JP2006257534A - Super low iron loss directional electrical steel sheet with excellent uniformity of magnetic properties - Google Patents

Abstract

An ultra-low iron loss directional electrical steel sheet having uniform magnetic properties over the entire surface of a coil by defining an appropriate film thickness distribution range of a TiN coating.
In a grain-oriented electrical steel sheet having TiN coatings on the front and back surfaces of a steel sheet, the average film thickness of the TiN coating on the entire front and back surfaces is t [ave.], And the maximum film thickness difference in the TiN film thickness distribution in the direction perpendicular to the rolling direction. Is Δt [C], and the maximum difference in thickness between the front and back surfaces at the same position is Δt [S].
(Δt [C] + 2 × Δt [S]) / (3 × t [ave.]) ≦ 0.3
Satisfy the relationship.
[Selection] Figure 4

Description

  The present invention relates to an ultra-low iron loss directional electrical steel sheet having excellent uniformity in magnetic properties having TiN coatings on the front and back surfaces of the steel sheet.

  A grain-oriented electrical steel sheet is a soft magnetic material mainly used as a core material for transformers and generators. In recent years, from the viewpoint of energy saving, the demand for reducing the energy loss of these electrical devices is increasing, and the grain-oriented electrical steel sheets used as iron core materials are required to have better magnetic properties than before. It has become. In particular, from the viewpoint of preventing global warming, in order to minimize power loss during power transmission / distribution from power plants, demands for reducing iron loss of grain-oriented electrical steel sheets are becoming stricter year by year. Iron loss is roughly classified into hysteresis loss and eddy current loss.

In order to reduce the iron loss of grain-oriented electrical steel sheets,
(1) Hysteresis loss is reduced by highly aligning the <001> axis, which is the easy axis of iron, in one direction (rolling direction) by secondary recrystallization.
(2) Reduce hysteresis loss by reducing impurities contained in the steel sheet or smoothing the surface,
(3) Reduce the eddy current loss by adding high resistivity element (mainly Si) to the steel sheet.
(4) It is effective to reduce the eddy current loss by reducing the thickness of the steel sheet. Also,
(5) A method of reducing eddy current loss by subdividing the magnetic domain by forming a specific shape of strain or groove on the surface of the steel sheet is also effective.

However, the reduction of iron loss by these conventional methods has already reached its limit, and it is time to develop a new method.
Recently, in order to obtain an even greater iron loss reduction effect, a high-tensile ceramic coating is applied to a grain-oriented electrical steel sheet with a smoothed surface using physical vapor deposition (PVD) or chemical vapor deposition (CVD). It is being considered to form.
For example, Patent Document 1 proposes a method of stably forming a uniform TiN film by using a PVD method (arc discharge method ion plating method). Patent Document 2 proposes an ultra-low iron loss directional electrical steel sheet that does not deteriorate over time by defining the Cl content in the film for a TiN film using a CVD method. Furthermore, Patent Document 3 proposes an ultra-low iron loss directional electrical steel sheet that can withstand strain relief annealing at high temperatures by defining the crystal form of the TiN coating.

The tension applied to the steel sheet by the TiN coating can be estimated from the physical properties of TiN and the steel sheet and the coating temperature. For example, when the TiN film is coated on the front and back surfaces of a grain-oriented electrical steel sheet having a thickness of 0.23 mm by the CVD method, if the TiN film thickness is 0.5 μm or more, the iron loss is reduced by 15 to 20% due to the tension effect. ing.
However, this is calculated on the assumption that the thickness of the TiN film, which is a tension-imparting film, is completely uniform over the entire surface of the steel sheet. It is extremely difficult to coat a uniform TiN film having no film thickness difference over the entire surface of the coil.

