JP5385039B2 - Powder for shot peening imparting slidability and surface compressive residual stress at the same time, and method for producing slidable member using the same - Google Patents

Description

  The present invention relates to a powder for shot peening that simultaneously imparts slidability and surface compressive residual stress, and a method for producing a slidable member formed by shot peening the powder.

  Generally, in the soft metal phase, sliding parts are often lubricated using liquid lubricants such as oil. However, liquid lubricants cannot be used for design reasons or are used in vacuum. If there is a restriction in the environment of use, such as being used, a solid lubricant is used. In recent years, as the social demand for energy problems increases, further reduction of friction of sliding members used in automobile engines and transmissions has been demanded.

  Therefore, in order to reduce the frictional resistance of the liquid lubricant used in the sliding part, a material having low viscosity tends to be used, and the thickness of the lubricant in the sliding part becomes thin, and the sliding members come into contact with each other. As the number of bearings used in possible boundary lubrication environments is increasing, it is necessary to develop members with high slidability and long stripping life even in boundary lubrication environments. The sliding part is covered.

  As a method of coating the sliding member with the solid lubricant, for example, as disclosed in JP 2002-161371 A (Patent Document 1) and JP 2007-10059 A (Patent Document 2), zinc, tin, etc. A film forming technique for shot peening a mixed powder of a soft metal powder and a solid lubricant powder such as molybdenum disulfide, or a soft metal powder or a solid lubricant powder alone is disclosed.

  In patent document 1, the adhesiveness of the coating film of a single solid lubricant having a low adhesion strength is improved by forming a coating film in which a solid lubricant powder such as molybdenum disulfide is dispersed in a soft metal. Therefore, a highly durable coating can be formed while maintaining the lubricity of the solid lubricant. In Patent Document 2, a sliding member having a small friction coefficient and excellent sliding performance can be obtained by controlling the coating area, thickness, and surface roughness of a coating formed on the sliding surface.

  In addition, as described in [(Tribology Conference Spring 2007 Proceedings, pages 123-124, “Longer Life of Rolling Bearing by Solid Lubricant Shot Coating)” (Non-Patent Document 1), a soft metal powder of tin or zinc is used. A technique for reducing the coefficient of friction of a sliding member by shot peening on the sliding member to form a soft metal film is disclosed.

Furthermore, regarding the hard phase, as another method for improving the peeling life under the boundary lubrication environment, shot peening is performed on a hard metal (such as high-speed steel) as disclosed in JP 2000-230544 A (Patent Document 3). Thus, there is a method of applying compressive residual stress to the surface. The powder used for these is generally harder than the base material to be shot peened, such as bearing steel.
JP 2002-161371 A JP 2007-10059 A JP 2000-230544 A [Tribology Conference Spring 2007, Proceedings, pages 123-124 "Extending the life of rolling bearings by shot coating with solid lubricant"]

  Since there is no powder that can be applied to both the soft metal phase and the hard phase described above at the same time, it is necessary to perform shot peening separately on the two types of hard powder and soft powder in order to use both. However, since shot peening is basically a batch process, there is a problem that the process is complicated and expensive.

  In order to solve the above-mentioned problems, the inventors have intensively developed and, as a result, shot peening powder containing a hard phase in the soft metal phase, while the surface is covered with the soft metal phase, Invented that compressive residual stress can be applied to the surface. The hardness of the hard phase is softer than that of general bearing steel, and it is possible to apply residual stress at Hv 300 or higher. Therefore, a soft metal film that reduces the coefficient of friction and a shot peening powder that can simultaneously apply surface compressive residual stress to the sliding surface of a rolling bearing in a harsh lubricating environment such as boundary lubrication, and the Provided is a method for producing a slidable member using

The gist of the invention is that
(1) The powder is characterized in that the soft metal phase having a Vickers hardness of HV100 or less is Sn, and the hard phase having a hardness exceeding HV100 is Sn—Cu alloy powder having Cu ₆ Sn ₅ and / or Cu ₃ Sn. A shot peening powder that simultaneously imparts slidability and surface compressive residual stress.

( 2 ) When manufacturing a sliding member from a raw material, it manufactures by carrying out shot peening using the powder as described in said (1 ), The manufacturing method of the sliding member characterized by the above-mentioned.
( 3 ) The slidable member manufacturing method according to ( 2 ), wherein the slidable member has a surface compressive residual stress of 600 to 1500 MPa.

