JP7370143B2 - Raceway members and rolling bearings - Google Patents

Description

The present invention relates to a raceway member and a rolling bearing.

Conventional raceway members are manufactured by subjecting them to heat treatment including hardening treatment and tempering treatment. Generally, the tempering treatment is carried out by housing the entire molded body, which is the object to be treated, in an atmospheric furnace. The raceway member manufactured in this manner contains a large amount of retained austenite. Therefore, when used in a high-temperature environment, the amount of retained austenite is gradually decomposed, and the dimensional changes over time of the raceway member become large.

It is preferable that the dimensional change rate of raceway members used in high-temperature environments is 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 kept low, it is possible to suppress the occurrence of creep due to loosening of the fit between the inner diameter surface of the inner ring and the shaft, and it is possible to suppress damage to the bearing.

Conventionally, as a measure to suppress the dimensional change rate of raceway members, a tempering treatment for reducing the average amount of retained austenite in the entire raceway member is known.

JP 2017-227334A 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 amount of retained austenite in the entire raceway member to 18% by volume or less.

JP2017-227334A

However, in the conventional tempering treatment method described above, since the entire molded body is tempered, residual austenite is decomposed in the entire molded body. Furthermore, in the above-mentioned conventional tempering treatment method, retained austenite is decomposed and martensite is decomposed in the entire molded body at the same time.

Therefore, track members manufactured by the conventional tempering process mentioned above are different from raceway members manufactured without being tempered under the above conditions because, for example, they are not planned to be used in high-temperature environments. Compared to this, the amount of martensite on the raceway surface is kept low, and the hardness of the raceway surface is low. As a result, in the former raceway member, the dimensional change rate of the circumferential surface located on the opposite side from 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 a lower level than in the latter raceway member. However, the hardness of the raceway surface has decreased.

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 circumferential surface is suppressed to a low level and a decrease in the hardness of the raceway surface is suppressed.

The raceway member according to the present invention is an annular raceway member made of carbon steel, and includes a raceway surface extending along the circumferential direction and another raceway member located on the opposite side of the raceway surface in the radial direction. It has a surface. The amount of retained austenite on the raceway surface is greater than the amount of retained austenite on other surfaces. The difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on other surfaces is 5% by volume or more. The variation in the amount of retained austenite on the raceway surface in the circumferential direction is 2% by volume or less.

The raceway member has been subjected to heat treatment including carbo-nitriding treatment, and the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the other surface is 10% by volume or more.

In the above raceway member, the hardness of the raceway surface is 650 Hv or more. The variation in hardness of the raceway surface in the circumferential direction is 20 HV or less.

In the track member, the other surface has a hardness of 600 Hv or more.
In the raceway member, the amount of retained austenite on the other surface is 5% by volume or less.

In the above raceway member, the overall average amount of retained austenite is 10% by volume or less.
In the raceway member, the rate of decrease in the amount of retained austenite in the radial direction from the raceway surface to the other surface is 2×10 ² volume %/m or more and 5×10 ³ volume %/m or less.

In the raceway member, the rate of decrease in hardness in the radial direction from the raceway surface to the other surface is 5×10 ³ HV/m or more and 4×10 ⁴ HV/m or less.

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 opposite side of 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 raceway member. The inner ring raceway surface is the raceway surface of the raceway member. The inner diameter surface is the other surface of the raceway 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 a decrease in hardness of the raceway surface is suppressed.

FIG. 1 is a cross-sectional view showing an example of a rolling bearing according to the present embodiment. FIG. 2 is a schematic diagram for explaining a method for measuring the amount of retained austenite in a bearing component according to the present embodiment. FIG. 3 is a top view showing an example of tempering treatment in the method for manufacturing a rolling bearing according to the present embodiment. 4 is a sectional view taken along arrow IV-IV in FIG. 3. FIG. 3 is a diagram showing an analytical model used for simulation analysis in Example 1. FIG. 6 is a graph showing the relationship between the heating temperature for the first circumferential surface and the temperature of the second circumferential surface at that time, obtained by simulation analysis using the analytical model shown in FIG. 5. FIG. 6 is a diagram showing the temperature distribution from the first circumferential surface to the second circumferential surface inside the heated member, obtained by simulation analysis using the analytical model shown in FIG. 5. FIG. 7 is a graph showing the relationship between variations in soaking temperature in the circumferential direction and variations in the amount of retained austenite in the circumferential direction, obtained by calculation in Example 2. 7 is a graph showing the relationship between variations in soaking temperature in the circumferential direction and variations in hardness in the circumferential direction, obtained by calculation in Example 2. 3 is a graph showing the temperature changes of the inner circumferential surface and the outer circumferential surface with respect to the heating time, as the experimental results in Example 3. 11 is an enlarged graph of a part of the temperature change of the inner circumferential surface shown in FIG. 10.

Embodiments will be described below with reference to the drawings. In addition, in the following drawings, the same reference numerals are given to the same or corresponding parts, and the description thereof will not be repeated.

<Configuration of rolling bearing>
The rolling bearing according to this embodiment is, for example, a radial ball bearing, more specifically a deep groove ball bearing 1 shown in FIG. 1. The deep groove ball bearing 1 includes an annular outer ring 11, an annular inner ring 12 arranged inside the outer ring 11, and rolling elements arranged between the outer ring 11 and the inner ring 12 and held in an annular retainer 14. A plurality of balls 13 are provided. The center axis of the outer ring 11 is arranged to overlap with the center axis of the inner ring 12. Note that the rolling bearing according to this embodiment may be, for example, a radial roller bearing, and more specifically a tapered roller bearing.

The outer ring 11 has an inner circumferential surface 11B and an outer circumferential surface 11C as an outer diameter surface. The inner peripheral surface 11B of the outer ring 11 is formed with an outer ring raceway surface 11A that extends along the circumferential direction. The inner ring 12 has an outer circumferential surface 12B facing the outer circumferential side in the radial direction, and an inner circumferential surface 12C serving 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. Inner ring 12 is arranged inside outer ring 11 such that inner ring raceway surface 12A faces 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 at the rolling surface 13A, and are arranged by the retainer 14 at a predetermined pitch in the circumferential direction. Thereby, the plurality of balls 13 are held on the annular orbits of the outer ring 11 and the inner ring 12 so as to be freely rollable. 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. Note that the inner ring 12 is the raceway member according to this embodiment.

The inner ring 12 has an inner ring raceway surface 12A that extends along the circumferential direction, and an inner peripheral surface 12C that is a circumferential surface that extends along the circumferential direction and also extends along the axial direction. The amount of retained austenite on the inner ring raceway surface 12A is greater than the amount of retained austenite on the inner peripheral surface 12C. The amount of retained austenite in the inner ring 12 shows a tendency to gradually decrease in the radial direction from the inner ring raceway surface 12A toward the inner peripheral surface 12C.

