JP2023081955A - Manufacturing method of raceway member - Google Patents

Abstract

To provide a raceway member which is suppressed in a dimension change rate of a circumferential face and also is suppressed in the lowering of the hardness of a raceway surface, and a rolling bearing.SOLUTION: An inner ring 12 is composed of carbon steel, and has an inner ring raceway surface 12A extending along a peripheral direction, and an internal peripheral face 12C extending along the peripheral direction and extending along an axial direction as a circumferential face. A residual austenite quantity of the inner ring raceway surface 12A is larger than a residual austenite quantity of the internal peripheral face 12C. A difference between the residual austenite quantity of the inner ring raceway surface 12A and the residual austenite quantity of the internal peripheral face 12C is equal to or larger than 5 vol%. A variation of the residual austenite quantity of the inner ring raceway surface 12A in the peripheral direction is equal to or smaller than 2 vol%.SELECTED DRAWING: Figure 1

Description

The present invention relates to raceway members and rolling bearings.

Conventional raceway members are manufactured through heat treatment including hardening and tempering. In general, the tempering treatment is carried out by placing the entire molded article to be treated in an atmosphere furnace. A 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 aging dimensional change of the raceway member increases.

It is preferable that the dimensional change rate of the race member used in a high-temperature environment 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 fitting between the inner diameter surface of the inner ring and the shaft, and damage to the bearing can be suppressed.

Conventionally, tempering treatment for reducing the average amount of retained austenite in the entire raceway member is known as a countermeasure for keeping the rate of dimensional change of the raceway member low.

Japanese Patent Application Laid-Open No. 2017-227334 discloses a technique of tempering a steel material at a temperature of 180° C. or more and 230° C. or less in order to make the average amount of retained austenite in the entire raceway member 18% by volume or less.

JP 2017-227334 A

However, in the conventional tempering treatment method, the entire compact is tempered, so the retained austenite is decomposed in the entire compact. Furthermore, in the conventional tempering treatment method, the retained austenite is decomposed and the martensite is decomposed in the entire compact.

For this reason, conventional track members manufactured by performing the above-described tempering treatment are not expected to be used in a high-temperature environment, for example, and are manufactured without being subjected to the above-described tempering treatment. Compared to , 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 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 as compared with 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 kept low and the decrease in hardness of the raceway surface is suppressed.

A raceway member according to the present invention is a raceway member made of carbon steel and provided in an annular shape. have a surface and The amount of retained austenite on the raceway surface is greater than the amount of retained austenite on the other surfaces. The difference between the amount of retained austenite on the raceway surface and the amount of retained austenite on the other surfaces is 5% by volume or more. Variation in the amount of retained austenite on the raceway surface in the circumferential direction is 2% by volume or less.

The raceway member is subjected to heat treatment including carbonitriding 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 raceway member, the hardness of the raceway surface is 650 Hv or more. 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 race member, the amount of retained austenite in 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 above 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.

A rolling bearing according to the present invention comprises an inner ring having an inner ring raceway surface and an inner diameter surface located opposite to the inner ring raceway surface, an outer ring having an outer ring raceway surface facing the inner ring raceway surface, an inner ring raceway surface and an outer ring. and a plurality of rolling elements in 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 kept low and the decrease in hardness of the raceway surface is suppressed.

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

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

<Structure 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. 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 by an annular retainer 14. A plurality of balls 13 are provided. The central axis of the outer ring 11 is arranged so as to overlap the central axis of the inner ring 12 . The rolling bearing according to the present embodiment may be, for example, a radial roller bearing, more specifically a tapered roller bearing.

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 in the circumferential direction is formed on an 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 in the circumferential direction is formed on an outer peripheral surface 12B of the inner ring 12 . The inner ring 12 is arranged inside the outer ring 11 such 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 retainer 14 . Thereby, the plurality of balls 13 are held on the annular raceway of the outer ring 11 and the inner ring 12 so as to be free to roll. With such a configuration, the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1 are rotatable relative to each other. In addition, the inner ring 12 is the raceway 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 along the axial direction. The amount of retained austenite in the inner ring raceway surface 12A is greater than the amount of retained austenite in the inner peripheral surface 12C. The amount of retained austenite in the inner ring 12 shows a tendency to gradually decrease from the inner ring raceway surface 12A toward the inner peripheral surface 12C in the radial direction.

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

The variation in the amount of retained austenite in 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 is arranged with a first region in which the amount of retained austenite exhibits a maximum value in the circumferential direction, and the first region and the first region are spaced apart in the circumferential direction. and a second region in which the amount of austenite exhibits 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.

Variation in the amount of retained austenite in the inner peripheral surface 12C in the circumferential direction is 2% by volume or less. In other words, the inner peripheral surface 12C is arranged with a third region in which the amount of retained austenite exhibits the maximum value in the circumferential direction, and is spaced apart from the third region in the circumferential direction. and a fourth region in which the amount of austenite exhibits a minimum value. The difference between the amount of retained austenite in the third region of the inner peripheral surface 12C and the amount of retained austenite in the fourth region 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 overlapping the fourth region in the radial direction.

