Method for manufacturing track members, method for manufacturing balls, and method for manufacturing rollers

Abstract

This manufacturing method for a raceway member having a raceway on which rolling elements roll comprises: a forging step for forging a metallic raw material, which includes a nonmetallic inclusion having a circle equivalent diameter of 2 μm or more, to obtain a forged member; a machining step for machining the forged member to obtain a machined member having a portion serving as a raceway; a determination step for examining the presence or absence of a nonmetallic inclusion having a predetermined size in a range to a first depth from directly below the surface of the machined member constituting a rolling surface, and for identifying a portion where the nonmetallic inclusion having the predetermined size is present; and a heat treatment step for heat-treating at least an entire surface portion constituting the rolling surface, in the surface of the determined member having undergone the determination step, to obtain a heat-treated member. When the presence of the nonmetallic inclusion having the predetermined size is confirmed in the determination step, a melting / solidifying step, in which a portion of the machined member including the confirmed nonmetallic inclusion is melted and then the melted raceway member is solidified, is performed before the heat treatment step.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a raceway member, a method for manufacturing balls, and a method for manufacturing rollers.

Background Art

[0002] Bearing materials used in rolling bearings and the like are required to have a long rolling fatigue life. The rolling fatigue life of a bearing is affected by non-metallic inclusions present in the material. Also, the larger the size of the non-metallic inclusions, the more likely internal-origin peeling, which affects the rolling fatigue life of the bearing, will occur.

[0003] Patent Document 1 proposes a bearing material having a specific composition in which S and O, which are non-metallic inclusion forming elements, are S: 0.025 mass% or less and O: 0.0012 mass% or less, respectively.

[0004] Patent Document 2 proposes a rolling bearing member made of low-purity steel in order to suppress the occurrence of internal-origin peeling caused by non-metallic inclusions and achieve a long life of the rolling bearing member, and the non-metallic inclusions present in the surface layer portion of the rolling surface of the rolling bearing member are crushed and reduced in diameter.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] A method for manufacturing a raceway member according to one aspect of the present disclosure is a method for manufacturing a raceway member having a raceway on which rolling elements roll, a forging step of forging a metal material containing non-metallic inclusions having an equivalent circle diameter of 2 μm or more into a forged member, A turning process in which the above-mentioned forged member is turned to obtain a turned member having a portion that will serve as a raceway, A determination step to investigate the presence or absence of non-metallic inclusions of a predetermined size in the range up to a first depth directly below the surface forming the turning surface of the turned member, and to identify the portion in which the non-metallic inclusions of the predetermined size exist. A heat treatment step in which, of the surfaces of the determined member after the above determination step, at least all of the surfaces that form the rolling surface are heat-treated to make it a heat-treated member, Equipped with, If the presence of a non-metallic inclusion of a predetermined size is confirmed in the above determination process, a portion of the turned member containing the confirmed non-metallic inclusion is melted before the above heat treatment process, and then a melting and solidification process is performed to solidify the melted material.

[0007] A method for manufacturing a ball according to one aspect of this disclosure is: A forging process in which a metallic material containing non-metallic inclusions with an equivalent circular diameter of 2 μm or more is forged to form a spherical forged member. A first grinding step in which the surface of the forged member is ground to obtain a first ground member, A determination step to investigate the presence or absence of non-metallic inclusions of a predetermined size in the range up to a third depth directly below the surface forming the rolling surface of the ground member, and to identify the portion where the non-metallic inclusions of the predetermined size are present. A heat treatment step in which the entire surface of the determined member after the above determination step is made into a heat-treated member, and A second grinding step in which the surface of a heat-treated member is ground to produce a second ground member, Equipped with, If the presence of non-metallic inclusions of a predetermined size is confirmed in the above determination process, a portion of the ground member containing the confirmed non-metallic inclusions is melted before the above heat treatment process, and then a melting and solidification process is performed to solidify the melted material.

[0008] A roller manufacturing method relating to one aspect of this disclosure is: A forging process in which a metallic material containing non-metallic inclusions with an equivalent circular diameter of 2 μm or more is forged to form a roller-shaped forged component. A first grinding step in which at least the circumferential surface of the forged member is ground to obtain a first ground member, A determination step to investigate the presence or absence of non-metallic inclusions of a predetermined size in the range up to a fourth depth directly below the surface forming the rolling surface of the ground member, and to identify the portion where the non-metallic inclusions of the predetermined size are present. A heat treatment step in which the entire surface of the determined member after the above determination step is made into a heat-treated member, and A second grinding step in which the surface of a heat-treated member is ground to produce a second ground member, Equipped with, If the presence of non-metallic inclusions of a predetermined size is confirmed in the above determination process, a portion of the ground member containing the confirmed non-metallic inclusions is melted before the above heat treatment process, and then a melting and solidification process is performed to solidify the melted material. [Brief explanation of the drawing]

[0009] [Figure 1] This is a process diagram illustrating a method for manufacturing a track member according to one embodiment of the present disclosure. [Figure 2] This is a process diagram illustrating the manufacturing methods used in the examples and comparative examples. [Modes for carrying out the invention]

[0010] <Problems that the present invention aims to solve> According to the inventions of Patent Documents 1 and 2, the lifespan of rolling bearing members can be extended. On the other hand, the invention described in Patent Document 1 aims to reduce non-metallic inclusions throughout the entire bearing member, making it expensive as a bearing material. Therefore, it was difficult to provide rolling bearing members at a low cost when using the bearing material described in Patent Document 1.

[0011] When implementing the invention of Patent Document 2, it is possible to reduce the size of non-metallic inclusions with a particle size of 30 μm or more to about 20 μm in maximum diameter. However, even when implementing the invention of Patent Document 2, it was difficult to further refine non-metallic inclusions with a smaller particle size.