For example, even in the thermal CVD method in which the film has good throwing power and a uniform coating can be obtained stably, it is affected by disturbance factors such as furnace temperature change, gas flow fluctuation, plate meandering, etc. A film thickness difference may occur in the width direction and the front and back surfaces. Similarly, in other coating methods such as plasma CVD and PVD, it is expected that it is difficult to obtain a uniform film thickness distribution on the entire surface of the coil.
Therefore, when industrially producing an ultra-low iron loss grain-oriented electrical steel sheet coated with a TiN coating, it is necessary to clarify and to strictly manage the allowable range of the TiN film thickness distribution on the front and back surfaces of the steel sheet.
However, none of the above-mentioned patent documents mentions the influence of the TiN film thickness distribution on the magnetic properties, and no such studies have been made heretofore.

JP 2004-353065 A JP 2004-197154 A JP 2004-238669 A

  Since the TiN film can apply a higher tension to the steel sheet than the conventional film, a non-uniform stress distribution is generated in the steel sheet even by a small difference in film thickness. When such a non-uniform stress distribution occurs, the shape and magnetic characteristics of the plate are significantly deteriorated. Therefore, when a TiN film is coated on a grain-oriented electrical steel sheet coil in an industrial production line, it is desired to obtain a uniform film thickness distribution in as wide an area as possible.

Such a TiN film cannot be synthesized by a conventional wet film coating method, and must be synthesized and coated by a dry film forming method such as a CVD method or a PVD method. However, in the steel industry, these CVD methods and PVD methods have hitherto been rarely used, and there is almost no knowledge about film thickness management at an industrial level.
Therefore, in order to prevent a decrease in yield that places an emphasis on film thickness uniformity and a large amount of poorly shaped materials and poorly characterized materials, it is possible to substantially reduce the iron loss (W _17/50 ≦ 0.75 W / kg). It is important to define an appropriate film thickness distribution range in which the material (1) can be obtained.

  The present invention has been developed in view of the above-mentioned circumstances, and by defining an appropriate film thickness distribution range of the TiN film, it is possible to achieve uniform magnetic properties that can stably obtain uniform iron loss over the entire surface of the coil. The purpose is to propose an excellent ultra-low iron loss grain-oriented electrical steel sheet.

That is, the present invention is a grain-oriented electrical steel sheet having TiN films on the front and back surfaces of the steel sheet, wherein the average film thickness of the TiN film on the entire front and back surfaces is t [ave.], And the TiN film thickness distribution in the direction perpendicular to the rolling is maximum. Where Δt [C] is the film thickness difference and Δt [S] is the maximum thickness difference between the front and back surfaces at the same position.
(Δt [C] + 2 × Δt [S]) / (3 × t [ave.]) ≦ 0.3
It is an ultra-low iron loss grain-oriented electrical steel sheet with excellent magnetic property uniformity characterized by satisfying the following relationship.

  According to this invention, by defining an appropriate film thickness distribution range of the TiN coating, it is possible to stably obtain an ultra-low iron loss directional electrical steel sheet having uniform magnetic characteristics over the entire surface of the coil.

First, the experimental results that led to the present invention will be described.
Frequency: 50Hz Magnetic flux density: Iron loss W _17/50 when excited to _1.7T is 0.85W / kg, and the surface is smoothed. Thickness: 0.23mm. A TiN film with a thickness of about 0.2, 0.6, and 1.0 μm is coated by the method, and then a sample with a width of 100 mm and a length of 300 mm is cut out for each condition, and the in-plane film thickness distribution is 10 mm. Measured at intervals, the average film thickness t [ave.] Was obtained.
Next, this sample was subjected to a heat treatment corresponding to strain relief annealing (800 ° C. × 3 hours in N ₂ gas), and then inserted into a single-plate magnetometer, and the iron loss W _17/50 was measured. .

