JP3743707B2 - Manufacturing method of ultra high magnetic flux density unidirectional electrical steel sheet - Google Patents

Description

【００４８】
［実施例２］
質量でＣ：０．０７５％、Ｓｉ：３．３５％、Ｍｎ：０．０８０％、Ｓ：０．０２５％、酸可溶性Ａｌ：０．０２５％、Ｎ：０．００８５％、Ｓｎ：０．０１４０％、Ｃｕ：０．０８％を含有し、かつＢｉ：０．００１５、０．０２３０％を含有するすスラブを、１３５０℃で加熱した後、直ちに圧延して２．４mm厚の熱延コイルとした。熱延コイルを冷間圧延して１．８mmとし、１０５０℃、１１５０℃、１２５０℃の３水準で１分間の焼鈍を施した。この後、冷間圧延により最終板厚０．２２mmにまで圧延した。その後は実施例１と同様に処理して製品としたコイルの製造条件と磁気特性を表２に示す。
【００４９】
【表２】

【００５０】
［実施例３］
実施例２で得られた、Ａ１、Ａ２、Ｂ１、Ｂ２について、通板方向に対して直角方向とのなす角が１２゜の方向に、５mm間隔で深さ１５μｍ、幅９０μｍの溝を形成したときの磁区制御前後の鉄損値を表３に示す。本発明条件を満足する条件で製造されたコイルは、鉄損特性に優れた方向性電磁鋼板となっている。
【００５１】
【表３】

【００５２】
［実施例４］
質量でＣ：０．０７０％、Ｓｉ：３．２５％、Ｍｎ：０．０７０％、Ｓｅ：０．０１８％、酸可溶性Ａｌ：０．０２５％、Ｎ：０．００８４％、Ｓｂ：０．０２５％、Ｍｏ：０．０１４％を含有し、かつＢｉ：０．０３５％を含有するすスラブを、１４００℃で加熱した後、直ちに圧延して２．５mm厚の熱延コイルとした。熱延コイルに１０００℃で焼鈍を施した後１．７mmまで冷間圧延したコイルを１０００〜１２００℃の間で５０℃毎に５水準とって１分間の焼鈍を施した。この後、冷間圧延により最終板厚０．２２mmにまで圧延した。その後は実施例１と同様に処理して製品としたコイルの製造条件と磁気特性を表４に示す。
本発明条件を満足する条件で製造されたコイルは、鉄損特性に優れた方向性電磁鋼板となっている。
【００５３】
【表４】

【００５４】
【発明の効果】
本発明により、Ｂｉを鋼中に含有する高磁束密度一方向性電磁鋼板の製造において、操業自由度が高く、安定製造可能な方法を提供することができる。
【図面の簡単な説明】
【図１】磁束密度Ｂ8 に及ぼすＢｉ含有量と仕上冷延前温度の影響を示す図。
【図２】鉄損に及ぼすＢｉ含有量と仕上冷延前温度の影響を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet that is mainly used as an iron core of a transformer or other electrical equipment. In particular, the present invention provides a method for producing a unidirectional electrical steel sheet having an extremely high magnetic flux density stably in the longitudinal direction of the coil by controlling the annealing temperature before finish cold rolling and the heating rate of decarburization annealing.
[0002]
[Prior art]
A grain-oriented electrical steel sheet used as a magnetic iron core in many electrical devices is usually a steel sheet containing 2 to 7% of Si and having a product crystal structure highly integrated in the {110} <001> orientation. The product characteristics of grain-oriented electrical steel sheets are evaluated by both iron loss characteristics and excitation characteristics. Reducing iron loss is effective in terms of energy saving because it reduces the loss of heat energy when used as an electrical device.
[0003]
On the other hand, increasing the excitation characteristics makes it possible to increase the design magnetic flux density of an electric device, which is effective for reducing the size of the device. Accumulating the crystal structure of the product in the {110} <001> orientation is effective in enhancing the excitation characteristics and reducing the iron loss. Therefore, many studies have been repeated in recent years, and various manufacturing techniques have been developed.
