Railway wheel and axle for railway vehicle

Abstract

The invention provides a railway wheel capable of suppressing crack extension. A railway wheel (100) according to the present disclosure includes a hub portion (10), a rim portion (20) including a tread (21) and a flange (22), and a plate portion (30). In a surface layer of a rim section (20) including a tread surface (21), the railway wheel (100) has an elastic limit [sigma] 0 of 430 MPa or more, an initial follow-up hardening coefficient C of 130 GPa or more, and a follow-up hardening coefficient reduction rate [gamma] of 400 or less. The initial follow-up hardening coefficient C and the follow-up hardening coefficient reduction rate gamma satisfy formula (1). # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a railway wheel and an axle used in a railway vehicle. Background Art

[0002] A railway vehicle travels on rails constituting a railway line. The railway vehicle has a plurality of railway wheels. The railway wheels support the railway vehicle and move while rotating on the rails in contact with the rails. Therefore, the railway wheels are loaded with repeated stress caused by rolling contact.

[0003] The surface of the railway wheel that contacts the top surface of the rail is called the tread. As one of the braking methods of railway vehicles, tread braking is known. Tread braking is a braking method in which a brake shoe is pressed against the tread of the railway wheel to generate friction between the tread and the brake shoe, and the railway vehicle is braked using the friction. When the railway vehicle is braked using the tread braking, friction heat is generated between the tread and the brake shoe.

[0004] Railway wheels are subjected to repeated stress due to rolling contact and frictional heat during braking of railway vehicles. There are cases where cracks are generated in railway wheels due to repeated stress and frictional heat. If the cracks extend, there is a possibility that the railway wheels will be damaged. Therefore, a railway wheel capable of suppressing cracks is sought.

[0005] Railway wheels capable of suppressing cracks are proposed in, for example, Japanese Patent Application Laid-Open No. 10-119503 (Patent Document 1) and Japanese National Publication No. 2001-517177 (Patent Document 2).

[0006] The railway wheel disclosed in Patent Document 1 is an integrally rolled wheel for railway vehicles in a shape in which the rim portion is displaced to a position outside the track relative to the hub portion. The railway wheel is characterized in that, when the dimension between the vertical lines respectively perpendicular to the axis from the center of the plate thickness near the end of the flange side curve of the rim portion fillet and the center of the plate thickness near the end of the flange opposite side curve of the hub portion fillet is set as the displacement amount δ of the rim portion relative to the hub portion, and the dimension between the vertical lines respectively perpendicular to the axis from the center of the plate thickness near the end of the flange side curve of the rim portion fillet and the center of the axial direction of the inner diameter of the rim portion is set as the displacement amount λ of the rim side plate portion, the displacement amount λ is greater than 5 mm, and the displacement amount δ is greater than 40 mm. In Patent Document 1, the thermal stress generated in the plate portion is suppressed by increasing the displacement amount δ of the plate portion. As a result, it is described in Patent Document 1 that a railway wheel with excellent performance against damage caused by thermal cracks generated on the tread and flange surface of the railway wheel can be obtained.

[0007] The railway wheel disclosed in Patent Document 2 has at least one recess formed in a portion where cracks may occur, and at least one surface covering layer is formed in the recess. The surface covering layer is composed of a base material and an additive. The base material is melted, in particular, by heat irradiation based on laser irradiation, and the additive is supplied to the melt, thereby giving the railway wheel characteristics different from those of the base material. The surface covering layer is formed in the recess as a plurality of linear bodies adjacent to each other filling the recess, and the outer surface of the surface covering layer is finished to a height consistent with the outer surface of the adjacent base material. In Patent Document 2, a surface protective layer is formed in a portion where cracks may occur by laser irradiation. As a result, it is described in Patent Document 2 that: surface fatigue and crack generation can be prevented, while deviation from a perfect circle and corrosion can be prevented.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 10-119503

[0011] Patent Document 2: Japanese Patent Application No. 2001-517177 Summary of the invention

[0012] Problem that the invention aims to solve

[0013] In addition, there are the following stages until the cracks generated in the railway wheel lead to damage. The first stage is the crack generation stage. As mentioned above, the tread is loaded with repeated stress caused by rolling contact with the rail. In addition, when the railway vehicle brakes, friction heat caused by friction with the brake shoe is generated on the tread. Since the friction heat is loaded in addition to the repeated stress caused by rolling contact, cracks are generated on the tread.

[0014] The second stage is the crack extension stage. The crack generated in the tread extends parallel to the tread or from the tread toward the inside of the railway wheel. If the driving force for crack extension in the surface layer of the railway wheel is high, the crack is easy to extend.

[0015] The third stage is the damage stage. The cracks extend and the railway wheel is damaged. If the railway wheel is damaged, the life of the railway wheel is shortened.

[0016] The railway wheel disclosed in Patent Document 1 suppresses the thermal stress generated in the plate portion. Thus, thermal cracks generated in the tread of the railway wheel are suppressed. The railway wheel disclosed in Patent Document 2 forms a surface protective layer on a portion where cracks may be generated. Thus, the generation of cracks is suppressed. That is, in Patent Documents 1 and 2, it is considered that the research is mainly conducted on suppressing the generation of cracks in the first stage.

[0017] The occurrence of cracks can be suppressed by the railway wheels disclosed in Patent Documents 1 and 2. However, in the railway wheels disclosed in Patent Documents 1 and 2, it is sometimes difficult to suppress the extension of the cracks that have occurred.

[0018] An object of the present disclosure is to provide a railway wheel capable of suppressing the extension of cracks and a railway vehicle axle including the railway wheel capable of suppressing the extension of cracks.

[0019] Solutions for solving problems

[0020] The railway wheel of the present disclosure comprises:

[0021] a hub portion constituting the inner peripheral portion of the railway wheel and having a through hole for inserting an axle of a railway vehicle;

[0022] a rim portion constituting an outer peripheral portion of the railway wheel, including a tread that contacts the top surface of a rail on which the railway vehicle travels, and a flange that protrudes to the outside of the tread in the radial direction of the railway wheel; and

[0023] an annular plate portion connecting the hub portion and the rim portion,

[0024] In the rim surface layer including the tread,

[0025] Elastic limitσ 0 The initial kinematic hardening coefficient C is 130 GPa or more, and the kinematic hardening coefficient reduction rate γ is 400 or less.

[0026] The initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ satisfy equation (1).

[0027]

Mathematical formula 1

[0028]

[0029] The railway vehicle axle disclosed in the present invention comprises:

[0030] the first railway wheel and the second railway wheel mentioned above; and

[0031] The axle is inserted into the through holes of the first railway wheel and the second railway wheel, and extends along the rotation axis direction of the first railway wheel and the second railway wheel.

[0032] Effects of the Invention

[0033] The railway wheel disclosed in the present invention can suppress the extension of cracks. The railway vehicle axle disclosed in the present invention can suppress the extension of cracks in the railway wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a diagram showing a FEM analysis model.

[0035] Figure 2 It is a longitudinal sectional view of the railway wheel according to the present embodiment.

[0036] Figure 3 It is a longitudinal sectional view of the railway vehicle wheel axle of this embodiment.

[0037] Figure 4 This is a graph showing the relationship between the crack extension rate da / dN and the 0.7% yield strength of the repeated stress-strain curve.

[0038] Figure 5 It is a figure which shows the heating pattern of the tread surface and the position of 15 mm depth from the tread surface in the case of one-stage cooling.

[0039] Figure 6 It is a figure which shows the heating pattern of the tread surface and the position of 15 mm depth from the tread surface in the case of two-stage cooling.

[0040] Figure 7 This is a schematic diagram showing a test piece in a repeated compression-tension test. DETAILED DESCRIPTION

[0041] [Technical concept of railway wheel disclosed in the present invention]

[0042] The present inventors have studied a method for suppressing the extension of cracks even when cracks are generated in the tread of a railway wheel.

[0043] The railway wheel load has repeated stress caused by rolling contact. Therefore, work hardening occurs in the railway wheel with repeated plastic deformation. Therefore, when studying the extension of cracks, it is necessary to consider the work hardening accompanied by repeated plastic deformation. As a model for expressing the stress-strain response of repeated plastic deformation, a nonlinear kinematic hardening law is known. The nonlinear kinematic hardening law is expressed by formula (2).

[0044]

Mathematical formula 2

[0045]

[0046] Here, σ eq : Equivalent stress (MPa), σ 0 : elastic limit (MPa), C: initial kinematic hardening coefficient (GPa), γ: kinematic hardening coefficient reduction rate.

[0047] In order to derive the formula (2), it is expressed as the formula (3).

[0048]

Mathematical formula 3

[0049]

[0050] In use peq When the formula (3) is derived, the formula (4) is obtained.

[0051]

Mathematical formula 4

[0052] f′(ε peq )=Cexp(-γε peq ) (4)

[0053] In ε peq = 0, f'(0) = C, and therefore the initial kinematic hardening coefficient C corresponds to the kinematic hardening coefficient when the plastic strain is 0. In other words, the initial kinematic hardening coefficient C corresponds to the slope of the graph of the stress-strain curve when the plastic strain is 0.

[0054] When the natural logarithm of both sides of equation (4) is taken, equation (5) is obtained.

[0055]

Mathematical formula 5

[0056] lnf′(ε peq )=-γε peq +lnC (5)

[0057] The kinematic hardening coefficient reduction rate γ corresponds to the slope of the linear function of equation (5). In other words, the kinematic hardening coefficient reduction rate γ corresponds to the slope of a graph with the natural logarithm of the kinematic hardening coefficient as the vertical axis and the plastic strain as the horizontal axis.

[0058] The equivalent stress σ of formula (2) eq Equivalent to the strength after work hardening. It is believed that if the strength after work hardening is high, the extension of cracks can be suppressed. In other words, it is believed that if the equivalent stress σ of formula (2) can be increased eq , then the extension of cracks can be suppressed.

[0059] On the other hand, the railway wheel begins to work harden when it starts running. If the work hardens at the beginning of running, the equivalent stress σ eq Rapidly increasing, it is easy to suppress the extension of cracks. Even if the same equivalent stress σ is finally reached eq In the case of , if work hardening is not carried out quickly, cracks will extend before work hardening, so it is not necessarily possible to suppress crack extension. eq When σ is too high, crack extension may not be suppressed. 0 When the MgO is high, the strength is high enough even if plastic deformation does not occur, so the extension of cracks is easily suppressed.

[0060] The present inventors have studied the σ that can suppress the extension of cracks. 0 The inventors further studied C (elastic limit), C (initial kinematic hardening coefficient) and γ (kinematic hardening coefficient reduction rate). The inventors used the Finite Element Method (FEM) to analyze and investigate how the crack extension rate changes when the material properties of the railway wheel are changed.

[0061] [FEM analysis method]

[0062] The FEM analysis was performed using the following method. Elastic-plastic FEM analysis was performed using ABAQUS Ver.6.14 (Dassault Systemes K.K.). Figure 1 The FEM analysis model is shown in . The model is set as a two-dimensional plane strain, the railway wheel test piece model is set as a plane, and the track test piece model is set as a circle. The railway wheel test piece model uses 8-node secondary elements, and the track test piece model uses 4-node primary elements. The diameter of the track test piece model is 75mm. The minimum element size of the railway wheel test piece model is set to 0.1mm in width and 0.1mm in length at the contact part with the track test piece model and its vicinity, except for the crack introduction part described later. In the railway wheel test piece model, the area with a width of 25mm and a length of 2mm including the contact part with the track test piece model is used as a finite element, and the area other than this is used as an infinite element. In the FEM analysis, in order to simulate rolling contact, a pressing load and a forced displacement in the rotation direction and the horizontal direction are applied to the track test piece model. Three cracks inclined relative to the surface of the railway wheel test piece model are introduced into the railway wheel test piece model. Its purpose is to simulate the situation where multiple cracks are generated on the surface of the railway wheel. The central crack among the three cracks was taken as the object for crack extension evaluation. Hereinafter, the central crack among the three cracks will also be referred to as the central crack. The angle of the crack relative to the surface of the railway wheel test piece model was set to 25°. The depth of the introduced crack was set to 0.8 mm, and the interval between the three cracks was set to 1.72 mm. The element size of the front end of the central crack was set to 0.08 mm in width and 0.08 mm in length. The number of nodes of the railway wheel test piece model was set to 16542, and the number of elements was set to 5488. The number of nodes of the track test piece model was set to 4250, and the number of elements was set to 4096. In the FEM analysis, the penetration of water into the crack under water lubrication conditions was simulated. Specifically, a non-compressible hydrostatic pressure element that fills the closed space formed by the crack and the surface of the track test piece model is defined. In addition, contact is defined on the crack surface.

[0063] In the FEM analysis, the rolling load was reproduced according to the following steps. (1) The rail test piece model was arranged at a position 7.5 mm away from the central crack. (2) A pressing load (Hertz stress) was applied to the MPC node arranged at the center of the rail test piece model. (3) The pressing load was kept constant and the multi-point constraint (MPC) node was given a forced displacement of rotation and horizontal movement, so that the rail test piece model rolled on the railway wheel test piece model. At this time, sliding was applied by offsetting the movement amount caused by rotation and the forced displacement amount of horizontal movement. The movement amount caused by rotation was set to a total of 15 mm. (4) The rail test piece model was moved to the initial position in a state where it was separated from the railway wheel test piece model by 0.09 mm. Five cycles were calculated with the above (1) to (4) as one cycle. The amount of water infiltration into the crack was calculated based on the volume of the closed space generated by the contact between the railway wheel test piece model and the rail test piece model in the second cycle. The calculation was performed up to the fifth cycle assuming that the volume of the fluid sealed in the second cycle did not change thereafter.

[0064] [Calculation method of driving force for crack extension]

[0065] The driving force for crack extension is obtained by calculating the stress expansion coefficient based on the FEM analysis results. Specifically, the stress expansion coefficient K of the open type (mode I) is calculated using equation (6): I and the stress expansion coefficient K of the shear type (mode II) II The calculation of the stress expansion coefficient uses the crack opening displacement obtained by FEM analysis in a local coordinate system having the tip of the central crack as the origin introduced into the railway wheel test piece model.

[0066]

Mathematical formula 6

[0067]

[0068] Here, E: Young's modulus (206 GPa), ν: Poisson's ratio (0.3), r: distance from the crack tip (m), U y : 1 / 2 of the crack opening displacement in the direction perpendicular to the crack surface (m), U x : 1 / 2 of the crack opening displacement in the direction parallel to the crack surface (m).

[0069] The U obtained by FEM analysis x , U y and the square root of r. K is calculated based on the slope and formula (2). I and K IIThe range of r for the linear approximation is based on the K value for the Hertzian stress of 1500 MPa. I The extension of rolling fatigue crack is a so-called mixed mode extension, which is caused by compression stress and shear stress, resulting in both open crack extension (mode I) and shear crack extension (mode II). Therefore, in order to evaluate the mixed mode crack extension, the stress expansion coefficient K is obtained using the Erdogan-Sih mixed mode criterion shown in formula (7): θ，max The crack extension angle θ σ The above calculations were performed using the analysis results of the fifth cycle, in which the values ​​were stable.

[0070]

Mathematical formula 7

[0071]

[0072] Here, θ σ is the angle of the maximum tangent stress on the circle centered at the crack front. II When >0, it becomes θ σ <0, in K II When <0, it becomes θ σ >0.

[0073] Table 1 shows the elastic limit σ in the above FEM analysis. 0 , fatigue crack extension rate based on Paris law when the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ change.

[0074] [Table 1]

[0075] Table 1

[0076]

[0077] The fatigue crack extension rate shown in the "da / dN (mm / cycle)" column of Table 1 was determined based on the formula (8).

[0078]

Mathematical formula 8

[0079]

[0080] Here, da / dN: crack extension rate (mm / cycle), ΔK θ , max : The variation range of stress expansion coefficient In addition, C and m are constants obtained in experiments (C = 3.93 × 10 －13, m=3.68). The larger the da / dN, the easier it is for the crack to extend. Test No. 1 is a material equivalent to Class-C (tread) as a standard of the Association of American Railroads' (American Railroad Association: AAR). Test No. 2 is a material equivalent to a wheel (tread) manufactured using the manufacturing method of the present application. Test Nos. 3 to 6 are hypothetically set materials with higher strength than Test No. 2. Test Nos. 4 to 6 in Table 1 are materials with higher strength than the elastic limit σ 0 The test numbers are the same except for the conditions. Comparing test numbers 4 to 6, it can be seen that da / dN decreases as the strength of the material increases. It can be seen that if the elastic limit σ 0 For example, if the pressure is 430 MPa or more, there is a possibility that a crack extension suppression effect equal to or higher than that of the conventional Class-C can be obtained.

[0081] On the other hand, the present inventors have studied ΔK as a driving force for crack extension. θ , max Further detailed research has revealed that ΔK is the driving force for crack extension. θ , max Substituting ε into equation (2) of the nonlinear kinematic hardening law peq = 0.007 when the equivalent stress σ eq There is a strong negative correlation. That is, it can be seen that ΔK, which is the driving force for crack extension, θ，max There is a strong negative correlation with the 0.7% yield strength of the repeated stress-strain curve. Therefore, the inventors investigated the relationship between the crack extension rate da / dN and the 0.7% yield strength of the repeated stress-strain curve. Figure 4 The relationship between the crack extension rate da / dN and the 0.7% yield strength of the repeated stress-strain curve is shown in FIG. Figure 4 The horizontal axis represents the 0.7% yield strength (MPa) of the repeated stress-strain curve. Figure 4 The vertical axis represents the crack extension rate da / dN (mm / cycle). Figure 4 As the 0.7% yield strength of the repeated stress-strain curve increases, the crack extension rate da / dN decreases exponentially. In particular, if the 0.7% yield strength of the repeated stress-strain curve is above 900 MPa, the crack extension rate da / dN (mm / cycle) becomes 4.83×10 -3 That is, if the 0.7% yield strength of the repeated stress-strain curve is 900 MPa or more, the crack extension rate becomes about half or less of that of Class-C, so it is considered that the rolling fatigue life is greatly extended.

[0082] Refer to Table 1 and Figure 4 , we know that: Taking the elastic limit σ 0 The initial kinematic hardening coefficient C is 430 MPa or more, the initial kinematic hardening coefficient C is 130 GPa or more, and the kinematic hardening coefficient reduction rate γ is 400 or less. If the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ satisfy equation (1), crack extension can be greatly suppressed compared with the existing Class-C. Equation (1) is obtained by substituting ε into equation (2) of the nonlinear kinematic hardening law. peq =0.007,σ eq =900, which is the equivalent stress value corresponding to 0.7% of the plastic strain. That is, it indicates the range of the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ when the 0.7% yield strength of the repeated stress-strain curve is 900 MPa or more.

[0083]

Mathematical formula 9

[0084]

[0085] The railway wheel 100 of the present embodiment completed based on the above findings has the following configuration. [1]

[0087] A railway wheel, comprising:

[0088] a hub portion constituting the inner peripheral portion of the railway wheel and having a through hole for inserting an axle of a railway vehicle;

[0089] a rim portion constituting an outer peripheral portion of the railway wheel, including a tread that contacts the top surface of a rail on which the railway vehicle travels, and a flange that protrudes to the outside of the tread in the radial direction of the railway wheel; and

[0090] an annular plate portion connecting the hub portion and the rim portion,

[0091] In the rim surface layer including the tread,

[0092] Elastic limitσ 0 The initial kinematic hardening coefficient C is 130 GPa or more, and the kinematic hardening coefficient reduction rate γ is 400 or less.

[0093] The initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ satisfy equation (1).

[0094]

Mathematical formula 10

[0095]

[0096] In the railway wheel of the present embodiment, the elastic limit σ 0The initial kinematic hardening coefficient C is 430 MPa or more, the initial kinematic hardening coefficient C is 130 GPa or more, the kinematic hardening coefficient reduction rate γ is 400 or less, and the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ satisfy the formula (1). Therefore, the extension of cracks can be suppressed. [2]

[0098] A wheel axle for a railway vehicle, comprising:

[0099] [1] the first railway wheel and the second railway wheel; and

[0100] The axle is inserted into the through holes of the first railway wheel and the second railway wheel, and extends along the rotation axis direction of the first railway wheel and the second railway wheel.

[0101] The railway vehicle axle of the present embodiment includes the railway wheel described in [1]. Therefore, the extension of cracks in the railway wheel can be suppressed.

[0102] [Structure of railway wheels]

[0103] Figure 2 1 is a longitudinal cross-sectional view of the railway wheel 100 of this embodiment. The longitudinal cross-section refers to a cross-section obtained by cutting the railway wheel 100 with a plane including the central axis X. Since the longitudinal cross-section of the railway wheel 100 is symmetrical with respect to the central axis X, Figure 2 1 shows only one side of the center axis X of the railway wheel 100. In the present embodiment, the direction in which the center axis X of the railway wheel 100 extends is referred to as an axial direction, and the radial direction of the railway wheel 100 is referred to as a radial direction.

[0104] Reference Figure 2 The railway wheel 100 includes a hub portion 10 , a rim portion 20 and a plate portion 30 .

[0105] The hub portion 10 is cylindrical with the central axis X as the axis center, and constitutes the inner peripheral portion of the wheel 100. In the hub portion 10, an axle (not shown) of a railway vehicle is inserted.

[0106] The rim portion 20 has a cylindrical shape with the central axis X as the axis center, and constitutes the outer peripheral portion of the railway wheel 100. The rim portion 20 is arranged outside the hub portion 10 in the radial direction.

[0107] The rim portion 20 includes a tread 21 and a flange 22. The tread 21 is provided on the outer peripheral surface of the railway wheel 100. That is, the tread 21 is an annular surface that faces outward in the radial direction. The tread 21 contacts the top surface of the rail on which the railway vehicle travels. The diameter of the tread 21 gradually increases toward the flange 22 side. The shape of the tread 21 is not particularly limited. The tread 21 can be, for example, conical or arc-shaped in the longitudinal cross-sectional view of the railway wheel 100.

[0108] The flange 22 is adjacent to the tread 21 in the axial direction. The flange 22 is provided at one end portion in the axial direction of the rim portion 20. In the present embodiment, the side where the flange 22 is located in the axial direction is referred to as the flange side, and the side opposite thereto is referred to as the flange opposite side. In other words, the surface side of the railway wheel 100 is the flange opposite side, and the back side of the railway wheel 100 is the flange side. The flange 22 protrudes to a position further outward than the tread 21 in the radial direction. When the railway vehicle is running on the track, the flange 22 is positioned on the inner side of the left and right tracks.

[0109] The surface of the flange 22 is connected to the tread 21. The connection portion between the surface of the flange 22 and the tread 21 is called a throat 23. The throat 23 is a curve including one or more arcs in a longitudinal cross-sectional view of the railway wheel 100, and smoothly connects the surface of the flange 22 and the tread 21.

[0110] The plate portion 30 has an annular shape, and connects the hub portion 10 on the inner circumference side and the rim portion 20 on the outer circumference side. The plate thickness of the plate portion 30 is smaller than the length of the hub portion 10 in the axial direction (hub width) and the length of the rim portion 20 in the axial direction (rim width) as a whole. The plate portion 30 has a surface on the opposite side of the flange and a back surface on the flange side. The inner circumferential ends of the surface and the back surface are connected to the outer circumferential surface 11 of the hub portion 10 by means of arc-shaped connecting portions 41a and 42a, respectively, in the longitudinal cross-sectional view. The outer circumferential ends of the surface and the back surface are connected to the inner circumferential surface 24 of the rim portion 20 by means of arc-shaped connecting portions 41b and 42b, respectively, in the longitudinal cross-sectional view.

[0111] The railway wheel 100 satisfies the above parameters in the rim surface layer including the tread 21. The rim surface layer refers to the range from the tread 21 to a depth of 15 mm along the radial direction of the railway wheel 100. If the rim surface layer satisfies the above parameters, the extension of cracks in the railway wheel 100 can be suppressed.

[0112] Figure 3 2 is a longitudinal cross-sectional view of the railway vehicle wheel axle 200 according to the present embodiment. The longitudinal cross-section refers to a cross-sectional view obtained by cutting the railway vehicle wheel axle 200 along a plane including the central axis Y. Figure 3 The railway vehicle axle 200 includes a first railway wheel 101 and a second railway wheel 102, and an axle 201. The first railway wheel 101 and the second railway wheel 102 are the above-mentioned railway wheels 100. The axle 201 is inserted into the through holes 60a and 60b of the first railway wheel 101 and the second railway wheel 102. The axle 201 extends along the rotation axis direction of the first railway wheel 101 and the second railway wheel 102.

[0113] [Elastic limit]

[0114] In the surface layer of the rim portion 20 including the tread 21, the elastic limit σ 0 430MPa or more. Elastic limit σ 0 The preferred lower limit of is 440 MPa, more preferably 450 MPa. Elastic limit σ 0 The upper limit of is not particularly limited, but is, for example, 900 MPa.

[0115] [Initial kinematic hardening coefficient]

[0116] In the surface layer of the rim portion 20 including the tread 21, the initial kinematic hardening coefficient C is 130 GPa or more. The preferred lower limit of the initial kinematic hardening coefficient C is 135 GPa, more preferably 140 GPa, further preferably 145 GPa, further preferably 150 GPa, further preferably 155 GPa, further preferably 160 GPa. The upper limit of the initial kinematic hardening coefficient C is not particularly limited, but is, for example, 200 GPa.

[0117] [Reduction rate of kinematic hardening coefficient]

[0118] In the surface layer of the rim portion 20 including the tread 21, the kinematic hardening coefficient reduction rate γ is 400 or less. The preferred upper limit of the kinematic hardening coefficient reduction rate γ is 390, more preferably 380, further preferably 370, further preferably 360, and further preferably 350. The lower limit of the kinematic hardening coefficient reduction rate γ is not particularly limited, but is, for example, 200.

[0119] [Method for measuring elastic limit, initial kinematic hardening coefficient, and kinematic hardening coefficient reduction rate]

[0120] The elastic limit σ of the railway wheel 100 is measured by the following method: 0 , initial kinematic hardening coefficient C, kinematic hardening coefficient reduction rate γ. First, repeat compression-tensile tests are performed to obtain repeated nominal stress-nominal strain curves. The nominal stress-nominal strain curve is rewritten as a true stress-true strain curve. Furthermore, the plastic strain in the true strain is calculated by subtracting the elastic strain from the true strain. The plastic strain in the true strain corresponds to the equivalent plastic strain, and the true stress at this time corresponds to the equivalent stress. The elastic limit σ is obtained by fitting the equivalent stress-equivalent plastic strain curve obtained in this way with formula (2) of the nonlinear kinematic hardening law. 0 , initial kinematic hardening coefficient C, kinematic hardening coefficient reduction rate γ. In addition, the 0.7% yield strength of the repeated stress-strain curve is obtained by substituting the equivalent plastic strain ε into the equation (2) of the nonlinear kinematic hardening law obtained by fitting. peq = 0.007 when the equivalent stress σ eq .

[0121] [Repeated compression-tension test]

[0122] The repeated compression-tension test was performed as follows: A cylindrical test piece was collected from the surface layer of the rim portion 20 of the railway wheel 100 so that the test piece length direction was in the circumferential direction of the railway wheel 100 . Figure 7 This is a schematic diagram of a test piece for a repeated compression-tensile test. The test piece is cylindrical with a maximum diameter of 15 mm, and the length of the parallel portion at the center of the length direction is 20 mm. The center of the cross section of the test piece perpendicular to the length direction is set at a position 7.5 mm deep from the tread 21 of the railway wheel 100 in the radial direction of the railway wheel 100. A repeated compression-tensile test was carried out using the collected test piece. The test was carried out using the Incremental Step method with a strain ratio of -1 and a strain rate of 0.04% / second. The strain variation range is set to 0.2%. The maximum amplitude of the strain is set to 1.0%. In addition, the cutoff number is set to 20 cycles. The repeated nominal stress-nominal strain curve is set to the first quadrant of the curve connecting the vertices of the hysteresis curve of the 20th cycle. Based on the repeated nominal stress-nominal strain curve obtained in this way and the above-mentioned method, the elastic limit σ is calculated. 0 , initial kinematic hardening coefficient C, and kinematic hardening coefficient reduction rate γ.

[0123] The chemical composition of the railway wheel 100 is not particularly limited. For example, the chemical composition of the railway wheel 100 may be, in mass%, C: greater than 0.70% and less than 1.35%, Si: less than 1.00%, Mn: 0.10% to 1.50%, P: 0% to 0.050%, S: 0% to 0.030%, N: less than 0.0200%, Al: 0% to 1.500%, Cu: 0% to 0.50%, Ni: 0% to 0.50%, Cr: 0% to 0.50%, V: 0% to 0.12%, Ti: 0% to 0.010%, Mo: 0% to 0.20%, Nb: 0% to 0.050%, and the balance is Fe and impurities. The microstructure of the railway wheel 100 is not particularly limited. The microstructure of the railway wheel 100 may be, for example, a microstructure of one or more selected from the group consisting of proeutectoid cementite, proeutectoid ferrite, bainite, and martensite, the total area ratio of which is 0% to 25%, and the balance is pearlite.

[0124] The area ratio of pearlite is calculated using the following method. Samples are collected from the center position of the thickness direction of the rim portion 20 of the railway wheel 100, the center position of the thickness direction of the plate portion 30, and the center position of the thickness direction of the hub portion 10. The observation surface of each sample is mirror-finished by mechanical grinding. Thereafter, the observation surface is corroded using a nitric acid ethanol solution (a mixture of nitric acid and ethanol). For any one field of view (200μm×200μm) within the observation surface after corrosion, a photo image is generated using a 500x optical microscope. The contrast between the quenched layer (martensite and / or bainite), proeutectoid cementite, and proeutectoid ferrite and pearlite is different. Therefore, the quenched layer and pearlite in the observation surface are determined based on the contrast. The area ratio of pearlite is calculated based on the determined total area of ​​pearlite and the area of ​​the observation surface.

[0125] [Method for manufacturing railway wheels]

[0126] An example of a method for manufacturing the above-mentioned railway wheel 100 will be described. This manufacturing method includes a blank manufacturing step, a forming step, a heat treatment step, and a cutting step. Each step will be described below.

[0127] [Blank material manufacturing process]

[0128] In the billet manufacturing process, molten steel having the above chemical composition is melted in an electric furnace or a converter, and then cast to form a casting (a slab or an ingot). The slab can be produced by continuous casting, or the ingot can be produced by mold casting.

[0129] The casting or ingot is hot-processed to produce a billet of a desired size. Examples of hot processing include hot forging, hot rolling, and the like. When the billet is produced by hot rolling, the billet is produced, for example, by the following method. In hot rolling, for example, a blooming mill is used. The casting is subjected to blooming rolling by the blooming mill to produce a billet. When a continuous rolling mill is provided downstream of the blooming mill, the steel material after blooming can be further hot-rolled by the continuous rolling mill to produce billets of smaller size. In the continuous rolling mill, a horizontal rolling mill having a pair of horizontal rolls and a vertical rolling mill having a pair of vertical rolls are alternately arranged in a row. The heating temperature of the heating furnace in hot rolling is not particularly limited, and is, for example, 1100°C to 1350°C. The billet is produced by the above manufacturing process.

[0130] In addition, the blank may be a casting (a cast sheet or an ingot). That is, the above-mentioned hot working may be omitted. Through the above-mentioned steps, the blank of the railway wheel 100 is manufactured. The blank is, for example, a cylindrical blank.

[0131] [Forming process]

[0132] In the forming step, the prepared blank is hot-worked to form an intermediate product in a wheel shape. Since the intermediate product has a wheel shape, it includes a hub portion 10, a plate portion 30, and a rim portion 20 including a tread 21 and a flange 22. The hot working is, for example, hot forging.

[0133] The preferred heating temperature of the blank during hot working is 1220° C. or higher. The cooling method of the intermediate product after hot working is not particularly limited and may be natural cooling or water cooling.

[0134] [Heat treatment process]

[0135] In the heat treatment process, the intermediate product formed into a wheel shape is subjected to tread quenching. Specifically, the intermediate product after the forming process (hot forging or hot rolling) is heated again to A cm The intermediate product is subjected to phase transformation point or above (reheating treatment). After heating, the tread 21 and the flange 22 are rapidly cooled (tread quenching). For example, the tread 21 and the flange 22 are rapidly cooled by spraying a cooling medium. The cooling medium is, for example, air, mist, or spray. In addition, during tread quenching, the plate portion 30 and the hub portion 10 are not water-cooled but naturally cooled.

[0136] Here, cooling that makes the cooling rate constant during tread quenching is referred to as one-stage cooling. Figure 5 1 is a diagram showing the heating pattern of the tread 21 and the position 15 mm deep from the tread 21 in the case of one-stage cooling. Hereinafter, the position 15 mm deep from the tread 21 is also referred to as the 15 mm depth position. Here, the 15 mm depth refers to the depth of 15 mm from the tread 21 in the radial direction of the railway wheel 100. Figure 5 In FIG. 1 , the heating pattern of the tread surface 21 is indicated by a solid line L1 . The heating pattern at a depth of 15 mm from the tread surface 21 is indicated by a dashed dotted line L2 .

[0137] In the case of one-stage cooling, in the tread 21, it is heated from the heating start temperature T0 to the reheating temperature T2 from time t0 to time t1. Thereafter, it is maintained at the reheating temperature T2 from time t1 to time t3. Then, it is cooled from the reheating temperature T2 to the cooling temperature T1 from time t3 to time t5. On the other hand, at the 15 mm depth position, heating and cooling take time compared with the tread 21. At the 15 mm depth position, it is heated from the heating start temperature T0 to the reheating temperature T2 from time t0 to time t2. Thereafter, it is maintained at the reheating temperature T2 from time t2 to time t4. Then, it is cooled from the reheating temperature T2 to the cooling temperature T1 from time t4 to time t6.

[0138] The cooling rate S1 of the tread 21 can be expressed by (T2-T1) / (t5-t3). On the other hand, the cooling rate S2 at the depth of 15 mm can be expressed by (T2-T1) / (t6-t4). The difference between t6 and t4 is larger than the difference between t5 and t3. That is, in the case of one-stage cooling, at the depth of 15 mm, the cooling rate is slower than that of the tread 21.

[0139] For example, by performing two-stage cooling, the cooling rate at the depth of 15 mm can be increased. Thus, the elastic limit σ at the depth of 15 mm can be controlled. 0 , initial kinematic hardening coefficient C and kinematic hardening coefficient reduction rate γ. Figure 6 2 is a diagram showing the heating pattern of the tread 21 and a position 15 mm deep from the tread 21 in the case of two-stage cooling. Figure 6 In FIG. 1 , the heating pattern of the tread surface 21 is indicated by a solid line L1 . The heating pattern at a depth of 15 mm from the tread surface 21 is indicated by a dashed dotted line L2 .

[0140] In the case of two-stage cooling, in the tread 21, heating is performed from the heating start temperature T0 to the reheating temperature T2 in the time from time t0 to time t1. Thereafter, the reheating temperature T2 is maintained from time t1 to time t3. Next, cooling is performed from the reheating temperature T2 to the first cooling temperature T3 in the time from time t3 to time t4. And, cooling is performed from the first cooling temperature T3 to the second cooling temperature T1 in the time from time t4 to time t5. The cooling rate from the reheating temperature T2 to the first cooling temperature T3 is referred to as the first cooling rate S10. The cooling rate from the first cooling temperature T3 to the second cooling temperature T1 is referred to as the second cooling rate S11. The second cooling rate S11 is made higher than the first cooling rate S10. For example, the first cooling rate S10 from the reheating temperature of 900°C to 1000°C to the first cooling temperature of 500°C to 550°C is set to 0.700°C / sec to 10.00°C / sec. The second cooling rate S11 from the first cooling temperature to the second cooling temperature of 300°C to 400°C is set to 1.40°C / sec to 25.0°C / sec. In this case, fine pearlite is precipitated on the tread 21 cooled at the first cooling rate S10. The tread 21 is cooled at the second cooling rate S11 at a stage where the structural change is reduced. The second cooling rate S11 is higher than the first cooling rate S10. As a result, the cooling rate S2 at the depth of 15 mm can be increased to control the elastic limit σ at the depth of 15 mm. 0 , initial kinematic hardening coefficient C and kinematic hardening coefficient reduction rate γ.

[0141] If the first cooling rate S10 is too high, the quenched layer (martensite) is excessively generated. The quenched layer is removed by the cutting process described later. If the quenched layer is excessively generated, the yield rate decreases. Therefore, the first cooling rate S10 is set to a cooling rate of 0.700℃ / second to 10.00℃ / second that can suppress the excessive generation of the quenched layer and enable fine pearlite to precipitate on the tread 21. Next, in order to increase the cooling rate S2 at a depth of 15mm, the second cooling rate S11 is set to 1.40℃ / second to 25.0℃ / second. The second cooling rate S11 is preferably a ratio of 2 to 2.5 times the first cooling rate S10.

[0142] For example, by rapidly cooling the tread 21 and flange 22 of the intermediate product under the above conditions, a railway wheel 100 is obtained in which the elastic limit σ 0 is 430 MPa or more, the initial kinematic hardening coefficient C is 130 GPa or more, the kinematic hardening coefficient reduction rate γ is 400 or less, and the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ satisfy the formula (1).

[0143] In the above description, the intermediate product is reheated, but the intermediate product after hot working may be directly subjected to tread quenching (without reheating).

[0144] The intermediate product after the tread quenching is tempered as needed. The tempering can be performed at a well-known temperature and time. The tempering temperature is, for example, 400°C to 600°C.

[0145] [Cutting process]

[0146] As described above, fine pearlite is formed on the surface layer of the tread 21 of the intermediate product after heat treatment, and a quenched layer is formed on the upper layer. When the railway wheel 100 is used, the quenched layer is removed by cutting because the wear resistance of the quenched layer is low. The cutting process can be performed by a well-known method.

[0147] Through the above steps, the railway wheel 100 of the present embodiment is manufactured.

[0148] [Manufacturing method of axle]

[0149] An example of a method for manufacturing the railway vehicle axle 200 according to the present embodiment will be described. The present manufacturing method includes an axle manufacturing process. The axle manufacturing process includes a preform manufacturing process and a heat treatment process.

[0150] [Pre-production process]

[0151] Molten steel is manufactured. The chemical composition of the molten steel is, for example, C: 0.45% to 0.59%, Si: 0.15% or more, P: 0% to 0.045%, S: 0% to 0.050%, V: 0.02% to 0.08%, and the balance is Fe and impurities. Molten steel is used to manufacture steel ingots. The steel ingots are hot forged to manufacture a rough product having an axle shape. The heating temperature of the steel ingot during hot forging can be within a well-known temperature range. The heating temperature is, for example, 1000°C to 1300°C. The manufactured rough product is subjected to quenching treatment and tempering treatment or normalizing treatment.

[0152] [Heat treatment process]

[0153] When quenching and tempering are performed, the upper limits of quenching and tempering are well-known conditions. Specifically, in the quenching process, the quenching temperature is set to A c3 The rough product is kept at the quenching temperature and then rapidly cooled by water cooling or oil cooling. In the tempering treatment, the tempering temperature is set to A c1 Below the phase transformation point. Keep the rough product at the tempering temperature and then cool it naturally. In the case of normalizing, keep the rough product at a temperature lower than A. c1 The heat treatment temperature with a high transformation point is followed by natural cooling. Alternatively, tempering treatment may be performed following normalizing treatment.

