JP5962565B2 - Planarization annealing method and manufacturing method of grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for flattening and annealing a grain-oriented electrical steel sheet and a method for producing a grain-oriented electrical steel sheet using the method for flattening annealing. In particular, the present invention is intended to advantageously improve iron loss.

  Oriented electrical steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and are required to have excellent magnetic properties such as magnetic flux density and iron loss. As a method for producing such a grain-oriented electrical steel sheet, a slab having a thickness of 100 to 300 mm is heated and then hot-rolled, and the obtained hot-rolled sheet is once or twice or more with intermediate annealing interposed therebetween. The final thickness was obtained by cold rolling, and after decarburization annealing, after applying an annealing separator, the final finish annealing was performed for the purpose of secondary recrystallization and purification, and the insulation coating was also baked. It is common to perform flattening annealing.

That is, generally, as disclosed in Patent Documents 1 to 3, after the slab is heated to a high temperature to dissolve the inhibitor component, it is reprecipitated in the steps after hot rolling and once. Alternatively, the primary recrystallized grain structure is controlled by two or more cold rollings sandwiching the intermediate annealing, and then the primary recrystallized structure is crystallized having a {110} <001> orientation in the rolling direction in the final finish annealing. The required magnetic properties are ensured by secondary recrystallization.
The <001> orientation is the direction of the easy axis of magnetization of iron, which makes use of the soft magnetic properties of iron, resulting in an iron core material with extremely low iron loss.
On the other hand, recently, as disclosed in Patent Document 4, a technique for expressing secondary recrystallized grains without using an inhibitor component has also been developed. In this case, high-temperature slab heating is not required. .

  Such grain-oriented electrical steel sheets are always required to have further reduced iron loss. For example, Patent Document 5 discloses a grain-oriented electrical steel sheet with low iron loss by appropriately controlling the amounts of Ni and Sb. It is disclosed that it can be obtained.

On the other hand, regarding flattening annealing, in Patent Document 6, the tension in the annealing furnace is made independent of the tension in the drying furnace prior to that, and the tension is reduced to 0.5 kg / mm ² (about 5 MPa) or less, thereby reducing iron loss. It is reported that it can be planned.
Patent Document 7 discloses that a high tension can be applied by controlling the particle diameter to a coarser side in a material to which Bi is added.

U.S. Patent No. 1965559 Japanese Patent Publication No. 40-15644 Japanese Patent Publication No.51-13469 JP 2000-129356 JP Japanese Patent No. 33757001 JP 59-96227 JP-A-8-269571

  However, recently, further cost reduction is required to increase the competitiveness of products, and production rationalization is an urgent task. There is an increasing need for shortening the time for flattening annealing focused in the present invention. However, within the range of the prior art, there has been a new problem that a desired iron loss cannot be obtained if the planarization annealing is shortened.

The present invention advantageously solves the above problem, and proposes a method for flattening annealing of grain-oriented electrical steel sheets that can effectively reduce the iron loss value after annealing even in a short period of flattening annealing. For the purpose.
Moreover, this invention aims at proposing the manufacturing method of the grain-oriented electrical steel sheet which can obtain the grain-oriented electrical steel sheet excellent in iron loss by using the above-mentioned planarization annealing method.

Now, the inventors have conducted intensive research to achieve the above-mentioned purpose.
As a result, it was newly found out that the iron loss can be reduced by devising the heat pattern of the flattening annealing even when the flattening annealing is shortened.
In other words, when a process that brings about a temperature change of 10 ° C or more within the soaking residence time in flattening annealing was intentionally added, residual strain that could not be removed sufficiently by conventional short-time flattening annealing was effectively removed. It has been sought to be done.

