Oriented particle-free electrical steel sheets, methods for stamping oriented particle-free electrical steel sheets, and dies for stamping oriented particle-free electrical steel sheets.

Abstract

The invention relates to an oriented non-grain electrical steel sheet which is an oriented non-grain electrical steel sheet comprising a silicon steel sheet as the base material, in which the silicon steel sheet has predetermined mechanical properties depending on the direction relative to the rolling direction, and the difference between the maximum and minimum values ​​of the diameters of the circular holes after stamping with a die is essentially round is 0.20% or less of the mean of the maximum and minimum values.

Description

Non-oriented electrical steel sheet, method for punching non-oriented electrical steel sheet, and die for punching non-oriented electrical steel sheet

[0001] The present invention relates to a non-oriented electrical steel sheet, a method for punching a non-oriented electrical steel sheet, and a punching die for a non-oriented electrical steel sheet. This application claims priority based on Japanese Patent Application No. 2021-061846 filed in Japan on March 31, 2021, and Japanese Patent Application No. 2021-099782 filed in Japan on June 15, 2021, the contents of which are incorporated herein by reference.

[0002] BACKGROUND ART In recent years, with the global increase in demand for electric devices such as motors, there has been an increase in demand for non-oriented electrical steel sheets used as materials for motors and the like.

[0003] Patent Document 1 describes a method for producing a motor core by punching a non-oriented electrical steel sheet, in which the circularity of the cutting edge of the punching die is controlled in accordance with the elongation percentage of the non-oriented electrical steel sheet.

[0004] Japanese Patent Publication No. 10-24333

[0005] Non-oriented electrical steel sheets used for motor stator cores are subjected to core annealing (stress relief annealing) to reduce iron loss after the stator core is punched out with a die. Specifically, the rotor core is first punched out from the non-oriented electrical steel sheet, then the inner diameter of the stator core is punched out, and then the outer diameter of the stator core is punched out. By applying heat to the stator core through core annealing, residual stress and strain are released, reducing iron loss. Note that while core annealing is applied to the stator core, annealing is generally not applied to the rotor core in order to increase its strength.

[0006] If the residual stress distribution in the stator core after punching it with a die is non-uniform, the shape change of the stator core due to the release of residual stress during core annealing will be non-uniform. As a result, the high roundness of the inner diameter of the stator core obtained before core annealing may be reduced by core annealing. One of the factors that causes the non-uniform residual stress distribution is the anisotropy of the mechanical properties of the non-oriented electrical steel sheet used for punching.

[0007] The technology described in Patent Document 1 controls the circularity of the cutting edge of a punching die in accordance with the elongation percentage of a non-oriented electrical steel sheet, and controls the dimensional accuracy of the processed non-oriented electrical steel sheet by the dimensions of the punching die, but does not anticipate controlling the circularity in consideration of the anisotropy of the mechanical properties of the non-oriented electrical steel sheet. Therefore, the technology described in Patent Document 1 has the problem of being unable to suppress a decrease in dimensional accuracy that corresponds to the anisotropy of the mechanical properties of the non-oriented electrical steel sheet being punched.

[0008] Therefore, an object of the present invention is to provide a non-oriented electrical steel sheet that can suppress a decrease in dimensional accuracy after working and core annealing. Another object of the present invention is to provide a method for punching a non-oriented electrical steel sheet and a die for punching a non-oriented electrical steel sheet that can suppress a decrease in dimensional accuracy after working and core annealing.

[0009] The gist of the present disclosure is as follows: (1) A non-oriented electrical steel sheet according to one embodiment of the present invention is a non-oriented electrical steel sheet including a silicon steel sheet as a base material, the silicon steel sheet having predetermined mechanical properties according to a direction relative to the rolling direction, and the difference between the maximum and minimum diameters of circular holes punched with a substantially circular die being 0.20% or less of the average of the maximum and minimum diameters.

[0010] (2) In the non-oriented electrical steel sheet described in (1) above, the predetermined mechanical properties may satisfy the following formula (1), where E0 is the Young's modulus in the rolling direction of the non-oriented electrical steel sheet, E90 is the Young's modulus in the direction perpendicular to the rolling direction, and E45 is the Young's modulus in the direction at an angle of 45 degrees from the rolling direction: 0.8100≦(E0+E90) / (2×E45)≦1.0000 (1).

[0011] (3) In the non-oriented electrical steel sheet described in (1) or (2) above, the predetermined mechanical property may satisfy the following formula (2), where r-value in the rolling direction of the silicon steel sheet is r0, r-value in the direction perpendicular to the rolling direction is r90, and r-value in the direction at 45 degrees from the rolling direction is r45: 1.0000≦(r0+r90) / (2×r45)≦1.3100 (2).

[0012] (4) In the non-oriented electrical steel sheet according to any one of (1) to (3) above, the predetermined mechanical properties may satisfy the following formula (3), where n0 is the n value in the rolling direction of the silicon steel sheet, n90 is the n value in the direction perpendicular to the rolling direction, and n45 is the n value in the direction at 45 degrees from the rolling direction: 0.8100≦(n0+n90) / (2×n45)≦1.0000 (3).

[0013] (5) In the non-oriented electrical steel sheet according to any one of (1) to (4) above, the predetermined mechanical properties may satisfy the following formula (4) when the yield ratio in the rolling direction of the silicon steel sheet is YR0, the yield ratio in the direction perpendicular to the rolling direction is YR90, and the yield ratio in the direction at an angle of 45 degrees from the rolling direction is YR45: 0.8300≦(YR0+YR90) / (2×YR45)≦1.0300 (4).

[0014] (6) In the non-oriented electrical steel sheet according to any one of (1) to (5) above, the base material has a chemical composition, in mass%, of C: 0.0010 to 0.0040%, Si: 2.5 to 4.5%, Al: 0.2 to 2.5%, Mn: 0.1 to 3.5%, P: more than 0% but not more than 0.10%, S: 0 to 0.0030%, N: 0 to 0.0030%, Ti: 0 to 0.0030%, Mo: 0.0010 to 0.10%, Cr: 0 to 0.10%, B: 0 to 0.0010%, Ni: 0 to 0.50%, Cu: 0 to 0.50%, Sn: 0 to 0.20%, Sb: 0 to 0.20%, It may contain Ca: 0 to 0.0050%, La: 0 to 0.0050%, Ce: 0 to 0.0050%, O: 0 to 0.10%, V: 0 to 0.10%, W: 0 to 0.10%, Zr: 0 to 0.10%, Nb: 0 to 0.10%, Mg: 0 to 0.10%, Bi: 0 to 0.10%, Nd: 0 to 0.10%, and Y: 0 to 0.10%, with the balance being Fe and impurities.

[0015] (7) A method for punching non-oriented electrical steel sheets according to another embodiment of the present invention is a method for punching non-oriented electrical steel sheets having a silicon steel sheet as a base material using a substantially cylindrical die, in which the diameter of the die in the direction relative to the rolling direction is determined based on mechanical property values ​​of the silicon steel sheet corresponding to the direction relative to the rolling direction of the silicon steel sheet, and the silicon steel sheet is punched.

