JPH10121213A - Grain-oriented electrical steel sheet that excels in iron loss characteristics in a low magnetic field compared to a high magnetic field and a method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a grain-oriented electrical steel sheet which is excellent in iron loss characteristics in a low magnetic field as compared with a high magnetic field and is suitable as a core of a small generator or a transformer. SOLUTION: Si: 1.5 to 7.0% and Mn: 0.03 to 2.5
%, And C, S and N are adjusted to C: 0.003% or less, S: 0.002% or less, and N: 0.002% or less, respectively. The number ratio is less than 1 mm: 25 to 98%, 4 mm to 7 mm: 45% or less, 7 mm or more: 10% or less, Al: 0.5 to 1.5%, Ti: 0.1 to 10 in the forsterite coating on the steel sheet surface.
% And B: contained in the range of 0.01 to 0.8%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high magnetic field, which is particularly advantageous in the use of grain-oriented electrical steel sheets used for generators and transformer cores, especially for small generators such as iron cores and EI cores. The present invention proposes a grain-oriented electrical steel sheet having excellent low-field iron loss characteristics and a method for producing the same.

[0002] It contains Si and has a crystal orientation of (110)
Oriented electrical steel sheets oriented in the [001] or (100) [001] direction are widely used as various iron core materials in the commercial frequency range because of their excellent soft magnetic properties. At this time, the characteristic required for the magnetic steel sheet is generally a loss when magnetized to 1.7 T at a frequency of 50 Hz.
It is important that the iron loss expressed by W _17/50 (W / kg) is low, and the iron loss of the iron core of large transformers and wound iron cores is a material with a low value of W _17/50. Have obtained results. However, the core of the small generator and the small transformer E
When the magnetic flux flowing inside the steel plate such as the I-core is complicated, there is a problem that the iron loss represented by W _17/50 of the material does not match the iron loss characteristics in the actual machine.

In recent years, with the progress of the energy crisis, transformers
It is required to reduce energy lost in
While efforts are being made to reduce losses,
The W _17/50Can not obtain a legitimate evaluation.
It was often difficult.

[0004]

2. Description of the Related Art Generally, in order to reduce iron loss of a material, a method of increasing electric resistance by containing Si effective to reduce eddy current loss, a method of reducing a steel sheet thickness, and a method of reducing a crystal grain size are known. There are known a method and a method of increasing the degree of integration of the crystal orientation to improve the magnetic flux density.

Among them, many techniques for improving the magnetic flux density have been studied so far. For example, Japanese Patent Publication No. Sho 51-2290 (a method of hot rolling a high magnetic flux density unidirectional magnetic steel sheet) has been disclosed. Al is added as an inhibitor component to steel, and slab heating is performed at a high temperature of 1300 ° C or higher.
The technology of performing hot finish rolling at high temperature for a short time and performing hot rolling at a hot rolling end temperature of 980 ° C or higher is also disclosed in
No. 6-23820 (heat treatment method for high magnetic flux density magnetic steel sheet) discloses that Al is added to steel, and after hot rolling, 1000 to 1200 ° C.
Very high magnetic flux density and to precipitate a fine AlN by hot-rolled sheet annealing and quenching process associated therewith at high temperatures, is disclosed a technique of applying a high pressure ratio of 80% to 95%, whereby at B ₁₀ and 1.95T And have obtained a material with low iron loss.

[0006] However, the method of improving the magnetic flux density by aligning the normal crystal orientation, which has been pursued in the past when reducing _{W17 / 50} , is to improve the iron loss characteristics of the EI core and the iron core of a small generator. Was not an effective method.

[0007]

As described above, as an alternative to the technique for improving the magnetic flux density, Si
We studied methods to increase the content, reduce the thickness of the steel sheet, and reduce the crystal grain size. However, there is a limit in that it is not preferable because it deteriorates the properties, and a method of reducing the thickness of the steel sheet has its own limit because it extremely increases the production cost.

[0008] Therefore, the present invention is characterized by claims 1 and 2
The object of the invention is to propose a grain-oriented electrical steel sheet having excellent iron loss characteristics in a low magnetic field as compared to a high magnetic field by optimizing a crystal grain size distribution of a product and a component composition of a forsterite coating. It is an object of the present invention to propose a method for manufacturing a grain-oriented electrical steel sheet.

Conventionally known techniques for controlling the crystal grain size of grain-oriented electrical steel sheets are disclosed in, for example,
Japanese Patent Publication No. 20745 (Unidirectional silicon steel sheet with extremely low iron loss and method for producing the same) discloses a method for producing a thin grain-oriented electrical steel sheet having an average crystal grain size of 1 to 6 mm.
No. 3 (Method for producing unidirectional silicon steel sheet with small iron loss)
A method of reducing the iron loss by setting the number ratio of crystal grains having a grain size of 2 mm or less to 15 to 70% is disclosed in Japanese Patent Publication No. 6-80172.
Japanese Patent Publication No. (oriented silicon steel sheet with low iron loss and a method for producing the same) proposes a technique for reducing iron loss by allowing fine grains having a grain size of 1.0 mm or more and 2.5 mm or less to exist in a mixed state. However, these are all magnetic flux density 1.
It is intended to reduce the iron loss W _17/50 in a high magnetic field of 7 T, and has not been studied for the iron loss in a low magnetic field.

[0010]

[Means for Solving the Problems] As a result of intensive studies, the inventors have increased the iron loss W _17/50 in a high magnetic field and increased the iron loss in a low magnetic field.
Reducing W _10/50, namely, reducing the value of W _10/50 / W _17/50, To that end, the grain size distribution of the products of the metal structure, a constant value or less fine grains and coarse grains It has been found out that the present invention can be achieved by appropriately controlling the number ratio of and by forming a film containing forsterite as a main component containing appropriate amounts of Al, Ti and B on the surface of the steel sheet. . That is, the gist of the present invention is as follows.

[0011] Si: 1.5 to 7.0 wt% and Mn: 0.03 to
It contains 2.5 wt%, and the contents of C, S and N are respectively C: 0.003 wt% or less, S: 0.002 wt% or less, and N: 0.
An electromagnetic steel sheet adjusted to 002 wt% or less, wherein the number ratio of the crystal grains penetrating in the thickness direction of the steel sheet in the in-plane direction of the steel sheet is less than 1 mm: 25 to 98%, and 4 mm or more and less than 7 mm: 45 % Or less and 7 mm or more: 10% or less. The steel sheet has a forsterite coating on the surface thereof, in which Al, Ti and B contain Al: 0.5 to 15 wt%, Ti: 0.1 to 10 wt% and B: A grain-oriented electrical steel sheet that is excellent in iron loss characteristics in a low magnetic field as compared with a high magnetic field, characterized by containing 0.01 to 0.8 wt% (first invention).

Si: 1.5 to 7.0 wt%, Mn: 0.03 to 2.5
wt% and Sb: 0.0010 to 0.080 wt%, and the contents of C, S and N are C: 0.003 wt% or less, and S: 0.
An electromagnetic steel sheet adjusted to 002 wt% or less and N: 0.002 wt% or less, wherein the number ratio of the crystal grains penetrating in the thickness direction of the steel sheet in the in-plane direction of the steel sheet is less than 1 mm: 25 to 98%. ,
4 mm or more and less than 7 mm: 45% or less and 7 mm or more: 10% or less. The steel sheet has a forsterite coating on the surface thereof, and Al, Ti and B are respectively contained in the coating.
A grain-oriented electrical steel sheet comprising 15 wt%, 0.1 to 10 wt% of Ti and 0.01 to 0.8 wt% of B and having excellent iron loss characteristics in a low magnetic field compared to a high magnetic field (second invention).

[0013] C: 0.005 to 0.070 wt%, Si: 1.5 to 7.0 wt%, Mn: 0.03 to 2.5 wt%, Al: 0.005 to 0.017 wt%, and N: 0.0030 to 0.0100 wt%, and Ti, Nb , B or Sb, one or more selected from the group consisting of Ti: 0.0005 to 0.0020 wt% Nb: 0.0010 to 0.010 wt% B: 0.0001 to 0.0020 wt% and Sb: 0.0010 to 0.080 wt% Into a silicon steel slab and heat it to a temperature of 1250 ° C or less using the slab as a raw material, or perform hot rolling directly or finish rolling in a temperature range of 800 to 970 ° C Then, it is rapidly cooled at a cooling rate of 10 ° C./s or more, wound around a coil at a temperature of 670 ° C. or less, and then heated at a rate of 5 to 25 ° C./s to 800 to 95 ° C.
After performing hot-rolled sheet annealing at a temperature range of 0 ° C. for 100 seconds or less, cold rolling at a reduction ratio of 80 to 95% by a tandem rolling mill, first recrystallization annealing, and Ti compound: 20wt
% And B: 0.04 to 1.0 are coated with the annealing separator containing wt%, the final annealing of heating and holding in an atmosphere containing of H ₂ from the raised middle of at least 850 ° C. above the temperature A method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics in a low magnetic field compared to a high magnetic field, characterized by being applied (third invention).

