Rotor for eddy current reduction gear

Abstract

To provide a rotor for an eddy current type reduction gear, excellent in high-temperature strength, and capable of reducing a gap between a cylindrical part of the rotor and a pole piece in constituting the eddy current type reduction gear.SOLUTION: A rotor for an eddy current type reduction gear includes a cylindrical part. The chemical composition of the cylindrical part comprises by mass% C: 0.05-0.15%, Si: 0.10-0.40%, Mn: 0.50-1.00%, P: 0.030% or less, S: 0.030% or less, Cr: over 0.10%-0.40%, Mo: 0.20-1.00%, Nb: 0.020-0.060%, V: 0.040-0.080%, sol.Al: 0.030-0.100%, B: 0.0005-0.0050%, N: 0.003-0.010%, Cu: 0-0.20%, Ni: 0-0.20%, and the balance: Fe and impurities.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a rotor, and more particularly to a rotor for an eddy current type retarder used in an eddy current type retarder. [Background technology]

[0002] Large vehicles such as buses and trucks are equipped with braking devices such as foot brakes and exhaust brakes. Recent large vehicles have also been equipped with eddy current reduction devices, which are also called retarders. For example, when traveling down a long, steep slope and it is difficult to slow the large vehicle down even with the engine brake and exhaust brake, the eddy current reduction device is activated. This further increases the braking force and effectively slows the large vehicle down.

[0003] There are two types of eddy current reduction gears: one that uses electromagnets and one that uses permanent magnets. An eddy current reduction gear using permanent magnets includes a rotor and a stator housed in the rotor. The rotor includes a cylindrical portion (drum), an annular wheel portion for fixing the rotor to the propeller shaft, and multiple arms connecting the cylindrical portion and the wheel portion. The stator includes a cylindrical body, multiple permanent magnets of two types with different polarities, and multiple pole pieces. The multiple permanent magnets with different polarities are arranged alternately in the circumferential direction on the outer peripheral surface of the cylindrical portion. The pole pieces are arranged with a gap between the inner peripheral surface of the cylindrical portion of the rotor and the permanent magnets. The cylindrical body of the stator, to which the multiple permanent magnets are attached, can rotate around its axis independently of the multiple pole pieces.

[0004] During braking, that is, when the eddy current reduction gear device is operating, the magnetic flux of the permanent magnets in the stator reaches the rotor through the pole pieces, forming a magnetic circuit between the permanent magnets and the cylindrical portion of the rotor. At this time, eddy currents are generated in the cylindrical portion of the rotor. The generation of eddy currents generates a Lorentz force. This Lorentz force becomes a braking torque and applies a braking force to the large vehicle. On the other hand, when not braking, that is, when the operation of the eddy current reduction gear device is stopped, the relative position of the permanent magnets with respect to the pole pieces is shifted so that the magnetic flux of the permanent magnets does not reach the rotor. In this case, a magnetic circuit is not formed between the permanent magnets and the cylindrical portion of the rotor. As a result, no eddy currents are generated in the cylindrical portion of the rotor, and no braking force is generated. Through the above operations, the eddy current reduction gear device performs braking and non-braking operations.

[0005] The braking force depends on the amount of eddy current generated in the cylindrical portion of the rotor during braking. Therefore, it is preferable that the amount of eddy current generated in the cylindrical portion of the rotor during braking is large. To increase the amount of eddy current generated during braking, it is preferable that the electrical resistance of the cylindrical portion of the rotor is low.

[0006] Furthermore, during braking, the rotor is heated by Joule heat generated along with the eddy currents, and the rotor temperature rises to approximately 650 to 700°C. On the other hand, when the eddy current reduction gear device is not braking, the rotor is rapidly cooled (air-cooled) by multiple cooling fins formed on the outer circumferential surface of the cylindrical portion. In other words, the rotor is subjected to thermal cycles due to repeated braking and non-braking. For this reason, the rotor of an eddy current reduction gear device must have high high-temperature strength.

[0007] Techniques for achieving high high-temperature strength while reducing electrical resistance in rotors for eddy current reduction gears are disclosed in Japanese Patent Laid-Open No. 8-49041 (Patent Document 1) and Japanese Patent Laid-Open No. 2020-180324 (Patent Document 2).

[0008] The rotor material for an eddy current reduction gear described in Patent Document 1 contains, by weight, 0.05-0.15% C, 0.10-0.40% Si, 0.5-1.0% Mn, 0.05% or less P, 0.50% or less Ni, 0.2-1.0% Mo, 0.01-0.03% Nb, 0.03-0.07% V, 0.0005-0.003% B, 0.02-0.09% Sol.Al, and 0.01% or less N, with the balance being essentially Fe. This document describes how the electrical resistance of the rotor material is reduced by reducing the contents of P, Ni, and Mn, which are elements that increase electrical resistance. Furthermore, the inclusion of B increases the high-temperature strength of the rotor material.

