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

Abstract

Provided is a method for manufacturing a grain-oriented electrical 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 manufacturing method comprises the following steps: a first groove forming step of forming a first groove formed by a plurality of grooves extending in a direction approximately parallel to the width direction on a cold-rolled steel sheet which is a material of a grain-oriented electromagnetic steel sheet; a secondary recrystallization annealing step for obtaining a grain-oriented electrical steel sheet by annealing the cold-rolled steel sheet in which the first groove is formed so that the easy magnetization axis of the cold-rolled steel sheet coincides with the longitudinal direction; and a second groove forming step for forming, in the grain-oriented electromagnetic steel sheet, a second groove comprising a plurality of grooves extending in a direction substantially parallel to the width direction by means of a contact-type groove forming process.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing directional electromagnetic steel sheets, directional electromagnetic steel sheets, and industrial products thereof. Background Technology

[0002] To improve the electromagnetic properties of directional electromagnetic steel sheets, a stress-relief annealing (SRA) domain control method is employed. This method enables domain control that combines heat resistance with improved iron loss by incorporating periodic grooves along the length of the directional electromagnetic steel sheet. Several process steps and groove formation methods have been previously proposed for this SRA domain control method.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 62-53579

[0006] Patent Document 2: Japanese Patent No. 6826604 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Regarding directional electromagnetic steel sheets, their magnetic properties require both significant reduction in iron loss (low iron loss) and high magnetic flux density, but these two characteristics are often contradictory. Ideally, to improve iron loss, deep grooves should be formed using lasers or etching that do not cause mechanical wear. However, forming deeper grooves leads to greater losses in the base material, resulting in a decrease in magnetic flux density. Furthermore, while attempting to form grooves through machining can suppress the decrease in magnetic flux density due to minimal losses in the base material, it also results in wear on the machining equipment due to contact with the steel sheet. The deeper the groove, the greater the wear on the machining equipment.

[0009] That is, when performing domain control, a groove depth of 20–25 μm and a groove pitch of 3–4 mm are required to achieve sufficient improvement in iron loss. When the base material is laser-processed according to these formation conditions, the magnetic flux density B8 will decrease 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 in, it is difficult to obtain the groove depth required for improving iron loss from the perspective of wear on the machining equipment.

[0010] In view of the above problems, the problem to be solved by the present invention is to provide a method for manufacturing a directional electromagnetic steel plate that takes into account both iron loss improvement and magnetic flux density, and to provide a directional electromagnetic steel plate that takes into account both iron loss improvement and magnetic flux density.

[0011] Solution to the problem

[0012] To address the aforementioned problems, according to one aspect of the present invention, a method for manufacturing a directional electromagnetic steel sheet is provided. This directional electromagnetic steel sheet is a steel sheet having multiple grooves formed along its length direction, extending in a direction substantially parallel to the width direction of the steel sheet. The manufacturing method includes the following steps: a first groove forming step of forming a first groove consisting of multiple grooves extending in a direction substantially parallel to the width direction on a cold-rolled steel sheet, which is the material of the directional electromagnetic steel sheet; a secondary recrystallization annealing step of annealing the cold-rolled steel sheet with the first grooves formed thereon, so that the easy magnetization axis of the cold-rolled steel sheet is aligned with the length direction to obtain the directional electromagnetic steel sheet; and a second groove forming step of forming a second groove consisting of multiple grooves extending in a direction substantially parallel to the width direction on the directional electromagnetic steel sheet using a contact-type groove forming process.

[0013] In the first groove forming step, the first groove can be formed by a non-contact groove forming process.

[0014] In the non-contact groove forming process, the first groove can be formed using one of laser, electron beam, and plasma.

[0015] In the first groove forming step, the first groove can be formed by mechanical groove forming process.

[0016] The first groove can be deeper than the second groove.

[0017] Furthermore, in order to solve the above problems, according to another aspect of the present invention, a directional electromagnetic steel plate is provided, which is a directional electromagnetic steel plate having a plurality of grooves formed in the length direction of the steel plate extending in a direction substantially parallel to the width direction of the steel plate, wherein the plurality of grooves are formed by a first groove where no fine particles are formed at the bottom of the groove and a second groove where fine particles are formed at the bottom of the groove.

[0018] The first groove can be deeper than the second groove.

[0019] It is possible that no subgrain boundary factor is formed in either the first or the second groove.

[0020] An industrial product manufactured using the aforementioned directional electromagnetic steel sheet is provided.

[0021] Solution to the problem

[0022] According to the present invention, a method for manufacturing a directional electromagnetic steel sheet that balances iron loss improvement and magnetic flux density can be provided, and a directional electromagnetic steel sheet that balances iron loss improvement and magnetic flux density can be provided. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating a directional electromagnetic steel plate according to one embodiment of the present invention.

[0024] Figure 2 This is a flowchart illustrating a method for manufacturing a directional electromagnetic steel sheet according to one embodiment of the present invention.

[0025] Figure 3A and Figure 3B This is a schematic diagram illustrating a directional electromagnetic steel plate according to one embodiment of the present invention.

