JP7147810B2 - Oriented electrical steel sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a grain-oriented electrical steel sheet, and more particularly, to a grain-oriented electrical steel sheet having linear grooves formed on the steel sheet surface and having excellent threadability.

Grain-oriented electrical steel sheets, which have excellent magnetic properties, are mainly used as iron core materials for transformers. Techniques for reducing iron loss in grain-oriented electrical steel sheets include a method of highly aligning secondary recrystallized grains in the steel sheet with the Goss orientation (sharpening) and increasing the film tension of the tension coating formed on the steel sheet surface. In addition to the thinning of the steel sheet, a method using surface processing of the steel sheet is known.

Iron loss reduction technology by surface processing of steel sheet is to reduce iron loss by introducing non-uniform strain on the surface of steel sheet by physical method, subdividing the width of the magnetic domain, and one of them is , a method of forming grooves on the surface of a finish-annealed steel sheet using toothed rolls (projection roll method). According to this method, the magnetic domains on the surface of the steel sheet can be subdivided by forming grooves, and the iron loss of the steel sheet can be reduced. It is also known that even when heat treatment such as strain relief annealing is performed after the grooves are formed, the introduced grooves do not disappear, so that the effect of reducing iron loss is maintained. However, in this method, the groove shape tends to be uneven due to the excessive wear of the toothed roll. There was a problem of increased cost.

Therefore, a method has been developed in which linear grooves are formed on the surface of a steel sheet by etching without using a mechanical means such as a toothed roll. Specifically, after a resist ink is applied in a pattern on the surface of the steel sheet before the forsterite coating is formed, the portions where the resist ink is not applied are selectively etched using a method such as electrolytic etching. By doing so, grooves are formed on the surface of the steel plate. In this method, since there is almost no mechanical wear of the device, maintenance is easier than in the method using toothed rolls.

By the way, it is known that a grain-oriented electrical steel sheet in which such linear grooves are formed is inferior in threadability to a grain-oriented electrical steel sheet in which no linear grooves are formed. This is due to the difference in plate thickness between the grooved portion and the non-grooved portion. Tension is applied to the steel sheet when the steel sheet is ejected from the coil and threaded, but if the tension is set according to the thickness of the non-grooved area, excessive stress is applied to the thin grooved area, causing it to break. increased risk of On the other hand, if the tension is set according to the grooved portion, the tension becomes insufficient in the grooved portion, causing meandering and shape defects, thereby degrading the threadability.

As a means for improving threadability, it is effective to prevent deterioration of the coil shape and reduce the tension required for shape correction or the like. As a technique for preventing deterioration of the coil shape, a technique for suppressing lateral strain deformation (buckling deformation due to its own weight) of the lower end portion of the coil in contact with the coil cradle during finish annealing has been disclosed.

For example, in Patent Documents 1 and 2, in order to suppress lateral strain deformation, by applying a grain refining agent to the lower end of the coil or applying processing deformation strain with a roll with protrusions, etc., A technique for intentionally refining the grains of the lower end of the coil to change the mechanical strength of the lower end of the coil is disclosed. By applying this technique, the mechanical strength of the lower end of the coil changes, making that part less likely to deform, and suppressing lateral strain to a certain extent.

In addition, in Patent Documents 3 to 6, in order to suppress lateral strain deformation, the secondary recrystallization of a belt-shaped portion with a constant width from the lower end of the coil is promoted to increase the crystal grain size at an early stage of the finish annealing and increase the temperature. A method for improving strength is disclosed. Furthermore, Patent Document 7 discloses a technique of introducing a melted and resolidified portion that is easily deformable to the lower end portion of the coil by laser irradiation. When these technologies are applied, the lateral strain is suppressed to some extent, and the tension required when the steel sheet is discharged from the coil and threaded is reduced. was inadequate for

JP-A-63-100131 JP-A-64-42530 JP-A-2-97622 JP-A-3-177518 JP-A-2000-38616 Japanese Patent Application Laid-Open No. 2001-323322 International Publication No. 2014-080763

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a grain-oriented electrical steel sheet having linear grooves formed on the surface of the steel sheet, the grain-oriented electrical steel sheet having excellent threadability. do.

The present inventors have obtained the following knowledge as a result of examining measures for improving the threadability of grain-oriented electrical steel sheets having grooves formed on the surface. In this specification, unless otherwise specified, the "end" of the steel plate or coil means the end of the steel plate or coil in the width direction.

(1) Since fracture troubles frequently occur after finish annealing (after secondary recrystallization structure is formed) in the manufacturing process of grain-oriented electrical steel sheets, the threadability of steel sheets after finish annealing should be improved. This is very important.

(2) In many cases, fractures start at the ends of the steel plate. Therefore, in order to improve the threadability of the steel plate, it is effective to increase the mechanical strength of both ends of the steel plate. It is important to refine the structure in the range up to at least 10 mm to an average crystal grain size of 5 mm or less. However, if the orientation of each crystal grain is substantially the same even if the crystal grains are refined, the slip system will be the same, and the yield strength in only a certain direction will be increased, so it is preferable that the crystal orientation is as random as possible. Therefore, it is necessary to set the frequency of existence of crystal grains having a deviation (deviation angle) of 10° or less from the Goss orientation to 50% or less.

