JP2010248568A - Rolling bearing for use in hydrogen atmosphere - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing which has long service life even when it is used in hydrogen atmosphere. <P>SOLUTION: In an inner ring 1 and an outer ring 2 of a deep groove ball bearing, the contents of carbon, silicon, manganese, chromium, molybdenum, sulfur, phosphorus and oxygen are within a predetermined range, respectively and the remainder is composed of iron and alloy steel which is an inevitable impurity. In addition, a structure change resistance value is ≥10. Furthermore, a hardening layer is formed in orbital planes 1a, 2a by performing quenching and tempering following carburizing treatment or carbonitriding treatment. The sum of carbon concentration and nitrogen concentration of the hardening layer is 0.5-1.5 mass%, the residual austenite amount is 20-45 vol.%. The surface hardness of the orbital planes 1a, 2a ia Hv 700-780, and hardness of a core part is Hv 550 or less. Compression residual stress in the peripheral direction at a depth position inside the orbital planes 1a, 2a by 100 μm is 100-500 MPa. The maximum peak height Rp of a rough curve in the axial directions of the orbital planes 1a, 2a is ≤0.2 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rolling bearing preferably used in a hydrogen atmosphere.

  Usually, a rolling bearing incorporated in a gas compressor is used in an atmosphere such as air or nitrogen. Therefore, as a method for extending the life of the rolling bearing, mainly the dimensional stability under a high temperature environment and the improvement of the seizure resistance at the time of high speed rotation. For example, Patent Document 1 discloses a rolling bearing excellent in dimensional stability in which high-temperature tempering is performed and the amount of retained austenite of a steel material is 5% by mass or less.

Further, rolling bearings used in corrosive gas are required to have excellent corrosion resistance. For example, Patent Document 2 discloses a rolling bearing that is excellent in corrosion resistance and seizure resistance, in which a bearing ring is made of martensitic stainless steel and a rolling element is made of ceramics.
On the other hand, as a technique for extending the life of a rolling bearing against hydrogen, a method of increasing the chromium content of steel constituting the race is conventionally known (see, for example, Patent Documents 3 and 4). This method takes into consideration that hydrogen is generated by the decomposition of the lubricating oil.

JP 2006-275131 A JP 2004-11896 A JP 2003-343577 A JP 2005-264216 A

  In recent years, from the viewpoint of environmental problems, development of technology using hydrogen (for example, a fuel cell) has progressed, and a compressor (hereinafter referred to as a hydrogen gas compressor) for compressing hydrogen gas is required. A rolling bearing incorporated in a hydrogen gas compressor may be used in a hydrogen atmosphere, and hydrogen is likely to enter the steel constituting the rolling bearing. When hydrogen intrudes into steel, the shear stress acting on the inside of the steel due to rolling contact with hydrogen causes a change in the martensitic structure of the steel into a structure called a white structure, which significantly increases the life of the rolling bearing. May decrease.

  Spherical roller bearings and relatively large ball bearings are often used for hydrogen gas compressors, but these types of rolling bearings are free from slippage between the rolling elements and the race. The amount is large and wear damage is likely to occur. Normally, an oxide film is formed on the metal surface, and the oxide film makes it difficult for wear damage to occur.However, since there is no oxygen in a hydrogen atmosphere and it is difficult to form an oxide film on the metal surface, wear damage occurs. Cheap. In addition, once wear occurs, the wear surface is chemically active, so hydrogen tends to enter the steel, and the above structural change is accelerated.

  Further, when a minute crack is generated due to generation of a white structure or wear damage, hydrogen embrittlement due to hydrogen occurs at the tip of the crack, so that the progress of the crack is facilitated. Normally, a crack generated in a rolling bearing propagates in parallel to the rolling direction and causes separation where the raceway surface is peeled thinly.However, when the crack progresses easily by hydrogen, a direction perpendicular to the rolling direction, that is, a direction perpendicular to the rolling direction, that is, Cracks may develop in the depth direction. If the crack propagates in the depth direction, the rolling bearing may be damaged.

From these facts, the rolling bearing incorporated in the hydrogen gas compressor is a countermeasure against the structural change due to hydrogen penetrating into steel, a countermeasure against wear damage in a hydrogen atmosphere, and a countermeasure against the progress of cracks in the depth direction. It is necessary to combine three.
However, since the rolling bearing disclosed in Patent Document 1 is not assumed to be used in a hydrogen atmosphere, none of the above three measures has been taken.

  In addition, since the rolling bearing disclosed in Patent Document 2 has a raceway made of stainless steel, measures against the structural change due to hydrogen entering the steel are taken, and the resistance to the structural change is high. Although the structure change is less likely to occur, neither a countermeasure against wear damage in a hydrogen atmosphere nor a countermeasure against the progress of cracks in the depth direction has been taken.

  Furthermore, since the rolling bearing disclosed in Patent Documents 3 and 4 assumes that a small amount of hydrogen generated by the decomposition of the lubricating oil enters the steel, the rolling bearing is used in a hydrogen atmosphere. Under such a harsh environment, the resistance to the tissue change was insufficient. In addition, measures against wear damage in a hydrogen atmosphere and measures against crack propagation in the depth direction have not been sufficient.

  Therefore, the present invention solves the problems of the prior art as described above, and is resistant to wear damage and cracks in the depth direction in addition to being less likely to change to a white structure even when used in a hydrogen atmosphere. It is an object of the present invention to provide a rolling bearing that does not easily develop and has a long life.

