JPH0742539B2 - High strength / high ductility tungsten alloy and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-ductility tungsten (hereinafter W) sintered alloy useful for a projectile (core material) penetrating a protective object and a high-speed rotating body, and a method for producing the same.

[0002]

2. Description of the Prior Art A core material must have high tensile strength, density and hardness, and must have sufficient ductility and toughness so as not to break before completely penetrating a protective body.
Further, the high-speed rotating body must have high tensile strength, Young's modulus and sufficient toughness so as not to be broken at high speed rotation. W sintered alloy is one of the materials having such characteristics.

In order to improve the above-mentioned various properties of the W sintered alloy, much research and development has been carried out in the past. In Japanese Examined Patent Publication No. 63-30391, the W grain size is 40 to 100 μm.
And nickel (hereinafter Ni) iron (hereinafter F)
Disclosed is a W sintered alloy in which e) is dissolved in a predetermined amount or more and the amount of oxygen and carbon in the alloy is limited to a predetermined amount or less. This alloy is said to be a high toughness W alloy with high elongation and impact value.

Japanese Unexamined Patent Publication (Kokai) No. 3-173738 discloses a W sintered alloy in which the grain size of W grains is 40 μm or less and a predetermined amount of nitrogen is solid-dissolved in the alloy. It is said that this alloy has improved both ductility and strength as compared with conventional ones.

However, there is a limit to simultaneously improving the elongation and toughness of the alloy only by controlling the W grain size and the intragranular solid solution element as in the prior art. It is generally said that it is effective to reduce the W grains in order to increase the strength of the W sintered alloy, but if so, sufficient ductility of the alloy cannot be obtained. In order to reduce the W grain size, it is necessary to lower the temperature of liquid phase sintering or shorten the sintering time in order to suppress the growth of W grains. However, if the growth of W grains is insufficient, the W grains are not sufficiently spherical in terms of microstructure, and therefore the contact area between adjacent W grains increases. Since the grain interface where W grains are in contact with each other is the weakest part in terms of microstructure, it has been considered that an increase in the surface causes ductility deterioration of the W alloy.

Further, in the conventional method for improving the characteristics of the W alloy by controlling the solid solution element in the W grain, special pretreatment of the raw material powder and control of the sintering atmosphere are required. Such work is troublesome, and there is a risk of defective products due to increased control factors during the product manufacturing process.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a W sintered alloy which has both high strength and ductility and can be manufactured by a simple manufacturing process. Another object of the present invention is to provide a method for producing a high-strength / high-ductility W alloy that requires no labor and is free from delicate process control factors.

[0008]

[Means for Solving the Problems] If the present inventors can prevent the coarsening of the grain size of W grains on the microstructure of W alloy and reduce the contact ratio at the W grain-W grain interface. The idea was that a W alloy with high strength and ductility could be produced. In order to realize this idea, as a result of repeatedly improving the alloy microstructure and developing manufacturing conditions such as sintering conditions, the present invention has been completed.

That is, the W sintered alloy of the present invention is a sintered alloy containing 85 to 98% by weight of tungsten and the balance of nickel and iron in the weight ratio of 5: 5 to 8: 2 as the main components. And the average grain size of the tungsten grains is 4
The average value of the contact ratio of the tungsten particles is 0 μm or less, and the contact ratio is <0.056 × W content weight% −5.0.
It is characterized in that the condition 1 is satisfied.

The method for producing a W sintered alloy of the present invention is
A metal powder mixture containing 85 to 98% by weight of tungsten and the balance of nickel and iron in a weight ratio of 5: 5 to 8: 2 as a main component is compression-molded to obtain a powder compact. In a method for producing a tungsten alloy, which comprises heating a body to a temperature above a liquid phase generation temperature of a nickel-iron alloy and sintering it; while maintaining a sintering temperature at 1500 ° C. or higher and maintaining a green compact at a liquid phase generation temperature or higher, (Sintering temperature-Liquid phase formation temperature) x integrated value of time is 1000 to 3000 ° C · min, and the cooling rate for cooling from the maximum temperature during sintering to the liquid phase formation temperature after holding is set to 8 ° C / min or more. Characterize.

