JP7529978B2 - Manufacturing method of grain-oriented electrical steel sheet - Google Patents

Description

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

Grain-oriented electrical steel sheets contain 0.5% to 7% by mass of Si, and the orientation of the crystal grains of the steel sheet is highly concentrated in the {110}<001> orientation, known as the Goss orientation. Grain-oriented electrical steel sheets have excellent magnetic properties and are used, for example, as iron core materials for stationary inductors such as transformers. Various developments have been made to improve the magnetic properties of electrical steel sheets. In particular, with the recent demand for energy saving, there is a demand for further reduction in iron loss in grain-oriented electrical steel sheets. To reduce the iron loss of grain-oriented electrical steel sheets, it is effective to increase the concentration of grains in the Goss orientation to improve the magnetic flux density and reduce hysteresis loss. In the manufacture of grain-oriented electrical steel sheets, the crystal orientation is controlled by utilizing a catastrophic grain growth phenomenon known as secondary recrystallization. To control the crystal orientation during secondary recrystallization, it is important to keep fine precipitates in the steel, called inhibitors, uniformly and stably present until the desired point in secondary recrystallization.

A typical method for reducing iron loss is to reduce eddy current loss by increasing the concentration of Si in steel, which increases the specific resistance. However, it is known that increasing the Si concentration makes the slab hard and brittle, and reduces workability. As a technique for improving workability during the manufacture of grain-oriented electrical steel sheets with 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. For example, Patent Document 1 describes a method for manufacturing silicon steel hot-rolled sheets in which a silicon steel slab containing 2.0 to 4.5 wt% Si is heated to a high temperature, subjected to hot rough rolling, and then subjected to hot finish rolling, in which the relationship between the entry thickness, exit thickness, surface temperature of the steel sheet at the time of bite, and temperature at a specified depth from the steel sheet surface at the time of bite is set within a specified range during hot rough rolling, thereby suppressing surface cracking during hot rolling.

WO 94/014549

The technology described in Patent Document 1 is related to the suppression of surface cracks during hot rolling, but in grain-oriented electrical steel sheets using slabs with high Si concentration, cracks occurring during cold rolling are also an issue. For example, when winding a steel strip around a reel during cold rolling, winding cracks can occur, and these cracks can become the starting point for breakage.

The present invention aims to solve the above problems and provide a method for manufacturing grain-oriented electrical steel sheets that can suppress cracking during cold rolling even when using slabs with high Si concentration.

The present disclosure encompasses the following aspects.
[1] A hot rolling process in which a slab having a slab composition containing, in mass%, C: 0.02% to 0.10%, Si: 2.5% to 4.5%, Mn: 0.01% to 0.30%, one or two of S and Se: 0.001% to 0.050%, acid-soluble Al: 0.01% to 0.05%, N: 0.002% to 0.020%, and the balance Fe and impurities is heated and hot-rolled to obtain a hot-rolled steel sheet;
A pickling process for obtaining a pickled sheet by immersing the hot-rolled steel sheet in a pickling solution, or by subjecting the hot-rolled steel sheet to hot-rolled sheet annealing to obtain a hot-rolled annealed sheet and then immersing the hot-rolled annealed sheet in a pickling solution;
A cold rolling process of cold rolling the pickled steel sheet to obtain a cold rolled steel sheet;
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 process in which an annealing separator containing MgO is applied to the surface of the primary recrystallization annealed sheet, and then finish annealing is performed to obtain a finish annealed sheet;
A flattening annealing process for applying an insulating coating to the finish annealed sheet and then flattening annealing the sheet.
the pickling solution contains one or more metals selected from the group consisting of Cu, Hg, Ag, Pb, Cd, Ni, Zn, and Co in an amount of 0.001% by mass or more and 0.100% by mass or less, and hydrochloric acid in an amount of 5% by mass or more and 20% by mass or less, based on hydrogen chloride.
[2] The method for producing a grain-oriented electrical steel sheet according to the above [1], wherein, 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.
[3] The method for producing a grain-oriented electrical steel sheet according to the above [1] or [2], wherein the heating of the slab is carried out at 1280°C or higher.
[4] The slab composition contains, in mass%, a part 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 producing a grain-oriented electrical steel sheet according to any one of the above [1] to [3], comprising one or more selected from the group consisting of:

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

The following describes exemplary embodiments of the present invention, but the present invention is not limited to the following embodiments. Unless otherwise specified, the notation "A to B" for numerical values A and B means "greater than or equal to A and less than or equal to B."

