JP2009222188A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing for achieving not only higher durability and higher smearing resistance but also higher dry-run performance in a foreign matter mixing environment, while suppressing the deterioration of the hardness of bearing components in a high temperature environment. <P>SOLUTION: An outer ring 11 and an inner ring 12 constituting the three-point contact ball bearing 1 is formed of steel which contains 0.11-0.15% carbon, 0.1-0.25% silicon, 0.15-0.35% manganese, 3.2-3.6% nickel, 4-4.25% chromium, 4-4.5% molybdenum, 1.13-1.33% vanadium, and iron and impurities in the rest. In a region including rolling surfaces 11A, 12A, nitrogen enriched layers 11B, 12B are formed each of which has a nitrogen concentration of 0.05 mass% or higher. A total value of the carbon concentration and the nitrogen concentration of the nitrogen enriched layers 11B, 12B is 0.55-1.9 mass%. On the other hand, a ball 13 is formed of ceramic. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rolling bearing, and more specifically to a rolling bearing provided with a rolling element made of ceramics.

  In recent years, with the progress of high performance and high efficiency of a mechanical device in which a rolling bearing is used, the rolling bearing tends to be required to have high durability under a severe use environment. Specifically, in a rolling bearing used in a foreign matter mixed environment where hard foreign matter enters inside, the rolling bearing is damaged early (with an operation time shorter than the calculated life of the bearing) due to the biting of the foreign matter. There is a case. Further, even when the applied load is relatively small, smearing may occur in a rolling bearing that rotates at a high speed. Furthermore, seizure may occur in a rolling bearing used in an environment where lubrication is insufficient. Moreover, when a rolling bearing is used in a high temperature environment, for example, a high temperature environment exceeding 200 ° C., the hardness of components (bearing components) constituting the rolling bearing may be reduced, and durability may be reduced.

  On the other hand, when the bearing part is made of steel, the strength at high temperature is improved by adding 4 mass% or more of chromium to the steel to improve the temper softening resistance of the steel, and the high temperature environment of the rolling bearing. The durability under can be improved. In addition, when the bearing part is made of steel having a carbon content of 0.15% by mass or less, in order to improve the durability in a foreign matter mixed environment, for example, carburizing treatment is performed on the bearing part in addition to the surface layer portion. After forming a region (carburized layer) having a higher carbon concentration than that in the region, a process for forming a nitrogen-enriched layer having a higher nitrogen concentration in the surface layer portion than in other regions, such as nitriding, is performed. Measures can be adopted.

  Here, in a bearing component made of steel having a high chromium content, for example, steel containing 4% by mass or more of chromium, a chemically stable oxide film is formed on the surface layer portion. Therefore, even if a normal nitriding treatment is performed, there is a problem that nitrogen does not enter the surface layer portion and a nitrogen-enriched layer is not formed. On the other hand, a countermeasure for forming a nitrogen-enriched layer by performing plasma nitriding has been proposed (see, for example, Patent Document 1). With respect to the control of the plasma nitriding treatment, for example, a method based on spectroscopic analysis of glow discharge and a method based on the current density of the current flowing through the workpiece have been proposed (see, for example, Patent Documents 2 and 3). ). As a result, a nitrogen-enriched layer can be formed on the surface layer portion of the bearing part made of steel containing 4% by mass or more of chromium.

In order to improve seizure resistance, a countermeasure has been proposed in which a ball as a bearing part is immersed in an organophosphorus compound to form a reaction film on the surface (for example, see Patent Document 4).
Japanese Patent Laid-Open No. 2-57675 JP-A-7-118826 Japanese Patent Laid-Open No. 9-3646 JP-A-9-133130

  However, even when a nitrogen-enriched layer is formed on the surface layer portion of a bearing part made of steel containing 4% by mass or more of chromium using the plasma nitriding treatment as described above, the characteristics of the bearing part are not sufficiently improved. There is a case. That is, when stress is repeatedly applied to the bearing parts as described above, peeling or fracture may occur at an early stage (decrease in fatigue strength). Further, when an impact stress is applied to the bearing component as described above, breakage may easily occur (decrease in toughness). In other words, in bearing parts made of steel containing 4% by mass or more of chromium, merely forming a nitrogen-enriched layer increases the hardness of the surface layer portion, but it is not always sufficient particularly in terms of fatigue strength and toughness. There is a problem in that it may not be possible to obtain proper characteristics.

  Also, the environment in which rolling bearings are used is becoming increasingly severe. For example, in rolling bearings used for jet engines such as aircraft, lubrication is temporarily performed in addition to suppressing the decrease in the hardness of bearing components in a high temperature environment, improving durability in a foreign matter mixed environment and improving smearing resistance. Therefore, improvement of seizure resistance (so-called improvement of dry run performance) is required when it is interrupted. Therefore, it cannot be said that conventional countermeasures including the countermeasures disclosed in Patent Documents 1 to 4 are sufficient.

  Accordingly, an object of the present invention is a rolling bearing capable of achieving not only suppression of hardness reduction of a bearing component in a high temperature environment, improvement in durability and contamination resistance in a foreign matter mixed environment, but also improvement in dry run performance. Is to provide.

  The rolling bearing according to the present invention has carbon of 0.11% by mass to 0.15% by mass, silicon of 0.1% by mass to 0.25% by mass, and 0.15% by mass to 0.35%. Manganese of not more than mass%, nickel of not less than 3.2 mass% and not more than 3.6 mass%, chromium of not less than 4 mass% and not more than 4.25 mass%, and molybdenum of not less than 4 mass% and not more than 4.5 mass% 1,3 to 1.33% by mass of vanadium, the balance is made of steel consisting of iron and impurities, and the region including the surface has a nitrogen concentration of 0.05% by mass or more. An enrichment layer is formed, and the total value of the carbon concentration and the nitrogen concentration in the nitrogen enrichment layer is 0.55% by mass or more and 1.9% by mass or less, and the race member is in contact with the race member. And a plurality of rolling elements arranged on the track. And the rolling element consists of ceramics.

  The present inventor has made a detailed study on the cause of a decrease in fatigue strength and toughness when a nitrogen-enriched layer is formed on a bearing part made of steel containing 4% by mass or more of chromium. As a result, it was found that the fatigue strength and toughness of the bearing parts are reduced due to the following phenomenon.

That is, when a nitrogen-enriched layer is formed on a bearing part made of steel containing 4% by mass or more of chromium by plasma nitriding as described above, the amount of nitrogen in the surface layer portion is the solid solubility limit of the steel constituting the bearing part. (Solution limit including nitrogen contained in the precipitate) is exceeded. Therefore, iron nitride (Fe ₃ N, Fe ₄ N, etc.) precipitated along the grain boundaries is formed in the steel constituting the bearing component. An iron nitride formed with a length of not less than 2 μm and a length of not less than 7.5 μm (hereinafter referred to as having an aspect ratio of not less than 2 and a length of not less than 7.5 μm along the grain boundary) The formed iron nitride is referred to as grain boundary precipitate), which may be the starting point of peeling and fracture.

  More specifically, when stress is repeatedly applied to the bearing component on which the grain boundary precipitate is formed, the grain boundary precipitate may become a stress concentration source, and a crack may occur. And since this crack progresses and it leads to peeling and a fracture | rupture, the fatigue strength of a bearing component falls. In addition, when an impact stress is applied to the bearing component on which the grain boundary precipitate is formed, the grain boundary precipitate promotes the generation and progress of cracks, so that the toughness may be lowered. That is, as a result of an excessive amount of nitrogen entering the surface layer portion of the bearing part, grain boundary precipitates are formed, and this can cause a decrease in fatigue strength and toughness of the bearing part.

  On the other hand, in the race member constituting the rolling bearing of the present invention, a nitrogen enriched layer having a nitrogen concentration of 0.05% by mass or more is formed in a region including the surface of the race member made of steel having an appropriate component composition. In addition, the formation of grain boundary precipitates can be suppressed by setting the total value of the carbon concentration and the nitrogen concentration in the nitrogen-enriched layer within an appropriate range. As a result, according to the race member constituting the rolling bearing of the present invention, it is made of steel containing 4% by mass or more of chromium, so that a decrease in hardness in a high temperature environment is suppressed, and a nitrogen enriched layer is formed on the surface layer portion. Can be provided, and a raceway member in which fatigue strength and toughness are sufficiently secured can be provided. The reason why the component ranges of steel constituting the raceway member and the nitrogen and carbon concentrations in the nitrogen-enriched layer are limited to the above ranges will be described below.

