Heating device and heating method for metal plate for electrical steel sheet, and method for manufacturing electrical steel sheet

Abstract

The present invention generates a large amount of seed crystals having a Goss orientation in a crystal structure before the primary recrystallization at an end part in the width direction of a metal plate for an electrical steel sheet. According to the present invention, an electrical conduction heating device (100) for a metal plate for an electrical steel sheet is provided with: a conveyance roll (110) for passing a band plate of a metal plate (1) for an electrical steel sheet after cold rolling and before primary recrystallization annealing; a first electrical conduction roll pair (120) for holding the metal plate (1) to be passed through at a predetermined pressure from both of the front surface side and the back surface side; a second electrical conduction roll pair (130) for holding the metal plate (1) to be passed through at a predetermined pressure from both of the front surface side and the back surface side, the second electrical conduction roll pair (130) being installed at a predetermined distance from the first energization roll pair (120) in the passing direction of the metal plate (1); and a high-frequency power supply (140) which is connected to the first electrical conduction roll pair (120) and the second electrical conduction roll pair (130) and is capable of heating the end part in the width direction of the metal plate (1) from a temperature that is equal to or higher than room temperature to a final temperature of 450°C to 1,000°C by means of a high-frequency current at a rate of 2,000°C / sec to 100,000°C / sec.

Description

Heating device and heating method for metal sheets for electromagnetic steel sheets, and manufacturing method for electromagnetic steel sheets

[0001] The present invention relates to a heating device and a heating method for metal sheets for electrical steel sheets, and a manufacturing method for 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 number of Goss-oriented grains, which have excellent magnetic properties, are present at the time of primary recrystallization. On the other hand, if a large number of Goss-oriented grains are generated in the crystalline structure after primary recrystallization, it is believed that the magnetic properties can be dramatically improved compared to conventional methods. Furthermore, as described below, it has been confirmed that the crystal grains grow from the edges toward the center of the metal sheet for electrical steel sheets, improving the magnetic properties.

[0008] As a result of extensive research conducted by the present inventors from the above viewpoints, as will be described in detail later, a new finding has been reached: by locally ultra-rapidly heating a metal sheet for 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 at the end portions of the metal sheet in the crystalline structure before primary recrystallization.

[0009] Patent Document 1 discloses a technique for partially and rapidly heating a cold-rolled steel sheet in 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 purpose. However, since heating by laser irradiation or electron beam irradiation is surface heating, only the surface of the steel sheet is heated preferentially, and the interior of the steel sheet is not easily heated. Furthermore, since heat is removed quickly after heating and it is difficult to maintain the temperature, this method may not be suitable as a means for locally heating metal sheets for electrical steel sheets. In particular, from the viewpoint that maintaining heat immediately after heating facilitates the growth of well-oriented Goss grains and results in a steel sheet suitable for grain-oriented electrical steel sheets, the heating method described in Patent Document 1, which removes heat quickly, is not suitable for the production of grain-oriented electrical steel sheets.

[0010] The present invention has been made in view of the above points, and aims to provide a heating device and a heating method for metal sheets for electrical steel sheets, and a method for manufacturing electrical steel sheets, which are capable of generating a large number of seed crystals having the Goss orientation at the sheet end portions in a crystalline structure before primary recrystallization.

[0011] In order to achieve the above object, the present invention provides a heating device for a metal sheet for an electromagnetic steel sheet, the heating device comprising: a conveying mechanism for passing a strip of a metal sheet for an electromagnetic steel sheet after cold rolling and before primary recrystallization annealing; a first pair of current-carrying rolls for holding the passing metal sheet from both the front and back sides with a predetermined pressure; a second pair of current-carrying rolls installed at a predetermined interval from the first pair of current-carrying rolls in the passing direction of the metal sheet and for holding the passing metal sheet from both the front and back sides with a predetermined pressure; and a high-frequency power source connected to the second current-carrying roll pair and capable of heating the end of the metal plate in the width direction of the metal plate 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 using a high-frequency current, wherein the first current-carrying roll pair and the second current-carrying roll pair each have a current-carrying roll that can be energized as at least one of the front and back rolls that make up the current-carrying roll pair.

[0012] According to the present invention, the width direction end portions of the metal plate can be heated at a rate of 2,000°C / sec to 100,000°C / sec from a temperature above room temperature to an ultimate temperature of 450°C to 1,000°C, and at a rate of 100,000°C / sec. This makes it possible to produce a large amount of seed crystals having the Goss orientation in the crystalline structure before primary recrystallization.

[0013] In the heating device for a metal sheet for an electromagnetic steel sheet, the diameter of each of the first pair of current-carrying rolls and the second pair of current-carrying rolls may be 300 mm or less.

[0014] In the heating device for a metal plate for an electromagnetic steel plate, the current-carrying roll may consist of two or more divided rolls divided in the width direction of the metal plate, and the divided rolls may be arranged at least at both ends of the metal plate in the width direction.

[0015] The heating device for the metal sheet for the electromagnetic steel sheet may further include a backup roll that supports the current-carrying roll.

[0016] In the heating device for a metal sheet for an electromagnetic steel sheet, the current-carrying roll may have a cooling mechanism for water-cooling the inside of the roll.

[0017] According to another aspect of the present invention, there is provided a heating device for a metal sheet for an electromagnetic steel sheet, the heating device comprising: a conveying mechanism for passing a strip of metal sheet for an electromagnetic steel sheet after cold rolling and before primary recrystallization annealing; an induction heating unit for induction heating the metal sheet being passed; and a high-frequency power supply connected to the induction heating unit, wherein the induction heating unit heats an end of the metal sheet in the width direction of the metal sheet by using a high-frequency current from the high-frequency power supply to heat an end of 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.

[0018] According to the present invention, the width direction end portions of the metal plate can be heated at a rate of 2,000°C / sec to 100,000°C / sec from a temperature above room temperature to an ultimate temperature of 450°C to 1,000°C, thereby making it possible to produce a large amount of seed crystals having the Goss orientation in the crystalline structure before primary recrystallization.

[0019] In the heating device for metal plates for electromagnetic steel plates, the induction heating unit has a pair of conductors connected to the high-frequency power supply so as to form an induction coil that circles the metal plate passing through and through the inside of the coil, and the pair of conductors includes a front-side conductor installed on the front side of the metal plate and a back-side conductor installed on the back side of the metal plate, and the front-side conductor and the back-side conductor may each be installed so as to cross the metal plate in the width direction when viewed in the thickness direction of the metal plate and so as to be spaced apart from each other in the direction in which the metal plate passes through.

[0020] In the heating device for metal plates for electromagnetic steel plates, the induction heating unit may have an induction coil and a magnetic core that concentrates the magnetic flux generated by the induction coil at the widthwise end of the metal plate so that the magnetic flux penetrates the metal plate in its thickness direction.

[0021] In the electric heating device for metal sheets for electromagnetic steel sheets, the high frequency power source may have a frequency of 1 kHz or more.

[0022] The heating device for metal sheets for electromagnetic steel sheets may further include a holding zone that maintains the temperature of the end portions in the width direction of the metal sheet, which has been heated 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, within a predetermined range for a predetermined period of time.

[0023] The heating device for a metal plate for an electromagnetic steel plate may further include a cooling section that cools the metal plate whose temperature is maintained by the retention zone.

[0024] According to another aspect, the present invention is 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, the method comprising the steps of: using the above-described apparatus for heating a metal sheet for use in an electrical steel sheet by applying electrical current, clamping the metal sheet with the first pair of electrical current-carrying rolls and the second pair of electrical current-carrying rolls at a predetermined pressure; and heating the widthwise ends of 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.