In addition, since the amount of strain remaining after the flattening annealing is extremely small, it is difficult to directly detect it.
Therefore, in the present invention, instead of detecting the residual strain, the residual strain amount is _calculated by the difference between the iron loss W _17/50 after the flattening annealing and the iron loss W _17/50 after the final strain relief annealing. I guessed it.
As a result, when a treatment that brings about a temperature change of 10 ° C. or more within the soaking residence time of the flattening annealing according to the present invention, the final distortion removal is performed from the iron loss W _17/50 after the flattening annealing. It was found that the value obtained by subtracting the iron loss W _17/50 after annealing can be suppressed to 0.020 W / kg or less.
Here, the processing called “final strain relief annealing” performed after the planarization annealing in the present invention is performed at a temperature equal to or higher than the highest temperature of the planarization annealing, thereby introducing the processing strain introduced at a low temperature such as room temperature. Not only is it considered to have an additional effect of releasing inevitable residuals of elastoplastic strain introduced during shape correction in the high temperature region of flattening annealing, so-called normal This is different from what is performed in order to release the elastoplastic strain introduced when shearing and punching are performed near room temperature in the strain relief annealing.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. Rewinding the grain-oriented electrical steel sheet coil after final finish annealing, containing C: 0.0050% or less, Si: 2.5-4.0% and Mn: 0.01-1.0%, the balance being Fe and unavoidable impurities. While flattening annealing,
800 to 900 ° C. The soaking temperature in said flattening annealing, while soaking residence time within 60 seconds, and at least one or more added Turkey a process of giving a temperature change of 10 to 30 ° C. in the residence time A method for flattening and annealing a grain-oriented electrical steel sheet characterized by:

2. In the planarization annealing, according to the amount of Si in the steel, the tension applied to the steel sheet in a temperature range of 800 ° C. or higher is divided into the following patterns (I) to (III): 2. A method for flattening and annealing a grain-oriented electrical steel sheet according to 1.
(I) If the Si content is 2.5% or more and less than 3.0% by mass%, additional tension: 10.0-15.0MPa
(II) When the Si content is 3.0% or more and less than 3.5% by mass%, additional tension: 7.5 to 12.5 MPa
(III) When the Si content is 3.5% or more and less than 4.0% by mass%, the applied tension: 5.0 to 10.0 MPa

3. 3. The method for flattening and annealing a grain-oriented electrical steel sheet according to the above 1 or 2, wherein a maximum temperature reached during the flattening annealing is 850 ° C. or higher.

4). The grain-oriented electrical steel sheet coil further includes, in mass%, Ni: 0.005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 0.50%, Cr: 0.01 to 1.50%, P: One or more kinds selected from 0.0050 to 0.50%, Nb: 0.0005 to 0.0100%, and Mo: 0.01 to 0.50% are contained. Flattening annealing method for steel sheet.

5. A method for producing a grain-oriented electrical steel sheet, comprising performing planarization annealing according to any one of claims 1 to 4 after final finish annealing in the production of a grain-oriented electrical steel sheet.

  ADVANTAGE OF THE INVENTION According to this invention, the deterioration of the iron loss which was conventionally anxious about planarization annealing can be improved effectively, and the grain-oriented electrical steel sheet of low iron loss can be obtained stably.

It is a figure which shows an example of the heat pattern of planarization annealing. It is a figure which shows the relationship between the temperature change ( _DELTA) T at the time of flattening annealing, and iron loss deterioration amount ( _{DELTA) W17 / 50} .

Hereinafter, the present invention will be specifically described.
First, the experimental results that led to the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
Steel containing C: 0.06%, Si: 3.6%, Mn: 0.06%, S: 0.01%, Se: 0.01%, sol. Al: 0.03%, N: 0.007%, the balance being Fe and inevitable impurities The slab was heated at 1380 ° C for 30 minutes, hot rolled into a 2.6mm thick hot rolled sheet, then subjected to hot rolled sheet annealing at 980 ° C for 1 minute, and then in the first cold rolling A cold rolled sheet having a thickness of 1.9 mm was obtained, and after intermediate annealing at 1050 ° C. for 1 minute, a final sheet thickness of 0.23 mm was obtained by a second cold rolling. Next, this final cold-rolled sheet is decarburized and annealed at 820 ° C for 2 minutes in wet hydrogen, and after applying and drying the annealing separator, it also serves as secondary recrystallization annealing and purification annealing. Final finish annealing was performed at 1200 ° C for 5 hours. Note that the amount of C after finish annealing was less than 20 ppm.

