JP2014080661A - Bearing part, rolling bearing and manufacturing method of bearing part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bearing part capable of securing high durability even in a severe use environment, and to provide a rolling bearing and a manufacturing method of the bearing part.SOLUTION: An outer ring 11, an inner ring 12 and a ball 13, as a bearing part, contain steel comprising 0.95 mass% to 1.10 mass% of carbon, 0.05 mass% to 0.35 mass% of silicon, 0.10 mass% to 0.50 mass% of manganese, 1.30 mass% to 2.00 mass% of chromium and the balance iron with impurities, an average nitrogen concentration at the surface region 11B, 12B and 13B within a depth of 20 μm from an outer ring rolling surface 11A, an inner ring rolling surface 12A and ball rolling surface 13A, which are surfaces rolling-contacting with other parts, is 0.2 mass% to 0.7 mass% and there are 5 or more per 100 μmof carbide having a diameter of 0.5 μm or less in surface layer regions 11B, 12B and 13B.

Description

  The present invention relates to a bearing component, a rolling bearing, and a manufacturing method of the bearing component, and more particularly to a bearing component, a rolling bearing, and a manufacturing method of the bearing component that can ensure high durability even in a severe use environment. It is.

As a measure for improving the durability of the bearing part, a carbonitriding process is known in which carbon and nitrogen are introduced into the surface layer of the bearing part prior to the quenching process (see, for example, Patent Document 1). It is known that the carbonitriding treatment improves the rolling fatigue life of the rolling bearing, particularly in an environment where hard foreign matter enters the rolling bearing (foreign matter intrusion environment). Carbonitriding process, ammonia, carbon monoxide, carbon dioxide and bearing components made of steel in an atmosphere containing hydrogen and heated to a temperature range of not lower than the A ₁ transformation point, to penetrate the carbon in the surface layer portion of the bearing parts, Or it is the process which makes nitrogen penetrate | invade into a surface layer part, suppressing the decarburization of a surface layer part.

For this carbonitriding treatment, the carbon concentration of the surface layer is adjusted to an appropriate level by adjusting a _c ^* defined by the following formula (1) and α defined by the formula (2) to an appropriate range. It is proposed to improve the efficiency of the carbonitriding process by increasing the nitrogen penetration rate (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 5-118336 JP 2007-277648 A

  However, even when the carbonitriding process as described above is performed on the bearing component, there is a problem that durability may be insufficient depending on the use environment.

  The present invention has been made to solve the above-mentioned problems, and its object is to provide a bearing component, a rolling bearing and a method for manufacturing the bearing component that can ensure high durability even in a severe use environment. It is to be.

The bearing component according to the present invention has a carbon content of 0.95 mass% to 1.10 mass%, silicon mass of 0.05 mass% to 0.35 mass%, and 0.10 mass% to 0.50 mass%. It is made of steel consisting of the balance iron and impurities, containing manganese of not more than mass% and chromium of not less than 1.30 mass% and not more than 2.00 mass%, and is deep from the contact surface that is the surface in rolling contact with other parts. The average nitrogen concentration in the surface layer region which is a region within 20 μm is 0.2% by mass or more and 0.7% by mass or less, and carbide (including carbonitride) having a diameter of 0.5 μm or less is 100 μm in the surface layer region. the presence of 5 or more per ^2.

  The inventor has studied in detail the cause of the phenomenon that the durability is insufficient even when the carbonitriding treatment is applied to the bearing component. As a result, the following knowledge was obtained and the present invention was conceived.

Bearing parts are formed by precipitation strengthening of the carbide by setting the state in which five or more carbides having a diameter of 0.5 μm or less are present per 100 μm ^{2 in} the surface layer region (the region having a depth of 20 μm or less from the contact surface) of the bearing component. The static load capacity is improved. Here, the state in which five or more carbides having a diameter of 0.5 μm or less exist in the surface layer region per 100 μm ² means that the bearing component is cut in a cross section perpendicular to the contact surface of the bearing component, and the surface layer region of the obtained cross section is When observed with a microscope, it means a state in which 5 or more carbides having a diameter of 0.5 μm or less are confirmed per 100 μm ² . Further, by setting the average nitrogen concentration in the surface layer region to 0.2% by mass or more, the durability (life) of the bearing component in a foreign matter mixed environment and the durability in a clean oil lubrication environment are sufficiently improved.

  However, when nitrogen is infiltrated into a steel containing a relatively large amount of chromium like the above steel, the solid solubility limit of carbon in a region where nitrogen has infiltrated becomes large. As a result, carbides are reduced and in some cases disappear. On the other hand, when the nitrogen concentration in the surface layer region exceeds 0.7% by mass, the hardenability of the surface layer region is lowered and an incompletely hardened structure is easily formed. In order to solve such a problem, it is effective to perform a diffusion process after the carbonitriding process. However, if diffusion treatment is carried out without taking any measures, nitrogen separation occurs in the surface layer region, resulting in a decrease in nitrogen concentration, and a nitrogen-enriched layer with a higher nitrogen concentration than the inside is formed near the surface of the bearing part. In spite of this, it has become clear that the nitrogen concentration in the surface layer region, which greatly affects the durability, is insufficient, which hinders the improvement of the durability of the bearing parts. That is, when a nitrogen enriched layer is formed by carbonitriding the bearing component, formation of an incompletely hardened structure due to excessive nitrogen amount, reduction or disappearance of carbides occurs. When the diffusion process is performed and the excessive amount of nitrogen is eliminated, the nitrogen concentration in the surface layer region becomes insufficient despite the formation of the nitrogen-enriched layer. The present inventor has found that such a phenomenon hinders the improvement of the durability of the bearing component, and has achieved an improvement in the durability of the bearing component by eliminating this phenomenon.

In the bearing component of the present invention, five or more carbides having a diameter of 0.5 μm or less per 100 μm ² exist in the surface layer region (region within a depth of 20 μm from the contact surface that is a rolling contact surface with other components). By doing so, the static load capacity of the bearing parts is sufficiently secured. And by making the average nitrogen concentration of the surface layer region 0.2 mass% or more and 0.7 mass% or less, both improvement in durability due to nitrogen penetration and avoidance of formation of incompletely hardened structure due to nitrogen penetration are achieved. doing. The above characteristics can be achieved by preventing nitrogen introduced into the surface region from being separated from the surface. Thus, according to the bearing component of the present invention, high durability can be ensured even in a severe use environment. The “contact surface” means a rolling surface of a raceway member such as a raceway, or a rolling surface of a rolling element such as a ball or roller (the surface of the ball, the outer peripheral surface of the roller).

  Here, the reason why the component composition of steel constituting the bearing part is set in the above range will be described.

