shaft member

Abstract

The shaft member (30) is made of steel and has an outer peripheral surface (30a) that contacts a rolling element (32). In a region of the shaft member in which the distance in the radial direction from the outer peripheral surface is equal to or less than a first distance (L1), the hardness is equal to or greater than 653 Hv. In a region of the shaft member in which the distance in the radial direction is equal to or greater than a second distance (L2), the amount of retained austenite is equal to or less than 7% by volume. The first distance is greater than the distance in the radial direction from the outer peripheral surface to a position (P) at which the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface. The second distance is equal to or less than 1.5 times the distance in the radial direction from the outer peripheral surface to the position at which the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface.

Description

Technical Field

[0001] This invention relates to shaft components. Background Technology

[0002] Patent Document 1 (Japanese Patent Application Publication No. 2010-1521) discloses a pinion shaft. The core of the pinion shaft disclosed in Patent Document 1 has a residual austenite content of 0% by volume. The hardness of the outer peripheral surface of the pinion shaft disclosed in Patent Document 1 is 650 Hv or higher.

[0003] The pinion shaft is used in a high-temperature environment under applied torque loads. Therefore, creep deformation occurs with use. The pinion shaft described in Patent Document 1 has a core with 0% retained austenite, thus suppressing creep deformation that occurs with use. Furthermore, the pinion shaft described in Patent Document 1 has an outer surface hardness of 650 Hv or higher, thus improving rolling fatigue life.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-1521 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] However, the inventors conducted in-depth research and found that the pinion shaft described in Patent Document 1 still has room for improvement in terms of creep resistance and rolling fatigue life. That is, because the depth of the surface hardening layer on the outer peripheral surface and the distance from the outer peripheral surface to the core of the pinion shaft described in Patent Document 1 are not specified, the creep resistance and rolling fatigue life are insufficient.

[0009] The present invention was made in view of the problems of the prior art described above. More specifically, the present invention provides a shaft member capable of suppressing creep deformation under high-temperature conditions with applied torque loads and improving rolling fatigue life.

[0010] means of solving technical problems

[0011] The shaft member of the first embodiment of the present invention is a steel shaft member having an outer peripheral surface that contacts the rolling element. In a region where the radial distance between the shaft member and the outer peripheral surface is less than or equal to a first distance, the hardness is 653 Hv or higher. In a region where the radial distance between the shaft member and the outer peripheral surface is greater than or equal to a second distance, the amount of retained austenite is 7% by volume or less. The first distance is greater than the radial distance from the outer peripheral surface to the location where the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface. The second distance is less than 1.5 times the radial distance from the outer peripheral surface to the location where the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface.

[0012] The second embodiment of the present invention has a steel shaft member having an outer peripheral surface that contacts the rolling element. In the region where the radial distance between the shaft member and the outer peripheral surface is less than or equal to a first distance, the hardness is 653 Hv or higher. In the region where the radial distance between the shaft member and the outer peripheral surface is greater than or equal to a second distance, the amount of retained austenite is 7% by volume or less. The first distance is at least 0.038 times the diameter when the diameter of the shaft member is less than 12 mm, at least 0.03 times the diameter when the diameter is 12 mm or more and less than 16 mm, at least 0.025 times the diameter when the diameter is 16 mm or more and less than 20 mm, and at least 0.02 times the diameter when the diameter is 20 mm or more. The second distance is less than 0.04 times the diameter when the diameter is less than 12 mm, less than 0.038 times the diameter when the diameter is 12 mm or more but less than 16 mm, less than 0.03 times the diameter when the diameter is 16 mm or more but less than 20 mm, and less than 0.025 times the diameter when the diameter is 20 mm or more.

[0013] The third-order shaft member of the present invention is a steel shaft member having an outer peripheral surface that contacts the rolling element. In the region where the radial distance between the shaft member and the outer peripheral surface is less than or equal to a first distance, the hardness is 653 Hv or higher. In the region where the radial distance between the shaft member and the outer peripheral surface is greater than or equal to a second distance, the amount of retained austenite is 7% by volume or less. The first distance is 0.02 times or more of the diameter when the diameter of the shaft member is 12 mm or less. The first distance is 0.015 times or more of the diameter when the diameter is greater than 12 mm. The second distance is 0.025 times or less of the diameter when the diameter is 12 mm or less. The second distance is 0.02 times or less of the diameter when the diameter is greater than 12 mm.

