JP2021011606A - Method for manufacturing bearing components - Google Patents

Abstract

To provide a method for manufacturing bearing components, in which a condition that satisfies a calculation formula for a tempering condition after hardening a bearing component is used by providing the calculation formula.SOLUTION: In a method for manufacturing bearing components, at first, a bearing component is prepared which is formed with a high carbon chromium bearing steel. The component is quenched so that surface hardness thereof becomes 64HRC or more and 66HRC or less. After the quenching step, the component is tempered under a temperature condition and a time condition that satisfy the following formula 1.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for manufacturing a component of a bearing, and particularly to a method for heat-treating the component.

When the bearing is used in a high temperature environment, the dimensional change of the component occurs due to the decomposition of the retained austenite contained in the metal structure of the component. Changes in the dimensions of the components lead to deterioration of rotational accuracy and damage such as creep. For this reason, bearings used in a high temperature environment are subjected to a treatment for suppressing dimensional changes.

One such process is, for example, the so-called subzero process disclosed in Japanese Patent Application Laid-Open No. 2002-3937 (Patent Document 1). The sub-zero treatment is a treatment for transforming retained austenite into martensite by cooling the components of the bearing after quenching below the freezing point.

Another such treatment is a tempering treatment under conditions stronger than usual. That is, the components of the bearing after quenching are tempered at a temperature higher than usual. As a result, the retained austenite in the component can be decomposed.

JP-A-2002-3937

In recent years, from the viewpoint of improving thermal efficiency and reducing environmental load, tempering treatment may be carried out by induction heating instead of an atmospheric furnace. However, induction heating is less productive than atmospheric furnaces. Therefore, when induction heating is used for the tempering treatment, high-temperature short-time heating is adopted from the viewpoint of compensating for low productivity. However, in that case, no tempering condition has been found at present for reducing the strain in a high temperature environment such as holding the temperature at 250 ° C. for 2500 hours so as to be within an allowable range.

The present invention has been made in view of the above problems. An object of the present invention is to provide a method for manufacturing bearing components in which distortion is suppressed in a high temperature environment.

In the method for manufacturing bearing components of the present invention, first, bearing components made of high carbon chromium bearing steel are prepared. The component is quenched so that the surface hardness is 64 HRC or more and 66 HRC or less. After the quenching step, the component is tempered under temperature and time conditions that satisfy the following equations.

If the tempering process is performed under the conditions satisfying the calculation formula provided by the present invention, the amount of strain of the processed component in a high temperature environment can be within an allowable range.

It is schematic cross-sectional view which shows an example of the structure of the bearing including the component part which concerns on this embodiment. It is a flowchart which shows roughly the manufacturing method of the component part of the bearing in this embodiment. It is the schematic which shows the mode of the test piece used for the evaluation of the manufacturing method of the component part of a bearing in this embodiment. It is a schematic diagram which shows the mode in which the tempering process is performed on the component part of a bearing in this Example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, with reference to FIG. 1, an example of a bearing composed of components that are tempered under the conditions according to the present embodiment will be described. FIG. 1 is a schematic cross-sectional view showing an example of a bearing configuration including components according to the present embodiment. With reference to FIG. 1, the bearing including the component according to the present embodiment is, for example, a deep groove ball bearing 10 (rolling bearing). The deep groove ball bearing 10 has an outer ring 11, an inner ring 12, and a ball 13 as constituent parts. The outer ring 11 has an outer ring rolling surface 11a on the inner peripheral surface. The inner ring 12 has an inner ring rolling surface 12a on the outer peripheral surface, and is arranged inside the outer ring 11 so that the inner ring rolling surface 12a faces the outer ring rolling surface 11a. The ball 13 has a rolling surface 13a and is arranged along the annular trajectory of the outer ring 11 and the inner ring 12. With such a configuration, the outer ring 11 and the inner ring 12 of the deep groove ball bearing 10 can rotate relative to each other. The balls 13 as these rolling parts are held together by the cage 14.

The outer ring 11 and the inner ring 12 as constituent parts of the deep groove ball bearing 10 are formed of, for example, JIS standard SUJ2 material, which is one of high carbon chrome bearing steels. Hereinafter, a method of manufacturing the bearing components of the present embodiment will be described with reference to FIG.

