JP6852966B2 - High-strength members for motors using non-oriented electrical steel sheets and their manufacturing methods - Google Patents

Description

The present invention relates to a high-strength member for a motor using a non-oriented electrical steel sheet.

In recent years, drive motors used in hybrid electric vehicles (HEVs) and electric vehicles (EVs) have been remarkably miniaturized and rotated at high speeds. In addition to the characteristics, there is an increasing demand for higher strength. In order to increase the strength of motor members, solid solution strengthening, precipitation strengthening, grain refinement strengthening, dislocation strengthening, transformation strengthening, etc. of non-oriented electrical steel sheets used as materials can be considered, but other than solid solution strengthening. Is not preferable for electrical steel sheets because it deteriorates magnetic properties. In addition, solid solution strengthening has a great effect on increasing strength while avoiding deterioration of magnetic properties, but at the same time, there are problems of increasing rolling load and brittle fracture, and there is an upper limit to the amount of addition from the viewpoint of productivity.

Conventionally, as shown in Patent Document 1, the bridge portion of the rotor core is work-hardened and heat-treated, and dislocations are fixed by C and N contained in the steel to strengthen the strength of the motor member. The method is disclosed. Further, Patent Document 2 discloses a technique for increasing rigidity by laminating rotors that have been work-hardened by a press or the like using an adhesive. Further, Patent Document 3 discloses a technique of further nitriding a rotor that has been work-hardened by a press or the like to improve wear resistance and fatigue characteristics.

Japanese Unexamined Patent Publication No. 2005-39963 Japanese Unexamined Patent Publication No. 2005-94940 Japanese Unexamined Patent Publication No. 2005-94941

However, when it is strengthened by the techniques of Patent Documents 1 to 3, it is not preferable as a member for a motor because the magnetic characteristics deteriorate. As described above, with the recent increase in high-speed rotation, it is desired to develop a technique for increasing the strength of motor members such as rotor cores without deteriorating the magnetic characteristics.

An object of the present invention is to provide a high-strength member for a motor having improved strength without deteriorating electromagnetic characteristics and a method for manufacturing the same.

In order to solve the above problems, the present inventors partially precipitate fine intermetallic compounds mainly composed of Al and Ni in places where reinforcement is required in motor members such as rotor cores to improve electromagnetic characteristics. It was found that the strength of the motor member can be improved without deterioration. The main point of the technique of the present invention is to partially generate dislocations in a part of a motor member that needs to be strengthened, and to use the dislocations as precipitation sites to precipitate an intermetallic compound of Al—Ni having a size as uniform as possible. The purpose is to improve the strength of the motor member without deteriorating the electromagnetic characteristics. According to the present invention, the following high-strength members for motors and methods for manufacturing the same are provided.

(1)
By mass%, Si: 2-4%, Al: 1-3%, Ni : 1.5-4%, Cr: 0.01-4%, Cu: 0.01-4%, A high-strength member for a motor made of a non-oriented electrical steel sheet containing Sn: 0.01 to 0.2% of 1 or 2 or more and composed of the balance Fe and unavoidable impurities.
^{30,000 pieces / μm 3} or more of Al—Ni intermetallic compounds having an average circle-equivalent diameter of 1 to 10 nm and a standard deviation of 1 or less, which are obtained on an area basis, are partially deposited in places where reinforcement is required. High-strength member for motors.

(2)
The high-strength member for a motor according to (1), wherein the high-strength member for a motor is a rotor core, and the portion requiring strengthening is an outer bridge portion.

( 3 )
The method for manufacturing a high-strength member for a motor according to any one of (1) and (2).
By mass%, Si: 2-4%, Al: 1-3%, Ni : 1.5-4%, Cr: 0.01-4%, Cu: 0.01-4%, After using a non-oriented electrical steel sheet containing 1 or 2 or more of Sn: 0.01 to 0.2% and consisting of the balance Fe and unavoidable impurities as a material to form a predetermined shape, the dislocation density is located where reinforcement is required. A method for manufacturing a high-strength member for a motor, which is subjected to plastic deformation having a value of 1 × 10 ¹⁴ / m ^{2 or more and further subjected to aging treatment at 400 to 600 ° C.}

( 4 )
The method for manufacturing a high-strength member for a motor according to (3 ), wherein the high-strength member for a motor is a rotor core, and the portion requiring strengthening is an outer bridge portion.

