JP6665737B2 - Method for preparing raceway surface of thrust type ball bearing - Google Patents

Description

  The present invention provides a thrust type that can be suitably used under severe conditions under high loads as parts of various machines and various machine tools used in steel, papermaking, wind power generation and mining, and automobiles and railway vehicles. The present invention relates to a method for producing a raceway surface of a ball bearing.

  BACKGROUND ART Various types of ball bearings are used in various machines and the like used in various fields such as steel, papermaking, wind power generation, and mining, as well as in automobiles and railway vehicles. Since these ball bearings are used under severe conditions under a high load, there is a possibility that cracks are locally generated.

  Usually, the fracture of the bearing is often caused by a phenomenon in which a fatigue crack propagates from a hard inclusion existing 50 to 200 μm directly below the surface to reach the surface, and the steel material surface peels off. This phenomenon occurs when rolling the steel bar that is the material of the bearing, because the amount of deformation of the steel that is the parent phase and the amount of deformation of the hard inclusion are different, a gap is created around the hard inclusion, and this gap is generated when rolling. This is called stress concentration, and it is the cause of fatigue crack initiation.

  In order to improve the rolling fatigue life by suppressing the occurrence of cracks, it is effective to roughly classify two methods, that is, a method of reducing the number of hard inclusions and a method of reducing voids around the hard inclusions. In particular, the latter method of reducing the voids around the hard inclusions, such as reducing the diameter of the hard inclusions and reducing the voids themselves generated during bar rolling, or applying a hydrostatic stress to the voids around the hard inclusions A method of crushing a gap is known.

  Methods for reducing the voids around inclusions by hydrostatic stress are disclosed in Patent Documents 1 and 2. Patent Literature 1 is a technique for reducing voids around hard inclusions by HIP. On the other hand, Patent Literature 2 discloses a technique for cold forging a mechanical component having a rolling portion and reducing a gap between the inclusion and the base material by hydrostatic stress generated at the time of cold forging.

Japanese Patent No. 5403945 Japanese Patent No. 5669128

  However, in the technology described in Patent Document 1, the time required to crush the voids is determined by the self-diffusion of iron atoms, so that it is necessary to maintain the temperature at a high temperature for a long time. In addition, the technology described in Patent Document 2 employs cold forging, so that the deformation resistance of the matrix is high and the elastic limit is high, so that it is difficult to crush the voids. Cracks may occur.

  The present invention has been made in view of the above circumstances, and is a method for manufacturing a raceway surface of a thrust type ball bearing that does not need to be maintained at a high temperature for a long time, and is used under a severe condition such as used under a high load. However, an object of the present invention is to provide a method of manufacturing a raceway surface of a thrust ball bearing that can be suitably used.

  The fatigue crack of the bearing is generated in an extremely narrow region from the surface of the mother phase in contact with the rolling ball to a position near the surface of 200 μm or less below the surface where the Hertz stress in the mother phase is maximized. If the adhesion between the inclusion and the matrix is increased in this region, the rolling life is improved. Conversely, even if there is a gap between the inclusion and the parent phase outside the above region, the rolling life is not affected.

  FIG. 1 shows the distribution of hydrostatic stress generated when a mold having an annular convex portion (the cross-sectional shape of a contact portion with the metal flat plate is arc-shaped) is pressed against a work (metal flat plate) having a thickness of 5 mm. FIG. As is apparent from the figure, simulating the case where the rolling grooves of the thrust type bearing were manufactured by hot forging, and pressing a mold having an annular convex portion on a flat plate, the mold was moved to a bottom dead center. At some point, a strongly compressed hydrostatic field is formed near the base material recess formed by the mold. The hydrostatic pressure field of this compression is larger than the hydrostatic stress of 200 MPa obtained by a normal hot isostatic press, and sufficiently covers the bearing fatigue crack initiation region (the region of 50 to 200 μm immediately below the surface of the flat metal plate). I have.

