JP5310510B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet suitable for a core material of a transformer.

  For grain-oriented electrical steel sheets, it is a common technique to preferentially recrystallize grains having Goss orientation during finish annealing using precipitates called inhibitors. For example, a technique using AlN and MnS described in Patent Document 1 and a technique using MnS and MnSe described in Patent Document 2 have been industrially put into practical use. Although the method using these inhibitors requires slab heating at a high temperature of 1300 ° C. or higher, it is a useful method for stably developing secondary recrystallized grains. Furthermore, in order to reinforce the action of these inhibitors, a technique that uses Pb, Sb, Nb, Te as a secondary agent is disclosed in Patent Document 3, Zr, Ti, B, Nb, Ta, V, Cr, Mo. Japanese Patent Application Laid-Open No. 2004-228688 discloses a technique that uses the secondarily.

  However, in the manufacture of grain-oriented electrical steel sheets using inhibitors, as described above, since slab heating at high temperatures is required, crystal grains are likely to be coarsened, and the occurrence of ear cracks in hot rolling is a major problem. is there. On the other hand, Patent Document 5 describes that Nb, which can be used as a secondary inhibitor as described above, is used as an element for preventing ear cracks during hot rolling.

Japanese Patent Publication No. 40-15644 Japanese Patent Publication No. 51-13469 Japanese Patent Publication No. 38-8214 JP-A-52-24116 Japanese Patent Publication No. 6-63031

  In patent document 5, in order to prevent an ear crack, when adding Nb to a grain-oriented electrical steel sheet, the addition amount is regulated within a range in which the magnetic characteristics do not deteriorate. However, among the magnetic properties, the magnetic flux density is a relatively good value, but the iron loss is not a satisfactory level and remains as a problem when adding Nb.

  Therefore, the inventors examined the reason for the deterioration of the iron loss characteristics. As a result, it became clear that the hysteresis loss increased due to Nb forming carbides in the steel, especially after the final finish annealing that served as secondary recrystallization annealing and purification annealing. .

Next, the inventors examined a method for reducing the hysteresis loss. Further, it has been found that the increase in hysteresis loss is approximately proportional to the amount of Nb added, and that the increase in hysteresis loss can be suppressed to some extent by limiting the amount of Nb added within a range in which the effect of improving the magnetic flux density can be maintained.
Hereinafter, experiments that have made the present invention successful will be described.

[Experiment 1]
In mass%, C: 0.045 to 0.062%, Si: 3.10 to 3.25%, Mn: 0.06 to 0.16%, Al: 0.022 to 0.025%, N: 0.007 to 0.009%, S: 0.012 to 0.015% and Sn: 0.032 to A steel slab containing 0.035%, further changing the amount of Nb added and making the balance Fe and unavoidable impurities by continuous casting, slab heating at 1250 ° C, then hot rolling to a thickness of 2.7mm Finished. Subsequently, after hot-rolled sheet annealing at 1100 ° C. for 20 seconds, the sheet thickness was finished to 0.30 mm by cold rolling. Then, after recrystallization annealing was performed at 80 ° C for 80 seconds, soaking conditions were applied, followed by application of an annealing separator mainly composed of MgO and a final finish annealing at 1200 ° C for 10 hours. .

The magnetic properties of the obtained samples were measured according to the method specified in JIS C 2550. FIG. 1 shows the relationship between the Nb amount, the magnetic flux density B ₈ and the hysteresis loss. The figure shows that when Nb is not added, the magnetic flux density B ₈ is low and the hysteresis loss is high, and when the Nb amount is 0.001 to 0.015% by mass, the hysteresis loss is low. .

In order to investigate this reason, when the cross section of the sample which measured the magnetic characteristic was observed with the optical microscope, the tendency for many fine precipitates to remain in steel was recognized as the Nb addition amount increased.
Precipitates in steel are known to inhibit the domain wall movement and deteriorate the hysteresis loss. However, in order to suppress this deterioration, it is necessary to limit the Nb addition amount to 0.015% by mass or less. I understood that.

