JP2012102344A - Grain-oriented electromagnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel sheet capable of being reduced in deterioration of magnetic properties after being sheared even when the electromagnetic steel sheet has a thickness of 0.220 mm or less, in the electromagnetic steel sheet used for a large transformer of a size as large as several meters.SOLUTION: The electromagnetic steel sheet has a composition containing, by mass, 0.005% or less C, 1.0-8.0% Si, and 0.005-1.0% Mn, further 10-50 mass ppm, in total, of one or more elements selected from among Nb, Ta, V and Zr, with the balance consisting of Fe and inevitable impurities, and is characterized in that at least 10% of each content of the Nb Ta, V and Zr is present in a precipitated state, the precipitated objects have diameters (circle-equivalent diameters) of 0.02-3 μm on the average, the number of intervening objects having diameters of 10 μm or more is less than 1 piece/mm, and the average grain diameter of the secondary recrystallization grains in the steel sheet is 5 mm or more.

Description

  The present invention relates to a grain-oriented electrical steel sheet suitable for use as a core material of a transformer, and the like, particularly to reduce deterioration of magnetic properties when shearing is performed.

  Electrical steel sheet is a material that is widely used as iron cores for various transformers, motors, etc. Especially, what is called grain-oriented electrical steel sheet, the orientation of its crystal grains is called the Goth orientation (110) [001] orientation Accumulated.

In producing such grain-oriented electrical steel sheets, it is a common technique to use secondary precipitates called inhibitors to recrystallize crystal grains having goth orientation during finish annealing. Yes.
For example, Patent Document 1 discloses a method of using AlN and MnS, and Patent Document 2 discloses a method of using MnS and MnSe, respectively, as the inhibitor component, and is used industrially. More recently, as proposed in Patent Document 3, there is a technique for developing Goss-oriented crystal grains by the action of secondary recrystallization even for steel sheets that do not contain an inhibitor component.

The technology described in Patent Document 3 reveals the grain boundary orientation angle dependence of the grain boundary energy possessed by the grain boundary when primary recrystallization occurs by eliminating impurities such as inhibitor components as much as possible. Thus, the secondary recrystallization of grains having Goth orientation is possible without using an inhibitor.
In this method, since the inhibitor component is unnecessary, a step of purifying the inhibitor component is unnecessary. In addition, there is no need to increase the temperature of the purification annealing, and the fine dispersion step in the steel of the inhibitor component is unnecessary, so the high-temperature slab heating that is essential for fine dispersion is no longer necessary. In addition, this method has a great merit in terms of maintenance of facilities and the like.

Among the characteristics of grain-oriented electrical steel sheets, the iron loss characteristic is the characteristic that directly leads to the energy loss of the product and is regarded as the most important. In order to improve the iron loss characteristic, it is _preferable to reduce a value represented by W _17/50 (energy loss at excitation magnetic flux density 1.7 T, excitation frequency 50 Hz).
Moreover, even in transformers that use grain-oriented electrical steel sheets, this iron loss characteristic is regarded as important, and even after the transformer is manufactured, its measurement is performed periodically in order to manage the iron loss characteristics in the actual machine. Need to be implemented.

Japanese Patent Publication No. 40-15644 Japanese Patent Publication No. 51-13469 JP 2000-129356 A

Generally, products of electromagnetic steel sheets are in sheet form, and are cut into a predetermined size when producing a transformer. As a cutting method, a shearing method (also referred to as slit processing) in which two blades are pressed from above and below like scissors (finally the blades pass each other) is generally used.
The processed surface of the steel plate thus sheared is torn off by the shearing force, and a large amount of strain is introduced into the steel plate. For this reason, the sheared electrical steel sheet has been a problem in that it tends to cause deterioration of magnetic properties due to the introduced strain.

As a method of reducing the deterioration of the magnetic characteristics due to the shearing process, there is a case where a strain relief annealing is performed in which annealing is performed at 700 to 900 ° C. for several hours after the shearing process. However, strain relief annealing is limited to small transformers with a size (length) of 500 mm or less, and cannot be applied to iron cores for large transformers with a size of several meters.
Therefore, there is a demand for a technique that can reduce the deterioration of magnetic properties when shearing is performed even in a magnetic steel sheet for large transformers having a size of several meters.
Furthermore, in recent years, the use of magnetic steel sheets with a thin plate thickness of 0.220 mm or less, which has been increasingly used in recent years, is more difficult to shear, so the amount of strain introduced increases, resulting in increased iron after shearing. There was a problem that the deterioration of the loss becomes larger.

As a result of intensive studies to solve the above-mentioned problems, the inventors have included a small amount of an element such as Nb to increase the amount of precipitates and control the size of the precipitates, in addition to the presence frequency of coarse inclusions. It was found that the iron loss deterioration at the time of shearing a thin electromagnetic steel sheet (thin material) as described above can be significantly reduced by limiting the above.
Hereinafter, experiments that have made the present invention successful will be described.