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 ring raceway surface 12A. Next, a second measurement point S2 displaced by θ (30°) in the circumferential direction when viewed from the first measurement point S1, and a third measurement displaced by θ (30°) in the circumferential direction when viewed from the second measurement point S2. A point S3, a fourth measurement point S4 displaced by θ (30°) in the circumferential direction when viewed from the third measurement point S3, and a fifth measurement point S4 displaced by θ (30°) in the circumferential direction when viewed from the fourth measurement point S4. A point S5 and a sixth measurement point S6 shifted by θ (30°) in the circumferential direction from the fifth measurement point S5 are set on the inner ring raceway surface 12A. In this manner, a plurality of measurement points S1 to S6 are set on the contact surface of the inner ring 12 along the circumferential direction at intervals of 30°. Each of the measurement points S1 to S6 is set at the central portion of the inner ring raceway surface 12A in the axial direction.

Furthermore, a seventh measurement point S7 located on the opposite side of the first measurement point S1 in the radial direction, an eighth measurement point S8 located on the opposite side of the second measurement point S2 in the radial direction, A ninth measuring point S9 located on the opposite side of the third measuring point S3, a tenth measuring point S10 located on the opposite side of the fourth measuring point S4 in the radial direction, and a fifth measuring point S5 in the radial direction. An eleventh measurement point S11 located on the opposite side to the radial direction, 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 of the inner ring raceway surface 12A in the circumferential direction is calculated as the difference between the maximum and minimum values of the amount of retained austenite measured at each of the measurement points S1 to S6. The variation in the amount of retained austenite of the inner peripheral surface 12C in the circumferential direction is calculated as the difference between the maximum and minimum values of the amount of retained austenite measured at the measurement points S7 to S12.

In addition, the difference between the amount of retained austenite in the inner ring raceway surface 12A and the amount of retained austenite in the inner peripheral surface 12C is obtained by measuring two of the plurality of measurement points S1 to S12 spaced apart in the radial direction. It is calculated as the minimum value of the difference in the amount of retained austenite between points.

The average amount of retained austenite in the entire 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 ring 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 peripheral surface 12C, the reduction rate of 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 higher, preferably 700 Hv or higher, and more preferably 750 Hv or higher. The hardness of the inner peripheral surface 12C is, for example, 600 Hv or more and 700 Hv or less. The hardness of each surface is measured according to the Vickers hardness test method defined in JIS (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 is arranged with a fifth region having a maximum hardness in the circumferential direction, and is spaced apart from the fifth region in the circumferential direction, and the hardness in the circumferential direction is and a sixth region in which is the minimum value. A difference in hardness between 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 overlapping with the fifth area. The second area is, for example, an area that overlaps with the sixth area.

The variation in hardness of the inner ring raceway surface 12A in the circumferential direction is calculated as the difference between the maximum and minimum hardness values measured at the measurement points S1 to S6. In addition, the difference between the hardness of the inner ring raceway surface 12A and the hardness of the inner peripheral surface 12C is the hardness between two measurement points spaced apart in the radial direction among the plurality of measurement points S1 to S12. calculated as the minimum difference in height.

From the inner ring raceway surface 12A to the inner peripheral surface 12C, the decrease rate of hardness in the radial direction is 5×10 ³ HV/m or more and 4×10 ⁴ HV/m or less. The decrease rate of 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 in the inner peripheral surface 12C compared to a conventional inner ring in which a conventional tempering treatment is performed and the inner ring raceway surface 12A has the same hardness. 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 undergone a conventional tempering treatment and that has an equal amount of retained austenite on the inner peripheral surface 12C. Therefore, the hardness of the inner ring raceway surface 12A is improved. The inner ring 12 achieves both improved dimensional stability of the inner peripheral surface 12C and improved hardness of the inner ring raceway surface 12A as compared with conventional inner rings.

The variation in the amount of retained austenite in the inner ring raceway surface 12A in the circumferential direction is suppressed to be equal to or greater than the variation in the amount of retained austenite in the raceway surface realized by conventional tempering treatment, and the present embodiment described later. It is realized by the tempering treatment according to the form of The variation in the amount of retained austenite in the inner peripheral surface 12C in the circumferential direction is suppressed more than the variation in the amount of retained austenite in the raceway surface realized by the conventional tempering treatment, and the tempering according to the present embodiment described later is suppressed. It is realized by return processing.

Furthermore, the inner ring 12 has a variation in the amount of retained austenite in the inner circumferential surface 12C in the circumferential direction compared to a conventional inner ring in which the conventional tempering treatment is performed and the inner ring raceway surface 12A has the same hardness. is reduced, variation in the dimensional change rate of the inner peripheral surface 12C in the circumferential direction is also suppressed. In addition, the inner ring 12 has a larger amount of retained austenite on the inner ring raceway surface 12A in the circumferential direction than a conventional inner ring that has undergone a conventional tempering treatment and has an equal amount of retained austenite on the inner peripheral 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 raceway surface 12A of the inner ring raceway surface 12A has variations in hardness in the circumferential direction compared to a conventional inner ring that has undergone a conventional tempering treatment and that has an equal amount of retained austenite in the inner peripheral surface 12C. is reduced by the same amount or more.

