JPH10121135A - Production of grain oriented silicon steel sheet with minimal iron loss and high magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize iron loss and to increase magnetic flux density by specifying, in particular, hot rolled plate annealing conditions and process annealing conditions, respectively. SOLUTION: It is necessary to regulate temp. rise rate, up to 800 deg.C, to (5 to 25) deg.C/s in order to finely precipitate AlN in the course of temp. raise at the time of hot rolled plate annealing and process annealing in a cold rolling process. By this procedure, precipitates are not coarsened but precipitated sufficiently, and a strong inhibiting power as inhibitor is obtained. Further, it is necessary to carry out the above annealing stages under the conditions of 900-1125 deg.C and <=150sec holding time. The lower limit temp. is set at 900 deg.C in order to coarsen the crystal structure after annealing to a prescribed size or above to obtain sufficient strength of the (110) grains, and the upper limit temp. and the holding time are set up in order to prevent the re-entering into solid solution of the AlN finely precipitated in the temp. rise stage. By this method, the strength of the (110) grain in the structure of primary recrystallized grains is increased, and as a result, secondary recrystallization, with high magnetic flux density and fine-grained structure, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention proposes a method for manufacturing a grain-oriented electrical steel sheet having extremely low iron loss and a high magnetic flux density, particularly among grain-oriented electrical steel sheets used for iron cores such as transformers and generators. Things.

[0002] It contains Si and has a crystal orientation of (110)
[001] orientation or (100) [001] orientation
Grain-oriented electrical steel sheets have excellent soft magnetic properties and
Widely used as various iron core materials in the
You. At that time, the characteristics required for electrical steel sheets are generally
Loss when magnetized to 1.7 T at a frequency of 50 Hz
 W _17/50It is important that the iron loss is low. Power generation
The iron loss of the iron core as a machine or transformer_17/50Is the value of
What can be greatly reduced by using lower materials?
W as iron loss_17/50Demand for low-cost materials is increasing year by year
Are being used.

[0003]

2. Description of the Related Art In general, in order to reduce iron loss of a material, a method of increasing an effective Si content to reduce an eddy current loss to increase electric resistance, a method of reducing a thickness of a steel sheet, a method of reducing a crystal grain, There is known a method of reducing the grain size, a method of increasing the degree of integration of crystal orientations, and improving the magnetic flux density. Among them, the method of increasing the Si content and the method of reducing the thickness of the steel sheet were examined.However, the method of increasing the Si content is preferable because excessive inclusion of Si deteriorates the rollability and workability. There is a limit, and the method of reducing the thickness of a steel sheet has a limit naturally because it extremely increases the manufacturing cost.

[0004] Among the above-mentioned techniques for improving the magnetic flux density, many studies have been made so far. For example, Japanese Patent Publication No. 46-23820 (heat treatment method for high magnetic flux density electromagnetic steel sheet) discloses a method for improving the magnetic flux density in steel. Al added and 10 after hot rolling
A proposal is made of a technique in which fine AlN is precipitated by hot-rolled sheet annealing at a temperature range of 00 to 1200 ° C and high temperature, followed by quenching, and a high-pressure reduction of 80 to 95% in the final cold rolling is performed. It is disclosed, and thereby obtain a very high magnetic flux density and 1.95T in B _10. This is because finely dispersed AlN
Has a strong effect as an inhibitor that suppresses the growth of primary recrystallized grains, and secondary recrystallizes only nuclei with excellent crystal orientation to obtain a product having a crystal structure with excellent orientation. It is assumed that.

However, in this technique, it is generally difficult to obtain a small iron loss by coarsening the crystal grains.
Further, since it is difficult to completely dissolve AlN into solid solution in hot-rolled sheet annealing, it has been difficult to stably obtain a product having a high magnetic flux density. The reason is that this technology requires that the final rolling reduction rate be 80-95%, thereby growing only a few nuclei with excellent crystal orientation and obtaining excellent magnetic flux density. This is because, although high magnetic flux density can be obtained, the density of secondary recrystallized grains is low and the crystal grains in the product are coarsened, so that the magnetic properties are unstable.

[0006] After that, with regard to the technology for producing a material using AlN as an inhibitor, Japanese Patent Publication No. 23647/1979 (a method for producing a high-grade unidirectional electrical steel sheet) and Japanese Patent Publication No.
No. 13846 (cold rolling method for obtaining a high magnetic flux density unidirectional silicon steel sheet having excellent characteristics),
Technology for performing aging treatment between cold rolling passes, and Japanese Patent Laid-Open No. 7-3
Attempts have been made to stabilize the magnetic properties of materials by a warm rolling technique as disclosed in Japanese Patent Application Publication No. 2006 (a cold rolling method for grain-oriented silicon steel sheets and a roll cooling device for a cold rolling mill). However, these methods are still insufficient to stably obtain a product having a high magnetic flux density, and the instability in production due to the essential reasons as described above has not been solved.

[0007]

As described above, when an attempt is made to obtain a high magnetic flux density by increasing the degree of integration of the crystal orientation, the crystal grains are inevitably coarsened and the magnetic characteristics become unstable. If crystal grains are refined to suppress this, conversely, the degree of integration in the crystal direction will decrease and the magnetic flux density will decrease. Due to such a trade-off state, materials with high magnetic flux density and extremely low iron loss have been used. It was difficult to stably produce.

In view of the above, the present invention eliminates the instability factor of coarsening of crystal grains in a product sheet inherently present in producing a grain-oriented electrical steel sheet using AlN as an inhibitor to reduce extremely low iron loss. the resulting, moreover aims to propose a method of manufacturing very high magnetic flux density oriented electrical steel sheet B ₈ is obtained.

[0009]

Means for Solving the Problems In order to solve the above trade-off state, the present inventors have focused on the precipitation and dispersion state of AlN, which is an inhibitor, and have taken a very different precipitation method from that of the prior art to achieve extremely fine particles. And found that a strong inhibitory effect on the growth of primary recrystallized grains was obtained, and the present invention was effectively utilized to achieve the present invention. That is, the gist of the present invention is as follows.

