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

Abstract

The present oriented electromagnetic steel sheet has a base steel sheet, a glass coating formed on the base steel sheet, and a tension imparting insulating coating formed on the glass coating, in the base steel sheet, a plurality of linear strain regions extending continuously or discontinuously in a direction intersecting a rolling direction are present, the width of each of the plurality of linear strain regions in the rolling direction is 210 μm or less, the plurality of linear strain regions are parallel to each other, the interval of the adjacent linear strain regions in the rolling direction is 10 mm or less, the magnetostriction λ 0‑pb when excited to 1.7 T after heat treatment at 800°C for 4 hours 0‑pa when excited to 1.7 T after heat treatment at 800°C for 4 hours 0‑pb satisfies 0.02 ≤ λ 0‑pa ≤ 0.20.

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. 2021-053619 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 such as magnetic susceptibility, plate thickness, film tension, impurity content, resistivity, grain size, and magnetic domain size all affect the level of iron loss. Even with the development of 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 shows 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, which improves iron loss characteristics 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 constant intervals.

[0008] Patent document 2 shows that a TEM with maximum intensity is obtained by passing the laser through a cross-section perpendicular to the beam propagation direction, where the laser intensity distribution is located near the center of the optical axis. 00 By setting the mode, the focusing diameter d [mm] of the irradiation beam in the rolling direction, the scanning linear velocity V [mm / s] of the laser beam, and the average output power P [W] of the laser to be in the range of 0 < d ≤ 0.2 and 0.001 ≤ P / V ≤ 0.012, a directional electromagnetic steel sheet with reduced iron loss can be obtained.

[0009] Furthermore, Patent Document 3 discloses a method for manufacturing a directional electromagnetic steel plate, in which the surface of the directional electromagnetic steel plate is irradiated with laser beams at equal intervals to improve its magnetic properties.

[0010] Patent document 3 shows that the laser is a pulsed oscillating Q-switched CO2 laser, and the irradiation beam shape is an ellipse with a major axis in the width direction of the plate. By setting the irradiation power density of the laser pulse to below the film damage threshold on the steel plate surface, the generation of laser irradiation marks is suppressed. Furthermore, by setting the length of the major axis of the elliptical beam to above the pulse beam irradiation interval in the width direction of the plate, the continuous pulse beams overlap on the steel plate surface, providing sufficient accumulated irradiation energy required for magnetic property improvement, suppressing laser irradiation marks, and achieving effective magnetic domain control.

[0011] On the other hand, in recent years, there has been a growing demand for reduced noise and vibration in electromagnetic applications such as transformers. This has led to a requirement for directional electromagnetic steel sheets used in transformer cores to be low-iron-loss materials suitable for low noise and low vibration. One contributing factor to the noise and vibration in transformers is reportedly the magnetostriction of directional electromagnetic steel sheets. Magnetostriction, as referred to here, is a vibration visible in the rolling direction of the directional electromagnetic steel sheet caused by a slight change in its shape due to variations in magnetization intensity when the sheet is energized with alternating current. The magnitude of this magnetostriction is 10. -6 Although the magnetostriction is on the order of magnitude and very small, it causes vibrations in the iron core, which propagate through external structures such as the transformer housing and become noise.

[0012] While laser irradiation of directional electromagnetic steel sheets as described in Patent Documents 1 to 3 is effective in reducing iron loss, it has the following drawback: the closed magnetic domains formed by laser irradiation increase magnetostriction, thereby degrading noise characteristics.

[0013] To address such issues, for example, Patent Document 4 discloses a directional electromagnetic steel plate with low iron loss and low noise when assembled into a transformer.

[0014] Patent document 4 shows 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 200 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 local strain introduced at periodic intervals relative to the rolling direction and in a direction that is transversely cut 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. Furthermore, an average of 1.8 or more of the 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 revealed that, with respect to the technology in Patent Documents 4 and 5, the improvement in noise characteristics is insufficient for the superior iron loss / noise balance required in recent years. Furthermore, it was found that magnetic domain control also damages the coating formed on the surface of the steel plate to impart insulation and tension to the directional electromagnetic steel plate, thus reducing the coating's adhesion.

[0018] Existing technical documents

[0019] Patent documents

[0020] Patent Document 1: Japanese Patent No. 4669565

[0021] Patent Document 2: Japanese Patent No. 4510757

[0022] Patent Document 3: Japanese Patent No. 3361709

[0023] Patent Document 4: Japanese Patent No. 6060988

[0024] Patent Document 5: Japanese Patent No. 6176282 Summary of the Invention

[0025] The problem that the invention aims to solve

[0026] As mentioned above, there has been no previously disclosed directional electromagnetic steel sheet and its manufacturing method that simultaneously and sufficiently improves iron loss characteristics and noise characteristics, while also taking into account the assurance of film adhesion.

[0027] The objective of this invention is to provide a directional electromagnetic steel sheet with excellent iron loss and noise characteristics (high iron loss improvement rate due to magnetic domain subdivision, low noise when assembled into a transformer, and excellent iron loss / noise balance) and a method for manufacturing the same. The objective is to preferably provide a directional electromagnetic steel sheet with excellent iron loss and noise characteristics, and consequently, excellent film adhesion.

[0028] Methods for solving problems

[0029] The present invention relates to the study of magnetic domain control conditions for obtaining directional electromagnetic steel sheets with excellent balance between iron loss and noise characteristics (iron loss / noise balance). The results show that, for the conditions under which energy rays are irradiated for magnetic domain control, a good iron loss / noise balance is achieved by increasing the input energy and decreasing the power density while controlling the shape of the energy rays on the irradiated surface. However, it is known that these steel sheets are prone to coating peeling starting from the energy ray irradiation area.

[0030] Directional electromagnetic steel sheets are irradiated with energy rays (laser beams, electron beams, etc.), causing the irradiated area to be rapidly heated and cooled. As a result, residual strain is generated from the surface near the irradiated area into the interior of the steel sheet, forming a strain region (residual strain region). Coating peeling easily originates from the energy ray irradiated area, but it is believed that in addition to damage to the coating at the irradiated area, the residual strain near the irradiated area is also a contributing factor. Considering these factors, the inventors attempted to adjust the energy ray irradiation conditions to a strain variable that maintains a good balance between iron loss and noise. The results showed that by adjusting the energy ray irradiation conditions and setting the width and formation interval of the strain region to a suitable range, a good balance between iron loss and noise can be obtained.

[0031] Furthermore, the inventors attempted to quantify the correlation between the corresponding variable and the magnitude of magnetostriction in directional electromagnetic steel sheets subjected to energy irradiation with increased input energy and reduced power density. The results showed that good film adhesion could be ensured by controlling the change in magnetostriction before and after specific heat treatment within a certain range.

[0032] Furthermore, the inventors conducted an in-depth investigation into the relationship between the structure of the compound phase constituting the coating and the coating adhesion. The results showed that by ensuring the MgAl₂O₄ phase formed in the coating remains in the lower part of the glass coating, better coating adhesion can be ensured.

[0033] The present invention was made in view of the above-mentioned insights. The main points of the present invention are as follows.

[0034] [1] One aspect of the present invention is a directional electromagnetic steel plate comprising: a base steel plate, a glass film formed on the base steel plate, and a tension-imparting insulating film formed on the glass film. In the base steel plate, there are multiple linear strain regions extending continuously or intermittently in a direction intersecting the rolling direction. The width of each of the multiple linear strain regions in the rolling direction is 210 μm or less. The multiple linear strain regions are parallel to each other, and the interval between adjacent linear strain regions in the rolling direction is 10 mm or less. The magnetostriction λ in μm / m at 1.7T excitation is... 0-pb The magnetostriction λ in μm / m after heat treatment at 800℃ for 4 hours and excitation to 1.7T 0-pa It satisfies the following equation (1).

[0035] 0.02≤λ 0-pb -λ 0-pa ≤0.20 (1)

[0036] [2] According to the directional electromagnetic steel plate described in [1], it is also possible that: the glass film contains a structure including MgAl2O4 phase and Mg2SiO4 phase as main phase, and in the cross section in the thickness direction, the glass film is divided into three regions of equal thickness along the thickness direction, and each region is set as 1 / 3 region, 2 / 3 region and 3 / 3 region from the side of the parent steel plate toward the side of the tension-bearing insulating film. When the area ratio of MgAl2O4 phase in the 1 / 3 region is set as S1, the area ratio of MgAl2O4 phase in the 2 / 3 region is set as S2 and the area ratio of MgAl2O4 phase in the 3 / 3 region is set as S3, the above S1, the above S2 and the above S3 satisfy the following formulas (2) to (4).

