JP2017057456A - High strength member for motor using non-oriented electromagnetic steel sheet and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength member for motor having improved strength without deteriorating electromagnetic property and a manufacturing method therefor.SOLUTION: There is provided a high strength member for motor having a non-oriented electromagnetic steel sheet containing, by mass%, Si:2 to 4%, Al:1 to 3%, Ni:1.5 to 4% and the balance Fe with inevitable impurities as a raw material and having intermetallic compounds of Al-Ni partially deposited in a location requiring reinforcement. The high strength member for motor is manufactured by making the above described raw material into a predetermined shape, adding plastic deformation with dislocation density of 1×10/mor more to the location requiring reinforcement and further conducting an aging treatment at 400 to 600°C.SELECTED DRAWING: Figure 1

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 (HEV) and electric vehicles (EV) have been remarkably miniaturized and rotated at high speed, and the motor components such as the rotor cores of these drive motors have electromagnetic properties such as low iron loss. 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 for materials can be considered. Is not preferable for electromagnetic steel sheets because it deteriorates the magnetic properties. In addition, solid solution strengthening has a great effect on increasing the strength while avoiding deterioration of magnetic properties, but at the same time, there are problems of increased rolling load and brittle fracture, so that the addition amount has an upper limit from the viewpoint of productivity.

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

JP-A-2005-39963 JP-A-2005-94940 Japanese Patent Laying-Open No. 2005-94941

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

  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-mentioned problems, the present inventors have partially deposited a fine intermetallic compound mainly composed of Al and Ni on a portion that needs to be strengthened in a motor member such as a rotor core, thereby improving electromagnetic characteristics. It has been found that the strength of the motor member can be improved without deterioration. The main point of the technology of the present invention is that a dislocation is partially generated in a portion that needs to be strengthened in a member for a motor, and the dislocation is used as a precipitation site to precipitate a uniform intermetallic compound of Al-Ni as much as possible. It 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 producing the same are provided.

(1)
High for motors that are made of non-oriented electrical steel sheets that contain Si: 2-4%, Al: 1-3%, Ni: 1.5-4%, and the balance Fe and inevitable impurities. A strength member,
A high-strength member for a motor, in which an Al—Ni intermetallic compound is partially deposited at a location that needs to be strengthened.

(2)
The high-strength member for motors according to (1), wherein the high-strength member for motors is a rotor core, and the portion that needs to be strengthened is an outer bridge portion.

(3)
In an area where the strengthening is necessary, an Al-Ni intermetallic compound having an average equivalent circle diameter of 1 to 10 nm and a standard deviation of 1 or less determined on an area basis is deposited in an amount of 30000 pieces / μm ³ or more. The high-strength member for motors according to any one of (1) and (2).

(4)
Furthermore, it contains 1 or 2 or more of Cr: 0.01-4%, Cu: 0.01-4%, Sn: 0.01-0.2% by mass%, (1)-(3) The high strength member for motors according to any one of claims.

(5)
In a mass%, Si: 2 to 4%, Al: 1 to 3%, Ni: 1.5 to 4%, and a non-oriented electrical steel sheet composed of the remaining Fe and inevitable impurities as a raw material and having a predetermined shape After that, a method for producing a high-strength member for a motor, in which plastic deformation is performed so that a dislocation density of 1 × 10 ¹⁴ / m ² or more is applied to a portion that needs to be strengthened, and further an aging treatment is performed at 400 to 600 ° C.

(6)
The manufacturing method of the high strength member for motors according to (5), wherein the high strength member for motors is a rotor core, and the portion requiring the reinforcement is an outer bridge portion.

(7)
The material further contains, in mass%, one or more of Cr: 0.01-4%, Cu: 0.01-4%, Sn: 0.01-0.2%, (5) or The manufacturing method of the high strength member for motors of any one of (6).

