JP2012031519A - Directional electromagnetic steel sheet and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a directional electromagnetic steel sheet excellent in both core loss and magnetostriction characteristics.SOLUTION: The method includes, when irradiating with a laser a directional electromagnetic steel sheet subjected to forsterite film formation followed by tensile strength coating formation to thereby reduce the core loss of the flat rolled electromagnetic steel sheet and strip, detecting the amount of forsterite film prior to tensile strength coating formation, as well as detecting the amount of tensile strength coating after tensile strength coating formation, collating these amounts of detection with the relation between the amounts of forsterite film and tensile strength coating in which the core loss after laser irradiation is within a target range and the laser irradiation conditions, the relation being evaluated in advance, and irradiating with a laser the directional electromagnetic steel sheet under the irradiation conditions obtained as the result of the collation.

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet having a low iron loss, which is suitable for iron core materials such as transformers.

The grain-oriented electrical steel sheet is mainly used as an iron core of a transformer and is required to have excellent magnetization characteristics, particularly low iron loss.
To that end, firstly, the secondary recrystallized grains in the steel plate must be highly aligned in the (110) [001] orientation (Goss orientation), and secondly, impurities present in the final product steel. It is necessary to reduce the amount of precipitates as much as possible.

However, since there is a limit to the control of crystal orientation and the reduction of impurities / precipitates, by introducing non-uniformity to the surface of the steel sheet using a physical method, the width of the magnetic domain is subdivided to reduce iron loss. A technology for reducing the magnetic field, that is, a magnetic domain fragmentation technology has been developed.
For example, Patent Document 1 discloses that the surface width of the final product plate is irradiated with a laser beam at intervals of several millimeters substantially perpendicular to the rolling direction, and a linear high dislocation density region is introduced into the steel sheet surface layer, thereby reducing the magnetic domain width. Techniques have been proposed for reducing iron loss by narrowing.

Usually, the surface layer of the product plate of the grain-oriented electrical steel sheet is composed of a forsterite film and a tension coating, and laser irradiation is performed after the tension coating. Reduction of iron loss by laser irradiation is achieved by applying thermal strain to the steel sheet by laser irradiation and, as a result, subdividing the magnetic domains.
On the other hand, both the forsterite film and the tension coating have the effect of imparting tensile stress to the steel sheet, and also have the effect of subdividing the magnetic domains. Therefore, the tension applied to the steel sheet by the forsterite film and the tension coating is one factor that affects the iron loss reduction effect by laser irradiation.
Conventionally, however, laser irradiation conditions are determined in advance for each material, and consideration is given to the effects of variations in the thickness of the forsterite film and tension coating formed on the actual steel sheet. There wasn't.

Japanese Patent Publication No.57-2252

  Laser irradiation on grain-oriented electrical steel sheets reduces iron loss due to the magnetic domain refinement effect. On the other hand, since distortion is introduced into the steel sheet, there is a side effect that magnetostriction increases and transformer noise worsens. Therefore, if a sufficient iron loss reduction effect is obtained, it is preferable to suppress the introduction of strain into the steel sheet by reducing the irradiation heat amount as much as possible.

  The present invention advantageously responds to the above-mentioned demand, and suppresses the introduction of excessive strain to the steel sheet in consideration of the influence of thickness variation in the forsterite film and tension coating during magnetic domain subdivision by laser irradiation. An object of the present invention is to propose an advantageous method for producing a grain-oriented electrical steel sheet excellent in both iron loss characteristics and magnetostriction characteristics.