Carbon: 0.11 mass% or more and 0.15 mass% or less In the steel which comprises a track member, if carbon is less than 0.11 mass%, the problem of the manufacturing cost rise of steel may generate | occur | produce. On the other hand, when carbon exceeds 0.15 mass%, problems such as an increase in core hardness and a decrease in toughness may occur. Therefore, carbon needs to be 0.11 mass% or more and 0.15 mass% or less.

Silicon: 0.1 mass% or more and 0.25 mass% or less In the steel which comprises a track member, if silicon is less than 0.1 mass%, the problem of the manufacturing cost rise of steel may generate | occur | produce. On the other hand, when silicon exceeds 0.25 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 0.1 mass% or more and 0.25 mass% or less.

Manganese: 0.15% by mass or more and 0.35% by mass or less In the steel constituting the race member, if manganese is less than 0.15% by mass, there may be a problem of an increase in steel manufacturing cost. On the other hand, when manganese 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, manganese needs to be 0.15 mass% or more and 0.35 mass% or less.

Nickel: 3.2 mass% or more and 3.6 mass% or less In the steel constituting the raceway member, if nickel is less than 3.2 mass%, there may be a problem that the effect of improving corrosion resistance, hardness and toughness is reduced. . On the other hand, when nickel exceeds 3.6 mass%, the problem of an increase in the amount of retained austenite may occur. Therefore, nickel needs to be 3.2 mass% or more and 3.6 mass% or less.

Chromium: 4% by mass or more and 4.25% by mass or less In the steel constituting the race member, when chromium is less than 4% by mass, there may be a problem that the temper softening resistance is lowered. On the other hand, when chromium exceeds 4.25 mass%, the problem that the solid solution of carbide is inhibited when quenching is performed may occur. Therefore, chromium needs to be 4 mass% or more and 4.25 mass% or less.

Molybdenum: 4% by mass or more and 4.5% by mass or less In the steel constituting the raceway member, when molybdenum is less than 4% by mass, there may be a problem that the temper softening resistance is lowered. On the other hand, when molybdenum exceeds 4.5 mass%, the problem that the manufacturing cost of steel rises may generate | occur | produce. Therefore, molybdenum needs to be 4 mass% or more and 4.5 mass% or less.

Vanadium: 1.13 mass% or more and 1.33 mass% or less In the steel constituting the raceway member, if vanadium is less than 1.13 mass%, the effect of reducing the temper softening resistance and refining the microstructure by adding vanadium is effective. The problem of fewer may occur. On the other hand, when vanadium exceeds 1.33 mass%, the problem that the manufacturing cost of steel rises may generate | occur | produce. Therefore, vanadium needs to be 1.13 mass% or more and 1.33 mass% or less.

Nitrogen concentration in the nitrogen-enriched layer: 0.05% by mass or more In the raceway member made of the above steel, in order to provide sufficient hardness to the surface layer portion and ensure wear resistance, the nitrogen concentration in the region including the surface It is necessary to form a nitrogen-enriched layer with 0.05% by mass or more. In order to further improve the wear resistance and the like, the nitrogen concentration on the surface of the race member is preferably 0.15% by mass or more.

Total value of nitrogen concentration and carbon concentration in the nitrogen-enriched layer: 0.55% by mass or more and 1.9% by mass or less In the raceway member made of the above steel, sufficient hardness is given to the surface layer part to provide wear resistance and the like. In order to secure it, it is important to manage not only the nitrogen concentration but also the carbon concentration. And, if the total value of the nitrogen concentration and the carbon concentration in the nitrogen-enriched layer is less than 0.55 mass, it is difficult to impart sufficient hardness to the surface layer portion to ensure wear resistance and the like. Found out. Therefore, the total value of the nitrogen concentration and the carbon concentration in the nitrogen-enriched layer needs to be 0.55% by mass or more. Further, in order to make it easy to provide sufficient hardness to the surface layer portion to ensure wear resistance and the like, the total value of the nitrogen concentration and the carbon concentration in the nitrogen-enriched layer is 0.7% by mass or more. It is preferable that

  On the other hand, in the raceway member made of the steel, when the nitrogen concentration in the surface layer portion increases, grain boundary precipitates are easily formed, and when the carbon concentration increases, the tendency becomes stronger. And this inventor discovered that it will become difficult to suppress formation of a grain-boundary precipitate when the total value of the nitrogen concentration and carbon concentration in a nitrogen enriched layer exceeds 1.9 mass%. Therefore, the total value of the nitrogen concentration and the carbon concentration in the nitrogen-enriched layer needs to be 1.9% by mass or less. Moreover, in order to further suppress the formation of grain boundary precipitates, the total value of the nitrogen concentration and the carbon concentration in the nitrogen-enriched layer is preferably 1.7% by mass or less. The carbon concentration and the nitrogen concentration refer to concentrations in the substrate (matrix) which is a region other than carbides and nitrides such as iron and chromium.

  Furthermore, in the rolling bearing of the present invention, the rolling element is made of ceramics. Thereby, generation | occurrence | production of smearing is suppressed, and since the track member and rolling element which mutually contact become a dissimilar material, seizure resistance improves. Moreover, the durability of the rolling element in a foreign matter mixed environment is improved by adopting a ceramic having a higher hardness than steel as the material of the rolling element. As a result, the improvement in the smearing resistance and the durability in the environment where foreign matters are mixed, and the improvement in the durability, for example, the dry run performance in an environment where the lubrication is insufficient are achieved. Moreover, since the rolling elements are made of ceramics, a decrease in hardness of the rolling elements in a high temperature environment is suppressed. Here, as the ceramic constituting the rolling element, for example, silicon nitride, sialon, alumina, zirconia, or the like can be employed.

  As described above, in the rolling bearing according to the present invention, the raceway member is made of steel containing 4% by mass or more of chromium, and the rolling element is made of ceramics, thereby suppressing a decrease in hardness of the bearing component in a high temperature environment. Is done. In addition, a nitrogen-enriched layer having an appropriate range of the total value of carbon concentration and nitrogen concentration is formed on the surface layer portion of the raceway member made of steel having an appropriate component composition, and the rolling element is made of ceramics. In addition, the durability of the bearing component in a foreign matter mixed environment is improved. Furthermore, by combining a rolling member made of ceramics with a raceway member made of steel, improvement in smearing resistance and improvement in dry run performance are achieved. As a result, according to the rolling bearing of the present invention, not only the hardness reduction of the bearing parts under a high temperature environment, the improvement of the durability and the smearing resistance in the environment containing foreign matters, but also the improvement of the dry run performance is achieved. Possible rolling bearings can be provided.

  In the rolling bearing, preferably, the nitrogen-enriched layer has a thickness of 0.1 mm or more. In the race member, the strength of the surface and the region immediately below the surface, specifically, the region within a distance of 0.1 mm from the surface is often important. Therefore, by setting the thickness of the nitrogen-enriched layer to 0.1 mm or more, it is possible to give sufficient strength to the race member. In order to further increase the strength of the raceway member, the thickness of the nitrogen-enriched layer is preferably 0.15 mm or more.

  In the rolling bearing, preferably, the nitrogen-enriched layer has a hardness of 800 HV or more. By setting the hardness of the nitrogen-enriched layer formed on the surface layer portion to 800 HV or higher, it is possible to ensure the strength of the race member more reliably.

  Preferably, in the rolling bearing, when the nitrogen-enriched layer is observed with a microscope, the number of iron nitrides having an aspect ratio of 2 or more and a length of 7.5 μm or more is 1 or less in a square region 5 field of view having a side of 150 μm. It is.

