Cold rolling method and production method for grain-oriented electromagnetic steel sheet, and cold rolling equipment line

Abstract

Provided is a technique enabling stable and high output production of a grain-oriented electromagnetic steel sheet excellent in magnetic characteristics when performing cold rolling using a single-stand rolling mill. In this cold rolling method for a grain-oriented electromagnetic steel sheet, when a cold rolled sheet having a final sheet thickness is obtained by cold rolling in which the total rolling reduction is 80% or more, the cold rolling is divided into preceding cold rolling and subsequent cold rolling. In the preceding cold rolling, rolling is performed to an intermediate plate thickness by using a tandem rolling mill. In the subsequent cold rolling, rolling is performed from the intermediate plate thickness to the final plate thickness in 1-3 passes of rolling by using a single-stand rolling mill having a work roll diameter of which the ratio is 0.60-1.35 with respect to the work roll diameter of the final stand of the tandem rolling mill used for the preceding cold rolling, whereby the difference between the maximum value and the minimum value of the magnetic flux density B8 in the plate width direction of the product plate is 0.005T or less. Also provided are a method for manufacturing a grain-oriented electromagnetic steel sheet using the cold rolling method, and a cold rolling equipment line used for the cold rolling.

Description

Cold rolling method and manufacturing method for grain-oriented electrical steel sheet, and cold rolling equipment train

[0001] The present invention relates to a method for cold rolling grain-oriented electrical steel sheets, a method for manufacturing grain-oriented electrical steel sheets with excellent magnetic properties using the cold rolling, and a cold rolling facility suitable for the cold rolling method. In this specification, the term "x to y" representing a range of numerical values ​​means not less than x and not more than y, and includes the boundary value.

[0002] Grain-oriented electrical steel sheets are steel sheets with excellent magnetic properties that have a crystalline structure in which the <001> orientation, which is the easy axis of magnetization of iron, is highly concentrated in the rolling direction of the steel sheet, i.e., the Goss orientation. Such grain-oriented electrical steel sheets are generally manufactured using steel materials containing approximately 4.5 mass% or less of Si. Grain-oriented electrical steel sheets often further contain inhibitors that cause secondary recrystallization, such as components that form MnS, MnSe, and AlN.

[0003] On the other hand, Patent Document 1 proposes a technique for inducing secondary recrystallization without the inclusion of inhibitor-forming components, known as the inhibitor-less process. This inhibitor-less process has the advantage of enabling low-cost production of grain-oriented electrical steel sheets because it does not require high-temperature slab heating, which is required when using inhibitors. However, this technique involves using highly purified steel material to induce secondary recrystallization through texture control, i.e., texture control (hereinafter also referred to as "texture inhibition"). Therefore, delicate control is required to engineer the texture.

[0004] In the production of grain-oriented electrical steel sheets, the cold rolling conditions are important from the viewpoint of appropriately controlling the texture. In particular, in the production of grain-oriented electrical steel sheets using steel materials that do not contain inhibitor-forming elements, the quality of the texture is extremely important because it significantly affects the quality of the magnetic properties.

[0005] As a technique for forming a good texture, for example, Patent Document 2 proposes a method of heat treating (aging) a steel sheet at a low temperature during cold rolling. Patent Document 3 also proposes a technique in which the cooling rate during hot-rolled sheet annealing or annealing before finish cold rolling (final cold rolling) is set to 30°C / s or more, and interpass aging is performed at a sheet temperature of 150 to 300°C for 2 minutes or more at least twice during finish cold rolling. Patent Document 4 also proposes a technique in which warm rolling is performed, in which the steel sheet temperature is increased during rolling, and dislocations introduced during rolling are immediately fixed with C (carbon) or N (nitrogen), utilizing the dynamic aging effect.

[0006] These techniques involve the diffusion of solute elements, C (carbon) and N (nitrogen), at low temperatures to fix dislocations introduced by rolling. By preventing dislocation movement in this way, shear deformation occurs during subsequent cold rolling, improving the rolling texture. The application of this technique can reduce the (111) fiber structure known as gamma fiber in the primary recrystallization texture after cold rolling. This effectively increases the frequency of the {110}<001>, or Goss orientation, which is advantageous for magnetic properties.

[0007] In addition, rolling mills used for the above-mentioned cold rolling generally include a single-stand reversing rolling mill (see, for example, Patent Document 5) and a tandem rolling mill consisting of multiple stands (see, for example, Patent Document 6). However, from the viewpoint of applying the above-mentioned technology, it is considered more advantageous to use a reversing rolling mill that can coil a rolled steel sheet at a high temperature and then hold the coil for a long time to perform so-called "aging treatment".

[0008] JP 2000-129356, JP 50-016610, JP 08-253816, JP 01-215925, JP 54-013846, JP 54-029182

[0009] As mentioned above, the prior art disclosed in Patent Documents 2 to 4 all utilize the effect of aging treatment, which promotes the diffusion of C and N in the steel by maintaining the steel sheet temperature at a high temperature during or after rolling, thereby fixing dislocations introduced during rolling. Therefore, when a tandem rolling mill is used, various studies have been conducted on the assumption that an extremely short aging treatment time is required between stands. Furthermore, when a reversing rolling mill is used, various studies have been conducted on the assumption that a relatively long aging treatment time is required after coiling. However, such aging treatment has a problem in that it is extremely limited by the equipment. For example, if an attempt is made to ensure a 1-hour aging treatment time, rolling must be interrupted for 1 hour during the reverse rolling, which significantly impairs productivity.

[0010] The present invention has been made in consideration of the above-mentioned problems of the conventional techniques, and its object is to provide a technique that enables stable and productive production of grain-oriented electrical steel sheets with excellent magnetic properties when cold rolling is performed using a single-stand rolling mill. Specifically, the present invention proposes a method for cold rolling grain-oriented electrical steel sheets and a method for producing grain-oriented electrical steel sheets using this cold rolling method, and also provides a cold rolling line suitable for these methods.