The tension imparted to the steel sheet by the forsterite film and the tension coating (hereinafter referred to as the film tension) has a magnetic domain refinement effect by reducing the magnetic domain structure called the lancet magnetic domain generated in the steel sheet, and further the laser. It also has the effect of enhancing the magnetic domain refinement effect by irradiation. Therefore, if the film tension is high, a sufficient magnetic domain refinement effect can be achieved even if the intensity of laser irradiation is lowered.
However, generally, for each raw steel plate coil, even in the same steel plate coil, the coating tension generally varies depending on the position in the longitudinal direction and the width direction.
In this regard, if the film thickness distribution of the film tension is detected prior to laser irradiation, it is possible to minimize the iron loss and at the same time suppress the transformer noise by performing laser irradiation under the optimum conditions accordingly. Conceivable.
The present invention is based on the above findings.

  Although it is possible to adjust the laser irradiation conditions by feeding back the iron loss value after film formation and the iron loss value after laser irradiation, this method does not increase the iron loss due to the film tension. In such a case, an excessive laser irradiation is performed on the coating, which may damage the coating and increase the iron loss deterioration.

That is, the gist configuration of the present invention is as follows.
1. After the forsterite film is formed, the grain-oriented electrical steel sheet on which the tension coating is formed is irradiated with a laser to reduce the iron loss of the electrical steel sheet.
The amount of forsterite film is detected before the tension coating is formed, and the amount of tension coating is detected after the tension coating is formed, and the detected iron loss after laser irradiation is within the target range. A method for producing a grain-oriented electrical steel sheet characterized by collating with the relationship between the amount of forsterite coating and tension coating and the laser irradiation conditions, and performing laser irradiation under the irradiation conditions obtained as a result of the collation .

2. When the amount of the tension coating is X (g / m ² ) and the amount of the forsterite film is Y (g / m ² ), the energy density U (mJ / mm ² ) of the laser irradiation is given by (1)
3.75 ≦ U × exp {1.6 × (0.07 × X + 0.05 × Y)} ≦ 6.25 --- (1)
2. The method for producing a grain-oriented electrical steel sheet according to 1 above, wherein the laser irradiation is performed under a condition that satisfies the following conditions.

3. A grain-oriented electrical steel sheet obtained by irradiating a laser on a surface having a forsterite film and a tension coating, wherein the amount of the tension coating is X (g / m ² ) and the amount of the forsterite film is Y (g / m ² ), the width W (μm) of the heat-affected region in the magnetic domain structure formed linearly at the laser irradiated portion is expressed by the following equation (2)
800 ≦ W × exp {1.6 × (0.07 × X + 0.05 × Y)} ≦ 1600 --- (2)
A grain-oriented electrical steel sheet characterized by satisfying the above relationship.

  According to the present invention, prior to laser irradiation, the amount of forsterite film and tension coating is detected, and laser irradiation is performed under appropriate irradiation conditions according to these detection amounts, thereby simultaneously reducing iron loss. In addition, magnetostriction and thus noise of the transformer can be reduced.

Hereinafter, the present invention will be specifically described.
In the present invention, it is important to detect the amount of forsterite film and tension coating, in other words, the film thickness prior to laser irradiation.
Since the tension of the forsterite film is mainly proportional to the amount of the forsterite film, the amount of the forsterite film of the coil is detected. At this time, a sample can be taken and analyzed from a certain position of the coil to obtain a representative value. More preferably, the amount of forsterite film is continuously detected and recorded. This can be converted into the amount of forsterite film (Mg ₂ SiO ₄ ) from the amount of oxygen by continuously measuring the amount of oxygen by fluorescent X-ray analysis before forming the tension coating.

  The tension coating tension is also proportional to the amount of coating. This can be taken as a representative value by taking a sample from a certain position of the coil and analyzing it at any time from tension coating formation to laser irradiation. More preferably, the amount of coating is continuously detected and recorded. This is because the coil is continuously subjected to oxygen analysis with fluorescent X-rays, and the oxygen amount resulting from the tension coating is calculated by excluding the oxygen amount resulting from the thickness of the forsterite film previously detected. And converted from the chemical composition (chemical formula) of the coating or detected by fluorescent X-ray analysis of components that are contained in the tension coating but not in the forsterite film (eg, phosphorus and chromium). The detected amount and the chemical composition (chemical formula) of the coating can be converted.

