JPH0797630A - Production of high magnetic flux density grain oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To stably produce a grain oriented silicon steel sheet having high magnetic flux density and remarkably small in core loss. CONSTITUTION:The compsn. of a steel is constituted of the one contg. 0.01 to 0.08% Al, 2.0 to 4.5% Si, 0.05 to 2.0% Cu, 0.0005 to 0.05% Bi and 0.001 to 0.06% S, and the balance Fe with inevitable impurities, and the hot rolled steel strip thereof is annealed according to necessary and is thereafter subjected to cold rolling for one time or >=two times including process annealing to regulate its thickness to a prescribed one, which is subjected to primary recrystallization annealing, is thereafter subjected to nitriding annealing according to necessary, is thereafter coated with a separation agent for annealing and is subjected to finish annealing. After the nitriding annealing, a separation agent for annealing essentially consisting of one or >=two kinds among alumina, silica, zirconia, strontium oxide and forsterite is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented silicon steel sheet (hereinafter referred to as grain-oriented magnetic sheet) having a high magnetic flux density and a low iron loss. Particularly, by not performing decarburization in the primary recrystallization annealing step, formation of an internal oxide layer harmful to magnetic properties is prevented, and B ₈ = 1.9 in the secondary recrystallization step (finish annealing step).
Express secondary recrystallization having a high magnetic flux density of 3 or more,
The process is completed without forming a forsterite (hereinafter referred to as glass) film on the surface of the steel sheet, and then magnetic domain subdivision, tension coating, etc. are performed to improve the iron loss characteristics. is there.

[0002]

2. Description of the Related Art In the production of grain-oriented electrical steel sheets, hot-rolled steel strips are annealed as necessary, and then cold-rolled once or twice or more with intermediate annealing, to a predetermined thickness, and then subjected to primary re-rolling. After crystal annealing, nitriding annealing is performed if necessary, and then an annealing separator is applied, and finish annealing is performed. Decarburization is generally performed in this primary recrystallization annealing. However, in recent years, many techniques have been reported in which decarburization in a molten steel state is used and decarburization in the primary recrystallization annealing process is omitted.

For example, JP-A-54-112317, JP-A-55-073818, and JP-A-57-114614.
No. 57-207114 and 58-100.
627, JP-A-61-91319 and JP-A-62-8.
3421, JP-A-1-119644, and JP-A1-2
12721, JP-A-1-309923, JP-A-1-
309924, JP-A-2-30714, JP-A-2-
141532, JP-A-3-111516, JP-A-3
-287721, JP-A-5-9666 and the like. However, it is difficult to produce a high magnetic flux density steel sheet to which the present invention is directed by these techniques, and even if possible, it is necessary to strictly control the production conditions for stable production. There are drawbacks such as. Further, as a technique for smoothing the surface of the steel sheet, there are chemical polishing, electrolytic polishing and the like disclosed in JP-A-64-83620.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a method for stably producing a grain-oriented electrical steel sheet having a high magnetic flux density. Furthermore, if the decarburization in the primary recrystallization annealing step is omitted, various difficulties are involved in producing a grain-oriented electrical steel sheet having a high magnetic flux density of B ₈ = 1.93 or more. If this can be solved, formation of an internal oxide layer that deteriorates iron loss formed during decarburization annealing can be reduced. Further, iron loss can be remarkably reduced by eliminating the formation of a glass film which is usually formed in the secondary recrystallization process and smoothing the plate surface. The present invention provides a method for solving these problems.

[0005]

Means for Solving the Problems In the means of the present invention, the components are C: 0.0005 to 0.004% by weight, Si: 2.0 to.
4.5% by weight, acid-soluble Al: 0.010 to 0.080
% By weight, N: 0.001 to 0.020% by weight, Cu:
0.050 to 2.00% by weight, Bi: 0.0005
0.050% by weight, S: 0.0010 to 0.060% by weight, the hot-rolled silicon steel strip consisting of the balance Fe and unavoidable impurities is annealed as needed, and then once or twice or more with intermediate annealing. This is to perform cold rolling to a predetermined plate thickness, perform primary recrystallization annealing, then perform nitriding annealing if necessary, apply an annealing separating agent, and perform finish annealing. Further, as the annealing separating agent, one or more kinds of alumina, silica, zirconia, strontium oxide and forsterite are contained as a main component.