[0025] According to the present invention, a 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, which makes it possible to produce a large amount of seed crystals having the Goss orientation in the crystalline structure before primary recrystallization.

[0026] According to another aspect, the present invention is a method for applying electric current to a metal sheet for use in an electrical steel sheet after cold rolling and before primary recrystallization annealing, the method comprising the step of using the above-described heating device for a metal sheet for use in an electrical steel sheet by induction heating to apply electric current to the induction heating section, thereby heating the widthwise ends of 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.

[0027] According to the present invention, the width direction end portions of the metal plate can be heated at a rate of 2,000°C / sec to 100,000°C / sec from a temperature above room temperature to an ultimate temperature of 450°C to 1,000°C, thereby making it possible to produce a large amount of seed crystals having the Goss orientation in the crystalline structure before primary recrystallization.

[0028] 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, subjecting the cold-rolled metal sheet to primary recrystallization annealing that also serves as decarburization annealing, forming an insulating layer mainly composed of MgO on the surface of the metal sheet after the primary recrystallization annealing, and subjecting the metal sheet with the insulating layer formed thereon to secondary recrystallization 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 heating to a metal sheet for use in an electrical steel sheet.

[0029] According to the present invention, in the process of heat treating the metal sheet (preheat treatment process) using the above-described method for heating a metal sheet for an electrical steel sheet, the widthwise ends of 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 a Goss orientation to be generated in the crystalline structure prior to primary recrystallization. This allows recrystallized grains to grow from the seed crystals as nuclei, resulting in an electrical steel sheet with a high-quality Goss orientation. As a result, the magnetic properties of the electrical steel sheet can be dramatically improved, and excellent metallurgical properties can be obtained.

[0030] According to the present invention, in the manufacturing process of an electrical steel sheet, it is possible to generate a large number of seed crystals having the Goss orientation at the end portions of a metal sheet for an electrical steel sheet in a crystalline structure before primary recrystallization, thereby making it possible to dramatically improve the magnetic properties of the resulting electrical steel sheet.

[0031] FIG. 1 is a side view showing the configuration of a heating apparatus for metal sheets for electromagnetic steel sheets according to a first embodiment of the present invention. FIG. 2 is a side view showing the configuration of a first modified example of the heating apparatus for metal sheets for electromagnetic steel sheets shown in FIG. 1. FIG. 3 is a bottom view, seen from the back surface side of the metal sheet, showing the configuration of a second modified example of the heating apparatus for metal sheets for electromagnetic steel sheets shown in FIG. 1. FIG. 4 is a cross-sectional view showing the configuration of a cooling mechanism for a current-carrying roll in the heating apparatus for metal sheets for electromagnetic steel sheets shown in FIG. 1. FIG. 5 is a top view showing the configuration of a heating apparatus for metal sheets for electromagnetic steel sheets according to a second embodiment of the present invention. FIG. 6 is a cross-sectional view, as seen in the width direction of the metal sheet, of the heating apparatus for metal sheets for electromagnetic steel sheets shown in FIG. 5. FIG. 7 is a cross-sectional view, as seen in the width direction of the metal sheet, showing the configuration of a first modified example of the heating apparatus for metal sheets for electromagnetic steel sheets shown in FIG. 5. FIG. 8 is a cross-sectional view, as seen in the material-passing direction of the metal sheet, showing the configuration of a second modified example of the heating apparatus for metal sheets for electromagnetic steel sheets shown in FIG. 5. FIG. 9 is a cross-sectional view, as seen in the material-passing direction of the metal sheet, showing the configuration of a third modified example of the heating apparatus for metal sheets for electromagnetic steel sheets according to a third embodiment of the present invention. FIG. 10 is a top view showing the configuration of a heating device for metal sheets for electromagnetic steel sheets according to a fourth embodiment of the present invention.

[0032] 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.

[0033] [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.

[0034] 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 from a temperature above room temperature to a high temperature (450°C to 1000°C) at a heating rate of 2000°C / sec to 100,000°C / sec (although the mechanism is currently unknown).

[0035] 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.)

[0036] Furthermore, since the current application time in the preliminary heat treatment (approximately 10 msec to 500 msec) is extremely short, a high current density is required, and the heating in the preliminary heat treatment is localized. Therefore, it is difficult to industrially realize the preliminary heat treatment by conventional induction heating or direct current heating between current-carrying rolls. For example, 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, heating to high temperatures causes sheet deformation and easy buckling.

[0037] Furthermore, in tests conducted by the present applicant, it was confirmed that in a coil for an electrical steel sheet that was subjected to gradient heating in the secondary recrystallization process, in which the ends of the coil were heated at a higher temperature and the center of the sheet was heated at a lower temperature than the ends, creating a temperature difference between the ends and the center, crystal grains grew from the ends of the steel sheet toward the center, and magnetic properties were improved (see, for example, JP 59-215419 A). Based on this knowledge, by locally and ultra-rapidly heating only the widthwise ends of a metal sheet for an electrical steel sheet, it is possible to generate a large number of seed crystals of recrystallized grains having the Goss orientation at the widthwise ends of the metal sheet, and it is possible to grow these seed crystals from the ends of the metal sheet toward the center during recrystallization.

[0038] If a portion of the locally heated region is insufficiently heated, there is a risk that sufficient seed crystals will not be generated in that portion. Therefore, it is necessary to stably heat the locally heated region at a predetermined temperature and a predetermined rate. Conversely, if a portion of the heated region is overheated, iron will melt at approximately 1500°C. Therefore, it is also important to avoid overheating by raising the temperature too high (controlling the temperature reached by heating the metal plate from a temperature above room temperature). Such temperature control is possible by adjusting the amount and time of current flowing through the metal plate using resistance heating or induction heating. In order to stably heat the metal plate to a predetermined temperature, in the case of resistance heating, it is necessary to contact the metal plate with a certain amount of rolling force, which serves as an electrode for conducting current, so that the metal plate for electrical steel sheet is stably electrified. On the other hand, in the case of induction heating, no rolling force is required because it is a non-contact method.

[0039] In order to satisfy the above conditions, a heating device for metal sheets for electrical steel sheets must have a mechanism for applying current while contacting the metal sheet for a predetermined period of time in the case of resistance heating. The inventors came up with the idea of ​​using a small-diameter current-carrying roll as such a current-carrying mechanism, and passing high-frequency current directly through the metal sheet during the short distance that the current-carrying roll contacts the metal sheet while rotating.

[0040] By directly applying a high-frequency current using such a small-diameter current-carrying roll, the current flows intensively toward the widthwise end portions of the metal sheet, so that localized, narrow-width (for example, about 1 mm to 10 mm) linear heating can be performed on the widthwise end portions of the metal sheet, and a large number of seed crystals can be produced on the widthwise end portions of the metal sheet.

[0041] Furthermore, as a heating device for metal sheets for electrical steel sheets that satisfies the above-mentioned conditions, in the case of induction heating, for example, by passing a high-frequency current through coil conductors (conductors constituting induction coils) arranged at intervals in the direction of passage of the metal sheet, the current flows concentratedly at the widthwise ends of the metal sheet, as in a direct current heating device, while the current density is low in the center of the sheet width, making it difficult for heating to occur. Therefore, although the sheet is heated rapidly to a high temperature, the sheet edges account for most of the heating, so only a small amount of input power is required.

[0042] 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.