FIG. 2 is a flowchart schematically showing a method of manufacturing bearing components according to the present embodiment. With reference to FIG. 2, first, the bearing components are prepared (S10). Specifically, for example, the outer ring 11 or the inner ring 12 of the deep groove ball bearing 10 shown in FIG. 1 is prepared. That is, in this step, the outer ring 11 or the inner ring 12 which is a component of the deep groove ball bearing 10 formed by JIS standard SUJ2 as a high carbon chrome bearing steel is prepared.

Next, the outer ring 11 or the inner ring 12 prepared in the step (S10) is quenched (S20). In the quenching step, the heated state is maintained for the above time, so that the volume ratio of carbides in the bearing components such as the outer ring 11 or the inner ring 12 after the quenching step (S20) is increased. The components are heated to 8% or more and 12% or less. As a method for measuring the volume ratio, there are a method for measuring the area ratio of carbides on the cut surface by image processing, an X-ray diffraction method, and the like.

After the heated state of the bearing component is maintained, the component is put into oil. As a result, the component is cooled and hardened so that its surface hardness is 64 HRC or more and 66 HRC or less. As described above, the component is hardened.

Next, after the above quenching step, the component is tempered (S30). In the present embodiment, it is preferable that high frequency induction heating is used in the tempering step (S30). That is, for example, a method is used in which a component to be processed is inserted into a space inside an induction coil that is wound a plurality of times, and a current is passed through the induction coil in that state to generate heat. At this time, the component is tempered under temperature and time conditions that satisfy the above formula (1).

In the above formula (1), T is the temperature of the surface of the component at the time of tempering (unit is K), and t is the time (unit is s) to keep the temperature of the surface of the component at the above temperature for tempering. Shown. Hereinafter, it is preferable to satisfy the above formula (1) as Example 1.

A test piece imitating the component parts of the deep groove ball bearing 10 was prepared, and the test piece was used for quenching treatment and tempering treatment in the same manner as the component parts. A test was conducted to determine whether or not the finished state was possible by comparing the dimensions before and after the heat treatment and measuring the strain.

The test was performed according to the procedure shown in FIG. With reference to FIG. 2 again, a test piece was first prepared (S10). Specifically, a test piece having a mode as shown in FIG. 3 was prepared. FIG. 3 is a schematic view showing an aspect of a test piece used for evaluating a method for manufacturing a bearing component in the present embodiment. With reference to FIG. 3, the test piece 20 used in this test is made of, for example, the same material as the outer ring 11 or inner ring 12 of the deep groove ball bearing 10 of FIG. That is, the test piece 20 was formed according to JIS standard SUJ2 as a high carbon chrome bearing steel. Further, the test piece 20 has a shape similar to that of the outer ring 11 or the inner ring 12 of FIG. That is, the test piece 20 was formed so as to have an annular shape in a plan view. The annular portion of the test piece 20 at the time of molding had an outer diameter A of 60 mm and an inner diameter B of 54 mm. The width C of the test piece 20 was set to 15 mm. In this way, the test piece 20 as a component of the bearing was prepared. Six test pieces 20 were prepared.

More specifically, high carbon chrome bearing steel SUJ2 was used for the test piece 20. Its chemical composition is as shown in Table 1 below. The unit of the numbers in the table is mass%. That is, for example, the carbon contained in the test piece 20 is 0.98% by mass.

With reference to FIG. 2 again, the prepared test piece 20 was then quenched (S20). The test piece 20 is heated so that the volume ratio of the carbides in the test piece 20 after the quenching step (S20) is 8% or more and 12% or less by maintaining the heated state for the above time. Was done.

After the test piece 20 was kept in a heated state, the test piece 20 was put into oil. As a result, the test piece 20 was cooled and cured so as to be 64 HRC or more and 66 HRC or less. As described above, the test piece 20 was quenched.

Next, after the above quenching step, the test piece 20 was tempered (S30). Specifically, each of the six test pieces 20 was tempered under the conditions of the surface temperature (tempering temperature) and the tempering time of the test pieces 20 at the time of different tempering as shown in Table 2 described later. That is, the test piece 1A, which is one of the six test pieces 20 (the same applies hereinafter), was tempered at a tempering temperature of 410 ° C. for 10800 seconds (3 hours). The test piece 2A was tempered at a tempering temperature of 420 ° C. for 7200 seconds (2 hours). The test piece 3A was tempered at a tempering temperature of 430 ° C. for 3600 seconds (1 hour). The test piece 4A was tempered at a tempering temperature of 440 ° C. for 3600 seconds (1 hour). The above test pieces 1A, 2A, 3A, and 4A satisfy the relationship of the inequality sign of the formula (1) by substituting the tempering temperature and the tempering time into the above formula (1). That is, the test pieces 1A, 2A, 3A, and 4A are test pieces as the present embodiment (the determination by the formula (1) is "OK"). That is, the test piece as this example is tempered under the temperature condition and the time condition satisfying the formula (1).