[0016] (8) In the method for punching non-oriented electrical steel sheets described in (7) above, when the Young's modulus of the silicon steel sheet in the rolling direction is E0, the Young's modulus in the direction perpendicular to the rolling direction is E90, the Young's modulus in the direction at 45 degrees from the rolling direction is E45, and Eave = (E0 + 2 × E45 + E90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di, the following formula (5) may be satisfied: 0.96 < (Ei / Eave) × (Di / D) ≦ 1.04 (5) where i = 0, 45, or 90, D0 is the diameter of the die in the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

[0017] (9) In the method for punching non-oriented electrical steel sheets described in (7) above, when the r-value in the rolling direction of the silicon steel sheet is r0, the r-value in the direction perpendicular to the rolling direction is r90, and the r-value in the direction at 45 degrees from the rolling direction is r45, and rave = (r0 + 2 × r45 + r90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di, the following formula (6) may be satisfied: 0.96 < (ri / rave) × (Di / D) ≦ 1.04 (6) where i = 0, 45, or 90, D0 is the diameter of the die corresponding to the rolling direction, D45 is the diameter of the die in the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

[0018] (10) In the method for punching non-oriented electrical steel sheets described in (7) above, when the n value in the rolling direction of the silicon steel sheet is n0, the n value in the direction perpendicular to the rolling direction is n90, and the n value in the direction at 45 degrees from the rolling direction is n45, and nave = (n0 + 2 × n45 + n90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di, the following formula (7) may be satisfied: 0.96 < (ni / nave) × (Di / D) ≦ 1.04 (7) where i = 0, 45, or 90, D0 is the diameter of the die in the rolling direction, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

[0019] (11) In the method for punching non-oriented electrical steel sheets described in (7) above, when the yield ratio of the silicon steel sheet in the rolling direction is YR0, the yield ratio in the direction perpendicular to the rolling direction is YR90, the yield ratio in the direction at an angle of 45 degrees from the rolling direction is YR45, and YRave = (YR0 + 2 × YR45 + YR90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di, the following formula (8) may be satisfied: 0.96≦(YRi / YRave) × (Di / D)≦1.04 (8) where i = 0, 45, or 90, D0 is the diameter of the die in the rolling direction, D45 is the diameter of the die corresponding to the direction at an angle of 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

[0020] (12) In the method for punching non-oriented electrical steel sheets according to any one of (7) to (11) above, the base material has a chemical composition, in mass%, of C: 0.0010 to 0.0040%, Si: 2.5 to 4.5%, Al: 0.2 to 2.5%, Mn: 0.1 to 3.5%, P: more than 0% but not more than 0.10%, S: 0 to 0.0030%, N: 0 to 0.0030%, Ti: 0 to 0.0030%, Mo: 0.0010 to 0.10%, Cr: 0 to 0.10%, B: 0 to 0.0010%, Ni: 0 to 0.50%, Cu: 0 to 0.50%, Sn: 0 to 0.20%, Sb: 0 to 0.20%, It may contain Ca: 0 to 0.0050%, La: 0 to 0.0050%, Ce: 0 to 0.0050%, O: 0 to 0.10%, V: 0 to 0.10%, W: 0 to 0.10%, Zr: 0 to 0.10%, Nb: 0 to 0.10%, Mg: 0 to 0.10%, Bi: 0 to 0.10%, Nd: 0 to 0.10%, and Y: 0 to 0.10%, with the balance being Fe and impurities.

[0021] (13) In another embodiment of the present invention, a punching die for a non-oriented electrical steel sheet is a substantially cylindrical die for punching a non-oriented electrical steel sheet having a silicon steel sheet as a base material, and the diameter of the die in a direction relative to the rolling direction of the silicon steel sheet is determined based on the mechanical property values ​​of the silicon steel sheet corresponding to the direction relative to the rolling direction.

[0022] (14) The die for punching non-oriented electrical steel sheets according to (13) above may satisfy the following formula (5) when the Young's modulus of the silicon steel sheet in the rolling direction is E0, the Young's modulus in the direction perpendicular to the rolling direction is E90, the Young's modulus in the direction at 45 degrees from the rolling direction is E45, and Eave = (E0 + 2 × E45 + E90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di: 0.96 < (Ei / Eave) × (Di / D) ≦ 1.04 (5) where i = 0, 45, or 90, and when a non-oriented electrical steel sheet is placed in the die, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

[0023] (15) The die for punching non-oriented electrical steel sheets according to (13) above may satisfy the following formula (6) when the r-value in the rolling direction of the silicon steel sheet is r0, the r-value in the direction perpendicular to the rolling direction is r90, and the r-value in the direction at 45 degrees from the rolling direction is r45, and rave = (r0 + 2 × r45 + r90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di: 0.96 < (ri / rave) × (Di / D) ≦ 1.04 (6) where i = 0, 45, or 90, and when a non-oriented electrical steel sheet is placed in the die, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

[0024] (16) The die for punching non-oriented electrical steel sheets according to (13) above may satisfy the following formula (7) when the n value in the rolling direction of the silicon steel sheet is n0, the n value in the direction perpendicular to the rolling direction is n90, the n value in the direction at 45 degrees from the rolling direction is n45, and nave = (n0 + 2 × n45 + n90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di: 0.96 < (ni / nave) × (Di / D) ≦ 1.04 (7) where i = 0, 45, or 90, and when a non-oriented electrical steel sheet is placed in the die, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

[0025] (17) The die for punching non-oriented electrical steel sheets described in (13) above may satisfy the following formula (8) when the yield ratio in the rolling direction of the silicon steel sheet is YR0, the yield ratio in the direction perpendicular to the rolling direction is YR90, the yield ratio in the direction at an angle of 45 degrees from the rolling direction is YR45, and YRave = (YR0 + 2 × YR45 + YR90) / 4, where D is the target diameter of the outer circumferential circle of the punched product after punching with the die and Di is the diameter of the die. 0.96≦(YRi / YRave)×(Di / D)≦1.04 (8) In formula (8), i=0, 45, 90, and when a non-oriented electrical steel sheet is placed in the die, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to a direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to a direction perpendicular to the rolling direction.

[0026] (18) In the die for punching non-oriented electrical steel sheets according to any one of (13) to (17), the base material has a chemical composition, in mass%, of C: 0.0010 to 0.0040%, Si: 2.5 to 4.5%, Al: 0.2 to 2.5%, Mn: 0.1 to 3.5%, P: more than 0% but not more than 0.10%, S: 0 to 0.0030%, N: 0 to 0.0030%, Ti: 0 to 0.0030%, Mo: 0.0010 to 0.10%, Cr: 0 to 0.10%, B: 0 to 0.0010%, Ni: 0 to 0.50%, Cu: 0 to 0.50%, Sn: 0 to 0.20%, It may contain Sb: 0-0.20%, Ca: 0-0.0050%, La: 0-0.0050%, Ce: 0-0.0050%, O: 0-0.10%, V: 0-0.10%, W: 0-0.10%, Zr: 0-0.10%, Nb: 0-0.10%, Mg: 0-0.10%, Bi: 0-0.10%, Nd: 0-0.10%, and Y: 0-0.10%, with the balance being Fe and impurities.

[0027] According to the above-described embodiment of the present invention, it is possible to provide a non-oriented electrical steel sheet that can suppress a decrease in dimensional accuracy after processing and core annealing. Also, according to the above-described embodiment of the present invention, it is possible to provide a method for punching a non-oriented electrical steel sheet and a die for punching a non-oriented electrical steel sheet that can suppress a decrease in dimensional accuracy after processing and core annealing.

[0028] 1 is a plan view illustrating a state in which the rotor core is inserted into the stator core, and FIG. 2 is a plan view for explaining how non-oriented electromagnetic steel sheets constituting the stator core shown in FIG. 1 are sequentially punched out by a male die.

[0029] A method for punching non-oriented electrical steel sheets and a die for punching non-oriented electrical steel sheets according to one embodiment of the present invention will be described below with reference to the drawings. A typical manufacturing process for non-oriented electrical steel sheets includes the steps of ironmaking, steelmaking, hot rolling, and cold rolling. After these steps are performed in order, strain caused during rolling is removed by annealing. Annealing restores or recrystallizes (primary recrystallization) the crystalline structure containing processing strain, thereby releasing the strain. Annealing also causes crystal grain growth. Note that annealing may be performed before cold rolling. Alternatively, cold rolling may be divided into multiple steps, with annealing and cold rolling repeated.

