WO2015098407A1

WO2015098407A1 - Machine component using powder compact and method for producing same

Info

Publication number: WO2015098407A1
Application number: PCT/JP2014/081250
Authority: WO
Inventors: 尚樹八代; 哲隆加古; 大平　晃也
Original assignee: Ntn株式会社; 尚樹八代; 哲隆加古; 大平　晃也
Priority date: 2013-12-26
Filing date: 2014-11-26
Publication date: 2015-07-02

Abstract

According to the present invention, a machine component having a radial crushing strength of more than 100 MPa is produced by: obtaining a powder compact by press molding a starting material powder which is mainly composed of a metal powder that is capable of forming an oxide film; and then forming an oxide film between particles of the metal powder that constitutes the powder compact by means of a water vapor treatment.

Description

Machine part using green compact and method for manufacturing the same

The present invention relates to a machine part using a green compact and a manufacturing method thereof. More specifically, the present invention relates to a mechanical part in which a green compact obtained by forming metal powder with a uniaxial working press or the like is made strong without sintering, and a method for manufacturing the same.

Conventionally, in the field of powder metallurgy, it has been common to mix raw material powders including metal powders and compact them, then sinter them in a furnace at a high temperature exceeding 800 ° C. . Hereinafter, a metal powder that has been molded is referred to as a green compact, and is further distinguished from a sintered body that has undergone a sintering process (see JIS Z 2500: 2000).

According to JIS Z 2500: 2000, powder metallurgy is a metallurgy technology department that manufactures metal powder or products from metal powder by forming and sintering processes, and is a technology different from casting and forging. In general, a product is manufactured by the following process.
(1) Mixing of raw material metal, lubricant, graphite powder, etc. (2) Compacting with pressure press etc. (3) Sintering below melting point (4) Correction (sizing)
(5) Post-processing such as heat treatment and oil impregnation (if necessary)

In particular, the sintering process (3) is generally performed in a high temperature range of 800 ° C. or more in the case of an iron-based material, and its cost accounts for 1/4 to 1/2 of the entire manufacturing cost. . Furthermore, since the green compact expands and contracts through a high temperature sintering process, the correction process (4) is indispensable in order to achieve the target dimensions or accuracy.

Through the sintering process, fusion between metal particles, necking occurs, and the strength is improved, but if sufficient strength is ensured by processing at a lower temperature, not only the production cost can be reduced, A change in dimensions can be suppressed, and the correction process can be omitted.

Conventionally, as a method for increasing the strength of a green compact other than sintering, the following studies have been made.

Patent Document 1 describes a method for strengthening a green compact in powder metallurgy. That is, after compression molding a metal powder with metal soap added as a molding lubricant, the green compact is heated to a temperature not lower than the melting point of the metal soap and not higher than the dewaxing temperature. It will increase significantly. The mechanism is presumed that the metal soap in the pores contained in the green compact melts by heat treatment, forms a continuous layer and solidifies, and the density of this layer increases the strength of the green compact. (See Claims of Patent Document 1, column 2, lines 10 to 12, column 3, lines 22 to 25).

Patent Document 2 describes that an iron-based “sintered” part is manufactured by bonding by a steam blackening process without sintering a green compact. The mechanism is that the whole surface of the green compact is covered with an oxide film by steam blackening treatment, and the surface particles are bonded and solidified to form an object having a predetermined strength as a whole ( (Second page, lower left column, lines 8 to 11 of Patent Document 2).

Japanese Examined Patent Publication No. 61-011282 Japanese Unexamined Patent Publication No. Sho 63-072803 Japanese Unexamined Patent Publication No. 04-198403

The purpose of the technique described in Patent Document 1 is to prevent chipping and cracking during conveyance of a green compact from a molding press or the like to a sintering furnace, and as such, it does not have strength as a product. . Therefore, of course, it does not suggest omission of the sintering process. After all, if you do not go through the sintering process at a high temperature after that, not only can you ensure enough strength to use as a product, but it is a pre-sintering process, so it will increase by 1 process compared to ordinary sintered products. On the other hand, it becomes a factor of cost increase.

