JPH0338323B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a unidirectional silicon steel sheet with excellent magnetic properties. As is well known, unidirectional silicon steel sheets are mainly used as iron cores for transformers and other electrical equipment, and are required to have excellent magnetic properties such as magnetization properties and iron loss properties. Recently, due to advances in manufacturing technology for silicon steel sheets, the magnetic flux density represented by the _B10 value (i.e., the magnetic flux density in the rolling direction that occurs when the magnetic field strength is 1000 A/m) has increased to 1.89T (Stella). In addition, as for iron loss characteristics, the W _17/50 value (i.e., the iron loss property when magnetized at a magnetic flux density of 1.7 T and a frequency of 50 Hz with a unidirectional silicon steel sheet of 0.30 mm thickness) It is now possible to obtain products with low iron loss (loss) of 1.10w/Kg or less. As mentioned above, a basic requirement for obtaining a silicon steel sheet having excellent magnetic properties is to sufficiently develop secondary recrystallized grains with (110) [001] orientation in the final annealing process. To achieve this, the existence of an inhibitor that strongly suppresses the growth of crystal grains with unfavorable crystal orientations other than the (110) [001] orientation during the secondary recrystallization process, and the presence of an inhibitor that strongly suppresses the growth of crystal grains with unfavorable crystal orientations other than the (110) [001] It is known that formation of a suitable primary recrystallized texture is necessary for sufficient development of secondary recrystallized grains. As the inhibitor, fine precipitates such as MnS, MnSe, AlN, etc. are generally used, and if necessary, grain boundary segregation type elements such as Sb, As, Bi, Pb, Sn, etc. are used in combination with the inhibitor. It has also been conventionally attempted to enhance the effect of the inhibitor. On the other hand, a suitable one
Regarding the formation of the next recrystallization texture, a method has traditionally been adopted that appropriately combines each process condition of hot rolling and cold rolling. Complicated processes such as rolling have also been employed in the past. By the way, recently there has been a trend in the manufacturing method of silicon steel slabs, which are the raw material for manufacturing silicon steel sheets, to change from the conventional one-block ingot method to the continuous casting method. A new problem has arisen that did not occur with slabs produced by the conventional ingot-forming method. In other words, in order to obtain fine precipitates such as MnS, MnSe, and AlN that act effectively as inhibitors, the slab must be heated to a high temperature of 1250°C or higher for a long time before hot rolling to sufficiently dissociate the inhibitor elements into solid solution. After this, it is necessary to control the cooling process during hot rolling so that the crystal grains are precipitated to an appropriate fine size. Due to these abnormally coarse grains, incompletely developed secondary recrystallized grains called band-like fine grain structures are formed in the silicon steel sheet, which can lead to deterioration of magnetic properties. . Several methods have already been proposed for improving magnetic properties by preventing the generation of the band-like fine grain structure as described above. For example, according to Japanese Patent Application Laid-open No. 55-119126,
When processing a material slab to a predetermined thickness by hot rolling, the structure immediately before recrystallization rolling is controlled so that it becomes a structure in which 3% or more of the γ phase is precipitated in the α phase matrix, and this is A method is disclosed in which recrystallization high pressure rolling is performed in a temperature range of ~960° C. so that the rolling reduction is 30% or more per pass. In addition, the present inventors have already proposed in Japanese Patent Application No. 56-31510 that a material slab contains a necessary amount of C according to the amount of Si, and a predetermined amount or more of γ phase is generated in a specific temperature range during hot rolling. discloses a method of splitting and destroying crystal grains that have grown coarsely during high-temperature heating of a material slab during the hot rolling process, thereby effectively preventing the formation of band-like fine grain structures in finished products. However, according to each of the above methods in which a predetermined amount or more of γ phase is generated during hot rolling, although the band-like fine grain structure of the product can be prevented, the desired magnetic properties may not always be sufficient. The prevention effect of the microstructure itself is extremely unstable, and in extreme cases, a fine grain structure may occur over the entire surface of the product, significantly degrading the magnetic properties. There was a problem that was missing. On the other hand, in recent years, methods have been developed for improving the primary recrystallization texture by effectively utilizing carbon or carbides contained in steel. For example, special public relations
Publication No. 14009 describes a hot rolled sheet before the first cold rolling.
Lenticular carbides with a size visible under an optical microscope (several μm) are precipitated within the crystal grains by rapidly cooling rapidly from a temperature of 790°C or higher to a temperature of 540°C or lower and then maintaining the temperature in a temperature range of 310 to 480°C. A method is disclosed. The relatively large-sized carbides produced by this method effectively act to split and refine the coarse hot-drawn elongated grains formed in the hot-rolling process, and prevent the development of secondary recrystallized grains. It is thought that this plays a role in eliminating crystal grains with the (110) to (110) [001] orientation, which are harmful to the cold rolling process, at the early stage of the cold rolling process. However, it has still been difficult to sufficiently improve magnetic properties using this method alone. More recently, methods have been developed that utilize solid solution C or fine carbides within crystal grains in the cold rolling process. For example, in Japanese Patent Publication No. 54-13846 and Japanese Patent Publication No. 54-29182, there are
Using AlN, the hot-rolled sheet is annealed at high temperature and then rapidly cooled.
A method is disclosed in which, when performing one hard cold rolling with a final cold rolling reduction of 80% or more, aging treatment is performed at least once between cold rolling passes. In this case, the aging treatment is carried out at a temperature of 50 to 350℃.
