JP4317484B2 - Manufacturing method of ultra high magnetic flux density grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a grain-oriented electrical steel sheet, which is a soft magnetic material that is most commonly used industrially as an iron core material for transformers, rotating machines, reactors, and the like, and particularly relates to a manufacturing method thereof.

  Oriented electrical steel sheets are the most commonly used soft magnetic materials in the industry as iron core materials for transformers, rotating machines, reactors, and the like. Oriented electrical steel sheets are expressed as <100> in the Miller index used in physics, and the crystal orientations that are most easily magnetized are relatively aligned for each crystal grain, and are therefore polycrystalline steel sheets. However, it is a desirable material as an industrial product having excellent magnetization characteristics in a specific direction as if it were a single crystal steel plate.

Oriented electrical steel sheets use a phenomenon generally referred to as secondary recrystallization to align the easy axis of crystal in a specific direction. N. Patent Document 1 by Goss, Patent Document 2 by Taguchi and Sakakura, Patent Document 3 by Imai and Saito, and the like. According to this technology, secondary recrystallization is performed by precipitating various compounds in addition to MnS as a second dispersed phase, commonly called an inhibitor, in steel containing a lot of silicon, and combining cold rolling and annealing. The next recrystallization is developed.
U. S. Pat. 1965559 (1934) Japanese Patent Publication No.33-4710 Japanese Patent Publication No. 38-8214

  By the way, in order to develop secondary recrystallization, it is generally said that high temperature annealing by box annealing is essential. That is, in order to grow only specific orientation grains to an extreme size to an abnormal extent, it may be thought that it is necessary to administer heat energy for a long time at a high temperature, but also the orientation of Goss orientation grains. It is also discussed that strict temperature control is necessary to increase the accuracy to the limit.

Therefore, the present inventors conducted an experiment to obtain the optimum temperature by hot-rolling and cold-rolling steels having appropriate components in publicly known literature and performing box annealing at various temperatures. However, the present inventors have come to recognize that this experiment is extremely difficult. That is, it was recognized that secondary recrystallization is not only a thermal process that requires a high temperature, but also a aging process that is time-dependent in its expression.
Specifically, it was sometimes observed that secondary recrystallization started and ended before reaching the target temperature if it took too long to raise the temperature to a target temperature. Therefore, the temperature was raised to a predetermined temperature at a sufficiently high speed so as not to cause such a situation, and the temperature was strictly controlled so as not to cause temperature unevenness in the steel sheet, and the experiment was repeated. However, further experimental difficulties occurred. When annealing a steel sheet, the crystal orientation and thus the magnetic properties often changed greatly when annealed with a single sheet for testing and when annealed with multiple layers closer to actual production. .

  Therefore, various conditions were tried to grasp this phenomenon, and it was found that there were conditions under which the secondary recrystallization orientation was extremely sharpened under certain conditions and the magnetic flux density was higher than that of conventional materials. For example, a B8 value indicating a magnetic flux density at a magnetizing force of 800 A / m was frequently obtained with a value of 1.98 T or more. Such a high B8 value was not obtained by one or two annealing, and three or more laminations were necessarily required, and were not found in the steel sheet located at the bottom of the lamination.

An object of the present invention is to clarify the conditions in which the secondary recrystallization orientation is extremely sharpened and the magnetic flux density is higher than that of a conventional material. In the present invention, the magnetic flux density is extremely high or the ultrahigh magnetic flux density means that B8 / Bs is 0.98 or more.
Therefore, in order to investigate the reason why such a phenomenon appears, it is necessary to examine the progress of secondary recrystallization, and the time to start and end secondary recrystallization using a material containing Al and N The annealing was interrupted at an intermediate point, and the crystal structure of the steel sheet was investigated.

  As a result, very interesting observation results were obtained. That is, the secondary recrystallized grains existed only in the vicinity of the outer edge of the steel plate, and extended in a column shape from both sides in the plate width direction to the center as if they were columnar crystals often found in the cast structure. Therefore, as a result of conducting various analyzes to examine the difference between the non-secondary recrystallized parts, it was found that there is a significant difference in the N amount at both parts. Certainly, the electrical steel sheet has a large decrease in the amount of N and S before and after the box annealing. In particular, in order to develop the magnetic properties of the final product, it is required to remove the precipitated dispersed phase, which is an inhibitor, called purification. It is done. That is, as a condition for forming the ultra-high magnetic flux density grain-oriented electrical steel sheet discovered this time, this purification proceeds in conjunction with the progress of secondary recrystallization. On the other hand, it was inferred that secondary recrystallization would progress along the slope of the degree of purification when it had a certain law.