The technique described in Patent Document 2 is that the green compact is subjected to steam blackening, particles are bonded to each other by an oxide film, and corrosion resistance is imparted. However, although it has “a certain level of strength and durability” (7th to 8th lines in the upper right column of the second page), it is not completely known how much strength can actually be obtained. In short, “there are some parts that are not required to be strong enough for the use of magnetic material parts, and it is intended to provide such parts that are easy to manufacture and inexpensive” (second page, upper left column, lines 10 to 12). Is. It is limited to applications where high strength is not required, such as soft magnetic material parts listed as specific examples. In fact, the material and density of the green compact that are considered to be important for increasing the strength of the green compact In addition, details such as steam treatment conditions are not disclosed.

The present invention provides a mechanical part having the same strength as a sintered product manufactured by the conventional technology at a lower cost by adopting another lower temperature treatment instead of this sintering process. It is something to be done.

Here, if the crushing strength according to JIS Z 2507 “Sintered bearing-crushing strength test method” is 100 MPa or more, it shall have the strength to withstand the use as a machine part. Also, according to JIS Z 2500 “powder and (metallurgical) terminology”, dimensional change is defined as an increase or decrease in green compact size caused by sintering. It shall mean the increase or decrease of the resulting green compact size.

As means for achieving such an object, the present inventors paid attention to steam treatment. In general, the steam treatment is also called homo-treatment, and the iron-based sintered material (after sintering) is reacted with steam while being heated to about 500 to 560 ° C in an oxidizing atmosphere, and the surface is mainly tetraoxidized. A film of triiron (Fe ₃ O ₄ ) is generated. The film thickness is said to be about 3-7 μm. Although there are few application examples to general steel materials, steam treatment has been widely used for a long time as an inexpensive surface treatment for sintered metals. The main treatment purposes are rust prevention, improvement of wear resistance, and sealing, and in addition, it is also effective for improvement of surface hardness and machinability (for example, see Patent Document 3). .

The present invention clarifies a method for obtaining a high-strength green compact by optimizing the material and density of the green compact, the steam treatment conditions, and the like. Here, high strength is a level that can withstand use as mechanical element parts such as sintered oil-impregnated bearings, rather than improving the chipping resistance of green compacts and the strength of soft magnetic material parts. Specifically, the crushing strength is 100 MPa or more.

In the conventional sintered body, the raw material powder is compacted by uniaxial pressing or the like, and then heated to a high temperature below the melting point (800 to 1,300 ° C. in the case of iron-based materials), thereby fusing particles ( Necking) is formed to increase the strength. In contrast, according to the present invention, an oxide film is formed on the surface of iron powder by reacting a green compact having a specific density with high-temperature water vapor at 400 to 550 ° C. in an oxidizing atmosphere. The oxide is mainly triiron tetroxide (Fe ₃ O ₄ ) when iron-based powder is used as the raw material powder. The oxide film formed between the particles of the raw material powder substitutes for the role of necking between the powder particles, and as a result, the green compact is strengthened.

Since the treatment temperature is lower than that in the normal sintering process, the dimensional change is small (± 0.1% or less before and after treatment). Therefore, it is possible to omit the sizing process that has been necessary for correcting the dimensions after sintering. In addition, the product and the mold for compacting can be easily designed. In addition, since the processing temperature is low, energy (electrical or thermal) required during processing can be reduced, processing steps can be reduced, and the manufacturing process and cost of the product can be shortened.

Since the steam treatment is an atmosphere treatment, it can be applied regardless of the shape and size of the product to be molded. In addition, the present invention is applicable as long as it is a material capable of forming an oxide film. Therefore, it is considered that the present invention is applicable not only to iron-based materials but also to metal materials having a large ionization tendency such as aluminum, magnesium, and chromium. In addition, although the atomizing method, the reduction method, the stamp method, the carbonyl method, etc. are known regarding the manufacturing method of raw material powder, this invention is applicable irrespective of the manufacturing method of raw material powder.

