JP2001011561A - Oxidation resistant tungsten alloy and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an alloy having superior oxidation resistance, heat resistance, and arc resistance and excellent in mass productivity and workability by providing a composition containing Cr in a specific weight percentage, at least one kind among iron group metals in a specific range of weight percentage, and W in a specific weight percentage or above and also regulating the density to a specific percentage of theoretical density. SOLUTION: The oxidation resistant tungsten alloy has a composition containing, by weight, 30-60% Cr, 0.5-3% of at least one kind among iron group metals, and >=37% W and has a density of >=85% of theoretical density. Preferred amount of iron group metals is 0.5-<1%, and it is also preferable to incorporate <=3% Ni and/or <=2% Fe among the iron group metals or to incorporate 0.1-2% Co among the iron group metals. Moreover, it is also preferable to incorporate >40-50% Cr. Further, it is also preferable to incorporate <=5% Mo and is also desirable to incorporate <=5% of either or both of Si and Al.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to oxidation resistance, heat resistance,
The present invention relates to an oxidation-resistant tungsten alloy having excellent arc resistance, that is, resistance to wear caused by an arc, and particularly useful for various electrodes for welding and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Generally, tungsten alloys have been used for various electrodes for welding and the like because of their excellent heat resistance and arc resistance. However, the oxidation resistance is insufficient, and a method for further improving the oxidation resistance has been sought. For example,
(1) "Powder and Powder Metallurgy" Vol. 16, No. 3, No. 145
On page 149 and in the same book, Vol. 17, No. 1, pages 13-18,
A method is disclosed in which Pd is mixed with W and Cr powders as a sintering accelerator, and after stamping, a tungsten alloy having excellent oxidation resistance is obtained by vacuum sintering or pressure sintering.

[0003] (2) Japanese Patent Publication No. 53-41087 discloses that Ni, Fe, M
High temperature tungsten alloys containing o and other additives are disclosed.

Further, (3) JP-B-54-33212, JP-A-51-136521, and JP-B-55-44-1.
No. 0653 discloses that W is not more than 26% by weight and 30% by weight.
An oxidation resistant heat resistant alloy containing less than Cr is disclosed.

Also, (4) Japanese Patent Application Laid-Open No. 61-26748 discloses an electrode material made of a tungsten alloy containing 15 to 40% by weight of Cr and the balance being W.

[0006]

However, the tungsten-chromium alloy described in the above (1) has considerably excellent oxidation resistance, but is not solid phase sintered at a temperature lower than the liquid phase appearance temperature. Therefore, the sintering density is low and organizational defects are likely to occur. Moreover, this alloy has poor ductility,
Due to the difficulty of cutting, its use has been limited.

Further, the tungsten alloy described in the above (2) has a small Cr content, so that the amount of increase in oxidation by heating in an oxidizing atmosphere is large, and the oxidation resistance is considerably insufficient. . For example, in some cases 1000
As a welding electrode material used at a high temperature exceeding ℃, a tungsten alloy having such a composition cannot be put to practical use.

Further, in the oxidation-resistant heat-resistant alloy described in the above (3), since the amount of W is small, the melting temperature is 1900 ° C.
, And the heat resistance was insufficient. Also, the amount of Cr is 3
Since it was less than 0% by weight, the oxidation resistance was insufficient, and it could not be used as a welding electrode material used at high temperatures as described above.

The electrode material described in (4) discloses that the oxidation resistance at 800 to 1200 ° C. is remarkably improved, but the sintering temperature is 1300 to 14
Sintering density of 50% of theoretical density
Or as low as 80%. For this reason, there are many systematic defects, and there is a drawback that oxidation easily proceeds to the inside of the alloy. As a result, the electrode material for welding used at a high temperature as described above still has a problem in oxidation resistance.

[0010] The present invention has been made in view of such circumstances, and an object of the present invention is to provide an alloy which overcomes the drawbacks of the prior art and is excellent in mass productivity and workability.

