JPS6022642B2 - Method for producing solid solution of hexagonal monocarbide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of a composite carbide for the purpose of replacing cemented carbide, particularly WC in the alloy, by MoC.

Conventionally, cemented carbide has WC as its main component, with Ti and Ta added to it.
, Nb, Mo, Hf, V, Cr, or other high-melting point metal carbides or carbonitrides are added according to the required properties of the alloy, and iron group metals are used as the bonding metals.

However, tungsten is a relatively expensive metal;
Since it is something that can only be found in very few places on earth,
It is considered as a so-called "strategic material," and its utilization can be said to have political value. Therefore, if the demand for cemented carbide, whose main component is WC, increases, it will naturally lead to resource problems.

If WC could be replaced with other high melting point metal carbides, the impact on the industry would be significant. Molybdenum monocarbide is the most promising substitute for this.

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 a single molybdenum monocarbide is still considered to be a pseudo-interference, and attempts have been made to stabilize MoC by collapsing it with tungsten carbide. This method was introduced in 1950 by W. Although this solid solution was first discovered by Robert Dawihl, not much research was done at the time as it was not considered to have any industrial value. Recently, with the rise in the value of W, (MoxWy)C [
Research on the use of solid lacquer bodies with a ratio of 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 present invention has MoC as the main component, Wa, Va
, regarding the stable production of solid solution carbide with Town A Group.

The feature of the present invention is that since carbide containing MoC as a main component is not stable at room temperature, other carbides such as WC are dissolved in solid solution at high temperature, the solid solution is cooled to room temperature, and mechanical treatment or thermal treatment that adds strain to the solid solution is performed. After the treatment, molybdenum carbide is converted into a WC type simple hexagonal type crystal structure by heating again to a temperature at which MoC is stabilized.

In general, in most cases of manufacturing methods for composite carbides, a uniform solid solution can be obtained by heating the carbides together or using a diffusion aid such as Co. However, in the case of a solid solution composition containing 70% or more of MoC, a uniform solution cannot be obtained only by interdiffusion at high temperature heating. This is because MoC is unstable at high temperatures, but (MOW)C, -x, and (MOW)3
This is because, since it decomposes into an intermediate solution such as C2, a WC type solid solution of (Mo.W)C cannot be obtained just by cooling it as it is. As a method for this stabilization, there is a method of once reacting at a high temperature to diffuse Mo2C and WC, and then holding it at a low temperature for a long time. [Samurai Sekisho 51-14 Suji 06 (
4)]. However, at low temperatures, (MOW)C4M, (M
It takes a considerable amount of time for diffusion and recrystallization to extract more (Mo.W)C from OW)3C2. If such a method is to be carried out industrially, ``in order to obtain a complete carbide, it must be heated in a furnace for a long time.
The productivity per furnace is low and a large number of furnaces are required for this purpose. 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 present inventors investigated various methods for industrially stable production of (Mo.W)C, and as a result, discovered a very efficient method.

That is, at high temperatures, Mo. Due to the diffusion reaction of W (Mo.W
) After the mixture of 2C+C double carbide and carbon is reduced to 0, it is quickly cooled to room temperature and left in the high temperature hydrogen reaction state.
Next, a carbide is obtained, in which case nearly a few percent of carbon remains in the powder layer. This primary carbide is made into a slightly finer powder by a mechanical crusher, and then heated again for a short time at a stable temperature of (Mo.W)C to convert it into (Mo.W)C powder, which is a complete monocarbide. I understand. If this mechanical pulverization is troublesome, use a continuous furnace or the like to speed up the quenching rate.The rapid contraction during cooling will cause distortion in the reactants, so heating again will cause the same solid solution reaction. may be promoted. In this way, the detailed reason why hexagonal monocarbide is stabilized by extremely short secondary heating when strain is applied to the primary reactant is unknown, but it appears that straining the primary reactant stabilizes hexagonal monocarbide. This is thought to cause a large number of lattice defects in the crystal lattice, and during secondary heating, atoms diffuse through these lattice defects.
2 in a very short time because the diffusion rate is significantly increased.
It is presumed that the hexagonal monocarbide is stabilized by the subsequent heating. Industrially, this method can be used in large quantities by combining continuous furnaces, and if a simple impact device is provided in the middle of the process, a stable carbide can be obtained at all times.

Furthermore, if the primary reactant has non-uniform parts, no matter how much the heating conditions are changed, a stable carbide cannot be obtained. 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, it is desirable that the primary heating temperature be 1400°C or higher to achieve the most effect.

If the temperature is below 1400 pm, the solid solution reaction between Mo2C and WC will not proceed.

Further, the secondary heating temperature is sufficiently satisfied if the temperature range is from 100 to 1800 oo. Diffusion reactions are difficult to occur below 1000 qo.

Moreover, if it exceeds 180,000, the solid melt of MoC and WC becomes unstable, and monocarbide of (MoW)C is not generated. This method is most effective when the MoC is 70% or more, and a significant effect can be achieved with compositions lacking MoC stability. 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 do not change even if this compound coexists with a BI type solid solution consisting of a group a metal such as Na, Va, and a nonmetallic component. Example 1 1 WC powder (24 g) and 2 F. Mo2C powder (71 g) were loaded with 4 carbon powders and 1 g of Co powder as a diffusion aid, and mixed in a dry ball mill for about 3 hours.

