JP4873770B2 - Unidirectional electrical steel sheet - Google Patents

Description

【００５５】
（実施例２）
実施例１の実験で用いた、３．４８％Ｓｉおよび０．０８１％Ｓｎの材料を用いて、熱延板焼鈍における均熱時間を、３０秒、６０秒および１５０秒とし、焼鈍温度を７００〜１２００℃に変更した。その他の工程条件は実施例１の実験と同一条件とした。磁気特性の測定結果を表２に、Ｂ８／Ｂｓに対する時間ｔ（秒）と温度Ｔ（Ｋ）の影響を図４に示す。ｔ（秒）とＴ（Ｋ）の関係が
ｌｏｇｔ（秒）≧５８０３．２／Ｔ（Ｋ）−２．８７４１
を満たせば、Ｂ８／Ｂｓ≧０．９６の高い二次再結晶ゴス方位集積度が得られていることが判る。
【００５６】
【表２】

【００５７】
【発明の効果】
本発明により、コストメリットが高い低温スラブ加熱−窒化処理を前提とするプロセスにおいて、高Ｓｉ化が可能となり、ゴス方位集積度が高く、二次再結晶粒径が小さく、鉄損が良好な一方向性電磁鋼板を製造することができる。
【図面の簡単な説明】
【図１】ＳｉおよびＳｎ含有量と二次再結晶ゴス方位集積度（Ｂ８／Ｂｓ）の関係を示す図である。
【図２】ＳｉおよびＳｎ含有量と一次再結晶の（１１０）面強度の関係を示す図である。
【図３】ＳｉおよびＳｎ含有量と一次再結晶の（１１１）面強度の関係を示す図である。
【図４】熱延板焼鈍の均熱温度Ｔ（Ｋ）および時間ｔ（秒）と二次再結晶ゴス方位集積度（Ｂ８／Ｂｓ）の関係を示す図である。
【図５】各Ｓｉ含有量における二次再結晶平均粒径とゴス方位集積度（Ｂ８／Ｂｓ）の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a unidirectional electrical steel having a crystal orientation (Goss orientation) aligned in one direction, which is used for an iron core material of electrical equipment such as a transformer. On the board It is related.
[0002]
[Prior art]
The unidirectional electrical steel sheet is composed of crystal grains having a so-called Goth orientation (representing a {110} <001> orientation in terms of Miller index) having a {110} plane and a rolling direction of the <100> axis. It is used as a soft magnetic material for transformers and generator cores. This steel plate must have good magnetic properties and iron loss properties as magnetic properties. The quality of the magnetization characteristics is determined by the level of magnetic flux density induced in the iron core in a constant magnetic field applied. Products with high magnetic flux density can reduce the size of the iron core. High magnetic flux density can be achieved by highly aligning the orientation of the steel plate crystal grains to {110} <001>. Normally, a value B8 at a magnetic field strength of 800 A / m is used as a representative value of the magnetic flux density.
[0003]
Iron loss is power loss that is consumed as thermal energy when a predetermined alternating magnetic field is applied to the iron core. For its quality, magnetic flux density, plate thickness, film tension, impurity content, specific resistance, crystal grains This affects the size of the. Among them, a high magnetic flux density and a large specific resistance are important for reducing the iron loss, and the development of a method for manufacturing a product having a low iron loss as much as possible at a low cost becomes an issue.
[0004]
Unidirectional electrical steel sheets are manufactured by secondary recrystallization using an inhibitor based on fine precipitates and texture control from cold rolling to primary recrystallization. Depends on. Moreover, although the specific resistance increases as the Si content increases, there is a problem that the texture deteriorates when the Si content is increased. Normally, the iron loss is represented by a loss W17 / 50 when magnetized to a magnetic flux density of 1.7 T at 50 Hz.
[0005]
By the way, the following four techniques are known as a manufacturing method of typical unidirectional electrical steel sheets that have been industrialized so far.
The first technique is M.M. F. Although it is a technique of the two-time cold rolling method using MnS which was disclosed in Japanese Patent Publication No. 30-3651 by Littmann, the magnetic flux density is not high. B8 is about 1.86T, and the ratio to the saturation magnetic flux density Bs (Goss orientation integration degree) is about 0.92 to 0.93.