Hold for more than 1 minute or within the temperature range of 300-600℃
It is said that it is necessary to hold for ~30 seconds and that it is effective to apply it multiple times. However, this method is uneconomical because the cold rolling efficiency is significantly reduced and the cost for heat treatment of the steel sheet is increased. Furthermore, in Japanese Patent Publication No. 19377, filed by the applicant,
When adding a combination of AlN and Sb as an inhibitor, in order to fully demonstrate the effect of this combination addition, slow cooling is performed at a temperature range of 700 to 900°C for 200 to 2000 seconds during cooling after intermediate annealing. A method is disclosed in which the temperature is immediately quenched to below 200°C. However, in order to achieve gradual cooling between 700 and 900 degrees Celsius for 200 to 2000 seconds using this method, the cooling zone of the continuous annealing furnace must be significantly modified to keep the steel plate heated to this temperature range. It is necessary to provide a long cooling zone for cooling, and continuous operation at extremely low speeds is required, resulting in a significant decrease in production efficiency and an increase in manufacturing costs, which is economically disadvantageous. Furthermore, both of these methods utilize a specific inhibitor, AlN or AlN-Sb, and can only be effective when combined with a strong cold rolling process of 80% or more. The texture is {111}<112
＞Directions are extremely concentrated, (110) [001]
The direction only shows weak accumulation as a subdirection;
This method is fundamentally different from the method of strongly accumulating the (110) [001] orientation, and these methods are used when manufacturing unidirectional silicon steel sheets using MnS and MnSe, which have been commonly used as inhibitors. It could not be applied. On the other hand, as one of the known methods for effectively utilizing carbon in steel to improve the texture within the range of the final cold rolling reduction suitable for this inhibitor, for example, Publication No. 56-3892 discloses a method in which cooling after intermediate annealing is performed between 600 and 300°C at a cooling rate of 150°C/min or more, and aging treatment is performed in the final cold rolling stage. In this case, the statute of limitations is 100
It is necessary to perform the aging treatment at ~400℃ for 5 seconds to 30 minutes at least once between cold rolling passes. Therefore, this also results in a decrease in cold rolling efficiency and an increase in heat treatment costs. Because it is economically disadvantageous,
There was a strong desire to develop a more efficient method. This invention was made in view of the above circumstances, and it eliminates and improves the various drawbacks of the conventional method for effectively utilizing C in steel, and makes it possible to efficiently and economically produce unidirectional silicon steel sheets with excellent magnetic properties. The purpose of this invention is to provide a method that enables production on an industrial scale. In other words, as a result of extensive experiments and studies in order to achieve the above-mentioned objectives, the present inventors found that, firstly, in order to control the amount of γ phase generated during hot rolling within an appropriate range, the amount of C was Adjust according to the amount of Si, the second
The third step is to decarburize a predetermined amount of C between the end of the hot rolling process and the intermediate annealing before the final cold rolling process, and the third step is to remove carbides in the grains of the steel sheet after the intermediate annealing before the final cold rolling process. By combining the above three requirements, we can efficiently and economically produce grain-oriented silicon steel sheets with excellent magnetic properties. They found that it could be obtained and came up with this invention. Specifically, the method for producing a unidirectional silicon steel sheet of the present invention includes C0.015~0.10%, Si2.8~4.0%, Mn0.02~0.15
% and contains one or two of S, Se, and Sb in a total amount of 0.008 to 0.080%, with the balance substantially consisting of Fe, hot-rolled;
The obtained hot-rolled steel sheet is cold-rolled two or more times with intermediate annealing at a final cold-rolling reduction of 40 to 80% to achieve a predetermined final thickness. In a method for manufacturing a series of unidirectional silicon steel sheets that undergoes charcoal annealing and final annealing, the amount of C in the silicon steel material is adjusted to the range expressed by the following formula according to the amount of Si, and the final annealing is performed after the hot rolling is completed. C from 0.006 to before the end of cold rolling
Decarburize by 0.020%, and in the cooling process after intermediate annealing before final cold rolling, rapidly cool within 30 seconds at a temperature range of 770 to 100℃, and immediately undergo aging treatment at a temperature of 150 to 250℃ for 2 to 60 seconds. or in the cooling process after the intermediate annealing.
By rapidly cooling the temperature range from 770 to 300℃ within 20 seconds, and then controlling the cooling time between 300 and 150℃ within the range of 8 to 30 seconds, carbides in the grains of the steel sheet can be removed. It is characterized in that the final cold rolling is carried out after controlling the precipitation state to be fine and sufficiently dispersed with a size of 100 to 500 Å. Note: 0.37 [Si%] + 0.27≦log ([C%] × 10 ³ ) ≦0.37 [Si%] + 0.57 However, [Si%] and [C%] represent the amount of Si and C contained in the steel, respectively. Represents weight %. The manufacturing method of the present invention will be explained in more detail below. First, to explain the findings in the process that led to this invention, the present inventors investigated the effect of the γ phase generated during hot rolling, and the following facts were confirmed. In other words, as mentioned above, the γ phase generated during hot rolling of the material slab is effective in splitting and destroying the crystal grains that have grown coarsely when the material slab is heated to high temperatures. It has a detrimental effect on fine precipitates, and sometimes excessive γ phase formation can significantly reduce the inhibitor's effectiveness and inhibit the sufficient development of secondary recrystallized grains. Therefore, the amount of γ phase formed must be appropriate. In addition, even if the amount of γ phase produced is within an appropriate range, after it plays the role of finely growing coarse grains during hot rolling, it will not be produced in the cold rolling process. We have newly discovered the fact that it is harmful to the formation of an appropriate crystal structure and texture. Therefore, the present inventors have conducted various research into ways to take advantage of the beneficial effects of the γ phase while also eliminating its harmful effects.As a result, the inventors have found that the amount of γ phase produced in the material during hot rolling should be within an appropriate range. The amount of C is adjusted according to the amount of Si, and an appropriate amount of decarburization is performed between the end of hot rolling and before the end of the final cold rolling process to reduce the amount of excessive γ phase formed. Control the intragrain carbides of a steel sheet before cold rolling to within a specific extremely small range that cannot be seen with an optical microscope, which has never been considered before, and sufficiently precipitate and disperse them. By this, the texture of the steel sheet after final cold rolling and decarburization annealing before final annealing can be improved to a state where the degree of accumulation of (110) [001] orientation is strong, and as a result, the
Highly aligned in the next recrystallization process (110) [001]
It was newly discovered that a unidirectional silicon steel sheet having excellent magnetic properties can be obtained by sufficiently growing oriented secondary recrystallized grains, leading to the completion of this invention. Each requirement of the present invention will be explained in more detail based on the experimental results of the present inventors that led to the completion of the present invention as described above. Figure 1 shows a total of 0.020 to 0.045% of Se and Sb and 0.03 to 0.09% of Mn as inhibitors, and Si contents of 2.8 to 3.1%, 3.3 to 3.5%, and 3.6 to 3.8%.
%, and the C content is 0.01~
A large number of continuously cast silicon steel slab specimens with changes in the range of 0.10% were heat-treated at 1400°C for 1 hour, then hot-rolled into hot-rolled sheets with a thickness of 2.5 mm, and then intermediately rolled by a known method. The iron loss W _17/50 was investigated for each product of unidirectional silicon steel plate obtained by finishing the final plate thickness to 0.30 mm through two cold rolling processes with annealing, and then performing decarburization annealing and final annealing. The relationship between the iron loss value and the Si content and C content of each continuously cast slab specimen is shown. In this test, the intermediate annealing atmosphere was varied from decarburizing to non-decarburizing, and the final cold rolling reduction was set in the range of 50 to 70%. The symbols ◎, ○, ●, and × in Fig. 1 indicate the size of the iron loss W _17/50 of the product, and the Si of each sample material stage.
