JPH07116547B2 - High toughness tungsten sintered alloy - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-toughness tungsten sintered alloy suitable for applications such as a core material and quill, which require high specific gravity and high toughness.

[Problems to be Solved by Conventional Techniques and Inventions] W-Ni-Fe based sintered alloys have been conventionally used for applications such as core material and quill, which require high specific gravity and high toughness. However, recently, from the viewpoint of improving the performance, demands for further improvement in toughness of the alloy have become stronger.

In order to meet such requirements, conventionally, for example, a raw material powder made of a predetermined ratio of tungsten, nickel, and iron is compacted and liquid-phase sintered, and then heat-treated by heating in vacuum and then rapidly cooling (Japanese Patent Application Laid-Open No. Sho-2004-96). No. 62-185805), and methods such as reducing the oxygen content and oxygen content in a tungsten sintered alloy (Japanese Patent Publication No. Sho 63-30391) are studied, while in the other, in the tungsten sintered alloy. The effect of various impurity components contained in toughness on toughness has been studied.

However, no proposal has been made to comprehensively control impurities that adversely affect toughness to obtain a tungsten sintered alloy having extremely high toughness on an industrial scale.

Therefore, the present inventors have made intensive studies on the influence of impurities on the tungsten sintered alloy, and as a result, have proposed the present invention. That is, an object of the present invention is to obtain an extremely high toughness tungsten sintered alloy on an industrial scale by controlling impurities.

[Means for Solving the Problems]

The first invention of the present application that achieves the above object is 90 to 98 wt% tungsten, the content of impurity components is P ≦ 8 ppm, As + Sb + Bi ≦ 20 ppm, Al + Ti ≦ 20 ppm, Cr + Mn + V ≦ 100 ppm, Si ≦ 20 ppm, C ≦ 100 ppm, and the balance Is composed of nickel (Ni) and iron (Fe), and the weight ratio of the nickel and iron is Ni / Fe = 0.5 to 4.

The second invention of the present application is tungsten 90 to 98 wt%, N
b10 to 100ppm, the impurity content is P ≦ 8ppm, As + Sb + Bi ≦ 20ppm, Al + Ti ≦ 20ppm, Cr + Mn + V ≦ 100ppm, Si ≦ 50ppm, C ≦ 200ppm, and the balance nickel (Ni) and iron (Fe). The weight ratio of nickel and iron is Ni / Fe = 0.5-4.

A third invention of the present application is the above-mentioned first or second invention, which contains 0.5 wt% or less of cobalt (Co).

The details will be described below.

The main composition of the sintered tungsten alloy of the present invention is 90 to 98 wt% tungsten (W), and the balance nickel (Ni) and iron (Fe). W content is to maintain a predetermined high density
90% or more is required. In addition, in order to secure the amount of the liquid phase that is completely densified in the liquid phase sintering step when manufacturing the tungsten sintered alloy, it is necessary to be 98 wt% or less. Ni and Fe are added as binders that generate a liquid phase during sintering to promote densification and enhance the ductility of the material. The added amount is 2 to 10 wt% of the alloy amount. 2 wt%
If it is less than the above, a sufficient liquid phase is not generated and the effect of increasing the density cannot be exhibited. On the other hand, if it exceeds 10 wt%, the W content becomes too small, and the high specific gravity of the alloy cannot be obtained. Also, with Ni
The weight ratio of Fe is preferably in the range of Ni: Fe = 0.5 to 4 in order to lower the liquid phase formation temperature and to carry out effective liquid phase sintering.

In addition, cobalt (C
o) can be added. Co is added to improve the strength of the sintered tungsten alloy,
If the content is too high, ductility will deteriorate, so 0.5 wt%
The following are appropriate:

Furthermore, the inventors of the present invention comprehensively understand the influence of various impurities that may be mixed in on the toughness of the product alloy when manufacturing the tungsten sintered alloy on an industrial scale, and by increasing the purity. We pursued the possibility of improving toughness. And in the process of research, I found the following facts.

Phosphorus (P) segregates at the grain boundaries during the cooling process after the heat treatment and deteriorates the impact value of the toughness. However, when the water-cooled cooling means is used for rapid cooling, there is no adverse effect up to about 10 ppm. However, when the cooling rate by Ar gas cooling means (≦ 20 ° C./min) is used as in the vacuum heat treatment step in the usual manufacturing on an industrial scale, the allowable amount is 8 ppm or less, which is extremely small.

Arsenic (As), antimony (Sb), bismuth (Bi) are P
Although it is an element that has the same adverse effect as the above, the degree of deterioration is small, and a total allowable amount of 20 ppm is recognized.

Aluminum (Al) and titanium (Ti) are usually contained as oxides. However, the ductility of W particles in the tungsten sintered alloy is significantly deteriorated by the amount of dissolved oxygen.
Therefore, the content of Al + Ti element by each oxide of Al and Ti is
If it exceeds 20ppm and remains in the tungsten sintered alloy,
These bound oxygen atoms form a solid solution with W atoms, and significantly deteriorate the toughness of the tungsten sintered alloy.

Chromium (Cr), manganese (Mn), and vanadium V) also have the same adverse effects as when the bound oxygen is Al and Ti, but Cr + Mn
It is acceptable if the total content of + V elements is 100 ppm or less.

