JPH11335736A - Production of high magnetic flux density grain oriented silicon steel sheet extremaly low in core loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon steel sheet extremely low in core loss by containing an element of a specified composition to a steel slab of a specified composition, hot rolling at a specific temp. and for a specific time and conducting a primary recystallization annealing at a specified temp. and a temp. rise rate. SOLUTION: To a steel slab, which contains, by weight, 0.03-0.095% C, 1.5-7.0% Si, 0.03-2.50% Mn, 0.003-0.040% independently or jointly S or Se, 0.0010-0.0070% B, 0.0005-0.1000% Bi, 30-120 wt.ppm N are added, further Al in the impurity is regulated to <=0.015% and V to <=0.010%. A hot rolling time is set to 50-220 sec and a hot rolling completion temp. to >=850 deg.C. The steel is subjected to rapid cooling at a cooling rate of >=30 deg.C/sec after hot rolling completion, is winded in a coil-like form at a temp. of <=700 deg.C. A temp. rise rate above 500 deg.C in a temp. rise process of primary recystallization annealing is set to >=8 deg.C/sec, an annealing temp. is set to 800-900 deg.C. The final cold rolling is conducted at a draft of 80-95%. In the case BN inhibitor is used, a silicon steel sheet having a low core loss and a high magnetic flux density is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high magnetic flux density grain-oriented electrical steel sheet suitable for downsizing transformers, among the grain-oriented silicon steel sheets used for iron cores of transformers and generators. The present invention relates to a manufacturing method capable of improving iron loss characteristics.

[0002]

2. Description of the Related Art Si has a crystal orientation of (11).
Oriented electrical steel sheets oriented in the 0) [001] or (100) [001] orientation are widely used as various iron core materials in the commercial frequency range because of their excellent soft magnetic properties. The properties required for electrical steel sheets in such applications include low iron loss, which is _generally expressed as W _17/50 (W / kg), which is the loss when magnetized to 1.7 T at a frequency of 50 Hz. is there. For iron cores and wound iron cores of large transformers, this W
_A material with a low _17/50 value has excellent iron loss characteristics in actual equipment. Here, the grain-oriented electrical steel sheet having a high magnetic flux density by improving the orientation of the crystal orientation described above is advantageous for downsizing of a transformer.

[0003] In a general manufacturing process of grain-oriented electrical steel sheets,
After containing the inhibitor component in the steel, the steel slab is heated at a high temperature to form a solid solution of the inhibitor, and then subjected to hot rolling to finely precipitate the inhibitor in the steel. The above-mentioned crystal orientation is obtained by selectively growing only crystal grains having a specific orientation using the phenomenon. In order to obtain a high magnetic flux density grain-oriented electrical steel sheet, a method in which AlN and MnS or a combination of AlN and MnSe is used as an inhibitor is often used because it is advantageous. As described above, when AlN is used as an inhibitor, AlN is used during secondary recrystallization.
Since N was easily affected by the atmosphere, the magnetic characteristics were sometimes unstable.

[0004] The inventors of the present invention have made efforts to search for other inhibitors, and have developed a technique for manufacturing a high magnetic flux density grain-oriented electrical steel sheet using a BN-based inhibitor. No. 301474). In addition, grain-oriented electrical steel sheets using this BN as an inhibitor have existed before,
For example, Japanese Patent Publication No. 58-43445 discloses 0.0006-0.
A technique using steel containing 0080 wt% B and 0.0100 wt% N is disclosed. However,
The magnetic flux density of the resulting material in the technique in -43445 discloses disclosed is a most about 1.89 T in the value of B _8, the magnetic flux density is not sufficient, the iron loss was not said to be less favorable . In contrast, the materials that the inventors have developed and applied for a patent earlier are those whose inhibitors are BN and MnS or BN
And MnSe, which are based on a manufacturing technique of changing hot rolling conditions in accordance with the Si content and the B content, so that a material having an extremely high magnetic flux density can be stably obtained.
Nevertheless, in transformers and the like in which grain-oriented electrical steel sheets are used, the demand for improved magnetic properties is not stopped from the viewpoints of product miniaturization and energy saving, etc. Low iron loss was required.

[0005]

The present invention relates to such a BN
It is an object of the present invention to propose a method capable of manufacturing an excellent grain-oriented electrical steel sheet having further low iron loss and high magnetic flux density when a system inhibitor is used.

[0006]

Means for Solving the Problems The inventors of the present invention effectively utilize not only the precipitation of BN as an inhibitor, but also the precipitation of silicon nitride in the course of the manufacturing process, and the texture of Bi contained in steel. It has been discovered that combining the techniques for effectively producing a control effect solves the above-mentioned problem.

[0007] Regarding the production technique of Bi-containing steel, Japanese Patent Application Laid-Open No. 56-18044 discloses a technique for producing Bi-oriented steel sheets in the production of grain-oriented electrical steel sheets using MnS or MnSe as an inhibitor.
And a technique for obtaining a high magnetic flux density by terminating the slab repressing treatment at 1050 ° C. or lower. Japanese Patent Publication No. 56-21331 discloses Bi and Al.
A technique is disclosed in which a combination of N and MnS and a combination of Bi, AlN and MnSe increase the magnetic flux density and obtain good characteristics of an iron loss value _{W17 / 50} . In addition, Tokuhei 7-621
In Example 3 of Japanese Patent Publication No. 76, a hot-rolled sheet of grain-oriented electrical steel containing Al, S and Bi was subjected to a hot-rolled sheet annealing at 1000 ° C. for 1 minute at 10 ° C. After intermediate annealing, the steel sheet is quenched and subjected to age rolling to obtain a grain-oriented electrical steel sheet having a high magnetic flux density. However, Japanese Patent Application Laid-Open No. 56-18044
The technique disclosed in the above publication was not sufficient as a value of the magnetic flux density. Further, in the techniques disclosed in Japanese Patent Publication No. 56-21331 and Japanese Patent Publication No. 7-62176, it is essential to use AlN as an inhibitor, so that the magnetic characteristics may fluctuate depending on the atmosphere of the secondary recrystallization annealing. However, the obtained iron loss value is unstable, so that it cannot be said that the technology is industrially sufficient. In this regard, the inventors have found that using BN as the primary inhibitor does not create these disadvantages.