C: 0.005 to 0.070 wt%, Si: 1.5 to 7.0 wt%, Mn: 0.03 to 2.5 wt%, Al: 0.005 to 0.017 wt%, and N: 0.0030 to 0.0100 wt%, and Ti, Nb , B or Sb, each containing Ti: 0.0005 to 0.0020 wt% Nb: 0.0010 to 0.010 wt% B: 0.0001 to 0.0020 wt% and Sb: 0.0010 to 0.080 wt%, Further, a molten steel containing one or two types of Cr or Sn at Cr: 0.0010 to 0.30 wt% and Sn: 0.0010 to 0.30 wt% is cast into a silicon steel slab. After hot-rolling by heating to a temperature or direct hot-rolling and finishing finish rolling in the temperature range of 800 to 970 ° C, quenching at a cooling rate of 10 ° C / s or more and temperature of 670 ° C or less At a temperature rise rate of 5 to 25 ° C./s to 800 to 95
After performing hot-rolled sheet annealing at a temperature range of 0 ° C. for 100 seconds or less, cold rolling at a reduction ratio of 80 to 95% by a tandem rolling mill, first recrystallization annealing, and Ti compound: 20wt
% And B: 0.04 to 1.0 are coated with the annealing separator containing wt%, the final annealing of heating and holding in an atmosphere containing of H ₂ from the raised middle of at least 850 ° C. above the temperature A method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics in a low magnetic field as compared to a high magnetic field, characterized by being performed (fourth invention).

The method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics in a low magnetic field compared to a high magnetic field according to the third or fourth invention, wherein electromagnetic stirring is performed during casting (fifth invention).

Here, the Ti compound contained in the annealing separator
What is TiO_Two, TiS, MgTiO_ThreeMeans compounds containing Ti
As B, the state of solid solution in MgO, nMgO
 B_TwoO _ThreeIn addition to the state of MgO in compounds such as
It may be contained as an additive in the annealing separator.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an experimental example which led to the present invention will be described below.

As a preliminary experiment, a good index for material evaluation of iron loss of an actual small generator and an iron core of an EI core was examined. As shown in Table 1, deterioration of iron loss in a high magnetic field was allowed and low magnetic field was evaluated. Good iron loss at
_10/50 (Iron loss at a magnetic flux density of 1.0 T: W / kg) / W
It was found that the value of _17/50 and the characteristics of the actual machine had a good correlation.

[0019]

[Table 1]

The reason for this is that, in the case of the actual machine, the distribution of the magnetic flux flowing in the steel sheet is non-uniform, so that the iron loss in a low magnetic field is more important. It is considered that the flow is improved in a direction to make the flow more uniform, and as a result, the iron loss of the actual machine is reduced. Further, when the materials a and b showing good actual machine characteristics were examined in Table 1, it was found that the crystal structure was fine.

Here, although there is a knowledge that a smaller crystal grain size is more advantageous for reducing iron loss than in the past, as described above, all of the materials up to now have a high iron loss W under a high magnetic field.
A study on the reduction of _17/50, no study from the viewpoint of improving the actual characteristics of the compact electric apparatus such like to reduce the iron loss of such EI core, in particular, iron loss W _{17
/ 50} acceptable iron loss W an increase of _10/50 and W _10/50 / W _17/50
From the viewpoint of reducing the value of, there has been no study on what size and distribution the crystal grain size should be controlled, and the appropriate distribution of the crystal grain size for that purpose has not been clarified.

On the basis of the results of the preliminary experiments, the iron loss in the product, the crystal grain size distribution of the steel sheet to reduce the values of W _10/50 and W _10/50 / W _17/50 , the production conditions thereof, etc. Various experiments and studies were performed.

Experiment 1 (Study of Al content, hot rolling conditions and hot rolled sheet annealing conditions) Ten slabs having the component composition of steel symbol I shown in Table 2 were used.
A hot-rolled sheet coil having a thickness of 2.4 mm was hot-rolled under the conditions of the symbols a to j shown in Table 3 and the slab having the component composition of the steel symbol III in Table 2 was used as a conventional manufacturing method. Symbol h
Hot-rolled under the conditions shown in (1) to obtain a hot-rolled sheet coil having a sheet thickness of 2.4 mm.

[0024]

[Table 2]

[0025]

[Table 3]

The cooling from the end of the hot rolling to the winding of the coil was all quenched at a cooling rate of 25.3 to 28.6 ° C./s.

Thereafter, all of these coils are divided into two parts.
One is annealed at 900 ° C for 60 seconds and the other is annealed at 1050 ° C for 60 seconds, pickled, and pickled by a tandem rolling mill.
After hot rolling to a thickness of 0.34 mm at a temperature of ℃, degreasing is performed
After decarburizing annealing at 850 ° C. for 2 minutes, applying an annealing separator containing 5% of TiO ₂ in MgO containing 0.1% of B, and applying N ₂ alone to a temperature of 600 ° C. when the temperature is raised. Atmosphere, followed by a mixed atmosphere of N ₂ : 25% and H ₂ : 75% up to a temperature of 1050 ° C., and thereafter, a final finish annealing in which the temperature is raised to a temperature of 1200 ° C. in an atmosphere of H ₂ alone and held for 5 hours. After the application, the unreacted annealing separator was removed.

Then, these steel sheets were coated with an insulating coating mainly composed of magnesium phosphate containing 40% of colloidal silica and baked at a temperature of 800 ° C. to obtain respective products.

Thereafter, each steel sheet from which the above-mentioned unreacted annealing separator was removed was macro-etched to measure the crystal grain size distribution, and a test piece of Epstein size was cut out from each product along the rolling direction at 800 ° C. After _performing strain relief annealing for 3 hours at the above temperature, iron losses W _10/50 and W _17/50 and magnetic flux density B ₈ at magnetic flux densities of 1.0 T and 1.7 T, respectively, were measured. In addition, EI from each product
After punching out a core for core and performing strain relief annealing, EI cores were manufactured by stacking, copper wire winding, etc., and the iron loss characteristics of these EI cores were also investigated. Table 4 summarizes the results of these investigations.

[0030]

[Table 4]

As shown in Table 4, the slab having the component composition of the conventional example (steel symbol III) was used as a material, and the hot rolling conditions (symbol h) of the conventional example were used.
(The grain size distribution does not change even if the product is produced by baking the insulating coating after finish annealing.) The number ratio of coarse grains with a grain size of 7 mm or more is large and the magnetic flux density Although B ₈ is also 1.96T and high product, looking at the iron loss characteristics, iron loss W at a high magnetic field _17/50
Is extremely small, whereas the iron loss W _10/50 in a low magnetic field is relatively large. Therefore, the value of W _10/50 / W _17/50 is large and the iron loss in a low magnetic field is excellent. Absent.

On the other hand, a slab (steel symbol I) of a component composition suitable for the present invention containing a small amount of Nb and having a low Al content was used as a raw material, and the slab heating temperature: 1200 ° C. or less, : 950 ° C or lower (800 ° C or higher), hot rolled sheet annealing temperature: 900 ° C (products marked as good in the remarks column in Table 4) have large iron loss at high magnetic field, but low magnetic field , The value of W _10/50 / W _17/50 is also small, and the iron loss as an EI core is extremely good. The feature of the crystal structure of these products is that the crystal grain size is smaller than that of the conventional production method, and it can be seen that the number ratio of the fine grains of less than 4 mm, especially less than 1 mm is large.

As a result of conducting experiments and studies on this point,
It has been found that the number ratio of crystal grains having a particle size of less than 1 mm needs to be 25% or more. However, the excessive presence of such fine grains greatly deteriorates the magnetic properties, and W _10/50
It was also found that the value itself deteriorated. By the way, using steel (steel symbol I) conforming to the present invention in Table 4 as a raw material, the hot rolling end temperature was too low or too high,
Or 98% of fine crystal grains with a grain size of less than 1 mm in products manufactured under conditions where the hot-rolled sheet annealing temperature is too high
W _10/50 and W _10/50 / W _17/50
Is remarkably deteriorated, and the iron loss characteristics of the EI core are inferior. Therefore, it is necessary to control the number ratio of crystal grains having a grain size of less than 1 mm to 25 to 98%.

Further, it is important to make the crystal grains having a grain size of 1 mm or more as small as possible. It is important to control the appearance of coarse crystal grains and to control the crystal grain size distribution within an appropriate range. I found it.

Next, various studies will be made on the reason why good iron loss characteristics in a low magnetic field were obtained by increasing the number ratio of fine crystal grains and optimizing the crystal grain size distribution as described above. added.

First, the method of depositing AlN as an inhibitor is novel, and AlN can be dispersed very finely and uniformly. Thus, it is considered that secondary recrystallization could be stably performed while crystal grains of less than 1 mm existed.

