JP5991026B2 - Manufacturing method of rolling bearing - Google Patents

Description

  The present invention relates to a rolling bearing for rotatably supporting rotating members of various rotating machine devices such as a main shaft of a wind turbine generator (windmill) or a rotating shaft constituting a transmission, a construction machine, an industrial robot, etc. Regarding improvements. Specifically, it is intended to realize a rolling bearing capable of suppressing the occurrence of peeling based on a structural change (white structural change) and ensuring sufficient durability even under severe use conditions. In particular, the present invention exhibits a remarkable effect when applied to a relatively large rolling bearing in which the diameter of the rolling element is 30 mm or more.

  For example, a radial ball bearing 1 as shown in FIG. 4 is incorporated in a rotation support portion of various rotary machine devices such as a rotation support portion of a main shaft constituting the wind power generator. The radial ball bearing 1 includes an outer ring 3 having an outer ring raceway 2 on an inner peripheral surface, an inner ring 5 having an inner ring raceway 4 on an outer peripheral surface, and an outer ring raceway 2 and an inner ring raceway 4 provided between the outer ring raceway 2 and the inner ring raceway 4. A plurality of balls 6 and 6 which are moving bodies are provided. These balls 6, 6 are held by a cage 7 so as to be able to roll while being arranged at equal intervals in the circumferential direction. Further, a radial tapered roller bearing 8 using a tapered roller as a rolling element as shown in FIG. 5, for example, is incorporated in the rotation support portion to which a large radial load is applied. The radial tapered roller bearing 8 includes an outer ring 3a having a conical concave outer ring raceway 2a on an inner peripheral surface, an inner ring 5a having a conical convex inner ring raceway 4a on an outer peripheral surface, the outer ring raceway 2a and the inner ring raceway 4a. Are provided with a plurality of tapered rollers 9, 9 each being a rolling element provided so as to be able to roll while being held by the cage 7 a. Further, out of both ends of the outer peripheral surface of the inner ring 5a, a large-diameter side flange 10 is formed at the large-diameter end, and a small-diameter flange 11 is formed at the small-diameter end. The small diameter side flange 11 may be omitted. Such a radial ball bearing 1 and a radial tapered roller bearing 8 are configured such that, for example, the outer rings 3 and 3a are fitted and fixed to the housing, and the inner rings 5 and 5a are fitted and fixed to the rotating shaft. The housing is rotatably supported.

  In the case of a rolling bearing formed by combining a pair of race rings and a plurality of rolling elements, including such a radial ball bearing 1 and a radial tapered roller bearing 8, any of the surfaces that are in rolling contact with each other in use. It is widely known that it peels off due to rolling fatigue and reaches the end of its life. As a form of such peeling, cracks are generated starting from non-metallic inclusions (oxide-based or TiN-based non-metallic inclusions) contained in the metal material constituting each component of the rolling bearing. There are cases in which cracks are generated starting from an indentation based on the mixing of foreign matters (internal origin type peeling) and peeling is caused (indentation starting type peeling).

  Furthermore, in some applications where the conditions of use are severe, the metal structure under the surface of the raceway or rolling surface (near the maximum shear stress position) turns white and cracks occur from that part, leading to delamination. There is also. The cause of such delamination based on changes in the metal structure (hereinafter referred to as “structural change-type delamination”) has not been fully elucidated, but at present, hydrogen generated when the lubricant is decomposed. It is considered that (hydrogen atom) penetrates into steel and causes hydrogen embrittlement, thereby promoting the occurrence of structural change and leading to peeling.

  Patent Documents 1 and 2 describe techniques for improving the rolling fatigue life by suppressing the occurrence of such structure change-type peeling by improving the components of grease sealed in rolling bearings or using grease. As a premise, there is described an invention intended to suppress generation of hydrogen and entry of hydrogen by applying a rust preventive oil to the surface of the raceway or each rolling element. However, depending on the application of the rolling bearing, grease may not be used and lubricating oil may have to be used. For this reason, the prior art described in Patent Documents 1 and 2 may not be applicable. In particular, in the case of a relatively large rolling bearing with a rolling element having a diameter of 30 mm or more, which is incorporated in the rotation support portion of the main shaft constituting the wind power generator, lubricating oil is used as a lubricant rather than grease. It is used frequently. In such a case, the techniques described in Patent Documents 1 and 2 are often not applicable. Furthermore, in a relatively large rolling bearing, for the purpose of facilitating the formation of an oil film or for the purpose of preventing wear, additives such as anti-wear agents are added to synthetic oils such as polyalkylene glycols and mineral oil, Often special lubricants are used. Such special lubricating oils, depending on their types, have a greater amount of hydrogen penetration into the steel than commonly used lubricating oils, and promote the occurrence of structural changes. .

  In addition, in a rolling bearing having a rolling element with a diameter of 30 mm or more, the contact area between the race and the rolling element is large, so that an oil film is hardly formed stably on the rolling contact portion, and local metal contact is likely to occur. Then, due to the metal contact, the lubricating oil decomposes and hydrogen is likely to be generated, and the generated hydrogen penetrates into the alloy steel constituting the race and the rolling elements, and the structure change type peeling as described above is performed. It tends to occur. Also, in the rotation support part where the direction of the torque acting on the rotation shaft changes temporarily or frequently on the rotation shaft of the transmission that transmits power by gears, the rotation is changed at the moment when the rotation direction changes. A large slip occurs between the rolling surface of the moving body and the raceway surface of the raceway. For this reason, due to the occurrence of metal contact due to the oil film breakage at the rolling contact portion, the lubricating oil decomposes and hydrogen is easily generated, and the generated hydrogen is contained in the alloy steel constituting the race and rolling elements. It becomes easy to invade. Therefore, in the large-sized rolling bearing incorporated in the rotation support portion as described above, the problem of the structure change type peeling due to the use of the lubricating oil is likely to be remarkable.

  Patent Document 3 describes an invention in which a structural change type peeling due to hydrogen is delayed by subjecting an alloy steel to which a large amount of Cr and Mo is added to carburizing or carbonitriding. However, when the content of carbide generating elements such as Cr and Mo increases, the surface C concentration tends to be as high as 1.5% or more during carburizing and carbonitriding depending on the heat treatment conditions. And when it becomes high, it becomes easy to produce | generate the huge carbide called a net-like carbide along the former austenite grain boundary which is the original austenite grain boundary before a martensitic structure. When such a net-like carbide is generated, cracks are easily generated and propagated along the net-like carbide, and the toughness is significantly reduced. For this reason, the technique described in Patent Document 3 may not be applied to a relatively large rolling bearing that requires high toughness.

