Non-oriented electrical steel sheet and method for producing the same

Abstract

Provided are a non-oriented electrical steel sheet that achieves both low iron loss in the high-frequency range and high ductility, and a method for producing the same. A non-oriented electrical steel sheet has a difference between an average Si content of a surface layer portion and an average Si content of an inner layer portion, and contains, in mass% in terms of an average content throughout an entire sheet thickness, particular amounts of C, Mn, Al, P, S, N, and O. The average Si content of the surface layer portion is 4.00% or more and 6.30% or less, the average Si content of the inner layer portion is 2.00% or more and 6.20% or less, ΔSi, which is the difference in average Si content between the surface layer portion and the inner layer portion, is 0.10% or more and 2.00% or less. The balance is Fe and unavoidable impurities, and formula (1) is satisfied: IB2 / IFe < 0.030 ··· (1) where, in formula (1), IB2 represents a diffraction peak intensity originating from a B2 phase of Fe3Si detected at around 2θ = 36.5° as measured by X-ray diffraction, and IFe represents a diffraction peak intensity originating from a ferrite phase detected at around 2θ = 77.6° as measured by X-ray diffraction.

Description

Non-oriented electrical steel sheet and its manufacturing method

[0001] The present invention relates to a non-oriented electrical steel sheet, particularly to a non-oriented electrical steel sheet suitable for motor cores, which combines low iron loss in the high frequency range with high ductility, and to a method for manufacturing the same.

[0002] Motors for hybrid electric vehicles and vacuum cleaners are driven at high frequencies of 400 Hz to 5 kHz in order to achieve compactness and high efficiency. Therefore, non-oriented electrical steel sheets used as core materials for such motors are required to have low high-frequency iron loss.

[0003] Increasing resistivity is an effective way to reduce high-frequency iron loss. Therefore, high-Si steels have been developed by increasing the Si content to increase resistivity. However, as the Si content increases, hardness increases and ductility decreases, making it difficult to process high-Si-content electrical steel sheets into motor cores and other products.

[0004] Therefore, as a method for improving the workability of electrical steel sheets with a high Si content, electrical steel sheets in which the formation of ordered phases is suppressed have been developed. For example, in Patent Document 1, in the cooling process after annealing, the temperature is held in the range of more than 600°C and not more than 700°C for 10 seconds or more, and then cooled from 600°C or less to at least 250°C or less at a cooling rate of 60°C / sec or more, thereby achieving a DO ３ An electrical steel sheet has been proposed that suppresses the increase in hardness and embrittlement of the steel sheet when the Si content is increased by using a material to which one or both of Ni: 0.1 to 5 mass % and Cu: 0.1 to 3 mass % are added in addition to the size of ordered clusters being 100 nm or less.

[0005] Patent No. 6375692

[0006] However, as a result of investigations conducted by the present inventors, when the method of adding Cu or Ni and rapidly cooling after annealing as proposed in Patent Document 1 is applied in a range in which the Si content exceeds 4.0 mass %, it is necessary to add a large amount of Cu or Ni and perform rapid cooling in order to suppress the ordered phase and maintain workability, which results in problems such as a decrease in saturation magnetic flux density and deterioration of iron loss due to distortion during cooling.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-oriented electrical steel sheet that achieves both low core loss and high ductility in the high frequency range, and a method for manufacturing the same.

[0008] As a result of intensive investigations into the above-mentioned problems, the present inventors have confirmed that when a certain amount or more of the B2 phase is formed in the surface layer of a non-oriented electrical steel sheet, the ductility of the non-oriented electrical steel sheet is significantly reduced, and have inferred that this is one of the causes of the reduction in ductility of the non-oriented electrical steel sheet.

[0009] Furthermore, through detailed investigations, the following findings were discovered: By controlling ΔSi, which is the difference in average Si content (average Si concentration) between the surface layer and the inner layer of a non-oriented electrical steel sheet, to an appropriate value, and also by controlling the cooling rate and tension applied to the steel sheet in the cooling process after the siliconizing diffusion treatment step in the manufacturing process, it is possible to suppress the formation of the B2 ordered phase in the surface layer of the non-oriented electrical steel sheet and improve the ductility of the non-oriented electrical steel sheet.

[0010] The present invention was made based on the above findings and as a result of further investigation, and the gist of the present invention is as follows.

[0011] [1] A non-oriented electrical steel sheet having a difference between the average Si content of the surface layer portion and the average Si content of the inner layer portion, where the range of 0 to t / 4 and the range of 3t / 4 to t are defined as a surface layer portion, and the range of more than t / 4 and less than 3t / 4 is defined as an inner layer portion, based on the sheet thickness t (mm), and the average Si content of the surface layer portion and the average Si content of the inner layer portion are contained in mass%, and the average contents across the entire sheet thickness are: C: 0.010% or less, Mn: 2.0% or less, Al: 2.0% or less, P: 0.20% or less, S: 0.005% or less, N: 0.010% or less, and O: 0.010% or less, the average Si content of the surface layer portion is 4.00% or more and 6.30% or less, and the average Si content of the inner layer portion is 2.00% or more and 6.20% or less, A non-oriented electrical steel sheet having a difference ΔSi between the average Si content of the surface layer portion and the average Si content of the inner layer portion of the steel sheet, which is 0.10% or more and 2.00% or less, with the remainder consisting of Fe and unavoidable impurities, and which satisfies the following formula (1): IB2 / IFe < 0.030 (1) In formula (1), IB2 is the Fe content appearing at around 2θ = 36.5° as measured by X-ray diffraction.３[2] The non-oriented electrical steel sheet according to [1], further comprising, in mass%, an average content across the entire sheet thickness of one or more of: Sn: 0.10% or less, Sb: 0.10% or less, Cu: 2.0% or less, Ni: 2.0% or less, Cr: 2.0% or less, Ca: 0.01% or less, Mg: 0.01% or less, and REM: 0.03% or less. [3] The non-oriented electrical steel sheet according to [1] or [2], further containing, in mass%, one or more elements selected from the group consisting of Mo: 0 to 0.050%, B: 0 to 0.0020%, Ti: 0 to 0.010%, Nb: 0 to 0.0050%, V: 0 to 0.050%, Pb: 0 to 0.020%, As: 0 to 0.020%, Zn: 0 to 0.010%, Co: 0 to 0.10%, Ge: 0 to 0.030%, and Ga: 0 to 0.030%, averaged across the entire sheet thickness.[4] A method for producing a non-oriented electrical steel sheet according to any one of [1] to [3] above, comprising, by mass%, Si: 4.5% or less, C: 0.010% or less, Mn: 2.0% or less, Al: 2.0% or less, P: 0.20% or less, S: 0.005% or less, N: 0.010% or less, and O: 0.010% or less, and optionally further comprising Sn: 0.10% or less, Sb: 0.10% or less, Cu: 2.0% or less, Ni: 2.0% or less, Cr: 2.0% or less, Ca: 0.01% or less, Mg: 0.01% or less, REM: 0.03% or less, Mo: 0 to 0.050%, B: 0 to 0.0020%, Ti: 0 to 0.010%, The method includes a siliconizing and diffusion treatment step of subjecting a steel sheet having a chemical composition containing one or more elements selected from Nb: 0-0.0050%, V: 0-0.050%, Pb: 0-0.020%, As: 0-0.020%, Zn: 0-0.010%, Co: 0-0.10%, Ge: 0-0.030%, and Ga: 0-0.030%, with the balance being Fe and unavoidable impurities, and a cooling step of cooling the steel sheet after the siliconizing and diffusion treatment step, wherein the diffusion treatment in the siliconizing and diffusion treatment step involves holding the steel sheet in a temperature range of 1250 to 1000°C for 10 seconds or more, and wherein the cooling step involves cooling the steel sheet in a temperature range of 600°C to 200°C with an average tension of 4.0 MPa or more applied to the steel sheet and an average cooling rate of 20.0°C / second or more, Furthermore, the total treatment time of the siliconizing treatment and the diffusion treatment satisfies (300 × t) seconds or more and (1500 × t) seconds or less (t: thickness of the steel sheet (mm)), and further the treatment time of the siliconizing treatment and the diffusion treatment satisfy the following formula (3): 4.00≦[Si]: base + 2.7 × exp(−0.003 × (T1 + T2) / t) + 0.0085 × T1 / t ≦ 6.30 (3) In formula (3), [Si] base is the Si content (%) of the steel sheet before the siliconizing and diffusion treatment step, t is the thickness (mm) of the steel sheet, T1 is the treatment time (seconds) of the siliconizing treatment, and T2 is the treatment time (seconds) of the diffusion treatment.

