WO2021100746A1 - Raceway member, rolling bearing, bearing ring for rolling bearing, and method for manufacturing bearing ring for rolling bearing - Google Patents

Abstract

An inner ring (12) is made from a steel and has an inner ring raceway surface (12A) that extends along a circumferential direction and an inner circumferential surface (12C) that serves as an inner circumferential surface extending along the circumferential direction and also extending along an axis direction. The amount of retained austenite in the inner ring raceway surface (12A) is larger than that in the inner circumferential surface (12C). The difference between the amount of retained austenite in the inner ring raceway surface (12A) and that in the inner circumferential surface (12C) is 3% by volume or more.

Description

Method for manufacturing raceway members, rolling bearings, raceway rings for rolling bearings, and raceway rings for rolling bearings

The present invention relates to a method for manufacturing a raceway member, a rolling bearing, a raceway ring of a rolling bearing, and a raceway ring of a rolling bearing.

The conventional track member is manufactured by performing a heat treatment including quenching treatment and tempering treatment. Generally, the tempering treatment is carried out by accommodating the entire molded product, which is the object to be treated, in the atmosphere furnace.

The dimensional change rate of the track member used in a high temperature environment is preferably kept low from the viewpoint of bearing life. For example, if the dimensional change rate of the inner diameter surface of the inner ring is suppressed to a low level, it is possible to suppress loosening of the fit between the inner diameter surface of the inner ring and the shaft to cause creep, and it is possible to suppress damage to the bearing.

Conventionally, as a measure to keep the dimensional change rate of the track member low, a tempering process for reducing the average residual austenite amount of the entire track member has been known.

Japanese Unexamined Patent Publication No. 2017-227334 discloses a technique for tempering a steel material at a temperature of 180 ° C. or higher and 230 ° C. or lower in order to reduce the average residual austenite amount of the entire track member to 18% by volume or less.

JP-A-2017-227334

However, in the conventional tempering treatment method, since the entire molded product is tempered, retained austenite is decomposed in the entire molded product. Further, in the conventional tempering treatment method, martensite is decomposed at the same time as retained austenite is decomposed in the entire molded product.

Therefore, in the conventional track member manufactured by performing the above-mentioned tempering treatment, for example, the track member manufactured without performing the tempering treatment under the above-mentioned conditions because it is not planned to be used in a high temperature environment. The amount of martensite in the raceway surface and the circumferential surface (hereinafter referred to as the anti-tracking surface) located on the opposite side of the raceway surface, that is, the inner diameter surface of the inner ring or the outer diameter surface of the outer ring is suppressed to be low. , The hardness of the track surface and the anti-track surface is low. Further, in the former track member, the amount of retained austenite is smaller than that of the latter track member, but since it is necessary to reduce the amount of decrease in hardness of the raceway surface, the amount of decomposition of retained austenite is small. Therefore, the effect of suppressing the dimensional change rate is not sufficient, and the hardness of the raceway surface and the anti-trackway surface is reduced.

A main object of the present invention is to provide a raceway member and a rolling bearing in which the dimensional change rate of the anti-track surface is suppressed to a low level and the decrease in hardness of the raceway surface and the anti-track surface is suppressed.

The track member according to the present invention has a track surface extending along the circumferential direction and an anti-track surface facing the opposite side to the track surface. The amount of retained austenite on the orbital plane is larger than the amount of retained austenite on the anti-orbital plane. The difference between the amount of retained austenite on the orbital plane and the amount of retained austenite on the anti-orbital plane is 3% by volume or more.

In the track member, the average residual austenite amount as a whole is 20% by volume or less.
In the track member, the average residual austenite amount as a whole is 10% by volume or less.

In the track member, the amount of retained austenite on the anti-track surface is 5% by volume or less.
In the track member, the hardness of the anti-track surface is 600 Hv or more.

The rolling bearing according to the present invention includes an inner ring having an inner ring raceway surface and an inner diameter surface located on the side opposite to the inner ring raceway surface, an outer ring having an outer ring raceway surface facing the inner ring raceway surface, and an inner ring raceway surface and an outer ring. It includes a plurality of rolling elements that come into contact with the raceway surface. The inner ring is the track member. The inner ring raceway surface is the raceway surface of the raceway member. The inner diameter surface is the anti-track surface of the track member.

According to the present invention, it is possible to provide a raceway member and a rolling bearing in which the dimensional change rate of the circumferential surface is suppressed to a low level and the decrease in hardness of the raceway surface and the anti-track surface is suppressed.

It is sectional drawing which shows an example of the rolling bearing which concerns on this embodiment. It is sectional drawing which shows another example of the rolling bearing which concerns on this embodiment. It is a flowchart of the manufacturing method of the rolling bearing which concerns on this embodiment. It is a top view which shows an example of the 1st tempering process in the manufacturing method of the rolling bearing which concerns on this embodiment. It is sectional drawing seen from the arrow VV in FIG. It is a graph which shows the relationship between the holding time (soaking time) at a tempering temperature required for reducing a predetermined amount from the initial residual austenite amount in the tempering treatment which concerns on this embodiment, and the initial residual austenite amount. It is a figure which shows the analysis model used for the simulation analysis about the temperature distribution of the member to be heated realized by the tempering process which concerns on this embodiment. It is a graph which shows the relationship between the heating temperature with respect to the 1st peripheral surface and the temperature of the 2nd peripheral surface at that time obtained by the simulation analysis using the analysis model shown in FIG. It is a graph which shows each temperature change of the 1st peripheral surface and the 2nd peripheral surface with respect to the heating time obtained by the simulation analysis using the analysis model shown in FIG. It is a figure which shows the temperature distribution of the member to be heated obtained by the simulation analysis using the analysis model shown in FIG. It is a top view of the inner ring 110. It is sectional drawing in XII-XII of FIG. It is sectional drawing of the inner ring 110 which concerns on a modification. It is a process drawing which shows the manufacturing method of the inner ring 110. It is a plane schematic diagram for demonstrating the tempering process S13. It is sectional drawing to explain the tempering process S13. It is a graph which shows the simulation result about the relationship between the heating time by a heating coil 130, and the temperature on the inner peripheral surface 120c and the outer peripheral surface 120d. It is a graph which shows the simulation result of the heating temperature of the outer peripheral surface 120d when the heating temperature of the inner peripheral surface 120c is changed.

Hereinafter, embodiments will be described with reference to the drawings. In the following drawings, the same or corresponding parts shall be given the same reference number, and the description thereof shall not be repeated.

<Structure of rolling bearing>
The rolling bearing according to the present embodiment is, for example, a radial ball bearing, and more specifically, a deep groove ball bearing 1 shown in FIG. The deep groove ball bearing 1 is a rolling element arranged between the annular outer ring 11, the annular inner ring 12 arranged inside the outer ring 11, and the outer ring 11 and the inner ring 12, and held by the annular cage 14. It is provided with a plurality of balls 13 which are. The central axis of the outer ring 11 is arranged so as to overlap the central axis of the inner ring 12.

The outer ring 11 has an inner peripheral surface 11B and an outer peripheral surface 11C as an outer diameter surface. An outer ring raceway surface 11A extending along the circumferential direction is formed on the inner peripheral surface 11B of the outer ring 11. The inner ring 12 has an outer peripheral surface 12B facing the outer peripheral side in the radial direction and an inner peripheral surface 12C as an inner diameter surface. An inner ring raceway surface 12A extending along the circumferential direction is formed on the outer peripheral surface 12B of the inner ring 12. The inner ring 12 is arranged inside the outer ring 11 so that the inner ring raceway surface 12A faces the outer ring raceway surface 11A.

The plurality of balls 13 are in contact with the outer ring raceway surface 11A and the inner ring raceway surface 12A on the rolling surface 13A, and are arranged at a predetermined pitch in the circumferential direction by the cage 14. As a result, the plurality of balls 13 are rotatably held on the annular orbits of the outer ring 11 and the inner ring 12. With such a configuration, the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1 can rotate relative to each other. The inner ring 12 is a track member according to the present embodiment.