Based on the above findings, repeated experiments with a small amount of Nb added may result in secondary recrystallized grains not appearing depending on manufacturing conditions, or secondary recrystallized grains having poor orientation and poor magnetic properties. Etc. have been recognized with considerable frequency.
In order to investigate this cause, the form of Nb before secondary recrystallization was examined, and it was found that Nb was present in the steel while forming fine precipitates. These precipitates are the carbides of Nb (NbC) described above, and it was speculated that NbC plays the role of an inhibitor.

Here, the generally known inhibitors MnSe and AlN are dissolved in a high temperature slab at about 1400 ° C. and then finely precipitated by subsequent hot rolling. Since then, annealing is not performed at such a temperature that the solid solution temperature is reached until secondary recrystallization occurs, and it is known that there is not much change in the particle size and distribution of MnSe and AlN.
However, considering the use of NbC as an inhibitor, since the solid solution temperature of NbC in Fe is low, there is a possibility that it will be dissolved in hot rolled sheet annealing or intermediate annealing. Furthermore, the process before the secondary recrystallization is a recrystallization annealing accompanied by decarburization, and is a process in which the amount of C in the steel is greatly reduced. For this reason, it is considered that the solid solution-precipitation temperature of NbC, which is a carbide, changes, and it becomes difficult to maintain a uniform and fine precipitate distribution state, and as a result, the magnetic properties of the steel sheet become unstable.

Therefore, in order to fully develop the function of NbC as an inhibitor, it is necessary that NbC is finely and uniformly distributed in the steel during secondary recrystallization. Therefore, it is necessary to have a process condition in which NbC is finely and uniformly distributed at a certain point in the manufacturing process of the steel sheet and the distribution is not changed until secondary recrystallization.
In view of this, the optimum process conditions for fully expressing the function of NbC as an inhibitor are the recrystallization annealing after the final cold rolling after the solid solution is formed by annealing immediately before the final cold rolling. It is presumed that it is important that the NbC is not dissolved again at the time of precipitation and subsequent recrystallization annealing.

Therefore, experiments were performed to variously change the annealing conditions immediately before the final cold rolling.
[Experiment 2]
By mass%, C: 0.062%, Si: 3.23%, Mn: 0.13%, S: 0.020%, acid-soluble Al: 0.025%, N: 0.008%, Sn: 0.13%, Nb: 0.004% and Cr: 0.07% A steel slab containing the remaining Fe and inevitable impurities was manufactured by continuous casting, heated at 1400 ° C., and then finished to a thickness of 2.4 mm by hot rolling. Thereafter, hot-rolled sheet annealing was performed at the holding temperature, holding time and cooling rate shown in Table 1, and then finished to a sheet thickness of 0.23 mm by cold rolling.

The continuous annealing described in the column of annealing type in Table 1 is a method in which a steel coil is discharged in a strip shape and a single plate is continuously annealed, and is characterized by short-time holding and short-time cooling. It is. On the other hand, batch annealing is a method in which a steel coil is kept in its shape in a furnace and annealed, and is characterized by long-term holding and long-time cooling.
Therefore, in this experiment, the annealing conditions are greatly different between the two.

The cooling rate in Table 1 is the cooling rate from 900 ° C. to 600 ° C., and is the average cooling rate calculated from the cooling time required from 900 ° C. to 600 ° C.
Then, after recrystallization annealing at 850 ° C for 60 seconds under a soaking condition of 50% N ₂ -50% H _{2 in a} humid atmosphere, an annealing separator mainly composed of MgO was applied, and 1200 ° C for 10 hours. Final finishing annealing was performed.

  Next, planarization annealing was performed under the conditions of 875 ° C. for 30 seconds, which also served to form a tension-imparting coating mainly composed of magnesium phosphate and boric acid. The magnetic properties of the obtained samples are measured by the method specified in JIS C 2550, and the measurement results are also shown in Table 1. From the table, it can be seen that the magnetic properties are good when the holding temperature is 900 ° C. or higher and the annealing type is continuous annealing.

  As described above, in order to utilize the inhibitor effect of NbC, it is important to dissolve the inhibitor component once and then precipitate finely and uniformly. That is, the reason why the magnetic properties are improved when the retention temperature is 900 ° C. or higher is that NbC is dissolved at the temperature or higher.

