阅读说明：本技术 涡电流式减速装置用转子 (Rotor for eddy current type speed reducer ) 是由 大泷奈央 冈田浩一 野口泰隆 今西宪治 田坂方宏 于 2020-04-21 设计创作，主要内容包括：本发明提供能够抑制涡电流式减速装置随着累积运转时间的增加所引起的高温强度的降低的、涡电流式减速装置用转子。本实施方式的涡电流式减速装置用转子(10)的圆筒部(11)的化学组成以质量％计包含C：0.05～0.15％、Si：0.10～0.40％、Mn：0.50～1.00％、P：0.030％以下、S：0.030％以下、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％、Cr：0～0.10％和剩余部分：Fe和杂质,显微组织中的马氏体和贝氏体的总面积率超过95.0％,等效圆直径为100～500nm的碳化物的数密度为0.35～0.75个/μm～(2)。(The invention provides a rotor for an eddy current type speed reducer, which can inhibit the reduction of high-temperature strength caused by the increase of accumulated operation time of the eddy current type speed reducer. The chemical composition of a cylindrical portion (11) of a rotor (10) for an eddy current reduction gear according to the present embodiment includes, in mass%: 0.05 to 0.15%, Si: 0.10 to 0.40%, Mn: 0.50-1.00%, P: 0.030% or less, S: 0.030% or less, Mo: 0.20 to 1.00%, Nb: 0.020 to 0.060%, V: 0.040-0.080%Al: 0.030 to 0.100%, B: 0.0005 to 0.0050%, N: 0.003 to 0.010%, Cu: 0-0.20%, Ni: 0-0.20%, Cr: 0-0.10% and the remainder: fe and impurities, the total area ratio of martensite and bainite in the microstructure exceeds 95.0%, and the number density of carbides with equivalent circle diameters of 100-500 nm is 0.35-0.75/mum 2 。)

1. A rotor for an eddy current type speed reducer, comprising a cylindrical portion,

the chemical composition of the cylindrical portion includes, in mass%:

C：0.05～0.15％、

Si：0.10～0.40％、

Mn：0.50～1.00％、

p: less than 0.030%,

S: less than 0.030%,

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％、

Cr: 0 to 0.10%, and

the rest is as follows: fe and impurities in the iron-based alloy, and the impurities,

the total area ratio of martensite and bainite in the microstructure exceeds 95.0%,

the number density of carbides having an equivalent circle diameter of 100 to 500nm is 0.35 to 0.75 piece/μm²。

2. The rotor for an eddy current deceleration device according to claim 1, wherein,

the chemical composition contains one or more elements selected from the following elements:

Cu：0.01～0.20％、

ni: 0.01 to 0.20%, and

Cr：0.01～0.10％。

Technical Field

The present invention relates to a rotor, and more particularly, to a rotor for an eddy current type speed reducer (retarder) used in an eddy current type speed reducer.

Background

Large vehicles such as buses and trucks are equipped with brake devices such as foot brakes and exhaust brakes. In recent large vehicles, there are vehicles equipped with an eddy current type reduction gear. Eddy current deceleration devices are also referred to as retarders. For example, when the vehicle travels on a steep downhill or the like, that is, when it is difficult to reduce the traveling speed of the large vehicle even if the engine brake and the exhaust brake are used in combination, the eddy current type deceleration device is operated. By operating the eddy current type speed reduction device, the braking force can be further increased, and the traveling speed of the large vehicle can be effectively reduced.

Eddy current type reduction gears are of a type using electromagnets and of a type using permanent magnets. An eddy current type speed reduction device using a permanent magnet includes a rotor and a stator accommodated in the rotor. The rotor includes, for example: the drive shaft includes a cylindrical portion (drum), an annular wheel portion for fixing the rotor to the drive shaft, and a plurality of arm portions connecting the cylindrical portion and the wheel portion. The stator is provided with: a cylindrical body, a plurality of permanent magnets of two types having different polarities, and a plurality of pole pieces. A plurality of permanent magnets having different polarities are alternately arranged on the outer circumferential surface of the cylindrical body in the circumferential direction. The pole piece is disposed between the inner circumferential surface of the cylindrical portion of the rotor and the permanent magnet. In the stator, a cylindrical body to which a plurality of permanent magnets are attached is independent of a plurality of pole pieces, and is rotatable around the axis of the cylindrical body.

During braking, that is, when the eddy current type reduction gear is operated, magnetic flux of the permanent magnet of the stator reaches the rotor through the pole piece, and a magnetic path is formed between the permanent magnet and the cylindrical portion of the rotor. At this time, an eddy current is generated in the cylindrical portion of the rotor. The lorentz force is generated as eddy currents are generated. The lorentz force becomes a braking torque, and applies a braking force to the large vehicle. On the other hand, when the eddy current type reduction gear unit is not braking, that is, when the operation is stopped, the relative positions of the permanent magnet and the pole piece are shifted, and the magnetic flux of the permanent magnet does not reach the rotor. In this case, no magnetic path is formed between the permanent magnets and the cylindrical portion of the rotor. Therefore, no eddy current is generated in the cylindrical portion of the rotor, and no braking force is generated. By the above operation, the eddy current type speed reduction device is switched between the braking operation and the non-braking operation (stop).

However, the braking force depends on the amount of eddy current generated in the cylindrical portion of the rotor at the time of braking. Therefore, it is preferable that the amount of eddy current generated in the cylindrical portion of the rotor during braking is large. In order to increase the amount of eddy current generated during braking, the cylindrical portion of the rotor preferably has a low resistance.

Further, during braking, the rotor is heated by joule heat generated together with the eddy current. On the other hand, during non-braking of the eddy current type reduction gear, the rotor is rapidly cooled (air-cooled) by the plurality of cooling fins formed on the outer circumferential surface of the cylindrical portion. That is, the rotor is loaded with thermal cycles through the repetition of braking and non-braking. Therefore, the eddy current type rotor for a reduction gear unit is required to have not only low electric resistance but also high-temperature strength.

Jp 8-49041 a (patent document 1) discloses a technique for reducing the electrical resistance of a rotor for an eddy current type speed reducer and obtaining high-temperature strength.

The rotor material for an eddy current type speed reducer described in patent document 1 contains, in mass%, C: 0.05 to 0.15%, Si: 0.10 to 0.40%, Mn: 0.5-1.0%, P: 0.05% or less, Ni: 0.50% or less, Mo: 0.2 to 1.0%, Nb: 0.01-0.03%, V: 0.03 to 0.07%, B: 0.0005 to 0.003%, Sol.Al: 0.02-0.09%, N: 0.01% or less, and the remainder substantially containing Fe. In this document, the electric resistance of the rotor material is reduced by reducing the contents of P, Ni, and Mn, which are elements that increase the electric resistance. Further, the high-temperature strength of the rotor material is improved by containing B.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 8-49041

Disclosure of Invention

Technical problem to be solved by the invention

However, as described above, the rotor is loaded with a thermal cycle due to repetition of braking and non-braking of the eddy current type deceleration device. If the cumulative operating time of the eddy current reduction gear is longer, the thermal cycle of the rotor load is increased, and the cumulative time during which the rotor is kept at a high temperature is also longer. Therefore, the high-temperature strength of the rotor may decrease as the cumulative operating time of the eddy current reduction gear increases. It is preferable that the rotor be capable of maintaining the high temperature strength of the rotor as much as possible even if the cumulative operating time of the eddy current type reduction gear is long.