  On the premise of such a fact, the present inventors have examined whether it is possible to use the hydrostatic stress at the time of hot forging to crush the gap existing between the inclusion and the matrix interface.

  The compressive hydrostatic stress field formed in the parent phase during hot forging depends on the distance from the surface of the parent phase, the amount of reduction of the die having the annular projection, and the forging temperature. FIG. 2 shows the hydrostatic stress when a mold is pressed into a work heated to 840 ° C. by 0.5 mm and the center of a concave groove formed in the work when producing a raceway surface corresponding to a 3/8 inch rolling ball. It is a graph which shows the relationship with the distance from the surface. The work in FIG. 2 is a hole-shaped disk having an inner diameter of 25 mm, an outer diameter of 52 mm, and a thickness of 5 mm. In addition, the mold in the figure has a convex portion having a radius of curvature of 4.76 mm and a radius of an annular convex portion core of 19.25 mm. As is clear from FIG. 2, the closer to the work surface, the greater the hydrostatic stress of compression. FIG. 3 shows the relationship between the hydrostatic stress and the amount of reduction at a position of 200 μm from the work surface when the amount of reduction was changed under the same forging temperature conditions as those in FIG. 2 for the work and the mold used in FIG. FIG. FIG. 4 shows the relationship between the hydrostatic stress at the position of 200 μm from the work surface and the forging temperature when the forging temperature condition was changed for the work and the die used in FIG. FIG. As is clear from FIG. 3, the hydrostatic stress increases almost in proportion to the amount of reduction. Further, as is clear from FIG. 4, the hydrostatic stress decreases as the forging temperature increases.

  Based on the results of FIG. 3 and FIG. 4, the present inventors utilize hydrostatic stress at the time of hot forging to determine the conditions under which the void existing between the inclusion and the matrix interface can be crushed. , Discussed in more detail. Since the increase in hydrostatic stress due to forging is instantaneous, a compressive hydrostatic stress of 200 MPa or more is required in order for the inclusions and the mother phase to adhere to each other. However, even when the indentation amount in FIG. 3 is 0.28 mm or more and the forging temperature in FIG. 4 is 940 ° C. or less, the compressive hydrostatic stress at a position of 200 μm from the work surface may be less than 200 MPa. Confirmed that there is.

  FIG. 5 is a diagram showing a region where the compressive hydrostatic stress at a position of 200 μm from the work surface is 200 MPa or more when the forging temperature (heating temperature during forging) and the indentation amount are respectively changed. In the figure, the colored portion is a region where the compressive hydrostatic stress is 200 MPa or more. According to the figure, even when the indentation amount is 0.28 mm or more and the forging temperature is 940 ° C. or less, there is a region where the hydrostatic stress at a position of 200 μm from the work surface is less than 200 MPa. Therefore, when setting the forging temperature and the indentation amount so that the compressive hydrostatic stress becomes 200 MPa or more, the result of FIG. 5 is more than the condition of simply adding the results of FIG. 3 and FIG. It turns out that it is more preferable to use.

  The present invention has been made based on the above findings, and the gist is as follows.

[1] A method for manufacturing a raceway surface of a thrust type ball bearing using an annular work having austenite as a main phase,
The die is pressed against a work and rolled so that the forging temperature T ₁ (° C.) during forging and the amount of press D (mm) of the die having an annular convex shape satisfy the following formula. Forging process to form a groove,
A martensite generation step of making the structure of the work in which the rolling grooves are formed a structure mainly composed of martensite,
A method for manufacturing a raceway surface of a thrust ball bearing, comprising:
T ₁ <−400D ² + 752D + 664 (1)

  [2] The method for producing a raceway surface of a thrust ball bearing according to the above [1], wherein the martensite generation step is a direct quench.

  [3] The method for producing a raceway surface according to the above [1], wherein the martensite generation step comprises slow cooling and quenching and tempering.

  [4] The method for producing a raceway surface of a thrust ball bearing according to the above [1], wherein the martensite generation step is a die quench.

