JP5953690B2 - Oriented electrical steel sheet and manufacturing method thereof - Google Patents

Description

  The present invention relates to a grain-oriented electrical steel sheet used for applications such as an iron core of a transformer and a manufacturing method thereof.

In recent years, the efficiency of energy use has progressed, and the demand for electrical steel sheets with high magnetic flux density and low iron loss has been increasing mainly by transformer manufacturers.
Here, the magnetic flux density can be improved by integration of the crystal orientation of the electromagnetic steel sheets to Goss orientation, for example, Patent Document 1, a manufacturing method of the grain-oriented electrical steel sheet having a magnetic flux density B ₈ of greater than 1.97T It is shown.

On the other hand, measures against iron loss have been considered from the viewpoints of high purity of material, high orientation, reduction of plate thickness, addition of Si and Al, subdivision of magnetic domains, etc. (for example, see Non-Patent Document 1) ). However, generally, the higher the magnetic flux density, the more the iron loss tends to deteriorate. This is because, when the crystal orientation is aligned, the magnetostatic energy is lowered, so that the magnetic domain width in the steel sheet is expanded and the eddy current loss is increased.
As a method for reducing eddy current loss, there is a method of performing magnetic domain subdivision by improving the film tension or introducing thermal strain. However, in the method of improving the film tension, as shown in Patent Document 2, since the strain region to be applied is in the vicinity of the elastic region and the tension is applied only to the surface layer of the ground iron, the iron loss is reduced. There is a problem that the effect is small.

On the other hand, methods of using a laser or an electron beam have been considered for introducing thermal strain, and it is known that all have an extremely high effect of improving iron loss by irradiation.
For example, Patent Document 3 _{discloses a} method for producing an electrical steel sheet having an iron loss with W _17/50 being _less than _0.8 W / kg by electron beam irradiation. Patent Document 4 discloses a method for reducing iron loss by applying laser irradiation to an electromagnetic steel sheet.

By the way, one of the problems of reducing iron loss by a technique using a laser or an electron beam is to improve productivity, that is, to improve irradiation efficiency. For example, when irradiating a pulsed laser whose magnetic characteristics are expected to be improved compared to a continuous laser, the Q-switched YAG laser has a pulse frequency of only about 10 kHz, so that a scanning speed of several tens of m / h or more is desired. Dozens of laser facilities are required to install in the line. As a result, the production cost increases significantly. Here, a technique that can improve the irradiation speed by using a CO ₂ laser and setting the frequency to about 100 kHz is disclosed in Patent Document 5 and the like.

  On the other hand, in order to reduce the iron loss of a steel sheet using an electron beam, there is a restriction that the introduction of vacuum equipment is essential, but by adjusting the current flowing in the deflection coil, the surface of the steel sheet can be adjusted at a speed of 20 m / s or more. It is possible to scan the electron beam.

Japanese Patent No. 4123679 Japanese Patent Publication No. 2-8027 Japanese Patent Publication No.7-65106 Japanese Patent Publication No.3-13293 JP-A-6-57333 Japanese Patent Laid-Open No. 2002-12918

"Recent Advances in Soft Magnetic Materials" 155/156 Nishiyama Memorial Technology Course, Japan Iron and Steel Institute, February 1, 1995

However, since the technique described in Patent Document 5 has a very large beam diameter of 0.8 mm, the region of the heat effect introduced into the steel sheet is excessively enlarged, and the iron loss compared to other methods with a smaller beam diameter. There is a problem that the improvement effect is small.
Further, in recent years, with increasing demand for grain-oriented electrical steel sheets mainly in Asia, further improvement in productivity has been demanded, and further improvement in irradiation speed has become a problem.

  The present invention has been developed in view of the above-described present situation, and even when the electron beam irradiation speed is increased more than before, the magnetic domain subdivision effect is sufficiently exerted and the direction has excellent magnetic properties. An object of the present invention is to provide a conductive electrical steel sheet and a method for producing the same.