The invention aims to provide a rotor for an eddy current type speed reducer, which has low resistance and high-temperature strength and can inhibit the reduction of the high-temperature strength of the eddy current type speed reducer caused by the increase of accumulated operation time.

Means for solving the problems

The rotor for an eddy current type reduction gear according to the present invention includes a cylindrical portion,

the chemical composition of the cylindrical portion includes, in mass%:

C：0.05～0.15％、

Si：0.10～0.40％、

Mn：0.50～1.00％、

p: less than 0.030%,

S: less than 0.030%,

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％、

Cr: 0 to 0.10%, and

the rest is as follows: fe and impurities in the iron-based alloy, and the impurities,

the total area ratio of martensite and bainite in the microstructure exceeds 95.0%,

the number density of carbides having an equivalent circle diameter of 100 to 500nm is 0.35 to 0.75 piece/μm²。

Effects of the invention

The rotor for an eddy current type speed reducer according to the present invention has a low electric resistance and a high-temperature strength, and can suppress a decrease in the high-temperature strength of the eddy current type speed reducer with an increase in the cumulative operating time.

Drawings

Fig. 1 is a front view of an eddy current type reduction gear to which a rotor for an eddy current type reduction gear according to the present embodiment is applied.

Fig. 2 is a cross-sectional view of the eddy current type reduction gear shown in fig. 1 in the axial direction of the propeller shaft when the eddy current type reduction gear is fixed to the propeller shaft.

Fig. 3 is a cross-sectional view (a cross-sectional view in a radial direction) perpendicular to an axial direction of the eddy current type deceleration device at the time of non-braking.

Fig. 4 is a cross-sectional view (a cross-sectional view in a radial direction) perpendicular to an axial direction of the eddy current type deceleration device at the time of braking.

Detailed Description

The present inventors have studied and studied means for making a rotor for an eddy current type speed reducer have a low electric resistance and a high-temperature strength and suppressing a decrease in the high-temperature strength of the eddy current type speed reducer with an increase in the cumulative operating time.

The present inventors have included C: 0.05 to 0.15%, Si: 0.10 to 0.40%, Mn: 0.50-1.00%, P: 0.030% or less, S: 0.030% or less, Mo: 0.20 to 1.00%, Nb: 0.020 to 0.060%, V: 0.040-0.080%, sol.Al: 0.030 to 0.100%, B: 0.0005 to 0.0050%, N: 0.003 to 0.010%, Cu: 0-0.20%, Ni: 0-0.20%, Cr: 0-0.10% and the remainder: fe and impurities, and quenched and tempered steel materials were used as rotors, and the electric resistance and the tensile strength TS0(MPa) at 650 ℃ were examined. In addition, a high-temperature holding test was performed by simulating the high-temperature strength when the cumulative operating time of the eddy current reduction gear unit was long. In the high temperature holding test, the steel material having the above chemical composition was held at 650 ℃ for 300 hours. The tensile strength TS1(MPa) at 650 ℃ of the retained steel material was determined. The difference between the tensile strength TS0 and the tensile strength TS1 is defined as a tensile strength difference Δ TS (mpa). As a result of the examination, even if the electric resistance can be kept low in the steel material having the above chemical composition, the tensile strength difference Δ TS between the tensile strength TS0 at 650 ℃ and the tensile strength TS1 after the high temperature holding test may become large, and the high temperature strength may be decreased more as the cumulative operating time increases.

Therefore, the present inventors have studied the mechanism of the decrease in high-temperature strength when the cumulative operating time of the eddy current reduction gear is longer. In a conventional rotor, quenching and tempering are performed after hot forging, and the high-temperature strength is improved by the dislocation density introduced by quenching. In this case, the high tensile strength can be maintained even at 650 ℃ by dislocation at the initial stage of operation of the eddy current type reduction gear. However, as the cumulative operating time of the eddy current reduction gear becomes longer, the high temperature holding time of the rotor becomes longer, and the dislocation density in the rotor significantly decreases. Therefore, when the high-temperature strength of the rotor for the eddy current reduction gear is ensured by the dislocation density, it is considered that the high-temperature strength is reduced as the cumulative operating time of the eddy current reduction gear becomes longer.

Therefore, the present inventors have studied the following: in the rotor including the steel material having the above chemical composition, the decrease in the high-temperature strength of the eddy current type reduction gear according to the increase in the cumulative operating time is suppressed by a mechanism different from the mechanism for increasing the high-temperature strength by the dislocation density.

In the above chemical composition, as the carbide to be produced, there is Mo carbide (Mo)₂C) Cementite, Nb carbide (NbC), V Carbide (VC), etc. Among these carbides, the finest carbides are Nb carbides and V carbides of MX type precipitates. The average equivalent circle diameter of the MX-type precipitates is 50nm or less. In the present specification, Nb carbides and V carbides are referred to as "fine carbides". On the other hand, Mo carbide and cementite are carbides larger than Nb carbide and V carbide of MX-type precipitates, and the equivalent circle diameter of Mo carbide and cementite is at most 100nm or more. In the present specification, Mo carbide and cementite having an equivalent circle diameter of 100 to 500nm are defined as "medium carbide".

The fine carbides and the medium carbides improve the high-temperature strength of the rotor by a precipitation strengthening mechanism. Therefore, the present inventors considered that if the dislocation density in the rotor is reduced compared to the conventional case and the high-temperature strength is secured by using precipitation strengthening of fine carbides and medium carbides instead of the dislocation density, the reduction of the high-temperature strength of the rotor caused by the increase of the cumulative operating time can be suppressed.

Therefore, the present inventors have studied the high-temperature strength of the rotor in which the number density of the fine carbides and the medium carbides is increased. However, as a result of the study, it was revealed that, in the case of increasing the number density of the fine carbide and the medium carbide, although the tensile strength TS0 at 650 ℃ could be increased, the tensile strength TS1 at 650 ℃ after the high temperature retention test became low, and the tensile strength difference Δ TS (═ TS0-TS1) might be significantly decreased.

Therefore, the present inventors investigated the cause. As a result, the present inventors have found the following. If the equivalent circle diameter is 100-500 nm, the medium-sized carbideNumber density (number/μm)²) If too small, the tensile strength TS0 at 650 ℃ is too low. Therefore, the number density of the medium size carbide has certain requirements. However, if the number density of the medium sized carbide is too high, many dislocations are trapped in the medium sized carbide within the rotor. Therefore, the rotor has a large amount of mesoscale carbides, but the dislocation density is too high. In this case, the high-temperature strength of the rotor is ensured by the precipitation strengthening mechanism by the fine carbides and the medium carbides and a large dislocation density. Therefore, when the rotor is kept at a high temperature for a long period of time, dislocations in the rotor disappear, and the high-temperature strength is significantly reduced.

