Manufacturing method for bearing components

Abstract

To provide a method for manufacturing a bearing component capable of efficiently eliminating gaps existing around a non-metallic inclusion.SOLUTION: In a method for manufacturing a bearing component, in order to reduce gaps between a non-metallic inclusion and a matrix in a region of a surface of a workpiece on which a load is applied when used as a bearing component, a rolling element is rolled in a contact manner and pressed to plastically deform the workpiece. Then, the workpiece after the plastic deformation is subjected to heat treatment to give it a Rockwell hardness of 58 HRC or more. As the rolling element, a sphere or roller can be used. Also, the rolling element can be pressed against the workpiece with a working surface pressure within a range of 3.5 GPa or more and 5.5 GPa or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a steel bearing component used for a bearing.

Background Art

[0002] Steel for bearings inevitably contains foreign substances called non-metallic inclusions due to its manufacturing process. In addition, in bearings manufactured through rolling or forging, gaps may be formed around non-metallic inclusions. This gap is considered to occur at the interface due to the difference in deformability between the non-metallic inclusion and the bearing steel, which is the matrix phase. This gap promotes the generation of cracks in the bearing component that undergoes rolling fatigue during use and may become the starting point of cracks. Therefore, in order to improve the life of the bearing, it is effective to reduce the gap around the non-metallic inclusion.

[0003] In Patent Document 1, plastic working (burnishing) is performed on the machined surface of the rolling component to fill the gap existing between the non-metallic inclusion and the matrix phase. Here, in the specific plastic working, the spherical pressing portion at the tip of the tool is pressed against the machined surface of the rolling component (inner ring). Although no clear disclosure is made regarding the details of this tool, judging from the description of the examples and the disclosed figures, while pressing the tool against the entire machined surface and moving it for processing, the minute uneven shape existing on the machined surface is flattened.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 describes a method in which a pressing part is pressed against the workpiece surface. However, such a processing method requires the introduction of specialized processing machines and tools, such as burnishing machines and cold rolling equipment. In contrast, the inventors of the present invention have found that by using rolling elements (rolling components such as those used in bearings) to perform plastic deformation on the workpiece surface by applying partial pressing using rolling contact, it is possible to efficiently fill the gap between non-metallic inclusions and the matrix phase. Furthermore, this method can be easily performed using, for example, a rolling fatigue testing machine used to evaluate the lifespan of bearings, and the processing time is also short. It has been found that the lifespan of parts utilizing this knowledge is improved, leading to the completion of the present invention. Patent Document 1 does not disclose any of the above-mentioned knowledge. [Means for solving the problem]

[0006] In the present invention's method for manufacturing bearing components, rolling elements are pressed against the surface of the workpiece in a region where a load is applied during use as a bearing component, thereby reducing the gap between the nonmetallic inclusions and the matrix phase, and causing plastic deformation of the workpiece. Then, the plastically deformed workpiece is subjected to heat treatment to impart a Rockwell hardness of 58 HRC or higher.

[0007] In the bearing component manufactured by the manufacturing method described above, the equivalent strain in the surface region from the surface of the load-applied area to a predetermined depth is greater than the equivalent strain in the non-surface region, which is the region outside the surface. Regarding the distance between the non-metallic inclusions contained in the bearing component and the matrix phase of the bearing component, i.e., the size of the gap, the size of the gap in the surface region is smaller than the size of the gap in the non-surface region, i.e., the gap is reduced.

[0008] The aforementioned processing using rolling elements allows for the formation of grooves in the areas where loads are applied during the use of bearing components. These grooves are formed during the manufacturing process of bearing components by applying partial pressing with rolling elements, followed by predetermined finishing processes and heat treatments (quenching and tempering, carburizing, carbonitriding, high-frequency induction hardening, etc.) to achieve the required hardness. Depending on the predetermined finishing process (grinding, etc.), the grooves may disappear. Even in that case, areas within the surface layer where the gap between nonmetallic inclusions and the matrix phase is reduced remain.

[0009] As the rolling elements, spheres or rollers can be used. These rolling elements may be those actually used in bearing components. Furthermore, the rolling elements can be pressed against the workpiece with a machining surface pressure in the range of 3.5 GPa to 5.5 GPa.

