JP2009235449A - Holder for rolling bearing, rolling bearing, and manufacturing method of holder for rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a holder for a rolling bearing and its manufacturing method capable of providing the high durability while suppressing any increase of the weight, and enhancing the dimensional accuracy and the dimensional stability, and the rolling bearing. <P>SOLUTION: The holder 14 consists of steel containing, by mass, ≥0.4% and <0.7% carbon, ≥0.15% and ≤0.35% silicon, ≥0.6% and ≤1.3% manganese, and the balance iron with impurities. A holder nitrogen enriched layer 14B in which the nitrogen concentration is higher than that in the inner part 14C is formed in an area including a surface 14A of the holder 14. In addition, the holder nitrogen enriched layer 14B contains the bainite structure, and the amount of the retained austenite is suppressed to ≤5 vol.%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a rolling bearing cage, a rolling bearing, and a method for manufacturing a rolling bearing cage, and more specifically, a rolling bearing made of steel containing 0.4% by mass or more and less than 0.7% by mass of carbon. The present invention relates to a cage, a manufacturing method thereof, and a rolling bearing provided with the rolling bearing cage.

  In recent years, with the improvement in performance of mechanical devices using rolling bearings, rolling bearings are often used in harsh environments. Therefore, the durability of the rolling bearing retainer that holds the rolling element as well as the race member and the rolling element that are components constituting the rolling bearing may be a problem. In particular, tapered roller bearings and needle roller bearings used in railway vehicle axles, drive motors, transmissions for automobiles and industrial machinery, etc. have large vibration during use, repeated rapid acceleration / deceleration, The cage may be damaged due to fatigue due to various factors such as a skew easily occurring in the moving body.

In response, various measures have been proposed, including measures to increase the thickness of the cage, and measures to increase the strength of the surface layer by applying soft nitriding or salt bath soft nitriding to the surface of the cage. (For example, see Patent Documents 1 to 3).
JP 2005-48827 A JP 2000-179554 A JP-A-2005-172200

  However, in view of the recent demand for higher performance for rolling bearings and the further severeness of the environment in which rolling bearings are used, the above measures are not necessarily sufficient. Specifically, in the measures for increasing the thickness of the cage, energy loss occurs due to an increase in the weight or size of the cage, and it is not possible to meet the recent demand for higher efficiency for mechanical devices. . Moreover, in the measure which simply performs the hardening process of the said surface layer part, sufficient intensity | strength as a whole cage | basket may not be obtained as a result of the intensity | strength inside a cage | basket being insufficient. Furthermore, along with the demand for higher precision for rolling bearings, the cage is also required to have improved dimensional accuracy and improved dimensional stability during use.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rolling bearing retainer capable of imparting high durability while suppressing an increase in weight and improving dimensional accuracy and dimensional stability, a manufacturing method thereof, and the rolling bearing. It is providing the rolling bearing which improved durability, suppressing the increase in a weight by providing the cage for use.

  The rolling bearing retainer according to one aspect of the present invention includes 0.4 mass% or more and less than 0.7 mass% carbon, 0.15 mass% or more and 0.35 mass% or less silicon, and 0.6 mass%. In the region including the surface, a nitrogen-enriched layer, which is a layer having a higher nitrogen concentration than the inside, is formed. ing. The nitrogen-enriched layer includes a bainite structure and the amount of retained austenite is suppressed to 5% by volume or less.

  The present inventor has made a detailed study on measures for imparting high durability while suppressing an increase in weight and improving dimensional accuracy and dimensional stability with respect to a rolling bearing cage. As a result, after forming a nitrogen-enriched layer on the surface of the cage made of steel having the appropriate component composition, the steel constituting the nitrogen-enriched layer includes a bainite structure and a residual austenite amount of 5%. It has been found that the following measures are effective measures. That is, in the rolling bearing retainer of the present invention, a nitrogen-enriched layer is formed in a region including the surface, and the nitrogen-enriched layer includes a bainite structure, thereby improving the durability of the surface layer portion. Further, the nitrogen-enriched layer includes a bainite structure, and the amount of retained austenite is suppressed to 5% by volume or less, so that heat treatment is performed compared to a cage having a general steel structure composed of martensite and retained austenite. As a result of the reduction in deformation, the dimensional accuracy is improved and the dimensional stability is also improved. Furthermore, not only the surface layer portion of the cage but also the internal strength is ensured by making the steel constituting the cage have the above-described composition. As a result, according to the rolling bearing retainer of the present invention, the rolling bearing retainer can provide high durability while suppressing an increase in the weight of the retainer and improve dimensional accuracy and dimensional stability. Can be provided. Hereinafter, the reason which limited the component range of steel to said range is demonstrated.

Carbon: 0.4 mass% or more and less than 0.7 mass% In the steel constituting the rolling bearing cage, if the carbon content is less than 0.4 mass%, the hardness, particularly the hardness inside the cage is insufficient, and the entire cage There is a possibility that the strength as will be insufficient. On the other hand, if the carbon content is 0.7% by mass or more, the cold workability of the material is deteriorated, and it becomes difficult to perform molding such as punching of a pocket for holding a rolling element in a cage, and heat treatment for facilitating this. Etc. may be newly required. Therefore, carbon needs to be 0.4 mass% or more and less than 0.7 mass%.