Based on the above findings, the present inventors considered that: in order to suppress a decrease in high-temperature strength after long-term retention at high temperatures, there is a range of suitable number density of medium-sized carbides that can sufficiently reduce dislocation density in the rotor while exhibiting a precipitation hardening mechanism, and the number density of medium-sized carbides is simply increased without utilizing precipitation hardening. Therefore, the present inventors have studied the following number density ranges: in the rotor including the steel material having the above chemical composition, the moderate-sized carbide having a high-temperature strength and capable of suppressing a decrease in high-temperature strength after being held at a high temperature for a long time is obtained in an appropriate range of the number density. As a result, it has been found that, in a rotor having the above-mentioned chemical composition and having a microstructure in which the total area ratio of martensite and bainite exceeds 95.0%, the number density of carbides (mesoscale carbides) having an equivalent circle diameter of 100 to 500nm is 0.35 to 0.75/μm²In this case, a low electric resistance and a high-temperature strength can be obtained, and even after the rotor is held at a high temperature for a long time, the reduction of the high-temperature strength can be effectively suppressed.

The rotor for an eddy current type speed reduction device according to the present embodiment completed by the above findings has the following configuration.

[1]

A rotor for an eddy current type speed reducer, comprising a cylindrical portion,

the chemical composition of the cylindrical portion includes, in mass%:

C：0.05～0.15％，

Si：0.10～0.40％，

Mn：0.50～1.00％，

p: less than 0.030 percent of the total weight of the composition,

s: less than 0.030 percent of the total weight of the composition,

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％，

cr: 0 to 0.10%, and

the rest is as follows: fe and impurities in the iron-based alloy, and the impurities,

the total area ratio of martensite and bainite in the microstructure exceeds 95.0%,

the number density of carbides having an equivalent circle diameter of 100 to 500nm is 0.35 to 0.75 piece/μm²，

A rotor for an eddy current type reduction gear.

[2]

The rotor for an eddy current type deceleration device according to the item [1], wherein,

the chemical composition contains one or more elements selected from the following elements

Cu：0.01～0.20％，

Ni: 0.01 to 0.20%, and

Cr：0.01～0.10％。

hereinafter, the rotor for an eddy current type speed reducer of the present embodiment will be described in detail.

[ Structure of Eddy Current type speed reduction device ]

Fig. 1 is a front view of an eddy current type reduction gear to which a rotor for an eddy current type reduction gear according to the present embodiment is applied. Referring to fig. 1, an eddy current type speed reduction device 1 includes a rotor 10 and a stator 20.

Fig. 2 is a cross-sectional view of the eddy current reduction gear 1 shown in fig. 1 in the axial direction of the propeller shaft 30 when the eddy current reduction gear 1 is fixed to the propeller shaft 30. Referring to fig. 2, in the present embodiment, the rotor 10 is fixed to the drive shaft 30. The stator 20 is fixed to a transmission device not shown. Referring to fig. 1 and 2, 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 has a through hole in the center. The thickness of the wheel portion 13 (the length of the transmission shaft 30 in the axial direction) is smaller than the thickness of the cylindrical portion 11 (the length of the transmission shaft 30 in the axial direction). Wheel portion 13 is fixed to transmission shaft 30 by inserting transmission shaft 30 in the through-hole. The arm portion 12 connects an end portion of the cylindrical portion 11 and the wheel portion 13, as shown in fig. 1 and 2. The cylindrical portion 11 has a plurality of cooling fins 11F formed on the outer circumferential surface thereof. 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 formed of separate members.

Fig. 3 is a cross-sectional view (a cross-sectional view in the radial direction) perpendicular to the axial direction of the eddy current type deceleration device 1 at the time of non-braking. Referring to fig. 3, 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 magnets 23 are alternately arranged on the outer circumferential surface of the magnet holding ring 21 in the circumferential direction. Of the surfaces of the permanent magnets 22, the surface facing the inner circumferential surface of the cylindrical portion 11 of the rotor 10 is the N-pole. Of the surfaces of the permanent magnets 22, the surface facing the outer circumferential surface of the magnet retaining ring 21 is the S-pole. Of the surfaces of the permanent magnets 23, the surface facing the inner circumferential surface of the cylindrical portion 11 of the rotor 10 is the S pole. Of the surfaces of the permanent magnets 23, the surface facing the outer circumferential surface of the magnet retaining ring 21 is the N-pole. The plurality of pole pieces 24 are arranged above the plurality of permanent magnets 22 and 23 and 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 circumferential surface of the cylindrical portion 11.

[ operation of braking and non-braking of eddy current type deceleration device 1]

Referring to fig. 3, if viewed from the radial direction of the eddy current reduction gear 1 during non-braking, each of the permanent magnets 22 and each of the permanent magnets 23 overlap two pole pieces 24 adjacent to each other. In other words, one pole piece 24 overlaps the permanent magnets 22 and 23 adjacent to each other when viewed from the radial direction of the eddy current reduction gear 1. At this time, the magnetic flux B flows through the stator 20 as shown in fig. 3. Specifically, the magnetic flux B flows between the permanent magnets 22 and 23, the pole piece 24, and the magnet retaining ring 21. Therefore, no magnetic path 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. 3, no braking force is generated.

Fig. 4 is a cross-sectional view (a cross-sectional view in the radial direction) perpendicular to the axial direction of the eddy current type deceleration device 1 at the time of braking. During braking, the magnet holding ring 21 in the stator 20 rotates, and the relative positions of the permanent magnets 22 and 23 and the pole piece 24 are shifted as compared with fig. 3. Specifically, in fig. 4, if the eddy current type speed reducer 1 is viewed from the radial direction during braking, each permanent magnet 22 or 23 overlaps only one pole piece 24, and does not overlap two pole pieces 24. At this time, as shown in fig. 4, 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 path is formed between the rotor 10 and the permanent magnet 22 or 23. At this time, an eddy current is generated in the cylindrical portion 11 of the rotor 10. The lorentz force is generated as eddy currents are generated. The lorentz force becomes a braking torque, and a braking force is generated.

As described above, the eddy current type reduction gear 1 generates a braking force by the eddy current generated in the rotor 10. Therefore, the amount of eddy current generated in the cylindrical portion 11 of the rotor 10 is preferably increased. This is because the braking force increases. The smaller the resistance of the cylindrical portion 11, the larger the amount of eddy current generated. Therefore, the cylindrical portion 11 of the rotor 10 preferably has a small resistance. In addition, the rotor 10 may be loaded with thermal cycles due to repeated braking and non-braking. As described above, recently, it is required to obtain high-temperature strength even at 650 ℃. The rotor 10 will be described in detail below.

[ rotor 10 for eddy current type reduction gear ]

[ chemical composition ]

The chemical composition of the cylindrical portion 11 of the rotor 10 for an eddy current type speed reducer according to the present embodiment contains the following elements. The "%" referred to in the element means mass% unless otherwise specified.

