JP3456352B2 - Grain-oriented electrical steel sheet with excellent iron loss characteristics and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in iron loss characteristics particularly advantageous among grain-oriented electrical steel sheets used for iron cores of generators and transformers, especially for iron cores and EI cores of small generators. It proposes a grain-oriented electrical steel sheet and its manufacturing method.

It contains Si and has a crystal orientation of (110)
The grain-oriented electrical steel sheet oriented in the [001] orientation or the (100) [001] orientation is widely used as various iron core materials in the commercial frequency range because it has excellent soft magnetic properties. At this time, the characteristic required for the electromagnetic steel sheet is generally the 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 large transformer cores and wound iron cores has a low value of W _17/50. The result is that However, E, which is a small generator core or small transformer,
When the magnetic flux flowing inside the steel plate such as the I-core is complicated, there was a problem that the iron loss represented by W _17/50 of the material and the iron loss characteristics in the actual machine did not match.

With the progress of the energy crisis in recent years, transformers
It is required to reduce energy lost in vain,
While efforts are being made to reduce losses, in the above cases materials
W _17/50In that case, a proper evaluation cannot be obtained.
It was sometimes 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 which is effective for reducing eddy current loss, a method of reducing a steel plate thickness, and a grain size are reduced. A method, a method of improving the magnetic flux density by further increasing the degree of integration of crystal orientations, and the like are known.

Among these, many methods have been studied so far for improving the magnetic flux density, and for example, Japanese Patent Publication No. 51-2290 (hot rolling method for high magnetic flux density unidirectional electrical steel sheet). Add Al as an inhibitor component to steel and heat the slab at a high temperature of 1300 ° C or higher,
A technique for performing hot finish rolling at high temperature in a short time and hot rolling at a hot rolling finish temperature of 980 ° C or higher is also disclosed in JP-B-4.
No. 6-23820 (heat treatment method for high magnetic flux density magnetic steel sheet), Al is added to the steel and 1000-1200 ° C. after hot rolling.
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.

However, when reducing W _17/50 , the conventional method of aligning the normal crystal orientations and improving the magnetic flux density 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]

From the above, as an alternative to the method for improving the magnetic flux density, Si
We examined methods of increasing the content, methods of reducing the steel plate thickness, and methods of reducing the crystal grain size. Among these, the method of increasing the Si content was found to contain too much Si for rollability and workability. There is not preferable limitations because degrading the sex, also there is a limit from the self not a in the a method of reducing the steel sheet thickness results in an increase in the extreme manufacturing cost.

Therefore, the invention according to claim 1 or 2
Of the present invention, the iron loss characteristics by optimizing the grain size distribution of the product and the component composition of the forsterite coating ,
It is an object of the present invention to propose a grain-oriented electrical steel sheet which is excellent in iron loss characteristics in a low magnetic field having a magnetic flux density of 1.0 T as compared with a high magnetic field having a magnetic flux density of 1.7 T. The purpose of the present invention is to propose a method for manufacturing a magnetic electrical steel sheet.

A well-known technique for controlling the crystal grain size of grain-oriented electrical steel sheets is disclosed in, for example, Japanese Patent Publication No.
A method for manufacturing a thin grain-oriented electrical steel sheet having an average crystal grain size of 1 to 6 mm is disclosed in Japanese Patent Publication No. 62-5692.
Publication No. 3 (Method for manufacturing unidirectional silicon steel sheet with low iron loss)
In order to reduce iron loss, the number ratio of crystal grains with a grain size of 2 mm or less should be 15-70%.
Japanese Patent Publication (oriented silicon steel sheet with low iron loss and method of manufacturing the same) proposes technologies for reducing iron loss by allowing fine particles with a grain size of 1.0 mm or more and 2.5 mm or less to exist in a mixed grain form. However, these are all magnetic flux density 1.
The purpose is to reduce the iron loss W _17/50 in a high magnetic field of 7 T, and the iron loss in a low magnetic field has not been studied.

[0010]

[Means for Solving the Problems] As a result of diligent research, the inventors increased iron loss W _17/50 in a high magnetic field and increased iron loss in a low magnetic field.
To reduce W _10/50 , that is, to reduce the value of W _10/50 / W _17/50 , in order to reduce the grain size distribution of the metal structure of the product, fine grains and coarse grains below a certain value The present invention has been newly found out that this can be achieved by appropriately controlling the number ratio of the above, and by forming a film containing forsterite as a main component containing Al, Ti and B in appropriate amounts on the surface of the steel sheet. . That is, the gist of the present invention is as follows.

Si: 1.5-7.0 wt% and Mn: 0.03-
It contains 2.5 wt% and the contents of C, S and N are C: 0.003 wt% or less, S: 0.002 wt% or less and N: 0.
002wt% or less , the balance Fe and unavoidable impurities
An electromagnetic steel sheet according to claim 1, wherein the number ratio of grain sizes of crystal grains penetrating in the plate thickness direction in the steel plate in-plane direction 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, a forsterite coating is provided on the surface of the steel sheet, and Al : 0.5 to 15 wt% and Ti: 0.1 to 10% in the coating.
wt% and B: 0.01 to 0.8 wt% are contained in the grain-oriented electrical steel sheet having excellent iron loss characteristics (first invention).

Further, Sb: 0.0010 to 0.080 wt% is contained
The grain-oriented electrical steel sheet having excellent iron loss characteristics according to the first aspect of the invention (second aspect of the invention).

C: 0.005-0.070 wt%, Si: 1.5-7.0 wt%, Mn: 0.03-2.5 wt%, Al: 0.005-0.017 wt% and N: 0.0030-0.0100 wt%, and Ti, Nb , B or Sb 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% , respectively. Molten steel consisting of balance Fe and unavoidable impurities is cast into a silicon steel slab, and the slab is used as a raw material.
After heating to a temperature of 1250 ° C or lower for hot rolling or direct hot rolling to finish rolling in the temperature range of 800 to 970 ° C, quenching is performed at a cooling rate of 10 ° C / s or more to 67
The coil is wound at a temperature of 0 ° C or less, and then the heating rate:
In the temperature range of 800 to 950 ℃, the temperature is raised in the range of 5 to 25 ℃ / s.
After hot-rolled sheet annealing for 100 seconds or less, cold rolling with a tandem rolling mill at a rolling reduction of 80 to 95%, primary recrystallization annealing, and Ti compound: 1 to 20 wt% and B: 0.04
It is characterized in that after applying an annealing separator containing 1.0 wt% to 1.0 wt%, a final finish annealing is performed in which the temperature is raised and held in an atmosphere containing H ₂ from a temperature of at least 850 ° C. or higher during heating. Method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics (third invention).