Silicon: 0.15% by mass or more and 0.35% by mass or less In the steel constituting the rolling bearing retainer, if silicon is less than 0.15% by mass, durability may be lowered. On the other hand, when silicon exceeds 0.35 mass%, the problem that the hardness of a raw material will rise and cold workability will fall may generate | occur | produce. Therefore, silicon needs to be 0.15 mass% or more and 0.35 mass% or less.

Manganese: 0.6% by mass or more and 1.3% by mass or less In the steel constituting the rolling bearing cage, if manganese is less than 0.6% by mass, the durability of the rolling bearing cage may be lowered. On the other hand, when manganese exceeds 1.3 mass%, the hardness of a raw material will raise and the problem that cold workability may fall may generate | occur | produce. Therefore, manganese needs to be 0.6 mass% or more and 1.3 mass% or less.

  The rolling bearing retainer according to another aspect of the present invention includes 0.4 mass% or more and less than 0.7 mass% carbon, 0.15 mass% or more and 0.35 mass% or less silicon, and 0.6 mass%. % To 1.3% by mass of manganese, and further containing at least one of 0.5% by mass or less of chromium and 0.5% by mass or less of molybdenum, and the balance iron and impurities. In a region including the surface, a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside is formed. The nitrogen-enriched layer includes a bainite structure and the amount of retained austenite is suppressed to 5% by volume or less.

  The rolling bearing retainer in another aspect of the present invention basically has the same configuration as the rolling bearing retainer in one aspect of the present invention, and exhibits the same operational effects. However, in the rolling bearing retainer according to another aspect of the present invention, considering the usage environment of the rolling bearing retainer and the like, the steel constituting the rolling bearing retainer further contains chromium of 0.5 mass% or less. And the cage for rolling bearings according to one aspect of the present invention described above in that it contains at least one of molybdenum and 0.5% by mass or less of molybdenum.

  According to the rolling bearing cage in another aspect of the present invention, the steel constituting the cage contains at least one of chromium of 0.5 mass% or less and molybdenum of 0.5 mass% or less. Thereby, while suppressing the addition amount of an alloy element, while improving durability of a surface layer part, the intensity | strength inside a holder | retainer can also be improved. In order to reliably improve the durability and internal strength of the surface layer portion, it is desirable that the chromium content is 0.3% by mass or more and the molybdenum content is 0.2% by mass or more.

  Here, in the rolling bearing retainer, the amount of retained austenite of the nitrogen-enriched layer is preferably 2% by volume or less. Thereby, the dimensional stability of the cage for rolling bearings is further improved. In general, in rolling bearing cages, the strength of the surface layer portion, specifically, the region having a thickness of about 0.15 mm including the surface is often important. For this reason, in the rolling bearing retainer, the thickness of the nitrogen-enriched layer is preferably 0.15 mm or more. Furthermore, from the viewpoint of improving durability, the nitrogen-enriched layer is preferably composed of a bainite structure, a martensite structure, and 5% by volume or less of retained austenite, from the viewpoint of improving dimensional stability. It is preferable that the bainite structure occupies 80% or more volume.

  Preferably, in the rolling bearing retainer of the present invention, the nitrogen-enriched layer comprises 0.7% by mass or more and 1.1% by mass or less of carbon, 0.1% by mass or more and 0.8% by mass or less of nitrogen. Is included.

  The carbon content of the steel constituting the rolling bearing cage greatly affects the hardness of the cage. The hardness of the cage is one of the important factors governing the durability of the cage. If the carbon content in the nitrogen-enriched layer is less than 0.7% by mass, it may be difficult to ensure sufficient hardness in the surface layer portion (nitrogen-enriched layer) of the cage. Therefore, the carbon content in the nitrogen-enriched layer is preferably 0.7% by mass or more. Moreover, when the carbon content in the nitrogen-enriched layer exceeds 1.1 mass%, large iron carbides are formed, which may adversely affect the durability of the cage. Therefore, the carbon content in the nitrogen-enriched layer is preferably 1.1% by mass or less.

On the other hand, nitrogen in the nitrogen-enriched layer has an effect of improving fatigue strength. The nitrogen in the steel lowers the temperature of the M _S point of the steel, to allow formation of more bainite structure at low temperatures. A bainite structure formed at a low temperature has high hardness and excellent fatigue strength. In order to clarify the effect of such nitrogen, the nitrogen content is preferably 0.1% by mass or more. Moreover, when the nitrogen content in steel exceeds 0.8 mass%, a void is formed in steel and there exists a possibility of reducing the durability of the holder | retainer which consists of the said steel. Furthermore, when the nitrogen content in the steel exceeds 0.8% by mass, the penetration of carbon into the steel becomes insufficient, and the strength of the cage made of the steel may be reduced. Therefore, the nitrogen content is preferably 0.8% by mass or less.

  In the rolling bearing retainer of the present invention, the surface hardness is preferably 50 HRC or more.

  As described above, the hardness of the cage is one of the important factors governing the durability of the cage. And when the hardness of the surface of a cage | basket is less than 50HRC, there exists a possibility that durability may become inadequate depending on the use environment etc. of the rolling bearing containing the said cage | basket. Therefore, the surface hardness is preferably 50 HRC or more. In view of ease of incorporation of the rolling elements into the cage, the hardness is preferably 58 HRC or less.

