JP4862370B2 - Primary recrystallization annealing equipment for grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to primary recrystallization annealing equipment for a grain-oriented electrical steel sheet equipped with a sensor capable of measuring on-line the crystal grain size of a steel sheet annealed in a continuous annealing furnace.

  A grain-oriented electrical steel sheet is a steel sheet used as a core material for electrical equipment such as transformers, and contains approximately 3% by mass of Si and has a texture that is accumulated in the Goss orientation ((100) [011] orientation). Have. The magnetic properties of such grain-oriented electrical steel sheets are better as the sharpness of the product texture is higher. Therefore, it is no exaggeration to say that the history of technical development of grain-oriented electrical steel sheets is the history of sharpening of the product texture.

  The grain-oriented electrical steel sheet is obtained by subjecting a steel slab containing about 3% by mass of Si to a final sheet thickness by cold rolling, followed by primary recrystallization annealing and further secondary recrystallization annealing. Manufactured. If necessary, intermediate annealing may be performed during hot-rolled sheet annealing or cold rolling. As described above, the product texture of the grain-oriented electrical steel sheet is formed by secondary recrystallization, but the sharpness is extremely sensitive to the texture and grain size of the primary recrystallized sheet.

  Therefore, the production conditions before primary recrystallization annealing, that is, the steel composition, rolling conditions, annealing conditions, etc. are controlled to optimize the texture and grain size of the primary recrystallized plate and sharpen the product texture. Many methods have been proposed in the past.

For example, in Patent Document 1 (Japanese Patent Publication No. 6-84524), the annealing conditions are such that the primary recrystallized grain size is measured online and the primary recrystallized grain size falls within an appropriate range for the steel sheet after annealing. The primary recrystallization annealing method for grain-oriented electrical steel sheets for controlling the above is described. Here, the iron loss having a good correlation with the crystal grain size is measured, and the primary recrystallized grain size is controlled by adjusting the furnace temperature and adjusting the plate passing speed so that the measurement result falls within an appropriate range. The method of doing is described. It is described that this is effective in preventing the occurrence of secondary recrystallization failure and stabilizing the magnetic flux density at a high level.
Japanese Patent Publication No. 6-84524

  On the other hand, in recent years, in the steel industry, reduction of manufacturing cost has become a bigger issue than before, and in manufacturing of grain-oriented electrical steel sheets, it has become important to reduce manufacturing cost by improving yield. In particular, in the grain-oriented electrical steel sheet, the product magnetic properties deteriorate in part of the width direction of the steel sheet, and an improvement has been desired for the yield reduction that occurs when the part is cut off.

  For such a problem, the method described in Patent Document 1 can measure only the crystal grain size based on the iron loss value averaged over the entire width of the steel sheet, and the crystal grain size in the width direction. It is not possible to measure fluctuations. Therefore, the product magnetic properties of grain-oriented electrical steel sheets deteriorate in part in the width direction of the steel sheet, and as a result, it has no effect at all on the problem of yield reduction caused by truncating that part. .

Therefore, in the production of grain-oriented electrical steel sheets, the present invention can measure the fluctuations in the crystal grain size in the steel sheet width direction in order to prevent a decrease in yield by suppressing the fluctuations in the crystal grain size in the steel sheet width direction. It aims at providing the primary recrystallization annealing equipment of a grain-oriented electrical steel sheet.

  The present inventors have investigated the cause of the product magnetic properties being deteriorated in part in the width direction of the steel sheet. As a result, it was found that fluctuations in the primary recrystallized grain size in the width direction of the steel sheet were the cause of the deterioration of the magnetic properties of the final product.

  However, the non-uniformity in the width direction of the steel sheet production conditions in all the steps before the primary recrystallization annealing can cause the primary recrystallization grain size variation in the width direction. Therefore, the present inventors investigated the primary recrystallized grain size in the width direction for many primary recrystallized annealing plates offline, and found the relationship between the pattern of the fluctuation in the width direction of the primary recrystallized grain size and the cause. It was investigated over a long period of time. Specifically, the metallographic structure was observed at an interval of 50 mm from the edge of the steel sheet after the primary recrystallization annealing, and the crystal grain size was measured as the equivalent circle diameter.