[ regarding essential elements ]

C：0.05～0.15％

Carbon (C) improves the hardenability of the steel material constituting the rotor, and improves the strength of the steel material. C also produces fine carbides such as Nb carbide and V carbide, and improves the high-temperature strength of the steel. C also generates Mo carbide and cementite (medium-sized carbide) with the equivalent circle diameter of 100-500 nm, and the high-temperature strength of the steel is improved. If the C content is less than 0.05%, the above-described effects cannot be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the C content exceeds 0.15%, the electric resistance of the steel material excessively increases even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. 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%, and still more preferably 0.08%. The upper limit of the C content is preferably 0.14%, more preferably 0.13%, and still more preferably 0.12%.

Si：0.10～0.40％

Silicon (Si) deoxidizes steel in a steel making process. Si also improves the hardenability of the steel material and improves the strength of the steel material. If the Si content is less than 0.10%, the above-described effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of the present embodiment. On the other hand, if the Si content exceeds 0.40%, the electrical resistance of the steel material increases excessively even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. 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%, and still more preferably 0.17%. The upper limit of the Si content is preferably 0.38%, more preferably 0.36%, further preferably 0.34%, further preferably 0.32%, further preferably 0.30%, further preferably 0.28%, further preferably 0.26%.

Mn：0.50～1.00％

Manganese (Mn) deoxidizes steel in a steel making process. Mn also increases the hardenability and the strength of the steel. If the Mn content is less than 0.50%, the above-described effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of the present embodiment. On the other hand, if the Mn content exceeds 1.00%, the electrical resistance of the steel material increases excessively even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. Therefore, the Mn content is 0.50 to 1.00%. The lower limit of the Mn content is preferably 0.56%, more preferably 0.58%, further preferably 0.60%, further preferably 0.62%, further preferably 0.64%, further preferably 0.66%, further preferably 0.68%. The upper limit of the Mn content is preferably 0.94%, more preferably 0.90%, and still more preferably 0.88%.

P: less than 0.030%

Phosphorus (P) is an impurity inevitably contained. That is, the P content exceeds 0%. P reduces hot workability and toughness of the steel. P also increases the electrical resistance of the steel. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. If the P content exceeds 0.030%, the hot workability and toughness of the steel material are significantly reduced and the braking force of the eddy current type speed reducer 1 is reduced even if the content of other elements is within the range of the present embodiment. Therefore, the P content is 0.030% or less. The upper limit of the P content is preferably 0.028%, more preferably 0.026%, and most preferably 0.025%. The P content is preferably as low as possible. However, an excessive decrease in the P content increases the manufacturing cost. Therefore, when considering general industrial production, the lower limit of the P content is preferably 0.001%, and more preferably 0.003%.

S: less than 0.030%

Sulfur (S) is an impurity inevitably contained. That is, the S content exceeds 0%. S reduces hot workability and toughness of the steel. If the S content exceeds 0.030%, the hot workability and toughness of the steel material are significantly reduced even if the content of other elements is within the range of the present embodiment. Therefore, the S content is 0.030% or less. The upper limit of the S content is preferably 0.025%, more preferably 0.022%, and still more preferably 0.020%. The S content is preferably as low as possible. However, an excessive reduction in the S content increases the manufacturing cost. Therefore, when considering general industrial production, the preferable lower limit of the S content is 0.001%, and more preferably 0.002%.

Mo：0.20～1.00％

Molybdenum (Mo) combines with C to form Mo carbide (Mo)₂C) In that respect The precipitates containing Mo carbides having an equivalent circle diameter of 100 to 500nm are 0.35 to 0.75 precipitates/μm²Under these conditions, the high-temperature strength of the steel material is improved. Mo also improves the hardenability of the steel. Mo also improves the toughness of the steel. If the Mo content is less than 0.20%, the effects cannot be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the Mo content exceeds 1.00%, the electrical resistance of the steel material increases excessively even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. Therefore, the Mo content is 0.20 to 1.00%. The lower limit of the Mo content is preferably 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 even more preferably 0.60%.

Nb：0.020～0.060％

Niobium (Nb) bonds with carbon to form Nb carbides (fine carbides), and precipitation strengthening improves the high-temperature strength of the steel material. Nb also suppresses coarsening of crystal grains. If the Nb content is less than 0.020%, the above-described effects cannot be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the Nb content exceeds 0.060%, the electrical resistance of the steel material increases excessively even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. If the Nb content exceeds 0.060%, the toughness of the steel is also lowered. Therefore, the Nb content is 0.020 to 0.060%. The lower limit of the Nb content is preferably 0.025%, more preferably 0.030%, further preferably 0.032%, and further preferably 0.034%. The preferable upper limit of the Nb content is 0.058%, more preferably 0.056%, still more preferably 0.054%, and still more preferably 0.052%.

V：0.040～0.080％

Vanadium (V) combines with carbon to form V carbide (fine carbide), and precipitation strengthening improves the high-temperature strength of the steel material. V also suppresses coarsening of crystal grains. If the V content is less than 0.040%, the above-described effect cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment. On the other hand, if the V content exceeds 0.080%, the electric resistance of the steel material excessively increases even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. If the V content exceeds 0.080%, the toughness of the steel is also lowered. 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 still more preferably 0.050%. The upper limit of the V content is preferably 0.075%, more preferably 0.070%, still more preferably 0.068%, still more preferably 0.066%, still more preferably 0.064%, and still more preferably 0.062%.

sol.Al：0.030～0.100％

Aluminum (Al) deoxidizes steel in a steel making process. Al also bonds with nitrogen (N) to form AlN, thereby refining the crystal grains of the steel material. If the sol.al content is less than 0.030%, the above-described effects cannot be sufficiently obtained even if the content of other elements is within the range of the present embodiment. On the other hand, if the sol.al content exceeds 0.100%, the electric resistance of the steel material excessively increases even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. Therefore, the content of sol.Al is 0.030 to 0.100%. The lower limit of the al content is preferably 0.040%, more preferably 0.050%, and still more preferably 0.052%. The upper limit of the al content is preferably 0.090%, more preferably 0.088%, more preferably 0.086%, more preferably 0.084%, more preferably 0.082%, and more preferably 0.080%.

B：0.0005～0.0050％

Boron (B) improves hardenability of the steel material, and improves high-temperature strength of the steel material. If the B content is less than 0.0005%, the effects cannot be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the B content exceeds 0.0050%, the toughness of the steel material decreases even if the content of other elements is within the range of the present embodiment. Therefore, the B content is 0.0005 to 0.0050%. The lower limit of the B content is preferably 0.0008%, more preferably 0.0010%, even more preferably 0.0012%, even more preferably 0.0014%, and even more preferably 0.0015%. The upper limit of the B content is preferably 0.0045%, more preferably 0.0040%, even more preferably 0.0035%, and even more preferably 0.0030%.

N：0.003～0.010％

Nitrogen (N) combines with Al to form AlN. AlN improves the high-temperature strength of the steel material by precipitation strengthening. AlN also makes the crystal grains of the steel material finer. If the N content is less than 0.003%, the above-described effects cannot be sufficiently obtained even if the contents of other elements are within the range of the present embodiment. On the other hand, if the N content exceeds 0.010%, the electric resistance of the steel material excessively increases even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. Therefore, the N content is 0.003 to 0.010%. The preferred lower limit of the N content is 0.004%. The upper limit of the N content is preferably 0.009%, more preferably 0.008%, still more preferably 0.007%, and still more preferably 0.006%.