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 5% by volume or more, preferably 10% by volume or more. The amount of retained austenite in the inner ring raceway surface 12A is, for example, 10% by volume or more, preferably 15% by volume or more. The amount of retained austenite in the inner circumferential surface 12C is, for example, less than 10% by volume, preferably 5% by volume or less. 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 conventional tempering treatment. This is realized by the tempering process according to the present embodiment, which will be described later. Note that 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 variation in the amount of retained austenite on the inner ring raceway surface 12A in the circumferential direction is 2% by volume or less. In other words, the inner ring raceway surface 12A has a first region in which the amount of retained austenite is at a maximum in the circumferential direction, and is arranged at a distance from the first region in the circumferential direction; and a second region in which the amount of austenite shows a minimum value. The difference between the amount of retained austenite in the first region and the amount of retained austenite in the second region of the inner ring raceway surface 12A is 2% by volume or less.

The variation in the amount of retained austenite on the inner circumferential surface 12C in the circumferential direction is 2% by volume or less. In other words, the inner circumferential surface 12C includes a third region in which the amount of retained austenite is at a maximum in the circumferential direction, and a third region that is spaced apart from the third region in the circumferential direction; and a fourth region in which the amount of austenite shows a minimum value. The difference between the amount of retained austenite in the third region and the amount of retained austenite in the fourth region of the inner peripheral surface 12C is 2% by volume or less. The first region is a region that overlaps the third region in the radial direction. The second region is a region that overlaps with the fourth region in the radial direction.

Note that the variation in the amount of retained austenite on each surface in the circumferential direction is calculated as follows. As shown in FIG. 2, first, a first measurement point S1 is set at an arbitrary location on the inner raceway surface 12A. Next, a second measurement point S2 is shifted by θ (30°) in the circumferential direction when viewed from the first measurement point S1, and a third measurement is shifted by θ (30°) in the circumferential direction when viewed from the second measurement point S2. Point S3, a fourth measurement point S4 shifted by θ (30°) in the circumferential direction as seen from the third measurement point S3, and a fifth measurement shifted by θ (30°) in the circumferential direction as seen from the fourth measurement point S4. Point S5 and a sixth measurement point S6 shifted by θ (30°) in the circumferential direction when viewed from the fifth measurement point S5 are set on the inner ring raceway surface 12A. In this way, a plurality of measurement points S1 to S6 are set on the contact surface of the inner ring 12 along the circumferential direction, shifted by 30 degrees. Note that each measurement point S1 to S6 is set at the center of the inner raceway surface 12A in the axial direction.

Further, a seventh measurement point S7 located on the opposite side to the first measurement point S1 in the radial direction, an eighth measurement point S8 located on the opposite side to the second measurement point S2 in the radial direction, A ninth measurement point S9 located on the opposite side to the third measurement point S3, a tenth measurement point S10 located on the opposite side to the fourth measurement point S4 in the radial direction, and a fifth measurement point S5 in the radial direction. An eleventh measurement point S11 located on the opposite side and a twelfth measurement point S12 located on the opposite side to the sixth measurement point S6 in the radial direction are set on the inner peripheral surface 12C.

The variation in the amount of retained austenite on the inner ring raceway surface 12A in the circumferential direction is calculated as the difference between the maximum value and the minimum value among the amounts of retained austenite measured at each measurement point S1 to S6. The variation in the amount of retained austenite on the inner circumferential surface 12C in the circumferential direction is calculated as the difference between the maximum value and the minimum value among the amounts of retained austenite measured at each measurement point S7 to S12.

Further, the difference between the amount of retained austenite on the inner ring raceway surface 12A and the amount of retained austenite on the inner circumferential surface 12C is determined by the difference between the amount of retained austenite on the inner ring raceway surface 12A and the amount of retained austenite on the inner circumferential surface 12C at two measurements arranged at intervals in the radial direction among the plurality of measurement points S1 to S12. It is calculated as the minimum value of the difference in retained austenite amount between points.

The overall average amount of retained austenite in the inner ring 12, that is, the average value calculated from the distribution of the amount of retained austenite in the radial direction from the inner raceway surface 12A to the inner peripheral surface 12C of the inner ring 12 is 20% by volume or less. Preferably, the average amount of retained austenite in the entire inner ring 12 is 10% by volume or less.

From the inner ring raceway surface 12A to the inner circumferential surface 12C, the rate of decrease in the amount of retained austenite in the radial direction is 2×10 ² volume %/m or more and 5×10 ³ volume %/m or less. The rate of decrease in the amount of retained austenite in the radial direction is calculated from the amount of retained austenite in the inner ring raceway surface 12A, the amount of retained austenite in the inner peripheral surface 12C, and the amount of retained austenite in the cross section of the inner ring 12 along the radial direction.

The hardness of the inner ring raceway surface 12A exceeds the hardness of the inner peripheral surface 12C. The difference between the hardness of the inner ring raceway surface 12A and the hardness of the inner peripheral surface 12C is, for example, 50 Hv or more, preferably 100 Hv or more. The hardness of the inner ring raceway surface 12A is, for example, 650 Hv or more, preferably 700 Hv or more, and more preferably 750 Hv or more. The hardness of the inner peripheral surface 12C is, for example, 600 Hv or more and 700 Hv or less. Note that the hardness of each surface is measured according to the Vickers hardness test method specified in the JIS standard (JJS Z 2244:2009).

The variation in hardness of the inner ring raceway surface 12A in the circumferential direction is 20 HV or less. In other words, the inner ring raceway surface 12A has a fifth region having a maximum hardness in the circumferential direction, and is arranged at a distance from the fifth region in the circumferential direction, and has a hardness in the circumferential direction. has a sixth region where the value is the minimum value. The difference between the hardness of the fifth region and the sixth region of the inner ring raceway surface 12A is 20 HV or less. The first area is, for example, an area that overlaps with the fifth area. The second area is, for example, an area that overlaps with the sixth area.

Incidentally, the variation in hardness of the inner ring raceway surface 12A in the circumferential direction is calculated as the difference between the maximum value and the minimum value of the hardnesses measured at the measurement points S1 to S6. Further, the difference between the hardness of the inner ring raceway surface 12A and the hardness of the inner circumferential surface 12C is determined by the difference in hardness between two measurement points spaced apart in the radial direction among the plurality of measurement points S1 to S12. It is calculated as the minimum value of the difference in height.

From the inner ring raceway surface 12A to the inner peripheral surface 12C, the rate of decrease in hardness in the radial direction is 5×10 ³ HV/m or more and 4×10 ⁴ HV/m or less. The rate of decrease in hardness in the radial direction is calculated from the hardness of the inner ring raceway surface 12A, the hardness of the inner peripheral surface 12C, and the hardness of the cross section of the inner ring 12 along the radial direction.

The inner ring 12 has a reduced amount of retained austenite on the inner circumferential surface 12C compared to a conventional inner ring that has been subjected to a conventional tempering treatment and has the same hardness as the inner ring raceway surface 12A. The dimensional change rate of the peripheral surface 12C is kept low. In addition, the inner ring 12 has an increased amount of martensite on the inner ring raceway surface 12A compared to a conventional inner ring that has been subjected to a conventional tempering treatment and has the same amount of retained austenite on the inner peripheral surface 12C. Therefore, the hardness of the inner ring raceway surface 12A is improved. Compared to conventional inner rings, the inner ring 12 achieves both improved dimensional stability of the inner circumferential surface 12C and improved hardness of the inner ring raceway surface 12A.