[0004]
One of typical techniques for improving the magnetic flux density is a manufacturing method disclosed in Japanese Patent Publication No. 40-15644. This is a production method in which AlN and MnS function as inhibitors and the rolling reduction in the final cold rolling step is a strong rolling exceeding 80%. By this method, a grain-oriented electrical steel sheet having a high magnetic flux density of B870 (magnetic flux density at 800 A / m) of 1.870 T or more is obtained by accumulating crystal grain orientations in the {110} <001> orientation.
[0005]
However, the magnetic flux density B8 based on this manufacturing method is from 1.88T to 1.95T at most, and shows only a value of about 95% of the saturation magnetic flux density 2.03T of 3% silicon steel. However, in recent years, social demands for energy and resource saving have become increasingly severe, and demands for reducing iron loss and improving magnetic properties of grain-oriented electrical steel sheets have become intense, and further improvements in magnetic flux density are strongly desired. ing.
[0006]
On the other hand, as a method of reducing iron loss, a method of performing laser treatment on a steel sheet disclosed in Japanese Patent Publication No. 57-2252, a method of introducing mechanical strain into a steel sheet in Japanese Patent Publication No. 58-2569, and the like, Various methods for subdividing the magnetic domains have been disclosed. When the magnetic domain is subdivided by the above method, the iron loss tends to decrease as the magnetic flux density increases. Therefore, the present situation is waiting for the emergence of means for further increasing the magnetic flux density B8 of the conventional grain-oriented electrical steel sheet and bringing it closer to the saturation magnetic flux density 2.03T of 3% silicon steel.
[0007]
In general, the iron loss of grain-oriented electrical steel sheets is graded according to JIS C2553 as W17 / 50 (energy loss under B8 1.7T, 50 Hz excitation conditions). In order to reduce the size of the transformer, when the excitation magnetic flux density is set to 1.7 T or higher, or even 1.7 T, the magnetic flux density of 1.7 T or higher is obtained locally in the transformer core. Therefore, there is a demand for a steel sheet with low iron loss in a high magnetic field (for example, W19 / 50).
[0008]
As a grain-oriented electrical steel sheet excellent in high magnetic field iron loss, Japanese Patent Application Laid-Open No. 2000-345306 discloses that the steel sheet has a crystal orientation of 5 degrees or less on average with respect to the ideal orientation of {110} <001>. Although the average of 180 ° C. magnetic domain width is more than 0.26 to 0.30 mm or less, or the area ratio of more than 0.4 mm of the magnetic domain width of the steel sheet is disclosed to be more than 3% to 20%, The obtained high magnetic field iron loss is the lowest, W19 / 50 = 1.13 W / kg, and a grain-oriented electrical steel sheet having further high magnetic field low iron loss is desired.
[0009]
As a technique for improving the magnetic flux density, Japanese Patent Publication No. 58-50295 proposes a temperature gradient annealing method. For the first time with this method, a product having a B8 of 1.95 T or more can be obtained. However, when this method is carried out at a factory-sized weight, there is a problem in industrial production because it involves heating energy from one end of the coil and cooling the other end to create a temperature gradient. It was.
[0010]
Japanese Patent Application Laid-Open No. 6-88171 discloses a method of adding 100 to 5000 g / T Bi to molten steel, and a product having B8 of 1.95 T or more can be obtained. The action of Bi increases the inhibitor strength to promote fine precipitation of inhibitors such as MnS and AlN, as disclosed in JP-A-6-207216, and deviates from the ideal {110} <001> orientation. This is considered to be advantageous for the selective growth of crystal grains having a small amount.
[0011]
In particular, the precipitation control of AlN, which is an inhibitor, has been deeply dependent on the annealing temperature before finish cold rolling of multiple cold rolling including hot-rolled sheet annealing, pre-cold rolling and pre-cold rolling, or intermediate annealing. Because it was well known that the temperature has been optimized.