Thereafter, the finish-annealed plate was baked by flattening annealing after removing the unreacted annealing separator and applying a glass coating.
As shown in FIGS. 1A to 1D, the flattening annealing is performed in the conventional heat pattern a (T ₁ = 860 ° C., ΔT = 0), heat pattern b (T ₁ = 820 to 857 ° C., T ₂ = 860 ° C., ΔT = T ₂ −T ₁ ), heat pattern c (T ₁ = 860 ° C., T ₂ = 840 to 857 ° C., ΔT = T ₁ −T ₂ ), heat pattern d (T ₁ = 830 to 840) C, T ₂ = 860 ° C., T ₃ = 830 to 840 ° C., ΔT = T ₂ −T ₁ = T ₂ −T ₃ ). At this time, soaking time, when the heat pattern a is a from the first T ₁ to the last 40 seconds, heat pattern b, and if the c is from start of T ₁ to the end of T ₂ 40 seconds In the case of the heat pattern d, the time from the beginning of T ₁ to the end of T ₃ was 40 seconds.

From the steel plate after flattening annealing, 10 test pieces for a single-plate magnetic test each having a rolling width direction of 100 mm and a length direction of 400 mm were cut out for each condition, and the iron loss W _{17/50 was measured} in accordance with JIS C 2556. Was measured. Thereafter, the test piece was subjected to strain relief annealing at 880 ° C. for 2 hours in a nitrogen atmosphere and cooled, and then the iron loss value was measured in the same manner as described above. Here, a value obtained by subtracting the iron loss value after strain relief annealing from the iron loss value after flattening annealing is defined as iron loss deterioration amount ΔW _17/50 .
The meaning of this ΔW _17/50 is the amount of iron loss deterioration due to strain that was introduced during the flattening annealing and remained after that, and remains in the strain relief annealing at a temperature higher than the maximum temperature of the flattening annealing. It is clarified by obtaining the standard value of iron loss by removing the strain.

FIG. 2 shows the result of the investigation on the iron loss deterioration ΔW _17/50 .
As shown in the figure, in the heat pattern a (ΔT = 0), which is the conventional heat pattern, the deterioration amount of iron loss exceeded 0.03 W / kg, whereas ΔT should be 10-30 ° C. It can be seen that the iron loss deterioration amount ΔW _17/50 can be significantly suppressed. In particular, in the heat pattern d in which the treatment for giving a predetermined temperature change within the soaking residence time is added twice, a further iron loss improvement effect is obtained.

  The reason why the deterioration of iron loss could be suppressed by adopting a heat pattern that changes the temperature during soaking in flattening annealing has not been fully elucidated, but the coil length in the soaking furnace It is thought that a moderate stress distribution is generated in the furnace due to the temperature difference in the direction, the deterioration of the shape in the coil width direction is improved, and the residual strain becomes difficult to remain.

Next, the reason why the steel plate composition after final finish annealing is limited to the above range in the present invention will be described.
Particularly important components in the present invention are C related to magnetic aging, Si having a function of increasing specific resistance, and Mn improving hot brittleness.
C: 0.0050% or less Since the magnetic aging tends to occur when the C content exceeds 0.0050%, the C content is 0.0050% or less. Preferably it is 0.0030% or less, More preferably, it is 0.0020% or less.

Si: 2.5-4.0%
Si increases the specific resistance of the steel sheet and contributes to the reduction of iron loss. However, if the content is less than 2.5%, the iron loss as expected in the present invention cannot be obtained. On the other hand, if the content exceeds 4.0%, the cold rolling property is impaired and the production becomes difficult. Therefore, the Si content is 2.5 to 4.0%. However, it is preferable to set it as 3.0 to 4.0% according to the request | requirement level with respect to an iron loss, More preferably, it is the range of 3.5 to 4.0%.

Mn: 0.01-1.0%
Mn is an element effective for preventing cracking during hot rolling due to hot brittleness. However, if the content is less than 0.01%, the effect cannot be said to be sufficient. On the other hand, if the content exceeds 1.0%, the magnetic properties are deteriorated. Therefore, the amount of Mn is set to 0.01 to 1.0%. Preferably it is 0.05 to 0.50% of range.