FIG. 1 shows the relationship between the average film thickness of the TiN film and the iron loss.
As is apparent from the figure, the iron loss of the material tends to decrease as the thickness of the TiN coating increases. That is, the tension imparting effect of the TiN coating can be confirmed.
However, although the film thickness is almost the same, the degree of iron loss reduction varies from sample to sample. Such variation in characteristics is not preferable as a product. However, increasing the total TiN film thickness to clear the lower limit of product characteristics not only increases the amount of TiCl ₄ used as a raw material, but also decreases the production efficiency.

Further, warpage was observed in samples having poor iron loss characteristics. When such a shape defect occurs, dimensional accuracy decreases when shearing, processing, and assembling as an iron core material, and there is a possibility that sufficient characteristics as an iron core may not be obtained.
Therefore, it is necessary to clarify the cause of the variation in the iron loss characteristic and appropriately deal with it.

Since the warpage of the plate is presumed to be caused by the non-uniformity of the tension-imparting film, as shown in FIG. 2, the average film thickness is the same level (about 0.6 μm). Samples were selected and investigated for changes in iron loss with respect to film thickness differences.
Here, the film thickness difference means that the maximum film thickness difference in the sheet width direction is Δt [C from the graph of the TiN film thickness distribution in the rolling perpendicular direction (also referred to as the sheet width direction) of each sample, as shown in FIG. On the other hand, the maximum difference between the front and back film thicknesses at the same place in the width direction is defined as Δt [S] and defined as (Δt [C] + 2 × Δt [S]) / (3 × t [ave.]).

FIG. 4 shows the relationship between the film thickness difference and the iron loss.
As shown in the figure, it can be seen that when the film thickness difference exceeds 0.3, the iron loss rapidly increases, that is, the magnetic characteristics deteriorate.
Therefore, the conditions for obtaining appropriate magnetic properties by TiN coating are as follows:
(Δt [C] + 2 × Δt [S]) / (3 × t [ave.]) ≦ 0.3
To satisfy the relationship.

As described above, the mechanism by which uniform magnetic properties can be obtained by controlling the film thickness difference on the steel sheet surface within the range satisfying Equation (1) is not necessarily clear at this stage, but is estimated as follows. ing.
That is, when there is a difference in film thickness between the front and back surfaces, the TiN tension differs between the front and back surfaces, so the steel sheet surface on the thicker side is stronger and the steel sheet surface on the thinner film side is pulled weaker. The plate warps so that the surface with strong tension is convex and the surface with weak is concave. When warping occurs in the plate, the magnetic properties are significantly degraded.
On the other hand, when the film thickness distribution occurs in the plate width direction, strong and weak parts are formed in the plane, but the effect on the plate shape is not as great as the difference in film thickness between the front and back surfaces, and the influence on the magnetic properties Relatively small. However, when the difference in thickness in the plate width direction becomes large, the plate shape is not a simple warp, and medium elongation, ear elongation, etc. become prominent, resulting in uneven stress distribution in the steel plate. Deteriorate.
Therefore, in order to improve the iron loss characteristics, it is necessary to keep not only the front and back surfaces but also the film thickness distribution in the plate width direction within an appropriate range. Therefore, in consideration of the difference between the front and back film thickness difference and the sheet width direction film thickness difference on the warp of the plate, that is, the stress distribution, in the present invention, the left side of Equation (1) is defined as a parameter representing the film thickness difference. It was.

  The film thickness distribution in the coil longitudinal direction of the grain-oriented electrical steel sheet was within 10% in all the investigated samples, and no influence on the iron loss characteristics was observed within this range. Accordingly, the film thickness distribution in the longitudinal direction is not particularly limited, but it goes without saying that it is preferably within 10%.

Moreover, in order to suppress the nonuniformity of the TiN film thickness that causes iron loss deterioration as much as possible and supply products with small variations, it is necessary to take effective measures when coating TiN.
As a result of intensive research, the inventors have made a cylindrical nozzle having slits parallel to the plate surface and perpendicular to the traveling direction of the plate at positions at equal intervals on the plate surface. When the TiN film was coated with the continuous CVD furnace provided, it was found that the plate shape of the material had a great influence on the uniformity of the TiN film.