[0026] Figure 4A and Figure 4B This is a schematic diagram illustrating a directional electromagnetic steel plate according to one embodiment of the present invention.

[0027] Figure 5A and Figure 5B This is a schematic diagram illustrating a directional electromagnetic steel plate according to one embodiment of the present invention.

[0028] Figure 6 This is a graph showing the relationship between the groove depth obtained by using only laser-based groove formation and by using only mechanical-based groove formation, and the iron loss improvement rate.

[0029] Figure 7 This is a graph showing the relationship between the groove depth obtained by using only laser-based groove formation and by using only mechanical-based groove formation, and the amount of B8 degradation.

[0030] Figure 8 This is a graph showing the iron loss improvement rate obtained by combining laser and mechanical methods according to one embodiment of the present invention.

[0031] Figure 9 This is a graph showing the relationship between the groove depth and the iron loss improvement rate of various combinations in one embodiment of the present invention.

[0032] Figure 10 This is a graph showing the amount of B8 degradation obtained by combining laser and mechanical methods according to one embodiment of the present invention.

[0033] Figure 11 This is a graph showing the relationship between the groove depth and the amount of B8 degradation for each combination in one embodiment of the present invention. Detailed Implementation

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, in this specification and the accompanying drawings, constituent elements having substantially the same functional structure are labeled with the same reference numerals, and repeated descriptions are omitted.

[0035] Furthermore, although details will be described later, in embodiments of the present invention, the cold-rolled steel sheet is transformed into a directional electromagnetic steel sheet by performing secondary recrystallization annealing on the cold-rolled steel sheet to make the orientation of the easy magnetization axis consistent, thereby manufacturing the directional electromagnetic steel sheet 10. Therefore, in the following description, the cold-rolled steel sheet as the material of the directional electromagnetic steel sheet 10 and the directional electromagnetic steel sheet with the crystal orientation consistent after secondary recrystallization are referred to together or separately as "steel sheet".

[0036] Directional electromagnetic steel sheet

[0037] First, a directional electromagnetic steel sheet 10 according to one embodiment of the present invention will be described. The directional electromagnetic steel sheet 10 of one embodiment of the present invention is a directional electromagnetic steel sheet 10 in which a plurality of grooves are formed in the length direction of the steel sheet, extending in a direction substantially parallel to the width direction of the steel sheet. The plurality of grooves are formed by a first groove 20 where fine particles are not formed at the bottom of the groove and a second groove 30 where fine particles are formed at the bottom of the groove. Here, fine particles refer to grains whose grain size is refined compared to the surrounding area at the bottom of the groove through localized machining or the like. The size of the fine particles is generally 20 to 200 μm, for example, about 50 μm. Furthermore, as a method for measuring the particle size, for example, the particle size can be measured according to the cross-section method of JIS (Japanese Industrial Standard) G0551:2020 in a plane parallel to the rolling surface at a distance of 1 / 2 the thickness of the steel sheet surface. As a directional electromagnetic steel sheet, for example, directional electrical steel strip of JIS C 2553:2012 can be used.

[0038] To improve the iron loss of the directional electromagnetic steel sheet 10, the first groove 20 and the second groove 30 formed on the surface of the directional electromagnetic steel sheet 10 are respectively formed in a manner that extends parallel to the width direction of the steel sheet, or from a direction that is parallel but slightly inclined to the side and is substantially parallel. Here, "substantially parallel" can mean within a range of 0 degrees and ±45 degrees, typically within a range of 0 degrees and ±30 degrees. In practice, from the perspective of avoiding breakage or fracture and balancing the improvement of iron loss with the amount of B8 deterioration, it can be within a range of +10 degrees and +20 degrees, or within a range of -20 degrees and -10 degrees. The reason for forming the slots at an angle relative to the width direction of the steel plate, in a roughly parallel direction, is that when the directional electromagnetic steel plate 10 is used as the core of a transformer, it is wound in a square-section manner to form the shape of the transformer core. Therefore, the extension direction of the slots needs to be different from the bending direction to prevent the directional electromagnetic steel plate 10 from breaking along the slot direction, starting from the slot, if the slot direction is the same as the bending direction. Therefore, the degree of inclination (inclination angle) of the slots relative to the width direction of the steel plate can be appropriately set, taking into account the fracture risk varying depending on the material and thickness of the steel plate. Furthermore, the first slot 20 and the second slot 30 can be formed on the front or back of the directional electromagnetic steel plate 10, or they can be formed on different surfaces. In addition, the first groove 20 can be formed using a laser, for example, with a scanning speed of 45m / s, a groove pitch of 3mm, a beam shape of 25×50μm, and a groove depth of 20μm, while the second groove 30 can be formed using machining, for example, with a groove pitch of 5mm and a groove depth of 10μm.

[0039] The first groove 20 can be formed using non-contact groove forming methods such as laser processing, etching, electron beam processing, and plasma processing. Alternatively, the first groove 20 can also be formed using contact groove forming methods such as stamping, where a mold with protrusions such as gears is pressed onto the surface of a steel plate. The second groove 30 is formed using contact groove forming methods such as machining.