[0011]

In order to achieve the above object, the present inventors have studied various compositions and sintering conditions of a tungsten alloy. As a result, they have reached the invention.

That is, according to the present invention, Cr is contained in an amount of 30% by weight or more and 60% by weight or less, and
The present invention provides an oxidation-resistant tungsten alloy characterized by containing not less than 3% by weight and not more than 3% by weight, and not less than 37% by weight of W, and having a density of not less than 85% of a theoretical density.
However, the alloy of the present invention may contain, in addition to the above components, unavoidable impurities that are mixed in from the raw materials and the production process thereof.

In the present invention, the basic composition described above,
o in an amount of 5% by weight or less.
Also included are those containing at least one of i and Al at 5% by weight or less.

The present invention also includes those having a carbon content of 1% by weight or less, especially 0.1% by weight or less.

The present invention also includes an electrode member for welding or the like using the above oxidation-resistant tungsten alloy.

The method for producing an oxidation-resistant tungsten alloy according to the present invention is characterized in that the Cr powder contains 30% by weight or more and 60% by weight or less, and at least one iron group metal powder contains 0.5% by weight or more and 3% by weight or less; A mixed powder containing 37 wt% or more of W powder is prepared and sintered in a non-oxidizing atmosphere at 1600 ° C. to 2700 ° C.

Further, in the above-mentioned production method, 5% by weight of Mo is used.
The present invention also includes a method of mixing and sintering, and a method of mixing and sintering at least one powder of Si and Al at 5% by weight or less.

Further, this sintering is carried out at a carbon monoxide partial pressure of 15%.
The method includes a method performed in a non-oxidizing atmosphere of 0 Pa or less, particularly 15 Pa or less.

[0019]

According to the present invention, in order to obtain heat resistance, W is the main component and its content is 37%.
% By weight or more. If a part of this W is small, it can be replaced by Mo having a high melting point and having a similar characteristic to W. However, if the Mo content exceeds 5% by weight of the whole alloy, the heat resistance may decrease due to a decrease in the melting temperature. Therefore, it is desirable that the Mo content is not more than this amount.

Next, in order to improve the oxidation resistance, and to reduce the amount of oxidation increase in an oxidizing atmosphere at a high temperature, particularly at an oxidizing atmosphere of 1000 ° C. or more, the tungsten alloy of the present invention contains
The content of r is 30% by weight or more, and more preferably, exceeds 40% by weight. On the other hand, the upper limit of Cr is set to 60% by weight. If Cr exceeds 60% by weight, in combination with W, the melting temperature is lowered and the heat resistance is lowered, and the hardness is increased, brittleness is liable to occur, and the workability of the alloy itself is lowered, which is not preferable. Preferably 50% by weight
It is as follows.

Further, in the present invention, N having a lower melting point than W is used.
i (melting point: 1,460 ° C.) and / or Fe (melting point: 1,
535 ° C.) to form a liquid phase with W at a relatively low temperature, thereby performing liquid phase sintering. In this way, the liquid phase of these components can be spread evenly between the particles, so that the densification by sintering is remarkably promoted. This also precipitates alloyed W during cooling and solidification, and promotes solid solution between W and Cr. By the above effects, a high-quality alloy having excellent oxidation resistance is obtained, and its density is 85% or more of the theoretical density.

Further, the tungsten alloy of the present invention has arc resistance (resistance to wear to an arc) in addition to the above-mentioned oxidation resistance.

Further, Co (melting point: 1,495 ° C.)
Addition of less than 10% by weight further improves oxidation resistance. However, 2
If the content exceeds 10% by weight, the oxidation resistance may be reduced rather than the composition without the additive. Since Ni, Fe and Co are easily dissolved in W, the sinterability can be easily increased if the total amount of these components is 0.5% by weight or more. However, if the content exceeds 3% by weight, oxidation resistance and heat resistance may be reduced, though no remarkable improvement in workability by cutting is observed. In order to maintain oxidation resistance and heat resistance, the content is more preferably less than 1% by weight.

