Rotor for Eddy Current Deceleration Device and Method for Manufacturing Rotor for Eddy Current Deceleration Device

Abstract

Provided are: an eddy-current-type reduction gear rotor having high strength at high temperatures and low electrical resistance; and a method for manufacturing the same. The eddy-current-type reduction gear rotor according to the present disclosure comprises a cylindrical part, the cylindrical part having a chemical composition satisfying formula (1) and comprising, in mass%, 0.05-0.15% of C, 0.01-0.15% of Si, 0.10-1.00% of Mn, 0.030% or less of P, 0.030% or less of S, 0.30-2.00% of Cr, 0.30-1.50% of Mo, 0.02-0.15% of V, 0.01-0.10% of Nb, 0.001-0.040% of sol. Al, 0.0005-0.0050% of B, and 0.001-0.010% of N with the remainder being Fe and impurities, and the cylindrical part further having a microstructure with a total surface area ratio of martensite and bainite of 99% or higher, and a yield stress at 700°C of 120-250 MPa.　(1): Cr + 4Si + 3 sol. Al + Mo ≤ 3.00

Description

Technical Field

[0001] The present disclosure relates to a rotor and a method for manufacturing a rotor, and more particularly to a rotor for an eddy current retarder and a method for manufacturing the same, which are used in an eddy current retarder.

Background Art

[0002] Large vehicles such as buses and trucks are equipped with braking devices such as foot brakes and exhaust brakes. In recent large vehicles, there have also appeared those equipped with an eddy current retarder as a braking device. The eddy current retarder is also called a retarder. For example, when traveling on a long downhill slope with a steep gradient, even when using an engine brake and an exhaust brake in combination, it is difficult to decelerate the traveling speed of a large vehicle. In such a case, the eddy current retarder is activated. By activating the eddy current retarder, the braking force can be further increased, and the traveling speed of the large vehicle can be effectively decelerated.

[0003] There are two types of eddy current retarders: those using electromagnets and those using permanent magnets. An eddy current retarder using a permanent magnet includes a rotor and a stator housed in the rotor. The rotor includes, for example, a cylindrical portion (drum), an annular wheel portion for fixing the rotor to a propeller shaft, and a plurality of arm portions connecting the cylindrical portion and the wheel portion. The stator includes a cylindrical body, a plurality of permanent magnets of two different polarities, and a plurality of pole pieces. The plurality of permanent magnets with different polarities are alternately arranged in the circumferential direction on the outer peripheral surface of the cylindrical body. The pole pieces are disposed between the inner peripheral surface of the cylindrical portion of the rotor and the permanent magnets. Among the stator, the cylindrical body to which the plurality of permanent magnets are attached is rotatable about the axis of the cylindrical body independently of the plurality of pole pieces.

[0004] During braking, that is, when the eddy current type deceleration device is operated, the magnetic flux of the permanent magnet of the stator reaches the rotor through the pole piece, and a magnetic circuit is formed between the permanent magnet and the cylindrical portion of the rotor. At this time, eddy currents are generated in the cylindrical portion of the rotor. Along with the generation of the eddy currents, Lorentz forces are generated. These Lorentz forces become braking torques and apply braking forces to large-sized vehicles. On the other hand, during non-braking, that is, when the operation of the eddy current type deceleration device is stopped, the relative position of the permanent magnet with respect to the pole piece is shifted so that the magnetic flux of the permanent magnet does not reach the rotor. In this case, a magnetic circuit is not formed between the permanent magnet and the cylindrical portion of the rotor. Therefore, 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 type deceleration device switches between the braking operation and the non-braking operation (stop).

[0005] Incidentally, the braking force depends on the amount of eddy current generated in the cylindrical portion of the rotor during braking. Specifically, the greater the amount of eddy current generated in the cylindrical portion of the rotor during braking, the higher the braking force. That is, in order to increase the amount of eddy current generated during braking and enhance the braking force, it is preferable that the electrical resistance of the cylindrical portion of the rotor be low.

[0006] Furthermore, during braking, the rotor is heated by Joule heat generated together with the eddy currents. On the other hand, during non-braking of the eddy current type deceleration device, the rotor is rapidly cooled (air-cooled) by a plurality of cooling fins formed on the outer peripheral surface of the cylindrical portion. That is, due to the repetition of braking and non-braking, a thermal cycle is loaded on the rotor. Therefore, the rotor for the eddy current type deceleration device is required to have not only low electrical resistance but also high high-temperature strength.

[0007] A technique for obtaining high high-temperature strength while reducing the electrical resistance in a rotor for an eddy current type deceleration device is disclosed in Japanese Patent Application Laid-Open No. 8-49041 (Patent Document 1).

[0008] The rotor material for the eddy current type speed reducer described in Patent Document 1 contains, by mass%, C: 0.05 to 0.15%, Si: 0.10 to 0.40%, Mn: 0.5 to 1.0%, P: 0.05% or less, Ni: 0.50% or less, Mo: 0.2 to 1.0%, Nb: 0.01 to 0.03%, V: 0.03 to 0.07%, B: 0.0005 to 0.003%, Sol.Al: 0.02 to 0.09%, and N: 0.01% or less, and the balance is substantially composed of Fe. In this document, 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, by containing B, the high-temperature strength of the rotor material is increased.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] As described above, in Patent Document 1, a rotor for an eddy current type speed reducer is provided that reduces electrical resistance while increasing high-temperature strength. However, it may be possible to obtain an eddy current type speed reducer that reduces electrical resistance while increasing high-temperature strength by a technique different from the technique disclosed in Patent Document 1.

[0011] An object of the present disclosure is to provide a rotor for an eddy current type speed reducer having high high-temperature strength and low electrical resistance, and a method for manufacturing the rotor for the eddy current type speed reducer.

Means for Solving the Problems

[0012] The rotor for an eddy current type speed reducer according to the present disclosure includes a cylindrical portion, and the cylindrical portion contains, by mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and, N: 0.001 to 0.010%, and contains the balance: Fe and impurities, and has a chemical composition satisfying formula (1), a microstructure with a total area ratio of martensite and bainite of 99% or more, and a yield stress of 120 to 250 MPa at 700 °C. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in formula (1), the content of the corresponding element is substituted in mass %.

[0013] The rotor for an eddy current reduction device according to the present disclosure is provided with a cylindrical portion, and the cylindrical portion in mass %, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and, N: 0.001 to 0.010%, and contains, further, Cu: 0.20% or less, Ni: less than 0.20%, and contains one or more elements selected from the group consisting of Ti: 0.050% or less, the balance: Fe and impurities, and has a chemical composition satisfying formula (1), a microstructure with a total area ratio of martensite and bainite of 99% or more, and has a yield stress of 120 to 250 MPa at 700 °C. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in each element symbol in formula (1), the content of the corresponding element is substituted in mass%.

[0014] The manufacturing method of the rotor for the eddy current decelerator according to the present disclosure is in mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, contains a preparation step of preparing an intermediate product having a chemical composition satisfying formula (1), consisting of the balance: Fe and impurities, a quenching step of performing quenching on the intermediate product, a tempering step of performing tempering on the intermediate product after the quenching step at a temperature below 700 °C to A c1 point, a processing step of processing the intermediate product after the tempering step to form a cylindrical portion, and a rotor forming step of manufacturing a rotor for an eddy current decelerator using the cylindrical portion. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in formula (1), the content of the corresponding element is substituted in mass%.