C: 0.025 to 0.095 wt%, Si: 1.5 to
7.0 wt%, Mn: 0.03 to 2.5 wt%, total of one or two of S or Se: 0.003 to 0.040 wt%, Al: 0.01
Using a silicon steel slab containing 0 to 0.030 wt% and N: 0.003 to 0.010 wt% as a raw material, the slab is heated to a temperature of 1350 ° C. or more, hot-rolled, and then subjected to hot-rolled sheet annealing. Cold rolling is performed by a cold rolling method or a twice cold rolling method with intermediate annealing to obtain a final cold-rolled sheet thickness, or after hot rolling, cold rolling is performed twice with intermediate annealing. After rolling and making it the final cold-rolled sheet thickness, it is subjected to primary recrystallization annealing, and then, after producing a grain-oriented electrical steel sheet by a series of steps of applying an annealing separating agent and then performing final finish annealing,
The temperature at which the hot finish rolling reduction rate is in the range of 85 to 99%, the finish rolling end temperature is in the range of 950 to 1150 ° C, and satisfies the following formula (1) from the relationship between the Si content and the Al content of the material. Perform hot rolling within the range, 20 ° C /
quenching at a cooling rate of 670 ° C or higher and coiling at a temperature of 670 ° C or lower, and both hot-rolled sheet annealing and intermediate annealing
The temperature is raised to a temperature of 0 ° C. at a heating rate of 5 to 25 ° C./s, and the holding time is 150 seconds or less in a temperature range of 900 to 1125 ° C., and cold rolling is performed once. Cold rolling is performed in the range of reduction ratio: 80 to 95% to obtain the final cold-rolled sheet thickness, or the first rolling is performed by double cold rolling in the range of reduction ratio: 15 to 60%. After the second annealing after the intermediate annealing
The first rolling is performed in a rolling reduction range of 80 to 95% to obtain a final cold-rolled sheet thickness, Ti compound: 1 to 20 wt%, and Ca: 0.01 to
The use of an annealing separator containing 3.0 wt% and the temperature increase of at least 900 ° C. or higher during the final finish annealing in an atmosphere containing H ₂ are sequentially combined. A method for producing a high magnetic flux density grain-oriented electrical steel sheet having extremely low iron loss (first invention).

[0011] The high magnetic flux density direction with extremely low iron loss according to the first invention, wherein cooling at the time of hot rolled sheet annealing or intermediate annealing immediately before final cold rolling is a quenching treatment for increasing the amount of solute C in the steel sheet. A method for producing a conductive electrical steel sheet (second invention).

[0012] The final cold rolling is performed at a temperature range of 90 to 350 ° C, or at a temperature range of 100 to 300 ° C.
The method for producing a high magnetic flux density grain-oriented electrical steel sheet having extremely low iron loss according to the first or second invention, wherein the inter-pass aging treatment is performed for a time range of 10 to 60 minutes (third invention).

[0013] Annealing before final cold rolling, 0.005 to 0.
The method for producing a high magnetic flux density grain-oriented electrical steel sheet having extremely low iron loss according to the first, second or third invention, characterized by performing decarburization of 025 wt% (fourth invention).

Here, the Ti compound means TiO ₂ , TiN, MgTi
O ₃ , FeTiO ₂ , SrTiO ₃ , TiS and other Ti-containing materials such as oxides, nitrides and sulfides.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an experimental example which led to the present invention will be described below. C: 0.08 wt% (hereinafter simply expressed as%), Si: 3.32%, Mn: 0.07%, Al: 0.024%, Se:
Two 250 mm thick silicon steel slabs each containing 0.020%, Sb: 0.040%, N: 0.008%, and the balance being Fe and inevitable impurities were heated to a temperature of 1380 ° C.

On the other hand, after rough rolling at a temperature of 1220 ° C. and a plate thickness of 45 mm, and finish rolling at a temperature of 1050 ° C. and a plate thickness of 2.2 mm, a large amount of cooling water is injected by spraying a large amount of cooling water. ° C /
The resultant was cooled at a cooling rate of s and wound around a coil at a temperature of 550 ° C. (referred to as a coil A). On the other hand, at a temperature of 1220 ° C, the thickness:
After rough rolling to 45 mm, finish rolling to a thickness of 2.2 mm at a temperature of 950 ° C, then spraying a large amount of cooling water
It was cooled at a cooling rate of 25 ° C./s and wound around a coil at a temperature of 550 ° C. (referred to as coil B).

Each of the coils A and B is divided into two (referred to as A-1, A-2 and B-1, B-2).
1 and B-1 hot-rolled sheet coils were heated at a rate of 12 ° C./s.
After heating to 1110 ° C. at a temperature of 1170 ° C., the hot rolled sheet coils of A-2 and B-2 were heated at a rate of 12 ° C./s at a temperature of 1170 ° C. Then, the hot rolled sheet was held for 30 seconds and then annealed.

These hot-rolled sheets are subjected to cold rolling at a temperature of 120 ° C. after pickling, to a final cold-rolled sheet thickness: 0.27 mm, and then to a degreasing treatment, and then to a 0.15% Ca the material obtained by adding TiO ₂ 4.5% in MgO in containing 0.08% of B is applied to the surface of the steel sheet as an annealing separating agent, wound to a coil, respectively.

Thereafter, the final finish annealing condition is 800
The temperature was raised to a temperature of 30 ° C. in a N ₂ atmosphere at a rate of 30 ° C./h, and the temperature in a temperature range of 800 to 1050 ° C. was increased in a mixed atmosphere of N ₂ : 25% and H ₂ : 75%. At a heating rate of 15 ° C / s, 105
The temperature rise in the temperature range of 0 to 1200 ° C. and the soaking in 1200 ° C. for 5 hours are performed in an H ₂ atmosphere, and the temperature rise rate in the temperature range of 1050 to 1200 ° C. is 20 ° C./s. The final finish annealing was performed by using a heat cycle and an atmosphere in which the temperature was rapidly cooled to a temperature of 800 ° C. in an H ₂ atmosphere, and a temperature of 800 ° C. or less was cooled in an N ₂ atmosphere.

After the final finish annealing, after removing the unreacted annealing separating agent, a tension coat composed of 50% colloidal silica and magnesium phosphate was applied and baked to obtain respective products. A specimen of Epstein size was cut out from each product thus obtained along the rolling direction, subjected to strain relief annealing at a temperature of 800 ° C. for 3 hours, and then subjected to iron loss W _17/50 and magnetic flux density at a magnetic flux density of 1.7 T. the B ₈ were measured to examine the average crystal grain size further these steel sheets macros etched to. Table 1 summarizes the results of these investigations.

[0021]

[Table 1]

As is clear from Table 1, symbol A indicates that the hot rolling (finish rolling) end temperature is high and the hot-rolled sheet annealing temperature is low.
The coil of -1 has an extremely high magnetic flux density (B ₈ ) and an extremely low iron loss (W _17/50 ) as compared with the symbol B-2 which is the conventional condition.
Has been obtained.

