JPH06346147A - Production of grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To stably produce a grain-oriented silicon steel sheet extremely high in magnetic flux density by subjecting a dead soft silicon steel slab having a specified compsn. to hot rolling and annealing, thereafter subjecting it to cold rolling into a cold rolled steel sheet, furthermore annealing it, thereafter executing nitriding treatment and successively subjecting it to finish annealing. CONSTITUTION:As for a silicon steel slab having a compsn. contg., by weight, 0.0005 to 0.004% C, 2.0 to 4.5% Si, 0.010 to 0.080% acid soluble Al, 0.001 to 0.020% N, 0.050 to 2.00% Cu and 0.010 to 0.060% S, and the balance Fe, rough rolling is started at 1000 to 1200 deg.C. After that, it is subjected to finish rolling into a hot rolled steel sheet. Next, it is annealed in the temp. range of 700 to 1100 deg.C in a short time of about 2min according to necessary. Subsequently, the surface is subjected to pickling treatment, and it us subjected to cold rolling for one time or >= two times including process annealing into a cold rolled sheet having a prescribed thickness. After that, heating is executed at 850 to 1050 deg.C for 1 to 200sec, and the surface of the cold rolled steel sheet is subjected to nitriding treatment while it is run in a mixed atmosphere of N2-H2-NH3. Finally, it is coated with an MgO series separation agent for annealing and is subjected to finish annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented silicon steel sheet (hereinafter referred to as grain-oriented electrical steel sheet).

[0002]

2. Description of the Related Art In the production of grain-oriented electrical steel sheet, a hot-rolled steel strip is annealed as required, and then cold-rolled once or twice or more with intermediate annealing to obtain a predetermined sheet thickness, and then, It is carried out by applying the annealing separation agent after performing the primary recrystallization annealing and performing the finish annealing. In this primary recrystallization annealing, decarburization is also generally performed. However, in recent years, many technologies have been reported in which decarburization in a molten steel state is used and decarburization in the primary recrystallization annealing step is omitted.

For example, JP-A-54-112317, JP-A-55-073818, JP-A-57-114614, JP-A-57-207114, JP-A-58-100627, JP-A-61-91319 and JP-A-62. -83421, JP-A-1-119644, JP-A-1-212721, JP-A-1-309923, JP-A-1-309924, JP-A-2
-30714, JP-A-2-141532, JP-A3-1
11516, JP-A-3-287721, and JP-A-5-96
There are many publications such as Japanese Patent No. 66. However, in order to stably manufacture the grain-oriented electrical steel sheet with these techniques, it is necessary to strictly control the production conditions.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a method for stably producing a grain-oriented electrical steel sheet.

[0005]

The means of the present invention comprises C:
0.0005-0.004% by weight, Si: 2.0-4.
5% by weight, acid-soluble Al: 0.010 to 0.080% by weight, N: 0.001 to 0.020% by weight, Cu: 0.0
Rough rolling and finish rolling of a silicon steel slab containing 50 to 2.00% by weight and S: 0.010 to 0.060% by weight (hereinafter simply referred to as "%") in a temperature range of 1000 to 1200 ° C. After making the hot rolled steel strip, 70
After annealing for a short time in the temperature range of 0 ° C to 1100 ° C, 1
Or two or more cold rollings with intermediate annealing
Specified plate thickness, 1 in the temperature range from 850 ℃ to 1050 ℃
After heating for 200 seconds or more and 200 seconds or less, nitriding treatment is performed in a state where the steel sheet is allowed to run, an annealing separator is applied, and finish annealing is performed.

In this case, the P H ₂ O / P H ₂ in the atmosphere at least after the heating of the primary recrystallization annealing is 0.06 or more and 4.0 or more.
Desired nitriding is efficiently performed by performing the nitriding treatment after the following. Even if nitriding is performed in this way, the nitride formed may not work effectively as an inhibitor when the partial pressure of nitrogen in the atmosphere of finish annealing is 50% or less. As described above, the nitrogen partial pressure is preferably 50% or more.