  Further, in Patent Document 4, the structure change caused by hydrogen is achieved by using bearing steel in which fine V-based carbides are precipitated by subjecting steel to which V is added to carburizing quenching or carbonitriding to quenching. An invention for delaying mold release is described. However, V is an expensive element, and the alloy steel containing V is also expensive, so it is difficult to reduce the cost. In addition, the crystal grain size of the prior austenite becomes coarse during the carburizing process or the carbonitriding process, and there is a problem that it is difficult to ensure fatigue strength due to the grain boundary fracture of the prior austenite.

  Furthermore, Patent Document 5 discloses an invention for realizing a rolling bearing that suppresses the occurrence of structural changes and suppresses cracks from progressing in the depth direction, thereby extending the life even under severe use conditions. Have been described. The invention described in Patent Document 5 includes any member of the outer ring, the inner ring, and each of the rolling elements, containing 2.5 to 5.0% by mass of Cr that can delay the penetration of hydrogen, and a core part. It is intended to reduce the hardness of the steel and ensure a high fracture toughness value. For this reason, in the case of the invention described in the above-mentioned Patent Document 5, any one of the above members is formed by adding 0.15 to 0.30% by mass of C, Si, Mn, Mo, Ni, Cu, S, P , Made of alloy steel containing appropriate amounts of Al, N, Ti and O. Then, the C + N concentration, the hardness, and the amount of retained austenite at a predetermined depth X position from the rolling contact surface of any one of the members are adjusted to appropriate values by carbonitriding or carburizing and quenching and tempering.

  In the case of the invention described in Patent Document 5 as described above, the hydrogen embrittlement resistance is improved and the structure is changed as compared with the conventional techniques known from Patent Documents 1 to 4 described above. In addition to suppressing the occurrence of cracks, it is possible to prevent the cracks from progressing in the depth direction, thereby extending the life even under severe use conditions. However, in the case of a rolling bearing used under extremely severe conditions, such as for a rotation support part of a main shaft of a wind turbine generator, used in a maintenance-free state for an extremely long time (for example, 20 to 30 years). Therefore, it is desired to ensure better durability.

JP 2002-327758 A JP 2003-106338 A JP 2005-314794 A JP 2008-280583 A JP 2010-196107 A

  In view of the circumstances as described above, the present invention more effectively suppresses the occurrence of structural changes due to hydrogen intrusion, can further extend the life, and can operate stably even under severe use conditions. The present invention has been invented to realize a rolling bearing capable of constituting a rotating support portion capable of rotating.

A rolling bearing that is an object of the present invention includes both first and second race rings and a plurality of rolling elements.
Of these, the first race ring has the first raceway surface on any surface.
Further, the second race ring has a second raceway surface on a surface facing the first raceway surface.
Furthermore, each said rolling element is provided between these 1st, 2nd track surfaces so that rolling is possible.

In particular, at least one member of said second bearing ring and the first bearing ring in the case of the manufacturing method of the rolling bearings of the present invention and the the rolling elements, C (carbon) 0 .10 to 0.30 mass%, Si (silicon) 0.2 to 0.5 mass%, Mn (manganese) 0.2 to 1.2 mass%, and Cr (chromium) 2.2 to 4. It is made of an iron-based alloy (alloy steel) containing 5% by mass and 0.1 to 1.0% by mass of Mo (molybdenum), and the remainder being Fe (iron) and inevitable impurities.

In the case of subject to the rolling bearing of the present invention, only setting the carburized layer or carbonitrided layer on the surface, the C concentration in the depth position of 50μm from the surface that the 1.5 to 2.0 mass% Can do . And, following 10μm maximum grain size of carbides at this depth position, the particle size of the prior austenite to 20μm or less.
Also, good Mashiku the prior SL in at least one of the members, the amount of retained austenite from the surface 50μm position, 30 to 60 volume%.

Moreover, in the case of the invention of the method for manufacturing a rolling bearing according to the present invention , first, an alloy steel material having the above composition is processed to obtain an intermediate material.
Thereafter, the intermediate material is subjected to heat treatment as shown in FIG. In this heat treatment, first, carburizing treatment or carbonitriding treatment is performed by holding the intermediate material in a state of being heated and maintained at 900 to 1000 ° C. within a range of FIG. 1 for a predetermined time (for example, 12 to 20 hours). Of course, when carburizing is performed, it is performed in a gas atmosphere containing a large amount of C, and when carbonitriding is performed, it is performed in a gas atmosphere containing a large amount of C and N, respectively. Next, in the range b of FIG. 1, a diffusion treatment is performed in which the temperature is maintained at a temperature higher by 10 ° C. or more than the temperature during the carburizing or carbonitriding treatment for a predetermined time (for example, 1 to 3 hours). If the treatment temperature of this diffusion treatment exceeds 1010 ° C., the prior austenite grain size tends to be coarsened. Therefore, the treatment temperature is preferably suppressed to 1010 ° C. or less.
Once the diffusion treatment as described above has been performed, it is then held at 800 to 880 ° C. for a predetermined time (for example, 1 to 3 hours) in the range of c in FIG. Apply oil cooling to immerse). Thereafter, a quenching process is performed in which the temperature is kept at 800 to 880 ° C. for a predetermined time (for example, 1 to 2 hours) in the range d of FIG. Next, in a range e shown in FIG. 1, in a state heated to 160 to 200 ° C., hold for a predetermined time (for example, 1 to 3 hours), and after tempering, cool in the furnace or outside the furnace (slow cooling) )
Then, a carburized layer or a carbonitrided layer is provided on the surface of the at least one member, and at a position of 50 μm from the surface of the member, the C concentration is 1.5% by mass or more, and the maximum particle size of the carbide is 10 μm. Hereinafter, the prior austenite grain size is set to 20 μm or less.