  Furthermore, it is important to determine in advance what kind of laser irradiation conditions should be adopted according to the film tension, and to be able to select appropriate laser irradiation conditions according to the film tension. .

In the present invention, based on these results, it is possible to minimize both the iron loss and the transformer noise by irradiating the laser under the optimum conditions according to the film tension.
Here, laser irradiation conditions typically indicate energy density, but in addition, laser output, beam diameter, scanning speed, irradiation point interval (in the case of pulsed laser), and repetition of linear irradiation in the rolling direction. It is conceivable to adjust the interval or the like alone or in combination.

In the present invention, in order to select an appropriate laser irradiation condition, it is effective to lower the laser output as the film tension increases. This is because the magnetic domain width is reduced as the coating tension increases, so that the desired iron loss can be improved even if the magnetic domain fragmentation effect by laser irradiation is reduced.
Specifically, when the amount of tension coating per side is X (g / m ² ) and the amount of forsterite coating per side is Y (g / m ² ), the energy amount of laser irradiation is per unit area. It is arranged by the amount of energy U (mJ / mm ² ).

That is, the energy density U (mJ / mm ² )
U = k × exp {−1.6 × (0.07 × X + 0.05 × Y)}
It was proved by the inventors' experimental investigation that it is particularly effective to set the constant k to about 5.0.
In addition, even if the irradiation energy amount is increased or decreased by about ± 25%, the effect variation is small, so in practice, the constant k is preferably in the range of 3.75 to 6.25.
Therefore, in the present invention, the above formulas are arranged,
3.75 ≦ U × exp {1.6 × (0.07 × X + 0.05 × Y)} ≦ 6.25 --- (1)
It is preferable that the following relational expression is satisfied.
In other words, the laser irradiation conditions in which the energy density U, the tension coating amount X (g / m ² ), and the forsterite coating amount Y (g / m ² ) satisfy the above formula (1) depend on the coating tension. Therefore, both iron loss and transformer noise can be effectively reduced.
In the above equation (1), the coefficients applied to X and Y reflect the degree of influence of the forsterite film amount and the tension coating amount on the film tension, respectively.

Furthermore, the inventors analyzed how the irradiation of the laser in this preferred range affects the magnetic domain fragmentation effect of the magnetic steel sheet by observing the magnetic domain structure by the magnetic colloid method (bitter method). As a result, the main magnetic domain observed in stripes on the magnetic steel sheet is good by limiting the width of the region exhibiting a magnetic domain structure disturbed by the thermal effect of laser irradiation (hereinafter referred to as a heat-affected region) to a predetermined range. As a result, it was revealed that the iron loss improvement effect can be obtained.
And the width W (μm) of the heat affected area is expressed by the following equation (2),
800 ≦ W × exp {1.6 × (0.07 × X + 0.05 × Y)} ≦ 1600 --- (2)
It was also revealed that meeting the requirements is essential.
Here, when the value of the middle side of the above formula (2) is smaller than 800, the amount of strain introduced is too small to sufficiently obtain the effect of reducing iron loss, while when larger than 1600, the strain is reduced. This is because the introduction amount is too large and the noise of the transformer increases or the iron loss increases.
The width W of the heat affected zone is a value obtained by measuring and averaging the width of the heat affected zone of about 1 m for every 500 m of the coil length.

In the present invention, any conventionally known manufacturing process is suitable for the process up to the tension coating process following the finish annealing. However, the laser irradiation on the grain-oriented electrical steel sheet needs to be after the formation of the forsterite film by finish annealing and the formation of the tension coating.
This is because it is the high temperature to develop the secondary recrystallized grains that have the Goss orientation characteristic of grain-oriented electrical steel sheets, and to form a forsterite film, or to form a tension coating to develop the tension effect. This is because such a high temperature treatment needs to be performed before the laser irradiation treatment of the present invention in order to remove or reduce the distortion introduced into the steel sheet by the laser irradiation treatment.

