Method for producing grain-oriented electrical steel sheet

Abstract

The present invention enables prolonged beam irradiation while maintaining high beam quality when applying magnetic domain fragmentation treatment through electron beam irradiation of the surface of a steel sheet. In a method for producing a grain-oriented electrical steel sheet according to the present invention, the output of an electron beam is set to 6 kW or less, and the rate of change of the bias voltage for obtaining the electron beam is set to -0.5 V / hr or less in the negative direction.

Description

Manufacturing method of grain-oriented electrical steel sheets

[0001] This invention relates to a method for manufacturing grain-oriented electrical steel sheets.

[0002] Grain-oriented electrical steel sheets are used as the core material for transformers. In these transformers, the heat loss (iron loss) that occurs when grain-oriented electrical steel sheets are magnetized with alternating current negatively affects the efficiency of the transformer, so the development of grain-oriented electrical steel sheets with low iron loss is underway. Here, the iron loss of grain-oriented electrical steel sheets mainly consists of hysteresis loss and eddy current loss.

[0003] Methods to improve hysteresis loss include highly orienting the (110)

[001] orientation, known as the GOSS orientation, in the rolling direction of the steel sheet, and reducing impurities in the steel sheet. Methods to improve eddy current loss include increasing the electrical resistance of the steel sheet by adding Si and applying coating tension in the rolling direction of the steel sheet. However, these methods have manufacturing limitations when pursuing further reductions in iron loss in grain-oriented electrical steel sheets.

[0004] Therefore, magnetic domain subdivision technology has been developed as a method to further reduce iron loss in grain-oriented electrical steel sheets. Magnetic domain subdivision technology is a technique that introduces non-uniformity of magnetic flux into steel sheets after finish annealing or after the baking of an insulating coating, using physical methods such as forming grooves and / or introducing localized strain. This subdivides the width of the 180° magnetic domains (main magnetic domains) formed along the rolling direction, thereby reducing iron loss in grain-oriented electrical steel sheets, especially eddy current loss.

[0005] For example, Patent Document 1 proposes a technique to improve iron loss from 0.80 W / kg or more to 0.70 W / kg or less by introducing linear grooves with a width of 300 μm or less and a depth of 100 μm or less on the surface of a steel plate. Patent Document 2 proposes a method to introduce localized thermal strain by irradiating the surface of a steel plate after secondary recrystallization with an electron beam in the width direction of the plate. Furthermore, in a transformer made using grain-oriented electrical steel sheet manufactured by this method, the iron loss (W) when excited at a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz is calculated. １７／５０It has been disclosed that the ratio can be improved to 0.680 W / kg or less.

[0006] Furthermore, the method for introducing linear grooves disclosed in Patent Document 1 is called heat-resistant magnetic domain refinement because the magnetic domain refinement effect does not disappear even if stress-relieving annealing is performed after the formation of the iron core. On the other hand, the method for introducing thermal strain disclosed in Patent Document 2 is called non-heat-resistant magnetic domain refinement because the effect of introducing thermal strain is lost due to stress-relieving annealing.

[0007] Non-heat-resistant magnetic domain subdivision treatment using electron beam irradiation is limited to applications such as transformers that do not require heat treatment. However, it has known advantages, such as the ability to electrically control the beam irradiation state, which makes it easier to achieve high-speed manufacturing during beam irradiation; the ability to impart thermal strain to deeper areas of the steel sheet by increasing the acceleration voltage, resulting in lower iron loss compared to lasers and plasma flames. On the other hand, when irradiating with an electron beam using a cathode, for example, there is a problem of gradually degrading beam quality. Here, beam quality refers to the focusing state and brightness of the beam when it reaches the steel sheet. And, in order to manufacture grain-oriented electrical steel sheets with low iron loss, it is effective to irradiate with a small beam diameter (high focusing state) and a high-intensity (high brightness) beam. Thus, deterioration of beam quality during operation means deterioration of the magnetic domain subdivision effect during operation. For this reason, periodic replacement of electron beam sources such as cathodes is necessary for stable production, and the equipment must be shut down at that time. However, a disadvantage of the electron beam irradiation process is that it requires the passage of steel plates under high vacuum conditions, resulting in longer downtime for restarting the equipment compared to other methods that can be performed in the atmosphere.

[0008] Incidentally, regulations on the high efficiency of transformers have been tightening globally in recent years. To satisfy this requirement, grain-oriented electrical steel sheets need to achieve both low iron loss and increased production. Among the many magnetic domain subdivision methods developed so far, as mentioned above, electron beam-based magnetic domain subdivision is advantageous for reducing iron loss, but disadvantageous for increasing production due to the periodic occurrence of long downtimes. Therefore, in magnetic domain subdivision methods using electron beams, the challenge is to develop methods that can increase the continuous operating time while maintaining high beam quality, that is, to extend the lifespan of electron beam irradiation. There are two aspects to the lifespan of electron beam irradiation referred to here: the time during which beam quality is maintained and the time during which beam output itself is produced. In this specification, the former is called the quality lifespan, and the latter is called the source lifespan (e.g., cathode lifespan).

[0009] Various studies have been conducted to extend the lifespan of the above-mentioned sources. For example, Patent Document 3 describes how to suppress malfunctions caused by abnormalities in the peripheral area of ​​the electron emission surface by selecting and removing cathodes with short quality lifespans in advance. Specifically, Patent Document 3 discloses a method for selecting cathodes to be removed, which involves investigating the amount of bias voltage fluctuation when a constant beam current is continuously emitted in a temperature-limited region.

[0010] Meanwhile, various methods are being considered to stabilize beam quality in order to extend the lifespan of the quality. For example, Patent Document 4 proposes a method to adjust the acceleration voltage using a control power supply in addition to adjusting the bias voltage in order to change the beam current while keeping the beam brightness constant. Furthermore, Patent Document 5 proposes a method to measure the beam current that has reached the non-irradiated object and to perform feedback control to adjust the filament power based on the relationship between filament power and beam current that has been acquired in advance.