<Experiment 1>
In mass%, C: 0.022%, Si: 3.39%, Mn: 0.08%, Sb: 0.030%, Sn: 0.050%, Cr: 0.05% and P: 0.010%, and in mass ppm, Al: 50ppm, A steel slab containing N: 50 ppm, S: 50 ppm and Nb: 41 ppm, the balance being Fe and unavoidable impurities is manufactured by continuous casting, and after slab heating at 1220 ° C., it is 2.4 by hot rolling. The thickness was mm. Next, hot-rolled sheet annealing was performed at 1050 ° C for 30 seconds, cold rolled to a thickness of 1.8 mm, and then subjected to intermediate annealing at 1000 ° C for 40 seconds, and then finished to a thickness of 0.15 mm by cold rolling. It was. After that, recrystallization annealing (primary recrystallization annealing) was performed in soaking conditions at 850 ° C. for 60 seconds and 50% by volume N ₂ -50% by volume H ₂ , and an annealing separator mainly composed of MgO was applied. After that, a final finish annealing (purification annealing) was performed for 10 hours at 1200 ° C. During final finish annealing (purification annealing), after maintaining the maximum temperature of the steel sheet at 1200 ° C, the cooling rate from 900 ° C to 500 ° C is variously changed from 5 to 300 ° C / h on average, and the temperature is lowered to room temperature. did. The reason why the cooling rate is changed is to variously change the amount of Nb-based precipitates remaining in the base iron even after the final finish annealing.
Thereafter, flattening annealing was performed under conditions of 900 ° C. and 15 seconds, which also served as a tension-imparting coating mainly composed of magnesium phosphate and boric acid.

The grain-oriented electrical steel sheet thus obtained was cut into a 30 mm × 280 mm size called an Epstein test piece. At this time, when cutting with a wire cutter slowly so as not to strain the steel, as described above, cutting with a shearing machine using an upper blade and a lower blade, which is a general cutting method of grain-oriented electrical steel sheets Two kinds of test pieces were prepared. The iron loss W _17/50 of the obtained sample was measured according to the method described in JIS C 2550.

In FIG. 1, the value obtained by subtracting the iron loss value of the sample cut with the wire cutter from the iron loss value of the sample cut with the shearing machine is ΔW (hereinafter, the same applies to the present invention), and this ΔW and Nb in the steel The result of having investigated about the relationship with content of is shown.
When cut with a shearing machine, as described above, strain remained in the steel sheet and the iron loss deteriorated. On the other hand, although cutting with a wire cutter took time, the steel sheet could be cut with almost no strain remaining.
Therefore, it is considered that ΔW shown in the figure substantially shows the iron loss amount deteriorated due to residual strain. Therefore, it can be seen from the figure that the amount of iron loss deteriorated by shearing can be reduced by containing Nb. However, it became clear at the same time that even if the Nb content was increased, ΔW might still be large.

The reason why the sample containing Nb as described above can reduce the iron loss deterioration due to shearing is not necessarily clear, but the inventors consider as follows.
A structural investigation of the Nb-containing material used in this experiment revealed that Nb formed precipitates and was dispersed in the steel. The diameter of the precipitate was about 0.02 μm for the small one and about 3 μm for the large one. In ordinary grain-oriented electrical steel sheets, there are almost no precipitates in such steel, and it is assumed that the presence of these precipitates contributed to the reduction of iron loss deterioration due to shearing.

On the other hand, the iron loss is deteriorated by shearing because strain accumulates at the sheared portion. Here, the accumulation of strain means that the iron atoms are regularly arranged in the iron crystal grains, the stress from the outside acts on the iron atoms and the iron atoms are distorted or irregularly arranged. It is a phenomenon that becomes.
However, if such precipitates exist in the regularly arranged iron atoms, when stress such as shearing is applied, stress concentration occurs around the precipitates, resulting in iron It is conceivable that a crack will occur before the arrangement of atoms is distorted. And if it thinks that accumulation | storage of the above-mentioned distortion will be relieved by this effect | action, the above-mentioned phenomenon can be demonstrated.

There are two types of Nb contained in the steel sheet, a solid solution state and a state in which precipitates are formed. As described above, it is considered important to form precipitates. Therefore, the Nb precipitation ratio (ratio of Nb content contained in the precipitate with respect to the total Nb content) was investigated for the sample containing 22 ppm of Nb.

In order to obtain the Nb precipitation ratio in the Nb precipitate, it is first necessary to obtain the total Nb content (content in the steel sheet: mass%). The total Nb content can be determined from the inductively coupled plasma emission spectroscopic analysis method (ICP emission spectroscopic analysis method) described in JIS G 1237. In the case of Ta, the content is determined by each method described in JIS G 1236, V in JIS G 1221, and Zr in JIS G 1232.
On the other hand, the content of Nb contained in the precipitate (content in the steel plate: mass%) is obtained by dissolving the steel plate by electrolysis and capturing (filtering) only the precipitate, and measuring the Nb weight in the precipitate, It can be calculated from the weight of the steel plate reduced by electrolysis and the Nb weight in the precipitate.
The quantitative value of the content of Nb contained in such a precipitate is specifically determined by the following method.

First, a product plate is cut into a size of 50 mm × 20 mm, and immersed in a 10% by mass HCl aqueous solution heated to 85 ° C. for 2 minutes to remove the product coating or film. Thereafter, the weight is measured, and electrolysis is performed using a commercially available electrolytic solution (10% by mass AA solution: 10% by mass acetylacetone-1% by mass tetramethylammonium chloride-methanol) until about 1 g is electrolyzed. Furthermore, in order to peel the deposit adhering to the product plate surface subjected to electrolysis, the product plate is immersed in an ethanol solution and ultrasonic waves are applied.
This ethanol solution and the electrolyte used in the above electrolysis contain precipitates, which are filtered by using 0.1 μm mesh filter paper (capable of capturing precipitates in the order of nm). To capture. After filtration, deposit the filtered precipitate together with filter paper in a platinum crucible at 700 ° C
Then, add Na ₂ B ₄ O ₇ and NaCO ₃ and heat at 900 ° C. for 15 minutes. After cooling this, it is further heated at 1000 ° C. for 15 minutes.