[0012] <Effects of the Invention of the Present Disclosure> According to the invention of the present disclosure, it is possible to manufacture a raceway member, a ball, and a roller in which internal-origin peeling is unlikely to occur.

[0013] <Outline of Embodiments of the Invention of the Present Disclosure> Under such circumstances, the present inventors have found a new method for manufacturing a rolling bearing member in which internal-origin peeling is unlikely to occur, and have completed the invention of the present disclosure. Hereinafter, an outline of embodiments of the invention of the present disclosure will be listed and described.

[0014] (1) The method for manufacturing a raceway member of the present disclosure is a method for manufacturing a raceway member having a raceway on which rolling elements roll, a forging step of forging a metal material containing non-metallic inclusions having an equivalent circle diameter of 2 μm or more into a forged member, a turning step of turning the forged member into a turned member having a portion that will become a raceway, a determination step of investigating the presence or absence of non-metallic inclusions of a predetermined size in a range up to a first depth directly below the surface forming the rolling surface of the turned member, and specifying a portion where the non-metallic inclusions of the predetermined size are present, a heat treatment step of heat-treating at least all of the surfaces of the determined member after the determination step that form the rolling surface to obtain a heat-treated member, comprising When the presence of non-metallic inclusions of a predetermined size is confirmed in the determination step, before performing the heat treatment step, a part of the turned member including the confirmed non-metallic inclusions is melted, and then a melting and solidification step of solidifying the melted material is performed.

[0015] According to the method for manufacturing a raceway member of this disclosure, non-metallic inclusions located directly beneath the rolling surface are refined, making it possible to manufacture a raceway member for a rolling bearing that is less prone to internal delamination. Furthermore, since the above manufacturing method selectively refines only the predetermined non-metallic inclusions whose presence has been confirmed in advance, it does not consume excess energy and is a manufacturing method with low CO2 emissions.

[0016] (2) The method for manufacturing the track member further comprises a surface treatment step performed after the heat treatment step, In the above surface treatment step, it is preferable to remove at least a portion of the surface forming the rolling surface of the heat-treated member from the surface to a second depth to obtain a surface-treated member. (3) In the above surface processing step, grinding and / or cutting steps are preferably performed.

[0017] (4) The method for manufacturing a ball according to the present disclosure includes a forging step of forging a metal material containing nonmetallic inclusions with an equivalent diameter of 2 μm or more to form a spherical forged member, A first grinding step in which the surface of the forged member is ground to obtain a first ground member, A determination step to investigate the presence or absence of non-metallic inclusions of a predetermined size in the range up to a third depth directly below the surface forming the rolling surface of the ground member, and to identify the portion where the non-metallic inclusions of the predetermined size are present. A heat treatment step in which the entire surface of the determined member after the above determination step is made into a heat-treated member, and A second grinding step in which the surface of a heat-treated member is ground to produce a second ground member, Equipped with, If the presence of non-metallic inclusions of a predetermined size is confirmed in the above determination process, a portion of the ground member containing the confirmed non-metallic inclusions is melted before the above heat treatment process, and then a melting and solidification process is performed to solidify the melted material.

[0018] According to the ball manufacturing method of this disclosure, non-metallic inclusions present near the surface are refined, and bearing balls that are less prone to internal delamination can be manufactured. Furthermore, since the above manufacturing method selectively refines only the predetermined non-metallic inclusions whose presence has been confirmed in advance, it does not consume excess energy and is a manufacturing method with low CO2 emissions.

[0019] (5) The manufacturing method described herein is A forging process in which a metallic material containing non-metallic inclusions with an equivalent circular diameter of 2 μm or more is forged to form a roller-shaped forged component. A first grinding step in which at least the circumferential surface of the forged member is ground to obtain a first ground member, A determination step to investigate the presence or absence of non-metallic inclusions of a predetermined size in the range up to a fourth depth directly below the surface forming the rolling surface of the ground member, and to identify the portion where the non-metallic inclusions of the predetermined size are present. A heat treatment step in which the entire surface of the determined member after the above determination step is made into a heat-treated member, and A second grinding step in which the surface of a heat-treated member is ground to produce a second ground member, Equipped with If the presence of non-metallic inclusions of a predetermined size is confirmed in the above determination process, a portion of the ground member containing the confirmed non-metallic inclusions is melted before the above heat treatment process, and then a melting and solidification process is performed to solidify the melted material.

[0020] According to the roller manufacturing method of this disclosure, non-metallic inclusions located directly beneath the rolling surface (circumferential surface of the roller) are refined, making it possible to manufacture bearing rollers that are less prone to internal origin delamination. Furthermore, since the above manufacturing method selectively refines only the predetermined non-metallic inclusions whose presence has been confirmed in advance, it does not consume excess energy and is a manufacturing method with low CO2 emissions.

[0021] <Details of Embodiments of the Invention Disclosed> Embodiments of the invention described herein will be described below. (First Embodiment) Figure 1 is a process diagram illustrating the manufacturing method of a track member according to this embodiment. Figure 1 illustrates the manufacturing method of the inner ring of a ball bearing as a method for manufacturing a track member having a track on which rolling elements run. The above method for manufacturing the inner ring is: The following steps are performed in this order: (a) forging, (b) turning, (c) judgment, (d) melting and solidification, (e) heat treatment, and (f) surface treatment. Except for the judgment step (c) and the melting and solidification step (d), known methods used in the manufacture of inner rings can be applied. The following explains each step in order.