The above-mentioned variation in the amount of retained austenite on the inner ring raceway surface 12A in the circumferential direction is suppressed to a level equal to or more than the variation in the amount of retained austenite on the raceway surface realized by conventional tempering treatment, and is suppressed to a level greater than the variation in the amount of retained austenite on the raceway surface achieved by conventional tempering treatment. This is realized by the tempering treatment according to the form. The above-mentioned variation in the amount of retained austenite on the inner peripheral surface 12C in the circumferential direction is suppressed more than the variation in the amount of retained austenite on the raceway surface realized by conventional tempering treatment. This is achieved through return processing.

Furthermore, the inner ring 12 has a variation in the amount of retained austenite on the inner circumferential surface 12C in the circumferential direction, compared to a conventional inner ring that has been subjected to a conventional tempering treatment and has the same hardness as the inner ring raceway surface 12A. Since this decreases, the variation in the dimensional change rate of the inner circumferential surface 12C in the circumferential direction is also suppressed to a low level. In addition, the inner ring 12 has a lower amount of retained austenite on the inner ring raceway surface 12A in the circumferential direction than a conventional inner ring that has been subjected to a conventional tempering treatment and has the same amount of retained austenite on the inner circumferential surface 12C. Since the variation is reduced to the same level or more, the variation in the amount of martensite on the inner ring raceway surface 12A in the circumferential direction is also reduced to the same level or more. Therefore, the inner ring 12 has a variation in hardness of the inner ring raceway surface 12A in the circumferential direction, compared to a conventional inner ring that has been subjected to a conventional tempering treatment and has the same amount of retained austenite on the inner peripheral surface 12C. has been reduced to the same level or even more.

<Manufacturing method for rolling bearings>
The rolling bearing according to this embodiment is manufactured by the method for manufacturing a rolling bearing according to this embodiment shown in FIG. As shown in FIG. 3, the method for manufacturing a rolling bearing according to the present embodiment includes a step (S10) of preparing a molded body to become the inner ring 12 (raceway member), and a quench hardening process for the molded body. (S20), a step (S30) of subjecting the quench-hardened compact to a tempering process, and a finishing process (S40) of grinding the tempered compact. Equipped with. The inner ring 12 is manufactured through the above steps (S10) to (S40). Furthermore, the method for manufacturing a rolling bearing according to the present embodiment further includes a step of preparing outer ring 11 and balls 13 and assembling inner ring 12, outer ring 11, and balls 13 (S50).

In step (S10), first, a steel material having a carbon steel composition is prepared. The steel material is made of hypereutectoid steel, for example. The steel material is prepared as, for example, a steel bar or a steel wire. Next, processing such as cutting, forging, and turning is performed on the steel material. As a result, a steel material (molded body) formed into the approximate shape of the inner ring 12 is produced. The molded body has a first circumferential surface facing inward in the radial direction and a second circumferential surface facing outward in the radial direction. By grinding the first circumferential surface in a post-process (S40), the inner circumferential surface 12C of the inner ring 12 is formed. By grinding the second circumferential surface in a post-process (S40), an inner ring raceway surface 12A of the inner ring 12 is formed.

In the step (S20), a quench hardening treatment is performed on the molded body prepared in the previous step (S10). In the step (S20), first, the molded body is subjected to carbo-nitriding treatment. Next, a nitrogen diffusion process is performed to diffuse the nitrogen that has entered the molded body by the carbo-nitriding process. Next, the entire molded body is heated to a temperature T ₁ at A ₁ point or higher, and held for a holding time t ₁ (soaking time) for soaking. Next, the molded body is cooled to a temperature T ₂ below the Ms point (martensitic transformation point). This cooling treatment is performed by immersing the target material in a cooling liquid such as oil or water. As a result, the target material is hardened. Note that the difference between the amount of retained austenite on the second circumferential surface and the amount of retained austenite on the first circumferential surface of the molded body subjected to the quench hardening treatment is less than 5% by volume.

In the step (S30), a tempering treatment is performed on the compact that has been subjected to the quench hardening treatment in the previous step (S20). In the tempering treatment, the second circumferential surface of the molded body is locally cooled by the cooling section, while the first circumferential surface is locally heated by the heating section. In other words, the second circumferential surface is continuously cooled from the start of heating to the first circumferential surface until the end of heating. Furthermore, in the tempering process, the cooling and heating are performed while the molded body is rotated along its circumferential direction relative to the cooling section and the heating section.

In the tempering process, the first circumferential surface of the compact is heated to a tempering temperature T ₃ and held for a holding time t ₂ (tempering time) for soaking. The temperature T ₄ reached at the second circumferential surface of the molded body is maintained below the tempering temperature T ₃ by performing the cooling during the tempering process. Note that the reached temperature is the highest temperature at the site whose temperature is being measured.

The tempering temperature _T3 and the holding time _t2 are set so that the amount of retained austenite on the inner circumferential surface 12C is equal to or less than a predetermined value from the viewpoint of realizing the dimensional stability required for the inner circumferential surface 12C. Ru. On the other hand, the attained temperature T ₄ of the second circumferential surface is set, for example, from the viewpoint of realizing the hardness required for the inner ring raceway surface 12A so that the hardness is equal to or higher than a predetermined value.

The tempering temperature T ₃ , holding time t ₂ , and reached temperature T ₄ set as described above can be realized, for example, by the heating method and cooling method shown in FIGS. 3 and 4.

As shown in FIGS. 3 and 4, the heating is performed, for example, by induction heating. The coil 30 as a heating section is arranged in the molded body 10 so as to face only the first circumferential surface 10C. Preferably, the heating is performed by high frequency induction heating. The coil 30 is supplied with an alternating current of 3 kHz or more. When the above-mentioned heating is performed by high-frequency induction heating, the temperature rise on the second circumferential surface 10A side in the radial direction is suppressed compared to induction heating in which an alternating current of a lower frequency is supplied to the coil 30. , the difference between the tempering temperature T ₃ and the attained temperature T ₄ increases. Note that the heating described above is not limited to induction heating, and may be, for example, contact heating, far-infrared heating, or the like. As shown in FIG. 3, the heating section may be provided to heat a portion of the molded body 10 in the circumferential direction. The coil 30 is arranged, for example, to face a portion of the molded body 10 in the circumferential direction in the radial direction. The heating by the heating unit is feedback-controlled so that the temperature of the first circumferential surface 10C measured by, for example, a thermocouple approaches a predetermined set temperature.