Carbon: 0.95% by mass or more and 1.10% by mass or less The carbon content greatly affects the hardness and carbide content of the bearing parts after quench hardening. By setting the carbon content of the steel to 0.95% by mass or more, sufficient hardness and carbide amount can be achieved without introducing much carbon into the steel by heat treatment. On the other hand, if the carbon content exceeds 1.10% by mass, a large carbide is formed at the time of manufacturing the steel, which may adversely affect the durability of the bearing component. Therefore, the carbon content is set to 0.95 mass% or more and 1.10 mass% or less.

Silicon: 0.05 mass% or more and 0.35 mass% or less Silicon contributes to the improvement of the temper softening resistance of steel. If the silicon content is less than 0.05% by mass, the temper softening resistance becomes insufficient, and the hardness of the contact surface decreases beyond the allowable range due to tempering after quench hardening and temperature rise during use of bearing parts. there's a possibility that. On the other hand, if the silicon content exceeds 0.35% by mass, the hardness of the material before quenching increases, and the workability in cold working when the material is formed into a bearing part is reduced. Therefore, the silicon content is set to 0.05% by mass or more and 0.35% by mass or less. Silicon promotes hydrogen embrittlement peeling of bearing parts. Therefore, the lower limit value of the silicon content is set lower than JIS standard SUJ2, which is the most common bearing steel. That is, when importance is attached to suppression of hydrogen embrittlement peeling, the silicon content can be less than 0.15% by mass lower than SUJ2.

Manganese: 0.10 mass% or more and 0.50 mass% or less Manganese contributes to the improvement of the hardenability of steel. If the manganese content is less than 0.10% by mass, this effect cannot be sufficiently obtained. On the other hand, if the manganese content exceeds 0.50% by mass, the hardness of the material before quenching increases, and the workability in cold working decreases. Therefore, manganese content was made into 0.10 mass% or more and 0.50 mass% or less.

Chromium: 1.30% by mass or more and 2.00% by mass or less Chromium contributes to improvement of hardenability of steel and improvement of rolling fatigue life of bearing parts. If the chromium content is less than 1.30% by mass, this effect cannot be sufficiently obtained. On the other hand, when the chromium content exceeds 2.00% by mass, there arises a problem that the material cost increases. Therefore, the chromium content is set to 1.30% by mass or more and 2.00% by mass or less. Note that when the silicon content is reduced as a measure against hydrogen embrittlement delamination, the hardenability of the steel may be insufficient. This lack of hardenability can be compensated by increasing the amount of chromium added. Therefore, the upper limit of the chromium content is set higher than JIS standard SUJ2, which is the most common bearing steel. In particular, when the silicon content is less than 0.15% by mass lower than SUJ2 with emphasis on suppression of hydrogen brittle exfoliation, the chromium content can exceed 1.60% by mass higher than SUJ2. .

  In the bearing component, preferably, the average nitrogen concentration is 0.7% by mass or less in the entire region within a depth of 20 μm from the surface.

  By doing so, not only the contact surface of the bearing part but also the region other than the contact surface, for example, the portion that is not ground after the formation of the nitrogen-enriched layer, such as a thin portion, is suppressed. Is done.

  In the bearing component, preferably, the hardness of the contact surface is 700 HV or more. Thereby, sufficient static load capacity can be given also to bearing parts used in a severe environment.

  In the bearing component, the amount of retained austenite on the contact surface is preferably 20% by volume or more and 35% by volume or less. Thereby, durability of the bearing component in a foreign material mixing environment can be improved, maintaining sufficient hardness in a contact surface.

  In the above bearing component, the total average retained austenite amount is preferably 18% by volume or less. By doing in this way, the improvement of the dimensional stability of bearing parts (inhibition of a dimensional change over time) can be achieved.

  Preferably, in the above-described bearing component, when the hardness distribution is measured in the depth direction in a cross section perpendicular to the contact surface after being held at 500 ° C. for 1 hour, the difference between the maximum value and the minimum value of the hardness is 130 HV or more. In such a bearing component, introduction of a sufficient concentration of nitrogen is ensured.

  The rolling bearing according to the present invention includes a race member and a rolling element disposed in contact with the race member. At least one of the race member and the rolling element is the bearing component. The rolling bearing of the present invention has high durability by including a bearing component capable of ensuring high durability even in a severe use environment as at least one of a race member and a rolling element.

The manufacturing method of the bearing component according to the present invention includes 0.95% by mass or more and 1.10% by mass or less of carbon, 0.05% by mass or more and 0.35% by mass or less of silicon, and 0.10% by mass or more. Containing 0.50% by mass or less of manganese and 1.30% by mass or more and 2.00% by mass or less of chromium, and preparing a molded body made of steel consisting of the remaining iron and impurities; By heating to a carbonitriding temperature in a carbonitriding atmosphere containing ammonia, carbon monoxide, carbon dioxide and hydrogen, the step of carbonitriding the molded body, and the carbonitrided molded body to ammonia, carbon monoxide, carbon dioxide And a step of diffusing nitrogen in the formed body by maintaining the diffusion temperature at a temperature equal to or lower than the carbonitriding temperature in a diffusion atmosphere containing carbon and hydrogen. When the partial pressure of undecomposed ammonia is P _N , the hydrogen partial pressure is P _H , a _c ^* is defined by the following formula (1), and α is defined by the following formula (2), a _c ^* in a carbonitriding atmosphere Is set to 0.88 to 1.27, α is set to 0.012 to 0.020, a _c ^* in the diffusion atmosphere is 0.88 to 1.27, and α is 0.003 to 0.012 Set to

In the bearing component manufacturing method of the present invention, a carbonitriding process and a diffusion process are sequentially performed on a molded body made of steel having the appropriate component composition. By performing this diffusion treatment, local excessive nitrogen in the molded body is eliminated, and formation of an incompletely hardened structure is suppressed. And in carrying out the diffusion treatment, by adjusting not only the above a _c ^* but also α to an appropriate value, the separation of nitrogen in the surface layer region in the diffusion treatment is suppressed, and the surface layer region having an appropriate nitrogen content Can be obtained. As a result, according to the bearing component manufacturing method of the present invention, it is possible to manufacture a bearing component capable of ensuring high durability even in a severe use environment.

  In the method for manufacturing the bearing component, a step of performing a tempering process for heating and cooling the molded body to a temperature range of 170 ° C. or higher and 220 ° C. or lower after the step of diffusing nitrogen in the molded body is further performed. You may have. Thereby, appropriate hardness can be provided to the contact surface of a bearing component, and sufficient static load capacity can be secured.

  As is apparent from the above description, according to the bearing component, rolling bearing and bearing component manufacturing method of the present invention, the bearing component, rolling bearing and bearing component capable of ensuring high durability even in a severe use environment. The manufacturing method of can be provided.