Furthermore, although uniaxial pressure molding was mentioned as a representative example of the green compacting method, it is applicable if a metal base material capable of forming an oxide film is exposed. Specifically, multi-axis CNC press molding, injection molding (MIM), and additional cold isostatic pressing (CIP) molding, etc. are possible. The molding method is not limited.

Generally, a lubricant powder such as metal soap or amide wax is mixed in the green compact to ensure lubrication between the powder to be molded, the mold and the powder, and the lubricant powder remains in the green compact. In the conventional method, it is decomposed because it is kept at a high temperature in the subsequent sintering process, and is not included in the sintered product. However, when the present invention is applied, the lubricant component may remain depending on the density, processing temperature, and holding time of the green compact. Therefore, it is desirable to take a technique in which a degreasing process for decomposing and removing the lubricant component is provided in advance prior to the steaming process, and the steaming process is continuously performed after the degreasing process. However, it has been confirmed that high strength can be achieved even if steam treatment is performed while a lubricant is contained without providing a degreasing step.

Usually, in a sintered part, the higher the density, the higher the strength. On the other hand, if the density of the green compact is too high, water vapor cannot penetrate into the green compact, and the formation of the oxide film is limited to the very surface layer of the green compact. However, if the powder density is too low, chipping and cracking may occur during handling (large rattra value), and there is a concern that the interparticle distance is too long to form an oxide film between the particles. For these reasons, the green density is 5.0 to 7.6 g / cm ³ , preferably 5.3 to 7.2 g / cm ³ , more preferably 6.0 g / cm ³ or more and less than 7.0 g / cm ^3. It is better to be in the range. The green density is based on the dimension measurement method.

Since the above machine parts are covered with an iron oxide film, their surface hardness is higher and the wear resistance is superior compared to a sintered body obtained by subjecting a green compact of the same composition to normal sintering. Yes. Further, according to the verification by the present inventors, when the above-mentioned mechanical part is a part that slides against the counterpart material through oil (for example, a sliding bearing, a gear, a cam, etc. used in an oil-lubricated environment), it is sintered. It has been found that it has better initial acclimation characteristics than the body. The reason for this is not clear, but as shown in FIG. 1, the surface of the above-described mechanical component (a green compact according to Example 8 to be described later) has an empty space on the order of several tens of μm remaining between the iron powders 11. In addition to the holes 12, micropores 14 on the order of several tens of nm are formed inside the iron oxide film 13 having a thickness of about several μm. Therefore, the oil impregnated in the micropores 14 is initially This may have contributed to the familiar characteristics.

According to this invention, the following effects can be obtained.

Bonding between particles (oxide film) by applying high-temperature water vapor to the green compact in an oxidizing atmosphere in a temperature range much lower than the sintering process (eg 400 to 550 ° C in the case of iron) ) To increase the strength. The high strength mentioned here specifically means a crushing strength of 100 MPa or more. If the crushing strength is 100 MPa or more, the strength is sufficiently high as compared with the prior art (Patent Documents 1 and 2), and the strength is practical enough for mechanical parts. For example, it is possible to provide a machine element part that can replace the conventional sintered oil-impregnated bearing.

Also, since the processing temperature is low, the dimensional change is small compared to sintering at high temperature. Therefore, the subsequent correction (sizing) step can be omitted. For the same reason, the manufacturing process is shortened and the cost can be reduced. For example, the dimensional change before and after the steam treatment is suppressed to less than ± 0.1% with respect to the green compact. Therefore, it becomes easy to design a product and a mold for compacting.

Furthermore, it is applicable regardless of the shape and size of the green compact. Since it is covered with an oxide film after the steam treatment, the rust prevention treatment becomes unnecessary. Depending on the processing temperature, an additive that denatures and decomposes at a temperature exceeding 500 ° C., for example, a material having slidability and lubricity, can be added to enhance the functionality of the product.

