Production method of grain-oriented electrical steel sheet

Abstract

To provide a production method of a grain-oriented electrical steel sheet in which the generation of edge cracks is reduced after finish annealing.SOLUTION: A production method of a grain-oriented electrical steel sheet includes a hot rolling step of heating and hot rolling an electrical steel material to obtain a hot-rolled steel sheet, a cold rolling step of subjecting the hot-rolled steel sheet to one cold rolling or two or more cold rolling with intermediate annealing therebetween to obtain a cold-rolled steel sheet, a primary recrystallization annealing step of subjecting the cold-rolled steel sheet to primary recrystallization annealing also serving as decarburization to obtain a primary recrystallization annealed sheet, and a finish annealing step of applying an annealing separator to the primary recrystallization annealed sheet to obtain a wound coil obtained by winding the primary recrystallization annealed sheet in a coil shape and subjecting the wound coil to finish annealing. Before the finish annealing step, the end surface of the wound coil, which becomes a mounting bottom surface of the wound coil during the finish annealing, is ground in an annular shape.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a grain-oriented electrical steel sheet that reduces the occurrence of edge cracks after finish annealing. [Background technology]

[0002] Grain-oriented electrical steel sheets are soft magnetic materials that are mainly used as iron core materials for transformers and generators. The easy axis of magnetization of iron <001> It has a crystal structure with a highly aligned orientation in the rolling direction of the steel plate. This texture is formed by the final annealing in the manufacturing process. , the so-called Goss orientation. <001> Preferential orientation of grains It is formed through secondary recrystallization, which causes giant growth.

[0003] The above-mentioned final annealing is performed by holding the temperature at 800°C or higher for a long time to preferentially grow the Goss-oriented grains. This generally consists of a secondary recrystallization annealing to induce secondary recrystallization, and a purification annealing to remove the inhibitor components used to induce secondary recrystallization by holding the steel at a temperature of around 1200°C for several hours. As mentioned above, the finish annealing of grain-oriented electrical steel sheets involves heat treatment at high temperatures for a long period of time. This is done by "batch annealing," in which the wire is annealed on a coil-by-coil basis. are.

[0004] The finish annealing of grain-oriented electrical steel sheets is performed with the coil winding axis in a vertical direction (up-end) as shown in Figure 1. The steel sheet coil 3 (hereinafter simply referred to as "coil") annealed in this manner is placed so that the coil end surface 6 contacts the base plate 4 and is then annealed. The upper surface of the installed coil is the coil end surface 5 .

[0005] However, after the finish annealing, cracks occur on the edges of the coil, which can cause breakage of the sheet or defects in shape when unwinding in the next process, resulting in a decrease in yield.

[0006] In order to suppress such coil defects after finish annealing, various methods have been proposed. For example, Patent Document 1 discloses a method of performing annealing with a base plate having a surface roughness of 5 mm or less and a spacer having a surface hardness of HV120 or more. Specifically, grain-oriented silicon steel sheet is cold-rolled, then subjected to decarburization annealing, coated with MgO as an annealing separator, and wound into a coil. The coil is then placed perpendicular to the coil winding axis direction and subjected to finish annealing. At this time, the surface roughness of the base plate on which the coil is placed is set to 5 mm or less, and the surface hardness of the spacer between the coil and base plate is set to HV120 or more, to prevent edge distortion from occurring at the bottom end surface of the coil.

[0007] Furthermore, Patent Document 2 discloses a method of grinding after trimming as a method of reducing edge cracks that occur during rolling by grinding. Specifically, the purpose is to increase the fracture surface ratio by side trimming a plastically worked hot-rolled steel strip and prevent the occurrence of saw edges in the subsequent cold rolling process. The saw edge prevention method is characterized by work-hardening the hot-rolled steel strip by plastic working, and then side-trimming it prior to the next process of cold rolling.

