JPH02163337A - Manufacture of high hardness tungsten liquid phase sintered alloy - Google Patents

Abstract

PURPOSE:To obtain the sintered alloy having high hardness and is homogeneous internally and externally by incorporating specified % of tungsten and one or more kinds among Cu, Fe, Ni and Co into a liquid phase sintered alloy material and subjecting the alloy material to hot working at a specified temp. at specified working rate. CONSTITUTION:To a liquid phase sintered alloy material, 90 to 98% tungsten and the balance one or more kinds among Cu, Fe, Ni and Co are incorporated. The material is subjected to hot working in the range of the temp. from 50 to 600 deg.C and 50 to 70% working rate. The sintered alloy is used as a projectile passing through an armor plate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a tungsten liquid phase sintered alloy which is particularly required to have high hardness as a projectile that penetrates armor plates.

[Conventional technology]

- the projectile has a high degree of tensile strength, Young's modulus,
Furthermore, it must have sufficient toughness so as not to break during high-speed rotation. Furthermore, in the case of armor-piercing projectiles, there has recently been an increasing demand for high hardness of Hv500 or more, and there is a tendency for such high hardness to be required locally, particularly only at the tip of the projectile.

Conventionally, as a method for manufacturing a projectile that meets the requirement of high hardness of Hv400 or more, there is a method proposed in Japanese Patent Publication No. 330803/1983. This thing is tungsten,
An alloy body formed by sintering and pressing iron and nickel powder is extruded from a nozzle and processed to reduce its cross-sectional area by 20%, thereby hardening it to Hv400 or higher. According to this method, spherical tungsten grains are plastically deformed into vertically elongated grains (first conventional example).

In addition, apart from the above, after cold working a sintered alloy of tungsten, iron, and nickel, it is aged at 500 to 700°C.
A method has been proposed to increase the temperature by more than Ivsoo (Second Conventional Example, [Powder and Powder Metallurgy] Vol. 35, No. 6, (1)
988) p. 92-97).

[Problem to be solved by the invention]

However, in the first conventional example, for example, Hv
When cold working is performed at a processing rate (cross-sectional area reduction rate) of 30% or higher in order to obtain a cross-sectional area of 500 or higher, there is a problem in that the material often breaks.

In addition, since the strength of tungsten sintered alloy is high, even if it is processed, the hardening due to processing does not reach the inside of the material.
Therefore, there was a problem that uniform hardness could not be obtained between the outside and inside of the material.

On the other hand, in the second conventional example, 500 to 7oo'c
Since the surface of the material oxidizes during aging, vacuum or non-oxidizing atmosphere equipment is required to prevent this, resulting in an increase in cost.

Furthermore, as mentioned above, when high hardness is required locally only at the tip of the projectile, there is a problem in that it is impossible to age-harden only the tip.

Therefore, the present invention has been made by focusing on the above-mentioned conventional problems, and its purpose is to obtain high hardness without destroying the material even when processed at a large processing rate, and to improve the material's hardness. The object of the present invention is to provide a method for manufacturing a high-hardness tungsten liquid phase sintered alloy that has uniform hardness on the outside and inside, is free from surface oxidation (and can be locally hardened).

[Means to solve the problem]

In order to achieve the above object, the present invention provides tungsten 90
~98% balance Cu, Fe, Ni, C.

It is characterized in that a liquid phase sintered alloy material containing one or more of the above is subjected to warm working at a temperature of 50 to 600°C and a working rate of 5 to 70%.

The inventor has determined that the tungsten liquid phase sintered alloy material has a
When processed at a warm temperature of ~600℃, at the same processing rate,
It has been found that higher hardness can be obtained when cold processing is performed (at room temperature).

This is thought to be because, unlike normal iron-based alloys, tungsten alloys have a high recrystallization temperature, so recovery phenomena do not occur during warm working in a temperature range of about 600°C. .

Furthermore, warm working has a higher dislocation density than cold working;
As a result, it is thought that the hardness becomes higher.

When producing tungsten sintered alloy, the main component is tungsten (W) powder, and the ii & 11 components are copper (Cu) powder with a lower melting point, iron (Fe) powder, nickel (N t ) powder, and cobalt powder. ) (C.

One or more types of powder (e.g. Nt-Fe, Ni-F
e-Co, etc.), the mixed powder is compression molded, and the resulting compression molded body is heated in a sintering furnace to a temperature slightly higher than the melting point of the subcomponents. As a result, only the powders of the mixed subcomponents are melted and a liquid phase is generated.

This liquid phase penetrates into the gaps between the tungsten particles due to surface tension, envelops the particles, and attracts them to each other.

As a result, changes occur in the tungsten particles, the tungsten particles are sintered together, and the volume of the compression molded body after sintering shrinks and becomes denser.

The tungsten content of the obtained sintered body must be 90% or more in order to maintain a predetermined high density.

Furthermore, in order to ensure the amount of liquid phase to be completely densified in the liquid phase sintering process, it is necessary that the amount is 98% or less.

That is, the subcomponent is added for the purpose of generating a liquid phase during sintering to promote densification and improve the ductility of the material, and the amount added is 2 to 10% of the amount of the alloy. If it is less than 2%, a sufficient liquid phase will not be generated and the densification effect cannot be achieved.

On the other hand, if it exceeds 10%, the tungsten content becomes too small, making it impossible to obtain a high specific gravity of the alloy.

In the present invention, processing such as compression processing, forging, or swaging is performed on the liquid phase sintered alloy material body at a predetermined temperature and processing rate to obtain a high hardness tungsten liquid phase sintered alloy. . The processing method may be one pass or multi-pass processing of two or more passes.