[0009] The rotor for an eddy current type reduction gear disclosed in Patent Document 2 has a cylindrical portion, and the chemical composition of the cylindrical portion is, in mass %, C: 0.05 to 0.15%, Si: 0.10 to 0.40%, Mn: 0.50 to 1.00%, P: 0.030% or less, S: 0.030% or less, Mo: 0.20 to 1.00%, Nb: 0.020 to 0.060%, V: 0.040 to 0.080%, and so l. The alloy consists of Al: 0.030 to 0.100%, B: 0.0005 to 0.0050%, N: 0.003 to 0.010%, Cu: 0 to 0.20%, Ni: 0 to 0.20%, Cr: 0 to 0.10%, and the balance: Fe and impurities, and satisfies formula (1) and formula (2), and the total area fraction of martensite and bainite in the microstructure is 95.0% or more. 0.060≦(51 / 93)Nb+V≦0.100 (1) 0.50 <Nb / V (2) Here, the content (mass %) of each element in formula (1) and formula (2) is substituted for the corresponding element symbol. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 8-49041 [Patent Document 2] Japanese Patent Publication No. 2020-180324 Summary of the Invention [Problem to be solved by the invention]

[0011] By reducing the gap between the cylindrical portion of the rotor and the pole pieces, it is possible to increase the amount of eddy currents generated during braking. Increasing the amount of eddy currents generated during braking increases the braking force of the eddy current reduction gear. However, as the rotor heats up during braking, a thick oxide film may form on the inner surface of the rotor over long-term use. For this reason, it was necessary to set the gap taking into account the thickness of this oxide film that may form. In this specification, the gap between the cylindrical portion of the rotor and the pole pieces (sometimes simply referred to as the gap) refers to the distance between the inner surface of the cylindrical portion of the rotor and the outer surface of the pole pieces.

[0012] The techniques disclosed in the above-mentioned Patent Documents 1 and 2 make it possible to obtain a rotor for an eddy current reduction gear having high high-temperature strength. However, Patent Documents 1 and 2 do not consider means for reducing the gap between the cylindrical portion of the rotor and the pole pieces.

[0013] An object of the present disclosure is to provide a rotor for an eddy current reduction gear that has excellent high-temperature strength and that, when used to form an eddy current reduction gear, can reduce the gap between the cylindrical portion of the rotor and the pole pieces. [Means for solving the problem]

[0014] The rotor for an eddy current reduction gear according to the present disclosure comprises: A cylindrical portion is provided, The chemical composition of the cylindrical portion is, in mass%, C: 0.05~0.15%, Si: 0.10 to 0.40% Mn: 0.50 to 1.00%, P:0.030% or less, S: 0.030% or less, Cr: more than 0.10%~0.40%, Mo: 0.20 to 1.00%, Nb: 0.020~0.060%, V: 0.040~0.080%, sol.Al: 0.030~0.100%, B: 0.0005~0.0050%, N: 0.003 to 0.010%, Cu: 0-0.20% Ni: 0 to 0.20%, and The balance consists of Fe and impurities. [Effects of the Invention]

[0015] The rotor for an eddy current reduction gear according to the present disclosure has high strength even when temperatures reach approximately 700° C. Furthermore, when an eddy current reduction gear is constructed using the rotor for an eddy current reduction gear according to the present disclosure, the gap between the cylindrical portion of the rotor and the pole pieces can be reduced. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing the relationship between the gap between the cylindrical portion of the rotor and the pole piece in the eddy current reduction gear device and the braking torque of the eddy current reduction gear device. [Figure 2] FIG. 2 is a front view of an eddy current reduction gear to which the eddy current reduction gear rotor of this embodiment is applied. [Figure 3] FIG. 3 is a cross-sectional view of the eddy current reduction gear shown in FIG. 2 in the axial direction of the propeller shaft when the eddy current reduction gear is fixed to the propeller shaft. [Figure 4] FIG. 4 is a cross-sectional view (radial cross-sectional view) perpendicular to the axial direction of the eddy current reduction gear device when not braking. [Figure 5] FIG. 5 is a cross-sectional view (radial cross-sectional view) perpendicular to the axial direction of the eddy current reduction gear device during braking. DETAILED DESCRIPTION OF THE INVENTION

[0017] The inventors have investigated and studied a rotor for an eddy current reduction gear that has excellent high-temperature strength and that, when used to construct an eddy current reduction gear, can reduce the gap between the cylindrical portion of the rotor and the pole piece.

[0018] When an eddy current reduction gear is used for a long period of time, an oxide film forms on the inner surface of the cylindrical portion of the rotor. If the cylindrical portion of the rotor comes into contact with the outer surfaces of the pole pieces, abnormal noise and vibration of the vehicle body will occur. Therefore, the gap between the cylindrical portion of the rotor and the pole pieces must be set taking into account the thickness of the oxide film that may form, so that the pole pieces will not come into contact with the cylindrical portion of the rotor even if a thick oxide film forms on the inner surface of the cylindrical portion of the rotor after long-term use.

[0019] On the other hand, the inventors thought that if the oxide film formed on the inner peripheral surface of the cylindrical portion of the rotor does not become thick even after long-term use of the eddy current reduction gear, the gap between the cylindrical portion of the rotor and the pole pieces could be made smaller. If the gap between the cylindrical portion of the rotor and the pole pieces could be made smaller, the braking torque of the eddy current reduction gear could be increased. The inventors investigated the relationship between the gap between the cylindrical portion of the rotor and the pole pieces within the eddy current reduction gear and the braking torque of the eddy current reduction gear. Specifically, an eddy current reduction gear rotor was manufactured, consisting of 0.09% C, 0.19% Si, 0.85% Mn, 0.009% P, 0.008% S, 0.17% Cr, 0.52% Mo, 0.029% Nb, 0.045% V, 0.066% sol. Al, 0.0018% B, 0.005% N, 0.01% Cu, 0.01% Ni, and the balance being Fe and impurities. The rotor had an outer diameter (diameter): 440 mm, an inner diameter (diameter): 390 mm, a cylindrical wall thickness: 11 mm, an axial length: 85 mm, 85 cooling fins, and an air gap: 1000 μm. The braking torque was measured when the propeller shaft rotation speed was 3000 rpm. Several rotors for eddy current reducer devices were manufactured with different cylindrical wall thicknesses to change the gap between the rotor's cylindrical portion and the pole pieces, without changing the chemical composition or other conditions. The braking torque when the cylindrical wall thickness was 11 mm and the air gap was 1000 μm was set to 1, and the braking torque ratio was calculated when the gap between the rotor's cylindrical portion and the pole pieces was changed. The results are shown in Figure 1.

