JP5825284B2 - Steel material processing method and grain-oriented electrical steel sheet processing method - Google Patents

Description

  The present invention relates to a method of processing a steel material using an electron beam, with a typical example of magnetic domain refinement treatment of grain-oriented electrical steel sheets.

In recent years, energy efficiency in various devices has been improved. For example, transformers are required to reduce energy loss during operation. The loss that occurs in this transformer mainly includes copper loss that occurs in the conductor and iron loss that occurs in the iron core. Furthermore, iron loss can be divided into hysteresis loss and eddy current loss, and it is known that improvement of the crystal orientation of the material and reduction of impurities are effective in reducing the former.
For example, Patent Document 1 discloses a method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic flux density and iron loss by optimizing the annealing conditions before final cold rolling.

Patent Document 2 _discloses that the iron loss W _17/50 , which was _0.80 W / kg or more before irradiation, is _reduced to 0.65 W / kg or less by irradiating a plasma arc to the steel sheet after secondary recrystallization. Techniques for reducing are shown.

Furthermore, Patent Document 3 obtains a transformer material with low iron loss and low noise by optimizing the film thickness and the average width of the magnetic domain discontinuities formed on the steel plate surface by electron beam irradiation. Technology is shown.
Here, the processing by the electron beam is advantageous in that speeding up of the beam deflection is achieved by electric control and that the heat affected zone is formed from the irradiation surface to a deeper portion by increasing the acceleration voltage. On the other hand, there is a handling difficulty that a high vacuum environment is essential. In particular, during electron beam irradiation, abnormal discharge (arcing) may occur, and current may flow in a portion different from the portion that is originally intended to be irradiated.

  As a cause of this abnormal discharge, it has been pointed out that water vapor inside the processing chamber and part of metal vapor from the molten pool in which the workpiece has melted enter between the electrodes inside the electron gun. And several methods have been proposed so far for suppressing this abnormal discharge.

For example, Patent Document 4 describes a method of sucking metal vapor that causes arcing by installing a vacuum pump under an electron gun. Furthermore, as a comparative example, a method of simply enlarging the working distance (WD) and a method of deflecting the beam are described.
Further, Patent Document 5 describes a method for preventing intrusion of metal vapor by deflecting a coil in multiple stages. Patent Document 6 describes a method of removing water vapor, which is a cause of abnormal discharge, by heating.
As described above, although many methods for suppressing abnormal discharge have been devised, it is still not possible to completely suppress them.

JP 2012-1741 A JP 2011-246782 A JP 2012-52230 A Japanese Utility Model Publication No. 62-77686 JP-A-8-287858 JP 2000-2149841 A

By the way, in the magnetic domain refinement process of the grain-oriented electrical steel sheet, as a cause of the occurrence of abnormal discharge, there is a substance that the steel sheet has melted and vaporized in addition to the water vapor.
The former arcing frequency due to water vapor is remarkable at the start-up of the apparatus, but as the evacuation time becomes longer, it decreases to a frequency causing almost no problem. In particular, in the magnetic domain fragmentation treatment of grain-oriented electrical steel sheets, the air-to-air exhaust device keeps the inside of the processing chamber in which the steel sheet is irradiated with the electron beam in a vacuum state. Unless it is brought in, the water vapor is hardly a problem. Moreover, even if there is some water vapor on the steel plate, it can be sufficiently removed in the front stage of the vacuum exhaust device having the differential pressure structure.

  Rather, it becomes a problem when the coating of the grain-oriented electrical steel sheet or the ground iron is melted and vaporized. In particular, when the coating is composed of a light element such as Mg and such a coating melts and vaporizes, the vaporized material easily reaches between the electrodes of the electron gun, and tends to cause abnormal discharge.

  The present invention proposes a method for appropriately performing the electron beam irradiation treatment on the steel having a directional electromagnetic steel sheet as a typical example even in the case where the abnormal discharge (arcing) occurs during the electron beam irradiation described above. The purpose is to do.

