JP5954527B2 - Ultra-thin electrical steel sheet with excellent high-frequency iron loss characteristics - Google Patents

Description

  The present invention relates to an ultrathin electrical steel sheet that is used for a core material such as a reactor and that has a plate thickness of less than 0.1 mm and excellent iron loss characteristics during high frequency excitation.

  In general, it is known that the iron loss of an electromagnetic steel sheet rapidly increases as the excitation frequency increases. However, the actual driving frequency of transformers and reactors is increased in order to reduce the size and increase the efficiency of the iron core. For this reason, heat generation due to iron loss of electromagnetic steel sheets has become a problem in many cases.

In order to reduce the iron loss of the steel sheet, a method of increasing the specific resistance of the steel by increasing the Si content is effective. However, when the amount of Si in the steel exceeds 3.5 mass%, the workability is remarkably lowered, and it is difficult to manufacture the electromagnetic steel sheet using the conventional rolling method. Therefore, various methods for producing a steel sheet having a high Si content have been proposed. For example, Patent Document 1 discloses a method of obtaining a magnetic steel sheet having a high Si content by spraying a non-oxidizing gas containing SiCl ₄ onto a steel sheet surface at a temperature of 1023 to 1200 ° C. and performing a siliconization treatment. Patent Document 2 discloses hot rolling with good cold rollability by rolling 4.5-7 mass% high Si steel with poor workability by optimizing rolling conditions in continuous hot rolling. A method of obtaining a plate is disclosed.

As a method of reducing iron loss other than increasing the amount of Si, it is effective to reduce the plate thickness. However, when manufacturing a steel plate by a rolling method using high Si steel as a raw material, there is a limit in reducing the plate thickness. Therefore, a method of increasing the Si content in the steel by cold rolling a low Si steel to a predetermined final plate thickness and then performing a siliconizing treatment in an SiCl ₄ containing atmosphere has been developed and already industrialized. It is disclosed that this method can give a gradient to the Si concentration in the plate thickness direction and is effective in reducing iron loss at a high excitation frequency (see Patent Documents 3 to 5).

However, in order to achieve even lower iron loss under high frequency excitation, the expected iron loss reduction effect can be obtained even if the plate thickness of the steel plate with the Si concentration gradient in the plate thickness direction is made thinner than 0.10 mm. It is clear that this is not possible. For example, Patent Document 6 describes a steel plate having a thickness of 0.05 mm in which high-frequency magnetic characteristics are improved by providing a component with a Si concentration gradient, but the iron loss W1 / 10k is 4.43 W. / Kg, it is not a low level.

Patent Document 7 discloses that when the plate thickness is reduced to 0.03 to 0.15 mm, good high-frequency magnetic characteristics can be obtained by accumulating the texture of the steel plate in the Goss orientation. . However, this method discloses a technique for improving the texture by adopting a process that requires a lot of time and cost for secondary recrystallization.

Japanese Patent Publication No. 05-049745 Japanese Patent Publication No. 06-057853 Japanese Patent No. 3948113 Japanese Patent No. 3948112 Japanese Patent No. 4073075 JP-A-11-199988 JP 2009-235529 A

  However, a steel sheet that employs a process such as the technique disclosed in Patent Document 7 to control the texture is excellent in magnetic properties, but cannot avoid a significant increase in product cost.

  The present invention has been made in view of the above-mentioned problems of the prior art, and the object thereof is to control the texture of the steel sheet, that is, to achieve a good high-frequency magnetism even in a textured steel sheet with less Goss orientation. An object of the present invention is to provide an electrical steel sheet having characteristics.

  The present inventors conducted extensive research to develop an electromagnetic steel sheet having good high-frequency magnetic properties even when the sheet thickness is as thin as less than 0.10 mm and the Goss orientation is small in the texture of the steel sheet. As a result, it has been found that it is effective to increase the Si concentration gradient in the plate thickness direction of the steel plate and to increase the ratio of the plate thickness penetrating grains, thereby completing the present invention.