[0012]
When Bi is contained in the raw material, in Japanese Patent Application Laid-Open No. Hei 6-212265, annealing before finish cold rolling of a plurality of cold rollings including hot-rolled sheet annealing or intermediate annealing is performed in a range of 850 ° C. to 1100 ° C. for 30 seconds. In JP-A-8-253815, the method of adjusting the annealing temperature before finish cold rolling by the excess Al amount in the steel, and in JP-A-11-124627, the average cooling rate of the hot-rolled sheet is used. And a method of controlling the annealing temperature prior to the final cold rolling to a range of 2400 × Bi amount (wt%) + 875 ° C. to 2400 × Bi amount (wt%) + 1025 ° C. according to the Bi content is disclosed. Yes. In any case, the proper range of the annealing temperature before finish cold rolling is characterized by a lower temperature than when Bi is not added.
[0013]
However, generally, annealing before finish cold rolling is not dedicated equipment for Bi-containing materials, so when the temperature of Bi-containing materials is lowered, the temperature must be changed between Bi-containing materials and non-containing materials. In some cases, however, a secondary recrystallization failure or a magnetic property failure having a low magnetic flux density may occur even after secondary recrystallization. Moreover, although temperature change may be implemented using the coil for temperature adjustment, since productivity is inhibited, it is unpreferable.
[0014]
Further, in JP-A-8-188824, Bi: 0.0005 to 0.05% is contained in the composition component of the material, and before decarburization annealing, an atmosphere in which P H ₂ O / P H ₂ is 0.4 or less is used. Among them, heat treatment is performed at a heating rate of 100 ° C./s or higher to a temperature range of 700 ° C. or higher to control the amount of SiO ₂ , stabilize the adsorption / desorption nitrogen behavior in finish annealing, and uniformly increase the magnetic flux in the coil. Techniques for obtaining density are disclosed. Since such heat treatment is generally performed with electric equipment such as induction heating or current heating, the H ₂ concentration is generally 4% or less from the viewpoint of explosion prevention.
[0015]
Therefore, in order to set the P H ₂ O / P H ₂ to an atmosphere of 0.4 or less, it is necessary to stabilize the operation at a low dew point, and it is necessary to install a dehumidifying equipment or the like, which requires equipment costs. Furthermore, the dew point must be controlled so as to be able to cope with slight fluctuations in the hydrogen concentration, resulting in a problem that the degree of freedom in operation becomes extremely small.
Therefore, secondary recrystallization failure in the longitudinal direction when annealing with a coil or magnetic property failure with low magnetic flux density may occur even if secondary recrystallization occurs, and stable industrial production has not yet been achieved.
[0016]
[Problems to be solved by the invention]
In view of the above problems, an object of the present invention is to provide a method of stably producing industrially with a high degree of freedom in operation in a grain-oriented electrical steel sheet having a very high magnetic flux density of B8 ≧ 1.94T.
[0017]
[Means for Solving the Problems]
The features of the present invention are as follows.
(1) By mass: C: 0.10% or less, Si: 2-7%, Mn: 0.02-0.30%,
Total of one or two selected from S and Se: 0.001 to 0.040%,
Acid-soluble Al: 0.010-0.065%, N: 0.0030-0.0150%,
Bi: 0.0005 to 0.05%
Is applied to the unidirectional electrical steel hot-rolled sheet composed of Fe and inevitable impurities, and the cold rolling is performed once or twice or more times with intermediate annealing between them. In the method for producing a grain-oriented electrical steel sheet, after applying decarburization annealing, applying an annealing separator, drying, and performing finish annealing, the maximum ultimate temperature of annealing before finish cold rolling falls within the range of the following formula according to the Bi content: The steel plate that is controlled and cold-rolled to the final thickness is heated to 700 ° C. or higher within 10 seconds or 100 ° C./second or higher , and PH ₂ O / PH ₂ is heated in an atmosphere of 0.6 to 0.8. Immediately after holding for 5 to 20 seconds at 700 ° C. or higher and performing pre-annealing to form SiO ₂ on the surface layer of the steel sheet, decarburization annealing is performed, and B8 ≧ 1.94T, which has a very high magnetic flux density and high Production of unidirectional electrical steel sheet with excellent magnetic iron loss Method.