  According to the present invention, it is possible to improve the strength of a high-strength member for a motor without deteriorating electromagnetic characteristics. As a result, it is possible to obtain a high-speed rotating motor that satisfies the characteristics required for recent hybrid electric vehicles (HEV), electric vehicles (EV), and the like, and a motor in which a magnet is incorporated in a rotor.

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 the rotor core at the time of high speed rotation.

  Embodiments of the present invention will be described below. As an example of a high-strength member for a motor, an embodiment 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, and the like 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 that is a rotor is inserted inside a cylindrical stator 10. The stator 10 is provided with a plurality of teeth 15 protruding toward the inner rotor core 11, and the teeth 15 are arranged radially with point symmetry with respect to the rotation center axis O of the rotor core 11. . A winding 16 is wound around each tooth 15 by a concentrated winding method to form a coil.

  As shown in FIG. 2, the rotor core 11 of this embodiment exemplifies an 8-pole rotor provided with 8 openings 20 into which magnets are inserted. The outer portion of each opening 20 is an outer bridge portion 21. In recent years, drive motors used in hybrid electric vehicles (HEV) and electric vehicles (EV) have been revolving at a high speed, and a strong centrifugal force acts on the bridge portion 21 during high-speed rotation.

  Here, according to the simulations of the present inventors, the stress distribution of the centrifugal force acting on the rotor core 11 during high-speed rotation has a result as shown in FIG. That is, in the rotor core 11 during high-speed rotation, strong stress acts on the outer bridge portion 21 (portion outside the dotted line 21 ′ in FIG. 3), and the portion in the vicinity of the corner portion outside each opening 20 (FIG. It has been found that stress concentration is particularly generated in the hatched area 22 in FIG. 3 and deformation of the rotor core 11 and fatigue failure are likely to occur.

  The present invention partially strengthens by depositing an Al-Ni intermetallic compound at a location where stress concentration is likely to occur in such a motor member.

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

Si: 2-4%
Si increases the specific resistance of steel, reduces eddy currents, lowers iron loss, and increases tensile strength, but the effect is small when the amount added is less than 2.0%. Moreover, since work hardening ability increases by addition, it also has the effect of increasing effectively the dislocation density by the process implemented before an aging heat processing. On the other hand, if Si exceeds 4%, the steel is embrittled and further the magnetic flux density of the product is lowered, so the content is made 4% or less.

Al: 1-3%
In the present invention, Al is an important element that is positively added as a constituent element of the intermetallic compound, but if it exceeds 3%, embrittlement becomes a problem, so the upper limit is made 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 precipitation strengthening of intermetallic compounds, at least 1% is contained. In addition, solute Al is known to have an effect of increasing electric resistance and improving iron loss. For this purpose, it is effective to contain more Al than that which forms Al—Ni precipitates.

Ni: 1.5-4%
Conventionally, Ni has generally been used mainly as a solid solution strengthening element or as a precipitation strengthening element such as carbide or nitride. In the present invention, Ni is contained in order to form an intermetallic compound with Al and develop precipitation strengthening due to the Al—Ni intermetallic compound. In order to develop precipitation strengthening by the intermetallic compound of Al—Ni, 1.5% or more of Ni is necessary. On the other hand, excessive addition deteriorates the ductility of the steel sheet and lowers the sheet-passability. In addition, the magnetic flux density is lowered and it is sometimes difficult to suppress preferable formation of intermetallic compounds in the production process. Further, the upper limit is made 4% in consideration of the addition cost.

  Moreover, the non-oriented electrical steel sheet (material) used for manufacturing the high-strength member for motors of the present invention is further contained in mass% as an optional component, Cr: 0.01 to 4%, Cu: 0.01 to 4 %, Sn: 0.01 to 0.2% or 1 or 2 or more. These elements are known as elements forming an intermetallic compound, and may contain 1 or 2 or more as necessary. However, excessive content deteriorates the ductility of the steel sheet and lowers the sheet passability, and may make it difficult to suppress preferable formation of intermetallic compounds in the production process. Further, considering the addition cost, 0.01 to 4% for Cr, 0.01 to 4% for Cu, and 0.01 to 0.2% for Sn.