Since the crucible is hardened in a bowl shape, the crucible is added to a 25 mass% HCl aqueous solution and heated at about 90 ° C. for 30 minutes to dissolve all the bowl-like substances. By analyzing this solution by the ICP emission spectroscopic analysis method described in JIS G1237, the mass of Nb in the precipitate is determined.
And this Nb mass is remove | divided by the mass of the product board (steel plate) decreased by electrolysis, and content (mass%) of Nb contained in a precipitate is calculated | required.
The Nb precipitation ratio can be obtained by further dividing the Nb content (mass%) contained in the precipitate thus obtained by the total Nb content (mass%) described above.

  The Nb precipitation rate in the sample was 65%. As a result of further investigations, it was found that at least 10% of the total Nb content is required to exhibit the effects of the present invention.

  From the above-described mechanism of improving the ΔW characteristic, it seems that the more the amount of precipitate-forming elements such as Nb remaining in the steel, the better the ΔW characteristic, but the precipitate is the iron itself of the raw material before processing. It also has the effect of deteriorating the loss characteristics. Therefore, it is preferable that the amount of precipitates is small in the range where the iron loss deterioration due to shearing is small. In this experiment, since the iron loss of the material itself was deteriorated in a material having an Nb content exceeding 50 ppm, it is considered that the content needs to be suppressed to 50 ppm or less.

  Further, in the case of a thin material having a plate thickness of 0.220 mm or less, even when the amount of precipitates satisfied the above-mentioned predetermined amount, there was a case where the deterioration of magnetic properties in shearing process was increased. Therefore, the inventors further conducted the following investigation on the cause.

Among the samples obtained in the above experiment, the cut surface of the sample cut with a shearing machine was examined with an optical microscope. As a result, despite the large amount of Nb in the precipitate, extremely coarse inclusions of 10 μm or more were observed in the sample having a large ΔW.
Accordingly, when the cut surface having a thickness of 0.15 mm was observed over a length of about 100 mm, 7 and 12 coarse inclusions of 10 μm or more were observed in the two types of samples having a large ΔW, respectively. On the other hand, coarse inclusions were not observed in the samples containing the same amount of Nb in the precipitates and having a small ΔW. Therefore, it can be said that the presence of coarse inclusions increases iron loss deterioration due to shearing.

Here, in the case of a thin material, the inventors consider the cause of the phenomenon as described above as follows.
As described above, in the present invention, accumulation of strain due to shearing is relaxed by precipitates, but if there are coarse inclusions, new stress concentration occurs there, and the arrangement of iron atoms is large in the vicinity thereof. It may be distorted, and as a result, ΔW may be deteriorated. Therefore, particularly in the case of a thin material, it is necessary to eliminate coarse inclusions as much as possible. Furthermore, as a result of investigating the presence frequency of coarse inclusions it was found that it is necessary to be less than 15 within an area of 15 mm ² (i.e., less than one in an area of 1 mm ^2).
In the present invention, since it is important that there are few inclusions on the shear plane when the steel plate is sheared, coarse inclusions are not the number per unit volume, but the inclusion per unit area of an arbitrary cross section. The number of objects shall be specified.

  Subsequently, the influence of the crystal grain size of secondary recrystallized grains on ΔW was investigated. This is because the strain accumulation due to shearing as described above is expected to be alleviated by the presence of a large number of crystal grain boundaries. Therefore, when the crystal grain size is small and there are many grain boundaries, the iron loss due to shearing is essentially the case. This is because the deterioration is small and the strain accumulation mitigation mechanism due to the precipitates described above may not be effective.

<Experiment 2>
% By mass, C: 0.037%, Si: 3.15%, Mn: 0.15%, Sb: 0.039%, Al: 31 mass ppm, N: 12 mass ppm, S: 21 mass ppm, and the balance Fe A steel slab made of unavoidable impurities is manufactured by continuous casting, heated to 1250 ° C, then hot rolled to a thickness of 2.0 mm, annealed at 1000 ° C for 15 seconds, and then cooled. Finished to a thickness of 0.20 mm by hot rolling.
Next, after recrystallization annealing in a 50% by volume N ₂ -50% by volume H ₂ humidified atmosphere at a temperature range of 800 to 880 ° C. and a soaking condition for 60 seconds, annealing separation mainly composed of MgO is performed. After the agent was applied, purification annealing (final finishing annealing) was performed for 10 hours in the temperature range of 1050 to 1230 ° C.
The reason for changing the recrystallization annealing temperature and the purification annealing temperature is to change the crystal grain size of the secondary recrystallization that occurs in the purification annealing.

  Next, flattening annealing was performed under the conditions of 900 ° C. for 30 seconds, which also served to form a tension-imparting coating mainly composed of magnesium phosphate and boric acid. Furthermore, it cut | disconnected to the above-mentioned Epstein test piece (30 mm x 280 mm) size. At this time, similarly to Experiment 1, wire cutter cutting and shearing were performed. The iron loss of the obtained sample was measured according to the method described in JIS C 2550.