When carrying out the invention of a method of manufacturing a rolling bearing of the above such present invention, for example, as the invention described in claim 2, as shown in FIG. 2, the diffusion treatment after the carburizing or carbonitriding 2, within the range f of FIG. 2, the air in the furnace or outside the furnace is maintained at 620 to 700 ° C., which is a temperature below the A1 transformation point of the alloy steel, for a predetermined time (for example, 4 to 12 hours). A process of cooling to room temperature (slow cooling) can be set.
Further, when carrying out the invention of the rolling bearing manufacturing method of the present invention as described above, preferably, as in the invention described in claim 3 , the at least one member is located at a position of 50 μm from the surface. The amount of retained austenite is 30 to 60% by volume.

  In the case of carrying out the present invention, the present invention is applied to any of the first and second race rings and the respective rolling elements, which are constituent members of a rolling bearing. Is determined in consideration of the structure and size of the rolling bearing (bearing name number) and operating conditions. Specifically, the durability of the entire rolling bearing can be improved by applying the present invention to the most inferior durability (the most easily peelable member). However, as a result of improving the durability of the member by applying the present invention to the member with the lowest durability as it is (when the present invention is not applied), the durability of the other member is When it is inferior to durability, the present invention can be applied to two or more kinds of members, and further to all members.

According to the rolling bearing manufactured by the manufacturing method of the rolling bearing of the present invention configured as described above, excellent durability can be ensured even in the case of a rolling bearing used under extremely severe conditions. That is, in the case of the present invention, the carbide in the surface layer portion of the component of the rolling bearing is refined as shown in FIG. 3A (the maximum particle size is suppressed to 10 μm or less). For this reason, the fracture toughness of this constituent member can be sufficiently increased, and a further durability improvement effect can be obtained with respect to the invention described in Patent Document 5 described above with respect to the structure change type peeling. That is, in the case of the present invention, fine carbides are formed on the surface layer portion of the constituent member, as is clear from comparison of FIG. 3A and FIG. 3B showing the conventional case. Since it exists in a large amount, the trapping effect of hydrogen by this carbide is excellent. In short, an extremely large number of hydrogen trap sites are present in the surface layer portion of the component member, and the total surface area thereof is large, and the effect of preventing the entry of hydrogen atoms into the component member becomes very excellent. As a result, the structure change (white structure change) due to the penetration of hydrogen into the alloy steel that constitutes the component is sufficiently suppressed, the occurrence of structure change-type peeling is suppressed, and even when the usage conditions are severe, sufficient durability Can be secured.

  And according to the manufacturing method of this invention, the structural member of the rolling bearing which refined the carbide | carbonized_material of the surface part as mentioned above can be manufactured stably. That is, in the case of the manufacturing method of the present invention, this component member is subjected to carburizing treatment or carbonitriding treatment under a predetermined condition on an alloy steel intermediate material having the above-described composition, and then the carburizing treatment. Alternatively, by performing diffusion treatment at a temperature higher than that of carbonitriding, large carbides generated near the surface can be sufficiently dissolved into the base structure. Further, by rapidly cooling from the state maintained at 800 to 880 ° C., formation of net carbide can be suppressed, and uniform and fine carbide can be obtained by C precipitated from the base structure. Furthermore, by subsequently quenching at 800 to 880 ° C., the grain size of the prior austenite that has become coarse by the above-described series of treatments can be returned to a normal size.

Next, in the present invention, the reason why the composition of the alloy steel and the heat treatment conditions constituting the structural member to suppress the structural change among the structural members of the rolling bearing will be described as described above.
First, the reason for regulating the composition of the alloy steel will be described.
[C: 0.10 to 0.30 mass%]
C is an element that dissolves in the base structure of the alloy steel by quenching and improves its hardness. Therefore, it is added to impart the necessary hardness to the constituent members.
When the content of C is less than 0.10% by mass, even if carburizing or carbonitriding is performed later, the core of the component (surface layer that is hardened by carburizing or carbonitriding) In the deeper portion, the hardness decreases as the depth increases, and the hardness of the portion where the hardness is constant regardless of the change in depth) is insufficient, ensuring the necessary rigidity as the component Things get harder.
On the other hand, if the C content exceeds 0.30% by mass, the hardness of the constituent members as a whole becomes too high. The component of the rolling bearing needs to have a sufficiently high hardness at the surface portion that is in rolling contact with the counterpart member. However, as far as the core portion is concerned, it is important to ensure toughness without excessively increasing the hardness. If the C content exceeds 0.30% by mass, it becomes difficult to ensure the toughness required for the core.
Therefore, the C content in the alloy steel is restricted to a range of 0.10 to 0.30 mass%.

[Si: 0.2 to 0.5% by mass]
Si dissolves in the base structure of the alloy steel and improves the hardenability. Further, it is added because it has the effect of stabilizing the martensite of the base structure, delaying the structural change due to hydrogen, and extending the life of the constituent members.
When the Si content is less than 0.2% by mass, the effect of improving the hardenability and the effect of delaying the structure change cannot be sufficiently obtained.
On the other hand, when the Si content exceeds 0.5% by mass, the carburizing property and the carbonitriding property are likely to deteriorate.
Therefore, the content of Si in the alloy steel is regulated to a range of 0.2 to 0.5 mass%.

[Mn: 0.2 to 1.2% by mass]
Mn is dissolved in the base structure of the alloy steel to improve the hardenability. Moreover, it has the effect of stabilizing the martensite in the base structure, delaying the structural change due to hydrogen, and extending the life of the structural member made of alloy steel. Furthermore, it has the effect of making it easy to produce retained austenite after heat treatment. The produced retained austenite delays the diffusion and accumulation of hydrogen in the alloy steel, thereby delaying the local occurrence of structural changes due to hydrogen and extending the life of components made of the alloy steel. Have
When the content of Mn is less than 0.20% by mass, the above-described effects such as delaying the tissue change cannot be obtained sufficiently.
On the other hand, when the Mn content exceeds 1.20% by mass, the prior austenite grain size becomes coarse or the residual austenite amount becomes excessive. The coarsening of the prior austenite grain size causes a decrease in toughness and a decrease in rolling fatigue life. In addition, since austenite expands when transformed into martensite, an excessive amount of retained austenite also leads to an inhibition of the shape and dimensional stability of the components made of the alloy steel.
Therefore, the Mn content in the alloy steel is restricted to a range of 0.2 to 1.2% by mass.
Even if the Mn content is within this range, the older the austenite grain size tends to become larger as the Mn content increases. Therefore, preferably, as in the invention described in claim 4, after carburizing treatment or carbonitriding treatment, after holding for a predetermined time at a temperature of 620 to 700 ° C., in the furnace (by furnace cooling) or outside the furnace The crystal grains are uniformly refined by cooling to room temperature in the air (by air cooling outside the furnace).

[Cr: 2.2 to 4.5% by mass]
Cr is an element that combines with C to form carbides, and there are more carbides that function as hydrogen trap sites to suppress structural changes associated with hydrogen intrusion into the alloy steel that constitutes the constituent members. It is important to make it. The function of generating such carbides becomes more prominent as the content of Cr (and Mo described below), which is a carbide generating element, increases. Cr also has a function of stabilizing carbide and martensite of the base structure. For this reason, the structure change by hydrogen is delayed more and there exists an effect which extends the lifetime of the said structural member. Furthermore, Cr also functions as a solid solution in the base structure of the alloy steel to improve the hardenability and increase the surface hardness required for the constituent members.
When the content of Cr is less than 2.2% by mass, not only the effect of delaying the structural change cannot be obtained sufficiently, but the generated carbide is refined (the maximum particle size is 10 μm or less). The effect of suppressing it to a sufficient level cannot be obtained.
On the other hand, when the Cr content exceeds 4.5% by mass, the carburizing property and the carbonitriding property are liable to be lowered, and it is difficult to sufficiently secure the surface hardness of the constituent member. Moreover, since Cr is an expensive element, if it is added excessively, the procurement cost of the alloy steel is increased. In addition, when added excessively, a predetermined hardness cannot be obtained unless the quenching temperature is increased, so that the productivity of the constituent members is lowered.
Therefore, the Cr content in the alloy steel is restricted to a range of 2.2 to 4.5 mass%.

[Mo: 0.1 to 1.0% by mass]
Mo, like Cr described above, is an element that forms a carbide by combining with C, and is important for making more carbide functioning as the hydrogen trap site. Mo also stabilizes carbides and the base structure martensite and austenite. For this reason, by adding Mo, the structural change by hydrogen is delayed and the lifetime of the said structural member can be extended. Furthermore, since Mo dissolves in the base structure of the alloy steel and improves the hardenability and temper softening resistance, the surface hardness after quenching can be increased.
When the Mo content is less than 0.1% by mass, not only the effect of delaying the structural change cannot be obtained sufficiently, but also the effect of refining the generated carbide can be sufficiently obtained. I can't.
On the other hand, when the Mo content exceeds 1.0% by mass, the machinability of the alloy steel decreases, and the productivity of the constituent members decreases. And since Mo is an expensive element, when it adds excessively, the procurement cost of alloy steel will raise easily.
Therefore, the Mo content in the alloy steel is restricted to a range of 0.1 to 1.0% by mass.

Next, the reason why the heat treatment conditions of the alloy steel having the above composition are regulated will be described.
[Carburizing treatment or carbonitriding treatment: 900 to 1000 ° C. for 12 to 20 hours]
Carburizing treatment or carbonitriding treatment is performed in order to increase the surface hardness of the constituent member and ensure the rolling fatigue life of the constituent member.
When the processing temperature is less than 900 ° C., a sufficient diffusion rate of C and N cannot be ensured, and the processing time becomes longer and the productivity of the constituent members is lowered.
On the other hand, when the processing temperature exceeds 1000 ° C., the prior austenite grains become coarse, which causes a decrease in toughness and a decrease in rolling fatigue life.
Therefore, the processing temperature of the carburizing process or the carbonitriding process is restricted to a range of 900 to 1000 ° C.
With respect to the time for holding at this processing temperature, an optimum carburizing or carbonitriding depth is selected according to the shape and size of the component (particularly, the relationship between the surface area and thickness). As described above, the present invention is effective when applied to a relatively large rolling bearing in which the diameter of the rolling element is 30 mm or more. If it is performed within a time range, a desired carburized layer or carbonitrided layer can be obtained.
When the treatment time is less than 12 hours, the thickness of the obtained carburized layer or carbonitrided layer becomes insufficient, and the rolling fatigue life of the component cannot be sufficiently secured.
On the other hand, when the treatment time exceeds 20 hours, the core region (thickness, width, or diameter) becomes smaller than the thickness of the carburized layer or carbonitrided layer (carburized layer or carbonitrided layer). Toughness is difficult to secure.
Therefore, the processing time is restricted to a range of 12 to 20 hours.
However, when processing components for small rolling bearings, the processing time can be less than 12 hours. On the other hand, when processing a component for an ultra-large rolling bearing, the processing time can be extended beyond 20 hours.
When performing the carburizing process or the carbonitriding process, the type and concentration of the gas fed into the furnace are adjusted in order to obtain an optimal amount of C or C + N. Specifically, the C concentration in the carburized layer or carbonitriding layer is controlled by controlling the flow rate of hydrocarbon gas such as propane or butane, and the N concentration in the carbonitriding layer is controlled by controlling the flow rate of ammonia gas. , Adjust each. Since this is a technique well-known in the technical field of carburizing or carbonitriding, detailed description is omitted.

[Diffusion treatment: Hold for 1 to 3 hours at a temperature 10 ° C. or higher than the temperature during carburizing or carbonitriding]
Diffusion treatment is an important requirement that characterizes the present invention, and by carrying out this diffusion treatment, carbides excessively precipitated near the surface of the component member during carburizing treatment or carbonitriding treatment are contained in the austenite of the base structure. Solid solution. The solid solution C is evenly distributed in the base organization. Even in each heat treatment performed after the diffusion treatment, uniform and fine carbides can be obtained.
Such a diffusion treatment is performed for 1 to 3 hours after the carburizing treatment or carbonitriding treatment at a temperature higher by 10 ° C. or more than the temperature during the carburizing treatment or carbonitriding treatment.
When the amount of temperature increase from the carburizing process or carbonitriding process to the diffusion process is less than 10 ° C., a sufficient carbide penetration effect cannot be obtained, and it becomes difficult to sufficiently refine the carbide in the surface layer portion. On the other hand, when the diffusion treatment temperature exceeds 1010 ° C., coarsening of prior austenite grains easily occurs. Therefore, this diffusion treatment temperature is preferably suppressed to 1010 ° C. or lower.
In such a diffusion process, regarding the holding time at a temperature of 10 ° C. or more higher than the temperature of the carburizing process or carbonitriding process, the shape and size of the component (particularly, the relationship between the surface area and the thickness). Regulate accordingly. As described above, the present invention is effective when applied to a relatively large rolling bearing with a rolling element having a diameter of 30 mm or more. Therefore, if the holding time is 1 to 3 hours, it is uniform and fine. Can be obtained.
However, when processing components for small rolling bearings, the holding time can be less than 1 hour. On the other hand, when processing the structural member for a very large rolling bearing, the processing time can be extended beyond 3 hours.