In addition, the reason why the continuous annealing type is effective is considered that the cooling rate is important.
As described above, since the cooling rate of the continuous annealing type is faster than that of the batch annealing type, it is considered that NbC exists in the steel in a supersaturated state while being in solid solution. That is, it is suggested here that there is an appropriate range for the cooling rate of the steel sheet.
As a result of further investigations, it was found that a cooling rate of 1 ° C./s or more was necessary to achieve a supersaturated state in which NbC was dissolved.

Next, since it is considered that the dispersion state of NbC depends on the rolling conditions, an experiment was conducted in which the rolling reduction ratio of cold rolling was changed.
[Experiment 3]
The steel slab of the component used in Experiment 2 was slab heated at 1400 ° C. and then finished to a thickness of 1.2 to 2.7 mm by hot rolling. After that, continuous annealing type hot-rolled sheet annealing held at 1050 ° C. for 90 seconds was performed, and finished to a sheet thickness of 0.23 to 0.35 mm by cold rolling. At this time, the cooling rate from 900 ° C. to 600 ° C. in the hot-rolled sheet annealing was 60 ° C./s. Moreover, the cold rolling reduction ratio was changed by producing various plate thicknesses after hot rolling and after cold rolling. Next, after recrystallization annealing at 850 ° C for 60 seconds in a soaking condition of 50% N ₂ -50% H _{2 in a} humid atmosphere, an annealing separator mainly composed of MgO was applied, and 1200 ° C for 10 hours. Final finishing annealing was performed. Thereafter, flattening annealing was performed under conditions of 875 ° C. for 30 seconds, which also served as a tension-imparting coating mainly composed of magnesium phosphate and boric acid.

The magnetic flux density B ₈ of the obtained sample was measured by the method defined in JIS C 2550, and the measurement result is shown in FIG. From the figure, it was found that the final cold rolling reduction ratio was 80% or more and the magnetic flux density B ₈ was good.
That is, it is presumed that it is necessary to introduce a large amount of strain due to rolling into the steel sheet in order for Nb that has been dissolved in supersaturation before cold rolling to uniformly form precipitates in the steel.

  The knowledge obtained from the above experiments is summarized below, and technically important points when using NbC as an inhibitor are described.

When Nb is added in a large amount, a precipitate is formed and remains in the steel of the final product plate, so that the iron loss is deteriorated. In order to suppress this iron loss deterioration, it is important to set the addition amount to 0.015% by mass or less.
It is considered that Nb forms fine precipitates of NbC and exhibits an inhibitor effect to improve the magnetic properties. However, since NbC has a low solid solution temperature, it may cause solid solution and reprecipitation even in an intermediate process, for example, an annealing process. Therefore, in order to fully exhibit the inhibitor effect, the NbC is kept in solid solution by annealing before the final cold rolling at 900 ° C. or higher, and the cooling rate at the time of annealing is increased, so that the solid solution remains in solution. It is considered that it is important to uniformly introduce rolling strain that can be a precipitation site of NbC into the steel sheet by creating a supersaturated state and setting the reduction ratio of the final cold rolling in the next step to 80%.

  Here, as expected from the above consideration, it is considered that NbC precipitates in the temperature raising process of recrystallization annealing, which is the next process of cold rolling. If this NbC is dissolved again, the inhibitor effect of NbC at the time of secondary recrystallization cannot be obtained. Therefore, it is considered essential that the recrystallization annealing temperature is 900 ° C. or lower in order to prevent solid solution. However, even when the temperature is kept at 900 ° C. or lower, NbC precipitates become coarse when held for a long time, and the inhibitor effect may not be exhibited.