  The rolling bearing according to the present invention includes the rolling bearing cage of the present invention. According to the rolling bearing of the present invention, by providing the rolling bearing cage of the present invention, it is possible to provide a rolling bearing with improved durability while suppressing an increase in weight.

A rolling bearing retainer manufacturing method according to one aspect of the present invention includes a step of preparing a steel member, a step of forming a nitrogen-enriched layer, and a step of transforming the nitrogen-enriched layer to bainite. . In the step of preparing the steel member, 0.4 mass% or more and less than 0.7 mass% carbon, 0.15 mass% or more and 0.35 mass% or less silicon, and 0.6 mass% or more and 1.3 mass% or less. A steel member is prepared, which is made of steel containing the remaining iron and impurities, and is formed and processed. In the step of forming a nitriding layer, by which the steel member is carbonitrided at a temperature of more than ₁ point A, the region including the surface of the steel member, nitrogen-enriched nitrogen concentration than the interior is higher layers A layer is formed. Then, a nitriding layer at a step of bainite transformation, the steel members, beyond the M _S point of the nitrogen-enriched layer, by maintaining the 300 ° C. temperature higher temperature below than M _S point, the nitrogen-enriched layer The nitrogen-enriched layer is transformed to bainite so that the amount of retained austenite becomes 5% by volume or less.

  In the method for manufacturing a rolling bearing retainer according to one aspect of the present invention, a nitrogen-enriched layer is formed in a region including the surface of the steel member having the appropriate component composition, and then the nitrogen-enriched layer is transformed into a bainite transformation. Process is adopted. As a result, a rolling bearing in which a nitrogen-enriched layer containing a bainite structure is formed in the surface layer portion, the internal hardness is sufficiently secured, the durability of the surface layer portion is improved, and the overall strength is also sufficiently secured. Can be manufactured. Furthermore, by carrying out the bainite transformation of the nitrogen enriched layer so that the amount of retained austenite in the nitrogen enriched layer is 5% by volume or less, a cage having a general steel structure composed of martensite and retained austenite is obtained. In comparison, it is possible to manufacture a cage in which deformation due to heat treatment is reduced, dimensional accuracy is improved, and dimensional stability is also improved. As a result, according to the method for manufacturing a rolling bearing cage in one aspect of the present invention, it is possible to provide high durability while suppressing an increase in the weight of the cage, and to improve dimensional accuracy and dimensional stability. Can be produced.

The manufacturing method of the rolling bearing cage in another aspect of the present invention includes a step of preparing a steel member, a step of forming a nitrogen enriched layer, and a step of transforming the nitrogen enriched layer. . In the step of preparing the steel member, 0.4 mass% or more and less than 0.7 mass% carbon, 0.15 mass% or more and 0.35 mass% or less silicon, and 0.6 mass% or more and 1.3 mass% or less. % Of manganese and further containing at least one of 0.5% by mass or less of chromium and 0.5% by mass or less of molybdenum, and is formed from a steel composed of the remaining iron and impurities, and is processed. A steel member is prepared. In the step of forming a nitriding layer, by which the steel member is carbonitrided at a temperature of more than ₁ point A, the region including the surface of the steel member, nitrogen-enriched nitrogen concentration than the interior is higher layers A layer is formed. Then, a nitriding layer at a step of bainite transformation, the steel members, beyond the M _S point of the nitrogen-enriched layer, by maintaining the 300 ° C. temperature higher temperature below than M _S point, the nitrogen-enriched layer The nitrogen-enriched layer is transformed to bainite so that the amount of retained austenite becomes 5% by volume or less.

  The method for manufacturing a rolling bearing retainer according to another aspect of the present invention basically has the same configuration as the method for manufacturing a rolling bearing retainer according to one aspect of the present invention, and has the same functions and effects. Play. However, in the method for manufacturing a rolling bearing cage according to another aspect of the present invention, considering the usage environment of the rolling bearing cage and the like, the steel constituting the steel member further contains 0.5 mass% or less of chromium and It differs from the method for manufacturing a rolling bearing retainer according to one aspect of the present invention in that it contains at least one of 0.5% by mass or less of molybdenum.

  According to the method for manufacturing a rolling bearing cage in another aspect of the present invention, the steel constituting the steel member is at least one of chromium of 0.5 mass% or less and molybdenum of 0.5 mass% or less. Thus, the rolling bearing cage can be manufactured in which the addition amount of the alloy element is suppressed, the durability of the surface layer portion is improved, and the strength inside the cage is also improved. In order to reliably improve the durability and internal strength of the surface layer portion, it is desirable that the chromium content is 0.3% by mass or more and the molybdenum content is 0.2% by mass or more.

Here, the point A ₁ in the case of heating the steel refers to a point that the structure of the steel corresponds to the temperature to start the transformation from ferrite to austenite. Further, the M _s point means a point corresponding to a temperature at which martensite formation starts when the austenitized steel is cooled.