[0040] In other words, the second trench 30 is formed in a contact manner, while the first trench 20 can be formed in either a contact or non-contact manner. However, as detailed below, in a contact manner, fine particles are generated at the bottom of the trench. In a non-contact manner other than etching, a factor (hereinafter referred to as "subgrain boundary factor") is generated that contributes to subgrain boundaries. However, as explained later, by performing a secondary recrystallization annealing between the formation of the first trench 20 and the formation of the second trench 30, the fine particles and subgrain boundary factor disappear, and therefore they are not present at the bottom of the first trench 20.

[0041] To elaborate, when a groove is formed using a contact-type groove forming method, fine particles generated during groove formation are present at the bottom of the groove immediately after its formation due to the compression of the steel plate at the bottom. On the other hand, when a groove is formed using a non-contact groove forming method, fine particles are not generated because there is no compression of the steel plate. However, the inventors have realized that when grooves are formed using non-contact methods involving thermal effects such as laser, electron beam, and plasma processing (hereinafter referred to as "thermal processing"), subgrain boundary factors are generated. Furthermore, even with non-contact methods, if grooves are formed using etching processes that do not involve thermal effects, neither fine particles nor subgrain boundary factors are generated.

[0042] Here, the aforementioned subgrain boundary factor refers to the factor that leads to the formation of subgrain boundaries when exposed to high-temperature environments, becoming the source (cause) of subgrain boundaries. The subgrain boundary factor is not easily identified at the time of groove formation because it has not yet become a subgrain boundary, but it becomes an easily identifiable subgrain boundary after undergoing heat treatment at around 800°C, such as stress-relief annealing. Furthermore, if the subgrain boundary factor grows into a subgrain boundary, it may lead to iron loss degradation, thus posing a problem. However, fine grains and subgrain boundaries (including those generated by the subgrain boundary factor) will disappear due to aging if subjected to prolonged high temperatures (e.g., around 1000°C or higher) such as secondary recrystallization annealing.

[0043] Therefore, since the first groove 20 is expected to be subjected to high temperatures for a long time after its formation, it can be formed using contact methods such as machining or non-contact methods such as laser processing. However, in machining, the cold-rolled sheet (base metal) used to form the first groove 20 is harder than the steel sheet after secondary recrystallization (directional electromagnetic steel sheet), making it more difficult to form deep grooves and causing the teeth to wear more easily. Furthermore, if etching is used, since no subgrain boundary factor is generated, there is no effect on iron loss deterioration due to subgrain boundary formation, but its manufacturing process and equipment are complex and costly. From this perspective, non-contact methods involving thermal effects are more advantageous, and laser processing is considered an advantageous method. Moreover, if the first groove 20 is formed by thermal processing, a deeper groove can be formed more easily and without concern for tooth wear compared to machining. Regarding grooves, it is known that within a certain depth range, such as below 25 μm, the deeper the groove, the more effective it is in improving iron loss. Therefore, if the first groove 20 is formed by thermal processing, a deeper groove with a higher iron loss improvement effect can be formed more easily.

[0044] On the other hand, by forming the second groove 30 in a contact manner, the base material loss is smaller compared to the non-contact manner. This not only suppresses the decrease in magnetic flux density caused by the base material loss but also does not generate sub-grain boundary factors. Therefore, even after stress relief annealing is performed after forming the second groove 30, the number of sub-grain boundaries does not increase. Thus, it is also possible to suppress the deterioration of the iron loss of industrial products such as transformers using the grain-oriented electrical steel sheet 10 compared to the iron loss of the grain-oriented electrical steel sheet 10 used as a material due to sub-grain boundaries.

[0045] In addition, it can be that a relatively deep first groove 20 is formed by thermal processing such as laser processing. Although the base material loss is large, its contribution to improving the iron loss is high. At the same time, the second groove 30 is formed by machining to suppress the base material loss (suppress the decrease in magnetic flux density) and form it into a groove shallower than the first groove 20. In this way, although the decrease in magnetic flux density caused by the first groove 20 is large, a significant iron loss improvement effect can be obtained. Although the iron loss improvement effect brought by the second groove 30 is small, an effect of suppressing the decrease in magnetic flux density can be obtained. Therefore, it is possible to balance the improvement of iron loss and magnetic flux density at a higher level. In addition, if the first groove 20 is laser processed and the second groove 30 is machined, such grain-oriented electrical steel sheets can be manufactured at a lower cost.

[0046] Furthermore, if thermal processing is adopted, the influence of the sub-grain boundary factor is greater. The influence of the sub-grain boundary factor is as follows: For example, when the grain-oriented electrical steel sheet 10 formed with the first groove 20 and the second groove 30 is wound into a transformer shape and then stress relief annealing is performed, if the second groove 30 is formed by thermal processing, the sub-grain boundary factor at its bottom will grow into sub-grain boundaries, resulting in the deterioration of the iron loss. For example, if the iron loss just after groove processing is denoted as W1, the iron loss after stress relief annealing is denoted as W2, the amount of iron loss deterioration due to processing strain is denoted as ΔW3, and the amount of iron loss deterioration due to the generation of sub-grain boundaries is denoted as ΔW4, then

[0047] W1 < W2 (the iron loss W2 after stress relief annealing increases and deteriorates)

[0048] W2 = W1 - ΔW3 + ΔW4

[0049] ΔW3 < ΔW4 (the amount of iron loss deterioration 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 W2 - ΔW4 and decreases. For the above reasons, the second groove 30 is preferably machined.