[0043] That is, the present invention provides an apparatus and method for preheating, which is important for controlling crystal orientation in the manufacture of electrical steel sheets. According to the present invention, by locally and ultra-rapidly heating a linear region near the widthwise edge of a metal sheet for electrical steel sheets before primary recrystallization annealing, a large number of seed crystals of recrystallized grains having Goss orientation are generated. These seed crystals can then be used as nuclei for crystal growth from the edge toward the center of the metal sheet. The preheating is a process for generating these 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 non-locally heated region (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, whereas recovery and recrystallization do not occur in the non-locally heated region.

[0044] Specifically, the device used for the preliminary heat treatment according to one embodiment of the present invention includes a conveying mechanism for passing a strip of a metal sheet for an electrical steel sheet after cold rolling and before primary recrystallization annealing, a first pair of current-carrying rolls that clamps the passing metal sheet from both the front and back sides with a predetermined pressure, a second pair of current-carrying rolls that are installed at a predetermined interval from the first pair of current-carrying rolls in the passing direction of the metal sheet and clamps the passing metal sheet from both the front and back sides with a predetermined pressure, and a roller that connects the first pair of current-carrying rolls to the second pair of current-carrying rolls. and a high-frequency power supply connected to a pair of current-carrying rolls and capable of heating the end of the metal plate in the width direction of the metal plate 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, wherein the first current-carrying roll pair and the second current-carrying roll pair each have a current-carrying roll that can be energized as at least one roll of a pair of front and back rolls that make up the current-carrying roll pair.

[0045] Furthermore, an apparatus used for preliminary heat treatment according to another embodiment of the present invention is an induction heating apparatus for metal for electromagnetic steel sheet, comprising: a conveying mechanism for passing a strip of metal sheet for electromagnetic steel sheet after cold rolling and before primary recrystallization annealing; an induction heating unit for induction heating the metal sheet being passed; and a high-frequency power supply connected to the induction heating unit, wherein the induction heating unit uses a high-frequency current from the high-frequency power supply to heat an end portion of the metal sheet in the width direction of 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.

[0046] Furthermore, a method for carrying out preliminary heat treatment according to the present invention is a method for electrically heating a metal sheet for use in an electrical steel sheet after cold rolling and before primary recrystallization annealing, comprising the step of using an electric heating device constituted by the above-mentioned electric heating device or induction heating device for a metal sheet for use in an electrical steel sheet to apply current to a pair of current-carrying rolls or an induction heating unit that holds the metal sheet at a predetermined pressure 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.

[0047] According to the above-described electric heating device and electric heating method for a metal sheet for an electrical steel sheet, seed crystals having a predetermined orientation (Goss orientation) can be generated at a predetermined density at the width direction ends of the metal sheet for an electrical steel sheet before primary recrystallization annealing. Preferred embodiments of the present invention, which have been completed based on the above findings, will now be described.

[0048] [First embodiment: direct resistance heating method] (resistance heating device 100) First, the configuration of a resistance heating device 100 as a heating device for metal sheets for electromagnetic steel sheets according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a side view showing the configuration of the resistance heating device 100 for metal sheets for electromagnetic steel sheets according to this embodiment.

[0049] As shown in FIG. 1 , the electric heating device 100 according to this embodiment mainly includes a transport roll 110 , a first pair of electric current rolls 120 , a second pair of electric current rolls 130 , and a high-frequency power source 140 .

[0050] The transport rolls 110 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 110, as long as it has a configuration that allows the strip of metal sheet 1 to pass through at a predetermined speed.

[0051] The first energized roll pair 120 is provided upstream of the second energized roll pair 130 in the direction of passage of the metal sheet 1, with a predetermined distance L between them, and includes an energized roll 121 arranged on the back side of the metal sheet 1, and a non-energized pressure roll 123 arranged on the front side of the metal sheet 1. In this embodiment, of the pair of front and back rolls constituting the first energized roll pair 120, only one roll is an energized roll and the other roll is a pressure roll, but both rolls may be energized rolls. The first energized roll pair 120 clamps the passing metal sheet 1 from both the front and back sides with a predetermined pressure. The pressure with which the energized roll pair 120 clamps the metal sheet 1 may be such that sparks do not occur in the space between the metal sheet 1 and the energized roll 121, and may be, for example, 10 N / mm ２If a spark occurs, there is a risk that the surfaces of the metal plate 1 and the current-carrying roll 121 may be melted and damaged.

[0052] The second energized roll pair 130 is provided downstream of the first energized roll pair 120 in the material passing direction of the metal sheet 1, with a predetermined distance L between them, and includes an energized roll 131 arranged on the back side of the metal sheet 1, and a non-energized pressure roll 133 arranged on the front side of the metal sheet 1. In this embodiment, of the pair of front and back rolls constituting the second energized roll pair 130, only one roll is an energized roll and the other roll is a pressure roll, but both rolls may be energized rolls. Similar to the first energized roll pair 120, this second energized roll pair 130 also clamps the passing metal sheet 1 from both the front and back sides with a predetermined pressure. This pressure is the same as in the case of the first current-carrying roll pair 120, and should be such that the metal plate 1 and the current-carrying roll 131 are in close contact with each other, and the optimum value should be determined based on the deformability of the roll, such as the Young's modulus of the pressure roll 133.

[0053] The diameter of each roll constituting the first current-carrying roll pair 120 and the second current-carrying roll pair 130 can be determined based on the relationship between the temperature reached by heating from a temperature above room temperature, the distance L between the current-carrying rolls (the distance between the current-carrying roll 121 and the current-carrying roll 131), and the conveying speed (material passing speed) of the metal sheet 1. For example, when the temperature reached from a temperature above room temperature (specifically, the temperature reached from room temperature) is 1000°C, the heating rate is 2,000°C / sec, and the conveying speed of the metal sheet 1 is 30 mpm to 60 mpm (0.5 m / sec to 1.0 m / sec), the distance L between the current-carrying rolls is 250 mm to 500 mm, and the diameter of the current-carrying rolls 121, 131 is preferably 200 mm (for 30 mpm) or less, or 450 mm (for 60 mpm) or less.

[0054] The material of the current-carrying rolls 121 and 131 is not particularly limited, but examples thereof include metals such as stainless steel and carbon steel whose surface is sprayed with ceramics or the like. However, if it is necessary to maintain the temperature for a short period of time during current heating of the metal sheet 1, current is passed to maintain the temperature, or the current-carrying rolls 121 and 131 themselves are maintained at their heating temperature without passing current through them. In this case, the material of the current-carrying rolls 121 and 131 is preferably a material whose main component is a nickel or chromium alloy that has a high resistance.

[0055] Furthermore, when it is necessary to rapidly cool the metal sheet 1 immediately after the heating by electrical conduction, it is preferable that the material of the current-carrying rolls 121 and 131 be a metal with good thermal conductivity, such as copper or a copper alloy, and that a cooling mechanism be provided to cool the current-carrying rolls 121 and 131. Such a cooling mechanism can prevent the temperature of the widthwise ends of the metal sheet 1 from rising too high. On the other hand, if the temperature of the widthwise ends of the metal sheet 1 rises too high without cooling the current-carrying rolls 121 and 131, the widthwise ends of the metal sheet 1 will expand, resulting in unstable contact between the current-carrying rolls 121 and 131 and the metal sheet 1 and the risk of sparks.

[0056] Here, the configuration of the cooling mechanism for cooling the current-carrying roll 121 and the current-carrying roll 131 will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view showing the configuration of the cooling mechanism for the current-carrying roll 121 and the current-carrying roll 131 in the resistance heating device 100.

