Grain-oriented magnetic steel sheet and method for manufacturing grain-oriented magnetic steel sheet

Abstract

The present disclosure provides a grain-oriented magnetic steel sheet capable of obtaining excellent magnetic properties, excellent iron loss properties, and further excellent noise properties. The grain-oriented magnetic steel sheet of the present disclosure includes a base steel sheet, and when crystal orientation is measured at measurement points arranged at intervals of 2 mm in each of a rolling direction and a direction orthogonal to the rolling direction on a surface of the base steel sheet using an X-ray diffraction method, the proportion R of the number of measurement points having an orientation difference of 15° or less from the {211} <011> orientation with respect to the total number of measurement points is 5% or less {211}<011> The proportion R of the number of measurement points having an orientation difference of 15° or less from the {110} <112> orientation with respect to the total number of measurement points is 5% or less {110}<112> The proportion R of the number of measurement points having an orientation difference of 15° or less from the {110} <001> orientation with respect to the total number of measurement points is 5% or less {110}<001> The proportion RL of the total length LI of the grain boundaries having an orientation difference of 15° or more with respect to the total length La of the grain boundaries of the crystal grains, i.e., the proportion of high-angle grain boundaries, is 5% or more and 30% or less.

Description

Technical Field

[0001] This disclosure relates to directional electromagnetic steel sheets (also known as "orientation electromagnetic steel sheets") and methods for manufacturing the same. Background Technology

[0002] Directional electromagnetic steel sheets, as soft magnetic materials, are mainly used in transformer cores. Directional electromagnetic steel sheets are primarily composed of {110} oriented steel, known as Gaussian orientation. <001> It consists of oriented grains (Gaussian-oriented grains). The size of Gaussian-oriented grains is on the order of millimeters. Through a phenomenon known as secondary recrystallization, Gaussian-oriented grains preferentially grow, thereby manufacturing directional electromagnetic steel sheets.

[0003] Directional electromagnetic steel sheets require excellent magnetic properties (high magnetic flux density and low iron loss). Regarding magnetic flux density, the higher the concentration of Gaussian-oriented grains, the better the magnetic flux density can be obtained.

[0004] On the other hand, iron loss is expressed as the sum of hysteresis loss and eddy current loss. Hysteresis loss depends on crystal orientation, etc. Eddy current loss depends on plate thickness, resistivity, domain size, etc. To reduce iron loss, reducing both hysteresis loss and eddy current loss is effective. As a method to reduce hysteresis loss, increasing the concentration towards Gaussian orientation is known. Furthermore, as a method to reduce eddy current loss, increasing the content of resistive elements such as Si, thinning the steel plate, or refining the magnetic domains are known methods.

[0005] Recently, methods to reduce iron loss by thinning the sheet thickness have been studied. However, when the sheet thickness is reduced, the cold rolling reduction rate in the manufacturing process of directional electromagnetic steel sheets becomes higher. In this case, it is sometimes impossible to consistently obtain excellent magnetic properties.

[0006] Therefore, methods for improving the magnetic properties of directional electromagnetic steel sheets even when the cold rolling reduction rate is high have been proposed in, for example, Japanese Patent Application Publication No. 6-145799 (Patent Document 1) and Japanese Patent Application Publication No. 7-62438 (Patent Document 2).

[0007] Patent Document 1 discloses a method for manufacturing directional electromagnetic steel sheets that involves two cold rolling processes with intermediate annealing. Specifically, hot rolling is completed at 850°C or higher, followed by immediate cooling, and the steel sheet is coiled at 600°C or lower. Then, before the first cold rolling, the steel sheet undergoes a carbide conditioning heat treatment at a temperature range of 650–900°C for 2–10 seconds. As a result, Patent Document 1 describes a method that enables the production of excellent magnetic flux density even in thinner directional electromagnetic steel sheets.

[0008] Patent Document 2 discloses a manufacturing method for directional electromagnetic steel sheets that undergo two or more cold rolling processes, including one intermediate annealing. In Patent Document 2, the final cold rolling reduction is 89% or more. Furthermore, the steel sheet rolled to its final thickness is heated to a temperature of 700°C or higher at a heating rate of 50°C / s or higher just before decarburization annealing. As a result, Patent Document 2 describes a method that yields excellent magnetic flux density and excellent iron loss.

[0009] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 6-145799 Patent Document 2: Japanese Patent Application Publication No. 7-62438 Summary of the Invention

[0010] The problem that the invention aims to solve Regarding the directional electromagnetic steel sheets proposed in Patent Documents 1 and 2, excellent magnetic flux density and excellent iron loss can also be obtained. However, excellent magnetic flux density and excellent iron loss can also be obtained by other means.

[0011] Recently, there has been a greater demand for reducing noise and vibration in transformers. Therefore, directional electromagnetic steel sheets are required to have excellent magnetic flux density, excellent iron losses, and excellent noise characteristics. Here, noise characteristics refer to the ability to sufficiently reduce noise and vibration when the directional electromagnetic steel sheet is mounted on a transformer.

[0012] One of the main reasons for reduced noise characteristics (i.e., the main cause of excessive noise and vibration) is the magnetostriction of directional electromagnetic steel sheets. Magnetostriction, as discussed here, refers to the vibration observed in the rolling direction of a directional electromagnetic steel sheet caused by a slight change in its shape due to alternating current when the sheet is energized with AC current. The magnitude of the magnetostriction is 10. -6 The magnetostriction is a very small value, but it causes the iron core to vibrate, which propagates to external structures such as the transformer's container and becomes noise. Neither Patent Document 1 nor Patent Document 2 mentioned above included any research on the noise characteristics.

[0013] The purpose of this disclosure is to provide a directional electromagnetic steel sheet that can achieve excellent magnetic properties, excellent iron loss properties, and consequently excellent noise properties.

[0014] Methods for solving problems The directional electromagnetic steel plate disclosed herein comprises a base steel plate, the chemical composition of which, by mass%, is: Si: 3.00–3.70%, Mn: 0.01–0.30%, N: 0.0001–0.0100%, C: 0.001–0.010%, sol.Al: 0–0.010%, one or more elements selected from the group consisting of S and Se: totaling 0–0.010%, Ti: 0–0.010%, Ni: 0–0.50%, Cr: 0–0.50%, Cu: 0–0.50%, P: 0–0.05%, Mo: 0–0.05%, Sn: 0–0.30%, Sb: 0–0.30%, Bi: 0–0.0150%, Ta: 0–0.05%, Nb: 0–0.010%, V: 0–0.50%, B: 0–0.010%, Te: 0–0.0150%, and the balance being Fe and impurities. When determining the crystal orientation using X-ray diffraction at measurement points spaced 2 mm apart in the rolling direction and in directions orthogonal to the rolling direction on the surface of the base steel plate, it is consistent with {211} <011> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {211}<011> Below 5%, with {110} <112> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<112> Below 5%, with {110} <001> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<001> The ratio of the total length LI of grain boundaries with an orientation difference of 15° or more obtained from the orientation difference at the measurement point to the total length La of the grain boundaries, i.e., the large-angle grain boundary ratio RL=LI / La, is 5% or more and less than 30%.

[0015] The method for manufacturing directional electromagnetic steel sheet disclosed herein includes a hot rolling process of hot rolling a slab to produce a hot-rolled steel sheet, wherein the composition of the slab, by mass%, is: Si: 3.00–3.70%, Mn: 0.01–0.30%, N: 0.0030–0.0150%, C: 0.010–0.100%, sol.Al: 0.010–0.050%, one or more selected from the group consisting of S and Se: totaling 0.010–0.050%, Ti: 0–0.010%, Ni: 0–0.50%, Cr: 0–0.50%, Cu: 0–0.50%, P: 0–0.05%, Mo: 0–0.05%, Sn: The composition is as follows: 0-0.30%, Sb: 0-0.30%, Bi: 0-0.0200%, Ta: 0-0.05%, Nb: 0-0.010%, V: 0-0.50%, B: 0-0.010%, Te: 0-0.0200%, with the balance consisting of Fe and impurities; a hot-rolled sheet annealing process for annealing hot-rolled steel sheets; a cold rolling process for cold-rolling hot-rolled steel sheets after the hot-rolled sheet annealing process to produce cold-rolled steel sheets; a decarburizing annealing process for cold-rolled steel sheets to produce decarburized annealed steel sheets; a final annealing process for applying an annealing separating agent to the decarburized annealed steel sheet and then performing final annealing; and an insulating coating forming process for forming an insulating coating on the surface of the final annealed sheet. In the cold rolling process, the cumulative reduction rate is set to be above 89% and below 93%. In the work rolls of the rolling mill stand where the first pass of cold rolling is performed, the axial arithmetic mean roughness Ra (μm), the ten-point mean roughness Rzjis (μm), and the diameter Dw (mm) of the work rolls satisfy equations (1) and (2).

[0016] 0.30≤Ra≤0.01Dw+3.08 (1) 3Ra≤Rzjis≤7Ra (2) Invention Effects The directional electromagnetic steel sheet disclosed herein exhibits excellent magnetic properties, excellent iron loss characteristics, and consequently, excellent noise characteristics. The manufacturing method of the directional electromagnetic steel sheet disclosed herein is capable of producing the aforementioned directional electromagnetic steel sheet. Attached Figure Description

[0017] Figure 1 This is a perspective view of the directional electromagnetic steel plate of this embodiment.

[0018] Figure 2 This is a schematic diagram of a tandem rolling mill used in a tandem rolling process.

[0019] Figure 3 This is a schematic diagram of a multi-stage rolling mill used in a reversible rolling process. Detailed Implementation

[0020] The inventors of this invention have studied directional electromagnetic steel sheets that exhibit excellent magnetic properties, excellent iron loss properties, and consequently, excellent noise properties. The results yielded the following insights.

[0021] The inventors first investigated and studied the reasons why the magnetic flux density of directional electromagnetic steel sheets could not always be adequately obtained under conditions of high cold rolling reduction. The result was that in directional electromagnetic steel sheets where sufficient magnetic flux density was not obtained, not only were there {110} <001> Oriented Gaussian grains, and an excess of {211} grains. <011> Oriented grains and having {110} <112> Oriented grains. It is believed that through these {211} <011> Oriented grains and {110} <112> Oriented grains grow through secondary recrystallization, which reduces the number of Gaussian oriented grains, resulting in a decrease in magnetic flux density.

[0022] Specifically, in the final annealing process of directional electromagnetic steel sheet manufacturing, the cold-rolled steel sheet in coil form after the cold rolling process is annealed in batches. Since the cold-rolled steel sheet is in coil form, it is annealed for a long time while maintaining a curved shape. It is believed that if secondary recrystallization occurs in the curved steel sheet, the deviation between the secondary recrystallization orientation and the matrix orientation increases depending on the curvature.

[0023] In the secondary recrystallization of directional electromagnetic steel sheets, grains with a high ratio of Σ9-corresponding orientation grain boundaries preferentially grow. Gaussian-oriented grains readily form Σ9-corresponding orientation grain boundaries. On the other hand, {211} <011> Oriented grains and {110} <112> Compared to Gaussian-oriented grains, oriented grains are less likely to form Σ9-corresponding orientation grain boundaries. Therefore, it is believed that {211} <011> Oriented grains and {110} <112> Compared to Gaussian oriented grains, oriented grains are more difficult to grow in the final annealing process.

[0024] However, as mentioned above, in the final annealing process, the cold-rolled steel sheet is in coil form. Therefore, as secondary recrystallization proceeds, the properties of the grain boundaries of the oriented grains change according to the curvature. Specifically, Gaussian oriented grains are difficult to form Σ9 corresponding orientation grain boundaries, while {211} <011> Oriented grains and {110} <112> Compared to Gaussian oriented grains, the formation difficulty of Σ9-oriented grain boundaries is mitigated. As a result, it is believed that {211} <011> Oriented grains and {110} <112> Oriented grains grow more readily. The higher the cumulative reduction rate during the cold rolling process, the more pronounced this phenomenon becomes.

[0025] Based on the above insights, the inventors believe that in directional electromagnetic steel sheets, by reducing {211} <011> Oriented grains and {110} <112> Increasing the proportion of Gaussian-oriented grains leads to superior magnetic flux density. Further research revealed that when measuring crystal orientation at 2mm intervals at measurement points on the surface of the base steel sheet of a directional electromagnetic steel sheet using X-ray diffraction, superior magnetic flux density can be obtained if the following conditions A to C are met.

[0026] (Requirement A) With {211} <011> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {211}<011> It is below 5%.

[0027] (Requirement B) With {110} <112> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<112> It is below 5%.

[0028] (Requirement C) With {110} <001> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<001> It is over 90%.

[0029] As described above, by maximizing the number of Gaussian-oriented grains within the grain, {211} is minimized. <011> Oriented grains and {110} <112> Orienting the grains increases the magnetic flux density. However, while excellent magnetic flux density can be obtained by satisfying requirements A through C, excellent iron loss and noise characteristics are sometimes not achieved. This shows that in directional electromagnetic steel sheets, an increase in magnetic flux density is not necessarily related to a decrease in iron loss.

[0030] Therefore, the present invention further investigated methods for reducing iron loss. As a result, the inventors discovered that the appropriate presence of large-angle grain boundaries in the microstructure improves iron loss.