[0006]
The second technique is a technique of making the final cold rolling reduction more than 80% by using “AlN + MnS” disclosed in Japanese Patent Publication No. 40-15644 by Taguchi et al. However, strict control of manufacturing conditions is required for industrial production. B8 is about 1.93T, and about 0.95 to 0.96 (Goss orientation integration degree) with respect to the saturation magnetic flux density Bs is obtained.
[0007]
The third technique is a technique of the double cold rolling method using “MnS (and / or MnSe) + Sb” disclosed in Japanese Patent Publication No. 51-13469 by Imachu et al. Inferior to technology. B8 is about 1.90T and is about 0.94 to 0.95 (Goth orientation integration degree) with respect to the saturation magnetic flux density Bs.
The above three types of techniques have the following problems in common. In any of the above techniques, the inhibitor is crowded before cold rolling. That is, by setting the slab heating temperature prior to hot rolling to over 1250 ° C., in fact, an extremely high temperature of 1300 ° C. or higher, coarse precipitates are once solid-dissolved, and in subsequent hot rolling or heat treatment, Precipitates are deposited finely and uniformly.
[0008]
However, increasing the slab heating temperature results from an increase in energy consumption during slab heating, an increase in equipment damage rate, etc., and in terms of material, yield loss due to scale loss and ear cracking, and coarsening of the slab crystal structure. A linear secondary recrystallization failure occurs, and this problem becomes remarkable particularly in a thin material and a high Si material.
In order to solve such a problem of the high temperature slab heating method, as a fourth technique, a technique of a low temperature slab heating method is disclosed in Japanese Patent Laid-Open Nos. 62-40315 and 5-112827. This is because the inhibitor necessary for the secondary recrystallization is built from the time after the decarburization annealing (primary recrystallization) is completed to the time before the secondary recrystallization appears in the final annealing, and the slab heating temperature is 1280 ° C, which is the same as that of ordinary steel. The technology is as follows. Inhibitors are (Al, Si) N formed by the penetration of N into the steel. Since the precipitation amount can ensure three times or more of the precipitation amount in the conventional high-temperature slab heating method, the inhibitor is strong and has high thermal stability.
[0009]
As a means to penetrate N into the steel, use the penetration of N from the atmosphere gas in the finish annealing temperature rise process, or after the decarburization annealing or after completion of the decarburization annealing, the strip is continuously lined. Is nitridation annealing? As a nitriding source, NH _Three An annealing atmosphere gas mixed with the above is used. By such a method, drastic cost reduction of the unidirectional electrical steel sheet could be achieved.
[0010]
Further, since this method uses a thermally stable inhibitor, a high magnetic flux density equivalent to that of the second technique can be obtained. B8 is about 1.93T, and the ratio (goth orientation integration degree) to the saturation magnetic flux density Bs is about 0.95 to 0.96.
[0011]
[Problems to be solved by the invention]
As a method of preventing abnormal crystal grain growth in the conventional high-temperature slab heating method, a technique has been adopted in which the amount of C is increased in accordance with the amount of Si to cause transformation during casting, thereby subdividing the crystal grains. . In this method, the higher the amount of Si, the higher the amount of C. However, the subsequent cold rolling becomes difficult, and the decarburization annealing process must be processed for a very long time. Therefore, it is difficult to increase the iron loss by increasing the amount of Si.
[0012]
On the other hand, in the manufacturing method using the low-temperature slab heating, the abnormal crystal grain growth that occurs in the high-temperature slab heating hardly occurs. High Si can be easily achieved without accompanying.
Therefore, the present inventors have promoted high Si based on the single cold rolling method of low temperature slab heating.
[0013]
However, when the Si content is increased while keeping the process conditions including the component composition as it is, the magnetic flux density B8 is deteriorated and it is difficult to obtain a predetermined low iron loss.