  In order to solve the above problems, the present invention has the following configuration. That is, the rolling bearing for a hydrogen atmosphere according to the present invention includes an inner ring having a raceway surface, an outer ring having a raceway surface facing the raceway surface of the inner ring, and a plurality of rolling rings arranged between the raceway surfaces. A rolling bearing comprising a rolling element and used in a hydrogen atmosphere, wherein at least one of the inner ring and the outer ring satisfies the following nine conditions.

  Condition 1: Carbon content is 0.15 mass% or more and 0.3 mass% or less, silicon content is 0.2 mass% or more and 1 mass% or less, and manganese content is 0.2 mass% or more. 2 mass% or less, chromium content is 6.5 mass% or more and 9.5 mass% or less, molybdenum content is 1 mass% or less, sulfur content is 0.02 mass% or less, and phosphorus content is The alloy steel is 0.02 mass% or less, the oxygen content is 12 mass ppm or less, and the balance is iron and inevitable impurities.

Condition 2: The content of silicon is Si%, the content of manganese is Mn%, the content of chromium is Cr%, the content of molybdenum is Mo%, 2.5 × Si% + 1.5 × The structure change resistance value calculated by the formula of Mn% + Cr% + 3 × Mo% is 10 or more.
Condition 3: A hardened layer is formed on the raceway surface by performing quenching and tempering after carburizing or carbonitriding.

Condition 4: The sum of the carbon concentration and the nitrogen concentration of the hardened layer is 0.9% by mass or more and 1.5% by mass or less.
Condition 5: The amount of retained austenite of the hardened layer is 20% by volume or more and 45% by volume or less. Condition 6: The surface hardness of the raceway surface is Hv 700 or higher and 780 or lower.
Condition 7: The hardness of the core part inside the hardened layer is Hv550 or less.

Condition 8: The compressive residual stress in the circumferential direction at a depth position inside 100 μm from the raceway surface is 100 MPa or more and 500 MPa or less.
Condition 9: The maximum peak height Rp of the roughness curve in the axial direction of the raceway surface is 0.2 μm or less.
In the rolling bearing for hydrogen atmosphere of the present invention, at least one of the inner ring and the outer ring is made of alloy steel containing silicon, manganese, chromium, and molybdenum, which are elements that suppress the diffusion of hydrogen in steel. Even if it is used in a hydrogen atmosphere, it does not easily change to a white structure. Further, since the content of impurity elements (sulfur, phosphorus, oxygen) in the alloy steel, the compressive residual stress in the vicinity of the raceway surface, and the hardness of the core portion are defined as suitable values, in the depth direction It is difficult for cracks to develop. Furthermore, since the maximum peak height Rp of the roughness curve along the axial direction of the raceway surface is 0.2 μm or less, wear due to metal contact hardly occurs, and a chemically active new surface is hardly generated. Therefore, in addition to being hard to cause wear damage, the penetration of hydrogen into the steel is also suppressed. Therefore, the rolling bearing for hydrogen atmosphere of the present invention has a long life even when used in a hydrogen atmosphere.

In the rolling bearing for a hydrogen atmosphere of the present invention, it is preferable that the rolling element is made of steel having a chromium content of 5 mass% to 18 mass%. Moreover, it is preferable that the said rolling element is comprised with ceramics.
Below, the critical significance of each numerical value (content of each alloy component contained in the alloy steel, etc.) relating to the inner ring, outer ring, rolling element, alloy steel, etc. in the present invention will be described.

[Carbon content]
Carbon (C) is an element for obtaining a hardness required as a rolling bearing by solid solution in the base by quenching. Moreover, it has the effect | action which combines with another alloy element and forms hard carbide | carbonized_material in alloy steel, and improves abrasion resistance. If the carbon content is less than 0.15% by mass, it may take a long time to sufficiently improve the carbon concentration on the surface in the carburizing process or the carbonitriding process. Moreover, the carbon content of the core part may be too low and the strength of the core part may be insufficient. On the other hand, if the carbon content exceeds 0.3% by mass, the toughness of the core portion becomes insufficient, and the rolling bearing may be easily broken due to the progress of cracks in the depth direction.

[About silicon content]
Silicon (Si) is an element that dissolves in the matrix to improve hardenability and improve temper softening resistance. In addition, it stabilizes the base structure, suppresses changes in the structure due to the penetration of hydrogen, and has an effect of suppressing a decrease in rolling life. If the silicon content is less than 0.2% by mass, these effects may not be sufficiently obtained. On the other hand, if the silicon content exceeds 1% by mass, carbon intrusion is inhibited during carburizing or carbonitriding, and the surface hardness of the raceway surface required for rolling fatigue resistance may be insufficient. There is. In consideration of the stability of the quality of the alloy steel, the silicon content is preferably 0.6% by mass or more and 0.8% by mass or less.

[About manganese content]
Manganese (Mn) is an element that dissolves in the matrix and improves hardenability. It also has an effect of assisting formation of retained austenite on the surface, which is important in the present invention. Furthermore, by solid-dissolving in the base as a substitutional element and stabilizing the base structure, the structure change due to hydrogen is suppressed, and the rolling life is reduced.

  There exists a possibility that said effect | action may become inadequate that content of manganese is less than 0.2 mass%. On the other hand, if the manganese content exceeds 1.2% by mass, the amount of retained austenite after quenching increases so that the hardness necessary for a rolling bearing may not be obtained. In consideration of the stability of the quality of the alloy steel, the manganese content is preferably 0.6% by mass or more and 1% by mass or less.