By adding at least one of Si and Al up to 5% by weight to the above basic composition, an oxide film which is stable even at high temperatures and has good adhesion is formed, and the oxidation resistance is improved. . However, when the content exceeds 5% by weight, the alloy is easily embrittled, and the workability at the time of cutting tends to be reduced.

As described above, since the alloy of the present invention has excellent oxidation resistance and arc resistance at high temperatures, it can be sufficiently used as a high-temperature welding electrode whose use temperature exceeds, for example, 1000 ° C. is there.

To sinter the alloy of the present invention, the alloy is sintered at a temperature of 1600 ° C. to 2700 ° C. in a non-oxidizing atmosphere, for example, in a vacuum or in an atmosphere containing a gas such as hydrogen. The reason why the temperature is set to 1600 ° C. or higher is to make a sufficient liquid phase appear to promote sintering. Also 2700
The reason why the temperature is set to not more than ° C. is to prevent oxidation and carburization, which deteriorate the alloy properties, because the tungsten alloy of the present invention is easily affected by the atmosphere during sintering.

When sintering in a hydrogen atmosphere, the dew point of the hydrogen used is desirably -22 ° C. or less in order to prevent oxidation of the Cr powder during the heating.

Further, since the tungsten alloy of the present invention is a material which is easily carburized during sintering, when a carbon monoxide gas is generated during sintering, the partial pressure of the gas should be 150 Pascal or less. Desirably, it is more preferably 15 Pascal or less. Above 150 Pascal, carburization proceeds easily, the carbon content may exceed 1% by weight, and carbides are easily formed. When carbides are formed, the alloy hardens and may become brittle. For example, the amount of carbon in the tungsten alloy is reduced to 0.1% by weight by carburization.
When the content exceeds 1, the hardness may gradually increase, and when it exceeds 1% by weight, the Rockwell C scale hardness may exceed 65 in some cases. In such a case, since sufficient ductility cannot be obtained, cutting may be difficult even if a tool made of cubic boron nitride having a high processing speed is used. Also,
Because of embrittlement, cracks and breakage are liable to occur not only during processing into an electrode shape or the like, but also during handling after sintering. If the carbon monoxide partial pressure in the atmosphere is 15 Pascal or less, the carbon content is 0.1% by weight or less, and there is no problem in production.

In the manufacturing method of the present invention, it is also possible to obtain a member by performing a net shape forming by a press in advance in consideration of a shrinkage ratio due to sintering, and thereafter sintering. In this case, post-processing such as cutting or grinding after sintering is not required, and the processing can be completed by simple processing such as barrel or blast.

Hereinafter, embodiments of the present invention will be described.

EXAMPLE W powder having an average particle size of 3.1 μm each,
2.8 μm Mo powder, 2.5 μm Cr powder, 3.6
A predetermined amount of Ni powder of 5.5 μm, Fe powder of 5.5 μm, Co powder of 1.4 μm, Si powder of 4.1 μm, and Al powder of 22 μm was mixed, and acetone was used as a solvent with an attritor for 8 hours. After wet mixing, the mixture was wet-sieved at 325 mesh and dried. As a binder for press,
1.5 wt% camphor was added and mixed, and the mixture was sieved with a 150-mesh dry sieve to obtain a raw material powder. This raw material powder was press-molded and held for 2 hours under each of the sintering conditions shown in Tables 1 to 3 to produce an alloy. The density ratios shown in Tables 1 to 3 are expressed in percentage by dividing the measured density of the obtained alloy by the theoretical density of the composition. In the oxidation test in the atmosphere, the test piece was placed in a high-purity alumina boat,
The heating was performed in a resistance heating type muffle furnace. Dimension is width 3
mm, a length of 7 mm, and a thickness of 3 mm. Each test piece was produced by cutting an alloy obtained by sintering.
The temperature was raised to 1000 ° C. in the atmosphere, and the temperature was kept at 1000 ° C. for 5 hours. The weight increased by the oxidation was confirmed, and this was divided by the total surface area of the test piece to calculate the oxidation weight increase. Tables 1 to 3 show the increase in oxidation as a measure of oxidation resistance.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

Sample Nos. 1, 12, 13, 18, 30, 3
2 is a comparative example and the others are examples. In the table, W in the alloy composition also contains unavoidable impurities mixed in from the raw materials and the manufacturing process.