Therefore, an experiment was conducted to investigate the relationship between the high temperature region holding time of recrystallization annealing and magnetic properties.
[Experiment 4]
The steel slab of the component used in Experiment 2 was slab heated at 1400 ° C. and then finished to a thickness of 2.7 mm by hot rolling. Then, it was subjected to continuous annealing type hot-rolled sheet annealing held at 1000 ° C for 90 seconds, and then finished to a thickness of 0.27 mm by cold rolling. The cooling rate from 900 ° C. to 600 ° C. in the hot-rolled sheet annealing was 45 ° C./s. Thereafter, recrystallization annealing was performed at a soaking temperature of 850 ° C. in a wet atmosphere of 50% N ₂ -50% H ₂ . At this time, the time during which the steel sheet was held at a temperature of 800 ° C. or higher (described as holding time in FIG. 3) was variously changed.
In addition, after applying an annealing separator mainly composed of MgO, a final finish annealing is carried out at 1200 ° C. for 10 hours, followed by a flattening annealing that also forms a tension-imparting coating mainly composed of magnesium phosphate and boric acid. The test was performed at 840 ° C for 30 seconds.

The magnetic properties of the obtained samples were measured by the method specified in JIS C 2550, and the measurement results are shown in FIG. From the figure, it was found that the magnetic flux density B ₈ gradually deteriorated as the holding time was increased. From this result, it can be said that the holding time needs to be 600 seconds or less. To further the magnetic flux density B ₈ good is desirably 200 seconds or less.

Through the experiments and discussions as described above, the inventors limited the amount of Nb, particularly its carbide, when used as an inhibitor, and annealed before final cold rolling, final cold rolling and recrystallization. It has been found that good magnetic properties can be obtained by controlling each annealing condition of annealing.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. C: 0.002-0.10 mass%, Si: 2.0-8.0 mass%, Mn: 0.005-1.0 mass%, S: 0.01-0.05 mass%, acid-soluble Al: 0.01-0.04 mass%, N: 0.003-0.015 mass%, A steel slab consisting of Sn: 0.01-0.20% by mass and Nb: 0.001-0.015% by mass, the balance Fe and inevitable impurities is hot-rolled and subjected to one or more cold rollings with intermediate annealing. In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing final finishing annealing after performing recrystallization annealing that also serves as decarburization to the obtained steel sheet.
Immediately before the final cold rolling, annealing is performed so that the average cooling rate from 900 ° C. to 600 ° C. is 1 ° C./s or more, and the reduction rate in the final cold rolling is 80%. And above
The recrystallization annealing is a method for producing a grain-oriented electrical steel sheet, characterized in that the temperature is 900 ° C. or less and the time during which the steel sheet is maintained at a temperature of 800 ° C. or more is 600 seconds or less.

  2. In the steel slab component, one or two selected from Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, and P: 0.005 to 0.50 mass% The method for producing a grain-oriented electrical steel sheet according to 1 above, comprising the above.

  3. In the steel slab component, Se: 0.003 to 0.050 mass%, Sb: 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Mo: 0.005 to 0.100 mass%, and B: 2 to 25 mass ppm The method for producing a grain-oriented electrical steel sheet according to 1 or 2 above, comprising one or more selected from the above.

  According to the present invention, a carbide of Nb can be efficiently used as an inhibitor, and thus a grain-oriented electrical steel sheet having good magnetic properties can be obtained.

It is a diagram showing a relationship between the added amount of Nb and the magnetic flux density B ₈ and the hysteresis loss. FIG. 6 is a diagram showing the relationship between the final cold rolling reduction and the magnetic flux density B ₈ . FIG. 5 is a diagram showing the relationship between the time of holding at a temperature of 800 ° C. or higher during recrystallization annealing and the magnetic flux density B ₈ .

Hereinafter, the present invention will be specifically described.
First, in the present invention, the reasons for limiting the constituent requirements of the present invention will be described. Hereinafter, unless otherwise specified, the component composition in steel and the like represents mass% and mass ppm.

C: 0.002 to 0.10%
When the content of C in the slab steel exceeds 0.10%, it becomes difficult to set C to 50 ppm or less, which is a content at which magnetic aging does not occur during decarburization annealing of the steel sheet. On the other hand, if it is less than 0.002%, the inhibitor effect of Nb carbide is not exhibited and the magnetic properties are deteriorated. Therefore, C is limited to 0.002 to 0.10%.