  Generally, grain oriented electrical steel sheets are annealed in a high temperature region around 1200 ° C. in a coil state in order to align the crystal orientation. At that time, warpage or middle elongation called a curl occurs in the steel plate, and the plate shape is not necessarily good. When such a steel plate is passed through the continuous CVD furnace described above, the distance between the nozzle gas outlet and the steel plate surface becomes asymmetrical on the front and back surfaces, and the TiN film formed on the steel plate surface by the CVD reaction becomes non-uniform. easy. Moreover, since the TiN coating tends to be thicker on the side closer to the nozzle of the steel plate (convex side) than on the far side (concave side), the tension acting on the steel plate also increases as the TiN film thickness increases and warps convexly. The part tends to warp more convexly, and the plate shape after the CVD process becomes worse.

  Therefore, when coating the TiN film, the influence of the material plate shape on the film thickness distribution was investigated, and if the warp (the warp amount in the plate width direction) was within 30% of the distance between the nozzle and the steel plate surface. It was found that TiN having a substantially uniform film thickness can be obtained.

  Moreover, when the plate | board shape of the grain-oriented electrical steel plate used for CVD processing is not favorable, it is necessary to perform shape correction in another process in advance. Furthermore, even a grain-oriented electrical steel sheet whose shape has been corrected before being charged into the CVD processing furnace may be deteriorated when heated to a high temperature of about 1000 ° C. necessary for performing TiN coating. In such a case, it is preferable to manufacture in a continuous CVD processing furnace having a function of correcting the shape of the material plate so that the shape can be corrected on the spot. In addition, the specific means of shape correction may be an increase in the tension in the furnace when the plate is passed, or a leveler device for shape correction may be installed on the entrance side of the furnace.

The present invention will be specifically described below.
As the grain-oriented electrical steel sheet to be used in the present invention, any conventionally known grain-oriented electrical steel sheet can be used, and particularly preferred component compositions are as follows. Unless otherwise specified, “%” in relation to ingredients means mass%.
In this invention, it is desirable to contain Si in 1.5 to 7.0% of range. That is, Si is an effective component for increasing the electrical resistance of the product and reducing the iron loss. However, if the content exceeds 7.0%, the hardness becomes high and it becomes difficult to manufacture and process. On the other hand, if it is less than 1.5%, transformation occurs during final finish annealing, and a stable secondary recrystallized structure cannot be obtained.

In addition to the above-mentioned elements, B, Bi, Sb, Mo, Te, Sn, P, Ge, As, Nb, Cr, as inhibitor components suitable for the manufacture of known grain-oriented electrical steel sheets are contained in steel. Ti, Cu, Pb, Zn and In can be contained alone or in combination.
Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets manufactured by such a method that does not use an inhibitor.

  On the other hand, C, S, Se, N and the like are harmful elements in terms of magnetic properties as impurities. Particularly, in order to deteriorate the iron loss, C: 0.003% or less, S and Se: 0.002 respectively in the final product. % Or less and N: 0.002% or less are preferable.

Moreover, the grain-oriented electrical steel sheet adjusted to the above component composition needs to be in a state in which there is no forsterite film on the surface after finish annealing.
As a method for that, the method of removing the forsterite film formed by the conventional method by pickling or polishing, or adjusting the composition of the annealing separator, to suppress the production of forsterite film on the steel sheet surface, Alternatively, it is possible to apply a method of substantially having a metal appearance by a method of forming the film so as to be easily peeled off and then cleaning and removing.
Furthermore, it is effective to reduce the iron loss value by subjecting the surface to a smoothing treatment. For example, the surface roughness is made as small as possible by pickling, thermal etching, chemical polishing, etc., and the surface is mirror finished, and the graining surface obtained by crystal orientation enhancement treatment by electrolysis in an aqueous halide solution It is done.
In addition, the state without a forsterite film includes a case where a film is not substantially formed, such as a small amount of forsterite being discrete or partly in the form of islands.