(3) As a means for increasing the mechanical strength of both ends of the steel sheet which is effective for improving the threadability of the steel sheet, it is effective to provide non-grooved portions in which no grooves are formed at both ends of the steel sheet. In order to improve the threadability more effectively, it is preferable not to form grooves at least in the range from both ends of the steel sheet to 1 mm in the width center direction.

(4) Since areas other than both ends of the steel sheet can also be fracture starting points, the grooves formed on the surface are continuously extended in the direction intersecting the rolling direction, and the grooves are formed discontinuously. It is also effective to prevent an increase in thin plate thickness due to the lap portion of the groove, which is easy to do, to improve the plate threadability.

The present invention has been made based on the above findings, and has the following configurations.
[1] A grain-oriented electrical steel sheet having grooves formed on its surface that extend in a direction intersecting the rolling direction and whose groove depth direction is the sheet thickness direction,
The structure is refined in a range of at least 10 mm in the width center direction from both ends in the width direction of the steel plate,
The refined structure with a width of 10 mm or less from both ends has an average grain size of 5 mm or less, and the frequency of existence of crystal grains having a deviation angle of 10° or less from the Goss orientation is 50% or less. is a grain-oriented electrical steel sheet.
[2] The grain-oriented electrical steel sheet according to [1], in which no grooves are formed in a range of at least 1 mm in the width center direction from both ends in the width direction of the surface of the steel sheet.
[3] The grain-oriented electrical steel sheet according to [1] or [2], wherein the grooves formed on the surface of the steel sheet continuously extend in a direction crossing the rolling direction.

According to the present invention, it is possible to provide a grain-oriented electrical steel sheet having linear grooves formed on the surface of the steel sheet and having excellent threadability.
According to the present invention, the mechanical strength of a grain-oriented electrical steel sheet coil having grooves formed on the surface of the steel sheet is greatly improved. A decrease in productivity due to breakage is prevented.

FIG. 1 is a graph showing the relationship between the steel sheet (structure) after each step and the fracture occurrence tension ratio. FIG. 2 is a graph showing the relationship between the grinding width from the edge of the steel sheet and the fracture occurrence tension ratio for steel sheets after finish annealing (secondary recrystallized structure) and after tension coating formation (secondary recrystallized structure). . FIG. 3 is a graph showing the relationship between the average grain size of the structure of the steel plate end region and the fracture occurrence tension ratio. FIG. 4 is a graph showing the relationship between the frequency of occurrence of secondary recrystallized grains in the steel sheet structure within a range of 10 mm in the width center direction from the edge of the steel sheet and the fracture occurrence tension ratio. FIG. 5 is a graph showing the relationship between the width of the groove-unformed portion from both ends of the steel plate in the width center direction and the fracture occurrence tension ratio. FIG. 6 is a diagram for explaining a formation pattern of linear grooves when forming linear grooves using a plurality of laser irradiation devices. FIG. 7 is an enlarged view of the wrap portion in the lower view of FIG. 6(c). FIG. 8 is a graph showing the relationship between the lap allowance and the fracture occurrence tension ratio. FIG. 9 is an explanatory diagram for explaining tissue observation regions. FIG. 10 is an explanatory diagram for explaining a method of setting a secondary recrystallized structure that serves as a reference when determining a region of a fine crystal structure. FIG. 11 is an explanatory diagram illustrating a method of measuring the number of grain boundary crossings per unit distance in the rolling direction at each pitch. 12A and 12B are explanatory diagrams for explaining a method for determining a region of a fine crystal structure. FIG.

<Experiment 1>
First, the results of an experiment that clarified the relationship between the structure of the edge of the steel sheet and the mechanical strength will be described. A cold-rolled plate with a thickness of 0.23 mm and a width of 800 mm coated with a resist ink on the surface is scanned with a laser in a direction perpendicular to the rolling direction, and the laser is irradiated at intervals of 5 mm in the rolling direction to apply resist. Ink was removed. In this method, the resist ink is peeled off (removed) from the portion irradiated with the laser. Laser irradiation is performed by installing two single-mode fiber lasers in the width direction of the steel sheet, using a galvanometer scanner method with a laser irradiation energy of 25 J / m and a laser scanning width of 400 mm, from one end to the other in the width direction of the steel plate. The resist ink was completely stripped continuously.

Next, the resist stripped sample was subjected to an electrolytic etching treatment to form grooves having a depth (in the plate thickness direction) of 20 μm and a width of 100 μm on the surface of the steel sheet, and the conditions were 820° C.×120 sec, N ₂ :H ₂ =40:60. (Volume ratio), decarburization annealing was performed at a dew point of 50°C. After that, both ends of the steel plate were ground to change the properties of subscales formed on the surface of the steel plate. At this time, the grinding width from both ends in the width direction of the steel plate to the width center direction was varied from 0 to 100 mm. Here, the grinding width at both ends of the steel plate (the grinding width at one end and the grinding width at the other end) was the same. Thereafter, application of an annealing separator, final annealing, formation of a tension coating, and the like were performed by a known method to produce a grain-oriented electrical steel sheet. For comparison, grain-oriented electrical steel sheets without grooves were also manufactured under the same manufacturing conditions except for the formation of grooves.