<Manufacturing method of rolling bearing>
The rolling bearing according to this embodiment is manufactured by the manufacturing method of the rolling bearing according to this embodiment shown in FIG. As shown in FIG. 3, the method of manufacturing a rolling bearing according to the present embodiment comprises a step (S10) of preparing a molded body to be the inner ring 12 (raceway member), and a quench hardening treatment of the molded body. (S20), a step (S30) of tempering the quench-hardening molded body, and a finishing step (S40) of grinding the tempered molded body. and The inner ring 12 is manufactured by the steps (S10) to (S40). Furthermore, the method of 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, for example, hypereutectoid steel. The steel material is prepared, for example, as a steel bar or steel wire. Next, processing such as cutting, forging, and turning is applied to the steel material. As a result, a steel material (formed body) formed into the approximate shape of the inner ring 12 is produced. The compact has a first circumferential surface facing radially inward and a second circumferential surface facing radially outward. Inner peripheral surface 12C of inner ring 12 is formed by grinding the first peripheral surface in a post-process (S40). Inner ring raceway surface 12A of inner ring 12 is formed by grinding the second circumferential surface in a post-process (S40).

In step (S20), a quench hardening treatment is performed on the compact prepared in the previous step (S10). In step (S20), first, the compact is subjected to carbonitriding treatment. Next, a nitrogen diffusion treatment is performed to diffuse the nitrogen that has permeated into the compact due to the carbonitriding treatment. Next, the entire compact is heated to a temperature T ₁ above point A ₁ and held for a holding time t ₁ (soaking time) for soaking. Next, the compact is cooled to a temperature _T2 below the Ms point (martensite transformation point). This cooling treatment is performed by immersing the target material in a coolant such as oil or water. As a result, the target material is quenched. In addition, the difference between the amount of retained austenite in the second peripheral surface and the amount of retained austenite in the first peripheral surface of the compact subjected to the quench hardening treatment is less than 5% by volume.

In the step (S30), a tempering treatment is performed on the formed body that has been subjected to the quench hardening treatment in the previous step (S20). In the tempering process, the first peripheral surface is locally heated by the heating unit while the second peripheral surface of the compact is locally cooled by the cooling unit. That is, the second peripheral surface is continuously cooled from the start of heating to the end of heating of the first peripheral surface. Furthermore, in the tempering process, the above-mentioned cooling and heating are performed while the formed body is relatively rotated along its circumferential direction with respect to the cooling section and the heating section.

In the tempering treatment, the first circumferential surface of the compact is heated to the tempering temperature _T3 and held for a holding time _t2 (tempering time) for soaking. The attained temperature _T4 of the second circumferential surface of the compact is kept below the tempering temperature _T3 by the cooling during the tempering process. It should be noted that the reached temperature is the maximum temperature at the site where the temperature is measured.

The tempering temperature _T3 and the holding time _t2 are set so that the amount of retained austenite in the inner peripheral surface 12C is equal to or less than a predetermined value from the viewpoint of realizing the dimensional stability required for the inner peripheral surface 12C. be. On the other hand, the attained temperature _T4 of the second peripheral surface is set so that the hardness is equal to or higher than a predetermined value from the viewpoint of realizing the hardness required for the inner ring raceway surface 12A, for example.

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

As shown in FIGS. 3 and 4, the heating is performed by induction heating, for example. A coil 30 as a heating portion is arranged in the compact 10 so as to face only the first peripheral surface 10C. Preferably, the heating is performed by high frequency induction heating. An alternating current of 3 kHz or more is supplied to the coil 30 . When the heating is performed by high-frequency induction heating, the temperature rise on the second peripheral surface 10A side in the radial direction is suppressed compared to induction heating in which an alternating current with a lower frequency is supplied to the coil 30. , the difference between the tempering temperature _T3 and the attained temperature _T4 increases. The heating is not limited to induction heating, and may be contact heating, far-infrared heating, or the like. As shown in FIG. 3, the heating section may be provided so as to heat a portion of the molded body 10 in the circumferential direction. The coil 30 is arranged, for example, so as 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 peripheral surface 10C measured by a thermocouple or the like 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 peripheral surface 10A of the compact 10. As shown in FIG. Preferably, the cooling is performed so as not to cool the first peripheral surface 10C. The cooling is performed so that the water supplied to the second peripheral surface 10A is not supplied to the first peripheral surface 10C. The injection part 31 as a cooling part is arranged, for example, so as to face only the second peripheral surface 10A in the molded body 10, and injects water to the second peripheral surface 10A. 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 so as 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, so as to face a portion of the molded body 10 in the circumferential direction in the radial direction. In addition, the cooling may be performed at least on a region of the second circumferential surface 10A that is to be ground in order to form the inner ring raceway surface 12A in the post-process (S40).