[0050] Specifically, according to the known manufacturing method of directional electromagnetic steel sheet 10, the steel sheet that has formed the first groove 20 through a groove formation process after cold rolling is subjected to a secondary recrystallization annealing at a heating temperature of approximately 1200 degrees Celsius to promote crystal growth and align the easy magnetization axis with the rolling orientation of the steel sheet. Therefore, through secondary recrystallization annealing, the fine grains and subgrain boundaries generated at the bottom of the groove due to the formation of the first groove 20 will disappear from the bottom of the first groove 20 due to aging. As a result, in the final state of becoming directional electromagnetic steel sheet 10, neither fine grains nor (non-existent) subgrain boundaries are formed at the bottom of the first groove 20. Therefore, there are no particular restrictions on the forming method for the first groove 20, and the choice can be made by comprehensively considering factors such as process and equipment costs.

[0051] Subsequently, a second groove 30 is formed on the surface of the steel sheet after secondary recrystallization annealing, according to a different forming pattern than the first groove 20 (e.g., groove pitch, groove depth, groove angle, etc.). The second groove 30 is formed by a groove forming method involving contact, such as machining. Therefore, at the bottom of the second groove 30, fine particles are formed as traces of machining. These fine particles do not age before finally becoming the directional electromagnetic steel sheet 10. Thus, in the grooves of the final directional electromagnetic steel sheet 10, the bottom of the second groove 30 is equivalent to still having fine particles formed.

[0052] Figure 1 A schematic diagram of a directional electromagnetic steel plate 10 according to an embodiment of the present invention is shown. The directional electromagnetic steel plate 10 according to an embodiment of the present invention, for example, has the following characteristics: Figure 1 The surface shown. As... Figure 1 As shown, multiple first grooves 20 are formed along the rolling direction (length direction) of the directional electromagnetic steel sheet 10 at a predetermined pitch, extending in a direction substantially parallel to the width direction of the directional electromagnetic steel sheet 10. For example, the first grooves 20 are formed using a laser, with a forming mode such as a scanning 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. These laser-formed first grooves 20 are heated in a subsequent secondary recrystallization annealing process, thereby preventing the retention of fine particles and subgrain boundaries at the bottom of the grooves.

[0053] On the other hand, as shown in the figure, a plurality of second grooves 30 are formed in the rolling direction of the directional electromagnetic steel sheet 10 at a predetermined pitch, extending in a direction substantially parallel to the width direction of the directional electromagnetic steel sheet 10 (but not necessarily parallel to the extension direction of the first groove). For example, the second grooves 30 are formed by machining, for example, according to a forming pattern of groove pitch of 5 mm and groove depth of 10 μm.

[0054] Thus, a directional electromagnetic steel sheet 10 is generated in which the first groove 20 and the second groove 30 coexist. In the directional electromagnetic steel sheet 10 generated in this way, the second groove 30, which is formed by machining, does not undergo secondary recrystallization caused by annealing, so fine particles still remain at the bottom of the groove.

[0055] In addition, Figure 1 In the diagram, the first groove 20 and the second groove 30 are depicted as segments divided into three or four parts in the width direction of the plate. This indicates that when forming grooves, if the length of the groove in the width direction that a single groove forming device can form is less than the width of the steel plate, multiple groove forming devices are arranged side by side in the width direction. Figure 1 In the case of 3 or 4 groove forming devices, each device is used to form a groove, thereby forming a groove (covering the entire length of the steel plate in the width direction). Repeated explanations of this case are omitted, as are Figures 3, 4, and 5 described later.

[0056] In the manner described above, a directional electromagnetic steel plate 10 is manufactured in which a plurality of first grooves 20, in which no fine particles or subgrain boundaries are formed at the bottom of the groove, and a plurality of second grooves 30, in which fine particles are formed at the bottom of the groove, coexist.

[0057] According to the above embodiment, a directional electromagnetic steel sheet is manufactured having a plurality of first grooves 20 with no fine grains or subgrain boundaries at the bottom, and a plurality of second grooves 20 with fine grains formed at the bottom, which can be formed in contact. The plurality of first grooves 20 with no fine grains or subgrain boundaries at the bottom can be formed by utilizing the fact that the fine grains, subgrain boundary factors, and subgrain boundaries at the bottom of the grooves disappear due to secondary recrystallization annealing. As a result, a directional electromagnetic steel sheet that balances iron loss improvement and magnetic flux density can be provided. That is, there are no subgrain boundaries or subgrain boundary factors in the first grooves 20 that cause iron loss deterioration. Furthermore, since the second grooves 30 are formed in contact, there are in principle no subgrain boundaries or subgrain boundary factors, and the base material loss that reduces magnetic flux density is also smaller. Therefore, based on the above-described directional electromagnetic steel sheet having both first grooves 20 and second grooves 30, the above-mentioned balance can be achieved. Furthermore, in the directional electromagnetic steel plate 10 manufactured in the above manner, there are no subgrain boundary factors in any of the slots. Therefore, even when using it to manufacture industrial products such as transformers, iron loss deterioration caused by subgrain boundary factor sub-glyphization will not occur. Thus, it is also possible to prevent further deterioration of the iron loss ratio after the second slot 30 has just been formed due to the manufacturing process of industrial products.