Further, it is known that the iron loss of the grain-oriented electrical steel sheet subjected to the magnetic domain refinement treatment becomes smaller as the orientation of secondary recrystallization is higher. B ₈ (magnetic flux density when magnetized at 800 A / m) is often used as a measure of orientation accumulation, but the grain-oriented electrical steel sheet used in the present invention preferably has B ₈ of 1.88 T or more, more preferably 1.92 T or more. Are preferred.
The magnetic flux density can be controlled by adjusting the components, and known methods such as adjusting the inhibitor components, rolling, and controlling the annealing conditions can be used.

  Further, in the present invention, the tension coating formed on the surface of the electrical steel sheet may be a conventionally known tension coating, but a glassy substance mainly composed of a phosphate such as aluminum phosphate or magnesium phosphate and silica. The tension insulating coating is preferred.

Laser irradiation is repeatedly performed linearly in a direction intersecting with the rolling direction of the steel sheet.
As an oscillator for introducing thermal distortion, a known method such as pulse oscillation of a YAG laser, CO ₂ laser, fiber laser or the like, or irradiation with continuous oscillation can be employed.
Here, the region where strain is introduced into the steel sheet by laser irradiation is as follows: width: 0.05 to 0.5 μm, depth: 5 to 40 μm, and repetition interval in the rolling direction: about 1 to 20 mm. It is preferable.

  Furthermore, in the present invention, “linear” includes not only a solid line but also a dotted line and a broken line. In the case where the laser irradiation is not continuous but discontinuous, an average value is used for the heat affected zone.

  The width of the heat-affected region caused by laser irradiation can be controlled by adjusting the laser spot diameter (rolling direction), output, and beam moving speed. Further, the width of the heat-affected region can be measured as the width of the region in which the main magnetic domain extending in a stripe shape in the rolling direction is disturbed by thermal stress by observing the magnetic domain in the irradiated portion. The magnetic domain observation can be performed by a known method such as the above-described bitter method or electron microscope method.

  In the present invention, in advance, the relationship between the laser irradiation conditions and the width of the heat-affected region in the magnetic domain structure caused by the irradiation is determined, and when producing a grain-oriented electrical steel sheet, from the amount of forsterite film and tension coating, By selecting an irradiation condition that provides W in the range satisfying the above formula (2), it becomes possible to stably obtain a certain iron loss even if the amount of forsterite film or tension coating varies. .

  In the present invention, the “direction intersecting the rolling direction” means an angle range within ± 30 ° with respect to the direction perpendicular to the rolling direction.

[Example 1]
After finishing annealing, a laser was continuously irradiated while continuously feeding a coil of a directional electrical steel sheet having a thickness of 0.23 mm, a width of 1 m, and a weight of 5 tons, which had been subjected to a tension coating treatment. This grain-oriented electrical steel sheet contains 3.4% by mass of Si, the magnetic flux density B ₈ is 1.93T, and the iron loss W _17/50 at 1.7T and 50Hz is 0.90W / kg. It is a grain-oriented electrical steel sheet, and the tension insulation coating is a general tension insulation coating obtained by baking a chemical solution composed of colloidal silica, magnesium phosphate, and chromic acid formed on the forsterite coating at 840 ° C.
Before forming the tension coating, the steel sheet is measured by oxygen analysis with fluorescent X-rays, and the forsterite coating amount Y (g / m ² ) is measured and recorded over the entire width. After forming the tension coating, the total length is analyzed by chromium analysis with fluorescent X-rays. The amount of tension coating X (g / m ² ) was measured and recorded over the entire width.

Next, laser irradiation treatment was performed. The laser transmitter is a Q-switched pulse type YAG laser with a beam diameter of 0.3 mm, a pulse repetition frequency of 25 kHz, and a galvano scanner with one oscillator arranged in a direction perpendicular to the rolling direction at a width of 200 mm. Was irradiated so as to draw at intervals of 5 mm.
The output during this irradiation
(a) 1.0mJ / mm ² constant,
(b) 2.0mJ / mm ² constant,
(c) 4.0mJ / mm ² constant,
(d) The measured total length, X and Y of the full width, the energy density U is U (mJ / mm ² ) = 5.0 × exp {−1.6 × (0.07 × X + 0.05 × Y)}
The following four conditions were set.
Three coils are processed for each condition, samples are taken for each ton from each coil, the iron loss of the material is measured (W _17/50 ), and 15 small test transformers are produced. The noise when excited at 1.7T and 50Hz was measured.
The measurement results are shown in Table 1.

  As shown in the table, when performed under the condition (d) that satisfies the conditions of the present invention, the iron loss average value, standard deviation and noise are all excellent, and stable low iron loss and low noise. It was confirmed that a grain-oriented electrical steel sheet suitable for the above can be manufactured.

[Example 2]
In the same manner as in the condition (d) of Example 1, the measured energy density (mJ / mm ² ) with respect to the total length and width of X and Y is expressed by the following equation: U = k × exp {−1.6 × (0.07 × X + 0.05 × Y)}
(K = U × exp {1.6 × (0.07 × X + 0.05 × Y)} is the middle side of equation (1) above)
, Laser irradiation was performed while changing the value of the constant k to 3.4, 3.75, 5.0, 6.25 and 6.6.
About the obtained raw material and the small transformer for a test, the iron loss and the noise level were evaluated by the same method as Example 1.

  The results are as shown in Table 2. In each case, the standard deviation of the iron loss was small, and a coil with a uniform and uniform iron loss could be manufactured. However, the average value of the iron loss is excellent under the condition that the value of the constant k is 3.75 or more and 6.25 or less, and it can be seen that it is more suitable as the laser irradiation condition for the steel sheet.

Example 3
A grain-oriented electrical steel sheet having a forsterite coating and a tension insulating coating was obtained in the same manner as in Example 1.
In addition, the forsterite coating amount Y (g / m ² ) was measured and recorded over the entire length and width of the steel sheet by oxygen analysis using fluorescent X-rays before forming the tension coating, and by chromium analysis using fluorescent X-rays after forming the tension coating. The amount of tension coating was recorded by measuring X (g / m ² ) over the entire length and width.

Next, laser irradiation treatment was performed. The laser transmitter is a Q-switched pulse type YAG laser with a beam diameter of 0.3 mm, a pulse repetition frequency of 25 kHz, and a galvano scanner with one oscillator arranged in a direction perpendicular to the rolling direction at a width of 200 mm. Was irradiated so as to draw at intervals of 5 mm.
Here, the iron loss becomes 0.75 W / kg or less according to the amount Y (g / m ² ) of forsterite film and the amount of tension coating X (g / m ² ) with the same steel plate in advance. The minimum output per pulse of the laser was investigated. Based on this data, a comparison was made between the case where the output was adjusted over the entire length and width direction (Condition A) and the case where the output was adjusted to a constant output (3.6 mJ / mm ² ) over the entire length and width (Condition B).
Three coils are processed for each condition, samples are taken for each ton from each coil, the iron loss of the material is measured (W _17/50 ), and 15 small test transformers are produced. The noise when excited at 1.7T and 50Hz was measured.
Table 3 shows the measurement results.

As shown in the table, depending on the amount of forsterite film Y (g / m ²⁾ Amount of tension coating X (g / m ^2), to adjust the laser conditions to minimize the output target iron loss is obtained When carried out by the method according to the present invention (Condition A), it is confirmed that a grain-oriented electrical steel sheet that is excellent in all of the average value, standard deviation and noise of iron loss and can be stably produced suitable for low iron loss and noise. It was done.

Example 4
Direction in which the amount of forsterite coating was changed by deliberately changing the oxidation of the atmosphere inside the annealing furnace and the amount of hydration of magnesia applied as an annealing separator in decarburization annealing performed before finish annealing After conducting annealing on the magnetic steel sheet coil, it is subjected to tension coating treatment, and the laser is continuously sent while continuously feeding the coil of directional magnetic steel sheet with a thickness of 0.23mm, width of 1m, and weight of 5 tons. Irradiated. This grain-oriented electrical steel sheet is a highly oriented grain-oriented electrical steel sheet containing 3.4% by mass of Si, selecting a coil with a magnetic flux density B ₈ of 1.93T, and iron loss W _{17 /} at 1.7T, 50Hz. ₅₀ was a grain-oriented electrical steel sheet in the range of 0.85 to 0.97 W / kg. The tension insulating coating is a general tension insulating coating obtained by baking a chemical solution made of colloidal silica, magnesium phosphate and chromic acid formed on the forsterite coating at 840 ° C.
Furthermore, before forming the tension coating, the steel sheet is measured by oxygen analysis with fluorescent X-rays, and the forsterite coating amount Y (g / m ² ) is measured and recorded over the entire width. The amount of tension coating X (g / m ² ) was measured and recorded over the entire width.

Next, laser irradiation treatment was performed. The laser transmitter is a continuous wave Yb fiber laser with a beam diameter of 0.3mm, and a galvano scanner with one oscillator arranged in a direction perpendicular to the rolling direction every 100mm in width, and the irradiation lines are drawn at intervals of 5mm. did. The width W (μm) of the heat-affected region in the magnetic domain structure when irradiated at an output of 10 to 400 W and a scanning speed of 5 to 30 m / s was obtained in advance, and the conditions for obtaining the necessary width were found.
Three coils are processed for each condition, samples are taken for each ton from each coil, the iron loss of the material is measured (W _17/50 ), and 15 small test transformers are produced. The noise when excited at 1.7T and 50Hz was measured.
Table 4 shows the measurement results.

  As shown in the table, the grain-oriented electrical steel sheet irradiated with laser with the width W of the heat-affected region satisfying the conditions of the present invention (the above formula (2)) is the average value of iron loss and the average value of noise. It was confirmed that the grain-oriented electrical steel sheet was good, stable with low iron loss and low noise.

Claims (3)

After the forsterite film is formed, the grain-oriented electrical steel sheet on which the tension coating is formed is irradiated with a laser to reduce the iron loss of the electrical steel sheet.
The amount of forsterite film is detected before the tension coating is formed, and the amount of tension coating is detected after the tension coating is formed, and the detected iron loss after laser irradiation is within the target range. A method for producing a grain-oriented electrical steel sheet characterized by collating with the relationship between the amount of forsterite coating and tension coating and the laser irradiation conditions, and performing laser irradiation under the irradiation conditions obtained as a result of the collation . When the amount of the tension coating is X (g / m ² ) and the amount of the forsterite film is Y (g / m ² ), the energy density U (mJ / mm ² ) of the laser irradiation is given by (1)
3.75 ≦ U × exp {1.6 × (0.07 × X + 0.05 × Y)} ≦ 6.25 --- (1)
The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the laser irradiation is performed under a condition that satisfies the requirements. A grain-oriented electrical steel sheet obtained by irradiating a laser on a surface having a forsterite film and a tension coating, wherein the amount of the tension coating is X (g / m ² ) and the amount of the forsterite film is Y (g / m ² ), the width W (μm) of the heat-affected region in the magnetic domain structure formed linearly at the laser irradiated portion is expressed by the following equation (2)
800 ≦ W × exp {1.6 × (0.07 × X + 0.05 × Y)} ≦ 1600 --- (2)
A grain-oriented electrical steel sheet characterized by satisfying the above relationship.