[0037] S1>S2>S3 (2)

[0038] (S1+S2+S3) / 3<0.50 (3)

[0039] S3 < 0.10 (4)

[0040] [3] Another aspect of the present invention is a method for manufacturing directional electromagnetic steel plates as described in [1] or [2], comprising the following steps: a hot rolling process of heating a steel billet and hot rolling it into a hot-rolled steel plate; a hot rolling annealing process of hot rolling annealing the hot-rolled steel plate; a pickling process of pickling the hot-rolled steel plate after the hot rolling annealing process; a cold rolling process of cold rolling the hot-rolled steel plate after the pickling process by performing a single cold rolling or multiple cold rolling with annealing to produce a cold-rolled steel plate; a decarburizing annealing process of decarburizing the cold-rolled steel plate; and coating the front and back surfaces of the cold-rolled steel plate after the decarburizing annealing process, which is a base material steel plate, with an annealing separating agent with MgO powder as the main component. After drying, a final annealing process is performed to form a glass film; 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 a magnetic domain subdivision process is performed by irradiating the surface of the tension-imparting insulating film of the directional electromagnetic steel plate with energy rays to form multiple linear strain regions in the base steel plate, wherein, in the magnetic domain subdivision process, the rolling direction spacing of adjacent linear strain regions in the multiple linear strain regions is 10 mm or less, and the energy ray output power P in W and the magnetic domain subdivision process in mm are used. 2 The calculated energy ray irradiation cross-sectional area S is defined by (P / S) in units of W / mm². 2 The calculated energy ray power density Ip satisfies the following equation (5). 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 (6), and...

[0041] The diameter dl of the energy beam perpendicular to the beam scanning direction, measured in μm, and the diameter dc of the beam scanning direction, defined by (dl / dc), satisfy the following equations (7) and (8), respectively.

[0042] 250≤Ip≤2000 (5)

[0043] 0.010 < Up ≤ 0.050 (6)

[0044] 0.0010 < dl / dc < 1.0000 (7)

[0045] 10 < dl < 200 (8)

[0046] [4] According to the manufacturing method of the directional electromagnetic steel plate described in [3], it is also possible that the above-mentioned energy ray is a laser beam.

[0047] [5] According to the manufacturing method of the directional electromagnetic steel plate described in [4], it is also possible that the laser beam is a fiber laser beam.

[0048] [6] The method for manufacturing the directional electromagnetic steel sheet according to any one of [3] to [5] may also include the following: the steel billet contains, by mass %: C: 0.010 to 0.200%, Si: 3.00 to 4.00%, sol.Al: 0.010 to 0.040%, Mn: 0.01 to 0.50%, N: less than 0.020%, S: 0.005 to 0.040%, P: less than 0.030%, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, with the remainder containing Fe and impurities.

[0049] [7] The manufacturing method of the directional electromagnetic steel sheet according to any one of [3] to [6] may also include: the above-mentioned decarburization annealing process having a heating process and a homogenization process, wherein the heating rate at 550 to 750°C in the above-mentioned heating process is set to 700 to 2000°C / second, and the oxygen potential is set to 0.0001 to 0.0100, and the above-mentioned homogenization process includes a first homogenization process in an atmosphere with an oxygen potential of 0.4 or higher and 0.8 or lower, wherein the annealing temperature is set to 800 to 900°C and the annealing time is set to 100 to 500 seconds, and a second homogenization process in an atmosphere with an oxygen potential of 0.1 or lower, wherein the annealing temperature is set to 850°C or higher and 1000°C or lower, and the annealing time is set to 5 seconds or higher and 100 seconds or lower.

[0050] [8] The method for manufacturing directional electromagnetic steel sheet according to any one of [3] to [7] may further include a nitriding treatment step for nitriding the cold-rolled steel sheet during or after the decarburizing annealing step.

[0051] Invention Effects

[0052] According to the above-described embodiments of the present invention, a directional electromagnetic steel sheet with good iron loss / noise balance and a method for manufacturing the same can be provided. Furthermore, according to a preferred embodiment of the present invention, a directional electromagnetic steel sheet with good iron loss / noise balance and excellent coating adhesion can be provided. Detailed Implementation

[0053] 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.

[0054] Furthermore, multiple linear strain (residual strain) regions are formed in the base steel plate, extending continuously or intermittently in a direction intersecting the rolling direction, and are generally parallel to each other. The width (width in the rolling direction) of each linear strain region is 210 μm or less, and the interval between adjacent linear strain regions in the rolling direction is 10 mm or less.

[0055] The directional electromagnetic steel plate of this embodiment will be described below.

[0056] <Base Material Steel Plate>

[0057] (Chemical composition)

[0058] The directional electromagnetic steel sheet of this embodiment has significant characteristics in the structure of the compound phase in the strain region (linear strain region) and the glass coating. The chemical composition of the base steel sheet used in the directional electromagnetic steel sheet is not limited and is preferably within a known range. For example, in order to obtain the characteristics generally required for a directional electromagnetic steel sheet, the following components are preferably included as the chemical composition. In this embodiment, unless otherwise specified, the percentages related to the chemical composition are by mass%.

[0059] C: Below 0.010%

[0060] Carbon (C) is an element effective for 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 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 preferably set to 0.010% or less. The C content is more preferably 0.005% or less. The lower the C content, the more preferred, but even if the C content is reduced to less than 0.0001%, the effect of microstructure control saturates, and only the manufacturing cost increases. Therefore, the C content can also be set to 0.0001% or more.

[0061] Si: 3.00~4.00%

[0062] Silicon (Si) is an element that increases the resistance of directional electromagnetic steel sheets and improves iron loss characteristics. When the Si content is less than 3.00%, a sufficient reduction in eddy current losses cannot be achieved. Therefore, the Si content is preferably set to 3.00% or more. More preferably, the Si content is 3.10% or more, and even more preferably 3.20% or more.

[0063] 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 preferably set to 4.00% or less. More preferably, the Si content is 3.80% or less, and even more preferably 3.70% or less.

[0064] Mn: 0.01~0.50%

[0065] Manganese (Mn) is an element that combines with sulfur (S) during the manufacturing process to form MnS. These precipitates function as inhibitors (inhibitors of normal grain growth), exhibiting 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 preferably set to 0.01% or more. More preferably, the Mn content is 0.02% or more.

[0066] 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 preferably set to 0.50% or less. More preferably, the Mn content is 0.20% or less, and even more preferably 0.10% or less.

[0067] N: below 0.010%

[0068] 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 preferably set to 0.010% or less. More preferably, the N content is 0.008% or less.

[0069] On the other hand, there is no specific lower limit for nitrogen content, but even if it is reduced to below 0.001%, only the manufacturing cost increases. Therefore, the nitrogen content can also be set above 0.001%.

[0070] sol.Al: 0.020% or less

[0071] Sol.Al (acid-soluble aluminum) is an element that combines with nitrogen (N) during the manufacturing process of directional electromagnetic steel sheets to form AlN, which functions as an inhibitor. However, if the Sol.Al content of 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 preferably set to 0.020% or less. More preferably, it is 0.010% or less, and even more preferably less than 0.001%. There is no particular requirement for a lower limit for the Sol.Al content, but even if it is reduced to less than 0.0001%, only the manufacturing cost increases. Therefore, the Sol.Al content can also be set to 0.0001% or more.

[0072] S: below 0.010%

[0073] 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 preferably set to 0.010% or less. The S content in the directional electromagnetic steel sheet is preferably as low as possible, for example, less than 0.001%. However, even if the S content in the directional electromagnetic steel sheet is reduced to less than 0.0001%, only the manufacturing cost increases. Therefore, the S content in the directional electromagnetic steel sheet can also be 0.0001% or more.

[0074] P: below 0.030%

[0075] 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 preferably set to 0.030% or less. More preferably, the P content is 0.020% or less, and even more preferably 0.010% or less.

[0076] The lower limit for phosphorus (P) content can include 0%, but 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.

[0077] Remaining components: Fe and impurities

[0078] The chemical composition of the base steel plate of the directional electromagnetic steel plate in this embodiment may also contain the elements described above, with the remainder being Fe and impurities. However, for the purpose of improving magnetic properties, Cu, Cr, Sn, Se, Sb, and Mo may be further included within the ranges shown below. These elements are also permitted to be included as impurities.

[0079] Furthermore, other than these elements, such as the presence of any one or two or more of W, Nb, Ti, Ni, Bi, Co, and V totaling less than 1.0%, will not hinder the effect of the directional electromagnetic steel plate of this embodiment.

[0080] Here, impurities refer to elements that are mixed in from the raw materials such as ore or scrap iron, or from the manufacturing environment, during the industrial manufacturing of the base steel plate. These are elements that are allowed to be present in a content that does not adversely affect the function of the directional electromagnetic steel plate of this embodiment.

[0081] Cr: 0–0.50%

[0082] Cr (chromium) is an element that helps increase the occupancy of Goss orientation in secondary recrystallization structures, thereby improving magnetic properties. To achieve the above effect, 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.

[0083] On the other hand, when the Cr content exceeds 0.50%, Cr oxide will form, reducing the magnetic properties. Therefore, the Cr content is preferably set to 0.50% or less. More preferably, the Cr content is 0.30% or less, and even more preferably 0.10% or less.

[0084] Sn: 0–0.50%

[0085] Sn (tin) is an element whose magnetic properties are improved through controlled recrystallization. To achieve this improvement in magnetic properties, 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.

