Manufacturing method of grain-oriented electrical steel sheet

Abstract

The present invention provides a means for suppressing propagation of edge cracking. The present invention provides a method for producing a grain-oriented electromagnetic steel sheet, the method comprising a step in which after hot rolling a silicon-containing steel slab, cold rolling is performed on the hot-rolled silicon-containing steel slab once, or two or more times with process annealing carried out therebetween, the cold-rolled silicon-containing steel slab is subjected to decarburization annealing, and after being applied with an annealing separator, the silicon-containing steel slab is wound into a coil and is subjected to finish annealing, and subsequently to flattening annealing. With respect to this method for producing a grain-oriented electromagnetic steel sheet, when the coil is introduced into a finish annealing furnace, a local strain having an indentation amount of 5 µm to 30 µm from the steel sheet surface is applied to a linear region which continuously or discontinuously extends in a direction that intersects the axial direction of the coil and is apart from an end of the coil in the axial direction, the end being in contact with a coil stage of the finish annealing furnace, by 5 mm to 20 mm in the axial direction, and the finish annealing is subsequently performed, thereby growing crystal grains that have a misorientation angle of 15 degrees or more from a Goss-oriented grain in 50% or more of the entire length of the linear region.

Description

[Technical field]

[0001] The present invention relates to a method for producing grain-oriented electrical steel sheet, and more particularly to a method for producing grain-oriented electrical steel sheet capable of preventing the growth of cracks that occur at the edges of steel sheet during flattening annealing, so-called edge cracks. [Background technology]

[0002] Grain-oriented electrical steel sheets are used as soft magnetic materials, mainly as iron core materials for transformers or rotating equipment, and are required to have high magnetic flux density, low core loss, and low magnetic distortion. In recent years, the energy situation has worsened and capital investment has increased due to aging power transmission facilities, so there is a growing need to supply grain-oriented electrical steel sheets with excellent magnetic properties as economically as possible. To obtain grain-oriented electrical steel sheets with excellent magnetic properties, the crystal grains must have the so-called Goss orientation, i.e., {110} <001> It is necessary to obtain a secondary recrystallized structure that is highly concentrated in the orientation.

[0003] Grain-oriented silicon steel sheet is produced by hot rolling a steel slab adjusted to a specified chemical composition to obtain a hot-rolled sheet, which is then annealed as necessary, and then cold-rolled once or at least twice with intermediate annealing in between. After decarburization annealing, the sheet is coated with an annealing separator, dried, wound into a coil under winding tension, and then finish-annealed in a specified atmosphere.

[0004] In the annealing furnace where the above-mentioned finish annealing is performed, the coil is placed with its winding shaft perpendicular to the surface of the coil support and is exposed to high temperature and long-term treatment. Therefore, defects frequently occur at the end of the coil (hereinafter also referred to as the edge) on the side that contacts the coil support. The most problematic defect that occurs at the coil end is edge cracks caused by deformation of the edge. After the finish annealing, flattening annealing is generally performed to flatten the coil and apply a coating. If there is an edge crack at this time, the tension applied to the steel sheet during flattening annealing increases the possibility that the edge crack will further progress. If the edge crack progresses too much, it will lead to the breakage of the steel sheet, which is a major hindrance to productivity. In addition, if there is an edge crack, it is necessary to remove the edge crack in a slitting process, which significantly reduces the product yield.

[0005] As a method for suppressing deformation of the edge portion that causes edge cracking, a method of imparting linear distortion to the edge portion, as described in Patent Documents 1 and 2, is known. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-204542 [Patent Document 2] JP 2001-323322 A Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there have been cases where edge cracks have been generated due to deformation of the coil ends, particularly in thin grain-oriented silicon steel sheets with a thickness of 0.20 mm or less. The techniques described in Patent Documents 1 and 2 have not necessarily been able to completely prevent such edge cracks, and there has been a demand for an improvement measure to prevent the progression of edge cracks from the coil ends. Therefore, an object of the present invention is to provide a method for preventing the progression of this edge crack. [Means for solving the problem]

[0008] The inventors investigated the progression of the above-mentioned edge cracks and discovered that the progression of edge cracks caused by deformation occurring at the coil edge into the inside of the coil can be suppressed by controlling the crystal grain orientation within a specific range within the linear strain portion imparted near the edge, and thus completed the present invention. That is, the gist of the present invention is as follows.

[0009] 1. A method for producing grain-oriented electrical steel sheet, comprising the steps of hot rolling a silicon-containing steel slab, cold rolling it once or at least twice with intermediate annealing, decarburization annealing, applying an annealing separator thereto, winding the slab into a coil, finish annealing the slab, and then flattening annealing the slab, a method for producing a grain-oriented electrical steel sheet, characterized in that, when the coil is loaded into a finish annealing furnace, a linear region that is spaced 5 mm or more and 20 mm or less in the coil axial direction from an axial end of the coil that contacts a coil support of the finish annealing furnace and extends continuously or discontinuously in a direction transverse to the axial direction is given a local strain with an indentation amount of 5 μm to 30 μm from the steel sheet surface, and then the finish annealing is performed, thereby generating crystal grains having a misorientation angle of 15 degrees or more from the Goss orientation grains in 50% or more of the total length of the linear region.

[0010] 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, further comprising the step of introducing a plurality of linear strain regions by imparting strain to the linear region. 3. The method for producing a grain-oriented electrical steel sheet according to 1 or 2 above, wherein the average heating rate in the finish annealing in a range of 500°C or higher and 800°C or lower is 25°C / h or less. Effect of the Invention

[0011] In the present invention, by introducing linear strain near the edge where edge cracks occur before secondary recrystallization, crystal grains different from the Goss orientation grains are generated in the strain-introduced portion during finish annealing, and the edge cracks can be prevented from progressing through the Goss grains. This makes it possible to reduce edge cut-off in the slitting process for silicon steel sheets that have undergone the final process, and improve product yield. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram showing a state in which a coil is placed in a finish annealing furnace. [Diagram 2] 13 is a diagram showing the suppression of the progression of edge cracks in the strain-introduced portion. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The production method of the present invention will be described in detail below. Grain-oriented silicon steel sheet is generally produced by hot rolling a steel slab adjusted to a predetermined chemical composition to obtain a hot-rolled sheet, which is then annealed as necessary, cold-rolled once or at least twice with intermediate annealing therebetween, and then decarburization annealing, followed by application of an annealing separator and drying. The coil is then wound up under a winding tension, and the coil is then finish-annealed in a predetermined atmosphere.

[0014] In the above-mentioned finish annealing, the present invention is characterized in that, when the coil is loaded into a finish annealing furnace, a local strain is imparted (with a push-in amount from the steel sheet surface of 5 μm to 30 μm) to a linear region that is spaced 5 mm or more and 20 mm or less in the coil axial direction from the axial end of the coil that contacts the coil support of the finish annealing furnace and extends continuously or discontinuously in a direction transverse to the axial direction, and then finish annealing is performed to generate fine crystal grains other than Goss oriented grains in 50% or more of the total length of the linear strain region. Each step will be specifically described below.

[0015] [Linear area] For example, as shown in Fig. 1, a coil pedestal 2 is provided in a finish annealing furnace 1. After a cold-rolled steel strip is wound into a coil, the coil 3 is placed on the coil pedestal 2 and subjected to finish annealing. A local strain is imparted to a linear region L that is placed on the coil pedestal 2 and is spaced from a coil end 30 on the side in contact with the pedestal 2 by 5 mm to 20 mm in the coil axial direction, and that extends continuously or discontinuously in a direction transverse to the axial direction. Specifically, the above-mentioned local strain is imparted to one end of the steel strip in the rolling direction, which is the coil end on the side in contact with the pedestal 2, after cold rolling.

[0016] Here, we will explain the reason why the linear region is spaced from the coil end (the side in contact with the support) by 5 mm to 20 mm in the coil axial direction (hereinafter, also referred to as the separation length).That is, if the separation length is less than 5 mm, the effect of preventing the propagation of edge cracks that occur at the edge is not sufficient, while if the separation length is more than 20 mm, the improvement in industrial yield is not sufficient.

[0017] The linear region is oriented in a direction transverse to the coil axis direction, preferably perpendicular to the coil axis direction. The linear region is preferably provided continuously, but may be discontinuous. In the case of discontinuous regions, it is desirable for the total continuous portion to be 80% or more of the total circumferential length of the coil perpendicular to the coil axis direction in order to obtain the effect of introducing strain described later.

[0018] [Distortion Introduction] Next, the method of applying strain to the linear region described above does not need to be particularly limited as long as strain is introduced, but for example, a method of pressing a roll or needle with a sharp contact surface, particularly a method of introducing strain using an abacus-bead-shaped carbide roll, is advantageously suited. In this case, it is essential to partially press the steel sheet surface to a depth of 5 μm to 30 μm in the thickness direction from the steel sheet surface.

[0019] The reason for setting the pushing amount to 5μm to 30μm is that, if the pushing amount is less than 5μm, the progress of the edge cracks is suppressed. On the other hand, if the pushing depth exceeds 30 μm, deformation in the vicinity of the edge of the steel sheet becomes large, making it difficult to wind the steel sheet.

[0020] [Linear strain area] The steel strip processed as above is coiled, and the coil is placed on a coil support in an annealing furnace so that the linear strain region where strain has been applied to the linear region is at the bottom end of the coil, and then finish annealing is performed. In the secondary recrystallization annealing of this finish annealing, a secondary recrystallized structure with Goss oriented grains is formed. In this case, in the linear strain region, recrystallization due to the introduced strain proceeds prior to secondary recrystallization, so that fine recrystallized grains remain in the linear strain region even after secondary recrystallization occurs around the linear region.

[0021] It is essential that the linear strain region has crystal grains having an orientation difference of 15 degrees or more from the Goss orientation in 50% or more of the total length of the linear region (total circumferential length of the coil). Here, the generation of crystal grains having an orientation difference of 15 degrees or more from the Goss orientation in the linear strain region means obtaining recrystallized grains having an orientation difference of 15 degrees or more from the Goss orientation that have grown 1 / 2 or more in the thickness direction of the steel sheet, and means that such crystal grains are present over 50% or more of the total length of the linear region (circumferential direction of the coil). In addition, in order to promote recrystallization having an orientation difference of 15 degrees or more, it is necessary to set the indentation amount in the linear region to 5 μm to 30 μm. Furthermore, it is preferable that the average heating rate in the region of 500 ° C. or more and 800 ° C. or less in the final annealing is 25 ° C. / h or less. The lower limit of the average heating rate in the temperature region is not particularly limited, but it can be, for example, 3 ° C. / h or more.

[0022] If the fine crystal grains other than the Goss grains are present over 50% or more of the entire length of the linear region, the edge cracks generated at the edge portion can be effectively prevented from progressing further inward than the linear region. That is, as shown in FIG. 2, which is a schematic diagram of the structure around the linear region from the edge portion of the steel sheet after secondary recrystallization annealing, the edge cracks that progress from the edge portion of the steel sheet to the inside of the steel sheet are blocked from progressing by the fine crystal grains of orientation other than the Goss grains generated in the strain introduction portion dispersing the stress of the edge crack progression. The crystal grains having a misorientation angle of 15 degrees or more from the Goss orientation grains are preferably present over 80% or more of the entire length of the linear region, and may be present over 100% of the entire length. It is more preferable that the crystal grains having a misorientation angle of 15 degrees or more and 55 degrees or less from the Goss orientation grains are present over 80% or more of the entire length of the linear region.

[0023] At least one linear strain region is required, and two or more may be provided within a range of 5 to 20 mm from the coil end, for example, 1 to 30. When multiple linear strain regions are provided, the spacing between the linear strain regions is preferably 0.5 mm or more, and the spacing may be, for example, 0.5 to 15 mm.

[0024] The present invention can reliably prevent the growth of edge cracks in grain-oriented electrical steel sheets by introducing strain into the linear regions, and is therefore applicable to any known grain-oriented electrical steel sheets. Therefore, the chemical composition of the grain-oriented electrical steel sheet is not particularly limited, but the chemical composition shown below can be adopted. C: 0.01 to 0.1 mass%, Si: 2.0-5.5 mass% and Mn: 0.02-2.5 mass% The basic composition is a composition containing the above, with the balance being iron and unavoidable impurities. The reasons for limiting the content of each component are as follows.

[0025] C: 0.01 to 0.1 mass% If the C content is less than 0.01%, the effect of improving the structure due to C may not be sufficient, whereas if the C content exceeds 0.1%, it may become difficult to remove C by decarburization annealing.

[0026] Si: 2.0-5.5 mass% Silicon is an element that increases the resistivity, which is the main function of electrical steel sheet. If the silicon content is less than 2.0%, the increase in resistivity is insufficient, whereas if the silicon content exceeds 5.5%, the cold rolling properties may deteriorate, making manufacturing difficult.

[0027] Mn: 0.02-2.5 mass% Mn has the effect of improving hot rolling properties, and if the content is less than 0.02%, the improvement effect is insufficient, while if the content exceeds 2.5%, the saturation magnetic flux density of the steel decreases, which may be disadvantageous in terms of practical application to transformers.

[0028] Furthermore, in addition to the above basic components, when an inhibitor is used, the material may contain Al: 0.01 to 0.04 mass%, N: 0.004 to 0.01 mass%, and, if necessary, one or more of S and Se in an amount of 0.005 mass% or more and 0.030 mass% or less. On the other hand, when no inhibitor is used, the alloy may contain Al: 0.003 to 0.01 mass%, N: 0.002 to 0.006 mass%, and S and Se each less than 0.005%.

[0029] Furthermore, in addition to the above basic components, The alloy may contain one or more selected from the group consisting of Ni: 0.01 to 0.4 mass%, Cr: 0.01 to 0.25 mass%, Cu: 0.01 to 0.30 mass%, P: 0.005 to 0.10 mass%, Sb: 0.005 to 0.10 mass%, Sn: 0.005 to 0.10 mass%, Bi: 0.005 to 0.10 mass%, Mo: 0.005 to 0.10 mass%, B: 0.0002 to 0.0025 mass%, Te: 0.0005 to 0.01 mass%, Nb: 0.001 to 0.01 mass%, V: 0.001 to 0.01 mass%, and Ta: 0.001 to 0.01 mass%. EXAMPLES

[0030] A steel slab containing C: 0.06 mass%, Si: 3.2 mass%, Mn: 0.05 mass%, Al: 0.005 mass%, and N: 0.004 mass% was heated to 1200°C, and then hot-rolled to a thickness of 2.5 mm. The slab was then annealed at 1000°C for 60 seconds, and cold-rolled once to a thickness of 0.19 mm. The cold-rolled sheet was decarburized in wet hydrogen at 820°C for 120 seconds, and wound into a coil. A linear strain was then imparted under various conditions shown in Table 1 to a linear region extending in a direction transverse to the axial direction at a position 8 mm from the edge of the decarburized annealed coil in the coil axial direction, to form a linear strain region. Next, the temperature rise conditions were changed in various ways, and the final annealing was performed. The final annealing was performed at a maximum temperature of 1180°C for 5 hours. After the finish annealing, the wire was subjected to flattening annealing at 800°C for 60 seconds to obtain a product coil.

[0031] The number of edge cracks exceeding 8 mm deep at the coil edge per 100 m and the maximum depth of the edge cracks were evaluated for the product coils thus obtained. Furthermore, the length ratio of crystal grains having a misorientation angle of 15 degrees or more from the Goss orientation grains in the linear strain region was investigated. That is, the length ratio of crystal grains was obtained by linearly analyzing the crystal orientation using an Electron Back-Scattering Pattern (EBSP) device in the center of the linear strain region toward the longitudinal direction of the coil. The results are shown in Table 1.

[0032] [Table 1] [Industrial Applicability]

[0033] According to the manufacturing method of the grain-oriented electrical steel sheet of the present invention, by introducing linear strain near the edge where the edge crack occurs before the secondary recrystallization, crystal grains different from the Goss orientation grains are generated in the strain-introduced portion during the final annealing, and the edge crack can be prevented from progressing inside the Goss grain. This makes it possible to reduce edge cutting in the slitting process for silicon steel sheet that has undergone the final process, improve product yield, and is highly useful in industry. [Explanation of symbols]

[0034] 1 Finish annealing furnace 2 Coil Support 3 Coil 30 Coil end L linear area

Claims

1. A method for producing a grain-oriented electrical steel sheet having a thickness of 0.20 mm or less, comprising the steps of hot rolling a silicon-containing steel slab, cold rolling the slab once or at least twice with intermediate annealing therebetween, decarburization annealing, applying an annealing separator thereto, winding the slab into a coil, finish annealing the slab, and then flattening annealing the slab, a linear region that is spaced from an axial end of the coil in contact with a coil support of the finish annealing furnace by 5 mm to 20 mm in the coil axial direction and extends continuously or discontinuously in a direction transverse to the axial direction when the coil is loaded into a finish annealing furnace, the linear region being indented by an amount of 5 μm to 30 μm from the steel sheet surface, and the finish annealing is then performed, thereby generating crystal grains having a misorientation angle of 15 degrees or more from the Goss orientation grains in 50% or more of the total length of the linear region.

2. The method for producing a grain-oriented electrical steel sheet according to claim 1 , wherein a plurality of linear strain regions are introduced by imparting strain to the linear region.

3. 3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein an average heating rate in the final annealing in a range of 500° C. or more and 800° C. or less is 25° C. / h or less.

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