Method for producing grain-oriented electrical steel sheet, and induction heating device

Abstract

A grain-oriented electrical steel sheet is produced by hot-rolling a steel raw material to form a hot-rolled sheet, cold-rolling the hot-rolled sheet to form a cold-rolled sheet having a final sheet thickness, subjecting the cold-rolled sheet to decarburization annealing that also serves as primary recrystallization annealing, and then subjecting the cold-rolled sheet to final annealing that performs secondary recrystallization, wherein, in the final cold rolling among the cold rolling, rolling is performed at least one pass or more in a temperature region in which the steel sheet temperature is 150-350 DEG C inclusive, and in the decarburization annealing, the average temperature rise rate T (DEG C / s) between 500-700 DEG C in the temperature rise process is set to 250 DEG C / s or more, and the average temperature rise rate T (DEG C / s) is set to 250 DEG C / s or more. A method for manufacturing a grain-oriented electromagnetic steel sheet having uniform and excellent magnetic characteristics in the sheet width direction by changing the time during which the temperature increase rate is reduced to 150 DEG C / s or less between 500 DEG C and 700 DEG C in accordance with the value of x / w (x: distance (mm) from the center of the sheet width and w: 1 / 2 (mm) of the sheet width) at each position in the sheet width direction, meanwhile, the invention provides an induction heating device for decarburization annealing of the method.

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of an oriented electromagnetic steel sheet and an induction heating device used in decarburization annealing of the manufacturing method. BACKGROUND

[0002] An oriented electromagnetic steel sheet is a soft magnetic material mainly used for transformer, generator core material, etc., and is a steel sheet having excellent magnetic properties of low iron loss and high magnetic flux density, because it has a crystal structure in which an easy magnetization axis of iron, i.e., {110} <001> orientation (Goss orientation), is highly consistent with a rolling direction of the steel sheet.

[0003] As a means for further reducing iron loss of the oriented electromagnetic steel sheet, it can be listed that the grains after secondary recrystallization annealing are highly gathered toward the Goss orientation. In order to improve the gathering degree of the secondary recrystallization grains toward the Goss orientation, it is important to: form a large number of Goss orientation grains in advance in the steel sheet structure at the time of primary recrystallization; and in the secondary recrystallization, make a difference in grain boundary mobility to make only sharp Goss orientation grains preferentially grow, i.e., optimize the texture of the steel sheet after the primary recrystallization.

[0004] As the primary recrystallization structure that can make only sharp Goss orientation grains grow preferentially, there are {111} <112> orientation grains and {411} <148> orientation grains, and by making them exist in the primary recrystallization structure in balance and at a high frequency, it is possible to highly gather the Goss orientation grains in the rolling direction in the secondary recrystallization annealing.

[0005] As a method of improving the existence ratio of the Goss orientation grains in the primary recrystallization structure, for example, Patent Literature 1 discloses a method of performing a low-temperature heat treatment on a cold-rolled sheet in cold rolling to perform aging treatment. In addition, Patent Literature 2 discloses a method of setting a cooling speed at the time of intermediate annealing before hot-rolled sheet annealing or final cold rolling (final cold rolling) to 30°C / s or more, and further performing interpass aging in which the steel sheet is held at a temperature of 150 to 300°C for 2 minutes or more twice or more in final cold rolling. Furthermore, Patent Literature 3 discloses a technology of performing warm rolling in which the steel sheet temperature is increased to perform rolling in cold rolling.

[0006] The technologies of the above Patent Documents 1 to 3 are all methods of raising the temperature of a steel sheet to an appropriate temperature before, during or between passes of cold rolling, promoting diffusion of solid-solution elements, i.e., carbon (C) and nitrogen (N), fixing dislocations introduced during cold rolling, suppressing movement of dislocations in subsequent rolling, and promoting shear deformation, thereby improving rolling texture. This is based on the view that nuclei of Goss-oriented grains in primary recrystallized structure are generated from shear bands introduced in {111}<112>-oriented worked structure. By applying these technologies, a large number of shear bands can be introduced in {111}<112>-oriented worked structure, thereby forming a large number of Goss-oriented grains in primary recrystallized structure.

[0007] In addition, by increasing the temperature increase rate during the heating process of decarburization annealing, it is also possible to promote formation of Goss-oriented grains in primary recrystallized structure. For example, Patent Document 4 discloses a method of performing rapid heating during the heating process of decarburization annealing. This technology suppresses development of γ-fiber texture ({111} / / ND) that is preferentially formed at a normal temperature increase rate by raising the temperature from room temperature to the vicinity of the recrystallization temperature in a short time using electric current heating or induction heating, and the like, thereby promoting generation of Goss-oriented grains that become nuclei of secondary recrystallized grains.

[0008] In addition, Patent Document 5 discloses a method of performing rapid heating at an average temperature increase rate of 50°C / s or more between 550°C and 700°C during the heating process of decarburization annealing, and reducing the temperature increase rate to 10°C / s or less and maintaining it for 1 to 10 seconds in any temperature region between 250°C and 550°C. This technology promotes recovery of {111}-oriented worked structure to suppress recrystallization by performing short-time maintenance between 250°C and 550°C as a recovery temperature region, thereby relatively increasing the presence ratio of Goss-oriented grains.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Application Publication No. S50-016610

[0012] Patent Document 2: Japanese Patent Application Publication No. H08-253816

[0013] Patent Document 3: Japanese Patent Application Publication No. H01-215925

[0014] Patent Document 4: Japanese Patent Application Publication No. H04-160114

[0015] Patent Document 5: Japanese Patent Application Publication No. 2014-152393 SUMMARY

[0016] PROBLEMS TO BE SOLVED BY THE INVENTION

[0017] However, the primary recrystallization texture is often not uniform in the width direction of the steel sheet. The reasons can be listed: the reduction in cold rolling becomes uneven in the width direction of the sheet due to edge drop formed in hot rolling, etc.; the grain size in the width direction of the steel sheet before cold rolling becomes uneven due to the inability to uniformly heat the width direction during annealing of the hot rolled sheet, etc. In addition, in the case of applying warm rolling in cold rolling as in the technologies disclosed in the above patent documents 1 to 3, the temperature of the end portion of the steel sheet decreases greatly due to heat dissipation, and the diffusion distance of carbon and nitrogen differs in the width direction of the sheet, which is also considered to be one of the reasons for the change in texture.

