JP3179549B2 - Manufacturing method of grain-oriented silicon steel sheet - Google Patents

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, and more particularly, to effectively recover AlN in a surface layer of a steel sheet lost during uniform annealing or intermediate annealing during annealing before final cold rolling. By doing so, it is intended to prevent the magnetic flux density from deteriorating due to the reduction in thickness of the product, and to maintain a high magnetic flux density.

[0002]

2. Description of the Related Art Grain-oriented silicon steel sheets are mainly used as core materials for transformers, and their magnetic properties are required to be high in magnetic flux density and low in iron loss. In recent years, due to advances in manufacturing technology, for example, in a steel sheet having a thickness of 0.23 mm, the magnetic flux density B ₈ (value at a magnetizing force of 800 A / m): 1.9
2T and iron loss characteristics W _17/50 (50 Hz, 1.7
It has become possible to produce excellent products on an industrial scale, such as the maximum magnetization value of T of 0.90 W / kg.

A material having the above excellent magnetic properties has a crystal structure in which the <001> orientation, which is the axis of easy magnetization of iron, is highly aligned in the rolling direction of the steel sheet. Such a texture is formed through a so-called secondary recrystallization phenomenon that preferentially grows crystal grains having the (110) [001] orientation during final finishing annealing during the production process of a grain-oriented silicon steel sheet. Is done. The basic requirement for sufficiently growing the secondary recrystallized grains having the (110) [001] orientation is that, in the secondary recrystallization process, crystal grains having an undesired orientation other than the (110) [001] orientation It is well known that the presence of an inhibitor for suppressing the growth of GaN and the formation of a primary recrystallized structure suitable for the secondary recrystallized grains of (110) [001] orientation to be sufficiently developed are essential. It is a fact. Here, as the inhibitor, fine precipitates such as MnS, MnSe and AIN are generally used, and in addition to these, a grain boundary segregation type element such as Sb and Sn is added in combination to reinforce the effect of the inhibitor. (For example, JP-B-51-13469, JP-B-54-32412).

Conventionally, those using MnS or MnSe as a main inhibitor have a small secondary recrystallized grain size, which is advantageous for reducing iron loss. However, in recent years, artificial grain boundaries have been artificially introduced by laser irradiation, plasma jet method, etc.
Since magnetic domain refinement can be achieved, the advantage due to the small size of the secondary recrystallized grain size has decreased, and it has become more important to increase the magnetic flux density instead.

A method of obtaining a grain-oriented silicon steel sheet having a high magnetic flux density has been known for a long time. For example, as described in JP-B-46-23820, (1) AlN is contained in steel as an inhibitor component. (2) rapid cooling of the annealing before final cold rolling to precipitate AlN; (3) reduction of final cold rolling to 80-95% and high pressure reduction; It is said that it can be manufactured by bonding. However, the above method has a drawback that when the thickness of the product is reduced, the magnetic flux density is rapidly deteriorated. For example, a product having a thickness of 0.25 mm or less, such as B ₈ : 1.94 T or more, which is recently oriented. It has been extremely difficult to stably produce excellent products.

[0006] In this regard, the present inventors have previously added Sb to a directional silicon steel material having AlN as a main inhibitor and improved the finish annealing method so that when the final thickness of the steel sheet is small, Have also found that an extremely high magnetic flux density can be obtained, and this is disclosed in JP-A-2-115319. However, even with the above method, it has not always been easy to industrially stably produce a material having a high magnetic flux density.

[0007]

As described above, when Sb is contained, a problem that secondary recrystallization does not occur in the production on an industrial scale occurs, and a material having a high magnetic flux density can be stably used. It was extremely difficult to get. That is, even if a material that can obtain an extremely high magnetic flux density when processed in a laboratory using a steel sheet after hot rolling, the magnetic flux density is low when a coil having the same composition is industrially processed, 2
The phenomenon that secondary recrystallization did not occur was often observed.

[0008] The inventors of the present invention have collected samples in each step and investigated the cause. As a result, it was found that no AlN, which is an inhibitor, was deposited on the surface layer of the steel sheet after the uniform annealing or the intermediate annealing. Identified the cause. That is, the loss of AlN lowers the inhibitory force of the steel sheet surface layer, and normal grain growth occurs during final finish annealing. As a result, failure of secondary recrystallization is a cause of failure in industrial production. Was determined.