Silicon (Si) and carbon (C) generate H ₂ O gas, which is a liquid phase hard-to-absorb gas, during sintering, and residual pores are formed in the sintered alloy, resulting in variations in elongation of the product alloy. Invite. This, Si, C has a property of reducing the solubility of H ₂ gas in the sintering process to be carried out with H ₂ in a gas flow, undissolved therefor H ₂
This is because H ₂ O gas is generated by combining with the water vapor in the atmosphere. Therefore, Si ≦ 20ppm, C ≦ 100ppm
And need to.

Niobium (Nb), on the contrary, has the property of increasing the solubility of H ₂ gas, and by adding a small amount of 10 to 100 ppm, the gas absorption in the liquid phase during sintering is improved. S
The harmful effects of i and C can be reduced. Therefore, if Nb is added, the regulation of the content of impure components is Si ≦ 20 ppm, C ≦ 100.
It is relaxed from ppm to Si ≦ 50ppm, C ≦ 200ppm.

Thus, according to the present invention, the toughness of the tungsten sintered alloy can be improved by positively controlling the specific impurities in the tungsten sintered alloy.

〔Example〕

 Examples of the present invention will be described below.

Different lots of hydrogen-reduced tungsten powder, carbonyl nickel powder, carbonyl iron powder, and hydrogen-reduced cobalt powder are used as raw material powders, and have different chemical composition through the manufacturing processes of mixing, molding, sintering, and heat treatment. A plurality of types of tungsten sintered alloys were manufactured and used as test pieces. A V-type mixer was used for mixing the raw material powders. A cold isostatic press was used for molding, and a molded product having a diameter of 20 mm and a length of 140 mm was obtained at a pressure of ² ton / cm ² . Using a pusher continuous sintering furnace,
After heat-treating at 1480 ℃ for 40 minutes in an H ₂ stream to sinter, 50
It was rapidly cooled at a cooling rate of ° C / min. Next, vacuum degree 10 ^-4 torr
Vacuum heat treatment was performed at 1150 ° C for 2 hours, and then cooled with Ar gas at a cooling rate of 20 ° C / min.

Table 1 shows the main component composition and the impurity content of the test object.
Nos. 1 to 8 are examples of the present invention, and No. 9 to
18 is a comparative example.

For each of the 18 types of DUTs thus formed,
The porosity, tensile strength, elongation, and Charpy impact value were measured, and the test results are also shown in Table 1. The porosity was calculated by the point calculation method. The tensile test was conducted at a gauge length of 16 mm and a test speed of 1 mm / min. The Charpy impact test specimen was 10 mm square, 55 mm long, and notched.

From Table 1, the tungsten sintered alloy of the present embodiment is largely in tensile strength of a minimum of 92.8kg / mm ² is 95 kg / mm ² or more, elongation is 30% base than 28.6% of the minimum impact value Is the lowest 3.4k
Except for g-m / cm ² , everything is 5 kg-m / cm ² or more. In addition,
In Nos. 5 and 8 of the examples, a large amount of Si and C are present in the impurities, but the addition of Nb is intended to improve the gas absorption in the liquid phase.

The tensile strength of the comparative example is 92.7 kg / mm ² or more, which is not much different from that of the example, but the elongation and impact value are significantly deteriorated in relation to impurities in comparison with the example. Was given.

That is, Comparative Examples Nos. 9, 10, and 17, 18 had a P content of 8 pp.
m or more, so that the impact value is 0.5 to 2.3 kg-m / cm ²
And is greatly reduced.

Comparative Example No. 11 has a total content of As, Sb, Bi of 20 ppm or more,
Therefore, the impact value remains at 1.9 kg-m / cm ² .

Comparative Example No. 12 has a total content of Al and Ti is 20 ppm or more, and Comparative Example No. 13 has a total content of Cr, Mn, V is 100 ppm or more, both are 2 kg-m / cm Only the impact value of ² units can be obtained.

Comparative Examples Nos. 14, 15 and 16 have a large content of Si or C which is a generation source of the liquid phase hardly-absorbent gas, and therefore the porosity is poor even if the impact value is high.

As described above, according to the present invention, the tungsten 90
~ 98wt%, the balance is made up of nickel and iron in the range of 0.5-4 by weight ratio, and 0.5w cobalt if necessary.
In the tungsten sintered alloy containing t%, the allowable content of a specific impurity component was regulated. As a result, it is possible to provide a tungsten sintered alloy having a significantly improved toughness and porosity on an industrial scale.

Claims (3)

[Claims] 1. Tungsten 90 to 98 wt%, impurity content P ≦ 8 ppm, As + Sb + Bi ≦ 20 ppm, Al + Ti ≦ 20 ppm, Cr + Mn + V ≦ 100 ppm, Si ≦ 20 ppm, C ≦ 100 ppm, balance nickel (Ni) and iron (Fe) ) And a weight ratio of nickel and iron is Ni / Fe = 0.5 to 4, a high toughness tungsten sintered alloy. 2. Tungsten 90 to 98 wt%, Nb 10 to 100 ppm, impurity content P ≦ 8 ppm, As + Sb + Bi ≦ 20 ppm, Al + Ti ≦ 20 ppm, Cr + Mn + V ≦ 100 ppm, Si ≦ 50 ppm, C ≦ 200 ppm, balance nickel ( Ni) and iron (Fe), and the weight ratio of the nickel and iron is Ni / Fe = 0.5 to 4, a high toughness tungsten sintered alloy. 3. A high toughness tungsten sintered alloy according to claim 1 or 2, wherein the high toughness tungsten sintered alloy contains 0.5 wt% or less of cobalt (Co).