Electrical resistance heating apparatus and electrical resistance heating method for metal plate for electromagnetic steel sheet, and method for manufacturing electromagnetic steel sheet

Abstract

Provided are: an electrical resistance heating apparatus and an electrical resistance heating method for a metal plate for an electromagnetic steel sheet, and a method for manufacturing an electromagnetic steel sheet, wherein a large amount of seed crystals having Goss orientation can be produced in a crystal structure prior to primary recrystallization. An electrical resistance heating apparatus (100) for a metal plate for an electromagnetic steel sheet comprises: a pair of electrodes (110) that are in locally dispersed contact with the front and back sides of a metal plate (1) for an electromagnetic steel sheet prior to primary recrystallization annealing after cold rolling, sandwiching the metal plate (1), and that apply current to the metal plate (1); a current control mechanism (150) for contacting the pair of electrodes (110) on the front and back sides of the metal plate (1) at predetermined positions for a predetermined time and then separating the electrodes (110) from the metal plate (1); a power supply (160) for heating the metal plate (1) from a temperature of room temperature or higher to a peak temperature of 450-1000°C at a rate of 2,000-100,000°C / sec; and a power supply circuit for connecting the electrodes (110) and the power supply (160).

Description

Electrical heating device and electric heating method for metal sheets for electromagnetic steel sheets, and manufacturing method for electromagnetic steel sheets

[0001] The present invention relates to an apparatus and method for applying electric heating to metal sheets for use in electrical steel sheets, and a method for manufacturing electrical steel sheets.

[0002] Electrical steel sheets are classified into two types: non-oriented electrical steel sheets, which are primarily used as iron core materials for rotating equipment such as motors and generators, and oriented electrical steel sheets, which are primarily used as iron core materials for stationary equipment such as transformers. Electrical steel sheets are required to have excellent magnetic properties, specifically, low iron loss to reduce energy loss in the equipment and high saturation magnetic flux density to enable equipment miniaturization. In particular, due to recent demands for energy conservation, further reductions in iron loss and high saturation magnetic flux density are required.

[0003] Grain-oriented electrical steel sheets are manufactured through the following process, as described in Non-Patent Document 1, for example. First, the steel sheet after cold rolling to a final sheet thickness (e.g., approximately 0.2 mm to approximately 0.4 mm) is subjected to decarburization annealing, thereby causing primary recrystallization of the crystalline structure and releasing the strain generated during rolling. Next, an insulating layer mainly composed of MgO is formed on the surface of the steel sheet after decarburization annealing, and then batch annealing is performed, thereby causing secondary recrystallization that selectively grows crystal grains oriented with good magnetic properties and forming an insulating coating. Furthermore, non-oriented electrical steel sheets, as described in Non-Patent Document 1, for example, form an insulating coating after primary recrystallization, and then grow crystal grains with random crystal orientations such that crystal grains oriented with good magnetic properties are distributed as evenly as possible on the steel sheet surface.

[0004] Thus, in the manufacture of electrical steel sheets, in order to improve magnetic properties such as low iron loss and high saturation magnetic flux density, it is important to control the crystal orientation, specifically, the size and arrangement of Goss-oriented grains, which have a {100}<001> orientation, also known as the Goss orientation. For example, in grain-oriented electrical steel sheets, the Goss-oriented grains are selectively grown by secondary recrystallization to increase the concentration of the Goss orientation, thereby increasing the longitudinal magnetic permeability and reducing iron loss of the steel sheet. In addition, in non-oriented electrical steel sheets, the crystal grains are grown so that the Goss-oriented grains are as evenly distributed as possible within the steel sheet, making the steel sheet more permeable to magnetism in all directions.

[0005] International Publication No. 2023 / 191029

[0006] Nippon Steel & Sumitomo Metal Corporation, "Color Illustrated Book: A Guide to the Future of Steel," Nippon Jitsugyo Publishing Co., Ltd., January 18, 2007, pp. 112-119

[0007] In the current manufacturing process for electrical steel sheets, only a small amount of Goss-oriented grains, which have excellent magnetic properties, are present at the time of primary recrystallization. However, if a large amount of Goss-oriented grains is generated in the crystalline structure after primary recrystallization, it is believed that the magnetic properties can be dramatically improved compared to conventional methods.

[0008] As a result of extensive research conducted by the present inventors from the above perspectives, they have obtained a new finding that, as will be described in detail later, by locally and ultra-rapidly heating a metal sheet for an electrical steel sheet before primary recrystallization annealing, it is possible to produce a large amount of crystals (seed crystals) that serve as nuclei of recrystallized grains having a Goss orientation in the crystalline structure before primary recrystallization.

[0009] Patent Document 1 discloses a technique for partially and rapidly heating a cold-rolled steel sheet during a decarburization annealing process in the production of grain-oriented electrical steel sheets, and describes irradiation with a laser beam or an electron beam as a means for this. However, because laser irradiation and electron beam irradiation are surface heating, only the surface of the steel sheet is heated preferentially, and the interior of the steel sheet is not easily heated. Furthermore, because these heating methods are non-contact heating, heat removal is rapid after heating, making it difficult to maintain the temperature, and they may not be suitable as localized heating methods for metal sheets for electrical steel sheets. Electrical steel sheets include non-oriented electrical steel sheets and grain-oriented electrical steel sheets. In particular, heating methods such as those described in Patent Document 1, which are non-contact and have rapid heat removal, are not suitable for the production of grain-oriented electrical steel sheets, because maintaining heat immediately after heating facilitates the growth of well-oriented Goss grains, thereby producing steel sheets suitable for grain-oriented electrical steel sheets.

[0010] The present invention has been made in view of the above points, and has an object to provide an electric heating apparatus and an electric heating method for metal sheets for electrical steel sheets, and a method for manufacturing electrical steel sheets, which are capable of generating a large amount of seed crystals having the Goss orientation in a crystalline structure before primary recrystallization.

[0011] In order to achieve the above object, the present invention is characterized by comprising: a pair of electrodes that are in locally dispersed contact with a metal sheet for use in an electrical steel sheet after cold rolling and before primary recrystallization annealing so as to sandwich the metal sheet from the front and back sides thereof and that pass a current through the metal sheet; a current control mechanism that controls the current flow by bringing the pair of electrodes into contact with the front and back sides of the metal sheet at predetermined positions on the metal sheet and separating the electrodes from the metal sheet after passing a current through the electrodes for a predetermined time; a power source that can heat the metal sheet from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec; and a power supply circuit that connects the electrodes and the power source.

[0012] According to the present invention, a metal plate can be locally heated from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec, which makes it possible to produce a large amount of seed crystals having the Goss orientation in the crystalline structure before primary recrystallization.

[0013] The electric heating device for metal plates for electromagnetic steel plates may further include a cylinder to which the electrodes are attached in an insulated state, a cylinder mounting base on which a plurality of the cylinders are arranged and which is parallel to the metal plate, a cylinder drive mechanism that causes the electrodes attached to the cylinders to extend and retract so as to contact and separate from the metal plate, and a base drive mechanism that causes the cylinder mounting base to move back and forth at least in the thickness direction of the metal plate, and the electric current control mechanism may have a drive control unit that controls the operation of the cylinder drive mechanism and the base drive mechanism, and a pressure adjustment unit that adjusts the pressure when the pair of electrodes are brought into contact with the metal plate.

[0014] In this case, the device may further include an electrode selection unit that selects the electrode to which electricity is to be applied from the power source.

[0015] Alternatively, the electrical heating device for metal plates for electromagnetic steel plates may further include a cylinder to which the electrodes are attached in an insulated state, a substantially cylindrical cylinder mounting base on which a plurality of the cylinders are arranged and which has a rotation axis in the width direction of the metal plate, a cylinder drive mechanism that extends and retracts the electrodes attached to the cylinder to bring them into contact with and away from the metal plate, and a base drive mechanism that rotates the cylinder mounting base along the rotation axis, and the electrical control mechanism may have a drive control unit that controls the operation of the cylinder drive mechanism and the base drive mechanism, and a pressure adjustment unit that adjusts the pressure when the pair of electrodes are brought into contact with the metal plate.

[0016] In this case, the electric heating device for metal sheets for electromagnetic steel sheets may further include a bypass current circuit provided in parallel with the power supply circuit.

[0017] Furthermore, the electric heating device for metal sheets for electromagnetic steel sheets may further include a substantially cylindrical electric roll having a plurality of the electrodes provided on its circumferential surface, the electrodes being insulated from each other, and having a rotation axis in the width direction of the metal sheet, and a roll drive mechanism that moves the electric roll back and forth at least in the thickness direction of the metal sheet, and the electric current control mechanism may include a drive control unit that controls the operation of the roll drive mechanism, and a pressure adjustment unit that adjusts the pressure when the pair of electrodes are brought into contact with the metal sheet.

[0018] The electrical heating device for a metal sheet for an electromagnetic steel sheet may further include a metal sheet conveying mechanism for passing a strip of the metal sheet through the electrical heating device.

[0019] The cylinder may be a spring cylinder, an air cylinder, a hydraulic cylinder, or an electric cylinder.

[0020] The electrical heating device for the metal plate for the electromagnetic steel plate may include a plurality of pairs of electrodes, and the electrode provided on the front side of the metal plate or the electrode provided on the back side of the metal plate may be common among the plurality of pairs of electrodes.

[0021] The current control mechanism may control the current flow so that spot heating is performed over the entire width of the metal plate.

[0022] The current control mechanism may control the current flow so that spot heating is performed only on the widthwise end portions of the metal plate.

[0023] The current control mechanism may keep the electrode in contact with the metal plate for a predetermined period of time after the current is passed through.

[0024] The electrode may have a flow path at its base end through which a cooling medium for cooling the electrode flows, and the tip end may be formed in a columnar shape that is thinner than the base end.

[0025] According to another aspect, the present invention is a method for applying electrical heating to a metal sheet for use in an electrical steel sheet after cold rolling and before primary recrystallization annealing, the method comprising the steps of: using the above-described electrical heating device for a metal sheet for an electrical steel sheet, bringing electrodes into contact with the metal sheet, and applying electricity to the electrodes for a predetermined time, thereby heating the metal sheet from a temperature equal to or higher than room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec.

[0026] Since the metal plate can be heated from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec, it is possible to produce a large amount of seed crystals having the Goss orientation in the crystalline structure before primary recrystallization.

[0027] According to yet another aspect, the present invention provides a method for producing an electrical steel sheet, comprising the steps of cold-rolling a metal sheet for use in an electrical steel sheet, and subjecting the metal sheet after the cold rolling to primary recrystallization annealing that also serves as decarburization annealing, characterized in that the method further comprises, after the cold rolling and before the primary recrystallization annealing, a step of heat-treating the metal sheet by the above-mentioned method for applying electrical heat to a metal sheet for use in an electrical steel sheet.

[0028] According to the present invention, in the process of heat treating the metal sheet (preheat treatment process) using the above-mentioned electrical heating method for a metal sheet for an electrical steel sheet, the metal sheet can be heated from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec. This allows a large amount of seed crystals having the Goss orientation to be generated in the crystalline structure before primary recrystallization. As a result, recrystallized grains grow from the seed crystals as nuclei, resulting in an electrical steel sheet having a large amount of Goss-oriented grains generated within the metal sheet surface. As a result, the magnetic properties of the electrical steel sheet can be dramatically improved, and excellent metallurgical properties can be obtained.