[Chromium content]
Chromium (Cr) is an element that dissolves in the base and improves hardenability, corrosion resistance, etc., and combines with carbon to form hard carbides in the alloy steel, thereby improving wear resistance. Moreover, it also has the effect | action which improves the resistance with respect to the structure | tissue change to the white structure | tissue important in this invention. That is, chromium has a function of reducing the rate at which hydrogen enters the alloy steel. Furthermore, even if hydrogen invades, it stabilizes the base tissue, thereby suppressing the rolling life due to hydrogen. There exists a possibility that said effect | action may become inadequate that content of chromium is less than 6.5 mass%. On the other hand, if the chromium content exceeds 9.5% by mass, carbon intrusion is inhibited during the carburizing or carbonitriding process, so that the surface hardness of the raceway surface necessary for rolling fatigue resistance is insufficient. There is a risk.

[Molybdenum content]
Molybdenum (Mo) has the effect | action which dissolves in a base | substrate and improves hardenability and temper softening resistance. Moreover, it has the effect | action which forms a hard carbide | carbonized_material in alloy steel and improves abrasion resistance and a rolling life. Furthermore, like chromium, it has the effect of reducing the rate at which hydrogen enters the alloy steel. Furthermore, even if hydrogen invades, it stabilizes the base tissue, thereby suppressing the change in structure due to the invasion of hydrogen and suppressing the decrease in rolling life due to hydrogen. If the molybdenum content exceeds 1% by mass, the cold workability and machinability may be insufficient, and the cost increases. In consideration of the stability of the quality of the alloy steel, the molybdenum content is preferably 0.2% by mass or more and 0.6% by mass or less.

[Sulfur content]
Since sulfur (S) forms manganese sulfide (MnS) and acts as an inclusion, it is preferable that the content of sulfur in the alloy steel is small. In addition, sulfur segregates at the crystal grain boundary and easily causes grain boundary cracking when hydrogen penetrates and lowers the toughness, so that there is a risk that the crack progresses in the depth direction. If the sulfur content exceeds 0.02 mass%, the toughness may be significantly lowered.

[About phosphorus content]
Phosphorus (P) segregates at the grain boundaries, and when hydrogen penetrates, it easily causes grain boundary cracks and lowers toughness. Therefore, there is a possibility that the cracks progress easily in the depth direction. If the phosphorus content exceeds 0.02% by mass, the toughness may be significantly lowered.
[Oxygen content]
Since oxygen (O) forms oxide-based non-metallic inclusions (for example, Al ₂ O ₃ ) that adversely affect the rolling life, it is preferable that the content in the alloy steel is small. When the oxygen content exceeds 12 ppm by mass, the rolling life may be significantly reduced.

[About tissue change resistance]
Silicon, manganese, chromium, and molybdenum have a function of suppressing the change in structure caused by hydrogen by strengthening the metal structure by forming a solid solution in the base of the metal structure as a substitutional element. Some of the above four elements form carbides or carbonitrides with carbon in the alloy steel. These carbides and carbonitrides strongly trap hydrogen, so that the hydrogen in the alloy steel is stress-concentrated. Accumulation in the water is suppressed, and a tissue change to a white tissue due to the penetration of hydrogen is suppressed.

  The strength of these actions varies depending on each alloy element, and the resistance of the alloy steel to the structural change is a structural change calculated by the formula 2.5 × Si% + 1.5 × Mn% + Cr% + 3 × Mo%. It can be defined by a resistance value. If this structure change resistance value is 10 or more, even if a rolling bearing is used in a hydrogen atmosphere, the structure change is suppressed, so that a reduction in the rolling life of the rolling bearing is suppressed.

  If the structure change resistance value is 10 or more, the rolling life of the rolling bearing is long in a hydrogen atmosphere, but if the structure change resistance value is 13 or more, high surface pressure, high rotation speed, high hydrogen pressure, etc. are severe. Since the structure change is suppressed even in a hydrogen atmosphere, a reduction in the rolling life of the rolling bearing is suppressed. In addition, it is preferable that a structure | tissue change resistance value is 16.8 or less for the reason mentioned above regarding the critical value of each alloy element.

[About carburizing and carbonitriding]
When manufacturing the inner ring and outer ring, for example, the material is processed into a predetermined shape by hot forging, turning, etc., carburized or carbonitrided, then quenched and tempered, and further subjected to grinding To finish. Since the alloy steel used in the present invention is a relatively high alloy, carbon and nitrogen tend to hardly enter the alloy steel when carburizing and carbonitriding are performed. Therefore, it is preferable to perform a pre-oxidation process as a pre-process before performing the carburizing process or the carbonitriding process, and then performing a carburizing process or a carbonitriding process after forming a non-dense oxide film on the surface. This pre-oxidation treatment is preferably carried out by holding at 800 ° C. or higher and 1000 ° C. or lower for 0.5 hour or longer and 1 hour or shorter in an oxygen-existing atmosphere.

[About the sum of carbon concentration and nitrogen concentration in the hardened layer]
Carbon and nitrogen in the hardened layer give the surface hardness of the raceway surface necessary for rolling bearings, suppress wear damage, increase the amount of retained austenite on the surface, decrease the hydrogen diffusion rate, and the structure It has the effect | action which suppresses a change. If the sum of the carbon concentration and the nitrogen concentration in the hardened layer is less than 0.9% by mass, the surface hardness of the raceway surface and the amount of retained austenite in the hardened layer may be insufficient. On the other hand, when it exceeds 1.5 mass%, a net-like carbide may be formed on the surface and the toughness may be lowered. Considering the stability of quality, the sum of the carbon concentration and the nitrogen concentration in the cured layer is preferably 1% by mass or more and 1.2% by mass or less.