The inner ring 12 has an inner ring raceway surface 12A extending along the circumferential direction and an inner peripheral surface 12C as a circumferential surface extending along the circumferential direction and extending along the axial direction. The amount of retained austenite on the inner ring raceway surface 12A is larger than the amount of retained austenite on the inner peripheral surface 12C. The amount of retained austenite in the inner ring 12 tends to gradually decrease from the inner ring raceway surface 12A to the inner peripheral surface 12C in the radial direction.

The difference between the amount of retained austenite on the inner ring raceway surface 12A and the amount of retained austenite on the inner peripheral surface 12C is 3% by volume or more. The difference between the amount of retained austenite on the inner ring raceway surface 12A and the amount of retained austenite on the inner peripheral surface 12C is, for example, 10% by volume or less, for example, less than 5% by volume. The above difference between the amount of retained austenite on the inner ring raceway surface 12A and the amount of retained austenite on the inner peripheral surface 12C exceeds the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the inner peripheral surface realized by the conventional tempering treatment. This is realized by the tempering process according to the present embodiment, which will be described later. The amount of retained austenite is calculated from the diffraction intensities of the martensite phase and the austenite phase measured by X-ray diffraction.

The amount of retained austenite on the inner peripheral surface 12C is, for example, 5% by volume or less, preferably less than 5% by volume. The amount of retained austenite on the inner ring raceway surface 12A is, for example, 10% by volume or more, preferably 15% by volume or more. The above difference between the amount of retained austenite on the inner ring raceway surface 12A and the amount of retained austenite on the inner peripheral surface 12C exceeds the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the inner peripheral surface realized by the conventional tempering treatment. This is realized by the tempering process in the method for manufacturing the inner ring 12 according to the present embodiment, which will be described later.

The average residual austenite amount of the entire inner ring 12, that is, the average value calculated from the distribution of the residual austenite amount in the radial direction from the inner ring raceway surface 12A to the inner peripheral surface 12C of the inner ring 12 is 20% by volume or less. The average residual austenite amount of the inner ring 12 as a whole is 20% by volume or less regardless of whether or not the carburizing and nitriding treatment is performed in the method for producing the inner ring 12. In the inner ring 12 which has not been subjected to the carburizing and nitrogen treatment in the production method, the average residual austenite amount of the entire inner ring 12 can be 10% by volume or less.

The hardness of the inner ring raceway surface 12A exceeds the hardness of the inner peripheral surface 12C. The hardness of the inner ring raceway surface 12A is, for example, 650 Hv or more, preferably 700 Hv or more. The hardness of the inner peripheral surface 12C is, for example, 600 Hv or more and 700 Hv or less. When the hardness of the inner peripheral surface 12C is 700 Hv, the hardness of the inner ring raceway surface 12A is, for example, 750 Hv or more. The hardness of each surface is measured according to the Vickers hardness test method specified in the JIS standard (JJS Z 2244: 2009).

The rolling bearing according to the present embodiment may be, for example, a radial roller bearing, and more specifically, a conical roller bearing 2 shown in FIG. The conical roller bearing 2 includes an annular outer ring 21 and an inner ring 22, a plurality of rollers 23 which are rolling elements, and an annular cage 24. An outer ring raceway surface 21A extending along the circumferential direction is formed on the inner peripheral surface of the outer ring 21, and an inner ring raceway surface 22A extending along the circumferential direction is formed on the outer peripheral surface of the inner ring 22. ing. The inner ring 22 is arranged inside the outer ring 21 so that the inner ring raceway surface 22A faces the outer ring raceway surface 21A.

The plurality of rollers 23 are in contact with the outer ring raceway surface 21A and the inner ring raceway surface 22A on the rolling surface 23A, and are arranged at a predetermined pitch in the circumferential direction by the cage 24. As a result, the roller 23 is rotatably held on the annular orbit of the outer ring 21 and the inner ring 22. Further, in the conical roller bearing 2, the apex of each of the cone including the outer ring raceway surface 21A, the cone including the inner ring raceway surface 22A, and the cone including the locus of the rotation axis when the roller 23 rolls is on the center line of the bearing. It is configured to intersect at one point. With such a configuration, the outer ring 21 and the inner ring 22 of the conical roller bearing 2 can rotate relative to each other. The inner ring 22 is a track member according to the present embodiment, like the inner ring 12. The inner ring 22 has the same configuration as the inner ring 12.

The inner ring 22 has an inner ring raceway surface 22A extending along the circumferential direction and an inner peripheral surface 22C as a circumferential surface extending along the circumferential direction and extending along the axial direction. The amount of retained austenite on the inner ring raceway surface 22A is larger than the amount of retained austenite on the inner peripheral surface 22C. The amount of retained austenite in the inner ring 22 tends to gradually decrease from the inner ring raceway surface 22A to the inner peripheral surface 22C in the radial direction.

The amount of retained austenite on the inner peripheral surface 22C is, for example, 5% by volume or less, preferably less than 5% by volume. The amount of retained austenite on the inner ring raceway surface 22A is, for example, 10% by volume or more, preferably 15% by volume or more. The above difference between the amount of retained austenite on the inner ring raceway surface 22A and the amount of retained austenite on the inner peripheral surface 22C exceeds the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the inner peripheral surface realized by the conventional tempering treatment. This is realized by the tempering process in the method for manufacturing the inner ring 22 according to the present embodiment described later.

The average residual austenite amount of the inner ring 22 as a whole, that is, the average value calculated from the distribution of the residual austenite amount in the radial direction from the inner ring raceway surface 22A to the inner peripheral surface 22C of the inner ring 22 is 20% by volume or less. The average residual austenite amount of the inner ring 22 as a whole is 20% by volume or less regardless of whether or not the carburizing and nitriding treatment is performed in the method for producing the inner ring 22. In the inner ring 22 which has not been subjected to the carburizing and nitrogen treatment in the production method, the average residual austenite amount of the entire inner ring 22 can be 10% by volume or less. The above difference between the amount of retained austenite on the inner ring raceway surface 22A and the amount of retained austenite on the inner peripheral surface 22C exceeds the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the inner peripheral surface realized by the conventional tempering treatment. This is realized by the tempering process according to the present embodiment, which will be described later.

The hardness of the inner ring raceway surface 22A exceeds the hardness of the inner peripheral surface 22C. The hardness of the inner ring raceway surface 22A is, for example, 650 Hv or more, preferably 700 Hv or more. The hardness of the inner peripheral surface 22C is, for example, 600 Hv or more and 700 Hv or less. When the hardness of the inner peripheral surface 22C is 700 Hv, the hardness of the inner ring raceway surface 22A is, for example, 750 Hv or more.

<Manufacturing method of rolling bearings>
The rolling bearing according to the present embodiment is manufactured by the method for manufacturing the rolling bearing according to the present embodiment shown in FIG. As shown in FIG. 3, the rolling bearing manufacturing method according to the present embodiment includes a step (S10) of preparing a molded body to be inner rings 12 and 22 (track members) and quenching of the molded body. A step of performing a hardening treatment (S20), a step of performing a tempering treatment on a molded product subjected to a quench hardening treatment (S30), and a finishing step of grinding a molded body subjected to the tempering treatment (S20). S40) and. Inner rings 12 and 22 are manufactured by the above steps (S10) to (S40). Further, the method for manufacturing a rolling bearing according to the present embodiment is a step of preparing outer rings 11 and 21 and balls 13 or rollers 23 and assembling inner rings 12, 22, outer rings 11 and 21 and balls 13 or rollers 23. (S50) is further provided.

In the process (S10), first, a steel material made of steel is prepared. The steel material is prepared as, for example, steel bar or steel wire. Next, the steel material is subjected to processing such as cutting, forging, and turning. As a result, a steel material (molded body) formed into the approximate shape of the inner rings 12 and 22 is produced. The molded body has a first peripheral surface 10C facing inward in the radial direction and a second peripheral surface facing outward in the radial direction. The inner peripheral surfaces 12C and 22C of the inner rings 12 and 22 are formed by grinding the first peripheral surface 10C in the subsequent step (S40). The inner ring raceway surfaces 12A and 22A of the inner rings 12 and 22 are formed by grinding the second peripheral surface in the post-process (S40).

