JP2012193394A - High face-pressure component excellent in pitching resistance and bending fatigue rigidity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high face-pressure component which makes soft-solid lubrication powder efficiently adhere to a soft metal membrane having slide performance by performing shot peening by using mixed powder after a steel ball and a soft metal are mixed, and can improve adhesiveness with a base material which forms a slide face.SOLUTION: The high face-pressure component excellent in the pitching resistance and the bending fatigue rigidity is characterized by mixing the steel ball and the soft metal and performing the shot peening by using the mixed powder in which a mixing ratio of the soft metal is 5 to 50 mass%. The soft metal is one or two or more kinds of either of Sn, Sn alloys or Cu, Cu alloys.

Description

  The present invention relates to parts made of steel for machine structure subjected to high surface pressure (hereinafter referred to as machine structure parts), such as gears, CVT, shafts, piston rings, cam followers manufactured by quenching, carburizing, carbonitriding, etc. The present invention relates to a machine structural component having excellent pitting resistance and bending fatigue strength used for high surface pressure parts such as crack parts.

  In general, mechanical structural parts, such as parts subjected to high surface pressure, such as gears, are formed by forming a steel material into a part shape by hot forging, cold forging, cutting, and the like, followed by heat treatment such as carburizing. Case-hardened steels such as JIS SCM420 and JIS SCR420 are mainly used as steel materials for such parts. Further, when strength is particularly required, high hardness and high compressive residual stress are imparted by shot peening after heat treatment.

  Also, lubrication of sliding parts such as gears is often performed using a liquid lubricant such as oil, but when the liquid lubricant cannot be used for design reasons, it is used in a vacuum. If there is a restriction in the usage environment such as a solid lubricant, a solid lubricant is used. Furthermore, in recent years, as the social demand for energy problems increases, further reduction in friction of sliding members used in automobile engines and transmissions is required.

  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. Since the number of parts used in the boundary lubrication environment is increasing, it is necessary to develop a long-life component that has high slidability even in the boundary lubrication environment. The moving part is covered.

  As a method for coating the sliding member with the solid lubricant, for example, as disclosed in JP-A-2002-161371 (Patent Document 1) and JP-A-2004-255522 (Patent Document 2), zinc or tin is used. A method is disclosed in which shot peening is performed on a sintered body of a mixed powder of a soft metal powder such as molybdenum disulfide powder such as molybdenum disulfide, or a mixed powder of a steel ball and molybdenum disulfide powder as a solid lubricant.

  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, solid lubricant powder such as molybdenum disulfide can be more penetrated into the sintered body by the collision energy of steel balls.

  JP 2007-10059 (Patent Document 3) discloses a film forming technique for shot peening a soft metal powder or a solid lubricant powder alone, and covers a coating area formed on a sliding surface, By controlling the thickness and surface roughness, it is said that a sliding member having a small friction coefficient and excellent sliding performance can be obtained.

  In JP 2009-209449 A (Patent Document 4), a powder comprising two phases of a phase composed of a soft metal and a phase composed of an alloy of the soft metal and other metal is shot peened. A technique for improving wear resistance and slidability is disclosed.

  In JP 2011-25346 A (Patent Document 5), a shot peening is performed on a film made of an alloy or an intermetallic compound of a soft metal such as Sn and one or more hard metals having higher hardness. For example, a technique is disclosed in which a soft metal is responsible for lubricity and an intermetallic compound is responsible for wear resistance.

  In JP 2011-25348 A (Patent Document 6), compressive residual stress is applied by shot peening using a powder formed by plating a soft metal film such as Sn on a steel ball. At the same time, a method is disclosed in which a soft metal on the surface is coated on a member to be processed and acts as a lubricant, and a low coefficient of friction lasts for a long time to obtain high sliding characteristics, wear resistance, and fatigue strength.