  However, since the alloy steel used in the present invention has a high structure change resistance value as described above, it tends to form carbides and carbonitrides. Therefore, when carburizing and carbonitriding are performed under the same conditions as normal carburized steel, carbon and nitrogen form carbides and carbonitrides on the extreme surface, so that carbon and nitrogen are difficult to diffuse inside. Therefore, when performing carburizing and carbonitriding, it is preferable to control the sum of the carbon concentration and nitrogen concentration on the surface by lowering the carbon potential and nitrogen potential in the atmosphere.

[Amount of retained austenite in the hardened layer]
The amount of retained austenite in the hardened layer can be controlled by the alloy components of the alloy steel and the heat treatment conditions (the conditions for carburizing, carbonitriding, quenching, and tempering).
Residual austenite is finely dispersed in martensite, and has a function of remarkably reducing the hydrogen diffusion rate by strongly trapping hydrogen that has entered the alloy steel from the raceway surface. This action suppresses the local concentration of hydrogen and delays the tissue change.

  There exists a possibility that said effect | action may become inadequate that the amount of retained austenites of a hardened layer is less than 20 volume%. On the other hand, if it exceeds 45% by volume, the surface hardness becomes insufficient and the rolling life may be reduced. Considering the stability of quality, the amount of retained austenite in the cured layer is preferably 25% by volume or more and 35% or less by volume.

[About surface hardness Hv of raceway]
The surface hardness of the raceway surface is a factor that affects the rolling life of the rolling bearing, and if it is less than Hv700, the rolling life of the rolling bearing may be insufficient. On the other hand, if the surface hardness of the raceway surface is more than Hv780, there is a risk that the strength is reduced due to the penetration of hydrogen. In addition, since it is difficult to measure the hardness of the outermost surface, the hardness at the depth position inside 100 μm from the outermost surface is measured, and in the present invention, this is the surface hardness. When measuring the surface hardness, the race is cut and the hardness at the depth position on the cut surface is measured.

[About the hardness of the core]
The hardness of the core is a factor that affects the progress of cracks in the depth direction due to the penetration of hydrogen. By reducing the hardness of the core, it is difficult for the strength to decrease due to the penetration of hydrogen. Moreover, since the fracture toughness value is increased by lowering the hardness of the core portion, it is difficult for cracks to progress in the depth direction. When the hardness Hv of the core part is more than 550, the above action may be insufficient.

[Compressive residual stress]
Since the compressive residual stress in the circumferential direction acts in the direction of closing the tip of the crack extending in the depth direction, the circumferential compressive residual stress has the effect of suppressing the progress of the crack in the depth direction and the cracking of the rolling bearing. Although the compressive residual stress by grinding is given to the raceway surface, since it is given only to the pole surface of the raceway surface, there is almost no action of suppressing the progress of cracks in the depth direction. Therefore, it is necessary to define the circumferential compressive residual stress applied to the depth position 100 μm inside from the raceway surface.

  If the circumferential compressive residual stress applied to the depth position 100 μm inside from the raceway surface is less than 100 MPa, the progress of cracks in the depth direction may not be sufficiently suppressed. On the other hand, if the circumferential compressive residual stress exceeds 500 MPa, the tensile residual stress generated inside the bearing ring increases in order to balance the compressive residual stress, so that the crack progress in the depth direction is accelerated. There is a case.

[About the maximum peak height Rp of the axial roughness curve of the raceway surface]
When there are protrusions on the raceway surface, metal contact is likely to occur between the raceway surface and the rolling surface of the rolling element. When metal contact occurs in a hydrogen atmosphere, an oxide film is difficult to be formed. Therefore, the portion where the metal contact occurs becomes a chemically active new surface, and adhesion wear tends to occur. Further, since hydrogen easily enters the alloy steel from the new surface, the occurrence of the structural change is accelerated. In general, the arithmetic average roughness Ra is used for managing the surface roughness, but there is no high correlation between the likelihood of wear damage in the hydrogen atmosphere and the arithmetic average roughness Ra.

  As a result of intensive studies, the present inventors have found that controlling the maximum peak height Rp of the roughness curve representing the height of the protrusion on the raceway surface is effective in suppressing wear damage in a hydrogen atmosphere. I found. If the maximum peak height Rp of the roughness curve along the axial direction of the raceway surface is more than 0.2 μm, metal contact occurs at the protrusions, adhesion wear of the raceway surface, and hydrogen penetration into the alloy steel. We found that is easy to occur.

  Since the alloy steel used in the present invention has a high structure change resistance value, silicon, manganese, chromium, and molybdenum form a hard carbide or carbonitride. Since these hard carbides and carbonitrides impair grindability, the maximum peak height Rp of the roughness curve tends to be larger than that of ordinary bearing steel. Therefore, in order to set the maximum peak height Rp of the roughness curve to 0.2 μm or less, it is necessary to suitably select the type of grindstone, the cutting speed, and the peripheral speed used in the grinding process. In consideration of the productivity and cost of the bearing rings, the maximum peak height Rp of the roughness curve is more preferably 0.1 μm or more and 0.2 μm or less.

[Materials that make up rolling elements]
Since rolling elements are less susceptible to damage than bearing rings, bearing steel, which is a material constituting rolling elements of general rolling bearings, bearing steel that has been subjected to carbonitriding, carburizing or carbonitriding The case-hardened steel subjected to the above can be employed without any problem as a material constituting the rolling element in the present invention.