One aspect of the present invention is
a hot rolling process of heating a slab having a slab composition containing, 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 or two of S and Se: 0.001% or more and 0.050% or less in total, acid-soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.020% or less, with the balance being Fe and impurities, and performing hot rolling to obtain a hot-rolled steel sheet;
A pickling process for obtaining a pickled sheet by immersing the hot-rolled steel sheet in a pickling solution, or by subjecting the hot-rolled steel sheet to hot-rolled sheet annealing to obtain a hot-rolled annealed sheet and then immersing the hot-rolled annealed sheet in a pickling solution;
A cold rolling process of cold rolling the pickled steel sheet to obtain a cold rolled steel sheet;
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 process in which an annealing separator containing MgO is applied to the surface of the primary recrystallization annealed sheet, and then finish annealing is performed to obtain a finish annealed sheet;
and a flattening annealing step of applying an insulating coating to the finish annealed sheet and then flattening annealing the sheet.

In one embodiment, the pickling solution contains 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 that function as inhibitors during finish annealing (typically MnS, MnSe, and AlN) are present in the steel, the inhibitors are finely precipitated in the steel sheet after hot rolling, and some of them are exposed on the steel sheet surface. The inventors noticed that cracks are likely to occur during cold rolling in the production of grain-oriented electrical steel sheets using slabs with a high Si concentration, and after investigating the cause of cracking, they found that corrosion occurs at the interface between the inhibitor on the steel sheet surface and the surrounding base material during pickling after hot rolling, and this corrosion is one of the causes of cracking. Specifically, when the scale on the steel sheet surface is removed by pickling, the inhibitor exposed on the steel sheet surface falls off due to the above-mentioned corrosion, forming fine recesses on the steel sheet surface, and it is believed that stress is concentrated in the recesses during the cold rolling process, causing cracking.

Corrosion at the interface between the inhibitor and the surrounding base material (mainly Fe) is believed to be due to the potential difference between the inhibitor and the base material. The present inventors have intensively studied means for suppressing this corrosion and found that it is effective to include a specific metal species in the pickling solution. In one embodiment, the pickling solution contains a metal component (sometimes simply referred to as a metal component in this disclosure) that is one or more metals selected from the group consisting of Cu, Hg, Ag, Pb, Cd, Ni, Zn, and Co. All of the Mn that constitutes the inhibitor has a relatively low standard electrode potential (standard oxidation-reduction potential) and a relatively high tendency to release electrons, but all of the metals that can constitute the metal component of this embodiment have a higher standard electrode potential than Mn and can be substituted for Mn to form sulfides or selenides. Such substitution is likely to occur near the surface of the inhibitor precipitate, which is the portion that comes into contact with the pickling solution, and is particularly likely to occur near the surface of the inhibitor precipitate exposed on the steel sheet surface. When Mn near the surface of the inhibitor precipitate is replaced with the metal component of this embodiment to form a sulfide or selenide of the metal component, the sulfide or selenide acts as a barrier to suppress the ionization of Mn inside the inhibitor precipitate, thereby reducing corrosion at the interface between the inhibitor and the base material. The metal component attached near 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 minor compared to when the metal component is not attached. In this way, the metal component of this embodiment advantageously contributes to corrosion inhibition at the interface between the inhibitor and the base material, and therefore to inhibitor shedding. In addition, the increase in volume due to the attachment of the metal component to the surface of the inhibitor precipitate also advantageously contributes to corrosion inhibition 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 preferred because they are easy to deposit on the steel sheet surface, are low cost, and have a low environmental impact.

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

In one embodiment, the pickling solution contains hydrochloric acid. Hydrochloric acid is advantageous in that it has a sufficient effect of removing scale from the steel sheet surface while being less likely to corrode the steel sheet surface. In one embodiment, the amount of hydrochloric acid in the pickling solution is 5% by mass or more and 20% by mass or less, preferably 6% by mass or more or 7% by mass or more, and preferably 19% by mass or less or 18% by mass or less, based on hydrogen chloride.

The manufacturing method for the grain-oriented electrical steel sheet according to this embodiment will be described in detail below.

[Slab composition]
First, the composition of the slab used in the grain-oriented electrical steel sheet according to this embodiment will be described. In the following, unless otherwise specified, the notation "%" represents "mass %". The remainder of the slab other than the elements described below is Fe and impurities.

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

The Si (silicon) content is 2.5% or more and 4.5% or less. Si increases the electrical resistance of the steel sheet, thereby reducing eddy current loss, which is one of the causes of iron loss. If the Si content is less than 2.5%, it is not preferable because it becomes difficult to sufficiently suppress the eddy current loss of the final grain-oriented electrical steel sheet. If the Si content exceeds 4.5%, it is not preferable because the workability of the grain-oriented electrical steel sheet decreases. 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.