[0011] To solve the above problems, the inventors have conducted extensive research focusing on the conditions for cold rolling a steel sheet after hot rolling. As a result, they have found that by dividing the cold rolling into a front stage and a rear stage, performing cold rolling using a tandem rolling mill in the front stage and a single-stand rolling mill in the rear stage, and controlling the reduction ratio and the work roll diameter ratio in the front and rear cold rolling stages within appropriate ranges, it is possible to productively and stably produce a grain-oriented electrical steel sheet that has excellent magnetic properties and small variations in the sheet width direction, which has led to the development of the present invention.

[0012] The present invention based on the above findings provides: (A) a method for cold rolling grain-oriented electrical steel sheet to produce a cold-rolled sheet of a final thickness by cold rolling at a total reduction of 80% or more, the cold rolling being divided into a front-stage cold rolling and a rear-stage cold rolling, and optionally intermediate annealing being performed between the front-stage cold rolling and the rear-stage cold rolling, and when the intermediate annealing is performed, the annealing temperature is set to 700°C or less, and in the front-stage cold rolling, a tandem rolling mill is used to roll the cold rolled sheet to a final thickness. The thickness is rolled to an intermediate thickness with a reduction ratio of 0.50 to 0.95 relative to the total reduction ratio in rolling, and in the latter stage of cold rolling, a single-stand rolling mill is used to roll from the intermediate thickness to the final thickness in 1 to 3 passes, and the ratio of the work roll diameter of the single-stand rolling mill to the work roll diameter of the final stand of the tandem rolling mill is set to a range of 0.60 to 1.35, thereby reducing the magnetic flux density B in the width direction of the product plate. ８ The present invention proposes a method for cold rolling grain-oriented electrical steel sheets, characterized in that the difference between the maximum and minimum values ​​of is 0.005T or less.

[0013] The cold rolling method for grain-oriented electrical steel sheet according to the present invention preferably comprises the following means: (a) winding the steel sheet after the first stage of cold rolling into a coil at a temperature of 80°C or higher, and then performing the second stage of cold rolling after at least 30 minutes have passed; and (c) performing the second stage of cold rolling using one single-stand rolling mill with different work roll diameters, or using multiple single-stand rolling mills with different work roll diameters.

[0014] The present invention also provides a composition containing 0.01 to 0.10 mass% of C, 2.0 to 4.5 mass% of Si, and 0.01 to 0.5 mass% of Mn, and further including, as inhibitor-forming components, Group A: 0.010 to 0.05 mass% of sol. Al and 0.004 to 0.012 mass% of N, Group B: 0.01 to 0.05 mass% in total of one or more selected from S and Se, and Group C: sol. Contains at least one component selected from Al: 0.010 to 0.05 mass%, N: 0.004 to 0.012 mass%, and at least one selected from S and Se: 0.01 to 0.05 mass% in total, and optionally contains Ni: 0.005 to 1.50 mass%, Cr: 0.005 to 0.3 mass%, Cu: 0.005 to 0.3 mass%, Sn: 0.005 to 0.3 mass%, Sb: 0.005 to 0.3 mass%, Mo: 0.005 to 0.3 mass%, Te: 0.005 to 0.3 mass%, Bi: 0.005 to 0.3 mass%. % as a whole, and at least one component selected from P: 0.005 to 0.3 mass%, with the balance being Fe and unavoidable impurities, is hot-rolled to form a hot-rolled sheet, and the hot-rolled sheet is cold-rolled at a total rolling reduction of 80% or more to form a cold-rolled sheet of a final thickness, and the cold-rolled sheet is subjected to primary recrystallization annealing that also serves as decarburization annealing, an annealing separator is applied to the steel sheet surface, and then secondary recrystallization is performed, followed by finish annealing for purification. In the cold rolling, by applying any of the above cold rolling methods, it is possible to obtain a magnetic flux density B ８ The present invention proposes a method for producing a grain-oriented electrical steel sheet characterized in that the difference between the maximum and minimum values ​​of is 0.005T or less.

[0015] The present invention also provides a steel sheet containing 0.01 to 0.10 mass% of C, 2.0 to 4.5 mass% of Si, 0.01 to 0.5 mass% of Mn, and sol. and optionally containing Ni: 0.005 to 1.50 mass%, Cr: 0.005 to 0.3 mass%, Cu: 0.005 to 0.3 mass%, Sn: 0.005 to 0.3 mass%, Sb: 0.005 to 0.3 mass%, Mo: 0.005 to 0.3 mass%, Te: 0.005 to 0.3 mass%, Bi: 0.005 to 0.3 mass%, and P: 0.005 to 0.3 mass%. A method for producing a grain-oriented electrical steel sheet, comprising: hot rolling a steel slab having a composition containing at least one element selected from the group consisting of 0.05% by mass and 0.3% by mass of iron, with the balance being Fe and unavoidable impurities; cold rolling the hot rolled sheet at a total rolling reduction of 80% or more to produce a cold rolled sheet of a final thickness; applying a primary recrystallization annealing that also serves as decarburization annealing to the cold rolled sheet; applying an annealing separator to the surface of the steel sheet; subsequently, subjecting the cold rolled sheet to secondary recrystallization; and then performing finish annealing for purification; wherein, in the cold rolling, by applying any of the above cold rolling methods, a magnetic flux density B in the sheet width direction is reduced. ８ The present invention proposes a method for producing a grain-oriented electrical steel sheet characterized in that the difference between the maximum and minimum values ​​of is 0.005T or less.

[0016] The present invention also relates to a cold rolling equipment train consisting of a front-stage cold rolling mill and a rear-stage cold rolling mill used in the cold rolling method of (a) or (b) above, characterized in that the front-stage cold rolling mill is a tandem rolling mill, the rear-stage cold rolling mill is a single-stand rolling mill, and the ratio of the work roll diameter of the rear-stage cold rolling mill to the work roll diameter of a final stand of the tandem rolling mill is within the range of 0.60 to 1.35.