[0058] Furthermore, setting the depth of the first groove 20 to be deeper than that of the second groove 30 can reduce the burden (wear, etc.) on contact-type equipment such as machining devices. In particular, if the first groove 20 is formed by thermal processing such as laser processing, a deep groove can be easily formed. Therefore, since there is a first groove 20 with sufficient depth and high iron loss improvement effect, and a second groove 30 with iron loss improvement effect while reducing the decrease in magnetic flux density, the above-mentioned balance can be achieved at a higher level as a whole. According to this embodiment, the directional electromagnetic steel plate 10 can eliminate the subgrain boundaries that cause iron loss deterioration by annealing, thereby achieving a balance between iron loss improvement and magnetic flux density.

[0059] [Manufacturing method of directional electromagnetic steel sheet]

[0060] Next, a method for manufacturing a directional electromagnetic steel plate 10 according to an embodiment of the present invention will be described. The method for manufacturing a directional electromagnetic steel plate 10 according to an embodiment of the present invention is a method for manufacturing a directional electromagnetic steel plate 10 having a plurality of grooves formed in the length direction of a steel plate extending in a direction substantially parallel to the width direction of the steel plate. Figure 2 This is a flowchart illustrating a method for manufacturing a directional electromagnetic steel plate 10 according to one embodiment of the present invention.

[0061] like Figure 2 As shown, if the manufacturing of the directional electromagnetic steel sheet 10 begins, in step S101, a first groove 20 consisting of a plurality of grooves extending in a direction substantially parallel to the width direction is formed on the cold-rolled steel sheet, which is the material of the directional electromagnetic steel sheet 10 (first groove forming step). Typically, a plurality of first grooves 20 extending in a direction substantially parallel to the width direction of the steel sheet (cold-rolled steel sheet) are formed on the surface of the cold-rolled steel sheet, which is the material of the directional electromagnetic steel sheet 10, after casting, hot rolling, annealing, and cold rolling and exiting from the finishing mill, in order to perform magnetic domain control. The first groove 20 is formed by one of the following methods: laser processing, etching processing, electron beam processing, plasma processing, and machining, according to a predetermined groove pitch, groove depth, or groove angle. Here, the groove angle is defined as the angle between the extension direction of the groove (the elongation direction of the groove) and the width direction of the steel sheet. Generally speaking, there is a trend that the larger the groove angle, the smaller the improvement in iron loss, and the greater the improvement in the deterioration of the magnetic flux density B8.

[0062] For example, the first groove 20 can be formed deeper than the second groove 30. Forming a first groove 20 that is deeper than the second groove 30 helps to improve the iron loss of the directional electromagnetic steel plate 10. Preferably, laser processing, which is easy to control in the depth direction and does not cause wear due to contact with the steel plate, is used. However, any method that can ensure the improvement of iron loss is acceptable. It is not limited to laser processing. Various non-contact methods such as electron beam processing and plasma processing, as well as mechanical processing, can also be used to form the groove.

[0063] Figure 3 shows a schematic diagram of a directional electromagnetic steel plate 10 according to one embodiment of the present invention. For example, Figure 3A The first groove 20 shown 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.

[0064] After the processing in step S101 is completed, proceed to step S102.

[0065] In step S102, the cold-rolled steel sheet with the first groove 20 is annealed to make the easy magnetization axis of the cold-rolled steel sheet consistent with the length direction of the steel sheet, thereby obtaining a directional electromagnetic steel sheet (secondary recrystallization annealing step).

[0066] To describe the process in more detail, as is known, the steel plate with the first groove 20 formed is subjected to decarburization annealing, for example, heating for 1 to 3 minutes at a temperature of 700°C to 900°C. Through decarburization annealing, the carbon concentration in the steel plate is adjusted, and an oxide layer mainly composed of silicon dioxide (SiO2) is formed on the surface of the decarburized steel plate. Subsequently, an annealing separating agent mainly composed of magnesium oxide (MgO) is coated onto the oxide layer on the surface of the decarburized steel plate, and the plate is then wound into a coil.

[0067] A steel sheet that has undergone decarburization annealing and has been coated with an annealing separating agent is inserted into a batch furnace while remaining in coil form. It is then subjected to heat treatment (secondary recrystallization annealing) at a heating time of 20–24 hours and a heating temperature of 1100°C–1300°C. Through this heat treatment, grains known as Gaussian grains, whose easy magnetization axis aligns with the rolling direction of the steel sheet, preferentially grow (resulting in secondary recrystallization). As a result, a directional electromagnetic steel sheet 10 with high crystal orientation (or crystal orientation) is obtained after secondary recrystallization annealing. Furthermore, during secondary recrystallization annealing, the oxide layer reacts with the annealing separating agent to form a glassy coating composed of magnesium olivine (Mg₂SiO₄) on the surface of the steel sheet, thereby forming the directional electromagnetic steel sheet 10.

