JP2019065365A - Manufacturing method of bearing part - Google Patents

Abstract

To provide a method for manufacturing a bearing part capable of implementing characteristics equal to or more than those manufactured by using an atmospheric furnace heat treatment.SOLUTION: The method for manufacturing a bearing part includes a process for preparing a steel part to be processed for the bearing part, and a process for performing heat treatment for cooling the part to be processed after heating the part. The heat treatment process includes heating the part to a heat treatment temperature of 900°C or more and 1000°C or less by locally heating the part, and cooling the part to be processed which is heated by using an oil cooling agent. In the heat treatment process, when the carbide area ratio in the part after the heat treatment is Y (unit: %) and the heat treatment temperature is X (unit: °C), the condition of the heat treatment is determined such that 6.600×10X-1.205X+5.539×10<Y and 1.160×10X-2.094X+9.472×10<Y are satisfied.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a method of manufacturing a bearing component, and more particularly to a method of manufacturing a bearing component including heat treatment.

  Atmosphere furnace heat treatment is usually used for heat treatment in the manufacturing process of bearing components. However, since it takes time to start up the heat treatment furnace and adjust the atmosphere, there is a disadvantage that the heat treatment furnace can not be easily stopped. In addition, atmosphere furnace heat treatment is not suitable for small lot production of bearing parts because mass production is assumed.

  As one of heat treatment methods capable of solving such a defect, heat treatment using induction heating can be mentioned. The induction heating is suitable for small lot production because the heating time is short and the bearing parts are treated individually (one treatment). Further, compared to the above-described heat treatment furnace, the induction heating apparatus can be activated and deactivated instantaneously, so it is not necessary to always arrange personnel in order to keep the heat treatment furnace operated as in the above heat treatment furnace. . From these advantages, induction heating is widely used for heat treatment of machine parts made of steel with a carbon concentration of about 0.5%.

  Further, as a technique of applying induction heating to the entire hardening of a part made of high carbon chromium bearing steel (for example, JIS standard SUJ2) which is an example of a material of the bearing part, it is disclosed, for example, in Japanese Patent Laid-Open No. 2006-083412. There is something. JP-A-2006-083412 discloses a technique for controlling the heating temperature and the heating time so as to be within predetermined ranges. However, in the said Unexamined-Japanese-Patent No. 2006-083412, the specific range of heating temperature, heating time, the cooling method after heating, and the reason for its determination are not disclosed.

Japanese Patent Application Publication No. 2006-083412

  By the way, when hydrogen intrudes into a bearing component made of steel, delayed fracture may occur due to the intruded hydrogen. Therefore, it is desirable to develop a process that makes it difficult for hydrogen to penetrate into the bearing components.

  In addition, the carbon concentration of JIS standard SUJ2 often used as a material of bearing parts is about 1.0%. In the bearing component consisting of SUJ2 before heat treatment, all carbon is present as carbide. In the conventional atmosphere furnace heat treatment, conditions are used such that about 60% of carbon in the bearing components dissolves in the matrix. By performing the heat treatment under such conditions, it is said that the performance as a bearing is the highest.

  Even when heat treating bearing components made of high carbon chromium bearing steel such as JIS standard SUJ2 by induction heating, it is desirable to heat treat under the conditions as described above, but high temperature short time heating such as induction heating locally It is extremely difficult to completely mimic the above-described atmosphere furnace heat treatment by the heat treatment method to be performed. However, the demand for small-lot production of bearing parts has been increasing in recent years, and development of a process that can guarantee the same quality as conventional atmosphere furnace heat treatment is also desired in such small-lot production.

  The present invention has been made to solve the problems as described above, and an object of the present invention is to use a heat treatment method in which hydrogen is less likely to intrude into bearing parts and local heating such as induction heating is performed. It is an object of the present invention to provide a method of manufacturing a bearing component capable of achieving the same or more characteristics as in the case of using the atmosphere furnace heat treatment.