[0018] If the primary recrystallization texture differs in the width direction of the sheet, the secondary recrystallization behavior also differs in the width direction, which becomes the reason for the fluctuation in the magnetic properties of the final product in the width direction of the sheet. In order to prevent this, it is possible to consider edge cutting of the end portion of the steel sheet after hot rolling or after cold rolling, etc., but the reduction in yield is inevitable.

[0019] The present application was completed in view of the above problems existing in the prior art, and aims to propose a manufacturing method of an oriented electromagnetic steel sheet having uniform and excellent magnetic properties in the width direction of the sheet, and to provide an induction heating device for decarburization annealing used in the method.

[0020] Method for solving the problem

[0021] The inventors have intensively studied a method for homogenizing the primary recrystallization texture in the width direction of the sheet in order to solve the above problem. As a result, it has been found that, in the final cold rolling in cold rolling, the temperature of the steel sheet is set to 150°C or higher, at least one pass or more of rolling is performed, and in decarburization annealing which serves as primary recrystallization annealing, when rapid heating is performed between 500°C and 700°C in the temperature rising process, the temperature rising rate is temporarily lowered in the middle of the way, and the time of this lowering is varied in the width direction of the sheet, thereby homogenizing the primary recrystallization structure after decarburization annealing in the width direction of the sheet, and thus the present application has been completed.

[0022] The present application based on the above insight proposes a manufacturing method of an oriented electromagnetic steel sheet, wherein a steel raw material is hot-rolled to produce a hot-rolled sheet, the hot-rolled sheet is cold-rolled once or cold-rolled twice or more with intermediate annealing to produce a cold-rolled sheet of a final sheet thickness, decarburization annealing that also serves as primary recrystallization annealing is performed on the cold-rolled sheet, and then final annealing that performs secondary recrystallization is performed, the manufacturing method being characterized in that, in the final cold-rolling among the above-mentioned cold-rolling once or cold-rolling twice or more, rolling is performed for at least one pass or more in a temperature range in which the temperature of the steel sheet is 150°C or higher and 350°C or lower, and in the above-mentioned decarburization annealing, the average temperature increase rate T (°C / s) between 500°C and 700°C in the temperature increase process is set to 250°C / s or higher, and in any temperature range between the above-mentioned 500°C and 700°C, the temperature increase rate at each position in the sheet width direction of the steel sheet is reduced to 150°C / s or lower only at a time t (s) that satisfies the following (1) formula, depending on the value of x / w at each position.

[0023] 200 / T x 0.2 (1 - x / w) ≤ t ≤ 200 / T x 0.8 (1 - x / w) (1)

[0024] where x is the distance from the center of the sheet width (mm), w is 1 / 2 of the sheet width (mm), but 0 ≤ x ≤ 0.9w.

[0025] The above-mentioned manufacturing method of an oriented electromagnetic steel sheet of the present application is characterized in that, in the above-mentioned final cold-rolling, rolling is performed for at least one pass or more in a temperature range in which the temperature is 30°C or higher and 130°C or lower, and then rolling is performed for at least one pass or more in a temperature range in which the temperature is 150°C or higher and 350°C or lower.

[0026] Further, the above-mentioned steel raw material used in the above-mentioned manufacturing method of an oriented electromagnetic steel sheet of the present application is characterized by having a composition containing C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.50 mass%, Al: 0.0100 to 0.0400 mass%, and N: 0.0050 to 0.0120 mass%, further containing at least one of S and Se in a total amount of 0.01 to 0.05 mass%, and the balance consisting of Fe and inevitable impurities.

[0027] Further, the above-mentioned steel raw material used in the above-mentioned manufacturing method of an oriented electromagnetic steel sheet of the present application is characterized by having a composition containing C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.50 mass%, Al: less than 0.0100 mass%, N: 0.0050 mass% or less, S: less than 0.0100 mass%, and Se: less than 0.0100 mass%, and the balance consisting of Fe and inevitable impurities.

[0028] Furthermore, the steel raw material used in the manufacturing method of the oriented electromagnetic steel sheet of the present invention is characterized in that, in addition to the above-mentioned composition, it further contains at least one component selected from Sb: 0.005-0.500 wt%, Cu: 0.01-1.50 wt%, P: 0.005-0.500 wt%, Cr: 0.01-1.50 wt%, Ni: 0.005-1.500 wt%, Sn: 0.01-0.50 wt%, Nb: 0.0005-0.0100 wt%, Mo: 0.01-0.50 wt%, B: 0.0010-0.0070 wt%, and Bi: 0.0005-0.0500 wt%.

[0029] Furthermore, the method for manufacturing the above-mentioned oriented electromagnetic steel sheet of the present invention is characterized in that a transverse induction heating device is used for rapid heating in the above-mentioned decarburization annealing.

[0030] In addition, the present invention is a transverse induction heating device used for rapid heating in the decarburization annealing process of the above-mentioned method for manufacturing oriented electromagnetic steel sheets.

[0031] Invention Effects

[0032] According to the present invention, it is possible to stably manufacture oriented electromagnetic steel plates with uniform and excellent magnetic properties in the width direction of the steel plate, thus making a significant contribution to improving the quality of the finished plates and increasing the yield. Attached Figure Description

[0033] Figure 1 This is a diagram illustrating the range of the heating rate reduction time in the width direction of the plate conforming to the present invention.

[0034] Figure 2 This is another figure illustrating the range of the heating rate reduction time in the width direction of the plate conforming to the present invention.

[0035] Figure 3 This is a schematic diagram illustrating a horizontal induction heating device. Detailed Implementation

[0036] First, the experiments that facilitated the development of this invention will be described.

