JPH0723516B2 - 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.

[Conventional technology]

The high-speed rotating body must have a high degree of tensile strength and Young's modulus, and must have sufficient toughness so as not to break during 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 mixed powder consisting of 85-97% tungsten powder and the balance nickel and iron powder.
Powder compacted under hydrostatic pressure of 4 ton / cm ² and the resulting compact is 0-
After liquid-phase sintering in a hydrogen stream having a dew point of 60 ° C., the sintered body is heated in 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]

The reason why liquid phase sintering is performed in an atmosphere having a dew point of 0 to −60 ° C. in the above conventional manufacturing method is to perform sufficient reduction and impurity removal.

However, according to the research conducted by the present inventor, in the case of such a dew point, oxygen and hydrogen solid-dissolved in the sintered body are 2 H + O = H ₂ O.
It was found that the H ₂ O generated by the reaction as described above becomes gas porosity, which rather causes the ductility of the sintered body to decrease. This decrease in ductility is a problem when actually using a high-speed rotating body made of a tungsten sintered alloy or a projectile penetrating a protective object.

Therefore, an object of the present invention is to solve the above-mentioned conventional problems by providing a manufacturing method in which the conditions of liquid phase sintering are specified in detail and a tungsten sintered alloy having high ductility is obtained. is there.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides tungsten 85-
At the time of compacting a mixed powder consisting of 97% and the balance nickel and iron powder under hydrostatic pressure, and then performing liquid phase sintering of the compact, the dew point of the atmosphere in the temperature range of 1430 ° C. or less during temperature rising. Of less than -5 ° C and then over 1430 ° C and in the temperature range of liquid phase sintering, the dew point of the atmosphere is -5 ° C to 5 ° C.
Below.

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. The tungsten content needs to be 85% or more to maintain a predetermined high density. 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 added amount is 3 to 15% of the alloy amount. 3%
Below, a sufficient liquid phase is not generated and the effect of increasing the density cannot be exhibited. On the other hand, if it exceeds 15%, the content of tungsten becomes too small, and the high specific gravity of the alloy cannot be obtained. Also, the composition ratio of nickel and iron is Ni: Fe = 5: 5 to N
It is desirable to adjust between i: Fe = 8: 2. The reason for this 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 becomes 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 . The molding of less than 1 ton / cm ^2,
Even if liquid phase sintering is performed, 2-3% of pores remain. 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 exceeding 4 ton / cm ² , the density becomes too high, and closed bores occur 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 and iron components form 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.

In the present invention, the moisture contained in the atmosphere in this liquid phase sintering step, that is, the dew point of the atmosphere is set in two stages. First, in the temperature range below 1430 ° C, the dew point is -5.
The temperature is raised below ℃. The reason is that oxygen or oxide adsorbed on the surface of the raw material powder is sufficiently reduced by hydrogen gas having a low dew point having a strong reducing power. The reaction at this time is O + H ₂ (g) = H ₂ O (g). If the dew point is -5 ° C or higher, this reaction does not occur and O cannot be removed.

The temperature of 1430 ° C. or less is for suppressing sintering and densification, facilitating gas flow to the inside of the molded body, and promoting the above reaction.

Next, in the temperature range over 1430 ° C, the dew point is -5 ° C to +5.
Temperature rising and subsequent liquid phase sintering are performed in a hydrogen atmosphere at ℃.

In this alloy system, when the sintering temperature exceeds 1430 ° C, the nickel and iron components melt and become true density, but in the melted liquid phase, hydrogen absorbed from the atmospheric gas and a small amount of unreduced residual oxygen are absorbed. Is melting in. At this stage, the dew point of the atmosphere is −
If the temperature is lower than 5 ° C, the reaction of O + 2H = H ₂ O (g) proceeds to generate water vapor, which is not discharged to the outside and remains as porosity even after sintering. Conversely, the dew point of the atmosphere is + 5 ° C
If it is set too high, oxygen due to the decomposition of H ₂ O gas is absorbed in the liquid phase and ductility is deteriorated.

According to the present invention, the dew point of the atmosphere in liquid phase sintering is 1430
By prescribing separately before and after ℃,
A tungsten sintered alloy having high ductility was obtained.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples.

Tungsten powder containing a total of 5 to 12% of nickel powder and iron powder was mixed using a V-type mixer, and the resulting mixed powder was compression-molded under a hydrostatic pressure of ² ton / cm ² , and then the molded body was Liquid phase sintering was performed at (1430 + α) ° C in hydrogen with various dew points. The obtained sintered body was heat-treated in vacuum at 1150 ° C. for 2 hours, and then the residual porosity was measured and the tensile test was performed to evaluate the quality.

The residual porosity was measured by observing the cross section of the material with an optical microscope and determining the area ratio of porosity by the lattice point method.

The tensile test was performed at a tensile speed of 1 mm / min using a test piece having a parallel portion of 4.0 mmφ and a gauge length of 30 mm.

Table 1 shows the chemical composition of the sample, the sintering conditions, and the results of quality evaluation. In addition, as a comparative example, the results obtained by changing the sintering conditions are also shown.

It can be seen from Table 1 that the material of this example has no residual porosity and exhibits high ductility as compared with the material of the comparative example.

〔The invention's effect〕

As described above, according to the present invention, tungsten 85
~ 97% and the balance powdered powder consisting of nickel and iron powders is pressed under hydrostatic pressure, and then the liquid phase sintering of the powder compact is performed in a temperature range of 1430 ° C or less during the temperature rise. The dew point should be less than -5 ° C, and then the dew point of the atmosphere should be -5 ° C or more and 5 ° C or more during the temperature rising over 1430 ° C and the temperature range of liquid phase sintering.
The temperature is set to be equal to or lower than ° C. Therefore, there is an effect that there is no residual porosity, the ductility of the tungsten sintered alloy can be remarkably enhanced, and a substantially excellent projectile and high-speed rotating body can be obtained.

Claims (1)

[Claims] 1. A powder mixture consisting of 85 to 97% tungsten and the balance nickel and iron powder is pressed under hydrostatic pressure, and then the liquid powder is sintered at 1430 ° C.
In the temperature range below, the dew point of the atmosphere is less than -5 ° C, and in the temperature range of the temperature rising above 1430 ° C and in the liquid phase sintering, the dew point of the atmosphere is -5 ° C to 5 ° C. Method for producing a sintered tungsten alloy.