The phenomenon that AlN in the surface layer of a steel sheet is lost by homogenizing annealing or intermediate annealing also occurs in steels containing no Sb. However, in these steels, such a phenomenon causes a particularly serious problem. Absent. According to the investigation by the inventors, it was found that during the final finish annealing, the re-nitriding of the steel sheet surface layer occurred before the secondary recrystallization, and AlN precipitates were formed again on the surface layer portion. did. In other words, in the final finish annealing performed in box annealing, excessive Al in the steel diffuses to the surface layer part because it is exposed to the nitrogen atmosphere for a long time before the secondary recrystallization (lower than 900 ° C), AlN is re-precipitated by combining with the nitrogen diffused from the steel, so that the restraining force of the steel sheet surface layer, which was lost for a while, is fortunately recovered just before the secondary recrystallization, so that this problem does not usually appear. It was. However, in the case of steel containing Sb, the recovery mechanism of the surface layer suppressing force does not work. This is because Sb segregates on the steel sheet surface and suppresses nitriding.
It is considered that it is extremely difficult to recover and precipitate AlN once disappeared again.

As a technique for strengthening the suppressing force of the steel sheet surface layer, nitrogen is used as an atmosphere during annealing of a grain-oriented silicon steel sheet containing Al, and the surface of the steel sheet is nitrided to precipitate AlN. Is a technology that enhances
It is disclosed in Japanese Patent Publication No. 50-19489. When the inventor actually tried this point, since the nitriding of the steel sheet containing Sb was suppressed by the above-mentioned phenomenon, the effect was thin and the magnetic properties of the product were not improved.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on a technique for avoiding a loss of the restraining force of the surface layer of a steel sheet in a grain-oriented silicon steel sheet containing AlN as an inhibitor and also containing Sb. As a result, in annealing before final cold rolling, a nitriding accelerator was applied to the steel sheet surface before annealing, and the partial pressure ratio of N ₂ in the annealing atmosphere was reduced to 20%.
In addition to the above, it has been found that by improving the cooling conditions in annealing before final cold rolling, a oriented silicon steel sheet having a high magnetic flux density can be stably obtained even when the sheet thickness is reduced. Introducing strain during the above-mentioned annealing during cooling effectively contributes to the improvement of magnetic flux density, and furthermore, the total partial pressure ratio of O ₂ + H ₂ O + CO _{2 in} the annealing atmosphere is set to 2% or more. It was also found that nitriding of the steel sheet surface layer was further promoted, and the suppressing power of the steel sheet surface layer could be further enhanced.

The present invention is based on the above findings. That is, the present invention provides a directional silicon steel material containing AlN as an inhibitor and also containing Sb,
After hot rolling, the reduction rate is 80
Up to 95% single cold rolling or final cold rolling reduction of 80 ~
Oriented silicon steel sheet is subjected to a series of steps of cold rolling twice with 95% intermediate annealing, followed by decarburization, primary recrystallization annealing, application of an annealing separator, and final finish annealing. Prior to annealing before final cold rolling, a nitriding accelerator is attached to the surface of the steel sheet, and the annealing is performed under the condition that the partial pressure ratio of N _{2 in} the atmosphere is 20% or more. After soaking, at a cooling rate of 15-500 ℃ / s 4
Rapidly cool to a temperature of 50-200 ° C, then a. Holding at the quenching attainment temperature for 10 to 90 seconds and then quenching, or b. A method for producing a grain-oriented silicon steel sheet, comprising performing any one of carbide precipitation control treatments in which a gradual cooling treatment of cooling at a cooling rate of 2 ° C./s or less from a quenching ultimate temperature is performed for 10 to 90 seconds (first invention) It is.

[0013] The present invention provides the first aspect, wherein
After quenching to a temperature of 450-200 ° C at a cooling rate of 500 ° C / s,
During or after the application of micro-strain of 0.005 to 3.0% from the quenching temperature to 200 ° C., a. 10 to 18
Cooling via hold for 0 seconds, or b. Manufacture of grain-oriented silicon steel sheet by performing any one of the carbide precipitation control treatments in which the temperature range from the quenching ultimate temperature to 200 ° C is gradually cooled at a cooling rate of 2 ° C / s or less for 10 to 180 seconds. It is a method (2nd invention).

Further, the present invention provides the first or second aspect of the present invention, wherein O ₂ in an annealing atmosphere before final cold rolling is further added.
This is a method for producing a grain-oriented silicon steel sheet (third invention), comprising setting the total partial pressure ratio of + H ₂ O + CO ₂ to 2% or more.