[0008] Furthermore, Patent Document 3 discloses a technique for partially covering the upper surface of a steel sheet coil with a heat insulating material when batch annealing is performed by covering a steel sheet coil placed up-end on a coil support with an inner cover.We propose a batch annealing method for steel sheet coils that can uniform the temperature distribution within the coil without significantly reducing production efficiency or energy efficiency and effectively prevent shape defects that occur during finish annealing. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 4-272137 [Patent Document 2] Japanese Patent Application Publication No. 9-141308 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-44322 Summary of the Invention [Problem to be solved by the invention]

[0010] However, although the technology of Patent Document 1 reduces the occurrence of edge distortion, it cannot eliminate the difference in expansion and contraction during the thermal cycle of heating, soaking, and cooling, which is the cause of coil buckling, and further improvement is required.

[0011] Furthermore, the technology of Patent Document 2 is a method in which trimming and grinding are performed after rolling, which has the problem of reducing the yield of steel sheets due to trimming.

[0012] Furthermore, the technology of Patent Document 3 covers the upper surface (end surface) and / or outer surface of the coil with insulating material to prevent uneven coil temperature caused by rapid heating, but does not disclose any technology to reduce cracks on the lower surface (end surface) of the coil, which forms the bottom surface on which the coil is placed.

[0013] Therefore, in order to solve the above-mentioned problems of the prior art, an object of the present invention is to propose a method for manufacturing grain-oriented electrical steel sheet that reduces the occurrence of edge cracks after finish annealing. [Means for solving the problem]

[0014] The inventors have conducted extensive research into a method for producing grain-oriented electrical steel sheets that can suppress edge cracks during finish annealing. As a result, it was found that the area where edge cracks frequently occurred after final annealing was on the bottom surface (coil end surface) of the coil during final annealing, and at a position approximately 35% of the total coil thickness based on the innermost circumference of the coil. Furthermore, it was discovered that the side surfaces (coil end surfaces) of the wound coil before finish annealing, which will become the bottom surfaces on which the coil is placed during finish annealing, are not uniform, and that there are areas at the coil ends where stress is locally concentrated.

[0015] The method for producing a grain-oriented electrical steel sheet according to the present invention, which advantageously solves the above problems, is configured as follows. [1] A method for manufacturing a grain-oriented electrical steel sheet, comprising: a hot rolling process in which an electrical steel material is heated and hot-rolled to form a hot-rolled steel sheet; a cold rolling process in which the hot-rolled steel sheet is subjected to one cold rolling or two or more cold rolling processes with intermediate annealing in between to form a cold-rolled steel sheet; a primary recrystallization annealing process in which the cold-rolled steel sheet is subjected to primary recrystallization annealing, which also serves as decarburization, to form a primary recrystallization annealed sheet; and a finish annealing process in which an annealing separator is applied to the primary recrystallization annealed sheet, the primary recrystallization annealed sheet is wound into a coil, and the wound coil is subjected to finish annealing. This is a method for producing a grain-oriented electrical steel sheet, characterized in that the end surface of the wound coil, which will become the bottom surface on which the wound coil is placed during annealing, is ground into an annular shape. [2] In the above [1], the grinding of the end surface of the wound coil is performed in a circular region of the end surface of the coil, which occupies 10% to 90% of the total thickness of the coil, including a position that is 35% of the total thickness of the coil based on the innermost circumference of the coil, in the coil thickness direction of the end surface of the coil. This is a manufacturing method of grain-oriented electrical steel sheet. [3] In the method for producing a grain-oriented electrical steel sheet according to the above [1] or [2], the grinding of the end surface of the wound coil is performed by a grinding amount of 1.0 mm or less in the coil width direction. [Effects of the Invention]

[0016] According to the present invention, before the finish annealing step, predetermined regions of the end faces of the wound coil, which will become the bottom faces on which the wound coil is placed during the finish annealing, are ground, thereby making it possible to suppress edge cracking. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram illustrating a batch annealing method for a steel sheet coil. [Figure 2]FIG. 2 is a diagram illustrating a grinding area on the end surface of a steel sheet coil. DETAILED DESCRIPTION OF THE INVENTION

[0018] A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described.

[0019] The method for producing a grain-oriented electrical steel sheet according to this embodiment includes a hot rolling step in which a raw electrical steel material is heated and hot-rolled to produce a hot-rolled steel sheet, and a cold rolling step in which the hot-rolled steel sheet is cold-rolled once or twice or more times with intermediate annealing in between to produce a cold-rolled steel sheet. The method then includes a primary recrystallization annealing step in which the cold-rolled steel sheet is subjected to primary recrystallization annealing, which also serves as decarburization, to produce a primarily recrystallization annealed steel sheet, and a finish annealing step in which an annealing separator is applied to the primarily recrystallization annealed steel sheet to produce a wound coil, which is then wound into a coil, and the wound coil is then finish annealed. In this method for producing a grain-oriented electrical steel sheet, prior to the finish annealing step, grinding is performed on the end surfaces of the wound coil, which will serve as the bottom surface on which the wound coil will be placed during the finish annealing, to prevent edge cracks.

[0020] <Electromagnetic steel material> The steel material to be used in the steel sheet production of this embodiment is not particularly limited as long as it has the chemical composition of a grain-oriented electrical steel sheet and is produced by a conventionally known method. Examples of methods for producing the steel material include a method in which molten steel obtained from a converter, electric furnace, or the like is melted by a commonly known refining process in which molten steel is subjected to secondary refining such as vacuum degassing to obtain a desired chemical composition, and then the steel is produced by a continuous casting method or an ingot casting-blooming rolling method.

[0021] <Hot rolling process> The steel material (slab) is subjected to hot rolling either without reheating or after reheating. When the steel material is reheated, the reheating temperature is preferably 1000°C or higher. If the temperature is lower than 1000°C, the rolling load becomes too high, making hot rolling difficult. The heated steel material is hot-rolled to obtain a hot-rolled sheet. There are no particular restrictions on the hot-rolling conditions according to this embodiment, and the hot-rolling may be performed by a commonly known method. Generally, the steel material is rough-rolled to form a sheet bar, and then finish-rolled and coiled to form a hot-rolled coil (hot-rolled steel sheet). For example, the conditions for the hot-rolling process according to this embodiment are preferably a finish-rolling temperature of 700°C or higher and 1100°C or lower, and a coiling temperature of 350°C or higher and 800°C or lower.

[0022] If necessary, the steel sheet obtained by the hot rolling may be subjected to a hot-rolled sheet annealing treatment in which annealing is performed. The hot-rolled sheet or hot-rolled annealed sheet obtained by the above hot rolling may further be subjected to a descaling treatment such as pickling, if necessary.

[0023] <Cold rolling process> Next, the hot-rolled sheet after hot rolling is annealed as necessary, and then cold-rolled once or twice or more times with intermediate annealing therebetween to obtain a final cold-rolled sheet. This cold rolling may be performed at room temperature, or may be warm rolling in which the steel sheet temperature is raised to a temperature higher than room temperature, for example, about 250°C.

[0024] <Primary recrystallization annealing process> Furthermore, the final cold-rolled sheet is subjected to primary recrystallization annealing. The purpose of this primary recrystallization annealing is to primary recrystallize the cold-rolled sheet having a rolled texture and adjust the primary recrystallized grain size to an optimal size for secondary recrystallization. Furthermore, by using a wet hydrogen-nitrogen or wet hydrogen-argon atmosphere as the annealing atmosphere, the carbon contained in the steel is decarburized and, at the same time, an oxide film is formed on the surface by the annealing atmosphere. For this purpose, the annealing temperature (holding temperature) of the primary recrystallization annealing is preferably in the range of approximately 800°C or higher but lower than 950°C. The oxide film formed during primary recrystallization annealing reacts with MgO applied to the steel sheet during the subsequent secondary recrystallization annealing to form a forsterite film. Therefore, the morphology of the oxide film after primary recrystallization annealing has a significant impact on the formation of surface films in subsequent processes.

[0025] <Finishing annealing process> Next, an annealing separator is applied to the surface of the steel sheet, and the steel sheet is wound into a coil. After that, the steel sheet coil 3 is placed so that the end surface 6 of the wound coil is in contact with the base plate 4 as shown in FIG. 1, and finish annealing is performed.

[0026] Before the finish annealing process, the winding coil end surface 6, which will be the bottom surface on which the winding steel sheet coil 3 is placed during finish annealing, is ground. Figure 2 shows the grinding method for the winding coil end surface 6. The shaded area is the grinding area 7. Grinding the winding coil end surface 6 increases the area on which the steel sheet coil 3 is placed, and distributes the stress on the coil end surface relative to the base plate, reducing the occurrence of edge cracks due to stress concentration. The wound coil end surface 6 is preferably ground in the coil annular region 7 of the coil end surface, which occupies 10% to 90% of the total coil thickness in the coil thickness direction. In order to distribute stress on the coil end surface by placing the coil, the coil annular region 7 of the coil end surface, which occupies 10% to 90% of the total coil thickness, is ground. Furthermore, when grinding the end surface 6 of the wound coil, it is preferable to set the grinding amount to 1.0 mm or less in the coil width direction. [Example]

[0027] The present embodiment will be specifically described below using examples, but the present invention is not limited to these examples.

[0028] A steel material containing 3% by mass of silicon was hot rolled, and then the hot-rolled steel sheet was cold rolled once to a thickness of 0.23 mm, decarburization annealed in a wet hydrogen atmosphere, MgO was applied to the surface as an annealing separator, the steel was wound into a coil, and the end faces of the wound coil were ground under the conditions shown in Table 1, followed by finish annealing. At the same time, a coil without grinding was also produced.

[0029] These coils were then subjected to flattening annealing and the occurrence of edge cracks was investigated. The results are shown in Table 1. It can be seen that the coil of the present invention had an improved number of edge cracks per 1000 m.

[0030] [Table 1] [Industrial Applicability]

[0031] The technology of the present invention can be applied not only to electrical steel sheets but also to all metal strip manufacturing methods that involve batch annealing processes for wound coils. [Explanation of symbols]

[0032] D: Coil winding direction 1: Inner cover 3: Steel coil 4: Base plate (coil support) 5, 6: End face of winding coil 7: Grinding area (coil ring area)

Claims

1. A method for manufacturing a grain-oriented electrical steel sheet, a hot rolling process in which the electromagnetic steel material is heated and hot rolled to form a hot-rolled steel sheet; a cold rolling step of subjecting the hot-rolled steel sheet to one cold rolling or two or more cold rolling steps with intermediate annealing therebetween to obtain a cold-rolled steel sheet; a primary recrystallization annealing step in which the cold-rolled steel sheet is subjected to primary recrystallization annealing, which also serves as decarburization, to obtain a primary recrystallization annealed sheet; a finish annealing step of applying an annealing separator to the primarily recrystallized annealed sheet, winding the primarily recrystallized annealed sheet into a coil, and then subjecting the wound coil to finish annealing; Including, a step of grinding the end surface of the wound coil, which will be the bottom surface on which the wound coil will be placed during the finish annealing, into an annular shape before the finish annealing step;

2. 2. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the grinding of the end surface of the wound coil is performed on an annular region of the end surface of the coil, the region occupying 10% to 90% of the total thickness of the coil in the coil thickness direction, including a position that is 35% of the total thickness of the coil based on the innermost periphery of the coil.

3. 3. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the grinding amount of the end surface of the wound coil is 1.0 mm or less in the coil width direction.

Images