Non-oriented electrical steel sheet, rotor core, motor, and method for manufacturing non-oriented electrical steel sheet

Abstract

Provided is a non-oriented electrical steel sheet capable of providing high strength and excellent magnetic characteristics and excellent in dimensional accuracy after punching. A non-oriented electrical steel sheet according to the present embodiment contains, in % by mass, 3.1-4.5% of Si, further, Ti, Si, Al, Zr, Nb, V, Mo, Cr, C, La, Ce and N satisfy formula (1) and formula (2), the tensile strength TS is higher than 570 MPa, the work hardening amount WH of formula (3) is less than 15 MPa, the average crystal grain size D (μm) satisfies formula (4), and the yield elongation is 0.5% or more.　(1): Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750; (2): Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000; (3): WH=Y2.0-YS; (4): D<80-Si×10

Description

[Technical Field]

[0001] The present disclosure relates to a non-oriented electrical steel sheet, a rotor core, a motor, and a method for manufacturing the non-oriented electrical steel sheet. [Background technology]

[0002] Non-oriented electrical steel sheets are widely used as materials for motor cores (iron cores). To obtain highly efficient motor cores, non-oriented electrical steel sheets are required to have excellent iron loss properties. Therefore, in order to manufacture non-oriented electrical steel sheets with excellent iron loss properties, steel sheets have been increasingly made with high alloys.

[0003] A motor core includes a stator core, which is a stator, and a rotor core, which is a rotor. Of the stator core and rotor core, the rotor core is particularly required to have both high strength and excellent magnetic properties (reduced iron loss degradation) for the following reasons: In recent years, motors for electric vehicles and hybrid vehicles have been designed to increase motor output by increasing the motor rotation speed. As a result, the load on the rotor core, which is the rotor, during motor operation has increased. Therefore, the rotor core is required to have high strength. In addition, because the rotor core is fixed to the rotating shaft, cooling it is difficult. Therefore, thermal management of the rotor core is also important. Iron loss in non-oriented electrical steel sheets ultimately becomes heat. Therefore, from the perspective of thermal management of the rotor core, it is necessary to reduce iron loss degradation of non-oriented electrical steel sheets.

[0004] A non-oriented electrical steel sheet having high strength and excellent magnetic properties is proposed in JP 2008-050686 A (Patent Document 1). In Patent Document 1, high strength and excellent magnetic properties are achieved by appropriately adjusting the chemical composition. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-050686 Summary of the Invention [Problem to be solved by the invention]

[0006] When manufacturing rotor cores from non-oriented electrical steel sheets, punching is performed on the non-oriented electrical steel sheets to produce punched products such as rotor core materials. High-alloy and high-strength non-oriented electrical steel sheets can be difficult to punch into the desired shape, resulting in reduced dimensional accuracy of the punched products. Specifically, unevenness may occur on the end surface (punched end surface) of the punched product after punching. When the punched end surface is uneven, when the punched product is assembled into a motor, it becomes difficult for the punched product to adhere to other components at the contact interface with the magnet, shaft, motor case, and other components. This creates challenges in fixing the motor core. Furthermore, it creates challenges in heat dissipation during thermal management of the motor core. Meanwhile, shear strain introduced into non-oriented electrical steel sheets causes deterioration of iron loss. This increases the heat generated by the motor core. Recently, rotor core materials have been punched into complex shapes to improve their functionality. As a result, the proportion of punched end faces in rotor core materials is increasing, and as a result, it is becoming increasingly important to reduce iron loss degradation caused by shear strain introduced into rotor core materials during punching.

[0007] An object of the present disclosure is to provide a non-oriented electrical steel sheet, a rotor core, a motor, and a method for manufacturing a non-oriented electrical steel sheet that has high strength and excellent magnetic properties and has excellent dimensional accuracy after punching. [Means for solving the problem]

[0008] The non-oriented electrical steel sheet of the present disclosure contains, by mass%, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0 to 0.100%, Cr: 0 to 2.000%, and La: 0 to 0.0100%. %, Ce: 0 to 0.0100%, B: 0 to 0.0010%, Zn: 0 to 0.0050%, Ga: 0 to 0.0050%, Ge: 0 to 0.0050%, As: 0 to 0.0100%, Ni: 0 to 0.500%, Cu: 0 to 0.500%, Sn: 0 to 0.200%, Sb: 0 to 0.100%, Ca: 0 to 0.0050%, Nd: 0 to 0.0010%, Mg: 0 to 0.0030%, and the remainder being Fe and impurities, satisfying formula (1) and formula (2). Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol. Furthermore, the non-oriented electrical steel sheet has a tensile strength TS higher than 570 MPa. For non-oriented electrical steel sheets, the stress at 2.0% strain is further increased to Y 2.0 (MPa) and the yield stress is YS (MPa), the amount of work hardening WH defined by formula (3) is less than 15 MPa. WH=Y 2.0 -YS (3) Furthermore, in the non-oriented electrical steel sheet, the average grain size D (μm) satisfies formula (4) and the yield elongation is 0.5% or more. D<80-Si×10 (4) Here, the element symbol in formula (4) is substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for that element symbol.

[0009] The rotor core of the present disclosure includes a plurality of rotor core blanks stacked on top of one another. The rotor core material is composed of, by mass%, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0 to 0.100%, Cr: 0 to 2.000%, La: 0 to 0.0100%, C e: 0-0.0100%, B: 0-0.0010%, Zn: 0-0.0050%, Ga: 0-0.0050%, Ge: 0-0.0050%, As: 0-0.0100%, Ni: 0-0.500%, Cu: 0-0.500%, Sn: 0-0.200%, Sb: 0-0.100%, Ca: 0-0.0050%, Nd: 0-0.0010%, Mg: 0-0.0030%, and the remainder being Fe and impurities, satisfying formula (1) and formula (2). Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol. The rotor core material also has a tensile strength TS higher than 570 MPa. Furthermore, for the rotor core material, the stress at 2.0% strain is 2.0 (MPa) and the yield stress is YS (MPa), the amount of work hardening WH defined by formula (3) is less than 15 MPa. WH=Y 2.0 -YS (3) Furthermore, the rotor core material has an average grain size D (μm) that satisfies formula (4) and a yield elongation of 0.5% or more. D<80-Si×10 (4) Here, the element symbol in formula (4) is substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for that element symbol.

[0010] The motor of the present disclosure includes the rotor core described above.

[0011] The method for manufacturing a non-oriented electrical steel sheet according to the present disclosure includes a hot rolling step, a cold rolling step, and a finish annealing step. In the hot rolling process, the slab is hot rolled to produce a hot-rolled steel sheet. In the cold rolling step, the hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet. In the finish annealing step, the cold-rolled steel sheet is subjected to finish annealing in a finish annealing furnace. In the final annealing step, the cold-rolled steel sheet is further annealed at a maximum temperature T1 of 950°C or less. Furthermore, the tension TE applied to the cold-rolled steel sheet at the maximum temperature T1 is set to 2.0 to 10.0 MPa. Furthermore, the residence time t0 (seconds) between the annealing temperatures T1 and 700°C in the heating zone, soaking zone, and cooling zone of the final annealing furnace, and the residence time t1 (seconds) between the annealing temperatures of 700°C and 500°C in the cooling zone satisfy formulas (A) and (B). t1-t0>0 (A) t1 / t0≦3.0 (B) Furthermore, in one or more locations selected from the heating zone, the soaking zone, and the cooling zone in the temperature range of 500°C or higher in the furnace atmosphere of the final annealing furnace, the hydrogen partial pressure P H2 (atm) versus water vapor partial pressure P H20 (atm) ratio is set to be higher than 0.05, or the oxygen concentration is set to be higher than 0.010%. Furthermore, the temperature gradient CG in the longitudinal direction of the cold-rolled steel sheet during the cooling process is set to 20°C / m or less. [Effects of the Invention]

[0012] The non-oriented electrical steel sheet of the present disclosure has high strength and excellent magnetic properties, and has excellent dimensional accuracy after punching. The rotor core and the motor of the present disclosure are manufactured using the non-oriented electrical steel sheet of the present disclosure as a raw material. The manufacturing method of the non-oriented electrical steel sheet of the present disclosure can manufacture the above-mentioned non-oriented electrical steel sheet of the present disclosure. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a stress-strain curve. [Figure 2] FIG. 2 is a schematic diagram showing an example of a stress-strain curve different from that shown in FIG. [Figure 3] FIG. 3 is a schematic diagram for explaining how to determine the yield point elongation when the upper yield point is not clear in the stress-strain curve. [Figure 4] FIG. 4 is a plan view showing an example of the rotor core of the present embodiment. [Figure 5] FIG. 5 is a plan view showing an example of the stator core of the present embodiment. [Figure 6] FIG. 6 is a schematic diagram for explaining the definition of punching flatness in the dimensional accuracy evaluation test after punching in the example. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors have investigated and studied the causes of the reduction in dimensional accuracy and the deterioration of magnetic properties of punched products (rotor core materials, etc.) when punching non-oriented electrical steel sheets, which have high strength and excellent magnetic properties. As a result, the present inventors have come to the following findings.

[0015] During punching, when a non-oriented electrical steel sheet is forced into a die by a punch, the portion of the steel sheet near the surface of the sheet that is pressed by the punch is forced in the thickness direction. Meanwhile, the portion of the steel sheet that is in contact with the die is pulled toward the chips. Thus, the direction of stress imparted to the steel sheet during punching varies in a complex manner. Therefore, after the steel sheet breaks during punching, the degree of springback when the stress is released varies depending on the thickness direction of the steel sheet. As a result, unevenness occurs on the end surface (punched end surface) of the punched product, reducing the dimensional accuracy of the punched product. This reduction in dimensional accuracy is particularly noticeable when the tensile strength of the steel sheet is higher than 570 MPa.

[0016] When a steel sheet is deformed by punching, multiple dislocations are introduced into the steel sheet. If the dislocations introduced by deformation become entangled and work hardening progresses, the amount of springback when the stress is released after the steel sheet breaks during punching increases further. As a result, unevenness occurs on the end surface of the punched product (punched end surface) after punching, reducing the dimensional accuracy of the punched product.

[0017] Furthermore, in non-oriented electrical steel sheets, dislocations are introduced due to the shear strain imparted during punching. These dislocations degrade the magnetic properties. As work hardening progresses, dislocations become entangled and remain in the steel sheet. As work hardening progresses, the iron loss of the steel sheet deteriorates.

[0018] Considering the above mechanism, the inventors thought that if the amount of work hardening could be reduced, the dimensional accuracy of the punched product after punching would be improved and iron loss deterioration could be suppressed. After further investigation, the inventors found that if the amount of work hardening WH defined by equation (3) is set to less than 15 MPa, excellent dimensional accuracy and excellent magnetic properties can be obtained after punching. WH=Y 2.0 -YS (3)

[0019] The present inventors further investigated means for making the work hardening amount WH less than 15 MPa, and as a result, the present inventors discovered the following.

[0020] Silicon (Si) restricts the slip systems through which dislocations can move. Increasing the Si content in steel sheet restricts the slip systems through which dislocations can move. This suppresses dislocation entanglement due to the occurrence of cross slip. As a result, an increase in dislocation density is suppressed.

[0021] Furthermore, solute C and solute N in steel sheets tend to lock onto dislocations. Dislocations with solute C or N stuck to them are less likely to move. Therefore, dislocations with solute C or N stuck to them tend to become entangled with moving dislocations. As a result, variations in dislocation density occur within the steel sheet. In order to reduce dislocations with solute C or N stuck to them, it is effective to reduce the solute C and N in the steel sheet.

[0022] In order to reduce the amount of solute C and N in a steel sheet, elements that have a high affinity for C and / or N may be added to the steel sheet to fix the C and N as precipitates. Si, Ti, and Zr have a high affinity for C and N. Nb, V, Mo, and Cr have a high affinity for C. Al, La, and Ce have a high affinity for N. Therefore, if the steel sheet contains one or more elements from this group, the amount of solute C and N in the steel sheet can be reduced.