  Thereafter, the base iron was exposed by pickling, and the crystal grain size of the secondary recrystallized grains was measured. As for the crystal grain size, the grain sizes of four Epstein test pieces were measured for each condition and averaged. In addition, when the component analysis of the ground iron was conducted, it was found that the mass% was C: 0.0014%, Si: 3.15%, Mn: 0.15%, Sb: 0.039%, Cr: 0.05%, P: 0.011%. The element was below the detection limit. FIG. 2 shows the relationship between ΔW obtained by the above-described method and the crystal grain size.

  In this experiment, since no precipitate forming element such as Nb remains, the effect obtained in Experiment 1 is not exhibited. Therefore, when the average particle size is large, ΔW is large, and when the average particle size is small, ΔW is small. That is, it is considered that the ΔW reduction effect due to the addition of an element that forms a precipitate such as Nb is exhibited when the average secondary grain size is 5 mm or more.

From the above experiments, the inventors have included 10 to 50 ppm of an element such as Nb in the final product plate of the grain-oriented electrical steel sheet having a large secondary recrystallized grain size and at least 10% thereof. It was found that iron loss deterioration during shearing can be suppressed by controlling the size of the precipitate and the amount of coarse inclusions.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. In mass%, C: 0.005% or less, Si: 1.0 to 8.0% and Mn: 0.005 to 1.0%, and one or more selected from Nb, Ta, V and Zr in a total of 10 to A steel plate with a content of 50 ppm by mass, the balance being Fe and inevitable impurities: 0.220 mm or less, and Nb, Ta, V and Zr are present as precipitates in at least 10% of the content, The diameter of the precipitate (equivalent circle diameter) is 0.02 to 3 μm on average, and the number of inclusions having a diameter of 10 μm or more is less than 1 per 1 mm ² , and the average grain size of secondary recrystallized grains of the steel sheet A grain-oriented electrical steel sheet having a diameter of 5 mm or more.

2. Further, Ni: 0.010 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%, Sn: 0.005 to 0.50%, Sb: 0.005 to 0.50%, Bi: 0.005 The grain-oriented electrical steel sheet according to 1 above, containing at least one selected from ˜0.50% and Mo: 0.005 to 0.100%.

3. The above-mentioned 1 characterized in that the steel sheet has linear grooves having a width of 50 to 1000 μm and a depth of 10 to 50 μm that intersect the rolling direction at an angle of 15 ° or less with respect to the direction perpendicular to the rolling direction of the steel sheet. Or the grain-oriented electrical steel sheet according to 2.

  ADVANTAGE OF THE INVENTION According to this invention, the magnetic characteristic deterioration resulting from a shearing process can be effectively suppressed in the grain-oriented electrical steel sheet of a thin material. As a result, it can be set as the iron core for transformers with little energy loss.

FIG. 5 is a diagram showing the relationship between the Nb content in steel and the iron loss deterioration amount (ΔW) due to shearing. FIG. 6 is a graph showing the relationship between the crystal grain size of secondary recrystallized grains and the amount of iron loss deterioration (ΔW) caused by shearing.

Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel sheet is limited to the above range in the present invention will be described. In addition, unless otherwise indicated, the% display and ppm display in a steel plate (base iron) component represent mass% and mass ppm, respectively.

C: 0.005% or less C is an element inevitably mixed in steel, but it is desirable to reduce it as much as possible because magnetic property deterioration occurs due to magnetic aging. However, it is difficult to remove completely, and 0.005% or less is acceptable from the viewpoint of manufacturing cost. Preferably it is 0.002% or less. Although there is no reason to specifically limit the lower limit of the C content, industrially, C is contained exceeding zero.

Si: 1.0-8.0%
Si is an element necessary for increasing the specific resistance of steel and improving iron loss in the final product plate, but its effect is poor at less than 1.0%. On the other hand, when it exceeds 8.0%, the saturation magnetic flux density of a steel plate falls remarkably. Therefore, Si is limited to 1.0 to 8.0%. A preferable lower limit of the Si content is 3.0%. Moreover, the upper limit with preferable Si content is 3.5%.

Mn: 0.005 to 1.0%
Mn is an element necessary for improving workability during hot rolling, but the amount added is 0.005%.
If the ratio is less than 1.0%, the workability improving effect is poor. On the other hand, if it exceeds 1.0%, secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, Mn is limited to 0.005 to 1.0%. The minimum with preferable Mn content is 0.02%. Moreover, the upper limit with preferable Mn content is 0.20%.

  In the present invention, as a precipitate forming element, one or more selected from Nb, Ta, V and Zr (hereinafter referred to as “Nb etc.”) are contained in a total range of 10 to 50 ppm. Is essential. This is because if Nb or the like is less than 10 ppm in total, precipitates for improving iron loss, which is the greatest feature of the present invention, are not generated sufficiently. On the other hand, if Nb and the like exceed 50 ppm in total, the iron loss characteristics of the material itself deteriorate as described above, so 50 ppm is set as the upper limit. Preferably, it is the range of 10-30 ppm.

The abundance (ratio) of the precipitates such as Nb described above is 10% or more, and the average diameter (equivalent circle diameter) of the precipitates needs to be in the range of 0.02 to 3 μm.
If the average diameter is less than 0.02 μm, the precipitates are too small and stress concentration is difficult to occur. On the other hand, if it exceeds 3 μm, the frequency (number) of the precipitates itself decreases, and the number of places where stress concentration occurs is reduced. A preferable average diameter of the precipitate is 0.05 to 3 μm. A more preferred lower limit is 0.12 μm, and a still more preferred lower limit is 0.33 μm. A more preferred upper limit is 1.2 μm, and a more preferred upper limit is 0.78 μm.
In addition, the rate of precipitation of precipitates such as Nb is preferably 20% or more, and more preferably 31% or more. More preferably, it is 48% or more. There is no need to set an upper limit, and there is no problem even if 100% is deposited.