  An example of a measurement result is shown in FIGS. Here, FIG. 1 is a measurement result in the width direction of the primary recrystallized grain size when the equiaxed crystal ratio of the slab is lowered due to a decrease in current of electromagnetic stirring during continuous casting. As shown in FIG. 1, it was recognized that the primary recrystallized grain size tends to be slightly coarser at about ¼ from both ends in the width direction of the steel sheet.

  FIG. 2 is a measurement result in the width direction of the primary recrystallized grain size when the temperature of the sheet bar width edge portion is lowered during rough rolling. As shown in FIG. 2, it was observed that the crystal grain size gradually increased toward both edge portions of the steel plate.

  FIG. 3 is a measurement result of the primary recrystallization grain size when the edge portion of the steel sheet is overheated in the heating zone of hot-rolled sheet annealing. As shown in FIG. 3, a tendency was observed in which the crystal grain size suddenly increased toward both edge portions of the steel sheet.

  As shown in FIGS. 1 to 3, it becomes clear that there is a variation pattern in the width direction of the primary recrystallized grain size inherent in the cause. For the identification of the cause and the solution of the problem, the primary in the width direction of the steel sheet It has been found that the measurement of the recrystallized grain size is extremely effective. Therefore, the inventors have made it possible to quickly identify the cause and solve the above problems by measuring the distribution of the primary recrystallization grain size in the width direction of the steel sheet, and contribute to a significant improvement in yield. Obtained knowledge.

  However, in the measurement of the crystal grain size based on the iron loss value described in Patent Document 1, only the crystal grain size averaged over the entire width of the steel sheet can be measured, and the crystal grain size in the width direction of the steel sheet can be measured. It is impossible to measure the distribution online. Therefore, the present inventors further examined a means capable of online measurement of the crystal grain size distribution in the width direction of the steel sheet. As a result, a crystal in the width direction of the steel sheet can be obtained by using a sensor having a configuration in which an excitation primary coil 402 and an output secondary voltage coil 403 are wound around a U-shaped core (iron core) 401 as shown in FIG. It has been found that the particle size distribution can be measured online.

  Here, in the above examination, the inventors input an alternating current to the excitation primary coil 402 for the various steel sheets after the primary recrystallization annealing using the sensor, and the output induced in the output secondary voltage coil 403. While conducting an experiment for detecting the voltage, the relationship between the crystal grain size measured from the optical microscope and the output voltage was examined. As a result, it was found that there is a good correlation between the crystal grain size measured from the optical microscope texture and the phase difference between the input voltage and the output voltage.

  Here, the phase difference can be measured by a commercially available lock-in amplifier. In the measurement, first, the input voltage signal is used as a reference signal for the lock-in amplifier, and the output voltage of the sensor is connected to the signal input of the lock-in amplifier. If the lock-in amplifier itself directly displays the phase difference Δθ, it may be used. When there is no direct display, it can be obtained by calculation using the arctan function from the X component output (cos Δθ) and the Y component output (sin Δθ) of the lock-in amplifier.

  That is, it has been found that the crystal grain size distribution in the width direction of the steel sheet can be measured online by measuring the crystal grain size at a plurality of locations in the width direction of the steel sheet using the sensor.

The present invention has been made based on the above findings and has the following characteristics.
[1] A primary recrystallization annealing facility for grain-oriented electrical steel sheets characterized in that on the outlet side of the continuous annealing furnace, sensors capable of measuring the crystal grain size of the steel sheets online are provided at two or more locations in the steel sheet width direction.
[2] Primary recrystallization annealing of a grain-oriented electrical steel sheet provided with one or more sensors on the outlet side of the continuous annealing furnace that can measure the grain size of the steel sheet online so as to be movable in the width direction of the steel sheet. Facility.
[3] In the above [1] or [2], the sensor capable of measuring the crystal grain size of the steel sheet on-line has a U-shaped core wound with an exciting primary coil and an output secondary voltage coil. Primary recrystallization annealing equipment for grain-oriented electrical steel sheets, characterized by
[4] The primary recrystallization annealing facility for grain-oriented electrical steel sheets according to any one of the above [1] to [3], wherein the measurement area of each sensor is 1/3 or less of the full width of the steel sheet.

  With the primary recrystallization annealing facility of the grain-oriented electrical steel sheet according to the present invention, it is possible to measure fluctuations in the width direction of the primary recrystallization grain size of the steel sheet on the exit side of the annealing furnace. As a result, regarding the magnetic property deterioration due to the fluctuation in the width direction of the primary recrystallized grain size, the cause can be quickly and easily identified from the pattern of fluctuation in the width direction of the primary recrystallized grain size. It became possible to keep the fluctuation of the crystal grain size in the width direction of the steel sheet low, and to improve the yield.

  The primary recrystallization annealing facility of the grain-oriented electrical steel sheet according to the present invention is characterized in that on the outlet side of the continuous annealing furnace, sensors capable of measuring the crystal grain size of the steel sheet online are provided at two or more locations in the width direction of the steel sheet. It is what.

  The continuous annealing furnace is equipment for primary recrystallization of cold-rolled sheets of grain-oriented electrical steel sheets by continuous annealing.

  On the outlet side of the continuous annealing furnace, sensors capable of measuring the crystal grain size of the steel sheet online are provided at two or more locations in the steel plate width direction, thereby measuring the crystal grain size in the steel plate width direction at at least two locations. It is possible to measure fluctuations in the primary recrystallized grain size in the width direction of the steel sheet. Here, for example, when two sensors are provided in the width direction of the steel plate, the area in which the crystal grain size is measured by each sensor is preferably 1/3 or less of the full width of the steel plate, and each sensor is located near the center in the width direction of the steel plate. And, by fixing and installing in the vicinity of one side end portion in the steel plate width direction, it becomes possible to measure the fluctuation of the primary recrystallized grain size in the steel plate width direction. Similarly, even when the sensors are installed at three or more locations, for example, when the sensors are provided at three locations, the area in which the crystal grain size is measured by each sensor is preferably set to 1/3 or less of the full width of the steel sheet. When the sensor is fixedly installed near the center in the width direction of the steel sheet and near the ends of both ends in the width direction of the steel sheet, and when provided at four locations, the area in which the crystal grain size is measured by each sensor is preferably 1 / th of the full width of the steel sheet. By setting each sensor to 4 or less and fixing them at substantially equal intervals in the steel plate width direction, it is possible to measure fluctuations in the primary recrystallized grain size in the steel plate width direction.

  Moreover, in this invention, you may make it equip the said continuous annealing furnace exit side with one or more sensors which can measure the crystal grain size of a steel plate on-line so that a movement in a steel plate width direction is possible. By measuring the crystal grain size at least at two or more locations in the steel plate width direction while moving the sensor, it is possible to measure fluctuations in the primary recrystallized grain size in the steel plate width direction. Here, it is preferable that the region in which the crystal grain size is measured by the sensor is 1/3 or less of the full width of the steel plate, as in the case of using the fixed sensor.

  Here, the size in the plate width direction of the measurement region by the sensor may be determined by the number of measurement points to be measured in the width direction of the steel plate. This is done by adjusting the core width and core length of the sensor described later. The measurement accuracy improves as the core length increases, but the price of the sensor increases. Therefore, it is preferably 1000 mm or less. If the core length is small, the measurement accuracy deteriorates. Is preferred.

  Hereinafter, the configuration of the sensor will be further described.

  FIG. 4 shows an example of the configuration of a sensor that can measure the crystal grain size of the steel sheet online. FIG. 4A is a front view of the sensor as viewed from the width direction of the steel sheet, and FIG. 4B is a side view of the sensor as viewed from the longitudinal direction of the steel sheet. As shown in FIG. 4, a sensor having a U-shaped core (iron core) 401 wound with an exciting primary coil 402 and an output secondary voltage coil 403 can be used as the sensor.

  Here, when the sensor having the configuration shown in FIG. 4 is used, the region in which the sensor measures the crystal grain size in the width direction of the steel plate 404 is the width of the U-shaped core 401 (w in FIG. 4B). ) And the region in which the crystal grain size is measured in the longitudinal direction of the steel plate 404 is a region corresponding to the length of the U-shaped core 401 (l in FIG. 4A). The average crystal grain size in this region is measured as the crystal grain size of the steel plate 404. The width w of the core 401 is preferably 1/3 or less of the full width of the steel plate. When the width w of the core 401 is 1/3 or less of the full width of the steel plate, the particle size distribution in the width direction can be measured with higher accuracy, and the cause of the width direction fluctuation can be easily identified.

  As the width w of the core 401 is reduced, the distribution of the crystal grain size in the width direction of the steel sheet can be measured with higher accuracy. However, if the width is too small, the accuracy of the measurement value itself is deteriorated. It is preferable to be 5 mm or more.

  The sensor is provided on the exit side of the continuous annealing furnace. Here, the outlet side of the continuous annealing furnace is often accompanied by an annealing separator coating apparatus and an annealing separator drying apparatus so that the steel sheets do not stick to each other in the secondary recrystallization annealing following the primary recrystallization annealing. . The installation position of the sensor is not particularly limited as long as it is on the exit side of the continuous annealing furnace, but before or after the annealing separator coating apparatus or the annealing separator drying apparatus, or the annealing separator coating apparatus and the annealing separator. You may install between drying apparatuses.

  An example of a method for measuring the crystal grain size using the sensor is described below. First, as shown in FIG. 4, both end surfaces of the U-shaped core 401 of the sensor are fixed at positions h = 10 mm away from the surface of the steel plate 404 subjected to primary recrystallization annealing. Next, an AC current of 50 Hz was input to the excitation primary coil 402 from a current supply device (not shown), and an output voltage waveform induced in the output secondary voltage coil 403 was detected by a voltage measurement device (not shown). Next, the phase difference between the input voltage and the output voltage is calculated by an arithmetic unit (not shown), and the crystal grain size is calculated from the relationship between the phase difference obtained in advance and the crystal grain size.

  Here, the distance h from the surface of the steel plate 404 is not limited to 10 mm, but it is better as it is smaller from the viewpoint of accurately measuring the crystal grain size on-line. However, if it is too small, the steel plate surface and the sensor may come into contact with each other.

  The alternating current input to the excitation primary coil 402 is not limited to 50 Hz, but is preferably in the range of 10 Hz to 1000 Hz from the viewpoint of measuring the crystal grain size with high accuracy.

  Here, the output voltage waveform of the output secondary voltage coil 403 varies depending on the primary recrystallization grain size of the steel sheet. In particular, the phase difference between the input voltage and the output voltage has a good correlation with the primary recrystallization grain size of the steel sheet as described above, and is suitable for grain size measurement. However, not only the phase difference between the input voltage and the output voltage but also a value measured from the voltage waveform of the output secondary coil, which is a value that can be correlated with the crystal grain size of the steel sheet, is applied to the present invention. However, the present invention is not limited to the phase difference.

  In the present invention, it is possible to accurately measure fluctuations in the crystal grain size in the width direction by providing the sensor having the above-described configuration at two or more locations in the width direction of the steel sheet, or by being movably provided in the width direction of the steel sheet by, for example, a rail. It becomes possible to do.

  FIG. 5 and FIG. 6 show an example in which the sensor having the above configuration is arranged in the steel plate width direction. FIG. 5 shows a case where sensors with a U-shaped core 502 having a width w are fixed in 20 positions in the width direction of the steel plate 501. FIG. 6 shows a case where a rail 603 is provided in the width direction of the steel plate 601, and a sensor whose width of the U-shaped core 602 is w is attached to the rail 603 so as to be movable.

  In the above, a case where a sensor having a U-shaped core (iron core) wound with an excitation primary coil and an output secondary voltage coil is used as a sensor capable of measuring the crystal grain size of a steel sheet online. However, for example, a known sensor such as a sensor using a method using ultrasonic attenuation as a sensor or a sensor using a method using a half-value width of an X-ray diffraction line may be used. However, the primary recrystallized grain size of grain-oriented electrical steel sheet is about 5 to 30 μm, and the most accurate and suitable for on-line crystal grain size measurement in this grain size range is the above-described excitation primary coil and output 2 This was the case where a sensor composed of a U-shaped core wound with a secondary voltage coil was used.

  Hereinafter, the result of having measured the crystal grain size of the width direction in the steel plate after primary recrystallization annealing using the sensor of the composition shown in Drawing 4 mentioned above is shown.

  As an example of the present invention, when the sensor is arranged as shown in FIG. 5 (Invention Example 1), when arranged as shown in FIG. 6 (Invention Example 2), as shown in FIG. Measurements were made for the case of arrangement (Invention Example 3) and the case of arrangement as shown in FIG. 8 (Invention Example 4). Here, the case shown in FIG. 5 shows the case where the width of the U-shaped core 502 of one sensor is 40 mm and 20 pieces are equally arranged in the steel plate width direction. In the case shown in FIG. 6, the width of the U-shaped core 602 of one sensor is set to 40 mm, and this sensor is moved in the steel plate width direction by the rail 603, while the width direction of the steel plate is divided into 20 parts. Measurements were made. In the case shown in FIG. 7, the width of the U-shaped core 702 of one sensor is set to 300 mm, and two of them are arranged in the steel plate width direction. In the case shown in FIG. 8, the width of the U-shaped core 802 of one sensor is 500 mm, and two of them are arranged in the steel plate width direction.

  Further, as a comparative example, as shown in FIG. 9, the measurement was performed when the width 902 of the U-shaped core of one sensor was set to 900 mm and one was arranged (Comparative Example 1).

  FIG. 10 shows the layout of the primary recrystallization annealing equipment used for this measurement. Here, 1001 is a steel plate coil before primary recrystallization annealing, 1002 is a heating zone of a continuous annealing furnace, 1003 is a soaking zone of the continuous annealing furnace, 1004 is a cooling zone of the continuous annealing furnace, 1005 is a sensor, and 1006 is an annealing separator. (Slurry mainly composed of MgO) Coating device, 1007 is an annealing separator drying furnace, 1008 is a steel plate coil after primary recrystallization annealing, and 1009 is a steel plate. In addition, the sensor arrange | positioned like the said invention examples 1-3 and the comparative example 1 was arrange | positioned in the said 1005 position.

  The steel plate 1009 used for the measurement is a steel slab composed of C: 0.06%, Si: 3.3%, Mn: 0.07%, Sol. Al: less than 100ppm, S: 20ppm, the balance Fe and unavoidable impurities. Slab heated at 1200 ° C for 20 min, hot rolled, then subjected to hot rolled sheet annealing at 1000 ° C for 30 sec, and used as a final cold rolled sheet with a thickness of 0.30 mm and a width of 1000 mm by cold rolling It was. This was subjected to primary recrystallization annealing at 850 ° C. × 100 s in a 50% H 2-50% N 2 atmosphere with a dew point of 55 ° C. and mass% in the continuous annealing furnace of the primary recrystallization annealing equipment shown in FIG. The crystal grain size in the width direction of the steel sheet was measured on the outlet side of the continuous annealing furnace.

  FIG. 11 shows the measurement results of Example 1 of the invention, FIG. 12 shows the measurement results of Example 2 of the invention, FIG. 13 shows the measurement results of Example 3 of the invention, and FIG. 14 shows the measurement results of Example 4 of the invention. FIG. 15 shows the measurement results of Comparative Example 1.

  As shown in FIGS. 11 to 14, it was confirmed that the primary recrystallized grain size in the steel sheet width direction can be measured with high accuracy by Examples 1-4 of the present invention. In the case of Invention Example 3 and Invention Example 4, it can be seen that the primary particle size is coarsened at the edge portion of the steel sheet, but from the Invention Example 4 where the core width is larger than 1/3 of the plate width. In the case of the present invention example 3 in which the core width is smaller than 1/3 of the plate width, the coarsening of the primary particle size at the edge portion can be detected more accurately, while in the case of the comparative example 1, the edge portion of the steel plate No coarsening of the crystal grain size could be detected.

  Subsequently, after subjecting to secondary recrystallization annealing at 1200 ° C. for 5 hours, an insulating coating was applied to obtain a product. As a result, the magnetic properties deteriorated at both edge portions 120 mm of the steel plate, and the yield was lowered as a result of cutting off the portions. However, according to Examples 1-4 of the present invention, the primary recrystallized grain size in the steel plate width direction increases sharply at the edge, and thus overheating occurs in the heating zone of hot-rolled sheet annealing. As a result, by lowering the temperature of the heating zone for hot-rolled sheet annealing, it was possible to prevent the deterioration of the magnetic properties in the subsequent products and to prevent the yield from being lowered.

It is a figure which shows the width direction measurement result of the primary recrystallized grain size by optical microscope observation when the slab equiaxed crystal ratio falls by the current fall of electromagnetic stirring at the time of continuous casting. It is a figure which shows the width direction measurement result of the primary recrystallized grain size by optical microscope observation when the temperature of a sheet bar width edge part falls at the time of rough rolling. It is a figure which shows the width direction measurement result of the primary recrystallized grain size by optical microscope observation when the edge part of a steel plate becomes overheating in the heating zone of hot-rolled sheet annealing. It is a figure which shows an example of a structure of the sensor which can measure the crystal grain diameter of the steel plate which concerns on this invention online. It is a figure which shows the case where the sensor whose width | variety of a U-shaped core is w is provided in 20 places fixed in the width direction of the steel plate which concerns on this invention. It is a figure which shows the case where a rail is provided in the width direction of the steel plate which concerns on this invention, and the sensor whose width | variety of a U-shaped core is w is attached to this rail so that a movement is possible. It is a figure which shows the case where the width | variety of the U-shaped core of one sensor which concerns on this invention shall be 300 mm, and it arrange | positions two in the steel plate width direction. It is a figure which shows the case where the width | variety of the U-shaped core of one sensor which concerns on this invention is 500 mm, and it arrange | positions two pieces in the steel plate width direction. It is a figure which shows the case where the width | variety of the U-shaped core of one sensor which concerns on a comparative example shall be 900 mm, and it arrange | positions one in the steel plate width direction. It is a figure which shows the layout of the primary recrystallization annealing equipment used for the measurement of the Example of this invention. It is a figure which shows the result of having measured the crystal grain size of the steel plate width direction which concerns on Example 1 of this invention. It is a figure which shows the result of having measured the crystal grain size of the steel plate width direction which concerns on Example 2 of this invention. It is a figure which shows the result of having measured the crystal grain size of the steel plate width direction which concerns on Example 3 of this invention. It is a figure which shows the result of having measured the crystal grain size of the steel plate width direction which concerns on Example 4 of this invention. It is a figure which shows the result of having measured the crystal grain size of the steel plate width direction which concerns on the comparative example 1. FIG.

Explanation of symbols

401, 502, 602, 702, 802 U-shaped core (iron core)
402 Excitation primary coil 403 Output secondary voltage coil 404, 501, 601, 701, 801, 909 Steel plate 603 Rail 1001 Steel plate coil before primary recrystallization annealing 1002 Heating zone of continuous annealing furnace 1003 Soaking zone of continuous annealing furnace 1004 Continuous annealing Furnace cooling zone 1005 Sensor 1006 Annealing separator coating device 1007 Annealing separator drying furnace 1008 Steel plate coil after primary recrystallization annealing

Claims (3)

On the outlet side of the continuous annealing furnace , a sensor that has a U-shaped core with an excitation primary coil and an output secondary voltage coil that can measure the crystal grain size of the steel sheet on-line is installed. In more than one place ,
When two sensors are provided in the steel sheet width direction, the sensors are fixedly installed near the center of the steel sheet width direction and near one end of the steel sheet width direction.
When three sensors are provided in the width direction of the steel sheet, each sensor is fixedly installed near the center of the width direction of the steel sheet and near both ends of the width direction of the steel sheet.
The primary recrystallization annealing equipment for grain-oriented electrical steel sheets, wherein when the sensors are provided at four or more locations, the sensors are fixedly arranged in the steel sheet width direction at substantially equal intervals . On the outlet side of the continuous annealing furnace , a sensor consisting of a U-shaped core with an excitation primary coil and an output secondary voltage coil that can measure the grain size of the steel sheet online is moved in the width direction of the steel sheet. Primary recrystallization annealing equipment for grain-oriented electrical steel sheets, characterized in that one or more are provided. The primary recrystallization annealing facility for grain-oriented electrical steel sheets according to claim 1 or 2 , wherein the measurement area of each sensor is 1/3 or less of the full width of the steel sheet.

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