  As described above, grain boundary precipitates, which are iron nitrides having an aspect ratio of 2 or more and a length of 7.5 μm or more, may reduce the characteristics such as fatigue strength and toughness of bearing parts. And when the inventor investigated the relationship between the fatigue strength of the bearing component and the number density of the grain boundary precipitates for the bearing component made of steel having the above component composition, when the nitrogen-enriched layer was observed with a microscope, It was found that the fatigue strength of the bearing component is reduced when the grain boundary precipitates are present at a number density of more than one in 5 fields of a square region having a side of 150 μm. Therefore, when the nitrogen-enriched layer is observed with a microscope, the fatigue strength of the raceway member can be improved by the number of grain boundary precipitates being one or less in a 5 visual field in a square region having a side of 150 μm. In order to further improve the fatigue strength of the raceway member, the number of the grain boundary precipitates is preferably 1 or less in the field of view of the square region 60 having a side of 150 μm.

  In the gas turbine engine, the rolling bearing may be used as a bearing that rotatably supports a rotating shaft that is a main shaft or a member that rotates by receiving the rotation of the main shaft with respect to a member adjacent to the rotating member. . The bearing that supports the rotating member (the main shaft or a member that rotates by the rotation of the main shaft) inside the gas turbine engine suppresses the decrease in the hardness of the bearing component in a high temperature environment, improves the durability in a foreign matter mixed environment, Improvements in smearing properties and dry run performance are required. Therefore, the rolling bearing of the present invention capable of achieving not only the suppression of hardness reduction of bearing components in a high temperature environment, the improvement of durability and the smearing resistance in an environment containing foreign substances, but also the improvement of dry run performance is a gas turbine. It is suitable as a bearing for supporting the rotating member inside the engine.

  The concentration of nitrogen and carbon in the nitrogen-enriched layer can be investigated by, for example, EPMA (Electron Probe Micro Analysis). The number density of the iron nitride (grain boundary precipitates) can be investigated, for example, as follows. That is, first, the bearing component is cut in a cross section perpendicular to the surface, and the cross section is polished. Thereafter, the cross section is corroded with an appropriate corrosive solution, and then the nitrogen-enriched layer is observed with a scanning electron microscope (SEM) or an optical microscope to take a photograph. Then, a square visual field having a side of 150 μm whose surface is defined as one side of the visual field is analyzed by an image analyzer, and the number of grain boundary precipitates is investigated. This is performed randomly in five or more visual fields, and the number of grain boundary precipitates per five visual fields is calculated.

  As is apparent from the above description, according to the rolling bearing of the present invention, not only the reduction in hardness of the bearing component in a high temperature environment, the improvement in the durability and the smearing resistance in a foreign matter mixed environment, but also the dry run It is possible to provide a rolling bearing capable of achieving an improvement in performance.

  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.

  FIG. 1 is a schematic view showing a configuration of a turbofan engine which is a gas turbine engine to which the rolling bearing of the present invention can be applied. With reference to FIG. 1, the structure of the turbofan engine in the present embodiment will be described.

  With reference to FIG. 1, a turbofan engine 70 includes a compression unit 71, a combustion unit 72, and a turbine unit 73. The turbofan engine 70 is disposed so as to surround the outer peripheral surface of the low-pressure main shaft 74 and the low-pressure main shaft 74 disposed from the compression section 71 through the combustion section 72 to the turbine section 73. 77.

  The compression unit 71 is connected to the low pressure main shaft 74 and surrounds the fan 75 having a plurality of fan blades 75A formed so as to protrude radially outward from the low pressure main shaft 74, and the combustion unit 72. A fan nacelle 76 extending toward the end and a compressor 81 arranged on the combustion portion 72 side when viewed from the fan 75 are included. The compressor 81 includes a low-pressure compressor 81A and a high-pressure compressor 81B disposed on the combustion unit 72 side when viewed from the low-pressure compressor 81A. The low pressure compressor 81A has a plurality of compressor blades 88 connected to the low pressure main shaft 74, projecting radially outward from the low pressure main shaft 74 side, and arranged side by side in a direction approaching the combustion unit 72 from the fan 75 side. Yes. The high pressure compressor 81B has a plurality of compressor blades 88 connected to the high pressure main shaft 77, projecting radially outward from the high pressure main shaft 77 side, and arranged side by side in a direction approaching the combustion unit 72 from the fan 75 side. is doing. Further, a core cowl 78 is disposed so as to surround the outer peripheral side of the low-pressure compressor 81A. The annular space between the core cowl 78 and the fan nacelle 76 constitutes a bypass channel 79.

  The combustion section 72 is connected to the high-pressure compressor 81B of the compression section 71, and includes a combustion chamber 82 having a fuel supply member and an ignition member (not shown). The turbine unit 73 includes a turbine 83 having a high-pressure turbine 83B and a low-pressure turbine 83A disposed on the opposite side of the combustion unit 72 when viewed from the high-pressure turbine 83B. Further, a turbine nozzle 84 for discharging the combustion gas in the turbine 83 to the outside is disposed on the opposite side of the low pressure turbine 83A from the high pressure turbine 83B. The low-pressure turbine 83A is connected to the low-pressure main shaft 74, has a plurality of turbine blades 87 that protrude radially outward from the low-pressure main shaft 74 side and are arranged side by side in a direction approaching the turbine nozzle 84 from the combustion chamber 82 side. ing. The high-pressure turbine 83B is connected to the high-pressure main shaft 77, protrudes radially outward from the high-pressure main shaft 77 side, and has a plurality of turbine blades 87 arranged side by side in a direction approaching the turbine nozzle 84 from the combustion chamber 82 side. Have.

  The low-pressure main shaft 74 and the high-pressure main shaft 77 as rotating members that are the main shaft or a member that rotates by receiving the rotation of the main shaft are members that are disposed adjacent to the low-pressure main shaft 74 and the high-pressure main shaft 77 by the rolling bearing 89. On the other hand, it is supported rotatably. That is, the rolling bearing 89 includes a low-pressure main shaft 74 or a high-pressure main shaft 77 as a rotating member that is a member that rotates in response to the rotation of the main shaft or the main shaft inside the turbofan engine 70 that is a gas turbine engine. Alternatively, it is rotatably supported with respect to a member adjacent to the high-pressure main shaft 77.

  Next, the operation of the turbofan engine 70 in the present embodiment will be described. Referring to FIG. 1, air on the side opposite to the combustion portion 72 as viewed from the fan 75, that is, on the front side of the turbofan engine 70 is surrounded by the fan nacelle 76 by the fan 75 rotating around the axis of the low-pressure main shaft 74. (Arrow α). A part of the taken-in air flows in the direction along the arrow β and is discharged to the outside through the bypass channel 79 as an air jet. This air jet becomes part of the thrust generated by the turbofan engine 70.

  On the other hand, the remaining portion of the air taken into the space surrounded by the fan nacelle 76 flows into the compressor 81 along the arrow γ. The air that has flowed into the compressor 81 is compressed by flowing inside the low-pressure compressor 81A having a plurality of compressor blades 88 rotating around the low-pressure main shaft 74 toward the high-pressure compressor 81B, and flows into the high-pressure compressor 81B. . Further, the air that has flowed into the high-pressure compressor 81B is further compressed by flowing toward the combustion chamber 82 through the inside of the high-pressure compressor 81B having a plurality of compressor blades 88 that rotate about the axis of the high-pressure main shaft 77, and enters the combustion chamber 82. Inflow (arrow δ).

  The air compressed in the compressor 81 and flowing into the combustion chamber 82 is mixed with fuel supplied into the combustion chamber by a fuel supply member (not shown) and then ignited by an ignition member (not shown). Thereby, combustion gas is generated in the combustion chamber 82. This combustion gas flows out of the combustion chamber 82 and flows into the turbine 83 (arrow ε).

  The combustion gas flowing into the turbine 83 collides with the turbine blade 87 connected to the high-pressure main shaft 77 in the high-pressure turbine 83B, thereby rotating the high-pressure main shaft 77 around the axis. As a result, the high-pressure compressor 81B having the compressor blade 88 connected to the high-pressure main shaft 77 is driven. Further, the combustion gas that has passed through the high-pressure turbine 83B collides with the turbine blade 87 connected to the low-pressure main shaft 74 in the low-pressure turbine 83A, thereby rotating the low-pressure main shaft 74 around the axis. As a result, the low pressure compressor 81A having the compressor blade 88 connected to the low pressure main shaft 74 and the fan 75 having the fan blade 75A connected to the low pressure main shaft 74 are driven.

  The combustion gas that has passed through the low-pressure turbine 83A is discharged from the turbine nozzle 84 to the outside. This jet of exhausted combustion gas becomes part of the thrust generated by the turbofan engine 70.

