JP2013133503A - Method of producing grain-oriented electromagnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a grain-oriented electromagnetic steel sheet, capable of preventing the deterioration of magnetic property and coating characteristics from occurring in a middle section of a wound coil, caused by temperature distribution in the coil, in the process of producing the same by subjecting a blank steel sheet in a coil form to finish annealing in a batch-type box-shaped annealing furnace.SOLUTION: The method of producing a grain-oriented electromagnetic steel sheet comprises: subjecting a steel sheet to primary recrystallization annealing after cold rolling; applying an annealing separating agent onto the surface thereof; winding it on a coil; and subjecting the resulting coil to finish annealing in a batch-type box-shaped annealing furnace. The method is characterized by making the inner diameter of the coil 700 mmφ or greater and cooling the inner diameter part of the coil in the process of increasing the temperature in the finish annealing.

Description

  The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet, and specifically relates to a finish annealing technique that can produce a grain-oriented electrical steel sheet that is excellent in magnetic characteristics and film characteristics over the entire length of a coil.

  In recent years, in order to prevent global warming, the demand for energy saving is increasing. As a result, grain-oriented electrical steel sheets used as core materials for transformers, electric motors, etc. are strongly required to have excellent magnetic properties with low core loss at commercial frequencies and high magnetic flux density even at low magnetic fields. It is coming.

  The grain-oriented electrical steel sheet is characterized in that it has a crystal structure in which the <001> orientation, which is the easy axis of iron, is highly accumulated in the rolling direction of the steel sheet. In this final annealing, high temperature annealing is performed to cause secondary recrystallization, and crystal grains called {110} <001> orientation grains, so-called “goth grains”, are preferentially grown giant.

In order to develop the secondary recrystallization and to form a forsterite (Mg ₂ SiO ₄ ) film on the surface of the steel sheet, heat treatment at a high temperature for a long time is required. For this reason, the finish annealing is generally performed in coil form using a batch type box annealing furnace. However, since the steel sheet finish-annealed with coil foam is secondarily recrystallized in a state of being wound around a coil, a coil set (winding habit) is generated. However, since the crystal orientation of the secondary recrystallized grains is determined by the crystal coordinate system corresponding to the primary recrystallization texture, the <001> orientation does not grow parallel to the plate surface, and FIG. Thus, the angle with respect to the plate surface changes in the length direction of the steel plate. Therefore, the crystal grain of the product plate that has been flattened by correcting the curl after the finish annealing is such that the orientation of the <001> orientation has changed in the longitudinal direction even within the same crystal grain as shown in FIG. Become. And since this change amount becomes so large that the winding diameter to a coil is small, the orientation integration degree of a product board will fall sequentially as it goes to the inner diameter side from the coil outer diameter side at the time of finish annealing. .

Furthermore, in the high magnetic flux density grain-oriented electrical steel sheet manufactured with a final cold rolling reduction of 80% or more, the secondary recrystallized grains have a grain size of several tens of millimeters. This is much larger than a general-purpose grain-oriented electrical steel sheet having a final cold rolling reduction of about 60% and a secondary recrystallization grain size of about 5 mm. FIG. 2 shows the result of investigating the influence of the tilt angle from the plate surface (hereinafter referred to as “β angle”) on the magnetic flux density B ₈ out of the deviation angle from the ideal Goss direction using a single crystal. It is shown. From this figure, it can be seen that the decrease in the magnetic flux density is small when the β angle is in the range of 0 to 2 °, but when the β angle exceeds 2 °, the magnetic flux density is decreased by 0.03 T per 1 °.

  As a technique for suppressing such a geometric increase in β angle due to the coil curvature, Patent Document 1 proposes a method in which the coil inner diameter in finish annealing is set to 600 mmφ or more. This method of increasing the inner diameter of the coil is correct in principle and is an extremely effective means.

Japanese Patent Publication No. 50-37128

  By the way, when finishing annealing a steel sheet with coil foam, there are problems such as coil deformation and buckling of the lower part of the coil due to non-uniform temperature in the coil at the time of temperature rise in addition to the problem of the above coil set. It has been known. Furthermore, there is a problem that the magnetic properties and film properties of the middle winding portion of the coil deteriorate. This problem is that when the steel sheet is finish-annealed with coil foam, in the heating process, the coil outer peripheral surface side and the inner peripheral surface side, which have a high temperature rising rate, try to thermally expand faster than the coil middle winding portion. In this case, the coil outer peripheral surface side can be freely thermally expanded, but the coil inner peripheral surface side is inhibited from thermal expansion by the coil middle winding portion. In other words, the coil middle winding portion is compressed by the coil inner peripheral surface side, and the coil is tightened. As a result, the annealing atmosphere between the steel sheets wound around the coil stays, and secondary recrystallization and forsterite film formation are inhibited, resulting in deterioration of magnetic properties and film characteristics such as film appearance and film adhesion. Will deteriorate.