Hereinafter, the present invention will be specifically described based on the experimental results which led to the present invention. As described above, the AlN in the surface layer of the steel sheet disappears by the uniform annealing or the intermediate annealing, and the suppressing force of the surface layer is lost. The cause of this is that the oxidation of Al and N in the steel on the surface progresses due to the oxide or oxidizing atmosphere on the surface of the steel sheet, so that a deficient layer of Al or N is formed near the surface, and as a result, This is because decomposition and disappearance proceed. Therefore, in order to suppress such a phenomenon, it is considered effective to nitride Al excessively present in steel.

Therefore, the present inventors first investigated the effect of N in the atmosphere. C: 0.07wt% (hereinafter simply indicated as%), Si: 3.3%, Mn:
0.08%, P: 0.005%, Se: 0.020%, Sb: 0.030%,
Al: 0.025% and N: 0.0080%, with the balance being substantially
After the silicon steel material having the composition of Fe is hot-rolled to a thickness of 2.0 mm by an ordinary method, after uniform annealing at 1000 ° C., cold-rolled to a thickness of 1.5 mm, and then 1100 ° C. in N ₂ , For 2 minutes. Analysis of N content in steel at this time showed 75 ppm
In this case, the amount of N was lower than that in the material stage. Then, the inventor next investigated the case where the gas flow rate of N ₂ flowing into the furnace was increased. That is, 1 to 1 g of sample
When l / min N ₂ gas was introduced, N in the steel after annealing was 79
It was found to increase to ppm. However, the above method requires a large amount of gas, which is extremely disadvantageous for industrial application.

[0017] Then, when exploring other methods,
In the process, it was found that a very small amount of CO gas contained in the exhaust gas hindered the nitriding of steel. Here, the mechanism by which a trace amount of CO gas inhibits nitriding of the steel is not clear, but it is considered that the generation of CO is caused by oxidation of C contained in the steel in the same manner as oxidation of Al and N. Therefore, in order to eliminate such adverse effects of CO, the gas flow rate was increased to promote the dissipation of CO. In addition, for unknown reasons, it has been newly found that it is effective to positively add a gas component such as H ₂ O, CO _{2, and} O ₂ that enhances the oxygen potential. The reason for this is that CO and H ₂ O, CO _2, O ₂
It is considered that the balance with the gas components has a subtle effect on the nitriding of steel.

FIG. 1 shows these H ₂ O, CO _2, O ₂ in N ₂ .
The results obtained by examining the amount of nitrogen in the steel after annealing in the case where the same experiment as described above was performed while variously changing the total partial pressure ratio of the steel. From the figure, it can be seen that when the total partial pressure ratio of H ₂ O, CO _{2, and} O ₂ is 2% or more, the same effect as when the N ₂ gas flow rate is increased can be obtained.

Therefore, in an annealing furnace in a factory, CO ₂ 1.5%,
Atmosphere gas with a dew point of 25 ° C and a balance of N ₂ balance (4.6% partial pressure ratio of CO ₂ + H ₂ O) was introduced, and the experiment was performed with actual coils. As a result, for part of the coil, B ₈ = 1.94
Although very good magnetic properties of 1 T were obtained, most were at low levels of about 1.76 to 1.86 T, which was not satisfactory.

Therefore, in order to overcome such difficulties, the idea of accelerating nitridation by applying a chemical agent to the surface layer of the steel sheet was examined by completely changing the idea from the conventional one. This has not been attempted so far, and as a result of the inventor's trial of a large number of reagents, a group of chemicals that promote nitriding of a steel sheet as described later has been found.

[0021] Now divided into three cold-rolled steel sheet having a thickness of 1.5mm as described above, one directly, the KNO ₃ aqueous solution to the other one of the 10% remaining one immersion in a 30% KNO ₃ solution After that, each was annealed at 1100 ° C. for 2 minutes in an atmosphere of 50% N ₂ , a dew point of 35 ° C., and the balance of H ₂ remaining. Analysis of the amount of N in the steel at this time revealed that the amount of N after annealing was 72 ppm for the former, which did nothing, while the latter was immersed in an aqueous KNO ₃ solution.
89 ppm and 96 ppm.