In addition to the above findings, it has been found that the effect of the above-mentioned silicon nitride can be effectively utilized by further restricting the contents of Al and V as impurities in steel to a certain value or less. The invention has been advantageously solved and the present invention has been completed.

That is, the present invention relates to C: 0.030 to 0.09.
5 wt%, Si: 1.5 to 7.0 wt%, Mn: 0.03 to 2.50 wt%, S
Or Se alone or in a total amount of 0.003 to 0.040 wt%, B: 0.00
A steel slab containing 10 to 0.0070 wt% is heated at a temperature of 1350 ° C. or more, then hot-rolled, and subjected to one or two or more cold rollings, and a final cold-rolling reduction of 80 to 95%. In the series of high magnetic flux density grain-oriented electrical steel sheet manufacturing methods in which the primary recrystallization annealing is performed after the final sheet thickness is applied under the following conditions, and then the annealing separator is applied, and then the final finishing annealing is performed, 0.0005 to 0.100 wt% and N in an amount of 30 to 120 wtppm, Al as an impurity is 0.015 wt% or less, and V is
0.010 wt% or less, hot rolling time is 50 to 220 seconds, and hot rolling end temperature is 850 ° C
After completion of hot rolling, quench at a cooling rate of 30 ° C / s or more, wind up in a coil at a temperature of 700 ° C or less, and raise the temperature at 500 ° C or more in the temperature rise process of primary recrystallization annealing. The temperature rate is 8 ° C / s or more, and the annealing temperature of this annealing is 800
This is a method for producing a high magnetic flux density grain-oriented electrical steel sheet having extremely low iron loss, characterized by a temperature of up to 900 ° C.

According to the present invention, Sb, S
One or two or more selected from n, Cu, Cr, Ni and Ge are contained in the range of 0.0010 to 0.080 wt% for Sb and 0.0010 to 1.30 wt% for Sn, Cu, Cr, Ni and Ge, respectively. After decarburizing annealing, N is introduced into the steel by 150 ~ until the start of secondary recrystallization.
Nitriding treatment to be contained in the range of 250 wtppm, formation of multiple grooves on the steel sheet surface after final cold rolling and before final finish annealing, or after final finish annealing, and suppression of film formation as an annealing separator It is more preferable to use a mold annealing separator and perform one or two or more of the steps of forming a tension coating after the final finish annealing.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the process of achieving the present invention will be described below based on experimental examples. (Experiment: Effects of hot rolling time, hot rolling end temperature, and intermediate annealing rate of N- and Bi-containing steel on magnetic properties)
After heating two steel slabs having a thickness of 250 mm shown in the ingot symbol A of Table 1 to 1410 ° C., they were rough-rolled to a thickness of 40 mm,
Next, a hot-rolled coil having a thickness of 2.4 mm was formed by hot finish rolling at 940 ° C. and 800 ° C., respectively. The time required for this hot rolling was 150 seconds as the temperature from the start of rough rolling to the end of finish rolling. The same hot rolling was performed on two steel slabs indicated by the ingot symbols B and C and the ingot symbol D in Table 1 as conventional steel components. After hot rolling, the coil was wound at a temperature of 600 ° C. after cooling at a cooling rate of 45 to 50 ° C./s by jet water cooling.

[0012]

[Table 1]

Thereafter, these coils were pickled and then cold-rolled to an intermediate plate thickness of 1.50 mm. After that, all of these coils are divided into two parts, one for 500 ° C as intermediate annealing.
Up to 20 ° C / s rapid heating up to 500 to 1050 ° C at an average rate of 10 ° C / s, and after heat treatment at that temperature for 60 seconds,
It was cooled to room temperature in 40 seconds (symbol 1). The other one is 50
Rapid heating up to 0 ° C at 20 ° C / s, holding at 600 ° C to eliminate rolling oil on steel sheet, and 1050 ° C at an average heating temperature of 3.0 ° C / s
After heating at that temperature for 60 seconds, it was cooled to room temperature in 40 seconds (symbol 2). After these intermediate annealings, each coil was pickled and rolled to a thickness of 0.22 mm by a Sendzimer rolling mill.

Thereafter, degreasing and decarburization annealing were performed at 850 ° C. for 2 minutes for primary recrystallization, and the rate of temperature rise between 500 and 850 ° C. was 20 ° C./s. Next, MgO to which 5% TiO ₂ was added was applied to the coil surface as an annealing separator, and a final finish annealing was performed. In this final annealing, N ₂ 100%
Temperature to 850 ° C at a rate of 30 ° C / h
C. for another 20 hours, and then heated up to 1050 ° C. at a rate of 12 ° C./h in a mixed atmosphere of 25% N ₂ and 75% H _2, and thereafter H ₂
The temperature was raised to 1200 ° C. in a 100% atmosphere, maintained for 5 hours, and then cooled.

After cooling, the unreacted annealing separator is removed and 50
% Of colloidal silica and an insulating coating containing magnesium phosphate as a main component, and baked at 800 ° C. to obtain a product. A specimen of Epstein size was cut out from each product along the rolling direction and subjected to strain relief annealing at 800 ° C. for 3 hours, and then the iron loss value W _17/50 and the magnetic flux density B ₈ at a magnetic flux density of 1.7 T were obtained. It was measured. Table 2 shows these values.
Are shown together.