[0029] According to the present invention, in the manufacturing process of an electrical steel sheet, a large amount of seed crystals having the Goss orientation can be generated in the crystalline structure before primary recrystallization, thereby making it possible to dramatically improve the magnetic properties of the obtained electrical steel sheet.

[0030] FIG. 10 is a side view schematically showing the configuration and operation of an electric heating device for metal sheets for electromagnetic steel sheets according to a first embodiment of the present invention. FIG. 11 is a block diagram showing the functional configuration of an electric heating device for metal sheets for electromagnetic steel sheets according to the first embodiment of the present invention. FIG. 12 is a diagram showing an example of a heating pattern by an electric heating device for metal sheets for electromagnetic steel sheets according to the present invention. FIG. 13 is a diagram showing an example of electrodes in an electric heating device for metal sheets for electromagnetic steel sheets according to the present invention. FIG. 14 is a side view schematically showing the configuration of a modified example of an electric heating device for metal sheets for electromagnetic steel sheets according to the first embodiment of the present invention. FIG. 15 is a block diagram showing the functional configuration of a modified example of an electric heating device for metal sheets for electromagnetic steel sheets according to the first embodiment of the present invention. FIG. 16 is a diagram showing an example of a heating pattern by an electric heating device for metal sheets for electromagnetic steel sheets according to the present invention. FIG. 17 is a diagram showing a modified example of electrodes in an electric heating device for metal sheets for electromagnetic steel sheets according to the present invention. FIG. 18 is a side view schematically showing the configuration and operation of an electric heating device for metal sheets for electromagnetic steel sheets according to a second embodiment of the present invention. FIG. 19 is a side view schematically showing the configuration and operation of an modified example of the electric heating device for metal sheets for electromagnetic steel sheets shown in FIG. FIG. 10 is a block diagram showing the functional configuration of an electric heating device for metal sheets for electromagnetic steel sheets according to the second embodiment of the present invention. 12 is a side view showing a schematic configuration of an electric heating device for a metal sheet for an electromagnetic steel sheet according to a third embodiment of the present invention. FIG. 13 is a block diagram showing a functional configuration of the electric heating device for a metal sheet for an electromagnetic steel sheet shown in FIG. 12. FIG. 14 is a top view showing an example of an upper electrode.

[0031] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0032] [Background and Overview of the Present Invention] Before describing preferred embodiments of the present invention, the background to the completion of the present invention and an overview of the present invention will be described first.

[0033] As described above, the present inventors have investigated a method for generating seed crystals (nuclei) in advance in a crystalline structure before primary recrystallization in order to grow recrystallized grains having good magnetic properties and metallurgical properties and a Goss orientation during annealing, such as secondary recrystallization annealing, in the manufacturing process of electrical steel sheets. Here, "good metallurgical properties" refers not only to a high probability of the existence of Goss-oriented grains but also to an environment that facilitates the growth of such grains. As a result, it has been experimentally found that a large number of seed crystals that serve as nuclei for recrystallized grains having a Goss orientation can be generated by subjecting a metal sheet for electrical steel sheets after cold rolling and before primary recrystallization annealing (decarburization annealing) to a preheat treatment in which the metal sheet is locally heated under pressure from a temperature above room temperature to a high temperature (450°C to 1000°C) at a heating rate of 2,000°C / sec to 100,000°C / sec. (The mechanism for this is currently unknown).

[0034] To realize the above preliminary heat treatment on an industrial scale, a specific means is required that allows for the above-mentioned ultra-rapid heating at 2,000°C / sec or more to be carried out continuously at predetermined intervals so as not to impair the productivity of electrical steel sheets. Further investigation by the present inventors has revealed that in order to achieve a heating rate of 2,000°C / sec, the current application time must be 500 msec or less (for example, approximately 10 msec to 500 msec). (This indicates that a technology that can raise the temperature to 1,000°C in 0.5 seconds is sufficient.)

[0035] Furthermore, because the current application time in the preliminary heat treatment is extremely short (approximately 10 msec to 500 msec), a high current density is required, and the heating in the preliminary heat treatment is localized. Therefore, it is difficult to industrially implement the preliminary heat treatment by conventional induction heating or direct current heating between current-carrying rolls. Specifically, conventional induction heating is insufficient in terms of current density, and it is difficult to achieve the ultra-rapid heating described above, which heats only an extremely narrow area while avoiding the effects of leakage magnetic flux. Furthermore, conventional heating between current-carrying rolls heats the entire strip of the metal sheet, making it impossible to selectively heat only the area where seed crystals are desired to be generated. Furthermore, conventional heating between current-carrying rolls poses the problem that, because the metal sheet for use in cold-rolled electrical steel sheets is thin, sheet deformation occurs and the sheet easily buckles when heated to high temperatures.

[0036] In the case of non-oriented electrical steel sheets, it is preferable to grow seed crystals evenly over the entire surface of the metal sheet for steel sheet, and it is necessary to heat multiple points at a predetermined distance in a short period of time. On the other hand, in the case of grain-oriented electrical steel sheets, it is necessary to heat so that seed crystals with the Goss orientation are present only at positions spaced a predetermined distance apart, rather than growing them evenly over the entire surface. Note that the predetermined distance in grain-oriented electrical steel sheets refers to a distance at which the seed crystals are likely to grow in a direction that provides good magnetic properties due to secondary recrystallization.

[0037] Furthermore, if some of the heated points are insufficiently heated, there is a risk that seed crystals will not be sufficiently generated in those areas. Therefore, it is necessary to stably heat the heated points at a predetermined temperature and a predetermined rate. Conversely, if some of the heated points are overheated, iron will melt at about 1500°C. Therefore, it is also important to avoid overheating (controlling the temperature reached by heating the metal sheet from a temperature above room temperature). Such temperature control can be achieved by adjusting the amount of current flowing through the electrodes and the current flow time using electrical heating, or by providing a cooling mechanism that can perform rapid cooling immediately after heating. In addition, to stably heat the metal sheet for electrical steel sheet at a predetermined temperature, it is necessary to contact the current-carrying electrodes with a certain amount of rolling force so that electrical current is stably applied to the metal sheet for electrical steel sheet.

[0038] A heating device for a metal sheet for use in an electrical steel sheet that satisfies the above-described conditions must be in contact with the metal sheet for a predetermined period of time. Such a heating device may have a current-carrying mechanism in which a current-carrying electrode contacts the metal sheet while it is stationary, moves the metal sheet a predetermined distance after heating, and then contacts the current-carrying electrode again, i.e., a batch-like current-carrying mechanism, or a mechanism in which the current-carrying electrode moves along with the metal sheet and conducts current. The inventors have conceived of such a current-carrying mechanism using a pair of electrodes that contact the metal sheet from both the front and back sides of the metal sheet for use in an electrical steel sheet, sandwiching the metal sheet between them, and passing current through the metal sheet in a point-like manner. For example, by arranging multiple pairs of such electrodes, localized point-like heating can be performed over the entire metal sheet, allowing multiple seed crystals to be generated throughout the metal sheet. The inventors have confirmed through the above-described experiments that point-like heating produces seed crystals with favorable recrystallized grains. Furthermore, when point-like heating is performed, the metal sheet undergoes slight deformation due to thermal expansion immediately after heating, but is quickly cooled, does not buckle, and maintains its original sheet shape.

[0039] The timing of the heating is after cold rolling and before primary recrystallization annealing (decarburization annealing). By generating a large amount of seed crystals that serve as nuclei for recrystallized grains having the Goss orientation before the primary recrystallization annealing, it is possible to generate a large amount of recrystallized grains having the Goss orientation, and the magnetic properties of the electrical steel sheet can be dramatically improved.

[0040] That is, the present invention provides an apparatus and method for preheating a metal sheet for electrical steel sheet to control crystal orientation, which is important in manufacturing electrical steel sheets. According to the present invention, by locally and ultra-rapidly heating a metal sheet for electrical steel sheet before primary recrystallization annealing, a large number of seed crystals of recrystallized grains having a Goss orientation are generated, and crystal growth can be achieved using these seed crystals as nuclei. The preheating is a process for generating these seed crystals that serve as nuclei. For example, in the preheating, Goss-oriented grains (coarse Goss-oriented grains) with a grain size of 5 μm or more are generated in the locally heated region (locally heated region), whereas the region not locally heated (non-locally heated region) retains a processed structure (very fine crystal grains), preventing the generation of coarse Goss-oriented grains. When local rapid heating is performed, recovery and recrystallization occur in the locally heated region, resulting in the generation of practical Goss-oriented grains and facilitating grain growth, but recovery and recrystallization do not occur in the non-locally heated region.

[0041] Specifically, the device used for the preliminary heat treatment according to the present invention is an electric heating device for a metal sheet for an electromagnetic steel sheet, comprising: a pair of electrodes that are in locally dispersed contact with the metal sheet from the front and back sides of the metal sheet for an electromagnetic steel sheet after cold rolling and before primary recrystallization annealing so as to sandwich the metal sheet, and that apply current to the metal sheet; a current control mechanism that brings the pair of electrodes into contact with the front and back sides of the metal sheet at predetermined positions on the metal sheet, and separates the electrodes from the metal sheet after applying current to the electrodes for a predetermined time; a power source that can heat the metal sheet from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec; and a power supply circuit that connects the electrodes and the power source.

[0042] Furthermore, a method for carrying out preliminary heat treatment according to the present invention is a method for conducting electrical heating of a metal sheet for use in an electrical steel sheet after cold rolling and before primary recrystallization annealing, the method comprising the steps of: using the electrical heating device for a metal sheet for an electrical steel sheet, bringing electrodes into contact with the metal sheet; and applying electricity to the electrodes for a predetermined time, thereby heating the metal sheet from a temperature equal to or higher than room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec.

[0043] According to the above-described electrical heating device and electrical heating method for a metal sheet for an electrical steel sheet, seed crystals having a predetermined orientation (Goss orientation) can be dispersed and generated at a predetermined density within the sheet surface of the metal sheet for an electrical steel sheet before primary recrystallization annealing.

[0044] First Embodiment: Batch Current Method Using Non-Rotating Electrodes (Electrical Heating Apparatus 100) First, the configuration of a direct current heating apparatus 100 for metal sheets for use in electromagnetic steel sheets according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a side view schematically illustrating the configuration and operation of the direct current heating apparatus 100 for metal sheets for use in electromagnetic steel sheets according to this embodiment. FIG. 2 is a block diagram illustrating the functional configuration of the direct current heating apparatus 100 for metal sheets for use in electromagnetic steel sheets according to this embodiment. Note that, for ease of explanation, FIG. 2 also illustrates components other than the functional configuration (electrodes, cylinder, cylinder mounting base, power supply) as blocks. FIG. 3 is a diagram illustrating an example of a heating pattern using the direct current heating apparatus 100 for metal sheets for use in electromagnetic steel sheets according to this embodiment.

[0045] As shown in Figures 1 and 2, the electric heating device 100 according to this embodiment is an electric current device including a group of electrodes fixedly arranged in pairs above and below the strip of metal sheet 1 for electromagnetic steel sheet at a predetermined interval, and mainly including a pair of electrodes 110, conveying rolls 120, a cylinder 130, a cylinder drive mechanism 135, a cylinder mounting base 140, a base drive mechanism 145, an electric current control mechanism 150, a power source 160, and a power supply circuit.

