JP2012087374A - Method for manufacturing grain-oriented electromagnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an advantageous method for manufacturing a grain-oriented electromagnetic steel sheet excellent in magnetic properties at all positions of a product coil by controlling β angles so as to be in a proper range covering a total length of the coil by suppressing variation of the β angles in a secondary recrystallized grain after finish-annealing.SOLUTION: The method for manufacturing a grain-oriented electromagnetic steel sheet includes primary recrystallization annealing performed to a cold rolled material of an electromagnetic steel sheet, and finish-annealing applied thereafter for performing secondary recrystallization in a state of a coil. The finish-annealing is performed being divided into two times or more so as to be performed before and after a rewinding process of the coil for changing a curvature radius of the steel sheet or/and reversing a code of the curvature of the steel sheet, and a secondary recrystallization ratio in the first finish-annealing is set to 5 to 90% in a surface ratio.

Description

  The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet, specifically, a grain-oriented electrical steel sheet that controls the crystal orientation of secondary recrystallized grains in the coil during finish annealing and has excellent magnetic properties over the entire length of the product coil. It relates to a method of manufacturing.

  The grain-oriented electrical steel sheet is obtained by applying an annealing separator containing MgO as a main component to the steel sheet surface after the primary recrystallization annealing that has been cold-rolled to the final sheet thickness and also performing decarburization annealing. Manufactured by performing final annealing that combines crystal annealing and purification annealing, then removing unreacted annealing separator and performing planarization annealing using a continuous annealing furnace for both planarization and baking of insulating coatings. It is common. Here, the finish annealing for the secondary recrystallization is not only to form a forsterite film on the surface of the steel sheet, but also to remove the impurity components in the steel and to purify it. Since it needs to be held, it is usually performed using a batch-type box annealing furnace with the steel sheet in a coiled state.

  Since the magnetic properties of grain-oriented electrical steel sheets are greatly influenced by the crystal orientation of secondary recrystallized grains, research and development of conventional grain-oriented electrical steel sheets mainly uses the crystal orientation of secondary recrystallized grains as a magnetic property. Efforts have been made to approach the ideal orientation, the so-called Goss orientation ((110) [001]). Here, as an index representing the deviation from the ideal orientation (Goss orientation) of the secondary recrystallized grains, which is important in relation to the magnetic properties of the grain-oriented electrical steel sheet, as shown in FIG. Deviation angle α and elevation angle β from the plate surface (among the three <001> axes, the angle formed by the <001> axis closest to the rolling direction and the plate surface; hereinafter also referred to as “β angle”). is there.

  In addition, since the α angle and the β angle are smaller, the degree of integration in the Goss direction is higher, so that it may be preferable for the iron loss characteristics. However, as β = 0 ° is approached, eddy current loss increases, and on the contrary, there arises a problem that iron loss characteristics deteriorate. Therefore, it is desirable to have an appropriate β angle in order to achieve low iron loss. Generally, in a material subjected to magnetic domain subdivision processing, α = 0 °, β = 0 ° and the magnetic domain subdivision In a material that is not subjected to the crystallization treatment, α = 0 ° and β = 2 ° are preferred.

  Among the deviation angles, control of the β angle is particularly important for stably realizing a low iron loss. However, in the finish annealing performed using a box-type annealing furnace with the steel sheet in a coiled state, the secondary recrystallized grains are, as shown in FIG. 2, the curvature of the steel sheet when wound on the coil. It grows in a certain direction regardless. Here, FIG. 2 schematically shows the growth direction of the secondary recrystallized grains in the steel plate of the coil inner winding portion having a large curvature.

  Therefore, when the steel sheet that has been secondary recrystallized by finish annealing is subsequently flattened, the β angle changes at the position inside the secondary recrystallized grains, that is, the nucleation position of secondary recrystallization. As shown in FIG. 3, the β angle fluctuates at the central part and the end part (grain boundary vicinity part) of the crystal grains due to bending back by flattening (hereinafter, this change amount is also referred to as “variation amount”). Say.) As a result, in the secondary recrystallized grains that have grown greatly, fluctuations in the β angle that greatly exceed 2 ° occur between the central part of the crystal grains and the vicinity of the grain boundary. When such a large change in the β angle occurs, the magnetic permeability is lowered, the amount of auxiliary magnetic domains called lancets is increased, and the iron loss characteristic is greatly lowered.

  In order to suppress such a phenomenon, it is effective to reduce the secondary recrystallization grain size, and various techniques have been developed conventionally. For example, Patent Document 1 has a waveform in which the final thick steel plate extends in a direction intersecting the rolling direction during secondary recrystallization, and the waveform is erased in the correction process after secondary recrystallization annealing. Then, a grain oriented electrical steel sheet in which a crystal structure in which the [001] axis is inclined by 4.0 ° or less with respect to the rolling surface is present in the secondary recrystallized grains is disclosed in Patent Document 2 as an annealing separator. In the process before coating, after the final thick steel plate is given a micro curve in the direction crossing the rolling direction, a unidirectional silicon steel plate is manufactured in a normal processing process including a straightening annealing process, and the product surface is microscopic. A low iron loss directional electrical steel sheet having a [001] axis inclined by 4 ° or less with respect to the rolling surface and imparting a small strain by applying strain is further cold-rolled in Patent Document 3. Form a corrugation in the direction crossing the rolling direction on the steel plate and remove the corrugated steel plate. Carbonization annealing, followed by secondary recrystallization annealing in a continuous strip method, then applying annealing separator, then performing purification annealing by box annealing, and then flattening the corrugated steel sheet A method for manufacturing a low iron loss grain-oriented electrical steel sheet is disclosed.