  Here, in the turbofan engine 70, a rolling bearing 89 that rotatably supports the low-pressure main shaft 74 or the high-pressure main shaft 77 with respect to a member adjacent to the low-pressure main shaft 74 or the high-pressure main shaft 77 is generated in the turbofan engine 70. It is used under high temperature environment due to the influence of heat. Further, hard foreign matters such as metal powder and carbon powder may enter the rolling bearing 89. For this reason, the rolling bearing 89 is required to suppress a decrease in the hardness of the bearing component in a high temperature environment and to improve durability in a foreign matter mixed environment. Further, in order to support the high speed rotation of the low pressure main shaft 74 or the high pressure main shaft 77, it is necessary to suppress the occurrence of smearing. Further, when the turbofan engine 70 is installed in an aircraft, even if the lubrication of the rolling bearing 89 is temporarily interrupted for some reason, the low-pressure spindle 74 or the high-pressure spindle is not seized until the lubrication is recovered. The rolling bearing 89 is required to have a dry run performance that continues to support the bearing 77 in a rotatable manner.

  On the other hand, when the rolling bearing 89 is a rolling bearing according to an embodiment of the present invention described below, the above requirement can be satisfied.

  FIG. 2 is a schematic cross-sectional view showing a configuration of a three-point contact ball bearing as a rolling bearing in an embodiment of the present invention. FIG. 3 is a schematic partial cross-sectional view showing an enlarged main part of FIG. With reference to FIGS. 2 and 3, a three-point contact ball bearing as a rolling bearing in an embodiment of the present invention will be described.

  Referring to FIG. 2, a three-point contact ball bearing 1 includes an annular outer ring 11 that is a race member, an annular inner ring 12 that is a race member disposed inside the outer ring 11, and an outer ring 11 and an inner ring 12. And a plurality of balls 13 as rolling elements that are disposed between and 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. The inner ring 12 includes a first inner ring 121 and a second inner ring 122, and has a structure divided at the axially central portion. A first inner ring rolling surface 121A and a second inner ring rolling surface 122A are formed on the outer peripheral surfaces of the first inner ring 121 and the second inner ring 122, respectively. The first inner ring rolling surface 121A and the second inner ring rolling surface 122A constitute an inner ring rolling surface 12A. Further, the plurality of balls 13 can contact and hold the first inner ring rolling surface 121A, the second inner ring rolling surface 122A, and the outer ring rolling surface 11A on the ball rolling surface 13A that is the outer peripheral surface. By being arranged at a predetermined pitch in the circumferential direction by the vessel 14, it is held so as to roll on an annular track. With the above configuration, the outer ring 11 and the inner ring 12 of the three-point contact ball bearing 1 can rotate relative to each other.

  Here, the outer ring 11 and the inner ring 12 that are raceway members are 0.11% by mass or more and 0.15% by mass or less of carbon, 0.1% by mass or more and 0.25% by mass or less of silicon, and 0.15% by mass. % To 0.35 mass% manganese, 3.2 mass% to 3.6 mass% nickel, 4 mass% to 4.25 mass% chromium, 4 mass% to 4.5 mass% % Of molybdenum and 1.13 mass% or more and 1.33 mass% or less of vanadium, and the balance is made of steel consisting of iron and impurities. Then, referring to FIG. 2, the outer ring nitrogen enrichment in which the nitrogen concentration is 0.05 mass% or more in the region including outer ring rolling surface 11 </ b> A and inner ring rolling surface 12 </ b> A which are the surfaces of outer ring 11 and inner ring 12. Layer 11B and inner ring nitrogen-enriched layer 12B are formed. Furthermore, the total value of the carbon concentration and the nitrogen concentration in the outer ring nitrogen-enriched layer 11B and the inner ring nitrogen-enriched layer 12B is 0.55 mass% or more and 1.9 mass% or less. Here, the impurities include inevitable impurities such as those derived from steel raw materials or those mixed in the manufacturing process.

Further, the balls 13 that are rolling elements are made of ceramics. More specifically, in the present embodiment, the balls 13 are made of a sintered body containing silicon nitride as a main component and the remaining impurities. Incidentally, the sintered body, aluminum oxide _{(Al 2 O} 3), may contain a sintering aid such as yttrium oxide _(Y 2 _{O 3).}

  In the outer ring 11 and the inner ring 12 that are race members of the three-point contact ball bearing 1 in the present embodiment, the outer ring rolling surface 11A and the inner ring rolling formed on the surface are made of steel having the appropriate component composition described above. An outer ring nitrogen-enriched layer 11B and an inner ring nitrogen-enriched layer 12B having a nitrogen concentration of 0.05% by mass or more are formed in a region including the surface 12A. Then, the total value of the carbon concentration and the nitrogen concentration in the outer ring nitrogen-enriched layer 11B and the inner ring nitrogen-enriched layer 12B is set to an appropriate range of 0.55 mass% or more and 1.9 mass% or less. Sufficient hardness is imparted to the part, and formation of grain boundary precipitates is suppressed. As a result, the outer ring 11 and the inner ring 12 that are the race members in the present embodiment are made of steel containing 4% by mass or more of chromium, a nitrogen-enriched layer is formed in the surface layer portion, and fatigue strength and This is a bearing component with sufficient toughness.

  Furthermore, in the three-point contact ball bearing 1 in the present embodiment, the balls 13 that are rolling elements are made of ceramics. Thereby, generation | occurrence | production of smearing is suppressed, and since the outer ring | wheel 11, the inner ring | wheel 12, and the ball | bowl 13 which contact mutually become a dissimilar material, seizure resistance improves. As a result, improvement in smearing resistance and durability in an environment with insufficient lubrication, for example, dry run performance, are achieved. Moreover, the durability of the ball 13 in a foreign matter mixed environment is improved by using ceramics having a higher hardness than steel as the material of the ball 13. Furthermore, since the balls 13 are made of ceramics, a decrease in the hardness of the balls 13 in a high temperature environment is suppressed. In addition, since the ball 13 is made of ceramics, the ball 13 is lighter than the ball 13 made of steel, and the centrifugal force acting on the ball 13 is reduced. It is suitable as a rolling bearing that supports a member that rotates at high speed.

  As described above, in the three-point contact ball bearing 1 in the present embodiment, the outer ring 11 and the inner ring 12 that are race members are made of steel containing 4% by mass or more of chromium, and the balls 13 that are rolling elements are formed. By being made of ceramics, a decrease in the hardness of the bearing component in a high temperature environment is suppressed. Further, the outer ring nitrogen in which the total value of the carbon concentration and the nitrogen concentration is within an appropriate range in the region including the outer ring rolling surface 11A and the inner ring rolling surface 12A of the outer ring 11 and the inner ring 12 made of steel having an appropriate component composition. While the enrichment layer 11B and the inner ring nitrogen enrichment layer 12B are formed, and the balls 13 are made of ceramics, the durability of the bearing component in a foreign matter mixed environment is improved. Further, by combining the outer ring 11 made of steel and the inner ring 12 with the ball 13 made of ceramics, the improvement of the smearing resistance and the improvement of the dry run performance are achieved. As a result, the three-point contact ball bearing 1 has achieved not only the suppression of hardness reduction of the bearing components in a high temperature environment, the improvement of the durability and the smearing resistance in a foreign matter mixed environment, but also the improvement of the dry run performance. It is a rolling bearing.

  Furthermore, the thicknesses of the outer ring nitrogen-enriched layer 11B and the inner ring nitrogen-enriched layer 12B formed on the outer ring 11 and the inner ring 12 are preferably 0.1 mm or more. Thereby, sufficient strength is imparted to the outer ring 11, the inner ring 12 and the ball 13.

  Furthermore, the outer ring nitrogen-enriched layer 11B and the inner ring nitrogen-enriched layer 12B preferably have a hardness of 800 HV or more. As a result, the strength of the outer ring 11 and the inner ring 12 can be more reliably ensured.

  Further, when the outer ring nitrogen-enriched layer 11B and the inner ring nitrogen-enriched layer 12B are observed with a microscope, the number of iron nitrides having an aspect ratio of 2 or more and a length of 7.5 μm or more is within 5 fields of a square region having a side of 150 μm. The number is preferably 1 or less. Thereby, the fatigue strength of the outer ring 11 and the inner ring 12 can be improved.