As a result of investigating the reason why such a good result was obtained, the following has become clear. That is, in the conventional method, γ transformation is caused during high-temperature soaking during hot-rolled sheet annealing, and after re-dissolution of AlN, re-precipitation in the cooling process is aimed at. It was found that in the coil of symbol A-1, which obtained the above results, extremely fine AlN was precipitated during the heating process of hot-rolled sheet annealing, and this resulted in a strong inhibitory action of the inhibitor.

Therefore, the first technical point of the present invention is that the annealing temperature of the hot-rolled sheet needs to be low so that the precipitated AlN does not re-dissolve and the Ostwald growth does not occur. Is a completely different technical idea.

The proper value of the annealing temperature of the hot-rolled sheet in the present invention is intended to make the grain size of the crystal structure after annealing appropriate. When the annealing temperature is excessively low, the re-rolling after rolling is performed. In the crystal structure, the strength of the (110) grains serving as nuclei for secondary recrystallization is insufficient, and secondary recrystallization with a good orientation cannot be obtained. Therefore, in order to obtain high strength of the (110) grains, it is necessary to coarsen the crystal structure after annealing the hot-rolled sheet to a certain size or more. For this purpose, it is necessary to raise the temperature to 900 ° C. or more. It is essential.

On the other hand, regarding the upper limit of the hot-rolled sheet annealing temperature,
As described above, the most important point is to prevent the re-dissolution of AlN, which is finely precipitated during the heating process, and Ostwald ripening. For this purpose, it is necessary to perform annealing at a temperature of 1125 ° C or less and a soaking time of 150 seconds or less. The precipitation phenomenon of AlN at the time of temperature rise during such annealing is almost 900 ° C.
However, since the size and distribution change depending on the heating rate, it is necessary to control the heating rate. If the heating rate is slower than 5 ° C./s, AlN tends to precipitate coarsely, and if it is faster than 25 ° C./s, the amount of AlN deposited becomes insufficient.

The cooling conditions after annealing do not need to be particularly limited. For example, a quenching treatment as described in Japanese Patent Publication No. 7-84615 (a method for producing a grain-oriented silicon steel sheet having excellent magnetic flux density) is used. The technique of precipitating fine carbide by means of improving the primary recrystallization texture is effective when applied to the present invention. Further, performing decarburization of the surface layer of the steel sheet during annealing can obtain more preferable results.

The second technical point is that as a prerequisite for effectively utilizing the technique of precipitating fine AlN in the process of increasing the temperature of hot-rolled sheet annealing, AlN is not precipitated in the hot rolling step. is there. Assuming that AlN
If AlN precipitates, AlN grows with AlN already deposited as a nucleus in the process of increasing the temperature of the hot-rolled sheet annealing, so that a small number of coarse AlN is present and the suppressing power is reduced.

A detailed examination of the process of fine precipitation of AlN during the heating process of hot-rolled sheet annealing revealed that a large number of ultrafine precipitates different from AlN already existed in the hot-rolled sheet.
These are the cores of AlN precipitation, and these ultrafine precipitates are sulfides such as MnS and CuS, MnSe, Cu
Consisting of selenides such as Se and their composite precipitates,
It was found that the hot finish rolling temperature was extremely fine in an appropriate range. That is, it was found that precipitation of AlN should be suppressed in a state where defects such as dislocations exist in the steel at high density. Here, when the finish rolling temperature is higher than the appropriate temperature, the density of the defects existing in the steel is reduced and a sufficient number of the above-mentioned ultrafine precipitates cannot be obtained. This precipitation becomes insufficient, and the precipitation density of ultra-fine precipitates decreases. Since these precipitates are ultrafine, a small amount of 0.003% or more is sufficient, but it is necessary to contain S and / or Se in the steel.

Means for preventing the precipitation of AlN in the hot rolling step include the following three points. One of them is to raise the temperature at the end of hot rolling (finish rolling) to make AlN exist in the steel in a supersaturated solid solution state. The precipitation temperature of AlN is
It is known that the temperature changes depending on the contents of Si and Al, so it is necessary to change the hot rolling end temperature in accordance with these contents. If the hot-rolling end temperature is too low, AlN precipitates in the hot rolling step, and in the above experiment, the symbol B-
In any case, the coil No. 2 is in a state where a small number of coarse AlN is precipitated as in the coil of symbol B-1 where the hot-rolled sheet annealing is performed at a low temperature, the suppression power is reduced, and secondary recrystallization failure occurs.

Another point is that the steel sheet is rapidly cooled after the completion of the hot rolling. That is, this leaves the supersaturated state
Al can be frozen in steel. If the cooling rate is low, AlN is likely to precipitate during the cooling process. Therefore, the required cooling rate is 20 ° C./s or more.

The other one is that the coil winding temperature after the completion of hot rolling is lowered. Since the coil is kept near that temperature for a long time, if the winding temperature is high, Al
This results in precipitation of N. For this reason, it is necessary to set the coil winding temperature to 670 ° C. or less.

Next, as described above, the appropriate range of the hot-rolling termination temperature related to the Si content and the Al content was examined.

Using various silicon steel slabs of 250 mm thickness having almost the same composition as in the above experiment except that the Si content and the Al content were intentionally changed, the hot rolling end temperature was changed. Each product was manufactured in the same process as the symbol A-1 in the above-described experiment except that the magnetic flux density B ₈ / B
_{The value of s} (B _s is the saturation magnetic flux density) was investigated. Figure 1 shows the effect of Si of the material on the degree of crystal orientation (B ₈ / B _s ) of the product.
4 is a graph showing the effects of the Al content, the Al content, and the hot rolling end temperature.

According to FIG. 1, in order to obtain an extremely high value of B ₈ / B _s of 0.98 or more, the hot rolling end temperature is 610 + 40X + Y or more, where X represents Si (%) and Y represents Al (ppm). And a temperature of 950 ° C or higher, and 750+
It is understood that the temperature must be 40X + Y or less and 1150 ° C or less. If the hot rolling end temperature is lower than the above range, AlN precipitates in the hot rolling step, and if the temperature is high, rolling in a high temperature range occurs and the width of the band structure of the hot-rolled sheet increases, resulting in good secondary re-rolling. It hinders crystal growth.

The third technical point is that the crystal size of the secondary recrystallized grains is reduced by lowering the annealing temperature. The reason for this is not clear, but by lowering the annealing temperature, the amount of γ transformation is reduced, and the crystal grains before rolling are substantially increased, and the (110)
It is presumed that the nucleation frequency of grains increased.

It is a well-known phenomenon that when the number of (110) grains increases in the primary recrystallized structure, the secondary recrystallized grains become finer. I always invited them. However, in the present invention, it is presumed that the effect of suppressing the strong inhibitor was obtained, and at the same time, the effect of improving the magnetic flux density was obtained at the same time as the secondary recrystallized grains were refined.

In the cold rolling step, a one-time cold rolling method in which a hot-rolled sheet is annealed and then a single cold-rolling is performed, and a hot-rolled sheet is annealed and then an intermediate after the first cold-rolling is performed. The second cold rolling method in which annealing is performed and then the second cold rolling is performed, or the second cold rolling is performed after the first cold rolling and the intermediate annealing is performed after the hot rolled sheet annealing is omitted. Any of the two cold rolling methods in which cold rolling is performed can be employed. In the annealing in the cold rolling step, AlN is precipitated during the temperature raising process, and attention must be paid to prevent Ostwald growth, re-solid solution and re-precipitation of the precipitated AlN, and hot-rolled sheet annealing and intermediate annealing are performed. It is important to take care to prevent Ostwald ripening, re-solid solution and re-precipitation of AlN precipitated even in the second annealing (intermediate annealing) in this case.

It is important that the rolling reduction of the final rolling be in the range of 80 to 95% as conventionally known.

As the next experiment, an investigation was made on the conditions of final finish annealing. C: 0.08%, Si: 3.38%, Mn: 0.
10% of 250 mm-thick silicon steel slabs each containing 14% each containing 07%, Al: 0.022%, Se: 0.020%, Sb: 0.035% and N: 0.008%, with the balance being Fe and unavoidable impurities. After heating at a temperature of 1250 ° C and rough rolling to a thickness of 45 mm at a temperature of 1250 ° C, finishing rolling to a thickness of 2.2 mm at a temperature of 1020 ° C is completed, and then a large amount of cooling water is injected. ° C /
Then, it was rapidly cooled at a cooling rate of s and wound up in a coil at a temperature of 550 ° C.

These hot rolled sheets were heated at a heating rate of 6.5 ° C./s, annealed at 1050 ° C. for 30 seconds, pickled, and then pickled at a temperature of 120 to 160 ° C. using a Sendzimer rolling mill. After being subjected to warm rolling to a final cold-rolled sheet thickness of 0.30 mm, each was subjected to degreasing treatment, followed by decarburization and primary recrystallization annealing at 850 ° C. for 2 minutes, respectively.

Subsequently, an annealing separator shown in Table 2 was applied to these decarburized annealed sheets, and then a final finish annealing was performed.
A heat pattern in which the temperature is raised to a temperature of 80 ° C. at a rate of 30 ° C./s, held for 7 hours, and then lowered, in an N ₂ atmosphere up to a temperature of 400 ° C., and thereafter in an atmosphere shown in Table 2. went.

[0043]

[Table 2]

Then, after removing the unreacted annealing separator from each steel sheet, an insulating coating mainly composed of magnesium phosphate containing 60% of colloidal silica was applied, and baked at a temperature of 800 ° C. .

A test piece of Epstein size was cut out from each of the products thus obtained along the rolling direction, subjected to strain relief annealing at a temperature of 800 ° C. for 3 hours, and then subjected to iron loss (W _{17) at} a magnetic flux density of 1.7 T. _{/ 50} ) and magnetic flux density (B ₈ ), and the average crystal grain size of each product plate was also measured. Table 3 summarizes the measurement results.

[0046]

[Table 3]

From Table 3, it can be seen that the products of the condition symbols A and B which were treated in the final finish annealing at a high temperature in an atmosphere of plain N ₂ were inferior in magnetic properties. This can be seen from the decrease in magnetic flux density and the value of the average crystal grain size that the nitriding of the steel sheet progressed and the crystal grains having poor orientation were recrystallized.

It is also understood that Ca and Ti are essential components to be contained in the annealing separator. On the steel sheet surface, S formed on the steel sheet surface during decarburization annealing
iO ₂ and MgO, which is the main component of the annealing separator, react during the final annealing to form a film containing forsterite (Mg ₂ SiO ₄ ) as a main component. It is considered that the addition causes the formation of nitrides or oxides of Ca and Ti in the coating, thereby enhancing the strengthening effect of the coating and increasing the tensile effect of the coating, thereby improving the magnetic properties.

The atmosphere of the final annealing plays an important role in the formation of oxides and nitrides in such a coating, and it is considered that it is necessary to enhance the reducibility especially in the middle to late stages of annealing. . In other words, the inclusion of strong reducing H ₂ in the atmosphere promotes the decomposition of nitrides in the steel and increases the Al content in the coating, and at the same time promotes the formation of the coating by the reducing atmosphere. It seems that it became possible to increase the amounts of Ti and Ca contained in the coating.

As a result of various searches for the component composition for achieving the effects of the present invention, in order to sufficiently precipitate AlN during the temperature raising process of hot-rolled sheet annealing, particularly for Al, an Al content of 0.010 It has been found that good results can be obtained in the range of 0.030%.

As described above, the present invention has been completed based on the knowledge obtained from the results of the above-described experiments and investigations. Next, with respect to the component composition and the manufacturing method of the grain-oriented electrical steel sheet of the present invention, the requirements for exhibiting the effects of the present invention, the range thereof, the operation, and the like will be described in detail. First, the component composition of the material will be described.

C: 0.025 to 0.095% When the content of C exceeds 0.095%, the amount of γ transformation becomes excessive, the distribution of Al during hot rolling becomes uneven, and the rise of hot-rolled sheet annealing and intermediate annealing increases. The uniformity of the distribution of AlN precipitated during the heating process is impaired, and the load of decarburization annealing is increased, so that poor decarburization tends to occur. On the other hand, if it is less than 0.025%, the effect of improving the structure cannot be obtained, and the secondary recrystallization becomes incomplete and the magnetic properties deteriorate. Therefore, its content is in the range of 0.025 to 0.095%.

Si: 1.5 to 7.0% Si is an essential component for increasing electric resistance and reducing iron loss. For this purpose, it is necessary to contain 1.5% or more. If it is contained, the processability deteriorates, and it becomes extremely difficult to manufacture and process the product. Therefore, its content is in the range of 1.5 to 7.0%.

Mn: 0.03 to 2.5% Mn is an important component because it increases the electric resistance and improves the hot workability at the time of production, like Si. For this purpose, it is necessary to contain 0.03% or more.
%, Magnetic properties are deteriorated by inducing γ transformation. Therefore, its content is in the range of 0.03 to 2.5%.

Al: 0.010 to 0.030%, N: 0.003 to 0.01
In addition to the above components, an inhibitor for inducing secondary recrystallization is required in the 0% steel, and it is essential to contain Al and N as inhibitor components. Al has a content of 0.01
If it is less than 0%, the amount of AlN precipitated during the heating process in hot-rolled sheet annealing or intermediate annealing is insufficient, and it is not possible to obtain a good secondary recrystallization. Conversely, if it exceeds 0.030%, AlN The precipitation temperature rises, and ordinary hot rolling makes it impossible to suppress the precipitation of AlN. Therefore, Al is 0.010-0.030
%.

If the content of N is less than 0.003%, the amount of AlN precipitated during the heating process of hot-rolled sheet annealing or intermediate annealing is insufficient, so that good secondary recrystallization cannot be obtained. .
If it exceeds 010%, it causes gasification and blistering in steel. Therefore, N should be contained in the range of 0.003 to 0.010%.

In addition to these, a small amount of S and / or Se
Must be contained. Those components in the steel
It precipitates as a Mn compound or a Cu compound, but has almost no effect as an inhibitor, and functions as a precipitation nucleus of AlN that precipitates during the heating process of hot-rolled sheet annealing or intermediate annealing. Since these are precipitations for nucleation of fine and high-density dispersion, a small amount is sufficient as the amount of precipitation, and S or Se alone or in combination with S. or S.
It is sufficient if the content is at least 003%. In addition, even if it is contained excessively, it is not harmful because only the excessive amount precipitates coarsely. However, if the content exceeds 0.040%, it precipitates at the grain boundaries and impairs the workability during hot rolling. Therefore, the content of S or Se alone or in combination is up to 0.040%.

Further, Sb, Sn, Bi, Te, Ge, P, Zn, In
Since Cr and Cr and the like have an auxiliary function of reinforcing the inhibitory force as inhibitors, it is preferable to include them in steel as needed. Their preferred content is 0.001 each
It is in the range of ~ 0.30%.

As for other additive components, for example, N
Since i, Co, Mo, and the like have the effect of improving the surface properties of the steel sheet, they can be appropriately included.

Next, the manufacturing method of the present invention will be described. The silicon steel slab adjusted to the above component composition can be manufactured by any conventionally known method.

The silicon steel slab is subjected to ordinary slab heating and then hot-rolled to form a hot-rolled sheet coil.
At this time, it is an important component of the present invention to set the slab heating temperature to 1350 ° C. or higher. This slab heating temperature is 1350
If the temperature is lower than ℃, the solid solution of the inhibitor is not sufficient and Al
A fine and uniform dispersion and precipitation state of N cannot be obtained.

In the hot rolling, known techniques such as a thickness reduction treatment and a width reduction treatment for uniformizing the structure can be added before and after the slab heating, as needed.

In hot rolling, the following four requirements are indispensable. First, the cumulative rolling reduction in finish rolling is to be in the range of 85 to 99%. This is because if the cumulative rolling reduction is less than 85%, the interval of the band structure in the hot-rolled sheet becomes large and it becomes harmful to the secondary recrystallization, and if it exceeds 99%, recrystallized grains are present in the hot-rolled sheet. And the state of dispersed precipitation of AlN in the cold rolling step becomes rough.

Second, the finish rolling end temperature T (° C.)
Temperature range from 950 ° C to 1150 ° C and Si (%)
Depending on X and Al (ppm) Y, it is necessary to make the range satisfying the following formula (1). 610 + 40X + Y ≦ T ≦ 750 + 40X + Y --- (1) When the finish rolling end temperature falls below the lower limit, Mn
Ultrafine precipitation of S becomes difficult, and AlN precipitates during rolling.
In the case where fine and uniform precipitation of N cannot be obtained and a product having desired magnetic properties cannot be obtained, and conversely, when the upper limit is exceeded,
There is a shortage of defects in the steel that result in ultra-fine precipitation of sulfides and selenides that become rolling nuclei at high temperatures and become AlN precipitation nuclei.As a result, products with the desired magnetic properties cannot be obtained because fine and uniform precipitation of AlN cannot be obtained. It is because it cannot be obtained.

Third, it is necessary to rapidly cool at a cooling rate of 20 ° C./s or more after the finish rolling. That is, the rapid cooling suppresses the precipitation of AlN in the supersaturated state, and increases the driving force for AlN precipitation during the temperature raising process in hot-rolled sheet annealing and intermediate annealing. Fourth, the coil winding temperature must be 670 ° C. or less. This is because, when the winding temperature exceeds 670 ° C., supersaturated AlN precipitates, the inhibitory power of the inhibitor is deteriorated, and a product having desired magnetic properties cannot be obtained.

In the cold rolling step, as described above, the sheet is annealed and then cold-rolled once, the sheet is annealed and the sheet is twice cold-rolled with intermediate annealing or hot-rolled. Any of the two-time cold rolling method that sandwiches intermediate annealing in which the strip annealing is omitted can be employed. In the first annealing (hot-rolled sheet annealing or intermediate annealing) in this cold rolling step, AlN, which is the essence of the present invention, is finely precipitated in the temperature raising process, and thereafter the annealing process and the second annealing (intermediate annealing) Has precipitated
It is extremely important to take care to prevent Ostwald ripening, re-dissolution and re-precipitation of AlN.

In the first annealing in the cold rolling step, that is, in the one-time cold rolling method and the two-time cold rolling method in which hot-rolled sheet annealing is performed, hot-rolled sheet annealing and hot-rolled sheet annealing are omitted.
In the cold rolling method, in order to cause AlN to be finely precipitated during the heating process of the intermediate annealing, the heating rate up to a temperature of 800 ° C. in the heating process is in a range of 5 to 25 ° C./s. It is necessary. This is because if the heating rate is less than 5 ° C./s, the precipitates are coarsely precipitated, and a strong inhibitory force as an inhibitor cannot be obtained. This is also because it becomes impossible to obtain a strong inhibitory force as an inhibitor.