  This problem cannot be improved even if the coil inner diameter is increased as in the technique of Patent Document 1. Rather, if the inner diameter of the coil is increased, the amount of heat input from the inner surface of the coil during finish annealing heating increases, and the temperature difference between the inner surface of the coil (inner diameter portion) and the middle winding portion increases, and the coil at the inner diameter portion of the coil increases. Detrimental effects such as deformation and deterioration of magnetic properties and film properties in the middle winding portion of the coil are caused.

  The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to produce a grain-oriented electrical steel sheet by finish annealing the steel sheet in coil form using a batch type box annealing furnace. It is an object of the present invention to propose an advantageous method for producing a grain-oriented electrical steel sheet capable of suppressing the deterioration of the magnetic characteristics and the film characteristics in the middle winding portion of the coil caused by the temperature distribution in the coil.

  The inventors have intensively studied to solve the above problems. As a result, the deterioration of the magnetic properties and film properties of the coil middle winding part is caused by the compressive stress applied to the coil middle winding part due to the temperature rise on the inner peripheral surface side of the coil being faster than that of the coil middle winding part. Therefore, it is only necessary to suppress the temperature rise of the coil inner peripheral surface with respect to the coil middle winding part and the coil outer peripheral surface, and for that purpose, it is only necessary to actively cool the coil inner peripheral surface in the heating process of finish annealing. The present invention has been developed.

  That is, the present invention is a method for producing a grain-oriented electrical steel sheet by cold rolling, followed by primary recrystallization annealing, winding a steel sheet coated with an annealing separator onto a coil, and finishing annealing in a batch type box annealing furnace. In the method for producing a grain-oriented electrical steel sheet, the inner diameter of the coil is set to 700 mmφ or more, and in the finish annealing, the inner peripheral surface of the coil is heated while being cooled.

  In the method for producing a grain-oriented electrical steel sheet according to the present invention, the temperature of the inner circumferential surface of the coil during heating is set to 20 ° C. or less with respect to the outer circumferential surface of the coil in the range of 600 to 800 ° C. at least. It is characterized by that.

  According to the present invention, it is possible to improve the temperature distribution in the coil generated during finish annealing of grain-oriented electrical steel sheets, reduce the compressive stress applied to the coil middle winding part, and prevent the deterioration of magnetic characteristics and film characteristics. This greatly contributes to improving the quality and yield of grain-oriented electrical steel sheets and, in turn, saving energy in transformers and electric motors.

It is a figure explaining the cause of deterioration of the magnetic characteristic of a coil inner diameter part. Is a graph showing the effect of tilt angle β is on the magnetic flux density B _8. It is a figure explaining the reason why the nonuniformity of the temperature distribution in a coil generate | occur | produces at the time of finish annealing heating. It is a figure explaining the temperature distribution in a coil which can reduce the compressive stress concerning a coil inner volume part. It is a schematic diagram which shows an example of the inner case which can cool a coil internal peripheral surface. Is a graph showing the relationship between the coil diameter and the magnetic flux density B _8. It is a graph which shows the relationship between a coil diameter and film adhesiveness (minimum bending peeling diameter). It is a figure which shows the temperature distribution in a coil at the time of the finish annealing in an Example.

In order to solve the above-mentioned problems, the inventors made the following considerations on the relationship between the temperature distribution in the coil and the compressive stress when the coil was heated by finish annealing.
Since the heating of the coil in the finish annealing is performed by radiant heat from the inner case placed on the coil, the coil is heated from the outer peripheral surface, the inner peripheral surface and the upper side surface of the coil as shown in FIG. Therefore, these portions are heated faster than the inside of the coil, and the temperature distribution in the radial direction in the coil is higher in the order of the coil outer peripheral surface side and the inner peripheral surface side as shown by the line A in FIG. The winding has the lowest temperature distribution. With such a temperature distribution, the coil outer peripheral surface side is not hindered by thermal expansion, but the inner peripheral surface side thermal expansion is hindered by the low-temperature middle winding portion. As a result, a large compressive stress is generated in the middle winding portion of the coil, causing deterioration of magnetic characteristics and film characteristics.
Therefore, as shown by the line B in FIG. 4, the temperature distribution in which the temperature of the coil inner peripheral surface is lower than that of the coil outer peripheral surface, and preferably the temperature gradually decreases from the coil outer peripheral surface side to the inner peripheral surface side. If it can be realized, thermal expansion will occur sequentially from the outer peripheral surface side of the coil as it is heated. Therefore, it is considered that no large compressive stress is generated in the middle winding portion of the coil, and the coil is not tightened.