The present invention based on the above findings is an electrical steel sheet containing C: less than 0.010 mass%, Si: 2-10 mass%, the balance being Fe and inevitable impurities, and a plate thickness of 0.01-0.08 mm. In the steel plate, the Si concentration in the steel plate is high in the plate thickness surface layer and low in the central portion, has a concentration distribution in which the concentration gradient in the plate thickness direction is 30 mass% / mm or more, and the number ratio of the plate thickness through grains is 50%. It is an ultrathin electrical steel sheet characterized by having a steel sheet structure in which the number ratio of crystal grains whose deviation angle from the Goss orientation is 15 ° or less is 4% or less.

  In addition to the above component composition, the electrical steel sheet according to the present invention further includes Mn: 0.005 to 1.0 mass%, Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu : 0.01 to 0.50 mass%, P: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Sb: 0.005 to 0.50 mass%, Bi: 0.005 to 0 It contains one or more selected from .50 mass%, Mo: 0.005 to 0.100 mass%, and Al: 0.02 to 6.0 mass%.

  According to the present invention, an ultra-thin electrical steel sheet having a plate thickness of less than 0.1 mm and excellent in high-frequency iron loss characteristics can be manufactured. Therefore, according to the present invention, it is possible to provide an ultra-thin electrical steel sheet suitable for use in iron core materials such as small transformers, motors, reactors, and the like that are required to have high-frequency iron loss characteristics.

It is a graph which shows the relationship between the Si concentration gradient of a plate | board thickness direction, and the high frequency iron loss W0.5 _{/ 20k} .

First, an experiment that triggered the development of the present invention will be described.
A steel slab containing C: 0.0082 mass%, Si: 3.10 mass% is hot-rolled to form a hot-rolled sheet having a thickness of 2.2 mm, pickled to remove the scale, and then cold-rolled. A cold-rolled sheet having a final thickness of 0.08 mm was used. Next, this cold-rolled sheet was subjected to a siliconizing treatment in a 10 vol% SiCl ₄ +90 vol% N ₂ atmosphere at a temperature of 1000 to 1200 ° C. for a time of 100 to 1400 seconds. In order to moderate the concentration gradient in the direction, diffusion annealing was performed at 1100 ° C. for 0 to 1200 seconds in an N ₂ atmosphere to produce steel sheets having various Si concentration gradients. In the above-mentioned siliconization treatment, the treatment conditions were adjusted so that the average Si amount in the thickness direction was about 5.5 mass% under any conditions.

  The magnetic properties of the steel sheet obtained as described above were measured by the method described in JIS C2550. Moreover, the cross section of the said steel plate was line-analyzed by EPMA, and the Si concentration gradient of the plate | board thickness direction was measured. Furthermore, the texture of the steel sheet surface layer was measured by X-ray diffraction. The Si concentration gradient is defined as a value obtained by dividing the difference between the maximum concentration and the minimum concentration of Si by ½ of the plate thickness.

FIG. 1 shows the relationship between the Si concentration gradient and the iron loss W _{0.5 / 20k} (iron loss when excited at a magnetic flux density of 0.05 T and a frequency of 20000 Hz). From this result, the iron loss decreases as the Si concentration gradient increases, and the iron loss reduction margin due to the increase in the concentration gradient is large until the Si concentration gradient is about 30 mass% / mm, but exceeds 30 mass% / mm. It can be seen that the reduction allowance becomes smaller. That is, it can be seen that in a thin steel plate having a thickness of 0.08 mm, good iron loss cannot be obtained unless the Si concentration gradient is increased to 30 mass% / mm or more.

  Moreover, in the measurement result by X-ray diffraction, the texture of the steel sheet surface layer is almost the same regardless of the difference in the siliconizing treatment conditions, and the number ratio of the crystal grains having Goss orientation is 0.6 to 1.2 in the whole. %. Here, the grain having the Goss orientation means a crystal grain having an orientation with a deviation angle of 15 ° or less from the Goss orientation. This indicates that a steel sheet having good iron loss characteristics can be obtained as shown in FIG. 1 even when the Goss orientation is small.

The reason why good high-frequency iron loss characteristics cannot be obtained without increasing the Si concentration gradient when the plate thickness is thin is not yet clear enough, but the inventors think as follows. Yes.
As described in Patent Document 3, when the plate thickness is thick, the magnetic flux when high-frequency excitation is concentrated near the surface layer of the steel plate, so the eddy current loss is reduced by increasing the permeability near the surface layer. it can. However, when the plate thickness is reduced, the distance between the surface layer and the center layer is reduced, so that a certain amount of magnetic flux also flows through the center layer.