Further, the sectional structure of each steel sheet was determined by the corrosion method using SE.
As observed in M, as shown in FIG. 2, no precipitation of AlN was observed in the surface layer of the steel sheet as it was annealed (FIG. 2 (a)). On the other hand, when KNO ₃ as a nitriding accelerator was applied (FIGS. (B) and (c)), clear fine precipitation of AlN was observed immediately below the subscale on the surface layer of the steel sheet.

Here, regarding the effect of the application of the nitriding accelerator,
The mechanism investigated and elucidated by the inventors will be described. In general, it is known that when Sb is present in steel, the form of an oxide film called a subscale formed on the surface changes significantly. That is, it is known that the oxide film becomes flat and dense due to the presence of Sb.
In general, decarburization, denitrification, carburization, and nitrification are inhibited in order to suppress the diffusion of carbon. FIG. 2A shows the case where the nitriding accelerator is not applied, and it can be seen that fine and fine subscales have been developed. In contrast, FIG.
(b) and (c) show the case where the nitriding accelerator was applied to the surface, but the sub-scale layer was destroyed and a pipe-like void (b) or a wide hollow layer
(c) is formed. It is considered that the nitriding is promoted because the atmospheric gas directly contacts the ground iron interface through such a pipe-shaped void or cavity layer.

By the way, a large number of fine precipitates were observed at the interface of the ferrous irons shown in FIGS. 2B and 2C.
It has been confirmed that it is AlN. Such a change in the subscale caused when the nitriding accelerator of KNO ₃ is applied to the surface is due to the alteration of the silica, which is a subscale product. When the extract was analyzed, it was found that when KNO ₃ was applied, K ₂ O was dissolved in silica. It is presumed that, due to the change in the surface tension of the silica, the shape changed and voids or cavities were formed.

Now, as an agent effective as a nitriding accelerator,
The following is what the inventors have found. KC
l, KNO ₃ , KF, KBr, K ₂ CO ₃ , KHCO ₃ , MgCl ₂ , Mg (NO ₃ ) ₂ , M
gF ₂ , MgBr ₂ , MgCO ₃ , CaCl ₂ , Ca (NO ₃ ) ₂ , CaF ₂ , NaCl, NaN
O ₃ , NaF, NaBr, Na ₂ CO ₃ , NaHCO _{3 and the} like. The attached amount of the agent is preferably in the range of 0.5 to 30 g / m ² per one side of the steel sheet. This is because if the coating weight is less than 0.5 g / m ^2, it is not enough to obtain the effect of accelerating nitriding, while 30
If it exceeds g / m ² , the properties of the steel sheet surface may be deteriorated. Any known method such as a method of applying with a roll, a method of applying with a spray, and an electrostatic coating can be applied.Also, even if the chemical is applied as a powder, it can be applied after dissolving in a solvent such as water. , May be applied and dried. As shown in FIG. 3, the coating timing is effective at any time prior to annealing before final cold rolling, and it is particularly effective to adhere immediately before annealing in order to maximize its effect.

Although the step of attaching the nitriding accelerator may be provided independently, it is more advantageous to connect the treatment to the annealing step before the final cold rolling. That is, when the cold rolling is performed once, the nitriding accelerator is applied before the homogenizing annealing immediately before the cold rolling, whereas when the cold rolling is performed twice, the second cold rolling is performed at the final cold rolling. Since the rolling is performed, the nitriding accelerator is attached before the intermediate annealing immediately before the rolling.

The annealing atmosphere before the final cold rolling requires that the N ₂ partial pressure ratio be 20% or more in order to promote nitriding. This is because if it is less than 20%, sufficient nitriding cannot be achieved even if a nitriding accelerator is attached, leading to deterioration of magnetic flux density. In addition, O ₂ and H ₂
The addition of 2% or more of O, CO ₂ as a source of oxygen potential at a total partial pressure ratio can reduce the CO generated during annealing.
It is more effective in removing the adverse effects of gas. The remaining gas components may contain a reducing gas such as H ₂ or a neutral gas such as Ar to keep the balance of the atmosphere composition. Therefore, ammonia decomposition gas (N ₂ = 25%, H ₂ = 75
%), And an atmosphere gas having a composition close to air, such as propane combustion gas, can provide a sufficient nitriding effect.
These atmosphere gas compositions need to be maintained at a predetermined composition during temperature rise and soaking, but during cooling, they can be replaced with other atmosphere gases due to little nitriding action.