Japanese Patent Publication No.57-61102 Japanese Patent Publication No.58-00747 Japanese Patent Publication No. 58-05969

  However, all of the techniques disclosed in Patent Documents 1 to 3 need to impart corrugated distortion in a direction intersecting the rolling direction of the steel sheet, but it is not possible to perform such processing on a cold-rolled steel sheet. It is unrealistic and impossible to put into practical use. Further, in the techniques disclosed in Patent Documents 1 to 3, it is necessary to greatly change the primary recrystallization texture in order to reduce the secondary recrystallization grain size while maintaining a high degree of secondary recrystallization orientation accumulation. Because there is a limit.

  The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to suppress the fluctuation of the β angle in the secondary recrystallized grains after finish annealing, and to make the β angle within the proper range over the entire coil length. The purpose of this is to propose an advantageous method for producing grain-oriented electrical steel sheets that are excellent in magnetic properties at all positions of product coils.

  In order to solve the above problems, the inventors diligently studied a method for controlling the β angle over the entire length of the coil by a method other than the prior art for refining secondary recrystallized grains. As a result, the fluctuation of the β angle in the secondary recrystallized grains is caused by bending and flattening the secondary recrystallized grains grown in one direction regardless of the curvature of the steel sheet when coiled. Since this occurs, using this phenomenon in reverse, finish annealing (secondary recrystallization annealing) is performed in multiple steps, and each time the secondary recrystallization proceeds by changing the curvature of the steel sheet, It is possible to suppress the fluctuation of the β angle in the secondary recrystallized grains to be small, and to control the fluctuation amount of the β angle to an appropriate range over the entire length of the coil, thereby improving the iron loss characteristics in all the product coils. The present invention has been conceived and the present invention has been completed.

  That is, the present invention provides a method for producing a grain-oriented electrical steel sheet by subjecting a cold-rolled electrical steel sheet material to primary recrystallization annealing and then performing secondary annealing in a coil state to produce the directional electrical steel sheet. This is a method for producing a grain-oriented electrical steel sheet characterized in that the secondary recrystallization rate in the first finish annealing is set to 5 to 90% in terms of area ratio.

  The grain-oriented electrical steel sheet manufacturing method of the present invention is characterized in that the radius of curvature of the steel sheet is changed before and after rewinding by rewinding the coil.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that the sign of the curvature of the steel sheet is reversed before and after rewinding by rewinding the coil.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that the finish annealing is performed in three or more times with a coil rewinding step in between.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that after the finish annealing, a magnetic domain refinement process is performed.

  According to the present invention, a grain-oriented electrical steel sheet having excellent magnetic characteristics over the entire length of the product coil can be manufactured, which not only improves product quality (magnetic characteristics) but also improves product yield and reduces manufacturing costs. Also contribute.

It is a figure explaining the alpha angle and beta angle in a grain-oriented electrical steel sheet. It is a figure explaining the distribution of the crystal orientation in a secondary recrystallized grain when carrying out secondary recrystallization of the steel plate of a coil state. It is a figure explaining the distribution of the crystal orientation in a secondary recrystallized grain when flattening the steel plate which carried out secondary recrystallization in the coil state. It is a graph which shows the relationship between the secondary recrystallization rate in the 1st finish annealing, and the average iron loss value of a product coil. It is a figure explaining the rewinding method of the coil by forward rewinding. It is a figure explaining the rewinding method of the coil by inversion rewinding. It is a figure explaining the secondary recrystallization in the second finish annealing when performing forward rewinding between the first finish annealing and the second finish annealing, (a) is the first finish annealing. The case where the generated secondary recrystallized grains grow as they are, (b) shows the case where new secondary recrystallized grains are generated from within the primary recrystallized grains. It is a figure explaining the secondary recrystallization in the 2nd finish annealing when reverse rewinding is performed between the 1st finish annealing and the 2nd finish annealing, and (a) occurs by the first finish annealing. (B) shows the case where new secondary recrystallized grains are generated from within the primary recrystallized grains. It is a figure explaining the influence which reverse rewinding has on distribution of β angle (in the case where secondary recrystallized grains generated by the first secondary recrystallization annealing grow by the second secondary recrystallization annealing).

The method for producing a grain-oriented electrical steel sheet according to the present invention comprises subjecting a cold-rolled Si-containing grain-oriented electrical steel sheet material (cold-rolled steel sheet) to primary recrystallization annealing and then subjecting it to secondary recrystallization in a coil state. When producing grain-oriented electrical steel sheets, the above-mentioned finish annealing is divided into multiple times with a coil rewinding process, and each time secondary recrystallization is performed by changing the curvature of the steel sheet when wound in a coiled state. By controlling the β angle fluctuation in the secondary recrystallized grains, the β angle fluctuation amount is controlled to an appropriate range over the entire coil length, and thereby the directionality with excellent magnetic characteristics over the entire coil length. This is a technique for obtaining electromagnetic steel sheets.
That is, the present invention performs the secondary recrystallization in the finish annealing in a plurality of times in order to suppress the fluctuation of the β angle in the secondary recrystallized grains and to control the fluctuation amount of the β angle to an appropriate range, It is characterized in that the curvature of the steel sheet in each finish annealing is changed each time.