[0016]

[Table 2]

From Table 2, the ingot symbol A indicates that the hot rolling end temperature is 94.
The product of symbol 1 under the condition of 0 ° C. and intermediate annealing had extremely good _iron loss value W _17/50 and magnetic flux density B ₈ , but the conventional components (ingot symbols B, C and D) It can be seen that all the products had inferior iron loss values.

As a result of vigorous investigations on the reason why a good result was obtained in the case of the steel ingot symbol A, the hot rolling temperature of 940 ° C. and the intermediate annealing condition symbol 1, the inventors found that the reason was as follows. I got the conclusion. That is, the first point is
In the ingot symbol A, it is N in the steel that functions as an inhibitor component. By rapid cooling after hot rolling, N existing in the supersaturation in the steel is nitrided in the initial stage of the first annealing of the cold rolling. It was finely precipitated as silicon, changed to (B, Si) N during the subsequent heating process, and further precipitated as fine BN in steel, which functioned as an extremely powerful inhibitor. In order to exert these functions sufficiently, it is necessary to contain N in the steel in an amount of 50 wtppm or more, and to reduce the content of nitride-forming components such as Al and V as impurities in the steel, and to improve the solidification. It is essential to effectively act as dissolved N.

The second point is that Bi containing Bi in steel coarsens crystal grains after annealing before final cold rolling (intermediate annealing corresponds to the experimental example). The purpose is to significantly increase the density of (110) [001] crystal grains in the texture of the primary recrystallization annealing after cold rolling. This effect can be further enhanced by increasing the temperature of the primary recrystallization to rapid heating. Further, Bi effectively acts as a suppressing force in a high temperature region in the final finish annealing. That is, silicon nitride decomposes at a high temperature of 800 ° C. or higher and cannot function as an inhibitor, but Bi has an effect of suppressing the growth of primary recrystallized grains at a higher temperature. 110)
It has the effect of promoting secondary recrystallization of crystal grains close to the [001] orientation.

Bi is an essential component of the present invention,
It has been confirmed that, for the first time, the primary recrystallization texture is improved to a certain extent by the presence of this component, and the secondary recrystallization becomes possible.

In order to increase the amount of solute N in steel, it is necessary to maintain the hot rolling end temperature at a high temperature and to keep the hot rolling time within a certain time. Further, after the hot rolling is completed, it is necessary to rapidly cool and wind the coil at a temperature as low as possible. If it is rolled slowly or at a high temperature, coarse silicon nitride precipitates in the steel, so that fine BN precipitates cannot be obtained in the cold rolling step, and a strong inhibitory effect cannot be obtained. When the coil is quenched and wound at a low temperature, some silicon nitride precipitates in the steel. However, the silicon nitride in this case is extremely fine and does not become harmful. When the hot rolling time is longer than a certain time, coarse BN precipitates in the steel, and it becomes impossible to obtain fine BN in cold rolling. Further, as described above, the solid solution N in the steel is fixed.
Even when a large amount of impurities such as Al and V are present, sufficient solid solution C cannot be obtained, so it is necessary to regulate the content of such impurities.

Next, in the temperature rise step of the first annealing in the cold rolling step, first, fine silicon nitride precipitates. At this time, annealing in a temperature range of 500 ° C. or more, which is the precipitation temperature of silicon nitride, is performed. It is necessary to set the heating rate to 5 ° C / s or faster. When the temperature is gradually increased, coarse silicon nitride precipitates, and the size of (B, Si) N and BN which subsequently precipitates also becomes coarse, so that a predetermined function as an inhibitor cannot be obtained. That is, the first technology of the present invention is that fine BN precipitates can be obtained by gradually replacing B of silicon nitride, which is finely precipitated in steel at a low temperature, with increasing temperature. It is. The annealing temperature of the first annealing in the cold rolling step needs to be 950 ° C. or higher. However, if it exceeds 1150 ° C., the upper limit is 1150 ° C. since finely precipitated BN gradually becomes coarse.

Next, in order to form a good texture, it is necessary to add Bi. However, the rolling reduction in the final cold rolling is also an important factor, and it is necessary to reduce the rolling reduction to 80 to 95%. It is.
In addition, the temperature increase rate of primary recrystallization annealing at 500 ° C
It is necessary to perform the rapid heating described above. That is, the texture is improved synergistically with the Bi-containing effect. Further, if the temperature of the primary recrystallization annealing is less than 800 ° C., sufficient development of the primary recrystallization texture is not recognized,
On the other hand, when the temperature exceeds 900 ° C., the primary recrystallized grain size becomes coarse, and it becomes impossible to provide a sufficient driving force at the time of secondary recrystallization, resulting in poor secondary recrystallization. The effect of improving the texture by the combination of the above conditions is accompanied by an increase in the (110) [001] orientation of the primary recrystallized grains, and appears as a sharpening of the secondary recrystallized grains. The result is favorable.