  Usually, electron beam irradiation performed for the purpose of reducing iron loss is performed by deflecting a beam from a width end portion of an irradiated material (electromagnetic steel sheet) to the other width end portion by a deflection coil. However, a plurality of electron guns may be used to divide the irradiation area with one.

Irradiation in the width direction of the steel sheet is performed by using a deflection coil so that the irradiation time repeats a long time (a ₁ ) and a short time (a ₂ ) along the irradiation position. In this case, the distance d (mm) between the long-time (a ₁ ) irradiation point and the subsequent long-time (a ₁ ) irradiation point is referred to as a dot pitch in the present invention. In the present invention, a ₂ since negligible sufficiently shorter than a _1, the inverse of a _1, can be regarded as a radiation frequency.

Here, if the irradiation frequency is increased, the scanning speed can be increased, but since the amount of heat input per unit length to the irradiation surface is reduced, the effect of reducing the iron loss is diminished.
Therefore, normally, when increasing the beam irradiation speed, the amount of heat input per unit time is increased by increasing the beam current. However, if the beam current becomes excessively high, the beam cannot be narrowed down by the focusing coil, so that the heat-affected zone is expanded and hysteresis loss is deteriorated.

Here, when irradiating the electromagnetic steel sheet with an electron beam in a point sequence,
(1) Scanning speed (m / s) = Irradiation frequency (Hz) x Dot pitch (m)
(2) Irradiation heat input per unit length (J / m) = {Acceleration voltage (V) x Beam current (A)} / {Irradiation frequency (Hz) x Dot pitch (m)}
There is a relationship.

    The inventors conducted experiments by trying to increase the scanning speed by increasing the dot pitch from the above formula (1), and as a result, the following knowledge was obtained.

FIGS. 1A and 1B schematically show the state of a heat-affected zone related to electron beam irradiation.
In the case of normal electron beam irradiation as shown in Fig. 1 (a), if the dot pitch exceeds 0.5 mm, even if the beam current is increased and the irradiation heat input per unit length of the steel sheet is increased. It was found that the iron loss was not reduced. Here, the irradiation conditions of the electron beam other than the heat-affected zone were set within the preferable range described later.

Next, the inventors set the length of the heat affected zone in the scanning direction of the electron beam (hereinafter, the irradiation direction also means the same direction) as L ₁ (μm) in addition to the irradiation heat input, and When the length of the heat-affected zone in the direction perpendicular to the scanning direction is L ₂ (μm), the ratio of L ₁ and L ₂ is thought to greatly affect the iron loss. Therefore, as shown in FIGS. 1B and 2, an attempt was made to slightly change the electron beam at each point in the heat affected zone.

That is, various tests were performed by adjusting the electron beam irradiation conditions so that the value of L ₁ / L ₂ was increased. As a result, by setting the ratio of L ₁ and L ₂ to a predetermined value, even if the dot pitch becomes wider than 0.5 mm, the iron loss can be sufficiently reduced without excessively increasing the beam current value. I found it possible. Furthermore, it has also been found that the hysteresis loss can be reduced because the amount of heat input is small.

Incidentally, by adjusting the ratio of L ₁ and L ₂ (irradiation signatures of the beam has an elliptical) technology, although in Patent Document 6, such a technology is merely an irradiation method of a laser irradiation mark is not generated It is just an explanation.

The present invention is based on the above-described knowledge, and the gist configuration is as follows.
1. It is a grain-oriented electrical steel sheet having point-like heat-affected zones formed by electron beam irradiation that is slightly changed along the scanning direction of the electron beam in the direction of 60 to 120 ° with respect to the rolling direction at predetermined intervals. And
When the length of the heat affected zone in the scanning direction of the electron beam is L ₁ (μm) and the length of the heat affected zone in the direction perpendicular to the scan direction is L ₂ (μm), these ratios (L ₁ / A grain-oriented electrical steel sheet characterized in that L ₂ ) is 1.2 or more.