It is a schematic sectional drawing which shows the structure of a deep groove ball bearing. It is the schematic fragmentary sectional view which expanded and showed the principal part of FIG. It is a schematic sectional drawing which shows the structure of a thrust roller bearing. FIG. 4 is a schematic partial cross-sectional view of the raceway ring of FIG. 3. It is a schematic sectional drawing of the roller of FIG. It is a flowchart which shows the outline of the manufacturing method of a rolling bearing. It is a figure which shows the density | concentration of carbon and nitrogen in the surface vicinity when _ac ^{* is set} to 0.8. It is a figure which shows the density | concentration of carbon and nitrogen in the surface vicinity when _ac ^* is 0.95. It is a figure which shows the density | concentration of nitrogen in the surface vicinity when (alpha) is 0.017. It is a figure which shows the density | concentration of nitrogen in the surface vicinity when (alpha) is 0.005. It is a figure which shows the relationship between nitrogen concentration, hardness, and a half value width. It is a photograph which shows a microstructure in case the average nitrogen concentration in a surface layer area | region is 1.0 mass%. It is a figure which shows the density | concentration of nitrogen in the surface vicinity in case (alpha) is 0. It is a figure which shows the density | concentration of nitrogen in the surface vicinity in case (alpha) is 0.005. It is a figure which shows the relationship between surface hardness and indentation depth. It is a figure which shows nitrogen concentration distribution just under a rolling surface. It is a figure which shows nitrogen concentration distribution just under a rolling surface. It is a figure which shows nitrogen concentration distribution just under a rolling surface. It is a figure which shows nitrogen concentration distribution just under a rolling surface. It is a figure which shows nitrogen concentration distribution just under a rolling surface. It is a figure which shows the shape of the peeling part vicinity after peeling generate | occur | produces. It is a figure which shows an example of the shape of an indentation. It is a figure which shows the relationship between the average nitrogen concentration in a surface layer area | region, and an indentation origin type | mold peeling lifetime. It is a figure which shows the relationship between the average nitrogen concentration in a surface layer area | region, and a cleaning oil lubrication lifetime. It is a figure which shows the relationship between a retained austenite amount and an indentation origin type | mold peeling lifetime. It is a figure which shows distribution of the amount of retained austenite in the surface vicinity. It is a figure which shows the relationship between a retained austenite amount and a dimensional change rate. It is a figure which shows the relationship between the hardness difference after hold | maintaining and cooling at 500 degreeC for 1 hour, and nitrogen concentration. It is a SEM photograph which shows the state where the carbide disappeared. It is a SEM photograph which shows the state by which the carbide | carbonized_material was hold | maintained. It is a figure which shows the influence of the presence of the carbide | carbonized_material on indentation depth.

  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 description thereof will not be repeated.

  First, an embodiment of the present invention will be described with reference to FIGS. 1 and 2 by taking a rolling bearing provided with bearing rings and balls as bearing parts as an example. The deep groove ball bearing 1 includes an outer ring 11 as a first race member as a bearing component, an inner ring 12 as a second race member as a bearing component, balls 13 as a plurality of rolling elements as bearing components, and a cage. 14. The outer ring 11 is formed with an outer ring rolling surface 11A as an annular first rolling surface. The inner ring 12 is formed with an inner ring rolling surface 12A as an annular second rolling surface facing the outer ring rolling surface 11A. Further, the balls 13 are formed with ball rolling surfaces 13A (the surfaces of the balls 13) as rolling elements rolling surfaces. The outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A are contact surfaces of these bearing components. The balls 13 are in contact with each of the outer ring rolling surface 11A and the inner ring rolling surface 12A on the ball rolling surface 13A, and are arranged at a predetermined pitch in the circumferential direction by an annular retainer 14. It is rotatably held on an annular track. With the above configuration, the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1 are rotatable relative to each other.

Referring to FIG. 2, the outer ring 11, the inner ring 12, and the ball 13 that are bearing parts are 0.95 mass% to 1.10 mass% carbon and 0.05 mass% to 0.35 mass%. Steel containing silicon, 0.10 mass% or more and 0.50 mass% or less, and 1.30 mass% or more and 2.00 mass% or less chromium, and the balance iron and impurities, such as JIS high standard It consists of SUJ2, which is a carbon chromium bearing steel. In the region including the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A as contact surfaces, nitrogen enriched layers 11D, 12D, having a higher nitrogen concentration than the inner 11C, 12C, 13C, 13D is formed respectively. In the surface layer regions 11B, 12B, and 13B whose distances from the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A as contact surfaces that are the surfaces of the nitrogen-enriched layers 11D, 12D, and 13D are within 20 μm. The average nitrogen concentration is 0.2% by mass or more and 0.7% by mass or less. Furthermore, 5 or more carbides having a diameter of 0.5 μm or less exist in 100 μm ² in the surface layer regions 11B, 12B, and 13B.

In the outer ring 11, the inner ring 12 and the ball 13 which are bearing parts in the present embodiment, the nitrogen concentration in the surface layer regions 11B, 12B and 13B below the contact surface is 0.2 mass% or more and 0.7 mass% or less. In the surface layer regions 11B, 12B, and 13B, there are five or more carbides having a diameter of 0.5 μm or less per 100 μm ² . As a result, the outer ring 11, the inner ring 12 and the ball 13 are bearing parts capable of ensuring high durability even in severe use environments. Further, it is more preferable that ten or more carbides exist in the region. The abundance (number) of the carbides can be confirmed by, for example, observing the region with a scanning electron microscope (SEM) and subjecting the observation result to image analysis processing.

  The outer ring 11, the inner ring 12 and the balls 13 preferably have an average nitrogen concentration of 0.7% by mass or less over the entire region within a depth of 20 μm from the surface. Thereby, not only the contact surfaces of the outer ring 11, the inner ring 12 and the balls 13, but also the formation of an incompletely hardened structure not only in the region other than the contact surface, for example, in the region that is not ground after the formation of the nitrogen-enriched layer. Is suppressed.

  Furthermore, the hardness of the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A, which are contact surfaces of the outer ring 11, the inner ring 12 and the ball 13, is preferably 700 HV or higher. Thereby, even when the outer ring 11, the inner ring 12 and the ball 13 are used in a harsh environment, a sufficient static load capacity can be ensured.

  In addition, the amount of retained austenite on the outer ring rolling surface 11A, the inner ring rolling surface 12A, and the ball rolling surface 13A, which are contact surfaces of the outer ring 11, the inner ring 12 and the ball 13, may be 20% by volume or more and 35% by volume or less. preferable. Thereby, durability of the outer ring 11, the inner ring 12 and the ball 13 in a foreign matter mixed environment can be improved while maintaining sufficient hardness on the outer ring rolling surface 11A, the inner ring rolling surface 12A and the ball rolling surface 13A. .