As shown in FIG. 4, the cooling is performed by supplying a cooling solvent such as water to the second circumferential surface 10A of the molded body 10. Preferably, the above cooling is performed so as not to cool the first circumferential surface 10C. The above cooling is performed such that the water supplied to the second circumferential surface 10A is not supplied to the first circumferential surface 10C. The injection part 31 as a cooling part is arrange|positioned so that it may oppose only 10 A of 2nd surrounding surfaces in the molded object 10, for example, and injects water to 10 A of 2nd surrounding surfaces. The flow rate of the cooling solvent injected from the injection part 31 is, for example, 20 L/min or more and 40 L/min or less. As shown in FIG. 3, the cooling section may be provided to cool a portion of the molded body 10 in the circumferential direction. The heating section and the cooling section are arranged, for example, so as to sandwich a portion of the molded body 10 in the circumferential direction in the radial direction. The injection part 31 is arranged, for example, to face a part of the molded body 10 in the circumferential direction and in the radial direction. Note that the above cooling may be performed on at least a region of the second circumferential surface 10A that will be subjected to grinding in order to form the inner ring raceway surface 12A in the subsequent step (S40).

The above heating and cooling are performed by rotating the molded body 10 in the circumferential direction with respect to the coil 30 and the injection section 31. The rotation is performed by, for example, a support section (not shown) that supports the molded body 10 and a drive section that rotates the support section in the circumferential direction. The support part is provided so as to support the downwardly facing end surface of the molded body 10, which is arranged such that the axial direction is along the vertical direction, for example. A part of the support part is arranged, for example, together with the molded body 10, the coil 30, and the injection part 31, in a chamber (not shown) in which the above-mentioned heating and cooling are performed, and the rest of the support part is arranged, for example, in a chamber (not shown) in which the above-mentioned heating and cooling are carried out. placed outside. The drive part is for example connected to said remainder of the support part and arranged outside said chamber. The rotational speed of the molded body 10 by the support section and the drive section is, for example, 100 rpm or more and 150 rpm or less.

In addition, the said tempering process may be implemented continuously with respect to the several molded object 10. In this case, the support portion may be provided to support from below the molded product located at the lowest position among the plurality of molded products 10 stacked in the axial direction and before being introduced into the chamber. . That is, the entire support part may be placed outside the chamber. In this case, the plurality of molded bodies 10 are, for example, after one of the molded bodies 10 is subjected to the above-mentioned tempering treatment, and then transported upward by the width of the one molded body 10 in the axial direction, The above-mentioned tempering process for the molded bodies 10 stacked under the one molded body 10 is started. The molded body 10 subjected to the above-mentioned tempering treatment is carried out of the chamber from, for example, an outlet provided above the chamber.

In addition, each setting value of tempering temperature _T3 , holding time _t2 , and attained temperature _T4 is set based on the following Numerical formula 1, Numerical formula 2, and Numerical formula 3, for example.

The above formula 1 is a prediction formula for predicting the relationship between the tempering temperature T ₃ (unit: °C) and the above-mentioned attained temperature T ₄ (unit: °C). The present inventors have discovered that the temperature within a heated member simulating a molded body when the heating is carried out by induction heating on the first circumferential surface and the cooling is carried out by jetting water on the second circumferential surface. The distribution was analyzed by simulation. The above equation 1 was determined by the inventors from the results of the above simulation analysis. As a result of the analysis, it was confirmed that the above-mentioned attained temperature T ₄ changes linearly with respect to the tempering temperature T ₃ (see FIG. 6). Details of the simulation analysis will be described later. In addition, when at least one of the heating method and the cooling method is implemented by a method different from the above, the above-mentioned formula 1 is changed to the prediction formula for the different method.

The above formula 2 is based on the temperature reached during tempering T (unit: K), the holding time t ₂ (unit: seconds), and the amount of retained austenite γ (unit: volume %) on the first circumferential surface after tempering. This is a prediction formula that predicts the relationship. R in the above formula 2 is a gas constant. The amount of retained austenite γ on the first circumferential surface after the tempering process is calculated by substituting the tempering temperature T ₃ for the final temperature T in Equation 2. The amount of retained austenite γ on the second circumferential surface after the tempering process is calculated by substituting the reached temperature T ₄ into the reached temperature T in Equation 2. The above formula 2 is derived from Non-Patent Document 1 (Tsuyoshi Inoue, "A new tempering parameter and its application to the integration method of tempering effect along a continuous temperature increase curve" Tetsu-to-Hagane, 66, 10 (1980) 1533.) This was experimentally determined by the present inventors based on the relational expression between hardness and tempering temperature described in .

The above formula 3 expresses the relationship between the temperature reached during tempering T (unit: K), the holding time t ₂ (unit: seconds), and the hardness M of the second peripheral surface after tempering (unit: HV). This is a prediction formula to predict. The hardness M of the first circumferential surface after the tempering treatment is calculated by substituting the tempering temperature T ₃ into the reached temperature T in Equation 3. The hardness M of the second circumferential surface after the tempering treatment is calculated by substituting the reached temperature T ₄ into the reached temperature T in Equation 3. The above formula 3 was experimentally determined by the present inventors based on the relationship between the amount of retained austenite and the tempering temperature described in JP-A-10-102137.

Specifically, each set value of the tempering temperature T ₃ , the holding time t ₂ , and the attained temperature T ₄ may be set, for example, as follows based on the above equations 1, 2, and 3.

First, from the above formula 2, the upper limit value of the tempering temperature T ₃ and the holding time are determined so that the amount of retained austenite on the first circumferential surface and the average amount of retained austenite in the entire molded body 10 are equal to or less than the above predetermined value. A lower limit value of t ₂ is set. Furthermore, from the above equation 3, the lower limit value of the attained temperature T ₄ and the upper limit value of the holding time t ₂ are set so that the hardness of the second circumferential surface is equal to or higher than the predetermined value. Next, from the above equation 1, the upper limit value of the above-mentioned reached temperature T ₄ when the upper limit value of the tempering temperature T ₃ set based on the above-mentioned equation 2 is realized is estimated. Alternatively, from the above equation 1, the lower limit value of the tempering temperature T 3 at which the lower limit value of the attained temperature T ₄ set based on the above equation ₃ is realized is estimated. Next, respective set values are determined based on the upper and lower limit values of the tempering temperature T ₃ , the ultimate temperature T ₄ , and the holding time t ₂ estimated as described above.

In the step (S40), at least the second circumferential surface 10A of the molded body 10 is subjected to a grinding process. Thereby, the inner ring 12 having the inner ring raceway surface 12A is formed. Note that when the first circumferential surface 10C of the molded body is not ground, the inner circumferential surface 12C is the first circumferential surface that has been subjected to a tempering process. Furthermore, when the first circumferential surface of the molded body is subjected to grinding, the inner circumferential surface 12C is a surface formed by grinding the first circumferential surface that has been subjected to a tempering process.

In the step (S50), the outer ring 11 and balls 13 are prepared. Next, the inner ring 12 manufactured in the previous step (S40) and the prepared outer ring 11 and balls 13 are assembled. As a result, the deep groove ball bearing 1 shown in FIG. 1 is manufactured.