Further, it is necessary that the annealing be performed at a temperature of 900 to 1125 ° C. for a holding time of 150 seconds or less.
That is, if the annealing temperature is excessively low, the strength of the (110) grains serving as nuclei for secondary recrystallization in the recrystallized structure after rolling is insufficient, and a secondary recrystallized structure having a good orientation cannot be obtained. In order to obtain sufficient strength of the (110) grains, it is necessary that the crystal structure after annealing is coarsened to a certain size or more. For this purpose, annealing at a temperature of 900 ° C. or more is indispensable. Also, regarding the upper limit of the annealing temperature,
The most important point is that the AlN deposited finely during the temperature raising process is not Ostwald-grown or re-dissolved.
For this purpose, set the annealing temperature to 1125 ° C or lower and maintain the holding time.
It must be less than 150 seconds. As described above, the present invention is characterized by lowering the annealing temperature. Thus, it becomes possible to increase the strength of the (110) grains in the structure of the primary recrystallized grains. Secondary recrystallization of a fine grain structure can be obtained.

Further, regarding the cooling process of the annealing,
Although not particularly required, quenching to increase the solid solution C in the steel after annealing or quenching to maintain fine quenching in the steel to precipitate fine carbides is not a product. This is effective in improving the magnetic characteristics of. Further, a known means for increasing the oxidizing property of the annealing atmosphere and decarburizing the surface layer of the steel sheet also works effectively.

Here, hot-rolled sheet annealing before final cold rolling,
The amount of decarburization in the intermediate annealing is preferably in the range of 0.005 to 0.025%. Due to such decarburization treatment, the C content of the surface layer of the steel sheet is reduced, and the amount of γ transformation during annealing is reduced, so that the inhibitory force of the inhibitor on the surface layer of the sheet thickness at which nuclei for secondary recrystallization is generated is enhanced, Preferred secondary recrystallization can be obtained. In order to obtain this effect, the C content of the steel sheet must be 0.005.
% Or more. However, if the content is reduced beyond 0.025%, the primary recrystallized structure is deteriorated, which is not preferable.

The second annealing (intermediate annealing) of the cold rolling twice after the hot-rolled sheet annealing is the same as the first annealing for maintaining the state of finely precipitated AlN and adjusting the crystal structure. Annealing at a temperature in the range of 900 to 1125 ° C for 150 seconds or less.

Regarding the rolling reduction of the cold rolling, it is necessary to make the rolling reduction of the final cold rolling in the range of 80 to 95% as conventionally known. This is because when the rolling reduction exceeds 95%, secondary recrystallization becomes difficult, and when the rolling reduction is less than 80%, a good orientation of the secondary recrystallized grains cannot be obtained, and the magnetic flux density of the product deteriorates.

The rolling reduction in the first rolling of the two-time cold rolling is in the range of 15 to 60%. If the rolling reduction is less than 15%, the mechanism of rolling recrystallization does not work and the crystal structure cannot be homogenized. Conversely, if it exceeds 60%, the crystal structure is integrated and the second rolling is performed. This is because the effect of (1) cannot be obtained.

Further, in the final cold rolling, warm rolling at a temperature range of 90 to 350 ° C. is performed as is well-known, or a pass for a time range of 10 to 60 minutes at a temperature range of 100 to 300 ° C. Performing the intermediate aging treatment has the effect of improving the primary recrystallized texture and more preferable results are obtained, and therefore, it is significant to apply the present invention to the present invention.

After the final cold rolling, a linear groove may be provided on the surface of the steel sheet for magnetic domain refinement as is known.

The steel sheet having the final cold-rolled thickness obtained by the above method is subjected to primary recrystallization annealing by a known method,
After applying an annealing separator containing a Ti compound in the range of 1 to 20% and Ca in a range of 0.01 to 3.0%, the temperature is raised at least from 900 ° C. to an atmosphere containing H ₂ from 900 ° C. or more. Anneal.

The reason why Ti and Ca are contained in the annealing separator is that oxides and nitrides of these components are generated in the coating formed by the final finish annealing, and the tensile effect of the coating due to these components is generated. This is because improvement is conceivable, and for this purpose, it is necessary to contain 1% or more of a Ti compound and 0.01% or more of Ca. However, when the Ti compound is contained in an amount exceeding 20%, a large amount of Ti penetrates into the steel to cause deterioration of the magnetic properties and inhibits the formation of the film, so that the Ca is included in an amount exceeding 3.0%. In such a case, the adhesion of the coating film is deteriorated. Therefore, the upper limits of these contents are set to 20% for the Ti compound and 3.0% for Ca.

In the final finish annealing, if nitriding of the steel sheet occurs during the annealing, secondary recrystallization of crystal grains having poor orientation is caused. Therefore, it is necessary that the atmosphere of the final finish annealing contains H ₂ at least at 900 ° C. or more. It is. The use of an atmosphere containing H ₂ plays an important role in the formation of oxides and nitrides in the above-mentioned film, and particularly in the middle to late stages of annealing at a temperature of 900 ° C. or more, the reducing property is enhanced. Is considered important.

In this final finish annealing, after removing the unreacted annealing separating agent, an insulating coating is applied to the steel sheet surface to obtain a product. If necessary, the steel sheet surface may be mirror-finished before coating. Alternatively, a tension coating may be used as the insulating coating, and the coating baking process may also serve as a flattening process.

Further, in order to reduce iron loss, the steel sheet after the second recrystallization is subjected to a plasma jet or laser irradiation as a well-known magnetic domain segmentation treatment, or a linear dent is formed by a projection roll. Or other processing can be performed.

[0081]

【Example】

Example 1 C: 0.08%, Si: 3.35%, Mn: 0.07%, Al: 0.022%,
A silicon steel slab containing 0.012% Se, 0.02% Sb and 0.008% N and the balance consisting of Fe and unavoidable impurities was heated to a temperature of 1410 ° C., and the sheet thickness was 45%.
rough rolling at a temperature of 1230 ° C on a sheet bar of 12 mm, finishing rolling to a rolling end temperature of 1020 ° C and a sheet thickness of 2.2 mm, cooling water is injected to cool at a cooling rate of 25 ° C / s and 600 ° C. At a temperature of 5 ° C. to form a hot rolled sheet.

The heating rate of the hot-rolled sheet to a temperature of 1100 ° C .:
The temperature was raised at 12.5 ° C./s, and after hot-rolled sheet annealing maintained at this temperature for 30 seconds, pickling was performed and cold-rolled to a sheet thickness of 1.5 mm.

