Railway vehicle wheels

Abstract

To provide a wheel for a railway vehicle that can ensure sufficient fatigue strength. [Solution] A wheel (100) includes a boss portion (10) that forms the inner periphery, a rim portion (20) that forms the outer periphery, and an annular plate portion (30) that connects the boss portion (10) and the rim portion (20). The rim portion (20) includes a tread surface (21) and a flange (22). The flange (22) is connected to one end of the tread surface (21) in the axial direction of the wheel (100) and protrudes outward from the tread surface (21) in the radial direction of the wheel (100). At the tread (21) of the rim portion (20), the circumferential compressive residual stress of the wheel (100) is 150 MPa or more at a position 0.5 mm deep from the surface of the tread (21), and at the corner (41) of the connection portion (40) between the boss portion (10) and the plate portion (30) located on the opposite side of the flange in the axial direction, the circumferential compressive residual stress is 5 MPa or more at a position 0.5 mm deep from the surface of the corner (41).

Description

[Technical Field]

[0001] The present disclosure relates to wheels for rail vehicles. [Background technology]

[0002] Railway vehicles have multiple wheels and run on rails. The wheel includes a boss portion that forms the inner periphery, a rim portion that forms the outer periphery, and an annular plate portion that connects the boss portion and the rim portion. The rim portion includes a tread and a flange. When the railway vehicle is running, the wheels support the railway vehicle and roll on the rails. At that time, the tread portion of the rim portion comes into strong contact with the rail and is subjected to frictional forces as well as compressive loads. For this reason, wear resistance is required of the wheels, especially the tread portion. In general, to improve the wear resistance of the tread portion, the tread portion is hardened during the wheel manufacturing process.

[0003] WO 2018 / 181862 (Patent Document 1) describes a technology related to tread hardening. The technology in Patent Document 1 focuses on the structure of a hypereutectoid steel wheel after hardening, and specifies the cooling rate during hardening on the tread and flange surfaces and the cooling rate during hardening on areas other than the tread and flange surfaces according to the chemical composition. Patent Document 1 describes that this technology forms a structure with excellent wear resistance on the tread and flange surfaces in a hypereutectoid steel wheel, and a structure with excellent toughness on areas other than the tread and flange surfaces. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 181862 Summary of the Invention [Problem to be solved by the invention]

[0005] Wheels are one of the important safety components of railway vehicles, and fatigue strength is also required. In Patent Document 1, the wear resistance of the tread and the toughness of parts other than the tread are examined, but fatigue strength is not examined, limited to wheels made of hypereutectoid steel.

[0006] The fatigue strength of wheels is evaluated, for example, according to the Japan Railway Rolling Stock Association standard (JRIS J 0405, 2010). In this evaluation, a load is applied to the wheel tread that comes into contact with the rail. During this evaluation, a vertical load is applied to the tread, assuming track conditions such as straight or curved tracks, and a lateral load is also applied to the flange as needed. When a lateral load is applied in addition to the vertical load, the magnitude of the resultant force is greater than when only a vertical load is applied, so high stress is expected to occur in the wheel.

[0007] Recent research has revealed that when a wheel is subjected to vertical and lateral loads, high stresses occur not only on the tread but also, depending on the wheel shape, at the corners of the joint between the boss and the plate, located on the opposite side of the flange in the axial direction of the wheel, or near those corners. In a wheel, the opposite side of the flange corresponds to the outer side in the track width direction, i.e., the front surface, and the flange side corresponds to the inner side in the track width direction, i.e., the back surface. In this specification, these corners are sometimes referred to as the "boss-side root of the plate surface." For this reason, the tread and the boss-side root of the plate surface of a wheel may be vulnerable to fatigue strength.

[0008] An object of the present disclosure is to provide a wheel for a railway vehicle that can ensure sufficient fatigue strength. [Means for solving the problem]

[0009] A railway vehicle wheel according to the present disclosure includes a boss portion constituting the inner periphery of the wheel, a rim portion constituting the outer periphery of the wheel, and an annular plate portion connecting the boss portion and the rim portion. The rim portion includes a tread surface and a flange. The flange is connected to one end of the tread surface in the axial direction of the wheel and protrudes outward from the tread surface in the radial direction of the wheel. At the tread surface of the rim portion, a compressive residual stress in the circumferential direction of the wheel is 150 MPa or more at a position 0.5 mm deep from the surface of the tread, and at a corner of the connection between the boss portion and the plate portion located on the opposite side of the flange in the axial direction, a compressive residual stress in the circumferential direction is 5 MPa or more at a position 0.5 mm deep from the surface of the corner. [Effects of the Invention]