[0015] The manufacturing method of the rotor for an eddy current decelerator according to the present disclosure is in mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, contains, and further Cu: 0.20% or less, Ni: 0.20% or less, and Ti: 0.050% or less, contains one or more elements selected from the group consisting of the balance: Fe and impurities, and prepares an intermediate product having a chemical composition satisfying formula (1); a preparation step, a quenching step of performing quenching on the intermediate product; a tempering step of performing tempering on the intermediate product after the quenching step at a temperature below 700°C to A c1 point; a machining step of machining the intermediate product after the tempering step to form a cylindrical portion; a rotor forming step of manufacturing a rotor for an eddy current decelerator using the cylindrical portion, and comprises. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in formula (1), the content of the corresponding element is substituted in mass%.

Advantages of the Invention

[0016] The rotor for the eddy current decelerator according to the present disclosure has high high-temperature strength and low electrical resistance. The manufacturing method of the rotor for the eddy current decelerator according to the present disclosure can manufacture the above-described rotor for the eddy current decelerator.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0018] The inventors of the present invention investigated and studied a technique for achieving both high high-temperature strength and low electrical resistance in a rotor for an eddy current decelerator. As a result, the following findings were obtained.

[0019] First, the inventors of the present invention focused on the chemical composition of the cylindrical portion of the rotor for the eddy current decelerator and variously studied methods for increasing the high-temperature strength of the rotor. As a result, it was found that the high-temperature strength of the rotor can be increased by increasing the Cr content in the chemical composition of the cylindrical portion of the rotor.

[0020] Specifically, the inventors focused on the yield stress at 700°C as the high-temperature strength of the rotor for the eddy current decelerator. The inventors further examined the rotor for the eddy current decelerator whose yield stress at 700°C satisfies 120 to 250 MPa from the viewpoint of chemical composition. As a result of the detailed examination by the inventors, the cylindrical portion of the rotor for the eddy current decelerator contains, in mass %, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, and further selectively contains one or more elements selected from the group consisting of Cu: 0.20% or less, Ni: 0.20% or less, and Ti: 0.050% or less, and the balance: Fe and impurities. It has been clarified that there is a possibility of obtaining a rotor for an eddy current decelerator whose yield stress at 700°C satisfies 120 to 250 MPa if the chemical composition is such.

[0021] On the other hand, in the chemical composition of the cylindrical portion of the rotor for the eddy current decelerator, if the content of the alloy element is increased, there is a concern that the electrical resistance of the rotor will increase. The effect of increasing the electrical resistance of the rotor varies depending on the element, and Cr has a high effect of increasing the electrical resistance among the above chemical compositions. Therefore, in the chemical composition of the cylindrical portion of the conventional rotor for the eddy current decelerator, the Cr content has been reduced as much as possible while increasing the high-temperature strength.

[0022] However, in the rotor for the eddy current type speed reducer according to the present embodiment, by deliberately increasing the Cr content in the chemical composition of the cylindrical portion to the above-mentioned range, the high-temperature strength of the rotor is increased. That is, a rotor for an eddy current type speed reducer including a cylindrical portion having the above-mentioned chemical composition with an increased Cr content is likely to have a high electrical resistance. Therefore, the present inventors have carefully studied a method for reducing the electrical resistance even in a rotor for an eddy current type speed reducer including a cylindrical portion having the above-mentioned chemical composition. As a result, it has been found that if the following formula (1) is further satisfied while having the above-mentioned chemical composition, there is a possibility of reducing the electrical resistance while maintaining the yield stress at 700 °C at 120 to 250 MPa. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, for each element symbol in formula (1), the content of the corresponding element is substituted in mass%.

[0023] Define F1 = Cr + 4Si + 3sol.Al + Mo. F1 is an index indicating the height of the electrical resistance in a rotor for an eddy current type speed reducer including a cylindrical portion having the above-mentioned chemical composition. If F1 is 3.00 or less, even when the Cr content is increased to 0.30 to 2.00%, the electrical resistance can be reduced. This point will be specifically described with reference to the drawings.

[0024] FIG. 1 is a diagram showing the relationship between F1 (= Cr + 4Si + 3sol.Al + Mo) and the electrical resistance (μΩcm) in the present embodiment. FIG. 1 is created using the F1 of each steel material and the result of the electrical resistance test, considering a steel material having the above-mentioned chemical composition, a microstructure with a total area ratio of martensite and bainite of 99% or more, and a yield stress of 120 to 250 MPa at 700 °C as a rotor for an eddy current type speed reducer. Referring to FIG. 1, in the relationship between F1 and the electrical resistance, it can be confirmed that if F1 is 3.00 or less, the electrical resistance of the steel material regarded as a rotor for an eddy current type speed reducer can be stably reduced to 20.5 μΩcm or less.

[0025] Therefore, in the rotor for the eddy current deceleration device according to the present embodiment, in the chemical composition of the cylindrical portion, in addition to the above-described chemical composition, F1 is set to 3.00 or less. As a result, the rotor for the eddy current deceleration device according to the present embodiment can achieve both high high-temperature strength and low electrical resistance.

[0026] Based on the above findings, the gist of the rotor for the eddy current deceleration device and the manufacturing method of the rotor for the eddy current deceleration device according to the present embodiment completed thereby is as follows.

[0027] [1] A rotor for an eddy current deceleration device, comprising a cylindrical portion, wherein the cylindrical portion in mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, contains the balance: Fe and impurities, and has a chemical composition that satisfies formula (1), a microstructure in which the total area ratio of martensite and bainite is 99% or more, and a yield stress of 120 to 250 MPa at 700°C, a rotor for an eddy current deceleration device. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in each element symbol in formula (1), the content of the corresponding element is substituted in mass%.

[0028] [2] A rotor for an eddy current reduction gear, comprising a cylindrical portion, wherein the cylindrical portion in mass %, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, and further Cu: 0.20% or less, Ni: 0.20% or less, and Ti: 0.050% or less, contains one or more elements selected from the group consisting of, the balance: Fe and impurities, has a chemical composition satisfying formula (1), and a microstructure with a total area ratio of martensite and bainite of 99% or more, a yield stress of 120 to 250 MPa at 700 °C, and has, a rotor for an eddy current reduction gear. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in formula (1), the content of the corresponding element is substituted in mass %.

[0029] [3] A method for manufacturing a rotor for an eddy current reduction gear, in mass %, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and, N: 0.001 to 0.010%, containing, the balance: Fe and impurities, and preparing an intermediate product having a chemical composition satisfying formula (1); a preparation step, a quenching step of performing quenching on the intermediate product; a tempering step of performing tempering on the intermediate product after the quenching step at a temperature below 700°C to A c1 point; a processing step of processing the intermediate product after the tempering step to form a cylindrical portion; a rotor forming step of manufacturing a rotor for an eddy current reduction device using the cylindrical portion, comprising: The method for manufacturing a rotor for an eddy current reduction device according to [1]. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in formula (1), the content of the corresponding element is substituted in mass%.

[0030] [4] A method for manufacturing a rotor for an eddy current reduction device, comprising: in mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and, Containing N: 0.001 to 0.010%, and further, Cu: 0.20% or less, Ni: 0.20% or less, and Ti: 0.050% or less, containing one or more elements selected from the group consisting of, The balance: consisting of Fe and impurities, and a preparation step of preparing an intermediate product having a chemical composition satisfying formula (1); A quenching step of performing quenching on the intermediate product; A tempering step of performing tempering on the intermediate product after the quenching step at a temperature below 700°C to A c1 point; A processing step of processing the intermediate product after the tempering step to form a cylindrical portion; A rotor forming step of manufacturing a rotor for an eddy current decelerator using the cylindrical portion, comprising: The method for manufacturing a rotor for an eddy current decelerator according to [2]. Cr + 4Si + 3sol.Al + Mo ≦ 3.00 (1) Here, in each element symbol in formula (1), the content of the corresponding element is substituted in mass%.

[0031] Furthermore, the gist of the rotor for an eddy current decelerator and the method for manufacturing the rotor for an eddy current decelerator according to the present embodiment can also be described as follows.