[0031] The effect of grain boundaries on iron loss is not fully understood, but the following reasons should be considered. Auxiliary magnetic domains form at locations with large-angle grain boundaries. These auxiliary domains disappear due to the tension of the insulating coating. When the auxiliary domains disappear, the magnetostatic energy increases. To mitigate this increase in magnetostatic energy, the domain walls are refined. When the domain walls are refined, the iron loss generated by the movement of the domain walls decreases. However, if the auxiliary domains become excessive, the magnetostriction, which is a cause of noise, increases.

[0032] Here, when determining crystal orientation using X-ray diffraction at measurement points spaced 2 mm apart in both the rolling direction and directions orthogonal to the rolling direction on the surface of the base steel sheet of directional electromagnetic steel sheet, the ratio of the total length LI of grain boundaries with an orientation difference of 15° or more obtained from the orientation difference at the measurement points to the total length La of grain boundaries is defined as the large-angle grain boundary ratio RL (=LI / La). Furthermore, an orientation difference of 1° or more is defined as a grain boundary.

[0033] If the proportion of large-angle grain boundaries (RL) is less than 5%, the proportion of large-angle grain boundaries is too low. In this case, there are excessively few auxiliary magnetic domains. Therefore, the refinement of the domain walls becomes insufficient, and excellent iron loss cannot be obtained.

[0034] On the other hand, if the proportion of large-angle grain boundaries (RL) exceeds 30%, the proportion of large-angle grain boundaries becomes excessive. In this case, auxiliary magnetic domains become excessive, and the movement of domain walls is hindered. As a result, hysteresis loss actually increases. Moreover, due to the excess of auxiliary magnetic domains, magnetostriction increases. Consequently, sufficient iron loss and excellent noise characteristics are not obtained.

[0035] If the proportion of large-angle grain boundaries (RL) is 5–30%, then a suitable amount of large-angle grain boundaries and auxiliary magnetic domains are present. Therefore, the domain walls are refined, and the number of auxiliary magnetic domains decreases. As a result, excellent iron loss can be obtained, and consequently, excellent noise characteristics can be achieved.

[0036] Based on the above insights, the inventors have completed a directional electromagnetic steel sheet of this embodiment having the following configuration.

[0037] The first type of directional electromagnetic steel plate includes a base steel plate, the chemical composition of which, by mass%, is: Si: 3.00–3.70%, Mn: 0.01–0.30%, N: 0.0001–0.0100%, C: 0.001–0.010%, sol.Al: 0–0.010%, one or more elements selected from the group consisting of S and Se: totaling 0–0.010%, Ti: 0–0.010%, Ni : 0~0.50%, Cr: 0~0.50%, Cu: 0~0.50%, P: 0~0.05%, Mo: 0~0.05%, Sn: 0~0.30%, Sb: 0~0.30%, Bi: 0~0.0150%, Ta: 0~0.05%, Nb: 0~0.010%, V: 0~0.50%, B: 0~0.010%, Te: 0~0.0150%, and the balance consists of Fe and impurities. When determining the crystal orientation using X-ray diffraction at measurement points spaced 2 mm apart in the rolling direction and in directions orthogonal to the rolling direction on the surface of the base steel plate, with {211} <011> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {211}<011> Below 5%, with {110} <112> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<112> Below 5%, with {110} <001> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<001> The ratio of the total length LI of grain boundaries with an orientation difference of 15° or more obtained from the orientation difference at the measurement point to the total length La of the grain boundaries, i.e., the large-angle grain boundary ratio RL=LI / La, is 5% or more and less than 30%.

[0038] The second type of directional electromagnetic steel sheet is the same as the first type of directional electromagnetic steel sheet, with the base steel sheet having a thickness of less than 0.19 mm.

[0039] The third type of directional electromagnetic steel plate is the first or second type of directional electromagnetic steel plate, and the chemical composition of the base steel plate, in mass percent, contains one or more elements selected from the group consisting of Ti: 0.001-0.010%, Ni: 0.01-0.50%, Cr: 0.01-0.50%, Cu: 0.01-0.50%, P: 0.01-0.05%, Mo: 0.01-0.05%, Sn: 0.01-0.30%, Sb: 0.01-0.30%, Bi: 0.0001-0.0150%, Ta: 0.01-0.05%, Nb: 0.001-0.010%, V: 0.01-0.50%, B: 0.001-0.010%, and Te: 0.0001-0.0150%.

[0040] The manufacturing method of the directional electromagnetic steel sheet of the first method is a manufacturing method of the directional electromagnetic steel sheet of any one of the first to third methods, which includes a hot rolling process, a hot-rolled sheet annealing process, a cold rolling process, a decarburization annealing process, a final annealing process, and an insulating coating formation process. In the hot rolling process, a slab is hot-rolled to produce a hot-rolled steel sheet. The composition of the slab, by mass%, is: Si: 3.00-3.70%, Mn: 0.01-0.30%, N: 0.0030-0.0150%, C: 0.010-0.100%, sol.Al: 0.010-0.050%, one or more selected from the group consisting of S and Se: totaling 0.010-0.050%, Ti: 0-0.01%. The composition is as follows: 0%, Ni: 0-0.50%, Cr: 0-0.50%, Cu: 0-0.50%, P: 0-0.05%, Mo: 0-0.05%, Sn: 0-30%, Sb: 0-0.30%, Bi: 0-0.0200%, Ta: 0-0.05%, Nb: 0-0.010%, V: 0-0.50%, B: 0-0.010%, Te: 0-0.0200%, with the balance consisting of Fe and impurities. In the hot-rolled sheet annealing process, the hot-rolled steel sheet is annealed. In the cold-rolling process, the hot-rolled steel sheet after the hot-rolled sheet annealing process is cold-rolled to produce a cold-rolled steel sheet. In the decarburizing annealing process, the cold-rolled steel sheet is decarburized and annealed to produce a decarburized annealed steel sheet. In the final annealing process, an annealing separating agent is applied to the decarburized annealed steel sheet before final annealing. In the insulating coating forming process, an insulating coating is formed on the surface of the final annealed plate. In the cold rolling process, the cumulative reduction rate is set to be above 89% and below 93%. In the work rolls of the rolling mill stand where the first pass of cold rolling is performed, the axial arithmetic mean roughness Ra (μm), the ten-point mean roughness Rzjis (μm), and the diameter Dw (mm) of the work rolls satisfy equations (1) and (2).

[0041] 0.30≤Ra≤0.01Dw+3.08 (1) 3Ra≤Rzjis≤7Ra (2) The second method for manufacturing directional electromagnetic steel plates is based on the first method for manufacturing directional electromagnetic steel plates. In the decarburization annealing process, the decarburization annealing temperature is set to 750–950°C, and the average heating rate from 400°C to 750°C is set to 100°C / second or more and 3000°C / second or less.

[0042] The third method of manufacturing directional electromagnetic steel sheet is based on the first or second method of manufacturing directional electromagnetic steel sheet, wherein in the cold rolling process, cold rolling begins from the front end of the hot-rolled steel sheet manufactured in the hot rolling process toward the rear end.

[0043] The directional electromagnetic steel plate of this embodiment will now be described. It should be noted that unless otherwise specified, the percentage (%) for elements refers to mass (%).

[0044] [Regarding the structure of directional electromagnetic steel sheets] Figure 1 This is a perspective view of the directional electromagnetic steel sheet according to this embodiment. In the figure, direction L refers to the rolling direction of the directional electromagnetic steel sheet. Direction W refers to the orthogonal rolling direction (plate width direction) of the directional electromagnetic steel sheet. Direction T refers to the normal direction (plate thickness direction) of the rolled surface of the directional electromagnetic steel sheet. It should be noted that the rolled surface of the directional electromagnetic steel sheet refers to the upper or lower surface of the directional electromagnetic steel sheet.

[0045] Reference Figure 1 In this embodiment, the directional electromagnetic steel plate 1 includes a base steel plate 10. The directional electromagnetic steel plate 1 may also include a lower coating 11 and an insulating coating 12. When the directional electromagnetic steel plate 1 includes a lower coating 11 and an insulating coating 12, the lower coating 11 is formed on the base steel plate 10. Figure 1 In this process, the lower coating 11 is formed on the surface of the base steel plate 10 in direct contact with the surface of the base steel plate 10. The lower coating 11 is either a primary coating mainly composed of magnesium olivine or an intermediate layer mainly composed of oxides such as silica and alumina. When reducing iron loss is a priority, the lower coating 11 is used as a primary coating. When punching workability is a priority, the lower coating 11 is used as an intermediate layer. The lower coating 11 is a known coating.

[0046] An insulating film 12 is formed on the lower film 11. For example... Figure 1 As shown, the lower coating 11 and the insulating coating 12 can also be formed on a pair of surfaces of the base steel plate 10 (i.e., on the surface and back of the base steel plate 10). The insulating coating 12 is a known insulating coating. The directional electromagnetic steel plate 1 may also have the base steel plate 10 and the insulating coating 12, but not the lower coating 11.

[0047] In addition, it is well known that directional electromagnetic steel sheets sometimes have a base steel sheet, a lower cladding and an insulating cladding, or sometimes have a base steel sheet and an insulating cladding.

[0048] [Regarding the chemical composition of the base steel plate 10] The chemical composition of the base steel plate 10 of the directional electromagnetic steel plate 1 contains the following elements.

[0049] Si: 3.00~3.70% Silicon (Si) increases the electrical resistance (resistivity) of the steel sheet, thereby reducing the iron loss of the directional electromagnetic steel sheet 1. If the Si content is less than 3.00%, the above effect cannot be fully obtained. On the other hand, if the Si content exceeds 3.70%, the steel sheet will become brittle.

[0050] Therefore, the Si content is 3.00–3.70%.

[0051] The preferred lower limit for the Si content is 3.05%, more preferably 3.10%, more preferably 3.15%, more preferably 3.20%, more preferably 3.25%, and more preferably 3.30%.

[0052] The preferred upper limit for the Si content is 3.65%, more preferably 3.60%, more preferably 3.55%, and more preferably 3.50%.

[0053] Mn: 0.01~0.30% Manganese (Mn) increases the resistivity of steel sheets, thereby reducing iron losses. Mn further improves the hot workability of the steel sheets and suppresses cracking during hot rolling. If the Mn content is less than 0.01%, the above effects cannot be fully obtained. On the other hand, if the Mn content exceeds 0.30%, the magnetic flux density of the directional electromagnetic steel sheet 1 will decrease, and the iron losses will also deteriorate.

[0054] Therefore, the Mn content is 0.01–0.30%.

[0055] The preferred lower limit for Mn content is 0.02%, more preferably 0.03%, and even more preferably 0.05%.

[0056] The preferred upper limit for Mn content is 0.28%, more preferably 0.25%, more preferably 0.20%, and more preferably 0.15%.

[0057] N: 0.0001~0.0100% Nitrogen (N) forms nitrides, which degrades the iron loss of the directional electromagnetic steel sheet 1. If the N content exceeds 0.0100%, the iron loss of the directional electromagnetic steel sheet 1 degrades significantly.

[0058] Therefore, the N content is 0.0001 to 0.0100%.

[0059] The preferred lower limit for N content is 0.0002%, and more preferably 0.0005%.

[0060] The preferred upper limit for N content is 0.0090%, more preferably 0.0050%, and even more preferably 0.0030%.

[0061] C: 0.001~0.010% Carbon (C) is an essential element in slabs to improve magnetic flux density. However, C is released from the steel sheet during the manufacturing process of the directional electromagnetic steel sheet 1. If more than 0.010% of C remains in the directional electromagnetic steel sheet 1 as a product, magnetic aging occurs, and the iron loss of the directional electromagnetic steel sheet 1 deteriorates.

[0062] The lower limit of C content is preferably low. However, excessively reducing the C content will increase manufacturing costs. Therefore, the lower limit of C content is set to be above 0.001%.

[0063] Therefore, the C content is 0.001–0.010%.

[0064] The preferred lower limit for C content is 0.002%, and more preferably 0.003%.

[0065] The preferred upper limit for C content is 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0066] sol.Al: 0~0.010% Acid-soluble aluminum (sol.Al) combines with nitrogen (N) during the manufacturing process of the directional electromagnetic steel sheet 1 to form AlN, acting as an inhibitor. However, if the sol.Al content exceeds 0.010%, Al-based inclusions will remain in the steel sheet. In this case, the iron loss of the directional electromagnetic steel sheet 1 deteriorates.

[0067] Therefore, the sol.Al content is below 0.010%. It should be noted that the sol.Al content can be 0%, meaning it ranges from 0% to 0.010%.

[0068] The preferred lower limit for the sol.Al content is 0.001%.

[0069] The preferred upper limit for the sol.Al content is 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0070] Choose one or more from the groups composed of S and Se: the total is 0 to 0.010%. Sulfur (S) and selenium (Se) combine with Mn during the manufacturing process to form fine MnS or MnSe, which act as inhibitors. Therefore, S and Se are essential elements in the slab. However, S and Se are released from the steel sheet during the manufacturing process of the directional electromagnetic steel sheet 1. If the total content of one or more of S and Se in the directional electromagnetic steel sheet 1 exceeds 0.010%, MnS or MnSe will remain in the steel sheet. In this case, the iron loss of the directional electromagnetic steel sheet 1 deteriorates.