The inventors diligently investigated the cause of this. First, since the saturation magnetic flux density Bs decreases as the Si content increases, B8 relative to the saturation magnetic flux density Bs is used as an index indicating the degree of orientation integration of goth secondary recrystallization. The ratio (B8 / Bs; hereinafter referred to as Goss direction integration degree) was useful, and in order to achieve good iron loss, it was found that the required Goss direction integration degree was required.
[0014]
However, it has been found that when the Si content is simply increased, the Goss orientation integration degree is deteriorated even in the Goss orientation integration degree, and a predetermined low iron loss cannot be obtained.
That is, it is necessary to elucidate the metallurgical change accompanying the increase of the Si content from the viewpoint of the primary recrystallization texture, and to develop a compensation technique for ensuring the required degree of Goss orientation integration even in high Si materials. It has been found.
[0015]
[Means for Solving the Problems]
The present inventors have investigated in detail the material changes accompanying the increase in Si, thereby elucidating the cause of the deterioration in Goss orientation integration and increasing the Si in the low-temperature slab heating-nitriding manufacturing process. The conditions for this were examined.
First, it was clarified that the deterioration of the Goss orientation accumulation degree with the increase in Si was caused by the decrease of the Goss orientation in the primary recrystallized structure.
[0016]
In addition, as a result of various investigations on the component composition design that compensates for the decrease in goth orientation, when the goth orientation of the primary recrystallized structure is effectively increased by adjusting the Sn content, the degree of goth orientation integration of the required secondary recrystallization It was discovered that the iron loss according to the Si content can be achieved.
That is, the gist of the present invention is the following (1 ) It is shown.
(1) By mass%, Si: 3.0-4.0%, Mn: 0.08-0.45%, Al: 0.001-0.035%, Cr: 0.01-0.25% And Sn,
0.107 × Si (%) − 0.31 ≦ Sn (%) ≦ 0.121 × Si (%) − 0.32
An electromagnetic steel containing the balance of Fe and inevitable impurities, B8 / Bs is 0.96 or more, and the average grain size of secondary recrystallized grains is 14 to 19.8 mm A unidirectional electrical steel sheet characterized by
[0017]
DETAILED DESCRIPTION OF THE INVENTION
First, the present invention will be described based on experimental results.
% By mass: Mn: 0.1%, S: 0.007%, Cr: 0.12%, acid-soluble Al: 0.029%, N: 0.0083%, and P: 0.030% Electromagnetic steel with base component content, C changed from 0.021 to 0.095%, Si changed from 2.85 to 3.74%, and Sn changed from 0.005 to 0.16%. The slab was heated at 1150 ° C. for 60 minutes and then hot rolled to obtain a 2.3 mm hot rolled sheet. And this hot-rolled sheet was subjected to annealing of “1120 ° C. × 30 seconds + 900 ° C. × 120 seconds”, and then rapidly cooled.
[0018]
The hot-rolled annealed plate was pickled and then cold-rolled to a 0.22 mm thick steel plate. By changing the annealing temperature and subjecting this steel plate to decarburization annealing, the average grain size of the primary recrystallized grains in the steel plate was adjusted to approximately 23 μm. Thereafter, nitridation annealing was performed at 750 ° C. × 30 seconds in a mixed gas of hydrogen, nitrogen and ammonia, and the nitrogen content of the steel sheet was adjusted to approximately 220 ppm. Next, MgO and TiO ₂ An annealing separation agent containing as a main component was applied, heated to 1200 ° C. at a heating rate of 10 ° C./hr, and then subjected to finish annealing at 1200 ° C. for 20 hours.
[0019]
After removing the excess annealing separator from the finish annealed plate and performing strain relief annealing, a tension coating treatment was performed and the iron loss was measured. The magnetic flux density was measured after removing the insulating film and the like in an acid solution in order to remove the influence of the film tension and interface properties. As for the magnetic flux density, the saturation magnetic flux decreases as the Si content increases, and the magnetic flux density B8 cannot reflect the sharpness of goth secondary recrystallization. Therefore, the Goss orientation integration degree was evaluated using the standard value of B8 / Bs. . The validity of B8 / Bs was confirmed by measuring the crystal orientation by X-ray diffraction.