[0068] Subsequently, the directional electromagnetic steel sheet 10, which is rolled into a roll, is unwound and unfolded into a sheet. While flattened, an insulating coating agent (coating liquid) is applied over the glass coating formed on the surface of the directional electromagnetic steel sheet 10. The directional electromagnetic steel sheet 10 coated with the insulating coating agent is annealed at a heating time of 10 to 120 seconds and a heating temperature of 800°C to 850°C, and the insulating coating agent is baked and cured to form an insulating coating on the surface of the directional electromagnetic steel sheet 10, thereby imparting electrical insulation properties and a specified surface tension to the directional electromagnetic steel sheet 10.

[0069] After the processing in step S102 is completed, proceed to step S103.

[0070] In step S103, a second groove 30, consisting of a plurality of grooves extending in a direction substantially parallel to the width direction, is formed on the directional electromagnetic steel plate 10 by machining (second groove forming step). The second groove 30 is formed by machining with gears or the like according to a predetermined groove pitch, groove depth, or groove angle.

[0071] For example, Figure 3B The second groove 30 shown is in Figure 3A The steel plate with the first groove 20 already formed is formed by machining (stamping) according to a second forming mode with a groove pitch of 5 mm, a groove depth of 10 μm, and a groove angle of 12 degrees. If stamping is used, the burden of chipping and tool wear when achieving a groove depth of more than 20 μm is relatively large, so it is difficult to continue. Therefore, on the one hand, a deeper groove (which is easier to improve iron loss) is formed as the first groove 20 by using a method such as laser processing, which is easy to process and has no wear problems, and on the other hand, a second groove 30 is formed by machining, which presses the steel plate into the groove during the groove formation without causing steel plate wear, so as not to cause magnetic flux density deterioration (magnetic flux density B8 is not easily deteriorated). This way, both iron loss improvement and magnetic flux density can be achieved. For example, to obtain the effect of iron loss improvement, a groove of 20 to 25 μm needs to be formed, but if this formation is carried out in step S101, the desired magnetic properties (iron loss improvement and avoidance of B8 deterioration) cannot be obtained.

[0072] Subsequently, when the insulating coating formed on the surface of the directional electromagnetic steel plate 10 disappears along with the formation of the second groove 30, an insulating coating can be formed on the surface of the directional electromagnetic steel plate 10 by applying an insulating coating agent (coating liquid) to the surface of the directional electromagnetic steel plate 10 again, and annealing it at a heating time of 10 to 120 seconds and a heating temperature of 800°C to 850°C and baking and curing the insulating coating agent, thereby obtaining the final directional electromagnetic steel plate 10.

[0073] The directional electromagnetic steel sheet 10 thus manufactured is shipped and used in appropriate industrial products, such as as a material for the core of a transformer.

[0074] Furthermore, in the above description, the second groove 30 is formed in step S103 after the insulating film is formed in step S102. However, the insulating film can be formed as long as secondary recrystallization occurs in step S102, or the insulating film can be formed after the second groove 30 is formed.

[0075] Furthermore, when grooves are formed by machining, fine particles are generated at the bottom of the groove due to compression of the steel plate. However, no fine particles are generated when grooves are formed by laser machining or etching. On the other hand, when grooves are formed by laser machining, thermal strain is introduced at the bottom (or the wall) of the groove, resulting in subgrain boundary factors. Such fine particles or subgrain boundaries will disappear due to aging if subjected to prolonged high temperatures (around 1000°C or higher) such as secondary recrystallization annealing.

[0076] Therefore, fine particles will exist at the bottom of the second groove 30 of the directional electromagnetic steel plate 10 (because it has not been subjected to high temperature for a long time after the groove is processed), while at the bottom of the first groove 20 (because it has been subjected to high temperature of secondary recrystallization annealing after the groove is processed), fine particles, subgrain boundaries, and subgrain boundary factors no longer exist.

[0077] Figure 4 shows a schematic diagram of a directional electromagnetic steel plate according to one embodiment of the present invention. As a result, along... Figure 4A In the cross-section of the directional electromagnetic steel plate 10 shown for line AA', as... Figure 4B As shown, fine particles remain at the bottom of the groove corresponding to the second groove 30, while at the bottom of the groove corresponding to the first groove 20, both fine particles and subgrain boundaries have disappeared.

[0078] Figure 5 shows a schematic diagram of a directional electromagnetic steel plate according to one embodiment of the present invention. There are no particular limitations on the forming mode, such as the slot pitch, slot depth, and slot angle, when forming the second slot 30 in the second slot forming step; for example, the mode shown in Figure 5 can also be used. That is, it is also possible to... Figure 5A The reference shown Figure 3A After the first groove 20 is formed on the steel plate, the surface of the steel plate, as shown... Figure 5B As shown, the second groove 30 is formed according to a different formation mode than that used when the first groove 20 was formed. For example, Figure 5B The second groove 30 shown is formed by machining according to a second forming mode with a groove pitch of 5 mm, a groove depth of 10 μm, and a groove angle of -12 degrees.

[0079] According to the above manufacturing method, a directional electromagnetic steel plate 10 can be manufactured in which multiple first grooves 20 without micro-grain and subgrain boundaries at the bottom are mixed with multiple second grooves 30 with micro-grain at the bottom. The directional electromagnetic steel plate 10 combines the first grooves 20 formed by laser processing or the like with a groove depth that is effective in improving iron loss, and the second grooves 30 formed by mechanical means that are effective in improving magnetic flux density and have less steel plate material loss, thus achieving a balance between improving iron loss and magnetic flux density.

[0080] [Example]

[0081] Figure 6 This is a graph showing the relationship between the groove depth obtained by using only laser-based groove formation and by using only mechanical-based groove formation, and the iron loss improvement rate. Figure 7 This is a graph showing the relationship between the groove depth obtained by using only laser-based groove formation and by using only mechanical-based groove formation, and the amount of B8 degradation.

[0082] The relationship between trench depth and iron loss improvement rate in existing trench formation methods using laser alone and those using mechanical methods alone is as follows: Figure 6 The curve shown is illustrated in the figure. Furthermore, the relationship between the groove depth and the amount of B8 degradation is as follows: Figure 7 The graph shown in the figure is as follows.

[0083] Regarding the method for measuring groove depth, a measuring device (Keyence (registered trademark) WI-5000, WI-001) is used to measure the groove depth. Specifically, the average measured height within any range of the ungrooved area on the steel plate surface is denoted as reference H0 (>0), and the height at the maximum depth of the groove is denoted as H (>0). Using the aforementioned measuring device, the length equivalent to their difference (H0-H) is measured to obtain the groove depth.

[0084] Furthermore, regarding the measurement methods for iron loss and magnetic flux density B8, the iron loss [W / kg] of the directional electromagnetic steel sheet is, for example, the iron loss when a magnetic field with a maximum magnetic flux density of 1.7 Tesla and a 50 Hz is applied to 10 sample sheets with dimensions of 60 [mm] × 300 [mm] and a sheet thickness of 0.23 [mm], and can be measured using an SST (Single Sheet Tester) measuring instrument. Additionally, the average iron loss of the raw material steel sheet is 0.85 [W / kg]. Furthermore, the magnetic flux density B8 can be, for example, set as the magnetic flux density generated when the aforementioned 10 sample sheets are magnetized under a magnetic field of 800 A / m. Additionally, the average magnetic flux density B8 of the raw material steel sheet is 1.92 [T (Tesla)].

[0085] At this point, the iron loss improvement rate can be defined as follows. That is, based on the iron loss of the raw material steel plate, the iron loss improvement rate of the directional electromagnetic steel plate is calculated in the following manner.

[0086] Iron loss improvement rate [%] = ((Iron loss of raw material steel plate) - (Iron loss of directional electromagnetic steel plate) / Iron loss of raw material steel plate) × 100

[0087] Here, raw material steel plate refers to steel plate that has not undergone the above-mentioned two groove forming steps of forming the first groove 20 and the second groove 30 in the coil of the same base material, that is, steel plate that has not formed the first groove 20 and the second groove 30.

[0088] Furthermore, the degradation amount ΔB8 of the magnetic flux density B8 can be defined as follows. That is, based on the magnetic flux density B8 of the raw material steel plate, the degradation amount ΔB8 of the directional electromagnetic steel plate is calculated in the following manner.

[0089] ΔB8[Gauss] = (Magnetic flux density B8(T) of raw material steel plate - Magnetic flux density B8(T) of directional electromagnet steel plate) × 10000

[0090] That is, in the formation of grooves using laser alone, when the groove depth is greater than 20 μm, the iron loss improvement rate can reach more than 11%, but the B8 degradation will become more than 300 Gauss. The reason for this is that the non-contact laser method can form relatively deep grooves. Due to the increase in leakage magnetic flux and static magnetic energy generated from the surface magnetic poles, the main magnetic domains are subdivided, thus making it easier to improve iron loss. However, on the other hand, it can be argued that the increased volume (amount) of steel sheet removed leads to an increased degradation of magnetic flux density B8.

[0091] On the other hand, in the case of slot formation using only mechanical methods, when the slot depth is 15–20 μm, the degradation of magnetic flux density B8 is below 200 Gauss, but it is impossible to achieve an iron loss improvement rate of over 11%. The reason for the poor iron loss improvement rate is that in contact-based slot formation, it is difficult to form deep slots due to tooth wear and chipping. Furthermore, regarding the good performance of magnetic flux density B8, it can be assumed that, as evidenced by the generation of fine particles, the base material of the steel plate is pressed into the bottom of the slot, thereby suppressing the loss of the base material of the steel plate and resulting in less loss.

[0092] In this embodiment, the first groove 20 is formed by laser processing according to a first forming mode with a scanning speed of 45 m / s, a groove pitch of 3 mm, a beam shape of 25 × 50 μm, and groove depths of 0 μm, 10 μm, 15 μm, 20 μm, and 25 μm obtained by adjusting the laser power. Furthermore, the second groove 30 is formed by stamping according to a second forming mode with a groove pitch of 5 mm and groove depths of 0 μm, 10 μm, 15 μm, and 20 μm obtained by adjusting the pressure of the tooth profile.