Next, this cold-rolled sheet coil was divided into two equal parts, and subjected to intermediate annealing in an H ₂ atmosphere at a dew point of 40 ° C. to reduce the C content.
At this time, one of them was annealed at 1080 ° C. for 50 seconds as a compatible example of the present invention, and the other was annealed at 1200 ° C. for 50 seconds as a comparative example.

These intermediate annealed sheets were each subjected to warm rolling at a steel sheet temperature of 220 ° C. to a final cold-rolled sheet thickness of 0.22 mm, and then degreased, and then decarburized at 850 ° C. for 2 minutes. After recrystallization annealing, an annealing separator containing 5% of TiO ₂ added to MgO containing 0.5% of Ca is applied, and then as final finishing annealing, a temperature of 30 ° C./h is applied to a temperature of 800 ° C. in an N ₂ atmosphere. 800 ° C. in a mixed atmosphere of N ₂ : 25% and H ₂ : 75% at a heating rate
From 1 to 1050 ° C at a rate of 12.5 ° C / h, then 25 ° C in an H ₂ atmosphere to 1200 ° C.
The temperature was raised at a rate of / h, maintained at this temperature for 6 hours, and then lowered. At this time, a treatment was performed in which the temperature was lowered to 600 ° C. in an H ₂ atmosphere and from 600 ° C. in an N ₂ atmosphere.

After the final annealing, the unreacted annealing separating agent was removed, and magnesium phosphate containing 60% of colloidal silica was applied as a tension coating and baked at a temperature of 800 ° C. to perform magnetic domain refining. Irradiation was carried out at a pitch of 6 mm with a plumb jet to produce products.

The measurement results of the magnetic properties investigated for these products are as follows.

As is clear from the above results, compared to the comparative example having a high intermediate annealing temperature, the conforming example of the present invention shows extremely excellent magnetic properties.

Example 2 1430 silicon steel slabs having various component compositions shown in Table 4 were used.
After heating to a temperature of ℃ ℃, a sheet bar with a thickness of 50mm is roughly rolled at a temperature of 1250 ℃, and then finish-rolled. For steels with symbols VII and X, the finish-rolling temperature is 1000 ℃ and for other steels At a finishing rolling temperature of 1030 ° C and a plate thickness of 2.6 mm, respectively, and then jet water to 35 ° C
/ S and cooled at a temperature of 550 ° C. into a coil to form a hot rolled sheet.

[0089]

[Table 4]

Further, these hot-rolled sheets were pickled, and the sheet thickness:
Cold-rolled to 1.8 mm, heated to 1080 ° C at a rate of 15 ° C / s, subjected to an intermediate treatment of 50 seconds in a 50 ° C H ₂ atmosphere, and then to 230 ° C steel sheet. Cold rolling at a final temperature of 0.26 mm was performed by warm rolling at a temperature.

These cold-rolled sheets were degreased and treated at 850 ° C.
Minutes after decarburization and primary recrystallization annealing, 0.35% Ca
MgO containing 0.07% B and 5% TiO ₂ , 2% Sr (O
After wound into a coil shape and coated with an annealing separating agent was added H) ₂ and 2% of SnO _2, as a final finish annealing, N ₂
In the atmosphere, the temperature was raised to a temperature of 850 ° C. at a rate of 30 ° C./h and maintained at a temperature of 850 ° C. for 25 hours. N ₂ : 25%, H ₂ : 75
% In a mixed atmosphere at a temperature of 1200 ° C: 15 ° C /
h, the temperature was maintained at this temperature in an H ₂ atmosphere for 5 hours, and then the temperature was lowered.

After removing the unreacted annealing separator, a tension coating containing 50% colloidal silica was applied and baked to obtain respective products. Table 5 summarizes the measurement results of the magnetic properties investigated for these products.

[0093]

[Table 5]

As is apparent from Table 5, all of the applicable examples of the present invention show good magnetic properties as compared with the comparative examples in which the content of Al, S + Se or N is out of the range of limitation of the present invention.

Example 3 C: 0.075%, Si: 3.35%, Mn: 0.07%, Al: 0.022
%, S: 0.004%, Sb: 0.02% and N: 0.0075%, the balance being a silicon steel slab (a) composed of Fe and unavoidable impurities, C: 0.073%, Si: 3.36%, Mn :
Silicon steel slab (b) containing 0.07%, Al: 0.024%, S: 0.002%, Sb: 0.02% and N: 0.0082%, with the balance being Fe and unavoidable impurities (b), C: 0.080
%, Si: 3.52%, Mn: 0.07%, Al: 0.030%, S: 0.00
8%, Sb: 0.02% and N: 0.0075%, with the balance being
Silicon steel slab (c) composed of Fe and unavoidable impurities and C: 0.073%, Si: 3.05%, Mn: 0.07%,
Al: 0.018%, S: 0.004%, Sb: 0.02% and N: 0.
0075%, the balance being four kinds of silicon steel slabs (d) composed of Fe and unavoidable impurities. After heating two each to a temperature of 1380 ° C., a sheet bar having a thickness of 35 mm Rough rolling and finishing rolling, the rolling end temperature is 985 ° C
After changing the thickness to 2.2 mm, jet water is sprayed and quenched at a cooling rate of 45 ° C / s.
It was wound around a coil at a temperature of 570 ° C. to form a hot rolled sheet.

Each of these hot-rolled sheets was subjected to hot-rolled sheet annealing at a heating rate of 15 ° C./s to 1100 ° C. and holding for 30 seconds, followed by pickling to make the intermediate sheet thickness: 1.5 mm. After cold rolling, intermediate annealing was performed.

In the intermediate annealing, a precipitation treatment of a carbide, which is maintained at a temperature of 1090 ° C. for 60 seconds, then rapidly cooled at a cooling rate of 40 ° C./s by spraying mist water and then maintained at a temperature of 350 ° C. for 30 seconds. went.

Thereafter, each steel sheet was rolled to a final cold-rolled sheet thickness: 0.22 mm while being subjected to an inter-pass aging treatment in a temperature range of 120 to 230 ° C. by a Sendzimir rolling mill.

These cold-rolled sheets were degreased, and as a magnetic domain refining treatment, grooves having a width of 50 μm and a depth of 20 μm were provided linearly at an angle of 15 degrees from the width direction of the steel sheet at a pitch of 4 mm in the longitudinal direction of the steel sheet. After that, decarburization and first recrystallization annealing at 850 ° C. for 2 minutes are performed, and MgO containing 0.22% of Ca and 0.08% of B is added to MgO.
An annealing separator containing 5% TiO ₂ and 3% SnO ₂ is applied and wound on a coil.
₂ Raise the temperature to 850 ° C at a rate of 30 ° C / h in an atmosphere and hold at 850 ° C for 25 hours. N ₂ : 25%, H ₂ :
Heating rate up to 1150 ° C in a 75% mixed atmosphere: 15 ° C
/ H, and the temperature was maintained for 5 hours in an H ₂ atmosphere, and then the temperature was reduced.