According to the present invention, it is possible to improve the strength of a high-strength member for a motor without deteriorating the electromagnetic characteristics. As a result, a high-speed rotary motor or a motor in which a magnet is incorporated in a rotor that satisfies the characteristics required for a hybrid electric vehicle (HEV) or an electric vehicle (EV) in recent years can be obtained.

It is explanatory drawing of the structure of a motor. It is explanatory drawing of a rotor core. It is explanatory drawing of the stress distribution of a rotor core at the time of high-speed rotation.

Hereinafter, embodiments of the present invention will be described. As an example of a high-strength member for a motor, a mode in which the present invention is applied to a rotor core of a permanent magnet built-in motor (IPM motor) used as a drive motor for an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, etc. will be described. ..

FIG. 1 is an explanatory diagram of the structure of a motor 1 with a built-in permanent magnet. A rotor core 11 which is a rotor is inserted inside the cylindrical stator 10. The stator 10 is provided with a plurality of teeth 15 projecting toward the rotor core 11 inside, and the teeth 15 are arranged radially symmetrically with respect to the rotation center axis O of the rotor core 11. .. A winding 16 is wound around each tooth 15 in a centralized winding manner to form a coil.

As shown in FIG. 2, the rotor core 11 of this form exemplifies an 8-pole rotor in which openings 20 for inserting magnets are provided at eight places. The outer portion of each opening 20 is the outer bridge portion 21. In recent years, drive motors used in hybrid electric vehicles (HEVs) and electric vehicles (EVs) have been remarkably rotated at high speeds, and a strong centrifugal force acts on the bridge portion 21 during high-speed rotations.

Here, according to the simulations of the present inventors, the stress distribution of the centrifugal force acting on the rotor core 11 at the time of high-speed rotation is as shown in FIG. That is, in the rotor core 11 during high-speed rotation, a strong stress acts on the outer bridge portion 21 (a portion outside the dotted line 21'in FIG. 3), and a portion near the outer corner portion of each opening 20 (FIG. 3). It was found that stress concentration was particularly generated in the shaded area 22 in 3), and deformation and fatigue fracture of the rotor core 11 were likely to occur.

The present invention partially strengthens the motor member by precipitating an intermetallic compound of Al—Ni at a location where stress concentration is likely to occur.

The non-oriented electrical steel sheet (material) used for manufacturing the high-strength member for a motor of the present invention contains Si: 2 to 4%, Al: 1 to 3%, and Ni: 1.5 to 4% in mass%. It is basically composed of the balance Fe and unavoidable impurities.

Si: 2-4%
Si increases the intrinsic resistance of steel, reduces eddy currents, reduces iron loss, and increases tensile strength, but the effect is small when the amount added is less than 2.0%. Further, since the work hardening ability is enhanced by the addition, there is also an effect of effectively increasing the dislocation density by the processing performed before the aging heat treatment. On the other hand, if Si exceeds 4%, the steel is embrittled and the magnetic flux density of the product is further reduced, so the content is set to 4% or less.

Al: 1-3%
In the present invention, Al is an important element positively added as a constituent element of an intermetallic compound, but if it exceeds 3%, embrittlement becomes a problem, so the upper limit is set to 3%. Al is usually added as a deoxidizing agent, but it is also possible to suppress the addition of Al and deoxidize with Si. On the other hand, in order to obtain the effect of strengthening the precipitation of the intermetallic compound, it is contained at least 1%. Further, the solid solution Al is known to have the effect of increasing the electric resistance and improving the iron loss, and for this purpose, it is effective to contain more Al than the Al—Ni precipitate is formed.

Ni: 1.5-4%
Conventionally, in general, Ni has been mainly used as a solid solution strengthening element or a precipitation strengthening element due to carbides, nitrides and the like. In the present invention, Ni is contained to form an intermetallic compound with Al and to develop precipitation strengthening due to the intermetallic compound of Al—Ni. In order to develop precipitation strengthening due to the intermetallic compound of Al—Ni, 1.5% or more of Ni is required. On the other hand, excessive addition may deteriorate the ductility of the steel sheet and reduce the passability, reduce the magnetic flux density, and make it difficult to suppress the preferable formation of the intermetallic compound in the manufacturing process. In addition, considering the addition cost, the upper limit is set to 4%.

