JPH10280041A - Production of grain-oriented silicon steel sheet having extremely excellent core loss characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high magnetic flux density grain-oriented silicon steel sheet having a good steel sheet shape and further having extremely excellent core loss. SOLUTION: In the method for producing a grain-oriented silicon steel hot rolled sheet contg. a process in which a steel contg., by weight, <=0.10% C, 2.5 to 7.0% Si and ordinary inhibitor components and the balance Fe with inevitable impurities is treated by an ordinary method, and the strip rolled approximately to a final product thickness is subjected to decarburizing annealing and is subjected to final finish annealing, at the time of subjecting the strip to the decarburizing annealing, immediately before this or in the temp. raising stage in the decarburizing annealing, rapid heating is executed by using conductive rolls, the sheet tension between the roll on the low temp. side and the roll on the high temp. side in the conductive rolls is regulated to 1.0 to 4.0 kg/mm<2> , the drawing down force in the roll on the high temp. side is regulated to 1.0 to 4.0 kg/mm by linear pressure, and the temp. of the roll on the high temp. side is regulated to >=200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high magnetic flux density unidirectional magnetic steel sheet which contains Si, has a good steel sheet shape, and has extremely excellent iron loss characteristics.

[0002]

2. Description of the Related Art Generally, the magnetic properties of a grain-oriented electrical steel sheet are as follows.
It is evaluated based on both iron loss characteristics and excitation characteristics. Increasing the excitation characteristics makes it possible to reduce the size of equipment that increases the design magnetic flux density.On the other hand, reducing the iron loss characteristics reduces the amount of heat energy lost when used as electrical equipment and reduces power consumption. This is effective in saving money. Furthermore, aligning the <100> axis of the crystal grains of the product in the rolling direction can enhance the magnetic properties and lower the iron loss properties. Technology was developed.

For example, Japanese Patent Publication No. 40-15644 discloses a method for manufacturing a grain-oriented electrical steel sheet in order to obtain a high magnetic flux density. This is a production method in which AlN + MnS is made to function as an inhibitor, and the rolling reduction in the final cold rolling step is a strong rolling exceeding 80%. According to this method, a grain-oriented electrical steel sheet having a high degree of integration of secondary recrystallized grains in the {110} <001> orientation and having a high magnetic flux density of B8 of 1.870 T or more can be obtained.

However, although this manufacturing method can reduce iron loss to some extent, the particle size of the secondary recrystallized macro is 1%.
Since it was as large as 0 mm, eddy current loss, which is a factor affecting iron loss, could not be reduced, and a good iron loss value could not be obtained. In order to improve this, Japanese Patent Publication No. 57-22
No. 52 discloses a method of subjecting a steel sheet to laser treatment, and Japanese Patent Publication No. 58-2569 discloses various methods of subdividing magnetic domains, such as a method of applying mechanical strain to a steel sheet. .

On the other hand, Japanese Patent Publication No. 6-51187 discloses a method for improving the magnetic characteristics by making the secondary recrystallized grains smaller. That is, the publication states that a steel sheet (strip) rolled at room temperature is heated at a heating rate of 140 ° C./sec or more to 657.
The steel sheet is subjected to ultra-rapid annealing to a temperature of not less than ℃, the steel sheet is decarbonized, subjected to a final high-temperature annealing treatment to perform secondary growth, whereby the steel sheet has a reduced secondary particle size and stress relief annealing treatment. Manufacturing methods with improved iron loss that persists without significant change thereafter are disclosed.

[0006] However, it is difficult to obtain iron loss comparable to the conventional magnetic domain refining simply by making the secondary particles finer by this manufacturing method. In particular, when the steel sheet is rapidly exposed to a high temperature by rapid heating, an oxide film having a different composition is formed (firelite (2MgO.SiO ₂ ) is preferentially formed), and MgO is applied in the final annealing. The formation of forsterite (2MgO.SiO ₂ ) is not always good, and there is a problem that sufficient magnetic properties cannot be obtained due to sufficient film tension.

[0007] In order to solve such a problem, the present inventors have proposed that PH ₂ O /
P H ₂ is proposed a method of heating treatment to 0.2 or less non-oxidizing atmosphere a temperature of more than 700 ° C. at 100 ° C. / sec or more heating speeds in, it is disclosed in JP-A-7-62436 . It also proposes using two pairs of direct-current heating rolls as a specific example of rapid heating.