[0010] The workpiece can be formed into a ring shape. In this case, the rolling elements can be rolled in a circumferential direction while making rolling contact with the workpiece. The hardness of the workpiece can be at least 99 HRB on the Rockwell hardness scale. If the hardness of the workpiece is higher than this, the effect of reducing the gap by machining with rolling elements will decrease. [Effects of the Invention]

[0011] According to the present invention, the gap between the non-metallic inclusion and the matrix phase in the region where a load is applied when used as a bearing component can be reduced, thereby improving the lifespan of the bearing component. [Brief explanation of the drawing]

[0012] [Figure 1] This is a flowchart illustrating the manufacturing method of bearing components. [Figure 2] This diagram illustrates a method for forming grooves in a roughly processed workpiece (grooving process). [Figure 3] This diagram illustrates the plastic deformation region and non-plastic deformation region that occur within the matrix during groove machining. [Figure 4]This is a top view of a test specimen in which Al2O3 particles and sintered material are embedded. [Figure 5] This figure shows a test specimen after applying tensile force to create gaps around the Al2O3 particles. [Figure 6] This is a diagram showing a test specimen with grooves formed on it. [Figure 7] The image shows a photograph of the region containing Al2O3 particles observed with an electron microscope in the example. [Figure 8] The comparative example is a photograph of the region containing Al2O3 particles observed with an electron microscope. [Modes for carrying out the invention]

[0013] This embodiment describes a method for manufacturing steel bearing components, specifically the process shown in Figure 1. Examples of steel used for bearing components include high-carbon chromium bearing steel materials specified in JIS G4805 (steel grades: SUJ2~5), carbon steel materials for machine structures specified in JIS G4051 (steel grades: S53C, SCr420, SCM420, SNCM220, SNCM420, SNCM815), and martensitic stainless steel bars specified in JIS G4303 (steel grades: SUS420J2, SUS440C, etc.).

[0014] In step S101 shown in Figure 1, a rough-machined part (workpiece described later) that will become the bearing component is prepared. The rough-machined part will undergo the processes described later in steps S102 to S104 to obtain the final bearing component. It is sufficient to obtain such a rough-machined part, and this can be prepared using known means.

[0015] For example, in the preparation of rough-machined products, an oxidation refining treatment of molten steel by an arc melting furnace or a converter in an electric furnace, a reduction refining treatment by a ladle furnace (LF), a reflux vacuum degassing treatment (RH treatment) by a reflux type vacuum degassing device (RH), a casting treatment of steel ingots by continuous casting or general ingot casting, and subsequent plastic processing are performed to manufacture steel materials of a predetermined shape. Here, as the plastic processing, hot rolling of steel ingots, hot forging, and subsequently, cold rolling, cold forging, and cold drawing may be performed. Further, examples of the shape of the steel material include bar steel, pipe material, and plain material.

[0016] Next, rough-machined products are formed by performing any one of hot forging, sub-hot forging, warm forging, cold forging, rolling forging, cold swaging, cold heading, drawing, or a combination thereof, or by performing heat treatment or turning for the purpose of softening or microstructure adjustment as necessary.

[0017] In step S102, using the rough-machined product prepared in the process of step S101 as the workpiece, a process of machining a groove (groove machining process) is performed on the workpiece. In this groove machining process, while pressing a rolling element against the surface of the rough-machined product (workpiece) with a predetermined load, the rolling element is rolled (in other words, pressed while rolling-contact with the rolling element), and the surface of the rough-machined product in contact with the rolling element is plastically deformed to form a groove. For example, on the same track, by rolling the rolling element while rolling-contact with the rough-machined product and orbiting in the circumferential direction of the rough-machined product, a groove having a desired shape can be formed along a predetermined track. The number of times the rolling element orbits may be once or a plurality of times.