Si: 2.0-8.0%
Si is an element necessary for increasing the specific resistance of steel and improving iron loss. However, if it is less than 2.0%, there is no effect of improving iron loss, while if it exceeds 8.0%, the workability of steel deteriorates. However, it is limited to 2.0 to 8.0% because rolling becomes difficult.

Sn: 0.01-0.20%
Sn is an essential element for reducing the iron loss by suppressing the coarsening of secondary grains that occurs when NbC is used as an inhibitor. If the addition amount is less than 0.01%, there is no effect of addition. On the other hand, if the addition amount exceeds 0.20%, the rollability of the steel sheet is remarkably deteriorated, so Sn is limited to 0.01 to 0.20%.

Nb: 0.001 to 0.015%
Nb is an element that forms the basis of the present invention, and is effective in preventing the cracking of the steel sheet. The present invention is characterized in that the carbide is used as an inhibitor. From the above-described experiment, if it is less than 0.001%, there is no effect as an inhibitor of NbC, while if it exceeds 0.015%, the domain wall movement is inhibited and the hysteresis loss is increased. Even within this range, the hysteresis loss tends to increase when Nb is large, so 0.005% or less is a suitable range.

  Here, Mn, S, acid-soluble Al and N are essential elements for forming a precipitate and exhibiting an inhibitor effect.

Each addition amount is Mn: 0.005-1.0%, S: 0.01-0.05%, acid-soluble Al: 0.01-0.04%, and N: 0.003-0.015%.
Mn is an element for improving the hot workability, but if it is less than 0.005%, there is no effect, while if it exceeds 1.0%, the magnetic flux density of the product plate decreases, so Mn is 0.005 to 1.0%. And
Further, other S, acid-soluble Al and N, when the addition amount is less than the lower limit amount, respectively, the formation amount of the inhibitor is small and the magnetic properties are deteriorated. On the other hand, when the upper limit amount is exceeded, the solid solution of Nb is dissolved. When the temperature becomes high and slab heating is performed, these inhibitors cannot be sufficiently dissolved. As a result, a fine and uniform distribution of the inhibitor is not achieved and the magnetic properties are deteriorated.

Although the basic components of the present invention have been described above, the present invention can appropriately contain other elements described below.
Ni: 0.010-1.50%
In the present invention, Ni can be added to improve the hot rolled sheet structure and improve the magnetic properties. If the amount added is less than 0.010%, the improvement of the magnetic properties is small. On the other hand, if it exceeds 1.50%, the secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, when Ni is added, 0.010 to 1.50% To do.

For the purpose of reducing iron loss, one or more selected from Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, and P: 0.005 to 0.50% can be added.
When the addition amount is less than the lower limit amount, the effect of reducing the iron loss is small. When the addition amount exceeds the upper limit amount, the secondary recrystallization becomes unstable and the iron loss increases.

Further, for the purpose of improving the magnetic flux density, Se: 0.003 to 0.050%, Sb: 0.005 to 0.50%, Bi: 0.005 to 0.50%, Mo: 0.005 to 0.100%, B: 2 to 25 ppm Two or more kinds can be added.
When the added amount is less than the lower limit amount, there is no effect of improving the magnetic properties, and when the upper limit amount is exceeded, the development of secondary recrystallized grains is suppressed and the magnetic properties are deteriorated.

Next, manufacturing conditions will be described.
The molten steel having the above components may be produced by a normal ingot forming method or a continuous casting method, or a thin cast piece having a thickness of 100 mm or less may be produced by a direct casting method.
Thereafter, the slab is subjected to slab heating for the purpose of dissolving the inhibitor component. In order to ensure sufficient solid solution, it is desirable to heat to 1400 ° C. or higher, but it is also desirable in terms of cost to make it low-temperature heating within the range where the inhibitor component can be dissolved. Thereafter, hot rolling is performed. At that time, from the viewpoint of inhibitor precipitation control, the temperature immediately after the end of hot rolling is preferably 900 ° C. or higher.