2. When the surface of the grain-oriented electrical steel sheet is irradiated with an electron beam in a direction of 60 to 120 ° with respect to the rolling direction to form a point-like heat-affected zone arranged at a predetermined interval,
By minutely changing the electron beam along the scanning direction of the electron beam, the length of the heat affected zone in the scanning direction: L ₁ (μm) and the length in the direction perpendicular to the scanning direction: L ₂ A method for producing a grain-oriented electrical steel sheet, wherein a ratio (L ₁ / L ₂ ) to (μm) is 1.2 or more.

  By following the present invention, the irradiation rate of the electron beam can be increased more than before without causing deterioration of the iron loss, so that the productivity of the electromagnetic steel sheet can be further improved.

(a) And (b) is the figure which showed typically the mode of the heat affected zone concerning irradiation of an electron beam. It is the figure which showed the length in the scanning direction of the electron beam in each point of a heat affected zone, and the length in the direction orthogonal to the scanning direction of a beam. It is a figure which compares and shows the irradiation time along the scanning direction of the electron beam by the presence or absence of a micro fluctuation.

Hereinafter, the present invention will be specifically described.
First, manufacturing conditions for the grain-oriented electrical steel sheet according to the present invention will be described.
In the present invention, the component composition of the slab for grain-oriented electrical steel sheet may be a component composition that causes secondary recrystallization. Further, when using an inhibitor, for example, when using an AlN-based inhibitor, Al and N, and when using an MnS / MnSe-based inhibitor, an appropriate amount of Mn and Se and / or S should be contained. Good. Of course, both inhibitors may be used in combination. The preferred contents of Al, N, S and Se in this case are Al: 0.01 to 0.065 mass%, N: 0.005 to 0.012 mass%, S: 0.005 to 0.03 mass%, and Se: 0.005 to 0.03 mass%, respectively. .

Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets in which the contents of Al, N, S and Se are limited and no inhibitor is used.
In this case, the amounts of Al, N, S and Se are preferably suppressed to Al: 100 mass ppm or less, N: 50 mass ppm or less, S: 50 mass ppm or less, and Se: 50 mass ppm or less, respectively.

The basic components and optional components of the slab for grain-oriented electrical steel sheets according to the present invention are specifically described as follows.
C: 0.08 mass% or less C is added to improve the hot-rolled sheet structure, but if it exceeds 0.08 mass%, it is difficult to reduce C to 50 mass ppm or less where no magnetic aging occurs during the manufacturing process. Therefore, the content is preferably 0.08% by mass or less. In addition, regarding the lower limit, since a secondary recrystallization is possible even for a material not containing C, it is not particularly necessary to provide it.

Si: 2.0 to 8.0 mass%
Si is an element effective in increasing the electrical resistance of steel and improving iron loss. However, if the content is less than 2.0% by mass, a sufficient iron loss reduction effect cannot be achieved, while 8.0% by mass. If it exceeds 1, the workability is remarkably lowered and the magnetic flux density is also lowered. Therefore, the Si content is preferably in the range of 2.0 to 8.0% by mass.

Mn: 0.005 to 1.0 mass%
Mn is an element necessary for improving the hot workability. However, if the content is less than 0.005% by mass, the effect of addition is poor, whereas if it exceeds 1.0% by mass, the magnetic flux density of the product plate decreases. The amount of Mn is preferably in the range of 0.005 to 1.0 mass%.

In addition to the above basic components, the following elements can be appropriately contained as magnetic property improving components.
Ni: 0.03-1.50 mass%, Sn: 0.01-1.50 mass%, Sb: 0.005-1.50 mass%, Cu: 0.03-3.0 mass%, P: 0.03-0.50 mass%, Mo: 0.005-0.10 mass% and Cr: At least one selected from 0.03 to 1.50 mass%
Ni is an element useful for improving the magnetic properties by improving the hot-rolled sheet structure. However, if the content is less than 0.03% by mass, the effect of improving the magnetic properties is small. On the other hand, if it exceeds 1.50% by mass, the secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, the amount of Ni is preferably in the range of 0.03 to 1.50 mass%.

Sn, Sb, Cu, P, Mo and Cr are elements useful for improving the magnetic properties, respectively, but if any of them is less than the lower limit of each component described above, the effect of improving the magnetic properties is small, If the upper limit amount of each component described above is exceeded, the development of secondary recrystallized grains is hindered.
The balance other than the above components is inevitable impurities and Fe mixed in the manufacturing process.

