WO2025079437A1 - Method for producing grain-oriented electrical steel sheet, grain-oriented electrical steel sheet, and industrial product - Google Patents

Abstract

The present invention provides a method for producing a grain-oriented electrical steel sheet in which a plurality of grooves that extends in a direction that is generally parallel to the width direction of a steel sheet is formed in the longitudinal direction of the steel sheet, the method including: a first groove formation step for forming a first groove comprising a plurality of grooves which extends in a direction that is generally parallel to the width direction on a cold-rolled steel sheet that serves as a material for the grain-oriented electrical steel sheet; a secondary recrystallization annealing step for annealing the cold-rolled steel sheet, on which the first groove has been formed, so as to align the easy axis of magnetization of the cold-rolled steel sheet in the longitudinal direction to form a grain-oriented electrical steel sheet; and a second groove formation step for forming a second groove comprising a plurality of grooves which extends in a direction that is generally parallel to the width direction on the grain-oriented electrical steel sheet using a contact-type groove formation process.

Description

Manufacturing method of grain-oriented electrical steel sheet, grain-oriented electrical steel sheet and industrial product

This disclosure relates to a method for manufacturing grain-oriented electrical steel sheets, grain-oriented electrical steel sheets, and industrial products.

In order to improve the electromagnetic properties of grain-oriented electromagnetic steel sheets, a stress relief annealing (SRA) magnetic domain control method is used, which allows magnetic domain control with heat resistance and iron loss improvement effects by providing periodic grooves in the longitudinal direction of the grain-oriented electromagnetic steel sheet. In this type of SRA magnetic domain control method, several process steps and groove formation methods have been proposed.

Special Publication No. 62-53579 Patent No. 6826604

Grain-oriented electrical steel sheet is required to have magnetic properties that improve iron loss (low iron loss) and have high magnetic flux density, but these are generally contradictory properties. In other words, to improve iron loss, it is desirable to create deep grooves using lasers or etching, which do not cause mechanical wear. However, making the grooves deeper results in a problem that the loss of base material increases, resulting in a decrease in magnetic flux density. Also, when grooves are created by machining, the loss of base material is not so great that the decrease in magnetic flux density can be suppressed, but there is a problem that the machining equipment is worn out due to contact with the steel sheet. The deeper the grooves are created, the greater the wear on the machining equipment.

In other words, when performing magnetic domain control, in order to obtain sufficient iron loss improvement, a groove depth of 20 to 25 μm and a groove pitch of 3 to 4 mm are required, but when the base material is laser processed according to these formation conditions, the magnetic flux density B8 decreases due to the removal of the base material. On the other hand, when the base material is machined according to these formation conditions, although the decrease in magnetic flux density B8 can be avoided to some extent by pressing the base material, it is difficult to obtain the groove depth required to improve iron loss due to wear on the machining equipment.

In consideration of the above problems, the object of the present invention is to provide a manufacturing method for grain-oriented electrical steel sheet that achieves both improved iron loss and magnetic flux density, and to provide a grain-oriented electrical steel sheet that achieves both improved iron loss and magnetic flux density.

In order to solve the above problems, according to one aspect of the present invention, there is provided a method for manufacturing a grain-oriented electromagnetic steel sheet in which a plurality of grooves extending in a direction substantially parallel to the width direction of the steel sheet are formed in the longitudinal direction of the steel sheet, the method comprising: a first groove forming step of forming a first groove consisting of a plurality of grooves extending in a direction substantially parallel to the width direction in a cold-rolled steel sheet that is the material for the grain-oriented electromagnetic steel sheet; a secondary recrystallization annealing step of annealing the cold-rolled steel sheet in which the first grooves are formed, thereby aligning the magnetization easy axis of the cold-rolled steel sheet in the longitudinal direction to form a grain-oriented electromagnetic steel sheet; and a second groove forming step of forming a second groove consisting of a plurality of grooves extending in a direction substantially parallel to the width direction in the grain-oriented electromagnetic steel sheet using a contact-type groove forming process.

The first groove forming step may involve forming the first groove by a non-contact groove forming process.

The non-contact groove forming process may use either a laser, an electron beam, or plasma to form the first groove.

The first groove forming step may involve forming the first groove by a mechanical groove forming process.

The first groove may be deeper than the second groove.

In order to solve the above problem, according to another aspect of the present invention, there is provided a grain-oriented electrical steel sheet having a plurality of grooves formed in the longitudinal direction of the steel sheet, the grooves extending in a direction approximately parallel to the width direction of the steel sheet, the plurality of grooves being formed of first grooves in which no fine grains are formed at the bottom of the grooves, and second grooves in which fine grains are formed at the bottom of the grooves.

The first groove may be deeper than the second groove.

　Sub-grain boundary factors may not be formed in the first and second grooves.

Industrial products are provided that are manufactured using the above-mentioned grain-oriented electrical steel sheet.

The present invention provides a method for manufacturing grain-oriented electrical steel sheet that achieves both improved iron loss and magnetic flux density, and can provide grain-oriented electrical steel sheet that achieves both improved iron loss and magnetic flux density.

FIG. 1 is a schematic diagram of a grain-oriented electrical steel sheet according to an embodiment of the present invention. FIG. 2 is a flow diagram illustrating a method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention. 3A and 3B are schematic diagrams of a grain-oriented electrical steel sheet according to one embodiment of the present invention. 4A and 4B are schematic diagrams of a grain-oriented electrical steel sheet according to one embodiment of the present invention. 5A and 5B are schematic diagrams of a grain-oriented electrical steel sheet according to one embodiment of the present invention. FIG. 6 is a diagram showing the relationship between groove depth and iron loss improvement rate in groove formation using only the laser method and groove formation using only the mechanical method. FIG. 7 is a diagram showing the relationship between the groove depth and the amount of B8 deterioration in groove formation using only the laser method and groove formation using only the mechanical method. FIG. 8 is a diagram showing an iron loss improvement rate by combining a laser method and a mechanical method according to an embodiment of the present invention. FIG. 9 is a diagram showing the relationship between the groove depth and the iron loss improvement rate for each combination according to one embodiment of the present invention. FIG. 10 is a diagram showing the amount of B8 deterioration resulting from a combination of the laser method and the mechanical method according to an embodiment of the present invention. FIG. 11 is a diagram showing the relationship between the groove depth and the amount of B8 deterioration for each combination according to one embodiment of the present invention.

Below, an embodiment of the present invention will be described with reference to the drawings. Note that in this specification and the drawings, components having substantially the same functional configurations are given the same reference numerals to avoid redundant description.

Although details will be described later, in an embodiment of the present invention, the cold-rolled steel sheet is annealed by secondary recrystallization to align the orientation of the easy axis of magnetization and convert it into a grain-oriented electromagnetic steel sheet to manufacture grain-oriented electromagnetic steel sheet 10. Therefore, in the following description, the cold-rolled steel sheet that is the material for grain-oriented electromagnetic steel sheet 10 and the grain-oriented electromagnetic steel sheet with the crystal orientation aligned after secondary recrystallization may be referred to simply as steel sheet, either together or individually.

[Grain-oriented electrical steel sheet]
First, a grain-oriented electrical steel sheet 10 according to an embodiment of the present invention will be described. The grain-oriented electrical steel sheet 10 according to an embodiment of the present invention is a grain-oriented electrical steel sheet 10 in which a plurality of grooves extending in a direction substantially parallel to the width direction of the steel sheet are formed in the longitudinal direction of the steel sheet, and the plurality of grooves are formed from a first groove 20 in which no fine grains are formed at the bottom of the groove, and a second groove 30 in which fine grains are formed at the bottom of the groove. Here, the fine grains are crystal grains whose size is reduced by partial machining or the like compared to the periphery of the bottom of the groove. The size of the fine grains is generally 20 to 200 μm, and may be, for example, about 50 μm. Note that, as a method for measuring the grain size, for example, the grain size is measured by the cutting method of JIS G0551:2020 in a plane parallel to the rolling surface at a depth of 1/2 the sheet thickness from the surface of the steel sheet. As the grain-oriented electrical steel sheet, for example, a grain-oriented electrical steel strip of JIS C 2553:2012 can be adopted.

The first groove 20 and the second groove 30 formed on the surface of the grain-oriented electromagnetic steel sheet 10 are each formed to extend parallel to the width direction of the steel sheet or in a direction that is slightly tilted from parallel, approximately parallel, for the purpose of improving the iron loss of the grain-oriented electromagnetic steel sheet 10. Approximately parallel here can be in the range of 0 degrees or more and ±45 degrees or less, and typically may be in the range of 0 degrees or more and ±30 degrees or less. In reality, in order to avoid fractures or breaks and to balance the improvement of iron loss and the amount of B8 degradation, it may be in the range of +10 degrees or more and +20 degrees or less, or in the range of -20 degrees or more and -10 degrees or less. The reason why the grooves are formed so as to be inclined in a direction substantially parallel to the width direction of the steel sheet is that, when the grain-oriented electromagnetic steel sheet 10 is used as an iron core of a transformer, a process of winding the sheet with a square cross section to form the shape of the iron core of the transformer is performed. In this process, the groove direction and the bending direction coincide with each other, so that the grain-oriented electromagnetic steel sheet 10 does not break along the groove direction starting from the groove, and the groove extension direction is made to be different from the bending direction. Therefore, the degree to which the grooves are inclined with respect to the width direction of the steel sheet (the inclination angle) can be appropriately set in consideration of the risk of breakage that differs depending on the material, thickness, etc. of the steel sheet. In addition, the first groove 20 and the second groove 30 may be formed on the front or back surface of the grain-oriented electromagnetic steel sheet 10, or may be formed on different surfaces. The first groove 20 may be formed using a laser according to a pattern, such as a scan speed of 45 m/s, a groove pitch of 3 mm, a beam shape of 25 x 50 μm, and a groove depth of 20 μm, and the second groove 30 may be formed using machining according to a pattern, such as a groove pitch of 5 mm and a groove depth of 10 μm.

The first groove 20 can be formed by a non-contact groove forming method such as laser processing, etching, electron beam processing, plasma processing, etc. The first groove 20 can also be formed by a contact groove forming method such as machining, such as a press process in which a die with protrusions such as gears is pressed against the surface of the steel plate. The second groove 30 is formed by a contact groove forming method such as machining.

In other words, while the second groove 30 is formed by a contact method, the first groove 20 can be formed by either a contact method or a non-contact method. However, as described in detail below, the contact method creates fine grains at the bottom of the groove. The non-contact method, except for etching, creates factors that cause subgrain boundaries (hereinafter simply referred to as subgrain boundary factors) at the bottom of the groove. However, as described below, the fine grains and subgrain boundary factors disappear by performing secondary recrystallization annealing between the formation of the first groove 20 and the formation of the second groove 30, so that they are no longer present at the bottom of the first groove 20.

To elaborate on this, when grooves are formed using a contact groove forming method, the steel plate is compressed at the bottom of the groove, and fine grains are generated at the bottom of the groove immediately after the groove is formed. On the other hand, when grooves are formed using a non-contact groove forming method, the steel plate is not compressed and fine grains are not generated, but the inventors have found that when grooves are formed using non-contact methods such as laser, electron beam, and plasma processing that involve heat (hereinafter simply referred to as thermal processing), subgrain boundary factors are generated. Even when using a non-contact method, when grooves are formed using etching processing that does not involve heat, neither fine grains nor subgrain boundary factors are generated.

The subboundary factors mentioned above are factors that are the origin (cause) of subboundaries that generate subboundaries when exposed to a high-temperature environment. Subboundary factors are not yet subboundaries at the time the grooves are formed, and are not easy to confirm, but they become subboundaries that are easy to confirm by undergoing heat treatment at about 800°C, such as stress relief annealing. In addition, when subboundary factors grow into subboundaries, this is problematic as it can cause iron loss deterioration, but fine grains and subboundaries (including those generated by subboundary factors) disappear through aging when exposed to long periods of high temperatures (for example, 1000°C or higher), such as secondary recrystallization annealing.

As described above, since the first groove 20 is to be exposed to high temperatures for a long time after formation, the first groove 20 may be formed by a contact method such as machining or a non-contact method such as laser processing. However, in the case of machining, since the cold-rolled sheet (base steel) used to form the first groove 20 is harder than the steel sheet (grain-oriented electromagnetic steel sheet) after secondary recrystallization, it is more difficult to form deep grooves and the teeth are more likely to wear. In addition, since the etching process does not generate subgrain boundary factors, there is no effect on iron loss deterioration due to subgrain boundary formation, but the manufacturing process and equipment are complicated and expensive. From this perspective, it is considered that the method involving heat among the non-contact methods is advantageous, and the laser processing is an advantageous method. Furthermore, if the first groove 20 is formed by thermal processing, it is possible to easily form a groove deeper than that formed by machining without worrying about tooth wear, etc. It is known that the deeper the groove is, the more effective it is in improving iron loss within a certain depth range, such as 25 μm or less. Therefore, if the first groove 20 is formed by thermal processing, it is relatively easy to form a deep groove that has a high iron loss improvement effect.

On the other hand, since the second grooves 30 are formed by the contact method, the loss of base material is smaller than in the non-contact method, the decrease in magnetic flux density due to the loss of base material is suppressed, and since subgrain boundary factors are not generated, the subgrain boundaries do not increase even if stress relief annealing is performed after the formation of the second grooves 30. Therefore, it is also possible to suppress the iron loss of industrial products such as transformers using the grain-oriented electromagnetic steel sheet 10 from being lower than the iron loss of the grain-oriented electromagnetic steel sheet 10 used as the material, due to the subgrain boundaries.

Also, the first groove 20 may be formed relatively deep by thermal processing such as laser processing, which causes a large loss of base material but contributes greatly to iron loss improvement, while the second groove 30 may be formed shallower than the first groove 20 while suppressing the loss of base material (suppressing the decrease in magnetic flux density) by machining. In this way, the first groove 20 has a large decrease in magnetic flux density but provides a large iron loss improvement effect, while the second groove 30 has a small iron loss improvement effect but provides an effect of suppressing the decrease in magnetic flux density, making it possible to achieve both iron loss improvement and magnetic flux density at a higher level. Furthermore, if the first groove 20 is laser processed and the second groove 30 is machined, it becomes possible to manufacture such grain-oriented electromagnetic steel sheet at a lower cost.

In thermal processing, the subgrain boundary factor has a large effect. For example, when the grain-oriented electrical steel sheet 10 with the first groove 20 and the second groove 30 formed therein is wound into a transformer shape and then stress relief annealing is performed, if the second groove 30 is formed by thermal processing, the subgrain boundary factor at the bottom of the second groove 30 grows into a subgrain boundary, deteriorating the iron loss. For example, if the iron loss immediately after groove processing is W1, the iron loss after stress relief annealing is W2, the amount of iron loss deterioration due to processing strain is ΔW3, and the amount of iron loss deterioration due to subgrain boundary formation is ΔW4, then
W1 < W2 (The iron loss W2 after stress relief annealing is high and deteriorates)
W2=W1-ΔW3+ΔW4
ΔW3<ΔW4 (because the iron loss deterioration amount ΔW4 due to sub-grain boundary formation is very large) However, if heat treatment is performed at 1000° C. or higher, ΔW4 disappears and the iron loss becomes small, W2−ΔW4. For this reason as well, it is preferable to machine the second grooves 30.

Specifically, the steel sheet in which the first grooves 20 are formed by groove formation performed after the cold rolling process is subjected to secondary recrystallization annealing at a heating temperature of about 1200 degrees in accordance with a known manufacturing method for grain-oriented electromagnetic steel sheet 10 so as to grow the crystals and align the axis of easy magnetization with the rolling direction of the steel sheet. Therefore, by performing secondary recrystallization annealing, the fine grains and subgrain boundaries generated at the bottom of the grooves by the formation of the first grooves 20 are aged and disappear from the bottom of the first grooves 20. As a result, in the final state of the grain-oriented electromagnetic steel sheet 10, neither fine grains nor subgrain boundaries are formed (exist) at the bottom of the first grooves 20. Therefore, there are no particular restrictions on the processing and formation means of the first grooves 20, and they can be selected taking into consideration the process and equipment costs, etc.

Then, second grooves 30 are formed on the surface of the steel sheet that has been subjected to secondary recrystallization annealing, with a formation pattern (e.g., groove pitch, groove depth, groove angle, etc.) different from that of the first grooves 20. The second grooves 30 are formed by a contact groove formation method such as machining. Therefore, fine grains are formed at the bottom of the second grooves 30 as traces of the machining, but these fine grains are not aged before finally becoming the grain-oriented electromagnetic steel sheet 10, so that among the grooves of the final grain-oriented electromagnetic steel sheet 10, the fine grains remain formed (exist) at the bottom of the grooves corresponding to the second grooves 30.

FIG. 1 shows a schematic diagram of a grain-oriented electromagnetic steel sheet 10 according to one embodiment of the present invention. The grain-oriented electromagnetic steel sheet 10 according to one embodiment of the present invention has a surface as shown in FIG. 1. As shown in FIG. 1, a plurality of first grooves 20 are formed in the rolling direction (longitudinal direction) of the grain-oriented electromagnetic steel sheet 10 at a predetermined pitch so as to extend in a direction approximately parallel to the sheet width direction of the grain-oriented electromagnetic steel sheet 10. For example, the first grooves 20 are formed using a laser according to a formation pattern such as a scan speed of 45 m/s, a groove pitch of 3 mm, a beam shape of 25×50 μm, and a groove depth of 20 μm. The first grooves 20 formed using such a laser are heated in the secondary recrystallization annealing performed later, so that fine grains and subgrain boundaries do not remain at the bottom of the grooves.

On the other hand, as shown in the figure, a plurality of second grooves 30 are formed at a predetermined pitch in the rolling direction of the grain-oriented electromagnetic steel sheet 10, extending in a direction substantially parallel to the sheet width direction of the grain-oriented electromagnetic steel sheet 10 (however, this does not have to be parallel to the extending direction of the first grooves). For example, the second grooves 30 are formed using machining according to a forming pattern, for example, with a groove pitch of 5 mm and a groove depth of 10 μm.

In this way, a grain-oriented electrical steel sheet 10 is produced that has a mixture of first grooves 20 and second grooves 30. In the grain-oriented electrical steel sheet 10 produced in this way, the second grooves 30 formed using machining do not undergo secondary recrystallization by annealing, so fine grains remain present at the bottom of the groove.

In FIG. 1, the first groove 20 and the second groove 30 are depicted as being divided into three or four stepped sections in the plate width direction. This indicates that when forming the grooves, the length in the plate width direction that can be formed by one groove forming device used for groove formation is smaller than the plate width of the steel plate, so that multiple groove forming devices (three or four in the case of FIG. 1) are lined up in the plate width direction and grooves are formed using each of these multiple groove forming devices to form grooves (whose overall length covers the entire plate width direction). Although a repeated explanation of this situation will be omitted, it is the same in FIG. 3, FIG. 4, and FIG. 5 described below.

In this way, a grain-oriented electromagnetic steel sheet 10 is manufactured that contains a mixture of a plurality of first grooves 20 in which fine grains and subgrain boundaries are not formed at the bottom of the groove portion, and a plurality of second grooves 30 in which fine grains are formed at the bottom of the groove portion.

According to the above-mentioned embodiment, a grain-oriented electromagnetic steel sheet is manufactured having a plurality of first grooves 20 that have no fine grains or subgrain boundaries at the bottom and can be formed by utilizing the disappearance of fine grains, subgrain boundary factors, and subgrain boundaries at the bottom of the groove due to secondary recrystallization annealing, and a plurality of second grooves 20 that have fine grains at the bottom and can be formed by a contact method. This makes it possible to provide a grain-oriented electromagnetic steel sheet that achieves both improved iron loss and magnetic flux density. That is, the first grooves 20 do not have subgrain boundaries and subgrain boundary factors that cause iron loss deterioration. In addition, since the second grooves 30 are formed by a contact method, they basically do not have subgrain boundaries and subgrain boundary factors, and the loss of base material that reduces magnetic flux density is small. Therefore, the above-mentioned compatibility can be achieved by a grain-oriented electromagnetic steel sheet having both the first grooves 20 and the second grooves 30 described above. In addition, in the grain-oriented electrical steel sheet 10 manufactured in this manner, there are no sub-boundary factors in any of the grooves, so even if this is used to manufacture industrial products such as transformers, there will be no iron loss deterioration due to the sub-boundary factors becoming sub-boundaries. Therefore, by manufacturing industrial products, it is possible to prevent iron loss from deteriorating more than after the formation of the second grooves 30.

Furthermore, if the first grooves 20 are made deeper than the second grooves 30, the burden (wear, etc.) on contact-type equipment such as machining devices can be reduced. In particular, if the first grooves 20 are formed by thermal processing such as laser processing, deep grooves can be easily formed. Therefore, the presence of the first grooves 20 that are deep enough and have a high iron loss improvement effect, and the second grooves 30 that have an iron loss improvement effect while reducing the decrease in magnetic flux density, allows the above compatibility to be achieved at a high level overall. In the grain-oriented electrical steel sheet 10 according to this embodiment, the subgrain boundaries that cause iron loss deterioration can be eliminated by annealing, and it is possible to achieve both iron loss improvement and magnetic flux density.

[Method of manufacturing grain-oriented electrical steel sheet]
Next, a method for manufacturing the grain-oriented electrical steel sheet 10 according to one embodiment of the present invention will be described. The method for manufacturing the grain-oriented electrical steel sheet 10 according to one embodiment of the present invention is a method for manufacturing the grain-oriented electrical steel sheet 10 in which a plurality of grooves extending in the longitudinal direction of the steel sheet and in a direction approximately parallel to the width direction of the steel sheet are formed. Figure 2 is a flow diagram illustrating the method for manufacturing the grain-oriented electrical steel sheet 10 according to one embodiment of the present invention.

As shown in FIG. 2, when the manufacture of the grain-oriented electromagnetic steel sheet 10 is started, in step S101, a first groove 20 consisting of a plurality of grooves extending in a direction approximately parallel to the width direction is formed in the cold-rolled steel sheet that is the material of the grain-oriented electromagnetic steel sheet 10 (first groove formation step). Typically, a plurality of first grooves 20 extending in a direction approximately parallel to the width direction of the steel sheet (cold-rolled steel sheet) are formed on the surface of the cold-rolled steel sheet that is the material of the grain-oriented electromagnetic steel sheet 10, which has been cast, hot-rolled, annealed, and cold-rolled and discharged from a finishing rolling mill, for magnetic domain control. The first grooves 20 are formed based on a predetermined groove pitch, groove depth, or groove angle using any of the following techniques: laser processing, etching, electron beam processing, plasma processing, or mechanical processing. Here, the groove angle is defined as the angle of the extension direction of the groove (the direction in which the groove extends) relative to the sheet width direction of the steel sheet. In general, as the groove angle increases, the iron loss improvement decreases, and the deterioration amount of the magnetic flux density B8 tends to improve.

For example, the first groove 20 may be formed deeper than the second groove 30. Forming the first groove 20 deeper than the second groove 30 is effective in improving the iron loss of the grain-oriented electromagnetic steel sheet 10. It is preferable to use laser processing, which allows easy control of the depth direction and does not cause wear due to contact with the steel sheet, but as long as the method can ensure iron loss improvement, it is not limited to laser processing, and various methods such as various non-contact methods such as electron beam processing and plasma processing, and mechanical processing can be used to form the grooves.

Figure 3 shows a schematic diagram of a grain-oriented electrical steel sheet 10 according to one embodiment of the present invention. For example, the first groove 20 shown in Figure 3A is formed, for example, by laser processing, with a groove pitch of 3 mm, a groove depth of 20 μm, and a groove angle of 10 degrees.

Once processing in step S101 is complete, proceed to step S102.

In step S102, the cold-rolled steel sheet with the first grooves 20 formed therein is annealed to align the magnetization easy axis of the cold-rolled steel sheet in the longitudinal direction of the steel sheet, thereby forming a grain-oriented electrical steel sheet (secondary recrystallization annealing step).

To explain the process in more detail, as is well known, the steel sheet having the first grooves 20 formed therein is subjected to decarburization annealing, for example, for a heating time of 1 to 3 minutes at a heating temperature of 700°C to 900°C. By decarburization annealing, the carbon concentration in the steel sheet is adjusted, and an oxide layer mainly made of silica (SiO ₂ ) is formed on the surface of the decarburization annealed steel sheet. Then, an annealing separator mainly made of magnesia (MgO) is applied to the oxide layer on the surface of the decarburization annealed steel sheet, and the steel sheet is wound into a coil.

The steel sheet that has been decarburized and annealed and coated with the annealing separator is inserted in a coiled state into a batch furnace and heat-treated for 20 to 24 hours at a heating temperature of 1100°C to 1300°C (secondary recrystallization annealing). This heat treatment preferentially grows crystals of so-called Goss grains, in which the rolling direction of the steel sheet coincides with the axis of easy magnetization (secondary recrystallization is generated). As a result, a grain-oriented electrical steel sheet 10 with high crystal orientation (crystal orientation) is obtained after secondary recrystallization annealing. During secondary recrystallization annealing, the oxide layer reacts with the annealing separator to form a glass coating made of forsterite (Mg ₂ SiO ₄ ) on the surface of the steel sheet, forming the grain-oriented electrical steel sheet 10.

Then, the coiled grain-oriented electromagnetic steel sheet 10 is unwound to stretch it into a sheet, and while it is stretched, an insulating coating agent (coating liquid) is applied onto the glass coating formed on the surface of the grain-oriented electromagnetic steel sheet 10. The grain-oriented electromagnetic steel sheet 10 to which the insulating coating agent has been applied is annealed for a heating time of 10 to 120 seconds at a heating temperature of 800°C to 850°C to bake the insulating coating agent, thereby forming an insulating coating on the surface of the grain-oriented electromagnetic steel sheet 10 and imparting electrical insulation to the grain-oriented electromagnetic steel sheet 10 and a predetermined tension to the surface.

Once processing in step S102 is complete, proceed to step S103.

In step S103, second grooves 30 consisting of multiple grooves extending in a direction approximately parallel to the width direction are formed in the grain-oriented electromagnetic steel sheet 10 using machining (second groove forming step). The second grooves 30 are formed according to a predetermined groove pitch, groove depth, or groove angle using machining using gears or the like.

For example, the second groove 30 shown in FIG. 3B is formed by machining (pressing) the steel plate on which the first groove 20 shown in FIG. 3A is formed according to a second formation pattern with a groove pitch of 5 mm, a groove depth of 10 μm, and a groove angle of 12 degrees. In press processing, achieving a groove depth of 20 μm or more is a heavy burden due to blade chipping and blade wear, and is difficult to carry out continuously. Therefore, while forming a deep groove (easy to improve iron loss) as the first groove 20 using a laser or the like that is easy to process and does not wear out, the second groove 30 is formed by separate machining that does not easily deteriorate the magnetic flux density (magnetic flux density B8 is not easily deteriorated) by pushing the steel plate into the groove during groove formation and not losing the steel plate, thereby making it possible to achieve both iron loss improvement and magnetic flux density. For example, to achieve the effect of improving iron loss, a groove of 20 to 25 μm needs to be formed, and if this is performed in step S101, the magnetic properties (improved iron loss and avoidance of B8 degradation) cannot be obtained.

　If the insulating coating formed on the surface of the grain-oriented electromagnetic steel sheet 10 subsequently disappears due to the formation of the second grooves 30, an insulating coating agent (coating liquid) is again applied to the surface of the grain-oriented electromagnetic steel sheet 10, and the sheet is annealed for a heating time of 10 to 120 seconds at a heating temperature of 800°C to 850°C to bake the insulating coating agent, thereby forming an insulating coating on the surface of the grain-oriented electromagnetic steel sheet 10 and producing the final grain-oriented electromagnetic steel sheet 10.

The grain-oriented electromagnetic steel sheet 10 thus manufactured is shipped and used in any suitable industrial product, for example as a material for the iron core of a transformer.

In the above description, the insulating coating is formed in step S102 and then the second groove 30 is formed in step S103. However, if the secondary recrystallization has already occurred in step S102, the insulating coating may be formed after the second groove 30 is formed.

When grooves are formed by machining, the steel plate is compressed at the bottom of the groove, generating fine grains, but when grooves are formed by laser processing or etching, fine grains do not occur. On the other hand, when grooves are formed by laser processing, thermal strain is introduced at the bottom of the groove (or the groove wall), generating subgrain boundary factors. Furthermore, these fine grains and subgrain boundaries disappear through aging when exposed to high temperatures (above about 1000°C) for long periods of time, such as during secondary recrystallization annealing.

As a result, fine grains are present at the bottom of the second grooves 30 of the grain-oriented electrical steel sheet 10 (because they have not been exposed to high temperatures for a long period of time after groove processing), but at the bottom of the first grooves 20, there are no fine grains, subgrain boundaries, or subgrain boundary factors (because they have been exposed to high temperatures associated with secondary recrystallization annealing after groove processing).

Figure 4 shows a schematic diagram of a grain-oriented electrical steel sheet according to one embodiment of the present invention. As a result, in the cross section of the grain-oriented electrical steel sheet 10 taken along line AA' as shown in Figure 4A, fine grains remain at the bottom of the groove corresponding to the second groove 30, while both the fine grains and the subgrain boundaries have disappeared at the bottom of the groove corresponding to the first groove 20, as shown in Figure 4B.

FIG. 5 shows a schematic diagram of a grain-oriented electrical steel sheet according to one embodiment of the present invention. The formation pattern of the groove pitch, groove depth, groove angle, etc., when forming the second grooves 30 in the second groove formation step is not particularly limited, but may be, for example, as shown in FIG. 5. That is, as shown in FIG. 5A, on the surface of the steel sheet after the first grooves 20 described above with reference to FIG. 3A are formed in the material steel sheet, the second grooves 30 may be formed according to a formation pattern different from the formation pattern in which the first grooves 20 were formed, as shown in FIG. 5B. For example, the second grooves 30 shown in FIG. 5B are formed by machining according to a second formation pattern with a groove pitch of 5 mm, a groove depth of 10 μm, and a groove angle of -12 degrees.

The above-mentioned manufacturing method allows the manufacture of a grain-oriented electromagnetic steel sheet 10 that has a mixture of a plurality of first grooves 20 that have no fine grains or subgrain boundaries at the bottom and a plurality of second grooves 30 that have fine grains at the bottom. The grain-oriented electromagnetic steel sheet 10 has both the first grooves 20 that have a groove depth that is effective for improving iron loss and are formed by laser processing or the like, and the second grooves 30 that are formed by a mechanical method and cause little loss of steel sheet base material and are effective for magnetic flux density, making it possible to achieve both improved iron loss and magnetic flux density.

[Example]
Fig. 6 is a diagram showing the relationship between the groove depth and the iron loss improvement rate in the case of groove formation by the laser method alone and groove formation by the mechanical method alone, and Fig. 7 is a diagram showing the relationship between the groove depth and the B8 deterioration amount in the case of groove formation by the laser method alone and groove formation by the mechanical method alone.

The relationship between groove depth and iron loss improvement rate for groove formation using only the conventional laser method and groove formation using only the mechanical method is shown in the graph in Figure 6. The relationship between groove depth and the amount of B8 degradation is shown in the graph in Figure 7.

The groove depth was measured using a measuring device (Keyence (registered trademark) WI-5000, WI-001). Specifically, the groove depth can be obtained by taking the measured average height in any area on the surface of the steel plate where there are no grooves as the reference H0 (>0) and the maximum depth of the groove as H (>0), and measuring the length equivalent to the difference (H0-H) using the measuring device.

As for the method of measuring the iron loss and magnetic flux density B8, the iron loss [W/kg] of the grain-oriented electrical steel sheet is the iron loss when a magnetic field of maximum magnetic flux density 1.7 Tesla and 50 Hz is applied to 10 test pieces having a size of 60 mm x 300 mm and a thickness of 0.23 mm, and can be measured with an SST (Single Sheet Tester) measuring device. The average iron loss of the base steel sheet is 0.85 [W/kg]. The magnetic flux density B8 can be the magnetic flux density generated when these 10 test pieces are magnetized in a magnetic field of 800 A/m, for example. The average magnetic flux density B8 of the base steel sheet is 1.92 [T (Tesla)].

In this case, the iron loss improvement rate can be defined as follows: That is, the iron loss improvement rate of the grain-oriented electrical steel sheet is calculated as follows, based on the iron loss of the base steel sheet.
Iron loss improvement rate [%] = ((iron loss of base steel sheet) - (iron loss of grain-oriented electromagnetic steel sheet) / iron loss of base steel sheet) x 100
Here, the base steel plate means a steel plate in which the two groove forming steps of forming the above-mentioned first groove 20 and second groove 30 have not been performed in the same base coil, i.e., a steel plate in which the first groove 20 and the second groove 30 have not been formed.

Further, the deterioration amount ΔB8 of the magnetic flux density B8 can be defined as follows: That is, the B8 deterioration amount ΔB8 of the grain-oriented electrical steel sheet is calculated as follows, using the magnetic flux density B8 of the base steel sheet as a reference.
ΔB8 [gauss] = (magnetic flux density B8 (T) of raw steel sheet - magnetic flux density B8 (T) of grain-oriented electrical steel sheet) x 10,000

In other words, when grooves are formed using the laser method alone, an iron loss improvement rate of 11% or more can be achieved for groove depths of 20 μm or more, but the B8 degradation amount is 300 gauss or more. This is thought to be because the non-contact laser method allows for the formation of relatively deep grooves, which generates leakage flux from the surface magnetic pole and increases magnetostatic energy, making it easier to subdivide the main magnetic domain and improve iron loss; on the other hand, the magnetic flux density B8 increases the volume (amount) of steel plate base material that is removed, which is thought to increase the amount of degradation.

On the other hand, when grooves are formed using the mechanical method alone, the deterioration in magnetic flux density B8 is less than 200 gauss at a groove depth of 15 to 20 μm, but an iron loss improvement rate of 11% or more cannot be achieved. The reason for the poor iron loss improvement rate is that with contact groove formation, it is difficult to form deep grooves due to wear of the tooth profile and chipping of the blade. Also, the reason for the good magnetic flux density B8 is thought to be that, as can be seen from the generation of fine grains, the base material of the steel plate is pushed into the bottom of the groove, minimizing the loss of the base material of the steel plate.

In this embodiment, the first groove 20 is formed by laser processing according to a first forming pattern with a scan speed of 45 m/s, a groove pitch of 3 mm, a beam shape of 25 x 50 μm, and groove depths of 0 μm, 10 μm, 15 μm, 20 μm, and 25 μm by adjusting the laser power. The second groove 30 is formed by press processing according to a second forming pattern with a groove pitch of 5 mm, and groove depths of 0 μm, 10 μm, 15 μm, and 20 μm by adjusting the pressure force of the tooth profile.

FIG. 8 is a diagram showing the iron loss improvement rate by combining a laser method and a mechanical method according to one embodiment of the present invention. FIG. 9 is a diagram showing the relationship between the groove depth and the iron loss improvement rate for each combination according to one embodiment of the present disclosure. According to the grain-oriented electromagnetic steel sheet 10 of this embodiment, which has a mixture of first grooves 20 formed by laser processing and second grooves 30 formed by press processing, the relationship between various combinations of groove depth by laser processing and groove depth by press processing and the iron loss improvement rate is the experimental results shown in FIG. 8 and FIG. 9. The combinations that achieved an iron loss improvement rate of 11% or more are the seven combinations highlighted in FIG. 8.

FIG. 10 is a diagram showing the amount of B8 degradation by a combination of a laser method and a mechanical method according to one embodiment of the present invention. FIG. 11 is a diagram showing the relationship between the groove depth and the amount of B8 degradation for each combination according to one embodiment of the present invention. The relationship between various combinations of groove depth by laser processing and groove depth by press processing and the iron loss improvement rate is the experimental results shown in FIG. 10 and FIG. 11. Of the seven combinations that achieved the iron loss improvement rate of 11% or more described above, the amount of B8 degradation is 200 gauss or less in three combinations: a combination of a laser processing groove depth of 10 μm and a press processing groove depth of 15 μm (amount of B8 degradation 180 gauss), a combination of a laser processing groove depth of 15 μm and a press processing groove depth of 5 μm (amount of B8 degradation 170 gauss), and a combination of a laser processing groove depth of 15 μm and a press processing groove depth of 10 μm (amount of B8 degradation 200 gauss).

Therefore, in this embodiment, it is believed that the optimal combination is a laser processing groove depth of 15 μm and a press processing groove depth of 10 μm, and the grain-oriented electromagnetic steel sheet 10 with grooves formed using the pattern formed by this combination achieves an iron loss improvement rate of 14.1% and a B8 degradation amount of 200 gauss, and is believed to be capable of achieving both iron loss improvement and magnetic flux density.

A similar groove depth may also be formed by electron beam or plasma processing, which are similar thermal processes. For example, the groove depth can be controlled by adjusting the accelerating voltage and current in the case of electron beams, and by adjusting the output current in the case of plasma.

　Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the specific embodiments described above, and various modifications and variations are possible within the scope of the gist of the present disclosure as set forth in the claims.

The entire disclosures of the specification, drawings and abstract contained in the Japanese application of Patent Application No. 2023-176056, filed on October 11, 2023, are incorporated herein by reference.

10 Grain-oriented electromagnetic steel sheet 20 First groove 30 Second groove

Claims (9)

A method for manufacturing a grain-oriented electrical steel sheet in which a plurality of grooves extending in a longitudinal direction of the steel sheet and in a direction substantially parallel to a width direction of the steel sheet are formed,
a first groove forming step of forming a first groove including a plurality of grooves extending in a direction substantially parallel to a width direction in a cold-rolled steel sheet that is a material for the grain-oriented electrical steel sheet;
A secondary recrystallization annealing step of annealing the cold-rolled steel sheet in which the first grooves are formed, thereby aligning the magnetization easy axis of the cold-rolled steel sheet in the longitudinal direction to form a grain-oriented electrical steel sheet;
and a second groove forming step of forming, in the grain-oriented electrical steel sheet, second grooves consisting of a plurality of grooves extending in a direction approximately parallel to the width direction, using a contact-type groove forming process. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the first groove forming step forms the first groove by a non-contact groove forming process. The method for manufacturing grain-oriented electrical steel sheet according to claim 2, wherein the non-contact groove forming process forms the first groove using either a laser, an electron beam, or plasma. The method for manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the first groove forming step forms the first groove by a mechanical groove forming process. The method for manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the first groove is deeper than the second groove. A grain-oriented electrical steel sheet having a plurality of grooves formed in the longitudinal direction of the steel sheet and extending in a direction substantially parallel to the width direction of the steel sheet,
the plurality of grooves are formed of first grooves in which no fine grains are formed at a bottom of the grooves, and second grooves in which fine grains are formed at a bottom of the grooves. The grain-oriented electrical steel sheet according to claim 6, wherein the first groove is deeper than the second groove. The grain-oriented electrical steel sheet according to claim 6 or 7, wherein the first groove and the second groove are free of sub-grain boundary factors. An industrial product manufactured using the grain-oriented electrical steel sheet according to any one of claims 6 to 8.