Grain-oriented electrical steel sheet and method for manufacturing the same

Abstract

The oriented electromagnetic steel sheet of the present application has a base steel sheet having a prescribed chemical composition, a glass coating formed on the base steel sheet, and a tension imparting insulating coating formed on the glass coating, on the surface of the base steel sheet, a plurality of linear strains continuously or intermittently extending in a direction intersecting the rolling direction exist, the interval p of the plurality of linear strains adjacent to each other in the rolling direction is 3.0 to 9.0 mm, the width of the linear strain is 10 to 250 μm, in an X-ray topography spectrum in a range of 1.50 mm in the rolling direction obtained from an X-ray topography image of the surface with the linear strain as the center, the half-value width of the peak of the X-ray topography spectrum containing the maximum value of the spectral intensity is 0.02 mm or more and 0.10 mm or less.

Description

Technical Field

[0001] This invention relates to directional electromagnetic steel sheets and their manufacturing methods.

[0002] This application claims priority based on Japanese Patent Application No. 2021-053618 filed on March 26, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Directional electromagnetic steel sheets are soft magnetic materials, primarily used as core materials for transformers. Therefore, directional electromagnetic steel sheets require magnetic properties such as high magnetization and low iron loss.

[0004] Iron loss refers to the electrical energy loss that is consumed as heat when the iron core is energized in an alternating magnetic field. From an energy-saving perspective, iron loss should be as low as possible. Factors affecting iron loss include magnetic susceptibility, plate thickness, film tension, impurity content, resistivity, grain size, and magnetic domain size. Even with current advancements in various technologies, research and development to reduce iron loss continues to improve energy conversion efficiency for directional electromagnetic steel sheets.

[0005] For example, Patent Document 1 discloses a method for manufacturing a directional electromagnetic steel sheet whose magnetic domains are controlled by laser irradiation. The method is characterized by the following steps: irradiating the surface of the directional electromagnetic steel sheet with a focused continuous-wave laser while scanning it along a direction inclined from the rolling direction of the sheet; and repeatedly performing the scanning of the continuous-wave laser at predetermined intervals. The average power of the continuous-wave laser is expressed as P (W), the scanning speed as Vc (mm / s), the predetermined interval as PL (mm), and the average irradiation energy density Ua is defined as Ua = P / (Vc × PL) (mJ / mm). 2 When ), it satisfies 1.0mm≤PL≤3.0mm and 0.8mJ / mm 2 ≤Ua≤2.0mJ / mm 2 .

[0006] Patent Document 1 demonstrates that it is possible to easily and ensure high productivity while reducing iron loss in both the L and C directions of the directional electromagnetic steel sheet.

[0007] Furthermore, Patent Document 2 discloses a method for manufacturing a directional electromagnetic steel sheet, wherein iron loss characteristics are improved by scanning and irradiating with a continuously oscillating laser beam to form linear closed magnetic domains that are approximately perpendicular to the rolling direction of the steel sheet and at approximately a certain interval.

[0008] Regarding Patent Document 2, it shows that the laser intensity distribution in the cross-section perpendicular to the beam propagation direction has the maximum intensity near the optical axis center for TEM 00 mode. For the converging diameter d [mm] of the irradiation beam in the rolling direction, the scanning line speed V [mm / s] of the laser beam, and the average output power P [W] of the laser, in the range of 0 < d ≤ 0.2 and 0.001 ≤ P / V ≤ 0.012, a grain-oriented electrical steel sheet with reduced iron loss can be obtained.

[0009] In addition, in Patent Document 3, a method for manufacturing a grain-oriented electrical steel sheet is disclosed, in which laser beams are irradiated on the surface of the grain-oriented electrical steel sheet at equal intervals to improve the magnetic properties.

[0010] Regarding Patent Document 3, the laser is a pulsed oscillation Q-switch CO2 laser, and the irradiation beam shape is an ellipse having a long axis in the plate width direction. In addition, it is shown that by setting the irradiation power density of the laser pulse below the film damage threshold of the steel sheet surface, the generation of laser irradiation marks is suppressed, and by setting the long axis length of the elliptical beam to be longer than the pulse beam irradiation interval in the plate width direction, continuous pulse beams are overlapped on the steel sheet surface, and the cumulative irradiation energy necessary and sufficient for improving the magnetic properties is given, and the laser irradiation marks are suppressed, thereby obtaining an effective magnetic domain control effect.

[0011] On the other hand, in recent years, there has been an increasing demand for reducing noise and vibration in electromagnetic application devices such as transformers. For the grain-oriented electrical steel sheet used in the iron core of a transformer, a material with low iron loss and suitable for low noise and low vibration is required. As one of the reasons for noise and vibration in the raw materials of transformers, magnetic strain of the grain-oriented electrical steel sheet is said to exist. Here, the so-called magnetic strain is the vibration seen in the rolling direction of the grain-oriented electrical steel sheet caused by a slight change in the shape of the grain-oriented electrical steel sheet accompanying the change in the magnetization intensity when the grain-oriented electrical steel sheet is excited with alternating current. The magnitude of this magnetic strain is a very small value on the order of 10 -6 order, but this magnetic strain causes vibration in the iron core, and it propagates in external structures such as the transformer tank and becomes noise.

[0012] Although laser irradiation on the grain-oriented electrical steel sheet as proposed in the above Patent Documents 1 to 3 is effective for reducing iron loss, there is the following problem: the closed magnetic domains formed by the strain imparted by laser irradiation increase the magnetic strain, resulting in deteriorated noise characteristics.

[0013] Regarding such a problem, for example, in Patent Document 4, a grain-oriented electrical steel sheet with low iron loss and low noise when incorporated into a transformer is disclosed.

[0014] Regarding Patent Document 4, it is shown that by forming closed magnetic domain regions with periodically varying widths in the rolling direction on the surface of a steel plate, each of the aforementioned closed magnetic domain regions satisfies the following conditions: the ratio of the maximum width Wmax to the minimum width Wmin in the rolling direction on the surface of the steel plate (Wmax / Wmin) is 1.2 or more and 2.2 or less; the average width Wave in the rolling direction on the surface of the steel plate is 80 μm or more and 250 μm or less; the maximum depth D in the thickness direction is 32 μm or more; and (Wave×D) / s is 0.0007 mm or more and 0.0016 mm or less, a better iron loss / noise balance than before can be achieved.

[0015] Furthermore, Patent Document 5 discloses a directional electromagnetic steel sheet, which is a directional electromagnetic steel sheet with localized strain introduced at periodic intervals relative to the rolling direction and in the direction transverse to the rolling direction. Linear closed magnetic domains are formed near the strain, and in the demagnetized state, magnetic domains with a rolling direction length of 1.2 mm or more extending from the closed magnetic domains along the rolling direction are formed. Moreover, an average of 1.8 or more magnetic domains are formed per 1 mm in the region along the closed magnetic domains. When the line interval of the closed magnetic domains is set to s (mm), the width of the closed magnetic domains: w (mm) and the depth of the closed magnetic domains in the plate thickness direction: h (μm) satisfy the relationship 4mm≤s≤1.5mm and hw / s≤0.9μm.

[0016] Patent document 5 suggests that the strain input index, expressed in hw / s, affects iron loss and noise.

[0017] However, the inventors' research has shown that, with respect to the technology in Patent Documents 4 and 5, the improvement in noise characteristics is not sufficient for the better iron loss / noise balance required in recent years.

[0018] Furthermore, as a technique for controlling closed magnetic domains, patent documents 6 and 7 disclose a method for manufacturing directional electromagnetic steel sheets that forms closed magnetic domains without damaging the coating, providing directional electromagnetic steel sheets with extremely low transformer iron loss and BF.

[0019] Furthermore, Patent Document 8 shows that by forming a closed magnetic domain shape that is advantageous for reducing iron loss by utilizing the characteristics of an electron beam, a directional electromagnetic steel sheet with low iron loss can be obtained over a wide range of sheet thicknesses.

[0020] Furthermore, Patent Document 9 discloses a directional electromagnetic steel plate for iron core, which has linear strain formed by an electron beam emitted from LaB6 in a direction of 60° to 120° relative to the rolling direction in the steel plate surface.

[0021] Furthermore, Patent Document 10 discloses a directional electromagnetic steel plate with excellent insulation and corrosion resistance, which controls the area ratio of beam irradiation marks in the beam irradiation domain, and a method for manufacturing the same.

[0022] However, Patent Documents 6-10 are all techniques for controlling closed magnetic domains to reduce iron losses or for improving the coating characteristics associated with closed magnetic domain control; they do not address closed magnetic domain control for achieving low noise. Therefore, regarding the techniques in Patent Documents 6-10, the improvement in noise characteristics is insufficient for the increasingly demanding iron loss / noise balance required in recent years.

[0023] Existing technical documents

[0024] Patent documents

[0025] Patent Document 1: Japanese Patent No. 4669565

[0026] Patent Document 2: Japanese Patent No. 4510757

[0027] Patent Document 3: Japanese Patent No. 3361709

[0028] Patent Document 4: Japanese Patent No. 6060988

[0029] Patent Document 5: Japanese Patent No. 6176282

[0030] Patent Document 6: Japanese Patent No. 6169695

[0031] Patent Document 7: Japanese Patent No. 6245296

[0032] Patent Document 8: International Publication No. 2014 / 068962

[0033] Patent Document 9: Japanese Patent No. 5954421

[0034] Patent Document 10: International Publication No. 2013 / 099272 Summary of the Invention

[0035] The problem that the invention aims to solve

[0036] As mentioned above, there has been no previously disclosed directional electromagnetic steel sheet and its manufacturing method that simultaneously and sufficiently improves both iron loss characteristics and noise characteristics.

[0037] The objective of this invention is to provide a directional electromagnetic steel sheet with excellent iron loss characteristics, particularly the iron loss improvement rate before and after magnetic domain control, and a method for manufacturing the same.

[0038] Methods for solving problems

[0039] Directional electromagnetic steel sheets are irradiated with energy beams such as laser beams or electron beams, causing the irradiated area to be rapidly heated and cooled. As a result, residual strain (thermal strain) is generated within the steel sheet near the irradiated area. If this residual strain is compressive strain in the rolling direction or tensile strain in the thickness direction, closed magnetic domains are generated in the region where this residual strain occurs. The formation of these closed magnetic domains generates leakage magnetic flux on the steel sheet surface, increasing the static magnetic energy. This high static magnetic energy state is energy unstable. Therefore, the magnetic domain structure of the steel sheet changes to a structure with reduced leakage magnetic flux. This structure with reduced leakage magnetic flux refers to a state with more 180° domain walls (parallel / anti-parallel to the rolling direction), known as "domain subdivision." This domain subdivision reduces abnormal eddy current losses, thus energy beam irradiation is beneficial for reducing iron losses. However, generally, if closed magnetic domains are formed, the degree of magnetic strain increases, thus increasing noise when integrated into transformers, etc.

