JPH0639641B2 - Method for producing tungsten sintered alloy - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a tungsten sintered alloy useful for a projectile penetrating a high speed rotating body or a protective object.

[Prior Art] A high-speed rotating body must have a high degree of tensile strength and Young's modulus, and also must have sufficient toughness so as not to break at high-speed rotation. The projectile must also have a high degree of tensile strength, density and hardness, yet be sufficiently ductile and tough to prevent the projectile from breaking before completely penetrating the protective object. .

A method for producing a tungsten alloy having a high specific gravity and a high ductility in order to meet such requirements is disclosed in JP-A-62-185843. This is a tungsten powder 8
A mixed powder of 5 to 97% and the balance of nickel and iron powder was compacted under hydrostatic pressure of 1 to 4 ton / cm ² , and the obtained compact was liquid-phase sintered in a hydrogen stream, The sintered body is subjected to heat treatment in which it is heated in a vacuum and then rapidly cooled.

By performing heat treatment of heating and quenching in a vacuum after the above-mentioned sintering, excess solid-solved hydrogen in the sintered body is removed, and grain boundary precipitation of impurities that cause embrittlement can be prevented, resulting in high ductility. Is said to be obtained.

[Problems to be Solved by the Invention]

In the high-speed rotating body and the projectile penetrating the protective object to which the tungsten alloy obtained by the above conventional manufacturing method is applied, the dimensional accuracy is strict, and finally the surface grinding by the centerless machine is essential. Process.

According to the results of the intensive studies by the present inventors, the ductility of the tungsten-nickel (W—Ni—Fe) -based sintered alloy is extremely sensitive to the residual stress on the surface, as is the case with ceramics. Therefore, it is found that if the surface grinding is applied by a centerless machine after the heat treatment for dehydrogenation and the heat treatment for rapid cooling in the above conventional example, the ductility is remarkably deteriorated, which is a problem in actual use. Was done.

Therefore, an object of the present invention is to solve the above-mentioned conventional problems by providing a method for producing a tungsten alloy capable of removing the adverse effect of residual stress on the surface after machining into a final shape.

[Means for solving problems]

In order to achieve the above object, the present invention provides a tungsten 85
˜97%, the mixed powder consisting of nickel and iron powder as the balance is compression molded, and then the compression molded body is densified by liquid phase sintering, and the obtained sintered body is processed into a final shape and then non-oxidized. After heating at 900 to 1400 ° C. in a neutral atmosphere, it is gradually cooled.

However, the slow cooling rate is preferably 30 ° C. or less.

The details will be described below.

The raw material powder used in the present invention is high-purity tungsten (W), nickel (Ni), and iron (Fe) powder.
Tungsten content is 85 in order to maintain a predetermined high density.
% Or more is required. Moreover, in order to secure the amount of the liquid phase which is completely densified in the liquid phase sintering step, it is necessary to be 97% or less. Nickel and iron are added for the purpose of generating a liquid phase during sintering, promoting densification, and increasing the ductility of the material. The addition amount is 3 to 15% of the alloy amount. If it is less than 3%, a sufficient liquid phase is not generated and the effect of increasing the density cannot be exhibited. On the other hand, if it is 15% or more, the content of tungsten becomes too small, and the high specific gravity of the alloy cannot be obtained. The composition ratio of nickel and iron is Ni:
It is desirable to adjust between Fe = 5: 5 and Ni: Fe = 8: 2. The reason is that in this composition range, the liquid phase generation temperature in the liquid phase sintering step is sufficiently lowered as compared with the case of nickel or iron alone, and eventually effective liquid phase sintering is possible.

Therefore, instead of a single powder of nickel and iron,
Even if both alloy powders having the above composition are used, the same effect can be obtained.

The pressure at the time of compression molding the mixture of the raw material powders is 1 to
The hydrostatic pressure is 4 ton / cm ² . In the case of molding at less than 1 ton / cm ² , 2-3% of pores remain even after liquid phase sintering. Therefore, the density of the compression molded article is too small to be completely densified, and the ductility is deteriorated. On the other hand, in the case of molding in excess of 4 ton / cm ² , on the contrary, the density becomes too high and a closed bore occurs in the compression molded body, so that it cannot be completely densified.

The reason why the hydrostatic pressure is used instead of the usual uniaxial compression is to increase the homogeneity of the alloy and thus the ductility by uniformly pressing from all sides.

Liquid phase sintering needs to be performed in hydrogen at 1430 ° C. or higher, which is the temperature at which the nickel / iron component forms a liquid phase.

The sintering time is a time required for complete densification, that is, 20 minutes or more, and 60 minutes or less is desirable in order to prevent coarse porosity from being generated during sintering.

Next, the sintered body is processed into a final shape. The processing method may be cutting, grinding, plastic working such as swaging, or a combination thereof.