[0071] Therefore, the total content of one or more selected items from the group consisting of S and Se is less than 0.010%. It should be noted that the total content of one or more selected items from the group consisting of S and Se can be 0%. That is, the total content of one or more selected items from the group consisting of S and Se is between 0 and 0.010%.

[0072] The preferred lower limit for the total content of one or more substances selected from the group consisting of S and Se is 0.001%.

[0073] The preferred upper limit for the total content of one or more selected from the group consisting of S and Se is 0.008%, more preferably 0.006%, and even more preferably 0.004%.

[0074] The chemical composition of the directional electromagnetic steel sheet 1 consists of Fe and impurities. Here, impurities refer to substances that are mixed in from the ore, waste, or manufacturing environment used as raw materials during the industrial manufacture of the base steel sheet 10 of the directional electromagnetic steel sheet 1, and are permissible within a range that does not adversely affect the directional electromagnetic steel sheet 1 of this embodiment. Impurities may include, for example, one or more selected from the group consisting of Ca: 0–0.001%, Mg: 0–0.002%, Ce: 0–0.002%, O: 0–0.01%, As: 0–0.10%, Co: 0–0.10%, Zr: 0–0.003%, W: 0–0.10%, Hf: 0–0.02%, Sc: 0–0.02%, Sr: 0–0.02%, Zn: 0–0.02%, Pb: 0–0.10%, Nd: 0–0.02%, REM: 0–0.02%, Ba: 0–0.02%, Cd: 0–0.02%, Pt: 0–0.02%, Au: 0–0.02%, Ga: 0–0.02%, Ge: 0–0.02%, Y: 0–0.02%, and La: 0–0.02%. In cases where multiple impurity elements are present, the total content of these multiple elements is 0 to 0.05%.

[0075] [About Optional Elements] The chemical composition of the base steel plate 10 of the directional electromagnetic steel plate 1 may also contain one or more elements selected from Ti: 0-0.010%, Ni: 0-0.50%, Cr: 0-0.50%, Cu: 0-0.50%, P: 0-0.05%, Mo: 0-0.05%, Sn: 0-0.30%, Sb: 0-0.30%, Bi: 0-0.0150%, Ta: 0-0.05%, Nb: 0-0.010%, V: 0-0.50%, B: 0-0.010%, and Te: 0-0.0150% to replace a portion of Fe. These elements are optional.

[0076] The following is an explanation of each element.

[0077] [Group 1: Ti] Ti: 0~0.010% Titanium (Ti) is an optional element and may be omitted. That is, the Ti content can be 0%.

[0078] In the presence of Ti, specifically when the Ti content exceeds 0%, Ti reduces the magnetic properties of the directional electromagnetic steel sheet 1. If the Ti content exceeds 0.010%, the magnetic properties of the directional electromagnetic steel sheet 1 are significantly reduced.

[0079] Therefore, the Ti content is 0 to 0.010%.

[0080] The Ti content is preferably as low as possible. However, excessive reduction in Ti content will increase manufacturing costs. Therefore, under normal industrial production conditions, the preferred lower limit for Ti content is 0.001%, and more preferably 0.002%.

[0081] The preferred upper limit for Ti content is 0.009%, more preferably 0.008%, more preferably 0.007%, and more preferably 0.005%.

[0082] [Group 2: Ni, Cr, Cu, P, and Mo] Ni, Cr, Cu, P, and Mo are all optional elements. These elements all cause changes in the microstructure during the manufacturing process, thereby improving the magnetic properties of the directional electromagnetic steel sheet 1.

[0083] Ni: 0~0.50% Nickel (Ni) is an optional element and can be omitted. That is, the Ni content can be 0%.

[0084] In the presence of Ni, i.e., when the Ni content exceeds 0%, Ni alters the microstructure formation behavior up to the final annealing process, promoting secondary recrystallization of Gaussian oriented grains. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if a small amount of Ni is present.

[0085] However, if the Ni content exceeds 0.50%, secondary recrystallization sometimes becomes unstable.

[0086] Therefore, the Ni content is 0 to 0.50%.

[0087] The preferred lower limit for Ni content is 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0088] The preferred upper limit for Ni content is 0.40%, more preferably 0.30%, more preferably 0.20%, and more preferably 0.15%.

[0089] Cr: 0~0.50% Chromium (Cr) is an optional element and may be omitted. That is, the Cr content can also be 0%.

[0090] In the presence of Cr, i.e., when the Cr content exceeds 0%, Cr alters the microstructure formation behavior up to the final annealing process, promoting secondary recrystallization of Gaussian oriented grains. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if a small amount of Cr is present.

[0091] However, if the Cr content exceeds 0.50%, Cr oxides will form in the steel plate. Therefore, the iron loss of the directional electromagnetic steel plate 1 deteriorates.

[0092] Therefore, the Cr content is 0 to 0.50%.

[0093] The preferred lower limit for Cr content is 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0094] The preferred upper limit for Cr content is 0.40%, more preferably 0.30%, more preferably 0.20%, and more preferably 0.15%.

[0095] Cu: 0~0.50% Copper (Cu) is an optional element and may be omitted. That is, the Cu content can be 0%.

[0096] In the presence of Cu, i.e., when the Cu content exceeds 0%, Cu alters the microstructure formation behavior up to the final annealing process, promoting secondary recrystallization of Gaussian oriented grains. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if a small amount of Cu is present.

[0097] However, if the Cu content exceeds 0.50%, the hot workability of the steel plate decreases.

[0098] Therefore, the Cu content is 0–0.50%.

[0099] The preferred lower limit for Cu content is 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0100] The preferred upper limit for Cu content is 0.40%, more preferably 0.30%, more preferably 0.20%, and more preferably 0.15%.

[0101] P: 0–0.05% Phosphorus (P) is an optional element and may be omitted. That is, the P content can also be 0%.

[0102] In the presence of phosphorus (P), i.e., when the P content exceeds 0%, P alters the microstructure formation behavior up to the final annealing process, promoting secondary recrystallization of Gaussian oriented grains. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if a small amount of P is present.

[0103] However, if the phosphorus content exceeds 0.05%, the workability of the steel plate decreases.

[0104] Therefore, the P content is 0–0.05%.

[0105] The preferred lower limit for P content is 0.01%.

[0106] The preferred upper limit for the P content is 0.04%, more preferably 0.03%, and even more preferably 0.02%.

[0107] Mo: 0–0.05% Molybdenum (Mo) is an optional element and can be omitted. That is, the Mo content can be 0%.

[0108] In the presence of Mo, i.e., when the Mo content exceeds 0%, Mo alters the microstructure formation behavior up to the final annealing process, promoting secondary recrystallization of Gaussian oriented grains. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if a small amount of Mo is present.

[0109] However, if the Mo content exceeds 0.05%, the workability of the steel plate decreases.

[0110] Therefore, the Mo content is 0–0.05%.

[0111] The preferred lower limit for Mo content is 0.01%, and more preferably 0.02%.

[0112] The preferred upper limit for Mo content is 0.04%, and more preferably 0.03%.

[0113] [Group 3: Sn, Sb, Bi, Ta, Nb, V, B, and Te] Sn, Sb, Bi, Ta, Nb, V, B, and Te are all optional elements. These elements all function as inhibitors, stabilizing secondary recrystallization.

[0114] Sn: 0~0.30% Tin (Sn) is an optional element and may not be present. That is, the Sn content can be 0%.

[0115] In the presence of Sn, Sn functions as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the directional electromagnetic steel sheet 1. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if a small amount of Sn is present.

[0116] However, if the Sn content exceeds 0.30%, the magnetic properties of the directional electromagnetic steel plate 1 will actually decrease.

[0117] Therefore, the Sn content is 0–0.30%.

[0118] The preferred lower limit for Sn content is 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0119] The preferred upper limit for Sn content is 0.25%, more preferably 0.20%, and even more preferably 0.15%.

[0120] Sb: 0~0.30% Antimony (Sb) is an optional element and can be omitted. That is, the Sb content can be 0%.

[0121] In the presence of Sb, Sb acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the directional electromagnetic steel sheet 1. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The above-mentioned effect can be achieved to a certain extent if a small amount of Sb is present.

[0122] However, if the Sb content exceeds 0.30%, the magnetic properties of the directional electromagnetic steel plate 1 will actually decrease.

[0123] Therefore, the Sb content is 0–0.30%.

[0124] The preferred lower limit for Sb content is 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0125] The preferred upper limit for Sb content is 0.25%, more preferably 0.20%, and even more preferably 0.15%.

[0126] Bi: 0~0.0150% Bismuth (Bi) is an optional element and can be omitted. That is, the Bi content can also be 0%.

[0127] In the presence of Bi, Bi acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the directional electromagnetic steel sheet 1. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The above-mentioned effect can be achieved to a certain extent if a small amount of Bi is present.

[0128] However, if the Bi content exceeds 0.0150%, the magnetic properties of the directional electromagnetic steel plate 1 will actually decrease.

[0129] Therefore, the Bi content is 0 to 0.0150%.

[0130] The preferred lower limit for Bi content is 0.0001%, more preferably 0.0005%, more preferably 0.0010%, and more preferably 0.0050%.

[0131] The preferred upper limit for Bi content is 0.0120%, more preferably 0.0100%, more preferably 0.0070%, and more preferably 0.0050%.

[0132] Ta: 0~0.05% Tantalum (Ta) is an optional element and can be omitted. That is, the Ta content can be 0%.

[0133] In the presence of Ta, Ta acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the directional electromagnetic steel sheet 1. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if a small amount of Ta is present.

[0134] However, if the Ta content exceeds 0.05%, the magnetic properties of the directional electromagnetic steel plate 1 will actually decrease.

[0135] Therefore, the Ta content is 0–0.05%.

[0136] The preferred lower limit for Ta content is 0.01%, and more preferably 0.02%.

[0137] The preferred upper limit for Ta content is 0.04%, and more preferably 0.03%.

[0138] Nb: 0~0.010% Niobium (Nb) is an optional element and can be omitted. That is, the Nb content can also be 0%.

[0139] In the presence of Nb, Nb acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the directional electromagnetic steel sheet 1. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The above effect can be achieved to a certain extent if a small amount of Nb is present. However, if the Nb content exceeds 0.010%, the magnetic properties of the directional electromagnetic steel sheet 1 actually decrease.

[0140] Therefore, the Nb content is 0 to 0.010%.

[0141] The preferred lower limit for Nb content is 0.001%, and more preferably 0.003%.

[0142] The preferred upper limit for Nb content is 0.008%, and more preferably 0.006%.

[0143] V: 0~0.50% Vanadium (V) is an optional element and can be omitted. That is, the V content can also be 0%.

[0144] In the presence of V, V acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the directional electromagnetic steel sheet 1. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if a small amount of V is present.

[0145] However, if the V content exceeds 0.50%, the magnetic properties of the directional electromagnetic steel plate 1 will actually decrease.

[0146] Therefore, the V content is 0–0.50%.

[0147] The preferred lower limit for the V content is 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0148] The preferred upper limit for the V content is 0.40%, more preferably 0.30%, and even more preferably 0.20%.

[0149] B: 0~0.010% Boron (B) is an optional element and may be omitted. That is, the B content can also be 0%.

[0150] In the presence of boron (B), B acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the directional electromagnetic steel sheet 1. As a result, the magnetic properties of the directional electromagnetic steel sheet 1 are improved. The aforementioned effect can be achieved to a certain extent if only a small amount of B is present.

[0151] However, if the B content exceeds 0.010%, the magnetic properties of the directional electromagnetic steel plate 1 will actually decrease.

[0152] Therefore, the content of B is 0 to 0.010%.

[0153] The preferred lower limit for the B content is 0.001%, more preferably 0.002%, and even more preferably 0.003%.

[0154] The preferred upper limit for the B content is 0.009%, more preferably 0.007%, and even more preferably 0.005%.

[0155] Te: 0~0.0150% Tellurium (Te) is an optional element and can be omitted. That is, the Te content can also be 0%.

[0156] In the presence of Te, Te acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of directional electromagnetic steel sheet 1. As a result, the magnetic properties of directional electromagnetic steel sheet 1 are improved. A small amount of Te can achieve this effect to a certain extent. However, if the Te content exceeds 0.0150%, the magnetic properties of directional electromagnetic steel sheet 1 actually decrease.

[0157] Therefore, the Te content is 0 to 0.0150%.

[0158] The preferred lower limit for Te content is 0.0001%, more preferably 0.0005%, more preferably 0.0010%, and more preferably 0.0050%.

[0159] The preferred upper limit for Te content is 0.0120%, more preferably 0.0100%, more preferably 0.0070%, and more preferably 0.0050%.

[0160] [Method for determining the chemical composition of directional electromagnetic steel sheet 1] The chemical composition of the directional electromagnetic steel plate 1 in this embodiment can be determined by a known compositional analysis method.