  FIG. 4 is a schematic cross-sectional view showing a configuration of a cylindrical roller bearing as a rolling bearing which is a modification of the present embodiment. FIG. 5 is a schematic partial cross-sectional view showing an enlarged main part of FIG. With reference to FIG. 4 and FIG. 5, the cylindrical roller bearing which is a modification of this Embodiment is demonstrated.

  Referring to FIG. 4, the cylindrical roller bearing 2 is disposed between an annular outer ring 21, an annular inner ring 22 disposed inside the outer ring 21, and the outer ring 21 and the inner ring 22. And a plurality of rollers 23 as rolling elements held by 24. The roller 23 has a cylindrical shape. An outer ring rolling surface 21 </ b> A is formed on the inner circumferential surface of the outer ring 21, and an inner ring rolling surface 22 </ b> A is formed on the outer circumferential surface of the inner ring 22. The outer ring 21 and the inner ring 22 are arranged so that the inner ring rolling surface 22A and the outer ring rolling surface 21A face each other. Further, the plurality of rollers 23 come into contact with the inner ring rolling surface 22A and the outer ring rolling surface 21A on the roller rolling surface 23A, which is the outer circumferential surface, and are arranged at a predetermined pitch in the circumferential direction by the cage 24. It is held on an annular track so as to be freely rollable. With the above configuration, the outer ring 21 and the inner ring 22 of the cylindrical roller bearing 2 can rotate relative to each other.

  Here, referring to FIG. 5, the outer ring 21 and the inner ring 22 of the cylindrical roller bearing 2 in this modified example correspond to the outer ring 11 and the inner ring 12 of the three-point contact ball bearing 1, and the roller 23 corresponds to the ball 13. It has the same structure and produces the same effect. That is, the outer ring 21 and the inner ring 22 that are raceway members are 0.11% by mass to 0.15% by mass of carbon, 0.1% by mass to 0.25% by mass of silicon, and 0.15% by mass. More than 0.35 mass% manganese, 3.2 mass% or more and 3.6 mass% nickel, 4 mass% or more and 4.25 mass% chromium, 4 mass% or more 4.5 mass% It contains the following molybdenum and 1.13 mass% or more and 1.33 mass% or less of vanadium, and is made of steel consisting of the remaining iron and impurities.

  Then, referring to FIG. 5, in the regions including outer ring rolling surface 21 </ b> A and inner ring rolling surface 22 </ b> A that are the surfaces of outer ring 21 and inner ring 22, the nitrogen concentration of the outer ring having a nitrogen concentration of 0.05 mass% or more is obtained. The inner layer 21B and the inner ring nitrogen-enriched layer 22B are formed. The total value of the carbon concentration and the nitrogen concentration in the outer ring nitrogen-enriched layer 21B and the inner ring nitrogen-enriched layer 22B is 0.55 mass% or more and 1.9 mass% or less.

  Furthermore, the roller 23 which is a rolling element is made of a sintered body mainly composed of ceramics, for example, silicon nitride.

  In the cylindrical roller bearing 2 in the present modification, as with the three-point contact ball bearing 1, the outer ring 21 and the inner ring 22 that are race members are made of steel containing 4% by mass or more of chromium and are rolling elements. Since the roller 23 is made of ceramic, a decrease in the hardness of the bearing component in a high temperature environment is suppressed. Further, the outer ring nitrogen in which the total value of the carbon concentration and the nitrogen concentration is within an appropriate range in the region including the outer ring rolling surface 21A and the inner ring rolling surface 22A of the outer ring 21 and the inner ring 22 made of steel having an appropriate component composition. While the enrichment layer 21B and the inner ring nitrogen enrichment layer 22B are formed, and the roller 23 is made of ceramics, the durability of the bearing component in a foreign matter mixed environment is improved. Furthermore, by combining the outer ring 21 made of steel and the inner ring 22 with the roller 23 made of ceramics, the smearing resistance is improved and the dry run performance is improved. As a result, the cylindrical roller bearing 2 is a rolling bearing that achieves not only a reduction in hardness of bearing components in a high-temperature environment, an improvement in durability and an improvement in smearing resistance in an environment containing foreign matter, but also an improvement in dry run performance. It has become.

  Next, a method for manufacturing the rolling bearing in the embodiment of the present invention will be described. FIG. 6 is a flowchart showing an outline of a method for manufacturing a rolling bearing in one embodiment of the present invention.

  Referring to FIG. 6, the rolling bearing manufacturing method in the present embodiment includes a race member manufacturing process including steps (S10) to (S110), and a rolling element manufacturing process including steps (S210) to (S250). And an assembling process implemented as a process (S300).

  First, the race member manufacturing process will be described. In the steel member preparation step implemented as the step (S10), 0.11% by mass to 0.15% by mass of carbon, 0.1% by mass to 0.25% by mass of silicon, and 0.15% by mass. % To 0.35 mass% manganese, 3.2 mass% to 3.6 mass% nickel, 4 mass% to 4.25 mass% chromium, 4 mass% to 4.5 mass% % Of molybdenum and 1.13 mass% or more and 1.33 mass% or less of vanadium, made of steel consisting of the remaining iron and impurities, and a steel member molded into the approximate shape of the raceway member is prepared. . Specifically, for example, an outer ring as a race member is formed by using a steel bar, steel wire, or the like containing the above components as a raw material, and performing processing such as cutting, forging, and turning on the steel bar, steel wire, etc. Steel members formed into schematic shapes such as 11 and 21 and inner rings 12 and 22 are prepared.

  Next, a heat treatment step is performed on the above-described steel member prepared in step (S10) to perform a heat treatment including a quenching treatment and a nitriding treatment. The heat treatment process includes a carburization process performed as the process (S20), a quenching process performed as the process (S30), a first tempering process performed as the process (S40), and a first process performed as the process (S50). As a 1st subzero process, the 2nd tempering process implemented as process (S60), 2nd subzero process implemented as process (S70), 3rd tempering process implemented as process (S80), and process (S90) It includes a plasma nitriding step to be performed and a diffusion step to be performed as step (S100). Details of this heat treatment step will be described later.

  Next, a finishing process in which finishing or the like is performed on the steel member that has been subjected to the heat treatment process is performed as a process (S110). Specifically, for example, polishing is performed on the outer ring rolling surfaces 11A and 21A, the inner ring rolling surfaces 12A and 22A, and the like of the steel member that has been subjected to the heat treatment process. Thereby, the track member in the present embodiment is completed, and the track member manufacturing process in the present embodiment is completed.

  Next, details of the above-described heat treatment step will be described. FIG. 7 is a diagram for explaining the details of the heat treatment step included in the raceway member manufacturing step in the present embodiment. In FIG. 7, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 7, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature.

Referring to FIG. 7, in the heat treatment step in the present embodiment, first, a carburizing step in which a steel member as a workpiece is carburized is performed. Specifically, for example, a steel member is heated to a temperature T ₁ that is a temperature equal to or higher than the A ₁ transformation point in a carburizing gas atmosphere containing carbon monoxide and hydrogen, and is held for a time t _1. Carbon enters the surface layer of the member. Thereby, a carburized layer having a high carbon concentration is formed in the region including the surface of the steel member as compared with the internal region which is a region other than the region including the surface.

Next, referring to FIG. 7, a quenching process is performed in which the steel member that has been subjected to the carburizing process is quenched. Specifically, the steel member is quenched and hardened by being cooled from a temperature T ₁ which is a temperature equal to or higher than the A ₁ transformation point to a temperature equal to or lower than the M _S point.

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.

Next, the 1st tempering process which performs a tempering process is implemented with respect to the steel member in which the quenching process was implemented. Specifically, referring to FIG. 7, for example, after a steel member is heated to a temperature T ₂ that is a temperature lower than the A ₁ transformation point in a reduced-pressure atmosphere (in a vacuum) and held for a time t ₂ , Tempering is performed by cooling. Thereby, the residual stress due to the quenching treatment of the steel member is relaxed, and the effect of suppressing the strain due to the heat treatment can be obtained.