The main composition of the W sintered alloy of the present invention has a W content of 85.
.About.98% by weight (hereinafter, w%) and the balance is Ni and Fe.
The W content needs to be 85% or more in order to maintain a predetermined high density. Further, 98% in order to ensure the amount of liquid phase that is completely densified in the liquid phase sintering step when manufacturing the W sintered alloy.
It must be: The content ratio by weight of Ni and Fe is set within the range of Ni: Fe = 5: 5 to 8: 2 in order to lower the liquid phase formation temperature and perform effective liquid phase sintering.
If necessary, cobalt can be added up to 5% as another component.

After compression molding of the mixed powder having the above composition ratio,
-The green compact is liquid-phase sintered by heating it to 1430 ° C or higher at which Fe melts. After the liquid phase sintering, the microstructure becomes a so-called heavy metal structure in which spherical W particles are surrounded by Ni-Fe and a matrix phase in which W is solid-dissolved. A trace amount of Ni, Fe gas components, etc. may be solid-dissolved in the W grains.

In the W alloy of the present invention, the average W grain in the microstructure is 40 μm or less, and the average contact ratio of the W grains is within the range represented by the following equation. 0.056x-5.01> y X: W content (%)
y: Contact rate If the W particle size exceeds 40 μm, sufficient alloy strength cannot be obtained. The lower limit of the grain size is not particularly limited, but if it is 10 μm or less, the upper limit of the contact rate of W grains may be exceeded and the ductility may be deteriorated. When the contact rate exceeds the range of the relational expression, the elongation deteriorates significantly. Here, the average grain size of W grains refers to the average value obtained by the section length measuring method.

The contact ratio of W grains is determined by the W content in the W alloy microstructure.
It is an index showing the existence ratio of the interface between the grains and the W grains. There are two types of interfaces of the microstructure of the W sintered alloy: an interface between W grains (C _WW ) and an interface between W grains and a liquid matrix phase (C _WL ). As shown in FIG. 1, an arbitrary line is drawn on the surface of the alloy where the microstructure is observed, and it is investigated whether the intersection of the line and the grain boundary is C _ww or C _WL . The contact rate is calculated by the following formula. Contact rate = (number of C _WW ) ÷ total number of interfaces = 2C _WW ÷ (2C _ww + C _WL ), where C _WW is doubled, one for each of the two W particles in contact. Each is based on the idea that there is an interface.

The average value of the contact ratio of W particles is 250 μm in length at 10 μm intervals in an optical microscope photograph at 400 × magnification.
50 lines are drawn in parallel and the average value of the contact ratio of the 50 lines is obtained.

In order to obtain the above-mentioned microstructure, the liquid phase sintering process of W alloy is controlled as follows. First, the holding temperature during liquid phase sintering is set to 1500 ° C. or higher, and the temperature is raised, held, and cooled so that the integrated value of (sintering temperature−liquid phase formation temperature) × time falls within the range of 1000 to 3000 ° C.min. In the cooling process after holding, the temperature from the holding temperature to the liquid phase formation temperature (around 1430 ° C.) is cooled at a cooling rate of 8 ° C./min or more.

The first feature of the W alloy sintering method of the present invention is that the sintering temperature is high. When the sintering temperature becomes high, the matrix phase in the molten state and the W
Since the interfacial energy with the grains is lowered, the angle formed by the contact portion between the W grains becomes large, and thereby the contact rate between the W grains can be reduced. As a result, the weakest W grain interface in the W sintered alloy can be reduced, and the ductility of the alloy can be improved.

The second characteristic is to suppress the coarsening of W grains which occurs during holding the alloy at a temperature higher than the liquidus formation temperature, so that the value of (sintering temperature-liquidus formation temperature) × time is within a certain range. That is the control within. As a result, it is possible to prevent the strength and ductility from being lowered due to the coarsening of W grains.