The diffusion treatment as described above can be carried out as it is after the carburizing treatment or carbonitriding treatment as described in FIG. 1 as described above, and again as described in the f range in FIG. After the carburizing treatment or carbonitriding treatment and before the diffusion treatment, the alloy steel is held at 620 to 700 ° C., which is a temperature not higher than the A1 transformation point, for a predetermined time (preferably 4 to 12 hours), and then in the furnace ( A step of cooling (gradual cooling) to room temperature can be set by furnace cooling) or in air outside the furnace (by air cooling outside the furnace). That is, when the temperature of the carburizing process or carbonitriding process is high and cooling from a high temperature, or when the Mn content is large as described above, the prior austenite grain size is likely to become coarse, and the metal structure is uneven. May occur.
By setting the diffusion treatment step as described above, the transformation treatment from austenite to cementite, pearlite, and ferrite can be completely completed, so that the prior austenite grain size can be uniformly refined. Although the optimal processing temperature of the said diffusion process changes with alloy components, when it is less than 620 degreeC or exceeds 700 degreeC, processing time becomes long and productivity is inhibited.

In any case, after the diffusion treatment, hold at 800 to 880 ° C. for a predetermined time (for example, 1 to 3 hours), and then rapidly cool to room temperature (for example, apply oil cooling immersed in quenching oil). Of these steps, the step of maintaining the temperature at 800 to 880 ° C. suppresses the precipitation of C from the base structure during the subsequent cooling, and the precipitated C is also made uniform and fine carbide, and the former austenite This is performed in order to suppress the coarsening of the particle size and to further prevent cracking during rapid cooling (oil cooling). When the holding temperature after the diffusion treatment is lower than 800 ° C., carbide growth due to C precipitated from the base structure occurs, and the effect of the diffusion treatment cannot be sufficiently obtained. In short, it becomes difficult to sufficiently refine the carbide in the surface layer portion due to C precipitated from the base structure. On the other hand, if the temperature rise exceeds 880 ° C., the effect of suppressing the coarsening of the prior austenite grain size cannot be obtained sufficiently, and the grain boundary fracture of the prior austenite can ensure fatigue strength and toughness. It becomes difficult.
As described above, even when the holding time is maintained at 800 to 880 ° C. after the diffusion treatment, it is appropriately regulated according to the shape and size (particularly, the relationship between the surface area and the thickness) of the structural member, When applied to such a relatively large rolling bearing, the holding time is 1 to 3 hours.
However, when processing components for small rolling bearings, the holding time can be less than 1 hour, and when processing components for ultra-large rolling bearings, the processing time can be reduced. Can be made longer than 3 hours.

[Quenching treatment: Hold at 800 to 880 ° C. for 1 to 2 hours and then rapidly cool to room temperature]
This quenching treatment is performed in order to increase the surface hardness of the constituent member. After holding the constituent member at a temperature of 800 to 880 ° C. for 1 to 2 hours, it is immersed in quenching oil (oil cooling). It is done by doing. When the quenching temperature is less than 800 ° C., the surface hardness after quenching is insufficient, and it becomes difficult to ensure a sufficient rolling fatigue life. On the other hand, if the quenching temperature exceeds 880 ° C., the amount of retained austenite in the constituent member becomes excessive, or coarsening of prior austenite grains occurs, and fatigue required for the constituent member It becomes difficult to ensure strength and toughness. Therefore, the quenching temperature is restricted to a range of 800 to 880 ° C.
In addition, regarding processing time, it regulates appropriately according to the shape and magnitude | size of the said structural member.

[Tempering treatment: held for 1 to 3 hours in a state heated to 160 to 200 ° C.]
This tempering process is performed in order to ensure the toughness required for the structural member. After maintaining the structural member at a temperature of 160 to 200 ° C. for 1 to 3 hours, air cooling or furnace cooling is performed. Do. When the tempering temperature is less than 160 ° C., it becomes difficult to ensure the required toughness, and the structure of the alloy steel becomes sensitive to hydrogen, and the structure changes easily due to hydrogen. On the other hand, when it exceeds 200 ° C., the amount of retained austenite decreases, and the effect of delaying the structural change due to hydrogen cannot be sufficiently obtained. Therefore, the tempering temperature is regulated to a range of 160 to 200 ° C.
In addition, regarding processing time, it regulates appropriately according to the shape and magnitude | size of the said structural member.