[0020] Referring to Figure 1, as the gap between the cylindrical part of the rotor and the pole pieces becomes smaller, the braking torque ratio increases. Also, compared to the region where the gap is larger (region where the gap is 1200 to 1500 μm), the amount of change in the braking torque ratio is larger in the region where the gap is small (region where the gap is 500 to 800 μm). In other words, it can be seen that the braking torque can be significantly increased in the region where the gap between the cylindrical part of the rotor and the pole pieces is small.

[0021] On the other hand, Joule heat generated along with eddy currents during braking heats the rotor to high temperatures (approximately 650 to 700°C), which accelerates oxidation on the inner circumferential surface of the rotor's cylindrical portion, and can lead to the formation of a thick oxide film over long periods of use. Therefore, while reducing the gap between the rotor's cylindrical portion and the pole pieces to suppress magnetic flux attenuation is an effective way to increase the braking torque of an eddy current reduction gear, it has been necessary to set the gap between the rotor's cylindrical portion and the pole pieces while taking into account the thickness of the oxide film that may form.

[0022] Therefore, the inventors specifically investigated means for maintaining high strength and suppressing the formation of oxide films, even when using at high temperatures up to approximately 700°C. As a result, they found that a Cr content of more than 0.10% to 0.40% in the cylindrical portion of the rotor is effective. The following is thought to be the reason why the Cr content of more than 0.10% to 0.40% suppresses the formation of oxide films. If the cylindrical portion of the rotor contains more than 0.10% to 0.40%, Cr oxides will form on or near the inner circumferential surface of the rotor when used at high temperatures (approximately 650 to 700°C). Cr oxides suppress the diffusion of oxygen from the atmosphere into the rotor interior and the diffusion of iron from the rotor interior to the rotor surface. This suppresses the formation of oxide films on the inner circumferential surface of the cylindrical portion of the rotor. If the cylindrical portion of the rotor contains more than 0.10% to 0.40% Cr, high-temperature strength will be further improved.

[0023] The rotor for an eddy current reduction gear according to this embodiment, which was completed based on the above findings, has the following features.

[0024] [1] A rotor for an eddy current reduction gear, A cylindrical portion is provided, The chemical composition of the cylindrical portion is, in mass%, C: 0.05~0.15%, Si: 0.10 to 0.40% Mn: 0.50 to 1.00%, P:0.030% or less, S: 0.030% or less, Cr: more than 0.10%~0.40%, Mo: 0.20 to 1.00%, Nb: 0.020~0.060%, V: 0.040~0.080%, sol.Al: 0.030~0.100%, B: 0.0005~0.0050%, N: 0.003 to 0.010%, Cu: 0-0.20% Ni: 0 to 0.20%, and The balance consists of Fe and impurities. Rotor for eddy current reduction gear.

[0025] [2] [1] A rotor for an eddy current type reduction gear according to the present invention, The chemical composition is Cu: 0.01 to 0.20%, and Ni: 0.01 to 0.20%, containing one or more elements selected from the group consisting of Rotor for eddy current reduction gear.

[0026] The rotor for an eddy current reduction gear of this embodiment will be described in detail below.

[0027] [Configuration of eddy current reducer] 2 is a front view of an eddy current reduction gear to which the rotor for an eddy current reduction gear of this embodiment is applied. Referring to FIG. 2, the eddy current reduction gear 1 includes a rotor 10 for an eddy current reduction gear (hereinafter simply referred to as rotor 10) and a stator 20.

[0028] FIG. 3 is a cross-sectional view of the eddy current reduction gear 1 shown in FIG. 2 in the axial direction of the propeller shaft when the eddy current reduction gear 1 is fixed to the propeller shaft. Referring to FIG. 3, in this embodiment, the rotor 10 is fixed to the propeller shaft 30, and the stator 20 is fixed to a transmission (not shown). Referring to FIGS. 2 and 3, the rotor 10 includes a cylindrical portion (drum) 11, an arm portion 12, and a wheel portion 13. The cylindrical portion 11 is cylindrical and has an inner diameter larger than the outer diameter of the stator 20. The wheel portion 13 is an annular member having an outer diameter smaller than the inner diameter of the cylindrical portion 11 and has a through hole in the center. The thickness of the wheel portion 13 is thinner than the thickness of the cylindrical portion 11. The propeller shaft 30 is inserted into the through hole and the wheel portion 13 is fixed to the propeller shaft 30. As shown in FIGS. 2 and 3, the arm portion 12 connects the end of the cylindrical portion 11 to the wheel portion 13. The cylindrical portion 11 has a plurality of cooling fins 11F formed on its outer circumferential surface.

[0029] FIG. 4 is a cross-sectional view (radial cross-sectional view) perpendicular to the axial direction of the eddy current reducer 1 when not braking. Referring to FIG. 4, the stator 20 includes a magnet retaining ring 21, a plurality of permanent magnets 22 and 23, and a plurality of pole pieces 24. The permanent magnets 22 and 23 are arranged alternately in the circumferential direction on the outer circumferential surface of the magnet retaining ring 21. Of the surfaces of the permanent magnet 22, the surface facing the inner circumferential surface of the cylindrical portion 11 of the rotor 10 is the north pole. Of the surfaces of the permanent magnet 23, the surface facing the inner circumferential surface of the cylindrical portion 11 of the rotor 10 is the south pole. The plurality of pole pieces 24 are arranged in the circumferential direction of the stator 20. The plurality of pole pieces 24 are arranged with gaps between the plurality of permanent magnets 22 and 23 and the inner circumferential surface of the cylindrical portion 11.