As described above, the intended purpose can be achieved by attaching the nitriding accelerator to the steel sheet surface and controlling the furnace atmosphere prior to annealing before final cold rolling. However, by further improving the cooling conditions after soaking in the annealing before the final cold rolling and controlling the precipitation of carbides, the magnetic flux density can be further improved. Then, next, the cooling conditions after soaking in the annealing before the final cold rolling will be described.

That is, as a cooling treatment after the soaking treatment of the annealing before the final cold rolling, the cooling treatment is performed at a rate of 15 to 500 ° C./s at 450 to 20 ° C./s.
Quench to 0 ° C. then a. Holding at the quenching attainment temperature for 10 to 90 seconds and then quenching, or b. Perform gradual cooling treatment for cooling at a cooling rate of 2 ° C / s or less from the quenching ultimate temperature for 10 to 90 seconds. Perform any of the treatments to control the precipitation of carbides to further improve the magnetic flux density. You can do it.

Here, if the quenching temperature exceeds 450 ° C.,
Since carbides are coarsely precipitated at the grain boundaries, there is no effect of improving the primary recrystallization texture. On the other hand, if the temperature is lower than 200 ° C., carbon is dissolved in a solid solution, or even if precipitated as carbide, the size is small. The effect of improving the crystal texture is small. If the cooling rate to the quenching temperature is less than 15 ° C / s, carbide precipitation starts at a high temperature, so that the primary recrystallization texture cannot be sufficiently improved. If the cooling rate is too high, it is difficult to control the quenched temperature.

Next, the precipitation control of the carbide after the quenching treatment may be either a constant temperature holding or a slow cooling treatment.
In the case of the slow cooling treatment, it is necessary to set the cooling rate to 2 ° C./s or less. This is because if the cooling rate exceeds 2 ° C./s, it becomes difficult to control the precipitation size of carbide. In each case, the processing time must be 10 to 90 seconds.
That is, if less than 10 seconds, the precipitation amount and size are insufficient, while if it exceeds 90 seconds, the precipitation size becomes coarse,
This is because the effect of improving the primary recrystallization texture is reduced.

By applying strain during the above-mentioned carbide precipitation treatment, the range of temperature and time for controlling carbide can be further expanded. Here, the precipitation temperature range of carbide is 500 ° C to 200 ° C.
In the range of ° C, the deposition time ranges from 10 seconds to 180 seconds,
If it is out of this range, the size, amount and position of precipitation of the carbide are inappropriate and the effect of improving the primary recrystallization texture is poor.

It is considered that the reason why the form of carbide precipitation can be controlled by imparting strain as described above is that the introduced dislocations serve as carbide precipitation nuclei. For this reason, when the strain is applied, the precipitation form of the carbide is stabilized. It is necessary that the distortion amount at which such an effect is obtained be 3.0% or less (preferably 0.05% or more). This is because if the strain amount exceeds 3.0%, the size of the precipitated carbide becomes too small, and the primary recrystallization texture is not sufficiently improved. The process of introducing such a small strain may be performed before or during the carbide precipitation control process as long as the process is performed at 500 to 200 ° C. for 10 to 180 seconds. Thus, the processing time in the carbide precipitation control processing is extended from 10 to 90 seconds without such a small strain introduction processing to 10 to 180 seconds.

Next, final cold rolling is performed.
The rolling reduction in the final cold rolling needs to be a high rolling reduction in order to obtain a high magnetic flux density as is known. Specifically, the rolling reduction needs to be 80 to 95% in both the cold rolling only once and the cold rolling twice. This is because if the rolling reduction is less than 80%, a high magnetic flux density cannot be obtained, while if it exceeds 95%, secondary recrystallization becomes difficult. Performing the aging treatment during the final cold rolling is advantageous in reducing iron loss of the product. In particular
The component system of the present invention containing Sb has an excellent feature that a remarkable improvement in magnetic flux density is recognized by a single aging treatment in a short time. After the final rolling, the steel sheet is subjected to degreasing treatment and then subjected to decarburization and primary recrystallization annealing.

Then, an annealing separator containing MgO as a main component is applied to the surface of the steel sheet, wound into a coil, subjected to final finish annealing, and then subjected to an insulating coating as necessary. It goes without saying that the magnetic domain refining process can be performed by other methods.

[0036]

The preferred composition of the grain-oriented silicon steel according to the present invention will be described. C is necessary for improving the hot-rolled structure, but if it is too much, decarburization becomes difficult.
It is preferably about 0.090%.