[0046] A pair of electrodes (sometimes referred to as "counter electrodes") 110 are electrodes that pass current through the metal sheet 1 by locally dispersing contact with the metal sheet 1 from the front and back sides thereof after cold rolling and before primary recrystallization annealing, sandwiching the metal sheet 1. The pair of electrodes comprises an upper electrode 111 disposed on the front side of the metal sheet 1 and a lower electrode 113 disposed on the back side of the metal sheet. Here, "locally dispersing contact" refers to a configuration in which the counter electrodes 110 are in contact with each other so that locally heated regions formed by sandwiching the metal sheet 1 between the counter electrodes 110 and locally rapid heating are present in multiple dispersed locations on the metal sheet 1. One or more upper electrodes 111 and lower electrodes 113, i.e., counter electrodes 110, may be arranged. As an example, as shown in the figure, multiple upper electrodes 111 and lower electrodes 113 are arranged at predetermined intervals in the width and length directions of the metal sheet 1. Specifically, the counter electrodes 110 are arranged at predetermined intervals (i.e., at equal intervals) across the entire width of the metal sheet 1 in the width direction of the metal sheet 1, and at predetermined intervals across a predetermined length in the longitudinal direction (material passing direction). In the electric heating device 100, the metal sheet 1 is sandwiched between the upper electrode 111 and the lower electrode 113 at a predetermined pressure for all of the counter electrodes 110, and current is applied to them all at once. By arranging the counter electrodes 110 and applying current as described above, spot heating by the electrodes 110 can be performed across the entire sheet surface of the metal sheet 1, that is, heating can be performed in a pattern suitable for non-oriented electrical steel sheets. A heating pattern suitable for non-oriented electrical steel sheets is, for example, a pattern in which spot heated portions HP are arranged in a lattice pattern (specifically, a staggered pattern) across the entire width direction of the metal sheet 1 (specifically, the entire sheet surface), as shown in FIG. 3 . Furthermore, by performing spot heating as described above, seed crystals can be generated over the entire surface of the metal plate 1.

[0047] The material of the electrode 110 is not particularly limited, but examples thereof include metals and alloys with good electrical conductivity, such as copper, chromium copper, and tungsten. A surface layer may be formed by thermal spraying of a conductive ceramic or cermet, a metal plating layer, ion plating, or the like. However, if it is necessary to maintain the temperature of the metal plate 1 for a short period of time after the metal plate 1 is heated by electrical current, electrical current is passed through the electrode 110 while it is in contact with the metal plate 1 to maintain the temperature. Alternatively, the electrode 110 continues to be in contact with the metal plate 1 even after the electrical current is stopped, and the temperature of the metal plate 1 is maintained at the heating temperature of the electrode 110 itself. In these cases, it is preferable that the material of the electrode 110 be a material primarily composed of a high-resistance nickel or chromium alloy, rather than a metal with good electrical conductivity, such as ordinary copper or chromium copper. Furthermore, when it is necessary to rapidly cool the metal sheet 1 immediately after the electrical heating of the metal sheet 1, it is preferable to use a metal with good thermal conductivity such as copper, a copper alloy, or a tungsten alloy as the material for the electrode 110, and further provide a cooling mechanism for cooling the electrode 110 so that the metal sheet 1 is cooled via the electrode 110. Rapid cooling immediately after heating tends to produce randomly oriented Goss grains, which is suitable for non-oriented electrical steel sheets. In addition, keeping the temperature immediately after heating tends to encourage the growth of well-oriented Goss grains, which is suitable for grain-oriented electrical steel sheets.

[0048] Here, the configuration of the cooling mechanism for cooling the electrode 110 will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view showing the cooling mechanism for the electrode 110 in the electric heating device 100.

[0049] 4A , the electrode 110 according to this embodiment has a closed tip end with a cavity 118 therein as a flow path for a cooling medium, and has a cooling pipe 119 near the center of the cavity 118. When cooling the electrode 110, cooling water as a cooling medium is caused to flow through the cooling pipe 119 from the rear end side of the electrode 110 toward the front end side. The cooling water flows from the open tip end of the cooling pipe 119, through the bottom of the cavity 118, and around the outside of the cooling pipe 119 from the front end side to the rear end side of the electrode 110. The electrode 110 according to this embodiment has such a cooling mechanism, which enables rapid cooling of the electrode 110.

[0050] The inventor's experiments have shown that maintaining the metal plate 1 at a high temperature for a short time (a few seconds) immediately after rapid heating can result in stable growth of Goss crystals with a better crystal orientation, i.e., better growth. To simultaneously achieve rapid cooling of the metal plate 1 via the electrode 110 and maintaining the temperature of the metal plate 1, the electrode 110 may have a hollow portion 118 at the base end T1, and the tip end T2 may be formed in a columnar shape that is thinner than the base end T1, as shown in FIG. 4(B). The tip end T2 is thinner than the portion of the base end T1 extending from the tip of the hollow portion 118 to the tip end T2. When the electrode 110 is shaped in this way, the temperature of the tip end T2 in contact with the metal plate 1 is less likely to decrease even when the electrode 110 is cooled by cooling water flowing through the hollow portion 118. Therefore, by continuing to press the electrode 110 against the metal plate 1 while flowing cooling water into the cavity 118 after the metal plate 1 has been rapidly heated, i.e., immediately after energization, the metal plate 1 can be maintained at a high temperature and then rapidly cooled. A material with high resistance may be used for the tip portion T2 of the electrode 110 so that the tip portion T2 is less likely to cool. The tip portion T2 and the base end portion T1 of the electrode 110 may be made of different materials. Furthermore, the tip portion T2 of the electrode 110 may have a self-heating structure.

[0051] The transport rolls 120 are an example of a metal sheet transport mechanism according to the present embodiment, and pass the strip of metal sheet 1 through the electric heating device 100. The metal sheet transport mechanism according to the present invention is not limited to the transport rolls 120, as long as it has a configuration that allows the strip of metal sheet 1 to pass through. The transport rolls 120 may be capable of continuously passing the strip of metal sheet 1 at a predetermined speed.

[0052] An electrode 110 (upper electrode 111 or lower electrode 113) is attached to the cylinder 130 in an insulated state. The type of cylinder 130 is not particularly limited, and various known cylinders such as a spring cylinder, an air cylinder, a hydraulic cylinder, and an electric cylinder can be used. More specifically, the electrode 110 is attached to the tip of a rod 133 provided in a cylinder 131 of the cylinder 130, and the rod 133 can move forward and backward relative to the metal plate 1 using the force of a spring, air pressure, hydraulic pressure, or the like, i.e., the rod 133 can extend and retract. The extension and retraction of the rod 133 allows the pair of electrodes 110 to contact the metal plate 1 so as to sandwich the metal plate 1 with a predetermined pressure.

[0053] The cylinder driving mechanism 135 extends and retracts the electrode 110 (upper electrode 111 or lower electrode 113) attached to the cylinder 130 (more specifically, the tip of the rod 133) so as to bring the electrode 110 into contact with and away from the metal plate 1. The driving of this cylinder driving mechanism 135 is controlled by a drive control unit 153 of the current control mechanism 150, which will be described later.

[0054] The cylinder mounting base 140 has a plate-like shape and is parallel to the metal plate 1, and has a plurality of cylinders 130 arranged thereon. Specifically, for example, the plurality of cylinders 130 are arranged at predetermined intervals in the longitudinal and width directions of the metal plate 1. The predetermined intervals between the cylinders 130 correspond to the intervals between the upper electrodes 111 (or lower electrodes 113), and are approximately the same as the intervals between the upper electrodes 111 (or lower electrodes 113). Furthermore, the electrodes 110 and the cylinder mounting base 140 must also be insulated from each other.

[0055] The base drive mechanism 145 reciprocates the cylinder mounting base 140 at least in the thickness direction of the metal plate 1. This allows the cylinder 130 to approach or move away from the front or back surface of the metal plate 1. If the cylinder mounting base 140 is installed so that the distance between the cylinder mounting base 140 and the front or back surface of the metal plate 1 is sufficiently short, it is not necessary to reciprocate the cylinder mounting base 140 in the thickness direction. Alternatively, the base drive mechanism 145 may be configured to reciprocate the cylinder mounting base 140 in the longitudinal direction (material passing direction) of the metal plate 1. This allows for a current application method in which the electrode 110 moves a predetermined distance in conjunction with the movement of the metal plate 1 while applying current, and after the current application is completed, the electrode 110 is returned to its original position, and another position on the metal plate 1 is applied current, as described below.

[0056] The current control mechanism 150 controls the current flow by contacting a pair of electrodes 110 (upper electrode 111 and lower electrode 113) on the front and back sides of the metal sheet 1 at predetermined positions, passing current through the electrodes 110 for a predetermined time, and then separating the electrodes 110 from the metal sheet 1. In the current heating device 100, the current control mechanism 150 controls the current flow so that spot heating is performed across the entire width of the metal sheet 1. Specifically, the current control mechanism 150 repeats the current flow control described above using the electrodes 110, thereby performing spot heating at multiple positions spaced apart by predetermined intervals in the longitudinal and width directions of the metal sheet 1 across the entire strip of the metal sheet 1. As a result, the metal sheet 1 is heated in a heating pattern suitable for non-oriented electrical steel sheets, in which spot heated portions HP are arranged in a grid pattern, as in the heating pattern shown in FIG. 3 . As a result, seed crystals of recrystallized grains having the Goss orientation can be formed at a plurality of positions spaced at predetermined intervals in the longitudinal and width directions of the metal sheet 1 over the entire strip of the metal sheet 1 .

[0057] The current control mechanism 150 includes a current control unit 151, a drive control unit 153, and a pressure adjustment unit 155. The current control unit 151 is connected to each electrode 110 and controls the amount and timing of current flow to each electrode 110. The drive control unit 153 controls the operation of the cylinder drive mechanism 135 and the base drive mechanism 145. The pressure adjustment unit 155 adjusts the pressure when the pair of electrodes 110 (the upper electrode 111 and the lower electrode 113) are brought into contact with the metal plate 1. The drive control unit 153 controls the operation of the cylinder drive mechanism 135 and the base drive mechanism 145 so that the electrode 110 contacts the metal plate 1 with the pressure adjusted by the pressure adjustment unit 155. The pressure control by the pressure adjustment unit 155 not only adjusts the contact area of ​​the electrode 110 to a constant value, but also adjusts the contact resistance between the electrode 110 and the metal plate 1, stabilizes current flow, and stabilizes the temperature of the contact portion of the electrode 110 with the metal plate 1. Pressure control is also used to control the amount of contact heat transfer from the metal plate 1 to the electrode 110 after electrical heating is completed.

[0058] The power supply 160 supplies to the electrode 110 electric power capable of heating the metal plate 1 from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec. The amount of current flowing from the power supply 160 to the electrode 110 is controlled by the current control unit 151 described above. The temperature of the metal plate 1 can be measured, for example, by a radiation thermometer or the like installed facing the central portion of the metal plate 1 in the width direction. The amount of current flowing to the electrode 110 is preferably controlled for each individual electrode, but may be controlled overall if the average current flow is known.