[0017] The cold rolling equipment train according to the present invention is a cold rolling equipment train consisting of a front-stage cold rolling mill and a rear-stage cold rolling mill used in the cold rolling method (c), wherein the front-stage cold rolling mill is a tandem rolling mill and the rear-stage cold rolling mill is a single-stand rolling mill, and a more preferable solution is that the rear-stage cold rolling mill consists of one single-stand rolling mill with a changeable work roll diameter or a plurality of single-stand rolling mills with different work roll diameters.

[0018] Furthermore, a more preferable solution for the cold rolling equipment train according to the present invention is one having at least one of the following configurations: (1) a function in which the tandem rolling mill controls the coil winding temperature by adjusting at least one of the temperature and flow rate of coolant sprayed onto at least one of the steel sheet surface and the work roll surface at the delivery side of the final stand; and (2) a heat retention device is disposed between the tandem rolling mill and a subsequent rolling mill, for maintaining the temperature of the steel sheet after cold rolling in the previous stage at 50°C or higher.

[0019] According to the present invention, it is possible to stably produce grain-oriented electrical steel sheets that not only have excellent magnetic properties but also have small variations in magnetic properties in the sheet width direction.

[0020] The work roll diameter ratio (WR diameter ratio) of the front-stage cold rolling mill and the rear-stage cold rolling mill is the difference ΔB between the maximum and minimum values ​​of magnetic flux density. ８ 1 is a graph showing the influence of the work roll diameter ratio (WR diameter ratio) between the front-stage cold rolling mill and the rear-stage cold rolling mill on the magnetic flux density and its variation.

[0021] First, the inventors conducted the following experiment to manufacture grain-oriented electrical steel sheets using steel materials that do not contain inhibitor-forming elements, for which texture control is particularly important, and investigated the conditions necessary to improve the magnetic properties.

[0022] (Experiment 1) A steel material (slab) containing 0.050 mass% C, 3.3 mass% Si, and 0.04 mass% Mn, and further containing less than 0.0050 mass% S, Se, and O, less than 0.0025 mass% N, with the balance being Fe and unavoidable impurities, was produced. This steel slab, which did not contain inhibitor-forming components, was heated to a temperature of 1100 ° C and hot-rolled to a hot-rolled sheet having a thickness of 3.0 mm. The hot-rolled sheet was then subjected to hot-rolled sheet annealing at 1000 ° C for 70 seconds to produce a hot-rolled annealed sheet. Next, the hot-rolled annealed sheet was subjected to a first stage of cold rolling using a five-stand tandem rolling mill with a work roll diameter of 250 mm in the final stand, in which the steel sheet temperature between the third stand and subsequent stands was 120°C or higher to roll it to the intermediate thickness shown in Table 1, and then wound into a coil. At this time, the sheet temperature (coiling temperature) during winding onto the coil was measured. Next, the steel sheet with the intermediate thickness was transported to a single-stand rolling mill with a work roll diameter of 200 mm and cold rolled for 1 to 4 passes shown in Table 1 to obtain a cold-rolled sheet with a final thickness of 0.22 mm. At this time, the time (elapsed time) from the end of the first stage of cold rolling to the start of the second stage of cold rolling was varied. Thereafter, the cold-rolled sheet with the final thickness was subjected to primary recrystallization annealing, which also served as decarburization annealing, an annealing separator was applied to the steel sheet surface, and then secondary recrystallization was performed, followed by finish annealing for purification to obtain a product sheet.

[0023] A test piece for magnetic measurement was taken from the longitudinal center position of the product sheet coil obtained in this way. The test piece was measured for magnetic flux density B ８ The magnetic flux density (magnetic flux density when a magnetic field of 800 A / m was applied) was measured, and the results are shown in Table 1. The table also shows the ratio of the reduction in the preceding cold rolling to the total reduction in the cold rolling (preceding cold rolling reduction / total reduction: hereinafter simply referred to as "reduction ratio"). Here, the reduction refers to the "amount of reduction in sheet thickness (mm) due to rolling."

[0024] The results in Table 1 show that the magnetic properties are relatively good when the reduction ratio is in the range of 0.50 to 0.95. Furthermore, among the conditions under which these relatively good magnetic properties are obtained, it can be seen that the magnetic properties are even better when the coiling temperature after the first cold rolling is 80°C or higher and the elapsed time between the first and second cold rolling is 30 minutes or longer.

[0025]

[0026] (Experiment 2) A steel material (slab) containing 0.03 mass% C, 3.2 mass% Si, and 0.06 mass% Mn, and further containing less than 0.0050 mass% S, Se, and O, less than 0.0025 mass% N, with the balance being Fe and unavoidable impurities, was produced. This steel slab containing no inhibitor-forming components was heated to a temperature of 1100 ° C and hot-rolled to a thickness of 3.0 mm and a width of 1000 mm. The hot-rolled sheet was then subjected to hot-rolled sheet annealing at 1000 ° C for 70 seconds to produce a hot-rolled annealed sheet. Next, the hot-rolled annealed sheet was subjected to a first-stage cold rolling using a five-stand tandem rolling mill with a work roll diameter of 250 mm in the final stand, in which the steel sheet temperature between the third stand and subsequent stands was 120°C or higher to roll it to an intermediate thickness of 0.6 mm. The sheet was then coiled at a temperature of 100°C. Next, 40 minutes after the end of the first-stage cold rolling, the sheet was subjected to a second-stage cold rolling using various single-stand rolling mills with different work roll diameters in two passes to produce a cold-rolled sheet with a final thickness of 0.22 mm. The work roll diameters used in the second-stage rolling were 14 types: 75 mm, 80 mm, 140 mm, 150 mm, 160 mm, 240 mm, 250 mm, 260 mm, 330 mm, 335 mm, 360 mm, 510 mm, 520 mm, and 530 mm. Thereafter, the cold-rolled sheet having the above-mentioned final thickness was subjected to primary recrystallization annealing which also served as decarburization annealing, an annealing separator was applied to the surface of the steel sheet, and then secondary recrystallization was carried out, followed by finish annealing for purification treatment to obtain a product sheet.

