RU2819013C2 - Sheet of anisotropic electrical steel and method of its production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to anisotropic electrical steel sheet and can be used in making transformer cores. Anisotropic electrical steel sheet comprises a base steel sheet, a glass coating formed on the base steel sheet, and a tension-imparting insulating coating formed on the glass coating. In the base steel sheet there are multiple linear deformations, which extend continuously or intermittently in the direction intersecting with the rolling direction, intervals in direction of rolling of multiple adjacent to each other linear deformations are 10 mm or less. In that area, where there are deformations, there is a closing domain, length d of the closing domain in the direction along the thickness of the sheet from the surface of the main steel sheet is 30–60 mcm, the length w of the closing domain in the rolling direction is 200 mcm or less. Ratio m/d of depth m from the surface of the main steel sheet, where the compression deformation in the rolling direction present in the closing domain exhibits the maximum value, to the said length d is in the range of more than 0.30 and less than 0.90. Sheet is made of steel containing, wt %: C 0.010 or less, Si 3.00–4.00, Mn 0.01–0.50, N 0.010 or less, sol. Al 0.020 or less, S 0.010 or less, P 0.030 or less, Cr 0–0.50, Sn 0–0.50, Cu 0–0.50, Se 0–0.020, Sb 0–0.50, Mo 0 –0.10, Fe and impurities are the rest.

EFFECT: sheet is characterized by improved characteristics of magnetic losses and noise characteristics.

2 cl, 1 dwg, 2 tbl, 29 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0001] The present invention relates to an anisotropic electrical steel sheet and a method for producing it. Priority is claimed to Japanese Patent Application No. 2021-053620, filed March 26, 2021, the contents of which are incorporated herein by reference.

BACKGROUND ART

[0002] Anisotropic electrical steel sheets are soft magnetic materials and are mainly used as transformer core materials. Therefore, anisotropic electrical steel sheets are required to have magnetic characteristics such as high magnetization characteristics and low magnetic losses. Magnetic losses represent the loss of power consumed in the form of thermal energy when the core is excited by an alternating magnetic field, and should be as small as possible from the point of view of energy savings. The degree of magnetic losses is affected by the magnetization coefficient, sheet thickness, coating tension, amount of impurities, electrical resistivity, grain sizes, magnetic domain sizes, etc. Although many technologies have been developed so far regarding anisotropic electrical steel sheets, research and development to reduce magnetic losses is still ongoing to improve energy efficiency.

[0003] For example, Patent Document 1 discloses a method for producing an anisotropic electrical steel sheet, including a step of irradiating the surface of an anisotropic electrical steel sheet with a focused beam of a continuous wave laser while scanning the anisotropic electrical steel sheet in a direction oblique with respect to the rolling direction, and a step of repeating the irradiation at displacement of areas scanned by continuous laser beams at specified intervals, and when the average power of continuous laser beams is designated as P (W), the scanning speed is designated as Vc (mm/s), the specified intervals are designated as PL (mm), and the average density irradiation energy Ua is designated as Ua = P/(Vc×PL) (mJ/mm ² ), magnetic domains control irradiation with laser beams in such a way that the conditions 1.0 mm ≤ PL ≤ 3.0 mm and 0.8 mJ/ are satisfied mm ² ≤ Ua ≤ 2.0 mJ/mm ² . Patent Document 1 shows that magnetic loss can be easily reduced in both the L direction and the C direction of an anisotropic electrical steel sheet while achieving high performance.

[0004] In addition, Patent Document 2 discloses a method for producing an anisotropic electrical steel sheet in which linear closing domains are formed approximately perpendicular to the rolling direction of the steel sheet at approximately constant intervals by scanning and irradiating with continuously oscillating laser beams to improve magnetic loss characteristics. Patent Document 2 shows that when the laser is in TEM ₀₀ mode, in which the intensity profile of the laser beam in the section perpendicular to the beam propagation direction has the maximum intensity near the center of the optical axis, and the diameter d [mm] of the focused irradiation beam in the rolling direction, Since the linear scanning speed V [mm/s] of the laser beam and the average power P [W] of the laser are in the ranges 0 < d ≤ 0.2 and 0.001 ≤ P/V ≤ 0.012, it is possible to obtain a sheet of anisotropic electrical steel with reduced magnetic losses.

[0005] In addition, Patent Document 3 discloses a method for producing an anisotropic electrical steel sheet in which the surface of the anisotropic electrical steel sheet is irradiated with a laser beam at regular intervals to improve magnetic characteristics. Patent Document 3 shows that the laser is a pulse-oscillating Q-switched CO ₂ laser, the shape of the irradiating beam is an ellipse, the main axis of which is located in the sheet width direction, the power density of the laser pulse is set equal to or less than the membrane damage threshold on the surface of the steel sheet, thereby suppressing the formation of a laser irradiation mark, and the major axis length of the elliptical beam is set equal to or larger than the pulse beam irradiation interval in the width direction of the sheet while suppressing the laser irradiation marks, whereby the continuous pulse beams are superimposed on each other each other on the surface of the steel sheet, a cumulative irradiation energy large enough to improve the magnetic performance is transmitted, and the effect of effectively controlling magnetic domains can be obtained.

[0006] In view of this, in recent years there has been a growing demand for reducing noise and vibration in electromagnetic equipment such as transformers, and the anisotropic electrical steel sheets that are used for transformer cores must be a material suitable not only for low magnetic losses, but also for low noise or low vibration. It is believed that one of the causes of noise or vibration in transformer materials is the magnetostriction of anisotropic electrical steel sheets. Magnetostriction referred to herein refers to vibration that occurs in the rolling direction of the anisotropic electrical steel sheet caused by a slight change in the external shape of the anisotropic electrical steel sheet due to a change in magnetization intensity when the anisotropic electrical steel sheet is excited by alternating currents. The magnitude of this magnetostriction is extremely small, on the order of 10 ^-6 , but this magnetostriction generates vibration in the cores that propagates into the external structure, such as a transformer tank, and turns into noise.

[0007] Laser irradiation of anisotropic electrical steel sheet proposed in the above-described Patent Documents 1 to 3 is effective in reducing magnetic loss, but there is a problem that the capping domain that is formed by laser irradiation increases magnetostriction, resulting in noise when a sheet of anisotropic electrical steel is embedded in a transformer, it becomes large (the noise characteristics deteriorate).

[0008] In view of such a problem, Patent Document 4, for example, discloses an anisotropic electrical steel sheet having low magnetic loss, which produces low noise when incorporated into a transformer. Patent Document 4 shows that when cap domain regions with periodically varying widths in the rolling direction are formed on the surface of the steel sheet, each of the cap domain regions satisfies the conditions in which the ratio (W _max /W _min ) of the maximum width W _max to the minimum width W _min in the rolling direction on the surface of the steel sheet is 1.2 or more and 2.2 or less, the average width W _ave in the rolling direction on the surface of the steel sheet is 80 µm or more and 250 µm or less, the maximum depth D in the thickness direction sheet is 32 μm or more, and (W _ave ×D)/s is 0.0007 mm or more and 0.0016 mm or less, it is possible to realize a more favorable magnetic loss/noise balance than in the prior art.

[0009] In addition, Patent Document 5 describes an anisotropic electrical steel sheet in which local deformations are introduced in a direction intersecting the rolling direction at periodic intervals in the rolling direction, in which linear portions of closing domains are formed near the deformations, comb magnetic ones are present in the demagnetized state domains having a length in the rolling direction of 1.2 mm or more, elongated in the rolling direction from the closing domain portion, and, in addition, in areas along the closing domain portions, an average of 1.8 or more magnetic domains per millimeter are formed, and in that case, if the linear intervals of the closing domains are designated as s (mm), the width of the closing domain section w (mm) and the depth of the closing domain section in the direction along the sheet thickness h (μm) satisfy the relations 4 mm ≤ s ≤ 1.5 mm and hw/ s ≤ 0.9 µm. Patent Document 5 assumes that the introduced strain amount represented by hw/s affects magnetic loss and noise.

[0010] However, in the methods of Patent Documents 4 and 5, it is assumed that special electron beam irradiation conditions are required to impart periodicity in the rolling direction to the widths of the trailing domains and to control the number of comb magnetic domains, and therefore it is difficult to obtain high productivity.

[0011] In addition, as a method for controlling the closing domain, for example, Patent Documents 6 and 7 disclose methods for producing anisotropic electrical steel sheet, in which the closing domain is formed without damaging the coating and providing an anisotropic electrical steel sheet having extremely low magnetic loss in a transformer and building factor (BF).

In addition, Patent Document 8 shows that an anisotropic electrical steel sheet with reduced magnetic loss over a wide range of sheet thickness can be obtained by forming a closure domain in a shape that is advantageous for reducing magnetic loss using the characteristics of the electron beam.

In addition, Patent Document 9 discloses an anisotropic electrical steel sheet for a core having linear deformations on the surface of the steel sheet generated by an electron beam emitted from LaB ₆ in directions at an angle of 60-120° relative to the rolling direction.

In addition, Patent Document 10 discloses an anisotropic electrical steel sheet with excellent insulating properties and corrosion resistance, in which the area ratio of beam irradiation marks in a beam irradiation region is controlled, as well as a method for producing it.

However, in all these methods, the trailing domains are controlled to reduce magnetic loss, and there has been no research regarding the trailing domain control to realize low noise.