As a typical example of steel material processing, magnetic domain subdivision processing by electron beam irradiation for coated grain-oriented electrical steel sheet is a method for suppressing abnormal discharge caused by the above-described work melting during electron beam irradiation. We studied earnestly. As a result, in the processing of grain-oriented electrical steel sheets, it is most effective to suppress damage to the coating and melting of the iron core. Specifically, the amount of heat applied per unit irradiation length of the electron beam can be reduced. It turned out to be good.
On the other hand, a reduction in the amount of heat applied per unit irradiation length of the electron beam leads to a reduction in the amount of thermal strain introduced into the grain-oriented electrical steel sheet and a concomitant reduction in eddy current loss improvement effect. In order to solve such a problem, the inventors have previously found that it is possible to suppress film melting by keeping the irradiation energy density constant while reducing the amount of irradiation heat per unit irradiation length. The effect was obtained. However, the degree of damage to the coating film caused by electron beam irradiation varies greatly depending on the coating properties. For example, when the adhesion between the coating film and the ground iron is extremely poor, the coating film damage is inevitably caused. Further, when the irradiation energy density is reduced, it is necessary to increase the number of irradiation beams of the electron beam, so that productivity is greatly impaired.

  For such a problem, it may be possible to predetermine irradiation conditions for increasing productivity within a range in which the coating is not damaged by investigating the coating properties in advance for each coil to be irradiated. However, even if the coating of grain-oriented electrical steel sheets is in the same coil, its properties may vary greatly depending on the location. On the other hand, the range in which the coating properties can be investigated is limited to a very small part of the coil. For this reason, it is difficult to reliably find the presence of a portion that is partially present in the coil and has poor film adhesion.

Therefore, the inventors diligently studied as follows a method that enables introduction of appropriate thermal strain by electron beam irradiation while avoiding film damage as much as possible.
Now, arcing is classified into two types: micro arcing in which the beam is not correctly output for a moment and large arcing that leads to the stop of the irradiation device. Micro arcing is an abnormal discharge phenomenon limited to a minute time, and usually occurs in a time of several milliseconds or less. On the other hand, large arcing is a case where insulation cannot be secured for a longer time. When this large arcing occurs, the device is stopped by the function of the safety device, which causes a great hindrance to production and causes damage.

  In the case of electron beam irradiation to a grain-oriented electrical steel sheet according to a typical application of the present invention, arcing is relatively light compared to welding premised on melting of a substance, and micro arcing accounts for most. . Even when large arcing occurs, there is a sign that micro arcing will occur several times in advance.

Furthermore, the present inventors have found that there is a certain correlation between the number of occurrences of micro arcing and the amount of damage to the coating, as shown in FIG. In this experiment, a directional electrical steel sheet with an insulating coating was scanned with an electron beam at a length of 100 mm with a setting of 2,000 irradiation if irradiated normally at a repetition interval of 5 mm in the rolling direction. . Thereafter, the ratio of the damaged part of the irradiation length of 100 mm was determined by observation with an optical microscope.
Therefore, it is important to suppress damage to the film in order to suppress micro arcing.

  The inventors of the present invention have made extensive studies based on such findings. As a result, arcing is detected in advance, and arcing can be performed by changing the electron beam irradiation conditions based on the number of occurrences per fixed time. It was conceived that a high magnetic domain fragmentation effect can still be obtained even if it is suppressed. That is, when a directional electromagnetic coil that easily breaks the coating as described above is passed, the frequency of occurrence of micro arcing increases, so the beam output is immediately reduced using the number of occurrences as a criterion. However, since the effect of reducing the iron loss is reduced by itself, the inventors have obtained new knowledge that it is important to shorten the irradiation line interval in the rolling direction at the same time.