[0161] First, when the directional electromagnetic steel plate 1 has a lower coating 11 and an insulating coating 12, the lower coating 11 and the insulating coating 12 are removed by the following method. Specifically, the directional electromagnetic steel plate 1 with the insulating coating 12 is immersed in a high-temperature alkaline solution to remove it. The composition, temperature, and immersion time of the alkaline solution can be adjusted appropriately. For example, the directional electromagnetic steel plate 1 with the insulating coating 12 is immersed in a sodium hydroxide aqueous solution of NaOH: 30-50% by mass + H2O: 50-70% by mass at 80-90°C for 5-10 minutes, followed by washing with water and drying. Through this process, the insulating coating 12 is removed from the directional electromagnetic steel plate 1.

[0162] Next, the insulating film 12 is removed, and the directional electromagnetic steel plate 1 with the remaining lower film 11 is immersed in high-temperature hydrochloric acid to remove it. The concentration, temperature, and immersion time of the hydrochloric acid can be adjusted appropriately. For example, to remove the insulating film 12, the directional electromagnetic steel plate 1 with the remaining lower film 11 is immersed in 30-40% by mass hydrochloric acid at 80-90°C for 1-5 minutes. The immersed directional electromagnetic steel plate 1 is then washed with water and dried. Through the above processes, a base steel plate 10 with the insulating film 12 and the lower film 11 removed is obtained.

[0163] The chemical composition of the obtained base steel plate 10 was determined using a known compositional analysis method according to JIS G0321:2017. Specifically, chips were collected from the directional electromagnetic steel plate 1. The collected chips were dissolved in acid to obtain a solution. ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) was performed on the solution to perform elemental analysis of the chemical composition. The C and S contents were determined using a known high-frequency combustion method (combustion-infrared absorption method). The N content was determined using a known inert gas melting-thermal conductivity method. For example, the chemical composition of the base steel plate 10 can be analyzed using a compositional analysis device (product name: ICPS-8000) manufactured by Shimadzu Corporation.

[0164] It should be noted that the content of each element is based on the significant figures specified in this embodiment, with the measured values ​​rounded to the minimum number of decimal places specified in this embodiment. For example, the Si content in this embodiment is defined as a value to two decimal places. Therefore, the Si content is set to a value to two decimal places obtained by rounding the third decimal place of the measured value.

[0165] Regarding the content of elements other than Si in the directional electromagnetic steel plate 1 of this embodiment, the measured value is rounded to the nearest digit as specified in this embodiment, and the value obtained is taken as the content of that element.

[0166] In addition, rounding means that if the last digit is less than 5, it is discarded; if the last digit is 5 or more, it is rounded up.

[0167] [Regarding the lower layer coating 11] As described above, the lower coating 11 can be either a primary coating or an intermediate layer. A primary coating is a known type of coating primarily composed of forsterite (Mg2SiO4). The forsterite content in the primary coating is 60% or more by mass. The primary coating is formed by reacting an annealing separating agent containing magnesium oxide with an oxide film such as SiO2 on the surface of the base steel plate 10 or with elements contained in the base steel plate 10 during final annealing. Therefore, the lower coating 11 has a composition derived from the chemical composition of the annealing separating agent and the base steel plate 10. For example, the lower coating 11 contains spinel (MgAl2O4). When reducing iron loss is a priority, the lower coating 11 is used as a primary coating. On the other hand, the intermediate layer is a coating primarily composed of silica and alumina. More specifically, the total content of silica and alumina in the intermediate layer is 60% or more by mass. When workability is a priority, the lower coating 11 is used as an intermediate layer.

[0168] [Regarding insulating film 12] An insulating coating 12 is formed on a lower coating 11. The insulating coating 12 ensures insulation between the stacked directional electromagnetic steel sheets 1 when multiple directional electromagnetic steel sheets 1 are used in a stacked configuration. The insulating coating 12 has a known structure. Specifically, the insulating coating 12 contains at least one inorganic material selected from metal chromate salts, metal phosphate salts, colloidal silica, Zr compounds, and Ti compounds. Preferably, the insulating coating 12 is a coating primarily composed of phosphate compounds. That is, the insulating coating 12 contains phosphate compounds. When the insulating coating 12 is primarily composed of phosphate compounds, the content of the phosphate compounds is 50% or more by mass%.

[0169] The insulating coating 12 may, for example, contain one or more compounds selected from the group consisting of colloidal silica and polytetrafluoroethylene, together with a phosphoric acid compound. The phosphoric acid compound may, for example, consist of one or more compounds selected from the group consisting of sodium phosphate, aluminum phosphate, and magnesium phosphate.

[0170] [Regarding the proportion of specific crystal orientations] Regarding the directional electromagnetic steel plate 1 of this embodiment, when measuring the crystal orientation using X-ray diffraction at measurement points arranged at 2mm intervals in each direction and in a direction orthogonal to the rolling direction on the surface of the base steel plate 10, the following requirements A to C are satisfied.

[0171] (Requirement A) With {211} <011> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {211}<011> It is below 5%.

[0172] (Requirement B) With {110} <112> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<112> It is below 5%.

[0173] (Requirement C) With {110} <001> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<001> It is over 90%.

[0174] The following is an explanation of requirements A through C.

[0175] With {110} <001> Compared to oriented Gaussian grains, it has {211} <011> Oriented grains and having {110} <112> Oriented grains have poor magnetic properties. Therefore, {211} <011> Oriented grains and {110} <112> The number of oriented grains should be as small as possible.

[0176] Specifically, if with {211} <011> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {211}<011> If it exceeds 5%, then {211} <011> Excessive grain orientation results in decreased magnetic properties.

[0177] Similarly, if the chemical composition of the base steel plate 10 meets the range of this embodiment, and if it is related to {110} <112> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<112> If it exceeds 5%, then {110} <112> Excessive grain orientation results in decreased magnetic properties.

[0178] Furthermore, if it is aligned with the Gaussian orientation, i.e. {110} <001> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<001> If the proportion is less than 90%, there are too few Gaussian oriented grains. Therefore, the magnetic properties become lower. Consequently, the noise characteristics may also decrease.

[0179] If conditions A to C are satisfied, then there are sufficiently numerous Gaussian-oriented grains, and {211} <011> Oriented grains and {110} <112> The oriented grains are sufficiently few. Therefore, excellent magnetic properties can be obtained. Specifically, excellent magnetic flux density can be obtained.

[0180] Number ratio R {211}<011> The preferred upper limit is 4%, and a further preferred limit is 3%.

[0181] Number ratio R {211}<011> The preferred lower limit is 1%, and the more preferred value is 0%.

[0182] Number ratio R{110}<112> The preferred upper limit is 4%, and a further preferred limit is 3%.

[0183] Number ratio R {110}<112> The preferred lower limit is 1%, and the more preferred value is 0%.

[0184] Number ratio R {110}<001> The preferred lower limit is 91%, further preferably 92%, further preferably 93%, and further preferably 94%.

[0185] Number ratio R {110}<001> The preferred upper limit is 96%, further preferably 97%, and even more preferably 98%.

[0186] [Regarding the proportion of large-angle grain boundaries (RL)] In the directional electromagnetic steel plate 1 of this embodiment, the ratio of the total length LI of the grain boundary with an orientation difference of 15° or more obtained from the orientation difference at the above-mentioned measurement point to the total length La of the grain boundary, i.e., the large angle grain boundary ratio RL=LI / La, is 5% or more and 30% or less.

[0187] As described in requirements A through C above, by maximizing the number of Gaussian-oriented grains in the grains, the {211} are minimized. <011> Oriented grains and {110} <112> Orienting the grains increases magnetic flux density. However, while excellent magnetic flux density can be obtained by satisfying conditions A through C, excellent iron loss is not necessarily achieved. This demonstrates that in directional electromagnetic steel sheets, an increase in magnetic flux density is not necessarily related to a decrease in iron loss.

[0188] On the other hand, as described above, the inventors have verified that the appropriate presence of large-angle grain boundaries improves iron loss. Specifically, auxiliary magnetic domains are formed at the locations where large-angle grain boundaries exist. If an appropriate amount of auxiliary magnetic domains are formed, the domain walls are refined, and iron loss is reduced.

[0189] If the proportion of large-angle grain boundaries (RL) is less than 5%, the proportion of large-angle grain boundaries is too low, resulting in an excessively small number of auxiliary magnetic domains. In this case, the refinement of the domain walls is insufficient. As a result, sufficiently low iron losses cannot be obtained.

[0190] On the other hand, if the proportion of large-angle grain boundaries (RL) exceeds 30%, the proportion of large-angle grain boundaries becomes excessive, resulting in an excess of auxiliary magnetic domains. In this case, the movement of the magnetic grating walls is hindered, and hysteresis losses increase. Consequently, sufficiently low iron losses cannot be obtained. Furthermore, if auxiliary magnetic domains become excessive, magnetostriction increases. It should be noted that if the proportion of large-angle grain boundaries (RL) exceeds 30%, the magnetic flux density may sometimes decrease.

[0191] If the proportion of large-angle grain boundaries (RL) is 5–30%, then a suitable amount of large-angle grain boundaries and auxiliary magnetic domains are present. Therefore, the domain walls are refined, and the excess amount of auxiliary magnetic domains is suppressed. As a result, excellent iron loss can be obtained, and consequently, excellent noise characteristics can be achieved.

[0192] The preferred lower limit for the large-angle grain boundary ratio RL is 6%, further preferably 7%, further preferably 8%, further preferably 10%, and further preferably 12%.

[0193] The preferred upper limit for the large-angle grain boundary ratio RL is 28%, further preferably 26%, further preferably 24%, and further preferably 22%.

[0194] [Method for determining crystal orientation at the measurement point] The crystal orientation at the measurement point can be determined by the following methods.

[0195] X-ray diffraction using the Laue method was performed on the rolled surface of the directional electromagnetic steel sheet 1. Specifically, one or more rectangular observation areas AR were selected from any location on the rolled surface of the directional electromagnetic steel sheet 1, with a length of 250 mm in the rolling direction and a length of 60 mm in the direction orthogonal to the rolling direction. n (n is a natural number). For the observation region AR n X-ray diffraction using the Laue method was performed at measurement points spaced 2 mm apart in both the rolling and width directions (3906 measurement points) to obtain the crystal orientation at each measurement point. The spot diameter was set to 1 mm. Based on the crystal orientation obtained at each measurement point, boundaries with orientation difference angles ranging from 1 to 180° were designated as grain boundaries. Furthermore, the regions enclosed by these grain boundaries were designated as grains. The X-ray source used in the Laue method was a W target, with the tube voltage set to 40 kV and the tube current set to 40 mA.

[0196] Determine each observation area AR n The total number of grains determined upon completion of the measurement is whether it is more than 100. If the number of grains is less than 100, another observation area AR is selected. n+1 The above-described X-ray diffraction was then performed. The determination was completed when the total number of crystal grains reached 100 or more.

[0197] Find the sum of {211} among all the measurement points after the measurement is completed. <011> The number of measurement points with an orientation difference of less than 15°. Based on the total number of measurement points completed and {211} <011> The number of measurement points with an orientation difference of less than 15° is calculated using the following formula to determine the proportion R. {211}<011> (%).

[0198] Number ratio R{211}<011> =and {211} <011> Number of measurement points with an orientation difference of less than 15° / Total number of measurement points completed × 100 Find the sum of {110} among all the measurement points after the measurement is completed. <112> The number of measurement points with an orientation difference of less than 15°. Based on the total number of measurement points completed and {110} <112> The number of measurement points with an orientation difference of less than 15° is calculated using the following formula to determine the proportion R. {110}<112> (%).

[0199] Number ratio R {110}<112> =and {110} <112> Number of measurement points with an orientation difference of less than 15° / Total number of measurement points completed × 100 Find the sum of {110} among all the measurement points after the measurement is completed. <001> The number of measurement points with an orientation difference of less than 15°. Based on the total number of measurement points completed and {110} <001> The number of measurement points with an orientation difference of less than 15° is calculated using the following formula to determine the proportion R. {110}<001> (%).

[0200] Number ratio R {110}<001> =and {110} <001> Number of measurement points with an orientation difference of less than 15° / Total number of measurement points completed × 100 Furthermore, AR will be applied to all observation areas where measurements have been completed. n The total length of the grain boundaries of all the grains identified is defined as La. Additionally, the total length of grain boundaries with an orientation difference angle of 15° or greater (large-angle grain boundaries) among the identified grain boundaries is defined as LI.

[0201] For example, if the number of crystal grains determined is more than 100 after the crystal orientation in the first observation area AR1 is determined, La and LI can be calculated using all the crystal grains determined in the observation area AR1.

[0202] On the other hand, if the number of grains determined after the measurement in observation area AR1 is less than 100, the measurement in the second observation area AR2 is performed. Then, if the total number of grains determined in observation areas AR1 and AR2 is more than 100 after the measurement in observation area AR2, La and LI are calculated using all the grains determined in observation areas AR1 and AR2.

[0203] As mentioned above, continue observing regions AR1 to AR2. nThe measurements were continued until the total number of identified grains reached 100 or more. Then, when the total number of grains reached 100 or more, measurements were performed on the entire observation area AR1 to AR2. n From all the grains identified in the sample, determine La and LI.

[0204] Using the obtained La and LI, the large-angle grain boundary ratio RL (%) is calculated using the following formula.

[0205] Large-angle grain boundary ratio RL=LI / La×100 Based on the crystal orientation at each measurement point, La and LI can be determined using OIMAnalysis, a product manufactured by TSL Solutions, Inc.