In the step (S20), a quench hardening treatment is performed on the molded product prepared in the previous step (S10). In the step (S20), first, a carburizing and nitriding treatment for carburizing and nitriding the molded product is carried out. Next, a nitrogen diffusion treatment for diffusing the nitrogen that has infiltrated into the molded body by the carburizing and nitrification treatment is carried out. Next, the whole of the molded body is heated to a temperature T ₁ of the above _point A, retention time t ₁ (soaking time) for soaking only be retained. Next, the molded product is cooled to a _{temperature T 2} below the Ms point (martensite transformation point). This cooling treatment is carried out by immersing the target material in a coolant such as oil or water. As a result, the target material is quenched. The quenching treatment is carried out under conditions such that the hardness of the hardened target material exceeds the hardness of the tempered target material described later. The difference between the amount of retained austenite on the second peripheral surface and the amount of retained austenite on the first peripheral surface 10C of the molded product subjected to the quench hardening treatment is less than 3% by volume. The amount of retained austenite on each of the first peripheral surface and the second peripheral surface of the molded product subjected to the quench hardening treatment (hereinafter referred to as the initial retained austenite amount) is not particularly limited. For example, it is 5% by volume or more and 13% by volume or less.

In the step (S30), the tempering treatment is performed on the molded product that has been quench-hardened in the previous step (S20). In the tempering treatment, the first tempering treatment as a conventional dimensional stabilization treatment in which the entire molded product is heated, and the first peripheral surface 10C while the second peripheral surface of the molded product is locally cooled. A second tempering process is performed in which the heat is locally heated. Local cooling of the second peripheral surface is continuously performed in the second tempering process from the start of heating to the end of heating of the first peripheral surface 10C.

The surface temperature of the first peripheral surface 10C of the molded product is maintained _{until the holding time t 2} (tempering time) elapses at the tempering _{temperature T 3.} The holding time t ₂ is the time from when the first peripheral surface 10C tempering temperature T ₃ is reached in the second tempering treatment to the end of heating. Surface temperature of the second circumferential surface of the green body, after being held by the first temperature reached T ₄ lower than the tempering temperature T _3, first reaches a temperature T ₄ or more tempering temperature T ₃ below the second temperature reached It is held at _{T 5} until the _{holding time t 3 elapses.} The holding time t ₃ is the time from when the second peripheral surface reaches the second reaching temperature T ₅ in the second tempering process until the heating of the second peripheral surface is completed. The second reached temperature T ₅ is, for example, equal to the _{tempering temperature T 3.}

The tempering temperature T ₃ and the holding time t ₂ are values in which the amount of retained austenite on the inner peripheral surfaces 12C and 22C is predetermined from the viewpoint of achieving the dimensional stability and hardness required for the inner peripheral surfaces 12C and 22C. It is set so that the hardness of the inner peripheral surfaces 12C and 22C is equal to or greater than a predetermined value. On the other hand, the first ultimate temperature T ₄ , the second ultimate temperature T ₅ , and the holding time t ₃ of the second peripheral surface are required for the hardness required for the inner ring raceway surfaces 12A and 22A and for the entire inner rings 12 and 22. From the viewpoint of realizing the dimensional stability, the hardness of the inner ring raceway surfaces 12A and 22A should be equal to or higher than the predetermined value, and the residual austenite amount of the inner ring raceway surfaces 12A and 22A should be equal to or lower than the predetermined value. Is set to.

The first tempering treatment and the second tempering treatment are carried out by, for example, the heating method and the cooling method shown in FIGS. 4 and 5.

As shown in FIGS. 4 to 5, the heating of the first peripheral surface 10C is carried out by, for example, induction heating using the first coil 30, preferably high frequency induction heating. The first coil 30 is arranged in the molded body 10 so as to face only the first peripheral surface 10C.

An alternating current of 3 kHz or higher is supplied to the first coil 30. When a high-frequency alternating current is supplied to the first coil 30, the temperature rises on the second peripheral surface 10A side in the radial direction as compared with the induction heating in which a lower-frequency alternating current is supplied to the first coil 30. Is suppressed, so that the difference between _{the tempering temperature T 3} and the first reached temperature T _{4 becomes large.}

As shown in FIGS. 4 and 5, the cooling of the second peripheral surface 10A is carried out by supplying a cooling solvent such as water to the second peripheral surface 10A of the molded body 10 by using, for example, the injection unit 31. To. Preferably, the cooling is carried out so as not to cool the first peripheral surface 10C. The cooling is carried out so that the water supplied to the second peripheral surface 10A is not supplied to the first peripheral surface 10C. The injection unit 31 is arranged so as to face the second peripheral surface 10A of the molded body 10 in the second tempering process, and injects water onto the second peripheral surface 10A. In the first tempering process, the first coil 30 and the injection unit 31 are arranged so as to sandwich the molded body 10 in the radial direction of the molded body 10, for example. The cooling may be performed on a region of the second peripheral surface 10A that is ground to form the inner ring raceway surfaces 12A and 22A at least in the subsequent step (S40).

The first tempering process and the second tempering process are carried out, for example, by relatively rotating the molded body 10, the first coil 30, and the injection unit 31 in the circumferential direction. The relative positions of the first coil 30 and the injection unit 31 are fixed throughout, for example, the second tempering process.

The first tempering process is carried out by putting the entire molded product into a heat treatment furnace heated to a temperature of 180 ° C. or higher and 230 ° C. or lower.

In the second tempering process, the first coil 30 heats the first peripheral surface 10C and the injection unit 31 cools the second peripheral surface 10A.

The set values of the tempering temperature T ₃ , the holding time t ₂ , the first reaching temperature T ₄ , the second reaching temperature T _5, and the holding time t ₃ are based on, for example, the following formulas 1, 2, and 3. Is set. The coefficients of the above formulas 1, 2 and 3 vary depending on the composition of the steel of the molded product, the amount of the initial retained austenite and the like.

The above formula 1 is a prediction formula for predicting the relationship between _{the tempering temperature T 3} (unit: ° C.) and the above first reached temperature T _{4 (unit: ° C.).} In the first tempering treatment, the present inventors consider a molded product in which the heating is carried out by induction heating on the first peripheral surface 10C and the cooling is carried out by jetting water on the second peripheral surface 10A. The temperature distribution in the member to be heated was simulated and analyzed. The above formula 1 was obtained by the present inventors from the results of the above simulation analysis. As a result of the analysis, _{it was confirmed that the first reached temperature T 4} changes linearly with respect to the tempering temperature T ₃ (see FIG. 8). The details of the simulation analysis will be described later. When at least one of the heating method and the cooling method is carried out by a method different from the above, the above formula 1 is changed to the prediction formula in the different method.

The above formula 2 is based on the reached temperature T (unit: K), holding time t (unit: seconds) during tempering treatment, and residual austenite amount γ (remaining austenite amount γ) on the first peripheral surface 10C or the second peripheral surface 10A after tempering treatment. It is a prediction formula that predicts the relationship of unit: volume%). The residual austenite amount γ of the first peripheral surface 10C after the second tempering treatment is obtained by substituting the _{tempering temperature T 3 for the ultimate temperature T in Equation 2} and substituting the holding time t 2 for the holding time t. Calculated. The residual austenite amount γ of the second peripheral surface 10A after the second tempering treatment _{is obtained by substituting the second reaching temperature T 5} for the reaching temperature T in Equation 2 and substituting the holding time t ₃ for the holding time t. It is estimated that the value is less than the calculated value by the amount of decomposition in the first tempering process. The above formula 2 is based on Non-Patent Document 1 (Takeshi Inoue, "Application of new tempering parameters and their application to the method of integrating the tempering effect along the continuous temperature rise curve", Iron and Steel, 66, 10 (1980) 1533.). It was experimentally obtained by the present inventors based on the relational expression between the hardness and the tempering temperature described in 1.