[0057] The current-carrying rolls 121 and 131 according to this embodiment have a hollow cylindrical shape, as shown in FIG. 4 , and include a cooling mechanism for water-cooling the interior of the rolls. The current-carrying rolls are cooled to prevent the roll shaft and the current-carrying roll body from being heated by the current flowing through the metal plate, and to prevent the rolls themselves from being heated by heat from the heated metal plate. In this cooling mechanism, the current-carrying rolls 121 and 131 can be cooled by flowing cooling water from one end of the current-carrying rolls 121 and 131 to the other end of the rolls. This flow of cooling water can cool the current-carrying rolls 121 and 131 from the inside. In this case, a spiral or the like can be provided on the inner circumferential surface 121a (131a) of the hollow current-carrying roll 121 (131) to increase the flow rate of the cooling water flowing through the current-carrying rolls 121 and 131, thereby further improving the cooling efficiency. Alternatively, although not shown, the current-carrying roll 121 and the current-carrying roll 131 may be cooled by heat exchange by forming them into a double-pipe structure or the like. By providing such a cooling mechanism, the current-carrying roll 121 and the current-carrying roll 131 according to this embodiment can rapidly cool the current-carrying roll 121 and the current-carrying roll 131, and can prevent the temperature of the metal sheet 1 from rising too high.

[0058] The high-frequency power supply 140 is connected to the first energized roll pair 120 and the second energized roll pair 130 by flexible electric wires 141 or the like. As a result, the first energized roll pair 120 and the second energized roll pair 130 form a current circuit via the metal plate 1. By passing a high-frequency current from the high-frequency power supply 140 through such a current circuit, current is passed from the energized roll 121 (or the energized roll 131) through the metal plate 1 to the energized roll 131 (or the energized roll 121). This allows the metal plate 1 to 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. The temperature of the metal plate 1 can be measured, for example, by a radiation thermometer or the like installed facing the heating unit on the widthwise end side of the metal plate 1.

[0059] The reason why the high-frequency power supply 140 is used as the power supply in this embodiment is as follows. When the high-frequency power supply 140 applies high-frequency current to the current-carrying rolls 121 and 131, due to the inductance of the metal sheet, the current flows unevenly toward the widthwise ends of the metal sheet 1, even if the current-carrying rolls 121 and 131 are in contact with the entire width of the metal sheet 1. Therefore, increasing the frequency of the high-frequency power supply 140 strengthens this tendency, and only the widthwise ends of the metal sheet 1 are heated. To achieve this effect, the frequency of the high-frequency power supply 140 is preferably 1 kHz or higher, and more preferably several tens of kHz or higher. Furthermore, by increasing the frequency of the high-frequency power supply 140, the width of the heated linear region at the widthwise ends of the metal sheet 1 can be narrowed. Although there is no particular upper limit for the frequency of the high-frequency power supply 140, for example, 400 kHz may be set as a practical upper limit.

[0060] As described above, by electrically heating the metal sheet 1 using the current-carrying rolls 121 and 131 connected to the high-frequency power supply 140, only a narrow linear region (see region H in FIG. 3 described later) at the widthwise end of the metal sheet 1 can be ultra-rapidly heated at a rate of 2,000°C / sec to 100,000°C / sec from a temperature above room temperature to an ultimate temperature of 450°C to 1,000°C. As a result, seed crystals of recrystallized grains having a Goss orientation can be formed in the linear region at the widthwise end of the metal sheet 1. Furthermore, because the first current-carrying roll pair 120 and the second current-carrying roll pair 130 are installed at a predetermined interval from each other in the direction of passage of the metal sheet 1, a heating time of 10 msec to 500 msec required to heat the metal sheet 1 from a temperature above room temperature to the ultimate temperature can be ensured for the metal sheet 1 passing through at high speed. Using only one of the current-carrying roll pairs would only ensure a heating time on the order of msec.

[0061] The inventors have confirmed through experiments that, for a cold-rolled metal sheet 1 for grain-oriented electrical steel sheet having a width of 1 m and a thickness of 0.23 mm, a linear region extending 2 mm from the widthwise end of the metal sheet 1 passing through at a conveying speed of 60 mpm (1000 mm / sec) can be heated from 20°C to 1000°C at a rate of approximately 10,000°C / sec under the following conditions (1) to (4): (1) Heating time: 0.098 seconds (2) Distance between the current-carrying roll 121 and the current-carrying roll 131: 100 mm (3) Diameter of the current-carrying roll 121 and the current-carrying roll 131: 50 mm (4) Frequency of high-frequency power source: 100 kHz, current of high-frequency power source: 350 A

[0062] (First Modification of Resistance Heating Apparatus 100) Here, a first modification of the present embodiment, a resistance heating apparatus 100-1, will be described with reference to Fig. 2. Fig. 2 is a side view showing the configuration of the resistance heating apparatus 100-1 for metal sheets for electromagnetic steel sheets, according to the first modification of the present embodiment.

[0063] 2, the resistance heating device 100-1 has the same configuration as the resistance heating device 100 according to the first embodiment described above, except that it further includes a backup roll 125, a backup roll 127, a backup roll 135, and a backup roll 137 that respectively support the current-carrying roll 121, the pressure roll 123, the current-carrying roll 131, and the pressure roll 133. Therefore, only the configuration of the backup roll will be described below.

[0064] As described above, when heating only a localized, narrow (e.g., approximately 1 mm to 10 mm) linear region at the widthwise end of the metal sheet 1, it is necessary to apply high-frequency current using small-diameter (e.g., 300 mm or less) current-carrying rolls 121 and 131. Here, the width of the metal sheet 1 for an electromagnetic steel sheet is often approximately 1 m, and it is difficult to contact a very small-diameter current-carrying roll, as described above, with the entire widthwise direction of the metal sheet 1, which is approximately 1 m wide, due to factors such as roll eccentricity and outer diameter accuracy. Therefore, contact between the current-carrying rolls 121 and 131 and the metal sheet 1 becomes unstable, which may result in sparks. The roll diameter and lower limit of the current-carrying rolls 121 and 131 are not particularly specified, but a practical lower limit of 50 mm may be used.

[0065] Therefore, in the modified example of the electric heating device 100-1, backup rolls 125 and 135 are provided to support at least the electric rolls 121 and 131 from the outside (the side opposite to the side that contacts the metal plate 1), so that the electric rolls 121 and 131 are in stable contact with each other across the entire width of the metal plate 1.

[0066] (Second Modification of Electrical Heating Apparatus 100) Next, a second modification of the present embodiment will be described with reference to Fig. 3. Fig. 3 is a bottom view of the configuration of the electric heating apparatus 100-2 for a metal sheet for an electromagnetic steel sheet according to the second modification of the present embodiment, as viewed from the back surface side of the metal sheet 1 (the surface side that comes into contact with the electric rolls 121 and 131).

[0067] 3, the electric heating device 100-2 has a configuration similar to that of the electric heating device 100 according to the first embodiment, except that instead of the electric roll 121 according to the first embodiment, the electric heating device 100-2 is a split electric roll 121-2 consisting of two split rolls 121A and 121B separated in the width direction of the metal sheet 1, and the split roll 121A and the split roll 121B are arranged at both ends in the width direction of the metal sheet 1. Therefore, only the configuration of the split electric roll will be described below.

[0068] As described in the first modified example, it is difficult to bring the current-carrying rolls 121-2 and 131, which have very small diameters, into contact with the entire width of the metal sheet 1, which has a width of about 1 m. Therefore, the contact between the current-carrying rolls 121-2 and 131 and the metal sheet 1 becomes unstable, which may result in sparks.

[0069] Therefore, in the modified example of the electric heating device 100-2, at least one of the two electric rolls 121-2, 131 (in the example shown in Figure 3, the electric roll 121-2) is made a split electric roll, so that the electric roll 121-2 can stably contact the widthwise end of the metal plate 1.