[0206] It should be noted that at measurement points with grain sizes of 1 mm or less, or at points equivalent to grain boundaries, crystal orientation identification can sometimes be difficult, resulting in poor identification. Therefore, at such measurement points (hereinafter referred to as poor measurement points), crystal orientation data from adjacent measurement points are used as a substitute. Specifically, among two measurement points adjacent to the poor measurement point in the rolling direction (+X and -X) and two measurement points adjacent to the poor measurement point in the width direction (+Y and -Y), crystal orientation data are used as substitutes in the order of +X, -X, +Y, -Y. First, the crystal orientation data of the +X measurement point is used as a substitute for the crystal orientation data of the poor measurement point. If the crystal orientation data at the +X measurement point is also poor, the crystal orientation data of the -X measurement point is used as a substitute. As described above, the data that can be used as substitutes are determined according to the order of priority. Furthermore, this method of using crystal orientation data as a substitute is set to the "Clean up" function in the above-mentioned OIM Analysis. The X direction is, for example, the rolling direction, and the Y direction is, for example, the width direction.

[0207] [Effects of the directional electromagnetic steel plate 1 in this embodiment] The directional electromagnetic steel plate 1 of this embodiment satisfies requirements A to C, and the large-angle grain boundary ratio RL is 5% to 30%. Therefore, excellent magnetic flux density can be obtained. Furthermore, after magnetic domain refinement treatment, excellent iron loss and excellent noise characteristics can be obtained.

[0208] [Preferred thickness of the base steel plate 10 for the directional electromagnetic steel plate 1 in this embodiment] The thickness of the base steel plate 10 of the directional electromagnetic steel plate 1 in this embodiment is not particularly limited. For example, the thickness of the base steel plate 10 can be 0.17 to 0.22 mm, which is the same as that of the base steel plate of a known directional electromagnetic steel plate.

[0209] The preferred thickness of the base steel plate 10 is 0.19 mm or less. In the directional electromagnetic steel plate 1 of this embodiment, even if the thickness of the base steel plate 10 is 0.19 mm or less, excellent magnetic flux density can be obtained, and after magnetic domain refinement treatment, excellent iron loss and excellent noise characteristics can be obtained.

[0210] [Other embodiments of the directional electromagnetic steel plate 1 in this implementation] In the directional electromagnetic steel plate 1 of this embodiment, it may also be formed with: a plurality of linear thermal strains that extend in a linear shape and are arranged in a direction perpendicular to the extension direction, or a plurality of grooves that extend in a linear shape and are arranged in a direction perpendicular to the extension direction.

[0211] Linear thermal strain or grooves are formed on the rolling surface of the directional electromagnetic steel sheet 1 through a known magnetic domain refinement process. The linear thermal strain or grooves refine the magnetic domains of the directional electromagnetic steel sheet 1. In the directional electromagnetic steel sheet 1 of this embodiment, excellent iron loss can be obtained after the magnetic domain refinement process.

[0212] [Manufacturing method of directional electromagnetic steel plate 1 according to this embodiment] An example of a method for manufacturing the directional electromagnetic steel sheet according to this embodiment will be described. The method for manufacturing the directional electromagnetic steel sheet 1 described below is an example for manufacturing the directional electromagnetic steel sheet 1 of this embodiment. Therefore, the directional electromagnetic steel sheet 1 of this embodiment can also be manufactured by other manufacturing methods besides the method described below. However, the manufacturing method described below is a preferred example of the method for manufacturing the directional electromagnetic steel sheet 1 of this embodiment.

[0213] [Manufacturing Process Flow] An example of the manufacturing method of the directional electromagnetic steel plate 1 in this embodiment includes the following steps 1 to 6.

[0214] (Process 1) Hot rolling process (Process 2) Hot-rolled plate annealing process (Process 3) Cold rolling process (Process 4) Decarburization annealing process (Step 5) Final annealing process (Process 6) Insulation film formation process It should be noted that the hot-rolled plate annealing process (process 2) is optional. Therefore, the hot-rolled plate annealing process can be implemented or not.

[0215] In terms of the manufacturing method of this embodiment, the following manufacturing conditions are further satisfied in the cold rolling process (process 3) and the decarburization annealing process (process 4).

[0216] (Condition 1) The cumulative reduction rate (RR) in the cold rolling process is above 89% and below 93%.

[0217] (Condition 2) In the work rolls of the rolling mill stand where the first pass of cold rolling is performed, the axial arithmetic mean roughness Ra (μm), the ten-point mean roughness Rzjis (μm), and the diameter Dw (mm) of the work rolls satisfy equations (1) and (2).

[0218] 0.30≤Ra≤0.01Dw+3.08 (1) 3Ra≤Rzjis≤7Ra (2) (Condition 3) The hot-rolled steel sheet, manufactured in the hot rolling process, is cold-rolled from the front end toward the rear end.

[0219] (Condition 4) During the heating process of the decarburization annealing process, the average heating rate HR in the range of 400℃~750℃ is set to be above 100℃ / second and below 3000℃ / second.

[0220] The following describes processes 1 through 6.

[0221] [(Process 1) Hot rolling process] In the hot rolling process, a slab is hot-rolled to produce a hot-rolled steel sheet. Here, the chemical composition of the prepared slab is adjusted so that the chemical composition of the directional electromagnetic steel sheet 1 meets the scope of this embodiment.

[0222] Specifically, the chemical composition of the slab, in mass percent, is as follows: Si: 3.00–3.70%, Mn: 0.01–0.30%, N: 0.0030–0.0150%, C: 0.010–0.100%, sol.Al: 0.010–0.050%, one or more selected from the group consisting of S and Se: totaling 0.010–0.050%, Ti: 0–0.010%, Ni: 0–0.50%, Cr: 0–0.50%, Cu: 0–0.50%, P: 0–0.05%, Mo: 0–0.05%, Sn: 0–0.30%, Sb: 0–0.30%, Bi: 0–0.0200%, Ta: 0–0.05%, Nb: 0–0.010%, V: 0–0.50%, B: 0–0.010%, Te: 0–0.0200%, and the balance consisting of Fe and impurities.

[0223] The preferred lower limit for Si content is 3.10%, and more preferably 3.20%.

[0224] The preferred upper limit for Si content is 3.60%, and more preferably 3.50%.

[0225] The preferred lower limit for Mn content is 0.02%, and more preferably 0.05%.

[0226] The preferred upper limit for Mn content is 0.28%, and more preferably 0.26%.

[0227] The preferred lower limit for N content is 0.0032%, and more preferably 0.0034%.

[0228] The preferred upper limit for N content is 0.0120%, and more preferably 0.0100%.

[0229] The preferred lower limit for C content is 0.012%, and more preferably 0.014%.

[0230] The preferred upper limit for C content is 0.090%, and more preferably 0.080%.

[0231] The preferred lower limit for the sol.Al content is 0.012%, and more preferably 0.014%.

[0232] The preferred upper limit for the sol.Al content is 0.048%, and more preferably 0.046%.

[0233] The preferred lower limit for the total content of S and Se is 0.012%, and more preferably 0.014%.

[0234] The preferred upper limit for the total content of S and Se is 0.048%, and more preferably 0.046%.

[0235] The preferred lower limit for Ti content is 0.001%, and more preferably 0.002%.

[0236] The preferred upper limit for Ti content is 0.008%, and more preferably 0.006%.

[0237] The preferred lower limit for Ni content is 0.01%, and more preferably 0.02%.

[0238] The preferred upper limit for Ni content is 0.40%, more preferably 0.30%, and even more preferably 0.20%.

[0239] The preferred lower limit for Cr content is 0.01%, and more preferably 0.02%.

[0240] The preferred upper limit for Cr content is 0.40%, more preferably 0.30%, and even more preferably 0.20%.

[0241] The preferred lower limit for Cu content is 0.01%, and more preferably 0.05%.

[0242] The preferred upper limit for Cu content is 0.40%, more preferably 0.30%, and even more preferably 0.20%.

[0243] The preferred lower limit for the P content is 0.01%, and more preferably 0.02%.

[0244] The preferred upper limit for the P content is 0.04%, and more preferably 0.03%.

[0245] The preferred lower limit for Mo content is 0.01%, and more preferably 0.02%.

[0246] The preferred upper limit for Mo content is 0.04%, and more preferably 0.03%.

[0247] The preferred lower limit for Sn content is 0.01%, and more preferably 0.02%.

[0248] The preferred upper limit for Sn content is 0.25%, and more preferably 0.20%.

[0249] The preferred lower limit for Sb content is 0.01%, and more preferably 0.02%.

[0250] The preferred upper limit for Sb content is 0.25%, more preferably 0.20%, and even more preferably 0.15%.

[0251] The preferred lower limit for Bi content is 0.0001%, and more preferably 0.0005%.

[0252] The preferred upper limit for Bi content is 0.0180%, more preferably 0.0150%, and even more preferably 0.0100%.

[0253] The preferred lower limit for Ta content is 0.01%, and more preferably 0.02%.

[0254] The preferred upper limit for Ta content is 0.04%, and more preferably 0.03%.

[0255] The preferred lower limit for Nb content is 0.001%, and more preferably 0.002%.

[0256] The preferred upper limit for Nb content is 0.008%, and more preferably 0.006%.

[0257] The preferred lower limit for V content is 0.01%, and more preferably 0.05%.

[0258] The preferred upper limit for V content is 0.40%, and more preferably 0.30%.

[0259] The preferred lower limit for the B content is 0.001%, and more preferably 0.002%.

[0260] The preferred upper limit for the B content is 0.008%, and more preferably 0.006%.

[0261] The preferred lower limit for Te content is 0.0001%, and more preferably 0.0005%.

[0262] The preferred upper limit for Te content is 0.0150%, and more preferably 0.0100%.

[0263] In this manufacturing method, AlN is used as an inhibitor. Therefore, the Al content in the slab's chemical composition falls within the range described above. When using a manufacturing method for directional electromagnetic steel sheets based on an inhibitor-free process, the Al content in the slab is less than 0.010%.

[0264] Slabs are manufactured through known steelmaking processes, continuous casting processes, or ingot casting and billet rolling processes. Slabs can also be produced in thicknesses of less than 100 mm by direct casting.

[0265] The hot rolling process using prepared slabs includes the following steps.

[0266] (Process 11) Heating process (Process 12) Rough rolling process (Process 13) Finishing rolling process The following describes steps 11 to 13.

[0267] [(Process 11) Heating Process] In the heating process, the slab is heated. For example, the slab is placed in a known heating furnace or a known soaking furnace for heating. The preferred heating temperature for the slab is 1100–1450°C.

[0268] [(Process 12) Rough rolling process] In the roughing process, the heated slab is subjected to rough rolling to produce a rough billet (intermediate steel plate). Here, roughing refers to hot rolling of the slab using a known roughing mill. The rough billet is the intermediate steel plate after the roughing process and before the finishing process begins. In the roughing process, the slab is subjected to multiple passes of pressing down using a roughing mill to produce the rough billet.

[0269] [(Process 13) Finishing rolling process] In the finishing rolling process, a known finishing rolling process is applied to the rough billet produced by the rough rolling process to manufacture hot-rolled steel sheet. Here, finishing rolling refers to hot rolling of the rough billet using a known finishing mill. In the finishing rolling process, a continuous rolling mill consisting of multiple finishing rolling mills arranged in series on a rolling production line is used to apply multiple rolling passes to the rough billet to manufacture hot-rolled steel sheet.

[0270] [(Process 2) Hot-rolled plate annealing process] The hot-rolled sheet annealing process is optional. That is, it can be omitted. When the hot-rolled sheet annealing process is performed, the hot-rolled steel sheet manufactured in the hot-rolling process is annealed. By performing the hot-rolled sheet annealing process, recrystallization occurs in the steel sheet's microstructure, improving its magnetic properties.

[0271] In the hot-rolled sheet annealing process, any known hot-rolled sheet annealing method can be performed. There are no particular limitations on the heating method for the hot-rolled steel sheet during hot-rolled sheet annealing; any known heating method can be used. The hot-rolled sheet annealing temperature is, for example, 800–1200°C. The holding time at the hot-rolled sheet annealing temperature is, for example, 10–300 seconds. It should be noted that when performing the hot-rolled sheet annealing process, pickling can be performed on the hot-rolled steel sheet after the hot-rolled sheet annealing process and before the cold-rolling process.

[0272] (Process 3) Cold rolling process In the cold rolling process, the hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet. As described above, the cold rolling process is carried out in either of the following two modes.

[0273] (Mode 1) After performing tandem rolling, reversible rolling is performed.

[0274] (Mode 2) Only reversible rolling is performed. The tandem rolling process and the reversible rolling process are explained.

[0275] [Sequential rolling process] In the tandem rolling process, cold rolling is performed using tandem rolling mills.

[0276] Figure 2 This is a schematic diagram of a tandem rolling mill. (Refer to...) Figure 2 The tandem rolling mill CM is positioned from upstream to downstream between the uncoiler (uncoiling device) 21 and the tension coiler (coiling device) 22.

[0277] Uncoiler 21 rewinds the hot-rolled steel sheet ST0. Tension coiler 22 winds the intermediate steel sheet ST1 manufactured by the tandem mill CM.