  Further, in the outer ring 11, the inner ring 12 and the ball 13, the total average retained austenite amount is preferably 18% by volume or less. Thereby, the improvement of the dimensional stability of the outer ring | wheel 11, the inner ring | wheel 12, and the ball | bowl 13 can be achieved.

  Further, when the outer ring 11, the inner ring 12 and the ball 13 are held at 500 ° C. for 1 hour, and the hardness distribution is measured in the depth direction in the cross section perpendicular to the contact surface, the difference between the maximum value and the minimum value of the hardness is 130HV. The above is preferable. In such outer ring 11, inner ring 12 and ball 13, introduction of a sufficient concentration of nitrogen is ensured.

  Next, with reference to FIGS. 3-5, the rolling bearing provided with the bearing components in other embodiment is demonstrated. The thrust needle roller bearing 2 has basically the same configuration as the deep groove ball bearing 1 and has the same effects. However, the thrust needle roller bearing 2 is different from the deep groove ball bearing 1 in the configuration of the raceway member and the rolling element. That is, the thrust needle roller bearing 2 has a disk-like shape, and a pair of race rings 21 as race members disposed so that one main surfaces thereof face each other, and a plurality of needle rollers 23 as rolling elements. And an annular retainer 24. The plurality of needle rollers 23 are in contact with a raceway rolling surface 21A formed on one main surface of the pair of raceways 21 facing each other on a roller rolling contact surface 23A that is an outer peripheral surface of the needle roller 23, and By being arranged at a predetermined pitch in the circumferential direction by the cage 24, the cage 24 is held so as to roll on an annular track. With the above configuration, the pair of race rings 21 of the thrust needle roller bearing 2 can rotate relative to each other.

  The bearing ring 21 of the thrust needle roller bearing 2 corresponds to the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1, and the needle roller 23 of the thrust needle roller bearing 2 corresponds to the ball 13 of the deep groove ball bearing. At the same time, the same nitrogen concentration and distribution state of carbides (including carbonitrides) are achieved. That is, the bearing ring 21 and the needle roller 23 have the same configuration as that of the deep groove ball bearing 1, the bearing ring rolling surface 21A (corresponding to the outer ring rolling surface 11A and the inner ring rolling surface 12A), the rolling contact surface 23A ( Corresponding to ball rolling surface 13A), surface layer regions 21B, 23B (corresponding to surface layer regions 11B, 12B, 13B), internal 21C, 23C (corresponding to internal 11C, 12C, 13C) and nitrogen-enriched layers 21D, 23D (nitrogen) Corresponding to the enriched layers 11D, 12D, and 13D). Thereby, the bearing ring 21 and the needle roller 23 are bearing parts that can ensure high durability even in a severe use environment.

  Next, a method for manufacturing the bearing component and the rolling bearing in the above embodiment will be described. With reference to FIG. 6, a molded object preparation process is first implemented as process (S10). In this step (S10), 0.95 mass% or more and 1.10 mass% or less carbon, 0.05 mass% or more and 0.35 mass% or less silicon, and 0.10 mass% or more and 0.50 mass% or less. A steel containing the following manganese and 1.30% by mass or more and 2.00% by mass or less of chromium and comprising the remaining iron and impurities, for example, a steel material comprising JIS standard SUJ2 is prepared. Specifically, for example, a steel bar or a steel wire having the above composition is prepared. Then, by performing processing such as forging and turning on the steel material, the steel material is formed into a shape such as an outer ring 11, an inner ring 12, a ball 13, a race ring 21, and a needle roller 23 shown in FIGS. A molded body is produced.

Next, a carbonitriding step is performed as a step (S20). In this step (S20), the formed body prepared in step (S10) is subjected to carbonitriding. This carbonitriding process can be performed as follows, for example. First, the molded body is preheated in a temperature range of about 780 ° C. to 820 ° C. for a period of 30 minutes to 90 minutes. Next, the molded body is carbonitrided by heating the preheated molded body to a carbonitriding temperature in a carbonitriding atmosphere containing ammonia, carbon monoxide, carbon dioxide and hydrogen. At this time, a _c ^* in the carbonitriding atmosphere is set to 0.88 to 1.27, and α is set to 0.012 to 0.020. Specifically, in an atmosphere in which α is adjusted by further introducing ammonia gas into an endothermic gas such as RX gas in which _ac ^* is adjusted by adding propane gas or butane gas as an enriched gas The molded body is heated and carbonitrided. The temperature of carbonitriding (carbonitriding temperature) can be, for example, 820 ° C. or higher and 880 ° C. or lower. The carbonitriding time can be set according to the desired nitrogen concentration of the nitrogen-enriched layer, and can be, for example, 4 hours or longer and 10 hours or shorter. Thereby, a nitrogen-enriched layer can be formed while appropriately distributing carbides in the surface layer region of the molded body.

Next, a diffusion step is performed as a step (S30). In this step (S30), nitrogen in the molded body is brought into the interior by being held at a diffusion temperature that is lower than the carbonitriding temperature in a diffusion atmosphere containing ammonia, carbon monoxide, carbon dioxide, and hydrogen. A diffusion process for diffusing is performed. At this time, a _c ^* in the diffusion atmosphere is set to 0.88 or more and 1.27 or less, and α is set to 0.003 or more and 0.012 or less. Specifically, in an atmosphere in which α is adjusted by further introducing ammonia gas into an endothermic gas such as RX gas in which _ac ^* is adjusted by adding propane gas or butane gas as an enriched gas The molded body is heated and the diffusion treatment is performed. The temperature (diffusion temperature) of the diffusion treatment can be, for example, 780 ° C. or more and 880 ° C. or less, and preferably 820 ° C. or more and 880 ° C. or less. Moreover, the time of the diffusion treatment can be set to, for example, 1 hour or more and 5 hours or less. As a result, while maintaining an appropriate distribution state of carbides in the surface layer region of the molded body, nitrogen is diffused to suppress the formation of an incompletely quenched structure, and nitrogen from the surface is suppressed to be separated from the surface region. The nitrogen concentration can be adjusted to an appropriate range.

  Next, a quenching process is implemented as process (S40). In this step (S40), the molded body on which the nitrogen-enriched layer is formed in steps (S20) to (S30) is quenched by being rapidly cooled from a predetermined quenching temperature. This quenching temperature can be, for example, 820 ° C. or higher and 880 ° C. or lower, and preferably 850 ° C. or higher and 880 ° C. or lower. The quenching treatment can be carried out, for example, by immersing the molded body in a quenching oil as a coolant maintained at a predetermined temperature. Further, in this step (S40), the region to be the surface layer portion below the contact surface in the molded body has an average of 20 ° C./sec or more in the temperature range from the quenching temperature to 600 ° C., and from the quenching temperature to 400 ° C. In this temperature range, it is preferable to cool at an average cooling rate of 30 ° C./sec or more. Thereby, the area | region which should become the surface layer part which hardenability fell by formation of the nitrogen rich layer can be hardened and hardened reliably.