The heating and cooling are performed by rotating the compact 10 in the circumferential direction with respect to the coil 30 and the injection section 31 . The rotation is carried out, for example, by a support section (not shown) that supports the molded body 10 and a driving section that rotates the support section in the circumferential direction. The support portion is provided so as to support the downward facing end face of the molded body 10 arranged such that the axial direction thereof extends along the vertical direction, for example. A part of the support 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 heating and the cooling are performed, and the rest of the support is, for example, in the chamber. placed outside. A drive part, for example connected to the rest of the support part, is arranged outside the chamber. The rotation speed of the molded body 10 by the supporting portion and the driving portion is, for example, 100 rpm or more and 150 rpm or less.

Note that the tempering treatment may be continuously performed on a plurality of compacts 10 . In this case, the support part may be provided so as to support from below the molded body positioned at the lowest position among the plurality of molded bodies 10 stacked in the axial direction and before being put into the chamber. . That is, the entire support may be arranged outside the chamber. In this case, for example, after one of the plurality of molded bodies 10 is subjected to the tempering treatment, the molded body 10 is conveyed upward by the width of the one molded body 10 in the axial direction. The above-described tempering treatment for the compacts 10 stacked under the one compact 10 is started. The molded body 10 that has undergone the tempering treatment is carried out of the chamber through, for example, a carry-out port provided above the chamber.

The set values of the tempering temperature _T3 , the holding time _t2 , and the ultimate temperature _T4 are set based on, for example, the following Equations 1, 2, and 3.

The formula 1 is a prediction formula for predicting the relationship between the tempering temperature T ₃ (unit: °C) and the ultimate temperature T ₄ (unit: °C). The present inventors have found that the temperature in the heated member simulating the molded body when the heating is performed by induction heating on the first peripheral surface and the cooling is performed by spraying water on the second peripheral surface The distribution was simulated and analyzed. Equation 1 above is obtained by the present inventors from the results of the above simulation analysis. As a result of the analysis, it was confirmed that the ultimate temperature _T4 changes linearly with respect to the tempering temperature _T3 (see FIG. 6). Details of the simulation analysis will be described later. Note that when at least one of the heating method and the cooling method is performed by a method different from the above, Equation 1 above is changed to a prediction formula for the different method.

The above formula 2 is the ultimate temperature T (unit: K) during tempering, the holding time t ₂ (unit: seconds), and the amount of retained austenite γ (unit: volume%) on the first peripheral surface after tempering. It is a prediction formula that predicts the relationship. R in Equation 2 above is a gas constant. The retained austenite amount γ of the first circumferential surface after tempering is calculated by substituting the tempering temperature _T3 for the attained temperature T in Equation (2). The amount of retained austenite γ of the second circumferential surface after tempering is calculated by substituting the reached temperature _T4 for the reached temperature T in Equation (2). Equation 2 above is derived from Non-Patent Document 1 (Takeshi Inoue, "New Tempering Parameters and Application to Integrating Method of Tempering Effect Along Its Continuous Temperature Rise Curve," Tetsu to Hagane, 66, 10 (1980) 1533.) was experimentally obtained 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 ultimate temperature T (unit: K) during tempering, the holding time t ₂ (unit: seconds), and the hardness M (unit: HV) of the second peripheral surface after tempering. It is a prediction formula for prediction. The hardness M of the first circumferential surface after tempering is calculated by substituting the tempering temperature _T3 for the ultimate temperature T in Equation 3. The hardness M of the second circumferential surface after tempering is calculated by substituting the ultimate temperature T4 in Equation 3 for the ultimate temperature _T4 . Equation 3 was obtained experimentally 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.

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

First, from the above formula 2, the upper limit of the tempering temperature T ₃ and the holding time so that the amount of retained austenite in the first peripheral surface and the average amount of retained austenite in the entire molded body 10 are equal to or less than the predetermined value. A lower bound for _t2 is set. Furthermore, from the above Equation 3, the lower limit of the attained temperature _T4 and the upper limit of the holding time _t2 are set such that the hardness of the second peripheral surface is equal to or higher than the predetermined value. Next, from Equation 1, the upper limit of the ultimate temperature _T4 when the upper limit of the tempering temperature T3 set based on Equation ₂ is realized is estimated. Alternatively, the lower limit value of the tempering _temperature T3 when the lower limit value of the ultimate temperature T4 set based on the above formula ₃ is realized is estimated from the above formula 1. Next, based on the upper and lower limits of the tempering temperature T ₃ , the ultimate temperature T ₄ , and the holding time t ₂ estimated as described above, respective set values are determined.

In the step (S40), at least the second peripheral surface 10A of the molded body 10 is ground. Thereby, the inner ring 12 having the inner ring raceway surface 12A is formed. When the first peripheral surface 10C of the compact is not ground, the inner peripheral surface 12C is the tempered first peripheral surface. Further, when the first peripheral surface of the compact is ground, the inner peripheral surface 12C is a surface formed by grinding the tempered first peripheral surface.

In step (S50), outer ring 11 and ball 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. Thereby, the deep groove ball bearing 1 shown in FIG. 1 is manufactured.