The essential components have been described above. In the present invention, the following elements can be appropriately contained as components that improve the magnetic properties more stably industrially. The balance is Fe and inevitable impurities.
Ni: 0.005-1.50%
Ni works to improve the magnetic properties by increasing the uniformity of the hot-rolled sheet structure, and for that purpose, it is preferable to contain 0.005% or more, but if the content exceeds 1.50%, the desired secondary recrystallization Ni is difficult to obtain, and the magnetic properties deteriorate, so it is desirable to contain Ni in the range of 0.005 to 1.50%.

Sn: 0.01-0.50%
Sn is a useful element that suppresses nitriding and oxidation of steel sheets during secondary recrystallization annealing and promotes secondary recrystallization of grains having good crystal orientation to improve magnetic properties. However, if it exceeds 0.50%, the cold rolling property deteriorates, so it is desirable to contain Sn in the range of 0.01 to 0.50%.

Sb: 0.005-0.50%
Sb is a useful element that effectively suppresses nitridation and oxidation of steel sheets during secondary recrystallization annealing, promotes secondary recrystallization of grains with good crystal orientation, and effectively improves magnetic properties. For the purpose, it is preferable to contain 0.005% or more, but if it exceeds 0.50%, the cold rolling property deteriorates, so Sb is preferably contained in the range of 0.005 to 0.50%.

Cu: 0.01 to 0.50%
Cu suppresses oxidation of the steel sheet during secondary recrystallization annealing, promotes secondary recrystallization of grains having a good crystal orientation, and effectively improves magnetic properties. However, if it exceeds 0.50%, the hot rolling property is deteriorated, so it is desirable to contain Cu in the range of 0.01 to 0.50%.

Cr: 0.01 to 1.50%
Cr has a function of stabilizing the formation of the forsterite film, and for that purpose, it is preferable to contain 0.01% or more, but when the content exceeds 1.50%, a desired secondary recrystallization can be obtained. Since it becomes difficult and the magnetic properties deteriorate, it is desirable to contain Cr in the range of 0.01 to 1.50%.

P: 0.0050-0.50%
P has a function of stabilizing the formation of the forsterite film. For that purpose, P is preferably contained in an amount of 0.0050% or more. However, if the content exceeds 0.50%, the cold rolling property deteriorates, so P is 0.0050 to It is desirable to make it contain in 0.50% of range.

Nb: 0.0005-0.0100%, Mo: 0.01-0.50%
Each of Nb and Mo has an effect of suppressing sag after hot rolling through suppression of cracking due to temperature change during slab heating. If any of these elements does not reach the lower limit value, the effect of suppressing the hege is small, whereas if the upper limit value is exceeded, the iron loss deteriorates when remaining to the final product by forming carbide or nitride. In order to cause it, it is desirable to make it contain in said range, respectively.

Next, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention will be described.
In the present invention, as long as a predetermined amount of C, Si, and Mn is contained after final finish annealing, the slab composition may be any method with or without using an inhibitor. As an example of a characteristic component in the slab stage, when an inhibitor is used, it is essential to contain C and the inhibitor components S, Se, and further Al and N. On the other hand, when an inhibitor is not used, it is essential to reduce the inhibitor components S, Se, and Al.

First, a preferred slab composition when using an inhibitor will be described.
C: 0.02-0.12%
C is an element useful not only for uniform refinement of the structure during hot rolling and cold rolling, but also for the development of Goss orientation, and at least 0.02% needs to be contained. However, if it exceeds 0.12%, decarburization becomes difficult and the Goss orientation is disturbed. Therefore, the upper limit is made 0.12%. Preferably it is 0.03 to 0.08% of range.
The Si amount and the Mn amount are the same as those described above in the steel plate composition after the final finish annealing.

S, Se: 0.005-0.05%
S and Se are elements that act as inhibitors by forming MnS and MnSe, respectively. However, if the amount of S and Se is less than 0.005%, securing of the suppressing force is not sufficient, while if it exceeds 0.05%, the effect is impaired. Therefore, 0.005 to 0.05% is set for both single addition and composite addition. Preferably it is 0.01 to 0.03% of range.