[0010] According to the railway vehicle wheel according to the present disclosure, fatigue strength can be sufficiently ensured. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a wheel for a railway vehicle according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing a schematic configuration of a cooling device used when manufacturing a railway vehicle wheel according to the first embodiment. [Figure 3] FIG. 3 is a vertical cross-sectional view showing a schematic configuration of a wheel for a railway vehicle according to a modified example of the first embodiment. [Figure 4] FIG. 4 is a vertical cross-sectional view showing a schematic configuration of a wheel for a railway vehicle according to another modified example of the first embodiment. [Figure 5] FIG. 5 is a vertical cross-sectional view showing a schematic configuration of a wheel for a railway vehicle according to the second embodiment. [Figure 6] FIG. 6 is a vertical cross-sectional view showing a schematic configuration of a wheel for a railway vehicle according to the third embodiment. [Figure 7] FIG. 7 is a diagram showing the relationship between the cooling rate ratio CVt / CVb of the tread surface to the base portion on the boss side of the plate surface and the residual stresses of the tread surface and the base portion on the boss side of the plate surface. DETAILED DESCRIPTION OF THE INVENTION

[0012] As mentioned above, the tread is hardened to improve its wear resistance. This hardening imparts compressive residual stress to the tread. If the tread is hardened to further improve its wear resistance, the compressive residual stress in the tread will increase. Since the tread can be a vulnerable part in terms of fatigue strength, it is thought that the compressive residual stress in the tread improves the fatigue strength of the wheel. However, it has become clear that simply hardening the tread increases the compressive residual stress in the tread, but at the base of the boss on the plate surface, the residual stress changes from compressive to tensile.

[0013] As described above, the boss-side root portion of the plate surface can be a vulnerable portion in terms of fatigue strength, and if tensile residual stress is applied to this root portion, the fatigue strength of the wheel may be reduced. Therefore, it is preferable that a relatively high compressive residual stress is applied to the tread, and that at least a compressive residual stress is applied to the boss-side root portion of the plate surface. Based on these considerations, the inventors have identified an appropriate balance of compressive residual stresses for the tread and the boss-side root portion of the plate surface, taking into account the hardening conditions.

[0014] A railway vehicle wheel according to an embodiment of the present disclosure has been completed based on the above findings.

[0015] A railway vehicle wheel according to this embodiment includes a boss portion constituting the inner periphery of the wheel, a rim portion constituting the outer periphery of the wheel, and an annular plate portion connecting the boss portion and the rim portion. The rim portion includes a tread surface and a flange. The flange is connected to one end of the tread surface in the axial direction of the wheel and protrudes outward from the tread surface in the radial direction of the wheel. At the tread surface of the rim portion, a compressive residual stress in the circumferential direction of the wheel is 150 MPa or more at a position 0.5 mm deep from the surface of the tread, and at a corner of the connection between the boss portion and the plate portion located on the opposite side of the flange in the axial direction, a compressive residual stress in the circumferential direction is 5 MPa or more at a position 0.5 mm deep from the surface of the corner (first configuration).

[0016] In the first configuration, the wheel circumferential compressive residual stress is 150 MPa or more at a position 0.5 mm deep from the tread surface of the rim, and the circumferential compressive residual stress is 5 MPa or more at a position 0.5 mm deep from the corner surface of the connection between the boss and plate, located on the opposite side of the flange in the axial direction. In other words, in addition to the large compressive residual stress imparted to the tread, which can be a vulnerable part in terms of fatigue strength, at least the base of the plate surface on the boss side, which can also be a vulnerable part in terms of fatigue strength like the tread, is imparted with compressive residual stress. Therefore, with the first configuration, sufficient fatigue strength can be ensured.

[0017] In the wheel according to the first configuration, the center of the rim portion in the axial direction may be located closer to the flange than the center of the boss portion in the axial direction (second configuration).

[0018] In the wheel according to the second configuration, the thickness centerline of the plate portion may be linear in a cross section including the wheel center axis, and may be inclined relative to the radial direction so as to move away from the flange as it moves radially outward. In this case, when the axial distance from the side farthest from the flange of the rim portion to the outer end that is the radially outer end of the thickness centerline is defined as Pw, and the axial length of the rim portion is defined as Wr, Pw / Wr may be less than 0.40 (third configuration).

[0019] In the wheel according to the first configuration, the center of the rim portion in the axial direction may be located on the opposite side of the flange from the center of the boss portion in the axial direction. In this case, the thickness centerline of the plate portion may be linear in a cross section including the central axis of the wheel. Furthermore, the outer end, which is the end located radially outward of both ends of the thickness centerline, may be located in the same position as the center of the rim portion in the axial direction, and the inner end, which is the end located radially inward of both ends of the thickness centerline, may be located in the same position as the center of the boss portion in the axial direction (fourth configuration).

[0020] In the wheel according to the first configuration, the center of the rim portion in the axial direction may be located at the same position as the center of the boss portion in the axial direction. In this case, the thickness centerline of the plate portion may have a straight line in a cross section including the central axis of the wheel. Furthermore, the outer end, which is the end located radially outward of both ends of the thickness centerline, may be located at the same position as the center of the rim portion in the axial direction, and the inner end, which is the end located radially inward of both ends of the thickness centerline, may be located at the same position as the center of the boss portion in the axial direction (fifth configuration).

