JPH0772331B2 - Sintered alloy with excellent high temperature wear resistance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sintered alloy having good oxidation resistance and seizure resistance at high temperatures, and therefore good high temperature wear resistance. The sintered alloy of the present invention is suitable as a sliding member that slides under high temperature and severe conditions. Typical sliding members in which the sintered alloy of the present invention is used include, for example, bearings used in heat treatment furnaces and bushes that support shafts of waste gate valves of superchargers used in internal combustion engines of automobiles.

The waste gate valve is a member that prevents the boost pressure from exceeding the set pressure. That is, this wastegate valve is closed when the engine speed is low, but is opened when the engine speed is high, and this opening bypasses the turbine inflow exhaust gas to the turbine outlet to control the turbine output. Therefore, it controls the supercharging pressure. The above exhaust gas is about 700
Since the temperature is as high as ℃ to 900 ℃, the turbine described above is considerably deteriorated, and thus sliding failure with the waste gate valve is likely to occur.

(Prior Art) Conventionally, sliding members that slide under high temperature and severe conditions are made of austenitic niresist cast iron or the like. However, a sliding member that slides under high temperature and severe conditions may not always be sufficient.

For example, in a waste gate valve used in a supercharger used in an internal combustion engine, further high temperature wear resistance and seizure resistance are required.

In addition, with the recent advances in performance of superchargers, the operating conditions have become even more severe.Therefore, the housing material has been changed from austenitic niresist cast iron to ferritic heat resistant cast iron in consideration of the improvement of heat crack resistance. It's starting. In a conventionally used wastegate valve bush, the wastegate valve bush is loosened due to a difference in thermal expansion between the wastegate valve bush and the ferrite-based housing.

(Problems to be Solved by the Invention) The present invention has been made against the background of the above-described conventional art. Therefore, the object of the present invention, in the high temperature range of 300 ℃ ~ 900 ℃, wear resistance, oxidation resistance, good seizure resistance,
It is to provide a sintered alloy having a small difference in thermal expansion even when the mating material is a ferritic material.

(Means for Solving the Problems) The sintered alloy of the present invention contains 10 to 18% by weight of chromium,
Molybdenum 0.5 to 6%, cobalt 0.4 to 7%, silicon 0.
04-1.8%, carbon 0.3% or less, unavoidable impurities 2% or less,
With the composition of the balance iron, the matrix is mainly composed of ferrite or martensite formed of stainless steel powder of ferritic or martensitic, the matrix has cobalt-based hard particles dispersed, The hard particles include cobalt, and an intermetallic compound composed of two or more kinds of molybdenum, silicon, and chromium, and, including cobalt, one or more kinds of molybdenum, silicon, chromium, and iron, and carbon. It is characterized by comprising at least one kind of the composite carbide of.

The matrix of the sintered alloy of the present invention is mainly composed of ferrite or martensite. Therefore, the sintered alloy of the present invention is excellent in heat resistance and oxidation resistance.

Hard particles are dispersed in the matrix. The cross-sectional shape of hard particles is generally round, and its size is usually 10-100.
Can be μ. The hard particles described above are composed of an intermetallic compound or a composite carbide (hereinafter, also referred to as double carbide). Here, the intermetallic compound contains cobalt and is composed of two or more of molybdenum, silicon, and chromium. The composite carbide contains cobalt and one or more of molybdenum, silicon, chromium, and iron, and carbon.

A typical intermetallic compound here is Co ₃ Mo ₂ Si. this
Co ₃ Mo ₂ Si has a hardness of HV 700 to 1100, which improves the wear resistance of the sintered alloy and also has a low attack on the mating material.

In the above-mentioned typical composite carbide, M ₆ C generally has a hardness of HV1100 to 1500 and improves the wear resistance of the sintered alloy. Here, M of M ₆ C includes cobalt, and means two or more of molybdenum, silicon, chromium, and iron.

The area ratio occupied by the hard particles in the tissue is 0.2 to 20.
% Is desirable. The reason is that if it is 0.2% or less, the hard particles are too small to contribute to the improvement of high temperature wear resistance, and if it is 20% or more, the cost tends to be high and the attacking property of the mating material tends to be high. The area ratio is more preferably 0.5 to 4%.

It is desirable that the above hard particles are uniformly dispersed in the matrix.

The sintered alloy according to the present invention is a cobalt-bonded powder that becomes hard particles, a graphite powder (added when hard particles of a composite carbide type are intended, but hard particles of hard particles of an intermetallic compound type are intended. Is basically not added to), and can be composed of a mixed powder containing a stainless steel powder serving as a matrix. Hereinafter, it will be described together with a preferable blending ratio.

(Cobalt-based alloy powder) Cobalt-based alloy powder is necessary to prevent sliding and sticking that tends to occur with the mating material, and if it is less than 2%, its effect is insufficient and the mating with the mating material is insufficient. Image sticking occurs. on the other hand
If it exceeds 10%, the oxidation resistance is deteriorated, the oxidative expansion of the sintered alloy itself may occur, and the tolerance with the mating material may be lost, resulting in a lock state.
Is appropriate.

In the case of 0% graphite, the cobalt alloy powder is, for example,
As an intermetallic compound having a structure of Co ₃ Mo ₂ Si, and in the case of adding graphite, M ₆ C type double carbide is generated, which contributes to improvement of wear resistance and seizure resistance.

As the composition of the cobalt-based alloy powder, Co is used as a base material, and it is possible to dilute it with one or both of Ni and Fe for the purpose of reducing the raw material cost. The total amount of Ni and Fe is 8
% Or less is desirable.

Mo and Si in the cobalt alloy powder are essential elements, and Cr is added when wear resistance is insufficient. If the Mo content is less than 25% and the Si content is less than 2%, the above effects are reduced.
If it exceeds 10% or Cr20%, the hardness of the cobalt-based alloy powder will not increase, so the density of the green compact will not increase sufficiently, and as a result, not only the oxidation resistance will decrease, but also the mold will be scratched during molding. It is not practical because it shortens the life of the die.

(Graphite powder) Graphite does not need to be added under use conditions that are not so severe, and is added when a sintered alloy is used under thermally severe conditions. This forms a double carbide with Co, Mo, Cr, etc. present in the cobalt-based alloy powder. When multiple carbides are formed, the hardness of the sintered alloy is improved to HV1100 to 1500 (HV700 to 1100 without addition of graphite powder), which not only improves wear resistance, but also causes multiple carbides to form in the matrix. Diffuses and strengthens the matrix. However, since addition of graphite lowers the oxidation resistance and forms retained austenite in part, addition of more than 0.3% will rather reduce the performance of the sintered alloy.

(Stainless Steel Powder) As the stainless steel powder, a stainless steel powder containing 11 to 18% by weight of chromium, 0 to 2% of molybdenum, and 0.03% or less of carbon can be adopted. If the chromium content is less than 11%, the oxidation resistance is insufficient, and if it exceeds 18%, the hardness of the stainless steel powder is high and the compressibility is reduced. Molybdenum is optionally added to the stainless steel powder. Molybdenum strengthens the matrix. However, if the molybdenum contained in the stainless steel powder exceeds 2%, the compressibility decreases. Carbon contained in stainless steel is preferably 0.03% or less from the viewpoint of ensuring compressibility. JIS-SUS41 is a typical stainless steel powder.
0L powder can be used. The average particle size of the above-mentioned stainless steel powder is preferably 50 to 100 μm. The reason is,
This is because if the average particle size of the stainless steel powder is 50 μm or less, the compressibility and moldability when forming a green compact are reduced, and if it is 100 μm or more, the sinterability is reduced.

(Matrix) When a mating material, such as a sintered alloy, is used for the wastegate burb bush, the housing as the mating material has insufficient heat-cracking resistance in conventional Ni-resist cast iron under severe heat load conditions. Therefore, in recent years, it is shifting to ferritic heat-resistant cast steel. Therefore, if the matrix of the sintered alloy is austenite type, thermal yielding occurs due to the difference in thermal expansion from the ferrite type housing, causing a problem. For example, when a sintered alloy is used for the waste gate valve bush, the press-fitting margin between the bush and the shaft is lost. Therefore, in order to alleviate the difference in thermal expansion, the matrix of the sintered alloy is mainly composed of ferrite or martensite.

(Manufacturing Method) The sintered alloy of the present invention can be formed as follows. The mixed powder obtained by mixing the alloy powder, the graphite powder, and the stainless steel powder as described above is compressed into a predetermined shape to form a green compact, and then the green compact is sintered. For the compression, a usual means such as molding with a die, or a means such as a rubber press can be used. The molding pressure is preferably 5 to 8 ton / cm ² . It is desirable that the green compact has a uniform density. The density of the green compact is preferably 6.0 to 6.8 g / cm ³ .

The reason for setting the above density value is as follows. That is, when the density is less than 6.0 g / cm ³ , the oxidation of the sintered alloy through the pores remarkably progresses, and the strength decreases. On the other hand, 6.
Molding exceeding 8 g / cm ³ is not practical because the mold life is shortened. Sintering of the green compact is preferably performed in a reducing atmosphere or vacuum. The reason for this is that, in an atmosphere other than this, the oxidation progresses along the grain boundaries of the stainless steel powder due to the atmosphere, resulting in a decrease in strength. Sintering is usually at 1150 to 1250 ℃, for example 30 to 60
Heat for 1 minute. If the temperature is lower than 1150 ° C, the sintering signal is insufficient, and if it exceeds 1250 ° C, the deformation is large and it is not practical. If the sintering time is less than 30 minutes, the sintering signal is insufficient, and if the sintering time exceeds 60 minutes, the progress of sintering is almost saturated. Therefore, the sintering time is preferably 30 minutes to 60 minutes.

By the way, the composition of the sintered alloy of the present invention has a weight ratio of chromium 10
.About.18%, molybdenum 0.5 to 6%, cobalt 0.4 to 7%, silicon 0.04 to 1.8%, carbon 0.3% or less and unavoidable impurities 2% or less, and the balance iron.

[Effects of the Invention] The sintered alloy of the present invention has the structure as described above. The sintered alloy having such a constitution has good oxidation resistance and seizure resistance at high temperatures. Therefore, it has excellent high temperature wear resistance. Furthermore,
Even when the mating material is a ferrite material, the problem of loosening due to the difference in thermal expansion can be improved.

In the sintered alloy of the present invention, the matrix is formed with a ferrite system, which is a metal layer having a carbon content lower than that of the austenite system, and a martensite system, and the carbon content is 0.3%.
Since it is kept low, it is advantageous for keeping the carbon amount in the matrix low, and therefore advantageous for ensuring the oxidation resistance of the matrix.

Therefore, when the sintered alloy of the present invention is applied to a sliding member that is slid under high temperature at high temperature, particularly to a bush of a wastegate valve used in a supercharger of an internal combustion engine of an automobile, the durability is remarkably improved. And the wear resistance of the sliding surface is reduced.

[Test Example] (Preparation of Sample of Present Invention) JIS-SUS410L (Fe-12% Cr) powder (average particle size 50 to 100 μm) was prepared as the stainless steel powder, and the cobalt alloy powder was 28% Mo in weight ratio. -8% Cr-2% Si cobalt-based alloy powder (average particle size 70 to 100 µm) was prepared.

Next, the above-mentioned stainless steel powder is mixed with cobalt-based alloy powder 5
%, And zinc stearate as a mold lubricant was added at an external weight of 1%. Then, add each of the above powders to a V-type mixer.
Mixed for minutes to obtain a mixed powder. And mixed powder 6ton
A green compact (density 6.2 g / cm ³ ) is molded with a molding pressure of f / cm ² , and the green compact is heated in a reducing atmosphere (hydrogen gas) at 1200 ° C.
Sintering was performed by heating for 45 minutes. Then, the sintered body was machined and used as a sample. The shape of the sample is cylindrical, and its size is 13 mm in outer diameter, 8 mm in inner diameter, and 26 m in total length.
m.

Samples were formed under the manufacturing conditions shown in Table 1 for Examples 2 to 4 by the same manufacturing method. In addition, in Example 4, the cobalt-based alloy powder used in Example 1 was used.

(Test of Samples of the Present Invention) Tests of the samples according to Examples 1 to 4 as described above at high temperature are performed under the following conditions (1) to (7), and the inner diameter dimension shrinkage of the cylindrical sample is performed. The measurement was performed by measuring the amount, the baking state, and the fastening state.

(1) Tests were carried out on a high temperature sliding tester simulating the supercharger shown in FIG. Sample 1 press-fitted into housing 2 40-60 μm
Pressed in. The shaft material 3 inserted in the hole of the sample 1 is JIS SUS304 steel material (tolerance gap 20 to 4 with the sample 1).
5 μm).

(2) The swing angle of the shaft material 3 is ± 20 °.

(3) The rocking speed of the shaft member 3 is 30 times / minute.

(4) Test temperature 800 ℃ (heated by heater 4 and thermocouple 5
(Measurement with) (5) Housing 2 is made of ferritic heat-resistant cast steel (Fe-7Cr
-3Si-1.3C).

(6) The test time is 100 hours.

(Test Results of Samples of the Present Invention) Table 2 shows the test results of Examples 1 to 4. The sample inner diameter dimension shrinkage amount according to Examples 1 to 4 is
It was about 13 to 25 μ. This is because the oxidation resistance is good.

As shown in Table 2, there were almost no seizure scratches between the samples according to Examples 1 to 4 and the shaft material 3 as the mating material. Also, no looseness occurred in the fastening state between the housing 2 and the sample 1. Sample 1 according to Examples 1 to 4
This is because the difference in thermal expansion between the housing and the housing 2 is small.

(Comparative Example) Samples were formed also in Comparative Examples 1 to 5. The manufacturing conditions of the samples of Comparative Examples 1 to 5 are shown in Table 1. The sample of Comparative Example 5 is JIS SUS made of ingot material.
It was made of 410L steel.

The sample of the comparative example was tested under the same conditions as the sample of the present invention. The test results of the sample of the comparative example, It is shown in Table 2. The contraction amount is 20μ in Comparative Example 1 and Comparative Example 2
However, in Comparative Example 3, 48 μ and in Comparative Example 4,
It was as large as 27μ.

In addition, in the sample of Comparative Example 5, seizure occurred with the shaft material 3. Further, in Comparative Examples 3 and 4, looseness occurred between the housing 2 and the sample 1.

The cobalt-based alloy powder compounded at the time of production is hard particles of cobalt-based, but as can be understood from Table 1, the cobalt-based alloy powder of Comparative Example 1 contains Co, but Mo, Si , Cr, only Mo is not contained, and graphite, which is an element for forming a composite carbon material, is not mixed, so that the wear resistance and seizure resistance are not sufficient, and thus the alloy of the present invention is not included.
In Comparative Example 2, Mo is too low as 0.3% as shown in Table 2, wear resistance and seizure resistance are not sufficient, and it is not included in the alloy of the present invention. In Comparative Example 3, as shown in Table 2, Co is too large at 9.3% and C is too large at 0.5%, so that it is not included in the alloy of the present invention. In Comparative Example 4, as can be understood from Table 1, the stainless steel powder forming the matrix of the sintered alloy is austenitic and is not included in the alloy of the present invention.

As described above, the product of the present invention exhibits extremely stable high-temperature oxidation resistance and seizure resistance as compared with the comparative example, and as a result, is excellent in high-temperature wear resistance.

[Brief description of drawings]

 FIG. 1 is a schematic diagram showing a test state.

Claims (5)

[Claims] 1. By weight ratio, chromium 10 to 18%, molybdenum 0.5 to 6%, cobalt 0.4 to 7%, silicon 0.04 to 1.8.
%, Carbon 0.3% or less, unavoidable irregularity 2% or less, the balance iron has a composition, and the matrix is formed of ferritic or martensitic stainless steel powder and is mainly composed of ferrite or martensite. , And has cobalt-based hard particles dispersed therein, the hard particles containing cobalt and an intermetallic compound of two or more of molybdenum, silicon and chromium, and molybdenum and cobalt. , Silicon, chrome,
A sintered alloy having excellent high-temperature wear resistance, comprising at least one kind of a composite carbide of carbon and one or more kinds of iron. 2. A sintered alloy having excellent high-temperature wear resistance according to claim 1, wherein the intermetallic compound is Co ₃ Mo ₂ Si. 3. The composite carbide is excellent in high-temperature wear resistance according to claim 1, wherein the composite carbide is M ₆ C (M contains cobalt and is two or more of molybdenum, silicon, chromium and iron). Sintered alloy. 4. The matrix is formed by sintering ferritic or martensitic stainless steel powder, and the composition of the stainless steel powder is chromium 11 to 11% by weight.
The sintered alloy having excellent high-temperature wear resistance according to claim 1, which has 18%, molybdenum 2% or less, and carbon 0.03% or less. 5. A sintered alloy having excellent high-temperature wear resistance according to claim 1, which is used for a bush of a waste gate valve used in a supercharger of an automobile.