[0023] Based on the above considerations, the inventors conducted an investigation from the viewpoint of chemical composition, and as a result, the inventors found that the composition is, in mass %, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0 to 0.100%, Cr: 0 to 2.000%, La: 0 to 0.0100%, Ce: 0 to 0.0100%, B: 0 to 0.0010%, Zn: 0 to 0.0050%, G It was believed that a non-oriented electrical steel sheet having a chemical composition consisting of a: 0-0.0050%, Ge: 0-0.0050%, As: 0-0.0100%, Ni: 0-0.500%, Cu: 0-0.500%, Sn: 0-0.200%, Sb: 0-0.100%, Ca: 0-0.0050%, Nd: 0-0.0010%, Mg: 0-0.0030%, and the balance being Fe and impurities, and further satisfying formulas (1) and (2), would achieve a tensile strength TS of more than 570 MPa, obtain excellent magnetic properties, and also improve dimensional accuracy after punching. Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol.

[0024] However, even if a non-oriented electrical steel sheet satisfies the above-mentioned characteristics, although it has high strength and excellent magnetic properties, there are still cases where sufficient dimensional accuracy cannot be obtained after punching. Therefore, the present inventors conducted further studies and obtained the following findings.

[0025] In punching, the amount of springback increases as work hardening progresses. However, if the yield point elongation ratio, in which deformation progresses without work hardening, is increased, the non-uniformity of deformation in the thickness direction is reduced, resulting in improved dimensional accuracy. If the yield point elongation is 0.5% or more, the dimensional accuracy after punching is further improved.

[0026] On the other hand, an increase in the Si content tended to decrease the yield point elongation. The reason for this is thought to be as follows: As mentioned above, Si is thought to suppress dislocation entanglement and contribute to the suppression of work hardening. However, work hardening also occurs due to dislocation pile-up. Increasing the Si content restricts the slip system, thereby limiting the source of dislocation generation. As a result, the yield point elongation is thought to decrease.

[0027] Based on the above findings, the inventors considered that increasing the number of dislocation sources and dispersing them would be an effective way to increase yield point elongation. Further investigation revealed that reducing the grain size to increase the number of grain boundaries, which are dislocation sources, increases yield point elongation. Specifically, the inventors discovered that if the average grain size D satisfies equation (4), the yield point elongation is likely to be 0.5% or more, improving the dimensional accuracy of the punched product after punching. D<80-Si×10 (4) Here, the Si content in mass % of the non-oriented electrical steel sheet is substituted for Si in formula (4).

[0028] The non-oriented electrical steel sheet of this embodiment has been completed based on the above technical concept, and its gist is as follows.

[0029] The non-oriented electrical steel sheet of the first configuration has, in mass%, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0 to 0.100%, Cr: 0 to 2.000%, and La: 0 to 0.010 0%, Ce: 0 to 0.0100%, B: 0 to 0.0010%, Zn: 0 to 0.0050%, Ga: 0 to 0.0050%, Ge: 0 to 0.0050%, As: 0 to 0.0100%, Ni: 0 to 0.500%, Cu: 0 to 0.500%, Sn: 0 to 0.200%, Sb: 0 to 0.100%, Ca: 0 to 0.0050%, Nd: 0 to 0.0010%, Mg: 0 to 0.0030%, and the remainder being Fe and impurities, satisfying formula (1) and formula (2). Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol. Furthermore, the non-oriented electrical steel sheet has a tensile strength TS higher than 570 MPa. For non-oriented electrical steel sheets, the stress at 2.0% strain is further increased to Y 2.0 (MPa) and the yield stress is YS (MPa), the amount of work hardening WH defined by formula (3) is less than 15 MPa. WH=Y 2.0 -YS (3) Furthermore, in the non-oriented electrical steel sheet of the first configuration, the average grain size D (μm) satisfies the formula (4), and the yield point elongation is 0.5% or more. D<80-Si×10 (4) Here, the element symbol in formula (4) is substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for that element symbol.

[0030] The non-oriented electrical steel sheet of the second configuration is the non-oriented electrical steel sheet of the first configuration, and contains, in mass%, Zr: 0.0001 to 0.0100%, Nb: 0.0001 to 0.0100%, V: 0.0001 to 0.0100%, Mo: 0.001 to 0.100%, Cr: 0.001 to 2.000%, La: 0.0001 to 0.0100%, Ce: 0.0001 to 0.0100%, B: 0.0001 to 0.0010%, Zn: 0.0001 to 0.0050%, It contains one or more elements selected from the group consisting of Ga: 0.0001 to 0.0050%, Ge: 0.0001 to 0.0050%, As: 0.0001 to 0.0100%, Ni: 0.001 to 0.500%, Cu: 0.001 to 0.500%, Sn: 0.001 to 0.200%, Sb: 0.001 to 0.100%, Ca: 0.0001 to 0.0050%, Nd: 0.0001 to 0.0010%, and Mg: 0.0001 to 0.0030%.

[0031] The rotor core of the first configuration includes a plurality of rotor core blanks stacked on top of each other. The rotor core material is composed of, by mass%, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0 to 0.100%, Cr: 0 to 2.000%, La: 0 to 0.0100%, C e: 0-0.0100%, B: 0-0.0010%, Zn: 0-0.0050%, Ga: 0-0.0050%, Ge: 0-0.0050%, As: 0-0.0100%, Ni: 0-0.500%, Cu: 0-0.500%, Sn: 0-0.200%, Sb: 0-0.100%, Ca: 0-0.0050%, Nd: 0-0.0010%, Mg: 0-0.0030%, and the remainder being Fe and impurities, satisfying formula (1) and formula (2). Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol. The rotor core material also has a tensile strength TS higher than 570 MPa. Furthermore, for the rotor core material, the stress at 2.0% strain is 2.0 (MPa) and the yield stress is YS (MPa), the amount of work hardening WH defined by formula (3) is less than 15 MPa. WH=Y 2.0 -YS (3) Furthermore, the rotor core material has an average grain size D (μm) that satisfies formula (4) and a yield elongation of 0.5% or more. D<80-Si×10 (4) Here, the element symbol in formula (4) is substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for that element symbol.

[0032] The rotor core of the second configuration is the rotor core of the first configuration, and the rotor core material contains, in mass%, Zr: 0.0001 to 0.0100%, Nb: 0.0001 to 0.0100%, V: 0.0001 to 0.0100%, Mo: 0.001 to 0.100%, Cr: 0.001 to 2.000%, La: 0.0001 to 0.0100%, Ce: 0.0001 to 0.0100%, B: 0.0001 to 0.0010%, and Zn: 0.0001 to 0.0050%. , Ga: 0.0001 to 0.0050%, Ge: 0.0001 to 0.0050%, As: 0.0001 to 0.0100%, Ni: 0.001 to 0.500%, Cu: 0.001 to 0.500%, Sn: 0.001 to 0.200%, Sb: 0.001 to 0.100%, Ca: 0.0001 to 0.0050%, Nd: 0.0001 to 0.0010%, and Mg: 0.0001 to 0.0030%.

[0033] The motor of this embodiment includes a rotor core having a first or second configuration.

[0034] The method for producing a non-oriented electrical steel sheet of this embodiment is a method for producing a non-oriented electrical steel sheet of the first or second configuration, and includes a hot rolling step, a cold rolling step, and a finish annealing step. In the hot rolling process, the slab is hot rolled to produce a hot-rolled steel sheet. In the cold rolling step, the hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet. In the finish annealing step, the cold-rolled steel sheet is subjected to finish annealing in a finish annealing furnace. In the final annealing step, the cold-rolled steel sheet is further annealed at a maximum temperature T1 of 950°C or less. Furthermore, the tension TE applied to the cold-rolled steel sheet at the maximum temperature T1 is set to 2.0 to 10.0 MPa. Furthermore, the residence time t0 (seconds) between the annealing temperatures T1 and 700°C in the heating zone, soaking zone, and cooling zone of the final annealing furnace, and the residence time t1 (seconds) between the annealing temperatures of 700°C and 500°C in the cooling zone satisfy formulas (A) and (B). t1-t0>0 (A) t1 / t0≦3.0 (B) Furthermore, in one or more locations selected from the heating zone, the soaking zone, and the cooling zone in the temperature range of 500°C or higher in the furnace atmosphere of the final annealing furnace, the hydrogen partial pressure P H2 (atm) versus water vapor partial pressure P H20 (atm) ratio is set to be higher than 0.05, or the oxygen concentration is set to be higher than 0.010%. Furthermore, the temperature gradient CG in the longitudinal direction of the cold-rolled steel sheet during the cooling process is set to 20°C / m or less.

[0035] The non-oriented electrical steel sheet of this embodiment will be described in detail below.

[0036] [Features of the non-oriented electrical steel sheet according to this embodiment] The non-oriented electrical steel sheet of this embodiment satisfies the following features 1 to 5. (Feature 1) The chemical composition, in mass%, is Si: 3.1-4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0-0.0100%, Nb: 0-0.0100%, V: 0-0.0100%, Mo: 0-0.100%, Cr: 0-2.000%, La: 0-0.0 100%, Ce: 0-0.0100%, B: 0-0.0010%, Zn: 0-0.0050%, Ga: 0-0.0050%, Ge: 0-0.0050%, As: 0-0.0100%, Ni: 0-0.500%, Cu: 0-0.500%, Sn: 0-0.200%, Sb: 0-0.100%, Ca: 0-0.0050%, Nd: 0-0.0010%, Mg: 0-0.0030%, and the remainder is Fe and impurities. (Feature 2) The above chemical composition further satisfies formula (1) and formula (2). Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol. (Feature 3) The tensile strength TS is higher than 570 MPa. (Feature 4) The stress at 2.0% strain is Y 2.0 (MPa) and the yield stress is YS (MPa), the amount of work hardening WH defined by formula (3) is less than 15 MPa. WH=Y 2.0 -YS (3) (Feature 5) The average grain size D (μm) satisfies formula (4), and the yield point elongation is 0.5% or more. D<80-Si×10 (4) Here, the element symbols in formula (4) are substituted with the corresponding element contents in mass %. Features 1 to 5 will be explained below.

[0037] [(Feature 1) Chemical composition] The chemical composition of the non-oriented electrical steel sheet of this embodiment contains the following elements. Note that "%" regarding the element content in the chemical composition of the non-oriented electrical steel sheet and the rotor core material means mass % unless otherwise specified. The non-oriented electrical steel sheet is also simply referred to as "steel sheet."

[0038] Si: 3.1 to 4.5% Silicon (Si) increases the resistivity of steel sheet and reduces eddy current loss. Si also dissolves in steel sheet to increase the strength of non-oriented electrical steel sheet. Si also restricts the slip systems through which dislocations can move. This suppresses dislocation entanglement and an increase in dislocation density. This improves dimensional accuracy after punching. If the Si content is less than 3.1%, the above effects cannot be fully achieved. On the other hand, if the Si content exceeds 4.5%, the punching workability of the non-oriented electrical steel sheet decreases. Therefore, the Si content is 3.1 to 4.5%. The lower limit of the Si content is preferably 3.2%, more preferably 3.3%, and even more preferably 3.4%. The upper limit of the Si content is preferably 4.4%, more preferably 4.3%, and even more preferably 4.2%.

[0039] C: 0.0025% or less Carbon (C) is unavoidably contained. In other words, the C content is greater than 0%. C increases the strength of the steel sheet. However, if the C content exceeds 0.0025%, the amount of solute C in the steel sheet will be excessive. In this case, solute C will adhere to dislocations during punching, restricting their movement. If there are many dislocations to which solute C adheres, the density of dislocations entangled with each other will also increase. As a result, unevenness is likely to occur in the punched product after punching, and the dimensional accuracy after punching will decrease. If the C content exceeds 0.0025%, excessive amounts of carbides and / or carbonitrides will be formed. As a result, iron loss will deteriorate. Therefore, the C content is 0.0025% or less. The lower limit of the C content is preferably 0.0001%, more preferably 0.0005%, even more preferably 0.0010%, even more preferably 0.0012%, even more preferably 0.0014%, and even more preferably 0.0016%. The upper limit of the C content is preferably 0.0024%, more preferably 0.0023%, even more preferably 0.0022%, and still more preferably 0.0021%.