In the present invention, after the final shape is machined, heat treatment such as heating and slow cooling is performed in a non-oxidizing atmosphere such as argon gas. The reason is that the adverse effect of the surface residual stress cannot be removed by performing mechanical processing such as surface grinding after the heat treatment, and the reason why the non-oxidizing atmosphere is set is that the oxidizing atmosphere significantly oxidizes.

The heat treatment temperature in the above non-oxidizing atmosphere is 900 to 1
The temperature of 400 ° C. is defined as below 900 ° C. because the residual stress of machining is not sufficiently removed (see FIG. 1).
This is because the product shape cannot be maintained at a temperature higher than 0 ° C. On the other hand, the cooling temperature is preferably a slow cooling rate of 30 ° C./min or less in order to prevent the occurrence of residual stress during cooling.

The heat treatment of the present invention is distinctly different from the conventional method of heating in vacuum immediately after liquid phase sintering and then quenching. That is, it is well known that the residual stress on the surface generally affects the material properties such as fatigue strength. In particular, as mentioned above, brittle materials such as ceramics and tungsten are sensitive to surface residual stress. No matter how carefully the material is processed, it is impossible to generate residual stress. The present inventors have found that this residual stress on the surface has an extremely large effect on the ductility of the tungsten sintered alloy. FIG. 2 shows the measurement results. The surface residual stress was measured by the half-value width midpoint method using X-ray diffraction. From FIG. 2, it can be seen that the elongation decreases in inverse proportion to the increase in the surface residual stress. In other words, removal of surface residual stress is very important for improving ductility.

According to the present invention, residual stress is removed by subjecting a predetermined compression-molded metal powder to liquid-phase sintering, then processing to a final shape, and then performing heat treatment of heating / slow cooling in a non-oxidizing atmosphere. The ductility was effectively improved.

〔Example〕

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

Tungsten powder 95 wt% -Nickel powder 3.5 wt%-
Iron powder was blended to a composition of 1.5 wt% and mixed using a V-type mixer. The obtained mixed powder was compression molded under a hydrostatic pressure of ² ton / cm ² , and the molded body was subjected to 40 ° C. in hydrogen at 1530 ° C.
Liquid phase sintering was performed for a minute. Subsequently, the sintered body was heat-treated in vacuum at 1200 ° C. for 2 hours and then machined into a tensile test piece.

This machining causes surface residual stress in the test piece.
This tensile test piece was heat-treated at 800 to 1400 ° C. for 1 hour in an argon atmosphere. The cooling rate at this time is 10 ℃
/ Min.

Table 1 shows the tensile test results. As a comparative example, a tensile test piece was not machined and then heat treated,
Also, the results of heat treatment in vacuum at 1000 ° C. for 1 hour after the machining and quenching at 50 / min are shown.

From Table 1, it can be seen that the method according to the present example exhibits higher elongation than those not subjected to heat treatment and those subjected to heating / quenching during machining.

Based on the above test results, a bullet as a projectile penetrating a protective object, which is a field of application of the present invention, was manufactured, and a penetration comparison for a multi-layered target was examined. Similar to Comparative Example 7 above, a projectile manufactured without heat treatment after final processing, and Comparative Examples 8 and 9
The penetration capability of a projectile manufactured under the same heat treatment conditions as
Then, the penetration capability of the projectile by the method of the present invention is 10
It was 0 or more.

[Effects of the Invention] As described above, according to the present invention, the tungsten 8
A mixed powder of 5 to 97% with the balance being nickel and iron powder is compression molded, and then the compression molded body is densified by liquid phase sintering, and the obtained sintered body is processed into a final shape. Heating was performed at 900 to 1400 ° C. in an oxidizing atmosphere, and slow cooling was performed at a predetermined rate. Therefore, the ductility of the tungsten sintered alloy in the final product shape can be remarkably enhanced, and a substantially excellent projectile and high-speed rotating body can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between heat treatment temperature and surface compressive residual stress in the tungsten alloy of the present invention, and FIG. 2 is a graph showing the relationship between surface compressive residual stress and elongation.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masao Nakai 4-2 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Metallurgical Industry Co., Ltd. (56) Reference JP-A-52-37503 (JP, A) )

Claims (2)

[Claims] 1. A mixed powder comprising 85 to 97% tungsten and the balance being powder of nickel and iron is compression-molded, and then the compression-molded body is densified by liquid phase sintering to obtain a sintered body having a final shape. After processed into 900-900mm in a non-oxidizing atmosphere
A method for producing a tungsten sintered alloy, which comprises heating at 1400 ° C. and then gradually cooling. 2. The method for producing a tungsten sintered alloy according to claim 1, wherein the slow cooling rate after heating in the non-oxidizing atmosphere is 30 ° C./min or less.