<Modified example>
In the above step (S20), carbo-nitriding treatment is performed, but carbo-nitriding treatment may not be performed. In this case, the amount of residual austenite in the molded body after the quenching treatment is generally smaller than that when the carburizing treatment is performed. Therefore, in this case, 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 smaller than that when the carbo-nitriding treatment is performed. However, in this case as well, since the above-mentioned tempering treatment has been carried out, the above-mentioned difference is larger than that of the conventional inner ring in which the above-mentioned tempering treatment has not been carried out. In other words, even in the inner ring 12 manufactured without carburizing and nitriding, the above-mentioned tempering treatment is performed, so that the amount of retained austenite on the inner ring raceway surface 12A and the amount of retained austenite on the inner circumferential surface 12C is different. The difference may be 5% by volume or more.

Further, the outer ring 11 as well as the inner ring 12 may be configured as a raceway member according to the present embodiment. In this case, the difference between the amount of retained austenite on the outer ring raceway surface 11A and the amount of retained austenite on the outer peripheral surface 11C as a circumferential surface is 5% by volume or more, preferably 10% by volume or more.

<Effect>
The inner ring 12 as a raceway member according to the present embodiment is an annular raceway member made of hypereutectoid steel, and has a raceway surface 12A extending along the circumferential direction and a raceway in the radial direction. It has an inner circumferential surface 12C located on the opposite side to the surface 12A. The amount of retained austenite on the raceway surface 12A is greater than the amount of retained austenite on the inner peripheral surface 12C. The difference between the amount of retained austenite on the raceway surface 12A and the amount of retained austenite on the inner peripheral surface 12C is 5% by volume or more. The variation in the amount of retained austenite on the raceway surface 12A in the circumferential direction is 2% by volume or less.

In conventional tempering treatment, the entire molded body is heated in an atmospheric furnace, so that residual austenite and martensite in the region that is to become the raceway surface is decomposed. Therefore, in the inner ring as the first comparative example manufactured by such 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 5% by volume. As a result, in the inner ring, there was a trade-off relationship between the dimensional stability of the inner diameter surface and the hardness of the raceway surface, and it was difficult to improve both simultaneously.

In addition, even if local heating is performed only on the first circumferential surface of the compact in the tempering process, if local cooling is not performed on the second circumferential surface, the second circumferential surface in the tempering process The temperature reached by the surface increases, and the decomposition of retained austenite and martensite progresses. As a result, even in the inner ring as a second comparative example manufactured by the tempering process in which only the above-mentioned heating is performed and the above-mentioned cooling is not performed, the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the inner diameter surface is 5 vol. less than %. As a result, also in the inner ring, there is a trade-off relationship between the dimensional stability of the inner diameter surface and the hardness of the raceway surface, and it is difficult to improve both simultaneously.

In contrast, in the tempering treatment according to the present embodiment, the first circumferential surface of the compact is locally heated and the second circumferential surface of the compact is locally cooled. The inner ring 12 is manufactured by being subjected to the tempering treatment according to the present embodiment. Therefore, the amount of retained austenite in the inner ring raceway surface 12A formed based on the second circumferential surface is 5% by volume or more greater than the amount of retained austenite in the inner circumferential surface 12C formed based on the first circumferential surface.

As a result, in the inner ring 12, the amount of retained austenite on the inner ring raceway surface 12A is greater than that in the inner rings of the first and second comparative examples, and the amount of retained austenite on the inner peripheral surface 12C is greater than that of the first comparative example and the second comparative example. It can be reduced compared to that of the inner ring of the second comparative example. In such an inner ring 12, the dimensional stability of the inner circumferential surface 12C and the hardness of the inner ring raceway surface 12A are simultaneously enhanced compared to the inner rings of the first comparative example and the second comparative example.

Further, in the inner ring 12, the amount of retained austenite on the inner peripheral surface 12C is the same as that of the inner rings of the first comparative example and the second comparative example, and the amount of retained austenite on the inner ring raceway surface 12A is the same as that of the inner ring of the first comparative example and the second comparative example. and may be increased compared to that of the inner ring of the second comparative example. In such an inner ring 12, the dimensional stability of the inner circumferential surface 12C is 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 surface 12A is equal to that of the inner rings of the first comparative example and the second comparative example. This is greatly improved compared to that of the inner ring of the second comparative example.

Furthermore, in the inner ring 12, the amount of retained austenite on the inner ring raceway surface 12A is the same as that of the inner rings of the first comparative example and the second comparative example, and the amount of retained austenite on the inner peripheral surface 12C is the same as that of the inner ring of the first comparative example and the second comparative example. and can be reduced compared to that of the inner ring of the second comparative example. In such an inner ring 12, the hardness of the inner ring raceway surface 12A is equal to that of the inner rings of the first comparative example and the second comparative example, and the dimensional stability of the inner circumferential surface 12C is equal to that of the inner ring of the first comparative example and the second comparative example. This is greatly improved compared to that of the inner ring of the second comparative example.

Further, as described above, the coil 30 and the injection section 31 are provided to heat and cool a part of the molded body 10 in the circumferential direction, and the heating and the cooling are applied to the coil 30 and the injection section 31. When applied to the molded body 10 that is fixed with There is a possibility that the temperature of the portion of the heated member that is arranged to face the connection point becomes lower than the temperature of other portions of the heated member that are arranged to face the annular portion in the radial direction.

On the other hand, in the tempering treatment according to the present embodiment, the heating and the cooling are performed by rotating the molded body 10 in the circumferential direction with respect to the coil 30 and the injection section 31. The inner ring 12 is manufactured by being subjected to the tempering treatment according to the present embodiment. Therefore, even if the coil 30 and the injection part 31 are provided to heat and cool a part of the molded body 10 in the circumferential direction as described above, the inner circumferential surface 12C formed based on the first circumferential surface The variation in the amount of retained austenite in the inner ring raceway surface 12A formed based on the second circumferential surface in the circumferential direction is 2% by volume or less. As a result, in the inner ring 12, the variation in the amount of retained austenite on the inner ring raceway surface 12A in the circumferential direction is reduced when the heating and cooling are applied to the molded body 10 fixed to the coil 30 and the injection part 31. Compared to that, it has been reduced. Furthermore, in the inner ring 12, the variation in the amount of retained austenite on the inner circumferential surface 12C in the circumferential direction is different from that when the heating and cooling are applied to the molded body 10 fixed to the coil 30 and the injection part 31. It has been reduced in comparison. In such an inner ring 12, the dimensional stability of the inner circumferential surface 12C in the circumferential direction is improved compared to the case where the heating and cooling are applied to the molded body 10 fixed to the coil 30 and the injection part 31. The variation and the variation in the hardness of the inner ring raceway surface 12A in the circumferential direction are simultaneously reduced.

In addition, when the heating part and the cooling part for carrying out the said tempering process are provided so that the whole compact 10 may be heated and cooled in the said circumferential direction, such a heating part and a cooling part Since this is more expensive than the coil 30 and the injection part 31, the manufacturing cost of the inner ring also increases. In other words, in the inner ring 12, although the manufacturing cost is reduced compared to an inner ring manufactured using such a heating section and a cooling section, variations in the dimensional stability of the inner circumferential surface 12C in the circumferential direction and At the same time, variations in hardness of the inner ring raceway surface 12A in the circumferential direction are reduced.