  In order to confirm this inference, experiments were conducted for various amounts of Al and N, and for various numbers of laminated sheets, steel plate sizes, and annealing temperatures. A similar experiment was also performed on steel using MnS and MnSe as inhibitors. As a result, under all conditions where an ultra-high magnetic flux density structure was obtained, it was confirmed that there were fewer inhibitor components such as N, S, Se, etc. in the secondary recrystallization site than in the non-secondary recrystallization part.

  Next, the reason why such a component variation occurs was examined. Paying attention to the fact that such a phenomenon appears only when the steel plates are laminated, an experiment was conducted by changing the lamination gap by applying MgO powder to the steel plate surface during lamination and changing the coating amount. Then, the larger the gap was, the more the development of the columnar structure was suppressed, and the spatial non-uniformity of the progress of purification was also eliminated. Furthermore, it should be noted that the total purification amount of the entire steel sheet was larger as the gap was larger. Based on this fact, further experiments were carried out considering that the amount of gas present in the gap between the steel plates might affect, and box annealing was performed in the same gap in two atmospheres of hydrogen and Ar. Then, a clear columnar structure was not obtained in Ar, but a remarkable columnar structure was obtained in hydrogen.

N, S, and Se in steel are considered to be purified by reacting with hydrogen in the atmosphere to form NH ₃ or H ₂ S, H ₂ Se, but the reaction rate depends on the hydrogen concentration in the atmosphere. . In other words, it can be considered that the replenishment speed of hydrogen consumed in the purification reaction determines the progress speed of the purification itself. Based on that model, when the stacking gap of the steel plates is sufficiently narrow, the movement of the replenished hydrogen and the purifying gas such as NH ₃ and H ₂ S removed by replacement, that is, the diffusion is delayed, and the speed of the secondary re- It can be considered that the local gradient of the degree of purification becomes prominent when the degree of progress of the crystal is reached.
Based on the above considerations, steel plates having undergone various components and process conditions were subjected to a secondary recrystallization annealing experiment, and a clear technical condition range was obtained, leading to the present invention.

That is, the gist of the present invention is as follows.
(1) It contains 2 to 7% by mass of Si and contains at least one of N and Al, or S and Mn, or a combination of Se and Mn, and the content thereof is one of N, S, and Se. Species or two or more of 0.015 to 0.04% by mass, C containing 0.03 to 0.1% by mass, the steel is melted, cast, hot-rolled after heating, cold-rolled In the method for producing a directional electrical steel sheet in which the obtained steel sheet is laminated in a sheet shape or wound in a tight coil shape and box annealed, the slab or ingot heating temperature prior to the hot rolling is 1250 ° C. or more, and Prior to box annealing, an annealing separator is applied to the surface of the steel sheet so that an effective gap between adjacent steel sheets can be 0.15 to 0.5 mm, and then the temperature is raised during heating to the holding temperature in box annealing. The speed is set to 100 ° C./hr or more, and continues to be 850 Performed retention annealed over 1hr at retention temperature between 100 ° C., and is characterized in that the temperature deviation within the dwelling scheduled within 25 ° C., the manufacturing method of the grain-oriented electrical steel sheet.

( 2 ) In the above (1) , characterized in that after cold rolling, nitriding is performed until the holding annealing of the box annealing, and N in the steel sheet is 0.015 to 0.04 mass%. The manufacturing method of the grain-oriented electrical steel sheet of description.
( 3 ) The method for producing a grain-oriented electrical steel sheet according to (1) or (2) , wherein hot-rolled sheet annealing is performed after hot rolling.
( 4 ) The method for producing a grain-oriented electrical steel sheet according to any one of (1) to ( 3 ), wherein the annealing is performed at 1100 ° C. or more after the holding annealing by box annealing.
( 5 ) The method for producing a grain-oriented electrical steel sheet according to any one of (1) to ( 4 ), wherein flattening annealing is performed after box annealing.
( 6 ) The method for producing a grain-oriented electrical steel sheet according to any one of (1) to ( 5 ), wherein an insulating coating is applied after box annealing.
( 7 ) The method for producing a grain-oriented electrical steel sheet according to any one of (1) to ( 6 ), wherein magnetic domain control is performed on the steel sheet.

  According to the present invention, an annealing method in which the crystal orientation selectivity in grain growth of secondary recrystallization is enhanced to the limit is established, and an ultrahigh magnetic flux density grain-oriented electrical steel sheet can be manufactured.

Next, an embodiment of the present invention will be described.
If the Si content is less than 2%, phase transformation occurs due to high-temperature annealing, and appropriate grain growth is hindered. If it exceeds 7%, the workability is extremely deteriorated and the effect of improving the magnetism is not recognized.

  As the inhibitor necessary for secondary recrystallization, one or more of AlN, MnS, and MnSe can be used. The amount of the inhibitor is N forming AlN, S forming MnS, or one or more of Se forming MnSe being less than 0.015%, secondary recrystallization becomes unstable, and there is a clear lack of inhibitors. Recognized. If it exceeds 0.04%, cracks and blisters called blisters occur during casting and hot rolling, so the content was made 0.04% or less.

  Addition of C to the steel is advantageous for sharpening the secondary recrystallization orientation. It can be seen that the primary recrystallization structure is sized and contributes to the progress of stable secondary recrystallization. This effect was observed when 0.03% or more was added. On the other hand, if added over 0.1%, the steel became brittle and hindered cold rolling and the like, so it was made 0.1% or less. Note that C deteriorates the magnetic properties in the final product or, if added in a large amount, induces a phase transformation during box annealing and inhibits secondary recrystallization, so it must be removed prior to secondary recrystallization. Yes, CO gasification decarburization in a humid atmosphere is effective.

  The upper limit of the effect of the steel plate lamination during the box annealing was investigated based on the above experiment, and an ultrahigh magnetic flux density steel plate could be obtained if it was 0.5 mm or less. At this time, if the surface of the steel sheet is coated with MgO powder or an annealing separator, the gap is filled and the effect is increased. In this case, considering the filling rate, (gap) × (1− (filling rate)) is 0. The same effect was obtained when the gas volume was .5 mm or less, that is, the gas volume substantially existing in the gap was equivalent to the 0.5 mm gap. This gap was exactly the same whether it was a stack of cut plates, a gap between plates when a tight coil was formed, or a gap formed by sandwiching a single plate with a block or a heat-resistant substrate.

  Incidentally, the measurement of the filling rate can be calculated by measuring the bulk density of the entire laminated steel sheet. For example, when applying MgO powder, the whole bulk volume is measured in the laminated state. Since the volume of only the steel sheet is obtained from the weight of the steel sheet and the specific gravity of the steel sheet, the difference between the bulk volume and the steel sheet volume is the total volume of the gap. Next, the weight in the state where the steel plates are laminated is measured, and the difference from the weight of only the steel plates is obtained. This is the weight of the coated MgO powder, and the total volume of MgO can be obtained by dividing by the specific gravity of MgO. That is, if the total volume of MgO is divided by the total volume of the gap, this is the filling rate. Further, by dividing the total volume of the gap by the number of the gaps, that is, (the number of laminated steel sheets-1), the volume per one gap is obtained, and the gap can also be calculated from this.

Next, regarding the box annealing conditions, first, the rate of temperature increase will be described.
The preferred heating rate depends on the subsequent holding temperature, especially when the holding temperature, that is, the temperature at which secondary recrystallization proceeds is high, the secondary recrystallization incubation time is short, and the heating is completed during that time. For example, if the holding temperature is about 1000 ° C., the incubation time is often about 1 hour. In this case, 1000 ° C./hr is required. . However, if the retention temperature was about 850 ° C., a latent time of several hours was observed. Among them, at a temperature increase of less than 100 ° C./hr, it was not possible to find a holding temperature, a steel component, and other production conditions for obtaining an ultrahigh magnetic flux density structure. hr.

  The box annealing was held for the purpose of starting and ending secondary recrystallization during this period, but it was found that the holding time was prolonged when this temperature was low. However, when the temperature is below 850 ° C., secondary recrystallization does not appear no matter how much the temperature is maintained, and finally, coarse graining or the like occurs in the surface layer region of the steel sheet, and a predetermined structure cannot be obtained. When the temperature exceeded 1100 ° C., normal grain growth developed and a secondary recrystallized structure could not be obtained. Even if the holding time is less than 1 hour, secondary recrystallization may occur, but when the atmosphere and inter-plate gap are adjusted so that an ultra-high magnetic flux density structure can be obtained, it will be less than 1 hr even at 1100 ° C. Therefore, it was set to 1 hr or more.

  Moreover, although it was the temperature fluctuation at the time of holding | maintenance, the start time of secondary recrystallization responded very sensitively to the temperature change. That is, during the course of secondary recrystallization, the degree of purification at the tip of the growth was examined, and even if this did not progress sufficiently, secondary recrystallization could proceed if the temperature rose slightly. It had become. In other words, columnar secondary recrystallized grains grow along the purification gradient, but when the temperature fluctuates to the high temperature side, new secondary recrystallized grains are generated at the tip of the growth end. This has hindered the formation of columnar structures. Thus, the temperature deviation enough to overturn the purification gradient significant for forming the columnar structure was more than 25 ° C. That is, if the temperature fluctuation during the progress of secondary recrystallization is 25 ° C. or less, a healthy columnar structure, that is, an ultrahigh magnetic flux density structure is sufficiently formed.

After the completion of secondary recrystallization, the precipitated dispersed phase present as an inhibitor is removed, so that the magnetic properties are remarkably improved. For this purpose, it was necessary to react with the atmosphere at a temperature of 1100 ° C. or higher.
In mass production, it is effective to perform hot-rolled sheet annealing in order to suppress variations in quality within the steel sheet. Although depending on the steel components, the effect was observed even at about 900 ° C., and about 1000 ° C. to 1100 ° C. was effective.
In addition, by applying an insulating coating on the surface of the steel sheet after box annealing, the actual machine magnetic characteristics when used in a laminated state in an electric device could be improved. Magnetic properties could also be improved by laser marking, groove formation, foreign matter contamination, and the like.

Steels having the components shown in Table 1 were melted and continuously cast at a thickness of 100 mm and a width of 400 mm to form a 1-ton slab, and then heated at 1300 ° C. to hot-roll to a plate thickness of 2 mm. It annealed at 1100 degreeC for 2 minutes, pickled, and cold-rolled to plate | board thickness 0.3mm. After dividing it into two coils with a width of 200 mm and decarburizing and annealing in an atmosphere of 850 ° C. for 2 minutes, N ₂ with a dew point of 60 ° C. and 25% of the remaining H ₂ , MgO powder was slurried on the surface. It was applied, dried and wound on a tight coil with an inner diameter of 400 mm. At this time, a coil with a winding weight of 20 kg and a large coil of 500 kg were prepared.

  Subsequently, heating to 1000 ° C. was maintained in dry hydrogen and the temperature was maintained, but the heating of the small coil was completed immediately in 30 minutes, but it took 12 hours for the large coil to reach 1000 ° C. After reaching 1000 ° C., the temperature was maintained for 3 hours within the range of temperature variation from 990 ° C. to 1010 ° C., subsequently heated to 1200 ° C., held for 20 hours, and cooled to room temperature. After performing the flattening annealing process at 850 ° C., the magnetic measurement was performed to obtain the B8 value.

  From Table 1, it can be seen that an extremely high B8 value was obtained when heating to 1000 ° C. with a sufficient temperature rise rate with a given component. At first glance, the B8 value seemed to be small in the E material, but the saturation magnetic flux density was lowered due to the high Si content, and the degree of crystal orientation integration was almost the same as that of the D material. A photograph of the crystal structure of the small coil material is shown in FIG. It can be observed that a remarkable columnar crystal structure extends from both widths of the steel plate toward the center.

  In the steel material, a sufficient secondary recrystallization structure was not obtained. In addition to the above steps, ammonia gas was added to the atmosphere in the latter half of the decarburization annealing, and the N content in the steel sheet was reduced to 0.02%. Then, box annealing is performed. At that time, the temperature is first held at 800 ° C. for 2 hours, then the small coil is heated to 1050 ° C. in 20 minutes, the large coil is heated to 1050 ° C. over 15 hours, and then 1150 After holding at 30 ° C. for 30 hours and then cooling and flattening, B8 of the small coil material reached 1.98T. On the other hand, the large coil was 1.88T.