Further, when the temperature at which the steel member is held in the step of transforming the nitrogen-enriched layer (hereinafter referred to as bainite transformation temperature) exceeds 300 ° C. higher than the _MS point, the hardness of the produced cage is increased. There is a risk of lowering the durability. Therefore, the bainite transformation temperature is required to be 300 ° C. higher temperatures less than M _S point. Furthermore, in order to improve the durability of the cage to be manufactured even more, the bainite transformation temperature is preferably at 250 ° C. higher temperatures less than M _S point. On the other hand, when the steel is cooled to a temperature below the _MS point, the steel undergoes martensitic transformation. Therefore, although the bainite transformation temperature needs to be higher than M _S point, considering precision of temperature control, it is preferable to 10 ° C. higher temperatures or higher than M _S point. Further, in consideration of use environment etc. of the cage, in order to improve the toughness of the cage, the bainite transformation temperature is preferably set to 0.99 ° C. higher temperatures or higher than M _S point.

Furthermore, in order to transform the nitrogen-enriched layer to a bainite transformation so that the amount of retained austenite in the nitrogen-enriched layer is 5% by volume or less, A steel heated to a temperature of _one point or higher is kept at the bainite transformation temperature for a sufficient time. There is a need to. Since the holding time changes depending on conditions such as the bainite transformation temperature and the steel component composition, it is necessary to set the holding time according to the conditions, but in the steel having the above component composition, the amount of retained austenite is 5% by volume or less. Therefore, it is preferable to set it for 60 minutes or more, and by setting it for 120 minutes or more, the amount of retained austenite can be reduced to 2 volume% or less which is a more preferable range. Further, when the steel is held at the bainite transformation temperature, the temperature of the steel may vary within the above temperature range, but it is desirable to keep the temperature constant when it is desired to easily control the amount of retained austenite. Furthermore, after the nitrogen-enriched layer is formed, the cooling rate from the _point A to the bainite transformation temperature, from the viewpoint of suppressing the generation of low strength perlite, be capable of suppressing cooling rate pearlite transformation preferably it is preferable that the 500 cooling rate of up to ° C. 200 ° C. / sec or more from _a point a in particular.

  As is apparent from the above description, according to the rolling bearing retainer, the rolling bearing, and the rolling bearing retainer manufacturing method of the present invention, while imparting high durability while suppressing an increase in weight, dimensions Provided is a rolling bearing cage capable of improving accuracy and dimensional stability, a manufacturing method thereof, and a rolling bearing having improved durability while suppressing an increase in weight by including the rolling bearing cage. can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

  FIG. 1 is a schematic diagram showing a configuration of a radial needle roller bearing as a rolling bearing provided with a rolling bearing cage in an embodiment of the present invention. FIG. 2 is a schematic partial cross-sectional view showing an enlarged main part of FIG. With reference to FIG. 1 and FIG. 2, the cage for rolling bearings and the rolling bearing according to one embodiment of the present invention will be described.

  1 and 2, a radial needle roller bearing 1 includes an annular outer ring 11 as a bearing ring, an annular inner ring 12 as a bearing ring arranged inside the outer ring 11, an outer ring 11 and an inner ring 12. And a plurality of needle rollers 13 as rolling elements held by an annular retainer 14. An outer ring rolling surface 11 </ b> A is formed on the inner circumferential surface of the outer ring 11, and an inner ring rolling surface 12 </ b> A is formed on the outer circumferential surface of the inner ring 12. And the outer ring | wheel 11 and the inner ring | wheel 12 are arrange | positioned so that 12A of inner ring | wheel rolling surfaces and 11A of outer ring | wheels may mutually oppose. Further, the plurality of needle rollers 13 are in contact with the inner ring rolling surface 12A and the outer ring rolling surface 11A in contact with the roller rolling surface 13A, which is the outer circumferential surface, and are arranged at a predetermined pitch in the circumferential direction by the cage 14. Therefore, it is held on an annular track so as to be freely rollable. With the above configuration, the outer ring 11 and the inner ring 12 of the radial needle roller bearing 1 are rotatable relative to each other.

  Here, the cage 14 that is a cage for a rolling bearing in the present embodiment includes 0.4 mass% or more and less than 0.7 mass% of carbon and 0.15 mass% or more and 0.35 mass% or less of silicon. And 0.6 mass% or more and 1.3 mass% or less of manganese, and the balance is made of steel consisting of iron and impurities. Referring to FIG. 2, a cage nitrogen enriched layer 14 </ b> B that is a layer having a higher nitrogen concentration than the inside 14 </ b> C is formed in a region including the surface 14 </ b> A of the cage 14. Furthermore, the cage nitrogen-enriched layer 14B includes a bainite structure, and the amount of retained austenite is suppressed to 5% by volume or less. Here, the impurities include inevitable impurities such as those derived from steel raw materials or those mixed in the manufacturing process.

  In the cage 14 as a rolling bearing cage in the present embodiment, the cage nitrogen-enriched layer 14B is formed in a region including the surface 14A, and the nitrogen-enriched layer 14B includes a bainite structure. The durability of the surface layer is improved. Further, the cage nitrogen-enriched layer 14B includes a bainite structure, and the retained austenite amount is suppressed to 5% by volume or less, so that the cage nitrogen-enriched layer 14B has a general steel structure composed of martensite and retained austenite. As a result, deformation due to heat treatment is reduced, dimensional accuracy is improved, and dimensional stability is also improved. Furthermore, the steel which comprises the said holder | retainer 14 shall have the said component composition, and not only the surface layer part of the holder | retainer 14 but the internal intensity | strength is also ensured. As a result, the retainer 14 in the present embodiment is a rolling bearing retainer that imparts high durability while suppressing an increase in weight and has improved dimensional accuracy and dimensional stability.