Preferably, the inner ring 12 is subjected to heat treatment including carbo-nitriding treatment. In this case, as described above, the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the circumferential surface may be 10% by volume or more. Therefore, in such an inner ring 12, the dimensional stability of the inner circumferential surface 12C and the hardness of the inner ring raceway surface 12A are simultaneously and greatly improved compared to the inner rings of the first comparative example and the second comparative example.

The tempering treatment according to the present embodiment can suppress decomposition of martensite on the second peripheral surface of the molded body, compared to conventional tempering treatment. Therefore, the hardness of the inner ring raceway surface 12A of the inner ring 12 may be 650 Hv or more. In other words, the hardness of the inner ring raceway surface 12A may exceed the hardness of the inner ring raceway surfaces of the first comparative example and the second comparative example. Furthermore, as described above, by the tempering treatment according to the present embodiment, the variation in the amount of retained austenite on the inner ring raceway surface 12A in the circumferential direction is reduced to 2% by volume or less. Therefore, the variation in hardness of the inner ring raceway surface 12A of the inner ring 12 in the circumferential direction can be 20 Hv or less.

The inner ring 12 is an inner ring of a deep groove ball bearing 1 or a tapered roller bearing, which is a radial bearing, and the inner circumferential surface 12C is a surface located on the opposite side from the inner ring raceway surface 12A in the radial direction. The deep groove ball bearing 1 including the inner ring 12 has both the dimensional stability of the inner circumferential surface 12C and the hardness of the inner ring raceway surface 12A compared to the deep groove ball bearings including the inner ring of the first comparative example and the second comparative example. Because it is reinforced, it has a long lifespan.

(Example 1)
A simulation analysis was conducted regarding the tempering treatment according to the embodiment described above. The simulation analysis was performed using heat conduction analysis using the finite element method. First, the heated member simulating the molded body was a ring made of JIS standard SUJ2 and having an axial thickness of 3 mm. Further, the heated member was subjected to the above-mentioned quenching treatment. The above-mentioned tempering process was simulated for this heated member using the analytical model shown in FIG. 5, and the temperature distribution inside the heated member at that time was analyzed. In this analytical model, tempering conditions were set in which the heating for the first circumferential surface of the molded body was induction heating, and the cooling for the second circumferential surface was water cooling. In addition, water cooling was simulated by giving an appropriate heat transfer coefficient to the second peripheral surface. In such an analytical model, the temperature distribution inside the molded body was analyzed when the heating temperature for the first circumferential surface, that is, the tempering temperature was set at 180° C. or higher and 490° C. or lower, and the holding time was set at 1 minute. The analysis results are shown in FIGS. 6 and 7.

FIG. 6 shows the relationship between the heating temperature and the temperature reached by the second circumferential surface that is being cooled, when the heating temperature for the first circumferential surface is 180°C or more and 490°C or less, and the holding time is 1 minute. It is a graph showing a relationship. The horizontal axis of FIG. 6 indicates the heating temperature (unit: °C) for the first circumferential surface, and the vertical axis of FIG. 6 indicates the reached temperature (unit: °C) of the second circumferential surface. As shown in FIG. 6, the temperature reached at the second circumferential surface changed linearly with respect to the heating temperature for the first circumferential surface. Equation 1 above was derived from the graph of FIG. From FIG. 6, by performing the above heating and the above cooling simultaneously, the temperature difference between the first circumferential surface and the second circumferential surface can be made sufficiently large, and the amount of retained austenite on the first circumferential surface and the amount of retained austenite on the second circumferential surface can be sufficiently increased. It was confirmed that the difference from the amount of retained austenite on the peripheral surface can be made 5% by volume or more.

FIG. 7 is a diagram showing the temperature distribution inside the heated member when 30 seconds have elapsed since the start of heating the first circumferential surface to a heating temperature of 350° C. and the above-mentioned cooling. As shown in FIG. 7, the temperature inside the heated member gradually decreases from the first circumferential surface to the second circumferential surface, and the amount of decrease relative to the temperature of the first circumferential surface is smaller than that of the first circumferential surface. It was confirmed that it changes linearly with the distance from Further, it was confirmed that even if the machining allowance of the grinding process in the above step (S50) is taken into account, the temperature reached in the region where the raceway surface is formed can be suppressed to a temperature at which decomposition of martensite can be sufficiently suppressed.

Further, the heating and cooling shown in FIG. 7 were performed on a member to be heated whose first circumferential surface and second circumferential surface before tempering had a residual austenite content of 14.4% by volume and a hardness of 780 Hv. In this case, the amount of retained austenite on the first circumferential surface is 2% by volume or less and the hardness of the first circumferential surface is 680Hv, whereas the amount of retained austenite on the second circumferential surface is 14.1% by volume and the hardness is 779Hv. Met.

(Example 2)
Regarding the tempering treatment according to the embodiment described above, the influence of temperature variations on the outer peripheral surface in the circumferential direction on the amount of retained austenite and hardness was evaluated based on Equations 2 and 3 above.

In FIG. 8, the maximum temperature (achieved temperature) of the first peripheral surface is 230°C or more and 400°C or less, and the minimum temperature of the first peripheral surface is 20°C, 50°C, or 80°C lower than the maximum temperature, And when the holding time is 1 minute, the relationship between the above maximum temperature and the difference Δγ between the amount of retained austenite when heated at the above maximum temperature and the amount of retained austenite when heated at the above minimum temperature. This is a graph showing. The amount of retained austenite when heated at the above maximum temperature is calculated by substituting the maximum temperature into the reached temperature T (unit: K) in the above formula (2), and calculating the holding time t ₂ ( Unit: seconds). The amount of retained austenite when heated at the above minimum temperature is determined by substituting the above minimum temperature into the reached temperature T (unit: K) in the above formula (2), and calculating the above holding time by the holding time t ₂ (in K) in the above formula (2). Unit: seconds).

The horizontal axis of FIG. 8 shows the maximum temperature (unit: °C), and the vertical axis of FIG. 8 shows the difference between the amount of retained austenite when heated at the above-mentioned minimum temperature and the amount of retained austenite when heated at the above-mentioned maximum temperature. Δγ (unit: volume %) is shown. In FIG. 8, there is a graph showing the relationship between the maximum temperature and the difference Δγ in the amount of retained austenite when the temperature difference ΔT is 20°C, and a graph showing the relationship between the maximum temperature and the difference Δγ in the amount of retained austenite when the temperature difference ΔT is 50°C. A graph showing the relationship with the difference Δγ and a graph showing the relationship between the maximum temperature and the difference Δγ in the amount of retained austenite when the temperature difference ΔT is 80° C. are shown. That is, in FIG. 8, the variation in the temperature of the inner peripheral surface in the circumferential direction is expressed as the difference ΔT between the maximum temperature and the minimum temperature, and the variation in the amount of retained austenite on the inner peripheral surface in the circumferential direction is represented by the retained austenite. The difference in quantity is expressed as Δγ.