100 pieces of the decarburized and annealed timber of Example 1 were cut into 200 mm × 800 mm and directly subjected to electric heating. Current flowed in the longitudinal direction of the plate and both ends were gripped by electrodes, but a thickness of 0.2 mm to 1 mm between each decarburization plate for a grip area of 200 mm x 10 mm in width so that the current would flow equally to all plates. A piece of the same size as the grip area was inserted and sandwiched, and the steel plate was lightly tensioned. As a result, the same gap as the thickness of the inserted piece was formed between the steel plates. The atmosphere composition was nitrogen and hydrogen 50% each. Since it was energized heating, the temperature rose very quickly, and it was heated to 980 ° C., but the required time was 5 minutes. Thereafter, the temperature was raised to 1000 ° C. over 2.5 hours, then immediately heated to 1250 ° C., held for 5 hours, and cooled to room temperature. Table 2 shows the relationship between the plate gap and the obtained B8 value.
From Table 2, it can be seen that the B8 value decreases as the plate gap increases.

Induction heating was also attempted with the same cut plate as in Example 2. This time, it is not necessary to energize the laminated plates, but in order to prevent fusion, a fiber refractory with a cotton shape was inserted thinly between the plates. At this time, pressure was applied in the plate surface direction of the steel plate in order to sufficiently reduce the plate gap. Table 3 shows the relationship between the gap between the plates, the refractory filling rate, and the obtained B8 value. The filling rate was calculated as a ratio of the actual volume obtained from the specific gravity measured separately and the bulk volume obtained from the gap, by actually measuring the weight of the refractory.
From Table 3, it can be seen that even if the gap is widened, if the refractory filling rate is increased and the effective gap is 0.5 mm or less, the effect is sufficiently exerted.

  The material in Table 1 has a very high magnetic flux density, and by itself, the usefulness is sufficiently enhanced for an electric device that utilizes magnetic attraction. However, the iron loss value is 1.2 W / magnetism at an excitation magnetic flux density of 1.7 T and 50 Hz. It was not good with kg. Therefore, when a phosphoric acid-based tension coating was applied to this material by baking, the iron loss value under the same conditions showed a good value of 0.95 W / kg. Furthermore, when laser scribing, groove formation by etching, groove formation by cemented carbide gear and subsequent strain relief annealing and Sb implantation technology were applied, the iron losses were 0.81, 0.85, 0.87, and 0.86 W, respectively. / Kg, an iron loss reduction effect that was astonishing was obtained.

It is a figure which shows the crystal structure photograph of the i material in an Example.

Claims (7)

It contains 2 to 7% by mass of Si, and contains at least one of N and Al, or S and Mn, or a combination of Se and Mn, and the content thereof is one or two of N, S, and Se The seed or more is 0.015-0.04% by mass, C is contained by 0.03-0.1% by mass, the steel is melted, cast, heated and then hot-rolled, cold-rolled, and obtained. In the manufacturing method of the grain-oriented electrical steel sheet in which the obtained steel sheet is laminated in sheet form or wound in a tight coil shape and box annealed, the slab or ingot heating temperature prior to the hot rolling is set to 1250 ° C. or more, and the box annealing is performed. Prior to applying an annealing separator to the steel sheet surface, the effective gap where the atmosphere can exist between adjacent steel sheets is set to 0.15 to 0.5 mm, and then the heating rate during heating to the holding temperature in box annealing is set to 100. Over 850/110 ° C. performed retention annealed over 1hr at retention temperature between, and is characterized in that the temperature deviation is within 25 ° C. within-holding Ordinary method of the grain-oriented electrical steel sheet. After cold rolling, a nitriding treatment is performed before the holding annealing of the box annealing, and N in the steel plate is 0.015.
The method for producing a grain-oriented electrical steel sheet according to claim 1, characterized in that the content is set to ˜0.04 mass%. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2 , wherein hot-rolled sheet annealing is performed after hot rolling. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3 , wherein the steel sheet is heated to 1100 ° C or higher after holding annealing by box annealing. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4 , wherein flattening annealing is performed after box annealing. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 5, wherein an insulating coating is applied after box annealing. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 6 , wherein magnetic domain control is performed on the steel sheet.

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