  The non-oriented electrical steel sheet (material) used for the production of the high strength member for motors of the present invention is based on the above component composition, and consists of the remainder Fe and inevitable impurities.

  C may degrade the magnetic properties, so 0.0400% or less is preferable. On the other hand, there is also an effect of increasing the work hardening ability and effectively increasing the dislocation density by 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, and if it is 0.0030% or less, the effect of suppressing magnetic aging is remarkable, and carbide etc. as the main means of increasing strength In the present invention in which no nonmetallic precipitate is used, it is more preferably 0.0020% or less, and further preferably 0.0015% or less. It may be 0%.

  Mn is effective as an element that increases the strength by solid solution, increases the electrical resistance, and improves the iron loss, and can be used according to a known technique in this embodiment. In addition, there is an effect of increasing the work hardening ability and effectively increasing the dislocation density by the processing performed before the aging heat treatment. From the viewpoint of increasing the strength, this is not particularly necessary in the present invention using a fine intermetallic compound. Although it may be 0%, in the industrial production method using iron ore as a raw material, about 0.01% is inevitably contained.

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

  Cu significantly reduces the saturation magnetic flux density Bs of iron, and B50 (magnetic flux density [T] when the magnetizing force is 5000 [A / m]). Since lowering of Bs and B50 leads to lowering of motor torque, in the present invention, non-oriented electrical steel sheets having high strength and low iron loss without requiring the inclusion of Cu, and without lowering of Bs and B50, and The manufacturing method can be realized. On the other hand, increasing strength by Cu precipitation is also known, and the present embodiment can also be used according to known techniques.

  For Nb, precipitates such as NbC are effective for increasing the strength, but these precipitates inhibit the domain wall movement and greatly deteriorate the iron loss. Therefore, it is not necessary to add Nb for this purpose. On the other hand, the solid solution Nb is effective not only for strengthening the solid solution but also for increasing the strength by refining the crystal grains and improving the high frequency characteristics, and can also be used in accordance with known techniques in this embodiment.

  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 work hardening ability is enhanced by the addition, and there is also an effect of effectively increasing the dislocation density by the processing performed before the aging heat treatment. If it exceeds 0.3%, brittleness is severe, and it is difficult to perform hot rolling and cold rolling on an industrial scale, so the upper limit is preferably set to 0.30%, more preferably 0.10%. It is as follows.

  Since S forms sulfides and may deteriorate magnetic properties, particularly iron loss, the S content is preferably as low as possible and may be 0%. In this invention, 0.020% or less is preferable, More preferably, it is 0.0040% or less, More preferably, it is 0.0020% or less, More preferably, it is 0.0010% or less.

  In addition, the non-oriented electrical steel sheet (material) used for the production of the high strength member for motors, for example, melts the steel containing the above components and forms a steel slab by continuous casting, then hot rolling, cold rolling and Obtained by annealing. Further, in addition to these steps, an insulating film formation or a decarburization step may be performed. In the annealing after cold rolling, it is desirable to quench particularly in the temperature range of 400 to 600 ° C. in order to suppress precipitation of Al—Ni intermetallic compounds.

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

Next, the plastic deformation which makes dislocation density 1 * 10 < ¹⁴ > / m < ² > or more is added to the location which needs reinforcement | strengthening. Plastic deformation can cause dislocations only in places where strengthening is required, for example, by pressing, shot blasting, or the like. In this way, since plastic deformation only needs to be applied to the portions that need to be strengthened, processing in a short time is possible. Further, for example, according to a method such as pressing or shot blasting, it is possible to select only a necessary portion and cause plastic deformation.