A method of manufacturing a bearing component according to the present disclosure includes the steps of preparing a steel processing target component to be a bearing component and performing a heat treatment for heating and cooling the processing target component. The step of performing the heat treatment includes a step of performing heat treatment of heating the processing target component locally to a heat treatment temperature of 900 ° C. or more and 1000 ° C. or less, and the heated processing target component using an oil coolant. And cooling. In the step of performing the heat treatment, when the carbide area ratio in the processing target part after the step of performing the heat treatment is Y (unit:%) and the heat treatment temperature is X (unit: ° C.)
6.600 × 10 ⁻⁴ X ² −1.205 X + 5.539 × 10 ² <Y
^{1.160 × 10 -3 X 2 -2.094X +} 9.472 × 10 2 <Y
The conditions of the heat treatment are determined so as to satisfy the following relationship.

  In this way, when performing heat treatment by locally heating the object to be processed using induction heating or the like, the quality of the object to be processed after heat treatment is subjected to atmosphere furnace heat treatment by satisfying the conditions described above It can be equal to or better than it was. Furthermore, by cooling the heated processing object under the above-described conditions, it is possible to prevent the entry of hydrogen into the processing object.

  According to the above, it is possible to obtain a bearing component having the same or more characteristics as in the case of using the atmosphere furnace heat treatment by using the heat treatment method for performing the local heating.

It is a flowchart for demonstrating the manufacturing method of the bearing components which concern on this embodiment. It is a graph for demonstrating the heat treatment conditions in the manufacturing method of the bearing components which concern on this embodiment. It is a graph which shows an example of the heat pattern of the heat processing in the manufacturing method of the bearing components which concern on this embodiment. It is a graph which shows the other example of the heat pattern of the heat processing in the manufacturing method of the bearing components which concern on this embodiment. It is a figure which shows the result of a temperature rising desorption analysis.

  Hereinafter, embodiments of the present invention will be described based on the drawings. In the following drawings, the same or corresponding parts have the same reference characters allotted and description thereof will not be repeated.

<Method of manufacturing bearing parts>
FIG. 1 is a flowchart for explaining a method of manufacturing a bearing using the method of manufacturing a bearing component according to the present embodiment. A method of manufacturing a bearing according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, first, the material preparation step (S10) is performed. Specifically, a steel processing object to be a bearing component is prepared. As an object to be processed, for example, a steel member to be a bearing component such as an outer ring, an inner ring, and a rolling element of a bearing is prepared. The steel that constitutes the object to be processed is, for example, a high carbon chromium bearing steel.

  Next, the heat treatment step (S20) is performed. The heat treatment step (S20) includes a heat treatment step (S21) for locally heating the object to be processed and a cooling treatment step (S22) for cooling the object to be heated. The heating temperature (heat treatment temperature) of the heating area in the object to be processed in the heat treatment step (S21) can be, for example, 900 ° C. or more and 1000 ° C. or less.

In the heat treatment step (S21), when the carbide area ratio of the processing target part after the heat treatment step is Y (unit:%) and the heat treatment temperature is X (unit: ° C.),
6.600 × 10 ⁻⁴ X ² −1.205 X + 5.539 × 10 ² <Y
^{1.160 × 10 -3 X 2 -2.094X +} 9.472 × 10 2 <Y
The conditions of the heat treatment are determined so as to satisfy the following relationship. The relationship between the carbide area ratio and the heat treatment temperature described above is shown in FIG. The horizontal axis in FIG. 2 indicates the heat treatment temperature (unit: ° C.), and the vertical axis indicates the carbide area ratio (unit:%). In the graph of FIG. 2, the solid line shows the equation 1 (6.600 × 10 ⁻⁴ X ² −1.205 × + 5.539 × 10 ² = Y), and the dotted line shows the equation 2 (1.160 × 10 ^{− 3 X 2 -2.094X + 9.472 × 10} 2 = Y) shows a. The above relationship indicates the area above the solid line showing Equation 1 and the dotted line showing Equation 2 in FIG.

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

  In the heat treatment step (S21), any method may be used as long as it is a means for locally heating the object to be processed, but for example, induction heating can be used. Further, in the heat treatment step (S21), the heat treatment temperature and the soaking time (time in 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.