[0070] In this modified example, only the current-carrying roll 121 on the inlet side (low-temperature side, upstream side in the material-passing direction) of the current-carrying heating device 100-2 is a split current-carrying roll, and the current-carrying roll 131 on the outlet side (high-temperature side, downstream side in the material-passing direction) of the current-carrying heating device 100-2 is an integrated current-carrying roll that is integral across the entire width direction of the metal sheet 1. However, the present invention is not limited to this example. For example, only the current-carrying roll 131 may be a split current-carrying roll, or both the current-carrying roll 121 and the current-carrying roll 131 may be split rolls. To more reliably prevent sparks, it is preferable that both the current-carrying roll 121 and the current-carrying roll 131 be split rolls.

[0071] (Electrical heating method) The electrical heating method for a metal sheet for an electromagnetic steel sheet according to this embodiment uses the electrical heating device 100 according to this embodiment described above (or the electrical heating device 100-1 or electrical heating device 100-2, which are modified examples thereof), and includes a preliminary heat treatment step of clamping the metal sheet 1 after cold rolling and before primary recrystallization annealing with a predetermined pressure between a first electrical roll pair 120 and a second electrical roll pair 130, and heating the metal sheet 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 by applying electricity to the electrical rolls 121 and 131 for 10 msec to 100 msec.

[0072] 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.

[0073] 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.

[0074] 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).

[0075] 1 , when the metal sheet 1 is transported into the electric heating device 100 by the transport rolls 110, the metal sheet 1 is first sandwiched between a first pair of electric rolls 120 installed on the upstream side in the material-passing direction (the entrance side of the electric heating device 100). Furthermore, when the metal sheet 1 passes through the material, the metal sheet 1 is also sandwiched between a second pair of electric rolls 130 installed on the downstream side in the material-passing direction (the exit side of the electric heating device 100) while still being sandwiched between the first pair of electric rolls 120.

[0076] In this state, the current-carrying roll 121 of the first current-carrying roll pair 120 and the current-carrying roll 131 of the second current-carrying roll pair 130 are energized with high-frequency current from the high-frequency power supply 140, and therefore the current-carrying roll 121 and the current-carrying roll 131 form a current circuit via the metal sheet 1. Furthermore, as described above, due to the inductance relationship, current flows only through the width-direction ends of the metal sheet 1 on the surface thereof, and therefore only linear regions at the width-direction ends of the metal sheet 1 are heated. At this time, by appropriately controlling the conveyance speed of the metal sheet 1, the heating time, the distance between the current-carrying roll 121 and the current-carrying roll 131, the diameters of the current-carrying roll 121 and the current-carrying roll 131, and the frequency and current amount of the high-frequency power supply 140, the metal sheet 1 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.

[0077] Here, while the metal sheet 1 is passing through the electric heating device 100, a current circuit is formed between the electric rolls 121 and 131 and the linear regions at the width direction ends of the metal sheet 1, and the strip of the metal sheet 1 is continuously transported. Therefore, according to the electric heating method of this embodiment, the width direction ends of the metal sheet 1 can be continuously ultra-rapidly heated, and therefore seed crystals having the Goss orientation can be produced in large quantities in the crystalline structure before primary recrystallization annealing without impairing the productivity of the electrical steel sheet.

[0078] [Second embodiment: induction heating method] (induction heating device 200) Fig. 5 is a top view showing the configuration of an induction heating device 200 as a heating device for metal sheets for electromagnetic steel sheets according to a second embodiment of the present invention. Fig. 6 is a cross-sectional view of the induction heating device shown in Fig. 5 as seen in the width direction of the metal sheet.

[0079] As shown in FIGS. 5 and 6, the induction heating device 200 according to this embodiment mainly includes an induction heating unit 210 and a high-frequency power supply 220 in addition to the transport rolls 110.

[0080] The induction heating section 210 is for induction heating the metal plate 1 passing therethrough, and includes, for example, a pair of conductors, i.e., one conductor pair 211 .

[0081] The conductor pair 211 is connected to a high-frequency power supply 220 so as to form an induction coil. The induction coil here is a primary closed circuit that circles around the passing metal sheet 1, i.e., the metal sheet 1 passes inside the coil, and forms a secondary closed circuit on the metal sheet 1.

[0082] The conductor pair 211 includes a front-side conductor 212 disposed on the front side of the metal plate 1 and a back-side conductor 213 disposed on the back side of the metal plate 1. The front-side conductor 212 and the back-side conductor 213 are each disposed so as to cross the metal plate 1 in the width direction when viewed in the thickness direction of the metal plate 1. That is, the length of each of the front-side conductor 212 and the back-side conductor 213 in the width direction of the metal plate 1 is longer than the width of the metal plate 1. The front-side conductor 212 and the back-side conductor 213 are disposed so as to be spaced apart from each other in the material-passing direction of the metal plate 1. Specifically, the front-side conductor 212 and the back-side conductor 213 are disposed with a predetermined distance K between them in the material-passing direction of the metal plate 1. In the illustrated example, the front-side conductor 212 is disposed downstream of the back-side conductor 213 in the material-passing direction of the metal plate 1; however, the front-side conductor 212 may also be disposed upstream of the back-side conductor 213 in the material-passing direction of the metal plate 1.

[0083] The high-frequency power supply 220 is connected to the induction heating unit 210 and supplies high-frequency power. The high-frequency power supply 220 is connected to the conductor pair 211 to form an induction coil, which is a primary closed circuit. When a high-frequency current is applied from the high-frequency power supply 220 to the conductor pair 211 that constitutes the induction coil, an induced current is induced on the surface of the metal sheet 1 facing the front-side conductor 212 and the back-side conductor 213 of the conductor pair 211, respectively, and a secondary closed circuit is formed between the portions facing the separated conductors through the widthwise ends of the metal sheet 1. At this time, the induced current is concentrated near the widthwise ends of the metal sheet 1, resulting in a high current density at these ends. On the other hand, the induced current density is lower in the portions of the metal sheet 1 directly below the coil conductors, such as the front-side conductor 212, i.e., the opposing portions, than at the widthwise ends. This allows ultra-rapid heating of only the widthwise ends of the metal sheet 1 from a temperature above room temperature to a temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec. Furthermore, even if an inexpensive high frequency power supply 220 for induction heating with a relatively low power density capability is used, the above-described ultra-rapid heating can be realized.

[0084] The above-described tendency of the induced current density becomes more pronounced when the frequency of the high-frequency power (current) from the high-frequency power supply 220 is high. For ultra-rapid heating, the frequency of the high-frequency power supply 220 is preferably 1 kHz or higher. Furthermore, by increasing the frequency of the high-frequency power supply 220, the width of the heated linear region at the widthwise end of the metal plate 1 can be narrowed. There is no particular upper limit for the frequency of the high-frequency power supply 220, but for example, 400 kHz may be set as a practical upper limit.

[0085] The distances of the front-side conductor 212 and the back-side conductor 213 to the metal plate 1 are set so as to obtain a sufficient induced current density at the widthwise ends of the metal plate 1. The above-mentioned predetermined interval K can be determined from the distances of the front-side conductor 212 and the back-side conductor 213 to the metal plate 1, the heating rate, the heating width of the widthwise ends of the metal plate 1, and the frequency of the high-frequency current. The predetermined interval K is preferably equal to or greater than the length of one coil conductor in order to efficiently pass current to the widthwise ends of the metal plate 1 and to locally heat the widthwise ends.