  Here, when finishing annealing is performed twice, the secondary recrystallization rate in the first finishing annealing is set to 5 to 90% in terms of the area ratio in the plate surface of the secondary recrystallized portion. There is a need. When the area ratio exceeds 90%, it is substantially the same as completing the secondary recrystallization only by the first finish annealing, and a huge secondary recrystallized grain is generated and the end of the secondary recrystallized grain ( This is because the maximum value of the β angle at the crystal grain boundary (the variation amount of the β angle in the grain) becomes large. Similarly, when the area ratio is less than 5%, it is substantially the same as completing the secondary recrystallization only by the second finish annealing, and a huge secondary recrystallized grain is formed, and the β angle within the grain is also produced. This is because the amount of fluctuation of becomes large. The recrystallization rate in the first finish annealing is preferably in the range of 30 to 70% in terms of area ratio.

The experiment that became the basis for the above limitation reasons will be described.
C: 0.05 mass%, Si: 3.2 mass%, Mn: 0.10 mass%, Se: 0.02 mass%, Sb: 0.04 mass%, Al: 0.020 mass%, N: 0.0050 mass% and Cu : A steel slab containing 0.05 mass% was heated to 1400 ° C. and hot-rolled into a hot-rolled sheet having a thickness of 2.0 mm, and then subjected to hot-rolled sheet annealing at 1100 ° C. × 60 seconds, and pickling And it cold-rolled to make a cold-rolled sheet having a thickness of 0.23 mm. Next, after performing primary recrystallization annealing also serving as decarburization annealing at 850 ° C. × 120 seconds, an annealing separator mainly composed of MgO is applied, wound around a coil having an inner diameter of 500 mm and an outer diameter of 1500 mm, and finish annealing. After that, unreacted MgO was washed and removed, and flattening annealing was performed to double the baking of the insulating film to obtain a product coil.

  In the above-mentioned finish annealing, heating is started at a temperature rising rate of 20 ° C./hr, and the temperature is once lowered in the middle of the temperature rising process or in the middle of soaking after heating to 1050 ° C. After the secondary recrystallization is interrupted, the forward rotation shown in FIG. 5 to be described later is performed to reverse the positions of the inner and outer coils, and the coil is wound around a coil having an inner diameter of 500 mmφ and an outer diameter of 1500 mmφ. The coil was again heated to a temperature of 1050 ° C. at a temperature increase rate of 20 ° C./hr to complete secondary recrystallization, and then subjected to a second finish annealing for purification at 1200 ° C. × 5 hr. At the time of rewinding after the first finish annealing, a sample was taken from the central portion in the length direction of the coil, and the secondary recrystallization rate in the first finish annealing was measured.

  Samples were taken from three locations, both in the longitudinal direction at both ends and in the center, of each product coil obtained as described above, and the iron loss was measured by the Epstein test method. The average iron loss value of the coil was used. FIG. 4 shows the relationship between the secondary recrystallization rate in the first finish annealing obtained as described above and the average iron loss value of the product coil. From this figure, it can be seen that the average iron loss value is improved when the secondary recrystallization rate by the first finish annealing is in the range of 5 to 90%, and further improved in the range of 30 to 70%.

  Further, the number of finish annealing is not limited to two as described above, and may be divided into three or more times in order to reduce the fluctuation of the β angle in the secondary recrystallized grains. In addition, when finishing annealing is performed in three times, the recrystallization rate in the first finishing annealing is in a range of 5 to 70%, and the area ratio of secondary recrystallization after the second finishing annealing is 30 to 30%. A range of 90% is preferable. However, since the manufacturing cost increases as the number of finish annealing increases, it is preferable that the upper limit is about 3 times from the viewpoint of manufacturability.

  In addition, the method of dividing the finish annealing into a plurality of times is preferably a method in which the temperature is lowered in the course of the secondary recrystallization after heating to the secondary recrystallization temperature or higher, and the method of interrupting the secondary recrystallization is realistic and preferable. The method for controlling the secondary recrystallization rate in finish annealing may be obtained by previously obtaining the relationship between the secondary recrystallization annealing temperature and time and the secondary recrystallization rate, and determining the annealing temperature and time accordingly. .

  In addition, as a method of changing the curvature of the steel sheet at each finish annealing each time, a method of rewinding the coil between each finish annealing is practical and preferable. Specifically, as shown in FIG. The method of rewinding and winding the subsequent coil as it is (hereinafter also referred to as “forward rewinding”), and reversing the winding direction of the coil after finish annealing as shown in FIG. There is a method (hereinafter also referred to as “reversal rewinding”) in which the front and back sides are reversed, and any of them can be used.

  Here, the normal rewinding in FIG. 5 will be described. As a result of performing the normal rewinding, the coil inner winding part (A end) in the last finish annealing moves to the coil outer winding part. The A end changes from a large curvature (small curvature radius) to a small curvature (large curvature radius). On the contrary, the coil outer winding part (B end) in the last finish annealing moves to the coil inner winding part. As a result, the B end changes from a small curvature (large curvature radius) state to a large curvature (small curvature radius). And change.