The above formula 3 is based on the reached temperature T (unit: K), holding time t (unit: seconds) during the tempering process, and hardness M (unit: unit) of the first peripheral surface 10C or the second peripheral surface 10A after the tempering process. : HV) is a prediction formula that predicts the relationship. The hardness M of the first peripheral surface 10C after the tempering process is calculated by substituting the _{tempering temperature T 3} for the ultimate temperature T in Equation 3 and substituting the holding time t _{3 for the holding time t.} The hardness M of the second peripheral surface 10A after the tempering treatment is estimated to be about a value calculated by substituting _{the second ultimate temperature T 5 for the ultimate temperature T in Equation 3.} The above formula 3 was experimentally obtained by the present inventors based on the relational expression between the amount of retained austenite and the tempering temperature described in JP-A-10-102137.

The tempering temperature T ₃ and the holding time t ₂ are such that the amount of retained austenite on the first peripheral surface 10C is equal to or less than the predetermined value and the hardness of the first peripheral surface 10C is based on the mathematical formulas 2 and 3. Is set so as to be equal to or greater than the above-mentioned predetermined value.

The first ultimate temperature T ₄ , the second ultimate temperature T _5, and the holding time t ₃ are such that the hardness of the second peripheral surface 10A is equal to or higher than the predetermined value based on the above equations 1, 2, and 3. Is set to be. Further, the second reaching temperature T ₅ and the holding time t ₃ are set so that the amount of retained austenite on the second peripheral surface 10A is equal to or less than the predetermined value.

The holding time t ₂ and the holding time t ₃ are set as follows, for example. First, the lower limit of the holding time t ₂ of the tempering temperature T ₃ in the tempering process is set to realize the initial residual austenite amount and the dimensional stability required for the inner rings 12 and 22. It is calculated from the upper limit of the residual austenite amount of 10C based on the above formula 2. _{Further, the lower limit of the holding time t 3} in the second tempering process is set to realize the initial residual austenite amount and the dimensional stability required for the inner rings 12 and 22, and the retained austenite on the second peripheral surface 10A is set. It is calculated from the upper limit of the amount based on the above formula 2.

Next, the upper limit of the holding time t ₃ is, the hardness lower limit of the first peripheral 10C which is set to achieve the hardness required for the inner ring 12, 22, based on the equation 3 Calculated. Further, the upper limit value of the holding time t ₃ is calculated based on the above formula 3 from the lower limit value of the hardness of the second peripheral surface 10A set to realize the hardness required for the inner rings 12 and 22. Will be done.

For example, the initial residual austenite amount of the molded product is 5% by volume, the upper limit of the retained austenite amount of the first peripheral surface 10C is 0% by volume, and the lower limit of the hardness of the first peripheral surface 10C is 670HV. Moreover, consider the case where the lower limit of the hardness of the second peripheral surface 10A is 700 HV. From the above formula 2, the graph shown in FIG. 6 is calculated. _{FIG. 6 shows the holding time t 2} (heating time) required to reduce the initial residual austenite amount by a predetermined amount when the _{tempering temperature T 3} is 350 ° C. in the tempering treatment according to the present embodiment. ) And the amount of initial retained austenite. The horizontal axis of FIG. 6 shows the initial residual austenite amount (unit:%) of the molded product before the tempering treatment, and the vertical axis of FIG. 6 shows the soaking time (unit: seconds) at 350 ° C. From FIG. 6, when the amount of retained austenite on the first peripheral surface from which the initial amount of retained austenite was 5% by volume should be reduced to 0% by volume by tempering, the holding time t _{2 with} respect to the first peripheral surface is 156 seconds or more. Is set. For example, of the holding time t ₂ , the lower limit of the holding time in the first tempering process is set as 156 seconds. On the other hand, according to the above formula 3, _{in the above tempering process in which the tempering temperature T 3} and the second reaching temperature T ₅ are 350 ° C., the hardness of the second peripheral surface 10A is 700 HV or more and the hardness of the first peripheral surface 10C. In order to set the hardness to 670 HV or more, the holding time t _{3 with} respect to the second peripheral surface 10A is set to 12 seconds or less. In this case, the holding time t ₂ is set to 168 seconds, which is the sum of 156 seconds and 12 seconds.

In the step (S40), at least the second peripheral surface 10A of the molded body 10 is ground. As a result, the inner rings 12 and 22 having the inner ring raceway surfaces 12A and 22A are formed. When the first peripheral surface 10C of the molded product is not ground, the inner peripheral surfaces 12C and 22C are the first peripheral surfaces that have been tempered. Further, when the first peripheral surface of the molded product is ground, the inner peripheral surfaces 12C and 22C are surfaces formed by grinding the first peripheral surface that has been tempered.

In the process (S50), the outer rings 11 and 21 and the balls 13 or rollers 23 are prepared. Next, the inner ring 12 manufactured in the previous step (S40), the prepared outer ring 11 and the ball 13 are assembled. As a result, the deep groove ball bearing 1 shown in FIG. 1 is manufactured. Alternatively, the inner ring 22 manufactured in the previous step (S40) and the prepared outer ring 21 and roller 23 are assembled. As a result, the conical roller bearing 2 shown in FIG. 2 is manufactured.

<Modification example>
In the above step (S20), carburizing and nitriding treatment is carried out, but the present invention is not limited to this. In the above step (S20), only the above quench hardening treatment may be carried out. In this case, the amount of retained austenite in the molded product after the quenching treatment is generally smaller than that in the case where the carburizing treatment is carried out. That is, the difference between the amount of retained austenite on the inner ring raceway surfaces 12A and 22A and the amount of retained austenite on the inner peripheral surfaces 12C and 22C due to the above tempering treatment is the difference between the inner ring 12 and the inner ring 12 It is smaller than that of 22. On the other hand, also in this case, since the tempering treatment is carried out, the difference becomes larger than that of the conventional inner ring in which the conventional tempering treatment is performed instead of the tempering treatment. The above difference between the inner rings 12 and 22 manufactured without performing the carburizing and nitriding treatment can be, for example, 3% by volume or more and 5% by volume or less.

Further, together with the inner rings 12 and 22, the outer rings 11 and 21 may also be configured as the track members according to the present embodiment. In this case, the amount of retained austenite on the outer ring raceway surface 11A is larger than the amount of retained austenite on the outer peripheral surface 11C as the circumferential surface, and the difference between the two is 3% by volume or more. Further, the amount of retained austenite on the outer ring raceway surface 21A is larger than the amount of retained austenite on the outer peripheral surface 21C as the circumferential surface, and the difference between the two is 3% by volume or more.

<Effect>
The inner rings 12 and 22 as the raceway members according to the present embodiment are made of steel and extend along the circumferential direction with the inner ring raceway surfaces 12A and 22A, and extend along the circumferential direction and along the axial direction. It has inner peripheral surfaces 12C and 22C as an extending circumferential surface. The amount of retained austenite on the inner ring raceway surfaces 12A and 22A is larger than the amount of retained austenite on the inner peripheral surfaces 12C and 22C. The difference between the amount of retained austenite on the inner ring raceway surfaces 12A and 22A and the amount of retained austenite on the inner peripheral surfaces 12C and 22C is 3% by volume or more.

In the conventional tempering process, the entire molded body is heated in the atmosphere furnace, so that retained austenite and martensite in the region that should be the raceway surface are decomposed. Therefore, in the inner ring as the first comparative example manufactured by the conventional tempering treatment, the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the inner diameter surface is less than 3% by volume. As a result, in the inner ring, the dimensional stability of the inner diameter surface and the hardness of the raceway surface showed a trade-off relationship, and it was difficult to increase both at the same time.

Further, in the tempering process, even if local heating is performed only on the first peripheral surface of the molded product, if local cooling is not performed on the second peripheral surface, the second period in the tempering process is performed. The reaching temperature of the surface becomes high, and the decomposition of retained austenite and martensite on the second peripheral surface side proceeds. As a result, the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the inner diameter surface is 3 volumes even in the inner ring as a second comparative example produced by the tempering treatment in which only the heating is performed and the cooling is not performed. It will be less than%. As a result, even in the inner ring, the dimensional stability of the inner diameter surface and the hardness of the raceway surface show a trade-off relationship, and it is difficult to increase both at the same time.