[0020]
In FIG. 1, the relationship between the crystal grain size of a hot-rolled sheet annealing board and a Goss orientation integration degree is shown. In order to obtain a high secondary recrystallization sharpness of B8 / Bs ≧ 0.96, it has been found that the Sn content needs to be increased according to the Si content. This is the first feature of the present invention. Here, in the material of B8 / Bs ≧ 0.96 in the figure, the iron loss decreased with the increase of the Si content, and it was confirmed that the effect of increasing the Si content can be exhibited. The iron loss improvement allowance was about 0.015 W / kg at W17 / 50 per 0.1% Si content.
[0021]
Next, the primary recrystallization texture was investigated in order to investigate the mechanism by which the required secondary recrystallization goth orientation accumulation degree can be secured by increasing the Sn content according to the Si content. The inverse surface strength was measured at 1 / 5t of the decarburized annealing plate, which is an intermediate process sample processed in FIG. FIG. 2 and FIG. 3 show the effects of the Si content and the Sn content on the (110) plane strength and (111) plane strength of primary recrystallization. It can be seen that (110) decreases and (111) increases as the amount of Si increases.
[0022]
It can also be seen that when the Sn amount is increased, (110) increases and (111) decreases. In other words, it is presumed that the change in the texture accompanying the increase in Si content acted in such a way that the increase in Sn content compensated.
Although the mechanism of the primary recrystallization texture on the secondary recrystallization Goss orientation accumulation degree is not clear at present, it is considered as follows.
[0023]
As described above, the degree of secondary recrystallization Goth orientation accumulation is considered to depend on the inhibitor strength and the primary recrystallization texture. In the present invention, the influence of primary recrystallization texture is considered to be large.
In general, for the primary recrystallization, the Goss orientation as the secondary recrystallization nucleus and the {111} <211> orientation in a corresponding orientation relationship with the Goss nucleus may be considered. In addition, it is considered that the Goss orientation forms deformation sites formed in the crystal grains by cold rolling, and that many Goss nuclei are formed when many deformation bands are formed in the crystal grains. On the other hand, {111} <211> is considered to increase {111} <211> when the vicinity of the crystal grain boundary before cold rolling is a recrystallization formation site and there are many deformations near the crystal grain boundary.
[0024]
In general, Si is known to be a solid solution strengthening element of iron, and it is considered that the strength in the crystal grains increases and the strength of the crystal grain boundaries relatively decreases as the amount of Si increases.
Therefore, in the steel sheet structure, the formation of deformation bands is suppressed and deformation near the crystal grain boundary is promoted, so that it is estimated that the amount of goth decreases and {111} <211> increases.
[0025]
On the other hand, Sn is known as a segregation element to crystal grain boundaries and the like, and it is considered that the grain boundary strength is relatively increased by the addition of Sn.
Therefore, when the Sn amount is increased, deformation near the crystal grain boundary is suppressed, and the formation of deformation bands in the crystal grains is relatively promoted, so that the amount of goth increases and {111} <211> decreases. It is estimated to be.
[0026]
In order to increase the degree of integration of secondary recrystallization goth orientation, it is thought that a quantitative balance between secondary recrystallization nuclei and corresponding orientation is important.
Therefore, when the amount of Si is increased alone, secondary recrystallization nuclei are insufficient with respect to the corresponding orientation, and the degree of integration of the secondary recrystallization goth orientation deteriorates.
Therefore, it is estimated that increasing the amount of Sn can compensate for the decrease in secondary recrystallization nuclei, balance the secondary recrystallization nuclei and the corresponding orientation, and increase the degree of Goss orientation integration in secondary recrystallization. Is done.
[0027]
From the above consideration, it is considered important that Sn is sufficiently segregated at the grain boundary before cold rolling in order to bring out the effect of Sn on the primary recrystallization texture. And in the segregation of Sn, the spreading | diffusion by annealing was considered important and the conditions of hot-rolled sheet annealing were examined.
Next, the result of having examined about the annealing conditions concerning a hot-rolled sheet is described.
