JP2018109204A - Bearing component and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bearing component capable of suppressing occurrence of crack without tempering immediately after quenching, and method for manufacturing the same.SOLUTION: In a bearing component according to the present disclosure, the amount of diffusible hydrogen after quenching and before tempering is 0.1 mass ppm or less. A method for manufacturing the bearing component according to the present disclosure includes a step of preparing a steel workpiece, a step of heating the workpiece to a heat treatment temperature of 900°C or higher and 1000°C or lower by locally heating the workpiece, and then a heat treatment step of cooling the workpiece. Heating in the heat treatment step is carried out in air or in an inert gas.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bearing component and a method for manufacturing the bearing component.

Conventionally, quenching and tempering have been widely performed as heat treatment for steel machine parts such as bearing parts. Quenching is performed by heating the workpiece to a heating temperature of A ₁ point or higher and then cooling it to the _MS point or lower. Tempering is performed by heating the workpiece after quenching to a temperature of A ₁ point or less.

  Conventionally, heating during quenching has been performed in an endothermic modified gas. The endothermic modified gas is a gas produced by reacting propane or butane with a catalyst at a high temperature. The endothermic denatured gas contains about 30% hydrogen.

  As described above, since the heating at the time of quenching has been performed in an atmosphere containing hydrogen, hydrogen penetrates into the workpiece during heating. Hydrogen in steel is known to cause cracking. This placement crack is caused by leaving the workpiece after quenching. This placement crack can be prevented by tempering. This is because, due to heating during tempering, hydrogen that has entered the workpiece during quenching diffuses to the vicinity of the surface and is discharged from the surface to the outside.

  In addition, although the prior art about this invention was demonstrated based on the general technical information which the applicant acquired, the information which should be disclosed as prior art document information before filing in the range which an applicant memorize | stores The applicant does not have

  From the standpoint of preventing cracking, it is preferable to perform tempering immediately after quenching. However, from the viewpoint of production management, tempering is not always possible immediately after quenching. Although it is conceivable to perform simple tempering in order to prevent cracking, performing such a process leads to deterioration in production efficiency.

  The present invention has been made in view of the above-mentioned problems of the prior art. More specifically, the present invention provides a bearing component and a method for manufacturing the same that can suppress the occurrence of cracks without performing tempering immediately after quenching.

The method of manufacturing a bearing component according to the present disclosure includes a step of preparing a steel workpiece and heating the workpiece locally to a heat treatment temperature of A ₁ point or more and 1000 ° C. or less, followed by cooling. Heat treatment step. Heating in the heat treatment step is performed in the air or in an inert gas.

  In the bearing component according to the present disclosure, the amount of diffusible hydrogen after quenching and before tempering is 0.1 mass ppm or less.

  According to the bearing component and the method for manufacturing the same according to the present disclosure, it is possible to suppress the occurrence of setting cracks without performing tempering immediately after quenching.

It is a flowchart for demonstrating the manufacturing method of the bearing components which concern on 1st Embodiment. It is a graph which shows the measurement result of hydrogen discharge | release amount. It is a flowchart for demonstrating the manufacturing method of the bearing components which concern on 2nd Embodiment. It is a graph which shows the relationship between the carbide area rate after a heat processing process, and the heat processing temperature. It is a graph which shows an example of the heat pattern in the heat treatment process in the manufacturing method of the bearing component concerning a 2nd embodiment. It is a graph which shows the other example of the heat pattern in the heat processing process in the manufacturing method of the bearing components which concerns on 2nd Embodiment.

  Hereinafter, 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 the description thereof will not be repeated.

(First embodiment)
Below, the bearing component which concerns on 1st Embodiment, and its manufacturing method are demonstrated. FIG. 1 is a flowchart for explaining a method of manufacturing a bearing component according to the first embodiment. As shown in FIG. 1, the bearing component manufacturing method according to the first embodiment includes a material preparation step S10 and a heat treatment step S20. The manufacturing method of the bearing component according to the first embodiment may further include a post-processing step S30. The bearing component manufacturing method according to the first embodiment may further include an assembly step S40.

  In the bearing component manufacturing method according to the first embodiment, a material preparation step S10 is first performed. In the material preparation step S10, a steel workpiece is prepared. The object to be processed is a steel member that serves as a bearing component such as an outer ring, an inner ring, or a rolling element of a bearing. The steel used for this workpiece is, for example, high carbon chrome bearing steel. High carbon chromium bearing steel is a steel type specified in JIS 4805: 2008.