[0008] It has been found that, although good magnetic properties can be obtained by this manufacturing method, a dense oxide layer may be formed on the steel sheet surface during rapid heating. When this oxide layer is formed, it becomes a barrier and affects the decarburizing action. That is, the carbon content in the product plate cannot be reduced, and as a result, the magnetic properties of the product deteriorate due to magnetic aging. In addition, if the decarburization time is increased for sufficient decarburization, the problem of magnetic aging can be solved. However, extending the decarburization time is not preferable because the production cost increases.

In the continuous heat treatment of a steel strip, there are various proposals for a method of using two pairs of energizing rolls for the rapid heating described above. For example, Japanese Patent Application Laid-Open No. Hei 7-292423 discloses that a plate tension (maximum 7 kg / mm ² ) necessary for obtaining the shape of a steel strip is applied between current-carrying rolls. Although the invention described in this publication does not target the magnetic properties, the plate tension is allowed up to 7 kg / mm ² , and applying such a large plate tension results in the deterioration of the magnetic flux density.

In Japanese Patent Application Laid-Open No. 5-54958, the rolling force per unit area between the high-temperature side roll of the current-carrying roll and the heated body (steel strip) is obtained by subtracting the unit tension from the yield point stress of the heated body. It is described as a value. The invention described in this publication is aimed at preventing the wear of the energizing roll and preventing the plate shape from deteriorating, and does not cover magnetic characteristics. That is, the application of the rolling force is regulated irrespective of the magnetic characteristics. Further, JP-A-6-293934
In the publication, when a cold-rolled steel sheet is continuously annealed using a current-carrying roll, the amount of temperature drop of the cold-rolled steel sheet that comes into contact with the high-temperature-side current-carrying roll is regulated in relation to the sheet thickness. As with the invention described in the above-mentioned publication, this is not intended for the magnetic characteristics and is regulated independently of the magnetic characteristics. Therefore, the above-described heat treatment using these energizing rolls cannot be applied to the production of a grain-oriented electrical steel sheet.

[0011]

The above-mentioned conventional heat treatment method using a current-carrying roll relates to a normal cold-rolled steel sheet, and it is difficult to derive a method for improving the magnetic properties from this. In addition, in the electric heating applied to the rapid heating before the decarburization annealing in the method for producing a grain-oriented electrical steel sheet, decarburization was an issue. The present invention has been made in view of the current situation of such a technology, and solves the conventional problems to provide a manufacturing method for stably obtaining a high magnetic flux density unidirectional magnetic steel sheet having a sufficiently low iron loss. To provide.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has the following constitution. That is, C: 0.10% or less by weight, Si:
The steel, containing 2.5-7.0% and the usual inhibitor components, the balance consisting of Fe and unavoidable impurities, is treated in the usual way, and the strip rolled to approximately the final product thickness is decarburized and annealed, In the method for producing a hot-rolled unidirectional electromagnetic steel sheet including a step of performing a finish annealing, when the strip is decarburized and annealed, immediately before or during the heating stage of the decarburization annealing, a current-carrying roll is used. The plate tension between the low-temperature roll and the high-temperature roll is 1.0 to 4.0 kg / mm ² , and the rolling force of the high-temperature roll is 1.0 to 4.0 kg / mm. mm, set the temperature of the hot roll to 20
This is a method for producing a high magnetic flux density unidirectional magnetic steel sheet having extremely excellent iron loss characteristics, which is characterized by being set to 0 ° C. or higher.

As described above, according to the present invention, when the rapid heating is carried out by using a current-carrying roll, the plate tension between the low-temperature roll and the high-temperature roll, the rolling force (linear pressure) at the high-temperature roll, In addition, by regulating the temperature of the high-temperature side roll to the above-described range, the plate shape of the strip is improved, and an appropriate strain is imparted to the strip, and the primary recrystallization after the primary recrystallization becomes the core of the secondary recrystallization. The formation of {110} <001> oriented grains is promoted, and fine secondary recrystallized grains are formed.
It is possible to obtain a grain-oriented electrical steel sheet having a high magnetic flux density of 1.91 (T) or more and extremely excellent iron loss characteristics of W17 / 50 and 0.82 W / kg or less. As described above, the present invention provides a method for manufacturing a grain-oriented electrical steel sheet that achieves both good sheet shape and excellent magnetic properties.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. FIG. 1 schematically shows an example of an electric heating device used in the present invention. A strip 1 is paired with each of the press rolls 5 and 6 and is connected to a low-temperature side electric conductor connected by a conductive member 2. Electric current is supplied by the roll 3 and the high-temperature-side current-carrying roll 4 and heated. Reference numeral 7 denotes a rolling force adjusting device for adjusting the stretching of the strip. Reference numeral 8 denotes an annular transformer connected to an external power supply. The electric heating device can be installed before the decarburizing annealing or incorporated in a heating step of the decarburizing annealing.