[0022] (a) Forging process: In this process (a), the annular material A is manufactured by forging a metallic material containing nonmetallic inclusions with an equivalent circular diameter of 2 μm or more. Examples of the above-mentioned metallic materials include steel materials in which the evaluation results of inclusions satisfy the parameters shown in Table 1 below, in measurements compliant with JIS G0555 (2003): Microscopic testing method for non-metallic inclusions in steel by point counting. [Table 1]

[0023] As for the metallic materials mentioned above, for example, steel materials whose inclusion evaluation results in measurements compliant with the ASTM E45 A method satisfy the parameters shown in Table 2 below can also be cited. [Table 2]

[0024] Steel materials that satisfy these parameters contain non-metallic inclusions with an equivalent circular diameter of 2 μm or larger. Furthermore, even steel materials that satisfy the parameters mentioned above may contain larger non-metallic inclusions with an equivalent circular diameter of 30 μm or more. Such non-metallic inclusions with an equivalent circular diameter of 30 μm or more tend to become the starting points for internal origin isolation.

[0025] The measurement of nonmetallic inclusions using methods compliant with JIS G0555 (2003) or ASTM E45 A, as described above, can be performed using commercially available nonmetallic inclusion measuring devices (for example, METALSPECTOR II-C manufactured by Toshiba Digital Solutions Corporation).

[0026] Examples of the above-mentioned metallic materials include carbon steels for machine structures such as S45C and S55C, high-carbon chromium bearing steels such as SUJ2, and alloy steels such as SAE5120 and SC420. These steels typically contain non-metallic inclusions with an equivalent circular diameter of 2 μm or more.

[0027] In the embodiments of this disclosure, whether or not the material (steel) contains nonmetallic inclusions with an equivalent circular diameter of 2 μm or more is determined by observing the cross-section of the material before forging and determining whether or not the equivalent circular diameter of the largest nonmetallic inclusion within the observation area is 2 μm or more. The above-mentioned equivalent circle diameter, also known as the Haywood diameter, refers to the diameter of a perfect circle that corresponds to the area of ​​the observed nonmetallic inclusion. In this process, spheroidizing annealing may be performed after forging.

[0028] (b) Turning process: In step (b), the outer circumference of the forged annular material A is turned to produce an annular material B having a portion that forms a raceway, including a surface 11a that forms the racing surface 1a. The annular material B is created by machining the end face 11b, outer circumference 11c, inner circumference 11d, etc. of the annular material A to a predetermined shape as needed, through grinding or other processes. Here, the surface 11a that forms the rolling surface 1a is the part that will be formed after subsequent melting and solidification processes and surface processing processes such as grinding. Typically, the surface 11a that forms the rolling surface 1a in this process is removed in a later process, and the part that was located directly below the surface 11a that forms the rolling surface 1a is exposed and becomes the rolling surface 1a. Furthermore, the parts that will become the track are the parts that will be formed through subsequent melting and solidification processes, as well as surface processing processes such as grinding.

[0029] (c) Judgment process: In this step (c), the area directly beneath the surface 11a that forms the rolling surface 1a of the annular material B is investigated to determine whether there are any nonmetallic inclusions of a predetermined size (for example, 30 μm or more in terms of equivalent circular diameter), and if they are present, their location is identified. In this embodiment, after identifying a portion containing nonmetallic inclusions of a predetermined size, a laser beam is selectively irradiated onto the identified portion to melt the portion containing the metallic inclusions, and then the melted annular material B is solidified. In this embodiment, the predetermined size of the nonmetallic inclusion can be set appropriately according to the required characteristics of the inner ring to be manufactured, and is not limited to 30 μm or more in terms of equivalent circular diameter. For example, the predetermined size of the nonmetallic inclusion may be 2 μm or more in terms of equivalent circular diameter.

[0030] In step (c), the depth from the surface 11a that forms the rolling surface 1a for investigating the presence or absence of nonmetallic inclusions of a predetermined size (first depth) can be determined by considering the depth at which the maximum shear stress of the completed inner ring occurs. The shear stress on the inner ring, generated by the rolling of the rolling elements, increases steadily from the rolling surface in the depth direction, reaching a maximum value at a certain depth, and then gradually decreasing in the depth direction from there. This depth at which the maximum shear stress is observed is called the depth at which the maximum shear stress occurs.

[0031] Furthermore, if the surface 11a forming the rolling surface 1a is removed by grinding or the like in a subsequent process, the first depth used to investigate the presence or absence of non-metallic inclusions should be determined taking into consideration the depth of this removed portion. Taking these factors into consideration, the first depth used to investigate the presence or absence of nonmetallic inclusions of a predetermined size is preferably the sum of the depth to which 90% of the maximum shear stress occurs and the depth to which the inclusions are removed in a subsequent process. If the presence of non-metallic inclusions of a predetermined size is confirmed to exist up to this depth directly below the surface 11a that forms the rolling surface 1a, the occurrence of internal source delamination can be suppressed by the refinement of the confirmed non-metallic inclusions.

[0032] The depth at which 90% of the maximum shear stress occurs is located at two points: one shallower and one deeper than the depth at which the maximum shear stress occurs. The preferred depth mentioned above, which is the sum of the depth at which 90% of the maximum shear stress occurs and the depth removed in the subsequent process, is intended to be the sum of the deeper of the two depths at which 90% of the maximum shear stress occurs and the depth removed in the subsequent process. In this specification, "the depth at which 90% of the maximum shear stress occurs" refers to the deeper of the two depths at which 90% of the maximum shear stress occurs, unless otherwise specified.