  Next, a heat treatment step S20 is performed. The heat treatment step S20 includes a heating step S21 and a cooling step S22. In the heat treatment step S20, a heating step S21 is first performed. In the heat treatment step S20, the cooling step S22 is performed after the heating step S21. The heat treatment step S20 may further include a tempering step S23. The tempering step S23 is performed after the cooling step S22.

  In the heat treatment step S20, the workpiece is heated. The processing object is heated locally. The heating of the workpiece is locally performed means that only the vicinity of the surface of the workpiece is a heating region. For the local heating, any conventionally known method can be used. For the local heating, for example, induction heating, laser irradiation, energization heating, or the like can be used.

The temperature in the heating region is called the heat treatment temperature. The heat treatment temperature is the surface temperature of the part being heated in the workpiece. The heat treatment temperature can be measured using, for example, a radiation thermometer. Heat treatment temperature may be a temperature of more than ₁ point A. The heat treatment temperature may be a temperature of more than _three points A. Heat treatment temperature is preferably, 1000 ° C. or less than or more ₁ point _A. More preferably, the heat treatment temperature is 900 ° C. or higher and 1000 ° C. or lower. Here, the _point A, the steel is a temperature for starting the austenitizing, the _three points A, is the temperature at which austenitization of the steel is completely performed.

  The workpiece is heated in an atmosphere that does not substantially contain hydrogen. The atmosphere containing substantially no hydrogen refers to an atmosphere having a hydrogen concentration such that hydrogen does not enter the workpiece during heating. For example, the workpiece may be heated in the atmosphere. Moreover, the workpiece may be heated in an inert gas. This inert gas is, for example, argon (Ar).

  When the workpiece is heated in an inert gas, it is difficult to form an oxide scale on the surface of the workpiece. If the oxide scale is formed on the surface of the workpiece, decarburization may cause burn cracking, deterioration of the appearance, softening of the surface, and the like. Therefore, when heating process S21 is performed in an inert gas, generation | occurrence | production of such a problem can be suppressed.

  In the cooling step S22, the workpiece is cooled. Cooling of the workpiece is performed using any conventionally known refrigerant. The refrigerant used for cooling the workpiece is, for example, oil or water.

In the cooling step S22, the object to be processed may be cooled, for example, to a temperature equal to or lower than the _MS point. The M _S point, when the austenitization and steel is cooled, the temperature to start martensite. Thereby, a hardening hardening layer is formed in the heating region of the workpiece.

  After the cooling step S22 is performed and before the tempering step S23 is performed, the amount of diffusible hydrogen in the workpiece is 0.1 mass ppm or less. After the cooling step S22 is performed and before the tempering step S23 is performed, the amount of diffusible hydrogen in the workpiece may be 0.06 mass ppm or less.

  Diffusible hydrogen refers to hydrogen that can freely diffuse in the crystal lattice of steel. The amount of diffusible hydrogen in the workpiece is measured by a thermal desorption analyzer. More specifically, the amount of diffusible hydrogen in the object to be processed is determined by using a temperature-programmed desorption analyzer within 30 minutes after the completion of the cooling step S22 in an Ar atmosphere at a rate of 100 ° C./h. Temperature-programmed desorption analysis is performed at a speed, which is determined by the integrated value of the amount of hydrogen released up to 200 ° C.

In the tempering step S23, the workpiece is tempered. Tempering is performed by a conventionally known method. That is, in tempering, the workpiece is heated to a predetermined temperature of A ₁ point or less (hereinafter referred to as tempering temperature) and held at the tempering temperature for a certain period of time (hereinafter referred to as holding time). Is done.

  The tempering step S23 is preferably performed immediately after the cooling step S22. However, the tempering step S23 may be performed after a lapse of time after the cooling step S22 is performed.

  Subsequently, a post-processing step S30 is performed. In post-processing process S30, the post-processing with respect to a process target object is performed. In the post-processing step S30, for example, machining such as cleaning of the workpiece, grinding or polishing of the workpiece is performed. As a result, the bearing component according to the first embodiment is manufactured from the workpiece.