The present invention has been completed as a result of intensive studies based on the above experiments and investigations. Hereinafter, with respect to the method for manufacturing a grain-oriented electrical steel sheet of the present invention, the requirements for obtaining the effects of the present invention, the range thereof, and the operation will be described in detail. First, the component composition range of the steel slab will be described. (C: 0.010 to 0.095 wt% (hereinafter simply referred to as “%”)) If the content of C exceeds 0.095%, poor decarburization is caused in the decarburization annealing step, and magnetic properties are deteriorated. On the other hand, if it is less than 0.010%, the effect of improving the structure by the γ transformation cannot be obtained, and the secondary recrystallization becomes incomplete and the magnetic properties deteriorate. Therefore, the content of C is set in the range of 0.010 to 0.095%. (Si: 1.5 to 7.0%) Si is an essential component for increasing electric resistance and reducing iron loss.
% Must be contained, but if the content exceeds 7.0%, the processability deteriorates and the production and processing of the product become extremely difficult. Therefore, the content of Si is 1.5 to 7.0.
% Range. (Mn: 0.03 to 2.50%) Like Si, Mn is an important component because it increases electrical resistance and improves hot workability during manufacturing. For this purpose, it is necessary to contain Mn in an amount of 0.03% or more. However, if it is contained in an amount exceeding 2.5%, γ transformation is induced to deteriorate magnetic properties. Therefore, Mn
Is in the range of 0.03 to 2.5%.

In addition to these components, an inhibitor for inducing secondary recrystallization is required in the steel, and it is necessary to contain B, N, S and / or Se as the inhibitor components. (B: 0.0010 to 0.0070%) If the content of B is less than 0.0010%, the amount of BN precipitated during the heating process of hot-rolled sheet annealing or intermediate annealing is insufficient, and a good secondary recrystallization cannot be obtained. ,on the other hand,
If it exceeds 0.0070%, BN precipitates during hot rolling, and its size becomes coarse. Therefore, the content of B is 0.0010 to
The range is 0.0070%. (N: 30 to 120 ppm) If the content of N is less than 30 ppm, the amount of silicon nitride, (B, Si) N and BN that precipitates during the temperature rise process of hot-rolled sheet annealing or intermediate annealing is insufficient. However, good secondary recrystallization cannot be obtained. On the other hand, if it exceeds 120 ppm, defects such as blisters are caused in the steel. Therefore, the content of N is in the range of 30 to 120 ppm.

Further, in addition to these inhibitor components,
It needs to contain some amount of S and / or Se. (Total of one or two of S or Se: 0.003 to 0.04
0%) S and / or Se precipitate in the steel as Mn compounds or Cu compounds. These compounds act as inhibitors and also precipitate in the process of increasing the temperature during hot-rolled sheet annealing and intermediate annealing. It has a function as a silicon precipitation nucleus.
For the expression of this function, the amount of precipitation for nucleation of fine high-density dispersion may be used alone or in combination.
It is sufficient if the content is 0.003% or more. On the other hand, when it is contained in excess, the excess precipitates out and functions as an inhibitor separately from BN. However, if the content exceeds 0.040%, it precipitates at the grain boundaries and impairs the workability during hot rolling.
Therefore, the total content of each of them alone or in combination of both is 0.003 to 0.040%.

(Bi: 0.0005 to 0.100%) Bi promotes the fine precipitation of silicon nitride and has the effect of improving the primary recrystallization texture, so that an extremely good texture can be obtained. For this purpose, it is necessary to contain 0.0005% or more. However, if the content exceeds 0.100%, it becomes difficult to perform cold rolling.
The range is 0.500%.

Further, Sb, Sn, Te, P, Pb, Zn, In and Cr
Etc. have an auxiliary function of reinforcing the inhibitory power as an inhibitor, so it is preferable to add them arbitrarily to steel, but among them, Sb, Sn, Cu, Cr, Ni and Ge act advantageously, so It is preferable to include one or more selected from the above. For this purpose Sb is 0.0010-0.
080% is preferable, and the content of Sn and Cr is 0.0010 to 0.0010%.
A content of 1.3% is preferred. Including Cu and Ni in steel has the effect of strengthening the inhibitor and improving the structure, which is advantageous for enhancing the effect of the present invention. For this purpose, it is preferable to contain each of these components in the range of 0.0010 to 1.30%. Other components are effective in the range of 0.0010 to 1.3%.

Further, the content of Al is 0.015% or less as an impurity,
Must be regulated to 0.010% or less.
That is, since these components combine with N in steel, the amount of solute N effective for producing silicon nitride is reduced. Therefore, excessive content deteriorates the magnetic properties of the product and is harmful. Therefore, it is necessary to regulate the Al content to 0.015% or less and the V content to 0.010% or less.

The steel slab for grain-oriented electrical steel sheets adjusted to the above-mentioned composition can be manufactured by any conventionally known method. Usually 200 ~
Although a slab having a thickness of 300 mm is used, there is no difference in the effects of the present invention even when a slab having a thickness of 30 to 100 mm is used. In this case, it is possible to omit the rough rolling step of hot rolling. The steel slab is heated to a high temperature for the solid solution of the inhibitor in the steel. Therefore, the slab heating temperature needs to be 1350 ° C. or higher. If the slab heating temperature is lower than 1350 ° C., the solid solution of the inhibitor is not sufficient, and BN is coarsely precipitated, resulting in secondary recrystallization failure. Also,
At the time of hot rolling, a known technique such as a thickness reduction treatment and a width reduction treatment for uniformizing the structure before and after slab heating can be optionally added. Further, when the slab is induction-heated, the temperature can be raised to a high temperature of 1400 ° C. or more in a very short time of 15 to 30 minutes.

In hot rolling, the following four requirements are indispensable. First, the time from the start to the end of rolling is set to 50 to 220 seconds. This is because if less than 50 seconds, precipitation of MnS and MnSe, CuS and CuSe, etc. becomes insufficient, and fine precipitation of BN in the cold rolling process is not obtained, while
If the time exceeds 220 seconds, BN precipitates coarsely during hot rolling, and in any case, a strong inhibitory effect cannot be obtained. Second, the hot rolling end temperature should be 850 ° C. or higher. If the hot-rolling end temperature is lower than 850 ° C, silicon nitride or BN starts to coarsely precipitate in the steel, resulting in deterioration of the inhibitory power of the inhibitor.