State of the Art Documents

Patent documents

[0012] [Patent Document 1] Japanese Patent No. 4669565

[Patent Document 2] Japanese Patent No. 4510757

[Patent Document 3] Japanese Patent No. 3361709

[Patent Document 4] Japanese Patent No. 6060988

[Patent Document 5] Japanese Patent No. 6176282

[Patent Document 6] Japanese Patent No. 6169695

[Patent Document 7] Japanese Patent No. 6245296

[Patent Document 8] International PCT Application Publication No. WO 2014/068962

[Patent Document 9] Japanese Patent No. 5954421

[Patent Document 10] International PCT Application Publication No. WO 2013/099272

DISCLOSURE OF INVENTION

Problems solved by the invention

[0013] As described above, anisotropic electrical steel sheets having both sufficiently improved magnetic loss and noise characteristics as well as methods for their production have not been disclosed. It is an object of the present invention to provide an anisotropic electrical steel sheet having excellent magnetic loss characteristics (in particular, magnetic loss improvement coefficient under energy beam irradiation) and noise characteristics, as well as a method for its production.

Remedies

[0014] In the anisotropic electrical steel sheet, the irradiated portion is quickly heated and cooled quickly when irradiated with an energy beam. As a result, deformation (permanent deformation) occurs in the steel sheet near the irradiated part. If this deformation is a compressive deformation in the rolling direction or a tensile deformation in the direction along the thickness of the sheet, a closing domain is formed in the region where this deformation is created. The formation of this trailing domain is the driving force behind the segmentation of 180° magnetic domains parallel/antiparallel to the rolling direction and is therefore beneficial for reducing magnetic losses. However, usually when the closing domain is formed, the degree of magnetostriction becomes large, which means that the noise when the steel sheet is embedded in the transformer becomes large (the noise characteristics deteriorate). The inventors of the present invention have conducted intensive studies on the relationship between the size of this closure domain, magnetic loss characteristics and noise characteristics. As a result of these studies, it was found that when the depth of the closure domain is controlled within a specified range, both low magnetic loss and low noise can be achieved after irradiation with an energy beam. In addition, it has been discovered that when not only the size of the closure domain but also the state of the voltages in the closure domain is controlled, a more excellent magnetic loss/noise balance can be obtained. The energy beam referred to herein refers to a laser beam or an electron beam.

[0015] The present invention has been made in view of the above-described findings. The essence of the present invention is as follows.

[1] The anisotropic electrical steel sheet according to one aspect of the present invention includes a main steel sheet, a glass coating formed on the main steel sheet, and a tension-imposing insulating coating formed on the glass coating, wherein a plurality of linear deformations are present in the main steel sheet, which extend continuously or discontinuously in a direction intersecting with the rolling direction, and the intervals in the rolling direction of a plurality of linear deformations adjacent to each other are 10 mm or less, in the region where deformations are present, there is a capping domain, the length d of the capping domain in the thickness direction sheet from the surface of the main steel sheet is 30-60 μm, the length w of the closing domain in the rolling direction is 200 μm or less, and the m/d ratio of the depth m from the surface of the main steel sheet where the compressive strain present in the closing domain in the rolling direction exhibits the maximum the value for said length d is in the range of more than 0.30 and less than 0.90.

[2] A method for producing an anisotropic electrical steel sheet according to another aspect of the present invention includes a step of segmenting magnetic domains on an anisotropic electrical steel sheet including a base steel sheet, a glass coating formed on the base steel sheet, and a tension imparting insulating coating, formed on a glass coating by irradiating the surface of the tension-inducing insulating coating with an energy beam to introduce a plurality of linear deformations that extend in a direction intersecting with the rolling direction in the vicinity of the surface of the base steel sheet, at the stage of segmenting magnetic domains among the plurality of linear deformations intervals in the rolling direction of adjacent with each other linear strains are 10 mm or less, the power density of the energy beam Ip in units of W/mm ² , which is determined as (P/S) using the output power of the energy beam P in units of W and the cross-sectional area of the energy beam when irradiated S in units of mm ² , satisfies the following expression (1), the energy beam input energy Up in units of J/mm, which is defined as (P/Vs) using the power beam output power P and the energy beam scanning speed Vs in units of mm/s, satisfies the following expression (2), and the beam size ratio, which is defined as (dl/dc) using the diameter dl in the direction perpendicular to the beam scanning direction and the diameter dc in the beam scanning direction of the energy beam in units of μm, and dl satisfy respectively the following expression (3) and the following expression (4):

250 ≤ IP ≤ 5200 (1)

0.007 < Up ≤ 0.050 (2)

0.0010 < dl/dc < 1.0000 (3)

10 ≤ dl < 200 (4).

Effects of the invention

[0016] According to the above-described aspects of the present invention, it is possible to provide an anisotropic electrical steel sheet having excellent magnetic loss characteristics and noise characteristics, as well as a manufacturing method thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a drawing showing an example of the contrast of magnetic domains observed in an electron backscatter image of a cross section of a steel sheet irradiated with an energy beam.

OPTIONS FOR IMPLEMENTING THE INVENTION

[0018] The anisotropic electrical steel sheet according to one embodiment of the present invention (the anisotropic electrical steel sheet of this embodiment) includes a base steel sheet, a glass coating formed on the base steel sheet, and a tensile insulating coating formed on the glass coating. In addition, in the main steel sheet, a plurality of linear deformations (residual deformations) extending continuously or intermittently in a direction intersecting the rolling direction are formed substantially parallel to each other, and intervals in the rolling direction of the plurality of linear deformations adjacent to each other are 10 mm or less. , in the region where deformation is present, there is a closing domain having a length d in the thickness direction of the sheet from the surface of the main steel sheet of 30-60 μm and a length w in the rolling direction of 200 μm or less, and the ratio m/d depth m from the surface of the base steel sheet, where the compressive strain present in the closing domain in the rolling direction exhibits a maximum value, to the length d of the closing domain in the sheet thickness direction is in the range of more than 0.30 and less than 0.90.

[0019] Next, the anisotropic electrical steel sheet of this embodiment will be described.

<Main steel sheet>

(Chemical composition)

[0020] The anisotropic electrical steel sheet of this embodiment is largely characterized by deformation and a locking domain, and the base steel sheet in the anisotropic electrical steel sheet is not limited in terms of chemical composition, which may be in a well-known range. For example, in order to obtain the characteristics that are generally required in anisotropic electrical steel sheets, the following chemical composition of a base steel sheet will be illustrated as an example. In this embodiment, "%" referring to chemical composition means "% by weight" unless otherwise indicated.

C: 0.010% or less

[0021] C (carbon) is an element effective for controlling the microstructure of a steel sheet in stages until the completion of the decarburization annealing step among the production steps. However, when the C content in the base steel sheet of the anisotropic electrical steel sheet, which is a sheet product, exceeds 0.010%, the magnetic characteristics (magnetic loss characteristics or magnetic flux density) are deteriorated. Therefore, in the base steel sheet of the anisotropic electrical steel sheet of this embodiment, the C content is preferably set to 0.010% or less. The C content is more preferably 0.005% or less. The C content is preferably as low as possible; however, when the C content is reduced to less than 0.0001%, the microstructure control effect becomes saturated and the production cost only increases. Therefore, the C content can be set to 0.0001% or more.

Si: 3.00-4.00%

[0022] Si (silicon) is an element that improves magnetic loss performance by increasing the electrical resistance of anisotropic electrical steel sheet. When the Si content is less than 3.00%, sufficient effect of reducing eddy current loss (Foucault current) cannot be obtained. Therefore, the Si content is preferably set to 3.00% or more. The Si content is more preferably 3.20% or more, and even more preferably 3.50% or more. On the other hand, when the Si content exceeds 4.00%, the anisotropic electrical steel sheet becomes brittle and its permeability is greatly deteriorated. In addition, the workability of the anisotropic electrical steel sheet is deteriorated, and the steel sheet may break during rolling. Therefore, the Si content is preferably set to 4.00% or less. The Si content is more preferably 3.80% or less, and even more preferably 3.70% or less.

Mn: 0.01-0.50%

[0023] Mn (manganese) is an element that combines with S to form MnS during production steps. These precipitates act as an inhibitor (an inhibitor of normal grain growth) and cause secondary recrystallization in the steel. Mn is also an element that further improves the hot workability of steel. In the case where the Mn content is less than 0.01%, it is not possible to obtain the above-described effect to a sufficient extent. Therefore, the Mn content is preferably set to 0.01% or more. The Mn content is more preferably 0.02% or more. On the other hand, when the Mn content exceeds 0.50%, secondary recrystallization does not occur, and the magnetic properties of the steel deteriorate. Therefore, in the base steel sheet of the anisotropic electrical steel sheet of this embodiment, the Mn content is preferably set to 0.50% or less. The Mn content is more preferably 0.20% or less, and even more preferably 0.10% or less.

N: 0.010% or less

[0024] N (nitrogen) is an element that combines with Al to form AlN, which functions as an inhibitor in production steps. However, when the N content exceeds 0.010%, the magnetic performance deteriorates due to the inhibitor remaining excessively in the base steel sheet. Therefore, in the base steel sheet of the anisotropic electrical steel sheet of this embodiment, the N content is preferably set to 0.010% or less. The N content is more preferably 0.008% or less, and even more preferably 0.005% or less. On the other hand, the lower limit of N content is not specifically defined; however, when N content is reduced to less than 0.001%, production costs only increase. Therefore, the N content can be set to 0.001% or more.

Sol. Al: 0.020% or less

[0025] Sol. Al (acid-soluble aluminum) is an element that combines with N to form AlN, which functions as an inhibitor during the production steps of anisotropic electrical steel sheet. However, when the sol. Al in the base steel sheet exceeds 0.020%, the magnetic performance is deteriorated due to the inhibitor remaining excessively in the base steel sheet. Therefore, in the main steel sheet of the anisotropic electrical steel sheet of this embodiment, the solution content is. Al is preferably set to 0.020% or less. Solvent content Al is more preferably 0.010% or less, and even more preferably less than 0.001%. Lower limit of sol. Al is not specifically defined; however, when the sol. Al is reduced to less than 0.0001%, production costs only increase. Therefore, the sol. Al may be set to 0.0001% or more.

S: 0.010% or less

[0026] S (sulfur) is an element that binds to Mn to form MnS, which functions as an inhibitor in production steps. However, when the S content exceeds 0.010%, the magnetic performance deteriorates due to excessive remaining inhibitor. Therefore, in the base steel sheet of the anisotropic electrical steel sheet of this embodiment, the S content is preferably set to 0.010% or less. The S content of the anisotropic electrical steel sheet is preferably as low as possible. For example, the S content is less than 0.001%. However, when the S content of the anisotropic electrical steel sheet is reduced to less than 0.0001%, production costs only increase. Therefore, the S content of the anisotropic electrical steel sheet may be 0.0001% or more.

P: 0.030% or less

[0027] P (phosphorus) is an element that deteriorates rolling processability. When the P content is 0.030% or less, excessive deterioration in rolling processability can be suppressed and destruction during production can be prevented. From such a point of view, the P content is preferably set to 0.030% or less. The P content is preferably 0.020% or less, and even more preferably 0.010% or less. The lower limit of P content may be 0%; however, the limit of sensitivity of chemical analysis is 0.0001%, which means that the actual lower limit of P content in practical steel sheets is 0.0001%. In addition, P is also an element that has the effect of improving texture and improving magnetic performance. In order to obtain this effect, the P content may be set to 0.001% or more, or may be set to 0.005% or more.

The rest: Fe and impurities.

[0028] The chemical composition of the base steel sheet in the anisotropic electrical steel sheet of this embodiment contains the above-described essential elements, and the rest may be Fe and impurities. However, for the purpose of improving magnetic characteristics and the like, Cu, Cr, Sn, Se, Sb and Mo may be further contained as optional elements in the ranges that will be shown below. It is also acceptable that these elements may be present as impurities. In addition, even when, for example, any one or more of W, Nb, Bi, Ti, Ni, Co and V are contained in a total amount of 1.0% or less as elements other than those specified, the effect of the anisotropic electrical steel sheet in this embodiment is not weakened. Here, impurities are elements that enter the composition from ore or scrap as raw materials, production environment, etc. during industrial production of the base steel sheet, and their contents are allowed in such quantities that do not adversely affect the performance of the anisotropic electrical steel sheet of this embodiment.

Cr: 0-0.50%

[0029] Cr (chromium) is an element that helps increase the occurrence of Goss orientation in the secondary recrystallization structure to improve magnetic characteristics. In order to obtain the above-described effect, the Cr content is preferably set to 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Cr content exceeds 0.50%, Cr oxide is formed and the magnetic performance is deteriorated. Therefore, the Cr content is preferably set to 0.50% or less. The Cr content is more preferably 0.30% or less, and even more preferably 0.10% or less.

Sn: 0-0.50%

[0030] Sn (tin) is an element that helps improve magnetic performance by controlling the primary recrystallization structure. In order to obtain the effect of improving magnetic performance, the Sn content is preferably set to 0.01% or more. The Sn content is preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Sn content exceeds 0.50%, the secondary recrystallization becomes unstable and the magnetic performance deteriorates. Therefore, the Sn content is preferably set to 0.50% or less. The Sn content is more preferably 0.30% or less, and even more preferably 0.10% or less.

Cu: 0-0.50%

[0031] Cu (copper) is an element that helps increase the occurrence of Goss orientation in the secondary recrystallization structure. Cu is an optional element in the base steel sheet of the anisotropic electrical steel sheet of this embodiment. Therefore, the lower limit of its content is 0%; however, to obtain the above-described effect, the Cu content is preferably set to 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes brittle during hot rolling. Therefore, in the main steel sheet of the anisotropic electrical steel sheet of this embodiment, the Cu content is preferably set to 0.50% or less. The Cu content is more preferably 0.30% or less, and even more preferably 0.10% or less.

Se: 0-0.020%

[0032] Se (selenium) is an element that has the effect of improving magnetic performance. Therefore Se may be contained. In the case where Se is contained, its content is preferably set to 0.001% or more in order to advantageously exhibit the magnetic performance improving effect. The Se content is more preferably 0.003% or more, and even more preferably 0.006% or more. On the other hand, when the Se content exceeds 0.020%, the adhesion of the glass coating is deteriorated. Therefore, the Se content is preferably set to 0.020% or less. The Se content is more preferably 0.015% or less, and even more preferably 0.010% or less.

Sb: 0-0.50%

[0033] Sb (antimony) is an element that has the effect of improving magnetic performance. Therefore Sb may be contained. In the case where Sb is contained, its content is preferably set to 0.005% or more so that the magnetic performance improving effect is advantageously exhibited. The Sb content is more preferably 0.01% or more, and even more preferably 0.02% or more. On the other hand, when the Sb content exceeds 0.50%, the adhesion of the glass coating is significantly deteriorated. Therefore, the Sb content is preferably set to 0.50% or less. The Sb content is more preferably 0.30% or less, and even more preferably 0.10% or less.

Mo: 0-0.10%

[0034] Mo (molybdenum) is an element having the effect of improving magnetic performance. Therefore Mo may be contained. In the case where Mo is contained, its content is preferably set to 0.01% or more in order to advantageously exhibit the magnetic performance improving effect. The Mo content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, when the Mo content exceeds 0.10%, cold rollability is deteriorated, and there is a possibility that the base steel sheet may break. Therefore, the Mo content is preferably set to 0.10% or less. The Mo content is more preferably 0.08% or less, and even more preferably 0.05% or less.

[0035] As described above, as an example, it is shown that the chemical composition of the base steel sheet in the anisotropic electrical steel sheet of this embodiment contains the above-described essential elements and the rest is Fe and impurities, or the chemical composition contains the above-described essential elements and further contains one or more of the specified optional elements, and the balance is Fe and impurities.

[0036] The chemical composition of the base steel sheet in the anisotropic electrical steel sheet of this embodiment can be measured after removing the glass coating and the tension-imposing insulating coating formed on the surface.

Specifically, an anisotropic electrical steel sheet is immersed in an aqueous solution of sodium hydroxide (80-90°C) containing NaOH: 30-50 wt.% and H ₂ O: 50-70 wt.%, for 7-10 minutes, resulting in whereupon the tension-providing insulating coating is removed. A sheet of anisotropic electrical steel, from which the tensile insulating coating has been removed, is washed with water, and after washing with water, it is dried by blowing with warm air for just under 1 minute. The dried anisotropic electrical steel sheet (anisotropic electrical steel sheet without tensile insulating coating) is immersed for 1-10 minutes in an aqueous solution of hydrochloric acid (80-90°C) containing 30-40 wt.% HCl, whereby the glass coating is removed. The main steel sheet is washed with water after immersion, and after washing with water, it is dried by blowing with warm air for just under 1 minute.

The base steel sheet can be extracted from the anisotropic electrical steel sheet by the above-described step.

The chemical composition of such a base steel sheet is obtained by a well-known component analysis method. Specifically, chips are created from a base steel sheet using a drill, the chips are collected, and the collected chips are dissolved in acid to form a solution. Elemental analysis of the chemical composition of this solution is performed using ICP-AES.

Here, the Si in the chemical composition of the base steel sheet is obtained using the method specified in JIS G 1212 (1997) (Methods for determination of silicon content). Specifically, when the above-described chips are dissolved in acid, silicon oxide precipitates, this precipitate (silicon oxide) is filtered with filter paper and its mass is measured, thereby obtaining the Si content.

The C content and S content are obtained by the well-known high-frequency combustion method (infrared absorption combustion method). Specifically, the above-described solution is burned by high-frequency heating in an oxygen flow, the resulting carbon dioxide and sulfur dioxide are detected, and the C content and S content are obtained as a result.

The N content is obtained using the inert gas melting thermal conductivity method.

(Deformations and closure domains)

[0037] In the main steel sheet included in the anisotropic electrical steel sheet of this embodiment, a plurality of linear deformations (residual deformations) generated by energy beam irradiation are present in the vicinity of the surface. The locations where deformation is present can be analyzed using the permanent deformation measurement method of X-ray diffraction, in which the surface of the steel sheet is irradiated with an X-ray beam.

A plurality of linear deformations extend in a direction intersecting with the rolling direction, individual deformations are substantially parallel to each other, and adjacent linear deformations are formed at intervals (distances from the center of one linear deformation to the center of an adjacent linear deformation in the rolling direction) of 10 mm or less in rolling direction.

In addition, it is known that especially when these strains are compressive strains in the rolling direction and tensile strains in the thickness direction of the sheet, regions magnetized in the thickness direction, which are called closure domains, are formed in those regions where deformation is present (areas where deformation is present when the surface of the steel sheet is viewed in a top view). When the sizes of the closure domains are equal to or larger than the specified size, the widths of the 180° magnetic domains are segmented, the Foucault current losses are reduced, and the magnetic losses are reduced. On the other hand, when the size of the closure domains becomes large, the magnetostriction when excitation of the closure domains by alternating current becomes large, and noise clearly appears in the transformers.