[0278] The tandem rolling mill CM performs multiple passes of continuous rolling on the uncoiled hot-rolled steel sheet ST0 to produce the intermediate steel sheet ST1.

[0279] A tandem rolling mill (CM) consists of multiple rolling stands (CMS1 to CMS1) arranged in a row from upstream to downstream. j (j is a natural number greater than 2). Each rolling mill stand (CMS) has a pair of horizontally extending work rolls WR1. The pair of work rolls WR1 contact the hot-rolled steel sheet to be cold-rolled, thus cold-rolling the hot-rolled steel sheet. The rolling mill stand (CMS) may also have multiple support rolls BR1. The support rolls BR1 support the work rolls WR1 and suppress the deflection of the work rolls WR1 during rolling.

[0280] In continuous rolling using a tandem rolling mill (CM), the step of pressing down the hot-rolled steel sheet using each rolling stand (CMS) as it passes through is called a "1-pass" pressing. Continuous rolling refers to pressing down the hot-rolled steel sheet using a tandem rolling mill (CM) in multiple passes. It should be noted that it is also possible to press down the hot-rolled steel sheet without using all the rolling stands (CMS) in the tandem rolling mill (CM). For example, if there are six rolling stands (CMS1 to CMS6) arranged in a tandem rolling mill (CM), passing the hot-rolled steel sheet through stand CMS6 without pressing it down is equivalent to performing five passes of continuous rolling.

[0281] [Reversible rolling process] Figure 3 This is a schematic diagram of a multi-stage rolling mill used in a reversible rolling process. (Refer to...) Figure 3 In the reversible rolling process, a multi-stage rolling mill SM is used to perform multiple passes of reversible rolling on the intermediate steel plate ST1 or hot-rolled steel plate ST0 after the tandem rolling process to produce cold-rolled steel plate ST2. In the following description, the intermediate steel plate ST1 and the hot-rolled steel plate ST0 will also be collectively referred to as steel plate ST.

[0282] A multi-segment rolling mill (SM) is, for example, a Sendzimir mill. A multi-segment rolling mill (SM) has a pair of work rolls (WR2) and multiple support rolls (BR2). In a multi-segment rolling mill (SM), the pair of work rolls (WR2) are supported by multiple support rolls (BR2), which greatly suppresses the deflection of the work rolls (WR2). This allows for a higher reduction. The pair of work rolls (WR2) includes an upper work roll (WR2U) and a lower work roll (WR2L). The lower work roll (WR2L) is positioned below the upper work roll (WR2U).

[0283] Here, when a reduction is applied to the steel plate ST as it passes through the multi-stage rolling mill SM, it is referred to as a "1-pass" reduction. In the case of reversible rolling, reduction is performed both as the steel plate ST moves from upstream to downstream and as it moves from downstream to upstream. More specifically, one pass of reduction is applied to the steel plate ST as it passes through the multi-stage rolling mill SM from upstream to downstream. Additionally, one pass of reduction is also applied to the steel plate ST as it passes through the same multi-stage rolling mill SM from downstream to upstream. That is, in the case of reciprocating reduction, two passes of reduction are applied to the steel plate ST. It should be noted that sometimes no reduction is applied to the steel plate ST as it passes through the multi-stage rolling mill SM.

[0284] In the cold rolling process, cold-rolled steel sheets are manufactured by performing either tandem rolling or reversible rolling (Mode 1) or only reversible rolling (Mode 2).

[0285] Manufacturing conditions in the cold rolling process In the cold rolling process, the following conditions 1 to 3 must be met.

[0286] (Condition 1) The cumulative reduction rate (RR) in the cold rolling process is above 89% and below 93%.

[0287] (Condition 2) In the work rolls of the rolling mill stand where the first pass of cold rolling is performed, the axial arithmetic mean roughness Ra (μm), the ten-point mean roughness Rzjis (μm), and the diameter Dw (mm) of the work rolls satisfy equations (1) and (2).

[0288] 0.30≤Ra≤0.01Dw+3.08 (1) 3Ra≤Rzjis≤7Ra (2) (Condition 3) The hot-rolled steel sheet, manufactured in the hot rolling process, is cold-rolled from the front end toward the rear end.

[0289] The following explains conditions 1 through 3.

[0290] [Regarding condition 1] The cumulative reduction rate (RR) in the cold rolling process is above 89% and below 93%.

[0291] When the cumulative reduction rate (RR) is too low, there is an excessive generation of {110}. <112> Oriented grains, excessively suppressing the formation of Gaussian oriented grains. Under conditions of excessively high cumulative reduction rate, {211} <011> Excessive formation of oriented grains and excessive suppression of Gaussian oriented grain formation result in the manufacture of directional electromagnetic steel sheet 1 failing to meet at least one of requirements A to C.

[0292] If the cumulative reduction rate (RR) is 89% or more and 93% or less, then the cumulative reduction rate (RR) is within an appropriate range. In this case, requirements A to C are satisfied in the manufactured directional electromagnetic steel sheet 1.

[0293] The preferred lower limit for cumulative reduction rate (RR) is 90%. The preferred upper limit for cumulative reduction rate (RR) is 92%.

[0294] [Regarding equation (1) of condition 2] In the work rolls of the rolling mill stand where the first pass of cold rolling is performed, the axial arithmetic mean roughness Ra (μm) of the work rolls and the diameter Dw (mm) of the work rolls satisfy equation (1).

[0295] 0.30≤Ra≤0.01Dw+3.08 (1) The arithmetic mean roughness Ra of the work roll affects factors A through C. When the arithmetic mean roughness Ra is too low, the strain introduced into the steel plate is excessively low. In this case, an excessive amount of {110} is generated. <112> Oriented grains, or {211} <011> Oriented grains are excessively suppressed in the formation of Gaussian oriented grains. As a result, at least one of requirements A to C is not satisfied in the manufactured directional electromagnetic steel sheet 1.

[0296] On the other hand, when the arithmetic mean roughness Ra is too high relative to the diameter Dw of the work roll, excessive strain is introduced into the steel sheet surface. In particular, the reduction in the first pass of cold rolling has a significant impact on the shear texture of the steel sheet surface formed during hot rolling. When excessive strain is introduced into the steel sheet surface by the work rolls of the rolling mill stand that performs the first pass of cold rolling, texture development is hindered. Therefore, {110} is excessively generated. <112> Oriented grains, or {211} <011> Oriented grains are excessively suppressed in the formation of Gaussian oriented grains. As a result, at least one of requirements A to C is not satisfied in the manufactured directional electromagnetic steel sheet 1.

[0297] When the arithmetic mean roughness Ra satisfies equation (1), the manufactured directional electromagnetic steel plate 1 satisfies requirements A to C.

[0298] The preferred lower limit for the arithmetic mean roughness Ra is 0.32 μm, and more preferably 0.34 μm.

[0299] The preferred upper limit for the arithmetic mean roughness Ra is 0.01Dw+3.00, and more preferably 0.01Dw+2.90.

[0300] In addition, the diameter Dw of the work roll is set to the arithmetic mean of the diameters of a pair of work rolls.

[0301] [Regarding equation (2) of condition 2] In the work rolls of the rolling mill stand where the first pass of cold rolling is performed, the axial arithmetic mean roughness Ra (μm) and ten-point mean roughness Rzjis (μm) of the work rolls satisfy equation (2).

[0302] 3Ra≤Rzjis≤7Ra (2) The ten-point average roughness Rzjis of the work roll is an indicator of the local size of the unevenness or concavity of the work roll. To achieve a certain range for the proportion of large-angle grain boundaries RL, slightly misaligned Gaussian-oriented grains need to undergo secondary recrystallization to become adjacent. The ten-point average roughness Rzjis affects the local variation of the steel sheet surface during cold rolling, influencing the offset of adjacent Gaussian-oriented grains. In other words, the ten-point average roughness Rzjis affects the proportion of large-angle grain boundaries RL.

[0303] When the ten-point average roughness Rzjis is too low relative to the arithmetic mean roughness Ra of the work roll, the orientation shift of adjacent Gaussian-oriented grains becomes too small. In this case, the proportion of large-angle grain boundaries RL becomes excessively low. On the other hand, when the ten-point average roughness Rzjis is too high relative to the arithmetic mean roughness Ra of the work roll, the orientation shift of adjacent Gaussian-oriented grains becomes too large. In this case, the proportion of large-angle grain boundaries RL becomes excessively high.

[0304] If the ten-point average roughness Rzjis satisfies equation (2), then the proportion of large-angle grain boundaries RL is above 5% and below 30%.

[0305] The preferred upper limit for the ten-point average roughness Rzjis is 6.5Ra, and more preferably 6.0Ra. The preferred lower limit for the ten-point average roughness Rzjis is 3.5Ra, and more preferably 4.0Ra.

[0306] [Methods for determining arithmetic mean surface roughness Ra and ten-point mean surface roughness Rzjis] The arithmetic mean roughness Ra and ten-point mean roughness Rzjis of the work rolls of the rolling mill stand are obtained by the following method.

[0307] On the surface of each of a pair of work rolls, three arbitrary locations are selected as measurement points, resulting in six measurement points. These three measurement points are arranged in a row along the axial direction of each work roll, with a spacing of 100 mm between each measurement point. At each measurement point, the arithmetic mean roughness Ra (μm) and the ten-point mean roughness Rzjis (μm) are measured axially along the work roll according to the method specified in JIS B 0601:2001. A contact roughness gauge is used for the measurements. The conditions for calculating the roughness profile are set as follows.

[0308] Measuring force: 0.75mN Stylus tip shape: 2μm R60° Cutoff value λc: 0.8mm Cutoff value λs: 2.5μm Number of intervals: 3 Measurement speed: 0.25 mm / s Reference length: 0.8mm Evaluation length: 16mm For example, a contact roughness meter can be used, such as the Mitutoyo SJ-210.

[0309] The arithmetic mean of the obtained arithmetic mean roughness of the six locations is set as the axial arithmetic mean roughness Ra (μm) of the work roll. Additionally, the arithmetic mean of the ten-point average roughness of the six locations is set as the axial ten-point average roughness Rzjis (μm) of the work roll.

[0310] [Regarding condition 3] In the manufacturing method of this embodiment, during the cold rolling process, cold rolling begins from the front end of the hot-rolled steel sheet manufactured in the hot rolling process, moving towards the rear end. That is, the rolling direction of the steel sheet at the start of cold rolling is aligned with the rolling direction of the steel sheet during hot rolling.

[0311] In the cold rolling process, if cold rolling begins from the front end of the hot-rolled steel sheet manufactured in the hot rolling process towards the rear end, the proportion of large-angle grain boundaries (RL) is less than 30%. The reason for this is unclear, but it is believed to be as follows: It is believed that if cold rolling begins from the front end of the hot-rolled steel sheet manufactured in the hot rolling process towards the rear end, a preferred rolling structure is formed in the shear deformation layer on the surface of the hot-rolled steel sheet, becoming a source of Gaussian orientation.

[0312] [(Process 4) Decarburization annealing process] In the decarburization annealing process, the cold-rolled steel sheet after the cold rolling process is decarburized and annealed, resulting in a primary recrystallization.

[0313] The decarburization annealing process includes the following steps.

[0314] (Process 41) Heating process (Process 42) Decarbonization process (Process 43) Cooling process In the heating process (process 41), the steel plate is heated to any temperature between 750 and 950°C (reaching temperature). In the decarburization process (process 42), the steel plate is held at a decarburization annealing temperature of 750–950°C to perform decarburization annealing, causing it to exhibit primary recrystallization. In the cooling process (process 43), the steel plate after the decarburization process is cooled using a known method. It should be noted that the reaching temperature and the decarburization annealing temperature can be the same, or the reaching temperature can be higher than the decarburization annealing temperature.

[0315] In this embodiment, during the heating process, the average heating rate HR in the temperature range of 400–750°C, corresponding to the recrystallization temperature region of the steel sheet, is significantly accelerated. This promotes the recrystallization of Gaussian-oriented grains. Consequently, the aggregation degree of Gaussian orientation after secondary recrystallization can be increased. As a result, the magnetic properties of the directional electromagnetic steel sheet can be improved.

[0316] The following is a detailed explanation of each process.

[0317] [(Process 41) Heating Process] In the heating process, the cold-rolled steel sheet after the cold rolling process is first loaded into a heat treatment furnace (decarburizing annealing furnace). It should be noted that the atmosphere inside the heat treatment furnace is set to a nitrogen and hydrogen mixture atmosphere (non-oxidizing atmosphere) with a dew point of -50 to 0°C. In the heat treatment furnace for decarburizing annealing in this embodiment, the cold-rolled steel sheet is heated to an arbitrary temperature of 750 to 900°C, for example, by high-frequency induction heating or electric heating. The heating process satisfies the following condition 4.

[0318] (Condition 4) The average heating rate (HR) within the temperature range of 400℃ to 750℃ is set to be above 100℃ / second and below 3000℃ / second.

[0319] [Regarding condition 4] In the heating process, the average heating rate of cold-rolled steel sheet within the temperature range of 400℃ to 750℃ is defined as the average heating rate HR (℃ / second).