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0022] First Embodiment [wheel] FIG. 1 is a longitudinal cross-sectional view showing the schematic configuration of a wheel 100 for a railway vehicle according to a first embodiment. The wheel 100 is attached to an axle (not shown) and rotates integrally with the axle about a central axis X. In this specification, the direction in which the central axis X extends may be referred to as the axial direction of the wheel 100, or simply as the axial direction. The axial direction corresponds to the track width direction. Furthermore, the circumferential direction and radial direction of the wheel 100 may be simply referred to as the circumferential direction or the radial direction, respectively. In this specification, unless otherwise specified, a longitudinal cross-section refers to a cross-section including the central axis X.

[0023] Referring to FIG. 1, a wheel 100 includes an annular boss portion 10, an annular rim portion 20, and an annular plate portion 30.

[0024] The boss portion 10 forms the inner periphery of the wheel 100. The boss portion 10 is connected to the plate portion 30 via a connecting portion 40.

[0025] The rim portion 20 forms the outer periphery of the wheel 100. The rim portion 20 is connected to the plate portion 30 via a connecting portion 50. The rim portion 20 includes a tread 21 and a flange 22. The flange 22 is connected to one end of the tread 21 in the axial direction of the wheel 100 and protrudes outward from the tread 21 in the radial direction of the wheel 100. The tread 21 is the surface that comes into contact with the rail. In this specification, the side of the wheel 100 closer to the flange 22 in the axial direction is referred to as the flange side, and the side farther from the flange 22 is referred to as the anti-flange side. From another perspective, the outer side of the wheel 100 in the track width direction is referred to as the anti-flange side, and the inner side in the track width direction is referred to as the flange side. For example, in the wheel 100 shown in Figure 1, the left side is the flange side and the right side is the anti-flange side.

[0026] The surface of the tread 21 is smoothly connected to the surface of the flange 22. Usually, the connection between the surface of the tread 21 and the surface of the flange 22 has a substantially arc shape when viewed in vertical cross section of the wheel 100. In this embodiment, the flange-side end (R stop) 212 of the connection between the surface of the tread 21 and the surface of the flange 22 is referred to as the flange-side end 212 of the tread 21. In addition, the anti-flange end 211 of the tread 21 is the connection between the tread 21 and the anti-flange side surface 24 of the rim portion 20. That is, in this embodiment, the range of the tread 21 is the range from end 211 to end 212.

[0027] In this embodiment, the center Cr of the rim portion 20 is located on the flange side in the axial direction relative to the center Cb of the boss portion 10. The center Cr of the rim portion 20 is the center of the width of the rim portion 20 in the axial direction, and the center Cb of the boss portion 10 is the center of the width of the boss portion 10 in the axial direction. Typically, in the axial direction, the flange-side side surface 23 of the rim portion 20 is located more inward in the raceway width direction than the flange-side side surface 11 of the boss portion 10.

[0028] The plate portion 30 is connected to the boss portion 10 via a connecting portion 40, and is connected to the rim portion 20 via a connecting portion 50. The plate portion 30 is inclined relative to the radial direction so as to move away from the flange 22 as it extends radially outward. The plate portion 30 includes a surface 31 on the opposite side to the flange and a back surface 32 on the flange side.

[0029] The connection portion 40 is a portion that connects the plate portion 30 and the boss portion 10. Hereinafter, the connection portion 40 will also be referred to as the inner peripheral connection portion 40. The connection portion 40 smoothly connects the plate portion 30 and the boss portion 10. The connection portion 40 includes a corner portion 41 on the anti-flange side and a corner portion 42 on the flange side. The anti-flange side corner portion 41 of the connection portion 40 corresponds to the boss side base portion 41 of the plate portion surface 31.

[0030] The connection portion 50 is a portion that connects the plate portion 30 and the rim portion 20. Hereinafter, the connection portion 50 will also be referred to as the outer peripheral side connection portion 50. The connection portion 50 smoothly connects the plate portion 30 and the rim portion 20. The connection portion 50 includes a corner portion 51 on the anti-flange side and a corner portion 52 on the flange side.

[0031] The surface of each of the corners 41, 42, 51, and 52 has a substantially arcuate shape in a vertical cross-sectional view of the wheel 100. The radius of curvature of each of the corners 41, 42, 51, and 52 can be determined appropriately.

[0032] The corner portion 41 is a portion of the inner peripheral connection portion 40 that is located on the anti-flange side. In this embodiment, an end (R-stop) 411 of the corner portion 41 on the plate portion 30 side is continuous with the surface 31 of the plate portion 30. In other words, the end 411 is the boundary between the plate portion 30 and the corner portion 41. An end (R-stop) 412 of the corner portion 41 on the boss portion 10 side is continuous with the outer peripheral surface 13 of the boss portion 10 on the anti-flange side. In other words, the end 412 is the boundary between the boss portion 10 and the corner portion 41.

[0033] The corner portion 42 is a portion of the inner peripheral connection portion 40 that is located on the flange side. In this embodiment, an end (R-stop) 421 of the corner portion 42 on the plate portion 30 side is continuous with the back surface 32 of the plate portion 30. In other words, the end 421 is the boundary between the plate portion 30 and the corner portion 42. An end (R-stop) 422 of the corner portion 42 on the boss portion 10 side is continuous with the outer peripheral surface 14 of the boss portion 10 on the flange side. In other words, the end 422 is the boundary between the boss portion 10 and the corner portion 42.

[0034] The corner portion 51 is a portion of the outer peripheral connecting portion 50 that is located on the anti-flange side. In this embodiment, an end (R end) 511 of the corner portion 51 on the plate portion 30 side is continuous with the surface 31 of the plate portion 30. In other words, the end 511 is the boundary between the plate portion 30 and the corner portion 51. An end (R end) 512 of the corner portion 51 on the rim portion 20 side is continuous with the inner circumferential surface 25 of the rim portion 20 on the anti-flange side. In other words, the end 512 is the boundary between the rim portion 20 and the corner portion 51.

[0035] The corner portion 52 is a portion of the outer peripheral connecting portion 50 that is located on the flange side. In this embodiment, an end (R-end) 521 of the corner portion 52 on the plate portion 30 side is continuous with the back surface 32 of the plate portion 30. In other words, the end 521 is the boundary between the plate portion 30 and the corner portion 52. An end (R-end) 522 of the corner portion 52 on the rim portion 20 side is continuous with the inner circumferential surface 26 on the flange side of the rim portion 20. In other words, the end 522 is the boundary between the rim portion 20 and the corner portion 52.

[0036] In this embodiment, of the end 411 of the corner 41 located on the anti-flange side facing the plate portion 30 and the end 421 of the corner 42 located on the flange side facing the plate portion 30, the one located more radially outward is defined as the inner peripheral end of the plate portion 30. Also, of the end 511 of the corner 51 located on the anti-flange side facing the plate portion 30 and the end 521 of the corner 52 located on the flange side facing the plate portion 30, the one located more radially inward is defined as the outer peripheral end of the plate portion 30. In the example shown in FIG. 1 , the end 411 of the corner 41 located on the anti-flange side and the end 511 of the corner 51 located on the anti-flange side are the inner peripheral end and the outer peripheral end of the plate portion 30, respectively.

[0037] The plate portion 30 has a plate thickness centerline A. The plate thickness centerline A is an imaginary line passing through the center of the plate thickness of the plate portion 30 extending from the boss portion 10 to the rim portion 20 in a vertical cross-sectional view of the wheel 100. The plate thickness centerline A passes through the middle between the front surface 31 and the back surface 32 of the plate portion 30, extending from the boss portion 10 side to the rim portion 20 side.

[0038] The plate thickness center line A has a straight line shape in a vertical cross-sectional view of the wheel 100. Here, the concept of a straight line does not only mean a perfect straight line, but also includes, for example, a very gentle arc with a curvature radius of 1000 mm or more, or a broken line. In other words, the plate thickness center line A may be any line that can be recognized as being substantially straight in a vertical cross-sectional view of the wheel 100. Because the plate thickness center line A is straight in a vertical cross-sectional view of the wheel 100, the plate portion 30 has a substantially flat plate shape and is not curved toward the flange side or the anti-flange side.

[0039] The thickness center line A has an outer end Aa and an inner end Ab. The outer end Aa is the end located radially outward of both end portions of the thickness center line A. In other words, the outer end Aa is the end located at the outer peripheral end 511 of the plate portion 30 of both end portions of the thickness center line A. The inner end Ab is the end located radially inward of both end portions of the thickness center line A. In other words, the inner end Ab is the end located at the inner peripheral end 411 of the plate portion 30 of both end portions of the thickness center line A.

[0040] The thickness center line A forms an angle θ with respect to the axial direction on the opposite side to the flange 22. In this embodiment, as described above, the plate portion 30 is inclined with respect to the radial direction so as to move away from the flange 22 as it moves radially outward. Therefore, the thickness center line A is inclined with respect to the radial direction so as to move away from the flange 22 as it moves radially outward. In this case, the angle θ of the thickness center line A is less than 90°. The angle θ is preferably 70° to 87.5°. The angle θ of the thickness center line A is also the angle that the tangent to the thickness center line A at the inner end Ab forms with respect to the axial direction on the anti-flange side.

[0041] The outer end Aa of the plate thickness centerline A is located on the anti-flange side of the center Cr of the rim portion 20. When the axial length of the rim portion 20 is defined as the rim width Wr and the axial distance from the anti-flange side surface 24 of the rim portion 20 to the outer end Aa of the plate thickness centerline A is defined as the plate portion position Pw, Pw / Wr is less than 0.40. It is preferable that Pw / Wr is 0.30 or more.

[0042] In this embodiment, compressive residual stress is imparted to the tread 21 of the rim portion 20 and the boss-side root portion 41 of the plate portion surface 31. Specifically, in the tread 21 of the rim portion 20, the compressive residual stress in the circumferential direction of the wheel 100 is 150 MPa or more at a position 0.5 mm deep from the surface of the tread 21. Also, in a corner portion 41 located on the anti-flange side in the axial direction of the connection portion 40 between the boss portion 10 and the plate portion 30, the compressive residual stress in the circumferential direction is 5 MPa or more at a position 0.5 mm deep from the surface of the corner portion 41.

[0043] Residual stress is measured using X-rays. The measurement is performed after removing 0.5 mm of the surface of each of the tread surface 21 of the rim portion 20 and the boss-side base portion 41 of the plate portion surface 31. This is because it is difficult to accurately measure residual stress near the surface due to the influence of damaged layers, etc. Therefore, the measurement depth position should be essentially 0.5 mm deep. For example, an error of about ±0.05 mm is allowed for the measurement depth.

[0044] The residual stress in the tread 21 and the boss-side root portion 41 of the plate surface 31 need only satisfy the specified residual stress at one location in each portion. However, it is preferable that the specified residual stress be satisfied over the entire area of ​​each portion. Specifically, it is preferable that the circumferential compressive residual stress of the wheel 100 be 150 MPa or more at a position 0.5 mm deep from the surface of the tread 21 over the entire area of ​​the tread 21 of the rim portion 20. Furthermore, it is preferable that the circumferential compressive residual stress be 5 MPa or more at a position 0.5 mm deep from the surface of the corner 41 over the entire area of ​​the corner 41 located on the anti-flange side in the axial direction of the connection portion 40 between the boss portion 10 and the plate portion 30.

[0045] [Method of manufacturing the wheel 100] Next, a description will be given of an example of a method for manufacturing the wheel 100 according to this embodiment. The method for manufacturing the wheel 100 includes a preparation step, a heating step, and a cooling step.

[0046] (preparation process) The preparation step is a step of preparing an intermediate product of the wheel 100. The intermediate product has a rough shape of the wheel 100 including the boss portion 10, the rim portion 20, and the plate portion 30. The material of the intermediate product is, for example, hypoeutectoid steel. Although not particularly limited, the chemical composition of the intermediate product may contain, in mass %, C: 0.62 to 0.72%, Si: 0.20 to 0.40%, Mn: 0.60 to 0.85%, P: 0.001 to 0.040%, S: 0.001 to 0.025%, Cu: 0.00 to 0.15%, Ni: 0.00 to 0.10%, Cr: 0.05 to 0.20%, Mo: 0.000 to 0.080%, and Al: 0.005 to 0.070%, with the balance being Fe and impurities. As an example, the chemical composition of the intermediate product is, in mass%, C: 0.65%, Si: 0.25%, Mn: 0.73%, P: 0.018%, S: 0.018%, Cu: 0.1%, Ni: 0.075%, Cr: 0.11%, Mo: 0.025%, Al: 0.04%, with the remainder being Fe and impurities.

[0047] The intermediate product is produced, for example, by the following method: Molten steel is produced using an electric furnace or a converter, etc. A material is produced using the molten steel. For example, a slab is produced by a continuous casting method. Alternatively, an ingot is produced by an ingot casting method. The slab or ingot is subjected to blooming or hot forging to produce a billet as a material. The material may be a slab produced by a continuous casting method. The shape of the material is preferably cylindrical.

[0048] The prepared material is used to form an intermediate product. Specifically, the material is cut in a direction perpendicular to the longitudinal direction. The cut material is formed into a railway wheel intermediate product having a rough shape of the wheel 100 by hot forging or hot rolling. The intermediate product is prepared in this manner.

[0049] (Heating process) The heating process is performed by heating the intermediate product of the wheel 100 to A c3 This is a process of heating above the A point. c3 The point is the temperature at which the transformation from ferrite to austenite is completed during heating. In the heating process, for example, the intermediate product is charged into a heating furnace and heated at A c3 The temperature is increased to a temperature equal to or higher than the temperature rise point. The temperature increase rate and the holding time at the heating temperature are set under well-known conditions. The heating temperature is, for example, 830°C. The holding time is, for example, 10,000 seconds.

[0050] (cooling process) The cooling step is a step of cooling the intermediate product of the wheel 100 that has been heated in the heating step. In the cooling step, the intermediate product is cooled using a cooling device 200. However, a known cooling device may also be used.

[0051] 2 is a side view showing a schematic configuration of a cooling device 200 used when manufacturing the wheel 100 according to this embodiment. The cooling device 200 includes a turntable 60 having a rotation shaft, and a plurality of refrigerant supply devices 70.

[0052] An intermediate product 100a is placed on the turntable 60. The side surface 12 of the boss portion 10 of the intermediate product 100a on the axial side opposite the flange is placed on the turntable 60. In other words, the intermediate product 100a is placed on the turntable 60 with the side surface 11 of the boss portion 10 on the axial side facing the flange upward. The turntable 60 rotates at a constant speed. The rotation speed of the turntable 60 is, for example, 10 rpm.

[0053] The multiple refrigerant supply devices 70 include multiple inner refrigerant supply devices 71 and multiple outer refrigerant supply devices 72. The inner refrigerant supply devices 71 are provided around the turntable 60, more inward than the rim portion 20 of the intermediate product 100a. The inner refrigerant supply devices 71 supply refrigerant to the inner peripheral portion of the intermediate product 100a. The inner refrigerant supply devices 71 have a refrigerant outlet 711. In this embodiment, the refrigerant outlet 711 is provided opposite the boss-side base portion 41 of the plate surface 31. The inner refrigerant supply devices 71 inject refrigerant from the refrigerant outlet 711 to mainly cool the surface of the boss-side base portion 41 of the plate surface 31.

[0054] The outer refrigerant supply device 72 is provided around the turntable 60, on the outer peripheral side of the rim portion 20 of the intermediate product 100a. The outer refrigerant supply device 72 supplies refrigerant to the outer periphery of the intermediate product 100a. The outer refrigerant supply device 72 has a refrigerant outlet 721 at its tip. The refrigerant outlet 721 is provided opposite the tread surface 21. The outer refrigerant supply device 72 injects refrigerant from the refrigerant outlet 721 to mainly cool the surface of the tread surface 21 of the rim portion 20.

[0055] The refrigerant is water. The water may be sprayed in liquid form or in particulate form. In this embodiment, the refrigerant from the inner refrigerant supply device 71 is sprayed in particulate form, and the refrigerant from the outer refrigerant supply device 72 is sprayed in liquid form. The amount of refrigerant supplied can be freely selected depending on the desired cooling rate. The amount of refrigerant supplied from the outer refrigerant supply device 72 is preferably 12 to 17 times the amount of refrigerant supplied from the inner refrigerant supply device 71.

[0056] In the cooling process, cooling water is supplied to the tread 21 and the surface of the boss-side root portion 41 of the plate surface 31. For 50 seconds from the start of the supply of cooling water, the intermediate product 100a is cooled so that the cooling rate ratio CVt / CVb, which is expressed as the ratio of the cooling rate CVt on the surface of the tread 21 to the cooling rate CVb on the surface of the root portion 41, is 4.7 or more and 6.9 or less.

[0057] In the cooling step, cooling with air may be performed in addition to cooling by the cooling device 200. For example, air may be sprayed onto the surface of the intermediate product 100a on the flange side in the axial direction.

[0058] The intermediate product 100a manufactured through the above steps is subjected to known product finishing, thereby manufacturing the wheel 100.

[0059] [effect] In the wheel 100 according to this embodiment, the circumferential compressive residual stress of the wheel 100 is 150 MPa or more at a position 0.5 mm deep from the surface of the tread 21 of the rim portion 20, and the circumferential compressive residual stress of the wheel 100 is 5 MPa or more at a position 0.5 mm deep from the surface of the corner 41 located on the opposite side of the flange in the axial direction of the connection portion 40 between the boss portion 10 and the plate portion 30. In other words, in addition to the large compressive residual stress imparted to the tread 21, which can be a part vulnerable to fatigue strength, at least the compressive residual stress is imparted to the boss-side root portion 41 of the plate portion surface 31, which, like the tread 21, can be a part vulnerable to fatigue strength. Therefore, the wheel 100 according to this embodiment can ensure sufficient fatigue strength.

[0060] [Modification of the first embodiment] Fig. 3 is a longitudinal cross-sectional view showing the schematic configuration of a wheel 100A according to a modified example of the first embodiment. In the example shown in Fig. 3, in the plate portion 30, the outer end Aa of the plate thickness center line A is located at the same position in the axial direction as the center Cr of the rim portion 20. Furthermore, the inner end Ab of the plate thickness center line A is located at the same position in the axial direction as the center Cb of the boss portion 10. Therefore, the plate portion 30 is inclined with respect to the radial direction so as to approach the flange 22 as it moves radially outward. In other words, the angle θ of the plate thickness center line A is greater than 90°, for example, 102°.

[0061] In this case as well, in addition to the large compressive residual stress being imparted to the tread 21, which may be a part vulnerable to fatigue strength, at least the compressive residual stress is imparted to the boss-side base portion 41 of the plate surface 31, which may also be a part vulnerable to fatigue strength like the tread 21. Therefore, as with the wheel 100, sufficient fatigue strength can be ensured.

[0062] Fig. 4 is a longitudinal cross-sectional view showing the schematic configuration of a wheel 100B according to another modified example of the first embodiment. In the example shown in Fig. 4, as in the example shown in Fig. 3, the outer end Aa of the plate thickness center line A is located at the same position in the axial direction as the center Cr of the rim portion 20. Furthermore, the inner end Ab of the plate thickness center line A is located at the same position in the axial direction as the center Cb of the boss portion 10.

[0063] Furthermore, in the example shown in FIG. 4, the plate portion 30 is curved in a wave-like shape in a vertical cross section. Specifically, the plate portion 30 has an arc-like shape on the outer periphery that is convex toward the flange side, and an arc-like shape on the inner periphery that is convex toward the anti-flange side. The radius of curvature of the arc on the outer periphery of the plate portion 30 is, for example, 165 mm, and the radius of curvature of the arc on the inner periphery of the plate portion 30 is, for example, 175 mm. The position where the radius of curvature of the plate portion 30 changes is the midpoint between the outer end Aa and the inner end Ab of the thickness center line A in the radial direction. In the example shown in FIG. 4, the thickness center line A is also curved in a wave-like shape in a vertical cross section. A tangent A1 at the inner end Ab of the thickness center line A forms an angle θ1 on the anti-flange side with respect to the axial direction. The angle θ1 is, for example, 102°.

[0064] In the example shown in FIG. 4, similar to the wheels 100 and 100A, sufficient fatigue strength can be ensured.

[0065] Second Embodiment Fig. 5 is a longitudinal cross-sectional view showing a schematic configuration of a railway vehicle wheel 100C according to the second embodiment. Referring to Fig. 5, railway vehicle wheel 100C according to the second embodiment differs from wheels 100, 100A, 100B according to the first embodiment and its variations in that a center Cr of rim portion 20 in the axial direction is located on the opposite flange side from a center Cb of boss portion 10 in the axial direction.

[0066] In the wheel 100C of the second embodiment, the outer end Aa of the thickness center line A is located at the same position in the axial direction as the center Cr of the rim portion 20. Furthermore, the inner end Ab of the thickness center line A is located at the same position in the axial direction as the center Cb of the boss portion 10. Furthermore, the thickness center line A of the plate portion 30 has a straight shape in a vertical cross section. Therefore, in the wheel 100C of the second embodiment, the plate portion 30 is inclined with respect to the radial direction so as to move away from the flange 22 as it moves radially outward. In other words, the angle θ of the thickness center line A is smaller than 90°, for example, 78°.

[0067] In wheel 100C of the second embodiment, similar to the first embodiment, large compressive residual stress is imparted to tread 21, which can be a part vulnerable to fatigue strength, and in addition, compressive residual stress is imparted to at least boss-side base portion 41 of plate surface 31, which can be a part vulnerable to fatigue strength like tread 21. Therefore, wheel 100C of the second embodiment can ensure sufficient fatigue strength, similar to wheels 100, 100A, and 100B.

[0068] Third Embodiment Fig. 6 is a longitudinal cross-sectional view showing a schematic configuration of a railway vehicle wheel 100D according to the third embodiment. Referring to Fig. 6, railway vehicle wheel 100D according to the third embodiment differs from wheels 100, 100A, 100B, 100C according to the first embodiment, its modifications, and the second embodiment in that a center Cr of rim portion 20 is positioned at the same position as a center Cb of boss portion 10 in the axial direction.

[0069] In the wheel 100D of the third embodiment, the outer end Aa of the thickness center line A is located at the same position as the center Cr of the rim portion 20 in the axial direction. Also, the inner end Ab of the thickness center line A is located at the same position as the center Cb of the boss portion 10 in the axial direction. Furthermore, the thickness center line A of the plate portion 30 has a straight shape in a vertical cross section. Therefore, in the wheel 100D of the third embodiment, the plate portion 30 is not substantially inclined with respect to the radial direction. That is, the angle θ of the thickness center line A is 90°.

[0070] In wheel 100D of the third embodiment, similar to the first and second embodiments, large compressive residual stress is imparted to tread 21, which can be a part vulnerable to fatigue strength, and in addition, compressive residual stress is imparted to at least boss-side base portion 41 of plate surface 31, which can be a part vulnerable to fatigue strength like tread 21. Therefore, wheel 100D according to the third embodiment can ensure sufficient fatigue strength, similar to wheels 100, 100A, 100B, and 100C.

[0071] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. [Example]

[0072] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0073] The intermediate product 100a was hardened, and the relationship between the cooling rate and residual stress at the tread surface 21 and the boss-side base portion 41 of the plate surface 31 was investigated. The temperature of each portion of the intermediate product 100a was measured while it was cooling. The temperature measurements were performed using a thermocouple. After cooling, the surface of each portion of the intermediate product 100a was electrolytically polished, and then the residual stress of each portion was measured. The residual stress measurements were performed using a portable X-ray residual stress measurement device μ-X360s manufactured by Pulstec Industrial Co., Ltd.

[0074] On the surface of the tread 21, the temperature was measured at a position 50 mm axially away from the end 211 on the anti-flange side. At this temperature measurement position, residual stress was measured at a position 0.5 mm deep from the surface of the tread 21. On the surface of the boss-side root 41 of the plate portion surface 31, the temperature was measured at a position 36 mm radially away from the outer peripheral edge of the side surface 12 on the anti-flange side of the boss portion 10. At this temperature measurement position, residual stress was measured at a position 0.5 mm deep from the surface of the boss-side root 41 of the plate portion surface 31.

[0075] During cooling of the intermediate product 100a, the cooling rate ratio CVt / CVb, which is expressed as the ratio of the cooling rate CVt of the tread surface 21 to the cooling rate CVb of the surface of the boss-side root portion 41 of the plate surface 31, was calculated for 50 seconds from the start of the supply of cooling water. Circumferential residual stress was measured for wheels manufactured when this cooling rate ratio CVt / CVb was 3.9 to 8.9.

[0076] Figure 7 shows the circumferential residual stress in the tread 21 and the boss-side root portion 41 of the plate surface 31 of wheels manufactured with each cooling rate ratio CVt / CVb. For the residual stresses shown in Figure 7, minus signs indicate compressive residual stress, and plus signs indicate tensile residual stress. The residual stress in the tread 21 was compressive residual stress regardless of the value of the cooling rate ratio CVt / CVb. As the value of the cooling rate ratio CVt / CVb increased, the compressive residual stress in the tread 21 increased. When the cooling rate ratio CVt / CVb was 4.7 or higher, the circumferential compressive residual stress in the tread 21 was 150 MPa or higher.

[0077] On the other hand, the residual stress in the boss-side root portion 41 of the plate surface 31 varied between compressive and tensile residual stresses depending on the value of the cooling rate ratio CVt / CVb. The residual stress in the boss-side root portion 41 of the plate surface 31 was compressive when the cooling rate ratio CVt / CVb was 6.9 or less, and the compressive residual stress decreased as the cooling rate ratio CVt / CVb increased within that range. The residual stress in the boss-side root portion 41 of the plate surface 31 was tensile when the cooling rate ratio CVt / CVb was greater than 6.9, and the tensile residual stress increased as the cooling rate ratio CVt / CVb increased within that range. When the cooling rate ratio CVt / CVb was 6.9 or less, the circumferential compressive residual stress in the boss-side root portion 41 of the plate surface 31 was 5 MPa or more.

[0078] From the above results, it became clear that by cooling the intermediate product 100a so that the cooling rate ratio CVt / CVb is 4.7 or more and 6.9 or less, it is possible to manufacture a wheel 100 in which the circumferential compressive residual stress of the tread surface 21 is 150 MPa or more and the circumferential compressive residual stress of the boss side base portion 41 of the plate portion surface 31 is 5 MPa or more. [Explanation of symbols]

[0079] 100,100A,100B,100C,100D: Wheel 10: Boss Section 20: Rim 21: Tread 22: Flange 24: Side 30: Board part 40: Connection 41: Corner A: Thickness center line Aa: outer end

Claims

1. A wheel for a railway vehicle, a boss portion that forms an inner circumferential portion of the wheel; a rim portion that forms an outer periphery of the wheel and includes a tread surface and a flange that is connected to one end of the tread surface in the axial direction of the wheel and protrudes outward from the tread surface in the radial direction of the wheel; an annular plate portion connecting the boss portion and the rim portion; Equipped with In the tread surface of the rim portion, a compressive residual stress in the circumferential direction of the wheel is 150 MPa or more at a position 0.5 mm deep from the surface of the tread surface, a corner of the connection portion between the boss portion and the plate portion that is located on the opposite side of the flange in the axial direction, wherein the compressive residual stress in the circumferential direction is 5 MPa or more at a position 0.5 mm deep from the surface of the corner.

2. 2. A wheel according to claim 1, A wheel, wherein a center of the rim portion in the axial direction is located on a flange side relative to a center of the boss portion in the axial direction.

3. 3. A wheel according to claim 2, a plate thickness center line of the plate portion has a straight line in a cross section including a central axis of the wheel, and is inclined with respect to the radial direction so as to move away from the flange as it extends outward in the radial direction, a wheel in which Pw is the axial distance from one of the two axial side surfaces of the rim portion that is farther from the flange to the outer end, which is the end that is located radially outward of both ends of the plate thickness centerline, and Wr is the axial length of the rim portion, and Pw / Wr is less than 0.

40.

4. 2. A wheel according to claim 1, a center of the rim portion in the axial direction is located on the opposite side to the flange with respect to a center of the boss portion in the axial direction, a thickness center line of the plate portion has a straight line shape in a cross section including a central axis of the wheel, an outer end portion, which is an end portion located outward in the radial direction, of both ends of the plate thickness centerline is disposed at the same position as the center of the rim portion in the axial direction; an inner end portion, which is the end portion located radially inward of both ends of the plate thickness centerline, is positioned at the same position as the center of the boss portion in the axial direction.

5. 2. A wheel according to claim 1, a center of the rim portion in the axial direction is disposed at the same position as a center of the boss portion in the axial direction, a thickness center line of the plate portion has a straight line shape in a cross section including a central axis of the wheel, an outer end portion, which is an end portion located outward in the radial direction, of both ends of the plate thickness centerline is disposed at the same position as the center of the rim portion in the axial direction; an inner end portion, which is the end portion located radially inward of both ends of the plate thickness centerline, is positioned at the same position as the center of the boss portion in the axial direction.

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