Third, after completion of the hot rolling, rapid cooling is performed at a cooling rate of 30 ° C./s or more. In other words, quenching suppresses the precipitation of BN and silicon nitride from the supersaturated state, and increases the fineness of silicon nitride and subsequent (B, Si) N and BN during the temperature rise process in hot-rolled sheet annealing and intermediate annealing. The driving force for precipitation will be increased. Fourth, set the coil winding temperature to 700
C. or lower. This is because when the winding temperature exceeds 700 ° C., silicon nitride and BN are coarsely precipitated from the supersaturated state, and the inhibitory power of the inhibitor is deteriorated, so that desired magnetic properties cannot be obtained.

In the cold rolling step, a one-time cold-rolling method after hot-rolled sheet annealing, a two-time cold-rolling method with intermediate annealing after hot-rolled sheet annealing, or a hot-rolled sheet annealing is omitted or reduced in temperature. Any of the two cold rolling methods with annealing can be adopted, and further, the three cold rolling methods can be adopted. In the first annealing (hot-rolled sheet annealing or intermediate annealing) heating step in this cold rolling step, fine precipitation of silicon nitride, which is the essence of the present invention, followed by (B, Si) N and finally Performs BN precipitation treatment.

For this purpose, in the first annealing in the cold rolling step, it is necessary to set the heating rate at 500 ° C. or more to 5 ° C./s or more and the annealing temperature to 1000 to 1150 ° C. . This is because if the annealing rate at 500 ° C. or more is less than 5 ° C./s, silicon nitride and BN begin to precipitate coarsely, resulting in a reduction in inhibitory power. However, 500 ℃
If it is less than 1, the temperature is too low for the precipitation of silicon nitride or the like, so that the precipitation of the inhibitor is not significantly affected.
Therefore, if the temperature of the hot-rolled sheet annealing is set to less than 500 ° C., this annealing is not regarded as the first annealing in the cold rolling step. 1000 ° C for the first annealing temperature in the cold rolling process
It is necessary that the above conditions be satisfied. At this temperature, all the fine silicon nitride precipitated in the early stage of the temperature rise is converted into BN. on the other hand,
When the temperature exceeds 1150 ° C, Ostwald growth of finely precipitated BN starts, and the suppressing power deteriorates due to coarsening of the precipitate.

Further, regarding the cooling process of the annealing,
Although there is no particular limitation, a quenching treatment for increasing the solid solution C in the steel after annealing, or a quenching treatment for precipitating fine carbide in the steel and a subsequent low-temperature holding treatment are performed. Is effective in improving the magnetic properties of the product. Here, the quenching process is a process of blowing a gas and / or a liquid onto a steel sheet as a cooling medium to cool the steel sheet so as to have a cooling rate faster than natural cooling, for example, blowing N ₂ gas, mist water or the like. This is the process of spraying jet water to cool the steel plate.

Further, a known means for increasing the oxidizing property in the annealing atmosphere and decarburizing the surface layer of the steel sheet also works effectively. The decarburization amount at this time is preferably in the range of 0.005 to 0.025%. By such decarburization treatment, the C content of the steel sheet surface layer portion is reduced, and the amount of γ transformation during annealing is reduced, so that the inhibitory force of the sheet thickness surface layer portion where nuclei of secondary recrystallization is generated is strengthened, A more preferable secondary recrystallization can be obtained.
To obtain this effect, the C content of the steel sheet is preferably reduced by 0.005% or more. However, when the content is reduced more than 0.025%, the primary recrystallized structure is deteriorated, which is not preferable.

Regarding the rolling reduction of the cold rolling, it is necessary to make the rolling reduction of the final cold rolling in the range of 80 to 95% as conventionally known. This is because when the rolling reduction exceeds 95%, secondary recrystallization becomes difficult, and when the rolling reduction is less than 80%, good secondary recrystallization orientation cannot be obtained, and in any case, the magnetic flux density in the product deteriorates. .

Further, in the final cold rolling, it is possible to carry out warm rolling or inter-pass aging as is known, so that the magnetic properties can be further improved. After the final cold rolling, it is also preferable to provide a linear groove on the surface of the steel sheet, which is a known magnetic domain refining means.

The steel sheet having the final thickness obtained by the above method is subjected to primary recrystallization annealing. It is particularly important to control the rate of temperature rise during this annealing. That is, if the rate of temperature increase at a temperature of 500 ° C. or more at which the primary recrystallization starts is less than 8 ° C./s, it becomes difficult to improve the primary recrystallization texture of the present invention containing Bi, resulting in high magnetic flux density and low magnetic flux density. The grain-oriented electrical steel sheet of the present invention having both iron loss cannot be obtained. Therefore, the heating rate in the temperature range
It is essential that the temperature be at least ° C / s. Further, the soaking temperature of the primary recrystallization annealing is set to a temperature range of 800 to 900 ° C. The primary recrystallized grains of Bi-containing steel have a low nucleation frequency of recrystallization, and thus tend to have a large size, and the driving force of the secondary recrystallized grains tends to decrease. In order to avoid this adverse effect, it is necessary to set the primary recrystallization temperature to 900 ° C. or less. But on the contrary
If the temperature is lower than 800 ° C., a desired primary recrystallized structure cannot be obtained, and the magnetic properties are deteriorated. The primary recrystallization annealing can also serve as decarburization annealing. However, in this case, if the annealing temperature is lower than 800 ° C., the decarburization becomes insufficient and the C content cannot be reduced to 0.002% or less. The desired magnetic characteristics cannot be obtained.