Al: 0.005-0.040%
Al is an element that acts as an inhibitor by forming N and AlN described later. However, if the amount of Al is less than 0.005%, the securing force is not sufficient, and if it exceeds 0.040%, the effect is impaired, so the amount of Al is made 0.005 to 0.040%. Preferably it is 0.01 to 0.030% of range.

N: 0.004 to 0.020%
N is an element that forms Al and AlN and acts as an inhibitor. However, if the amount of N is less than 0.004%, it is not sufficient to secure the suppressive force. On the other hand, if it exceeds 0.020%, the effect is impaired, so the amount of N is made 0.004 to 0.020%. Preferably it is 0.005 to 0.010% of range.

The above-described inhibitor components MnS, MnSe, and AlN may be used alone or in combination.
The elements described above are necessary elements in the slab stage, but Ni, Sn, Sb, Cu, Cr, P, Nb, Mo, and the like described above can be added to further improve the magnetic characteristics.
The contents of these elements and the reasons for their limitation are the same as described above.

Next, a preferred slab composition when no inhibitor is used will be described.
C: 0.08% or less C is an element useful for improving the primary recrystallized texture. However, if the content exceeds 0.08%, the primary recrystallized texture is deteriorated. Therefore, an inhibitor is not used. In some cases, the content is 0.08% or less. A desirable addition amount from the viewpoint of magnetic properties is in the range of 0.01 to 0.06%. If the required magnetic property level is not so high, C may be set to 0.01% or less in order to omit or simplify the decarburization in the primary recrystallization annealing.
The Si amount and the Mn amount are the same as those described above in the steel plate composition after the final finish annealing.

S, Se and O: each less than 50 ppm When the amounts of S, Se and O are each 50 ppm or more, it is difficult to obtain a desired secondary recrystallization. This is because coarse oxides and MnS and MnSe coarsened by slab heating make the primary recrystallized structure non-uniform. Therefore, S, Se, and O must all be suppressed to less than 50 ppm.

sol.Al: less than 100ppm
Al forms a dense oxide film on the surface, which may make it difficult to control the amount of nitridation during nitridation or inhibit decarburization. Therefore, Al is suppressed to less than 100 ppm in terms of sol.Al. did.

N: 80 ppm or less In order to create a texture by applying inhibitorless, it is necessary to suppress the N content to 80 ppm or less. This is because if the amount of N exceeds 80 ppm, adverse effects such as the effect of grain boundary segregation and the formation of trace amounts of nitrides cause deterioration of the texture. Moreover, since it may cause defects such as “fluff” at the time of slab heating, it is necessary to suppress it to 80 ppm or less. Desirably, it is 60 ppm or less.

The elements described above are necessary elements in the slab stage, but Ni, Sn, Sb, Cu, Cr, P, Nb, Mo, and the like described above can be added to further improve the magnetic characteristics.
The contents of these elements and the reasons for their limitation are the same as described above.

Next, a specific manufacturing process will be described.
Steel slabs adjusted to the preferred component composition as described above, when the inhibitor component is added, it is heated to 1250 ° C or higher due to the solid solution of the inhibitor component, and then subjected to hot rolling, while the inhibitor is not used. For this, it is desirable to use hot rolling with heating below 1250 ° C.
Next, after performing hot-rolled sheet annealing as necessary, the final product thickness is obtained by cold rolling twice or more times with one or intermediate annealing.

Thereafter, when grooves for magnetic domain subdivision are formed, grooves in a direction substantially perpendicular to the rolling direction may be formed by electrolytic treatment. This is followed by decarburization annealing that serves the purpose of primary recrystallization and subscale formation. However, these may be implemented separately for each purpose. After the decarburization annealing, an annealing separator for preventing seizure in the final finish annealing that is subsequently applied is applied.
In addition, as an adjustment of the inhibitor, the amount of N or S in the steel can be adjusted by nitriding or sulfurating during the heating process from decarburization annealing to final finish annealing.
After decarburization annealing, after winding on the coil, after final finishing annealing for the purpose of secondary recrystallization and purification annealing, after removing unreacted annealing separator, baking and shape of insulating coating Perform flattening annealing that also serves as correction.