Further, the non-oriented electrical steel sheet (material) used for manufacturing the high-strength member for a motor of the present invention has Cr: 0.01 to 4% and Cu: 0.01 to 4 in mass% as optional components. %, Sn: 0.01 to 0.2% may contain 1 or 2 or more. These elements are known as elements forming an intermetallic compound, and can contain 1 or 2 or more as required. However, if it is excessively contained, the ductility of the steel sheet is deteriorated and the sheet-passability is lowered, and it may be difficult to suppress the preferable formation of the intermetallic compound in the manufacturing process. Further, considering the addition cost, Cr is 0.01 to 4%, Cu is 0.01 to 4%, and Sn is 0.01 to 0.2%.

The non-oriented electrical steel sheet (material) used for manufacturing the high-strength member for a motor of the present invention is based on the above component composition, and is composed of the balance Fe and unavoidable impurities.

Since C may deteriorate the magnetic characteristics, it is preferably 0.0400% or less. On the other hand, it also has the effect of increasing the work hardening ability and effectively increasing the dislocation density due to the processing performed before the aging heat treatment. From the viewpoint of manufacturing cost, it is advantageous to reduce the amount of C by degassing equipment at the molten steel stage. If it is 0.0030% or less, the effect of suppressing magnetic aging is remarkable, and carbides, etc. are the main means of increasing the strength. In the present invention in which the non-metal precipitate of No. 1 is not used, the content is more preferably 0.0020% or less, further preferably 0.0015% or less. It may be 0%.

Mn is also effective as an element for increasing the strength by solid solution, increasing the electric resistance, and improving the iron loss, and can be used according to the known technique in this embodiment as well. It also has the effect of increasing the work hardening ability and effectively increasing the dislocation density due to the processing performed before the aging heat treatment. From the viewpoint of increasing the strength, it is not particularly required in the present invention utilizing the fine intermetallic compound. 0% may be used, but in an industrial manufacturing method using iron ore as a raw material, about 0.01% is inevitably contained.

Since N deteriorates the magnetic characteristics like C, it is preferably 0.0400% or less. The content also has the effect of increasing the work hardening ability and effectively increasing the dislocation density due to the processing performed before the aging heat treatment. In particular, in the present invention, it is preferable that N is low in order to avoid the formation of a strong nitride with Al, and if it is 0.0027% or less, the effect of suppressing the deterioration of characteristics due to magnetic aging and the formation of fine nitrides is remarkable, which is more preferable. May be 0.0022%, more preferably 0.0015% or less, or 0%.

Cu significantly lowers the saturation magnetic flux density Bs of iron, and also significantly lowers B50 (magnetic flux density [T] when the magnetization force is 5000 [A / m]). Since a decrease in Bs and B50 leads to a decrease in motor torque, in the present invention, the inclusion of Cu is not essential, and the non-oriented electrical steel sheet having high strength and low iron loss is not accompanied by a decrease in Bs and B50. The manufacturing method can be realized. On the other hand, it is also known that the strength is increased by Cu precipitation, and this embodiment can also be used according to a known technique.

Nb is not necessary to be added for this purpose because precipitates such as NbC are effective for increasing the strength, but these precipitates hinder the movement of the domain wall and significantly deteriorate the iron loss. On the other hand, the solid solution Nb is effective not only for strengthening the solid solution but also for increasing the strength and improving the high frequency characteristics by refining the crystal grains, and can be used according to the known technique in this embodiment as well.

P is an element having a remarkable effect of increasing the tensile strength by strengthening the solid solution, but it is not necessary to add it for this purpose. It may be 0%. On the other hand, the addition also has the effect of increasing the work hardening ability and effectively increasing the dislocation density due to the processing performed before the aging heat treatment. If it exceeds 0.3%, embrittlement becomes severe and processing such as hot spreading and cold spreading on an industrial scale becomes difficult. Therefore, the upper limit is preferably 0.30%, more preferably 0.10%. It is as follows.

Since S may form sulfides and deteriorate magnetic properties, particularly iron loss, the content of S is preferably as low as possible and may be 0%. In the present invention, it is preferably 0.020% or less, more preferably 0.0040% or less, still more preferably 0.0020% or less, still more preferably 0.0010% or less.

For non-oriented electrical steel sheets (materials) used in the manufacture of high-strength members for motors, for example, steel containing the above components is melted and continuously cast to form steel slabs, which are then hot-rolled, cold-rolled and Obtained by annealing. Further, in addition to these steps, an insulating film forming step or a decarburization step may be performed. In the annealing after cold rolling, it is particularly desirable to rapidly cool the temperature range of 400 to 600 ° C. in order to suppress the precipitation of the intermetallic compound of Al—Ni.

The non-oriented electrical steel sheet (material) thus obtained is formed into a predetermined shape required as a motor member by, for example, punching. In this case, the non-oriented electrical steel sheet is still soft at the material stage, and can be easily processed into the shape of a motor member.

Next, plastic deformation with a dislocation density of 1 × 10 ¹⁴ / m ^{2 or more is applied to the portion requiring strengthening.} The plastic deformation can cause dislocations only in the parts that need to be strengthened by, for example, pressing or shot blasting. Since plastic deformation only needs to be applied to the parts that need to be strengthened in this way, processing in a short time is possible. Further, for example, by a method such as pressing or shot blasting, it is possible to select and plastically deform only necessary parts.

Next, after applying plastic deformation, aging treatment is performed at 400 to 600 ° C. In this case, the entire motor member may be heat-treated, but only the parts that need to be strengthened may be heated by, for example, laser heating, infrared heating, high-frequency heating, or the like. Since it is sufficient to heat only the part that needs to be strengthened in this way, it is possible to process in a short time, and the heating energy can be reduced, which is economical. Further, for example, according to a method such as laser heating, infrared heating, high frequency heating, etc., it is possible to select and heat-treat only necessary parts.

To set the dislocation density of the parts that need to be strengthened by plastic deformation to 1 × 10 ¹⁴ / m ² or more, the dislocations are sufficiently generated at the necessary parts in the member before the aging treatment, and the dislocations are used as precipitation sites for strengthening. This is because the intermetallic compound of Al—Ni having a uniform size as much as possible is dispersed and precipitated at the required location. If the dislocation density is ^{less than 1 × 10 14} / m ² , the precipitation sites of the intermetallic compounds are insufficient, and after aging, an intermetallic compound of Al—Ni having a ^{number density of 30,000 / μm 3 or more cannot be obtained.} It ends up. Further, when the number density of the intermetallic compounds of Al-Ni is small, the average value of the equivalent circle diameters of the intermetallic compounds becomes larger than 10 nm, and the size variation of each intermetallic compound becomes large, and the standard deviation becomes large. Exceeds 1. If the dislocation density before the aging treatment ^{exceeds 3 × 10 16} / m ² , the electromagnetic characteristics deteriorate, and after the aging, the size, standard deviation, and number density of the Al—Ni intermetallic compound are determined by the present invention. There is a risk of going out of the range of. Therefore, it is desirable that the dislocation density before the aging treatment is 3 × 10 ¹⁶ / m ^{2 or less.}

The aging treatment is performed at 400 to 600 ° C. If the temperature is lower than 400 ° C, a sufficient intermetallic compound cannot be obtained, while if the temperature exceeds 600 ° C, the formed intermetallic compound becomes coarse. The holding time at this time is preferably 1 to 120 minutes. If it is too short, a sufficient intermetallic compound cannot be obtained, while if it is too long, the formed intermetallic compound becomes coarse. In addition, the heating rate, cooling rate, and the like may also affect the state of the precipitate, which is a feature of the present invention. These heat treatment conditions are determined in consideration of components, productivity, etc. according to the desired characteristics. It is easy for a person skilled in the art to determine appropriate conditions by several trials according to the technical idea of the present invention.

Through the above manufacturing process, the intermetallic compound of Al—Ni having an average value of the equivalent circle diameter of 1 to 10 nm and a standard deviation of 1 or less, which is obtained on an area basis, can be obtained in places where strengthening is required. , 30,000 pieces / μm ³ or more can be precipitated. As a result, it is possible to improve the strength of the high-strength member for the motor without deteriorating the electromagnetic characteristics.

If a large amount of coarse compounds having an average value of the equivalent circle diameter of the intermetallic compound exceeding 10 nm are produced, the efficiency of increasing the strength may decrease and the magnetic characteristics may also deteriorate. In the present invention, the strength of the electrical steel sheet is improved while maintaining excellent magnetic properties and thermal conductivity by generating a fine-sized intermetallic compound at a high density in a portion of the member that needs to be strengthened. On the other hand, if the average value of the equivalent circle diameters of the intermetallic compounds is less than 1 nm, the reinforcing ability becomes small. In order to further increase the strength reliably, it is necessary that the sizes of the individual intermetallic compounds are uniform so that the standard deviation of the equivalent circle diameter is 1 or less. If this standard deviation exceeds 1, the size of the intermetallic compound becomes non-uniform, and there is a risk that the thermal conductivity in particular may decrease. As the intermetallic compounds of Al-Ni to form in the steel material, NiAl, such as Ni ₃ Al is commonly known. Further, it is known that the elemental ratios of these compounds fluctuate considerably, and those containing some impurity elements also correspond to the present invention.

From the viewpoint of increasing the strength, the number density of the intermetallic compound to be deposited at the portion of the member that needs to be strengthened needs to be 30,000 / μm ³ or more. Controlling the intermetallic compound size and number density is important from the viewpoint of achieving both excellent strength and magnetic properties. Since the present invention does not utilize the miniaturization of the crystal structure as the main means for increasing the strength, the crystal grain size can be adjusted to the optimum range from the viewpoint of magnetic properties. Since the size and density of the intermetallic compound that contributes to high strength can be controlled not only by the components but also by the final heat treatment, the crystal grain size is the maximum reached temperature of recrystallization annealing and its temperature before this heat treatment, for example. It is possible to control the intermetallic compound independently of the control of the intermetallic compound depending on the retention time in the region and the like. The crystal grain size is usually 300 μm or less, and is preferably controlled to 30 to 250 μm. More preferably, it is 60 to 200 μm. Generally, when the frequency of the exciting current when using the motor member is high, it is preferable to keep the crystal grains fine. Further, even if the grain size is coarsened to several cm by using secondary recrystallization or the like as in the grain-oriented electrical steel sheet, the effect of the present invention is not impaired at all.

As an example, a mode in which the present invention is applied to a rotor core of a motor with a built-in permanent magnet (IPM motor) has been described, but the present invention is not limited to such a mode. The present invention can also be applied to other motor members that are required to have both strength and magnetic characteristics, such as the outer peripheral portion of an induction motor (IM motor) slot.

The vacuum-melted hot-rolled steel sheet shown in Table 1 was pickled, cold-rolled to a thickness of 0.20 mm, and annealed. From the annealed plate, a stator core with an outer diameter of 112 mm, an inner diameter of 56 mm, and 24 slots, and a 4-pole IMP rotor with an outer diameter of 55 mm were prototyped. After laminating the rotor core, the bridge portion was compression-deformed in the plate thickness direction with a mold to change the amount of compression, so that the dislocation density in the example of the present invention was adjusted to ^{1 × 10 14} / m ^{2 or more.} Then, the aging treatment was carried out at 550 ° C. × 2 hours. Table 1 shows the maximum efficiency of the motor prototyped for each material and the rotation speed at which the outer diameter of the rotor was measured while changing the rotor rotation speed and the outer circumference started to deform. The maximum efficiency of the motor prototyped this time was 87% or more, and those exceeding 89% were accepted. In Table 1, the numerical values outside the scope of the present invention are underlined.

In the rotor without aging treatment, the outer circumference of the rotor started to deform at 15,000 to 22,000 rotations, but in the rotor with aging treatment, no deformation was observed up to 25,000 rotations or more. ..

Further, the maximum efficiency of 92% was obtained with the addition of Cr and Sn, and no deformation was observed up to about 35,000 rotations after the aging treatment with the addition of Cu.

Claims (4)

By mass%, Si: 2-4%, Al: 1-3%, Ni : 1.5-4%, Cr: 0.01-4%, Cu: 0.01-4%, A high-strength member for a motor made of a non-oriented electrical steel sheet containing Sn: 0.01 to 0.2% of 1 or 2 or more and composed of the balance Fe and unavoidable impurities.
^{30,000 pieces / μm 3} or more of Al—Ni intermetallic compounds having an average circle-equivalent diameter of 1 to 10 nm and a standard deviation of 1 or less, which are obtained on an area basis, are partially deposited in places where reinforcement is required. High-strength member for motors. The high-strength member for a motor according to claim 1, wherein the high-strength member for a motor is a rotor core, and the portion requiring strengthening is an outer bridge portion. The method for manufacturing a high-strength member for a motor according to any one of claims 1 or 2.
By mass%, Si: 2-4%, Al: 1-3%, Ni: 1.5-4%, Cr: 0.01-4%, Cu: 0.01-4%, After using a non-oriented electrical steel sheet containing 1 or 2 or more of Sn: 0.01 to 0.2% and consisting of the balance Fe and unavoidable impurities as a material to form a predetermined shape, the dislocation density is located where reinforcement is required. 1x10 ¹⁴ / M ² A method for manufacturing a high-strength member for a motor, which is subjected to the above plastic deformation and further subjected to an aging treatment at 400 to 600 ° C. The method for manufacturing a high-strength member for a motor according to claim 3, wherein the high-strength member for a motor is a rotor core, and the portion requiring strengthening is an outer bridge portion.

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