If the content of Si is too small, the electric resistance becomes small and good iron loss characteristics cannot be obtained. On the other hand, if the content is too large, cold rolling becomes difficult. Therefore, the range of about 2.5 to 4.5% is preferable.

As for the inhibitor, AlN is particularly advantageous for obtaining a high magnetic flux density. Therefore, in the present invention, AlN is used as the inhibitor. However, if the amount is too large, fine precipitation becomes difficult. It is preferable that acid-soluble Al ≦ 0.15% and 0.0030 ≦ N ≦ 0.020%.

In this case, S and Se may be additionally contained as an inhibitor-forming element. Such S and Se
Is effective as an inhibitor because it precipitates as MnS or MnSe, and among them, MnSe is preferable because it has a strong suppressing effect even when the final finished plate thickness is particularly small. The range of S and Se suitable for finely depositing such MnS and MnSe is about 0.01 to 0.04% in both cases of single use and combined use. Note that Mn is required as an inhibitor component as described above, but if it is too large, it is difficult to form a solution, so the range of 0.05 to 0.15% is preferable.

Further, in the present invention, it is essential that Sb be contained in the steel, and the content is preferably about 0.005 to 0.08%. By including such Sb, a product having an extremely high magnetic flux density can be obtained even when the thickness of the steel sheet is small. This is because the segregation effect of Sb on the steel sheet surface and crystal grain boundaries effectively acts, and the inhibitor inhibitory effect is maintained even when the steel sheet thickness is small.

In addition to the above, in order to improve magnetism, C
Inhibitor reinforcing elements such as u, Cr, Bi, Sn, B, and Ge can also be added as appropriate, and the range may be a known range.
Also, to prevent surface defects due to hot embrittlement, 0.0
Mo addition in the range of 05 ≦ Mo ≦ 0.020% is preferred.

For the production process of the steel material, a known production method is applied, and the produced ingot or slab is regenerated as required, adjusted in size, and heated.
Hot roll. The final strip thickness of the steel strip after hot rolling is obtained by one cold rolling or two cold rollings with intermediate annealing.
Prior to the annealing treatment before the final cold rolling, a nitriding accelerator is attached to the surface of the steel sheet, and then the above-described controlled cooling and the carbide precipitation control treatment are performed. The treatment temperature in this annealing is desirably set to a high temperature of about 850 to 1200 ° C. for solutionizing AlN.

[0043]

EXAMPLES Example 1 Steel slabs having various component compositions shown in Table 1 (symbols A to H)
Was hot-rolled according to a conventional method to obtain a hot-rolled coil having a thickness of 2.2 mm. After that, uniform annealing was performed at 1000 ° C. for 90 seconds, and an intermediate plate thickness of 1.50 mm was obtained by cold rolling. Then, a 10% aqueous solution of KHCO ₃ as a nitriding accelerator was roll-coated on the surface of the steel sheet in an amount such that the adhesion amount per one side after drying was 4 g / m ² .
Then, in an atmosphere of 40% N ₂ , dew point: 40 ° C. and the remaining H ₂ ,
After an intermediate anneal of 00 ° C for 90s, it is rapidly cooled to 350 ° C at a rate of 50 ° C / s, then passed through a slow cooling zone with a cooling rate of about 1.5 ° C / s for 12 seconds, and then allowed to cool to the atmosphere did. After that, each steel strip was cold-rolled to a final thickness of 0.22 mm, subjected to electrolytic degreasing, decarburized in wet hydrogen at 850 ° C for 2 minutes, and subjected to primary recrystallization annealing. After applying an annealing separator (containing 5% of TiO ₂ ) as a main component, a final finishing annealing was performed at 1200 ° C. for 10 hours. Thereafter, a tension coating was applied to the surface, and a part thereof was subjected to a magnetic domain refinement treatment at a pitch of 8 mm by a known plasma jet method. Table 2 shows the results of examining the magnetic properties of the steel sheet thus obtained before and after the magnetic domain refining treatment.

[0044]

[Table 1]

[0045]

[Table 2]

Example 2 A billet F shown in Table 1 was hot-rolled according to a conventional method.
1.8 mm and 1.5 mm hot rolled sheets were used. Then 1000 ℃, 90s
After uniform annealing, allow to cool naturally, 1.2 mm and 1.0 mm, respectively.
After the first cold rolling to a thickness of mm
After dipping in a 15% KNO ₃ aqueous solution and drying to attach 1.4 g / m ² of KNO ₃ , the other is left as it is, N ₂ : 40%, dew point: 30 ° C.,
Intermediate annealing was performed at 1100 ° C. and 50 s in an atmosphere with the balance of H ₂ remaining. At this time, the cooling was rapidly cooled to 350 ° C at an average speed of 60 ° C / s and then gradually cooled to 310 ° C at a speed of 2 ° C / s while applying 0.01% strain through a slow cooling box equipped with bending rolls. Water decree. After that, the thickness of 1.2 mm is 0.18
mm, whereas the one with 1.0 mm was cold rolled to a final thickness of 0.15 mm, but with a thickness of 0.60 mm and 0.50 mm, respectively.
After aging treatment at 00 ° C for 2 minutes, the final cold rolling was continued.

After the final cold rolling, degreased and placed in wet hydrogen at 850 ° C.
After 2 minutes of decarburization and primary recrystallization annealing, an annealing separator mainly containing MgO (including 10% TiO ₂ ) was applied, followed by final finishing annealing at 1200 ° C for 10 hours. . afterwards,
A tension coating was applied to the surface, and an electron beam was irradiated at a pitch of 5 mm to perform a magnetic domain refining treatment. Table 3 shows the results obtained by examining the magnetic properties of the steel sheet thus obtained.

[0048]

[Table 3]

Example 3 A billet G shown in Table 1 was hot-rolled according to a conventional method.
A hot-rolled sheet having a thickness of 2.4 mm was used. This coil is called a, b, c,
d, 5 is divided into e, after both with the K ₂ CO ₃ is per side 3 g / m ² applied as a nitriding accelerator has been annealed for 90 seconds at 1175 ° C., the N ₂ partial pressure ratio of the atmosphere at that time, a is 10%, b
Is 23%, c is 45%, d and e are 75%, e is CO ₂ 2%
dp (dew point) 20 ° C was added. The remaining gas is H ₂
Balanced. The cooling of this annealing is a method of spraying mist, and after cooling from 1175 ° C to 330 ° C at an average cooling rate of 40 ° C / s, a constant temperature treatment of 330 ° C for 20 seconds is performed in the preservation zone, It was allowed to cool naturally. Thereafter, each was cold-rolled to a final thickness of 0.30 mm, and the intermediate thickness was once aged at 300 ° C. for 1 minute. After cold rolling, degrease and decarburize in wet hydrogen at 850 ° C for 2 minutes.
After primary recrystallization annealing, MgO is mainly used (2%
SrSO ₄ ) After applying the annealing separator,
A final finish annealing of 0 hours was performed. Thereafter, a tension coating was applied to the surface, and the magnetic properties were measured. Table 4 shows the values at this time.

[0050]

[Table 4]

Example 4 The billet F shown in Table 1 was hot-rolled according to a conventional method.
A hot-rolled coil with a thickness of 2.2 mm was used. After that, uniform annealing was performed at 1000 ° C. for 90 seconds, and an intermediate plate thickness of 1.50 mm was obtained by cold rolling. Next, a 15% aqueous solution of K ₂ CO ₃ as a nitriding accelerator was spray-coated on the surface of the steel sheet in an amount such that the adhesion amount per one side after drying was 2.5 g / m ² . Thereafter, the steel sheet is divided into three parts, one of which is subjected to intermediate annealing at 1100 ° C for 60 seconds in an atmosphere of 60% N ₂ , a dew point of 35 ° C and the rest of H ₂ , and is sprayed with mist to 40 ° C / s to 330 ° C. And then slowly cooled at a rate of 1.5 ° C./s for 20 seconds and then poured into water (coil a).

Another coil was subjected to intermediate annealing at 1100 ° C. for 60 seconds in an atmosphere of 60% N ₂ , a dew point of 35 ° C. and the remaining H ₂ , and then sprayed with a mist at 40 ° C./s to 350 ° C. The mixture was rapidly cooled at a speed and then gradually cooled at a rate of 2 ° C./s for 15 seconds while applying a 0.3% strain through a slow cooling box equipped with a bending roll, and then put into water (coil b). Further, the remaining coil is subjected to intermediate annealing at 1100 ° C for 60 seconds in an atmosphere of 60% N ₂ , dew point 35 ° C and remaining H ₂ , and then blasted to quench at 80 ° C at a rate of 35 ° C / s. And put into water (coil c).