[5] Die quench is performed so that the forging heating temperature T ₂ (° C.), die quench end temperature T ₃ (° C.), and forging heating time t (hr) satisfy the following formula. The method for producing a raceway surface of the thrust type ball bearing described in the above.
^{_{T 3 <4.17 × 10 -3 T}} 2 2 -8.18T 2 -15.7log 10 (t) -2.98 × 10 3 / t / T 2 +4142 (2)

  [6] The method for producing a raceway surface of a thrust ball bearing according to any one of the above [1] to [5], wherein the temperature of the workpiece is 840 ° C. or lower and the rolling groove is formed.

  [7] The method for producing a raceway surface of a thrust ball bearing according to any one of [1] to [6], wherein the rolling grooves are formed so that the rolling reduction is 0.4 mm or more.

  In the method for producing a raceway surface of a thrust ball bearing according to the present invention, the relationship between the amount of reduction of the die and the forging temperature is improved. As a result, according to the present invention, the raceway surface of the thrust type ball bearing can be manufactured without having to hold at a high temperature for a long time. Further, according to the present invention, the gap between the inclusion and the base material can be crushed immediately below the raceway surface, and the inclusion and the parent phase can be brought into close contact with each other. It can be suitably used, and the life can be extended.

FIG. 1 shows the distribution of hydrostatic stress generated when a mold having an annular convex portion (the cross-sectional shape of a contact portion with the metal flat plate is arc-shaped) is pressed against a work (metal flat plate) having a thickness of 5 mm. FIG. FIG. 2 shows the relationship between the hydrostatic stress when a mold is pressed against a work heated to 840 ° C. and the distance from the work surface in producing a raceway surface corresponding to a ／ inch rolling ball. It is a graph. FIG. 3 shows the hydrostatic stress and the reduction amount (indentation amount) at a position of 200 μm from the work surface when the reduction amount is changed under the same forging temperature condition as the condition in FIG. 2 for the work and the die used in FIG. FIG. FIG. 4 shows the relationship between the hydrostatic stress at the position of 200 μm from the work surface and the forging temperature when the forging temperature condition was changed for the work and the die used in FIG. FIG. FIG. 5 is a diagram showing a region where the hydrostatic stress at a position of 200 μm from the workpiece surface is 200 MPa or more when the forging temperature and the indentation amount are respectively changed. FIG. 6 is a graph showing the results of the rolling fatigue test (the relationship between the cumulative failure probability (%) and the life (number of repetitions)).

  Hereinafter, an embodiment of a method for producing a raceway surface of a thrust type ball bearing according to the present invention (hereinafter, referred to as “the present embodiment”) will be described. Note that the present embodiment does not limit the present invention. The components of the present embodiment include components that can be easily replaced by those skilled in the art, or components that are substantially the same. Furthermore, various forms (for example, preferable forms) included in the present embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  The method for producing a raceway surface of a thrust ball bearing according to the present embodiment is a method for producing a raceway surface using an annular work having austenite as a main phase. In addition, since the raceway surface manufacturing method according to the present embodiment has a thrust type ball bearing in mind, it corresponds to the axial raceway plate corresponding to the inner ring and the outer ring among the general components of the thrust ball bearing. This is a method of producing a raceway surface for a housing washer. Here, the expression "austenite as the main phase" means that austenite is most contained in the structure of the work.

  The workpiece can include any component as long as it is a component included in general steel. That is, the work can include, for example, Fe, C, Si, Mn, P, S, Cu, Ni, Cr, Al, O, and unavoidable impurities, and the component composition range of these elements is not particularly limited. Here, the unavoidable impurities are components that can be contained in ore or scrap as a raw material when a work is industrially produced, or components that can be mixed due to a production environment or the like, and Means components not added to On the other hand, the structure of the workpiece is most austenite, and the remainder is composed of ferrite and various carbides (inclusions).