[0154] The rough product that has been quenched and tempered or normalized is subjected to machining as needed. Thereafter, the rough product is subjected to high-frequency quenching. In the high-frequency quenching, the surface layer of the rough product is made thicker than A by high-frequency heating. c3 After reaching a temperature with a high phase transition point, the product is rapidly cooled. The rapid cooling method is, for example, water cooling. The rough product subjected to high frequency quenching may also be subjected to final machining as required. In other words, machining is an arbitrary processing step. In addition, when machining is performed, machining (turning and grinding) is performed within a range that can ensure a hardened layer of the desired depth.

[0155] The axle 201 of the present embodiment is manufactured by the above-described manufacturing method.

[0156] The axle 201 is press-fitted into the through-hole of the manufactured railway wheel 100 to manufacture the railway vehicle axle 200 of the present embodiment.

[0157] [Example]

[0158] By changing the cooling rate, the elastic limit σ 0 , the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ of the test piece. The test piece was used to carry out repeated compression-tension tests.

[0159] Molten steel having the following chemical composition is produced: C: greater than 0.70% and less than 1.35%, Si: less than 1.00%, Mn: 0.10% to 1.50%, P: 0% to 0.050%, S: 0% to 0.030%, N: less than 0.0200%, Al: 0% to 1.500%, Cu: 0% to 0.50%, Ni: 0% to 0.50%, Cr: 0% to 0.50%, V: 0% to 0.12%, Ti: 0% to 0.010%, Mo: 0% to 0.20%, Nb: 0% to 0.050%, and the balance is Fe and impurities. The molten steel is cast in a mold with a diameter of 513 mm to produce steel ingots, and each ingot is cut into 300 mm in length. The cut ingots are heated to 1200°C and then hot forged to produce wheels with a diameter of 965 mm.

[0160] After the manufactured wheel was heated at 900°C for two hours, so-called tread quenching was performed, in which water was sprayed from a nozzle while the wheel was rotated to cool it. During the tread quenching, the cooling rate from 900°C to 550°C, i.e., the first cooling rate, and the cooling rate from 550°C to 400°C, i.e., the second cooling rate, were changed. The first cooling rate and the second cooling rate are shown in Table 2. After the tread quenching, tempering treatment (a treatment of cooling in the atmosphere after holding at 450°C for two hours) was performed. In test number 12, high-temperature tempering treatment (a treatment of cooling in the atmosphere after holding at 650°C for two hours) was further performed after the tempering treatment. Test number 14 is equivalent to the previous Class-C, and is a material in which the first cooling rate and the second cooling rate were not changed. In this way, railway wheels of each test number were manufactured.

[0161] [Table 2]

[0162] Table 2

[0163]

[0164] Test pieces were prepared from the railway wheels of each test number. The test pieces of each test number were used to carry out repeated compression-tension tests using the method described in the above-mentioned [Repeated Compression-Tension Test]. The elastic limit σ of the test piece of each test number was calculated. 0 , initial kinematic hardening coefficient C, kinematic hardening coefficient reduction rate γ. The results are shown in Table 2. In addition, FEM analysis was performed under the above conditions to find the ratio of the crack extension rate (da / dN (mm / cycle)) of each test number to the crack extension rate (da / dN (mm / cycle)) of test number 14 (conventional Class-C). The results are shown in Table 2 ((da / dN) / (da / dN) Class－C ) column.

[0165] [Evaluation results]

[0166] Referring to Table 2, in test numbers 7 to 10, the elastic limit σ of the test piece simulating the railway wheel is 0 The initial kinematic hardening coefficient C is 430 MPa or more, the initial kinematic hardening coefficient C is 130 GPa or more, the kinematic hardening coefficient reduction rate γ is 400 or less, and the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ satisfy equation (1). As a result, the ratio of the crack extension rate to the conventional Class-C ((da / dN) / (da / dN) Class－C ) is 0.500 or less. Test Nos. 7 to 10 can further suppress the extension of cracks compared to conventional railway wheels.

[0167] On the other hand, in test numbers 11 and 12, the elastic limit σ 0 Less than 430MPa, the initial kinematic hardening coefficient C is less than 130GPa, and the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ do not satisfy equation (1). As a result, the ratio of the crack extension rate to Class-C ((da / dN) / (da / dN) Class－C ) is greater than 0.500. Test Nos. 11 and 12 failed to further suppress the extension of cracks compared to conventional railway wheels.

[0168] In test numbers 13 and 14, the initial kinematic hardening coefficient C is less than 130 GPa, and the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ do not satisfy equation (1). As a result, the ratio of the extension rate of the crack to Class-C ((da / dN) / (da / dN) Class－C ) is greater than 0.500. Test Nos. 13 and 14 failed to further suppress the extension of cracks compared to conventional railway wheels.

[0169] The embodiments of the present disclosure are described above. However, the above embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above embodiments, and the above embodiments can be appropriately modified and implemented within the scope of the present disclosure.

[0170] Description of Reference Numerals

[0171] 10. hub portion; 20. rim portion; 21. tread; 22. flange; 30. plate portion; 60. through hole; 100. railway wheel.

Claims

1. A railway wheel, comprising: a hub portion constituting the inner peripheral portion of the railway wheel and having a through hole for inserting an axle of a railway vehicle; a rim portion constituting an outer peripheral portion of the railway wheel, including a tread that contacts the top surface of a rail on which the railway vehicle travels, and a flange that protrudes to the outside of the tread in the radial direction of the railway wheel; and an annular plate portion connecting the hub portion and the rim portion, In the rim surface layer including the tread, The elastic limit σ0 is 430MPa or more, the initial kinematic hardening coefficient C is 130GPa or more, and the kinematic hardening coefficient reduction rate γ is 400 or less. Among them, the initial kinematic hardening coefficient C and the kinematic hardening coefficient reduction rate γ satisfy formula (1), 2. A wheel axle for a railway vehicle, comprising: The first railway wheel and the second railway wheel according to claim 1; as well as The axle is inserted into the through holes of the first railway wheel and the second railway wheel, and extends along the rotation axis direction of the first railway wheel and the second railway wheel.

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