[0027] A sample material having a total width of 1000 mm was taken from the center position in the longitudinal direction of the product sheet coil obtained in this way, and 10 test pieces each having a width of 100 mm and a length of 300 mm, with the rolling direction as the length direction, were taken from the sample material, and the magnetic flux density B of each test piece was measured using a single sheet magnetic measuring instrument. ８ (magnetic flux density when a magnetic field of 800 A / m is applied) is measured, and the magnitude of variation in the plate width direction ΔB ８ The magnetic flux density B ８ The magnitude of variation ΔB ８ is expressed as the difference between the maximum and minimum values.

[0028] FIG. 1 shows the relationship between the ratio of the work roll diameters used in the front and rear cold rolling stages ((rear-stage WR diameter / front-stage WR diameter), hereinafter simply referred to as the "WR diameter ratio") and the magnetic flux density B ８ The magnitude of variation ΔB ８ From this figure, it can be seen that the magnetic flux density B ８ The magnitude of variation ΔB ８ It can be seen that the variation is reduced, with the value being 0.005 T or less. Therefore, it was found that in order to suppress the variation in the magnetic properties of the product sheet, it is necessary to control the ratio of the work roll diameter used in the subsequent cold rolling to the work roll diameter used in the preceding cold rolling within an appropriate range.

[0029] The technology according to this embodiment was completed by further improving the above experimental results.

[0030] Next, the chemical composition of the steel material (slab) used to manufacture the grain-oriented electrical steel sheet according to this embodiment will be described. Hereinafter, the unit of content "%" for the chemical composition represents "mass %" unless otherwise specified.

[0031] C: 0.01 to 0.10% C is an element effective in improving the primary recrystallization texture, and from the viewpoint of achieving this effect, a C content of 0.01% or more is included. However, if the C content exceeds 0.10%, it actually leads to deterioration of the primary recrystallization texture. In addition, excessive C content makes it difficult to reduce the C content to a level that does not cause magnetic aging, for example, 0.003% or less, by decarburization annealing. Therefore, the C content is set to the range of 0.01 to 0.10%. Preferably, the C content is 0.02% or more, and preferably, the C content is 0.08% or less.

[0032] Si: 2.0 to 4.5% Si is an element that is effective in increasing the resistivity of steel and improving iron loss. From the viewpoint of obtaining the above effect, Si is contained in an amount of 2.0% or more. However, if the Si content exceeds 4.5%, cold rolling property is significantly reduced, so the upper limit is set to 4.5%. Preferably, the Si content is 2.5% or more, and more preferably, the Si content is 4.0% or less.

[0033] Mn: 0.01 to 0.5% Mn has the effect of improving workability in hot rolling and is also a useful element from the viewpoint of controlling the formation of an oxide film during primary recrystallization annealing, so the content is set to 0.01% or more. However, if the Mn content exceeds 0.5%, the primary recrystallization texture deteriorates, leading to deterioration of magnetic properties, so the upper limit is set to 0.5%. Preferably, the Mn content is 0.03% or more, and preferably, the Mn content is 0.2% or less.

[0034] The components other than C, Si and Mn differ depending on whether a precipitation-type inhibitor such as AlN, MnS or MnSe is used to induce secondary recrystallization or whether no such inhibitor is used.

[0035] First, we will explain the use of a precipitation-type inhibitor to induce secondary recrystallization. When AlN is used as the inhibitor, the Al content is preferably in the range of 0.010 to 0.05% in terms of sol. Al (acid-soluble Al), and the N content is preferably in the range of 0.004 to 0.012%. If the sol. Al content is less than 0.010%, the amount of precipitated AlN is too small, resulting in an insufficient inhibitor effect, causing poor secondary recrystallization and a decrease in magnetic flux density. On the other hand, if the sol. Al content exceeds 0.05%, secondary recrystallization tends to become unstable. Furthermore, if the N content is less than 0.004%, AlN does not precipitate properly during intermediate processes such as hot rolling and hot-rolled sheet annealing, making it difficult to control the crystal grain size during hot-rolled sheet annealing, intermediate annealing, and even primary recrystallization annealing. On the other hand, if the N content exceeds 0.012%, surface defects known as blisters occur frequently. Therefore, it is preferable that the Al and N contents are within the above ranges. From the viewpoint of stabilizing the inhibitor during secondary recrystallization, the sol. Al content is more preferably 0.010% or more, and more preferably 0.035% or less. The N content is more preferably 0.008% or more, and more preferably 0.012% or less.

[0036] The N content of the steel sheet can be increased by applying a nitriding treatment in a process prior to finish annealing, and therefore, in the material stage, for example, in a steel slab, the N content may be 0.008% or less as long as it is 0.004% or more. When nitriding is performed, the N content may be increased to about 0.05% from the viewpoint of appropriately controlling the primary recrystallized grain size and obtaining the inhibitor strength required for secondary recrystallization.

[0037] On the other hand, when a sulfide such as MnS or a selenide such as MnSe is used as an inhibitor, it is preferable to contain at least one selected from S and Se in a total range of 0.01 to 0.05%. If the total content of S and Se is less than 0.01%, the absolute amount of inhibitor will be insufficient. On the other hand, if it exceeds 0.05%, it will be difficult to purify by finish annealing. S and Se may be added alone, and in that case, their respective contents are preferably in the range of 0.01 to 0.05%. More preferably, the total content of S and Se is 0.015% or more, and more preferably, the total content of S and Se is 0.040% or less.

[0038] When an inhibitor is used to induce secondary recrystallization, the above-mentioned AlN-based inhibitor may be used in combination with an MnS-based inhibitor or an MnSe-based inhibitor.

[0039] On the other hand, as disclosed in Patent Document 1, when developing secondary recrystallized grains without using a precipitation-type inhibitor, it is preferable to reduce the contents of Al, N, S, and Se, which are components that form inhibitors, as much as possible. Specifically, it is preferable to reduce the Al content to less than 0.010% sol. Al, the S content to 0.0050% or less, the Se content to 0.0050% or less, and the N content to 0.0050% or less. If the contents of each element are outside the above ranges, it becomes difficult to obtain a secondary recrystallized structure due to the effect of texture inhibition. Furthermore, it is preferable to keep the N content within the above range in order to prevent the formation of Si nitrides during the purification treatment of the final annealing.