The present invention will be described in detail below. As a method for producing a grain-oriented electrical steel sheet without decarburizing in the primary recrystallization annealing step, the inventors of the present invention have disclosed JP-A-57-114.
Although the technique disclosed in Japanese Patent No. 614 was developed, this method had a drawback that the magnetic flux density was relatively low (Example B).
₈ = 1.88). Further, as a technique for producing a steel sheet having a high magnetic flux density, Japanese Patent Application Laid-Open No. 57-89439 (Example B ₈
= 1.97) and has been developed Sho 57-207114 Patent Publication (Example B ₈ = 1.94) also may stably such a high magnetic flux density can not be obtained by the present. As a result of diligent research on the cause, (1) the primary recrystallized plate has few (110) [001] -oriented crystal grains that become nuclei for secondary recrystallization, and (2) the growth of crystal orientations other than the secondary recrystallized grains. Insufficient inhibitor to prevent the above-mentioned phenomenon, and further, (3) (110) [001] secondary recrystallized grains preferentially grow, and compared with the primary recrystallized plate produced by the conventional manufacturing process, Turned out to be few.

To overcome these drawbacks, C: 0.0
005 to 0.004%, Si: 2.0 to 4.5%, acid-soluble Al: 0.010 to 0.080%, N: 0.001
~ 0.020%, Cu: 0.050-2.00%, S:
Rough rolling of a silicon steel slab containing 0.010 to 0.060% of components is started in a temperature range of 1000 ° C to 1200 ° C, and finish rolling is performed to form a hot rolled steel strip, and then 700 if necessary. After performing short-time annealing in the temperature range of ℃ to 1100 ℃, cold rolling is performed once or twice or more with intermediate anneal to obtain a predetermined plate thickness, and in the temperature range of 850 ℃ to 1050 ℃ for 1 second. After heating within 200 seconds, nitriding is performed in a state where the steel sheet is allowed to run after heating, an annealing separator is applied, and finish annealing is performed.

In this case, desired nitriding can be efficiently performed by performing nitriding treatment after setting P H ₂ O / P H ₂ in the atmosphere after heating of the primary recrystallization annealing to 0.06 or more and 4.0 or less. Done. If the nitrogen partial pressure in the atmosphere of finish annealing is 50% or less, the formed nitride may not work effectively as an inhibitor.
The inventors have found that it is preferable to set the nitrogen partial pressure to 50% or more at a temperature of not less than 0 ° C, and have completed the present invention.

There is a prior art disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-77525 regarding a method for manufacturing a grain-oriented electrical steel sheet having substantially the same structure as the present invention. The prior art is characterized in that after decarburization annealing, the steel sheet is subjected to a nitriding treatment in a running state, an annealing separator is applied, and then high-temperature finish annealing is performed. The crude hot rolling start temperature in the present invention is 1200 ° C. or lower, and this condition is also the same as this prior art. The most different structural difference between the present invention and this prior art is firstly the steel composition and secondly the primary recrystallization annealing conditions.

Although Cu is not added in the prior invention, Cu is added in the range of 0.05% to 2% in the present invention, and Cu is positively utilized. It is point 1. Further, in this prior invention, when S is contained in an amount of 0.012% or more, secondary recrystallization failure occurs, so S is preferably made 0.007% or less. However, in the present invention, S is required to be 0.010% or more, and up to about 0.04%, the higher the S, the more stable the secondary recrystallization. The present invention and this prior art are completely different in the effect of S. The range of S and the difference in its action and effect are the second points that are different in the components.

According to the prior invention, when the content of C is 0.025% or less, the secondary recrystallization becomes unstable, and the magnetic flux density of the product decreases to 1.8 Tesla even when the secondary recrystallization is performed.
In the present invention, C is 0.
Although it is 004% or less, the secondary recrystallization is stable, and the magnetic flux density shows a high value of 1.8 Tesla or more. The third difference is that the amount of C before primary recrystallization is different from that of the prior invention in terms of components.

As will be described in detail later, the composition of the present invention and the prior invention is that both the sulfide and the nitride and the solid solution Cu are utilized in the state of C of 0.004% or less as the inhibitor of the present invention. That's why it's different. In the present invention, C is 0.004% or less and S is 0.
A steel sheet containing Cu in an amount of 010% or more and 0.05% to 2.00% is subjected to primary recrystallization annealing without decarburization at a temperature of 850 ° C. or more and then subjected to nitriding treatment.