[0033] In this step, the presence or absence of nonmetallic inclusions of a predetermined size is investigated in the range from the surface 11a forming the rolling surface 1a to a first depth. In this step, the presence or absence of nonmetallic inclusions may be investigated in the entire range from the surface 11a forming the rolling surface 1a to the first depth, or it may be investigated in only a part of the range. When investigating only a portion of the area, for example, the investigation of the region close to the surface 11a that forms the rolling surface 1a (for example, the region 100 μm from the surface) can be omitted, and the investigation of the remaining region on the first depth side can be performed.

[0034] In step (c), a method such as ultrasonic testing can be used to identify areas where non-metallic inclusions of a predetermined size are present. As the ultrasonic testing method described above, for example, the pulsed reflection method can be used, and this pulsed reflection method may be the vertical testing method, the oblique testing method, or the phased array method. In the ultrasonic testing method described above, the ultrasonic frequency used can be, for example, 25 to 125 MHz. The investigation of non-metallic inclusions using the ultrasonic testing method described above can be performed using an ultrasonic testing device 20 (for example, HIS3 HF manufactured by KJTD).

[0035] In the method for manufacturing the track member according to this embodiment, (d) a determination step is performed to identify the portion containing nonmetallic inclusions of a predetermined size before the melting and solidification step, and the portion containing nonmetallic inclusions of a predetermined size is selectively melted, so that nonmetallic inclusions that can cause internal source delamination can be efficiently reduced in size. Furthermore, because the laser light is selectively irradiated only where needed, it can significantly contribute to reducing CO2 emissions during the manufacturing process.

[0036] When this process (c) is performed, there are cases in which areas containing nonmetallic inclusions of a predetermined size are identified, and cases in which nonmetallic inclusions of a predetermined size are not detected. Then, if a portion containing nonmetallic inclusions of a predetermined size is identified, the (d) melting and solidification process is performed on the identified portion. On the other hand, if no nonmetallic inclusions of a predetermined size are detected, the (d) melting and solidification process is omitted, and the (e) heat treatment process is performed immediately afterward.

[0037] (d) Melting and solidification process: In step (d), at least a portion of the raceway portion of the annular material B, which is a turned member, is melted. Specifically, the portion containing a nonmetallic inclusion of a predetermined size, which was identified in step (c) above, is melted. When a portion of the surface of the annular material B is irradiated with laser light, the surface layer up to a predetermined depth, including the surface irradiated with laser light, is melted. The portion melted by the laser light is cooled and solidified when the laser irradiation is stopped or the point of laser irradiation is moved.

[0038] According to step (d), since it is sufficient for the portion containing the nonmetallic inclusions to be melted, if the nonmetallic inclusions are located near the surface of the portion that forms the orbit, only the shallow portion near the surface needs to be melted. If the nonmetallic inclusions are located in a deeper portion away from the surface of the portion that forms the orbit, it is necessary to melt the deeper portion away from the surface as well. Therefore, in step (d), the depth of the melted portion may be adjusted depending on the location of the nonmetallic inclusions. In other words, the laser irradiation conditions may be changed depending on the location of the nonmetallic inclusions.

[0039] However, frequently changing the laser irradiation conditions to alter the depth of the melted portion can lead to decreased productivity. Therefore, it is preferable to irradiate the same annular material B under the same conditions. In this case, it is preferable to irradiate the material with laser light under conditions that allow melting to at least the first depth mentioned above. On the other hand, the maximum depth of the melted portion is not particularly limited, as long as the melted portion does not penetrate to the inner circumference 11d of the annular material B.

[0040] The depth of the melted portion should be determined by considering the depth at which the maximum shear stress occurs in the completed inner ring. It is preferable that the depth be greater than or equal to the sum of the depth at which 90% of the maximum shear stress occurs and the depth removed in a subsequent process (preferably the first depth). The depth of the melted portion is preferably about 120-200% of the sum of the depth at which 90% of the maximum shear stress occurs and the depth to which the material is removed in a subsequent process. The preferred depth for the melted portion cannot be generalized, as it depends on the depth at which maximum shear stress occurs and the depth to be removed in the finishing process, but it is usually around 300 to 2000 μm.

[0041] In this step (d), nonmetallic inclusions that were present in the part to be melted before melting are refined. While it's difficult to generalize as it depends on the type of nonmetallic inclusion and the melting and solidification conditions, nonmetallic inclusions with an equivalent circular diameter of approximately 30-60 μm can, for example, be refined to an equivalent circular diameter of approximately 0.1-1.0 μm.

[0042] The laser 10 used in this process can be any laser capable of melting nonmetallic inclusions. Specifically, it is preferable that the laser beam irradiation area be heated to 2500°C or higher. Specific examples of laser 10 include, for instance, YAG lasers, YVO lasers, semiconductor lasers, and fiber lasers.

[0043] In this process, by scanning the laser beam and changing the irradiation position of the laser beam over time, the melting and solidification of the steel material can be performed continuously. Furthermore, by adjusting the output and movement speed of the laser beam, the depth of the melted area and the cooling rate after melting can be adjusted. Specifically, the depth of the melted area can be increased by increasing the output of the laser beam or decreasing the movement speed of the laser 10. On the other hand, the cooling rate can be increased by increasing the movement speed of the laser 10.

[0044] In this process, the cooling rate of the molten portion is preferably such that the cooling rate of the surface of the molten portion is 1200 to 10000°C / sec. This cooling rate is suitable for the refinement of non-metallic inclusions. The above cooling rate can be calculated based on the temperature change measured using a thermometer with sufficient time resolution, such as a radiation thermometer.

[0045] After this process is completed, in the area directly below the surface 11a forming the rolling surface 1a, up to the sum of the depth to which 90% of the maximum shear stress occurs and the depth to be removed in a subsequent process, there are no non-metallic inclusions with an equivalent circular diameter of 30 μm or more, or only small amounts are present. In this case, internal source delamination is suppressed over a long period of time.