  In addition, the heat processing temperature means the surface temperature of the part currently heated in the workpiece. In the heat treatment step (S21), when the temperature of the object to be processed is maintained within the predetermined temperature range as described above, the heat treatment temperature is maintained within the predetermined temperature range. It may be an average value of the surface temperature of the object to be processed during the period (for example, 60 seconds before the start of cooling to the start of cooling, or 30 seconds before the start of cooling to the start of cooling). Alternatively, when the surface temperature of the object to be processed changes to some extent during the heat treatment step (S21) (for example, the surface temperature is gradually rising), the heat treatment temperature is a constant temperature before the start of cooling. It may be the highest temperature (maximum heating temperature) among surface temperatures changing in a period (for example, from 60 seconds before the start of cooling to the start of cooling, or from 30 seconds before the start of cooling to the start of cooling) . The heat treatment temperature can be measured, for example, using a radiation thermometer. In addition, the soaking time is, for example, a predetermined temperature range including the heat treatment temperature (for example, a temperature range of heat treatment temperature ± 30 ° C.) after the surface temperature of the portion heated in the workpiece becomes equal to or higher than the heat treatment temperature. It means the time maintained at (more preferably, the time maintained at a predetermined temperature range above the heat treatment temperature). In practice, the time from the surface temperature of the heated portion of the object to be processed to the heat treatment temperature or higher and the start of cooling of the object to be processed can be used as the soaking time.

  As the heat pattern in the heat treatment described above, for example, a heat pattern as shown in FIGS. 3 and 4 can be used. In FIG. 3 and FIG. 4, the horizontal axis is time (unit: second), and the vertical axis is heat treatment temperature (unit: ° C.). FIG. 3 shows the case where the heat treatment temperature is 900 ° C. and the soaking time is about 60 seconds. FIG. 3 shows the case where the heat treatment temperature during the soaking time is almost as set. FIG. 4 shows the case where the soaking time is about 30 seconds, and the heat treatment temperature during the soaking time fluctuates to some extent.

  When the object to be processed is cooled in the cooling treatment step (S22), the object to be processed (for example, a heated region) is cooled to a temperature equal to or lower than the Ms point using an oil-based coolant. For example, the object to be processed may be cooled from the heat treatment temperature described above to a temperature of 500 ° C. or less. In addition, when austenitized steel is cooled, Ms point means the point corresponded to the temperature which starts martensite formation here. In this way, a quench-hardened layer can be formed in the area that has been heated in the object to be processed.

  In the cooling process step (S22), the entire object to be processed may be cooled, or only the heated region may be cooled. In addition, in the cooling process step (S22), any method can be used as a method of cooling the processing object. For example, as a method of cooling the processing object, a method of immersing the processing object in a bath containing an oil-based coolant, or a method of spraying an oil-based coolant on the processing object may be used.

  The oil-based coolant is a coolant mainly composed of oil. As oil, mineral oil can be used. Also, additives may be added to the oil.

  Next, the post-processing step (S30) is performed. Specifically, a cleaning process of the object to be processed, and a machining process such as a grinding process and a polishing process may be performed. In the post-processing step (S30), bearing components such as an inner ring, an outer ring, and rolling elements are manufactured from the object to be processed. The above steps (S10) to (S30) correspond to the method of manufacturing the bearing component of the present embodiment.

  Next, an assembly process (S40) is performed. In this step (S40), the bearing is manufactured by assembling the bearing component obtained by the above-described method of manufacturing the bearing component. Thus, the method of manufacturing the bearing according to the present embodiment is implemented.

  In this way, the quality of the object to be processed after heat treatment can be made equal to or higher than in the case of using the atmosphere furnace heat treatment, so bearing components and bearings having characteristics equal to or more than the case of using the atmosphere furnace heat treatment It can be manufactured.

  In the above-described bearing component manufacturing method (steps (S10) to (S30)), in the step of performing heat treatment (heat treatment step (S21)), as described above, the workpiece may be heated by induction heating . In this case, since induction heating can easily perform startup and shutdown of the heating apparatus and is suitable for manufacturing bearing components in small lots, bearings of the same or higher quality as those using atmosphere furnace heat treatment Parts can be easily manufactured in small lots.