[0018] By using a jig that enables rotation while holding the rolling elements, the rolling elements can be rolled while being pressed against the rough workpiece. As a jig for maintaining the rotation of the rolling elements, for example, a cage for a shaft can be used. Also, in order to prevent the test piece from rotating as the rolling elements rotate, a jig or mechanism for holding the test piece is necessary. Further, since the rolling elements roll between two objects, a member is also necessary that is disposed on the opposite side so as to sandwich the rolling elements together with the test piece to be processed. As a mechanism for sandwiching the rolling elements, for example, a mechanism for sandwiching the rolling elements vertically by an upper plate and a lower plate, or a mechanism for sandwiching the rolling elements between the inner ring and the outer ring of a bearing component can be used.

[0019] Also, in the mechanism for sandwiching the rolling elements vertically, when it is desired to perform groove processing on the rough workpiece used as the lower plate, if the hardness of the upper plate is low, when the rolling elements are rolled while being held by the cage, grooves due to the rolling elements are formed deeper in the upper plate, and the upper plate and the cage come into contact, and groove processing on the lower plate (rough workpiece) may no longer be able to continue. To avoid this, as the material of the upper plate, it is necessary to select a material harder than the lower plate (rough workpiece). Here, the hardness of the lower plate (rough workpiece) is not particularly limited. Also, in order to prevent seizure of the rough workpiece due to rolling, it is desirable to supply lubricating oil to the rolling part (the contact part of the rolling elements and the rough workpiece) during rolling. Since the groove processing itself is performed in a short time, the lubricating oil may be only applied to the rolling part in advance.

[0020] The groove may be formed in the region that receives the load generated during the use of the bearing component, and the position where the groove is formed can be determined in advance according to the position of the region that receives the load. Also, since the groove is formed by pressing while causing the rolling elements to rollingly contact, the shape of the groove becomes a shape along the outer shape of the rolling elements, and the width of the groove depends on the size of the rolling elements. Therefore, if the region that receives the load in the bearing component has been determined in advance, rolling elements of a size that can cover the width of this region can be used.

[0021] Spheres can be used as rolling elements. Rollers can also be used. When forming grooves, it is desirable to use multiple rolling elements to ensure stable groove formation. When using multiple rolling elements, all rolling elements should roll on the same track. The load applied to press the rolling elements against the rough workpiece (workpiece) should be a load that can form grooves in the rough workpiece; for example, a machining surface pressure within the range of 3.5 GPa to 5.5 GPa can be set. Note that as grooves are formed, the contact state between the rolling elements and the rough workpiece (workpiece) changes, and the machining surface pressure may decrease. However, it is sufficient to ensure the aforementioned machining surface pressure (3.5 GPa to 5.5 GPa) at the start of groove formation. The material used for the rolling elements should be a material that can form grooves in the rough workpiece (workpiece), and can be appropriately selected from known materials. Rolling elements used in bearing components may also be reused.

[0022] In this embodiment, the processing is performed by partial pressing of the rough workpiece (workpiece), and the processing load is relatively low, so cold processing is possible, and the following various advantages can be obtained.

[0023] First, when machining at a hot temperature, oil cannot be used to prevent ignition, which can result in seizing during groove formation. In contrast, cold machining allows for the use of lubricating oil during the process, thus preventing seizing. Furthermore, cold working allows for more efficient filling of the gap between non-metallic inclusions and the matrix phase compared to hot working. This is advantageous in that it improves the lifespan of bearing components by closing the gap. However, groove machining is not limited to cold working.

[0024] In the bearing component obtained by the manufacturing method of this embodiment, the equivalent strain in the surface region is greater than the equivalent strain in the non-surface region. This reduces the gap between the non-metallic inclusion and the matrix phase in the surface region, thereby improving the lifespan of the bearing component. Here, the surface region includes the surface of the groove formed by the groove machining process and extends from the groove surface to a predetermined depth. The predetermined depth can be 500 μm or less. According to the manufacturing method of this embodiment, the surface region can be formed in the region up to the predetermined depth described above. The non-surface region is the area inside the bearing component other than the surface region.