Next, the 1st subzero process which performs a subzero process is implemented with respect to the steel member in which the 1st tempering process was implemented. Specifically, with reference to FIG. 7, the steel member, for example, liquid nitrogen is sprayed is cooled to a temperature T ₃ at a temperature of less than 0 ° C., is sub-zero treatment by being held for a time t ₃ The Thereby, the residual austenite produced | generated by the hardening process of the steel member transforms into a martensite, and effects, such as stabilization of the structure of steel, are acquired.

Next, the 2nd tempering process which performs a tempering process is implemented with respect to the steel member in which the 1st subzero process was implemented. Specifically, referring to FIG. 7, for example, the steel member is heated to a temperature T ₄ that is a temperature below the A ₁ transformation point in a vacuum, held for a time t ₄ , and then cooled. Tempered. Thereby, the residual stress due to the sub-zero treatment of the steel member is relaxed, and effects such as suppression of strain can be obtained.

Next, a second subzero process is performed in which the subzero process is performed again on the steel member that has been subjected to the second tempering process. Specifically, with reference to FIG. 7, the steel member, for example, liquid nitrogen is sprayed is cooled to a temperature T ₅ at a temperature of less than 0 ° C., is sub-zero treatment by being held for a time t ₅ The Thereby, the residual austenite produced | generated by the hardening process of the steel member further transforms into a martensite, and the effect that the structure | tissue of steel is stabilized more is acquired.

Next, the 3rd tempering process which performs a tempering process again is implemented with respect to the steel member in which the 2nd subzero process was implemented. Specifically, referring to FIG. 7, as in the second tempering step, the steel member is heated to a temperature T ₆ that is a temperature lower than the A ₁ transformation point in a vacuum and held for a time t ₆ . And then tempering by cooling. Here, the temperatures T ₆ and t ₆ can be the same conditions as the temperatures T ₄ and t _{4 in} the second tempering step. As a result, the residual stress that can be generated by the sub-zero treatment of the steel member in the second sub-zero process is relaxed, and effects such as suppression of strain can be obtained.

Next, a plasma nitriding step for performing a plasma nitriding process is performed on the steel member on which the third tempering step has been performed. Specifically, referring to FIG. 7, for example, selected from the group consisting of nitrogen (N ₂ ), hydrogen (H ₂ ), methane (CH ₄ ), and argon (Ar) so that the pressure is 50 Pa or more and 5000 Pa or less. A steel member is inserted into a plasma nitriding furnace into which at least one of the above is introduced and heated to a temperature T ₇ under conditions of a discharge voltage of 50 V to 1000 V and a discharge current of 0.001 A to 100 A. after being held for a time t _7, the steel member is treated plasma nitriding by being cooled. Thereby, nitrogen penetrate | invades into the surface layer part of a steel member, a nitrogen enriched layer is formed, and the intensity | strength of the said surface layer part improves. Here, the temperature T ₇ can be, for example, 300 ° C. or more and 550 ° C. or less, and the time t ₇ can be 1 hour or more and 80 hours or less. The heat treatment conditions such as the temperature T ₇ and the time t ₇ take into account the allowance in the finishing process performed in the finishing process, and the grain boundary precipitate layer (grain boundary precipitate is formed in the plasma nitriding process). The thickness of the layer) can be determined to be equal to or less than the thickness that can be removed in the finishing process.

When the steel constituting the steel member is AMS standard 6278 (AISI standard M50NiL), the pressure in the plasma nitriding step is 50 Pa to 1000 Pa, the discharge voltage is 50 V to 600 V, and the discharge current is 0.001 A to 300 A. The temperature T ₇ is preferably 350 ° C. or higher and 450 ° C. or lower, and the time t ₇ is preferably 1 hour or longer and 50 hours or shorter.

Next, the diffusion process which performs a diffusion process is implemented with respect to the steel member in which the plasma nitriding process was implemented. Specifically, referring to FIG. 7, for example, the steel member is diffusion-treated by being heated to a temperature T ₈ in a vacuum and held for a time t ₈ . Here, the temperature T ₈ can be 300 ° C. or higher and 480 ° C. or lower, preferably 300 ° C. or higher and 430 ° C. or lower, and the time t ₈ can be 50 hours or longer and 300 hours or shorter. Thereby, nitrogen which penetrate | invaded steel can be made to reach | attain a desired area | region, suppressing that the hardness increase of the surface layer part by nitrided layer formation is canceled. And by carrying out this diffusion process, even if the depth of penetration of nitrogen in the plasma nitriding process is limited to a range in which the grain boundary precipitate layer can be removed in the finishing process, the nitrogen that has entered the steel is desired. It is possible to reach even the area. Through the above steps, the heat treatment step in this embodiment is completed.

  As described above, according to the heat treatment method in the present embodiment, the surface layer portion of steel containing 4% by mass or more of chromium is nitrided to form a high hardness nitrogen-enriched layer, and grain boundary precipitates Can be suppressed.

  In addition, according to the raceway member manufacturing step in the above embodiment, it is made of steel containing 4% by mass or more of chromium, and the surface layer portion is nitrided to form a high hardness nitrogen-enriched layer, and the grain boundary Track members (outer rings 11, 21, inner rings 12, 22, etc.) in which the generation of precipitates is suppressed can be manufactured. As a result, as described above, the region including the surface (outer ring rolling surfaces 11A, 21A, inner ring rolling surfaces 12A, 22A, etc.) of the race members (outer rings 11, 21, inner rings 12, 22, etc.) in the present embodiment. A nitrogen enriched layer having a thickness of 0.1 mm or more and a hardness of 800 HV or more, wherein the nitrogen concentration is 0.05% by mass or more, and the total value of the carbon concentration and the nitrogen concentration is 0.55% by mass or more and 1.9% by mass or less. When forming and cutting the nitrogen-enriched layer in a cross section perpendicular to the surface and observing five fields of view of a square of 150 μm on a side including the surface at random using an optical microscope or SEM, the grain boundary The number of detected precipitates can be 1 or less. Here, the carbon concentration and the nitrogen concentration in the nitrogen-enriched layer are controlled, for example, by adjusting the processing time of plasma nitriding performed in the plasma nitriding step and the processing time of diffusion processing performed in the diffusing step. Can do.

  On the other hand, referring to FIG. 6, in the rolling element manufacturing step, first, as a step (S210), a powder preparation step of preparing ceramic powder is performed. Specifically, ceramics employed as a material constituting the rolling elements, for example, silicon nitride powder is prepared. Next, as the step (S220), a mixing step is performed in which a sintering aid is added to and mixed with the ceramic powder prepared in the step (S210).

  Next, referring to FIG. 6, a molding step of molding the mixture of the ceramic powder and the sintering aid into a schematic shape of the rolling element is performed as a step (S230). Specifically, the mixture of the ceramic powder and the sintering aid is subjected to molding using a technique such as press molding, casting molding, extrusion molding, rolling granulation, etc. 13 and a molded body formed into a general shape such as the roller 23 are produced.

  Next, as a step (S240), a sintering step in which the molded body is sintered is performed. Specifically, the molded body is sintered using a pressure sintering method such as HIP (Hot Isostatic Press) or GPS (Gas Pressure Sintering). Thus, a sintered body having a schematic shape such as the outer rings 11 and 21 and the inner rings 12 and 22 is obtained.

  Next, a finishing process for completing the rolling member is performed by performing a finishing process in which the surface of the sintered body obtained in the process (S240) is processed and a region including the surface is removed. S250). Specifically, by polishing the surface (rolling surface) of the sintered body obtained in the sintering step, the balls 13 and rollers 23 as the rolling elements are completed. With the above steps, the rolling element manufacturing step in the present embodiment is completed.

  Then, referring to FIG. 6, an assembly process in which the completed bearing parts are combined to assemble a rolling bearing is performed as a process (S300). Specifically, the three-point contact ball bearing 1 is assembled by combining the outer ring 11, the inner ring 12, and the ball 13 produced by the above-described process and a separately prepared cage 14. Thereby, the rolling bearing in the present embodiment is completed.

  In the above embodiment, a three-point contact ball bearing and a cylindrical roller bearing have been described as examples of the rolling bearing of the present invention. However, the rolling bearing of the present invention is not limited to this, for example, a deep groove ball bearing or an angular ball. The present invention can be applied to various rolling bearings such as a bearing and a thrust needle roller bearing.