When the present invention is further carried out, the primary recrystallization annealing is performed at a temperature of 900 ° C. or higher and 1050 ° C. or lower for 1 second or longer and 10 minutes or longer.
Heating for seconds or less, and the temperature rising process of the final annealing 8
Heating 00 ° C or higher in an atmosphere of 50% or higher nitrogen,
The nitrogen content of the steel sheet before finish annealing is 0.006 to 0.050.
It is desirable that the content is wt%.

The present invention will be described in detail below. First, the conditions for stabilizing and developing secondary recrystallization having a magnetic flux density of 1.93 or more in the primary recrystallization annealing step without performing decarburization annealing will be described. As a method for producing a grain-oriented electrical steel sheet without decarburization in the primary recrystallization annealing step, the inventors have developed the technique disclosed in Japanese Patent Laid-Open No. 57-114614, but this method can reduce the magnetic flux density. It had the disadvantage of being relatively low (Example B ₈ = 1.88). Further, as a technique for manufacturing a steel sheet having a high magnetic flux density, Japanese Patent Application Laid-Open No. 57-8943
9 No. (Example B ₈ = 1.97) or, JP 57-2
No. 07114 (Example B ₈ = 1.94) was also developed, but such a high magnetic flux density may not be stably obtained in some cases.

As a result of diligent research into the cause, the main orientation of the secondary recrystallization was found in the primary recrystallized plate (110) [00
1) The existence amount of the orientation is small, that is, the crystal orientation that becomes the nucleus of the secondary recrystallization is small, and the inhibitor that should prevent the growth of the crystal orientation other than the secondary recrystallized grains is insufficient. It was found that the action and effect of preferentially growing only the 110) [001] oriented secondary recrystallized grains is smaller than that of the primary recrystallized plate produced by the conventional manufacturing process.

In the present invention, Cu, Bi and S are respectively replaced by C
u: 0.050 to 2.00% by weight, Bi: 0.0005
It was discovered that these drawbacks can be overcome by limiting the content to the range of .about.0.050% by weight and S: 0.0010 to 0.060% by weight (weight% is simply expressed as "%" in the following description). Has been completed. The reason why this effect occurs will be described below.

First, it has been found that when Cu is contained in an amount of 0.050 to 2.00%, the crystal orientation serving as a nucleus is increased, and further, there is an effect of inhibiting the growth of crystal grains other than the secondary recrystallized grains. In this case, the effect is that the Cu content is 0.5%.
It has been found that the above is remarkable. Further, it was found that the effect becomes remarkable when Cu is 0.05% or more, and the effect becomes larger as Cu increases. If the Cu content is 0.05% or more, the amount and size of Cu sulfide do not change even if the Cu amount is increased. Therefore, the addition of Cu facilitates the growth of secondary recrystallized grains. It is considered that this is because the inhibitor effect as sulfide) and the solid solution Cu itself have an effect of inhibiting the growth of crystal grains other than the secondary recrystallized grains.

Next, it has been found that when Bi is contained in an amount of 0.0005 to 0.050%, only the (110) [001] oriented secondary recrystallized grains are preferentially grown. This is due to the fact that Bi is refined in sulfide,
Is involved in being uniformly finely dispersed.

Next, the reason why S is limited to the range of 0.0010 to 0.060% is that the effect of is exhibited. That is, in the material component of the present invention, when S is less than 0.005%, it becomes difficult to find secondary recrystallized grains, and when secondary recrystallized, secondary recrystallized grains deviated from the (110) [001] orientation We found that the expression was high. That is, in this component system, S gives the effect of.

When S is present in an amount of 0.001% or more, fine sulfides are observed, and the fine sulfides exert the effect of. S is effective even if it is 0.06%, but if S is large, cracks are likely to occur in the hot rolling step. Especially, if the amount of Bi added is large, this tendency is promoted. Therefore, in the present invention, the upper limit is 0.060%. did.

N forms (Al, Si) N and acts as an inhibitor, but the effect is not exhibited unless it is 0.001% or more at the stage of slab. If 0.02% or more is contained, surface scratches called blister occur. However, in the state before finish annealing, the range of 0.006% or more and 0.06% is desirable. This is 0.006 in nitrogen before finish annealing.
% Or less than 0.06%, secondary recrystallization tends to be less likely to occur, and even if secondary recrystallization occurs, the magnetic flux density is significantly deteriorated. When the nitrogen content is low, the reason why secondary recrystallization is difficult to develop is that the inhibitor as a nitride is insufficient, so that crystal grains with various orientations grow, and secondary recrystallization occurs. The reason why the magnetic flux density is low is that the secondary recrystallization occurs at a low temperature, and in that case, the probability that the secondary recrystallization orientation is a secondary recrystallization grain other than the (110) [001] orientation increases. .