[0320] Strain accumulates in cold-rolled steel sheets manufactured through the cold rolling process. If the average heating rate HR is less than 100°C / s, the strain energy that drives recrystallization will be released before recrystallization begins. In this case, a sufficient amount of Gaussian-oriented grains cannot be generated in the cold-rolled steel sheet after one recrystallization process (i.e., the cold-rolled steel sheet after the decarburization annealing process).

[0321] If the average heating rate (HR) is 100°C / s or higher, primary recrystallization occurs in the cold-rolled steel sheet under conditions of sufficient strain energy accumulation. Therefore, a sufficient amount of Gaussian-oriented grains can be generated in the cold-rolled steel sheet after primary recrystallization. Consequently, in the subsequent final annealing process, a large number of Gaussian-oriented grains remain when secondary recrystallization occurs. This increases the degree of Gaussian orientation aggregation after secondary recrystallization. As a result, the magnetic properties of directional electromagnetic steel sheets can be improved, and deviations in magnetic properties can be suppressed.

[0322] Furthermore, there is no specific upper limit to the average heating rate HR. However, even if the average heating rate HR is made faster than 3000 °C / second, the above effect will saturate. Therefore, the upper limit of the average heating rate HR is 3000 °C / second.

[0323] The preferred lower limit for the average heating rate HR is 150°C / second, and more preferably 200°C / second.

[0324] The average heating rate HR was determined using the following method. Multiple thermometers for measuring the surface temperature of the steel plate were installed inside the heat treatment furnace. These thermometers were arranged from upstream to downstream of the furnace. The average heating rate HR (°C / second) was calculated based on the temperature of the steel plate measured by the thermometers and the time taken for the steel plate temperature to rise from 400°C to 750°C.

[0325] [(Process 42) Decarbonization process] In the decarburization process, the cold-rolled steel sheet after the heating process is held at a decarburization annealing temperature to perform decarburization annealing. This causes the cold-rolled steel sheet to exhibit primary recrystallization. The atmosphere in the decarburization process can be a known atmosphere, such as a non-oxidizing atmosphere containing hydrogen and nitrogen. The oxygen potential Po is set, for example, to 0.01–0.60. By performing decarburization annealing, carbon is removed from the steel sheet, resulting in primary recrystallization. There are no particular limitations on the decarburization annealing temperature or the holding time at the decarburization annealing temperature. The decarburization annealing temperature is, for example, 750–950°C. The holding time at the decarburization annealing temperature is, for example, 15–150 seconds.

[0326] [(Process 43) Cooling Process] In the cooling process, the cold-rolled steel sheet after the decarburization process is cooled to room temperature using known methods to produce a decarburized annealed steel sheet. The cooling method can be air cooling or water cooling. Preferably, the cold-rolled steel sheet after the decarburization process is allowed to cool naturally. Through the above steps, a decarburized annealed steel sheet is manufactured in the decarburization annealing process.

[0327] (Step 5) Final annealing process In the final annealing process, an annealing separating agent is applied to the decarburized annealed steel plate, and the decarburized annealed steel plate coated with the annealing separating agent is subjected to final annealing to produce the final annealed steel plate.

[0328] The final annealing process includes the following steps.

[0329] (Step 51) Annealing Separating Agent Coating Step (Step 52) Annealing process The following is a description of each process.

[0330] [(Process 51) Annealing Separator Coating Process] In the annealing release agent coating process, an annealing release agent is applied to a decarburized annealed steel plate. Specifically, an aqueous slurry containing an annealing release agent is applied to the decarburized annealed steel plate. The aqueous slurry is prepared by adding water to the annealing release agent and stirring.

[0331] Annealing separators can be primarily composed of magnesium oxide (MgO), or primarily composed of silicon dioxide and aluminum oxide. "Primary component" refers to a content of 60.0% or more by mass in the annealing separator. In addition to MgO, or in addition to silicon dioxide and aluminum oxide, annealing separators may also contain known additives.

[0332] When minimizing iron loss, annealing separators primarily consist of MgO. When workability is a priority, annealing separators primarily consist of silica and alumina.

[0333] In the annealing release agent coating process, an aqueous slurry of annealing release agent is coated onto the surface of the decarburized annealed steel sheet. The steel sheet coated with the annealing release agent is then rolled into a coil. After the steel sheet is rolled into a coil, an annealing process is performed.

[0334] [(Process 52) Annealing process] The steel sheet after the annealing separating agent coating process undergoes an annealing process to induce secondary recrystallization. The final annealing process is carried out by loading the coiled steel sheet into a heat treatment furnace. The manufacturing conditions in the annealing process are as follows. It should be noted that the furnace atmosphere in the annealing process is a known atmosphere.

[0335] Final annealing temperature: 800~1200℃ Holding time at final annealing temperature: 5–60 hours If the final annealing temperature is below 800°C, sufficient secondary recrystallization is not observed, and the purification process to remove precipitates used for secondary recrystallization is inadequate. Therefore, the magnetic properties of the manufactured directional electromagnetic steel sheet are reduced. On the other hand, even if the final annealing temperature exceeds 1200°C, the effect on secondary recrystallization and purification is low, and problems such as steel sheet deformation occur. If the final annealing temperature is between 800 and 1200°C, provided the holding time is appropriate as described above, sufficient secondary recrystallization is observed, and the magnetic properties are improved. Furthermore, a primary coating is formed on the surface of the steel sheet.

[0336] Through the above manufacturing processes, the final annealed steel plate is manufactured in the final annealing process.

[0337] It should be noted that the final annealing process removes various elements from the steel sheet to some extent. In particular, elements such as S, Al, and N, which act as inhibitors, are significantly removed. Furthermore, a lower coating (primary coating or intermediate layer) is formed on the surface of the directional electromagnetic steel sheet after the final annealing process.

[0338] [(Process 6) Insulation Coating Formation Process] In the insulating coating forming process, an insulating coating (insulating coating) forming agent is applied to the final annealed steel sheet. Then, the final annealed steel sheet coated with the insulating coating forming agent is subjected to heat treatment. Thus, an insulating coating (insulating film) is formed on the final annealed steel sheet.

[0339] Specifically, a known insulating coating forming agent containing at least one of the following inorganic substances—such as metal chromate salts, metal phosphate salts, colloidal silica, Zr compounds, and Ti compounds—is applied to the surface of the final annealed steel sheet (on the lower coating layer). The final annealed steel sheet coated with the insulating coating forming agent is then baked. Thus, a known insulating coating is formed on the primary coating layer.

[0340] [Other optional procedures] [Nitriding treatment process] The manufacturing method of the directional electromagnetic steel sheet 1 in this embodiment can also, as needed, perform a nitriding treatment process after the decarburization annealing process (process 4) and before the final annealing process (process 5). The nitriding treatment process can be performed under known conditions. The nitriding treatment temperature is, for example, 700 to 850°C. The atmosphere in the nitriding treatment furnace (nitriding treatment atmosphere) is, for example, an atmosphere containing gases with nitriding capabilities such as hydrogen, nitrogen, and ammonia.

[0341] If the nitriding temperature is above 700°C or below 850°C, nitrogen easily penetrates into the steel sheet during nitriding. If nitriding is performed within this temperature range, the nitrogen content within the steel sheet can be preferably ensured. Therefore, it is preferable to form fine AlN in the steel sheet before secondary recrystallization. As a result, secondary recrystallization is preferably exhibited during final annealing. It should be noted that the holding time of the steel sheet at the nitriding temperature is not particularly limited, for example, 10 to 60 seconds.

[0342] [Magnetic domain refinement process] The directional electromagnetic steel sheet of this embodiment can also undergo a magnetic domain refinement process after the final annealing process (process 5) or the insulating coating formation process (process 6), as needed. In the magnetic domain refinement process, a laser with a magnetic domain refinement effect is irradiated onto the surface (rolled surface) of the directional electromagnetic steel sheet to form linear thermal strain on the surface of the steel sheet, or grooves are physically formed on the surface of the steel sheet. In this case, a directional electromagnetic steel sheet with superior magnetic properties can be manufactured.

[0343] Through the above manufacturing process, the directional electromagnetic steel plate 1 of this embodiment can be manufactured.

[0344] The present invention will now be specifically described through examples. These examples are for confirming the effectiveness of the method for manufacturing the directional electromagnetic steel sheet of this embodiment, and do not limit the present invention.

[0345] [Example 1] Using slabs with the chemical compositions shown in Table 1 (Table 1A, Table 1B, Table 1C, Table 1D), directional electromagnetic steel sheets as shown in Table 3 (Table 3A and Table 3B) are manufactured.

[0346] Specifically, the slabs shown in Table 1 (Table 1A, Table 1B, Table 1C, Table 1D) were prepared.

[0347] The prepared slabs are subjected to a hot rolling process. Specifically, the slabs of each test number are heated to 1340°C in a heating furnace. The heated slabs are then hot rolled to produce hot-rolled steel sheets with the thicknesses (mm) shown in Table 3 (Table 3A, Table 3B).

[0348] For hot-rolled steel sheets after the hot rolling process, a hot-rolled annealing process was carried out at a hot-rolled sheet annealing temperature of 900-1200℃ for a holding time of 10-300 seconds.

[0349] After the hot-rolled sheet annealing process, a cold rolling process is carried out to manufacture cold-rolled steel sheets with the thickness (mm) shown in Table 3 (Table 3A, Table 3B). The cumulative reduction rate RR (%), arithmetic mean roughness Ra (μm) of the work rolls of the first rolling stand, diameter Dw (mm) of the work rolls of the first rolling stand, ten-point mean roughness Rzjis (μm) of the work rolls of the first rolling stand, rolling direction and cold rolling mode of the first cold rolling pass are shown in Table 3 (Table 3A, Table 3B).

[0350] Here, in Table 3 (Table 3A, Table 3B), the meaning of "T" in the "Evaluation" column of "Equation (1)" is that the arithmetic mean roughness Ra satisfies Equation (1), and the meaning of "F" is that the arithmetic mean roughness Ra does not satisfy Equation (1). The meaning of "Same direction" in the "Rolling direction of the first pass" column is that cold rolling begins from the front end of the hot-rolled steel sheet manufactured in the hot rolling process towards the rear end, and the meaning of "opposite direction" is that cold rolling begins from the rear end of the hot-rolled steel sheet manufactured in the hot rolling process towards the front end. In the "Cold rolling mode" column, the meaning of "T+R" is that reversible rolling was performed after tandem rolling (i.e., mode 1 was implemented as cold rolling), and the meaning of "R" is that only reversible rolling was performed (i.e., mode 2 was implemented as cold rolling).

[0351] It should be noted that the arithmetic mean roughness Ra and ten-point mean roughness Rzjis of the work rolls in the first cold rolling pass are measured based on the above-mentioned [methods for measuring arithmetic mean roughness Ra and ten-point mean roughness Rzjis].

[0352] A decarburization annealing process is performed on the cold-rolled steel sheet after the cold rolling process. Specifically, the atmosphere of the decarburization annealing furnace is set to a nitrogen and hydrogen mixed gas atmosphere (non-oxidizing atmosphere) with a dew point of -30℃. The average heating rate HR (℃ / s) in the temperature range of 400~750℃ is shown in Table 3 (Table 3A, Table 3B). After heating to a temperature of 800~950℃, it is held at 800~950℃ for 120~150 seconds. The oxygen potential Po in the atmosphere at this time is set to 0.01~0.60.

[0353] An annealing separating agent with MgO as the main component is coated on the surface of the decarburized annealed steel sheet. Then, the decarburized annealed steel sheet coated with the annealing separating agent is rolled into a coil.

[0354] The coil is subjected to final annealing to produce a final annealed steel sheet. The final annealing temperature is set to 1100–1200°C, and the holding time at the final annealing temperature is set to 5–30 hours.

[0355] An insulating coating formation process is then performed on the steel sheet after the final annealing process. Specifically, an insulating coating forming agent, mainly composed of colloidal silica and phosphate, is applied to the surface of the final annealed steel sheet for each test number. Then, the final annealed steel sheet coated with the insulating coating forming agent is baked under the same conditions to form an insulating coating on the lower coating (first coating). Through the above manufacturing process, directional electromagnetic steel sheets for each test number are manufactured.

[0356] It should be noted that the chemical composition of each test number of the directional electromagnetic steel sheet was determined based on the above-described method for determining the chemical composition of directional electromagnetic steel sheet 1. The results are shown in Table 2 (Table 2A, Table 2B, Table 2C, Table 2D) for the base steel sheet of each test number. It should also be noted that a composition analysis apparatus (product name: ICPS-8000) manufactured by Shimadzu Corporation was used as the testing apparatus.

[0357] [Evaluation Test] The following evaluation tests were conducted on the manufactured directional electromagnetic steel sheets.

[0358] (Experiment 1) Number ratio R {211}<011> Number ratio R {110}<112> and the ratio of the number R {110}<001> Determination test (Experiment 2) Determination of the proportion of large-angle grain boundaries (RL) (Experiment 3) Magnetic Flux Density Measurement Experiment (Experiment 4) Evaluation of iron loss of directional electromagnetic steel sheet after magnetic domain refinement treatment (Experiment 5) Evaluation of magnetostriction of directional electromagnetic steel sheet after domain refinement treatment The following describes Experiments 1 through 5.