  Further, an assembly process S40 is performed. In the assembly step S40, the assembly of the bearing component according to the first embodiment is performed. More specifically, when the bearing component according to the first embodiment is a bearing component, the bearing is manufactured by assembling it.

  The effects of the bearing component and the manufacturing method thereof according to the first embodiment will be described below by comparing with a comparative example. The bearing component manufacturing method according to the comparative example includes a material preparation step S10 and a heat treatment step S20, similarly to the method for manufacturing a mechanical part according to the embodiment.

  However, in the method for manufacturing a bearing component according to the comparative example, the heating step S21 is performed in the endothermic modified gas. In this respect, the manufacturing method of the bearing component according to the comparative example is different from the manufacturing method of the bearing component according to the first embodiment.

  As described above, the endothermic gas contains hydrogen. As a result, in the method for manufacturing a bearing component according to the comparative example, hydrogen gas enters the workpiece. Therefore, the amount of diffusible hydrogen in the workpiece after the cooling step S22 and before the tempering step S23 exceeds 0.1 mass ppm. In this respect, the bearing component according to the comparative example is different from the bearing component according to the first embodiment.

  In the method for manufacturing a bearing component according to the comparative example, when the tempering step S23 is not performed immediately after the cooling step S22 and the tempering step S23 is performed after a considerable time has elapsed, due to the influence of diffusible hydrogen in the workpiece, There is a risk of cracking.

  On the other hand, in the bearing component manufacturing method according to the first embodiment, the concentration of diffusible hydrogen in the workpiece is low. Therefore, even if the tempering step S23 is not performed immediately after the cooling step S22 and the tempering step S23 is performed after a lapse of a considerable time, it is difficult for cracks to occur. For this reason, according to the bearing component and the manufacturing method thereof according to the first embodiment, it is possible to suppress the occurrence of cracks without deteriorating the production efficiency.

<Test conditions and test results>
Below, the result of the test conducted in order to confirm the effect of the bearing component which concerns on 1st Embodiment, and its manufacturing method is demonstrated.

(1) Sample The sample used in this test is a steel ring made of SUJ2 specified in JIS 4805: 2008. This steel ring has an outer diameter of 60 mm, an inner diameter of 54 mm, and a width of 15 mm.

(2) Heat treatment conditions When furnace heating is performed in an endothermic denatured gas (hereinafter referred to as a comparative example), holding is performed at a heat treatment temperature of 850 ° C. for 30 minutes. When heating was performed using induction heating in an inert gas (hereinafter referred to as an example), heating was performed to 950 ° C. in about 10 seconds, and then 950 ° C. was performed for 15 seconds. In addition, the cooling after a heating performed immersion immersion in oil in any case.

(3) Measurement conditions After performing the above heat treatment, each sample was cut into a size of about 35 g. This cut sample was subjected to temperature programmed desorption analysis in an Ar atmosphere at a temperature rising rate of 100 K / h, and an integrated value of the amount of released hydrogen until reaching 200 ° C. was calculated. This evaluated the amount of diffusible hydrogen that entered the steel ring during heat treatment.

(4) Test Results FIG. 2 is a graph showing the measurement results of the hydrogen release amount. As shown in FIG. 2, in the comparative example, the integrated value of the hydrogen release amount until reaching 200 ° C. was 0.92 mass ppm. On the other hand, in the examples, the integrated value of the hydrogen release amount until reaching 200 ° C. was 0.06 mass ppm. As described above, according to the bearing component and the manufacturing method thereof according to the first embodiment, it is experimentally confirmed that mixing of diffusible hydrogen during heating into the steel is suppressed, and consequently, cracking is suppressed. It was.

(Second Embodiment)
Below, the bearing component which concerns on 2nd Embodiment, and its manufacturing method are demonstrated. In the following, differences from the first embodiment will be mainly described, and the same description will not be repeated.

  FIG. 3 is a flowchart showing a method for manufacturing a bearing component according to the second embodiment. The manufacturing method of the bearing component according to the second embodiment includes a material preparation step S10 and a heat treatment step S20. The bearing component manufacturing method according to the second embodiment may further include a post-processing step S30. The bearing component manufacturing method according to the second embodiment may further include an assembly step S40. In these respects, the bearing component manufacturing method according to the second embodiment is the same as the bearing component manufacturing method according to the first embodiment.

  However, as described below, the bearing component manufacturing method according to the second embodiment differs from the bearing component manufacturing method according to the first embodiment in the details of the heat treatment conditions of the heat treatment step S20.