When the nitrogen content is high, the secondary recrystallization orientation is bad because the inhibitor as a nitride is strong, and the secondary recrystallization appears at high temperature. In this case, similar to secondary recrystallization that occurs at low temperature, secondary recrystallization with various orientations occurs. The reason why secondary recrystallization may not appear when the nitrogen content is high is that the inhibitor rapidly weakens at high temperature and only secondary recrystallized grains cannot grow.

As the content of Si increases, the specific resistance increases and the eddy current loss of the product decreases. Therefore, the more Si, the better. The reason why Si is limited to 2% or more is that the lower limit is set to 2% because eddy current loss is large and it is not preferable below this range. However, Si becomes more likely to crack in the cold rolling process as the added amount increases. This tendency becomes more remarkable as C is higher. Since the steel of the present invention has a C content of 0.004% or less in the cold rolling process, it is less likely to be cracked than conventional materials, but if Si is 4.5% or more, it requires special measures for cold rolling and is economically manufactured. Therefore, the upper limit was set to 4.5% because it defeats the purpose of the present invention.

Although Al forms (Al, Si) N and acts as an inhibitor, the effect is not exhibited unless the content of the acid-soluble Al is 0.01% or more, so the lower limit was made 0.01%. The upper limit is set to 0.08% because if Al is present in excess of this, it will not work effectively as an inhibitor.

When the hot rolling start temperature is 1200 ° C. or higher, secondary recrystallization becomes unstable with the components of the present invention, and the probability that the magnetic flux density of the product will be 1.80 Tesla or less increases, so that it cannot be used as an industrial manufacturing method. . The reason why the secondary recrystallization becomes unstable is that the crystal grain size is large in high temperature hot rolling, so that the recrystallization in the hot rolling process is insufficient, and the magnetic flux density is low even after the secondary recrystallization. The reason is that the primary recrystallized grains become small due to the high temperature heating, and as a result, the secondary recrystallized temperature is lowered and the secondary recrystallized grains having a bad orientation are developed. Good magnetic properties can be obtained even when the hot rolling start temperature is 1000 ° C. or lower, but a lot of energy required for hot rolling is required, and the surface of the steel sheet is easily scratched during hot rolling, which is not economical.

In the conventional method for producing grain-oriented electrical steel sheet, the steel sheet cold rolled to the final thickness has a C content of 0.04% to 0.08%.
%, It is necessary to perform decarburization in addition to recrystallization in the primary recrystallization annealing. In order to decarburize C to 0.004% or less by primary recrystallization annealing, it is usually 820 ° C.
To 860 ° C. for 120 seconds or more is required. In this case, when the heating temperature is 900 ° C. or higher, an internal oxide layer harmful to decarburization is formed on the surface of the steel sheet and decarburization becomes difficult, so the heating temperature is suppressed to 900 ° C. or lower.

However, since the steel sheet of the present invention does not require decarburization, the main purpose is to recrystallize it in the primary recrystallization annealing. Therefore, since it is sufficient to heat at the recrystallization temperature or higher, there is no upper limit of the heating temperature. The heating time may be short. However, in order to obtain particularly good magnetic properties, primary recrystallization annealing is performed for 1 second or longer at a temperature of 900 ° C. or higher and 1050 ° C. or lower.
It is preferable to perform heating for 0 seconds or less. Heating temperature to 10
It is preferable that the temperature is 50 ° C. or lower because good magnetic properties can be obtained even at a heating temperature higher than 50 ° C., but sometimes stable good properties cannot be obtained due to deterioration of magnetic properties.
This is because heating at such a high temperature is uneconomical.

The heating time of 1 second or longer is preferable because good magnetic properties can be obtained if the heating time is longer than 10 seconds, and the heating time of 10 seconds or shorter is preferable even when the heating time is longer than this. This is because magnetic characteristics can be obtained, but sometimes stable and good characteristics cannot be obtained due to deterioration of magnetic characteristics, and it is uneconomical to heat for a long time.