  However, when used in a severe hydrogen atmosphere where the hydrogen pressure is higher, when the slip between the bearing ring and the rolling element is large, when the rotational speed of the rolling bearing is high, or when the load received by the rolling bearing is When the usage environment of the rolling bearing is severe, such as when it is high, it is preferable to use steel having a chromium content of 5 mass% or more and 18 mass% or less as a material constituting the rolling element. Chromium has the effect of reducing the rate at which hydrogen enters the steel. Moreover, even if hydrogen invades, it stabilizes the base structure, thereby suppressing the rolling life from being reduced due to hydrogen intrusion.

There exists a possibility that said effect | action may become inadequate that content of chromium is less than 5 mass%. On the other hand, if it exceeds 18% by mass, coarse eutectic carbides are formed, and the rolling life may be insufficient. Considering the stability of the quality of the steel, the chromium content is more preferably 12% by mass or more and 18% by mass or less.
Further, ceramics can be used as a material constituting the rolling elements. Ceramics are particularly suitable when the usage environment of the rolling bearing is more severe because the strength of the bearing is small and the friction coefficient with the race is small and wear damage of the race is less likely to occur. The type of ceramic is not particularly limited, but silicon nitride or a composite ceramic of alumina and zirconia is preferable.

  The rolling bearing for a hydrogen atmosphere of the present invention has a long life, in addition to being less likely to undergo a structural change to a white structure even when used in a hydrogen atmosphere, and to be less prone to wear damage and crack propagation in the depth direction.

It is a fragmentary longitudinal cross-section which shows the structure of the deep groove ball bearing which is one Embodiment of the rolling bearing for hydrogen atmosphere which concerns on this invention.

An embodiment of a rolling bearing for a hydrogen atmosphere according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial longitudinal sectional view showing a structure of a deep groove ball bearing which is an embodiment of a rolling bearing for a hydrogen atmosphere according to the present invention.
The deep groove ball bearing of FIG. 1 includes an inner ring 1 having a raceway surface 1a on an outer peripheral surface, an outer ring 2 having a raceway surface 2a facing the raceway surface 1a of the inner ring 1 on an inner peripheral surface, and both raceway surfaces 1a and 2a. There are provided a plurality of rolling elements 3 arranged so as to be capable of rolling, a cage 4 for holding the rolling elements 3 between both raceway surfaces 1a, 2a, and sealing devices 5, 5 such as rubber seals. The cage 4 and the sealing device 5 may not be provided.

  The inner ring 1 and the outer ring 2 have a carbon content of 0.15% by mass to 0.3% by mass, a silicon content of 0.2% by mass to 1% by mass, and a manganese content of 0.8%. 2 mass% or more and 1.2 mass% or less, chromium content is 6.5 mass% or more and 9.5 mass% or less, molybdenum content is 1 mass% or less, and sulfur content is 0.02 mass% or less. The phosphorus content is 0.02 mass% or less, the oxygen content is 12 mass ppm or less, and the balance is composed of iron and an unavoidable impurity alloy steel (condition 1).

In this alloy steel, assuming that the silicon content is Si%, the manganese content is Mn%, the chromium content is Cr%, and the molybdenum content is Mo%, 2.5 × Si% + 1. The tissue change resistance value calculated by the formula 5 × Mn% + Cr% + 3 × Mo% is 10 or more (Condition 2).
Furthermore, the inner ring 1 and the outer ring 2 are manufactured by performing quenching and tempering subsequent to the carburizing process or the carbonitriding process, and the raceway surfaces 1a and 2a are hardened layers cured by the heat treatment as described above. (Not shown) is formed (condition 3).

  The sum of the carbon concentration and the nitrogen concentration of this hardened layer is 0.9 mass% or more and 1.5 mass% or less (Condition 4). Moreover, the amount of retained austenite of this hardened layer is 20 volume% or more and 45 volume% or less (Condition 5). Furthermore, the surface hardness of the raceway surfaces 1a and 2a is Hv 700 or more and 780 or less (Condition 6). Further, a core (not shown) that is not cured by the above-described heat treatment is disposed inside the cured layer, and the hardness of the core is Hv550 or less (Condition 7). Further, a compressive residual stress in the circumferential direction of 100 MPa or more and 500 MPa or less is applied to a depth position inside 100 μm from the raceway surfaces 1 a and 2 a (Condition 8). Furthermore, the maximum peak height Rp of the roughness curves in the axial direction of the raceway surfaces 1a and 2a is 0.2 μm or less (condition 9).

  Since such deep groove ball bearings satisfy the above conditions 1 to 9, in addition to being hard to undergo a structural change to a white structure even when used in a hydrogen atmosphere, wear damage and cracks in the depth direction are prevented. It is difficult to develop and has a long life. Therefore, it is suitable as a rolling bearing used in a hydrogen atmosphere like a rolling bearing incorporated in a compressor that compresses hydrogen gas. Although these conditions 1-9 should just satisfy | fill only one of the inner ring | wheel 1 and the outer ring | wheel 2, it is preferable that both the inner ring | wheel 1 and the outer ring | wheel 2 satisfy | fill.