[0025] Furthermore, increasing the depth and equivalent strain of the surface region, and widening the groove, allows for a larger area of ​​gap closure. The depth and equivalent strain of this surface region, as well as the groove width, vary depending on the machining pressure and the hardness of the matrix (workpiece). When the workpiece hardness is the same and the machining pressure is increased, both the depth and equivalent strain of the surface region increase, and the groove width also widens. Conversely, when the machining pressure is the same and the workpiece hardness is increased, plastic deformation becomes less likely, both the depth and equivalent strain of the surface region decrease, and the groove width narrows. Also, if the machining pressure and the workpiece hardness are too high, the workpiece undergoes significant work hardening, making it more prone to cracking at the groove edges.

[0026] From the above, it is important to adjust not only the machining surface pressure mentioned earlier, but also the hardness of the workpiece. When forming grooves in a cold state, it is desirable that the hardness of the workpiece be at least 99 HRB on the Rockwell hardness scale. If the workpiece is harder than this, the effect of reducing the gap by machining with rolling elements will decrease. The hardness of the rolling elements used to form the grooves should be such that they are used as rolling elements in ordinary bearing components. For example, a Rockwell hardness of 58 HRC or higher is a guideline, and more preferably 60 HRC or higher. However, depending on the hardness of the rough workpiece, rolling elements with a hardness of 58 HRC or less can also be selected.

[0027] An example of the groove machining process described above will be explained using Figure 2. In Figure 2, a groove 11 is formed by pressing a spherical rolling element 20 against the upper surface of a ring-shaped rough workpiece 10 and rolling it in the direction of arrow D (circumferential direction of the rough workpiece 10). Three rolling elements 20 are used here, and the three rolling elements 20 roll on the same trajectory. In groove machining using rolling elements 20, for example, a device with a mechanism similar to that used in thrust-type rolling fatigue tests can be used for groove machining.

[0028] Figure 3 is a cross-sectional view showing the contact area between the rolling element 20 and the rough workpiece 10 in the example shown in Figure 2. The surface of the rough workpiece 10 undergoes plastic deformation due to the load F1 from the rolling element 20. Here, the region R1 shown in Figure 3 (the area indicated by hatching) is the region within the rough workpiece 10 that undergoes plastic deformation (hereinafter referred to as the "plastic deformation region"). The boundary BL shown in Figure 3 indicates the boundary between the plastic deformation region R1 and the region that does not undergo plastic deformation (hereinafter referred to as the "non-plastic deformation region") R2 within the rough workpiece 10. The plastic deformation region R1 corresponds to the surface region described above, and the non-plastic deformation region R2 corresponds to the non-surface region described above.

[0029] As shown in Figure 3, when the rolling element 20 is pressed against the rough workpiece 10, the plastic deformation region R1 receives a load F1 from the rolling element 20 and a restraining force F2 from the non-plastic deformation region R2. Here, as can be seen from Figure 3, the load F1 acts in multiple radial directions of the rolling element 20, and the restraining force F2 acts as a reaction force to the load F1. When such load F1 and restraining force F2 act on the plastic deformation region R1, if there is a gap between the non-metallic inclusion and the matrix in the plastic deformation region R1, the matrix is ​​deformed in a direction toward the non-metallic inclusion, making it easier to fill the gap.

[0030] In Patent Document 1, as described above, machining is performed by pressing the tool against the entire workpiece surface while moving the tool. This flattens minute irregularities across the entire workpiece surface. Patent Document 1 also presents machining of the entire workpiece surface using a forming roll and mandrel, assuming cold rolling. In contrast, in this embodiment, grooves are formed in a portion of the rough-machined workpiece that follow the outer shape of the rolling element. This eliminates the need to move the tool to machine the entire workpiece surface as in Patent Document 1, and the need to prepare forming rolls and mandrels for machining. It also allows for the reduction of gaps around non-metallic inclusions only in the area that will experience rolling fatigue when used as a bearing component. Furthermore, as described above, by placing the rolling element between the rough-machined workpiece (workpiece) and the opposing member (countering member), and applying a load to the rolling element through the countering member while performing groove machining, it becomes possible to perform simple machining without the need for special machining equipment or tools as in Patent Document 1. In these respects, this embodiment differs from Patent Document 1. The differences from Patent Document 1 will be explained in more detail below.

