JP2002241906A - Grain-oriented silicon steel sheet having excellent coating film characteristic and magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grain-oriented silicon steel sheet which has excellent directionality and on which forsterite film with superior adhesion is formed, and particularly, a grain-oriented silicon steel sheet which contains Bi as an inhibitor and has coarsely grown secondary recrystallized grains and on which forsterite film with superior adhesion is formed. SOLUTION: The grain-oriented silicon steel sheet has the forsterite film on the surface. Grain size is 10-150 mm in the rolling direction, and the area ratio of the secondary crystallized grains in which the <001> axis has an angle of <=5 deg. with respect to the rolling direction is >=80% based on the surface area of the steel sheet. The forsterite film with superior adhesion is formed by regulating the cooling rate through the temperature region of 1100-700 deg.C to (8 to 30) deg.C/h in the cooling step of the final finish annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet for use in iron cores of transformers and other electrical equipment, and more particularly to a grain-oriented electrical steel sheet having both excellent film properties and excellent magnetic properties.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets used as core materials for transformers and generators are most required to have high magnetic flux density and low iron loss. To meet this demand, many means have been adopted to date, for example, as disclosed in Japanese Patent Publication No. 33-4710 and Japanese Patent Publication No. 40-15644, Al is contained in the raw material, which is finally cooled. The above object is achieved by precipitating AlN as a strong inhibitor by annealing before rolling and by setting the final cold rolling reduction under a high pressure of 81 to 95%.

Further, Sn, As, Bi, Sb, B, Pb, Mo, T
It is also known that the addition of an inhibitor component such as e, V, or Ge is effective in improving the degree of integration of the secondary recrystallized grains in the rolling direction of the <001> axis, It is actually used. Among them, it is classified as a Group 5B element in the periodic table
P, As, Sb, and Bi segregate at the grain boundaries and work together with the main inhibitors, such as MnS, MnSe, Cu _2-x S, Cu _2-x Se, and AlN, to enhance the suppression of normal grain growth. It is known to enhance magnetic properties. In particular, Bi has been attracting attention as a strong element that has a low solubility in iron, and thus has a strong effect of suppressing the normal grain growth by the grain boundary segregation effect, and thus has a very high crystal orientation in the <001> direction. The grain-oriented electrical steel sheet having a thickness of 30 mm or more is being obtained.

In a grain-oriented electrical steel sheet, it is generally important to form a forsterite coating on the surface together with an insulating tension coating formed thereon to reduce iron loss and magnetostriction. A number of means have been proposed for producing a forsterite-like coating that is uniform and even. For example, Japanese Patent No. 3081118 discloses that a crystal grain size is generated on a steel sheet surface having a diameter of 1 mm to 6 mm,
A technique has been disclosed in which the amount of spinel in an oxide film containing forsterite as a main component is 5% or more.

[0005] By these means, it has become possible to produce a forsterite coating having high uniformity in appearance and good adhesion to a high magnetic flux density grain-oriented electrical steel sheet. However, especially when manufacturing a grain-oriented electrical steel sheet by processing a material containing Bi as an inhibitor component, crystal grains grow enormously, and in such a case, a forsterite coating film with excellent characteristics is not necessarily produced. I couldn't let it. For example, when flattening annealing is performed after the final finish annealing, a phenomenon in which a part of the forsterite coating is peeled off from the steel plate was observed. However, the cause and the solution remain unclear, and this has been a bottleneck for the practical use of grain-oriented electrical steel sheets having excellent orientation and, consequently, high magnetic flux density.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a grain-oriented electrical steel sheet on which a forsterite coating having excellent orientation and good adhesion is formed. In particular, the present invention contains Bi as an inhibitor,
An object of the present invention is to provide a grain-oriented electrical steel sheet in which a forsterite coating film with good adhesion is formed on a grain-oriented electrical steel sheet in which secondary recrystallized grains have grown to a large extent.

[0007]

Means for Solving the Problems The present inventors investigated the cause of deterioration of the forsterite coating of a grain-oriented electrical steel sheet having a high degree of integration of secondary recrystallized grains in the <001> axis rolling direction. As a result, it was clarified that the deterioration of the forsterite coating occurred during cooling during final finish annealing, and as a countermeasure, it was formed by extending the residence time in the 1100 ° C to 700 ° C region in the cooling stage during final finish annealing. The present inventors have found that it is effective to have a forsterite coating, and have completed the present invention.

