Railway wheel

Abstract

To provide a railway wheel that exhibits superior wear resistance and further enables suppression of a quenched layer.SOLUTION: A railway wheel of the present disclosure comprises: a rim portion; a boss portion; and a plate portion disposed between the rim portion and the boss portion and linked to the rim portion and the boss portion, wherein the railway wheel comprises in mass%: C: 0.65-0.84%, Si: 0.10-1.00%, Mn: 0.05-0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, and Sn: more than 0.50% to 1.50%, with the remainder being Fe and impurities. In the microstructure of the rim portion, the pearlite area ratio is 95.0% or more. A formula (1) is satisfied. Sn / Mn≥2.0 (1).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to railway wheels.

Background Art

[0002] Railway vehicles run on rails that make up the track. Railway vehicles are equipped with a plurality of railway wheels. The railway wheels support the railway vehicle, come into contact with the rails, and move while rotating on the rails. Therefore, the railway wheels are worn due to contact with the rails. Recently, for the purpose of improving the efficiency of railway transportation, an increase in the loading weight on railway vehicles and an increase in the speed of railway vehicles have been promoted. As a result, an improvement in the wear resistance of railway wheels is required.

[0003] An example of a method for manufacturing railway wheels is as follows. A steel slab is hot-worked to form an intermediate product in the shape of a railway wheel. Heat treatment (tread quenching) is performed on the formed intermediate product. In tread quenching, after heating the intermediate product, the rim portion of the intermediate product (especially the tread and flange portions of the rim portion) is rapidly cooled. As a result, fine pearlite with high wear resistance is generated in the matrix structure of the surface layer portion of the tread.

[0004] However, a quenched layer is formed on the upper layer of the fine pearlite in the surface layer portion of the tread after tread quenching. The quenched layer is a hard layer composed of martensite, or a hard layer composed of martensite and bainite. During the use of railway wheels, the quenched layer is easily worn. Therefore, after tread quenching, the quenched layer formed on the outermost surface of the tread is removed by cutting to expose the fine pearlite on the tread. Through the above steps, railway wheels are manufactured.

[0005] When the above-mentioned quenched layer is formed deeply, the cutting amount increases in the cutting process of the quenched layer, and the yield may deteriorate. Furthermore, the cutting time may increase. Therefore, a technique for suppressing the formation of the quenched layer is required.

[0006] A technique for obtaining wear resistance of a railway wheel and suppressing the formation of a hardened layer is proposed in Patent Document 1 (International Publication No. 2021-193808).

[0007] The railway wheel disclosed in Patent Document 1 has a chemical composition in mass % of C: 0.80 to 1.15%, Si: 1.00% or less, Mn: 0.10 to 1.20%, P: 0.050% or less, S: 0.030% or less, Al: 0.005 to 0.190%, N: 0.0200% or less, Nb: 0.005 to 0.050%, Cr: 0 to 0.25%, V: 0 to 0.12%, and the balance being Fe and impurities. In the microstructure of the rim portion, the area ratio of primary cementite is 0.1 to 1.5%, the area ratio of pearlite is 95.0% or more, and the formula (1) (100Nb / (C + 0.5Si + 0.8Mn + 15Al + 40Cr + 10V) ≧ 0.070) is satisfied. In this railway wheel, by satisfying the above chemical composition and further satisfying formula (1), wear resistance is obtained and the hardened layer formed in the tread hardening process is suppressed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The railway wheel disclosed in Patent Document 1 obtains wear resistance and further suppresses the hardened layer. However, wear resistance may be obtained and the hardened layer may be suppressed by means different from those of Patent Document 1.

[0010] An object of the present disclosure is to provide a railway wheel capable of obtaining excellent wear resistance and further suppressing the hardened layer.

Means for Solving the Problems

[0011] The railway wheel according to the present disclosure is a rim portion, a boss portion, and a plate portion disposed between the rim portion and the boss portion and connecting the rim portion and the boss portion, The chemical composition of the railway wheel is, by mass%, C: 0.65 to 0.84%, Si: 0.10 to 1.00%, Mn: 0.05 to 0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, and Sn: more than 0.50% to 1.50%, and the balance consists of Fe and impurities, In the microstructure of the rim portion, the pearlite area ratio is 95.0% or more, satisfies formula (1). Sn / Mn ≧ 2.0 (1) Here, in each element symbol in formula (1), the content in mass% of the corresponding element in the chemical composition is substituted.

[0012] The railway wheel according to the present disclosure is a rim portion, a boss portion, and a plate portion disposed between the rim portion and the boss portion and connecting the rim portion and the boss portion, The chemical composition of the railway wheel is, by mass%, C: 0.65 to 0.84%, Si: 0.10 to 1.00%, Mn: 0.05 to 0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, and Sn: more than 0.50% to 1.50%, and further contains one or more selected from the group consisting of Group 1 to Group 4, and the balance consists of Fe and impurities, In the microstructure of the rim portion, the pearlite area ratio is 95.0% or more, satisfies formula (1). [Group 1] Cu: 0.20% or less, Ni: 0.20% or less, Mo: 0.20% or less, and Cr: 0.50% or less, one or more selected from the group consisting of [Group 2] Al: 0.050% or less, and Nb: 0.030% or less, one or more selected from the group consisting of [Group 3] V: 0.10% or less, and Ti: 0.030% or less, one or more selected from the group consisting of [Group 4] B: 0.0050% or less Sn / Mn ≥ 2.0 (1) Here, for each element symbol in formula (1), the content in mass % of the corresponding element in the chemical composition is substituted. [Advantages of the Invention]

[0013] The railway wheel of the present disclosure can obtain excellent wear resistance and further suppress the quenched layer. [Brief Description of the Drawings]

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0015] The inventors have studied railway wheels that can obtain excellent wear resistance and further suppress the hardened layer. As a result, the inventors have obtained the following findings.

[0016] First, the inventors studied the chemical composition suitable for railway wheels. As a result, the inventors considered that a chemical composition in mass% of C: 0.65 to 0.84%, Si: 0.10 to 1.00%, Mn: 0.05 to 0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, Cu: 0 to 0.20%, Ni: 0 to 0.20%, Mo: 0 to 0.20%, Cr: 0 to 0.50%, Al: 0 to 0.050%, Nb: 0 to 0.030%, V: 0 to 0.10%, Ti: 0 to 0.030%, B: 0 to 0.0050%, and the balance being Fe and impurities is appropriate as a railway wheel.

[0017] The inventors studied means for enhancing wear resistance and suppressing the hardened layer in railway wheels that satisfy the above chemical composition. As a result, the inventors obtained the following findings.

[0018] The element that particularly contributes to the formation of the hardened layer in the above chemical composition is Mn. Therefore, if the Mn content is reduced, the formation of the hardened layer is suppressed.