[0086] On the other hand, when the Sn content exceeds 0.50%, secondary recrystallization becomes unstable, and the magnetic properties deteriorate. Therefore, the Sn content is preferably set to 0.50% or less. The Sn content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0087] Cu: 0–0.50%

[0088] Cu (copper) is an element that contributes to increasing the proportion of Goss orientation in secondary recrystallization structures. Cu is an optional element in the base steel sheet of this embodiment. Therefore, its content is limited to 0%, but to achieve the aforementioned effect, it is preferable to set the Cu content to 0.01% or more. More preferably, the Cu content is 0.02% or more, and even more preferably 0.03% or more.

[0089] 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, it is preferable to set the Cu content to 0.50% or less. More preferably, the Cu content is 0.30% or less, and even more preferably 0.10% or less.

[0090] Se: 0~0.020%

[0091] Selenium (Se) is an element that improves magnetic properties. Therefore, it may be included in the composition of Se. When Se is included, it is preferable to set the content to 0.001% or more in order to effectively improve magnetic properties. The Se content is preferably 0.003% or more, and more preferably 0.006% or more.

[0092] On the other hand, if the Se content exceeds 0.020%, the adhesion of the glass coating deteriorates. Therefore, it is preferable to set the Se content to 0.020% or less. More preferably, the Se content is 0.015% or less, and even more preferably 0.010% or less.

[0093] Sb: 0~0.500%

[0094] 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.

[0095] On the other hand, if the Sb content exceeds 0.500%, the adhesion of the glass coating deteriorates significantly. Therefore, it is preferable to set the Sb content to 0.500% or less. More preferably, the Sb content is 0.300% or less, and even more preferably 0.100% or less.

[0096] Mo: 0–0.10%

[0097] Mo (molybdenum) is an element that improves magnetic properties. Therefore, it may be included in the composition of the molybdenum. 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.

[0098] On the other hand, if the Mo content exceeds 0.10%, cold rollability may deteriorate, leading to breakage. Therefore, it is preferable to set the Mo content to 0.10% or less. More preferably, the Mo content is 0.08% or less, and even more preferably 0.05% or less.

[0099] As described above, the chemical composition of the base steel plate of the directional electromagnetic steel plate illustrated in 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.

[0100] 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.

[0101] Specifically, the tension is applied to the insulating film by immersing the directional electromagnetic steel plate in an aqueous solution of sodium hydroxide containing 30-50% by mass of NaOH and 50-70% by mass of H2O at 80-90°C for 7-10 minutes.

[0102] The directional electromagnetic steel sheet, after the tension-insulating film has been removed, is washed with water and then dried with a warm air blower for less than 1 minute. The glass film is then removed by immersing the dried directional electromagnetic steel sheet (without the tension-insulating film) in an aqueous solution of hydrochloric acid containing 30-40% by mass and at 80-90°C for 1-10 minutes.

[0103] The impregnated steel plate is washed with water, and then dried with a warm air blower for less than 1 minute.

[0104] Through the above procedures, the base steel plate can be removed from the directional electromagnetic steel plate.

[0105] The chemical composition of the base steel plate is determined using well-known compositional analysis methods. Specifically, a drilling machine is used to generate shavings from the base steel plate. These shavings are 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.

[0106] 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.

[0107] 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.

[0108] The nitrogen content is determined using the well-known inert gas melting-thermal conductivity method.

[0109] (Strain Region)

[0110] In the base steel plate of the directional electromagnetic steel plate of this embodiment, there are multiple linear strain regions (residual strain regions) formed by irradiation with energy rays.

[0111] These multiple linear strain regions extend along the surface of the base steel plate in a direction intersecting the rolling direction. Each strain region is parallel (with a deviation of approximately 5° allowed in actual manufacturing), and its width along the rolling direction is less than 210 μm. Adjacent linear strain regions are formed at intervals of less than 10 mm along the rolling direction. By setting the strain regions as described above, a good balance between iron loss and noise can be achieved.

[0112] The location of strain can be analyzed using residual strain measurement techniques based on X-ray diffraction (e.g., K. Iwata, et al., J. Appl. Phys. 117.17A910 (2015)). Furthermore, if energy ray irradiation marks can be identified on the steel plate surface, these marks can be directly identified as strain regions.

[0113] Furthermore, it is known that when the strain (residual strain) is compressive strain in the rolling direction and tensile strain in the thickness direction, a region magnetized along the thickness direction, known as closed magnetic domains, is formed in the region where the strain exists (strain region).

[0114] In this embodiment, "extending along a direction intersecting the rolling direction" means that the direction of the strain region's extension is within 30° of the direction perpendicular to the rolling direction. If it deviates from this angle range, the 180° magnetic domain subdivision effect of the steel plate is reduced, and a sufficient iron loss reduction effect cannot be obtained.

[0115] The strain region can exist continuously as a straight line or intermittently extending in one direction (e.g., as a dashed line), but from the perspective of improving iron loss, a continuous existence is preferred. The linear strain region is formed by irradiation with energy rays. The type of energy ray is not particularly limited, but commonly used lasers or electron beams are preferred. When irradiating with an electron beam, the atmosphere during electron beam irradiation needs to be set to a vacuum with a vacuum level below a certain value, which raises concerns about increased production costs.

[0116] Furthermore, if the rolling direction spacing between adjacent linear strain regions exceeds 10 mm, the domain subdivision effect of the 180° magnetic domains is reduced, resulting in insufficient improvement in iron loss. Therefore, the rolling direction spacing between adjacent linear strain regions is set to 10 mm or less. The spacing between multiple linear strain regions is preferably approximately equal.

[0117] Narrowing the irradiation spacing generally reduces iron loss, but if it is reduced excessively, the domain subdivision effect saturates, eddy current losses essentially cease to decrease, and the increase in hysteresis losses caused by strain becomes significant, worsening iron loss. Furthermore, noise characteristics may deteriorate. Therefore, the spacing in the rolling direction between adjacent linear strain regions is preferably set to 3 mm or more.

[0118] Here, the spacing between adjacent strain regions in the rolling direction is the distance between the center of a linear strain region and the center of an adjacent linear strain region in the rolling direction.

[0119] The length of the strain in the width direction is not limited, but it is preferable to extend 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 must satisfy d1 ≤ 3 × d0. d0 can be in the range of 50 μm or more and 50 mm or less.

[0120] Furthermore, if the proportion of the strain region on the surface of the base steel plate becomes excessively large, the overall strain of the base steel plate increases, leading to increased total hysteresis loss, deterioration of iron loss, and degradation of noise characteristics. Therefore, the width of the strain region is set to 210 μm or less. Preferably, it is 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0121] In the directional electromagnetic steel sheet of this embodiment, the state related to strain is further defined by the change in magnetostriction during specific heat treatment. Specifically, the magnetostriction λ at 1.7T excitation is... 0-pb The magnetostriction λ after being heat-treated at 800℃ for 4 hours and then excited to 1.7T 0-pa It satisfies the following equation (1).

[0122] 0.02≤λ 0-pb -λ 0-pa ≤0.20(μm / m) (1)

[0123] Under the condition of satisfying the above equation (1), it becomes possible to ensure a good iron loss / noise balance.

[0124] This formula is considered to be a formula that evaluates not only the strain quantity but also the distribution of strain and the state of lattice defects that constitute strain, which are introduced into the base steel plate by energy ray irradiation. By setting the strain to be within the range of Equation (1) as the strain release factor caused by heat treatment at 800°C for 4 hours and the relationship with magnetostriction, a good balance between iron loss and noise can be achieved.

[0125] A change in magnetostriction of less than 0.02 μm / m before and after heat treatment indicates that an appropriate amount of strain was not introduced during energy ray irradiation, or that the strain is not easily released by heat treatment. In this case, a good iron loss / noise balance cannot be achieved. On the other hand, a change in magnetostriction of more than 0.20 μm / m before and after heat treatment indicates that excessive strain was introduced during energy ray irradiation, or that the strain is easily excessively released by heat treatment. In this case, a good iron loss / noise balance also cannot be achieved.

[0126] <Glass Coating>

[0127] In the directional electromagnetic steel sheet of this embodiment, a glass film is formed on the surface of the base steel sheet.

[0128] The glass coating is an inorganic coating with magnesium silicate as its main component. It is formed by reacting an annealing separating agent containing magnesium oxide (MgO) applied to the surface of the base steel sheet during final annealing with the surface components of the base steel sheet. The glass coating has a composition derived from the annealing separating agent and the base steel sheet, containing a microstructure comprising the Mg₂SiO₄ phase (more than 50% by area) and the MgAl₂O₄ phase as the main phases. In addition to these phases, it sometimes contains less than 1% precipitates.

[0129] The area occupied by each phase (area ratio) is determined by the composition of the oxides obtained by energy-dispersive X-ray analysis in a scanning electron microscope attached to a cross-section of the glass film thickness. The region containing Mg, Al, and O, with an Al concentration of 5% or more, is designated as the MgAl2O4 phase, and the region with a Si concentration of 5% or more is designated as the Mg2SiO4 phase.