Judgments were made according to the content as shown in Table 1 below.

[Table] Also, the broken lines A, B, C, D,
E is the estimated value of the amount of γ phase formed at 1150℃ during hot rolling, and the amount of γ phase formed is 40%, 30%, and 20%, respectively.
%, 10% and 0% cases are shown. Here, the amount of γ phase produced substantially changes depending on the amount of Si, the amount of C, and the temperature.
D and E are the correlations between the measured values of the amount of γ phase generated in the equilibrium state at 1150°C and the amount of Si and C in the steel, which were determined by experiments for silicon steel specimens with various amounts of Si and C. This is calculated from the following equation (1) derived from . γ%=67log([C%]×10 ₃ )−25[Si%]−8……(1
) As is clear from Figure 1 and Table 1, the absolute iron loss level that is judged to be good differs depending on the Si content, but depending on the Si content, the iron loss W _17/50 is excellent.
It has been found that the appropriate range of the amounts is limited between the dashed lines D and B, that is, when the amount of γ phase produced is within the range of 10 to 30%. However, unlike the equilibrium state, the γ phase generated during the hot rolling process is metastable, and it is difficult to accurately grasp the amount of γ phase generated during actual hot rolling at 1150°C. Therefore, it is not practical to limit the amount by the amount of γ phase produced, so if the estimated γ phase produced by the above equation (1) is 10~
It is considered appropriate to limit the range of the amount of C according to the amount of Si in the material so that it falls within the range of 30%. Based on this idea, in this invention, C
The range of C content was derived from the above equation (1), and this was determined as the appropriate range of C content to obtain an excellent level of iron loss. That is, the appropriate range of this C amount is expressed by the following equation (2). 0.37[Si%]+0.27≦log([C%]×10 ³ )≦0.37[Si%]+0.57...(2) This is the first characteristic requirement of this invention. If the C amount is insufficient than the lower limit of the appropriate C amount range according to the Si amount shown by the above formula (2), and therefore the composition corresponds to less than 10% of the γ phase formation amount during hot rolling, , the crystal structure of the product showed a clear band-like fine grain structure, and deterioration of magnetic properties was observed. In addition, products with a composition in which the amount of γ phase produced during hot rolling is 10% or more, as shown by line D in Figure 1, have almost no band-like fine grains and are mostly composed of normally developed secondary recrystallized grains. It turned out that it was. Therefore, in order to split and destroy the coarse crystal grains that have grown abnormally during the hot rolling process when heating the slab at high temperatures, and to prevent the generation of band-like fine grains in the product, it is necessary to generate a γ phase of a predetermined amount or more. ,
It has been found that the required predetermined amount of the γ phase can be achieved by including an amount of C so that 10% or more of the γ phase is generated during hot rolling in an equilibrium state depending on the amount of Si contained. On the other hand, if the amount of C is significantly excessive,
In other words, if the composition corresponds to a composition in which the amount of γ phase produced during hot rolling exceeds 30%, the crystal structure of the product becomes a fine-grained structure with incomplete development of secondary recrystallization, and exhibits extremely poor magnetic properties. Ta. As mentioned above, depending on the amount of Si, the band-shaped grain structure in the product can only be improved if the amount of C is such that γ phase will be produced in the range of 10 to 30% in equilibrium during hot rolling. It is possible to prevent the generation of a fine-grained structure on the entire surface where the generation or development of secondary recrystallized grains is incomplete, and therefore, limiting the amount of C according to the amount of Si using equation (2) above is extremely effective in improving magnetic properties. It turned out to be effective. However, even within the range of 10 to 30% of the amount of γ phase produced in Figure 1, there are still some particles with insufficient iron loss characteristics, and this is seen from the viewpoint of industrial production where stability of magnetic properties is required. From, C according to the above formula (2),
Regulation of the amount of Si alone is still not satisfactory. Therefore, the present inventors conducted research to further improve this and found that 0.006 to 0.020% of C was decarburized during the process from the end of the hot rolling process to the intermediate annealing before the final cold rolling process. They found that it is effective to stably obtain excellent magnetic properties, and made this the second characteristic requirement of the present invention. This requirement was clarified from the following experimental results by the inventors. That is, among the test materials used in the experiment shown in FIG. The magnetic properties of the product and the C characteristics immediately after the end of the hot rolling process and after the intermediate annealing before the final cold rolling of the sample material whose composition is within the range corresponding to 10 to 30% of the amount of γ phase formed at 1150°C during hot rolling. As a result of a detailed investigation of the relationship between the content difference, that is, the decarburization amount ΔC, the results shown in FIG. 2A and B were obtained. In Figure 2, the white circles indicate the group with Si content of 2.8 to 3.1%, and the black circles indicate the group with Si content of 3.3 to 3.5%.
Each group is shown below. As is clear from Figure 2 A and B, excellent magnetic properties are stably obtained when the decarburization amount ΔC is 0.006% or more and 0.020% or less, and C
It has been found that when the ratio is less than 0.006% or more than 0.020%, the magnetic flux density is insufficient and the iron loss also shows a large value, making it impossible to obtain sufficient magnetic properties. In addition, the amount of decarburization during the period from hot rolling to final cold rolling in the production of ordinary silicon steel sheets is about 0.005% or less, so the amount of decarburization in the method of this invention is 0.006 to 0.020% compared to that in the conventional method. Since the amount of decarburization is larger than the normal decarburization amount, when carrying out the method of the present invention, it is usually necessary to carry out active decarburization treatment such as making the intermediate annealing atmosphere decarburizing. In this way, by performing a suitable amount of strong decarburization between the end of hot rolling and before the final cold rolling, it is possible to compensate for the unsatisfactory points of the first requirement explained earlier and to maintain stable excellent magnetic properties. It became possible to obtain it. As mentioned above, the fact that an appropriate amount of decarburization is effective in improving and stabilizing magnetic properties is due to the following crystal structure,
This is also clear from the texture observation results. In other words, when the amount of decarburization is appropriate, the grain size before final cold rolling is uniform and appropriate, and the primary recrystallization texture is improved to a favorable state showing strong accumulation of (110) [001] orientation. As a result, the crystal structure of the product is one in which normal secondary recrystallized grains are sufficiently developed. On the other hand, when the amount of decarburization is insufficient, the grains in the primary recrystallized texture are irregular and lumpy carbides remain, and the primary recrystallized texture has a weak accumulation of (110) [001] orientations. <112> The structure has an inappropriate structure with dispersed orientation, resulting in a mixture of fine grains.