  Further, in the method of manufacturing the bearing component, the steel constituting the component to be processed may be high carbon chromium bearing steel. In this case, it is possible to secure the quality after heat treatment equal to or higher than that in the case of using the atmosphere furnace heat treatment for the bearing component made of high carbon chromium bearing steel.

In the method of manufacturing the bearing component, in the step (S21) of performing the heat treatment,
900 ° C. ≦ X ≦ 950 ° C.
8% ≦ Y ≦ 12%
The conditions of the heat treatment may be determined so as to satisfy the following relationship. In this case, the quality of the object to be processed after the heat treatment can be reliably made equal to or higher than the case of using the atmosphere furnace heat treatment.

<Basic concept of derivation of heat treatment conditions>
According to the study of the inventor of the present invention, there are two differences among the differences in the heat treatment method of performing local heating such as induction heating to the atmosphere furnace heat treatment, which are considered to affect the bearing characteristics. The first difference is that induction heating is high-temperature short-time heating. The second difference is that, in induction heating, it is basically difficult to make the amount of carbon dissolved constant within the part, and the amount of carbon dissolved (solid solution amount of carbon) varies within the part. is there.

  Such variations in the amount of dissolved carbon in the bearing component are expected to affect the dimensional stability, static load capacity, and crushing value of the bearing component. Therefore, if the upper and lower limits of the amount of solid solution of carbon at which the values of these characteristics are equal to or higher than the atmosphere furnace heat-treated product are investigated, it can be regarded as the allowable solid solution concentration range of carbon inside the bearing component. Further, since the heat treatment temperature also affects the above-mentioned characteristics, the allowable range of the heat treatment temperature is determined by investigating the range of the heat treatment temperature at which the value of these characteristics is equal to or higher than the atmosphere furnace heat treated product. Then, by using the range of the solid solution amount of carbon and the range of the heating temperature described above, when the entire bearing component is included in the range, it can be determined that the quality is equal to or higher than the atmosphere furnace heat-treated product. .

  Therefore, the influence of the solid solution amount of carbon and the heat treatment temperature on the bearing characteristics was investigated, and the heat treatment conditions capable of obtaining the same quality as the atmosphere furnace heat treated product were determined by the following test.

  In addition, it is difficult to directly measure the solid solution amount of carbon. Therefore, the carbide area ratio in the processing object (bearing part) after heat treatment was used as a substitute index. It is possible to calculate an approximate amount of solid solution of carbon from the carbide area ratio.

<On the sample used to derive the 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 materials of the chemical components described above, the carbide area ratio before heat treatment is calculated to be 15.1% from the above carbon concentration.

(2) Heat treatment method In the samples used in the following tests, the test levels of the area fraction of carbide were 4%, 8% and 12%, and the test levels of the heating temperature were 900 ° C, 950 ° C and 1000 ° C. In addition, the heat processing time (soaking time) in each heating temperature for making a carbide area ratio into 4%, 8%, and 12% in the said material is as showing in the following Table 2.

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

  In the sample used for the test, the following heat treatment was performed to realize the above-described carbide area ratio. Specifically, as a sample, a steel ring made of JIS standard SUJ2 having a size of 60.3 mm in outer diameter, 53.7 mm in inner diameter, and 15.3 mm in axial direction is induction heated by a single turn coil. The output of the power supply (for supplying power to the coil) connected to the coil is controlled by feeding back the measured temperature of the ring surface (the surface of the portion being inductively heated by the coil), and the ring surface Temperature is raised to a predetermined temperature (specifically, 900.degree. C., 950.degree. C. or 1000.degree. C.). The time for the temperature of the ring surface to rise to the above-described predetermined temperature from the start of the heat treatment is, for example, about 5 seconds.

  After the ring surface is heated to a predetermined temperature, the power supplied to the coil is controlled so as to hold the ring for a specific time (heat treatment time) at the predetermined temperature (soaking). Then cool the ring. As a cooling method, the ring was cooled by immersing the ring in oil having a temperature of 70 ° C. (quenching treatment). For example, the heat pattern shown in FIG. 3 can be adopted as the heat pattern of such heat treatment.