This invention is based on said knowledge, The summary structure is as follows.
(1) When a steel material is irradiated with an electron beam to continuously process the steel material,
When arcing is detected during the irradiation of the electron beam and arcing that occurs at a certain time interval within a certain elapsed time occurs N times or more, the electrons after the Nth occurrence are detected. Steel material processing method that reduces beam irradiation current.

(2) The steel material processing method according to (1), wherein the N is 3.

(3) The irradiation current of the electron beam after the time when the N-th occurrence is reduced by 5 to 30% of the irradiation current of the electron beam when the N-th occurrence is described in (1) or (2) Steel material processing method.

(4) When the surface of the grain-oriented electrical steel sheet moving on the transport line is irradiated with an electron beam linearly in a direction intersecting with the rolling direction of the steel sheet, repeated at intervals in the rolling direction of the steel sheet. ,
Arcing is detected during the irradiation of the electron beam, and 0.05 [m] / VL [m / s] within an elapsed time of 1000 [m] / v [m / s] (v: scanning speed of the electron beam) When arcing that occurs at a time interval of (VL: moving speed of the steel plate in the transfer line) occurs three times or more, the irradiation current after the third time occurs is the third time. A method for processing grain-oriented electrical steel sheets that reduces within a range of 5 to 30% of the irradiation current of the electron beam at the time.

(5) The mutual interval between the electron beam irradiation lines after the third occurrence is reduced within a range of 5 to 30% of the mutual interval between the electron beam irradiation lines at the third occurrence (4) ) Processing method for grain-oriented electrical steel sheet.

  According to the present invention, the number of occurrences of micro arcing, and further, the occurrence of large arcing can be suppressed to the maximum, so that the product yield can be improved, the re-coating step of the coating can be omitted, The phenomenon that the irradiation is stopped) is suppressed, so that it is possible to suppress the deterioration of characteristics such as magnetism, and its industrial significance is great.

It is a graph which shows the relationship between the frequency | count of generation | occurrence | production of arcing, and the amount of damage of a film. It is a figure explaining the measuring method of micro arcing.

The steel material processing method of the present invention will be described below by taking an example of magnetic domain subdivision processing by electron beam irradiation to grain-oriented electrical steel sheets.
First, the electron beam irradiation conditions are determined within suitable conditions described later in consideration of characteristics (for example, iron loss and magnetostriction) desired to be obtained after irradiation. At this time, the irradiation energy condition that does not destroy the coating film may be obtained in advance within the possible range by reflecting the coating property investigated in advance. From the viewpoint of productivity, it is preferable to make the distance between the irradiation beams of the electron beams as wide as possible. However, excessively widening increases the output required for magnetic domain subdivision, leading to an increase in arcing. It is necessary to pay attention to this point. In addition, said prior investigation is evaluating the minimum round bar diameter which produces the film fracture of a winding surface, for example, when a grain-oriented electrical steel sheet is wound around a round bar. The smaller the diameter is, the stronger the film can withstand higher stresses, and therefore, there is a tendency that even if the electron beam energy is increased, the film is not easily broken.

Subsequently, the directional electromagnetic steel sheet is irradiated with an electron beam under the determined conditions. If micro arcing occurs at time t during the electron beam irradiation, after a predetermined time tA has elapsed from the time t (= 0), and within a predetermined elapsed time tB. Measure the micro arcing that occurs. If it is not measured within the elapsed time tB, the process returns to the above process with t (= 0) being the first micro arcing occurrence time measured for the first time (see FIG. 2A).
On the other hand, when measured within the elapsed time tB, the time (the occurrence time of arcing that occurred earliest within the above time) is t (2) (however, the numbers in parentheses indicate the number of arcing counted) ), And the micro arcing that occurs before the time tB after a certain time tA has elapsed is measured. When micro arcing is measured, the time is t (3), and micro arcing that occurs before the time tB passes after a certain time tA has elapsed is measured (see FIG. 2B).
Note that, when micro arcing occurs before the time tA elapses after the occurrence of micro arcing, it is not counted, and micro arcing that occurs after tA elapses is counted as the next micro arcing (see FIG. 2C). As shown in FIG.2 (c), this operation is repeated and a count number is accumulated.

Such a measurement process is repeated until t (NA) + tA> tB, and the counted number of times of arcing NA occurring within the elapsed time of tB is obtained. When this NA is equal to or greater than a certain value NC, film damage is likely to occur, and irradiation defects due to arcing increase. Therefore, in order to suppress this, the output of the electron beam is reduced by a certain amount.
The arcing threshold NC is preferably 3 or more. This is because the occurrence of arcing once or twice can often occur regardless of the ease of destruction of the film due to dust, moisture, and oil adhering to the steel plate only partially.

  Further, it is preferable to reduce the output of the electron beam in the range of 5 to 30% of the electron beam irradiation conditions until the NC is measured. The reason is that if it exceeds 30%, the effect of magnetic domain fragmentation becomes insufficient, while if it is less than 5%, the effect of suppressing film damage becomes insufficient.

  At the same time in the above processing, the total energy amount (proportional to the output / line spacing) per unit line length in the line direction (conveyance direction) is the same as before the output reduction of the electron beam. It is preferable to shorten the beam irradiation line interval in the range of 5 to 30% of the electron beam irradiation time until the NC is measured. Here, if it is less than 5%, the effect of magnetic domain fragmentation becomes insufficient. On the other hand, if it is more than 30%, the line spacing becomes excessively narrow and the productivity is lowered.

  If micro arcing occurs even after the above electron beam irradiation condition change, NA may be measured according to the above and the same procedure as above may be followed. When the irradiation treatment of one electromagnetic steel sheet coil is completed, the next electromagnetic steel sheet coil is set and the irradiation treatment is performed. At this time, if the coating properties of the electromagnetic steel sheet coil are considered to be equivalent, irradiation is continued under the same conditions. If the film properties are unknown, it may be returned to the condition where the irradiation line interval is large again.

  Furthermore, the number of occurrences of arcing may be detected using a known method (for example, Japanese Patent Laid-Open No. 63-290693 and Japanese Patent Publication No. 5-32157), or other methods. As another method, for example, a spark generated when the insulating coating is vaporized may be observed and replaced by the number of times.

  It is to be noted that the above-described arcing has been known to be detected when it occurs (for example, Japanese Patent Application Laid-Open No. 63-290693 and Japanese Patent Publication No. 5-32157). Incidentally, Japanese Patent Laid-Open No. 63-290693 also shows a method of changing machining conditions by detecting arcing.

Next, specific conditions will be shown as a particularly suitable example when magnetic domain subdivision of a grain-oriented electrical steel sheet is performed.
[Minimum time interval for arcing occurrence tA = 0.05 [m] / VL [m / s], Maximum measurement time tB = 1000 [m] / v [m / s]]
In the electron beam irradiation process described above, even if a magnetic steel sheet coil having a high arcing frequency is passed, measures are taken to suppress the arcing frequency as quickly as possible. Since the purpose of the present invention is to increase the irradiation time, it is necessary to determine whether the irradiation conditions should be changed in the shortest possible time.

Therefore, the elapsed time tB is a maximum measurement time, and it is preferable to set tB = 1000 [m] / v [m / s]. Where v is the scanning speed [m / s] of the electron beam.
The above equation is the minimum time required for the electron beam to scan a length of 1000 m. Since the occurrence frequency of arcing is proportional to the scanning length of the electron beam, it is empirically known that the presence or absence of occurrence of arcing can be sufficiently determined if it is 1000 m.

Here, assuming that the scanning speed of the electron beam is 50 m / s, tB = 20 sec, 1 coil length is 2500 m, and the steel plate moving speed (line speed) is 50 m / min (0.83 m / s) in the transfer line. The amount used for the determination for changing the irradiation condition is less than 1% of the total coil length. However, on the other hand, arcing in a short time that occurs in an excessively short region only reflects the extremely local surface properties of the coil. The frequency of treatment for shortening the line interval increases, and the productivity is excessively impaired. Therefore, a time limit of tA (time corresponding to a coil length of 50 mm = 0.05 m) is also provided.
That is, the above-mentioned fixed time tA is the minimum arcing occurrence time interval, and it is preferable that tA = 0.05 [m] / VL [m / s]. However, VL is the moving speed of the grain-oriented electrical steel sheet on the transport line. The reason why tA is set as described above is that the surface characteristics that are extremely different from each other in the coil are mostly present within a length range within 50 mm in the longitudinal direction of the coil.

[NC: 3 times or more]
Next, with respect to the threshold NC of the number of times of arcing, it is difficult to say that the average information of the steel sheet is reflected once or twice. That is, the occurrence of arcing once or twice can often occur regardless of the ease of destruction of the film due to dust, moisture, and oil adhering to the steel plate only partially. However, since it is arcing, it is preferable to reduce it as much as possible, and the number of times is preferably 3 times.

[Condition change x: 5 to 30%]
The amount of change in the electron beam irradiation condition is to change (reduce) at least 5% of either or both of the irradiation current and the mutual distance between the electron beam irradiation lines in order to reliably obtain the effect of suppressing the destruction of the film. Is preferred. On the other hand, if it is changed excessively, either or both of the irradiation current and the mutual interval between the electron beam irradiation lines will be reduced more than necessary, and the productivity will be significantly impaired. Is preferred.

Next, the electron beam irradiation conditions in the present invention will be described for each condition.
[Acceleration voltage Va: 40 to 300kV]
A higher acceleration voltage is advantageous in achieving a narrow beam diameter, which is advantageous for magnetic domain fragmentation of grain-oriented electrical steel sheets, but if it is 40 kV or less, it is difficult to narrow the beam diameter and the effect of reducing iron loss is small. Become. On the other hand, if it is 300 kV or more, the apparatus becomes excessively large due to X-ray shielding, resulting in poor maintainability and accompanying productivity reduction.

[Electron beam diameter (half width of beam profile): 100-500μmφ]
When the beam diameter is less than 100μmφ, it is necessary to take measures such as extremely reducing the working distance (WD). In that case, the distance that can be deflected by one electron beam source is greatly reduced. Resulting in. As a result, in order to irradiate a wide coil of about 1200 mm, a large number of electron guns are required, reducing maintenance and productivity.
On the other hand, if it is larger than 500 μmφ, a sufficient iron loss reduction effect cannot be obtained. This is because the beam irradiation area (volume of the thermal strain introduction portion) of the steel sheet is excessively increased and the hysteresis loss is deteriorated.

[Electron beam irradiation pattern]
While the electron beam having the above acceleration voltage and beam diameter is scanned on the steel plate surface, linear thermal strain is applied to the inside of the steel plate. What is necessary is just to set suitably the output of the electron beam at this time, and the scanning speed on a steel plate so that it may become conditions favorable for the reduction in iron loss of a steel plate. The scanning of the electron beam may be a continuous one that continues to move constantly or a dot-like one that is repeatedly moved and stopped without any problem.

  Further, it is desirable that the direction in which the thermal strain is introduced has a deviation angle of 30 ° or less from the direction perpendicular to the rolling. In general, magnetic domains are subdivided by thermal strain introduced in a direction crossing the easy axis of magnetization. Therefore, in the grain-oriented electrical steel sheet mainly formed with Goss-oriented grains, if there is a thermal strain directed in the direction perpendicular to the rolling, the magnetic domain is sufficiently subdivided, while on the other hand, it is shifted from the direction perpendicular to the rolling Therefore, an excessive thermal strain is formed in the steel, which becomes an obstacle to the domain wall motion and deteriorates the iron loss.

  Further, the linear thermal strain is periodically formed with a certain interval in the rolling direction. This interval (line interval) is preferably 3 to 15 mm. When the line spacing is narrow, the strain region formed in the steel becomes excessively large, and not only iron loss (hysteresis loss) is deteriorated but also productivity is deteriorated. On the other hand, if it is too wide, no matter how much the reflux magnetic domain is expanded in the depth direction, the effect of subdividing the magnetic domain becomes poor and the iron loss is not improved.

[Processing chamber pressure: 3 Pa or less]
When the processing chamber pressure exceeds 3 Pa, the electrons generated from the electron gun are scattered by the residual gas, which has a thermal effect on the iron and reduces the energy of the electrons that form the reflux magnetic domain. Therefore, it is difficult to improve iron loss.

  Form a forsterite film (materials A, B, C) with different film strength on a grain-oriented electrical steel sheet containing 3.2% Si by mass in the base iron, and then apply a phosphate-based tension film on top of it. After the formation, magnetic domain fragmentation was performed by irradiating an electron beam according to the following conditions. At that time, the occurrence of micro arcing was measured, and the irradiation condition of the electron beam was adjusted as shown in Table 1. Table 2 shows the results of investigating the number of arcing occurrences per 1000 m, the iron loss of the grain-oriented electrical steel sheet after the electron beam irradiation treatment, and the electron beam processing time in the treatment of the 2000 m long steel sheet coil.

Electron beam irradiation conditions: scanning speed 30m / s, acceleration voltage 70kV, irradiation width (coil width) 200mm, processing chamber pressure 0.1Pa
The grain-oriented electrical steel sheets were slit to 200 mm from a 1200 mm wide coil and used as experimental materials. Therefore, if the materials are the same, the magnetic properties are almost equal. The electron beam irradiation condition was changed only once during one coil irradiation.

Here, the measurement of micro arcing was performed by detecting the decrease in acceleration voltage and abnormal current as disclosed in Japanese Patent Application Laid-Open No. 63-290693.
The magnetic properties were measured by sampling 50 SST specimens every 20 m from the center of the coil width and averaging them. In addition, the irradiation part before and after the condition change was always collected.

  As shown in Tables 1 and 2, it can be seen that examples satisfying the scope of the present invention have good magnetic properties. It can also be seen that Nos. 5 and 7 with tA, tB, NC, and x being more appropriate conditions have good magnetism and achieve high-speed processing.

Claims (5)

When the steel material is irradiated with an electron beam to continuously process the steel material,
When arcing is detected during the irradiation of the electron beam and arcing that occurs at a certain time interval within a certain elapsed time occurs N times or more, the electrons after the Nth occurrence are detected. Steel material processing method that reduces beam irradiation current.   The steel material processing method according to claim 1, wherein N is three.   The steel material processing method according to claim 1 or 2, wherein the irradiation current of the electron beam after the Nth time is reduced by 5 to 30% of the irradiation current of the electron beam when the Nth time is generated. In repetitively performing the irradiation of the electron beam linearly in the direction intersecting the rolling direction of the steel sheet at intervals in the rolling direction of the steel sheet on the surface of the directional electromagnetic steel sheet moving on the transport line,
Arcing is detected during the irradiation of the electron beam, and 0.05 [m] / VL [m / s] within an elapsed time of 1000 [m] / v [m / s] (v: scanning speed of the electron beam) When arcing that occurs at a time interval of (VL: moving speed of the steel plate in the transfer line) occurs three times or more, the irradiation current after the third time occurs is the third time. A method for processing grain-oriented electrical steel sheets that reduces within a range of 5 to 30% of the irradiation current of the electron beam at the time. 5. The mutual interval between the electron beam irradiation lines after the third time is reduced within a range of 5 to 30% of the mutual interval between the electron beam irradiation lines when the third time occurs. 6. A method for processing grain-oriented electrical steel sheets.

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