[0014] In the aforementioned shaft components, the steel may contain 0.10% by weight or more and 0.40% by weight of carbon, 0.10% by weight or more and 2.50% by weight of silicon, 0.30% by weight or more and 1.20% by weight of manganese, 1.20% by weight of chromium, and 0.30% by weight of molybdenum.

[0015] In the aforementioned shaft components, the steel may contain 0.90% or more and 1.20% or less carbon, 0.10% or more and 2.50% or less silicon, 0.50% or less manganese, 1.20% or more and 1.70% or less chromium, and 0.08% or less molybdenum.

[0016] In the aforementioned shaft components, the steel may contain 0.90% or more and 1.20% or less carbon, 0.10% or more and 2.50% or less silicon, 0.80% or more and 1.30% or less manganese, 0.80% or more and 1.30% or less chromium, and 0.08% or less molybdenum.

[0017] The aforementioned shaft component can be subjected to carburizing or carburizing and nitriding treatment on its outer peripheral surface. The amount of retained austenite on the outer peripheral surface can be more than 10% by volume and less than 40% by volume. The aforementioned shaft component can be a pinion shaft for a planetary gear assembly.

[0018] The effects of the invention

[0019] The shaft member according to the first and second embodiments of the present invention can suppress creep deformation under high temperature conditions with applied torque loads and improve rolling fatigue life. Attached Figure Description

[0020] Figure 1 This is a front view of the planetary gear assembly 100.

[0021] Figure 2 yes Figure 1 Sectional view II-II in the diagram.

[0022] Figure 3 This is an enlarged sectional view of the shaft member 30 near the outer peripheral surface 30a.

[0023] Figure 4 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.015 times the outer diameter D1 and the outer diameter D1.

[0024] Figure 5 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.02 times the outer diameter D1 and the outer diameter D1.

[0025] Figure 6 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.025 times the outer diameter D1 and the outer diameter D1.

[0026] Figure 7It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.03 times the outer diameter D1 and the outer diameter D1.

[0027] Figure 8 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.038 times the outer diameter D1 and the outer diameter D1.

[0028] Figure 9 This is a process diagram showing the manufacturing method of the shaft component 30.

[0029] Figure 10 This is a schematic diagram used to illustrate the content of the four-point bending test.

[0030] Figure 11 This is a graph showing the relationship between the amount of residual austenite in test piece W and the amount of warpage in test piece W during a four-point bending test.

[0031] Figure 12 This is a graph showing the relationship between the change in the amount of residual austenite in test piece W before and after the four-point bending test and the amount of warpage of test piece W.

[0032] Figure 13 It is a graph showing the relationship between the radial distance of the shaft member 30 to the outer peripheral surface 30a and the maximum shear stress. Detailed Implementation

[0033] The detailed description of the embodiments is given with reference to the accompanying drawings. Throughout this document, the same or corresponding parts are labeled with the same reference numerals, and repeated descriptions will not be repeated.

[0034] (Structure of the planetary gear device and the shaft member of the embodiment)

[0035] The structure of the planetary gear device (hereinafter referred to as "planetary gear device 100") of the embodiment and the shaft member (hereinafter referred to as "shaft member 30") of the embodiment will be described below.

[0036] Figure 1 This is a front view of the planetary gear assembly 100. Figure 2 yes Figure 1 Sectional view II-II in the diagram. (See example...) Figure 1 and Figure 2 As shown, the planetary gear assembly 100 includes an internal gear 10, a shaft member 20, a sun gear 21, a shaft member 30, planetary gears 31, and a carrier 40. Figure 1 (Illustrations omitted). Planetary gear unit 100, for example, a speed reducer used in an automobile transmission.

[0037] The internal gear 10 has an annular shape. The internal gear 10 has an inner circumferential surface and an outer circumferential surface. Multiple teeth are formed on the inner circumferential surface of the internal gear 10 along the circumferential direction of the internal gear 10. The teeth of the internal gear 10 protrude radially inward from the inner circumferential surface of the internal gear 10.