It is a photograph (SEM image) of a section of an example of the present invention. It is the figure which showed FIG. 1A typically. It is a front view of a friction and abrasion tester. It is a side view of a friction abrasion tester. It is a graph which shows the convergence value of the friction coefficient in a friction abrasion test (with external oil supply). It is a graph which shows transition of the friction coefficient in a friction wear test (with external oil supply). It is a graph which shows the specific wear amount in a friction wear test (with external oil supply). It is a graph which shows the convergence value of the friction coefficient in a friction abrasion test (without external oil supply). It is a graph which shows transition of the friction coefficient in a friction wear test (without external oil supply). It is a graph which shows the specific wear amount in a friction wear test (without external oil supply).

Hereinafter, embodiments of the present invention will be described using specific examples.

Tests of Examples 1 to 13 and Comparative Examples 1 to 10 using reduced iron powder as the base metal powder, electrolytic copper powder as the second metal component, and amide wax powder lubricant as the compacting lubricant Pieces were made and various tests were performed. The test piece is ring-shaped and the dimensions are as follows.
Inner diameter: φ12mm
Outer diameter: φ20mm
Length: 7mm

Examples 1 to 5
Electrolytic copper powder is 2 wt. %, Lubricant is 0.7 wt. Is added to the mold made of alloy tool steel SKD11, and uniaxial press molding is performed at various molding pressures, so that five cylindrical powder compacts having different green density (g / cm ³ ) are obtained. Got the body. Thereafter, the lubricant component contained in the green compact was degreased at 350 ° C. for 90 minutes and then steamed at 500 ° C. for 40 minutes to obtain Examples 1 to 5. The green density (g / cm ³ ) of Examples 1 to 5 was as follows.
Example 1: 5.3
Example 2: 6.0
Example 3: 6.5
Example 4: 7.0
Example 5: 7.2

Examples 6-9
In order to confirm the influence of the difference in the treatment temperature of the steam treatment, a green compact corresponding to Example ^{3 and having} a green compact density of 6.5 g / cm ³ was degreased at 350 ° C. for 90 minutes in the same manner as in Examples 1 to 5. Then, Examples 6 to 9 were obtained by steaming for 40 minutes at the following four treatment temperatures.
Example 6: 350 ° C.
Example 7: 400 ° C
Example 8: 450 ° C
Example 9: 550 ° C

Examples 10 and 11
In order to confirm the effect of the difference in the treatment time of the steam treatment, two samples with different treatment times were prepared. That is, Example 3 equivalent, the green compact green density 6.5 g / cm ^3, after having degreased for 90 minutes in a likewise 350 ° C. Examples 1 to 5, in 500 ° C., only the next time steam Examples 10 and 11 were obtained by processing.
Example 10: 20 minutes Example 11: 80 minutes

Examples 12 and 13
In order to confirm the effect of material differences, two samples with different materials were prepared. That is, as in Example 3, each powder was uniaxially pressed to a compact density of 6.5 g / cm ³ , degreased at 350 ° C. for 90 minutes as in Examples 1 to 5, and then 500 Steam treatment was carried out at 40 ° C. for 40 minutes. The composition of the powder used in each example is as follows.
Example 12: Only reduced iron powder (Cu 0%) was mixed with 0.7 wt. Example 13: Electrolytic copper powder was 20 wt. %, Lubricant is 0.7 wt. % Added powder

Comparative Examples 1-5
Comparative examples 1 to 5 were obtained by omitting the degreasing step at 350 ° C. for 90 minutes and the subsequent steam treatment step in Examples 1 to 5, that is, in a state where the powder was compacted.

Comparative Examples 6 and 7
Comparative examples 6 and 7 were obtained by omitting the degreasing process at 350 ° C. for 90 minutes and the subsequent water vapor treatment process in Examples 12 and 13, that is, in a state where the powder was compacted.