As shown in FIG. 8, the larger the temperature difference ΔT, the larger the difference Δγ in the amount of retained austenite. Further, the larger the temperature difference ΔT, the higher the maximum temperature at which the difference Δγ in the amount of retained austenite showed the maximum value. The maximum value of the difference Δγ in the amount of retained austenite is 2.8 volume % when the temperature difference ΔT is 20 °C, 6.6 volume % when the temperature difference ΔT is 50 °C, and 9.6 volume % when the temperature difference ΔT is 80 °C. there were.

In FIG. 8, the plot where the maximum temperature is 300°C in the graph when the temperature difference ΔT is 20°C shows the amount of retained austenite when heated to 300°C and the amount of retained austenite when heated to 280°C. This indicates that the difference is 2% by volume or more.

In Figure 8, the plot where the maximum temperature is 290°C in the graph when the temperature difference ΔT is 20°C is the amount of retained austenite when heated to 290°C and the amount of retained austenite when heated to 270°C. This indicates that the difference between the two is 2% by volume or less. In FIG. 8, the plot in which the maximum temperature is 250°C in the graph when the temperature difference ΔT is 20°C shows the amount of retained austenite when heated to 250°C and the amount of retained austenite when heated to 230°C. This indicates that the difference between the two is 1% by volume or less.

In FIG. 9, the maximum temperature of the first peripheral surface is 230°C or more and 400°C or less, the minimum temperature of the first peripheral surface is 20°C, 50°C, or 80°C lower than the maximum temperature, and the holding time is It is a graph showing the relationship between the maximum temperature and the difference ΔHV between the hardness when heated at the maximum temperature and the hardness when heated at the minimum temperature, when one minute is set. The hardness when heated at the above maximum temperature is calculated by substituting the above maximum temperature into the attained temperature T (unit: K) in the above formula (3), and the above holding time being the holding time t ₂ (unit: K) in the above formula (3). : seconds). The hardness when heated at the above minimum temperature is determined by substituting the above minimum temperature into the attained temperature T (unit: K) in the above formula (3), and the above holding time being the holding time t ₂ (unit: K) in the above equation (3). : seconds).

The horizontal axis of FIG. 9 shows the maximum temperature (unit: °C), and the vertical axis of FIG. 9 shows the difference ΔHV (unit: HV). In FIG. 9, a graph showing the relationship between the maximum temperature and the hardness difference ΔHV when the temperature difference ΔT is 20°C, and a graph showing the relationship between the maximum temperature and the hardness difference ΔHV when the temperature difference ΔT is 50°C. A graph showing the relationship with ΔHV and a graph showing the relationship between the maximum temperature and the hardness difference ΔHV when the temperature difference ΔT is 80° C. are shown. That is, in FIG. 9, the variation in temperature of the inner circumferential surface in the circumferential direction is expressed as the difference ΔT between the maximum temperature and the minimum temperature, and the variation in the hardness of the inner circumferential surface in the circumferential direction is expressed as the difference ΔT between the maximum temperature and the minimum temperature. It is expressed as the difference ΔHV.

As shown in FIG. 9, the larger the temperature difference ΔT, the larger the hardness difference ΔHV. Furthermore, the larger the temperature difference ΔT, the higher the maximum temperature at which the hardness difference ΔHV showed the maximum value. The maximum value of the hardness difference ΔHV was 10.6HV when the temperature difference ΔT was 20°C, 28.0HV when the temperature difference ΔT was 50°C, and 47.3HV when the temperature difference ΔT was 80°C. The higher the maximum temperature, the smaller the hardness difference ΔHV.

As shown in FIG. 9, when the temperature difference ΔT was 20° C., the hardness difference ΔHV was 20 HV or less. In the graph when the temperature difference ΔT is 20°C, each plot where the maximum temperature is 350°C or higher has a difference of 10 HV between the hardness when heated to 350°C or higher and the hardness when heated to 330°C or higher. It shows that:

In other words, in the calculation results shown in FIGS. 8 and 9, the smaller the variation in the temperature of the outer circumferential surface in the circumferential direction, the more suppressed the variation in the amount of retained austenite and the variation in hardness of the outer circumferential surface in the circumferential direction. .

(Example 3)
Each temperature of the first circumferential surface and the second circumferential surface of the molded body and each temperature change in the tempering treatment according to the embodiment described above were evaluated. First, a plurality of members to be heated made of SUJ2 defined in the JIS standard and arranged in an annular shape were prepared. The width of each heated member in the radial direction, that is, the distance between the inner circumferential surface and the outer circumferential surface, was set to be 3 mm or more and 7 mm or less. Next, a plurality of thermocouples and a wireless measurement unit for collecting the output of each thermocouple are prepared, and the inner peripheral surface corresponding to the first peripheral surface of the partial area in the circumferential direction of each heated member is One thermocouple was fixed to each outer peripheral surface corresponding to the second peripheral surface. The thermocouple fixed to the inner peripheral surface of the partial region was arranged to overlap in the radial direction with the thermocouple fixed to the outer peripheral surface of the partial region.

Next, as an example, each member to be heated to which a thermocouple was attached was subjected to the above heating and the above cooling in the tempering treatment according to the embodiment described above. Specifically, in a state where the member to be heated is supported by the support section and rotated in the circumferential direction of the member to be heated by the drive section, the inner circumferential surface of the member to be heated is induction heated by the heating section. At the same time, the outer peripheral surface of the member to be heated was cooled by the cooling section (cooling jacket). The heating section and the cooling section heat and cool a portion of the member to be heated in the circumferential direction. That is, in the heating and cooling, the distance between the partial area of the heated member to which the thermocouple is fixed and the heating section and the cooling section changes as the driving section rotates the heated member. It was carried out under heating conditions. The heating and cooling were started at the same time.

The rotation speed of the heated member by the drive section was set to be 100 rpm or more and 150 rpm or less. The heating by the heating section was feedback-controlled so that the temperature of the inner circumferential surface measured by the thermocouple approached a predetermined heating temperature (soaking temperature) of the inner circumferential surface. Feedback control was performed using a DA converter and a programmable logic controller. The flow rate of the cooling liquid injected from the cooling unit onto the outer circumferential surface of the heated member was set to 20 L/min or more and 40 L/min or less. The changes in temperature of the inner circumferential surface and outer circumferential surface of each member to be heated during such heat treatment were evaluated.

FIGS. 10 and 11 show typical evaluation results for the heated member with a radial width of 3 mm at a rotational speed of 100 rpm, an attained temperature of the inner circumferential surface of 250° C., and a coolant flow rate of 20 L. 3 is a graph showing temperature changes when heat treatment is performed at a rate of 1/min. The horizontal axis in FIGS. 10 and 11 is the heating time (unit: seconds), and the vertical axis in FIGS. 10 and 11 is the measured temperature (unit: °C) of the inner peripheral surface and the outer peripheral surface. FIG. 11 is a partially enlarged view showing a temperature change within a predetermined time after the temperature of the inner circumferential surface reaches a predetermined ultimate temperature among the temperature changes of the inner circumferential surface shown in FIG. 10.