That is, according to the present invention, the composition including the forsterite coating film has a mass ratio of Si: 2.5 to 7.0%, Mn: 0.02
0.5%, Mg: 0.01-0.3%, O: 0.01-0.5% and Al: 0.0
A grain-oriented electrical steel sheet containing from 0.05 to 0.03%, and containing a total of 8% or less of components other than Fe including these components,
<001> Secondary recrystallized grains whose axis is 5 ° or less with respect to the rolling direction and the grain size in the rolling direction is 10 to 150 mm have an area ratio of 80% or more of the steel sheet surface area, and the cooling process of final finish annealing 1 in
It has a forsterite coating produced at a cooling rate between 100 and 700 ° C of 8 to 30 ° C / h.

[0009] In the above, Bi further 0.001 to 0.20%
To contain, or Cr in addition to 0.015 to 0.5
It is preferable to contain 0%.

[0010] The grain-oriented electrical steel sheet of the present invention preferably has a surface provided with a tension imparting insulating coating or a magnetic domain refinement treatment.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described. The most important aspect of the present invention is that a cooling rate of 1100 ° C. to 700 ° C. is set to 8 to 30 ° C./h in a cooling process of final finish annealing. Since it has a manufactured forsterite coating, this point will be described first based on experimental data, and then various conditions required for carrying out the present invention will be described step by step.

(Relationship between Magnetic Flux Density and Coating Properties) As described above, it is empirically known that the formation of a forsterite coating becomes unstable in a grain-oriented electrical steel sheet having a high magnetic flux density. However, the cause of such a phenomenon and the quantitative relationship were not clear. The present inventors conducted the following experiments to clarify these points.

(Experiment 1) C: 0.08% (mass%, hereinafter the same unless otherwise specified), Si: 3.4%, Mn: 0.08%, Se: 0.02%,
Al: 0.030%, N: 0.0082%, Cu: 0.15%, Bi: 0.010%, with the remainder being substantially processed from a steel ingot made of Fe by a conventional method to form a hot-rolled sheet. After annealing, it was cold rolled into a cold rolled sheet having a sheet thickness of 0.23 mm. After performing decarburization annealing on the obtained cold-rolled sheet, an annealing separator containing MgO as a main component was applied thereto, and final finish annealing was performed. This final finish annealing is performed in a nitrogen (hereinafter, referred to as N ₂ ) atmosphere up to 750 ° C., from 750 ° C. to 1150 ° C.
° C. until N _2: 25 vol%, (hereinafter referred to as H ₂₎ hydrogen: heating at a rate of both 18 ° C. / h with 75 vol% of the atmosphere, the atmosphere H ₂
And purify by holding at 1180 ° C for 8 hours, and then cool from 1180 ° C to 500 ° C at 15 ° C / h.

In the above series of steps, a secondary recrystallized sheet was obtained by changing the temperature of hot-rolled sheet annealing from 850 ° C. to 1150 ° C. every 50 ° C. The magnetic flux density B ₈ of the obtained secondary recrystallized plate is
1.92T, 1.93T, 1.94
T, 1.95T, 1.96T, 1.97T, 1.98T. The average grain size (rolling direction) of the secondary recrystallized grains is 6.3mm, 8.5mm,
12.2mm, 20.6mm, 23.4mm, 37.8mm, 52.2mm.

Table 1 shows the results of the visual judgment of the appearance of the coating of the secondary recrystallized sheet having these various magnetic flux densities and average particle diameters (rolling directions) and the evaluation results of the bending adhesion. The bending adhesion was determined by applying an insulating tension coating containing magnesium phosphate and colloidal silica as main components to the obtained secondary recrystallized plate and winding it around a round bar having various diameters. It was evaluated by the small diameter.

[0016]

[Table 1]

As is clear from Table 1, the steel sheets produced in Experiment 1 all have good film visual judgment results and have a thickness of 20 mm.
It was determined to have the following flexural peeling diameter, to cause no practical problem at all, and to be excellent in film properties. However, the above results do not agree with the empirical rule that when the magnetic flux density is high and the crystal grain size is large, the film properties are inferior. In order to elucidate the cause, the influence of the cooling rate during the cooling of the final finish annealing was clarified by the following experiment 2.

(Experiment 2) C: 0.082%, Si: 3.25%, Mn: 0.078%, Se: 0.025%, Al:
0.030%, N: 0.0092%, Cu: 0.15%, Sn: 0.08%, Bi: 0.02
A steel ingot (A) containing 0% and the balance substantially consisting of Fe;
0.078%, Si: 3.45%, Mn: 0.072%, S: 0.025%, Cu: 0.15
%, Sn: 0.08%, Bi: 0.020%, and the remainder was substantially treated with a steel ingot (B) substantially composed of Fe to obtain a 2.6 mm hot-rolled sheet, which was then heated at 1000 ° C. for 65 seconds. After the holding, a hot-rolled sheet was quenched at 30 ° C./s for annealing. After pickling, the obtained hot-rolled sheet is cold-rolled to an intermediate sheet thickness of 1.8 mm, then subjected to intermediate annealing at a temperature of 950 to 1150 ° C., and further subjected to normal cold rolling to a sheet thickness of 0.8 mm. The lower part was rolled to a final sheet thickness of 0.23 mm by warm rolling at an average of 200 ° C. to obtain a cold-rolled sheet. On the obtained cold rolled sheet
After decarburizing annealing at 825 ° C., an annealing separator containing MgO as a main component was applied and wound into a coil having a diameter of 500 mm to perform final finish annealing. Final finish annealing is 10 between 700 and 1100 ° C.
The mixture was heated at 1 ° C / h, purified in 1175 ° C for 5 hours in pure hydrogen, and then cooled at a rate of 35 ° C / h between 1100 and 700 ° C.