[0031] In this embodiment, by forming grooves along the outer shape of the rolling elements, it becomes easier to apply load F1 and restraining force F2 to the plastic deformation region R1, as shown in Figure 3. As a result, it becomes easier to fill the gaps present in the plastic deformation region R1, and to fill the gaps throughout the groove 11. On the other hand, in Patent Document 1, although the pressing portion is pressed against the workpiece surface, the purpose is to flatten minute irregularities on the workpiece surface. Therefore, compared to the case where grooves are formed as in this embodiment, it becomes more difficult to form the plastic deformation region R1 shown in Figure 3, and it becomes more difficult to apply load F1 and restraining force F2 to the plastic deformation region R1. Accordingly, according to this embodiment, it becomes easier to efficiently fill the gaps present around the nonmetallic inclusions compared to Patent Document 1.

[0032] Fatigue cracks in bearing components are thought to occur near the depth from the raceway surface where the Hertzian contact stress is maximum (200 μm or less for typical bearing components), just below the raceway surface of the bearing component. The plastic deformation region R1 of the above-described embodiment can be formed to cover at least the range in which fatigue cracks occur, so that the gaps present in the plastic deformation region R1 are filled, thereby eliminating the gaps around non-metallic inclusions that cause fatigue cracks and improving the lifespan of the bearing component.

[0033] When the groove machining process described above is performed, a raised area may form around the groove 11. In this case, the raised area can be removed by grinding. Alternatively, the surface of the groove 11 may be smoothed by polishing. Also, as described above, depending on the predetermined finishing process (such as grinding), the groove 11 may disappear. These processes can be performed between steps S102 and S103 in Figure 1. Furthermore, if the amount of grinding or polishing is small, this grinding or polishing may be combined with the process in step S104 described later.

[0034] Returning to Figure 1, in step S103, the rough-machined part (workpiece) that has undergone groove machining is subjected to heat treatment. This heat treatment is performed to give the rough-machined part (workpiece) a predetermined hardness, and examples include quenching and tempering such as full quenching (deep quenching and tempering), carburizing and quenching and tempering, carburizing and nitriding and quenching and tempering, carburizing and nitriding and quenching and tempering, high-frequency induction quenching and tempering, and nitriding treatment. Here, the predetermined hardness is preferably 58 HRC or higher on the Rockwell hardness scale, and more preferably 60 HRC or higher. When using a surface hardening method among the heat treatment methods described above, the hardness mentioned above refers to the hardness near the surface of the part.

[0035] In step S104, the rough-machined part (workpiece) that has undergone heat treatment (S103) is subjected to finishing and raceway surface polishing. The final bearing component can be obtained by finishing the rough-machined part (workpiece) and smoothing the raceway surface through polishing. [Examples]

[0036] Steel with the chemical composition shown in Table 1 below, and the remainder consisting of Fe and unavoidable impurities, was prepared. This steel type is SUJ2 as specified in JIS G4805.

[0037] [Table 1]

[0038] The SUJ2 steel mentioned above was melted in an arc melting furnace, then reduced in a ladle refining furnace to remove impurities and excess oxygen. Further oxygen reduction was achieved through reflux vacuum degassing. Next, a steel ingot was produced by continuous casting, and a steel bar with a diameter of φ65 mm was produced by hot rolling of the steel ingot. The steel bar was then subjected to normalizing by holding it at 900°C for 1.5 hours and then air-cooling, followed by spheroidizing annealing by heating it to a maximum temperature of 800°C and then slowly cooling it. From this steel bar, a ring-shaped test piece 100 (see Figure 4) was produced.

[0039] Here, the outer diameter of test piece 100 is 54 mm, and the inner diameter is 29 mm. The steelmaking process shown here is an example of a manufacturing method when SUJ2 steel is produced in an electric furnace, and the heat treatment method shown is a general pretreatment for processing SUJ2 steel. These methods should be appropriately selected according to the manufacturing method of the bearing component and the type of steel. The size of test piece 100 is merely the shape used to confirm the effect in this embodiment, and therefore the present invention is not particularly dependent on the shape of test piece 100.