[0011] Japanese Patent Publication No. 6-22179, Japanese Patent Publication No. 2012-36445, Japanese Patent Publication No. 2016-225358, International Publication No. 2016 / 110996, Japanese Patent Publication No. 2010-62374

[0012] Patent Document 3 describes a method that can suppress the downward deviation in quality life associated with longer continuous operating times. Therefore, it can be useful from the perspective of extending the life of the beam source. However, the technology in Patent Document 3 does not lead to a fundamental improvement in quality life and source life (cathode life). Furthermore, Patent Documents 4 and 5 are highly effective in maintaining beam quality, and therefore can be useful from the perspective of extending beam quality life. On the other hand, there was a concern that the increased filament power and application of control voltage would accelerate the wear of the cathode tip as a beam source, potentially degrading both quality life and cathode life. Therefore, from the perspective of achieving both low iron loss and increased production in grain-oriented electrical steel sheets, none of these methods are yet sufficient, and the development of methods for further improving the life of quality and the beam source is desired.

[0013] The present invention has been made in view of the above circumstances, and aims to provide a method for manufacturing grain-oriented electrical steel sheets that enables long-term operation of the beam irradiation while maintaining high beam quality when performing magnetic domain subdivision treatment using electron beam irradiation.

[0014] The inventors of the present invention have diligently conducted research to solve the above problem and have obtained the following findings. First, they investigated the cause of the deterioration of beam quality when continuously operating a magnetic domain refinement treatment that irradiates the surface of grain-oriented electrical steel sheets with an electron beam. For electron beam irradiation, a LaB is used as the beam source. ６ A cathode equipped with a sintered body chip (cathode chip) and a heater was used. This LaB ６ A heater was placed between the sintered chip, and the chip was heated by the DC current from the heater and its resistive heating. Furthermore, a third electrode (Wöhnert electrode) was placed between the cathode and anode, to which a negative bias voltage was applied to the cathode, allowing adjustment of the brightness (amount of emitted electrons) and focusing state (beam crossover) of thermionic electrons emitted from the cathode. In this way, LaB ６An electron beam was irradiated using a thermionic electron gun with a sintered chip as the electron source. The electron beam was irradiated for a long period of 30 days under conditions of constant beam output. During this time, the beam current and heater current were also feedback controlled to remain constant. To investigate the cathode state during magnetic domain subdivision, the trends of the beam current, heater current (current flowing through the heater), heater voltage (voltage generated across the heater), and bias voltage were acquired during irradiation.

[0015] As a result of obtaining the above time-dependent trends, the beam current and heater current, which are feedback-controlled to remain constant, were constant as controlled. On the other hand, the bias voltage and heater voltage showed a decreasing trend. The inventors speculate the following regarding this decrease in bias voltage. That is, for example, as a cathode chip, LaB ６ When an electron beam is irradiated from a cathode using a sintered chip, this LaB ６ The sintered chip is continuously heated to a high temperature of approximately 1700°C. Therefore, when used as a radiation source for extended periods, LaB ６ As the cathode evaporates and / or oxidizes, the amount of emitted electrons per unit area decreases, and the beam quality gradually deteriorates. It is thought that the bias voltage decreases to compensate for this reduced amount of emitted electrons. Therefore, this decrease in bias voltage associated with the continuous operation time of the cathode is considered to be a change caused by the depletion of the beam source, such as the cathode. Thus, it is estimated that the change in bias voltage over time can serve as an indicator of the source lifetime (cathode lifetime).

[0016] Furthermore, when the bias voltage decreases, as mentioned above, the amount of electrons emitted per unit area from the source decreases, and in order to control the beam current to a constant level, the emission area of ​​the electron beam also increases. At this time, the aberration of the focusing coil changes due to the increase in emission area, and therefore the appropriate beam focusing conditions also change. However, normally, the beam focusing settings are not changed during electron beam irradiation, so it is possible that the focused state and / or brightness of the electron beam when it reaches the surface of the steel plate will be inferior. Therefore, it is possible that the beam quality deteriorates as a result of the decrease in bias voltage due to the continuous operating time of the source such as the cathode. Thus, it was estimated that the change in bias voltage over time can also serve as an indicator of quality life.

[0017] Through the above investigations, the inventors have found that when applying magnetic domain refinement treatment to the surface of a steel plate by electron beam irradiation, the trend in both the quality life of the electron beam and the source life (cathode life) of the electron beam manifests as a decrease in bias voltage. Therefore, in order to achieve both extended quality life and source life in electron beam irradiation, the inventors have found that it is effective to control the rate of change of the bias voltage during electron beam irradiation, or more specifically, the amount of decrease in bias voltage per unit time.

[0018] However, the above reasoning cannot explain the decrease in heater voltage. When the heater voltage decreases while the heater current remains constant, that is, the heater output decreases. And when the heater output decreases, the LaB during electron beam irradiation decreases. ６ This leads to a decrease in the temperature of the sintered chip. In this case, the amount of electrons emitted per unit area from the cathode decreases, and in order to maintain the beam current, the bias voltage also decreases. In other words, a decrease in heater voltage during electron beam irradiation is also considered to be one of the factors causing a decrease in bias voltage. From the above further investigation, we have also found that by suppressing the decrease in heater voltage when irradiating with an electron beam, or by controlling the heater output to be constant, it is possible to suppress the decrease in bias voltage and, as a result, further improvement in quality life is possible.

[0019] Therefore, the inventors of the present invention conducted further investigations on the cause of the decrease in the heater voltage during the irradiation of the electron beam. When the cathode where the decrease in the heater voltage was confirmed was disassembled and its state was examined in detail, it was confirmed that a large number of deposits were present on the surface of the heater. When the components of these deposits were analyzed, LaB ６ derived from the cathode chip and metals derived from the members constituting the cathode were detected. These deposits have a lower electrical resistance than the heater that heats the cathode chip. Therefore, it was newly found that when these substances with low electrical resistance adhere to the surface of the heater, the electrical resistance of the heater also decreases, and as a result, the heater voltage decreases. Furthermore, such evaporation of the cathode chip due to the irradiation of the electron beam occurs both above and below the chip. That is, it was also revealed that the surface of the cathode chip is similarly consumed along with the irradiation of the electron beam, and the chip after use is thinner than before use. When such thinning occurs, the distance between the tip of the cathode chip and the anode (the distance between the cathode and the anode) increases. Since the electric field applied to the cathode is inversely proportional to the distance between the cathode and the anode, it was also found from this point that the electron emission ability of the cathode decreases.

[0020] Therefore, in order to suppress the decrease in the heater voltage during electron beam irradiation or to keep the heater output constant, it is effective to prevent the adhesion of external substances to the heater; furthermore, it was found that in addition to this, it is effective to provide a mechanism for keeping the tip position of the cathode chip constant. And based on this, further findings were obtained that the quality life can be further improved.

[0021] The present invention has been made based on the above findings, and the main configuration of the present invention is as follows. [1] A method for manufacturing a grain-oriented electrical steel sheet by irradiating at least one surface of a steel sheet with an electron beam to perform magnetic domain refinement treatment, wherein the output of the electron beam is 6 kW or less, and the rate of change of the bias voltage used to obtain the electron beam is -0.5 V / hr or less in the negative direction. A method for manufacturing a grain-oriented electrical steel sheet, characterized by this.

[0022] [2] The method for manufacturing a grain-oriented electrical steel sheet according to [1] above, wherein the electron beam source is thermoelectrons.

[0023] [3] When irradiating the electron beam from the cathode using a cathode having a heater for heating the line source, monitor the voltage and current in the heater, and control the output in the heater to be constant to perform the irradiation of the electron beam. The method for manufacturing a directionally electromagnetic steel sheet according to [2] above.

[0024] [4] When irradiating the electron beam from the cathode using a cathode having a heater for heating the line source, the cathode further includes a mechanism for suppressing the adhesion of substances from the outside to the heater. The method for manufacturing a directionally electromagnetic steel sheet according to [2] above.

[0025] [5] The method for manufacturing a directionally electromagnetic steel sheet according to [4] above, further comprising a mechanism for adjusting the relative spatial position of the cathode in the optical axis direction.

[0026] According to the present invention, when performing a magnetic domain refinement treatment on a steel sheet by electron beam irradiation, it is possible to provide a method for manufacturing a directionally electromagnetic steel sheet that realizes long-time operation of beam irradiation while maintaining high beam quality. In other words, according to the method for manufacturing a directionally electromagnetic steel sheet of the present invention, for the electron beam used in the magnetic domain refinement treatment, both the quality life and the beam generation source life can be extended. Therefore, according to the manufacturing method of the present invention, a directionally electromagnetic steel sheet showing low iron loss can be favorably mass-produced, and thus has an excellent industrial effect.

[0027] It is a graph showing the relationship between the change rate ΔV of the bias voltage and the change amount ΔW of the iron loss, which is the result of Experiment 1. It is a schematic diagram showing a part of the thermionic gun used in Experiment 2 and some examples.

[0028] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible without departing from the gist of the present invention. First, the experiments that led to the completion of the present invention will be described.

[0029] (Experiment 1) First, an investigation was conducted on the influence of the deterioration of the beam quality during electron beam irradiation, that is, the decrease in the bias voltage, on the domain refinement effect on the steel plate. A steel slab having the component composition shown in Table 1 was used. The balance other than the elements shown in Table 1 is Fe and inevitable impurities. Using this steel slab, a steel strip of a non-oriented electrical steel sheet with a thickness of 0.20 mm (however, before the domain refinement treatment) manufactured by a general manufacturing process was used as a test material.

[0030]

[0031] From this test material, a single plate test piece with a size of 500 mm in the rolling direction and 500 mm in the sheet width direction was cut out. Then, under the following conditions, the test piece was irradiated with an electron beam to perform domain refinement treatment, and the cathode was continuously operated for a long time. For the irradiation of the electron beam, a thermionic gun having a cathode equipped with LaB ６ and a heater was used, and the heater current was set to a constant value of 10 A to heat the cathode (LaB ６ chip). Also, the acceleration voltage of the electron beam was set to 60 kV, the beam current was set to 10 mA, and the beam output was set to 0.6 kW. Regarding the thermionic gun set at this output, heating was continued for 30 days, and the electron beam was continuously irradiated to the beam collector to simulate the wear of the cathode during long-term operation.

[0032] The domain refinement treatment on the steel plate as a single plate test piece was carried out on the first day of the domain refinement treatment performed before the irradiation of the electron beam to the beam collector, and then every 24 hours (that is, during the simulation of the wear of the cathode), for each of the four single plate test pieces. The domain refinement treatment was carried out by irradiating the one side of the above steel plate with an electron beam periodically at intervals of 6 mm in the rolling direction and in a direction perpendicular to the rolling direction. Also, during the 30-day electron beam irradiation, the bias voltage was recorded every 24 hours simultaneously.

[0033] Further, for each single plate test piece after the domain refinement treatment by electron beam irradiation, according to the single plate magnetic measurement method described in JIS C 2556:2015, the iron loss (single plate iron loss: W １７／５０ ) of the non-oriented electrical steel sheet was measured. Here, W １７／５０This refers to the heat loss when a single sheet of grain-oriented electrical steel is magnetized with alternating current at a magnetic flux density of 1.7 T and a frequency of 50 Hz in the rolling direction of the specimen. Iron loss measurements were performed on each specimen after magnetic domain refinement treatment from day 1 to the end of day 30. The iron loss for the grain-oriented electrical steel that underwent magnetic domain refinement treatment on day N is given by W. Ｎ The iron loss for each day was then calculated.

[0034] These series of experiments were conducted under the same conditions as described above, except for the heater current, which was varied between 10 and 16 A. By changing only the heater current, the experiment was conducted under conditions that changed the cathode heating temperature, i.e., the degree of cathode wear over time. The relationship between the rate of change (decrease rate) of the bias voltage ΔV and the change in iron loss ΔW under these various cathode conditions was then investigated.

[0035] Here, the rate of change of the bias voltage ΔV (unit: V / hr) is the bias voltage V at the beam output at the start of beam irradiation (day 1 as described above in this experiment). ｉ Based on the unit V (volts), in this experiment, the bias voltage at the beam output up to the end of each beam irradiation until the end of the 30th day as described above was measured. ｔ The average slope can be calculated using the least squares method from the trend over time (unit: hr, hour).

[0036] Next, W Ｎ The graph was plotted against the heating time of the thermionic electron gun (cathode), and the slope dW was calculated using the least squares method. The change in iron loss ΔW (unit: W / kg) can be obtained by multiplying this dW by the total heating time of the thermionic electron gun.

[0037] Figure 1 shows the relationship between the rate of change of bias voltage ΔV and the change in iron loss ΔW, as determined above. Figure 1 is a graph with ΔV on the horizontal axis and ΔW on the vertical axis. As shown in Figure 1, it can be seen that as ΔV increases in the negative direction, in other words, as the value of ΔV becomes negatively large towards the right on the horizontal axis of the graph, ΔW also increases. The inventors believe that this result reflects the fact that as the bias voltage decreases more significantly with respect to the electron beam irradiation time, the appropriate focusing conditions also change more significantly from the initial settings, and as a result the magnetic domain subdivision effect of the electron beam irradiated onto the steel plate is impaired.