[0086] 7 is a cross-sectional view of an induction heating device 200-1 according to a first modification of this embodiment, viewed in the width direction of a metal plate. The induction heating section 210 of the induction heating device 200-1 has conductor pairs 211A and 211B similar to the conductor pair 211 described above, i.e., has two conductor pairs 211.

[0087] The front-side conductor 212A of the conductor pair 211A is disposed opposite the back-side conductor 213B of the conductor pair 211B across the metal plate 1. That is, the front-side conductor 212A of the conductor pair 211A and the back-side conductor 213B of the conductor pair 211B are located at the same position in the material-passing direction of the metal plate 1. On the other hand, the back-side conductor 213A of the conductor pair 211A is disposed opposite the front-side conductor 212B of the conductor pair 211B across the metal plate 1. That is, the back-side conductor 213A of the conductor pair 211A and the front-side conductor 212B of the conductor pair 211B are located at the same position in the material-passing direction of the metal plate 1.

[0088] At the widthwise end of the metal plate 1, the conductor pair 211A and the conductor pair 211B are connected to a high-frequency power supply 220 (see FIG. 6 ) so that the induced current induced in the induction coil formed by the conductor pair 211A and the induced current induced in the metal plate by the induction coil formed by the conductor pair 211B reinforce each other rather than destructively. That is, currents of the same phase flow up and down in the coil conductors, and currents of opposite phase flow in the longitudinal direction.

[0089] In this example, even if the distance between the conductors constituting the conductor pair is short, that is, even if the induction heating device 200-1 is small, the above-described ultra-rapid heating can be achieved.

[0090] (Second Modification of Induction Heating Device 200) FIG. 8 is a cross-sectional view taken in the direction in which the metal plate 1 passes, showing the configuration of an induction heating device 200-2 according to a second modification of this embodiment.

[0091] The induction heating unit 210 of the induction heating device 200-2 forms a magnetic flux that penetrates the metal plate 1 in its thickness direction, and heats the metal plate 1 by an induced current generated in the metal plate 1 by this magnetic flux. That is, the induction heating unit 210 heats the metal plate 1 by a TF (Transverse Flux: perpendicular magnetic flux) method.

[0092] As shown in Fig. 8, the induction heating unit 210 includes a front-side magnetic core 214 disposed on the front side of the metal plate 1 and a back-side magnetic core 215 disposed on the back side of the metal plate 1. The front-side magnetic core 214 and the back-side magnetic core 215 are provided with induction coils 214a and 215a, respectively, and the magnetic flux generated by the induction coils 214a and 215a is concentrated at the widthwise ends of the metal plate 1 so as to penetrate the metal plate 1 in its thickness direction. Furthermore, the front-side magnetic core 214 and the back-side magnetic core 215 are each disposed so as to cross the metal plate 1 in the widthwise direction when viewed in the thickness direction of the metal plate 1. In other words, the length of the front-side magnetic core 214 and the back-side magnetic core 215 in the widthwise direction of the metal plate 1 is longer than the width of the metal plate 1.

[0093] The front-side magnetic core 214 is formed in an inverted U-shape when viewed in the direction in which the metal plate 1 passes, with a portion facing the widthwise end of the metal plate 1 protruding toward the metal plate 1. Meanwhile, the back-side magnetic core 215 is formed in a U-shape when viewed in the direction in which the metal plate 1 passes, with a portion facing the widthwise end of the metal plate 1 protruding toward the metal plate 1. Furthermore, induction coils 214a and 215a are provided in the front-side magnetic core 214 and the back-side magnetic core 215, respectively, so that magnetic flux flows along the shape of the core. When high-frequency current is applied from the high-frequency power supply 220 (see FIG. 6 ) to the induction coils 214a and 215a, a closed circuit of magnetic flux is formed between the front-side magnetic core 214 and the back-side magnetic core 215, penetrating the widthwise end of the metal plate 1 in the thickness direction of the metal plate 1. This induces an induced current that is concentrated at the widthwise end of the metal plate 1, resulting in high current density at the end. This allows only the widthwise ends of the metal plate 1 to be ultra-rapidly 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.

[0094] The shapes of the front-side magnetic core 214 and the back-side magnetic core 215 and the distance to the metal plate 1 are set so as to avoid problems such as overheating or the heating range not being limited to a specific area.

[0095] (Third Modification of Induction Heating Device 200) FIG. 9 is a cross-sectional view of an induction heating device 200-3 according to a third modification of this embodiment, taken in the direction in which the metal plate 1 passes.

[0096] Similar to that of induction heating device 200-2, induction heating section 210 of induction heating device 200-3 forms a magnetic flux that penetrates metal plate 1 in its thickness direction, and heats metal plate 1 by an induced current generated in metal plate 1 by this magnetic flux. That is, induction heating section 210 heats metal plate 1 by a TF (Transverse Flux: perpendicular magnetic flux) method.

[0097] 9, the induction heating unit 210 of the induction heating device 200-3 is different from that of the induction heating device 200-2 and includes a first magnetic core 216 installed on one widthwise side of the metal plate 1 and a second magnetic core 217 installed on the other widthwise side of the metal plate 1. The first magnetic core 216 and the second magnetic core 217 are provided with induction coils 216a and 217a, respectively, and the magnetic flux generated by the induction coils 216a and 217a is concentrated at the widthwise ends of the metal plate 1 so as to penetrate the metal plate 1 in its thickness direction.

[0098] The first magnetic core 216 is formed in a C-shape when viewed in the material-passing direction of the metal plate 1 so as to sandwich an end portion on one side in the width direction of the metal plate 1, with a portion facing the front side and a portion facing the back side of the end portion of the metal plate 1 each protruding toward the metal plate 1. On the other hand, the second magnetic core 217 is formed in an inverted C-shape when viewed in the material-passing direction of the metal plate 1 so as to sandwich an end portion on the other side in the width direction of the metal plate 1, with a portion facing the front side and a portion facing the back side of the end portion of the metal plate 1 each protruding toward the metal plate 1. In addition, induction coils 216a and 217a are provided in the first magnetic core 216 and the second magnetic core 217, respectively, so that magnetic flux flows along the shape of the core. When high-frequency current is applied to induction coils 216a and 217a from high-frequency power supply 220 (see FIG. 6), induction coils 216a and 217a each individually form a closed circuit of magnetic flux that penetrates corresponding widthwise ends of metal plate 1 in the thickness direction of metal plate 1. This induces an induced current that concentrates at the widthwise ends of metal plate 1, increasing the current density at those ends. This allows ultra-rapid heating of only the widthwise ends of 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.

[0099] The shapes of the first magnetic core 216 and the second magnetic core 217 and the distance to the metal plate 1 are set so as to avoid problems such as overheating or the heating range not being limited to a specific area.

[0100] (Induction Heating Method) The induction heating method for a metal plate for an electromagnetic steel plate according to this embodiment includes a preliminary heat treatment step of using the induction heating device 200 according to this embodiment described above (or its modified examples, induction heating device 200-1, induction heating device 200-2, induction heating device 200-3) to apply electricity to the induction heating unit 210 for 10 msec to 100 msec, thereby 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.

[0101] 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.

[0102] 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.

[0103] 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).

[0104] Specifically, when a high-frequency current is supplied from the high-frequency power supply 220 while the metal sheet 1 is passing through, as described above, the current density of the induced current becomes high only at the widthwise end of the metal sheet 1, and therefore only the linear region at that end is heated. At this time, by appropriately controlling the conveying speed of the metal sheet 1, the heating time, the dimensions and position of the induction heating unit 210, and the frequency and current amount of the high-frequency power supply 220, the metal sheet 1 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.