[0040] Furthermore, when a precipitation-type inhibitor is not used, it is preferable to reduce the contents of the nitride-forming elements Ti, Nb, B, Ta and V to 0.0050% or less, respectively, from the viewpoint of preventing interference with the texture inhibition action and suppressing deterioration of iron loss.

[0041] The steel material used to manufacture the grain-oriented electrical steel sheet according to this embodiment essentially consists of Fe and unavoidable impurities, except for the above-mentioned components. However, from the viewpoint of improving the hot-rolled sheet structure and enhancing magnetic properties, Ni may be contained in the range of 0.005 to 1.50% in addition to the above-mentioned components. Furthermore, for the purpose of improving magnetic properties, at least one element selected from the group consisting of grain boundary segregation elements Cr, Cu, Sn, Sb, Mo, Te, Bi, and P may be contained in the range of 0.005 to 0.3% each.

[0042] Next, a method for manufacturing the grain-oriented electrical steel sheet according to this embodiment will be described. First, a steel material (slab) that is the raw material for the grain-oriented electrical steel sheet can be produced by melting steel that satisfies the above-mentioned chemical composition using a commonly known refining process, and then by a conventional continuous casting method or an ingot-making and blooming rolling method.

[0043] Next, the steel material (slab) is heated to an appropriate temperature and then subjected to hot rolling. If the steel slab contains precipitation-type inhibitor-forming elements, the heating temperature of the steel slab is preferably in the range of 1350 to 1450°C in order to completely dissolve Al, Se, S, etc. On the other hand, if the steel slab does not contain precipitation-type inhibitor-forming elements, the heating temperature of the steel slab is preferably 1250°C or less. This is because if the heating temperature of the steel slab is too high, the inhibitor-forming elements that have dissolved during heating will precipitate non-uniformly as fine grains during hot rolling. This will locally inhibit grain boundary migration, resulting in a non-uniform grain size distribution and inhibiting the development of secondary recrystallized grains.

[0044] The conditions for hot rolling following heating of the steel slab may be in accordance with the usual methods used in the production of grain-oriented electrical steel sheets. Furthermore, the steel sheet after the hot rolling, i.e., the hot-rolled sheet, may be subjected to hot-rolled sheet annealing for the purpose of improving magnetic properties, or may not be subjected to hot-rolled sheet annealing in order to prioritize production costs.

[0045] Next, the hot-rolled sheet after the hot rolling or hot-rolled sheet annealing is subjected to cold rolling. This cold rolling is the most important step in this embodiment and must be performed while satisfying the following conditions. First, the cold rolling in this embodiment must be performed separately in an earlier stage and a later stage, and the total reduction of the earlier and later stages of cold rolling must be 80% or more. If the total reduction is less than 80%, the dislocation density introduced by rolling cannot be sufficiently increased, dislocation fixation by strain aging cannot be promoted, and the texture cannot be improved. A preferred total reduction is 84% ​​or more, and a preferred total reduction is 96% or less. Here, the "total reduction" refers to the sum of the thickness reduction amounts due to cold rolling, i.e., the percentage of the value obtained by dividing the total reduction amount by the thickness before cold rolling.

[0046] Furthermore, intermediate annealing between the first and second cold rolling stages can be optionally performed. When intermediate annealing is performed, the annealing temperature must be set to 700°C or less. If annealing is performed at a temperature exceeding 700°C during cold rolling, the rolled structure will recover and recrystallize, and the dislocations introduced by cold rolling will disappear, resulting in a deterioration of the magnetic properties of the grain-oriented electrical steel sheet. Therefore, the annealing temperature for intermediate annealing is limited.

[0047] Furthermore, when switching from the first cold rolling stage to the second cold rolling stage, it is necessary to control the ratio of the reduction amount of the first cold rolling stage to the total reduction amount of the cold rolling stage, i.e., the reduction ratio, within the range of 0.50 to 0.95. Here, the total reduction amount in cold rolling is the difference between the hot-rolled sheet thickness and the final cold-rolled sheet thickness, and the reduction amount of the first cold rolling stage refers to the thickness reduction amount in the first cold rolling stage. By setting the reduction ratio of the first cold rolling stage within the above range, sufficient dislocation density can be accumulated in the steel sheet. If the reduction ratio is less than 0.50, dislocation density will not be sufficiently accumulated, while if it exceeds 0.95, the texture improvement effect of the second cold rolling stage, which is a feature of this embodiment, will not be fully achieved. Note that the preferred reduction ratio is 0.60 or more, and the preferred reduction ratio is 0.80 or less.

[0048] It is also important that the first stage cold rolling is performed using a tandem rolling mill consisting of multiple rolling mills to roll to an intermediate plate thickness, and the second stage cold rolling is performed using a single-stand rolling mill to roll from the intermediate plate thickness to the final plate thickness in one to three passes. By setting the number of passes in the second stage cold rolling to three or less, the reduction rate per pass in a state in which dislocations are locked can be increased, and the formation of deformation bands can be further promoted.

[0049] Furthermore, the ratio of the work roll diameter of the rolling mill used in the latter cold rolling to the work roll diameter of the final stand of the tandem rolling mill used in the former cold rolling (WR diameter ratio) must be within the range of 0.60 to 1.35. The reason for making the work roll diameter used in the latter cold rolling closer to that of the former cold rolling, as described above, is believed to be as follows. That is, in order to continue to inherit and develop the rolling texture formed in the former cold rolling in the latter cold rolling, it is preferable that the work roll diameter of the latter cold rolling be closer to that of the former work roll. As a result, changes in the deformation mode in the sheet width direction can be suppressed, and variations in magnetic properties in the sheet width direction can be reduced. The preferable WR diameter ratio is 0.65 or more, and the preferable WR diameter ratio is 1.25 or less.

[0050] When the subsequent cold rolling is performed in two or three passes, as long as the work roll diameter is within the range that satisfies the above-mentioned conditions, each pass may be performed using work rolls of different diameters in a single rolling mill, or each pass may be performed using a plurality of rolling mills having work rolls of different diameters.