Comparative Examples 8-10
Comparative Examples 8 to 10 were obtained by sintering three types of green compacts of Fe only, Fe + 2% Cu and Fe + 20% Cu described in Comparative Examples 6, 3, and 7 at 1100 ° C. for 30 minutes.
Comparative Example 8: Fe only (sintered Comparative Example 6)
Comparative Example 9: Fe + 2% Cu (Sintered Comparative Example 3)
Comparative Example 10: Fe + 20% Cu (sintered Comparative Example 7)

Evaluation Method The mechanical properties of the obtained test piece were evaluated based on the results of the measurement of the crushing strength performed in accordance with JIS Z 2507. The test apparatus used is Autograph AG-5000A manufactured by Shimadzu Corporation. The crushing strength refers to the strength of a cylindrical sintered body or green compact determined by a certain method from the crushing load, and the crushing load refers to a cylindrical sintered body or green compact that is parallel to the axis. This is the load when cracks begin to occur due to compression on the surface.

Table 1 shows the criteria for determining the crushing strength. That is, as shown in the left column of the same table, the crushing strength (unit: MPa) is divided into four stages of less than 50, 50 or more, less than 100, 100 or more, less than 150, or 150 or more. , ◎.

In addition, using an image size measuring device (manufactured by Keyence Corporation, IM-6000), the inner diameter and outer diameter of the test piece were measured before and after the steam treatment, and before and after the treatment with respect to the dimensions before the treatment. The percentage of change was calculated and used as the dimensional change rate. For the determination of the dimensional change rate, the larger numerical value of the inner diameter and the outer diameter was adopted.

Table 2 shows the criteria for the rate of dimensional change. That is, as shown in the left column of the table, the dimensional change rate (unit:%) is divided into three stages of ± 0.1 or more, less than ± 0.1, and less than ± 0.05, and the symbols Δ and ○ , ◎.

Next, evaluation results will be described.
(I) About the green density In order to confirm the influence of the green density on the crushing strength and the dimensional change rate, for the 2% Cu—Fe green compacts of Examples 1 to 5 having different green density, Steam treatment was carried out at 500 ° C. for 40 minutes. Table 3 shows the determination results of the crushing strength and the dimensional change rate in this case.

In Examples 1 to 5, the crushing strength is improved by the steam treatment. Specifically, except that Example 1 having a green density of 5.3 g / cm ³ is less than 100 MPa, the crushing strength is 100 MPa in Examples 2 to 5 having a green density of 6.0 g / cm ³ or more. That's it. However, Example 4 of the green density 7.0 g / cm ^3, also 7.2 g / cm ³ in Example 5, the dimensional change ratio was slightly worse. Moreover, the crushing strength of Example 5 is inferior to that of Example 4 having a green density of 7.0 g / cm ³ . From this, it can be seen that the higher the green density is not necessarily better.

In light of the test results, the green density is 5.0 to 7.6 g / cm ³ , preferably 5.3 to 7.2 g / cm ³ , more preferably 6.0 g / cm ³ or more and less than 7.0 g / cm ^3. It is better to be in the range. In particular, Examples 2 and green density is in the range of less than 6.0 g / cm ³ or more 7.0 g / cm ³ 3 is, with regard radial crushing strength, with respect to dimensional change, suffice as machine parts is there.

In each of Comparative Examples 1 to 5 in which the steam treatment was not performed, the crushing strength was less than 50 MPa. In Comparative Examples 1 to 5, neither steam treatment nor sintering was performed, so the dimensional change rate was not measured. Since Comparative Example 9 having a green compact density of 6.5 g / cm ³ was sintered at 1100 ° C. × 30 min, the crushing strength was 150 MPa or more, but the dimensional change rate was ± 0.1% or more. Met.