The content of Mn (manganese) is 0.01% or more and 0.30% or less. Mn forms MnS, MnSe, etc., which are inhibitors that affect secondary recrystallization. If the content of Mn is less than 0.01%, the absolute amount of MnS and MnSe that cause secondary recrystallization is insufficient, which is not preferable. If the content of Mn is more than 0.30%, it is not preferable because it becomes difficult for Mn to be dissolved in solid solution during slab heating. In addition, if the content of Mn is more than 0.30%, it is not preferable because the precipitate size of MnS and MnSe, which are inhibitors, tends to become coarse, and the optimal size distribution as an inhibitor is impaired. Therefore, the content of Mn is 0.01% or more and 0.30% or less, preferably 0.02% or more and 0.15% or less, more preferably 0.03% or more and 0.13% or less, and more preferably 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 inhibitors together with the above-mentioned Mn. Both S and Se may be contained in the slab, but at least one of them should be contained in the slab. If the total content of S and Se is outside the above range, it is not preferable because a sufficient inhibitor effect cannot be obtained. 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 0.040% or less.

The content of acid-soluble Al (acid-soluble aluminum) is 0.01% or more and 0.05% or less. Acid-soluble Al constitutes an inhibitor necessary for manufacturing grain-oriented electrical steel sheets with high magnetic flux density. If the content of acid-soluble Al exceeds 0.05%, the AlN precipitated as an inhibitor becomes coarse, which is not preferable because it reduces the inhibitor strength. In addition, if the content of acid-soluble Al is less than 0.01%, the inhibitor strength is low and is not preferable. Therefore, the content of acid-soluble Al is 0.01% or more and 0.05% or less, and preferably 0.01% or more and 0.04% or less.

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

In addition, in addition to the above-mentioned elements, the slab used in the manufacture of the directional electrical steel sheet of this embodiment may contain, in order to improve the magnetic properties, one or more elements selected from the group consisting of, 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, in place of a portion of the remaining Fe. In one embodiment of the slab, the Cu content may be, in mass%, 0.0005% or more, the Cr content may be 0.02% or more, the Bi content may be 0.0005% or more, the Sb content may be 0.005% or more, the Mo content may be 0.005% or more, the Sn content may be 0.005% or more, and the Ni content may be 0.005% or more.

A slab is formed by casting molten steel adjusted to the composition described above. The method for casting the slab is not particularly limited. In research and development, even if a steel ingot is formed in a vacuum melting furnace or the like, the same effects as when a slab is formed can be confirmed for the above components. Below, the preferred embodiments of each process for manufacturing grain-oriented electrical steel sheet from a slab are further explained.

[Hot rolling process]
In this process, the slab is heated and hot-rolled to obtain a hot-rolled steel sheet. In one embodiment, the heating temperature of the slab may be preferably 1280°C or higher, or 1300°C or higher, from the viewpoint of dissolving the inhibitor components (e.g., MnS, MnSe, AlN, etc.) in the slab to obtain a good inhibitor effect. In this case, the upper limit of the heating temperature of the slab is not particularly specified, but 1450°C is preferable from the viewpoint of equipment protection. Alternatively, in one embodiment, the heating temperature of the slab may be preferably less than 1280°C, or 1250°C or lower, from the viewpoint of reducing the burden on the heating furnace during hot rolling, reducing the amount of scale generation, and downstream processing of inhibitor control.

The heated slab is hot-rolled to produce hot-rolled steel sheet. The thickness of the hot-rolled steel sheet after processing is preferably 1 mm or more, since the temperature of the steel sheet is unlikely to decrease, and the precipitation of inhibitors in the steel can be stably controlled. It is also preferably 10 mm or less, since the rolling load in the cold rolling process can be reduced.

[Pickling process]
In this process, a pickled sheet is obtained by immersing the hot-rolled steel sheet in a pickling solution, or by annealing the hot-rolled steel sheet to obtain a hot-rolled annealed sheet, and then immersing the hot-rolled annealed sheet in a pickling solution. In the method of this embodiment, pickling using a pickling solution containing a metal component that is a specific metal species is performed before cold rolling, which can suppress the inhibitor from falling off due to corrosion at the interface between the inhibitor and the base material on the steel sheet surface, and can reduce cracks 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 process from the viewpoint of reducing roll wear in cold rolling.