The next recrystallization is in a state of poor development. In addition, in the case of excessive decarburization, the grain size before the final cold rolling is uneven and coarse grains are dispersed, making it inappropriate, and the primary recrystallization texture also decreases in the (110) [001] orientation. Therefore, after the secondary recrystallization, the crystal grains are extremely coarse, and the crystal orientation of these is (110) [001]
Many of the bearings were slightly deviated from the normal direction, and the magnetic properties were therefore insufficient. As _mentioned above, the present inventors have found that an appropriate amount of decarburization is effective in improving and stabilizing magnetic properties. As a result of our efforts to develop a grain-oriented silicon steel sheet with extremely excellent properties of less than 1.00W/Kg, we have discovered that carbides within the grains of the steel sheet cannot be seen with an optical microscope after intermediate annealing before final cold rolling. By combining the above two requirements with a process that controls the precipitation within a specific extremely small range that cannot be achieved and causes the precipitation to occur in a sufficiently large amount, the texture before final annealing can be made into a state where the accumulation of (110) [001] orientation is even stronger. can be improved,
As a result, we newly discovered that secondary recrystallized grains with highly aligned (110) [001] orientation are formed in the secondary recrystallization process during final annealing, resulting in excellent magnetic properties. The third characteristic requirement of the present invention is a treatment for controlling carbides within the crystal grains. The effect of the third requirement will be explained below based on the experimental results of the present inventors. The material used in the experiment was C0.045
%, Si3.20%, Mn0.06%, Se0.025%, and
It is a hot-rolled plate with a thickness of 3.0 mm that has a composition of 0.020% Sb and is finished through normal steel manufacturing, continuous casting, and hot rolling. After annealing such a hot-rolled plate at 950°C for 2 minutes, it was pickled and subjected to the first cold rolling to give an intermediate plate thickness of 0.75mm. After intermediate annealing at 900°C for 3 minutes,
The final cold rolling was carried out with a rolling reduction of 60%, resulting in a final thickness of 0.30 mm. Next, decarburization annealing was performed in a wet hydrogen atmosphere at 800℃, and after coating with MgO, final annealing was performed at 1200℃×10
Time holding annealing was performed to obtain a unidirectional silicon steel plate product. In the above experiment, the decarburization amount ΔC in the intermediate annealing between the cold rolling processes was set to three levels: 0.002%, which is the conventional standard, 0.012%, which is within the limited range of this invention, and 0.025%, which is excessive decarburization. In addition, cooling to 770℃ or less in the cooling process after intermediate annealing is oil quenching (rapid cooling corresponding to a cooling time of about 10 seconds at 770 to 100℃), and immediately aging treatment at 200℃.
It was carried out by varying the time between ~200 seconds. The relationship between the intragrain carbide precipitate size and magnetic properties in the steel sheet after this aging treatment, that is, the steel sheet after intermediate annealing and before final cold rolling, and also the relationship between the carbide precipitate size and 200
Figure 3 shows the relationship with the aging treatment time at °C. The magnetic property plot in Figure 3 shows that the amount of decarburization ΔC is
If 0.002%, mark ○; if ΔC0.012%, mark ●;
The case where ΔC is 0.025% is indicated by a mark ◎. Moreover, as a comparative material in FIG. 3, a sample is shown which was forced air cooled at a cooling rate corresponding to a cooling time of 98 seconds between 770 and 100° C., which is generally used in industrial continuous annealing. As is clear from Fig. 3, the amount of decarburization is
Appropriate amount (● mark) within the requirements of 200
When the aging treatment time at °C is about 10 to 20 seconds, the magnetic flux density B ₁₀ value is 1.94T or more, and the iron loss W _17/50 is
Exhibits extremely excellent magnetic properties of less than 1.00W/Kg,
In addition, the carbide precipitation size in this case is 100 to 500
It is clear that it is in the range of Å. Also, an electron micrograph of the carbide precipitation state in this case (10,000x magnification)
is shown in Figure 4A. However, this electron micrograph is
After intermediate annealing before final cold rolling, the samples were rapidly cooled from 770 to 100°C for 22 seconds, and then immediately aged at 200°C for 10 seconds.The average carbide grain size was 200 Å, and the carbide It is clear that the particles are uniformly and abundantly dispersed. On the other hand, in the case of oil quenching after intermediate annealing (no aging treatment) and aging treatment at 200℃ for 2 seconds, it is clear that the magnetic properties are insufficient regardless of the amount of decarburization, and in this case, the crystallization No intragranular carbide was observed or only a small amount of intragranular carbide was precipitated locally. Furthermore, when the aging treatment at 200°C was performed for 30 seconds or longer, it was clear that the magnetic properties were insufficient regardless of the amount of decarburization, and in this case, the precipitated size of intracrystalline carbides exceeded 500 Å. For reference, an electron micrograph (10,000x magnification) of the state of carbide precipitation before the final cold rolling of a comparative material subjected to industrial standard cooling (cooling time between 770 and 100°C for approximately 98 seconds) after intermediate annealing. is shown in Figure 4B. In this case, the average grain size of intragrain carbide precipitation is approximately 700 Å,
In addition, the magnetic properties were as poor as those obtained when the material was rapidly cooled after intermediate annealing and then subjected to aging treatment at 200°C for 30 seconds or more. Furthermore, from Fig. 3, we can see that when the amount of decarburization ΔC is at the conventional normal level (○ mark) and when there is excessive decarburization (◎
It is clear from the mark) that even if the material is rapidly cooled after intermediate annealing and then immediately subjected to aging treatment at 200°C for about 10 to 20 seconds, the magnetic properties are slightly improved, but not significantly. From the above experimental results, it is possible to improve the magnetic properties by applying a treatment that reduces the carbide size within the crystal grains within the range of 100 to 500 Å after intermediate annealing and before final cold rolling, sometimes on materials with an appropriate amount of decarburization. It turned out that the problem could be improved significantly. Furthermore, the present inventors (A) did not actively decarburize in the intermediate annealing process, and did not perform rapid cooling in the cooling process after the intermediate annealing before the final cold rolling, but instead carried out standard cooling (cooling time required between 770 and 100°C). (approximately 90 seconds), (B) intermediate annealing process