In the high magnetic field according to the third invention, the molten steel further contains one or two kinds of Cr or Sn at Cr: 0.0010 to 0.30 wt% and Sn: 0.0010 to 0.30 wt%. In comparison, a method for producing a grain-oriented electrical steel sheet which is excellent in iron loss characteristics in a low magnetic field (fourth invention).

A method for manufacturing a grain-oriented electrical steel sheet having excellent iron loss characteristics in a low magnetic field as compared with a high magnetic field according to the third or fourth invention, which is characterized by performing electromagnetic stirring during casting (fifth invention).

Here, the Ti compound contained in the annealing separator.
And is TiO₂, TiS, MgTiO₃Means compounds containing Ti, etc.
However, as B, the state of solid solution in MgO or nMgO.
 B₂O ₃In addition to the state existing in MgO with compounds such as
It may be added as an additive to the annealing separator.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION First, experimental examples that have led to the present invention will be described below.

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

[0019]

[Table 1]

The reason for this is that, in the case of an actual machine, the distribution of the magnetic flux flowing in the steel sheet is non-uniform, so iron loss in a low magnetic field is more important, and iron loss in a high magnetic field is rather high. It is thought that this is because the flow of is improved to be more uniform, and as a result, the iron loss of the actual machine is reduced. Further, when the materials a and b which showed good actual machine properties in Table 1 were investigated, it was found that the crystal structure was fine grain.

Here, although it is known that it is advantageous to reduce the crystal grain size to reduce the iron loss as compared with the prior art, as described above, all of the iron loss W of the material in the high magnetic field has been described so far.
_There is no research from the viewpoint of improving the actual machine characteristics of small electric devices such as reducing iron loss such as EI core, especially iron loss W _17
Allowing an increase of _{/ 50} , iron loss W _10/50 or W _10/50 / W _17/50
There has been no research on what size and distribution of the crystal grain size should be controlled from the viewpoint of reducing the value of, and the proper distribution of the crystal grain size for that purpose has not been clarified.

Based on the results of this preliminary experiment, the steel grain size distribution and manufacturing conditions for reducing the iron loss in products and the values of W _10/50 and W _10/50 / W _17/50 Various experiments and studies were conducted.

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

[0024]

[Table 2]

[0025]

[Table 3]

All the cooling from the end of hot rolling to the coil winding was done by quenching at a cooling rate of 25.3 to 28.6 ° C./s.

After that, these coils are all divided into two,
One is hot-rolled sheet annealing at 900 ° C for 60 seconds and the other at 1050 ° C for 60 seconds, then pickled, and then tandem
After hot rolling at a temperature of ℃ to a thickness of 0.34 mm, degreasing is performed.
After decarburization annealing at 850 ° C for 2 minutes and applying an annealing separator containing 5% of TiO ₂ in MgO containing 0.1% of B, N ₂ alone is heated up to a temperature of 600 ° C. Atmosphere, then a mixed atmosphere of N ₂ : 25% and H ₂ : 75% up to a temperature of 1050 ° C., and then a final finishing annealing in which H ₂ alone is heated to a temperature of 1200 ° C. and held for 5 hours. After the application, the unreacted annealing separator was removed.

Next, an insulating coating containing magnesium phosphate containing 40% of colloidal silica as a main component was applied to these steel sheets and baked at a temperature of 800 ° C. to obtain respective products.

Thereafter, the steel plates from which the above unreacted annealing separator has been removed are macro-etched to measure the grain size distribution, and Epstein-sized test pieces are cut out from each product along the rolling direction at 800 ° C. After the strain relief annealing was performed at the temperature of 3 hours, the iron loss W _10/50 and W _17/50 and the magnetic flux density B ₈ at the magnetic flux densities of 1.0 T and 1.7 T were measured, respectively. Also, from each product, EI
The cores for cores were punched out, subjected to strain relief annealing, and then EI cores were produced by stacking, copper wire winding, etc., and the iron loss characteristics of these EI cores were also investigated. The results of these investigations are summarized in Table 4.

[0030]

[Table 4]

From Table 4, the slab (steel symbol III) having the composition of the conventional example is used as the material, and the hot rolling conditions (symbol h) of the conventional example are used.
The steel sheet after finish annealing manufactured in (the grain size distribution does not change even after baking the insulating coating after finish annealing) has a large number ratio of coarse crystal grains with a grain size of 7 mm or more, and the magnetic flux density. B _{8 is} also a high product of 1.96 T, but looking at the iron loss characteristics, iron loss in high magnetic field W _17/50
Is extremely small, but the iron loss W _10/50 in the low magnetic field is relatively large, and therefore the value of W _10/50 / W _17/50 is large and it can be said that the iron loss in the low magnetic field is excellent. Absent.

On the other hand, a slab (steel code I) having a composition that complies with the present invention and containing a small amount of Nb and a small Al content is used as a material, and the slab heating temperature is 1200 ° C. or less and the hot rolling end temperature is : Products manufactured at 950 ° C or lower (800 ° C or higher) and hot-rolled sheet annealing temperature: 900 ° C (marked as good in the remarks column in Table 4) have large iron loss in high magnetic fields, but low magnetic fields The core loss is low and therefore the value of W _10/50 / W _17/50 is also small, and the core loss as an EI core is also very good. The characteristic of the crystal structure of these products is that the crystal grain size is smaller than that of the conventional manufacturing method, and it is understood that the number ratio of fine grains of less than 4 mm, particularly less than 1 mm is large.

As a result of conducting experiments and studies on this point,
It was found that it is necessary to set the number ratio of crystal grains having a grain size of less than 1 mm to 25% or more. However, the excessive presence of such fine particles significantly deteriorates the magnetic properties and W _10/50
It also became clear that it deteriorates the value of. By the way, using a steel (steel symbol I) compatible with the invention of Table 4 as a material, the hot rolling end temperature is too low or too high,
Alternatively, for products manufactured under conditions where the hot-rolled sheet annealing temperature is too high, the number ratio of fine crystal grains with a grain size of less than 1 mm is 98%.
W _10/50 and W _10/50 / W _17/50
Value is significantly deteriorated, and the iron loss characteristics of the EI core are also 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 fine as possible, and it is important to suppress the appearance of coarse crystal grains and control the grain size distribution within a proper range. I knew it was.

Next, various studies will be further conducted 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 precipitating AlN as an inhibitor is novel, and it is possible to disperse AlN extremely finely and uniformly. It is considered that, as a result, the secondary recrystallization could be stably performed even though the crystal grains of less than 1 mm were present.