The flattening annealing is an indispensable process performed to correct the winding gusset of the coil formed by the final finish annealing. In the present invention, the heat pattern during the flattening annealing is important.
The purpose of the present invention is to shorten the flattening annealing, so the soaking residence time is set to 60 seconds or less. Preferably it is within 50 seconds, more preferably within 40 seconds.
In addition, in the present invention, it is important to add at least one treatment that brings about a temperature change of 10 to 30 ° C. within the soaking residence time. The direction of temperature change is effective for both increasing and decreasing the temperature, and both may be incorporated in a series of heat patterns.
In addition, the soaking temperature in the flattening annealing is 800 ° C. or more from the point of the straightening effect, but the maximum temperature achieved during the flattening annealing is desirably 850 ° C. or more for the purpose of achieving a short time, More desirably, it is 860 ° C or higher. The upper limit is set to 900 ° C. because the insulation coating deteriorates when it exceeds 900 ° C.

Furthermore, the tension applied to the coil during the flattening annealing is preferably controlled as in the following (I) to (III) according to the amount of Si in the steel.
(I) When Si content is 2.5% or more and less than 3.0%, additional tension: 10.0-15.0MPa
(II) When the Si content is 3.0% or more and less than 3.5%, additional tension: 7.5 to 12.5 MPa
(III) When Si content is 3.5% or more and less than 4.0%, additional tension: 5.0 to 10.0 MPa
As described above, the additional tension is adjusted according to the amount of Si in the steel, because the higher the amount of Si, the easier the plastic deformation occurs at high temperatures, so the optimum tension value to be applied decreases. Yes.

  In the present invention, any conventionally known heat-resistant or non-heat-resistant magnetic domain fragmentation method can be applied. For the non-heat-resistant type, it is effective to subject the steel sheet surface in any step after secondary recrystallization to magnetic domain refinement using an electron beam or continuous laser. However, there is no damage to the insulating coating on the surface deeper than the laser, re-coating can be eliminated, and this is advantageous in terms of economy. Of the heat-resistant molds, the method of etching the final cold-rolled plate is reasonable because a base coating and an insulating coating are subsequently applied.

Example 1
Steel containing C: 0.06%, Si: 3.6%, Mn: 0.06%, S: 0.01%, Se: 0.01%, sol. Al: 0.03% and N: 0.007%, the balance being Fe and inevitable impurities The slab was heated at 1380 ° C for 30 minutes, hot rolled into a 2.6mm thick hot rolled sheet, then subjected to hot rolled sheet annealing at 980 ° C for 1 minute, and then in the first cold rolling A cold rolled sheet having a thickness of 1.9 mm was obtained, and after intermediate annealing at 1050 ° C. for 1 minute, a final sheet thickness of 0.23 mm was obtained by a second cold rolling. Next, this final cold-rolled sheet is decarburized and annealed at 820 ° C for 2 minutes in wet hydrogen, and after applying and drying the annealing separator, it also serves as secondary recrystallization annealing and purification annealing. Final finish annealing was performed at 1200 ° C for 5 hours. Note that the amount of C after finish annealing was less than 20 ppm.
Then, this finish-annealed plate was baked by flattening annealing shown in Table 1 after removing the unreacted annealing separator and applying a glass coating.

From the steel plate after flattening annealing, 10 test pieces for a single-plate magnetic test each having a rolling width direction of 100 mm and a length direction of 400 mm were cut out for each condition, and the iron loss W _{17/50 was measured} in accordance with JIS C 2556. Was measured. Thereafter, the test piece was subjected to strain relief annealing at 880 ° C. for 2 hours in a nitrogen atmosphere, cooled, and the iron loss W _17/50 was measured in the same manner as described above.
Table 1 shows iron loss W _17/50 after flattening annealing, iron loss W _17/50 and ΔW _17/50 after strain relief annealing.