[0028]
Using the material of 3.48% Si and 0.081% Sn used in the experiment of FIG. 1, the soaking time of hot-rolled sheet annealing was 30 seconds, 60 seconds, and 150 seconds, and the annealing temperature was 700. Changed to ~ 1200 ° C. Other process conditions were the same as those in the experiment of FIG. The influence of time t (second) and temperature T (K) on B8 / Bs is shown in FIG.
In order to obtain B8 / Bs ≧ 0.96 from the figure, the time t is
logt (seconds) ≧ 5803.2 / T (K) −2.8741
It turns out that it is important to be within the range. This is the second feature of the present invention.
[0029]
The above formula almost coincides with the relationship between the temperature and time at which Sn diffuses about 20 μm of the crystal grain radius of the hot-rolled annealed plate calculated from the diffusion constant of Sn in αFe.
That is, if the condition of the above formula is satisfied, it is considered that Sn is sufficiently diffused into the crystal grain boundary and segregation is possible. Then, it is presumed that the above-described effect on the primary recrystallization texture of Sn is exhibited, and a good degree of secondary recrystallization goth orientation integration is obtained.
[0030]
Next, in the product obtained by applying the invention having the above characteristics, parameters characterizing the secondary recrystallization structure were analyzed. For the secondary recrystallization macroplate used in FIG. 1, the average particle size of the secondary recrystallization was measured. The secondary recrystallized grain size tends to increase as the Si amount increases and decrease as the Sn amount increases. This tendency is in agreement with the above-described tendency of the primary recrystallization texture with respect to the amount of goth (110), and it is estimated that the amount of secondary recrystallization nuclei has changed.
[0031]
Therefore, the relationship between the secondary recrystallized grain size and B8 / Bs was arranged, considering that there is an appropriate secondary recrystallized grain size for obtaining high B8 / Bs. The result is shown in FIG.
As can be seen from the figure, the secondary recrystallization average particle size for obtaining B8 / Bs ≧ 0.96 is in the range of 14 to 21 μm, and the present invention is also characterized by the secondary recrystallization particle size of the product. I found This is the third feature of the present invention including the contents of Si and Sn.
[0032]
When magnetic domain subdivision such as laser processing is not performed, a smaller crystal grain size is advantageous for iron loss improvement, and the present invention is characterized as a low iron loss material from the viewpoint of B8 / Bs of the product and crystal grain size. .
Next, the reason for limitation related to the component composition of the present invention will be described.
Si is an important element for effectively increasing the specific resistance of a product and obtaining low iron loss, and its content is determined according to the iron loss to be targeted. When the Si content is less than 3.0%, it is difficult to obtain a product having a low iron loss. On the other hand, when the Si content exceeds 4.0%, the cold rolling property of the material becomes problematic.
[0033]
The Sn content (Sn (%)), which is the first feature of the present invention, is described in detail in the description of FIG. 1, and the range is related to the Si content (Si (%)).
0.107 × Si (%) − 0.31 ≦ Sn (%) ≦ 0.121 × Si (%) − 0.32
In the range.
[0034]
If Sn is not positively added, about 0.01% is mixed as a playing element, but below this, the effect of improving the magnetic properties is not exhibited. On the other hand, if added in a large amount, segregation to the surface becomes remarkable in addition to segregation to the crystal grain size, and this suppresses oxidation characteristics important for decarburization and primary film formation. 16%.
[0035]
C is contained in an amount of about 0.02 to 0.10% at the slab stage for organization control, but is removed in a later decarburization annealing step. If C remains in the product, the magnetic properties deteriorate due to aging, so the C content in the product is preferably as low as possible. Usually, it is removed to 100 ppm or less by decarburization annealing.
When the C content is less than 0.02% at the slab stage, secondary recrystallization becomes unstable, and even when secondary recrystallization occurs, the Goss orientation accumulation degree (B8 / Bs) is as low as 0.94 or less. It will be a thing. On the other hand, when the C content exceeds 0.10%, the secondary recrystallization is stabilized, but the Goss orientation accumulation degree is deteriorated and the decarburization annealing time is also increased, thereby impairing the productivity.