[0105] The induction heating method according to the present embodiment also makes it possible to continuously and ultra-rapidly heat the width direction ends of the metal sheet 1, and therefore it is possible to produce a large amount of seed crystals having the Goss orientation in the crystalline structure before primary recrystallization annealing without impairing the productivity of the electrical steel sheet.

[0106] [Third embodiment] Fig. 10 is a top view showing the configuration of a heating apparatus 300 for a metal sheet for an electrical steel sheet according to a third embodiment of the present invention. As shown in Fig. 10, the heating apparatus 300 according to this embodiment includes a retention zone 310 in addition to the configuration of the induction heating apparatus 200 shown in Fig. 5.

[0107] The heat retention zone 310 maintains the temperature of the widthwise end of the metal sheet 1, which has been heated from room temperature or higher to a target temperature of 450°C to 1000°C at a rate of 2,000°C / sec to 100,000°C / sec, within a predetermined range for a predetermined time. The predetermined range is, for example, 450°C to 1000°C. The predetermined time may be, for example, 0.1 seconds or longer. If the temperature of the widthwise end of the metal sheet 1 is maintained for 0.1 seconds or longer, the structure of the locally heated region can be favorably controlled to a recovered structure or a recrystallized structure. The above-mentioned maintenance time is preferably 0.2 seconds or longer, more preferably 0.3 seconds or longer, and even more preferably 0.4 seconds or longer. Meanwhile, the upper limit of the maintenance time is not particularly limited and may be, for example, 10 seconds or shorter. This maintenance time has a fundamental effect on the formation of coarse Goss-oriented grains (Goss-oriented grains with a grain size of 5 μm or more) that are close to the ideal Goss orientation.

[0108] The retention zone 310 is provided downstream of the induction heating unit 210 in the direction in which the metal sheet 1 passes, and heats the metal sheet 1 so as to compensate for the temperature drop of the rapidly heated metal sheet 1. The heating method of the retention zone 310 may be an induction heating method like the induction heating unit 210 according to the second embodiment and its modified examples, or may be another induction heating method. The heating method of the retention zone 310 may also be a method that uses radiant heat from an electric heater, or a method that sprays a heating medium such as heated gas or mist from a nozzle.

[0109] As a result of further research, the inventors have found that holding the high temperature for a short period of time after ultra-rapid heating of the widthwise end portions of the metal sheet 1 allows Goss grains to grow stably with a better crystal orientation, i.e., metallurgically improving. Therefore, according to this embodiment, the widthwise end portions of the metal sheet 1 that have been ultra-rapidly heated can be held at a constant high temperature for a certain period of time or more, thereby producing even better quality Goss grains. Furthermore, when using electric power to heat the retention zone 310, only an amount of electric power sufficient to prevent the widthwise end portions of the metal sheet 1 from cooling is sufficient.

[0110] Furthermore, the heating device according to this embodiment may be provided with an induction heating device configuration other than that shown in Fig. 5 or the configuration of the electric heating device shown in Fig. 1, etc., instead of the induction heating device configuration shown in Fig. 5. Heating in the retention zone 310 may be performed continuously, or may be performed intermittently to suppress temperature fluctuations (specifically, temperature rise).

[0111] (Heating method) The electric heating method for a metal sheet for an electromagnetic steel sheet according to this embodiment includes the preparatory heat treatment step described above in the resistance heating method according to the first embodiment or the induction heating method according to the second embodiment. The electric heating method according to this embodiment also includes, in the preparatory heat treatment step, a holding step in which the temperature of the width direction end portions of the metal sheet 1, which has been 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, is maintained at a certain level or higher by using the heat retention zone 310.

[0112] 11 is a top view showing the configuration of a heating apparatus 400 for a metal sheet for an electromagnetic steel sheet according to a fourth embodiment of the present invention. As shown in Fig. 11, the heating apparatus 400 according to this embodiment includes a cooling section 410 in addition to the configuration of the induction heating apparatus 200 in Fig. 5 and the retention zone 310.

[0113] The cooling section 410 cools the metal plate 1 to reduce the effects of heating or the effects of heating and heat retention. The cooling section 410 may cool only the widthwise ends of the metal plate 1 by cooling only the portions of the metal plate 1 other than the widthwise ends, or it may cool the entire metal plate 1. The cooled portions are prevented from undergoing unnecessary changes to the metal structure. The cooling section 410 is provided downstream of the retention zone 310 in the material passing direction of the metal plate 1, and specifically, is provided adjacent to the retention zone 310 and downstream of the retention zone 310 in the material passing direction of the metal plate 1. The cooling method of the cooling section 410 is, for example, a method in which a cooling medium such as low-temperature gas or mist is sprayed from a nozzle.

[0114] According to this embodiment, the thermal influence on the metal plate 1 can be alleviated, and therefore, Goss-oriented grains of higher quality can be obtained.

[0115] Moreover, the heating device according to this embodiment may have the configuration of an induction heating device other than that shown in Fig. 5 or the configuration of the electric heating device shown in Fig. 1, etc., instead of the configuration of the induction heating device shown in Fig. 5. Furthermore, the heating device according to this embodiment may omit the retention zone 310.

[0116] (Heating method) The electric heating method for a metal sheet for an electromagnetic steel sheet according to this embodiment includes the above-mentioned preliminary heat treatment step of the resistance heating method according to the first embodiment or the induction heating method according to the second embodiment. The electric heating method according to this embodiment may also include the holding step of the heating method according to the third embodiment in the preliminary heat treatment step. Furthermore, the electric heating method according to this embodiment includes the step of cooling the heated metal sheet 1 or the heated and warmed metal sheet 1 by a cooling unit 410 in the preliminary heat treatment step.

[0117] (Method for manufacturing electrical steel sheet) The method for manufacturing electrical steel sheet according to the present disclosure includes a cold rolling step, a primary recrystallization annealing step, an insulating layer forming step, and a secondary 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.

[0118] In the cold rolling process, the metal sheet 1 for an electrical steel sheet is cold rolled to a final sheet 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 in a linear region at the width direction end 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.

[0119] The linear region at the widthwise end of the metal plate 1 may be, for example, a locally narrow region of approximately 1 mm to 10 mm. Heating a region narrower than 1 mm is difficult using current heating or induction heating with the heating device of this embodiment, even if a high-frequency power source is used and the frequency is increased, because the heat is uniformed by heat transfer. On the other hand, if the region is wider than 10 mm, the area proportion of Goss-oriented grains that cannot grow outside the locally heated region increases, making it difficult to achieve the effect of localized rapid heating.

[0120] After the preliminary heat treatment step, a primary recrystallization annealing step is performed, in which the pre-heat-treated metal plate 1 is annealed to decarburize it. During this annealing, the seed crystals formed 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 time are small particles on the order of several tens of micrometers.

[0121] Next, in the insulating layer formation process, an insulating layer mainly composed of MgO is formed on the surface of the metal sheet 1 after the primary recrystallization annealing. In the subsequent secondary recrystallization annealing process, the metal sheet 1 on which the insulating layer has been formed is batch annealed, so that the Goss-oriented grains formed in the primary recrystallization annealing grow into large grains visible to the naked eye. During this process, the Goss-oriented grains formed in the primary recrystallization annealing grow from the widthwise end sides toward the center of the metal sheet 1. During this process, the insulating layer also becomes an insulating coating; specifically, MgO in the insulating layer reacts at the high temperature caused by annealing to form an insulating coating.

[0122] 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.