On the other hand, in the tempering treatment according to the present embodiment, since the second peripheral surface 10A is locally cooled in the second tempering treatment, the temperature of the second peripheral surface 10A is set to the temperature of the first peripheral surface 10C. some of the time of the holding time t _2, which is held in the tempering temperature T _3, is held in the first ultimate temperature T ₄ lower than the tempering temperature T _3. The first ultimate temperature T ₄ can be made lower than the ultimate temperature of each of the second peripheral surfaces of the first comparative example and the second comparative example by the above cooling. Therefore, in the tempering treatment according to the present embodiment, decomposition of retained austenite and martensite on the second peripheral surface 10A side is suppressed as compared with the first comparative example and the second comparative example. As a result, in the inner rings 12 and 22 manufactured by performing the tempering treatment according to the present embodiment, the residual austenite amount of the inner ring raceway surfaces 12A and 22A formed based on the second peripheral surface is determined. The amount of retained austenite on the inner peripheral surfaces 12C and 22C formed based on the first peripheral surface is 3% by volume or more larger than the amount of retained austenite.

As a result, in the inner rings 12 and 22, the amount of retained austenite on the inner ring raceway surfaces 12A and 22A is larger than that of the inner rings of the first and second comparative examples, and the amount of retained austenite on the inner peripheral surfaces 12C and 22C is large. It can be reduced as compared with that of the inner ring of the first comparative example and the second comparative example. In such inner rings 12 and 22, the dimensional stability of the inner peripheral surfaces 12C and 22C and the hardness of the inner ring raceway surfaces 12A and 22A are simultaneously enhanced as compared with the inner rings of the first comparative example and the second comparative example. There is.

Further, in the inner rings 12 and 22, the amount of retained austenite on the inner peripheral surfaces 12C and 22C is the same as that of the inner rings of the first and second comparative examples, and the amount of retained austenite on the inner ring raceway surfaces 12A and 22A. Can be increased as compared with that of the inner ring of the first comparative example and the second comparative example. In such inner rings 12 and 22, the dimensional stability of the inner peripheral surfaces 12C and 22C is made equivalent to that of the inner rings of the first comparative example and the second comparative example, and the hardness of the inner ring raceway surfaces 12A and 22A is high. It is greatly improved as compared with that of the inner ring of the first comparative example and the second comparative example.

Further, in the inner rings 12 and 22, the amount of retained austenite on the inner ring raceway surfaces 12A and 22A is equal to that of the inner rings of the first and second comparative examples, and the amount of retained austenite on the inner peripheral surfaces 12C and 22C. Can be reduced as compared with that of the inner ring of the first comparative example and the second comparative example. In such inner rings 12 and 22, the hardness of the inner ring raceway surfaces 12A and 22A is the same as that of the inner rings of the first comparative example and the second comparative example, and the dimensional stability of the inner peripheral surfaces 12C and 22C is improved. It is greatly improved as compared with that of the inner ring of the first comparative example and the second comparative example.

Further, it is manufactured by performing only the second tempering treatment in the tempering treatment, the tempering temperature of the tempering treatment _{is equal to the tempering temperature T 3} , and the reaching temperature of the second peripheral surface is the first reaching temperature. Consider the inner ring as a third comparative example equivalent to T _4. In the third comparative example, since the temperature reached by the second peripheral surface in the tempering process is sufficiently lower than the tempering temperature, a large amount of residual austenite remains on the second peripheral surface side. As a result, the overall average retained austenite amount of the third comparative example may be relatively large, and the overall dimensional stability of the third comparative example may be lower than the required specifications.

On the other hand, in the tempering treatment according to the present embodiment, the second tempering treatment is performed after the first tempering treatment. In the first tempering treatment, the entire molded body is heated. Therefore, the amount of retained austenite on the inner ring raceway surfaces 12A and 22A formed based on the second peripheral surface 10A is smaller than the amount of retained austenite on the inner ring raceway surface of the third comparative example. As a result, the average residual austenite amount of the inner rings 12 and 22 as a whole is also smaller than that of the third comparative example, and the overall dimensional stability of the inner rings 12 and 22 is improved as compared with that of the third comparative example.

The inner rings 12 and 22 are manufactured after undergoing carburizing and nitriding treatment. In this case, the average residual austenite amount of the inner rings 12 and 22 is, for example, 5% by volume or more and 25% by volume or less. In such inner rings 12 and 22, the dimensional stability of the inner peripheral surfaces 12C and 22C and the hardness of the inner ring raceway surfaces 12A and 22A are simultaneously and greatly improved as compared with the first comparative example and the second comparative example. There is. Further, the overall dimensional stability of the inner rings 12 and 22 is higher than that of the third comparative example.

The inner rings 12 and 22 may be manufactured without undergoing carburizing and nitrification treatment. In this case, the total average retained austenite amount of the inner rings 12 and 22 can be 10% by volume or less. Therefore, in such inner rings 12 and 22, the dimensional stability of the inner peripheral surfaces 12C and 22C and the hardness of the inner ring raceway surfaces 12A and 22A are at the same time as compared with the inner rings of the first comparative example and the second comparative example. It has improved significantly.

The hardness of the inner ring raceway surfaces 12A and 22A of the inner rings 12 and 22 is 700 Hv or more. The tempering treatment according to the present embodiment can suppress the decomposition of martensite on the second peripheral surface of the molded product as compared with the conventional tempering treatment. Therefore, the hardness of the inner ring raceway surfaces 12A and 22A may exceed the hardness of the raceway surfaces of the inner rings of the first comparative example and the second comparative example.

The inner rings 12 and 22 are the inner rings of the deep groove ball bearing 1 or the conical roller bearing 2 which are radial bearings, and the inner peripheral surfaces 12C and 22C are surfaces located on the opposite sides of the inner ring raceway surfaces 12A and 22A in the radial direction. is there. The deep groove ball bearing 1 provided with the inner ring 12 has higher dimensional stability of the inner peripheral surface 12C and hardness of the inner ring raceway surface 12A at the same time than the deep groove ball bearings provided with the inner rings of the first comparative example and the second comparative example. Because it is a bearing, it has a long life. The conical roller bearing 2 provided with the inner ring 22 has the dimensional stability of the inner peripheral surface 22C and the hardness of the inner ring raceway surface 22A at the same time as compared with the conical roller bearings having the inner rings of the first comparative example and the second comparative example. Because it is enhanced, it has a long life.

The details of the above simulation analysis regarding the second tempering process according to the present embodiment will be described below. The simulation analysis was performed by heat conduction analysis by the finite element method. First, the member to be heated simulating the molded body was made of JIS standard SUJ2 and was a ring having a thickness of 3 mm in the axial direction. Further, it was assumed that the member to be heated was subjected to the above quenching treatment. The tempering process of the member to be heated was simulated using the analysis model shown in FIG. 7, and the temperature distribution inside the member to be heated at that time was analyzed. In this analysis model, tempering conditions were set in which the heating of the first peripheral surface of the molded product was induced and the cooling of the second peripheral surface was water cooling. In addition, an appropriate heat transfer coefficient was given to the second peripheral surface to simulate water cooling. In such an analysis model, the temperature distribution inside the molded body was analyzed when the heating temperature with respect to the first peripheral surface, that is, the tempering temperature was 180 ° C. or higher and 490 ° C. or lower, and the holding time was 1 minute. The analysis results are shown in FIGS. 8 to 10.

FIG. 8 shows the heating temperature and the ultimate temperature of the cooled second peripheral surface when the heating temperature for the first peripheral surface is 180 ° C. or higher and 490 ° C. or lower and the holding time is 1 minute. It is a graph which shows the relationship. The horizontal axis of FIG. 8 indicates the heating temperature (unit: ° C.) with respect to the first peripheral surface, and the vertical axis of FIG. 8 indicates the ultimate temperature (unit: ° C.) of the second peripheral surface. As shown in FIG. 8, the temperature reached by the second peripheral surface changed linearly with respect to the heating temperature with respect to the first peripheral surface. The above formula 1 was derived from the graph of FIG. From FIG. 8, by performing the heating and the cooling at the same time, the temperature difference between the first peripheral surface and the second peripheral surface can be sufficiently increased, and the residual austenite amount and the inner peripheral surface of the inner ring raceway surface can be sufficiently increased. It was confirmed that the difference from the amount of retained austenite in the above can be 3% by volume or more.