The AlN precipitation method which has been conventionally performed is as follows.
As disclosed in Japanese Examined Patent Publication No. 46-23820, by making AlN into a solid solution state in hot-rolled sheet annealing, re-precipitating in the cooling process of hot-rolled sheet annealing, and controlling the cooling rate at that time. This is a method to control the precipitation size of AlN. On the other hand, the AlN precipitation method that has obtained good results in this experiment is a novel method of keeping AlN in a solid solution state until hot rolling and precipitating AlN in the temperature rising process of hot-rolled sheet annealing. .

In such a method, in order to finely precipitate AlN, the solubility product of AlN is lowered, so that the Al content is made smaller than the conventional suitable value, the precipitation temperature of AlN is lowered, and hot rolling is performed. Prevents precipitation during the process, sets the hot rolling finish temperature to 800 ° C or more, and sets the hot-rolled coil winding temperature.
It is necessary to suppress the precipitation of AlN in the hot rolling process at 670 ° C or lower. The need to keep the coil winding temperature low is to suppress the supersaturated AlN 3 that precipitates when the coiling temperature is high.

Further, Al in a supersaturated state after hot rolling
In order to suppress the precipitation of N, it is naturally required that the cooling rate from the end of hot rolling to the coil winding is also high. For this purpose, a cooling rate of 10 ° C / s or more is required. I found out.

Further, as the hot-rolled sheet annealing, the conventional high-temperature annealing such as the temperature of 1150 ° C. which aims at the solid solution of AlN is extremely harmful, and in addition, the fine particles precipitated during the temperature rising process are added. In order to suppress the Ostwald growth of AlN as well, the annealing temperature was 950 ° C or less, which is 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. It has been conventionally known that it is advantageous that the size of the primary recrystallized grains that are eroded by the silkworm is uniform and small in order to rapidly grow the secondary recrystallized grains. Further, as a cause of increasing the size of primary recrystallized grains and a cause of increasing non-uniformity, coarsening of crystal grains of steel material in a stage before hot rolling or cold rolling is also a cause. It is well known. However, before hot rolling, high temperature slab heating is inevitable for solid solution of the inhibitor, and of course, the crystal grain size of the steel material before hot rolling increases. Therefore, the primary recrystallized grain size naturally increases when the inhibitor grain growth suppressing force is weak, and for example, JP-A-6-172861 (a thick unidirectional electrical steel sheet having excellent magnetic properties). Production method), the primary recrystallized grain size becomes as coarse as 18 to 35 μm.

From this point of view, the conditions for obtaining the good iron loss characteristics in the low magnetic field in the above experiment are indicated by the slab heating temperature as low as around 1200 ° C. and the annealing condition of the hot rolled sheet as low as around 900 ° C. As described above, these are the best conditions for suppressing the growth of crystal grains of the steel material before hot rolling or cold rolling to obtain the finer and more uniform primary recrystallization structure. It can be said to be a technical technology.

Further, from the viewpoint of not coarsening the crystal grains of the steel material before hot rolling, it is more effective that the cast structure of the steel is fine. For example, the molten metal during casting is subjected to electromagnetic stirring treatment to form a columnar shape. The method of suppressing the growth of crystals has a great effect. A method of directly rolling the slab without heating it is also preferable from this viewpoint.

Experiment 2 (Influence of AlN Precipitating Nucleation Component and Effect of Hot Rolling Rate of Hot Rolled Sheet) Experiments and studies were carried out on fine precipitation of AlN in the temperature rising process of hot rolled sheet annealing. Six slabs having the composition of the steel symbol XI shown in Table 2 above and one slab having the composition of the steel symbol V were hot-rolled under the conditions shown in the symbol b of the above Table 3 to obtain the sheet thickness. : A 2.4 mm hot rolled sheet coil was used. At this time, the cooling rate from the end of hot rolling to the coil winding was 26.5 ° C / s.

These hot-rolled sheets were subjected to hot-rolled sheet annealing at 900 ° C. for 60 seconds. At this time, regarding the hot-rolled sheets using the slab of steel symbol XI, 2.5, 3.7, 5.4, 12.7, 23 and 28 ° C
The heating rate was changed to / s, and for the hot-rolled sheet using the slab with the steel symbol V, the heating rate was 12.2 ° C / s.

After that, these annealed plates were pickled, and the thickness was 0.34 mm in a temperature range of 100 to 160 ° C. by a tandem rolling mill.
After hot rolling, degreasing treatment was performed, and after decarburization annealing at 850 ° C for 2 minutes, 7% T was added to MgO containing 0.05% B.
After applying the annealing separator containing iO ₂ ,
An atmosphere of N ₂ alone up to a temperature of ℃, then a mixed atmosphere of N ₂ : 25% and H ₂ : 75% up to a temperature of 850 ° C, and thereafter H
After subjected to final annealing and holding for 5 hours after heating to a temperature of 1180 ° C. in ₂ alone atmosphere to remove unreacted annealing separator, respectively.

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

Then, in the same manner as in Experiment 1, the grain size distribution of each steel sheet after removal of the unreacted annealing separator, the magnetic properties of each product, and the iron loss of the EI core produced using each product were determined. Each was investigated. The results of these investigations are summarized in Table 5.

[0049]

[Table 5]

From Table 5, a slab (steel code V) in which Ti, Nb, B, Sb or the like as a component composition does not conform to the present invention
The product plate made from is large with the number ratio of fine crystal grains of 1 mm or less exceeding 98%, and the magnetic flux density B ₈ is 1.68.
It is as low as T, and the iron loss in low and high magnetic fields is generally poor.

On the other hand, in the case of a product made of a slab (steel code XI) conforming to the present invention with a slight amount of B added, the rate of temperature rise during hot-rolled sheet annealing is in the range of 5 to 25 ° C./s. In that case, excellent iron loss in a low magnetic field and excellent iron loss in the EI core were obtained. When the rate of temperature rise is out of the above range, the number ratio of fine crystal grains having a grain size of less than 1 mm increases to more than 98%, and iron loss in a low magnetic field is poor. Therefore, the conditions for obtaining good low magnetic field characteristics are:
It is necessary that the number ratio of crystal grains having a grain size of less than 1 mm is within a certain range.