  Here, when the Si concentration gradient is applied, since the Si concentration in the center layer is not high, the permeability is not high, and the eddy current loss in the center layer is expected to increase. As a result, although the eddy current loss is reduced due to the magnetic permeability in the steel sheet surface layer, the effect of reducing the iron loss when viewed as the whole steel sheet cannot be obtained due to the increase in the eddy current loss in the center layer. It is presumed that this is the reason why good iron loss characteristics cannot be obtained when the plate thickness is reduced.

From this point of view, it is expected that the iron loss increases as the Si concentration gradient increases, but the above experimental results do not.
Therefore, the inventors focused on the change in the lattice constant of iron when Si was dissolved. The Fe lattice is a body-centered cubic lattice at room temperature, but it is known that the Fe lattice contracts when Si is dissolved and Fe atoms are replaced with Si atoms. That is, when the silicon content is increased by increasing the Si content of the steel sheet surface layer, the steel sheet surface layer tends to shrink. However, since the steel sheet center layer has a low Si content and a small amount of shrinkage, the steel sheet surface layer is in a state where tensile stress is applied from the center layer. This is exactly the same as when a tension coating is applied to the steel sheet surface, and it is considered that the eddy current loss is reduced by the effect of this tensile stress.

  Since the magnitude of the tensile stress generated on the steel sheet surface is considered to depend on the Si concentration gradient, increasing the Si concentration gradient can increase the tensile stress on the steel plate surface and increase the eddy current loss reduction allowance. It is considered possible. That is, it is considered that the iron loss degradation due to the magnetic flux flowing to the center layer is offset by increasing the Si concentration gradient.

  Furthermore, based on the above idea, it is presumed that the crystal grain boundary affects the stress distribution in the steel sheet. That is, since it is considered that the crystal grain boundary has an effect of relaxing the stress, it is preferable that the crystal grain boundary that is parallel to the tensile stress (in the direction parallel to the plate surface) is smaller, and therefore the crystal existing in the steel sheet is present. It is considered that the grains are desirably plate-thickness through grains in which there are no crystal grain boundaries parallel to the steel plate surface.

  As described above, the inventors of the present invention have made it possible to increase the ratio of the plate thickness through grains in the crystal grains in addition to extremely increasing the Si concentration gradient in the electromagnetic steel sheet having a small thickness, thereby increasing the iron during high frequency excitation. The inventors have found that the loss can be greatly reduced, and have completed the present invention.

Next, the component composition of the electrical steel sheet (product board) of the present invention will be described.
The electrical steel sheet of the present invention needs to have a component composition of C: less than 0.010 mass% and Si: 2 to 10 mass%.
C: Less than 0.010 mass% C is more desirable as it is smaller because C causes magnetic aging and deteriorates magnetic properties. However, excessive reduction of C causes an increase in manufacturing cost. Therefore, C is limited to less than 0.010 mass% where magnetic aging does not cause a practical problem. Preferably it is less than 0.005 mass%.

Si: 2 to 10 mass%
Si is an indispensable element that increases the specific resistance of steel and improves iron loss characteristics, and it is necessary to contain 2 mass% or more on the average of the total thickness. The reason for this is that in the present invention, which presupposes a large Si concentration gradient in the plate thickness direction, the Si maximum concentration in the vicinity of the surface layer needs to exceed 4 mass% at which the magnetic permeability increases. This is because if the minimum density of 0 is 0 mass%, the average thickness is 2 mass%. However, if the content exceeds 10 mass%, the saturation magnetic flux density is significantly reduced. Therefore, in this invention, Si is taken as the range of 2-10 mass% on the average of all the board thickness.

  In addition, as can be seen from FIG. 1, the electrical steel sheet of the present invention has a concentration in which the Si concentration in the steel sheet is high in the plate thickness surface layer and low in the center, and the concentration gradient in the plate thickness direction is 30 mass% / mm or more. It is necessary to have a distribution. Preferably, it is 50 mass% / mm or more.