As shown in Figures 10 and 11, after reaching the predetermined ultimate temperature of 250°C, the temperature of the inner peripheral surface changed in a wave-like manner within the temperature range of 240°C to 260°C. . As shown in FIG. 11, after the temperature of the inner circumferential surface reaches the final temperature, the amplitude of the temperature change on the inner circumferential surface is 15°C or less, and the frequency of the temperature change on the inner circumferential surface is equal to that of the heated member. It was almost the same as the number of rotations. From this result, it can be seen that the temperature change on the inner circumferential surface after the temperature of the inner circumferential surface reaches the final temperature is mainly due to the distance between the partial area of the heated member and the heating section and the cooling section. It was confirmed that this was caused by a change.

As shown in FIG. 10, after reaching 100°C, the temperature of the outer peripheral surface changed in a wave-like manner within a temperature range of 80°C to 120°C. As shown in FIG. 11, after the temperature of the outer peripheral surface reached 100° C., the temperature of the inner peripheral surface reached 250° C. relatively quickly. After the temperature of the inner circumferential surface reached 250° C., the amplitude of the temperature change on the outer circumferential surface was 30° C. or less, and the frequency of the temperature change on the outer circumferential surface was approximately equal to the number of rotations of the member to be heated. The heated member shown in FIGS. 10 and 11 had a heat transfer coefficient of about 19000 W/m ² K at the outer peripheral surface. Furthermore, in the heated member according to this example, no uneven discoloration due to surface oxidation after heating was observed.

On the other hand, as a comparative example, each heated member to which a thermocouple was attached was subjected to heat treatment that differed from the above example only in that it was not rotated in the circumferential direction. In the heated member according to the comparative example, the variation in temperature of the inner circumferential surface in the circumferential direction was estimated to be several tens of degrees Celsius or more based on uneven discoloration due to surface oxidation after heating.

From the above evaluation results, it was confirmed that the variation in temperature of the inner circumferential surface and outer circumferential surface in the circumferential direction during the tempering treatment was reduced by rotating the member to be heated.

Furthermore, it was confirmed that the temperature change on the outer circumferential surface after the temperature of the inner circumferential surface reached the final temperature while the member to be heated was rotated was mainly dependent on the rotational speed of the member to be heated. Furthermore, if other evaluation results not shown in FIGS. 10 and 11 are taken into account, the heat transfer coefficient at the outer circumferential surface is determined by the number of rotations of the heated member by the drive unit and the number of rotations of the heated member from the cooling unit. It was confirmed that this is controlled by the flow rate of the coolant, etc.

(Example 4)
Regarding the tempering treatment according to the embodiment described above, the influence of the temperature distribution in the radial direction on the distribution of the amount of retained austenite in the radial direction was evaluated based on the simulation results of Example 1 and Equation 2. Similarly, the influence of the temperature distribution in the radial direction on the hardness distribution in the radial direction was evaluated based on the simulation results of Example 1 and Equation 3 above.

The temperature of each portion of the member to be heated in the radial direction estimated from the above simulation results was substituted for the reached temperature T in the above equation (2), and the amount of retained austenite at each portion was estimated. As a result, the rate of decrease in the amount of retained austenite in the radial direction from the second circumferential surface to the first circumferential surface of the member to be heated, that is, the rate of decrease in the amount of retained austenite with respect to the distance from the second circumferential surface is 2×10 ² volume %/m or more and 5×10 ³ volume %/m or less.

The temperature of each portion of the member to be heated in the radial direction estimated from the simulation results was substituted for the reached temperature T in the above equation (3), and the hardness of each portion was estimated. As a result, the rate of decrease in hardness in the radial direction from the second circumferential surface to the first circumferential surface of the member to be heated, that is, the rate of decrease in hardness with respect to the distance from the second circumferential surface is 5×10 ³ HV/m. It was 4×10 ⁴ HV/m or less.

Furthermore, the distribution of the amount of retained austenite in the radial direction of the member to be heated used in Example 3 was evaluated. Furthermore, the distribution of hardness in the radial direction of the heated member used in Example 3 was evaluated. The evaluation method was as described in the above embodiment.

In the heated member having a radial width of 7 mm and subjected to heat treatment at a rotational speed of 100 rpm, a temperature reached at the inner circumferential surface of 250° C., and a coolant flow rate of 20 L/min, the residual austenite decreases. The hardness reduction rate was 2×10 ² volume %/m, and the hardness reduction rate was 5×10 ³ HV/m. In the heated member having a radial width of 3 mm and subjected to heat treatment at a rotation speed of 150 rpm, a temperature reached at the inner circumferential surface of 400° C., and a coolant flow rate of 40 L/min, the residual austenite decreases. The hardness reduction rate was 5×10 ³ volume %/m, and the hardness reduction rate was 4×10 ⁴ HV/m.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the claims rather than the above description, and it is intended that equivalent meanings to the claims and all changes within the scope are included.

1 deep groove ball bearing, 10 molded body, 10A second peripheral surface, 10C first peripheral surface, 11 outer ring, 11A outer ring raceway surface, 12C inner peripheral surface, 12B outer peripheral surface, 12 inner ring, 12A inner ring raceway surface, 13 balls, 13A Rolling surface, 14 cage, 30 coil, 31 injection section.

Claims (8)

A raceway member made of hypereutectoid steel and provided in an annular shape,
a raceway surface extending along the circumferential direction;
and another surface located on the opposite side to the raceway surface in the radial direction,
The amount of retained austenite on the raceway surface is greater than the amount of retained austenite on the other surface,
The difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the other surface is 5% by volume or more,
The amount of retained austenite on the other surface is 2% by volume or less,
The variation in the amount of retained austenite on the raceway surface in the circumferential direction is 2% by volume or less,
A raceway member , wherein the raceway surface has a hardness of 750 Hv or more . Heat treatment including carbo-nitriding treatment is applied.
The raceway member according to claim 1, wherein the difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the other surface is 10% by volume or more. The raceway member according to claim 1 or 2, wherein a variation in hardness of the raceway surface in the circumferential direction is 20 HV or less. The track member according to any one of claims 1 to 3, wherein the other surface has a hardness of 600 Hv or more. The raceway member according to any one of claims 1 to 4, wherein the overall average retained austenite amount is 10% by volume or less . Any one of claims 1 to 5, wherein the rate of decrease in the amount of retained austenite in the radial direction from the raceway surface to the other surface is 2×10 ² volume %/m or more and 5×10 ³ volume %/m or less. The track member according to item 1. According to any one of claims 1 to 5, the rate of decrease in hardness in the radial direction from the raceway surface to the other surface is 5 x 10 ³ HV/m or more and 4 x 10 ⁴ HV/m or less. The track member described. an inner ring having an inner ring raceway surface and an inner diameter surface located on the opposite side of the inner ring raceway surface;
an outer ring having an outer ring raceway surface facing the inner ring raceway surface;
comprising a plurality of rolling elements in contact with the inner ring raceway surface and the outer ring raceway surface,
The inner ring is the raceway member according to any one of claims 1 to 7,
the inner ring raceway surface is the raceway surface of the raceway member,
the inner diameter surface is the other surface of the raceway member,
The rolling bearing, wherein the distance between the inner ring raceway surface and the inner diameter surface is 3 mm or more and 7 mm or less .

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