In the prior invention, before the primary recrystallization annealing, C: 0.
A steel sheet containing 025% to 0.075% or less and S in the range of 0.012% is recrystallized, and subsequently at a temperature of 800 ° C to 850 ° C in an atmosphere containing water vapor, 1
Decarburization is performed by heating for 20 seconds or more, and then nitriding treatment is performed. That is, the purpose of the steel composition and the primary recrystallization annealing is different between the present invention and the prior invention.

Since decarburization is unnecessary in the steel of the present invention, recrystallization annealing may be completed in a non-decarburizing atmosphere. In this case, until the recrystallized grain growth is completed, after a possible reducing atmosphere, it continues to nitriding treatment continuously, but the P H ₂ O / P H ₂ atmosphere before the nitriding treatment 0.
By setting the ratio to be not less than 06 and not more than 4.0, secondary recrystallization is stable and good magnetic characteristics can be obtained.

By combining the above components and the respective conditions of the primary recrystallization annealing, the secondary recrystallization, which was impossible in the prior invention in the present invention, is stabilized, and the magnetic flux density is 1.8.
At present, the metallurgical principle of whether or not Tesla can be secured is not clear at this point. At the present time, the reason why the combination effect is generated from the experimental fact is interpreted as follows.

First, the components will be described. Cu is 0.05
When it is contained in an amount of 0 to 2.00%, (1) (110) [00
1) The number of crystal grains that may become azimuth secondary recrystallized nuclei increases (see FIG. 1), and further there is an action effect of inhibiting the growth of crystal grains other than the secondary recrystallized grains of (2). Do you get it. In this case, it was discovered that the effect of (1) becomes remarkable especially when the Cu content is 0.5% or more. Further, it was found that the effect of (2) becomes remarkable when Cu is 0.05% or more, and the effect becomes larger as Cu increases.

When the morphology of precipitates was examined by an electron microscope, when Cu was 0.05% or more, the amount and size of Cu sulfide did not change even if the amount of Cu was increased.
The fact that the addition of u facilitates the growth of secondary recrystallized grains has an inhibitor effect as a precipitate (sulfide) and an effect that solid solution Cu itself prevents the growth of crystal grains other than the secondary recrystallized grains. It is thought to be because. In order to confirm this point, when the amount of Cu added was increased in a sample containing no S,
The more u, the more stable the results of secondary recrystallization are obtained.
It was speculated that solid solution Cu has such an effect (see Example 3).

Next, S is limited to the range of: 0.010 to 0.060% because the effects of (2) and (3) are exhibited. That is, in the material component of the present invention, S is 0.01%
It was found that when the amount is less than the above, secondary recrystallized grains are hard to develop, and when secondary recrystallized, secondary recrystallized grains deviated from (110) [001] increase. That is, S is interpreted as giving the effects of (2) and (3) in this component system.

Although the mechanism is not clear, S is 0.
When it is present in an amount of 01% or more, many fine Cu-based sulfides are observed, and it is interpreted that these fine Cu-based sulfides exert the effects of (2) and (3). Although S is effective even if it is 0.06%, cracks are likely to occur in the hot rolling process when S is large, so in the present invention, the upper limit is made 0.060%. This effect of S is exhibited only when it coexists with Cu, and it is presumed that the presence of S rather makes secondary recrystallization unstable if Cu is not added as in the prior invention. .

Next, the metallurgical reasons for selecting the primary recrystallization annealing conditions different from those of the prior invention will be described. As mentioned earlier,
In the prior art, it is necessary to heat at 820 ° C. to 860 ° C. for 120 seconds or more in a decarburizing atmosphere in the primary recrystallization annealing step. In this case, when the heating temperature is 900 ° C. or higher, a 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. In this decarburization annealing step, an internal oxide layer is formed on the surface of the steel sheet, and this internal oxide layer changes its form in the finish annealing step, but remains in the final product, deteriorating the magnetic properties, especially iron loss.