  Further, after the above-described heat treatment, tempering was performed on the ring. The tempering conditions were a tempering temperature of 180 ° C. and a holding time of 2 hours, which are standard conditions.

Aging dimensional stability test
The bearings change in size as the residual austenite decomposes during use. In order to reduce the accuracy of the bearing, the dimensional change is required to be less than a certain standard.

(1) Sample After the above-described heat treatment, 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 a sample, nine types were prepared by the combination of the heating temperature (900 ° C., 950 ° C., 1000 ° C.) and the carbide area ratio in the above-described heat treatment as shown in Table 2.

(2) Test and result About the nine types of samples mentioned above, the change of the outside dimension before and behind the process on the conditions of heating temperature 230 degreeC and holding time 2 hours was measured. The results are shown in Table 3.

Here, the dimensional change rate is defined as (absolute value of D ₁ −D ₀ ) / D ₀ where D0 is the outer diameter of the sample before the treatment and D1 is the outer diameter of the sample after the treatment. Be done. The measurement position of the outer diameter of the sample was the same position before and after the high temperature holding. The measurement of the outer diameter was evaluated in two directions crossing 90 ° as viewed from the center of the ring-shaped sample. Also, n = 3 for each level.

In Table 3, assuming that the dimensional change rate is less than 70 × 10 ^-5 is regarded as equal to or higher than the atmosphere furnace heat-treated product, it is accepted (OK judgment), and the dimensional change rate ^rejects 70 × 10 ^-5 or more (Judgement of NG). As can be seen from Table 3, the samples which can ensure the aged dimensional stability equal to or higher than the atmosphere furnace heat-treated product from this result have a carbide area ratio of 8% and 12% when the heat treatment temperature is 900 ° C and 950 ° C. The sample has a carbide area ratio of 12% when the heat treatment temperature is 1000.degree.

In addition, when the approximation function is obtained from the test data described above and the condition that the dimensional change is less than 70 × 10 ⁻⁵ is obtained, 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 acts on the bearing, plastic deformation occurs, but in order for the rolling element of the bearing to roll smoothly, it is required that the amount of plastic deformation of the rolling element is 1/10000 or less of the diameter of the rolling element.

(1) Sample The ring after heat treatment described above was polished and wire-cut to obtain a sample of 6 mm long × 15 mm wide × 3 mm thick. The 6 mm × 15 mm surface of the sample was mirror polished. Similar to the aged dimensional stability test described above, nine types of samples were prepared by the combination of the heating temperature and the carbide area ratio.

  In addition, for comparison, after performing atmosphere furnace heat treatment as a heat treatment to a sample made of steel rings of the same composition and size as the heat treatment, a sample (sample of a comparative example) which is machined to have the same size is also prepared. did.

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

  In Table 4, the column of indentation depth shows the average value of the indentation depths measured for a plurality of samples for each sample, and the column of standard deviation shows the standard deviation of the data of the indentation depth. Then, in the column of judgment, those which are less likely to have an indentation than the samples of the atmosphere furnace heat treatment at a significance level of 95% are indicated as pass (OK), and those which are likely to have an indentation are indicated as failure (NG). Moreover, "-" was displayed on the column of determination about what is not applicable to the said reference | standard.

  From this result, it can be seen that the samples for which the indication in the judgment column is OK and "-" exhibit a static load capacity equal to or higher than the atmosphere furnace heat-treated product. Specifically, when the heat treatment temperature is 900 ° C. and 950 ° C., the samples having a carbide area ratio of 8% and 12% show static load capacity equal to or higher than the atmosphere furnace heat-treated product.

  Also, if the approximation function is obtained from the test data described above, and the standard deviation is 0.015 μm, the area at which the quality equal to or higher than that of the atmosphere furnace heat-treated product can be secured. When the heat treatment temperature is 950 ° C., the carbide area ratio is 4.8% or more. When the heat treatment temperature is 1000 ° C., the carbide area ratio is 13.2% or more.

<Crushing strength test>
The crushing strength may be required for the bearings, and the following tests were performed.

(1) Sample After the above-described heat treatment, 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 a sample, nine types were prepared by the combination of the heating temperature (900 ° C., 950 ° C., 1000 ° C.) and the carbide area ratio in the above-described heat treatment as shown in Table 2. Also, n = 3 for each level.

  In addition, for comparison, after performing atmosphere furnace heat treatment as a heat treatment to a sample made of steel rings of the same composition and size as the heat treatment, a sample (sample of a comparative example) which is machined to have the same size is also prepared. did.

(2) Test and Results For each sample, load was applied at a constant speed across the data from the radial direction, and the load leading to crushing was measured. Also, the fracture stress was calculated from the load. The results are shown in Table 5.

  In the column of judgment in Table 5, even if the standard deviation is taken into consideration, those with lower crush strength than the atmosphere furnace heat treated product are displayed as rejection (NG), and the standard deviation is considered equal to or higher than the atmosphere furnace heat treated product. About what can secure crushing strength, it displayed as "-".

  From this result, it is understood that the sample in which the indication of the judgment column is "-" can exhibit a crushing strength equal to or higher than the atmosphere furnace heat-treated product. Specifically, when the heat treatment temperature is 900 ° C. and 950 ° C., a sample having a carbide area ratio of 8% and 12% can exhibit a crush strength equal to or higher than the atmosphere furnace heat-treated product.

  In addition, when an approximation function is obtained from the test data described above, and the standard deviation is 150MPa, the carbide area ratio is 4 when the heat treatment temperature is 900 ° C. when a range capable of ensuring the quality equal to or higher than the atmosphere furnace heat treated product is calculated. When the heat treatment temperature is 950 ° C., the carbide area ratio is 5.4% or more. 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 means of high temperature short time heating such as induction heating is used for quenching of high carbon chromium bearing steel such as JIS standard SUJ2, performance equal to or better than atmosphere furnace heat treated product can be surely realized. Is the case where the heat treatment temperature is 900 ° C. and 950 ° C. and the carbide area ratio is 8% and 12%. Here, looking at each data, in any test results, the heat treatment temperature and the carbide area ratio are monotonously increasing or monotonously decreasing. Therefore, it is considered that the heat treatment condition corresponding to the region (region indicated by hatching in FIG. 2) surrounded by the four points obtained this time can realize the quality equal to or higher than the atmosphere furnace heat-treated product.

  Therefore, it is the area | region between 8%-12% of the carbide | carbonized_material area ratio which can ensure the quality more than an atmosphere furnace heat-treated product reliably at the heat processing temperature of 900 degreeC or more and 950 degrees C or less.

  Further, Table 6 shows the range of the carbide area ratio which is equal to or higher than the quality of the atmosphere furnace heat-treated product obtained from the approximation function of each test result.

With regard to the relationship between the range of the carbide area ratio shown in Table 6 and the heat treatment temperature, the approximation function can be obtained as follows:
Aging size:
6.600 × 10 ⁻⁴ X ² −1.205 X + 5.539 × 10 ² <Y (Conditional Expression 1)
Static load capacity:
1.160 × 10 ⁻³ X ² −2.094 X + 9.472 × 10 ² <Y (Conditional Expression 2)
Collapse test:
5.000 × 10 ⁻⁴ X ^{2 −} 8.970 × 10 ⁻¹ X + 4.063 × 10 ² <Y (Conditional Expression 3)
It becomes. Here, Y is a carbide area ratio (%), and X is a heat treatment temperature (° C.).

  And the range which can ensure the quality more than the atmosphere furnace heat treatment goods is a case where the carbide area ratio Y satisfies the said conditional expressions 1-3 in the range whose heat processing temperature X is 900 degreeC or more and 1000 degrees C or less.

  Here, in the heat treatment temperature range of 900 ° C. or more and 1000 ° C. or less, X satisfying conditional expression 1 always satisfies conditional expression 3 as well. Therefore, conditional expression 3 may not be taken into consideration. For this reason, the range in which the quality equal to or higher than that of the atmosphere furnace heat-treated product can be ensured is when the carbide area ratio Y satisfies the conditional expression 1 and the conditional expression 2 in the heat treatment temperature range of 900 ° C. or more and 1000 ° C. or less.

<Study of heat treatment conditions where hydrogen hardly penetrates>
In addition to the amount of carbon solid solution in the bearing component, the amount of hydrogen intruded into the bearing component also affects the bearing characteristics. Specifically, it is known that delayed fracture occurs due to hydrogen intruding into the bearing component. The inventors focused on the coolant used in the cooling process after induction heating, and investigated the influence of the difference in the coolant on the amount of hydrogen intruding into the bearing component.

(1) Sample In this test, a material consisting of the chemical components shown in Table 1 was used.

(2) Heat treatment method A steel ring made of JIS standard SUJ2 having the chemical components shown in Table 1 and having an outer diameter of 60.3 mm, an inner diameter of 53.7 mm, and an axial width of 15.3 mm as a sample Induction heating with a single turn coil. After the temperature of the ring surface is raised to 950 ° C., the ring is soaked at 950 ° C. for about 15 seconds. Then, the ring was cooled to 100 ° C. by immersing the ring in a coolant. After cooling, the ring was tempered. The tempering conditions were a tempering temperature of 230 ° C. and a holding time of 2 hours.

  As a coolant, bright quenching oil (bright quenching oil H-2050 manufactured by Nippon Grease Co., Ltd.) or a water-soluble coolant (Solqueque WP-2000S manufactured by Nippon Grease Co., Ltd.) was used. When using a quenching oil as a coolant, the ring was cooled by immersing the ring in quenching oil at 70 ° C. In the case of using an aqueous solution as a coolant, the ring was cooled by immersing the ring in an aqueous solution at 30 ° C.

  Moreover, after performing atmosphere furnace heat processing with respect to the sample which is a steel property ring of the same composition and size, the said sample was cooled by immersing the heated sample in hardening oil. Thereafter, the sample was tempered. The atmosphere furnace heat treatment conditions were a temperature of 850 ° C. in the atmosphere furnace and a holding time of 2 hours. In the atmosphere furnace heat treatment, an endothermic modified gas called RX gas (registered trademark) composed of gases such as nitrogen, carbon monoxide, carbon dioxide and hydrogen was used.

(3) Test and result The amount of hydrogen which entered into each sample was measured by temperature programmed desorption analysis (Hydrogenus steel in steel measuring system, JTF-20AII manufactured by J. Science Lab., Ltd.).

  FIG. 5 is a diagram showing the results of thermal desorption analysis. The horizontal axis of FIG. 5 indicates the temperature, and the vertical axis indicates the amount of hydrogen released from the sample per minute. No. in the figure. The test result indicated by 1 is the test result of the sample subjected to the atmosphere furnace heat treatment. No. The test result shown by 2 is a test result of a sample cooled using an aqueous solution after induction heating. No. The test result shown by 3 is a test result of a sample cooled using quenching oil after induction heating.

  As shown in FIG. 1 and No. Hydrogen was released from the sample of 2 between 200 ° C. and 400 ° C. On the other hand, no. No hydrogen was released from the sample of 3 between 200 ° C. and 400 ° C. From this, No. Samples subjected to atmosphere furnace heat treatment of No. 1 and No. 1 Although hydrogen penetrated into the sample cooled with the aqueous solution after induction heating of No. 2, No. 6 It can be seen that hydrogen hardly infiltrated into the sample cooled by the quenching oil after induction heating of 3. Further, from the amount of hydrogen released at 200 ° C. to 400 ° C., it can be seen that more hydrogen penetrates the sample subjected to the atmosphere furnace heat treatment than the sample cooled with quenching oil after induction heating.