  As described above, when the soft metal according to the present invention is collided with the counterpart material at a high speed, the powder surface adheres to the counterpart material at the time of the collision, and is transferred to form a film, and the soft metal is formed on the surface When shot peening is performed with a shot powder having a coating, a compressive residual stress is applied to the surface by the core powder, and at the same time, a soft metal on the surface covers the mating material and acts as a lubricant.

Hereinafter, embodiments of the present invention will be described in detail based on an Sn-Cu alloy that is an example of the present invention. FIG. 1 is a Sn-Cu binary phase diagram. From FIG. 1, the two-phase composition of the Sn phase, which is a soft metal, and the alloy composed of the soft metal and Cu, Cu ₆ Sn ₅ and Cu ₃ Sn, can be obtained when Sn is 61% by mass or more. The film is desirably Sn: 65 to 95% by mass. Therefore, Cu has a component composition of 5 to 35% by mass.

In the powder, the ratio of the soft metal Sn phase, the hard phase Cu ₆ Sn ₅ and the Cu ₃ Sn phase changes depending on the amount of Cu. Therefore, if Sn is less than 61 to 65% by mass, a soft Sn film is not sufficiently formed. On the other hand, when Sn exceeds 95 to 100% by mass, no increase in surface compressive residual stress is observed. Examples of the method for forming the alloy powder having the above-described composition include pulverization of a cast material, atomization with gas or water, cutting and pulverization of a wire by an underwater spinning method, and pulverization of a ribbon by liquid quenching. These can be properly used depending on the required particle size and shape.

  Further, it is desirable that the Vickers hardness HV as a soft metal is 100 or less, and the hardness of the hard phase is Hv 300 or more, which is softer than the hardness of general bearing steel. For example, when Vickers hardness HV as a soft metal is set to 100 or less and a powder in which a hard phase having a Vickers hardness HV of 200 or more is dispersed in the soft metal, only the soft metal is deformed at the time of collision. Although it adheres to the surface, compressive residual stress is imparted to the surface by deforming both the hard phase and the mating surface.

  In addition, when there is a possibility of adverse effects such as polishing the mating material or coating material when the hard phase slides, it is possible to coat only the soft metal Sn phase by heat-treating the powder and coarsening the hard phase. . When the heat treatment is performed at a temperature range of 160 to 415 ° C. for 1 hour or longer, the finely dispersed hard phase becomes coarse.

  The alloy powder is formed on the surface of the sliding member by a shot peening method. The average film thickness of the formed film is 0.5 to 2.5 μm. If the average film thickness is less than 0.5 μm, the lubrication effect is not sufficient, and the friction coefficient as a bearing used in a boundary lubrication environment in which sliding members may come into contact with each other cannot be sufficiently obtained. Moreover, since the effect will be saturated when it exceeds 2.5 micrometers, the range was 0.5-2.5 micrometers.

  The shot peening method forms a film by causing the powder to collide with the sliding member at a high speed, so that high adhesion can be obtained in a short time, and it is not necessary to heat the sliding member, so that the sliding property It is suitable as a method for forming a film. As conditions for shot peening, powder is injected for 1 to 20 minutes using compressed air having a pressure of 0.4 to 0.8 MPa. At this time, a compressive stress is given to the sliding member surface because there is a hard phase in the powder.

  The compressive stress formed on the surface of the sliding member is in the range of 600 to 1500 MPa. The reason for this range is that Sn, which is a soft metal, acts to lower the frictional resistance during sliding, and 600 MPa or more is necessary to obtain the effect, and if it exceeds 1500 MPa, the life of the member The range was set to 600 to 1500 MPa. Preferably, the pressure is 600 to 1200 MPa.

  In the present invention, the sliding member refers to a member having a sliding surface that is in sliding contact with the counterpart member. Specific examples of the sliding member are mechanical parts that perform contact movement on a cylindrical surface, a spherical surface, a flat surface, and the like. For example, a cam and a cam follower, a piston ring, a fuel injection device, and a friction that constitute an automobile engine. Plates, crack parts, slide members constituting slide bearings, rolling bearings, retainers for slide bearings, and the like can be raised.