The remainder of the chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current reduction gear 1 of the present embodiment contains Fe and impurities. Here, the impurities are those which can be tolerated in a range where ore or scrap as a raw material or impurities mixed from a production environment or the like do not adversely affect the cylindrical portion 11 of the rotor 10 of the present embodiment when the cylindrical portion 11 of the rotor 10 of the present embodiment is industrially produced.

[ with respect to optional elements ]

Further, the chemical composition of the cylindrical portion 11 of the rotor 10 of the eddy current reduction gear 1 according to the present embodiment may contain one element or two or more elements selected from Cu, Ni, and Cr instead of part of Fe. These elements are optional elements and improve the hardenability of the steel.

Cu：0～0.20％

Copper (Cu) is an optional element, and may not be contained. That is, the Cu content may be 0%. If contained, Cu improves the hardenability of the steel material and improves the high-temperature strength of the steel material. The effect can be obtained to a certain extent only by containing a small amount of Cu. However, if the Cu content exceeds 0.20%, the electrical resistance of the steel material increases excessively even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear unit brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current type reduction gear unit 1 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. Therefore, the Cu content is 0 to 0.20%. The lower limit of the Cu content is preferably more than 0%, more preferably 0.01%, and still more preferably 0.02%. The upper limit of the Cu content is preferably 0.15%, more preferably 0.12%, and still more preferably 0.10%.

Ni：0～0.20％

Nickel (Ni) is an optional element, and may not be contained. That is, the Ni content may be 0%. When Ni is contained, the hardenability of the steel material is improved, and the high-temperature strength of the steel material is improved. The effect can be obtained to a certain extent only by containing a small amount of Ni. However, if the Ni content exceeds 0.20%, the electrical resistance of the steel material increases excessively even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current type reduction gear 1 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. Therefore, the Ni content is 0 to 0.20%. The lower limit of the Ni content is preferably more than 0%, more preferably 0.01%, still more preferably 0.02%, and still more preferably 0.03%. The upper limit of the Ni content is preferably 0.15%, more preferably 0.12%, and still more preferably 0.10%.

Cr：0～0.10％

Chromium (Cr) is an optional element, and may not be contained. That is, the Cr content may be 0%. When Cr is contained, it improves the hardenability of the steel material and improves the high-temperature strength of the steel material. The effect can be obtained to a certain extent only by containing a small amount of Cr. However, if the Cr content exceeds 0.10%, the electrical resistance of the steel material increases excessively even if the content of other elements is within the range of the present embodiment. In this case, when the eddy current type reduction gear 1 brakes, the amount of eddy current flowing through the cylindrical portion 11 of the rotor 10 of the eddy current type reduction gear 1 decreases. As a result, the braking force of the eddy current type speed reduction device 1 is reduced. Therefore, the Cr content is 0 to 0.10%. The lower limit of the Cr content is preferably more than 0%, more preferably 0.01%, and still more preferably 0.02%. The upper limit of the Ni content is preferably 0.09%, more preferably 0.08%, even more preferably 0.07%, even more preferably 0.06%, and even more preferably 0.05%.

[ regarding the microstructure ]

In the microstructure of the cylindrical portion 11 of the rotor 10 of the present embodiment, the total area ratio of martensite and bainite exceeds 95.0%. That is, the microstructure of the cylindrical portion 11 of the eddy current type rotor 10 for a reduction gear according to the present embodiment is a structure mainly including martensite and/or bainite. The "martensite and bainite" referred to in the present 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 less than 5.0%.

In addition to martensite, bainite, and ferrite, precipitates and inclusions typified by the carbide described above are present in the microstructure of the cylindrical portion 11. However, the total area ratio of these precipitates and inclusions is very small and negligible compared to the area ratios of martensite, bainite, and ferrite.

In addition, in the microstructure observation described later, it is extremely difficult to distinguish martensite from bainite. On the other hand, ferrite can be extremely easily distinguished from martensite and bainite by contrast. Therefore, in the microstructure observation, regions other than ferrite are regarded as "martensite and bainite".

The strength is also affected by the microstructure of the cylindrical portion 11 of the eddy current type rotor 10 for a deceleration device according to the present embodiment. In the microstructure of the cylindrical portion 11 of the rotor 10 for an eddy current type speed reducer according to the present embodiment, if the total area ratio of martensite and bainite is 95.0% or less and the area ratio of ferrite is 5.0% or more, the number density of the medium-sized carbide is 0.35 to 0.75 pieces/μm²Sufficient high-temperature strength cannot be obtained. On the other hand, if the total area ratio of martensite and bainite exceeds 95.0% and the area ratio of ferrite is less than 5.0%, the content of each element in the chemical composition is within the range of the present embodiment, and the number density of medium-sized carbides is 0.35 to 0.75 pieces/μm²On the premise of (1), higher high-temperature strength can be obtained at 650 ℃.

Here, the total area ratio of martensite and bainite and the area ratio of ferrite in the microstructure can be measured by the following methods. A sample is taken from the center 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 the observation field (200. mu. m.times.100. mu.m) described later can be secured. In the surface of the sample, an observation surface including the observation field is mirror-polished. The mirror-polished sample was immersed in a nital solution for about 10 seconds to perform etching, and the tissue was visualized on the observation surface. Observation of the tissue visualized by etching with an optical microscope of 500 timesObservation is performed in any one of the in-plane visual fields (observation visual fields). The visual field area of the observation visual field is 20000 mu m²(200. mu. m.times.100. mu.m). As described above, in the observation field, ferrite can be easily distinguished from martensite and bainite based on the contrast. Therefore, the ferrite in the observation field of view is identified, and the area of the identified ferrite is determined. The area ratio (%) of ferrite was determined by dividing the area of ferrite by the total area of the observation field. 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 equation.

The total area ratio of martensite and bainite is 100.0-area ratio of ferrite

[ number density of carbides (medium-sized carbides) having an equivalent circle diameter of 100 to 500nm ]

In addition, the number density of carbide (medium-sized carbide) having an equivalent circle diameter of 100 to 500nm in the cylindrical portion 11 of the rotor 10 of the present embodiment is 0.35 to 0.75 piece/μm². If the number density of the medium size carbide is less than 0.35 pieces/μm²Even if the contents of the respective elements in the chemical composition are within the range of the present embodiment, the total area ratio of martensite and bainite in the microstructure exceeds 95.0%, and the area ratio of ferrite is less than 5.0%, the number density of the medium carbide is too low. Therefore, sufficient high-temperature strength cannot be obtained. On the other hand, if the number density of the medium size carbide exceeds 0.75 pieces/μm²Even if the contents of the respective elements in the chemical composition are within the range of the present embodiment, the total area ratio of martensite and bainite in the microstructure exceeds 95.0%, and the area ratio of ferrite is less than 5.0%, the number density of the medium carbide is too high. In this case, a large number of dislocations are trapped in the medium-sized carbide, and the dislocation density is also too high. Therefore, although a high-temperature strength is obtained, the reduction in high-temperature strength due to the increase in the cumulative operating time of the eddy current reduction gear increases.