As described above, it is known that the strip is heated by a current-carrying roll. However, in order to improve magnetic properties, the present invention requires that the conditions of the current-carrying roll used during rapid heating during decarburization annealing be adjusted appropriately. To choose. That is, in the present invention, the strip is flattened between the low-temperature side roll and the high-temperature side roll and stretched appropriately when heating by energization, thereby improving the plate shape. That is, flattening is performed over the entire width direction, and for this purpose, a tension of 1.0 kg / mm ² or more is required. On the other hand, when the inter-roll tension becomes too high, the texture (100) <025> after the temporary recrystallization.
Tend to increase, which affects the sharpness of the secondary recrystallization orientation in the rolling direction and lowers the magnetic flux density. Therefore, in order to make the magnetic flux density B8 of the final product not less than 1.91 (T), it is necessary that the tension does not exceed 4 kg / mm ² . Preferably 1.5 to 3.0 kg / mm ²
It is good to do.

In the present invention, the rolling force applied to the high-temperature roll is regulated. That is, a linear pressure of 1.0 to 4.0 kg /
mm. Foreign matter may adhere to the surface of the energizing roll or irregularities may be formed due to abrasion. If the linear pressure is low, the contact becomes uneven and sparks may occur at the contact point with the strip. In order to prevent this, the rolling force is preferably set to a linear pressure of 1.0 kg / mm or more, and the plate shape becomes good. However, applying an excessively large linear pressure is not preferable for the shape because the strip heated at a high temperature has low deformation resistance and is easily deformed.
The zero plane increases, affects the stability of secondary recrystallization, and causes magnetic flux density and iron loss to deteriorate. Therefore, the linear pressure is limited to 4.0 kg / mm, and this is set as the upper limit. Preferably, the pressure is 1.5 to 3.0 kg / mm.

FIG. 2 shows that in the process of manufacturing a grain-oriented electrical steel sheet having a thickness of 0.22 mm, rapid heating performed in a heating stage of decarburization annealing is performed by a current-carrying roll. In each case, the relationship between the high-temperature side roll and the magnetic characteristics (B8) is shown. That is, the product of FIG.
077 (wt)%, Si: 3.25%, Mn: 0.08
%, P: 0.01%, S: 0.03%, Al: 0.03
%, N: 0.01%, Cu: 0.08%, Sn: 0.0
%, With the balance being substantially Fe, a continuous cast slab is hot-rolled into a 2.4 mm thick hot-rolled sheet, annealed at 1120 ° C for 1 minute, and then at 220 ° C for 1 minute on the way. The sheet was finished to a sheet thickness of 0.26 mm by cold rolling. When the cold rolled sheet was decarburized and annealed, the temperature was raised using a current-carrying roll shown in FIG. 1, and decarburization annealing was performed at 840 ° C. × 180 seconds. After that, an annealing separator is applied and finish annealing is performed for 120 minutes.
It was obtained by performing at 0 ° C. × 24 hours.

As is apparent from FIG. 2, 1.91 (T)
It can be seen that in order to obtain the above high magnetic flux density (B8), the inter-roll tension should be 4 kg / mm ² or less, and the linear pressure on the high temperature side should be 4 kg / mm or less.

Further, in the present invention, by setting the temperature of the high-temperature side roll to 200 ° C. or more, heat removal from the high-temperature strip heated by the current-carrying member is suppressed, and deterioration of magnetic properties is prevented. That is, when the temperature of the high-temperature side roll is 200
At low temperatures below ℃, the hot strip that comes in contact with it causes a shape change due to heat removal, and the introduced strain changes the texture to obtain an appropriate dive angle of the secondary recrystallization orientation to the plate surface. This is because both magnetic flux density and iron loss deteriorate. Preferably, the temperature is 300 ° C. or higher. The temperature of the high-temperature side roll can be raised by an appropriate heating means, for example, an induction heating means.

Hereinafter, the production process of the present invention will be described in more detail. First, the reasons for limiting the steel components are as follows. C
Is 0.10% or less. If the amount is more than this, the time required for decarburization becomes longer, which is economically disadvantageous. The lower limit of Si is set to 2.5% in order to improve iron loss, but if it is too large, it is likely to break during cold rolling and processing becomes difficult, so the upper limit is set to 7.0%.

Further, in order to manufacture a grain-oriented electrical steel sheet, the following component elements can be added as ordinary inhibitor components. When MnS is used as an inhibitor, Mn and S are added. Mn is desirably 0.015 to 0.15% in order to obtain an appropriate dispersion state of MnS. S is an element necessary for forming MnS and (Mn · Fe) S.
1-0.05% is desirable. Se may be added instead of S, or both may be added.