[0093] Figure 8This is a graph showing the iron loss improvement rate obtained by combining laser and mechanical methods according to one embodiment of the present invention. Figure 9 This is a graph showing the relationship between the groove depth and the iron loss improvement rate of various combinations of one embodiment of the present disclosure. Based on the directional electromagnetic steel plate 10 of this embodiment, which contains a first groove 20 formed by laser processing and a second groove 30 formed by stamping, it can be seen that the relationship between various combinations of groove depths obtained by laser processing and groove depths obtained by stamping and the iron loss improvement rate is as follows: Figure 8 and Figure 9 The experimental results are shown in the figure. Figure 8 The seven highlighted combinations shown are those that achieve an iron loss improvement rate of over 11%.

[0094] Figure 10 This is a graph showing the amount of B8 degradation obtained by combining laser and mechanical methods according to one embodiment of the present invention. Figure 11 This is a graph showing the relationship between the groove depth and B8 degradation amount for various combinations of groove depths obtained by laser processing and stamping processing, as well as the iron loss improvement rate. Figure 10 and Figure 11 The experimental results are shown in the figure. Among the seven combinations that achieved an iron loss improvement rate of over 11%, the following three combinations had a B8 degradation of no more than 200 Gauss: the combination of a laser-processed groove depth of 10 μm and a stamping groove depth of 15 μm (B8 degradation of 180 Gauss), the combination of a laser-processed groove depth of 15 μm and a stamping groove depth of 5 μm (B8 degradation of 170 Gauss), and the combination of a laser-processed groove depth of 15 μm and a stamping groove depth of 10 μm (B8 degradation of 200 Gauss).

[0095] Therefore, it can be considered that the combination of a laser processing groove depth of 15μm and a stamping processing groove depth of 10μm is optimal in this embodiment; the directional electromagnetic steel plate 10 obtained by forming the groove according to the forming mode of this combination achieves an iron loss improvement rate of 14.1% and a B8 degradation of 200 Gauss, which can be considered to be able to balance iron loss improvement and magnetic flux density.

[0096] Alternatively, the same groove depth can also be achieved using electron beam or plasma processing, both of which are thermal processing methods. For example, when using an electron beam, the groove depth can be controlled by adjusting the accelerating voltage and current, while when using plasma, the groove depth can be controlled by adjusting the output current.

[0097] The embodiments of this disclosure have been specifically described above, but this disclosure is not limited to the specific embodiments described above. Various modifications and alterations can be made within the scope of the key points of this disclosure as recorded in the claims.

[0098] The entire contents of the description, drawings and abstract contained in Japanese Patent Application No. 2023-176056, filed on October 11, 2023, are incorporated herein by reference.

[0099] Explanation of reference numerals in the attached figures

[0100] 10. Directional Electromagnetic Steel Sheet

[0101] 20 First slot

[0102] 30 Second slot

Claims

1. A method for manufacturing a directional electromagnetic steel sheet, wherein the directional electromagnetic steel sheet is a steel sheet having a plurality of grooves formed in the length direction of the steel sheet extending in a direction substantially parallel to the width direction of the steel sheet, the manufacturing method being characterized by comprising the following steps: The first groove forming step is to form a first groove consisting of a plurality of grooves extending in a direction substantially parallel to the width direction on a cold-rolled steel sheet, which is the material of directional electromagnetic steel sheet. The cold-rolled steel sheet with the first groove is annealed to make the easy magnetization axis of the cold-rolled steel sheet consistent with the length direction, thereby obtaining a secondary recrystallization annealing step for a directional electromagnetic steel sheet. as well as A second groove forming step involves forming a second groove on the directional electromagnetic steel plate by means of a plurality of grooves extending in a direction substantially parallel to the width direction.

2. The method for manufacturing a directional electromagnetic steel plate as described in claim 1, wherein, In the first groove forming step, the first groove is formed by a non-contact groove forming process.

3. The method for manufacturing a directional electromagnetic steel plate as described in claim 2, wherein, In the non-contact groove forming process, the first groove is formed using one of laser, electron beam, and plasma.

4. The method for manufacturing the directional electromagnetic steel plate according to any one of claims 1 to 3, wherein, In the first groove forming step, the first groove is formed by mechanical groove forming process.

5. The method for manufacturing the directional electromagnetic steel plate according to any one of claims 1 to 4, wherein, The first groove is deeper than the second groove.

6. A directional electromagnetic steel plate, characterized in that it has a plurality of grooves formed along its length direction extending substantially parallel to the width direction of the steel plate, wherein... The plurality of grooves are formed by a first groove at the bottom of which no fine particles are formed and a second groove at the bottom of which fine particles are formed.

7. The directional electromagnetic steel plate as described in claim 6, wherein, The first groove is deeper than the second groove.

8. The directional electromagnetic steel plate as described in claim 6 or 7, wherein, No subgrain boundary factor was formed in either the first or the second groove.

9. An industrial product, characterized in that, The industrial product is manufactured using the directional electromagnetic steel sheet as described in any one of claims 6 to 8.

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