The conventional method of depositing AlN is as follows.
As disclosed in JP-B-46-23820, AlN is made into a solid solution state in hot-rolled sheet annealing, reprecipitated in the cooling process of hot-rolled sheet annealing, and the cooling rate at that time is controlled. This is a method to control the size of AlN precipitate. On the other hand, the AlN precipitation method that obtained good results in this experiment is a novel method that keeps AlN in a solid solution state until hot rolling and precipitates AlN during the heating process of hot-rolled sheet annealing. .

In this method, in order to precipitate AlN finely, the solubility content of AlN is reduced, so that the Al content is made lower than the conventional preferable value, the precipitation temperature of AlN is lowered, and hot rolling is performed. Precipitation in the process is difficult, hot rolling end temperature is 800 ℃ or more, hot rolled coil winding temperature
It is necessary to set the temperature to 670 ° C. or lower to suppress the precipitation of AlN in the hot rolling step. The necessity of keeping the coil winding temperature low is to suppress supersaturated AlN from being precipitated when the winding temperature is high.

Further, the supersaturated Al after hot rolling
In order to suppress the precipitation of N, the cooling rate between the end of hot rolling and coil winding must be high, and for this purpose, a cooling rate of 10 ° C./s or more is required. It turned out to be.

As for hot-rolled sheet annealing, conventional high-temperature annealing at a temperature of 1150 ° C., which aims at solid solution of AlN, is extremely harmful. In order to suppress the Ostwald ripening of AlN, the annealing temperature was 950 ° C or less, which was extremely low which was completely unsuitable in the past.

The second innovative technique is to improve the primary recrystallization structure to obtain a suitable secondary recrystallization. Conventionally, it is known that it is advantageous that the size of the primary recrystallized grains consumed by the silkworm is uniform and small for rapid growth of the secondary recrystallized grains. Further, the cause of the increase in the size of the primary recrystallized grains and the increase in the non-uniformity are also caused by the coarsening of the crystal grains of the steel material before hot rolling or cold pressing. It is well known. However, before hot rolling, it is necessary to perform high-temperature slab heating in order to form a solid solution of the inhibitor, and accordingly, the crystal grain size of the steel material before hot rolling naturally increases. For this reason, when the inhibitory effect on the grain growth of the inhibitor is weak, the primary recrystallized grain size naturally increases, for example, as disclosed in Japanese Patent Application Laid-Open No. HEI 6-172861 (a unidirectional electrical steel sheet having a large thickness and excellent magnetic properties). ), The primary recrystallized grain size is as coarse as 18 to 35 μm.

From this point, the conditions under which good iron loss characteristics in a low magnetic field were obtained in the above experiment were set to a low slab heating temperature of about 1200 ° C. and a low temperature hot rolled sheet annealing condition of about 900 ° C. As described above, these are excellent conditions for suppressing the growth of crystal grains of the steel material before hot rolling and before cold rolling and for obtaining a fine and uniform primary recrystallized structure. Technology.

Further, from the viewpoint of not enlarging the crystal grains of the steel material before hot rolling, it is more effective that the steel casting structure is fine. For example, the molten metal being cast is subjected to electromagnetic stirring to form a columnar shape. The effect of the method for suppressing the development of crystals is enormous. In addition, a method of directly rolling a slab without heating is also preferable from this viewpoint.

Experiment 2 (Effect of AlN precipitation nucleation component and effect of heating rate of hot-rolled sheet) Experiments and examinations were performed on fine precipitation of AlN in the heating process of hot-rolled sheet annealing. Six slabs having the composition of steel symbol XI shown in Table 2 above and one slab having the composition of steel symbol V were hot-rolled under the conditions shown in symbol b of Table 3 above. : A hot-rolled coil of 2.4 mm was used. At this time, the cooling rate from the end of hot rolling to the time of coil winding was 26.5 ° C./s.

These hot-rolled sheets were annealed at 900 ° C. for 60 seconds. At this time, the hot-rolled sheets using the slabs of steel symbol XI were 2.5, 3.7, 5.4, 12.7, 23 and 28 ℃
/ S, and the heating rate was changed, and the hot-rolled sheet using the slab of steel symbol V was set at a heating rate of 12.2 ° C./s.

Thereafter, these annealed sheets were pickled, and the sheet thickness was 0.34 mm in a temperature range of 100 to 160 ° C. by a tandem rolling mill.
After warm-rolling, a degreasing treatment is performed, and after decarburizing annealing at 850 ° C. for 2 minutes, 7% T in MgO containing 0.05% B
After applying the annealing separator with iO ₂ added,
° C. to a temperature N ₂ alone atmosphere, then, to a temperature of _{850 ℃ N 2: 25%,} H 2: 75% of the mixed atmosphere, thereafter H
₍₂ ) After performing a final finish annealing in which the temperature was raised to a temperature of 1180 ° C. in a single atmosphere and maintained for 5 hours, an unreacted annealing separator was removed.

Further, these steel sheets were coated with an insulating coating mainly composed of magnesium phosphate containing 40% of colloidal silica, and baked at a temperature of 800 ° C. to obtain respective products.

Thereafter, in the same manner as in Experiment 1, the crystal grain size distribution of each steel sheet after removing the unreacted annealing separating agent, the magnetic properties of each product, and the iron loss of the EI core manufactured using each product, etc. Each was investigated. Table 5 summarizes the results of these investigations.

[0049]

[Table 5]

From Table 5, it can be seen that slabs in which Ti, Nb, B, Sb, etc. do not conform to the present invention as a component composition (steel symbol V)
The materials and the products plate particle size is the number ratio of less fine grain 1mm greater than 98%, and the magnetic flux density B ₈ also 1.68
T is low, and iron loss at low magnetic field and high magnetic field is generally poor.

On the other hand, in the case of a product made of a slab (steel symbol XI) containing a small amount of B and conforming to the present invention, the rate of temperature rise in hot-rolled sheet annealing is in the range of 5 to 25 ° C./s. In this case, excellent iron loss in a low magnetic field and excellent iron loss in an EI core are obtained. When the heating rate is out of the above range, the number ratio of the fine crystal grains having a particle size of less than 1 mm is also increased to more than 98%, and iron loss in a low magnetic field is inferior. Therefore, conditions under which good low magnetic field characteristics can be obtained include:
It is necessary that the number ratio of crystal grains having a particle size of less than 1 mm be within a certain range.

As a result of investigating the cause of obtaining such a result, it was found that there was a large difference in the distribution of precipitated AlN after the temperature was raised in hot-rolled sheet annealing. In other words, extremely fine precipitates of 1.0 to 5.0 nm existed in high density at a high density immediately after the temperature was raised in hot-rolled sheet annealing under the conditions (including the material) where good magnetic properties and crystal grain distribution were obtained. On the other hand, when the steel symbol V is used as the material or when the heating rate is as fast as 28 ° C / s,
Insufficient amount of N was deposited and the rate of temperature rise was 2.5 ° C / s or 3.
For the slower one at 7 ° C / s, the precipitated AlN was coarse, 5.0 to 20 nm. It is considered that such a difference in the precipitation state of the inhibitor affected the secondary recrystallization and changed the crystal structure of the product.

Therefore, in order to control the precipitation of AlN in a fine and high-density state during the heating process of hot-rolled sheet annealing, it is important to control the heating rate, and if this rate is too slow, AlN precipitates coarsely. Conversely, if the speed is too high, the amount of AlN precipitated will be insufficient.

For controlling the precipitation of AlN, not only the control of the heating rate but also the trace components in the base steel and the hot rolling temperature are important. That is, it was found that the presence of Ti, Nb, B and Sb increased the precipitation nuclei of AlN. Among these, for Ti, Nb and B, extremely fine precipitates are formed in the hot finish rolling, and these precipitates are used as nuclei for precipitation, and AlN precipitates during the heating process of hot-rolled sheet annealing. In addition, the segregation of Sb at the crystal grain boundaries suppresses the coarse precipitation of AlN at the crystal grain boundaries and increases the substantial concentration of solid solution Al and solid solution N in the crystal grains to increase the frequency of formation of AlN precipitate nuclei. I understood that.

For this purpose, the hot rolling end temperature is set to 970 ° C.
It is necessary to: When the hot-rolling end temperature is high, even these ultrafine precipitates serving as precipitation nuclei for AlN do not precipitate, and uniform fine precipitation of AlN during the heating process of hot-rolled sheet annealing becomes impossible.