[0059] When the pair of electrodes 110 and the power source 160 are connected by a flexible wire 170 or the like, a circuit is formed consisting of the upper electrode 111, the lower electrode 113, and the power source 160, and a power supply circuit is formed to include the flexible wire 170 or the like.

[0060] (Modification of Resistance Heating Apparatus 100) Here, with reference to Figs. 5 to 7, a description will be given of a resistance heating apparatus 100-2 according to a modification of this embodiment. Fig. 5 is a side view schematically showing the configuration of a modification 100-2 of the resistance heating apparatus 100 for metal sheets for electromagnetic steel sheets shown in Fig. 1. Fig. 6 is a block diagram showing the functional configuration of the resistance heating apparatus 100-2 for metal sheets for electromagnetic steel sheets. Note that, for ease of explanation, Fig. 6 also shows configurations other than the functional configuration (electrode selection unit) as blocks. Fig. 7 is a diagram showing an example of a heating pattern by the resistance heating apparatus 100-2 for metal sheets for electromagnetic steel sheets according to this embodiment.

[0061] As shown in FIGS. 5 and 6 , in the electrical heating device 100-2, a pair of electrodes 110 are connected to a power source 160 via an electrode selector 180 and a flexible electric wire 170. The electrode selector 180 selects a counter electrode 110 to which current is applied from the power source. For example, the electrode selector 180 is provided on the cylinder 130 while electrically connected to the electrode 110. The counter electrode 110 selected by the electrode selector 180 is controlled by a current controller 151. The amount of current flowing from the power source 160 to the electrode 110 via the electrode selector 180 is also controlled by the current controller 151. While it is preferable to control the amount of current flowing to the electrode 110 via the electrode selector 180 on an individual electrode basis, it may also be controlled collectively if the average current flow is known. As long as electrical connection between the electrode selector 180 and each of the electrodes 110 is possible, the electrode selector 180 may be attached directly to the electrode 110 or to the cylinder 130.

[0062] In the electric heating device 100-2, the power supply circuit is a circuit composed of an upper electrode 111, a lower electrode 113, an electrode selection unit 180, and a power supply 160, as a result of a pair of electrodes 110 and a power supply 160 being connected by a flexible electric wire 170 and an electrode selection unit 180, etc.

[0063] Furthermore, in the electric heating device 100-2, the base driving mechanism 145 may be configured to move the cylinder mounting base 140 also in the width direction of the metal plate 1. In this case, it is not necessary for the counter electrode 110 to be disposed across the entire width of the metal plate 1.

[0064] In the electric heating device 100-2, the electric current control mechanism 150 controls the electric current by clamping the metal plate 1 with a predetermined pressure between a predetermined counter electrode 110 or all of the counter electrodes 110, and then passing electric current through the electrode selection unit 180 to only the predetermined counter electrode 110 for a predetermined time and then separating it from the metal plate 1.

[0065] For example, in the electric heating device 100-2, the current control mechanism 150 controls current flow so that spot heating is performed across the entire width of the metal sheet 1. Specifically, the current control mechanism 150 repeats the above-described current control using the electrodes 110 while appropriately moving the cylinder mounting base 140 in the longitudinal and width directions, thereby performing spot heating at multiple positions spaced apart by a predetermined distance across the entire strip of the metal sheet 1. This makes it possible to heat the metal sheet 1 with a heating pattern suitable for non-oriented electrical steel sheets, in which spot heated portions HP are arranged in a grid pattern, as in the heating pattern of FIG. 3 .

[0066] Furthermore, in the electric heating device 100-2, the current control mechanism 150 may control current flow so that spot heating is performed only on the widthwise ends of the metal sheet 1. Specifically, the current control mechanism 150 performs the above-described current control using the electrodes 110 while appropriately moving the cylinder mounting base 140 in the longitudinal and widthwise directions, thereby performing spot heating at multiple positions at a predetermined interval in the longitudinal direction of the metal sheet 1 on the widthwise end of the strip of the metal sheet 1. This allows the metal sheet 1 to be heated in a heating pattern suitable for grain-oriented electrical steel sheets, as exemplified in FIG. 7 . The heating pattern in FIG. 7 is a pattern in which spot-heated portions HP are arranged in a linear row at each widthwise end of the metal sheet 1. As a result of this heating, seed crystals of recrystallized grains having a Goss orientation can be formed at multiple positions at a predetermined interval on each widthwise end of the metal sheet 1 throughout the entire length of the metal sheet 1. By forming seed crystals in this manner, when heating proceeds from the widthwise end sides of the coiled metal sheet 1 strip in the secondary recrystallization step described below, Goss crystals grow from the widthwise end sides toward the center, resulting in the formation of a grain-oriented electrical steel sheet. Heating at 2,000°C / sec may require a current of several thousand to several tens of thousands of amperes for each counter electrode 110, depending on the sheet thickness. However, in the electric heating device 100-2, current is not supplied to all of the counter electrodes 110 at once, so the power source 160 does not need to have a large capacity.

[0067] (Electrical heating method) The electrical heating method for a metal sheet for an electromagnetic steel sheet according to this embodiment includes a preliminary heat treatment step of using the electrical heating device 100 or electrical heating device 100-2 according to this embodiment described above to bring a pair of electrodes 110 into contact with the metal sheet 1 after cold rolling and before primary recrystallization annealing, and heating the metal sheet 1 from a temperature equal to or higher than room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec by applying electricity to the electrodes 110 for a predetermined time.

[0068] In the preliminary heat treatment step, the heating rate should be 2,000°C / sec or more at the center of the locally heated region as viewed in the thickness direction and at 1 / 5 of the thickness of the metal plate 1. If the heating rate is 2,000°C / sec or more, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. It is more preferable that the heating rate be 10,000°C / sec or more. Furthermore, although it is not necessarily necessary to specify an upper limit for the heating rate, it may be set to 100,000°C / sec or less for convenience of equipment such as thermocouples used for measurement.

[0069] The 1 / 5 portion of the plate thickness of the metal plate 1 means a depth corresponding to 1 / 5 of the steel plate thickness from the surface of the metal plate 1 in the plate thickness direction.

[0070] Furthermore, in the preliminary heat treatment step, the temperature reached at the center of the locally heated region as viewed from the thickness direction and at 1 / 5 of the thickness of the metal plate 1 should be 450°C to 1000°C. If the temperature reached is 450°C or higher, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The temperature reached may be 700°C or higher, particularly 800°C or higher, or even 900°C or higher, or even 1000°C. The upper limit of the temperature reached should be equal to or lower than the melting point of the material (metal plate 1).

[0071] Specifically, when the electric heating device 100 is used, as shown in FIG. 1A, the metal plate 1 is transported into the electric heating device 100 by the transport rolls 120, and the drive control unit 153 controls the base drive mechanism 145, which moves the cylinder mounting base 140 in the thickness direction of the metal plate 1 so as to approach the metal plate 1. The same applies when the electric heating device 100-2 is used. Furthermore, the drive control unit 153 controls the cylinder drive mechanism 135, which operates the cylinder 130 so as to extend the electrodes 110 (upper electrode 111 and lower electrode 113) and bring them into contact with the metal plate 1, as shown in FIG. 1B. At this time, in the case of the electric heating device 100, the pressure adjustment unit 155 adjusts the pressure at which the electrodes 110 contact the metal plate 1, and the drive control unit 153 controls the cylinder drive mechanism 135 so that all of the electrodes 110 contact the metal plate 1 with the adjusted pressure. In the case of the electric heating device 100-2, the pressure is adjusted so that at least a part of the predetermined electrodes 110 contacts the metal plate 1.

[0072] After the pressure at which all of the electrodes 110 or at least certain of the electrodes 110 contact the metal plate 1 reaches a predetermined pressure, a predetermined amount of current is passed through all of the electrodes 110 via the flexible electric wires 170, or through the certain of the electrodes 110 via the flexible electric wires 170 and the electrode selection unit 180, for a predetermined time to heat the metal plate 1. At this time, the amount of current passed through each electrode 110 and the time for which the current is passed are controlled by the current control unit 151 so that the metal plate 1 is heated from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec.

[0073] After the heating is completed, the drive control unit 153 controls the cylinder drive mechanism 135, and the cylinder drive mechanism 135 operates the cylinder 130 so as to shorten the electrodes 110 (upper electrode 111 and lower electrode 113) and move them away from the metal plate 1.

[0074] Here, if the temperature of the metal sheet 1 needs to be maintained for a short period of time after the electrical heating, electrical current can be applied to maintain the temperature while the electrode 110 is in contact with the metal sheet 1, or the electrode 110 can be maintained at the heating temperature of the electrode 110 itself, which has been heated by a current flowing through the metal sheet 1 without passing any current through the electrode 110 while the electrode 110 is in contact with the metal sheet 1. Also, the electrode 110 in contact with the metal sheet 1 can be rapidly cooled immediately after the electrical heating. Even in this case, the metal sheet 1 can be maintained at a high temperature even after the electrical heating by, for example, configuring the electrode 110 as shown in FIG. 4(B). That is, the metal sheet 1 can be maintained at a high temperature for a predetermined time after the electrical heating and then rapidly cooled. As a result, it is possible to prevent the metal sheet 1 from being maintained at an unnecessarily high temperature, which would otherwise prevent the production of high-quality Goss-oriented grains.

[0075] In the case of the resistance heating apparatus 100, the current application method in the resistance heating method according to this embodiment may be, for example, a semi-batch method. The semi-batch method is a method in which the passage of the metal sheet 1 transported into the resistance heating apparatus 100 is temporarily stopped, and after the current application is completed, the metal sheet 1 is passed through a predetermined distance and then current is applied again. In other words, the passage of the metal sheet 1 transported into the resistance heating apparatus 100 is stopped each time current is applied. The semi-batch method of current application using the resistance heating apparatus 100 enables semi-continuous ultra-rapid heat treatment of a long strip of metal sheet 1. Furthermore, the current application method in the resistance heating method according to this embodiment may be a method in which current is applied while the electrode 110 moves a predetermined distance in conjunction with the continuous passage (movement) of the metal sheet 1, and after the current application is completed, the electrode 110 is returned to its original position and current is applied to another position on the metal sheet 1. In this current application method, the base drive mechanism 145, controlled by the drive control unit 153, reciprocates the cylinder mounting base 140 in the longitudinal direction (material passing direction) of the metal sheet 1, thereby moving the position of the electrode 110. This type of current application by the resistance heating device 100 enables continuous ultra-rapid heat treatment of a strip of long metal sheet 1. In addition, in the case of the resistance heating device 100-2, the above-mentioned semi-batch method is used as the current application method. However, in the case of the resistance heating device 100-2, unlike the case of the resistance heating device 100, the electrode 110 may be moved in at least one of the width direction and the longitudinal direction while the metal sheet 1 is stopped.

[0076] (Method for manufacturing an electrical steel sheet) The method for manufacturing an electrical steel sheet according to this embodiment includes a cold rolling step and a primary recrystallization annealing step, and further includes the above-mentioned preliminary heat treatment step after the cold rolling step and before the primary recrystallization annealing step. In addition, in the case of a grain-oriented electrical steel sheet, the manufacturing method according to this embodiment further includes a secondary recrystallization annealing step.