After the primary recrystallization annealing, an annealing separator is applied to the surface of the steel sheet and is subjected to final finish rolling. In the final finish annealing, the steel sheet undergoes secondary recrystallization, and the steel sheet is further purified in a high-temperature region to obtain desired magnetic properties.
In addition, by blending Al ₂ O ₃ and chloride in the annealing separator, it becomes a film formation suppressing type annealing separator, and the formation of a forsterite film which is usually formed after final finish annealing is suppressed, It is also possible to form a new tension film after finish annealing. As the tension coating for this purpose, any known coating such as a ceramic coating, a vitreous coating, a mixture of both, and metal plating is suitable.

It is also possible to perform a nitriding treatment in which N is contained in the steel in the range of 150 to 250 wtppm from after the primary recrystallization annealing to the start of the secondary recrystallization. For this purpose, known techniques such as heat treatment in an NH ₃ atmosphere after decarburizing annealing, inclusion of a nitride in an annealing separator, and nitriding atmosphere in the final finish annealing atmosphere can be applied.

Furthermore, a conventionally well-known magnetic domain refining treatment for forming a plurality of grooves on the surface of the steel sheet between after the final rolling and before the final finish annealing or after the final finish annealing can be performed. After the final annealing, an insulation coating is applied and baked as required, and a flattening process is performed to obtain a product. Furthermore, in order to reduce iron loss on the steel sheet after the flattening process, a process of applying a plasma jet or a laser beam in a linear manner as a well-known domain refining process or providing a linear dent by a projection roll is performed. It can also be applied.

[0043]

EXAMPLES (Example 1) Ingot numbers A,
Continuously cast molten steel with the composition of B, E, F, G, H and I into a 250 mm thick slab, at a temperature of 1180 ° C
After holding for 3 hours, reduce the width of the slab by 40 mm and reduce the thickness to 230 mm, then put it into an induction heating furnace, raise the temperature to 1410 ° C in 30 minutes and soak for 10 minutes After that, hot rolling was started. In this hot rolling, the sheet thickness was 35 mm in rough rolling and 1.8 mm in finishing rolling, and the hot rolling time was 120 seconds. The hot rolling end temperature was 930 to 950 ° C. After the hot rolling was completed, the steel sheet was quenched at a rate of 55 to 65 ° C / s by spraying jet water onto the steel sheet, and wound up at 600 to 630 ° C.

[0044]

[Table 3]

Thereafter, each coil was subjected to hot rolled sheet annealing at 1100 ° C. for 40 seconds. In this hot-rolled sheet annealing, after preheating to 300 ° C, the temperature was raised to 500 ° C in 15 seconds, further raised to 1100 ° C at a rate of 12 ° C / s, and then quenched with mist water at a rate of 35 ° C / s. .
The annealing atmosphere was a mixed atmosphere of 50% N ₂ and 50% H ₂ having a dew point of 55 ° C., and 0.012% of C was decarburized from the surface layer of the steel sheet. After this, each coil is pickled, rolled to a final sheet thickness of 0.22 mm by a Sendzimer mill at a rolling pass exit temperature of 170 to 250 ° C, and two or more passes at a temperature of 220 ° C or more, and degreased. Decarburization annealing was performed at 850 ° C for 2 minutes. The annealing rate at 500 to 850 ° C for this decarburizing annealing was 20 ° C / s.

Next, MgO containing 5% of TiO ₂ was applied to the coil surface as an annealing separator, and the temperature was raised up to 850 ° C.
Atmosphere of N ₂ 100%, mixed atmosphere of 25% N ₂ and 75% H ₂ until the temperature rise process up to 1150 ° C, then heat up to 1200 ° C in H ₂ 100% atmosphere and hold for 5 hours Finish annealing was performed, after which the unreacted annealing separator was removed. These coils are further coated with an insulating coating based on magnesium phosphate containing 50% colloidal silica.
The product was baked at 800 ° C, and the surface of the steel sheet was irradiated with a plasma jet linearly at 5 mm intervals in the rolling direction.

An SST test piece having a width of 100 mm and a length of 400 mm was cut out from each product along the rolling direction, and the iron loss value W _17/50 and the magnetic flux density B ₈ at a magnetic flux density of 1.7 T were measured. . These values are summarized in FIG. 1 in relation to the Bi content. As shown in FIG. 1, the grain-oriented electrical steel sheet manufactured using the ingots A, F, G, H, and I having a suitable Bi content of the present invention has a low iron loss in addition to a high magnetic flux density. Magnetic properties are obtained.

(Example 2) A molten steel having a composition indicated by ingot symbols J and K in Table 3 was cast by a continuous casting machine while performing electromagnetic stirring to form a slab having a thickness of 220 mm. In melting each ingot, by changing the degree of impurity cleaning treatment,
The ingot symbol J changed the Al content in the range of 0.001 to 0.032%, and the ingot symbol K changed the V content in the range of 0.003 to 0.025%.

The slab after casting is charged into an induction heating furnace,
The temperature was raised to 1390 ° C. for 1 hour in N ₂ gas to perform hot rolling. In this hot rolling, 45 mm in rough rolling and 2.0 mm in finishing rolling
The hot rolling time was 120 to 140 seconds.
The temperature at the end of hot rolling was 970 to 990 ° C, and the cooling rate from the end of hot rolling to coil winding was 65 to 70 ° C / s. Further, the coil winding temperature was 550 to 620 ° C.