[0038] The shaft member 20 has a cylindrical shape. The position of the central axis of the shaft member 20 coincides with the position of the central axis of the internal gear 10. The sun gear 21 has an inner circumferential surface and an outer circumferential surface. Multiple teeth are formed on the outer circumferential surface of the sun gear 21 along the circumferential direction of the sun gear 21. The teeth of the sun gear 21 protrude radially outward from the outer circumferential surface of the sun gear 21. A central hole is formed at the center of the sun gear 21, penetrating the sun gear 21 along the thickness direction. The shaft member 20 is mounted to the sun gear 21 by fitting into the central hole of the sun gear 21.

[0039] The shaft member 30 has a cylindrical shape. The shaft member 30 has an outer peripheral surface 30a. The detailed structure of the shaft member 30 will be described below. A planetary gear 31 is disposed between the internal gear 10 and the sun gear 21. A central hole is formed at the center of the planetary gear 31, extending through the planetary gear 31 in the thickness direction. The outer diameter of the shaft member 30 is D1.

[0040] Planetary gear 31 has an inner circumferential surface 31a and an outer circumferential surface 31b. The inner wall surface of the center hole of planetary gear 31 is the inner circumferential surface 31a. Multiple teeth are formed on the outer circumferential surface 31b along the circumferential direction of planetary gear 31. The teeth of planetary gear 31 protrude radially outward from the outer circumferential surface 31b. The teeth of planetary gear 31 mesh with the teeth of internal gear 10 and sun gear 21.

[0041] The shaft member 30 is inserted into the center hole of the planetary gear 31. That is, the shaft member 30 is a so-called pinion shaft. The shaft member 30 is rotatably supported by an inner circumferential surface 31a. More specifically, a plurality of rolling elements 32 are arranged between the outer circumferential surface 30a and the inner circumferential surface 31a. From another viewpoint, the outer circumferential surface 30a is the surface of the shaft member 30 that contacts the rolling elements 32. The rolling elements 32 are, for example, needle rollers. The outer diameter of the rolling element 32 is an outer diameter D2. The outer diameter D2 is less than 0.5 times the outer diameter D1. A carrier 40 is fixed to one axial end of the shaft member 30.

[0042] By rotating the shaft member 20, which serves as the input shaft, around its central axis, the sun gear 21 rotates around the central axis of the shaft member 20. The teeth of the planet gear 31 mesh with the teeth of the sun gear 21 and the internal gear 10, thus the planet gear 31 revolves around the sun gear 21 as the sun gear 21 rotates. The revolution of the planet gear 31 is transmitted to the carrier 40 via the shaft member 30, causing the output shaft (not shown), which is fixed on the carrier 40, to rotate around its central axis. In this way, the rotation of the input shaft is slowed down and transmitted to the output shaft through the planetary gear assembly 100.

[0043] <Detailed Structure of the Shaft Member in the Embodiment>

[0044] The detailed structure of shaft member 30 is described below.

[0045] The shaft member 30 is made of steel. The steel constituting the shaft member 30 is preferably steel of the first, second, or third composition below.

[0046] As shown in Table 1, the steel in the first composition contains 0.10% to 0.40% by weight of carbon, 0.10% to 2.50% by weight of silicon, 0.30% to 1.20% by weight of manganese, 1.20% to 1.20% by weight of chromium, and 0.30% to 0.30% by weight of molybdenum. Alternatively, the steel in the first composition may be free of chromium and molybdenum. The remainder of the steel in the first composition is iron and unavoidable impurities.

[0047] [Table 1]

[0048]

[0049] As shown in Table 2, the steel in the second composition contains 0.90% to 1.20% by weight of carbon, 0.10% to 2.50% by weight of silicon, 0.50% to 0.50% by weight of manganese, 1.20% to 1.70% by weight of chromium, and 0.08% to 0.08% by weight of molybdenum. Alternatively, the steel in the second composition may be molybdenum-free. The remainder of the steel in the second composition is iron and unavoidable impurities.

[0050] [Table 2]

[0051]

[0052] As shown in Table 3, the steel of the third component contains 0.90% to 1.20% by weight of carbon, 0.10% to 2.50% by weight of silicon, 0.80% to 1.30% by weight of manganese, 0.80% to 1.30% by weight of chromium, and 0.08% by weight of molybdenum. Alternatively, the steel of the third component may also be molybdenum-free. The remainder of the steel of the third component is iron and unavoidable impurities.

[0053] [Table 3]

[0054]

[0055] Figure 3 This is an enlarged sectional view of the shaft member 30 near the outer peripheral surface 30a. Figure 3 A cross-section through the central axis of shaft member 30 is shown. (Example) Figure 3 As shown, the shaft member 30 has a first region 30b and a second region 30c.

[0056] The first region 30b is located on the outer peripheral surface 30a. The first region 30b is the region in the radial direction of the shaft member 30 that is at a distance less than or equal to the distance L1 from the outer peripheral surface 30a. In the first region 30b, the hardness is 653 Hv or higher (58 HRC or higher).

[0057] Position P is defined as the location where the maximum shear stress reaches 650 MPa when the rolling element 32 contacts the outer peripheral surface 30a. The distance L1 is greater than the radial distance from the outer peripheral surface 30a to the shaft member 30 at position P. Furthermore, the maximum contact surface pressure when the rolling element 32 contacts the outer peripheral surface 30a is, for example, 2000 MPa or more and 4000 MPa or less.

[0058] The maximum shear stress when the rolling element 32 contacts the outer peripheral surface 30a is obtained as a function of the distance from the outer peripheral surface 30a by substituting equations (2) and (3) into equation (1). Therefore, the position P can be determined based on this function.

[0059] [Mathematical Expression 1]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065] K1 = (c + y) 2 +z 2 K2 = (cy) 2 +z 2

[0066] b is the contact width between the rolling element 32 and the outer peripheral surface 30a, and c is the minor axis radius of the contact ellipse.

[0067] μ is the coefficient of friction between the contact surfaces, P max The maximum contact pressure between the rolling element 32 and the outer peripheral surface 30a

[0068] The second region 30c is the region where the radial distance between the shaft member 30 and the outer peripheral surface 30a is greater than or equal to the distance L2. In the second region 30c, the amount of retained austenite is less than 7% by volume. Alternatively, the amount of retained austenite in the second region 30c can be 0% by volume.

[0069] The distance L2 is, for example, greater than or equal to the distance L1. However, the distance L2 can also be less than or equal to the distance L1. From another perspective, the first region 30b and the second region 30c can overlap each other radially in the shaft member 30. If the distance L2 is too large, the second region 30c will become too thin and unable to suppress creep deformation. Therefore, the distance L2 is less than 1.5 times the radial distance from the outer peripheral surface 30a to the shaft member 30 at position P. Preferably, the distance L2 is less than 1.3 times the radial distance from the outer peripheral surface 30a to the shaft member 30 at position P.

[0070] Figure 4 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.015 times the outer diameter D1 and the outer diameter D1. Figure 5 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.02 times the outer diameter D1 and the outer diameter D1. Figure 6 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.025 times the outer diameter D1 and the outer diameter D1.

[0071] Figure 7 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.03 times the outer diameter D1 and the outer diameter D1. Figure 8 It is a graph showing the relationship between the maximum shear stress at the position where the radial distance between the shaft member 30 and the outer peripheral surface 30a reaches 0.038 times the outer diameter D1 and the outer diameter D1.

[0072] In calculation Figures 4-8 When the curve is shown, the maximum contact surface pressure between the rolling element 32 and the outer peripheral surface 30a, the outer diameter D1, the outer diameter D2, the contact width between the rolling element 32 and the outer peripheral surface 30a, the Young's modulus, the Poisson's ratio and the coefficient of friction are the values ​​shown in Table 4.

[0073] [Table 4]

[0074]

[0075] Considering Figures 4-8The curves shown and the heat treatment deviations used to form the first region 30b are as shown in Tables 5 and 6, if the minimum value of the exemplary distance L1 and the maximum value of the distance L2 are calculated for each outer diameter D1 and outer diameter D2 respectively.

[0076] [Table 5]

[0077]

[0078] [Table 6]

[0079]

[0080] Carburizing is preferably performed on the outer peripheral surface 30a. Carburizing and nitriding can also be performed on the outer peripheral surface 30a. Carburizing is preferably performed until the carbon concentration on the outer peripheral surface 30a reaches 0.7% by weight or more. Carburizing and nitriding are preferably performed until the carbon concentration and nitrogen concentration on the outer peripheral surface 30a reach 0.7% by weight or more and 0.3% by weight or more, respectively.

[0081] The amount of retained austenite on the outer peripheral surface 30a is preferably 10% by volume or more and 40% by volume or less. If the amount of retained austenite in the region at a distance of 0.01 times the outer diameter D1 from the outer peripheral surface 30a is 10% by volume or more and 40% by volume or less, it is sufficient to achieve "the amount of retained austenite on the outer peripheral surface 30a is 10% by volume or more and 40% by volume or less".

[0082] The hardness of region 30b was determined using the Vickers hardness test method specified in JIS standard (JIS Z2244:2009). The amount of retained austenite in region 30b and region 30c was determined by X-ray diffraction. Specifically, the amount of retained austenite was obtained by comparing the integrated intensity of the X-ray diffraction peak of austenite with the integrated intensity of the X-ray diffraction peak of the phases other than austenite in the steel.

[0083] <Method for manufacturing shaft components according to the embodiments>

[0084] Figure 9 This is a process diagram illustrating the manufacturing method of the shaft component 30. (Example) Figure 9 As shown, the manufacturing method of shaft component 30 includes a preparation process S1, a carburizing and nitriding process S2, a quenching process S3, a tempering process S4, and a post-treatment process S5.

[0085] In preparation step S1, the component to be processed is prepared. In carburizing and nitriding treatment step S2, the outer peripheral surface of the component to be processed is subjected to carburizing and nitriding treatment. The carburizing and nitriding treatment is performed by heating and holding the component to be processed in a carbon and nitrogen-containing atmosphere. The atmosphere gas used for carburizing and nitriding treatment includes, for example, RX gas, enriched gas, and ammonia. The heating and holding temperature during carburizing and nitriding treatment is, for example, a temperature above the Al phase transformation point of the steel constituting the component to be processed.

[0086] In the quenching process S3, firstly, the workpiece is heated and held at a temperature above the Al phase transformation point. This generates austenite in the steel constituting the workpiece. Secondly, in the quenching process S3, the workpiece is rapidly cooled to M... S The temperature below the phase transformation point. Thereby, a portion of the austenite formed by the above heating and holding becomes martensite, and the remainder becomes retained austenite.

[0087] In the tempering process S4, the workpiece is heated and held at a temperature below the Al phase transformation point. This decomposes some of the retained austenite remaining after the quenching process S3. In the post-processing process S5, the workpiece is finished (grinding, lapping, etc.) and cleaned. The product is manufactured through the above processes. Figure 3 Shaft member 30 of the structure shown.

[0088] To further reduce the amount of retained austenite in the workpiece, a cryogenic treatment process S6 can be performed after quenching process S3 and before tempering process S4. In cryogenic treatment process S6, the workpiece is cooled to M... f Temperatures below the phase transformation point. This allows a portion of the retained austenite remaining after quenching step S3 to transform into martensite.

[0089] Distances L1 and L2 are adjusted by appropriately adjusting the heating temperature and holding time in the tempering process S4 and the cooling temperature in the cryogenic treatment process S6.

[0090] (Effects of the planetary gear device and shaft member of the embodiment)

[0091] The effects of the planetary gear assembly 100 and the shaft component 30 are explained below.

[0092] When the distance L1 is less than the radial distance from the outer peripheral surface 30a to position P of the shaft member 30, sufficient hardness cannot be ensured at position P. As a result, the rolling fatigue life of the shaft member 30 may become insufficient. However, since the distance L1 is greater than the radial distance from the outer peripheral surface 30a to position P of the shaft member 30, sufficient hardness (more specifically, a hardness of 653 Hv or higher) can be ensured at position P. Therefore, the rolling fatigue life can be improved by means of the shaft member 30.

[0093] Figure 10 This is a schematic diagram used to illustrate the four-point bending test. For example... Figure 10 As shown, the four-point bending test of the test piece W is carried out by applying loads to positions P3 and P4 while the piece is supported at positions P1 and P2.

[0094] The test specimen W has dimensions of 140 mm in length, 20 mm in width, and 3 mm in thickness. Positions P1 and P2 are positioned symmetrically with respect to the length of the test specimen W. The distance between positions P1 and P2 is 120 mm. The distance between positions P3 and P4 is 60 mm. Positions P3 and P4 are also positioned symmetrically with respect to the length of the test specimen W. A load is applied to the test specimen W such that the maximum bending stress applied to the test specimen W reaches 200 MPa. This load is applied from the second surface Wb side to the first surface Wa side of the test specimen W. Under the applied load, the test specimen W is held in the atmosphere at 130°C for 50 hours. The warpage of the test specimen W is the distance between the end of the second surface Wb along the length of the test specimen W and the position on the second surface Wb where the distance from that end is maximized.

[0095] Figure 11 This is a graph showing the relationship between the amount of retained austenite in specimen W and the amount of warpage in specimen W during a four-point bending test. For example... Figure 11 As shown, the smaller the amount of retained austenite in the test piece W before the four-point bending test, the smaller the warpage of the test piece W. Therefore, by keeping the amount of retained austenite in the second region 30c below 7% by volume, creep deformation of the shaft member 30 can be suppressed.

[0096] However, when the distance L2 is greater than 1.5 times the radial distance from the outer peripheral surface 30a to the shaft member 30 at position P, the second region 30c becomes too thin, and sometimes the effect of suppressing creep deformation is insufficient due to the amount of retained austenite being less than 7% by volume. On the other hand, since the distance L2 is less than 1.5 times the radial distance from the outer peripheral surface 30a to the shaft member 30 at position P, creep deformation can be sufficiently suppressed.

[0097] Figure 12This is a graph showing the relationship between the change in the amount of residual austenite in test piece W before and after the four-point bending test and the amount of warpage in test piece W. Figure 12 As shown, there is no particular phase between the change in the amount of residual austenite in the test piece W before and after the four-point bending test and the amount of warpage of the test piece W.

[0098] On the other hand, such as Figure 11 As shown, when the test piece W is formed with SUJ3 as specified in JIS standard (JIS G4805:2019), the warpage of the test piece W is smaller compared to that formed with SUJ2 as specified in JIS standard. That is, the alloy composition in the steel constituting the shaft member 30 has an effect on the creep deformation of the shaft member 30.

[0099] Compared to SUJ2, SUJ3 contains relatively more silicon and manganese. The first composition of the steel has a relatively higher silicon content compared to SUJ2 and SUJ3. The second and third compositions of the steel also have relatively higher silicon and manganese contents compared to SUJ2 and SUJ3. Therefore, by forming the shaft member 30 with steels from the first to third compositions, creep deformation can be further suppressed.

[0100] With a low carbon concentration in the steel, the dislocation density in the martensite generated by quenching is smaller, making it less prone to dislocation movement during high-temperature holding. The carbon concentration of the third-component steel is relatively lower than that of SUJ2 and SUJ3. Therefore, by forming the shaft member 30 with the third-component steel, creep deformation can be further suppressed.

[0101] Increasing the chromium content in steel promotes creep deformation. The steels in compositions one through three, due to their relatively low chromium content, are able to suppress creep deformation. Furthermore, suppressing the chromium content in the steel results in lower steel costs.

[0102] When the outer peripheral surface 30a is carburized or carburized and nitrided, the rolling fatigue life of the shaft member 30 is further improved due to the increased hardness of the outer peripheral surface 30a. When the amount of retained austenite on the outer peripheral surface 30a is more than 10% and less than 40%, the presence of retained austenite suppresses stress concentration and indentation, further improving the rolling fatigue life in the environment with foreign matter intrusion.

[0103] The planetary gear assembly 100, having a shaft member 30 as a pinion shaft, is able to suppress the rolling fatigue life and creep deformation of the pinion shaft.

[0104] (Variation Example 1)

[0105] From the perspective of production efficiency, as shown in Tables 5 and 6, it is sometimes difficult to vary the distances L1 and L2 according to the outer diameters D1 and D2. In this case, the same effect can be achieved by varying the distances L1 and L2 according to each outer diameter D1. More specifically, when the outer peripheral surface 30a of the shaft member 30 is in maximum contact with the rolling element 32 at a maximum contact pressure of 4000 MPa, the distances L1 and L2 can be set according to each outer diameter D1 as shown in Table 7.

[0106] [Table 7]

[0107]

[0108] (Variation Example 2)

[0109] Figure 13 This is a graph showing the relationship between the radial distance of the shaft member 30 to the outer peripheral surface 30a and the maximum shear stress. In the calculation... Figure 13 When plotting the curve, the outer diameter D1 is 18mm and the outer diameter D2 is 3.5mm. Furthermore, in calculating... Figure 13 When the curve is plotted, the maximum contact surface pressure between the outer peripheral surface 30a and the rolling element 32 is 2164 MPa.

[0110] like Figure 13 As shown, based on the outer diameter D1, outer diameter D2, and the maximum contact surface pressure between the outer peripheral surface 30a and the rolling element 32, the maximum shear stress applied to the shaft member 30 may sometimes be less than 650 MPa. Even in this case, it is necessary to consider preventing damage to the surface initiation point. In this case, if the second region 30c is too thin, it will be difficult to suppress creep deformation. From this point of view, when the outer peripheral surface 30a of the shaft member 30 is in contact with the rolling element 32 at the maximum contact surface pressure with a maximum shear stress of less than 650 MPa, the distances L1 and L2 can also be set according to the outer diameter D1 as shown in Table 8.

[0111] [Table 8]

[0112]

[0113] The embodiments of the present invention have been described above, but various modifications can be made to these embodiments. The scope of the present invention is not limited to the above embodiments. The scope of the present invention is defined by the claims and is intended to include all modifications with the same meaning and scope as the claims.

[0114] Industrial availability

[0115] This embodiment is particularly advantageously applicable to pinion shafts and planetary gear assemblies using pinion shafts.

[0116] Symbol Explanation

[0117] 10 Internal Gears

[0118] 20-axis component

[0119] 21 Sun Gear

[0120] 30-axis component

[0121] 30a outer peripheral surface

[0122] 30b First Zone

[0123] 30c Second Zone

[0124] 31 Planetary Gears

[0125] 31a Inner circumferential surface

[0126] 31b outer peripheral surface

[0127] 32 Rolling element

[0128] 40 racks

[0129] 100 Planetary Gear Assembly

[0130] D1 outer diameter

[0131] D2 outer diameter

[0132] P position

[0133] P1 position

[0134] P2 position

[0135] P3 position

[0136] P4 position

[0137] L1 distance

[0138] L2 distance

[0139] S1 Preparation Process

[0140] S2 Carburizing and Nitriding Process

[0141] S3 Quenching process

[0142] S4 Tempering Process

[0143] S5 Post-processing

[0144] S6 Cryogenic Treatment Process

[0145] W test piece.

Claims

1. Shaft member, which is a steel shaft member. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is greater than the radial distance from the outer peripheral surface to the location where the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface. The second distance is less than 1.5 times the radial distance from the outer peripheral surface to the location where the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface. The steel contains 0.10% by weight or more and 0.40% by weight of carbon, 0.10% by weight or more and 2.50% by weight of silicon, 0.30% by weight or more and 1.20% by weight of manganese, 1.20% by weight of chromium and 0.30% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

2. Shaft member, which is a steel shaft member. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is at least 0.038 times the diameter when the diameter of the shaft member is less than 12 mm, at least 0.03 times the diameter when the diameter is 12 mm or more and less than 16 mm, at least 0.025 times the diameter when the diameter is 16 mm or more and less than 20 mm, and at least 0.02 times the diameter when the diameter is 20 mm or more. The second distance is less than 0.04 times the diameter when the diameter is less than 12 mm, less than 0.038 times the diameter when the diameter is 12 mm or more but less than 16 mm, less than 0.03 times the diameter when the diameter is 16 mm or more but less than 20 mm, and less than 0.025 times the diameter when the diameter is 20 mm or more. The steel contains 0.10% by weight or more and 0.40% by weight of carbon, 0.10% by weight or more and 2.50% by weight of silicon, 0.30% by weight or more and 1.20% by weight of manganese, 1.20% by weight of chromium and 0.30% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

3. Shaft members, which are steel shaft members. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is at least 0.02 times the diameter when the diameter of the shaft member is less than 12 mm, and at least 0.015 times the diameter when the diameter is greater than 12 mm. The second distance is less than 0.025 times the diameter when the diameter is less than 12 mm, and less than 0.02 times the diameter when the diameter is greater than 12 mm. The steel contains 0.10% by weight or more and 0.40% by weight of carbon, 0.10% by weight or more and 2.50% by weight of silicon, 0.30% by weight or more and 1.20% by weight of manganese, 1.20% by weight of chromium and 0.30% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

4. Shaft members, which are steel shaft members. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is greater than the radial distance from the outer peripheral surface to the location where the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface. The second distance is less than 1.5 times the radial distance from the outer peripheral surface to the location where the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface. The steel contains 0.90% by weight and less than 1.20% by weight of carbon, 0.10% by weight and less than 2.50% by weight of silicon, less than 0.50% by weight of manganese, 1.20% by weight and less than 1.70% by weight of chromium and less than 0.08% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