−10 × ln (A) + 1100 ≦ B ≦ −10 × ln (A) +1220
Where A: Bi content (ppm)
B: Annealing temperature before finish cold rolling (° C)
(2) The highest ultimate temperature of annealing before finish cold rolling is controlled within the following range according to the Bi content, and high magnetic field iron with an ultrahigh magnetic flux density of B8 ≧ 1.94T as described in (1) above A method for producing a unidirectional electrical steel sheet excellent in loss.
−10 × ln (A) + 1130 ≦ B ≦ −10 × ln (A) +1220
Where A: Bi content (ppm)
B: Annealing temperature before finish cold rolling (° C)
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
In order to obtain a so-called ultra-high magnetic flux density unidirectional electromagnetic steel sheet more stably, the present inventors have conducted various studies, and as a result, the temperature increase rate of primary recrystallization annealing is set to 100 ° C./second or more. In this case, it was found from the following experiment that the annealing temperature before finish cold rolling and the Bi content have a great influence on the magnetic properties.
[0019]
C: 0.075%, Si: 3.25%, Mn: 0.08%, S: 0.025%, acid-soluble Al: 0.026%, N: 0.008 by mass within the scope of the present invention. %, And Bi: 0.0001 to 0.03%, and variously modified slabs for unidirectional electromagnetic steel plates were heated at 1400 ° C. as a starting material and then hot rolled to a 2.3 mm hot rolled sheet It was.
Subsequently, various changes were made to the maximum temperature reached in hot-rolled sheet annealing in the range of 950 to 1230 ° C., followed by pickling and cold rolling to finish a steel sheet having a thickness of 0.22 mm. Thereafter, the temperature was raised to 850 ° C. at a rate of 500 ° C./second in an atmosphere of P H ₂ O / P H ₂ : 0.6, and then decarburization annealing was performed at 800 ° C. in a humid atmosphere. Further, after applying an annealing separator mainly composed of MgO, finish annealing was performed at 1200 ° C. for 20 hours.
This annealed steel sheet was baked with an insulating film composed mainly of phosphate and colloidal silica, and the magnetic domain was controlled by laser irradiation. The laser irradiation conditions are an irradiation row interval of 6.5 mm, an irradiation point interval of 0.6 mm, and an irradiation energy of 0.8 mJ / mm ² . Thereafter, magnetic measurement was performed.
[0020]
1 and 2 show the effects of the Bi content and the annealing temperature before finish cold rolling on the magnetic flux density B8 and iron loss. As the Bi content is increased, the annealing temperature before finish cold rolling, which provides high magnetic flux density and low iron loss, tends to decrease, and B8 ≧ 1.94 T and W19 / 50 ≦ 1.20 w / kg can be obtained. If the Bi content is A (ppm),
−10 × ln (A) + 1100 ≦ temperature before finish cold rolling (° C.) ≦ −10 × ln (A) +1220
In particular, excellent magnetic properties were obtained.
−10 × ln (A) + 1130 ≦ temperature before finishing cold rolling (° C.) ≦ −10 × ln (A) +1220
It was in the range.
[0021]
In the above experiment, the method by one cold rolling was explained, but the same result was obtained when cold rolling was performed twice with intermediate annealing.
[0022]
Conventionally, when Bi is contained in the material, the primary recrystallized grain size tends to be coarse as disclosed in JP-A-11-124627, and the annealing temperature before finish cold rolling is lowered to reduce AlN or the like. Therefore, it has been essential to refine the precipitation-dispersed inhibitor in order to suppress the coarsening of the primary recrystallized grain size. For this reason, since the annealing temperature fluctuation | variation before finish cold rolling arises between Bi non-containing materials, the magnetic characteristic stable in the longitudinal direction was not acquired.