(B) Treatment temperature In order to confirm the effect of the treatment temperature of the steam treatment on the crushing strength and the dimensional change rate, the treatment temperature was set for a 2% Cu—Fe compact with a compact density of 6.5 g / cm ^3. Instead, steam treatment was carried out for 40 minutes each. Table 4 shows the determination results of the crushing strength and the dimensional change rate in this case.

Regarding the crushing strength, the processing temperature was 350 MPa in Example 6, 400 ° C in Example 7, 550 ° C in Example 9 and 550 ° C in Example 9 at 100 MPa or more, and the processing temperature at 450 ° C in Example 8 and the processing temperature at 500 ° C. In Example 3, it was 150 MPa or more. The maximum dimensional change rate was less than ± 0.1% in all Examples, and was less than ± 0.05% in Examples 3, 8, 7, and 6 in which the processing temperature was 500 ° C. or less. In Example 6 at a treatment temperature of 350 ° C., some red rust (Fe ₂ O ₃ ) was generated, and it was not possible to form only the originally intended Fe ₃ O ₄ film. In Examples 7, 8, 3, and 9 where the treatment temperature was higher than that of Example 6, no red rust was observed.

In light of the test results, the treatment temperature of the water vapor treatment is 400 ° C. or higher, preferably 400 ° C. or higher and 550 ° C. or lower, more preferably 450 ° C. or higher and 500 ° C. or lower. Regarding the processing temperature, if the test results of Example 3 at 500 ° C. and Example 9 at 550 ° C. are compared, it can be seen that the higher the processing temperature, the better. In particular, it has been found that the crushing strength and the dimensional change rate are suitable at a processing temperature lower than 500 to 560 ° C., which is a general processing temperature of conventional steam processing.

(C) Treatment time In order to confirm the effect of the treatment time of the steam treatment on the crushing strength and the dimensional change rate, it was measured at 500 ° C. with respect to a 2% Cu—Fe compact with a compact density of 6.5 g / cm ^3. The water vapor treatment was carried out by changing the treatment time. Table 5 shows the determination results of the crushing strength and the dimensional change rate in this case.

As can be seen from Table 5, each of Examples 10, 3, and 11 had a crushing strength of 150 MPa or more and a dimensional change rate of less than ± 0.1%. In light of this result, it is considered that a sufficient effect can be obtained if the water vapor treatment time is 20 minutes or longer.

In Comparative Example 3, the crushing strength was less than 50 MPa, but the dimensional change rate was not measured because neither steam treatment nor sintering was performed. In Comparative Example 9, the crushing strength was 150 MPa or more, but the dimensional change rate was ± 0.1% or more.

(D) Difference in material In order to confirm the effect of the material on the crushing strength and the dimensional change rate, the powder density is obtained by using a powder in which different percentages of electrolytic copper powder are added to the reduced iron powder as the base material. A green compact of 6.5 g / cm ³ was molded and subjected to steam treatment at 500 ° C. for 40 minutes. Table 6 shows the determination results of the crushing strength and the dimensional change rate of each test piece in this case.

The ratio of electrolytic copper powder to reduced iron powder was 0 wt. %, Example 3 was 2 wt. %, Example 13 was 20 wt. The crushing strength was 100 MPa or more in all cases. In these investigated compositions, the iron ratio was 80 wt. It can be seen that the crushing strength of 100 MPa or more is achieved even when the amount is reduced to%, and the dimensional change rate is less than ± 0.1% in any composition.

In the case of Comparative Examples 8, 9, and 10 sintered at 1100 ° C., the dimensional change rate is ± 0.1% or more, so that it is understood that the dimensional change is smaller when only the steam treatment is performed. In Comparative Examples 6, 3, and 7, the crushing strength was less than 50 MPa, but the dimensional change rate was not measured because neither steam treatment nor sintering was performed.

Next, the following tests were conducted in order to evaluate the friction and wear characteristics of the examples of the present invention.