  Here, instead of the steel, the cage 14 is 0.4 mass% or more and less than 0.7 mass% carbon, 0.15 mass% or more and 0.35 mass% or less silicon, 0.6 Steel containing at least one of manganese and 0.5 mass% or less of chromium and 0.5 mass% or less of molybdenum, the balance being iron and impurities. You may be comprised from. Thereby, while suppressing the addition amount of an alloy element, while improving the durability of a surface layer part, the intensity | strength of the inside 14C of the holder | retainer 14 can also be improved.

  Furthermore, the cage nitrogen-enriched layer 14B preferably contains 0.7% by mass or more and 1.1% by mass or less of carbon and 0.1% by mass or more and 0.8% by mass or less of nitrogen. Thereby, while ensuring the hardness in the surface 14A enough, formation of the large carbide | carbonized_material by excess carbon and formation of the void by excess nitrogen can be suppressed, and the durability of the holder | retainer 14 can be improved.

  Furthermore, the hardness of the surface 14A included in the cage nitrogen-enriched layer 14B is preferably 50 HRC or more. Thereby, sufficient fatigue strength can be ensured.

  Next, a rolling bearing retainer according to an embodiment of the present invention and a method of manufacturing a rolling bearing provided with the rolling bearing retainer will be described. FIG. 3 is a flowchart showing an outline of a rolling bearing retainer and a method of manufacturing a rolling bearing provided with the rolling bearing retainer according to an embodiment of the present invention.

  Referring to FIG. 3, in the rolling bearing retainer and the rolling bearing manufacturing method according to the present embodiment, first, a steel material preparation step is performed as a step (S100). Specifically, in this step (S100), 0.4 mass% or more and less than 0.7 mass% carbon, 0.15 mass% or more and 0.35 mass% or less silicon, and 0.6 mass% or more. A steel containing 1.3% by mass or less manganese and the balance iron and impurities, for example, a steel bar made of JIS standards S45C and S50C, a steel wire, and the like is prepared. In the step (S100), 0.4 mass% or more and less than 0.7 mass% carbon, 0.15 mass% or more and 0.35 mass% or less silicon, 0.6 mass% or more and 1.3 mass% or less. Steel bar, steel wire, which contains not more than 0.5% by mass of manganese and further contains at least one of 0.5% by mass or less of chromium and 0.5% by mass or less of molybdenum, with the balance being iron and impurities. Etc. may be prepared.

  Next, a forming step is performed as a step (S200). Specifically, in step (S200), the steel material prepared in step (S100) is subjected to processing such as cutting, punching, and turning, so that the steel material is formed into the approximate shape of cage 14. Is done. This process (S100) and (S200) comprise the steel member preparation process which prepares the steel member which consists of steel and was shape-processed by the rough shape of the cage for rolling bearings.

  Next, the carbonitriding process implemented as process (S300) and the heat treatment process including the bainite transformation process implemented as process (S400) are implemented. Details of this heat treatment step will be described later.

  Next, as a process (S500), a finishing process in which a finishing process or the like is performed on the steel member that has been subjected to the heat treatment process is performed. Specifically, for example, a finishing process is performed on the surface 14A of the steel member on which the heat treatment process has been performed. Thereby, the retainer 14 in this Embodiment is completed and the manufacturing method of the rolling bearing retainer in this Embodiment is completed.

  Further, as step (S600), an assembly step in which the completed rolling bearing retainer is assembled and the rolling bearing is assembled is performed. Specifically, a radial needle is formed by combining a cage 14 which is a rolling bearing cage in the present embodiment manufactured by the above-described procedure, and an outer ring 11, an inner ring 12 and a needle roller 13 which are separately prepared. The roller bearing 1 is assembled. Thereby, the rolling bearing of the present invention is completed.

  Next, details of the heat treatment step will be described. FIG. 4 is a diagram for explaining the details of the heat treatment step included in the method of manufacturing a rolling bearing retainer in the present embodiment. In FIG. 4, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 4, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature.

Referring to FIG. 3, in the heat treatment step in the present embodiment, first, a carbonitriding step (step (S300)) in which a steel member as an object to be processed is carbonitrided. Specifically, referring to FIG. 4, for example, a steel member is heated to a temperature T ₁ which is a temperature equal to or higher than the A ₁ transformation point in a mixed atmosphere of a carburizing gas containing carbon monoxide and hydrogen and ammonia gas, by being held for a time t _1, the carbon and nitrogen from penetrating the surface layer of the steel member. As a result, a carbonitriding layer having a higher carbon concentration and nitrogen concentration is formed in the region including the surface of the steel member than in the internal region that is a region other than the region including the surface. This carbonitriding layer corresponds to the cage nitrogen-enriched layer 14B in the present embodiment.

Next, referring to FIG. 4, the steel member carbonitriding process is completed, is 300 ° C. higher temperature below the temperature than M _S point above M _S point of the nitrogen-enriched layer from _one or more points A temperature cooling step is cooled to temperature T ₂ is performed. Specifically, the steel member carbonitriding process is implemented, for example, is immersed in the salt bath, it is cooled to a temperature T _2. The cooling of the steel member in this cooling step is performed at a cooling rate at which the steel member does not undergo pearlite transformation. The cooling rate at which the steel member does not undergo pearlite transformation can be determined in consideration of, for example, the CCT (Continuous Cooling Transformation) diagram of the steel constituting the steel member.

Next, referring to FIG. 4, the bainite transformation step of the steel member is maintained at a temperature T ₂ (step (S400)) is performed. Specifically, in step (S400), steel members which are cooled to a temperature T ₂ in the cooling step, by being held for the time t ₂ to temperature T _2, the cage nitrogen formed on the steel member The enriched layer 14B undergoes bainite transformation, and a bainite structure is formed. Thereafter, the M _S point below the temperature of the steel member is a nitrogen-enriched layer, for example by being air-cooled, the heat treatment step in the present embodiment is completed. Here, the temperatures T ₁ and T ₂ and the times t ₁ and t ₂ can be determined according to the composition of the steel member and the usage environment of the rolling bearing including the cage to which the heat treatment step is applied, For example, the temperature T ₁ can be 750 ° C. to 900 ° C., the T ₂ can be 350 ° C. to 550 ° C., the time t ₁ can be 0.5 hours to 2 hours, and the time t ₂ can be 1 hour to 3 hours. .

  The cage 14 and the radial needle roller bearing 1 according to the above embodiment can be manufactured by the rolling bearing cage and the rolling bearing manufacturing method including the heat treatment steps described above.

  In the present embodiment, the rolling bearing cage constituting the radial needle roller bearing has been described as an example of the rolling bearing cage of the present invention. However, the rolling bearing cage of the present invention is not limited to this. I can't. The cage for a rolling bearing of the present invention may be a cage constituting, for example, a thrust needle roller bearing, a radial tapered roller bearing, a thrust tapered roller bearing, a cylindrical roller bearing, a large ball bearing, or the like. Further, as steel applicable to the rolling bearing cage of the present invention, specifically, steels such as JIS standards S38C, S40C, S43C, S45C, S48C, S50C, S53C, S55C, S58C and SAE standard 1070, Or what added manganese in the range of 1.3 mass% or less in these steels, what added chromium and molybdenum in the range of 0.5 mass% or less to these steels, etc. are mentioned.

  Embodiment 1 of the present invention will be described below. A sample subjected to heat treatment by the heat treatment step in the above embodiment was produced, and an experiment was conducted to investigate the material characteristics and durability of the sample. The experimental procedure is as follows.

  First, a method for manufacturing a sample is described. In the preparation of the sample, first, 0.4 mass% or more and less than 0.7 mass% carbon, 0.15 mass% or more and 0.35 mass% or less silicon, 0.6 mass% or more and 1.3 mass% or less. % Steel and containing steel and impurities, JIS S55C steel and S45C steel are prepared, and steel members corresponding to the shape of the sample according to each test item described later. Molded. Then, the sample was produced by implementing the following three types of heat processing with respect to the said steel member. The finishing process after the heat treatment was basically not performed, and only necessary areas were polished. For the heat treatment, the heat treatment of an example for producing a sample having the same configuration as the rolling bearing cage of the present invention and the heat treatment of Comparative Examples A and B for producing a sample outside the scope of the present invention were performed.

(Example)
The steel member was heat-treated by the heat treatment step in the embodiment described above based on FIG. Here, referring to FIG. 4, the carbonitriding step is a mixed gas of RX gas and ammonia in which the carbon potential (C _P ) value of the atmosphere is controlled to 1.0 and the concentration of undecomposed ammonia is controlled to 0.2% by volume. This was performed by inserting a steel member into an atmosphere furnace and heating. Here, the temperature T ₁ was 850 ° C., and the time t ₁ was 60 minutes. Thereafter, the bainite transformation step was carried out by immersing the steel member subjected to carbonitriding in a quenching salt bath and maintaining it at a constant temperature. At this time, temperature _{T 2} is 250 ° C., the time _{t 2} was set to 3.5 hours. Thereby, the penetration depth of carbon on the surface of the steel member was about 0.4 mm, the penetration depth of nitrogen was about 0.3 mm, and the surface layer portion into which nitrogen had penetrated had a bainite structure (carbonitriding + bainite transformation). ;Example).

(Comparative Example A)
Steel members were produced in the same manner as in the above examples, and the carbonitriding process was performed under the same conditions. Then, by immersing the steel member during tempering Nyuabura, by cooling from a temperature of more than ₁ point A to M _S point below the temperature was carried out quenching. Further, the steel member was tempered by heating to 200 ° C. and holding for 120 minutes (carbonitriding + quenching + tempering; Comparative Example A).

(Comparative Example B)
A steel member was prepared in the same manner as in the above example, heated to 580 ° C. and subjected to gas soft nitriding for 100 minutes. Then, it cooled to room temperature by air-cooling (gas soft nitriding; the comparative example B).

  Next, a method for investigating material characteristics and durability will be described. The investigation of material properties and durability is as follows: (1) hardness, (2) heat treatment deformation (roundness), (3) dimensional stability, (4) crack strength, (5) crack fatigue strength, (6) retention The test was conducted on 6 items of the fatigue strength of the vessel. Hereinafter, the investigation method for each item will be described.

(1) Hardness Using S55C as a material, a ring-shaped test piece having an outer diameter of φ24 mm, an inner diameter of φ18.5 mm, and a height of 7 mm was produced, and the hardness was measured. The measurement position was an end face, and the end face was polished and measured with a Vickers hardness meter.

(2) Heat treatment deformation (roundness)
About the ring-shaped test piece similar to (1), the roundness before and after the heat treatment was measured, and the deformation amount was calculated from the difference. The experiment was performed on five ring-shaped test pieces, and the amount of deformation due to heat treatment was evaluated based on the ratio of the average value to Comparative Example A.

(3) Dimensional stability For the ring-shaped test piece similar to (1), after polishing the outer peripheral surface, the ratio between the original outer diameter and the outer diameter after heating to 230 ° C. and holding for 2 hours is Calculated. The test was performed on three ring-shaped test pieces, and the dimensional stability was evaluated by the ratio of the average value to Comparative Example A.

(4) Crack strength Using the same ring-shaped test piece as in (1), the test piece was compressed in the radial direction with an Amsler type tester, and the stress value at the time of failure was recorded as the cracking strength. Assuming the state of the actual rolling bearing cage, the inner peripheral surface was not polished. The said test was done about three ring-shaped test pieces, and the crack strength was evaluated by the ratio with respect to the Example of the average value.

(5) Crack fatigue strength Using the same ring-shaped test piece as in (1), a stress of 800-1500 MPa was applied to the inner peripheral surface at a repetition rate of 50 Hz in the radial direction by a hydraulic shaker (servo pulser manufactured by Shimadzu Corporation). A stress was repeatedly applied to the test piece under the condition that is applied. As in the above (4), the actual state of the rolling bearing cage was assumed, and the inner peripheral surface was not polished. Then, the number of repeated stresses and the load at which the test piece broke was recorded, and after performing this multiple times, the test results were statistically processed, and the test piece was destroyed by repeating the stress load 10 ⁷ times. The expected stress value (10 ⁷ times strength) was calculated. Then, this was evaluated by the ratio of ¹⁰⁷ times the strength of the Example.

(6) Fatigue strength of cage The fatigue strength test of the cage was carried out by the following test method after producing an actual cage using S45C as a material. FIG. 5 is a schematic cross-sectional view showing a test piece for fatigue strength of a cage. FIG. 6 is a schematic diagram for explaining a test method for the fatigue strength of the cage. FIG. 7 is a schematic cross-sectional view for explaining a method for testing the fatigue strength of the cage.

  Referring to FIG. 5, after a steel material made of S45C is prepared and processed, the above heat treatment is performed, so that the cage shape is held with an outer diameter of 41.9 mm, an inner diameter of 35.8 mm, and a height of 19.8 mm. A vessel 71 was made. Thereafter, the needle roller 72 was fitted into the pocket portion of the cage, and the fatigue test piece 70 was assembled. Then, with reference to FIG. 6 and FIG. 7, the said fatigue test piece 70 was set to the cage fatigue tester 80, and the test was implemented. In the fatigue test, first, the fatigue test piece 70 is penetrated so that the outer peripheral surface of the fatigue test piece 70 faces the inner peripheral surface of the cylindrical through hole formed in the fixed scale 84 of the cage fatigue tester 80. They were inserted into the holes, and both were fixed by the fixed load pieces 83. Next, the swing shaft 81 was inserted into the inner diameter portion of the fatigue test piece 70, and the swing shaft 81 and the fatigue test piece 70 were fixed by the swing side load piece 82. In this state, the test was performed by swinging the swing shaft 81 in the circumferential direction. The load torque was ± 2940 N · cm, the load speed was 700 cpm, and lubrication was performed by applying turbine oil VG32. Then, the time until the cage retainer 71 of the fatigue test piece 70 broke down under the conditions was recorded as the life, and the fatigue strength was evaluated by the ratio of the life to the life of the example.

  Next, test results will be described. Table 1 shows the test results of the above (1) to (6).

(1) Hardness With reference to Table 1, the hardness of Example and Comparative Example A was 650 HV (58 HRC) or more, and the hardness of Comparative Example B was 550 HV (52.3 HRC). Therefore, the hardness of the surface layer portion was a sufficient value in any sample. However, the internal hardness that is not affected by the surface hardening treatment such as carburizing and nitriding was about 500 HV in Example B and Comparative Example A, whereas Comparative Example B had a hardness of 500 HV or more. . Therefore, although the cage having the same configuration as that of Comparative Example B has no problem in the hardness of the surface layer portion, the strength of the entire cage may be insufficient because the internal hardness is insufficient. I understood.

(2) Heat treatment deformation amount As shown in Table 1, the heat treatment deformation amount of the example and the comparative example B was significantly smaller than that of the comparative example A. This is presumably because Comparative Example A was heat-treated with martensitic transformation, whereas Example and Comparative Example B were not heat-treated with martensitic transformation. In particular, although Example A was heated to a temperature of A ₁ point or higher in the heat treatment, it was then transformed uniformly by being held at the bainite transformation temperature, so that the strain associated with the heat treatment was small and the amount of deformation was suppressed. It is considered a thing.

(3) Dimensional stability As shown in Table 1, the amount of dimensional change in Example and Comparative Example B was significantly smaller than that in Comparative Example A. This is because, in Comparative Example A, deformation accompanied by decomposition of retained austenite occurred during quenching occurred, whereas in Example and Comparative Example B where heat treatment accompanied by martensite transformation was not performed, the deformation occurred. This is thought to be because there was not.

(4) Crack strength Referring to Table 1, the crack strength of the examples was much larger than those of Comparative Examples A and B. This is considered to be due to the fact that the bainite structure contained in the test piece of the example is excellent in crack strength, and in Comparative Example B, the internal hardness was insufficient as described above.

(5) Crack fatigue strength With reference to Table 1, the crack fatigue strength of the Example was higher than Comparative Example A. This is considered to be due to the fact that the bainite structure contained in the test piece of the example is excellent in crack fatigue strength. In addition, the crack fatigue strength of the comparative example B with insufficient internal hardness is low.

(6) Fatigue strength of cage As shown in Table 1, the fatigue strength of the examples clearly shows Comparative Examples A and B having the conventional configuration even under the same conditions as the actual cage usage state. It was confirmed that the cage of the example was a cage having excellent durability.

  From the above experimental results, it was confirmed that according to the example of the present invention, it is possible to provide a rolling bearing cage capable of providing high durability and improving dimensional accuracy and dimensional stability.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  A rolling bearing cage, a rolling bearing, and a rolling bearing cage manufacturing method according to the present invention include a rolling bearing cage that requires high durability and excellent dimensional accuracy and dimensional stability, a manufacturing method thereof, and It can be applied particularly advantageously to rolling bearings.

It is the schematic which shows the structure of the radial needle roller bearing provided with the cage for rolling bearings. It is a schematic fragmentary sectional view which expands and shows the principal part of FIG. It is a flowchart which shows the outline of the manufacturing method of a rolling bearing provided with the cage for rolling bearings and the said cage for rolling bearings. It is a figure for demonstrating the detail of the heat treatment process included in the manufacturing method of the cage for rolling bearings. It is a schematic sectional drawing which shows the test piece of the fatigue strength of a holder | retainer. It is the schematic for demonstrating the test method of the fatigue strength of a holder | retainer. It is a schematic sectional drawing for demonstrating the test method of the fatigue strength of a holder | retainer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Radial needle roller bearing, 11 outer ring, 11A outer ring rolling surface, 12 inner ring, 12A inner ring rolling surface, 13 needle roller, 13A roller rolling surface, 14 cage, 14A surface, 14B cage nitrogen enriched layer, 14C Internal, 70 Fatigue test piece, 71 Cage type cage, 72 Needle roller, 80 Cage fatigue tester, 81 Oscillation shaft, 82 Oscillation side load piece, 83 Fixed side load piece, 84 Fixed scale

Claims (7)

0.4% by mass or more and less than 0.7% by mass of carbon, 0.15% by mass or more and 0.35% by mass or less of silicon, and 0.6% by mass or more and 1.3% by mass or less of manganese. Composed of steel, the balance iron and impurities,
In the region including the surface, a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside is formed,
The nitrogen-enriched layer includes a bainite structure, and the retained austenite amount is suppressed to 5% by volume or less. 0.4% by mass or more and less than 0.7% by mass of carbon, 0.15% by mass or more and 0.35% by mass or less of silicon, and 0.6% by mass or more and 1.3% by mass or less of manganese. And further comprising at least one of 0.5% by mass or less of chromium and 0.5% by mass or less of molybdenum, and is composed of steel consisting of the remaining iron and impurities,
In the region including the surface, a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside is formed,
The nitrogen-enriched layer includes a bainite structure, and the retained austenite amount is suppressed to 5% by volume or less.   The nitrogen-rich layer contains 0.7% by mass or more and 1.1% by mass or less of carbon and 0.1% by mass or more and 0.8% by mass or less of nitrogen. Roller bearing cage.   The rolling bearing retainer according to any one of claims 1 to 3, wherein the surface has a hardness of 50 HRC or more.   The rolling bearing provided with the cage for rolling bearings of any one of Claims 1-4. 0.4% by mass or more and less than 0.7% by mass of carbon, 0.15% by mass or more and 0.35% by mass or less of silicon, and 0.6% by mass or more and 1.3% by mass or less of manganese. And a step of preparing a formed steel member composed of steel composed of the remaining iron and impurities, and
Forming a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside in a region including the surface of the steel member by carbonitriding the steel member at a temperature of A ₁ point or higher;
It said steel member, beyond the M _S point of the nitrogen-enriched layer, the M by holding 300 ° C. higher temperature below the temperature than _the point _S, the amount of retained austenite of the nitrogen-enriched layer is 5 vol% or less And a step of transforming the nitrogen-enriched layer to a bainite transformation. 0.4% by mass or more and less than 0.7% by mass of carbon, 0.15% by mass or more and 0.35% by mass or less of silicon, and 0.6% by mass or more and 1.3% by mass or less of manganese. And a step of preparing a formed steel member comprising at least one of chromium of 0.5% by mass or less and molybdenum of 0.5% by mass or less, and composed of steel composed of the remaining iron and impurities. ,
Forming a nitrogen-enriched layer that is a layer having a higher nitrogen concentration than the inside in a region including the surface of the steel member by carbonitriding the steel member at a temperature of A ₁ point or higher;
It said steel member, beyond the M _S point of the nitrogen-enriched layer, the M by holding 300 ° C. higher temperature below the temperature than _the point _S, the amount of retained austenite of the nitrogen-enriched layer is 5 vol% or less And a step of transforming the nitrogen-enriched layer to a bainite transformation.

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