As a result of investigating the cause of obtaining such a result, it was found that there is a large difference in the distribution of precipitated AlN after the temperature rise of the hot rolled sheet annealing. That is, as for the precipitated AlN immediately after the temperature rising of the hot-rolled sheet annealing under the conditions (including the material) that provided good magnetic properties and crystal grain distribution, extremely fine particles of 1.0 to 5.0 nm existed at high density. On the other hand, for those made of the steel symbol V and those with a high heating rate of 28 ° C / s, Al
The amount of N precipitation is insufficient, and the heating rate is 2.5 ° C / s or 3.
For the slower 7 ° C / s, the precipitated AlN was coarser at 5.0 to 20 nm. It is considered that such a difference in the precipitation state of the inhibitor affects the secondary recrystallization and changes the crystal structure of the product.

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

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

For this purpose, the hot rolling end temperature is set to 970 ° C.
You will need to: When the hot rolling finish temperature is high, even these ultrafine precipitates that become AlN precipitation nuclei do not precipitate, and uniform fine precipitation of AlN cannot be achieved during the temperature rising process of hot-rolled sheet annealing.

As described above, the inhibitor precipitation control of the present invention is carried out by 1) decreasing the AlN precipitation temperature due to the low Al content and the accompanying decrease in the slab heating temperature, and 2) adding a small amount of the AlN precipitation nucleation component and performing hot work. 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 the end of hot rolling to coil winding And control of AlN precipitation during hot rolling by controlling the upper limit of coil winding temperature, 4) Al in the heating process by controlling the heating rate of hot-rolled sheet annealing
Fine and uniform precipitation of N, 5) Reinforcing solid solution of AlN by controlling the upper limit of annealing temperature of hot rolled sheet, and suppressing coarsening of crystal grains due to Ostwald growth. Become.

Experiment 3 (Study 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 chemical 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 plate thickness of 2.4 mm. At this time, the cooling rate from the end of hot rolling to the 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 was subjected to warm rolling in the temperature range of 120 to 180 ° C. by the tandem rolling mill, and the second annealed plate was subjected to a large amount of coolant on the surface of the material to be rolled by the tandem rolling mill. It is jetted and rolled at a steel plate temperature in the range of 50 to 80 ° C., and the third annealed plate is subjected to an aging treatment in the temperature range of 150 to 220 ° C. between rolling passes by a reverse rolling mill and rolled. The fourth annealed plate was subjected to rolling at a steel plate 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.

After that, each cold-rolled sheet was degreased at 850 ° C.
It was decarburized for 2 minutes and converted to MgO containing 0.05% B.
7% TiO₂Apply the annealing separator with added to the steel plate surface
To 700 ° C when the temperature is raised₂Alone atmosphere, that
After that, until the temperature of 850 ℃, N ₂: 25%, H₂: 75% mixed
Combined atmosphere, then H₂Raises the temperature to 1180 ℃ in a single atmosphere
After performing final finishing annealing that keeps for 5 hours after warming,
Each unreacted annealing separator was removed.

[0060] In addition, the respective baked products at temperatures of applying an insulating coating composed mainly of magnesium phosphate containing 60% colloidal silica in these steel plates 800 ° C.. Then, in the same manner as in Experiment 1, the grain size distribution of each steel sheet after removal of the unreacted annealing separator, the magnetic properties of each product, and the iron loss of the EI core produced using each product were investigated. . Table 6 shows these survey results.
Are shown together.

[0061]

[Table 6]

As shown in Table 6, in the case of rolling using the tandem rolling mill, as compared with the case of using the reverse rolling mill, low magnetic field iron loss W _10/50 , iron loss of high magnetic field and low magnetic field Ratio W
_Good iron loss at _10/50 / W _17/50 and EI core, especially 50 ~ 50% when warm-rolled in the temperature range of 120-180 ℃.
W _10/50 is slightly higher than that when rolled in the temperature range of 80 ° C, but the value of W _10/50 / W _17/50 is small and it is excellent in iron loss of EI core. The diameter distribution is also appropriate.

Generally, the aging treatment in the warm rolling or rolling process has a function of changing the rolling deformation texture of the crystal, and becomes a nucleus of secondary recrystallization in the primary recrystallization structure after rolling recrystallization (110). ) It is known to increase the production density of crystal grains in the [001] orientation. To this end, Japanese Patent Publication No. 54-13
As disclosed in Japanese Patent No. 846 (cold rolling method for obtaining a high magnetic flux density unidirectional silicon steel sheet having excellent characteristics), conventionally, an aging treatment between rolling passes by a reverse type rolling mill such as a Sendzimer mill. Therefore, it has been considered appropriate to diffuse C.

However, as shown in this experimental result, the aging treatment between the passes by the reverse rolling was not effective, but the rolling by the tandem rolling mill was effective. Considering the difference between the two, the strain rate during rolling is relatively small in the inter-pass aging treatment by reverse rolling, and there is sufficient time between rolling passes, which inevitably occurs due to the heat generated due to processing strain during that time. On the other hand, static aging occurs due to the diffusion phenomenon of C to dislocations, whereas in tandem rolling, the strain rate during rolling is relatively high, and the time between rolling passes is extremely short, so static aging does not easily occur. During the pass, dislocations are proliferated and at the same time, dynamic strain aging occurs due to diffusion of C into dislocations.

[0065] The results of this experiment, it tandem rolling method having excellent than the warm rolling is always rolled in it and tandem rolling superior reverse rolling method, furthermore, that the path between the aging treatment is detrimental in the reverse rolling system Shows. Thus, high strain rate and dynamic strain aging work effectively, while static aging has a detrimental effect.

From these, it can be said that the tandem system 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 system is preferably 90 ° C. or higher.

Experiment 4 (Study of Appropriate Forsterite Coating) An experiment relating to the coating of the present invention will be described. Table 2 above
Nine slabs of steel symbol IX shown in Table 1 were hot-rolled under the condition of 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 coil winding was 14.5 ° C / s.

These hot-rolled sheets were annealed at 900 ° C. for 30 seconds at a temperature rising rate of 6.5 ° C./s, pickled, and then tandem-rolled in a temperature range of 120 to 160 ° C. 0.34
After hot rolling to mm, it was degreased and decarburized at 850 ° C for 2 minutes.

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

[0070]

[Table 7]

At this time, on the surface of the steel sheet, SiO ₂ generated in the surface layer of the steel sheet during decarburization annealing and MgO which is the main component of the annealing separator are used.
Reacts during the final annealing and forsterite (Mg ₂ Si
Although a coating film containing O ₄ ) as a main component is formed, the contents of B, Ti and Al in the coating films of these steel sheets were measured.

After the unreacted annealing separation and removal, each steel plate is further 60
% Of colloidal silica was applied as an insulating coating containing magnesium phosphate as a main component, and the product was baked at a temperature of 800 ° C.

After that, in the same manner as in Experiment 1, the grain size distribution of each steel sheet after 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 were measured. And so on. The results of these investigations are summarized in Table 8.

[0074]

[Table 8]

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

As described above, the reason why the iron loss in a low magnetic field is improved by increasing the amount of these components in the coating film is that such components are present in the form of nitride or oxide, and the coating film as a whole is probably present. It is thought that this is due to the fact that the coefficient of thermal expansion is decreased and, as a result, the tension effect is improved.

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

That is, by containing H ₂ having a strong reducing property in the atmosphere, the decomposition of the nitride in the steel can be promoted and the Al content in the film can be increased. At the same time, the film formation can be performed in the reducing atmosphere. It can promote and increase the amount of Ti and B in the coating. Incidentally, Al does not need to be particularly added to the annealing separator, since Al migrates from the steel, the final finish annealing atmosphere is controlled as in the present invention to promote the migration of Al into the coating, and It is only necessary to suppress the Al that migrates into the unreacted annealing separator.

Further, it was also found that the components contained in the steel have important functions in the cooling process of final finishing performed in an N ₂ atmosphere, baking annealing and strain relief annealing of the insulating coating. That is, there is an advantage that the adverse effects of nitriding of steel due to annealing in an N ₂ atmosphere can be suppressed by Ti, B and Sb existing in the steel. Ti and B are concentrated at the coating interface in contact with the base iron to form BN and TiN, which suppresses the penetration of N into the steel (base iron) and enhances 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 existing 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, strengthening the tension of the coating and the It was clarified by considering the results of this experiment that it works effectively to suppress nitriding and contributes to the reduction of iron loss in the low magnetic field of the product.

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

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 and 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 crystal grains of 4 to 7 mm exceeds 45% and when the number ratio of crystal grains of 7 mm or more exceeds 10%, good iron loss in the EI core is observed. There is no chance of getting it.

FIG. 3 shows the products of various experiments.
3 is a graph showing the relationship between the content of Al, Ti and B in the forsterite coating and the iron loss of the EI core when the crystal grain size distribution is within the range 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.

As a result of earnest research based on the experiments and investigations as described above, the present invention has been completed.

Next, the essential and preferred conditions for obtaining the effects of the present invention and their actions will be described. First, the constitutional requirements of the grain-oriented electrical steel sheet of the present invention, which has excellent iron loss characteristics in a low magnetic field as compared with a high magnetic field, will be described.

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

Si: 1.5 to 7.0 wt% (hereinafter simply expressed as%) Si is an effective component for increasing the electrical resistance of the product and reducing the iron loss.
If it is contained in excess of%, the hardness becomes high and manufacturing and processing become difficult. Therefore, its content is more than 1.5%, 7.0
% Or less.

Mn: 0.3-2.5% Mn has a function of increasing electric resistance like Si, and
It has the function of facilitating hot working during manufacturing. For this
It is necessary to contain 0.03% or more, but if it exceeds 2.5%, γ-transformation is induced during the heat treatment to deteriorate the magnetic properties, so the content should be 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 is essential. When these impurities exceed this value, they have a detrimental effect on the magnetic properties and particularly deteriorate iron loss.

In addition to these components, the following components can be contained if necessary. 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 that are added to the steel to improve the microstructure are added to promote good secondary recrystallization. It remains in the product afterwards. Furthermore, the inclusion of a small amount of components such as Ti and B produces nitrides and oxides at the interface between the coating and the base iron, which is also advantageous in terms of magnetic properties in a low magnetic field.

Here, in particular, the inclusion of Sb is preferable because it has the effect of suppressing the nitriding of the base iron during stress relief annealing, and for this purpose, it is essential to contain 0.0010% or more. %, The toughness of the steel sheet deteriorates and it becomes difficult to process. Therefore, the content is 0.0010 to 0.080.
The appropriate range is%.

The surface of such a grain-oriented electrical steel sheet is used in the presence of an insulating material, and an insulating coating containing forsterite (Mg ₂ SiO ₄ ) as a main component formed during final finishing annealing is used. A topcoat may also be applied over the insulating coating.

Further, controlling the trace components in the forsterite coating is one of the essential constituents 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 is enhanced and the iron loss in the low magnetic field region of the product is improved. 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, the inclusion of excessive amounts of Al: more than 15%, Ti: more than 10% and B: more than 0.8% is not suitable because the hardness of the coating is excessively increased and the adhesion of the coating is deteriorated. Therefore, it is necessary to contain Al: 0.5 to 15%, Ti: 0.1 to 10% and B: 0.01 to 0.8% in the coating film.

Here, the method for measuring the concentrations of these components in the coating will be described. The oxygen content (fO) of the steel sheet, Al
The content (fAl), Ti content (fTi) and B content (fB) were analyzed, and then the forsterite coating was removed by pickling, and then the oxygen content (sO) and Al content of the steel sheet were again detected. 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
As the Al content in the coating is (fAl-sAl) ÷ f × 100 (%), the Ti content in the coating is (fTi-sTi) ÷ f × 100 (%) B content in the coating The amount can be calculated by (fB-sB) ÷ f × 100 (%).

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

In the grain-oriented electrical steel sheet of the present invention, the target crystal grains are those penetrating in the plate thickness direction. The grain size of the crystal grain is represented by the diameter of a circle having the same area as the area of the crystal grain on the surface of the steel sheet (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 taken as the average crystal grain size.

The ratio of the number of crystal grains having a grain size in the in-plane direction of the steel sheet of less than 1 mm is 25 to 98%, 4 mm
As a result, the number ratio of crystal grains of less than 7 mm is 45% or less and 7
It is necessary that the number ratio of crystal grains of mm or more is 10% or less.

A crystal grain of 7 mm or more has an effect of increasing iron loss in a low magnetic field as compared with a high magnetic field, and in order to improve the characteristics of an actual machine, it is suppressed to a number ratio of 10% or less. 7
It is essential to suppress the number ratio of crystal grains less than mm to 45% or less. Increasing the number ratio of crystal grains of less than 4 mm, especially 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 should be 25% or more. However, if it exceeds 98%, the iron loss in a low magnetic field increases conversely, resulting in deterioration of actual machine characteristics, so the upper limit is made 98%.

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

By adjusting the contents 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, limiting conditions, preferable conditions and the reasons therefor will be described as constituents of the method for producing a grain-oriented electrical steel sheet of the present invention which is excellent in iron loss characteristics in a low magnetic field as compared with a high magnetic field. First, the composition of ingredients will be described.

C: 0.005-0.070% C is a feature of the present invention in that the content of C is 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 temperature rising process of hot-rolled sheet annealing becomes non-uniform and good at low magnetic fields. 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 properties also deteriorate. Therefore, its content is limited to the range of 0.005 to 0.070%.

Si: 1.5-7.0% 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, but more than 7.0%. If it is contained as a component, the workability is deteriorated and it becomes extremely difficult to manufacture or process the product. Therefore, its content should be in the range of 1.5 to 7.0%.

Mn: 0.03 to 2.5% Mn is a necessary component because it raises the electrical resistance like Si and improves the hot workability during manufacturing. For this purpose, it is necessary to contain 0.03% or more, but 2.5%
If it is contained in excess of 0.1%, γ-transformation is induced and the magnetic properties are deteriorated, so the content is made 0.03 to 2.5%.

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

Al: 0.005-0.017%, N: 0.0030-0.01
If the content of 00% Al is less than 0.005%, the amount of AlN precipitated during the temperature rising process of hot-rolled sheet annealing is insufficient. On the other hand, if it exceeds 0.017%, it will be
Since solid solution of lN becomes difficult and the solid solution temperature of AlN rises, AlN precipitates in the hot rolling process, which is one of the features of this invention in the temperature rising process of hot-rolled sheet annealing. As a result, fine precipitation of AlN becomes impossible and good iron loss characteristics cannot be obtained in a low magnetic field. If slab heating is performed at a high temperature around 1400 ° C in order to eliminate this deficiency, the crystal grain size of the product becomes coarser, the iron loss in the high magnetic field decreases, and the iron loss in the low magnetic field increases. 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, N is a component constituting AlN, so it is necessary to contain 0.0030% or more. However, if the content exceeds 0.0100%, it is gasified in the steel and causes defects such as blistering, so its content is 0.0030%.
The range is to 0.0100%. Furthermore, in this invention, Ti,
It is essential to include one or more selected from Nb, B or Sb.

These components have a function of forming fine precipitates in the hot rolling and increasing AlN precipitation nuclei in the temperature rising process of the hot rolling annealing in the next step.
The respective contents for obtaining such action and effect are as follows: Ti: 0.0005% or more, Nb: 0.0010% or more, B: 0.0001
% And Sb: 0.0010 %% or more is required. However, Ti: 0.0020% over, Nb: 0.010% over, B: 0.0020
% And Sb: If contained in excess of 0.080%, mechanical properties such as bend properties of the product will deteriorate. Therefore, the contents of Ti are 0.0005 to 0.0020%, Nb is 0.0010 to 0.010%, and B is 0.0001 to 0.0020%.
% And Sb are in the range of 0.0010 to 0.080%.

Other additional components are not necessarily required to obtain a grain-oriented electrical steel sheet having a good iron loss characteristic in a low magnetic field as compared with a high magnetic field. Since it has the effect of improving the surface properties of the above, it is preferable to contain it, and it is also possible to appropriately contain Bi, Te and the like.

Next, the manufacturing process conditions will be described. Steel adjusted to the above component composition by a conventional method is usually hot-rolled sheet coil by hot rolling after being subjected to slab heating, this slab heating temperature can be 1250 ℃ or less It is an important constituent 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 increases in the distribution of crystal grains in the product, and iron loss in a low magnetic field increases. From the above, the slab heating temperature is 1250 ° C or lower in order to obtain good grain distribution and magnetic properties. Furthermore, in recent years, a method of directly hot rolling after continuous casting without performing slab heating has been developed, but since the slab temperature hardly rises in this method,
As a matter of course, the method is suitable as a method for manufacturing the grain-oriented electrical steel sheet of the present invention.

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

After 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. Furthermore, it is essential to control the coil winding temperature to 670 ° C or lower. This is also because when the coiling temperature exceeds 670 ° C, AlN precipitates and deteriorates the magnetic properties.

By the above control, the hot rolled sheet coil in which precipitation of AlN in the hot rolling is suppressed is subjected to hot rolled sheet annealing.
It is the originality of this invention that this hot-rolled sheet annealing is performed at an extremely low temperature. The temperature and time compatibility conditions for 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 if the annealing time exceeds 100 seconds, the grain size of the steel sheet before cold rolling becomes coarse, resulting in 1
If the annealing temperature of the hot-rolled sheet is less than 800 ℃, the A
lN becomes insufficiently precipitated.

Furthermore, the point that AlN is precipitated during the temperature rising process of this hot rolled sheet is the newest technology of the present invention, but it is also essential to control the temperature rising rate of such annealing within the range of 5 to 25 ° C / s. It becomes the condition of. That is, this is because the heating rate is 5 ° C.
If it is less than / s, AlN coarsely precipitates and causes deterioration of magnetic properties. On the other hand, if it exceeds 25 ° C / s, the amount of AlN precipitates becomes insufficient and similarly deteriorates magnetic properties. .

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

[0116] Here, the tandem rolling mill is a rolling mill for rolling by rolling between a pair of rolls, which is continuously arranged in the rolling direction, and is capable of rolling continuously on one direction of rolling. It means that.

By rolling with such a tandem rolling mill, it is possible to suppress harmful static aging between rolling passes, and increase the strain rate to obtain a good rolling texture. That is, by this, the primary recrystallization texture is improved in the direction of promoting the secondary recrystallization grain growth, promoting the nucleation and growth of fine crystal grains, and the grain size of the product is less than 1 mm. Promotes stable generation of crystal grains with a grain size of 1 to 4 mm. At this time, by raising the temperature of the steel sheet during rolling, it is possible to induce dynamic strain aging and obtain a more preferable effect. A suitable rolling temperature for this purpose is a steel sheet temperature in the range of 90 to 300 ° C.

In the case of reverse rolling such as a Zenzimer rolling mill, static aging is inevitably accompanied, and a primary recrystallized structure which is inferior in the growth property of secondary recrystallized grains is formed and the number of crystal grains less than 1 mm. If the ratio is excessively increased, the iron loss in the product is deteriorated not only in the high magnetic field iron loss but also in the low magnetic field iron loss, and the iron loss characteristic in the actual machine becomes poor.

Further, the reduction ratio of the cold rolling is 80 to 95.
%. This is one of the products when the rolling reduction is less than 80%.
When the ratio of the number of crystal grains less than mm is reduced and the high magnetic field iron loss is reduced, the low magnetic field iron loss increases and the iron loss characteristics in the actual machine become poor. Conversely, when the rolling reduction exceeds 95%, This is because the ratio of the number of crystal grains of less than 1 mm in the product becomes excessively large, the low magnetic field iron loss increases, and the iron loss characteristics in the actual machine also become poor.

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

The reason why an atmosphere containing H ₂ from a temperature of at least 850 ° C. or higher during the temperature rising of the final finish annealing is used because of the inclusion of the Ti compound and B in the annealing separator is to accelerate the decomposition of AlN. Or for increasing the Ti and B contents in the forsterite coating formed after the final finish annealing to enhance the tension effect of the coating and improve the iron loss in the low magnetic field region.

For this purpose, 1% or more of the Ti compound and B are added.
It is necessary to contain 0.04% or more. That is, when the amount is less than these values, the amount of Ti and B contained in the coating is insufficient even by controlling the atmosphere during the temperature increase in final finish annealing, and the desired magnetic properties cannot be obtained. When the content of B exceeds 1.0% and the content of B exceeds 1.0%, the hardness of the coating is excessively increased and the adhesion of the coating is deteriorated.

Further, during the temperature rising of the final finish annealing, 850
When annealing is performed in an atmosphere of N ₂ above the temperature of ℃,
Decomposition of AlN is delayed, Al is not rapidly transferred from the base steel to the film, and the film formation reaction is also delayed, and
The concentration of Ti and B does not occur, and the desired magnetic characteristics cannot be obtained.

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

[0125]

【Example】

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

After that, degreasing treatment is performed at a temperature of 850 ° C. for 2 hours.
Decarburization annealing for 1 minute, apply the annealing separator with 7% TiO ₂ in MgO containing 0.12% B,
At the time of heating up to a temperature of 500 ° C, an atmosphere of N ₂ alone, then 10
After a final atmosphere of up to 50 ° C mixed atmosphere of N ₂ : 25% and H ₂ : 75%, and then a temperature of 1200 ° C for 5 hours in a single atmosphere of H _{2 and} then a final finishing annealing, unreacted annealing Each separating agent was removed. 40% more for these coils
An insulating coating containing magnesium phosphate as a main component containing colloidal silica was applied and baked at a temperature of 800 ° C to obtain each product.

Then, the content of Al: Ti and B in the forsterite coating of each steel sheet from which the unreacted annealing separator was removed was analyzed, and the steel sheet was macro-etched to measure the distribution of crystal grain size. . Epstein-sized test pieces were cut from each product along the rolling direction at 800 ° C.
After performing stress relief annealing for 3 hours at the temperature of 1.0T and
Iron loss values at magnetic flux density of 1.7 T W _10/50 , W _17/50
And the magnetic flux density B ₈ were measured. Further, iron cores for EI cores were punched out from each product, strain relief annealing was performed, stacking work, copper wire winding work, etc. were respectively made, and the iron loss characteristics of these EI cores were also investigated. The results of these investigations are summarized in Table 9.

[0128]

[Table 9]

As shown in Table 9, the grain-oriented electrical steel sheet conforming to the present invention is superior to the high magnetic field characteristic in the iron loss characteristic in the low magnetic field, and the iron loss in the actual machine is very good.

Example 2 Molten steel having the chemical composition of steel symbol XII shown in Table 2 above was cast into a slab by a continuous casting machine while performing electromagnetic stirring, and the six slabs were subjected to the conditions shown by symbol b in Table 3 above. Were hot-rolled to obtain 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 the coil winding was changed to 4.7, 8.8, 11.6, 15.6, 26.5 and 55.8 ° C / s. These hot-rolled sheet coils were annealed at a temperature of 900 ° C. for 30 seconds, and the heating rate was 12.6 ° C./s. Then, these coils were pickled and warm-rolled at a temperature of 100 to 160 ° C. by a tandem rolling mill to a thickness of 0.29 mm.

After that, degreasing treatment is performed at a temperature of 850 ° C. for 2 hours.
After decarburization annealing for 1 minute, it was added to MgO containing 0.05% B.
4% TiO₂Applying an annealing separator with added to the steel plate surface
The temperature rises to 500 ° C₂Alone atmosphere, then 85
N up to a temperature of 0 ° C₂: 25%, H ₂ : 75% mixed atmosphere,
After that H₂ Hold for 5 hours after raising the temperature to 1180 ℃ in a single atmosphere
After carrying out the final finishing annealing, the unreacted annealing separator
Were removed respectively. These coils have an additional 50%
The main component is magnesium phosphate containing a colloidal silica
Apply an insulating coating and bake at a temperature of 800 ° C
Each product.

Thereafter, in the same manner as in Example 1, quantitative analysis of Al, Ti and B in the forsterite coating and the crystal grain size distribution of the steel sheet from which the unreacted annealing separator was removed and the magnetic properties of the product were obtained. And the iron loss etc. of the EI core produced using each product were investigated respectively. The results of these surveys are summarized in Table 10.

[0133]

[Table 10]

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

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

After that, degreasing treatment is performed at a temperature of 850 ° C. for 2 hours.
Decarburization annealing for 1 minute, and then 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, an atmosphere of N ₂ alone up to a temperature of 800 ° C, then 1050
Up to ℃ temperature, mixed atmosphere of N ₂ : 25%, H ₂ : 75%,
After that, after performing final finish annealing in which the temperature was raised to 1200 ° C. in a single atmosphere of H _{2 and} held for 5 hours, the unreacted annealing separator was removed. Each of these coils was further coated with an insulating coating containing magnesium phosphate as a main component containing 60% of colloidal silica, and baked at a temperature of 800 ° C to obtain each product.

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

[0138]

[Table 11]

As shown in Table 11, the slab heating temperature is 1250 ° C.
The grain-oriented electrical steel sheet which satisfies the requirements of this invention with the hot-rolled sheet annealing temperature of 900 ° C or less is excellent in the iron loss characteristics in the low magnetic field as compared with the high magnetic field characteristics, and the iron loss in the actual machine is extremely good. is there.

Example 4 Molten steel having a component 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 the symbol b in Table 3 above, and respectively (a) 2.0 mm, (b) 2.2 mm, (c) 2.5 mm, (d) 2.7 m
m, (e) 3.2 mm, (f) 3.6 mm, (g) 13 mm thick hot rolled sheet coil. At this time, the cooling rate from the end of hot rolling to the coil winding was 27.5 ° C / s. These hot-rolled sheet 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 coil reduction rate of (a) is 76%, the coil reduction rate of (b) is 78%, and (c)
The coil rolling ratio is 80%, and the coil rolling ratio in (d) is 82%.
%, The coil rolling reduction of (e) is 85%, the coil rolling reduction of (f) is 86%, and the coil rolling reduction 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.

After that, each coil is degreased at 850 ° C.
Decarburization annealing for 2 minutes at the temperature of 0.08% B
7% TiO in MgO₂Annealing agent with added
Applied to N and up to a temperature of 700 ° C₂ Single atmosphere,
After that, N up to a temperature of 850 ℃ ₂ : 25%, H₂ : 75% mixed
Combined atmosphere, then H₂ Temperature rises to 1200 ℃ in a single atmosphere
After final finishing annealing of holding for 5 hours, then unreacted
The annealing separator was removed respectively. These coils are even more
Magnesium phosphate containing 60% colloidal silica
Apply an insulating coating consisting mainly of
The product was baked at a certain degree.

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

[0143]

[Table 12]

As shown in Table 12, the reduction ratio of cold rolling was 80 to
The grain-oriented electrical steel sheet satisfying the constituent requirements of the present invention of 95% is superior to the high magnetic field characteristic in the iron loss characteristic in the low magnetic field, and the iron loss in the actual machine is extremely good.

Example 5 Molten steel having the chemical 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 sheet coils each having a thickness of 2.4 mm.
At this time, the cooling rate from the end of hot rolling to the coil winding was 14.5 ° C / s. These hot-rolled sheet coils were subjected to hot-rolled sheet annealing at a temperature rising rate of 6.5 ° C / s and at a temperature of 900 ° C for 30 seconds, pickled, and then cooled to 170 by a tandem rolling mill.
Warm rolling was performed at a temperature of ~ 220 ° C, and each was rolled to a thickness of 0.34 mm.

After that, each coil is degreased at 850 ° C.
After performing decarburization annealing at the temperature of 2 minutes, each coil was subjected to final finish annealing by using the annealing separator having the composition shown in Table 6 and the annealing atmosphere conditions. Final finish annealing is 1180
A heat pattern was used in which the temperature was raised to 30 ° C. at a heating rate of 30 ° C., held for 7 hours, and then lowered. After that, the unreacted annealing separator was removed. These coils were further coated with an insulating coating composed mainly of magnesium phosphate containing 60% colloidal silica and baked at a temperature of 800 ° C.

Then, in the same manner as in Example 1, quantitative analysis of Al, Ti and B in the forsterite coating and the crystal grain size distribution of the steel sheet from which the unreacted annealing separator was removed and the magnetic properties of the product were obtained. And the iron loss etc. of the EI core produced using each product were investigated respectively. The results of these surveys are summarized in Table 13.

[0148]

[Table 13]

As shown in Table 13, the grain-oriented electrical steel sheet in which the composition of the annealing separator and the atmosphere condition of the final finish annealing satisfy the constituent requirements of the invention has iron loss in a low magnetic field as compared with high magnetic field characteristics. Excellent properties and extremely good iron loss in actual equipment.

[0150]

EFFECTS OF THE INVENTION Of the present invention, the inventions of claims 1 and 2 are grain-oriented electrical steel sheets which specify the grain size distribution and composition of the forsterite coating. Using the specified material, hot rolling conditions, cold rolling conditions, annealing separator composition and final finishing annealing conditions are specified to produce the grain-oriented electrical steel sheet, and the grain-oriented electrical steels 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 machines such as small generators and transformers that use this as an iron core. it can.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the number ratio of crystal grain sizes having a grain size of less than 1 mm and the iron loss of the 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 a forsterite coating for a crystal grain size distribution which conforms to the scope of the present invention.
It is a graph which shows the relationship between content and the iron loss of EI core.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C22C 38/06 C22C 38/06 H01F 1/16 H01F 1/16 B (72) Inventor Atsuto Honda Atsushi Mizushima Kawasaki, Kurashiki City, Okayama Prefecture 1-chome (without street number) Kawasaki Steel Co., Ltd. Mizushima Steel Works (72) Inventor Kunihiro Senda 1-chome (without street number) Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture Kawasaki Steel Co., Ltd. Mizushima Steel Works (56) References 7-268470 (JP, A) JP 5-304016 (JP, A) JP 52-153827 (JP, A) JP 60-145382 (JP, A) JP 60-59045 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00 303 B21B 3/02 C21D 8/12 C21D 9/46 501 C22C 38/04 C22C 38/06 H01F 1/16

Claims (5)

(57) [Claims] 1. Si: 1.5 to 7.0 wt% and Mn: 0.03 to 2.
5% by weight, and the contents of C, S and N were C: 0.003 wt% or less, S: 0.002 wt% or less and N: 0.
002 wt% or less , with no balance of Fe and unavoidable impurities
Which is a magnetic steel sheet, wherein the number ratio of grain sizes 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 surface of the steel sheet has a forsterite coating, and Al : 0.5 to 15 wt%, Ti: 0.1 to 10 wt% and B:
A grain-oriented electrical steel sheet with excellent iron loss characteristics, characterized by containing 0.01 to 0.8 wt%. 2. Sb: 0.0010 to 0.080 wt% is further contained.
The grain- oriented electrical steel sheet having excellent iron loss characteristics according to claim 1 . 3. C: 0.005-0.070 wt%, Si: 1.5-7.0 wt%, Mn: 0.03-2.5 wt%, Al: 0.005-0.017 wt% and N: 0.0030-0.0100 wt%, and Ti , Nb, B or Sb selected from the group consisting of one or more selected from 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% Then, a molten steel consisting of the balance Fe and unavoidable impurities is cast into a silicon steel slab, and the slab is used as a raw material.
After heating to a temperature of 1250 ° C or lower for hot rolling or direct hot rolling to finish rolling in the temperature range of 800 to 970 ° C, quenching is performed at a cooling rate of 10 ° C / s or more to 67
The coil is wound at a temperature of 0 ° C or less, and then the heating rate:
In the temperature range of 800 to 950 ℃, the temperature is raised in the range of 5 to 25 ℃ / s.
After hot-rolled sheet annealing for 100 seconds or less, cold rolling with a tandem rolling mill at a rolling reduction of 80 to 95%, primary recrystallization annealing, and Ti compound: 1 to 20 wt% and B: 0.04
It is characterized in that after applying an annealing separator containing 1.0 wt% to 1.0 wt%, a final finish annealing is performed in which the temperature is raised and held in an atmosphere containing H ₂ from a temperature of at least 850 ° C. or higher during heating. Method for producing grain-oriented electrical steel sheet with excellent iron loss characteristics. 4. The iron according to claim 3, wherein the molten steel further contains one or two kinds of Cr or Sn at Cr: 0.0010 to 0.30 wt% and Sn: 0.0010 to 0.30 wt%. A method for manufacturing a grain-oriented electrical steel sheet having excellent loss characteristics. 5. The method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics according to claim 3, wherein electromagnetic stirring is performed during casting.