[0023]
However, as shown in FIG. 1, when the temperature increase rate of primary recrystallization annealing or decarburization annealing is rapidly increased to 100 ° C./second or more, the annealing temperature before finish cold rolling is higher than that of the conventional Bi-containing material. The proper range is heated. For example, as described above, in JP-A-6-212265, annealing before finish cold rolling is set to a range of 850 to 1100 ° C., but in the present invention, the temperature is higher than this. By increasing the frequency of primary recrystallization nuclei by rapid temperature increase and reducing the primary recrystallized grain size, the annealing temperature before finish cold rolling can be made higher than before. Fluctuation suppression became possible.
[0024]
In addition, as the Bi addition amount increases, the appropriate temperature range before the finish cold rolling is lowered, but since the primary recrystallized grain size becomes coarse due to the increase in Bi addition amount, the temperature before the finish cold rolling is lowered. The primary recrystallized grain size is adjusted.
[0025]
Furthermore, when Bi was added, it discovered that the direction-oriented electrical steel sheet excellent in the high magnetic field iron loss was obtained by carrying out moderate preheating before decarburization annealing after heating up rapidly. This is because, when Bi is contained in the material, the secondary recrystallized grains are coarsened and the magnetic domain width is widened, so that the high magnetic field iron loss is deteriorated. However, it is considered that the pre-annealing sufficiently provides the effect of imparting the tension of the coating obtained after the secondary coating is applied, and the magnetic field is subdivided to improve the high magnetic field iron loss.
[0026]
The reason why the film tension is improved by the pre-annealing is not clear, but the amount of SiO _{2 in the} surface layer portion of the steel sheet changes depending on the pre-annealing time held immediately after heating. The SiO ₂ content is estimated to represent the SiO ₂ coating of the surface layer portion, by optimizing the SiO ₂ coverage, as to optimize the internal oxide layer structure on subsequent decarburization annealed sheets It is considered that the film adhesion is improved and the film tension is increased as a structure in which the primary film and the base iron interface are complicated during the subsequent finish annealing.
[0027]
Next, the component conditions of this invention are demonstrated.
If C exceeds 0.10%, decarburization annealing after cold rolling requires a long time for decarburization, which is not economical, and decarburization tends to be incomplete, which is called magnetic aging in products. Since it causes a defect, it is not preferable.
[0028]
Si is an extremely effective element for increasing the electrical resistance of steel and reducing the eddy current loss that constitutes part of the iron loss, but if it is less than 2%, the eddy current loss of the product cannot be suppressed. On the other hand, if it exceeds 7.0%, the workability is remarkably deteriorated and cold rolling at room temperature becomes difficult, which is not preferable.
[0029]
Mn is an important element forming MnS and / or MnSe called an inhibitor that influences secondary recrystallization. If it is less than 0.02%, the absolute amount of MnS and MnSe necessary for causing secondary recrystallization is insufficient, which is not preferable. On the other hand, if it exceeds 0.3%, not only the solid solution during slab heating becomes difficult, but also the precipitation size during hot rolling tends to become coarse, and the optimum size distribution as an inhibitor is impaired.
[0030]
S and / or Se are important elements for forming the above-described Mn and MnS and / or MnSe. If the amount deviates from the above range, a sufficient inhibitor effect cannot be obtained, so it is necessary to limit it to 0.001 to 0.040%.
[0031]
Acid-soluble Al is a main inhibitor constituent element for a high magnetic flux density unidirectional electrical steel sheet. If it is less than 0.010%, it is not preferable because it is insufficient in quantity and insufficient in inhibitor strength. On the other hand, if it exceeds 0.065%, AlN precipitated as an inhibitor becomes coarse, and as a result, the strength of the inhibitor is lowered, which is not preferable.
[0032]
N is an important element for forming the acid-soluble Al and AlN described above. If the above range is exceeded, a sufficient inhibitor effect cannot be obtained, so it is necessary to limit the content to 0.0030 to 0.0150%.