As a result of the research of the inventors of the present invention, it has been found that with respect to the size of the capping domain that is formed and present in the region where deformation is present, if its length d in the sheet thickness direction from the surface of the main steel sheet is from 30 to 60 μm, and its length w in the rolling direction is 200 μm or less, magnetic loss is reduced, and the problem of noise that becomes apparent can be suppressed.

In addition, the present inventors discovered for the first time that noise can be further reduced by controlling the strain distribution in the closing domain. That is, in the case where the ratio m/d of the depth m from the surface of the main steel sheet, where the compressive strain present in the closing domain in the rolling direction exhibits a maximum value, to the said length d is in the range of more than 0.30 and less than 0.90 , noise is further reduced.

[0038] In this embodiment, the fact that the linear strains extend in a direction intersecting with the rolling direction means that the extension directions of the linear strains are within a range of 30° or less in angle of deviation from the direction perpendicular to the rolling direction (that is, are in the range of 60-120° relative to the rolling direction). When the extension direction deviates from this angular range, the segmentation effect of the 180° magnetic domains of the steel sheet becomes weak, and sufficient magnetic loss reducing effect cannot be obtained.

The deformation may be present continuously in a linear form or may be present intermittently in one direction (eg, in the form of a dotted line).

In addition, when the intervals in the rolling direction of a plurality of linear deformations adjacent to each other are more than 10 mm, the segmentation effect of 180° magnetic domains becomes weak, and therefore the magnetic loss reducing effect is insufficient. Therefore, each of the intervals in the rolling direction of adjacent linear deformations is set to 10 mm or less. It is preferable that the intervals of the plurality of linear deformations be substantially equal.

When irradiation steps become narrow (intervals of multiple linear deformations become narrow), magnetic losses decrease; however, when the irradiation steps become equal to or less than a certain threshold value, the total hysteresis loss increases, the magnetic loss deteriorates, and there are cases where the noise performance deteriorates. Therefore, each of the intervals in the rolling direction of adjacent linear deformations is preferably set to 3 mm or more.

The length of the deformation in the width direction of the sheet is not limited, but the deformation is preferably formed from one end to the other end of the base steel sheet in the width direction. In the case where the steel sheet is irradiated with the energy beam periodically (intermittently), during irradiation of the steel sheet with the energy beam in the width direction in specific steps, it is preferable that the major axis (length along the width direction) d00 of the part irradiated by the energy beam and the length d01 along the width directions between the parts not irradiated by the energy beam, each of which is enclosed between two parts irradiated by the energy beam, satisfied the condition d01 ≤ 3×d00. d00 may be in the range of 50 µm or more and 50 mm or less.

[0039] In addition, as described above, the capping domains that are formed due to the generation of strains are the driving force behind the segmentation of 180° magnetic domains, which is beneficial in reducing magnetic loss, but there was a problem that the degree of magnetostriction increases from - behind the trailing domains, and the noise becomes greater.

Traditionally, measures such as increasing the energy beam irradiation step or decreasing the input energy of the energy beam have been taken to suppress noise degradation. However, such measures are merely a means of improving noise performance by sacrificing to a certain extent the effect of improving magnetic loss by irradiation with an energy beam, assuming that the magnetic loss performance and noise performance are in a compromise relationship.

In contrast, as a result of the research of the inventors of the present invention, it has been found that in anisotropic electrical steel sheets, when the closure domain regions are formed shallowly below the surface (localized in the surface layer), the magnetic loss characteristics can be improved while suppressing the deterioration of the noise characteristics. In particular, it has been found that when the length d in the sheet thickness direction of the capping domain present in the region where the deformation has been generated is set to 60 μm or less, it is possible to improve the magnetic loss performance while suppressing the deterioration of noise performance. Therefore, the length d of the closing domain in the sheet thickness direction from the surface of the main steel sheet is set to 60 μm or less.

On the other hand, when the length d of the capping domain in the sheet thickness direction is less than 30 μm, the effect of improving magnetic loss cannot be obtained. Therefore, the length d is set to 30 μm or more.

In addition, when the length w of the closing domain in the rolling direction of the main steel sheet is more than 200 μm, the volume of the closing domain increases and the degree of magnetostriction increases. Therefore, the length w of the capping domain is set to 200 μm or less. The length w of the closure domain is preferably 150 μm or less, and more preferably 100 μm or less. On the other hand, the length w of the closing domain in the rolling direction of the main steel sheet is preferably 50 μm or more.

In addition, the m/d ratio of the depth m from the surface of the main steel sheet, where the compressive strain present in the closing domain in the rolling direction exhibits a maximum value, to the length d is set in the range of more than 0.30 and less than 0.90. The reason for further noise reduction by controlling m/d is unclear, but it is assumed that when the value of m/d is 0.90 or more, since the depth at which compressive strain in the rolling direction is present in the closing domain is large, the closure domain is further stabilized, and the external magnetic field required to make the closure domain disappear becomes larger, causing the harmonic component of the magnetostriction waveform to become large and the noise to become large. Therefore, m/d is set to less than 0.90. On the other hand, m/d in the range of 0.30 or less is difficult to realize under a range of laser or electron beam irradiation conditions in actual surgery. Therefore, m/d is set to greater than 0.30.

[0040] The dimensions of the closing domain (length in the thickness direction of the sheet and length in the rolling direction) are estimated by observing the electron reflected image of an inclined anisotropic electrical steel sheet in a scanning electron microscope.

In particular, from a sheet of anisotropic electrical steel having residual deformations and closing domains, a section is obtained perpendicular to the direction along the width of the sheet (section in the direction along the thickness of the sheet), and then technological deformations on the surface of this section are removed using a beam of argon ions. When obtaining a section perpendicular to the width direction of the sheet, the section is cut so that the angle of deviation from the {110} crystallographic plane of iron becomes less than 1° around the ND axis (direction perpendicular to the surface of the sample). After this, the resulting cross-section is irradiated with an electron beam in a scanning electron microscope to obtain an image in reflected electrons. The sample to be analyzed is left tilted at approximately 45-80°. When a magnetic domain is present in the sample being analyzed, the trajectories of the incident or reflected electrons in the sample change due to the Lorentz force depending on the direction of magnetization in the magnetic domain, and thus a contrast is created in the image in the reflected electrons due to the magnetic domain. Based on this contrast, the trailing domain is determined, and its dimensions are considered to be the dimensions of the trailing domain.

Next, a method for determining the closure domain by contrast will be described. Fig. 1 shows an example of an electron reflected image of a section parallel to the sheet thickness direction and the rolling direction at a position where the steel sheet was irradiated with an energy beam. As shown in FIG. 1, the electron backscatter image shows that the region where streak contrast is observed (SPR region surrounded by white and black dotted lines in FIG. 1) is present in the steel sheet directly below the area irradiated by the energy beam. In this region, the structure of the magnetic domain differs from the structure of the environment due to the influence of residual deformations introduced during irradiation with an energy beam. In this embodiment, such an area (surrounded by the dotted lines in Fig. 1) where the pixel intensities change at intervals of 2-10 μm in the rolling direction within an amplitude of 0.4% or more of the average pixel intensities (striped pattern contrast shown) , is considered as a closing domain, and its dimensions are considered as the dimensions of a closing domain. The average pixel intensity referred to here refers to the average intensity of the pixels in the area where the banding pattern is observed.

Strain in the capping domain is assessed by taking a section perpendicular to the sheet width direction (section in the sheet thickness direction) and then performing an electron backscatter diffraction (EBSD) mapping measurement. During EBSD strain acquisition, EBSD images are stored at high resolution and the shift between images is measured, converting that shift into a strain value. For example, EBSD images are saved at 956x956 pixels and used to calculate deformation. The method of converting the shear between EBSD images into strain is well known in the literature, and the strain can be calculated using commercially available software such as CrossCourt4 from BLG Vantage or the like. Thereby, the depth from the surface of the steel sheet is calculated where the compressive strain in the rolling direction exhibits its maximum value.

<Glass cover>

[0041] In the anisotropic electrical steel sheet of this embodiment, a glass coating is formed on the surface of the main steel sheet. Glass coating is an inorganic coating containing magnesium silicate as the main component. The glass coating is formed by the reaction between an annealing separator containing magnesium oxide (MgO) deposited on the surface of the base steel sheet and a component on the surface of the base steel sheet during final annealing, and has a composition derived from the annealing separator and the base steel sheet component (more specifically , a composition containing Mg ₂ SiO ₄ as the main component).

<Tension Insulation Coating>

[0042] In the anisotropic electrical steel sheet of this embodiment, a tension-imposing insulating coating is formed on the surface of the glass coating.

The tension imparting insulating coating imparts electrical insulating properties to the anisotropic electrical steel sheet, thereby reducing Foucault current loss while improving the magnetic loss of the anisotropic electrical steel sheet. In addition, according to the tensile insulating coating, in addition to the electrical insulating properties described above, various properties such as corrosion resistance, heat resistance and slip resistance can be obtained.

In addition, the tension-imposing insulating coating has the function of applying tension to the anisotropic electrical steel sheet. When tension is applied to the anisotropic electrical steel sheet to promote the movement of domain walls in the anisotropic electrical steel sheet, the magnetic loss of the anisotropic electrical steel sheet can be improved.

The tensile insulating coating may be a well-known coating that is formed, for example, by applying and calcining a coating liquid containing a metal phosphate and silica as main components on the surface of the glass coating.

<Main steel sheet thickness: 0.17-0.30mm>

[0043] The thickness of the base steel sheet in the anisotropic electrical steel sheet of this embodiment is not limited, but is preferably 0.17 to 0.30 mm in consideration of not only low magnetic loss, but also application in transformer cores that require low level noise and low vibration. The smaller the thickness of the sheet, the more favorable the effect of reducing Foucault current loss can be obtained and the more favorable the magnetic loss can be obtained, and therefore the preferred upper limit of the thickness of the base steel sheet is 0.30 mm. However, to produce a base steel sheet with a thickness of less than 0.17 mm, special equipment becomes necessary, which is not preferable from a production point of view, for example, due to increased production costs. Therefore, the industry's preferred lower limit for sheet thickness is 0.17 mm.

<Production method>

[0044] The anisotropic electrical steel sheet of this embodiment can be produced by a production method including the following steps.

(i) A hot rolling step by heating and then hot rolling a steel billet containing, in mass%, C: 0.01-0.20%, Si: 3.0-4.0%, sol. Al: 0.010-0.040%, Mn: 0.01-0.50%, N: 0.020% or less, S: 0.005-0.040%, P: 0.030% or less, Cu: 0-0.50%, Cr: 0-0.50%, Sn: 0-0.50%, Se: 0-0.020%, Sb: 0-0.50%, Mo: 0-0.10%; and the rest is Fe and impurities, producing hot-rolled steel sheet,

(ii) a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet to obtain a hot-rolled and annealed steel sheet,

(iii) a cold rolling step of performing cold rolling one or more times with intermediate annealing therebetween of the hot rolled and annealed steel sheet to obtain a cold rolled steel sheet,

(iv) a decarburization annealing step of performing decarburization annealing on the cold rolled steel sheet to obtain a decarburization annealing steel sheet,

(v) a final annealing step of applying an annealing separator to the decarburization annealed steel sheet and then performing final annealing to obtain a final annealed steel sheet,

(vi) a step of forming an insulating coating by forming a tension-imposing insulating coating on the surface of the finally annealed steel sheet, and

(vii) the stage of segmentation of magnetic domains with the introduction of linear thermal deformations into the surface of the tension-inducing insulating coating by irradiation with an energy beam.

These stages will be described in detail below. In the following description, in the event that the conditions in each step are not described, it is possible to carry out each step by suitably applying well-known conditions.

<Hot rolling stage>

[0045] At the hot rolling stage, for example, a steel billet such as a slab containing, in wt.%, C: 0.01-0.20%, Si: 3.0-4.0%, sol. Al: 0.010-0.040%, Mn: 0.01-0.50%, N: 0.020% or less, S: 0.005-0.040%, P: 0.030% or less, Cu: 0-0.50%, Cr: 0-0.50%, Sn: 0-0.50%, Se: 0-0.020%, Sb: 0-0.50%, Mo: 0-0.10%, and the rest is Fe and impurities, heat and then subjected to hot rolling to obtain hot rolled steel sheet. The heating temperature of the steel billet is preferably set in the range of 1100-1450°C. The heating temperature is more preferably 1300-1400°C. The hot rolling conditions are not particularly limited and can be set as appropriate based on the required characteristics. The thickness of the hot-rolled steel sheet is preferably in the range of, for example, 2.0 mm or more and 3.0 mm or less.

<Annealing stage of hot rolled sheet>

[0046] The hot-rolled sheet annealing step is a step of annealing the hot-rolled steel sheet produced in the hot rolling step to obtain a hot-rolled and annealed steel sheet. When this annealing treatment is performed, recrystallization occurs in the structure of the steel sheet, and it becomes possible to realize advantageous magnetic characteristics. In the hot-rolled sheet annealing step of this embodiment, the hot-rolled steel sheet produced in the hot rolling step can be annealed according to a well-known method to obtain a hot-rolled and annealed steel sheet. The means for heating the hot-rolled steel sheet during annealing is not particularly limited, and a well-known heating method can be used. In addition, the annealing conditions are also not particularly limited, and it is possible to anneal the hot-rolled steel sheet, for example, in a temperature range of 900-1200°C for 10 seconds to 5 minutes.

<Cold rolling stage>

[0047] In the cold rolling step, cold rolling, including multiple passes, of the hot-rolled and annealed steel sheet is performed after annealing the hot-rolled sheet to obtain a cold-rolled steel sheet having a thickness of 0.17-0.30 mm. Cold rolling may be cold rolling that is performed once (a series of cold rolling without intermediate annealing), or may be performed multiple times, including intermediate annealing, with the cold rolling stopped and intermediate annealing performed at least once or more before the final pass of the step cold rolling. In the case where intermediate annealing is performed, the hot-rolled steel sheet is preferably kept at a temperature of 1000-1200°C for 5-180 seconds. The annealing atmosphere is not particularly limited. The number of times of intermediate annealing is preferably 3 or less in view of the production cost. In addition, the surface of the hot-rolled and annealed steel sheet can be etched before the cold rolling stage.

[0048] In the cold rolling step, the hot-rolled and annealed steel sheet can be cold-rolled according to a well-known method to obtain a cold-rolled steel sheet. For example, you can make sure that the final rolling reduction is in the range of 80-95%. If the final rolling reduction is less than 80%, there is a high probability that Goss nuclei in which the {110}<001> orientation has a high degree of development in the rolling direction cannot be obtained, which is not preferable. On the other hand, if the final rolling reduction exceeds 95%, there is an increased likelihood that the secondary recrystallization will become unstable in the subsequent final annealing step, which is not preferable. When the final rolling reduction is set to fall within the above-described range, Goss nuclei in which the {110} <001> orientation has a high degree of development in the rolling direction can be obtained, and the instability of secondary recrystallization can be suppressed. The final rolling reduction is the cumulative cold rolling reduction and is the cumulative cold rolling reduction after final process annealing if process annealing is performed.

<Decarburization Annealing Stage>

[0049] In the decarburization annealing step, decarburization annealing of the resulting cold-rolled steel sheet is performed to obtain a decarburization annealing steel sheet. In the decarburization annealing stage, the decarburization annealing conditions are not limited, as long as the cold-rolled steel sheet undergoes primary recrystallization, and C, which has a negative effect on the magnetic performance, can be removed from the steel sheet, and, as an illustrative example, the cold-rolled steel sheet is kept in an annealing atmosphere (furnace atmosphere), where the oxidation degree (PH ₂ O/PH ₂ ) is set to 0.3-0.6, at an annealing temperature of 800-900°C for 10-600 seconds.

<Nitriding stage>

[0050] The nitriding treatment may be performed between the decarburization annealing step and the final annealing step described below.

For example, in the nitriding step, the decarburization-annealed steel sheet is maintained at about 700-850° C. in a nitriding treatment atmosphere (an atmosphere containing a gas having nitriding ability such as hydrogen, nitrogen or ammonia). Here, it is preferable to carry out nitriding so that the N content of the decarburization-annealed steel sheet after the nitriding step reaches 40 to 1000 parts per million on a mass basis ( ^ppm ). When the N content of the decarburization-annealed steel sheet after nitriding is less than 40 ^ppm , AlN is not released in the decarburization-annealing steel sheet sufficiently, and there is a possibility that AlN will not act as an inhibitor. Therefore, in the case where AlN is used as an inhibitor, the N content of the decarburization-annealed steel sheet after nitriding is preferably set to 40 ^ppm or more.

On the other hand, if the N content of the decarburization-annealed steel sheet exceeds 1000 ^ppm , AlN is excessively present in the steel sheet even after secondary recrystallization in the final annealing is completed. Such AlN causes deterioration of magnetic losses. Therefore, the N content of the decarburization-annealed steel sheet after the nitriding step is preferably set to 1000 ^ppm or less.

<Final annealing stage>

[0051] In the final annealing step, a predetermined annealing separator is applied to the decarburization-annealed steel sheet produced by the decarburization annealing step or further subjected to nitriding, and then final annealing is performed. Final annealing is usually carried out over a long period of time in a state where the steel sheet is coiled. Therefore, before final annealing, an annealing separator is applied to the decarburization-annealed steel sheet and dried to prevent seizing between the inner and outer sides of the sheet in the roll.

As the applied annealing separator, an annealing separator containing MgO as a main component (for example, containing 80 mass% or more of MgO) is used. Using an annealing separator containing MgO as the main component, a glass coating can be formed on the surface of the base steel sheet. If MgO is not the main component, the primary coating (glass coating) will not form. The reason for this is that the primary coating is a compound of Mg ₂ SiO ₄ or MgAl ₂ O ₄ and the Mg required for the formation reaction is insufficient.

Final annealing can be carried out under conditions such that, for example, in a gas atmosphere containing hydrogen and nitrogen, the temperature is raised to 1150-1250°C, and then the cold-rolled steel sheet is annealed for 10-60 hours.

<Insulation coating formation stage>

[0052] In the insulating coating forming step, a tensile insulating coating is formed on one surface or both surfaces of the cold-rolled steel sheet after final annealing. Conditions for forming the tensile insulation coating are not particularly limited, and the film-forming liquid can be applied and dried in a well-known manner using a well-known insulation coating forming liquid. When a tensile insulating coating is formed on the surface of a steel sheet, the magnetic characteristics of the anisotropic electrical steel sheet can be further improved.

The surface of the steel sheet on which the tensile insulating coating is to be formed may be a surface on which optional pre-treatment such as alkali degreasing treatment and the like has been performed before applying the film-forming liquid. or etching with hydrochloric acid, sulfuric acid, phosphoric acid, etc., or may be a final annealed surface on which no pre-treatments have been performed.

The insulating coating that is formed on the surface of the steel sheet is not particularly limited as long as it can be used as the insulating coating of anisotropic electrical steel sheets, and a well-known insulating coating can be used. Illustrative examples of such insulating coatings are composite insulating coatings containing an inorganic substance as a main component and additionally containing an organic substance. In this case, the composite insulating coating is an insulating coating containing at least any inorganic substance, such as a metal chromic acid salt, a metal phosphate salt, colloidal silica, a Zr compound or a Ti compound, as a main component, in which fine particles of organic matter are dispersed resin. Particularly from the point of view of reducing the environmental burden during production, which is more and more in demand in recent years, an insulation coating for which a metal phosphate, a binder with Zr or Ti, or their carbonate or ammonium salt.

<Magnetic domain segmentation stage>

[0053] In the magnetic domain segmentation step, the surface of the tensile insulating coating is irradiated with an energy beam (laser beam or electron beam), thereby introducing a plurality of linear deformations extending in a direction intersecting with the rolling direction near the surface of the base steel sheet (from the surface to the inner part of a steel sheet). In the magnetic domain segmentation step, a plurality of linear strains (thermal strains generated by rapid heating by irradiation with an energy beam and subsequent rapid cooling) are generated at predetermined intervals in the rolling direction, and these intervals (that is, the intervals of linear strains adjacent to each other) are set equal 10mm or less in rolling direction.

When the intervals of multiple linear deformations in the rolling direction are more than 10 mm, the effect of improving magnetic loss is insufficient. Therefore, deformations are generated by irradiating the tension-imposing insulating coating with an energy beam at intervals in the rolling direction of 10 mm or less.

The energy beam can be continuous radiation or pulsed radiation. Examples of the type of laser beam include a fiber laser, a YAG laser, or a CO ₂ laser. The electron beam may be a continuous beam or an intermittent beam.

[0054] In addition, as described above, in order to obtain an anisotropic electrical steel sheet providing both low magnetic loss and low noise, strains are introduced into the base steel sheet and closure domains are formed shallowly below the surface. Specifically, the tensile insulating coating is irradiated with an energy beam such that the energy beam power density Ip, which is determined as P/S using the energy beam output power P in units of W and the energy beam irradiation cross-sectional area S in units of ^mm2 , satisfies the following expression (1), and the energy beam input energy in units of J/mm, which is defined as P/Vs using the energy beam output power P and the energy beam scanning speed Vs in units of mm/s, satisfies the following expression (2).

[0055] 250 ≤ Ip ≤ 5200 Expression (1)

0.007 < Up ≤ 0.050 Expression (2)

[0056] When Ip is less than 250, the irradiation effect cannot be obtained sufficiently, and magnetic loss is not improved sufficiently. Therefore the IP is 250 or more. On the other hand, when Ip becomes larger than 5200, the depth of the trailing domain increases and the noise performance deteriorates. Therefore the IP is 5200 or less. The IP is preferably 2000 or less, more preferably 1750 or less, and even more preferably 1500 or less. In this case, the noise performance is more excellent. In addition, when Up is 0.007 or less, the irradiation effect cannot be obtained sufficiently and the magnetic loss is not improved sufficiently. Therefore Up is more than 0.007. On the other hand, when Up becomes larger than 0.050, the depth of the trailing domain increases and the noise performance deteriorates. Therefore Up is 0.050 or less.

[0057] Moreover, in the method for producing an anisotropic electrical steel sheet of this embodiment, when irradiated with an energy beam, the beam aspect ratio is controlled to satisfy the following expression (5), wherein the beam aspect ratio is determined by (dl/dc) using diameter dl in the direction perpendicular to the scanning direction of the beam, in units of μm and diameter dc in μm in the scanning direction of the energy beam beam in units of μm.

[0058] 0.0010 < dl/dc < 1.0000 (5)

[0059] When the beam aspect ratio is 0.0010 or less, heat is generated due to beam irradiation, input energy supply efficiency is reduced, and sufficient magnetic domain segmentation effect (magnetic loss reduction effect) cannot be obtained. Therefore, the beam aspect ratio is more than 0.0010. On the other hand, when the beam aspect ratio is 1.0000 or more, the volume in which the residual stress is present increases and the noise performance becomes poor. Therefore, the beam aspect ratio is less than 1.0000. The beam aspect ratio is preferably less than 0.0500, and more preferably less than 0.0050.

[0060] In addition, the diameter dl of the energy beam in the direction perpendicular to the scanning direction of the beam, in units of μm, is made to satisfy the following expression (6).

[0061] 10 ≤ dl < 200 (6)

[0062] For an energy beam such as a laser or electron beam, it is difficult in industry to narrow the beam diameter to less than 10 μm. Therefore dl is 10 or more. On the other hand, when dl becomes 200 or more, excessive thermal deformation is introduced beyond the magnetic domain segmentation effect, resulting in noise performance deteriorating. Therefore, dl is less than 200. dl is preferably less than 150, and more preferably less than 100.

[0063] In the method for producing an anisotropic electrical steel sheet of this embodiment, as described above, irradiation is performed with an energy beam having a relatively high Ip in a state where the beam aspect ratio is small. Such irradiation is not usually performed. The reason for this is that it is believed that decreasing the beam aspect ratio leads to dispersion of the irradiation energy and weakens the effect of increasing Ip. However, the inventors of the present invention first discovered that the above-described irradiation conditions are preferable as a result of studies based on new findings that control of the spatial distribution of strains is important from the point of view of simultaneously reducing magnetic losses and noise.

Examples

[0064] The hot rolling step was performed on slabs containing 3.0 wt.% Si (steel billets containing, in wt.%, C: 0.03%, Si: 3.0%, sol. Al: 0.040%, Mn: 0.05%, N: 0.005%, S: 0.005%, P: 0.01%, and the rest is Fe and impurities). Specifically, the slabs were heated to 1350°C, and then hot rolling of the slabs was performed in order to produce hot-rolled steel sheets with a thickness of 2.3 mm.

The hot-rolled sheet annealing step was performed on hot-rolled steel sheets after the hot rolling step at an annealing temperature of 900°C to 1200°C for a holding time of 10 to 300 seconds.

Thereafter, cold rolling was performed one or more times with intermediate annealing in between to obtain cold-rolled steel sheets with a thickness of 0.17-0.30 mm.

Decarburization annealing was performed on these cold-rolled steel sheets under conditions where the cold-rolled steel sheets were kept at 800-850°C for 100-200 seconds. The well-known humid atmosphere containing hydrogen and nitrogen was formed as the decarburization annealing atmosphere.

After decarburization annealing, steel sheets No. 4, 6 and 13 were kept at 700-850°C for 10-60 seconds in a well-known nitriding treatment atmosphere (an atmosphere containing a gas having nitriding ability such as hydrogen, nitrogen or ammonia), and nitriding treatments were carried out so that the N contents of the decarburization-annealed steel sheets were 40-1000 ^ppm .

An annealing separator containing magnesium oxide (MgO) as the main component was applied to the surfaces of steel sheets, and final annealing of steel sheets Nos. 4, 6 and 13 was performed after nitriding, and the other steel sheets after decarburization annealing. The final annealing temperature in the final annealing step was 1200°C, and the holding time at the final annealing temperature was 20 hours.

An insulating coating composition containing colloidal silica and phosphate as the main components was applied to the surfaces (glass coatings) of steel sheets (anisotropic electrical steel sheets) after cooling in a final annealing step, and then calcined to form tension-inducing insulating coatings.

An anisotropic electrical steel sheet of each steel sheet number was produced using the above-described steps.

[Analysis of the chemical composition of the main steel sheet]

[0065] The chemical composition of the base steel sheet in the anisotropic electrical steel sheet with each steel sheet number before magnetic domain segmentation obtained by the above method was obtained by the following method. First, the tensile insulating coating was removed from each anisotropic electrical steel sheet. Specifically, an anisotropic electrical steel sheet was immersed in an aqueous sodium hydroxide solution (80-90°C) containing NaOH: 30-50 wt% and H ₂ O: 50-70 wt% for 7-10 minutes. The anisotropic electrical steel sheet after immersion (the anisotropic electrical steel sheet from which the tension imparting insulating coating has been removed) was washed with water. After rinsing with water, the anisotropic electrical steel sheet was dried by blowing warm air for just under one minute.

The glass coating was then removed from the anisotropic electrical steel sheet. Specifically, an anisotropic electrical steel sheet was immersed in an aqueous solution of hydrochloric acid (80-90°C) containing 30-40 wt.% HCl for 1-10 minutes. Therefore, the glass coating was removed from the base steel sheet. The base steel sheet was washed with water after immersion. After rinsing with water, the anisotropic electrical steel sheet was dried by blowing warm air for just under one minute.

The base steel sheet was extracted from the anisotropic electrical steel sheet using the above-described step.

The chemical composition of the recovered base steel sheet was obtained using a well-known component analysis method. Specifically, chips were created from a base steel sheet using a drill, and these chips were collected. The collected shavings were dissolved in acid to form a solution. Elemental analysis of the chemical composition of this solution was performed using ICP-AES. Si in the chemical composition of the base steel sheet was obtained using the method described in JIS G 1212 (1997) (Methods for determination of silicon content). In particular, when the above-described chips were dissolved in acid, silicon oxide precipitated. This precipitate (silicon oxide) was filtered with filter paper and its mass was measured, thereby obtaining the Si content. The C content and S content were obtained using the well-known high-frequency combustion method (infrared absorption combustion method). Specifically, the above-described solution was combusted by high-frequency heating in an oxygen flow, the resulting carbon dioxide and sulfur dioxide were detected, and the C content and S content were obtained. The N content was obtained using an inert gas melting thermal conductivity method. The chemical composition of the base steel sheet was obtained using the above-described analysis method. The chemical composition of the steel sheet (base steel sheet) with each steel sheet number was as follows, in mass%: C: 0.001%, Si: 3.0%, sol. Al: less than 0.001%, Mn: 0.05%, N: 0.002%, S: less than 0.001%, P: 0.01%, and the rest is Fe and impurities.

[Evaluation of magnetic characteristics]

[0066] Although not shown in the table, in order to estimate the magnetic loss improvement factor, the magnetic losses were evaluated before segmenting the magnetic domains. A sample having a width of 60 mm and a length of 300 mm, including the position of the center of the sheet along the width, was taken from an anisotropic electrical steel sheet with each steel sheet number. The direction along the sample length was set parallel to the rolling direction. The sample taken was kept at 800°C for 2 hours in a nitrogen atmosphere having a dew point of 0°C or lower, and the strain introduced during sample collection was removed. Magnetic loss W _17/50 (W/kg) with the frequency set to 50 Hz and the maximum magnetic flux density set to 1.7 T was measured in accordance with JIS C2556 (2015) using this sample.

[0067] Subsequently, segmentation of the magnetic domains of the anisotropic electrical steel sheet with each number of steel sheet was performed by laser irradiation or electron beam irradiation of the surface of the steel sheet under the conditions shown in Table 1 using a fiber laser or electron beam, then the dimensions of the trailing domain were examined and performed tests to evaluate noise performance and magnetic performance. Laser irradiation was performed in an atmosphere, and electron beam irradiation was performed in a vacuum (vacuum level: 0.2 Pa).

[0068] [Table 1] Steel Sheet No. Magnetic domain segmentation stage Energy Beam IP Up dl/dc dl Type of energy beam Angle between the scanning direction of the energy beam and the direction perpendicular to the rolling direction Spacing in rolling direction W/mm ² J/mm µm degrees mm 1 Laser 267 0.006 0.0524 100 Laser 8 6 2 Laser 251 0.008 0.0393 100 Laser 28 5 3 Laser 293 0.008 0.0287 80 Laser 5 4 4 Laser 375 0.015 0.0212 90 Laser 8 8 5 Laser 589 0.019 0.0894 160 Laser 10 5 6 Laser 440 0.026 0.0605 170 Laser 18 6 7 Laser 409 0.045 0.0516 190 Laser 17 8 8 Laser 650 0.033 0.0628 200 Laser 22 5 9 Laser 84 0.080 0.0091 200 Laser 10 9 10 Laser 550 0.037 0.0115 105 Laser 15 3 eleven Laser 283 0.043 0.0082 125 Laser 3 5 12 Laser 255 0.036 0.0059 150 Laser 3 4 13 Laser 1800 0.045 0.0452 120 Laser 9 7 14 Laser 90 0.036 0.0027 130 Laser 20 6 15 Laser 95 0.020 0.0293 200 Laser 5 4 16 Laser 260 0.038 0.0092 190 Laser 1 7 17 Laser 1048 0.044 0.0293 140 Laser 1 3 18 Laser 1643 0.042 0.0611 165 Laser 20 5 19 Laser 300 0.053 0.0072 135 Laser 10 6 20 Laser 252 0.048 0.0061 195 Laser 10 8 21 Laser 5250 0.008 2.5447 180 Laser 22 7 22 Laser 5125 0.008 0.7000 197 Laser 1 10 23 Laser 2000 0.050 0.1278 197 Laser 1 12 24 Laser 1923 0.008 0.0302 50 Laser 3 7 25 Laser 5250 0.004 0.1963 50 Laser 6 5 26 Laser 250 0.037 0.0623 225 Laser 15 3 27 Electron beam 1600 0.040 0.0600 170 Electron beam 3 5 28 Laser 1100 0.030 0.0008 20 Laser 2 5 29 Laser 1070 0.050 1.3000 200 Laser 2 5

[Distribution of closure domains in energy beam treated steel sheet]

[0069] The cross-sectional dimensions of the closing domain in the thickness direction of each anisotropic electrical steel sheet were estimated by the above-described method by observing the electron reflected image using a scanning electron microscope. From a sheet of anisotropic electrical steel having residual deformation and a closing domain, a section was obtained perpendicular to the direction along the width of the sheet (section in the direction along the thickness of the sheet), and then technological deformations on the surface of this section were removed using a beam of argon ions at an accelerating voltage of 1 kV. When obtaining a section perpendicular to the sheet width direction, the section was cut so that the angle of deviation from the iron {110} crystallographic plane was less than 1° around the ND axis (the direction perpendicular to the surface of the sample). The sample was tilted at an angle of 70 degrees in a scanning electron microscope and the cross section was irradiated with an electron beam to obtain an electron backscatter image. The accelerating voltage of the electron beam was set to 20 kV. The evaluation results are shown in Table 2.

[Estimation of strain in the closing domain]

[0070] Strains (residual strains) in the closure domain were assessed by taking a cross-section in the thickness direction of the sheet and then performing electron backscatter diffraction (EBSD) mapping measurements. The sample, tilted at 70 degrees, was irradiated with an electron beam to obtain an EBSD image. EBSD images were saved at 956 × 956 pixels and used to calculate strain. Strain calculations were performed using CrossCourt4 software from BLG Vantage. Thus, we calculated the depth from the surface of the steel sheet where the compressive strain in the rolling direction exhibited its maximum value.

[Noise Performance Evaluation]

[0071] A sample having a width of 100 mm and a length of 500 mm was taken from each anisotropic electrical steel sheet. The direction along the length of the sample was chosen to correspond to the rolling direction RD, and the direction along the width was chosen to correspond to the direction along the sheet width TD.

The magnetostriction of this sample was measured by the AC magnetostriction method using a magnetostriction meter. The instrument used to measure magnetostriction was a device including a laser Doppler vibrometer, an excitation coil, an excitation power supply, a magnetic flux detection coil, an amplifier and an oscilloscope.

Specifically, an alternating magnetic field was applied to the sample so that the maximum magnetic flux density was 1.7 Tesla in the rolling direction. The change in sample length caused by the expansion and contraction of magnetic domains was measured using a laser Doppler vibrometer, and the magnetostriction signal was obtained. Fourier analysis of the obtained magnetostriction signal was performed to obtain the amplitude Cn of each frequency component fn (n is a natural number equal to 1 or more) of the magnetostriction signal. The magnetostriction level LVA (dB) represented by the following expression was obtained using the A-correction factor αn of each frequency component fn.

LVA=20 × Log(√(∑(ρc × 2π × fn × αn × Cn/√2) ² )/Pe0)

Here ρc is the intrinsic acoustic impedance, set to 400. Pe0 is the minimum audible sound pressure, set to Pe0=2×10 ^-5 (Pa). The values given in Table 2 of JIS C 1509-1 (2005) were used as the A-correction factor αn.

Based on the obtained level of magnetostriction (LVA), the noise characteristics were assessed according to the following criteria. When the magnetostriction level was less than 60 dBA, the anisotropic electrical steel sheet was considered superior in terms of noise performance.

The results are shown in Table 2.

[Evaluation of magnetic characteristics]

[0072] A sample having a width of 60 mm and a length of 300 mm, including the position of the center of the sheet along the width, was taken from an anisotropic electrical steel sheet with each steel sheet number. The direction along the sample length was set parallel to the rolling direction. The sample taken was kept at 800°C for 2 hours in a nitrogen atmosphere having a dew point of 0°C or lower, and the strain introduced during sample collection was removed.

Magnetic flux density (T) was obtained by single sheet magnetic performance test (SST test) in accordance with JIS C2556 (2015) using this sample. In particular, a magnetic field of 800 A/m was applied to the sample and the magnetic flux density (T) was determined.

In addition, the magnetic loss W _17/50 (W/kg) with the frequency set to 50 Hz and the maximum magnetic flux density set to 1.7 T was measured in accordance with JIS C2556 (2015) using this sample.

The measurement results are shown in Table 2.

[0073] Here, the improvement factor (%) of magnetic loss before and after irradiation with an energy beam was determined as 100 × the difference in magnetic loss before and after irradiation with an energy beam/magnetic loss before irradiation with an energy beam, and the improvement factor of magnetic loss was 5.0 % or more was considered acceptable. The measurement results of the magnetic loss improvement factor are shown in Table 2.

[0074]

[Table 2] Steel Sheet No. Permanent deformation Trailing domain Distribution of residual deformations in the direction along the sheet thickness Magnetic characteristics Noise characteristics Note Angle between the direction of the extent of permanent deformation and the direction perpendicular to the rolling direction Spacing in rolling direction Linear form Length in direction along sheet thickness, d Length in rolling direction, w Thickness of main steel sheet Depth where there is a maximum value of compressive strain in the rolling direction, m m/d Magnetic losses
W _17/50 Magnetic flux density Magnetic loss improvement factor degrees mm µm µm mm µm - W/kg Tl % dB 1 8 6 Continuous 29 100 0.27 25 0.87 0.82 1.91 2.4 49 Comparative example 2 28 5 Intermittent thirty 100 0.17 26 0.87 0.72 1.91 7.3 49 Example according to the invention 3 5 4 Continuous 31 80 0.17 27 0.86 0.73 1.91 6.9 49 Example according to the invention 4 8 8 Continuous 37 90 0.22 32 0.87 0.74 1.91 8.1 51 Example according to the invention 5 10 5 Continuous 41 160 0.22 34 0.83 0.73 1.91 10.4 55 Example according to the invention 6 18 6 Intermittent 41 170 0.22 35 0.84 0.72 1.91 10.5 55 Example according to the invention 7 17 8 Continuous 44 190 0.22 37 0.84 0.72 1.90 10.8 56 Example according to the invention 8 22 5 Continuous 45 200 0.22 38 0.84 0.71 1.91 12.2 58 Example according to the invention 9 10 9 Intermittent 24 200 0.27 20 0.84 0.82 1.92 2.4 51 Comparative example 10 15 3 Continuous 45 105 0.17 35 0.78 0.70 1.90 10.4 54 Example according to the invention eleven 3 5 Continuous 41 125 0.27 34 0.82 0.76 1.91 9.4 54 Example according to the invention 12 3 4 Continuous 35 150 0.17 29 0.83 0.71 1.91 9.6 53 Example according to the invention 13 9 7 Intermittent 54 120 0.17 26 0.48 0.68 1.90 12.4 58 Example according to the invention 14 20 6 Continuous 28 130 0.27 24 0.86 0.83 1.92 1.2 48 Comparative example 15 5 4 Continuous thirty 200 0.17 28 0.93 0.73 1.91 6.9 61 Comparative example 16 1 7 Continuous 34 190 0.22 thirty 0.89 0.73 1.91 10.0 54 Example according to the invention 17 1 3 Intermittent 50 140 0.22 23 0.46 0.71 1.90 11.9 58 Example according to the invention 18 20 5 Intermittent 53 165 0.22 25 0.47 0.71 1.90 12.4 58 Example according to the invention 19 10 6 Intermittent 63 135 0.27 31 0.49 0.74 1.90 12.2 61 Comparative example 20 10 8 Continuous 31 197 0.17 27 0.88 0.70 1.91 10.5 55 Example according to the invention 21 22 7 Continuous 62 180 0.27 29 0.47 0.73 1.89 13.2 63 Comparative example 22 1 10 Continuous 57 200 0.17 25 0.44 0.66 1.90 14.8 59 Example according to the invention 23 1 12 Continuous 56 200 0.17 25 0.45 0.75 1.91 3.8 53 Comparative example 24 3 7 Continuous 34 50 0.22 23 0.67 0.73 1.90 9.9 57 Example according to the invention 25 6 5 Continuous 61 50 0.22 thirty 0.49 0.71 1.90 12.3 61 Comparative example 26 15 3 Continuous 29 225 0.17 22 0.76 0.65 1.90 16.7 61 Comparative example 27 3 5 Intermittent 60 200 0.22 28 0.47 0.72 1.90 10.4 59 Example according to the invention 28 3 4 Continuous 10 20 0.22 3 0.30 0.73 1.90 1.5 48 Comparative example 29 4 5 Continuous 63 200 0.22 32 0.51 0.71 1.91 15.0 63 Comparative example

[0075] As can be seen from Table 1 and Table 2, in the examples of the present invention, the dimensions of the capping domain (d and w) and the m/d ratio of the depth m from the surface of the base steel sheet, where the compressive strain present in the capping domain in the rolling direction exhibited a maximum value , to length d were within the scope of the present invention. As a result, the magnetic performance was excellent, the magnetic loss improvement factors were also high, and the noise performance was excellent. On the other hand, in the comparative examples, the sizes of the tail domain or the m/d ratio were outside the scope of the present invention. As a result, at least one of the improvement ratios of magnetic loss and noise performance was poor.

[0076] In steel sheet No. 1, the input energy of the energy beam Up was low, and in steel sheet No. 14, the power density of the energy beam Ip was low, and the lengths of the closing domains in the thickness direction of the sheet were not sufficient. As a result, the magnetic loss improvement factors did not reach 5.0%.

In the No. 9 steel sheet, the input energy of the energy beam Up was large, but the power density of the energy beam Ip was low, and therefore the length of the closing domain in the thickness direction of the sheet was not sufficient. As a result, the magnetic loss improvement factors did not reach 5.0%.

In the No. 15 steel sheet, the energy beam power density Ip was low and the m/d ratio was large. As a result, the noise performance was poor.

In the No. 19 steel sheet, the input energy of the Up energy beam was too large, and therefore the length of the capping domain in the thickness direction of the sheet was too long. As a result, the noise performance was poor.

In the No. 21 steel sheet, the power density of the energy beam Ip was too high, and therefore the length of the closing domain in the thickness direction of the sheet was too long. As a result, the noise performance was poor.

In steel sheet No. 23, the interval in the rolling direction of adjacent linear deformations exceeded 10 mm. As a result, the magnetic loss improvement factors did not reach 5.0%.

In the No. 25 steel sheet, the input energy of the energy beam Up was small, the power density of the energy beam Ip was high, and the length of the closing domain in the thickness direction of the sheet was too long. As a result, the noise performance was poor.

In the No. 26 steel sheet, the length of the energy beam irradiation mark in the rolling direction was too long, and the length of the capping domain in the rolling direction exceeded 200 μm. As a result, the noise performance was poor.

In the No. 28 steel sheet, the aspect ratio of the energy beam irradiation mark was too small, sufficient energy beam irradiation effect could not be obtained due to the influence of heat generation, and the length of the closing domain in the thickness direction of the sheet was not sufficient. As a result, the magnetic loss improvement factors did not reach 5.0%.

In the No. 29 steel sheet, the aspect ratio of the energy beam irradiation mark was too large, and the length of the capping domain in the thickness direction of the sheet was too long. As a result, the noise performance was poor.

INDUSTRIAL APPLICABILITY

[0077] According to the present invention, it is possible to provide an anisotropic electrical steel sheet having excellent magnetic loss characteristics and noise characteristics, as well as a production method thereof. Therefore, the present invention has high industrial applicability.

BRIEF DESCRIPTION OF REFERENCE SYMBOLS

[0078] ND: vertical direction to the sheet surface

TD: direction along the sheet width

RD: rolling direction

S: surface

SPR: area where banding pattern is observed

EIrD: energy beam irradiation direction

Claims (19)

1. An anisotropic electrical steel sheet containing: main steel sheet; a glass coating formed on a base steel sheet; And a tensile insulating coating formed on the glass cover, wherein a plurality of linear deformations are present in the base steel sheet, which extend continuously or discontinuously in a direction intersecting with the rolling direction, the intervals in the rolling direction of a plurality of linear deformations adjacent to each other are 10 mm or less, in the area where deformation is present, there is a closing domain, the length d of the closing domain in the sheet thickness direction from the surface of the main steel sheet is 30-60 μm, the length w of the closing domain in the rolling direction is 200 μm or less, the m/d ratio of the depth m from the surface of the main steel sheet, where the compressive strain present in the closing domain in the rolling direction exhibits a maximum value, to said length d is in the range of more than 0.30 and less than 0.90, and the chemical composition of the base steel sheet contains, wt.%: C: 0.010 or less, Si: 3.00-4.00, Mn: 0.01-0.50, N: 0.010 or less, sol. Al: 0.020 or less, S: 0.010 or less, P: 0.030 or less, Cr: 0-0.50, Sn: 0-0.50, Cu: 0-0.50, Se: 0-0.020, Sb: 0-0.50, Mo: 0-0.10, and the rest is Fe and impurities. 2. A method for producing anisotropic electrical steel sheet according to claim 1, including: a step of segmenting magnetic domains with respect to an anisotropic electrical steel sheet including a base steel sheet, a glass coating formed on the base steel sheet, and a tension-imposing insulating coating formed on the glass coating, irradiating the surface of the tension-imposing insulating coating with an energy beam to introduce a plurality of linear deformations that extend in a direction intersecting with the rolling direction in the vicinity of the surface of the base steel sheet, wherein at the stage of magnetic domain segmentation, among the plurality of linear deformations, the intervals in the rolling direction of linear deformations adjacent to each other are 10 mm or less, The energy beam power density Ip in units of W/ ^mm2 , which is defined as (P/S) using the energy beam output power P in units of W and the irradiated energy beam cross-sectional area S in units of ^mm2 , satisfies the following expression (1), the energy beam input energy Up in units of J/mm, which is defined as (P/Vs) using the energy beam output power P and the energy beam scanning speed Vs in units of mm/s, satisfies the following expression (2), and beam size ratio, which is defined as (dl/dc) using the diameter dl in the direction perpendicular to the beam scanning direction and the diameter dc in the beam scanning direction of the energy beam in units of μm, and dl satisfy respectively the following expression (3) and the following expression ( 4): 250 ≤ Ip ≤ 5200 (1); 0.007 < Up ≤ 0.050 (2); 0.0010 < dl/dc < 1.0000 (3); 10 ≤ dl < 200 (4).