[0037] Experiment 1

[0038] A steel billet containing C: 0.033% by mass, Si: 3.4% by mass, Mn: 0.07% by mass, sol.Al: 0.0081% by mass, N: 0.0052% by mass, S: 0.0030% by mass, and Se: 0.0030% by mass, with the balance being Fe and unavoidable impurities, is heated to 1220°C and then hot-rolled to produce a hot-rolled sheet with a thickness of 2.0 mm. Next, the hot-rolled sheet is subjected to hot-rolled annealing at 1000°C for 60 seconds, and then cold-rolled in one pass to produce a cold-rolled sheet with a final thickness of 0.20 mm. It should be noted that the above cold rolling is a warm rolling process where the temperature of the steel sheet immediately before the rolls bite into the workpiece is raised to 200°C using induction heating. Next, sample materials were cut from the above-mentioned cold-rolled sheet. When the distance from the center of the sheet width was set as x (mm) (x=0 at the center of the sheet width) and half the width of the sheet width was set as w (mm), multiple samples of Epstein test piece size (30mm × length 280mm) were cut from the above-mentioned sample material at five positions in the sheet width direction: x=0, 0.2w, 0.4w, 0.6w and 0.8w.

[0039] Next, the samples were subjected to decarburization annealing, which also served as a recrystallization annealing, with a homogenization temperature of 850°C and a homogenization time of 100 s. During this process, the average heating rate between 500°C and 700°C was set to 300°C / s, and under certain conditions, the heating rate was reduced to 120°C / s only for the time shown in Table 1 when reaching 600°C. Then, an annealing separating agent with MgO as the main component was coated onto the surface of the decarburized annealed samples, followed by a final annealing for secondary recrystallization. Afterward, an insulating coating solution containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was coated onto the surface of the final annealed samples, and a simulated planarization annealing heat treatment was performed at 800°C for 30 s, followed by baking to produce product plate samples. It should be noted that the average heating rate of 300°C / s between 500°C and 700°C is the average heating rate excluding the time spent reducing the heating rate.

[0040] For the product plate sample with the dimensions of the Epstein test piece obtained as described above, the iron loss W was determined according to JIS Z 2550. 17 / 50 The difference between the maximum and minimum values ​​of iron loss in the width direction of the plate was calculated, and the results are shown in Table 1.

[0041]

[0042] As shown in Table 1, when rapid heating is performed between 500 and 700°C, if the heating rate is temporarily reduced within the above temperature range, and the time for reducing the heating rate is longer in the middle of the plate width and shorter at the ends of the plate width, the difference between the maximum and minimum values ​​of the iron loss in the plate width direction becomes less than 0.04 W / kg, and uniform magnetic properties can be obtained in the plate width direction.

[0043] Regarding the reason why uniform magnetic properties can be obtained in the width direction when the time for temporarily reducing the heating rate is longer in the central part of the plate width and shorter at the ends of the plate width during rapid heating, as described above, the inventors believe as follows.

[0044] Due to factors such as edge reduction during hot rolling, the cold rolling reduction rate is lower at the wide ends of the plate compared to the central portion. This means that the deformation during cold rolling is smaller at the wide ends. Furthermore, the plate temperature is lowered more easily at the wide ends due to heat dissipation than in the central portion during cold rolling. For these reasons, the diffusion distance of carbon and nitrogen in the steel at the wide ends is smaller, and dislocations formed during rolling are more difficult to fix. Therefore, the amount of shear bands introduced into the cold-rolled microstructure at the wide ends, which serve as sites for Gaussian-oriented grain formation during primary recrystallization, is less than in the central portion. Thus, shortening the time for reducing the heating rate at the wide ends promotes the recrystallization of Gaussian-oriented grains, while extending the time for reducing the heating rate in the central portion inhibits it. As a result, it is believed that the number of Gaussian-oriented grains after primary recrystallization annealing becomes more uniform along the width of the plate.

[0045] Next, based on the above experimental results, the inventors conducted an experiment to investigate the appropriate time for reducing the heating rate according to the position in the width direction of the plate.

[0046] <Experiment 2>

[0047] For five Epstein test piece sizes of cold-rolled sheets cut in Experiment 1 with different positions along the width direction, decarburization annealing, which also served as a recrystallization annealing, was performed. The homogenization temperature was set to 850℃ and the homogenization time to 100s. During this decarburization annealing, the average heating rate between 500℃ and 700℃ was set to 300℃ / s. The time required to reduce the heating rate to 110℃ / s along the width direction when reaching 650℃ was changed to... Figure 1 The eight conditions are shown. Next, an annealing separating agent with MgO as the main component is coated onto the surface of the sample after decarburization annealing, and a final annealing is performed for secondary recrystallization. Then, an insulating coating solution containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 is coated onto the surface of the final annealed sample, and a simulated planarization annealing heat treatment at 800℃ for 30s is performed before baking to produce a product plate sample.

[0048] For the product plate sample with the dimensions of the Epstein test piece obtained as described above, the iron loss W was determined according to JIS Z 2550. 17 / 50 The difference between the maximum and minimum iron loss values ​​in the width direction of the plate is shown in Table 2.

[0049]

[0050] As shown in Table 2, under the condition that the time t for all the temperature reduction at positions x=0, 0.2w, 0.4w, 0.6w and 0.8w in the width direction satisfies the following equation (1), the difference between the maximum and minimum iron loss values ​​in the width direction becomes less than 0.04W / kg, and uniform magnetic properties can be obtained in the width direction.

[0051] 200 / T×0.2(1-x / w)≤t≤200 / T×0.8(1-x / w)…(1)

[0052] Where x is the distance from the center of the plate width (mm), and w is 1 / 2 of the plate width (mm), but 0≤x≤0.9w.

[0053] This invention was completed based on the above-mentioned new insights and further research.

[0054] Next, the composition of the steel raw material (steel billet) used in the manufacture of the oriented electromagnetic steel sheet of the present invention will be described. It should be noted that, as the steel raw material used in the manufacture of the present invention, conventionally known steel raw materials used in the manufacture of oriented electromagnetic steel sheets can be used, but from the viewpoint of obtaining excellent magnetic properties, the following composition is preferred.

[0055] C: 0.01~0.10% by mass

[0056] Carbon (C) is an element that precipitates by forming fine carbides and helps improve the texture of primary recrystallization. However, when the C content is less than 0.01% by mass, the amount of fine carbides precipitated is insufficient, and the aforementioned texture improvement effect may be inadequate. On the other hand, when it exceeds 0.10% by mass, it may be difficult to reduce it to below 0.0050% by mass without magnetic aging by decarburization annealing. Therefore, the C content is preferably set in the range of 0.01 to 0.10% by mass. More preferably, it is in the range of 0.015 to 0.08% by mass.

[0057] Si: 2.0–4.5% by mass

[0058] Si is an effective element for improving iron loss by increasing the resistivity of steel. However, when the Si content is less than 2.0% by mass, the aforementioned iron loss reduction effect cannot be fully obtained. On the other hand, when it exceeds 4.5% by mass, the workability is significantly reduced, making rolling difficult. Therefore, the Si content is preferably set in the range of 2.0 to 4.5% by mass. More preferably, it is set in the range of 2.5 to 4.0% by mass.

[0059] Mn: 0.01~0.50% by mass

[0060] Mn is an element required to improve hot workability. When the Mn content is less than 0.01% by mass, it is difficult to obtain the aforementioned improvement in hot workability. On the other hand, when it exceeds 0.50% by mass, the primary recrystallization texture may deteriorate, making it difficult to obtain secondary recrystallized grains with a high degree of Gaussian orientation. Therefore, the Mn content is preferably set in the range of 0.01 to 0.50% by mass. More preferably, it is set in the range of 0.03 to 0.45% by mass.

[0061] Regarding the components other than C, Si, and Mn mentioned above, the differences depend on whether an inhibitor is used during secondary recrystallization.

[0062] Specifically, when using an inhibitor for secondary recrystallization and employing AlN as the inhibitor, in addition to C, Si, and Mn, it is preferable that the content of Al and N be in the range of 0.0100–0.0400% by mass and 0.0050–0.0120% by mass. When the Al and N contents are below the lower limits mentioned above, it is difficult to obtain the desired inhibitory effect. On the other hand, when the contents exceed the upper limits mentioned above, the dispersion of the precipitate becomes uneven, and it is also difficult to obtain the desired inhibitory effect.

[0063] In addition to AlN, when sulfides (MnS, Cu2S, etc.) and selenides (MnSe, Cu2Se, etc.) are used as inhibitors, the inhibitor-forming components preferably contain at least one of S and Se in a total mass percentage range of 0.0100 to 0.0500%. When the total content of S and Se is below the lower limit mentioned above, it is difficult to obtain a sufficient inhibitory effect. On the other hand, when it exceeds the upper limit mentioned above, the dispersion of the precipitate becomes uneven, and it is also difficult to obtain a sufficient inhibitory effect. It should be noted that the sulfides and selenides mentioned above can precipitate together.

[0064] On the other hand, when secondary recrystallization does not utilize inhibitors, it is preferable to minimize the components that form inhibitors. Specifically, it is preferable that Al: less than 0.0100% by mass, N: less than 0.0050% by mass, S: less than 0.0100% by mass, and Se: less than 0.0100% by mass.

[0065] In the steel raw material for manufacturing oriented electromagnetic steel sheets of the present invention, the balance other than the above-mentioned basic components is substantially Fe and unavoidable impurities. However, in order to improve magnetic properties, at least one of the following components may be added in addition to the above-mentioned components: Sb: 0.005-0.500 wt%, Cu: 0.01-1.50 wt%, P: 0.005-0.500 wt%, Cr: 0.01-1.50 wt%, Ni: 0.005-1.500 wt%, Sn: 0.01-0.50 wt%, Nb: 0.0005-0.0100 wt%, Mo: 0.01-0.50 wt%, B: 0.0010-0.0070 wt%, and Bi: 0.0005-0.0500 wt%. Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi are elements useful for improving magnetic properties. If they are within the above range, the improvement in magnetic properties can be achieved without hindering the development of secondary recrystallized grains.

[0066] Next, the manufacturing method of the oriented electromagnetic steel sheet of the present invention will be described.

[0067] The steel raw material (steel billet) for manufacturing oriented electromagnetic steel sheets of the present invention is preferably manufactured by the following method: the steel having the composition described above is smelted by a generally known refining process, which involves secondary refining of molten steel obtained by vacuum degassing or the like using a converter, electric furnace or the like, and then the steel raw material is produced by a generally known continuous casting method or ingot-bill rolling method.

[0068] Next, the steel billet is heated to a specified temperature and then hot-rolled into a hot-rolled sheet. From the viewpoint of ensuring hot rollability, the heating temperature of the steel billet is preferably set to about 1050°C or higher. There is no particular upper limit to the heating temperature, but when it exceeds 1450°C, it approaches the melting point of steel, making it difficult to maintain the shape of the billet. Therefore, it is preferable to set it to 1450°C or lower.

[0069] Hot rolling of steel billets after heating can be performed under generally known conditions without particular restrictions.

[0070] Next, the hot-rolled steel sheet (hot-rolled plate) can be annealed as needed. It should be noted that when annealing the hot-rolled plate, generally known conditions can be used without particular restrictions.

[0071] The hot-rolled steel sheet or the annealed hot-rolled steel sheet, after being descaled by pickling or mechanical methods as needed, is then cold-rolled to produce a cold-rolled sheet with a final thickness (product thickness). This cold rolling can be performed in a single cold rolling operation to achieve the final thickness, or it can be performed in two or more cold rolling operations with intermediate annealing. It should be noted that the final thickness is preferably set within the range of 0.1 mm to 1.0 mm.

[0072] Furthermore, the reduction rate of the final cold rolling in the aforementioned cold rolling process is preferably set to a range of 60% or more and 95% or less. Here, the aforementioned final cold rolling refers to the last cold rolling process performed in one or more cold rolling processes. For example, when only one cold rolling process is performed, that one rolling process is the final cold rolling process; when two or more cold rolling processes are performed, the last rolling process is the final cold rolling process.

[0073] In this invention, during the final cold rolling process, at least one pass of rolling is required at a rolling temperature of 150°C or higher and 350°C or lower. Performing cold rolling at this temperature for at least one pass promotes the diffusion of dissolved carbon and the fixation of dislocations, efficiently introducing shear bands that serve as nucleation sites for Gaussian-oriented grains during primary recrystallization, thereby further enhancing magnetic properties. When the rolling temperature is below 150°C, the dislocation fixation caused by dissolved carbon is insufficient, and the increase in Gaussian-oriented grains during primary recrystallization cannot be expected. On the other hand, when the rolling temperature exceeds 350°C, the lubrication condition deteriorates significantly due to the evaporation of the rolling oil used for lubrication. A preferred rolling temperature is in the range of 180°C or higher and 300°C or lower. It should be noted that the rolling temperature mentioned above refers to the temperature of the steel plate immediately before the rolls bite into the workpiece.

[0074] Furthermore, in the aforementioned final cold rolling, by performing at least one pass of rolling at a low-temperature region (above 30°C and below 130°C) followed by at least one pass of rolling at a high-temperature region (above 150°C and below 350°C), the increase in Gaussian-oriented grains during primary recrystallization can be further improved. {111} <112> The orientation is a rolling-stable orientation that does not change due to rolling. Therefore, rolling is first performed in a low-temperature region to achieve {111} <112> The structure is well-developed, and then further rolling in a high-temperature region can efficiently increase the {111} sites that become Gaussian-oriented grain nucleation sites during primary recrystallization. <112> Shear bands formed in the processing structure. When the rolling temperature in the low-temperature region is below 30°C, plate cracking may occur, significantly reducing productivity. On the other hand, above 130°C, {111} <112> The microstructure actually decreases. The preferred rolling temperature in the low-temperature region is above 40°C and below 100°C.

[0075] Furthermore, when the final cold rolling is performed in three or more passes, the positions of the low-temperature and high-temperature passes are unrestricted, as long as rolling is performed in the low-temperature region followed by rolling in the high-temperature region. For example, if rolling in the low-temperature region (above 30°C and below 130°C) is designated as low-temperature, and rolling in the high-temperature region (above 150°C and below 350°C) is designated as high-temperature, then in the case of three-pass final cold rolling, rolling can be performed in any of the following sequences: low-temperature-high-temperature, high-temperature-low-temperature-high-temperature, low-temperature-low-temperature-high-temperature, or low-temperature-high-temperature-low-temperature. However, when rolling in the high-temperature-low-temperature-low-temperature or high-temperature-high-temperature-low-temperature sequence, an increase in Gaussian orientation cannot be expected.

[0076] Next, the cold-rolled sheet to the final thickness is subjected to decarburization annealing, which also serves as a recrystallization annealing. Regarding the decarburization conditions (conditions during homogenization) in this decarburization annealing, known conditions can be used without particular limitation, but for example, conditions of 720–870°C for 60–150 s in a moist hydrogen atmosphere are preferred. Through this decarburization annealing, the carbon content in the steel sheet is reduced to below 0.0050% by mass, at which magnetic aging does not occur.

[0077] However, in this decarburization annealing, it is important that the heating process from 500°C to 700°C during the heating phase up to the aforementioned homogenization temperature is characterized as rapid heating with an average heating rate of 250°C / s or more. Here, the average heating rate between 500°C and 700°C in this invention refers to the average heating rate over the time excluding the period of temporary reduction in heating rate described later. When the average heating rate is less than 250°C / s, the Gaussian orientation grains after the first recrystallization are insufficient, and good iron loss cannot be obtained. A preferred average heating rate is 300°C / s or more. It should be noted that rapid heating can also be performed in a temperature range outside the 500°C to 700°C range.

[0078] Furthermore, during the aforementioned decarburization annealing heating process, it is necessary to temporarily reduce the heating rate to below 150°C / s at any temperature between 500 and 700°C during the rapid heating. When the steel plate temperature is below 500°C, even with a reduced heating rate, the recrystallization behavior of the Gaussian-oriented grains will not change, and the effect of adjusting the number of Gaussian-oriented grains in the primary recrystallization cannot be achieved. On the other hand, when the temperature exceeds 700°C, even with a reduced heating rate, recrystallization is already largely complete, and similarly, the effect of adjusting the number of Gaussian-oriented grains in the primary recrystallization cannot be achieved.

[0079] Furthermore, in this invention, it is necessary to vary the time for temporarily reducing the heating rate according to the position in the plate width direction. This invention eliminates the differences in steel sheet microstructure in the plate width direction caused by various manufacturing conditions up to decarburization annealing by varying the time for temporarily reducing the heating rate in the plate width direction during rapid heating in decarburization annealing. In particular, when warm rolling is used in the final cold rolling, a temperature difference occurs in the plate width direction, and the primary recrystallization texture easily becomes uneven in the plate width direction; therefore, this technique is preferably applied when warm rolling is performed.

[0080] The time t during the rapid heating process that temporarily reduces the heating rate to below 150°C / s is longer in the central part of the plate width and shorter at the ends of the plate width. Specifically, it is important that this variation satisfies the following equation (1). When t is shorter than the left side of equation (1), there will be too many Gaussian-oriented grains in that part, and the local iron loss will decrease. Conversely, when t is longer than the right side of equation (1), the recrystallization of Gaussian-oriented grains in that part will be suppressed, and the local iron loss will increase. As a result, it is impossible to obtain uniform magnetic properties in the plate width direction. It should be noted that the plate width range that satisfies the above equation (1) is set to (0≤x≤0.9w) because, in the case of transverse induction heating during rapid heating, the induced current is concentrated at the ends of the plate width, and therefore it may not be possible to satisfy equation (1) across the entire width. Of course, it is preferable to satisfy equation (1) across the entire width.

[0081] 200 / T×0.2(1-x / w)≤t≤200 / T×0.8(1-x / w)…(1)

[0082] Where x is the distance from the center of the plate width (mm), and w is 1 / 2 of the plate width (mm), but 0≤x≤0.9w.

[0083] Furthermore, the temporarily reduced heating rate needs to be below 150°C / s. If the heating rate is higher than this, the effect of suppressing recrystallization of Gaussian-oriented grains becomes insufficient. While there is no particular limitation on the lower limit of the reduced heating rate, it is preferably 10°C / s or higher. The duration of the aforementioned temporary reduction in heating rate can be determined by measuring the steel plate temperature during the heating process using a thermocouple or similar device and then differentiating the steel plate temperature over time.

[0084] Here, the rapid heating during the decarburization annealing process and the reduction of the heating rate midway can be implemented by: connecting two or more electric heating devices or solenoid induction heating devices in series along the through-plate direction of the steel plate; designating any interval between these two or more devices as a heating rate reduction interval; and appropriately adjusting the output power of the rapid heating devices and the through-plate speed (linear velocity) of the steel plate. Additionally, to prevent heat loss from the wide ends of the plate, edge heaters can also be installed in the heating rate reduction interval.

[0085] As mentioned above, connecting two or more rapid heating devices in series presents the problem of requiring significant cost and space. However, as a rapid heating device, for example using... Figure 3 The schematic diagram illustrates a transverse induction heating device in which a heating coil wound around an iron core is positioned above and below a steel plate, and an alternating magnetic flux generated within the iron core flows along the thickness of the steel plate. This magnetic field is used to heat the steel plate. In this transverse induction heating device, the induced current flows along the shape of the heating coil within the plate surface, while no induced current flows in the portion of the steel plate opposite the iron core. Therefore, the heating rate temporarily decreases as the steel plate passes through the iron core portion, and this phenomenon can be used to reduce the overall heating rate. Furthermore, the time of this reduction in heating rate can be adjusted by changing the output power or linear velocity of the induction heating device. Additionally, since the induced current flows at the wider end of the plate, heat dissipation at the wider end is also suppressed. Moreover, the reduction in heating rate occurs within a single induction heating device, thus eliminating space constraints. Therefore, a transverse induction heating device is suitable for use in this invention.

[0086] Furthermore, in order to vary the heating rate reduction time along the width of the plate using the aforementioned transverse induction heating device, the coil diameter along the plate width can be made larger at the center of the plate width and gradually smaller towards the ends of the plate width. Additionally, the heating coil of the aforementioned transverse induction heating device can be any shape such as circular, rectangular, or elliptical, but as mentioned above, it is preferable that the coil diameter along the plate width varies along the plate width.

[0087] Next, the cold-rolled sheet that has undergone the above-mentioned decarburization annealing is coated with an annealing separating agent on the surface of the steel sheet, and then subjected to a final annealing process for secondary recrystallization. As the annealing separating agent, any known annealing separating agent can be used without particular limitation. Examples include annealing separating agents with MgO as the main component and TiO2 or other additives added as needed, or annealing separating agents with SiO2 or Al2O3 as the main components.

[0088] For steel sheets that have undergone the aforementioned final annealing, it is preferable to apply an insulating coating liquid to the steel sheet surface after removing any unreacted annealing separating agent remaining on the steel sheet surface, and then bake it by simultaneously performing a planarization annealing to correct the shape of the steel sheet deteriorated due to the final annealing, thereby producing a finished product sheet. It should be noted that the formation of the insulating coating can also be carried out on other production lines. The type of insulating coating is not particularly limited, but when forming a tension-imparting insulating coating that imparts tensile tension on the steel sheet surface, it is preferable to apply a phosphate-colloidal silica slurry disclosed in Japanese Patent Application Publication Nos. 50-79442, 48-39338, and 56-75579, and bake it at a temperature of approximately 800°C.

[0089] In addition, if it is desired to further reduce iron loss, magnetic domain refinement can be carried out by known methods such as forming grooves on the surface of the steel plate in any process after the above-mentioned cold rolling, mechanically forming strain regions on the surface of the steel plate after final annealing, or forming thermal strain regions by irradiating with laser beams, electron beams, etc.

[0090] Example 1

[0091] A steel billet containing C: 0.035% by mass, Si: 3.3% by mass, Mn: 0.05% by mass, sol.Al: 0.0084% by mass, N: 0.0051% by mass, S: 0.0031% by mass, and Se: 0.0031% by mass, with the balance being Fe and unavoidable impurities, is heated to 1260°C and then hot-rolled to produce a hot-rolled sheet with a thickness of 2.0 mm. Next, the hot-rolled sheet is subjected to hot-rolled annealing at 1000°C for 60 seconds, and then cold-rolled in one pass to produce a cold-rolled sheet with a final thickness of 0.20 mm. It should be noted that the above cold rolling is performed using induction heating to raise the steel sheet temperature to 250°C.

[0092] Next, the above-mentioned cold-rolled sheet was subjected to decarburization annealing, which was also a recrystallization annealing, with the soaking temperature set at 850°C and the soaking time set at 100s. During the heating process of decarburization annealing, the average heating rate T (°C / s) between 500°C and 700°C varied as shown in Table 3. For some steel sheets, the heating rate at each position in the width direction was reduced to the "reduced heating rate" shown in Table 3 only at the time t expressed by the following formula (2) when the temperature reached 620°C. Next, an annealing separating agent with MgO as the main component was coated on the surface of the steel sheet after decarburization annealing, and a final annealing was performed for secondary recrystallization. Next, an insulating coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was coated on the surface of the steel sheet after final annealing, and a planarization annealing was performed at 800°C for 30s for baking to produce the finished sheet.

[0093] t=200 / T×0.5×(1-x / w)…(2)

[0094] Where x is the distance from the center of the plate width (mm), and w is 1 / 2 of the plate width (mm), but 0≤x≤0.9w.

[0095] From the obtained product plate, at positions x=0, 0.2w, 0.4w, 0.6w, and 0.8w (x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm)), cut Epstein test pieces with a width of 30mm and a length of 280mm. The iron loss W is then measured according to JIS Z 2550. 17 / 50 The average value of iron loss in the width direction of the plate and the difference between the maximum and minimum values ​​were calculated and recorded in Table 3. As shown in Table 3, under the condition that the average heating rate is above 250℃ / s and the reduced heating rate is below 150℃ / s, the average value of iron loss is as low as below 0.84W / kg, and the difference in iron loss is suppressed to below 0.04W / kg.

[0096]

[0097]

[0098]

[0099] Example 2

[0100] A steel billet containing C: 0.06 wt%, Si: 3.4 wt%, Mn: 0.06 wt%, sol.Al: 0.0250 wt%, N: 0.0090 wt%, S: 0.01 wt%, and Se: 0.01 wt%, with the balance being Fe and unavoidable impurities, and containing inhibitory components, is heated to 1400°C and then hot-rolled to produce a hot-rolled plate with a thickness of 2.0 mm. Next, the hot-rolled plate undergoes a first cold rolling to produce an intermediate plate thickness of 1.2 mm. Then, after intermediate annealing at 1100°C for 80 s in an atmosphere of N2: 75 vol% + H2: 25 vol%, with a dew point of 46°C, a second cold rolling (final cold rolling) is performed using a tandem mill to produce a cold-rolled plate with a final thickness of 0.20 mm. At this point, the flow rate of the cooling medium sprayed onto the steel plate is adjusted to achieve a final cold rolling temperature of 160°C to 250°C.

[0101] Next, the cold-rolled sheet was subjected to decarburization annealing, which also served as a recrystallization annealing, with a soaking temperature of 850°C and a soaking time of 100 seconds. During the heating process of this decarburization annealing, a transverse induction heating device was used, with an average heating rate of 300°C / s between 500°C and 700°C for rapid heating. Then, when the steel sheet temperature reached 650°C midway through the induction heating process, the output power and linear velocity of the induction heating device were adjusted so that the time it took for the heating rate T to reach 100°C / s in the width direction was... Figure 2 The six conditions are shown. Next, an annealing separating agent with MgO as the main component is coated onto the surface of the decarburized annealed steel sheet, followed by final annealing for secondary recrystallization. Then, an insulating coating solution containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 is coated onto the surface of the final annealed steel sheet, followed by planarization annealing at 800℃ for 30 seconds and baking to produce the finished product sheet.

[0102] From the obtained product plate, at positions x=0, 0.2w, 0.4w, 0.6w, and 0.8w (x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm)), cut Epstein test pieces with a width of 30mm and a length of 280mm. The iron loss W is then measured according to JIS Z 2550. 17 / 50 The average value of the iron loss in the width direction and the difference between the maximum and minimum values ​​were calculated and recorded in Table 4. Table 4 shows that for steel plates where the heating rate was reduced during rapid heating under the condition that equation (1) is satisfied at all positions in the width direction, the difference between the maximum and minimum values ​​of the iron loss in the width direction is less than 0.04 W / kg. Therefore, it can be seen that even when using raw materials containing inhibitor-forming components to manufacture oriented electromagnetic steel plates, the magnetic properties in the width direction can be homogenized by applying this invention.

[0103] 200 / T×0.2(1-x / w)≤t≤200 / T×0.8(1-x / w)…(1)

[0104] Where x is the distance from the center of the plate width (mm), and w is 1 / 2 of the plate width (mm), but 0≤x≤0.9w.

[0105]

[0106] Example 3

[0107] Steel billet A, composed of C: 0.035 wt%, Si: 3.3 wt%, Mn: 0.05 wt%, sol.Al: 0.0084 wt%, N: 0.0051 wt%, S: 0.0031 wt%, and Se: 0.0031 wt%, with the balance being Fe and unavoidable impurities, and containing no inhibitory components, and steel billet B, composed of C: 0.06 wt%, Si: 3.4 wt%, Mn: 0.06 wt%, sol.Al: 0.0250 wt%, N: 0.0095 wt%, S: 0.01 wt%, and Se: 0.01 wt%, with the balance being Fe and unavoidable impurities, and containing inhibitory components, are heated to 1300℃ and then hot-rolled into hot-rolled plates with a thickness of 2.0 mm. Next, the hot-rolled sheet manufactured from the aforementioned billet A is hot-rolled and annealed at 1000°C for 60 seconds, then cold-rolled once to obtain a cold-rolled sheet with a final thickness of 0.20 mm. On the other hand, the hot-rolled sheet manufactured from the aforementioned billet B is hot-rolled and annealed at 1000°C for 60 seconds, then cold-rolled once to obtain an intermediate thickness of 1.2 mm. After intermediate annealing at 1100°C for 80 seconds in an atmosphere of N2: 75 vol% + H2: 25 vol%, dew point 46°C, a second cold-rolled sheet is obtained to obtain a cold-rolled sheet with a final thickness of 0.20 mm. It should be noted that the cold rolling to obtain the final thickness (final cold rolling) in the above-mentioned cold rolling processes is performed in 4 passes, according to the steel plate temperatures listed in Table 5.

[0108] Next, the cold-rolled sheet was subjected to decarburization annealing, which was also a recrystallization annealing, with a soaking temperature of 850°C and a soaking time of 100s. During the decarburization annealing process, the average heating rate between 500°C and 700°C was set to 300°C / s. When the temperature reached 600°C, the heating rate at each position in the width direction of the sheet was reduced to 100°C / s only within the time t calculated by the following formula (2). It should be noted that the steel sheets No. 323, 324, 325 and 326 in Table 5 were rapidly heated by maintaining a heating rate of 300°C / s (without reducing the heating rate).

[0109] t=200 / T×0.5×(1-x / w)…(2)

[0110] Where x is the distance from the center of the plate width (mm), and w is 1 / 2 of the plate width (mm), but 0≤x≤0.9w.

[0111] Next, an annealing separating agent with MgO as the main component is coated on the surface of the steel plate after decarburization annealing, and a final annealing is performed for secondary recrystallization. Then, an insulating coating solution containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 is coated on the surface of the steel plate after the final annealing, and a planarization annealing at 800℃ for 30s is performed for baking to produce the finished product plate.

[0112] From the obtained product plate, at positions x=0, 0.2w, 0.4w, 0.6w, and 0.8w (x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm)), cut Epstein test pieces with a width of 30mm and a length of 280mm. The iron loss W is then measured according to JIS Z 2550. 17 / 50 The average value of the iron loss in the width direction and the difference between the maximum and minimum values ​​were calculated, and the results are recorded in Table 5. Table 5 shows that for steel plates that have undergone at least one pass of rolling at a temperature above 150℃ and below 350℃ in the final cold rolling process, the iron loss W of the finished plate... 17 / 50 All values ​​are below 0.84 W / kg, which is considered good. Furthermore, for steel plates that have undergone at least one rolling pass at a temperature above 30°C and below 130°C, and at least one rolling pass at a temperature above 150°C and below 350°C, the iron loss W of the finished plate is... 17 / 50 All values ​​are below 0.80 W / kg, which is considered a better value. On the other hand, for steel plates that have undergone warm rolling but do not meet the heating conditions of this invention during decarburization annealing, the difference between the maximum and minimum values ​​of iron loss in the width direction is above 0.06 W / kg, showing significant fluctuations.

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119]

[0120]

[0121] Example 4

[0122] Steel containing C: 0.036 wt%, Si: 3.4 wt%, Mn: 0.06 wt%, sol.Al: 0.0072 wt%, N: 0.0050 wt%, S: 0.0031 wt%, and Se: 0.0031 wt%, and with other components including Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi as shown in Table 6, with the balance consisting of Fe and unavoidable impurities, and without any inhibitory components, was melted to produce a steel billet. The billet was then heated to 1210°C and hot-rolled to produce a hot-rolled plate with a thickness of 2.0 mm. The hot-rolled plate was then annealed at 1000°C for 60 seconds and cold-rolled once (final cold rolling) using a tandem mill to produce a cold-rolled plate with a final thickness of 0.20 mm. It should be noted that in this final cold rolling, the flow rate of the cooling medium sprayed onto the steel plate is adjusted so that the temperature of the steel plate during rolling reaches 250℃~300℃.

[0123] Next, the cold-rolled sheet was subjected to decarburization annealing, which also served as a recrystallization annealing, with a homogenization temperature of 850°C and a homogenization time of 100 s. During the decarburization annealing heating process, a transverse induction heating device was used, similar to that in Example 2, with an average heating rate between 500°C and 700°C set to 300°C / s for rapid heating. The time for reducing the heating rate to 110°C / s in the width direction when the steel sheet temperature reached 650°C was set to the same as in Example 2. Figure 2 The conditions are the same as in No. 1. Next, after coating the surface of the decarburized annealed steel sheet with an annealing agent mainly composed of MgO, a final annealing is performed for secondary recrystallization. Then, an insulating coating solution containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 is applied to the surface of the final annealed steel sheet, and a planarization annealing at 800℃ for 30 seconds is performed before baking to produce the finished product sheet.

[0124] From the obtained product plate, at positions x=0, 0.2w, 0.4w, 0.6w, and 0.8w (x: distance from the center of the plate width (mm), w: 1 / 2 of the plate width (mm)), cut Epstein test pieces with a width of 30mm and a length of 280mm. The iron loss W is then measured according to JIS Z 2550. 17 / 50The average value of the iron loss in the width direction of the product plate and the difference between the maximum and minimum values ​​were calculated, and the results are recorded in Table 6. Table 6 shows that for product plates manufactured according to the conditions of the method of the present invention, using steel billets containing at least one of Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi as the steel raw material, and employing a transverse induction heating device during the decarburization annealing heating process, the average value of the iron loss in the width direction is below 0.80 W / kg, and the difference between the maximum and minimum values ​​of the iron loss in the width direction is below 0.04 W / kg, exhibiting uniform and excellent magnetic properties in the width direction.

[0125]

Claims

1. A method for manufacturing an orientation-oriented electromagnetic steel sheet, wherein, The manufacturing method involves hot rolling steel raw materials to produce hot-rolled sheets, then subjecting the hot-rolled sheets to one cold rolling or two or more cold rolling processes including intermediate annealing to produce cold-rolled sheets of a final thickness. The cold-rolled sheets are then subjected to decarburization annealing, which also serves as a recrystallization annealing, followed by a final annealing process for secondary recrystallization. The characteristic of this manufacturing method is that... In the final cold rolling of one or more cold rolling processes, at least one rolling pass is performed in a temperature range of 150°C to 350°C. In the decarburization annealing, the average heating rate T (°C / s) between 500°C and 700°C is set to be 250°C / s or more. Furthermore, in any temperature range between 500°C and 700°C, the heating rate at each position in the width direction of the steel plate is reduced to 150°C / s or less only at the time t (s) that satisfies the following equation (1), based on the x / w value at each position. 200 / T×0.2(1-x / w)≤t≤200 / T×0.8(1-x / w)…(1) Where x is the distance from the center of the plate width (mm), and w is 1 / 2 of the plate width (mm), but 0≤x≤0.9w.

2. The method for manufacturing the oriented electromagnetic steel sheet according to claim 1, characterized in that, In the final cold rolling, after at least one pass of rolling is performed in a temperature range of 30°C or higher and 130°C or lower, at least one pass of rolling is performed in a temperature range of 150°C or higher and 350°C or lower.

3. The method for manufacturing an orientation-oriented electromagnetic steel sheet according to claim 1 or 2, characterized in that, The steel raw material comprises C: 0.01-0.10% by mass, Si: 2.0-4.5% by mass, Mn: 0.01-0.50% by mass, Al: 0.0100-0.0400% by mass and N: 0.0050-0.0120% by mass, and further comprises at least one of S and Se totaling 0.01-0.05% by mass, with the balance consisting of Fe and unavoidable impurities.

4. The method for manufacturing an orientation-oriented electromagnetic steel sheet according to claim 1 or 2, characterized in that, The steel raw material contains C: 0.01-0.10% by mass, Si: 2.0-4.5% by mass, Mn: 0.01-0.50% by mass, Al: less than 0.0100% by mass, N: less than 0.0050% by mass, and S: Less than 0.0100% by mass and Se: less than 0.0100% by mass, the balance being composed of Fe and unavoidable impurities.

5. The method for manufacturing an orientation-oriented electromagnetic steel sheet according to claim 3 or 4, characterized in that, The steel raw material, in addition to the aforementioned composition, also contains at least one component selected from the following: Sb: 0.005–0.500 wt%, Cu: 0.01–1.50 wt%, P: 0.005–0.500 wt%, Cr: 0.01–1.50 wt%, Ni: 0.005–1.500 wt%, Sn: 0.01–0.50 wt%, Nb: 0.0005–0.0100 wt%, Mo: 0.01–0.50 wt%, B: 0.0010–0.0070 wt%, and Bi: 0.0005–0.0500 wt%.

6. The method for manufacturing the oriented electromagnetic steel sheet according to any one of claims 1 to 5, characterized in that, Rapid heating in the decarburization annealing is performed using a transverse induction heating device.

7. A transverse induction heating device for rapid heating in the decarburization annealing process of the manufacturing method of the oriented electromagnetic steel sheet according to any one of claims 1 to 5.

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