  In the electrical steel sheet of the present invention, the balance other than C and Si is Fe and inevitable impurities. However, Mn, Ni, Cr, Cu, P, Sn, Sb, Bi, Mo, and Al are contained in the following ranges for the purpose of improving hot workability and improving magnetic properties such as iron loss and magnetic flux density. It is preferable to do so.

Mn: 0.005 to 1.0 mass%
Mn is preferably contained in the range of 0.005 to 1.0 mass% in order to improve the workability during hot rolling. This is because, if it is less than 0.005 mass%, the effect of improving the workability is small, whereas if it exceeds 1.0 mass%, the magnetic properties are deteriorated. However, Mn is an element that is difficult to reduce, and since it is mixed in an impurity level of about 0.01 mass%, it does not have to be added.

Ni: 0.010 to 1.50 mass%
Ni can be added because it has the effect of improving the magnetic properties. When the addition amount is less than 0.010 mass%, the effect of improving the magnetic properties is small. On the other hand, when the addition amount exceeds 1.50 mass%, the saturation magnetic flux density decreases. Therefore, it is preferable to add Ni in the range of 0.010 to 1.50 mass%.

Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, P: 0.005 to 0.50 mass%, Al: 0.02 to 6.0 mass%, Sn: 0.005 One or more selected from 0.50 mass%, Sb: 0.005-0.50 mass%, Bi: 0.005-0.50 mass%, and Mo: 0.005-0.100 mass%. These are all effective elements for reducing iron loss. In order to obtain such an effect, it is preferable to contain one or more elements within the above range. When the content is less than the lower limit, there is no effect of reducing iron loss. On the other hand, when the content exceeds the upper limit, the saturation magnetic flux density is lowered, which is not preferable.

Next, the plate thickness and crystal structure of the electrical steel sheet of the present invention will be described.
The thickness of the electromagnetic steel sheet of the present invention is less than 0.10 mm. This is because the problem caused by the plate thickness clarified in the present invention occurs at a plate thickness of less than 0.10 mm. However, if the thickness is less than 0.01 mm, it is difficult to roll to the final plate thickness or pass through the siliconization equipment, and the productivity is significantly hindered, so the lower limit of the plate thickness is 0.01 mm. .

  Moreover, the electrical steel sheet of the present invention requires that the number of through-thickness grains is 50% or more of all crystal grains. As described above, since the grain boundaries parallel to the plate surface have the effect of relaxing the tensile stress generated on the steel plate surface, it is desirable that there are more through-thickness through-grains without crystal grain boundaries parallel to the plate surface. is there. Therefore, in the present invention, the ratio of the number of plate-thickness through grains is 50% or more. Preferably, it is 75% or more.

  The electrical steel sheet of the present invention is required to have a texture of 4% or less in terms of the number of crystal grains whose deviation angle from the Goss orientation is 15 ° or less with respect to all crystal grains. This is because the present invention is intended for a steel sheet with a small Goss orientation. Note that the texture of the electrical steel sheet according to the present invention is sufficient if the steel sheet surface layer is measured because the sheet thickness is thin and there are many through-grains.

Next, the manufacturing method of the electrical steel sheet of this invention is demonstrated.
The electromagnetic steel sheet of the present invention can be manufactured using a general method as a manufacturing method of the electromagnetic steel sheet. That is, the steel adjusted to the above-mentioned predetermined component composition is melted to form a steel slab, hot-rolled, and the obtained hot-rolled sheet is subjected to hot-rolled sheet annealing as necessary, once or in the middle Cold rolling at least twice with annealing is performed to obtain a cold-rolled sheet having a final thickness, and a siliconizing treatment is performed, and an insulating coating is coated as necessary.

  The steel slab having the component composition described above may be manufactured by a normal ingot-bundling rolling method or a continuous casting method, or a thin cast piece having a thickness of 100 mm or less may be manufactured by a direct casting method. . Thereafter, the steel slab is reheated by an ordinary method and subjected to hot rolling, but may be hot rolled immediately after casting without being reheated. In the case of a thin cast slab, hot rolling may be performed, or hot rolling may be omitted and the process may proceed to the next step.

  The heating temperature when the slab is reheated before hot rolling is preferably 1250 ° C. or less from the viewpoint of energy cost.