  In the heat treatment step S20, the following formulas 1 and 2 are satisfied when the carbide area ratio in the workpiece to be processed after the heat treatment step S20 is Y (unit:%) and the heat treatment temperature is X (unit: ° C.). As such, the conditions for the heat treatment are determined.

Formula 1: 6.600 × 10 ⁻⁴ X ² −1.205X + 5.539 × 10 ² <Y
Formula 2: 1.160 × 10 ⁻³ X ² −2.094X + 9.472 × 10 ² <Y
The carbide area ratio is measured by mirror-polishing a workpiece, corroding the polished surface, photographing the polished surface with a scanning electron microscope, and analyzing the photographed image.

  FIG. 4 is a graph showing the relationship between the carbide area ratio and the heat treatment temperature after the heat treatment step S20. In FIG. 4, the horizontal axis represents the heat treatment temperature (unit: ° C.). In FIG. 4, the vertical axis represents the carbide area ratio (unit:%).

In the graph of FIG. 4, the solid line graph represents Formula 1 (6.600 × 10 ⁻⁴ X ² −1.205X + 5.539 × 10 ² = Y), and the dotted line graph represents Formula 2 (1.160 × 10 ^{− 3} X ² -2.094X + 9.472 × 10 ² = Y). The above relationship shows a region above the solid line indicating Expression 1 and the dotted line indicating Expression 2 in FIG.

  Specifically, in the region where the heat treatment temperature is 900 ° C. or more and 950 ° C. or less, it is above the solid line graph (formula 1), and in the region where the heat treatment temperature is 950 ° C. or more and 1000 ° C. or less, the dotted line graph (formula 2 The region above the graph) is a region that satisfies the above relationship. Further, as the above relationship, a relationship between the carbide area ratio and the heat treatment temperature of 900 ° C. ≦ X ≦ 950 ° C. and 8% ≦ Y ≦ 12% may be adopted. This relationship is shown as a shaded portion in FIG.

  In the heating step S <b> 21, any method can be used as long as it is a means for locally heating the workpiece, as in the method for manufacturing the bearing component according to the first embodiment. For example, induction heating can be used as means for locally heating the workpiece.

  In the heating step S21, the heat treatment temperature and the soaking time (the time during which the temperature of the object to be processed is maintained in a certain temperature range including the heat treatment temperature) are determined so as to satisfy the above relationship.

  When the temperature of the workpiece is maintained within a certain temperature range as described above before the workpiece is cooled, the heat treatment temperature is maintained within the certain temperature range. The average value of the surface temperature of the workpiece in a period (for example, a period from 60 seconds before the start of cooling to the start of cooling, or a period from 30 seconds before the start of cooling to the start of cooling) may be used. When the surface temperature of the object to be processed has changed to some extent before the object to be processed is cooled (for example, the surface temperature gradually increases), the heat treatment temperature is maintained for a certain period before the start of cooling. Even if it is the highest temperature (maximum heating temperature) among the surface temperatures that are changing (for example, the period from 60 seconds before the start of cooling to the start of cooling, or the period from 30 seconds before the start of cooling to the start of cooling). Good.

  The soaking time is maintained within a predetermined temperature range including the heat treatment temperature (for example, a heat treatment temperature ± 30 ° C. temperature range) after the surface temperature of the heated part of the workpiece becomes equal to or higher than the heat treatment temperature, for example. It is the time (more preferably the time during which the temperature is maintained within a predetermined temperature range equal to or higher than the heat treatment temperature). Practically, as the soaking time, the time from when the surface temperature of the heated part of the workpiece is equal to or higher than the heat treatment temperature until the cooling of the workpiece is started can be used.

  FIG. 5 is a graph showing an example of a heat pattern in the heating step S21 in the method for manufacturing a bearing component according to the second embodiment. FIG. 6 is a graph showing another example of a heat pattern in the heating step S21 in the method for manufacturing a bearing component according to the second embodiment. 5 and 6, the horizontal axis indicates time (unit: second), and the vertical axis indicates the heat treatment temperature (unit: ° C.). FIG. 5 shows a case where the heat treatment temperature is 900 ° C. and the soaking time is about 60 seconds. FIG. 5 shows a case where the heat treatment temperature during the soaking time is substantially as set. FIG. 6 shows a case where the soaking time is about 30 seconds and the heat treatment temperature during the soaking time varies to some extent.

The cooling step S22 in the bearing component manufacturing method according to the second embodiment is the same as the bearing component manufacturing method according to the first embodiment. That is, in the method for manufacturing a bearing component according to the second embodiment, in the cooling step S22, the workpiece is cooled. Cooling of the workpiece is performed using any conventionally known refrigerant. For example, the workpiece may be cooled to a temperature equal to or lower than the _MS point.

  In the induction heating, the heating device can be easily started up and down. Therefore, induction heating is suitable for manufacturing bearing parts in a small lot. Therefore, in the method for manufacturing a bearing component according to the second embodiment, when induction heating is used as a means for locally heating a workpiece, a bearing component having a quality equal to or higher than that when using atmospheric furnace heat treatment is used. It can be easily manufactured in small lots.

  In the method for manufacturing a bearing part according to the second embodiment, the steel constituting the part to be processed may be a high carbon chromium bearing steel. In this case, the quality after the heat treatment equivalent to or higher than that in the case of using the atmospheric furnace heat treatment can be ensured for the bearing component made of the high carbon chromium bearing steel.

In the bearing component manufacturing method according to the second embodiment, in the heat treatment step S20,
900 ℃ ≦ X ≦ 950 ℃
8% ≦ Y ≦ 12%
The conditions for the heat treatment may be determined so as to satisfy the relationship. In this case, the quality of the workpiece after the heat treatment can be reliably made equal to or higher than that when the atmosphere furnace heat treatment is used.

<Basic concept for derivation of heat treatment conditions>
According to the study of the present inventor, there are two differences that are considered to affect the bearing characteristics among the differences in the heat treatment method that performs local heating such as induction heating with respect to the atmospheric furnace heat treatment. The first difference is that induction heating is high-temperature and short-time heating. The second difference is that, in principle, it is difficult for induction heating to make the carbon penetration constant within the part, and the carbon penetration (carbon solid dissolution) varies within the part. is there.

  Variations in the amount of carbon dissolved in bearing parts are expected to affect the aging stability, static load capacity, and crushing value of bearing parts. Therefore, if the upper and lower limits of the carbon solid solution amount in which the values of these characteristics are equal to or higher than those of the atmosphere furnace heat treated product are investigated, it can be regarded as the allowable carbon solid solution concentration range inside the bearing part.

  Heat treatment temperature is also expected to affect the above properties. Therefore, the allowable range of the heat treatment temperature is determined by investigating the range of the heat treatment temperature at which these characteristic values are equal to or higher than those of the atmosphere furnace heat treatment product.

  Then, by using the above-described range of the carbon solid solution amount and the range of the heating temperature, when the entire bearing component is included in the range, it can be determined that the quality is equal to or higher than that of the atmosphere furnace heat treatment product. . Therefore, the effects of the carbon solid solution amount and the heat treatment temperature on the bearing characteristics were investigated, and the conditions for obtaining the same quality as the atmosphere furnace heat treatment product were obtained by the following tests.

  It is difficult to directly measure the amount of carbon solid solution. Therefore, the carbide area ratio in the workpiece (bearing part) after heat treatment was used as an alternative index. It is possible to calculate an approximate amount of carbon solid solution from the carbide area ratio.

<Samples used to derive heat treatment conditions>
(1) Sample The chemical composition of the sample material used in the test is shown in the table.

Assuming that all the carbides are composed of Fe ₃ C in the material of the chemical component described above, the carbide area ratio before the heat treatment is calculated from the above-described carbon concentration to be 15.1%.

(2) Heat treatment method In the samples used in the following tests, the carbide area ratio test levels were 4%, 8%, and 12%. Moreover, the test level of heating temperature was 900 degreeC, 950 degreeC, and 1000 degreeC. In addition, the heat treatment time (soaking time) at each heating temperature for setting the carbide area ratio to 4%, 8%, and 12% in the above materials is as shown in Table 2 below.

  Table 2 shows the heat treatment time (unit: seconds) required to obtain a predetermined carbide area ratio when each heating temperature is employed. For example, as shown in Table 2, when the heating temperature is 900 ° C., the heat treatment time necessary for setting the carbide area ratio to 4% is 316 seconds.

  In the sample used for the test, the following heat treatment was performed in order to realize the above-described carbide area ratio. As a sample used for the test, a steel ring made of SUJ2 defined in JIS 4805: 2008 was used. The outer diameter of the steel ring is 60.3 mm, the inner diameter is 53.7 mm, and the width in the axial direction is 15.3 mm.

  The heating step S21 was performed by induction heating using a single turn coil in an inert gas. The output of the power supply (to supply power to the single turn coil) connected to the single turn coil is controlled by feeding back the measured temperature of the steel ring surface (the surface of the part that is inductively heated by the single turn coil). It was. The surface temperature of the steel ring was raised to a predetermined temperature (specifically, 900 ° C., 950 ° C. or 1000 ° C.). In addition, it took about 5 seconds until the temperature of the steel ring surface rose to the predetermined temperature described above from the start of the heat treatment.

  After the surface of the steel ring was heated to a predetermined temperature, the power supplied to the single turn coil was controlled so that the ring was held at the predetermined temperature for a specific time (heat treatment time) (soaking).

  Then, cooling process S22 was performed and the steel ring was cooled. As a cooling method, the steel ring was cooled by immersing the steel ring in oil at a temperature of 70 ° C. (quenching treatment). As the heat pattern for such heat treatment, for example, the heat pattern shown in FIG. 5 can be adopted.

  A tempering step S23 was performed after the cooling step S22. The tempering conditions were a standard tempering temperature of 180 ° C. and a holding time of 2 hours.

<Aged dimensional stability test>
The bearings change in size as the retained austenite decomposes during use. Since the dimensional change reduces the accuracy of the bearing, it is required to be below a certain standard.

(1) Sample After the heat treatment step S20 described above, the sample was polished to prepare a ring-shaped sample having an outer diameter of 60 mm, an inner diameter of 54 mm, and an axial width of 15 mm. As shown in Table 2, nine types of samples were prepared by combining the heating temperature (900 ° C., 950 ° C., 1000 ° C.) and the carbide area ratio in the heat treatment described above.

(2) Test and Results For the nine types of samples described above, changes in the external dimensions before and after treatment under the conditions of a heating temperature of 230 ° C. and a holding time of 2 hours were measured. The results are shown in Table 3.

Here, the dimensional change rate is (the absolute value of D ₁ −D ₀ ) / D ₀ when the outer diameter of the sample before the treatment is D ₀ and the outer diameter of the sample after the treatment is D _1. Is defined. The measurement position of the outer diameter of the sample was the same before and after holding at high temperature. The measurement of the outer diameter was evaluated in two directions intersecting 90 ° when viewed from the center of the ring-shaped sample. In addition, n = 3 for each level.

In Table 3, a dimensional change rate of less than 70 × 10 ⁻⁵ was regarded as being equivalent to or higher than that of the atmosphere furnace heat treated product, and was determined to be acceptable (OK determination). In Table 3, a dimensional change rate of 70 × 10 ⁻⁵ or more was regarded as unacceptable (NG judgment). As can be seen from Table 3, from this result, the samples capable of securing aged dimensional stability equal to or higher than that of the atmosphere furnace heat treated product have a carbide area ratio of 8% and 12% when the heat treatment temperatures are 900 ° C. and 950 ° C. This is a sample whose carbide area ratio is 12% when the heat treatment temperature is 1000 ° C.

Further, when an approximate function is obtained from the test data described above and the condition that the dimensional change rate is less than 70 × 10 ⁻⁵ is obtained, when the heat treatment temperature is 900 ° C., the carbide area ratio is 4.0% or more and the heat treatment temperature is In the case of 950 ° C., the carbide area ratio is 4.8% or more, and in the case where the heat treatment temperature is 1000 ° C., the carbide area ratio is 8.9% or more.

<Static load capacity test>
When a large load is applied to the bearing, plastic deformation occurs. However, in order for the rolling element of the bearing to roll smoothly, the amount of plastic deformation of the rolling element is required to be 1 / 10,000 or less of the diameter of the rolling element.

(1) Sample A sample having a size of 6 mm long × 15 mm wide × 3 mm thick was obtained by polishing and wire cutting the ring after the heat treatment step S20 described above. A 6 mm × 15 mm surface of the sample was mirror-polished. Nine types of samples were prepared by combining the heating temperature and the carbide area ratio in the same manner as in the aged dimensional stability test described above.

  For comparison, a sample (comparative example sample) having the same size was prepared by performing an atmosphere furnace heat treatment as a heat treatment on a sample having the same composition and then performing machining.

(2) Test and Results A 3/8 inch ceramic ball was pressed against the mirror-polished surface of the sample with a constant test load. And the depth of the indentation produced by the plastic deformation in the said surface was evaluated. The test load was 471 N corresponding to Pmax 4 GPa in Hertz contact. In addition, n = 3 for each level. The results are shown in Table 4.

  The column of indentation depth in Table 4 shows an average value of indentation depths measured for each sample. The column of standard deviation in Table 4 shows the standard deviation of the indentation depth data. And in the column of judgment of Table 4, the thing which is hard to make an indentation from the sample of atmosphere furnace heat treatment with a significance level of 95% is displayed as pass (OK), and the thing which is easy to make an indentation is displayed as failure (NG). In addition, "-" is displayed in the judgment column for items that do not meet the above criteria.

  From this result, it can be seen that the sample in which the display in the judgment column is OK and “−” shows a static load capacity equal to or higher than that of the atmosphere furnace heat treatment product. Specifically, when the heat treatment temperatures are 900 ° C. and 950 ° C., the samples having a carbide area ratio of 8% and 12% show a static load capacity equal to or higher than that of the atmospheric furnace heat treatment product.

  In addition, when an approximate function is obtained from the test data described above and a standard deviation is set to 0.015 μm and a range that can ensure a quality equivalent to or better than that of an atmosphere furnace heat treatment product is calculated, when the heat treatment temperature is 900 ° C., the carbide area ratio When the heat treatment temperature is 950 ° C., the carbide area ratio is 4.8% or more, and when the heat treatment temperature is 1000 ° C., the carbide area ratio is 13.2% or more.

<Crush strength test>
The crushing strength may be required for the bearing, and the following tests were conducted.

(1) Sample A ring-shaped sample having an outer diameter of 60 mm, an inner diameter of 54 mm, and an axial width of 15 mm was prepared by polishing the sample after the heat treatment step S20 described above. As shown in Table 2, nine types of samples were prepared by combining the heating temperature (900 ° C., 950 ° C., 1000 ° C.) and the carbide area ratio in the heat treatment described above. In addition, n = 3 for each level.

  For comparison, a sample (comparative example sample) having the same size was prepared by performing an atmosphere furnace heat treatment as a heat treatment on a sample having the same composition and then performing machining.

(2) Test and Results For each sample, a load was applied at a constant speed with a material sandwiched from the radial direction, and the load that resulted in crushing was measured. Moreover, the fracture stress was calculated from the load. The results are shown in Table 5.

  In the judgment column of Table 5, those having a crushing strength lower than that of the atmosphere furnace heat treated product even if the standard deviation is taken into consideration are displayed as “NG” (NG). “−” Is indicated for the material that can secure the crushing strength.

  From this result, it can be seen that the sample in which the display in the judgment column is “−” can show a crushing strength equivalent to or higher than that of the atmosphere furnace heat treatment product. Specifically, when the heat treatment temperatures are 900 ° C. and 950 ° C., a sample with a carbide area ratio of 8% or 12% can exhibit a crushing strength equal to or higher than that of the atmosphere furnace heat treatment product.

  Further, when an approximate function is obtained from the test data described above and a range in which a quality equivalent to or better than that of the atmospheric furnace heat treatment product can be secured when the standard deviation is 150 MPa, the carbide area ratio is 4 when the heat treatment temperature is 900 ° C. When the heat treatment temperature is 950 ° C., the carbide area ratio is 5.4% or more, and when the heat treatment temperature is 1000 ° C., the carbide area ratio is 9.3% or more.

<Examination of heat treatment conditions>
From the above results, when high temperature short time heating means such as induction heating is used for quenching of high carbon chrome bearing steel such as SUJ2 as defined in JIS 4805: 2008, performance equal to or better than that of atmosphere furnace heat treated products is obtained. This can be reliably realized when the heat treatment temperatures are 900 ° C. and 950 ° C. and the carbide area ratio is 8% and 12%.

  Looking at each data, all the test results are monotonously increasing or monotonically decreasing with respect to the heat treatment temperature and carbide area ratio. Therefore, it is considered that the quality equivalent to or higher than that of the atmosphere furnace heat-treated product can be realized even by the heat treatment condition corresponding to the region surrounded by the four points obtained this time (the region indicated by the oblique lines in FIG. 4).