FIG. 9 is a graph showing the temperature changes of the first peripheral surface and the second peripheral surface with respect to the elapsed time from the start of heating with the heating temperature of the first peripheral surface to 420 ° C. and the above-mentioned cooling. The horizontal axis of FIG. 9 indicates the elapsed time (unit: seconds) from the start of heating, and the vertical axis of FIG. 9 indicates the temperatures (unit: ° C.) of the first peripheral surface and the second peripheral surface. As shown in FIG. 9, about 5 seconds after the start of heating, the temperature of the first peripheral surface reached 390 ° C., which is 90% of the tempering temperature. Similarly, the temperature of the second peripheral surface reached 220 ° C., which is 90% of the temperature estimated from the above equation 1, about 5 seconds after the start of heating. Further, after the temperature of the second peripheral surface reached the above-estimated temperature, the temperature rise of the second peripheral surface was suppressed even though the heating of the first peripheral surface was continued. That is, it was confirmed that the temperature rise of the second peripheral surface was sufficiently suppressed by the above water cooling.

FIG. 10 is a diagram showing the temperature distribution inside the member to be heated when 30 seconds have passed since the start of heating and cooling at a heating temperature of 350 ° C. for the first peripheral surface. As shown in FIG. 10, the temperature inside the member to be heated gradually decreases from the first peripheral surface to the second peripheral surface, and the amount of decrease from the temperature of the first peripheral surface is the first circumference. It was confirmed that it changed linearly with respect to the distance from the surface. Further, it was confirmed that the temperature reached in the region where the raceway surface is formed can be suppressed to a temperature at which the decomposition of martensite can be sufficiently suppressed, even when the grinding allowance in the above step (S50) is taken into consideration.

Further, the heating and cooling shown in FIG. 10 were carried out on the member to be heated having a residual austenite amount of 14.4% by volume and a hardness of 780Hv on the first peripheral surface and the second peripheral surface before the tempering treatment. In this case, the amount of retained austenite on the first peripheral surface is 2% by volume or less and the hardness of the first peripheral surface is 680Hv, whereas the amount of retained austenite on the second peripheral surface is 14.1% by volume and the hardness is 779Hv. Met.

On the other hand, when the conventional tempering treatment is carried out on a member to be heated in which the amount of retained austenite on the first and second peripheral surfaces before the tempering treatment is 14.4% by volume and the hardness is 780 Hv, the first The difference between the amount of retained austenite on the peripheral surface and the amount of retained austenite on the second peripheral surface was less than 5% by volume.

As described above, it was confirmed that according to the method for manufacturing the raceway member according to the present embodiment, it is possible to manufacture an inner ring in which the amount of retained austenite on the raceway surface is 5% by volume or more larger than the amount of retained austenite on the first peripheral surface. .. Further, according to the method for manufacturing a track member according to the present embodiment, the amount of residual austenite on the first peripheral surface is lower and the residual austenite on the second peripheral surface is lower than that in the conventional method for manufacturing a track member including tempering treatment. It was confirmed that an inner ring with a high amount of austenite could be produced.

(Structure of raceway ring of rolling bearing according to embodiment)
The configuration of the raceway ring of the rolling bearing according to the embodiment will be described below.

The raceway ring of the rolling bearing according to the embodiment is, for example, an inner ring of a deep groove ball bearing (hereinafter, referred to as "inner ring 110"). However, the raceway ring of the rolling bearing according to the embodiment is not limited to this. The raceway ring of the rolling bearing according to the embodiment may be an outer ring of a deep groove ball bearing, or may be a raceway ring of a rolling bearing other than the deep groove ball bearing.

The inner ring 110 is made of hardened steel. That is, this steel contains martensite crystal grains and retained austenite crystal grains. This steel may contain other than martensite crystal grains and retained austenite crystal grains (for example, ferrite crystal grains and carbide grains). This steel is, for example, SUJ2, which is a high carbon chrome bearing steel defined in the JIS standard (JIS G 4805: 2008).

FIG. 11 is a plan view of the inner ring 110. FIG. 12 is a cross-sectional view taken along the line XII-XII of FIG. As shown in FIGS. 11 and 12, the inner ring 110 has an annular shape. The inner ring 110 has a central axis A.

The inner ring 110 has a first end surface 110a and a second end surface 110b, an inner peripheral surface 110c, and an outer peripheral surface 110d. The first end surface 110a, the second end surface 110b, the inner peripheral surface 110c, and the outer peripheral surface 110d may be collectively referred to as the surface of the inner ring 110.

The first end face 110a and the second end face 110b form end faces in a direction along the central axis A (hereinafter, referred to as "axial direction"). The second end surface 110b is the opposite surface of the first end surface 110a in the axial direction.

The inner peripheral surface 110c extends in a direction along the circumference centered on the central axis A (hereinafter, referred to as "circumferential direction"). The inner peripheral surface 110c faces the central axis A side. The inner peripheral surface 110c is connected to the first end surface 110a and the second end surface 110b. The inner ring 110 is fitted to a shaft (not shown) on the inner peripheral surface 110c.

The outer peripheral surface 110d extends in the circumferential direction. The outer peripheral surface 110d faces the side opposite to the central axis A. That is, the outer peripheral surface 110d is the opposite surface of the inner peripheral surface 110c in the direction orthogonal to the central axis A and passing through the central axis A (hereinafter, referred to as “diameter direction”).

The outer peripheral surface 110d has a raceway surface 110da. The outer peripheral surface 110d is recessed on the inner peripheral surface 110c side in the raceway surface 110da. The raceway surface 110da has an arc shape in a cross-sectional view passing through the central axis A. The raceway surface 110da is a surface that comes into contact with a rolling element (not shown). The anti-orbital plane is a plane on the opposite side of the orbital plane 110da in the radial direction. In the inner ring 110, the inner peripheral surface 110c is an anti-track surface.

The amount of retained austenite on the inner peripheral surface 110c, which is the anti-orbital plane, is smaller than the amount of retained austenite on the raceway surface 110da. The average value of the amount of retained austenite in the steel constituting the inner ring 110 is preferably 10% by volume or less. The "average value of the amount of retained austenite in the steel constituting the inner ring 110" is a plurality of points arranged at equal intervals between the raceway surface 110da and the inner peripheral surface 110c along the radial direction of the inner ring 110. It is a value obtained by integrating the distribution curve of the retained austenite amount obtained by the measurement along the circumferential direction and dividing it by the cross-sectional area of the raceway ring (inner ring 110) parallel to the circumferential direction.

The difference between the amount of retained austenite on the inner peripheral surface 110c and the amount of retained austenite on the raceway surface 110da is preferably 3% by volume or more. The amount of retained austenite on the inner peripheral surface 110c is preferably 5% by volume or less.

The amount of retained austenite in the steel constituting the inner ring 110 is measured by an X-ray diffraction method. More specifically, the amount of retained austenite is obtained by comparing the intensities of the diffraction peaks of each phase obtained by irradiating with X-rays.

The minimum value of compressive residual stress on the raceway surface 110 da is 100 MPa or more. In the region where the distance from the raceway surface 110 da is 0.2 mm or less, the compressive residual stress is preferably 100 MPa or less. The residual stress on the orbital plane 110 da is measured by the X-ray diffraction method. More specifically, the residual stress on the raceway surface 110da is measured based on the change in the diffraction peak angle when the raceway surface 110da is irradiated with X-rays.

The hardness on the raceway surface 110da is higher than the hardness on the inner peripheral surface 110c. The hardness of the raceway surface 110da and the hardness of the inner peripheral surface 110c are preferably 700 Hv or more. The hardness of the raceway surface 110da and the hardness of the inner peripheral surface 110c are measured according to the Vickers hardness test method defined in the JIS standard (JIS Z 2244: 2009).