As can be seen from the data in Tables 1 to 3, the tungsten alloy of the present invention has excellent oxidation resistance,
It was found that if the oxidation weight gain at 5 ° C. for 5 hours was 3.0 mg / cm ² or less, it could be used as a welding electrode used at a sufficiently high temperature.

A high-frequency TIG welding test and an arc start test were performed using the tungsten alloy of the present invention as a welding electrode. As a result, arc stability and wear resistance due to arc resistance (arc resistance) compared to pure W electrode material
In this respect, good performance was exhibited.

Although the embodiments of the oxidation-resistant tungsten alloy of the present invention have been described above, the present invention is not limited to the above embodiments. Also,
Specific mixing method as exemplified for the production method,
Not limited to the mixing conditions, it can be manufactured by any other method.

[0038]

According to the present invention, the alloy of the present invention has good oxidation resistance, heat resistance and arc resistance, and can be used stably for various electrodes, particularly for welding.

Claims (16)

[Claims] (1) Cr is contained in an amount of 30% by weight or more and 60% by weight or less,
0.5% by weight or more and 3% by weight of at least one iron group metal
Or less, and containing 37% by weight or more of W and having a theoretical density of 8
An oxidation-resistant tungsten alloy characterized by being at least 5%. 2. The oxidation-resistant tungsten alloy according to claim 1, wherein the amount of the iron group metal is 0.5% by weight or more and less than 1% by weight. 3. The oxidation-resistant tungsten alloy according to claim 1, wherein the iron-containing metal contains 3% by weight or less of Ni and / or 2% by weight or less of Fe. 4. The oxidation-resistant tungsten alloy according to claim 1, wherein the iron-containing metal contains 0.1% by weight or more and 2% by weight or less of Co. 5. The oxidation-resistant tungsten alloy according to claim 1, which contains more than 40% by weight and not more than 50% by weight of Cr. 6. The oxidation-resistant tungsten alloy according to claim 1, which contains 5% by weight or less of Mo. 7. At least one of Si and Al is 5% by weight.
The oxidation-resistant tungsten alloy according to any one of claims 1 to 6, further comprising: 8. The oxidation-resistant tungsten alloy according to claim 1, wherein the carbon content is 1% by weight or less. 9. The oxidation-resistant tungsten alloy according to claim 8, wherein the carbon content is 0.1% by weight or less. 10. The oxidation-resistant tungsten alloy according to claim 1, wherein the hardness is 65 or less in Rockwell C scale hardness. 11. An electrode member comprising the oxidation-resistant tungsten alloy according to claim 1. 12. Cr powder in an amount of 30% by weight to 60% by weight.
Hereinafter, at least one powder of the iron group metal is added in an amount of 0.5% by weight.
A method for preparing an oxidation-resistant tungsten alloy, comprising preparing a mixed powder containing at least 3 wt% and not more than 37 wt% of W powder and sintering in a non-oxidizing atmosphere at 1600 ° C. to 2700 ° C. . 13. The method for producing an oxidation-resistant tungsten alloy according to claim 12, wherein 5% by weight or less of Mo powder is mixed. 14. The method for producing an oxidation-resistant tungsten alloy according to claim 12, wherein 5% by weight or less of at least one powder of Si and Al is mixed. 15. The method for producing an oxidation-resistant tungsten alloy according to claim 12, wherein the sintering is performed in a non-oxidizing atmosphere having a carbon monoxide partial pressure of 150 Pascal or less. 16. Sintering is performed in a non-oxidizing atmosphere having a carbon monoxide partial pressure of 15 Pascal or less.
6. The method for producing an oxidation-resistant tungsten alloy according to 5.