The secondary recrystallized plate thus obtained is
Flattened annealing at 830 ° C, coated with insulating tension coating mainly composed of magnesium phosphate and colloidal silica to obtain a product. Under the same conditions as in Experiment 1, magnetic flux density B ₈ , average grain size (rolling direction) Was measured and the film properties were observed. Table 2 shows the results.

[0020]

[Table 2]

As is clear from Table 2, in Experiment 2, the appearance and adhesion of the coating film greatly depend on the magnetic flux density and the crystal grain size. This is considered to be because in Experiment 2, the cooling rate during the final finish annealing was increased. Experiment 2 also differs from Experiment 1 in that the coil was wound into a coil shape and subjected to flattening annealing after final finishing annealing. The following experiment 3 was performed to clarify the effect of the magnetic flux density and the crystal grain size on the film characteristics when the cooling rate was increased.

(Experiment 3) C: 0.065%, Si: 3.35%, Mn: 0.0635%, Se: 0.030%, A
l: 0.028%, N: 0.0095%, Cu: 0.12%, the remainder is a steel ingot substantially consisting of Fe processed by a conventional method to a thickness of 2.9 mm
Was obtained. 800 to 1180 for this hot rolled sheet
The hot-rolled sheet was annealed at a temperature of 30 ° C. for a holding time of 30 seconds, followed by warm rolling with intermediate annealing interposed therebetween to obtain a final sheet thickness of 0.23 mm.

After the obtained steel sheet was subjected to decarburizing annealing at 850 ° C., an annealing separating agent containing MgO as a main component was applied thereto, and the diameter was 500 mm.
And subjected to final finish annealing. In the final finish annealing, first, from room temperature to 700 ° C under N ₂ atmosphere, average 15 ° C /
h, 700-850 ° C is heated at 10 ° C / h, and between 850 and 1150 ° C is heated at 10 ° C / h in a mixed atmosphere of H ₂ : 70 vol% and N ₂ : 30 vol%, and then at 1150 ° C 15h and purified and held in pure H _2, and as further cooled between 1100 ° C. to 700 ° C. at a rate of 35 ° C. / h. The obtained steel sheet was subjected to an insulating tension coating containing magnesium phosphate and colloidal silica as main components, followed by flattening annealing at 830 ° C.

In the above experiments, the conditions of hot-rolled sheet annealing, intermediate annealing, and warm rolling were appropriately combined to vary the crystal grain size and crystal orientation distribution of the secondary recrystallized grains after final finish annealing. It is. FIGS. 1 and 2 show the results of investigations on the magnetic flux density and the film appearance of the product plate obtained in this manner. FIG. 1 shows that the magnetic flux density is remarkably improved when the grain size is 10 to 150 mm and the area ratio of the crystal grains whose <001> axis is 5 ° or less from the rolling direction is 80% or more. On the other hand, from FIG. 2, the area ratio occupied by crystal grains having a particle size of 10 to 150 mm is
At 80% or more, the tendency of the film to deteriorate becomes remarkable, especially when the area ratio of the crystal grains whose <001> axis is 5 ° or less from the rolling direction is 80% or more.

According to the above-mentioned experiments 1 to 3, the deterioration of the film was caused when the cooling rate during the final finish annealing was relatively large, the crystal grains were large, and the <001> axis was highly accumulated in the rolling direction. It was clarified that it was easy to occur. The mechanism is considered as follows. However, this is not necessarily definitive and is not a requirement that constitutes the present invention.