[0123] (Improvement of Magnetic Properties) Improvement of the magnetic properties of cold-rolled steel sheets for electrical steel sheets that were subjected to preheat treatment using the heating device (electrical heating device or induction heating device) according to this embodiment was confirmed as follows.

[0124] 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 a preliminary heat treatment using the heating device described above. The heating was performed only on a localized linear region of a narrow width (e.g., approximately 1 mm to 10 mm) at the widthwise end of the metal sheet 1, forming a locally heated region.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] In both the direct current method and the induction heating method, the heating rate, the maximum temperature, and the holding time after reaching the maximum temperature were controlled by changing the current flow, the current flow time, the electrode holding time after current flow, etc. in a composite manner as described in the above embodiment. Specific conditions are shown in Table 1 below. Note that "No treatment" in the table indicates that localized rapid heating was not performed.

[0131] 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.

[0132] In Table 1, "heating width" represents the width of the locally heated region relative to a sheet width of 1000 mm, and corresponds to the width of the linear region at the edge in the width direction. Furthermore, the "locally heated section ratio" of the local heating conditions represents the ratio (percentage) of the above-mentioned "heating width" to the sheet width. Note that, in local heating, the edge (extreme edge) of the steel sheet in the width direction tends to be heated the most, and the heating rate, maximum temperature achieved, and holding time in Table 1 are based on this edge, and the heating width and locally heated section ratio refer to the region in which the temperature rises to 90% of the edge.

[0133]

[0134] 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 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 steel sheet nitrogen content 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 one of the following conditions, and held at 1200°C for 20 hours in a hydrogen atmosphere. Normal: Heating from 1000°C to 1200°C at 15°C / hour Slow heating: Heating from 1000°C to 1200°C at 7.5°C / hour

[0135] 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.

[0136]

[0137] Among Nos. 1 to 18, 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.

[0138] The present invention is useful for a heating device and a heating method for metal sheets for electromagnetic steel sheets having excellent magnetic properties, and for a method for manufacturing electromagnetic steel sheets.

[0139] 1 Metal plate for electromagnetic steel plate 100, 100-1, 100-2 Electric heating device 110 Transport roll 120 First energized roll pair 121 Energized roll 121-2 Split type energized roll 123 Pressing roll 125, 127 Backup roll 130 Second energized roll pair 131 Energized roll 133 Pressing roll 135, 137 Backup roll 140, 220 High frequency power supply 141 Flexible electric wire 200, 200-1, 200-2, 200-3 Induction heating device 210 Induction heating section 211, 211A, 211B Conductor pair 214 Front surface side magnetic core 214a, 215a, 216a, 217a Induction coil 215 Back surface side magnetic core 216 First magnetic core 217 Second magnetic core 300, 400 Heating device 310 Heating zone 410 Cooling section L Distance between current-carrying rolls K Distance between conductors

Claims

1. A conveying mechanism for passing a strip of metal sheet for use in an electrical steel sheet after cold rolling and before primary recrystallization annealing; a first pair of current-carrying rolls for holding the passing metal sheet from both the front and back sides with a predetermined pressure; a second pair of current-carrying rolls installed at a predetermined distance from the first pair of current-carrying rolls in the direction of passing of the metal sheet and for holding the passing metal sheet from both the front and back sides with a predetermined pressure; and a high-frequency power source connected to the first pair of current-carrying rolls and the second pair of current-carrying rolls, which is capable of heating the edge of the metal sheet in the width direction of 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. The heating device for a metal sheet for an electromagnetic steel sheet, characterized in that the first current-carrying roll pair and the second current-carrying roll pair each have a current-carrying roll that can be energized as at least one roll of a pair of front and back rolls that make up the current-carrying roll pair.

2. A heating device for metal sheets for electromagnetic steel sheets according to claim 1, characterized in that the diameter of each of the rolls constituting the first pair of current-carrying rolls and the second pair of current-carrying rolls is 300 mm or less.

3. A heating device for metal sheets for electromagnetic steel sheets according to claim 1 or 2, characterized in that the current-carrying roll is made up of two or more divided rolls divided in the width direction of the metal sheet, and the divided rolls are arranged at least at both ends of the metal sheet in the width direction.

4. The heating device for metal sheets for electrical steel sheets according to claim 1 or 2, further comprising a backup roll for supporting the current-carrying roll.

5. A heating device for metal sheets for electromagnetic steel sheets according to claim 1 or 2, characterized in that the current-carrying roll has a cooling mechanism for water-cooling the inside of the roll.

6. A heating device for metal sheets for electromagnetic steel sheets, comprising: a transport mechanism for passing a strip of metal sheet for electromagnetic steel sheets after cold rolling and before primary recrystallization annealing; an induction heating unit for induction heating the passing metal sheet; and a high-frequency power source connected to the induction heating unit, wherein the induction heating unit uses high-frequency current from the high-frequency power source to heat the edges of the metal sheet in the width direction 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.

7. The heating device for metal sheets for electromagnetic steel sheets according to claim 6, characterized in that the induction heating unit has a pair of conductors connected to the high-frequency power supply so as to form an induction coil that circles around the metal sheet being passed through and the metal sheet passes inside the coil, the pair of conductors including a front-side conductor installed on the front side of the metal sheet and a back-side conductor installed on the back side of the metal sheet, the front-side conductor and the back-side conductor being each installed so as to traverse the metal sheet in the width direction when viewed in the thickness direction of the metal sheet and so as to be spaced apart from each other in the direction in which the metal sheet is passed through.

8. A heating device for metal plates for electromagnetic steel plates as described in claim 6, wherein the induction heating section comprises: an induction coil; and a magnetic core that concentrates the magnetic flux generated by the induction coil at the widthwise end of the metal plate so that the magnetic flux penetrates the metal plate in its thickness direction.

9. A heating device for metal sheets for electromagnetic steel sheets according to any one of claims 1, 2, and 6-8, characterized in that the frequency of the high frequency power source is 1 kHz or higher.

10. A heating device for metal sheets for electrical steel sheets according to any one of claims 1, 2, and 6-8, further comprising a holding zone for maintaining the temperature of the end portions in the width direction of the metal sheet, which has been 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, within a predetermined range for a predetermined period of time.

11. The heating device for metal sheets for electrical steel sheets according to claim 10, further comprising a cooling section for cooling the metal sheet whose temperature is maintained by the heat retention zone.

12. A method for applying electrical current to heat a metal sheet for use in an electromagnetic steel sheet after cold rolling and before primary recrystallization annealing, comprising the steps of: using the heating device for metal sheets for use in an electromagnetic steel sheet as defined in claim 1, clamping the metal sheet with the first pair of current-carrying rolls and the second pair of current-carrying rolls at a predetermined pressure; and applying current to the current-carrying rolls for a predetermined period of time, thereby heating the widthwise ends of 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.

13. 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 step of applying electrical current for a predetermined period of time using the heating device for metal sheets for use in an electrical steel sheet as defined in claim 6, thereby heating the widthwise edges of 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.

14. A method for manufacturing an electromagnetic steel sheet, comprising the steps of: cold-rolling a metal sheet for use in an electromagnetic steel sheet; subjecting the metal sheet after the cold rolling to primary recrystallization annealing, which also serves as decarburization annealing; forming an insulating layer mainly composed of MgO on the surface of the metal sheet after the primary recrystallization annealing; and subjecting the metal sheet with the insulating layer formed thereon to secondary recrystallization annealing, characterized in that the method for manufacturing an electromagnetic steel sheet further comprises, after the cold rolling and before the primary recrystallization annealing, a step of heat-treating the metal sheet by the heating method for a metal sheet for use in an electromagnetic steel sheet according to claim 12 or 13.

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