Then, after cold rolling to a final plate thickness of 0.22 mm, electrolytic degreasing was performed for all three members, and then the wet plate was immersed in wet hydrogen.
Perform decarburization and primary recrystallization annealing at 50 ° C for 2 minutes.
After applying an annealing separator mainly containing gO (including 5% TiO ₂ and 3% Sr (OH) ₂ .8H ₂ O), a final finish annealing was performed at 1200 ° C. for 10 hours. Thereafter, a tension coating was applied to the surface, and the magnetic properties were measured. Table 5 shows the values at this time.

[0054]

[Table 5]

[0055]

As described above, according to the present invention, a grain-oriented silicon steel sheet having an extremely high magnetic flux density can be stably obtained regardless of the thickness of a product.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the total partial pressure ratio of H ₂ O, CO ₂ and O _{2 in} an annealing atmosphere and the amount of N in steel after annealing.

FIG. 2 (a) is a microscopic metallographic photograph showing a cross section of the surface layer of a steel sheet after normal annealing in Sb-containing silicon steel.
(B) and (c) are microstructure micrographs each showing a cross section of the steel sheet surface layer after annealing when the nitriding accelerator according to the present invention is applied to the steel sheet surface.

FIG. 3 is a block diagram showing a manufacturing method according to the present invention in the order of steps.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahiro Suga 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Technical Research Division (56) References JP-A-2-115319 (JP, A) JP-A Sho 59-190324 (JP, A) JP-A-62-202024 (JP, A) JP-A-3-72025 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 8/12 C23C 8/26 C22C 38/00 303 C22C 38/60

Claims (3)

(57) [Claims] 1. The method according to claim 1, wherein the inhibitor contains AlN as an inhibitor and contains Sb.
After the hot rolling of a grain-oriented silicon steel material containing the following, uniform cold annealing followed by one cold rolling with a reduction of 80 to 95% or a final reduction of 80 to 95% Oriented silicon steel sheet is subjected to a series of steps of cold rolling twice with 95% intermediate annealing, followed by decarburization, primary recrystallization annealing, application of an annealing separator, and final finish annealing. Prior to annealing before final cold rolling, a nitriding accelerator is attached to the surface of the steel sheet, and the annealing is performed at a partial pressure ratio of N ₂ of 20% in the atmosphere.
In addition to the above conditions, after the soaking in the annealing, at a cooling rate of 15 to 500 ° C./s
Rapidly cool to a temperature of 450-200 ° C, then a. Holding at the quenching attainment temperature for 10 to 90 seconds and then quenching, or b. A method for producing a grain-oriented silicon steel sheet, comprising performing any one of carbide precipitation control treatments in which a slow cooling treatment of cooling at a cooling rate of 2 ° C / s or less from a quenching ultimate temperature is performed for 10 to 90 seconds. 2. The method according to claim 1, wherein the composition contains AlN as an inhibitor and contains Sb.
After the hot rolling of a grain-oriented silicon steel material containing the following, uniform cold annealing followed by one cold rolling with a reduction of 80 to 95% or a final reduction of 80 to 95% Oriented silicon steel sheet is subjected to a series of steps of cold rolling twice with 95% intermediate annealing, followed by decarburization, primary recrystallization annealing, application of an annealing separator, and final finish annealing. Prior to annealing before final cold rolling, a nitriding accelerator is attached to the surface of the steel sheet, and the annealing is performed at a partial pressure ratio of N ₂ of 20% in the atmosphere.
In addition to the above conditions, after the soaking in the annealing, at a cooling rate of 15 to 500 ° C./s
Quenching to a temperature of 450-200 ° C., and then applying or after applying a micro strain of 0.005-3.0% from the quenching temperature to 200 ° C., a. 10 to 18
Cooling via hold for 0 seconds, or b. A grain-oriented silicon steel sheet characterized by performing any one of carbide precipitation control treatments in which a temperature range from the quenching ultimate temperature to 200 ° C is gradually cooled at a cooling rate of 2 ° C / s or less for 10 to 180 seconds. Manufacturing method. 3. The method for producing a grain-oriented silicon steel sheet according to claim 1, wherein the total partial pressure ratio of O ₂ + H ₂ O + CO ₂ in the atmosphere during annealing before final cold rolling is 2% or more.