[0040] N: 0.0025% or less Nitrogen (N) is inevitably contained. In other words, the N content is greater than 0%. N increases the strength of steel sheets. Even if even a small amount of N is contained, the above effects can be obtained to some extent. However, if the N content exceeds 0.0025%, the amount of solute N in the steel sheet will be excessive. In this case, the solute N will attach to dislocations during punching, restricting their movement. If there are many dislocations to which solute N is attached, the density of dislocations entangled with each other will also increase. As a result, unevenness is likely to occur in the punched product after punching, and the dimensional accuracy after punching will decrease. If the N content exceeds 0.0025%, excessive amounts of nitrides and / or carbonitrides will be formed. As a result, iron loss will deteriorate. Therefore, the N content is 0.0025% or less. The lower limit of the N content is preferably 0.0001%, more preferably 0.0005%, even more preferably 0.0010%, even more preferably 0.0012%, even more preferably 0.0014%, and even more preferably 0.0016%. The upper limit of the N content is preferably 0.0024%, more preferably 0.0023%, even more preferably 0.0022%, and still more preferably 0.0021%.

[0041] O: 0.0400% or less Oxygen (O) is unavoidably contained. In other words, the O content is greater than 0%. O forms oxides that reduce the magnetic properties of the steel sheet. Therefore, the O content is 0.0400% or less. The O content is preferably as low as possible. However, excessive reduction in the O content increases production costs. Therefore, from the viewpoint of industrial productivity, the lower limit of the O content is preferably 0.0001%, more preferably 0.0010%, and even more preferably 0.0020%. The upper limit of the O content is preferably 0.0370%, more preferably 0.0350%, even more preferably 0.0300%, and still more preferably 0.0200%.

[0042] P:0.100% or less Phosphorus (P) is unavoidably contained. In other words, the P content is greater than 0%. P increases the strength of steel sheets. Even if even a small amount of P is contained, the above effects can be obtained to some extent. However, if the P content exceeds 0.100%, the steel sheet becomes embrittled, the workability deteriorates, and cracks may occur in the steel sheet during cold rolling. Therefore, the P content is 0.100% or less. The lower limit of the P content is preferably 0.001%, more preferably 0.005%, and even more preferably 0.007%. The upper limit of the P content is preferably 0.090%, more preferably 0.080%, and even more preferably 0.070%.

[0043] S: 0.0050% or less Sulfur (S) is an unavoidable impurity. In other words, the S content is greater than 0%. S generates MnS, which deteriorates iron loss. Therefore, the S content is 0.0050% or less. The S content is preferably as low as possible. However, excessive reduction in the S content increases production costs. Therefore, from the viewpoint of industrial productivity, the lower limit of the S content is preferably 0.0001%, more preferably 0.0003%, and even more preferably 0.0005%. The upper limit of the S content is preferably 0.0047%, more preferably 0.0045%, even more preferably 0.0040%, even more preferably 0.0030%, even more preferably 0.0025%, and even more preferably 0.0020%.

[0044] [Elements that reduce solute C and / or solute N] The chemical composition of the non-oriented electrical steel sheet of this embodiment further includes Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0-0.0100%, Nb: 0-0.0100%, V: 0-0.0100%, Mo: 0-0.100%, Cr: 0-2.000%, La: 0-0.0100%, and Ce: 0-0.0100%. These elements fix solute C and / or solute N in the steel sheet to form precipitates such as carbides, carbonitrides, or nitrides. As a result, these elements reduce the solute C and solute N, which are factors that reduce dimensional accuracy after punching.

[0045] Ti:0.0100% or less Titanium (Ti) is unavoidably contained. In other words, the Ti content is greater than 0%. Ti combines with C and / or N to form precipitates, reducing the amount of solute C and N. This improves the dimensional accuracy after punching. Ti also increases the strength of the steel sheet by forming precipitates. Even if even a small amount of Ti is contained, the above effects can be obtained to some extent. However, if the Ti content exceeds 0.0100%, excessive precipitates are formed, resulting in deterioration of magnetic properties. Therefore, the Ti content is 0.0100% or less. The lower limit of the Ti content is preferably 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The upper limit of the Ti content is preferably 0.0090%, more preferably 0.0080%, even more preferably 0.0070%, even more preferably 0.0060%, and still more preferably 0.0055%.

[0046] Mn: 2.0% or less Manganese (Mn) is unavoidably included. In other words, the Mn content is greater than 0%. Mn combines with C to form carbides, reducing the amount of solute C. Mn also increases the resistivity of the steel sheet and reduces eddy current loss. Even if even a small amount of Mn is included, the above effects can be achieved to some extent. However, if the Mn content exceeds 2.0%, the magnetic flux density of the steel sheet decreases. Therefore, the Mn content is 2.0% or less. The lower limit of the Mn content is preferably 0.1%, more preferably 0.2%, and even more preferably 0.5%. The upper limit of the Mn content is preferably 1.8%, more preferably 1.6%, and even more preferably 1.4%.

[0047] Al: 1.500% or less Aluminum (Al) is inevitably included. In other words, the Al content is greater than 0%. Al combines with N to form nitrides, reducing the amount of solute N. This improves dimensional accuracy after punching. Furthermore, Al increases the strength of the steel sheet by forming nitrides. Even if even a small amount of Al is included, the above effects can be achieved to some extent. However, if the Al content exceeds 1.500%, an excessive amount of oxide is produced in the steel sheet, resulting in deterioration of the magnetic properties. Therefore, the Al content is 1.500% or less. The lower limit of the Al content is preferably 0.001%, more preferably 0.004%, even more preferably 0.005%, even more preferably 0.010%, even more preferably 0.050%, and even more preferably 0.100%. The upper limit of the Al content is preferably 1.450%, more preferably 1.400%, even more preferably 1.300%, even more preferably 1.100%, and even more preferably 0.900%. In this specification, the Al content means the content of sol. Al (acid-soluble Al).

[0048] Zr: 0 to 0.0100% Zirconium (Zr) may not be contained, that is, the Zr content may be 0%. When contained, that is, when the Zr content is more than 0%, Zr combines with C and / or N to form precipitates, reducing the amount of solute C and N. As a result, Zr improves the dimensional accuracy after punching. Zr also increases the strength of the steel sheet by forming precipitates. Even if even a small amount of Zr is contained, the above effects can be obtained to some extent. However, if the Zr content exceeds 0.0100%, excessive precipitates are formed, which deteriorates the magnetic properties. Therefore, the Zr content is 0 to 0.0100%. The lower limit of the Zr content is preferably 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The upper limit of the Zr content is preferably 0.0095%, more preferably 0.0090%, even more preferably 0.0080%, and still more preferably 0.0070%.

[0049] Nb: 0 to 0.0100% Niobium (Nb) may not be contained, that is, the Nb content may be 0%. When Nb is contained, it combines with C to form carbides and reduces the amount of solute C. As a result, Nb improves the dimensional accuracy after punching. Furthermore, Nb increases the strength of the steel sheet by forming carbides. Even if even a small amount of Nb is contained, the above effects can be obtained to some extent. However, if the Nb content exceeds 0.0100%, excessive carbides are formed, which deteriorates the magnetic properties. Therefore, the Nb content is 0 to 0.0100%. The lower limit of the Nb content is preferably 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The upper limit of the Nb content is preferably 0.0090%, more preferably 0.0080%, even more preferably 0.0070%, even more preferably 0.0050%, even more preferably 0.0040%, even more preferably 0.0030%, and even more preferably 0.0025%.

[0050] V: 0 to 0.0100% Vanadium (V) may not be contained, that is, the V content may be 0%. When V is contained, that is, when the V content exceeds 0%, V combines with C to form carbides and reduce the amount of solute C. As a result, V improves the dimensional accuracy after punching. Furthermore, V increases the strength of the steel sheet by forming carbides. Even if even a small amount of V is contained, the above effects can be obtained to some extent. However, if the V content exceeds 0.0100%, excessive carbides are formed, which deteriorates the magnetic properties. Therefore, the V content is 0 to 0.0100%. The lower limit of the V content is preferably 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The upper limit of the V content is preferably 0.0090%, more preferably 0.0080%, even more preferably 0.0070%, even more preferably 0.0050%, even more preferably 0.0040%, even more preferably 0.0030%, and even more preferably 0.0025%.

[0051] Mo: 0 to 0.100% Molybdenum (Mo) may not be contained, that is, the Mo content may be 0%. When contained, that is, when the Mo content exceeds 0%, Mo combines with C to form carbides and reduce the amount of solute C. As a result, Mo improves the dimensional accuracy after punching. Mo also increases the strength of the steel sheet by forming carbides. Even if even a small amount of Mo is contained, the above effects can be obtained to some extent. However, if the Mo content exceeds 0.100%, excessive carbides are formed, which deteriorates the magnetic properties. Therefore, the Mo content is 0 to 0.100%. The lower limit of the Mo content is preferably 0.001%, more preferably 0.005%, even more preferably 0.010%, and still more preferably 0.030%. The upper limit of the Mo content is preferably 0.090%, more preferably 0.080%, and even more preferably 0.070%.

[0052] Cr: 0 to 2.000% Chromium (Cr) may not be contained, that is, the Cr content may be 0%. When contained, that is, when the Cr content is more than 0%, Cr combines with C to form carbides and reduce the amount of solute C. As a result, Cr improves the dimensional accuracy after punching. Cr also increases the strength of the steel sheet. Even if even a small amount of Cr is contained, the above effects can be obtained to some extent. However, if the Cr content exceeds 2.000%, excessive carbides are formed, which deteriorates the magnetic properties. Therefore, the Cr content is 0 to 2.000%. The lower limit of the Cr content is preferably 0.001%, more preferably 0.005%, even more preferably 0.010%, and still more preferably 0.050%. The upper limit of the Cr content is preferably 1.800%, more preferably 1.500%, even more preferably 1.400%, and still more preferably 1.000%.

[0053] La: 0 to 0.0100% Lanthanum (La) is an optional element and may not be contained, that is, the La content may be 0%. When contained, that is, when the La content exceeds 0%, La combines with N to form nitrides, reducing the amount of solute N. As a result, La improves the dimensional accuracy after punching. Furthermore, La increases the strength of the steel sheet by forming nitrides. Even if even a small amount of La is contained, the above effects can be obtained to some extent. However, if the La content exceeds 0.0100%, excessive nitrides are formed in the steel sheet, which deteriorates the magnetic properties. Therefore, the La content is 0 to 0.0100%. The lower limit of the La content is preferably 0.0001%, more preferably 0.0005%, even more preferably 0.0010%, and still more preferably 0.0020%. The upper limit of the La content is preferably 0.0090%, more preferably 0.0080%, even more preferably 0.0075%, and still more preferably 0.0070%.

[0054] Ce: 0 to 0.0100% Cerium (Ce) is an optional element and may not be contained, that is, the Ce content may be 0%. When contained, that is, when the Ce content is more than 0%, Ce combines with N to form nitrides, reducing the amount of solute N. As a result, Ce improves the dimensional accuracy after punching. Ce also increases the strength of the steel sheet by forming nitrides. Even if even a small amount of Ce is contained, the above effects can be obtained to some extent. However, if the Ce content exceeds 0.0100%, excessive nitrides are formed in the steel sheet, resulting in deterioration of the magnetic properties. Therefore, the Ce content is 0 to 0.0100%. The lower limit of the Ce content is preferably 0.0001%, more preferably 0.0005%, even more preferably 0.0010%, and still more preferably 0.0015%. The upper limit of the Ce content is preferably 0.0090%, more preferably 0.0080%, and even more preferably 0.0070%.

[0055] The balance of the chemical composition of the non-oriented electrical steel sheet of this embodiment is composed of Fe and impurities. Here, the impurities are those that are mixed in from raw materials such as ore and scrap, or from the manufacturing environment, during industrial production of the non-oriented electrical steel sheet. The content of these impurities is permissible within a range that does not adversely affect the non-oriented electrical steel sheet of this embodiment.

[0056] The non-oriented electrical steel sheet of this embodiment may further contain B: 0-0.0010%, Zn: 0-0.0050%, Ga: 0-0.0050%, Ge: 0-0.0050%, As: 0-0.0100%, Ni: 0-0.500%, Cu: 0-0.500%, Sn: 0-0.200%, Sb: 0-0.100%, Ca: 0-0.0050%, Nd: 0-0.0010%, and Mg: 0-0.0030%. All of these elements are optional and may not be contained. Each element will be described below.