However, since the main purpose of the steel sheet of the present invention is to recrystallize in the primary recrystallization annealing, the recrystallization temperature is set in an atmosphere which suppresses the formation of internal oxidation which causes a bad influence on the iron loss of such a product. Since the above heating is sufficient, it becomes easy to obtain good magnetic characteristics. Therefore, there is no upper limit of the heating temperature and the heating time may be short. Since the heating temperature need only be recrystallized, it may be 700 ° C. or higher. However, the heating temperature of 900 ° C. or higher is preferable because when primary recrystallization is performed at a temperature below this temperature, the primary recrystallization may be different depending on the component system. Because the crystal grain size is small, the magnetic flux density of the product may decrease as a result.

The upper limit of the heating temperature is set to 1050 ° C. or lower when good magnetic properties can be obtained even at heating temperatures higher than this temperature, but sometimes stable magnetic properties cannot be obtained due to deterioration of magnetic properties. This is because it is uneconomical to heat at such a high temperature. The heating time is set to 1 second or longer because good magnetism and characteristics can be obtained if the heating time is longer than this, and the upper limit is set to 200 seconds or shorter.
Good magnetic properties can be obtained with heating time longer than this,
If the heating time is too long, the surface properties will be unfavorable to the subsequent nitriding treatment, and as a result, the magnetic properties of the product may deteriorate and stable and good properties may not be obtained, and it is uneconomical to heat for a long time. This is because.

In this case, P H ₂ O / P in the atmosphere before heating
H ₂ was 0.06 or less, it is preferable that the P H ₂ O / P H ₂ atmosphere before the nitriding treatment start 0.06 to 4.0 thereafter. By treating in such an atmosphere, the magnetic properties of the product are improved and it is easy to continue nitriding in the nitriding step, so it is particularly effective when an element that is difficult to be nitrided is added. Due to the combination of the above component effects and the effect of primary recrystallization annealing, secondary recrystallization is stable with a material of C <0.005% or less, which is impossible in the prior invention, as the starting material, and the magnetic flux density is in the direction of 1.8 Tesla or more. We believe that it has become possible to manufacture high-quality silicon steel sheets.

Other components in the method of the present invention, hot rolling conditions, and treatment conditions after hot rolling will be described below. The higher the Si content, the more the specific resistance increases and the eddy current loss of the product decreases. Therefore, the more Si the better, in order to reduce the eddy current loss. 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. In the steel of the present invention, since C is already 0.004% or less in the cold rolling process, it is less likely to crack as compared with the conventional material, but Si4.5%
In the above description, the upper limit was set to 4.5% because the cold rolling requires special measures and the purpose of the present invention is to economically manufacture.

Al forms (Al, Si) N and acts as an inhibitor, but the effect is not exhibited unless the content of 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 it exceeds this amount, it will not work effectively as an inhibitor. 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 slab stage, so the lower limit was made 0.001%. The upper limit is set to 0.02% because if it is contained more than this, surface scratches called blister occur.

When the hot rolling start temperature is 1200 ° C. or higher, the secondary recrystallization becomes unstable with the components of the present invention, the secondary recrystallization becomes stable, and the probability that the magnetic flux density of the product will be 1.80 Tesla or less increases. However, it cannot be adopted 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 if the starting temperature for rough hot rolling is 1000 ° C or lower, but it requires a large amount of energy for hot rolling and is not economical because the surface of the steel sheet is easily scratched during hot rolling. The starting temperature was 1000 ° C or higher.

The atmosphere of finish annealing may be the same as that of the conventional finish annealing of 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 characteristics can be obtained. It is preferable to heat. 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 may be 100%, but 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.

By the way, the nitrogen content of the steel of the present invention is 0.001% or more and 0.
The range is preferably 020% or less, but is preferably 0.006% or more and 0.06% in the state before finish annealing.
This is because even before nitrogen is 0.006% or below 0.06% in the state before finish annealing, secondary recrystallization tends to be difficult to occur, or even when secondary recrystallization occurs, the magnetic flux density is remarkably high. This is because it gets worse.

When the nitrogen content is low, the secondary recrystallization is difficult to occur because the inhibitor as a nitride is insufficient and the crystal grains having various orientations grow. Even if appears, the magnetic flux density is low,
Due to lack of inhibitor as nitride, secondary recrystallization occurs at low temperature, and the secondary recrystallization orientation in that case is (11
0) The probability of secondary recrystallized grains other than the [001] orientation increases.

