JP7378201B2 - Manufacturing method of bearing parts - Google Patents

Description

The present invention relates to a method of manufacturing a bearing component.

Tempering is an important heat treatment to improve the dimensional stability of bearing components. Bearing parts for bearings used in high-temperature environments are required to have greater dimensional stability. Therefore, bearing parts of bearings used in high-temperature environments are tempered under stronger conditions (longer time, higher temperature) than usual.

In recent years, from the viewpoint of improving thermal efficiency and reducing environmental impact, tempering is sometimes performed by induction heating instead of heating in an atmospheric furnace. Tempering by induction heating is disadvantageous from the viewpoint of productivity compared to tempering by heating in an atmospheric furnace. In order to compensate for such disadvantages, in tempering by induction heating, heating is performed at a higher temperature and in a shorter time than in tempering by heating in an atmospheric furnace.

As tempering by induction heating, for example, the tempering method described in Patent Document 1 (Japanese Unexamined Patent Publication No. 2013-221199) is known. In the tempering method described in Patent Document 1, tempering is performed by heating at a temperature of 180° C. or more and 300° C. or less for 3 seconds or more and 10 seconds or less.

Japanese Patent Application Publication No. 2013-221199

However, according to the findings of the present inventors, the bearing parts of a bearing tempered according to the tempering method described in Patent Document 1 have a lower dimensional change rate after long-term use in a high-temperature environment. There is room for improvement.

The present invention has been made in view of the problems of the prior art as described above. More specifically, the present invention provides a method for manufacturing a bearing component that can improve the rate of dimensional change after long-term use in a high-temperature environment.

A method for manufacturing a bearing component according to one embodiment of the present invention includes the steps of: hardening a workpiece made of high carbon chromium bearing steel to form a hardened layer; and tempering the workpiece. and a process. The hardening is performed so that the hardness of the hardened layer is 64HRC or more and 68HRC or less. Tempering is performed so that the relationship -logt+1.13×10 ⁴ /T<17.9 is satisfied, where the heating temperature is T (unit: Kelvin) and the holding time is t (unit: seconds). be exposed.

In the method for manufacturing a bearing component described above, the quenching may be performed such that the area ratio of carbide in the quenched hardened layer is 8% or more and 12% or less.

In the above method for manufacturing a bearing component, heating during tempering may be performed by high frequency induction heating.

In the above method for manufacturing a bearing component, the heating time for tempering may be 260° C. or more and 320° C. or less, and the holding time for tempering may be 300 seconds or more and 3600 seconds or less.

In the above method for manufacturing bearing parts, after being held at 160°C in the atmosphere for 2500 hours, the external dimensional change rate of the workpiece after tempering is 2 x 10 ^-4 or less. Good too.

In the above method for manufacturing a bearing component, the high carbon chromium bearing steel may be SUJ2 defined in the JIS standard.

According to the method for manufacturing a bearing component according to one aspect of the present invention, the rate of dimensional change after long-term use in a high-temperature environment can be improved.

FIG. 2 is a top view of a bearing component according to an embodiment. FIG. 2 is a sectional view taken along line II-II in FIG. 1; FIG. 3 is a process diagram showing a method for manufacturing a bearing component according to an embodiment. It is a top view of the workpiece member 20 prepared in preparation process S1. 5 is a sectional view taken along line VV in FIG. 4. FIG.

Details of embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and overlapping explanations will not be repeated.

(Configuration of bearing parts according to embodiment)
Below, the structure of the bearing component according to the embodiment will be explained.

FIG. 1 is a top view of a bearing component according to an embodiment. FIG. 2 is a sectional view taken along line II-II in FIG. As shown in FIGS. 1 and 2, the bearing component according to the embodiment is, for example, an inner ring 10 of a rolling bearing. Although the bearing component according to the embodiment is not limited to this, the inner ring 10 will be described below as an example.

The inner ring 10 has an upper surface 10a, a bottom surface 10b, an inner circumferential surface 10c, and an outer circumferential surface 10d. The top surface 10a and the bottom surface 10b constitute end surfaces in the direction along the central axis 10e of the inner ring 10. The bottom surface 10b is the opposite surface to the top surface 10a.