[0030] After the stator core is punched out using a die, the non-oriented electrical steel sheet used for the stator core is subjected to core annealing (stress relief annealing) to reduce iron loss. By applying heat during core annealing, residual stress and strain are released, reducing iron loss.

[0031] If the residual stress distribution in the stator core after punching the stator core with a die is uneven during core annealing, the shape of the stator core will change unevenly due to the release of the residual stress, which may result in a decrease in the high roundness of the inner diameter of the stator core that was achieved before core annealing.

[0032] FIG. 1 is a plan view showing a rotor core inserted into a stator core. In FIG. 1, the stator core 21 is formed by laminating non-oriented electromagnetic steel sheets in a direction perpendicular to the plane of the page. The stator core 21 includes an outer core back 22 and a plurality of teeth 23 protruding inward from the core back 22. A rotor core 30 is inserted inside the tips of the teeth 23. The rotor core 30 includes a rotor core 31 and a plurality of magnets 32 disposed on the outer periphery of the rotor core 31 and facing the tips of the teeth 23. The outer periphery of the stator core 21 is held by a case 50. A shaft 60 passes through the center of the rotor core 31 and is fixed to the rotor core 31. The shaft 60 is supported by the case 50 (or another fixing member) to be rotatable about the center O, with the center O of the shaft 60 aligned with the center of the inner diameter of the stator core 21.

[0033] In FIG. 1 , the inner diameter of the stator core is specifically the inner diameter D of the tips of the teeth 23. If the circularity of this inner diameter D decreases due to the shape change of the stator core 21 accompanying the release of residual stress as described above, the gap between the tips of the teeth 23 and the rotor core 31 becomes uneven. This increases the cogging torque when the rotor core 30 rotates. The increased cogging torque can cause uneven rotation, vibration, noise, and the like. Furthermore, if the circularity of the inner diameter of the stator core 21 decreases further, problems such as the rotor core 31 of the rotor core 30 hitting the tips of the teeth 23 can occur.

[0034] JIS B0621 (1984) "Definition and Display of Geometric Deviation" defines "circularity as the magnitude of deviation of a circular shape from a geometrically correct circle." It also states that the display of circularity is "when a circular shape is sandwiched between two concentric geometric circles, circularity is expressed as the difference in radius between the two circles with the smallest distance between them, and is displayed as circularity mm or circularity μm."

[0035] In this embodiment, the evaluation criterion for roundness is the ratio obtained by dividing the difference between the maximum and minimum diameters of the circles by the average diameter. The maximum diameter of the circles is the diameter of the larger of the two concentric circles described in JIS B0621 (1984), and the minimum diameter of the circles is the diameter of the smaller of the two concentric circles. The average diameter is the average of the maximum and minimum diameters of the circles. Therefore, the evaluation criterion for roundness in this embodiment corresponds to the ratio obtained by dividing the roundness, which is the difference in radius between the two concentric circles when the distance between them is minimum, by the average radius of the two circles described in JIS B0621 (1984).

[0036] If the ratio of the difference between the maximum and minimum values ​​of inner diameter D to the average diameter exceeds 0.20%, the gap between the tips of teeth 23 and rotor core 31 will become uneven, causing rotation irregularities, vibration, noise, etc. Furthermore, problems such as the rotor core 31 of rotor core 30 hitting the tips of teeth 23 will occur, so the ratio of the difference between the maximum and minimum values ​​of inner diameter D to the average diameter is set to 0.20% or less. This ratio is preferably 0.15% or less, and more preferably 0.10% or less. A smaller ratio is preferable, so no lower limit is set.

[0037] One of the factors that causes the residual stress distribution in the stator core to become non-uniform is the anisotropy of the mechanical properties of the non-oriented electrical steel sheet used for punching. If the anisotropy of the mechanical properties is large, the residual stress release during core annealing will vary depending on the direction. In other words, if the anisotropy of the mechanical properties of the non-oriented electrical steel sheet used for punching is large, the stator core will deform (shrink) during core annealing, and the amount of this deformation will vary depending on the direction of residual stress release. Therefore, even if the inner diameter of the stator core is punched out to a perfect circle before core annealing, the roundness of the inner diameter of the stator core after core annealing will decrease, increasing errors in motor manufacturing control.

[0038] In this embodiment, the dimensions of the cylindrical die used to punch the stator core are determined based on the mechanical properties of the non-oriented electrical steel sheet to be punched, i.e., the anisotropy of the silicon steel sheet used as the base material. As the mechanical properties, for example, at least one of Young's modulus, r-value, n-value, and yield ratio is focused on. These characteristic values ​​have anisotropy, with values ​​varying depending on the direction relative to the rolling direction. Therefore, the dimensions of the punching die used to punch the inner diameter of the stator core are determined based on this anisotropy. Specifically, the diameter of the die relative to the rolling direction of the silicon steel sheet is determined based on the mechanical property values ​​of the silicon steel sheet that correspond to the direction relative to the rolling direction of the silicon steel sheet. This makes it possible to provide a motor core with reduced loss of roundness after core annealing. This determination will be described in detail later. Conventionally, a technique has been known for improving the roundness of a stator core after punching by increasing the isotropy of the tensile strength (TS) of the mechanical properties of non-oriented electrical steel sheet. However, improving the isotropy of tensile strength does not necessarily improve the isotropy of other mechanical properties, such as Young's modulus, accordingly, leaving room for improvement in preventing a decrease in the roundness of the inner diameter of the stator core after core annealing. Furthermore, manufacturing a non-oriented electrical steel sheet with improved isotropy of all mechanical properties, including Young's modulus, of the steel sheet to be punched requires a very complicated process, resulting in excessively high manufacturing costs. Furthermore, changing the texture of a non-oriented electrical steel sheet from one rich in {111} to one rich in {100} and / or {110} to improve magnetic properties increases the anisotropy of mechanical properties, such as Young's modulus. Therefore, in order to further improve the roundness of the stator core after punching, improvements to the punching method and the die to be used have been desired, assuming that the non-oriented electrical steel sheet to be punched has anisotropy in mechanical properties. The present embodiment has been made in light of this background, and the punching method for the stator core and the dimensions of the punching die are determined depending on the anisotropy of the mechanical properties of the non-oriented electrical steel sheet to be punched. An example is shown below.

[0039] Taking Young's modulus as an example, the larger the Young's modulus, the smaller the residual stress after punching the stator core inner diameter, and the smaller the deformation when the residual stress is released by core annealing. Therefore, depending on the anisotropy of Young's modulus, it is recommended to reduce the corresponding mold dimensions in the in-plane direction where the Young's modulus is larger, and increase the corresponding mold dimensions in the in-plane direction where the Young's modulus is smaller. This makes it possible to achieve a perfect circle for the stator core inner diameter not only after punching but also after core annealing. Furthermore, the larger the r-value, the greater the change in width / thickness due to tensile stress during punching, and the greater the residual stress under conditions where the width is constrained. Therefore, depending on the anisotropy of the r-value, it is recommended to reduce the corresponding mold dimensions in the in-plane direction where the r-value is larger, and increase the corresponding mold dimensions in the in-plane direction where the r-value is smaller. Furthermore, the larger the n-value and yield ratio, the smaller the deformation from the start of plastic deformation to fracture and the smaller the residual stress. Therefore, depending on the anisotropy of the n value and yield ratio, it is advisable to make the dimensions of the corresponding mold smaller in the in-plane direction of the plate where the n value and / or yield ratio is larger, and larger in the direction where the n value and / or yield ratio is smaller.