  Next, a tempering step is performed as a step (S50). In this step (S50), the molded body that has been quenched in the step (S40) is tempered. Specifically, for example, the tempering treatment is performed by holding the compact in an atmosphere heated to a temperature range of 170 ° C. or higher and 220 ° C. or lower for a period of time of 0.5 hours to 4 hours. Furthermore, the tempering temperature may be 180 ° C. or higher and 210 ° C. or lower.

  Next, a finishing process is performed as a process (S60). In this step (S60), the contact surface, which is a surface that comes into contact with other components by processing the molded body tempered in step (S50), that is, the outer ring rolling surface 11A of the deep groove ball bearing 1, The ring rolling surface 12A and the ball rolling surface 13A, and the raceway rolling surface 21A and the rolling contact surface 23A of the thrust needle roller bearing 2 are formed. As the finishing process, for example, a grinding process can be performed. The outer ring 11, inner ring 12, ball 13, race ring 21, needle roller 23, etc., which are bearing parts in the present embodiment, are completed through the above steps.

  Furthermore, an assembly process is performed as a process (S70). In this step (S70), the outer ring 11, the inner ring 12, the ball 13, the race ring 21, the needle roller 23 produced in steps (S10) to (S60) and the cages 14 and 24 prepared separately are assembled. Together, the deep groove ball bearing 1 and the thrust needle roller bearing 2 in the above embodiment are assembled. Thereby, the manufacturing method of the rolling bearing in this Embodiment is completed.

  Here, in order to set the average nitrogen concentration in the surface layer region, which is a region within a depth of 20 μm from the contact surface, to 0.2 mass% or more and 0.7 mass% or less, in the above steps (S20) to (S30), Nitrogen-rich in the compact so that the nitrogen concentration in the surface layer regions 11B, 12B, 13B, 21B, and 23B below the contact surface is 0.2% by mass or more and 0.7% by mass or less by finishing in the subsequent step (S60). A layer is formed. That is, in consideration of the allowance in the step (S60), the amount of nitrogen is adjusted so that the nitrogen concentration in the surface layer portion after completion of the contact surface can be 0.2% by mass or more and 0.7% by mass or less. Adjusted nitrogen-enriched layers 11D, 12D, 13D, 21D, and 23D are formed. At this time, it is preferable to suppress the generation of an incompletely hardened structure by setting the nitrogen concentration to 0.7% by mass or less even in a region where the surface layer portion is not removed by finishing (for example, a thin portion). For this purpose, it is necessary to adjust the nitrogen concentration in the surface layer region to 0.7 mass% or less at the time of completion of the step (S30).

  Furthermore, in order to set the hardness of the contact surface to 700 HV or higher, it is necessary to appropriately set the heating temperature in the step (S50). Specifically, the tempering temperature can be set to 170 ° C. or higher and 220 ° C. or lower, for example. Further, in order to adjust the amount of retained austenite of the outer ring 11, the inner ring 12, the ball 13, the race ring 21, and the needle roller 23 to an appropriate value, it is necessary to adjust the quenching temperature in the step (S40).

  With the above procedure, the bearing component and the rolling bearing in the present embodiment can be manufactured.

  Note that the deep groove ball bearing and the thrust roller bearing described in the above embodiment and the bearing components constituting them are examples of the rolling bearing and the bearing component of the present invention. The rolling bearing and bearing component of the present invention can be applied to various types of rolling bearings.

An experiment was conducted to confirm the necessity of atmosphere control during carbonitriding. Specifically, carbon nitride treatment was performed on a test piece made of SUJ2 while changing the values of a _c ^* and α, and an experiment was conducted to confirm the carbon concentration and nitrogen concentration near the surface.

FIG. 7 shows carbon and nitrogen concentration distributions when carbonitriding for 2.5 hours is performed in an atmosphere in which a _c ^* is adjusted to 0.80 and α is set to 0.017. FIG. 8 shows carbon and nitrogen concentration distributions when carbonitriding is performed for 2.5 hours in an atmosphere where a _c ^* is 0.95 and α is 0.017. 7 and 8, the thin line indicates the carbon concentration distribution, and the thick line indicates the nitrogen concentration distribution. Since α is the same value, nitridation is normal in both cases. However, in FIG. 7, since a _c ^* is less than 0.88, carbide near the surface disappears, and the carbon of the parent phase is slightly removed. Yes.

9 shows the nitrogen concentration distribution when carbonitriding for 5 hours is performed in an atmosphere where a _c ^* is 1 and α is 0.017. FIG. 10 shows a _c ^* is 1 and α is 0. A nitrogen concentration distribution when carbonitriding for 5 hours is performed in an atmosphere of 005 is shown. The carbonitriding time is the same, but in FIG. 10 where α is small, the amount of nitrogen intrusion is smaller than in FIG. 9 where α is in an appropriate range.

From the above experimental results, it can be seen that the management of a _c ^* and α during the carbonitriding process is important. And it can be said that it is necessary to maintain a _c ^* in the range of 0.88 to 1.27 and α in the range of 0.012 to 0.02.

  An experiment was conducted to confirm the necessity of diffusion treatment after carbonitriding. Specifically, the carbonitriding process which changed conditions on the test piece which consists of SUJ2 was performed, the sample from which nitrogen concentration differs was produced, and the experiment which investigates the relationship between nitrogen concentration, surface hardness, and half width was conducted. Here, the “half-value width” means the half-value width of the peak (142.3 to 170.2 °) corresponding to martensite measured using the Kα ray of the Cr tube.

  FIG. 11 shows the relationship between the nitrogen concentration (average nitrogen concentration), the surface hardness, and the half-value width in the surface layer region obtained as a result of the experiment. Referring to FIG. 11, when the nitrogen concentration in the surface layer region is 0.7% by mass or more, the hardness is 700 HV or less, and the half-value width is 7.0 or less. From this, it can be seen that when the nitrogen concentration in the surface layer region is 0.7% by mass or more, an incompletely hardened structure is generated in the region. FIG. 12 is a photograph of the microstructure when the nitrogen concentration in the surface layer region is 1.0 mass%. From this photograph, it is confirmed that an incompletely hardened structure is formed near the surface. As described above, from the viewpoint of avoiding the formation of an incompletely quenched structure near the surface, the nitrogen concentration in the surface layer region that has a great influence on the rolling fatigue life should be 0.7% by mass or less. Is confirmed.