[0077] In the cold rolling process, the metal sheet 1 for an electrical steel sheet is cold rolled to a final thickness (for example, approximately 0.2 mm to approximately 0.4 mm). After this cold rolling process, a preliminary heat treatment process is carried out. In the preliminary heat treatment process, a large number of seed crystals are generated at predetermined intervals throughout the entire length and width directions of the metal sheet 1. These seed crystals have a Goss orientation. Note that the preliminary heat treatment process has already been described in detail, so a detailed description thereof will be omitted here.

[0078] After the preliminary heat treatment step, a primary recrystallization annealing step is performed, in which the pre-heat-treated metal sheet 1 is annealed to decarburize it. During this annealing, the seed crystals generated in the preliminary heat treatment step undergo primary recrystallization, becoming Goss-oriented grains with excellent magnetic properties. The recrystallized grains (Goss-oriented grains) at this stage are small particles on the order of 10 to 20 μm. When manufacturing a non-oriented electrical steel sheet, the primary recrystallization annealing step may be completed, or a step of forming an insulating film on the surface of the metal sheet 1 may be performed thereafter.

[0079] On the other hand, when manufacturing grain-oriented electrical steel sheets, an insulating layer, typically consisting mainly of MgO, is subsequently formed on the surface of the metal sheet 1 after primary recrystallization annealing in an insulating layer formation process. In the subsequent secondary recrystallization annealing process, the metal sheet 1 with the insulating layer formed thereon is batch-annealed, causing the Goss-oriented grains formed in the primary recrystallization annealing to grow into large crystals visible to the naked eye. During this process, the insulating layer becomes an insulating coating; specifically, the MgO in the insulating layer reacts at the high temperature of the annealing to form an insulating coating. The spacing between the counter electrodes 110 in the electric heating device 100 is set so that the secondary recrystallized crystal grains can grow smoothly relative to each other. Since the size of the secondary recrystallized crystal grains is generally up to about 50 mm, the spacing is set to, for example, about 50 mm.

[0080] The electrical steel sheet according to this embodiment manufactured through the above-described steps produces a large number of seed crystals having the Goss orientation in the preliminary heat treatment step, and recrystallized grains grow from these seed crystals as nuclei, resulting in a steel sheet with a large number of Goss-oriented grains produced within the metal sheet surface, which allows for dramatically improved magnetic properties of the electrical steel sheet.

[0081] (Improvement of Magnetic Properties) Improvement of the magnetic properties of the cold-rolled steel sheet for the electrical steel sheet that was subjected to preliminary heat treatment using the electrical heating device 100 or the electrical heating device 100-2 according to this embodiment was confirmed as follows.

[0082] First, steel containing 0.06% by mass of C, 3.4% by mass of Si, 0.10% by mass of Mn, 0.006% by mass of S, 0.026% by mass of Al, and 0.008% by mass of N was hot-rolled and cold-rolled to a cold-rolled steel sheet having a thickness of 0.22 mm. This steel sheet was subjected to electrical heating using the electrical heating device 100 described above. The heating pattern was as shown in FIG. 3, and a localized heating region was formed.

[0083] Then, the above-mentioned cold-rolled steel sheet (cold-rolled steel sheet after local rapid heating and before primary annealing) was subjected to primary annealing (decarburization annealing). In the primary annealing, the cold-rolled steel sheet was heated at a heating rate of 100°C / sec and held at 830°C for 90 seconds. In the decarburization annealed steel sheet after the primary annealing, many Goss-oriented grains were present in the locally heated region, and these grains also underwent grain growth. On the other hand, almost no Goss-oriented grains were observed in the non-locally heated region.

[0084] The steel sheet after decarburization annealing was further nitrided, and then coated with an annealing separator mainly composed of MgO, followed by secondary annealing. The secondary annealing conditions were a hydrogen-nitrogen atmosphere, a heating rate of 15°C / hour, and a holding time of 1200°C for 20 hours. The resulting steel sheet was subjected to macro-etching to reveal grain boundaries. Observation of the steel sheet after macro-etching at the location corresponding to the localized heated region revealed that multiple secondary recrystallized grains had grown from the location corresponding to the localized heated region, and that secondary recrystallized grains had spread from the center of the location corresponding to the localized heated region. Furthermore, in the location corresponding to the localized heated region, fine grains of 2 mm or less were sometimes observed as traces of the localized heated region, but not in other cases. Although the secondary recrystallized macrostructure may change slightly depending on the local heating conditions, the degree of integration of the Goss orientation can be increased compared to when localized heat treatment is not performed, resulting in increased magnetic permeability and reduced iron loss. This increases the magnetic flux density B of the steel sheet. ８ (magnetic flux density when excited at 800 A / m) was improved. ８ improved from 1.911 T to 1.943 T. It can be confirmed that the crystal orientation of the secondary recrystallization obtained in this way has an extremely small deviation from the ideal Goss orientation.

[0085] (Modification of Electrode 110) FIG. 8 illustrates a modification of the electrode 110. As shown in FIG. 8, the lower electrode 113 provided on the back side of the metal plate 1 may be common to the pair of electrodes 110. Alternatively, the upper electrode 111 provided on the front side of the metal plate 1 may be common to the pair of electrodes 110. In this case, the common electrode 110 is disposed on a base 185 having a shape similar to that of the cylinder mounting base 140. For stable current flow, the common electrode 110 is preferably insulated except for the portion corresponding to the contact position with the upper electrode, or the common electrode 110 is preferably shaped so that only the portion near the contact position is raised. The base drive mechanism 145 reciprocates the base 185 at least in the thickness direction of the metal plate 1. One of the pair of electrodes 110 may be common, not only when an electrode selector 180 is provided as in the illustrated example, but also when an electrode selector 180 is not provided as in the resistance heating device 100 of FIG. 1.

[0086] [Second embodiment: continuous current application method using rotating electrodes] (Current heating device 200) Next, the configuration of a current application heating device 200 for metal sheets for electromagnetic steel sheets according to a second embodiment of the present invention will be described with reference to Figs. 9 and 11. Fig. 9 is a side view schematically showing the configuration and operation of the current application heating device 200 for metal sheets for electromagnetic steel sheets according to this embodiment. Fig. 11 is a block diagram showing the functional configuration of the current application heating device for metal sheets for electromagnetic steel sheets according to this embodiment. Note that in Fig. 11, as in Fig. 2, components other than the functional components (electrodes, cylinder, cylinder mounting base, power supply) are also shown as blocks for ease of explanation.

[0087] As shown in Figures 9 and 11, the electric heating device 200 according to this embodiment is an electric current device including a pair of upper and lower electrode groups that are fixed to a rotating shaft and rotate in synchronization with the material passing speed of the metal sheet for electromagnetic steel sheet, and mainly includes a pair of electrodes 210, conveying rolls 220, a cylinder 230, a cylinder drive mechanism 235, a cylinder mounting base 240, a base drive mechanism 245, an electric current control mechanism 250, a power source 260, a power supply circuit, and a bypass electric current circuit.

[0088] The pair of electrodes 210 are electrodes that are in locally dispersed contact with the metal sheet 1 for an electrical steel sheet after cold rolling and before primary recrystallization annealing, sandwiching the metal sheet 1 from the front and back sides, and pass current through the metal sheet 1. The pair of electrodes 210 consists of an upper electrode 211 arranged on the front side of the metal sheet 1 and a lower electrode 213 arranged on the back side of the metal sheet. The upper electrode 211 and the lower electrode 213 are each fixedly installed on a substantially cylindrical cylinder mounting base 240 having a rotation axis, and rotate in synchronization with the passing speed of the metal sheet 1. Furthermore, the upper electrodes 211 and the lower electrodes 213, i.e., the counter electrodes 110, are each arranged at predetermined intervals (i.e., at equal intervals) across the entire width of the metal sheet 1 in the width direction of the metal sheet 1. Furthermore, the upper electrodes 211 and the lower electrodes 213 may each be arranged at equal intervals along the circumferential direction of the cylinder mounting base 240. Furthermore, by arranging a plurality of upper electrodes 211 and lower electrodes 213 as described above and rotating the pair of electrodes 210 in synchronization with the speed at which the metal sheet 1 passes, it is possible to perform spot heating by the electrodes 210 over the entire surface of the metal sheet 1. In other words, it is possible to heat in a pattern suitable for non-oriented electrical steel sheets, as in the heating pattern shown in Fig. 3. As a result, seed crystals can be generated over the entire surface of the metal sheet 1.

[0089] The electrode 210 preferably has a curved tip so that it can maintain stable point contact with the metal plate 1 for a predetermined period of time while rotating along the rotation axis and so as not to scratch the steel plate.

[0090] The material and cooling mechanism of the electrode 210 are the same as those of the electrode 110 according to the first embodiment described above, and therefore detailed description thereof will be omitted.

[0091] Furthermore, the configurations and functions of the transport roll 220, the cylinder 230, and the cylinder drive mechanism 235 are similar to those of the transport roll 120, the cylinder 130, and the cylinder drive mechanism 135 according to the first embodiment, respectively, and therefore detailed description thereof will be omitted. Note that Fig. 9 (and Fig. 10 described later) shows an example in which the cylinder 230 is a spring cylinder.

[0092] The cylinder mounting base 240 has a substantially cylindrical shape with a rotation axis in the width direction of the metal plate 1 and multiple cylinders 230 arranged thereon. Specifically, for example, the multiple cylinders 230 are arranged at predetermined intervals in the width direction of the metal plate 1 (the rotation axis direction of the cylinder mounting base 240). Furthermore, on the cylindrical side surface of the cylinder mounting base 240, only one set of cylinders 230 (a set of multiple cylinders 230 arranged at the same circumferential position in the rotation axis direction) may be arranged in the circumferential direction, or multiple sets of cylinders 230 may be arranged at predetermined intervals in the circumferential direction. Note that FIG. 4 shows an example in which four sets of cylinders 230 are arranged in the circumferential direction. The predetermined circumferential intervals between the cylinders 230 (calculated as the central angle around the rotation axis; the same applies to the second embodiment) correspond to the circumferential intervals between the upper electrodes 211 (or lower electrodes 213) and are approximately the same as the circumferential intervals between the upper electrodes 211 (or lower electrodes 213). Furthermore, the electrode 210 and the cylinder mounting base 240 must also be insulated from each other.

[0093] The base drive mechanism 245 rotates the cylinder mounting base 240 along its rotation axis, whereby the electrode 210 attached to the cylinder 230 transitions from a state of contacting the surface of the metal plate 1 at an oblique angle θ to a state of contacting the surface of the metal plate 1 perpendicularly as the cylinder mounting base 240 rotates, and then returns to a state of contacting the surface of the metal plate 1 at the same angle θ again, before being separated from the metal plate 1.