[0038] The product specifications for grain-oriented electrical steel sheets are W １７／５０ The grades are divided into increments of 0.05 W / kg. Therefore, when determining the upper limit of operational stability, ΔV such that ΔW ≤ 0.04 W / kg from Figure 1, it was found that this is achievable when ΔV is -0.5 V / hr or smaller in the negative direction (to the left on the horizontal axis of the graph). Accordingly, when performing magnetic domain refinement treatment on steel plates by electron beam irradiation, it is essential to suppress the rate of decrease in bias voltage so that ΔV ≥ -0.5 V / hr and to irradiate the beam while controlling the cathode state as a method to improve the quality life of the beam.

[0039] Furthermore, the inventors also investigated the effect of beam output during electron beam irradiation. Except for various changes in beam output, the electron beam was emitted in the same manner as in Experiment 2 No. 1 described later. The time elapsed when electron beam emission became impossible was defined as the cathode lifetime T. limit (Unit: time (hr)) was used for verification. As a result, when the beam output was set to more than 6 kW, T limit A significant decrease in performance was observed, and a trend of noticeably shorter cathode life was confirmed. In other words, by controlling the beam output to 6 kW or less, a good cathode life could be ensured.

[0040] (Experiment 2) Next, we investigated methods to improve the quality lifetime of the electron beam while keeping ΔV within the specified range, and to further improve the source lifetime of the electron beam (cathode lifetime). Cathodes (LaB) that underwent various additional controls as described in Table 2 ６ Using a chip, an electron beam was emitted under the conditions of an initial heater current of 12A, an initial heater voltage of 10V, an initial acceleration voltage of 120kV, and a beam output of 6kW. For comparison, the experiment was also conducted without the above additional control. Furthermore, in each control method No., the heater current was set near the boundary between the temperature-limited region and the space-charge-limited region, and attempts were made to emit the electron beam every 50 hours while controlling so that ΔV ≥ -0.5V / hr. The temperature-limited region is the region in which the amount of beam emitted increases as the cathode temperature increases, and the space-charge-limited region is the region in which the amount of beam emitted hardly changes even if the cathode temperature is increased. The boundary can be confirmed from the beam emission characteristics with respect to the cathode temperature, i.e., the heater current. During this experiment, the cathode heating state under the above conditions was continuously maintained. The time elapsed when electron beam emission became impossible was defined as the cathode lifetime T. limit Each was recorded in hours (in hours). The results are shown in Table 2.

[0041]

[0042] Here, we will explain in detail the deposition prevention plates used in control methods No. 5 and 6 in Table 2. Figure 2 shows a schematic diagram of a part of the thermionic electron gun used under the above control conditions in Experiment 2. The thermionic electron gun 1 in Figure 2 comprises: a cathode 20 having a cathode tip 21 and a heater 22; an anode 30 facing the cathode 20 and connected to the cathode via an accelerating power supply 31; and a Wehnelt electrode 40 positioned between the cathode 20 and the anode 30 and connected to the cathode 20 via a bias power supply 41. The heater 22 is positioned on either side of the cathode tip 21, and the current from the heater power supply 23 and its resistive heating heat the cathode tip 21, causing thermionic electrons to be emitted from the cathode 20. The thermionic electrons then travel as an electron beam through the Wehnelt electrode 40 and then between the anode 30 towards the irradiated object, which is the grain-oriented electrical steel sheet.

[0043] Here, the thermionic electron gun 1 in Figure 2 is further equipped with an adhesion suppression mechanism 24, more specifically an evaporation prevention plate 24, in front of the lower surface of the outer circumferential surface constituting the heater 22, which faces the same direction as the direction in which the cathode tip 21 protrudes. Further investigation by the inventors revealed that the adhesion of external substances to the heater is mainly caused by the evaporation of constituent components of the cathode tip. Therefore, since it is effective to prevent evaporation that occurs between the cathode tip and the heater, a cathode with a structure that includes a mechanism to suppress the adhesion of external substances in front of the heater was used.

[0044] The adhesion suppression mechanism, such as a deposition prevention plate, is not particularly limited, but when the opposing surfaces of the heater 22, such as a carbon heater, and the adhesion suppression mechanism 24 are provided facing each other, it is preferable that the area of ​​the opposing surface of the adhesion suppression mechanism 24 is larger than the area of ​​the opposing surface of the heater 22 (the lower surface in the above description of Figure 2). Furthermore, it is even more preferable that the adhesion suppression mechanism is provided so as to face the source with an opposing surface having a larger area than the area of ​​the surface of the source, such as a cathode tip 21, that faces the beam projector.

[0045] Next, the tip position holding mechanism used in control method No. 6 in Table 2 will be explained in detail with reference to Figure 2. However, the tip position holding mechanism itself is not shown in Figure 2. When the direction connecting the point where the electron beam is emitted to the point where the electron beam irradiates the steel plate is defined as the optical axis, the thermionic electron gun 1 is configured with the positional relationship of the cathode tip 21, the Wehnelt electrode 40, and the anode 30 in order along this optical axis. Here, if only the position of the cathode tip 21 changes in the direction of the optical axis, the influence of the bias voltage applied from the Wehnelt electrode 40 will change. As described above, according to the inventors' findings, the cathode tip 21 becomes thinner with electron beam irradiation, so if no control is applied, the relative position between the cathode tip 21 and the Wehnelt electrode 40 changes, which becomes a factor that causes the rate of decrease in the bias voltage to become negatively large. In addition, the cathode-anode distance between the tip of the cathode tip 21 and the anode 30 also increases, leading to a deterioration of beam quality.

[0046] Therefore, when controlling the output of the electron beam during repeated electron beam irradiation, it is effective to further provide a mechanism (not shown) that can adjust the relative spatial position of the cathode 20 in the optical axis direction so that the relative position between the cathode tip 21 and the Wehnelt electrode 40 does not change even if the cathode tip is worn out. With such a cathode spatial position adjustment mechanism, even if the cathode tip becomes thinner due to repeated electron beam irradiation, the relative spatial position between the cathode tip 21 and the anode 30 can be kept constant.