If the number density of the medium-sized carbide is 0.35 to 0.75 pieces/μm²The contents of the elements in the chemical composition are within the scope of the present embodimentOn the premise that the total area ratio of martensite and bainite in the inner periphery and the microstructure exceeds 95.0% and the area ratio of ferrite is less than 5.0%, the rotor of the present embodiment has high-temperature strength, and can sufficiently suppress a decrease in high-temperature strength of the eddy current reduction gear caused by an increase in the cumulative operating time. Specifically, the tensile strength TS0 at 650 ℃ is 250MPa or more, and the tensile strength difference Δ TS at 650 ℃ before and after the high-temperature holding test is less than 50 MPa. The fine carbide particles have an equivalent circle diameter of 50nm or less and are very fine, and it is difficult to quantitatively measure the number density. Further, even if the cumulative operating time in the high temperature region becomes long, the change in the shape of the fine carbide is very small. Therefore, the fine carbide does not have much influence on the suppression of the decrease in the high-temperature strength with the increase in the cumulative operating time.

The preferred lower limit of the number density of the medium size carbide is 0.38 pieces/μm²More preferably 0.40 particles/. mu.m²More preferably 0.42 pieces/. mu.m²More preferably 0.44 pieces/. mu.m²More preferably 0.46 pieces/. mu.m²More preferably 0.48 particles/. mu.m². The preferable upper limit of the number density of the medium size carbide is 0.70 pieces/μm²More preferably 0.68 pieces/. mu.m²More preferably 0.66 pieces/. mu.m²More preferably 0.64 particles/. mu.m²More preferably 0.62 particles/. mu.m²。

[ method for measuring number density of Medium-sized carbide ]

The number density of the medium sized carbide can be measured by the following method. A sample is taken from the center of the wall thickness of the cylindrical portion 11 of the rotor 10. Of the surfaces of the sample, the surface corresponding to the cross section perpendicular to the central axis direction of the cylindrical portion 11 was taken as an observation surface. The observation surface of the sample was mirror-polished. The observation surface after mirror polishing was etched with a nital solution. The observation surface after etching was observed with a Scanning Electron Microscope (SEM) at 10000 times in any 5 fields (field area per 1 field was 12 μm × 9 μm).

Determine each assay confirmed in 5 fieldsEquivalent circular diameter of the discharge. The equivalent circle diameter can be obtained by known image processing. Among the precipitates, those having an equivalent circle diameter of 100 to 500nm can be considered as Mo carbides and/or cementites in the steel material having the chemical composition according to the present embodiment. Therefore, precipitates having an equivalent circle diameter of 100 to 500nm are considered as medium-sized carbides. Based on the number of identified mesoscale carbides (carbides having an equivalent circle diameter of 100 to 500 nm) and the total area of 5 visual fields (540 μm)²) The number density (number/μm) of the mesoscale carbide was determined²)。

[ method for measuring resistance ]

The resistance of the cylindrical portion 11 of the rotor 10 can be determined by a measurement method according to JIS C2526 (1994). Specifically, a test piece including the thickness center position of the cylindrical portion 11 of the rotor 10 is collected. The test piece was a standard test piece of 3 mm. times.4 mm. times.60 mm. The resistance (. mu. OMEGA.cm) of the test piece was determined by the double bridge method at room temperature (20. + -. 15 ℃ C.).

[ method for measuring tensile Strength at 650 ℃ ]

The tensile strength (MPa) at 650 ℃ of the cylindrical portion of the rotor for an eddy current type reduction gear can be determined by a measurement method based on JIS G0567 (2012). Specifically, a tensile test piece was taken from the center of the thickness of the cylindrical portion 11 of the rotor 10. The length of the parallel portion of the tensile test piece was 40mm, the diameter of the parallel portion was 6mm, and the parallel portion was parallel to the central axis of the cylindrical portion 11. The tensile test piece was heated using a heating furnace so that the temperature of the tensile test piece reached 650 ℃. The retention time at 650 ℃ was set to 10 minutes. A tensile test was conducted in air on a 650 ℃ tensile test piece to obtain a stress-strain curve. The tensile strength TS0(MPa) was obtained from the obtained stress-strain curve.

[ method of measuring the tensile Strength Difference Delta TS at 650 ℃ before and after the high temperature holding test ]

The tensile strength difference Δ TS can be obtained in the following direction. Specifically, the tensile test piece was collected from the center of the thickness of the cylindrical portion 11 of the rotor 10 in the same manner as the method of measuring the tensile strength at 650 ℃. Using the collected tensile test piece, a high temperature holding test was performed. Specifically, the tensile test piece was held at 650 ℃ for 300 hours using a heating furnace. The 650 ℃ tensile test piece after the lapse of the retention time was subjected to a tensile test in air to obtain a stress-strain curve. The tensile strength TS1(MPa) was obtained from the obtained stress-strain curve. Using the obtained tensile strengths TS0 and TS1, the tensile strength difference Δ TS (MPa) at 650 ℃ before and after the high temperature holding test was obtained by the following formula.

ΔTS＝TS0-TS1

As described above, in the cylindrical portion 11 of the rotor 10 for an eddy current type speed reducer according to the present embodiment, the total area ratio of martensite and bainite in the microstructure exceeds 95.0%, and the number density of carbide (medium-sized carbide) having an equivalent circle diameter of 100 to 500nm is 0.35 to 0.75 pieces/μm². Therefore, the eddy current type rotor 10 for a speed reducer of the present embodiment has a low electric resistance and a high-temperature strength, and can sufficiently suppress a decrease in the high-temperature strength of the eddy current type speed reducer with an increase in the cumulative operating time. Specifically, the resistance is 20.0. mu. omega. cm or less, the tensile strength TS0 at 650 ℃ is 250MPa or more, and the difference Δ TS in tensile strength at 650 ℃ before and after the above-mentioned high-temperature holding test is 50MPa or less.

[ production method ]

An example of a method of manufacturing the rotor 10 for an eddy current type speed reducer according to the present embodiment will be described. The manufacturing method described later is an example for manufacturing the eddy current type rotor 10 for a speed reducer according to the present embodiment. Therefore, the rotor 10 for an eddy current type speed reducer having the above-described configuration can be manufactured by a manufacturing method other than the manufacturing method described later. However, the manufacturing method described later is a preferred example of the manufacturing method of the rotor 10 for an eddy current type speed reducer according to the present embodiment.

The method for manufacturing the rotor 10 for an eddy current type reduction gear according to the present embodiment includes the steps of: a raw material preparation step of preparing a raw material for the cylindrical portion 11 of the rotor 10 for an eddy current type reduction gear; a hot forging and hot rolling step of hot forging and hot rolling the prepared raw material to produce an intermediate product corresponding to the cylindrical portion 11; a thermal refining step of subjecting the intermediate product to quenching and tempering; a machining step of cutting the inner and/or outer circumferential surfaces of the intermediate product to form the cylindrical portion 11 and the plurality of fins 11F; and a rotor forming step of manufacturing the rotor 10 for the eddy current type speed reducer using the wheel portion 13, the arm portion 12, and the cylindrical portion 11. Hereinafter, each step will be explained.

[ raw Material preparation Process ]

In the raw material preparation step, a raw material having a chemical composition in which the content of each element is within the range of the present embodiment is prepared. The raw material may be supplied by a third party. Raw materials can also be manufactured. In the case of manufacturing, for example, the following method is used.

Molten steel having a chemical composition in which the contents of the respective elements are within the ranges of the present embodiment is produced. The refining method is not particularly limited, and a known method may be used. For example, molten iron produced by a known method is refined in a converter (primary refining). The molten steel discharged from the converter is subjected to known secondary refining. In the secondary refining, alloying elements are added to adjust the composition, thereby producing molten steel having a chemical composition in which the content of each element is within the range of the present embodiment.

The molten steel produced by the refining method described above is used to produce a raw material by a well-known casting method. For example, steel ingots are manufactured by an ingot casting method using molten steel. Further, a billet or billet can be manufactured by a continuous casting method using molten steel. Or heating the manufactured square billet or steel ingot to 1000-1300 ℃, and then performing hot working to manufacture a steel billet. Examples of the hot working include hot rolling and hot forging. The produced billet (billet produced by continuous casting or billet produced by hot working a square billet or a steel ingot) is used as a material of the rotor 10 for an eddy current type reduction gear.

[ Hot forging and Hot Rolling Process ]

The raw material prepared in the raw material preparation step is subjected to hot forging and hot rolling to produce an intermediate product corresponding to the cylindrical portion 11. Firstly, heating the raw material to 1000-1300 ℃. The heated raw material is subjected to hot forging to be formed into a predetermined size. After the hot forging, hot rolling is further performed to manufacture a cylindrical intermediate product.

[ thermal refining Process ]

The intermediate product produced by the hot forging and hot rolling steps is subjected to a thermal refining step. Specifically, the intermediate product is subjected to quenching treatment and then to tempering treatment.

[ quenching treatment ]

First, the intermediate product is subjected to quenching treatment. The quenching temperature is 860-930 ℃. If the quenching temperature is less than 860 ℃, Mo carbide and cementite produced by the hot forging step cannot be sufficiently solid-dissolved. In this case, in the tempering treatment in the next step, undissolved Mo carbide and carburized body remaining in the intermediate product after the quenching treatment coarsen. As a result, the number density of the medium size carbide is lowered. Further, if the quenching temperature is less than 860 ℃, the microstructure of the intermediate product maintained at the quenching temperature does not become an austenite single phase. Therefore, the structure after the quenching treatment contains not only martensite and/or bainite but also ferrite. The upper limit of the tempering temperature is not particularly limited, and is, for example, 930 ℃. Therefore, the quenching temperature is 860-930 ℃. The lower limit of the quenching temperature is preferably 865 ℃ and more preferably 870 ℃. If the quenching temperature is too high, the austenite becomes coarse. Therefore, the upper limit of the quenching temperature is preferably 920 ℃, and more preferably 910 ℃.

The holding time of the quenching temperature in the quenching treatment is not particularly limited, and is, for example, 1.0 to 2.0 hours.

[ tempering treatment ]

Tempering the intermediate product after the quenching treatment. Fine carbides and medium carbides are produced by tempering. The tempering temperature T is 660-700 ℃. If the tempering temperature T is less than 660 ℃, the number density of the medium-sized carbide is less than 0.35 pieces/mu m². In this case, the precipitation amount of the fine carbide and the medium carbide is insufficient, and thus the high-temperature strength is lowered. On the other hand, if the tempering temperature T exceeds 700 ℃, the medium carbides coarsen, and the number density of the medium carbides is less than 0.35 pieces/μm². Therefore, the high temperature strength becomesLow. In addition, a part of the microstructure may be transformed into austenite. Therefore, the tempering temperature T is 660-700 ℃. The lower limit of the tempering temperature T is preferably 670 ℃, and more preferably 680 ℃.

The tempering treatment further satisfies the following formula.

1400≤(T+273.15)×(1+log(t))+(Mo/96+C/12)×20000≤1800 (1)

Here, "T" in the formula (1) is substituted for the tempering temperature T (. degree. C.), and "T" is substituted for the tempering retention time (hours). The symbol of an element in the formula (1) is substituted into the content (mass%) of the corresponding element.

Definition F1 ═ T +273.15 (1+ log (T)) + (Mo/96+ C/12) x 20000. F1 is an index of the amount of precipitated medium-sized carbides. If F1 is less than 1400 deg.C, medium-sized carbide with a number density of less than 0.35/μm cannot be sufficiently produced even if the tempering temperature is 660-700 deg.C². On the other hand, if F1 exceeds 1800, the amount of medium carbides produced is excessive and the number density of the medium carbides exceeds 0.75 pieces/. mu.m, even if the tempering temperature is 660 to 700 ℃². As a result, the high-temperature strength significantly decreases as the cumulative operating time of the eddy current reduction gear increases.

When F1 is 1400-1800, the number density of the medium-sized carbide is 0.35-0.75 pieces/μm². Therefore, excellent high-temperature strength can be obtained, and a significant decrease in high-temperature strength caused by an increase in the cumulative operating time of the eddy current reduction gear can be sufficiently suppressed. The lower limit of F1 is preferably 1410, more preferably 1420. The upper limit of F1 is preferably 1790, more preferably 1780, and still more preferably 1770.

[ machining Process ]

The outer circumferential surface of the tempered intermediate product is machined to form cooling fins 11F. The machining may be performed by a known method. Through the above steps, the cylindrical portion 11 is manufactured.

[ rotor Forming Process ]

The arm portion 12 attached to the wheel portion 13 is attached to the manufactured cylindrical portion 11, and the rotor 10 for an eddy current type speed reducer is manufactured. The mounting method may be welding or other methods.

The eddy current type rotor 10 for a reduction gear according to the present embodiment can be manufactured by the above manufacturing method. The eddy current type rotor 10 for a speed reducer according to the present embodiment is not limited to the above-described manufacturing method, and if the eddy current type rotor 10 having the above-described configuration can be manufactured, the eddy current type rotor 10 for a speed reducer according to the present embodiment may be manufactured by a manufacturing method other than the above-described manufacturing method. However, the above-described manufacturing method is a suitable example of manufacturing the rotor 10 for an eddy current type speed reducer of the present embodiment.

Examples

Molten steels having the chemical compositions of table 1 were produced.

The blank portion in table 1 means that the content of the corresponding element is less than the detection limit. For example, the Cu content of test No. 1 indicates a value rounded to the third decimal place of 0%. The Ni content of test No. 1 was 0% after rounding to the third decimal place. The Cr content in test No. 1 was 0% after rounding to the third decimal place. A30 kg cylindrical steel ingot having a diameter of 120mm was produced by an ingot casting method using molten steel.

The steel ingot was heated to 1200 ℃ and then hot forged to produce a steel sheet having a thickness of 40mm as a pseudo intermediate product. The intermediate product was quenched at a quenching temperature shown in table 2. The holding time at the quenching temperature is 1.1 to 1.7 hours. The quenched intermediate product was tempered at a tempering temperature and F1 shown in table 2. Through the above-described manufacturing process, pseudo rotors (steel plates) of respective test numbers of the rotor for the pseudo eddy current type speed reducer were manufactured.