<Modification>
In the above step (S20), the carbonitriding treatment is performed, but the carbonitriding treatment may not be performed. In this case, the amount of retained austenite in the molded body after quenching treatment is generally smaller than that when carburizing treatment is performed. Therefore, the difference between the amount of retained austenite in the inner ring raceway surface 12A and the amount of retained austenite in the inner peripheral surface 12C in this case is smaller than that in the case where the carbonitriding treatment is performed. However, even in this case, since the tempering treatment is performed, the difference is larger than that of the conventional inner ring which is not subjected to the tempering treatment. In other words, even in the inner ring 12 manufactured without the carbo-nitriding treatment, the amount of retained austenite in the inner ring raceway surface 12A and the amount of retained austenite in the inner peripheral surface 12C are reduced by the tempering treatment. The difference can be 5% by volume or more.

Further, together with the inner ring 12, the outer ring 11 may also be configured as a raceway member according to the present embodiment. In this case, the difference between the amount of retained austenite in the outer ring raceway surface 11A and the amount of retained austenite in the outer peripheral surface 11C as the 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 made of hypereutectoid steel and is a raceway member provided in an annular shape. It has an inner peripheral surface 12C located on the opposite side of the surface 12A. The amount of retained austenite on the raceway surface 12A is greater than the amount of retained austenite on the inner circumferential surface 12C. The difference between the amount of retained austenite in the raceway surface 12A and the amount of retained austenite in the inner peripheral surface 12C is 5% by volume or more. Variation in the amount of retained austenite on the raceway surface 12A in the circumferential direction is 2% by volume or less.

In the conventional tempering treatment, the entire molded body is heated in an atmosphere furnace, so the retained austenite and martensite in the region that should become the raceway surface are 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, the inner ring has a trade-off relationship between the dimensional stability of the inner diameter surface and the hardness of the raceway surface, and it has been difficult to improve both at the same time.

Also, in the tempering process, even if only the first peripheral surface of the molded body is locally heated, if the second peripheral surface is not locally cooled, the second peripheral surface in the tempering process The surface reaches a higher temperature, and decomposition of retained austenite and martensite proceeds. As a result, the difference between the retained austenite amount on the raceway surface and the retained austenite amount on the inner diameter surface was 5 volumes even in the inner ring as the second comparative example manufactured by the tempering treatment in which only the heating was performed and the cooling was not performed. %. As a result, even in this 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 at the same time.

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

As a result, in the inner ring 12, the amount of retained austenite on the inner ring raceway surface 12A is greater than that of 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 inner ring of the first and second comparative examples. 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 peripheral surface 12C and the hardness of the inner ring raceway surface 12A are simultaneously enhanced as compared with the inner rings of the first and second comparative examples.

In addition, in the inner ring 12, the amount of retained austenite in the inner peripheral surface 12C is the same as that of the inner rings in the first and second comparative examples, and the amount of retained austenite in the inner ring raceway surface 12A is the same as in the first comparative example. and can 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 peripheral surface 12C is equivalent to that of the inner rings of the first and second comparative examples, and the hardness of the inner ring raceway surface 12A is the same as that of the inner rings of the first and second comparative examples. This is greatly improved compared to that of the inner ring of the second comparative example.

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 and second comparative examples, 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 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 the same as that of the inner rings of the first and second comparative examples, and the dimensional stability of the inner peripheral surface 12C is the same as that of the first and second comparative examples. This is greatly improved compared to that of the inner ring of the second comparative example.

In addition, as described above, the coil 30 and the injection section 31 are provided so as 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 it is applied to the compact 10 fixed by the heating, the magnetic flux density decreases in the vicinity of the connection between the annular portion of the coil 30 and the lead portions connected to both ends of the annular portion, and the radial direction of the member to be heated is reduced. There is a possibility that the temperature of the portion of the heated member that is arranged to face the connection point in the above may be lower than the temperature of the other portion of the heated member that is arranged to face the annular portion in the radial direction.

In contrast, in the tempering process according to the present embodiment, the heating and the cooling are performed by rotating molded body 10 in the circumferential direction with respect to coil 30 and jetting section 31 . The inner ring 12 is manufactured by performing the tempering treatment according to the present embodiment. Therefore, even if the coil 30 and the injection part 31 are provided so as to heat and cool a part of the molded body 10 in the circumferential direction as described above, the inner peripheral surface 12C formed based on the first peripheral surface The variation in the amount of retained austenite in the inner ring raceway surface 12A formed on the basis of the second circumferential surface and the second circumferential surface is 2% by volume or less in the circumferential direction. As a result, in the inner ring 12, the variation in the amount of retained austenite of the inner ring raceway surface 12A in the circumferential direction is the same as that when the molded body 10 fixed to the coil 30 and the injection portion 31 is subjected to the heating and the cooling. reduced by comparison. Furthermore, in the inner ring 12, the variation in the amount of retained austenite on the inner peripheral surface 12C in the circumferential direction is similar to that in the case where the molding 10 fixed to the coil 30 and the injection part 31 is subjected to the above heating and cooling. reduced in comparison. In such an inner ring 12, the dimensional stability of the inner circumferential surface 12C in the circumferential direction is higher than in the case where the heating and cooling are applied to the compact 10 fixed to the coil 30 and the injection portion 31. Variation and variation in hardness of the inner ring raceway surface 12A in the circumferential direction are reduced at the same time.