[0051] Furthermore, it is preferable that the steel sheet after the first stage of cold rolling is coiled at a temperature of 80°C or higher, and the second stage of cold rolling is carried out after at least 30 minutes have elapsed. By satisfying the above conditions, dislocation fixation due to strain aging is promoted, and the texture improvement effect can be further enhanced. The preferred coiling temperature is 100°C or higher, and the elapsed time is 60 minutes or longer.

[0052] In addition, from the viewpoint of maintaining the steel sheet temperature at 80°C or higher after the completion of the front-stage cold rolling, the tandem rolling mill used for the front-stage cold rolling according to this embodiment preferably has a function of controlling the coil winding temperature by adjusting the temperature and / or flow rate of coolant sprayed onto the steel sheet surface and / or the work roll surface at the outlet side of the final stand of the tandem rolling mill. Generally, cold rolling is often performed while supplying rolling oil at 70°C or lower to the rolls. Therefore, in order to maintain the steel sheet temperature at 80°C or higher during coil winding, it is preferable to have a function of wiping the oil so that the rolling oil does not come into contact with the steel sheet after cold rolling, or to perform control such as blowing off the rolling oil with high-pressure gas or air. From the viewpoint of productivity, performing the front-stage and rear-stage rolling continuously increases efficiency, but deliberately setting a time of 30 minutes or more is also an important factor.

[0053] Furthermore, from the viewpoint of promoting aging, the rolling mill used for cold rolling the grain-oriented electrical steel sheet according to this embodiment preferably has a heat retention device disposed between the front-stage tandem rolling mill and the rear-stage rolling mill for maintaining the temperature of the steel sheet after the front-stage cold rolling at 50° C. or higher. The temperature of the steel sheet at the start of cold rolling is not particularly limited and includes so-called warm rolling, but if the temperature of the steel sheet at the start of cold rolling becomes too high, a problem of rolling oil burning occurs, so the temperature is preferably 280° C. or lower.

[0054] Next, the cold-rolled sheet having reached the final thickness is subjected to primary recrystallization annealing, which also serves as decarburization annealing. The purpose of this primary recrystallization annealing is to recrystallize the cold-rolled sheet having a rolled texture to adjust it to a primary recrystallization texture optimal for secondary recrystallization, to reduce the carbon content in the steel to a level at which magnetic aging does not occur, and to form an oxide film necessary for forsterite film formation on the steel sheet surface. Therefore, the primary recrystallization annealing is preferably performed at a temperature of 750 to 900°C in an oxidizing wet hydrogen-nitrogen or wet hydrogen-argon atmosphere. Furthermore, the heating rate during primary recrystallization annealing is preferably rapid heating of 50°C / s or more to improve the texture.

[0055] After the primary recrystallization annealing, the steel sheet is coated with an annealing separator. This annealing separator preferably contains magnesia (MgO) as its main component, and forms a forsterite film on the steel sheet surface after the final annealing. It is preferable to add an appropriate amount of an auxiliary agent such as a Ti oxide or an Sr compound to this annealing separator to make the forsterite film uniform and improve its peeling resistance.

[0056] The steel sheet coated with the annealing separator is wound into a coil and allowed to undergo secondary recrystallization, after which it is subjected to finish annealing at a temperature of 1100°C or higher to form a forsterite film and to remove impurities such as inhibitor-forming components from the steel sheet (purification treatment). ２ The atmosphere is N ２ , Ar, H ２ Alternatively, it is preferable to use any of these mixed gases. By this purification treatment, the inhibitor-forming components Al, N, S, and Se contained in the steel sheet are reduced to impurity levels, specifically, Al: 0.008 mass% or less, N: 0.003 mass% or less, S: 0.003 mass% or less, and Se: 0.005 mass% or less. In order to more advantageously carry out secondary recrystallization in the above-mentioned finish annealing, the steel sheet may be isothermally held at a temperature near the secondary recrystallization temperature for a long period of time, or may be slowly heated in the above-mentioned temperature range.

[0057] Next, the steel sheet after the above-mentioned finish annealing is preferably subjected to planarization annealing for shape correction. Furthermore, in the above-mentioned planarization annealing, an insulating coating may be applied to the surface of the steel sheet and baked. The type of this insulating coating is not particularly specified. For example, from the viewpoint of reducing iron loss, the techniques disclosed in JP-A-50-79442 and JP-A-48-39338 can be applied. These techniques involve applying a coating liquid containing phosphate, chromate, and colloidal silica to the surface of the steel sheet and baking it at a temperature of about 800°C to form a tension-imparting insulating coating. Furthermore, from the viewpoint of further reducing iron loss, a magnetic domain refinement treatment may be performed by forming grooves on the surface of the steel sheet in any step after cold rolling, or by irradiating the surface of the steel sheet after the finish annealing with an electron beam or laser beam to introduce thermal strain.

[0058] The grain-oriented electrical steel sheet according to this embodiment manufactured as described above not only has excellent magnetic properties but also has small variations in the magnetic properties in the sheet width direction. Specifically, the magnetic flux density B ８ The magnitude of variation, that is, the difference between the maximum and minimum values, ΔB ８ is 0.005T or less.