[0030] [Regarding braking and non-braking operations of the eddy current reduction gear 1] 4, when not braking, each permanent magnet 22 or 23 overlaps with two adjacent pole pieces 24 when viewed in the radial direction of the eddy current reducer 1. In this case, as shown in FIG. 4, magnetic flux B flows within the stator 20, specifically, between the permanent magnets 22 and 23, the pole piece 24, and the magnet retaining ring 21. In this case, no magnetic circuit is formed between the rotor 10 and the permanent magnets 22 and 23, and no Lorentz force is generated in the rotor 10. Therefore, no braking force is applied.

[0031] FIG. 5 is a cross-sectional view (radial cross-sectional view) perpendicular to the axial direction of the eddy current reduction gear device 1 during braking. During braking, the magnet retaining ring 21 in the stator 20 rotates, shifting the relative positions of the permanent magnets 22 and 23 with respect to the pole pieces 24 compared to FIG. 4. Specifically, in FIG. 5, when viewed radially of the eddy current reduction gear device 1 during braking, each permanent magnet 22 or 23 overlaps only one pole piece 24 and does not overlap both pole pieces 24. Therefore, as shown in FIG. 5, magnetic flux B flows among the magnet retaining ring 21, the permanent magnet 22 or 23, the pole piece 24, and the cylindrical portion 11. In this case, a magnetic circuit is formed between the rotor 10 and the permanent magnet 22 or 23. At this time, eddy currents are generated in the cylindrical portion 11 of the rotor 10. The generation of eddy currents generates a Lorentz force. This Lorentz force becomes a braking torque, generating a braking force.

[0032] As described above, the eddy current reduction gear 1 applies magnetic flux B to the rotor 10, generating a braking force due to the eddy currents that are generated. Therefore, a smaller distance between the inner circumferential surface of the cylindrical portion 11 of the rotor 10 and the outer circumferential surface of the pole pieces 24 (the gap G between the cylindrical portion 11 of the rotor 10 and the pole pieces 24) reduces the attenuation of magnetic flux B before it acts on the cylindrical portion 11 of the rotor 10, thereby achieving a high braking force. Therefore, the cylindrical portion 11 of the rotor 10 is preferably made of a material that undergoes minimal deformation even when subjected to thermal cycles caused by repeated braking and debraking, and that is resistant to the formation of an oxide film. Because the rotor 10 of the eddy current reduction gear 1 is used at high temperatures of 650°C to 700°C, a material with high strength and oxidation resistance at these temperatures is required. The rotor 10 will be described in detail below.

[0033] [Regarding the rotor 10 for eddy current reduction gear] [Chemical composition] The chemical composition of the cylindrical portion 11 of the rotor 10 for an eddy current type reduction gear of this embodiment contains the following elements: "%" relating to elements means mass % unless otherwise specified.

[0034] C: 0.05 to 0.15% Carbon (C) improves the hardenability of steel and increases its strength. Furthermore, C forms fine precipitation-strengthened carbides, such as Nb carbide and V carbide, thereby improving the high-temperature strength of the steel. If the C content is less than 0.05%, the above-mentioned effects cannot be sufficiently achieved, even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the C content exceeds 0.15%, the electrical resistance of the steel increases excessively, even if the contents of other elements are within the ranges of this embodiment. This reduces the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current reduction gear device 1. In this case, the braking force of the eddy current reduction gear device 1 decreases. Therefore, the C content is 0.05 to 0.15%. The lower limit of the C content is preferably 0.06%, more preferably 0.07%. The upper limit of the C content is preferably 0.14%, more preferably 0.13%, and even more preferably 0.12%.

[0035] Si: 0.10 to 0.40% Silicon (Si) deoxidizes steel during the steelmaking process. Si also improves the hardenability and strength of steel. If the Si content is less than 0.10%, the above effects cannot be sufficiently achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Si content exceeds 0.40%, the electrical resistance of the steel increases excessively even if the contents of other elements are within the ranges of this embodiment, and the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases when the eddy current reduction gear device 1 is braking. In this case, the braking force of the eddy current reduction gear device 1 decreases. Therefore, the Si content is 0.10 to 0.40%. The lower limit of the Si content is preferably 0.12%, more preferably 0.15%. The upper limit of the Si content is preferably 0.38%, more preferably 0.36%.

[0036] Mn: 0.50 to 1.00% Manganese (Mn) deoxidizes steel during the steelmaking process. Mn also improves the hardenability and strength of steel. If the Mn content is less than 0.50%, the above effects cannot be sufficiently achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mn content exceeds 1.00%, the electrical resistance of the steel increases excessively even if the contents of other elements are within the ranges of this embodiment, and the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current reduction gear device 1 decreases. In this case, the braking force of the eddy current reduction gear device 1 decreases. Therefore, the Mn content is 0.50 to 1.00%. The lower limit of the Mn content is preferably 0.58%, more preferably 0.60%, and even more preferably 0.62%. The upper limit of the Mn content is preferably 0.94%, more preferably 0.90%, and even more preferably 0.88%.