Thereafter, after removing the unreacted annealing separator, a tension coating containing 50% of colloidal silica was applied and baked to obtain respective products. Table 6 summarizes the measurement results of the magnetic properties investigated for these products.

[0101]

[Table 6]

As is clear from Table 6, the S content was 0.00
3% and hot finish rolling end temperature (T) is 610
+ 40X + Y ≦ T ≦ 750 All of the applicable examples of the present invention satisfying + 40X + Y show extremely low iron loss values.

Example 4 Ten slabs each having the component composition of the symbol VII shown in Table 4 above were heated to a temperature of 1400 ° C., and then roughly rolled into a sheet bar having a thickness of 50 mm. Finish rolling was performed at 1060 ° C. and a thickness of 2.7 mm, and then jet water was injected to quench at a cooling rate of 40 ° C./s and wound at 600 ° C. in a coil to form a hot rolled sheet.

These hot-rolled sheets were heated at a heating rate of 17 ° C./s for 11 hours.
After hot-rolled sheet annealing, which is heated to a temperature of 00 ° C and held for 60 seconds, is pickled, cold-rolled to a final cold-rolled sheet thickness of 0.30 mm, degreased, and 850 ° C for 2 minutes. , And primary recrystallization annealing.

Thereafter, after applying each of the annealing separators shown in Table 2 above, the final finish annealing is performed in a N ₂ atmosphere up to a temperature of 400 ° C., and thereafter the final holding temperature is reduced.
Each treatment was performed in the atmosphere shown in Table 2 except that the temperature was changed to 1200 ° C. The heat pattern at that time is 25 up to a temperature of 1200 ° C.
The temperature was raised at a rate of ° C / s, and the temperature was maintained for 8 hours and then lowered.

After the final annealing, the unreacted annealing separating agent is removed, then aluminum phosphate containing 60% colloidal silica is applied and baked at a temperature of 800 ° C.
As a magnetic domain refining treatment, a plasma jet was linearly irradiated at a pitch of 7 mm to obtain products. Table 7 summarizes the measurement results of the magnetic properties investigated for these products.

[0107]

[Table 7]

As is clear from Table 7, all of the applicable examples of the present invention show extremely low iron loss.

[0109]

The present invention uses a material having a limited component composition, specifies hot rolling conditions, hot-rolled sheet annealing conditions and intermediate annealing conditions, and finely precipitates AlN precipitation nuclei by annealing before cold rolling. In addition, to specify the other manufacturing conditions such as the composition of the annealing separator, to produce a grain-oriented electrical steel sheet, according to the present invention, to produce a high magnetic flux density oriented silicon steel sheet with extremely low iron loss Therefore, it is possible to advantageously respond to the recent demand for lower iron loss of the iron core material.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of the Si and Al contents of a material and the hot rolling end temperature on the degree of integration (B ₈ / B _s ) of the crystal orientation of a product.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kunihiro Senda, 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. Chome (without address) Mizushima Works, Kawasaki Steel Corporation (72) Inventor Chisuko Goto 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture (without address) Inside Mizushima Works, Kawasaki Steel Corporation

Claims (4)

[Claims] 1. C: 0.025-0.095 wt%, Si: 1.5-7.
0 wt%, Mn: 0.03 to 2.5 wt%, one of S or Se
Species or total of 2 types: 0.003 to 0.040 wt%, Al: 0.010
A silicon steel slab containing -0.030 wt% and N: 0.003 -0.010 wt% is used as a raw material, and the slab is heated to a temperature of 1350 ° C or more, hot-rolled, and then subjected to hot-rolled sheet annealing.
Cold rolling is performed by a cold rolling method or a twice cold rolling method with intermediate annealing to obtain a final cold-rolled sheet thickness, or after hot rolling, cold rolling is performed twice with intermediate annealing. After rolling to the final cold-rolled sheet thickness, subjecting it to primary recrystallization annealing, and then applying an annealing separator, and then performing the final finish annealing, a series of steps to produce a grain-oriented electrical steel sheet, Hot rolling in which the final rolling finish temperature is in the range of 950 to 1150 ° C and the temperature range satisfies the following formula (1) from the relationship between the Si content and the Al content of the material. After the completion of hot rolling, quench at a cooling rate of 20 ° C./s or more
Coiling at a temperature of less than or equal to ℃, hot-rolled sheet annealing and intermediate annealing are both raised to a temperature of 800 ℃ at a heating rate of 5 to 25 ℃ / s, 900 to 1125 ℃
Cold rolling is performed in a temperature range of 80 to 95% by a single cold rolling method under the condition that the holding time is 150 seconds or less. After the first rolling is performed in the range of 15 to 60% by the cold rolling method twice, and then the second rolling is performed after the intermediate annealing, the rolling is reduced to 80:
To be in the range of ~ 95%, to obtain a final cold-rolled sheet thickness, using an annealing separator containing 1 to 20 wt% of Ti compound and 0.01 to 3.0 wt% of Ca, at least during the temperature rise during final finish annealing. A method for producing a high magnetic flux density grain-oriented electrical steel sheet having extremely low iron loss, which is sequentially combined with increasing the temperature from 900 ° C. or higher in an atmosphere containing H ₂ . [Note] 610 + 40X + Y≤T≤750 + 40X + Y --- (1) T: Finish rolling end temperature (° C) X: Si (wt%) Y: Al (wtppm) 2. The high magnetic flux with extremely low iron loss according to claim 1, wherein the cooling at the time of hot-rolled sheet annealing or intermediate annealing immediately before the final cold rolling is a quenching treatment for increasing the amount of solute C in the steel sheet. Method for producing density-oriented electrical steel sheet. 3. The final cold rolling is performed at a temperature of 90 to 350 ° C. or at a temperature of 100 to 300 ° C.
The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to claim 1 or 2, wherein an inter-pass aging treatment is performed for a time range of up to 60 minutes. 4. Annealing before final cold rolling is performed in a range of 0.005 to 0.02.
4. The method for producing a high magnetic flux density grain-oriented electrical steel sheet having extremely low iron loss according to claim 1, wherein decarburization of 5 wt% is performed.