The atmosphere of the finish annealing may be the same as that of the finish annealing of the conventional grain-oriented electrical steel sheet. However, if nitrogen is annealed in an atmosphere of 50% or more in the temperature of finish annealing, stable and good magnetic properties can be obtained. Therefore, heating process 800 ° C or more in finish annealing should be heated in an atmosphere of nitrogen 50% or more. Is preferred. In this case, the reason why the temperature is limited to 800 ° C. or higher is that there is little influence at a temperature lower than this. The amount of nitrogen is 1
Although it may be 00%, when hydrogen is not contained at all, if oxygen or the like is mixed in the atmosphere, the steel sheet may be oxidized, which is not preferable. Therefore, it is preferable to mix a few% of hydrogen.

Next, a technique for smoothing the surface of the primary recrystallized plate thus formed without forming a film in the secondary recrystallization annealing process will be described. The inventors of the present invention have studied the same method as the method of applying the annealing separator mainly composed of MgO, that is, the application with an aqueous slurry, and the alumina (Al
₂ O ₃ ), silica (SiO ₂ ), zirconia (Zr
O ₂ ), strontium oxide (SrO), and forsterite (Mg ₂ SiO ₄ ) have an average particle size within a certain range,
I found it possible. That is, it was found that particularly good results were obtained when the average particle size of these substances was 0.5 to 10.0 μm.

In this case, if the powder having a particle size of less than 0.5 μm can be effectively applied as a water slurry, alumina (Al ₂ O
₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ),
When strontium oxide (SrO) and forsterite (Mg ₂ SiO ₄ ) particles themselves are activated because the average particle size is small, they are sintered to form a film and the metal surface does not appear. There is. Also, 1
If it exceeds 0.0 μm, the water slurry is unstable and precipitates immediately when stirring is stopped, it is difficult to apply, the surface of the steel sheet is difficult to get due to the coarse particles, and not only a smooth surface is not obtained but also the magnetic properties are It may cause a problem of deterioration.

In the case of coating methods other than water slurry coating, the average of alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), strontium oxide (SrO), and forsterite (Mg ₂ SiO ₄ ) is also used. The particle size is 0.
5 to 10.0 μm is preferable. Here, what is referred to as an average particle diameter is a particle diameter at which 50% by weight passes. Annealing containing one or more of alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), strontium oxide (SrO), and forsterite (Mg ₂ SiO ₄ ) as a main component. It does not hurt to add a little rust preventive to the separating agent.

Embodiments of the present invention will be described below. C: 0.
0005 to 0.0040%, Si: 2.0 to 4.5%,
Acid-soluble Al: 0.010 to 0.080%, N: 0.0
01-0.020%, Cu: 0.050-2.00%,
S: 0.0010 to 0.060%, molten steel consisting of balance Fe and unavoidable impurities in a normal process or continuously cast into a slab, and then hot-rolled from a temperature range of 1200 ° C to 1000 ° C. Rolled steel plate or hot rolled steel strip. This hot rolled steel sheet or hot rolled steel strip has a temperature of 750 ° C to 1
Annealing is performed in the temperature range of 200 ° C.

Further, these hot-rolled steel sheets or hot-rolled steel strips are cold-rolled without such hot-rolled sheet annealing. Then, the material after cold rolling is subjected to primary recrystallization annealing in a temperature range of 700 ° C to 1050 ° C. After this annealing, nitriding treatment with ammonia is performed to strengthen the inhibitor. Then, the recrystallized plate is coated with an annealing separator and enters a finish annealing furnace. At this time, alumina (Al ₂ O ₃ ) and silica (Si
O ₂ ), zirconia (ZrO ₂ ), strontium oxide (SrO), and forsterite (Mg ₂ SiO ₄ ).
The annealing separator containing at least one of the above as a main component is applied.

The temperature rising rate of the finish annealing is the same as that of the ordinary grain-oriented electrical steel sheet. The atmosphere at the time of raising the temperature of the finish annealing is neutral or reducing as in the case of the ordinary grain-oriented electrical steel sheet, but the nitrogen partial pressure is preferably 50% or more in the temperature range exceeding 800 ° C. It should be noted that mixing an inert gas such as argon or helium for adjusting the nitrogen partial pressure does not matter. After the completion of the secondary recrystallization, it is kept at a high temperature (about 1200 ° C.) with 100% hydrogen for purification. After finishing annealing, magnetic domain subdivision processing such as laser beam irradiation is performed if necessary.

