Test method for rolling fatigue strength

Abstract

To provide a method for testing rolling fatigue strength which can evaluate fatigue characteristics of a gear material more easily and more precisely.SOLUTION: A method for testing rolling fatigue strength according to an embodiment of the present invention has an evaluation material having an axis of rotation and at least one partner material having an axis of rotation, and evaluates the rolling fatigue strength of the evaluation material by bringing a rotary surface of the evaluation material and a rotary surface of the partner material in contact with each other and causing the evaluation material and the partner material to rotate in opposite directions while applying a load on the evaluation material. In the method, a burn-in evaluation parameter SR is not larger than 9.00, a yield parameter RD is not larger than 0.85, a sliding rate of the evaluation material σ12 is in the range of -300% to -60%, and root-mean-square roughness Rq of a contact surface of the evaluation material in contact with the partner material and a contact surface of the partner material in contact with the evaluation material is not larger than 1.00 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for testing rolling fatigue strength. [Background technology]

[0002] Traditionally, the rolling fatigue strength (pitting strength) of surface-hardened steel used in gears is often evaluated by a two-cylinder rolling fatigue test. The two-cylinder rolling fatigue test is a test in which a roller-shaped test piece is brought into contact with another roller, and the rolling fatigue of the test piece is evaluated by controlling the surface pressure of the contact surface and the rotational speed of each roller.

[0003] For example, in Patent Document 1, a small roller with a diameter of 26 mm and a large roller with a diameter of 130 mm and a crowning of 150 mm are used as test specimens, and the pitting strength is measured with a slip ratio of 80%, a rotation speed of 1000 rpm for the small roller, and a surface pressure of 2800 MPa or 3000 MPa. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-132936 [Non-patent literature]

[0005] [Non-Patent Document 1] Ichiro Nakahara, Strength of Materials, Volume 2, Yokendo, Tokyo (1971), pp. 116-132. [Non-Patent Document 2] Masatoshi Tokuda, Mechanical Design, Vol. 24, No. 12 (1980), pp. 26-30. [Non-Patent Document 3] Tedric A. Harris, "Rolling Bearing Analysis", John Wiley & Sons Inc., p.110-143. [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, electric vehicles have emerged and are gaining market share. Compared to conventional gasoline-engine vehicles, electric vehicles tend to experience higher loads on their gears (surface pressure, rotational speed, slip ratio, etc.), requiring higher strength from the steel used as the gear material. As a result, when evaluating steel materials used for electric vehicle gears, it has become necessary to conduct tests under higher loads.

[0007] In conventional two-cylinder rolling fatigue tests, when evaluating the rolling fatigue strength of high-strength materials under high load, seizure can occur during the test. This can lead to problems such as being unable to obtain appropriate test results, or having to reduce the rotation speed during the test to avoid seizure, resulting in a test that takes a long time.

[0008] Furthermore, when evaluating steel materials that will be used as gear components, especially those requiring surface hardening treatment (particularly gas carburizing, vacuum carburizing, or nitriding), the materials are subjected to fatigue testing only after undergoing surface hardening treatment under the same conditions as the gears. Conventional two-cylinder rolling fatigue tests have a drawback: when high-load tests are performed, the inside of the material being evaluated can undergo plastic deformation during the test, making it difficult to obtain appropriate test results for evaluating surface fatigue strength.

[0009] This invention has been made in view of the above circumstances, and the object of this invention is to provide a rolling fatigue strength test method using a two-cylinder rolling fatigue test, which can evaluate the fatigue characteristics of gear materials more simply and more accurately. [Means for solving the problem]

[0010] The inventors of this invention have conducted extensive research and obtained the following findings. (a) In a two-cylinder rolling fatigue test, increasing the slip ratio increases the tangential force on the surface of the test roller (evaluation material), making surface-initiated pitting fatigue more likely to occur. (b) By changing the diameter of each roller in the two-cylinder rolling test, the shear stress distribution generated inside the test roller can be controlled, and by positioning the high-stress region in the surface hardened layer of the test roller, the influence of the core hardness (the hardness near the center of the roller axis of the test roller) can be reduced. (c) Although the amount of heat generation increases with an increase in the slip ratio and there is a possibility that the rollers may seize, seizure can be suppressed by restricting the contact area between the rollers. Based on the above findings, the inventors have developed a method for evaluating rolling fatigue strength.

[0011] The gist of the present invention completed based on the above findings is as follows. [1] A test method for rolling fatigue strength according to one aspect of the present invention includes an evaluation material having a rotating shaft and one or more mating materials having a rotating shaft, bringing the rotating surface of the evaluation material into contact with the rotating surface of the mating material, while applying a load to the evaluation material, rotating the evaluation material and the mating material in opposite directions to each other, and evaluating the rolling fatigue strength of the evaluation material. A test method for rolling fatigue strength, wherein the area A (mm 2 ) and the slip ratio σ 12 of the contact surface of the evaluation material with the mating material when the load is acting are used to calculate the seizure evaluation parameter S R by formula (1), satisfying S xy ≤ 9.00, and the depth position Dτ xy from the contact surface of the evaluation material where the conjugate maximum shear stress τ xy of the evaluation material occurs is used to calculate Dτ c ' from formula (2), and the yield parameter R D calculated from formula (3) using Dτ 12 ' and the effective hardened layer depth D S R = A × (σ 12 / 100) 2 ··· Formula (1) Dτ xy '=2Dτ xy ...Equation (2) R D =Dτ xy ' / D c ...Equation (3) [2] In the rolling fatigue strength test method described in [1] above, the shape of the contact surface between the evaluation material and the mating material may be elliptical, and the area A may be calculated by formula (4) using the major axis radius a (mm) and the minor axis radius b (mm). A = πab ... Equation (4) [3] In the rolling fatigue strength test method described in [2] above, the radius R of the contact portion of the evaluation material that comes into contact with the mating material. 11 It may be between 2 and 100 mm. [4] In the rolling fatigue strength test method described in [2] or [3] above, the crowning R of the contact portion of the evaluation material that comes into contact with the mating material 12 It may be 1 mm or more. [5] In the rolling fatigue strength test method described in any of [2] to [4] above, the radius R of the contact portion of at least one of the one or more mating materials that contacts the evaluation material. 21 The size can be between 2mm and 100mm. [6] In the rolling fatigue strength test method described in any of [2] to [5] above, the crowning R of the contact portion of at least one of the one or more mating materials 22 It may be 1 mm or more. [7] In the rolling fatigue strength test method described in [1] above, the shape of the contact surface between the evaluation material and the mating material is rectangular, and the area A is equal to the contact length L in the direction of the principal axis. s Alternatively, the contact width 2w in the circumferential direction may be used to calculate the contact width using equation (5). A = 2wL s ...Equation (5) [8] In the rolling fatigue strength test method described in [7] above, the length l2 in the rotational axis direction of the contact portion in the evaluation material that contacts the mating material may be 1 mm or more. [9] In the rolling fatigue strength test method described in [7] or [8] above, the rotational axial length l of the contact surface of at least one of the one or more mating materials that contacts the evaluation material. 21 It may be 1 mm or more. [Effects of the Invention]

[0012] According to the above-described embodiment of the present invention, the fatigue characteristics of gear materials can be evaluated more simply and accurately. In particular, the above-described embodiment of the present invention can be used to evaluate the rolling fatigue characteristics of small gear steels used in electric vehicles and the like. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram illustrating a test method for measuring rolling fatigue strength according to one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the major axis radius a and minor axis radius b at the contact surface of the evaluation material in the first embodiment. [Figure 3] This is a front view of the evaluation material in the same embodiment. [Figure 4] This is a front view of the mating material in the same embodiment. [Figure 5] This is a front view of the evaluation material in the second embodiment. [Figure 6] This is a front view of the mating material in the same embodiment. [Figure 7] This is a schematic diagram illustrating the contact length Ls and contact width 2w at the contact surface of the evaluation material in the same embodiment. [Figure 8] This is a front view showing a modified example of the evaluation material. [Figure 9] This is a front view showing a modified example of the evaluation material. [Figure 10] This is a front view showing a modified version of the mating material. [Figure 11] This is a front view showing a modified version of the mating material. [Figure 12] This is a front view showing a modified example of the evaluation material. [Modes for carrying out the invention]

[0014] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0015] A rolling fatigue strength test method according to one embodiment of the present invention, as shown in Figure 1, involves bringing the rotation surface (contact surface 111) of a cylindrical evaluation material 1 having a rotation axis C1 into contact with the rotation surface (contact surface 211) of a cylindrical mating material 2 having a rotation axis C2, applying a load from the mating material 2 to the evaluation material 1, and rotating the evaluation material 1 and the mating material 2 in opposite directions around their respective rotation axes C1 and C2 as centers of rotation to evaluate the rolling fatigue strength of the evaluation material 1. The contact surface S is the contact surface of the evaluation material 1 when a load is applied from the contact surface 211 of the mating material 2 to the contact surface 111 of the evaluation material 1.

[0016] The evaluation material 1 and the mating material 2 can be rotated at independent rotational speeds while maintaining contact. That is, by rotating the evaluation material 1 and the mating material 2 in opposite directions at different peripheral speeds, slippage can be induced between the contact surfaces 111 and 211, allowing for a test that replicates the slippage that occurs in the operating environment of gears. Of course, it is also possible to rotate the evaluation material 1 and the mating material 2 in opposite directions at equal peripheral speeds to conduct a fatigue test without slippage. In the rolling fatigue strength test method of this embodiment, the method for calculating the seizure evaluation parameters, which will be described later, differs depending on the shape of the contact surface between the evaluation material and the mating material. Therefore, this embodiment will be described below for each shape of the contact surface between the evaluation material and the mating material.

[0017] <First Embodiment> [Seizure evaluation parameter S] R [9.00 or less] The rolling fatigue strength test method according to this embodiment involves measuring the area A (mm²) of the contact surface S between the evaluation material 1 and the mating material 2 when a load is applied from the mating material 2. 2 ) and slip ratio σ 12 Therefore, S calculated from equation (1) R The value is 9.00 or less.R This parameter relates to the seizure of the contact surface 111 of the evaluation material 1. In this paper, S R The unit is mm 2 That is the case.

[0018] S R =A(σ 12 / 100) 2 ...Equation (1)

[0019] If the mating material 2 is, for example, crown-shaped, with a contact portion 21 that contacts the evaluation material 1 becoming gradually convex from the end towards the center, as shown in Figure 4, then the contact surface S between the evaluation material 1 and the mating material 2 will be elliptical, as shown in Figure 2. The major axis radius of the elliptical contact surface S is a (mm), and the minor axis radius of the ellipse is b (mm). Using the major axis radius a (mm) and the minor axis radius b (mm), the area A of the contact surface S is expressed by the following equation (2). The major axis of the contact surface S is parallel to the rotation axis C1 of the evaluation material 1, and the minor axis of the contact surface S is perpendicular to the major axis of the contact surface S at the contact surface S.

[0020] A = πab ... Equation (2)

[0021] The major axis radius a and minor axis radius b are calculated using a method based on Non-Patent Document 1 (Ichiro Nakahara, Mechanics of Materials, Volume 2, Yokendo, Tokyo (1971), pp. 116-132).

[0022] slip ratio σ 12 This is the relative peripheral velocity of the evaluation material 1 with respect to the mating material 2, and is expressed by the following equation (3).

[0023] σ 12 [%]=(2×π×R 11 ×u1 / 60-2×π×R 21 (×u² / 60) / (2×π×R) 11 ×u1 / 60)...Equation (3) Here, R 11 : Radius perpendicular to the rotation axis C1 of the contact portion 11 in the evaluation material 1 R 21 : The radius perpendicular to the rotation axis C2 of the contact portion 21 in the mating material 2 u1: Rotational speed of evaluation material 1 [rpm] u2: Rotational speed of the mating material 2 [rpm] That is the case.

[0024] In equation (3) above, 2 × π × R 11 ×u1 / 60 represents the peripheral velocity (m / s) at the minimum radius position in the contact area 11 of the evaluation material 1, and 2×π×R 21 ×u2 / 60 represents the peripheral velocity (m / s) at the maximum radius position in the contact area 21 of the mating material 2.

[0025] seizure evaluation parameter S R The seizure evaluation parameter S is 9.00 or less. R If the value exceeds 9.00, the amount of heat generated by friction at the contact surface between the evaluation material 1 and the mating material 2 increases, causing oil film breakdown and seizure between the evaluation material 1 and the mating material 2. Seizure evaluation parameter S R From the viewpoint of preventing seizure, the seizure evaluation parameter S is preferably 8.50 or less, and more preferably 8.00 or less. R The lower limit is not particularly restricted from the standpoint of preventing seizure, but the seizure evaluation parameter S R A small value means a small test load, which leads to a longer test time. Therefore, the seizure evaluation parameter S R Preferably, it is 0.05 or higher, and more preferably 0.10 or higher.

[0026] From equations (1) to (3) above, the seizure evaluation parameter S R In order to make it 9.00 or less, the major axis radius a, minor axis radius b, and the radius R of the cross section perpendicular to the rotation axis C1 at the contact portion 11 of the evaluation material 1 must be 11 (See Figure 3) The radius R of the cross-section perpendicular to the rotation axis C2 at the contact portion 21 of the mating material 2. 21 (See Figure 4) The rotational speed u1 at the contact portion 11 of the evaluation material 1 and the rotational speed u2 at the contact portion 21 of the mating material 2 can be changed.

[0027] [Slip ratio σ 12 [-300 to -60%] In this embodiment, as described above, the seizure evaluation parameter S R The measurement conditions are set using the following: This is done while considering the balance between the shape and material of the evaluation material 1 and the mating material 2, and the major axis radius a and minor axis radius b of the contact surface S calculated based on the applied load, and the slip ratio σ 12 This means setting the seizure evaluation parameter S. R Within the range where it is 9.00 or less (i.e., within the range where seizing can be suppressed), slip ratio σ 12 It is possible to set it to a small value (a value with a large slip rate), and the slip rate σ is smaller than -60% (a value with a large slip rate). 12 Furthermore, seizure can be suppressed even when testing under high load. In this disclosure, the slip ratio σ 12 The test could be performed without problems down to a minimum of -300%. From the perspective of suppressing seizure, the slip ratio σ 12 Preferably, it is -280% or higher, and more preferably -260% or higher.

[0028] If the gears are used in electric vehicles as envisioned in this disclosure, the slip ratio σ that occurs in gears used in real-world environments is... 12 It is thought to be around -150%. As mentioned above, in this embodiment, the slip ratio σ 12 By setting the slip ratio σ to -60% or less, testing can be conducted under conditions close to those of gears in a real environment. From the perspective of more accurately reproducing tests that simulate the operating environment of gears, the slip ratio σ 12 Preferably, it is -80% or less, more preferably -100% or less, or -120% or less.

[0029] As previously mentioned, when the conventional two-cylinder test was performed on surface-hardened cylindrical specimens under high load, plastic deformation occurred internally, making it impossible to perform a proper test. The inventors investigated this problem and found that in the conventional two-cylinder test, shear stress acts at a depth from the surface, resulting in plastic deformation at a depth where the effect of the surface hardening treatment does not extend. The inventors then developed the yield parameter R, which will be described later. DBy appropriately adjusting this, we were able to suppress internal plastic deformation even under high-load testing.

[0030] [Yield parameter R D [0.85 or less] The rolling fatigue strength test method according to this embodiment is Dτ xy Dτ calculated from equation (4) xy 'and the effective hardened layer depth D at the contact portion 11 of the evaluation material 1 c And, the yield parameter R calculated from equation (5) is D The value of Dτ is 0.85 or less. xy In evaluation material 1, the maximum conjugate shear stress τ xy This is the depth position from the contact surface S at the contact portion 11 of the evaluation material 1 when a load is applied.

[0031] Dτ xy '=2×Dτ xy ...Equation (4) R D =Dτ xy ' / D c ...Equation (5)

[0032] A shear stress acts at the contact surface S, and a conjugate shear stress acts inward from the contact surface S, conjugated to the shear stress. Due to the conjugate shear stress, fatigue cracks occur inward from the contact surface S, causing the contact surface 111 of the evaluation material 1 to peel off and wear away. The shear stress at the contact surface S occurs near the boundary of the contact surface S, and the conjugate shear stress is 0 at the surface, reaching a maximum value τ at a certain depth. max It will become.

[0033] In two-cylinder rolling fatigue tests conducted under low slip ratio conditions, the tangential force is relatively smaller compared to gears. Therefore, pitting will not occur unless the test surface pressure is increased to increase the frictional force at the contact point. Consequently, in two-cylinder rolling fatigue tests with increased surface pressure, the influence of the conjugate shear stress mentioned above cannot be ignored.

[0034] Maximum conjugate shear stress τ xyThe location where this occurs is the depth position (maximum conjugate shear stress position) Dτ from the contact surface S. xy This is the value corresponding to z0 described in Non-Patent Document 2 (Masatoshi Tokuda, Machine Design, Vol. 24, No. 12 (1980), pp. 26-30). Specifically, it is expressed by the following equation (6).

[0035]

number

[0036] In equation (6) above, b is the minor axis radius of the contact surface S, and t is the value calculated by equation (7) below.

[0037]

number

[0038] In equation (7) above, b is the minor axis radius of the contact surface S, and a is the major axis radius of the contact surface S. Furthermore, equation (7) above is obtained by modifying equation (8) shown in Non-Patent Document 2. Note that the above is written on the premise that the shape of the contact surface S is elliptical. The case where the shape of the contact surface S is rectangular will be described later.

[0039]

number

[0040] D in equation (5) c This is the effective hardened layer depth at the contact area of ​​the evaluation material 1, and specifically, it is the depth from the contact surface 111 of the evaluation material 1 to the position where the Vickers hardness is 513 Hv.

[0041] Effective cured layer depth D of evaluation material 1 cThe effective hardened layer depth D is calculated as follows: A cross-section perpendicular to the rotation axis C1 is obtained from the center position of the contact portion 11 of the evaluation material 1. At each cross-section, the Vickers hardness Hv is measured in accordance with JIS Z2244:2020, with a load of 0.20 kgf, starting at a position 0.03 mm in the depth direction from the contact surface, and increasing to a depth of 0.05 mm, 0.10 mm, and so on, up to a depth of 2.00 mm. Measurements are taken at a total of three locations at 120-degree intervals in the circumferential direction of the cross-section, and the average of the radial length (depth) up to the position where the measured Vickers hardness Hv is 513 Hv is taken. c Let's assume that.

[0042] The yield parameter R is expressed by equation (5). D If R exceeds 0.85, the conjugate shear stress in the interior of the evaluation material 1 is relatively too high compared to the conjugate shear stress generated in the effective hardened layer of the evaluation material 1, causing yielding to occur inside the evaluation material 1. As a result, the interior of the evaluation material 1 hardens, and this hardening causes pitting originating from the interior of the evaluation material 1, making it impossible to accurately reproduce the test that simulates the operating environment of gears. Therefore, R D The value should be 0.85 or less. D Preferably, it is 0.75 or less, and more preferably 0.70 or less.

[0043] [Evaluation Material 1] Next, we will explain evaluation material 1 in detail. Evaluation material 1 is composed of, for example, surface-hardened steel in which the surface is harder than the interior. Surface-hardened steel is a type of steel used, for example, in gears of electric vehicles. For example, steel in which the carbon concentration on the surface is higher than the carbon concentration inside and the surface is hardened, or steel in which the nitrogen concentration on the surface is higher than the nitrogen concentration inside and the surface is hardened, is used as evaluation material 1, and its rolling fatigue strength is evaluated.

[0044] Table 1 shows the distribution of Vickers hardness Hv for a surface-hardened steel whose rolling fatigue strength is evaluated, as an example of evaluation material 1. Vickers hardness Hv was measured according to JIS Z2244:2020, with a load of 0.20 kgf, at the distances from the surface shown in Table 1. It can be seen that in surface-hardened steel, hardened by gas carburizing, vacuum carburizing, or nitriding, the Vickers hardness Hv decreases towards the interior. Note that in the example shown in Table 1, the effective hardened layer depth D of the surface-hardened material treated by gas carburizing is shown. C The ECD (in Table 1) is 0.77 mm, and the effective hardened layer depth D of the surface hardened material treated by vacuum carburizing. C The ECD (in Table 1) is 0.45 mm, and the effective hardened layer depth D of the surface-hardened material treated by nitriding. C The ECD (in Table 1) is 0.14 mm.

[0045] [Table 1]

[0046] Next, the shape of the evaluation material 1 will be described in detail with reference to Figure 3. Figure 3 is a front view of the evaluation material 1. As shown in Figure 2, the evaluation material 1 is substantially cylindrical with a rotation axis C1, and the shape of the cross section perpendicular to the rotation axis C1 is circular at any position along the direction of the rotation axis C1. The evaluation material 1 comprises a contact portion 11 which is the part that comes into contact with the mating material 2, and a main body portion 12 connected to both ends of the contact portion 11. Hereinafter, the direction along the rotation axis C1 may be referred to as the axial direction, and the direction perpendicular to the rotation axis C1 may be referred to as the radial direction.

[0047] (Contact portion 11) The contact portion 11 is a smaller diameter portion than the main body portion 12. The contact portion 11 has a contact surface 111 located at its radial end that contacts the mating material 2. The contact portion 11 consists of tapered portions 11a, 11a connected to the main body portion 12, and a cylindrical portion 11b of approximately the same diameter along the rotation axis C1 between the tapered portions 11a, 11a.

[0048] The radius R of the contact portion 11 in the evaluation material 1 11 is preferably 2 to 100 mm. The radius R of the contact portion 11 11 refers to the minimum radius perpendicular to the rotation axis C1 in the contact portion 11. The radius R of the contact portion 11 11 If it is 2 mm or more, since the area of the contact surface S when a load acts becomes small, a high surface pressure can be applied with a low load. As a result, the maximum shear stress position Dτ xy can be shifted from the rotation axis C1 side to the contact surface S side. Also, since a high surface pressure can be applied with a low load, the amount of heat generated by friction is reduced, and seizure can be made less likely to occur. On the other hand, if the radius R of the contact portion 11 11 is too small, deflection may occur depending on the load, and the amount of deflection may become large, causing bending fatigue failure in some cases. However, if the radius R of the contact portion 11 11 is 2 mm or more, the occurrence of bending fatigue failure can be suppressed. The radius R of the contact portion 11 11 is more preferably 3 mm or more, and even more preferably 4 mm or more.

[0049] Also, if the radius R of the contact portion 11 11 is too large, since the area of the contact surface S when a load acts becomes too large, it may not be possible to apply a high surface pressure unless a large load is applied. When a large load is applied, the maximum shear stress position Dτ xy shifts from the contact surface S side to the rotation axis C1 side, and yielding may occur inside the contact portion 11 and work hardening may occur. Also, when a large load is applied, the amount of heat generated by friction becomes large, and seizure is likely to occur. However, by setting the radius R of the contact portion 11 11 to 100 mm or less, yielding inside the contact portion 11 and seizure on the contact surface S can be suppressed. The radius R of the contact portion 11 11 is more preferably 75 mm or less, and even more preferably 65 mm or less.

[0050] The crowning R of the contact portion 11 in the evaluation material 1 12 is preferably 1 mm or more. The crowning R 12This is the radius R of the cross-section parallel to the rotation axis C1, which includes the rotation axis C1. 11 This value is expressed as the radius of curvature of the contact portion 11 at the position having the crowning R of the contact portion 11. 12 If the thickness is 1 mm or more, a high surface pressure can be applied to the contact surface 111 with a small load. This allows for the maximum shear stress position Dτ xy The rotation axis can be moved from the C1 side to the contact surface 111 side. Crowning R of the contact portion 11 12 It is more preferably 10 mm or more, and even more preferably 100 mm or more. On the other hand, Crowning R 12 If the distance is less than 1 mm, elastic deformation due to contact with the mating material 2 and crowning radius due to the increase in the number of cycles will occur. 12 Wear at the location where crowning R 12 If a position other than the one having contact with the mating material 2, or crowning R 12 The outer side of the position having the feature comes into contact with the mating material 2, and there is a risk that the contact portion 11 will experience uneven wear.

[0051] Axial length of contact portion 11 (length in the direction of rotation axis C1) l 11 This is not particularly limited and may be changed as appropriate. For example, the length l of the contact portion 11. 11 This may be changed according to the length of the tapered portion 11a of the contact portion 11 in the direction of the rotation axis C1.

[0052] (Root mean square roughness Rq is 1.00 μm or less) The root mean square roughness Rq of the contact surface 111 in the evaluation material 1 is 1.00 μm or less. If the contact surface 111 is too rough, large protrusions on the contact surface 111 may plastically deform during testing, creating new surfaces, and seizing may occur on these new surfaces. However, if the root mean square roughness Rq of the contact surface 111 is 1.00 μm or less, there will be fewer large localized protrusions, and seizing can be suppressed. The root mean square roughness Rq of the contact surface 111 is preferably 0.90 μm or less, and more preferably 0.80 μm or less. On the other hand, it is preferable that the lower limit of the root mean square roughness Rq of the contact surface 111 be small. The root mean square roughness Rq of the contact surface 111 may be, for example, 0.02 μm or more, or 0.03 μm or more.

[0053] The root mean square roughness Rq is measured according to the method compliant with JIS B0601:2013.

[0054] (Main body 12) The main body 12 is the part that is gripped when performing rolling fatigue testing. The diameter φ and axial length l of the main body 12 are specified. 12 There are no particular restrictions.

[0055] [Opponent Material 2] Next, the mating material 2 will be described in detail with reference to Figure 4. Figure 4 is a front view of the mating material 2. As shown in Figure 4, the mating material 2 is cylindrical with a rotation axis C2, and the shape of the cross section perpendicular to the rotation axis C2 is circular at any position along the rotation axis C2. The mating material 2 has a contact portion 21 which is the part that comes into contact with the evaluation material 1. Hereinafter, the direction along the rotation axis C2 will be referred to as the axial direction, and the direction perpendicular to the rotation axis C2 will be referred to as the radial direction.

[0056] (Contact portion 21) The contact portion 21 has a contact surface 211 positioned at its radial end that contacts the evaluation material 1. The contact portion 21 has a convex crown that is convex when viewed from a direction perpendicular to the rotation axis C2 of the mating material 2. In other words, when viewed from a direction perpendicular to the rotation axis C2 of the mating material 2, the diameter of the contact portion 21 (the distance from the rotation axis C2 to the contact surface 211) increases from both axial ends toward the axial center.

[0057] Radius R of the contact portion 21 in the mating material 2 21 The radius R of the contact portion 21 is preferably 2 to 100 mm. 21 This refers to the maximum radius perpendicular to the rotation axis C2 at the contact portion 21. Radius R of the contact portion 21 21 If the thickness is 2 mm or more, the area of ​​the contact surface S becomes smaller, allowing a high surface pressure to be applied with a small load. As a result, in the evaluation material 1, the position of the maximum shear stress Dτ xy The pressure can be shifted from the rotation axis C1 side to the contact surface 111 side. Furthermore, because high surface pressure can be applied with a small load, the amount of heat generated due to friction is reduced, making seizure less likely. On the other hand, the radius R of the contact portion 21... 21 If the radius R of the contact portion 21 is too small, deflection may occur depending on the load, and if the amount of deflection becomes large, bending fatigue failure may occur. 21 If the radius is 2 mm or more, the occurrence of bending fatigue failure can be suppressed. Radius R of the contact portion 21 21 The diameter is preferably 3 mm or more, and more preferably 4 mm or more.

[0058] Also, the radius R of the contact portion 21 21 If the size is too large, the area of ​​the contact surface 211 becomes too large, and it may not be possible to apply high surface pressure without applying a high load. When a high load is applied, the position Dτ of the maximum shear stress in the evaluation material 1 xy The friction shifts from the contact surface 111 side to the shaft side, causing yielding to occur inside the contact portion 11 of the evaluation material 1, and work hardening may occur. Also, when a large load is applied, the amount of heat generated due to friction increases, making seizure more likely. However, the radius R of the contact portion 21 21By keeping the radius R of the contact portion 21 of the evaluation material 1 to 100 mm or less, yielding within the contact portion 11 and seizing on the contact surface 211 can be suppressed. 21 Preferably, it is 90 mm or less, and more preferably 80 mm or less.

[0059] Crowning radius of the contact portion 21 in the mating material 2 22 It is preferable that it is 1 mm or more. Crowning R 22 This is the radius R of the cross-section parallel to the rotation axis C2, which includes the rotation axis C2. 21 This value is expressed as the radius of curvature of the contact portion 21 at the position having the crowning R of the contact portion 21. 22 If the thickness is 1 mm or more, a high surface pressure can be applied to the contact surface 211 with a small load. This allows for the maximum shear stress position Dτ in the evaluation material 1. xy The rotation axis can be moved from the C1 side to the contact surface 111 side. Crowning R of the contact portion 21 22 The diameter is preferably 10 mm or more, and more preferably 15 mm or more. On the other hand, Crowning R 22 If it is less than 1 mm, elastic deformation due to contact with evaluation material 1 and crowning R due to increasing number of cycles will occur. 22 Wear at the location where crowning R 22 If a position other than the one having contact with the evaluation material 1, or Crowning R 22 The outer side of the position having the feature may come into contact with the evaluation material 1, potentially causing uneven wear of the contact portion 21.

[0060] The root mean square roughness Rq of the contact surface 211 on the mating material 2 is preferably 1.00 μm or less. If the contact surface 211 is too rough, large protrusions on the contact surface 211 may plastically deform during testing, creating new surfaces, and seizing may occur on these new surfaces. However, if the root mean square roughness Rq of the contact surface 211 is 1.00 μm or less, there will be fewer large localized protrusions, and seizing can be suppressed. The root mean square roughness Rq of the contact surface 211 is more preferably 0.90 μm or less, and even more preferably 0.80 μm or less. On the other hand, a smaller root mean square roughness Rq of the contact surface 211 is preferable. The root mean square roughness Rq of the contact surface 211 may be, for example, 0.02 μm or more, or 0.03 μm or more.

[0061] The root mean square roughness Rq is measured according to the method compliant with JIS B0601:2013.

[0062] Up to this point, the evaluation material 1 and the opponent material 2 used in the rolling fatigue test method according to this embodiment have been described. When the rolling fatigue test is performed, a load is applied from the opponent material 2 to the evaluation material 1, and after the contact surface 111 of the evaluation material 1 and the contact surface 211 of the opponent material 2 come into contact, the evaluation material 1 and the opponent material 2 rotate in opposite directions at a predetermined speed.

[0063] The evaluation material 1 mentioned above is Crowning R 12 It has, and the opposing material 2 is Crowning R 22 Because it has this property, stress concentration is less likely to occur compared to the evaluation material 1A and counter material 2A in the second embodiment described later, and more stable test results can be obtained.

[0064] Next, an example of a manufacturing method for the evaluation material and counter material used in the rolling fatigue test method according to this embodiment will be described. The manufacturing method for the evaluation material and counter material described below is merely an example, and the evaluation material and counter material having the above-described characteristics are not limited to the evaluation material and counter material manufactured by the manufacturing method described below, but are considered the evaluation material and counter material in this invention.

[0065] The evaluation material and the counter material include an intermediate product manufacturing process for producing an intermediate product, and a heat treatment process for heat-treating the intermediate product.

[0066] In the intermediate product manufacturing process, intermediate products having a predetermined shape are manufactured. For example, molten steel having a predetermined chemical composition is manufactured, and a slab or bloom is manufactured using the continuous casting method with this molten steel. Alternatively, an ingot may be manufactured using the ingot-making method with the molten steel. Next, the slab or ingot is hot-worked to manufacture a billet. The billet is hot-worked to manufacture a steel bar or wire rod. The hot-working may be hot-rolling or hot-forging. To homogenize the grain size of the microstructure after hot-forging, normalizing in accordance with JIS B 6911:2010 "Normalizing and Annealing of Steel" or isothermal annealing (IA) for the purpose of reducing the hardness of the material may be performed before the machining process described later. The manufactured steel bar or wire rod is cold-forged or machined to process it into a predetermined shape to produce an intermediate product. Machining may include cutting or drilling. The shape of the intermediate product is formed by well-known methods.

[0067] In the heat treatment process, the intermediate product is heat-treated. For example, the intermediate product manufactured in the intermediate product manufacturing process is subjected to surface hardening heat treatment. Furthermore, tempering may be performed on the intermediate product after surface hardening heat treatment. Further machining (such as cutting) may be performed on the intermediate product after quenching. Surface hardening heat treatment refers to, for example, gas carburizing, vacuum carburizing, nitriding, etc. These treatment conditions are carried out according to generally known conditions. Surface hardening treatments such as shot peening may be performed to increase the compressive residual stress on the surface layer of the part after surface hardening heat treatment.

[0068] <Second Embodiment> The rolling strength test method according to the second embodiment differs from the first embodiment in that the shape of the contact surface S between the evaluation material and the mating material is parallel to the axis of rotation when viewed from the front. This is due to the difference in shape between the evaluation material and the mating material compared to the first embodiment. The second embodiment will be described below with reference to Figures 5 to 7. Figure 5 is a front view of the evaluation material 1A in the second embodiment. Figure 6 is a front view of the mating material 2A in this embodiment. Figure 7 shows the contact length L at the contact surface S of the evaluation material in this embodiment. s This is a schematic diagram illustrating the contact width 2w.

[0069] [Evaluation Material 1A] As shown in Figure 5, evaluation material 1A is cylindrical in shape, has approximately the same diameter along the axial direction, and has a radius of R 11 In other words, evaluation material 1A differs from evaluation material 1 in the first embodiment in that the main body portion and the contact portion are not separated. Therefore, it can be said that all parts of evaluation material 1A except the axial end are the contact portion 11A.

[0070] The axial length l2 of the contact portion 11A that contacts the mating material 2A in the evaluation material 1A is preferably 1 mm or more. Since the evaluation material 1A has approximately the same diameter along the rotation axis C1, the length of the evaluation material 1A in the direction of the rotation axis C1 becomes the axial length l2 of the contact portion 11A. If the axial length l2 of the contact portion 11A is 1 mm or more, the contact area becomes smaller, which affects the seizure evaluation parameter S described later. R This becomes smaller. In addition, by applying a high surface pressure to the contact surface 111 with a small load, the maximum shear stress position Dτ xy It is possible to move it from the rotation axis C1 side to the contact surface 111 side. If multiple mating materials 2A are provided, the length of the mating material 2A with the shortest contact surface 211A in the direction of the rotation axis C2 is set as the thickness t1 of the contact portion 11A, and it is preferable that the thickness t1 is 1 mm or more.

[0071] At both axial ends of evaluation material 1A, the radius of curvature in plan view is R. 13It has edges 13, 13. The shape of the edges 13 is not particularly limited and can be, for example, R chamfer, C chamfer, or thread chamfer. When the shape of the edges 13 is C chamfer or thread chamfer, the radius of curvature R 13 The center of the circle of curvature is defined as a point at the same distance from both ends of the chamfered portion, and the radius of curvature is defined as the distance from this center to the end of the chamfered portion.

[0072] [Opponent material 2A] As shown in Figure 6, the mating material 2A is cylindrical in shape, has approximately the same diameter along the axial direction, and has a radius of R 22 In other words, the mating material 2A differs from the mating material 2 in the first embodiment from the evaluation material 1 in the first embodiment in that the contact surface 211A at the contact portion 21A is parallel to the rotation axis C2 of the mating material 2A.

[0073] The mating material 2A has a radius of curvature of R at both axial ends of the contact portion 21A. 21 It has edges 21a, 21a. In this case, the axial length l of the contact surface 211A 21 This can be expressed by the following equation (9), where L2 is the axial length of the mating material 2A.

[0074] l 21 ≤L2-2×R 21 ...Equation (9)

[0075] The shape of the edge portion 21a is not particularly limited and can be, for example, R chamfer, C chamfer, or thread chamfer. When the shape of the edge portion 21a is C chamfer or thread chamfer, the radius of curvature R 21 The center of the circle of curvature is defined as a point at the same distance from both ends of the chamfered portion, and the radius of curvature is defined as the distance from this center to the end of the chamfered portion.

[0076] Axial length l of contact surface 211A 21 It is preferable that the contact area is 1 mm or more. This reduces the contact area, which affects the seizure evaluation parameter S described later. R This becomes smaller. In addition, by applying a high surface pressure to the contact surface 111 with a small load, the maximum shear stress position Dτ xyIt is possible to move it from the rotation axis C1 side to the contact surface 111 side.

[0077] Since the evaluation material 1A and the mating material 2A described above have simpler shapes compared to the evaluation material 1 and mating material 2 in the first embodiment, processing to prepare them is easy.

[0078] [Seizure evaluation parameter S] R ] When a load is applied from the mating material 2A to the evaluation material 1A, the contact surface S of the evaluation material 1A with the mating material 2A becomes rectangular with a width of 2w (mm), as shown in Figure 7. At this time, the length in the direction of the rotation axis C1 at the contact surface S of the evaluation material 1A when the load is applied is L. s If (mm), the area A of the contact surface S is expressed by the following equation (10).

[0079] A = 2wL s ...Equation (10)

[0080] The axial length l2 of the contact portion 11A in the evaluation material 1A is equal to the axial length l of the contact surface 211A in the mating material 2A. 21 When it is longer than the axial length l of the contact surface 211A in the mating material 2A 21 Contact length L s The axial length l2 of the contact portion 11A in the evaluation material 1A is equal to the axial length l of the contact surface 211A in the mating material 2A. 21 When it is shorter than the contact length L, the axial length l2 of the contact surface 111A in the evaluation material 1A is equal to the contact length L s This is the result.

[0081] seizure evaluation parameter S R This is calculated using the area A calculated by equation (10). In the second embodiment as well, the seizure evaluation parameter S R It is 9.00 or less.

[0082] [Slip ratio σ 12 [-300 to -60%] Slip ratio σ of evaluation material 1A 12The slip ratio σ of evaluation material 1A is calculated according to the above formula (3). 12 This is -300 to -60%, similar to the first embodiment.

[0083] [Yield parameter R D [0.85 or less] As described in Non-Patent Document 3, when two cylinders (evaluation material 1A and mating material 2A) are in line contact, b / a = 0 (because crowning R12 and R22 are infinite, 2a → ∞), and from equation (5) above, the value of t cannot be 0.5, so from equation (8), t = 1.00. That is, the conjugate maximum shear stress τ xy This occurs at position Dτ in the depth direction from the contact surface S. xy From equation (6), this becomes 0.5b. To distinguish it from the first embodiment, if we conveniently set b to w, then the conjugate maximum shear stress τ xy This occurs at position D in the depth direction from the contact surface S. τxy This corresponds to 0.5W. Yield parameter R D This can be obtained from the above formulas (4) and (5), and is 0.85 or less in the second embodiment as well.

[0084] The evaluation material 1A and the counter material 2A may be manufactured in the same manner as in the second embodiment.

[0085] The present invention has been described above based on one embodiment of the present invention. As in the first and second embodiments, the seizure evaluation parameter S R This can be calculated using formula (1). The embodiments described above are merely illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and produces similar effects is included within the technical scope of the present invention.

[0086] <Modified form of the first embodiment> For example, in the first embodiment, the evaluation material 1 described above had a shape having a tapered portion 11a, but the evaluation material may be an evaluation material 1B with a shape as shown in Figure 8. In the evaluation material 1B, the contact portion 11B has a concave crown that is concave when viewed from a direction perpendicular to the rotation axis C1 of the evaluation material 1B. In other words, when viewed from a direction perpendicular to the rotation axis C1 of the evaluation material 1B, the diameter of the contact portion 11B (distance from the rotation axis C1 to the contact surface 111B) decreases from both ends in the axial direction toward the axial center.

[0087] Furthermore, for example, the evaluation material may have the shape shown in Figure 9, and the mating material may have the shape shown in Figure 10. In the evaluation material 1C shown in Figure 9, the contact portion 11C is a larger diameter portion than the main body portion 12C. In the evaluation material 1C, the contact portion 11C consists of tapered portions 11c, 11c connected to the main body portion 12C, and a cylindrical portion 11d of approximately the same diameter along the rotation axis C1 between the tapered portions 11c, 11c. On the other hand, in the mating material 2C shown in Figure 10, the contact portion 21C has a concave crown that is concave when viewed from a direction perpendicular to the rotation axis C2 of the mating material 2C. In other words, when viewed from a direction perpendicular to the rotation axis C2 of the mating material 2C, the diameter of the contact portion 21C (distance from the rotation axis C2 to the contact surface 211C) decreases from both ends in the axial direction toward the axial center. Furthermore, if the contact portion 11C is larger in diameter than the main body portion 12C, as in the evaluation material 1C, or if it has a convex crown that is convex when viewed from a direction perpendicular to the rotation axis C1, the radius R of the contact portion 11C 11 This refers to the maximum radius perpendicular to the rotation axis C1 at the contact portion 11C. Furthermore, if the contact portion 21 has a concave crown that is concave when viewed from a direction perpendicular to the rotation axis C2, as in the case of the mating material 2C, then the radius R of the contact portion 21C is... 21 This refers to the minimum radius perpendicular to the rotation axis C2 at the contact portion 21C.

[0088] Furthermore, the mating material may have, for example, a main body portion (not shown) on both axial sides of the contact area that does not come into contact with the evaluation material.

[0089] Furthermore, in the rolling fatigue testing method according to the present invention, the number of mating materials that are rotated in contact with a single evaluation material is not limited to one, but may be multiple.

[0090] <Modified form of the second embodiment> Furthermore, for example, in the second embodiment, the mating material 2A described above had substantially the same diameter along the direction of the rotation axis C2, but the mating material may be a mating material 2D having the shape shown in Figure 11. In a front view, the contact surface 211D of the mating material 2D is parallel to the rotation axis C2, similar to the mating material 2A, but it may have steps on its outer circumference other than the contact surface 211D.

[0091] Furthermore, the mating material may have, for example, a main body portion (not shown) on both axial sides of the contact area that does not come into contact with the evaluation material.

[0092] Furthermore, the axial length of the contact portion may be appropriately changed within a range where the contact length of the contact surface in the evaluation material is longer than the contact length of the contact surface in the mating material. For example, the shape of the evaluation material may be an evaluation material 1D having a contact portion 11D which is the part that contacts the mating material, and a main body portion 12D connected to both ends of the contact portion 11D, as shown in Figure 12. The contact portion 11D is a portion with a smaller diameter than the main body portion 12D. The contact portion 11D has a contact surface 111D which contacts the mating material, located at its radial end. The contact portion 11D is composed of cylindrical portions 11b of approximately the same diameter along the rotation axis C1 between tapered portions 11a, 11a connected to the main body portion.

[0093] Furthermore, in the rolling fatigue test method according to the present invention, the number of mating materials that are rotated in contact with a single evaluation material is not limited to one, but may be multiple. Of the one or more mating materials, the contact length l of at least one mating material. 21 It is preferable that the thickness be 1 mm or more. This further suppresses seizing. [Examples]

[0094] The present invention will be described in more detail below with reference to examples. The examples described below are merely examples of the present invention and do not limit it.

[0095] <Example 1> [Manufacturing of evaluation materials] The evaluation materials were manufactured using the following method. Steels SCr420, SCM420, SCM435, SCM822, SNCM220, and SACM645, having chemical compositions conforming to JIS G 4053 standards, were melted in a 300 kg vacuum melting furnace to produce molten steel, and each molten steel was cast to produce ingots. These ingots were hot forged into 250 mm diameter round bars. Hot forging was performed at a temperature between 1100°C and 1200°C, and after forging, the bars were allowed to cool in the atmosphere. Normalizing was performed on each bar (vacuum-melted material) in accordance with JIS B 6911:2010 "Normalizing and annealing of steel".

[0096] Next, each 250 mm diameter steel bar was machined after normalizing to produce evaluation materials with the shapes shown in Figure 3 and Table 2. A main body section with a diameter of φ24 mm was provided on both axial sides of the contact area. The axial length of each main body section was l 12 The length of the contact area was set to 60 mm. 11 The length was set to 28 mm. Therefore, the length L of the evaluation material was set to 148 mm.

[0097] [Table 2]

[0098] Each prepared evaluation material was subjected to a surface hardening heat treatment by gas carburizing, vacuum carburizing, or nitriding. The conditions for gas carburizing, vacuum carburizing, and nitriding were as follows: In the gas carburizing treatment (gas carburizing, quenching, and tempering), each evaluation material was held at 930°C for 80 minutes in an atmosphere with a carbon potential CP of 1.0% (carburizing process). Subsequently, the carbon potential CP was reduced to 0.8%, and the rough test specimens were held at 930°C for 60 minutes (diffusion process). After that, each evaluation material was cooled to 850°C, held at 850°C for 30 minutes, and then cooled in oil at 60°C (quenching process). After cooling, each evaluation material was subjected to a tempering treatment. The tempering temperature was 180°C, and the holding time at the tempering temperature was 120 minutes. In the vacuum carburizing treatment, a carburizing process was first carried out by introducing acetylene gas at a furnace pressure of 100 Pa or less. The carburizing process was performed at a temperature of 930°C for a holding time of 30 minutes. After the carburizing process, a diffusion process was carried out. During the diffusion process, the introduction of acetylene gas was stopped and the furnace pressure was kept below 10 Pa. The temperature during the diffusion process was set to 930°C for a holding time of 10 minutes. After the diffusion process, a quenching process was carried out. During the quenching process, the temperature was set to 850°C for a holding time of 30 minutes. After the holding time, the material was cooled in oil at 60°C. After the quenching process, a tempering process was carried out. During the tempering process, the temperature was set to 180°C for a holding time of 120 minutes. In the nitriding treatment, NH3, H2, and N2 gases were introduced into the furnace under atmospheric pressure and held at 570°C for 180 minutes. After the holding time, the material was cooled in oil at 60°C. Vickers hardness Hv was determined by taking cross-sections at 10 locations in the contact area of ​​the evaluation material and measuring the hardness distribution. In detail, for each cross-section, the Vickers hardness Hv is measured in accordance with JIS Z2244:2020, with a load of 0.20 kgf, starting at a point 0.03 mm from the contact surface in the depth direction, and increasing to 0.05 mm, 0.10 mm, and so on, up to a depth of 2.00 mm. Measurements are taken at three locations, every 120 degrees of the cross-section, and the average of the radial length (depth) up to the position where the measured Vickers hardness Hv is 513 Hv is used as the effective hardened layer depth D. c That's what I decided.

[0099] [Manufacturing of the counterpart material] The mating material was manufactured using the following method: Using steel that meets the SCM420 standard of JIS G 4053:2016, the mating material shown in Figure 4 and Table 2 was manufactured using a general manufacturing process, namely "normalizing → test piece processing → eutectoid carburizing in a gas carburizing furnace → low-temperature tempering → polishing".

[0100] The Vickers hardness Hv at a position 0.05 mm from the surface of the mating material, i.e., at a depth of 0.05 mm, ranged from 740 to 760, and the depth at which the Vickers hardness Hv was 513 was in the range of 0.8 to 1.0 mm. The Vickers hardness Hv at a depth of 0.05 mm and the depth at which the Vickers hardness Hv was 513 for each evaluated material were determined by the following method. Specifically, a cross section perpendicular to the rotation axis C2 was obtained from the center position of the contact area of ​​the evaluated material, and at each cross section, the Vickers hardness was measured in accordance with JIS Z2244:2020, with a load of 0.20 kgf, starting at a position 0.03 mm from the contact surface in the depth direction, at depths of 0.05 mm, 0.10 mm, and thereafter in 0.05 mm increments up to a depth of 2.00 mm. The hardness values ​​obtained from the measurements were plotted based on the depth of the measurement location. The depth at which the line connecting each point corresponds to the target value was identified as the depth at which the Vickers hardness Hv is 513.

[0101] [evaluation] The seizure and plastic deformation of each manufactured evaluation material were evaluated using the following method. After finishing the main body of the evaluation material to remove heat treatment strain, the evaluation material and the mating material were subjected to a two-cylinder rolling fatigue test. The contact surface of the evaluation material and the contact surface of the mating material were brought into contact, and the surface pressure p0 shown in Table 3 was applied, followed by rotations in opposite directions at the rotational speeds shown in Table 3. The surface pressure p0 shown in the table was calculated using the following equation (11), which is shown in equation (6.49) of Non-Patent Document 1.

[0102]

number

[0103] In equation (11) above, P is the load, a is the semi-major radius, and b is the semi-minor radius.

[0104] The number of cycles to terminate the two-cylinder rolling fatigue test is 1.0 × 10⁻⁶, which represents the fatigue limit required for typical steel. 7 The number of repetitions was set to 1. However, if vibration occurred during the test, it was determined that plastic deformation had occurred inside the evaluation material, and the rotation of both the evaluation material and the mating material was stopped. If the rotation was stopped before reaching the specified number of repetitions, the contact surface of the evaluation material was observed after the rotation stopped. If the test continued to the specified number of repetitions without being stopped midway, the contact surface was observed after the test was completed. If no signs of seizure were found on these contact surfaces, it was determined that no seizure had occurred. The occurrence of vibration was confirmed using a vibration meter installed in the testing machine.

[0105] Confirmation of the occurrence of plastic deformation inside the evaluation material during the test is performed before the test and after 1 × 10 cycles. 6 After the first round, a cross-section perpendicular to the rotation axis C1 was obtained from the center position of the contact area of ​​the evaluated material, and the hardness distribution was measured. Specifically, in each cross-section, starting from a position 0.050 mm in the depth direction from the contact surface, ΔHv = (1 × 10) was measured every 0.025 mm. 6 The Vickers hardness after each test cycle was calculated as (Vickers hardness after the test cycle) - (Vickers hardness before the test), and the average value of ΔHv at each depth was calculated. Of the average values ​​of ΔHv at each depth, the largest value was used to determine ΔHv. max And ΔHv max If the value was less than 50 Hv, it was determined that there was no plastic deformation inside the evaluated material. Note that the test specimens used for measuring the cross-sectional hardness distribution before the test and 1 × 10⁻¹⁰ 6 The specimens used for measuring the cross-sectional hardness distribution after each test were all different. The results are shown in Table 3.

[0106] [Table 3]

[0107] As described above, the major axis radius a, minor axis radius b, and slip ratio σ of the contact surface between the evaluation material and the mating material when a load is applied. 12 Using this, the seizure evaluation parameter S is calculated by equation (1). RThe value is 9.00 or less, and the conjugate maximum shear stress τ of the evaluated material is also satisfied. xy The depth position Dτ from the contact surface of the evaluation material where this occurs. xy Dτ calculated from equation (4) using xy 'and the effective hardened layer depth D of the evaluation material. c And, the yield parameter R calculated from equation (5) is D In cases where the value is 0.85 or less, seizure does not occur, and 1 × 10 6 No plastic deformation (yielding) occurred inside the evaluated material after repeated testing. Therefore, the evaluation parameter S R The yield parameter R is 9.00 or less. D It was found that a two-cylinder rolling fatigue test with a coefficient of 0.85 or less allows for a simpler and more accurate evaluation of the rolling fatigue strength of surface-hardened steel used in gears.

[0108] Comparative Example 27 uses the seizure evaluation parameter S. R Because the value exceeded 9.00, seizing occurred on the contact surface of the evaluation material before the number of repeated trials was sufficient, making it impossible to obtain appropriate measurement results. Comparative Example 28 has a yield parameter R D Because it exceeded 0.85, the number of repetitions was 1 × 10 6 Plastic deformation occurred within the evaluation material after the specified number of cycles. Therefore, it is unlikely that appropriate measurement results can be obtained even if the test is conducted up to the specified number of cycles. In Comparative Example 29, the radius R of the evaluation material 11 The sample size was very small (1 mm), and the evaluation material broke during the test, making it impossible to obtain measurement results. In Comparative Example 30, the crowning R of the evaluation material was 12 It is smaller than 1 mm, Crowning R 12 Because contact with the mating material occurred at locations other than those containing the specified element, measurement results could not be obtained. In Comparative Example 31, the radius R of the mating material 21 The measurement was very small, only 1 mm, and the mating material broke during the test, making it impossible to obtain measurement results. In Comparative Example 32, the crowning radius of the mating material 22It is smaller than 1 mm, Crowning R 22 Because the evaluation material came into contact with locations other than those containing the specified element, measurement results could not be obtained. In comparative examples 33 and 34, the surface roughness of the evaluation material and the mating material was high, resulting in burning on the contact surface of the evaluation material before the number of cut-off cycles was reached, making it impossible to obtain appropriate measurement results.

[0109] <Example 2> [Manufacturing of evaluation materials] The evaluation materials were manufactured using the following method. Steels SCr420, SCM420, SCM435, SCM822, SNCM220, and SACM645, having chemical compositions conforming to JIS G 4053 standards, were melted in a 300 kg vacuum melting furnace to produce molten steel, and each molten steel was cast to produce ingots. These ingots were hot forged into 250 mm diameter round bars. Hot forging was performed at a temperature between 1100°C and 1200°C, and after forging, the bars were allowed to cool in the atmosphere. Normalizing was performed on each bar (vacuum-melted material) in accordance with JIS B 6911:2010 "Normalizing and annealing of steel".

[0110] Next, machining was performed on each 250 mm diameter steel bar after normalizing to produce evaluation materials with the shapes shown in Figure 5 and Table 4.

[0111] [Table 4]

[0112] Each prepared evaluation material was subjected to a surface hardening heat treatment by gas carburizing, vacuum carburizing, or nitriding. The conditions for gas carburizing, vacuum carburizing, and nitriding were as follows: In the gas carburizing treatment (gas carburizing, quenching, and tempering), each evaluation material was held at 930°C for 80 minutes in an atmosphere with a carbon potential CP of 1.0% (carburizing process). Subsequently, the carbon potential CP was reduced to 0.8%, and the rough test specimens were held at 930°C for 60 minutes (diffusion process). After that, each evaluation material was cooled to 850°C, held at 850°C for 30 minutes, and then cooled in oil at 60°C (quenching process). After cooling, each evaluation material was subjected to a tempering treatment. The tempering temperature was 180°C, and the holding time at the tempering temperature was 120 minutes. In the vacuum carburizing treatment, a carburizing process was first carried out by introducing acetylene gas at a furnace pressure of 100 Pa or less. The carburizing process was performed at a temperature of 930°C for a holding time of 30 minutes. After the carburizing process, a diffusion process was carried out. During the diffusion process, the introduction of acetylene gas was stopped and the furnace pressure was kept below 10 Pa. The temperature during the diffusion process was set to 930°C for a holding time of 10 minutes. After the diffusion process, a quenching process was carried out. During the quenching process, the temperature was set to 850°C for a holding time of 30 minutes. After the holding time, the material was cooled in oil at 60°C. After the quenching process, a tempering process was carried out. During the tempering process, the temperature was set to 180°C for a holding time of 120 minutes. In the nitriding treatment, NH3, H2, and N2 gases were introduced into the furnace under atmospheric pressure and held at 570°C for 180 minutes. After the holding time, the material was cooled in oil at 60°C. Vickers hardness Hv was determined by taking cross-sections at 10 locations in the contact area of ​​the evaluation material and measuring the hardness distribution. In detail, for each cross-section, the Vickers hardness Hv is measured in accordance with JIS Z2244:2020, with a load of 0.20 kgf, starting at a point 0.03 mm from the contact surface in the depth direction, and increasing to 0.05 mm, 0.10 mm, and so on, up to a depth of 2.00 mm. Measurements are taken at three locations, every 120 degrees of the cross-section, and the average of the radial length (depth) up to the position where the measured Vickers hardness Hv is 513 Hv is used as the effective hardened layer depth D. c That's what I decided.

[0113] [Manufacturing of the counterpart material] The mating material was manufactured using the following method: Using steel that meets the SCM420 standard of JIS G 4053:2016, the mating material shown in Figure 6 and Table 4 was manufactured using a general manufacturing process, namely "normalizing → test piece processing → eutectoid carburizing in a gas carburizing furnace → low-temperature tempering → polishing".

[0114] The Vickers hardness Hv at a position 0.05 mm from the surface of the mating material, i.e., at a depth of 0.05 mm, ranged from 740 to 760, and the depth at which the Vickers hardness Hv was 513 was in the range of 0.8 to 1.0 mm. The Vickers hardness Hv at a depth of 0.05 mm and the depth at which the Vickers hardness Hv was 513 for each evaluated material were measured in the same manner as in Example 1.

[0115] [evaluation] The seizure and plastic deformation of each manufactured evaluation material were evaluated using the following method. After finishing the main body of the evaluation material to remove heat treatment strain, the evaluation material and the mating material were subjected to a two-cylinder rolling fatigue test. The contact surface of the evaluation material and the contact surface of the mating material were brought into contact, and the surface pressure p0 shown in Table 5 was applied, followed by rotations in opposite directions at the rotational speeds shown in Table 5. The surface pressure p0 shown in the table was calculated by replacing πab with 2wL in the above formula (11).

[0116] The number of cycles to terminate the two-cylinder rolling fatigue test and the occurrence of plastic deformation inside the evaluated material during the test were confirmed using the same method as in Example 1. The results are shown in Table 5.

[0117] [Table 5]

[0118] As described above, the contact width L in the principal axis direction, the contact width w in the circumferential direction, and the slip ratio σ of the contact surface between the evaluation material and the mating material when a load is applied. 12 Using this, the seizure evaluation parameter S is calculated by equation (1). R The value is 9.00 or less, and the conjugate maximum shear stress τ of the evaluated material is also satisfied. xyThe depth position Dτ from the contact surface of the evaluation material where this occurs. xy Dτ calculated from equation (4) using xy 'and the effective hardened layer depth D of the evaluation material. c And, the yield parameter R calculated from equation (5) is D In cases where the value is 0.85 or less, seizure does not occur, and 1 × 10 6 No plastic deformation (yielding) occurred inside the evaluated material after repeated testing. Therefore, the evaluation parameter S R The yield parameter R is 9.00 or less. D It was found that a two-cylinder rolling fatigue test with a coefficient of 0.85 or less allows for a simpler and more accurate evaluation of the rolling fatigue strength of surface-hardened steel used in gears.

[0119] Comparative Example 59 uses the seizure evaluation parameter S. R Because the value exceeded 9.00, seizing occurred on the contact surface of the evaluation material before the number of repeated trials was sufficient, making it impossible to obtain appropriate measurement results. Comparative Example 60 has a yield parameter R D Because it exceeded 0.85, the number of repetitions was 1 × 10 6 Plastic deformation occurred within the evaluation material after the specified number of cycles. Therefore, it is unlikely that appropriate measurement results can be obtained even if the test is conducted up to the specified number of cycles. In Comparative Example 61, the radius R of the evaluation material 11 The sample size was very small (1 mm), and the evaluation material broke during the test, making it impossible to obtain measurement results. In Comparative Example 62, the outermost thickness of the evaluation material was small at 1 mm, making it impossible to detect pitting and obtain measurement results. In Comparative Example 63, the radius R of the mating material 21 The measurement was very small, only 1 mm, and the mating material broke during the test, making it impossible to obtain measurement results. In Comparative Example 64, the outermost thickness of the mating material was small at 1 mm, so pitting could not be detected and measurement results could not be obtained. In comparative examples 65 and 66, the surface roughness of the evaluation material and the counter material was high, resulting in burning on the contact surface of the evaluation material before the number of cut-off cycles was reached, making it impossible to obtain appropriate measurement results. Comparative Example 70 uses the seizure evaluation parameter S. R Because the value exceeded 9.00, seizing occurred on the contact surface of the evaluation material before the number of repeated trials was sufficient, making it impossible to obtain appropriate measurement results.

[0120] Thus, in the present invention, the seizure evaluation parameter S R , yield parameter R D , the slip ratio σ of the evaluated material 12 Furthermore, fatigue test conditions are set while adjusting the root mean square roughness Rq of the evaluation material and the mating material within an appropriate range. This suppresses seizure on the surface of the evaluation material and avoids plastic deformation inside, even when testing under high loads (slip ratio, high surface pressure, and high rotational speed), allowing the suitability of the steel material to be evaluated under higher loads than before.

[0121] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention. [Explanation of Symbols]

[0122] 1,1A,1B Evaluation Material 11,11A,11B Contact part 11a, 11c Tapered section 11b, 11d Cylindrical section 12, 12A, 12B Main Unit 13 Edge 111,111A,111B Contact surface 121,121A,121B surface 2,2B Opposing material 21,21B Contact part 21a Edge 211,211A,211B Contact surface C1 rotation axis C2 rotation axis S: Contact surface of the evaluation material when a load is applied.

Claims

1. A rolling fatigue strength test method comprising an evaluation material having a rotating shaft and one or more mating materials having a rotating shaft, wherein the rotating surface of the evaluation material and the rotating surface of the mating material are brought into contact, and while a load is applied to the evaluation material, the evaluation material and the mating material are rotated in opposite directions to evaluate the rolling fatigue strength of the evaluation material, The area A (mm²) of the contact surface between the evaluation material and the mating material when the load is applied. ２ ) and slip ratio σ １２ Using this, the seizure evaluation parameter S is calculated by equation (1). Ｒ The value is 9.00 or less, and The conjugate maximum shear stress τ of the aforementioned evaluation material ｘｙ The depth position Dτ from the contact surface of the evaluation material where this occurs. ｘｙ Dτ calculated from equation (2) using ｘｙ 'and the effective hardened layer depth D of the evaluation material ｃ And, the yield parameter R calculated from equation (3) is Ｄ If the value is 0.85 or less, The slip rate σ of the evaluation material １２ is -300 to -60%, The root mean square roughness Rq of the contact surface of the evaluation material that comes into contact with the mating material, and the root mean square roughness Rq of the contact surface of the mating material that comes into contact with the evaluation material, is 1.00 μm or less. A method for testing rolling fatigue strength, characterized by the following: S Ｒ =A(σ １２ / 100) ２ ・・・formula (1) Dτ ｘｙ =2Dτ ｘｙ ・・・Form (2) R Ｄ =Dτ ｘｙ ' / D ｃ ...Form (3)

2. The rolling fatigue strength test method according to claim 1, wherein the shape of the contact surface between the evaluation material and the mating material is elliptical, and the area A is calculated by formula (4) using the major axis radius a (mm) and the minor axis radius b (mm). A=πab...Formula (4)

3. The radius R of the contact portion in the evaluation material that contacts the mating material. １１ The rolling fatigue strength test method according to claim 2, wherein the distance is 2 to 100 mm.

4. Crowning radius of the contact portion in the evaluation material that contacts the mating material. １２ A method for testing rolling fatigue strength according to claim 2 or 3, wherein the thickness is 1 mm or more.

5. The radius R of the contact portion in at least one of the one or more mating materials that contacts the evaluation material. ２１ A method for testing rolling fatigue strength according to claim 2 or 3, wherein the distance is 2 mm to 100 mm.

6. Crowning R of the contact portion of at least one of the one or more mating materials ２２ A method for testing rolling fatigue strength according to claim 2 or 3, wherein the thickness is 1 mm or more.

7. The shape of the contact surface between the evaluation material and the mating material is rectangular, and the area A is equal to the contact length L of the contact surface in the direction of rotation. ｓ A method for testing rolling fatigue strength according to claim 1, wherein the rolling fatigue strength is calculated by formula (5) using the contact width 2w in the circumferential direction perpendicular to the rotation axis direction at the contact surface. A = 2wL ｓ ...Form (5)

8. The length l in the rotational axis direction of the contact portion in the evaluation material that comes into contact with the mating material. ２ The rolling fatigue strength test method according to claim 7, wherein the thickness is 1 mm or more.

9. The rotational axis length l of the contact surface in at least one of the one or more mating materials that contacts the evaluation material. ２１ A method for testing rolling fatigue strength according to claim 7 or 8, wherein the thickness is 1 mm or more.

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