Decarburizing annealing is applied to a cold-rolled steel sheet containing AlN as an inhibitor, and an annealing separator containing MgO as a main component is applied thereto, followed by final finish annealing. When formed, Al in the steel is taken into the coating, and a spinel oxide containing Al is formed in the forsterite coating. The thermal expansion coefficient of a forsterite coating containing such a spinel oxide is small. On the other hand, the thermal expansion coefficient of the ground iron portion of the steel sheet is larger than that of the forsterite coating, so that when the steel is cooled from a high temperature of 1100 ° C or more to room temperature, strong tension is applied to the base steel by the forsterite coating. Will work.
The magnetic domains of the magnetic steel sheet are subdivided by this tension, and iron loss is reduced. However, when the cooling rate is large and the tension is excessive, if there is a place at the interface between the forsterite coating and the ground iron that cannot withstand the above-described force, the coating and the steel plate (base steel) may be formed at that location. Cracks are likely to occur between them. As a result, film degradation appears on the product after flattening annealing,
At the same time, the effect of imparting tension by the film is lost, and the effect of reducing iron loss is also reduced. Such a phenomenon is considered to occur also in the process of manufacturing a normal grain-oriented electrical steel sheet, but is particularly remarkable when the magnetic flux density is high and the crystal grain size is large.

The cause of the deterioration of the film properties when the crystal grains are large is that the final finish annealing is industrially performed in a state of being wound in a coil shape. That is,
In such a case, the forsterite coating is also formed with the same curvature as the steel sheet wound in a coil shape, so if flattening annealing is performed after the formation of the forsterite coating, the forsterite coating is formed at the end of the secondary recrystallized grains. A bending moment occurs in the stellite coating. If the crystal grains are small, the bending moment is small, and the force is dispersed because the grain boundaries (crystal ends) are large. However, this bending moment increases as the secondary recrystallized grain size increases, so that the crystal grain size increases. When is large, cracks occur in the forsterite coating, and also in the interface between the coating and the steel plate, leading to coating defects.

On the other hand, it is considered that there are two reasons why the deterioration of the coating properties becomes remarkable in a steel sheet having a high magnetic flux density.
First, for steel sheets with high magnetic flux density, <001>
It is pointed out that the crystal grains are inevitably enlarged during the secondary recrystallization because the axes are oriented very accurately and the number thereof is small. Second, since there is almost no difference in orientation between adjacent secondary recrystallized grains, it is difficult to alleviate thermal strain applied to the entire steel sheet during cooling during final finish annealing.

In any case, when the cooling rate at the time of the final finish annealing is high, the coating is liable to deteriorate. The following experiment 4 was carried out in order to elucidate this phenomenon quantitatively and to solve the film defect caused by the cooling process at the time of final finish annealing.

(Experiment 4) C: 0.06%, Si: 3.3%, Mn: 0.07%, Se: 0.02%, Al: 0.02
%, N: 0.008%, Cu: 0.15%, and Sn: 0.08%, and a silicon steel slab substantially consisting of Fe, with the balance substantially consisting of Fe, was processed into a decarburized annealed sheet having a sheet thickness of 0.23 mm. An annealing separator consisting of 100 parts by mass of MgO, 12 parts by mass of TiO ₂ , 6 parts by mass of Sr (OH) _{2, and} 3 parts by mass of MgSO ₄ was applied to the steel sheet so that the amount became 13 g / m ² per one surface of the steel sheet. It was wound into a coil having an inner diameter of 500 mm and an outer diameter of 1200 mm and was subjected to final annealing. The final finish annealing is performed at a heating rate between room temperature and 830 ° C. in a nitrogen atmosphere at an average of 20 ° C./h.
At 20 ° C. for 20 hours, and then heated to 1180 ° C. at 12 ° C./h in a mixed atmosphere of H ₂ : 75% and N ₂ : 25%, and further heated to 1180 ° C. in a hydrogen atmosphere.
Purification was performed at 5 ° C. for 5 hours. Cooling of the final finish annealing is performed between 1,100 and 700 ° C, 5, 7, 9, 12, 15, 19, 23,
The cooling rates were 27, 32, and 40 ° C / h. The obtained secondary recrystallized plate is subjected to an insulating tension coating containing magnesium phosphate and colloidal silica as main components, and further 830 ° C.
For flattening annealing.

The products thus obtained were _examined for magnetic properties (magnetic flux density, iron loss W _17/50 ) and coating properties (coating appearance, bending adhesion). Table 3 shows the results. As shown in Table 3, it can be seen that under conditions where the cooling rate at 1100 to 700 ° C during the final finish annealing was from 9 ° C / h to 27 ° C / h, it is possible to manufacture a product with excellent iron loss and coating appearance. . By repeating such an experiment, it was confirmed that if the cooling rate at 1100-700 ° C was changed from 8 ° C / h to 30 ° C / h during final finish annealing, it would be possible to manufacture products with excellent iron loss and coating appearance. did it. When the cooling rate is less than 8 ° C./h, there is no problem in the film properties, but the iron loss deteriorates. It is considered that the reason is that iron atoms move in a direction to lower the tension by self-diffusion of iron in a high-temperature region, and as a result, the tension generated due to a difference in thermal expansion between the steel sheet and the forsterite coating is lost. Therefore, the above cooling rate should not be unnecessarily low but should be 8 ° C./h or more.

