Method for manufacturing grain-oriented electrical steel sheets and rolling equipment therefor

Abstract

To provide a production method of an oriented electrical steel sheet with extremely low iron loss by further enhancing the effect of strain aging during rolling.SOLUTION: Disclosed is a production method of an oriented electrical steel sheet comprising: a hot rolling step in which a steel slab is hot-rolled to form a hot-rolled steel sheet; a hot-rolled sheet annealing step in which the hot-rolled steel sheet is optionally annealed to form a hot-rolled annealed sheet; a cold rolling step in which the hot-rolled steel sheet or the hot-rolled annealed sheet is cold-rolled once or twice or more including intermediate annealing to form a cold-rolled steel sheet having a final sheet thickness; a decarburizing annealing step in which the cold-rolled steel sheet is decarburized and annealed to form a decarburizing annealed sheet; and a finishing annealing step in which the decarburizing annealed sheet is subjected to secondary recrystallization annealing. In the cold rolling to make the final thickness of the cold rolling step, a steel sheet surface vibration step for imposing vibration to the steel sheet surface is performed between at least one passes. In the steel sheet surface vibration step, it is preferable that the surface of the steel sheet is irradiated with acoustic waves, the sound pressure on the surface of the steel sheet is 30 dB or more, and the temperature of the steel sheet is 50°C or more and 400°C or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to the production of a grain-oriented electrical steel sheet having excellent magnetic properties.

Background Art

[0002] A grain-oriented electrical steel sheet is a soft magnetic material used as a core material for transformers and generators. It is a steel sheet with excellent magnetic properties, having a crystal structure in which the {110}<001> orientation, i.e., the so-called Goss orientation, which is the easy magnetization axis of iron, is highly aligned in the rolling direction of the steel sheet.

[0003] As a method for enhancing the aggregation in the Goss orientation, for example, Patent Document 1 discloses a method of heat-treating a cold-rolled steel sheet during cold rolling at a low temperature and performing an aging treatment. Further, Patent Document 2 discloses a technique in which the cooling rate during hot-rolled sheet annealing or intermediate annealing before final cold rolling is set to 30°C / sec or more, and further, during final cold rolling, inter-pass aging at a sheet temperature of 150 to 300°C for 2 minutes or more is performed two or more times. Furthermore, Patent Documents 3 to 5 disclose techniques that utilize dynamic strain aging in which the temperature of the steel sheet during rolling is increased to perform warm rolling, thereby immediately fixing the dislocations introduced during rolling with C or N.

[0004] All of the techniques of these Patent Documents 1 to 3 maintain the steel sheet temperature at an appropriate temperature before cold rolling, during rolling, or between passes of rolling. Thereby, carbon (C) and nitrogen (N), which are solid solution elements, are diffused at a low temperature, the dislocations introduced by cold rolling are fixed, the movement of dislocations in subsequent rolling is hindered, more shear deformation is caused, and the rolling texture is improved. By applying these techniques, a large number of Goss orientation seed crystals are formed at the time of the primary recrystallized sheet. By the grain growth of these Goss orientation seed crystals during secondary recrystallization, the aggregation in the Goss orientation after secondary recrystallization can be enhanced.

[0005] Furthermore, as a technique to further enhance the effect of strain aging described above, Patent Document 4 describes a method in which fine carbides are precipitated in the steel during the annealing process immediately preceding the final cold rolling of the cold rolling process, and this final rolling is divided into two parts: a first half and a second half. In the first half of the final rolling, rolling is performed at a low temperature of 140°C or less with a reduction ratio in the range of 30-75%, while in the second half, rolling is performed at a high temperature of 150-300°C with at least two reduction passes, and the total reduction ratio of the first and second halves combined is 80-95%. This method discloses a technique for obtaining a material that is stably and highly concentrated in the Goss orientation. In addition, Patent Document 5 describes a method of applying 0.5 kg / mm² before tandem cold rolling. 2 A technique has been disclosed in which fine carbides are precipitated in steel by applying heat treatment at 50 to 150°C for 30 seconds to 30 minutes under the above tension conditions. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 50-016610 [Patent Document 2] Japanese Patent Application Publication No. 08-253816 [Patent Document 3] Japanese Patent Application Publication No. 01-215925 [Patent Document 4] Japanese Patent Application Publication No. 09-157745 [Patent Document 5] Japanese Patent Application Publication No. 04-120216 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In recent years, the demand for low-iron-loss grain-oriented electrical steel sheets has been steadily increasing due to societal demands for energy conservation, and the development of technologies to manufacture low-iron-loss grain-oriented electrical steel sheets is required. To achieve this, it is necessary to enhance the effect of strain aging during rolling. However, the prior art disclosed in the above-mentioned patent document has the following problems.