This mixed powder was heated to 190°C in a hydrogen stream using a Yuman furnace.
The temperature was raised to 0 qo and heated for about 1 hour. After heating, the furnace temperature was lowered to 136,000 and maintained at this temperature for 6 hours. The carbide obtained after 6 hours was taken out into the furnace and analyzed for carbon content, and the results were as shown in Table 1.

In addition, the crystal form of the solid carbide was examined using X-rays. The results are shown in FIG. 11a. Table 1 In Table 1, nearly 3% of free carbon remained, and only 21% of the carbon that reacted with the blended carbon.

Furthermore, in the X-ray diffraction results shown in FIG. 1-a, many Mo2C peaks remained, and no monocarbide formation was observed. Next, this unreacted primary carbide was pulverized in a ball mill for 2 hours, and then heated again at a temperature of 136,000° C. As a result, it changed to the carbide shown in Table 2. Table 2 Reaction rate reached 97%,
As a result of examining the carbide by line diffraction, it was found that all of the carbides changed to a WC type crystal form as shown in FIG. 1-b.

The peak of Mo2C was almost reduced. C in this carbide
A prototype (Mo.W)C-10%Co alloy was made by mixing O powder, but it had exactly the same structure as the WC-Co alloy.
It was possible to sufficiently replace the WC layer. Example 2 A trial production of solid solution carbide of (MoB5W,5)C was attempted using the blending ratio shown in Example 1.

Insert the graphite boat containing the mixed powder into a vacuum furnace and heat it for 18 minutes.
The temperature was raised to 00oo over about 3 hours, heated at the maximum temperature for 1 hour, and then cooled to room temperature in 1 feeding time. 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 35.7%. This X-ray diffraction result Table 3 is shown in FIG. 21a, and a large amount of MQC remained as expected.

MoC monocarbide is not formed in conventional composite carbide manufacturing methods. Next, this powder was phase-pulverized in a jaw machine, then inserted into a Tamman furnace heated at 1350 oo and heated for about 4 hours. Table 4 shows the results of investigating the characteristics of this carbide. Table 4 The X-ray results are shown in Figure 2-b.

The Mo2C peak almost disappeared, and all the crystals became WC type crystals. For comparison, a mixed powder with the same composition was similarly placed in a graphite boat and heated to 1800 oo in a vacuum furnace.
After heating for 1 hour at
Heated for a calm time. When the obtained sample was examined, it was found that it contained almost only hexagonal monocarbide. By the way 1
A large amount of Mo2C was observed in the sample heated at 350q0 for 1 hour. It has been found that any primary carbide can be converted into monocarbide using the method of the present invention.

Example 3 Powder having the same composition as in Example 2 was placed in a graphite boat and heated in a vacuum furnace at 170,000 °C for 1 hour.

This sample was rapidly cooled to room temperature in batches of three powders, and then heated at 01400o0 in a nitrogen stream for 1 hour. When the sample was examined after cooling, it was found that it was almost only hexagonal monocarbide, and chemical analysis revealed that it was (Mo84.9W15.1) (C97
．． 3N2.7). Example 4 The body is (M○, W) (C, N) and some MO public and (T
Four phases of i, Ta, Mo, W) (C, N) and Co coexisted.

When cutting steel with this heat-generating body, it showed good cutting characteristics. 8 (Mo, W) (C, N) obtained in Example 4
% by weight, (Ti,Ta,W)C by 8% by weight, Co by weight%

[Brief explanation of the drawing]

1-a, FIG. 11b, FIG. 2-a, and FIG. 2-b are all charts showing the X-ray diffraction results of solid solutions according to examples of the present invention. After mixing 12% by weight using the green method, it was stamped and the green compact was
Vacuum sintering was performed at 45,000 for 1 hour. Obtained sintered diagram l-o Figure l-b Figure 2-o Figure 2-b

Claims (1)

[Claims] 1. In the production of a solid solution consisting of one or more hard phases having a simple hexagonal crystal structure in a composite carbide or carbonitride of molybdenum and tungsten, after mixing raw material powders. , a hexagonal monomer characterized in that the mixed powder is heated at a temperature of 1400°C or higher, then cooled once to room temperature, the primary reactant is distorted, and then heated again at a temperature of 1000°C to 1800°C. Method for producing solid solutions of carbides. 2 In claim 1, the mixed powder is heated to 1400°C.
A method for producing a solid solution of hexagonal monocarbide, which comprises applying pulverization or similar mechanical strain to a reactant heated at a temperature above. 3 In claim 1, the mixed powder is
By rapidly cooling the reactant heated above ℃ to room temperature, the primary reactant is strained, and then heated to 100℃ again.
A method for producing a solid solution of hexagonal monocarbide, which comprises heating at a temperature of 0°C to 1800°C. 4 In Claim 1, the content of molybdenum is 70
A method for producing a solid solution of hexagonal monocarbide, characterized in that the hexagonal monocarbide is at % or more.