[0046] (e) Heat treatment process: In step (e), the intermediate material C, in which nonmetallic inclusions have been refined through the melting and solidification process, or the annular material B, in which no nonmetallic inclusions were detected and therefore the melting and solidification process was omitted, is subjected to heat treatment to produce the intermediate material D, which is a heat-treated component. As the above heat treatment, for example, quenching and tempering may be performed. Alternatively, as the above heat treatment, carburizing or carbonitriding may be performed. Examples of the above-mentioned hardening methods include through hardening, high-frequency induction hardening, and flame hardening. Furthermore, the above-mentioned hardening may be whole hardening or partial hardening. The above-mentioned partial hardening is performed on at least the entire surface 11a that forms the rolling surface 1a formed on the annular material B or intermediate material C.

[0047] (f) Surface processing process: In step (f), the surface 11a that forms the rolling surface 1a of the heat-treated intermediate material D is surface-processed to form an inner ring E having a rolling surface 1a finished to a predetermined precision. Furthermore, in this process, it is preferable that the surface 11a forming the rolling surface 1a is machined, as well as the end face and inner circumference of the intermediate material D, to obtain an inner ring E having an end face 1b and inner circumference 1d finished to a predetermined precision. In this process (f), surface treatment can be performed by, for example, grinding or cutting.

[0048] In step (f), the surface 11a forming the rolling surface 1a of the intermediate material D is removed to a predetermined depth (second depth). At this time, the depth to be removed is set such that the depth of the portion that melted and solidified in the melting and solidification step remaining after removal (or the depth at which no predetermined nonmetallic inclusions were found in the determination step) is greater than or equal to the depth at which a stress of 90% of the maximum shear stress occurs. Therefore, in step (c) described above, the preferred depth for investigating the presence or absence of nonmetallic inclusions is the sum of the depth to which 90% of the maximum shear stress occurs and the depth to which the inclusions are removed in a subsequent step.

[0049] By performing these steps (a) to (f), the inner ring of a rolling bearing can be manufactured. In the inner ring manufactured in this embodiment, there are no non-metallic inclusions with a particle size of 30 μm or larger in equivalent diameter up to the depth where 90% of the maximum shear stress occurs directly below the rolling surface, or if there are, only small amounts, so internal delamination is less likely to occur over a long period of time. Furthermore, according to this embodiment, the inner ring can be manufactured with low CO2 emissions.

[0050] (Second Embodiment) This embodiment relates to a method for manufacturing balls as rolling bearing components. The method for manufacturing a ball according to this embodiment is: The following steps are performed in this order: (a) forging, (b) first grinding, (c) judgment, (d) melting and solidification, (e) heat treatment, and (f) second grinding. At this time, known methods used in the manufacture of balls for rolling bearings can be applied to all steps except for (c) judgment and (d) melting and solidification. The following describes each step in order. Here, we will explain each step focusing on the differences from the first embodiment.

[0051] (a) Forging process: In this process (a), the spherical intermediate material F is produced by forging a metallic material containing nonmetallic inclusions with an equivalent circular diameter of 2 μm or more. Examples of the above-mentioned metal material include those used in the first embodiment. In this process, spheroidizing annealing may be performed after forging.

[0052] (b) First grinding process: In this process (b), the surface of the forged intermediate material F is ground to produce a spherical intermediate material G. Although burrs and other imperfections are present on the surface of the intermediate material F manufactured in the forging process described above (a), by performing this process (B), the burrs and other imperfections are removed, and an intermediate material G with a relatively smooth surface is produced.

[0053] (c) Judgment process: In step (c), a region extending to a certain depth from the surface of the spherical intermediate material G is investigated, and areas containing nonmetallic inclusions of a predetermined size (for example, a circular equivalent diameter of 30 μm or more) are identified. As a method for identifying the areas where non-metallic inclusions are present, for example, the ultrasonic testing method used in the first embodiment can be employed. Furthermore, in this process (C), the depth from the surface of the spherical intermediate material G (third depth) used to investigate the presence or absence of nonmetallic inclusions of a predetermined size is preferably the sum of the depth at which 90% of the maximum shear stress occurs and the depth at which the material is removed in a subsequent process.

[0054] In this process, if a portion containing nonmetallic inclusions of a predetermined size is identified, the (d) melting and solidification process is performed on that portion. On the other hand, if no nonmetallic inclusions of a predetermined size are detected in this process, the (d) melting and solidification process is omitted, and the (e) heat treatment process is performed immediately afterward.

[0055] (d) Melting and solidification process: In this process (d), a portion of the ground intermediate material G is melted. Specifically, the portion containing non-metallic inclusions of a predetermined size, which were identified in the determination process (c) above, is melted. By going through this process (d), the intermediate material G becomes a spherical intermediate material H in which the nonmetallic inclusions just below the surface are refined. The melting of the above-mentioned intermediate material G may be carried out in the same manner as in the first embodiment. Furthermore, the solidification of the molten portion can be carried out in the same manner as in the first embodiment.

[0056] In this embodiment as well, the depth of the melted portion should be determined by considering the depth at which the maximum shear stress occurs in the finished ball, and should be greater than or equal to the sum of the depth at which 90% of the maximum shear stress occurs and the depth removed in a subsequent process (preferably a third depth). The depth of the melted portion is preferably about 120-200% of the sum of the depth at which 90% of the maximum shear stress occurs and the depth to which the material is removed in a subsequent process. While it's difficult to give a definitive answer regarding the preferred depth of the melted portion, it's typically around 300 to 2000 μm. Furthermore, if the identified nonmetallic inclusion particles can be melted, the depth of the melted portion may be shallower than the third depth described above.