[0057] [B, Zn, Ga, Ge and As] B, Zn, Ga, Ge, and As are impurities in the non-oriented electrical steel sheet of this embodiment.

[0058] B: 0 to 0.0010% Boron (B) is an optional element and may not be contained, that is, the B content may be 0%. When B is contained, that is, when the B content exceeds 0%, B forms nitrides, which inhibit recrystallization during final annealing. Therefore, the B content is 0 to 0.0010%. An excessive reduction in the B content increases production costs, so from the viewpoint of industrial productivity, the lower limit of the B content is preferably 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%. The upper limit of the B content is preferably 0.0009%, more preferably 0.0008%, and even more preferably 0.0007%.

[0059] Zn: 0 to 0.0050% Zinc (Zn) is an optional element and may not be contained, that is, the Zn content may be 0%. When Zn is contained, that is, when the Zn content exceeds 0%, no particular problem occurs as long as the Zn content is 0.0050% or less. Therefore, the Zn content is 0 to 0.0050%. An excessive reduction in the Zn content increases production costs, and therefore, from the viewpoint of industrial productivity, the lower limit of the Zn content is preferably 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%. The upper limit of the Zn content is preferably 0.0020%, more preferably 0.0010%, and even more preferably 0.0005%.

[0060] Ga: 0 to 0.0050% Gallium (Ga) is an optional element and may not be contained, that is, the Ga content may be 0%. When Ga is contained, that is, when the Ga content exceeds 0%, no particular problem occurs as long as the Ga content is 0.0050% or less. Therefore, the Ga content is 0 to 0.0050%. An excessive reduction in the Ga content increases production costs, and therefore, from the viewpoint of industrial productivity, the lower limit of the Ga content is preferably 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%. The upper limit of the Ga content is preferably 0.0040%, more preferably 0.0035%, even more preferably 0.0030%, even more preferably 0.0020%, even more preferably 0.0010%, and even more preferably 0.0005%.

[0061] Ge: 0 to 0.0050% Germanium (Ge) is an optional element and may not be contained, that is, the Ge content may be 0%. When Ge is contained, that is, when the Ge content exceeds 0%, no particular problem occurs as long as the Ge content is 0.0050% or less. Therefore, the Ge content is 0 to 0.0050%. An excessive reduction in the Ge content increases production costs, and therefore, from the viewpoint of industrial productivity, the lower limit of the Ge content is preferably 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%. The upper limit of the Ge content is preferably 0.0040%, more preferably 0.0035%, even more preferably 0.0030%, even more preferably 0.0020%, even more preferably 0.0010%, and even more preferably 0.0005%.

[0062] As: 0 to 0.0100% Arsenic (As) is an optional element and may not be contained, that is, the As content may be 0%. When As is contained, that is, when the As content exceeds 0%, no particular problem occurs as long as the As content is 0.0100% or less. Therefore, the As content is 0 to 0.0100%. An excessive reduction in the As content increases production costs. Therefore, from the viewpoint of industrial productivity, the lower limit of the As content is preferably 0.0001%, more preferably 0.0002%, even more preferably 0.0003%, even more preferably 0.0005%, and even more preferably 0.0010%. The upper limit of the As content is preferably 0.0070%, more preferably 0.0060%, even more preferably 0.0050%, and still more preferably 0.0030%.

[0063] [Ni and Cu] Ni and Cu are optional elements. Both Ni and Cu increase the strength of the non-oriented electrical steel sheet.

[0064] Ni: 0 to 0.500% Nickel (Ni) is an optional element and may not be contained, that is, the Ni content may be 0%. When contained, that is, when the Ni content exceeds 0%, Ni increases the strength of the non-oriented electrical steel sheet. Even if even a small amount of Ni is contained, the above effect can be obtained to some extent. However, if the Ni content exceeds 0.500%, the steel sheet becomes embrittled and the workability deteriorates. Therefore, the Ni content is 0 to 0.500%. The lower limit of the Ni content is preferably 0.001%, more preferably 0.005%, even more preferably 0.010%, even more preferably 0.020%, even more preferably 0.050%, and even more preferably 0.100%. The upper limit of the Ni content is preferably 0.450%, more preferably 0.400%, even more preferably 0.350%, even more preferably 0.300%, and even more preferably 0.250%.

[0065] Cu: 0 to 0.500% Copper (Cu) is an optional element and may not be contained, that is, the Cu content may be 0%. When Cu is contained, that is, when the Cu content exceeds 0%, Cu increases the strength of the non-oriented electrical steel sheet. Even if even a small amount of Cu is contained, the above effect can be obtained to some extent. However, if the Cu content exceeds 0.500%, the steel sheet becomes embrittled and the workability deteriorates. Therefore, the Cu content is 0 to 0.500%. The lower limit of the Cu content is preferably 0.001%, more preferably 0.005%, even more preferably 0.010%, even more preferably 0.030%, even more preferably 0.050%, and even more preferably 0.100%. The upper limit of the Cu content is preferably 0.450%, more preferably 0.400%, even more preferably 0.350%, even more preferably 0.250%, and still more preferably 0.150%.

[0066] [Sn and Sb] Sn and Sb are optional elements. Both Sn and Sb reduce the iron loss of non-oriented electrical steel sheets.

[0067] Sn: 0 to 0.200% Tin (Sn) is an optional element and may not be contained, that is, the Sn content may be 0%. When Sn is contained, that is, when the Sn content is more than 0%, Sn segregates on the surface of the steel sheet and suppresses oxidation and nitridation during final annealing. Sn also improves the texture of the steel sheet and increases the magnetic flux density, thereby reducing the iron loss of the non-oriented electrical steel sheet. Even if even a small amount of Sn is contained, the above effects can be achieved to some extent. However, if the Sn content exceeds 0.200%, the steel sheet becomes embrittled and the workability deteriorates. Therefore, the Sn content is 0 to 0.200%. The lower limit of the Sn content is preferably 0.001%, more preferably 0.003%, even more preferably 0.005%, even more preferably 0.010%, even more preferably 0.030%, and even more preferably 0.050%. The upper limit of the Sn content is preferably 0.180%, more preferably 0.160%, even more preferably 0.150%, and still more preferably 0.120%.

[0068] Sb: 0 to 0.100% Antimony (Sb) is an optional element and may not be contained, that is, the Sb content may be 0%. When Sb is contained, that is, when the Sb content is more than 0%, Sb, like Sn, segregates on the surface of the steel sheet and suppresses oxidation and nitridation during finish annealing. Sb also improves the texture of the steel sheet and increases the magnetic flux density, thereby reducing the iron loss of the non-oriented electrical steel sheet. Even if even a small amount of Sb is contained, the above effects can be achieved to some extent. However, if the Sb content exceeds 0.100%, the steel sheet becomes embrittled and the workability deteriorates. Therefore, the Sb content is 0 to 0.100%. The lower limit of the Sb content is preferably 0.001%, more preferably 0.005%, even more preferably 0.010%, and still more preferably 0.030%. The upper limit of the Sb content is preferably 0.080%, more preferably 0.070%, even more preferably 0.060%, and still more preferably 0.050%.

[0069] [Ca, Nd and Mg] Ca, Nd, and Mg are optional elements. Ca, Nd, and Mg all promote the growth of crystal grains during finish annealing, thereby improving the magnetic properties of non-oriented electrical steel sheets.

[0070] Ca: 0 to 0.0050% Calcium (Ca) is an optional element and may not be contained, that is, the Ca content may be 0%. When contained, that is, when the Ca content is more than 0%, Ca combines with S during the casting of molten steel to form coarse precipitates, which are coarse sulfides and / or coarse oxysulfides. The particle size of the coarse precipitates is approximately 1 to 2 μm. The coarse precipitates adsorb fine inhibitors, such as MnS, TiN, and AlN, with particle sizes of approximately 100 nm, which are formed in the steel sheet during manufacturing processes after the casting process. This suppresses the inhibition of grain growth by the inhibitors during final annealing. Therefore, grain growth is promoted during final annealing. As a result, the magnetic properties of the non-oriented electrical steel sheet are improved. Even if even a small amount of Ca is contained, the above effects can be obtained to some extent. However, if the Ca content exceeds 0.0050%, excessive coarse precipitates are formed, which inhibits recrystallization and grain growth during the final annealing process. Therefore, the Ca content is 0 to 0.0050%. The lower limit of the Ca content is preferably 0.0001%, more preferably 0.0005%, and even more preferably 0.0010%. The upper limit of the Ca content is preferably 0.0045%, more preferably 0.0040%, and even more preferably 0.0035%.

[0071] Nd: 0 to 0.0010% Neodymium (Nd) is an optional element and may not be contained, that is, the Nd content may be 0%. When Nd is contained, that is, when the Nd content is more than 0%, Nd forms coarse precipitates in the same way as Ca, and suppresses the inhibition of grain growth by inhibitors during final annealing. Therefore, grain growth is promoted during final annealing. As a result, the magnetic properties of the non-oriented electrical steel sheet are improved. Even if even a small amount of Nd is contained, the above effects can be obtained to some extent. However, if the Nd content exceeds 0.0010%, excessive coarse precipitates are formed, which inhibits recrystallization and grain growth during the final annealing process. Therefore, the Nd content is 0 to 0.0010%. The lower limit of the Nd content is preferably 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%. The upper limit of the Nd content is preferably 0.0008%, more preferably 0.0006%, and even more preferably 0.0004%.

[0072] Mg: 0 to 0.0030% Magnesium (Mg) is an optional element and may not be contained, that is, the Mg content may be 0%. When Mg is contained, that is, when the Mg content is more than 0%, Mg, like Ca, forms coarse precipitates and suppresses the inhibition of grain growth by inhibitors during final annealing. Therefore, grain growth is promoted during final annealing. As a result, the magnetic properties of the non-oriented electrical steel sheet are improved. Even if even a small amount of Mg is contained, the above effects can be obtained to some extent. However, if the Mg content exceeds 0.0030%, excessive coarse precipitates are formed, which inhibits recrystallization and grain growth during the final annealing process. Therefore, the Mg content is 0 to 0.0030%. The lower limit of the Mg content is preferably 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%. The upper limit of the Mg content is preferably 0.0025%, more preferably 0.0020%, even more preferably 0.0015%, and still more preferably 0.0010%.

[0073] [Method for measuring the chemical composition of non-oriented electrical steel sheets] The chemical composition of the non-oriented electrical steel sheet of this embodiment can be measured by a known elemental analysis method in accordance with JIS G0321:2017. Specifically, chips are collected from the steel sheet using a drill. The collected chips are dissolved in acid to obtain a solution. The solution is subjected to ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) to perform elemental analysis of the chemical composition. The C content and S content are determined by a known high-frequency combustion method (combustion-infrared absorption method). The N content is determined by a known inert gas fusion-thermal conductivity method. The O content is determined by a known inert gas fusion-infrared absorption method.

[0074] The content of each element is determined by rounding off the measured value to the nearest significant digit based on the significant digits specified in this embodiment. For example, the Si content of the steel sheet in this embodiment is determined to one decimal place. Therefore, the Si content is determined to one decimal place by rounding off the measured value to one decimal place.

[0075] Similarly, the contents of other elements other than the Si content of the steel sheet of this embodiment are also determined by rounding off the measured value to the smallest digit specified in this embodiment, and this is the content of the element.

[0076] Rounding off means rounding down if the fraction is less than 5, and rounding up if the fraction is 5 or more.

[0077] [(Feature 2) Regarding Equation (1) and Equation (2)] The non-oriented electrical steel sheet of this embodiment further satisfies formulas (1) and (2). Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol.

[0078] [Regarding formula (1)] Equation (1) is an equation for sufficiently reducing the amount of solute C in a steel sheet by forming carbides or carbonitrides. The left side of equation (1) is composed of elements that bond with C to form carbides or carbonitrides. When equation (1) is satisfied, carbides or carbonitrides are sufficiently formed, thereby sufficiently reducing the amount of solute C.