Furthermore, it is preferable that the rolling element 3 is comprised with the steel or ceramics whose chromium content is 5 mass% or more and 18 mass% or less.
In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, in the present embodiment, a deep groove ball bearing has been described as an example of a hydrogen atmosphere rolling bearing, but the present invention can be applied to various types of rolling bearings other than deep groove ball bearings. . For example, radial rolling bearings such as angular contact ball bearings, self-aligning ball bearings, cylindrical roller bearings, tapered roller bearings, needle roller bearings, and self-aligning roller bearings, and thrust types such as thrust ball bearings and thrust roller bearings This is a rolling bearing.

〔Example〕
Rolling bearings were manufactured by the method described below. The alloy steel having the composition as in the above condition 1 is formed into a shape of a raceway by forging and cutting or only by cutting. Next, pre-oxidation treatment, carburization treatment (or carbonitriding treatment), quenching, and tempering are performed in this order to form a hardened layer containing residual austenite on the surface, and then polishing is performed to finish the track. Completed the wheel.

  The pre-oxidation treatment was performed by holding at 800 to 1000 ° C. for 0.5 to 1 hour in an atmosphere (for example, air) in which oxygen exists. Moreover, the carburizing process was performed by air cooling or oil cooling after holding | maintaining at 900-1000 degreeC for 4 to 20 hours in the mixed gas atmosphere of RX gas and enriched gas. Further, the carbonitriding process was performed by air cooling or oil cooling after holding at 900 to 1000 ° C. for 4 to 20 hours in a mixed gas atmosphere of RX gas, enriched gas, and ammonia gas.

  The quenching performed after the carburizing process or the carbonitriding process was performed by oil cooling or gas cooling after holding at 950 to 1050 ° C. Moreover, the tempering performed after this hardening was performed by hold | maintaining at 160-240 degreeC, and cooling by furnace or air. The rolling rings (inner and outer rings) thus obtained were combined with rolling elements, cages and seals to form rolling bearings.

  Below, the example which manufactured the deep groove ball bearing is shown. Using the alloy steel of steel type B in Table 1 as a raw material, the inner ring for a deep groove ball bearing of the reference number 6316 and the same method as above (the heat treatment adopts carbonitriding among carburizing and carbonitriding) An outer ring was manufactured. As a rolling element, a ball composed of steel type O shown in Table 1 was used. These inner rings, outer rings, and rolling elements were assembled to obtain a deep groove ball bearing having a nominal number 6316.

  When the sum of the carbon concentration and the nitrogen concentration of the hardened layer formed by the heat treatment on the raceway surfaces of the inner ring and the outer ring of this deep groove ball bearing was measured using an electron beam microanalyzer (EPMA), 1.5 masses each. % And 1.2% by mass. Moreover, when the amount of retained austenite of the hardened layer was measured using an X-ray diffractometer, it was 25% by volume and 30% by volume, respectively.

  Next, the example which manufactured the self-aligning roller bearing is shown. An inner ring and an outer ring for a spherical roller bearing having a nominal number 22218 were manufactured by the same method as described above (carbonitriding was adopted for heat treatment) using alloy steel of steel type B shown in Table 1. As the rolling elements, rollers composed of steel type N shown in Table 1 were used. These inner rings, outer rings, and rolling elements were assembled to obtain a self-aligning roller bearing having a nominal number 22218.

  When the sum of the carbon concentration and the nitrogen concentration of the hardened layer formed by the heat treatment on the raceway surfaces of the inner and outer rings of this self-aligning roller bearing was measured using an electron beam microanalyzer (EPMA). They were 9% by mass and 1.1% by mass. Moreover, when the amount of retained austenite of the hardened layer was measured using an X-ray diffractometer, it was 30% by volume and 35% by volume, respectively.

  Next, the example which manufactured the thrust ball bearing is shown. Using the alloy steels of steel types A to K shown in Table 1 as raw materials, an inner ring and an outer ring for a thrust ball bearing having a nominal number 51305 were manufactured by the same method as described above. As the rolling elements, balls composed of steel types G (SUJ2), M, N, O or ceramics P, Q shown in Table 1 were used. These inner rings, outer rings, and rolling elements were assembled to obtain a thrust ball bearing having a nominal number 51305. However, the number of balls was three in order to facilitate adjustment of the surface pressure.

These thrust ball bearings were subjected to a rolling fatigue test under the following two test conditions in a hydrogen atmosphere to determine the life (L ₅₀ ) at which the cumulative failure probability was 50%.
・ Test condition A
Hydrogen pressure: 0.12 MPa
Surface pressure: 3.1 GPa
Rotational speed: 1000min ^-1
Lubricating oil: Lubricating oil whose ISO viscosity grade is ISO VG32-Test condition B
Hydrogen pressure: 0.4 MPa
Surface pressure: 3.1 GPa
Rotational speed: 1000min ^-1
Lubricating oil: Lubricating oil whose ISO viscosity grade is ISO VG68 Table 2 shows the test results under test condition A. Also, the structure change resistance value of alloy steel, the content of heat treatment (carburizing or carbonitriding), the sum of carbon concentration and nitrogen concentration in the hardened layer, the amount of retained austenite in the hardened layer, the surface hardness of the raceway, the core Table 2 also shows the hardness of the surface, the compressive residual stress in the circumferential direction at a depth of 100 μm from the raceway surface, the arithmetic mean roughness Ra of the raceway surface, and the maximum peak height Rp of the raceway surface roughness curve. .

  The sum of the carbon concentration and the nitrogen concentration in the cured layer was measured using an electron beam microanalyzer (EPMA). The amount of retained austenite and compressive residual stress were measured using an X-ray diffractometer. Furthermore, the lifetime in Table 2 is shown as a relative value when the lifetime of Comparative Example 5 is 1.