[0057] After this process (d) is completed, nonmetallic inclusions with an equivalent circular diameter of 30 μm or more are either not present or present in small quantities in the portion of the intermediate material H from the surface to the depth where 90% of the maximum shear stress occurs and the depth to be removed in the subsequent process. In this case, the balls manufactured through subsequent processes will have internal origin peeling suppressed over a long period of time.

[0058] (e) Heat treatment process: In step (e), intermediate material G in which no nonmetallic inclusions were found in the above determination step, or intermediate material H in which the nonmetallic inclusions were refined after the above melting and solidification step, is subjected to heat treatment to produce spherical intermediate material I, which is a heat-treated component. The same type and method as the heat treatment in the first embodiment are used for the heat treatment described above.

[0059] (f) Second grinding process: In step (f), the heat-treated intermediate material I is ground to form a ball J having a rolling surface finished to a predetermined precision. In step (f), the surface of the intermediate material I is removed to a predetermined depth (fifth depth). At this time, the depth to be removed is set so that the depth of the portion that melted and solidified in the melting and solidification step, from the remaining surface after removal, is greater than or equal to the depth at which a stress of 90% of the maximum shear stress occurs.

[0060] By performing these processes (a) to (f), the balls of the rolling bearing are manufactured. In the balls manufactured in this embodiment, there are no non-metallic inclusions with a particle size of 30 μm or larger in equivalent circular diameter up to the depth where 90% of the maximum shear stress occurs from the surface, or if there are, only small amounts, so internal delamination is less likely to occur over a long period of time. Furthermore, according to this embodiment, balls can be manufactured with low CO2 emissions.

[0061] (Third embodiment) This embodiment relates to a method for manufacturing rollers used as rolling bearing components. The manufacturing method of rollers according to this embodiment is The following steps are performed in this order: (a) forging, (b) first grinding, (c) judgment, (d) melting and solidification, (e) heat treatment, and (f) second grinding. At this time, known methods used in the manufacture of rollers for rolling bearings can be applied to all steps except for (c) judgment and (d) melting and solidification. The following describes each step in order. Here, we will explain each step focusing on the differences from the first and second embodiments.

[0062] (a) Forging process: In this process (a), the roller-shaped intermediate material K is manufactured by forging a metallic material containing nonmetallic inclusions with an equivalent circular diameter of 2 μm or more. Examples of the above-mentioned metal material include those used in the first embodiment. In this process, spheroidizing annealing may be performed after forging.

[0063] (b) First grinding process: In step (b), at least the circumferential surface of the forged intermediate material K is ground to produce a roller-shaped intermediate material L. When producing the intermediate material L, it is preferable to also grind the end face of the intermediate material K. Although burrs and other imperfections are present on the circumferential surface of the intermediate material K manufactured in the forging process described above (a), by performing this process (B), the burrs and other imperfections are removed, and an intermediate material L with a relatively smooth circumferential surface is produced.

[0064] (c) Judgment process: In step (c), a region extending to a certain depth from the circumferential surface of the roller-shaped intermediate material L is investigated, and a portion containing nonmetallic inclusions of a predetermined size (for example, a circular equivalent diameter of 30 μm or more) is identified. As a method for identifying the areas where non-metallic inclusions are present, for example, the ultrasonic testing method used in the first embodiment can be employed. Furthermore, in this step (C), the depth from the circumferential surface of the intermediate material L with a predetermined shape for investigating the presence or absence of nonmetallic inclusions of a predetermined size (fourth depth) is preferably the sum of the depth at which 90% of the maximum shear stress occurs and the depth at which the material is removed in a subsequent step.

[0065] In this process, if a portion containing nonmetallic inclusions of a predetermined size is identified, the (d) melting and solidification process is performed on that portion. On the other hand, if no nonmetallic inclusions of a predetermined size are detected in this process, the (d) melting and solidification process is omitted, and the (e) heat treatment process is performed immediately afterward.

[0066] (d) Melting and solidification process: In this process (d), a portion of the intermediate material L, which is a ground component, is melted. Specifically, the portion containing non-metallic inclusions of a predetermined size, which were identified in the determination process (c) above, is melted. Through this process (d), the intermediate material L becomes an intermediate material M in which the non-metallic inclusions directly beneath the circumferential surface are refined. The melting of the intermediate material L described above may be carried out in the same manner as in the first embodiment. Furthermore, the solidification of the molten portion can be carried out in the same manner as in the first embodiment.

[0067] In this embodiment as well, the depth of the melted portion should be determined by considering the depth at which the maximum shear stress occurs when the material is completed. The depth should be greater than or equal to the sum of the depth at which 90% of the maximum shear stress occurs and the depth removed in a subsequent process (preferably the fourth depth). The depth of the melted portion is preferably about 120-200% of the sum of the depth at which 90% of the maximum shear stress occurs and the depth to which the material is removed in a subsequent process. While it's difficult to give a definitive answer regarding the preferred depth of the melted portion, it's typically around 300 to 2000 μm. Furthermore, if the identified nonmetallic inclusion particles can be melted, the depth of the melted portion may be shallower than the fourth depth described above.

[0068] After this process (d) is completed, nonmetallic inclusions with an equivalent circular diameter of 30 μm or more are either not present or present in small quantities in the portion of the intermediate material M from the circumferential surface to the sum of the depth to which 90% of the maximum shear stress occurs and the depth to be removed in the subsequent process. In this case, internal delamination is suppressed over a long period of time as the product is manufactured through subsequent processes.