[0032]

[Table 3]

The cooling rate in the above cooling process is controlled.
The range of 1100 ° C. to 700 ° C. is defined as a range in which the formation of forsterite is completed, self-diffusion of iron atoms occurs, and a change due to the cooling rate can be expected. In other words, at temperatures above 1100 ° C, the formation of forsterite is still continuing, so there is no point in controlling the cooling rate.On the other hand, at temperatures below 700 ° C, self-diffusion of iron atoms hardly occurs, and the change due to the cooling rate does not change. I can't expect it at all.

As described above, as clarified in Experiments 1-4, in the final finish annealing, the secondary recrystallized grains were formed so that the crystal grain size was 10-150 mm in the rolling direction and the <001> axis was in the rolling direction.
By controlling the area ratio of crystal grains of 5 ° or less to be 80% or more of the steel sheet surface, and by setting the cooling rate of 1100 to 700 ° C to 8 to 30 ° C / h in the cooling process of final finish annealing Thus, it is possible to obtain a grain-oriented electrical steel sheet having excellent magnetic properties and excellent film properties.

In the present invention, 80% or more of the steel sheet area is covered with crystal grains having a crystal grain size in the rolling direction of 10 mm or more and 150 mm or less and the <001> axis aligned at 5 ° or less with respect to the rolling direction. The reason for this is clear from the above experimental results. That is, when the crystal grain size in the rolling direction is less than 10 mm, film deterioration does not occur, and the crystal grain size in the rolling direction is 150 m
If it exceeds m, when the steel sheet is wound into a coil shape and the steel sheet subjected to final finish annealing is returned to a flat state, the inclination of the orientation of the crystal grains in the direction perpendicular to the sheet surface at the edge of the crystal grains increases, and the magnetic flux density Is to be reduced. The <001> axis is 5 ° in the rolling direction.
The reason why the following is set is to secure a high magnetic flux density.

Hereinafter, the most important points of the present invention are as described above. Hereinafter, various points that are important in practicing the present invention will be described. First, in the present invention, the composition of the starting material is 8% or less in total of components other than Fe in mass ratio, and C:
0.01 to 0.10%, Si: 2.5 to 7.0%, Mn: 0.02 to 0.5% and Al: 0.015 to 0.050% as an inhibitor component, N: 0.005 to 0.0
It is preferable to contain 15% and the balance substantially consist of Fe and inevitable impurities. The reason for limiting the total amount of components other than Fe to 8% or less in this way is that when the content other than Fe is too high, the saturation magnetic flux density decreases, so that the <001> axis of the crystal is aligned in the rolling direction. also because the magnetic flux density B ₈ is deteriorated.

C is an element effective for improving the hot-rolled structure by utilizing transformation and is an element effective for generation of Goss-oriented grains. It is necessary to contain C in an amount of 0.01% or more. If the content exceeds the above range, poor decarburization may occur. Therefore, it is preferable that the content be in the range of 0.01 to 0.10%.

It is necessary to contain 2.5% or more of Si in order to improve iron loss. However, if it is too much, it is likely to be broken when forming a transformer, and it becomes difficult to work, so the upper limit is made 7.0%. Mn
Is also an element necessary for increasing electric resistance and improving hot workability at the time of production. 0 for this purpose.
It is necessary that the content be 02% or more, but if it exceeds 0.5%, the magnetic properties deteriorate, so the content is set in the range of 0.02 to 0.5%. Note that the content of Si and Mn in the product is also in the range described above.

It is preferable to contain Al and N as the inhibitor component. Of these, Al is 0.015-0.0
It is necessary to contain 50%. Al content 0.015%
If less than, it is not possible to obtain good secondary recrystallized grains due to insufficient amount of AlN to be precipitated, while if more than 0.050%, it is difficult to uniformly disperse to a size functioning as an inhibitor, which is not preferable. . Therefore, Al is 0.015
To 0.050%. If N is contained at 0.005% or more, it gasifies in the steel and causes defects such as blisters.
5 to 0.015% is to be contained.

The content of Al in the product is 0.005 to 0.005.
It is essential to set it to 0.03%. If less than 0.005%, the oxide of Al does not exist on the surface of the steel sheet, the effect of imparting tension by the forsterite coating does not become large, and therefore, it is possible to produce a unidirectional magnetic steel sheet having a low iron loss aimed at by the present invention. This is because it is not possible and no coating defects occur.
On the other hand, the reason why the upper limit of the Al content in the product is set to 0.03% is that if it is present in excess, the precipitates in the steel will be too large, hindering the domain wall movement and increasing the iron loss.

Other inhibitor components include Se,
S can be used alone or in combination. These elements precipitate as Mn compounds or Cu compounds in the steel, but it is desirable to contain a total of 0.010% or more in order to maintain the effect of suppressing the growth of primary recrystallized grains. However, if the total content of these exceeds 0.040%, even if the slab heating temperature is increased, it is not possible to completely form a solid solution, and when used as an element, it is better to contain them in the range of 0.010 to 0.040%. . When these elements are not used as inhibitor elements and a method of omitting high-temperature heating of the slab is adopted, the content of these elements is preferably 0.010% or less in total.

In the present invention, it is particularly preferable to use Bi as an inhibitor element. Bi acts to highly accumulate the <001> axis of secondary recrystallized grains in the rolling direction,
In addition, when Bi is contained in order to make crystal grains grow extremely large, the effect of improving the film is remarkably exhibited by applying the present invention. However, its content is 0.005%
If it is less than 0.20%, the expected effect cannot be obtained. On the other hand, if it exceeds 0.20%, uniform dispersion becomes difficult, which is rather detrimental. Therefore, Bi is preferably contained at 0.005 to 0.20%. In addition,
Since Bi may escape from the steel to some extent during the final annealing, if the Bi content in the starting material is 0.005 to 0.20%, the Bi content in the product will be 0.001 to 0.20% .

In addition to the above, Cu, Sn, Sb, Mo, B, As, T
Known inhibitor elements such as e and P can be supplementarily contained. The preferred content range of these elements is 0.05 to 0.5% for Cu and Sn, and 0.005 for Sb, As, Mo, Te, and P.
0.10.10%, and B is 0.0010-0.0060%.

In addition to the above elements, for example, the addition of Ge or Co has an effect of improving the surface properties of the steel sheet.
It is preferable to contain it in the range of 5%. In particular, Cr has an effect of accelerating the forsterite formation reaction.
It is preferable to contain it in the range of 0.5%. When the content is less than 0.05%, the effect is not sufficiently exhibited.On the other hand, when the content is more than 0.5%, not only the coating improvement effect is saturated but also the magnetic flux density tends to decrease. It is better to be in the range of 0.5%. Also, since the grain-oriented electrical steel sheet of the present invention has a forsterite coating,
Contains 0.01 to 0.3% of Mg and 0.01 to 0.5% of O. If Mg is less than 0.01%, the forsterite film is too small to generate the desired tension, and if more than 0.3%, the coating thickness becomes excessively large with respect to the steel sheet thickness, and the magnetic flux density decreases. Mg for O
For the same reason as above, the lower limit was set to 0.01% and the upper limit was set to 0.5%.

The starting material having the above composition is usually 1350
After being heated to a temperature of at least ° C., a hot-rolled coil is formed by hot rolling. However, a lower heating temperature can be employed when the composition has a composition that precludes the blending of elements that require a high temperature for solution, such as Se and S. Hot rolling may be performed by a conventional method, for example, the finish-rolling exit temperature is 800 to 1100.
° C, coil winding temperature 700 ° C or less.

In the cold rolling step, the cold rolling process is performed once to obtain the final thickness by rolling once after the hot rolling plate annealing, or, if necessary, after the hot rolling plate annealing process, the first cold rolling process is performed. A cold rolling twice method in which rolling is performed, then intermediate annealing is performed, and second cold rolling is performed can be adopted. The rolling reduction of the cold rolling is preferably in the range of 60 to 90%, more preferably 80 to 90%. The conditions of hot-rolled sheet annealing and intermediate annealing are preferably 800 to 1200
C, more preferably within the range of 1000 to 1200 C. In the final cold rolling, warm rolling or aging treatment between passes is performed as necessary. Warm rolling is preferably performed in the range of 120 to 300 ° C, more preferably 180 to 250 ° C, and aging between passes is preferably performed at 150 to 350 ° C for 1 minute or more. In the decarburization annealing performed after cold rolling, the heating rate is 60
It is effective to perform rapid heating between 0 and 750 ° C at 10 ° C / s or more. By appropriately combining these means within the above preferred range, the primary recrystallization texture is improved, and thus the <001> axis of the crystal grains after the secondary recrystallization is within the scope of the present invention, with respect to the rolling direction. A steel sheet can be obtained in which the area ratio of crystal grains having a crystal grain size of 5 ° or less and a grain size in the rolling direction of 10 to 150 mm is 80% or more of the steel sheet surface area. Further, after the final cold rolling, it is possible to perform a magnetic domain refining treatment for providing linear grooves on the surface of the steel sheet.

The steel sheet after decarburization annealing obtained by this method is coated with an annealing separator mainly composed of MgO,
It is wound in a coil shape and subjected to final finish annealing. At that time, it is free to include a Ti compound, an Sr compound, an Sb compound, or Ca or B in the annealing separator. Further, after decarburizing annealing, it is also possible to perform a nitriding treatment for containing N in a range of 300 ppm or less in the steel before the start of the secondary recrystallization,
As a result, it is possible to manufacture a product having more excellent film characteristics and magnetic characteristics.

The conditions for the final finish annealing are characterized by the cooling conditions after the purification stage, as already shown in Experiments 1 to 4. That was already detailed. Other conditions may be according to a conventionally known method. Note that at least 1050 ° C. or more, preferably 900 ° C. or more in the temperature rise process of the final finish annealing, it is necessary to set the annealing atmosphere to an H ₂ -containing atmosphere. Thereby, the formation of oxides and nitrides in the coating formed during the final finish annealing is performed smoothly, and a coating that gives high tension to the steel sheet can be formed.

After the final finish annealing, after removing the unreacted separating agent, an insulating tension coating mainly containing magnesium phosphate and colloidal silica is applied to the surface of the steel sheet.
Bake. Generally, the product is further subjected to flattening annealing, but the application and baking process of the insulating tension coating may also serve as the flattening process. In addition, in order to obtain an iron loss reduction effect on the steel sheet after the secondary recrystallization, known magnetic domain refining treatment, for example, formation of a linear region by plasma jet or laser irradiation, or formation of a linear dent region by a projection roll You are also free to do.

[0050]

[Example] (Example 1) C: 0.08%, Si: 3.65%, Mn: 0.07%, P: 0.003%, S: 0.00
3%, Al: 0.027%, Se: 0.020%, Sb: 0.060%, Cr: 0.25
%, N: 0.0092%, Bi: 0.020%, and a silicon steel slab consisting essentially of iron was charged into a gas heating furnace, heated to 1180 ° C., held for 30 minutes, and then heated to 1400% by induction heating. 20 at ℃
Heated for 2.5 minutes and hot rolled to a thickness of 2.5 mm by hot rolling. The obtained hot-rolled sheet is subjected to hot-rolled sheet annealing at 1000 ° C. for 30 seconds, then pickled, subjected to primary cold rolling to a thickness of 1.7 mm, and subjected to intermediate annealing at 1080 ° C. for 2 minutes, A cold rolled sheet having a final thickness of 0.23 mm was formed by secondary cold rolling at a maximum temperature of 220 ° C.

The atmosphere of the obtained cold rolled sheet in a uniform process was P (H ₂
0) / P (H ₂ ) was subjected to decarburization annealing at 850 ° C. for 100 seconds in an atmosphere of 0.45. An annealing separator was applied to the obtained decarburized annealed sheet at 7 g / m ² per one side of the steel sheet, wound around a coil, and subjected to final finish annealing. At this time, the composition of the annealing separator was MgO: 1.
00 parts by mass, TiO ₂ : 10 parts by mass, Sr (OH) ₂ : 3 parts by mass, SnO ₂ :
It was 1 part by mass. The conditions for final finish annealing were as follows: heating from room temperature to 870 ° C in a nitrogen atmosphere for 70 hours;
After holding at 70 ° C for 10 hours, the atmosphere was H ₂ : 50% and N ₂ : 50%
And heated to 1200 ° C., and then the atmosphere was switched to an argon (Ar) atmosphere to start cooling. The predetermined cooling rate shown in Table 4 was between 1100 and 700 ° C.

[0052]

[Table 4]

The thus obtained finish-annealed plate was coated with an insulating tension coating mainly composed of magnesium phosphate containing colloidal silica, flattened at 830 ° C. for 10 seconds, and further subjected to plasma flame. The product was subjected to a magnetic domain refining treatment by irradiation of the product. From the obtained product,
A sample having a length of 500 mm and a width of 500 mm was collected and subjected to magnetic measurement by SST. The measurement results are also shown in Table 4. As is evident from Table 4, when manufactured by a method compatible with the present invention, the film appearance, adhesion, and magnetic properties are excellent.

Example 2 21 kinds of silicon steel slabs having the composition shown in Table 5 and the balance substantially consisting of iron were put in a gas heating furnace.
After heating at 1150 ° C for 60 minutes, 1430 in 50 minutes in induction heating furnace
After heating to 14 ° C., it was kept at 1430 ° C. for 15 minutes. This was extracted from the furnace and formed into a 40 mm-thick sheet bar by three-pass rough rolling, followed by hot rolling to form a 2.2 mm-thick hot-rolled sheet and winding at 550 ° C. The obtained hot-rolled sheet was annealed at 950 ° C. for 1 minute, and cooled to room temperature at 30 ° C./s. This was subjected to primary cold rolling to an intermediate thickness of 1.5 mm, and then 1120 ° C, 3
Intermediate annealing was performed for 0 second, and the temperature was reduced to room temperature at 35 ° C./s. Then, a final sheet thickness of 0.20 mm was obtained by secondary cold rolling at an average sheet temperature of 170 ° C.

[0055]

[Table 5]

The obtained cold-rolled sheet was etched by resist etching at an angle of 75 ° with respect to the rolling direction, an interval of 3.5 mm, a depth of 20 μm, and a width of 17 mm.
After forming grooves in a linear shape of 0 μm, decarburization annealing was performed. The conditions for decarburizing annealing are as follows: heating rate up to 850 ° C is 25 ° C / s,
P (H ₂ 0) / P (H ₂ ) is 0.39 for the oxidizing property of the atmosphere in the overheating process, and P (H ₂₀ ) / P (H ₂ ) is 0.42 for the oxidizing property of the atmosphere in the soaking process. The temperature was 850 ° C. and the soaking time was 150 seconds. The obtained decarburized annealed plate has 12 parts by mass of TiO ₂ and 2 parts by mass of MgO 100 parts by mass.
An annealing separator of Sr (OH) ₂ was applied and wound into a coil to perform final annealing.

The final finish annealing is performed between 700 ° C. and 850 ° C. at 20 ° C./h.
Heat in N ₂ atmosphere with r, H ₂ : 70% between 850 ° C and 1150 ° C,
N ₂ : Heat at 10 ° C / hr in a 30% mixed atmosphere, then 1150 ° C
The atmosphere was changed to H ₂ atmosphere, and the purification was performed at 1200 ° C. for 12 hours. The cooling rates between 1100 and 700 ° C. are shown in Table 6 (slab symbols A to K) and Table 7 (slab symbols L to U). It was performed under conditions.

[0058]

[Table 6]

[0059]

[Table 7]

The resulting final annealed plate was coated with an insulating tension coating containing magnesium phosphate and colloidal silica as main components and subjected to flattening annealing to obtain a product. Table 6 also shows the magnetic properties and coating properties of the obtained product. After the unreacted separating agent was removed from the final annealed plate by washing with water, the components with the coating were analyzed. Table 8 shows the results. It can be seen that when the content of Mg is in the range of 0.01 to 0.300% and the content of O is in the range of 0.010 to 0.500%, a forsterite coating having an appropriate thickness is formed. As described above, when manufactured by a method conforming to the present invention, the film appearance, adhesion, and magnetic properties are excellent.

[0061]

[Table 8]

[0062]

According to the present invention, as described above, secondary recrystallized grains
The deterioration of the forsterite coating on grain-oriented electrical steel sheets with a high degree of integration in the rolling direction of the <001> axis was solved by extending the residence time in the 1100 ° C to 700 ° C region in the cooling stage during final finish annealing. Thereby, it becomes possible to obtain a grain-oriented electrical steel sheet having extremely excellent coating properties and magnetic properties. In particular, the present invention is directed to a directionally oriented steel sheet containing Bi as an inhibitor, in which so-called secondary recrystallized particles have grown to a large size, in which a forsterite coating with good adhesion is formed and has excellent coating properties and magnetic properties. It is possible to obtain a conductive magnetic steel sheet.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a crystal grain size, a crystal orientation, and magnetic properties.

FIG. 2 is a diagram showing a relationship between a crystal grain size, a crystal orientation, and a film appearance.

Continued on the front page (72) Inventor Kunihiro Senda 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. None) Kawasaki Steel Corporation Mizushima Works F-term (reference) 5E041 AA11 BC08 HB14

Claims (5)

[Claims] 1. A composition containing a forsterite coating containing Si by weight: 2.5 to 7.0%, Mn: 0.02 to 0.5%, and Mg: 0.01 to 1.
Contains 0.3%, O: 0.01 to 0.5% and Al: 0.005 to 0.03%, and a total of 8% of components other than Fe including these components
The grain-oriented electrical steel sheet is as follows, the <001> axis is 5 ° or less to the rolling direction, and the secondary recrystallized grains having a grain size in the rolling direction of 10 to 150 mm have an area ratio of 80 to the sheet surface area Excellent for coating and magnetic properties characterized by having a forsterite coating produced at a cooling rate between 1100 and 700 ° C in the cooling process of final finish annealing of 8 to 30 ° C / h. Oriented magnetic steel sheet. 2. The method according to claim 1, wherein Bi is 0.001 to 0.20.
A grain-oriented electrical steel sheet with excellent coating and magnetic properties characterized by containing 3. The method according to claim 1, further comprising:
A grain-oriented electrical steel sheet having excellent coating and magnetic properties, characterized by containing 015 to 0.50%. 4. The grain-oriented electrical steel sheet according to claim 1, wherein the grain-oriented electrical steel sheet has a surface provided with a tension imparting insulating coating. steel sheet. 5. The grain-oriented electrical steel sheet according to claim 1, wherein the grain-oriented electrical steel sheet has been subjected to a magnetic domain refining treatment. .