Next, hot-rolled sheet annealing is performed as necessary. In order to obtain good magnetic properties, the hot-rolled sheet annealing temperature is preferably 800 ° C. or higher and 1150 ° C. or lower. This is because when the hot-rolled sheet annealing temperature is less than 800 ° C., the band structure at the time of hot-rolling remains, making it difficult to achieve a sized primary recrystallized structure. Development may be impeded. On the other hand, when the hot-rolled sheet annealing temperature exceeds 1150 ° C., the grain size after the hot-rolled sheet annealing is excessively coarsened, which is a very disadvantageous structure for realizing a sized primary recrystallized structure.
In the present invention, when the cold rolling is performed only once, the hot-rolled sheet annealing is necessarily performed, but in this case, the hot-rolled sheet annealing is performed immediately before the final cold rolling. It is essential that the hot-rolled sheet annealing temperature is 900 ° C. or higher, and it is also essential that the cooling rate from 900 ° C. to 600 ° C. is 1 ° C./s or more on average.

  It can also be set as the process of performing recrystallization annealing, after giving cold rolling of 2 or more times which interpose intermediate annealing as needed after hot-rolled sheet annealing. At that time, the final cold rolling at the end of the multiple cold rolling is the final cold rolling. When the intermediate annealing is the annealing immediately before the final cold rolling, the conditions for the intermediate annealing are as follows: temperature: 900 ° C. or higher, 900 ° C. It is essential that the cooling rate from 1 to 600 ° C. is 1 ° C./s or more on average.

  In the present invention, it is essential that the rolling reduction of the final cold rolling is 80% or more. Preferably it is 85% or more, more preferably 87% or more. Further, the temperature of the cold rolling is raised to 100 ° C. to 300 ° C., and the aging treatment is performed once or a plurality of times during the cold rolling in the range of the rolling temperature of 100 to 300 ° C. This is advantageous for improving the magnetic properties by changing the recrystallized texture.

  In addition, it is essential that the recrystallization annealing is performed at 900 ° C. or lower, and the time for which the steel sheet is held at a temperature of 800 ° C. or higher is 600 seconds or shorter. At this time, since decarburization is required, it is desirable that the atmosphere be a humid atmosphere. After recrystallization annealing, a technique for increasing the amount of Si by a siliconization method may be used in combination.

After that, when forming a forsterite film with an emphasis on iron loss, a secondary recrystallized structure is developed and a forsterite film is developed by applying a finish annealing after applying an annealing separator mainly composed of MgO. It is possible to form.
Also, if the forsterite film is not required with emphasis on punching workability, do not use an annealing separator, or use MgO that forms a forsterite film, but use silica, alumina, etc. .
When applying these annealing separators, it is effective to perform electrostatic coating that does not bring in moisture. Further, a heat resistant inorganic material sheet (silica, alumina, mica, etc.) may be used.

The final finish annealing is desirably performed at 800 ° C. or higher for secondary recrystallization. In order to complete the secondary recrystallization, it is desirable to hold at a temperature of 800 ° C. or higher for 20 hours or longer. If the forsterite film is not formed with emphasis on punchability, the secondary recrystallization should be completed, so the holding temperature is preferably in the range of 850 to 950 ° C. It is also possible to end.
In the case where the iron loss is regarded as important or the forsterite film is formed in order to reduce the noise of the transformer, it is desirable to raise the temperature to about 1200 ° C.

  After final finish annealing, it is effective to perform water washing, brushing, and pickling in order to remove the attached annealing separator. Thereafter, flattening annealing and correcting the shape are advantageous for reducing iron loss.

  In the case where the steel plates are laminated and used, it is effective to provide an insulating coating on the surface of the steel plate before or after the flattening annealing in order to improve iron loss. This insulating coating is preferably a coating that can apply tension to the steel sheet to reduce iron loss. In addition, if a method of forming a coating layer by forming an inorganic material on the surface of a steel sheet by a tension coating application method using a binder, physical vapor deposition method, or chemical vapor deposition method is adopted, the coating layer has excellent adhesion and significant iron loss reduction. It is desirable because of its effect.

  In order to reduce iron loss, it is desirable to perform magnetic domain fragmentation. Any of the conventionally known methods can be used as the magnetic domain subdividing method. However, a groove is formed in the final product plate, a thermal strain or shock strain is introduced linearly by laser or plasma, or a final finishing plate. A method in which a groove is previously formed in an intermediate product such as a cold-rolled sheet having reached a thickness can be suitably used.