[0032] [1] A rotor for an eddy current decelerator, comprising: A cylindrical portion, The cylindrical portion, in mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, N: 0.001 to 0.010%, Cu: 0 to 0.20%, Ni: 0 to 0.20%, Ti: 0 to 0.050%, and, the balance: Fe and impurities, having a chemical composition satisfying formula (1), a microstructure with a total area ratio of martensite and bainite of 99% or more, a yield stress of 120 to 250 MPa at 700 °C, and having, a rotor for an eddy current reduction device. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in formula (1), the content of the corresponding element is substituted in mass %.

[0033] [2] The rotor for an eddy current reduction device according to [1], wherein the chemical composition is Cu: 0.01 to 0.20%, Ni: 0.01 to 0.20%, and, Ti: 0.001 to 0.050%, containing at least one element selected from the group consisting of a rotor for an eddy current reduction device.

[0034] [3] A method for manufacturing a rotor for an eddy current reduction device, in mass %, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, N: 0.001 to 0.010%, Cu: 0 to 0.20%, Ni: 0 to 0.20%, Ti: 0 to 0.050%, and, the balance: Fe and impurities, and prepare an intermediate product having a chemical composition satisfying formula (1); a preparation step of a quenching step of performing quenching on the intermediate product; a tempering step of performing tempering on the intermediate product after the quenching step at a temperature below 700 °C to c1 less than the A point; a processing step of processing the intermediate product after the tempering step to form a cylindrical portion; a rotor forming step of manufacturing a rotor for an eddy current reduction device using the cylindrical portion, comprising: The method for manufacturing a rotor for an eddy current reduction device according to [1] or [2]. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in formula (1), the content of the corresponding element is substituted in mass%.

[0035] [4] The method for manufacturing a rotor for an eddy current reduction device according to [3], wherein the chemical composition is Cu: 0.01 to 0.20%, Ni: 0.01 to 0.20%, and, Ti: 0.001 to 0.050%, and contains at least one element selected from the group consisting of The method for manufacturing a rotor for an eddy current reduction device.

[0036] Hereinafter, the rotor for an eddy current reduction device of the present embodiment will be described in detail.

[0037] [Configuration of Eddy Current Reduction Device] FIG. 2 is a front view of an eddy current deceleration device 1 to which the rotor for the eddy current deceleration device of the present embodiment is applied. Referring to FIG. 2, the eddy current deceleration device 1 includes a rotor 10 and a stator 20.

[0038] FIG. 3 is an axial cross-sectional view of the eddy current deceleration device 1 when the eddy current deceleration device 1 shown in FIG. 2 is fixed to the propeller shaft 30. Referring to FIG. 3, in the present 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. More specifically, the rotor 10 includes a cylindrical portion 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 having a through hole at the center. The thickness of the wheel portion 13 (the axial length of the propeller shaft 30) is thinner than the thickness of the cylindrical portion 11 (the axial length of the propeller shaft 30). The wheel portion 13 inserts the propeller shaft 30 into the through hole and 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 and the wheel portion 13. Note that a plurality of cooling fins 11F are formed on the outer peripheral surface of the cylindrical portion 11. The cylindrical portion 11, the arm portion 12, and the wheel portion 13 may be integrally formed. The cylindrical portion 11, the arm portion 12, and the wheel portion 13 may be configured by separate and independent members.

[0039] FIG. 4 is a cross-sectional view (radial cross-sectional view) perpendicular to the axial direction of the eddy current type speed reduction device 1 when not in braking. Referring to FIG. 4, the stator 20 includes a magnet holding ring 21, a plurality of permanent magnets 22 and 23, and a plurality of pole pieces 24. The plurality of permanent magnets 22 and the permanent magnet 23 are alternately arranged in the circumferential direction on the outer peripheral surface of the magnet holding ring 21. Among the surfaces of the permanent magnet 22, the surface facing the inner peripheral surface of the cylindrical portion 11 of the rotor 10 is the N pole. Among the surfaces of the permanent magnet 22, the surface facing the outer peripheral surface of the magnet holding ring 21 is the S pole. Among the surfaces of the permanent magnet 23, the surface facing the inner peripheral surface of the cylindrical portion 11 of the rotor 10 is the S pole. Among the surfaces of the permanent magnet 23, the surface facing the outer peripheral surface of the magnet holding ring 21 is the N pole. The plurality of pole pieces 24 are arranged above the plurality of permanent magnets 22 and 23 and are arranged in the circumferential direction of the stator 20. The plurality of pole pieces 24 are arranged between the plurality of permanent magnets 22 and 23 and the inner peripheral surface of the cylindrical portion 11.

[0040] [Regarding the braking and non-braking operations of the eddy current type speed reduction device 1] Referring to FIG. 4, when not in braking, when viewed in the radial direction of the eddy current type speed reduction device 1, each permanent magnet 22 and each permanent magnet 23 are arranged so as to overlap with two adjacent pole pieces 24. In other words, when viewed in the radial direction of the eddy current type speed reduction device 1, one pole piece 24 is arranged so as to straddle the adjacent permanent magnets 22 and 23. In this case, the magnetic flux B flows through the stator 20 as shown in FIG. 4. Specifically, the magnetic flux B flows between the permanent magnets 22 and 23, the pole pieces 24, and the magnet holding ring 21. Therefore, no magnetic circuit is formed between the rotor 10 and the permanent magnets 22 and 23, and no Lorentz force is generated on the rotor 10. Therefore, in FIG. 4, the braking force does not act.

[0041] FIG. 5 is a cross-sectional view (radial cross-sectional view) perpendicular to the axial direction of the eddy current type deceleration device 1 during braking. During braking, the magnet holding ring 21 in the stator 20 rotates, shifting the relative positions of the permanent magnets 22 and 23 with respect to the pole piece 24 as compared to FIG. 4. Specifically, in FIG. 5, during braking, when viewed in the radial direction of the eddy current type deceleration device 1, each permanent magnet 22 or 23 is disposed directly below the pole piece 24. That is, each of the permanent magnets 22 and 23 is arranged so as to overlap only one pole piece 24. In this case, as shown in FIG. 5, the magnetic flux B flows between the magnet holding ring 21, the permanent magnet 22 or 23, the pole piece 24, and the cylindrical portion 11. Therefore, 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. Along with the generation of the eddy currents, Lorentz forces are generated. These Lorentz forces become braking torques, generating braking forces.

[0042] As described above, the eddy current type deceleration device 1 generates a braking force by the eddy currents generated in the rotor 10. Therefore, it is preferable that the amount of eddy currents generated in the cylindrical portion 11 of the rotor 10 is large. This is because the braking force becomes large. The smaller the electrical resistance of the cylindrical portion 11, the larger the amount of eddy currents generated. Therefore, it is preferable that the cylindrical portion 11 of the rotor 10 has a small electrical resistance. The rotor 10 is further subjected to thermal cycles by repeating braking and non-braking. As described above, recently, it has been required to obtain not only a low electrical resistance but also a high high-temperature strength. Hereinafter, the rotor 10 will be described in detail.

[0043] [Regarding the Rotor 10 for Eddy Current Type Deceleration Device] [Chemical Composition] The chemical composition of the cylindrical portion 11 of the rotor 10 for the eddy current type deceleration device of the present embodiment contains the following elements. “%” regarding the elements means mass % unless otherwise specified.

[0044] [Regarding Essential Elements] C: 0.05 to 0.15% Carbon (C) enhances the hardenability of the steel material constituting the rotor and increases the strength of the steel material. C further forms fine carbides such as V carbide and medium carbides such as cementite to increase the high-temperature strength of the steel material. If the C content is less than 0.05%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the C content exceeds 0.15%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material excessively increases. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases during braking of the eddy current type deceleration device 1. As a result, the braking force of the eddy current type deceleration device 1 decreases. If the C content exceeds 0.15%, furthermore, even if the contents of other elements are within the range of this embodiment, the toughness of the steel material may decrease. Therefore, the C content is 0.05 to 0.15%. The preferable lower limit of the C content is 0.06%, more preferably 0.07%, and even more preferably 0.08%. The preferable upper limit of the C content is 0.14%, more preferably 0.13%, and even more preferably 0.12%.