  As can be seen from Table 2, in Examples 1 to 6, the alloy composition of the alloy steel, the structure change resistance value, the sum of the carbon concentration and the nitrogen concentration of the hardened layer, the amount of retained austenite of the hardened layer, the raceway Since the surface hardness of the surface, the hardness of the core, the compressive residual stress, and the maximum peak height Rp of the raceway surface roughness curve are within the scope of the present invention, there is little decrease in life even when used in a hydrogen atmosphere. Also, wear damage was difficult to occur. Therefore, the rolling life was long. In particular, Examples 1 to 3 had a longer life because the alloy composition, the sum of the carbon concentration and the nitrogen concentration of the hardened layer, and the amount of retained austenite of the hardened layer were in a more preferable range.

On the other hand, in Comparative Example 1, since the carbon content of the alloy steel constituting the bearing ring is low, the difference in hardness between the surface layer portion (hardened layer) and the core portion becomes large, and as a result, the compressive residual stress Is out of the scope of the present invention. Therefore, a tensile residual stress accompanying the compressive residual stress is generated in the core portion, so that the rolling life is lowered.
In Comparative Example 2, the alloy steel constituting the race ring has a low silicon content and a high oxygen content. For this reason, the resistance to the change in structure due to the penetration of hydrogen is low, and the amount of oxide inclusions increases, resulting in a short life.

  Furthermore, since the comparative example 3 has high carbon content and sulfur content of the alloy steel which comprises a bearing ring, the toughness of a core part is low. Therefore, when a minute crack is generated, the speed at which the crack progresses in the depth direction is increased, resulting in a short life. Furthermore, since the carbon content of the alloy steel which comprises a bearing ring was low, the comparative example 4 had the low resistance with respect to the said structure | tissue change by the penetration | invasion of hydrogen, and was short life. Further, Comparative Example 5 had a short life because the alloy composition was within the range of the present invention, but the structure change resistance value was less than 10.

  Furthermore, in Comparative Example 6, the carbonitriding conditions are inappropriate, and the sum of the carbon concentration and the nitrogen concentration of the hardened layer is high, and accordingly, the surface hardness of the raceway surface is increased. As a result, the strength was significantly reduced when hydrogen entered, and the life was short. Furthermore, in Comparative Example 7, the carburizing conditions are inappropriate, and the sum of the carbon concentration and the nitrogen concentration of the hardened layer is low, and accordingly, the surface hardness of the raceway surface is low. As a result, the rolling fatigue strength of the base structure was lowered and the life was short.

  Furthermore, in Comparative Example 8, since the quenching and tempering conditions are inappropriate, the amount of retained austenite and the compressive residual stress of the cured layer are low. As a result, the structure change due to the invasion of hydrogen is likely to occur, and further, the generated microcracks tend to progress in the depth direction, resulting in a short life. Furthermore, in Comparative Example 9, since the quenching and tempering conditions are inappropriate, the amount of retained austenite in the cured layer is high. As a result, the surface hardness of the raceway surface was reduced and the service life was short.

  Further, in Comparative Examples 10 and 11, alloy steels of the same type as in Examples 5 and 6 were used, heat treatment was performed under the same conditions, and only the grinding conditions were changed to change the surface roughness (arithmetic mean roughness) of the raceway surface. Only Ra and the maximum peak height (Rp) of the roughness curve are different. In Comparative Examples 10 and 11, the arithmetic average roughness Ra is smaller than those in Examples 5 and 6, but the maximum peak height Rp of the roughness curve is large. For this reason, wear tends to occur in a hydrogen atmosphere and the penetration of hydrogen accelerates, resulting in a short life.

  Next, Table 3 shows the test results under test condition B. Also, the structure change resistance value of alloy steel, the content of heat treatment (carburizing or carbonitriding), the sum of carbon concentration and nitrogen concentration in the hardened layer, the amount of retained austenite in the hardened layer, the surface hardness of the raceway surface, the core Table 3 shows the hardness of the surface, the compressive residual stress in the circumferential direction at a depth of 100 μm from the raceway surface, the arithmetic average roughness Ra of the raceway surface, and the maximum peak height Rp of the raceway roughness curve. .

  The track rings of Examples 21 to 26 and Comparative Examples 21 to 31 are the same as the track rings of Examples 1 to 6 and Comparative Examples 1 to 11, respectively, and only the rolling element material is different. For example, in Example 1 and Example 21, the raceway is the same and only the rolling elements are different.

  In the case of test condition B, since the hydrogen pressure is high, measures against hydrogen are also required for the rolling elements. Therefore, steel types M, N, O or ceramics P, Q were used as the material constituting the rolling elements. The sum of the carbon concentration and the nitrogen concentration in the cured layer was measured using an electron beam microanalyzer (EPMA). The amount of retained austenite and compressive residual stress were measured using an X-ray diffractometer. Furthermore, the lifetime in Table 3 is shown as a relative value when the lifetime of Comparative Example 21 is 1.

  As can be seen from Table 3, in Examples 21 to 26, the alloy composition of the alloy steel constituting the race ring, the structure change resistance value, the sum of the carbon concentration and the nitrogen concentration of the hardened layer, the amount of retained austenite of the hardened layer, the raceway The surface hardness of the surface, the hardness of the core, the compressive residual stress, and the maximum peak height Rp of the roughness curve of the raceway surface are within the scope of the present invention, so the life is reduced even when used in a high-pressure hydrogen atmosphere. There was little, and abrasion damage was hard to occur. Therefore, the rolling life was long. In particular, Examples 21 to 23 had a longer life because the alloy composition, the sum of the carbon concentration and the nitrogen concentration of the hardened layer, and the amount of retained austenite of the hardened layer were in a more preferable range. Moreover, since the rolling element is also made of a preferable material, the rolling element has a long life without being damaged.