[0036]
Moreover, in order to adjust the γ phase ratio as in the past, adjusting the C content in accordance with the Si content in the steelmaking process does not impair the characteristics of the present invention.
One of the characteristics in the component system of the starting material (electromagnetic steel slab) of the present invention is that it contains S and Se alone or in combination of 0.015% or less, preferably 0.0070% or less. As is well known, S and Se form MnS and MnSe, respectively, and have an action of suppressing grain growth. In the present invention, it is characterized in that an inhibitor necessary for developing secondary recrystallized grains is built in after decarburization annealing, and that fine precipitates are dispersed before cold rolling, primary recrystallized grains In the present invention in which the diameter is adjusted to obtain a high magnetic flux density and a low iron loss, this is not preferable.
[0037]
Therefore, the content of S and / or Se is set to 0.015% or less. Moreover, reducing the content of S and / or Se has a great effect in reducing the ear cracks during hot rolling.
Mn is a forming element of MnS or MnSe, and it is preferable that Mn is as much as possible in order to make the inhibitor effect harmless. If the content is too small, even in the case of low-temperature slab heating at 1250 ° C. or lower, MnS or MnSe partially dissolves, the primary recrystallized grain size becomes unstable, and the magnetic properties vary. On the other hand, if the amount is too large, an excessive transformation structure is affected, making it difficult to obtain a product having a high magnetic flux density. The appropriate Mn content is 0.08 to 0.45%.
[0038]
Al combines with N to form AlN, but in the present invention, it is essential to form (Al, Si) N by nitriding the steel after the subsequent step, that is, primary recrystallization. Therefore, a certain amount or more of free Al is necessary. Therefore, 0.020 to 0.035% is added as acid-soluble Al. This Al is slightly reduced in products due to oxidation during decarburization annealing and purification during finish annealing.
[0039]
N needs to be 0.0035 to 0.012% in the slab stage. If the N content exceeds 0.012%, the surface of the steel plate called blisters will swell, and it will be difficult to adjust the primary recrystallization structure. The lower limit of the N content is preferably 0.0035%. When the N content is less than 0.0035%, it becomes difficult to develop secondary recrystallized grains.
[0040]
Note that N functions as an inhibitor in combination with the nitriding treatment described later, and is removed during purification in finish annealing. Since N also causes aging, it is better that it is less in the product, and is usually suppressed to 50 ppm or less.
Since Cr has the effect of mitigating the suppression of decarburization and oxidation due to the surface segregation of Sn, which is a feature of the present invention, its addition is essential. The lower limit of the Cr content is 0.01% contained as a playing element, and more than this is intentionally added. On the other hand, when a large amount of Cr is added, excessive oxidation occurs, and conversely, film formation is inhibited. Considering the load of addition cost, the upper limit is made 0.25%.
[0041]
In addition, inclusion of trace amounts of P, Cu, Sb, Ni, Bi, V, Nb, B, etc. does not impair the features of the present invention.
Next, the manufacturing process of the present invention will be described. An electromagnetic steel slab is obtained by melting steel in a melting furnace such as a converter or electric furnace, vacuum degassing treatment as necessary, and then performing continuous casting or rolling after ingot casting. It is done. Thereafter, slab heating prior to hot rolling is performed.
[0042]
In the production process of the present invention, the slab heating temperature is a low temperature of 1280 ° C. or less, and the consumption of heating energy is reduced, and the AlN in the steel is not completely dissolved but incompletely dissolved. . Naturally, MnS (Se) having a high solid solution temperature is also in an incomplete solid solution state due to the component design of high Mn and low S (Se). Immediately after the slab heating, rough hot rolling and finish hot rolling are performed by a normal method to obtain a hot rolled plate having a thickness of 2 to 3 mm.