  The average diameter of the precipitates such as Nb is preferably obtained by observing the cross section of the obtained sample with a scanning electron microscope, photographing about 10 fields of view at a magnification of about 10000 times, and obtaining the average equivalent circle diameter by image analysis. . Further, the ratio of precipitates (precipitation ratio) can be measured by the method described in Experiment 1.

  As the precipitate forming element, one or more selected from Nb, V and Zr are preferable from the viewpoint that it is difficult to form defects in the steel sheet during hot rolling. Nb is particularly preferable from the viewpoint of reducing defects during hot rolling.

Here, in order to adjust the precipitate diameter and precipitation ratio of Nb and the like, it is effective to control the maximum attained steel plate temperature during the purification annealing and the subsequent cooling rate from 900 ° C. to 500 ° C. The reason for this is that these precipitates can be adjusted in size and ratio by bringing the purification annealing to a high temperature, once forming a solid solution, and reprecipitation when cooled.
In the above phenomenon, as in the general precipitation phenomenon, when the cooling rate is fast, the amount of the precipitate is reduced (partly remains in solid solution), and the diameter of the precipitate is also reduced. On the other hand, when the cooling rate is low, the opposite is true.

Furthermore, in the present invention, as described above, it is necessary to reduce coarse inclusions as much as possible. Specifically, it is necessary to limit the presence frequency of inclusions having a diameter (equivalent circle diameter) of 10 μm or more to less than 1 per 1 mm ² . This is because, as described above, the strain accumulation due to the shearing process is alleviated by the precipitates, but when coarse inclusions exist, stress concentration occurs there, so iron near the coarse inclusions. This is because the atomic arrangement is greatly distorted.

Note that the number density of coarse inclusions is roughly 100 mm in length when the cut surface of the sample cut with a shearing machine is observed with an optical microscope, and the diameter (equivalent circle diameter) present in the region is 10 μm or more. It is possible to calculate the number of inclusions and convert them per mm ² .
Here, in the present invention, precipitates are mainly carbides, oxides and nitrides such as Nb, and coarse inclusions are mainly impurities such as flux and alumina in the molten steel, and the above The precipitate is coarsened to 10 μm or more.

In addition, in order to achieve the ΔW reduction effect due to the addition of the precipitate forming element, as described above, the average particle size of the secondary recrystallized grains of the material needs to be 5 mm or more. Note that this grain size is generally used for electrical steel sheets for large transformers of several meters, which was also mentioned in the problem to be solved by the present invention. By controlling the temperature rate and atmosphere, the average particle size can be controlled to 5 mm or more. Further, the average particle size of the secondary recrystallized grains is preferably measured by the method described in Experiment 2.
Here, a method of reducing ΔW by setting the average grain size of secondary recrystallized grains to less than 5 mm is also possible, but this is not preferable because problems such as a decrease in the absolute value of iron loss and magnetic flux density occur.

The basic components and configurations of the present invention have been described above.
In the present invention, the elements described below can be appropriately contained as required.
Ni: 0.010-1.50%
Ni can be added to improve the magnetic properties. In this case, when the addition amount is less than 0.010%, the improvement width of the magnetic characteristics is small. On the other hand, if it exceeds 1.50%, secondary recrystallization may become unstable and the magnetic properties may deteriorate. Therefore, Ni is preferably in the range of 0.010 to 1.50%.

Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%
In order to reduce the iron loss, at least one of Cr, Cu and P can be added.
However, when each addition amount is less than the above lower limit amount, the effect of reducing iron loss is poor. On the other hand, when the above upper limit is exceeded, the development of secondary recrystallized grains is suppressed, and the iron loss increases. Therefore, it is preferable to make it contain in said range, respectively.

Sn: 0.005-0.50%, Sb: 0.005-0.50%, Bi: 0.005-0.50%, Mo: 0.005-0.100%
For the purpose of improving the magnetic flux density, at least one of Sn, Sb, Bi and Mo can be added.
However, when the amount of each additive is less than the above lower limit, the effect of improving the magnetic properties is poor. On the other hand, when the above upper limit is exceeded, the development of secondary recrystallized grains is suppressed and the magnetic properties are deteriorated. Therefore, it is preferable to make it contain in said range, respectively.

  Furthermore, in the present invention, the surface of the steel sheet has an angle within 15 ° with respect to the direction perpendicular to the rolling direction (in the present invention, the direction perpendicular to the rolling direction), and the width in the direction intersecting with the rolling direction. : It is preferable to form a linear groove having a depth of 50 to 1000 μm and a depth of 10 to 50 μm. By such groove formation, the magnetic domain subdivision effect is exhibited, and the iron loss is further reduced. The groove interval (pitch) is preferably about 2 to 7 mm. The “straight line shape” includes not only a solid line but also a dotted line and a broken line that are continuous in a line shape.