When AlN is used as an inhibitor, acid-soluble Al and N are added. Acid soluble A
l is 0.01 to 0.1 in order to obtain a proper dispersion state of AlN.
04% is desirable. N is also 0.003 to obtain AlN.
-0.02% is desirable. In addition, Cu, Sn, Sb,
Cr, Bi, and Mo are used to strengthen inhibitors.
At 0% or less, at least one kind may be added.

Next, the molten steel containing the above-mentioned components is made into a slab by a usual ingot casting method or a continuous casting method, and is hot-rolled to obtain an intermediate-thick strip. Further, a strip casting method can also be applied to the present invention.

Next, after performing hot-rolled sheet annealing, a strip having a final product thickness is obtained by performing cold rolling twice or more including one to intermediate annealing. Or, without applying hot-rolled sheet annealing,
Strips of the final product thickness can also be obtained by two or more cold rollings including intermediate annealing. When performing two or more cold rollings including intermediate annealing, the first rolling is performed with a rolling reduction of 5 to 50.
%, Hot-rolled sheet annealing and intermediate annealing are preferably performed at 950 to 1200 ° C. for 30 seconds to 30 minutes. The next final cold rolling reduction is preferably 85% or more. 85% lower limit
This is because below this, a Goss nucleus having a {110} <001> orientation with a high degree of integration in the rolling direction cannot be obtained.

In the cold rolling process, the final thickness is obtained through each thickness step by a plurality of passes during the cold rolling.
In order to improve the magnetic properties, the steel sheet may be given a thermal effect of maintaining the steel sheet at a temperature range of 100 ° C. or more for 1 minute or more in at least one or more sheet thickness stages in the pass.

The strip rolled to the final product thickness is subjected to a heat treatment. This heat treatment is performed by using the above-described current-carrying roll.
Rapid heating to a temperature of 700 ° C. or more at a heating rate of at least seconds. The lower limit of the heating rate at this time is set to 100 ° C./sec. Below this, the {110} <001> orientation grains after the primary recrystallization, which are the nucleus of the secondary recrystallization, decrease, and the fine secondary This is because recrystallized grains cannot be obtained. The lower limit temperature of the heat treatment is set to 700 ° C. because recrystallization does not start below this temperature.

In this rapid heating treatment, the atmosphere of the steel sheet is preferably in a wet hydrogen atmosphere of P H ₂ O / P H ₂ ≤ 4.2 due to the problem of decarburization. Except for such an atmosphere, a dense oxide layer is formed on the surface of the steel sheet, and the decarburization property in the subsequent decarburization annealing is reduced. That is, in the decarburizing annealing step in the manufacturing process of the grain-oriented electrical steel sheet, the carbon content is set to 20 ppm in order to prevent magnetic aging.
You have to decarburize to: For that purpose, it is necessary to suppress the formation of a dense oxide layer formed on the surface of the steel sheet and not to suppress the reaction between carbon and oxygen.

Conventionally, the atmosphere P H ₂ O /
It is known that the P H ₂ in 0.15 to 0.75, knowledge of the atmosphere in the heating step, JP-A-7-6
100 ° C./s only with the invention disclosed in Japanese Patent No. 2436
It is disclosed that PH ₂ O / P H ₂ ≦ 0.2 at the above heating rate.

However, when a rapid heating treatment is performed, the formation of a dense oxide layer formed on the surface of the steel sheet cannot be sufficiently suppressed in this atmosphere. In order to solve such a problem, the rapid heat treatment is performed in a wet hydrogen atmosphere of P H ₂ O / P H ₂ ≦ 4.2, thereby suppressing the formation of a dense oxide layer formed on the steel sheet surface. Very good decarburization. In addition, in order to achieve the above object, PH ₂ O /
The lower limit of P H ₂ is preferably set to 0.4.

In this energization heating, the atmosphere needs to be kept at room temperature in order to use electric equipment. In this case, only about 1 to 3% of hydrogen can be contained in the atmosphere due to the danger of explosion due to hydrogen. In the case where the amount of hydrogen is as small as 1 to 3%, it is desirable to increase the dew point. However, setting the dew point to 30 ° C. or higher may be limited because electric appliances may have an adverse effect such as dew condensation. It is preferable to use the above atmosphere from the viewpoint of desirability.