As a result of experiments, it was confirmed that the processing temperature is preferably within the range of 50°C to 600''C, and the processing rate is preferably within the range of 5 to 70%.

If the temperature is less than 50° C., the deformation resistance during processing is large, so the material is likely to be destroyed, and the material is also deformed unevenly, making it difficult to obtain uniform hardness.

On the other hand, when the temperature exceeds 600°C, oxidation of the material is promoted.

As for the processing rate, if it is less than 5%, sufficient strain cannot be applied to the material, and the hardness will not increase to the desired value. On the other hand, if it exceeds 70%, extremely large force will be required for processing, making it impractical.

The reason why warm working of tungsten liquid phase sintered alloy material under such conditions results in an alloy having higher hardness than that obtained by cold working at room temperature is considered as follows.

In other words, the crystal structure of tungsten is a body-centered cubic lattice, and when processed in a warm region, interstitial solid solution atoms such as carbon (C) and nitrogen (N) become distorted around dislocations that multiply as the process progresses. It is attracted to the tension side by field interaction, creating the so-called Cottrell atmosphere. As a result, the movement of dislocations is resisted and the strength increases.

In other alloys, such as mild steel, the above effects occur at 250-300°C. If the temperature is higher than this, the strength decreases because the mobility of dislocations increases due to thermal vibration and the resistance decreases.

In addition, in iron-chromium (Fe-Cr) alloy, 500
When the temperature exceeds .degree. C., C1N in the Cottrell atmosphere is used as chromium carbonitride, and the strength similarly decreases.

Tungsten is a high melting point metal (melting point 3380°C),
The recrystallization temperature (1500°C) is also high. Therefore, even if the temperature is increased, the Cottrell atmosphere created by warm working is maintained, and it is considered that the strength does not deteriorate even at higher temperatures.

It is thought that when warm working is performed, tungsten undergoes dynamic strain aging due to the above-described repeated proliferation and fixation of dislocations, resulting in a structure with a very high dislocation density.

Thus, according to the present invention, a material with higher hardness than when cold worked at room temperature can be obtained, and by raising the temperature, deformation resistance is reduced, and uniform hardness can be obtained throughout the material. This is especially important for high strength materials such as tungsten.

In addition, local hardening can be realized by applying warm working to a limited area, for example, only to the tip of the material.

Embodiments of the present invention will be described below with reference to the drawings.

[Example 1] Tungsten powder 95wt% - Nickel powder 3.5w% -
The iron powder was blended to a composition of 1.5 wt % and mixed using a ■ type mixer. The obtained mixed powder was compression molded under a hydrostatic pressure of 2 tOn/crA, and the molded product was heated at 1530°C in hydrogen.
Liquid phase sintering was carried out for 40 minutes. Next, the sintered body was heated to 1200℃.
After heat treatment in vacuum for 2 hours, the specimens were machined into tensile specimens.

A tensile test was conducted on this test piece under different temperature conditions.

Figure 1 shows the test results. At temperatures below 50°C, there is little elongation. On the other hand, it can be seen that the tensile strength and 0°2% yield strength decrease as the temperature increases.

Next, the composition was changed to tungsten powder 97wt% nickel powder 2
．． 1 wt% - iron powder 0.9 wt%,
A plurality of samples were prepared by compression molding, liquid phase sintering, and heat treatment in the same manner as above. Then put them at 20″C (room temperature) and 50°C.
, 200, 400, and 600°C, and the Vickers hardness was measured.

The test results are shown in Figure 2. Those cold-worked at room temperature break at a reduction in area (RA) of 50%, and the hardness at that time is Hv. It was 460. On the other hand, the temperature 50
, 200, 400, and 600°C, there was no breakage even when the RA reached 70%, and the hardness at that time was Hv480. Hv525. Hv
560. Hv605, clearly showing the effect of increasing hardness due to warm working.

[Example 2] As in Example 1, tungsten powder 97 wt% nickel powder 2.1 w L% - iron powder 0.9 wt% was compression molded → liquid phase sintered → heat treated, and then heated to 20°C. (room temperature) and 50,200°C, and the hardness distribution from the outside to the inside of the material was measured.

The test results are shown in Figure 3. For those cold-worked at room temperature, a rapid decrease in hardness was observed from the surface to the center of the sample. On the other hand, those subjected to warm working at a temperature of 50.200'C showed uniform hardness from the outside to the inside, clearly demonstrating its homogeneity.

〔Effect of the invention〕

As explained above, according to the present invention, a tungsten liquid phase sintered alloy material of a predetermined composition is subjected to warm working at a temperature of 50 to 600°C and a working rate of 5 to 70%. I took it as a thing. Therefore, there is an effect that high hardness, which cannot be obtained by cold working alone, can be obtained uniformly inside and outside without destroying the material. Moreover, the effect that the material can be partially hardened is obtained. A further advantage is that oxidation problems that occur with conventional age hardening do not occur.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between temperature and tensile properties of tungsten liquid phase sintered alloys, Figure 2 is a graph showing the relationship between processing rate and hardness in the present invention and the conventional example, using processing temperature as a parameter, and Figure 3 is a graph of the present invention. It is a graph comparing the homogeneity of curing between the invention and a conventional example.

Claims (1)

[Claims] (1) Tungsten 90-98%, balance Cu, Fe, N
For liquid phase sintered alloy materials containing one or more of Co.
A method for producing a high-hardness tungsten liquid phase sintered alloy, characterized by performing warm working within a range of 70%.