[0040] Next, a drill hole 101 with a diameter of 4.5 mm and a depth of 6 mm (see Figure 4) was machined into one side of the test piece 100 (which was designated as the top surface) using a micro-drill. Multiple artificial spherical Al2O3 particles 102, which simulate non-metallic inclusions, were prepared, and a sintered material 103 (hereinafter referred to as "sintered material") made by mixing these particles with powder having the same composition as the main components of the steel described above was embedded in the drill hole 101. The diameter of the Al2O3 particles 102 was approximately 150 μm, and the gaps formed between the drill hole 101 and the multiple Al2O3 particles 102 were filled with the sintered material 103.

[0041] The reason for preparing a sintered material 103 containing multiple Al2O3 particles 102 that simulate nonmetallic inclusions will now be explained. The steel produced in the above steelmaking process has high cleanliness with respect to nonmetallic inclusions, that is, the frequency of nonmetallic inclusions is low, making it difficult to easily confirm the effect of reducing the gaps around nonmetallic inclusions in this invention. To facilitate this confirmation, the aforementioned sintered material 103 was prepared.

[0042] After filling the drill hole 101 with sintered material 103 containing Al2O3 particles 102, the sintered material 103 containing Al2O3 particles 102 was pressed into contact with the matrix of the test piece 100 by HIP (Hot Isostatic Pressing). Specifically, when performing HIP processing, first, the sintered material 103 filling the drill hole 101 is secured to prevent it from coming loose as needed, the test piece 100 is placed in a low-carbon steel container, a mandrel is inserted into the inner diameter hole formed in the test piece 100, and then the container is sealed. After vacuuming the inside of the container, it is held at a predetermined pressure (e.g., 147 MPa) and a predetermined temperature (e.g., 1170°C) for a predetermined time (e.g., 5 hours) and then slowly cooled, thereby pressing the Al2O3 particles 102 and sintered material 103 into contact with the matrix of the test piece 100.

[0043] After the HIP (Heat Ion Pressing) process, normalizing and spheroidizing annealing were performed using the same method as described above. Turning was then performed to remove the container holding the test piece 100, and the test piece 100 was reshaped and polished.

[0044] Next, a tensile force was applied to the test specimen 100 in a predetermined direction using a tensile testing machine. As a result, the test specimen 100 deformed as shown in Figure 5, and this deformation formed a gap S around the Al2O3 particles 102. This gap S simulates the gap that may exist around non-metallic inclusions in bearing components, and in this embodiment, the gap S was intentionally formed.

[0045] Next, a test specimen (Example) 100 was prepared in which groove processing was performed according to the method of the present invention on the test specimen 100 shown in Figure 5, and a test specimen (Comparative Example) 100 was prepared in which groove processing was not performed according to the method of the present invention on the test specimen 100 shown in Figure 5. In this case, since groove processing was not performed on the test specimen (Comparative Example) 100, gaps S remain formed around the Al2O3 particles 102.

[0046] In the grooving process, grooves 104 were formed on the surface of the test piece 100 in areas where Al2O3 particles 102 with gaps S were embedded to a depth of approximately 50-300 μm from the surface, as shown in Figure 6. The grooves 104 are formed along the circumferential direction of the ring-shaped test piece 100 and are also formed on circular tracks. In the example shown in Figure 6, the grooves 104 are formed in positions that overlap with some of the Al2O3 particles 102 within the aforementioned depth range. However, the width of the grooves 104 depends on the size of the rolling elements and the machining pressure during the grooving process, so depending on the selection, it is also possible to form grooves 104 in positions that overlap with all of the Al2O3 particles 102. In the grooving process of the embodiment, spherical rolling elements made of quenched and tempered SUJ2 steel with a diameter of 9.525 mm were used, and the rolling elements were pressed against the test piece 100 with machining pressures of 4.0 GPa and 4.5 GPa, respectively, and grooves 104 were formed by rotating the rolling elements in the circumferential direction. The width of groove 104 is approximately 2.5 mm, and the depth of groove 104 is approximately 170 μm.