[0045] Si: 0.01 - 0.15% Silicon (Si) deoxidizes the steel in the steelmaking process. Si further enhances the hardenability of the steel material and increases the strength of the steel material. If the Si content is less than 0.01%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the Si content exceeds 0.15%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material excessively increases. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases during braking of the eddy current type deceleration device 1. As a result, the braking force of the eddy current type deceleration device 1 decreases. Therefore, the Si content is 0.01 to 0.15%. The preferable lower limit of the Si content is more than 0.01%, more preferably 0.02%, and even more preferably 0.03%. The preferable upper limit of the Si content is 0.12%, more preferably 0.10%, and even more preferably less than 0.10%.

[0046] Mn: 0.10 - 1.00% Manganese (Mn) deoxidizes steel in the steelmaking process. Mn further increases the hardenability of the steel material and increases the strength of the steel material. If the Mn 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 sufficiently obtained. On the other hand, if the Mn content exceeds 1.00%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material excessively increases. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases during the braking of the eddy current type deceleration device 1. As a result, the braking force of the eddy current type deceleration device 1 decreases. If the Mn content exceeds 1.00%, furthermore, even if the contents of other elements are within the range of this embodiment, the austenite phase becomes stable and A c1 The transformation point drops, and there may be a case where the tempering temperature cannot be raised to 700 °C or higher. Therefore, the Mn content is 0.10 to 1.00%. The preferable lower limit of the Mn content is 0.15%, more preferably 0.20%, still more preferably 0.25%, and still more preferably 0.30%. The preferable upper limit of the Mn content is 0.95%, more preferably 0.90%, still more preferably 0.85%, and still more preferably 0.80%.

[0047] P: 0.030% or less Phosphorus (P) is an impurity that is inevitably contained. That is, the P content is more than 0%. P reduces the hot workability and toughness of the steel material. P further increases the electrical resistance of the steel material. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases during braking of the eddy current decelerator 1. As a result, the braking force of the eddy current decelerator 1 decreases. If the P content exceeds 0.030%, even if the contents of other elements are within the range of this embodiment, the hot workability and toughness of the steel material are significantly reduced, and furthermore, the braking force of the eddy current decelerator 1 decreases. Therefore, the P content is 0.030% or less. The preferable upper limit of the P content is 0.028%, more preferably 0.026%, and even more preferably 0.025%. It is preferable that the P content is 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 0.001%, more preferably 0.003%.

[0048] S: 0.030% or less Sulfur (S) is an impurity that is inevitably contained. That is, the S content is more than 0%. S reduces the hot workability and toughness of the steel material. S further increases the electrical resistance of the steel material. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases during braking of the eddy current decelerator 1. As a result, the braking force of the eddy current decelerator 1 decreases. If the S content exceeds 0.030%, even if the contents of other elements are within the range of this embodiment, the hot workability and toughness of the steel material are significantly reduced, and furthermore, the braking force of the eddy current decelerator 1 decreases. Therefore, the S content is 0.030% or less. The preferable upper limit of the S content is 0.025%, more preferably 0.022%, and even more preferably 0.020%. It is preferable that the S content is as low as possible. However, excessive reduction of the S content increases the manufacturing cost. Therefore, considering normal industrial production, the preferable lower limit of the S content is 0.001%, more preferably 0.002%.

[0049] Cr: 0.30 - 2.00% Chromium (Cr) enhances the hardenability of steel materials and increases the high-temperature strength of steel materials. Cr further forms carbides to increase the high-temperature strength of steel materials. If the Cr content is less than 0.30%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the Cr content exceeds 1.30%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material will increase excessively. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current decelerator 1 decreases during braking of the eddy current decelerator 1. As a result, the braking force of the eddy current decelerator 1 decreases. Therefore, the Cr content is 0.30 to 2.00%. The preferable lower limit of the Cr content is 0.35%, more preferably 0.40%, still more preferably 0.45%, and even more preferably 0.50%. The preferable upper limit of the Cr content is 1.90%, more preferably 1.80%, still more preferably 1.75%.

[0050] Mo: 0.30 to 1.50% Molybdenum (Mo) enhances the hardenability of steel materials and increases the high-temperature strength of steel materials. Mo further forms carbides to increase the high-temperature strength of steel materials. Mo further enhances the toughness of steel materials. If the Mo content is less than 0.30%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the Mo content exceeds 1.50%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material will increase excessively. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current decelerator 1 decreases during braking of the eddy current decelerator 1. As a result, the braking force of the eddy current decelerator 1 decreases. Therefore, the Mo content is 0.30 to 1.50%. The preferable lower limit of the Mo content is 0.32%, more preferably 0.35%, still more preferably 0.38%, and even more preferably 0.40%. The preferable upper limit of the Mo content is 1.40%, more preferably 1.35%, still more preferably 1.30%, and even more preferably 1.25%.

[0051] V: 0.02 to 0.15% Vanadium (V) forms carbides to enhance the high-temperature strength of steel materials. V further suppresses the coarsening of crystal grains. If the V content is less than 0.02%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the V content exceeds 0.15%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material excessively increases. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases during the braking of the eddy current type decelerator 1. As a result, the braking force of the eddy current type decelerator 1 decreases. Therefore, the V content is 0.02 to 0.15%. The preferable lower limit of the V content is 0.03%, more preferably 0.04%, and even more preferably 0.05%. The preferable upper limit of the V content is 0.13%, more preferably 0.11%, and even more preferably 0.10%.

[0052] Nb: 0.01 - 0.10% Niobium (Nb) forms carbides to enhance the high-temperature strength of steel materials. Nb further suppresses the coarsening of crystal grains. If the Nb content is less than 0.01%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the Nb content exceeds 0.10%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material excessively increases. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases during the braking of the eddy current type decelerator 1. As a result, the braking force of the eddy current type decelerator 1 decreases. Therefore, the Nb content is 0.01 to 0.10%. The preferable lower limit of the Nb content is 0.02%, more preferably 0.03%, and even more preferably 0.04%. The preferable upper limit of the Nb content is 0.09%, more preferably 0.08%, and even more preferably 0.06%.

[0053] sol.Al: 0.001 - 0.040% Aluminum (Al) combines with nitrogen (N) to form AlN, which refines the crystal grains of steel. If the sol.Al content is less than 0.001%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the sol.Al content exceeds 0.040%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel will increase excessively. When the electrical resistance of the steel increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 during braking of the eddy current decelerator 1 decreases. As a result, the braking force of the eddy current decelerator 1 decreases. Therefore, the sol.Al content is 0.001 to 0.040%. The preferable lower limit of the sol.Al content is 0.005%, more preferably 0.010%, and even more preferably 0.015%. The preferable upper limit of the sol.Al content is less than 0.040%, more preferably 0.038%, even more preferably 0.035%, and even more preferably 0.030%. Note that the "sol.Al" content referred to in this specification means the content of "acid-soluble Al".

[0054] B: 0.0005 to 0.0050% Boron (B) increases the hardenability of the steel material and increases the high-temperature strength of the steel material. If the B content is less than 0.0005%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the B content exceeds 0.0050%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material will increase excessively. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases during the braking of the eddy current type deceleration device 1. As a result, the braking force of the eddy current type deceleration device 1 decreases. If the B content exceeds 0.0050%, furthermore, the toughness of the steel material may decrease. Therefore, the B content is 0.0005 to 0.0050%. The preferable lower limit of the B content is 0.0008%, more preferably 0.0010%, still more preferably 0.0012%, still more preferably 0.0014%, and still more preferably 0.0015%. The preferable upper limit of the B content is 0.0045%, more preferably 0.0040%, still more preferably 0.0035%, and still more preferably 0.0030%.

[0055] N: 0.001 to 0.010% Nitrogen (N) forms AlN and / or TiN to increase the high-temperature strength of the steel material. AlN and / or TiN further refine the crystal grains of the steel material. If the N content is less than 0.001%, even if the contents of other elements are within the range of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the N content exceeds 0.010%, even if the contents of other elements are within the range of this embodiment, BN is formed to reduce the high-temperature strength of the steel material. Therefore, the N content is 0.001 to 0.010%. The preferable lower limit of the N content is 0.002%. The preferable upper limit of the N content is 0.009%, more preferably 0.008%, still more preferably 0.006%, and still more preferably 0.005%.

[0056] The remainder of the chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current type speed reducer 1 according to the present embodiment consists of Fe and impurities. Here, the impurities are those mixed from ores, scraps, or manufacturing environments as raw materials when industrially manufacturing the cylindrical portion 11 of the rotor 10 of the present embodiment, and are those allowed within a range that does not adversely affect the cylindrical portion 11 of the rotor 10 of the present embodiment.

[0057] [Regarding optional elements] The chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current type speed reducer 1 according to the present embodiment may further contain one or more elements selected from the group consisting of Cu, Ni, and Ti in place of a part of Fe. All of these elements are optional elements and increase the high-temperature strength of the steel material.

[0058] Cu: 0 to 0.20% Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. When Cu is contained, Cu increases the hardenability of the steel material and increases the high-temperature strength of the steel material. If even a little Cu is contained, the above effects can be obtained to a certain extent. However, if the Cu content exceeds 0.20%, even if the contents of other elements are within the range of the present embodiment, the electrical resistance of the steel material excessively increases. If the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current type speed reducer 1 decreases during braking of the eddy current type speed reducer 1. As a result, the braking force of the eddy current type speed reducer 1 decreases. Therefore, the Cu content is 0 to 0.20%, and when Cu is contained, the Cu content is 0.20% or less. The preferable lower limit of the Cu content is more than 0%, more preferably 0.01%, still more preferably 0.02%, and still more preferably 0.03%. The preferable upper limit of the Cu content is 0.15%, more preferably 0.12%, and still more preferably 0.10%.

[0059] Ni: 0 to 0.20% Nickel (Ni) is an optional element and may not be contained. That is, the Ni content may be 0%. When Ni is contained, Ni enhances the hardenability of the steel material and increases the high-temperature strength of the steel material. Even if 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 range of this embodiment, the electrical resistance of the steel material will increase excessively. If the electrical resistance of the steel material increases, when the eddy current type deceleration device 1 is braked, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current type deceleration device 1 will decrease. As a result, the braking force of the eddy current type deceleration device 1 will decrease. Therefore, the Ni content is 0 to 0.20%, and when Ni is contained, the Ni content is 0.20% or less. The preferable lower limit of the Ni content is more than 0%, more preferably 0.01%, still more preferably 0.02%, and still more preferably 0.03%. The preferable upper limit of the Ni content is 0.15%, more preferably 0.12%, and still more preferably 0.10%.

[0060] Ti: 0 to 0.050% Titanium (Ti) is an optional element and may not be contained. That is, the Ti content may be 0%. When Ti is contained, Ti forms titanium carbonitride to increase the high-temperature strength of the steel material. Ti further forms TiN to suppress the coarsening of crystal grains. Even if a small amount of Ti is contained, the above effects can be obtained to a certain extent. However, if the Ti content exceeds 0.050%, even if the contents of other elements are within the range of this embodiment, the electrical resistance of the steel material will increase excessively. If the electrical resistance of the steel material increases, when the eddy current type decelerator 1 is braked, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current type decelerator 1 will decrease. As a result, the braking force of the eddy current type decelerator 1 will decrease. If the Ti content exceeds 0.050%, furthermore, the toughness of the steel material will decrease. Therefore, the Ti content is 0 to 0.050%, and when Ti is contained, the Ti content is 0.050% or less. The preferable lower limit of the Ti content is more than 0%, more preferably 0.001%, still more preferably 0.003%, and still more preferably 0.005%. The preferable upper limit of the Ti content is 0.040%, more preferably 0.030%, and still more preferably 0.020%.

[0061] [Regarding formula (1)] The chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current type decelerator 1 of this embodiment satisfies the following formula (1) in addition to satisfying the above chemical composition. Cr + 4Si + 3sol.Al + Mo ≦ 3.00 (1) Here, the content of the corresponding element in the chemical composition of the cylindrical portion 11 of the rotor 10 of this embodiment is substituted in mass% for each element symbol in formula (1).

[0062] F1(=Cr + 4Si + 3sol.Al + Mo) is an index indicating the height of electrical resistance in the rotor 10 for an eddy current reduction device having a cylindrical portion 11 with the above-described chemical composition. That is, F1 is an index indicating the height of electrical resistance on the premise that the cylindrical portion 11 of the rotor 10 for the eddy current reduction device has the above-described chemical composition. If F1 exceeds 3.00, even if the element content in the chemical composition is within the range of this embodiment, the electrical resistance of the steel material will increase excessively. When the electrical resistance of the steel material increases, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current reduction device 1 decreases during braking of the eddy current reduction device 1. As a result, the braking force of the eddy current reduction device 1 decreases. Therefore, in the chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current reduction device 1 of this embodiment, F1 is 3.00 or less. As a result, the rotor 10 of this embodiment can not only enhance the high-temperature strength but also sufficiently reduce the electrical resistance.

[0063] In the chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current reduction device 1 of this embodiment, the preferable upper limit of F1 is 2.95, more preferably 2.90, still more preferably 2.85, and still more preferably 2.80. In the chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current reduction device 1 of this embodiment, the lower limit of F1 is not particularly limited. However, in the cylindrical portion 11 of the rotor 10 of the eddy current reduction device 1 of this embodiment on the premise of the above-described chemical composition, the lower limit of F1 is determined from the lower limit values of each component. That is, in the cylindrical portion 11 of this embodiment, the lower limit of F1 obtained from the above-described chemical composition is 0.64. In this embodiment, F1 is taken as the value obtained by rounding off the third decimal place of the calculated numerical value.

[0064] [Regarding the microstructure] The cylindrical portion 11 of the rotor 10 of the present embodiment has a microstructure in which the total area ratio of martensite and bainite is 99% or more. That is, the microstructure of the cylindrical portion 11 of the rotor 10 for the eddy current type speed reducer of the present embodiment is mainly composed of martensite and / or bainite. "Martensite and bainite" as used in this specification also includes tempered martensite and tempered bainite. In the microstructure of the cylindrical portion 11 of the rotor 10 of the present embodiment, the remainder other than martensite and bainite is ferrite. That is, the area ratio of ferrite is 1% or less.

[0065] In addition, in the microstructure of the cylindrical portion 11, in addition to martensite, bainite, and ferrite, there are also precipitates typified by the above-mentioned carbides and inclusions. However, these precipitates and inclusions are extremely small, and it is difficult to confirm their area by the microstructure observation described later. Therefore, when obtaining the area ratios of martensite, bainite, and ferrite, the precipitates and inclusions are to be ignored. Thus, the precipitates and inclusions existing in martensite and bainite are included in the area ratios of martensite and bainite, and the precipitates and inclusions existing in ferrite are included in the area ratio of ferrite.

[0066] Also, in the microstructure observation described later, it is extremely difficult to distinguish between martensite and bainite. On the other hand, ferrite, martensite, and bainite can be extremely easily distinguished by contrast. Therefore, in the microstructure observation, the region other than ferrite is recognized as "martensite and bainite".

[0067] The microstructure of the cylindrical portion 11 of the rotor 10 for the eddy current type reduction gear of the present embodiment also affects the strength. In the microstructure of the cylindrical portion 11 of the rotor 10 for the eddy current type reduction gear of the present embodiment, when the total area ratio of martensite and bainite is 99% or less and the area ratio of ferrite exceeds 1%, sufficient high-temperature strength cannot be obtained even if the above-described chemical composition including F1 is satisfied. On the other hand, if the total area ratio of martensite and bainite is 99% or more and the area ratio of ferrite is 1% or less, high high-temperature strength can be obtained on the premise that the content of each element in the chemical composition is within the range of the present embodiment.

[0068] In the present embodiment, the total area ratio of martensite and bainite and the area ratio of ferrite 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 later can be secured. Of the surface of the sample, an observation surface including the above-described observation field is mirror-polished. The mirror-polished sample is immersed in nital solution for about 10 seconds for etching to reveal the structure on the observation surface. Any one field (observation field) in the observation surface where the structure is revealed by etching is observed with an optical microscope at 500 times magnification. The field area of the observation field is 20000 μm 2 (200 μm × 100 μm).

[0069] As described above, in the observation field, ferrite, martensite, and bainite can be easily distinguished based on the contrast. Therefore, ferrite in the observation field is specified, and the area of the specified ferrite is obtained. The area of ferrite is divided by the total area of the observation field to obtain the area ratio (%) of ferrite. Note that the area ratio (%) of ferrite is a value obtained by rounding off the second decimal place of the calculated value. As described above, in the microstructure of the cylindrical portion 11 of the rotor 10 of the present embodiment, the remainder other than ferrite is martensite and / or bainite. Therefore, the total area (%) of martensite and bainite is obtained by the following formula. Total area ratio of martensite and bainite = 100.0 - area ratio (%) of ferrite

[0070] [High-temperature strength] The cylindrical portion 11 of the rotor 10 of the present embodiment has a yield stress of 120 to 250 MPa at 700°C. The yield stress referred to in this specification means the 0.2% proof stress obtained in the tensile test at 700°C described below. In the cylindrical portion 11 of the rotor 10 of the present embodiment, if the yield stress at 700°C is less than 120 MPa, the desired high-temperature strength cannot be obtained. On the other hand, in the cylindrical portion 11 of the rotor 10 of the present embodiment, if the yield stress at 700°C exceeds 250 MPa, the high-temperature strength becomes too high, and the toughness of the cylindrical portion 11 may decrease. Therefore, in the present embodiment, the cylindrical portion 11 of the rotor 10 has a yield stress of 120 to 250 MPa at 700°C.

[0071] The preferable lower limit of the yield stress at 700°C of the cylindrical portion 11 of the rotor 10 of the present embodiment is 125 MPa, and more preferably 130 MPa. The preferable upper limit of the yield stress at 700°C of the cylindrical portion 11 of the rotor 10 of the present embodiment is 245 MPa, and more preferably 240 MPa.

[0072] In the present embodiment, the yield stress (MPa) at 700°C of the cylindrical portion 11 of the rotor 10 is obtained by conducting a tensile test in accordance with JIS G 0567 (2012). Specifically, a tensile test piece is taken from the central position of the wall thickness of the cylindrical portion 11 of the rotor 10. The tensile test piece has a parallel portion length of 40 mm and a parallel portion diameter of 6 mm. The parallel portion of the tensile test piece is parallel to the central axis of the cylindrical portion 11. The tensile test piece is heated using a heating furnace to bring the temperature of the tensile test piece to 700°C and held for 10 minutes. A tensile test is conducted on the tensile test piece held at 700°C for 10 minutes in the atmosphere to obtain a stress-strain curve. The 0.2% proof stress based on the offset method is defined as the yield stress (MPa) from the obtained stress-strain curve. In the present embodiment, the yield stress (MPa) at 700°C is the value obtained by rounding off the first decimal place of the calculated numerical value.

[0073] [Electrical resistance] The cylindrical portion 11 of the rotor 10 according to the present embodiment has the above-described chemical composition including the formula (1) and the above-described microstructure. As a result, the cylindrical portion 11 of the rotor 10 according to the present embodiment exhibits low electrical resistance even when the yield stress at 700 °C is 120 to 250 MPa. In the present embodiment, the electrical resistance of the cylindrical portion 11 can be evaluated by a method conforming to JIS C 2526 (1994).

[0074] Specifically, a test piece including the central position of the thickness of the cylindrical portion 11 of the rotor 10 is taken. The test piece is a standard test piece of 3 mm × 4 mm × 60 mm. At room temperature (20 ± 15 °C), the electrical resistance (μΩcm) of the test piece is obtained by the double bridge method. In the present embodiment, the electrical resistance (μΩcm) of the test piece is a value obtained by rounding off the second decimal place of the calculated numerical value. If the obtained electrical resistance is 20.5 μΩcm or less, it can be evaluated that the cylindrical portion 11 has low electrical resistance.

[0075] [Manufacturing method] An example of a manufacturing method of the rotor 10 for the eddy current type reduction gear according to the present embodiment will be described. The manufacturing method described hereinafter is an example for manufacturing the rotor 10 for the eddy current type reduction gear according to the present embodiment. Therefore, the rotor 10 for the eddy current type reduction gear 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 rotor 10 for the eddy current type reduction gear according to the present embodiment.

[0076] The manufacturing method of the rotor 10 for the eddy current type reduction gear according to the present embodiment includes a preparation step of manufacturing an intermediate product corresponding to the cylindrical portion 11, a quenching step of performing quenching on the prepared intermediate product, a tempering step of performing tempering on the quenched intermediate product, a processing step of processing the tempered intermediate product to form the cylindrical portion 11, and a rotor forming step of manufacturing the rotor 10 for the eddy current type reduction gear using the cylindrical portion 11. Hereinafter, each step will be described.

[0077] [Preparation step] In the preparation process, an intermediate product having the above-described chemical composition is prepared. The intermediate product here corresponds to the cylindrical portion 11. If the intermediate product has the above-described chemical composition, the manufacturing method of the intermediate product is not particularly limited. The preparation process may include, for example, a process of preparing a material (material preparation process) and a process of performing hot working on the prepared material to manufacture the intermediate product (hot working process). Hereinafter, the case including the material preparation process and the hot working process will be described in detail.

[0078] [Material Preparation Process] In the material preparation process, a material having a chemical composition with each element content within the range of the present embodiment is prepared. The material may be supplied from a third party. The material may be manufactured. When manufacturing, for example, it is manufactured by the following method.

[0079] Molten steel having a chemical composition with each element content within the range of the present embodiment is manufactured. The refining method is not particularly limited, and a well-known method may be used. For example, refining (primary refining) in a converter is performed on hot metal manufactured by a well-known method. Well-known secondary refining is performed on the molten steel tapped from the converter. In the secondary refining, alloying elements for component adjustment are added to manufacture molten steel having a chemical composition with each element content within the range of the present embodiment.

[0080] Using the molten steel manufactured by the above-described refining method, a material is manufactured by a well-known casting method. For example, an ingot may be manufactured by an ingot casting method using molten steel. Alternatively, a bloom or a billet may be manufactured by a continuous casting method using molten steel. After heating the manufactured bloom or ingot to 1000 to 1300 °C, hot working may be performed to manufacture a billet. The hot working is, for example, hot rolling, hot forging, etc. The manufactured billet (a billet manufactured by continuous casting or a billet manufactured by hot working a bloom or an ingot) is used as the material for the rotor 10 of the eddy current decelerator.

[0081] [Hot Working Process] Hot working is performed on the material prepared in the material preparation process to manufacture an intermediate product corresponding to the cylindrical portion 11. The hot working may be hot forging, or may be hot forging and hot rolling. In this case, first, the material is heated to 1000 to 1300 °C. Hot forging is performed on the heated material to form it into a predetermined dimension. After hot forging, hot rolling may be further performed.

[0082] As described above, an intermediate product is prepared in the preparation process. The intermediate product may be prepared by the above-described material preparation process and hot working process, or may be prepared by purchasing an intermediate product manufactured by a third party. Hereinafter, the quenching process will be described in detail.

[0083] [Quenching Process] In the quenching process, quenching is performed on the intermediate product prepared in the above-described preparation process. In this specification, "quenching" means quenching intermediate products at A 3 points or more. In the quenching process, the quenching temperature is, for example, 880 °C or higher. In this specification, the quenching temperature means the temperature of the intermediate product before quenching. If the quenching temperature is too low, precipitates such as carbides may not dissolve sufficiently in the microstructure of the intermediate product. In this case, in the tempering process described later, the precipitates coarsen, and the high-temperature strength of the manufactured rotor 10 decreases. If the quenching temperature is too low, furthermore, the microstructure of the intermediate product does not transform into a single austenite phase, and ferrite may remain in the microstructure of the manufactured rotor 10 in an amount exceeding 1%. In this case, the high-temperature strength of the rotor 10 decreases. Therefore, in this embodiment, a preferable quenching temperature is 880 °C or higher. In the quenching process according to this embodiment, a more preferable lower limit of the quenching temperature is 890 °C, and more preferably 900 °C. The upper limit of the quenching temperature is not particularly limited, but is, for example, 970 °C.

[0084] In the quenching process, when the intermediate product is heated and held and then rapidly cooled, the time for holding at the quenching temperature is, for example, 0.5 to 3.0 hours. In the quenching process, it is sufficient if the intermediate product can be cooled at a cooling rate faster than natural cooling. Methods for rapidly cooling the intermediate product include, for example, water cooling, mist cooling, and oil cooling. In the quenching process, the average cooling rate from the cooling start temperature (quenching temperature) to 400°C is, for example, 2 to 20°C / sec. The tempering process will be described in detail below.

[0085] [Tempering process] In the tempering process, the intermediate product that has been quenched in the quenching process is tempered. c1 The tempering temperature is preferably 700°C to 100°C. c1 The tempering temperature is less than the tempering temperature point. Usually, the higher the tempering temperature, the lower the high-temperature strength tends to be. However, as described above, in the rotor 10 according to the present embodiment, the Cr content is increased in the chemical composition of the cylindrical portion 11. Therefore, in the tempering process according to the present embodiment, tempering at a high temperature can also be performed.

[0086] Here, when tempering is performed on an intermediate product having the above-mentioned chemical composition, if the tempering temperature is 700°C or higher, the rotor 10 is heated by Joule heat generated together with eddy currents during braking, and even if the temperature reaches a high temperature exceeding 650°C and reaching approximately 700°C, changes in the microstructure are unlikely to occur. Also, if the tempering temperature is less than 700°C, the toughness of the steel material may decrease. Therefore, the tempering temperature is preferably 700°C or higher. On the other hand, if the tempering temperature is A c1 If the tempering temperature is above this point, austenite may remain in part of the microstructure of the intermediate product, or precipitates such as carbides may become coarse. In this case, the high-temperature strength may decrease. Therefore, in the tempering process according to this embodiment, the tempering temperature is set to 700° C. to 700° C. c1 It is preferable that the holding time for tempering is, for example, 0.5 to 5.0 hours. The cooling method after tempering is, for example, natural cooling.

[0087] [Processing Step] In the processing step, the intermediate product that has been tempered in the above-mentioned tempering step is processed to form the cylindrical portion 11. Specifically, the cooling fins 11F are formed by machining the outer peripheral surface of the intermediate product after tempering. The machining can be carried out by a well-known method. Through the above steps, the cylindrical portion 11 is manufactured.

[0088] [Rotor Forming Step] In the rotor forming step, the manufactured cylindrical portion 11 is used to manufacture the rotor 10 for the eddy current type reduction gear. Specifically, the arm portion 12 attached to the wheel portion 13 is attached to the manufactured cylindrical portion 11 to manufacture the rotor 10 for the eddy current type reduction gear. The attachment method may be welding or other methods.

[0089] By the above manufacturing method, the rotor 10 for the eddy current type reduction gear of the present embodiment can be manufactured. Note that the rotor 10 for the eddy current type reduction gear of the present embodiment is not limited to the above manufacturing method, and if the rotor 10 for the eddy current type reduction gear having the above configuration can be manufactured, the rotor 10 for the eddy current type reduction gear of the present embodiment may be manufactured by other manufacturing methods other than the above manufacturing method. However, the above manufacturing method is a preferred example for manufacturing the rotor 10 for the eddy current type reduction gear of the present embodiment. Hereinafter, the rotor 10 for the eddy current type reduction gear according to the present embodiment will be described more specifically by way of examples.

Example

[0090] Steel having the chemical composition shown in Table 1 was manufactured. Also, F1 (= Cr + 4Si + 3sol.Al + Mo) obtained from the chemical composition shown in Table 1 and the above-mentioned definition is shown in Table 1.

[0091]

Table 1

[0092] The "-" in Table 1 means that the content of the corresponding element was less than the detection limit. For example, the Cu content and Ni content of Test No. 1 mean that the rounded value to the third decimal place was 0%. The Ti content of Test No. 1 means that the rounded value to the fourth decimal place was 0%. Using molten steel, cylindrical ingots with a diameter of 120 mm and a weight of 30 kg were produced by the ingot casting method.

[0093] After heating the ingot to 1250 °C, hot forging was carried out to produce a steel plate with a thickness of 30 mm as a pseudo-intermediate product. For the pseudo-intermediate product, quenching (oil cooling) was carried out by holding it at the quenching temperature (°C) shown in Table 2 for the quenching time (hours) and then rapidly cooling. Tempering was carried out on the pseudo-intermediate products of each test number after quenching. Specifically, tempering was carried out by holding it at the tempering temperature (°C) shown in Table 2 for the tempering time (hours). Through the above manufacturing process, pseudo-rotors (steel plates) of each test number, which simulated the rotor for the eddy current decelerator, were produced.

[0094]

Table 2

[0095] [Evaluation Test] The following evaluation tests were carried out on the pseudo-rotors of each test number produced.

[0096] [Microstructure Observation Test] Samples were taken from the central position of the plate thickness of the pseudo-rotors of each test number. After mirror-polishing the surface of the samples, they were immersed in nital solution for about 10 seconds for etching to reveal the microstructure. An arbitrary 1 field of view (observation field of view) on the surface where the microstructure was revealed by etching was observed with an optical microscope at 500 times magnification. The field area of the observation field of view was 20000 μm 2 (200 μm × 10 It was 0 μm. By contrast, the phases in the observation field of view were specified. As a result, the microstructure in the observation field of view consisted of martensite, bainite, and ferrite. The area of the specified ferrite was determined. The ferrite area ratio (%) was determined by dividing the ferrite area by the total area of the observation field of view. As described above, in the microstructure in the observation field of view, the remainder other than ferrite was martensite and / or bainite. Therefore, the total area (%) of martensite and bainite was determined by the following formula. Total area ratio of martensite and bainite = 100.0 - ferrite area ratio For the pseudo-rotors of each test number, the obtained total area ratio (%) of martensite and bainite is shown in Table 2.

