JP2022022481A - Method for manufacturing grain-oriented electromagnetic steel sheet - Google Patents

Abstract

To provide a method for manufacturing grain-oriented electromagnetic steel sheet in which cracking during cold rolling can be suppressed even when a high Si concentration slab is used.SOLUTION: Provided is a method for manufacturing grain-oriented electromagnetic steel sheet that comprises a hot rolling step, an arbitrary hot rolling sheet annealing step, a pickling step, a cold rolling step, a primary recrystallization annealing step, a finish annealing step, and a flattening annealing step. In the pickling step, a pickling solution that contains one or more metals selected from the group consisting of Cu, Hg, Ag, Pb, Cd, Ni, Zn and Co by 0.001 mass% or more and 0.100 mass% or less, and hydrochloric acid in an amount of 5 mass% or more and 20 mass% or less based on hydrogen chloride is used.SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet.

The grain-oriented electrical steel sheet is a steel sheet containing about 0.5% by mass to 7% by mass of Si, and the orientation of the crystal grains of the steel sheet is highly integrated in the {110} <001> orientation called the Goss orientation. Since the grain-oriented electrical steel sheet has excellent magnetic characteristics, it is used, for example, as an iron core material for a static induction device such as a transformer. Conventionally, various developments have been made to improve the magnetic properties of electrical steel sheets. In particular, with the recent demand for energy saving, further reduction of iron loss is required for grain-oriented electrical steel sheets. In order to reduce the iron loss of the grain-oriented electrical steel sheet, it is effective to increase the degree of integration in the Goss direction with respect to the orientation of the crystal grains of the steel sheet to improve the magnetic flux density and reduce the hysteresis loss. In the production of grain-oriented electrical steel sheets, the crystal orientation is controlled by utilizing a catastrophic grain growth phenomenon called secondary recrystallization. In order to control the crystal orientation by secondary recrystallization, it is important to allow fine precipitates in steel called inhibitors to be uniformly and stably present up to a desired time point of secondary recrystallization.

A typical method for reducing iron loss is to reduce the eddy current loss by increasing the concentration of Si in the steel, which increases the intrinsic resistance. However, it is known that when the Si concentration is increased, the slab becomes hard and brittle, and the workability is lowered. As a technique for improving the workability of grain-oriented electrical steel sheets having a high Si concentration, a technique for controlling the properties of the steel sheet surface by optimizing the conditions of the hot rolling process or the hot-rolled sheet annealing process has been proposed. ing. For example, in Patent Document 1, a silicon steel slab containing Si: 2.0 to 4.5 wt% is heated at a high temperature to perform hot rough rolling, and then hot finish rolling is performed. In the manufacturing method of, in the case of hot rough rolling, rolling at the first stand is performed by rolling on the inlet side plate thickness, the exit side plate thickness, the surface temperature of the steel plate at the time of biting, and the predetermined depth from the surface of the steel plate at the time of biting. A method of suppressing surface cracking in hot rolling by keeping the relationship between the temperatures in the above range within the specified range will be described.

International Publication No. 94/014549

The technique described in Patent Document 1 relates to suppressing surface cracking in hot rolling, but in a grain-oriented electrical steel sheet using a slab having a high Si concentration, the occurrence of cracking during cold rolling is also a problem. It has become. For example, when a steel strip is wound around a reel in cold rolling, winding cracks may occur, and the cracks may be the starting point to cause fracture.

An object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing grain-oriented electrical steel sheets, which can suppress cracking during cold rolling even when a slab having a high Si concentration is used.

The present disclosure includes the following aspects.
[1] In terms of mass%, C: 0.02% or more and 0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.30% or less, S and Se. The total of one or two of them: 0.001% or more and 0.050% or less, acid-soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.020% or less. A hot rolling step of heating a slab having a slab composition consisting of the balance Fe and impurities and hot rolling to obtain a hot-rolled steel sheet.
By immersing the hot-rolled steel plate in a pickling solution, or by immersing the hot-rolled steel plate in a pickling solution after obtaining a hot-rolled annealed plate. The pickling process to obtain a pickling plate and
A cold rolling step of obtaining a cold-rolled steel sheet by cold-rolling the pickling plate, and
A primary recrystallization annealing step of subjecting the cold-rolled steel sheet to primary recrystallization annealing to obtain a primary recrystallization annealed sheet,
A finish annealing step of applying an annealing separator containing MgO to the surface of the primary recrystallization annealed plate and then performing finish annealing to obtain a finish annealed plate.
Including a flattening annealing step of applying an insulating film to the finish annealing plate and then performing flattening annealing.
The pickling solution contains 0.001% by mass or more and 0.100% by mass or less of one or more metals selected from the group consisting of Cu, Hg, Ag, Pb, Cd, Ni, Zn and Co, and hydrochloric acid. A method for manufacturing a directional electromagnetic steel plate, which comprises an amount of 5% by mass or more and 20% by mass or less based on hydrogen chloride.
[2] In the pickling step, the pH of the pickling solution is −1.5 or more and less than 7.0, the liquid temperature is 15 ° C. or more and 100 ° C. or less, and the immersion is performed for 5 seconds or more and 200 seconds or less. The method for manufacturing a directional electromagnetic steel plate according to [1].
[3] The method for manufacturing a grain-oriented electrical steel sheet according to the above [1] or [2], wherein the heating of the slab is performed at 1280 ° C. or higher.
[4] The slab composition is, instead of a part of the Fe, by mass%.
Cu: 0.5000% or less,
Cr: 0.50% or less,
Bi: 0.0200% or less,
Sb: 0.500% or less,
Mo: 0.500% or less,
Sn: 0.500% or less, and Ni: 0.500% or less,
The method for manufacturing a grain-oriented electrical steel sheet according to any one of the above [1] to [3], which contains one kind or two or more kinds selected from the group consisting of.

According to one aspect of the present invention, there can be provided a method for manufacturing a grain-oriented electrical steel sheet that can suppress cracking during cold rolling even when a slab having a high Si concentration is used.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. Unless otherwise specified, the notation "A to B" for the numerical values A and B means "A or more and B or less".

One aspect of the present invention is
By mass%, C: 0.02% or more and 0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.30% or less, one of S and Se Or the total of the two types: 0.001% or more and 0.050% or less, acid-soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.020% or less, and the balance Fe A hot rolling step of heating a slab having a slab composition composed of impurities and hot rolling to obtain a hot-rolled steel sheet.
By immersing the hot-rolled steel plate in a pickling solution, or by immersing the hot-rolled steel plate in a pickling solution after obtaining a hot-rolled annealed plate. The pickling process to obtain a pickling plate and
A cold rolling step of obtaining a cold-rolled steel sheet by cold-rolling the pickling plate, and
A primary recrystallization annealing step of subjecting the cold-rolled steel sheet to primary recrystallization annealing to obtain a primary recrystallization annealed sheet,
A finish annealing step of applying an annealing separator containing MgO to the surface of the primary recrystallization annealed plate and then performing finish annealing to obtain a finish annealed plate.
Provided is a method for manufacturing a grain-oriented electrical steel sheet, which comprises a flattening annealing step of applying an insulating film to the finished annealed plate and then performing flattening annealing.

In one embodiment, the pickling solution comprises a metal component that is one or more metals selected from the group consisting of Cu, Hg, Ag, Pb, Cd, Ni, Zn and Co.

When components (typically MnS, MnSe and AlN) that function as inhibitors during finish annealing are present in the steel, the inhibitors are finely deposited on the steel sheet after hot rolling, and some of them are finely deposited on the steel sheet. It is exposed on the surface. The present inventors focused on the fact that cracks are likely to occur during cold rolling in the production of directional electromagnetic steel sheets using slabs with a high Si concentration, and investigated the cause of the cracks. Occasionally, it was found that corrosion occurs at the interface between the inhibitor on the surface of the steel sheet and the base metal around it, and this corrosion contributes to the cracking. Specifically, when the scale on the surface of the steel sheet is removed by pickling, the inhibitor exposed on the surface of the steel sheet falls off due to the above corrosion, so that fine recesses are formed on the surface of the steel sheet, and the recesses are formed in the cold rolling process. It is considered that cracks occur due to the concentration of stress on the steel sheet.

Corrosion at the interface between the inhibitor and the base material around it (main component is Fe) is considered to be due to the potential difference between the inhibitor and the base material. As a result of diligent studies on means for suppressing this corrosion, the present inventors have found that it is effective to include a specific metal species in the pickling solution. In one embodiment, the pickling solution is a metal component that is one or more metals selected from the group consisting of Cu, Hg, Ag, Pb, Cd, Ni, Zn and Co (in the present disclosure, it is simply referred to as a metal component). There is also.). All of the Mns constituting the inhibitor have a relatively low standard electrode potential (standard oxidation-reduction potential) and have a relatively high tendency to emit electrons, but all the metals that can form the metal component of the present embodiment are compared with Mn. The standard electrode potential is high and can be replaced with Mn to form a sulfide or selenium. Such substitution is likely to occur in the vicinity of the surface of the inhibitor precipitate which is in contact with the pickling solution, and in particular, is likely to occur in the vicinity of the surface of the inhibitor precipitate exposed on the surface of the steel sheet. When Mn near the surface of the inhibitor precipitate is replaced with the metal component of the present embodiment to form a sulfide or selenium of the metal component, the sulfide or selenium becomes a barrier and the inside of the inhibitor precipitate. Since the ionization of Mn is suppressed, corrosion at the interface between the inhibitor and the base metal is reduced. The metal component adhering to the vicinity of the surface of the inhibitor precipitate also has a potential difference that is base or noble with respect to Fe of the base material, but the degree of corrosion at the interface is slight compared to the case where the metal component is not adhered. Is. As described above, the metal component of the present embodiment advantageously contributes to the suppression of corrosion at the interface between the inhibitor and the base material, and thus the suppression of the inhibitor from falling off. In addition, the increase in volume due to the adhesion of the metal component to the surface of the inhibitor precipitate also contributes to corrosion suppression by reducing the gap at the interface between the inhibitor and the base material.

Among the metals that can be used as metal components, Cu and Ni are preferable from the viewpoints that they are easily deposited on the surface of the steel sheet, the cost is low, and the load on the environment is small.

In one embodiment, the content of the metal component in the pickling solution is 0.001% by mass or more and 0.100% by mass or less. The content thereof is 0.001% by mass or more, preferably 0.002% by mass or more, or 0.003% by mass or more, or 0.004% by mass in one embodiment from the viewpoint of satisfactorily obtaining the ionization inhibitory effect of the inhibitor. % Or more, preferably 0.100% by mass or less in one embodiment, from the viewpoint of preventing inconveniences during primary recrystallization (insufficient decarburization, insufficient formation of oxide film, etc.) due to excessive precipitation of metal components. It is 0.080% by mass or less, or 0.060% by mass or less. The amount of the metal component in the pickling solution can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometery).

In one embodiment, the pickling solution comprises hydrochloric acid. Hydrochloric acid has a sufficient effect of removing scale from the surface of the steel sheet, but is advantageous in that it does not easily corrode the surface of the steel sheet. The amount of hydrochloric acid in the pickling solution may be 5% by mass or more and 20% by mass or less, preferably 6% by mass or more, or 7% by mass or more, preferably 7% by mass or more, based on hydrogen chloride. It may be 19% by mass or less, or 18% by mass or less.

Hereinafter, the method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment will be specifically described.

[Slab component composition]
First, the component composition of the slab used for the grain-oriented electrical steel sheet according to the present embodiment will be described. In the following, unless otherwise specified, the notation "%" means "mass%". Further, the rest of the slab other than the elements described below is Fe and impurities.

The content of C (carbon) is 0.02% or more and 0.10% or less. C has various roles, but when the C content is less than 0.02%, the crystal grain size becomes excessively large when the slab is heated, resulting in iron loss of the final grain-oriented electrical steel sheet. It is not preferable because it increases the value. When the C content is more than 0.10%, the decarburization time becomes long and the manufacturing cost increases during decarburization after cold rolling, which is not preferable. Further, when the C content is more than 0.10%, decarburization tends to be incomplete, which may cause magnetic aging in the final grain-oriented electrical steel sheet, which is not preferable. Therefore, the content of C is 0.02% or more and 0.10% or less, preferably 0.03% or more and 0.09% or less, and more preferably 0.04% or more and 0.08% or less. be.

The content of Si (silicon) is 2.5% or more and 4.5% or less. Si reduces the eddy current loss, which is one of the causes of iron loss, by increasing the electric resistance of the steel sheet. When the Si content is less than 2.5%, it becomes difficult to sufficiently suppress the eddy current loss of the final grain-oriented electrical steel sheet, which is not preferable. When the Si content is more than 4.5%, the workability of the grain-oriented electrical steel sheet is deteriorated, which is not preferable. Therefore, the Si content is 2.5% or more and 4.5% or less, preferably 2.7% or more and 4.0% or less, and more preferably 2.9% or more and 3.7% or less. be.

The content of Mn (manganese) is 0.01% or more and 0.30% or less. Mn forms MnS, MnSe and the like, which are inhibitors that influence secondary recrystallization. If the Mn content is less than 0.01%, the absolute amounts of MnS and MnSe that cause secondary recrystallization are insufficient, which is not preferable. When the Mn content is more than 0.30%, it is not preferable because it becomes difficult to dissolve Mn during slab heating. Further, when the Mn content is more than 0.30%, the precipitation sizes of the inhibitors MnS and MnSe tend to be coarse, and the optimum size distribution as an inhibitor is impaired, which is not preferable. Therefore, the Mn content is 0.01% or more and 0.30% or less, preferably 0.02% or more and 0.15% or less, and more preferably 0.03% or more and 0.13% or less. More preferably, it is 0.05% or more and 0.10% or less.

The total content of S (sulfur) and Se (selenium) is 0.001% or more and 0.050% or less. S and Se form an inhibitor together with Mn described above. Both S and Se may be contained in the slab, but at least one of them may be contained in the slab. If the total content of S and Se is out of the above range, a sufficient inhibitory effect cannot be obtained, which is not preferable. Therefore, the total content of S and Se is 0.001% or more and 0.050% or less, preferably 0.001% or more and 0.040% or less, and more preferably 0.005% or more and 0. It is 040% or less.

The content of acid-soluble Al (acid-soluble aluminum) is 0.01% or more and 0.05% or less. The acid-soluble Al constitutes an inhibitor necessary for producing a grain-oriented electrical steel sheet having a high magnetic flux density. When the content of the acid-soluble Al is more than 0.05%, AlN precipitated as an inhibitor becomes coarse and the inhibitor strength is lowered, which is not preferable. When the content of acid-soluble Al is less than 0.01%, the inhibitor strength is low, which is not preferable. Therefore, the content of acid-soluble Al is 0.01% or more and 0.05% or less, preferably 0.01% or more and 0.04% or less.

The content of N (nitrogen) is 0.002% or more and 0.020% or less. N forms the inhibitor AlN together with the acid-soluble Al described above. If the content of N is out of the above range, a sufficient inhibitory effect cannot be obtained, which is not preferable. Therefore, the content of N is 0.002% or more and 0.020% or less, preferably 0.002% or more and 0.015% or less, and more preferably 0.002% or more and 0.012% or less. More preferably, it is 0.005% or more and 0.012% or less.

Further, in addition to the above-mentioned elements, the slab used for producing the directional electromagnetic steel plate according to the present embodiment has Cu: 0. 5000% or less, Cr: 0.50% or less, Bi: 0.0200% or less, Sb: 0.500% or less, Mo: 0.500% or less, Sn: 0.500% or less, and Ni: 0.500 It may contain one kind or two or more kinds selected from the group consisting of% or less. In the slab according to one embodiment, the Cu content may be 0.0005% or more, the Cr content may be 0.02% or more, and the Bi content may be 0.0005 in mass%. % Or more, Sb content may be 0.005% or more, Mo content may be 0.005% or more, and Sn content may be 0.005% or more. Often, the Ni content may be 0.005% or more.

A slab is formed by casting molten steel adjusted to the composition of the components described above. The method of casting the slab is not particularly limited. Further, in research and development, even if a steel ingot is formed in a vacuum melting furnace or the like, the same effect as when a slab is formed can be confirmed for the above components. Hereinafter, preferred embodiments of each step for manufacturing grain-oriented electrical steel sheets from slabs will be further described.

[Hot rolling process]
In this step, a hot-rolled steel sheet is obtained by heating the slab and performing hot rolling. In one embodiment, the heating temperature of the slab is preferably 1280 ° C. or higher, or 1300 ° C. from the viewpoint of solidly dissolving the inhibitor component (for example, MnS, MnSe, AlN, etc.) in the slab to obtain a good inhibitor effect. The above may be sufficient, and the upper limit of the heating temperature of the slab in this case is not particularly determined, but is preferably 1450 ° C. from the viewpoint of equipment protection. Alternatively, the heating temperature of the slab is preferably less than 1280 ° C or 1250 ° C or less from the viewpoints of reducing the load on the heating furnace, reducing the amount of scale generated, and lowering the process of inhibitor control during hot spreading. It's okay.

The heated slab is hot-rolled and processed into a hot-rolled steel sheet. The thickness of the hot-rolled steel sheet after processing is preferably 1 mm or more, for example, because the temperature of the steel sheet does not easily decrease and the precipitation of inhibitors in the steel can be stably controlled. For example, 10 mm or less is preferable in that it can be lowered.

[Pickling process]
In this step, the hot-rolled steel plate is immersed in a pickling solution, or the hot-rolled steel sheet is annealed to obtain a hot-rolled annealed plate and then the hot-rolled annealed plate is immersed in a pickling solution. , Get a pickling plate. In the method of the present embodiment, pickling using a pickling solution containing a metal component which is a specific metal species is performed before cold rolling to obtain an inhibitor due to corrosion of the interface between the inhibitor and the base metal on the surface of the steel sheet. It is possible to suppress falling off and reduce cracking during cold rolling. Pickling is performed at least once after hot rolling and before primary recrystallization annealing. In one aspect, pickling is performed before the cold rolling step from the viewpoint of reducing roll wear in cold rolling.

The pickling solution contains the above-mentioned metal components and acids. The pH of the pickling solution is -1.5 or more and less than 7.0 in one embodiment. The solution that can be prepared in reality has a pH of -1.5 or higher. When the pH of the pickling solution is 7.0 or more, the scale removing effect by pickling is insufficient, which is not preferable. It is advantageous that the pH of the pickling solution is −1.5 or more and less than 7.0 from the viewpoint of precipitating the metal component on the surface of the steel sheet to a desired degree. The pH is preferably less than 2.0, more preferably less than 1.0.

The liquid temperature of the pickling solution is 15 ° C. or higher and 100 ° C. or lower in one embodiment. When the temperature of the pickling solution is less than 15 ° C., the scale removing effect by pickling is insufficient, which is not preferable. If the temperature of the pickling solution exceeds 100 ° C., it becomes difficult to handle the pickling solution, which is not preferable. The fact that the temperature of the pickling solution is 15 ° C. or higher and 100 ° C. or lower is also advantageous from the viewpoint of precipitating the metal component on the surface of the steel sheet to a desired degree. The liquid temperature may be preferably 22 ° C. or higher, 24 ° C. or higher, or 26 ° C. or higher, and preferably 98 ° C. or lower, 96 ° C. or lower, or 94 ° C. or lower.

The time for the steel sheet to be immersed in the pickling solution is 5 seconds or more and 200 seconds or less in one embodiment. When the steel sheet is immersed in the pickling solution for less than 5 seconds, the scale removing effect by pickling becomes insufficient, which is not preferable. If the time for the steel sheet to be immersed in the pickling solution is more than 200 seconds, the equipment becomes long, which is not preferable. The immersion time may be preferably 10 seconds or longer, 20 seconds or longer, or 30 seconds or longer, and preferably 150 seconds or shorter, or 100 seconds or shorter.

[Cold rolling process]
In this step, the pickled sheet is rolled by one cold rolling or a plurality of cold rolling with intermediate annealing sandwiched between them to obtain a cold-rolled steel sheet. Cold rolling may be performed a plurality of times with intermediate annealing and / or pickling in between.

The steel sheet may be heat-treated at about 300 ° C. or lower between cold rolling passes, between rolling roll stands, or during rolling. Such heating is preferable in that the magnetic properties of the final grain-oriented electrical steel sheet can be improved. The hot-rolled steel sheet may be rolled by, for example, three or more cold rollings, but the cold rolling may be performed once or twice in order to increase the manufacturing cost. preferable. For example, when cold rolling is performed by reverse rolling such as Z-Mill mill, the number of passes in each cold rolling is not particularly limited, but 9 times or less is preferable from the viewpoint of manufacturing cost. The rolling reduction of the steel sheet in the cold rolling step may be appropriately designed so as to obtain a cold-rolled steel sheet having a desired thickness, and may be, for example, 80% to 95%.

[Primary recrystallization annealing process]
Next, in this step, the cold-rolled steel sheet is subjected to primary recrystallization annealing. In a typical embodiment, the primary recrystallization annealing step includes a heating step and a decarburization annealing step. The cold-rolled steel sheet is decarburized and annealed in the decarburization annealing step after undergoing the temperature raising step. It is preferable that the steps from the temperature raising step to the decarburization annealing step are continuously performed.

(Heating process)
In the temperature raising step, the temperature of the cold-rolled steel sheet is raised to a desired decarburization annealing temperature. It is desirable that the rate of temperature rise is appropriately controlled according to the temperature range. In one embodiment, the average temperature rise rate in the temperature range of 30 ° C. to 400 ° C. may be 50 ° C./sec or more from the viewpoint of suppressing the oxidation of the metal component deposited on the surface of the steel sheet, and the ease of passing the sheet is improved. From the viewpoint, it may be 600 ° C./sec or less. The average heating rate between 400 ° C. and 500 ° C. does not require any special control, but may be the same as that exemplified above as the average heating rate between 30 ° C. and 400 ° C., for example. In one embodiment, the average heating rate between 500 ° C. and 750 ° C. may be 100 ° C./sec or more from the viewpoint of increasing the amount of Goss directional grains before finish annealing of the cold-rolled steel sheet, and the equipment cost and From the viewpoint of manufacturing cost, it may be 3000 ° C./sec or less. In one embodiment, the average heating rate between 750 ° C. and 800 ° C. may be 500 ° C./sec or more from the viewpoint of suppressing the formation of SiO ₂ that inhibits decarburization during decarburization and quenching, and the equipment cost. And from the viewpoint of manufacturing cost, it may be 2000 ° C./sec or less. Such rapid temperature rise can be carried out, for example, by using an energization heating method or an induction heating method. The temperature raising step may be carried out by a plurality of devices. The temperature rise rate can be measured by measuring the steel plate temperature using a radiation thermometer or the like, but if it is difficult to measure the steel plate temperature, these can be estimated by inferring each heat pattern of temperature rise and cooling. You may estimate the temperature of. Further, the temperature on the entrance side and the temperature on the exit side of the steel sheet to the temperature riser in the temperature rise step may be set as a temperature rise start point and a temperature rise end point.

(Decarburization annealing process)
After the temperature raising step, a decarburization annealing step is performed. In a normal embodiment, the decarburization annealing step comprises a leveling heat treatment. The soaking heat treatment may be carried out at 900 ° C. or lower, for example, 750 ° C. to 900 ° C. in a moist atmosphere containing hydrogen and / or nitrogen. The decarburization annealing temperature may be the same as or lower than the temperature rise completion temperature of the above-mentioned temperature rise step. The soaking heat treatment may be performed once or twice or more. For example, when the leveling heat treatment is performed twice, the first leveling heat treatment and the second leveling heat treatment, the steel sheet is once cooled (for example, cooled to room temperature) and then reheated after the completion of the first leveling heat treatment, or cooled. The second leveling heat treatment may be performed without this. In one embodiment, the decarburization annealing step may include a first leveling heat treatment performed at 800 ° C. to 900 ° C. and a second leveling heat treatment performed at 900 ° C. to 1000 ° C.

The oxygen potential of the atmosphere of soaking heat, that is, the ratio of the partial pressure of water vapor _PH2O and the partial pressure of hydrogen _{PH2 (P H2O / PH2} ratio) in the atmosphere, promotes internal oxidation well and uniformly oxidizes the surface of the steel plate. From the viewpoint of forming a film, it may be 0.2 or more, and from the viewpoint of obtaining good magnetic properties, it may be 0.8 or less. Further, for example, when the first leveling heat treatment and the second leveling heat treatment are performed, the _PH2O / _PH2 ratio of the first leveling heat treatment is within the above range, and the _PH2O / _PH2 ratio of the second leveling heat treatment is 0. It may be less than 2, for example, 0.01 or more and less than 0.2.

In the primary recrystallization annealing step, the dew point temperature of the atmosphere between 30 ° C and 800 ° C suppresses the oxidation of the metal in the steel sheet and suppresses the formation of SiO ₂ due to external oxidation to promote decarburization satisfactorily. Therefore, the temperature may be 0 ° C. or lower, and may be −50 ° C. or higher from the viewpoint of promoting internal oxidation satisfactorily.

[Nitriding treatment]
After the cold rolling step and before finish annealing, further nitriding may be performed for the purpose of strengthening the inhibitor. In one embodiment, the nitriding treatment may be carried out after the leveling heat treatment and before the finish annealing, for example, in the order of leveling heat treatment-nitriding treatment-finishing annealing, first leveling heat treatment-second leveling heat treatment-nitriding treatment-finishing. The order may be the order of annealing, or the order of first leveling heat treatment-nitriding treatment-second leveling heat treatment-finish baking.

[Finishing annealing process]
Subsequently, for the purpose of forming a primary film and secondary recrystallization, the steel sheet (primary recrystallization annealed sheet) after the primary recrystallization annealing step is subjected to finish annealing. In a typical embodiment, the primary recrystallization annealed plate before finish annealing is coated with an annealing separator containing MgO as a main component for the purpose of preventing seizure between steel sheets, forming a primary film, controlling secondary recrystallization behavior, and the like. Will be done. In the finish annealing, a purification treatment may be performed after the heat treatment of the steel sheet.

[Flatration annealing process]
After finish annealing, an insulating film (for example, an insulating film containing aluminum phosphate or colloidal silica as a main component) may be applied to the surface of the steel sheet for the purpose of imparting insulation and tension to the steel sheet. Next, flattening annealing may be performed for the purpose of baking the insulating film and flattening the shape of the steel sheet by finish annealing.

Further magnetic domain control processing may be performed depending on the use of the obtained grain-oriented electrical steel sheet.

By the steps exemplified above, a grain-oriented electrical steel sheet having excellent magnetic characteristics can be manufactured. The grain-oriented electrical steel sheet that can be manufactured by the method of the present embodiment is processed into a wound steel core or a product core during the production of a transformer, and can be applied to a desired application.

In the production of grain-oriented electrical steel sheets by the method of the present embodiment, the breaking frequency is preferably 0.9 times / 1000 tons or less, or 0.8 times / 1000 tons or less. The smaller the breaking frequency, the more desirable.

Hereinafter, embodiments of the present invention will be further described with reference to examples, but the present invention is not limited to the following examples.

<Manufacturing of grain-oriented electrical steel sheets>
[Example 1]
A slab having the slab composition shown in Table 1 was obtained. After heating the slab at 1350 ° C., hot rolling was performed to obtain a hot rolled steel strip having a thickness of 2.3 mm. Next, the hot-rolled steel strip was heated to 1120 ° C. and recrystallized, and then annealed at 900 ° C., which is a lower temperature than this, to obtain a hot-rolled plate annealed steel strip. The hot-rolled annealed steel strip was pickled under the pickling conditions shown in Table 2, and then cold-rolled to a final product plate thickness of 0.220 mm. At that time, the breaking frequency per 1000 tons generated in the second pass is shown in Table 2.
The breaking frequency is the ratio of the number of breakings occurring in the second pass to the amount of passing through a plurality of coils having the slab composition shown in Table 1 as a result of passing at least 200 tons.
The results are shown in Table 2.

As shown in Table 2, even when a slab with a high Si content of 3.30 to 3.65% is used by controlling to appropriate pickling conditions, the frequency of wrapping crack breakage in the second pass of cold rolling is 1. Good results were obtained at times / 1000 tons or less.

The grain-oriented electrical steel sheet obtained by the method of the present disclosure can be suitably applied to various applications requiring good magnetic properties.

Claims (4)

By mass%, C: 0.02% or more and 0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.30% or less, one of S and Se Or the total of the two types: 0.001% or more and 0.050% or less, acid-soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.020% or less, and the balance Fe A hot rolling step of heating a slab having a slab composition composed of impurities and hot rolling to obtain a hot-rolled steel sheet.
By immersing the hot-rolled steel plate in a pickling solution, or by immersing the hot-rolled steel plate in a pickling solution after obtaining a hot-rolled annealed plate. The pickling process to obtain a pickling plate and
A cold rolling step of obtaining a cold-rolled steel sheet by cold-rolling the pickling plate, and
A primary recrystallization annealing step of subjecting the cold-rolled steel sheet to primary recrystallization annealing to obtain a primary recrystallization annealed sheet,
A finish annealing step of applying an annealing separator containing MgO to the surface of the primary recrystallization annealed plate and then performing finish annealing to obtain a finish annealed plate.
Including a flattening annealing step of applying an insulating film to the finish annealing plate and then performing flattening annealing.
The pickling solution contains 0.001% by mass or more and 0.100% by mass or less of one or more metals selected from the group consisting of Cu, Hg, Ag, Pb, Cd, Ni, Zn and Co, and hydrochloric acid. A method for manufacturing a directional electromagnetic steel plate, which comprises an amount of 5% by mass or more and 20% by mass or less based on hydrogen chloride. In the pickling step, the pH of the pickling solution is −1.5 or more and less than 7.0, the liquid temperature is 15 ° C. or more and 100 ° C. or less, and the immersion is performed for 5 seconds or more and 200 seconds or less. The method for manufacturing a directional electromagnetic steel plate according to the description. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein the heating of the slab is performed at 1280 ° C. or higher. The slab composition is, in mass%, instead of a portion of the Fe.
Cu: 0.5000% or less,
Cr: 0.50% or less,
Bi: 0.0200% or less,
Sb: 0.500% or less,
Mo: 0.500% or less,
Sn: 0.500% or less, and Ni: 0.500% or less,
The method for manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, which contains one kind or two or more kinds selected from the group consisting of.