If 0.006 to 0.020% decarburization is performed and standard cooling is performed without rapid cooling in the cooling process after intermediate annealing before final cold rolling, (C) without active decarburization in intermediate annealing process, (D) If the temperature range of 770 to 100℃ is rapidly cooled within 30 seconds in the cooling process after intermediate annealing, and then immediately subjected to aging treatment at 200℃ for about 10 to 20 seconds, (D)
If 0.006 to 0.020% decarburization is performed and the same rapid cooling and aging treatment as in (C) above is performed in the cooling process after intermediate annealing before final cold rolling, the above four types of (A) to (D) When examining the Goss orientation strength of the surface layer of the decarburized annealed sheet before final annealing for the cold rolled sheet obtained by the treatment, it was found that:
The results shown in FIG. 5 were obtained. From Figure 5, when neither decarburization nor rapid cooling-aging treatment is performed
Compared to (A), the Goss orientation strength is about 1.5 times higher in the case of decarburization only (B) and the case of quenching-aging treatment only (C), and furthermore, the It was confirmed that when both the quenching and quenching-aging treatments were applied (D), the Goss orientation strength was approximately 1.7 times higher than that of (A). The reason why the Goss orientation strength is increased by the method of the present invention is considered to be as follows. That is, by decarburizing an appropriate amount, the recrystallization initiation temperature becomes lower in the intermediate annealing before the final cold rolling, which is advantageous for the growth of Goss grains, which are said to recrystallize at a constant temperature, and further increases the recrystallization temperature. The reduction in the amount of α-γ transformation during soaking after crystallization prevents the randomization of the texture and improves the texture to one with strong accumulation in the Goss orientation. In addition, the uniform precipitation and dispersion of ultrafine carbides before the final cold rolling plays a role in expanding the difference in the amount of internal strain accumulation depending on the initial crystal orientation during the final cold rolling, and the subsequent decarburization annealing. When recrystallizing during the heating process, crystal grains with the (110) [001] orientation and crystal orientations in its vicinity, which have a large amount of strain accumulated inside the crystal after cold rolling, start recrystallizing early and preferentially. , it is estimated that a primary recrystallized structure with a stronger Goss orientation is formed.
Therefore, in the method of the present invention, the synergistic effect of the above two effects improves the texture to have a stronger accumulation of Goss orientation. On the other hand, if the amount of decarburization before the final cold rolling is insufficient, the primary recrystallized texture before the final cold rolling will have uneven grain size, fine crystal grains will be distributed in clusters, and the primary recrystallized texture will be has a weak accumulation of (110)[001] directions,
It has an unsuitable structure with relatively strong (111) <112> orientations dispersed, and it is necessary to perform rapid cooling before the final cold rolling.
Even if fine carbides of 100 to 500 Å are precipitated and dispersed uniformly, the effect is small, and as a result, the crystal structure of the product is in a state of poor secondary recrystallization in which fine grains are mixed. In addition, in the case of excessive decarburization, the grain size before the final cold rolling becomes uneven and inappropriate with coarse grains dispersed, and the primary recrystallization texture also becomes (110) [001].
Orientation is decreasing. In addition, due to excessive decarburization, the amount of carbides precipitated was insufficient during cooling during the intermediate elevating and slowing before the final cold rolling, and the desired amount of fine carbides could not be secured by rapid cooling, resulting in However, the crystal structure of the product obtained from this state is dominated by extremely coarse secondary recrystallized grains, and many of these coarse grains have an orientation slightly deviated from the (110) [001] orientation, and therefore are magnetically There is a tendency for the characteristics to become insufficient and the iron loss value to increase. As detailed above, extremely low loss values and sufficiently high magnetic flux densities can be obtained only when a suitable amount of decarburization before the final cold rolling is combined with the desired intra-grain carbide size. Even if the amount of decarburization is within an appropriate range, intragranular carbides are not precipitated or have grown to a size exceeding 500 Å, or conversely, even if the intragranular carbide precipitation size is within the range of 100 to 500 Å, it is necessary to If the amount of decarburization is too much or too little, the initial magnetic properties cannot be obtained. Next, a specific method for sufficiently precipitating ultrafine carbides within the range of 100 to 500 Å within the crystal grains before the final cold rolling as described above will be described. Figure 6 shows the aging treatment temperature, treatment time, and grain interior when the cooling time is 22 seconds between 770 and 100 degrees Celsius after intermediate aging, and the aging treatment is immediately performed in the temperature range of 100 to 300 degrees Celsius. The relationship with carbide precipitation size is shown. From Figure 6, 100 ~
In order to precipitate ultrafine carbides within the range of 500 Å, it was found that it is appropriate to hold the temperature in the temperature range of 150 to 250°C for 2 to 60 seconds, but as long as the temperature is low. . During the cooling after the intermediate elevating and slowing before the final cold rolling, the amount of solid solution of C reaches its maximum at 770°C, so if the cooling rate in the region below 770°C is slow, it will take until the precipitation of fine carbides begins. Coarse carbides precipitate at grain boundaries etc., making it impossible to obtain a predetermined amount of precipitated and dispersed fine carbides, making it impossible to improve the texture.
Cooling before aging treatment was performed by rapidly cooling between 770 and 100°C within 30 seconds. Furthermore, the present inventors have discovered that the temperature range of the cooling process after the intermediate rise and slowing has been particularly overlooked in the past.
We attempted to develop a method that eliminates the need for aging treatment after cooling by strictly controlling the cooling process below 300℃. In other words, as can be understood from Fig. 6, we focused on the fact that ultrafine carbides precipitate within the grains at a temperature range of 300°C or lower and approximately 150°C or higher, and from 770°C to 300°C, we rapidly cooled in the same manner as above. An attempt was made to precipitate intragranular ultrafine carbides during cooling between 300 and 150 degrees Celsius by cooling at various cooling rates over a temperature range of 150 degrees Celsius. Specifically, during cooling after intermediate annealing before final cold rolling, the temperature between 770 and 300°C is rapidly cooled by mist jet cooling for a cooling time of 15 seconds, and then quenched at 300°C.
When cooling the temperature range below ℃ at various cooling rates from water cooling to natural cooling, we investigated the relationship between the cooling time between 300 and 150℃, the size of intragranular carbide precipitation, and the magnetic properties of the product. The results shown in the figure were obtained. However, the amount of decarburization in the intermediate annealing before the final cold rolling is 0.012%, which is within the scope of this invention. From Figure 7, it is clear that in order to obtain an intragranular carbide precipitate size of 100 to 500 Å, the required cooling time between 300 and 150°C should be selected within the range of 8 to 30 seconds; It has become clear that extremely low iron loss values and sufficiently high magnetic velocity densities can be obtained in this case. As mentioned above, within the grains of the steel sheet before the final cold rolling,
An industrial method for dispersing and precipitating ultrafine carbides with a size of 100 to 500 Å is to heat between 770 and 100°C during the cooling process of intermediate annealing before final annealing.
A method of rapidly cooling within 30 seconds and then immediately aging at a temperature of 150 to 250℃ for 2 to 60 seconds, or
Rapid cooling between 770 and 300℃ within 20 seconds, followed by 300℃
It has become clear that a method of controlling the time required for cooling between 8 and 30 seconds between temperatures of 150 DEG C. and 150 DEG C. is appropriate. All of these methods can be easily implemented industrially, but the latter method in particular has the advantage of allowing efficient continuous furnace operation due to shortening of cooling time. Next, the reason for limiting the composition of the silicon steel material applied to the method of the present invention will be explained. Si is an effective element for increasing resistivity and reducing iron loss; if it is less than 2.8%, a sufficiently low iron loss value cannot be achieved, and on the other hand, if it exceeds 4.0%, it becomes extremely brittle. The content was limited to a range of 2.8 to 4.0% because cold rolling workability would be reduced and normal industrial cold rolling would be difficult. In general, products with lower penetration loss can be obtained by increasing the Si content within the range of 2.8 to 4.0%, but in actual operation, increasing the Si content not only increases the Si raw material cost. In other words, a decrease in cold rolling yield leads to an increase in cost, so it is necessary to appropriately select the Si content depending on the desired iron loss level to be obtained. As mentioned above, C should be adjusted within the range of formula (2) according to the amount of Si. In other words, the amount of γ phase formed at 1150°C during hot rolling as shown in Figure 1 is approximately 10~
It is necessary to keep the C content within the range equivalent to 30%.
An example of a specific numerical value based on the above formula (2) is the following second value.
As shown in the table.

[Table] However, if the C content is less than 0.015%, the Si content will be 2.8 to 4.0%.
The required amount of γ phase is not secured within the range of C.
If the amount exceeds 0.10%, the decarburization process will take a long time,
Since this is economically disadvantageous, it is necessary to satisfy the above formula (2) within the range of 0.015 to 0.10% of C. Mn, S, Se, and Sb are all added as inhibitors and are necessary to suppress the growth of primary recrystallized grains in the final annealing and to sharply develop secondary recrystallized grains with (110) [001] orientation. It is an element. However, if the total amount of Mn 0.02 to 0.15%, one or two of S and Se, and Sb exceeds the range of 0.008 to 0.080%, secondary recrystallization will become unstable. Since the desired excellent magnetic properties would not be obtained, it was limited to the above range. The silicon steel material to which the method of the present invention is applied is not particularly limited other than the above-mentioned components, but may contain grain boundary segregated elements such as As, Bi, etc.
Pb, Sn, Te, etc. may be added alone or in combination to enhance the effect of the inhibitor. However, the addition of these grain boundary segregation type elements does not particularly affect the specific effects of this invention. Next, the entire process of manufacturing a unidirectional silicon steel plate by the method of the present invention will be explained in order of process. The silicon steel slab used in this invention may be obtained by the conventional ingot-blowing method or by the continuous casting method, but
The method of the present invention is particularly effective in stabilizing and improving magnetic properties when continuously cast slabs are used. In the method of this invention, a silicon steel slab is heated to about 1250°C or higher, then hot rolled by a known method to form a hot rolled plate with a thickness of 1.2 to 5.0 mm, and heated to 750 to 1100°C as necessary. Normalizing annealing at 750-1100℃ followed by cold rolling two or more times with intermediate annealing at 750-1100℃ to achieve a final plate thickness of 0.15~
The final cold-rolled sheet is 0.50mm. During this process, during the process from after hot rolling to before final cold rolling, that is, during self-annealing after hot-rolling, or at least one of the normalizing annealing or intermediate annealing, the atmosphere is removed. Adjust to carbonaceous properties and decarburize by 0.006 to 0.020% in total. The decarburizing strength of the decarburizing annealing atmosphere should be adjusted appropriately depending on the composition of the material, plate thickness, annealing time, etc. Also, when using the self-annealing time after winding the hot-rolled coil, there is a It is also possible to perform decarburization annealing of the hot rolled sheet by a method such as applying an oxide such as Fe ₂ O ₃ or the like. In addition, in the cooling process of intermediate annealing before the final cold rolling in the cold rolling process, each of the cooling methods described above is used to form a 100 to 500
Ultrafine carbides with a size of 100 Å are precipitated sufficiently, and then cold rolled to a product thickness at a final cold rolling reduction of 40 to 80%. In this invention, the crystal structure is made uniform by performing appropriate decarburization and fine carbide precipitation treatment before the final cold rolling, and the (110) [001]
This effect promotes a strong accumulation of orientation, but this effect cannot be obtained when the final cold rolling reduction is less than 40% or exceeds 80%, and is only achieved when the final cold rolling reduction is in the range of 40 to 80%. It will be done. After the cold rolling process described above is completed, C is usually heated in a wet hydrogen atmosphere at a temperature range of 750 to 850°C.
Perform decarburization annealing to decarburize to 0.003% or less. Then, after applying an annealing separator such as MgO, final annealing is performed. This final annealing is performed at a temperature of approximately 1000°C or higher, preferably in the range of 1050 to 1250°C, for several hours in order to remove impurity elements such as S, Se, and N, and to form an electrically insulating coating mainly composed of forsterite. It is desirable to maintain the above. In this final annealing, when performing high-temperature annealing at 900°C or higher, it is necessary to use hydrogen as an annealing atmosphere to promote the removal of impurities.
When low temperature holding annealing is performed at about 820 to 900°C, any of hydrogen, nitrogen, and argon may be used as the atmosphere. Examples of this invention will be described below. Example 1 A large number of 2.5 mm thick continuous cast slabs containing 3.35% Si, 0.050% C, 0.06% Mn, 0.023% Se and 0.020% Sb were subjected to known hot rolling. After annealing at 950°C for 2 minutes, each hot-rolled sheet was pickled, the intermediate plate thickness was 0.75 mm by the first cold rolling, and then P _H2O /P _H2 = 0.003〜
The decarburization amount ΔC was adjusted to 0.002% and 0.025%, which are outside the range of this invention, and 0.013%, which is within the range of this invention, respectively, by treatment in a wet hydrogen atmosphere in the range of 0.35%.