  Therefore, it is in the region where the heat treatment temperature is 900 ° C. or more and 950 ° C. or less and the carbide area ratio is 8% or more and 12% or less that can ensure the same or better quality as the atmosphere furnace heat treatment product.

  Table 6 shows the range of the carbide area ratio obtained from the approximate function of each test result and having a quality equivalent to or better than that of the atmosphere furnace heat-treated product.

When an approximate function is obtained for the relationship between the carbide area ratio range and the heat treatment temperature shown in Table 6 (in the following conditional expressions, Y is the carbide area ratio (%), and X is the heat treatment temperature (° C.)). is there),
Aged dimensions:
6.600 × 10 ⁻⁴ X ² −1.205X + 5.539 × 10 ² <Y (conditional expression 1)
Static load capacity:
1.160 × 10 ⁻³ X ² −2.094X + 9.472 × 10 ² <Y (Condition 2)
Crush test:
5.000 × 10 ⁻⁴ X ² −8.970 × 10 ⁻¹ X + 4.063 × 10 ² <Y (conditional expression 3)
It becomes.

  And the range which can ensure the quality equivalent to or better than the atmosphere furnace heat treated product is the case where the carbide area ratio Y satisfies the above conditional expressions 1 to 3 in the heat treatment temperature X range of 900 ° C. or higher and 1000 ° C. or lower.

  Here, in the range of the heat treatment temperature of 900 ° C. or higher and 1000 ° C. or lower, X satisfying conditional expression 1 always satisfies conditional expression 3. Therefore, conditional expression 3 need not be considered. For this reason, the range which can ensure the quality equivalent to or better than the atmosphere furnace heat treated product is a case where the carbide area ratio Y satisfies the conditional expression 1 and the conditional expression 2 in the heat treatment temperature range of 900 ° C. to 1000 ° C.

  Although the embodiment of the present invention has been described above, the above-described embodiment can be variously modified. Further, the scope of the present invention is not limited to the above-described embodiment. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The above embodiments are particularly advantageously applied to bearing parts using induction heating and their manufacture.

  S10 Material preparation step, S20 heat treatment step, S21 heating step, S22 cooling step, S23 tempering step, S30 post-treatment step, S40 assembly step, X heat treatment temperature, Y carbide area ratio.

Claims (8)

Preparing a steel workpiece,
A heat treatment step of locally heating the workpiece to a heat treatment temperature of A ₁ or more and 1000 ° C. or less and then performing a heat treatment for cooling,
The method for manufacturing a bearing component, wherein the heating in the heat treatment step is performed in an atmosphere substantially free of hydrogen.   The method for manufacturing a bearing component according to claim 1, wherein the heating in the heat treatment step is performed in an inert gas. The heat treatment step includes a step of tempering the workpiece.
The method for manufacturing a bearing part according to claim 1, wherein the amount of diffusible hydrogen in the workpiece after the cooling is performed and before the tempering is 0.1 mass ppm or less. . The heat treatment temperature is 900 ° C. or higher and 1000 ° C. or lower,
In the heat treatment step, when the carbide area ratio of the workpiece after the heat treatment step is Y (unit:%) and the heat treatment temperature is X (unit: ° C.),
6.600 × 10 ⁻⁴ X ² −1.205X + 5.539 × 10 ² <Y
1.160 × 10 ⁻³ X ² −2.094X + 9.472 × 10 ² <Y
The method for manufacturing a bearing part according to any one of claims 1 to 3, wherein the conditions for the heat treatment are determined so as to satisfy the relationship. In the heat treatment step,
900 ℃ ≦ X ≦ 950 ℃
8% ≦ Y ≦ 12%
The manufacturing method of the bearing component according to claim 4, wherein the conditions for the heat treatment are determined so as to satisfy the relationship.   The method for manufacturing a bearing part according to claim 1, wherein in the heat treatment step, the workpiece is heated by induction heating.   The said steel which comprises the said workpiece is a manufacturing method of the bearing components of any one of Claims 1-6 which are high carbon chromium bearing steel.   A bearing component that is after quenching and has an amount of diffusible hydrogen before tempering of 0.1 mass ppm or less.

Images