  Embodiment 1 of the present invention will be described below. A sample having the same structure as the race member constituting the rolling bearing of the present invention was actually produced using the heat treatment method in the above embodiment, and generation of grain boundary precipitates in the surface layer portion was suppressed. A confirmation experiment was conducted. The experimental procedure is as follows.

  First, 0.11% by mass to 0.15% by mass of carbon, 0.1% by mass to 0.25% by mass of silicon, 0.15% by mass to 0.35% by mass of manganese, 3.2 mass% or more and 3.6 mass% or less nickel, 4 mass% or more and 4.25 mass% or less chromium, 4 mass% or more and 4.5 mass% or less molybdenum, and 1.13 mass% or more A steel material of AMS standard 6278 (AISI standard M50NiL), which contains 1.33 mass% or less of vanadium and is composed of the remaining iron and impurities, is prepared and processed to have an outer diameter of 40 mm, an inner diameter of 30 mm, and a thickness. A test piece of t16 mm was produced.

Next, a heat treatment step using the steel heat treatment method described with reference to FIG. 7 in the above embodiment was performed on the test piece. Here, T ₁ , t ₁ , T ₂ , t ₂ , T ₃ , t ₃ , T ₄ , t ₄ , T ₅ , t ₅ , T ₆ and t ₆ are the test pieces after the third tempering step. The hardness was determined to be 58 to 65 HRC, T ₇ was 430 ° C., t ₇ was 10 hours, T ₈ was 430 ° C., and t ₈ was 160 hours. In the plasma nitriding step, as the treatment temperature _{T 7} during plasma nitridation is 430 ° C., the discharge voltage 200V or 450V or less controlled the discharge current at 5A below the range of 1A. Further, in the plasma nitriding process, gas is introduced into the furnace at a ratio of nitrogen (N ₂ ): hydrogen (H ₂ ) = 1: 1 so that the pressure in the furnace during plasma nitriding is 267 Pa or more and 400 Pa or less. did.

  Furthermore, in the diffusion step, the diffusion treatment is performed so that the test piece is heated in an atmosphere furnace adjusted to a nitrogen atmosphere, and the sum of the carbon concentration and the nitrogen concentration on the surface of the test piece is 1.9% by mass or less. It was implemented. As described above, a test piece on which the same heat treatment step as in the above embodiment was performed was used as a sample of an example of the present invention (Example A).

On the other hand, the heat treatment process which abbreviate | omitted the diffusion process was implemented with respect to the test piece which consists of AMS specification 6278 similarly produced from the heat processing method of steel demonstrated based on FIG. 7 in the said embodiment. Here, T ₁ , t ₁ , T ₂ , t ₂ , T ₃ , t ₃ , T ₄ , t ₄ , T ₅ , t ₅ , T ₆ and t ₆ are the test pieces after the third tempering step. The hardness was determined to be 58 to 65 HRC, T ₇ was 480 ° C., and t ₇ was 30 hours. In the plasma nitriding step, the discharge voltage was controlled in the range of 200 V to 450 V and the discharge current in the range of 1 A to 5 A so that the processing temperature T ₇ during plasma nitriding was 480 ° C. Further, in the plasma nitriding step, nitrogen (N ₂ ): hydrogen (H ₂ ): methane (CH ₄ ) = 79: 80: 1 is set so that the pressure in the furnace during plasma nitriding is 267 Pa or more and 400 Pa or less. Gas was introduced into the furnace at a rate. The test piece subjected to the above heat treatment method was used as a sample of a comparative example of the present invention (Comparative Example A).

  And the sample of Example A and Comparative Example A produced as described above was cut in a cross section perpendicular to the surface, and the cross section was polished. Further, after the polished cross section was corroded with a corrosive liquid, five fields of view of a square having a side of 150 μm including the surface were randomly observed.

  Next, experimental results will be described. FIG. 8 is an optical micrograph of the microstructure near the surface of Example A. FIG. 9 is a diagram showing the hardness distribution in the vicinity of the surface of Example A. FIG. 10 is a graph showing the distribution of carbon and nitrogen concentrations in the vicinity of the surface of Example A. FIG. 11 is an optical micrograph of the microstructure near the surface of Comparative Example A. FIG. 12 is a diagram showing the hardness distribution in the vicinity of the surface of Comparative Example A. FIG. 13 is a graph showing the distribution of carbon and nitrogen concentrations in the vicinity of the surface of Comparative Example A. 8 and 11, the upper part of the photograph corresponds to the surface side of the sample. 9 and 12, the horizontal axis indicates the depth (distance) from the surface, and the vertical axis indicates the hardness (the unit is Vickers hardness). 10 and 13, the horizontal axis indicates the depth (distance) from the surface, the vertical axis indicates the carbon and nitrogen concentrations, the thin line indicates the carbon concentration, and the thick line indicates the nitrogen concentration.

  Referring to FIG. 8, in the surface layer portion of the sample of Example A of the present invention, grain boundary precipitates (iron nitride formed with an aspect ratio of 2 or more and a length of 7.5 μm or more) It is not observed and has a good microstructure. 9 and 10, the region within 0.05 mm in depth from the surface of the sample of Example A has a sufficient hardness of 950 HV or more, and a sufficient amount of nitrogen has entered. is doing. Therefore, by performing finishing such as polishing on the surface of the steel member subjected to the same heat treatment as in Example A, the nitrogen concentration is 0.05% by mass or more, and the total value of the carbon concentration and the nitrogen concentration is 0. When a nitrogen-rich layer having a thickness of 0.1 mm or more and a thickness of 0.1 mm or more and a hardness of 800 HV or more is formed and the nitrogen-rich layer is observed with a microscope, One or less machine parts can be manufactured within 5 fields of view of a square area of 150 μm per side.

  On the other hand, referring to FIG. 11, a large number of grain boundary precipitates 90 are observed in the surface layer portion of the sample of Comparative Example A which is outside the scope of the present invention. 12 and 13, the region within a depth of 0.05 mm from the surface of the sample of Comparative Example A has a sufficient hardness of 950 HV or more, as in Example A, and A sufficient amount of nitrogen has penetrated. Therefore, even when a finishing process such as polishing is performed on the surface of the steel member that has been subjected to the same heat treatment as in Comparative Example A, a high-hardness surface layer portion is formed, but grain boundary precipitates remain in the surface layer portion. Machine parts to be obtained. Such a bearing component cannot be said to have sufficient fatigue strength and toughness as described above.

  As mentioned above, according to the manufacturing method of the raceway member which adopted the heat treatment method in the above-mentioned embodiment, it is made of steel containing 4% by mass or more of chromium, and a nitrogen-enriched layer is formed in the surface layer part, and It was confirmed that it was possible to produce a race member with sufficient fatigue strength and toughness.

  Embodiment 2 of the present invention will be described below. An experiment was conducted to investigate an appropriate heating temperature range in the diffusion step of the heat treatment method described in the above embodiment. The experimental procedure is as follows.

  First, 0.11% by mass to 0.15% by mass of carbon, 0.1% by mass to 0.25% by mass of silicon, 0.15% by mass to 0.35% by mass of manganese, 3.2 mass% or more and 3.6 mass% or less nickel, 4 mass% or more and 4.25 mass% or less chromium, 4 mass% or more and 4.5 mass% or less molybdenum, and 1.13 mass% or more A steel material of AMS standard 6278 (AISI standard M50NiL), which contains 1.33 mass% or less of vanadium and is composed of the remaining iron and impurities, is prepared and processed to have an outer diameter of 40 mm, an inner diameter of 30 mm, and a thickness. A test piece of t16 mm was produced.

  Next, of the heat treatment process using the steel heat treatment method described with reference to FIG. 7 in the above embodiment for the test piece, the carburization process to the third tempering process are examples of the first example. It carried out like the case of A. And the process similar to a diffusion process was implemented by hold | maintaining the said test piece at the temperature of 430 degreeC-570 degreeC for various time, and the hardness of the carburized layer was measured. More specifically, the hardness was measured at 9 points in a region where the distance from the surface of the test piece was 0.2 mm or more and 0.4 mm or less, and the minimum hardness was calculated. Furthermore, the measurement result was analyzed based on the reaction kinetics, and the relationship between the heat treatment time (diffusion time) at each heating temperature in the diffusion step and the hardness of the carburized layer was calculated.