  As shown in Table 1, when an appropriate temperature change is applied at the time of soaking in the flattening annealing according to the present invention, the deterioration of the iron loss is greatly suppressed as compared with the conventional short-time flattening annealing. I was able to.

Example 2
The slab materials of No. 1 to No. 10 shown in Table 2 were heated at 1200 ° C for 30 minutes for No. 2 and 25 minutes at 1400 ° C for others, and hot rolled to 2.2 mm After forming a thick hot-rolled sheet, it was subjected to hot-rolled sheet annealing at 980 ° C. for 1 minute. Next, for Nos. 1 to 4, the final plate thickness was 0.23 mm by the first cold rolling. For the remaining Nos. 5-10, a cold-rolled sheet with a thickness of 1.6 mm is obtained by the first cold rolling, and after intermediate annealing at 1050 ° C. for 1 minute, No. 5-7 is obtained by the second cold rolling. The final plate thickness of 0.23 mm and No. 8 to 10 was 0.18 mm. Next, this final cold-rolled sheet is decarburized and annealed at 820 ° C for 2 minutes in wet hydrogen, and after applying and drying the annealing separator, it also serves as secondary recrystallization annealing and purification annealing. Final finish annealing was performed at 1200 ° C for 5 hours. Note that the amount of C after finish annealing was less than 20 ppm.
Then, this finish-annealed plate was baked by flattening annealing shown in Table 2 after removing the unreacted annealing separator and applying a glass coating. At this time, the maximum reached temperature during soaking was 870 ° C., and the total time during soaking was 45 seconds. The tension applied during soaking was 8.0 MPa.

From the steel plate after flattening annealing, 10 test pieces for a single-plate magnetic test each having a rolling width direction of 100 mm and a length direction of 400 mm were cut out for each condition, and the iron loss W _{17/50 was measured} in accordance with JIS C 2556. Was measured. Thereafter, the test piece was subjected to strain relief annealing at 890 ° C. for 2 hours in a nitrogen atmosphere, cooled, and the iron loss W _17/50 was measured in the same manner as described above.
Table 2 shows ΔW _17/50 together with ΔT.

  As shown in Table 2, it can be seen that when an appropriate temperature change is applied during soaking in the flattening annealing according to the present invention, deterioration of the iron loss can be significantly suppressed.

Claims (5)

Rewinding the grain-oriented electrical steel sheet coil after final finish annealing, containing C: 0.0050% or less, Si: 2.5-4.0% and Mn: 0.01-1.0%, the balance being Fe and unavoidable impurities. While flattening annealing,
800 to 900 ° C. The soaking temperature in said flattening annealing, while soaking residence time within 60 seconds, and at least one or more added Turkey a process of giving a temperature change of 10 to 30 ° C. in the residence time A method for flattening and annealing a grain-oriented electrical steel sheet characterized by: In the flattening annealing, according to the amount of Si in the steel, the tension applied to the steel sheet in a temperature range of 800 ° C. or higher is divided into the following patterns (I) to (III): Item 2. A method for flattening and annealing a grain-oriented electrical steel sheet according to Item 1.
(I) If the Si content is 2.5% or more and less than 3.0% by mass%, additional tension: 10.0-15.0MPa
(II) When the Si content is 3.0% or more and less than 3.5% by mass%, additional tension: 7.5 to 12.5 MPa
(III) When the Si content is 3.5% or more and less than 4.0% by mass%, the applied tension: 5.0 to 10.0 MPa   3. The method for flattening and annealing a grain-oriented electrical steel sheet according to claim 1, wherein a maximum temperature reached during the flattening annealing is 850 ° C. or higher.   The grain-oriented electrical steel sheet coil further includes, in mass%, Ni: 0.005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 0.50%, Cr: 0.01 to 1.50%, P: The directionality according to any one of claims 1 to 3, comprising one or more selected from 0.0050 to 0.50%, Nb: 0.0005 to 0.0100%, and Mo: 0.01 to 0.50%. A method for flattening annealing of electrical steel sheets.   A method for producing a grain-oriented electrical steel sheet, comprising performing planarization annealing according to any one of claims 1 to 4 after final finish annealing in the production of a grain-oriented electrical steel sheet.

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