  Further, the reverse rewinding of FIG. 6 will be described. By performing this reverse rewinding, the coil inner winding portion (A end) and the coil outer winding portion (B end) in the last finish annealing are respectively positioned in the coil and The curvature (curvature radius) changes as described above, but in addition, the bending direction of the steel sheet, that is, the sign of the curvature is also reversed. Therefore, since this rewinding has a larger amount of change in the curvature of the steel sheet than the normal rewinding, the effect of suppressing the fluctuation of the β angle is great as will be described later.

  As described above, the present invention stops the grain growth in the middle of the growth of the secondary recrystallized grains, and completes the secondary recrystallization while rewinding the coil to change the curvature of each part of the coil. Is to be controlled within an appropriate range. Therefore, the coil inner diameter and outer diameter during the first and second (or third and subsequent) finish annealing are considered after the final finish annealing in consideration of the length and thickness of the steel sheet, the size of the secondary recrystallized grains, etc. It is necessary to select an appropriate value so that the fluctuation amount (or maximum value) of the β angle becomes the smallest over the entire length of the coil after completion of the secondary recrystallization.

Hereinafter, the method of the present invention in which the finish annealing is divided into two times and will be specifically described.
FIG. 7A is a diagram showing the progress of secondary recrystallization of the coil inner winding portion (A end) when secondary recrystallization is stopped halfway in the first finish annealing. This shows a state where secondary recrystallized grains and primary recrystallized grains coexist. In this case, since the secondary recrystallized grains do not grow enormously as in the case of the finish annealing of the prior art, the deviation angle (β) between the [001] axis and the steel plate surface in the secondary recrystallized grains The variation in angle is smaller than that in FIG.

  Here, after the first finish annealing, when the coil is rewound by the forward rewinding shown in FIG. 5, the end A of the coil inner winding portion at the first finish annealing is directed to the coil outer winding portion. As a result, the large curvature (small curvature radius) of the steel sheet at the A end changes to a small curvature (large curvature radius). And in this state, when the second finish annealing is performed again and the secondary recrystallization proceeds, the secondary recrystallized grains generated by the first finish annealing grow as they are, and a huge secondary recrystallization occurs. Either a secondary recrystallized nucleus is formed from the primary recrystallized grain due to the internal strain caused by the change in curvature due to re-rolling or the secondary recrystallized grain grows. Such a phenomenon is thought to occur.

  FIG. 7B shows the former case, that is, the case where the secondary recrystallized grains generated by the first finish annealing grow as they are to form huge secondary recrystallized grains. In this case, as can be seen from FIG. 7B, the curvature of the steel sheet at the second finish annealing is smaller than that at the first finish annealing, so even if the secondary recrystallized grains grow as they are. The amount of fluctuation of the β angle in the secondary recrystallized grains does not increase as in FIG. As a result, in addition to a decrease in the β angle in the first finish annealing, an increase in the β angle in the second finish annealing is suppressed, so the β angle in the grains after the completion of the secondary recrystallization is reduced. It is expected that the amount of fluctuation will be smaller and the iron loss characteristics will be improved.

  On the other hand, FIG. 7C shows the latter case, that is, the case where new secondary recrystallized grains are generated from the primary recrystallized grains in the second finish annealing. In this case, the newly generated secondary recrystallized grains nucleate without being affected by the β angle of the secondary recrystallized grains generated by the first finish annealing, so that the β angle is close to 0 °. Grain will grow from the state. As a result, the amount of fluctuation of the β angle in the secondary recrystallized grains is smaller than in the case of FIG. 7B in which the secondary recrystallization generated by the first finish annealing grows as it is. Further, in this case, secondary recrystallized grains generated by the second finish annealing are added to the secondary recrystallized grains generated by the first finish annealing, and a crystal is formed at the boundary of the secondary recrystallized grains. Since grain boundaries and pseudo grain boundaries are formed, the same magnetic domain refinement effect as that obtained by refining secondary recrystallized grains can be obtained. As a result, in combination with the effect of improving the iron loss by suppressing the fluctuation of the β angle, a greater improvement in the iron loss characteristic is expected.

Furthermore, when the reverse rewinding shown in FIG. 6 is performed, the iron loss characteristic can be further improved as compared with the case of the forward rewinding described above.
This is because when the rewinding is performed, the A end of the coil inner winding part at the time of the first finish annealing not only moves to the coil outer winding part, but also the bending direction of the steel sheet is reversed. As a result, since the large curvature (small curvature radius) of the steel sheet at the A end changes to a small curvature (large curvature radius), the sign of the curvature is also reversed, so that the curvature of the steel sheet is greater than in the case of forward rewinding. The amount of change is large. And even when the second finish annealing is performed in this state, the secondary recrystallized grains generated by the first finish annealing grow as they are to form huge secondary recrystallized grains, or the primary It is considered that any of the phenomenon that new secondary recrystallization nuclei are generated from the recrystallized grains and the grains grow is caused.