[0359] [(Experiment 1) Number ratio R] {211}<011> Number ratio R {110}<112> and the ratio of the number R {110}<001> [Determination Test] Based on the method described above [method for determining crystal orientation at the measurement point], the proportion R of directional electromagnetic steel plates for each test number was calculated. {211}<011> (%), proportion of items R {110}<112> (%) and proportion of numbers R {110}<001>(%). The obtained values ​​are shown in Table 4 (Table 4A, Table 4B).

[0360] [(Experiment 2) Determination of the proportion of large-angle grain boundaries (RL)] Based on the method described above in [Method for determining crystal orientation at the measurement point], the large-angle grain boundary ratio RL (%) of the directional electromagnetic steel plates for each test number was calculated. The obtained values ​​are shown in "LI / La (%)" in Table 4 (Table 4A, Table 4B).

[0361] [(Experiment 3) Magnetic Flux Density Measurement Experiment] Magnetic domain refinement using laser irradiation was performed on the directional electromagnetic steel sheets for each test number. In this laser irradiation process, the irradiation spacing in the rolling direction was set to 4 mm. Furthermore, the energy density Ua was set to 1.25 mJ / mm². 2 .

[0362] Test pieces were collected from the center of the width of the directional electromagnetic steel sheet after magnetic domain refinement. The dimensions of the test piece were set as 60 mm in the width direction × 300 mm in the rolling direction × sheet thickness. According to JIS C2556:2015, the magnetic flux density B8(T) was determined by applying a magnetic field of 800 A / m to the test piece through a single-plate magnetic property test (SST test). The obtained magnetic flux density B8 is shown in "B8(T)" in Table 4 (Table 4A, Table 4B). If the magnetic flux density B8 is 1.921 T or higher, it is considered to have obtained excellent magnetic flux density. Furthermore, if the magnetic flux density B8 is less than 1.700 T, it is considered that poor secondary recrystallization has occurred, and tests 1, 2, 4, and 5 were not performed.

[0363] [(Experiment 4) Evaluation of iron loss of directional electromagnetic steel sheet after magnetic domain refinement treatment] Test specimens were collected from the center of the width of a directional electromagnetic steel sheet after domain refinement. The dimensions of the test specimens were set to 100mm × 500mm × sheet thickness. According to JIS C2556:2011, using the test specimens, the iron loss W was determined when the frequency was set to 50Hz and the maximum magnetic flux density was set to 1.700T. 17 / 50 (W / kg). The obtained iron loss W 17 / 50 The “W” shown in Table 4 (Table 4A, Table 4B) 17 / 50 (W / kg)

[0364] In each test, the following conditions were considered to indicate that excellent iron loss was achieved.

[0365] (1) When the plate thickness is 0.22mm, the iron loss W 17 / 50 It is below 0.703 W / kg.

[0366] (2) When the plate thickness is 0.19 mm, the iron loss W 17 / 50 It is below 0.669 W / kg.

[0367] (3) When the plate thickness is 0.17mm, the iron loss W 17 / 50 It is below 0.625 W / kg.

[0368] [(Experiment 5) Evaluation of magnetostriction of directional electromagnetic steel sheet after magnetic domain refinement treatment] The magnetostriction of directional electromagnetic steel plates for each test number was determined using the following method. The test piece collected in Test 4 above was used as the test piece. The magnetostriction measuring device included a laser Doppler vibrometer, an excitation coil, an excitation power supply, a flux detection coil, an amplifier, and an oscilloscope.

[0369] Magnetostriction was determined using the aforementioned magnetostriction measuring apparatus via AC magnetostriction measurement. Specifically, an AC magnetic field was applied to the test piece with a maximum magnetic flux density of 1.700 T in the rolling direction. The change in sample length caused by the expansion and contraction of magnetic domains was measured using a laser Doppler vibrometer, yielding the magnetostriction signal. Fourier analysis was performed on the obtained magnetostriction 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 magnetostriction velocity level LVA (dB) shown in the following formula was calculated.

[0370] LVA=20×Log(√(Σ(ρc×2π×fn×αn×Cn / √2) 2 ) / Pe0) Here, ρc is the inherent acoustic impedance, ρc = 400. Pe0 is the minimum audible 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).

[0371] The obtained magnetostrictive velocity level (LVA) is shown in Table 4. If the obtained magnetostrictive velocity level (LVA) is below 58.04 dB, it is judged that excellent noise characteristics have been obtained.

[0372] [Evaluation Results] Referring to Tables 1 (Tables 1A to 1D) and 2 (Tables 2A to 2D), the directional electromagnetic steel plates of test numbers 1 to 47 meet requirements A to C, and the proportion of large-angle grain boundaries RL (=LI / La) is 5% to 30%. Therefore, after refinement treatment, an excellent magnetic flux density B8 is obtained. Furthermore, after magnetic domain refinement treatment, excellent iron loss is obtained, and thus excellent noise characteristics are obtained.

[0373] On the other hand, regarding tests 48 to 53, condition 1 was not met during the manufacturing process. Therefore, any of the requirements A to C is outside the scope of this invention. As a result, a sufficient magnetic flux density B8 cannot be obtained. Consequently, sufficient iron loss cannot be obtained, and consequently, sufficient noise characteristics cannot be obtained.

[0374] Regarding tests 54-60, under manufacturing process condition 2, the arithmetic mean roughness Ra of the work roll in the first pass does not satisfy equation (1). Therefore, any of the requirements A to C is outside the scope of this invention. As a result, sufficient magnetic flux density B8, insufficient iron loss, or insufficient noise characteristics cannot be obtained.

[0375] Regarding tests 61 and 62, under manufacturing process condition 2, the ten-point average roughness Rzjis of the work roll in the first pass does not meet the upper limit of equation (2). Therefore, the large-angle grain boundary ratio RL (=LI / La) exceeds 30%. As a result, a sufficient magnetic flux density B8 cannot be obtained. In addition, sufficient iron loss cannot be obtained, and consequently, sufficient noise characteristics cannot be obtained.

[0376] Regarding test number 63, under manufacturing process condition 2, the ten-point average roughness Rzjis of the work roll in the first pass does not satisfy the lower limit of equation (2). Therefore, the large-angle grain boundary ratio RL (=LI / La) is less than 5%. As a result, although sufficient magnetic flux density B8 is obtained, sufficient iron loss is not obtained.

[0377] Regarding test number 64, manufacturing process condition 3 is not met. Therefore, the proportion of large-angle grain boundaries RL (=LI / La) exceeds 30%. As a result, sufficient iron loss is not obtained, and consequently, sufficient noise characteristics are not achieved.

[0378] Tests 65 and 66 do not meet manufacturing process condition 4. Therefore, the quantity ratio R {110}<001> (Requirement C) is less than 90%. As a result, a sufficient magnetic flux density B8 cannot be obtained. In addition, sufficient iron loss cannot be obtained, and consequently, sufficient noise characteristics cannot be obtained.

[0379] Regarding test number 67, the Si content in the slab and the directional electromagnetic steel sheet was too high. Therefore, the steel sheet fractured during the manufacturing process. Consequently, no evaluation test was conducted.

[0380] Regarding experiment number 68, the Si content in the slab and directional electromagnetic steel sheet was too low. Therefore, after further domain refinement treatment, sufficient iron loss could not be obtained.

[0381] Regarding test number 69, the Mn content in the base steel of the slab and the directional electromagnetic steel sheet was too high. Therefore, the magnetic flux density B8 was less than 1.700T.

[0382] Regarding test number 70, the Mn content in the base steel of the slab and the directional electromagnetic steel sheet was too low. Therefore, the magnetic flux density B8 was less than 1.700T.

[0383] Regarding test number 71, the nitrogen content of the slab was too high; regarding test number 72, the nitrogen content of the slab was too low. Therefore, the magnetic flux density B8 is less than 1.700T.

[0384] Regarding test number 73, the carbon content of the slab was too high; regarding test number 74, the carbon content of the slab was too low. Therefore, the magnetic flux density B8 is less than 1.700T.

[0385] Regarding test number 75, the sol.Al content of the slab was too high; regarding test number 76, the sol.Al content of the slab was too low. Therefore, the magnetic flux density B8 is less than 1.700T.

[0386] Regarding tests 77-82, the combined S and Se content of the slabs is outside the scope of this invention. Therefore, the magnetic flux density B8 is less than 1.700T.

[0387] The embodiments of this disclosure have been described above. However, the above embodiments are merely illustrative examples for implementing this disclosure. Therefore, this disclosure is not limited to the above embodiments, and can be implemented by appropriately modifying the above embodiments without departing from its spirit.

[0388] Explanation of reference numerals in the attached figures 1. Directional Electromagnetic Steel Sheet 10. Base steel plate 11. Lower layer coating 12. Insulating film.

Claims

1. A directional electromagnetic steel sheet comprising a base steel sheet, wherein the chemical composition of the base steel sheet is, by mass%, Si: 3.00–3.70%, Mn: 0.01–0.30%, N: 0.0001–0.0100%, C: 0.001–0.010%, sol.Al: 0–0.010%, one or more elements selected from the group consisting of S and Se: totaling 0–0.010%, Ti: 0–0.010%, N i: 0–0.50%, Cr: 0–0.50%, Cu: 0–0.50%, P: 0–0.05%, Mo: 0–0.05%, Sn: 0–0.30%, Sb: 0–0.30%, Bi: 0–0.0150%, Ta: 0–0.05%, Nb: 0–0.010%, V: 0–0.50%, B: 0–0.010%, Te: 0–0.0150%, and the balance consisting of Fe and impurities. When determining the crystal orientation using X-ray diffraction at measurement points spaced 2 mm apart in the rolling direction and in directions orthogonal to the rolling direction on the surface of the base steel plate, the crystal orientation is similar to {211}. <011> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {211}<011> Below 5%, with {110} <112> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<112> Below 5%, with {110} <001> The proportion R of the number of measurement points with an orientation difference of less than 15° relative to the total number of measurement points. {110}<001> The ratio of the total length LI of grain boundaries with an orientation difference of 15° or more obtained from the orientation difference at the measurement point to the total length La of the grain boundaries, i.e., the large-angle grain boundary ratio RL=LI / La, is 5% or more and less than 30%.

2. The directional electromagnetic steel plate according to claim 1, wherein, The thickness of the base steel plate is less than 0.19 mm.

3. The directional electromagnetic steel plate according to claim 1, wherein, The chemical composition of the base steel plate, expressed as a percentage by mass, contains one or more components selected from the group consisting of Ti: 0.001–0.010%, Ni: 0.01–0.50%, Cr: 0.01–0.50%, Cu: 0.01–0.50%, P: 0.01–0.05%, Mo: 0.01–0.05%, Sn: 0.01–0.30%, Sb: 0.01–0.30%, Bi: 0.0001–0.0150%, Ta: 0.01–0.05%, Nb: 0.001–0.010%, V: 0.01–0.50%, B: 0.001–0.010%, and Te: 0.0001–0.0150%.

4. A method for manufacturing a directional electromagnetic steel sheet according to any one of claims 1 to 3, comprising: A hot rolling process for producing hot-rolled steel sheets by hot rolling a slab, wherein the slab composition, by mass%, is: Si: 3.00–3.70%, Mn: 0.01–0.30%, N: 0.0030–0.0150%, C: 0.010–0.100%, sol.Al: 0.010–0.050%, one or more elements selected from the group consisting of S and Se: totaling 0.010–0.050%, Ti: 0–0.010%. Ni: 0-0.50%, Cr: 0-0.50%, Cu: 0-0.50%, P: 0-0.05%, Mo: 0-0.05%, Sn: 0-0.30%, Sb: 0-0.30%, Bi: 0-0.0200%, Ta: 0-0.05%, Nb: 0-0.010%, V: 0-0.50%, B: 0-0.010%, Te: 0-0.0200%, and the balance consists of Fe and impurities; The hot-rolled steel sheet is subjected to an annealing process. A cold rolling process that involves cold rolling the hot-rolled steel sheet after the annealing process to produce a cold-rolled steel sheet; The decarburizing annealing process of decarburizing annealing the cold-rolled steel sheet to produce decarburized annealed steel sheet; The final annealing process involves applying an annealing separating agent to the decarburized annealed steel sheet and then performing final annealing; and The insulating film forming process involves forming an insulating film on the surface of the final annealed plate. In the cold rolling process, the cumulative reduction rate is set to be above 89% and below 93%. In the work rolls of the rolling mill stand where the first pass of cold rolling is performed, the axial arithmetic mean roughness Ra in μm, the ten-point mean roughness Rzjis in μm, and the diameter Dw in mm of the work roll satisfy equations (1) and (2). 0.30≤Ra≤0.01Dw+3.08 (1) 3Ra≤Rzjis≤7Ra (2).

5. The method for manufacturing a directional electromagnetic steel plate according to claim 4, wherein, In the decarburization annealing process, the decarburization annealing temperature is set to 750-950°C, and the average heating rate from 400°C to 750°C is set to be above 100°C / second and below 3000°C / second.

6. The method for manufacturing a directional electromagnetic steel plate according to claim 4, wherein, In the cold rolling process, cold rolling begins from the front end of the hot-rolled steel sheet manufactured in the hot rolling process toward the rear end.

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