[0047] For the example and comparative example test pieces 100, the grooved surface was polished in the depth direction until the vicinity of the maximum diameter of the Al2O3 particles was exposed. Then, the Al2O3 particles 102 were observed using an optical microscope from directly above the groove 104 (i.e., from the direction in which the grooved surface could be observed). The observed test piece 100 was formed by pressing rolling elements against the test piece 100 with a machining surface pressure of 4.5 GPa. For the example test piece 100, as shown in Figure 7, it was confirmed that there were no gaps S around the Al2O3 particles 102, and that the gaps S were filled. On the other hand, for the comparative example test piece 100, as shown in Figure 8, it was confirmed that gaps S remained around the Al2O3 particles 102.

[0048] Next, for the test piece 100 of the example, which was prepared separately using the same method as described above, the grooves 104 formed by pressing the rolling elements were removed by polishing in order to smooth the surface of the grooved surface. At this time, although the grooves 104 were removed by polishing, the area where the gaps around the inclusions were filled during the groove machining process remained. Next, bearing parts with a hardness (Rockwell hardness) of 58 HRC or higher were manufactured by performing quenching and tempering treatment on the test piece 100 of the example and comparative example. Dislocations introduced into the microstructure of the steel due to the equivalent strain applied during the groove machining process are eliminated through recovery and recrystallization during this heat treatment process, but the effect of reducing the gaps around nonmetallic inclusions is maintained even after heat treatment. A more desirable hardness for bearing parts is 60 HRC or higher.

[0049] A thrust-type rolling fatigue test was performed on the bearing components described above. In the thrust-type rolling fatigue test, a race (model number 51305) of a single thrust bearing made of SUJ2 was used as the upper plate, and test piece 100 was used as the lower plate. Between the upper and lower plates, three rolling elements were placed at equal intervals (120° pitch) on a circular track with a diameter of 38.5 mm using a cage. Here, steel balls made of SUJ2 with a diameter of 9.525 mm were used as rolling elements. For test piece 100, which is the embodiment, the rolling elements (steel balls) were positioned so as to overlap with the location where the groove 104 was formed on the circumference and the position of the Al2O3 particles embedded below it. For test piece 100, which is the comparative example, the rolling elements (steel balls) were positioned so as to overlap with the location where the Al2O3 particles 102 were embedded.

[0050] For the thrust-type rolling fatigue test, a load was applied to the rolling elements (steel balls) such that a maximum Hertz contact stress of 5.3 GPa was applied to 100 test specimens (example / comparative example). The load cycle speed was set to 1800 cycles / min, and the specimens were immersed in an ISO VG68 oil bath for lubrication. This thrust-type rolling fatigue test was performed at room temperature.

[0051] Based on the results of the thrust-type rolling fatigue test described above, the total number of rotations until delamination occurs in 10% of the test specimens 100 from the short-life side was determined based on the Weibull distribution function, and this was calculated as L 10 Lifespan was defined as the lifespan. Comparative example L 10 L in the examples and comparative examples when the lifespan is indexed to 1.0 10 The lifespan is shown in Table 2 below.

[0052] [Table 2]

[0053] As shown in Table 2 above, according to the example, L is greater than in the comparative example. 10 Lifespan improved. As shown in Figures 7 and 8, in the embodiment, no gap S remained around the nonmetallic inclusion, so the lifespan was longer than in the comparative example where the gap S was present. 10It can be seen that life expectancy has improved. [Explanation of Symbols]

[0054] 10: Roughly machined part, 11: Groove, 20: Rolling element, 100: Test piece, 101: Drill hole, 102: Al2O3 particles, 103: Sintered material, 104: Grooves

Claims

1. On the surface of the workpiece, within the area where a load is applied when used as a bearing component, a spherical rolling element is pressed against the workpiece with a processing pressure in the range of 4.0 GPa to 4.5 GPa while rolling contact is made, thereby plastically deforming the workpiece and forming grooves along the outer shape of the rolling element. A method for manufacturing bearing components, characterized by performing a heat treatment on the workpiece after plastic deformation to impart a Rockwell hardness of 58 HRC or higher.

2. The workpiece is formed in a ring shape, The method for manufacturing a bearing component according to claim 1, characterized in that the groove is formed by rotating the rolling elements in a circular motion while they are in contact with the workpiece in the circumferential direction.

3. The method for manufacturing a bearing component according to claim 1 or 2, characterized in that the hardness of the workpiece is at least 99 HRB on the Rockwell hardness scale.

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