[0019] By the way, in order to enhance the wear resistance of railway wheels, it is effective to increase the hardness of the pearlite in the microstructure (hereinafter also referred to as pearlite hardness). Pearlite is a lamellar structure in which soft ferrite and hard cementite are alternately arranged in layers. If the hardness of the soft ferrite is increased, the pearlite hardness increases. Mn dissolves in ferrite and increases the hardness of ferrite by solid solution strengthening. As a result, the pearlite hardness is increased. Thereby, the wear resistance of railway wheels is enhanced.

[0020] Therefore, when the Mn content is reduced, although the formation of the hardened layer can be suppressed, the wear resistance of the railway wheel will decrease. Thus, the inventors investigated elements that, like Mn, solid-solution strengthen ferrite and are less likely to contribute to the formation of the hardened layer. As a result, the inventors focused on Sn.

[0021] Sn has a higher solid-solution strengthening ability for ferrite than Mn. Furthermore, Sn is less likely to form a hardened layer compared to Mn. Therefore, the inventors considered adding Sn while reducing the Mn content. As a result, the inventors first found that by further containing more than 0.50% of Sn in the above chemical composition, it is possible to enhance the wear resistance while suppressing the formation of the hardened layer.

[0022] However, even for railway wheels having the above chemical composition, there were still cases where it was not possible to fully achieve both improved wear resistance and suppression of the formation of the hardened layer. Thus, the inventors further investigated. As a result, the inventors obtained the following findings.

[0023] Although Sn is effective for solid-solution strengthening of ferrite, it reduces the hot workability of the steel material. Therefore, it is not preferable to contain an excessive amount of Sn. Therefore, to increase the hardness of ferrite, not only Sn but also a certain amount of Mn content is required.

[0024] Based on the above findings, the inventors considered that it is necessary to appropriately adjust the Sn content and the Mn content in order to achieve both improved wear resistance and suppression of the formation of the hardened layer. Thus, the inventors investigated and examined the relationship between the Sn content and the Mn content, and the wear resistance and the formation of the hardened layer in the above chemical composition. As a result, the inventors found that by further containing more than 0.50% to 1.50% of Sn in the above chemical composition and adjusting so that the Sn content and the Mn content satisfy formula (1), excellent wear resistance can be obtained and the hardened layer can also be sufficiently suppressed. Sn / Mn≧2.0 (1) Here, for each element symbol in formula (1), the content in mass% of the corresponding element in the chemical composition is substituted.

[0025] The railway wheel of the present embodiment completed based on the above technical idea has the following configuration.

[0026] [1] A railway wheel, a rim portion, a boss portion, and a plate portion disposed between the rim portion and the boss portion and connecting the rim portion and the boss portion. The chemical composition of the railway wheel is, by mass%, C: 0.65 to 0.84%, Si: 0.10 to 1.00%, Mn: 0.05 to 0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, and Sn: more than 0.50% to 1.50%, and the balance consists of Fe and impurities. In the microstructure of the rim portion, the pearlite area ratio is 95.0% or more, satisfying formula (1), A railway wheel. Sn / Mn ≧ 2.0 (1) Here, in each element symbol in formula (1), the content in mass% of the corresponding element in the chemical composition is substituted.

[0027] [2] A railway wheel, a rim portion, a boss portion, and a plate portion disposed between the rim portion and the boss portion and connecting the rim portion and the boss portion. The chemical composition of the railway wheel is, by mass%, C: 0.65 to 0.84%, Si: 0.10 to 1.00%, Mn: 0.05 to 0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, and containing Sn: 0.50% to 1.50%, further containing one or more selected from the group consisting of the first group to the fourth group, and the balance consisting of Fe and impurities, in the microstructure of the rim portion, the pearlite area ratio is 95.0% or more, satisfying formula (1), a railway wheel. [First group] Cu: 0.20% or less, Ni: 0.20% or less, Mo: 0.20% or less, and Cr: 0.50% or less, one or more selected from the group consisting of [Second group] Al: 0.050% or less, and Nb: 0.030% or less, one or more selected from the group consisting of [Third group] V: 0.10% or less, and Ti: 0.030% or less, one or more selected from the group consisting of [Fourth group] B: 0.0050% or less Sn / Mn ≥ 2.0 (1) Here, in formula (1), the content in mass% of the corresponding element in the chemical composition is substituted for each element symbol.

[0028] [3] The railway wheel according to [2], wherein the chemical composition contains the first group, a railway wheel.

[0029] [4] The railway wheel according to [2] or [3], wherein the chemical composition contains the second group, a railway wheel.

[0030] [5] The railway wheel according to any one of [2] to [4], wherein the chemical composition contains the third group, a railway wheel.

[0031] [6] The railway wheel according to any one of [2] to [5], wherein the chemical composition contains the fourth group, Railway wheel.

[0032] [7] The railway wheel according to [1], satisfying formula (2A), Railway wheel. 115.4×Sn + 165.4×Mn ≥ 100.0 (2A) Here, for each element symbol in formula (2A), the content in mass% of the corresponding element in the chemical composition is substituted.

[0033] [8] The railway wheel according to any one of [2] to [6], satisfying formula (2), Railway wheel. 115.4×Sn + 886.9×V + 509.2×Mo + 165.4×Mn - 1328040×B ≥ 100.0 (2) Here, for each element symbol in formula (2), the content in mass% of the corresponding element in the chemical composition is substituted. When an element is not contained, "0" is substituted for the corresponding element symbol.

[0034] Hereinafter, the railway wheel of the present embodiment will be described in detail. Note that, unless otherwise specified, "%" regarding an element means mass%.

[0035] [Configuration of railway wheel] Figure 1 is a cross-sectional view including the central axis of the railway wheel according to the present embodiment. Referring to Figure 1, the railway wheel 1 is disc-shaped and includes a boss portion 2, a plate portion 3, and a rim portion 4. The boss portion 2 is cylindrical and is disposed at the central portion of the railway wheel 1 in the radial direction of the railway wheel 1 (the direction perpendicular to the central axis). The boss portion 2 has a through hole 21. The central axis of the through hole 21 coincides with the central axis of the railway wheel 1. A railway axle (not shown) is inserted into the through hole 21. The thickness T2 of the boss portion 2 is thicker than the thickness T3 of the plate portion 3. The rim portion 4 is formed at the edge of the outer periphery of the railway wheel 1. The rim portion 4 includes a tread surface 41 and a flange portion 42. The tread surface 41 is connected to the flange portion 42. When the railway wheel 1 is in use, the tread surface 41 and the flange portion 42 are in contact with the rail surface. The thickness T4 of the rim portion 4 is thicker than the thickness T3 of the plate portion 3. The plate portion 3 is disposed between the boss portion 2 and the rim portion 4 and is connected to the boss portion 2 and the rim portion 4. Specifically, the inner peripheral edge portion of the plate portion 3 is connected to the boss portion 2, and the outer peripheral edge portion of the plate portion 3 is connected to the rim portion 4. The thickness T3 of the plate portion 3 is thinner than the thickness T2 of the boss portion 2 and the thickness T4 of the rim portion 4.