[0079] [Regarding formula (2)] Equation (2) is an equation for sufficiently reducing solute N by forming nitrides or carbonitrides. The left side of equation (2) is composed of elements that bond with N to form nitrides or carbonitrides. When equation (2) is satisfied, nitrides or carbonitrides are sufficiently formed, thereby sufficiently reducing solute N.

[0080] [(Feature 3) Tensile strength TS] The non-oriented electrical steel sheet of this embodiment has a tensile strength TS of more than 570 MPa, that is, the non-oriented electrical steel sheet of this embodiment has high strength. The lower limit of the tensile strength TS of the non-oriented electrical steel sheet of this embodiment is preferably 575 MPa, and more preferably 580 MPa. There is no particular upper limit to the tensile strength TS, but when Features 1 and 2 are satisfied, the upper limit to the tensile strength TS is, for example, 750 MPa.

[0081] [Method for measuring stress-strain curve] The tensile strength TS of the non-oriented electrical steel sheet of this embodiment is measured by the following method. A JIS No. 5 tensile test piece, as specified in JIS Z2241:2011, is taken from the non-oriented electrical steel sheet. Using the taken tensile test piece, a tensile test is carried out in air at room temperature in accordance with JIS Z2241:2011 to obtain a stress-strain curve. The tensile strength TS (MPa) is determined from the obtained stress-strain curve.

[0082] [(Feature 4) Work hardening amount WH] In the non-oriented electrical steel sheet of this embodiment, the stress at 2.0% strain is further set to Y 2.0 (MPa) and the yield stress is YS (MPa), the amount of work hardening WH defined by formula (3) is less than 15 MPa. WH=Y 2.0 -YS (3)

[0083] If dislocations grow excessively during punching, there is a high possibility that dislocations anchored by solute C or solute N will increase. If dislocations anchored by solute C or solute N increase, regions with a high density of dislocations intertwined with each other will be formed locally. In this case, unevenness is likely to occur in the punched product after punching, and sufficient dimensional accuracy cannot be obtained.

[0084] The amount of work hardening WH correlates with the dislocation density. If the amount of work hardening WH is less than 15 MPa, the dislocation density is sufficiently suppressed during punching. Therefore, the occurrence of dislocations where solute C or solute N is fixed can be sufficiently suppressed. Therefore, the occurrence of irregularities caused by punching in the punched product after punching is suppressed, and sufficient dimensional accuracy can be obtained.

[0085] The upper limit of the amount of work hardening WH is preferably 14 MPa, more preferably 13 MPa, even more preferably 12 MPa, even more preferably 11 MPa, and even more preferably 10 MPa. The work-hardening amount WH is preferably as low as possible. In consideration of industrial productivity, the lower limit of the work-hardening amount WH is preferably 2 MPa, more preferably 1 MPa, and most preferably 0 MPa.

[0086] [Work hardening amount WH evaluation test] The amount of work hardening WH can be determined by the following method: A tensile test as described in the above [Method for measuring a stress-strain curve] is carried out to obtain a stress-strain curve. Fig. 1 is a schematic diagram of an example of a stress-strain curve. Referring to Fig. 1, the maximum value of stress within the strain range of 0 to 0.2% plastic strain is defined as "yield strength YS" (MPa). In Figure 1, an upper yield point P0 occurs on the stress-strain curve when the strain is in the range L0 of 0 to 0.2% plastic strain. Therefore, when the stress-strain curve has an upper yield point as in Figure 1, the stress at the upper yield point P0 is taken as the yield strength YS (MPa).

[0087] On the other hand, in the case of a stress-strain curve in which the upper yield point P0 does not occur, as in the stress-strain curve shown in Figure 2, when the strain is in the range L0 from 0 to 0.2% plastic strain, the stress at the position of 0.2% plastic strain becomes the maximum value. Therefore, in this case, the 0.2% proof stress is taken as the yield strength YS (MPa).

[0088] 1 and 2, the stress at 2.0% strain in the stress-strain curve is expressed as Y 2.0 (MPa).

[0089] The obtained yield strength YS (MPa) and stress Y 2.0 (MPa) and calculate the amount of work hardening WH (MPa) using equation (3). 2.0 In this case, WH is defined as 0 (MPa).

[0090] [(Feature 5) Average grain size D] Furthermore, in the non-oriented electrical steel sheet of this embodiment, the average grain size D (μm) satisfies the formula (4), and the yield point elongation is 0.5% or more. D<80-Si×10 (4) Here, the Si content in mass % in the chemical composition of the non-oriented electrical steel sheet is substituted for Si in formula (4).

[0091] Let Fn be defined as follows: Fn=80-Si×10 If the average grain size D (μm) is less than Fn, the number of dislocation sources during deformation can be increased and the dislocation sources can be dispersed. In this case, dislocations do not occur locally during deformation of the steel sheet during punching, but are dispersed. This suppresses dislocation entanglement. As a result, the yield elongation tends to be 0.5% or more, and non-uniformity of deformation in the sheet thickness direction during punching can be reduced. As a result, dimensional accuracy after punching can be improved.

[0092] The lower limit of the average crystal grain size D is preferably 10 μm, more preferably 15 μm, and even more preferably 20 μm. The upper limit of the average crystal grain size D is preferably 75-Si×10 (μm), more preferably 70-Si×10 (μm), and even more preferably 65-Si×10 (μm).

[0093] The lower limit of the yield elongation is preferably 0.6%, more preferably 0.7%, even more preferably 1.0%, and even more preferably 1.5%. The upper limit of the yield elongation is not particularly limited, but is about 7.0%.

[0094] [Method for measuring average grain size D] The average grain size D is determined by the following method. The cross section (L cross section) parallel to the rolling direction of the non-oriented electrical steel sheet is used as the observation surface. The observation surface is mirror-polished, and then etched using a nital solution. The etched observation surface is observed using an optical microscope at a magnification of 100x, and a photographic image of the observation field is generated. Using the photographic image, the average grain size D (μm) is determined by the method of calculating the number of grains within a rectangular area, described below, in accordance with JIS G0551:2013 "Steel - Microscopic test method for grain size."

[0095] Specifically, a rectangular area is drawn on the L-section, surrounded by lines parallel to the thickness direction and the surface direction (rolling direction), in an area consisting only of recrystallized grains, excluding unrecrystallized regions. This rectangular area is the observation field. The area A of the rectangular area is 0.5 mm 2 The area of ​​one rectangle is 0.5mm 2If this is not possible, draw multiple rectangular areas so that the total area A of the rectangular areas is 0.5 mm 2 Make sure it is above that.

[0096] The number of crystal grains in the rectangular region is counted. Specifically, the number of crystal grains that exist inside the rectangular region and do not touch any of the sides of the rectangular region is defined as N1. The number of crystal grains that intersect with any of the four sides of the rectangular region excluding the four corners (the four vertices of the rectangle) is defined as N2. 0.5mm 2 The number of all rectangular areas drawn to secure the above area is N3. The total area of ​​the rectangular areas is A (mm 2 ) and the numbers of crystal grains N1 to N3, the average crystal grain size D (μm) is calculated by the formula (I).

number

[0097] [Method for measuring yield elongation] The yield elongation is determined using the following method. A tensile test piece is taken from the non-oriented electrical steel sheet. A tensile test is carried out in air at room temperature in accordance with JIS Z2241:2011 to determine the yield elongation (%). A JIS No. 5 tensile test piece is used.

[0098] If the upper yield point is not clearly visible, the yield elongation (%) is determined using the following method. Referring to Figure 3, the yield strength YS (MPa) is determined from the stress-strain curve obtained by the tensile test based on the method described in the above-mentioned [Work Hardening Amount WH Evaluation Test]. The strain value at the determined yield strength YS is designated as ε1. In the stress-strain curve after strain value ε1, the maximum strain value ε2 is identified in the region where the stress remains within the range of the yield stress YS ±1.0% as the strain increases. Using ε1 and ε2, the yield elongation is calculated using the following formula: Yield elongation (%) = ε2 - ε1

[0099] [Effects of the non-oriented electrical steel sheet according to this embodiment] The non-oriented electrical steel sheet of this embodiment satisfies Features 1 to 5. Therefore, the non-oriented electrical steel sheet of this embodiment has high strength and sufficient magnetic properties, and yet also has excellent dimensional accuracy after punching.

[0100] [Manufacturing method for non-oriented electrical steel sheets] An example of a method for manufacturing the non-oriented electrical steel sheet of this embodiment will be described. The method for manufacturing the non-oriented electrical steel sheet of this embodiment includes the following steps. (Process 1) Hot rolling process (Process 2) Hot-rolled sheet annealing process (Process 3) Cold rolling process (Process 4) Finishing annealing process Of the above steps 1 to 4, step 2 is an optional step. In other words, step 2 does not have to be performed. Each step will be described below.

[0101] [(Process 1) Hot rolling process] In the hot rolling process, the slab is hot-rolled to produce a hot-rolled steel sheet. The slab is produced by a well-known method, for example, by continuous casting.

[0102] The prepared slab is subjected to hot rolling. The various conditions for hot rolling are not particularly limited. The slab heating temperature is, for example, 1100 to 1200°C. The finish rolling temperature is, for example, 800 to 1100°C. The coiling temperature is, for example, 700 to 800°C. Through the above steps, a hot-rolled steel sheet is manufactured.

[0103] [(Process 2) Hot-rolled sheet annealing process] The hot-rolled sheet annealing step is an optional step. That is, the hot-rolled sheet annealing step may or may not be performed. When performed, the hot-rolled sheet annealing step involves annealing the hot-rolled steel sheet. The hot-rolled sheet annealing may be box annealing or continuous annealing. The annealing conditions in the hot-rolled sheet annealing step are not particularly limited. In the case of box annealing, the annealing temperature is, for example, 750°C to 850°C, and the holding time at the annealing temperature is, for example, 1 hour to 30 hours. In the case of continuous annealing, the annealing temperature is, for example, 900°C to 1000°C, and the holding time at the annealing temperature is, for example, 1 second to 100 seconds. If necessary, a well-known pickling treatment may be performed on the hot-rolled steel sheet before annealing in the hot-rolled sheet annealing step and / or the hot-rolled steel sheet after annealing.

[0104] [(Process 3) Cold rolling process] In the cold rolling process, cold rolling is performed on the hot-rolled steel sheet produced in the hot rolling process or the hot-rolled steel sheet after the hot-rolled sheet annealing process to produce a cold-rolled steel sheet. Cold rolling may be performed once or multiple times. When cold rolling is performed multiple times, intermediate annealing may be performed after cold rolling and before the next cold rolling is performed.

[0105] [(Process 4) Finishing annealing process] The cold-rolled steel sheet manufactured by carrying out the cold rolling process is subjected to finish annealing in a finish annealing furnace. In the finish annealing, the cold-rolled steel sheet finished to the final thickness is annealed to recrystallize and grow crystal grains. In the finish annealing process, the following conditions 1 to 5 are satisfied. (Condition 1) Anneal at a maximum temperature T1 (℃) of 950℃ or less. (Condition 2) The tension TE applied to the cold-rolled steel sheet at the maximum temperature T1 (°C) is set to 2.0 to 10.0 MPa. (Condition 3) The residence time t0 (seconds) between the annealing temperatures T1 and 700°C in the heating zone, soaking zone, and cooling zone of the finish annealing furnace, and the residence time t1 (seconds) between 700 and 500°C in the cooling zone satisfy formulas (A) and (B). t1-t0>0 (A) t1 / t0≦3.0 (B) (Condition 4) In the furnace atmosphere of the final annealing furnace, at one or more locations selected from the heating zone, the soaking zone, and the cooling zone in the temperature range of 500°C or higher, the hydrogen partial pressure P H2 (atm) versus water vapor partial pressure P H20 The ratio (atm) is set to be higher than 0.05, or the oxygen concentration is set to be higher than 0.010% by volume. (Condition 5) The temperature gradient CG in the longitudinal direction of the cold-rolled steel sheet during the cooling process is set to 20°C / m or less. Conditions 1 to 5 will be explained below.

[0106] [(Condition 1) Maximum temperature reached T1] The maximum temperature T1 is set to 950°C or less. If the maximum temperature T1 exceeds 950°C, solution of carbides and nitrides occurs in the steel plate. As a result, the work hardening amount WH defined by formula (3) becomes 15 MPa or more. Therefore, the maximum temperature T1 is set to 950°C or less. A known temperature is sufficient as the lower limit of the maximum temperature T1. For example, the lower limit of the maximum temperature T1 is 800°C.