Example 1
A steel slab composed of the components shown in Table 2 and the balance Fe and inevitable impurities was manufactured by continuous casting, heated at 1420 ° C., and then finished to a thickness of 2.7 mm by hot rolling. Next, after hot-rolled sheet annealing was performed at 1000 ° C for 30 seconds and a cooling rate from 900 ° C to 600 ° C at 25 ° C / s, the thickness was reduced to 0.30 mm (rolling rate 88.9%) by cold rolling. Finished. Thereafter, recrystallization annealing was performed at 830 ° C. for 60 seconds in a 40% N ₂ -60% H ₂ humid atmosphere. At this time, the time for which the steel sheet was held at a temperature of 800 ° C. or higher was about 120 seconds.
Further, after applying an annealing separator mainly composed of MgO, final finishing annealing was performed at 1200 ° C. for 6 hours. Thereafter, planarization annealing was performed under the conditions of 870 ° C. for 15 seconds, which also served as a tension-imparting coating mainly composed of magnesium phosphate and boric acid.
The magnetic properties of the obtained samples are measured by the method specified in JIS C 2550 and are also shown in Table 2.

  As is clear from the table, it can be seen that all of the electrical steel sheets having the composition of the present invention have good magnetic properties under the above-described manufacturing conditions.

(Example 2)
C: 0.026%, Si: 3.31%, Mn: 0.05%, S: 0.013%, acid-soluble Al: 0.035%, N: 0.011%, Nb: 0.010% and Sn: 0.05%, remaining Fe and inevitable impurities A steel slab was manufactured by continuous casting, heated at 1400 ° C, and then finished to a thickness of 2.3 mm by hot rolling.
Next, hot-rolled sheet annealing was performed at the holding temperature and holding time shown in Table 3 and the cooling rate from 900 ° C to 600 ° C, and then finished to a sheet thickness of 0.23 mm (reduction rate 90%) by cold rolling. . Thereafter, recrystallization annealing was performed in a 50% N ₂ -50% H ₂ humid atmosphere under a soaking condition of 850 ° C. for 60 seconds. At this time, the time for which the steel sheet was kept at a temperature of 800 ° C. or higher was about 150 seconds. Further, after applying an annealing separator mainly composed of MgO, final finishing annealing was performed by holding at 1200 ° C. for 10 hours. Thereafter, planarization annealing was performed under conditions of 850 ° C. for 40 seconds, which also served as a tension-imparting coating mainly composed of magnesium phosphate and boric acid. The magnetic properties of the obtained samples are measured by the method specified in JIS C 2550 and are also shown in Table 3.

  As shown in the table, according to the present invention, in accordance with the present invention, the electrical steel sheet that has been subjected to hot-rolled sheet annealing at a cooling rate of 900 ° C. to 600 ° C. with a selected holding temperature and holding time has good magnetic properties. It is.

(Example 3)
C: 0.077%, Si: 3.22%, Mn: 0.13%, S: 0.022%, acid-soluble Al: 0.028%, N: 0.009%, Nb: 0.005%, Sn: 0.06%, Cr: 0.07% and P: 0.010 %, The remainder Fe and inevitable impurities were produced by continuous casting, and after slab heating at 1400 ° C., as shown in Table 4, it was finished to a thickness of 1.5 to 2.7 mm by hot rolling. Then, after performing hot-rolled sheet annealing held at 1050 ° C. for 90 seconds, as shown in Table 4, it was finished to a sheet thickness of 0.23 to 0.35 mm by cold rolling.
The cooling rate from 900 ° C. to 600 ° C. for hot-rolled sheet annealing was 25 ° C./s. Thereafter, recrystallization annealing was performed in a humid atmosphere of 50% N ₂ -50% H _{2 at} 840 ° C. for 80 seconds. At this time, the time for which the steel plate was held at a temperature of 800 ° C. or higher was about 140 seconds. Further, after applying an annealing separator mainly composed of MgO, final finishing annealing was carried out at 1200 ° C. for 10 hours. Thereafter, planarization annealing was performed under conditions of 850 ° C. for 40 seconds, which also served as a tension-imparting coating mainly composed of magnesium phosphate and boric acid.
The rolling reduction of the obtained sample was calculated, and its magnetic properties were measured by the method specified in JIS C 2550. The results are also shown in Table 4.