The pickling solution contains the above-mentioned metal components and acid. In one embodiment, the pH of the pickling solution is -1.5 or more and less than 7.0. Solutions that can actually be prepared have a pH of -1.5 or more. If the pH of the pickling solution is 7.0 or more, the effect of removing scale by pickling becomes insufficient, which is not preferable. A pickling solution having a pH of -1.5 or more and less than 7.0 is advantageous from the viewpoint of precipitating the desired amount of metal components on the steel sheet surface. The pH is preferably less than 2.0, more preferably less than 1.0.

In one embodiment, the temperature of the pickling solution is 15°C or higher and 100°C or lower. If the temperature of the pickling solution is lower than 15°C, the effect of removing scale by pickling becomes insufficient, which is not preferable. If the temperature of the pickling solution exceeds 100°C, the handling of the pickling solution becomes difficult, which is not preferable. A temperature of the pickling solution of 15°C or higher and 100°C or lower is advantageous from the viewpoint of precipitating the desired degree of metal components on the steel sheet surface. The temperature of the pickling solution may be preferably 22°C or higher, or 24°C or higher, or 26°C or higher, and may be preferably 98°C or lower, or 96°C or lower, or 94°C or lower.

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

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

Between passes of cold rolling, between rolling roll stands, or during rolling, the steel sheet may be heat-treated at about 300°C or less. Such heating is preferable in that it can improve the magnetic properties of the final grain-oriented electrical steel sheet. The hot-rolled steel sheet may be rolled by cold rolling, for example, three or more times, but since multiple cold rolling increases the manufacturing cost, it is preferable to perform cold rolling once or twice. For example, when cold rolling is performed by reverse rolling such as a Sendzimir mill, the number of passes in each cold rolling is not particularly limited, but is preferably 9 times or less from the viewpoint of manufacturing cost. The reduction ratio of the steel sheet in the cold rolling process may be appropriately designed so that a cold-rolled steel sheet of the desired thickness is obtained, and may be, for example, 80% to 95%.

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

(Heating process)
In the temperature increasing step, the cold-rolled steel sheet is heated to a desired decarburization annealing temperature. It is desirable that the heating rate is appropriately controlled according to the temperature range. In one embodiment, the average heating rate in the temperature range of 30°C to 400°C may be 50°C/sec or more from the viewpoint of suppressing oxidation of the metal components precipitated on the steel sheet surface, and may be 600°C/sec or less from the viewpoint of ease of sheet passing. The average heating rate between 400°C and 500°C does not require special control, but may be the same as the average heating rate between 30°C and 400°C exemplified above. 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-oriented grains before the finish annealing of the cold-rolled steel sheet, and may be 3000°C/sec or less from the viewpoint of equipment cost and manufacturing cost. 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 generation of SiO ₂ that inhibits decarburization during decarburization annealing, and may be 2000 ° C./sec or less from the viewpoint of equipment costs and manufacturing costs. Such rapid heating can be performed, for example, by using an electric heating method or an induction heating method. The heating process may be performed by a plurality of devices. The heating rate can be measured by measuring the steel sheet temperature using a radiation thermometer or the like, but if it is difficult to measure the steel sheet temperature, these temperatures may be estimated by analogizing the heat patterns of heating and cooling. In addition, the entry and exit temperatures of the steel sheet to the heating device in the heating process may be the heating start and end points.

(Decarburization annealing process)
After the temperature increase step, a decarburization annealing step is performed. In a typical embodiment, the decarburization annealing step includes a soaking treatment. The soaking treatment may be performed in a wet atmosphere containing hydrogen and/or nitrogen at 900° C. or less, for example, 750° C. to 900° C. The decarburization annealing temperature may be the same as the temperature increase end temperature of the above-mentioned temperature increase step, or may be higher or lower than this. The soaking treatment may be performed once or twice or more. For example, when the soaking treatment is performed twice, that is, the first soaking treatment and the second soaking treatment, the second soaking treatment may be performed by cooling the steel sheet once (for example, to room temperature) after the first soaking treatment is completed, and then reheating, or without cooling. In one embodiment, the decarburization annealing step may include a first soaking treatment performed at 800° C. to 900° C. and a second soaking treatment performed at 900° C. to 1000° C.

The oxygen potential of the soaking atmosphere, i.e., the ratio of the water vapor partial pressure P _H2O to the hydrogen partial pressure P _H2 in the atmosphere (P _H2O /P _H2 ratio) may be 0.2 or more from the viewpoint of favorably progressing internal oxidation and forming a uniform oxide film on the steel sheet surface, and may be 0.8 or less from the viewpoint of obtaining favorable magnetic properties. Furthermore, for example, when the first soaking and the second soaking are performed, the P _H2O /P _H2 ratio of the first soaking may be in the above range, and the P _H2O /P _H2 ratio of the second soaking may be less than 0.2, 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. may be 0 ° C. or lower from the viewpoint of suppressing oxidation of the metal in the steel sheet and suppressing the generation of _SiO2 due to external oxidation to smoothly proceed with decarburization, and may be −50 ° C. or higher from the viewpoint of smoothly proceeding with internal oxidation.