[0037] P:0.030% or less Phosphorus (P) is an unavoidable impurity. In other words, the P content is greater than 0%. P reduces the hot workability and toughness of the steel. P also increases the electrical resistance of the steel and reduces the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current reduction gear device 1. If the P content exceeds 0.030%, the hot workability and toughness of the steel significantly deteriorate, even if the contents of other elements are within the ranges of this embodiment, and the braking force of the eddy current reduction gear device 1 also deteriorates. Therefore, the P content is 0.030% or less. The preferred upper limit of the P content is 0.028%, more preferably 0.026%, and even more preferably 0.025%. The P content is preferably as low as possible. However, excessive reduction of the P content increases manufacturing costs. Therefore, considering normal industrial production, the preferred lower limit of the P content is 0.001%, more preferably 0.003%.

[0038] S: 0.030% or less Sulfur (S) is an unavoidable impurity. In other words, the S content is greater than 0%. S reduces the hot workability and toughness of the steel material. If the S content exceeds 0.030%, the hot workability and toughness of the steel material will be significantly reduced even if the contents of other elements are within the ranges of this embodiment. Therefore, the S content is 0.030% or less. A preferred upper limit of the S content is 0.025%, more preferably 0.022%, and even more preferably 0.020%. The S content is preferably as low as possible. However, excessive reduction of the S content increases production costs. Therefore, considering normal industrial production, a preferred lower limit of the S content is 0.001%.

[0039] Cr: More than 0.10%~0.40% Chromium (Cr) improves the hardenability of steel and enhances its high-temperature strength. Furthermore, Cr improves the high-temperature oxidation resistance of steel and suppresses the formation of oxide films. If the Cr content is 0.10% or less, sufficient high-temperature oxidation resistance cannot be obtained, even if the contents of other elements are within the ranges of this embodiment. However, if the Cr content exceeds 0.40%, the electrical resistance of the steel increases excessively, even if the contents of other elements are within the ranges of this embodiment. Even if the gap between the cylindrical portion 11 of the rotor 10 and the pole pieces is reduced, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current reduction device 1 decreases, resulting in a decrease in the braking force of the eddy current reduction device 1. Therefore, the Cr content is greater than 0.10% and up to 0.40%. The preferred lower limit of the Cr content is 0.11%, more preferably 0.12%. The preferred upper limit of the Cr content is 0.38%, more preferably 0.35%.

[0040] Mo: 0.20 to 1.00% Molybdenum (Mo) improves the hardenability of steel and enhances high-temperature strength through solid solution strengthening and precipitation strengthening (dispersion strengthening) by Mo carbide (MoC). Mo also enhances the toughness of steel. If the Mo content is less than 0.20%, the above effects cannot be fully achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mo content exceeds 1.00%, the electrical resistance of the steel increases excessively, even if the contents of other elements are within the ranges of this embodiment. This reduces the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current reduction gear device 1. In this case, the braking force of the eddy current reduction gear device 1 decreases. Therefore, the Mo content is 0.20 to 1.00%. The preferred lower limit of the Mo content is 0.25%, more preferably 0.30%, even more preferably 0.35%, and even more preferably 0.40%. The upper limit of the Mo content is preferably 0.90%, more preferably 0.80%, even more preferably 0.70%, and still more preferably 0.60%.

[0041] Nb: 0.020 to 0.060% Niobium (Nb) combines with carbon to form Nb carbides, which enhance the high-temperature strength of the steel material through precipitation strengthening. Nb also suppresses grain coarsening. If the Nb content is less than 0.020%, the above effects cannot be sufficiently achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Nb content exceeds 0.060%, the electrical resistance of the steel material increases excessively, even if the contents of other elements are within the ranges of this embodiment, and the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current reduction gear device 1 decreases. In this case, the braking force of the eddy current reduction gear device 1 decreases. If the Nb content exceeds 0.060%, the toughness of the steel material further decreases. Therefore, the Nb content is 0.020 to 0.060%. The preferred lower limit of the Nb content is 0.025%, more preferably 0.030%, even more preferably 0.032%, and even more preferably 0.034%. The upper limit of the Nb content is preferably 0.058%, more preferably 0.056%, and even more preferably 0.054%.

[0042] V: 0.040~0.080% Vanadium (V) combines with carbon to form V carbides, which enhance the high-temperature strength of the steel material through precipitation strengthening. V also suppresses grain coarsening. If the V content is less than 0.040%, the above effects cannot be fully achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the V content exceeds 0.080%, the electrical resistance of the steel material increases excessively, even if the contents of other elements are within the ranges of this embodiment. This reduces the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current reduction gear device 1. In this case, the braking force of the eddy current reduction gear device 1 decreases. If the V content exceeds 0.080%, the toughness of the steel material further decreases. Therefore, the V content is 0.040 to 0.080%. The lower limit of the V content is preferably 0.044%, more preferably 0.048%, and even more preferably 0.050%. The upper limit of the V content is preferably 0.075%, and even more preferably 0.070%.

[0043] sol.Al: 0.030~0.100% Aluminum (Al) deoxidizes steel during the steelmaking process. Furthermore, Al combines with N to form AlN, which refines the grain size of the steel. If the sol. Al content is less than 0.030%, the above-mentioned effects cannot be sufficiently achieved, even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the sol. Al content exceeds 0.100%, the electrical resistance of the steel increases excessively, even if the contents of other elements are within the ranges of this embodiment. This reduces the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current reduction gear device 1. In this case, the braking force of the eddy current reduction gear device 1 decreases. Therefore, the sol. Al content is 0.030 to 0.100%. The lower limit of the sol. Al content is preferably 0.040%, more preferably 0.050%. The upper limit of the sol. Al content is preferably 0.090%.

[0044] B: 0.0005 to 0.0050% Boron (B) improves the hardenability of steel materials and enhances their high-temperature strength. If the B content is less than 0.0005%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the B content exceeds 0.0050%, the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the B content is 0.0005 to 0.0050%. A preferred lower limit of the B content is 0.0010%, more preferably 0.0012%, and even more preferably 0.0014%. A preferred upper limit of the B content is 0.0045%, more preferably 0.0040%, even more preferably 0.0035%, and even more preferably 0.0030%.

[0045] N: 0.003 to 0.010% Nitrogen (N) combines with Al to form AlN, thereby refining the grain size of the steel. If the N content is less than 0.003%, the above effect cannot be sufficiently achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the N content exceeds 0.010%, the electrical resistance of the steel increases excessively, even if the contents of other elements are within the ranges of this embodiment, and the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases when the eddy current reduction gear device 1 is braking. In this case, the braking force of the eddy current reduction gear device 1 decreases. Therefore, the N content is 0.003 to 0.010%. A preferable lower limit of the N content is 0.004%. A preferable upper limit of the N content is 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0046] The remainder of the chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current reducer 1 of this embodiment is composed of Fe and impurities. Here, the impurities refer to substances that are mixed in from raw materials such as ore or scrap or the manufacturing environment when industrially manufacturing the cylindrical portion 11 of the rotor 10 of this embodiment, and are acceptable within a range that does not adversely affect the cylindrical portion 11 of the rotor 10 of this embodiment.

[0047] [Optional elements] The chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current reducer 1 of this embodiment may further contain one or more elements selected from Cu and Ni in place of a portion of Fe. These elements are optional and improve the hardenability of the steel material.

[0048] Cu: 0 to 0.20% Copper (Cu) is an optional element and may not be contained. In other words, the Cu content may be 0%. When contained, Cu improves the hardenability of the steel material and increases the high-temperature strength of the steel material. Even if even a small amount of Cu is contained, the above effects can be obtained to some extent. However, if the Cu content exceeds 0.20%, even if the contents of other elements are within the ranges of this embodiment, the electrical resistance of the steel material increases excessively, and the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current reduction device 1 during braking of the eddy current reduction device 1 decreases. In this case, the braking force of the eddy current reduction device 1 decreases. Therefore, the Cu content is 0 to 0.20%. The preferred lower limit of the Cu content is more than 0%, more preferably 0.01%, and even more preferably 0.02%. The preferred upper limit of the Cu content is 0.15%, more preferably 0.12%, and even more preferably 0.10%.

[0049] Ni: 0 to 0.20% Nickel (Ni) is an optional element and may not be contained. In other words, the Ni content may be 0%. When contained, Ni improves the hardenability of the steel material and increases the high-temperature strength of the steel material. Even if even a small amount of Ni is contained, the above effects can be obtained to some extent. However, if the Ni content exceeds 0.20%, even if the contents of other elements are within the ranges of this embodiment, the electrical resistance of the steel material increases excessively, and the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current reduction device 1 during braking of the eddy current reduction device 1 decreases. In this case, the braking force of the eddy current reduction device 1 decreases. Therefore, the Ni content is 0 to 0.20%. The lower limit of the Ni content is preferably greater than 0%, more preferably 0.01%, even more preferably 0.02%, and even more preferably 0.03%. The upper limit of the Ni content is preferably 0.15%, even more preferably 0.12%, and even more preferably 0.10%.

[0050] [Microstructure] The microstructure of the cylindrical portion 11 of the rotor 10 for an eddy current type reduction gear of this embodiment is a structure mainly composed of martensite and / or bainite. For example, the total area ratio of martensite and bainite is 95% or more. The remainder other than martensite and bainite is ferrite. Note that, since it is extremely difficult to distinguish between martensite and bainite in microstructural observation, the region other than ferrite is recognized as "martensite and bainite."

[0051] [Microstructure observation method] In this embodiment, the total area ratio of martensite and bainite in the microstructure can be measured by the following method. A sample is taken from the center position of the wall thickness of the cylindrical portion 11 of the rotor 10. The size of the sample is not particularly limited as long as an observation field (200 μm × 100 μm) described below can be secured. The surface of the sample, including the observation field, is mirror-polished. After mirror polishing, the sample is immersed in a nital solution for about 10 seconds to etch the sample, revealing the structure on the observation surface. An arbitrary field (observation field) within the observation surface, where the structure has been revealed by etching, is observed using an optical microscope at 500x magnification. The observation field has a field area of ​​20,000 μm. 2 The observation field is set to (200 μm × 100 μm). Ferrite can be easily distinguished from martensite and bainite based on the contrast. Therefore, the ferrite in the observation field is identified and the area of ​​the identified ferrite is calculated. The area of ​​the ferrite is divided by the total area of ​​the observation field to calculate the area ratio (%) of ferrite. The total area ratio (%) of martensite and bainite is calculated using the following formula. Total area ratio of martensite and bainite = 100 - area ratio of ferrite

[0052] [Manufacturing method] An example of a method for manufacturing the rotor 10 for an eddy current reduction device of this embodiment will be described below. The manufacturing method described below is one example for manufacturing the rotor 10 for an eddy current reduction device of this embodiment. Therefore, the rotor 10 for an eddy current reduction device having the above-described configuration may be manufactured by a manufacturing method other than the manufacturing method described below. However, the manufacturing method described below is a preferred example of a method for manufacturing the rotor 10 for an eddy current reduction device of this embodiment.

[0053] A method for manufacturing the rotor 10 for an eddy current reduction gear of this embodiment includes, for example, the following steps. (Process 1) Material preparation process (Process 2) Hot processing process (Process 3) Tempering treatment process (Process 4) Machining process (Step 5) Rotor formation process Each step will be described below.

[0054] [(Process 1) Material preparation process] In the material preparation step, a material having an element content within the range of this embodiment is prepared. The material may be supplied by a third party. The material may also be manufactured. When manufacturing the material, for example, it may be manufactured by the following method.

[0055] Molten steel is produced having a chemical composition in which the content of each element falls within the range of this embodiment. The refining method is not particularly limited, and any known method may be used. In the refining, alloy elements are added to adjust the composition, thereby producing molten steel having a chemical composition in which the content of each element falls within the range of this embodiment.

[0056] The molten steel produced by the above-described refining method is used to produce a material by a well-known casting method. For example, an ingot is produced by ingot casting using the molten steel. Alternatively, a bloom or billet may be produced by continuous casting using the molten steel. The produced bloom or ingot may be heated to 1000 to 1300°C and then hot-worked to produce a billet. Examples of hot-working include hot rolling and hot forging. The produced billet (a billet produced by continuous casting, or a billet produced by hot-working a bloom or ingot) is used as the material for the rotor 10 for an eddy current reduction gear.

[0057] [(Process 2) Hot processing process] The material prepared in the material preparation step is subjected to hot working (hot forging and / or hot rolling) to manufacture an intermediate product corresponding to the cylindrical portion 11. First, the material is heated to 1000 to 1300°C. The heated material is subjected to hot forging to form it into predetermined dimensions. After hot forging, hot rolling is further performed to manufacture a cylindrical intermediate product. The heated material may be subjected to hot forging or hot rolling to manufacture a cylindrical intermediate product.

[0058] [(Process 3) Tempering treatment process] The intermediate product produced by the hot working process is subjected to a tempering process. The tempering process includes the following steps. The main manufacturing conditions for each step are also listed. (Step 31) Quenching process Recommended quenching temperature: 870~930℃ Preferred retention time: 0.5 to 3.0 hours (Step 32) Tempering process Recommended tempering temperature: 660~710℃ Preferred retention time: 0.5 to 3.0 hours

[0059] [(Step 31) Quenching process] First, the intermediate product is quenched. The quenching temperature is 870 to 930°C. The time for holding at the quenching temperature is not particularly limited, but is, for example, 0.5 to 3.0 hours. If the quenching temperature is less than 870°C, the microstructure of the intermediate product will not be austenite single phase, and ferrite will remain in the quenched structure in addition to martensite and / or bainite, resulting in insufficient high-temperature strength. On the other hand, if the quenching temperature is more than 930°C, the austenite grains will coarsen, reducing the toughness and high-temperature oxidation resistance of the rotor 10. Therefore, the quenching temperature is 870 to 900°C. A known method for quenching during the quenching process will suffice. For example, water cooling or oil cooling is used as the quenching method during the quenching process.

[0060] [(Step 32) Tempering treatment step] The intermediate product after quenching is subjected to tempering. The tempering temperature is 660 to 710°C. The time for holding at the tempering temperature is not particularly limited, but is, for example, 0.5 to 3.0 hours. If the tempering temperature is less than 660°C, sufficient strength cannot be obtained. On the other hand, if the tempering temperature exceeds 710°C, softening due to tempering becomes too great, and in this case too, sufficient strength cannot be obtained. Therefore, the tempering temperature is set to 660 to 710°C.

[0061] [(Process 4) Machining process] The inner and outer peripheral surfaces of the tempered intermediate product are machined. At this time, cooling fins 11F are formed on the outer peripheral surface. The machining can be performed by a well-known method. Through the above steps, the cylindrical portion 11 is manufactured.

[0062] [(Step 5) Rotor formation process] The arm portion 12 attached to the wheel portion 13 is attached to the manufactured cylindrical portion 11, thereby manufacturing the rotor 10 for the eddy current reduction gear. The attachment method may be welding or another method.

[0063] The eddy current reduction gear rotor 10 of this embodiment can be manufactured by the above manufacturing method. Note that the manufacturing method for the eddy current reduction gear rotor 10 of this embodiment is not limited to the above manufacturing method, and the eddy current reduction gear rotor 10 of this embodiment may be manufactured by a manufacturing method other than the above manufacturing method as long as the eddy current reduction gear rotor 10 having the above configuration can be manufactured. However, the above manufacturing method is a suitable example for manufacturing the eddy current reduction gear rotor 10 of this embodiment. [Example]

[0064] Molten steel having the chemical composition shown in Table 1 was produced.

[0065] [Table 1]

[0066] A blank space in Table 1 means 0% in the number of decimal places specified in the embodiment. In other words, it means that the content of the corresponding element is 0% when rounded to the nearest decimal place specified in the embodiment. For example, the Cr content specified in this embodiment is specified to two decimal places. Test No. 14 in Table 1 means that the measured Cr content was 0% when rounded to three decimal places.

[0067] Using the molten steel of each test number, a 180 kg cylindrical ingot was produced by ingot casting. A portion of the ingot was cut out, heated to 1200°C, and then hot forged to produce a 40 mm thick steel plate as a pseudo-intermediate product. The pseudo-intermediate product was quenched at a quenching temperature of 900°C. The holding time at the quenching temperature was 1.5 hours, and the cooling method was water cooling. The quenched pseudo-intermediate product was tempered at a tempering temperature of 690°C. The holding time at the tempering temperature was 2 hours, and the cooling method was air cooling. Using the above manufacturing process, a pseudo rotor (steel plate) of each test number was produced, simulating a rotor for an eddy current reduction gear. The microstructure of the pseudo rotor (steel plate) of each test number was mainly composed of martensite and / or bainite, and the total area ratio of martensite and bainite was 95% or more.

[0068] [Tensile test at 700℃] The yield strength (MPa) at 700°C of each manufactured pseudo rotor was determined using a measurement method in accordance with JIS G 0567 (2012). Specifically, tensile test specimens were taken from each pseudo rotor. The parallel portion of the tensile test specimen had a length of 40 mm, a gauge length of 30 mm, and a diameter of 6 mm. The tensile test specimens were heated to 700°C using a heating furnace. A tensile test was performed on the 700°C tensile test specimens in air to obtain stress-strain curves. The 0.2% proof stress based on the offset method was defined as the yield strength (MPa) from the obtained stress-strain curves. The obtained yield strengths (MPa) at 700°C are shown in Table 2.

[0069] [Table 2]

[0070] Only for test numbers with a yield strength of 140 MPa or more at 700°C, rotors for eddy current reduction gears were manufactured for thermal load durability tests. Specifically, the ingots for test numbers 1 to 4, 14, and 15 were heated to 1200°C and then hot forged to produce cylindrical blanks. The cylindrical blanks were quenched by holding them at 900°C for 1.5 hours and then water-cooled, and then tempered by holding them at 690°C for 2 hours and then air-cooled. The blanks were then machined, and an arm attached to a wheel was attached by welding to produce the rotors for eddy current reduction gears. The rotors had an outer diameter (diameter) of 440 mm, an inner diameter (diameter) of 390 mm, a cylindrical wall thickness of 11 mm, and an axial length of 85 mm. The rotors had 81 cooling fins on their outer circumferential surface.

[0071] [Heat load durability test] A thermal load endurance test was conducted on the manufactured rotors with test numbers 1 to 4, 14, and 15. In the thermal load endurance test, the rotor was rotated at 3,000 rpm and subjected to a thermal cycle by repeatedly switching between braking and non-braking states. Specifically, the rotor was placed in a braking state, and when the rotor temperature reached 700°C, the brake state was switched back to non-braking. When the rotor temperature cooled to 100°C, the brake state was switched back to braking. This cycle was repeated 20,000 times, resulting in a thermal cycle with a minimum temperature of 100°C and a maximum temperature of 700°C. After the 20,000 thermal cycles, the cylindrical portion of the rotor was cut at the center of its axial length, and the thickness of the oxide film formed on the inner surface of the cylindrical portion of the rotor was measured by observing the cut surface. The measured oxide film thicknesses are shown in Table 3.

[0072] [Table 3]

[0073] [Evaluation results] Referring to Tables 2 and 3, the pseudo rotors of test numbers 1 to 4 had a yield strength of 140 MPa or more at 700°C, and had high strength at 700°C. The rotors of test numbers 1 to 4 had oxide films of 500 μm or less in thickness formed after the thermal cycle. In other words, it was found that the rotors of test numbers 1 to 4 can reduce the gap G between the cylindrical portion of the rotor and the pole piece when used in an eddy current reduction gear device.

[0074] On the other hand, in test number 5, the C content was too low, and therefore the yield strength at 700°C was less than 140 MPa, which was too low.

[0075] In test number 6, the Si content was too low, so the yield strength at 700°C was less than 140 MPa, which was too low.

[0076] In test number 7, the Mn content was too low, so the yield strength at 700°C was less than 140 MPa, which was too low.

[0077] In test number 8, the Mo content was too low, so the yield strength at 700°C was less than 140 MPa, which was too low.

[0078] In test number 9, the V content was too low, so the yield strength at 700°C was less than 140 MPa, which was too low.

[0079] In test number 10, the Nb content was too low, so the yield strength at 700°C was less than 140 MPa, which was too low.

[0080] In test number 11, the Al content was too low, so the yield strength at 700°C was less than 140 MPa, which was too low.

[0081] In test number 12, the B content was too low, so the yield strength at 700°C was less than 140 MPa, which was too low.

[0082] In test number 13, the N content was too low, so the yield strength at 700°C was less than 140 MPa, which was too low.

[0083] The Cr content of the rotors of test numbers 14 and 15 was too low. As a result, the thickness of the oxide film formed after the thermal cycle exceeded 500 μm for the rotors of test numbers 14 and 15. In other words, it was found that the rotors of test numbers 14 and 15 cannot reduce the gap G between the cylindrical portion of the rotor and the pole piece when used in an eddy current reduction gear device.

[0084] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure. [Explanation of symbols]

[0085] 1 Eddy current reduction device 10 rotors 11 Cylindrical part 12 Arm section 13 Wheel section 20 Stator

Claims

1. A rotor for an eddy current reduction gear, A cylindrical portion is provided, The chemical composition of the cylindrical portion is, in mass%, C: 0.05-0.15%, Si: 0.10-0.40%, Mn: 0.50-1.00%, P: 0.030% or less, S: 0.030% or less, Cr: more than 0.10% to 0.40%, Mo: 0.20-1.00%, Nb: 0.020-0.060%, V: 0.040-0.080%, sol. Al: 0.030 to 0.100%, B: 0.0005-0.0050%, N: 0.003-0.010%, Cu: 0 to 0.20%, Ni: 0 to 0.20%, and The balance is composed of Fe and impurities, In the microstructure of the cylindrical portion, the total area ratio of martensite and bainite is 95% or more. Rotor for eddy current reduction gear.

2. 2. The rotor for an eddy current type reduction gear according to claim 1, The chemical composition is Cu: 0.01 to 0.20%, and Ni: 0.01 to 0.20%; containing one or more elements selected from the group consisting of: Rotor for eddy current reduction gear.

Images