  FIG. 8B shows the case of the former case, that is, the case where the secondary recrystallized grains generated by the first finish annealing grow as they are to form huge secondary recrystallized grains. In this case, in addition to the small β angle in the first finish annealing, as can be seen from FIG. 8 (b), as a result of the reversal of the curvature by the rewinding, the steel plate in the second finish annealing The plate surface is in a direction (direction closer to the steel plate surface) along the grain growth direction of the secondary recrystallized grains generated by the first finish annealing. As a result, the fluctuation amount of the β angle in the secondary recrystallized grains is further reduced as compared with the case of FIG. 7B, and it is expected that the iron loss characteristic is further improved.

  FIG. 8C shows the latter case, that is, a case where new secondary recrystallized grains are generated from the primary recrystallized grains in the second finish annealing. Also in this case, newly generated secondary recrystallized grains are grown from a state close to β angle = 0 ° without being affected by the β angle of the secondary recrystallized grains generated in the first finish annealing. Therefore, the fluctuation amount of the β angle is smaller than that in the case of FIG. 8B where the secondary recrystallization generated in the first finish annealing grows as it is. In addition, the generation of new secondary recrystallized grains has the same effect as the refinement of secondary recrystallized grains. Furthermore, when this rewinding is performed, since the amount of change in the curvature of the steel sheet is larger than in the case of normal rewinding, the probability that a new secondary recrystallized grain will occur from within the primary recrystallized grain, It becomes higher than the case of normal rewinding. As a result, the variation amount of the β angle in the case of FIG. 8C is the case of FIG. 8B in which the secondary recrystallization generated by the first finish annealing is grown as it is, or the above-described FIG. 7B. And it becomes smaller than the case of FIG.7 (c). Therefore, when reverse rewinding is performed, a greater iron loss improvement effect can be expected than when forward rewinding is performed.

Here, the case where the secondary recrystallized grains generated by the first finish annealing (secondary recrystallization annealing) grow as they are after reversal rewinding to form huge secondary recrystallized grains will be described.
FIG. 9 shows an electrical steel sheet material after primary recrystallization that simulates a coil inner winding part with an inner diameter of 24 inches (600 mmφ) and is curved to a curvature radius of 300 mm, by a conventional finish annealing method (one finish annealing). The distribution of β angles in the secondary recrystallized grains when the secondary recrystallized grains are grown 20 mm forward and backward from the nucleation position toward the rolling direction into giant grains having a grain size of 40 mm, and the present invention In the first finish annealing, secondary recrystallized grains were grown by 10 mm forward and backward from the nucleation position toward the rolling direction from the nucleation position, and then the curvature radius was the same 300 mm and only the bending direction was changed. After reversing, the distribution of the β angle in the grains when the second re-annealing grains are subsequently grown and the secondary recrystallized grains are grown to obtain secondary recrystallized grains having a grain size of 40 mm is expressed by β at the nucleation position. The comparison is shown with an angle = 0 °. From this figure, in the conventional finish annealing method in which secondary recrystallization is completed by one finish annealing, the maximum β angle at the end of the secondary recrystallized grain (grain boundary) reaches 4 °. In contrast, in the finish annealing method of the present invention, the maximum value of the β angle is halved to about 2 °, which is close to the ideal β angle (2 °).

  In FIG. 9, it is assumed that the β angle = 0 ° at the secondary recrystallization nucleation position, but the actual β angle of the secondary recrystallization nuclei is in the range of about ± 3 °, and the rolling direction Grain growth is not necessarily uniform. Therefore, in the conventional finish annealing method in which the secondary recrystallization is completed by one finish annealing, the maximum value of the β angle in the secondary recrystallized grains is larger than the calculated value (4 °), and the magnetic characteristics Will be greatly degraded. In this regard, the finish annealing method of the present invention can suppress an increase in the amount of fluctuation of the β angle even when the secondary recrystallized grains become large, and new secondary recrystallized grains are generated by the second finish annealing. Sometimes, the same effect as the refinement of crystal grains can be obtained, so the iron loss improvement effect is extremely large.

  In the above description, the coil inner winding portion (A end) at the first finish annealing is described as an example, but the coil outer winding portion (B end in FIGS. 5 and 5) at the first finish annealing is also described. The iron loss reduction effect can be obtained in exactly the same manner. That is, the coil outer winding (B end) at the time of the first finish annealing becomes the coil inner winding when the forward rotation rewinding in FIG. 5 is performed, and the curvature of the steel sheet is small (the curvature radius is large). In the case of changing to large (the radius of curvature is small) and performing reverse rewinding in FIG. 6, in addition to the change in the radius of curvature, the bending direction of the steel sheet (the sign of the curvature) also changes. Therefore, the coil outer winding part (B end) at the time of the first finish annealing is also the same as the inner winding part (A end), suppressing the fluctuation of the β angle in the secondary recrystallized grains and imparting an appropriate β angle, and Thus, the effect of refining crystal grains can be obtained. Therefore, the grain-oriented electrical steel sheet manufactured by the method according to the present invention (finish annealing method) suppresses the variation of β angle in the secondary recrystallized grains at all positions in the coil and has an appropriate β angle. Therefore, the iron loss characteristics can be excellent over the entire length of the product coil.

  As described above, the manufacturing method (finish annealing method) according to the present invention has a β angle of about 2 ° which is ideal for realizing a low iron loss when the magnetic domain subdivision process is not performed. Since it can be applied uniformly over the entire length, it is easy to obtain a grain-oriented electrical steel sheet that is particularly highly integrated in the Goss orientation, that is, α≈0 °, β = 0-2 °, and magnetic domain refinement treatment. An excellent effect is obtained when used in a method for producing a directional electrical steel sheet having a high magnetic flux density that is not applied. However, in the manufacturing method of the present invention, it is needless to say that the magnetic domain fragmentation treatment may be performed.

If the manufacturing method of the grain-oriented electrical steel sheet of the present invention is a method for producing a grain-oriented electrical steel sheet that is secondarily recrystallized in a coil state using a box annealing furnace, it is particularly limited except that finish annealing is performed under the above-described conditions. Can be applied without.
In addition, the production method of the present invention can be applied regardless of the difference in the mechanism for causing secondary recrystallization. For example, a directional electromagnetic wave that causes secondary recrystallization using an inhibitor such as AlN, MnS, or MnSe. The present invention can be applied to both a method for producing a steel sheet and a method for producing a grain-oriented electrical steel sheet that causes secondary recrystallization without using the inhibitor component.

  In addition, as a steel raw material used for the manufacturing method of this invention, when using an inhibitor, for example, C: 0.005-0.080 mass%, Si: 2.0-5.0 mass%, Mn: 0.03 In steel containing ˜0.20 mass%, Al, N, S, and Se were added as sol. Al: 0.010-0.120 mass%, N: 0.005-0.015 mass%, S: 0.005-0.020 mass%, Se: 0.01-0.04 mass% suitably contained, and further A steel to which Sb, Bi, Mo, Cu, P, Sn or the like is appropriately added as a reinforcing element that enhances the inhibitor effect can be suitably used. Of the above components, C is mainly removed during decarburization annealing, and S, Se, N, Al, P, and the like are removed during purification annealing in the second half of finish annealing.

  On the other hand, as a steel material when no inhibitor is used, C: 0.02 mass% or less, Si: 1.0 to 5.0 mass%, Al: 0.0100 mass% or less, N: 0.0050 mass% or less Any steel can be suitably used as long as it has B, Nb, V, S, Se and P having an inhibitory effect reduced to 0.0050 mass% or less. In addition, in order to improve an iron loss characteristic, in said steel, Mn: 0.02-2.0 mass%, Ni: 0.005-2.0 mass%, Sn: 0.01-2.0 mass%, Sb: You may add 0.005-0.5 mass%, Cu: 0.01-2.0 mass%, Mo: 0.01-0.50 mass%, Cr: 0.01-2.0 mass% suitably.

  C: 0.05 mass%, Si: 3.2 mass%, Mn: 0.10 mass%, S: 0.02 mass%, Sb: 0.04 mass%, Al: 0.020 mass%, N: 0.0050 mass% and Cu : A steel slab containing 0.05% by mass is heated to 1400 ° C. and hot-rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm, and then subjected to hot-rolled sheet annealing at 1100 ° C. for 60 seconds, and then an acid Washed and cold-rolled to obtain a cold-rolled sheet having a final sheet thickness of 0.23 mm. Next, after subjecting to primary recrystallization annealing at 850 ° C. × 120 seconds, which also serves as recrystallization annealing and decarburization annealing, an annealing separator mainly composed of MgO is applied to the steel sheet surface and dried, and an inner diameter of 500 mmφ and an outer diameter The coil was wound around a 1500 mmφ coil and subjected to finish annealing by the following two methods using a box annealing furnace.

(Method A: conventional finish annealing method)
After heating to 1200 ° C. at a rate of temperature increase of 20 ° C./hr, finish annealing was performed to complete secondary recrystallization and purification by one annealing that was held for 50 hr.
(Method B: Finish annealing method of the present invention)
After raising the temperature to 1050 ° C. at 20 ° C./hr, the secondary recrystallization is progressed halfway through the first finish annealing immediately followed by cooling, interrupting the finish annealing and cooling, as shown in FIG. After rewinding, the positions of the inner and outer coils are reversed and wound on a coil having an inner diameter of 500 mmφ and an outer diameter of 1500 mmφ. After that, the coil is heated to 1200 ° C. at 20 ° C./hr, and then 1200 ° C. × A second finish annealing for purification at 5 hr was performed to complete the secondary recrystallization. When rewinding after the first finish annealing, the progress of secondary recrystallization was confirmed with a sample taken from the central part in the length direction of the coil. As a result, the secondary recrystallization was 40% in area ratio. Completed and the rest remained primary recrystallized grains.

Next, unreacted MgO is washed and removed from the surface of the steel sheet after the finish annealing obtained as described above, and subjected to continuous annealing that combines the baking of the insulating coating and the flattening annealing to obtain a grain-oriented electrical steel sheet (product coil). . At that time, samples were taken from the inner and outer windings of the product coil, and the magnetic properties (magnetic flux density B ₈ , iron loss W _17/50 ) were measured by the Epstein test method, and the results were measured during purification annealing. Table 1 shows a comparison by position within the coil.