[0047] Such a cathode spatial position adjustment mechanism may, depending on the usage conditions, be a chip position holding mechanism that allows the cathode 20 (cathode tip 21) to descend in the optical axis direction (move toward the anode 30). Alternatively, the cathode spatial position adjustment mechanism may be a mechanism that allows the anode 30 to rise in the optical axis direction (move toward the cathode 20), or a mechanism that can perform both of the above operations. Evaporation of the cathode tip is mainly determined by the vacuum level, temperature, and usage time. Therefore, in No. 6 of Table 2, the change in the amount of evaporation of the cathode tip over time in the actual usage environment was measured in advance, a calibration curve was created, and a chip position holding mechanism with a feedback mechanism according to the usage time was used. Then, the electron beam was continuously irradiated while adjusting the relative spatial position of the cathode along the optical axis direction using this chip position holding mechanism.

[0048] Since a high voltage is applied between the cathode and anode, it is preferable that the cathode spatial position adjustment mechanism be a built-in mechanism of the electron beam irradiation equipment such as a thermionic electron gun, rather than an external mechanism. For example, a cathode spatial position adjustment mechanism could be a structure in which the cathode or anode is attached to a stage that moves up and down in the optical axis direction according to the usage time.

[0049] As shown in Table 2, in case No. 1, where no additional control is applied to the cathode other than the ΔV mentioned above, the cathode lifetime T limit It was 1000hr. Also, in the case of No. 2, which increased the acceleration voltage by 10% from No. 1, and No. 3, which increased the heater output (also called heater power) by 15%, although the beam quality could be maintained, T limitThe cathode lifetime was 900 hours, indicating a decrease in cathode life. This is thought to be because, while increasing the acceleration voltage or heater output can compensate for the reduced beam emission capacity due to cathode use, it also accelerates the wear of the cathode itself. Therefore, we believe that the cathode lifetime decreased, especially when emitting high-power electron beams such as in magnetic domain subdivision processing.

[0050] On the other hand, in No. 4, where the heater output was adjusted to be constant and the electron beam was irradiated, an increase in cathode lifetime was observed compared to Nos. 2 and 3. This is thought to be because the load on the cathode was reduced compared to Nos. 2 and 3, making it possible to improve cathode lifetime while maintaining beam quality. Furthermore, the method in No. 4 also showed an improvement in cathode lifetime compared to No. 1. This is thought to be because, by controlling the heater output to be constant, the load on the cathode was reduced compared to No. 3, resulting in a greater improvement in the cathode's beam emission capacity than the accelerated cathode wear due to increased heater current. In No. 4, the heater output was kept constant by monitoring the heater current and heater voltage during electron beam irradiation and using feedback control to keep their product constant.

[0051] Furthermore, in the case of No. 5, which was fitted with a deposition prevention plate as an adhesion suppression mechanism and irradiated with an electron beam, T limit This improved significantly to 1500hr. This is because if the cathode heating continues, the cathode itself will be consumed, and the LaB radiation source will also be consumed. ６ Both the deposition on the heater and the resulting decrease in the cathode's electron emission capacity occur. Methods No. 2 to 4 address the electron emission capacity issue but accelerate the cathode's wear. In contrast, method No. 5 does not accelerate the cathode's wear. ６ As a result of suppressing deposition on the heater, the lifespan was limited solely by cathode wear, which is thought to be the reason why the cathode lifespan was significantly improved compared to Nos. 1-4.

[0052] Furthermore, in the case of No. 6, which was irradiated with an electron beam and equipped with a chip position holding mechanism as a spatial position adjustment mechanism for the cathode in addition to the above-mentioned deposition prevention plate, an improvement effect equivalent to or better than that of No. 5 was confirmed in terms of cathode life. This is because under the conditions of No. 5, LaB ６ Although deposition on the heater was suppressed, LaB ６ The previous method had not been able to address the thinning of the chip due to evaporation. In contrast, with method No. 6, by combining a deposition prevention plate and a chip position holding mechanism, we were able to maintain a constant spatial position of the cathode relative to the Wehnelt electrode and the anode, resulting in an even longer cathode lifespan.

[0053] Based on the above results, it was found that the following methods are effective in further improving cathode lifetime while maintaining beam quality: controlling the heater output to a constant value; providing a mechanism to suppress the adhesion of external materials to the heater, specifically by installing an anti-deposition plate on the cathode; and further, in addition to the anti-deposition plate, installing a mechanism (tip position holding mechanism) that adjusts the relative spatial position of the cathode along the optical axis.

[0054] (Method for manufacturing grain-oriented electrical steel sheets) In the manufacturing method of the present invention, when applying a magnetic domain subdivision treatment to a steel sheet by irradiating at least one surface of the steel sheet with an electron beam, the output of the electron beam and the rate of change of the bias voltage required to obtain the beam of said output (time change of bias voltage) are controlled to a predetermined range. By controlling both the beam output and the rate of change of the bias voltage during electron beam irradiation to a predetermined range, the quality life of both the electron beam and the beam source life can be extended. As a result, the magnetic domain subdivision treatment can be performed for a long time while increasing the magnetic domain subdivision effect on the steel sheet. Therefore, according to the manufacturing method of the present invention, a larger quantity of grain-oriented electrical steel sheets exhibiting lower iron loss can be obtained.

[0055] [Electron Beam Output] The electron beam output must be 6 kW or less. If the electron beam output exceeds 6000 W, the wear on the beam source, such as the cathode, becomes severe, leading to a decrease in the source life (cathode life). From this viewpoint, it is preferable to set the electron beam output to 5000 W (5 kW) or less. On the other hand, the higher the electron beam output, the greater the thermal strain introduced into the steel plate, thus increasing the magnetic domain subdivision effect. From this viewpoint, it is preferable to set the electron beam output to 500 W (0.5 kW) or more. The electron beam output can be controlled, for example, by adjusting the bias voltage so that the beam current under a constant acceleration voltage becomes a constant value.

[0056] [Percentage change of bias voltage ΔV] As described above, the percentage change of bias voltage with respect to time during electron beam irradiation must be ΔV ≥ -0.5V / hr (less than or equal to -0.5V / hr in the negative direction), preferably ΔV ≥ -0.4V / hr (less than or equal to -0.4V / hr in the negative direction), and more preferably ΔV ≥ -0.2V / hr (less than or equal to -0.2V / hr in the negative direction). By keeping the percentage change of bias voltage below the above upper limit in the negative direction (to the right on the horizontal axis of the graph in Figure 1), the beam quality can be maintained well even if electron beam irradiation is performed for a long period of time, such as a cumulative total of 720 hours (equivalent to 30 days) or more, or even 960 hours (equivalent to 40 days) or more. As a result, good magnetic domain subdivision processing can be applied to more grain-oriented electrical steel sheets, and low iron loss can be achieved for more grain-oriented electrical steel sheets. Furthermore, the rate of change of the bias voltage is typically ΔV ≤ 0V / hr (greater than or equal to 0V / hr in the negative direction) due to the performance of the electron beam irradiation device. The range of the rate of change of the bias voltage is preferably -0.5V / hr ≤ ΔV ≤ 0V / hr, more preferably -0.4V / hr ≤ ΔV ≤ 0V / hr, and even more preferably -0.2V / hr ≤ ΔV ≤ 0V / hr.

[0057] Here, the rate of change of the bias voltage ΔV can be calculated in the manner described above in Experiment 1. That is, since the beam output is often constant during magnetic domain subdivision processing, the initial bias voltage V at the start of production (start of electron beam irradiation) ｉ Based on this, the bias voltage V at any irradiation time t.ｔ This is constantly monitored. Then, from the trend of the obtained bias voltage with respect to irradiation time, the average slope with respect to irradiation time, calculated using the least squares method, can be defined as ΔV.

[0058] [Control Method for ΔV] One of the key manufacturing conditions in this invention is to control ΔV so that it does not become negative above a predetermined value. There are mainly two factors that cause ΔV to increase in the negative direction during electron beam irradiation. One is that the beam source itself, such as the cathode, is consumed, and the amount of emitted electrons decreases. The other is that external substances, such as cathode chips, adhere to the heater, reducing the heater output and thus the amount of emitted electrons. Regarding the former, it is difficult to deal with because the rate of consumption is determined by various factors such as the source temperature (cathode temperature) and the vacuum level of the electron gun chamber. However, according to the inventors' studies, by controlling the output of the electron beam to 6 kW or less, the load on the beam source, such as the cathode, can be reduced, and the consumption of the beam source itself can be suppressed. As a result, it is easier to effectively suppress the increase of ΔV in the negative direction.

[0059] The latter can be controlled by methods such as those listed below. One method is to monitor the heater current and heater voltage during electron beam irradiation and perform feedback control so that the heater output, which is their product, remains constant. Another method is to attach a mechanism such as a plate to the cathode that can suppress the adhesion of foreign matter to the heater. One such mechanism that suppresses the adhesion of external substances from components other than the heater is a deposition prevention plate that can prevent deposition originating from the cathode chip. If the material of the deposition prevention plate is a porous material such as ceramics, there is a concern that gas will be released during heating, causing oxidation of the cathode chip. Therefore, it is preferable to use a metal material such as W or Al alloy that is resistant to high temperatures as the material of the deposition prevention plate. Further methods include adjusting the position of the cathode relative to the anode and / or the Wehnert electrode so that the spatial position of the cathode relative to the anode and / or the Wehnert electrode is maintained, even if the beam source is worn down and becomes thinner. Mechanisms that enable such adjustment include the cathode chip position holding mechanism and the anode position holding mechanism mentioned above. The effect can be further enhanced by using a mechanism to suppress the adhesion of external materials and a mechanism to adjust the relative spatial position of the cathode in combination. In this way, the increase of ΔV into the negative can be suppressed even more effectively.

[0060] [Composition of Steel Sheet] In the manufacturing method of the present invention, the steel sheet to be subjected to magnetic domain refinement treatment is not particularly limited and can be obtained according to the conventional method for manufacturing grain-oriented electrical steel sheets before magnetic domain refinement treatment. The composition of the slab for grain-oriented electrical steel sheets should be any composition that causes secondary recrystallization. When using inhibitors, for example, in the case of an AlN-based inhibitor, Al and N should be included in appropriate amounts, and in the case of a MnS / MnSe-based inhibitor, Mn and Se and / or S should be included in appropriate amounts. Of course, both inhibitors may be used in combination. In this case, the preferred content of Al, N, S and Se is, respectively, Al: 0.010 to 0.065 mass%, N: 0.0050 to 0.0120 mass%, S: 0.005 to 0.030 mass%, and Se: 0.005 to 0.030 mass%.

[0061] Furthermore, the present invention can also be applied to obtain grain-oriented electrical steel sheets that do not use inhibitors and have limited Al, N, S, and Se content. In this case, it is preferable to limit the Al, N, S, and Se content to less than 0.010 mass%, less than 0.0050 mass%, less than 0.005 mass%, and less than 0.005 mass%, respectively.

[0062] The basic components of slabs for grain-oriented electrical steel sheets and other optional additives are described in detail below. C: 0.08 mass% or less. C can be suitably added to improve the structure of the hot-rolled sheet. However, if the C content exceeds 0.08 mass%, it becomes difficult to decarburize to 50 mass ppm or less during the manufacturing process, so it is preferable to keep the C content at 0.08 mass% or less. Furthermore, since secondary recrystallization occurs even in materials without C, no lower limit is set for the C content. That is, the C content may be 0 mass%.

[0063] Si: 2.0 to 8.0 mass% Si is an effective element for increasing the electrical resistance of steel and improving iron loss, and can therefore be suitably added. When the Si content is 2.0 mass% or more, the effect of reducing iron loss is further enhanced. On the other hand, when the Si content is 8.0 mass% or less, it becomes easier to suppress the decrease in workability and sheet treadability, and also easier to suppress the decrease in magnetic flux density. For this reason, it is preferable to have a Si content in the range of 2.0 to 8.0 mass%.

[0064] Mn: 0.005 to 1.0 mass% Mn is an effective element for improving hot workability and can therefore be suitably added. When the Mn content is 0.005 mass% or more, this effect is more easily obtained. On the other hand, when the Mn content is 1.0 mass% or less, it is easier to suppress the decrease in the magnetic flux density of the product plate. For this reason, it is preferable to have a Mn content in the range of 0.005 to 1.0 mass%.

[0065] It is preferable that the slab for grain-oriented electrical steel sheets has the above elements as its basic components. In addition to the above basic components, the slab may optionally contain the following further elements. The following elements are effective in improving magnetic properties: One or more selected from Ni: 0.01 to 1.50 mass%, Sn: 0.01 to 1.50 mass%, Sb: 0.005 to 1.50 mass%, Cu: 0.03 to 3.0 mass%, P: 0.03 to 0.50 mass%, Mo: 0.005 to 0.10 mass%, and Cr: 0.03 to 1.50 mass%.

[0066] Ni is an effective element for improving the structure of hot-rolled sheets and enhancing their magnetic properties, and can therefore be suitably added. A Ni content of 0.01% by mass or more, and more preferably 0.03% by mass or more, further enhances the effect of improving magnetic properties. A Ni content of 1.50% by mass or less can suppress the instability of secondary recrystallization, making it easier to reduce the risk of deterioration of the magnetic properties of the product sheet. Therefore, when Ni is included, the Ni content is preferably in the range of 0.01 to 1.50% by mass, and more preferably in the range of 0.03 to 1.50% by mass.

[0067] Furthermore, Sn, Sb, Cu, P, Mo, and Cr are also elements that can further improve magnetic properties, and the improvement in magnetic properties is more easily obtained when the content of each element is above the lower limit mentioned above. On the other hand, when the content of each component is below the upper limit mentioned above, the risk of suppressing the growth of secondary recrystallized grains is reduced, and the deterioration of magnetic properties is more easily suppressed. For this reason, when Sn, Sb, Cu, P, Mo, and Cr are included, it is preferable that the content of each element be within the above range.

[0068] Furthermore, the remainder of the mixture consists of Fe and unavoidable impurities.

[0069] [Steel Sheet Manufacturing Process] The process for manufacturing steel sheets before magnetic domain subdivision is not particularly limited. As an example, a slab having the above-mentioned component composition is subjected to hot rolling, and the resulting hot-rolled sheet is then annealed. Next, the resulting hot-rolled and annealed sheet is subjected to one or two cold rollings to finish it into a steel strip with a final thickness. After that, this steel strip is subjected to decarburization annealing, an annealing separating agent is applied, and then it is wound into a coil and subjected to final annealing for the purpose of secondary recrystallization. After final annealing, the steel strip is subjected to planarization annealing to form an insulating film (an insulating film that can impart tension to the steel sheet), and it can be made into a steel sheet.

[0070] [Magnetic Domain Refinement Treatment of Steel Sheet] Then, one or both sides of the obtained steel sheet are irradiated with an electron beam under the above-described conditions to perform magnetic domain refinement treatment and obtain a grain-oriented electrical steel sheet. The manufacturing method of the present invention may include only the above-described predetermined non-heat-resistant magnetic domain refinement step on the steel sheet as the magnetic domain refinement treatment, or it may further include a heat-resistant magnetic domain refinement step such as electrolytic etching or groove formation by laser irradiation on the steel sheet (steel strip) in any step after cold rolling.

[0071] The following describes an example of irradiation conditions when performing magnetic domain refinement by electron beam irradiation. Examples of electron beam sources include thermionic electron guns and electrolytic emission electron guns. Among these, for magnetic domain refinement applications, it is preferable to use a thermionic electron source because it can obtain a higher brightness electron beam, and therefore it is preferable to use a thermionic electron gun.

[0072] [Acceleration Voltage] A higher acceleration voltage is preferable because it increases the straight-line propagation of electrons and reduces the thermal impact on the outside of the beam-irradiated area in the steel plate. For this reason, the acceleration voltage is preferably 60 kV or higher, more preferably 90 kV or higher, and even more preferably 120 kV or higher. On the other hand, if the acceleration voltage is too high, it becomes difficult to shield the X-rays generated by the electron beam irradiation. Therefore, from a practical standpoint, the acceleration voltage is preferably 300 kV or lower, and more preferably 200 kV or lower.

[0073] [Beam Current] From the viewpoint of reducing the beam diameter, a smaller beam current is preferable. This is because if the beam current is large, the beam diameter tends to widen due to Coulomb repulsion, and the beam quality when it reaches the steel plate tends to be poor. For this reason, it is preferable to set the beam current to 40 mA or less. On the other hand, if the beam current is too small, there will be insufficient energy to create strain in the steel plate. For this reason, it is preferable to set the beam current to 0.5 mA or more.

[0074] [Vacuum level in the beam irradiation area] Electron beams are scattered by gas molecules, causing an increase in beam diameter and / or halo diameter, a decrease in energy, etc. Therefore, a high vacuum level in the beam irradiation area is preferable, and it is preferable to keep the pressure at 3 Pa or less. There is no particular lower limit on the vacuum level in the beam irradiation area, but if it is lowered too much, the cost of the vacuum system, such as vacuum pumps, will increase. Therefore, in practice, a pressure of 10 Pa is preferable. -5 It is preferable to use a pressure of Pa or higher.

[0075] [Beam Diameter] The beam diameter (spot diameter) during electron beam irradiation is preferable as it allows for localized distortion to be introduced into the steel plate. From this viewpoint, the beam diameter is preferably 300 μm or less, more preferably 280 μm or less, and even more preferably 260 μm or less. In this specification, beam diameter refers to the full width at half maximum of the electron beam profile obtained by the slitting method using a slit with a width of 30 μm.

[0076] [Beam Deflection Speed] The slower the beam deflection speed, the greater the amount of heat incident on a unit length of steel plate. Therefore, a slower beam deflection speed is preferable. However, if the beam deflection speed is excessively high, a larger power supply is required to generate the amount of heat necessary to introduce thermal strain into the steel plate, leading to larger equipment. Therefore, a beam deflection speed of 400 m / s or less is preferable. However, if the beam deflection speed is excessively low, the processing area per unit time decreases, resulting in a decrease in manufacturing efficiency. Therefore, a beam deflection speed of 5 m / s or more is preferable.

[0077] [Angle between the thermal strain formation direction and the plate width direction] The greater the deviation of the stretching direction of the thermal strain formation portion from the plate width direction, the fewer magnetic poles are generated at the interface between the recirculating magnetic domain and the main magnetic domain, thus degrading the magnetic domain subdivision effect. Therefore, the angle between the stretching direction of the thermal strain formation portion and the plate width direction is preferably within ±30°, and may be 0° (parallel to the plate width direction). In other words, the direction in which the electron beam is irradiated onto the steel plate is preferably within ±30° of the plate width direction of the steel plate, and may be parallel to the plate width direction.

[0078] In addition to the processes and manufacturing conditions described above, known methods for manufacturing grain-oriented electrical steel sheets can be used as appropriate.

[0079] Next, the present invention will be specifically described based on examples. The following examples illustrate preferred examples of the present invention and do not limit the invention in any way. It is also possible to implement the invention with modifications to the extent that they are in line with the spirit of the invention, and such modifications are also included within the technical scope of the present invention.

[0080] A steel slab having the component composition shown in Table 3 was used. The remainder of the elements other than those shown in Table 3 consisted of Fe and unavoidable impurities. Using this steel slab, a strip of grain-oriented electrical steel sheet (before magnetic domain refinement treatment) was manufactured using a general manufacturing process. An insulating coating capable of applying tension to the steel sheet was formed on both sides of this grain-oriented electrical steel sheet using a general process. Then, on one side of the insulating coating of the grain-oriented electrical steel sheet, an electron beam was irradiated in a direction perpendicular to the rolling direction of the steel sheet (steel strip) and at 6 mm intervals in the rolling direction, under the conditions shown in Table 4 and described later, to continuously perform magnetic domain refinement treatment.

[0081]

[0082] For electron beam irradiation, LaB is used as the electron source. ６A thermionic electron gun was used, comprising a cathode with a cathode tip and heater; an anode; and a Wehnelt electrode as a third electrode placed between the cathode and anode. In some examples, a cathode further equipped with a 70 mm square deposition prevention plate between the cathode tip and heater was used (see Figure 2). In some further examples, the cathode was mounted on a stage equipped with a mechanism (cathode tip position holding mechanism) that lowered the cathode toward the steel plate along the optical axis according to the usage time of the cathode, based on a calibration curve of the evaporation rate of the cathode tip that was prepared in advance. This tip position holding mechanism allowed electron beam irradiation to be performed while maintaining a constant relative spatial position between the cathode (cathode tip), the Wehnelt electrode and the anode, even if the cathode tip became thinner with use.

[0083] Electron beam irradiation was performed with an initial heater current of 12A, an initial heater voltage of 12V, an initial acceleration voltage of 120kV, and a beam output of 1, 3, 6, or 6.5kW. The steel strip was continuously irradiated with the electron beam until the beam output ceased or for 1500 hours. Furthermore, for each irradiation, electron beam irradiation was performed under four control conditions: no special control (shown as "No Control Method" in Table 4); the heater current and / or heater voltage were adjusted to maintain a constant heater output (shown as "Constant Heater Output" in Table 4); a cathode with an anti-deposition plate placed between the cathode tip and the heater (shown as "Anti-Deposition Plate Added" in Table 4); and in addition to the anti-deposition plate, the aforementioned tip position holding mechanism was further installed to adjust the relative spatial position of the cathode (shown as "Anti-Deposition Plate Added + Tip Position Holding Mechanism Added" in Table 4).

[0084] During electron beam irradiation of the steel sheet (steel strip) on which the above insulating coating was formed, the bias voltage was constantly monitored, and the rate of change ΔV of the bias voltage was calculated using the same method as in the experiment described above. In addition, for the steel strip of grain-oriented electrical steel sheet in the area where magnetic domain refinement treatment was performed, samples were taken at the beginning of operation (when electron beam irradiation started, i.e., when the cathode started heating), and thereafter every 50 hours, and test pieces measuring 280 mm in the rolling direction and 100 mm in the sheet width direction were cut out. For these test pieces, the iron loss of the grain-oriented electrical steel sheet (single sheet iron loss: W) was measured according to the single-sheet magnetic measurement method described in JIS C2556:2015. １７／５０ The iron loss was measured. From the obtained iron loss, the change in iron loss ΔW from the initial stage of beam irradiation operation was calculated using the same method as in the experiment described above.

[0085] The results are shown in Table 4. From Table 4, it can be confirmed that the increase in iron loss is well suppressed by keeping the beam output within a predetermined range and the rate of change of the bias voltage ΔV within a predetermined range. In other words, it can be confirmed that the quality life of the cathode in electron beam irradiation is increased by satisfying the requirements of the present invention. Furthermore, from Table 4, it can be confirmed that by satisfying the requirements of the present invention, it is possible to irradiate with the electron beam for a longer operating time (usage time) while suppressing the increase in iron loss. In other words, it can be confirmed that both the quality life and the cathode life are improved by satisfying the requirements of the present invention. Furthermore, it can be confirmed that this effect is further enhanced by controlling the heater output to a constant value. Furthermore, it can be confirmed that this effect is further enhanced by using a cathode equipped with a deposition prevention plate. And it can be confirmed that this effect is further enhanced by installing a cathode tip position holding mechanism in addition to the deposition prevention plate to adjust the relative spatial position of the cathode to a constant value.

[0086] As a result, for example, even when the cathode operating time is extended to 1500 hours, the increase in iron loss of the steel plate can be reduced to ΔW = 0.025 (W / kg) or less. Furthermore, for example, even when the cathode operating time is extended to 1500 hours, the increase in iron loss of the steel plate can be reduced to ΔW = 0.015 (W / kg) or less.

[0087]

[0088] The method for manufacturing grain-oriented electrical steel sheets of the present invention can be effectively used, for example, in the field of mass production of highly efficient transformers.

[0089] 1 Thermionic electron gun 20 Cathode 21 Cathode chip 22 Heater 23 Heater power supply 24 Deposition suppression mechanism (deposition prevention plate) 30 Anode 31 Accelerator power supply 40 Third electrode (Wehnert electrode) 41 Bias power supply

Claims

1. A method for manufacturing grain-oriented electrical steel sheets, comprising irradiating at least one surface of a steel sheet with an electron beam to perform magnetic domain refinement, characterized in that the output of the electron beam is 6 kW or less, and the rate of change of the bias voltage used to obtain the electron beam is -0.5 V / hr or less in the negative direction.

2. The method for manufacturing grain-oriented electrical steel sheets according to claim 1, wherein the electron beam source is a thermionic electron.

3. A method for manufacturing a grain-oriented electrical steel sheet according to claim 2, wherein when irradiating the cathode with the electron beam using a cathode equipped with a heater for heating the radiation source, the voltage and current in the heater are monitored and controlled so that the output of the heater remains constant when irradiating with the electron beam.

4. The method for manufacturing grain-oriented electrical steel sheets according to claim 2, wherein when irradiating the electron beam from the cathode using a cathode equipped with a heater for heating the radiation source, the cathode further comprises a mechanism for suppressing the adhesion of external substances to the heater.

5. The method for manufacturing grain-oriented electrical steel sheet according to claim 4, further comprising a mechanism for adjusting the relative spatial position of the cathode in the optical axis direction.

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