The inner peripheral surface 10c and the outer peripheral surface 10d are continuous with the top surface 10a and the bottom surface 10b. The outer peripheral surface 10d constitutes a raceway surface of the inner ring 10. A raceway groove is formed on the outer peripheral surface 10d. In the raceway groove, the outer circumferential surface 10d is depressed toward the inner circumferential surface 10c. The shape of the raceway groove is partially circular in cross-sectional view.

The inner ring 10 has a ring-like shape in plan view (when viewed from a direction perpendicular to the top surface 10a and the bottom surface 10b).

Inner ring 10 is made of steel, for example. The steel that constitutes the inner ring 10 is, for example, bearing steel. The steel constituting the inner ring 10 is preferably high carbon chromium bearing steel defined in the JIS standard (JIS G 4805:2008). It is more preferable that the steel forming the inner ring 10 is SUJ2 defined in the JIS standard (JIS G 4805:2008).

The inner ring 10 has a hardened layer 10f. The hardened layer 10f is arranged on the surface of the inner ring 10. More specifically, the hardened layer 10f is arranged on the top surface 10a, the bottom surface 10b, the inner peripheral surface 10c, and the outer peripheral surface 10d.

The hardness of the inner ring 10 in the hardened layer 10f is preferably 60HRC or less. The hardness of the inner ring 10 in the quench hardened layer 10f is determined according to the method specified in the JIS standard (JIS Z 2245:2011).

The dimensional change rate of the inner ring 10 after being maintained at 160° C. for 2500 hours in the atmosphere is 2×10 ⁻⁴ or less. The dimensional change rate after being held at 160° C. for 2500 hours in the atmosphere is preferably 1.5×10 ⁻⁴ or less. It is more preferable that the dimensional change rate after being held at 160° C. for 2500 hours in the atmosphere is 1.0×10 ⁻⁴ or less.

The dimensional change rate of the inner ring 10 is measured by the following method. First, the outer diameter of the inner ring 10 (that is, the distance between the outer peripheral surfaces 10d across the center axis 10e in a cross section passing through the center axis 10e) before holding at 160° C. for 2500 hours is measured. Second, the inner ring 10 is held at 160° C. for 2500 hours in the atmosphere. Thirdly, the outer diameter of the inner ring 10 after being held at 160° C. for 2500 hours in the atmosphere is measured. Fourthly, the difference between the outer diameter of the inner ring 10 before holding at 160°C in the atmosphere for 2500 hours and the outer diameter of the inner ring 10 after holding at 160°C in the air for 2500 hours is calculated as follows: Divided by the outer diameter of the inner ring 10 before being held at 160° C. for 2500 hours. Thereby, the dimensional change rate of the inner ring 10 after being held at 160° C. for 2500 hours in the atmosphere can be obtained.

(Method for manufacturing bearing parts according to embodiment)
Below, a method for manufacturing a bearing component according to an embodiment will be described.

FIG. 3 is a process diagram showing a method for manufacturing a bearing component according to an embodiment. As shown in FIG. 3, the method for manufacturing a bearing component according to the embodiment includes a preparation step S1, a hardening step S2, a tempering step S3, and a post-processing step S4.

In the preparation step S1, the workpiece 20 is prepared. FIG. 4 is a top view of the workpiece 20 prepared in the preparation step S1. FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. As shown in FIGS. 4 and 5, the workpiece 20 has an upper surface 20a, a bottom surface 20b, an inner peripheral surface 20c, and an outer peripheral surface 20d. The bottom surface 20b is the opposite surface to the top surface 20a. The top surface 20a and the bottom surface 20b constitute end surfaces in the direction along the central axis 20e of the workpiece 20.

The inner peripheral surface 20c and the outer peripheral surface 20d are continuous with the top surface 20a and the bottom surface 20b. A raceway groove is formed on the outer peripheral surface 20d. In the raceway groove, the outer peripheral surface 20d is depressed toward the inner peripheral surface 20c. The shape of the raceway groove is partially circular in cross-sectional view.

The workpiece member 20 has a ring-like shape in plan view (when viewed from a direction perpendicular to the top surface 20a and the bottom surface 20b).

The workpiece member 20 is made of, for example, steel. The steel that constitutes the workpiece member 20 is, for example, bearing steel. The steel constituting the workpiece member 20 is preferably high carbon chromium bearing steel defined in the JIS standard (JIS G 4805:2008). It is more preferable that the steel constituting the workpiece member 20 is SUJ2 defined in the JIS standard (JIS G 4805:2008).

The hardening process S2 is performed after the preparation process S1. In the hardening step S2, a hardened layer 10f is formed. The hardening process S2 includes a heating process S21 and a cooling process S22. In the heating step S21, the workpiece 20 is heated to a temperature equal to or higher than the _A1 transformation point of the steel constituting the workpiece 20 (hereinafter referred to as "first temperature"), and heated for a predetermined time (hereinafter referred to as "first temperature"). , referred to as the "first time").

The _A1 transformation point is the temperature at which the ferrite phase contained in the steel constituting the workpiece 20 starts to transform into the austenite phase. The first temperature is, for example, 900°C or more and 1000°C or less. The first temperature is preferably 900°C or more and 950°C or less.

The higher the first temperature and the longer the first time, the more the amount of carbon dissolved in the austenite phase increases. As the amount of carbon dissolved in the austenite phase increases, the hardness of the hardened layer 10f increases when the austenite phase transforms into the martensite phase in the cooling step S22. The first temperature and the first time are appropriately selected so that the hardness of the hardened layer 10f after the hardening step S2 is 64HRC or more and 68HRC or less.

As described above, the higher the first temperature and the longer the first time, the more the amount of carbon dissolved in the austenite phase increases. As a result, the amount of carbide remaining in the hardened layer 10f after the hardening step S2 is reduced. It is preferable that the first temperature and the first time are appropriately selected such that the carbide area ratio in the hardened layer 10f after the hardening step S2 is 8 percent or more and 12 percent or less.

The carbide area ratio in the quenched hardened layer 10f is measured by the following method. First, mirror polishing of the workpiece 20 after the hardening step S2 is performed. Second, corrosion of the mirror-polished surface is performed. This corrosion is carried out using a corrosive solution (Piracle) containing picric acid and alcohol. Thirdly, the corroded mirror-polished surface is observed using an SEM (Scanning Electron Microscope). Then, by performing image analysis on the SEM image acquired from the corroded mirror-polished surface, the area ratio of the carbide phase in the quench-hardened layer 10f is calculated.

The cooling step S22 is performed after the heating step S21. In the cooling step S22, the workpiece 20 is cooled to a temperature below the Ms transformation point. The M _S transformation point is the temperature at which the austenite phase formed in the heating step S21 starts transforming into the martensite phase. Cooling of the workpiece 20 in the cooling step S22 is performed by oil cooling or water cooling.

Note that not all of the austenite phase formed in the heating step S21 transforms into a martensite phase, and a part of it remains as an austenite phase (this remaining austenite phase is hereinafter referred to as a "residual austenite phase"). ).

The tempering step S3 is performed after the hardening step S2. The tempering step S3 is performed by holding the workpiece 20 at a temperature below the _A1 transformation point (hereinafter referred to as "second temperature") for a predetermined time (hereinafter referred to as "second time"). It will be done. The heating in the tempering step S3 is preferably performed by high frequency induction heating.

In the tempering step S3, part of the martensite phase and retained austenite phase contained in the hardened layer 10f is decomposed into a ferrite phase and a cementite phase. In the tempering step S3, part of the martensite phase and the retained austenite phase is decomposed into a ferrite phase and a cementite phase, so that the inner ring 10 is included in the hardened layer 10f after being used for a long time in a high-temperature environment. The martensite phase and retained austenite phase that are formed in this way become difficult to decompose.

As a result, the dimensional change rate of the inner ring 10 after being used in a high temperature environment for a long time is improved. Further, in the tempering step S3, part of the martensite phase and the retained austenite phase is decomposed into a ferrite phase and a cementite phase, so that the hardness of the hardened layer 10f decreases.

The second temperature is preferably 260°C or more and 320°C or less. The second time is preferably 300 seconds or more and 3600 seconds or less.

When the second temperature is T (unit: Kelvin) and the second time is t (unit: seconds), the second temperature and second time are -logt+1.13×10 ⁴ /T<17.9. Selected to satisfy the relational expression.

It is preferable that the tempering step S3 is performed such that the hardness of the hardened layer 10f after the tempering step S3 is 60 HRC or less.

Post-processing step S4 is performed after tempering step S3. In the post-processing step S4, post-processing is performed on the workpiece member 20. In the post-processing step S4, for example, the workpiece member 20 is cleaned, and the surface of the workpiece member 20 is subjected to mechanical processing such as grinding or polishing. Through the above steps, the inner ring 10 is manufactured.

(Effects of the bearing component manufacturing method according to the embodiment)
The effects of the bearing component manufacturing method according to the embodiment will be explained below.

According to the knowledge discovered by the present inventors, the hardening step S2 is performed such that the hardness of the hardened layer 10f after the hardening step S2 is 64HRC or more and 68HRC or less, and the tempering step S3 is performed such that the hardness is -logt+1. When the process is carried out to satisfy the relational expression 13×10 ⁴ /T<17.9, the inner ring 10 after being held at 160° C. for 2500 hours in the atmosphere (i.e., after passing through the quenching process S2 and the tempering process S3) The dimensional change rate of the workpiece 20) can be 2×10 ⁻⁴ or less.

(Dimensional change rate measurement test)
Below, a dimensional change rate measurement test conducted to confirm the effects of the bearing component manufacturing method according to the embodiment will be described.

<Test material>
In the above dimensional change rate measurement test, Samples 1 to 6 were used as test materials. Samples 1 to 6 are ring-shaped members.

The outer diameter (the value obtained by doubling the distance between the outer peripheral surface and the central axis) of Samples 1 to 6 was 60 mm. The inner diameter of Samples 1 to 6 (the value obtained by doubling the distance between the inner peripheral surface and the central axis) was 54 mm. The width (distance between the top surface and the bottom surface) of Samples 1 to 6 was 15 mm.

The steel used for Samples 1 to 6 was SUJ2, which is a high carbon chromium bearing steel specified in the JIS standard (JIS G 4805:2008). Table 1 shows the chemical compositions of the steels constituting Samples 1 to 6.

<Heat treatment conditions>
Table 2 shows the conditions of the heat treatment (quenching step S2 and tempering step S3) performed on samples 1 to 6.

As shown in Table 2, in the hardening step S2 performed on Samples 1 to 6, the first temperature was 950°C. The second temperature was set so that the carbide area ratio in the hardened layer 10f of Samples 1 to 6 after the hardening step S2 was 8% or more and 12% or less. The cooling step S22 was performed by oil cooling.

The tempering step S3 performed on sample 1 was performed under the conditions that the second temperature was 260° C. and the second time was 3600 seconds. The tempering step S3 performed on sample 2 was performed under the conditions that the second temperature was 280° C. and the second time was 1000 seconds. The tempering step S3 performed on sample 3 was performed under the conditions that the second temperature was 300° C. and the second time was 300 seconds. The tempering step S3 performed on sample 4 was performed under the conditions that the second temperature was 320° C. and the second time was 300 seconds.

The tempering step S3 performed on sample 5 was performed under the conditions that the second temperature was 260° C. and the second time was 100 seconds. The tempering step S3 performed on sample 6 was performed under the conditions that the second temperature was 280° C. and the second time was 10 seconds. Note that the tempering step S3 for samples 1 to 6 was performed using high frequency induction heating.

<Dimensional change rate measurement results>
Table 3 shows the dimensional change rates of Samples 1 to 6 after being held at 160° C. for 2500 hours in the atmosphere. In Table 3, the case where the dimensional change rate was 2×10 ⁻⁴ or less was evaluated as “OK”, and the case where the dimensional change rate was over 2×10 ⁻⁴ was evaluated as “NG”. In addition, in Table 3, if the value of -logt+1.13×10 ⁴ /T is less than 17.9, it is evaluated as “OK”, and if the value of −logt+1.13×10 ⁴ /T is 17.9 or more, it is evaluated as “OK”. In some cases, it was rated as "NG".

As shown in Table 3, the dimensional change rate of Sample 1 after being held at 160° C. for 2500 hours in the atmosphere was 1.6×10 ⁻⁴ . The dimensional change rate of Sample 2 after being held in the atmosphere at 160° C. for 2500 hours was 1.4×10 ⁻⁴ . The dimensional change rate of Sample 3 after being held at 160° C. for 2500 hours in the atmosphere was 1.3×10 ⁻⁴ . The dimensional change rate of Sample 4 after being held at 160° C. for 2500 hours in the atmosphere was 0.7×10 ⁻⁴ .

The dimensional change rate of Sample 5 after being held at 160° C. for 2500 hours in the atmosphere was 3.1×10 ⁻⁴ . The dimensional change rate of Sample 6 after being held at 160° C. for 2500 hours in the atmosphere was 3.8×10 ⁻⁴ .

In sample 1, the value of -logt+1.13×10 ⁴ /T was 17.6. In sample 2, the value of -logt+1.13×10 ⁴ /T was 17.4. In sample 3, the value of -logt+1.13×10 ⁴ /T was 17.2. In sample 4, the value of -logt+1.13×10 ⁴ /T was 16.6.

In sample 5, the value of -logt+1.13×10 ⁴ /T was 18.4. In sample 6, the value of -logt+1.13×10 ⁴ /T was 18.7.

As mentioned above, in Samples 1 to 4, the dimensional change rates after being held at 160° C. for 2500 hours in the atmosphere were all evaluated as "OK". On the other hand, in Samples 5 and 6, the dimensional change rates after being held at 160° C. for 2500 hours in the atmosphere were all evaluated as “NG”.

Furthermore, as described above, in samples 1 to 4, all values of -logt+1.13×10 ⁴ /T were evaluated as "OK". On the other hand, in samples 5 and 6, all values of -logt+1.13×10 ⁴ /T were evaluated as "NG".

In this way, the judgment results of "OK"/"NG" based on the dimensional change rate after 2500 hours of holding at 160°C in the atmosphere and "OK"/"NG" based on the value of -logt+1.13×10 ⁴ /T are shown. In view of the fact that the results are consistent with the "NG" determination result, the hardness of the hardened layer 10f is 64HRC or more and 68HRC or less, and the tempering step S3 is -logt+1.13×10 ⁴ / When the process is performed to satisfy the relational expression T<17.9, the inner ring 10 after being held at 160° C. for 2500 hours in the atmosphere (i.e., the workpiece 20 that has undergone the quenching process S2 and the tempering process S3) It has been experimentally confirmed that the dimensional change rate of the material can be reduced to 2×10 ⁻⁴ or less.

Although the embodiments of the present invention have been described above, the embodiments described above can be modified in various ways. Moreover, the scope of the present invention is not limited to the above-described embodiments. The scope of the present invention is indicated by the claims, and is intended to include all changes within the meaning and range equivalent to the claims.

The above-described embodiments are particularly advantageously applied to a method of manufacturing a bearing component.

10 inner ring, 10a top surface, 10b bottom surface, 10c inner peripheral surface, 10d outer peripheral surface, 10e center axis, 10f quenched hardened layer, 20 workpiece member, 20a top surface, 20b bottom surface, 20c inner peripheral surface, 20d outer peripheral surface, 20e center Shaft, S1 preparation process, S2 quenching process, S21 heating process, S22 cooling process, S3 tempering process, S4 post-treatment process.

Claims (4)

A process of quenching a workpiece made of high carbon chromium bearing steel to form a quenched hardened layer;
comprising a step of tempering the workpiece,
The hardening is performed such that the hardness of the hardened layer is 64HRC or more and 68HRC or less,
For the tempering, -logt+1.13×10 ⁴ /T<17.9, where the heating temperature for the tempering is T (unit: Kelvin) and the holding time for the tempering is t (unit: seconds). carried out in a way that satisfies the relationship with
The heating during the tempering is performed by high frequency induction heating,
The heating temperature is 260°C or more and 320°C or less,
The method for manufacturing a bearing component , wherein the holding time is 300 seconds or more and 3600 seconds or less . 2. The method for manufacturing a bearing component according to claim 1, wherein the quenching is performed such that the area ratio of carbide in the quench-hardened layer is 8 percent or more and 12 percent or less. Claim 1 or Claim 2 , wherein after being held at 160°C in the atmosphere for 2500 hours, the external dimensional change rate of the workpiece after the tempering is 2 x 10 ^-4 or less. Method of manufacturing the bearing parts described. The method for manufacturing a bearing component according to any one of claims 1 to 3 , wherein the high carbon chromium bearing steel is SUJ2 specified in the JIS standard.

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