[0107] [(Condition 2) Tension TE at maximum temperature T1] The tension TE applied to the cold-rolled steel sheet at the maximum temperature T1 is set to 2.0 to 10.0 MPa. Specifically, the tension TE is applied in the rolling direction (longitudinal direction) of the cold-rolled steel sheet. If the tension TE is less than 2.0 MPa, dislocation sources are not sufficiently obtained in the steel sheet, and in this case, even if the non-oriented electrical steel sheet satisfies formula (4), the yield point elongation will be less than 0.5%. On the other hand, if the tension TE exceeds 10.0 MPa, residual strain occurs in the steel sheet, and in this case, the amount of work hardening WH becomes 15 MPa or more.

[0108] [(Condition 3) Regarding stay times t0 and t1] In the finish annealing, the residence time t0 (seconds) between the annealing temperatures T1 and 700°C in the heating zone, soaking zone, and cooling zone of the finish annealing furnace, and the residence time t1 (seconds) between 700 and 500°C in the cooling zone satisfy the formulas (A) and (B). t1-t0>0 (A) t1 / t0≦3.0 (B) Here, residence time t0 includes the time during the heating process from 700°C to the maximum temperature T1 in the heating zone, soaking zone, and cooling zone, the holding time at the maximum temperature T1, and the time during the cooling process from the maximum temperature T1 to 700°C. Residence time t1 corresponds to the time from 700 to 500°C in the cooling zone, and does not include the time during the heating process (heating zone) from 500 to 700°C.

[0109] In the annealing temperature range of T1 to 700°C, carbides and nitrides are likely to dissolve, and solute C and solute N are likely to be formed. On the other hand, the temperature range of 700 to 500°C is a temperature range in which carbides, carbonitrides, and nitrides are likely to be formed. Solute C and solute N bind to dislocations and inhibit dislocation movement. As the number of dislocations whose movement is inhibited increases, dislocation entanglement increases. Therefore, in the non-oriented electrical steel sheet of this embodiment, solute C and solute N are reduced as much as possible.

[0110] FA is defined as follows: FA=t1-t0 FA corresponds to the left side of formula (A). When FA is greater than 0, that is, when the residence time t1 is longer than the residence time t0, the dissolved carbon and nitrogen can be re-immobilized as carbides, carbonitrides, and nitrides while suppressing the solutionization of carbides and nitrides that were formed before the final annealing. This reduces the amount of dissolved C and N in the steel sheet. As a result, the work hardening amount WH can be reduced to less than 15 MPa.

[0111] FB is defined as follows: FB=t1 / t0 F B corresponds to the left side of formula (B). If F B exceeds 3.0, solute C and solute N remaining in the steel sheet without precipitating as precipitates will lock to dislocations. In this case, dislocations are more likely to pile up, increasing the amount of work hardening WH. If F B is 3.0 or less, the amount of work hardening WH can be sufficiently suppressed.

[0112] [(Condition 4) Oxygen potential] In the final annealing, the hydrogen partial pressure P is further increased in one or more locations selected from the heating zone, the soaking zone, and the cooling zone in the temperature range of 500°C or higher in the furnace atmosphere of the final annealing furnace. H2 (atm) versus water vapor partial pressure P H20 (atm) ratio is set to be higher than 0.05, or the oxygen concentration is set to be higher than 0.010%.

[0113] The hydrogen partial pressure P in the atmosphere inside the finishing annealing furnace H2 (atm) versus water vapor partial pressure P H20 The ratio of the oxygen potential (atm) to the oxygen concentration (atm) is defined as the oxygen potential. When the oxygen potential is higher than 0.05 or the oxygen concentration is higher than 0.010% in one or more locations selected from the heating zone, soaking zone, and cooling zone in the temperature range of 500°C or higher in the furnace atmosphere of a finish annealing furnace, decarburization of the steel sheet during finish annealing is promoted. In this case, the amount of solute C in the steel sheet can be sufficiently reduced. As a result, the work hardening amount WH can be reduced to less than 15 MPa.

[0114] [(Feature 5) Temperature gradient CG in the longitudinal direction of cold-rolled steel sheets during the cooling process] During the cooling process, the temperature gradient in the longitudinal direction (rolling direction) of the cold-rolled steel sheet from the maximum temperature T1 to 500°C is defined as CG (°C / m). The temperature gradient CG is calculated based on the sheet running distance from the maximum temperature T1 to 500°C and the temperature difference obtained by subtracting 500°C from the maximum temperature T1. If the temperature gradient CG during the cooling process exceeds 20°C / m, residual strain will occur in the steel plate due to thermal strain. In this case, the work hardening amount WH will be 15 MPa or more. Therefore, the temperature gradient CG should be 20°C / m or less.

[0115] [Other processes] In the above-described manufacturing method, a coating step may be carried out after the final annealing step. In the coating step, an insulating coating is applied to the surface of the non-oriented electrical steel sheet after the final annealing step. The type of insulating coating is not particularly limited. The insulating coating may be an organic component or an inorganic component.

[0116] The non-oriented electrical steel sheet of this embodiment can be manufactured by the above manufacturing method. Note that the manufacturing method of the non-oriented electrical steel sheet of this embodiment is not particularly limited as long as Features 1 to 5 are satisfied.

[0117] [About the rotor core] The rotor core of this embodiment is manufactured using the non-oriented electrical steel sheet of this embodiment as a material. Fig. 4 is a plan view showing an example of a rotor core 1. Referring to Fig. 4, the rotor core 1 includes a plurality of rotor core materials 2. The rotor core materials 2 are plate-shaped. More specifically, the rotor core materials 2 are disk-shaped. The rotor core 1 is configured by stacking the plurality of rotor core materials 2.

[0118] The shape of the rotor core material 2 is not particularly limited as long as it is plate-shaped. FIG. 4 shows the rotor core material 2 for a permanent magnet synchronous motor as an example. However, the rotor core material 2 may have other shapes as long as it is plate-shaped. For example, when the motor is a reluctance motor, the rotor core material 2 may be plate-shaped with a plurality of salient poles, or may be plate-shaped with a plurality of through-holes that serve as flux barriers. Furthermore, when the motor is an induction motor, the rotor core material 2 may have a plurality of through-holes in which induced current paths made of copper or aluminum die-cast or the like are installed.

[0119] As described above, the rotor core material 2 is a punched product manufactured by punching the non-oriented electrical steel sheet of this embodiment. Therefore, the rotor core material 2 satisfies the above-mentioned features 1 to 5. Specifically, the rotor core material 2 contains, in mass %, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0 to 0.100%, Cr: 0 to 2.000%, and La: 0 to 0.010 0%, Ce: 0 to 0.0100%, B: 0 to 0.0010%, Zn: 0 to 0.0050%, Ga: 0 to 0.0050%, Ge: 0 to 0.0050%, As: 0 to 0.0100%, Ni: 0 to 0.500%, Cu: 0 to 0.500%, Sn: 0 to 0.200%, Sb: 0 to 0.100%, Ca: 0 to 0.0050%, Nd: 0 to 0.0010%, Mg: 0 to 0.0030%, and the remainder being Fe and impurities, satisfying formula (1) and formula (2). Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol. Furthermore, rotor core material 2 has a tensile strength TS higher than 570 MPa. For rotor core material 2, the stress at 2.0% strain is further increased to Y 2.0 (MPa) and the yield stress is YS (MPa), the amount of work hardening WH defined by formula (3) is less than 15 MPa. WH=Y 2.0 -YS (3) Furthermore, in the rotor core material 2, the average crystal grain size D (μm) satisfies the formula (4), and the yield elongation is 0.5% or more. D<80-Si×10 (4) Here, the element symbol in formula (4) is substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for that element symbol.

[0120] [About the stator core] Note that a stator core may be manufactured using the non-oriented electromagnetic steel sheet of this embodiment as a material. Fig. 5 is a plan view of a stator core 3. Referring to Fig. 5, the stator core 3 includes a plurality of stator core materials 4. The stator core materials 4 are in the shape of an annular plate. The stator core 3 is configured by stacking a plurality of stator core materials 4.

[0121] The stator core material 4 includes a plurality of teeth 41. The plurality of teeth 41 are arranged with gaps between each other in the circumferential direction of the stator core material 4. Each tooth 41 extends in the radial direction of the stator core material 4.

[0122] The stator core material 4 is manufactured by punching the non-oriented electrical steel sheet of this embodiment and then performing stress relief annealing. Therefore, the stator core material 4 satisfies the above-mentioned features 1 and 2.

[0123] Specifically, the stator core material 4 contains, in mass %, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0 to 0.100%, Cr: 0 to 2.000%, and La: 0 to 0.010 0%, Ce: 0 to 0.0100%, B: 0 to 0.0010%, Zn: 0 to 0.0050%, Ga: 0 to 0.0050%, Ge: 0 to 0.0050%, As: 0 to 0.0100%, Ni: 0 to 0.500%, Cu: 0 to 0.500%, Sn: 0 to 0.200%, Sb: 0 to 0.100%, Ca: 0 to 0.0050%, Nd: 0 to 0.0010%, Mg: 0 to 0.0030%, and the remainder being Fe and impurities, satisfying formula (1) and formula (2). Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) Here, the element symbols in formulas (1) and (2) are substituted with the corresponding element content in mass %. If the corresponding element is not contained, "0" is substituted for the element symbol.

[0124] [Method for measuring the chemical composition of rotor core material 2 and stator core material 4] The chemical compositions of the rotor core material 2 and the stator core material 4 can be measured based on the method described in the above-mentioned [Method for measuring the chemical composition of non-oriented electrical steel sheet]. Specifically, chips are collected from the rotor core material 2 or the stator core material 4 using a drill. The collected chips are dissolved in acid to obtain a solution. ICP-AES is performed on the solution to perform elemental analysis of the chemical composition. The C content and S content are determined using the well-known high-frequency combustion method (combustion-infrared absorption method). The N content is determined using the well-known inert gas fusion-thermal conductivity method. The O content is determined using the well-known inert gas fusion-infrared absorption method.

[0125] [Method for measuring the stress-strain curve of rotor core material 2] The tensile strength TS of the rotor core material 2 is measured using the following method. A JIS No. 5 tensile test piece, as specified in JIS Z2241:2011, is taken from the rotor core material 2. If a JIS No. 5 tensile test piece cannot be taken due to the small size of the rotor core material 2, a scaled-down test piece of the JIS No. 5 tensile test piece is taken from the rotor core material 2. Using the collected tensile test specimen, a tensile test is conducted in air at room temperature in accordance with JIS Z2241:2011 to obtain a stress-strain curve. The tensile strength TS (MPa) is calculated from the obtained stress-strain curve. When conducting a tensile test using a scaled test specimen, the test is conducted based on the strain rate specified in Appendix JB of the above standard.

[0126] [Work hardening amount WH evaluation test for rotor core material 2] The amount of work hardening WH of the rotor core material 2 is determined by the method described in the above-mentioned [Work hardening amount WH evaluation test]. At this time, the stress-strain curve used is the stress-strain curve obtained by the above-mentioned [Method for measuring the stress-strain curve of the rotor core material 2].

[0127] [Method for measuring the average crystal grain size D of rotor core material 2] The average crystal grain size D of the rotor core material 2 is determined by the method described above in [Method for measuring average crystal grain size D]. Note that the cross section (L cross section) of the rotor core material 2 parallel to the rolling direction is used as the observation surface.

[0128] [Method for measuring yield elongation of rotor core material 2] The yield elongation of the rotor core material 2 is determined by the following method. Specifically, a JIS No. 5 tensile test piece is taken from the rotor core material 2. A tensile test is conducted in air at room temperature in accordance with JIS Z2241:2011 to determine the yield elongation (%). Note that if a JIS No. 5 tensile test piece cannot be taken because the rotor core material 2 is too small, a scaled-down JIS No. 5 tensile test piece is taken from the rotor core material 2. When a tensile test is conducted using a scaled-down test piece, the test is conducted based on the strain rate specified in Appendix JB of the above standard.

[0129] If the upper yield point is not clearly visible, the yield elongation (%) is determined using the following method. Referring to Figure 3, the yield strength YS (MPa) is determined from the stress-strain curve obtained by the tensile test based on the method described above in the "Test for evaluating the amount of work hardening, WH, of rotor core material 2" section. The strain value at the determined yield strength YS is designated as ε1. In the stress-strain curve after strain value ε1, the maximum strain value ε2 is identified in the region where the stress remains within the range of the yield stress YS ±1.0% as the strain increases. Using ε1 and ε2, the yield elongation is determined using the following equation. Yield elongation (%) = ε2 - ε1

[0130] [Method of manufacturing rotor core 1] The rotor core 1 is manufactured by the following method. The rotor core blank 2 is manufactured by punching from the non-oriented electrical steel sheet of this embodiment. Specifically, the rotor core blank 2 is punched out by punching. The punched rotor core blanks 2 are stacked to manufacture the rotor core 1.

[0131] [About the motor] The motor of this embodiment includes the rotor core 1 described above. The motor further includes a well-known stator core. Because the motor of this embodiment includes the rotor core of this embodiment, the rotor core has high strength and sufficient magnetic properties.

[0132] The stator core 3 described above may be used as the stator core included in the motor core. The stator core 3 is manufactured by the following method. Using the non-oriented electromagnetic steel sheet of this embodiment as a material, a stator core blank 4 is manufactured by punching. A plurality of stator core blanks 4 are stacked to manufacture the stator core 3.

[0133] The stator core material 4 manufactured by punching using the non-oriented electrical steel sheet of this embodiment has high dimensional accuracy. Therefore, it is superior in terms of dimensional accuracy to conventional stator cores manufactured using non-oriented electrical steel sheets with a tensile strength of over 570 MPa. The stator core 3 manufactured using the non-oriented electrical steel sheet of this embodiment is subjected to stress relief annealing after laminating the stator core material 4. This makes it possible to achieve higher efficiency in motors incorporating the stator core 3. [Example]

[0134] Non-oriented electrical steel sheets having the chemical compositions shown in Table 1 (Tables 1A to 1C) were produced by the following method.

[0135] [Table 1A]

[0136] [Table 1B]

[0137] [Table 1C]

[0138] In Table 1C, "T" in the "Formula (1)" column means that formula (1) is satisfied, and "F" means that formula (1) is not satisfied. In the "Formula (2)" column, "T" means that formula (2) is satisfied, and "F" means that formula (2) is not satisfied.

[0139] The slabs (steel billets) were hot-rolled to produce hot-rolled steel sheets with a thickness of 2.0 mm. The slab heating temperature was 1100 to 1200°C. The finish rolling temperature was 800 to 1100°C. The coiling temperature was 700 to 800°C. The hot-rolled steel sheets were subjected to hot-rolled sheet annealing by continuous annealing, in which the sheets were soaked at 1000°C for 60 seconds. The steel sheets after the hot-rolled sheet annealing were cold-rolled to produce cold-rolled steel sheets with a thickness of 0.25 mm.

[0140] The cold-rolled steel sheets were subjected to final annealing. The maximum temperature reached in final annealing, T1 (°C), tension, TE (MPa), residence time, t0 (seconds) and residence time, t1 (seconds), FA, FB, and oxygen potential, P H20 / P H2 The oxygen concentration (%) and temperature gradient CG (°C / m) are shown in Table 2. Non-oriented electrical steel sheets with each test number were manufactured by the above manufacturing process.

[0141] [Table 2]

[0142] [Evaluation test] The following evaluation tests were carried out on the non-oriented electrical steel sheets with each test number. (Test 1) Chemical composition measurement test (Test 2) Tensile strength TS measurement test (Test 3) Work hardening amount WH evaluation test (Test 4) Measurement test of average crystal grain size D (Test 5) Yield elongation measurement test (Test 6) Magnetic property evaluation test (Test 7) ​​Dimensional accuracy evaluation test after punching Tests 1 to 7 will be explained below.

[0143] [(Test 1) Chemical composition measurement test] The chemical composition of the non-oriented electrical steel sheet of each test number was determined according to the method described above in [Method for measuring the chemical composition of non-oriented electrical steel sheet]. As a result, the chemical composition of the non-oriented electrical steel sheet of each test number was as shown in Table 1 (Table 1A to Table 1C).

[0144] [(Test 2) Tensile strength TS measurement test] The tensile strength TS (MPa) of the non-oriented electrical steel sheet of each test number was determined according to the method described above in [Method for measuring stress-strain curve]. The obtained tensile strengths TS (MPa) are shown in Table 3.

[0145] [Table 3]

[0146] [(Test 3) Work hardening amount WH evaluation test] The work hardening amount WH (MPa) of the non-oriented electrical steel sheets of each test number was determined according to the method described in the above-mentioned [Work hardening amount WH evaluation test]. The obtained work hardening amounts WH (MPa) are shown in Table 3.

[0147] [(Test 4) Measurement test of average crystal grain size D] The average grain size D (μm) of the non-oriented electrical steel sheets of each test number was determined according to the method described above in [Method for measuring average grain size D]. The obtained average grain size D is shown in Table 3.

[0148] [(Test 5) Yield elongation measurement test] The yield elongation (%) of the non-oriented electrical steel sheet with each test number was determined according to the method described in the "Method for measuring yield elongation" above. The obtained yield elongation (%) is shown in Table 3. In Table 3, "80-Si×10" indicates the Fn value. In addition, in the "Equation (4)" column in Table 3, "T" means that equation (4) is satisfied, and "F" means that equation (4) is not satisfied.

[0149] [(Test 6) Magnetic property evaluation test] The magnetic flux density B can be calculated by the following method. 50 (T) and iron loss W 5 / 1000 (W / kg) was calculated. [Magnetic flux density B 50 Evaluation Test] For each test number of non-oriented electrical steel sheet, the magnetic flux density B in the rolling direction (L direction) 50(L) , and magnetic flux density B in the direction perpendicular to the rolling direction (C direction) 50(C) Specifically, Epstein test pieces were cut out in the L and C directions from the non-oriented electrical steel sheets of each test number in accordance with JIS C 2550-1:2011. The cut-out Epstein test pieces were subjected to the electrical steel strip test method in accordance with JIS C 2550-1:2011 and 2550-3:2011, and the magnetic flux density B at 5000 A / m in the L and C directions was measured. 50(L) (T) and B 50(C) (T) was measured. The magnetic flux density B in the L direction 50(L) (T) and C direction magnetic flux density B 50(C) The arithmetic mean value of the magnetic flux density B 50 (T). The obtained magnetic flux density B 50 (T) is shown in Table 3.

[0150] [Iron loss W 5 / 1000 Evaluation Test] The above-mentioned magnetic flux density B 50Epstein test specimens were prepared in the same manner as in the evaluation tests. The Epstein test specimens were cut out in two ways: by shear cutting with a clearance of 20 μm, and by electrical discharge machining. In other words, two types of test specimens were prepared for each test number: Epstein test specimens cut out by shear cutting, which simulates punching, and Epstein test specimens cut out by electrical discharge machining. Each Epstein test specimen was subjected to the electromagnetic steel strip test method in accordance with JIS C 2550-1:2011 and 2550-3:2011, and the iron loss W at 1000 Hz and 0.5 T in the L direction (rolling direction) and C direction (direction perpendicular to the rolling direction) was measured. 5 / 1000(L) (W / kg) and iron loss W 5 / 1000(C) (W / kg) was measured. Iron loss in the L direction (rolling direction) W 5 / 1000(L) and iron loss W in the C direction (direction perpendicular to the rolling direction) 5 / 1000(C) The arithmetic mean value of (W / kg) is the iron loss W 5 / 1000 (W / kg). Iron loss W in Epstein test piece by shear cutting 5 / 1000 (W / kg) in Table 3. 5 / 1000 The iron loss in the Epstein test piece by EDM is shown in the "Shear Cutting" column of "(W / kg)". 5 / 1000 (W / kg) in Table 3. 5 / 1000 (W / kg)" is shown in the "Electric Discharge Machining" column. Iron loss during shear cutting W 5 / 1000 (W / kg) to iron loss W in EDM 5 / 1000 (W / kg) is subtracted from the iron loss deterioration amount ΔW 5 / 1000 (W / kg) Iron loss deterioration amount ΔIron loss W 5 / 1000 (W / kg) are shown in Table 3.

[0151] [(Test 7) ​​Dimensional accuracy evaluation test after punching] The dimensional accuracy of each non-oriented electrical steel sheet after punching was evaluated using the following test. Ring-shaped samples (punched products) with an inner diameter of 90 mm and an outer diameter of 100 mm were prepared from each non-oriented electrical steel sheet by punching using a die with a clearance of 8% of the sheet thickness. The ring-shaped samples were then cut at 45° intervals around the normal to the non-oriented electrical steel sheet from the rolling direction of the non-oriented electrical steel sheet to obtain eight test pieces. Each test piece was embedded in resin, and the cut surface was polished by 1 mm or more to eliminate the effects of deformation during cutting. After polishing, the cut surfaces near the punched end surface on the inner circumferential surface and the punched end surface on the outer circumferential surface were observed using an optical microscope at 100x magnification. As shown in Figure 6, a line segment 20 was drawn connecting point P1, where the sagging surface 10 transitions to the punched end surface 11, and the burr tip P2 of the punched end surface 11. A line segment 21 is drawn that is parallel to the line segment 20 and tangent to the punched end surface 11 that protrudes from the line segment 20. The distance d between the line segment 20 and the line segment 21 is determined. The arithmetic mean value of the distances d determined for eight test pieces (eight on the cut surface near the punched end surface on the inner peripheral surface side, eight on the cut surface near the punched end surface on the outer peripheral surface side, a total of 16 on the inner peripheral surface side and the outer peripheral surface side) was defined as the punched flatness (μm). The obtained punched flatness is shown in Table 3 under "Punched Flatness (μm)".

[0152] [Evaluation results] Referring to Tables 1 to 3, Test Nos. 1 to 30 satisfied Features 1 to 5. Therefore, the non-oriented electrical steel sheets with these test Nos. had a magnetic flux density B 50 is 1.60T or more, and the iron loss W 5 / 1000 Iron loss W in shear cutting 5 / 1000 Iron loss deterioration amount ΔW minus 5 / 1000 The flatness of the punched portion was 25 μm or less, and excellent dimensional accuracy was obtained after punching.

[0153] On the other hand, test numbers 31 to 34 did not satisfy formula (1) or formula (2). Therefore, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained during punching. Furthermore, the iron loss degradation amount ΔW 5 / 1000was more than 2.0, and excellent magnetic properties were not obtained.

[0154] In test numbers 35 and 36, the Si content was too low. Therefore, the tensile strength TS was too low. Furthermore, the work hardening amount WH was 15 MPa or more. As a result, the iron loss deterioration amount ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained.

[0155] In test numbers 37 and 38, the Si content was too low. As a result, the work hardening amount WH was 15 MPa or more. As a result, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained during punching. Furthermore, the iron loss degradation amount ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained.

[0156] Test Nos. 39 and 40 did not satisfy Condition 1 in the finish annealing process. As a result, the work hardening amount WH was 15 MPa or more. Furthermore, formula (4) was not satisfied, and the yield point elongation was less than 0.5%. As a result, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained during punching. Furthermore, the iron loss degradation amount ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained.

[0157] In test numbers 41 and 42, the tension TE at the maximum temperature T1 was too low. Therefore, the yield elongation was less than 0.5%. As a result, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained during punching. Furthermore, the iron loss degradation ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained.

[0158] In test numbers 43 and 44, the tension TE at the maximum temperature T1 was too high. As a result, the work hardening amount WH was 15 MPa or more. As a result, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained during punching. Furthermore, the iron loss degradation amount ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained.

[0159] In test numbers 45 and 46, FA did not satisfy formula (A) during the finish annealing process. Therefore, the work hardening amount WH was 15 MPa or more. As a result, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained during punching. Furthermore, the iron loss degradation amount ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained.

[0160] In test numbers 47 and 48, FB did not satisfy formula (B). Therefore, the work hardening amount WH was 15 MPa or more. As a result, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained during punching. Furthermore, the iron loss degradation amount ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained.

[0161] Test Nos. 49 and 50 did not satisfy Condition 4 in the finish annealing process. Therefore, the work hardening amount WH was 15 MPa or more. As a result, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained during punching. Furthermore, the iron loss degradation amount ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained.

[0162] In test numbers 51 and 52, the temperature gradient CG was too large. As a result, the work hardening amount WH exceeded 15 MPa. As a result, the punching flatness exceeded 25 μm, and sufficient dimensional accuracy was not obtained after punching. Furthermore, the iron loss degradation amount ΔW 5 / 1000 was more than 2.0, and excellent magnetic properties were not obtained. [Example]

[0163] Using the non-oriented electrical steel sheets of test numbers 1 to 30 of Example 1, rotor cores having the shape shown in FIG. 4 were manufactured. Specifically, punching was performed on the non-oriented electrical steel sheets of each test number. In the punching process, rotor core blanks were produced by punching using a die with a clearance of 8% of the sheet thickness. Multiple rotor core blanks were stacked to form the rotor core. The diameter of the rotor core blank was 70 mm.

[0164] The following evaluation tests were carried out on the rotor cores with each test number. (Test 1) Tensile strength TS measurement test (Test 2) Work hardening amount WH evaluation test (Test 3) Measurement test of average crystal grain size D (Test 4) Yield elongation measurement test (Test 5) Magnetic property evaluation test (Test 6) Dimensional accuracy evaluation test after punching Tests 1 to 6 will be explained below.

[0165] [(Test 1) Tensile strength TS measurement test] The rotor core blank was separated from the rotor core. The tensile strength TS (MPa) of the rotor core blank was determined according to the method described above in [Method for measuring the stress-strain curve of rotor core blank 2]. The dimensions of the tensile test specimen taken from the rotor core blank were a parallel section width of 2.50 mm, a gauge length of 5.00 mm, a thickness of 0.25 mm, and a total length of 25 mm. The tensile strength TS (MPa) of the rotor core blank is shown in Table 4.

[0166] [(Test 2) Work hardening amount WH evaluation test] The work-hardening amount WH of the rotor core material was determined according to the method described in the above-mentioned [Work-hardening amount WH evaluation test for rotor core material 2]. The work-hardening amount WH (MPa) of the obtained rotor core material is shown in Table 4.

[0167] [(Test 3) Measurement test of average crystal grain size D] The rotor core blank was separated from the rotor core. The average crystal grain size D (μm) of the rotor core blank was determined according to the method described in the above-mentioned [Method for measuring the average crystal grain size D of rotor core blank 2]. The average crystal grain size D (μm) of the obtained rotor core blank is shown in Table 4.

[0168] [(Test 4) Yield elongation measurement test] The rotor core blank was separated from the rotor core. The yield elongation (%) of the rotor core blank was determined according to the method described above in [Method for measuring yield elongation of rotor core blank 2]. The dimensions of the tensile test specimen taken from the rotor core blank were a parallel section width of 2.50 mm, a gauge length of 5.00 mm, a thickness of 0.25 mm, and a total length of 25 mm. The yield elongation (%) of the rotor core blank is shown in Table 4.

[0169] [(Test 5) Magnetic property evaluation test] The rotor core material was separated from the rotor core. From the separated rotor core material, small test pieces of extractable dimensions for single-plate magnetic measurement were created using electric discharge machining. The size of the small test pieces was 10 mm x 20 mm x plate thickness. Using a small test piece and a single sheet tester, the magnetic flux density B of the rotor core material was measured in accordance with the Single Sheet Tester (SST) method described in JIS C 2556:2015. 50 (T) and iron loss W 5 / 1000 (W / kg) was calculated. The magnetic flux density B of the obtained rotor core material 50 (T) and iron loss W 5 / 1000 (W / kg) are shown in Table 4.

[0170] [(Test 6) Dimensional accuracy evaluation test after punching] After punching, the rotor core blank was cut at 45° intervals around its central axis to obtain eight test pieces, including the outer peripheral surface of the blank. Each test piece was embedded in resin, and the cut surface was polished at least 1 mm to eliminate the effects of deformation during cutting. After polishing, the cut surface near the outer peripheral surface of the blank was observed using an optical microscope at 100x magnification. As shown in Figure 6, a line segment 20 was drawn connecting point P1, where the sagging surface 10 transitions to the punched end surface 11, and the burr tip P2 of the punched end surface 11. A line segment 21 was drawn parallel to line segment 20 and tangent to the punched end surface 11 protruding from line segment 20. The distance d between line segment 20 and line segment 21 was calculated. The arithmetic mean value of the distances d measured for the eight test pieces (a total of eight) was used as the punched flatness (μm). The punched flatness (μm) of the resulting rotor core blank is shown in Table 4. It should be noted that the punched end surface at the time of punching may not be maintained on the inner peripheral surface side of the rotor core blank due to processing such as when inserting the shaft. Therefore, as described above, the dimensional accuracy was evaluated on the punched end surface in the vicinity of the outer peripheral surface of the rotor core blank.

[0171] [Table 4]

[0172] [Evaluation results] As shown in Table 4, the rotor core materials with test numbers 1 to 30 satisfied features 1 to 5. Therefore, the rotor core materials with these test numbers had a punching flatness of 25 μm or less, and were excellent in dimensional accuracy after punching. In addition, the rotor core materials had a magnetic flux density B 50 is 1.60T or more, and iron loss W 5 / 1000 The magnetic flux density was 16.9 W / kg or less, and high strength and excellent magnetic properties were obtained.

[0173] While preferred embodiments of the non-oriented electrical steel sheet of the present disclosure have been described above, the non-oriented electrical steel sheet of the present disclosure is not limited to these examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the ideas described in the claims, and it is understood that these modifications or alterations also fall within the technical scope of the non-oriented electrical steel sheet of the present disclosure.

Claims

1. A non-oriented electrical steel sheet, In mass%, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0-0.100%, Cr: 0-2.000%, La: 0 to 0.0100%, Ce: 0 to 0.0100%, B: 0 to 0.0010%, Zn: 0 to 0.0050%, Ga: 0 to 0.0050%, Ge: 0 to 0.0050%, As: 0 to 0.0100%, Ni: 0 to 0.500%, Cu: 0 to 0.500%, Sn: 0-0.200%, Sb: 0 to 0.100%, Ca: 0-0.0050%, Nd: 0 to 0.0010%, Mg: 0 to 0.0030%, and the balance being Fe and impurities, satisfying formula (1) and formula (2); Tensile strength TS is higher than 570 MPa, The stress at 2.0% strain is Y ２．０ (MPa) and the yield stress is YS (MPa), the work hardening amount WH defined by the formula (3) is less than 15 MPa, The average grain size D (μm) satisfies formula (4) and the yield elongation is 0.5% or more. Non-oriented electrical steel sheet. Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) WH=Y ２．０ -YS (3) D<80-Si×10 (4) Here, the element symbols in formulas (1), (2), and (4) are substituted with the corresponding element contents in mass%. When the corresponding element is not contained, "0" is substituted for the element symbol.

2. The non-oriented electrical steel sheet according to claim 1, In mass%, Zr: 0.0001 to 0.0100%, Nb: 0.0001 to 0.0100%, V: 0.0001 to 0.0100%, Mo: 0.001-0.100%, Cr: 0.001-2.000%, La: 0.0001 to 0.0100%, Ce: 0.0001 to 0.0100%, B: 0.0001 to 0.0010%, Zn: 0.0001 to 0.0050%, Ga: 0.0001-0.0050%, Ge: 0.0001 to 0.0050%, As: 0.0001 to 0.0100%, Ni: 0.001 to 0.500%, Cu: 0.001 to 0.500%, Sn: 0.001-0.200%, Sb: 0.001 to 0.100%, Ca: 0.0001-0.0050%, Nd: 0.0001 to 0.0010%, and Mg: 0.0001 to 0.0030%; Non-oriented electrical steel sheet.

3. A rotor core material is provided which is laminated on top of one another; The rotor core material is In mass%, Si: 3.1 to 4.5%, C: 0.0025% or less, N: 0.0025% or less, O: 0.0400% or less, P: 0.100% or less, S: 0.0050% or less, Ti: 0.0100% or less, Mn: 2.0% or less, Al: 1.500% or less, Zr: 0 to 0.0100%, Nb: 0 to 0.0100%, V: 0 to 0.0100%, Mo: 0-0.100%, Cr: 0-2.000%, La: 0 to 0.0100%, Ce: 0 to 0.0100%, B: 0 to 0.0010%, Zn: 0 to 0.0050%, Ga: 0 to 0.0050%, Ge: 0 to 0.0050%, As: 0 to 0.0100%, Ni: 0 to 0.500%, Cu: 0-0.500%, Sn: 0-0.200%, Sb: 0 to 0.100%, Ca: 0-0.0050%, Nd: 0 to 0.0010%, Mg: 0 to 0.0030%, and the balance being Fe and impurities, satisfying formula (1) and formula (2); Tensile strength TS is higher than 570 MPa, The stress at 2.0% strain is Y ２．０ (MPa) and the yield stress is YS (MPa), the work hardening amount WH defined by the formula (3) is less than 15 MPa, The average grain size D (μm) satisfies formula (4) and the yield elongation is 0.5% or more. Rotor core. Si / 28+Ti / 48+Nb / 93+V / 51+Zr / 91+Mo / 96+Cr / 52>C / 12×750 (1) Si / 28+Al / 27+Ti / 48+Zr / 91+La / 139+Ce / 140>N / 14×1000 (2) WH=Y ２．０ -YS (3) D<80-Si×10 (4) Here, the element symbols in formulas (1), (2), and (4) are substituted with the corresponding element contents in mass%. When the corresponding element is not contained, "0" is substituted for the element symbol.

4. The rotor core according to claim 3, The rotor core material is In mass%, Zr: 0.0001 to 0.0100%, Nb: 0.0001 to 0.0100%, V: 0.0001 to 0.0100%, Mo: 0.001-0.100%, Cr: 0.001-2.000%, La: 0.0001 to 0.0100%, Ce: 0.0001 to 0.0100%, B: 0.0001 to 0.0010%, Zn: 0.0001 to 0.0050%, Ga: 0.0001-0.0050%, Ge: 0.0001 to 0.0050%, As: 0.0001 to 0.0100%, Ni: 0.001 to 0.500%, Cu: 0.001 to 0.500%, Sn: 0.001-0.200%, Sb: 0.001 to 0.100%, Ca: 0.0001-0.0050%, Nd: 0.0001 to 0.0010%, and Mg: 0.0001 to 0.0030%; Rotor core.

5. A rotor core according to claim 3 or 4, Motor.

6. A method for producing a non-oriented electrical steel sheet according to claim 1 or 2, a hot rolling process in which hot rolling is performed on the slab to produce a hot-rolled steel sheet; a cold rolling step of cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; A finish annealing step of performing finish annealing on the cold-rolled steel sheet in a finish annealing furnace, In the finish annealing step, Annealing the cold-rolled steel sheet at a maximum temperature T1 of 950 ° C. or less, The tension TE applied to the cold-rolled steel sheet at the maximum temperature T1 is set to 2.0 to 10.0 MPa, a residence time t0 (seconds) between the annealing temperatures T1 and 700°C in the heating zone, soaking zone, and cooling zone of the finish annealing furnace, and a residence time t1 (seconds) between the annealing temperatures of 700 and 500°C in the cooling zone satisfy formulas (A) and (B), In the furnace atmosphere of the finish annealing furnace, at one or more locations selected from the heating zone, the soaking zone, and the cooling zone in a temperature range of 500 ° C. or higher, a hydrogen partial pressure P Ｈ２ (atm) relative to the water vapor partial pressure P Ｈ２０ (atm) ratio is higher than 0.05, or the oxygen concentration is higher than 0.010%, The temperature gradient CG in the longitudinal direction of the cold-rolled steel sheet during the cooling process is 20 ° C. / m or less. Manufacturing method for non-oriented electrical steel sheets. t1-t0>0 (A) t1 / t0≦3.0 (B)

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