[0029]

【Example】

Example 1 C: 0.001%, Si: 2.90%, Mn: 0.75
%, S: 0.030%, Cu: 0.10%, Al: 0.
027%, N: 0.007%, other unavoidable impurities and Bi: 0.0055%, Bi: 0.0097%, B
i: Three kinds of slabs containing 0.0153% were formed into hot-rolled sheets by a known method. Then, it was heated at 900 ° C. for 2 minutes and cooled with water. After pickling, cold rolling was performed to a thickness of 0.29 mm. Next, heating was performed for 10 seconds at temperatures of 850 ° C, 900 ° C, and 9500 ° C.

Next, MgO is applied and 95% N ₂ −
After heating to 1200 ° C. at a temperature rising rate of 15 ° C./hr in an atmosphere of H ₂ , 50% N ₂ —H ₂ and 25% N ₂ —H ₂ , 100%
It was heated in an H ₂ atmosphere for 20 hours and then cooled. Then, strain relief annealing was performed to measure the magnetic properties. The results are shown in Table 1. For comparison, a material containing no Bi was also treated, but it is found that the magnetic flux density is lower than that of the steel of the present invention. As is apparent from the table, the material produced by the method of the present invention has a remarkably good magnetic flux density.

[0031]

[Table 1]

Example 2 C: 0.001%, Si: 2.90%, Mn: 0.07
5%, S: 0.030%, Cu: 1.00%, Al:
A slab containing 0.024%, N: 0.007%, other unavoidable impurities and Bi: 0.0128% was formed into a hot-rolled sheet by a known method. Then, it was heated at 900 ° C. for 2 minutes and cooled with water. After pickling, cold rolling was performed to a thickness of 0.29 mm. Then it was heated at a temperature of 850 ° C. and 950 ° C. for 10 seconds.

Next, MgO is applied and heated to 1200 ° C. at a temperature rising rate of 15 ° C./hr in an atmosphere of 95% N ₂ —H ₂ and then,
It was heated in a 100% H ₂ atmosphere for 20 hours and then cooled. Then, strain relief annealing was performed to measure the magnetic properties. The results are shown in Table 2. For comparison, a material containing no Bi was treated in the same process, but the magnetic flux density was slightly lower than that of the steel of the present invention. As is apparent from the table, the magnetic flux density of the material produced by the method of the present invention is remarkably good.

[0034]

[Table 2]

Example 3 C: 0.0019%, Si: 2.92%, Mn: 0.0
79%, S: 0.028%, Cu: 1.00%, Al:
0.024%, N: 0.0069%, Bi: 0.002
A slab containing 6% and other unavoidable impurities was formed into a hot-rolled sheet by a known method. Then, it was heated at 900 ° C. for 2 minutes and cooled with water. After pickling, cold rolling was performed to a thickness of 0.29 mm. Next, after heating at a temperature of 950 ° C. for 10 seconds, nitriding treatment was performed.

Next, MgO is applied and heated to 1200 ° C. at a temperature rising rate of 15 ° C./hr in an atmosphere of 95% N ₂ —H ₂ and then,
It was heated in a 100% H ₂ atmosphere for 20 hours and then cooled. Then, strain relief annealing was performed to measure the magnetic properties. The results are shown in Table 3. For comparison, a material containing no Bi was treated in the same process, but the magnetic flux density was lower than that of the steel of the present invention.

As can be seen from the table, the magnetic flux density of the material produced by the method of the present invention is remarkably good.
According to the method of the present invention, the material in which the nitrogen content before secondary recrystallization was 387 ppm had poor iron loss in spite of the extremely high magnetic flux density.
The orientation of the secondary recrystallization was extremely close to the ideal (110) [001] orientation, and the iron loss was remarkably reduced by applying the domain refinement treatment.

[0038]

[Table 3]

Example 4 C: 0.001%, Si: 2.90%, Mn: 0.07
5%, S: 0.030%, Cu: 0.10%, Al:
A slab containing 0.027%, N: 0.007%, and other unavoidable impurities was formed into a hot-rolled sheet by a known method. Then 9
The mixture was heated at 00 ° C for 2 minutes and cooled with water. After pickling, cold rolling was performed to a thickness of 0.29 mm. Next, primary recrystallization was performed in a reducing atmosphere, and subsequently nitriding treatment was performed. Next, Al ₂ O ₃ having an average particle diameter of 4.0 μm was applied in a water slurry state.
For comparison, an annealing separator containing MgO as a main component was applied in a water slurry state.