On the other hand, after carrying out the same test piece from the carburizing step to the third tempering step in the same manner as in Example A of Example 1, the plasma nitriding step and the diffusion step were actually carried out, Experiments were also conducted to confirm the hardness distribution. In the plasma nitriding step, the discharge voltage is controlled in the range of 200 V to 450 V, the discharge current is controlled in the range of 1 A to 5 A and maintained for 1 hour so that the processing temperature T ₇ during plasma nitridation is 480 ° C. Nitriding was performed. Furthermore, in the plasma nitriding step, gas was introduced into the furnace at a ratio of nitrogen (N ₂ ): hydrogen (H ₂ ) = 1: 1 so that the pressure in the furnace during plasma nitriding was 267 Pa or more and 400 Pa or less. . Further, a diffusion step of holding at 480 ° C. for 50 hours was performed on the test piece for which the plasma nitriding step was completed. And the hardness distribution in the surface layer part of the test piece before and behind implementing a diffusion process was measured.

  Next, the results of the experiment will be described. FIG. 14 is a diagram (Abami plot) showing the relationship between the heat treatment time (diffusion time) at each heating temperature in the diffusion step and the hardness of the carburized layer, obtained as a result of the analysis based on the reaction kinetics. In FIG. 14, the horizontal axis indicates the heat treatment time (diffusion time), and the vertical axis indicates the hardness of the carburized layer. FIG. 15 is a diagram showing the hardness distribution of the surface layer portion of the test piece before the diffusion step and the test piece subjected to the diffusion step held at 480 ° C. for 50 hours. In FIG. 15, the horizontal axis indicates the depth (distance) from the surface, and the vertical axis indicates the hardness. In FIG. 15, the rhombus indicates the hardness of the test piece before the diffusion process, and the square indicates the hardness of the test piece after the diffusion process held at 480 ° C. for 50 hours.

  Referring to FIG. 14, the hardness of the carburized layer of the test piece decreases in a shorter time as the diffusion temperature is higher, but when the diffusion temperature reaches 480 ° C., the hardness decreases even when the diffusion treatment is performed for 200 hours. The width becomes 50 HV or less, and the influence of the decrease in the hardness of the base material (the hardness in the region of the carburized layer where there is no influence of nitrogen intrusion due to plasma nitriding) on the hardness of the surface layer portion is reduced. Further, when the diffusion temperature is 460 ° C., even when the diffusion treatment is performed for 200 hours, the decrease in hardness is 30 HV or less, and the influence of the decrease in the hardness of the base material on the hardness of the surface layer is further reduced. Further, when the diffusion temperature is 430 ° C., even when the diffusion treatment is performed for 200 hours, the decrease in hardness becomes 10 HV or less, and the decrease in the hardness of the base material hardly affects the hardness of the surface layer portion.

  On the other hand, referring to FIG. 15, when the diffusion step of holding at 480 ° C. for 50 hours is performed, the actual decrease in the base material hardness is almost the same as the analysis result of FIG. 14, and the analysis result of FIG. Is considered to be consistent with the actual heat treatment results.

  From the above experimental results, the heating temperature (diffusion temperature) in the diffusion step is a viewpoint that allows nitrogen that has entered the steel to reach a desired region while suppressing the influence of the decrease in the hardness of the base material on the hardness of the surface layer portion. Therefore, it is necessary to set the temperature to 480 ° C. or lower, and preferably 460 ° C. or lower. Furthermore, by setting the heating temperature to 430 ° C. or lower, the diffusion step can be carried out with almost no influence on the hardness of the surface layer portion due to the decrease in the hardness of the base material. In addition, from the viewpoint of suppressing the influence of the decrease in the hardness of the base material on the hardness of the surface layer portion, it is preferable to lower the heating temperature in the diffusion step, but the nitrogen that has entered the steel reaches the desired region. Therefore, the heating temperature is preferably set to 300 ° C. or higher in order to avoid the time required for the operation from exceeding the allowable limit in the actual production process.

  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.

  The bearing component of the present invention can be particularly advantageously applied to a rolling bearing that is required to have improved durability under severe conditions.

It is the schematic which shows the structure of the turbofan engine which can apply the rolling bearing of this invention. It is a schematic sectional drawing which shows the structure of a three-point contact ball bearing. FIG. 3 is a schematic partial cross-sectional view showing an enlarged main part of FIG. 2. It is a schematic sectional drawing which shows the structure of a cylindrical roller bearing. FIG. 5 is a schematic partial cross-sectional view showing an enlarged main part of FIG. 4. It is a flowchart which shows the outline of the manufacturing method of a rolling bearing. It is a figure for demonstrating the detail of the heat processing process included in a track member preparation process. 2 is an optical micrograph of the microstructure near the surface of Example A. FIG. It is a figure which shows the hardness distribution in the surface vicinity of Example A. FIG. 4 is a graph showing the distribution of carbon and nitrogen concentrations in the vicinity of the surface of Example A. 4 is an optical micrograph of a microstructure in the vicinity of the surface of Comparative Example A. 6 is a diagram showing a hardness distribution in the vicinity of the surface of Comparative Example A. FIG. 6 is a graph showing the distribution of carbon and nitrogen concentrations in the vicinity of the surface of Comparative Example A. FIG. It is a figure (Abami plot) which shows the relationship between the heat processing time (diffusion time) in each heating temperature of a spreading | diffusion process, and the hardness of a carburized layer. It is a figure which shows the hardness distribution of the surface layer part of the test piece which performed the spreading | diffusion process hold | maintained at 480 degreeC for the test piece before performing a spreading | diffusion process for 50 hours.

Explanation of symbols

  1 3-point contact ball bearing, 2 cylindrical roller bearing, 11, 21 outer ring, 11A, 21A outer ring rolling surface, 11B, 21B outer ring nitrogen enriched layer, 12, 22 inner ring, 12A, 22A inner ring rolling surface, 12B, 22B Inner ring nitrogen-enriched layer, 121 first inner ring, 121A first inner ring rolling surface, 122 second inner ring, 122A second inner ring rolling surface, 13 balls, 13A ball rolling surface, 14, 24 cage, 23 rollers, 23A Roller rolling surface, 70 Turbo fan engine, 71 Compression section, 72 Combustion section, 73 Turbine section, 74 Low pressure spindle, 75 Fan, 75A fan blade, 76 Fan nacelle, 77 High pressure spindle, 78 Core cowl, 79 Bypass flow path, 81 compressor, 81A low pressure compressor, 81B high pressure compressor, 82 combustion chamber, 83 turbine, 83A low pressure turbine, 3B high pressure turbine, 84 a turbine nozzle, 87 a turbine blade, 88 a compressor blade, 89 a rolling bearing, 90 grain boundary precipitates.

Claims (5)

2. 0.11% by mass to 0.15% by mass of carbon, 0.1% by mass to 0.25% by mass of silicon, 0.15% by mass to 0.35% by mass of manganese, 2 mass% or more and 3.6 mass% or less nickel, 4 mass% or more and 4.25 mass% or less chromium, 4 mass% or more and 4.5 mass% or less molybdenum, 1.13 mass% or more 1. It contains 33% by mass or less of vanadium, and is composed of steel consisting of the balance iron and impurities, and in the region including the surface, a nitrogen enriched layer having a nitrogen concentration of 0.05% by mass or more is formed. The total value of the carbon concentration and the nitrogen concentration in the nitrogen enriched layer is 0.55% by mass or more and 1.9% by mass or less, and the race member,
A plurality of rolling elements disposed on an annular track in contact with the track member;
The rolling element is a rolling bearing made of ceramics.   The rolling bearing according to claim 1, wherein the nitrogen-enriched layer has a thickness of 0.1 mm or more.   The rolling bearing according to claim 1, wherein the nitrogen-enriched layer has a hardness of 800 HV or more.   When the nitrogen-enriched layer is observed with a microscope, the number of iron nitrides having an aspect ratio of 2 or more and a length of 7.5 μm or more is 1 or less in 5 fields of a square region having a side of 150 μm. 4. The rolling bearing according to any one of 3 above.   The inside of a gas turbine engine WHEREIN: The rotating member which is a member rotated by receiving the rotation of the main shaft or the main shaft is rotatably supported with respect to a member adjacent to the rotating member. Rolling bearing according to item.