[0043]
In order to obtain a product having good magnetic properties, annealing before the final cold rolling is essential from the viewpoint of segregation of Sn grain boundaries. That is, when single cold rolling is employed, it is necessary to specify conditions for hot-rolled sheet annealing, and when two or more cold rollings are employed, it is necessary to specify conditions for intermediate annealing. As described in detail in the explanation of FIG. 3, the annealing conditions are set as a soaking time t (second) and a soaking temperature T (K),
logt (seconds) ≧ 5803.2 / T (K) −2.8741
It is important to control within the range. Since the above equation is related to the diffusion distance of Sn in Fe, in the case of a two-stage cycle such as “1120 ° C. × 30 seconds + 900 ° C. × 120 seconds”, it was calculated according to the soaking of the left and right terms, respectively. Judgment must be made based on the cumulative results. Even if it implements well-known techniques, such as rapid cooling, after annealing for control of a primary recrystallization texture, the characteristic of this invention is not inhibited.
[0044]
Then, the process conditions after cold rolling are demonstrated. In the present invention, hot-rolled sheet annealing is performed, and then cold rolling is performed once in a cold rolling state of 80% or more, or a final rolling reduction rate of 80% or more is inserted through intermediate annealing for adjusting the reduction rate. It is premised on the final cold rolling under strong pressure to obtain the final sheet thickness by the above cold rolling. Cold rolling is performed by a normal method. In order to obtain a high magnetic flux density, it is preferable to finely adjust the rolling reduction or perform an aging treatment between passes.
[0045]
The steel sheet cold-rolled to the final thickness is subjected to decarburization annealing. In addition to decarburization, the decarburization annealing has a role of generating an oxide layer necessary for adjusting the primary recrystallization structure and forming a film. This is usually performed in wet hydrogen or nitrogen gas at a temperature range of 800 to 900 ° C. The primary recrystallization particle size is preferably 15 to 30 μm.
Next, nitriding is performed. The conditions for the nitriding treatment are known conditions related to strip nitriding, nitriding during finish annealing, and the like. In the case of strip nitriding, it is advantageous for nitriding that the annealing temperature is 650 to 850 ° C. In order to stably develop good secondary recrystallized grains, the amount of nitrogen is required to be 120 ppm or more, preferably 150 ppm or more.
[0046]
After this, MgO and TiO are known by a known method. ₂ An annealing separation agent containing as a main component is applied and finish annealing is performed at a temperature of 1100 ° C. or higher. The conditions for the finish annealing may be known conditions, and it is effective to adjust the atmosphere or slow the heating rate in order to increase the degree of Goss direction integration.
In the product obtained by the present invention, the above-mentioned components of Si, Mn, Al, Cr and Sn are important. In particular, the quantitative relationship between Si and Sn is characteristic. N and S are excluded from the essential components because they are purified during the finish annealing. Al is also reduced during finish annealing, but since AlN is used as an inhibitor, the lower limit is made 0.001%.
[0047]
Further, as a characteristic of the secondary recrystallization structure, B8 / Bs as a simple index of the Goss orientation accumulation degree is 0.95 or more, preferably 0.96 or more, and the secondary recrystallization average particle diameter is 12 It is important that it is ˜25 mm, preferably 14 to 21 mm. However, the upper limit of the secondary recrystallization average particle diameter was set to 19.8 mm in Table 1 based on the maximum value 19.8 (mm) of the inventive examples. The grain size can be measured by a method of counting the number of crystal grain sizes and converting from an average area to a circle-equivalent grain size, a method using an image analysis processing device, or the like.
[0048]
The coil after finish annealing is subjected to shape correction annealing or insulating coating, but can be subjected to magnetic domain subdivision treatment by laser, plasma, mechanical method, etching, or other methods as necessary.
[0049]
【Example】
Example 1
% By mass: Mn: 0.1%, S: 0.007%, Cr: 0.12%, acid-soluble Al: 0.029%, N: 0.0083%, and P: 0.030% Electromagnetic steel with base component content, C changed from 0.021 to 0.095%, Si changed from 2.85 to 3.74%, and Sn changed from 0.005 to 0.16%. The slab was heated at 1150 ° C. for 60 minutes and then hot-rolled to obtain a hot-rolled sheet having a thickness of 2.3 mm.
[0050]
The hot-rolled sheet was annealed at “1120 ° C. × 30 seconds + 900 ° C. × 120 seconds” and then rapidly cooled. The hot-rolled annealed plate was pickled and cold-rolled to a steel plate having a thickness of 0.22 mm. The steel sheet was decarburized and annealed by changing the annealing temperature to adjust the primary recrystallized grain size to 23 μm.
Thereafter, nitridation annealing was performed at 750 ° C. for 30 seconds in a mixed gas of hydrogen, nitrogen, and ammonia, and the nitrogen content of the steel sheet was adjusted to approximately 220 ppm. Next, MgO and TiO ₂ An annealing separation agent containing as a main component was applied, heated to 1200 ° C. at 10 ° C./hr, and then annealed at 1200 ° C. for 20 hours.
[0051]
After removing the excess annealing separator from the finish annealed plate and performing strain relief annealing, a tension coating treatment mainly comprising colloidal silica and aluminum phosphate was performed, and the iron loss was measured. The magnetic flux density (B8 and Bs) was measured after the treatment of removing the insulating film and the like in an acid solution in order to remove the influence of the film tension and interface properties. Moreover, the secondary recrystallization average particle diameter was measured by image processing from the same sample.
[0052]
The measurement results are shown in Table 1. FIG. 1 shows the relationship between the crystal grain size of the hot-rolled sheet annealed sheet and the Goss orientation integration degree. Sn content calculated from Si content is
0.107 × Si (%) − 0.31 ≦ Sn (%) ≦ 0.121 × Si (%) − 0.32
In this range, a high degree of secondary recrystallization goth orientation integration of B8 / Bs ≧ 0.96 is obtained.
[0053]
On the other hand, the result of arranging the relationship between the secondary recrystallized grain size and B8 / Bs is shown in FIG. The secondary recrystallization average particle diameter for obtaining B8 / Bs ≧ 0.96 is 12 to 25 mm, preferably 14 to 21 mm.
[0054]
[Table 1]

[0055]
(Example 2)
Using the materials of 3.48% Si and 0.081% Sn used in the experiment of Example 1, the soaking time in hot-rolled sheet annealing was 30 seconds, 60 seconds and 150 seconds, and the annealing temperature was 700. Changed to ~ 1200 ° C. Other process conditions were the same as those in the experiment of Example 1. The measurement results of the magnetic properties are shown in Table 2, and the influence of time t (second) and temperature T (K) on B8 / Bs is shown in FIG. The relationship between t (seconds) and T (K)
logt (seconds) ≧ 5803.2 / T (K) −2.8741
It can be seen that a high secondary recrystallization Goth orientation integration degree of B8 / Bs ≧ 0.96 is obtained.
[0056]
[Table 2]

[0057]
【Effect of the invention】
According to the present invention, in a process premised on low-temperature slab heating-nitriding treatment with high cost merit, high Si can be achieved, Goth orientation integration degree is high, secondary recrystallized grain size is small, and iron loss is good. A grain-oriented electrical steel sheet can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between Si and Sn content and secondary recrystallization goth orientation integration degree (B8 / Bs).
FIG. 2 is a diagram showing the relationship between Si and Sn content and (110) plane strength of primary recrystallization.
FIG. 3 is a graph showing the relationship between Si and Sn content and (111) plane strength of primary recrystallization.
FIG. 4 is a diagram showing the relationship between the soaking temperature T (K) and time t (seconds) of hot-rolled sheet annealing and the degree of secondary recrystallization Goth orientation integration (B8 / Bs).
FIG. 5 is a diagram showing the relationship between secondary recrystallization average grain size and Goth orientation integration degree (B8 / Bs) at each Si content.

Claims (1)

% By mass, Si: 3.0-4.0%, Mn: 0.08-0.45%, Al: 0.001-0.035%, Cr: 0.01-0.25%, and Sn
0.107 × Si (%) − 0.31 ≦ Sn (%) ≦ 0.121 × Si (%) − 0.32
An electromagnetic steel containing the balance of Fe and inevitable impurities, B8 / Bs is 0.96 or more, and the average grain size of secondary recrystallized grains is 14 to 19.8 mm A unidirectional electrical steel sheet characterized by

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