[0033]
Furthermore, Sn is effective as an element for stably obtaining secondary recrystallization of a thin product, and also has an effect of reducing the secondary recrystallization particle size, and therefore may be added as necessary. In order to obtain this effect, addition of 0.05% or more is necessary, and when it exceeds 0.50%, the action is saturated, so addition of 0.50% or less is necessary from the viewpoint of cost increase. Good.
[0034]
Cu is effective as a primary film formation stabilizing element for Sn-added steel, and is added if necessary. If it is less than 0.01%, the effect is small, and if it exceeds 0.40%, the magnetic flux density of the product is lowered, which is not preferable.
[0035]
Sb and / or Mo are effective as an element for stably obtaining secondary recrystallization of a thin product, and may be added as necessary. In this case, in order to obtain this effect, addition of 0.0030% or more is necessary, and when it exceeds 0.30%, the action is saturated, so that it is 0.30% or less from the viewpoint of cost increase. limit.
[0036]
Bi is an essential element contained in the slab in the stable production of the ultrahigh magnetic flux density unidirectional electrical steel sheet of B8 ≧ 1.94T according to the present invention, and has an effect of improving the magnetic flux density. If it is less than 0.0005%, the effect cannot be sufficiently obtained, and if it exceeds 0.05%, not only the effect of improving the magnetic flux density is saturated but also cracking occurs at the end of the hot rolled coil, which is not preferable. .
[0037]
Next, the stable manufacturing method of the ultrahigh magnetic flux density material according to the present invention will be described.
The molten steel for producing an ultra high magnetic flux density grain-oriented electrical steel sheet with the components adjusted as described above is cast by an ordinary method. There is no particular limitation on the casting method. Then, it is rolled into a hot rolled coil by ordinary hot rolling.
Subsequently, finish cold rolling after hot-rolled sheet annealing, or multiple times of cold rolling including intermediate annealing, or multiple times of cold rolling including intermediate annealing after hot-rolled sheet annealing, finish the product sheet thickness. In the annealing before cold rolling, the crystal structure is homogenized and AlN precipitation is controlled.
[0038]
The feature of the present invention is to control the annealing temperature before finish cold rolling within the following range.
−10 × ln (A) + 1100 ≦ B ≦ −10 × ln (A) +1220
Where A: Bi content (ppm), B: Annealing temperature before finish cold rolling (° C)
When this temperature is too low, AlN is excessively finely precipitated, so that the primary recrystallization grain size is reduced and the magnetic flux density is lowered. Therefore, the temperature must be −10 × ln (A) + 1100 ° C. or more. On the other hand, when this temperature is high, the primary recrystallization grain size becomes coarse and secondary recrystallization becomes unstable, so that the upper limit is −10 × ln (A) + 1220 ° C.
[0039]
The strips rolled to the final product thickness are decarburized and annealed. Before decarburizing and annealing the steel sheet cold-rolled to the final thickness, it is heated to a temperature range of 700 ° C. or higher at a heating rate of 100 ° C./second or higher. As for this heating rate, an average heating rate up to the highest temperature of 20 to 700 ° C. or higher is shown. Particularly, a heating rate from 300 ° C. to 700 ° C. is important, and the average heating rate of this part is 100 ° C./second. When it is slower, the {110} <001> grains serving as secondary recrystallization nuclei do not increase, and secondary recrystallization becomes unstable. Even when the maximum temperature reached 700 ° C. or lower, {110} <001> grains do not increase, so 700 ° C. is the lower limit.
As a heating method for achieving such a high heating rate, induction heating or current heating is preferably employed.
[0040]
In addition, it is preferable to perform pre-annealing at 700 ° C. or higher for 5 to 20 seconds after rapid heating, since the high magnetic field iron loss is improved. When the pre-annealing temperature is lower than 700 ° C., appropriate SiO ₂ is not formed.
If the pre-annealing time exceeds 20 seconds, a sufficient amount of SiO ₂ is secured, but poor decarburization occurs. On the other hand, when the pre-annealing time is less than 5 seconds, an appropriate SiO ₂ cannot be ensured, so that Bi is not concentrated and Bi is excessively concentrated at the interface, and the film adhesion is deteriorated.