[0130] In this embodiment, the directional electromagnetic steel sheet preferably has a defined structure in which the compound phase constituting the glass coating has a specified structure. Specifically, in the cross-section of the directional electromagnetic steel sheet in the thickness direction, the glass coating is divided into three regions of equal thickness along the thickness direction. Each region is designated as 1 / 3 region, 2 / 3 region, and 3 / 3 region from the side of the parent steel sheet toward the surface of the steel sheet. Furthermore, when the area ratio of the MgAl2O4 phase in the 1 / 3 region is set as S1, the area ratio of the MgAl2O4 phase in the 2 / 3 region is set as S2, and the area ratio of the MgAl2O4 phase in the 3 / 3 region is set as S3, it is preferable to satisfy the following formulas (2) to (4).

[0131] In cross-sectional observation, the leading edge of the glass film also exhibits drastically uneven or separated island-like regions. In this embodiment, a sufficient length of 20 mm or more is observed along a direction parallel to the steel plate surface. The total thickness of the glass film is defined as the distance between the location where the glass film penetrates deepest into the parent steel plate and the outermost surface of the steel plate in the thickness direction where the glass film is located. The thicknesses of the aforementioned 1 / 3, 2 / 3, and 3 / 3 regions are then determined. Furthermore, in the calculation of the area ratio of the MgAl2O4 phase in each region, the total area of ​​each region, which becomes the denominator, is the "region as glass film" that also includes the island-like regions. That is, in the leading edge region of the glass film, i.e., the 1 / 3 region, the "region as glass film" is prone to drastically uneven or separated island-like regions. Although there are many Fe phases within the same thickness range, the Fe phase regions are not included in the area (total area) of the region that becomes the denominator in the calculation of the area ratio of the MgAl2O4 phase. Therefore, the total area of ​​the 1 / 3 region generally becomes smaller than the total area of ​​the 2 / 3 and 3 / 3 regions.

[0132] S1>S2>S3 (2)

[0133] (S1+S2+S3) / 3<0.50 (3)

[0134] S3 < 0.10 (4)

[0135] Under the condition that equations (2) to (4) are satisfied, it indicates that the MgAl2O4 phase, which is a mixed phase, exists unevenly on the side of the base steel plate in the glass film.

[0136] In the 1 / 3 region, the MgAl2O4 phase is a compound phase that enhances the adhesion of the film. This 1 / 3 region of the glass film is the area bonded to the base steel plate. The interface between the glass film and the base steel plate generally exhibits a complex, uneven shape, also resembling a "root." Through this morphology, the glass film and the base steel plate are strongly bonded through a so-called anchoring effect. Therefore, even if the MgAl2O4 phase is present to a certain extent in this region, cracks that could become the starting point for film peeling are unlikely to occur.

[0137] Therefore, it is preferable that the MgAl2O4 phase is non-uniformly present in the 1 / 3 region of the glass film. From the viewpoint of adhesion, it is preferable that the MgAl2O4 phase is also as non-uniformly present as possible on the side of the base steel plate in the 1 / 3 region. The form in which the MgAl2O4 phase is (only) non-uniformly present at the interface between the glass film and the base steel plate can be said to be one of the most preferred forms.

[0138] On the other hand, the MgAl2O4 phase is a compound phase that should be avoided from forming in the 3 / 3 region. If the MgAl2O4 phase is present in the 3 / 3 region of the glass film, it becomes the starting point for crack initiation, and the film adhesion is significantly reduced. Therefore, S3 < 0.10 is preferred, more preferably S3 < 0.05, and S3 = 0 is the most preferred state. Furthermore, if the proportion of the MgAl2O4 phase in the whole is 0.50 or more, a peeling starting point is generated between the MgAl2O4 phase and the Mg2SiO4 phase. Therefore, the area fraction (S1 + S2 + S3) / 3 of the MgAl2O4 phase in the glass film is preferably less than 0.50, more preferably less than 0.30.

[0139] By applying a coating in this morphology, a good balance of iron loss / noise can be ensured in steel sheets with the aforementioned strain (magnetostrictive changes caused by heat treatment), and further, good coating adhesion can be achieved. The reason for this is not clear, but it can be considered as follows.

[0140] The directional electromagnetic steel sheet of this embodiment achieves a good iron loss / noise balance through irradiation conditions, represented by energy beam irradiation with increased input energy and reduced power density, but it also becomes more prone to coating peeling from the laser irradiation area. This suggests that the strain formed in the directional electromagnetic steel sheet of this embodiment is different from the general strain distribution to date. Therefore, it is anticipated that when stress is applied to the directional electromagnetic steel sheet, a higher peeling stress than before will act on the interface between the base steel sheet and the glass coating in the strain region. It is believed that this peeling stress is mitigated by the non-uniform existence of the MgAl2O4 phase in the glass coating on the base steel sheet side. It is unclear whether this mitigation is caused by the stress generated by the non-uniform existence configuration of the dissimilar phases being due to the mitigation of peeling stress caused by residual strain, or whether the non-uniform existence configuration of the dissimilar phases itself has a strong resistance to peeling stress. However, considering that the improved coating adhesion effect brought about by the non-uniform existence configuration of the MgAl2O4 phase specified in this embodiment plays a significant role in the strain-controlled magnetic domain material shown in this embodiment, it is believed that this combination has a particularly preferred interaction.

[0141] Furthermore, the possibility that not only the energy ray irradiation conditions, but also the non-uniform distribution of the MgAl2O4 phase in the glass coating itself, may have a qualitative impact on the strain of the energy ray irradiated section, making the iron loss / noise balance even better. A detailed analysis of the influence of the interaction between strain and glass coating morphology on the iron loss / noise balance or sealing performance is anticipated in future studies.

[0142] In the directional electromagnetic steel sheet of this embodiment, even directional electromagnetic steel sheets that achieve a good iron loss / noise balance through irradiation conditions such as energy beam irradiation with increased input energy and reduced power density can achieve sufficient coating adhesion. Specifically, the residual coating area ratio when the directional electromagnetic steel sheet is wound onto a round bar with a diameter of 20 mm and bent back to its original shape is 90% to 100%. This residual coating area ratio is used as an indicator of the quality of coating adhesion. The residual coating area ratio is preferably 95% or more.

[0143] The residual film area percentage is evaluated through a bending tightness test. An 80mm × 80mm flat test piece taken from a directional electromagnetic steel plate with a film is wound onto a 20mm diameter round rod, then unfolded flat. The area of ​​the film (glass film and / or tension insulation film) that has not peeled off from the electromagnetic steel plate is measured. The value obtained by dividing the area without peeling by the area of ​​the steel plate is defined as the residual film area percentage (%). For example, a transparent film with a 1mm grid scale can be placed on the test piece, and the area of ​​the film that has not peeled off can be measured.

[0144] <Tension imparts insulation film>

[0145] In the directional electromagnetic steel plate of this embodiment, a tension-insulating film is formed on the surface of the glass film.

[0146] Tension-imbued insulating films reduce eddy current losses and improve iron losses in directional electromagnets by imparting electrical insulation to them. Furthermore, in addition to the aforementioned electrical insulation properties, tension-imbued insulating films can also provide various other properties such as corrosion resistance, heat resistance, and smoothness.

[0147] 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.

[0148] Tension imparts an insulating coating, preferably a known coating formed by applying a coating solution with metal phosphates and silica as the main components to the surface of a glass coating and then baking it.

[0149] <Base steel plate thickness: 0.17~0.30mm>

[0150] 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, the preferred upper limit for the base steel plate thickness is 0.30 mm. However, manufacturing base steel plates thinner than 0.17 mm requires specialized equipment, increasing manufacturing costs and making it less desirable from a production standpoint. Therefore, the industrially preferred lower limit for the plate thickness is 0.17 mm.

[0151] <Manufacturing Method>

[0152] The directional electromagnetic steel sheet of this embodiment can be manufactured by a manufacturing method including the following steps.

[0153] (i) The hot rolling process of heating a steel billet and hot rolling it into a hot-rolled steel sheet;

[0154] (ii) The hot-rolled steel sheet is subjected to a hot-rolled annealing process;

[0155] (iii) A pickling process for pickling the hot-rolled steel plate after the above-mentioned hot-rolled plate annealing process.

[0156] (iv) A cold rolling process in which the hot-rolled steel sheet after the pickling process is subjected to one cold rolling or multiple (two or more) cold rolling processes with annealing to produce a cold-rolled steel sheet.

[0157] (v) A decarburizing annealing process is performed on the above-mentioned cold-rolled steel sheet;

[0158] (vi) After the above-mentioned decarburization annealing process of the cold-rolled steel sheet as the base material, the front and back surfaces are coated with an annealing separating agent with MgO powder as the main component and dried, and then the final annealing is carried out to form a glass film.

[0159] (vii) A tension-imparting insulating film is formed on the glass film to obtain a film forming process of 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.

[0160] (viii) A magnetic domain subdivision process in which the surface of the insulating film is irradiated with energy rays to form multiple linear strain regions in the base steel plate by applying the tension of the directional electromagnetic steel plate.

[0161] In the manufacturing method of the directional electromagnetic steel sheet of this embodiment, the conditions in the magnetic domain subdivision process, which specifically controls the state of strain, and the conditions in the decarburization annealing process, which specifically controls the morphology of the MgAl2O4 phase in the glass film, are characteristic conditions.