[0069] (e) Heat treatment process: In step (e), intermediate material L in which no nonmetallic inclusions were found in the above determination step, or intermediate material M in which nonmetallic inclusions were refined after the above melting and solidification step, is subjected to heat treatment to produce intermediate material N in a roller shape, which is a heat-treated component. The same type and method as the heat treatment in the first embodiment are used for the heat treatment described above.

[0070] (f) Second grinding process: In step (f), the heat-treated intermediate material N is ground on its circumferential surface to become a roller O having a rolling surface finished to a predetermined accuracy. When the circumferential surface of the intermediate material N is ground, the end face of the intermediate material N may also be ground. In step (f), the circumferential surface of the intermediate material N is removed from the surface to a predetermined depth (sixth depth). At this time, the depth to be removed is set so that the depth of the portion that melted and solidified in the melting and solidification step from the remaining surface after removal is greater than or equal to the depth at which a stress of 90% of the maximum shear stress occurs.

[0071] By performing these processes (a) to (f), the rollers of the rolling bearing are manufactured. In the materials manufactured according to this embodiment, non-metallic inclusions with a particle size of 30 μm or larger in equivalent circular diameter are either absent or present in small quantities from the circumferential surface to the depth where 90% of the maximum shear stress occurs, making it less likely for internal delamination to occur over a long period of time. Furthermore, according to this embodiment, rollers can be manufactured with low CO2 emissions.

[0072] (Other embodiments) In each embodiment of this disclosure, the predetermined size (reference value) of the nonmetallic inclusions may be set appropriately according to the required characteristics of the manufactured product. For example, it may be 40 μm or more in equivalent circular diameter, 50 μm or more in equivalent circular diameter, 100 μm or more in equivalent circular diameter, etc. On the other hand, if the reference value is less than 30 μm, the cost increase relative to performance will be large, so it is preferable to set the reference value in the range of 30 μm or more.

[0073] The products manufactured by the manufacturing method according to the embodiments of this disclosure are not limited to inner rings, balls, and rollers, which are components of rolling bearings. The manufacturing method according to the embodiments of this disclosure can also be used to manufacture track members having tracks on which rolling elements travel, such as the outer ring of a rolling bearing. [Examples]

[0074] Next, the invention of this disclosure will be described in more detail based on examples. The invention of this disclosure is not limited to these examples. As an example, a disk for thrust-type life evaluation was fabricated, and non-metallic inclusions and rolling life were evaluated. The results are shown in Table 4. Figure 2 is a diagram illustrating the manufacturing process used in the examples and comparative examples. As shown in Figure 2, the determination step and the melting and solidification step were performed in Examples 1 and 2, whereas the determination step and the melting and solidification step were not performed in Comparative Example 1.

[0075] (Comparative Example 1) (1) Five disc-shaped materials with a diameter of 60 mm and a thickness of 12 mm were produced by forging and turning a material made of SUJ2. In addition, after the forging process, the disc-shaped materials that were not turned were subjected to spheroidizing annealing.

[0076] (2) Next, the disc-shaped material was subjected to heat treatment. The heat treatments described above consisted of a quenching process, which involved heating at 830°C for 35 minutes followed by oil cooling, and a tempering process, which involved heating at 180°C for 120 minutes.

[0077] (3) On one side of the disc-shaped material that has undergone the above heat treatment, a grinding process is applied as a surface treatment. Through this process, the evaluation discs (5 discs) for Comparative Example 1 were completed.

[0078] (Examples 1 and 2) (1) Ten disc-shaped materials were produced in the same manner as in step (1) of Comparative Example 1. (2) An ultrasonic flaw detection device (KJTD, HIS3 HF) was used to investigate the presence or absence of nonmetallic inclusions with an equivalent diameter of 30 μm or more in the disc-shaped material. The frequency of the ultrasonic flaw detection device was 80 MHz. In this investigation, an ultrasonic flaw detection device was moved to trace a circle with a diameter of approximately 38.5 mm and a line width of 2 mm to check for the presence of non-metallic inclusions with an equivalent circular diameter of 30 μm or more on one side of a disc-shaped material. The depth investigated was 300 μm from the surface.

[0079] As a result, the presence of non-metallic inclusions with an equivalent diameter of 30 μm or more was confirmed in all 10 disc-shaped materials. After the investigation, the number of non-metallic inclusions was calculated for each equivalent circular diameter, and the average number per disc-shaped material was determined. The results are shown in Table 3.

[0080] [Table 3]

[0081] Next, of the 10 disc-shaped materials whose presence or absence of nonmetallic inclusions was investigated, 5 were used in Example 1 and the remaining 5 were used in Example 2. (Example 1) (3) The disc-shaped material produced by steps (1) and (2) above was subjected to a melting and solidification process in which a portion of one side thereof was irradiated with laser light. In the melting and solidification process, a fiber laser was used, and the disc-shaped material was irradiated with laser light under the conditions of laser A shown in Table 4. The laser light was irradiated in a manner that traced the circumference of a circle with a diameter of approximately 38.5 mm, which was investigated in step (2) above. The laser light melted the disc-shaped material to a depth of 300 μm from the surface, and then solidified.

[0082] (4) After the melting and solidification process described above was completed, heat treatment and surface treatment were performed in the same manner as in steps (2) and (3) of Comparative Example 1. Through this process, the evaluation discs (5 discs) for Example 1 were completed.

[0083] (Example 2) (3) The disc-shaped material produced by steps (1) and (2) above was subjected to a melting and solidification process in which a portion of one side thereof was irradiated with laser light. In the melting and solidification process, a fiber laser was used, and the disc-shaped material was irradiated with laser light under the conditions of laser B shown in Table 4. The laser light was irradiated in a manner that traced the circumference of a circle with a diameter of approximately 38.5 mm, which was investigated in step (2) above. The laser light melted the disc-shaped material to a depth of 300 μm from the surface, and then solidified. In Example 2, the evaluation discs (5 discs) for Example 2 were completed in the same manner as in Example 1, except that the laser light was irradiated onto a portion of one side of the disc-shaped material under the conditions of laser B shown in Table 4.

[0084] [Table 4]

[0085] [Evaluation of non-metallic inclusions] For each of the evaluation discs prepared in the examples and comparative examples, the presence or absence of non-metallic inclusions with an equivalent diameter of 30 μm or more in the disc-shaped material was investigated using an ultrasonic flaw detection device (HIS3 HF, manufactured by KJTD). The frequency of the ultrasonic flaw detection device was 80 MHz. In this investigation, an ultrasonic flaw detection device was moved to trace a circle with a diameter of approximately 38.5 mm and a line width of 2 mm to check for the presence of non-metallic inclusions with an equivalent circular diameter of 30 μm or more on one side of a disc-shaped material. The depth investigated was 300 μm from the surface. In both Example 1 and Example 2, no nonmetallic inclusions with an equivalent diameter of 30 μm or larger were observed on one side of the disc-shaped material. On the other hand, the comparative example's evaluation disc had nonmetallic inclusions with an equivalent diameter of 30 μm or larger on one side of the disc-shaped material. The number of nonmetallic inclusions with an equivalent diameter of 30 μm or larger is shown in Table 5.

[0086] [Evaluation of rolling life] Rolling fatigue tests were performed on five evaluation discs for each embodiment and five evaluation discs for the comparative example using a Mori-type thrust-type rolling fatigue testing machine, and the L10 life of the bearings was predicted. Furthermore, the relative L10 lifespans of the evaluation discs for Example 1 and Example 2, with the L10 lifespan of the evaluation disc for Comparative Example 1 set to 1, were calculated as the L10 lifespan ratio. The results are shown in Table 5. The L10 lifespan ratios for the evaluation discs for the embodiments and comparative examples are shown in Table 5.

[0087] [Table 5]

[0088] As shown in Table 5, it has become clear that bearing members with extended lifespan can be manufactured according to the embodiments of this disclosure. [Explanation of symbols]

[0089] 1a: Rolling surface 1b: End face 1d: Inner circumference 10: Laser 11a: Surface that forms the rolling surface 20:Ultrasonic flaw detection equipment A,B,C,D: Intermediate material E: Inner circle

Claims

1. A method for manufacturing a track member having a track on which rolling elements travel, A forging process to produce a forged component by forging a metallic material containing non-metallic inclusions with an equivalent circular diameter of 2 μm or more. A turning process in which the forged member is turned to obtain a turned member having a portion that will serve as a raceway, A determination step of investigating the presence or absence of nonmetallic inclusions of a predetermined size in the range up to a first depth directly below the surface forming the turning surface of the turned member, and identifying the portion in which the nonmetallic inclusions of the predetermined size exist. A heat treatment step in which, of the surfaces of the determined member after the determination step, at least all of the surfaces that form the rolling surface are heat-treated to make it a heat-treated member, Equipped with, A method for manufacturing a track member, wherein, if the presence of a non-metallic inclusion of a predetermined size is confirmed in the determination step, a portion of the turned member containing the confirmed non-metallic inclusion is melted before the heat treatment step, and then a melting and solidification step is performed to solidify the melted material.

2. The process further comprises a surface treatment step performed after the heat treatment step, The surface treatment step involves removing at least a portion of the surface forming the rolling surface of the heat-treated member from the surface to a second depth to obtain a surface-treated member. A method for manufacturing a track member according to claim 1.

3. The method for manufacturing a track member according to claim 2, wherein the surface processing step involves grinding and / or cutting.

4. A forging process to forge a metallic material containing non-metallic inclusions with an equivalent diameter of 2 μm or more into a spherical forged component. A first grinding step in which the surface of the forged member is ground to obtain a first ground member, A determination step of investigating the presence or absence of nonmetallic inclusions of a predetermined size in the range up to a third depth directly below the surface forming the rolling surface of the ground member, and identifying the portion in which the nonmetallic inclusions of the predetermined size exist. A heat treatment step in which the entire surface of the determined member after the determination step is made into a heat-treated member, and A second grinding step in which the surface of a heat-treated member is ground to produce a second ground member, Equipped with, A method for manufacturing a ball, wherein if the presence of a non-metallic inclusion of a predetermined size is confirmed in the determination step, a portion of the ground member containing the confirmed non-metallic inclusion is melted before the heat treatment step, and then a melt-solidification step is performed to solidify the melted material.

5. A forging process in which a metal material containing non-metallic inclusions with an equivalent circular diameter of 2 μm or more is forged to form a roller-shaped forged member. A first grinding step in which at least the circumferential surface of the forged member is ground to obtain a first ground member, A determination step of investigating the presence or absence of nonmetallic inclusions of a predetermined size in the range up to a fourth depth directly below the surface forming the rolling surface of the ground member, and identifying the portion in which the nonmetallic inclusions of the predetermined size exist. A heat treatment step in which the entire surface of the determined member after the determination step is made into a heat-treated member, and A second grinding step in which the surface of a heat-treated member is ground to produce a second ground member, Equipped with, A roller manufacturing method comprising: if the presence of a non-metallic inclusion of a predetermined size is confirmed in the determination step, a portion of the ground member containing the confirmed non-metallic inclusion is melted before the heat treatment step, and then a melt-solidification step is performed to solidify the melted material.

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