In addition, when the heating unit and the cooling unit for performing the tempering treatment are provided so as to heat and cool the entire molded body 10 in the circumferential direction, such a heating unit and the cooling unit is more expensive than the coil 30 and the injection part 31, so the manufacturing cost of the inner ring also increases. In other words, the inner ring 12 is less expensive to manufacture than an inner ring manufactured using such a heating section and a cooling section. 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 carbonitriding. 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 can be 10% by volume or more. Therefore, in such an inner ring 12, the dimensional stability of the inner peripheral 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 and second comparative examples.

The tempering treatment according to the present embodiment can suppress the decomposition of the martensite on the second peripheral surface of the formed body as compared with the conventional tempering treatment. Therefore, the hardness of the inner ring raceway surface 12A of the inner ring 12 can be 650 Hv or more. That is, the hardness of the inner ring raceway surface 12A can exceed the hardness of the inner ring raceway surfaces of the first and second comparative examples. Furthermore, as described above, the tempering treatment according to the present embodiment reduces the variation in the amount of retained austenite in the inner ring raceway surface 12A in the circumferential direction 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 the inner ring of the deep groove ball bearing 1 or tapered roller bearing, which is a radial bearing, and the inner peripheral surface 12C is a surface located on the opposite side of the inner ring raceway surface 12A in the radial direction. The deep groove ball bearing 1 including the inner ring 12 has the dimensional stability of the inner peripheral surface 12C and the hardness of the inner ring raceway surface 12A at the same time as compared with the deep groove ball bearings including the inner rings of the first and second comparative examples. It has a long service life because it is enhanced.

(Example 1)
A simulation analysis was performed with respect to the tempering process according to the embodiment described above. Simulation analysis was performed by heat conduction analysis using the finite element method. First, the member to be heated simulating the above compact was a ring made of JIS SUJ2 and having a thickness of 3 mm in the axial direction. Also, the member to be heated was subjected to the above quenching treatment. The tempering process was simulated for this heated member using the analysis model shown in FIG. 5, and the temperature distribution inside the heated member at that time was analyzed. In this analysis model, tempering conditions were set such that the first peripheral surface of the compact was heated by induction heating, and the second peripheral surface was cooled by water cooling. Also, water cooling was simulated by giving an appropriate heat transfer coefficient to the second circumferential surface. In such an analysis model, the temperature distribution inside the compact was analyzed when the heating temperature for 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. 6 and 7 show the analysis results.

FIG. 6 shows the difference between the heating temperature and the temperature of the second peripheral surface that is subjected to the cooling 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 showing the relationship. The horizontal axis of FIG. 6 indicates the heating temperature (unit: °C) for the first peripheral surface, and the vertical axis of FIG. 6 indicates the reached temperature (unit: °C) of the second peripheral surface. As shown in FIG. 6, the reached temperature of the second peripheral surface changed linearly with respect to the heating temperature of the first peripheral surface. Equation 1 was derived from the graph of FIG. From FIG. 6, 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 amount of retained austenite on the first peripheral surface and the second 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 member to be heated when 30 seconds have passed since the heating with the heating temperature of 350° C. for the first circumferential surface and the cooling described above. As shown in FIG. 7, the temperature inside the heated member gradually decreases from the first peripheral surface toward the second peripheral surface, and the amount of decrease in the temperature of the first peripheral surface is the same as that of the first peripheral surface. It was confirmed that it changed linearly with the distance from Moreover, 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 machining allowance in the grinding process in the step (S50) is taken into consideration.

Moreover, the heating and cooling shown in FIG. 7 were performed on a heated member having a retained austenite amount of 14.4% by volume and a hardness of 780 Hv in the first and second peripheral surfaces before tempering treatment. When the amount of retained austenite in the first peripheral surface is 2% by volume or less and the hardness of the first peripheral surface is 680Hv, the amount of retained austenite in the second peripheral 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 effect of the variation in the temperature of 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 (reaching 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 maximum temperature and the difference Δγ between the amount of retained austenite when heated at the maximum temperature and the amount of retained austenite when heated at the minimum temperature It is a graph showing. The amount of retained austenite when heated at the maximum temperature is obtained by substituting the maximum temperature for the reached temperature T (unit: K) in the above formula (2), and the holding time is the holding time t ₂ ( unit: seconds). The amount of retained austenite when heated at the minimum temperature is obtained by substituting the minimum temperature for the reached temperature T (unit: K) in the above formula (2), and the holding time is the holding time t ₂ ( unit: seconds).

The horizontal axis of FIG. 8 indicates the maximum temperature (unit: ° C.), and the vertical axis of FIG. 8 indicates the difference between the amount of retained austenite when heated at the minimum temperature and the amount of retained austenite when heated at the maximum temperature. Δγ (unit: volume %) is shown. In FIG. 8, 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 the relationship between the maximum temperature and the amount of retained austenite when the temperature difference ΔT is 50° C. A graph showing the relationship between 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 temperature variation of the inner peripheral surface in the circumferential direction is represented 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 the retained austenite. The amount difference 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. Moreover, the maximum temperature at which the difference Δγ in the amount of retained austenite exhibits the maximum value was higher as the temperature difference ΔT was larger. The maximum value of the difference Δγ in the amount of retained austenite is 2.8% by volume when the temperature difference ΔT is 20°C, 6.6% by volume when the temperature difference ΔT is 50°C, and 9.6% by 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. difference is 2% by volume or more.

In FIG. 8, in the graph when the temperature difference ΔT is 20 ° C., the maximum temperature is 290 ° C. The plot shows the amount of retained austenite when heated to 290 ° C. and the amount of retained austenite when heated to 270 ° C. difference is 2% by volume or less. In FIG. 8, the plot where 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. difference is 1% by volume or less.

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 5 is a graph showing the relationship between the highest temperature and the difference ΔHV between the hardness when heated at the highest temperature and the hardness when heated at the lowest temperature, when the time is 1 minute. The hardness when heated at the maximum temperature is obtained by substituting the maximum temperature for the reaching temperature T (unit: K) in the above formula (3), and the holding time is the holding time t ₂ (unit: K) in the formula (3). : seconds). The hardness when heated at the lowest temperature is obtained by substituting the lowest temperature for the reaching temperature T (unit: K) in the above formula (3), and the holding time is the holding time t ₂ (unit: K) in the formula (3). : seconds).

The horizontal axis of FIG. 9 indicates the maximum temperature (unit: ° C.), and the vertical axis of FIG. 9 indicates the difference ΔHV (unit: HV). In FIG. 9, a graph showing the relationship between the maximum temperature and the difference ΔHV in hardness when the temperature difference ΔT is 20° C., and the difference in hardness and the maximum temperature when the temperature difference ΔT is 50° C. 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 temperature variation 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 hardness variation of the inner peripheral surface in the circumferential direction is the hardness. The difference is expressed as ΔHV.

As shown in FIG. 9, the greater the temperature difference ΔT, the greater the hardness difference ΔHV. Moreover, the maximum temperature at which the difference ΔHV in hardness shows the maximum value was higher as the temperature difference ΔT was larger. The maximum hardness difference ΔHV was 10.6 HV when the temperature difference ΔT was 20°C, 28.0 HV when the temperature difference ΔT was 50°C, and 47.3 HV 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 each plot where the maximum temperature is 350 ° C. or higher in the graph when the temperature difference ΔT is 20 ° C., the difference between the hardness when heated to 350 ° C. or higher and the hardness when heated to 330 ° C. or higher is 10 HV. It shows that:

That is, in the calculation results shown in FIGS. 8 and 9, the smaller the variation in the temperature of the outer peripheral surface in the circumferential direction, the more suppressed the variation in the amount of retained austenite and the variation in hardness on the outer peripheral surface in the circumferential direction. .

(Example 3)
Each temperature and each temperature change of the first peripheral surface and the second peripheral surface of the formed body in the tempering treatment according to the embodiment described above were evaluated. First, a plurality of members to be heated, which were made of SUJ2 specified in JIS and were provided in a ring shape, were prepared. The radial width of each member to be heated, that is, the distance between the inner peripheral surface and the outer peripheral surface was set to 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 region in the peripheral direction of each heated member and the 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 area was arranged so as to overlap the thermocouple fixed to the outer peripheral surface of the partial area in the radial direction.

Next, as an example, each member to be heated to which a thermocouple was attached was subjected to the above heating and cooling in the tempering process according to the above embodiment. Specifically, when the inner peripheral surface of the member to be heated is induction-heated by the heating portion while the member to be heated is supported by the supporting portion and rotated in the circumferential direction of the member to be heated by the driving portion. 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 region of the member to be heated to which the thermocouple is fixed and the heating unit and the cooling unit changes as the member to be heated is rotated by the driving unit. It was carried out under heating conditions. The heating and cooling were started at the same timing.

The number of revolutions of the member to be heated by the drive unit was set to 100 rpm or more and 150 rpm or less. The heating by the heating unit was feedback-controlled so that the temperature of the inner peripheral surface measured by the thermocouple approaches a predetermined heating temperature (soaking temperature) of the inner peripheral surface. Feedback control was performed using a DA converter and a programmable logic controller. The flow rate of the coolant injected from the cooling unit to the outer peripheral surface of the member to be heated was set to 20 L/min or more and 40 L/min or less. Changes in the temperatures of the inner and outer peripheral surfaces of the members to be heated in such heat treatment were evaluated.

FIG. 10 and FIG. 11 show typical evaluation results for a member to be heated having a width of 3 mm in the radial direction at a rotational speed of 100 rpm, a temperature reached on the inner peripheral surface of 250° C., and a coolant flow rate of 20 L. /min is a graph showing temperature changes when heat treatment is performed. 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 temperatures of the inner and outer peripheral surfaces (unit: °C). FIG. 11 is a partially enlarged view showing temperature changes within a predetermined time period after the temperature of the inner peripheral surface reaches a predetermined temperature, among the temperature changes of the inner peripheral surface shown in FIG.

As shown in FIGS. 10 and 11, the temperature of the inner peripheral surface reached a predetermined temperature of 250° C., and then changed in a wavy manner within the temperature range of 240° C. or more and 260° C. or less. . As shown in FIG. 11, after the temperature of the inner peripheral surface reaches the target temperature, the amplitude of the temperature change of the inner peripheral surface is 15° C. or less, and the frequency of the temperature change of the inner peripheral surface is that of the heated member. It was almost the same as the number of revolutions. From this result, the temperature change of the inner peripheral surface after the temperature of the inner peripheral surface reaches the target temperature is mainly due to the distance between the partial region of the member to be heated and the heating section and the cooling section. It was confirmed that this was caused by the change.

As shown in FIG. 10, the temperature of the outer peripheral surface, after reaching 100° C., changed in a wave-like manner within the temperature range of 80° C. or higher and 120° C. or lower. 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 peripheral surface reached 250° C., the amplitude of the temperature change of the outer peripheral surface was 30° C. or less, and the frequency of the temperature change of the outer peripheral surface was substantially equal to the rotational speed of the heated member. In the member to be heated shown in FIGS. 10 and 11, the heat transfer coefficient on the outer peripheral surface was about 19000 W/m ² K. Furthermore, in the heated member according to the example, no uneven discoloration due to surface oxidation after heating was observed.

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

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

Furthermore, it was confirmed that the temperature change of the outer peripheral surface after the temperature of the inner peripheral surface reaches the target temperature while the member to be heated is rotated depends mainly on the rotation speed of the member to be heated. Furthermore, considering other evaluation results not shown in FIGS. 10 and 11, the heat transfer coefficient on the outer peripheral surface depends on the number of rotations of the heated member by the drive section and the amount of heat supplied to the heated member by the cooling section. It was confirmed that it is controlled by the flow rate of the cooling liquid, etc.

(Example 4)
Regarding the tempering treatment according to the embodiment described above, the effect 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 above. Similarly, the effect 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 simulation results was substituted for the ultimate temperature T in the above equation (2) to estimate the amount of retained austenite in each portion. As a result, the rate of decrease in the amount of retained austenite in the radial direction from the second peripheral surface to the first peripheral surface of the heated member, that is, the rate of decrease in the amount of retained austenite with respect to the distance from the second peripheral surface was 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 ultimate 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 peripheral surface to the first peripheral surface of the member to be heated, that is, the rate of decrease in hardness with respect to the distance from the second peripheral surface was 5×10 ³ HV/m. It was more than 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 hardness distribution in the radial direction of the member to be heated used in Example 3 was evaluated. The evaluation method was as described in the above embodiment.

In the heated member having a width of 7 mm in the radial direction and subjected to heat treatment at a rotation speed of 100 rpm, an inner peripheral surface temperature of 250 ° C., and a cooling liquid flow rate of 20 L / min, the decrease in retained austenite The rate of decrease was 2×10 ² volume %/m, and the rate of decrease in hardness was 5×10 ³ HV/m. In the heated member having a width of 3 mm in the radial direction and subjected to heat treatment at a rotation speed of 150 rpm, an inner peripheral surface temperature of 400 ° C., and a cooling liquid flow rate of 40 L / min, the decrease in retained austenite The rate of decrease was 5×10 ³ volume %/m, and the decrease rate of hardness was 4×10 ⁴ HV/m.

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

Reference Signs List 1 deep groove ball bearing 10 compact 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 ball 13A rolling surface, 14 retainer, 30 coil, 31 injection part.

Claims (9)

A track member made of carbon steel and provided in an annular shape,
a raceway surface extending along the circumferential direction;
and another surface located on the opposite side of 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 surfaces,
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,
A raceway member, wherein variation in the amount of retained austenite in the raceway surface in the circumferential direction is 2% by volume or less. Heat treatment including carbonitriding treatment is applied,
2. The raceway member according to claim 1, wherein the difference between the amount of retained austenite on said raceway surface and the amount of retained austenite on said other surface is 10% by volume or more. The raceway surface has a hardness of 650 Hv or more,
3. The raceway member according to claim 1, wherein variation in hardness of said raceway surface in said 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 amount of retained austenite in said other surface is 5% by volume or less. The track member according to any one of claims 1 to 5, wherein the average amount of retained austenite in the whole is 10% by volume or less. 7. 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, according to any one of claims 1 to 6. The track member according to item 1. 7. The method according to any one of claims 1 to 6, wherein the decrease rate of hardness in the radial direction from the raceway surface to the other surface is 5× ¹⁰ HV/m or more and 4×10 ⁴ HV/m or less. A track member as described. an inner ring having an inner ring raceway surface and an inner diameter surface located 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 in contact with the inner ring raceway surface and the outer ring raceway surface,
wherein the inner ring is the raceway member according to any one of claims 1 to 8,
The inner ring raceway surface is the raceway surface of the raceway member,
A rolling bearing, wherein the inner diameter surface is the other surface of the raceway member.

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