Steel sheets during the above manufacturing process and after completion of the final process, specifically after etching (cold-rolled structure), after decarburization annealing (primary recrystallized structure), after finish annealing (secondary recrystallized structure), tension coating After forming (secondary recrystallized structure), a steel plate with grooves and a steel plate without grooves were subjected to a tensile force (hereinafter referred to as "breaking tension") until fracture occurred on a trial basis. and fracture of the steel sheet (structure) after each process.

The results were expressed as a ratio of the fracture initiation tension of the steel plate with grooves (with grooves) to the fracture initiation tension of the steel plate without grooves (without grooves) (hereinafter referred to as the fracture initiation tension ratio). The test was performed at room temperature of 25°C. The reason why both ends of the steel plate were ground was to change the secondary recrystallization behavior by changing the properties of the subscale, and to change the mechanical strength of the steel plate due to the change in the structure of both ends of the steel plate.

FIG. 1 shows the relationship between the steel sheet (structure) after each process and the fracture occurrence tension ratio, which was investigated for the steel sheet without grinding (grinding width 0 mm). From Fig. 1, when grooves are formed on the surface of the steel sheet, the tension at which fracture occurs is greatly reduced when the secondary recrystallized structure (after finish annealing) is reached. It turns out that it is important to consider when .

FIG. 2 shows the relationship between the grinding width from the edge of the steel sheet and the fracture occurrence tension ratio for steel sheets after finish annealing (secondary recrystallized structure) and after tension coating formation (secondary recrystallized structure). The horizontal axis indicates the width (mm) ground from the ends (both ends) of the steel plate in the direction of the width center. It can be seen that by grinding both ends of the steel sheet by at least 10 mm or more in the direction of the center of the width, the decrease in the tension at breakage is greatly suppressed, and the threadability is improved. In order to investigate the reason why the threadability was improved by grinding, each ground steel plate was pickled and etched and its structure was observed. As a result of observation, it was found that the structure of the ground portion (the region where the sub-scale property changed due to grinding) had a fine crystal structure with an average crystal grain size of 0.8 mm.

In addition, in the present invention, the region of the refined structure (microcrystalline structure) is determined by the following method. A method for determining a region of fine crystal structure in the present invention will be described with reference to FIGS. 9 to 12. FIG.
(i) An area of 100 mm in the total width of the steel sheet and 100 mm in the rolling direction of the steel sheet is used as the structure observation area (Fig. 9). Structure observation and crystal orientation measurement are performed for a region of [100 mm in the width direction]×[100 mm in the rolling direction] at the center in the sheet width direction (Fig. 10).
(ii) From the crystal orientation measurement results, if the frequency of existence of crystal grains with a deviation angle of 10° or less from the Goss orientation is 90% or more in the above [width direction 100 mm] × [rolling direction 100 mm] region, The area is set as a "standard secondary recrystallization structure" (Fig. 10).
(iii) From the results of structure observation, grain boundaries intersecting the rolling direction are measured at 5 mm pitches over the entire width of the steel sheet (Fig. 11).
(iv) Calculate the number of intersections per unit distance in the rolling direction at each pitch (Fig. 11).
(v) If points with a crossing number that is twice or more the average crossing number in the reference secondary recrystallized structure (region) appear continuously, the range (between pitches) is the fine crystal structure (FIG. 12).

In addition, when crystal orientation analysis was performed on the fine crystal structure, the frequency of existence of crystal grains with a deviation angle of 10 ° or less from the Goss orientation was 5% or less, and most of them were not secondary recrystallized structures, but primary crystal grains. It was found that the recrystallized grains were normal grain growth due to finish annealing after grinding. From the above results, it can be concluded that, in the steel sheet whose main structure is the secondary recrystallization structure, the decrease in the tensile strength at break of the grooved steel sheet is greatly suppressed because the mechanical strength is increased by the fine grain structure at both ends of the steel strip. is considered to be the cause.

The crystal orientation measurement in the present invention is measured at a pitch of 1 mm using the X-ray Laue method. angle). In the present invention, the measurement was performed with respect to an area of 100 mm in the total width of the steel plate×rolling direction of the steel plate (see FIG. 9). The frequency of existence of crystal grains with a deviation angle from the Goss orientation of 10° or less is defined as crystals with a deviation angle (deviation amount) from the Goss orientation of 10° or less in a region of 10 mm from the plate edge to the center of the plate width. Find the area of the grain, and the ratio to the area of the region up to 10 mm [(area of the crystal grain with a deviation angle from the Goss orientation of 10 ° or less / area of the region from the edge of the plate to 10 mm in the width center direction) × 100] is the existence frequency, and the deviation angle is defined as √(α ² +β ² ). The α angle is the deviation angle of the secondary recrystallized grain orientation from the (110) <001> ideal orientation in the rolling surface normal direction (ND) axis, and the β angle is the rolling perpendicular direction (TD) axis of the secondary recrystallized grain orientation. is the angle of deviation from the (110) <001> ideal orientation. The average crystal grain size in the area from the edge of the plate to 10 mm in the width center direction is determined by observing the crystal grains present in the area with an optical microscope or microscope, and measuring the number of crystal grains and the area of the area. It was obtained from the equivalent diameter.

<Experiment 2>
Next, the relationship between the average grain size and breaking tension was investigated. Differences from Experiment 1 are as follows. In this experiment, grinding was not performed. Instead, after applying an annealing separator, an additional boric acid solution was sprayed with a nozzle in a range of 10 mm in the width center direction from each steel plate end, and then baking treatment was performed. gone. At that time, the concentration of the boric acid aqueous solution was varied from 0% by mass to 10% by mass. Other than that, the experiment was conducted in the same manner as Experiment 1. The reason why the aqueous boric acid solution was applied is that boron penetrates into the steel sheet during the final annealing and affects the secondary recrystallization behavior.

FIG. 3 shows the relationship between the average grain size of the steel plate after the formation of the tension coating and the fracture occurrence tension ratio in the range where the boric acid solution was sprayed (the range of 10 mm in the width center direction from the edge of the steel plate). When the average crystal grain size in the above range was 5 mm or less, the fracture occurrence tension ratio varied greatly. However, it was found that when the average crystal grain size exceeds at least 5 mm, the decrease in fracture initiation tension cannot be suppressed. In addition, when the average grain size is in the range of 2 to 5 mm, the fracture occurrence tension ratio varies greatly, suggesting that factors other than the average grain size have an effect.

Observation of the structure with an average grain size of 2 to 5 mm in the above range revealed that secondary recrystallized grains and primary recrystallized grains often coexist. On the other hand, when the average grain size is 1 mm or less, the primary recrystallized structure is dominant, and when the average grain size exceeds 5 mm, the secondary recrystallized structure is dominant. Such changes in the structure are considered to be due to the addition of boric acid. Therefore, regarding the samples having an average crystal grain size of 5 mm and 3 mm in the above range, the relationship between the existence frequency of secondary recrystallized grains (here, crystal grains with a deviation angle from the Goss orientation of 10 ° or less) and the fracture occurrence tension ratio was examined. investigated. The results are shown in FIG. 4. If the frequency of existence of secondary recrystallized grains is 50% or less, it is possible to suppress the decrease in the tensile strength at break of the grooved steel sheet, and the improvement of the threadability becomes remarkable. found.

<Experiment 3>
As a further measure to improve the threadability, we investigated not to intentionally form grooves in the regions of both ends of the steel plate. If grooves are not formed, the effect of refining the magnetic domain cannot be obtained, so there is a problem of deterioration in magnetic properties. buckling deformation due to deformation, and deformation due to stress caused by the difference in temperature distribution due to overheating during coil annealing occurs at the upper end of the coil, and a certain range from both ends of the steel plate inevitably becomes a portion where products cannot be extracted. Therefore, if the groove-unformed portion necessary for improving the strip threading property is not large, the groove-unformed portion will fit in the portion where such a product cannot be collected.

A cold-rolled plate having a thickness of 0.18 mm and a width of 800 mm obtained by a known method was coated with a resist ink by known gravure offset printing. At that time, the coating pattern has an uncoated portion extending in the direction intersecting the rolling direction of the steel plate, and the both ends of the steel plate are intentionally uncoated in the range of 0 to 15 mm in the width center direction from both ends of the steel plate. A range that does not form a part is provided. That is, the application pattern was adjusted so that the subsequent electrolytic etching formed a non-grooved portion in which no groove was formed in the range of 0 to 15 mm from both ends of the steel sheet in the width center direction. After that, by electrolytic etching and resist stripping in an alkaline solution, linear grooves having a width of 200 μm and a depth of 25 μm were formed at intervals of 4.5 mm at an inclination angle of 7.5° with respect to the direction perpendicular to the rolling direction. formed. Then, an additional heat treatment was applied to a range of 10 mm from both ends of the steel sheet in the width center direction by an edge heater to change the inhibitor state and the primary recrystallized grain size of that section. After that, after performing decarburization annealing with atmospheric oxidation degree P(H ₂ O)/P(H ₂ ) = 0.55, soaking temperature: 840 ° C. for 60 seconds, applying an annealing separator by a known method, Finish annealing, tension coating application, etc. were performed to make a product. The evaluation of the tension at break was performed in the same manner as in Experiments 1 and 2.

FIG. 5 shows the relationship between the width in the direction of the width center from both ends of the steel plate in the non-grooved portion and the fracture occurrence tension ratio. In this evaluation sample, the frequency of existence of secondary recrystallized grains was 20% and the average grain size was 4 mm in the structure within 10 mm from both ends heated by the edge heater. As shown in FIG. 5, even if there is no non-grooved portion (the width of the non-grooved portion is 0 mm), a significant decrease in the tensile strength at break of the steel plate with grooves is suppressed, and the threadability is not significantly deteriorated. However, by setting the width of the non-grooved portion from the edge of the steel sheet to 1 mm or more, the decrease in the tensile strength at break of the steel sheet with the groove formed is further suppressed, and the deterioration of the threadability is suppressed. It became clear. The width of the non-grooved portion from the steel plate edge is preferably 2 mm or more.

<Experiment 4>
It was clarified that improving the structure of the edge region of the steel sheet greatly improved the threadability, but we investigated whether further improvement is possible by improving the groove formation behavior in the secondary recrystallization structure. Groove formation may be formed by a single continuous groove (a groove extending continuously in a direction intersecting the rolling direction) as shown in FIG. In the case of forming grooves by etching after peeling off, a plurality of laser irradiation devices may be used to connect linear resist peelings. In other words, it is not necessary to scan the entire width of the steel sheet with the laser beams emitted from the respective irradiation devices. In this case, there occurs a portion where the groove is discontinuous in the extending direction of the groove. In this case, if the grooves are formed as shown in FIG. 6(b), the core loss will be deteriorated. It is common to form grooves so that they overlap with each other. Hereinafter, a region where grooves adjacent to each other in the sheet width direction overlap each other when projected onto a projection plane orthogonal to the groove width direction is referred to as a lap portion (see FIG. 6A). If a groove is formed to have a lap portion, the area where the strip thickness is thin becomes large at the lap portion. decided to investigate.

A cold-rolled plate having a plate thickness of 0.20 mm and a plate width of 1200 mm obtained by a known method in which a resist ink is applied to the surface is subjected to a known laser processing method using three laser oscillators to determine the lap allowance between adjacent grooves. Grooves were formed while changing Here, the lap allowance (%) is expressed by (lap width/groove width) x 100, and the lap width is the overlap in the groove width direction when adjacent grooves in the width direction overlap in the groove width direction. Width is indicated (see bottom view of FIG. 6(c) and enlarged view of the wrap portion of FIG. 7). For example, as shown in the upper diagram of FIG. 6(c), when the adjacent grooves are completely overlapped in the groove width direction, the lap allowance is 100%, and as shown in FIG. If the grooves are separated from each other in the groove width direction, the lapping allowance is 0%. Linear grooves having a width of 50 μm and a depth (thickness direction) of 15 μm were formed at intervals of 3.0 mm in the rolling direction at an inclination angle of 3.0° with respect to the direction orthogonal to the rolling direction. Then, an additional heat treatment was applied to a range of 10 mm from both ends of the steel sheet in the width center direction by an edge heater to change the inhibitor state and the primary recrystallized grain size of that section. After that, after performing decarburization annealing with atmospheric oxidation degree P(H ₂ O)/P(H ₂ ) = 0.55, soaking temperature: 840 ° C. for 60 seconds, applying an annealing separator by a known method, Finish annealing, tension coating application, etc. were performed to make a product. The evaluation of the tension at break was performed in the same manner as in Experiments 1 and 2. In the structure in the range of 10 mm in the width center direction from each edge heated by the edge heater, the existence frequency of secondary recrystallized grains was 5% and the average grain size was 2 mm.

The evaluation results are shown in FIG. As shown in Fig. 6(a), there is a tendency for the fracture occurrence tension ratio to decrease (thickness to deteriorate) due to the existence of the lap portion (0% lap margin) where the ends of adjacent grooves do not overlap. However, the decrease in fracture occurrence tension ratio was suppressed as the lap allowance increased. From the above, it has been found that the lapping allowance is preferably 5% or more, and more preferably, a continuous groove (lapping allowance of 100%) is formed.

Based on the above results, the present invention will be specifically described. The following description shows a preferred embodiment of the present invention, and the present invention is not limited by the following description.

[Grain-oriented electrical steel sheet]
TECHNICAL FIELD The present invention relates to a grain-oriented electrical steel sheet having grooves formed on its surface. Hereinafter, the chemical composition of the steel material (slab) of the grain-oriented electrical steel sheet of the present invention will be described. The grain-oriented electrical steel sheet is not particularly limited and can be used arbitrarily. However, from the viewpoint of reducing iron loss, it is preferable to have a chemical composition containing Si in the range of 2.0 to 8.0% by mass. In addition, it is more preferable to have a component composition containing 2.5 to 4.5% by mass of Si from the viewpoint of plate threadability.

The chemical composition other than Si suitable for the steel material (slab) used for manufacturing the grain-oriented electrical steel sheet of the present invention is as follows. Of course, the composition is not limited to the following, and the application of the present invention reliably improves the threadability of any electrical steel sheet compared to the steel sheet before application.

C: 0.01 to 0.08% by mass
C is an element necessary for improving the texture during primary recrystallization, and is preferably contained in an amount of 0.01% by mass or more in order to obtain the effect. On the other hand, if the C content exceeds 0.08% by mass, it becomes difficult to reduce the C content by decarburization annealing to 0.0050% by mass or less where magnetic aging does not occur. Therefore, C is preferably in the range of 0.01 to 0.08% by mass. More preferably, it is in the range of 0.03 to 0.07% by mass.

Mn: 0.005 to 1.0% by mass
Mn is an element effective in improving hot workability, but if it is less than 0.005% by mass, the above effect cannot be obtained, while if it exceeds 1.0% by mass, the magnetic flux density decreases become. Therefore, Mn is preferably in the range of 0.005 to 1.0% by mass. More preferably, it is in the range of 0.010 to 0.2% by mass.

In addition, the basic components other than the above components of the steel material used for manufacturing the grain-oriented electrical steel sheet of the present invention differ depending on whether or not an inhibitor is used to cause secondary recrystallization.

When using an inhibitor to cause secondary recrystallization, for example, when using an AlN-based inhibitor, Al and N are respectively Al: 0.01 to 0.065% by mass, N: 0.005 to 0 012% by mass, and when using an MnS/MnSe-based inhibitor, Se and/or S are respectively added to S: 0.005 to 0.03% by mass and Se: 0.005% by mass. It is preferably contained in the range of up to 0.03% by mass.

On the other hand, when an inhibitor is not used to cause secondary recrystallization, Al, N, S, and Se, which are inhibitor-forming components, are Al: 0.0100% by mass or less, N: 0.0050% by mass, respectively. Hereinafter, it is preferable to reduce S to 0.0050% by mass or less and Se to 0.0050% by mass or less.

In addition to the basic components described above, the steel material used for manufacturing the grain-oriented electrical steel sheet of the present invention further contains Ni: 0.03 to 1.50 in addition to the above component composition for the purpose of improving magnetic properties. Mass %, Sn: 0.01 to 1.50 mass %, Sb: 0.005 to 1.50 mass %, Cu: 0.03 to 3.0 mass %, P: 0.03 to 0.50 mass % , Mo: 0.005 to 0.10% by mass, and Cr: 0.03 to 1.50% by mass.

Ni is an element useful for improving the structure of the hot-rolled sheet and improving the magnetic properties. However, if it is less than 0.03% by mass, the above effect is small, while if it exceeds 1.50% by mass, the secondary recrystallization becomes unstable and the magnetic properties deteriorate. Sn, Sb, Cu, P, Mo and Cr are elements useful for improving magnetic properties. , the growth of secondary recrystallized grains is inhibited.

In the steel material used for manufacturing the grain-oriented electrical steel sheet of the present invention, the balance other than the above components is Fe and unavoidable impurities. In addition, since C is decarburized in primary recrystallization annealing, and Al, N, S and Se are purified in finish annealing, these components are unavoidable in steel sheets after finish annealing (grain-oriented electrical steel sheets as products). The content is reduced to the level of a typical impurity.

[heating]
A slab having the above component composition is heated according to a conventional method. The heating temperature is preferably 1150 to 1450°C.

[Hot rolling]
After the heating, hot rolling is performed. After casting, hot rolling may be performed immediately without heating. In the case of thin cast slabs, hot rolling may be performed, or hot rolling may be omitted. When hot rolling is carried out, it is preferable to carry out the rolling temperature of the final pass of rough rolling at 900° C. or higher and the rolling temperature of the final pass of finish rolling at 700° C. or higher.

[Hot-rolled sheet annealing]
After that, the hot-rolled sheet is annealed as necessary. At this time, the hot-rolled sheet annealing temperature is preferably in the range of 800 to 1100° C. in order to develop the Goss texture in the product sheet to a high degree. If the hot-rolled sheet annealing temperature is lower than 800°C, the band structure in the hot rolling remains, making it difficult to achieve a primary recrystallized structure with uniform grains and inhibiting the development of secondary recrystallization. . On the other hand, if the hot-rolled sheet annealing temperature exceeds 1100° C., the crystal grain size after the hot-rolled sheet annealing becomes too coarse, making it extremely difficult to achieve a primary recrystallized structure with uniform grains.

[Cold rolling]
After that, cold rolling is performed once or twice or more with intermediate annealing. The intermediate annealing temperature is preferably 800°C or higher and 1150°C or lower. Also, the intermediate annealing time is preferably about 10 to 100 seconds.

[Decarburization annealing]
After that, decarburization annealing is performed. In the decarburization annealing, the annealing temperature should be 750 to 900° C., the oxidizing atmosphere P(H ₂ O)/P(H ₂ ) should be 0.25 to 0.60, and the annealing time should be about 50 to 300 seconds. is preferred.

[Application of annealing separator]
After that, an annealing separator is applied. The annealing separator preferably contains MgO as a main component and is applied in an amount of about 8 to 15 g/m ² .

[Finish annealing]
After that, finish annealing is performed for the purpose of secondary recrystallization and formation of a forsterite coating. It is preferable that the annealing temperature is 1100° C. or higher and the annealing time is 30 minutes or longer.

[Planarizing annealing and tension coating formation]
Flattening annealing can be performed at the same time as the application and baking of the coating liquid when forming the tension coating, and the shape can be corrected. The flattening annealing is preferably performed at an annealing temperature of 750 to 950° C. for an annealing time of about 10 to 200 seconds.

In addition, in the present invention, a tension coating is formed on the surface of the steel sheet before or after flattening annealing. The tension coating here means a coating (tension coating) that applies tension to the steel sheet in order to reduce iron loss. Tension coatings include insulating tension coatings. Examples of tension coatings include phosphate-based coatings containing silica, and ceramic coatings by physical vapor deposition, chemical vapor deposition, or the like.

[Groove forming step]
A method for forming grooves in the grain-oriented electrical steel sheet according to the present embodiment is not particularly limited, and grooves can be formed by known methods such as a laser method, a press machine method, and an etching method. The groove formation timing is not particularly limited, either a cold-rolled sheet having the final thickness, a primary recrystallization annealing sheet after decarburization annealing, or a secondary recrystallization annealing sheet after finish annealing. . The above three methods are preferable from the viewpoint of process reduction because the final flattening annealing can remove strain due to grooving. However, the effect of the present invention is not impaired even if the product sheet after the tension coating is formed is grooved.

By forming grooves so that ungrooved portions are formed in a range of 1 mm or more in the width center direction from both ends of the steel plate, that is, grooves are not formed in a range of at least 1 mm in the width center direction from both ends of the steel plate. By forming grooves in the grooves, the board threadability is further improved. The non-grooved portion causes deterioration of the magnetic properties, but even if a coil shape countermeasure such as that shown in Patent Document 1 is taken, a shape defect in the range of 15 to 35 mm in the width center direction from the end of the steel plate Occurrence is inevitable. Therefore, the formation of the non-grooved portion according to the present invention does not become a new yield reduction factor. Further, it is preferable to form the groove continuously in the width direction of the steel sheet, ie, to form the groove continuously in the width direction of the steel sheet, because this reduces the ratio of the area where the thickness of the steel sheet is thin, thereby improving the threadability of the steel sheet.

[Steel sheet (coil) edge refinement process]
The most important point of the present invention is that (a) it is effective to increase the mechanical strength of both ends of the steel sheet (coil), and the steel sheet structure is reduced to an average grain size of 5 mm or less in the range of at least 10 mm from both ends of the steel sheet in the width center direction. (b) Even if the crystal grains are refined, if the orientation of each crystal grain is almost the same, the slip system will be the same, so the yield strength will only increase in a certain direction. Therefore, at least the frequency of existence of crystal grains having a deviation angle of 10° or less from the Goss orientation is set to 50% or less.

The method of making the average crystal grain size 5 mm or less and the frequency of existence of crystal grains with a deviation angle of 10° or less from the Goss orientation 50% or less is not particularly limited, but a means that affects the secondary recrystallization behavior is adopted. It is more preferable to promote normal grain growth of primary recrystallized grains. As means for influencing the secondary recrystallized grains, (a) the properties of the subscale are changed by grinding or oxidation by laser irradiation, and the nitriding and inhibitor decomposition behavior during finish annealing are changed only in a specific range at the edge of the steel sheet. (b) B, Ti, Sr, Sn, etc., which are known as elements that affect secondary recrystallization, are newly added only to the target range of the steel plate edge during the annealing separator coating process. . Alternatively, if it has already been added, the amount added is changed. Although the technique for changing the amount added is not particularly limited, it is preferable to once apply an ordinary annealing separator to the entire surface, and then additionally supply the above elements from a nozzle or the like to the target range of the edge of the steel sheet. (c) It is also effective to coarsen the inhibitor properties and the primary recrystallized grain size. It is also effective to provide a temperature gradient in the width direction of the steel sheet by heating from both ends of the steel sheet (coil), thereby bringing the end regions of the steel sheet into an overheated state. It should be noted that the refinement range (region of the fine crystal structure) necessary for improving threadability is sufficient if it is 10 mm in width from the edge of the steel sheet. Form defects of 15 to 35 mm are unavoidable. Therefore, even if the non-grooved portion is formed as described above, it does not become a new cause of lowering the yield. The average crystal grain size is preferably 3 mm or less, more preferably 1 mm or less. The frequency of existence of the crystal grains is preferably 35% or less, more preferably 20% or less. Although the upper limit of the refinement range is not particularly limited, for example, the structure can be refined in the range of 35 mm in the width center direction from both ends of the steel plate, and the structure in the range of 25 mm in the width center direction from both ends of the steel plate can be refined. It can be miniaturized.

EXAMPLES Next, the present invention will be specifically described based on examples. The following examples show preferred examples of the present invention, and the present invention is not limited by the examples. The embodiments of the present invention can be modified as appropriate within the scope of the gist of the present invention, and all of them are included in the technical scope of the present invention.

As the grain-oriented electrical steel sheet, C: 0.02 mass%, Si: 3.25 mass%, Mn: 0.09 mass%, Al: 0.012 mass%, N: 0.008 mass%, S: 0 005% by mass and Se: 0.01% by mass, a steel slab containing an inhibitor-forming component is hot-rolled according to a conventional method, and hot-rolled sheet is annealed at 900° C. for 60 seconds. , and cold rolled into a 0.23 mm cold-rolled sheet. Thereafter, grooves were formed by (a) gravure offset printing + electrolytic etching method, (b) projection roll method, and (c) laser processing method (laser irradiation + electrolytic etching). Tables 1 and 2 show information about the shape of the formed groove, such as groove width, groove depth, presence or absence of a lap portion, and lap allowance.

Next, decarburization annealing is performed at a soaking temperature of 830° C. for 300 seconds, after which an annealing separator containing MgO as a main component is applied, and finish annealing is performed for the purpose of secondary recrystallization, forsterite film formation, and purification. was performed at 1200° C. for 30 hours. After removing the unreacted separating agent, a coating liquid consisting of 60% by mass of colloidal silica and aluminum phosphate was applied and baked at 800° C. to form a tension coating. This coating application process also serves as flattening annealing.

As means for refining the grains in both end regions of the steel plate, (a) additional oxidation treatment by laser irradiation to the target range after decarburization annealing, (b) additional addition of TiO ₂ to the target range after applying the annealing separator, (c) After annealing the hot-rolled sheet, it was realized by subjecting the edge of the steel sheet to additional heat treatment with an edge heater for a soaking time of 20 seconds. The grain refinement range and the frequency of existence of crystal grains with a deviation of 10° or less from the Goss orientation are determined by changing the laser irradiation range/laser irradiation energy, the additional _TiO2 coating range/coating amount, and the additional heating range/heating temperature. It was realized by A sample was taken from the steel sheet after the finish annealing, and the grain refinement (refinement) range (region of the fine crystal structure), the average grain size, and the crystal grain frequency with a deviation angle from the Goss orientation of 10 ° or less were measured in Experiment 1. It was evaluated by the same method as described.

The average crystal grain size (mm) in the structure in the grain refinement range shown in Tables 1 and 2, and the frequency (%) of crystal grains with a deviation angle of 10° or less from the Goss orientation are fine grains from both ends to 10 mm in the width center direction. The average grain size (mm) in the grained structure and the frequency (%) of crystal grains with a deviation angle of 10° or less from the Goss orientation are shown, respectively. In addition, in the structure from one end (end 1) in the width direction of the steel plate to 10 mm in the width center direction and the structure from the other end (end 2) in the width direction of the steel plate to 10 mm in the width center direction, the average grain size (mm), and when the frequency (%) of crystal grains with a deviation angle of 10° or less from the Goss orientation is different, the respective maximum values are shown. In addition, when the refined structure is less than 10 mm in the width center direction from both ends, the average crystal grain size (mm) in the refined structure in the region from both ends to 10 mm in the width center direction, the deviation from the Goss orientation The frequency (%) of crystal grains with an angle of 10° or less is shown. For example, No. in Table 1. The average crystal grain size (mm) in the structure in the grain refinement range of 1-7, and the frequency (%) of crystal grains with a deviation angle of 10° or less from the Goss orientation are the structures from the end 1 to the width center direction 5 mm. , the average grain size (mm) in the structure from the end 2 to 5 mm in the width center direction, and the maximum value of the existence frequency (%) of crystal grains with a deviation angle of 10° or less from the Goss orientation. The average grain size (mm) in the structure in the grain refinement range of 1-9, and the frequency (%) of grains with a deviation angle of 10° or less from the Goss orientation are the structures from the edge 1 to the width center direction 10 mm The average grain size (mm) and the frequency (%) of crystal grains with a deviation angle of 10° or less from the Goss orientation are shown.

Here, the fracture initiation tension (ratio to the fracture initiation tension of a steel sheet with no groove formed) after finish annealing (intermediate process material) and after tension coating formation (product sheet) was investigated. Evaluation results are shown in Tables 1 and 2. The fracture initiation tension ratios shown in Tables 1 and 2 are obtained using the larger value of the fracture initiation tensions after the finish annealing and after the formation of the tension coating. It should be noted that the closer the ratio of tension at breakage to 1, the higher the tension at breakage and the better the plate threadability.

As can be seen from the results shown in Tables 1 and 2, the grain-oriented electrical steel sheets that satisfy the requirements of the present invention are higher than those outside the scope of the present invention, regardless of the method of forming grooves or the method of refining the steel plate end regions. It can be seen that the tensile strength ratio at which breakage occurs is also high, and that it has good threadability.

Claims (3)

A grain-oriented electrical steel sheet in which grooves extending in a direction intersecting the rolling direction and having groove depths in the plate thickness direction are formed on the surface,
The structure is refined in a range of at least 10 mm in the width center direction from both ends in the width direction of the steel plate,
The refined structure from both ends to 10 mm in the width center direction has an average grain size of 5 mm or less, and the frequency of existence of crystal grains having a deviation angle of 10° or less from the Goss orientation is 50% or less. Oriented electrical steel sheet. 2. The grain-oriented electrical steel sheet according to claim 1, wherein no grooves are formed in a range of at least 1 mm from both ends in the width direction of the surface of the steel sheet to the center of the width. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the grooves formed on the surface of the steel sheet continuously extend in a direction crossing the rolling direction.

Images