  Furthermore, as a material forming the sliding member, for example, bearing steel such as high carbon chrome bearing steel such as SUJ2, case hardening steel such as SCM420 and SCr420, and stainless steel such as SUS440 is subjected to quenching and tempering treatment. And those subjected to carburizing treatment or carbonitriding treatment and quenching and tempering treatment.

Hereinafter, the present invention will be specifically described with reference to examples.
Sn-Cu alloy powders having various compositions shown in Table 1 were produced by gas atomization. After confirming with a scanning electron microscope that the produced powder had a structure in which the intermetallic compound was finely dispersed, the produced powder was classified to a particle size of 105 to 38 μm, and the sliding member was classified using the classified powder. A lubricious coating was formed by shot peening on the sliding surface under the conditions of an injection pressure of 0.4 MPa and an injection time of 5 minutes. On the other hand, as a sliding member, bearing steel whose JIS symbol used for a general bearing is SUJ2 was quenched to the hardness of HRC60 and used.

The average film thickness of the formed film was observed by a scanning electron microscope after cutting a portion corresponding to the sliding surface of the test piece and mirror-finishing its cross section by buffing. Observation was carried out for 5 fields at 1000 times with EPMA (Electron Probe Microanalyzer), and the average was obtained. At that time, the concentration of Cu was 3% or less at the maximum and was hardly detected. The surface compressive residual stress was measured using X-rays. Further, the sliding member has a length in the diameter 26mm and small roller of 28mm, and carried a roller pitting test using this soft film single L ₅₀ life was compared (50% of life damage) and. For flexible film single L ₅₀ life, at least twice: ◎, less than two times or more 1-fold: ○, 0.5 times or more than 1 time: △, less than 0.5 times: was ×.

表１に示すように、Ｎｏ．１〜６は本発明例であり、Ｎｏ．７〜１０は比較例である。

As shown in Table 1, no. Nos. 1 to 6 are examples of the present invention. 7 to 10 are comparative examples.

Comparative Example No. 7 is a case where Sn is 100%, that is, a soft film alone, and the surface compressive residual stress is small. This case was used as a reference for the roller pitching test (L ₅₀ ). Comparative Example No. No. 8 has a small soft phase and a large hard phase, so the surface compressive residual stress is too large, which affects the life of the sliding member and shortens the life of the sliding member. Comparative Example No. 9 is Comparative Example No. Since the soft phase is smaller than 8, the hard phase is large, and the average film thickness is thin, the surface compressive residual stress is increased, and the life of the sliding member is further shortened.

  Comparative Example No. Reference numeral 10 denotes a case where no treatment is performed. At that time, the surface compressive stress is small, and the life of the sliding member is short. On the other hand, No. which is an example of the present invention. Since 1-6 satisfy | fill all the conditions of this invention, it turns out that the lifetime of the sliding member is extended 2 times or more compared with the case where a soft metal is single.

As described above, a film made of an alloy or intermetallic compound of hard metal Sn-Cu alloy powder is Cu ₆ Sn ₅ and / or Cu ₃ Sn with soft metal and more hardness of S n By forming it using shot peening, etc., only the soft metal deforms and adheres to the surface at the time of collision, but the hard phase deforms on both the hard phase and the mating sliding member, This formed film to which compressive residual stress is applied contains an intermetallic compound that is harder than soft metal and softer than sliding members such as bearings as a base material. In this formed film, the soft metal is lubricated. When the metal compound is aimed for wearability and initial wearability, a sliding film with high sliding performance and durability can be formed, and the life of the sliding member can be improved.

It is a Sn-Cu binary state diagram.

Claims (3)

Sliding the Vickers hardness as a powder is characterized in that the Sn-Cu alloy powder hard phase is Cu ₆ Sn ₅ and / or Cu ₃ Sn with hardness HV100 following soft metal phase exceeds Sn, HV100 For shot peening that simultaneously imparts surface properties and surface compressive residual stress. When manufacturing a sliding member from a raw material, it manufactures by carrying out shot peening using the powder of Claim 1, The manufacturing method of the sliding member characterized by the above-mentioned. The method for producing a slidable member according to claim 2 , wherein the surface compressive residual stress of the slidable member is 600 to 1500 MPa.

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