[0036] [Features of the railway wheel of the present embodiment] The railway wheel of the present embodiment satisfies the following Features 1 to 3.

[0037] (Feature 1) The chemical composition is, by mass%, C: 0.65 to 0.84%, Si: 0.10 to 1.00%, Mn: 0.05 to 0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, Sn: more than 0.50% to 1.50%, Cu: 0 to 0.20%, Ni: 0 to 0.20%, Mo: 0 to 0.20%, Cr: 0 to 0.50%, Al: 0 to 0.050%, Nb: 0 to 0.030%, V: 0 to 0.10%, Ti: 0 to 0.030%, B: 0 to 0.0050%, and the balance consists of Fe and impurities. (Feature 2) In the microstructure of the rim portion, the pearlite area ratio is 95.0% or more. (Feature 3) The above chemical composition satisfies formula (1). Sn / Mn ≧ 2.0 (1) Here, the content of each element symbol in formula (1) is substituted with the content in mass % of the corresponding element in the chemical composition.

[0038] [(Characteristic 1) Regarding the chemical composition] The chemical composition of the railway wheel of this embodiment contains the following elements.

[0039] C: 0.65 - 0.84% Carbon (C) increases the hardness of the steel and enhances the wear resistance of the railway wheel 1. When the C content is less than 0.65%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be fully obtained. On the other hand, if the C content exceeds 0.84%, even if the contents of other elements are within the range of this embodiment, the toughness of the railway wheel 1 decreases. Therefore, the C content is 0.65 - 0.84%. The preferable lower limit of the C content is 0.67%, more preferably 0.69%, and even more preferably 0.70%. The preferable upper limit of the C content is 0.82%, more preferably 0.80%, even more preferably 0.77%, and even more preferably 0.73%.

[0040] Si: 0.10 - 1.00% Silicon (Si) solid-solution strengthens ferrite to increase the hardness of the steel. If the Si content is less than 0.10%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be fully obtained. On the other hand, if the Si content exceeds 1.00%, even if the contents of other elements are within the range of this embodiment, the toughness of the railway wheel 1 decreases. If the Si content exceeds 1.00%, furthermore, the hardenability of the steel becomes too high and martensite is likely to be generated. In this case, the thickness of the hardened layer formed on the tread surface during tread hardening increases. As a result, the cutting amount increases and the yield decreases. If the Si content exceeds 1.00%, furthermore, during the use of the railway wheel 1, the rim portion 4 is burned by the frictional heat generated between the brake. In this case, the crack resistance of the steel may decrease. Therefore, the Si content is 0.10 to 1.00%. The preferable lower limit of the Si content is 0.15%, more preferably 0.20%, still more preferably 0.25%. The preferable upper limit of the Si content is 0.90%, more preferably 0.80%, still more preferably 0.70%, still more preferably 0.60%, still more preferably 0.50%.

[0041] Mn: 0.05 to 0.80% Manganese (Mn) solid-solution strengthens ferrite to increase the hardness of the steel. Mn further forms MnS to improve the machinability of the steel. If the Mn content is less than 0.05%, even if the contents of other elements are within the scope of this embodiment, these effects cannot be obtained. On the other hand, if the Mn content exceeds 0.80%, even if the contents of other elements are within the scope of this embodiment, the hardenability of the steel becomes too high. In this case, the thickness of the hardened layer increases, and the yield during the manufacturing process decreases. Further, when the railway wheel 1 is in use, the rim portion 4 is hardened due to the frictional heat generated between the brake. In this case, the crack resistance of the steel may decrease. Therefore, the Mn content is 0.05 to 0.80%. The preferable lower limit of the Mn content is 0.06%, more preferably 0.07%, still more preferably 0.08%. The preferable upper limit of the Mn content is 0.75%, more preferably 0.70%, still more preferably 0.65%, still more preferably 0.60%, still more preferably 0.55%.

[0042] P: 0.050% or less Phosphorus (P) is an impurity inevitably contained. P segregates at grain boundaries and reduces the toughness of the steel. Therefore, the P content is 0.050% or less. The P content is preferably as low as possible. However, excessive reduction of the P content increases the manufacturing cost. Therefore, considering normal industrial production, the preferable lower limit of the P content is over 0%, more preferably 0.001%, still more preferably 0.002%, and even more preferably 0.003%. The preferable upper limit of the P content is 0.040%, more preferably 0.025%, still more preferably 0.020%, and even more preferably 0.015%.

[0043] S: 0.040% or less Sulfur (S) is inevitably contained. S forms MnS and improves the machinability of steel. If even a little S is contained, the above effect can be obtained to a certain extent. However, if the S content exceeds 0.040%, the MnS in the steel coarsens and the toughness of the steel decreases. Therefore, the S content is 0.040% or less. The S content is preferably as low as possible. However, excessive reduction of the S content increases the manufacturing cost. Therefore, considering normal industrial production, the lower limit of the S content is over 0%, more preferably 0.001%, still more preferably 0.002%, and even more preferably 0.005%. The preferable upper limit of the S content is 0.030%, more preferably 0.025%, still more preferably 0.020%, and even more preferably 0.015%.

[0044] N: 0.0200% or less Nitrogen (N) is an impurity inevitably contained. If the N content exceeds 0.0200%, even if the contents of other elements are within the scope of this embodiment, AlN coarsens and the toughness of the steel decreases. Therefore, the N content is 0.0200% or less. The preferable lower limit of the N content is over 0%, more preferably 0.0001%, still more preferably 0.0002%, and even more preferably 0.0003%. The preferable upper limit of the N content is 0.0180%, more preferably 0.0150%, still more preferably 0.0130%, still more preferably 0.0100%, and still more preferably 0.0080%.

[0045] Sn: Over 0.50% to 1.50% Tin (Sn) solid-solution strengthens the ferrite in pearlite to increase the hardness of the steel. Sn further narrows the interlamellar spacing of pearlite. Thereby, the hardness of pearlite increases. If the Sn content is 0.50% or less, these effects cannot be sufficiently obtained. On the other hand, if the Sn content exceeds 1.50%, even if the contents of other elements are within the range of this embodiment, the toughness of the railway wheel 1 decreases. If the Sn content exceeds 1.50%, furthermore, the hot workability of the steel decreases. Therefore, the Sn content is over 0.50% to 1.50%. The preferable lower limit of the Sn content is 0.55%, more preferably 0.60%, still more preferably 0.65%, and still more preferably 0.70%. The preferable upper limit of the Sn content is 1.40%, more preferably 1.30%, still more preferably 1.25%, and still more preferably 1.20%.