[0040] More specifically, when the anisotropy of the mechanical properties of the non-oriented electrical steel sheet to be punched is Young's modulus, where E0 is the Young's modulus in the rolling direction, E90 is the Young's modulus in the direction perpendicular to the rolling direction, and E45 is the Young's modulus in the direction at 45 degrees from the rolling direction, and Eave is defined as (E0 + 2 × E45 + E90) / 4, the dimensions of the die in the rolling direction, the direction perpendicular to the rolling direction, and the direction at 45 degrees from the rolling direction (Di; where i = 0, 45, 90) are determined so as to satisfy the following formula (5) for the target inner diameter D of the core after punching. This allows for the provision of a motor core with the desired circularity. In this specification, the "target inner diameter D of the core after punching" refers to the target value of the outer circumference of the punched product after punching with the die.

[0041] 0.96≦(Ei / Eave)×(Di / D)≦1.04 (5) where i=0, 45, 90.

[0042] If the value of (Ei / Eave) × (Di / D) is outside the range of formula (5), the roundness after core annealing tends to decrease, so the value of (Ei / Eave) × (Di / D) is set to 0.96 or more and 1.04 or less. The value of (Ei / Eave) × (Di / D) is preferably 0.97 or more, and more preferably 0.98 or more. The value of (Ei / Eave) × (Di / D) is preferably 1.03 or less, and more preferably 1.02 or less.

[0043] Furthermore, if the anisotropy of the mechanical properties of the non-oriented electrical steel sheet to be punched is the r-value, and the r-value in the rolling direction is defined as r0, the r-value in the direction perpendicular to the rolling direction as r90, and the r-value in the direction at 45 degrees from the rolling direction as r45, and rave is defined as (r0 + 2 × r45 + r90) / 4, then the dimensions of the die in the rolling direction, the direction perpendicular to the rolling direction, and the direction at 45 degrees from the rolling direction (Di; where i = 0, 45, or 90) are determined so as to satisfy the following formula (6) for the target inner diameter D of the core after punching. This makes it possible to provide a motor core with the desired roundness.

[0044] 0.96≦(ri / rave)×(Di / D)≦1.04 (6) where i=0, 45, 90.

[0045] If the value of (ri / rave) × (Di / D) is outside the range of formula (6), the roundness after core annealing tends to decrease, so the value of (ri / rave) × (Di / D) is set to 0.96 or more and 1.04 or less. The value of (ri / rave) × (Di / D) is preferably 0.97 or more, and more preferably 0.98 or more. The value of (ri / rave) × (Di / D) is preferably 1.03 or less, and more preferably 1.02 or less.

[0046] Furthermore, if the anisotropy of the mechanical properties of the non-oriented electrical steel sheet to be punched is an n-value, and the n-value in the rolling direction is defined as n0, the n-value in the direction perpendicular to the rolling direction as n90, and the n-value in the direction at 45 degrees from the rolling direction as n45, and nave is defined as (n0 + 2 × n45 + n90) / 4, then the dimensions of the die in the rolling direction, the direction perpendicular to the rolling direction, and the direction at 45 degrees from the rolling direction (Di; where i = 0, 45, 90) are determined so as to satisfy the following formula (7) for the target inner diameter D of the core after punching. This makes it possible to provide a motor core with the desired roundness.

[0047] 0.96≦(ni / nave)×(Di / D)≦1.04 (7) where i=0, 45, 90.

[0048] If the value of (ni / nave) × (Di / D) is outside the range of formula (7), the roundness after core annealing tends to decrease, so the value of (ni / nave) × (Di / D) is set to 0.96 or more and 1.04 or less. The value of (ni / nave) × (Di / D) is preferably 0.97 or more, and more preferably 0.98 or more. The value of (ni / nave) × (Di / D) is preferably 1.03 or less, and more preferably 1.02 or less.

[0049] Furthermore, when the anisotropy of the mechanical properties of the non-oriented electrical steel sheet to be punched is the yield ratio, the yield ratio in the rolling direction is defined as YR0, the yield ratio in the direction perpendicular to the rolling direction as YR90, and the yield ratio in the direction at 45 degrees from the rolling direction as YR45, and YRave is defined as (YR0 + 2 × YR45 + YR90) / 4, the dimensions of the mold in the rolling direction, the direction perpendicular to the rolling direction, and the direction at 45 degrees from the rolling direction are determined so as to satisfy the following formula (8) for the target inner diameter D of the core after punching. This makes it possible to provide a motor core with the desired roundness.

[0050] 0.96≦(YRi / YRave)×(Di / D)≦1.04 (8) where i=0, 45, 90.

[0051] If the value of (YRi / YRave) × (Di / D) is outside the range of formula (8), the roundness after core annealing tends to decrease, so the value of (YRi / YRave) × (Di / D) is set to 0.96 or more and 1.04 or less. The value of (YRi / YRave) × (Di / D) is preferably 0.97 or more, and more preferably 0.98 or more. The value of (YRi / YRave) × (Di / D) is preferably 1.03 or less, and more preferably 1.02 or less.

[0052] Furthermore, the non-oriented electrical steel sheet before and after being punched using the above-mentioned die satisfies the following conditions depending on the anisotropy of the mechanical properties of the silicon steel sheet base material. Even after punching and core annealing, no significant changes in texture occur. In other words, the conditions described below are applicable regardless of whether they are before or after punching or core annealing.

[0053] When the anisotropy of the mechanical properties of a non-oriented electrical steel sheet is Young's modulus, where E0 is the Young's modulus in the rolling direction of the non-oriented electrical steel sheet, E90 is the Young's modulus in the direction perpendicular to the rolling direction, and E45 is the Young's modulus in the direction at an angle to the rolling direction, the non-oriented electrical steel sheet of this embodiment satisfies the following formula (1), and the difference between the maximum and minimum diameters of circular holes obtained by punching the steel sheet is 0.20% or less of the average diameter: 0.8100≦(E0+E90) / (2×E45)≦1.0000 (1)

[0054] If the value of (E0 + E90) / (2 × E45) is outside the range of formula (1), even when a disk is punched using a die that satisfies formula (5), the circularity after core annealing will decrease. Therefore, the value of (E0 + E90) / (2 × E45) is set to 0.8100 or more and 1.0000 or less. The value of (E0 + E90) / (2 × E45) is preferably 0.8300 or more, and more preferably 0.8500 or more. The value of (E0 + E90) / (2 × E45) is preferably 0.9800 or less, and more preferably 0.9600 or less. Note that a steel sheet whose Young's modulus satisfies formula (1) can be produced by appropriately controlling the steel composition, rolling, and annealing conditions.

[0055] Furthermore, when the anisotropy of the mechanical properties of a non-oriented electrical steel sheet is the r-value, and the r-value in the rolling direction of the non-oriented electrical steel sheet is defined as r0, the r-value in the direction perpendicular to the rolling direction as r90, and the r-value in the direction at 45 degrees from the rolling direction as r45, the non-oriented electrical steel sheet of this embodiment satisfies the following formula (2), and the difference between the maximum and minimum diameters of circular holes obtained by punching the steel sheet is 0.2% or less of the average diameter: 1.0000≦(r0+r90) / (2×r45)≦1.3100 (2)

[0056] If the value of (r0 + r90) / (2 × r45) is outside the range of formula (2), even if a disk is punched using a die that satisfies formula (6), the circularity after core annealing will decrease, so the value of (r0 + r90) / (2 × r45) is set to 1.0000 or more and 1.3100 or less. The value of (r0 + r90) / (2 × r45) is preferably 1.0500 or more, more preferably 1.1000 or more. The value of (r0 + r90) / (2 × r45) is preferably 1.2600 or less, more preferably 1.2100 or less. Note that steel sheets whose r-value satisfies formula (2) can be manufactured by appropriately controlling the steel composition, rolling, and annealing conditions.

[0057] Furthermore, when the anisotropy of the mechanical properties of a non-oriented electrical steel sheet is represented by an n-value, where the n-value in the rolling direction of the non-oriented electrical steel sheet is defined as n0, the n-value in the direction perpendicular to the rolling direction as n90, and the n-value in the direction at 45 degrees from the rolling direction as n45, the non-oriented electrical steel sheet of this embodiment satisfies the following formula (3), and the difference between the maximum and minimum diameters of circular holes obtained by punching the steel sheet is 0.2% or less of the average diameter: 0.8100≦(n0+n90) / (2×n45)≦1.0000 (3)

[0058] If the value of (n0 + n90) / (2 × n45) is outside the range of formula (3), even if a disk is punched using a die that satisfies formula (7), the circularity after core annealing will decrease. Therefore, the value of (n0 + n90) / (2 × n45) is set to 0.8100 or more and 1.0000 or less. The value of (n0 + n90) / (2 × n45) is preferably 0.8300 or more, and more preferably 0.8500 or more. The value of (n0 + n90) / (2 × n45) is preferably 0.9800 or less, and more preferably 0.9600 or less. Note that steel sheets whose n value satisfies formula (3) can be produced by appropriately controlling the steel composition, rolling, and annealing conditions.

[0059] Furthermore, when the anisotropy of the mechanical properties of a non-oriented electrical steel sheet is the yield ratio, and the yield ratio in the rolling direction of the non-oriented electrical steel sheet is defined as YR0, the yield ratio in the direction perpendicular to the rolling direction as YR90, and the yield ratio in the direction at an angle of 45 degrees from the rolling direction as YR45, the non-oriented electrical steel sheet of this embodiment satisfies the following formula (4), and the difference between the maximum and minimum diameters of circular holes obtained by punching the steel sheet is 0.2% or less of the average diameter: 0.8300≦(YR0+YR90) / (2×YR45)≦1.0300 (4)

[0060] If the value of (YR0 + YR90) / (2 × YR45) is outside the range of formula (4), even when a disk is punched using a die that satisfies formula (8), the roundness after core annealing will decrease. Therefore, the value of (YR0 + YR90) / (2 × YR45) is set to 0.8300 or more and 1.0300 or less. The value of (YR0 + YR90) / (2 × YR45) is preferably 0.8500 or more, and more preferably 0.8700 or more. The value of (YR0 + YR90) / (2 × YR45) is preferably 1.0100 or less, and more preferably 0.9900 or less. Steel sheets whose yield ratio satisfies formula (4) can be produced by appropriately controlling the steel composition, rolling, and annealing conditions.

[0061] The Young's modulus, r value, n value, and yield ratio are all obtained by tensile testing, and the method conforms to the standard (JIS Z 2241 (2011)). In this embodiment, the Young's modulus, r value, n value, and yield ratio of the non-oriented electrical steel sheet are measured based on this standard on the non-oriented electrical steel sheet before core annealing. However, as described above, there is no significant change in the texture even after punching and core annealing. In other words, these property values ​​(Young's modulus, r value, n value, and yield ratio) do not change even after punching and core annealing, so the property values ​​measured before core annealing can be considered to be maintained even after core annealing. An overview of each property value is explained below. In the tensile test, a rectangular tensile test specimen conforming to JIS Z 2241 (2011) is pulled by applying force to both ends, and the magnitude of the load and the change in shape of the test specimen are measured as the load is increased.

[0062] As the load is increased, the strain increases in proportion to the magnitude of the load, but once the yield point is reached, this proportionality relationship no longer holds. The region up to this point is the elastic region, and the ratio of stress to strain in the elastic region is Young's modulus. In the elastic region, when the load is removed, the strain becomes 0 and the material returns to its original state. A material with a high Young's modulus requires a high stress to impart a certain strain. For example, the Young's modulus of single crystal iron is smallest in the <100> direction and largest in the <111> direction.

[0063] Once the yield point is reached, the material will not return to its original state even if the load is removed. This region is the plastic region, and once the yield point is passed, even a slight load will cause strain and elongation. This region is called the yield elongation. If further load is applied here, the material will enter a region where strain increases as the force increases. This is the uniform elongation region, and the r value (Lankford value) is the ratio of the logarithmic strain εw in the width direction to the logarithmic strain εt in the thickness direction when a uniform elongation is applied to the parallel portion of the test piece.

[0064] r≡εw / εt (11) where εw=ln(w / W) and εt=ln(t / T), where w / W is the strain in the width direction and t / T is the strain in the thickness direction.

[0065] For example, in the {111}<112> orientation, which is often found in steel sheets for automobile bodies, the r-value change between 0 and 90 degrees is small, at about 2, but in the {100}<001> orientation, the r-value is maximum in the 0° and 90° directions and is 0 in the 45° direction. In the {110}<001> orientation of grain-oriented electrical steel sheets, the r-value is 1 in the 0° direction, reaches a minimum near the 45° direction, and then increases rapidly as the orientation tilts toward the 90° direction, reaching infinity in the 90° direction.

[0066] After that, the tensile test piece reaches a certain load and begins to elongate even at loads smaller than that, eventually leading to breakage. If the tensile strength, which is the maximum load, is represented by P and the load at the yield point is represented by Py, the yield ratio is given by the following equation (12): Yield ratio = Py / P (12)

[0067] Furthermore, when it is assumed that the following n-th power hardening equation (Equation (13)) holds between the true strain ε and the true stress σ, the power n in the equation is the n value. σ = Cεn (13)

[0068] When measuring the n-value, the relationship between stress σN and strain εN is measured at five or more points from the end of yield elongation to the maximum load point using a tensile test piece conforming to JIS Z 2241, using a method conforming to the standard (JIS Z 2241). Based on these measurements, true stress σ and true strain ε are calculated using equations (14) and (15), and plotted on a logarithmic scale with strain (lnε) on the horizontal axis and stress (lnσ) on the vertical axis. The gradient of the line indicated by the measurement points represents the n-value. σ = (1 + εN)σN (14) ε = ln(1 + εN) (15)

[0069] The deformation of steel plate progresses due to work hardening, and the n-value can be considered a characteristic value that represents the work hardening behavior of plate material in the early stages of deformation. Materials with a high n-value therefore have the tendency to easily expand the plastic deformation region. Therefore, the n-value is also called the work hardening coefficient or strain hardening exponent.

[0070] The non-oriented electrical steel sheet according to this embodiment has been described above. The thickness of the non-oriented electrical steel sheet according to this embodiment may be 0.35 mm or less, and more preferably 0.30 mm or less. On the other hand, excessive thinning significantly reduces the productivity of the steel sheet and motors, so the thickness is preferably 0.10 mm or more, and more preferably 0.15 mm or more.

[0071] The thickness may be measured using a micrometer. If the non-oriented electrical steel sheet to be measured has an insulating coating on its surface, the insulating coating should be removed before the measurement.

[0072] FIG. 2 is a plan view illustrating how the non-oriented electromagnetic steel sheet 110 constituting the stator core 21 shown in FIG. 1 is sequentially punched out by the male dies 100, 102, and 104. First, the non-oriented electromagnetic steel sheet 110 is punched out by the cylindrical male die 100. The punched circular portion becomes the rotor core. Next, the male die 102 punches out the spaces between the portions that will become the teeth 23. Next, the cylindrical die 104 punches out the portion corresponding to the outer diameter of the stator core 21, thereby punching out the outer diameter. The outer diameter Dm of the male die 100 corresponds to the inner diameter D of the stator core 21. The male die 100 and the female die 110 are configured so that the outer diameter Dm of the male die 100 satisfies Di in the above-described formulas (5) to (8). Furthermore, the male die 100 and the female die 110 are configured so that the outer diameter of the male die 104 satisfies Di in the above-described formulas (5) to (8). The die for punching non-oriented electrical steel sheets according to this embodiment includes male dies 100, 104 and female dies corresponding to the male dies 100, 104. The outer diameter of the male dies 100, 104 may be smaller than the inner diameter of the female dies corresponding to the male dies 100, 104 by the amount of a predetermined clearance required for punching.

[0073] The non-oriented electrical steel sheet according to this embodiment includes a silicon steel sheet as a base material, and a known non-oriented electrical steel sheet can be used as this silicon steel sheet. An example of a preferred chemical composition of the base material will be described below. Note that "%" in the following chemical components means "mass %." Furthermore, numerical ranges indicated with "to" include both the lower and upper limits.

[0074] The chemical composition of the base material is, in mass %, 3.0% to 6.0% Si, with the remainder being Fe and impurities. There are no particular limitations on the other elements. However, in this embodiment, in addition to Si, Fe, and impurities, elements may be contained within a range that does not impair the effects of the present invention. For example, it is acceptable to replace a portion of Fe with the following elements within the following ranges. The content ranges of representative selected elements are as follows:

[0075] C: 0.0010-0.0040%, Si: 2.5-4.5%, Al: 0.2-2.5%, Mn: 0.1-3.5%, P: more than 0%, 0.10% or less, S: 0-0.0030%, N: 0-0.0030%, Ti: 0-0.0030%, Mo: 0.0010-0.10%, Cr: 0-0.10%, B: 0-0.0010%, Ni: 0-0.50%, Cu: 0-0.50%, Sn: 0-0.20%, Sb: 0-0.20%, Ca: 0-0.0050%, La: 0 to 0.0050%, Ce: 0 to 0.0050%, O: 0-0.10%, V: 0-0.10%, W: 0-0.10%, Zr: 0-0.10%, Nb: 0-0.10%, Mg: 0-0.10%, Bi: 0-0.10%, Nd: 0-0.10%, Y: 0-0.10%.

[0076] The above-mentioned optional elements may be contained according to their intended purpose, so there is no need to set a lower limit, and they may not be substantially contained. Furthermore, even if these optional elements are contained as impurities, the effects of this embodiment are not impaired. Furthermore, since it is difficult to achieve a C content of 0% in practical steel sheets during manufacturing, the C content may be greater than 0%. Furthermore, impurities refer to elements that are unintentionally contained, and refer to elements that are mixed in from raw materials such as ore, scrap, or the manufacturing environment during industrial production of base steel sheets. The upper limit of the total impurity content may be, for example, 5%. Excessive Sn and Sb content may increase the {110}<001> orientation, resulting in increased anisotropy of the Young's modulus. Therefore, the respective contents of Sn and Sb are preferably 0.01% or less.

[0077] The chemical composition of the base material may be measured by a general steel analysis method. For example, the chemical composition of the base steel plate may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, for example, a 35 mm square test piece may be obtained from the center of the base steel plate after coating removal, and the composition may be determined by measuring it using a Shimadzu ICPS-8100 or similar (measuring device) under conditions based on a pre-created calibration curve. C and S may be measured using a combustion-infrared absorption method, and N may be measured using an inert gas fusion-thermal conductivity method.

[0078] The above chemical composition is that of the silicon steel sheet used as the base material. If the non-oriented electrical steel sheet to be measured has an insulating coating or the like on its surface, the coating is removed by a known method before measuring the chemical composition.

[0079] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea described in the claims of the present disclosure and that achieves similar effects is included within the technical scope of the present disclosure. Furthermore, although the present embodiments illustrate the case where circular holes are punched in a non-oriented electrical steel sheet, the present embodiments can also be applied to the case where holes having shapes other than circular are punched.

[0080] The present disclosure will be specifically described below using examples. Note that the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present disclosure, and the present disclosure is not limited to the conditions in the examples. The present disclosure may adopt various conditions as long as they do not deviate from the gist of the disclosure and achieve its objectives. Note that underlines in Tables 1 to 6 indicate conditions that are outside the scope or preferred range of the present invention, unfavorable mold conditions, or unfavorable characteristic values.

[0081] Example 1 A 3 mm thick hot-rolled sheet containing, by mass%, 3.0% Si, 0.5% Al, 0.2% Mn, and 0.0020% C, with the balance being Fe and impurities, was prepared and annealed at 800°C to 1100°C for 1 to 10 minutes to obtain a hot-rolled annealed sheet. The hot-rolled annealed sheet was cold-rolled to a thickness of 0.4 mm to 2.0 mm, annealed at 800°C to 1100°C for 1 to 10 minutes (intermediate annealing), and cold-rolled again to obtain a 0.2 mm thick cold-rolled sheet. The cold-rolled sheet was annealed at 750°C for 30 seconds (finish annealing) to obtain non-oriented electrical steel sheets (Nos. A1 to A17 (Materials 1A to 1Q)) having the mechanical properties (Young's modulus) shown in Table 1. The obtained non-oriented electrical steel sheets (Materials 1A to 1Q) were punched using the dies shown in Table 2, and then core annealed at 750°C for 2 hours. As a result, for Nos. A1 to A8, which used materials 1A to 1H satisfying formula (1), when punched with any of dies 1R to 1Z satisfying formula (5), the predetermined dimensions with high circularity that satisfied the above-mentioned evaluation criteria were obtained. On the other hand, for Nos. A9 to A15, which used materials other than 1A to 1H (1J to 1Q), none of the dies used satisfied formula (5), and therefore the predetermined dimensions with high circularity that satisfied the evaluation criteria were not obtained. Furthermore, for No. A17, which used material 1J that did not satisfy formula (1), the circularity decreased even when punched with a die that satisfied formula (5), and the predetermined dimensions with high circularity that satisfied the evaluation criteria were not obtained. Furthermore, for No. Although A16 uses a material 1A that satisfies formula (1), the mold did not satisfy formula (5), so the circularity decreased and the predetermined dimensions of high circularity that meet the evaluation criteria could not be obtained. The target diameter D of the outer circumferential circle of the punched product after punching was set to 120 mm. Here, the predetermined dimensions of high circularity that meet the evaluation criteria means that the value of the maximum value - minimum value of the diameter after punching and core annealing is 0.20% or less of the average diameter (target diameter), and when the target diameter is 120 mm, the diameter after punching and core annealing falls within the range of 120 mm ± 0.12 mm.

[0082]

[0083]

[0084] Example 2 A 3 mm thick hot-rolled sheet containing, by mass%, 3.0% Si, 0.5% Al, 0.2% Mn, and 0.0020% C, with the balance being Fe and impurities, was prepared and annealed at 800°C to 1100°C for 1 to 10 minutes to obtain a hot-rolled annealed sheet. The hot-rolled annealed sheet was cold-rolled to a thickness of 0.4 mm to 2.0 mm, annealed at 800°C to 1100°C for 1 to 10 minutes (intermediate annealing), and cold-rolled again to obtain a 0.2 mm thick cold-rolled sheet. The cold-rolled sheet was annealed at 750°C for 30 seconds (finish annealing) to obtain non-oriented electrical steel sheets (Nos. B1 to B17 (Materials 2A to 2Q)) having the mechanical properties (r-values) shown in Table 3. The obtained non-oriented electrical steel sheets (materials 2A to 2Q) were punched using the dies shown in Table 4, and then core annealed at 750°C for 2 hours. As a result, for Nos. B1 to B8, which used materials 2A to 2H satisfying formula (2), when punched with any of dies 2R to 2Z satisfying formula (6), a high degree of circularity and the predetermined dimensions satisfying the above-mentioned evaluation criteria were obtained. On the other hand, for Nos. B9 to B15, which used materials other than 2A to 2H (2J to 2Q), none of the dies used satisfied formula (6), and therefore the high degree of circularity and the predetermined dimensions satisfying the evaluation criteria were not obtained. Furthermore, for No. A17, which used material 2N not satisfying formula (2), the circularity decreased even when punched with a die satisfying formula (6), and the high degree of circularity and the predetermined dimensions satisfying the evaluation criteria were not obtained. Furthermore, for No. Although B16 uses a material 2A that satisfies formula (1), the mold did not satisfy formula (6), so the circularity decreased and the predetermined dimensions of high circularity that meet the evaluation criteria could not be obtained. The target diameter D of the outer circumferential circle of the punched product after punching was set to 120 mm. Here, the predetermined dimensions of high circularity that meet the evaluation criteria mean that the value of the maximum value - minimum value of the diameter after punching and core annealing is 0.20% or less of the average diameter (target diameter), and when the target diameter is 120 mm, the diameter after punching and core annealing falls within the range of 120 mm ± 0.12 mm.

[0085]

[0086]

[0087] Example 3 A 3 mm thick hot-rolled sheet containing, by mass%, 3.0% Si, 0.5% Al, 0.2% Mn, and 0.0020% C, with the balance being Fe and impurities, was prepared and annealed at 800°C to 1100°C for 1 to 10 minutes to obtain a hot-rolled annealed sheet. The hot-rolled annealed sheet was cold-rolled to a thickness of 0.4 mm to 2.0 mm, annealed at 800°C to 1100°C for 1 to 10 minutes (intermediate annealing), and cold-rolled again to obtain a 0.2 mm thick cold-rolled sheet. The cold-rolled sheet was annealed at 750°C for 30 seconds (finish annealing) to obtain non-oriented electrical steel sheets (Nos. C1 to C17 (Materials 3A to 3Q)) having the mechanical properties (n values) shown in Table 5. The obtained non-oriented electrical steel sheets (materials 3A to 3Q) were punched using the dies shown in Table 6, and then core annealed at 750°C for 2 hours. As a result, for Nos. C1 to C8, which used materials 3A to 3H satisfying formula (3), when punched with any of dies 3R to 3Z satisfying formula (7), the predetermined dimensions with high circularity that satisfied the above-mentioned evaluation criteria were obtained. On the other hand, for Nos. C9 to C15, which used materials other than 3A to 3H (3J to 3Q), none of the dies used satisfied formula (7), and therefore the predetermined dimensions with high circularity that satisfied the evaluation criteria were not obtained. Furthermore, for No. C17, which used material 3J that did not satisfy formula (3), the circularity decreased even when punched with a die that satisfied formula (7), and the predetermined dimensions with high circularity that satisfied the evaluation criteria were not obtained. Furthermore, for No. Although C16 uses a material 3A that satisfies formula (3), the mold did not satisfy formula (7), so the circularity decreased and the predetermined dimensions of high circularity that meet the evaluation criteria could not be obtained. The target diameter D of the outer circumferential circle of the punched product after punching was 120 mm. Here, the predetermined dimensions of high circularity that meet the evaluation criteria are those in which the value of the maximum value - minimum value of the diameter after punching and core annealing is 0.20% or less of the average diameter (target diameter), and when the target diameter is 120 mm, the diameter after punching and core annealing is within the range of 120 mm ± 0.12 mm.

[0088]

[0089]

[0090] Example 4 A 3 mm thick hot-rolled sheet containing, by mass%, 3.0% Si, 0.5% Al, 0.2% Mn, and 0.0020% C, with the balance being Fe and impurities, was prepared and annealed at 800°C to 1100°C for 1 to 10 minutes to obtain a hot-rolled annealed sheet. The hot-rolled annealed sheet was cold-rolled to a thickness of 0.4 mm to 2.0 mm, annealed at 800°C to 1100°C for 1 to 10 minutes (intermediate annealing), and cold-rolled again to obtain a 0.2 mm thick cold-rolled sheet. The cold-rolled sheet was annealed at 750°C for 30 seconds (finish annealing) to obtain non-oriented electrical steel sheets (Nos. D1 to D17 (Materials 4A to 4Q)) having the mechanical properties (yield ratio) shown in Table 7. The obtained non-oriented electrical steel sheets (materials 4A to 4Q) were punched using the dies shown in Table 8, and then core annealed at 750°C for 2 hours. As a result, for Nos. D1 to D8, which used materials 4A to 4H satisfying formula (4), when punched with any of dies 4R to 4Z satisfying formula (8), the predetermined dimensions with high circularity that satisfied the above-mentioned evaluation criteria were obtained. On the other hand, for Nos. D9 to D15, which used materials other than 4A to 4H (4J to 4Q), none of the dies used satisfied formula (8), and therefore the predetermined dimensions with high circularity that satisfied the evaluation criteria were not obtained. Furthermore, for No. D17, which used material 4J that did not satisfy formula (4), the circularity decreased even when punched with a die that satisfied formula (8), and the predetermined dimensions with high circularity that satisfied the evaluation criteria were not obtained. Furthermore, for No. Although D16 uses material 4E, which satisfies formula (4), the mold did not satisfy formula (8), so the circularity decreased and the predetermined dimensions of high circularity that meet the evaluation criteria could not be obtained. The target diameter D of the outer circumferential circle of the punched product after punching was 120 mm. Here, the predetermined dimensions of high circularity that meet the evaluation criteria mean that the value of the maximum value - minimum value of the diameter after punching and core annealing is 0.20% or less of the average diameter (target diameter), and when the target diameter is 120 mm, the diameter after punching and core annealing falls within the range of 120 mm ± 0.12 mm.

[0091]

[0092]

[0093] 21 stator core 22 core back 23 teeth 30 rotor core 31 rotor core 32 magnet 50 case 60 shaft 100, 102, 104 male mold 110 non-oriented electromagnetic steel sheet

Claims

1. A non-oriented electrical steel sheet having a silicon steel sheet as a base material, the silicon steel sheet having predetermined mechanical properties corresponding to a direction relative to the rolling direction, and the difference between the maximum and minimum diameters of a circular hole after punching with a substantially circular die is 0.20% or less of the average of the maximum and minimum values.

2. The non-oriented electrical steel sheet according to claim 1, wherein the predetermined mechanical properties satisfy the following formula (1) when the Young's modulus in the rolling direction of the silicon steel sheet is E0, the Young's modulus in the direction perpendicular to the rolling direction is E90, and the Young's modulus in the direction at 45 degrees from the rolling direction is E45: 0.8100≦(E0+E90) / (2×E45)≦1.0000...(1) 3. The non-oriented electrical steel sheet according to claim 1 or 2, wherein the predetermined mechanical property satisfies the following formula (2) when the r-value in the rolling direction of the silicon steel sheet is r0, the r-value in the direction perpendicular to the rolling direction is r90, and the r-value in the direction at 45 degrees from the rolling direction is r45: 1.0000≦(r0+r90) / (2×r45)≦1.3100...(2) 4. The non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the predetermined mechanical properties satisfy the following formula (3) when the n-value in the rolling direction of the silicon steel sheet is n0, the n-value in the direction perpendicular to the rolling direction is n90, and the n-value in the direction at 45 degrees from the rolling direction is n45: 0.8100≦(n0+n90) / (2×n45)≦1.0000...(3) 5. The non-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the predetermined mechanical properties satisfy the following formula (4) when the yield ratio in the rolling direction of the silicon steel sheet is YR0, the yield ratio in the direction perpendicular to the rolling direction is YR90, and the yield ratio in the direction at an angle of 45 degrees from the rolling direction is YR45: 0.8300≦(YR0+YR90) / (2×YR45)≦1.0300...(4) 6. The chemical composition of the base material is, in mass%, C: 0.0010-0.0040%, Si: 2.5-4.5%, Al: 0.2-2.5%, Mn: 0.1-3.5%, P: over 0%, 0.10% or less, S: 0-0.0030%, N: 0-0.0030%, Ti: 0-0.0030%, Mo: 0.0010-0.10%, Cr: 0-0.10%, B: 0-0.0010%, Ni: 0-0.50%, Cu: 0-0.50%, Sn: 0-0.20%, Sb: 0-0.20%, Ca: 0-0.0050%, 6. The non-oriented electrical steel sheet according to any one of claims 1 to 5, comprising La: 0-0.0050%, Ce: 0-0.0050%, O: 0-0.10%, V: 0-0.10%, W: 0-0.10%, Zr: 0-0.10%, Nb: 0-0.10%, Mg: 0-0.10%, Bi: 0-0.10%, Nd: 0-0.10%, and Y: 0-0.10%, with the balance being Fe and impurities.

7. A method for punching a non-oriented electrical steel sheet having a silicon steel sheet as a base material using a substantially cylindrical die, comprising determining the diameter of the die in a direction relative to the rolling direction based on mechanical property values ​​of the silicon steel sheet corresponding to the direction relative to the rolling direction of the silicon steel sheet, and punching the silicon steel sheet.

8. The method for punching non-oriented electrical steel sheets according to claim 7, wherein, when the Young's modulus of the silicon steel sheet in the rolling direction is E0, the Young's modulus in the direction perpendicular to the rolling direction is E90, the Young's modulus in the direction at 45 degrees from the rolling direction is E45, and Eave = (E0 + 2 × E45 + E90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di, the following formula (5) is satisfied: 0.96 < (Ei / Eave) × (Di / D) ≦ 1.04 (5) where, in formula (5), i = 0, 45, 90, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

9. The method for punching non-oriented electrical steel sheets according to claim 7, wherein, when the r-value in the rolling direction of the silicon steel sheet is r0, the r-value in the direction perpendicular to the rolling direction is r90, the r-value in the direction at 45 degrees from the rolling direction is r45, and rave = (r0 + 2 × r45 + r90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di, the following formula (6) is satisfied: 0.96 < (ri / rave) × (Di / D) ≦ 1.04 (6) where, in formula (6), i = 0, 45, 90, D0 is the diameter of the die corresponding to the rolling direction, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

10. The method for punching non-oriented electrical steel sheets according to claim 7, wherein, when the n value of the silicon steel sheet in the rolling direction is n0, the n value in the direction perpendicular to the rolling direction is n90, the n value in the direction at 45 degrees from the rolling direction is n45, and nave = (n0 + 2 × n45 + n90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di, the following formula (7) is satisfied: 0.96 < (ni / nave) × (Di / D) ≦ 1.04 (7) where, in formula (7), i = 0, 45, 90, D0 is the diameter of the die corresponding to the rolling direction, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

11. The method for punching non-oriented electrical steel sheets according to claim 7, wherein, when the yield ratio of the silicon steel sheet in the rolling direction is YR0, the yield ratio in the direction perpendicular to the rolling direction is YR90, the yield ratio in the direction at 45 degrees from the rolling direction is YR45, and YRave = (YR0 + 2 × YR45 + YR90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di, the following formula (8) is satisfied: 0.96≦(YRi / YRave) × (Di / D)≦1.04 (8) where i = 0, 45, 90, D0 is the diameter of the die corresponding to the rolling direction, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

12. The chemical composition of the base material is, in mass%, C: 0.0010-0.0040%, Si: 2.5-4.5%, Al: 0.2-2.5%, Mn: 0.1-3.5%, P: over 0%, 0.10% or less, S: 0-0.0030%, N: 0-0.0030%, Ti: 0-0.0030%, Mo: 0.0010-0.10%, Cr: 0-0.10%, B: 0-0.0010%, Ni: 0-0.50%, Cu: 0-0.50%, Sn: 0-0.20%, Sb: 0-0.20%, Ca: 0-0.0050%, 12. The method for punching a non-oriented electrical steel sheet according to any one of claims 7 to 11, characterized in that the steel sheet contains La: 0-0.0050%, Ce: 0-0.0050%, O: 0-0.10%, V: 0-0.10%, W: 0-0.10%, Zr: 0-0.10%, Nb: 0-0.10%, Mg: 0-0.10%, Bi: 0-0.10%, Nd: 0-0.10%, and Y: 0-0.10%, with the balance being Fe and impurities.

13. A punching die for non-oriented electromagnetic steel sheet, comprising a substantially cylindrical die for punching a non-oriented electromagnetic steel sheet having a silicon steel sheet as a base material, wherein the diameter of the die in a direction relative to the rolling direction of the silicon steel sheet is determined based on the mechanical property values ​​of the silicon steel sheet according to the direction relative to the rolling direction.

14. A punching die for non-oriented electrical steel sheets according to claim 13, which satisfies the following formula (5) when the Young's modulus of the silicon steel sheet in the rolling direction is E0, the Young's modulus in the direction perpendicular to the rolling direction is E90, the Young's modulus in the direction at 45 degrees from the rolling direction is E45, and Eave = (E0 + 2 × E45 + E90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di: 0.96 < (Ei / Eave) × (Di / D) ≦ 1.04 ... (5) where, in formula (5), i = 0, 45, 90, and when a non-oriented electrical steel sheet is placed in the die, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

15. A punching die for non-oriented electrical steel sheets according to claim 13, which satisfies the following formula (6) when the r-value in the rolling direction of the silicon steel sheet is r0, the r-value in the direction perpendicular to the rolling direction is r90, the r-value in the direction at 45 degrees from the rolling direction is r45, and rave = (r0 + 2 × r45 + r90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di: 0.96 < (ri / rave) × (Di / D) ≦ 1.04 ... (6) where, in formula (6), i = 0, 45, 90, and when a non-oriented electrical steel sheet is placed in the die, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling.

16. A punching die for non-oriented electrical steel sheets according to claim 13, which satisfies the following formula (7) when the n value in the rolling direction of the silicon steel sheet is n0, the n value in the direction perpendicular to the rolling direction is n90, the n value in the direction at 45 degrees from the rolling direction is n45, and nave = (n0 + 2 × n45 + n90) / 4, the target diameter of the outer circumferential circle of the punched product after punching with the die is D, and the diameter of the die is Di: 0.96 < (ni / nave) × (Di / D) ≦ 1.04 ... (7) where, in formula (7), i = 0, 45, 90, and when a non-oriented electrical steel sheet is placed in the die, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to the direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling.

17. A punching die for non-oriented electrical steel sheet as recited in claim 13, which satisfies the following formula (8), when the yield ratio of the silicon steel sheet in the rolling direction is YR0, the yield ratio in the direction perpendicular to the rolling direction is YR90, and the yield ratio in a direction at 45 degrees from the rolling direction is YR45, YRave = (YR0 + 2 × YR45 + YR90) / 4, a target diameter of an outer circumferential circle of a product punched with the die is D, and a diameter of the die is Di. 0.96≦(YRi / YRave)×(Di / D)≦1.04 (8) In formula (8), i = 0, 45, 90, and when a non-oriented electrical steel sheet is placed in the die, D0 is the diameter of the die corresponding to the rolling direction of the silicon steel sheet, D45 is the diameter of the die corresponding to a direction at 45 degrees from the rolling direction, and D90 is the diameter of the die corresponding to the direction perpendicular to the rolling direction.

18. The chemical composition of the base material is, in mass%, C: 0.0010-0.0040%, Si: 2.5-4.5%, Al: 0.2-2.5%, Mn: 0.1-3.5%, P: over 0%, 0.10% or less, S: 0-0.0030%, N: 0-0.0030%, Ti: 0-0.0030%, Mo: 0.0010-0.10%, Cr: 0-0.10%, B: 0-0.0010%, Ni: 0-0.50%, Cu: 0-0.50%, Sn: 0-0.20%, Sb: 0-0.20%, Ca: 0-0.0050%, 18. The punching die for non-oriented electrical steel sheet according to any one of claims 13 to 17, characterized in that it contains La: 0-0.0050%, Ce: 0-0.0050%, O: 0-0.10%, V: 0-0.10%, W: 0-0.10%, Zr: 0-0.10%, Nb: 0-0.10%, Mg: 0-0.10%, Bi: 0-0.10%, Nd: 0-0.10%, and Y: 0-0.10%, with the balance being Fe and impurities.

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