In addition, as described in [Tribology Conference 2007 Spring 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 slid. A technique for reducing the friction coefficient of a sliding member by shot peening on a moving member and forming a soft metal film is disclosed.
JP 2002-161371 A JP 2004-255522 A JP 2007-10059 A JP 2009-209449 A JP 2011-25346 A JP 2011-25348 A [Tribology Conference Spring 2007, Proceedings, pages 123-124 "Extending the life of rolling bearings by shot coating with solid lubricant"]

  However, in the technique described in Patent Document 1 described above, it is very difficult to mix homogeneously a soft metal powder such as tin or lead and particles of a solid lubricant such as molybdenum disulfide or graphite because their densities are greatly different. It is difficult to obtain a film in which the solid lubricant is uniformly dispersed on the sliding surface, and sufficient sliding properties may not be obtained due to poor film adhesion and adhesion efficiency.

  Also in the technique described in Patent Document 2, it is very difficult to uniformly mix the particles of a solid lubricant such as a steel ball and molybdenum disulfide because their densities are very different from each other. It is difficult to obtain the material penetration effect. With the technique described in Patent Document 3, the softness of the solid lubricant film on the sliding surface is low, such as tin or zinc, so the adhesion and wear resistance are low, and the film cannot withstand long-term use. There is sex.

  Further, in the technique described in Patent Document 4, since the hardness of the shot powder is low, the material to be treated cannot obtain sufficient hardness and compressive residual stress, the bending fatigue strength is not sufficient, and the adhesion is further low. A sufficient pitching life may not be obtained. Further, in the technique described in Patent Document 5, there is a high possibility that sufficient sliding characteristics and bending fatigue strength can be obtained, but it is expected that the cost of the powder is high because only a metal such as Sn or Cu is used. The

  In the technique described in Patent Document 6, it is very expensive to form a soft metal film on a steel ball by a method such as plating. Furthermore, since the technique described in Non-Patent Document 1 is a soft metal such as tin or zinc, which has a low strength of the solid lubricant film on the sliding surface, as in Cited Document 3, the adhesion and wear resistance are low and long. The membrane may not withstand the use of time.

  As a result of diligent development to solve the problems as described above, the inventors mixed a soft solid lubricating powder such as Sn with a steel ball used for imparting compressive residual stress, and then mixed the mixture. By performing shot peening using powder, this soft solid lubricating powder can efficiently adhere as a soft metal film with sliding properties, and at the same time, it can improve the adhesion with the base material that forms the sliding surface. I found it.

  In the first place, pitching and wear are phenomena that occur when the metal surfaces rub against each other, but when this soft metal film is present at the interface where the part contacts the part, this film itself reduces the metal contact between the parts, and Pitching life and wear resistance are improved by reducing frictional resistance because it works as a lubricant. Furthermore, as described above, when the steel ball is shot using a mixed powder such as Sn, the surface of the material to be treated is made of a steel ball even though a soft metal film is formed on the surface of the material to be treated. The effect of shot peening works simultaneously with film formation, the processed surface of the material to be processed is work hardened to increase the surface hardness, and the compressive residual stress is increased, resulting in pitching life and wear resistance. And the bending fatigue strength can be improved.

The gist of the invention is that
(1) A high surface pressure component excellent in pitting resistance and bending fatigue strength, characterized by mixing steel balls and soft metal, and shot peening mixed powder having a soft metal mixing ratio of 5 to 50% by mass. .
(2) Shot peening is performed on a mixed powder in which the soft metal according to (1) is one or more of Sn, Sn alloy, Zn, Zn alloy, Cu, and Cu alloy. It is a high surface pressure component with excellent pitching and bending fatigue strength.

  As described above, after mixing the high hardness shot peening powder such as the spherical shape and the soft solid lubricating powder such as Sn according to the present invention, the soft solid lubricating powder is made slidable by performing shot peening with this mixed powder. Efficiently attaches a soft metal film, and at the same time improves adhesion to the base material that forms the sliding surface. This film provides lubrication and increases the pitching life and wear resistance. It is done.

  Furthermore, although the film is formed, the surface of the workpiece is affected by the effect of strong working with steel balls, so that the pitching life, wear resistance, and bending fatigue strength can be improved. In this way, even if mixed powder is used, the other powder is an extra powder when viewed from one powder, but both have the same characteristics without causing adverse effects. In this case, it has an extremely excellent effect.