<Modification example>
FIG. 13 is a cross-sectional view of the inner ring 110 according to the modified example. As shown in FIG. 13, an immersion layer 110e may be formed on the surface of the inner ring 110. The nitrogen concentration in the steel located in the immersion layer 110e is higher than the nitrogen concentration in the steel located in the steel other than the immersion layer 110e. The nitrogen concentration in steel is measured by EPMA (Electron Probe Micro Analyzer).

When the nitriding layer 110e is formed on the surface of the inner ring 110, the average value of the amount of retained austenite in the steel constituting the inner ring 110 is preferably 20% by volume or less.

(Method of manufacturing a raceway ring of a rolling bearing according to an embodiment)
The method of manufacturing the inner ring 110 will be described below.

FIG. 14 is a process diagram showing a manufacturing method of the inner ring 110. As shown in FIG. 14, the method for manufacturing the inner ring 110 includes a preparation step S11, a quenching step S12, a tempering step S13, and a post-treatment step S14. In the preparation step S11, the annular machined member 120 to be the inner ring 110 is prepared by going through the quenching step S12, the tempering step S13, and the post-treatment step S14.

When the nitrification layer 110e is formed on the surface of the inner ring 110, the surface of the member 120 to be processed is subjected to a nitrification treatment prior to the quenching step S12. The immersion treatment is performed by holding the member 120 to be processed at a predetermined temperature for a predetermined time in, for example, an atmospheric gas containing nitrogen (for example, ammonia (NH _{3) gas).}

In the quenching step S12, the member 120 to be processed is quenched. The quenching step S12 includes a heating step S121 and a cooling step S122. In the heating step S121, the member 120 to be processed _{is heated to a temperature of one} A point or higher and held for a predetermined time. A ₁ point is the temperature at which ferrite in steel begins to transform into austenite. By performing the heating step S121, austenite crystal grains are generated in the steel constituting the processing target member 120.

The cooling step S122 is performed after the heating step S121. In the cooling step S122, the member 120 to be processed is cooled to a temperature equal to or lower than the Ms point. The Ms point is the temperature at which the transformation from austenite to martensite begins. Therefore, in the cooling step S122, some of the austenite crystal grains in the steel constituting the processing target member 120 become martensite crystal grains.

In the cooling step S122, the temperature is lowered below the Ms point and at or near the Mf point. The Mf point is the temperature at which the transformation from austenite to martensite ends. That is, in the cooling step S122, a so-called sub-zero treatment (deep cooling treatment) is performed. As a result, the amount of retained austenite in the steel constituting the work target member 120 is considerably reduced.

The tempering step S13 is performed after the quenching step S12. In the tempering step S13, the member 120 to be processed is tempered.

FIG. 15 is a schematic plan view for explaining the tempering step S13. FIG. 16 is a schematic cross-sectional view for explaining the tempering step S13. As shown in FIGS. 15 and 16, the heating in the tempering step S13 is performed by, for example, induction heating.

More specifically, it is performed by inducing and heating the inner peripheral surface 120c by rotating the heating coil 130 in the circumferential direction along the inner peripheral surface 120c of the member 120 to be processed. When the inner peripheral surface 120c is heated by the heating coil 130, the outer peripheral surface 120d of the member 120 to be processed is cooled by a cooling liquid such as water injected from the injection unit 131.

FIG. 17 is a graph showing the simulation results regarding the relationship between the heating time by the heating coil 130 and the temperatures on the inner peripheral surface 120c and the outer peripheral surface 120d. In FIG. 17, the horizontal axis represents the heating time (unit: seconds) by the heating coil 130, and the vertical axis represents the temperature (unit: ° C.) on the inner peripheral surface 120c and the outer peripheral surface 120d. The simulation of FIG. 17 was performed under the conditions that the heating temperature of the inner peripheral surface 120c was 420 ° C., the outer peripheral surface 120d was water-cooled, and the distance between the inner peripheral surface 120c and the outer peripheral surface 120d was 3 mm. As shown in FIG. 17, in the tempering step S13, the heating temperature of the outer peripheral surface 120d is lower than the heating temperature of the inner peripheral surface 120c.

FIG. 18 is a graph showing a simulation result of the heating temperature of the outer peripheral surface 120d when the heating temperature of the inner peripheral surface 120c is changed. In FIG. 18, the horizontal axis represents the heating temperature (unit: ° C.) of the inner peripheral surface 120c, and the vertical axis represents the heating temperature (unit: ° C.) of the outer peripheral surface 120d. The simulation of FIG. 18 was performed under the same conditions as the simulation of FIG. 17, except that the heating temperature of the inner peripheral surface 120c was changed. As shown in FIG. 18, the heating temperature of the outer peripheral surface 120d is a linear expression of the heating temperature of the inner peripheral surface 120c. Assuming that the heating temperature of the inner peripheral surface 120c is x and the heating temperature of the outer peripheral surface 120d is y, y = a × x + b (a is a positive number less than 1 and b is a positive number). Is called "Equation 1").

For example, as described in Japanese Patent Application Laid-Open No. 10-102137, the volume ratio (M ₁ ) of retained austenite in the steel constituting the work target member 120 after the tempering step S13 is performed is tempered. _{Using the volume ratio (M 0} ), heating temperature (T), and heating time (t) of the retained austenite in the steel constituting the member 120 to be processed before the step S13 is performed _{, M 1} = M ₀ × {A. × exp (−Q / RT) × t ⁿ } (A, Q and n are constants, R is a gas constant) (hereinafter, this equation is referred to as “Equation 2”).

Therefore, by appropriately adjusting the heating temperature and heating time of the inner peripheral surface 120c by the heating coil 130, the heating temperature of the outer peripheral surface 120d can be appropriately adjusted, and accordingly, the volume ratio of the retained austenite in the inner peripheral surface 120c. And the volume ratio of retained austenite on the outer peripheral surface 120d can be adjusted as appropriate.

For example, as described in References (Takeshi Inoue, "New Tempering Parameters and Application to Tempering Integration Method Along Its Continuous Temperature Curve", Iron and Steel, 66, 10 (1980), 1533). The hardness (Hv) of the steel constituting the work target member 120 after the tempering step S13 is determined by using the heating time (t) and the heating temperature (T) as Hv = c × log + d / T + e ( c, d and e are constants). Therefore, the hardness of the inner peripheral surface 120c can be appropriately adjusted by appropriately adjusting the heating temperature and the heating time of the inner peripheral surface 120c by the heating coil 130.

In the post-treatment step S14, post-treatment is performed on the member 120 to be processed. This post-treatment includes grinding of the processing target member 120, cleaning of the processing target member 120, and the like. With the above, the manufacturing process of the inner ring 110 is completed.

(Effect of the bearing ring of the rolling bearing according to the embodiment)
The effect of the inner ring 110 will be described below.

In the inner ring 110, since the amount of retained austenite on the anti-orbital plane (inner peripheral surface 110c) is smaller than the amount of retained austenite on the raceway surface 110da, the retained austenite is transformed into martensite over time, so that the inner peripheral surface 110c The dimensional change of is small. Therefore, in the inner ring 110, the fitting with the shaft is hard to loosen, and the creep resistance on the anti-track surface can be improved.

In the inner ring 110, the amount of retained austenite on the inner peripheral surface 110c is smaller than the amount of retained austenite on the raceway surface 110da (from another viewpoint, the amount of decrease in retained austenite on the inner peripheral surface 110c is the amount of retained austenite on the raceway surface 110da. The shrinkage on the inner peripheral surface 110c side after the end of the tempering step S13 is larger than that on the raceway surface 110da side.

Due to this difference in the amount of shrinkage, compressive residual stress acts on the raceway surface 110da. In the inner ring 110, the difference between the amount of retained austenite on the inner peripheral surface 110c and the amount of retained austenite on the raceway surface 110da is 3% by volume or more, so that the raceway surface 110da has a large compressive residual stress (specifically, , The minimum value is 100 MPa or more). Therefore, according to the inner ring 110, the rolling fatigue characteristics on the raceway surface 110 da can be improved.