The above-mentioned rapid heating treatment can be carried out before the decarburizing annealing to be performed next, or it can be incorporated in the decarburizing annealing step as a heating step of the decarburizing annealing. It is preferable because the number is small. In the case of a process in which the slab heating temperature in hot rolling is set to a low temperature and only AlN is used as an inhibitor, a nitriding treatment may be added in an ammonia atmosphere.

Further, by applying an annealing separator such as MgO and performing a final annealing at 1100 ° C. or more for secondary recrystallization and purification, a fine film such as forsterite is formed on the surface of the steel sheet. Obtain secondary recrystallized grains. By further applying an insulating film on a film such as forsterite, a grain-oriented electrical steel sheet having extremely low iron loss characteristics is manufactured.

The magnetic properties obtained as described above maintain a low iron loss that does not change even after subsequent strain relief annealing. In addition, in order to further improve iron loss in the obtained product, it is possible to subject the above-mentioned grain-oriented electrical steel sheet to a treatment for subdividing magnetic domains.

[0034]

Next, embodiments of the present invention will be described. C: 0.0
78%, Si: 3.25%, Mn: 0.08%, P:
0.01%, S: 0.03%, Al: 0.03%, N:
A slab manufactured by a continuous casting method consisting of 0.01%, Cu: 0.08%, Sn: 0.1%, and the remainder substantially made of Fe was hot-rolled into a 2.3 mm hot-rolled sheet. Hot rolled sheet 110
After annealing at 0 ° C. × minutes, a cold rolled sheet having a sheet thickness of 0.22 mm was produced in the middle stage by cold rolling at 220 ° C. × 5 minutes.

The cold-rolled sheet was subjected to decarburizing annealing at 840 ° C. × 180 seconds.
It was applied for 24 hours.

The rapid heating in the heating stage of the decarburizing annealing was performed by using two pairs of energizing rolls as shown in FIG. 1 under various conditions.
Atmosphere and hydrogen + _{nitrogen, P H 2 O / P H} 2: 0.54
Humid atmosphere. Table 1 shows the pass-through conditions of the current-carrying roll, and the shape and magnetic properties (magnetic flux density B) of the obtained product.
8 (T) and iron loss W17 / 15 (W / kg).

[0037]

[Table 1]

In Table 1, conditions 2 to 4 and 6 are examples of the present invention, and 1, 5, 7 to 11 are comparative examples. Condition 1 had poor shape due to low inter-roll tension of 0.9, and Condition 6
Has a low magnetic flux density because the exit side (high temperature side) roll temperature is low. In condition 7, since the inter-roll tension is as high as 7.0, the magnetic flux density is low, and the iron loss is also poor. In condition 8, the inter-roll tension is too high at 8.0, so that the iron loss value is high, the magnetic flux density is low, and the shape is not good. Condition 9 has a high exit roll reduction force and good shape, but has a reduced magnetic flux density and iron loss. Condition 10 is inferior in shape due to low exit roll reduction force. Under condition 11, the shape is deteriorated due to the low exit roll temperature, and the iron loss is poor. In contrast, all of the examples of the present invention are excellent in shape, magnetic flux density, and iron loss.

[0039]

As described above, according to the present invention, by adjusting the inter-roll tension, the rolling force and the temperature of the high-temperature roll during rapid heating by the energizing roll, the secondary recrystallization orientation is sharpened in the rolling direction. It is possible to optimize and stabilize the dive angle of the plate surface for the crystallization and secondary recrystallization, and thereby to manufacture a high magnetic flux density unidirectional magnetic steel sheet having extremely excellent iron loss characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a current-carrying member heating device of the present invention.

FIG. 2 is a diagram showing a relationship between a high-temperature roll linear pressure and a magnetic flux density for each tension between rolls during heating of an electric conductor.

Claims (1)

[Claims] C. 0.10% or less by weight, Si:
The steel, containing 2.5-7.0% and the usual inhibitor components, the balance consisting of Fe and unavoidable impurities, is treated in the usual way, and the strip rolled to approximately the final product thickness is decarburized and annealed, In the method for producing a hot-rolled unidirectional electromagnetic steel sheet including a step of performing a finish annealing, when the strip is decarburized and annealed, immediately before or during the heating stage of the decarburization annealing, a current-carrying roll is used. The plate tension between the low-temperature side roll and the high-temperature side roll is 1.0 to 4.0 kg / mm ² , and the rolling force of the high-temperature side roll is 1.0 to 4.0 kg / mm ² in linear pressure. , Set the temperature of the hot roll to 20
A method for producing a high magnetic flux density unidirectional magnetic steel sheet having extremely excellent iron loss characteristics, wherein the temperature is 0 ° C. or higher.