Hereinafter, the present invention will be described in detail.
In the present invention, a steel ball and a soft metal are mixed, and the mixing ratio of the soft metal is 5 to 50% by mass. That is, since both of the present invention are metals, shot peening is performed in a severe lubrication environment such as a boundary lubrication environment by shot peening a mixed powder in which a soft metal is mixed in a ratio of 5 to 50% by mass to a steel ball having a similar specific gravity. Thus, it is possible to efficiently form a soft metal film that exhibits slidability and to enhance its adhesion. However, if the mixing ratio is less than 5% by mass, it is difficult to obtain a sufficient soft metal film because the amount of the soft metal powder is too small, and conversely if it exceeds 50% by mass, the pressure-bonding effect by the steel ball decreases. Since the adhesiveness of the film is lowered, the range is made 5 to 50% by mass. Preferably, it is 10 to 40% by mass. Note that steel balls and soft metal powder having substantially the same particle size are mixed in such a ratio that the soft metal powder is 5 to 50% by mass. This mixing is performed for 30 minutes to 1.5 hours using a V-type mixer.

  Examples of the steel balls according to the present invention described above include powdered high-speed steel and Fe-B alloys. Examples of the soft metal include Sn, Sn alloy, Zn, Zn alloy, Cu, and Cu alloy. A steel ball having a Vickers hardness of 800 to 1500 HV and an average particle size of 30 to 60 μm is used, and a soft metal powder having an average particle size of 30 to 60 μm is used. The shot peening conditions are to form a soft metal on the sliding surface by using a shot peening device and accelerating and spraying under conditions of a pressure of 0.4 to 1.0 MPa and an injection time of 5 to 20 minutes. .

Hereinafter, the present invention will be specifically described with reference to examples.
A steel made of 0.2C-0.25Si-0.75Mn-1.05Cr-0.15Mo-remaining Fe, which is JIS SCM420, was melted in a 100 kg vacuum melting furnace to obtain steel. Next, this steel was hot forged at 1200 ° C., and the roller pitching test piece base material was a round bar with a diameter of 32 mm, and the rotary bending fatigue test piece base material was a round bar with a diameter of 20 mm. Next, the steel bar was heated to 900 ° C., held for 1 hour, air-cooled and normalized, and then a roller pitching test piece having the shape shown in FIG. 1 and a rotating bending fatigue test piece having the shape shown in FIG. It produced, and carburizing quenching by gas carburizing and tempering were performed according to the carburizing quenching and tempering conditions shown in FIG. 3, respectively.

  The mixed powder for shot peening is a high-speed steel, or a powder that is a steel ball for shot peening having an average particle size of 44 μm and a Vickers hardness of 1200 HV, and Sn is a soft metal having an average particle size of 44 μm. Zn, Cu powder, or an alloy thereof was prepared by mixing for 1 hour using a V-type mixer so as to have the composition of the present invention example and the comparative example. FIG. 4 is a scanning electron micrograph of the mixed powder when Fe-9Cr-6B is 75 mass% and Sn powder is 25 mass%. As shown in this figure, it can be seen that the Sn powder 2 is dispersed in the steel ball powder 1. Such a mixed powder was shot peened into a roller pitching test piece and a rotating bending fatigue test piece. The shot peening conditions were a gas pressure of 0.7 MPa and a shot time of 10 minutes.

  The soft metal coverage on the surface after the shot was observed from the surface of the roller pitching test piece using EPMA (Electron Probe Microanalyzer) at five times with five fields of view, and the area occupied by the soft metal with respect to the field of view The quotient with the area of is shown as a percentage. For example, the Sn coverage was 77% when the powder high-speed steel was 75% by mass and the Sn powder was 25% by mass. The thickness of the soft metal was obtained by observing five sections of a section obtained by cutting a roller pitching test piece at a magnification of 5000 times with a scanning electron microscope (SEM), measuring each of the six fields, and averaging. When the content of Sn was 75% by mass and the Sn powder was 25% by mass, the thickness was 1.6 μm. When all the particles having an average particle diameter of 44 μm were shot with Sn powder under the same shot peening conditions, the Sn coverage was 79% and a film thickness of 1.8 μm was obtained. Therefore, despite the fact that the amount of Sn used in the mixed powder was a quarter due to the collision energy of the steel ball, it was possible to obtain the same film as when using the entire amount of Sn powder, compared with the steel ball. Thus, the consumption of expensive Sn powder could be suppressed, and the Sn film could be formed four times more efficiently with the film formation rate.

  In addition, in order to evaluate the adhesion of the film, the interface with the film of the cross-sectional sample for SEM was analyzed by SEM / EDS, and the diffusion of Sn into the test piece was measured. %, Sn was detected even at a point of 0.5 μm or less from the film interface, but Sn was not detected at 0.5 μm or less in the test piece shot with Sn alone. This is due to the effect that the Sn film was mechanically pressed by the collision energy of the steel ball, and it is considered that the mixed powder in which Sn diffused deeper has higher film adhesion.

  As described above, the mixed powder of the steel ball and the soft metal powder collides with the member to be treated at a high speed, and the soft metal powder surface adheres to the member to be treated at the time of the collision and is transferred to the soft member. By simultaneously applying the collision energy of the steel balls when the metal film is formed, the film can be efficiently formed and at the same time a film with high adhesion can be formed.

  As a result, when shot peening is performed with a mixed powder of steel balls and soft metal powder, the soft metal is stably coated on the processing member in a highly adhesive state, works as a lubricant, and maintains a low coefficient of friction for a long period of time. Thus, the pitting resistance and wear resistance are stably maintained for a long time. In addition, despite the presence of the coating, the surface hardness is increased by work hardening by the projection of the steel ball powder, and since a large compressive residual stress is applied to the surface, not only the wear resistance is sufficient, The surface fatigue characteristics and fatigue strength are also improved, and the effect of the present invention is great.

Subsequently, a roller pitching test and a rotating bending fatigue test were performed, and the results of the comparative examples and the examples of the present invention were covered with the soft metal, the average film thickness, the surface compressive residual stress, the surface hardness, the roller pitching life, and the rotating bending. The fatigue strength is shown in Tables 1 and 2. The rotational bending fatigue strength was evaluated by 10 ⁷ cycle strength. The roller pitting life and the rotational bending fatigue strength in Tables 1 and 2 are shown as strength ratios when the strength of Comparative Example 1 (when shot peening is not performed) is 1.0.

  As seen in Table 1 and Table 2, in the present invention example, a steel ball and a soft metal are mixed, and the film is formed by shot peening using a powder in which the mixing ratio of the soft metal is 5 to 50% by mass. A soft metal film having a good adhesion with a thickness of 0.5 μm or more and good lubricity can be applied, and the surface can provide high hardness and high compressive residual stress despite the presence of the film. Therefore, it has become possible to obtain excellent properties such as a roller pitching life of 3 times or more and a rotational bending fatigue strength of 1.3 times or more.

  As described above, the steel ball according to the present invention is mixed with a soft metal, and shot peening is performed using a powder in which the mixing ratio of the soft metal is 5 to 50% by mass. It is possible to attach a good film, and the surface can be applied with high hardness and high compressive residual stress. I was able to.

It is a figure which shows a roller pitching test piece. It is a figure which shows a rotation bending fatigue test piece. It is a figure which shows the heat cycle of carburizing quenching and tempering conditions. It is a scanning electron micrograph of mixed powder.

1 Steel ball powder 2 Sn powder



Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (2)

A high surface pressure component excellent in pitting resistance and bending fatigue strength, characterized by mixing a steel ball and a soft metal and shot peening a mixed powder having a soft metal mixing ratio of 5 to 50% by mass. Pitching resistance and bending characterized by shot peening a mixed powder in which the soft metal according to claim 1 is one or more of Sn, Sn alloy, Zn, Zn alloy, Cu, and Cu alloy High surface pressure parts with excellent fatigue strength.

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