JP2003193141A - Method of producing grain oriented silicon steel sheet having excellent coating property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably produce a grain oriented silicon steel sheet which has excellent coating properties by causing secondary recrystallization without using an inhibitor. <P>SOLUTION: The grain oriented silicon steel sheet is produced by using a steel slab produced by using molten steel having a composition containing, by mass, ≤0.08% C, 2.0 to 8.0% Si, 0.005 to 3.0% Mn, and 0.005 to 0.3% Cu, and in which the content of Al is reduced to <100 ppm, and the contents of S and Se are reduced to ≤50 ppm, respectively. In this case, as for the steel sheet directly before decarburizing annealing, the concentration ratio of Cu in the surface layer part to that in the central part of the sheet thickness is controlled to ≥1.2, and the concentration ratio of Si is controlled to ≤0.90. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used for a transformer iron core and the like, and particularly to improve the coating properties thereof. Is. [0002] In the production of grain-oriented electrical steel sheets, precipitates called inhibitors are used to preferentially remove {110} <001> -oriented grains called goth-oriented grains during final finish annealing. Subsequent recrystallization is used as a common technique. For example, Japanese Patent Publication No. 40-15644 discloses a method using AlN, MnS as an inhibitor.
Japanese Patent Publication No. 51-13469 discloses an inhibitor.
A method using MnS and MnSe is disclosed, and both are industrially put into practical use. Apart from these, a technique for adding CuSe and BN is disclosed in Japanese Patent Publication No. 58-42244, and Ti, Zr,
A method using a nitride such as V is disclosed in Japanese Patent Publication No. 46-40855. [0003] The method using these inhibitors is a useful method for stably developing secondary recrystallized grains. However, since the precipitates must be finely dispersed, slab heating before hot rolling is performed. It is necessary to carry out at a high temperature of 1300 ° C or higher. However, high-temperature heating of the slab has problems such as an increase in equipment cost and an increase in the amount of scale generated during hot rolling, resulting in a decrease in yield and complicated maintenance of the equipment. On the other hand, a method for producing a grain-oriented electrical steel sheet without using an inhibitor is disclosed in JP-A-64-55339.
No. 2-57635, No. 7-76732 and No. 7-197126. What is common to these techniques is that the {110} plane is intended to grow preferentially using surface energy as the driving force. In order to effectively use the surface energy difference, it is necessary to reduce the plate thickness in order to increase the contribution of the surface. For example, in the technique disclosed in Japanese Patent Laid-Open No. 64-55339, the thickness is limited to 0.2 mm or less, and in the technique disclosed in Japanese Patent Laid-Open No. 2-57635, the thickness is limited to 0.15 mm or less. However, since the thickness of the grain-oriented electrical steel sheet that is currently used is almost 0.20 mm or more, it is difficult to produce a normal grain-oriented electrical steel sheet by the method using the surface energy as described above. Furthermore, in the method using the surface energy, the final finish annealing must be performed while suppressing the formation of the surface oxide layer. For example, an annealing separator such as MgO cannot be applied and annealed. An oxide film similar to that of a normal grain-oriented electrical steel sheet cannot be formed after annealing. For example, a silicate coating is a coating formed when MgO is applied as a main component as an annealing separator, but this coating not only gives tension to the steel sheet surface, but also a phosphate that is applied and baked on it. It is responsible for ensuring the adhesion of the insulation tension coating mainly composed of.
Therefore, when there is no such silicate, the iron loss is greatly deteriorated. In this respect, the hot rolling reduction ratio is 30% or more without forming a silicate film and using an inhibitor component.
A technique for performing secondary recrystallization by setting the hot-rolled sheet thickness to 1.5 mm or less is disclosed in JP-A-11-61263, and a technique for performing orientation accumulation of secondary recrystallized grains in the Goss orientation is disclosed in JP-A 2000-1293.
No. 56 discloses a problem that iron loss is inferior because there is no surface oxide film. However, in the above method, a silicate film having a good appearance and sufficient adhesion cannot be formed as compared with a conventional grain-oriented electrical steel sheet using an inhibitor. [0007] Typical precipitates used as inhibitors include MnS, MnSe, AlN and the like. The effect of reducing these components on film formation is investigated. In particular, S, Se
In the case of electrical steel sheets that do not contain Si,
It was found that the shape of the subscale mainly composed of O ₂ changed significantly. That is, in general, since S and Se have an effect of suppressing internal oxidation, if S or Se in a range included in a grain-oriented electrical steel sheet using a normal inhibitor is contained, the subscale moves into the steel sheet. Oxidation progress is moderately suppressed, resulting in a relatively thin and dense film, but when it is not contained, SiO ₂ exhibits a generation behavior mainly consisting of dendritic growth inside the steel sheet, and then an annealing separator. It was found that the silicate coating formed by the reaction with the above is not dense and does not show sufficient adhesion. Similarly, Al is considered to have an effect of relatively suppressing the formation of SiO ₂ by oxidizing Al instead of Si. Therefore, when Al concentration is reduced, S and Se are reduced. As with the reduction, the subscale form during decarburization annealing deteriorates. Conventionally, many methods for improving the quality of the subscale coating after decarburization annealing have been proposed, but all of them are premised on steel components including inhibitor components.
It did not change the form of the subscale significantly. The present invention has been developed in view of the above circumstances, and in the case of producing a grain-oriented electrical steel sheet using a steel containing no inhibitor as a raw material, a silicate film having excellent adhesion to the steel sheet. It is an object of the present invention to propose a novel method for producing a grain-oriented electrical steel sheet having excellent coating properties. Means for Solving the Problems The elucidation process of the present invention will be described below. As a result of intensive studies to solve the above problems, the inventors have focused on the effect of Cu element addition on the film formation. In other words, were investigated the effect of Cu addition on subscale formed during decarburization annealing the component system containing no inhibitor component, the addition of an appropriate amount of Cu, the sub-scale SiO ₂ principal was mainly dendritic It was found that the shape changed to a thin and dense oxide film mainly composed of spherical or lamellar shapes. However, if a large amount of Cu is added in advance to the steel output component, surface cracking is likely to occur during hot rolling, and the surface properties of the final product may be deteriorated. Therefore, it is important to increase the Cu concentration only in the vicinity of the surface involved in surface oxidation during decarburization annealing. As for the addition of Cu to the grain-oriented electrical steel sheet, Japanese Patent Laid-Open No. 4-341519 discloses a method of adding into steel as a means for reinforcing the inhibition effect, and Japanese Patent Laid-Open No. 3-240922. Discloses a technique for adhering Cu to the surface of a steel sheet after decarburization annealing as means for improving the bend characteristics as well as the magnetic characteristics. However, all of these are based on steel components including an inhibitor component, and no consideration is given to a component system that does not include an inhibitor component. The inventors have also paid attention to Si itself, which is the main raw material for SiO ₂ , as a component that changes the subscale form. In other words, in hot-rolled sheet annealing or intermediate annealing in a series of production processes of grain-oriented electrical steel sheets leading to decarburization annealing, when the steel sheet surface is oxidized to form an oxide scale, the outermost layer Si is consumed. The Si concentration in the vicinity of the surface is lower than that in the central part of the plate thickness. Therefore, by utilizing this decrease in the concentration of Si on the surface, rapid growth of SiO ₂ during decarburization annealing of component systems that do not contain inhibitor components is suppressed, and the subscale morphology is changed from dendritic to spherical or lamellar. It becomes possible to change the shape. As described above, the present invention has been studied on the influence of the Cu and Si concentration distribution in the surface layer of the steel sheet immediately after decarburization annealing on the form of the subscale formed during decarburization annealing. It has been completed. That is, in the present invention, the mass% is C: 0.08.
%, Si: 2.0 to 8.0%, Mn: 0.005 to 3.0% and
Cu: 0.005 to 0.3%, Al less than 100 ppm, S, Se
Steel slabs manufactured using molten steel each reduced to 50 ppm or less are hot-rolled and then subjected to hot-rolled sheet annealing as necessary, followed by one or more cold rollings sandwiching intermediate annealing Then, after decarburization annealing, in the method of manufacturing a grain-oriented electrical steel sheet that is subjected to final finish annealing by applying an annealing separator, the steel layer immediately before decarburization annealing, the surface layer portion Cu to the center of the plate thickness This is a method for producing a grain-oriented electrical steel sheet having excellent coating properties, characterized in that the concentration ratio of Si is 1.20 or more and the concentration ratio of Si is 0.90 or less. DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below. First, the experimental results that led to the present invention will be described. In addition, unless otherwise indicated, the "%" display regarding a component means the mass% (mass%). C: 40 ppm, Si:
3.40%, Mn: 0.25%, Al: 30ppm, S: 5ppm, Se: 5
A steel slab containing ppm, N: 10 ppm and Cu: 0.05%, the balance being Fe and inevitable impurities, is heated to 1150 ° C after continuous casting, and then hot-rolled to a thickness of 2.5 mm by hot rolling Then, at 1000 ° C., the oxygen potential [P
(H ₂ O) / P (H ₂ )] after hot-rolled sheet annealing in an atmosphere of 0.50, then 0.30 mm by cold rolling twice with intermediate annealing
Finished to the final thickness. At this time, the oxygen potential of the intermediate annealing is kept constant at P (H ₂ O) / P (H ₂ ) = 0.35, while the annealing time and the subsequent pickling conditions are variously changed over the thickness direction. The final cold-rolled sheet with Cu and Si concentration distribution was prepared. Subsequently, these were decarburized and annealed in a wet hydrogen atmosphere at 830 ° C., and after that, a final finishing annealing was performed in which the temperature was raised to 1120 ° C. after application of a sintered pure fiber mainly composed of MgO. The results of examining the appearance and bending adhesion of the forsterite film of the final annealed plate thus obtained are shown in Table 1 together with the results of examining the concentration ratio of the surface layer to the center of the thickness of Cu and Si. Here, the concentration ratio of Cu and Si is GDS.
(Glow Discharge Spectrometer) was used to examine the strength distribution in the plate thickness direction, and the evaluation was made by the ratio of the values obtained by removing the background from the measured strength at the plate thickness center and the surface. In addition,
The measurement method is not limited to GDS as long as it can evaluate the concentration of Cu or Si, but SIMS (Secondary Ion Mass Spe
ctroscopy) or other chemical analysis or other chemical analysis. The bending adhesion was evaluated by the minimum diameter at which the film was not peeled off by bending the sample along a round bar having various diameters. [Table 1] As shown in the table, when the Cu concentration ratio is 1.20 or more and the Si concentration ratio is 0.90 or less, a forsterite film having good coating appearance and excellent bending adhesion can be obtained. I understand. In contrast, the Cu concentration ratio and
When either of the Si concentration ratios was not suitable, a good appearance could not be obtained or sufficient bending adhesion could not be obtained. Here, the Si concentration distribution on the surface is mainly
Control can be performed by forming a surface oxide containing Si during intermediate annealing, consuming Si near the surface, and then removing the formed surface oxide by pickling or grinding. Moreover, not only the adjustment of the annealing time as in the above-described experimental example, but also control is possible by changing the oxidizing property and annealing temperature of the annealing atmosphere.
What is necessary is just to adjust Si density | concentration at the time of hot-rolled sheet annealing. On the other hand, regarding the concentration of Cu on the surface,
The pickling conditions performed after the annealing are important. That is, Cu dissolves with nitric acid having oxidizing power, but when pickling with hydrochloric acid or phosphoric acid having weak oxidizing power, Cu does not dissolve but only Fe dissolves.
The concentration of Cu can be relatively increased. However, if the pickling time is long or the concentration is high, it is advantageous for increasing the Cu concentration, but the surface low Si layer formed during annealing is reduced by pickling, so it is appropriate. Needless to say, the acid concentration, liquid temperature, and treatment time must be selected. In the present invention, the reason why secondary recrystallization occurs in steel containing no inhibitor component is not necessarily clear, but is considered as follows. Now, as a result of intensive studies on the reason why Goss orientation grains undergo secondary recrystallization, the inventors have found that the orientation difference angle in the primary recrystallization structure is 20 to 20
It was discovered that the grain boundaries at 45 ° play an important role and reported in Acta Material Vol. 45 (1997), p. 1285. That is, the primary recrystallization structure, which is the state immediately before the secondary recrystallization of the grain-oriented electrical steel sheet, is analyzed, and the grain boundary orientation difference angle is about the grain boundary around each crystal grain having various crystal orientations. When the ratio of the grain boundaries to 20 to 45 ° with respect to the whole was investigated, it was clarified that the Goss orientation had the highest frequency. Grain boundaries with misorientation angles of 20-45 ° are experimental data by CG Dunn et al. (AIME Transaction 188 (1949) 368
According to page), it is a high energy grain boundary. This high energy grain boundary has a messy structure with a large free space within the grain boundary. Grain boundary diffusion is a process in which atoms move through the grain boundary. Therefore, grain boundary diffusion is faster in a high energy grain boundary with a large free space in the grain boundary. It is known that secondary recrystallization occurs with the growth of precipitates called inhibitors, which is controlled by diffusion rate. Precipitates on high energy grain boundaries
Since coarsening preferentially progresses during finish annealing, the pinning is preferentially released and grain boundary migration starts, indicating the mechanism by which goth grains grow. The inventors have further developed this study, and the essential factor of secondary recrystallization of Goss-oriented grains is the distribution of high energy grain boundaries in the primary recrystallization structure, and the role of inhibitors is It has been found that there is a difference in moving speed between high energy grain boundaries and other grain boundaries. Therefore, according to this theory, without using an inhibitor,
If a difference in the moving speed of the grain boundary can be generated, secondary recrystallization can be performed. The impurity elements present in the steel are likely to segregate at the grain boundaries, particularly at high energy grain boundaries, and therefore when there are many impurity elements, there is a difference in the moving speed between the high energy grain boundaries and other grain boundaries. It is thought that is missing. In this regard, if the influence of the impurity elements as described above can be eliminated by increasing the purity of the material, the inherent difference in the moving speed depending on the structure of the high energy grain boundary becomes obvious, and the two goss-oriented grains are It is considered that next recrystallization is possible. Furthermore, in order to enable stable secondary recrystallization using the grain boundary moving speed difference, it is important to keep the primary recrystallization structure as uniform as possible in the particle size distribution. This is because, when a uniform grain size distribution is maintained, the crystal grains other than the Goss orientation grains have a low frequency of low energy grain boundaries with a low grain boundary moving speed, and thus the grain growth is suppressed. By so-called Texture Inhibition effect,
This is because secondary recrystallization proceeds as selective grain growth of goth-oriented grains having the highest frequency of high energy grain boundaries with a high grain boundary moving speed. On the other hand, when the grain size distribution is not uniform, normal grain growth using the grain size difference between adjacent crystal grains as a driving force occurs. Texture Inhibi to be selected
The selective effect of goth-oriented grains does not occur unless the effect is exhibited. However, in industrial production, it is practically difficult to completely remove the inhibitor component, so it is inevitably contained. However, when the hot rolling heating temperature is high, a small amount of solid solution dissolved after heating is present. As a result of the non-uniform fine precipitation of the inhibitor component as an impurity during hot rolling, grain boundary migration is locally suppressed, the particle size distribution becomes extremely nonuniform, and the development of secondary recrystallization is inhibited. Therefore, it is the first to reduce the inhibitor component, but in order to avoid the fine precipitation of the trace amount of the inhibitor component inevitably mixed, in order to make it harmless, the heating temperature before hot rolling is within a rollable range, It is effective to keep it as low as possible. Next, the reason why the component composition of the material slab is limited to the above range in the present invention will be described. C: 0.08% or less Magnetic aging does not occur when the C content exceeds 0.08% 50ppm
C is limited to 0.08% or less because it is difficult to reduce it to below. Si: 2.0 to 8.0% Si is an element useful for increasing the electrical resistance of steel and reducing iron loss, so 2.0% or more is contained. However, if the content exceeds 8.0%, the workability is remarkably lowered and cold rolling becomes difficult. Therefore, the Si content is limited to the range of 2.0 to 8.0%. Mn: 0.005 to 3.0% Mn is an element useful for improving the hot workability, but if the content is less than 0.005%, its addition effect is poor,
On the other hand, if it exceeds 3.0%, the magnetic flux density will be reduced, so the Mn content should be in the range of 0.005 to 3.0%. Cu: 0.005 to 0.3% Cu is required to be contained at least 0.005% in order to obtain the above-described film improvement effect. However, if it exceeds 0.3%, surface cracks occur during hot rolling, and the surface of the product. Since the properties may deteriorate, the Cu content is limited to a range of 0.005 to 0.3%. Al: less than 100 ppm, S and Se are 50p each
In addition, it is indispensable to reduce the content of Al, which is an impurity element, to less than 100 ppm, and to reduce S and Se to 50 ppm or less, preferably 30 ppm or less, in order to achieve good secondary recrystallization. In addition, N and nitride-forming elements such as Ti, Nb, B, Ta, and V can be reduced to 50 ppm or less to prevent deterioration of iron loss and ensure good workability. It is valid. As described above, the essential component and the suppressing component have been described. However, in the present invention, other elements described below can be appropriately contained. Ni: 0.005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to
At least one Ni selected from 0.50%, P: 0.005 to 0.50%, and Cr: 0.01 to 1.50% is a useful element that improves the magnetic properties by improving the hot rolled sheet structure. However, if the content is less than 0.01%, the improvement in magnetic properties is small. On the other hand, if it exceeds 1.50%, secondary recrystallization becomes unstable and the magnetic properties deteriorate.
0.005 to 1.50%. Sn, Sb, P, and Cr are elements useful for improving the iron loss. If any of the elements does not satisfy the lower limit of the above range, the effect of improving the iron loss is small. Since the development of the next recrystallized grains is inhibited, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%,
It is necessary to contain P in the range of 0.005 to 0.50% and Cr: 0.01 to 1.5%. Next, the manufacturing process of the present invention will be described. The molten steel adjusted to the above preferred component composition is refined by a known method using a converter, an electric furnace, etc., and if necessary, after vacuum treatment, etc., using a normal ingot forming method or continuous casting method Manufacture slabs. Also, using direct casting method, 100
A thin cast slab having a thickness of mm or less may be directly produced. The slab is heated and hot-rolled by a normal method, but may be subjected to hot rolling immediately after casting without being heated. In the case of a thin slab, hot rolling may be performed, or the hot rolling may be omitted and the subsequent process may be performed as it is. It is particularly desirable to suppress the slab heating temperature before hot rolling to 1250 ° C. or less in order to reduce the amount of scale generated during hot rolling. Also,
It is desirable to lower the slab heating temperature in order to realize a uniform sized primary recrystallized structure by making the crystal structure finer and the harmful effects of the unavoidably mixed inhibitor components. Next, hot-rolled sheet annealing is performed as necessary.
In order to develop Goss tissue in the product board,
The hot-rolled sheet annealing temperature is preferably in the range of 800 to 1100 ° C. This is because when the annealing temperature of the hot-rolled sheet is less than 800 ° C, the band structure in the hot-rolling remains and it becomes difficult to realize the primary recrystallized structure of the sized particles, thereby inhibiting the development of secondary recrystallization. On the other hand, when the hot-rolled sheet annealing temperature exceeds 1100 ° C, the unavoidably mixed inhibitor components dissolve and re-precipitate non-uniformly during cooling, making it difficult to achieve a sized primary recrystallized fabric. This is also because the development of secondary recrystallization is inhibited. Further, when the hot-rolled sheet annealing temperature exceeds 1100 ° C., the grain size after hot-rolled sheet annealing is too coarse, which is extremely disadvantageous for realizing a primary recrystallized structure of sized particles. After the hot-rolled sheet annealing, the steel sheet is subjected to cold rolling at least once with one or more intermediate annealings, followed by decarburization annealing.
C does not cause magnetic aging 50ppm or less, preferably 30ppm
Reduce to: In the cold rolling described above, the rolling temperature is raised to 100 to 250 ° C, or the aging treatment in the range of 100 to 250 ° C is performed once or a plurality of times during the cold rolling, It is effective in developing Gothic tissue. The decarburization annealing after the final cold rolling is preferably performed at a temperature of 700 to 1000 ° C. using a humid atmosphere. Moreover, you may use together the technique which increases Si amount by the siliconization method after decarburization annealing. Here, by appropriately controlling the annealing temperature, time, atmospheric oxidation degree, and pickling conditions in hot-rolled sheet annealing and intermediate annealing until the above decarburization annealing, the surface layer part with respect to the center part of the sheet thickness Cu concentration ratio
It is important to control 1.20 or more and Si concentration ratio to 0.90 or less. In the present invention, the surface layer portion of the steel sheet is
Thickness up to 1/10 depth. For example, when the thickness is 0.30mm, it means up to 30μm from the surface of the steel plate. Thereafter, a secondary recrystallization structure is developed and a silicate film is formed by applying a final finish annealing by applying an annealing separator. Final finish annealing must be performed at 800 ° C or higher for secondary recrystallization.
The heating rate up to 0 ° C. does not have a great influence on the magnetic properties, so any conditions are acceptable. Thereafter, flattening annealing is performed to correct the shape. Then, after the above-described flattening annealing, for the purpose of improving the iron loss, it is advantageous to provide an insulating coating that imparts tension to the steel sheet surface. Furthermore, it goes without saying that known magnetic domain refinement techniques can be applied. Example 1 C: 200 ppm, Si: 3.30%, Mn: 0.20%, Al: 25 ppm,
A steel slab containing S: 4 ppm, Se: 5 ppm, N: 12 ppm and Cu: 0.10%, with the balance being Fe and inevitable impurities, was hot-rolled after continuous casting, and then 950 ° C. for 60 seconds. After hot-rolled sheet annealing, it was pickled and finished to a final sheet thickness of 0.35 mm by cold rolling. At this time, the annealing temperature and oxygen potential in the hot-rolled sheet annealing and the pickling conditions after the hot-rolled sheet annealing were changed variously, and various kinds of Cu in the sheet thickness direction were changed.
And the final cold rolled sheet with Si concentration distribution was fabricated. In addition,
The pickling temperature was constant at 80 ° C. and the pickling time was 60 seconds. Next, these were decarburized and annealed at 830 ° C in a wet hydrogen atmosphere,
Then, after applying an annealing separator mainly composed of MgO, 1120
Final finish annealing was performed to raise the temperature to 0 ° C. The results of examining the appearance and bending adhesion of the forsterite film of the final annealed plate thus obtained, together with the results of examining the concentration ratio of the surface layer part to the center part of the thickness of Cu and Si using GDS, It is shown in 2. [Table 2] As is clear from the figure, the Cu concentration ratio is 1.20.
Sample Nos. 1 and 2 having a Si concentration ratio of 0.90 or less were able to obtain a forsterite film having a uniform and good appearance and excellent bending adhesion. On the other hand, all of the sample Nos. 3 to 5 in which the scale formation at the time of hot-rolled sheet annealing was insufficient or the subsequent pickling conditions were inappropriate,
Because the Cu concentration ratio and Si concentration ratio are out of the appropriate range, the entire fosterite film is thin or incompletely formed.
The film adhesion was also poor. Example 2 C: 300 ppm, Si: 3.40%, Mn: 0.30%, Al: 40 ppm,
S: 5 ppm, Se: 4 ppm, N: 15 ppm and Cu: 0.25%
The steel slab having a composition of Fe and unavoidable impurities is hot-rolled after continuous casting, and then in an atmosphere having an oxygen potential [P (H ₂ O) / P (H ₂ )] of 0.60 1000
After hot-rolled sheet annealing for 60 seconds at ℃, sandwich intermediate annealing 2
The final sheet thickness was 0.30 mm by cold rolling.
At this time, the intermediate annealing condition is 1000 ° C., 60 seconds, the oxygen potential during annealing and the subsequent pickling conditions are variously changed,
The final cold-rolled sheets with various Cu and Si concentration distributions in the sheet thickness direction were prepared. Subsequently, these were decarburized and annealed at 840 ° C. in a wet hydrogen atmosphere, and then a final finish annealing was performed in which the temperature was raised to 1100 ° C. after applying an annealing separator mainly composed of CaO. The results of examining the appearance and bending adhesiveness of the silicate coating on the final annealed plate thus obtained, together with the results of examining the concentration ratio of the surface layer portion with respect to the center portion of the thickness of Cu and Si using GDS, 3 shows. [Table 3] As shown in the table, Sample Nos. 1 and 2 whose Cu concentration ratio and Si concentration ratio satisfy the scope of the present invention both have a uniform and good appearance and excellent bending adhesion. A silicic oxide coating could be obtained. On the other hand, all of the sample Nos. 3 to 5 where the scale formation during the intermediate annealing was insufficient, or the subsequent pickling was excessive, and the Cu concentration ratio and the Si concentration ratio were out of the appropriate ranges, were all silicates. The film was thin or was hardly formed and was incomplete, and the film adhesion was inferior. Thus, according to the present invention, when a grain-oriented electrical steel sheet is produced by a method of causing secondary recrystallization without using an inhibitor, the Cu of the surface layer portion with respect to the center portion of the plate thickness is produced. By appropriately controlling the concentration ratio and the Si concentration ratio, it is possible to stably obtain a grain-oriented electrical steel sheet having a silicate film having good coating appearance and excellent coating adhesion.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuyuki Hayakawa             1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama             Shi) Kawasaki Steel Co., Ltd. Mizushima Works (72) Inventor Mitsumasa Kurosawa             1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama             Shi) Kawasaki Steel Co., Ltd. Mizushima Works F-term (reference) 4K033 AA02 JA04 LA02 RA04 SA02                       TA01                 5E041 AA02 CA02 HB15 NN01

Claims (1)

[Claim 1] In mass%, C: 0.08% or less, Si: 2.0 to
8.0%, Mn: 0.005 to 3.0% and Cu: 0.005 to 0.3%
A steel slab manufactured using molten steel containing less than 100 ppm Al and less than 50 ppm each of S and Se is hot-rolled and then subjected to hot-rolled sheet annealing as necessary.
In a method for producing grain-oriented electrical steel sheets, which is subjected to cold rolling at least twice with intermediate or intermediate annealing, followed by decarburization annealing, and then applying final finish annealing by applying an annealing separator, immediately before decarburization annealing. For the steel sheet, the concentration ratio of Cu in the surface layer portion relative to the center portion of the plate thickness is 1.20 or more, and the concentration ratio of Si is 0.
A method for producing a grain-oriented electrical steel sheet having excellent coating properties, characterized by being 90 or less.