[0059] Example 1 A steel slab containing 0.040 mass% C, 3.3 mass% Si, and 0.05 mass% Mn, with the remaining components shown in Table 2, and the balance consisting of Fe and unavoidable impurities, was produced. The steel slab was heated to a temperature of 1200°C and then hot-rolled to a hot-rolled sheet having a thickness of 2.5 mm. The hot-rolled sheet was then subjected to hot-rolled sheet annealing at 1000°C for 60 seconds. The hot-rolled sheet after the hot-rolled sheet annealing was then rolled to the intermediate thickness shown in Table 2 using a four-stand tandem rolling mill with a work roll diameter of 400 mm in the final stand, with the steel sheet temperature between stands from the third pass onwards being 150°C or higher. The steel sheet was then subjected to a pre-coiling cold rolling process at a temperature of 110°C. Some of the coils after the first cold rolling were then subjected to intermediate annealing at 1000°C for 30 seconds. Next, after 30 minutes or more had elapsed since the end of the first cold rolling, the cold-rolled sheet with the intermediate thickness was rolled into a cold-rolled sheet with a final thickness of 0.27 mm using a single-stand rolling mill with a work roll diameter of 300 mm, with the number of passes shown in Table 2. The cold-rolled sheet with the final thickness was then rapidly heated from 400°C to 700°C at a heating rate of 80°C / s, and then subjected to primary recrystallization annealing, which also served as decarburization annealing, at 850°C for 40 seconds in a wet hydrogen atmosphere. Next, an annealing separator mainly composed of MgO was applied to the surface of the steel sheet after the first recrystallization annealing, and dried. Subsequently, secondary recrystallization was performed, followed by finish annealing for purification. Next, a coating liquid for an insulating coating containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2 was applied to the surface of the steel sheet after the above-mentioned finish annealing, and the steel sheet was subjected to flattening annealing at 850°C for 30 seconds, which served both to bake the insulating coating and to correct the shape, to obtain a product sheet.

[0060] From the longitudinal center of the product sheet coil thus obtained, a test piece of 30 mm width x 280 mm length with the rolling direction as the longitudinal direction was cut out with a total weight of 500 g or more, and the magnetic flux density B ８ At the same time, ten test pieces each having a width of 100 mm and a length of 300 mm, with the rolling direction as the length direction, were taken from the position adjacent to the position where the Epstein test piece was taken, in the width direction of the sheet. The magnetic flux density B ８ Measure the difference between the maximum and minimum values ​​ΔB ８ was calculated and the magnitude of the variation in the plate width direction was evaluated.

[0061] The results of the above measurements are also shown in Table 2. From Table 2, it can be seen that all of the steel sheets that satisfy the conditions of this embodiment not only have excellent magnetic properties but also have a high magnetic flux density B ８ Variation in the width direction of the plate ΔB ８ It can be seen that the value is reduced to 0.005T or less.

[0062]

[0063] (Example 2) C: 0.05 mass%, Si: 3.4 mass%, Mn: 0.08 mass%, Al: 0.015 mass%, N: 0.006 mass%, S: 0.003 mass% and Se: 0.012 mass%, with the balance being Fe and unavoidable impurities. A steel slab having a component composition was heated to a temperature of 1400 ° C. and hot-rolled to a thickness of 2.0 mm. Then, the hot-rolled sheet was subjected to hot-rolled sheet annealing at 1080 ° C. × 60 s, and then rolled to an intermediate thickness of 0.7 mm using a 4-stand tandem rolling mill with a work roll diameter of 400 mm in the final stand. The steel sheet temperature between the stands after the third pass was 150 ° C. or higher. The cold rolling was performed at a temperature of 100 ° C. before being wound into a coil. Next, after 40 minutes or more have passed since the previous stage of cold rolling, the cold-rolled sheet having the intermediate thickness was rolled in two passes using different single-stand rolling mills having five different work roll diameters of 80 mm, 250 mm, 330 mm, 500 mm, and 580 mm to obtain a cold-rolled sheet having a final thickness of 0.25 mm. Next, the cold-rolled sheet having the final thickness was subjected to primary recrystallization annealing, which also served as decarburization annealing, at 850°C for 120 seconds in a wet hydrogen atmosphere. Thereafter, a coating of TiO, mainly composed of MgO, was applied to the surface of the steel sheet after the primary recrystallization annealing. ２ After secondary recrystallization, the steel sheet was subjected to finish annealing in which it was held at 1,200°C for 10 hours for purification. Next, a coating liquid for an insulating coating containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2 was applied to the surface of the steel sheet after the finish annealing, and the steel sheet was subjected to flattening annealing at 850°C for 30 seconds, which served both to bake the insulating coating and to correct the shape, to produce a product sheet.

[0064] A sample material was taken from the center of the length of the product sheet coil thus obtained, and 10 test pieces each measuring 30 mm in width and 280 mm in length were taken from the sample material in the sheet width direction, with the rolling direction as the length direction. The magnetic flux density B ８ (magnetic flux density when a magnetic field of 800 A / m was applied) was measured.

[0065] 2 shows the influence of the work roll diameter ratio (WR diameter ratio) of the front and rear cold rolling mills on the magnetic flux density and its variation in the sheet width direction (maximum value - minimum value) based on the above measurement results. From this figure, it can be seen that the steel sheet satisfying the conditions of this embodiment has a magnetic flux density B ８ and the magnetic flux density B in the plate width direction is good. ８ It can be seen that the variation in is suppressed to 0.005T or less.

[0066] (Example 3) In Example 1, the steel sheet (intermediate plate thickness 0.6 mm) produced from Steel 1 after the first stage of cold rolling was subjected to the second stage of cold rolling, in which the steel sheet was rolled in one pass each using a single stand rolling mill with a work roll diameter of 330 mm and a single stand rolling mill with a work roll diameter of 250 mm (a total of two passes). Thereafter, a grain-oriented electrical steel sheet product coil was produced under the same conditions as in Example 1. A sample material was taken from the center in the longitudinal direction of the product plate coil thus obtained, and from the sample material, ten test pieces with a width of 30 mm and a length of 280 mm, with the length direction being the rolling direction, were taken from the plate width direction, and the magnetic flux density B ８ As a result, the magnetic flux density B ８ were all within the range of 1.922±0.002 T. From this result, it was confirmed that, as long as the ratio of the diameter of the WR used in each pass of the latter-stage cold rolling to the diameter of the WR in the preceding stage satisfies the conditions of this embodiment, the effect of reducing the variation in magnetic flux density in the sheet width direction can be obtained even when the latter-stage cold rolling is performed using a plurality of single-stand rolling mills with different work roll diameters.

[0067] The technology of the present invention can also be applied to other steel products in which texture is controlled by utilizing carbon in the steel.

Claims

1. A method for cold rolling grain-oriented electrical steel sheets, comprising cold rolling at a total reduction rate of 80% or more to produce a cold-rolled sheet having a final thickness, The cold rolling is divided into a front-stage cold rolling and a rear-stage cold rolling, Optionally, an intermediate annealing is performed between the first cold rolling and the second cold rolling; When the intermediate annealing is performed, the annealing temperature is set to 700°C or less, In the first stage cold rolling, a tandem rolling mill is used to roll the steel sheet to an intermediate thickness with a reduction ratio relative to the total reduction in the cold rolling being in the range of 0.50 to 0.95; In the latter stage cold rolling, a single stand rolling mill is used to roll the sheet from the intermediate plate thickness to the final plate thickness in 1 to 3 passes, By setting the ratio of the work roll diameter of the single stand rolling mill to the work roll diameter of the final stand of the tandem rolling mill to be in the range of 0.60 to 1.35, the magnetic flux density B in the width direction of the product plate ８ The method for cold rolling grain-oriented electrical steel sheets is characterized in that the difference between the maximum and minimum values ​​of is 0.005T or less.

2. 2. The method for cold rolling grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet after the first stage of cold rolling is wound into a coil at a temperature of 80°C or higher, and then the second stage of cold rolling is carried out after at least 30 minutes have elapsed.

3. 2. The method for cold rolling grain-oriented electrical steel sheet according to claim 1, wherein the latter stage of cold rolling is performed using one single-stand rolling mill with different work roll diameters, or using a plurality of single-stand rolling mills with different work roll diameters.

4. Contains C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, and Mn: 0.01 to 0.5 mass%, Further, as inhibitor-forming components, the composition contains at least one component selected from Group A: sol. Al: 0.010 to 0.05 mass% and N: 0.004 to 0.012 mass%, Group B: one or more selected from S and Se: 0.01 to 0.05 mass% in total, and Group C: sol. Al: 0.010 to 0.05 mass%, N: 0.004 to 0.012 mass%, and at least one selected from S and Se: 0.01 to 0.05 mass% in total, Optionally, at least one component selected from Ni: 0.005 to 1.50 mass%, Cr: 0.005 to 0.3 mass%, Cu: 0.005 to 0.3 mass%, Sn: 0.005 to 0.3 mass%, Sb: 0.005 to 0.3 mass%, Mo: 0.005 to 0.3 mass%, Te: 0.005 to 0.3 mass%, Bi: 0.005 to 0.3 mass%, and P: 0.005 to 0.3 mass% is contained; A method for producing a grain-oriented electrical steel sheet, comprising the steps of hot rolling a steel slab having a component composition with the balance being Fe and unavoidable impurities to form a hot-rolled sheet, cold rolling the hot-rolled sheet at a total reduction rate of 80% or more to form a cold-rolled sheet of a final thickness, subjecting the cold-rolled sheet to primary recrystallization annealing which also serves as decarburization annealing, applying an annealing separator to the surface of the steel sheet, and then subjecting the cold-rolled sheet to secondary recrystallization followed by finish annealing for purification, In the cold rolling, by applying the cold rolling method according to any one of claims 1 to 3, the magnetic flux density B in the plate width direction is ８ The method for producing a grain-oriented electrical steel sheet, characterized in that the difference between the maximum and minimum values ​​of is 0.005T or less.

5. Contains C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.5 mass%, and further contains sol. Al: less than 0.010 mass%, S: 0.0050 mass% or less, Se: 0.0050 mass% or less, and N: 0.0050 mass% or less, Optionally, at least one component selected from Ni: 0.005 to 1.50 mass%, Cr: 0.005 to 0.3 mass%, Cu: 0.005 to 0.3 mass%, Sn: 0.005 to 0.3 mass%, Sb: 0.005 to 0.3 mass%, Mo: 0.005 to 0.3 mass%, Te: 0.005 to 0.3 mass%, Bi: 0.005 to 0.3 mass%, and P: 0.005 to 0.3 mass% is contained; A method for producing a grain-oriented electrical steel sheet, comprising the steps of hot rolling a steel slab having a component composition with the balance being Fe and unavoidable impurities to obtain a hot-rolled sheet, cold rolling the hot-rolled sheet at a total rolling reduction of 80% or more to obtain a cold-rolled sheet of a final thickness, subjecting the cold-rolled sheet to primary recrystallization annealing which also serves as decarburization annealing, applying an annealing separator to the surface of the steel sheet, and then subjecting the cold-rolled sheet to secondary recrystallization and then finish annealing for purification, In the cold rolling, by applying the cold rolling method according to any one of claims 1 to 3, the magnetic flux density B in the plate width direction is ８ The method for producing a grain-oriented electrical steel sheet, characterized in that the difference between the maximum and minimum values ​​of is 0.005T or less.

6. A cold rolling equipment train comprising a front-stage cold rolling mill and a rear-stage cold rolling mill used in the cold rolling method according to claim 1, the front-stage cold rolling mill is a tandem rolling mill, and the rear-stage cold rolling mill is a single-stand rolling mill; a ratio of the work roll diameter of the cold rolling mill in the latter stage to the work roll diameter of the final stand of the tandem rolling mill is within a range of 0.60 to 1.

35.

7. A cold rolling equipment train comprising a front-stage cold rolling mill and a rear-stage cold rolling mill used in the cold rolling method according to claim 3, the front-stage cold rolling mill is a tandem rolling mill, and the rear-stage cold rolling mill is a single-stand rolling mill; 7. The cold rolling equipment train according to claim 6, wherein the downstream cold rolling mill comprises one single-stand rolling mill capable of changing the work roll diameter or a plurality of single-stand rolling mills having different work roll diameters.

8. (1) A function of the tandem rolling mill controlling the coil winding temperature by adjusting at least one of the temperature and flow rate of the coolant sprayed onto at least one of the steel plate surface and the work roll surface at the delivery side of the final stand; and (2) A heat retention device is disposed between the tandem rolling mill and the subsequent rolling mill, for maintaining the temperature of the steel sheet after the previous cold rolling at 50°C or higher.

8. The cold rolling equipment train according to claim 6, characterized in that it has at least one of the following configurations: