JPS60218461A - Sliding member having excellent wear resistance at high temperature and its production - Google Patents

Abstract

PURPOSE:To produce inexpensively a sliding member having excellent resistance to wear, heat and corrosion at a high temp. by molding and sintering the powder of an austenitic stainless steel then heating and nitriding the powder in an atmosphere contg. gaseous NH3. CONSTITUTION:The powder of an austenitic stainless steel contg. 15-30% Cr, 10-25% Ni, 0.2-0.7% N, <5% Mo and <2% unavoidable impurities is compacted and molded to a prescribed shape. After the green compact thereof is sintered in a reducing or inert gaseous atmosphere, the green compact is subjected to a nitriding treatment for 30-120min at 700-1,000 deg.C in a neutral or inert gaseous atmosphere contg. 10-50vol% gaseous NH3. The material which is uniformly dispersed with hard Cr2N particles having 1-10mu size in the austenite matrix and is suitable for a sliding member such as bushing or the like of a waste gate valve to be used for a supercharger of an automobile requiring the resistance to wear at a high temp. is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a sliding member with excellent high-temperature wear resistance. The sliding member of the present invention is suitable as a sliding member that slides under severe conditions such as high temperatures and no or insufficient supply of lubricating oil. The sliding member of the present invention is suitable, for example, for a bushing that supports the shaft of a waste gate valve of a supercharger used in an internal combustion engine of an automobile, and a bearing used for a heat treatment furnace.

To explain the waste gate valve further, it is a member that prevents the supercharging pressure from exceeding a set pressure. That is, this wastegate valve is closed when the engine speed is low, but opens when the engine speed is high, and by opening, the exhaust gas flowing into the turbine is bypassed to the turbine outlet, thereby controlling the turbine output. , which controls the boost pressure.

The bushing supporting the waste gate valve is 8
They slide at high temperatures of 00 to 900°C, and the high temperatures make it impossible or difficult to use lubricating oil, making them prone to wear.

Furthermore, since the bushings come into contact with the high temperature exhaust gas, the degree of oxidation corrosion is quite severe.

[Prior Art] As the performance of sliding members used in internal combustion engines has improved in recent years, the sliding conditions have become even more severe. Therefore, various research and development efforts have been made to further improve wear resistance, heat resistance, and corrosion resistance. ing. For example, a metal powder made by blending hard particles with a grain size of about 10 to 100 with austenitic stainless steel powder has been developed, and a metal powder made by molding and sintering the metal powder has been developed. Although this product has improved high-temperature abrasion resistance and burning resistance because hard particles are dispersed therein, the cost is high because it contains special hard particles. Furthermore, the bonding force between the hard particles and the matrix was not so strong, and there was a risk that the hard particles would fall off during sliding.

On the other hand, if the sliding member is made of a stainless steel material that does not contain hard particles, the increase in cost can be suppressed, but the high-temperature wear resistance and the burning resistance are inferior.

[Object of the Invention] The present invention has been accomplished against the background of the above-mentioned prior art. Therefore, the object of the present invention is to achieve high temperatures, particularly from 800°C to 90°C.
The object of the present invention is to provide a sliding member that has good wear resistance, heat resistance, and corrosion resistance in the 0° C. range, and is also inexpensive.

[Summary of the Invention] The sliding member of the present invention is a sliding member in which at least a part of the surface is a sliding surface, and the sliding member has chromium 15 to 30.
mf&%, nickel 10-25! IIm%, nitrogen 0.2
It is composed of a sintered body consisting of ~0.7% by weight, 0.5% by weight or less of molybdenum, 2% by weight or less of unavoidable impurities, and the balance iron, and has a structure in which chromium nitride is dispersed in an austenite matrix. It is characterized by having

Further, the manufacturing method of the present invention includes a first step of molding and sintering austenitic stainless steel powder to form a sintered body, and a step of forming the sintered body in a gas nitriding atmosphere at a temperature of 700 to 100%.
The second step is to nitride the sintered body by heating it at 0° C. for 30 to 120 minutes to form a nitride in the matrix.

[Detailed Description of the Structure of the Invention] The sliding member of the present invention refers to a member that moves while in contact with a mating member. In this case, the surface constitutes a sliding surface. In this case, the entire surface may be a sliding surface, or only a portion of the surface may be a sliding surface.

A typical sliding member is a bushing that supports the shaft of a wastegate valve.

The structure of the sliding member of the present invention is that fine chromium nitrides are dispersed in an austenite matrix. Since the sliding member has austenite as a matrix, it has excellent heat resistance and corrosion resistance. The grain size of austenite is 50
It is preferable to have a thickness in the range of ~150μ. The reason is that it is convenient for improving strength, creep resistance, and corrosion resistance.

The fine chromium nitride typically has a size of 1 to 10 microns. It is presumed that the chromium nitride is CrzN.

The density ratio of the sintered body related to the sliding material of the present invention is generally 8
It is 5-90%. In addition, the surface hardness is generally about 40OHV i in terms of Vickers hardness of load No. 1ka.

The composition of the base material of the sliding member of the present invention is 15 to 30% by weight of chromium, 10 to 25% by weight of nickel, and 5% by weight of molybdenum.
Below, unavoidable impurities are 2% by weight or less, and the balance is iron. The reason for having the above composition is as follows.

That is, chromium is dissolved in the austenite matrix to improve the heat resistance and oxidation resistance of the matrix. However, in the present invention, since Cr2N is precipitated, the chromium concentration in the matrix is correspondingly lowered. Therefore, the chromium content is 1511! If the amount is less than 30% by weight, the solid solution effect in the matrix will be extremely low (on the other hand, if it exceeds 30% by weight, the improvement in the effect will reach a plateau).

Nickel forms a solid solution in the austenite matrix, promotes austenitization, and improves heat resistance and corrosion resistance. However, if it is less than 10%, austenitization is insufficient, and if it exceeds 25%, no further improvement in the effect can be expected.

Molybdenum is dissolved in the austenite matrix and improves heat resistance and oxidation resistance. However, if it exceeds 5%, the matrix becomes extremely brittle.

As the gas nitriding atmosphere, an atmosphere in which 10 to 5 Qvo 1% of N1]3 gas is added to a neutral or reducing gas is generally used. N1-13 decomposes at high temperatures, generates nascent N, forms a chromium nitride layer, and contributes to wear resistance. However, the effect is low below 10vo1%, and 50vo1
%, no increase in effectiveness can be expected and costs will increase. Nitride can also be formed by high temperature treatment in a neutral or reducing atmosphere containing nitrogen. In this case, if the nitrogen content is less than 20 VO 1%, the effect will be small.

It is desirable to have fewer impurities. Unavoidable impurities include c1s+, Mn% pss, and the like. Carbon is
Generally, it is preferably 0.2% by weight or less.

Now, a typical method for manufacturing the sliding part agent of the present invention (1)
) to (4) will be explained.

(1) First, austenitic stainless steel powder is compression molded into a predetermined shape to form a green compact. A typical austenitic stainless steel powder is JIS-8US3.
16m powder can be used. This J IS-8U
The composition of S316L powder is chromium 16.00-18.
00%, nickel 12%~15.00%, molybdenum 2
．． 00-3.00%, Carbon 0.030% or less, Silicon 1.00% or less, Manganese 2.00% or less, Phosphorus 0.0
45% or less, and sulfur 0.030% or less. The average particle size of the stainless steel powder is preferably in the range of 50 to 100 microns. As a compression means when forming a powder compact, ordinary means can be used. For example, a mechanical press, a hydraulic press, etc. can be selected as needed. Molding pressure is 5-8t
It is preferable to do this at onf/cm2.

(2) After producing the green compact as described above, the green compact is sintered. The atmosphere during sintering is selected from various atmospheres such as hydrogen gas, reducing gas such as ammonia decomposition gas, inert gas such as argon gas, and vacuum. Sintering is 115
This is preferably carried out by heating at 0 to 1250°C for 30 to 60 minutes. When manufactured in this manner, the matrix of the sliding member can be made of austenite with good corrosion resistance.

(3) Heating the sintered body produced as above at 700 to 1000'C for a predetermined time in a gas nitriding atmosphere,
This causes nitrogen to diffuse into the interior of the sintered body, thereby performing nitriding. The reason for setting the temperature to 700 to 1000℃ is that
At temperatures below 10°C, N decomposed from the atmosphere diffuses into the metal structure and is insufficient to form sufficient nitrides.
This is because if the temperature exceeds 00°C, a brittle and thick nitrided layer is formed on the surface, which reduces the sliding wear resistance, which is not preferable. The heating time is preferably about 60 minutes. As a special example of nitriding treatment, urea or the like can be used.

[Effects of the Invention] The sliding member of the present invention has the structure as described above. As shown in the test example described below, the sliding member with such a structure
It has good wear resistance, heat resistance, and corrosion resistance at high temperatures, particularly from 800 to 900°C. Therefore, it is suitable for sliding members used in internal combustion engines of automobiles, where sliding conditions have become more severe in recent years as performance has improved. In particular, when the present invention is applied to a bushing for a waste gate valve, the amount of wear caused by the sliding motion of the bushing is significantly reduced as shown in the test examples described below.

Furthermore, the problem of adhesion to the mating material can be almost eliminated or reduced. The reason for this is presumed to be that the fine chromium nitrides described above are dispersed in the ausbunite matrix.

According to the manufacturing method of the present invention, the above-mentioned excellent properties can also be obtained.
A sliding member can be manufactured.

[Test Example] (Preparation of sample of the product of the present invention) Stainless steel powder with an average particle size of 50 to 100μ was heated to a pressure of 6
tonf/am2, outer diameter 12IIIl11 inner diameter 61
1III11 After forming a bearing-shaped compact with a height of 26 m and m, sintering was performed at 1200° C. for 60 minutes in a reducing atmosphere. After that, A in a gas nitriding atmosphere,
BIC at 800℃ for 60 minutes, D at 1000℃ for 60 minutes.
The sample was prepared by heating for 0 minutes.

Sample ASB obtained in this way, (composition of D,
Table 1 shows the density ratio and surface hardness.

(Testing Samples of the Present Invention) Samples A, B, and C1D formed through the steps described above were tested. The test was conducted under the following conditions (1) to (8), and the changes in the inner diameter of the sample, amount, adhesion status, sliding marks, etc. were measured.

(1) The sliding material is a wastegate valve bottle of a supercharging device used in an automobile internal combustion engine. This bottle was fitted into a bearing-shaped sample.

The material of the bottle is ausbunite stainless steel.

(2) The swing angle mark of the bottle, which is the mating material, is about ±306.

(3) The rocking speed is 60 times/min.

(4) The atmosphere during rocking is exhaust gas at about 700 to 900°C discharged from an internal combustion engine.

(Fuel: unleaded gasoline) (5) The housing of the supercharger is Ni-Resist
Made from cast iron.

(6) A repeated temperature cycle of 900° C. and room temperature was used as the test temperature.

(7) The test time is 100 hours. - (Test results of samples of products of the present invention) The test results are shown in Table 2. In both cases, an oxide film is formed on the sample surface, and the inner diameter is smaller in the 1 method. Especially sample A
, B had an inner diameter dimension change of 5μ. Also sample ASB,
C: There was little or no synonymy between D and the other material. Furthermore, materials A, B, C, and I) all had very few sliding marks. Also, samples A, B, 'C,
Both D have excellent oxidation resistance, and self-judgment (Excellent...A)
, moderate...B1 poor...C) and was palanque.

(Preparation of Sample of Comparative Example) Sample E of Comparative Example was prepared from a sintered alloy of Table 1 and Table 2 of austenitic stainless steel powder, which has been conventionally used as a sliding member that slides at high temperatures.

Here, the composition of sample E is J15-8M51 species.

(Tests and test results of samples of comparative examples) Tests of samples of comparative examples were conducted under the same conditions as the samples of the products of the present invention. The test results for the comparative samples are shown in Table 2.

The growth of the oxide film on the surface was large, and peeling and falling off were observed in some parts, and as shown in Table 2, the inner diameter dimensional change was as large as 150μ, which was approximately 30 times that of samples Δ and B, which are products of the present invention. The change was Φ.

Patent applicant: Toyota Motor Corporation Tokyo Sintered Metal Co., Ltd. Agent: Patent Attorney Hiroshi Okawa Patent attorney Osamu Fujitani Same patent attorney Akio Maruyama

Claims (7)

[Claims] (1) In a sliding member in which a small part of the surface is a sliding surface, the sliding member is made of chromium 15-30!11 m 1t%, nickel 10-25% by weight, nitrogen 0.2-0.7 type. It is characterized by a sintered body consisting of 5% by weight or less of molybdenum, 2% by weight or less of unavoidable impurities, and the balance iron, and has a structure in which 1comb nitride is dispersed in an austenite matrix. A sliding member with excellent high-temperature wear resistance. (2) A sliding member with excellent high-temperature wear resistance according to claim 1, wherein the chromium nitride has a size of 1 to 10 μm. (3) A sliding member with excellent high-temperature wear resistance according to claim 1, wherein the chromium nitride is CrtN. (4) The sliding member having excellent 1181i temperature wear resistance as described in claim 1 is a bushing of a waste gate valve used in a supercharging device of an automobile. (5) A first step of molding and sintering the austenitic stainless steel powder to form a sintered body, and heating the sintered body in a gas nitriding atmosphere at 700 to 1000°C for 30 to 120 degrees Celsius.
A method for manufacturing a sliding member having excellent high-temperature wear resistance, comprising a second step of heating the sintered body for 1 minute to nitride the sintered body to form a nitride in the matrix. (6) The method for producing a sliding member with excellent high-temperature wear resistance according to claim 5, wherein an atmosphere in which 10 to 5 Qvol of NH3 gas is added to a neutral or reducing gas is used as the gas nitriding atmosphere. (7) The method for manufacturing a sliding member with excellent high-temperature wear resistance as set forth in claim 5, wherein the gas nitriding atmosphere contains nitrogen at 20 VO 1% or more.