Next, the slab having the above-described component composition is heated and subjected to hot rolling according to a conventional method, but may be immediately hot rolled after casting without being heated. 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.
Furthermore, hot-rolled sheet annealing is performed as necessary. At this time, in order to develop a goth structure at a high level in the product plate, a range of 800 to 1100 ° C. is preferable as the hot-rolled sheet annealing temperature. When the hot-rolled sheet annealing temperature is less than 800 ° C, the band structure in hot rolling remains, making it difficult to achieve a sized primary recrystallization structure and inhibiting the development of secondary recrystallization. . On the other hand, when the hot-rolled sheet annealing temperature exceeds 1100 ° C., the grain size after the hot-rolled sheet annealing is excessively coarsened, so that it is very difficult to realize a sized primary recrystallized structure.

  After hot-rolled sheet annealing, after performing cold rolling of 1 time or 2 times or more sandwiching intermediate annealing, recrystallization annealing is performed and an annealing separator is applied. After applying the annealing separator, a final finish annealing is performed for the purpose of secondary recrystallization and forsterite film formation.

  After the final finish annealing, it is effective to correct the shape by performing flattening annealing. In the present invention, an insulating coating is applied to the steel sheet surface before or after planarization annealing. Here, in the present invention, this insulating coating means a coating (hereinafter referred to as tension coating) that can apply tension to a steel sheet in order to reduce iron loss. Examples of the tension coating include silica-containing inorganic coating, physical vapor deposition, and ceramic coating by chemical vapor deposition.

  In the present invention, the magnetic domain refinement treatment is performed by irradiating the grain-oriented electrical steel sheet after the final finish annealing or tension coating described above with an electron beam under the following conditions.

Next, an electron beam irradiation method according to the present invention will be described.
First, the electron beam irradiation conditions will be described.
Acceleration voltage: 40-300kV
The acceleration voltage is 40 kV or higher. The higher the acceleration voltage, the smaller the irradiation beam current required to obtain the same output. As a result, it is preferable because the beam diameter can be reduced and excessive increase in hysteresis loss can be suppressed. However, if it exceeds 300 kV, the irradiation beam current becomes excessively small, and fine adjustment of the beam current may be difficult.

Irradiation diameter: 250 μm or less If the irradiation diameter is large, the heat-affected zone expands and iron loss (hysteresis loss) deteriorates. Therefore, the irradiation diameter is preferably 250 μm or less.
The measurement of the irradiation diameter was defined by the half width of a current (or voltage) curve obtained by a known slit method. In addition, there is no limitation on the lower limit of the irradiation diameter, but if it is too small, the beam energy density becomes excessively high, it becomes easy to generate irradiation marks, and the voltage resistance and rust resistance deteriorate, so that it is about 100 μm or more. It is preferable to do this.

Line spacing: 1-15mm
In the present invention, the electron beam irradiation is performed by scanning from the width end to the width end of the irradiated material by the deflection coil, and the same scanning is repeated at a certain interval in the line direction of the irradiated material. In the present invention, this interval is called a line interval.
Here, if the line spacing is narrower than 1 mm, the heat-affected zone is expanded and the iron loss (hysteresis loss) may be deteriorated. On the other hand, when the width is larger than 15 mm, the magnetic domain is not sufficiently subdivided and the iron loss tends not to be improved. Therefore, the line spacing in the present invention is preferably in the range of 1 to 15 mm.

Processing chamber pressure: 3 Pa or less When the pressure in the processing chamber exceeds 3 Pa, electrons generated from the electron gun are scattered and the energy of the electrons that have a thermal effect on the ground iron is reduced. There is a risk that iron loss will not be improved. There is no particular lower limit, and the lower the pressure, the better.
Needless to say, it is preferable to adjust the convergence current in advance so that the beam in the width direction becomes uniform when the beam is deflected in the width direction.

  The electron beam is irradiated linearly from the width end of the steel sheet to the other width end while repeating the intermittent motion described below. However, it is important that the direction from the start point to the end point is 60 to 120 ° from the rolling direction. This is because the magnetic domain fragmentation effect by the electron beam is not sufficiently exhibited when the direction is deviated from the above.

In the present invention, it is most important that the length in the irradiation direction of each heat-affected zone is at least 1.2 times the length in the perpendicular direction. This is because when the length ratio is smaller than 1.2, that is, when L ₁ / L ₂ is smaller than 1.2, as described above, the magnetic domain fragmentation by the electron beam is not sufficiently performed, and the iron loss reduction effect is reduced. Because it will end up. Therefore, L ₁ / L ₂ is 1.2 or more.

Here, in order to set L ₁ / L ₂ to 1.2 or more, as shown in FIG. 1B, the electron beam is slightly changed along the scanning direction of the electron beam applied to the surface of the irradiated material. . Due to such fluctuation, the heat-affected zone becomes an ellipse having a long axis in the scanning direction or a shape close thereto. Then, such a heat-affected zone may be irradiated in the width direction at a predetermined interval (for example, the dot pitch in FIG. 1B). Incidentally, although the upper limit of L _{1 /} L ₂ is not particularly limited, but is preferably 1.5 or less from the viewpoint of reducing iron loss effect. The predetermined interval does not necessarily need to be regular, and irregular intervals can be allowed.

FIG. 3 shows a comparison of irradiation times along the scanning direction of the electron beam depending on the presence or absence of minute fluctuations. As shown in the figure, if it is slight change, (shown in figure x ₁₎ area which the electron beam is irradiated, compared with the scanning direction in the case of not slight change (shown in the figure x ₂₎ Expand to. A preferable range of the dot pitch is 0.2 to 0.8 mm.

As a simple method for determining the heat irradiation area in the present invention, when a sample with a film is irradiated with an electron beam, it can be determined by looking at the shape (irradiation trace) of film peeling caused by irradiation heat it can. Further, when there is no coating or when the irradiation mark is visually unclear, the heat irradiation region can be measured from the strain distribution using EBSP or the like.

  If the irradiation traces observed by the above method can be confirmed at a set dot pitch or more, check whether the shape of one irradiation trace is the elliptical shape or a shape close thereto. If it is such a shape, it can be determined that the electron beam has undergone minute fluctuations.

  On the other hand, when irradiation marks can be confirmed at an interval narrower than the set dot pitch, it is considered that the above-mentioned minute fluctuation occurs and temperature unevenness occurs in one heat-affected zone, and a plurality of irradiation marks are generated. Therefore, the interval between the irradiation marks is measured, and the two irradiation marks whose intervals are the narrowest are handled as one irradiation mark. Then, for example, the adjustment of the dot pitch is repeated until the average interval between the 20 irradiation traces is about the set dot pitch. After that, the shape of the newly determined irradiation mark is measured, and if it is an ellipse or a shape close thereto, it can be determined that a minute fluctuation of the electron beam is made.

In the present invention, as shown in FIGS. 2 and 3, each heat-affected zone is a local region in which one dot including a minute variation region irradiates the steel plate for a ₁ second. At this time, the irradiation beam spot is considered as a circular shape having a beam diameter measured by a known slit method. However, when L ₁ / L ₂ ≧ 1.2, it is clear from the observation results by the inventors that the irradiation trace is in the range of the length in the electron beam scanning direction / the length in the perpendicular direction ≧ 1.2. ing. Therefore, even if the exact L ₁ and L ₂ are unknown, it can be determined that the electron beam according to the present invention has undergone minute fluctuations as long as it has the irradiation mark shape described above.

  Here, the reciprocal of the irradiation frequency is the irradiation time per dot, but in the case of minute fluctuation, the irradiation time of the minute fluctuation is included.

  In this invention, except the process and manufacturing conditions mentioned above, the manufacturing conditions of the grain-oriented electrical steel sheet which performs a magnetic domain refinement process using the conventionally well-known electron beam are applicable.

The present invention is a grain-oriented electrical steel sheet that radiates an electron beam in a direction of 60 to 120 ° with respect to the rolling direction and forms point-like heat-affected zones at predetermined intervals by satisfying the above-described conditions. When the length of the point-like heat-affected zone in the scanning direction of the electron beam is L ₁ (μm) and the length in the direction perpendicular to the scanning direction is L ₂ (μm), these ratios (L ₁ / L ₂ ) can be 1.2 or more. As a result, even if the scanning speed of electron beam irradiation is high, a grain-oriented electrical steel sheet with low iron loss can be obtained.

Steel slabs with the composition shown in Table 1 are manufactured by continuous casting, heated to 1430 ° C, hot rolled into a hot rolled sheet with a thickness of 1.6mm, and then hot rolled at 1000 ° C for 10 seconds. Plate annealing was performed.
Next, intermediate annealing was performed by cold rolling to an intermediate plate thickness of 0.55 mm, atmosphere oxidation degree PH ₂ O / PH ₂ = 0.37, temperature: 1100 ° C., and time: 100 seconds. Then, after removing the surface subscale by hydrochloric acid pickling, cold rolling was performed again to obtain a cold-rolled sheet having a sheet thickness of 0.23 mm.
Next, after decarburization annealing was performed at atmospheric oxidation degree PH ₂ O / PH ₂ = 0.45 and soaking temperature: 850 ° C. for 150 seconds, an annealing separator mainly composed of MgO was applied. Then, final finish annealing for the purpose of secondary recrystallization and purification was performed at 1180 ° C. for 60 hours.
In this final finish annealing, the average cooling rate in the cooling process in the temperature range of 700 ° C. or higher was changed. Next, a tension coating composed of 50% colloidal silica and magnesium phosphate was applied, and the iron loss was measured. The iron loss was 0.56 to 0.58 W / kg in eddy current loss (1.7 T, 50 Hz).

Then, the magnetic domain fragmentation process which irradiates an electron beam on each irradiation condition shown in Table 2 was performed, and the iron loss of the obtained steel plate was measured based on JIS C2556.
Table 3 shows the measurement results.

Comparing symbols 1 and 2, 3 and 4, and 6 and 7, by increasing L ₁ / L ₂ to 1.2 or more, the magnitude of the total iron loss change before and after electron beam irradiation (the absolute _value of ΔW _17/50 It can be seen that even when the values are substantially equal, the hysteresis loss is low and the scanning speed represented by dot pitch × frequency is high.

Further, looking at symbol 5, it can be seen that even if L ₁ / L ₂ is greater than 1.00, the iron loss is not sufficiently reduced unless it is 1.2 or more. On the other hand, comparing symbols 6 and 8, when the frequency is simply increased, the beam current is increased, and the scanning speed is increased, the effect of reducing the iron loss is reduced due to the increase in hysteresis loss. It turns out that it will become.

  In the above embodiment, the grain-oriented electrical steel sheet mainly containing an inhibitor component has been described. However, it has been confirmed that the same result can be obtained for a steel sheet having a so-called inhibitorless component.

Claims (2)

It is a grain-oriented electrical steel sheet having point-like heat-affected zones formed by electron beam irradiation that is slightly changed along the scanning direction of the electron beam in the direction of 60 to 120 ° with respect to the rolling direction at predetermined intervals. And
When the length of the heat affected zone in the scanning direction of the electron beam is L ₁ (μm) and the length of the heat affected zone in the direction perpendicular to the scan direction is L ₂ (μm), these ratios (L ₁ / A grain-oriented electrical steel sheet characterized in that L ₂ ) is 1.2 or more. When the surface of the grain-oriented electrical steel sheet is irradiated with an electron beam in a direction of 60 to 120 ° with respect to the rolling direction to form a point-like heat-affected zone arranged at a predetermined interval,
By minutely changing the electron beam along the scanning direction of the electron beam, the length of the heat affected zone in the scanning direction: L ₁ (μm) and the length in the direction perpendicular to the scanning direction: L ₂ A method for producing a grain-oriented electrical steel sheet, wherein a ratio (L ₁ / L ₂ ) to (μm) is 1.2 or more.

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