  Further, since the work is processed into a shaft raceway or a housing raceway of a thrust type ball bearing, it has an annular shape. In the following description, the track surface is formed by the same operation for both the shaft washer and the housing washer.

  Under such a premise, the method for producing a raceway surface of a thrust ball bearing of the present embodiment includes the following (A) forging step and (B) martensite generation step.

(A) Forging Step In the forging step, the forging temperature T ₁ (° C.) and the indentation amount D (mm) of the die having the annular convex shape satisfy the following formula. To form rolling grooves.
T ₁ <−400D ² + 752D + 664 (3)

  The mold only needs to have a shape suitable for forming a raceway surface on each of the shaft raceway and the housing raceway of the thrust type ball bearing. More specifically, any other shape can be used as long as the convex portion, which is a component of the mold, is shaped so that it can be continuously abutted in the circumferential direction of both washers at the center in the width direction of the two washers. It is not particularly limited.

  The above equation shows the colored portion shown in FIG. 5. In this region, the hydrostatic stress at a position of 200 μm from the work surface becomes 200 MPa or more, the adhesion between the inclusion and the matrix increases, and the rolling life is improved. .

The heating temperature of the workpiece is given the martensite step described below, it is A ₃ transformation temperature or more of the steel, martensite step without raising the temperature of the workpiece after forging the martensite step Is preferred in that it can be carried out. The forging in the present embodiment is a concept including any of hot pressing, warm forging, hot forging, and sub-hot forging, and is a technique that can be applied in a wide range of forging fields.

  On the other hand, when the forging temperature exceeds 940 ° C., the deformation resistance of the steel work is excessively small, and the compressive hydrostatic stress generated during forging is excessively small. Specifically, when the forging temperature is higher than 940 ° C., the compressive hydrostatic stress may be less than 200 MPa, the gap around the hard inclusion may not be sufficiently collapsed, and the hard inclusion may not adhere to the matrix. is there. For this reason, the forging temperature is preferably set to 940 ° C. or lower. It is more preferable to set the forging temperature to 840 ° C. or lower, because the voids around the hard inclusions are further crushed and the hard inclusions adhere to the matrix more highly.

  Further, as for the amount of reduction in pressing the mold against the work, the larger the amount, the higher the hydrostatic pressure stress, and the more the inclusions can be securely adhered to the parent phase by crushing the gap. Specifically, when the rolling amount is less than 0.27 mm, the compressive hydrostatic stress may be less than 200 MPa, and voids may remain and the inclusions may not adhere to the matrix. For this reason, the amount of reduction is preferably 0.27 mm or more. In addition, it is more preferable that the amount of reduction is 0.4 mm or more, because the inclusions adhere to the matrix more highly.

  Thus, in the forging process, by limiting the relationship between the forging temperature and the amount of reduction to a suitable range, the gap around the hard inclusion is reliably crushed, and furthermore, the inclusion can be brought into close contact with the matrix. it can.

(B) Martensite generation step Next, in the martensite generation step, the structure of the work in which the rolling grooves are formed as described above is a structure mainly composed of martensite. Here, the organization mainly composed of martensite means an organization in which martensite is most contained among the organization of the work.

  As the martensite generation step, (1) direct quench, (2) slow cooling and quenching and tempering, and (3) die quench can be employed. The quenching and tempering after slow cooling can ensure the strength of the work and prevent quenching.

  Here, the slow cooling includes, for example, air cooling the forged work. Further, the direct quench is a concept including any heat treatment method as long as the work after forging is quenched with water or oil while hot (before the transformation starts). In addition, the die quench is a concept including any heat treatment method as long as it is a heat treatment method that removes heat from a work after pressing a mold against the work after forging.

  In particular, when the die quench is adopted, there are the following advantages. That is, after forging, the die is stopped at the bottom dead center, and cooled while being pressed against the work, the surface of the work in contact with the die is extracted and quenched by the die, and the vicinity of the raceway surface formed on the work is 80%. % Or more becomes martensite. Such die quenching reduces heat treatment strain and transforms the parent phase from austenite to martensite while hydrostatic stress is applied. Therefore, transformation plasticity occurs during transformation, the voids around the hard inclusions are reduced at a higher level, and the adhesion between the matrix and the hard inclusions is significantly improved.

Here, it is preferable to perform the die quench so that the heating temperature T ₂ (° C.) during forging, the die quench end temperature T ₃ (° C.), and the heating time t (hr) during forging satisfy the following formula.
^{_{T 3 <4.17 × 10 -3 T}} 2 2 -8.18T 2 -15.7log 10 (t) -2.98 × 10 3 / t / T 2 +4142 (4)

  By performing the die quench so as to satisfy the above equation, the work is rapidly cooled to a temperature equal to or lower than the martensite transformation start temperature, so that 85% or more of the vicinity of the raceway surface formed on the work becomes martensite. Thereby, transformation plasticity further occurs during transformation, the voids around the hard inclusions are reduced at a remarkably high level, and the adhesion between the matrix and the hard inclusions is further improved.

  When a high carbon chromium bearing steel material (SUJ2) is used as the work, if the work at the time of forging is heated at 930 ° C. for 1 hour, the martensite transformation start temperature (Ms point) is about 150 ° C., and 840 If the heating is performed at 1 ° C. for 1 hour, the Ms point is about 230 ° C. This is because the higher the heating temperature, the higher the spheroidized cementite solid solution, the higher the carbon concentration of the matrix, and the lower the martensitic transformation temperature. For this reason, from the viewpoint of abrasion resistance, it is preferable to set the heating temperature of the work to 840 ° C. or lower and form the rolling grooves in a state where the solid solution of the spheroidized cementite is small. In particular, when a die quench is adopted, the mold temperature must be kept at 100 ° C. or lower, and when forging and die quench are repeated, the mold needs to be water-cooled.

  Also, in any of the case of employing direct quench, the case of employing slow cooling and quenching and tempering, and the case of adopting die quench, after the structure of the work becomes a structure mainly composed of martensite, the forged part is formed. It is preferable to adjust the roughness of the surface by performing a lapping process on the surface.

  In the method of manufacturing the raceway surface of the thrust ball bearing according to the present embodiment described above, the raceway surface of the ball bearing can be manufactured in a situation where the increase in the compressive hydrostatic stress, which is called forging, is realized instantaneously. Therefore, according to the method of the present embodiment, it is not necessary to hold the steel material at a high temperature for a long time as in the related art, so that the raceway surface can be quickly manufactured.

  Further, in the method of manufacturing the raceway surface of the thrust ball bearing according to the present embodiment, due to the limitation on the relationship between the forging temperature and the rolling reduction, the gap around the hard inclusion is surely crushed, Can be in close contact with the phase. Therefore, according to the method of the present embodiment, the ball bearing can be suitably used even under a high load condition, and the life thereof can be extended.

  Hereinafter, the effects of the present invention will be demonstrated by examples.

  Rolled material of SUJ2 round bar of φ60 having the chemical components shown in Table 1 (unit is% by mass) and the balance being Fe and inevitable impurities was spheroidized to obtain an outer diameter of 52 mm, an inner diameter of 72.2 mm and a thickness of 5 mm. A test piece (work) of 0.5 mm was cut out.

  Next, the work thus obtained was forged. Forging is carried out using a forging tester (load capacity: 6000 kN: manufactured by AIDA), and a top metal (material RF06) having a convex portion (having a circular arc cross section having a curvature radius R of 4.76 mm and being annular). A raceway surface (rolling groove) was formed on the work using a mold and a flat lower mold. Thereafter, the work was cooled to room temperature. Table 2 shows the forging conditions and cooling conditions of the work.

  For Levels 1, 2, 4 to 10, the upper die was held at the bottom dead center during forging, the work was cooled to the die quench end temperature (die quench), and then tempering heat treatment was performed at 160 ° C. for 1.5 hours. For Levels 6 and 9, a 0.3 mm groove was formed by cutting, and the rolling reduction during forging was set to 0.3 mm, so that the groove depth of the final shape was 0.6 mm, which was the same as other levels. It was made to become. Similarly, for Levels 7 and 8, a groove of 0.15 mm is formed by cutting, and the rolling reduction during forging is set to 0.45 mm, so that the groove depth of the final shape is 0.6 mm, which is the same as other levels. It was made to become.

  In Level 3, after forging, the work was cooled to room temperature by air cooling, heated at 840 ° C. for 30 minutes, quenched with 60 ° C. oil, and further tempered at 160 ° C. for 1.5 hours. In Level 4, after forging, the work was immersed in oil at 60 ° C., cooled, and then tempered at 160 ° C. for 1.5 hours.

  Each of the workpieces was manufactured in a number of 10 pieces, and rolling grooves were wrapped as finishing processing, and a thrust rolling fatigue test was performed.

  As for Level 4, two out of 10 sheets were warped, so the Level 4 rolling fatigue test was performed on 8 sheets.

The conditions of the rolling fatigue test were performed using three rolling balls made of Si ₃ N _{4 having} a ／ inch diameter and a load of 8.5 kN. The rolling fatigue test endured 1.5 × 10 ⁸ cycles. FIG. 6 shows the result.

  As is clear from FIG. 6, so-called Weibull values (for example, L50 life and L10 life) show excellent values for works of levels 1 to 7 in which the relationship between the forging temperature and the amount of reduction is within the predetermined range of the present application. I have. This is because, for Levels 1 to 7, the inclusions and the base material can be brought into close contact with each other immediately below the raceway surface, and the ball bearing can be suitably used even under high load conditions.

  On the other hand, for the levels 8 and 9 in which the forging temperature or the rolling reduction is not within the predetermined range in the present application, the Weibull value does not show an excellent value. This is because, for Levels 8 and 9, it is insufficient to closely contact the inclusions and the base material immediately below the raceway surface, and the ball bearings have not been suitably used under high load conditions.

  On the other hand, at level 10, the die quench end temperature is high, and the martensite fraction near the raceway surface formed on the work is insufficient, so that the fatigue life is reduced.

Claims (7)

A method for producing a raceway surface of a thrust type ball bearing using an annular work having austenite as a main phase,
The die is pressed against a work and rolled so that the forging temperature T ₁ (° C.) during forging and the amount of press D (mm) of the die having an annular convex shape satisfy the following formula. Forging process to form a groove,
A martensite generation step of making the structure of the work in which the rolling grooves are formed a structure mainly composed of martensite,
A method for manufacturing a raceway surface of a thrust ball bearing, comprising:
T ₁ <−400D ² + 752D + 664 (1)   The method for producing a raceway surface of a thrust ball bearing according to claim 1, wherein the martensite generation step is a direct quench.   The track surface manufacturing method according to claim 1, wherein the martensite generation step includes slow cooling and quenching and tempering.   The method for producing a raceway surface of a thrust ball bearing according to claim 1, wherein the martensite generation step is die quench. As during forging heating temperature T _{2 (°} C.) and die quenching end temperature T _{3 (°} C.) and heating time during forging t (hr) satisfy the following equation, performs die-quenching, thrust-type of claim 4 How to make ball bearing raceway surface.
^{_{T 3 <4.17 × 10 -3 T}} 2 2 -8.18T 2 -15.7log 10 (t) -2.98 × 10 3 / t / T 2 +4142 (2)   The method for producing a raceway surface of a thrust type ball bearing according to any one of claims 1 to 5, wherein the rolling groove is formed by setting the temperature of the work to 840 ° C or lower.   The method for producing a raceway surface of a thrust ball bearing according to any one of claims 1 to 6, wherein the rolling groove is formed such that a reduction amount is 0.4 mm or more.