On the other hand, in Comparative Example 21, the carbon content of the alloy steel constituting the bearing ring is low, so the difference in hardness between the surface layer portion (hardened layer) and the core portion becomes large, and as a result, the compressive residual stress Is out of the scope of the present invention. Therefore, a tensile residual stress accompanying the compressive residual stress is generated in the core portion, so that the rolling life is lowered.
In Comparative Example 22, the alloy steel constituting the race ring has a low silicon content and a high oxygen content. For this reason, the resistance to the change in structure due to the penetration of hydrogen is low, and the amount of oxide inclusions increases, resulting in a short life.

  Furthermore, since the comparative example 23 has high carbon content and sulfur content of the alloy steel which comprises a bearing ring, the toughness of a core part is low. Therefore, when a minute crack is generated, the speed at which the crack progresses in the depth direction is increased, resulting in a short life. Further, in Comparative Example 24, since the carbon content of the alloy steel constituting the race was low, the resistance to the structural change due to the penetration of hydrogen was low, and the life was short. Furthermore, although the alloy composition was within the range of the present invention in Comparative Example 25, the structure change resistance value was less than 10, so the life was short.

  Further, in Comparative Example 26, the carbonitriding conditions are not suitable, and the sum of the carbon concentration and the nitrogen concentration of the hardened layer is high, and accordingly, the surface hardness of the raceway surface is increased. As a result, the strength was significantly reduced when hydrogen entered, and the life was short. Furthermore, in Comparative Example 27, the carburizing conditions are inappropriate, and the sum of the carbon concentration and the nitrogen concentration of the hardened layer is low, and accordingly, the surface hardness of the raceway surface is low. As a result, the rolling fatigue strength of the base structure was lowered and the life was short.

  Further, in Comparative Example 28, the hardening and tempering conditions are unsuitable, so the amount of retained austenite and compressive residual stress of the cured layer is low. As a result, the structure change due to the invasion of hydrogen is likely to occur, and further, the generated microcracks tend to progress in the depth direction, resulting in a short life. Furthermore, in Comparative Example 29, the amount of retained austenite in the hardened layer is high because the conditions for quenching and tempering are inappropriate. As a result, the surface hardness of the raceway surface was reduced and the service life was short.

  Further, in Comparative Examples 30 and 31, alloy steels of the same type as those in Examples 25 and 26 were used, heat treatment was performed under the same conditions, and only the grinding conditions were changed to change the surface roughness (arithmetic average roughness) of the raceway surface. Only Ra and the maximum peak height (Rp) of the roughness curve are different. In Comparative Examples 30 and 31, the arithmetic average roughness Ra is smaller than those in Examples 25 and 26, but the maximum peak height Rp of the roughness curve is large. For this reason, wear tends to occur in a hydrogen atmosphere and the penetration of hydrogen accelerates, resulting in a short life.

DESCRIPTION OF SYMBOLS 1 Inner ring 1a Raceway surface 2 Outer ring 2a Raceway surface 3 Rolling element

Claims (3)

An inner ring having a raceway surface, an outer ring having a raceway surface facing the raceway surface of the inner ring, and a plurality of rolling elements arranged to roll between the raceway surfaces, and used in a hydrogen atmosphere. A rolling bearing for a hydrogen atmosphere, wherein at least one of the inner ring and the outer ring satisfies the following nine conditions.
Condition 1: Carbon content is 0.15 mass% or more and 0.3 mass% or less, silicon content is 0.2 mass% or more and 1 mass% or less, and manganese content is 0.2 mass% or more. 2 mass% or less, chromium content is 6.5 mass% or more and 9.5 mass% or less, molybdenum content is 1 mass% or less, sulfur content is 0.02 mass% or less, and phosphorus content is The alloy steel is 0.02 mass% or less, the oxygen content is 12 mass ppm or less, and the balance is iron and inevitable impurities.
Condition 2: The content of silicon is Si%, the content of manganese is Mn%, the content of chromium is Cr%, the content of molybdenum is Mo%, 2.5 × Si% + 1.5 × The structure change resistance value calculated by the formula of Mn% + Cr% + 3 × Mo% is 10 or more.
Condition 3: A hardened layer is formed on the raceway surface by performing quenching and tempering subsequent to carburizing or carbonitriding.
Condition 4: The sum of the carbon concentration and the nitrogen concentration of the hardened layer is 0.9% by mass or more and 1.5% by mass or less.
Condition 5: The amount of retained austenite of the hardened layer is 20% by volume or more and 45% by volume or less. Condition 6: The surface hardness of the raceway surface is Hv 700 or higher and 780 or lower.
Condition 7: The hardness of the core part inside the hardened layer is Hv550 or less.
Condition 8: The compressive residual stress in the circumferential direction at a depth position inside 100 μm from the raceway surface is 100 MPa or more and 500 MPa or less.
Condition 9: The maximum peak height Rp of the roughness curve in the axial direction of the raceway surface is 0.2 μm or less.   2. The rolling bearing for a hydrogen atmosphere according to claim 1, wherein the rolling element is made of steel having a chromium content of 5 mass% to 18 mass%.   The rolling element for a hydrogen atmosphere according to claim 1, wherein the rolling element is made of ceramics.

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