The reason why the cooling rate from the holding temperature to the liquid phase formation temperature after the holding is set to 8 / min or more is that the high temperature structure is solidified as it is by increasing the cooling rate. It should be noted that if the temperature raising rate is extremely slow, the W particles become coarse during the temperature raising, so it is preferable that the rate is relatively high (for example, 8 ° C./min or more).

[0020]

Example Hydrogen-reduced tungsten powder, carbonyl nickel powder, and carbonyl iron powder were used as raw material powders, and mixed with a V-type mixer to have the composition shown in Table 1. Diameter of mixed powder 20
It was filled in a rubber mold having a length of 140 mm and a length of 140 mm, and was pressed using a cold isostatic press. Put the green compact in the hydrogen sintering furnace and
A reduction treatment of 0 ° C. × 1 hr and a pre-sintering of 1350 ° C. × 1 hr were performed. After that, the temperature rising rate is 5 ° C / min to 25 ° C / m
In, the temperature was raised to 1450 to 1650 ° C, which is the sintering temperature, and held for 1 min to 40 min, and then the cooling rate was 1 ° C / m.
The temperature was changed to in to 25 ° C / min and sintering was performed to obtain W alloy sintered bodies of Examples and Comparative Examples. After sintering, vacuum heat treatment was performed at 1150 ° C. for 2 hours for the purpose of H ₂ removal treatment. The liquid phase production temperature in this example was 1430 ° C. Table 1 shows the sintering conditions of the alloy of this experiment, the microstructure of the obtained alloy and the result of the tensile test.

[0021]

[Table 1]

FIG. 2 shows micrographs of the microstructures of the W sintered alloys of Example (A) and Comparative Example (B). In Example (A), although the W particle size was as small as 34 μm, the liquid phase was well wrapped around the W particle size.
The W grain interface is reduced. A graph showing the relationship between tensile strength and elongation of the alloys of Examples and Comparative Examples is shown in FIG. As is clear from this graph, the W alloys of the examples of the present invention are
The balance between tensile strength and elongation is remarkably improved as the alloy of the comparative example.

[0023]

As is apparent from the above description, the present invention exhibits the following effects. Since the W grain size of the W sintered alloy is small and the brittle W grain interface is small, the strength and ductility of the alloy are improved in a well-balanced manner. By improving the relatively simple manufacturing condition of controlling the temperature during sintering, a W sintered alloy having both high strength and ductility can be manufactured. As a result, it is possible to provide a low-cost, high-quality, high-strength / high-toughness W sintered alloy.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method of measuring a W grain-W grain contact rate.

FIG. 2 is a micrograph showing a microstructure of a W sintered alloy according to Example (A) and Comparative Example (B) of the present invention.

FIG. 3 is a graph showing tensile properties of W sintered alloys according to Examples and Comparative Examples of the present invention.

Claims (2)

[Claims] 1. 85 to 98% by weight of tungsten, and
A sintered alloy containing nickel and iron in a weight ratio of 5: 5 to 8: 2 as the main constituent, the grain size of tungsten grains being 40 μm or less on average, and the contact rate of tungsten grains. Average value of contact rate <0.056 × W
A high-strength, high-ductility tungsten alloy, characterized by satisfying the condition of content weight% -5.01. 2. 85 to 98% by weight of tungsten, and
A metal powder mixture containing nickel and iron in a weight ratio of 5: 5 to 8: 2 as the main component is compression molded to obtain a green compact, and the green compact is used to generate a liquid phase of a nickel-iron alloy. In a method for producing a tungsten alloy which is heated to a temperature or higher and is sintered; the maximum temperature during sintering is 1500 ° C. or higher, and while the green compact is kept above the liquid phase formation temperature (sintering temperature-liquid phase formation temperature) × The integrated value of time is 1000 to 3000 ° C.
The method for producing a high-strength, high-ductility tungsten alloy is characterized in that the cooling rate after cooling is from the maximum temperature during sintering to the liquid phase formation temperature after holding is 8 ° C / min or more.