Two types of test pieces, the above-mentioned Example 2 in which the green compact was subjected to the steam treatment and the Comparative Example 11 in which the green compact of the comparative example 2 not subjected to the steam treatment was subjected to sintering treatment at 1100 ° C. × 30 min. Was made. The number of test pieces was three each. These test pieces were immersed in a lubricating oil (hydraulic hydraulic oil, Shell Terrace S2M68, ISO viscosity VG68 equivalent) and vacuum impregnated at 70 ° C. for 1 hour or more.

The friction and wear test was performed using a testing machine shown in FIG. This testing machine includes an arm 22 that can swing around a rotating shaft 21, a mating member 24 that is provided below the arm 22, and that is fixed to the rotating shaft 23, and a felt that slides on the outer peripheral surface of the mating member 24. And a pad 25. The test piece W is attached to the lower surface of the arm 22. The mating member 24 has an outer diameter of 40 mm, an outer diameter surface sub-curvature R of 60 mm, a surface roughness of 0.01 μm Ra or less, and a Vickers hardness of 780 HV or more, and is made of, for example, SUJ2 hardened steel. The felt pad 25 is impregnated with the same lubricating oil as the lubricating oil impregnated in the test piece W. A predetermined weight 26 is attached to the arm 22, and the test piece W is pressed against the mating member 24 from above with a predetermined load. Under a maximum contact surface pressure of Hertz of 0.5 GPa and room temperature (25 ° C.), 0 The mating member 24 was rotated for 30 minutes at a rotational speed of .05 m / s. At this time, the frictional force generated between the test piece W and the mating member 24 was detected by the load cell 27 provided on the arm 22. Further, after the rotation, the specific wear amount was calculated from the size of the indentation formed on the test piece W.

From the following three items obtained in the above test, the friction and wear characteristics of Example 2 (steam-treated product) and Comparative Example 11 (sintered product) were evaluated.
-Convergence value of friction coefficient-Initial running-in characteristic-Specific wear amount In this test, the "convergence value of friction coefficient" means the average value of the friction coefficient for 10 minutes at the end of the test. In addition, the initial running-in characteristic refers to the transition of the friction coefficient at the initial stage of the test.

The result of the convergence value of the friction coefficient is shown in FIG. As shown in the figure, the convergence value of the friction coefficient of Example 2 is substantially equal to the convergence value of the friction coefficient of Comparative Example 11.

Fig. 4 shows the results of changes in the friction coefficient. As shown in the figure, the transition of the friction coefficient was different between Example 2 and Comparative Example 11. Specifically, Comparative Example 11 showed a high coefficient of friction exceeding 0.2 at the beginning of the test and then decreased to about 0.15 in about 1 minute, but 5 to 5 until the final level was reached. It took about 10 minutes. On the other hand, Example 2 showed a low coefficient of friction from the beginning of the test, and the coefficient of friction decreased to a level equivalent to that at the end of the test within 0 or several seconds. From this, it can be said that Example 2 which is a steam-treated product has an initial familiarity characteristic superior to Comparative Example 11 which is a sintered product.

The result of the specific wear amount is shown in FIG. As shown in the figure, the specific wear amount of Comparative Example 11 was 400 to 800 × 10 ⁻¹⁰ mm ³ / (N · m), whereas Example 2 was 50 to 250 × 10 ^{− It was 10} mm ³ / (N · m). Thus, the specific wear amount of Example 2 was 1/2 or less of the specific wear amount of Comparative Example 11. From this, it can be said that Example 2 which is a steam-treated product has better wear resistance than Comparative Example 11 which is a sintered product.

From the above results, Example 2 which is a steam-treated product has a convergence value of the friction coefficient equivalent to that of Comparative Example 11 which is a sintered product, and is more excellent in initial familiarity characteristics than Comparative Example 11 which is a sintered product. In addition, it was confirmed to have wear resistance.

Next, a frictional wear test similar to that described above was performed with the felt pad 25 shown in FIG. 2 removed and without external lubrication. The test time was 5 minutes. Further, the “convergence value of the friction coefficient” in this test was the friction coefficient at the end of the test.