[ Table 2]

[ evaluation test ]

The following evaluation tests were carried out on the fabricated pseudo rotors of the respective test numbers.

Samples were collected from the plate thickness center positions of the pseudo rotors of the respective test numbers. After the surface of the sample was mirror-polished, the sample was immersed in a nital solution for about 10 seconds to perform etching, thereby visualizing the tissue. An arbitrary 1 field (observation field) of view of the surface where the tissue was exposed by etching was observed by an optical microscope at 500 magnifications. The visual field area of the observation visual field is 20000 mu m²(200. mu. m.times.100. mu.m). Through the contrast, the phases in the observation field of view are identified. As a result, the microstructure in the observation field included martensite, bainite, and ferrite. The area of the identified ferrite is determined. The area ratio (%) of ferrite was determined by dividing the area of ferrite by the total area of the observation field. As described above, in the microstructure in the observation field, the remainder other than ferrite is martensite and/or bainite. Therefore, the total area (%) of martensite and bainite is obtained by the following equation.

The total area ratio of martensite and bainite is 100.0-area ratio of ferrite

The area ratio (%) of ferrite obtained is shown in table 2. The total area ratio (%) of martensite and bainite is shown in Table 2.

[ measurement test of number Density of Medium-sized carbides ]

Samples were collected from the plate thickness center positions of the pseudo rotors of the respective test numbers. The observation surface of the sample was mirror-polished. The observation surface after mirror polishing was etched with a nital solution. The observation surface after etching was observed with a Scanning Electron Microscope (SEM) at 10000 times in 5 random fields (field area per 1 field was 12 μm × 9 μm). The equivalent circle diameter of each precipitate confirmed in 5 visual fields was determined. Among the precipitates, precipitates having an equivalent circle diameter of 100 to 500nm are considered as Mo carbides and/or cementites, and thus precipitates having an equivalent circle diameter of 100 to 500nm are considered as medium carbides. Based on the number of mesoscale carbides (carbides having an equivalent circle diameter of 100 to 500 nm) and the total area of 5 visual fields (540 μm)²) To find the medium carbonNumber density of compounds (units/μm)²). The number density of the resulting mesoscale carbides is shown in table 2.

[ method for measuring resistance ]

The resistance of the pseudo rotor of each test number at room temperature was determined by a measurement method based on JIS C2526 (1994). Specifically, the test piece was collected from the plate thickness center position of the pseudo rotor of each test number. The test piece had dimensions of 3 mm. times.4 mm. times.60 mm. The resistance (. mu. OMEGA.cm) of the test piece was determined by the double bridge method at room temperature. The obtained resistance (. mu. OMEGA.cm) is shown in Table 2.

[ tensile test at 650 ]

The tensile strength TS0(MPa) at 650 ℃ of each test number of the trochoid was determined by a measurement method based on JIS G0567 (2012). Specifically, tensile test pieces were collected from the plate thickness center positions of the pseudo rotors of the respective test numbers. The length of the parallel portion of the tensile test piece was 40mm, and the diameter of the parallel portion was 6 mm. The parallel portion of the tensile test piece was parallel to the rolling direction of the pseudo rotor (steel plate). The tensile test piece was heated using a heating furnace so that the temperature of the test piece reached 650 ℃. The retention time at 650 ℃ was set to 10 minutes. A tensile test was conducted in air on a 650 ℃ tensile test piece to obtain a stress-strain curve. The tensile strength TS0(MPa) is defined from the resulting stress-strain curve. The tensile strength TS0(MPa) at 650 ℃ obtained is shown in Table 2.

[ measurement test of tensile Strength Difference Delta TS at 650 ℃ before and after high temperature holding test ]

The tensile strength difference Δ TS of the pseudo rotors of the respective test numbers was obtained in the following direction. In the same manner as in the above-mentioned 650 ℃ tensile test, a test piece was taken from the center of the thickness of the pseudo rotor. The length of the parallel portion of the tensile test piece was 40mm, and the diameter of the parallel portion was 6 mm. The parallel portion of the tensile test piece was parallel to the rolling direction of the pseudo rotor (steel plate). The tensile test piece was kept at 650 ℃ for 300 hours using a heating furnace. The 650 ℃ tensile test piece after the lapse of the retention time was subjected to a tensile test in air to obtain a stress-strain curve. From the obtained stress-strain curve, tensile strength TS1(MPa) was obtained. Using the obtained tensile strengths TS0 and TS1, the tensile strength difference Δ TS at 650 ℃ before and after the high temperature holding test was obtained by the following equation. The obtained tensile strength difference Δ TS is shown in table 2.

ΔTS＝TS0-TS1

[ test results ]

Referring to table 2, the chemical compositions of the pseudo rotors of test nos. 1 to 7 each contain an appropriate amount of each element, and the total area ratio of martensite to bainite is 95.0% or more. And the medium-sized carbide has a number density of 0.35 to 0.75 particles/μm². Therefore, the resistance is 20.0 μ Ω cm or less, and the resistance is sufficiently low as a rotor of an eddy current type reduction gear. Furthermore, the tensile strength TS0 at 650 ℃ was 250MPa or more, and the excellent high-temperature strength was exhibited. Further, the tensile strength difference Δ TS was 50MPa or less, and the decrease in high-temperature strength after the high-temperature holding test was sufficiently suppressed.

On the other hand, in test No. 8, the Mo content and the B content were too low. Thus, the tensile strength TS0 at 650 ℃ is less than 250 MPa.

In test No. 9, the C content was too low. Thus, the tensile strength TS0 at 650 ℃ is less than 250 MPa.

In test No. 10, the C content was too high. In addition, the Cr content is too high. Therefore, the resistance is too high.

In test No. 11, the contents of the respective elements were appropriate, but the quenching temperature was too low. Therefore, the total area ratio of martensite and bainite is 95.0% or less. As a result, the tensile strength TS0 at 650 ℃ was less than 250 MPa.

In test No. 12, the contents of the respective elements were appropriate, but the tempering temperature was too high. Thus, the medium carbide number density is less than 0.35 pieces/μm². As a result, the tensile strength TS0 at 650 ℃ was less than 250 MPa.

In test No. 13, the contents of the respective elements were proper, but the F1 value was less than the lower limit of formula (1). Thus, the medium carbide number density is less than 0.35 pieces/μm². As a result, the tensile strength TS0 at 650 ℃ was less than 250 MPa.

In test No. 14, the contents of the respective elements were proper, but the F1 value exceeded the upper limit of formula (1). Therefore, the number density of the medium-sized carbide is excessive0.75 pieces/mu m². As a result, the tensile strength difference Δ TS exceeded 50 MPa.

The embodiments of the present invention are explained above. However, the described embodiments are only examples for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiments, and the embodiments can be appropriately modified and implemented without departing from the scope of the present invention.

Description of the symbols

1 eddy current type speed reducer

10 rotor

11 cylindrical part

12 arm part

13 wheel part

20 stator