard solid solution containing molybdenum according to claim 1, wherein the compound of molybdenum and tungsten is a hydroxide or an oxide. 3. Contains molybdenum according to claim 1, characterized in that when stirring and mixing molybdenum and tungsten ammonium salts in a solution, the free hydrochloric acid concentration in the solution is set to 0.1 to 5 normal. Method for producing hard solid solutions. 4 A mixture of alloy powder consisting of a solid solution of molybdenum and tungsten and carbon with a coefficient of 5 or less of Fe and Ni. A method for producing a hard solid solution containing molybdenum according to claim 1, characterized in that a metal such as Co is added and reacted.