JP4604827B2 - Manufacturing method of unidirectional electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a unidirectional electrical steel sheet having excellent magnetic properties and coating properties at a low cost.

  The grain-oriented electrical steel sheet is mainly used as an iron core material for transformers and other electric devices, and is required to have excellent magnetic properties such as magnetic flux density and iron loss value. As a general manufacturing method, a slab having a thickness of 100 to 300 mm is heated to a high temperature of about 1350 ° C. or more, hot-rolled, and then subjected to hot-rolled sheet annealing as necessary, or once or A complex process in which the final sheet thickness is obtained by cold rolling at least twice with intermediate annealing, and after decarburization annealing, an annealing separator is applied, followed by final finishing annealing for the purpose of secondary recrystallization and purification. The crystal grains of {110} <001> orientation are grown by secondary recrystallization during final finish annealing.

  In order to effectively develop such secondary recrystallization, it is necessary to first disperse a precipitated dispersed phase called an inhibitor that suppresses the growth of primary recrystallized grains to a uniform and appropriate size. . As such an inhibitor, those having low solubility in steel such as sulfides, Se compounds and nitrides represented by MnS, MnSe, AlN and BN are used, and slab heating before hot rolling is used. At times, a method in which the inhibitor is completely dissolved and finely precipitated in the subsequent steps is employed. In this case, in order to sufficiently dissolve the inhibitor, it is necessary to perform slab heating at a temperature of about 1350 to 1400 ° C., which is about 200 ° C. higher than the slab heating temperature of ordinary steel.

However, high temperature slab heating as described above has the following drawbacks.
(A) The energy intensity is high for high temperature heating.
(B) Melt scale is likely to occur and slab sag is likely to occur, so that surface defects of the product are likely to occur.
(C) Overdecarburization of the slab surface layer is likely to occur.

  In order to solve the problems (b) and (c), an induction heating furnace is employed, but the problem of an increase in energy cost remains. Therefore, many studies have been made to reduce the slab heating temperature in order to save energy and reduce costs.

  For example, Patent Document 1 discloses a technique for lowering the slab heating by setting Mn to 0.08 to 0.45% and S to 0.007% or less, and Patent Document 2 discloses adding Cr to this. A technique for stabilizing secondary recrystallization is disclosed. All of these are characterized in that the amount of S is reduced to achieve solid solution of MnS during slab heating. However, these techniques have a problem that variations in magnetic characteristics in the coil width direction and the longitudinal direction are likely to occur, and have been limited to laboratory-scale manufacturing means. The cause is destabilization of secondary recrystallization due to insufficient function of an inhibitor that substitutes for MnS. The above-mentioned technique contains 0.010 to 0.060% of acid-soluble Al and 0.0030 to 0.0130% of N and uses AlN as an inhibitor. However, since the slab heating temperature is low and AlN cannot be completely dissolved, The magnetic properties were not stabilized due to insufficient inhibitory force or partial fluctuations in inhibitory force.

  As means for making up for such drawbacks, Patent Document 3 discloses a technique for stabilizing secondary recrystallization by promoting nitrogen absorption during secondary recrystallization annealing. A similar technique for nitriding during secondary recrystallization annealing by adding nitride in the annealing separator and stabilizing secondary recrystallization is also disclosed in Patent Document 4. However, the technique of nitriding during secondary recrystallization annealing still cannot sufficiently stabilize the expression of secondary recrystallization due to differences in the amount of nitriding in the longitudinal and width directions of the coil. .

  In order to solve the above problems, Patent Document 5, Patent Document 6, and Patent Document 7 disclose techniques for stabilizing secondary recrystallization by nitriding a steel plate after decarburization annealing and before secondary recrystallization annealing. It was done. However, the method of performing the nitriding treatment before the secondary recrystallization annealing has a problem of requiring new equipment and increasing the cost.

  On the other hand, various attempts have been made to produce grain-oriented electrical steel sheets without using inhibitors that have been considered essential so far. For example, Patent Literature 8, Patent Literature 9, Patent Literature 10, and Patent Literature 11 disclose techniques that utilize tertiary recrystallization. However, since these are all methods that utilize a surface energy difference, Limited to thin thickness. Therefore, the thickness of the grain-oriented electrical steel sheet currently used as a product is almost 0.20 mm or more, and it is difficult to manufacture a normal product by the above method.

However, in recent years, as an important point in the development of secondary recrystallization, in addition to the presence of an inhibitor, the orientation difference angle between adjacent crystal grains in the primary recrystallization structure has attracted attention. That is, it is reported in Non-Patent Document 1 that a grain boundary (high energy grain boundary) having an azimuth difference angle of 20 to 45 ° plays an important role, and based on this, a directional electromagnetic without using an inhibitor is reported. Steel plate research has been actively conducted again.
For example, Patent Document 12 discloses a technique (inhibitorless method) capable of industrially producing a grain-oriented electrical steel sheet without including an inhibitor component in a steel slab.

In order to improve and stabilize the properties of the grain-oriented electrical steel sheet produced by this inhibitorless method, Patent Document 13 suppresses the contents of N and S according to [ppmN] ² + [ppmS] ² ≦ 6400, The rate of temperature increase from 600 ° C. to 750 ° C. in decarburization annealing is controlled to 15 ° C./s or more, and the atmospheric oxidizing property P (H, which is the ratio of water vapor partial pressure to hydrogen partial pressure in the soaking process of decarburization annealing ₂ O) / P (H ₂ ) is a technique for controlling the range to 0.6 or less, and Patent Document 14 contains 0.1 to 9.0 parts by weight of Ti oxide as an annealing separator with respect to 100 parts by weight of MgO. And the final finish annealing includes a step of holding in the temperature range of 900 ° C. to 1050 ° C. for 5 hours to 15 hours in an atmosphere having an inert gas content of 50 vol% or more. A technology that retains in the temperature range of 950 ° C or higher in the process for 2 hours or more and 10 hours or less is more special In Reference 15, the crystal grain size in the steel sheet after the primary recrystallization annealing is in the range of 8 to 25 μm, and the average heating rate of 800 to 900 ° C. in the temperature raising process of the secondary recrystallization annealing is 0.5 to 5 ° C./h. A technique is disclosed in which the difference in the amount of nitrogen in the steel sheet between 900 ° C. and 800 ° C. is set in the range of −10 ppm to +25 ppm in the temperature raising process of the secondary recrystallization annealing.

JP 59-56522 JP 59-190325 A JP 62-70521 A Japanese Patent Laid-Open No. 62-40315 JP-A-2-200732 JP-A-4-183817 JP-A-4-235222 JP-A-64-55339 JP-A-2-57635 Japanese Unexamined Patent Publication No. 7-76732 Japanese Unexamined Patent Publication No. 7-197126 JP 2000-129356 JP Japanese Patent Laid-Open No. 2001-158919 Japanese Patent Laid-Open No. 2004-190053 JP 2004-218024 A Act Material 45 (1997) 1285

  However, when compared to grain-oriented electrical steel sheets manufactured using conventional inhibitors, there are still inferior magnetic properties and stability of the coating properties, especially when the steel sheet is wound into a coil and subjected to final finish annealing. Due to the fact that the magnetic properties and film properties may deteriorate in the width direction or longitudinal direction of the strip, it is still necessary to stably produce products with excellent quality and further improve the yield. It left room for improvement.

  The present invention has been developed in view of the above-described situation, and has a uniform forsterite insulating coating that has no defects over the entire width and length of the coil and that has excellent adhesion, and has excellent magnetic properties. It aims at proposing the method which can manufacture a steel plate at low cost.

The elucidation process of the present invention will be described below.
The inventors first tried to improve and stabilize the magnetic characteristics and film characteristics based on the techniques of Patent Documents 14 and 15 already proposed. Unless otherwise specified, “%” in relation to ingredients means mass%.

  First, regarding the material components, the upper limits of acid-soluble Al and N were required to be less than 100 ppm and less than 60 ppm, respectively, as in the above technology, but acid-soluble Al should contain a trace amount of 40 ppm or more. Therefore, the oxide film formed on the steel sheet surface during decarburization annealing becomes dense, the increase and decrease in nitrogen during secondary recrystallization annealing is suppressed, and the accumulation of secondary recrystallized grains in the Goss orientation improves, and the magnetic It has been found that the properties are improved. Therefore, the component range of acid-soluble Al is set to 40 ppm or more and less than 100 ppm. Further, N was found to be contained in an amount of 30 ppm or more in order to suppress the increase or decrease in nitrogen during secondary recrystallization annealing, so the component range was set to 30 ppm or more and less than 60 ppm. Furthermore, in order to produce a grain-oriented electrical steel sheet by the inhibitorless method, the upper limit of (S + 0.405Se) needs to be less than 50 ppm. This is because, when the total amount of these is 50 ppm or more, secondary recrystallization becomes difficult and the magnetic properties deteriorate.

Furthermore, Sb very effectively suppresses the increase in the amount of steel sheet nitrogen during secondary recrystallization annealing, so it is an indispensable element for obtaining excellent magnetic properties and stabilizing magnetic properties. In order to exert the effect sufficiently, it is necessary to add 0.03% or more. However, if it exceeds 0.30%, the decarburization at the time of decarburization annealing becomes very bad and unsuitable for industrial mass production, so the component range must be 0.03% or more and 0.30% or less. .
However, Sb, on the other hand, is very effective in reducing the oxidation rate of the steel sheet during decarburization annealing, so increasing the amount of Sb is thought to result from a decrease in the amount of oxide in the decarburized annealing plate subscale. Increased product coating defects.

Therefore, as a result of intensive investigations on means for suppressing this film defect, it has been newly found that increasing the amount of Mn in steel according to the amount of Sb is effective for suppressing this defect.
That is, when Sb: 0.03% or more and 0.30% or less and Mn: {0.04 + Sb (%)}% or more and 0.50% or less, it is found that a grain-oriented electrical steel sheet having excellent magnetic properties and film properties can be stably produced. It was. The upper limit of the Mn amount is 0.30% because the upper limit value of the Sb amount is 0.30%. Therefore, the upper limit of the Mn amount should be at least the lower limit value (0.34%) in that case. Not only is it disadvantageous in terms of cost, but also causes a decrease in magnetic flux density, so 0.50% was set.

  Secondly, regarding the composition of the annealing separator, as disclosed in Patent Document 14, even in the inhibitorless component system, it is effective to improve the film properties by adding a Ti compound to magnesia. Therefore, as a result of examining the proper blending amount of the Ti compound in the component system of the present invention, as a result of applying an annealing separator containing 0.3 to 8 parts by weight of the Ti compound in terms of Ti with respect to 100 parts by weight of magnesia. Has been found to be effective in improving coating properties.

  Finally, as for the secondary recrystallization annealing pattern, disclosed in Patent Document 15 is “the average temperature increase rate from 800 ° C. to 900 ° C. in the temperature increase process of secondary recrystallization annealing is 0.5 to 5 ° C./h. Based on the technology of `` within the range '', as a result of examining the temperature increase pattern of secondary recrystallization annealing in the component system of the present invention, the residence time in the temperature range of 800 ° C to 900 ° C is 40 hours to 150 hours It has been found effective to improve the magnetic properties.

In addition to these, the inventors have also studied the effect of the finish rolling conditions during hot rolling in the inhibitorless component system on the fluctuation of the magnetic properties in the coil longitudinal direction.
As a result, by changing the inlet temperature during finish rolling to 940 ° C or higher and the outlet temperature to 800 ° C or higher and 900 ° C or lower, fluctuations in the magnetic properties in the coil longitudinal direction can be suppressed, improving magnetic properties. Newly found to be effective.

  That is, in the inhibitorless component system of the present invention, it is desirable that S and Se as impurities are less, but in actual operation, S is contained to some extent as an impurity, so that MnS and Cu are present in the steel. CuS is formed. When the influence on the secondary recrystallization expression by MnS or CuS greatly changes in the longitudinal direction of the coil, it causes the magnetic characteristics to fluctuate greatly in the longitudinal direction of the coil. In order to suppress the fluctuation as much as possible and further improve the characteristics, it has been determined that the above finish rolling conditions are extremely effective.

In addition, the inventors have also studied the influence of the composition of the annealing separator in the inhibitorless component system on the properties and magnetic properties of the forsterite insulating coating.
This is because many proposals have been made to improve the coating properties and magnetic properties by controlling the composition of the annealing separator, but most of them are MnS, MnSe, AlN, etc. This is because those using an inhibitor or those that form an inhibitor such as (Al, Si) N by nitriding after decarburization annealing, and in the inhibitorless component system, there has been little research on these.

Therefore, when the additive other than the Ti compound to be blended in the annealing separator was examined, in addition to the Ti compound, magnesia: 100 parts by weight, and 0.2 to 5 parts by weight of the Sr compound in terms of Sr However, it has been found that there is an effect in further improving the magnetic characteristics and the film characteristics.
That is, as long as the steel sheet is wound into a coil shape and subjected to final finish annealing, there is a certain difference in annealing conditions such as heat history and atmosphere in the inner, middle, and outer winding portions of the coil. However, it has been found that it is extremely effective to add the above additives to the annealing separator in order to suppress the difference in magnetic properties and film properties due to the difference as much as possible and further improve the properties. It is.

The present invention has been developed based on the above findings, and the gist of the present invention is as follows.
(1) By mass%, C: 0.01 to 0.10%, Si: 2.5 to 4.5%, acid-soluble Al: 40 ppm to less than 100 ppm, N: 30 ppm to less than 60 ppm, Sb: 0.03 to 0.30%, Mn: {0.04 + Sb ( %)}% Or more and 0.50% or less and (S + 0.405Se): Hot rolling after heating a silicon steel slab containing less than 50 ppm and the balance of Fe and inevitable impurities at a temperature of 1250 ° C or less Then, after performing hot-rolled sheet annealing as necessary, perform cold rolling at least once with intermediate or intermediate annealing, followed by decarburization and primary recrystallization annealing, followed by annealing separation with magnesia as the main component In the method for producing a unidirectional electrical steel sheet comprising a series of steps for applying a final finishing annealing consisting of secondary recrystallization annealing and purification annealing after applying the agent,
a) The finish rolling entry temperature during hot rolling should be 940 ° C or more and the finish rolling exit temperature should be 800 ° C or more and 900 ° C or less,
b) In the annealing separator, magnesia: 0.3 to 8.0 parts by weight of Ti compound in terms of Ti with respect to 100 parts by weight,
c) In the Atsushi Nobori process of secondary recrystallization annealing, manufacturing method of an oriented electrical steel sheet you characterized in that the residence time in the temperature range of 800 ° C. or higher 900 ° C. or less than 40 hours or more 150 hours.

In (2) above (1), further in the annealing separator, magnesia with respect to 100 parts by weight of the Sr compound one oriented electrical steel sheet you characterized by the inclusion 0.2-5 parts by weight Sr terms Production method.

(3) In the above (1) or (2), the silicon steel slab is further mass%, Sn: 0.03-0.50%, Cu: 0.03-0.50%, Ni: 0.03-0.50%, Cr: 0.03-0.30 %, P: 0.01~0.10% and Mo: 0.005 to 0.10% 1 kind or production method of an oriented electrical steel sheet you characterized by containing two or more kinds selected from among.

  According to the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties can be produced at low cost by low-temperature slab heating using a material in which an inhibitor component is not contained in the steel slab, that is, Al, S, etc. are at an impurity level. Can be obtained at

Hereinafter, the experimental results that led to the present invention will be described.
(Experiment 1)
C: 0.02 to 0.06%, Si: 3.0 to 3.5%, acid-soluble Al: 40 ppm to less than 100 ppm, N: 30 ppm to less than 60 ppm, Sb: 0.01 to 0.30%, Mn: 0.05% to 0.50%, (S + 0.405Se ): Less than 50 ppm, Cu: 0.01 to 0.50%, Cr: 0.01 to 0.30%, P: 0.002 to 0.10% of the component range, with the balance being a large number of vacuum steel ingots with a composition of Fe and inevitable impurities, 1200 After heating to ° C., hot rolling was performed, and after hot-rolled sheet annealing at 950 to 1100 ° C., the final sheet thickness was rolled to 0.29 mm by cold rolling. Then, after decarburization and primary recrystallization annealing at a temperature of 800 to 900 ° C. in H ₂ —H ₂ O—N ₂ , magnesia is the main component, and magnesia: 0.1 to 20.0 weight with respect to 100 parts by weight After applying a part of TiO ₂ containing annealing separator, in the secondary recrystallization annealing temperature rise process, the residence time in the temperature range of 800 ° C or more and 900 ° C or less is set to 10 hours or more and 200 hours or less A final finish annealing consisting of recrystallization annealing and purification annealing was performed. Thereafter, the sample was washed with water to remove the unreacted annealing separator, and after the appearance of the coating film of the sample was examined, a coating containing magnesium phosphate, colloidal silica and chromic acid as main components was applied.
The magnetic properties (magnetic flux density B ₈ , iron loss W _17/50 ) and film adhesion of the samples thus obtained were investigated. The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.

First, among the large number of samples, Mn is 0.08 to 0.14%, Sb is 0.04 to 0.06%, and the results of investigating the effect of the amount of TiO ₂ added in the annealing separator on the film adhesion. As shown in FIG.
As shown in the figure, although there are some exceptions, magnesia: When TiO ₂ is added 0.3 to 8 parts by weight in terms of Ti with respect to 100 parts by weight, relatively good film adhesion can be obtained. I understand.

Similarly, it is a component that satisfies Mn: 0.08-0.14% and Sb: 0.04-0.06%. During the temperature increase process of secondary recrystallization annealing, the residence time in the temperature range of 800 ° C or higher and 900 ° C or lower becomes the magnetic property. The result of investigating the influence is shown in FIG.
As shown in the figure, although there are some exceptions, it can be seen that relatively excellent magnetic properties can be obtained when the residence time in the temperature range of 800 ° C to 900 ° C is 40 hours to 150 hours. .

Based on the above analysis results, magnesia: 0.3 to 8 parts by weight of TiO ₂ in terms of Ti is added to 100 parts by weight, and in the temperature range of 800 ° C to 900 ° C in the temperature rising process of secondary recrystallization annealing. The effect of the amount of Mn and Sb in the material on the magnetic properties and film properties was investigated under the condition that the residence time was 40 hours or more and 150 hours or less. The obtained results are shown in FIGS. 3 (a) and 3 (b).
According to the figure, when Sb is 0.03% or more and Mn: {0.04 + Sb (%)}% or more, it is understood that a grain-oriented electrical steel sheet excellent in both magnetic properties and film properties can be obtained.

  In addition, as a technique for improving the film properties by increasing the amount of Mn in steel, there is a technique disclosed in Patent Document 3 and the like. However, according to examples, these contain 0.02 to 0.03% of acid-soluble Al as an inhibitor. A material using AlN, a material containing 0.02 to 0.03% of acid-soluble Al was subjected to nitriding after decarburization annealing, or nitrogen absorption was promoted during secondary recrystallization to use AlN as an inhibitor. The purpose of increasing the amount of Mn was to improve the tension and adhesion of the forsterite film by forming an appropriate amount of MnO by high-temperature oxidation on the steel sheet surface layer during finish annealing.

However, unlike the above technique, the inhibitor-less component system of the present invention contains less than 100 ppm of acid-soluble Al in the raw material component. The film formation process when acid-soluble Al is contained in an amount of about 0.02% or more is described in “Journal of Materials Engineering and performance Vol.3 (1994) p. 214 (“ Glass Film Structure of Grain-Oriented Silicon Steel Using Aluminum Nitride as Inhibitor ” ) ”And“ Materials and Processes CAMP-ISIJ, Vol.6 (1993) -676 (Structural Analysis of Finished Annealed Films on Directional Silicon Steel Sheets) ”. Different from the case. Therefore, it can be estimated that the influence of the amount of Mn in steel is different between the case where the acid-soluble Al content is 0.02 to 0.03% and the case where it is not.
That is, the above-described findings are novel findings obtained particularly in relation to the amount of Sb under an inhibitorless component system different from the material component of the grain-oriented electrical steel sheet using the conventional inhibitor.

Furthermore, in the inhibitorless component system, when the amount of Mn in steel is increased in accordance with the amount of Sb, the reason why the coating properties are improved is also different from the mechanism of the prior art described above. That is, as described above, Sb is very effective in reducing the oxidation rate of the steel sheet during decarburization annealing. Therefore, when the amount of Sb increases, as shown in FIG. And the defects of the product coating presumed to be increased.
On the other hand, when the amount of Mn in the steel is increased, as shown in FIG. 5, the amount of oxide generated during the decarburization annealing increases, so that the reduction in the subscale amount due to the increase in the Sb amount can be compensated.

In addition, as sub-scale oxides, the amount of firelite and silica produced increases as Mn increases. Especially in the component system in which the amount of (S + 0.405Se) is less than 50 ppm, when the amount of Mn is increased, (Fe, An increase in the amount of firelite generated represented by the chemical formula of Mn) ₂ SiO ₄ also contributes to the improvement of the coating. That is, in the secondary recrystallization annealing in which the residence time of the temperature rising process of 800 ° C. or more and 900 ° C. or less, which is one of the constituent elements of the present invention, is 40 hours or more and 150 hours or less, in the temperature range of 800 ° C. or more and 900 ° C. or less. The main reaction of film formation is not the reaction of the following formula (1) in which magnesia and silica react directly to form forsterite, but a part of Fe or Mn in the firelite is substituted with Mg (2) Since the reaction is an olivine formation reaction (olivine formation reaction), it is considered that the formation of a film is more likely to proceed when a certain amount of firelite is present in the decarburized annealed plate subscale, and the final film characteristics are improved.
Further, when the Mn ratio is increased in (Fe, Mn) ₂ SiO ₄ , the substitution of Mg is more likely to proceed in the olivine formation reaction, that is, the olivine formation reaction is likely to proceed, and the amount of Mn in the steel is increased. This is considered to be one of the reasons why the film properties are improved. In addition, when the amount of Sb is increased while keeping the amount of Mn constant, the olivine formation reaction becomes slower. Therefore, the reason why the coating properties deteriorate when the Sb content is increased is thought to be due to the fact that the oxide content of the decarburized annealing plate subscale decreases and the olivine formation reaction slows down during the secondary recrystallization annealing process. However, the fact that both can be improved at the same time by increasing the Mn content is considered to be a reason why the increase in Mn can compensate for the deterioration of the coating properties due to the increase in Sb.
2MgO + SiO ₂ → Mg ₂ SiO ₄ --- (1)
(Fe, Mn) ₂ SiO ₄ + MgO → (Fe, Mn) _2-X Mg _X SiO ₄ + [Mg _1-X , (Fe, Mn) _X ] O --- (2)

Fig. 6 shows that after applying an annealing separator mainly composed of magnesia to a decarburized annealing plate with different raw material components, holding the sample at 850 ° C for 50 hours, and then extracting the sample surface by Fourier transform infrared absorption spectroscopy (FT- (IR).
(a) Compared to the sample with Mn: 0.09% + Sb: 0.04%, the sample at (b) Mn: 0.09% + Sb: 0.06% stopped at the low wavenumber side at about 1030cm ^-1 in (a). It can be seen that olivine formation is slow, but in the sample of (c) Mn: 0.12% + Sb: 0.06%, olivine formation progresses more than (b), and it is understood that (a) is equal to or higher.

In JP-A-6-184638, the Fe and Mn content in the oxide film component {(Fe, Mn) O} a · {SiO ₂ } b generated in the decarburization annealing step is (FeO + MnO) / oxide film. among by total SiO ₂ as 0.10 to 0.50, and the oxide film in the total SiO ₂ is decarburization annealing as a 0.6 to 1.7 g / m ^2, it has a uniform glass film, excellent direction of the magnetic properties Although the technology for producing a tempered electrical steel sheet is disclosed, the purpose of this technique is good in the method of producing a directional electrical steel sheet in which a nitriding treatment is performed after decarburization annealing to form an (Al, Si) N-based inhibitor. Therefore, the technical contents are different from those of the present invention which is intended to produce a grain-oriented electrical steel sheet having excellent magnetic characteristics and film characteristics in an inhibitorless component system.

(Experiment 2)
Based on the results of Experiment 1, when a factory experiment was conducted with a component system with Mn and Sb contents of Sb: 0.03% or more and Mn: {0.04 + Sb (%)}% or more, fluctuations in the magnetic characteristics in the coil longitudinal direction There was a case. In particular, during hot rolling, there was a tendency for the magnetic characteristics to deteriorate significantly toward the tail end in the longitudinal direction of the coil.
In the factory coil, as it reaches the tail end in the longitudinal direction of the coil, the entry temperature during finish rolling decreases, while the rolling speed increases and the finish rolling exit temperature increases.
Therefore, an experiment was conducted to investigate the influence of the finish rolling entry temperature and the finish rolling exit temperature on the magnetic properties during hot rolling.

That is, C: 0.04%, Si: 3.2%, acid-soluble Al: 50ppm, N: 35ppm, Sb: 0.04%, Mn: 0.10%, (S + 0.405Se): 25ppm, the balance being Fe and inevitable A slab for grain-oriented silicon steel sheet having an impurity composition was heated to 1200 ° C. and then hot rolled into a hot rolled sheet having a thickness of 2.2 mm. At that time, the finish rolling entry temperature during hot rolling was variously changed between 900-1100 ° C. and the finish rolling exit temperature was varied between 740-1000 ° C. Thereafter, hot-rolled sheet annealing was performed at 1050 ° C. for 30 seconds, and then the final cold-rolled sheet thickness was 0.29 mm by cold rolling. Subsequently, these cold-rolled sheets were degreased to clean the surface, and then decarburized and annealed in an H ₂ —H ₂ O—N ₂ atmosphere.

After that, after applying an annealing separator containing magnesia as a main component and 4 parts by weight of TiO ₂ with respect to 100 parts by weight of magnesia, 800 ° C. to 900 ° C. in the temperature raising process of the secondary recrystallization annealing. Final finish annealing was performed, which consisted of secondary recrystallization annealing and purification annealing with a residence time in the following temperature range of 60 hours. Then, after washing with water and removing the unreacted annealing separator, a coating containing magnesium phosphate, colloidal silica and chromic acid as main components was applied.
The magnetic properties (magnetic flux density B ₈ ) of each product thus obtained were investigated.
The obtained results are shown in FIG. 7 where the horizontal axis is the finish rolling entry temperature during hot rolling and the vertical axis is the finish rolling exit temperature.

  As shown in the figure, good magnetic properties can be obtained when the finish rolling entry temperature is 940 ° C or higher and the finish rolling exit temperature is 800 ° C or more and 900 ° C or less.

This is presumably because no significant change occurs in the precipitation state of MnS or CuS due to S contained as an impurity under these conditions.
Therefore, it is considered that the fluctuation of the magnetic characteristics in the coil longitudinal direction can be suppressed by performing hot rolling so as to meet this condition over the entire length of the coil.

(Experiment 3)
C: 0.05%, Si: 3.35%, acid-soluble Al: 70ppm, N: 40ppm, Sb: 0.05%, Mn: 0.12%, (S + 0.405Se): 20ppm, Cu: 0.10%, Cr: 0.05%, P: A slab for directional silicon steel sheets with a composition of 0.015%, the balance being Fe and inevitable impurities, and heated to 1200 ° C, and hot rolled into a hot rolled sheet with a thickness of 2.0mm . At that time, hot rolling was performed so that the finish rolling entry temperature was in the range of 940 to 1100 ° C. and the finish rolling exit temperature was in the range of 800 to 900 ° C. over the entire length of the coil. Thereafter, hot-rolled sheet annealing was performed at 1025 ° C. for 30 seconds, and then the final cold-rolled sheet thickness was 0.285 mm by cold rolling. At this time, the final cold rolling was performed such that the steel plate temperature immediately after the exit side of the rolling roll was 150 to 250 ° C. for at least one pass. Subsequently, these cold-rolled sheets were degreased to clean the surface, and then decarburized and annealed in an H ₂ —H ₂ O—N ₂ atmosphere.

Then, magnesia as the main component, magnesia: 100 parts by weight, 0-10 parts by weight of TiO _{2 in} terms of Ti and 0-8 parts by weight of SrSO ₄ or Sr (OH) ₂ · 8H ₂ O in terms of Sr The final finish consisting of secondary recrystallization annealing and purification annealing with a residence time of 80 hours in the temperature range of 800 ° C or higher and 900 ° C or lower in the temperature increase process of secondary recrystallization annealing after the applied annealing separator It was subjected to annealing. Then, after washing with water to remove the unreacted annealing separator, a coating containing magnesium phosphate, colloidal silica and chromic acid as main components was applied.
The magnetic characteristics (magnetic flux density B ₈ , iron loss W _17/50 ), coating appearance and coating adhesion of each product coil thus obtained were evaluated. The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.
The obtained results are shown in FIG. 8 with the horizontal axis representing magnesia: TiO ₂ content relative to 100 parts by weight (Ti equivalent) and the vertical axis representing Sr compound content relative to 100 parts by weight magnesia (Sr equivalent).
From the figure, it can be seen that excellent product characteristics are obtained when 0.3 to 8 parts by weight of TiO ₂ in terms of Ti is added to 100 parts by weight of magnesia. In particular, it is found that particularly excellent product characteristics are obtained when the Sr compound is used in combination with 0.2 to 5 parts by weight in terms of Sr with respect to 100 parts by weight of magnesia.

Next, the reason why the component composition of the silicon steel slab is limited to the above range in the present invention will be described.
C: 0.01-0.10%
C is an element necessary for improving the primary recrystallization structure. However, if the content is less than 0.01%, a good primary recrystallization structure cannot be obtained. On the other hand, if it exceeds 0.10%, decarburization annealing is not possible. Since the decarburization load increases and the productivity decreases, the C amount is limited to 0.01 to 0.10%.

Si: 2.5-4.5%
Si is an element useful for increasing the electrical resistance of steel and reducing eddy current loss, and in the present invention, it is necessary to contain 2.5% or more. However, if it exceeds 4.5%, cold rolling becomes extremely difficult, so the Si content is limited to 2.5-4.5%.

Acid-soluble Al: 40 ppm or more and less than 100 ppm In order to produce a grain-oriented electrical steel sheet by producing secondary recrystallization by an inhibitorless method, the impurity element Al needs to be less than 100 ppm. However, a small amount of acid-soluble Al of 40 ppm or more densifies the oxide film formed on the steel sheet surface during decarburization annealing, suppresses the increase and decrease of nitrogen during secondary recrystallization annealing, and reduces the gossip of secondary recrystallized grains. Since it is effective for improving the accumulation in the orientation and improving the magnetic properties, in the present invention, the acid-soluble Al is contained in the range of 40 ppm or more and less than 100 ppm.

N: 30 ppm or more and less than 60 ppm Similarly, in order to produce a grain-oriented electrical steel sheet by causing secondary recrystallization by an inhibitorless method, N as an impurity element needs to be less than 60 ppm. However, in order to suppress the increase and decrease of nitrogen during the secondary recrystallization annealing, it is better to contain 30 ppm or more. Therefore, in the present invention, N is contained in the range of 30 ppm or more and less than 60 ppm.

Sb: 0.03-0.30%
Sb very effectively suppresses the increase in the amount of steel sheet nitrogen during secondary recrystallization annealing, so it is an indispensable element for obtaining excellent magnetic properties and stabilizing magnetic properties. It is necessary to add 0.03% or more in order to fully exhibit. However, if the content exceeds 0.30%, the decarburization property at the time of decarburization annealing becomes very bad and unsuitable for industrial mass production, so the Sb content is limited to 0.03 to 0.30%.

Mn: {0.04 + Sb (%)}% or more and 0.50% or less The problem with producing grain-oriented electrical steel sheets with excellent magnetic properties and coating properties using Sb in an inhibitorless component system is the amount of Sb added. It is in the deterioration of the film properties when increased. In order to solve this problem, it is effective to increase the amount of Mn according to the amount of Sb, so the lower limit of the amount of Mn was set to {0.04 + Sb (%)}%. Since the upper limit of the Sb amount is 0.30%, the upper limit of the Mn amount should be at least the lower limit (0.34%) in that case, and addition of a certain amount or more is cost Not only is it disadvantageous, but also causes a decrease in magnetic flux density, so 0.50% was set.

(S + 0.405Se): less than 50 ppm Impurity elements S and Se are made less than 50 ppm with (S + 0.405Se) in order to produce a grain-oriented electrical steel sheet by producing secondary recrystallization by an inhibitorless method. There is a need. This is because when the amount of (S + 0.405Se) is 50 ppm or more, secondary recrystallization becomes difficult and the magnetic properties are deteriorated.

The basic components have been described above. In the present invention, the following elements can be appropriately contained for the purpose of improving magnetic properties and film properties.
Sn: 0.03-0.50%
Sn is an element that improves and stabilizes magnetic properties. However, if the content is less than 0.03%, the effect of addition is poor. On the other hand, if it exceeds 0.50%, a good primary recrystallized structure cannot be obtained. , Sn content is preferably in the range of 0.03-0.50%.

Cu: 0.03-0.50%
Cu is an element having an action of suppressing deterioration of magnetic properties by suppressing oxynitriding of the steel sheet surface layer. However, if the content is less than 0.03%, the effect of addition is poor. On the other hand, if it exceeds 0.50%, defects called “baldness” tend to occur on the surface, so the Cu content is in the range of 0.03 to 0.50%. Is preferred.

Ni: 0.03-0.50%
Ni is an element having an effect of improving the texture and improving the magnetic flux density. However, if the content is less than 0.03%, the effect of addition is poor. On the other hand, even if added over 0.50%, not only the effect is insufficient, but the rolling property may be deteriorated. It is preferable to be in the range of ~ 0.50%.

Cr: 0.03-0.30%
Cr is an element effective for improving the film properties, but if it is less than 0.03%, a remarkable improvement effect cannot be obtained. On the other hand, if it exceeds 0.30%, the magnetic properties tend to deteriorate, so the Cr content is 0.03 to 0.30. % Is preferable.

P: 0.01-0.10%
P has a function of improving the magnetic flux density by improving the texture after cold rolling and recrystallization by grain boundary segregation. However, if the content is less than 0.01%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.10%, a good primary recrystallized structure cannot be obtained. Therefore, the P content is preferably in the range of 0.01 to 0.10%.

Mo: 0.005-0.10%
Mo has the effect of improving the surface properties. However, if the content is less than 0.005%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.10%, the decarburization property during decarburization annealing deteriorates, so the Mo amount is preferably in the range of 0.005 to 0.10%. .

Next, preferred production conditions for the grain-oriented electrical steel sheet of the present invention will be described.
The molten steel adjusted to the above components is cast by a continuous steel casting method or an ingot-making method by a steel making method conventionally used, and a slab is produced with a lump process interposed as necessary. Further, a thin cast piece having a thickness of 100 mm or less may be directly produced using a direct casting method.

  Next, the slab is heated according to a normal method, and then hot rolled to form a hot rolled coil. The slab heating temperature at this time shall be 1250 degrees C or less for energy cost reduction. This is because high-temperature slab heating exceeding 1250 ° C. is meaningless in the present invention by the inhibitorless method and only increases the cost.

  In the above hot rolling process, as shown in FIG. 7, it is important to set the inlet temperature during finish rolling to 940 ° C or higher and the outlet temperature after finish rolling to 800 ° C or higher and 900 ° C or lower. As a result, fluctuations in the magnetic characteristics in the coil longitudinal direction can be effectively suppressed.

  After the above-described hot rolling, hot-rolled sheet annealing is performed as necessary, and then a cold-rolled sheet having a final thickness is obtained by one or more cold rolling or two or more cold rollings sandwiching intermediate annealing. The cold rolling may be performed at room temperature, or may be performed at a temperature higher than room temperature, for example, about 150 to 300 ° C. for rolling. Moreover, you may perform the aging treatment in the range of 150-300 degreeC in the middle of cold rolling once or several times.

Next, decarburization and primary recrystallization annealing are performed on the final cold rolled sheet in a wet hydrogen atmosphere. It is desirable that the residual C content be 0.004% or less by this decarburization annealing.
Thereafter, an annealing separator mainly composed of magnesia is applied to the surface of the steel plate subjected to the decarburization annealing as a slurry, and then dried. Here, in order to obtain good film properties, it is necessary to apply an annealing separator containing 0.3 to 8 parts by weight of Ti compound in terms of Ti with respect to 100 parts by weight of magnesia. Here, as the Ti compound, TiO ₂ , TiO ₃ .H ₂ O, TiO. (OH) ₂ , Ti (OH) ₄ or the like can be used. In addition, combining 0.2 to 5 parts by weight of an Sr compound in terms of Sr with respect to 100 parts by weight of magnesia is effective in further improving and stabilizing magnetic properties and film properties. As such an Sr compound, SrSO ₄ , Sr (OH) ₂ .8H ₂ O, SrCO ₃ , Sr (NO) _{3 and the} like can be used.

In addition, for the purpose of further improving the uniformity of the film properties, in the annealing separator, oxides such as CaO, sulfides such as MgSO ₄ .7H ₂ O and SnSO ₄ , Na ₂ B ₄ O ₇ One or more selected from B compounds such as Sb ₂ O ₃ and Sb ₂ (SO ₄ ) ₃ can also be added as appropriate.

  Moreover, it is preferable to use the magnesia used for the annealing separator in the range of 1 to 5% of hydration amount (reduced by ignition at 1000 ° C. for 1 hour after hydration at 20 ° C. for 60 minutes). . This is because if the amount of hydration of magnesia is less than 1%, the formation of forsterite film is insufficient, while if it exceeds 5%, the amount of moisture brought between the coil layers becomes too large and the amount of additional oxidation of the steel sheet is large. Therefore, there is a possibility that a good forsterite film cannot be obtained. The citric acid activity (CAA40) at 30 ° C. is preferably 30 to 160 seconds. The reason is that if the citric acid activity (CAA40) is less than 30 seconds, the reactivity is too strong and the forsterite is generated abruptly and easily peels off. On the other hand, if it exceeds 160 seconds, the reactivity is too weak and the forsterite is generated. This is because does not progress.

Further, the annealing separator is preferably applied in a range of about 4 to 10 g / m ² per one side of the steel sheet. This is because if the coating amount is less than 4 g / m ^2, the formation of forsterite becomes insufficient. On the other hand, if it exceeds 10 g / m ² , the forsterite film is excessively formed and becomes thick. Because it invites.

After that, final finish annealing consisting of secondary recrystallization annealing and purification annealing is performed. Here, the secondary recrystallization annealing is performed in the temperature range of 800 ° C to 900 ° C for a residence time of 40 hours to 150 hours. It is necessary to keep the time below.
This is because if the residence time in the temperature range of 800 ° C. or more and 900 ° C. or less is out of the above range, the magnetic characteristics are deteriorated as shown in FIG.

Thereafter, a phosphate-based insulating coating, preferably an insulating coating that imparts tension, is applied to the steel sheet surface to obtain a product. The type of insulating coating is not particularly limited, but any conventionally known insulating coating is suitable. For example, a coating solution containing phosphate-chromic acid-colloidal silica described in JP-A-50-79442 and JP-A-48-39338 is applied to a steel plate and baked at about 800 ° C. The method is preferred.
Furthermore, performing a known magnetic domain refinement after the final cold rolling, after the final finish annealing, or after forming the insulating coating is effective in further reducing iron loss.

Example 1
A steel slab having the component composition shown in Table 1 was heated to 1200 ° C. in a gas heating furnace, and then hot rolled into a hot rolled sheet having a sheet thickness of 2.2 mm. During this hot rolling, the entry side temperature and the exit side temperature during finish rolling were controlled within the ranges shown in Table 2 over the entire length of the coil.
Then, after hot-rolled sheet annealing at 1050 ° C. for 30 seconds, the final sheet thickness was 0.29 mm by cold rolling. Thereafter, after decarburization and primary recrystallization annealing, an annealing separator mainly composed of magnesia was applied, and final finishing annealing consisting of secondary recrystallization annealing and purification annealing was performed. Table 2 shows the composition of the annealing separator and the secondary recrystallization annealing conditions (retention time of 800 ° C. or more and 900 ° C. or less). Thereafter, an insulating coating mainly composed of magnesium phosphate, chromic acid and colloidal silica was applied.

Table 2 shows the results of examining the magnetic flux density (B ₈ ), iron loss (W _17/50 ), coating appearance and coating adhesion for each product thus obtained.
The coating adhesion was evaluated by the minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters at intervals of 5 mm as the bending adhesion of the coating.

  As is apparent from Table 2, all of the inventive examples produced under the conditions according to the present invention have good magnetic properties and coating properties.

Example 2
A steel slab having the composition shown in Table 3 was heated to 1200 ° C. in a gas heating furnace, and then hot rolled to form a hot rolled sheet having a thickness of 2.0 mm. During this hot rolling, the entry side temperature and the exit side temperature during finish rolling were controlled within the ranges shown in Table 4 over the entire length of the coil.
Then, after hot-rolled sheet annealing at 1035 ° C. for 60 seconds, the final sheet thickness was 0.285 mm by cold rolling. At this time, the final cold rolling was performed such that the steel plate temperature immediately after the exit side of the rolling roll was 150 to 250 ° C. for at least one pass. Then, after decarburization and primary recrystallization annealing, an annealing separator mainly composed of magnesia was applied, and final finishing annealing consisting of secondary recrystallization annealing and purification annealing was performed. Table 4 shows the composition of the annealing separator and the secondary recrystallization annealing conditions (retention time of 800 ° C. or more and 900 ° C. or less). Thereafter, an insulating coating mainly composed of magnesium phosphate, chromic acid and colloidal silica was applied.

Table 4 shows the results of examining the magnetic flux density (B ₈ ), iron loss (W _17/50 ), coating appearance, and coating adhesion of each product thus obtained.

  As is apparent from Table 4, all of the inventive examples produced under the conditions according to the present invention obtained good magnetic properties and coating properties.

Example 3
A steel slab having the composition shown in Table 5 was heated to 1240 ° C. in a gas heating furnace, and then hot rolled to form a hot rolled sheet having a sheet thickness of 2.7 mm. During this hot rolling, the inlet side temperature and outlet side temperature during finish rolling were controlled within the ranges shown in Table 6 over the entire length of the coil.
Then, the sheet thickness was 1.6 mm by cold rolling, and after intermediate annealing at 1020 ° C. for 45 seconds, the final sheet thickness was 0.22 mm by cold rolling. At this time, the final cold rolling was performed such that the steel plate temperature immediately after the exit side of the rolling roll was 150 to 250 ° C. for at least one pass. Next, after decarburization and primary recrystallization annealing, an annealing separator mainly composed of magnesia was applied, and final finish annealing including secondary recrystallization annealing and blunt annealing was performed. Table 6 shows the composition of the annealing separator and the secondary recrystallization annealing conditions (retention time of 800 ° C. or higher and 900 ° C. or lower). Thereafter, an insulating coating mainly composed of magnesium phosphate, chromic acid and colloidal silica was applied.

Table 6 shows the results of examining the magnetic flux density (B ₈ ), iron loss (W _17/50 ), coating appearance and coating adhesion of each product thus obtained.

  As is apparent from Table 6, all of the inventive examples produced under the conditions according to the present invention exhibit good magnetic properties and coating properties.

TiO ₂ content in annealing separator is a diagram showing the effect on film adhesion. It is a figure which shows the influence which the residence time in the temperature range of 800 degreeC or more and 900 degrees C or less has on a magnetic characteristic in the temperature rising process of secondary recrystallization annealing. It is a figure which shows the influence which the amount of Mn and Sb in a raw material has on a magnetic characteristic and a film characteristic. It is a figure which shows the influence which the amount of Sb in a raw material has on the oxygen basis weight (per one side) of a decarburization annealing board subscale. It is a figure which shows the influence which the amount of Mn in a raw material has on the amount of oxygen areal weight (per one side) of a decarburization annealing board subscale. It is a figure which shows the FT-IR measurement result of the steel plate surface after annealing for 50 hours at 850 degreeC during secondary recrystallization annealing. It is a figure which shows the influence which the finish rolling entrance temperature and the finish rolling exit side temperature at the time of hot rolling exert on a magnetic characteristic. TiO ₂ and Sr compound amount in the annealing separator is a diagram showing the effect on product properties.

Claims (3)

In mass%, C: 0.01-0.10%, Si: 2.5-4.5%, acid-soluble Al: 40ppm or more, less than 100ppm, N: 30ppm or more, less than 60ppm, Sb: 0.03-0.30%, Mn: {0.04 + Sb (%)} % Or more and 0.50% or less and (S + 0.405Se): less than 50ppm, the balance is Fe and unavoidable impurities, silicon steel slab is heated at a temperature of 1250 ℃ or less, then hot-rolled and necessary Depending on the condition, after hot-rolled sheet annealing is performed, cold rolling is performed once or two or more times with intermediate annealing, followed by decarburization and primary recrystallization annealing, and then an annealing separator mainly composed of magnesia is applied. Then, in the method for producing a unidirectional electrical steel sheet comprising a series of steps of performing final finishing annealing consisting of secondary recrystallization annealing and purification annealing,
a) The finish rolling entry temperature during hot rolling should be 940 ° C or more and the finish rolling exit temperature should be 800 ° C or more and 900 ° C or less,
b) In the annealing separator, magnesia: 0.3 to 8.0 parts by weight of Ti compound in terms of Ti with respect to 100 parts by weight,
c) In the Atsushi Nobori process of secondary recrystallization annealing, manufacturing method of an oriented electrical steel sheet you characterized in that the residence time in the temperature range of 800 ° C. or higher 900 ° C. or less than 40 hours or more 150 hours. According to claim 1, further in the annealing separating agent, magnesia To 100 parts by weight, manufacturing method of an oriented electrical steel sheet you characterized by the inclusion 0.2-5 parts by weight of Sr compound Sr terms. 3. The silicon steel slab according to claim 1, wherein the silicon steel slab is further mass%, Sn: 0.03-0.50%, Cu: 0.03-0.50%, Ni: 0.03-0.50%, Cr: 0.03-0.30%, P: 0.01- 0.10% and Mo: 0.005 to 0.10% manufacturing method of an oriented electrical steel sheet you characterized in that it contains one or more kinds selected from among.

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