As described above, the inhibitor precipitation control according to the present invention includes: 1) a decrease in the AlN precipitation temperature due to a low Al content and a corresponding decrease in the slab heating temperature; Generation of precipitation nuclei by lowering the finish rolling temperature (upper limit of hot rolling end temperature) 3) Lower limit of hot rolling end temperature, lower limit of cooling rate from end of hot rolling to coil winding And control of AlN precipitation in hot rolling by controlling the upper limit of coil winding temperature. 4) Control of Al during precipitation by controlling the heating rate of hot-rolled sheet annealing.
Unprecedented technological ideas and means, such as fine and uniform precipitation of N, 5) suppression of coarsening of crystal grains due to re-dissolution of AlN and Ostwald ripening by the upper limit of the annealing temperature of the hot-rolled sheet. Become.

Experiment 3 (Examination of Cold Rolling Method) An experiment which is the basis of the cold rolling technique for obtaining good results will be described. Four slabs having the component composition of steel symbol VIII shown in Table 2 above were hot-rolled under the conditions of symbol b shown in Table 3 above to obtain hot-rolled sheet coils each having a thickness of 2.4 mm. At this time, the cooling rate from the end of hot rolling to the time of coil winding was 17.5 ° C./s. These hot rolled sheets were annealed at 900 ° C. for 30 seconds at a heating rate of 7.8 ° C./s, pickled, and then cold rolled to a sheet thickness of 0.34 mm.

At this time, the first annealed plate is subjected to warm rolling in a temperature range of 120 to 180 ° C. by a tandem rolling mill, and the second annealed plate is coated with a large amount of coolant on the surface of the material to be rolled by a tandem rolling mill. Injecting and rolling at a steel sheet temperature in the range of 50 to 80 ° C., the third annealed sheet is subjected to aging treatment in a temperature range of 150 to 220 ° C. between rolling passes by a reverse type rolling mill and rolled, The fourth annealed sheet was rolled at a steel sheet temperature in the range of 50 to 80 ° C. by injecting a large amount of coolant onto the surface of the material to be rolled by a reverse rolling mill.

Thereafter, each cold-rolled sheet is subjected to a degreasing treatment,
Decarburization treatment for 2 minutes, MgO containing 0.05% B
7% TiO_TwoOf annealed separating agent added to steel sheet surface
From the temperature up to 700 ° C_TwoA single atmosphere, that
After that, N until the temperature of 850 ℃ _Two: 25%, H_Two: 75% blend
Atmosphere, H_TwoTemperature rises to 1180 ° C in a single atmosphere
After performing the final finish annealing that holds for 5 hours after warming,
Each unreacted annealing separator was removed.

Further, an insulating coating containing 60% of colloidal silica and containing magnesium phosphate as a main component was applied to these steel sheets and baked at a temperature of 800 ° C. to obtain respective products. Thereafter, in the same manner as in Experiment 1, the crystal grain size distribution of each steel sheet after the removal of the unreacted annealing separator, the magnetic properties of each product, and the iron loss of the EI core made using each product were investigated. . Table 6 shows the results of these surveys.
Are shown together.

[0061]

[Table 6]

[0062] As shown in Table 6, compared with the case of using a reverse rolling mill, when rolled with a tandem mill, downfield iron loss W _10/50, iron loss of the high magnetic field and low magnetic field Ratio W
_10/50 / W _17/50 and good core loss in EI core, especially 50-200 when warm rolling in the temperature range of 120-180 ° C.
_W10 / ₅₀ is slightly higher than when rolled in a temperature range of 80 ° C, but the value of _W10 / ₅₀ / _W17 / ₅₀ is small and excellent in iron loss of the EI core. The diameter distribution is also appropriate.

In general, the aging treatment in the warm rolling or the rolling step has a function of changing the rolling deformation texture of the crystal, and becomes the core of the secondary recrystallization in the primary recrystallization structure after the rolling recrystallization (110). It is known to increase the generation density of [001] crystal grains. For this purpose, Japanese Patent Publication No. 54-13
As disclosed in Japanese Patent Publication No. 846 (cold rolling method for obtaining a high magnetic flux density unidirectional silicon steel sheet having excellent characteristics), conventionally, aging treatment between rolling passes by a reverse type rolling mill such as a Zenjima mill is conventionally performed. Thus, it was considered appropriate to promote the diffusion of C.

However, as shown in the experimental results, the aging treatment between the passes by the reverse rolling was not effective, and the rolling by the tandem rolling mill was effective. Considering the difference between these two, in the inter-pass aging treatment by reverse rolling, the strain rate during rolling is relatively low, and there is enough time between the rolling passes and the heat generated due to processing strain during that In contrast to static aging due to the diffusion phenomenon of C to dislocations, in tandem rolling, the strain rate during rolling is relatively large, and the time between rolling passes is extremely short, so that static aging is unlikely to occur. During the pass, while the dislocations are being propagated, dynamic strain aging due to the diffusion of C into the dislocations occurs simultaneously.

The experimental results show that the tandem rolling method is superior to the reverse rolling method, that the warm rolling in tandem rolling is superior to the constant rolling method, and that the aging treatment between passes is harmful in the reverse rolling method. Is shown. Thus, high strain rates and dynamic strain aging are effective, whereas static aging has a detrimental effect.

From the above, it can be said that the tandem method is the most excellent as the final cold rolling method of the present invention. Furthermore, in order to further improve the effect of dynamic strain aging, the rolling temperature in the tandem rolling method is preferably set to 90 ° C. or higher.

Experiment 4 (Study of Appropriate Forsterite Coating) An experiment on the coating of the present invention will be described. Table 2 above
9 were subjected to hot rolling under the conditions of the symbol b shown in Table 3 above to obtain a hot-rolled sheet coil having a sheet thickness of 2.4 mm. At this time, the cooling rate from the end of hot rolling to the time of coil winding was 14.5 ° C./s.

These hot-rolled sheets were annealed at 900 ° C. for 30 seconds at a heating rate of 6.5 ° C./s. After pickling, the sheet thickness was adjusted by a tandem rolling mill in a temperature range of 120 to 160 ° C .: 0.34
After being warm-rolled to a diameter of 0.5 mm, each was subjected to a degreasing treatment and a decarburization treatment at 850 ° C. for 2 minutes.

Thereafter, these decarburized steel sheets were coated with annealing separators having different compositions as shown in Table 7, and then heated in the atmosphere shown in Table 7 to a temperature of 1180 ° C. at a rate of 30 ° C./s. After the final annealing was performed in a heat pattern in which the temperature was lowered after holding for 7 hours, the unreacted annealing separator was removed.

[0070]

[Table 7]

At this time, on the surface of the steel sheet, SiO ₂ formed on the surface layer of the steel sheet during the decarburizing annealing and MgO, which is a main component of the annealing separating agent, were added.
Reacts at the time of final finish annealing to forsterite (Mg ₂ Si
Although the coating mainly composed of O ₄ ) was formed, the contents of B, Ti and Al in the coatings of these steel sheets were measured.

Each steel sheet after the unreacted annealing separation removal was further 60
% Of colloidal silica, and an insulating coating containing magnesium phosphate as a main component was applied and baked at a temperature of 800 ° C. to obtain respective products.

Thereafter, in the same manner as in Experiment 1, the crystal grain size distribution of each steel sheet after the removal of the unreacted annealing separator, the magnetic properties of each product sheet, and the iron loss of the EI core produced using each product sheet. And so on. Table 8 summarizes the results of these investigations.

[0074]

[Table 8]

As shown in Table 8, the crystal grain size distributions were all within the proper range of the present invention, but the iron loss characteristics under a low magnetic field were clearly determined by the contents of Al, Ti and B in the coating. The higher the content, the better the iron loss characteristics. The contents of Al, Ti and B in the coating vary depending on their contents in the annealing separator and the final finish annealing atmosphere conditions.

As described above, the reason why the iron loss in a low magnetic field is improved by the increase of these components in the coating film is probably that such components exist in the form of nitrides and oxides, and the coating film as a whole It is considered that this is because the thermal expansion coefficient is reduced, and as a result, the tension effect is improved.

The nitrogen atmosphere in the final annealing plays an important role in the formation of oxides and nitrides in the coating, and it is important to enhance the reducibility especially in the middle to late stages of annealing. .

That is, by containing H ₂ having a strong reducing property in the atmosphere, the decomposition of nitrides in steel can be promoted and the Al content in the coating can be increased. It promotes and can increase the amount of Ti and B in the coating. Incidentally, even if Al is not particularly added to the annealing separator, since Al transfers from the steel, the final finish annealing atmosphere is controlled as in the present invention to promote the transfer of Al into the coating, and It suffices if Al that migrates into the unreacted annealing separator can be suppressed.

It has also been found that the components contained in the steel have an important effect in the cooling process of the final finishing performed in the N ₂ atmosphere, the baking annealing of the insulating coating and the strain relief annealing. That is, there is an advantage that the adverse effect of the nitriding of the steel due to the annealing in the N ₂ atmosphere can be suppressed by Ti, B and Sb present in the steel. Ti and B are concentrated at the coating interface in contact with the base iron and generate BN and TiN to suppress the penetration of N into steel (base iron) and increase the coating strength. Sb is concentrated at the interface between the coating and the base iron. Has the effect of suppressing nitriding.