  In order to efficiently form a relatively high concentration (for example, 0.2% by mass or more) nitrogen-enriched layer, a high-concentration nitrogen-enriched layer is formed on the surface of the workpiece by carbonitriding. Then, it is preferable to adopt a process for performing a diffusion treatment. At this time, the formation of an incompletely hardened structure can be suppressed by setting the nitrogen concentration in the vicinity of the surface to 0.7 mass% or less by diffusion treatment. If the nitrogen concentration in the surface layer of the entire part is reduced to 0.7% by mass or less by diffusion treatment, incompletely hardened structures remain in the product even in areas that are not processed in the subsequent process (for example, thinning parts). Is done.

  An experiment was conducted to confirm the necessity of atmosphere control in the diffusion treatment. Specifically, after carbonitriding the test piece made of SUJ2, the diffusion treatment was performed by changing the α value, and an experiment was conducted to investigate the effect of the α value on the nitrogen concentration in the surface layer region. It was. FIG. 13 shows the nitrogen concentration distribution near the surface when α is 0, and FIG. 14 shows when the α is 0.005.

As shown in FIG. 13, when the diffusion treatment is performed in an atmosphere where α is 0, that is, _PN is 0, it can be seen that nitrogen is detached from the surface and the nitrogen concentration in the surface layer region is lowered. On the other hand, when the value of α is set to 0.005, it can be seen that the above-described separation of nitrogen is suppressed and a surface region having an appropriate nitrogen concentration is obtained. From this, it is understood that it is important to manage the value of α also in the diffusion process. And according to examination of this inventor, the surface layer area | region which has suitable nitrogen concentration is obtained by setting the value of (alpha) to the range of 0.003-0.012.

  In the diffusion treatment after the carbonitriding treatment, it is general that only the carbon potential is adjusted without introducing ammonia into the atmosphere. However, according to the study of the present inventor, it is considered that the nitrogen concentration in the surface layer region is lowered by such a diffusion treatment, and the improvement of the durability of the bearing component is hindered. And the durability improvement of a bearing component is achieved by setting the value of (alpha) in the range of 0.003-0.012 in a spreading | diffusion process.

  Experiments were conducted to investigate the relationship between surface hardness and static load capacity. Specifically, a test piece made of SUJ2 was prepared, and after carbonitriding, diffusion, and quenching were performed under the same conditions, samples with different surface hardness were produced by changing the tempering temperature. Then, the surface hardness of the sample was measured, and a ball made of silicon nitride having a diameter of φ9.525 mm was pressed against the surface of the sample with a constant load to form an indentation. And the depth of the formed indentation (residual indent after removing the load) was investigated. The experimental results are shown in FIG. In FIG. 15, the horizontal axis indicates the stress applied to the surface, and the vertical axis indicates the depth of the indentation.

  Referring to FIG. 15, the depth of the indentation becomes deeper as the surface hardness becomes lower. Only when the surface hardness is 700 HV or higher and the hardness is 730 HV, the indentation depth is allowed even when used in applications requiring high static load capacity. From this, it can be said that the hardness at the contact surface of the bearing component is preferably 700 HV or more.

  An experiment was conducted to investigate the influence of nitrogen concentration in the surface layer on the durability of the bearing ring of a rolling bearing. Specifically, a rolling fatigue life test was performed in a state where indentations were formed on the rolling surface of the race (inner ring). The experimental procedure is as follows.

  The test was conducted using a deep groove ball bearing of JIS standard 6206 model number (inner diameter 30 mm, outer diameter 62 mm, width 16 mm, 9 rolling elements, manufactured by SUJ2). First, an inner ring was produced by the same procedure as in the above embodiment. At this time, the concentration distribution of nitrogen entering the inner ring surface is controlled by adjusting the partial pressure of undecomposed ammonia, hydrogen partial pressure, carbon activity, heat treatment time, quenching temperature, etc. in the atmosphere during carbonitriding did. For comparison, an inner ring without carbonitriding was also produced. As a result, inner rings having the five nitrogen concentration distributions shown in FIGS. 16 to 20 were obtained. Here, in FIGS. 16 to 20, the horizontal axis indicates the distance from the surface (rolling surface), and the vertical axis indicates the nitrogen concentration. Moreover, the concentration distribution measurement of nitrogen was implemented twice for each condition, and the measurement results twice are shown in FIGS.

  Next, indentations were formed on the obtained inner ring. Here, as a method for evaluating the life of a rolling bearing that simulates an actual use environment, a life test under lubrication mixed with foreign matter may be performed. This test method operates by mixing particles having a particle diameter of 100 to 180 μm (hardness of about 800 HV) produced by gas atomization into the lubricating oil of a rolling bearing and evaluating the failure life. The reason why the particle size is 100 to 180 μm is that hard foreign substances having a particle size of about 100 μm at the maximum may be mixed in an actual use environment. Under such foreign matter-mixed lubrication, an indentation is formed on the bearing component due to the hard foreign matter, and indentation origin type separation is generated in which the indentation starts as a starting point. FIG. 21 shows the surface shape (indentation shape) of the raceway ring damaged by the life test under the foreign matter mixed lubrication. In FIG. 21, the horizontal axis indicates the distance from the reference point along the surface (rolling surface), and the vertical axis indicates the height. From the reference point on the horizontal axis to the vicinity of 0.3 mm, the initial rolling surface corresponds to the indentation from 0.3 mm to 1.1 mm, and the region of 1.1 mm or more corresponds to the peeled portion. From FIG. 21, it can be seen that the indentation formed by the hard foreign matter has a depth of about 15 to 20 μm.

  In addition, the shape and microstructure of the raised portion of the indentation are major factors that determine the life. The shape of the raised portion of the indentation is considered to be determined by the microstructure of the material up to the depth of the indentation. Moreover, the microstructure of steel changes with the nitrogen concentration. From these facts, it is considered that the lifetime in an environment where hard foreign matter intrudes depends not only on the surface nitrogen concentration but also on the nitrogen concentration from the surface to the indentation depth.

  As described above, the indentation depth is about 20 μm at the maximum. For this reason, in the present specification and the like, the region from the surface to a depth of 20 μm is defined as the surface layer region, and attention is paid to the average nitrogen concentration in the surface layer region. Specifically, the average nitrogen concentration in the surface layer region is obtained by performing line analysis in the depth direction with EPMA (Electron Probe Micro Analysis) on a cross section perpendicular to the surface, and calculating an average value from the surface to a depth of 20 μm. Can be investigated.