  No. Sample No. 1 and No. 1 No. 3 is compared with No. 3 sample. It can be seen that hydrogen penetrates into the sample 1. No. Sample No. 1 and No. 1 The conditions after the cooling process are the same as for the sample No. 3, but the method of the heat treatment is different. From this, No. It is considered that hydrogen penetrated into the sample 1 at the time of heat treatment. In the atmosphere furnace heat treatment, the heat treatment is performed in a mixed gas containing propane, butane and hydrogen as described above. It is considered that hydrogen contained in the mixed gas intruded into the sample during heating. On the other hand, in the induction heat treatment, the heat treatment is performed in the atmosphere or in an inert gas, so the sample is not heated in an atmosphere containing hydrogen. Therefore, it is considered that hydrogen did not penetrate into the sample during heating.

  No. Sample No. 2 and No. No. 3 is compared with No. 3 sample. It can be seen that hydrogen is intruding into the second sample. No. Sample No. 2 and No. The samples No. 3 and No. 3 differ from each other only in the cooling treatment conditions. It is considered that hydrogen penetrated from the aqueous solution during the cooling process to the sample No. 2.

  No. Sample No. 1 and No. 1 No. 2 is compared with sample No. 2. No. 2 than No. 2 sample. It can be seen that a large amount of hydrogen is invading the sample 1. From this, it can be understood that the amount of hydrogen entering during the atmosphere furnace heat treatment is larger than the amount of hydrogen entering from the aqueous solution during the cooling process.

  From this point of view, in terms of the amount of hydrogen intruding into the bearing component, the induction heat-treated product can ensure the quality more than the atmosphere furnace heat-treated product. Also, from the viewpoint of the amount of hydrogen intruding into the bearing parts, bearing parts of higher quality can be manufactured using an oil-based coolant rather than a water-soluble coolant.

  Here, it is known that a water-soluble coolant generally has a higher cooling capacity than an oil-based coolant. Therefore, by induction heating only the surface area of the object to be heated and then spraying the water-soluble coolant to the object to be heated, the heat can be instantaneously cooled before it diffuses to the inside, and a very thin hardening is achieved. Layers can be created. In addition, when a water-soluble coolant is used, not only the surface heat but also the internal heat can be reduced quickly even if it is intended to obtain a thick hardened layer, so a structure other than martensite is mixed It can be expected to be effective in preventing such situations. Since such an effect can be expected, a water-soluble coolant is often used during the cooling process. However, when considered from the viewpoint of the amount of hydrogen intruding into the bearing components, bearing components of higher quality can be manufactured using an oil-based coolant rather than a water-soluble coolant.

  Although the embodiments of the present invention have been described above, various modifications of the above-described embodiments are possible. 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 present embodiment is particularly advantageously applied to a method of manufacturing a bearing component using induction heating.

  S10 material preparation process, S20 heat treatment process, S21 heat treatment process, S22 cooling process process, S30 post processing process, S40 assembly process.

Claims (4)

Preparing a steel processing target part to be a bearing part;
Heat treatment for heating and then cooling the part to be processed;
The step of performing the heat treatment includes a step of performing a heat treatment of heating the processing target component locally to a heat treatment temperature of 900 ° C. or more and 1000 ° C. or less, and an oily coolant for the heated processing target component Performing a cooling process of using and cooling,
In the step of performing the heat treatment, when the carbide area ratio in the part to be processed after the step of performing the heat treatment is Y (unit:%) and the heat treatment temperature is X (unit: ° C.)
6.600 × 10 ⁻⁴ X ² −1.205 X + 5.539 × 10 ² <Y
^{1.160 × 10 -3 X 2 -2.094X +} 9.472 × 10 2 <Y
A method of manufacturing a bearing component, wherein the conditions of the heat treatment are determined so as to satisfy the following relationship.   The manufacturing method of the bearing component of Claim 1 which heats the said process target component by induction heating in the process of performing the said heat processing.   The method of manufacturing a bearing component according to claim 1, wherein the steel constituting the processing target component is a high carbon chromium bearing steel. In the step of performing the heat treatment,
900 ° C. ≦ X ≦ 950 ° C.
8% ≦ Y ≦ 12%
The manufacturing method of the bearing component of any one of Claims 1-3 in which the conditions of the said heat processing are determined so that the relationship of may be satisfied.

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