[0046] The balance of the chemical composition of the railway wheel according to this embodiment consists of Fe and impurities. Here, the impurities mean those mixed from ores, scraps, or manufacturing environments as raw materials when the railway wheel of this embodiment is industrially manufactured, and are allowed within a range that does not adversely affect the railway wheel of this embodiment.

[0047] [Regarding Optional Elements] The chemical composition of the railway wheel 1 according to this embodiment may further contain one or more selected from the group consisting of Group 1 to Group 4. [Group 1] Cu: 0.20% or less, Ni: 0.20% or less, Mo: 0.20% or less, and, One or more selected from the group consisting of less than 0.50% Cr [Group 2] Al: less than 0.050%, and Nb: less than 0.030%, one or more selected from the group consisting of [Group 3] V: less than 0.10%, and Ti: less than 0.030%, one or more selected from the group consisting of [Group 4] B: less than 0.0050% The elements of Group 1 to Group 4 will be described below.

[0048] [Regarding Group 1 (Cu, Ni, Mo, and Cr)] The chemical composition of the railway wheel 1 of the present embodiment may contain one or more selected from the group consisting of Cu, Ni, Mo, and Cr in place of a part of Fe. All of these elements increase the hardness of the steel.

[0049] Cu: less than 0.20% Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. When contained, Cu increases the hardness of the steel by solid solution strengthening. As a result, the wear resistance of the railway wheel 1 increases. However, if the Cu content exceeds 0.20%, even if the contents of other elements are within the range of the present embodiment, the hot workability of the steel decreases. Therefore, the Cu content is 0 to 0.20%, and when contained, the Cu content is 0.20% or less. The lower limit of the Cu content is preferably more than 0%, more preferably 0.01%, more preferably 0.02%, more preferably 0.05%, and more preferably 0.10%. The upper limit of the Cu content is preferably 0.17%, more preferably 0.15%, more preferably 0.12%, and more preferably 0.10%.

[0050] Ni: less than 0.20% Nickel (Ni) is an optional element and may not be contained. That is, the Ni content may be 0%. When contained, Ni increases the hardness and toughness of the steel. However, if the Ni content exceeds 0.20%, even if the contents of other elements are within the scope of this embodiment, the hardenability becomes excessively high and the thickness of the hardened layer after tread hardening increases excessively. Therefore, the Ni content is 0 to 0.20%, and when contained, the Ni content is 0.20% or less. The lower limit of the Ni content is preferably more than 0%, more preferably 0.01%, still more preferably 0.02%, and still more preferably 0.05%. The upper limit of the Ni content is preferably 0.17%, more preferably 0.15%, still more preferably 0.12%, and still more preferably 0.10%.

[0051] Mo: 0.20% or less Molybdenum (Mo) is an optional element and may not be contained. That is, the Mo content may be 0%. When contained, Mo increases the hardness of the steel. As a result, the wear resistance of the railway wheel 1 is enhanced. However, if the Mo content exceeds 0.20%, even if the contents of other elements are within the scope of this embodiment, the hardenability becomes excessively high and the thickness of the hardened layer after tread hardening increases excessively. Therefore, the Mo content is 0 to 0.20%, and when contained, the Mo content is 0.20% or less. The lower limit of the Mo content is preferably more than 0%, more preferably 0.01%, still more preferably 0.02%, and still more preferably 0.05%. The upper limit of the Mo content is preferably 0.18%, more preferably 0.15%, still more preferably 0.12%, still more preferably 0.10%, and still more preferably 0.07%.

[0052] Cr: 0.50% or less Chromium (Cr) is an optional element and may not be contained. That is, the Cr content may be 0%. When contained, Cr narrows the interlamellar spacing of pearlite. As a result, the hardness of pearlite increases significantly. However, if the Cr content exceeds 0.50%, even if the contents of other elements are within the range of this embodiment, the hardenability becomes excessively high and the thickness of the hardened layer after tread hardening increases excessively. Therefore, the Cr content is 0 to 0.50%, and when contained, the Cr content is 0.50% or less. The lower limit of the Cr content is preferably more than 0%, more preferably 0.01%, still more preferably 0.02%, still more preferably 0.03%, still more preferably 0.05%. The upper limit of the Cr content is preferably 0.45%, more preferably 0.40%, still more preferably 0.35%, still more preferably 0.30%, still more preferably 0.25%, still more preferably 0.20%.

[0053] [Regarding the second group (Al and Nb)] The chemical composition of the railway wheel 1 of this embodiment may contain one or more selected from the group consisting of Al and Nb in place of a part of Fe. All of these elements form carbides or nitrides and suppress the coarsening of crystal grains due to the pinning effect.

[0054] Al: 0.050% or less Aluminum (Al) is an optional element and may not be contained. That is, the Al content may be 0%. When contained, Al combines with N to form AlN and refines the crystal grains. By refining the crystal grains, the toughness of the steel increases. However, if the Al content exceeds 0.050%, even if the contents of other elements are within the range of this embodiment, non-metallic inclusions increase and the toughness of the steel decreases. Therefore, the Al content is 0 to 0.050%, and when contained, the Al content is 0.050% or less. The lower limit of the Al content is preferably more than 0%, more preferably 0.001%, still more preferably 0.005%, still more preferably 0.010%, still more preferably 0.020%, and still more preferably 0.030%. The upper limit of the Al content is preferably 0.045%, more preferably 0.040%, and still more preferably 0.035%. Note that the Al content referred to in this specification means the acid-soluble Al (sol.Al) content.

[0055] Nb: 0.030% or less Niobium (Nb) is an optional element and may not be contained. That is, the Nb content may be 0%. When contained, Nb combines with C during heating for surface hardening in the manufacturing process of railway wheels to form fine NbC. The fine NbC functions as pinning particles to suppress the coarsening of austenite during heating. Therefore, the prior austenite grain size is maintained fine, and the hardenability of the steel is suppressed. As a result, the formation of the hardened layer during the manufacturing process of the railway wheel 1 is suppressed. Nb also enhances the toughness of the steel material by suppressing the coarsening of the prior austenite grain size. On the other hand, if the Nb content exceeds 0.030%, even if the contents of other elements are within the range of this embodiment, the NbC coarsens and the toughness of the steel material rather decreases. Therefore, the Nb content is 0 to 0.030%, and when contained, the Nb content is 0.030% or less. The lower limit of the Nb content is preferably more than 0%, more preferably 0.010%, still more preferably 0.012%, and still more preferably 0.015%. The upper limit of the Nb content is preferably 0.025%, more preferably 0.020%, and still more preferably 0.017%.