[0094] The current control mechanism 250 controls the current flow by contacting a pair of electrodes 210 (upper electrode 211 and lower electrode 213) on the front and back sides of the metal sheet 1 at predetermined positions, passing current through the electrodes 210 for a predetermined time, and then separating the electrodes 210 from the metal sheet 1. In the current heating device 200, the current control mechanism 250 controls the current flow so that spot heating is performed across the entire width of the metal sheet 1. Specifically, the current control mechanism 250 repeats the current flow control described above using the electrodes 210, thereby performing spot heating at multiple positions spaced apart by predetermined intervals in the longitudinal and width directions of the metal sheet 1 across the entire strip of the metal sheet 1. As a result, the metal sheet 1 is heated in a heating pattern suitable for non-oriented electrical steel sheets, in which spot heated portions HP are arranged in a grid pattern, as in the heating pattern shown in FIG. 3 . As a result, seed crystals of recrystallized grains having the Goss orientation can be formed at a plurality of positions spaced at predetermined intervals in the longitudinal and width directions of the metal sheet 1 over the entire strip of the metal sheet 1 .

[0095] The current control mechanism 250 includes a current control unit 251, a drive control unit 253, and a pressure adjustment unit 255. The current control unit 251 is connected to each electrode 210 and controls the amount and timing of current flow to each electrode 210. The drive control unit 253 controls the operation of the cylinder drive mechanism 235 and the base drive mechanism 245. The pressure adjustment unit 255 adjusts the pressure when the pair of electrodes 210 (the upper electrode 211 and the lower electrode 213) are brought into contact with the metal plate 1. The drive control unit 253 controls the operation of the cylinder drive mechanism 235 and the base drive mechanism 245 so that the electrode 210 contacts the metal plate 1 at the pressure adjusted by the pressure adjustment unit 255. Note that in this embodiment, current is not applied to all of the portions of the electrode 210 that are in contact with the metal plate 1. Instead, current is applied only from the time when the pressure at which the electrode 210 contacts the metal plate 1 reaches a predetermined pressure after the electrode 210 contacts the metal plate 1, while maintaining a pressure equal to or greater than the predetermined pressure.

[0096] The power supply 260 supplies to the electrode 210 electric power capable of heating the metal plate 1 from a temperature above room temperature to an ultimate temperature of 450° C. to 1000° C. at a rate of 2,000° C. / sec to 100,000° C. / sec. The amount of current flowing from the power supply 260 to the electrode 210 is controlled by the current control unit 251 described above.

[0097] The power supply circuit is a circuit that is configured by connecting the pair of electrodes 210 and the power supply 260 with flexible electric wires 270 or the like, and is therefore configured of the upper electrode 211, the lower electrode 213, and the power supply 260. The electrode 210 may be connected to the power supply 260 from a sliding brush 241 attached to the rotation shaft of the cylinder mounting base 240 via the flexible electric wires 270 or the like.

[0098] Here, a protection mechanism that equalizes the load on the power supply 260 is required to protect the power supply 260 and ensure stable current flow to the metal plate 1 even when the current flow to the metal plate 1 is intermittent. That is, a large current needs to flow through the power supply circuit to rapidly heat up to a high temperature in a short time. However, as the cylinder mounting base 240 rotates, if a section where current cannot flow is reached, current stops flowing in the power supply circuit, and if a section where current can flow (a section where the electrode 210 contacts the metal plate 1 with a predetermined pressure) is reached, a large current flows in the power supply circuit. Repeated occurrences of this phenomenon place a heavy burden on the power supply 260, resulting in unstable current flow (loss of control, excessive inrush current, etc.), breakdowns, sparks, etc.

[0099] Therefore, in this embodiment, the electric heating device 200 is provided with a bypass current circuit as such a protection mechanism. This bypass current circuit is a dummy load circuit provided in parallel with the power supply circuit. For example, a resistor 277 is connected to the power supply 260 by a flexible wire 270 or the like, resulting in a circuit composed of the resistor 277 and the power supply 260. By providing such a bypass current circuit, current always flows to either the power supply circuit or the bypass current circuit, leveling the load and ensuring stable current flow. The bypass current circuit continuously flows a current that does not place a load on the power supply 260, thereby preventing a sudden large current from flowing through a state where no current is flowing through the circuit (preventing the circuit from going into a shutdown state) and reducing the burden on the power supply 260. When it is desired to pass current to the electrode 210, a resistor 277 may be provided so that the bypass current circuit has a higher resistance than the power supply circuit, making it easier for current to flow to the electrode 210.

[0100] (Modification of Resistance Heating Apparatus 200) Here, a modification of the present embodiment, a resistance heating apparatus 200-2, will be described with reference to Fig. 10. Fig. 10 is a side view schematically showing the configuration and operation of a modification 200-2 of the resistance heating apparatus 200 for metal sheets for electromagnetic steel sheets shown in Fig. 9.

[0101] 10 , in the resistance heating device 200-2, the tip of the lower electrode 213-2 has a plate-like shape parallel to the metal plate 1, and the contact between the lower electrode 213-2 and the metal plate 1 is surface contact rather than point contact, which is different from the lower electrode 213 in the above-described resistance heating device 200. The lower electrode 213-2 is attached to the tip of a rod 233 inside a cylinder 230, and can be extended and retracted by the cylinder 230. The lower electrode 213-2 may be extended by the cylinder 230 when current is applied so that it comes into contact with the metal plate 1, or it may be in a state where it is always in contact with the metal plate 1 and current is applied only while the upper electrode 211 is in contact with the metal plate 1.

[0102] 10, the cylinder mounting base 240 on the back side of the metal plate 1, on which the cylinder 230 with the lower electrode 213-2 attached is disposed, is shown to have the same shape as the cylinder mounting base 240 on the front side of the metal plate 1. However, since the cylinder mounting base 240 on the back side does not necessarily need to rotate, it may have a plate-like shape similar to the cylinder mounting base 140 according to the first embodiment.

[0103] The other configurations and operations of the electric heating device 200-2 are similar to those of the above-described electric heating device 200, and therefore detailed description thereof will be omitted.

[0104] (Electrical heating method) The electrical heating method for a metal sheet for an electrical steel sheet according to this embodiment includes a preliminary heat treatment step in which, using the electrical heating device 200 according to this embodiment described above, a pair of electrodes 210 is brought into contact with the metal sheet 1 after cold rolling and before primary recrystallization annealing, and an electric current is applied to the electrodes 210 for a predetermined time, thereby heating the metal sheet 1 from a temperature equal to or higher than room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec.

[0105] Specifically, as shown in FIGS. 9 and 11 , when the metal sheet 1 is transported into the electric heating device 200 by the transport rolls 220, the drive control unit 253 controls the base drive mechanism 245, which rotates the cylinder mounting base 240. At this time, the rotation of the cylinder mounting base 240 is synchronized with the passing speed of the metal sheet 1. Furthermore, the drive control unit 253 controls the cylinder drive mechanism 235, which, when the electrodes 210 (upper electrode 211 and lower electrode 213) come into contact with the metal sheet 1, shortens (retreats) the electrodes 210, thereby operating the cylinder 230 so that the electrodes 210 are in contact with the metal sheet 1 for a predetermined time. At this time, the pressure adjustment unit 255 adjusts the pressure at which the electrodes 210 come into contact with the metal sheet 1, and the drive control unit 253 controls the cylinder drive mechanism 235 so that the electrodes 210 come into contact with the metal sheet 1 at the adjusted pressure.

[0106] After the pressure at which the electrode 210 contacts the metal plate 1 reaches a predetermined pressure, a predetermined amount of current is passed through a flexible electric wire 270 connected to the electrode 210 via a sliding brush 241 attached to a cylinder mounting base 240 for a predetermined time, thereby heating the metal plate 1. At this time, the amount of current passed through the electrode 210 via the flexible electric wire 270 and the current passing time are controlled by a current control unit 251 so that the metal plate 1 is heated from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec. In FIG. 9 , the period during which current is passed through the electrode 210 is indicated by a double-headed arrow. In this embodiment, current is not passed throughout the entire time the electrode 210 is in contact with the metal plate 1, but is passed only from the time when the pressure at which the electrode 210 contacts the metal plate 1 reaches a predetermined pressure until the pressure equal to or higher than the predetermined pressure is reached (while the electrode 210 is positioned as indicated by the double-headed arrow in FIG. 9 ). By heating the metal plate 1 in this manner, seed crystals that serve as nuclei for the growth of recrystallized grains can be produced.

[0107] After heating is completed, the drive control unit 253 controls the base drive mechanism 245, which further rotates the cylinder mounting base 240, and also controls the cylinder drive mechanism 235, which operates the cylinder 230 to gradually extend the electrode 210 (upper electrode 211 and lower electrode 213) as the cylinder mounting base 240 rotates, and may continue to keep it in contact with the metal plate 1 for a predetermined period of time.

[0108] Here, when it is necessary to maintain the temperature of the metal plate 1 for a short period of time, as described above, current is passed through the electrode 210 while it is in contact with the metal plate 1 to maintain the temperature, or the electrode 210 itself is maintained at its heating temperature without passing current through it. Also, as in the first embodiment described above, the electrode 210 in contact with the metal plate 1 may be rapidly cooled immediately after the heating by passing current through it.

[0109] The current supply method in the resistance heating method according to this embodiment is a method in which the electrode 210 intermittently contacts the metal plate 1 while rotating and moves while being in contact with the metal plate 1 and conducting current. In this embodiment, no current flows through the circuit while no current is being applied to the metal plate 1. Although current may be applied by turning the power supply on and off, in the case of the resistance heating method according to this embodiment, since the current application time is short, if the rise time until the current reaches a predetermined set current cannot be ignored, as described above, a certain amount of current flows through the bypass current supply circuit even while no current is being applied to the metal plate 1 so as not to place a load on the power supply 260.

[0110] (Method for manufacturing an electromagnetic steel sheet) The method for manufacturing an electromagnetic steel sheet according to this embodiment includes a cold rolling step and a primary recrystallization annealing step, and further includes the above-mentioned preliminary heat treatment step after the cold rolling step and before the primary recrystallization annealing step. Each step in the method for manufacturing an electromagnetic steel sheet according to this embodiment is the same as that of the first embodiment described above, except for the configuration of the electric heating device 200 used in the preliminary heat treatment step, more specifically, the arrangement of the electrodes 210, which is different from the arrangement of the electrodes 110 according to the first embodiment, the shape of the cylinder mounting base 240, which is different from the cylinder mounting base 140 according to the first embodiment, and the inclusion of a bypass current circuit 275, and so detailed description thereof will be omitted.

[0111] The electrical steel sheet according to this embodiment manufactured through the above-described steps, like the first embodiment, produces a large number of seed crystals having the Goss orientation in the preliminary heat treatment step, and recrystallized grains grow from these seed crystals as nuclei, resulting in a steel sheet with a large number of Goss-oriented grains produced within the metal sheet surface, which allows for dramatically improved magnetic properties of the electrical steel sheet.

[0112] [Third embodiment: other current application method using rotating electrodes] (Current heating device 300) Next, the configuration of a current application heating device 300 for metal sheets for electromagnetic steel sheets according to a third embodiment of the present invention will be described with reference to Figs. 12 to 14. Fig. 12 is a side view schematically showing the configuration of the current application heating device 300 for metal sheets for electromagnetic steel sheets according to this embodiment. Fig. 13 is a block diagram showing the functional configuration of the current application heating device for metal sheets for electromagnetic steel sheets according to this embodiment. Note that in Fig. 13, as in Fig. 2 and other figures, components other than the functional components (electrodes, current-carrying rolls, power supply) are also shown as blocks for ease of explanation. Fig. 14 is a top view showing an example of an upper electrode.