  In addition, it is recommended to form grooves for magnetic domain subdivision at any stage from the final cold rolling to the product shipment because it is effective in reducing iron loss. Further, the magnetic domain subdivision is not limited to the groove forming method, and a strain applying method is also effective.

A TiN film is formed on the surface of the directional electrical steel sheet strip having no film thus obtained.
As a method for coating the TiN film, either a CVD method or a PVD method may be used.
In particular, when coating a TiN film by continuous CVD, as described above, the coating operation is performed under a condition in which the warp (the warp amount in the plate width direction) is within 30% with respect to the distance between the nozzle and the steel plate surface. It is important to obtain TiN having a substantially uniform film thickness.
In addition, it is particularly advantageous to install a shape correction device on the entry side of the continuous CVD processing furnace to reduce the warpage of the steel sheet supplied into the furnace in advance.

Example 1
The iron loss W _17/50 is 0.845 W / kg and the surface is smoothed. The directional electrical steel sheet with a surface thickness of 0.23 _mm is passed through a continuous CVD furnace heated to 1100 ° C in various conditions. TiTi ₄ gas was supplied to coat the TiN coating on the front and back surfaces of the steel plate. Thereafter, a sample of width: 100 mm × length: 300 mm was cut out, and the film thickness distribution was measured at intervals of 10 mm.
Subsequently, an insulating film having a thickness of about 1 μm was applied and baked on the obtained sample, and further subjected to strain relief annealing in N ₂ gas at 800 ° C. for 3 hours.
The sample thus obtained was inserted into a single plate magnetometer, and the iron loss W _17/50 was measured.
The obtained results are shown in Table 1 in relation to the TiN film thickness distribution.

  As shown in the table, the iron loss was reduced as a whole by the TiN coating, but a remarkable iron loss reduction effect of 10% or more was recognized particularly in the inventive examples.

Example 2
In a continuous CVD furnace equipped with cylindrical nozzles that have slits parallel to the plate surface and perpendicular to the direction of plate travel, at a constant distance from the plate surface, supply at a constant temperature of 1100 ° C Under the gas conditions, various steel plates with a thickness of 0.23 mm and a width of 350 mm and different amounts of warpage in the width direction were passed, and each was coated with a TiN coating. Thereafter, the TiN film thickness distribution in the plate width direction was investigated on the front and back surfaces of the steel plate.
The obtained results are shown in Table 2 in relation to the amount of material warpage.

  As apparent from the table, when the coating operation was performed under the condition that the warpage amount in the plate width direction was less than 30% of the nozzle-plate interval, the film thickness difference could be suppressed to a low level. As a result, effective iron loss reduction is expected.

It is the graph which showed the relationship between the average film thickness of a TiN film, and an iron loss. It is the graph which showed the relationship between the average film thickness of a TiN film, and the variation in an iron loss. It is the figure which showed the calculation point of the film thickness difference in this invention. It is the graph which showed the relationship between a film thickness difference (0.5 micrometer <= t [ave.] <= 0.7 micrometer), and an iron loss.

Claims (1)

A grain-oriented electrical steel sheet having TiN coatings on the front and back surfaces of the steel plate, wherein the average film thickness of the TiN coating on the entire front and back surfaces is t [ave.], And the maximum film thickness difference in the TiN film thickness distribution in the direction perpendicular to the rolling is Δt. [C] and when the maximum difference in thickness between the front and back surfaces at the same position is Δt [S], these are expressed by the following equation (1)
(Δt [C] + 2 × Δt [S]) / (3 × t [ave.]) ≦ 0.3
An ultra-low iron loss grain-oriented electrical steel sheet with excellent magnetic property uniformity characterized by satisfying the above relationship.

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