[0097] [Tensile test at 700°C] The yield stress (MPa) at 700°C of the pseudo-rotors of each test number was determined by a tensile test in accordance with JIS G 0567 (2012). Specifically, tensile test pieces were taken from the pseudo-rotors of each test number. The length of the parallel part of the tensile test piece was 40 mm, and the diameter of the parallel part was 6 mm. The tensile test pieces were heated to 700°C using a heating furnace and held for 10 minutes. A tensile test was carried out on the tensile test pieces held at 700°C for 10 minutes in the air to obtain a stress-strain curve. The 0.2% proof stress determined based on the offset method from the obtained stress-strain curve was taken as the yield stress (MPa). For the pseudo-rotors of each test number, the obtained yield stress (MPa) at 700°C is shown in Table 2.

[0098] [Method for measuring electrical resistance] The electrical resistance at room temperature of the pseudo-rotors of each test number was determined by a method in accordance with JIS C 2526 (1994). Specifically, test pieces were taken from the pseudo-rotors of each test number. The size of the test piece was 3 mm × 4 mm × 60 mm. The electrical resistance (μΩcm) of the test piece was determined by the double bridge method at room temperature. For the pseudo-rotors of each test number, the obtained electrical resistance (μΩcm) is shown in Table 2.

[0099] [Test results] Referring to Table 1 and Table 2, the content of each element in the chemical composition of the dummy rotors of Test Nos. 1 to 15 was appropriate, satisfying Formula (1), and the total area ratio of martensite and bainite was 99% or more. As a result, the yield stress at 700 °C satisfied 120 to 250 MPa, showing sufficiently high high-temperature strength as the rotor of the eddy current decelerator. Furthermore, the electrical resistance was 20.5 μΩcm or less, showing sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0100] On the other hand, for the dummy rotor of Test No. 16, the quenching temperature was too low, and the total area ratio of martensite and bainite was less than 99%. As a result, the yield stress at 700 °C was less than 120 MPa, and it did not show sufficiently high high-temperature strength as the rotor of the eddy current decelerator.

[0101] For the dummy rotor of Test No. 17, the tempering temperature was too low. As a result, the yield stress at 700 °C exceeded 250 MPa, and it did not show the desired mechanical properties as the rotor of the eddy current decelerator.

[0102] For the dummy rotors of Test Nos. 18 to 22, F1 was too high. As a result, the electrical resistance exceeded 20.5 μΩcm, and it did not show sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0103] For the dummy rotor of Test No. 23, the C content was too low. As a result, the yield stress at 700 °C was less than 120 MPa, and it did not show sufficiently high high-temperature strength as the rotor of the eddy current decelerator.

[0104] For the dummy rotor of Test No. 24, the C content was too high. As a result, the electrical resistance exceeded 20.5 μΩcm, and it did not show sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0105] For the dummy rotor of Test No. 25, the Si content was too high. As a result, the electrical resistance exceeded 20.5 μΩcm, and it did not show sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0106] The dummy rotor of Test No. 26 had too high an Mn content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator. Also, because the Mn content was too high, the austenite phase became stable and the A c1 transformation point dropped, and it was necessary to perform low-temperature tempering. As a result, the yield stress at 700 °C exceeded 250 MPa and did not show the desired mechanical properties as the rotor of the eddy current decelerator.

[0107] The dummy rotor of Test No. 27 had too high a P content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0108] The dummy rotor of Test No. 28 had too high an S content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0109] The dummy rotor of Test No. 29 had too low a Cr content. As a result, the yield stress at 700 °C was less than 120 MPa and did not show a sufficiently high high-temperature strength as the rotor of the eddy current decelerator.

[0110] The dummy rotor of Test No. 30 had too high a Cr content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0111] The dummy rotor of Test No. 31 had too high a Mo content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0112] The dummy rotor of Test No. 32 had too high a V content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0113] The dummy rotor of Test No. 33 had too high an Nb content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0114] The dummy rotor of Test No. 34 had too high a sol.Al content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0115] The dummy rotor of Test No. 35 had too high a B content. As a result, the electrical resistance exceeded 20.5 μΩcm and did not show a sufficiently low electrical resistance as the rotor of the eddy current decelerator.

[0116] The dummy rotor of Test No. 36 had too high an N content. As a result, the yield stress at 700 °C was less than 120 MPa and did not show a sufficiently high high-temperature strength as the rotor of the eddy current decelerator.

[0117] 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 the above-described embodiments can be appropriately modified and implemented without departing from the spirit thereof.

Description of Reference Numerals

[0118] 1 Eddy current decelerator 10 Rotor 11 Cylindrical portion 12 Arm portion 13 Wheel portion 20 Stator

Claims

1. A rotor for an eddy current reduction gear, comprising: a cylindrical portion, wherein the cylindrical portion has, by mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, and consists of the balance: Fe and impurities, and has a chemical composition satisfying formula (1); a microstructure in which the total area ratio of martensite and bainite is 99% or more; and a yield stress of 120 to 250 MPa at 700°C. A rotor for an eddy current reduction gear. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in each element symbol in formula (1), the content of the corresponding element is substituted in mass%.

2. A rotor for an eddy current reduction gear, comprising: a cylindrical portion, wherein the cylindrical portion has, by mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, sol.Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, and further contains Cu: 0.20% or less, Ni: 0.20% or less, and Ti: 0.050% or less, and consists of the balance: Fe and impurities, and has a chemical composition satisfying formula (1); a microstructure in which the total area ratio of martensite and bainite is 99% or more; and a yield stress of 120 to 250 MPa at 700°C. A rotor for an eddy current reduction gear. Cr + 4Si + 3sol.Al + Mo ≤ 3.00 (1) Here, in each element symbol in formula (1), the content of the corresponding element is substituted in mass%.

3. A method for manufacturing a rotor for an eddy current reduction gear, comprising: by mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, ​ ​ ​ ​ Sol. Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, are contained, The balance: Fe and impurities, and prepare an intermediate product having a chemical composition satisfying formula (1); a preparation step, A quenching step of performing quenching on the intermediate product, For the intermediate product after the quenching step, a tempering step is performed in which tempering is carried out by holding at a temperature of less than 700 °C to A c1 and a tempering step of performing tempering by holding at a temperature of less than the A point A processing step of processing the intermediate product after the tempering step to form a cylindrical portion, A rotor forming step of manufacturing a rotor for an eddy current reduction device using the cylindrical portion, and comprising: The method for manufacturing a rotor for an eddy current reduction device according to claim 1. Cr + 4Si + 3Sol. Al + Mo ≤ 3.00 (1) Here, in each element symbol in formula (1), the content of the corresponding element is substituted in mass%.

4. A method for manufacturing a rotor for an eddy current reduction device, In mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.15%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 2.00%, Mo: 0.30 to 1.50%, V: 0.02 to 0.15%, Nb: 0.01 to 0.10%, Sol. Al: 0.001 to 0.040%, B: 0.0005 to 0.0050%, and N: 0.001 to 0.010%, are contained, and further Cu: 0.20% or less, Ni: 0.20% or less, and Ti: 0.050% or less, contains one or more elements selected from the group consisting of, The balance: Fe and impurities, and prepare an intermediate product having a chemical composition satisfying formula (1); a preparation step, A quenching step of performing quenching on the intermediate product, For the intermediate product after the quenching step, a tempering step is carried out in which tempering is performed by holding at a temperature of less than 700 °C to point A c1 and a tempering step of performing tempering by holding at a temperature of less than point A A processing step of processing the intermediate product after the tempering step to form a cylindrical portion, A rotor forming step of manufacturing a rotor for an eddy current reduction device using the cylindrical portion, and comprising: The method for manufacturing a rotor for an eddy current reduction device according to claim 2. Cr + 4Si + 3Sol. Al + Mo ≤ 3.00 (1) Here, in each element symbol in formula (1), the content of the corresponding element is substituted in mass%.

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