  Next, after plastic deformation, an aging treatment is performed at 400 to 600 ° C. In this case, the entire motor member may be heat-treated, but only the portions that need to be strengthened may be heated by, for example, laser heating, infrared heating, high-frequency heating, or the like. In this way, it is sufficient to heat only the portion that needs to be strengthened, so that it is possible to perform processing 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, or high-frequency heating, it is possible to select and heat-treat only necessary portions.

The dislocation density of the portion that needs to be strengthened by plastic deformation is set to 1 × 10 ¹⁴ / m ² or more because the dislocation is sufficiently generated in the necessary portion in the member before the aging treatment, and the dislocation is used as a precipitation site for strengthening. This is because an Al—Ni intermetallic compound that is as uniform in size as possible is dispersed and deposited in the necessary locations. If the dislocation density is less than 1 × 10 ¹⁴ / m ² , the precipitation site of the intermetallic compound is insufficient, and an Al—Ni intermetallic compound having a number density of 30000 / μm ³ or more cannot be obtained after aging. End up. In addition, when the number density of Al—Ni intermetallic compounds is small, the average value of the equivalent circle diameter of the intermetallic compounds is larger than 10 nm, and the variation in the size of each intermetallic compound is also increased. Will exceed 1. Incidentally, when the dislocation density before the aging treatment exceeds 3 × 10 ¹⁶ / m ² , the electromagnetic characteristics are deteriorated, and the size, standard deviation, and number density of the Al—Ni intermetallic compound after aging are further reduced. May fall out of the range. Therefore, it is desirable that the dislocation density before aging treatment is 3 × 10 ¹⁶ / m ² or less.

  The aging treatment is performed at 400 to 600 ° C. When the temperature is lower than 400 ° C., sufficient intermetallic compounds cannot be obtained. On the other hand, when the temperature exceeds 600 ° C., the formed intermetallic compounds become coarse. In this case, the holding time is preferably 1 to 120 minutes. If it is too short, a sufficient intermetallic compound cannot be obtained. On the other hand, if it is too long, the formed intermetallic compound becomes coarse. In addition, the heating rate, the cooling rate, and the like may affect the state of precipitates that is a feature of the present invention. These heat treatment conditions are determined in consideration of components, productivity and the like according to the target characteristics. A person skilled in the art can easily determine appropriate conditions by several trials in accordance with the technical idea of the present invention.

By passing through the manufacturing process as described above, an Al—Ni intermetallic compound having an average equivalent circle diameter of 1 to 10 nm and having a standard deviation of 1 or less is obtained at an area where strengthening is required. 30000 / μm ³ or more can be deposited. As a result, it is possible to improve the strength of the high-strength member for motors without deteriorating electromagnetic characteristics.

In addition, when a large amount of coarse compounds having an average equivalent circle diameter of an intermetallic compound exceeding 10 nm is generated, the efficiency of increasing the strength is lowered and the magnetic characteristics may be deteriorated. In the present invention, the strength of the electrical steel sheet is improved while maintaining excellent magnetic properties and thermal conductivity by generating high-density intermetallic compounds at high density at locations where strengthening is required in the member. On the other hand, if the average value of the equivalent circle diameter of the intermetallic compound is less than 1 nm, the strengthening ability is small. Furthermore, in order to reliably achieve high strength, 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. When this standard deviation exceeds 1, the size of the intermetallic compound becomes non-uniform, and there is a possibility that the thermal conductivity is particularly lowered. As the intermetallic compounds of Al-Ni to form in the steel material, NiAl, such as Ni ₃ Al it is commonly known. In addition, it is known that the element ratio of these compounds varies considerably, and those containing some impurity elements also correspond to the present invention.

From the viewpoint of increasing the strength, the number density of intermetallic compounds to be deposited at locations where strengthening is required in the member is required to be 30000 / μm ³ or more. Control of the intermetallic compound size and number density is important from the viewpoint of achieving both excellent strength and magnetic properties. In the present invention, since the refinement of the crystal structure is not used as a main means for increasing the strength, the crystal grain size can be adjusted to an optimum range from the viewpoint of magnetic properties. Since the size and density of the intermetallic compounds that contribute to high strength can be controlled not only by the components but also by the final heat treatment, the crystal grain size can be controlled before the heat treatment. The control can be performed independently of the control of the intermetallic compound by the holding time in the region. The crystal grain size is usually 300 μm or less, preferably 30 to 250 μm. More preferably, it is 60-200 micrometers. In general, when the frequency of the excitation current when using a motor member is high, it is preferable to keep the crystal grains fine. Further, the effect of the present invention is not impaired at all even if the crystal grain size is increased to several centimeters using secondary recrystallization or the like as in the case of grain-oriented electrical steel sheets.

  In addition, although the form which applied this invention was demonstrated to the rotor core of a permanent magnet built-in motor (IPM motor) as an example, this invention is not limited to this form. For example, the present invention can also be applied to other motor members that require both strength and magnetic properties, such as the slot outer periphery of an induction motor (IM motor).

The hot-rolled steel sheet melted in vacuum shown in Table 1 was pickled, cold-rolled to a thickness of 0.20 mm, and annealed. From the annealed plate, a stator core having an outer diameter of 112 mm, an inner diameter of 56 mm, 24 slots, an outer diameter of 55 mm, and a 4-pole IMP rotor was manufactured. After laminating the rotor core, the bridge portion was subjected to compression deformation in the plate thickness direction with a die, and the amount of compression was changed to adjust the dislocation density to 1 × 10 ¹⁴ / m ² or more. Thereafter, an aging treatment was performed at 550 ° C. for 2 hours. Table 1 shows the maximum efficiency of the motor prototyped with each material and the rotational speed at which the outer diameter of the rotor was measured while changing the rotor rotational speed and the outer periphery started to deform. The maximum efficiency of the prototype motor was 87% or more, and exceeded 89%. In Table 1, numerical values outside the range of the present invention are underlined.

  The rotor that had not been subjected to aging treatment started to deform at 15,000 to 22,000 revolutions, but the one that did not undergo deformation until 25,000 revolutions or more was obtained with aging treatment. .

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

Claims (7)

High for motors that are made of non-oriented electrical steel sheets that contain Si: 2-4%, Al: 1-3%, Ni: 1.5-4%, and the balance Fe and inevitable impurities. A strength member,
A high-strength member for a motor, in which an Al—Ni intermetallic compound is partially deposited at a location that needs to be strengthened.   The high-strength member for motors according to claim 1, wherein the high-strength member for motors is a rotor core, and the portion requiring the reinforcement is an outer bridge portion. In an area where the strengthening is necessary, an Al-Ni intermetallic compound having an average equivalent circle diameter of 1 to 10 nm and a standard deviation of 1 or less determined on an area basis is deposited in an amount of 30000 pieces / μm ³ or more. The high-strength member for motors according to any one of claims 1 and 2.   Furthermore, in mass%, it contains 1 or 2 or more of Cr: 0.01-4%, Cu: 0.01-4%, Sn: 0.01-0.2%, Any one of Claims 1-3 The high-strength member for motors according to 1. In a mass%, Si: 2 to 4%, Al: 1 to 3%, Ni: 1.5 to 4%, and a non-oriented electrical steel sheet composed of the remaining Fe and inevitable impurities as a raw material and having a predetermined shape After that, a method for producing a high-strength member for a motor, in which plastic deformation is performed so that a dislocation density of 1 × 10 ¹⁴ / m ² or more is applied to a portion that needs to be strengthened, and further an aging treatment is performed at 400 to 600 ° C.   The method for producing a high-strength member for a motor according to claim 5, wherein the high-strength member for a motor is a rotor core, and the portion requiring the reinforcement is an outer bridge portion.   The said raw material further contains 1 or 2 or more of Cr: 0.01-4%, Cu: 0.01-4%, Sn: 0.01-0.2% by the mass%. The method for producing a high-strength member for a motor according to any one of 6.