[0040] The inventors investigated the relationship between irradiation conditions such as laser beams or electron beams and iron loss and noise characteristics. The results showed that while reducing the input energy of the laser beam or electron beam improved noise characteristics, insufficient magnetic domain control and inadequate improvement in iron loss characteristics occurred under these conditions.

[0041] Therefore, the inventors further investigated a method for improving iron loss characteristics without deteriorating noise characteristics. The results showed that, during the manufacturing process, by controlling the irradiation conditions of laser beams or electron beams, and the decarburization annealing conditions, sufficient magnetic domain subdivision can be achieved even with low input energy of the laser beams or electron beams, thus achieving both low iron loss and low noise after irradiation.

[0042] This invention is made in view of the above-mentioned insights. The main points of this invention are as follows.

[0043] [1] One embodiment of the directional electromagnetic steel plate of the present invention comprises a base steel plate, a glass film formed on the base steel plate, and a tension-imparting insulating film formed on the glass film. The base steel plate comprises, by mass%, 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, P: 0.030% or less, S: 0.010% or less, Sn: 0-0.50%, Cu: 0-0.50%, Cr: 0-0.50%, Se: 0-0.020%, Sb: 0-0.500%, Mo: 0- 0.10%, the remainder: chemical composition of Fe and impurities. On the surface of the above-mentioned base steel plate, there are multiple linear strains that extend continuously or intermittently in a direction intersecting with the rolling direction. The interval p between the multiple linear strains that are adjacent to each other in the rolling direction is 3.0 to 9.0 mm. The width of the linear strains is 10 to 250 μm. In the X-ray morphology spectrum obtained from the surface X-ray morphology image, in a range of 1.50 mm in the rolling direction with the linear strains as the center, the half-width of the peak of the X-ray morphology spectrum containing the maximum value of the spectral intensity is 0.02 mm or more and 0.10 mm or less.

[0044] [2] According to the directional electromagnetic steel sheet described in [1], wherein an X-ray beam is irradiated over a range of 3.0 mm in the rolling direction centered on the linear strain of the surface described above, and the minimum value of the X-ray reflection intensity of the (310) surface is set to I. min The background intensity is set to I0, and an X-ray beam is irradiated over a 3.0 mm area in the rolling direction centered on the linear strain on the back side. The minimum value of the X-ray reflection intensity of the resulting diffraction surface (310) is set to J. min When the background intensity is set to J0, the above I min The above I0, the above J min The above J0 can also satisfy the following equation (2).

[0045] 0.02≤|J0-J min | / |I0-I min |≤1.00(2)

[0046] [3] According to the directional electromagnetic steel sheet described in [1] or [2], the above chemical composition of the above-mentioned base steel sheet may also include any one or both of Sn: 0.01 to 0.50% and Cu: 0.05 to 0.50%.

[0047] [4] Another aspect of the present invention is a method for manufacturing a directional electromagnetic steel plate as described in [1] or [2], which includes the following steps: manufacturing a directional electromagnetic steel plate containing, by mass %: C: 0.010–0.200%, Si: 3.00–4.00%, Mn: 0.01–0.50%, N: less than 0.020%, Sol.Al: 0.010–0.040%, P: less than 0.030%, S: 0.005–0.040%, ... The steel billet, with a chemical composition of Sn: 0-0.50%, Cu: 0-0.50%, Bi: 0-0.020%, Cr: 0-0.50%, Se: 0-0.020%, Sb: 0-0.500%, Mo: 0-0.10%, and the remainder being Fe and impurities, is heated and then hot-rolled to obtain a hot-rolled steel plate. The hot-rolled steel plate is then subjected to a hot-rolled annealing process. Finally, the hot-rolled steel plate after the annealing process undergoes a single or intermediate... The process includes: a cold rolling process for obtaining cold-rolled steel sheets by multiple cold rolling processes involving intermittent annealing; a decarburizing annealing process for decarburizing the cold-rolled steel sheets; a finished product annealing process for forming a glass film by coating the front and back surfaces of the cold-rolled steel sheets (which serve as the base steel sheets) with an annealing separating agent with MgO as the main component, drying them, and then performing finished product annealing; a film forming process for obtaining a directional electromagnetic steel sheet having the base steel sheet, a glass film formed on the base steel sheet, and a tension-imparting insulating film formed on the glass film; and a magnetic domain subdivision process for irradiating the surface of the tension-imparting insulating film of the directional electromagnetic steel sheet with energy rays to impart multiple linear strains to the base steel sheet, wherein in the magnetic domain subdivision process, the rolling direction interval of adjacent linear strains among the multiple linear strains is 3.0 to 9.0 mm, and the energy ray output power P in W and mm are used. 2 The calculated energy ray irradiation cross-sectional area S is defined by (P / S) in units of W / mm². 2The calculated energy ray power density Ip satisfies the following equation (3). Using the above-mentioned energy ray output power P and energy ray scanning speed Vs in mm / s, the energy ray input energy Up in J / mm defined by (P / Vs) satisfies the following equation (4). Furthermore, using the above-mentioned energy ray diameter dl in μm perpendicular to the beam scanning direction and the above-mentioned beam scanning direction diameter dc, the beam aspect ratio defined by (dl / dc) and the above-mentioned dl respectively satisfy the following equations (5) and (6). In the above-mentioned decarburization annealing process, the heating rate S1 in the first temperature range of 550 to 750°C is set to 500°C / s or more, the heating rate S2 in the second temperature range of 750 to 800°C is set to 800°C / s or more, or the heating rate S2 in the second temperature range is set to 50°C / s or more, and the atmosphere dew point in the second temperature range is set to -50°C to 20°C.

[0048] 250≤Ip≤2000(3)

[0049] 0.005 <Up≤0.050(4)

[0050] 0.001 <dl / dc<1.000(5)

[0051] 10≤dl<200(6)

[0052] [5] In the manufacturing method of the directional electromagnetic steel sheet according to [4], a nitriding treatment process for nitriding the cold-rolled steel sheet may be further provided between the above-mentioned decarburization annealing process and the above-mentioned finished product annealing process.

[0053] [6] In the method for manufacturing directional electromagnetic steel sheet according to [4] or [5], the above chemical composition of the steel billet may also include any one or both of Sn: 0.01 to 0.50% and Cu: 0.05 to 0.50%.

[0054] Invention Effects

[0055] According to the above-described solution of the present invention, a directional electromagnetic steel sheet with excellent iron loss characteristics and noise characteristics, and a method for manufacturing the same, can be provided. Attached Figure Description

[0056] Figure 1 It is a diagram representing the geometry of X-ray morphology measurements.

[0057] Figure 2 This is a diagram representing an example of image data showing X-ray topography.

[0058] Figure 3 This is a diagram showing an example of the distribution curve (line profile) of the intensity of reflected diffracted X-rays.

[0059] Figure 4 This is a diagram illustrating the dynamic diffraction based on multiple scattering in X-ray diffraction.

[0060] Figure 5 This diagram illustrates the kinematic and kinetic diffraction processes in X-ray diffraction. Detailed Implementation

[0061] A directional electromagnetic steel sheet according to one embodiment of the present invention (the directional electromagnetic steel sheet of this embodiment) comprises a base steel sheet having a predetermined chemical composition, a glass film formed on the base steel sheet, and a tension-imparting insulating film formed on the glass film.

[0062] Furthermore, on the surface of the base steel plate, a plurality of linear strains (thermal strains) are formed in a direction that is approximately parallel to the rolling direction and extends continuously or intermittently in a direction that intersects the rolling direction, or more specifically, at an angle (φ) of 60 to 120° relative to the rolling direction. The interval (p) between the plurality of adjacent linear strains in the rolling direction is 3.0 to 9.0 mm, and the width (length in the direction orthogonal to the extension direction) of each of the plurality of linear strains, as determined by X-ray morphology, is 10 to 250 μm.

[0063] Furthermore, in the directional electromagnetic steel sheet of this embodiment, in the X-ray morphology spectrum obtained from the surface X-ray morphology image, within a range of 1.50 mm in the rolling direction centered on the linear strain (a range of ±0.75 mm in the rolling direction from the linear strain), the half-width of the peak of the X-ray morphology spectrum containing the maximum value of the spectral intensity is 0.02 mm or more and 0.10 mm or less.

[0064] The directional electromagnetic steel plate of this embodiment will be described below.

[0065] <Base Material Steel Plate>

[0066] (Chemical composition)

[0067] The directional electromagnetic steel sheet of this embodiment exhibits significant characteristics in its linear strain state, and the chemical composition of the base steel sheet used in the directional electromagnetic steel sheet is not limited. However, in order to obtain the characteristics generally required for directional electromagnetic steel sheets, the following ranges are set. In this embodiment, the percentages (%) of each element are (%) unless otherwise specified.

[0068] C: Below 0.010%

[0069] Carbon (C) is an element effective in controlling the microstructure of steel sheets during the manufacturing process up to the completion of the decarburization annealing process. However, if the C content exceeds 0.010%, the magnetic properties (iron loss characteristics, magnetic flux density) of the directional electromagnetic steel sheet used as the finished product decrease. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the C content is set to 0.010% or less. The C content is preferably 0.005% or less. The lower the C content, the better, but even if the C content is reduced to less than 0.0001%, the effect of microstructure control saturates, resulting only in increased manufacturing costs. Therefore, the C content can also be set to 0.0001% or more.

[0070] Si: 3.00~4.00%

[0071] Silicon (Si) is an element that increases the resistance of directional electromagnetic steel sheets and improves iron loss characteristics. When the Si content is below 3.00%, a sufficient reduction in eddy current losses cannot be achieved. Therefore, the Si content is set to 3.00% or more. The Si content is preferably 3.20% or more, and more preferably 3.50% or more.

[0072] On the other hand, if the Si content exceeds 4.00%, the directional electromagnetic steel sheet becomes brittle, and its through-sheet properties deteriorate significantly. Furthermore, the machinability of the directional electromagnetic steel sheet decreases, and the sheet may break during rolling. Therefore, the Si content is set to 4.00% or less. Preferably, the Si content is 3.80% or less, and more preferably 3.70% or less.

[0073] In steel billets such as slabs, some of the silicon (Si) is sometimes consumed in the formation of a glass coating with Mg2SiO4 as the main component. Therefore, the Si content in directional electromagnetic steel sheets can be reduced compared to when the steel is tapped.

[0074] Mn: 0.01~0.50%

[0075] Manganese (Mn) is an element that combines with sulfur (S) during the manufacturing process to form MnS. This precipitate functions as an inhibitor (an inhibitor of normal grain growth) and exhibits secondary recrystallization in steel. Mn also improves the hot workability of steel. When the Mn content is below 0.01%, the aforementioned effects cannot be sufficiently obtained. Therefore, the Mn content is set to 0.01% or more. The Mn content is preferably 0.02% or more, and more preferably 0.05% or more.

[0076] On the other hand, if the Mn content exceeds 0.50%, secondary recrystallization will not occur, and the magnetic properties of the steel will decrease. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the Mn content is set to 0.50% or less. The Mn content is preferably 0.20% or less, and more preferably 0.10% or less.

[0077] N: below 0.010%

[0078] Nitrogen (N) is an element that combines with Al during the manufacturing process to form AlN, which functions as an inhibitor. However, if the N content exceeds 0.010%, the magnetic properties decrease due to the excessive residual inhibitor in the base steel sheet. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the N content is set to 0.010% or less. The N content is preferably 0.008% or less, and more preferably 0.005% or less.

[0079] On the other hand, there is no specific lower limit for nitrogen content, but even if it is reduced to below 0.0001%, it only increases manufacturing costs. Therefore, the nitrogen content can also be set to above 0.0001%.

[0080] Sol.Al: 0.020% or less

[0081] Sol.Al (acid-soluble aluminum) is an element that combines with nitrogen (N) during the manufacturing process to form AlN, which functions as an inhibitor. However, if the Sol.Al content in the base steel sheet exceeds 0.020%, the magnetic properties decrease due to the excessive residual inhibitor in the base steel sheet. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the Sol.Al content is set to 0.020% or less. The Sol.Al content in the directional electromagnetic steel sheet is preferably as low as possible. For example, the Sol.Al content is 0.010% or less, or less than 0.001%, or even 0%.

[0082] On the other hand, there is no specific lower limit for the Sol.Al content, but even if it is reduced to below 0.0001%, it only increases the manufacturing cost. Therefore, the Sol.Al content can also be set to above 0.0001%.

[0083] P: below 0.030%

[0084] Phosphorus (P) is an element that reduces workability during rolling. By setting the P content to 0.030% or less, excessive reduction in rolling workability can be prevented, and breakage during manufacturing can be suppressed. From this point of view, the P content is set to 0.030% or less. The P content is preferably 0.020% or less, and more preferably 0.010% or less.

[0085] There is no lower limit to the phosphorus (P) content; it can include 0%. However, since the detection limit for chemical analysis is 0.0001%, the substantive lower limit for P content in practical steel plates is 0.0001%. Furthermore, P is also an element that improves texture and magnetic properties. To achieve this effect, the P content can be set to 0.001% or higher, or 0.005% or higher.

[0086] S: below 0.010%

[0087] Sulfur (S) is an element that combines with Mn during the manufacturing process to form MnS, which functions as an inhibitor. However, when the S content exceeds 0.010%, the magnetic properties decrease due to the excessive residual inhibitor. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the S content is set to 0.010% or less. The S content in the directional electromagnetic steel sheet is preferably as low as possible. For example, it can be less than 0.0001%, or even 0%. However, even if the S content in the base steel sheet of the directional electromagnetic steel sheet is reduced to less than 0.0001%, only the manufacturing cost increases. Therefore, the S content can also be 0.0001% or more.

[0088] Remaining components: Fe and impurities

[0089] The chemical composition of the base steel plate of the directional electromagnetic steel plate in this embodiment may also contain the aforementioned essential elements, with the remainder being Fe and impurities. However, for the purpose of improving magnetic properties, Sn, Cu, Cr, Se, Sb, and Mo may be included as optional elements within the ranges shown below. These elements are also permitted to be included as impurities.

[0090] Furthermore, other than these elements, such as the presence of any one or two or more of W, Nb, Bi, Ti, Ni, Co, and V totaling less than 1.0%, will not hinder the effect of the directional electromagnetic steel plate of this embodiment.

[0091] Here, impurities refer to elements that are introduced into the raw materials, such as ores, waste, or the manufacturing environment, during the industrial manufacturing of the base steel plate. These are elements whose content is permissible and does not adversely affect the function of the directional electromagnetic steel plate of this embodiment.

[0092] Sn: 0-0.50%

[0093] Sn (tin) is an element that increases Goss orientation and is effective in refining secondary recrystallized grains. If the secondary recrystallized grains are small, sufficient improvement in iron loss can be achieved even with low energy input during domain refinement. To achieve this effect, it is preferable to set the Sn content to 0.01% or more. More preferably, the Sn content is 0.02% or more, and even more preferably 0.03% or more. However, the presence of Sn raises concerns about a decrease in the occupancy of the Goss orientation in the secondary recrystallized structure. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, when Sn is present, it is preferable to include it simultaneously with Cu, as described later.

[0094] On the other hand, when the Sn content exceeds 0.50%, secondary recrystallization becomes unstable, and the magnetic properties deteriorate. Therefore, even when Sn is present, the Sn content is set to be 0.50% or less. The Sn content is preferably 0.30% or less, and more preferably 0.20% or less.

[0095] Cu: 0–0.50%

[0096] Cu (copper) is an element that contributes to increasing the proportion of Goss orientation in secondary recrystallization structures. To achieve the above-mentioned effects, it is preferable to set the Cu content to 0.05% or more. More preferably, the Cu content is 0.06% or more, and even more preferably 0.07% or more.

[0097] On the other hand, when the Cu content exceeds 0.50%, the steel sheet becomes brittle during hot rolling. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, even if it contains Cu, the Cu content is set to 0.50% or less. The Cu content is preferably 0.30% or less, and more preferably 0.20% or less.

[0098] Cr: 0–0.50%

[0099] Chromium (Cr) is an element that improves magnetic properties. Although the reason is unclear, it is believed to have effects such as increasing the proportion of Goss orientation in secondary recrystallization structures, thereby improving magnetic properties. To obtain the above effects, it is preferable to set the Cr content to 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.

[0100] On the other hand, when the Cr content exceeds 0.50%, Cr oxide will form, reducing magnetic properties. Therefore, even when it is present, the Cr content is set to 0.50% or less. The Cr content is preferably 0.30% or less, and more preferably 0.10% or less.

[0101] Se: 0~0.020%

[0102] Selenium (Se) is an element that improves magnetic properties. Therefore, it may be included in the composition of the element. When Se is included, it is preferable to set the Se content to 0.001% or more in order to effectively improve magnetic properties. More preferably, the Se content is 0.003% or more, and even more preferably 0.006% or more.

[0103] On the other hand, if the Se content exceeds 0.020%, the adhesion of the glass coating deteriorates. Therefore, even when it is present, the Se content is set to 0.020% or less. The Se content is preferably 0.015% or less, and more preferably 0.010% or less.

[0104] Sb: 0~0.500%

[0105] Antimony (Sb) is an element that improves magnetic properties. Therefore, it may be included in the composition of Sb. When Sb is included, it is preferable to set the content to 0.005% or more in order to effectively improve magnetic properties. More preferably, the Sb content is 0.010% or more, and even more preferably 0.020% or more.

[0106] On the other hand, if the Sb content exceeds 0.500%, the adhesion of the glass coating deteriorates significantly. Therefore, even when Sb is present, the Sb content is set to 0.500% or less. The Sb content is preferably 0.300% or less, and more preferably 0.100% or less.

[0107] Mo: 0–0.10%

[0108] Mo (molybdenum) is an element that improves magnetic properties. Therefore, it may be included in the composition of the element. When Mo is included, it is preferable to set the Mo content to 0.01% or more in order to effectively improve the magnetic properties. More preferably, the Mo content is 0.02% or more, and even more preferably 0.03% or more.

[0109] On the other hand, if the Mo content exceeds 0.10%, cold rollability may deteriorate, leading to breakage. Therefore, even when it is present, the Mo content is set to 0.10% or less. The Mo content is preferably 0.08% or less, and more preferably 0.05% or less.

[0110] As described above, the chemical composition of the base steel plate of the directional electromagnetic steel plate of this embodiment contains the aforementioned essential elements and the remaining portion contains Fe and impurities, or contains the aforementioned essential elements, further contains one or more optional elements, and the remaining portion contains Fe and impurities.

[0111] The chemical composition of the base steel plate of the directional electromagnetic steel plate in this embodiment can be measured after removing the glass film formed on the surface and the tension-imposed insulating film.

[0112] Specifically, the tension-imparting insulating film is removed by immersing the directional electromagnetic steel sheet in an aqueous sodium hydroxide solution at 80-90°C containing 30-50% NaOH and 50-70% H2O for 7-10 minutes. The directional electromagnetic steel sheet after removing the tension-imparting insulating film is then washed with water and dried using a warm air blower for less than 1 minute. The dried directional electromagnetic steel sheet (without the tension-imparting insulating film) is then immersed in an aqueous hydrochloric acid solution containing 30-40% HCl at 80-90°C for 1-10 minutes to remove the glass film. The immersed base steel sheet is then washed with water and dried using a warm air blower for less than 1 minute.

[0113] Through the above procedures, the base steel plate can be removed from the directional electromagnetic steel plate.

[0114] The chemical composition of the base steel plate is determined using well-known compositional analysis methods. Specifically, a drill bit is used to generate powder from the base steel plate, which is then collected and dissolved in acid to obtain a solution. ICP-AES is then performed on the solution to perform elemental analysis of its chemical composition.

[0115] Here, the Si content in the chemical composition of the base steel plate is determined using the method specified in JIS G 1212 (1997) (quantitative method for silicon). Specifically, if the above-mentioned shredded material is dissolved in acid, silicon oxide precipitates out as a precipitate. Therefore, the precipitate (silicon oxide) is filtered with filter paper, its mass is measured, and the Si content is determined.

[0116] The C and S contents are determined using the well-known high-frequency combustion method (combustion-infrared absorption method). Specifically, the solution is burned in an oxygen stream by high-frequency heating, and the produced carbon dioxide and sulfur dioxide are measured to determine the C and S contents.

[0117] The nitrogen content is determined using the well-known inert gas melting-thermal conductivity method.

[0118] (Linear strain)

[0119] In the base steel sheet of the directional electromagnetic steel sheet of this embodiment, near the surface, there exist residual strains, i.e., multiple linear strains (thermal strains), formed by irradiation with energy rays such as laser beams or electron beams. These multiple linear strains extend continuously or intermittently along directions with an angle φ of 60 to 120° relative to the rolling direction (directions intersecting the rolling direction). The strain can exist continuously as a straight line or intermittently along one direction (e.g., as a dotted line).

[0120] It is known that the strain (residual strain) formed by irradiation with energy rays is compressive strain in the rolling direction and tensile strain in the thickness direction. Within the strained area and below it in the thickness direction, a region magnetized along the thickness direction, known as closed magnetic domains, is formed. When the size of the closed magnetic domain is larger than a specified size, the 180° domain width is subdivided, reducing eddy current losses and iron losses. On the other hand, if the size of the closed magnetic domain increases, the magnetic strain during AC excitation increases, and the transformer noise becomes more pronounced.

[0121] The inventors conducted research and found that by controlling the width of the strain formed on the surface and the strain introduction state in the plate thickness direction, iron loss can be reduced (iron loss characteristics improved), and the manifestation of noise problems can be suppressed (noise characteristics improved).

[0122] As mentioned above, the closed magnetic domains formed along with residual strain are beneficial for reducing iron losses because they are the driving force for 180° domain subdivision. However, this leads to problems such as increased magnetic strain due to closed domains and increased noise (deterioration of noise characteristics) when integrated into the transformer. Previously, countermeasures such as increasing the irradiation spacing of energy rays or reducing the input energy of energy rays were implemented to suppress noise characteristic deterioration. However, such solutions are merely means of improving noise characteristics at the expense of iron loss and noise characteristics, sacrificing the iron loss improvement effect brought about by energy ray irradiation to a certain extent.

[0123] The inventors conducted research on this topic and found that by introducing strain into the directional electromagnetic steel sheet to form shallow (locally existing on the surface) closed magnetic domain regions, it is possible to suppress the deterioration of noise characteristics and improve iron loss characteristics. In other words, the inventors discovered that controlling the spatial distribution of strain is important from the viewpoint of simultaneously reducing iron loss and noise. The spatial distribution of strain can be identified using X-ray diffraction analysis methods such as X-ray morphology.

[0124] Although details are described below, in regions with particularly strong strain introduction, such as those irradiated with high-energy rays, the lattice is disrupted to a degree that does not cause diffraction itself (high-strain introduction region). In X-ray morphology, such regions appear white because they do not cause diffraction itself. Therefore, the X-ray morphology spectrum obtained from the image shows low intensity (low pixel values).

[0125] On the other hand, in regions where residual strain (regions with low dislocation density) is introduced, although diffraction phenomena occur, the X-ray morphology image appears blackish. Therefore, the X-ray morphology spectrum obtained from the image shows high intensity (high pixel value). The residual strain region causing this diffraction phenomenon has a magnetic domain subdivision effect (iron loss improvement effect), but on the other hand, the crystal lattice itself is not damaged. Therefore, the adverse effects on noise are limited.

[0126] Therefore, it is important to introduce an appropriate amount of residual strain region that induces diffraction phenomena in order to achieve both excellent iron loss characteristics and excellent noise characteristics.

[0127] In the directional electromagnetic steel sheet of this embodiment, in order to take into account both excellent iron loss characteristics and excellent noise characteristics, the width of each of the multiple linear strains measured by X-ray morphology is 10 to 250 μm. Furthermore, in the X-ray morphology spectrum obtained from the surface X-ray morphology image, within a range of 1.50 mm in the rolling direction centered on the linear strain, the half-width of the peak of the X-ray morphology spectrum containing the maximum value of the spectral intensity is 0.02 mm or more and 0.10 mm or less.

[0128] If the width of the linear strain is less than 10 μm, the improvement in iron loss will not be achieved. Furthermore, setting the beam diameter to less than 10 μm is difficult industrially. Therefore, the strain width is set to 10 μm or more. Preferably, the strain width is 50 μm or more.

[0129] On the other hand, if the strain width exceeds 250 μm, the volume of the closed magnetic domains formed with the strain increases, and the degree of magnetic strain becomes greater. Therefore, the strain width is set to 250 μm or less. The strain width is preferably 200 μm or less, and more preferably 150 μm or less.

[0130] Furthermore, when the half-width at half-maximum (WWHM) of the X-ray morphology spectrum peaks is less than 0.02 mm, the strain induction range is small, and no iron loss improvement effect is obtained. On the other hand, when the WWHM exceeds 0.10 mm, excessive strain is introduced, and no noise characteristic improvement effect is obtained. The preferred range for the WWHM of the X-ray morphology spectrum peaks is 0.03 mm or more and 0.08 mm or less, and the more preferred range is 0.03 mm or more and 0.06 mm or less.

[0131] The half-width at half-maximum (WHM) of the peaks in X-ray morphology spectra is influenced by the crystal orientation of the parent material. Therefore, to achieve a predetermined WHM, it is necessary to increase the heating rate of decarburization annealing, as described below, to improve the sharpness of the Goss orientation crystal orientation. When the Goss orientation crystal orientation sharpness is poor, the WHM exceeds 0.10 mm when implementing strain-induced domain control, resulting in no improvement in noise characteristics.

[0132] The width of the linear strain was determined using X-ray morphology (XRT) (e.g., the Rigaku XRTmicron X-ray morphology imaging system) by the following method. The target of the X-ray source was set to Cu, and the voltage and current were set to 40 kV and 30 mA, respectively. The CCD resolution in the detector was set to Binning 1 × 1 (5.4 μm). The CCD field of view size was set to 17 mm × 13.5 mm (3326 pixels × 2540 pixels), and the digital resolution was set to 16 bits (65536 gray levels).

[0133] First, an X-ray beam is irradiated onto a steel plate sample according to the Bragg diffraction conditions. The diffracted X-ray beam is then exposed using a detector (CCD camera), thereby acquiring mapping data of the diffracted X-ray intensity. The diffracted X-ray intensity is converted into color density, and the scanned X-ray area is represented as a color density distribution image. This yields an X-ray morphology image (mapping data of diffracted X-ray intensity). The greater the diffracted X-ray intensity, the more concentrated the color density of the X-ray morphology image tends to become (negative display). Furthermore, sometimes a rocking curve measurement is used to adjust the measurement position to maximize the intensity. Specifically, a curve is scanned with the horizontal axis set to the incident angle θs (°) of the X-rays and the vertical axis set to the diffracted X-ray intensity; the point at which the strongest intensity is found is θs. max (°). However, in this invention, it is set that θs(°) = θs max X-ray topography images are obtained at positions of + to 0.09 (corresponding to the same method as the weak beam method used in dark-field imaging with transmission electron microscopy (TEM)). For example, the peak position of the rocking curve can also be determined by setting the X-ray topography imaging position to θs = 32.9200° and θd = 83.4400° relative to the incident angle of X-rays θs (°) = 32.8343° and the exit angle of X-rays θd = 83.5257°. Figure 2 An example of an X-ray topography image is shown below.

[0134] During the measurement, for example, a sample with a width of 50 mm in the width direction (TD direction) and a rolling direction of 150 mm is collected from a directional electromagnetic steel plate. An X-ray beam (Cu Kα line) is irradiated onto the surface of this sample in a manner that satisfies the Bragg diffraction condition relative to the desired diffraction plane (hkl). The intensity of the reflected diffracted X-rays is measured using a high-resolution CCD camera or the like, and a mapping image of the diffracted X-ray intensity is generated (see reference). Figure 1 At this point, TDI (Time Delay Integration) scanning is not performed, so that a still image (snap shot) of the diffraction image is captured while the sample is stationary. Through the diffraction X-rays from various locations on the sample, each pixel of the CCD camera is exposed and charge is accumulated. Therefore, by scanning the sample, the intensity mapping data of the diffraction X-rays is made by reading out the exposure charge at each location.

[0135] The condition where the RD axis (rolling direction) of the sample is parallel to the incident and reflection directions of the X-ray beam is called the g=222 measurement condition or the diffraction plane (222) condition. On the other hand, the condition where the TD axis of the sample is parallel to the incident and reflection directions of the X-ray beam is called the g=310 measurement condition or the diffraction plane (310) condition. In this embodiment, unless otherwise specified, the measurement condition adopts the diffraction plane (310) condition.

[0136] Based on the mapping image, multiple linear regions extending at approximately equal intervals along an angle φ of 60 to 120° relative to the rolling direction of the steel plate, and with an intensity lower than the average X-ray diffraction intensity of the overall mapping data (appearing as whitish due to the light color concentration), are identified as linear strain introduced by energy rays.

[0137] The width of the linear strain and the half-width of the peaks in the X-ray morphology spectrum were determined using the following method. Specifically, the location of the lowest intensity at the linear strain in the X-ray morphology image obtained using the above method was defined as the center of the strain. Color density data (pixel values) were obtained by connecting the desired two points along a straight line centered on the strain, within a 1.50 mm range in the rolling direction (±0.75 mm in the rolling direction with the linear strain as the center). This data was then processed as follows: Figure 3 As shown, the graph is plotted with the horizontal axis representing the measurement location and the vertical axis representing the pixel value, resulting in a distribution curve (line profile) of the reflected diffracted X-ray intensity (this curve is called the X-ray morphology spectrum. The pixel value on the vertical axis corresponds to the reflected diffracted X-ray intensity).

[0138] In this line profile, the maximum value of the reflection intensity is set to I. max Set the background intensity to I0, and in the area containing Imax The peaks of the X-ray morphology spectrum (including I) max Furthermore, within a continuous curve range where the intensity is greater than I0, the connecting spectral intensity is defined as |I max The length between two points of -I0| / 2 is set as the half-value width. From the perspective of removing spectral noise, the value obtained by measuring the same location several times and accumulating the results can also be used. The X-ray morphology spectrum can also be approximated as a continuous curve through fitting. The continuous curve range containing the center position of the strain and with a reflection intensity less than I0 is set as a linear strain. The reflection intensity in the region of linear strain is set as Iz. The strain width is set as the length connecting two points of Iz = 0 in a direction parallel to the rolling direction of the steel plate sample.

[0139] Generally, the greater the strain of a crystal lattice, the stronger the intensity of the diffracted X-rays; it weakens as the strain decreases, and becomes constant when the strain is zero (extinction effect). In crystal lattices with very small strain, such as... Figure 4 As shown, the traveling wave in the incident direction of the X-rays and the diffracted wave after scattering at the diffraction plane, after multiple interference (multiple scattering), propagate as reflected diffracted X-rays from the crystal surface (kinetic diffraction). Multiple interference within the crystal occurs in diffraction planes continuously formed with uniform and consistent lattice spacing, where the wavelength of the diffracted wave corresponds to the diffraction plane spacing formed by the strain-free crystal lattice. On the other hand, in regions where localized high strain exists, since uniform and consistent lattice spacing is not formed, multiple interference does not occur; instead, diffracted waves are generated with wavelengths corresponding to the strained lattice plane spacing, which are locally scattered only once (see reference). Figure 5 The wavelength of the diffracted wave generated in the locally strained region differs from the wavelength of the diffracted wave generated by multiple scattering in the unstrained region. Therefore, the diffracted wave generated in the strained region does not get caught up in the multiple scattering in the unstrained region and propagates within the crystal, exiting as reflected diffracted X-rays from the crystal surface (kinetic diffraction). Generally, regarding the intensity of diffracted X-rays, kinetic diffraction is stronger than dynamic diffraction (extinction effect). Furthermore, regions with locally introduced large amounts of strain exhibit strong spectral intensity through kinetic diffraction (e.g., setting the maximum value to I). max On the other hand, the spectral intensity of areas with less strain (the base material) becomes a certain value (e.g., set to I) through the extinction effect. o Furthermore, the localized areas where strain becomes excessive and the crystal lattice is disordered do not induce Bragg diffraction themselves, resulting in weak spectral intensity (e.g., setting the minimum value to I). min ).

[0140] In the directional electromagnetic steel sheet of this embodiment, the extension directions of multiple linear strains on the surface of the base steel sheet deviate from the direction perpendicular to the rolling direction by an angle of up to 30°. In other words, the multiple linear strains extend continuously or intermittently along a direction with an angle φ of 60° to 120° relative to the rolling direction. If they deviate from this angle range, the 180° magnetic domain subdivision effect of the steel sheet becomes less, and a sufficient iron loss reduction effect is not obtained.

[0141] Furthermore, the spacing between adjacent linear residual strains in the rolling direction is set to 3.0–9.0 mm. If the spacing in the rolling direction exceeds 9.0 mm, the domain subdivision effect of the 180° magnetic domains is reduced, resulting in insufficient improvement in iron loss. On the other hand, narrowing the spacing between the multiple linear residual strains (narrowing the irradiation spacing) tends to reduce iron loss, but if it falls below a certain threshold, the total hysteresis loss increases, leading to a deterioration in iron loss, and sometimes, a deterioration in noise characteristics. Therefore, the spacing between adjacent residual strains in the rolling direction is set to 3.0 mm or more. The multiple linear residual strains are preferably approximately parallel and their spacing is approximately equal.

[0142] The length of the residual strain in the width direction is not limited, but it is preferably formed from one end of the base steel plate in the width direction to the other end. In the case of discontinuous (intermittent) energy beam irradiation, when energy beam irradiation is performed on the steel plate at specific intervals relative to the width direction, the major axis (length along the width direction) d0 of the energy beam irradiation section and the length d1 along the width direction of the energy beam non-irradiation zone sandwiched between the two energy beam irradiation sections preferably satisfy d1 ≤ 3 × d0. d0 can be in the range of 50 μm or more and 50 mm or less.

[0143] The interval between adjacent linear thermal strains (the distance in the rolling direction from the center of the linear strain to the center of the adjacent linear strain) can be determined using X-ray morphology, with the strain location determined under the conditions described above.

[0144] Furthermore, in the directional electromagnetic steel sheet of this embodiment, an X-ray beam is irradiated over a range of 3.0 mm in the rolling direction centered on the linear strain of the surface, and the minimum value of the X-ray reflection intensity of the (310) surface is set to I. min The background intensity was set to I0, and an X-ray beam was irradiated over a 3.0 mm area in the rolling direction centered on the linear strain on the back side. The minimum X-ray reflection intensity of the resulting diffraction surface (310) was set to J. min When the background intensity is set to J0, the above I min The above I0, the above J minThe J0 mentioned above preferably satisfies the following equation (2). In this case, the iron loss characteristics and noise characteristics are further improved.

[0145] 0.02≤|J0-J min | / |I0-I min |≤1.00(2)

[0146] By satisfying equation (2), a strain distribution that is more favorable for noise characteristics is obtained. This satisfies |J0-J min | / |I0-I min This means that the number of closed magnetic domains near the back surface is less than the number of closed magnetic domains near the surface. Although the reason is unclear, it is believed that strain on the back surface of the strain-introduced surface may also have an iron loss improvement effect, if |J0-J min | / |I0-I min If the value is 0.02 or higher, this effect can be achieved.

[0147] On the other hand, although the reason is unclear, in |J0-J min | / |I0-I min When the value exceeds 1.00, meaning the number of closed magnetic domains on the back side exceeds the number of closed magnetic domains introduced on the surface, the noise characteristics become more prone to degradation. Therefore, it is believed that by using |J0-J min | / |I0-I min Setting it to 1.00 or below will yield better iron loss and noise characteristics.

[0148] Furthermore, the X-ray reflection intensity of the diffraction surface (310) within a range of 3.0 mm (±1.5 mm) in the rolling direction centered on the linear strain on the surface and back is determined by the following method.

[0149] That is, if it is a surface, an X-ray topography image (strain distribution image) is obtained under the above conditions. On the obtained image, a point with strain is selected, and on a straight line parallel to the rolling direction (RD direction) from this point, point A (+0.075 mm) and point B (-0.075 mm) are connected by straight lines. Color density data (pixel values) are obtained relative to the straight line connecting A and B. By plotting this with the horizontal axis representing the measurement position and the vertical axis representing the pixel value (diffraction intensity), a distribution curve (line profile) of the reflected diffracted X-ray intensity is obtained. The diffraction intensity at the position where the diffraction intensity of point A and the diffraction intensity of point B are averaged is set to I0. Furthermore, the diffraction intensity at the position with the lowest diffraction intensity is set to I. min .

[0150] Furthermore, if it is the reverse side, the diffraction intensity at the average position of the diffraction intensity of the starting and ending points of the straight line will be set as J0, and the diffraction intensity at the position with the lowest diffraction intensity will be set as J... min .

[0151] <Glass Coating>

[0152] In the directional electromagnetic steel sheet of this embodiment, a glass film is formed on the surface of the base steel sheet. The glass film may also be formed on only one side of the base steel sheet, but it is preferable to form it on both sides.

[0153] The glass coating is an inorganic coating with magnesium silicate as the main component. The glass coating is formed by reacting an annealing separating agent containing magnesium oxide (MgO) applied to the surface of the base steel sheet during the annealing process with the surface components of the base steel sheet. It has a composition derived from both the annealing separating agent and the base steel sheet (more specifically, a composition with Mg2SiO4 as the main component).

[0154] <Tension imparts insulation film>

[0155] In the directional electromagnetic steel sheet of this embodiment, a tension-imparting insulating film is formed on the surface of the glass film. The tension-imparting insulating film may be formed on only one side, but preferably on both sides.

[0156] Tension imparts an insulating film to directional electromagnetic steel sheets, thereby reducing eddy current losses and improving iron losses. Furthermore, by using tension to impart an insulating film, in addition to the aforementioned electrical insulation properties, various other characteristics such as corrosion resistance, heat resistance, and smoothness can also be obtained.

[0157] Furthermore, tension imparts the function of applying tension to the insulating film on the directional electromagnetic steel sheet. By applying tension to the directional electromagnetic steel sheet, the movement of the magnetic domain walls within the sheet becomes easier, thereby improving the iron loss of the directional electromagnetic steel sheet.

[0158] Tension imparts an insulating coating, preferably a known coating formed by applying a coating solution with phosphate and colloidal silica as the main components to the surface of a glass coating and then baking it.

[0159] <Base steel plate thickness: 0.17~0.30mm>

[0160] The thickness of the base steel plate for the directional electromagnetic steel plate in this embodiment is not limited, but considering its applicability in the core of transformers requiring low iron loss, low noise, and low vibration, a thickness of 0.17 to 0.30 mm is preferred. A thinner plate thickness allows for greater reduction in eddy current losses and results in better iron loss; therefore, a more preferred thickness for the base steel plate is 0.23 mm or less, and a further preferred thickness is 0.20 mm or less. Manufacturing a base steel plate thinner than 0.17 mm requires specialized equipment, increasing manufacturing costs and making it less desirable from a production standpoint. Therefore, an industrially preferred thickness is 0.17 mm or more, and more preferably 0.18 mm or more.

[0161] <Manufacturing Method>

[0162] The directional electromagnetic steel sheet of this embodiment can be manufactured by a manufacturing method including the following steps.

[0163] (i) A hot rolling process in which a steel billet having a chemical composition comprising, by mass%, C: 0.010–0.200%, Si: 3.00–4.00%, Mn: 0.01–0.50%, N: less than 0.020%, Sol.Al: 0.010–0.040%, P: less than 0.030%, S: 0.005–0.040%, Sn: 0–0.50%, Cu: 0–0.50%, Bi: 0–0.020%, Cr: 0–0.50%, Se: 0–0.020%, Sb: 0–0.500%, Mo: 0–0.10%, with the remainder being Fe and impurities, is heated and then hot rolled to obtain a hot-rolled steel plate.

[0164] (ii) The hot-rolled steel sheet is subjected to a hot-rolled annealing process;

[0165] (iii) A cold rolling process in which the hot-rolled steel sheet after the above-mentioned hot-rolled steel sheet annealing process is subjected to one or multiple cold rolling processes with intermediate annealing to obtain a cold-rolled steel sheet.

[0166] (iv) Decarburization annealing process for the above-mentioned cold-rolled steel sheet;

[0167] (v) A finished product annealing process in which a glass film is formed by coating the front and back sides of the cold-rolled steel sheet after the above-mentioned decarburization annealing process of the steel sheet as the base material with an annealing separating agent with MgO as the main component and drying it, and then performing finished product annealing.

[0168] (vi) A film forming process in which a tension-imparting insulating film is formed on the glass film to obtain a directional electromagnetic steel plate having the base steel plate, a glass film formed on the base steel plate, and a tension-imparting insulating film formed on the glass film; and

[0169] (vii) A magnetic domain subdivision process in which the surface of the insulating film is irradiated with energy rays to impart multiple linear strains to the base steel plate under the tension of the directional electromagnetic steel plate.

[0170] The following is a detailed description of these procedures. In the following description, unless a particular condition for each procedure is specified, generally known conditions may be applied to perform each procedure.

[0171] <Hot Rolling Process>

[0172] In the hot rolling process, a steel billet having a chemical composition, for example, containing (by mass%) C: 0.010–0.200%, Si: 3.00–4.00%, Mn: 0.01–0.50%, N: less than 0.020%, Sol.Al: 0.010–0.040%, P: less than 0.030%, S: 0.005–0.040%, Sn: 0–0.50%, Cu: 0–0.50%, Bi: 0–0.020%, Cr: 0–0.50%, Se: 0–0.020%, Sb: 0–0.500%, Mo: 0–0.10%, with the remainder being Fe and impurities, is heated and then hot-rolled to obtain a hot-rolled steel sheet. The heating temperature of the steel billet is not particularly limited, but is preferably set within the range of 1100–1450°C. The heating temperature is more preferably 1300~1400℃.

[0173] There are no particular limitations on the hot rolling conditions; they can be set appropriately based on the required characteristics. The thickness of the hot-rolled steel sheet obtained by hot rolling is preferably in the range of 2.0 mm or more and 3.0 mm or less.

[0174] The chemical composition of the billet is set to the range described above because the chemical composition of the base steel plate is obtained by taking into account the following manufacturing processes.

[0175] <Hot-rolled sheet annealing process>

[0176] The hot-rolled sheet annealing process is a process of annealing hot-rolled steel sheets manufactured through the hot rolling process. By performing this annealing treatment, recrystallization occurs in the steel sheet structure, enabling the achievement of good magnetic properties.

[0177] In the hot-rolled sheet annealing process of this embodiment, the hot-rolled steel sheet manufactured by the hot-rolling process can be annealed according to a known method. There are no particular limitations on the means of heating the hot-rolled steel sheet during annealing; a known heating method can be used. Furthermore, there are no particular limitations on the annealing conditions; for example, the hot-rolled steel sheet can be annealed in a temperature range of 900–1200°C for 10 seconds to 5 minutes.

[0178] <Cold rolling process>

[0179] In the cold rolling process, hot-rolled steel sheets after the annealing process are subjected to cold rolling in multiple passes to obtain cold-rolled steel sheets with a thickness of 0.17–0.30 mm. Cold rolling can be a single cold rolling (a series of cold rollings without intermediate annealing), or it can be a multiple cold rolling process with intermediate annealing, in which the cold rolling is interrupted before the final pass of the cold rolling process and at least one or two intermediate annealings are performed.

[0180] When performing intermediate annealing, it is preferable to hold the temperature at 1000–1200°C for 5–180 seconds. The annealing atmosphere is not particularly limited. Considering manufacturing costs, the number of intermediate annealing cycles is preferably no more than 3.

[0181] Alternatively, the surface of the hot-rolled steel sheet can be pickled under known conditions before the cold rolling process.

[0182] In the cold rolling process of this embodiment, a cold-rolled steel sheet can be produced by cold rolling a hot-rolled steel sheet according to a known method. For example, the final reduction rate can be set to a range of 80% or more and 95% or less. If the final reduction rate is less than 80%, {110} cannot be obtained. <001> The likelihood of Goss nuclei having a high degree of aggregation in the rolling direction increases, which is undesirable. On the other hand, when the final reduction rate exceeds 95%, the likelihood of secondary recrystallization becoming unstable in the finished product annealing process, which is a subsequent process, increases, and is therefore undesirable. By setting the final reduction rate within the above range, {110} can be obtained. <001> The orientation of the Goss nucleus in the rolling direction has a high degree of aggregation and suppresses the instability of secondary recrystallization.

[0183] The so-called final reduction rate is the cumulative reduction rate of cold rolling. In the case of intermediate annealing, it is the cumulative reduction rate of cold rolling after final intermediate annealing.

[0184] <Decarburization Annealing Process>

[0185] In the decarburizing annealing process, the obtained cold-rolled steel sheet is decarburized and annealed. In the decarburizing annealing, the cold-rolled steel sheet undergoes a recrystallization process, and carbon that adversely affects magnetic properties is removed from the steel sheet.

[0186] In the decarburization annealing process, the number of Goss nuclei is increased, resulting in finer secondary recrystallized grains obtained during the final annealing process (described later). If grain boundaries are considered to function as magnetic poles (sources of leakage flux), then the overall magnetic static energy of the system is improved through the refinement of the secondary recrystallized grains. That is, due to the high driving force for magnetic domain refinement, it becomes possible to achieve both low iron loss and low noise without relying on excessive closure of magnetic domains.

[0187] In the manufacturing method of the directional electromagnetic steel sheet of this embodiment, in order to increase the number of Goss nuclei, the heating rate in the temperature range of 550–750°C (the first temperature range) is accelerated and the residence time in this temperature range is shortened during the decarburization annealing heating. Specifically, if the heating rate in the first temperature range is less than 500°C / second, the increase in Goss nuclei becomes insufficient. Therefore, the heating rate in the temperature range of 550–750°C is set to 500°C / second or more. There is no upper limit to the heating rate, but if the heating rate is set to exceed 2000°C / second, there is concern that the equipment load will become too high. Therefore, the heating rate in the temperature range of 550–750°C can also be set to 2000°C / second or less. By decarburizing and annealing under such conditions, the sharpness of the crystal orientation after secondary recrystallization is close to the ideal Goss orientation. That is, a secondary recrystallized structure with a relatively small dispersion of crystal orientation can be obtained. By strain introduction of such a structure under the conditions described later, it becomes possible to achieve both low iron loss and low noise.

[0188] However, if heating is carried out in the temperature range of 550–750°C at a heating rate of 500°C / second or higher, the oxide film formed on the surface of the steel plate in this temperature range is essentially SiO2. This is because SiO2 has the fastest formation rate compared to other oxide films. Since SiO2 has the effect of inhibiting decarburization, it is preferable from the viewpoint of promoting decarburization to prevent excessive SiO2 film thickness.

[0189] In the manufacturing method of the directional electromagnetic steel sheet of this embodiment, even when heating is performed at a heating rate of 500°C / second or higher in the temperature range of 550 to 750°C, by accelerating the heating rate of the temperature range of 750 to 800°C (the second temperature range), or by accelerating the heating rate of the temperature range of 750 to 800°C and controlling the dew point atmosphere, it is possible to avoid the formation of a thick film of SiO2 generated in the temperature range of 550 to 750°C.

[0190] Specifically, when only the heating rate is controlled, the heating rate in the 750–800°C temperature range is set to 800°C / second or higher. A heating rate lower than 800°C / second cannot adequately suppress SiO2 growth (thickening of the oxide film). The preferred heating rate in the 750–800°C temperature range is 1000°C / second or higher. There is no upper limit to the heating rate, but setting it above 2000°C / second raises concerns about excessive device load. Therefore, the heating rate in the 750–800°C temperature range can also be set below 2000°C / second.

[0191] Furthermore, when simultaneously controlling the heating rate and atmosphere dew point within the temperature range of 750–800°C (the second temperature range), from the viewpoint of suppressing SiO2 growth, the heating rate is set to 50°C / second or higher, while maintaining the atmosphere dew point at -50 to 20°C. When the atmosphere dew point exceeds 20°C or the heating rate is lower than 50°C / second, SiO2 growth cannot be sufficiently suppressed. On the other hand, a lower atmosphere dew point is preferred. Therefore, no specific lower limit is set, but achieving a temperature below -50°C requires specialized equipment, which is not preferable for industrial applications. Therefore, the lower limit of the atmosphere dew point can also be set to -50°C.

[0192] There are no particular restrictions on the atmosphere in the first temperature range; well-known conditions can be applied.

[0193] <Nitriding treatment process>

[0194] Nitriding can also be performed between the decarburization annealing process and the finished product annealing process described later.

[0195] In the nitriding process, for example, cold-rolled steel sheets after decarburization annealing are maintained at approximately 700–850°C in a nitriding atmosphere (an atmosphere containing nitriding gases such as hydrogen, nitrogen, and ammonia). Here, it is preferable to nitrid the steel sheet with a nitrogen content of 40–1000 ppm by mass. If the nitrogen content of the nitrided cold-rolled steel sheet is less than 40 ppm, AlN may not be sufficiently precipitated within the cold-rolled steel sheet, and AlN will not function as an inhibitor. Therefore, when AlN is used as an inhibitor, the nitrogen content of the nitrided cold-rolled steel sheet is preferably set to 40 ppm or higher.

[0196] On the other hand, when the nitrogen content in cold-rolled steel sheet exceeds 1000 ppm, excessive AlN remains in the steel sheet even after secondary recrystallization during finished annealing. This AlN contributes to iron loss degradation. Therefore, the nitrogen content in nitrided cold-rolled steel sheet is preferably set to 1000 ppm or less.

[0197] <Finished product annealing process>

[0198] In the finished product annealing process, after applying a specified annealing release agent to one or both sides of the cold-rolled steel sheet obtained in the decarburization annealing process or further nitrided, finished product annealing is performed. Finished product annealing is generally carried out for a long time while the steel sheet is rolled into a coil. Therefore, before finished product annealing, in order to prevent sand from adhering to the inside and outside of the coil, an annealing release agent is applied to the cold-rolled steel sheet and allowed to dry.

[0199] As the annealing separating agent for coating, an annealing separating agent with MgO as the main component (e.g., containing more than 80% by weight) is used. By using an annealing separating agent with MgO as the main component, a glass coating can be formed on the surface of the base steel sheet. Without MgO as the main component, a primary coating (glass coating) will not form. This is because the primary coating is a Mg₂SiO₄ or MgAl₂O₄ compound, thus lacking the Mg necessary for the formation reaction.

[0200] The finished product can be annealed, for example, by heating to 1150-1250°C in an atmosphere containing hydrogen and nitrogen, and annealing for 10-60 hours in that temperature range.

[0201] <Coating Formation Process>

[0202] In the coating formation process, a tension-imparting insulating coating is formed on one or both sides of the finished annealed cold-rolled steel sheet. There are no particular limitations on the conditions for forming the tension-imparting insulating coating; any known insulating coating treatment solution can be used, and the solution can be applied and dried using known methods. By forming a tension-imparting insulating coating on the steel sheet surface, the magnetic properties of the directional electromagnetic steel sheet can be further improved.

[0203] The surface of the steel plate on which the insulating film (tension imparts the insulating film) is formed can be any pre-treated surface that has undergone degreasing treatment with alkali or pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid or other similar substances before the coating treatment liquid is applied, or it can be the original surface of the finished product after annealing without such pre-treatment.

[0204] The insulating film formed on the surface of the steel plate is not particularly limited as long as it is used as an insulating film for directional electromagnetic steel plates, and known insulating films can be used. Examples of such insulating films include those with phosphates and colloidal silica as main components. Furthermore, composite insulating films with inorganic materials as the main body and further containing organic materials can be included. Here, a composite insulating film is, for example, an insulating film with at least one of inorganic materials such as chromate salts, metal phosphate salts, colloidal silica, Zr compounds, and Ti compounds as the main body, and with finely dispersed organic resin particles. Especially from the viewpoint of reducing the environmental impact of manufacturing processes, which has increased in recent years, insulating films using coupling agents of metal phosphate salts or Zr or Ti, or their carbonates or ammonium salts, as starting materials are sometimes used.

[0205] <Magnetic domain subdivision process>

[0206] In the magnetic domain subdivision process, by irradiating an energy ray such as a laser beam or an electron beam onto the surface of a film with tension applied, multiple linear strains extending in a direction forming an angle φ of 60 to 120° with respect to the rolling direction are introduced near the surface of the base steel plate (from the surface to the inside of the steel plate). In the magnetic domain subdivision process, multiple linear strains (thermal strains generated by rapid heating by irradiating an energy ray and subsequent rapid cooling) are formed at a prescribed interval in the rolling direction, and the interval (i.e., the interval (p) between adjacent strains) is set to 3.0 to 9.0 mm in the rolling direction.

[0207] If the interval p in the rolling direction of the multiple linear strains exceeds 9.0 mm, the iron loss improvement effect is insufficient.

[0208] Examples of the energy ray include a laser beam and an electron beam. The laser beam can be a continuous-wave laser or a pulsed laser. Examples of the type of laser beam include fiber laser, YAG laser, or CO2 laser. The electron beam can be a continuous beam or an intermittent beam.

[0209] In addition, as described above, in order to obtain a grain-oriented electrical steel sheet that兼顾低铁损和低噪音 (兼顾 low iron loss and low noise), in the magnetic domain subdivision process, by irradiating an energy ray from the film with tension insulation, strain is introduced with respect to the base steel plate, and closed magnetic domains with a shallow depth from the surface are formed.

[0210] Specifically, using the laser output power P in units of W and the laser irradiation cross-sectional area S in units of mm 2 calculated, the laser beam is irradiated in such a way that the laser power density Ip defined by P / S satisfies the following formula (3), and using the laser output power P and the laser scanning speed Vs in units of mm / second, the laser input energy Up per unit J / mm defined by (P / Vs) satisfies the following formula (4).

[0211] 250 ≤ Ip ≤ 2000 Formula (3)

[0212] 0.005 < Up ≤ 0.050 Formula (4)

[0213] When Ip is lower than 250, insufficient energy is input, and the magnetic domain subdivision effect (iron loss improvement effect) cannot be obtained. Therefore, Ip is 250 or more. Ip is preferably 500 or more.

[0214] On the other hand, if Ip exceeds 2000, excess thermal strain is introduced beyond the magnetic domain subdivision effect, resulting in deterioration of the noise characteristics. Therefore, Ip is 2000 or less. Ip is preferably 1750 or less, more preferably 1500 or less.

[0215] It should be noted that there is an incorrect expression "兼顾低铁损和低噪音" in the original text which is directly translated as it is. It might be a wrong or incomplete description in the original Chinese. You may want to double-check the accuracy of this part in the original content.Furthermore, when Up is below 0.005, the irradiation effect is insufficient, and iron loss is not adequately improved. Therefore, Up should exceed 0.005. On the other hand, if Up exceeds 0.050, the noise characteristics deteriorate. Therefore, Up should be below 0.050.

[0216] Here, a laser beam is used as a specific example, but the same applies to other energy beam methods such as electron beams.

[0217] Furthermore, in the manufacturing method of the directional electromagnetic steel plate in this embodiment, when irradiated by energy rays, the diameter dl of the energy ray perpendicular to the beam scanning direction (scanning direction) and the diameter dc of the beam scanning direction, measured in units of μm, are controlled in such a way that the beam length-to-width ratio defined by (dl / dc) satisfies the following formula (5).

[0218] 0.001 <dl / dc<1.000(5)

[0219] When the beam aspect ratio is below 0.001, heat loss occurs due to beam irradiation, reducing the efficiency of energy input and failing to achieve sufficient magnetic domain subdivision (iron loss improvement). Therefore, the beam aspect ratio must exceed 0.001.

[0220] On the other hand, when the beam aspect ratio is 1.000 or higher, heat removal associated with beam irradiation is not caused, but instead, residual stress is generated, and the low-noise effect is not achieved. Therefore, the beam aspect ratio is lower than 1.000. The beam aspect ratio is preferably lower than 0.050, and more preferably lower than 0.005.

[0221] Furthermore, the diameter dl of the energy ray, measured in μm and perpendicular to the beam scanning direction, satisfies the following equation (6).

[0222] 10≤dl<200(6)

[0223] It is difficult to produce bundles with a dl value below 10 in industrial applications. Therefore, dl values ​​above 10 are preferred.

[0224] On the other hand, if dl is 200 or higher, the residual thermal strain is introduced beyond the magnetic domain subdivision effect, thereby degrading the noise characteristics. Therefore, dl is below 200. dl is preferably below 150, and more preferably below 100.

[0225] In the manufacturing method of the directional electromagnetic steel plate of this embodiment, as described above, a relatively strong Ip energy ray is irradiated with a beam of small aspect ratio. Such irradiation is generally not performed. This is because it is believed that reducing the beam aspect ratio would cause the irradiation energy to disperse, thus reducing the effect of increasing Ip.

[0226] However, the inventors conducted research based on the new insight that controlling the spatial distribution of strain is important from the viewpoint of simultaneously reducing iron loss and noise, and as a result, they discovered for the first time the preferred irradiation conditions described above.

[0227] Example

[0228] As shown in Table 1, prepare steel billets with different chemical compositions for each steel number (A-G).

[0229] Next, directional electromagnetic steel sheets were manufactured using the various steel billets (Experiments No. 1 to 28).

[0230] Specifically, steels B, E, and F are heated to a temperature ranging from 1100 to 1200°C and then hot-rolled to produce hot-rolled steel sheets with a thickness of 2.3 ± 0.3 mm. Similarly, steel billets A, C, D, and G are heated to a temperature ranging from 1300 to 1400°C and then hot-rolled to produce hot-rolled steel sheets with a thickness of 2.3 ± 0.3 mm.

[0231] Next, the obtained hot-rolled steel sheet was subjected to hot-rolled annealing. Specifically, the hot-rolled steel sheet was annealed at an annealing temperature of 1000–1200°C and a holding time of 10–200 seconds.

[0232] Next, after removing the surface oxide scale from the hot-rolled annealed steel sheet by pickling, it is subjected to one or two cold rolling processes with annealing to produce a cold-rolled steel sheet with a base material thickness of 0.19 to 0.23 mm.

[0233] The obtained cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Table 2. Furthermore, the homogenization process during decarburization annealing was carried out at a temperature of 800–840°C for 100–150 seconds. The degree of oxidation was controlled at (PH2O / PH2) = 0.3–0.5. For tests No. 2, 5, 6, 9, 10, 14, 16, 18, 23, 26, and 27 using steels B, E, and F, nitriding treatment was further performed.

[0234] Next, the cold-rolled steel sheet undergoes a finished product annealing process. Specifically, an annealing release agent with magnesium oxide (MgO) as the main component (more than 80% by weight) is coated on the surface of the cold-rolled steel sheet.

[0235] Next, the cold-rolled steel sheet coated with annealing release agent was annealed at 1000-1300°C to produce a steel sheet with a glass coating on the base steel sheet.

[0236] Next, a coating forming process is performed on the steel plate. Specifically, an insulating coating forming liquid mainly composed of colloidal silica and phosphate is applied to the surface of the steel plate (more specifically, the surface of the glass coating as a primary coating) and then heat-treated (baked). As a result, a directional electromagnetic steel plate is obtained, comprising a base steel plate, a glass coating formed on the base steel plate, and a tension-imparting insulating coating formed on the glass coating.

[0237]

[0238] Table 2

[0239]

[0240] [Analysis of the chemical composition of the base steel plate]

[0241] The chemical composition of the base steel sheet of the directional electromagnetic steel sheet before magnetic domain subdivision according to the above-mentioned principles is determined by the following method.

[0242] First, tension was removed from the directional electromagnetic steel sheets of each test No., and an insulating film was applied. Specifically, the directional electromagnetic steel sheets were immersed in an aqueous sodium hydroxide solution containing 30–50% by mass of NaOH and 50–70% by mass of H₂O at 80–90°C for 7–10 minutes. The immersed directional electromagnetic steel sheets (after removing the tension and applying the insulating film) were then washed with water. After washing, they were dried using a warm air blower for less than 1 minute.

[0243] Next, the glass coating is removed from the directional electromagnet sheet, which lacks the tensile strength to impart an insulating coating. Specifically, the directional electromagnet sheet is immersed in an aqueous solution of hydrochloric acid containing 30-40% by mass of HCl at 80-90°C for 1-10 minutes. This removes the glass coating from the base steel sheet. The immersed base steel sheet is then washed with water. After washing, it is dried using a warm air blower for less than 1 minute. Through these steps, the base steel sheet is removed from the directional electromagnet sheet.

[0244] The chemical composition of the extracted base steel plate was determined using well-known component analysis methods. Specifically, the base steel plate was pulverized using a drill bit, and the pulverized material was collected. The collected pulverized material was dissolved in acid to obtain a solution. ICP-AES was performed on the solution to perform elemental analysis of the chemical composition. The Si content in the base steel plate was determined using the method specified in JIS G 1212 (1997) (quantitative method for silicon). Specifically, if the pulverized material was dissolved in acid, silicon oxide precipitated as a precipitate. The precipitate (silicon oxide) was filtered through filter paper, its mass was measured, and the Si content was determined. The C and S contents were determined using a well-known high-frequency combustion method (combustion-infrared absorption method). Specifically, the solution was burned in an oxygen stream by high-frequency heating, and the carbon dioxide and sulfur dioxide produced were detected to determine the C and S contents. The N content was determined using a well-known inert gas melting-thermal conductivity method. The chemical composition of the base steel plate was determined using the above analytical methods. The results are shown in Table 3.

[0245] Table 3

[0246]

[0247] Although not shown in the table, the iron loss before domain subdivision was evaluated for the directional electromagnetic steel plates of each test No. to assess the iron loss improvement rate. Samples measuring 60 mm in width and 300 mm in length, including the center of the plate width, were collected from the directional electromagnetic steel plates of each test No. The length direction of the samples was set parallel to the rolling direction. The collected samples were held at 800°C for 2 hours in a nitrogen atmosphere with a dew point below 0°C to implement strain removal introduced at the time of sample collection.

[0248] Using this sample, the iron loss W was measured when the frequency was set to 50 Hz and the maximum magnetic flux density was set to 1.7 T. 17 / 50 (W / kg)

[0249] Subsequently, for each test No., the directional electromagnetic steel plate was irradiated with energy rays using continuous wave laser or intermittent wave laser under the conditions shown in Tables 4 and 5, thereby performing magnetic domain subdivision. For the directional electromagnetic steel plates after magnetic domain subdivision, noise characteristics and magnetic properties were evaluated through tests.

[0250] [Noise Characteristics Evaluation]

[0251] For a sample with a width of 60 mm and a length of 300 mm that has undergone the above-mentioned magnetic domain control, the magnetic strain was measured using an AC magnetic strain measurement device. The magnetic strain measurement device was configured to include a laser Doppler vibrometer, an excitation coil, an excitation power supply, a magnetic flux detection coil, an amplifier, and an oscilloscope.

[0252] Specifically, an alternating magnetic field is applied to the sample with a maximum magnetic flux density of 1.7T in the rolling direction. A laser Doppler vibrometer is used to measure the change in sample length caused by the expansion and contraction of magnetic domains, obtaining a magnetic strain signal. Fourier analysis is performed on the obtained magnetic strain signal to determine the amplitude Cn of each frequency component fn (n is a natural number greater than 1). Using the A correction coefficient αn for each frequency component fn, the magnetic strain velocity level LVA (dB) is calculated as shown in the following formula.

[0253] LVA=20×Log(√(Σ(ρc×2π×fn×αn×Cn / √2) 2 ) / Pe0)

[0254] Where ρc is the inherent acoustic impedance, set to ρc = 400. Pe0 is the minimum audible pressure, using Pe0 = 2 × 10⁻⁶. -5 (Pa). The correction factor αn used the value recorded in Table 2 of JIS C 1509-1 (2005).

[0255] Based on the obtained magnetic strain velocity level (LVA), noise characteristics are evaluated according to the following criteria. If the LVA is below 60 dBA, it is considered "excellent noise characteristics." If it is below 50 dBA, it is considered "particularly excellent." A LVA above 60 dBA is considered "insufficient noise characteristics."

[0256] The results are shown in Table 5.

[0257] [Magnetic Property Evaluation]

[0258] As a magnetic property, the improvement in iron loss brought about by magnetic domain control was evaluated by the iron loss improvement rate.

[0259] Using a sample with a width of 60 mm and a length of 300 mm that underwent the aforementioned domain control, the iron loss W was measured when the frequency was set to 50 Hz and the maximum magnetic flux density was set to 1.7 T. 17 / 50 (W / kg)

[0260] Then, using the iron loss W measured here 17 / 50 (W / kg) and iron loss W measured before domain control 17 / 50 (W / kg) is used as [(iron loss before domain control - iron loss after domain control) × 100] / iron loss before domain control to calculate the iron loss improvement rate (%).

[0261] When the iron loss improvement rate is above 5%, it is judged as "having an iron loss improvement effect"; when the iron loss improvement rate is above 10%, it is judged as "having a significant iron loss improvement effect".

[0262] However, for materials with iron loss exceeding 0.85 W / kg after domain control, the improvement rate of domain control should not be used to determine "insufficient magnetic properties".

[0263] In addition, the magnetic flux density (T) was determined using the same sample through a single-plate magnetic property test (SST test). Specifically, a magnetic field of 800 A / m was applied to the sample, and the magnetic flux density (T) was determined.

[0264] The results are shown in Table 5.

[0265] In this evaluation, regarding magnetic properties and noise characteristics, only those that "have an effect on improving iron loss" and "have excellent noise characteristics" are designated as qualified, i.e., invention examples. If at least one of the magnetic properties and noise characteristics is "insufficient noise characteristics" or "insufficient magnetic properties", it is designated as a "comparative example".

[0266] Table 4

[0267]

[0268]

[0269] As can be seen from Tables 1 to 5, the magnetic and noise characteristics of Tests No. 1 to 12 and 21, 24 to 28, which are examples of the invention, are excellent. That is, "the iron loss improvement rate is more than 5%" and "the iron loss after magnetic domain control is less than 0.85 W / kg" and "the magnetic strain rate level is less than 60 dBA".

[0270] For tests No. 5–11 and No. 21, the iron loss improvement rate exceeded 10%, and the magnetic strain velocity level was below 50 dBA, which are particularly good characteristics. This is because Ip and Up, which are laser irradiation conditions, are within a more favorable control range.

[0271] Although Ip and Up, which are laser irradiation conditions, in Tests No. 1 to 4 and Test No. 12 are outside the preferred or more preferred range, the effects of the invention can be enjoyed because they meet the scope of the present invention.

[0272] In contrast, tests No. 13–20, 22, and 23 served as comparative examples, and at least one of their magnetic and noise characteristics was inferior.

[0273] Regarding Experiment No. 13, the heating process during decarburization annealing falls outside the scope of this invention. Specifically, in Experiment No. 13, the orientation sharpness of the Goss grains in the secondary recrystallization structure is insufficient. Therefore, although strain-introducing conditions are implemented within the scope of this invention, the half-width of the X-ray morphology spectrum falls outside the scope of this invention, resulting in poor noise characteristics.

[0274] Decarburization in Experiment No. 14 was insufficient. Therefore, even after domain control, the iron loss exceeded 0.85 W / kg, and the iron loss improvement rate was low.

[0275] In Experiment No. 15, the linear strain intervals exceeded 9.0 mm. As a result, due to the wide strain introduction intervals, the frequency of secondary recrystallized grains without magnetic domain control increased. Consequently, the magnetic domain control effect was insufficient, and the iron loss improvement rate did not reach 5%.

[0276] The linear strain interval in Test No. 16 was less than 3.0 mm. Due to excessive strain introduction, the noise characteristics were poor.

[0277] The strain-imposing conditions of experiments No. 17-20 are outside the scope of this invention.

[0278] Experiment No. 17 failed to achieve the desired magnetic domain subdivision effect due to its small Ip value, and Experiment No. 20 failed to achieve the desired effect due to its small Up value. Consequently, the half-width of the X-ray morphology spectrum deviated from the range of this invention, and the iron loss improvement rate did not reach 5%.

[0279] Due to the large Ip in Experiment No. 18 and the large Up in Experiment No. 19, the half-width of the X-ray morphology spectrum deviates from the range of this invention, resulting in poor noise characteristics.

[0280] Experiment No. 22 failed to achieve the desired low-noise effect because the beam aspect ratio exceeded 1.000, resulting in the half-width of the X-ray morphology spectrum falling outside the scope of this invention.

[0281] In Experiment No. 23, the diameter dl in the direction perpendicular to the beam scanning direction was over 200 μm, which increased the strain width and introduced residual thermal strain, thus failing to achieve a low-noise effect.

[0282] Industrial availability

[0283] According to the present invention, a directional electromagnetic steel sheet with excellent iron loss characteristics and noise characteristics, and a method for manufacturing the same, are available, and have high industrial applicability.

Claims

1. A grain-oriented electrical steel sheet characterized by, It has: a base steel sheet, a glass coating film formed on the base steel sheet, and a tension imparting insulating film formed on the glass coating film, the base steel sheet has a chemical composition containing, in mass%, C: 0.010% or less, Si: 3.00 to 4.00%, Mn: 0.01 to 0.50%, N: 0.010% or less, Sol. Al: 0.020% or less, P: 0.030% or less, S: 0.010% or less, Sn: 0 to 0.50%, Cu: 0 to 0.50%, Cr：0～0.50％、 Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, the remainder: Fe and impurities, on the surface of the base steel sheet, a plurality of linear strains continuously or discontinuously extending in a direction intersecting the rolling direction, the interval p of the plurality of linear strains adjacent to each other in the rolling direction is 3.0 to 9.0 mm, the width of the linear strain is 10 to 250 μm, in an X-ray topography spectrum in a range of 1.50 mm in the rolling direction centered on the linear strain obtained from an X-ray topography image of the surface, the half-value width of the peak of the X-ray topography spectrum containing the maximum value of the spectral intensity is 0.02 mm or more and 0.10 mm or less.

2. The grain-oriented electrical steel sheet according to claim 1, characterized by X-ray beam is irradiated in a range of 3.0 mm in the rolling direction centering on the linear strain of the surface, and a minimum value of the X-ray reflection intensity of the (310) plane is set as I min The background intensity is set as I0, X-ray beam is irradiated in a range of 3.0 mm in the rolling direction centering on the linear strain of the back surface, and a minimum value of the X-ray reflection intensity of the resulting diffraction plane (310) plane is set as J min When the background intensity is set as J0, the I min , the I0, the J min , the J0satisfy the following formula (2), 0.02 < | J0 - J min | | I0 - I min ≤ 1.00 (2).

3. The grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that, The chemical composition of the base steel sheet contains either or both of Sn: 0.01 to 0.50% and Cu: 0.05 to 0.50%.

4. A method of manufacturing a grain-oriented magnetic steel sheet, characterized by, It is a method of manufacturing the oriented electromagnetic steel sheet according to claim 1 or 2, having the following steps: a hot rolling step of heating a billet having a chemical composition containing, in mass%, C: 0.010 to 0.200%, Si: 3.00 to 4.00%, Mn: 0.01 to 0.50%, N: 0.020% or less, Sol. Al: 0.010 to 0.040%, P: 0.030% or less, S: 0.005 to 0.040%, Sn: 0 to 0.50%, Cu: 0 to 0.50%, Bi: 0 to 0.020%, Cr: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, and the remainder: Fe and impurities, and then performing hot rolling to obtain a hot-rolled steel sheet; a hot-rolled sheet annealing step of performing hot-rolled sheet annealing on the hot-rolled steel sheet; a cold rolling step of performing cold rolling on the hot-rolled steel sheet after the hot-rolled sheet annealing step, once or a plurality of times with intermediate annealing interposed; a decarburization annealing step of performing decarburization annealing on the cold-rolled steel sheet; a finished product annealing step of forming a glass coating film by applying an annealing separator containing MgO as a main component to the surface and back surface of the cold-rolled steel sheet after the decarburization annealing step as a base steel sheet and drying it, and then performing finished product annealing; a coating film forming step of forming a tension imparting insulating film on the glass coating film to obtain an oriented electromagnetic steel sheet having the base steel sheet, the glass coating film formed on the base steel sheet, and the tension imparting insulating film formed on the glass coating film; and and A surface of the grain-oriented magnetic steel sheet to which the insulating coating is given is irradiated with an energy ray, and a magnetic domain subdivision process of giving a plurality of linear strains to the base steel sheet is performed, In the magnetic domain subdivision process, An interval of the rolling direction of adjacent linear strains in the plurality of linear strains is 3.0 to 9.0 mm, using an energy ray output power P in units of W and an energy ray irradiation cross-sectional area S in units of mm 2 An energy ray power density Ip defined by (P / S) in units of W / mm 2 satisfies the following equation (3) An energy ray input energy Up defined by (P / Vs) in units of J / mm satisfies the following equation (4), and A beam aspect ratio defined by (dl / dc) using a diameter dl in a direction perpendicular to a beam scanning direction in units of μm using the energy ray and a diameter dc of the beam scanning direction, and the dl respectively satisfy the following equation (5) and the following equation (6), In the decarburization annealing process, A temperature rising rate S1 in a first temperature range of 550 to 750°C is set to 500°C / sec or more, A temperature rising rate S2 in a second temperature range of 750 to 800°C is set to 800°C / sec or more, or the temperature rising rate S2 in the second temperature range is set to 50°C / sec or more, and an atmospheric dew point in the second temperature range is set to -50°C to 20°C, 250 ≤ Ip ≤ 2000 (3) 0.005 < Up ≤ 0.050 (4) 0.001 < dl / dc < 1.000 (5) 10≤dl<200 (6)。 5. The method of producing a grain-oriented electrical steel sheet according to claim 4, characterized in that, Between the decarburization annealing process and the finished product annealing process, a nitriding treatment process of performing a nitriding treatment on the cold-rolled steel sheet is further provided.

6. The method of producing a grain-oriented electromagnetic steel sheet according to claim 4 or 5, characterized in that, The chemical composition of the steel billet includes any one or both of Sn: 0.01 to 0.50%, and Cu: 0.05 to 0.50%.

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