  Therefore, in order to realize the temperature distribution as shown by the line B in FIG. 4, the inner case shown in FIG. 5 can be improved by improving the inner case covered on the coil during finish annealing and cooling the inner peripheral surface of the coil. Was made. The inner case 3 is provided with an outer tube 4a facing the inner peripheral surface 1a of the coil and an inner tube 4b on the inner side at the center of the upper surface of the inner case 3 that covers the steel sheet coil 1 placed on the up end. As shown by the arrow in FIG. 5, the cooling gas 6 is provided in the inner tube 4b of the cylindrical recess 4 having a double-pipe structure. Then, the blown cooling gas 6 is caused to flow in the gap between the inner tube 4b and the outer tube 4a, so that the cooling gas 6 flows smoothly and the outer tube 4a is efficiently cooled. The inner peripheral surface 1a can be efficiently cooled.

Therefore, the following experiment was performed using the inner case.
C: 0.07 mass%, Si: 3.3 mass%, Mn: 0.06 mass%, Al: 0.02 mass%, N: 0.008 mass%, Se: 0.02 mass% and Sb: 0.04 mass% Then, a steel slab having a composition composed of Fe and inevitable impurities as the balance is heated to 1420 ° C., and then hot-rolled to form a hot-rolled sheet having a thickness of 2.3 mm, and annealed at 1000 ° C. for 30 seconds. After the first cold rolling, a cold rolled sheet having an intermediate thickness of 1.8 mm is formed, and after intermediate annealing at 1120 ° C. for 30 seconds, the temperature of the steel sheet is raised to 220 ° C. by processing heat generation. A second cold rolling was performed to obtain a cold rolled sheet having a final sheet thickness of 0.23 mm.

Next, after subjecting to primary recrystallization annealing also serving as decarburization at 840 ° C. for 120 seconds in a wet hydrogen atmosphere with a dew point of 60 ° C., an annealing separator mainly composed of MgO is applied to the steel sheet surface and dried. The inner diameter is 1000 mm, the outer diameter is 2000 mm, the coil A and the inner diameter is 500 mm, and the outer diameter is 2000 mm. The coil B is wound around two types of coils. The temperature was raised to 1170 ° C. in a (N ₂ + H ₂ ) mixed atmosphere, and finish annealing was performed for 5 hours in an H ₂ atmosphere.

In the finish annealing, an inner case having a cylindrical recess having a double-pipe structure shown in FIG. 5 is used, and the atmospheric temperature is set in the inner tube of the cylindrical recess between 800 and 1170 ° C. in the heating process of the finish annealing. The N ₂ gas was supplied at 500 Nm ³ / hr to cool the inner peripheral surface of the coil. Further, the temperature of the heating process is an intermediate portion between the inner diameter and the outer diameter of the coil, that is, a coil coupled to a central portion of the plate width at a position where the coil diameter is 1250 mm in the coil A and a position where the coil diameter is 900 mm in the coil B. It was set as the measured temperature.

Next, after the finish annealing, after removing the unreacted annealing separator from the steel sheet surface, a coating liquid composed of 50 mass% colloidal silica and magnesium phosphate is applied so that the double-sided weight is 10 g / m ² . A flattening annealing was performed at a temperature of 840 ° C. while applying a tension of 9 MPa to form an insulating film, thereby obtaining a product coil.

Samples were collected from the positions of the coil diameter 500 mm (the inner diameter part of the coil B), 700 mm, 1000 mm (the inner diameter part of the coil A), 1500 mm and 2000 mm (the outer diameter part) of the product coil thus obtained, and rolled. The magnetic flux density B _{8 in the} direction and the adhesion between the forsterite film were evaluated. The film adhesion was evaluated with the minimum diameter at which the test piece of rolling direction: 30 mm × rolling perpendicular direction: 300 mm was wound around a round bar having various outer diameters and bent at 180 degrees, and the film peeling of the bent portion did not occur. .

The above experimental results, in Figure 6 the relationship between the coil diameter and the magnetic flux density B _8, shown in and Figure 7 the relationship between the coil diameter and the film adhesion (minimum bend Peeling diameter). From these results, a directional electrical steel sheet with good magnetic flux density and good film adhesion can be obtained over the entire length of the coil by heating and finishing annealing the coil A having a larger coil inner diameter while cooling the inner peripheral surface side. I understand that.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
The steel slab used for the material of the grain-oriented electrical steel sheet of the present invention may be produced according to a conventional method such as a continuous casting method or an ingot-bundling rolling method, and is not particularly limited. Further, a thin cast piece having a thickness of 100 mm or less manufactured by a direct casting method can also be used.
Also, the component composition of the steel slab may be any conventionally known grain-oriented electrical steel sheet and is not particularly limited, but any component having the following component composition can be suitably used.

C: 0.01-0.10 mass%
C is not only an element useful for improving the crystal structure of a hot-rolled sheet using phase transformation, but also an element useful for generating goth-oriented grains, and is contained at least 0.01 mass%. Is preferred. On the other hand, when it contains exceeding 0.10 mass%, it will become difficult to decarburize to 0.005 mass% or less by decarburization annealing and magnetic aging does not occur. Therefore, C contained in the steel slab is preferably in the range of 0.01 to 0.10 mass%.

Si: 2.0 to 4.5 mass%
Si is an element useful for increasing the specific resistance of steel, reducing eddy current loss, and reducing iron loss, and is preferably contained in an amount of 2.0 mass% or more. However, if added over 4.5 mass%, the steel becomes brittle and it is difficult to manufacture by cold rolling. Therefore, Si is preferably in the range of 2.0 to 4.5 mass%.

Mn: 0.01 to 0.5 mass%
Since Mn has an effect of improving the hot workability of steel, it is preferable to add 0.01 mass% or more. However, if added over 0.5 mass%, the primary recrystallization texture deteriorates, secondary recrystallized grains highly accumulated in the Goth orientation are difficult to obtain, and the magnetic properties deteriorate. Therefore, Mn is preferably in the range of 0.01 to 0.5 mass%.

As an important component other than the C, Si and Mn contained in the steel slab, there is an inhibitor component.
This inhibitor component must be contained when an inhibitor is used to develop secondary recrystallization. For example, when AlN is used as an inhibitor, Al: 0.010 to 0.030 mass%, N : In the range of 0.0030 to 0.0100 mass%, and when MnS and / or MnSe is used as an inhibitor, S and Se are preferably contained alone or in total in the range of 0.010 to 0.030 mass%. . In addition, the said inhibitor utilized for secondary recrystallization may be only 1 type, and may use 2 or more types.

  On the other hand, as in the technique disclosed in Japanese Patent Application Laid-Open No. 2000-129356, when secondary recrystallization is expressed using the effect of suppressing the grain boundary migration of solute nitrogen without using an inhibitor, Al, Inhibitor components such as N, S, Se, and B are desirably reduced as much as possible. For example, Al: 0.0100 mass% or less, N: 0.0050 mass% or less, S: 0.0050 mass% or less, and Se: 0.0050 mass. It is preferable to reduce to less than%.

  Further, the grain-oriented electrical steel sheet of the present invention, in addition to the essential components described above, assists the action of an inhibitor and further improves iron loss and magnetic properties, so that Cr: 0.1 mass% or less, Ni: 0. 5 mass% or less, Mo: 0.1 mass% or less, Cu: 0.10 mass% or less, Nb: 0.05 mass% or less, Sb: 0.01 to 0.10 mass%, Sn: 0.01 to 0.20 mass%, and P: One or more selected from 0.05 mass% or less can be contained. However, addition of these elements beyond the above range causes embrittlement of the steel and causes cracking and fracture in hot rolling and cold rolling, resulting in a decrease in product yield. preferable.

  Next, the steel slab is reheated to a predetermined temperature, and then hot-rolled to form a hot-rolled sheet, and after performing hot-rolled sheet annealing as necessary, or without performing hot-rolled sheet annealing, A cold-rolled sheet having a final thickness is obtained by cold rolling at least twice with intermediate or intermediate annealing. In the cold rolling, from the viewpoint of developing a goth structure in the primary recrystallized structure, the steel plate temperature is raised to 100 to 250 ° C. by processing heat generation, or a temperature of 100 to 250 ° C. during the cold rolling. It is preferable to apply aging between passes once or a plurality of times.

  Next, the cold-rolled sheet having the final thickness is subjected to primary recrystallization annealing. In addition, this primary recrystallization annealing is also performed in the wet hydrogen atmosphere at a temperature of 750 to 900 ° C. in the case where the C content in the steel slab is high, and the C content is 0.0050 mass% or less. It is desirable to reduce it to 0.0030 mass% or less.

  The steel sheet after the primary recrystallization annealing is then batch coated with an annealing separator mainly composed of MgO on the steel sheet surface, dried, wound into a coil, subjected to secondary recrystallization, and a forsterite film is formed. It is preferable to perform finish annealing at a temperature of 1000 ° C. or higher using a box-type annealing furnace of the type.

At this time, in the present invention, the inner diameter of the coil during the above-mentioned finish annealing is set to 700 mmφ or more, and the inner peripheral surface of the coil is cooled in the heating process of the final annealing, and the temperature of the inner peripheral surface of the coil is set to the coldest spot in the coil. It is desirable to make it lower than the temperature.
Here, the reason for cooling the inner peripheral surface of the coil in the heating process of the finish annealing is that the temperature distribution in the radial direction in the coil is changed from the outer diameter side to the inner diameter side as shown by the line B in FIG. By controlling the temperature so that the temperature gradually decreases or the temperature distribution is close to that, the compressive stress of the inner coil of the coil caused by the thermal expansion of the inner diameter of the coil is suppressed, and the magnetic properties are extended over the entire length. This is to obtain a product coil having excellent coating properties.

  The reason why the coil inner diameter is 700 mmφ or more is that when the coil inner diameter is less than 700 mmφ, the curvature (curvature) of the coil inner diameter portion is large, the amount of azimuth deterioration accompanying flattening annealing increases, and the magnetic characteristics deteriorate. Further, when the coil inner diameter is less than 700 mmφ, the surface area of the inner peripheral surface of the coil is reduced, so that the inner peripheral surface of the coil is not sufficiently cooled, and the temperature distribution in the coil as shown by line B in FIG. 4 can be realized. It will be difficult.

  It is ideal to control the temperature distribution in the coil during the heating process of finish annealing as shown by line B in FIG. However, in reality, it is difficult not only to lower the temperature of the inner peripheral surface of the coil below the coldest temperature, but excessive cooling of the inner peripheral surface slows the temperature rise rate of the entire coil, and the annealing time. Will be extended. In addition, if the compressive stress received by the middle winding portion of the coil is within a range that does not adversely affect the magnetic characteristics and the film characteristics, it should be acceptable even if the temperature of the inner peripheral surface of the coil is higher than the coldest temperature. Therefore, in the present invention, the coil inner peripheral surface is cooled, and the temperature of the coil inner peripheral surface being heated is controlled to 20 ° C. or less with respect to the coil outer peripheral surface at least in the range of the temperature of 600 to 800 ° C. Is preferred. That is, this temperature range is a temperature range where grain boundary migration starts in the secondary recrystallization, and stress in this temperature range greatly affects the secondary recrystallization.

  The method for cooling the inner peripheral surface of the coil is not limited to the above-described method using the inner case in which the cylindrical concave portion of the double tube structure shown in FIG. There is no particular limitation on the method. For example, a method of cooling by installing a cooling tower for ejecting a cooling gas at the inner diameter of the coil may be used.

  After finishing annealing, the steel sheet after finish annealing is used to remove the unreacted annealing separator from the surface of the steel sheet, and if necessary, apply a coating solution of an insulating coating, and perform flattening annealing that combines this baking and shape correction. Product plate. In addition, in order to further reduce iron loss, the insulating coating is preferably a tension applying coating in which phosphate and colloidal silica are mixed.

  C: 0.07 mass%, Si: 3.3 mass%, Mn: 0.06 mass%, Al: 0.02 mass%, N: 0.008 mass%, Se: 0.02 mass% and Sb: 0.04 mass% Then, a steel slab having a composition composed of Fe and inevitable impurities as the balance is heated to 1420 ° C., and then hot-rolled to form a hot-rolled sheet having a thickness of 2.3 mm, and annealed at 1000 ° C. for 30 seconds. Was given. Next, the hot-rolled sheet is made into a cold-rolled sheet having an intermediate sheet thickness of 1.8 mm by the first cold rolling, subjected to intermediate annealing at 1120 ° C. for 30 seconds, and then the steel sheet temperature is increased to 220 ° C. by processing heat generation. The second cold rolling was performed to obtain a cold rolled sheet having a final sheet thickness of 0.23 mm. Next, after performing primary recrystallization annealing also serving as decarburization at 840 ° C. for 120 seconds in a wet hydrogen atmosphere with a dew point of 60 ° C., an annealing separator mainly composed of MgO was applied to the steel sheet surface, and Table 1 The coil having the inner diameter and outer diameter shown in FIG.

Thereafter, the coil, in a batch annealing _furnace, N 2 -H ₂ mixed atmosphere at a temperature raised to 1170 ° C., subjected to finish annealing to 5 hours under an _{H 2} atmosphere. In the finish annealing, an inner case having a cylindrical recess having a double-pipe structure shown in FIG. 5 is used, and when the furnace temperature in the heating process is between 400 and 1170 ° C., the cylindrical recess has an atmospheric temperature of N. _Two gases were supplied at 500 Nm ³ / hr to heat the coil inner peripheral surface while cooling. Further, in the heating process, the temperature in the coil at the time of finish annealing is obtained by winding a thermocouple in the central part of the three plate widths of the inner peripheral surface of the coil, the outer peripheral surface, and the middle winding part of the coil (intermediate part of the coil inner diameter and outer diameter). Changes were measured. In addition, the said cooling gas was controlled by the temperature of a coil inner volume part.

Next, the coil after the finish annealing is applied with a coating solution of 50 mass% colloidal silica and magnesium phosphate so that the weight per side is 10 g / m ² after removing the unreacted annealing separator, While applying tension, planarization annealing was performed at a temperature of 840 ° C. to form an insulating film, thereby obtaining a product coil.

The inner diameter of the product coil obtained by thus, the central part and the test piece was taken from each position of the outer diameter was evaluated the adhesion of the rolling direction of the magnetic flux density B ₈ and the forsterite film. The film adhesion was evaluated with the minimum diameter at which the test piece of rolling direction: 30 mm × rolling perpendicular direction: 300 mm was wound around a round bar having various outer diameters and bent at 180 degrees, and the film peeling of the bent portion did not occur. .

The measurement results are shown in Table 1. From Table 1, by directing the coil inner diameter to 700 mmφ or more and cooling the coil inner diameter portion, a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties can be obtained over the entire length of the coil. No. It can be seen that 4 is the most effective.
Further, FIG. 8 shows that the No. 1 at the time when the outer peripheral surface of the coil reached 800 ° C. during the heating process based on the temperature measurement results at three points in the coil radial direction. It is the figure which estimated the temperature distribution in a coil of the example of 3, 4, and 6. FIG. No. of invention example with thick coil thickness. 3 is a comparative example No. 3 having the same wall thickness. 6, the temperature distribution is improved, but the inner circumferential surface temperature of the coil is slightly higher than that of the middle winding portion of the coil. On the other hand, No. of the invention example with thin coil thickness. No. 4 shows a temperature distribution close to ideal, which is considered to have greatly improved the magnetic characteristics and the film characteristics.

  The technology of the present invention is not limited to finish annealing of grain-oriented electrical steel sheets, and can be applied to batch annealing of cold-rolled steel sheets, for example.

1: Steel plate coil 1a: Coil inner peripheral surface 1b: Coil outer peripheral surface 2: Heating furnace of annealing furnace 2a: Burner 3: Inner case (inner cover)
4: cylindrical recess 4a: outer tube of cylindrical recess 4b: inner tube of cylindrical recess 5: cooling nozzle 6: cooling gas

Claims (2)

In the method of producing a grain-oriented electrical steel sheet by cold rolling, primary recrystallization annealing, winding a steel sheet coated with an annealing separator on a coil, and finish annealing in a batch type box annealing furnace,
The inner diameter of the coil is 700 mmφ or more, and
The method for producing a grain-oriented electrical steel sheet, wherein the finish annealing is performed while cooling the inner circumferential surface of the coil. The direction according to claim 1, wherein the temperature of the inner peripheral surface of the coil being heated is set to 20 ° C. or less with respect to the outer peripheral surface of the coil at least in the range of 600 to 800 ° C. by the cooling. Method for producing an electrical steel sheet.

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