[0056] [Regarding Group 3 (V and Ti)] The chemical composition of the railway wheel 1 of this embodiment may contain one or more selected from the group consisting of V and Ti in place of a part of Fe. All of these elements form either carbide, nitride, or carbonitride to precipitate-strengthen the steel.

[0057] V: 0.10% or less Vanadium (V) is an optional element and may not be contained. That is, the V content may be 0%. When contained, V forms either carbide, nitride, or carbonitride to precipitate-strengthen the steel (specifically, ferrite in the steel). As a result, the hardness of the railway wheel 1 increases and the wear resistance improves. However, if the V content exceeds 0.10%, the hardenability increases and the thickness of the hardened layer after tread hardening increases excessively. Therefore, the V content is 0 to 0.10%, and when contained, the V content is 0.10% or less. The lower limit of the V content is preferably more than 0%, more preferably 0.01%, still more preferably 0.02%, and still more preferably 0.03%. The upper limit of the V content is preferably 0.09%, more preferably 0.08%, and still more preferably 0.07%.

[0058] Ti: 0.030% or less Titanium (Ti) is an optional element and may not be contained. That is, the Ti content may be 0%. When contained, Ti forms either carbide, nitride, or carbonitride to precipitate-strengthen the steel (specifically, ferrite in the steel). As a result, the hardness of the railway wheel 1 increases and the wear resistance improves. However, if the Ti content exceeds 0.030%, the hardenability increases and the thickness of the hardened layer after tread hardening increases excessively. Therefore, the Ti content is 0 to 0.030%, and when contained, the Ti content is 0.030% or less. The lower limit of the Ti content is preferably more than 0%, more preferably 0.001%, still more preferably 0.002%, and still more preferably 0.003%. The upper limit of the Ti content is preferably 0.020%, more preferably 0.010%, and even more preferably 0.005%.

[0059] [Regarding Group 4 (B)] The chemical composition of the railway wheel 1 of the present embodiment may contain B in place of a part of Fe.

[0060] B: 0.0050% or less Boron (B) is an optional element and may not be contained. That is, the B content may be 0%. When contained, B reduces the cooling rate dependence of the pearlite transformation temperature and makes the hardness distribution of the wheel tread uniform. However, if the B content exceeds 0.0050%, the hardenability increases and the thickness of the hardened layer after tread hardening excessively increases. Therefore, the B content is 0 to 0.0050%, and when contained, the B content is 0.0050% or less. The lower limit of the B content is preferably more than 0%, more preferably 0.0001%, even more preferably 0.0003%, and even more preferably 0.0005%. The upper limit of the B content is preferably 0.0040%, more preferably 0.0030%, and even more preferably 0.0025%.

[0061] [(Feature 2) Regarding the microstructure of the rim portion of the railway wheel] The railway wheel of the present embodiment further satisfies the following Feature 2. (Feature 2) In the microstructure of the rim portion, the pearlite area ratio is 95.0% or more.

[0062] In the microstructure of the rim portion 4 of the railway wheel 1 of the present embodiment, the area ratio of pearlite is 95.0% or more. Among the microstructures of the rim portion 4, the phases other than pearlite are, for example, martensite, bainite, and proeutectoid ferrite, etc.

[0063] [Method for measuring the pearlite area ratio] The pearlite area ratio in the microstructure of the rim portion 4 is determined by the following method. A sample is taken from the central position in the thickness direction of the rim portion 4 (the central position of the thickness T4 in FIG. 1). The observation surface of each sample is polished to a mirror finish by mechanical polishing. Then, etching is performed on the observation surface using 3% nitric acid alcohol (nital etching solution). For an arbitrary one field (500 μm × 500 μm) in the observation surface of the etched sample, a photographic image is generated using an optical microscope with a magnification of 200 times. In the observation surface, each phase (pearlite, primary ferrite, martensite, and bainite) has a different contrast. Therefore, based on the contrast, the pearlite in the microstructure can be discriminated. Based on the contrast, the pearlite is specified. The area ratio (%) of the pearlite is determined based on the total area of the specified pearlite and the area of the observation field.

[0064] [(Feature 3) Regarding Equation (1)] The railway wheel of the present embodiment further satisfies Equation (1). Sn / Mn ≧ 2.0 (1) Here, for each element symbol in Equation (1), the content in mass % of the corresponding element in the chemical composition is substituted.

[0065] Define Fn1 as follows. Fn1 = Sn / Mn

[0066] Fn1 corresponds to the left side of Equation (1). Fn1 is an index for enhancing the wear resistance of the railway wheel that satisfies Feature 1 and Feature 2 and further suppressing the quenched layer. Among the elements in the above chemical composition, Sn increases the pearlite hardness of the railway wheel. On the other hand, Mn has a lower effect of increasing the pearlite hardness of the railway wheel compared to Sn. Further, Mn increases the hardenability, and the quenched layer of the railway wheel may become thick. In the present disclosure, the hardness of the microstructure with a pearlite area ratio of 95.0% or more is defined as the pearlite hardness.

[0067] If Fn1 is less than 2.0, the Sn content is too low relative to the Mn content. In this case, the pearlite hardness may be excessively reduced, or the hardened layer depth may be excessively thick, or both may occur.

[0068] If Fn1 is 2.0 or more, the Sn content is sufficiently high relative to the Mn content. Therefore, on the premise of satisfying Feature 1 and Feature 2, excellent wear resistance of the railway wheel can be obtained, and furthermore, the hardened layer can be suppressed.

[0069] The preferable lower limit of Fn1 is 2.5, more preferably 3.0, still more preferably 3.5, and even more preferably 4.0. The upper limit of Fn1 is not particularly limited, but for example, it is 14.0.

[0070] [Regarding the effects of the railway wheel of the present embodiment] The railway wheel of the present embodiment satisfies Features 1 to 3. Therefore, in the railway wheel of the present embodiment, excellent wear resistance can be obtained, and furthermore, the hardened layer can be suppressed.

[0071] [Regarding the uses of the railway wheel of the present embodiment] The railway wheel of the present embodiment is suitable for railway vehicle applications.

[0072] [Preferred forms of the railway wheel of the present embodiment] Preferably, the railway wheel of the present embodiment satisfies Features 1 to 3, and further satisfies the following Feature 4.

[0073] (Feature 4) Preferably, the railway wheel of the present embodiment further satisfies Formula (2). 115.4×Sn + 886.9×V + 509.2×Mo + 165.4×Mn - 1328040×B ≧ 100.0 (2) Here, for each element symbol in Formula (2), the content in mass % of the corresponding element in the chemical composition is substituted. When an element is not contained, "0" is substituted for the corresponding element symbol. In addition, when the chemical composition of the railway wheel does not contain V, Mo, and B which are optional elements (that is, when V, Mo, and B are 0%), Equation (2) becomes the following Equation (2A). 115.4×Sn + 165.4×Mn ≥ 100.0 (2A)

[0074] Define Fn2 as follows. Fn2 = 115.4×Sn + 886.9×V + 509.2×Mo + 165.4×Mn - 1328040×B In addition, when the chemical composition of the railway wheel does not contain V, Mo, and B which are optional elements (that is, when V, Mo, and B are 0%), define Fn2 as follows. Fn2 = 115.4×Sn + 165.4×Mn

[0075] Fn2 corresponds to the left side of Equation (2) or Equation (2A). Fn2 is an index for enhancing the rolling contact fatigue damage resistance characteristics of the railway wheel that satisfies Features 1 to 3.

[0076] Here, as disclosed in Patent Document 2 (Japanese Patent No. 7239082), there is a positive correlation between the rolling contact fatigue damage resistance characteristics and the 0.7% proof stress obtained from the repeated stress-strain curve (hereinafter also referred to as the repeated S-S curve). That is, if the 0.7% proof stress in the repeated S-S curve of the railway wheel increases, the rolling contact fatigue damage resistance characteristics of the railway wheel increase. This will be described below.

[0077] The railway wheel is loaded with repeated stress due to rolling contact. At this time, if the tread surface of the railway wheel is work-hardened, the strength of the tread surface increases. Thereby, the propagation of cracks is suppressed, and the rolling contact fatigue damage resistance characteristics of the railway wheel increase.

[0078] As a model for expressing the stress-strain response in repeated plastic deformation, the equation of the non-linear kinematic hardening rule shown in Equation (I) is known. σ eq = σ 0 + C / γ{1 - exp(-γε peq )} (I) Here, σ in Equation (I) eqis the equivalent stress (MPa), σ 0 is the elastic limit (MPa), C is the initial kinematic hardening coefficient (GPa), γ is the kinematic hardening coefficient reduction rate, ε peq is the equivalent plastic strain.

[0079] The equivalent stress σ in Equation (I) eq corresponds to the strength after work hardening. If the strength after work hardening is high, crack propagation can be suppressed. That is, if the equivalent stress σ eq can be increased, crack propagation can be suppressed.

[0080] Here, the fatigue crack propagation rate da / dN (mm / cycle), which is an index of crack propagation, is expressed by Equation (II) based on the Paris law. da / dN = C(ΔK) m = C(ΔK θ、max ) m (II) Here, ΔK in Equation (II) θ、max is the range of stress intensity factor (MPa√m). Also, C and m are constants obtained from experiments (C = 3.93×10 -13 , m = 3.68).

[0081] When examining the correlation between the equivalent stress σ defined by Equation (I) eq and the fatigue crack propagation rate da / dN defined by Equation (II), when ε peq = 0.007 is substituted into Equation (I), the equivalent stress σ eq (i.e., 0.7% proof stress) and the fatigue crack propagation rate da / dN defined by Equation (II) show a strong negative correlation as shown in Figure 4. Specifically, referring to Figure 4, as the 0.7% proof stress in the repeated S - S curve increases, the crack propagation rate da / dN exponentially decreases. If the crack propagation rate da / dN is low, it means that the resistance to rolling fatigue damage characteristics is high. That is, the higher the 0.7% proof stress in the repeated S - S curve, the higher the resistance to rolling fatigue damage characteristics.

[0082] Among the elements in the above chemical composition, Sn, V, Mo, and Mn increase the 0.7% yield strength in the repeated S-S curve of the railway wheel. On the other hand, B decreases the 0.7% yield strength in the repeated S-S curve of the railway wheel. If Fn2 is less than 100.0, the contents of Sn, V, Mo, and Mn are too low relative to the B content. In this case, even if the railway wheel satisfies Features 1 to 3, sufficient resistance to rolling contact fatigue damage characteristics cannot be obtained. Therefore, Fn2 is 100.0 or more.

[0083] The preferable lower limit of Fn2 is 110.0, more preferably 120.0, and even more preferably 140.0. The upper limit of Fn2 is not particularly limited, but for example, it is 400.0.

[0084] [Manufacturing Method of Railway Wheel of the Present Embodiment] Hereinafter, the manufacturing method of the railway wheel of the present embodiment will be described. The manufacturing method of the railway wheel described hereinafter is an example of the manufacturing method of the railway wheel of the present embodiment. Therefore, the railway wheel having the above-described configuration may be manufactured by other manufacturing methods other than the manufacturing method described hereinafter. However, the manufacturing method described hereinafter is a preferable example of the manufacturing method of the railway wheel of the present embodiment.

[0085] An example of the manufacturing method of the present embodiment includes the following steps. (Step 1) Stock Preparation Step (Step 2) Forming Step (Step 3) Heat Treatment Step (Step 4) Machining Step Hereinafter, each step will be described.

[0086] [(Step 1) Stock Preparation Step] In the stock preparation step, molten steel having the above-described chemical composition is produced using an electric furnace or a converter, etc. The produced molten steel is cast into a casting material (cast slab or ingot). A cast slab may be produced by continuous casting, or an ingot may be produced by casting into a mold.

[0087] The ingot or slab is hot-worked to produce a steel material for railway wheels (hereinafter also referred to as the steel material) of a desired size. The hot working is, for example, hot forging, hot rolling, etc. When producing the steel material by hot rolling, for example, the steel material is produced by the following method. In hot rolling, for example, a slabbing mill is used. The material is subjected to slabbing rolling by the slabbing mill to produce the steel material. When a continuous rolling mill is installed downstream of the slabbing mill, hot rolling may be further performed on the steel material after slabbing rolling using the continuous rolling mill to produce a smaller-sized steel material. In the continuous rolling mill, a horizontal stand having a pair of horizontal rolls and a vertical stand 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, but is, for example, 1100 to 1350 °C. Through the above manufacturing process, the steel material for railway wheels is produced.

[0088] Note that the steel material for railway wheels may be a casting (ingot or slab). That is, the above hot working may be omitted. Through the above process, the steel material for railway wheels, which is the material of the railway wheel, is produced. The steel material for railway wheels is, for example, a cylindrical material.

[0089] [(Process 2) Forming Process] In the forming process, an intermediate product in the shape of a wheel is formed by hot working using the prepared steel material for railway wheels. Since the intermediate product has the shape of a wheel, it includes a boss portion, a plate portion, and a rim portion including a tread surface and a flange portion. The hot working is, for example, hot forging, hot rolling, etc. The cooling method of the intermediate product after hot working is not particularly limited. Air cooling or water cooling may be used.

[0090] [(Process 3) Heat Treatment Process] In the heat treatment process, surface hardening of the tread is performed on the formed intermediate product in the shape of a wheel. Specifically, the intermediate product after the forming process (hot forging or hot rolling) is heated to a temperature above the A c3 transformation point or the A cmReheat above the transformation point and hold for soaking for 30 to 150 minutes (reheat treatment). After heating, the tread and flange portions of the intermediate product are quenched rapidly (tread quenching). For example, the tread and flange portions are cooled by a cooling medium. The cooling medium is, for example, air, mist, spray, salt bath, etc., and is not particularly limited as long as it has a cooling rate at which a desired structure can be obtained. Further, the temperature and holding time of the cooling medium are not particularly limited. Thereby, in the tread and flange portions of the rim portion, a hardened layer (martensite) on the outermost surface and a hard pearlite structure below it are formed.

[0091] For the intermediate product after tread quenching, tempering is carried out as necessary. The tempering temperature is, for example, 400 to 600 °C.

[0092] [(Process 4) Machining process] As described above, fine pearlite is formed on the surface layer of the tread of the intermediate product after the heat treatment process, and a hardened layer composed of martensite is formed on the upper layer. In the use of railway wheels, the wear resistance of martensite is low. Therefore, the hardened layer is removed by well-known machining.

[0093] Through the above processes, the railway wheel of the present embodiment is manufactured.

Example

[0094] The effects of the railway wheel of the present embodiment will be further specifically described by examples. The conditions in the following examples are one example of the conditions adopted to confirm the feasibility and effects of the railway wheel of the present embodiment. Therefore, the railway wheel of the present embodiment is not limited to this one example of conditions.

[0095] Molten steel having the chemical compositions shown in Table 1A and Table 1B was produced. In the following description, Table 1A and Table 1B are also collectively referred to as "Table 1". "-" in Table 1 indicates that the corresponding element content is below the impurity level.

[0096]

Table 1A

[0097] [Table 1B]

[0098] The material preparation process of the manufacturing process of railway wheels was simulated, and ingots of each test number were manufactured by the ingot casting method using the above molten steel. Next, the forming process of the manufacturing process of railway wheels was simulated, and the ingots were hot forged to manufacture round bar T with a diameter of 35 mm.

[0099] [Evaluation Test] For round bar T of each test number, the following evaluation tests were carried out. (Test 1) Measurement test of hardening layer depth (Test 2) Measurement test of pearlite hardness (Test 3) Measurement test of 0.7% yield strength in repeated S-S curve Hereinafter, Tests 1 to 3 will be described.

[0100] [(Test 1) Measurement test of hardening layer depth] The hardening layer depth of round bar T of each test number was evaluated by the following method. From round bar T with a diameter of 35 mm of each test number, Jominy test pieces with a diameter of 25 mm and a length of 100 mm were prepared. The central axis of the Jominy test piece was coincident with the central axis of round bar T. Using the Jominy test piece, a Jominy one-end hardening test conforming to JIS G 0561:2020 was carried out. Specifically, the Jominy test piece was held in a furnace at 950 °C, which is a temperature at or above the transformation point or A c3 transformation point or A cm transformation point for 30 minutes to make the structure of the Jominy test piece a single austenite phase. Then, one-end hardening (water cooling) was carried out. Specifically, water was sprayed on one end of the Jominy test piece for cooling.

[0101] After water cooling, in the Jominy test piece on which water cooling was performed, corresponding positions separated from each other by 180° were mechanically polished to a thickness of 0.4 mm over the entire length of the Jominy test piece and removed, and the hardness of both side surfaces was measured. Specifically, from one end (water-cooled end) of both side surfaces of the Jominy test piece, at regular intervals in the axial direction, Rockwell hardness (HRC) tests were performed using a C scale conforming to JIS Z 2245:2021. The measurement interval of HRC was set to a pitch of 1.5 mm up to less than 3.0 mm from the water-cooled end, a pitch of 2.0 mm at positions from 3.0 mm or more to less than 15.0 mm from the water-cooled end, and a pitch of 5.0 mm at positions 15.0 mm or more from the water-cooled end. A Jominy curve was obtained by averaging the Rockwell hardness measured on both side surfaces of the Jominy test piece. From the obtained Jominy curve, the quenched layer depth was determined by the following method.

[0102] Figures 2 and 3 are graphs schematically showing the Jominy curves obtained by the above-described Jominy one-end quenching test. Referring to Figure 2, in the Jominy curve, the Rockwell hardness rapidly decreases in the depth direction from the water-cooled end. Thereafter, the Rockwell hardness gradually increases and then gradually decreases with the distance A from the water-cooled end and the Rockwell hardness B as the apexes. Here, there may be a case like Figure 3 where there is no gradual increase in the Rockwell hardness after the rapid decrease in the Rockwell hardness as shown in Figure 2. The inflection point where the Rockwell hardness rapidly decreases in the depth direction from the water-cooled end and the Rockwell hardness gradually decreases is defined as the distance A from the water-cooled end and the Rockwell hardness B. The region from the water-cooled end to the distance A is defined as the "quenched layer", and the region in the depth direction from the distance A is defined as the "base material". Here, the distance A from the water-cooled end is defined as the "quenched layer depth (mm)". Based on the Jominy curves of each test number, the distance A from the water-cooled end was specified to determine the quenched layer depth (mm). The obtained quenched layer depths are shown in the "Quenched layer depth (mm)" column in Table 2.

[0103]

Table 2

[0104] [(Test 2) Measurement Test of Pearlite Hardness] In accordance with the above [(Test 1) Measurement Test of Quenched Layer Depth], the Jominy end quenching test of round bar T for each test number was carried out. Referring to FIGS. 2 and 3, Rockwell hardness B was defined as the "pearlite hardness (HRC)" in the base material. Rockwell hardness B was specified from the Jominy curve of each test number to obtain the pearlite hardness (HRC). The obtained pearlite hardness is shown in the "pearlite hardness (HRC)" column in Table 2.

[0105] [(Test 3) Measurement Test of 0.7% Endurance in Repeated S-S Curve] The 0.7% endurance in the repeated S-S curve of round bar T for each test number was evaluated by the following method. Round bar S with a diameter of 17 mm and a length of 140 mm was machined from round bar T for each test number by cutting.

[0106] For this round bar S, quenching simulating the tread quenching in the manufacturing process of railway wheels was carried out. Specifically, for round bar S of each test number, soaking was performed at a heat treatment temperature of 900 °C for 30 minutes. After soaking, in order to form a pearlite structure, round bar S was taken out of the furnace and immersed in a salt bath at 550 °C. The immersion time in the salt bath was 3 minutes. Then, round bar S was taken out of the salt bath and air-cooled to room temperature (25 °C).

[0107] From round bar S, cylindrical test piece 100 shown in FIG. 5 was sampled so that the longitudinal direction of the test piece for the repeated stress-strain test (hereinafter also referred to as the repeated S-S test) was the longitudinal direction of round bar S. Referring to FIG. 5, the total length 106 of test piece 100 was 130 mm, the length of parallel portion 101 at the longitudinal center of test piece 100 was 20 mm, and the length of gripping portion 102 located at both ends of parallel portion 101 was 41 mm. The diameter 103 of parallel portion 101 was 6 mm, and the diameter 104 of gripping portion 102 was 15 mm. The radius of curvature 105 between parallel portion 101 and gripping portion 102 was 20 mm. Furthermore, the surface roughness of parallel portion 101 was 0.4 μm, and the surface roughness of gripping portion 102 was 1.6 μm.

[0108] The repeated S-S test was carried out using the test piece 100. The repeated S-S test was performed using a hydraulic servo fatigue testing machine (manufactured by Shimadzu Corporation). The repeated S-S test was conducted by the Incremental Step method with a maximum amplitude of strain of 1.2%. The strain increment per waveform was 2.0×10 -1 %, the strain waveform was a triangular wave, and after applying a repeated load of 20 blocks, the test was terminated. Here, the strain was measured with an extensometer attached to the parallel part of the test piece. The gauge length of the extensometer was 12.5 mm, the strain ratio was -1, and the strain rate was 4×10 -2 % / second. The strain, load, and stroke in the repeated S-S test were measured at a sampling frequency of 10 Hz.

[0109] Next, the nominal stress-nominal strain hysteresis loop obtained from the above repeated S-S test was obtained. The absolute value of the nominal stress at the absolute value of the nominal strain at the apex of the hysteresis loop obtained from the 20th block of repeated load was averaged, and the repeated S-S curve was obtained by plotting the averaged nominal stress and nominal strain. The stress value at which the plastic strain in the repeated S-S curve becomes 0.7% was defined as the 0.7% proof stress (MPa). The obtained 0.7% proof stress is shown in the column of "0.7% proof stress (MPa)" in Table 2.

[0110] [Test Results] Referring to Table 1 and Table 2, the round bar T manufactured by simulating the manufacturing process of the railway wheels of Test Nos. 1 to 23 satisfied Features 1 to 3. Therefore, in the round bar T of these test numbers, the pearlite hardness was 40.0 HRC or more and the quenched layer depth was 15.0 mm or less, so excellent wear resistance was obtained and the quenched layer could be further suppressed.

[0111] In particular, the round bar T manufactured by simulating the manufacturing process of the railway wheels of Test Nos. 1 to 13, 15 to 18, 20, 22, and 23 satisfied not only Features 1 to 3 but also Feature 4. Therefore, compared with Test Nos. 14, 19, and 21 that did not satisfy Feature 4, the 0.7% proof stress in the repeated S-S curve was 650 MPa or more, and excellent rolling fatigue damage resistance characteristics were obtained.

[0112] On the other hand, in Test No. 24, the Sn content was too low. As a result, the pearlite hardness was less than 40.0 HRC. Consequently, sufficient wear resistance could not be obtained.

[0113] In Test No. 25, Fn1 was too low. As a result, the pearlite hardness was less than 40.0 HRC. Consequently, sufficient wear resistance could not be obtained.

[0114] In Test Nos. 26 and 27, Fn1 was too low. As a result, the case depth was more than 15.0 mm. Consequently, the case layer could not be sufficiently suppressed.

[0115] In Test No. 28, Fn1 was too low. As a result, the pearlite hardness was less than 40.0 HRC and, furthermore, the case depth was more than 15.0 mm. Consequently, sufficient wear resistance could not be obtained and, furthermore, the case layer could not be sufficiently suppressed.

[0116] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for carrying out the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and the above-described embodiments can be appropriately modified and implemented without departing from the spirit thereof.

Claims

1. A railway wheel, comprising: a rim portion; a boss portion; a plate portion disposed between the rim portion and the boss portion and connecting the rim portion and the boss portion; The chemical composition of the railway wheel is, by mass percentage: C: 0.65 to 0.84%, Si: 0.10 to 1.00%, Mn: 0.05 to 0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, and Sn: more than 0.50% to 1.50%, and the balance consists of Fe and impurities; In the microstructure of the rim portion, the pearlite area ratio is 95.0% or more, satisfying formula (1); A railway wheel. Sn / Mn ≥ 2.0 (1) Here, in formula (1), the content of the corresponding element in the chemical composition is substituted for each element symbol.

2. A railway wheel, comprising: a rim portion; a boss portion; a plate portion disposed between the rim portion and the boss portion and connecting the rim portion and the boss portion; The chemical composition of the railway wheel is, by mass percentage: C: 0.65 to 0.84%, Si: 0.10 to 1.00%, Mn: 0.05 to 0.80%, P: 0.050% or less, S: 0.040% or less, N: 0.0200% or less, and Sn: more than 0.50% to 1.50%, and further contains one or more selected from the group consisting of Group 1 to Group 4, and the balance consists of Fe and impurities; In the microstructure of the rim portion, the pearlite area ratio is 95.0% or more, satisfying formula (1); A railway wheel. [Group 1] Cu: 0.20% or less, Ni: 0.20% or less, Mo: 0.20% or less, and Cr: 0.50% or less, one or more selected from the group consisting of [Group 2] Al: 0.050% or less, and Nb: 0.030% or less, one or more selected from the group consisting of [Group 3] V: 0.10% or less, and Ti: 0.030% or less, one or more selected from the group consisting of [Group 4] B: 0.0050% or less Sn / Mn ≥ 2.0 (1) Here, in formula (1), the content of the corresponding element in the chemical composition is substituted for each element symbol.

3. The railway wheel according to claim 2, wherein the chemical composition contains the Group 1. A railway wheel.

4. The railway wheel according to claim 2, wherein the chemical composition contains the Group 2. A railway wheel.

5. The railway wheel according to claim 2, wherein the chemical composition contains the Group 3. A railway wheel.

6. The railway wheel according to claim 2, wherein The chemical composition contains the fourth group, Railway wheel.

7. The railway wheel according to claim 1, satisfying formula (2A), Railway wheel. 115.4 × Sn + 165.4 × Mn ≥ 100.0 (2A) Here, for each element symbol in formula (2A), the content in mass % of the corresponding element in the chemical composition is substituted.

8. The railway wheel according to any one of claims 2 to 6, satisfying formula (2), Railway wheel. 115.4 × Sn + 886.9 × V + 509.2 × Mo + 165.4 × Mn - 1328040 × B ≥ 100.0 (2) Here, for each element symbol in formula (2), the content in mass % of the corresponding element in the chemical composition is substituted. When an element is not contained, "0" is substituted for the corresponding element symbol.

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