On the other hand, the test piece 1B was tempered at a tempering temperature of 410 ° C. for 3600 seconds (1 hour). The test piece 2B was tempered at a tempering temperature of 420 ° C. for 1800 seconds (0.5 hours). The above test pieces 1B and 2B do not satisfy the relationship of the inequality sign of the formula (1) by substituting the tempering temperature and the tempering time into the above formula (1). That is, the test pieces 1B and 2B are test pieces as comparative examples (the judgment by the formula (1) is "NG").

The tempering process was performed by the following method. FIG. 4 is a schematic view showing a mode in which a tempering step is performed on the component parts of the bearing in this embodiment. With reference to FIG. 4, high frequency induction heating using the induction coil 30 was used in the tempering step. That is, the test piece 20 to be processed is inserted into the space inside the induction coil 30 that is wound a plurality of times at intervals in the vertical direction of FIG. In this state, a current I1 is passed through the induction coil 30. The direction of flow of this current I1 is reversed at regular intervals. In this way, a magnetic field is generated in the space inside the induction coil 30 due to the current I1 flowing through the induction coil 30. Then, the test piece 20 generates heat due to the induced loss. Further, if the direction in which the current I1 flows changes, the magnetic field inside the induction coil 30 also changes. Due to this change in the magnetic field, an eddy current due to electromagnetic induction flows. If an eddy current flows through the test piece 20, the test piece 20 generates heat. As described above, heat generation due to the induced loss and the eddy current is generated in the test piece 20. Tempering treatment was performed using this heat generation.

At the stage when the above tempering treatment was completed, the dimensions of each test piece 20 were measured. Specifically, the outer diameter A, inner diameter B, and width C (see FIG. 2) of each of the test pieces 1A to 4A and 1B to 2B were measured.

Next, after the above measurement, each test piece 20 was kept warm in the air at 250 ° C. for 2500 hours. After keeping warm in the air, the dimensions of each test piece 20 were measured again. Again, the outer diameter A, inner diameter B and width C (see FIG. 2) of each of the test pieces 1A to 4A and 1B to 2B were measured. The strain values of the outer diameter A, the inner diameter B, and the width C were obtained from the dimensions of each test piece 20 before and after the heat retention in the atmosphere for 2500 hours. The average value of the three strain values of A, B, and C was determined to be the strain value of the entire test piece 20. If the value of the strain is 2.0 × 10 ^-4 or less, the tempering condition is considered to be suitable for the test piece, and the judgment based on the strain is “OK”. On the other hand, if the value of the strain exceeds 2.0 × 10 ^-4 , the tempering condition is not suitable for the test piece, and the judgment based on the strain is “NG”.

The conditions of the tempering process of each test piece treated as described above and the evaluation results are shown in Table 2 below.

From Table 2, the test piece 20 that was tempered under the conditions of the tempering temperature and the tempering time satisfying the above formula (1) can suppress the strain generated after being kept warm in the high temperature atmosphere for a long period of time within an allowable range. It turned out. On the other hand, from Table 2, the test piece 20 that was tempered under the conditions of the tempering temperature and the tempering time that did not satisfy the above formula (1) had a strain generated after being kept warm in the high temperature atmosphere for a long period of time from the allowable range. Was also found to grow.

The features described this time may be applied so as to be appropriately combined within a technically consistent range.

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

10 Deep groove ball bearings, 11 outer ring, 11a outer ring rolling surface, 12 inner ring, 12a inner ring rolling surface, 13 balls, 13a rolling surface, 14 cage, 20 test piece, 30 induction coil.

Claims (3)

The process of preparing bearing components made of high carbon chrome bearing steel,
A step of quenching the component parts so that the surface hardness is 64 HRC or more and 66 HRC or less.
A method for manufacturing a bearing component, comprising: after the quenching step, the component is tempered under temperature and time conditions that satisfy the following equations.

The bearing according to claim 1, wherein in the quenching step, the component is heated so that the volume ratio of carbides in the component after the quenching step is 8% or more and 12% or less. How to manufacture the components of. The method for manufacturing a bearing component according to claim 1 or 2, wherein high-frequency induction heating is used in the tempering step.

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