From Table 1, in the grain-oriented electrical steel sheet manufactured by the conventional finish annealing method (Method A), good magnetic properties are obtained in the coil outer winding portion during the purification annealing, but in the coil inner winding portion, the magnetic flux density is obtained. B ₈ is low, is larger iron loss _{W 17/50.} On the other hand, in the grain-oriented electrical steel sheet manufactured by the finish annealing method (B method) of the present invention, good magnetic properties are obtained over the entire length regardless of the position of the coil.
This is because, in the conventional finish annealing method, the secondary recrystallization is completed at the curvature radii of 250 mm and 750 mm in the coil inner winding portion and the outer winding portion, respectively. In particular, since the fluctuation amount of the β angle of the coil inner winding is large, the iron loss characteristic is greatly deteriorated. On the other hand, in the finish annealing method of the present invention, secondary recrystallized grains grow with curvature radii of 250 mm and 750 mm, respectively, in the coil inner winding portion and the outer winding portion in the first finish annealing. By performing the normal rewinding shown, the relationship is reversed in the second finish annealing, and secondary recrystallized grains grow at the curvature radii of 750 mm and 250 mm, respectively. Fluctuations can be kept small. Furthermore, in the finish annealing method of the present invention, an appropriate β angle can be imparted to the coil outer winding portion where the β angle becomes too small in the conventional finish annealing method. As a result, since the fluctuation amount of the β angle in the secondary recrystallized grains is made uniform over the entire length of the coil, it is considered that a low iron loss can be realized as compared with the conventional finish annealing method.

Steel slab containing C: 0.05 mass%, Si: 3.2 mass%, Mn: 0.10 mass%, S: 0.02 mass%, Al: 0.020 mass% and N: 0.0050 mass% at 1400 ° C After heating, it is hot-rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm, subjected to hot-rolled sheet annealing at 1100 ° C. × 60 seconds, pickled, and subjected to sheet thickness 1. The intermediate plate thickness was 5 mm, and after intermediate annealing at 1050 ° C. × 60 seconds, the cold rolled plate having a final plate thickness of 0.23 mm was obtained by final cold rolling. Next, after subjecting to primary recrystallization annealing at 850 ° C. × 120 seconds, which also serves as recrystallization annealing and decarburization annealing, an annealing separator mainly composed of MgO is applied to the steel sheet surface and dried, and an inner diameter of 500 mmφ and an outer diameter The coil was wound around a 1500 mmφ coil and subjected to finish annealing by the following two methods using a box annealing furnace.
(A 'method: conventional finish annealing method)
After heating up to 900 ° C. at a rate of temperature increase of 15 ° C./hr, holding for 30 hr to complete secondary recrystallization, finish annealing was performed to purify at 1200 ° C. × 5 hr.
(Method C: Finish annealing method of the present invention)
After heating to 900 ° C. at 15 ° C./hr and continuing the secondary recrystallization halfway through the first finish annealing that is held for 10 hr, the finish annealing is interrupted and cooled, and the rewinding shown in FIG. The positions and front and back of the inner and outer windings of the coil are reversed and wound on a coil having an inner diameter of 500 mmφ and an outer diameter of 1500 mmφ, and then this coil is heated to 900 ° C. at 30 ° C./hr and held for 30 hr. After the next recrystallization was completed, a second finish annealing was performed to purify at 1200 ° C. × 5 hr. When rewinding after the first finish annealing, the progress of secondary recrystallization was confirmed with a sample taken from the central portion in the length direction of the coil. As a result, the secondary recrystallization was found to be 50% in area ratio. Completed and the rest remained primary recrystallized grains.

Next, unreacted MgO is washed and removed from the surface of the steel sheet after the finish annealing obtained as described above, and subjected to continuous annealing that combines the baking of the insulating coating and the flattening annealing to obtain a grain-oriented electrical steel sheet (product coil). . At that time, samples were taken from the inner and outer windings of the product coil, and the magnetic properties (magnetic flux density B ₈ , iron loss W _17/50 ) were measured by the Epstein test method, and the results were measured during purification annealing. Table 2 shows a comparison by position within the coil.

From Table 2, in the grain-oriented electrical steel sheet manufactured by the conventional finish annealing method (A ′ method), good magnetic properties are obtained in the coil outer winding portion during the purification annealing, but in the coil inner winding portion, the magnetic flux low density _{B 8,} is larger iron loss value _{W 17/50.} On the other hand, in the grain-oriented electrical steel sheet manufactured by the finish annealing method (C method) of the present invention, good magnetic properties are obtained over the entire length regardless of the position of the coil. Moreover, the magnetic properties of the grain-oriented electrical steel sheet produced by the conventional finish annealing method are not significantly different from the magnetic properties of the comparative example of Example 1, whereas it was produced by the finish annealing method (Method C) of the present invention. The magnetic properties of the grain-oriented electrical steel sheet are further improved over the magnetic properties of the inventive example (Method B) of Example 1, and the difference from the comparative example is large.
This is because, in the finish annealing method (Method B) of the present invention of Example 1, the rewinding after the first finish annealing is performed by the forward rewinding shown in FIG. In the example finish annealing method (C method), since the rewinding after the first finish annealing is performed by reversal rewinding that reverses the bending direction of the steel plate shown in FIG. 6, the variation in β angle is smaller. In addition to being suppressed, it is considered that a pseudo grain boundary was introduced and the effect of refining secondary recrystallized grains was developed.