[0008] In techniques that heat the steel sheet during rolling, as described in Patent Documents 1-3, the rise in steel sheet temperature leads to insufficient rolling lubrication, resulting in a decrease in yield due to deterioration of the steel sheet shape. Therefore, there is an upper limit to the steel sheet temperature during aging. Consequently, there is also an upper limit to the magnetic improvement effect. Furthermore, while techniques that perform carbide deposition treatment in the annealing process before the final cold rolling, as described in Patent Documents 4 and 5, enhance the effect of strain aging, there is a need for techniques that further enhance the effect of strain aging.

[0009] The present invention aims to provide a method for manufacturing grain-oriented electrical steel sheets with extremely low iron loss by further enhancing the effect of strain aging during rolling, and rolling equipment for rolling grain-oriented electrical steel sheets used in this method. [Means for solving the problem]

[0010] To solve the above problems, the inventors diligently studied methods to enhance the effect of strain aging during rolling. The experiments that led to this invention are described below.

[0011] A steel slab was prepared with a composition by mass of C:0.037%, Si:3.4%, Mn:0.05%, S:31ppm, Se:31ppm, N:50ppm, and sol.Al:85ppm, with the remainder being Fe and unavoidable impurities. This steel slab was then heated to 1210°C and hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.0 mm.

[0012] The above hot-rolled steel sheet was subjected to hot-rolled annealing at 1000°C for 60 seconds to obtain a hot-rolled annealed sheet, which was then wound into a coil. The obtained hot-rolled annealed sheet was rolled five times using a Zenzimir rolling mill to produce a cold-rolled steel sheet with a thickness of 0.20 mm. During this process, between the first and second passes, an 8000 Hz sound wave was irradiated for 10 minutes using a sound wave generator at the sound pressure shown in Figure 1. The sound pressure was measured by placing a sound pressure meter near the surface of the steel sheet coil. The steel sheet was maintained at 80°C during sound wave irradiation. For comparison, a sample was also prepared that was only kept at a constant temperature without sound wave irradiation.

[0013] Subsequently, the cold-rolled steel sheet underwent primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. After that, an annealing separating agent mainly composed of MgO was applied to the surface of the steel sheet, followed by finish annealing to induce secondary recrystallization. A coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2 was applied to the surface of the steel sheet after the secondary recrystallization annealing, and planarization annealing was performed at 800°C for 30 seconds to form the product coil.

[0014] Samples were cut from the product coil so that the total weight was 500g or more, and the iron loss was measured by performing an Epstein test. The results are shown in Figure 1. From Figure 1, it can be seen that materials irradiated with sound waves that produced a sound pressure of 30dB or more near the surface of the steel sheet during cold rolling exhibited low iron loss of 0.82 W / kg or less.

[0015] The inventors believe the mechanism by which iron loss was reduced in the above experiment is as follows: By irradiating the steel plate with sound waves and forcing it to vibrate slightly, repeated bending deformation is applied to the steel plate. As a result, the lattice spacing near the material surface is expanded, and the mobility of carbon atoms, which are interstitial solid solution elements, increases. This promotes the diffusion of carbon in the steel to dislocations, and as a result of the enhanced effect of strain aging, the secondary recrystallized plate structure is thought to have accumulated more in the Goss orientation. Based on these findings, further investigations were conducted, and the present invention was completed.

[0016] The method for manufacturing grain-oriented electrical steel sheets according to the present invention, developed based on the above findings, is configured as follows. [1] A method for manufacturing grain-oriented electrical steel sheets, comprising: a hot rolling step of hot rolling a steel slab to obtain a hot-rolled steel sheet; optionally, a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet to obtain a hot-rolled annealed sheet; a cold rolling step of cold rolling the hot-rolled steel sheet or the hot-rolled annealed sheet once or two or more times with an intermediate annealing in between to obtain a cold-rolled steel sheet having a final thickness; a decarburization annealing step of decarburizing the cold-rolled steel sheet to obtain a decarburized annealed sheet; and a finish annealing step of secondary recrystallization annealing the decarburized annealed sheet, wherein in the cold rolling to obtain the final thickness of the cold rolling step, a steel sheet surface vibration step of vibrating the steel sheet surface is performed between at least one pass. [2] In the steel sheet surface vibration step described in [1] above, sound waves are irradiated onto the steel sheet so that the sound pressure on the surface of the steel sheet is 30 dB or more, which is a method for manufacturing grain-oriented electrical steel sheets. [3] The method for manufacturing grain-oriented electrical steel sheets in which, in the steel sheet surface vibration step described in [1] or [2] above, the steel sheet temperature is set to 50°C or higher and 400°C or lower. [4] In any one of [1] to [3] above, the steel slab contains, by mass%, C: 0.01 to 0.10%, Si: 2.0 to 4.5%, and Mn: 0.01 to 0.5%, and Group A: Al: 0.0100 to 0.0400%, N: 0.0050 to 0.0120%, and at least one of S and Se totaling 0.01 to 0.05%, Group B: Al: less than 0.0100%, S: 0.0100% or less, Se: 0.0100% or less, and This is a method for manufacturing grain-oriented electrical steel sheets, wherein the composition contains one of the components from the group N: 0.0050% or less, with the remainder being Fe and unavoidable impurities. [5] The method for manufacturing grain-oriented electrical steel sheets, wherein the steel slab further contains, by mass%, at least one component from groups C to E described below, as described in [4] above. Group C; at least one selected from Sb: 0.005~0.50%, Cu: 0.01~1.50%, P: 0.005~0.500%, Cr: 0.01~1.50%, Ni: 0.005~1.500%, Sn: 0.01~0.50%, Nb: 0.0005~0.0100%, Mo: 0.01~0.50%, B: 0.0010~0.007%, and Bi: 0.0005~0.0500%. Group D; Ti: 0.0005~0.0400%, V: 0.001~0.020% and W: At least one type selected from 0.001 to 0.020% Group E; at least one selected from Zn: 0.0005 to 0.020%, Zr: 0.001 to 0.020%, Pb: 0.0001 to 0.0100%, As: 0.001 to 0.020%, Ag: 0.001 to 0.050%, Au: 0.001 to 0.050%, Ga: 0.0001 to 0.0050%, Ge: 0.0001 to 0.0050%, Ca: 0.0005 to 0.020%, Mg: 0.0005 to 0.020%, REM: 0.0005 to 0.0200% and Hf: 0.001 to 0.020%.

[0017] Based on the above findings, the rolling equipment for the grain-oriented electrical steel sheet according to the present invention developed is configured as follows [6] A rolling equipment for grain-oriented electrical steel sheet rolling, comprising a device for irradiating sound waves with a sound pressure level of 30 dB or more on the steel sheet surface.

Effect of the Invention

[0018] According to the present invention, the effect of strain aging during rolling can be further enhanced, and a grain-oriented electrical steel sheet with extremely low iron loss can be manufactured.

Brief Description of the Drawings

[0019] [Figure 1] It is a graph showing the influence of the sound pressure of the sound wave irradiated on the steel sheet surface on the iron loss of the steel sheet.

Embodiments for Carrying Out the Invention

[0020] First, the rolling equipment for manufacturing grain-oriented electrical steel sheet according to the present embodiment will be described. <Rolling Equipment> The production of the grain-oriented electrical steel sheet according to the present embodiment includes a hot rolling process, an optional hot rolled sheet annealing process, a cold rolling process, a decarburization annealing process, and a finish annealing process, and in the cold rolling process, a steel sheet surface vibration process is carried out. Devices and equipment for carrying out the hot rolling process, the hot rolled sheet annealing process, the decarburization annealing process, and the finish annealing process can use known ones. Also, the type of rolling mill for cold rolling is not particularly limited. For example, a tandem rolling mill, a reversing rolling mill, etc. are suitable.

[0021] The sound wave irradiation device used in the steel sheet surface vibration process is preferably a device that irradiates sound waves with a sound pressure level of 30 dB or higher. The frequency of the sound waves is preferably 10 Hz or higher. More preferably 100 Hz or higher. It is also preferable that it be 500 Hz or higher, 1000 Hz or higher, and even more preferably 3000 Hz or higher. The upper limit is preferably 100 kHz. Furthermore, the sound wave irradiation device is preferably installed between the stands in a tandem rolling mill, and preferably installed on one or both winders of the rolling mill in a reverse rolling mill.

[0022] Next, a method for manufacturing grain-oriented electrical steel sheets according to this embodiment will be described. The manufacturing method for grain-oriented electrical steel sheets according to this embodiment includes a hot rolling step, an optional hot-rolled sheet annealing step, a cold rolling step, and a finish annealing step. In the hot rolling step, a steel slab is hot-rolled to obtain a hot-rolled steel sheet. In the hot-rolled sheet annealing step, the hot-rolled steel sheet is annealed to obtain a hot-rolled annealed sheet. In the cold rolling step, the hot-rolled steel sheet or hot-rolled annealed sheet is cold-rolled once or two or more times with an intermediate annealing in between to obtain a cold-rolled steel sheet having a final thickness. In the decarburization annealing step, the cold-rolled steel sheet is decarburized annealed to obtain a decarburized annealed sheet. In the finish annealing step, the decarburized annealed sheet is subjected to secondary recrystallization annealing.

[0023] In this embodiment, in the cold rolling process that determines the final thickness of the sheet metal, a steel sheet surface vibration process is performed between at least one pass. Here, the cold rolling process that determines the final thickness refers to the cold rolling process if it does not include intermediate annealing, and if it includes intermediate annealing, it refers to the cold rolling process after the last intermediate annealing, where the thickness of the steel sheet after that cold rolling process becomes the final thickness.

[0024] <Steel slab> The steel slab (steel material) of this embodiment can be manufactured by methods such as steelmaking-continuous casting or ingot formation-blot rolling. In steelmaking, molten steel obtained in a converter or electric furnace can be refined to the desired composition through secondary refining such as vacuum degassing.

[0025] The composition of the steel slab can be the same as that used for manufacturing grain-oriented electrical steel sheets. It is preferable to include C, Si, and Mn in order to obtain grain-oriented electrical steel sheets with excellent magnetic properties. Examples of C, Si, and Mn content are as follows. In the following description, "%" in relation to the composition means "mass%" unless otherwise specified.

[0026] C: 0.01~0.10% Carbon (C) is an element necessary to improve the primary recrystallized texture by fixing dislocations introduced during the final cold rolling. Since this technology promotes carbon diffusion by ultrasonic irradiation, C content is most preferable. If the C content exceeds 0.10%, it may be difficult to reduce it to 0.0050% or less, where magnetic aging does not occur, through decarburization annealing. On the other hand, if the C content is less than 0.01%, the texture improvement effect may be insufficient. Therefore, the C content is preferably 0.01 to 0.10%, and more preferably 0.01 to 0.08%.

[0027] Si: 2.0~4.5% Si is an effective element for increasing the electrical resistance of steel and improving iron loss. If the Si content exceeds 4.5%, the workability decreases significantly, which may make it difficult to manufacture by rolling. On the other hand, if the Si content is less than 2.0%, it may be difficult to obtain a sufficient effect of reducing iron loss. Therefore, the Si content is preferably between 2.0% and 4.5%, and more preferably between 2.5% and 4.5%.

[0028] Mn: 0.01~0.5% Mn is an element necessary to improve hot workability. If the Mn content exceeds 0.5%, the primary recrystallized texture deteriorates, and it may become difficult to obtain secondary recrystallized grains with a high concentration of Goss orientations. On the other hand, if the Mn content is less than 0.01%, it may become difficult to obtain sufficient hot rollability. Therefore, the Mn content is preferably 0.01 to 0.5%, and more preferably 0.03 to 0.5%.

[0029] <Use of inhibitors> Group A: Al: 0.0100~0.0400%, N: 0.0050~0.0120%, and at least one of S and Se totaling 0.01~0.05% The component composition preferably includes C, Si, and Mn, as well as Al: 0.0100~0.0400% and N: 0.0050~0.0120% as inhibitor components in secondary recrystallization. If the Al and N content is below the above lower limit, it may be difficult to obtain the desired inhibitor effect. On the other hand, if it exceeds the above upper limit, the dispersion state of the precipitate will become heterogeneous, and it may be difficult to obtain the desired inhibitor effect. Furthermore, in addition to Al and N, at least one of S and Se may be included as an inhibitor component in a total of 0.01~0.05%. By including these, sulfides such as MnS and Cu2S, and selenides such as MnSe and Cu2Se can be formed. The sulfides and selenides may precipitate in combination. When the S content, Se content, or their sum is above the lower limit, a sufficient inhibitory effect can be obtained. When it is below the upper limit, the dispersion of the precipitate becomes uniform, and a sufficient inhibitory effect can be obtained.

[0030] <Inhibitorless> Group B; Al: less than 0.0100%, S: 0.0100% or less, Se: 0.0100% or less, and N: 0.0050% or less. The component composition can also be adapted to an inhibitor-free system by suppressing the Al content to less than 0.0100%. In this case, the N content should be N: 0.0050% or less, S: 0.0100% or less, and Se: 0.0100% or less.

[0031] To improve magnetic properties, in addition to the elements of the basic composition described above, at least one component from groups C to E below may be included as an optional additive element.

[0032] Group C; at least one selected from Sb: 0.005-0.50%, Cu: 0.01-1.50%, P: 0.005-0.500%, Cr: 0.01-1.50%, Ni: 0.005-1.500%, Sn: 0.01-0.50%, Nb: 0.0005-0.0100%, Mo: 0.01-0.50%, B: 0.0010-0.007%, and Bi: 0.0005-0.0500%. Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi are elements useful for improving magnetic properties, and it is preferable to include them within the above ranges if they are to obtain a sufficient magnetic property improvement effect without inhibiting the development of secondary recrystallized grains.

[0033] Group D; at least one selected from Ti: 0.0005~0.0400%, V: 0.001~0.020%, and W: 0.001~0.020%. Ti, V, and W all form fine carbides and nitrides, which refine the crystal grains after intermediate annealing, thereby improving bending properties and sheet treadability. However, below the lower limit, the above effects cannot be fully obtained, while adding more than the upper limit may lead to saturation of the above effects and an increase in raw material costs.

[0034] Group E: At least one selected from Zn: 0.005-0.020%, Zr: 0.001-0.020%, Pb: 0.0001-0.0100%, As: 0.001-0.020%, Ag: 0.001-0.050%, Au: 0.001-0.050%, Ga: 0.0001-0.0050%, Ge: 0.0001-0.0050%, Ca: 0.0005-0.020%, Mg: 0.0005-0.020%, REM: 0.0005-0.0200%, and Hf: 0.001-0.020%. Zn, Zr, Pb, As, Ag, Au, Ga, Ge, Ca, Mg, REM, and Hf all have the effect of reinforcing grain boundaries by concentrating at them or forming compounds at the grain boundaries, thereby suppressing the occurrence of defects caused by grain boundary fracture. However, if the content is below the lower limit, the above effect cannot be sufficiently obtained, while if it is added in excess of the upper limit, the above effect will saturate, which may lead to an increase in raw material costs.

[0035] The steel slab used in this embodiment consists of Fe and unavoidable impurities, with the remainder being the elements of the basic composition described above and any optional additives. However, for the purpose of further improving magnetic properties, corrosion resistance, tensile strength, fatigue properties, castability, and treadability, and improving productivity through scrap utilization, trace elements such as In, Te, Ce, Os, Re, Ta, Y, La, and Yb may be included in place of a portion of the remaining Fe, in a total amount of 5.0% or less, preferably 2.0% or less, and more preferably 1.0% or less. Furthermore, elements other than those listed above may be included in the steel as unavoidable impurities, as long as they do not impair the effects of this embodiment.

[0036] The remainder of the steel slab's composition consists of Fe and unavoidable impurities. For example, it may contain 0.0060% or less of O (oxygen). Note that the content of optional additives below the lower limit is acceptable as unavoidable impurities because it does not affect the properties of the grain-oriented electrical steel sheet in this embodiment.

[0037] <Hot rolling process> The manufacturing method of this embodiment involves hot-rolling a steel slab to produce a hot-rolled steel sheet. The steel slab can be heated before being subjected to hot-rolling. From the viewpoint of ensuring hot-rollability, the heating temperature is preferably 1050°C or higher. There is no particular upper limit to the heating temperature, but temperatures above 1450°C are close to the melting point of steel, making it difficult to maintain the shape of the slab, so it is preferable to keep the temperature below 1450°C. Other hot rolling conditions are not particularly limited, and known conditions can be applied.

[0038] <Hot-rolled sheet annealing process> Hot-rolled steel sheets may optionally be subjected to hot-rolled sheet annealing. In this case, the annealing conditions are not particularly limited, and known conditions can be applied.

[0039] <Cold rolling process> Hot-rolled steel sheets are annealed as needed, and then cold-rolled to produce cold-rolled steel sheets. Descaling by pickling or other methods may be performed before cold rolling.

[0040] The cold-rolled steel sheet may be formed to its final thickness in a single cold-rolling process, or it may be formed to its final thickness by two or more cold-rolling processes with an intermediate annealing in between. The total reduction ratio of the cold rolling is preferably 70% to 95%. The reduction ratio of the final cold-rolling is preferably 60% to 95%. The final thickness is preferably 0.1 mm to 1.0 mm.

[0041] <Steel plate surface vibration process> Sound waves are irradiated onto the steel sheet surface during at least one pass of cold rolling to determine the final sheet thickness. This irradiation is thought to partially expand the spacing between the crystal lattice of the steel sheet, making it easier for dissolved carbon to move between the crystal lattices, thereby promoting the diffusion of dissolved carbon into dislocations.

[0042] Here, "pass" refers to the process of rolling a steel plate once by one rolling mill. The rolling process at each stand of a tandem rolling mill is also called a pass, as is the rolling process of a reverse rolling mill. "Pass interval" refers to the time between passes.

[0043] The sound pressure of the sound waves irradiated onto the steel plate is preferably 30 dB or higher. If the sound pressure is less than 30 dB, the vibrations that should be imparted to the steel plate by the irradiated sound waves may be hindered by the rigidity of the steel plate itself, and the effect of promoting the diffusion of solid solution carbon may not be sufficiently obtained. A sound pressure of 60 dB or higher is more preferable, and even more preferable is 80 dB or higher. The sound pressure can be measured by installing a sound pressure meter near the surface of the steel plate. Furthermore, there is no upper limit on the sound pressure. However, from the viewpoint of preventing noise pollution, a sound pressure of 150 dB or less is preferable, and even more preferable is 130 dB or less.

[0044] The frequency of the sound waves to be irradiated is not particularly limited and can be set according to the thickness and rigidity of the steel plate coil. From the viewpoint of ensuring the number of vibrations per unit time, it is preferable that the frequency be 10 Hz or higher. Furthermore, the higher the frequency, the higher the directivity of the sound waves, making it easier to control the sound wave irradiation position. Therefore, it is more preferable that the frequency of the sound waves be 100 Hz or higher, and more preferably 500 Hz or higher, 1000 Hz or higher, and even more preferably 3000 Hz or higher. There is no particular upper limit to the frequency of the sound waves, but it is preferable that it be 100 kHz or lower, and more preferably 80 kHz or lower.

[0045] The irradiation of the steel sheet may be performed while heating the steel sheet. Since the diffusion of carbon in steel is a thermally activated physical phenomenon, heating can further promote the diffusion of carbon into dislocations. Therefore, the temperature of the steel sheet when irradiating with sound waves is preferably 50°C or higher, and more preferably 80°C or higher. If the steel sheet temperature is too high, insufficient lubrication during rolling may result in defects in the shape of the steel sheet, which may reduce the yield. Therefore, the upper limit of the steel sheet temperature is preferably 400°C or lower, and more preferably 350°C or lower. The method of heating the steel sheet between passes is not particularly limited. For example, methods that utilize the heat generated during processing during rolling or methods that blow high-temperature air generated externally onto the steel sheet coil can be applied.

[0046] The type of rolling mill used for cold rolling to achieve the final plate thickness is not particularly limited. For example, tandem rolling mills and reverse rolling mills are suitable. In the case of a tandem rolling mill, the ultrasonic irradiation device can be installed between the stands, and in the case of a reverse rolling mill, it can be installed on one or both winders.

[0047] Furthermore, the means of vibrating the surface of the steel plate are not limited to sound wave irradiation. For example, one method involves bringing a vibrator that applies mechanical vibration to the steel plate, or applying an alternating magnetic field to the steel plate to vibrate it through magnetostriction.

[0048] <Decarburization annealing process> In this embodiment, a cold-rolled steel sheet having a final thickness can be decarburized and then subjected to secondary recrystallization annealing to obtain a grain-oriented electrical steel sheet. An insulating coating may be applied after secondary recrystallization annealing.

[0049] The conditions for decarburization annealing are not particularly limited. Generally, decarburization annealing often combines with primary recrystallization annealing, and this embodiment can also combine with primary recrystallization annealing. In that case, for example, annealing conditions such as 800°C for 2 minutes in a warm hydrogen atmosphere can be used.

[0050] <Finishing annealing process> After decarburizing and annealing the cold-rolled steel sheet, a finish annealing is performed for secondary recrystallization. Before the finish annealing, an annealing release agent can be applied to the surface of the steel sheet. The annealing release agent is not particularly limited and may include, for example, one mainly composed of MgO with TiO2 added as needed, or one mainly composed of SiO2 or Al2O3.

[0051] After finish annealing, it is preferable to apply an insulating coating to the surface of the steel plate and bake it, and if necessary, to flatten the shape of the steel plate by annealing. The type of insulating coating is not particularly limited, but when forming an insulating coating that imparts tensile tension to the surface of the steel plate, it is preferable to use a coating solution containing phosphate-colloidal silica and bake it at about 800°C. [Examples]

[0052] [Example 1] A steel slab was prepared with a composition by mass of C:0.037%, Si:3.4%, Mn:0.05%, S:31ppm, Se:31ppm, N:50ppm, and sol.Al:85ppm, with the remainder being Fe and unavoidable impurities. This steel slab was then heated to 1210°C and hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.0 mm.

[0053] The hot-rolled steel sheet described above was subjected to hot-rolled annealing at 1000°C for 60 seconds and wound into a coil. The resulting hot-rolled and annealed sheet was rolled into a cold-rolled steel sheet with a thickness of 0.20 mm in five rolling passes using a Zenzimir rolling mill. During this process, 300 Hz sound waves were irradiated onto the steel sheet surface for 5 minutes using a sound wave generator, with the sound pressure on the steel sheet surface set to 50 dB between the passes shown in Table 1. The steel sheet was held at the temperature shown in Table 1 during sound wave irradiation. Subsequently, the cold-rolled steel sheet underwent primary recrystallization annealing, which also served as decarburization annealing, at a soaking temperature of 840°C for a soaking time of 100 seconds. After that, an annealing separating agent mainly composed of MgO was applied to the surface of the steel sheet, followed by finish annealing to induce secondary recrystallization. A coating solution containing phosphate, chromate, and colloidal silica in a weight ratio of 3:1:2 was applied to the surface of the steel sheet after the secondary recrystallization annealing described above, and planar annealing was performed at 800°C for 30 seconds to form the product coil.

[0054] Samples were cut from the product coil so that the total weight was 500g or more, and the iron loss was measured by performing an Epstein test. The results are shown in Table 1. The iron loss W17 / 50 represents the iron loss at a frequency of 50Hz and a maximum magnetic flux density of 1.7T. The same applies below.

[0055] Materials that were irradiated with sound waves at least once between each pass (conditions No. 1-15, 17-28) showed low iron loss of 0.84 W / kg or less. Furthermore, under conditions where the steel plate temperature was maintained at 50°C or higher during sound wave irradiation (conditions No. 7-15, 17-25), the iron loss was 0.82 W / kg or less, indicating improved magnetism.

[0056] [Table 1]

[0057] [Example 2] A steel slab was used with a composition on a mass basis containing C:0.06%, Si:3.4%, Mn:0.06%, N:90ppm, sol.Al:250ppm, S:0.02%, and Se:0.02%, with the remainder being Fe and unavoidable impurities. The steel slab was then heated to 1400°C and hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.0 mm.

[0058] The hot-rolled steel sheet described above was subjected to hot-rolled annealing at 1000°C for 60 seconds and wound into a coil. The resulting hot-rolled annealed sheet was subjected to the first cold-rolling in a tandem rolling mill (roll diameter 300 mm, 5 stands). Next, it underwent intermediate annealing at 1100°C for 80 seconds in an atmosphere of 75 vol% N2, 25 vol% H2, and a dew point of 46°C. Then, it underwent final cold-rolling in a tandem rolling mill (roll diameter 300 mm, 5 stands) to obtain a cold-rolled steel sheet with a thickness of 0.20 mm. During the final cold-rolling, sound wave irradiation devices were installed between each stand, and sound waves of sound pressure and frequency were irradiated between the stands shown in Table 2. The sound pressure was measured with a sound pressure meter attached near the surface of the steel sheet. The frequency was adjusted using the sound wave irradiation device. Furthermore, during the final rolling process, the steel sheet temperature between the stands where sonic irradiation was performed was adjusted to various temperatures shown in Table 2 by adjusting the amount of strip coolant injected. The steel sheet temperature was measured using an infrared thermometer.

[0059] Subsequently, the cold-rolled steel sheet underwent primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. After that, an annealing separating agent mainly composed of MgO was applied to the surface of the steel sheet, followed by finish annealing to induce secondary recrystallization. A coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2 was applied to the surface of the steel sheet after the secondary recrystallization annealing, and flattening annealing was performed at 800°C for 30 seconds to form the product coil.

[0060] Test specimens were cut from the product coil so that the total weight was 500g or more, and the iron loss was measured by performing the Epstein test. The results are shown in Table 2.

[0061] Even when using steel slabs with a large amount of inhibitor added, and including intermediate annealing in the cold rolling process, it can be seen that the iron loss is good when the final cold rolling is performed under specified sonic irradiation conditions.

[0062] [Table 2]

[0063] [Example 3] Steel was melted down to form a steel slab. This slab was then heated to 1210°C and hot-rolled to form a 2.0 mm thick hot-rolled steel sheet.

[0064] The hot-rolled steel sheet described above was subjected to hot-rolled annealing at 1000°C for 60 seconds and wound into a coil. The resulting hot-rolled annealed sheet was rolled into a cold-rolled steel sheet with a thickness of 0.20 mm in one tandem rolling pass using a tandem rolling mill (roll diameter 300 mm, number of stands 5). During the final cold rolling, a sound wave irradiation device was installed between the first and second stands, and 4000 Hz sound waves at a sound pressure of 70 dB were irradiated onto the passing steel sheet. The temperature and pressure were measured using a sound pressure meter attached near the surface of the steel sheet. The temperature of the steel sheet between the first and second stands was adjusted to 100°C. Subsequently, the cold-rolled steel sheet underwent primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. After that, an annealing separating agent mainly composed of MgO was applied to the surface of the steel sheet, followed by finish annealing to induce secondary recrystallization. A coating solution containing phosphate, chromate, and colloidal silica in a weight ratio of 3:1:2 was applied to the surface of the steel sheet after the secondary recrystallization annealing described above, and planar annealing was performed at 800°C for 30 seconds to form the product coil.

[0065] Test specimens were cut from the product coil so that the total weight was 500g or more, and the iron loss was measured by performing the Epstein test. The results are shown in Table 3.

[0066] Steel sheets to which at least one of the following elements is added show an iron loss of less than 0.77 W / kg and further improved properties.

[0067] [Table 3]

[0068] [Example 4] A steel was melted down to form a steel slab, which had a composition of C: 0.06%, Si: 3.4%, and Mn: 0.06% by mass, with N: 90 ppm, sol.Al: 250 ppm, S and Se: 0.02% each, and other components selected from groups C to E as shown in Tables 4-1 and 4-2, with the remainder being Fe and unavoidable impurities. The steel slab was then heated to 1400°C and hot-rolled to form a hot-rolled steel sheet with a thickness of 2.0 mm.

[0069] The hot-rolled steel sheet described above was subjected to hot-rolled annealing at 1000°C for 60 seconds and wound into a coil. The resulting hot-rolled annealed sheet was rolled into a cold-rolled steel sheet with a thickness of 0.20 mm in one tandem rolling pass using a tandem rolling mill (roll diameter 300 mm, number of stands 5). During the final cold rolling, a sound wave irradiation device was installed between the first and second stands, and 4000 Hz sound waves at a sound pressure of 70 dB were irradiated onto the passing steel sheet. The temperature and pressure were measured using a sound pressure meter attached near the surface of the steel sheet. The temperature of the steel sheet between the first and second stands was adjusted to 100°C. Subsequently, the cold-rolled steel sheet underwent primary recrystallization annealing, which also served as decarburization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. After that, an annealing separating agent mainly composed of MgO was applied to the surface of the steel sheet, followed by finish annealing to induce secondary recrystallization. A coating solution containing phosphate, chromate, and colloidal silica in a weight ratio of 3:1:2 was applied to the surface of the steel sheet after the secondary recrystallization annealing described above, and planar annealing was performed at 800°C for 30 seconds to form the product coil.

[0070] Test specimens were cut from the product coil so that the total weight was 500g or more, and the iron loss was measured by performing the Epstein test. The results are shown in Tables 4-1 and 4-2.

[0071] Tables 4-1 and 4-2 show that even when using steel slabs with a large amount of inhibitor added, steel sheets with one or more of Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi added have an iron loss of 0.77 W / kg or less, indicating further improvement in properties. In addition, steel sheets with at least one component selected from groups A and B, Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, Bi, Ti, V, W, Zn, Zr, Pb, As, Ag, Au, Ga, Ge, Ca, Mg, REM, and Hf added all have an iron loss W17 / 50 lower than 0.82 W / kg, indicating that the magnetic property improvement effect by sound wave irradiation of the present invention is obtained without any problems.

[0072] [Table 4-1]

[0073] Table 4-2

Claims

1. The hot rolling process involves hot rolling a steel slab to produce a hot-rolled steel sheet, Optionally, the hot-rolled steel sheet is annealed to form a hot-rolled annealed sheet; A cold rolling process in which the hot-rolled steel sheet or the hot-rolled annealed sheet is subjected to cold rolling once or two or more times with an intermediate annealing in between, to obtain a cold-rolled steel sheet having a final thickness, The decarburization annealing process involves subjecting the aforementioned cold-rolled steel sheet to decarburization annealing to obtain a decarburized annealed sheet. A finish annealing step is performed on the decarburized annealed plate, in which secondary recrystallization annealing is performed. Includes, In the cold rolling process to obtain the final sheet thickness, a steel sheet surface vibration process is performed between at least one pass, in which vibration is applied to the surface of the steel sheet. A method for manufacturing grain-oriented electrical steel sheets, wherein the steel sheet surface vibration step involves setting the steel sheet temperature to 50°C or higher and 400°C or lower, and the vibration is performed by irradiating the sheet with sound waves having a predetermined frequency of 10 Hz or higher and 10,000 Hz or lower.

2. The method for manufacturing grain-oriented electrical steel sheets according to claim 1, wherein in the steel sheet surface vibration step, sound waves are irradiated onto the steel sheet so that the sound pressure on the surface of the steel sheet is 30 dB or more.

3. The aforementioned steel slab is, by mass%, C: 0.01 to 0.10%, Si: 2.0–4.5% and Mn: 0.01~0.5% It contains, Group A; Al: 0.0100-0.0400%, N: 0.0050–0.0120% and At least one of S and Se in total, 0.01 to 0.05% Group B; Al: Less than 0.0100% S: 0.0100% or less, Se: 0.0100% or less and N: 0.0050% or less, The composition contains components from any one of the following groups, with the remainder being Fe and unavoidable impurities. A method for manufacturing grain-oriented electrical steel sheets according to claim 1 or 2.

4. The method for producing a grain-oriented electrical steel sheet according to claim 3, wherein the steel slab further contains, by mass%, at least one component from groups C to E described below. Group C; Sb: 0.005 to 0.50%, Cu: 0.01 to 1.50%, P: 0.005-0.500%, Cr: 0.01-1.50%, Ni: 0.005-1.500%, Sn: 0.01-0.50%, Nb: 0.0005 to 0.0100%, Mo: 0.01-0.50%, B: 0.0010–0.007% and Bi: 0.0005-0.0500% At least one of the following, Group D; Ti: 0.0005 to 0.0400%, V: 0.001–0.020% and W: 0.001-0.020% At least one of the following, Group E; Zn: 0.0005-0.020%, Zr: 0.001 to 0.020%, Pb: 0.0001 to 0.0100%, As: 0.001 to 0.020%, Ag: 0.001-0.050%, Au: 0.001 to 0.050%, Ga: 0.0001-0.0050%, Ge: 0.0001 to 0.0050%, Ca: 0.0005-0.020%, Mg: 0.0005-0.020%, REM: 0.0005–0.0200% and Hf: 0.001-0.020% At least one of the following.

5. A rolling mill for grain-oriented electrical steel sheets, comprising a device that irradiates sound waves of a predetermined frequency of 10 Hz to 10,000 Hz, with a sound pressure level of 30 dB or more on the surface of the steel sheet, at least one location between passes where the cold-rolled steel sheet temperature for the final thickness of the cold-rolling process is 50°C to 400°C.

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