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

[Finish annealing process]
Next, for the purpose of forming a primary coating and secondary recrystallization, the steel sheet after the primary recrystallization annealing step (primarily recrystallized annealed sheet) is subjected to finish annealing. In a typical embodiment, an annealing separator mainly composed of MgO is applied to the primarily recrystallized annealed sheet before the finish annealing for the purpose of preventing seizure between the steel sheets, forming a primary coating, controlling the secondary recrystallization behavior, etc. In the finish annealing, a purification treatment may be performed after the heat treatment of the steel sheet.

[Planarization annealing process]
After the final annealing, an insulating coating (e.g., an insulating coating mainly composed of aluminum phosphate or colloidal silica) may be applied to the surface of the steel sheet for the purpose of imparting insulation and tension to the steel sheet. Then, planarization annealing may be performed for the purpose of baking the insulating coating and planarizing the shape of the steel sheet by the final annealing.

Depending on the application of the resulting grain-oriented electrical steel sheet, further magnetic domain control processing may be performed.

By using the process exemplified above, it is possible to manufacture grain-oriented electrical steel sheets with excellent magnetic properties. The grain-oriented electrical steel sheets that can be manufactured by the method of this embodiment can be processed into wound cores or stacked cores during transformer manufacturing and can be used for the desired applications.

In the production of grain-oriented electrical steel sheets using the method of this embodiment, the fracture frequency is preferably 0.9 times/1000 tons or less, or 0.8 times/1000 tons or less. The lower the fracture frequency, the more desirable it is.

The following provides further explanation of exemplary aspects of the present invention using 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. The slab was heated at 1350 ° C. and then hot-rolled to obtain a hot-rolled steel strip having a thickness of 2.3 mm. The hot-rolled steel strip was then heated to 1120 ° C. for recrystallization, and then annealed at a lower temperature, 900 ° C., to obtain a hot-rolled 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 thickness of 0.220 mm. The frequency of fractures per 1000 tons occurring in the second pass was shown in Table 2.
The breakage frequency is the ratio of the number of breakages that occurred on the second pass to the amount of sheet that was passed when at least 200 tons of multiple coils having the slab composition shown in Table 1 were passed.
The results are shown in Table 2.

As shown in Table 2, by controlling the pickling conditions appropriately, good results were obtained, with the frequency of winding cracking failure during the second cold rolling pass being less than 1 time per 1,000 tons, even when using slabs with a high Si content of 3.30 to 3.65%.

The grain-oriented electrical steel sheet obtained by the method disclosed herein can be suitably applied to various applications that require good magnetic properties.

Claims (4)

a hot rolling process of heating a slab having a slab composition containing, 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 or two of S and Se: 0.001% or more and 0.050% or less in total, acid-soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.020% or less, with the balance being Fe and impurities, and performing hot rolling to obtain a hot-rolled steel sheet;
A pickling process for obtaining a pickled sheet by immersing the hot-rolled steel sheet in a pickling solution, or by subjecting the hot-rolled steel sheet to hot-rolled sheet annealing to obtain a hot-rolled annealed sheet and then immersing the hot-rolled annealed sheet in a pickling solution;
A cold rolling process of cold rolling the pickled steel sheet to obtain a cold rolled steel sheet;
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 process in which an annealing separator containing MgO is applied to the surface of the primary recrystallization annealed sheet, and then finish annealing is performed to obtain a finish annealed sheet;
A flattening annealing process for applying an insulating coating to the finish annealed sheet and then flattening annealing the sheet.
The pickling solution contains one or more metals selected from the group consisting of Cu, Hg, Ag, Pb, Cd, Ni, Zn, and Co in an amount of 0.001% by mass or more and 0.100% by mass or less, and hydrochloric acid in an amount of 5% by mass or more and 20% by mass or less based on hydrogen chloride ,
In the pickling step, Mn near the surface of inhibitor precipitates exposed on the surface of the hot-rolled annealed sheet is replaced with the metal to form sulfides or selenides of the metal . The method for producing grain-oriented electrical steel sheet according to claim 1, wherein in the pickling process, 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 producing grain-oriented electrical steel sheet according to claim 1 or 2, in which the heating of the slab is performed at 1280°C or higher. The slab composition is, in mass %, replacing a part 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 producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, further comprising one or more selected from the group consisting of: