Grain-oriented electrical steel sheet and method for manufacturing the same

Abstract

The present invention provides a grain-oriented magnetic steel sheet which can enjoy the effect of reducing iron loss due to a groove and effectively suppresses the decrease in magnetic flux density. The grain-oriented magnetic steel sheet has a prescribed linear groove, and for each linear groove, the proportion of a flat portion defined as prescribed in the total length of the linear groove is 30% to 90%, and in a surface area of 100 cm 2 The number of portions in which the flat portion is continuous with a prescribed length is 10 or more, and the ratio of ten-point average roughness Rzj to average depth D is 0.1 to 1.

Description

Technical Field

[0001] This invention relates to a superior directional electromagnetic steel sheet used as a transformer core, in which the magnetic domain refinement effect does not disappear due to stress-relief annealing, and a method for manufacturing the same. Background Technology

[0002] Directional electromagnetic steel sheets containing Si with crystal orientations in the (110)

[001] and (100)

[001] orientations are widely used as core materials in various commercial frequency domains due to their excellent soft magnetic properties. Among the required characteristics of electromagnetic steel sheets, the loss at a maximum magnetic flux density of 1.7T when magnetized at a frequency of 50Hz, i.e., W... 17 / 50 Iron loss expressed in (W / kg) is important. That is, this is because by using W 17 / 50 Materials with low iron loss can significantly reduce iron loss in generators and transformers at the main commercial frequency domain of 50Hz AC current.

[0003] Moreover, there is a growing demand year by year for the development of materials that can reduce iron loss.

[0004] As a method to reduce iron loss in directional electromagnetic steel sheets, a common approach is to refine magnetic domains. Among these methods, a heat-resistant magnetic domain refinement method is known, which utilizes the static magnetic energy generated by the free magnetic poles produced on the sidewalls of the grooves to refine magnetic domains by forming grooves on the surface of the steel sheet that extend in a direction intersecting the rolling direction.

[0005] Methods for forming grooves on the surface of steel plates include raised roller engraving, electrolytic etching, and laser processing. Optimizations have been proposed for the depth, width, spacing between grooves, and angle between the groove wall and the surface of the steel plate.

[0006] For example, Patent Document 1 discloses the design of the shape of a groove formed on the surface of a steel plate by electrolytic etching, Patent Document 2 discloses the formation of a linear groove by laser processing, and the further formation of a recess at the bottom of the groove. Additionally, Patent Document 3 discloses a method for suppressing processing strain when forming a groove by mechanical processing.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 4719319

[0010] Patent Document 2: Japanese Patent Application Publication No. 2018-131680

[0011] Patent Document 3: Japanese Patent Application Publication No. 2010-168615 Summary of the Invention

[0012] In addition, there has been a recent search for a method to determine the iron loss W in the magnetization region, which is not only the maximum magnetic flux density of 1.7T as mentioned above, but also a method to determine the grade of steel sheet. 17 / 50 Directional electromagnetic steel sheet with small size and excellent iron loss in regions magnetized with low magnetization force at low magnetic flux density such as 1.0 to 1.5T, and excellent magnetic properties such as magnetic flux density B8 in regions magnetized with high magnetization force such as 800 A / m.

[0013] In heat-resistant magnetic domain refinement techniques based on groove formation, it is known that deepening the groove is effective in improving the domain refinement effect. However, this method has the following problem: since the volume of the substrate iron and the volume of the groove are correspondingly reduced, the magnetic flux density decreases. This problem still exists in Patent Document 1. Furthermore, when designing processing methods as in Patent Documents 2 and 3, problems exist in terms of reduced productivity or increased manufacturing costs.

[0014] The present invention was developed in view of the above-mentioned actual situation, and aims to provide a directional electromagnetic steel plate that, by designing an electrolytic etching method during the formation of grooves in the steel plate, suppresses the decrease in magnetic flux density and further improves iron loss without reducing its productivity.

[0015] In addition, the present invention aims to provide a method for manufacturing the directional electromagnetic steel plate.

[0016] To address the aforementioned issues, the inventors formed linear grooves on the final cold-rolled steel sheet using various methods and evaluated the magnetic properties after secondary recrystallization. During the repetition of this experiment, it was discovered that in steel sheets with a flat and slightly rough bottom surface of the linear groove, the improvement in iron loss was greater than the deterioration in magnetic flux density. Through detailed investigation, a suitable shape for the bottom surface of the groove was discovered, thus completing this invention.

[0017] The present invention is based on the above insights, and the main structure of the present invention is as follows.

[0018] 1. A directional electromagnetic steel sheet, characterized in that it has linear grooves on one side surface, extending in a direction intersecting the rolling direction, wherein when the average depth of the linear groove is set to D, the average width is set to W, and the ten-point average roughness of the roughness curve at the center of the width is set to Rzjis, for each linear groove,

[0019] The proportion of flat portions in the total length of the linear groove is 30% to 90%. The aforementioned flat portions are defined as the portion whose absolute value of the difference between its depth and the average depth D is less than 1 / 10 of the average depth D.

[0020] With a surface area of ​​100cm² 2In the above-mentioned flat portion, the number of continuous portions with a length of at least 1.3 times the average width W is 10 or more, and

[0021] The ratio of the ten-point average roughness Rzjis to the average depth D, i.e., Rzjis / D, is 0.1 to 1.

[0022] 2. According to the directional electromagnetic steel plate described in 1 above, wherein the average absolute value of the elevation of the five peaks from the highest peak to the fifth highest peak in the roughness curve at the center of the width of the linear groove is set as Pa, and the average absolute value of the elevation of the five valleys from the lowest valley to the fifth lowest valley is set as Va, Pa and Va satisfy the following equation (4):

[0023] Va≤Pa≤15μm······(4).

[0024] 3. A method for manufacturing a directional electromagnetic steel sheet, characterized in that the directional electromagnetic steel billet undergoes at least a final cold rolling process, and further undergoes two recrystallization annealing processes.

[0025] After the final cold rolling and before the two recrystallization annealing processes, an insulating masking agent is applied to the surface of the steel plate. The masking agent is removed linearly in a direction intersecting the rolling direction by laser irradiation in an inactive atmosphere, and then electrolytic etching is performed to form linear grooves.

[0026] 4. The method for manufacturing a directional electromagnetic steel plate according to 3 above, wherein after removing the masking agent linearly, the plate is placed in an electrolytic cell within 10 seconds to perform the electrolytic etching.

[0027] According to the present invention, iron loss can be effectively improved by the magnetic domain refinement effect of the grooves formed on the surface of the steel plate. Therefore, the directional electromagnetic steel plate according to the present invention can enjoy the iron loss improvement effect brought about by the formation of the grooves and suppress the reduction of magnetic flux density. Attached Figure Description

[0028] Figure 1 This diagram illustrates the shape of the bottom of the tank formed by electrolytic etching.

[0029] Figure 2 It means Figure 1 A diagram showing the flat portion at the bottom of the groove.

[0030] Figure 3 It means Figure 1 The diagram shows Rzjis at the bottom of the groove. Detailed Implementation

[0031] The present invention will now be described in detail.

[0032] The heat-resistant magnetic domain refinement based on the formation of linear grooves (hereinafter, unless otherwise specified, "groove" refers to linear grooves) in this invention is achieved by increasing the static magnetic energy through magnetic poles generated on the side of the groove, thereby generating new 180° magnetic domain walls for elimination, and narrowing the domain width. Furthermore, if the domain width is narrowed in this way (resulting in magnetic domain refinement), the movement distance of the domain walls when the steel plate is magnetized is shortened, thus reducing the energy loss, i.e., iron loss, during the movement of the domain walls.

[0033] To demonstrate the aforementioned mechanism, magnetic poles need to be generated, and importantly, an interface between materials with different magnetic permeabilities needs to be created. However, in the technique utilizing a slot described above, the difference in magnetic permeability between iron and air is taken into account. Therefore, if a slot is formed, the following problems arise: the effective magnetic permeability of the steel plate decreases accordingly with the volume of the slot, and the magnetic flux density B8 value at 800 A / m, which is another indicator of magnetic properties, decreases.

[0034] Therefore, if a large number of magnetic poles are generated to improve the magnetic domain refinement effect, it will result in a decrease in effective permeability and magnetic flux density. In addition, since the magnetic poles are only generated on the side of the groove, when the groove is formed on one side of the steel plate (the plane on one side), there is a problem that the magnetic domain refinement effect brought about by the groove formation is difficult to extend to the center of the steel plate in the thickness direction or the back side (the plane on the other side).

[0035] Therefore, in order to solve the above-mentioned problems, the inventors have studied the shape of the groove, especially the shape of the bottom surface of the groove, in order to maximize the effects brought about by the groove formation without causing adverse effects. This is because, in observing the groove shapes produced by existing groove forming techniques, it was noted that the groove depth changes and that this change affects iron loss. It was believed that by achieving an ideal groove shape that nearly fully guides the effect of magnetic domain refinement and minimizes the reduction in the effective permeability of the steel plate, further reduction in iron loss can be achieved.

[0036] As a result, the following insights were obtained: it is effective to make the bottom surface of the linear groove smooth and to provide concave and convex parts that meet the specified conditions.

[0037] That is, the inventors have discovered that satisfying the two requirements of having a flat portion with a small depth variation of a certain length or more on the bottom surface of the groove and having a concave-convex portion with a large depth variation in addition to the flat portion is suitable for solving the above-mentioned problems and effectively exerting the magnetic domain refinement effect brought about by the formation of the groove.

[0038] Next, the reasons for limiting each constituent element of the present invention will be described.

[0039] First, the linear grooves of the present invention are formed on one side surface of the steel plate (one side surface). This is because the grooves of the present invention are formed only on one side surface of the steel plate, and the magnetic domain refinement effect brought about by the formation of the grooves will also affect the center or back side of the steel plate in the thickness direction (the other side surface).

[0040] In addition, the spacing of the above-mentioned linear grooves is not particularly limited, but is preferably in the range of 2.0 mm to 5.0 mm.

[0041] The bottom surface of the linear groove of the present invention is preferably substantially flat. This is because if the absolute value of the variation (d-D) of the measured value d of the groove depth (hereinafter referred to as groove depth d) relative to the average depth D of the linear groove (hereinafter referred to as average depth D) exceeds 1 / 10 of the average depth D, there is a tendency that even if the groove depth d is increased, the iron loss will not decrease. It should be noted that the average depth D is the average value of the groove depth d measured at the center in the groove width direction, and the variation of the groove depth d is the difference between the groove depth d measured at the center in the groove width direction and the average depth D.

[0042] The mechanism of the aforementioned phenomenon of this variation (d-D) (if the variation is large, there is a tendency for the iron loss not to decrease even if the groove depth is increased) is not yet clear. However, it is presumed that this is because when the variation of the groove depth d in the same groove is large, the shallow part of the groove with insufficient magnetic domain refinement and the deep part of the groove with increased hysteresis loss due to the reduction of the base iron volume coexist. Therefore, even if the optimal average groove depth is formed, the iron loss will not decrease at all.

[0043] In this invention, the portion in the linear groove where the absolute value of the variation (d-D) is less than 1 / 10 of the average depth D, i.e., that satisfies the following formula (1), is defined as a "flat portion".

[0044] -0.10D≤(d-D)≤0.10D····(1)

[0045] Furthermore, the number of flat sections with a continuous length L of at least 1.3 times the average width W in the direction of the linear groove extension, i.e., the number of flat sections with a continuous length L satisfying the following formula (2), is required for any steel plate with a surface area of ​​100 cm². 2 There are at least 10 parts in the middle.

[0046] 1.3W≤L····(2)

[0047] This is because if the number of the aforementioned sections is less than 10, the flat portion of the groove bottom is too short to fully guide the magnetic domain refinement effect, and the reduction in the effective magnetic permeability of the steel plate cannot be minimized. It should be noted that the surface area of ​​any of the aforementioned steel plates is 100 cm². 2 If every 1m 2Twenty samples were taken from the steel plate, which can be said to represent the whole.

[0048] Furthermore, the proportion of flat portions in the total length of each groove needs to be 30% to 90%. Preferably, it is 40% to 90%.

[0049] It should be noted that although the requirements for the grooves described above are specified in each groove, it is sufficient if 90% of all grooves satisfy these requirements. That is, if there are 100 grooves, it is sufficient if at least 90 grooves satisfy the above requirements.

[0050] An example of determining the groove depth along the extension direction of a linear groove is shown below. Figures 1-3 . Figure 1 The measurement results of the groove depth were used to record the aforementioned "flat section" diagram. Figure 2 It should be explained that... Figure 2 The part marked "L" is a continuous interval of "flat section".

[0051] In this invention, as described above, it is necessary to form a flat portion where W and L satisfy the following formula (2). This is because: since the wider W is, the smaller the volume of the base iron, it is necessary to reduce the portion with large variations in the bottom surface of the groove, and reduce the interval that is insufficient for the reduction of the base iron volume or the depth required for the refinement of magnetic domains.

[0052] 1.3W≤L····(2)

[0053] On the other hand, the bottom surface of the linear groove of the present invention is not completely flat, but has portions other than the flat portion, i.e., uneven portions with a predetermined height or depth. If the groove is flat as described above, the effect of the groove depth formed on the steel plate surface being the optimal depth is greater, but the allowable range is narrowed, and the cost of production management increases. Therefore, by intentionally leaving rough portions in the flat groove, it is possible to balance the magnetic domain refinement effect and characteristic stabilization brought about by the formation of the groove.

[0054] It should be noted that, in this invention, the uneven portion is defined as the part in the linear groove where the absolute value of the variation (d-D) exceeds 1 / 10 of the average depth D. Furthermore, in this invention, the ten-point average roughness Rzjis according to JIS B 0601-2001 is 100% or less relative to the average depth D.

[0055] Specifically, such as Figure 3 As shown, a range of 2 mm in length is arbitrarily selected from the cross-sectional curve at the center of the groove. Within this range, the ten-point average roughness Rzjis according to JIS B 0601-2001 needs to be 0.1 to 1 relative to the average depth D, which satisfies the following equation (3).

[0056] 0.1≤Rzjis / D≤1 ·····(3)

[0057] Although the reason is not yet clear, it is believed that the iron loss increases when deviating from the range of equation (3) above. It should be noted that Rzjis is preferably 20% to 50% of the average depth D. In other words, Rzjis / D is preferably 0.2 to 0.5.

[0058] In addition, in the roughness curve at the center of the width of the linear groove, when the average absolute value of the elevation of the five peaks from the highest peak to the fifth highest peak is set as Pa, and the average absolute value of the elevation of the five valleys from the lowest valley to the fifth lowest valley is set as Va, the above Pa and the above Va preferably satisfy the following equation (4).

[0059] Va≤Pa≤15μm····(4)

[0060] This is because if Pa and Va exceed 15 μm, the deviation from the target groove depth becomes larger, making it difficult to achieve the desired magnetic domain refinement effect locally. Furthermore, the valley portion further reduces the proportion of iron in the steel plate; therefore, as mentioned above, Va ≤ Pa is preferred. It should be noted that in this invention, the aforementioned peak refers to the upward-convex vertex in the roughness curve, and the aforementioned valley refers to the downward-concave lowest point in the roughness curve. Additionally, the absolute value of the aforementioned elevation refers to the absolute value of the distance from the peak or lowest point from the average depth D. Furthermore, this specification is based on the roughness curve measured at the cross-section at the center of each groove, and preferably, at least one out of every ten grooves satisfies the above formula (4).

[0061] The composition of the steel plate used in this invention is not particularly limited as long as it is the same as that used in existing directional electromagnetic steel plates. The following describes representative components.

[0062] [Ingredients]

[0063] Si: 2.0% by mass to 5.0% by mass

[0064] Si is an element required to increase the resistivity of steel and reduce iron loss. If the content is less than 2.0% by mass, the above effects are insufficient; on the other hand, if it exceeds 5.0% by mass, the processability decreases, making it difficult to roll and manufacture. Therefore, the Si content of the steel plate used in this invention is preferably in the range of 2.0 to 5.0% by mass. More preferably, it is in the range of 2.5 to 4.5% by mass.

[0065] It should be noted that there are no particular limitations on the elements other than Si contained in the steel sheet, as long as they are components of existing known directional electromagnetic steel sheets and contain a normal amount of components that undergo secondary recrystallization during the normal manufacturing process of directional electromagnetic steel sheets. Furthermore, the remaining components beyond this normal amount are Fe and unavoidable impurities.

[0066] The method for manufacturing the directional electromagnetic steel sheet of the present invention will be described below.

[0067] The present invention employs the following method: In the manufacturing method of a directional electromagnetic steel sheet, which involves hot rolling and other known processes, followed by final cold rolling, and then two recrystallization annealings and the treatment of an insulating tension film after the two recrystallization annealings, an insulating masking agent is applied to the surface of the steel sheet after the final cold rolling and before the two recrystallization annealings. The masking agent is removed linearly in a direction intersecting the rolling direction by laser irradiation in an inactive atmosphere, and then electrolytic etching is performed to form linear grooves.

[0068] It should be noted that the aforementioned intersecting direction refers to a direction with an angle within ±30 degrees that is perpendicular to the rolling direction (orthogonal direction).

[0069] In this invention, during the process of linearly removing the masking agent by laser irradiation after coating and drying an insulating masking material, laser irradiation is performed in an inactive atmosphere. This is to suppress the formation of an oxide film on the steel plate surface from laser irradiation to electrolytic etching, prevent the groove shape formed by electrolytic etching from becoming uneven, and make the bottom of the groove flatter.

[0070] Preferably, the area subjected to laser irradiation is close to the electrolytic cell where electrolytic etching is performed.

[0071] In addition, in order to flatten the bottom of the tank, it is preferable to place the steel plate into the electrolytic tank within 10 seconds after irradiating the steel plate with a laser and removing the masking agent in a linear fashion.

[0072] It should be noted that Rzjis, Pa, and Va, which are related to roughness, can be optimized by adjusting the electrolytic current and time during etching.

[0073] Example

[0074] The embodiments of the present invention will be described below.

[0075] In this embodiment, a steel billet containing the components shown in Table 1 below, with the remainder being Fe and unavoidable impurities, is hot-rolled using conventional methods to produce a hot-rolled steel sheet. This is further cold-rolled twice, including intermediate annealing, to produce a cold-rolled steel sheet with a thickness of 0.23 mm. Then, a sample is cut from the center portion, removing more than 100 mm from both edges in the width direction of the steel sheet, to obtain a cold-rolled steel sheet with a width of 30 mm and a length of 280 mm.

[0076] [Table 1]

[0077]

[0078] Then, the conditions for the groove formation process are set as follows: 3 conditions.

[0079] (I) An insulating masking agent is coated on the surface of the steel plate. The masking agent is removed linearly in a direction orthogonal to the rolling direction by laser irradiation in an inactive atmosphere. Then, grooves are formed by electrolytic etching.

[0080] (II) The groove is formed by pressing down the linear protruding roller.

[0081] (III) No groove forming process is performed

[0082] The target width of the linear grooves is 40–80 μm, formed in the rolling direction at intervals of 2.0–5.0 mm in a direction orthogonal to the width direction of the steel plate. Electrolytic etching is performed in a NaCl bath. Furthermore, during the formation of the grooves by electrolytic etching, the Rzjis, Pa, and Va of the linear grooves are adjusted by modifying the electrolytic current and electrolytic time, and the target groove depth is further adjusted to between 20–28 μm. Additionally, the proportion of flat portions in the total length of the linear grooves is varied by adjusting the laser output and the exposure time to the atmosphere from laser irradiation to electrolytic etching. Ten test pieces are prepared for each processing condition and groove depth.

[0083] These test pieces underwent a primary recrystallization annealing treatment that also served as decarburization annealing. They were then coated with an annealing separating agent primarily composed of MgO, and after final annealing, an insulating film was applied to create magnetic property evaluation test pieces. After stress-relief annealing at 800℃ for 2 hours, the iron loss W of the test piece was measured using a single-plate magnetic property test. 17 / 50 The difference in iron loss between the iron loss and that without the groove forming process (as described in III above) is taken as the iron loss improvement amount ΔW. 17 / 50 An evaluation was conducted. The shape of the groove was measured using a laser microscope.

[0084] The shape of the groove described above is measured. The portion where the absolute value of the variation (d-D) is less than 1 / 10 of the average depth D is defined as the flat portion. The length of the flat portion of each groove containing this portion is accumulated and divided by the accumulated length of the groove (total length). The resulting value is taken as the percentage of the flat portion.

[0085] In addition, in order to convert the number of parts in the flat section that satisfy the above formula (2) into the number of steel plates per 100cm 2 The surface area makes the average number of flat parts of the 10 confirmed test pieces above 119 times (=100 / (0.3×2.8)).

[0086] According to the relationship between the groove shape and iron loss shown in Table 2, it can be seen that by properly managing the proportion of the flat portion and the roughness Rzjis in the total length of the linear groove, the magnetic domain refinement effect brought about by the groove formation can be stabilized, and the iron loss can be further improved.

[0087] [Table 2]

[0088]

Claims

1. A directional electromagnetic steel plate, characterized in that, A linear groove is formed on one side of the surface, extending in a direction intersecting the rolling direction. When the average depth of the linear groove is set to D, the average width to W, and the average roughness of ten points on the roughness curve at the center of the width is set to Rzjis, for each linear groove... The proportion of flat portions in the total length of the linear groove is 30% to 90%, and the flat portion is defined as the portion whose absolute value of the difference between its depth and the average depth D is less than 1 / 10 of the average depth D. With a surface area of ​​100cm² 2 In this case, the number of continuous portions with a length at least 1.3 times the average width W in the flat portion is 10 or more, and The ratio of the ten-point average roughness Rzjis to the average depth D, i.e., Rzjis / D, is 0.1 to 1.

2. The directional electromagnetic steel plate according to claim 1, wherein, When Pa is defined as the average absolute value of the elevation of the five peaks from the highest peak to the fifth highest peak in the roughness curve at the center of the width of the linear groove, with the average depth D as the reference, and Va is defined as the average absolute value of the elevation of the five valleys from the lowest valley to the fifth lowest valley, with the average depth D as the reference, Pa and Va satisfy the following equation (4): Va≤Pa≤15μm ••••••(4) 3. A method for manufacturing a directional electromagnetic steel plate, which is the method for manufacturing a directional electromagnetic steel plate as described in claim 1 or 2, characterized in that, The directional electromagnetic steel billet shall undergo at least a final cold rolling process, followed by two recrystallization annealing processes. After the final cold rolling and before the second recrystallization annealing, an insulating masking agent is applied to the surface of the steel plate. The masking agent is removed linearly in a direction intersecting the rolling direction by laser irradiation in an inactive atmosphere, and then electrolytic etching is performed to form linear grooves.

4. The method for manufacturing a directional electromagnetic steel plate according to claim 3, wherein, After removing the masking agent linearly, the electrolytic etching is performed within 10 seconds by placing the sample into an electrolytic cell.

Images