After this, each coil was preheated at 200 ° C.
After the temperature was raised to 500 ° C. in 15 seconds and further raised to 1100 ° C. at a rate of 15 ° C./s, the temperature was maintained for 30 seconds, and mist water was sprayed to rapidly cool. The annealing atmosphere at this time was an air-fuel ratio of 0.95 and a dew point.
Using 45 ° C fuel gas, decarburize the surface layer of steel sheet to reduce C content
0.020% reduction. After this, pickling is performed, followed by warm rolling at a stand exit temperature of 250 ° C. by a Sendzimir rolling mill and aging between passes at 150 to 230 ° C. for 10 to 40 minutes to a final sheet thickness of 0.34 mm. Rolled.

Next, after degreasing, decarburizing annealing was performed at 820 ° C. for 2 minutes. The rate of temperature rise in this decarburizing annealing at 500 to 820 ° C was 14 ° C / s. Next, MgO containing 7% TiO ₂ and 2% strontium sulfate was applied to the coil surface as an annealing separating agent, and a final finish annealing was performed. The conditions of the final annealing were as follows: a heating rate of 35 ° C./h, and N ₂ 10
0% atmosphere, 30 minutes before the temperature rise to 1150 ° C
% N ₂ and 70% H ₂ mixed atmosphere, and thereafter 11% in H ₂ 100% atmosphere
After the temperature was raised to 80 ° C, the temperature was maintained for 5 hours. Then, the unreacted annealing separator was removed. These coils have an additional 60
% Of colloidal silica, and an insulating coating containing aluminum phosphate as a main component, and baked at 800.degree.

A test piece of Epstein size was cut out from each product along the rolling direction and subjected to strain relief annealing at 800 ° C. for 3 hours, and then the iron loss value W at a magnetic flux density of 1.7 T was obtained.
_17/50 and the magnetic flux density was measured B _8. The results of these measurements are shown in FIGS. As shown in these figures, it is understood that the Al content and the V content as impurities need to be restricted to 0.015% or less for Al and 0.010% or less for V.

(Example 3) Ingot symbols L, M and N in Table 3
A steel slab having a thickness of 70 mm having the composition shown in Table 1 was melted and cast into six pieces each. These slabs were charged into a heating furnace of an electric heating type, heated to 1350 ° C., and then hot-rolled by a finishing mill to form a 2.4 mm hot-rolled coil. At this time, the rolling speed of the six coils of the ingot symbol L was changed to change the hot rolling time to 22 seconds, 43 seconds, 53 seconds, 126 seconds, 225 seconds and 36 seconds.
Change the temperature to 5 seconds, set the hot rolling end temperature to 900 to 950 ° C, and rapidly cool at a rate of 45 to 50 ° C / s from the end of hot rolling to 650
It was wound up in a coil at ℃. For the coil of ingot symbol M, the hot rolling time was set to 160 seconds, and the amount of roll coolant was changed to change the rolling end temperature to 1050 ° C, 1000 ° C,
Change to 0 ° C, 870 ° C, 840 ° C and 810 ° C, then 38-45
After water cooling at a cooling rate of ° C / s, the coil was wound at 550 to 620 ° C to form a hot rolled coil. Further, the hot rolling time of all six coils of the ingot symbol N was 160 seconds and the hot rolling end temperature was 98 seconds.
After the hot rolling was completed at 0 to 1000 ° C., the steel sheet was rapidly cooled at a cooling rate of 45 to 67 ° C./s and wound into a coil at 640 to 660 ° C.

These coils were annealed at 500 ° C., pickled, and cold rolled to 1.80 mm by a tandem rolling mill.
After that, as intermediate annealing, the temperature was raised at a rate of 20 ° C./s to 500 ° C., and then raised to 1030 ° C. at a rate of 12 ° C./s.After holding for 60 seconds, jet water was jetted for 30 seconds. A heat treatment for cooling was performed. After that, each coil was rolled to a final thickness of 0.26 mm with a Sendzimer rolling mill, degreased, and electrolytically etched to a depth of 20 μm, a width of 120 μm, and a groove extending in a direction perpendicular to the rolling direction in the surface of the steel sheet by rolling in a rolling direction. Repeat interval 5 mm
It was formed repeatedly. After that, decarburizing annealing was performed at 820 for 2 minutes. At this time, for the steel ingot symbols L and N, the rate of temperature increase from 500 to 820 ° C was 17 ° C / s, and
For each coil, a heating rate of 500 to 820 ° C
4.0 ° C / s, 6.2 ° C / s, 8.5 ° C / s, 16.5 ° C / s, 20 ° C / s and
Changed to 35 ° C / s. Then at 800 ° C. 10% NH ₃ and 70% N ₂
When the 20% H ₂ Metropolitan nitriding treatment in an atmosphere for 30 seconds consisting of the N content in the steel was increased 120 to 150 DEG ppm.

Thereafter, MgO containing 7% TiO ₂ and 2% tin oxide was applied to the coil surface as an annealing separating agent, and a final finish annealing was performed. The conditions for this final finish annealing were as follows:
° C. / and h, N ₂ 100% of the atmosphere up to 950 ° C. of in heating, mixed atmosphere subsequent until the course of temperature elevation up to 1180 ℃ 35% N ₂ and 65% H _2, thereafter H ₂ 100% The atmosphere was kept for 5 hours. Then, 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.

A specimen of Epstein size was cut out from each product along the rolling direction, subjected to strain relief annealing at 800 ° C. for 3 hours, and then the value of iron loss W at a magnetic flux density of 1.7 T was obtained.
_17/50 and the magnetic flux density was measured B _8. The results of these measurements are shown in Tables 4, 5 and 6. From each table, it can be seen that in the product satisfying the manufacturing conditions of the present invention, both high magnetic flux density and low iron loss are obtained.

[0057]

[Table 4]

[0058]

[Table 5]

[0059]

[Table 6]

Example 4 Ingot symbols A to A shown in Table 3
Each slab having the composition of R is subjected to electromagnetic stirring while 24
Cast into a 0 mm thick slab. These slabs were heated to 1220 ° C in a gas furnace, further charged in an induction heating furnace, heated to 1430 ° C by gradual heating for 2 hours, and hot-rolled to a thickness of 2.0 mm by hot rough rolling and finish rolling. A rolled coil was used. The rolling time of this hot rolling was 180 seconds, and the hot rolling end temperature was 95 seconds.
0 to 980 ° C, and after hot rolling, cool at 55 ° C / s
It was wound at 580 ° C.

After pickling, the coils were made to have an intermediate sheet thickness of 1.40 mm by a tandem rolling mill consisting of four stands, and then subjected to intermediate annealing. In this intermediate annealing, the temperature was raised to 500 ° C at a rate of 14 ° C / s, then raised to 1100 ° C at a rate of 18 ° C / s, soaked for 40 seconds, and then rapidly cooled to 35 ° C / s by jetting jet water. And Moreover, the annealing atmosphere is 70% at a dew point of 50 ° C. H ₂ and 30%
Decarburize from the surface of steel sheet as N ₂ atmosphere to reduce C content to 0.015
%. Thereafter, using the same tandem rolling mill, the third and fourth stand-side roll bites were subjected to warm rolling such that the maximum sheet temperature at the exit side was 220 to 280 ° C. to a final sheet thickness of 0.19 mm.

Thereafter, a degreasing treatment is performed, a decarburization treatment is performed at 850 ° C. for 2 minutes, a temperature rising rate of 500 to 850 ° C. is set to 14 ° C., and MgO containing 6% TiO ₂ and strontium hydroxide is added.
Was applied to the coil surface as an annealing separator, and was subjected to final finish annealing. The annealing conditions at this time were as follows: the temperature was raised to 850 ° C. in N ₂ at a rate of 35 ° C./h, and then maintained at 850 ° C. for 25 hours.
Thereafter, the atmosphere was a mixed atmosphere of 20% N ₂ and 80% H ₂ until 1100 ° C., and after that, the temperature was raised to 1180 ° C. in an atmosphere of 100% H ₂ and maintained for 5 hours. After annealing, remove the unreacted annealing separating agent, apply an insulating coating mainly composed of magnesium phosphate containing 60% colloidal silica, bake it at 800 ° C, and form a plasma jet linearly at 5 mm intervals. To give a product.

An SST test piece having a width of 100 mm and a length of 400 mm was sampled from each product along the rolling direction, and the iron loss value W _17/50 and the magnetic flux density B ₈ at a magnetic flux density of 1.7 T were measured. Table 7 shows the measurement results. From Table 7, it can be seen that, in the product having the component composition range of the present invention, an extremely excellent value was obtained in the iron loss in the low magnetic flux density region.

[0064]

[Table 7]

[0065]

As described above in detail, according to the method of the present invention, it is possible to produce an excellent grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between Bi content and magnetic properties.

FIG. 2 is a diagram showing the effect of Al content as an impurity in steel on magnetic properties.

FIG. 3 is a diagram showing the effect of the V content as an impurity in steel on magnetic properties.

Claims (5)

[Claims] C: 0.030 to 0.095 wt%, Si: 1.5 to 7.
A steel slab containing 0 wt%, Mn: 0.03 to 2.50 wt%, S or Se alone or in a total of 0.003 to 0.040 wt%, and B: 0.0010 to 0.0070 wt% is heated at a temperature of 1350 ° C. or more, and then heated. Cold rolling at least once or twice, under the condition that the rolling reduction of the final cold rolling is 80 to 95% to make the final sheet thickness and then perform the primary recrystallization annealing, and then the annealing separator After applying,
A series of methods for producing a high magnetic flux density grain-oriented electrical steel sheet to be subjected to final finish annealing, wherein the steel slab contains 0.0005 to 0.100 wt% of Bi and 30 to 120% of N.
wtppm and 0.015 wt% Al as an impurity
Hereinafter, V is regulated to 0.010 wt% or less, the hot rolling time is 50 to 220 seconds, the hot rolling end temperature is 850 ° C or more, and after the hot rolling is completed, 30 ° C / s.
Cool rapidly at the above cooling rate and wind it into a coil at a temperature of 700 ° C or less, and set the heating rate at 500 ° C or more in the temperature rise process of primary recrystallization annealing to 8 ° C / s or more, and set the annealing temperature for this annealing. 800 to 90
A method for producing a high magnetic flux density grain-oriented electrical steel sheet having extremely low iron loss, wherein the temperature is set to 0 ° C. 2. Sb, Sn, Cu, Cr, Ni and Ge in a steel slab.
One or two or more selected from Sb is 0.0010 to 0.080
wt%, Sn, Cu, Cr, Ni and Ge are 0.0010-1.30wt respectively
%. The method for producing a high magnetic flux density grain-oriented electrical steel sheet having extremely low iron loss according to claim 1, wherein the content is in the range of%. 3. The method according to claim 1, wherein after the decarburizing annealing, the steel is subjected to a nitriding treatment for containing N in a range of 150 to 250 wt ppm in the steel before the start of the secondary recrystallization. Manufacturing method of high magnetic flux density grain-oriented electrical steel sheet with low iron loss. 4. The extremely iron loss according to claim 1, wherein a plurality of grooves are formed on the surface of the steel sheet between after final cold rolling and before final finish annealing or after final finish annealing. Method for producing high magnetic flux density grain-oriented electrical steel sheet with low density. 5. An extremely ferrous iron according to claim 1, wherein an annealing separating agent of a film formation suppressing type is used as the annealing separating agent, and a tension coating is formed after the final finish annealing. Manufacturing method of high magnetic flux density grain-oriented electrical steel sheet with low loss.