5. Shaft members, which are steel shaft members. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is at least 0.038 times the diameter when the diameter of the shaft member is less than 12 mm, at least 0.03 times the diameter when the diameter is 12 mm or more and less than 16 mm, at least 0.025 times the diameter when the diameter is 16 mm or more and less than 20 mm, and at least 0.02 times the diameter when the diameter is 20 mm or more. The second distance is less than 0.04 times the diameter when the diameter is less than 12 mm, less than 0.038 times the diameter when the diameter is 12 mm or more but less than 16 mm, less than 0.03 times the diameter when the diameter is 16 mm or more but less than 20 mm, and less than 0.025 times the diameter when the diameter is 20 mm or more. The steel contains 0.90% by weight and less than 1.20% by weight of carbon, 0.10% by weight and less than 2.50% by weight of silicon, less than 0.50% by weight of manganese, 1.20% by weight and less than 1.70% by weight of chromium and less than 0.08% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

6. Shaft members, which are steel shaft members. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is at least 0.02 times the diameter when the diameter of the shaft member is less than 12 mm, and at least 0.015 times the diameter when the diameter is greater than 12 mm. The second distance is less than 0.025 times the diameter when the diameter is less than 12 mm, and less than 0.02 times the diameter when the diameter is greater than 12 mm. The steel contains 0.90% by weight and less than 1.20% by weight of carbon, 0.10% by weight and less than 2.50% by weight of silicon, less than 0.50% by weight of manganese, 1.20% by weight and less than 1.70% by weight of chromium and less than 0.08% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

7. Shaft members, which are steel shaft members. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is greater than the radial distance from the outer peripheral surface to the location where the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface. The second distance is less than 1.5 times the radial distance from the outer peripheral surface to the location where the maximum shear stress reaches 650 MPa when the rolling element contacts the outer peripheral surface. The steel contains 0.90% by weight or more and 1.20% by weight of carbon, 0.10% by weight or more and 2.50% by weight of silicon, 0.80% by weight or more and 1.30% by weight of manganese, 0.80% by weight or more and 1.30% by weight of chromium and 0.08% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

8. Shaft members, which are steel shaft members. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is at least 0.038 times the diameter when the diameter of the shaft member is less than 12 mm, at least 0.03 times the diameter when the diameter is 12 mm or more and less than 16 mm, at least 0.025 times the diameter when the diameter is 16 mm or more and less than 20 mm, and at least 0.02 times the diameter when the diameter is 20 mm or more. The second distance is less than 0.04 times the diameter when the diameter is less than 12 mm, less than 0.038 times the diameter when the diameter is 12 mm or more but less than 16 mm, less than 0.03 times the diameter when the diameter is 16 mm or more but less than 20 mm, and less than 0.025 times the diameter when the diameter is 20 mm or more. The steel contains 0.90% by weight or more and 1.20% by weight of carbon, 0.10% by weight or more and 2.50% by weight of silicon, 0.80% by weight or more and 1.30% by weight of manganese, 0.80% by weight or more and 1.30% by weight of chromium and 0.08% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

9. Shaft member, which is a steel shaft member. It has an outer peripheral surface that contacts the rolling element. The first distance is defined as the radial distance from the outer peripheral surface of the shaft member to the portion with a hardness of 653Hv. The radial distance from the outer peripheral surface to the location where the retained austenite content is 7% by volume is defined as the second distance. The first distance is at least 0.02 times the diameter when the diameter of the shaft member is less than 12 mm, and at least 0.015 times the diameter when the diameter is greater than 12 mm. The second distance is less than 0.025 times the diameter when the diameter is less than 12 mm, and less than 0.02 times the diameter when the diameter is greater than 12 mm. The steel contains 0.90% by weight or more and 1.20% by weight of carbon, 0.10% by weight or more and 2.50% by weight of silicon, 0.80% by weight or more and 1.30% by weight of manganese, 0.80% by weight or more and 1.30% by weight of chromium and 0.08% by weight of molybdenum, with the remainder being iron and unavoidable impurities.

10. The shaft member according to any one of claims 1 to 9, wherein, The outer peripheral surface is subjected to carburizing or carburizing and nitriding treatment. The amount of retained austenite on the outer peripheral surface is more than 10% by volume and less than 40% by volume.

11. The shaft member according to any one of claims 1 to 9, wherein, It is the pinion shaft used in planetary gear systems.

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