These two materials were heated to 1200 ° C.
The temperature was raised in a 5% N ₂ -5% H ₂ atmosphere while maintaining the temperature rising rate of 15 ° C./Hr, and after reaching 1200 ° C., 100% hydrogen was obtained and the temperature was maintained for 20 hours. After finishing annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The characteristics of the obtained product are shown in Table 4. The magnetic properties were also investigated for the material that was only subjected to strain relief annealing after finish annealing.

[0041]

[Table 4]

Example 5 C: 0.0019%, Si: 2.92%, Mn: 0.0
79%, S: 0.028%, Cu: 1.00%, Al:
0.024%, N: 0.0069%, Bi: 0.026
A slab containing% and other unavoidable impurities was formed into a hot-rolled sheet by a known method. Then, it was heated at 900 ° C. for 2 minutes and cooled with water. After pickling, cold rolling was performed to a thickness of 0.29 mm. Next, primary recrystallization annealing was performed in a reducing atmosphere and nitriding treatment was performed to adjust the amount of nitrogen to 400 ppm. Next, A having an average particle size of 4.0 μm
1 ₂ O ₃ was applied as a water slurry. For comparison, an annealing separator containing MgO as a main component was applied in a water slurry state.

These two kinds of materials were heated to 1200 ° C.
The temperature was raised in a 5% N ₂ -5% H ₂ atmosphere while maintaining the temperature rising rate of 15 ° C./Hr, and after reaching 1200 ° C., 100% hydrogen was obtained and the temperature was maintained for 20 hours. After finishing annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The characteristics of the obtained product are as shown in Table 5. The magnetic properties were also investigated for the material that was only subjected to strain relief annealing after finish annealing.

[0044]

[Table 5]

Example 6 C: 0.0019%, Si: 2.92%, Mn: 0.0
79%, S: 0.010%, Cu: 0.85%, Al:
0.029%, N: 0.0069%, Bi: 0.030
A slab containing% and other unavoidable impurities was formed into a hot-rolled sheet by a known method. Then, after pickling, cold rolling is performed to a thickness of 0.
It was set to 29 mm. Next, primary recrystallization annealing was performed in a reducing atmosphere and nitriding treatment was performed to adjust the nitrogen content to 1150 ppm. Next, Al ₂ O ₃ having an average particle diameter of 4.0 μm was applied in a water slurry state. For comparison, an annealing separator containing MgO as a main component was applied in a water slurry state.

These two kinds of materials were heated to 1200 ° C.
The temperature was raised in a 5% N ₂ -5% H ₂ atmosphere while maintaining the temperature rising rate of 15 ° C./Hr, and after reaching 1200 ° C., 100% hydrogen was obtained and the temperature was maintained for 20 hours. After finishing annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The characteristics of the obtained product are as shown in Table 6. The magnetic properties were also investigated for the material that was only subjected to strain relief annealing after finish annealing.

[0047]

[Table 6]

[0048]

According to the present invention, 0.004% in the molten steel state
A technique has been provided in which a grain-oriented electrical steel sheet having an extremely high magnetic flux density can be easily obtained at low cost using the following silicon steel containing C as a material. The industrial value of the present invention is enormous.

Claims (2)

[Claims] 1. A silicon hot-rolled steel strip is annealed as required, and then cold-rolled once or twice or more with an intermediate anneal to obtain a predetermined plate thickness, and after primary recrystallization annealing, In the method for producing a grain-oriented silicon steel sheet in which an annealing separator is applied after performing nitriding annealing as necessary, and a finish annealing is performed, the composition of the hot-rolled silicon steel strip is C: 0.0005 to 0.004% by weight, Si: 2.0-4.5% by weight, acid-soluble Al: 0.010-0.080% by weight, N: 0.001-0.020% by weight, Cu: 0.050-2.00% by weight, Bi: 0.0005 to 0.050% by weight S: 0.0010 to 0.060% by weight, balance Fe and inevitable impurities. 2. The high magnetic flux according to claim 1, wherein after the nitriding annealing, an annealing separator containing one or more of alumina, silica, zirconia, strontium oxide and forsterite as a main component is applied. A method for manufacturing a density-oriented silicon steel sheet.