Fig. 6 shows the result of the convergence of the friction coefficient in the friction and wear test without external lubrication. As shown in the figure, the convergence value of the friction coefficient of Example 2 is substantially equal to the convergence value of the friction coefficient of Comparative Example 11.

Fig. 7 shows the results of changes in the friction coefficient in the friction and wear test without external lubrication. As shown in the figure, Comparative Example 11 showed a high friction coefficient exceeding 0.15 at the beginning of the test, and decreased to a level equivalent to the convergence value over about 1 minute. On the other hand, Example 2 shows a low coefficient of friction that is substantially equivalent from the beginning to the end of the test. From this, it can be said that Example 2 which is a steam-treated product has an initial familiarity characteristic superior to Comparative Example 11 which is a sintered product.

The result of the specific wear amount in the friction wear test without external oil supply is shown in FIG. As shown in the figure, the specific wear amount of Comparative Example 11 was 3000 to 7000 × 10 ⁻¹⁰ mm ³ / (N · m), whereas Example 2 was 1600 to 2500 × 10 ^{− It was 10} mm ³ / (N · m). Thus, the specific wear amount of Example 2 was 1/2 or less of the specific wear amount of Comparative Example 11. From this, it can be said that Example 2 which is a steam-treated product has better wear resistance than Comparative Example 11 which is a sintered product.

From the above results, even when there is no external lubrication, as in the case of external lubrication, Example 2 which is a steam-treated product has a convergent value of the friction coefficient equivalent to that of Comparative Example 11 which is a sintered product. In addition, it was confirmed that the material had better initial conformability and wear resistance than Comparative Example 11 which was a sintered product.

Although the embodiments of the present invention have been described with specific examples, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the claims. Is possible.

Since the mechanical component of the present invention has a crushing strength exceeding 100 MPa, it can be used as a substitute for a conventional sintered metal component. Specific examples of sintered metal parts include sliding parts and magnetic iron cores. Examples of the sliding parts include those that slide with a mating member via lubricating oil, such as bearings, gears, cams, and the like that are used in an oil-lubricated environment. Examples of the bearing include a sliding bearing that slides and supports a mating member (shaft) through oil, specifically, a sintered oil-impregnated bearing and a fluid dynamic pressure bearing. In addition, the mechanical component of the present invention is not limited to the replacement of a sintered machine component for high-load use, but can of course be replaced with a sintered metal component for a lighter load application.

Claims

A green compact obtained by pressure-molding a raw material powder mainly composed of a metal powder capable of forming an oxide film, wherein the oxide film is formed between the particles of the metal powder, and has a crushing strength exceeding 100 MPa. Machine parts.
The machine part according to claim 1, wherein the green compact has a green density in a range of 5.0 to 7.6 g / cm 3 by a dimensional measurement method.
The machine part according to claim 1 or 2, wherein the oxide film is formed by steam treatment.
The machine part according to claim 3, wherein a treatment temperature of the steam treatment is 400 ° C or higher and 550 ° C or lower.
The machine part according to any one of claims 1 to 4, further comprising a sliding surface that slides against a mating member through a lubricating oil.
A raw material powder made mainly of a metal powder capable of forming an oxide film is pressed to obtain a green compact, and an oxide film is formed between particles of the metal powder constituting the green compact by steam treatment. A method for producing a machine part having a crushing strength exceeding 100 MPa, comprising forming.
The method for manufacturing a machine part according to claim 6, wherein the green compact has a green density in a range of 5.0 to 7.6 g / cm 3 by a dimensional measurement method.
The method for manufacturing a machine part according to claim 6 or 7, wherein the steam treatment is performed after degreasing the powder lubricant component added for molding contained in the green compact.
The method for manufacturing a machine part according to any one of claims 6 to 8, wherein a treatment temperature of the steam treatment is 400 ° C or higher and 550 ° C or lower. *