  Next, hot-rolled sheet annealing is performed as necessary. The annealing temperature of this hot-rolled sheet annealing is preferably set to a temperature range of 800 to 1150 ° C. in order to obtain good magnetic properties and not to generate irregularities called ridging on the steel sheet. When the annealing temperature is less than 800 ° C., a band structure in hot rolling remains, and it becomes difficult to obtain a primary recrystallized structure of sized particles, and magnetic characteristics are deteriorated. On the other hand, when the annealing temperature exceeds 1150 ° C., the grain size after the hot-rolled sheet annealing becomes too coarse, and it becomes difficult to obtain a primary recrystallized structure of sized particles.

  The hot-rolled sheet after hot rolling or after hot-rolled sheet annealing is pickled and descaled to obtain a cold-rolled sheet having a final sheet thickness by one or more cold rollings sandwiching intermediate annealing. In addition, performing the temperature of cold rolling to the temperature of 100-300 degreeC, or performing an aging treatment once or in the temperature range of 100-300 degreeC in the middle of cold rolling is magnetic. It is effective for improving the characteristics.

Thereafter, the cold-rolled sheet after the cold rolling is subjected to a siliconizing treatment. For the above-described siliconization treatment, a vapor phase siliconization method using SiCl ₄ as a reaction atmosphere, which has already been industrialized, can be applied. However, even if it is not such a gas phase reaction method, even a solid phase siliconization method in which a steel sheet is sandwiched between silica sheets and annealed and siliconized, a Si concentration gradient can be imparted in the thickness direction. May be.

In the case of the above-described vapor phase siliconization method for the siliconization treatment, in order to control the Si concentration gradient, it is desirable to appropriately adjust the treatment temperature, treatment time, and atmospheric gas (reaction gas). In addition, it is preferable to cool immediately after the siliconization treatment in order to suppress a decrease in concentration gradient due to Si diffusion. Moreover, in order to raise the ratio of the plate | board thickness penetration grain of the crystal grain in a product board, it is preferable that the siliconization process temperature shall be 1050 degreeC or more, and 1150 degreeC or more is more preferable.
It is preferable to apply an insulating coating to the steel plate that has been subjected to the siliconization treatment in order to ensure the insulating properties of the steel plate when used after being laminated.

C: 0.0035% by mass, Si: 2.58% by mass, the remainder comprising Fe and unavoidable impurities is melted and continuously cast into a steel slab. The steel slab is reheated to a temperature of 1150 ° C. After heating, it was hot-rolled to obtain a hot-rolled sheet having a thickness of 1.8 mm, pickled, and cold-rolled to obtain a cold-rolled sheet having a final thickness of 0.05 mm. Subsequently, the cold-rolled sheet was subjected to a silicon dip treatment at 1200 ° C. for 180 seconds in a 10 vol% SiCl ₄ +90 vol% Ar atmosphere. In addition, it was 74 mass% / mm when the Si density | concentration gradient of the steel plate thickness direction after a siliconization process was investigated. Thereafter, in order to reduce the Si concentration gradient, diffusion annealing was performed at a temperature of 1100 ° C. for a time in the range of 0 to 1200 seconds described in Table 1.

When the texture of the steel sheet surface layer thus obtained was examined by an X-ray diffraction method, the ratio of crystal grains having a deviation angle of 15 ° or less from the Goss orientation in any steel sheet was 0.4 to 0.8. %.
Further, the magnetic properties of the obtained steel sheet were measured by the method described in JIS C2550. Furthermore, the cross section of the obtained steel plate was observed with an optical microscope over a length of 50 mm, the ratio of the plate thickness through grains to the total crystal grains was measured, and the results are also shown in Table 1.

From Table 1, it can be seen that a steel sheet having a Si concentration gradient suitable for the present invention has extremely good magnetic characteristics during high-frequency excitation. Incidentally, Patent Document 6 describes a steel plate having a thickness of 0.05 mm and an iron loss W _{1 / 10k} of 4.43 W / kg with an Si concentration gradient and improved high-frequency magnetic characteristics. W _{1 / 10k} and W _{0.5 / 20k} cannot be directly compared because the measurement conditions are different, but show almost the same value empirically. Therefore, comparing the iron loss values of the two, it can be seen that the iron steel sheet of the present invention has a much lower iron loss. This difference is presumed that, in the present invention, in addition to increasing the Si concentration gradient, increasing the ratio of the plate thickness through grains contributed.