[The amount of C (C concentration) at a depth of 50 μm from the surface and the size of carbide on the surface layer: 1.5 to 2.0 mass%, 10 μm or less]
This condition is important for trapping the hydrogen atoms that have entered the component member during the operation of the rolling bearing and suppressing the occurrence of structure change type separation on the component member.
That is, the hydrogen that causes the structure change type peeling is generated by the decomposition of the lubricant (lubricating oil), penetrates into the alloy steel from the surface (the raceway surface or the rolling surface) of the constituent member, and diffuses. Then, the hydrogen diffused in the alloy steel locally accumulates at the position where the shear stress is the highest, and accelerates the structural change to lead to peeling.
On the other hand, since nitrides and carbides trap hydrogen atoms, the formation of nitrides and carbides at a depth of 50 μm from the surface, that is, the formation of nitrides and carbides in the vicinity of the surface allows the hydrogen that penetrates from the surface to enter the inside (depth 50 μm It has the effect of suppressing the diffusion to the position where the shear stress is highest (trapping hydrogen on the surface portion).
In the case of the present invention, in order to sufficiently obtain the trap effect of the carbides among these, the amount of C and the size of the carbides are defined. That is, the trap effect increases as the amount of C after the carburizing or carbonitriding process described above increases, and a large amount of fine carbides are precipitated (the total surface area of all the carbides is wide). Can be sufficiently suppressed.
Therefore, in the case of the present invention, the C content at a depth of 50 μm from the surface is set to 1.5% or more.
However, when the amount of C after carburizing or carbonitriding is as high as 1.5% or more, in the conventional heat treatment method, C that cannot be completely dissolved in the base structure precipitates and grows as a carbide. The particle size becomes large. As described above, when a large amount of carbide is generated along the prior austenite grain boundary and becomes a state called net-like carbide, cracks are easily generated and propagated along the carbide, and the toughness is increased. It will drop significantly.
In particular, the alloy steel that forms the component of the rolling bearing in the present invention has a Cr content of 2.2 to 4.5 mass%, a Mo content of 0.1 to 1.0 mass%, and a carbide generating element. Since it is contained in a large amount, carbide tends to be large.
On the other hand, in the case of the present invention, by performing the diffusion treatment, an alloy steel containing a large amount of the carbide generating element is used, and the amount of C after carburizing or carbonitriding is 1.5% or more. Even in this case, there is no large carbide, and fine carbide can be generated uniformly. That is, when the diffusion treatment is not performed, as shown in FIG. 3B, a carbide having a large particle size (net-like carbide) is generated in the alloy steel, whereas the diffusion treatment is performed. By applying, a large number of fine and uniform carbides can be generated as shown in FIG. As described above, such a fine and uniform carbide exhibits an excellent hydrogen trap effect. And the structure change type peeling by hydrogen can be suppressed and the durability of the said structural member can be improved.
Such an effect becomes more excellent as the particle size of each carbide is smaller when the total amount of carbide is the same. Specifically, when the maximum value of the particle size of each carbide is 10 μm or less, a remarkable effect can be obtained as compared with the conventional case. In other words, the effects described above cannot be obtained if large carbides having a maximum particle size exceeding 10 μm are produced in large quantities. As is clear from the above description, the smaller the particle size of the carbide, the better. Therefore, the minimum value of the particle size is not particularly restricted.

[Amount of retained austenite at a depth of 50 μm from the surface: 30 to 60% by volume]
Residual austenite in this portion is present in a large amount in order to delay the local accumulation of hydrogen in the stress concentration portion, suppress the structure change type peeling due to hydrogen, and improve the durability of the constituent members.
That is, the retained austenite in the metal structure has a crystal structure different from that of martensite, which is the base structure of the alloy steel, and has an effect of reducing the hydrogen diffusion constant due to the crystal structure. Therefore, if the amount of retained austenite from the surface to a depth of 50 μm is increased, the diffusion rate of hydrogen entering from the surface can be reduced. Durability can be improved.
Such an effect cannot be sufficiently obtained when the amount of retained austenite at the position is less than 30% by volume. On the other hand, when the amount of retained austenite at the position exceeds 60% by volume, the stability of the shape and dimensions of the constituent members is hindered. That is, as described above, since austenite expands when transformed into martensite, if the amount of retained austenite is excessive, it is difficult to ensure the stability of the shape and dimensions of the constituent members.
Therefore, the amount of retained austenite at the position is regulated to a range of 30 to 60% by volume.
The amount of retained austenite at this position can be appropriately regulated by regulating the components of the alloy steel and controlling the amount of C or C + N and the conditions for quenching and tempering. Generally, the greater the amount of carbon dissolved in the base structure, the greater the amount of retained austenite. Therefore, the greater the amount of C or C + N, the higher the quenching temperature and the lower the tempering temperature, The austenite amount tends to increase.

The diagram which shows the implementation condition of the heat processing of the manufacturing method corresponding to Claim 3 among this invention. The diagram which similarly shows the implementation condition of the heat processing of the manufacturing method corresponding to Claim 4. The microscope picture for comparing the magnitude | size of the carbide | carbonized_material which exists in the surface layer part of the alloy steel which comprises the structural member of a rolling bearing about the case (A) of this invention, and the conventional case (B). The partial cut perspective view of the radial ball bearing used as the object of the present invention. The partial cut perspective view of a radial tapered roller bearing.

  The feature of the present invention is that by devising the composition of the members constituting the rolling bearing, the C concentration at a predetermined position, the particle size of carbide, the prior austenite particle size, the amount of retained austenite, and the heat treatment method for obtaining these characteristics, It is in the point which aims at the durable improvement of the said structural member by suppressing the structure change type | mold peeling by hydrogen. The structure of the rolling bearing itself is the same as that of various types of conventionally known rolling bearings such as the radial ball bearing 1 shown in FIG. 4 and the radial tapered roller bearing 8 shown in FIG. Is omitted.

An experiment conducted for confirming the effect of the present invention will be described.
In the experiment, 13 types of alloy steels with different compositions described in Table 1 below were prepared.
In Table 1, numerical values shown in parentheses are values that are out of the technical scope of the present invention.
In the experiment, the alloy steels listed in Table 1 were subjected to predetermined forming and heat treatments, respectively, to form a Charpy test piece and an inner ring for a single row deep groove type radial ball bearing having an identification number of 6317 (inner diameter: 85 mm, Width: 41 mm). And the evaluation test of toughness was performed using the Charpy test piece, and the evaluation test of the rolling life was performed using the inner ring. Hereinafter, each processing condition, test condition, and test result will be described.

[Toughness evaluation test]
This toughness evaluation test was carried out by the “Charpy impact test method for metal materials” defined in JIS Z 2242: 2005. In order to obtain a Charpy test piece to be used for this purpose, the material made of “steel type A” or “steel type L” in Table 1 is cut into an intermediate material of a predetermined shape, and then this intermediate material And 7 kinds of test pieces belonging to the technical scope of the present invention (Examples 1 to 7) and seven kinds of test specimens outside the technical scope of the present invention (Examples 1 to 7) Comparative Examples 1 to 7) were prepared.

Regarding the numerical values in Table 2, the numerical values shown in parentheses are values that are out of the technical scope of the present invention.

In addition, the carburizing process or carbonitriding process described in Table 2 was performed by maintaining the temperature described in Table 2 for 14 hours. In either case, the gas concentration in the carburizing the flow rate of propane and ^{0.025m 3 / h, 0.025m 3 /} h flow rate of propane in the carbonitriding process, the flow rate of ammonia 0.1 m ³ / h did.
Moreover, after the carburizing treatment or the carbonitriding treatment, except for Comparative Example 1, a diffusion treatment was performed for 2 hours at the temperatures described in Table 2 above. However, in Examples 2 and 7, the diffusion treatment was performed after holding for 10 hours at the temperatures shown in Table 2 and then cooling to room temperature. After the diffusion treatment, except for Comparative Examples 2 and 3, oil cooling was performed after holding at the temperature described in Table 2 for 2 hours. Comparative Example 2 was oil cooled immediately after the diffusion treatment, and Comparative Example 3 was furnace cooled as it was without maintaining the temperature after the diffusion treatment.
Further, as a quenching treatment, each test piece was held at the temperature described in Table 2 for 1.5 hours, and then oil-cooled to room temperature. Further, as the tempering treatment, each was held at the temperature described in Table 2 for 2 hours, and then cooled to room temperature.
After these series of heat treatments, grinding and finishing were respectively performed to obtain 15 types of Charpy test pieces having a notch shape of 10RC notch and a size of 10 mm × 10 mm × 55 mm.

Of the 14 types of test pieces described in Table 2, the seven types of test pieces described as Examples 1 to 7 are also used as alloy steels having compositions belonging to the technical scope of the present invention. The heat treatment belonging to the range is performed, and the C amount, the carbide size, the retained austenite amount, and the prior austenite particle size at a depth of 50 μm from the surface are all within the technical scope of the present invention. And it was confirmed that the test pieces of Examples 1 to 7 each had a Charpy impact value as high as 40 J / cm ² or more and excellent toughness.
On the other hand, in all of Comparative Examples 1 to 7, any requirement shown in parentheses is out of the technical scope of the present invention, and the Charpy impact value is 30 J / cm ² at the maximum, It was low compared with the Examples, and the toughness was inferior.
The reason is considered as follows. First, since Comparative Example 1 is not subjected to diffusion treatment, Comparative Example 3 is furnace-cooled after diffusion treatment, Comparative Example 4 is low in the amount of increase in diffusion treatment temperature, and Comparative Example 5 is holding temperature after diffusion treatment. Therefore, it is considered that the maximum particle size of the carbide is large and the toughness is lowered. In addition, Comparative Example 2 was oil cooled after diffusion treatment, and Comparative Example 6 was high in carburizing temperature, holding temperature after diffusion treatment, and quenching temperature, so that the prior austenite grain size was increased and toughness was reduced. Conceivable. Further, in Comparative Example 7, the C content was outside the technical range of the present invention (excess) during the composition of the alloy steel, so it is considered that the hardness of the core portion was excessive and the toughness was lowered.

[Rolling fatigue life evaluation test]
In this test, only the inner ring of the single row deep groove type radial ball bearing (inner diameter: 85 mm, outer diameter: 180 mm, width: 41 mm, ball diameter: 30.2 mm) having the identification number 6317 is shown in Table 1 above. Of the 13 types of alloy steel, 12 types of alloy steel except L were used, and the outer ring and ball were made of SUJ2 as defined in JIS G 4805. This is because the inner ring raceway provided on the outer peripheral surface of the inner ring is the most severe under the evaluation test conditions performed in this example, and is easily peeled off. In Comparative Example 9, the inner ring was also made of SUJ2 (alloy steel M) for comparison.

In order to produce a total of 25 types of test pieces (inner rings) described in Table 3 as Examples 8 to 19 and Comparative Examples 8 to 20, the steel material (extruded steel bar) was obtained by cutting it into a predetermined size. The raw material was subjected to hot rolling, spheroidizing annealing, and turning to form the shape of the inner ring as a test piece, and then heat-treated under the conditions shown in Table 3 above. Specifically, the carburizing process or the carbonitriding process was performed by holding at the temperature described in Table 3 for 14 hours. In either case, the gas concentration in the carburizing the flow rate of propane and ^{0.025m 3 / h, 0.025m 3 /} h flow rate of propane in the carbonitriding process, the flow rate of ammonia 0.1 m ³ / h did.
Moreover, after the carburizing process or the carbonitriding process, except for the comparative example 14, the diffusion process hold | maintained at the temperature described in Table 3 for 2 hours, respectively was performed. However, Examples 9, 14, 17 and Comparative Examples 12 and 20 were each subjected to diffusion treatment after being held at the temperatures shown in Table 3 for 10 hours and cooled to room temperature. After the diffusion treatment, the samples were kept at the temperatures shown in Table 3 for 2 hours except for Comparative Examples 15 and 16, and then cooled with oil. Comparative Example 15 was oil-cooled after diffusion treatment, and Comparative Example 16 was furnace-cooled after diffusion treatment.

Further, as a quenching treatment, each test piece was kept at the temperature described in Table 3 for 1.5 hours, and then oil-cooled to room temperature. Further, as the tempering treatment, each was held at the temperature described in Table 3 for 2 hours, and then cooled to room temperature.
After these series of heat treatments, the inner ring, which is a test piece, obtained by grinding and finishing, respectively, was combined with the outer ring, balls, and a cage to form a radial ball bearing with a nominal number of 6317. The inner ring has a thickness of 14.75 mm, and the distance between the innermost surface of the inner ring and the innermost surface of the inner ring (the radial thickness of the thinnest part of the inner ring central portion) is 8.67 mm. .

The conditions of the rolling fatigue life evaluation test performed using the sample as described above are as follows.
Radial load: 53.2kN
Rotation conditions: inner ring rotation speed: 2000min ^-1
Lubrication conditions: Forced circulation of high traction oil (synthetic oil for transmission) In addition, three inner rings, each of which is a test piece, are made in a total of 75, and a rolling fatigue life test is performed on each of the above conditions under the conditions described above. The average life was obtained, and this average life was described in the column of life ratio in the above table as the rolling fatigue life of Examples 8 to 19 and Comparative Examples 8 to 20, respectively. In addition, this life ratio is the rolling of each example and comparative example when the rolling fatigue life of the radial ball bearing incorporating the inner ring of steel type M (manufactured by SUJ2) is 1.0. It is the ratio of fatigue life. Further, in the rolling fatigue life test, in the radial ball bearing in which peeling occurred, all peeling occurred in the inner ring raceway portion on the outer peripheral surface of the inner ring, and a white structure was observed in the peeling portion.

  Regarding the rolling fatigue life evaluation test whose results are shown in Table 3 above, Examples 8 to 19 all have inner rings made of alloy steel within the technical scope of the present invention. Is within the scope. Furthermore, the C amount at a depth of 50 μm from the surface, the carbide size, the retained austenite amount, and the prior austenite grain size were all within the technical scope of the present invention. For this reason, any of the radial ball bearings had a lifespan more than five times that of the standard radial ball bearing of Comparative Example 8, and no peeling occurred. In addition, the test regarding the said Examples 8-19 was interrupted on the way.

On the other hand, Comparative Examples 8 to 20 all have a shorter rolling fatigue life than Examples 8 to 19, and observation of the metal structure of the inner ring cross section performed after the test reveals a change in structure due to hydrogen. It was done. The reasons are considered as follows.
First, in all of Comparative Examples 8 to 13, the components of the alloy steel constituting the inner ring are outside the technical scope of the present invention. Comparative Example 8 is a standard SUJ2 radial ball bearing, and the amount of C, Cr, Mo, amount of C at a depth of 50 μm from the surface, and the amount of retained austenite are all the techniques of the present invention. It was out of the target range. Moreover, because it is a baked steel, the core has excessive hardness and low toughness.

Further, Comparative Example 9 has a C amount and a Cr amount, and Comparative Example 10 has a Mo amount less than that of the alloy steel used in the present invention, so that the amount of carbide is insufficient and a sufficient hydrogen trapping effect is obtained. Life is short.
In Comparative Example 11, the amount of Si is larger than that of the alloy steel used in the present invention, and the carburizing property is lowered. Therefore, the C amount at a depth of 50 μm from the surface is low, and the life is short.
In Comparative Example 12, since the amount of Mn and the amount of Mo are larger than those of the alloy steel used in the present invention, the prior austenite grain size is large and the life is short. Also, since the amount of retained austenite at a depth of 50 μm from the surface is large, the dimensional stability is also poor.
In Comparative Example 13, the amount of Si and the amount of Mn are less than that of the alloy steel used in the present invention, respectively, so the amount of retained austenite at a depth of 50 μm from the surface is small and the life is short.

Furthermore, as for Comparative Examples 14-20, as for the heat processing conditions, all are outside the technical scope of this invention.
Since Comparative Example 14 was not subjected to diffusion treatment, Comparative Example 16 was furnace-cooled after diffusion treatment, and Comparative Example 17 had a small increase in diffusion treatment temperature, Comparative Example 18 was retained after diffusion treatment. Since the temperature is low, the size of the carbide is large and the hydrogen trapping effect cannot be obtained sufficiently, both of which have a short life.
Since Comparative Example 15 was oil-cooled after diffusion treatment, and Comparative Example 19 was high in carburizing temperature, holding temperature after diffusion treatment, and quenching temperature, the prior austenite grain size was large and the life was short.
In Comparative Example 20, since the tempering temperature is high, the amount of retained austenite at a depth of 50 μm from the surface is small and the life is short.

The rolling bearing of the present invention can improve the rolling fatigue life due to excellent fracture toughness while suppressing the structural change caused by hydrogen even under the condition where hydrogen easily enters. For this reason, the rolling bearing of the present invention uses a relatively large size rolling bearing in which a lubricating oil is used as a lubricant and high toughness is required, and the rolling element diameter is 30 mm or more. It is most suitable as a rolling bearing used to support a main shaft of the motor, a rotating shaft constituting a transmission, a construction machine, an industrial robot, or the like.
However, the present invention is not limited to these applications, and can be widely applied to rolling bearings for various applications, and is not limited to single-row deep groove type radial ball bearings, but includes radial types and axial types. In addition, it can be widely applied to tapered roller bearings, cylindrical roller bearings, and self-aligning roller bearings.

DESCRIPTION OF SYMBOLS 1 Radial ball bearing 2, 2a Outer ring raceway 3, 3a Outer ring 4, 4a Inner ring raceway 5, 5a Inner ring 6 Ball 7, 7a Cage 8 Radial tapered roller bearing 9 Tapered roller 10 Large diameter side collar 11 Small diameter side collar

Claims (3)

A first raceway having a first raceway surface on any surface, a second raceway having a second raceway surface on a surface opposite to the first raceway surface, and the first and second A rolling bearing comprising a plurality of rolling elements provided so as to be freely rollable between both raceway surfaces,
At least one member of the first raceway ring, the second raceway ring, and each of these rolling elements, C is 0.10 to 0.30 mass%, Si is 0.2 to 0.5. Mass%, Mn 0.2-1.2 mass%, Cr 2.2-4.5 mass%, Mo 0.1-1.0 mass%, respectively, the remainder being Fe and inevitable impurities After processing the iron-based alloy material made into an intermediate material,
The intermediate material is subjected to a carburizing treatment or carbonitriding treatment at 900 to 1000 ° C., and then subjected to a diffusion treatment that is held for a predetermined time at a temperature 10 ° C. higher than the temperature at the time of the carburizing treatment or carbonitriding treatment, By holding at 800 to 880 ° C. for a predetermined time and quenching, then quenching at 800 to 880 ° C., then tempering at 160 to 200 ° C. and then cooling in the furnace or outside the furnace ,
A carburized layer or a carbonitrided layer is provided on the surface of the at least one member, and at a position of 50 μm from the surface of the member, the C concentration is 1.5% by mass or more, and the maximum particle size of the carbide is 10 μm or less, A method for manufacturing a rolling bearing in which the prior austenite grain size is 20 μm or less. Before the diffusion treatment after the carburizing or carbonitriding treatment, comprising the step of cooling at a predetermined time holding furnace from or outside the furnace in air at six hundred twenty to seven hundred ° C., according to claim 1 rolling bearing Manufacturing method. Wherein in at least one of the members, the amount of retained austenite from the surface 50μm position, 30 to 60 volume%, the manufacturing method of the rolling bearing according to any one of claims 1-2.