As described above, the components such as Ti, B and Sb present in the steel have an advantageous effect not only in the annealing during the manufacturing process but also in the strain relief annealing of the product, thereby strengthening the coating film and reducing the strength of the ground iron. It has been clarified by examining the experimental results that they function effectively in suppressing nitriding and contribute to reducing the low-field iron loss of products.

The results obtained from Experiments 1 to 4 are shown in FIGS.
3 collectively. FIG. 1 shows the number ratio of crystal grains having a grain size of less than 1 mm, the iron loss of the EI core, and the iron loss ratio W _10/50 / of the product.
It is a graph which shows the relationship with _{W17 / 50} . As is apparent from this figure, the number ratio of crystal grains having a particle size of less than 1 mm is 25 to 98.
%, Good values are obtained.

FIG. 2 is a graph showing the relationship between the number ratio of crystal grains of 4 mm or more and less than 7 mm, the number ratio of crystal grains of 7 mm or more, and the iron loss of the EI core. As is clear from this figure, when the number ratio of the crystal grains of 4 to 7 mm exceeds 45%, and when the number ratio of the crystal grains of 7 mm or more exceeds 10%, good iron loss in the EI core is obtained. There is no possibility.

FIG. 3 shows, among products of various experiments,
4 is a graph showing the relationship between the Al, Ti, and B contents in the forsterite coating and the iron loss of the EI core when the crystal grain size distribution is within the scope of the present invention. As is clear from this figure, excellent iron loss in the EI core is obtained only when all of the contents of Al, Ti and B satisfy the constituent requirements of the present invention.

The present invention has been completed as a result of intensive studies based on the experiments and investigations described above.

Next, essential conditions and preferable conditions for obtaining the effects of the present invention and their operations will be described. First, the constituent requirements of the grain-oriented electrical steel sheet of the present invention, which is more excellent in iron loss characteristics in a low magnetic field than in a high magnetic field, will be described.

The grain-oriented electrical steel sheet of the present invention contains the following components as essential and preferred components.

Si: 1.5 to 7.0 wt% (hereinafter simply expressed as%) Si is an effective component for increasing the electric resistance of the product and reducing iron loss. For this purpose, 1.5% or more is contained.
%, The hardness becomes high and production and processing become difficult. Therefore, its content is more than 1.5%, 7.0
% Or less.

Mn: 0.3-2.5% Mn has the effect of increasing the electric resistance like Si, and
Has the effect of facilitating hot working during manufacturing. To do this
The content must be 0.03% or more. However, if the content exceeds 2.5%, γ transformation is induced at the time of heat treatment to deteriorate magnetic properties. Therefore, the content is set to 0.03% or more and 2.5% or less.

As impurities, C is 0.003% or less, more preferably 0.001% or less, and both S and N are 0.002% or less.
%, More preferably 0.001% or less. If these impurities exceed this value, they have a detrimental effect on magnetic properties, and particularly deteriorate iron loss.

In addition to these components, the following components can be contained as required. That is, B, Sb, Ge, P, Sn, C added to steel as an inhibitor component
Components such as u, Cr, Pb, Zn, and In, and Mo, Ni, and Co added to the steel to improve the structure are added to promote the secondary recrystallization favorably. It remains in the product afterwards. Furthermore, the inclusion of a trace amount of components such as Ti and B generates nitrides and oxides at the interface between the coating and the base iron, which is advantageous in the magnetic properties in a low magnetic field.

[0091] Here, the content of Sb is particularly preferable since it has an effect of suppressing the nitriding of ground iron during strain relief annealing and the like. For this purpose, it is essential that the content be 0.0010% or more. %, The toughness of the steel sheet deteriorates and processing becomes difficult, so the content is 0.0010 to 0.080%.
A range of% is appropriate.

The surface of such a grain-oriented electrical steel sheet is used in the presence of an insulator, and an insulating coating mainly composed of forsterite (Mg ₂ SiO ₄ ) formed at the time of final finish annealing is used. An overcoat may further be applied over the insulating coating.

Further, controlling a trace component in the forsterite coating is one of the essential components of the present invention. That is, it is necessary to include Al, Ti and B in the coating. By including these components, the tension effect of the coating film is enhanced, and the iron loss in the low magnetic field region of the product is improved. In order to obtain this effect, Al: 0.
It is necessary to contain 5% or more, Ti: 0.1% or more and B: 0.01% or more. However, excessive contents of Al: more than 15%, Ti: more than 10% and B: more than 0.8% are not suitable because they excessively increase the hardness of the coating and conversely deteriorate the adhesion of the coating. Therefore, it is necessary to contain Al in the range of 0.5 to 15%, Ti: 0.1 to 10% and B: 0.01 to 0.8% in the coating.

Here, a method for measuring the concentration of these components in the coating will be described. With only the forsterite coating on the steel sheet surface, the oxygen content (fO), Al
After analyzing the content (fAl), Ti content (fTi) and B content (fB), the forsterite film was removed by pickling, and then the oxygen content (sO) and Al content of the steel sheet were again measured. The amount (sAl), Ti content (sTi) and B content (sB) are analyzed. Thus, the amount of forsterite coating is almost
f = (fO-sO) × Mg 2 SiO 4 ÷ 0 4 = (fO-sO) × 140.6 ÷ 64
The Al content in the coating is (fAl-sAl) ÷ f × 100 (%) The Ti content in the coating is (fTi-sTi) ÷ f × 100 (%) The B content in the coating The amount can be calculated as (fB-sB) ÷ f × 100 (%).

[0095] Next, each essential requirement for crystal grains constituting the grain-oriented electrical steel sheet of the present invention and its operation will be described.

[0096] In the grain-oriented electrical steel sheet of the present invention, the target crystal grains are those penetrating in the thickness direction. The grain size of a crystal grain is represented by the diameter of a circle having the same area as the area of the crystal grain on the steel sheet surface (equivalent circle diameter), and the average grain size is the number of crystal grains contained in a certain area. The area is divided, and the equivalent circle diameter of this value is defined as the average crystal grain size.

The number ratio of the crystal grains having a crystal grain size of less than 1 mm in the in-plane direction of the steel sheet is 25 to 98%,
As described above, the number ratio of crystal grains of less than 7 mm
It is necessary that the number ratio of crystal grains of not less than mm is 10% or less.

Crystal grains of 7 mm or more have an effect of increasing iron loss in a low magnetic field as compared with a high magnetic field. In order to improve the characteristics of an actual machine, the number ratio is suppressed to 10% or less. 7
It is essential that the number ratio of crystal grains having a size less than mm be suppressed to 45% or less. Increasing the number ratio of crystal grains of less than 4 mm, particularly the number ratio of crystal grains of less than 1 mm, is extremely effective in improving iron loss in a low magnetic field, and the number ratio of crystal grains of less than 1 mm is 25% or more. However, if it exceeds 98%, the iron loss in a low magnetic field increases and the characteristics of actual equipment deteriorate, so the upper limit is made 98%.

In order to increase the iron loss in a high magnetic field and to reduce the iron loss in a low magnetic field to improve the characteristics of the actual device, it is important to make the crystal grain size extremely small and keep it within a certain range. Therefore, it is an essential technique to increase the crystal grains of less than 4 mm, especially the crystal grains of less than 1 mm.

By controlling the content of Al, Ti and B in the coating film together with the control of the crystal grains, it is possible to obtain a product having excellent iron loss characteristics in a low magnetic field as compared with a high magnetic field. Become.

Next, the limiting conditions, the preferable conditions, and the reasons thereof will be described as constituent components of the method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics in a low magnetic field compared to a high magnetic field according to the present invention. First, the component composition of the material will be described.

C: 0.005 to 0.070% It is a feature of the present invention that the content of C is set to 0.070% or less. That is, if it exceeds 0.070%, the amount of γ transformation becomes excessive, the distribution of Al during hot rolling becomes non-uniform, and the distribution of AlN precipitated during the heating process of hot-rolled sheet becomes non-uniform. High magnetic properties cannot be obtained. On the other hand, if the content is less than 0.005%, the effect of improving the structure cannot be obtained, and the secondary recrystallization becomes incomplete, and the magnetic characteristics also deteriorate. Therefore, its content is limited to the range of 0.005 to 0.070%.

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

Mn: 0.03 to 2.5% Mn is a necessary component for increasing electric resistance and improving hot workability at the time of manufacturing like Si. For this purpose, it is necessary to contain 0.03% or more, but 2.5%
If contained in excess of, the γ transformation is induced and the magnetic properties are degraded, so the content should be in the range of 0.03 to 2.5%.

In addition to these components, an inhibitor component for inducing good secondary recrystallization is required to be contained in the steel material, and it is essential to contain Al and N.

Al: 0.005 to 0.017%, N: 0.0030 to 0.01
If the content of 00% Al is less than 0.005%, the amount of AlN precipitated during the heating process of hot-rolled sheet annealing becomes insufficient. On the other hand, if the content exceeds 0.017%, the slab temperature becomes lower at around 1200 ° C.
Since the solid solution of lN becomes difficult and the solid solution temperature of AlN rises, AlN precipitates in the hot rolling step, and during the hot-rolled sheet annealing, which is one of the features of the present invention, the temperature rise process. The fine precipitation of AlN becomes impossible, and good iron loss characteristics in a low magnetic field cannot be obtained. In addition, if slab heating is performed at a high temperature around 1400 ° C to eliminate this defect, the crystal grain size of the product is coarsened, resulting in a reduction in iron loss in a high magnetic field and an increase in iron loss in a low magnetic field. And the iron loss in the actual machine deteriorates. Therefore, it is necessary to contain Al in the range of 0.005 to 0.017%.

On the other hand, since N is a component constituting AlN, it is necessary to contain 0.0030% or more. However, if the content exceeds 0.0100%, gasification occurs in the steel, causing defects such as blisters.
The range is ~ 0.0100%. Further, in the present invention, Ti,
It is essential to include one or more selected from Nb, B and Sb.

These components have the effect of forming fine precipitates in hot rolling and increasing the number of AlN precipitate nuclei in the temperature raising process of hot rolling sheet annealing in the next step.
The contents for obtaining such effects are as follows: Ti: 0.0005% or more, Nb: 0.0010% or more, B: 0.0001%
% And Sb: 0.0010 %% or more are required. However, Ti: more than 0.0020%, Nb: more than 0.010%, B: 0.0020%
% And Sb: more than 0.080%, the mechanical properties such as the bend properties of the product deteriorate. Accordingly, the contents of Ti are in the range of 0.0005 to 0.0020%, Nb is in the range of 0.0010 to 0.010%, and B is 0.0001 to 0.0020%, respectively.
% And Sb are in the range of 0.0010 to 0.080%.

The other additive components are not necessarily required to obtain a grain-oriented electrical steel sheet having better iron loss characteristics in a low magnetic field than in a high magnetic field. It is effective to improve the surface properties of these, so that it is preferable to include them, and it is also possible to appropriately add Bi, Te, or the like.

Subsequently, the manufacturing process conditions will be described. Steel that has been adjusted to the above-mentioned composition by a conventional method is usually subjected to slab heating and then hot-rolled into a hot-rolled sheet coil.However, the slab heating temperature can be set to a temperature of 1250 ° C or less. This is an important component of the invention. That is, when slab heating is performed at a high temperature, the ratio of coarse crystal grains of 7 mm or more in the distribution of crystal grains in a product increases, and iron loss in a low magnetic field increases. For this reason, in order to obtain good crystal grain distribution and magnetic properties, the slab heating temperature is 1250 ° C. or less. Furthermore, in recent years, a method of directly performing hot rolling after continuous casting without performing slab heating has been developed, but since this method hardly raises the slab temperature,
As a matter of course, this is a method suitable as a method for manufacturing a grain-oriented electrical steel sheet of the present invention.

In hot rolling, the hot rolling end temperature is set to 8
It is essential that the temperature be in the range of 00 to 970 ° C. When the hot-rolling end temperature is lower than 800 ° C, AlN precipitates in the steel and causes deterioration of the magnetic properties.On the other hand, when the temperature exceeds 970 ° C, nucleation sites for AlN precipitation are formed in the steel. The amount and distribution of precipitates formed become insufficient and the magnetic properties deteriorate.

After the completion of hot rolling, it is necessary to cool at a cooling rate of 10 ° C./s or more. This is because, at a cooling rate of less than 10 ° C./s, AlN precipitates during cooling and the magnetic properties deteriorate. In addition, it is essential to control the coil winding temperature to 670 ° C or less. This is also because if the winding temperature exceeds 670 ° C., AlN precipitates and the magnetic properties deteriorate.

By such control, hot-rolled sheet annealing is performed on the hot-rolled sheet coil in which AlN precipitation during hot rolling is suppressed.
It is an original point of the present invention that the hot-rolled sheet annealing is performed at an extremely low temperature. The suitable conditions for the temperature and time of this hot-rolled sheet annealing are that the holding time is within 100 seconds in the temperature range of 800 to 950 ° C. That is, the hot-rolled sheet annealing temperature is 95
If the temperature exceeds 0 ° C or the annealing time exceeds 100 seconds, the crystal grains of the steel sheet before cold rolling become coarse, and as a result, 1
The secondary recrystallization failure occurs due to an increase in the secondary recrystallized grain size. If the hot-rolled sheet annealing temperature is lower than 800 ° C, the A
Insufficient precipitation of lN.

Further, the point of precipitation of AlN in the process of raising the temperature of the hot-rolled sheet is the most new technology of the present invention. However, it is also essential to control the rate of temperature rise of such annealing within the range of 5 to 25 ° C./s. Is the condition. That is, this means that the temperature rise rate is 5 ° C.
If the rate is less than 25 ° C./s, AlN precipitates coarsely, leading to deterioration of magnetic properties. Conversely, if the rate exceeds 25 ° C./s, the amount of AlN deposited becomes insufficient, and the magnetic properties also deteriorate. .

After hot rolling annealing, the final cold rolled sheet thickness is obtained by one cold rolling. At this time, it is an essential condition to perform cold rolling by a tandem rolling mill.

Here, a tandem rolling mill is a rolling machine that passes between roll pairs and rolls, and is continuously arranged in a rolling direction, and can be continuously rolled with respect to a one-way rolling of a steel sheet. Means

Rolling in such a tandem rolling mill can suppress harmful static aging between rolling passes, increase the strain rate, and obtain a good rolling texture. In other words, the primary recrystallization texture is improved in such a way as to promote the grain growth of the secondary recrystallization, the nucleation and growth of fine crystal grains are promoted, and the crystal grains having a grain size of less than 1 mm in the product are improved. And stable generation of crystal grains having a particle size of 1 to 4 mm. At this time, by increasing the temperature of the steel sheet during rolling, it is possible to cause dynamic strain aging and obtain a more favorable effect. As the rolling temperature for this purpose, the range of 90 to 300 ° C. in the temperature of the steel sheet is appropriate.

In the case of reverse rolling such as a Sendzimer rolling mill, a primary recrystallized structure inevitably accompanied by static aging and inferior in growth of secondary recrystallized grains is formed, and the number of crystal grains less than 1 mm is generated. The ratio is excessively increased, and the iron loss in the product is degraded not only in the high-field iron loss but also in the low-field iron loss, and the iron loss characteristics in the actual machine become poor.

Further, the rolling reduction of the cold rolling is set to 80 to 95.
%. If the rolling reduction is less than 80%,
If the number ratio of crystal grains of less than mm is reduced and the iron loss in the low magnetic field is increased in spite of the reduction in the iron loss in the high magnetic field, the iron loss characteristics in the actual machine become poor, and if the rolling reduction exceeds 95%, This is because the number ratio of the crystal grains of less than 1 mm in the product becomes excessive, the iron loss in the low magnetic field increases, and the iron loss characteristics in the actual machine also become poor.

After cold rolling, primary recrystallization annealing is performed, and then an annealing separator containing 1 to 20% of a Ti compound and 0.04 to 1.0% of B is applied.
From a temperature of 50 ° C. or more, final finish annealing is performed in an atmosphere containing H ₂ . Here, it is important to suppress nitriding of the steel sheet during the primary recrystallization annealing and the final finish annealing as much as possible.

The reason that the Ti compound and B are contained in the annealing separator and the atmosphere containing H ₂ is used from a temperature of at least 850 ° C. or more in the course of raising the temperature of the final finish annealing is to promote the decomposition of AlN. This is because the content of Ti or B in the forsterite coating formed after the final annealing is increased, and the tensile effect of the coating is increased to improve iron loss in a low magnetic field region.

For this purpose, a Ti compound is contained in an amount of 1% or more and B is added.
It is necessary to contain 0.04% or more. That is, if the value is less than these values, the amount of Ti or B contained in the coating film is insufficient even by controlling the atmosphere during the final annealing temperature rise, and the desired magnetic properties cannot be obtained. When the content exceeds 1.0% and B is contained in excess of 1.0%, the hardness of the coating becomes excessively high and the adhesion of the coating deteriorates.

Further, during the final finish annealing, the temperature was raised to 850
If more than the temperature of ℃ was annealed in an atmosphere of N ₂ plain,
The decomposition of AlN is delayed, so that the Al does not rapidly move from the base iron to the coating, and the coating formation reaction is also delayed, and
The enrichment of Ti and B does not occur, and the predetermined magnetic characteristics cannot be obtained.

After the final finish annealing, an insulating coating is applied and baked as required, and further flattening annealing is performed to obtain a product.

[0125]

【Example】

Example 1 Molten steel having a component composition of steel symbols I to XV shown in Table 2 above was continuously cast into a slab while performing electromagnetic stirring to form a slab.
Each one was hot-rolled under the conditions shown in Table 3 above to obtain a hot-rolled coil having a thickness of 2.4 mm. The cooling rate between the end of hot rolling and coil winding is 1
Rapid cooling was performed at 5.3 to 18.6 ° C / s. After this, all of these coils are split into two, one at a temperature of 900 ° C for 60 seconds, the other
Hot rolled sheet annealing was performed at a temperature of 1050 ° C. for 60 seconds. further,
After pickling, these coils were rolled at a temperature of 150 ° C. by a tandem rolling mill to a thickness of 0.34 mm.

Thereafter, a degreasing treatment was performed, and the temperature was set at 850 ° C. for 2 hours.
Minutes of decarburizing annealing, and applying an annealing separator containing 7% TiO ₂ in MgO containing 0.12% B to the steel sheet surface,
Temperature to N ₂ alone atmosphere during heating 500 ° C., followed by 10
After a final finish annealing in which the temperature is raised to a temperature of 1200 ° C. in a mixed atmosphere of N ₂ : 25% and H ₂ : 75% up to a temperature of 50 ° C. and then H ₂ alone and then maintained at 1200 ° C. for 5 hours, unreacted annealing Each separating agent was removed. These coils are 40% more
An insulating coating mainly composed of magnesium phosphate containing colloidal silica was applied and baked at a temperature of 800 ° C. to obtain respective products.

Thereafter, the content of Al: Ti and B in the forsterite coating was analyzed for each steel sheet from which the unreacted annealing separator was removed, and the steel sheet was macro-etched to measure the crystal grain size distribution. . Also, cut out Epstein size test specimens from each product along the rolling direction at 800 ° C.
After 3 hours of strain relief annealing at a temperature of 1.0 T and
Iron loss values at 1.7 T flux density W _10/50 , W _17/50
And magnetic flux density B ₈ were measured. Furthermore, EI cores were punched out of each product, subjected to strain relief annealing, piled up, wound with copper wires, etc., and each of the EI cores was manufactured. The iron loss characteristics of these EI cores were also investigated. Table 9 summarizes the results of these investigations.

[0128]

[Table 9]

As shown in Table 9, the grain-oriented electrical steel sheet conforming to the present invention has excellent iron loss characteristics in a low magnetic field as compared with high magnetic field characteristics, and has extremely good iron loss in an actual machine.

Example 2 A molten steel having the composition of steel symbol XII shown in Table 2 above was formed into a cast slab by a continuous casting machine while performing electromagnetic stirring, and the six slabs were subjected to the conditions shown in Symbol b in Table 3 above. And hot rolled sheet coils each having a thickness of 2.2 mm. At this time, the cooling rate from the end of hot rolling to coil winding was changed to 4.7, 8.8, 11.6, 15.6, 26.5, 55.8 ° C./s. These hot rolled sheet coils were subjected to hot rolled sheet annealing at a temperature of 900 ° C. for 30 seconds, at which time the rate of temperature rise was 12.6 ° C./s. The coils were then pickled and warm rolled to a thickness of 0.29 mm by a tandem mill at a temperature of 100-160 ° C.

Thereafter, a degreasing treatment was performed and the temperature was set at 850 ° C. for 2 hours.
Minutes of decarburization annealing in MgO containing 0.05% B
4% TiO_TwoCoated steel sheet with annealing additive
Up to a temperature of 500 ° C_TwoAlone atmosphere, then 85
N up to 0 ° C_Two: 25%, H _Two : 75% mixed atmosphere,
H_Two After heating to 1180 ° C in a single atmosphere, keep for 5 hours
After the final finish annealing, the unreacted annealing separator
Were respectively removed. These coils provide an additional 50%
Main component is magnesium phosphate containing lodal silica
Apply insulation coating and bake at 800 ℃
Each was a product.

Thereafter, in the same manner as in Example 1, the quantitative analysis of Al, Ti and B in the forsterite coating on the steel sheet from which the unreacted annealing separator was removed, the crystal grain size distribution, and the magnetic properties of the product In addition, the iron loss of the EI core manufactured using each product was investigated. Table 10 summarizes the results of these surveys.

[0133]

[Table 10]

As shown in Table 10, the grain-oriented electrical steel sheet satisfying the constitutional requirements of the present invention having a cooling rate of 10 ° C./s or more after completion of hot rolling and coil winding is compared with the high magnetic field characteristics. It has excellent iron loss characteristics in low magnetic fields and extremely good iron loss in actual equipment.

Example 3 Of the four slabs cast with molten steel having the composition of steel symbol XIV shown in Table 2 above while performing electromagnetic stirring, and one slab cast with molten steel stopped, electromagnetic stirring was performed. The four slabs were hot-rolled under the conditions of a, b, e and f shown in Table 3 above to obtain a hot-rolled coil having a thickness of 2.6 mm. Condition e in Table 3
Hot rolling was performed (sheet thickness: 2.6 mm). At this time, the cooling rate from the end of hot rolling to coil winding was a rapid cooling of 21.6 to 26.2 ° C./s. Thereafter, these coils were all divided into two parts, one of which was subjected to hot rolled sheet annealing at a temperature of 900 ° C. for 60 seconds and the other at a temperature of 1050 ° C. for 60 seconds. Further, these coils were warm-rolled to a thickness of 0.26 mm by a tandem rolling mill at a temperature of 120 ° C. after pickling.

Thereafter, a degreasing treatment was performed and the temperature was set at 850 ° C. for 2 hours.
Minutes of decarburizing annealing, and applying an annealing separator containing 5% TiO ₂ in MgO containing 0.1% B to the steel sheet surface,
At the time of temperature rise, the atmosphere of N ₂ alone up to the temperature of 800 ℃, then 1050
Up to a temperature of 25 ° C., a mixed atmosphere of N ₂ : 25%, H ₂ : 75%,
Thereafter, after a final finish annealing in which the temperature was raised to 1200 ° C. and the temperature was maintained for 5 hours in an atmosphere of H ₂ alone, unreacted annealing separators were removed. Each of these coils was further coated with an insulating coating mainly composed of magnesium phosphate containing 60% of colloidal silica and baked at a temperature of 800 ° C. to obtain products.

Thereafter, in the same manner as in Example 1, the quantitative analysis of Al, Ti and B in the forsterite coating on the steel sheet from which the unreacted annealing separator was removed, the crystal grain size distribution, and the magnetic properties of the product And EI made using each product
Core iron loss was investigated. Table 11 summarizes the results of these surveys.

[0138]

[Table 11]

[0139] As shown in Table 11, the slab heating temperature was 1250 ° C.
A grain-oriented electrical steel sheet that satisfies the requirements of the present invention, which has a hot-rolled sheet annealing temperature of 900 ° C or less, has excellent iron loss characteristics in a low magnetic field compared to a high magnetic field characteristic, and has extremely good iron loss in an actual machine. is there.

Example 4 Molten steel having a composition of steel symbol VIII shown in Table 2 above was cast into a slab by a continuous casting machine while performing electromagnetic stirring. Seven of these slabs were hot-rolled under the conditions indicated by symbol b in Table 3 above, and (a) 2.0 mm, (b) 2.2 mm, (c) 2.5 mm, and (d) 2.7 m, respectively.
m, (e) 3.2 mm, (f) 3.6 mm, and (g) 13 mm in thickness. At this time, the cooling rate from the end of hot rolling to the time of coil winding was 27.5 ° C./s. These hot-rolled coils have a heating rate of 7.8 ° C / s and a temperature of 900 ° C.
The hot rolled sheet was annealed for 30 seconds, pickled, and then cold rolled to a thickness of 0.49 mm. Therefore, the rolling reduction of the coil of (a) is 76%, the rolling reduction of the coil of (b) is 78%,
The rolling reduction of the coil is 80%, and that of (d) is 82
%, The reduction of the coil of (e) is 85%, the reduction of the coil of (f) is 86%, and the reduction of the coil of (g) is 96%. At this time, these coils were subjected to warm rolling by a tandem rolling mill at a temperature of 120 to 180 ° C.

Thereafter, each coil was subjected to a degreasing treatment, and 850 ° C.
Decarburizing annealing for 2 minutes at a temperature of 0.08% B
7% TiO in MgO_TwoSteel sheet surface
To a temperature of 700 ° C when the temperature rises._Two A single atmosphere,
After that, until the temperature reaches 850 ° C, N _Two : 25%, H_Two : 75% blend
Atmosphere, H_Two Temperature rise to 1200 ° C in a single atmosphere
After final annealing for 5 hours, then unreacted
Each of the annealing separators was removed. These coils are
Phosphate containing 60% colloidal silica
Apply an insulating coating mainly composed of
Degrees were baked products.

Thereafter, in the same manner as in Example 1, the quantitative analysis of Al, Ti and B in the forsterite coating on the steel sheet from which the unreacted annealing separator was removed, the crystal grain size distribution, and the magnetic properties of the product The iron loss of the EI core manufactured using each product was investigated. Table 12 shows the results of these surveys.
Are shown together.

[0143]

[Table 12]

As shown in Table 12, the rolling reduction of the cold rolling was 80 to
A grain-oriented electrical steel sheet satisfying the requirements of the present invention of 95% has excellent iron loss characteristics in a low magnetic field as compared with high magnetic field characteristics, and has extremely good iron loss in an actual machine.

Example 5 Molten steel having the composition of steel symbol I shown in Table 2 above was cast into a slab while performing electromagnetic stirring with a continuous casting machine. Nine of these slabs were hot-rolled under the conditions indicated by the symbol "b" in Table 3 above to obtain hot-rolled coil coils each having a thickness of 2.4 mm.
At this time, the cooling rate from the end of hot rolling to the time of coil winding was 14.5 ° C./s. These hot rolled sheet coils were subjected to hot rolled sheet annealing at a heating rate of 6.5 ° C./s and a temperature of 900 ° C. for 30 seconds.
Warm rolling was performed at a temperature of about 220 ° C., and each was rolled to a thickness of 0.34 mm.

Thereafter, each coil was subjected to a degreasing treatment, and 850 ° C.
After the decarburizing annealing for 2 minutes at the above temperature, each coil was subjected to the final finish annealing using the annealing separator having the composition shown in Table 6 and the annealing atmosphere conditions. Final finishing annealing is 1180
The temperature was raised to a temperature of 30 ° C. at a rate of 30 ° C./s, held for 7 hours, and then lowered. Thereafter, the unreacted annealing separator was removed. These coils were further coated with an insulating coating based on magnesium phosphate containing 60% colloidal silica and baked at 800 ° C.

Then, in the same manner as in Example 1, the quantitative analysis of Al, Ti and B in the forsterite coating on the steel sheet from which the unreacted annealing separator was removed, the crystal particle size distribution, and the magnetic properties of the product In addition, the iron loss of the EI core manufactured using each product was investigated. Table 13 summarizes the results of these surveys.

[0148]

[Table 13]

As shown in Table 13, the grain-oriented electrical steel sheet in which the composition of the annealing separating agent and the atmosphere conditions of the final finish annealing satisfy the constitutional requirements of the present invention are compared with the high magnetic field characteristics in the iron loss at a low magnetic field. Excellent characteristics and extremely good iron loss in actual machine.

[0150]

The first and second aspects of the present invention relate to a grain-oriented electrical steel sheet for specifying the grain size distribution and the composition of the forsterite coating, and the third to fifth aspects of the invention relate to the component composition. Using the specified material, hot-rolling conditions, cold-rolling conditions, annealing separator composition and final finish annealing conditions are specified to produce grain-oriented electrical steel sheets, and the grain-oriented electrical steel sheets of these inventions and According to its manufacturing method, it becomes a grain-oriented electrical steel sheet that excels in iron loss characteristics in a low magnetic field compared to a high magnetic field, and greatly improves the iron loss characteristics of actual equipment such as small generators and transformers using this as an iron core it can.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the number ratio of crystal grains having a grain diameter of less than 1 mm, the iron loss of an EI core, and the iron loss ratio W _10/50 / W _17/50 .

FIG. 2 is a graph showing the relationship between the number ratio of crystal grains having a grain size of 4 mm or more and less than 7 mm, the number ratio of crystal grains having a grain size of 7 mm or more, and the iron loss of the EI core.

FIG. 3 shows Al, Ti and B in the forsteritic coating for those having a grain size distribution within the scope of the present invention.
It is a graph which shows the relationship between content and iron loss of an EI core.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/06 C22C 38/06 H01F 1/16 H01F 1/16 B (72) Inventor Kenichi Sadahiro 1 Mizushima Kawasaki Dori, Kurashiki City, Okayama Prefecture Chome (without address) Kawasaki Steel Corporation, Mizushima Works (72) Inventor Atsuto Honda 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi

Claims (5)

[Claims] (1) Si: 1.5 to 7.0 wt% and Mn: 0.03 to 2.
5 wt%, and the contents of C, S and N are respectively: C: 0.003 wt% or less, S: 0.002 wt% or less, and N: 0.
An electromagnetic steel sheet adjusted to 002 wt% or less, wherein the number ratio of the crystal grains penetrating in the thickness direction of the steel sheet in the in-plane direction of the steel sheet is less than 1 mm: 25 to 98%, and 4 mm or more and less than 7 mm: 45% or less and 7mm or more: 10% or less. The steel sheet has a forsterite coating on the surface, and Al, Ti and B are each contained in Al: 0.5 to 15 wt%, T
A grain-oriented electrical steel sheet containing 0.1 to 10% by weight of i: and 0.01 to 0.8% by weight of B, which is excellent in iron loss characteristics in a low magnetic field compared to a high magnetic field. 2. Si: 1.5 to 7.0 wt%, Mn: 0.03 to 2.5 wt%
% And Sb: 0.0010 to 0.080 wt%, and the contents of C, S and N are respectively 0.003 wt% or less and S: 0.00
An electromagnetic steel sheet adjusted to 2 wt% or less and N: 0.002 wt% or less, wherein the number ratio of crystal grains penetrating in the thickness direction of the steel sheet in the in-plane direction of the steel sheet is less than 1 mm: 25 to 98 %, 4 mm or more and less than 7 mm: 45% or less and 7 mm or more: 10% or less. The steel sheet has a forsterite coating on the surface thereof, and Al, Ti and B are each contained in the coating of Al: 0.5 to 15 wt%. , T
A grain-oriented electrical steel sheet containing 0.1 to 10% by weight of i: and 0.01 to 0.8% by weight of B, which is excellent in iron loss characteristics in a low magnetic field compared to a high magnetic field. 3. The composition contains 0.005 to 0.070 wt% of C, 1.5 to 7.0 wt% of Si, 0.03 to 2.5 wt% of Mn, 0.005 to 0.017 wt% of Al, and 0.0030 to 0.0100 wt% of N. , Nb, B or Sb, each containing at least one of Ti: 0.0005 to 0.0020 wt% Nb: 0.0010 to 0.010 wt% B: 0.0001 to 0.0020 wt% and Sb: 0.0010 to 0.080 wt% The molten steel is cast into a silicon steel slab, and the slab is heated to a temperature of 1250 ° C or less and hot-rolled, or directly hot-rolled and finish-rolled in a temperature range of 800 to 970 ° C. After quenching is completed, it is rapidly cooled at a cooling rate of 10 ° C./s or more, wound around a coil at a temperature of 670 ° C. or less, and then heated at a rate of 5 to 25 ° C./s to 800 to 95 ° C.
After performing hot-rolled sheet annealing at a temperature range of 0 ° C. for 100 seconds or less, cold rolling at a reduction ratio of 80 to 95% by a tandem rolling mill, first recrystallization annealing, and Ti compound: 20wt
% And B: 0.04 to 1.0 are coated with the annealing separator containing wt%, the final annealing of heating and holding in an atmosphere containing of H ₂ from the raised middle of at least 850 ° C. above the temperature A method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics in a low magnetic field as compared with a high magnetic field. 4. An alloy containing C: 0.005 to 0.070 wt%, Si: 1.5 to 7.0 wt%, Mn: 0.03 to 2.5 wt%, Al: 0.005 to 0.017 wt%, and N: 0.0030 to 0.0100 wt%, and Ti , Nb, B or Sb, each containing at least one of Ti: 0.0005 to 0.0020 wt% Nb: 0.0010 to 0.010 wt% B: 0.0001 to 0.0020 wt% and Sb: 0.0010 to 0.080 wt% Further, a molten steel containing one or two kinds of Cr or Sn at Cr: 0.0010 to 0.30 wt% and Sn: 0.0010 to 0.30 wt% is cast into a silicon steel slab, and the slab is used as a material at 1250 ° C. Perform hot rolling by heating to the following temperature, or finish rolling in the temperature range of 800 to 970 ° C by direct hot rolling, then quench at a cooling rate of 10 ° C / s or more and 670 ° C or less At a temperature of 800 to 95 ° C / s.
After performing hot-rolled sheet annealing at a temperature range of 0 ° C. for 100 seconds or less, cold rolling at a reduction ratio of 80 to 95% by a tandem rolling mill, first recrystallization annealing, and Ti compound: 20wt
% And B: 0.04 to 1.0 are coated with the annealing separator containing wt%, the final annealing of heating and holding in an atmosphere containing of H ₂ from the raised middle of at least 850 ° C. above the temperature A method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics in a low magnetic field as compared with a high magnetic field. 5. The method for producing a grain-oriented electrical steel sheet according to claim 3, wherein electromagnetic stirring is performed during casting.