[0162] 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.

[0163] <About the chemical composition of steel billets>

[0164] The chemical composition of the steel billet supplied for the heating process is not limited, but in order to obtain the properties generally required for directional electromagnetic steel sheets, the following components are preferably included as the chemical composition. In the following description, unless otherwise specified, "%" is used to indicate "mass %". The steel billet is, for example, a slab.

[0165] C: 0.010~0.200%

[0166] Carbon (C) is an element that exhibits an improving effect on magnetic flux density. However, when the C content in the billet exceeds 0.200%, the steel undergoes a phase transformation during secondary recrystallization annealing (i.e., final annealing), and secondary recrystallization is not sufficiently achieved, resulting in poor magnetic flux density and iron loss characteristics. Therefore, it is preferable to set the C content of the billet to 0.200% or less. The lower the C content, the better for reducing iron loss. From the viewpoint of reducing iron loss, the C content is more preferably 0.150% or less, and even more preferably 0.100% or less.

[0167] On the other hand, when the carbon content of the billet is less than 0.010%, the improvement in magnetic flux density cannot be obtained. Therefore, the carbon content of the billet is set to 0.010% or more. The carbon content is preferably 0.040% or more, and more preferably 0.060% or more.

[0168] Si: 3.00~4.00%

[0169] Silicon (Si) is an element highly effective at increasing the resistivity of steel and thus reducing eddy current losses, which constitute part of iron losses. When the Si content in the billet is less than 3.00%, the steel undergoes a phase transformation during secondary recrystallization annealing, and secondary recrystallization is insufficient, resulting in poor magnetic flux density and iron loss characteristics. Therefore, the Si content in the billet is preferably set to 3.00% or more. More preferably, it is 3.10% or more, and even more preferably 3.20% or more.

[0170] On the other hand, when the Si content exceeds 4.00%, the steel sheet becomes brittle, and the permeability during manufacturing processes deteriorates significantly. Therefore, the Si content of the steel billet is preferably set to 4.00% or less. More preferably, the Si content of the steel billet is 3.80% or less, and even more preferably 3.60% or less.

[0171] sol.Al: 0.010~0.040%

[0172] Sodium soluble aluminum (sol.Al) is a major constituent element of compounds known as inhibitors in the secondary recrystallization of directional electromagnetic steel sheets. From the viewpoint of secondary recrystallization performance, it is an essential element in the base steel sheet of this embodiment. When the sol.Al content in the billet is less than 0.010%, AlN, which functions as an inhibitor, is not sufficiently generated, secondary recrystallization becomes insufficient, and the iron loss characteristics are not improved. Therefore, the sol.Al content in the billet is preferably set to 0.010% or more. More preferably, it is 0.015% or more, and even more preferably 0.020%.

[0173] On the other hand, when the sol.Al content exceeds 0.040%, the embrittlement of the steel plate becomes significant. Therefore, the sol.Al content of the billet is preferably set to 0.040% or less. More preferably, the sol.Al content is 0.035% or less, and even more preferably 0.030% or less.

[0174] Mn: 0.01~0.50%

[0175] Manganese (Mn) is an important element in the formation of MnS, which is one of the main inhibitors of MnS formation. When the Mn content in the billet is less than 0.01%, the absolute amount of MnS required for secondary recrystallization is insufficient. Therefore, the Mn content in the billet is preferably set to 0.01% or more. More preferably, it is 0.03% or more, and even more preferably 0.06% or more.

[0176] On the other hand, when the Mn content in the billet exceeds 0.50%, a phase transformation occurs in the steel during secondary recrystallization annealing, and secondary recrystallization is not fully carried out, resulting in poor magnetic flux density and iron loss characteristics. Therefore, the Mn content in the billet is set to 0.50% or less. More preferably, the Mn content is 0.40% or less, and even more preferably, 0.30% or less.

[0177] N: below 0.020%

[0178] Nitrogen (N) is an element that reacts with the aforementioned acid-soluble Al to form AlN, which functions as an inhibitor. When the N content in the billet exceeds 0.020%, cavities (voids) are generated in the steel sheet during cold rolling, and the strength increases, while the sheet's passability deteriorates during manufacturing. Therefore, it is preferable to set the N content in the billet to 0.020% or less. The N content is more preferably 0.015% or less, and even more preferably 0.010% or less. As long as AlN is not used as an inhibitor, the lower limit of the N content can include 0%. However, since the detection limit for chemical analysis is 0.0001%, the practical lower limit of the N content in practical steel sheets is 0.0001%. On the other hand, in order to combine with Al to form AlN, which functions as an inhibitor, the N content in the billet is preferably 0.001% or more, and more preferably 0.005% or more.

[0179] S: 0.005~0.040%

[0180] Sulfur (S) is an important element that reacts with Mn to form MnS, which acts as an inhibitor. When the S content in the steel billet is below 0.005%, a sufficient inhibitory effect cannot be obtained. Therefore, it is preferable to set the S content in the steel billet to 0.005% or more. More preferably, the S content is 0.010% or more, and even more preferably 0.020% or more.

[0181] On the other hand, when the sulfur content in the billet exceeds 0.040%, it becomes a cause of hot brittleness, making hot rolling significantly more difficult. Therefore, the sulfur content in the billet is preferably set to 0.040% or less. More preferably, the sulfur content is 0.035% or less, and even more preferably 0.030% or less.

[0182] P: below 0.030%

[0183] 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 preferably set to 0.030% or less. More preferably, the P content is 0.020% or less, and even more preferably 0.010% or less.

[0184] The lower limit for phosphorus (P) content can include 0%, but 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.

[0185] Remaining components: Fe and impurities

[0186] The chemical composition of the steel billet used in the manufacture of the directional electromagnetic steel sheet in this embodiment is based on the elements mentioned above, with the remainder being Fe and impurities. However, for the purpose of improving magnetic properties, it may be further enriched with Cu, Cr, Sn, Se, Sb, and Mo within the range shown below.

[0187] Here, impurities refer to elements that are mixed in from the raw materials such as ore, scrap iron, or the manufacturing environment during the industrial manufacturing of the base steel plate. These are elements that are allowed to be present in a content that does not adversely affect the function of the directional electromagnetic steel plate of this embodiment.

[0188] Cu: 0–0.50%

[0189] Cu (copper) is an element that contributes to increasing the proportion of Goss orientation in secondary recrystallization structures and improving the adhesion of glass films. To achieve these effects, it is preferable to set the Cu content to 0.02% or more. More preferably, the Cu content is 0.03% or more.

[0190] On the other hand, when the Cu content exceeds 0.50%, the steel sheet becomes brittle during hot rolling. Therefore, it is preferable to set the Cu content of the billet to 0.50% or less. More preferably, the Cu content is 0.30% or less, and even more preferably 0.10% or less.

[0191] Cr: 0–0.50%

[0192] Like Sn and Cu described later, Cr (chromium) is an element that helps increase the proportion of Goss orientation in the secondary recrystallization structure, thereby improving magnetic properties and enhancing the adhesion of the glass film. To achieve these effects, it is preferable to set the Cr content to 0.02% or more, and more preferably to 0.03% or more.

[0193] On the other hand, when the Cr content exceeds 0.50%, Cr oxide will form, reducing the magnetic properties. Therefore, the Cr content is preferably set to 0.50% or less. More preferably, the Cr content is 0.30% or less, and even more preferably 0.10% or less.

[0194] Sn: 0–0.50%

[0195] Sn (tin) is an element that improves magnetic properties. Therefore, it can be included. When Sn is included, it is preferable to set the content to 0.005% or more in order to fully exert the effect of improving magnetic properties. If both magnetic properties and film adhesion are considered, the Sn content is preferably 0.02% or more, and more preferably 0.03% or more.

[0196] On the other hand, if the Sn content exceeds 0.50%, the adhesion of the glass coating deteriorates significantly. Therefore, it is preferable to set the Sb content to 0.50% or less. The Sn content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0197] Se: 0~0.020%

[0198] 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 content to 0.001% or more to maximize the effect of improving magnetic properties. If both magnetic properties and film adhesion are considered, the Se content is more preferably 0.003% or more, and even more preferably 0.006% or more.

[0199] On the other hand, if the Se content exceeds 0.020%, the glass coating deteriorates significantly. Therefore, it is preferable to set the upper limit of the Se content to 0.020%. More preferably, the Se content is 0.015% or less, and even more preferably 0.010% or less.

[0200] Sb: 0~0.500%

[0201] Antimony (Sb) is an element that improves magnetic properties. Therefore, it can be included in the composition of Sb. When Sb is included, it is preferable to set its content to 0.001% or more in order to effectively improve magnetic properties. If both magnetic properties and film adhesion are considered, the Sb content is more preferably 0.005% or more, and even more preferably 0.010% or more.

[0202] On the other hand, if the Sb content exceeds 0.500%, the glass coating deteriorates significantly. Therefore, it is preferable to set the upper limit of the Sb content to 0.500%. More preferably, the Sb content is 0.300% or less, and even more preferably 0.100% or less.

[0203] Mo: 0–0.10%

[0204] Mo (molybdenum) is an element that improves magnetic properties. Therefore, it may be included in the composition of the molybdenum. 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.

[0205] On the other hand, if the Mo content exceeds 0.10%, cold rollability may deteriorate, leading to breakage. Therefore, it is preferable to set the Mo content to 0.10% or less. More preferably, the Mo content is 0.08% or less, and even more preferably 0.05% or less.

[0206] <Hot Rolling Process>

[0207] In the hot rolling process, a steel billet with a specified chemical composition is heated and then hot-rolled to obtain a hot-rolled steel sheet. The heating temperature of the steel billet is preferably set in the range of 1100–1450°C. More preferably, the heating temperature is 1300–1400°C.

[0208] 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 is preferably in the range of 2.0 mm or more and 3.0 mm or less.

[0209] <Hot-rolled sheet annealing process>

[0210] The hot-rolled sheet annealing process is a process of annealing hot-rolled steel sheets produced through the hot-rolling process to produce hot-rolled annealed steel sheets. Through this annealing treatment, recrystallization occurs in the steel sheet structure, resulting in good magnetic properties.

[0211] In the hot-rolled sheet annealing process of this embodiment, hot-rolled steel sheets manufactured through the hot-rolling process can be annealed to produce hot-rolled annealed steel sheets by following known methods. There are no particular limitations on the means of heating the hot-rolled steel sheet during annealing; known heating methods 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.

[0212] <Cold rolling process>

[0213] In the cold rolling process, hot-rolled annealed steel sheets after hot rolling 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 performed by interrupting the cold rolling process before the final pass and performing at least one or two intermediate annealings, thereby performing multiple cold rollings with intermediate annealings.

[0214] When performing intermediate annealing, it is preferable to set the temperature to 1000–1200°C and the time to be 5 to 180 seconds. The annealing atmosphere is not particularly limited. Considering manufacturing costs, the number of intermediate annealing cycles is preferably no more than 3.

[0215] In addition, the surface of hot-rolled annealed steel sheets can be pickled before the cold rolling process.

[0216] In the cold rolling process of this embodiment, a cold-rolled steel sheet can be produced by cold rolling a hot-rolled annealed 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 final 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.

[0217] 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.

[0218] <Decarburization Annealing Process>

[0219] The decarburization annealing process is an important process for controlling the state of the MgAl2O4 phase in the glass coating. When the MgAl2O4 phase is set to the aforementioned state, the decarburization annealing process, which includes a heating process and a homogenization process, must have the heating rate set at 700–2000 °C / second (550–750 °C) and the oxygen potential set at 0.0001–0.0100 during the heating process. The homogenization process includes a first homogenization process in an atmosphere with an oxygen potential of 0.4 or higher and 0.8 or lower, where the annealing temperature is set at 800–900 °C and the annealing time is set at 100–500 seconds; and a second homogenization process in an atmosphere with an oxygen potential of 0.1 or lower, where the annealing temperature is set at 850 °C or higher and 1000 °C or lower, and the annealing time is set at 5 seconds or higher and 100 seconds or lower.

[0220] The second soaking process (second heat treatment) can be carried out after the first soaking process (first heat treatment) with a temperature reduction, or it can be carried out continuously after the first heat treatment without a temperature reduction.

[0221] The reason why the state of the MgAl2O4 phase in the glass film becomes the preferred state by carrying out decarburization annealing within the above range is not clear, but it is considered as follows.

[0222] The glass coating is formed by the reaction of MgO, which is applied to the surface of the steel sheet before final annealing as an annealing separating agent, with Si contained in the base steel sheet. As the reaction proceeds along with the final annealing, the interface between the glass coating and the base steel sheet advances within the base steel sheet, and the leading edge of the glass coating on the base steel sheet side develops in a complex, uneven shape resembling the aforementioned "root".

[0223] In this process, the MgAl2O4 phase is formed by the reaction of MgO with Al in the base steel sheet, but it is believed that there are roughly two pathways. One is the case where MgO in the annealing separating agent reacts directly with Al supplied from the base steel sheet. The other is the case where MgO in the annealing separating agent first reacts with Si originating from the base steel sheet to form the Mg2SiO4 phase, and then further reacts with Al to transform into the MgAl2O4 phase. In the former case, it is believed that the MgAl2O4 phase is generated in an earlier stage of the glass film formation process. On the other hand, in the latter case, it is believed that since Mg and O are temporarily fixed as oxides of Si, the formation of the MgAl2O4 phase occurs in a later stage of the glass film formation process. If it is believed that the formation of the glass film with the Mg2SiO4 phase as the main phase is achieved by the progression of the oxide region in the base steel sheet, then the MgAl2O4 phase formed in the earlier stage is considered to be configured as a residue on the surface side of the glass film. Conversely, it is believed that the MgAl2O4 phase formed in a later stage is disposed on the interface side between the glass film and the base steel plate. Taking this into account, it can be presumed that setting the situation so that MgO and Si present on the surface of the base steel plate during the final annealing preferentially reacts, in order to keep the MgAl2O4 phase formed in the glass film on the base steel plate side, is preferable.

[0224] The decarburizing annealing conditions of this embodiment are designed to ensure that a sufficient amount of SiO2 is formed on the surface of the steel sheet after the decarburizing annealing process. Specifically, if the surface of the steel sheet after the decarburizing annealing process is covered with a sufficient amount of SiO2, and an annealing separating agent primarily composed of MgO is further coated onto its surface, and the reaction of the annealing separating agent begins during the final annealing, MgO preferentially forms the Mg2SiO4 phase in the initial stage of the reaction. As a result, the presence of the MgAl2O4 phase in the glass film becomes a preferred state. Conversely, without the aforementioned decarburizing annealing conditions, since a sufficient amount of SiO2 is not present on the surface of the steel sheet after the decarburizing annealing process, when the reaction of the annealing separating agent begins during the final annealing, MgO reacts directly with the Al-containing base steel sheet in the initial stage of the reaction, forming the MgAl2O4 phase. As a result, the presence of the MgAl2O4 phase in the glass film becomes an undesirable state.

[0225] The glass coating formed on the surface of the base steel sheet after undergoing the above-mentioned thermal process in the decarburization annealing process is a preferred form. By implementing magnetic domain control under suitable laser processing conditions, it becomes possible to manufacture directional electromagnetic steel sheets with good iron loss / noise balance and better coating adhesion.

[0226] <Nitriding treatment process>

[0227] Nitriding can also be performed during the decarburization annealing process, or after the decarburization annealing process and before the final annealing process described later.

[0228] In the nitriding process, for example, cold-rolled steel sheets after the homogenization process of decarburization annealing are maintained at approximately 700–850°C in a nitriding atmosphere (an atmosphere containing nitriding gases such as hydrogen, nitrogen, and ammonia). 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 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.

[0229] 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 final 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.

[0230] <Final Annealing Process>

[0231] In the final annealing process, the cold-rolled steel sheet obtained in the decarburization annealing process, or after further nitriding, is coated with a specified annealing release agent and then subjected to final annealing. Final annealing is generally carried out for a long time while the steel sheet is rolled into a coil. Therefore, before final annealing, to prevent the inside and outside of the coil from sticking together, an annealing release agent is applied to the cold-rolled steel sheet and allowed to dry.

[0232] As the annealing separating agent for coating, an annealing separating agent with MgO as the main component (e.g., containing more than 80% by mass) 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 required for the formation reaction.

[0233] The final annealing can be carried out, for example, by annealing in an atmosphere containing hydrogen and nitrogen at a temperature of 1150–1250°C for 10–60 hours.

[0234] <Insulating film formation process>

[0235] In the insulating film formation process, a tension-imposed insulating film is formed on one or both sides of the final annealed cold-rolled steel sheet. There are no particular limitations on the conditions for forming the tension-imposed insulating film; any known insulating film treatment solution can be used, and the solution can be applied and dried using known methods. By forming a tension-imposed insulating film on the steel sheet surface, the magnetic properties of the directional electromagnetic steel sheet can be further improved.

[0236] The surface of the steel plate on which the insulating film (tension imparts the insulating film) is formed can be a surface that has undergone any pretreatment before the coating treatment liquid is applied, such as degreasing with alkali or pickling with hydrochloric acid, sulfuric acid, phosphoric acid, etc., or it can be the original surface after final annealing without any pretreatment.

[0237] The tension formed on the surface of the glass film (formed on the base steel plate through the glass film) imparts a certain degree of tension to the insulating film. As long as the insulating film is used as an insulating film for directional electromagnetic steel plates, there are no particular limitations, and known insulating films can be used. Examples of such insulating films include composite insulating films that are primarily composed of inorganic materials and further contain organic materials. Here, a composite insulating film is, for example, an insulating film that is primarily composed of at least one of inorganic materials such as metal chromate salts, metal phosphate salts, colloidal silica, Zr compounds, and Ti compounds, and disperses fine organic resin particles. In particular, 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 preferred.

[0238] <Magnetic domain subdivision process>

[0239] In the magnetic domain subdivision process, energy rays are irradiated onto the surface of the tension-imposed insulating film to introduce multiple linear strains extending in a direction intersecting the rolling direction onto the surface of the base steel sheet. In the magnetic domain subdivision process, regions (strain regions) with multiple substantially parallel linear strains (thermal strains generated by rapid heating and subsequent rapid cooling using energy ray irradiation) existing along the rolling direction are formed in the base steel sheet at predetermined intervals, but the intervals (i.e., the intervals between adjacent strain regions) are set to 10 mm or less in the rolling direction.

[0240] If the interval between multiple linear strain regions in the rolling direction exceeds 10 mm, the iron loss improvement effect is insufficient. Therefore, energy rays are irradiated along each rolling direction at intervals of less than 10 mm to form strain (residual strain).

[0241] There are no particular limitations on the types of energy rays. Commonly used lasers or electron beams can be applied.

[0242] When laser irradiation is applicable, the laser beam can be a continuous wave laser or a pulsed laser, but a continuous wave laser is preferred. Furthermore, between laser beams and electron beams, laser beams are preferred. This is because a vacuum environment is necessary in the electron beam irradiation process, increasing production costs. Therefore, this embodiment implements a magnetic domain subdivision process using a laser beam. The laser beam is, for example, a fiber laser beam.

[0243] Furthermore, as mentioned above, in order to obtain a directional electromagnetic steel sheet that balances low iron loss and low noise and has excellent film adhesion, strain is introduced relative to the base steel sheet.

[0244] Specifically, the energy output power P, measured in W, and the energy output power P, measured in mm, are used. 2 The energy ray irradiation cross-sectional area S is calculated, and the energy ray power density Ip defined by P / S satisfies the following equation (5). Furthermore, the energy ray output power P and the energy ray scanning speed Vs in mm / s are used to irradiate the energy ray input energy Up in J / mm defined by P / Vs in the following equation (6).

[0245] Equation (5) is 250≤Ip≤2000

[0246] 0.010 < Up ≤ 0.050 (Equation 6)

[0247] When Ip is below 250, insufficient energy is invested, and the magnetic domain subdivision effect (iron loss improvement effect) cannot be obtained. Therefore, Ip should be above 250. Ip is preferably above 500.

[0248] On the other hand, if Ip exceeds 2000, the magnetic domain subdivision effect is exceeded, resulting in residual thermal strain and deterioration of noise characteristics. Therefore, Ip is 2000 or less. Ip is preferably 1750 or less, and more preferably 1500 or less.

[0249] Furthermore, when Up is below 0.010, the irradiation effect is insufficient, and iron loss is not improved. On the other hand, if Up exceeds 0.050, the noise characteristics deteriorate.

[0250] 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 in the direction 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 (7).

[0251] 0.0010 < dl / dc < 1.0000 (7)

[0252] When the beam aspect ratio is below 0.0010, 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 0.0010.

[0253] On the other hand, if the beam aspect ratio is 1.0000 or higher, heat removal associated with beam irradiation will not occur, but instead, residual stress will be generated, and a low-noise effect cannot be obtained. Therefore, the beam aspect ratio is lower than 1.0000. The beam aspect ratio is preferably lower than 0.0500, and more preferably lower than 0.0050.

[0254] Furthermore, the diameter dl of the energy ray in the direction perpendicular to the beam scanning direction, measured in μm, satisfies the following equation (8).

[0255] 10 < dl < 200(8)

[0256] For typical laser sources, it is difficult to set the beam diameter below 10 μm. Therefore, the dl exceeds 10.

[0257] 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.

[0258] 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.

[0259] However, the inventors conducted research based on the novel 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.

[0260] Example

[0261] A slab with the chemical composition listed in Table 1 is manufactured. The slab is then subjected to a hot rolling process. Specifically, the slab is heated to 1350°C and then hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.3 mm.

[0262] The hot-rolled steel sheet after the hot rolling process is subjected to an annealing process at an annealing temperature of 900-1200℃ for a holding time of 10-300 seconds.

[0263] Afterwards, multiple cold rolling processes were carried out to obtain cold-rolled steel sheets with a thickness of 0.17–0.27 mm.

[0264] The cold-rolled steel sheet was decarburized and annealed under the conditions shown in Tables 2A and 2B.

[0265] After decarburization annealing, for tests No. 11, 13, and 15, the steel sheets were held at 700–850°C for 10–60 seconds in a well-known nitriding atmosphere (an atmosphere containing hydrogen, nitrogen, and ammonia, etc., which have nitriding capabilities) to make the N content of the cold-rolled steel sheets after decarburization annealing above 40 ppm and below 1000 ppm.

[0266] For experiments No. 11, 13, and 15, after nitriding, and for all others after decarburization annealing, an annealing separating agent with magnesium oxide (MgO) as the main component was applied to the surface of the steel plate, followed by a final annealing process. The final annealing temperature in the final annealing process was 1200℃, and the holding time at the final annealing temperature was 20 hours.

[0267] After the final annealing process, an insulating coating based on colloidal silica and phosphate is applied to the surface (on the glass film) of the cooled steel sheet (directional electromagnetic steel sheet), followed by baking to form a tension-imparting insulating film. Through the above process, directional electromagnetic steel sheets of each test number are manufactured.

[0268]

[0269] Table 2A

[0270]

[0271] Table 2B

[0272]

[0273] [Analysis of the chemical composition of the base steel plate]

[0274] The chemical composition of the base steel sheet for each test No. of directional electromagnetic steel sheet before magnetic domain subdivision, obtained according to the above-described method, was determined by the following method. First, the tension-insulating coating was removed from the directional electromagnetic steel sheet of each test No. Specifically, the directional electromagnetic steel sheet was 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 sheet (after removing the tension-insulating coating) was then washed with water. After washing, it was dried using a warm air blower for less than 1 minute.

[0275] 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.

[0276] The chemical composition of the extracted base steel plate was determined using well-known component analysis methods. Specifically, the base steel plate was drilled to produce powder, which was then collected. The collected powder was dissolved in acid to obtain a solution. ICP-AES was performed on the solution to perform elemental analysis of the chemical composition. For the Si content in the base steel plate, it was determined using the method specified in JIS G1212:1997 (quantitative method for silicon). Specifically, if the powder was dissolved in acid, silicon oxide precipitated. This precipitate (silicon oxide) was filtered through filter paper, and its mass was measured to determine the Si content. 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 using high-frequency heating, and the produced carbon dioxide and sulfur dioxide 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 method. The chemical composition of the steel plate (base steel plate) for each test No. is shown in Table 3. In Table 3, "-" indicates that the content of the corresponding element is below the detection limit.

[0277] [Magnetic Property Evaluation]

[0278] Although not shown in the table, samples measuring 60 mm in width and 300 mm in length, including the central portion of the plate width, were collected from the directional electromagnetic steel plates of each test No. The sample length 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.

[0279] Using this sample, the magnetic flux density (T) was determined by a single-plate magnetic property test (SST test) according to JIS C2556 (2015). Specifically, a magnetic field of 800 A / m was applied to the sample, and the magnetic flux density (T) was determined.

[0280] Furthermore, using the aforementioned sample, according to JIS C2556 (2015), 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)

[0281] Table 3

[0282]

[0283] Furthermore, for the directional electromagnetic steel plates (after the tension-imposed insulating film was formed) of each obtained Test No., the surface of the steel plate was irradiated with energy rays using a laser (fiber laser or pulsed laser) or an electron beam under the conditions shown in Tables 4A and 4B, thereby performing magnetic domain subdivision and conducting evaluation tests on noise and magnetic properties. In addition, after determining the total thickness of the glass film using the above method, the area fractions S1, S2, and S3 of the MgAl2O4 phase in each region were also measured.

[0284] Table 4A

[0285]

[0286] Table 4B

[0287]

[0288] [Noise Characteristics and Magnetostriction Evaluation]

[0289] Samples measuring 100 mm in width and 500 mm in length were collected from directional electromagnetic steel sheets. The length direction of the sample corresponds to the rolling direction RD, and the width direction corresponds to the sheet width direction TD.

[0290] For the samples, magnetostriction was measured using a magnetostriction measuring device via AC magnetostriction measurement. The magnetostriction measuring device was configured to include a laser Doppler vibrometer, excitation coil, excitation power supply, magnetic flux detection coil, amplifier, and oscilloscope.

[0291] Specifically, an alternating magnetic field is applied to the sample with a maximum magnetic flux density of 1.7T and a frequency of 50Hz in the rolling direction. The change in sample length caused by the stretching of magnetic domains is measured using a laser Doppler vibrometer, yielding a magnetostrictive signal. Fourier analysis is performed on the obtained magnetostrictive signal to determine the amplitude Cn of each frequency component fn (n being a natural number greater than 1). Using the A correction coefficient αn for each frequency component fn, the magnetostrictive velocity level LVA (dB) is calculated as shown in the following formula.

[0292] LVA=20×Log(√(Σ(ρc×2π×fn×αn×Cn / √2) 2 ) / Pe0)

[0293] Where ρc is the inherent acoustic impedance, set to ρc = 400. Pe0 is the minimum sound pressure level, using Pe0 = 2 × 10⁻⁶. -5(Pa). The correction factor αn uses the value recorded in Table 2 of JIS C 1509-1 (2005).

[0294] The noise characteristics are evaluated based on the following criteria for the obtained magnetostrictive velocity level (LVA). If the magnetostrictive velocity level is below 60 dBA, the noise characteristics are considered excellent.

[0295] Furthermore, the magnetostriction λ is obtained from the aforementioned magnetostriction signal. 0-p (μm / m). Specifically, the length Lp (μm) of the test piece (steel plate) under the above excitation conditions with a magnetic flux density of 1.7T and the length L0 (m) of the test piece with a magnetic flux density of 0T, through λ 0-p It can be calculated as (Lp-L0) / L0.

[0296] Furthermore, for steel plates that underwent heat treatment at 800℃ for 4 hours, the magnetostriction λ was similarly measured when the frequency was set to 50Hz and the maximum magnetic flux density was set to 1.7T. 0-p (μm / m). Furthermore, the magnetostriction before heat treatment is set to λ. 0-pb The magnetostriction after heat treatment is set to λ. 0-pa Find λ 0-pb -λ 0-pa .

[0297] The results are shown in Tables 5A, 5B, 6A, and 6B.

[0298] [Magnetic Property Evaluation]

[0299] Samples measuring 60 mm in width and 300 mm in length, including the central portion of the plate width, were collected from the directional electromagnetic steel plates of each test No. The length of the sample 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 during sample collection.

[0300] Using this sample, the magnetic flux density (T) was determined by a single-plate magnetic property test (SST test) according to JIS C2556 (2015). Specifically, a magnetic field of 800 A / m was applied to the sample, and the magnetic flux density (T) was determined.

[0301] Furthermore, using the aforementioned sample, according to JIS C2556 (2015), 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). An iron loss improvement rate of 5.0% or higher is considered excellent. The measurement results are shown in Tables 6A and 6B.

[0302] [Capsule adhesion]

[0303] The coating adhesion (residual coating area ratio) of the directional electromagnetic steel sheet was determined using the method described above. If the residual coating area ratio was 50% or higher, the coating adhesion was considered acceptable (evaluation 0); if it was 90% or higher, the coating adhesion was considered excellent (evaluation ◎). The evaluation results were recorded in Tables 6A and 6B.

[0304] Table 5A

[0305]

[0306] Table 5B

[0307]

[0308] Table 6A

[0309]

[0310] Table 6B

[0311]

[0312] As can be seen from Tables 1 to 6B, the presence of a strain region and λ is preferred. 0-pb -λ 0-pa For the steel plate within the scope of this invention (example of the invention), a good balance between iron loss and noise can be ensured. Furthermore, regarding λ... 0-pb -λ 0-pa For steel plates within the scope of this invention that can ensure a good balance between iron loss and noise, the residual area ratio of the film is sufficiently high when the area ratio of the MgAl2O4 phase in the glass film in each region satisfies the preferred relationship, thus ensuring good adhesion.

[0313] On the other hand, regarding λ 0-pb -λ 0-pa For steel plates that are outside the scope of this invention and for which a good balance between iron loss and noise cannot be ensured, the effect of the area ratio of the MgAl2O4 phase in the glass coating on the residual area ratio of the coating is unclear.

[0314] Industrial availability

[0315] According to the present invention, a directional electromagnetic steel sheet with good iron loss / noise balance and a method for manufacturing the same can be provided. Furthermore, according to a preferred embodiment of the present invention, a directional electromagnetic steel sheet with good iron loss / noise balance and excellent coating adhesion can be provided. Therefore, it has high industrial applicability.

Claims

1. A directional electromagnetic steel plate, characterized in that, It possesses: Base material steel plate, Glass film formed on the base steel plate, and The tension formed on the glass film imparts an insulating coating. In the base steel plate, there exist multiple linear strain regions that extend continuously or intermittently in a direction intersecting the rolling direction. The width of each of the plurality of linear strain regions in the rolling direction is less than 210 μm. The plurality of linear strain regions are parallel to each other, and the spacing between adjacent linear strain regions in the rolling direction is less than 10 mm. Magnetostriction λ in μm / m at excitation up to 1.7T 0-pb The magnetostriction λ in μm / m after heat treatment at 800°C for 4 hours and excitation to 1.7T. 0-pa It satisfies the following equation (1), The chemical composition of the base steel plate contains: C: less than 0.010%, Si: 3.00-4.00%, Mn: 0.01-0.50%, N: less than 0.010%, sol.Al: less than 0.020%, S: less than 0.010%, P: less than 0.030%, Cr: 0-0.50%, Sn: 0-0.50%, Cu: 0-0.50%, Se: 0-0.020%, Sb: 0-0.500%, Mo: 0-0.10%, with the remainder being Fe and impurities. The glass coating contains a structure comprising a MgAl2O4 phase and a Mg2SiO4 phase as the main phase. In the cross-section along the thickness direction of the plate, the glass coating is divided into three regions of equal thickness. These regions are designated as 1 / 3, 2 / 3, and 3 / 3 regions, respectively, from the side of the base steel plate towards the side where tension is applied to the insulating coating. The area fraction of the MgAl2O4 phase in the 1 / 3 region is set as S1, the area fraction of the MgAl2O4 phase in the 2 / 3 region is set as S2, and the area fraction of the MgAl2O4 phase in the 3 / 3 region is set as S3. S1, S2, and S3 satisfy the following equations (2) to (4). 0.02≤λ 0-pb -l 0-pa ≤0.20 (1) S1>S2>S3 (2) (S1+S2+S3) / 3<0.50 (3) S3＜0.10 (4)。 2. A method for manufacturing a directional electromagnetic steel plate, characterized in that, It is a method for manufacturing the directional electromagnetic steel plate according to claim 1, comprising the following steps: The hot rolling process involves heating a steel billet and hot rolling it into a hot-rolled steel plate. The hot-rolled steel sheet is subjected to a hot-rolled annealing process. A pickling process is performed on the hot-rolled steel plate after the annealing process. The cold rolling process involves subjecting the hot-rolled steel sheet after the pickling process to a single cold rolling or multiple cold rolling processes with annealing to produce a cold-rolled steel sheet. The decarburizing annealing process is performed on the cold-rolled steel sheet. After the decarburization annealing process of the cold-rolled steel sheet used as the base material, an annealing separating agent with MgO powder as the main component is coated on the front and back sides and dried, and then a final annealing process is carried out to form a glass film. A film forming process is performed by forming a tension-imparting insulating film 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 The tension of the directional electromagnetic steel sheet is imparted to the surface of the insulating film by irradiation with energy rays, forming a magnetic domain subdivision process that creates multiple linear strain regions in the base steel sheet. In the magnetic domain subdivision process, The rolling direction spacing between adjacent linear strain regions in the plurality of linear strain regions is less than 10 mm. Using energy ray output power P in W and in mm 2 The calculated energy ray irradiation cross-sectional area S is defined by (P / S) in units of W / mm². 2 The calculated energy ray power density Ip satisfies the following equation (5), Using the energy ray output power P and the 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 (6), and, Using the diameter dl of the energy beam perpendicular to the beam scanning direction in units of μm and the diameter dc of the beam scanning direction, the beam aspect ratio defined by (dl / dc) and dl satisfy the following equations (7) and (8), respectively. The decarburization annealing process includes a heating process and a homogenization process. The heating rate during the heating process (550–750°C) is set to 700–2000°C / second, and the oxygen potential is set to 0.0001–0.0100. The homogenization process includes a first homogenization process in an atmosphere with an oxygen potential of 0.4 or higher and 0.8 or lower, wherein the annealing temperature is set to 800-900°C and the annealing time is set to 100-500 seconds; and a second homogenization process in an atmosphere with an oxygen potential of 0.1 or lower, wherein the annealing temperature is set to 850-1000°C and the annealing time is set to 5-100 seconds. 250≤Ip≤2000 (5) 0.010 < Up ≤ 0.050 (6) 0.0010 < dl / dc < 1.0000 (7) 10＜dl＜200 (8)。 3. The method for manufacturing a directional electromagnetic steel plate according to claim 2, characterized in that, The energy beam is a laser beam.

4. The method for manufacturing a directional electromagnetic steel plate according to claim 3, characterized in that, The laser beam is a fiber laser beam.

5. The method for manufacturing a directional electromagnetic steel plate according to any one of claims 2 to 4, characterized in that, The steel billet contains, by mass percent, C: 0.010–0.200%, Si: 3.00–4.00%, sol.Al: 0.010–0.040%, Mn: 0.01–0.50%, N: less than 0.020%, S: 0.005–0.040%, P: less than 0.030%, Cu: 0–0.50%, Cr: 0–0.50%, Sn: 0–0.50%, Se: 0–0.020%, Sb: 0–0.500%, Mo: 0–0.10%, with the remainder being Fe and impurities.

6. The method for manufacturing a directional electromagnetic steel plate according to any one of claims 2 to 5, characterized in that, In or after the decarburizing annealing process, there is a further nitriding process to nitrid the cold-rolled steel sheet.

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