When the average value of the amount of retained austenite in the steel constituting the inner ring 110 is 10% by volume or less (when the nitriding layer 110e is formed, it is 20% by volume or less). , The transformation of retained austenite to martensite with the passage of time is less likely to occur, and the creep resistance can be further improved.

By performing the sub-zero treatment in the cooling step S122, the average value of the amount of retained austenite in the steel constituting the inner ring 110 is 10% by volume or less (20% by volume when the nitriding layer 110e is formed). The following) can be used. If the average value of the amount of retained austenite in the steel is reduced before the tempering step S13, the time required for the tempering step S13 can be shortened, and the inner peripheral surface 110c is heated in the tempering step S13. The temperature can be lowered. As a result, the hardness can be maintained not only on the raceway surface 110da but also on the inner peripheral surface 110c.

<Experimental example>
Samples 1 to 4 were prepared as samples to be used in the experiment. Samples 1 to 4 are annular members formed by SUJ2 defined in JIS standards. The surfaces of Sample 1 and Sample 2 have not been subjected to nitrification treatment. The surfaces of Samples 3 and 4 are subjected to a nitrogen immersion treatment. The sample 1 and the sample 3 are not subjected to the sub-zero treatment in the cooling step S122, and the samples 2 and the sample 4 are subjected to the sub-zero treatment in the cooling step S122. A tempering step S13 is performed on Samples 1 to 4.

As shown in Table 1, the amount of retained austenite on the orbital surface of Sample 1 was 11% by volume. On the other hand, the amount of retained austenite on the orbital surface of Sample 2 was 7% by volume. The amount of retained austenite on the orbital surface of Sample 3 was 31% by volume, while the amount of retained austenite on the orbital surface of Sample 4 was 16% by volume.

Since the amount of retained austenite in the steel constituting the member 120 to be machined decreases in the tempering step S13 from the raceway surface to the anti-track plane, the inner ring 110 is formed by performing the subzero treatment in the cooling step S122. The average value of the amount of retained austenite in the steel can be 10% by volume or less (20% by volume or less when the immersion layer 110e is formed).

Tempering step S13 was performed on sample 2. At this time, the heating temperature on the inner peripheral surface side of the sample 2 was set to 300 ° C., and the outer peripheral surface side of the sample 2 was water-cooled. The heating time was set so that the difference between the amount of retained austenite on the outer peripheral surface and the retained austenite on the inner peripheral surface was 3% by volume based on the formulas 1 and 2.

As shown in Table 2, in the sample 2 before the tempering step S13 was performed, the residual tensile stress was acting on the outer peripheral surface, but in the sample 2 after the tempering step S13 was performed, the residual tensile stress was acting. A compressive residual stress of 100 MPa or more was generated at a position where the distance from the outer peripheral surface was up to 0.2 mm. From this, it is possible that a compressive residual stress of 100 MPa or more is generated on the raceway surface 110da because the difference between the amount of retained austenite on the inner peripheral surface 110c and the amount of retained austenite on the raceway surface 110da is 3% by volume or more. It was also clarified experimentally.

It should be considered that the embodiments and examples disclosed this time are examples in all respects and are not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.

1 Deep groove ball bearing, 2 Conical roller bearing, 10 Molded body, 10A 2nd peripheral surface, 10C 1st peripheral surface, 11,21 outer ring, 11A, 21A outer ring raceway surface, 12C, 22C inner peripheral surface, 12B, 22B outer peripheral surface , 12, 22 inner ring, 12A, 22A inner ring raceway surface, 13 ball, 13A, 23A rolling surface, 14, 24 cage, 30 first coil, 31 injection part, 32 second coil, 110 inner ring, 110a first end surface , 110b second end surface, 110c inner peripheral surface, 110d outer peripheral surface, 110da orbital surface, 110e quenching layer, 120 machining target member, 120c inner peripheral surface, 120d outer peripheral surface, 130 heating coil, 131 injection part, A central axis, S11 preparation process, S12 quenching process, S13 tempering process, S14 post-treatment process, S121 heating process, S122 cooling process.

Claims (17)

1. The orbital plane extending along the circumferential direction,
   It has an anti-orbital plane facing the opposite side of the orbital plane,
   The amount of retained austenite on the orbital plane is larger than the amount of retained austenite on the anti-orbital plane.
   A raceway member in which the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the anti-tracking surface is 3% by volume or more.
2. The track member according to claim 1, wherein the average residual austenite amount as a whole is 20% by volume or less.
3. The track member according to claim 1, wherein the average residual austenite amount as a whole is 10% by volume or less.
4. The orbital member according to any one of claims 1 to 3, wherein the amount of retained austenite on the anti-orbital surface is 5% by volume or less.
5. The track member according to any one of claims 1 to 4, wherein the hardness of the anti-track surface is 600 Hv or more.
6. An inner ring having an inner ring raceway surface and an inner diameter surface located on the side opposite to the inner ring raceway surface,
   An outer ring having an outer ring raceway surface facing the inner ring raceway surface,
   A plurality of rolling elements that come into contact with the inner ring raceway surface and the outer ring raceway surface are provided.
   The inner ring is the track member according to any one of claims 1 to 5.
   The inner ring raceway surface is the raceway surface of the raceway member.
   A rolling bearing in which the inner diameter surface is the anti-track surface of the track member.
7. The raceway ring of a rolling bearing
   The raceway ring is made of hardened steel and has a surface having an inner peripheral surface and an outer peripheral surface.
   One of the inner peripheral surface and the outer peripheral surface includes a raceway surface.
   The other of the inner peripheral surface and the outer peripheral surface is an anti-orbital surface.
   The amount of retained austenite in the steel on the anti-track surface is smaller than the amount of retained austenite in the steel on the raceway surface.
   The difference between the amount of retained austenite in the steel on the raceway surface and the amount of retained austenite in the steel on the anti-track surface is 3% by volume or more.
   The minimum value of compressive residual stress on the raceway surface is 100 MPa or more, which is the raceway ring of the rolling bearing.
8. The raceway ring of the rolling bearing according to claim 7, wherein the average value of the residual austenite amount in the steel is 10% by volume or less.
9. An immersion layer is formed on the surface.
   The raceway ring of the rolling bearing according to claim 7, wherein the average value of the amount of retained austenite in the steel is 20% or less.
10. The raceway ring of a rolling bearing according to any one of claims 7 to 9, wherein the hardness of the steel on the raceway surface and the hardness of the steel on the anti-track surface are 700 Hv or more.
11. The raceway ring of the rolling bearing according to any one of claims 7 to 9, wherein the amount of retained austenite in the steel on the anti-track surface is 5% by volume or less.
12. The rolling bearing raceway ring according to any one of claims 7 to 11, wherein the steel is SUJ2, a high carbon chrome bearing steel defined in JIS standards.
13. A step of preparing a member to be processed made of steel, which is annular and has a first peripheral surface and a second peripheral surface which is an opposite surface in the radial direction of the first peripheral surface.
    A quenching process for quenching the member to be processed and
    It is provided with a tempering process for tempering the member to be processed.
    The quenching step includes a heating step of heating the processing target member to the A ₁ transformation point or more temperature of the steel, and a cooling step of cooling the processing target member to a temperature below Mf point of the steel ,
    The tempering step is a method for manufacturing a raceway ring of a rolling bearing, which is performed by heating the second peripheral surface while cooling the first peripheral surface.
14. The method for manufacturing a raceway ring of a rolling bearing according to claim 13, wherein the tempering step is performed while rotating the machining target member around the central axis of the machining target member.
15. The method for manufacturing a raceway ring of a rolling bearing according to claim 13, wherein in the tempering step, the first peripheral surface is cooled by injecting a cooling liquid.
16. The method for manufacturing a raceway ring of a rolling bearing according to any one of claims 13 to 15, wherein in the tempering step, the second peripheral surface is heated by induction heating.
17. The method for manufacturing a raceway ring of a rolling bearing according to any one of claims 13 to 16, wherein in the tempering step, the second peripheral surface is heated so that the average temperature becomes 300 ° C. or higher. ..

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