When the nitrogen content is high, the secondary recrystallization is difficult to develop. The reason is that the inhibitor as a nitride is so strong that the secondary recrystallization cannot be expressed up to a high temperature and the inhibitor becomes weak at a high temperature. This is because the crystal grains that it has undergone secondary recrystallization growth or so-called fine grains are generated and secondary recrystallization does not occur.

Embodiments of the present invention will be described below. C: 0.
0005 to 0.015%, Si: 2.0 to 4.5%, acid-soluble Al: 0.010 to 0.080%, N: 0.00
1 to 0.020%, Cu: 0.050 to 2.00%,
S: 0.010 to 0.060%, the balance of Fe and unavoidable impurities is used as a molten steel in a normal process or continuously cast into a slab, and then hot rolled from a temperature range of 1200 ° C to 1000 ° C. Hot-rolled steel sheet or hot-rolled steel strip.
This hot rolled steel sheet or hot rolled steel strip is 750 to 1200.
Annealing is performed in the temperature range of ° C. Further, these hot rolled steel sheets or hot rolled steel strips are cold rolled without such hot rolled sheet annealing.

The material after cold rolling is 700 to 105.
Primary recrystallization annealing is performed in the temperature range of 0 ° C. In the latter stage of this annealing, nitriding treatment is performed in an ammonia-containing atmosphere to strengthen the inhibitor. The recrystallized plate is then coated with an annealing separator and enters a finish annealing furnace. The temperature rising rate of finish annealing is
It is similar to that of a normal unidirectional 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.

[0035]

【Example】

Example 1 C: 0.0010%, Si: 2.90%, Mn: 0.0
Four types of slabs A containing 75%, Al: 0.027%, N: 0.008% as main components and different Cu and S contents.
To D (see Table 1) were heated at a temperature of 1100 ° C. for 2 hours, then rough-rolled and finish-rolled to obtain hot-rolled sheets having a thickness of 2.3 mm. Then, it was heated at 900 ° C. for 2 minutes and cooled with water. After pickling, cold rolling was performed to a thickness of 0.35 mm.

Next, after heating at a temperature of 850 ° C. for 180 seconds,
It was continuously nitrided in an atmosphere of N ₂ -H ₂ -NH ₃ in the cooling process. Next, MgO is applied and heated to 1200 ° C. at a temperature rising rate of 15 ° C./hr in an atmosphere of 25% N ₂ —H ₂ and then 10
The mixture was heated in a 0% 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.

[0037]

[Table 1]

As is clear from Table 1, the material produced by the method of the present invention had a high magnetic flux density and a low iron loss, whereas the comparative material had a low magnetic flux density and a high iron loss.

Example 2 C: 0.001%, Si: 2.95%, Mn: 0.07
8%, S: 0.026%, Cu: 0.98%, N: 0.
Three types of slabs A to C (see Table 2) having 007% as a main component and different Al contents were rough rolled at 1070 ° C. to obtain a hot-rolled sheet having a thickness of 2.5 m. Then, it was heated at 900 ° C. for 2 minutes and cooled with water. After pickling, cold rolling is performed to a thickness of 0.
It was set to 29 mm. Next, after heating for 180 seconds at a temperature of 950 ° C., nitriding treatment was continuously performed in an N ₂ —H ₂ —NH ₃ atmosphere in the cooling process.

Next, MgO is applied, and 95% N ₂ --H ₂ ,
After heating to 1200 ° C. at a temperature rising rate of 15 ° C./hr in an atmosphere of 50% N ₂ —H ₂ and 25% N ₂ —H ₂ , 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. A material containing no Cu or S was also processed for comparison, but in this case, 10
0% secondary recrystallization did not occur and the magnetic properties were remarkably poor (B ₈ : 1.42 Tesla, W _17/50 : 3.43 w / kg). It can be seen that the material produced by the method of the invention has remarkably good magnetic properties.

[0041]

[Table 2]

As is clear from Table 2, the materials produced by the method of the present invention have remarkably good magnetic properties.