C: 0.0071 mass%, Si: 3.75 mass%, Mn: 0.07 mass%, the remainder of which is made of Fe and inevitable impurities are melted and continuously cast into a steel slab, and the steel slab Is heated again to a temperature of 1200 ° C., hot rolled to a hot rolled sheet with a thickness of 2.3 mm, annealed at 1000 ° C. for 30 seconds, pickled and cold rolled. Thus, a cold-rolled sheet having a final thickness of 0.03 mm was obtained. Thereafter, the cold-rolled sheet was subjected to a siliconizing treatment in a 20 vol% SiCl ₄ +80 vol% N ₂ atmosphere under the conditions of changing the temperature and time shown in Table 2.

  When the texture of the steel sheet surface layer thus obtained was measured by an X-ray diffraction method, the proportion of crystal grains whose deviation angle from the Goss orientation was 15 ° or less was in the range of 0.8 to 3.2%. It was in. Further, the magnetic properties of the obtained steel sheet were measured by the method described in JIS C2550, and the cross section of the obtained steel sheet was observed with an optical microscope over a length of 50 mm. The percentage was measured.

  The results of the above measurements are also shown in Table 2. From Table 2, it can be seen that a steel sheet in which both the Si concentration gradient and the plate thickness penetrating grain are compatible with the present invention has extremely good magnetic characteristics during high-frequency excitation.

Except for Si, steels having various composition shown in Table 3 were melted, continuously cast into steel slabs, reheated to a temperature of 1200 ° C., and then hot-rolled to obtain a plate thickness of 2.7 mm. A hot-rolled sheet, pickled, and cold-rolled to obtain a final cold-rolled sheet having a thickness of 0.080 mm. Thereafter, the cold-rolled sheet is 1200 ° C. × 100 seconds in a 15 vol% SiCl ₄ +85 vol% N ₂ atmosphere. The siliconization treatment was applied.

Table 3 shows the results of component analysis of the steel sheet thus obtained and the results of measuring the Si concentration gradient in the thickness direction. In addition, the amount of Si in Table 3 is an average value in the thickness direction after the siliconization treatment. Moreover, when the texture of the obtained steel sheet surface layer was measured by an X-ray diffraction method, the ratio of crystal grains whose deviation angle from the Goss orientation was 15 ° or less was within the range of 0.3 to 0.8%. Met.
Further, the magnetic properties of the obtained steel sheet were measured by the method described in JIS C2550. Furthermore, the cross section of the obtained sample was observed with an optical microscope over a length of 50 mm, and the ratio of the plate thickness penetrating grains among the total crystal grains was measured.

  The measurement results are also shown in Table 3. From Table 3, it can be seen that a steel sheet in which the steel component, Si concentration gradient, and the ratio of the plate thickness penetrating grains are all within the scope of the present invention has extremely good magnetic properties during high-frequency excitation.

Claims (2)

In the electrical steel sheet containing C: less than 0.010 mass%, Si: 2-10 mass%, the balance being Fe and inevitable impurities, and having a plate thickness of 0.01-0.08 mm ,
The Si concentration in the steel sheet has a concentration distribution in which the plate thickness surface layer is high and the central portion is low, and the concentration gradient in the plate thickness direction is 30 mass% / mm or more,
An ultra-thin electromagnetic wave characterized by having a steel sheet structure in which the number ratio of through-thickness grains is 50% or more and the number ratio of crystal grains whose deviation angle from Goss orientation is 15 ° or less is 4% or less steel sheet. In addition to the above component composition, the magnetic steel sheet further comprises Mn: 0.005 to 1.0 mass%, Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.00. 01-0.50 mass%, P: 0.005-0.50 mass%, Sn: 0.005-0.50 mass%, Sb: 0.005-0.50 mass%, Bi: 0.005-0.50 mass% The ultra-thin electromagnetic according to claim 1, comprising one or more selected from Mo: 0.005 to 0.100 mass% and Al: 0.02 to 6.0 mass%. steel sheet.

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