As shown in the table, of the magnetic properties, the iron loss since the thickness of the high-impact, when compared with the value of the magnetic flux density B _8, the reduction ratio in accordance with the present invention, even better magnetic flux density both of the steel plate It turns out that it is.

Example 4
C: 0.066%, Si: 3.15%, Mn: 0.16%, S: 0.014%, acid-soluble Al: 0.027%, N: 0.009%, Nb: 0.002%, Sn: 0.05%, Cr: 0.07% and Ni: 0.04 %, The balance Fe and unavoidable impurities were produced by continuous casting, heated at 1400 ° C. and then hot rolled to a thickness of 2.8 mm. Next, hot-rolled sheet annealing was performed at 1000 ° C. for 40 seconds, and the sheet thickness was 1.8 mm by cold rolling. Thereafter, intermediate annealing was performed at 1025 ° C. for 30 seconds. The cooling rate from 900 ° C. to 600 ° C. at this time was 34 ° C./s. Furthermore, the sheet thickness was 0.23 mm by cold rolling. Subsequently, recrystallization annealing was performed in a 50% N ₂ -50% H ₂ humid atmosphere. At this time, the holding temperature and the time during which the steel plate was held at a temperature of 800 ° C. or higher were carried out under various conditions shown in Table 5.

  Further, after applying an annealing separator mainly composed of MgO, final finishing annealing was performed by holding at 1250 ° C. for 4 hours. Thereafter, planarization annealing was performed under conditions of 850 ° C. for 40 seconds, which also served as a tension-imparting coating mainly composed of magnesium phosphate and boric acid. Further, the magnetic domain was subdivided by plasma irradiation. In this condition, linear thermal strain having a thickness of 200 μm was introduced at intervals of 7 mm in parallel with the width direction of the steel sheet. The magnetic properties of the obtained samples are measured by the method specified in JIS C 2550 and are also shown in Table 5.

  As shown in the table, when the holding temperature and the time of holding the steel sheet at a temperature of 800 ° C. or higher are in the range according to the present invention, it can be seen that all the steel sheets have good magnetic properties.

  According to the present invention, it is possible to obtain an iron core material having excellent magnetic properties, particularly iron loss values, and thus contribute to the manufacture of high-quality transformers and electric motors.

Claims (3)

C: 0.002-0.10 mass%, Si: 2.0-8.0 mass%, Mn: 0.005-1.0 mass%, S: 0.01-0.05 mass%, acid-soluble Al: 0.01-0.04 mass%, N: 0.003-0.015 mass%, A steel slab consisting of Sn: 0.01-0.20% by mass and Nb: 0.001-0.015% by mass, the balance Fe and inevitable impurities is hot-rolled and subjected to one or more cold rollings with intermediate annealing. In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing final finishing annealing after performing recrystallization annealing that also serves as decarburization to the obtained steel sheet.
Immediately before the final cold rolling, annealing is performed so that the average cooling rate from 900 ° C. to 600 ° C. is 1 ° C./s or more, and the reduction rate in the final cold rolling is 80%. And above
The recrystallization annealing is a method for producing a grain-oriented electrical steel sheet, characterized in that the temperature is 900 ° C. or less and the time during which the steel sheet is maintained at a temperature of 800 ° C. or more is 600 seconds or less.   In the steel slab component, one or two selected from Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, and P: 0.005 to 0.50 mass% The method for producing a grain-oriented electrical steel sheet according to claim 1, comprising the above.   In the steel slab component, Se: 0.003 to 0.050 mass%, Sb: 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Mo: 0.005 to 0.100 mass%, and B: 2 to 25 mass ppm The method for producing a grain-oriented electrical steel sheet according to claim 1, comprising one or more selected from the above.

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