Example 3 C: 0.003%, Si: 2.87%, Mn: 0.07
6%, Al: 0.026%, Cu: 1.00%, N:
Two types of slabs A and B (see Table 3) having 0.007% as a main component and different S contents were heated at a temperature of 1100 ° C. for 1 hour and immediately followed by rough hot rolling to obtain hot rolled sheets. 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, 180 at 850 ° C. and 900 ° C.
After second heating, nitriding was continuously performed in an N ₂ —H ₂ —NH ₃ atmosphere in the cooling process. Next, MgO is applied and 25% N ₂ −
After heating in an atmosphere of H ₂ to 1200 ° C. at a heating rate 15 ° C. / hr, and cooled after heated for 20 hours at 100% H ₂ atmosphere.
Then, strain relief annealing was performed to measure the magnetic properties. The results are shown in Table 3. The comparative material containing only 0.001% S also exhibited 100% secondary recrystallization, but the magnetic properties were remarkably poor.

[0045]

[Table 3]

As is apparent from Table 3, the materials produced by the method of the present invention have remarkably good magnetic properties.

Example 4 C: 0.0028%, Si: 2.87%, Mn: 0.0
76%, S: 0.020%, Cu: 1.00%, Al:
A slab containing 0.026%, N: 0.0069%, and other unavoidable impurities was heated at a temperature of 1150 ° C. for 1 hour and then hot rolling was immediately started to obtain a hot rolled sheet. Then, it was heated at 900 ° C. for 2 minutes and cooled with water. After pickling, cold rolling is performed to a thickness of 0.
It was set to 45 mm and 0.35 mm.

Next, after heating for 180 seconds at a temperature of 850 ° C., nitriding treatment was performed. Next, MgO is applied and 95% N ₂ -H ₂
After heating to 1200 ° C. at a temperature rising rate of 15 ° C./hr in the above atmosphere, heating was performed 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 4.
Shown in. For comparison, a material having Cu and S of 0.001% or less was treated in the same process, but the magnetic flux density was remarkably low and the iron loss was large as compared with the steel of the present invention.

[0049]

[Table 4]

As is clear from Table 4, the materials produced by the method of the present invention have remarkably good magnetic properties.

Example 5 C: 0.001%, Si: 2.88%, Mn: 0.08
6%, Al: 0.026%, Cu: 0.082%, N:
Two types of slabs A and B (see Table 5) having 0.008% as a main component and different S contents were made 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, 900 ℃, 9
After heating for 180 seconds at a temperature of 50 ° C, N ₂ -H _2-
Nitriding was continuously performed in an NH ₃ atmosphere.

Next, MgO was applied, and 95% N ₂ --H ₂ ,
After heating to 1200 ° C. at a temperature rising rate of 15 ° C./hr in a 50% N ₂ —H ₂ atmosphere and a 25% N ₂ —H ₂ atmosphere, heating was performed 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 5. S is 0.00
The comparative material containing only 1% had poor magnetic properties even when the secondary recrystallization was unstable or when the secondary recrystallization was 100%.

[0053]

[Table 5]

As is clear from Table 5, the materials produced by the method of the present invention have remarkably good magnetic properties.

[0055]

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 by using the following silicon steel containing C as a raw material. The industrial value of the present invention is enormous.

[Brief description of drawings]

1] Cu addition amount and (110) <uv of primary recrystallized plate
It is a chart showing the relationship of w> strength.

Claims (1)

[Claims] 1. 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% 0.020% by weight, Cu: 0.050 to 2.00% by weight, S: 0.010 to 0.060% by weight 1 of a silicon steel slab containing the balance Fe and unavoidable impurities.
After starting rough rolling in the temperature range of 000 ° C to 1200 ° C, and subsequently performing finish rolling to form a hot rolled steel strip, after performing short-time annealing in the temperature range of 700 ° C to 1100 ° C as necessary, Cold rolling is performed once or twice or more with intervening intermediate annealing to obtain a predetermined thickness, and nitriding is performed in a state where the steel sheet is allowed to run after heating in the temperature range of 850 ° C to 1050 ° C for 1 second to 200 seconds. A method for manufacturing a grain-oriented silicon steel sheet, which comprises applying an annealing separator and performing finish annealing.