  Next, the suitable manufacturing method of the grain-oriented electrical steel sheet of this invention is described. The main process of this manufacturing method can utilize the manufacturing process of a normal grain-oriented electrical steel sheet. That is, the slab manufactured using the molten steel with the predetermined component adjustment as described above is hot-rolled and subjected to hot-rolled sheet annealing as necessary on the obtained hot-rolled sheet once or Apply cold rolling at least twice with intermediate annealing to the final sheet thickness, then recrystallize the steel sheet, and then perform purification annealing, flattening annealing as necessary, and then coating It is a series of steps of giving.

This is the case of adjusting the components in molten steel. However, if the amount of C exceeds 0.10%, it will be difficult to reduce it to 50 ppm (0.005%) or less, which does not cause magnetic aging in the subsequent processes. Then, it is desirable to set it as 0.10% or less.
Further, there is no problem even if Si is finally adjusted in an amount of 1.0 to 8.0%, which is a necessary amount, at the stage of component adjustment in molten steel. On the other hand, when using a method of increasing the amount of Si by siliconizing or the like in the process after the slab manufacturing, the amount of Si in the molten steel can be finally suppressed to be less than the necessary amount.

Nb, Ta, V and Zr, which are the main components of the present invention, are difficult to add and reduce in the process after the molten steel stage, and the necessary amount should be added at the stage of component adjustment in the molten steel described above. Is most desirable.
In addition to the above, at least inhibitor components (Al and N that are AlN forming elements, Mn and S that are MnS forming elements, Mn and Se that are MnSe forming elements, Ti and N that are TiN forming elements, etc.) One set can contain appropriate amounts according to conventional methods.

  Here, it is important in the present invention to reduce coarse inclusions as much as possible. For that purpose, secondary refining in vacuum is carried out at the steelmaking stage, and the time for the secondary refining is 10 minutes or more, preferably 20 minutes or more. In addition, when casting with a continuous casting machine, it is desirable to perform electromagnetic stirring or the like at the start of casting to promote floating of insoluble inclusions in molten steel and suppress inclusion settling.

The molten steel having the above-described components may be produced as a slab by a normal ingot-making method or a continuous casting method, or a thin cast piece having a thickness of 100 mm or less may be produced by a direct casting method. The slab is heated and hot-rolled by a normal method, but may be hot-rolled immediately without being heated after casting. In the case of a thin slab, hot rolling may be performed, or the hot rolling may be omitted and the process may proceed as it is.
As the slab heating temperature before hot rolling, a high temperature of about 1400 ° C. is usually employed in a component system including an inhibitor component. On the other hand, in a component system that does not contain an inhibitor component, a low temperature of 1250 ° C. or lower is usually employed, which is advantageous in terms of cost.

  Next, hot-rolled sheet annealing is performed as necessary. In order to obtain good magnetism, the hot-rolled sheet annealing temperature is preferably 800 ° C or higher and 1150 ° C or lower. This is because when the hot-rolled sheet annealing temperature is less than 800 ° C, the band structure in the hot-rolled remains, and it becomes difficult to realize a sized primary recrystallized structure. However, the effect of promoting the development of secondary recrystallization is relatively small. On the other hand, when the hot-rolled sheet annealing temperature exceeds 1150 ° C., the crystal grains after the hot-rolled sheet annealing are coarsened. Therefore, also in this case, it becomes difficult to realize a primary recrystallized structure having a sized particle.

  After hot-rolled sheet annealing, re-annealing is performed after performing at least one cold rolling with intermediate annealing as required. It is effective for further improving the magnetic properties that the temperature of the cold rolling is in the range of 100 ° C to 300 ° C and that the aging treatment in the range of 100 to 300 ° C is performed once or multiple times during the cold rolling. It is. In the case of performing recrystallization annealing, when decarburization is necessary, the atmosphere is a moist atmosphere, but when decarburization is not necessary, it may be performed in a dry atmosphere. After recrystallization annealing, a technique for increasing the amount of Si by a silicon immersion method may be further applied.

After that, when forming a forsterite film with an emphasis on iron loss, a secondary recrystallized structure is developed and a forsterite film is developed by applying a finish annealing after applying an annealing separator mainly composed of MgO. It is possible to form.
If the forsterite film is not actively formed with emphasis on punchability, do not use the annealing separator or use silica or alumina without using MgO that forms the forsterite film even if it is applied. It is good. When applying these annealing separators, it is effective to perform electrostatic coating that does not bring in moisture. Further, a heat resistant inorganic material sheet (silica, alumina, mica) may be used.

  The finish annealing is sufficient if it is a temperature at which secondary recrystallization occurs, but it is desirable to perform the annealing at 800 ° C. or higher. Also, the annealing conditions for completing the secondary recrystallization are desirable, and it is desirable to hold at a temperature of 800 ° C. or higher for 20 hours or longer. If the forsterite film is not formed with emphasis on punchability, the secondary recrystallization should be completed, so the holding temperature is preferably about 850 to 950 ° C, and the finish annealing may be completed by this holding treatment. Is possible. When a forsterite film is formed in order to emphasize iron loss or reduce transformer noise, it is advantageous to raise the temperature to about 1200 ° C.

In cooling the high-temperature annealing, it is desirable to cool at a rate of 5 to 100 ° C./h in a temperature range of at least 900 ° C. to 500 ° C. When cooling from a holding temperature of less than 900 ° C., it is desirable to cool at a rate of 5 to 100 ° C./h in the temperature range from the holding temperature to 500 ° C. This is because if the cooling rate in the above temperature range exceeds 100 ° C./h, the precipitates may become too fine or may not precipitate in a solid solution. On the other hand, if it is less than 5 ° C./h, the diameter of the precipitate becomes too large, or the cooling time becomes long and the productivity may be lowered.
A more preferable lower limit of the cooling rate is 7.8 ° C./h. A more preferable upper limit of the cooling rate is 30 ° C./h, and a more preferable upper limit of the cooling rate is 14 ° C./h from the viewpoint of obtaining a stable result.

  After finish annealing, it is desirable to perform water washing, brushing, and pickling in order to remove the attached annealing separator. After that, it is effective to reduce the iron loss by performing flattening annealing to correct the shape.

  In the case where the steel plates are laminated and used, in order to improve iron loss, it is effective to apply an insulating coating to the steel plate surface before or after the flattening annealing. In order to reduce iron loss, a coating that can impart tension to the steel sheet is desirable. Adopting a method of coating the surface of the steel sheet with an inorganic substance by a tension coating application method, physical vapor deposition method, chemical vapor deposition method, etc., through a binder is particularly effective because it has excellent coating film adhesion and a significant iron loss reduction effect. desirable.

  In order to reduce iron loss, it is desirable to perform magnetic domain fragmentation. As the treatment method, as is generally done, a groove is formed in the final product plate, thermal strain or impact strain is introduced linearly by laser or plasma, and the final finished plate thickness is adjusted. The method of putting a groove | channel beforehand in intermediate products, such as a cold-rolled board which reached | attained, is illustrated.

  Moreover, as a suitable manufacturing method of the iron core using the steel plate of the present invention, for example, there is a method of manufacturing the iron core by shearing the steel plate of the present invention and laminating without strain relief annealing. This manufacturing method is particularly advantageous when a large iron core is manufactured by shearing into a large plate (for example, the longest side is longer than 500 mm). The number of steel plates stacked, the size and shape of the steel plates obtained by shearing, the presence or absence of the grooves and their dimensions, and the presence and type of coating may be selected as appropriate based on conventional knowledge.

<Example 1>
Steel slabs were produced by continuous casting by melting steel slabs containing the components shown in Table 1 and the balance Fe and unavoidable impurities. At the time of smelting, secondary refining was performed in vacuum, and the frequency of inclusions was adjusted by changing the time. After slab heating at 1400 ° C., it was finished to a thickness of 2.4 mm by hot rolling. Thereafter, hot-rolled sheet annealing was performed at 1000 ° C. for 40 seconds, and then a thickness of 1.8 mm was obtained by cold rolling. Further, an intermediate annealing at 900 ° C. was performed, and then a thickness of 0.20 mm was finished by cold rolling.

Then, after recrystallization annealing under a soaking condition at 850 ° C. for 90 seconds in a 60% by volume N ₂ -40% by volume H ₂ wet atmosphere, an annealing separator mainly composed of MgO is applied. Purification annealing was performed at 6 ° C. for 6 hours. In the purification annealing, the cooling rate from 900 ° C. to 500 ° C. was controlled in the range of 1 to 50 ° C./h, and the Nb precipitate diameter and precipitation ratio were manipulated. Thereafter, planarization annealing was performed at 850 ° C. for 20 seconds.

  The obtained sample was cut into a size of 30 mm × 280 mm. The cutting at this time was performed under two conditions: wire cutter cutting and shearing. The magnetic properties of the obtained samples are measured by the method described in JIS C 2550, and the magnetic properties of the samples obtained by cutting with a wire cutter are shown in Table 1.

  Furthermore, for each of the iron losses obtained by the two cutting methods, ΔW obtained by subtracting the iron loss of the sample obtained by cutting with the wire cutter from the iron loss of the sample cut by the shearing machine is shown in Table 1. It is written together. Next, the sample after the magnetic measurement was pickled to remove the film, and the crystal grain size of the secondary recrystallized grains was measured. The results are also shown in Table 1 together with the results of investigating the Nb precipitate size, the precipitation ratio, and the presence frequency of inclusions of 10 μm or more.

  As shown in the table, all of the invention examples in which the crystal grain size, the Nb precipitate size and precipitation ratio, and the presence frequency of inclusions satisfy the appropriate range of the present invention have good magnetic properties, and It can be seen that ΔW is small and iron loss deterioration due to shearing is small.

<Example 2>
By immersing the product plate of grain-oriented electrical steel sheet containing the components shown in Table 2 and adjusting the frequency of inclusions by changing the secondary refining time in hot hydrochloric acid at 90 ° C. for 6 minutes, The coating and forsterite film were removed and the plate thickness was reduced to 0.10 mm. After that, annealing is performed in a humidified atmosphere at 850 ° C for 70 seconds and 60% by volume N ₂ -40% by volume H ₂ wet atmosphere to provide an internal oxide layer of SiO ₂ and an annealing separator mainly composed of MgO is applied. After that, a forsterite film was formed again by carrying out purification annealing at 1200 ° C. for 2 hours.
Thereafter, planarization annealing was performed at 900 ° C. for 30 seconds under the condition of forming a tension-imparting coating mainly composed of magnesium phosphate and boric acid. In this way, a sample having a thickness of 0.10 mm was obtained. The obtained sample was cut into a 30 mm × 280 mm size of an Epstein test piece. At this time, the cutting was performed under two conditions, that is, cutting with a wire cutter so that the steel was not distorted and cutting with a shearing machine.

  The magnetic properties such as iron loss and ΔW obtained by the two cutting methods are obtained in the same procedure as in Example 1, and the obtained ΔW is also shown in Table 2. Further, since the crystal grain size of the secondary recrystallized grains does not change even when the plate thickness is reduced, the value of Example 1 is used. The values are also shown in Table 2.

  Here, the components in the ground iron in Table 2 are the results of a component survey performed on a sample from which the film has been removed after the pickling treatment. Moreover, as a result of investigating precipitates and the like, the average precipitate diameter was 0.60 to 1.77 μm, which was within the scope of the present invention. The other survey results are also shown in Table 2.

  As described above, the precipitate diameter of Nb is within the scope of the present invention, and as shown in Table 2, the crystal diameter of secondary recrystallized grains, the precipitation ratio of Nb, etc., and the frequency of inclusions However, it can be seen that all of the invention examples satisfying the appropriate range of the present invention have good magnetic properties, small ΔW, and small iron loss deterioration due to shearing.

<Example 3>
Contains C: 0.052%, Si: 3.35%, Mn: 0.20%, Cr: 0.06%, Al: 250ppm, N: 80ppm, S: 35ppm, P: 0.008%, Sb: 0.036% and Nb: 30ppm, the balance A steel slab composed of Fe and inevitable impurities was produced by continuous casting, and the frequency of inclusions was adjusted by changing the time of secondary refining in vacuum during melting. Further, after slab heating at 1400 ° C., the thickness was 2.4 mm by hot rolling. Next, after hot-rolled sheet annealing at 1000 ° C. for 40 seconds, it was cold rolled to a thickness of 1.8 mm, intermediate annealed at a temperature range of 700 to 120 ° C., and then cold rolled to a thickness of 0.18 mm Finished in steel plate.

Subsequently, linear grooves having a width of 100 μm and a depth of 25 μm were formed on the surface of the steel plate at an 8 mm pitch so as to form an angle of 80 ° with the rolling direction. Then, after applying recrystallization annealing at 800-900 ° C for 90 seconds in a 60% by volume N ₂ -40% by volume H ₂ humidified atmosphere, an annealing separator mainly composed of MgO is applied. Then, purification annealing was performed at 1220 ° C. for 6 hours.

Thereafter, planarization annealing was performed at 850 ° C. for 20 seconds. The reason why the intermediate annealing temperature and the recrystallization annealing temperature are variously changed is to change the size of the grain size after the secondary recrystallization.
The obtained sample was cut into an Epstein test piece of 30 mm × 280 mm size. At this time, it performed on two conditions, the case where a wire cutter is cut | disconnected, and the case of the cutting | disconnection by a shearing machine.

  Further, the magnetic properties of the test piece were measured by the method described in JIS C 2550. Table 3 shows the magnetic properties of the samples obtained by cutting with a wire cutter. Furthermore, for each of the iron losses obtained by the two cutting methods, the value ΔW obtained by subtracting the iron loss of the sample cut by the wire cutter from the iron loss of the sample cut by the shearing machine is also shown in Table 3. .

Further, the sample after the magnetic measurement was pickled to remove the film, and the crystal grain size of the secondary recrystallized grains was measured. The results are also shown in Table 3 together with the results of investigation of the Nb precipitate diameter, the precipitation ratio, and the existence frequency of inclusions.
The results of the investigation of the components in the steel sheet with the above-mentioned coating removed were as follows: C: 0.0016%, Si: 3.35%, Mn: 0.20%, Cr: 0.06%, P: 0.008%, Sb: 0.036%, Nb : 19 ppm, and the component composition satisfied the requirements of the present invention. Furthermore, as a result of conducting a precipitate investigation, the average precipitate diameter was 0.52 to 1.22 μm, which was within the scope of the present invention.

  As shown in the table, all of the invention examples in which the crystal grain size, the precipitation ratio of Nb, and the frequency of inclusions satisfy the appropriate range of the present invention have good magnetic properties, and have small ΔW and shearing. It can be seen that the iron loss deterioration due to processing is small.

ADVANTAGE OF THE INVENTION According to this invention, the grain-oriented electrical steel sheet of the thin material which reduced effectively the magnetic characteristic degradation at the time of a shearing process can be obtained. As a result, an iron core with less iron loss can be obtained, and thus a large-scale transformer with high energy efficiency can be manufactured.

Claims (3)

In mass%, C: 0.005% or less, Si: 1.0 to 8.0% and Mn: 0.005 to 1.0%, and one or more selected from Nb, Ta, V and Zr in a total of 10 to A steel plate with a content of 50 ppm by mass, the balance being Fe and inevitable impurities: 0.220 mm or less, and Nb, Ta, V and Zr are present as precipitates in at least 10% of the content, The diameter of the precipitate (equivalent circle diameter) is 0.02 to 3 μm on average, and the number of inclusions having a diameter of 10 μm or more is less than 1 per 1 mm ² , and the average grain size of secondary recrystallized grains of the steel sheet A grain-oriented electrical steel sheet having a diameter of 5 mm or more.   Further, Ni: 0.010 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%, Sn: 0.005 to 0.50%, Sb: 0.005 to 0.50%, Bi: 0.005 The grain-oriented electrical steel sheet according to claim 1, comprising at least one selected from -0.50% and Mo: 0.005-0.100%. A straight groove having a width of 50 to 1000 µm and a depth of 10 to 50 µm intersecting with the rolling direction at an angle of 15 ° or less with respect to the direction perpendicular to the rolling direction of the steel plate is provided on the surface of the steel plate. The grain-oriented electrical steel sheet according to 1 or 2.

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