  Based on the above examination results, the inner ring has an indenter for measuring the Rockwell hardness of a conical diamond at the center of the groove bottom of the rolling surface (an indenter having a spherical surface with a curvature of 0.2 mm at the apex of a cone having an apex angle of 120 °). ) Was pressed with a load of 196 N to form an indentation. When the shape of the formed indentation was measured with a three-dimensional surface shape apparatus, it was confirmed that the raised shape at the periphery of the indentation was substantially symmetrical with respect to the axial direction and the circumferential direction with the center of the indentation as the axis of symmetry. FIG. 22 shows a typical indentation shape. The applied indentations were 30 per inner ring, and were formed at equal intervals in the circumferential direction (that is, every 12 ° of the central angle).

  The bearings were assembled by combining rolling elements, cages and the like in addition to the normal outer ring that was not subjected to carbonitriding and formed no indentation on the inner ring thus produced. The obtained bearing was subjected to a life test. The test results are shown in FIG. In addition, bearings in which the formation of indentations was omitted in the same procedure were created, and the life in a normal clean oil lubrication environment was also investigated. FIG. 24 shows the test results of the life in the clean oil lubrication environment.

  23 and 24, the horizontal axis represents the average nitrogen concentration in the surface layer region, and the vertical axis represents the time (L10 life) when the cumulative failure probability is 10%. Referring to FIG. 23, when the average nitrogen concentration in the surface layer region is 0.2% by mass or more, the indentation origin type peeling life is twice or more as compared with the case where the average nitrogen concentration is 0. Referring to FIG. 24, when the average nitrogen concentration in the surface layer region is 0.2% by mass or more, the life in the clean oil lubrication environment is also more than twice that in the case where the average nitrogen concentration is 0. Yes.

  From the above experimental results, it was confirmed that the average nitrogen concentration in the surface layer region should be 0.2% by mass or more in order to obtain a clear effect of formation of the nitrogen-enriched layer (carbonitriding treatment). . Further, from the experimental results described in Example 2 above, considering that the average nitrogen concentration in the surface layer region should be 0.7% by mass or less in order to suppress the formation of an incompletely quenched structure, it is appropriate. It can be said that the surface nitrogen concentration is 0.2% by mass or more and 0.7% by mass or less.

  An experiment was conducted to investigate the relationship between the amount of retained austenite on the contact surface and the indentation-origin peel life. Specifically, a sample was prepared in which the average nitrogen concentration in the surface layer region was constant (0.4% by mass), and the amount of retained austenite was changed by changing the tempering temperature. A starting-type peel life test was conducted. The experimental results are shown in FIG. In FIG. 25, the horizontal axis represents the amount of retained austenite on the rolling surface of the inner ring, and the vertical axis represents the L10 life.

  Referring to FIG. 25, the indentation origin peeling life becomes longer as the amount of retained austenite increases. When the amount of retained austenite is 20% by volume or more, the indentation origin type peeling life is twice or more that of the case of the average nitrogen concentration of 0 in Example 5. On the other hand, if the amount of retained austenite exceeds 35% by volume, the hardness on the rolling surface (contact surface) may be insufficient. From the above examination results, it can be said that the amount of retained austenite at the contact surface is preferably 20% by volume or more and 35% by volume or less.

  Experiments were conducted to investigate the relationship between retained austenite content and dimensional stability of the entire part. Specifically, by preparing a ring-shaped test piece made of SUJ2 having an outer diameter φ: 60 mm, an inner diameter φ: 54 mm, and an axial length t: 15 mm, and performing heat treatment such as carbonitriding under different conditions Quenched and hardened samples with different overall average retained austenite amounts were obtained. The residual austenite amount distribution of the sample is shown in FIG. In FIG. 26, the horizontal axis indicates the distance from the surface, and the vertical axis indicates the amount of retained austenite. Based on FIG. 26, the average amount of retained austenite of the entire sample was calculated. In the legend of FIG. 26, “quenching temperature−tempering temperature−average nitrogen concentration in surface layer region” is displayed. For example, the display of 850 ° C.-180 ° C.-N 0.4 mass% indicates that the quenching temperature is 850 ° C., the tempering temperature is 180 ° C., and the average nitrogen concentration in the surface layer region is 0.4% by mass.

  The sample was held at 120 ° C. for 2500 hours. And the outer diameter of the sample before and behind the said process was measured, and dimensional stability was evaluated by the change rate (value which remove | divided the variation | change_quantity by the outer diameter before a change). Here, the treatment of holding at 120 ° C. for 2500 hours is to accelerate and generate the secular dimensional change that appears over a long period in the actual machine. The test results are shown in Table 1. FIG. 27 shows the relationship between the average retained austenite amount and the dimensional change rate. In FIG. 27, the horizontal axis represents the average retained austenite amount in each sample, and the vertical axis represents the dimensional change rate of the outer diameter.

With reference to Table 1 and FIG. 27, it can be said that the average retained austenite amount of the entire part is preferably 18% by mass or less from the viewpoint of setting the aging change rate to 60 × 10 ⁻⁵ or less which is a preferable value.

  As described in Example 5 above, in order to impart sufficient durability to the bearing component, the average nitrogen concentration in the surface layer region needs to be 0.2% by mass or more. Here, the nitrogen concentration can be confirmed by, for example, EPMA as described above. However, performing quality confirmation using EPMA in the mass production process of bearing parts complicates the quality confirmation work. Therefore, it is desirable that quality confirmation in the mass production process is performed by a simpler method. Therefore, the present inventor has studied a method for confirming the quality by utilizing the fact that nitrogen that has entered the steel improves the temper softening resistance.

  Specifically, a quench-hardened sample having different nitrogen concentrations (carbonitrided) is prepared, the sample is subjected to a heat treatment held at 500 ° C. for 1 hour, and the cross-sectional hardness distribution of the sample after the heat treatment An experiment was conducted to measure. Here, nitrogen does not penetrate into the center of the sample, and the center has the smallest temper softening resistance. Therefore, the hardness of the central portion is the lowest. On the other hand, the surface layer portion into which nitrogen has entered has a temper softening resistance corresponding to the nitrogen concentration. Therefore, the surface layer portion has a hardness higher than that of the center portion and has a hardness corresponding to the nitrogen concentration. FIG. 28 shows the relationship between the nitrogen concentration and the hardness difference. In FIG. 28, the horizontal axis represents the nitrogen concentration, and the vertical axis represents the difference between the maximum value and the minimum value in the cross-sectional hardness distribution.

  Referring to FIG. 28, the difference in hardness after the heat treatment is greatest when the nitrogen concentration is about 0.2 to 0.3% by mass. Further, in the range where the nitrogen concentration is 0.2% by mass or more and 0.3% by mass or less, the hardness difference is 130HV or more with a probability of 95% or more. Therefore, when the hardness distribution is measured in the depth direction in a cross section perpendicular to the surface after being held at 500 ° C. for 1 hour, if the difference between the maximum value and the minimum value of the hardness is 130 HV or more, the nitrogen concentration is 0.00. It can be judged that it is 2 mass% or more. By adopting such a determination method, it is possible to easily check the quality of bearing parts.

When bearing steel such as JIS standard SUJ2 containing Cr is infiltrated into the steel by carbonitriding or the like, the Cr concentration in the base material decreases and the austenite single phase region expands. The limit concentration increases. As a result, if a carbonitriding treatment with a high concentration (for example, forming a nitrogen-enriched layer of 0.2% by mass or more) is performed without taking any special measures, even if decarburization does not occur, carbide (carbonitride) Decrease or disappear. Here, from the viewpoint of increasing the strength of the bearing component, it is considered preferable to leave the carbide and utilize the precipitation strengthening function of the carbide. In the method for manufacturing a bearing component of the present invention, the value of a _c ^* is set to 0.88 or more and 1.27 or less, and carburization is performed faster than the increase in the carbon solid solubility limit of the nitrogen-enriched layer. The disappearance is suppressed. An experiment was conducted to confirm the effect of this carbide remaining. FIG. 29 is a cross-sectional SEM photograph of a sample made of SUJ2 that has been subjected to carbonitriding by a conventional carbonitriding method. In the photograph of FIG. 29, the carbide is almost lost. In contrast, FIG. 30 is a cross-sectional SEM photograph of a sample made of SUJ2 that has been subjected to carbonitriding by the carbonitriding method (with the value of a _c ^* being 1) employed in the method for manufacturing a bearing component of the present invention. is there. In the photograph of FIG. 30, there are five or more carbides having a diameter of 0.5 μm or less per 100 μm ² .

And in order to confirm the effect of the said carbide | carbonized_material, the carbonitriding process was implemented on the test piece which consists of SUJ2 on different conditions, and the sample which made hardness 750HV, changing the abundance (number density) of a carbide | carbonized_material was produced. An experiment was conducted to measure the depth of indentation formed by pressing a ball made of silicon nitride having a diameter of 9.525 mm against the surface of the sample. The experimental results are shown in FIG. In FIG. 31, the horizontal axis indicates the pressing pressure of the silicon nitride balls, and the vertical axis indicates the depth of the indentation formed by pressing the balls. Further, in FIG. 31, square marks correspond to measurement results of samples in which carbides disappeared, and diamond marks correspond to measurement results of samples having 5 or more carbides having a diameter of 0.5 μm or less per 100 μm ² .

Referring to FIG. 31, in the sample in which 5 or more carbides (carbonitrides) having a diameter of 0.5 μm or less exist per 100 μm ² in comparison with the sample in which the carbides are lost even though the hardness is the same. It is confirmed that the depth of the indentation is reduced. From the above experimental results, from the viewpoint of improving the static load capacity of the bearing component, it is preferable that five or more carbides (carbonitrides) having a diameter of 0.5 μm or less exist per 100 μm ^{2 in} the surface layer region of the bearing component. It can be said.

  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.

  INDUSTRIAL APPLICABILITY The bearing component, rolling bearing, and bearing component manufacturing method of the present invention can be applied particularly advantageously to bearing components, rolling bearings, and bearing component manufacturing methods that are required to ensure high durability even in severe use environments. .

  DESCRIPTION OF SYMBOLS 1 Deep groove ball bearing, 2 Thrust needle roller bearing, 11 Outer ring, 11A Outer ring rolling surface, 11B, 12B, 13B, 21B, 23B Surface region, 11C, 12C, 13C, 21C, 23C Inside, 11D, 12D, 13D, 21D , 23D Nitrogen-enriched layer, 12 inner ring, 12A inner ring rolling surface, 13 balls, 13A ball rolling surface, 14, 24 cage, 21 bearing ring, 21A bearing ring rolling surface, 23 needle roller, 23A rolling contact surface .

Claims (9)

0.95 mass% or more and 1.10 mass% or less carbon, 0.05 mass% or more and 0.35 mass% or less silicon, 0.10 mass% or more and 0.50 mass% or less manganese, Containing 30% by mass or more and 2.00% by mass or less of chromium, and made of steel composed of the remaining iron and impurities,
The average nitrogen concentration in the surface layer region, which is a region within a depth of 20 μm from the contact surface that is a rolling contact surface with other parts, is 0.2% by mass or more and 0.7% by mass or less,
A bearing component in which five or more carbides having a diameter of 0.5 μm or less exist per 100 μm ^{2 in the} surface layer region.   The bearing component according to claim 1, wherein the average nitrogen concentration is 0.7 mass% or less in the entire region within a depth of 20 μm from the surface.   The bearing component according to claim 1, wherein the contact surface has a hardness of 700 HV or more.   The bearing part of any one of Claims 1-3 whose amount of retained austenite in the said contact surface is 20 volume% or more and 35 volume% or less.   The bearing component according to any one of claims 1 to 4, wherein an overall average retained austenite amount is 18% by volume or less.   The difference between the maximum value and the minimum value of hardness is 130 HV or more when the hardness distribution is measured in the depth direction in a cross section perpendicular to the contact surface after being held at 500 ° C for 1 hour. The bearing component according to any one of claims. A track member;
A rolling element arranged in contact with the raceway member,
At least any one of the said track member and the said rolling element is a rolling bearing which is a bearing component of any one of Claims 1-6. 0.95 mass% or more and 1.10 mass% or less carbon, 0.05 mass% or more and 0.35 mass% or less silicon, 0.10 mass% or more and 0.50 mass% or less manganese, Containing 30% by mass or more and 2.00% by mass or less of chromium, and preparing a formed body made of steel composed of the remaining iron and impurities;
Carbonitriding the molded body by heating the molded body to a carbonitriding temperature in a carbonitriding atmosphere containing ammonia, carbon monoxide, carbon dioxide and hydrogen;
Nitrogen in the molded body is diffused by holding the carbonitrided molded body at a diffusion temperature that is lower than the carbonitriding temperature in a diffusion atmosphere containing ammonia, carbon monoxide, carbon dioxide, and hydrogen. A process of
The undecomposed ammonia partial pressure P _N, the hydrogen partial pressure of P _H, the following equation a _c ^* (1), when defined by the following equation alpha (2), is a _c ^* in the carbonitriding atmosphere 0.88 to 1.27, α is set to 0.012 to 0.020, a _c ^* in the diffusion atmosphere is 0.88 to 1.27, and α is 0.003 to 0.012 A manufacturing method for bearing parts, set to
  9. The method according to claim 8, further comprising a step of performing a tempering treatment in which the molded body is heated to a temperature range of 170 ° C. or higher and 220 ° C. or lower after the step of diffusing nitrogen in the molded body. The manufacturing method of the bearing components as described.