In the subsequent cooling process, the cooling time between 770 and 100℃ is 22 seconds, and then the temperature is immediately increased to 200℃.
℃ aging treatment (A) without, (B) 10 seconds, (C) 40 seconds
It was applied in different types. Then, final rolling was carried out at a reduction rate of 60% to a thickness of 0.30 mm, and the plate was heated at 830°C in a wet hydrogen atmosphere.
Decarburization annealing was performed for 3 minutes, and after applying MgO slurry, purification annealing was performed at 120°C for 10 hours as a final annealing, and then an insulating coating was applied to obtain a unidirectional silicon steel sheet product. The results of measuring the magnetic properties of these products are shown in Table 3 in correspondence with each process condition.

[Table] As is clear from Table 3, Sample 7 has a decarburization amount ΔC of 0.002%, which is less than the range of this invention.
In both No. 8 and No. 9, sufficiently low iron loss values were not obtained. Of these samples 7, 8, and 9, sample 8, in which the carbide precipitate size is within the range of this invention, has a slightly improved magnetism because the fine grain generation rate in the product is 0%. However, the desired low iron loss value could not be obtained. In addition, sample 13 had an excessive decarburization amount ΔC of 0.025%.
In both Nos. 14 and 15, the fine grain generation rate was 0%, but the secondary recrystallized grains became coarse, and although the magnetic flux density was sufficient, a low iron loss value could not be obtained. On the other hand, Sample 11, which satisfied all the requirements of the present invention, had a sufficiently low iron loss value and high magnetic flux density. Samples 10 and 12, in which the amount of decarburization ΔC is within the range of the present invention but the carbide precipitation size is outside the range of the present invention, both had high magnetic flux density and considerably low iron loss values, but were not in accordance with the present invention. Ultra-low iron loss value as shown in example (sample 11),
However, it was not possible to obtain an ultra-high magnetic flux density. Example 2 Si3.35%, C0.050%, Mn0.06%, Se0.023%,
A large number of 2.5 mm thick hot-rolled plates obtained by performing known hot rolling on continuous cast slabs containing 0.020% Sb were annealed at 950°C for 2 minutes, and then pickled. The intermediate plate thickness was made 0.75 mm by cold rolling, and then during intermediate annealing at 950°C for 2 minutes, the continuous annealing atmosphere was changed to P _H2O /P _H2 = 0.003 to 0.35 using a known method.
The amount of decarburization was adjusted to 0.002%, 0.025%, which is outside the range of this invention, and 0.013%, which is within the range of this invention, and in the subsequent cooling process, the amount of decarburization was varied within the range of 770 to 300°C. The required cooling time was set to 17 seconds or 70 seconds, and then the required cooling time between 300 and 150°C was controlled to 15 seconds or 50 seconds. Then, after final cold rolling with a rolling reduction of 60% to a thickness of 0.30 mm, decarburization annealing was performed at 830°C for 3 minutes in wet hydrogen, and after applying MgO slurry, final annealing was performed.
Purification annealing was performed at 1200°C for 10 hours, and then an insulating coating was applied to obtain a unidirectional silicon steel plate product. The results of examining the magnetic properties of these products are shown in Table 4 in correspondence with each condition.

[Table] As is clear from Table 4, sample 18 that satisfies each requirement of this invention is compared with other samples, that is, samples of comparative examples that lack one or more of the requirements of this invention. , a significantly high magnetic flux density and a significantly low core loss value were obtained, making it a satisfactory unidirectional silicon steel sheet. Example 3 C0.049%, Si3.30%, Mn0.080%, S0.026%,
Regarding a 2.7 mm thick hot rolled plate obtained by performing known hot rolling on a continuously cast slab containing 0.026% Sb,
After pickling, intermediate cold rolling to 0.77mm thickness, then 980℃×
Intermediate annealing for 1.5 minutes was performed in a wet hydrogen atmosphere with P _H2O /P _H2 = 0.25 to achieve a decarburization amount ΔC of 0.015%, and cooling after the intermediate annealing took 12 seconds from 770℃ to 300℃. The time required between 300°C and 150°C was 20 seconds, and the final cold rolling was then carried out to a thickness of 0.27 mm at a rolling reduction of 65%. After that, 830℃ x 3 in a wet hydrogen atmosphere
After applying decarburization annealing for 1 minute and applying MgO slurry, as final annealing, purification annealing was performed at 1200°C x 10 hours after holding at 840°C for 60 hours during heating, and then an insulating coating was applied. A unidirectional silicon steel plate product (sample No. 31) was obtained. For comparison, a hot-rolled sheet with the same composition and thickness as used in the above-mentioned inventive example was 0.77 mm after pickling.
It is intermediately cold rolled to a thick thickness and then subjected to intermediate annealing at 980°C for 1.5 minutes in a normal atmosphere to achieve a decarburization amount of 0.002%.
Cooling after intermediate annealing takes 47 seconds between 770℃ and 300℃, and 45 seconds between 300℃ and 150℃.
0.27 seconds and then final cold rolling with a rolling reduction of 65%.
Finished in mm thickness. Thereafter, decarburization annealing, application of MgO slurry, final annealing, and insulation coating were performed in the same manner as in the case of the present invention example, to obtain a unidirectional silicon steel sheet product (sample No. 30) according to the comparative example. Table 5 shows the results of measuring the magnetic properties of these products.

[Table] As is clear from Table 5, the product of the present invention example (sample No. 31) manufactured by the method of the present invention is:
It was found that the magnetic properties were superior to that of the comparative product (sample No. 30). Example 6 C0.051%, Si3.25%, Mn0.085%, S0.021%,
A 2.0 mm thick hot-rolled plate obtained by performing known hot rolling on a continuously cast slab containing 0.005% Se and 0.026% Sb was washed with wet hydrogen at P _H2O /P _H2 = 0.20 after pickling. Hot-rolled plate annealing at 930°C for 2.5 minutes in an atmosphere (decarburization amount ΔC
= 0.008%), then intermediate cold rolled to a thickness of 0.70 mm, and then heated at 950°C in a wet hydrogen atmosphere with P _H2O /P _H2 = 0.20.
x Intermediate annealing for 2 minutes (decarburization amount ΔC = 0.009%), and cooling after the intermediate annealing is from 770℃ to 100℃
Immediately after cooling, the time required for
Aging treatment was performed at 225°C for 30 seconds, and the reduction rate was further reduced.
It was finished with a final cold rolling of 67% to a thickness of 0.23mm. After that, decarburization annealing was performed at 830°C for 3 minutes in a wet hydrogen atmosphere, and after applying MgO slurry, the final annealing was performed at 850°C for 55 hours and then at 1200°C for 10 minutes.
A unidirectional silicon steel sheet product (sample No. 33) according to an example of the present invention was obtained by subjecting it to purification annealing for a period of time and then applying an insulating coating. For comparison, a hot-rolled sheet with the same composition and thickness as the above-mentioned inventive example was annealed at 930°C for 2.5 minutes (decarburization amount ΔC = 0.002%), and then pickled and
After intermediate rolling to a thickness of mm, intermediate annealing was performed at 950°C for 2 minutes (decarburization amount ΔC = 0.002%), and cooling after the intermediate annealing was performed for 67 seconds between 770°C and 100°C. , the statute of limitations was not applied. Further, after final cold rolling with a rolling reduction of 67% to a thickness of 0.23 mm, decarburization annealing, application of MgO slurry, final annealing, and insulating coating were performed in the same manner as in the example of the present invention. Table 6 shows the results of measuring the magnetic properties of these products.

[Table] As is clear from Table 6, the product of the example of the present invention (sample No. 33) obtained by the method of the invention has superior magnetic properties compared to the product of the comparative example (sample No. 32). It has characteristics. As is clear from the above explanation, according to the manufacturing method of the present invention, the amount of C in the material is adjusted to an appropriate range according to the amount of Si, and the amount of decarburization after hot rolling and before final cold rolling is adjusted to an appropriate range. Moreover, by appropriately controlling the carbides in the grains of the steel sheet before final cold rolling, unidirectional silicon has extremely excellent magnetic properties such as a significantly high magnetic flux density and a significantly low iron loss value that were previously unobtainable. It is possible to stably obtain steel sheets, and unidirectional silicon steel sheets with extremely excellent properties can be obtained without requiring slow cooling at a special high temperature or long-term aging treatment, making it suitable for industrial use. Even when implemented on a large scale, various effects such as high productivity and economy can be obtained.

[Brief explanation of drawings]

Figure 1 is a graph showing the influence of the amount of Si and C contained in the material on the iron loss value of the product, and Figure 2 is a graph showing the effect of the amount of decarburization ΔC after hot rolling before final cold rolling on the magnetic properties of the product. A graph showing the influence, Figure 3 shows the amount of decarburization during intermediate annealing and the amount of decarburization at 200℃ after intermediate annealing.
A graph showing the relationship between aging treatment time, magnetic properties, and carbide precipitation size during aging treatment. Figure 4 is an electron micrograph at a magnification of 10,000 times showing the carbide precipitation state of the steel sheet before final cold rolling. A shows the case where intermediate annealing is followed by rapid cooling and aging treatment according to the present invention, B shows the case where intermediate annealing is followed by standard cooling according to the conventional method, and Figure 5 shows the surface layer of the steel sheet after decarburization annealing. A graph comparing the Goss orientation strength of according to the presence or absence of decarburization in the intermediate annealing process and the presence or absence of rapid cooling-aging treatment after intermediate annealing,
Figure 6 is a graph showing the relationship between aging treatment conditions and carbide precipitation size when the intermediate annealing before the final cold rolling is followed by rapid cooling and further aging treatment. This is a graph showing the relationship between the required cooling time between 300 and 150°C, the carbide precipitation size, and the magnetic properties when the cooling time between 770 and 300°C is rapidly cooled and the required cooling time between 300 and 150°C is varied.

Claims (1)

[Claims] 1 C0.015 to 0.10% (weight%, same hereinafter), Si2.8
~4.0%, Mn0.02~0.15%, and one or both of S and Se and Sb in a total amount of 0.008
A silicon steel material containing ~0.080% Fe with the remainder being substantially Fe is hot rolled, and the resulting hot rolled steel sheet is cold rolled two or more times with intermediate annealing in between to achieve a final cold rolling reduction of 40~ In a series of methods for manufacturing unidirectional silicon steel sheets, the C contained in the silicon steel material is applied within a range of 80% to finish the sheet to a predetermined thickness, and the cold rolled sheet is then subjected to decarburization annealing and final annealing. The amount is determined according to the amount of Si within the range expressed by the following formula: 0.37 [Si%] + 0.27 ≦ log ([C%] × 10 ³ ) ≦ 0.37 [Si%] + 0.57, and hot After the end of rolling and before the end of final cold rolling, increase C from 0.006 to
0.020% decarburization, and in the cooling process after intermediate annealing before final cold rolling, the steel plate is rapidly cooled after intermediate annealing so that the cooling time from 770 to 100℃ is within 30 seconds, and immediately after intermediate annealing to 150 to 100℃. A method for producing a unidirectional silicon steel sheet with excellent magnetic properties, which comprises subjecting the steel sheet to an aging treatment for 2 to 60 seconds within a temperature range of 250°C, and then subjecting it to final cold rolling. 2 C0.015-0.10% (weight%, same below), Si2.8
~4.0%, Mn0.02~0.15%, and one or both of S and Se and Sb in a total amount of 0.008
A silicon steel material containing ~0.080% Fe with the remainder being substantially Fe is hot rolled, and the resulting hot rolled steel sheet is cold rolled two or more times with intermediate annealing in between to achieve a final cold rolling reduction of 40~ In a series of methods for manufacturing unidirectional silicon steel sheets, the C contained in the silicon steel material is applied within a range of 80% to finish the sheet to a predetermined thickness, and the cold rolled sheet is then subjected to decarburization annealing and final annealing. The amount is determined according to the amount of Si within the range expressed by the following formula: 0.37 [Si%] + 0.27 ≦ log ([C%] × 10 ³ ) ≦ 0.37 [Si%] + 0.57, and hot After the end of rolling and before the end of final cold rolling, increase C from 0.006 to
0.020% decarburization, and in the cooling process after intermediate annealing before final cold rolling, the cooling time between 770 and 300°C is controlled within 20 seconds, and the subsequent 300 to 300°C
1. A method for producing a unidirectional silicon steel sheet with excellent magnetic properties, which comprises cooling at 150° C. by controlling the cooling time within a range of 8 to 30 seconds, and then performing final cold rolling.