C: 0.05 mass%, Si: 3.2 mass%, Mn: 0.10 mass%, S: 0.02 mass%, Sb: 0.04 mass%, Al: 0.0050 mass%, N: 0.0030 mass%, and Cu : A steel slab containing 0.05 mass% was heated to 1250 ° C., then hot-rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm, and subjected to hot-rolled sheet annealing at 1100 ° C. × 60 seconds, and then an acid Washed and cold-rolled to obtain a cold-rolled sheet having a final sheet thickness of 0.23 mm. Next, after performing primary recrystallization annealing at 850 ° C. × 120 seconds, which is both recrystallization annealing and decarburization annealing, the following A ″ method applies an annealing separator mainly composed of MgO, In the C ′ and D methods, a grain-oriented electrical steel sheet is manufactured by winding up a coil having an inner diameter of 500 mmφ and an outer diameter of 1500 mmφ without applying an annealing separation good, and performing a final annealing by the following three methods using a box annealing furnace. did.
(A ″ method: conventional finish annealing method)
After heating to 900 ° C. at a rate of temperature increase of 10 ° C./hr, holding for 50 hr to complete secondary recrystallization, finish annealing was performed to purify at 1200 ° C. × 5 hr.
(C ′ method: finish annealing method of the present invention)
After heating up to 900 ° C. at 10 ° C./hr, the secondary recrystallization is progressed halfway through the first finish annealing that is held for 20 hr, and then the finish annealing is interrupted and cooled, and an annealing separator mainly composed of MgO. Is applied and dried, and the positions and front and back of the inner and outer windings of the coil are reversed by reversing rewinding as shown in FIG. 6 and wound around a coil having an inner diameter of 500 mmφ and an outer diameter of 1500 mmφ. After the temperature was raised to 900 ° C. in hr, the secondary recrystallization was completed by holding for 40 hr, and then a second finish annealing was performed to purify at 1200 ° C. × 5 hr. When rewinding after the first finish annealing described above, the progress of secondary recrystallization was confirmed with a sample taken from the central portion in the length direction of the coil. As a result, secondary recrystallization was observed at an area ratio of 60%. Completed and the rest remained primary recrystallized grains.
(Method D: Finish annealing method of the present invention)
After raising the temperature to 900 ° C. at 10 ° C./hr and performing the first finish annealing for 10 hours, the secondary recrystallization is progressed halfway, then the finish annealing is interrupted and cooled, and the inversion shown in FIG. By rewinding, the positions and front and back of the inner and outer coils of the coil were reversed and wound around a coil having an inner diameter of 500 mmφ and an outer diameter of 1500 mmφ to obtain a coil having an inner diameter of 500 mmφ and an outer diameter of 1500 mmφ.
Next, after the coil was heated to 900 ° C. at 30 ° C./hr and subjected to second finish annealing for 10 hours, secondary recrystallization was further advanced, and then the finish annealing was interrupted and cooled. The positions of the inner and outer coils and the front and back of the coil were reversed by the reversal rewinding shown in FIG.
Thereafter, the temperature is raised at 30 ° C./hr, and after secondary recrystallization is completed at 900 ° C. × 20 hr, an annealing separator containing MgO as a main component is applied, and the third finish is purified at 1200 ° C. × 5 hr. Annealed. The progress of secondary recrystallization was confirmed with the samples collected during the rewinding after the first finish annealing and after the second finish annealing, and the area ratio was 30% and 60%, respectively. The next recrystallization was completed, and the rest remained primary recrystallized grains.

  Next, unreacted MgO is washed and removed from the surface of the steel sheet after finish annealing obtained as described above, and after continuous annealing that combines baking of the insulating coating and flattening annealing, it is 10 ° with respect to the direction perpendicular to the rolling direction. In the inclined direction, a plasma jet was linearly irradiated at intervals of 8 mm to perform magnetic domain subdivision treatment to obtain a grain-oriented electrical steel sheet (product coil). Next, samples are taken from the inner and outer windings of the product coil obtained as described above, the magnetic properties are measured with an SST tester (Single Strip Tester), and the results are classified according to the position in the coil during purification annealing. Table 3 shows a comparison.

From Table 3, in the grain-oriented electrical steel sheet manufactured by the conventional finish annealing method (A ″ method), the magnetic properties were improved by applying the magnetic domain subdivision treatment, but the coil outer winding during the purification annealing again in part, the magnetic flux density _{B 8} is low, is larger iron loss value _{W 17/50.} On the other hand, in the grain-oriented electrical steel sheet manufactured by the finish annealing method (C ′ method, D method) of the present invention, the finish annealing was performed by changing the curvature of the steel sheet by rewinding the coil. Combined with the effect of the subdividing treatment, good magnetic properties are obtained over the entire length regardless of the position of the coil. In particular, in the D method in which the coil is rewound twice, the magnetic characteristics are remarkably improved.

Claims (5)

In the method of producing a grain-oriented electrical steel sheet by subjecting a cold-rolled electrical steel sheet material to primary recrystallization annealing and then subjecting it to secondary recrystallization in a coiled state, the above-mentioned finish annealing is performed by a coil rewinding step. A method for producing a grain-oriented electrical steel sheet, characterized in that the secondary recrystallization rate in the first finish annealing is 5 to 90% in terms of area ratio. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the curvature radius of the steel sheet is changed before and after the rewinding by rewinding the coil. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein the sign of the curvature of the steel sheet is reversed before and after the rewinding by rewinding the coil. The method for manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the finish annealing is performed three or more times with a coil rewinding step in between. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein a magnetic domain refinement treatment is performed after the finish annealing.

Images