[0113] As shown in Figures 12 and 13, the electric heating device 300 according to this embodiment is an electric current device including a pair of upper and lower electrode groups that are provided on the surface of a rotating electric current roll, and is mainly equipped with a pair of electrodes 310, a transport roll 320, electric current rolls 330 and 332, a roll drive mechanism 340, an electric current control mechanism 350, a power source 360, and a power supply circuit.

[0114] The pair of electrodes 310 are electrodes that are in localized dispersed contact with the metal sheet 1 for an electrical steel sheet after cold rolling and before primary recrystallization annealing, sandwiching the metal sheet 1 from the front and back sides, and pass current through the metal sheet 1, and consist of an upper electrode 311 arranged on the front side of the metal sheet 1 and a lower electrode 313 arranged on the back side of the metal sheet.

[0115] The upper electrode 311 is provided on the circumferential surface of a substantially cylindrical current-carrying roll 330 having a rotation axis in the width direction of the metal sheet 1, and rotates as the current-carrying roll 330 rotates. The upper electrodes 311 are insulated from each other by an insulating layer 331. For example, as shown in FIG. 14(A), a plurality of upper electrodes 311 are arranged at predetermined intervals (i.e., at equal intervals) across the entire width of the metal sheet 1 in the width direction of the metal sheet 1. However, as shown in FIG. 14(B), a single upper electrode 211 may be arranged across the entire width of the metal sheet 1 in the width direction of the metal sheet 1. Alternatively, a plurality of upper electrodes 211 may be arranged at equal intervals in the circumferential direction of the current-carrying roll 330, i.e., along the peripheral surface.

[0116] The lower electrode 313 is, for example, common to the counter electrodes 310 and is provided so as to cover the entire peripheral surface of a substantially cylindrical current-carrying roll 330 having a rotation axis in the width direction of the metal sheet 1. The lower electrode 313 may rotate in synchronization with the material passing speed of the metal sheet 1, or may not rotate at all. When the lower electrode 313 does not rotate, it may be configured similarly to the lower electrode 213-2 of the above-described resistance heating device 200-2.

[0117] By arranging the upper electrode 311 and the lower electrode 313 as described above and rotating at least the upper electrode 311, it is possible to perform point heating or line heating by the electrode 310 over the entire surface of the metal plate 1. As a result, it is possible to generate seed crystals over the entire surface of the metal plate 1.

[0118] The material and cooling mechanism of the electrode 310 may be the same as those of the electrode 110 according to the first embodiment described above.

[0119] Furthermore, the configuration of the transport roll 320 is the same as that of the transport roll 120 according to the first embodiment, and therefore a detailed description thereof will be omitted.

[0120] The current-carrying roll 330 has a substantially cylindrical shape with a rotation axis in the width direction of the metal sheet 1, and a plurality of upper electrodes 311 are provided on the circumferential surface, with the upper electrodes 311 being insulated from one another by an insulating layer 331. In the current-carrying roll 330, the plurality of upper electrodes 311 are provided, for example, at predetermined intervals in the width direction of the metal sheet 1 (the direction of the rotation axis of the current-carrying roll 330). In addition, in the current-carrying roll 330, only one upper electrode 311 may be provided in the circumferential direction, or multiple upper electrodes 311 may be provided at predetermined intervals in the circumferential direction. Note that FIG. 12 shows an example in which four upper electrodes 311 are arranged in the circumferential direction.

[0121] The current-carrying roll 330 can be fabricated, for example, as follows: A conductive cylindrical member is prepared, and a portion of the circumferential surface of the cylindrical member is ground to form convex portions that will become the upper electrodes 311 on the circumferential surface. Next, an insulating material such as alumina or zirconia is sprayed onto the cylindrical member, and the member is polished to form an insulating layer 331 that exposes the upper electrodes 311, which are the current-carrying portions. This completes the current-carrying roll 330. Note that after forming the convex portions that will become the upper electrodes 311, the spaces between the convex portions may be made into the insulating layer 331 without spraying the insulating material. However, spraying the insulating material as described above and then polishing the convex portions is preferable because this stabilizes current flow from the upper electrodes 311 and prevents the convex portions from causing scratches on the metal sheet 1.

[0122] The current-carrying roll 332 has a substantially cylindrical shape with a rotation axis in the width direction of the metal sheet 1 , and its peripheral surface serves as the lower electrode 313 .

[0123] The roll drive mechanism 340 rotates the current-carrying rolls 330, 332 along their rotation axes. Due to the rotation by the roll drive mechanism 340, the upper electrode 311 provided on the current-carrying roll 330 contacts the sheet surface of the metal sheet 1 and then separates from it. However, the lower electrode 313 remains in contact with the sheet surface of the metal sheet 1. The roll drive mechanism 340 also reciprocates the current-carrying rolls 330, 332 in the thickness direction of the metal sheet 1. This allows the current-carrying rolls 330, 332 to contact or separate from the front or back surface of the metal sheet 1, and also allows the contact pressure between the current-carrying rolls 330, 332 and the metal sheet 1 to be changed.

[0124] The current control mechanism 350 controls the current flow by contacting a pair of electrodes 310 (upper electrode 311 and lower electrode 313) on the front and back sides of the metal sheet 1 at predetermined positions, passing current through the electrodes 310 for a predetermined time, and then separating the electrodes 310 from the metal sheet 1. In the current heating device 300, when the upper electrode 311 is provided as shown in FIG. 14 , the current control mechanism 350 controls the current flow so that spot heating is performed across the entire width of the metal sheet 1. Specifically, the current control mechanism 350 repeats the current flow control described above using the electrodes 310, thereby performing spot heating at multiple positions spaced apart by predetermined intervals across the entire strip of the metal sheet 1, for example, in the longitudinal and width directions of the metal sheet 1. As a result, the metal sheet 1 is heated in a heating pattern suitable for non-oriented electrical steel sheets, in which spot heated portions HP are arranged in a grid pattern, as in the heating pattern shown in FIG. 3 . As a result, seed crystals of recrystallized grains having the Goss orientation can be formed at a plurality of positions spaced at predetermined intervals in the longitudinal and width directions of the metal sheet 1 over the entire strip of the metal sheet 1. Note that although the metal sheet 1 may be heated in a heating pattern in which the spot heated portions are arranged randomly, by heating the metal sheet 1 in a heating pattern in which the spot heated portions are arranged in a lattice pattern as described above, the material properties of the manufactured non-oriented electrical steel sheet can be made uniform.

[0125] The current control mechanism 350 has a current control unit 351, a drive control unit 353, and a pressure adjustment unit 355. The current control unit 351 is connected to each electrode 310, and controls the amount and timing of current flowing through each electrode 310. The drive control unit 353 also controls the operation of the roll drive mechanism 340. The pressure adjustment unit 355 also adjusts the pressure when the pair of electrodes 310 (upper electrode 311 and lower electrode 313) are brought into contact with the metal plate 1. The drive control unit 353 controls the operation of the roll drive mechanism 340 so that the electrodes 310 come into contact with the metal plate 1 at the pressure adjusted by the pressure adjustment unit 355.

[0126] The power supply 360 supplies to the electrode 310 electric power capable of heating the metal plate 1 from a temperature above room temperature to an ultimate temperature of 450° C. to 1000° C. at a rate of 2,000° C. / sec to 100,000° C. / sec. The amount of current flowing from the power supply 360 to the electrode 310 is controlled by the current control unit 351 described above.

[0127] The power supply circuit is a circuit configured by connecting the pair of electrodes 310 and the power supply 360 with flexible electric wires 370 or the like, and is therefore configured of the upper electrode 311, the lower electrode 313, and the power supply 360. The electrode 310 may be connected to the power supply 360 from a sliding brush 371 attached to the rotation shaft of the current-carrying rolls 330 and 332 through the flexible electric wires 370 or the like.

[0128] In this embodiment, a bypass energization circuit may be provided, similar to the second embodiment.

[0129] (Electrical heating method) The electrical heating method for a metal sheet for an electrical steel sheet according to this embodiment includes a preliminary heat treatment step in which, using the electrical heating device 300 according to this embodiment described above, a pair of electrodes 310 is brought into contact with the metal sheet 1 after cold rolling and before primary recrystallization annealing, and an electric current is applied to the electrodes 310 for a predetermined time, thereby heating the metal sheet 1 from a temperature equal to or higher than room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec.

[0130] Specifically, when the metal sheet 1 is transported into the electric heating device 300 by the transport rolls 320, the drive control unit 353 controls the roll drive mechanism 340, which rotates the electric rolls 330 and 332. At this time, the rotation of the electric rolls 330 and 332 is synchronized with the passage of the metal sheet 1. Furthermore, the drive control unit 353 controls the roll drive mechanism 340, and when the upper electrode 311 contacts the metal sheet 1, the cylinder drive mechanism 235 stops the rotation of the electric rolls 330 and 332 in synchronization with the stopping of the passage of the metal sheet 1, thereby keeping the electrode 210 in contact with the metal sheet 1 for a predetermined time. At this time, the pressure adjustment unit 355 adjusts the pressure at which the electrode 310 contacts the metal sheet 1, and the drive control unit 353 controls the roll drive mechanism 340 so that the electrode 310 contacts the metal sheet 1 at the adjusted pressure.

[0131] After the pressure at which the electrode 310 contacts the metal plate 1 reaches a predetermined pressure, a predetermined amount of current is passed through a flexible electric wire 370 connected to the electrode 310 via a sliding brush 371 attached to the current-carrying rolls 330 and 332 for a predetermined time, thereby heating the metal plate 1. At this time, the amount of current passed through the flexible electric wire 370 and the time for passing the current are controlled by a current control unit 351 so that the metal plate 1 is heated from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec.

[0132] After the heating is completed, the drive control unit 353 controls the roll drive mechanism 340, and the roll drive mechanism 340 resumes the rotation of the conductive rolls 330, 332 in accordance with the resumption of the passage of the metal plate 1, thereby separating the upper electrode 311 from the metal plate 1.

[0133] Here, if it is necessary to maintain the temperature of the metal sheet 1 for a short period of time after the current-carrying heating, current is passed through the electrode 110 while it is in contact with the metal sheet 1 before the rotation of the current-carrying rolls 330, 332 is resumed, or the electrode 110 is kept in contact with the metal sheet 1 and no current is passed through the electrode 110, thereby maintaining the temperature at the heating temperature of the electrode 110 itself. Also, as in the first embodiment described above, the electrode 310 in contact with the metal sheet 1 may be rapidly cooled immediately after the current-carrying heating. Note that, when the metal sheet 1 is moved by the payout device and the winding device and the current-carrying rolls 330, 332 rotate following the rotation of the metal sheet 1, the roll drive mechanism 340 does not need to have a function to rotate the current-carrying rolls 330, 332.

[0134] The current flow method in the electric heating method according to this embodiment is a method in which the passage of the metal plate 1 and the rotation of the electrode 310 are temporarily stopped each time the rotating electrode 310 comes into contact with the metal plate 1 in order to allow current to flow.

[0135] (Method for manufacturing an electrical steel sheet) The method for manufacturing an electrical steel sheet according to this embodiment includes a cold rolling step and a primary recrystallization annealing step, and further includes the above-mentioned preliminary heat treatment step after the cold rolling step and before the primary recrystallization annealing step. Each step in the method for manufacturing an electrical steel sheet according to this embodiment is the same as that in the first embodiment described above, except for the configuration of the electric heating device 300 used in the preliminary heat treatment step, and therefore detailed description thereof will be omitted.

[0136] The electrical steel sheet according to this embodiment manufactured through the above-described steps, like the first embodiment, produces a large number of seed crystals having the Goss orientation in the preliminary heat treatment step, and recrystallized grains grow from these seed crystals as nuclei, resulting in a steel sheet with a large number of Goss-oriented grains produced within the metal sheet surface, which allows for dramatically improved magnetic properties of the electrical steel sheet.

[0137] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention.

[0138] The effects of the present invention will be specifically explained using examples. The conditions in the examples are examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0139] A steel (steel type A) containing 0.06 mass% C, 3.4 mass% Si, 0.10 mass% Mn, 0.006 mass% S, 0.026 mass% Al, and 0.008 mass% N was hot-rolled and cold-rolled to form a cold-rolled steel sheet having a thickness of 0.22 mm. This steel sheet was subjected to localized rapid heating as the preliminary heat treatment described in the above embodiment.

[0140] In the localized, dispersed-contact resistance heating (spot resistance heating), a copper electrode with a diameter of 3 mm was used in the contact area with the steel sheet, and the electrode shape, electrode pressure, current, current application time, and electrode holding time after current application were varied in a complex manner to control the heating rate, maximum temperature, and holding time from the time the maximum temperature was reached until cooling to 700°C (holding time at 700°C or higher). Specific conditions are shown in Table 1 below. Note that "untreated" in the table indicates that localized rapid heating was not performed.

[0141] The manufactured steel sheets were measured based on EBSD (Electron Backscattering Diffraction Pattern) to confirm the presence of Goss-oriented grains having a grain size of 5 μm or more. The EBSD measurement was performed on a plane parallel to the steel sheet surface and 20 μm in the sheet thickness direction, and the IQ (Image Quality) value and crystal orientation were measured in 0.5 μm steps in a region including the locally heated region.

[0142] The "rolling direction spacing" and "width direction spacing" in Table 1 represent the spacing in the rolling direction and the direction perpendicular to the rolling direction at which the localized heated regions are arranged on the plate surface of the cold-rolled steel plate. The localized heated regions are evenly arranged at equal intervals in the rolling direction and the direction perpendicular to the rolling direction. For example, if both the "rolling direction spacing" and the "width direction spacing" are 100 mm or less, localized heated regions are arranged in all the divided sections. On the other hand, if either the "rolling direction spacing" or the "width direction spacing" exceeds 100 mm, there are divided sections in which no localized heated regions are arranged. Note that, among all the divided sections, the divided sections having localized heated regions are arranged so as not to be unevenly distributed.

[0143] Furthermore, in Table 1, the "locally heated section ratio" of the local heating conditions represents the area ratio of the divided sections in which the locally heated regions are arranged on the sheet surface of the cold-rolled steel sheet. Specifically, a 100 mm x 100 mm area on the sheet surface is defined as a divided section, and when it is confirmed for at least 100 divided sections whether the locally heated regions are arranged within these divided sections, the value obtained by dividing the sum of the areas of the divided sections in which the locally heated regions are arranged by the area of ​​all the divided sections corresponds to the "locally heated section ratio," and the value is shown as a percentage in Table 1.

[0144]

[0145] The produced cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Table 2 below. In the decarburization annealing, the degree of oxidation (PH) in the annealing atmosphere (furnace atmosphere) was measured. ２ O / PH ２) was set to 0.13. Furthermore, the decarburization-annealed steel sheet was nitrided at 750°C in a nitrogen-hydrogen-ammonia atmosphere to set the nitrogen content of the steel sheet to 220 ppm. Furthermore, an annealing separator mainly composed of MgO was applied, and finish annealing was performed. In the finish annealing, the steel sheet was heated to 1000°C at a heating rate of 15°C / hour in a mixed atmosphere of hydrogen and nitrogen, and then heated to 1200°C under the following conditions, and held at 1200°C for 20 hours in a hydrogen atmosphere. Normal: Heat from 1000°C to 1200°C at a rate of 15°C / hour

[0146] After the final annealing, the steel sheets were coated with an insulating coating solution mainly composed of colloidal silica and phosphate, with chromic anhydride added as needed, and baked to form an insulating coating. The obtained electrical steel sheets were evaluated for various properties. The evaluation results are shown in Table 2 below. Specifically, the magnetic flux density B ８ (magnetic flux density when excited at 800 A / m) and iron loss W １７／５０ (power loss per unit weight at an AC frequency of 50 Hz and an excitation magnetic flux density of 1.7 T) was evaluated.

[0147]

[0148] Among Nos. 1 to 14, the steel sheets according to the present invention have a magnetic flux density B ８ , iron loss W １７／５０ Specifically, the magnetic flux density B ８ is 1.920 or more, iron loss W １７／５０ On the other hand, in the steel sheet of the comparative example, the magnetic flux density B ８ , iron loss W １７／５０ was in a lower position.

[0149] INDUSTRIAL APPLICABILITY The present invention is useful for an electric heating device and an electric heating method for metal sheets for electromagnetic steel sheets having excellent magnetic properties, and for a method for manufacturing electromagnetic steel sheets.

[0150] 1 Metal plate for electromagnetic steel plate 100, 200, 200-2, 300 Electric heating device 110, 210, 310 Electrode 111, 211, 311 Upper electrode 113, 213, 313-2, 313 Lower electrode 118 Cavity 119 Cooling pipe 120, 220, 320 Transport roll 130, 230 Cylinder 135, 235 Cylinder drive mechanism 140, 240 Cylinder mounting base 145, 245 Base drive mechanism 150, 250, 350 Current control mechanism 151, 251, 351 Current control unit 153, 253, 353 Drive control unit 155, 255, 355 Pressure adjustment unit 160, 260, 360 Power supply 170, 270, 370 Flexible wire 180 Electrode selection unit 275 Bypass current supply circuit 330, 332 Current supply roll 340 Roll drive mechanism

Claims

1. An electric heating device for metal sheet for electrical steel sheet, comprising: a pair of electrodes that are in locally dispersed contact with the front and back sides of a metal sheet for electrical steel sheet after cold rolling and before primary recrystallization annealing, sandwiching the metal sheet and passing current through the metal sheet; a current control mechanism that controls the current flow by bringing the pair of electrodes into contact with the front and back sides of the metal sheet at predetermined positions on the metal sheet and separating the electrodes from the metal sheet after passing current through them for a predetermined time; a power source that can heat the metal sheet from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec; and a power supply circuit that connects the electrodes and the power source.

2. The electric heating device for metal sheets for electromagnetic steel sheets according to claim 1, further comprising: a cylinder to which the electrodes are attached in an insulated state; a cylinder mounting base on which a plurality of the cylinders are arranged and which is parallel to the metal sheet; a cylinder drive mechanism that extends and retracts the electrodes attached to the cylinders to bring them into contact with and away from the metal sheet; and a base drive mechanism that moves the cylinder mounting base back and forth at least in the thickness direction of the metal sheet, wherein the current control mechanism has a drive control unit that controls the operation of the cylinder drive mechanism and the base drive mechanism, and a pressure adjustment unit that adjusts the pressure when the pair of electrodes are brought into contact with the metal sheet.

3. The electric heating device for metal sheets for electrical steel sheets according to claim 2, further comprising an electrode selection unit that selects the electrodes to which electricity is to be applied from the power source.

4. An electric heating device for metal sheets for electromagnetic steel sheets as set forth in claim 1, further comprising: a cylinder to which the electrodes are attached in an insulated state; a substantially cylindrical cylinder mounting base on which a plurality of the cylinders are arranged and which has a rotation axis in the width direction of the metal sheet; a cylinder drive mechanism that extends and retracts the electrodes attached to the cylinder to bring them into contact with and away from the metal sheet; and a base drive mechanism that rotates the cylinder mounting base along the rotation axis, wherein the current control mechanism has a drive control unit that controls the operation of the cylinder drive mechanism and the base drive mechanism, and a pressure adjustment unit that adjusts the pressure when the pair of electrodes are brought into contact with the metal sheet.

5. The electrical heating device for metal sheets for electromagnetic steel sheets according to claim 4, further comprising a bypass current circuit provided in parallel with the power supply circuit.

6. An electric heating device for metal sheets for electromagnetic steel sheets as described in claim 1, further comprising: a substantially cylindrical current-carrying roll having a plurality of electrodes provided on its circumferential surface, the electrodes being insulated from each other, and having a rotation axis in the width direction of the metal sheet; and a roll drive mechanism for reciprocating the current-carrying roll at least in the thickness direction of the metal sheet, wherein the current control mechanism has a drive control unit for controlling the operation of the roll drive mechanism, and a pressure adjustment unit for adjusting the pressure when the pair of electrodes are brought into contact with the metal sheet.

7. An electric heating device for metal sheets for electromagnetic steel sheets according to any one of claims 1 to 6, further comprising a metal sheet transport mechanism for passing the metal sheet strip through the electric heating device.

8. The electric heating device for metal sheets for electromagnetic steel sheets according to any one of claims 2 to 5, wherein the cylinder is a spring cylinder, an air cylinder, a hydraulic cylinder or an electric cylinder.

9. An electric heating device for metal sheets for electromagnetic steel sheets according to any one of claims 1 to 3 and 6, comprising a plurality of pairs of electrodes, and wherein the electrode provided on the front side of the metal sheet or the electrode provided on the back side of the metal sheet is common to a plurality of pairs of electrodes.

10. An electric heating device for metal sheets for electromagnetic steel sheets as described in any one of claims 1 to 6, wherein the current control mechanism controls the current so that spot heating is performed across the entire width of the metal sheet.

11. An electric heating device for metal sheets for electromagnetic steel sheets according to any one of claims 1 to 6, wherein the current control mechanism controls the current so that spot heating is performed only on the widthwise ends of the metal sheet.

12. An electric heating device for metal sheets for electromagnetic steel sheets according to any one of claims 1 to 3, wherein the current control mechanism keeps the electrodes in contact with the metal sheets for a predetermined period of time even after current is passed through.

13. An electric heating device for metal sheets for electromagnetic steel sheets as described in claim 12, wherein the electrodes have a flow path at their base ends through which a cooling medium flows to cool the electrodes, and the tip ends are formed in a columnar shape that is thinner than the base ends.

14. A method for applying electrical current to a metal sheet for use in an electrical steel sheet after cold rolling and before primary recrystallization annealing, comprising the steps of: using an electrical heating device for metal sheets for use in an electrical steel sheet as defined in any one of claims 1 to 6, bringing the electrodes into contact with the metal sheet, and applying electricity to the electrodes for a predetermined period of time, thereby heating the metal sheet from a temperature above room temperature to an ultimate temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec.

15. A method for producing an electromagnetic steel sheet, comprising the steps of: cold-rolling a metal sheet for use in an electromagnetic steel sheet; and subjecting the metal sheet after the cold rolling to primary recrystallization annealing, which also serves as decarburization annealing, characterized in that the method further comprises, after the cold rolling and before the primary recrystallization annealing, a step of heat-treating the metal sheet by the method for applying electrical heating to a metal sheet for use in an electromagnetic steel sheet as defined in claim 14.

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