[0041]
Next, decarburization annealing is performed, but the above heat treatment may be incorporated into the temperature increase.
The atmosphere of decarburization annealing that continues after the soaking is the same as usual. That is, a mixed atmosphere of H ₂ and H ₂ O or H ₂ , H ₂ O and an inert gas is set, and P H ₂ O / P H ₂ is set in a range of 0.15 to 0.65. In addition, the amount of residual carbon after decarburization annealing needs to be 50 ppm or less similarly to the normal case. When only AlN is used as an inhibitor, the steel sheet may be nitrided by annealing in an ammonia-containing atmosphere after decarburization annealing, and inhibitor formation may be performed at this stage.
[0042]
After decarburization annealing, an annealing separator mainly composed of MgO is applied to the steel sheet and dried. At this time, about 1 to 40% of TiO ₂ may be added to MgO, and preferably the coating amount is 5 g / m per side. ² or more.
[0043]
Further, a final finish annealing at 1100 ° C. or higher is performed for the purpose of primary film formation, secondary recrystallization, and purification. In many cases, after the final finish annealing, an insulating film is further applied on the primary film. In particular, an insulating film obtained by baking a coating liquid mainly composed of phosphate and colloidal silica has a large applied hearing ability to the steel sheet, and is effective for further improving iron loss.
Further, the unidirectional electrical steel sheet may be subjected to so-called magnetic domain subdivision processing such as laser irradiation, plasma irradiation, groove processing by tooth roll or etching.
[0044]
[Example 1]
C: 0.080% by mass, Si: 3.30%, Mn: 0.080%, S: 0.025%, acid-soluble Al: 0.026%, N: 0.0082%, and Bi: 0, 0.0030, 0.0150, 0.0380% soot slab was heated at 1350 ° C. and then hot rolled to a thickness of 2.3 mm. , Annealing was performed at 4 levels of 1210 ° C. for 1 minute. Thereafter, it was rolled to a final thickness of 0.22 mm by cold rolling.
[0045]
Further, when the obtained strip was decarburized and annealed, the temperature increase rate from 300 ° C. to 850 ° C. was increased to 850 ° C. at 400 ° C./second, and immediately after that, P H ₂ O / PH ₂ = 0.8. Pre-annealing was performed at 850 ° C. for 5 seconds in an atmosphere, and decarburization annealing was performed in a uniform temperature of 840 ° C. and wet hydrogen.
[0046]
Thereafter, an annealing separator containing MgO as a main component was applied, and high temperature annealing was performed in a hydrogen gas atmosphere at a maximum temperature of 1200 ° C. for 20 hours. After removing excess MgO from the obtained steel sheet and forming an insulating film mainly composed of colloidal silica and phosphate on the formed forsterite film, a magnetic domain was controlled by laser irradiation. The laser irradiation conditions are an irradiation row interval of 6.5 mm, an irradiation point interval of 0.6 mm, and an irradiation energy of 0.8 mJ / mm ² . The manufacturing conditions and magnetic characteristics at this time are shown in Table 1.
The coil manufactured under the conditions satisfying the conditions of the present invention is a grain-oriented electrical steel sheet having excellent iron loss characteristics.
[0047]
[Table 1]

[0048]
[Example 2]
By mass: C: 0.075%, Si: 3.35%, Mn: 0.080%, S: 0.025%, acid-soluble Al: 0.025%, N: 0.0085%, Sn: 0.00. A slab containing 0140%, Cu: 0.08% and Bi: 0.0015, 0.0230% was heated at 1350 ° C. and immediately rolled to a 2.4 mm thick hot rolled coil It was. The hot-rolled coil was cold-rolled to 1.8 mm and annealed at three levels of 1050 ° C., 1150 ° C., and 1250 ° C. for 1 minute. Thereafter, it was rolled to a final thickness of 0.22 mm by cold rolling. Table 2 shows the manufacturing conditions and magnetic characteristics of the coil processed as a product after that in the same manner as in Example 1.
[0049]
[Table 2]

[0050]
[Example 3]
For A1, A2, B1, and B2 obtained in Example 2, grooves having a depth of 15 μm and a width of 90 μm were formed at intervals of 5 mm in an angle of 12 ° with the direction perpendicular to the sheet passing direction. Table 3 shows iron loss values before and after magnetic domain control. The coil manufactured under the conditions satisfying the conditions of the present invention is a grain-oriented electrical steel sheet having excellent iron loss characteristics.
[0051]
[Table 3]

[0052]
[Example 4]
By mass: C: 0.070%, Si: 3.25%, Mn: 0.070%, Se: 0.018%, acid-soluble Al: 0.025%, N: 0.0084%, Sb: 0.00. A slab containing 025%, Mo: 0.014% and Bi: 0.035% was heated at 1400 ° C. and then immediately rolled into a 2.5 mm thick hot rolled coil. The hot-rolled coil was annealed at 1000 ° C. and then cold-rolled to 1.7 mm. The coil was annealed for 1 minute at 1000 to 1200 ° C. at 5 levels every 50 ° C. Thereafter, it was rolled to a final thickness of 0.22 mm by cold rolling. Table 4 shows the manufacturing conditions and magnetic characteristics of the coil processed as a product after that in the same manner as in Example 1.
The coil manufactured under the conditions satisfying the conditions of the present invention is a grain-oriented electrical steel sheet having excellent iron loss characteristics.
[0053]
[Table 4]

[0054]
【The invention's effect】
According to the present invention, in the production of a high magnetic flux density unidirectional electrical steel sheet containing Bi in steel, it is possible to provide a method having a high degree of freedom in operation and capable of stable production.
[Brief description of the drawings]
FIG. 1 is a graph showing the effects of Bi content and temperature before finish cold rolling on magnetic flux density B8.
FIG. 2 is a graph showing the effects of Bi content and temperature before finish cold rolling on iron loss.

Claims (2)

C: 0.10% or less by mass,
Si: 2 to 7%,
Mn: 0.02 to 0.30%,
Total of one or two selected from S and Se: 0.001 to 0.040%, acid-soluble Al: 0.010 to 0.065%,
N: 0.0030 to 0.0150%,
Bi: 0.0005 to 0.05%
Is applied to the unidirectional electrical steel hot-rolled sheet composed of Fe and inevitable impurities, and the cold rolling is performed once or twice or more times with intermediate annealing between them. In the method for producing a grain-oriented electrical steel sheet, after applying decarburization annealing, applying an annealing separator, drying, and performing finish annealing, the maximum ultimate temperature of annealing before finish cold rolling falls within the range of the following formula according to the Bi content: The steel plate that is controlled and cold-rolled to the final thickness is heated to 700 ° C. or higher within 10 seconds or 100 ° C./second or higher , and PH ₂ O / PH ₂ is heated in an atmosphere of 0.6 to 0.8. Immediately after holding for 5 to 20 seconds at 700 ° C. or higher and performing pre-annealing to form SiO ₂ on the surface layer of the steel sheet, decarburization annealing is performed, and B8 ≧ 1.94T, which has a very high magnetic flux density and high Production of unidirectional electrical steel sheet with excellent magnetic iron loss Method.
−10 × ln (A) + 1100 ≦ B ≦ −10 × ln (A) +1220
Where A: Bi content (ppm)
B: Annealing temperature before finish cold rolling (° C) The maximum attained temperature of annealing before finish cold rolling is controlled within the following range in accordance with the Bi content, and the super high magnetic flux density of B8 ≥ 1.94T according to claim 1, which is excellent in high magnetic field iron loss. A method for producing grain-oriented electrical steel sheets.
−10 × ln (A) + 1130 ≦ B ≦ −10 × ln (A) +1220
Where A: Bi content (ppm)
B: Annealing temperature before finish cold rolling (° C)

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