[0012] According to the present invention, it is possible to provide a non-oriented electrical steel sheet that achieves both low iron loss and high ductility in the high frequency range, and a method for manufacturing the same.

[0013] According to the present invention, a non-oriented electrical steel sheet can be obtained that combines low iron loss and high ductility and is suitable as a material for motor cores. The non-oriented electrical steel sheet of the present invention has low iron loss characteristics in the high-frequency range, for example, 400 Hz to 5 kHz. The non-oriented electrical steel sheet of the present invention is suitable as a material for motors used in hybrid electric vehicles and vacuum cleaners that are driven in such high-frequency ranges. The non-oriented electrical steel sheet of the present invention is a material that can reduce defects such as cracks that occur during punching and crimping, and therefore has the advantage of being able to reduce iron loss in motors manufactured by punching and crimping.

[0014] Fig. 1 is a schematic diagram showing the structure of a non-oriented electrical steel sheet according to one embodiment of the present invention. Fig. 2 is a schematic diagram showing an example of a Si content profile in the sheet thickness direction of a non-oriented electrical steel sheet. Fig. 3 is a graph showing the relationship between the average Si content in the surface layer portion of a non-oriented electrical steel sheet and IB2 / IFe. Fig. 4 is a graph showing the relationship between IB2 / IFe and total elongation of a non-oriented electrical steel sheet. Fig. 5 is a graph showing the relationship between the difference (ΔSi) in the average Si content between the surface layer portion and the inner layer portion of a non-oriented electrical steel sheet and IB2 / IFe.

[0015] The present invention will be specifically described below. Note that the following description shows examples of preferred embodiments of the present invention, and the present invention is not limited thereto.

[0016] Fig. 1 is a schematic diagram showing the structure of a non-oriented electrical steel sheet according to one embodiment of the present invention. Fig. 2 is a schematic diagram showing an example of a Si content profile in the sheet thickness direction of the non-oriented electrical steel sheet. The vertical axis in Fig. 2 indicates the position in the sheet thickness direction, with 0 representing one surface of the non-oriented electrical steel sheet and t representing the other surface of the non-oriented electrical steel sheet.

[0017] As shown in Fig. 2, the non-oriented electrical steel sheet of the present invention (hereinafter sometimes simply referred to as "electrical steel sheet") has a Si content distribution in which the Si content decreases from the surface toward the center of the sheet thickness. Note that the Si content distribution may be a distribution in which the Si content changes continuously throughout the entire region in the sheet thickness direction of the electrical steel sheet, or may be a Si content distribution in which the Si content changes continuously on the surface side of the electrical steel sheet and is constant in the center of the sheet thickness.

[0018] Here, if we define the ranges of 0 to t / 4 and 3t / 4 to t as surface layer portions, and the range of more than t / 4 and less than 3t / 4 as inner layer portions, taking the total sheet thickness t (mm) of the electrical steel sheet as the reference, then as shown in Figure 1 , a non-oriented electrical steel sheet 1 according to one embodiment of the present invention can be said to consist of inner layer portions 10 and surface layer portions 20 located on both sides of inner layer portion 10. As will be described later, non-oriented electrical steel sheet 1 has a difference in average Si content between surface layer portions 20 and inner layer portions 10.

[0019] [Composition] First, the composition of the non-oriented electrical steel sheet of the present invention will be described. In the following description, "%" representing the content of each element represents "mass %" unless otherwise specified. Furthermore, the content of each element represents the average content across the entire sheet thickness unless otherwise specified. However, since the content of Si differs between the surface layer and the inner layer, the average Si content in each region is shown.

[0020] The non-oriented electrical steel sheet of the present invention may have a chemical composition containing Si, C, Mn, Al, P, S, N, and O, with the balance being Fe and unavoidable impurities. First, C, Mn, Al, P, S, N, and O will be described.

[0021] C: 0.010% or less The carbon contained in electrical steel sheets forms carbides, causing magnetic aging and degrading iron loss characteristics. Furthermore, the carbides formed in the steel sheet become fracture initiation sites, reducing ductility. Therefore, the upper limit of the carbon content is limited to 0.010%. The carbon content is preferably 0.007% or less. While the lower limit of the carbon content is not particularly specified, it is preferably 0.0001% from the viewpoint of reducing decarburization costs in the refining process. The carbon content is more preferably 0.0005% or more.

[0022] Mn: 2.0% or less Mn is an element that increases the resistivity of electrical steel sheets and reduces iron loss. Furthermore, Mn has the effect of suppressing the fine precipitation of sulfides. On the other hand, if the Mn content exceeds 2.0%, slab cracking and the like occur, deteriorating the operability of the steelmaking process. Therefore, the upper limit of the Mn content is set to 2.0%. The lower limit of the Mn content is not particularly specified and may be, for example, 0.001%. From the viewpoint of more effectively enjoying the above-mentioned effects, the Mn content is preferably 0.01% or more.

[0023] Al: 2.0% or less Al is a useful element that increases the resistivity of steel and reduces iron loss. However, if the Al content exceeds 2.0%, rolling becomes difficult, so the upper limit of the Al content is set to 2.0%. Reducing the Al content to 0.01% or less improves the texture and increases the magnetic flux density. Therefore, when magnetic flux density is important, the Al content is preferably set to 0.01% or less. The Al content is more preferably 0.003% or less. There is no particular lower limit for the Al content, but an excessive reduction leads to increased refining costs, so the Al content is preferably set to 0.0001% or more.

[0024] P: 0.20% or less P is a useful element used to adjust the strength of steel. However, if the P content exceeds 0.20%, the steel becomes embrittled and difficult to roll, so the upper limit of the P content is set to 0.20%. There is no particular lower limit for the P content, but from the viewpoint of reducing the cost of dephosphorization in the refining process, it is preferably set to 0.001%.

[0025] S: 0.005% or less S forms fine precipitates such as MnS, which inhibit grain growth during annealing and adversely affect iron loss characteristics. Furthermore, the precipitates act as fracture initiation sites, reducing ductility. In particular, when the S content exceeds 0.005%, the adverse effects become significant, so the upper limit of the S content is limited to 0.005%. The S content is preferably 0.003% or less. While there is no particular lower limit for the S content, from the viewpoint of reducing the cost of desulfurization in the refining process, the S content is preferably 0.0005% or more.

[0026] N: 0.010% or less, O: 0.010% or less N and O are elements that form fine precipitates, inhibit grain growth during stress relief annealing, and adversely affect iron loss characteristics. In particular, when the contents of N and O each exceed 0.010%, the adverse effects become significant, so the upper limits of N and O are each limited to 0.010%. The contents of N and O are preferably each 0.003% or less. There are no particular lower limits for the N and O contents, but from the viewpoint of reducing refining costs in the refining process, the N and O contents are preferably 0.0001% or more.

[0027] Next, Si will be described.

[0028] The average Si content of the surface layer portion is 4.00% or more and 6.30% or less, and the average Si content of the inner layer portion is 2.00% or more and 6.20% or less. Si is an element that increases the electrical resistance of the electrical steel sheet and reduces eddy current loss. Due to the skin effect, eddy currents tend to concentrate in the surface layer portion of the electrical steel sheet, so increasing the Si content of the surface layer portion compared to the inner layer portion can effectively reduce iron loss. If the average Si content of the surface layer portion is less than 4.00% or the average Si content of the inner layer portion is less than 2.00%, eddy current loss cannot be effectively reduced. Therefore, the average Si content of the surface layer portion is set to 4.00% or more. The average Si content of the surface layer portion is preferably 4.20% or more, more preferably 4.50% or more. The average Si content of the inner layer portion is set to 2.00% or more. The average Si content of the inner layer portion is preferably 2.50% or more, more preferably 3.00% or more. On the other hand, if the average Si content in the surface layer portion exceeds 6.30%, it becomes difficult to maintain high ductility even when the ΔSi conditions and manufacturing method of the present invention described below are applied. Therefore, the Si content in the surface layer portion is set to 6.30% or less. Furthermore, the upper limit of the average Si content in the inner layer portion is set to 6.20% in accordance with the ΔSi conditions described below. The average Si content in the surface layer portion is preferably set to 6.10% or less, more preferably 6.00% or less. Furthermore, the Si content in the inner layer portion is preferably set to 6.00% or less, more preferably 5.80% or less.

[0029] A steel sheet according to one embodiment of the present invention may have a composition containing the above-mentioned components as basic components, with the balance consisting of Fe and inevitable impurities. Here, a steel sheet according to one embodiment of the present invention preferably contains only the above-mentioned basic components and the balance consisting of Fe and inevitable impurities. Inevitable impurities are impurities that are inevitably mixed in from raw materials, manufacturing processes, manufacturing equipment, etc., and are permissible to be contained within a range that does not impair the objects and effects of the present invention. Examples of raw materials include iron ore, reduced iron, and scrap.

[0030] In addition to the above components, a non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more elements selected from Sn, Sb, Cu, Ni, Cr, Ca, Mg, and REM. These elements may be optionally contained, and the content of each of these elements may be 0 mass%.

[0031] Sn: 0.10% or less, Sb: 0.10% or less Both Sn and Sb have the effect of significantly improving the texture, increasing the magnetic flux density, and further reducing hysteresis loss. However, if the Sn and Sb contents exceed 0.10%, the effect saturates, and manufacturability and costs increase. Therefore, when Sn and Sb are contained, the Sn and Sb contents are each set to 0.10% or less. When Sn and Sb are contained, there are no particular restrictions on the lower limits of their respective contents, but from the viewpoint of making it easier to obtain the above effects, it is preferable that the Sn and Sb contents are each 0.001% or more.

[0032] Cu: 2.0% or less, Ni: 2.0% or less, Cr: 2.0% or less Cu, Ni, and Cr are each elements that increase the resistivity of steel and reduce iron loss. However, if the Cu, Ni, and Cr contents exceed 2.0%, the effect of reducing iron loss saturates, resulting in increased costs. Therefore, when Cu, Ni, and Cr are contained, their respective contents are set to 2.0% or less. When Cu, Ni, and Cr are contained, the lower limits of their respective contents are not particularly limited, but from the viewpoint of making it easier to obtain the above effects, it is preferable that the Cu, Ni, and Cr contents are each 0.001% or more.

[0033] Ca: 0.01% or less, Mg: 0.01% or less, REM: 0.03% or less. Ca, Mg, and REM (rare earth metals) each form sulfides to fix S, improve grain growth during stress relief annealing, and contribute to reducing iron loss. However, excessive inclusion of these elements may result in poor economic efficiency. Therefore, when Ca, Mg, and REM are contained, the Ca and Mg contents are each set to 0.01% or less, and the REM content is set to 0.03% or less. When Ca, Mg, and REM are contained, the lower limits of their respective contents are not particularly limited. However, in order to more easily obtain the above-mentioned effects, the Ca, Mg, and REM contents are preferably set to 0.001% or more. Note that REM is a collective term for 17 elements, including Sc, Y, and lanthanoids. One or more of these 17 elements may be contained as REM, and the REM content here refers to the total content of these elements.

[0034] A non-oriented electrical steel sheet according to one embodiment of the present invention may further contain, in addition to the above-mentioned components, one or more elements selected from Mo, B, Ti, Nb, V, Pb, As, Zn, Co, Ge, and Ga.

[0035] Mo: 0 to 0.050%, B: 0 to 0.0020% Mo and B are elements that are effective in improving the toughness of steel plate. However, if the Mo content exceeds 0.050% or the B content exceeds 0.0020%, iron loss increases significantly. Therefore, when Mo and B are contained, the upper limit of the Mo content is set to 0.050%, and the upper limit of the B content is set to 0.0020%. When Mo and B are contained, there are no particular restrictions on the lower limits of their respective contents, but from the viewpoint of more easily achieving the above-mentioned effects, it is preferable that the Mo and B contents are each 0.0005% or more.

[0036] Ti: 0-0.010%, Nb: 0-0.0050%, V: 0-0.050%, Pb: 0-0.020%. Ti, Nb, V, and Pb are elements that form fine precipitates and refine crystal grains, thereby improving the hardness of steel sheets. However, if the Ti content exceeds 0.010%, the Nb content exceeds 0.0050%, the V content exceeds 0.050%, and the Pb content exceeds 0.020%, hysteresis loss increases significantly. Therefore, when Ti, Nb, V, and Pb are contained, the upper limits of the Ti content are 0.010%, the Nb content exceeds 0.0050%, the V content exceeds 0.050%, and the Pb content exceeds 0.020%. When Ti, Nb, V, and Pb are contained, the lower limit of each content is not particularly limited. However, in order to more easily obtain the above-mentioned effects, it is preferable that the contents of Ti, V, and Pb are each 0.002% or more, and the Nb content is 0.0005% or more.

[0037] As: 0 to 0.020% As is an element that has the effect of improving the hardness of steel sheet. However, if the As content exceeds 0.020%, the steel becomes embrittled and rolling becomes difficult. Therefore, when As is contained, the upper limit of the As content is set to 0.020%. The lower limit of the As content is not particularly limited, but is preferably set to 0.0005% from the viewpoint of suppressing refining costs in the refining process.

[0038] Zn: 0 to 0.010% Zn is an element that has the effect of coarsening inclusions and reducing iron loss. However, if the Zn content exceeds 0.010%, not only does the above effect saturate, but the steel becomes embrittled and difficult to roll. For this reason, when Zn is contained, the upper limit of the Zn content is set to 0.010%. When Zn is contained, there is no particular restriction on the lower limit of the Zn content, but from the viewpoint of making it easier to obtain the above effect, the Zn content is preferably 0.0005% or more.

[0039] Co: 0 to 0.10% Co is an element that has the effect of improving magnetic flux density. However, if the Co content exceeds 0.10%, the steel becomes embrittled and rolling becomes difficult. Therefore, when Co is contained, the upper limit of the Co content is set to 0.10%. When Co is contained, there is no particular restriction on the lower limit of the Co content, but from the viewpoint of making it easier to obtain the above-mentioned effect, the Co content is preferably 0.0010% or more.

[0040] Ge: 0 to 0.030%, Ga: 0 to 0.030% Both Ge and Ga are elements that significantly improve texture and increase magnetic flux density. However, if the Ge and Ga contents exceed 0.030%, the effects saturate, and manufacturability and costs increase. Therefore, when Ge and Ga are contained, the Ge and Ga contents are each set to 0.030% or less. When Ge and Ga are contained, there are no particular lower limits for their respective contents, but from the viewpoint of more easily achieving the above effects, it is preferable that the Ge and Ga contents are each 0.0005% or more.

[0041] When the content of any of the above optional components is less than the respective preferred lower limit values ​​mentioned above, the component is considered to be contained as an unavoidable impurity.

[0042] In the electrical steel sheet of the present invention, in addition to the above-mentioned composition, the reflection intensity derived from the ordered phase measured by X-ray diffraction and ΔSi, which is the difference in average Si concentration between the surface layer and the inner layer of the electrical steel sheet, are specified. ３It is well known that an ordered phase of the B2 phase is formed in the surface layer of an electrical steel sheet. This ordered phase suppresses dislocation movement, which causes a decrease in the workability of the material (electrical steel sheet). The inventors have confirmed that the B2 phase formed in the surface layer of an electrical steel sheet significantly affects the elongation of the material (electrical steel sheet), and that the formation of a certain amount or more of the B2 phase in the surface layer of an electrical steel sheet significantly reduces the ductility of the electrical steel sheet. They have inferred that this is one of the causes of the decrease in ductility of the electrical steel sheet. Through detailed investigation, they have discovered the following: By controlling ΔSi, which is the difference in average Si content between the surface layer and the inner layer of an electrical steel sheet, and by controlling the cooling rate and the tension applied to the steel sheet to appropriate values ​​during the cooling process after the siliconizing diffusion treatment in the manufacturing process of the electrical steel sheet, the formation of the B2 phase in the surface layer can be suppressed, thereby improving the ductility of the electrical steel sheet.

[0043] Based on the above-mentioned results of the study, the present invention specifies that the following formula (1) be satisfied: IB2 / IFe < 0.030 (1) where IB2 is the Fe content measured by X-ray diffraction at 2θ = 36.5°. ３ IFe is the diffraction peak intensity derived from the B2 phase of Si, and IFe is the diffraction peak intensity derived from the ferrite phase that appears around 2θ = 77.6° as measured by X-ray diffraction. Note that "around" takes into consideration the shift of the diffraction peak. Usually, the shift is in the range of about ±0.1°. For example, when the shift is taken into consideration, Fe ３ The diffraction peak derived from the B2 phase of Si usually appears in the range of 2θ=36.4° to 36.6°. The diffraction peak derived from the ferrite phase usually appears in the range of 2θ=77.5° to 77.7°. However, the magnitude of the shift may vary depending on sample preparation, etc. In the present invention, the diffraction peak derived from the Fe phase, which appears around 2θ=36.5°, is determined from the diffraction peak measured by X-ray diffraction. ３ The diffraction peak intensity derived from the B2 phase of Si and the diffraction peak intensity derived from the ferrite phase that appears around 2θ = 77.6° can be measured. IB2 / IFe on the left side of equation (1) is the magnitude of the reflection peak IB2 derived from the B2 phase relative to the reflection peak IFe derived from the base steel, and a larger value of IB2 / IFe indicates a larger amount of B2 phase formed in the surface layer of the electrical steel sheet.

[0044] FIG. 3 shows the relationship between the Si content in the surface layer and IB2 / IFe, and FIG. 4 shows the relationship between IB2 / IFe and the total elongation of the electrical steel sheet. The electrical steel sheets used for the measurements were prepared as follows. A slab having the composition of sample symbol A in Table 1 below was hot-rolled, annealed at 950°C for 30 seconds, and then cold-rolled to produce a cold-rolled sheet with a thickness of 0.1 mm. The cold-rolled sheet was siliconized at 1200°C, and the holding time of the diffusion treatment (annealing time) was adjusted to set the difference in average Si concentration between the surface layer and the inner layer of the electrical steel sheet, ΔSi, to approximately 0.2% (siliconizing diffusion treatment process). After the siliconizing diffusion treatment process, the electrical steel sheet was cooled in the temperature range from 600°C to 200°C under the following cooling condition 1 (cooling process) to produce an electrical steel sheet. (Cooling condition 1) Average tension: 5.0 MPa, average cooling rate: 50°C / sec

[0045] The method of applying tension to the steel sheet in the temperature range from 600°C to 200°C is not particularly limited, but examples include a method of applying tension between rolls by controlling the peripheral speed of rolls that transport the steel sheet, and a method of applying tension by bending with rolls. The tension can be calculated, for example, by multiplying the total value of the loads (kgf) of the load cells on the left and right sides of the roll by the cross-sectional area of ​​the steel sheet (= sheet thickness (mm) × sheet width (mm)) (mm ２ ) and converting to MPa. The average tension in the temperature range from 600°C to 200°C is the average value of the tension applied to the steel sheet in the temperature range from 600°C to 200°C. Specifically, the average tension is the arithmetic average of the tensions obtained per second as described above from 600°C to 200°C. Furthermore, the above temperatures refer to the surface temperatures of the steel sheet, and can be measured using a surface thermometer or the like. Furthermore, the above average cooling rate refers to the average cooling rate of the steel sheet surface. The above average cooling rate is calculated as (600°C - 200°C) / cooling time (seconds) from 600°C to 200°C.

[0046] The total elongation of the electrical steel sheet was measured by taking a JIS No. 5 test piece from the electrical steel sheet prepared as described above and conducting a tensile test at a strain rate of 40% / min. The IB2 / IFe was measured by taking a sample from the electrical steel sheet and conducting X-ray diffraction measurement using a Co target Kα ray source and an output of 40 kV × 135 mA, and detecting the Fe３ The calculation was based on the diffraction peak intensity (IB2) derived from the B2 phase of Si and the diffraction peak intensity (IFe) derived from the ferrite phase appearing near 2θ=77.6°.

[0047] As can be seen from the results in Figure 3, the value of IB2 / IFe increases gradually with increasing Si content in the surface layer portion up to around 0.030, and then rises sharply above 0.030. Furthermore, as can be seen from the results in Figure 4, a correlation exists between IB2 / IFe and the total elongation of the electrical steel sheet. From this, it can be seen that when IB2 / IFe is 0.030 or more, the value of IB2 / IFe rises sharply, and accordingly, the total elongation of the electrical steel sheet also drops sharply. For this reason, IB2 / IFe is set to less than 0.030. On the other hand, since the smaller the B2 phase, the better, so no lower limit is set for IB2 / IFe. As an example, IB2 / IFe may be 0.005 or more.

[0048] The present invention further specifies that ΔSi, which is the difference in average Si content between the surface layer and the inner layer of the electrical steel sheet, is 0.10% or more and 2.00% or less.

[0049] Figure 5 shows the relationship between ΔSi and IB2 / IFe when the average tension applied to the steel sheet in the temperature range from 600 ° C to 200 ° C during cooling was 1.0 MPa, 4.0 MPa, and 5.0 MPa. The electrical steel sheets used for the measurements were produced in the same manner as above. However, by adjusting the holding time (annealing time) of the diffusion treatment, ΔSi was changed to set the average Si content of the surface layer to 6.2%, and the average cooling rate in the temperature range from 600 ° C to 200 ° C during cooling was set to 50 ° C / s, and the average tension applied to the steel sheet was set to 1.0 MPa, 4.0 MPa, and 5.0 MPa. The electrical steel sheets were produced by measuring the Si content distribution in the cross section in the sheet thickness direction using an EPMA (Electron Probe Micro Analyzer) and calculating the difference in the average Si content between the surface layer and the inner layer.

[0050] The average Si content of the surface layer portion was determined by measuring the Si concentration at 0.5 μm intervals in the thickness direction of the surface layer portion (in the range of 0 to t / 4 or in the range of 3t / 4 to t) using EPMA, and the average value was taken as the average Si content of the surface layer portion.The average Si content of the inner layer portion was determined by measuring the Si concentration at 0.5 μm intervals in the thickness direction of the inner layer portion (in the range of more than t / 4 and less than 3t / 4) using EPMA, and the average value was taken as the average Si content of the inner layer portion.

[0051] As shown in Fig. 5, in the cooling step after the siliconizing diffusion treatment step, for samples in which the average tension was 5.0 MPa and 4.0 MPa in the temperature range from 600°C to 200°C, IB2 / IFe was 0.030 or more when ΔSi was less than 0.10 mass%, but IB2 / IFe became less than 0.030 by setting ΔSi to 0.1 mass% or more. For this reason, in order to suppress the B2 phase in the surface layer of the electrical steel sheet and improve the elongation of the electrical steel sheet, ΔSi is set to 0.10 mass% or more.

[0052] The mechanism behind this is not entirely clear, but it is speculated that the tensile stress generated in the surface layer by ΔSi inhibits the formation of an ordered phase. On the other hand, when ΔSi exceeds 2.00 mass%, the effect of reducing IB2 / IFe saturates, and the internal stress due to ΔSi increases, resulting in an increase in iron loss. Therefore, the upper limit of ΔSi is set to 2.00 mass%.

[0053] [Sheet Thickness] If the non-oriented electrical steel sheet is too thin, it may be difficult to handle during manufacturing processes such as cold rolling and annealing, which tends to increase manufacturing costs. Therefore, the sheet thickness t of the non-oriented electrical steel sheet is preferably 0.01 mm or more. On the other hand, if the non-oriented electrical steel sheet is too thick, eddy current loss tends to increase, and total iron loss tends to increase. Therefore, the sheet thickness t of the non-oriented electrical steel sheet is preferably 0.35 mm or less.

[0054] [Iron Loss] In the present invention, it is preferable that the iron loss (total iron loss): W10_1k (W / kg) at a frequency of 1 kHz and a maximum magnetic flux density of 1.0 T and the plate thickness: t (mm) satisfy the following formula (2): W10_1k / (t+0.1)<145 (2)

[0055] When the iron loss of a non-oriented electrical steel sheet satisfies the relationship of the above formula (2), heat generation in a stator core manufactured using the corresponding non-oriented electrical steel sheet is suppressed, and as a result, motor efficiency can be further improved. Note that, because iron loss depends on the sheet thickness, the above formula (2) specifies an upper limit value for iron loss taking into account the influence of the sheet thickness. In the present invention, it is determined that a non-oriented electrical steel sheet has low iron loss in the high frequency range when the iron loss of the sheet satisfies the relationship of the above formula (2).

[0056] [Total elongation] The non-oriented electrical steel sheet of the present invention preferably has a total elongation of 6.0% or more. Total elongation is measured by preparing a JIS No. 5 test piece from the non-oriented electrical steel sheet and conducting a tensile test at a strain rate of 40% / min. If the non-oriented electrical steel sheet satisfies the above conditions, the occurrence of product defects such as cracking of the material can be suppressed when the sheet is processed into a motor core by punching or crimping. In the present invention, if the total elongation of the non-oriented electrical steel sheet satisfies the above range, it is determined that the sheet has high ductility.

[0057] [Manufacturing Method] The non-oriented electrical steel sheet of the present invention can be manufactured by, but is not particularly limited to, a siliconizing method. When the siliconizing method is used, for example, a base steel sheet (steel sheet before siliconizing diffusion treatment) having a constant Si content in the thickness direction is subjected to siliconizing diffusion treatment, thereby increasing the Si content in the surface layer portions on both sides of the base steel sheet.

[0058] The method of siliconizing and diffusion treatment is not particularly limited, and any method can be used. For example, siliconizing treatment can be performed by a CVD method to increase the Si content at the surface of the base steel sheet, followed by a heat treatment to diffuse the Si into the interior of the base steel sheet. The Si contents in the surface layer and the inner layer can be controlled by adjusting the increase in the Si content at the surface of the base steel sheet by the CVD method and the heat treatment conditions for the diffusion treatment. A non-oriented electrical steel sheet obtained by siliconizing and diffusion treatment by the CVD method has, for example, a Si content profile in the sheet thickness direction as shown in Figure 2.

[0059] The Si-containing gas used in the siliconizing treatment is not particularly limited, and may be SiH ４ , Si ２ H ５ , SiCl４ Among these, SiCl ４ The gas used for the siliconizing treatment is preferably SiCl ４ When using SiCl, the siliconizing temperature is preferably in the range of 1000 to 1250°C, more preferably 1150 to 1250°C. ４ The concentration of is preferably 1.0 to 50% by volume. The treatment time of the siliconizing treatment is the holding time at the siliconizing treatment temperature.

[0060] After the siliconizing treatment, a diffusion treatment is performed in which the temperature is maintained at 1250 to 1000°C in a non-oxidizing atmosphere containing no Si for 10 seconds or more. The Si content of the surface layer, the Si content of the inner layer, and ΔSi can be adjusted by adjusting the treatment time of the diffusion treatment (the holding time at the diffusion treatment temperature). In this case, for a steel sheet having a thickness of t, if the total treatment time of the siliconizing treatment and the diffusion treatment exceeds (1500 × t) seconds, ΔSi becomes less than 0.10% by mass. On the other hand, if the total treatment time is less than (300 × t) seconds, ΔSi becomes more than 2.00% by mass. Therefore, to achieve a ΔSi of 0.10% by mass or more and 2.00% by mass or less, the total treatment time of the siliconizing treatment and the diffusion treatment is set to (300 × t) seconds or more and (1500 × t) seconds or less. Note that t is the thickness (mm) of the steel sheet. In this embodiment, the thickness of the base steel sheet and the thickness of the final non-oriented electrical steel sheet are the same.

[0061] The siliconizing and diffusion treatment times (holding times at the siliconizing and diffusion temperatures) are adjusted according to the target siliconization amount (Si content in the surface layer) by adjusting the concentration and flow rate of the Si-containing gas, the Si content and thickness of the base steel sheet, the siliconizing temperature, and other factors. The siliconizing treatment time T1 (seconds) and the diffusion treatment time T2 (seconds) required to control the Si content in the surface layer to 4.00% or more and 6.30% or less can be experimentally determined. As an example, when a sample (base steel sheet) with a thickness t (mm) is siliconized at a siliconizing temperature of 1000 to 1250°C and then diffused at a diffusion temperature of 1000 to 1250°C, preferably when siliconizing at a siliconizing temperature of 1150 to 1250°C and then diffused at a diffusion temperature of 1150 to 1250°C, the following formula (3) is preferably satisfied. In the examples described below, the Si content in the surface layer was controlled using the following formula (3). 4.00≦[Si] base + 2.7 × exp(−0.003 × (T1 + T2) / t) + 0.0085 × T1 / t ≦ 6.30 (3) In formula (3), [Si] base is the Si content (%) of the steel sheet (base steel sheet) before the siliconizing and diffusion treatment step, t is the sheet thickness (mm) of the steel sheet (base steel sheet), T1 is the treatment time (seconds) of the siliconizing treatment, and T2 is the treatment time (seconds) of the diffusion treatment.

[0062] After the siliconizing treatment and the diffusion treatment (siliconizing and diffusion treatment), the steel sheet is cooled in a cooling step in the temperature range from 600°C to 200°C, with an average tension of 4.0 MPa or more applied to the steel sheet and an average cooling rate of 20.0°C / sec or more.

[0063] (Composition of Base Steel Sheet) The composition of the base steel sheet (steel sheet before siliconizing diffusion treatment) in the manufacturing process of the non-oriented electrical steel sheet of the present invention is the same as the composition of the non-oriented electrical steel sheet described above, except for Si. The contents of each element other than Si and the reasons for limiting them are the same as those described above, so explanations will be omitted here except for Si.

[0064] Si content (mass%) of base steel sheet: 4.5% or less If Si exceeds 4.5%, the steel sheet becomes very brittle and may break during sheet threading or cold rolling. Therefore, the Si content of the base steel sheet is preferably 4.5% or less. The Si content of the base steel sheet is more preferably 4.0% or less. Although no lower limit is particularly specified, if the Si content of the base steel sheet is less than 1.0%, it takes longer to achieve the target Si content of the non-oriented electrical steel sheet by siliconizing treatment, which reduces manufacturability. Therefore, when manufacturing non-oriented electrical steel sheet by the CVD method, the Si content of the base steel sheet is preferably 1.0% or more.

[0065] Based on the above-mentioned findings, in the present invention, in order to improve the effect of suppressing the formation of the B2 phase in the surface layer, heat treatment is performed in the cooling step after the siliconizing and diffusion treatment step by controlling the average cooling rate and tension to appropriate values ​​so that IB2 / IFe is less than 0.030. To achieve this, the diffusion treatment in the siliconizing and diffusion treatment step involves holding the steel sheet at 1250 to 1000°C for 10 seconds or more, and also performing treatment such that the total treatment time of the siliconizing and diffusion treatments is a predetermined time, and then in the cooling step, the average tension applied to the steel sheet is set to 4.0 MPa or more in the temperature range from 600°C to 200°C, and the average cooling rate is set to 20.0°C / second or more.

[0066] The reason for holding the steel sheet at 1250 to 1000°C for 10 seconds or more during the diffusion treatment in the siliconizing diffusion treatment process is to make the steel sheet structure into a disordered phase state. Even if the holding time is extended, the effect saturates, so holding for a long time is not necessary.

[0067] In the cooling process, the B2 phase begins to form in the range of 600°C or less, and ordered transformation occurs up to around 200°C. Therefore, the cooling rate in the temperature range from 600°C to 200°C is important. If the average cooling rate in the temperature range from 600°C to 200°C is less than 20.0°C / sec, the formation of the B2 phase cannot be suppressed. For this reason, the average cooling rate in the temperature range from 600°C to 200°C is specified to be 20.0°C / sec or more. On the other hand, although there is no upper limit specified for the average cooling rate in this temperature range, if it is 200.0°C / sec or less, the influence of iron loss deterioration due to cooling strain can be easily suppressed. Therefore, it is preferable that the average cooling rate in this temperature range be 200.0°C / sec or less.

[0068] Furthermore, as a result of further investigations, the inventors have found that in addition to the cooling rate in the above temperature range, the tension applied to the steel sheet during the cooling process in the above temperature range also affects the suppression of the formation of the B2 phase in the surface layer of the steel sheet. Referring again to FIG. 5 , as shown in FIG. 5 , in samples with average tensions of 5.0 MPa and 4.0 MPa during the cooling process, IB2 / IFe was less than 0.030 when ΔSi was 0.10 mass% or more. On the other hand, in samples with average tensions of 1.0 MPa during the cooling process, IB2 / IFe was 0.030 or more even when ΔSi was 2.00 mass% or more. Based on this, it is specified that the average tension applied to the steel sheet in the temperature range from 600°C to 200°C is 4.0 MPa or more.

[0069] On the other hand, although there is no upper limit specified for the average tension applied to the steel sheet in the above temperature range, an average tension of 100 MPa or more may cause the steel sheet to break. Therefore, the average tension is preferably 100 MPa or less, and more preferably 50 MPa or less.

[0070] Note that, because the B2 phase does not form in a temperature range above 600°C, the cooling rate and tension during the cooling process from after the siliconizing diffusion treatment to 600°C do not affect the formation of the B2 phase. Therefore, the cooling rate and tension in the temperature range from after the siliconizing diffusion treatment to 600°C are not particularly specified. However, since the cooling rate that can be achieved without burdening the equipment is 300°C / sec or less, the average cooling rate in this temperature range is preferably 300°C / sec or less. Furthermore, from the viewpoint of manufacturability, the average cooling rate is preferably 1.0°C / sec or more. The tension in this temperature range is also not particularly specified. However, since an average tension applied to the steel sheet in this temperature range exceeding 10.0 MPa can cause the steel sheet to break, a tension of 10.0 MPa or less is preferred. On the other hand, an average tension of less than 0.5 MPa in this temperature range may cause shape deterioration due to deflection, so the average tension in this temperature range is preferably 0.5 MPa or more.

[0071] In order to confirm the effects of the present invention, non-oriented electrical steel sheets were manufactured according to the procedure described below, and their magnetic properties were evaluated. However, the present invention is not limited to the following examples.

[0072] (Steel Slabs) First, steel slabs with sample symbols A to AJ were prepared, each having the composition shown in Table 1. The contents of elements other than Si in the steel slabs used (C, Mn, Al, P, S, N, O, Sn, Sb, Cu, Ni, Cr, Ca, Mg, REM, Mo, B, Ti, Nb, V, Pb, As, Zn, Co, Ge, and Ga) did not change throughout the manufacturing process, and were therefore equal to the average contents across the entire thickness of the finally obtained non-oriented electrical steel sheet.

[0073] (Hot rolling, hot-rolled sheet annealing) The steel slab was hot-rolled to form a hot-rolled steel sheet, which was then subjected to hot-rolled sheet annealing at 950°C for 30 seconds.

[0074] (Cold rolling) Next, the hot-rolled steel sheets after the hot-rolled sheet annealing were subjected to cold rolling to obtain cold-rolled steel sheets having a sheet thickness t shown in Table 2. However, the hot-rolled steel sheets using the steel slabs with sample symbols C, F, H, and J fractured in the cold rolling process (denoted as "fracture occurred during cold rolling" in Table 1), and therefore no treatment after cold rolling was performed. It is believed that these hot-rolled steel sheets fractured in the cold rolling process because the content of at least one of Si, Mn, Al, and P was excessive.

[0075] (Siliconizing Diffusion Treatment) The obtained cold-rolled steel sheet (base steel sheet) was subjected to siliconizing diffusion treatment to obtain a non-oriented electrical steel sheet. ２ Gas and SiCl ４ The steel sheet was siliconized at 1200°C by CVD in an atmosphere containing a mixture of these at a volume ratio of 10:1 to increase the Si content in the surface layer of the steel sheet. ２ The steel sheets were subjected to a diffusion treatment (heat treatment) at 1200° C. in an atmosphere to diffuse Si from the surface layer thereof into the interior. The treatment times for the siliconizing treatment and the diffusion treatment are shown in Table 2.

[0076] (Cooling step) The steel sheets after siliconizing diffusion treatment were cooled (quenched) under the cooling conditions shown in Table 2. From the diffusion treatment temperature to 600°C, all samples were cooled at an average tension of 1.0 MPa and an average cooling rate of 10°C / sec, and from 600°C to a temperature range of at least 200°C, cooling was performed while controlling the average cooling rate and average tension to be within the cooling conditions shown in Table 2. Non-oriented electrical steel sheets were produced by the above steps.

[0077] (Si content) The obtained non-oriented electrical steel sheets were embedded in a carbon mold, and the Si content distribution in the cross section in the sheet thickness direction was measured using EPMA. Using the total steel sheet thickness t (mm) as the reference, the ranges of 0 to t / 4 and 3t / 4 to t were defined as the surface layer, and the range of more than t / 4 and less than 3t / 4 was defined as the inner layer. Then, from the Si content distribution obtained by EPMA, the average Si content in the surface layer and inner layer of the non-oriented electrical steel sheet, and the difference between these values, ΔSi, were calculated. The measurement results are also shown in Table 2.

[0078] As mentioned above, the contents of elements other than Si (C, Mn, Al, P, S, N, O, Sn, Sb, Cu, Ni, Cr, Ca, Mg, REM, Mo, B, Ti, Nb, V, Pb, As, Zn, Co, Ge, and Ga) do not change throughout the manufacturing process, and therefore the contents of these elements in the finally obtained non-oriented electrical steel sheet are equal to the contents of these elements in the steel slab used.

[0079] (Iron Loss) Test pieces measuring 30 mm wide and 280 mm long were taken from each of the obtained non-oriented electrical steel sheets, and the iron loss (W10_1k (W / kg)) at a maximum magnetic flux density of 1.0 T and a frequency of 1 kHz was measured in an Epstein test in accordance with JIS C2550-1:2011. In the Epstein test, equal amounts of L-direction test pieces, taken so that the length direction of the test pieces was the rolling direction (L direction), and C-direction test pieces, taken so that the length direction of the test pieces was the direction perpendicular to the rolling direction (C direction), were used, and the average values ​​of the magnetic properties in the L direction and C direction were evaluated. The measurement results are also shown in Table 2. In Table 2, samples in which the iron loss and sheet thickness t (mm) satisfied the relationship in the following formula (2) were marked with "Good" in the "Equation (2) Judgment" column, and samples in which the relationship was not satisfied were marked with "Poor." When the iron loss of a non-oriented electrical steel sheet satisfies the relationship of the following formula (2), it can be determined that the sheet has low iron loss in the high frequency range: W10 — 1k / (t+0.1) < 145 (2)

[0080] As can be seen from the results shown in Table 2, the non-oriented electrical steel sheets that satisfied the conditions of the present invention had excellent properties, such as low high-frequency iron loss.

[0081] (B2 phase) A 30 mm square sample was taken from each of the obtained non-oriented electrical steel sheets, and X-ray diffraction measurement was performed on the sample surface to measure the reflection intensity. The measurement was performed by irradiating X-rays with an output of 40 kV x 135 mA using Kα rays from a Co target as a radiation source. Based on the above measurement results, Fe, which appears around 2θ = 36.5°, ３ The diffraction peak intensity derived from the B2 phase of Si was defined as IB2, and the diffraction peak intensity derived from the ferrite phase appearing around 2θ = 77.6° as IFe, and IB2 / IFe was calculated. The calculation results of IB2 / IFe are also shown in Table 2. In Table 2, those that satisfied the following formula (1) were marked with "Good" in the "Determination of formula (1)", and those that did not were marked with "Poor". IB2 / IFe < 0.030 ... (1)

[0082] As can be seen from the results shown in Table 2, the non-oriented electrical steel sheets that satisfied the conditions of the present invention had an IB2 / IFe ratio of less than 0.030, and were able to suppress the formation of the B2 phase.

[0083] (Ductility) From each of the obtained non-oriented electrical steel sheets, JIS No. 5 test pieces (parallel portion length 60 mm, parallel portion width 25 mm) with the rolling direction (L direction) as the longitudinal direction were prepared by cutting, and tensile tests were performed at least five times under the condition of a strain rate of 40% / min to measure total elongation. The average values ​​are also shown in Table 2. If the total elongation of a non-oriented electrical steel sheet is 6.0% or more, it can be determined that it has high ductility.

[0084] As can be seen from the results shown in Table 2, the non-oriented electrical steel sheet of the present invention can achieve both low core loss and high ductility in the high frequency range.

[0085]

[0086]

[0087] 1 Non-oriented electrical steel sheet 10 Inner layer portion 20 Surface layer portion

Claims

1. A non-oriented electrical steel sheet having a difference in the average Si content of the surface layer portion and the average Si content of the inner layer portion, where the sheet thickness t (mm) is defined as the range of 0 to t / 4 and the range of 3t / 4 to t, and the range of more than t / 4 and less than 3t / 4, and the average Si content of the surface layer portion is defined as the range of more than t / 4 and less than 3t / 4, the average Si content of the surface layer portion being 4.00% or more and 6.30% or less, and the average Si content of the inner layer portion being 2.00% or more and 6.20% or less, and the average Si content of the inner layer portion being 2.00% or more and 6.20% or less, A non-oriented electrical steel sheet having a difference ΔSi between the average Si content of the surface layer portion and the average Si content of the inner layer portion of the steel sheet, which is 0.10% or more and 2.00% or less, with the remainder consisting of Fe and unavoidable impurities, and which satisfies the following formula (1): IB2 / IFe < 0.030 (1) In formula (1), IB2 is the Fe content appearing at around 2θ = 36.5° as measured by X-ray diffraction. ３ IFe is the diffraction peak intensity derived from the B2 phase of Si, and IFe is the diffraction peak intensity derived from the ferrite phase that appears near 2θ=77.6° as measured by X-ray diffraction.

2. The non-oriented electrical steel sheet according to claim 1, further comprising, in mass%, at an average content across the entire sheet thickness, one or more elements selected from the group consisting of Sn: 0.10% or less, Sb: 0.10% or less, Cu: 2.0% or less, Ni: 2.0% or less, Cr: 2.0% or less, Ca: 0.01% or less, Mg: 0.01% or less, and REM: 0.03% or less.

3. The non-oriented electrical steel sheet according to claim 1 or 2, further comprising, in mass%, one or more elements selected from the group consisting of Mo: 0-0.050%, B: 0-0.0020%, Ti: 0-0.010%, Nb: 0-0.0050%, V: 0-0.050%, Pb: 0-0.020%, As: 0-0.020%, Zn: 0-0.010%, Co: 0-0.10%, Ge: 0-0.030%, and Ga: 0-0.030%, averaged across the entire sheet thickness.

4. A method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 3, containing, by mass%, Si: 4.5% or less, C: 0.010% or less, Mn: 2.0% or less, Al: 2.0% or less, P: 0.20% or less, S: 0.005% or less, N: 0.010% or less, and O: 0.010% or less, and optionally further containing Sn: 0.10% or less, Sb: 0.10% or less, Cu: 2.0% or less, Ni: 2.0% or less, Cr: 2.0% or less, Ca: 0.01% or less, Mg: 0.01% or less, REM: 0.03% or less, Mo: 0 to 0.050%, B: 0 to 0.0020%, Ti: 0 to 0.010%, The method includes a siliconizing and diffusion treatment step of subjecting a steel sheet having a chemical composition containing one or more elements selected from Nb: 0-0.0050%, V: 0-0.050%, Pb: 0-0.020%, As: 0-0.020%, Zn: 0-0.010%, Co: 0-0.10%, Ge: 0-0.030%, and Ga: 0-0.030%, with the balance being Fe and unavoidable impurities, and a cooling step of cooling the steel sheet after the siliconizing and diffusion treatment step, wherein the diffusion treatment in the siliconizing and diffusion treatment step involves holding the steel sheet in a temperature range of 1250 to 1000°C for 10 seconds or more, and wherein the cooling step involves cooling the steel sheet in a temperature range of 600°C to 200°C with an average tension of 4.0 MPa or more applied to the steel sheet and an average cooling rate of 20.0°C / second or more, Furthermore, the total treatment time of the siliconizing treatment and the diffusion treatment satisfies (300 × t) seconds or more and (1500 × t) seconds or less (t: thickness of the steel sheet (mm)), and further, the treatment time of the siliconizing treatment and the diffusion treatment satisfy the following formula (3): 4.00≦[Si] base + 2.7 × exp(−0.003 × (T1 + T2) / t) + 0.0085 × T1 / t ≦ 6.30 (3) In formula (3), [Si] base is the Si content (%) of the steel sheet before the siliconizing and diffusion treatment step, t is the thickness (mm) of the steel sheet, T1 is the treatment time (seconds) of the siliconizing treatment, and T2 is the treatment time (seconds) of the diffusion treatment.