JP2006022820A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase a service life even under any lubricating conditions such as a low viscosity severe lubrication, a foreign matter environment, and a clean oil lubrication. <P>SOLUTION: An infinite number of micro recessed dents are formed at random at least in the surfaces of rolling elements, the surface roughness parameter Ryni of the surface in which the dents are formed is set within the range of 0.4 μm ≤ Ryni ≤ 1.0 μm, and sk value is set to -1.6 or less. At least one of the outer and inner rings and the rolling elements of the rolling bearing comprises a nitrogen-enriched layer, and the grain number of the austenitic crystal grains of the nitrogen-enriched layer exceeds 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rolling bearing, and can be applied to, for example, a roller bearing used in a shaft support portion of an automobile transmission.

  JP-A-2-16821 and JP-A-6-42536 describe rolling bearings in which minute irregularities are formed on the surface of a rolling element to improve oil film forming ability.

In the above prior art, as a countermeasure against damage due to poor lubrication such as peeling damage of roller bearings, a minute concave recess is provided on the rolling surface of the roller and / or the raceway surface of the inner and outer rings, and the surface roughness is set to the parameter Rqni. The value Rqni (L) / Rqni (C) of the ratio between the axial surface roughness Rqni (L) and the circumferential surface roughness Rqni (C) is 1.0 or less, and the surface roughness The parameter Sk value is set to −1.6 or less, so that a long life is obtained even when the mating surface is rough or has a good finish.
Japanese Patent Laid-Open No. 2-168021 (page 2, upper left column, line 14 to upper right column, second line) JP-A-6-042536 (paragraph number 0009)

  In recent years, parts where rolling bearings such as automobile transmissions are used are becoming smaller and higher in output, and the usage environment such as lower viscosity of the lubricating oil tends to become higher load and higher temperature. For this reason, bearings are changing to a more severe lubrication environment than ever, and surface-origin separation due to poor lubrication, fatigue life is reduced due to high surface pressure, and delamination in a foreign environment is more likely to occur. . Therefore, it is necessary to improve the service life under any lubrication conditions such as low-viscosity severe lubrication, foreign matter environment, and clean oil lubrication.

  When the surface roughness is expressed by the parameter Rqni, a conventional concave portion having a concave shape has a ratio value Rqni (L) / Rqni of the axial surface roughness Rqni (L) and the circumferential surface roughness Rqni (C). (C) is 1.0 or less (Rqni ≧ 0.10), and the surface roughness parameter Sk value is set to −1.6 or less. Although it is designed to have a long service life, the effect may not be sufficiently exhibited when the oil film thickness is extremely thin under low viscosity dilute lubrication.

  According to the present invention, in a rolling bearing in which an infinite number of minute concave recesses are provided at least on the surface of a rolling element, a surface roughness parameter Ryni of the surface provided with the recesses is 0.4 μm ≦ Ryni ≦ 1.0 μm. And the Sk value is −1.6 or less, and at least one of the outer member, the inner member, and the rolling element constituting the rolling bearing has a nitrogen-enriched layer. In addition, the grain size number of the austenite crystal grains in the nitrogen-enriched layer is in a range exceeding # 10.

  Here, the parameter Ryni is the average value of the maximum height for each reference length, that is, the reference length is extracted in the direction of the average line from the roughness curve, and the interval between the peak line and the valley bottom line of this extracted portion is the roughness curve. It is a value measured in the direction of the vertical magnification (ISO 4287: 1997).

  The parameter Sk indicates the degree of skewness (skewness) of the roughness curve (ISO 4287: 1997), and is a statistic that is a measure of the asymmetry of the uneven distribution. The Sk value is close to 0 in a symmetric distribution such as a Gaussian distribution. That is, when the concave and convex portions are deleted, negative values are obtained, and in the opposite case, positive values are obtained. The Sk value can be controlled by selecting the rotational speed of the barrel sander, the processing time, the amount of workpiece input, the type and size of the chip, and the like. By setting the Sk value to -1.6 or less in both the width direction and the circumferential direction, the hollow with a minute concave shape becomes an oil reservoir, and even when compressed, there is little oil leakage in the sliding direction and the right-angle direction, so that an oil film is formed. Excellent, oil film formation is good, and has the effect of minimizing surface damage.

  As is well known, a rolling bearing is a mechanical element that supports a shaft that rotates or swings by a rolling motion of a rolling element (ball or roller). Usually, the rolling element is freely rollable between the inner ring raceway and the outer ring raceway. However, the rolling element has no inner ring with the outer peripheral surface of the shaft as the direct raceway surface, for example, the inner peripheral surface of the gear directly on the raceway. There is also a type that does not have a surface outer ring. The use of the inner member and the outer member is not limited to the inner ring and the outer ring, and does not exclude a shaft or gear having a raceway surface. In addition, at least the surface of the rolling element is intended not to exclude the formation of a micro-concave recess on the raceway surface. Also, when the rolling element is a roller, not only the rolling surface is used. That is, it does not exclude the case where a concave portion having a minute concave shape is also formed on the end surface.

  The nitrogen-enriched layer is a layer with an increased nitrogen content formed on the raceway (outer ring or inner ring) or the surface layer of the rolling element, and can be formed by a process such as carbonitriding, nitriding, or nitriding. . The nitrogen content in the nitrogen-enriched layer is preferably in the range of 0.1% to 0.7%. If the nitrogen content is less than 0.1%, there will be no effect, and the rolling life especially under the foreign matter mixing conditions will be reduced. When the nitrogen content is more than 0.7%, voids called voids are formed, or the retained austenite increases so much that the hardness does not come out, resulting in a short life. For the nitrogen-enriched layer formed on the raceway, the nitrogen content is a value at the surface layer of 50 μm of the raceway surface after grinding, and can be measured by, for example, EPMA (wavelength dispersion type X-ray microanalyzer).

  In addition, the rolling fatigue life can be greatly improved by the finer austenite grain size as the grain size number of the austenite crystal grains exceeds 10. If the austenite grain size number is 10 or less, the rolling fatigue life is not greatly improved. Usually 11 or more. Although it is desirable that the austenite particle size is finer, it is usually difficult to obtain a particle size number exceeding # 13. In addition, the austenite grains of the bearing parts described above do not change either in the surface layer portion having the nitrogen-enriched layer or in the inside thereof. Therefore, the target position of the above crystal grain size number range is the surface layer portion and the inside. The austenite crystal grain is a crystal grain based on the trace of the austenite crystal grain boundary immediately before quenching after the quenching treatment, for example.

  The invention of claim 2 provides at least a random number of minute concave depressions on the surface of the rolling element, the rolling element has a nitrogen-enriched layer, and the grain size of austenite crystal grains in the nitrogen-enriched layer It is a rolling bearing characterized in that the number is in a range exceeding 10th.

  According to a third aspect of the present invention, in the rolling bearing of the second aspect, a surface roughness parameter Ryni of the surface provided with the recess is in a range of 0.4 ≦ Ryni ≦ 1.0 μm.

  According to a fourth aspect of the present invention, in the rolling bearing of the first or third aspect, a surface roughness parameter Rymax of the surface provided with the recess is 0.4 to 1.0. The parameter Rymax is the maximum value of the maximum height for each reference length (ISO 4287: 1997).

  According to a fifth aspect of the present invention, in the rolling bearing of the first, third, or fourth aspect, when the surface roughness of the surface provided with the recess is represented by a parameter Rqni, the axial surface roughness Rqni (L) and the circumferential direction The ratio value Rqni (L) / Rqni (C) to the surface roughness Rqni (C) is 1.0 or less. The parameter Rqni is the square root of the value obtained by integrating the square of the height deviation from the roughness center line to the roughness curve in the section of the measurement length and averaging the section, and is also called the root mean square roughness. (ISO 4287: 1997). Rqni is obtained by numerical calculation from the cross-sectional curve and roughness curve recorded in an enlarged manner, and measured by moving the stylus of the roughness meter in the width direction and the circumferential direction.

  The invention of claim 6 is the rolling bearing according to claim 1, 3, 4 or 5, characterized in that the nitrogen content in the nitrogen-enriched layer is in the range of 0.1% to 0.7%. Is.

  According to a seventh aspect of the present invention, in the rolling bearing according to the sixth aspect, the at least one member is a bearing ring, and the nitrogen content is a value at a surface layer of 50 μm of the raceway surface after grinding. It is characterized by.

  According to the present invention, an oil film forming ability is improved by providing an innumerable number of minute concave concaves on the surface of the rolling element, and the oil film thickness is extremely thin under low viscosity and dilute lubrication. But it has a long life. In particular, the surface roughness parameter Ryni of the surface provided with the indentation is set within a range of 0.4 μm ≦ Ryni ≦ 1.0 μm, and is suppressed to be smaller than before, thereby preventing oil film breakage even under lean lubrication. It is possible, and a long life can be obtained even under conditions where the oil film thickness is extremely thin compared to conventional products. As for the Sk value, −1.6 or less is a range advantageous for oil film formation in terms of the shape and distribution of the surface recess depending on the processing conditions.

  In addition, by forming a nitrogen-enriched layer and then refining the austenite grain size to a particle size number of 11 or more, the rolling fatigue life is greatly improved, and excellent crack resistance strength and aging resistance change are obtained. be able to.

  A rolling bearing has an inner ring, an outer ring, and rolling elements as main components. Then, an infinite number of minute concave recesses are randomly formed on at least one of the rolling surfaces and end surfaces of the rolling elements and the raceway surfaces of the inner and outer rings (and the large rib surface for the inner ring of the tapered roller bearing) to form a minute rough surface. It is faced. This minute rough surface has a surface roughness parameter Ryni of a surface provided with a depression within a range of 0.4 μm ≦ Ryni ≦ 1.0 μm, and an Sk value of −1.6 or less, preferably −4.9. ~ -1.6. Further, the surface roughness parameter Rymax of the surface provided with the depression is 0.4 to 1.0. Furthermore, when the surface roughness is obtained in each of the axial direction and the circumferential direction of each surface and displayed by the parameter Rqi, the ratio of the axial surface roughness Rqni (L) to the circumferential surface roughness Rqni (C) The value Rqni (L) / Rqni (C) is 1.0 or less, and the parameter Sk value of the surface roughness is −1.6 or less in both the axial direction and the circumferential direction. As the surface processing for obtaining such a fine rough surface, a desired finished surface can be obtained by special barrel polishing, but a shot or the like may be used.

The measurement method and conditions of the parameters Ryni, Rymax, Sk, Rqni are exemplified as follows. When measuring the surface properties represented by these parameters for components such as rolling elements and rolling rings of rolling bearings, a single measured value can be relied on as a representative value. Should be measured.
Parameter calculation standard: JIS B 0601: 1994 (Surfcom JIS 1994)
Cut-off type: Gaussian Measurement length: 5λ
Cut-off wavelength: 0.25mm
Measurement magnification: × 10000
Measurement speed: 0.30 mm / s
Measurement location: Roller center measurement number: 2
Measuring device: Surface roughness measuring device Surfcom 1400A (Tokyo Seimitsu Co., Ltd.)
FIG. 1 shows a first example of a rolling bearing. The rolling bearing 1 is a needle roller bearing in which a needle roller 2 is incorporated in an outer ring 3 as a rolling element, and a counter shaft 4 is supported by the needle roller 2. It is supposed to be. A description will be given of the results of manufacturing a plurality of types of needle roller bearings having surface treatments with different finishing surfaces on the surface of the needle rollers and performing a life test. As shown in FIG. 2, the needle roller bearing used for the life test has 15 outer diameters Dr = 33 mm, an inner diameter dr = 25 mm, a diameter D = 4 mm of the needle roller 2, and a length L = 25.8 mm. It is a bearing with the cage | basket 5 using the needle roller of this. Three types of test roller bearings with different surface roughness finishes were produced. That is, there are a bearing A (comparative example) subjected to superfinish after grinding, and a bearing B (comparative example) and a bearing C (example) in which an infinite number of minute concave recesses are formed. FIGS. 3 to 5 show the finished surface condition of the needle roller of each test bearing. 3 shows the surface roughness of the bearing A, FIG. 4 shows the surface roughness of the bearing B, and FIG. 5 shows the surface roughness of the bearing C. Table 1 shows a list of characteristic value parameters of the surface finish of each test bearing. For Rqni (L / C), the bearings B and C are 1.0 or less, and the bearing A is a value around 1.0.

The test apparatus used is a radial load tester 11 as schematically shown in FIG. 6, and the test bearings 1 are attached to both sides of the rotating shaft 12, and the test is performed by applying rotation and load. The finish of the inner race (mating shaft) used for the test is Ra 0.10 to 0.16 μm of the polished finish. The outer race (outer ring) is also common. The test conditions are as follows.
Bearing radial load: 2000kgf
Rotation speed: 4000rpm
Lubricant: Crisecoil H8 (2 cst under test conditions)
FIG. 7 shows the life test results under the oil film parameter Λ = 0.13. The vertical axis of the figure represents the L10 life (h). As is clear from the figure, bearing A was 78h and bearing B was 82h, while bearing C was 121h. As this data shows, the bearing C as an example can obtain a long-life effect even under extremely severe lubrication conditions where the oil film parameter Λ = 0.13.

  Next, FIG. 8 shows a tapered roller bearing as a second example of the rolling bearing. The tapered roller bearing is a radial bearing that uses a tapered roller 16 as a rolling element, and a plurality of tapered rollers 16 are interposed between a raceway of the outer ring 13 and a raceway of the inner ring 14 so as to be able to roll. During operation, the rolling surface 17 of the tapered roller 16 is in rolling contact with the raceway of the outer ring 13 and the inner ring 14, and the large end surface 18 of the tapered roller 16 is in sliding contact with the inner surface of the large collar 15 of the inner ring 14. Therefore, in the case of the tapered roller 16, an infinite number of minute concave recesses may be formed on the large end surface 18 in addition to the rolling surface 17. Similarly, in the case of the inner ring 14, an infinite number of minute concave recesses may be formed on the inner surface of the large brim 5 in addition to the raceway surface.

  Conventional tapered roller bearings A and B (comparative example) in which the rolling surface of the tapered roller is finished to be smooth, and bearings C to E in which numerous indentations having a small concave shape are randomly formed on the rolling surface of the tapered roller. The life test conducted for (Comparative Example) and bearings F and G (Examples) will be described (see Table 2). The bearings A to G used are tapered roller bearings having an outer diameter of 81 mm and an inner diameter of 45 mm. In addition, the rolling surfaces of the rollers in the bearings A and B of the comparative example are processed by super finishing (superfinishing) after grinding, and are not subjected to indentation processing. The rolling surfaces of the rollers C to E of the comparative example and the bearings F and G of the example are formed with a myriad of indentations of minute concave shapes randomly by barrel polishing special processing. For Rqni (L / C), roller bearings C to E, F, and G are 1.0 or less, and roller bearings A and B are values around 1.0.

  A peeling test was performed using a two-cylinder testing machine shown in FIG. 10, and the metal contact rate was evaluated. In FIG. 10, a driving side cylinder 22 (D cylinder: Driver) and a driven side cylinder 24 (F cylinder: Follower) are attached to one end of each rotating shaft, and two rotating shafts 26, 28 are pulleys 30, 32, respectively. Can be driven by a separate motor. The shaft 26 on the D cylinder 22 side was driven by a motor, and the F cylinder 24 was free-rolled to follow the D cylinder 22. For the F cylinder 24, two types of comparative examples and examples were prepared for the surface treatment. Details of the test conditions are shown in Table 3.

  The comparison data of metal contact ratio is shown in FIG. In this figure, the horizontal axis represents the elapsed time, the vertical axis represents the metal contact rate, FIG. 9B shows the metal contact rate of the rolling surface of the roller in the bearing of the example, and FIG. 9A shows the bearing of the comparative example. The metal contact ratios of the rolling surfaces of the rollers are shown respectively. Comparing these figures, it can be clearly confirmed that the metal contact ratio is improved in the embodiment as compared with the comparative example. In other words, the oil film formation rate (= 100% −metal contact rate) is about 10% at the start of operation and 2 at the end of the test (after 2 hours) in the bearing of the example compared to the bearing of the comparative example. % Improvement.

  Next, FIG. 11 shows a cross section of a deep groove ball bearing as another example of a rolling bearing. This rolling bearing is composed mainly of an outer ring 34, an inner ring 36, a plurality of rolling elements 38 that are freely rollable between the raceway of the outer ring 34 and the raceway of the inner ring 36, and a cage 40. ing. The rolling elements 38 are balls here, and are held by the retainer 40 at predetermined intervals in the circumferential direction. At least one bearing component of the outer ring 34, the inner ring 36 and the rolling element 38 constituting the rolling bearing has a nitrogen-enriched layer. A heat treatment including a carbonitriding process will be described as a specific example of the process for forming the nitrogen-enriched layer.

FIG. 12 is a diagram for explaining a heat treatment method for a rolling bearing in the embodiment of the present invention, and FIG. 13 is a diagram for explaining a modification thereof. FIG. 12 is a heat treatment pattern showing a method of performing primary quenching and secondary quenching, and FIG. 13 shows a method of cooling the material to below the A ₁ transformation point temperature during quenching, and then reheating and finally quenching. It is the heat processing pattern shown. In these figures, in the treatment T ₁ , the carbon is sufficiently dissolved while carbon and nitrogen are diffused in the steel base, and then cooled to less than the A ₁ transformation point. Next, in the process T ₂ of the in the figure, then reheated to a temperature lower than the A ₁ transformation point temperature or higher and treatment T _1, subjected to oil quenching from there.

  By the above heat treatment, the crack strength can be improved and the aging rate of dimensional change can be reduced while carbonitriding the surface layer portion as compared with conventional carbonitriding and quenching, that is, carbonitriding as it is, followed by quenching as it is. The rolling bearing of the present invention manufactured by the heat treatment pattern shown in FIG. 12 or FIG. 13 has a microstructure in which the grain size of austenite crystal grains is less than or equal to one half of the conventional one. The bearing component subjected to the above heat treatment has a long life against rolling fatigue, can improve the cracking strength, and can also reduce the rate of dimensional change over time. Since a heat treatment step for lowering the secondary quenching temperature is performed to refine the crystal grains, the amount of retained austenite is reduced in the surface layer and inside, and as a result, excellent crack strength and aging resistance can be obtained.

  FIG. 14 is a diagram showing the microstructure of bearing parts, particularly austenite grains. FIG. 14A shows a bearing component according to an example of the present invention, and FIG. 14B shows a conventional bearing component. That is, FIG. 14A shows the austenite grain size of the bearing ring of the rolling bearing according to the embodiment of the present invention to which the heat treatment pattern shown in FIG. 12 is applied. For comparison, FIG. 14B shows the austenite grain size of the bearing steel obtained by the conventional heat treatment method. FIGS. 15 (a) and 15 (b) show the austenite grain sizes illustrating FIGS. 14 (a) and 14 (b). From the structure showing the austenite grain size, the conventional austenite grain size is No. 10 in the JIS standard grain size number, and according to the heat treatment method of FIG. 12 or FIG. 13, No. 12 fine grains can be obtained. Moreover, the average particle diameter of Fig.14 (a) was 5.6 micrometers as a result of measuring by the intercept method.

  Next, examples will be described.

(Example I)
Using JIS standard SUJ2 material (1.0 wt% C-0.25 wt% Si-0.4 wt% Mn-1.5 wt% Cr), (1) measurement of hydrogen content, (2) crystal grain size (3) Charpy impact test, (4) Fracture stress value measurement, and (5) Rolling fatigue test. Table 4 shows the results.

  The manufacturing history of each sample is as follows.

  Samples A to D (examples of the present invention): carbonitriding 850 ° C., holding time 150 minutes. The atmosphere was a mixed gas of RX gas and ammonia gas. In the heat treatment pattern shown in FIG. 12, primary quenching was performed from a carbonitriding temperature of 850 ° C., and then secondary quenching was performed by heating to a temperature range of 780 ° C. to 830 ° C. lower than the carbonitriding temperature. However, Sample A having a secondary quenching temperature of 780 ° C. was excluded from the test because of insufficient quenching.

  Samples E and F (comparative examples): The carbonitriding treatment was carried out with the same history as the invention examples A to D, and the secondary quenching temperature was 850 ° C. to 870 ° C., which is a carbonitriding temperature of 850 ° C.

  Conventional carbonitrided product (comparative example): carbonitrided at 850 ° C., holding time of 150 minutes. The atmosphere was a mixed gas of RX gas and ammonia gas. Quenching was performed as it was from the carbonitriding temperature, and secondary quenching was not performed.

Normal quenching product (comparative example): without any carbonitriding treatment, it was quenched by heating to 850 ° C. Secondary quenching was not performed.

  Next, the test method will be described.

(1) Measurement of hydrogen amount The amount of hydrogen was determined by analyzing the amount of non-diffusible hydrogen in the steel using a DH-103 type hydrogen analyzer manufactured by LECO. The amount of diffusible hydrogen is not measured. The specification of this LECO DH-103 type hydrogen analyzer is shown below.

Analysis range: 0.01 to 50.00 ppm
Analysis accuracy: ± 0.1 ppm or ± 3% H (whichever is greater)
Analysis sensitivity: 0.01ppm
Detection method: Thermal conductivity method Sample weight size: 10 mg to 35 mg (maximum: diameter 12 mm × length 100 mm)
Heating furnace temperature range: 50 ° C to 1100 ° C
Reagents: Anhydrone Mg (ClO ₄ ) ₂ , Ascarite NaOH
Carrier gas: nitrogen gas, gas dosing gas: hydrogen gas, both gases have a purity of 99.99% or more and a pressure of 40 psi (2.8 kgf / cm ² ).

  The outline of the measurement procedure is as follows. A sample collected with a dedicated sampler is inserted into the hydrogen analyzer together with the sampler. Internal diffusible hydrogen is directed to the thermal conductivity detector by a nitrogen carrier gas. This diffusible hydrogen is not measured in this example. Next, a sample is taken out from the sampler, heated in a resistance heating furnace, and non-diffusible hydrogen is guided to the thermal conductivity detector by nitrogen carrier gas. The amount of non-diffusible hydrogen can be known by measuring the thermal conductivity with a thermal conductivity detector.

(2) Measurement of crystal grain size The crystal grain size was measured based on the JIS G 0551 steel austenite grain size test method.

(3) Charpy impact test The Charpy impact test was performed based on the Charpy impact test method of the metal material of JIS Z2242. As a test piece, a U-notch test piece (JIS No. 3 test piece) shown in JIS Z 2202 was used.

(4) Measurement of Fracture Stress Value FIG. 16 is a diagram showing a test piece for a static crush strength test (measurement of a fracture stress value). The load until it is broken by applying a load in the P direction in the figure is measured. Thereafter, the obtained fracture load is converted into a stress value by the following bending beam stress calculation formula. In addition, a test piece is not restricted to the test piece shown in FIG. 16, You may use the test piece of another shape.

Assuming that the fiber stress on the convex surface of the test piece of FIG. 16 is σ ₁ and the fiber stress on the concave surface is σ ₂ , σ ₁ and σ ₂ are obtained by the following equations (Mechanical Engineering Handbook A4 Knitting Material Dynamics A4-40) . Here, N is the axial force of the cross section including the axis of the annular specimen, A is the cross-sectional area, e ₁ is the inner radius, and e ₂ is the outer radius. Further, κ is a section modulus of the curved beam.
σ ₁ = (N / A) + {M / (Aρ ₀ )} [1 + e ₁ / {κ (ρ ₀ + e ₁ )}]
σ ₂ = (N / A) + {M / (Aρ ₀ )} [1-e ₂ / {κ (ρ ₀ −e ₂ )}]
κ = − (1 / A) ∫A {η / (ρ ₀ + η)} dA
(5) Rolling fatigue life Table 2 shows the test conditions for the rolling fatigue life test. FIG. 17 is a schematic view of a rolling fatigue life tester. FIG. 17A is a front view, and FIG. 17B is a side view. In FIG. 17A and FIG. 17B, the rolling fatigue life test piece 48 is driven by the drive roll 42 and rotates in contact with the ball 46. The ball 46 is a 3/4 inch ball and is guided by the guide roll 44 to roll while exerting a high surface pressure with the rolling fatigue life test piece 48.

  The test results of Example I shown in Table 4 will be described as follows.

(1) Amount of hydrogen Conventional carbonitrided products that have undergone carbonitriding have a very high value of 0.72 ppm. This is thought to be because ammonia (NH ₃ ) contained in the carbonitriding atmosphere decomposed and hydrogen entered the steel. On the other hand, in Samples B to D, the hydrogen content is reduced to almost half of 0.37 to 0.40 ppm. This amount of hydrogen is at the same level as that of ordinary hardened products.

  By reducing the amount of hydrogen described above, embrittlement of steel due to hydrogen solid solution can be reduced. That is, the reduction in the amount of hydrogen greatly improves the Charpy impact value of Samples B to D of the present invention example.

(2) Crystal grain size When the secondary quenching temperature is lower than the quenching (primary quenching) temperature during carbonitriding, that is, in the case of Samples B to D, the austenite grains are prominent as the grain size numbers 11 to 12. Has been refined. The austenite grains of the samples E and F, the conventional carbonitrided product and the normal quenching product have a crystal grain size number 10, and are coarser than the samples B to D of the examples of the present invention.

(3) Charpy impact test According to Table 1, the Charpy impact value of the samples B to D of the present invention example is 6 compared to the Charpy impact value of the conventional carbonitrided product being 5.33 J / cm ^2. A high value of .30 to 6.65 J / cm ² is obtained. Among these, the one where secondary quenching temperature is low shows the tendency for a Charpy impact value to become high. The normally hardened product has a high Charpy impact value of 6.70 J / cm ² .

(4) Measurement of fracture stress value The fracture stress value corresponds to the crack resistance strength. According to Table 4, the conventional carbonitrided product has a fracture stress value of 2330 MPa. Compared to this, the fracture stress values of Samples B to D were improved to 2650 to 2840 MPa. The fracture stress value of the normal quenching product is 2770 MPa, and the improved cracking resistance strength of Samples B to D is estimated to have a great effect by reducing the hydrogen content, along with the refinement of austenite crystal grains.

(5) According to the rolling contact fatigue test Table 4, normally quenched sample has to reflect to have no carbonitrided layer in the surface layer portion, the rolling fatigue life L ₁₀ is the lowest. Compared to this, the rolling fatigue life of the conventional carbonitrided product is 3.1 times. The rolling fatigue life of Samples B to D is significantly improved as compared with the conventional carbonitrided product. Samples E and F are almost equivalent to conventional carbonitrided products.
In summary, Samples B to D of the present invention have a reduced hydrogen content, an austenite grain size of 11 or more, and improved Charpy impact value, crack resistance strength and rolling fatigue life. .

Example II
Next, Example II will be described. A series of tests were performed on the following X material, Y material, and Z material. JIS standard SUJ2 material (1.0% by weight C-0.25% by weight Si-0.4% by weight Mn-1.5% by weight Cr) is used for the heat treatment material. did. The manufacturing history of the X material to the Z material is as follows.
X material (comparative example): Only normal quenching (not carbonitriding).
Y material (comparative example): quenching directly after carbonitriding (conventional carbonitriding quenching). Carbonitriding temperature 845 ° C, holding time 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas.
Z material (example of the present invention): bearing steel subjected to the heat treatment pattern of FIG. Carbonitriding temperature 845 ° C, holding time 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas. The final quenching temperature was 800 ° C.

(1) Rolling fatigue life Test conditions and test equipment for rolling fatigue life are as shown in Table 5 and FIG. 17 as described above. The rolling fatigue life test results are shown in Table 6.

According to Table 6, the Y material of the comparative example shows 3.1 times the L ₁₀ life of the X material that was subjected only to normal quenching in the comparative example (the life that one of the 10 test pieces breaks), The effect of extending the life by carbonitriding is recognized. On the other hand, the Z material of the present invention example has a long life of 1.74 times that of the B material and 5.4 times that of the X material. The main reason for this improvement is thought to be the refinement of the microstructure.

(2) Charpy impact test The Charpy impact test was performed by the method according to the above-mentioned JISZ2242 using the U notch test piece. The test results are shown in Table 7.

  The Charpy impact value of the Y material (comparative example) subjected to carbonitriding was not higher than that of the normal quenching X material (comparative example), but the Z material obtained the same value as the X material.

(3) Test of Static Fracture Toughness Value FIG. 18 is a diagram showing a test piece of a static fracture toughness test. About 1 mm of pre-crack was introduced into the notch portion of the test piece, and then a static load by three-point bending was applied to determine the fracture load P. The following formula (I) was used for calculation of the fracture toughness value (K ₁ c value). The test results are shown in Table 8.
K1c = (PL√a / BW ² ) {5.8−9.2 (a / W) +43.6 (a / W) ²
−75.3 (a / W) ³ +77.5 (a / W) ⁴ } (I)

  Since the precrack depth is larger than the carbonitrided layer depth, there is no difference between the X material and the Y material of the comparative example. However, the Z material of the present invention example was able to obtain a value about 1.2 times that of the comparative example.

(4) Static Crush Strength Test A static crush strength test piece having the shape shown in FIG. 16 was used as described above. In the figure, a static crushing strength test was performed by applying a load in the P direction. The test results are shown in Table 9.

  The Y material subjected to carbonitriding has a slightly lower value than the normal quenching X material. However, the Z material of the example of the present invention has a static crushing strength higher than that of the Y material, and a level comparable to that of the X material is obtained.

(5) Aged dimensional change rate The measurement results of the aged dimensional change rate at a holding temperature of 130 ° C. and a holding time of 500 hours are shown in Table 7 together with the surface hardness and the retained austenite amount (50 μm depth).

  It can be seen that the Z material of the example of the present invention is suppressed to half or less compared to the dimensional change rate of the Y material having a large amount of retained austenite.

(Example III)
Table 13 shows the results of tests conducted on the relationship between the nitrogen content and the rolling life under the contamination condition. In this test, the tapered roller bearing shown in FIG. 8 is used, and in Examples 1 to 5, all of the outer ring 13, the inner ring 14, and the tapered roller 16 are manufactured by the heat treatment pattern shown in FIG. In addition, an infinite number of minute concave recesses shown in Tables 1 and 2 are formed on the surface of the tapered roller. Comparative Example 1 is a standard quenched product, and Comparative Example 2 is a standard carbonitrided product. Comparative Example 3 is a case where the same treatment as in the embodiment of the present invention was performed, but only the amount of nitrogen was excessive. The test conditions are as follows.
Test bearing: Tapered roller bearing 30206 (both inner and outer rings and rollers are made of JIS high carbon chrome bearing steel class 2 (SUJ2))
Radial load: 17.64kN
Axial load: 1.47kN
Rotation speed: 2000rpm
1g / L of hard foreign matter

  From Table 11, regarding Examples 1 to 5, it can be seen that the nitrogen content and the foreign substance lifetime are in a substantially proportional relationship. However, in Comparative Example 3 where the nitrogen content is 0.72, the upper limit of the nitrogen content is preferably 0.7 in light of the fact that the rolling life under the mixing of foreign matters is extremely reduced.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Sectional drawing of a needle roller bearing. Sectional drawing of the needle roller bearing used for the life test. The roughness curve figure which shows the finished surface condition of the rolling element in a test bearing. The roughness curve figure which shows the finished surface condition of the rolling element in a test bearing. The roughness curve figure which shows the finished surface condition of the rolling element in a test bearing. Schematic of a test apparatus. The graph which shows a life test result. Sectional drawing of a tapered roller bearing. A is a graph showing the metal contact rate of the comparative example, and B is a graph showing the metal contact rate of the example. Overall schematic diagram of a two-cylinder testing machine. The schematic sectional drawing which shows the rolling bearing in embodiment of this invention. The figure explaining the heat processing method of the rolling bearing in embodiment of this invention. The figure explaining the modification of the heat processing method of the rolling bearing in embodiment of this invention. It is a figure which shows the microstructure of a bearing component, especially an austenite grain, Comprising: (a) is a bearing component of the example of this invention, (b) is a conventional bearing component. (A) shows the austenite grain boundary illustrated in FIG. 14 (a), and (b) shows the austenite grain boundary illustrated in FIG. 14 (b). The figure which shows the test piece of a static crushing strength test (measurement of a fracture stress value). It is the schematic of a rolling fatigue life test machine, (a) is a front view, (b) is a side view. The figure which shows the test piece of a static fracture toughness test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling bearing 2 Rolling element 2a Indentation 3 Outer ring 4 Opposite shaft 5 Cage

Claims (7)

In a rolling bearing in which a large number of minute concave depressions are randomly provided on the surface of the rolling element,
The surface roughness parameter Ryni of the surface provided with the recess is in the range of 0.4 μm ≦ Ryni ≦ 1.0 μm, and the Sk value is −1.6 or less,
At least one of the outer member, the inner member, and the rolling element constituting the rolling bearing has a nitrogen-enriched layer, and the austenite crystal grain size number in the nitrogen-enriched layer is 10 A rolling bearing characterized by being in a range exceeding the number.   A range in which at least the surface of the rolling element is randomly provided with an infinite number of minute concave recesses, the rolling element has a nitrogen-enriched layer, and the austenite grain size number in the nitrogen-enriched layer is greater than 10 A rolling bearing characterized by   The rolling bearing according to claim 2, wherein a surface roughness parameter Ryni of the surface provided with the depression is in a range of 0.4 ≦ Ryni ≦ 1.0 μm.   The rolling bearing according to claim 1 or 3, wherein a surface roughness parameter Rymax of the surface provided with the recess is in a range of 0.4 to 1.0.   When the surface roughness of the surface provided with the depression is represented by the parameter Rqni, the ratio value Rqni (L) / Rqni (R) of the axial surface roughness Rqni (L) and the circumferential surface roughness Rqni (C) 5. The rolling bearing according to claim 1, wherein C) is 1.0 or less.   The rolling bearing according to claim 1, 3, 4, or 5, wherein the nitrogen content in the nitrogen-enriched layer is in the range of 0.1% to 0.7%. The rolling bearing according to claim 6, wherein the at least one member is a bearing ring, and the nitrogen content is a value at a surface layer of 50 μm of the raceway surface after grinding.