Method for manufacturing grain-oriented electromagnetic steel sheet and rolling apparatus for manufacturing electromagnetic steel sheet

Abstract

Provided is a method for manufacturing an oriented electromagnetic steel sheet with low iron loss and less variation in iron loss, which can be stably manufactured using a tandem mill. The method for manufacturing an oriented electromagnetic steel sheet includes the following steps: hot-rolling a steel blank to produce a hot-rolled sheet, cold-rolling the hot-rolled sheet once or more than twice with intermediate annealing to produce a cold-rolled sheet with a final sheet thickness, then decarburizing the cold-rolled sheet and performing secondary recrystallization annealing; and performing final cold-rolling using a tandem mill, wherein the final cold-rolling is performed by heating the hot-rolled sheet to a temperature range of 70-200°C, then cooling to below 60°C, and then introducing the sheet into the first pass of the tandem mill.

Description

Technical Field

[0001] This invention relates to a method for manufacturing an orientation-oriented electromagnetic steel sheet with excellent magnetic properties. Background Technology

[0002] Oriented electromagnetic steel sheets are soft magnetic materials used as core materials for transformers and generators. They are steel sheets with excellent magnetic properties, characterized by a highly consistent crystalline structure with the iron's easy magnetization axis, i.e., {110}<001> orientation (Gaussian orientation), in the rolling direction of the steel sheet.

[0003] As a method to improve integration towards Gaussian orientation, Patent Document 1 discloses a method for heat-treating and aging cold-rolled sheets at low temperatures. Patent Document 2 discloses a technique where the cooling rate during annealing of hot-rolled sheets or intermediate annealing before final cold rolling is 30°C / s or more, and further, during final cold rolling, inter-pass aging is performed at a temperature of 150–300°C for at least two passes of at least two minutes. Furthermore, Patent Document 3 discloses a technique utilizing dynamic strain aging, which involves warm rolling by increasing the temperature of the steel sheet during rolling, immediately fixing dislocations introduced during rolling with C and N.

[0004] The techniques described in these patent documents 1-3 all involve maintaining the steel sheet temperature at an appropriate level before, during, or between cold rolling passes. This allows carbon (C) and nitrogen (N), which are solid solution elements, to diffuse at low temperatures, fixing dislocations introduced during cold rolling, suppressing dislocation movement during subsequent rolling, further inducing shear deformation, and improving the rolling texture. Through the application of these techniques, a large number of Gaussian-oriented seed crystals are formed during the first recrystallization. These Gaussian-oriented seed crystals grow during the second recrystallization, thereby improving the integration of Gaussian orientation after the second recrystallization.

[0005] Furthermore, as a technique to further improve the aforementioned strain aging effect, Patent Document 4 discloses the following technique: In the annealing process prior to the final cold rolling in the cold rolling process, fine carbides are precipitated in the steel. The final rolling is divided into a first half and a second half. In the first half, the steel is rolled at a low temperature of 140°C or below with a reduction rate of 30-75%. In the second half, at least two reduction passes are performed at a high temperature of 150-300°C. The total reduction rate of the first and second halves is then increased to 80-95%, thereby stably obtaining a material with a high degree of integration in Gaussian orientation. Additionally, Patent Document 5 discloses the following technique: Before tandem cold rolling, a 0.5 kg / mm² annealing process is applied... 2 Under tension of more than one type, heat treatment is carried out at 50-150°C for 30 seconds to 30 minutes, thereby precipitating fine carbides in the steel.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 50-016610

[0009] Patent Document 2: Japanese Patent Application Publication No. 08-253816

[0010] Patent Document 3: Japanese Patent Application Publication No. 01-215925

[0011] Patent Document 4: Japanese Patent Application Publication No. 09-157745

[0012] Patent Document 5: Japanese Patent No. 3160281 Summary of the Invention

[0013] In recent years, due to the social demand for energy conservation, the need for low-iron-loss oriented electromagnetic steel sheets has been increasing, necessitating the development of technologies for the stable mass production of low-iron-loss oriented electromagnetic steel sheets.

[0014] Here, continuous rolling mills, compared to reversible mills like Sendzimir, have a higher throughput per hour, which is beneficial for the mass production of oriented electromagnetic steel sheets. However, in the techniques disclosed in Patent Documents 1 and 2 that implement inter-pass aging during rolling, the desired effects cannot be achieved when the distance between passes is short and the linear speed is high, as in continuous rolling.

[0015] Furthermore, in the rolling method disclosed in Patent Document 3, which involves heating at the inlet side of a continuous rolling mill, the improvement in iron loss is insufficient, as described below. Here, it is assumed that the primary recrystallized Gaussian-oriented grains nucleate from shear bands introduced into the {111}<112> matrix structure, which is one of the rolling stable orientations. In the method disclosed in Patent Document 3, which involves heating at the inlet side of the continuous rolling mill and rolling at that temperature, it is difficult to form a {111}<112> matrix structure. As a result, the amount of Gaussian-oriented grains in the primary recrystallized structure is insufficient, and therefore, the iron loss is not considered to be adequately improved.

[0016] Furthermore, in the techniques described in Patent Documents 4 and 5, which involve carbide precipitation treatment during the annealing process prior to final cold rolling, the precipitation morphology of the carbides changes over time depending on the elapsed period from the precipitation treatment to final cold rolling, resulting in textural variations. Consequently, there is a problem of increased deviation in iron loss of the product coil.

[0017] Therefore, the purpose of this invention is to solve the above-mentioned problems existing in the prior art and to provide a method for manufacturing oriented electromagnetic steel sheets with low iron loss and low iron loss that can be stably produced using a continuous rolling mill.

[0018] To solve the above problems, the inventors conducted repeated and in-depth research on methods for heat treatment before cold rolling. The following describes the experiments that led to the present invention.

[0019] A steel billet with the following composition is heated to 1210°C and then hot-rolled to produce a hot-rolled plate with a thickness of 2.0 mm. The composition contains, by mass %: C: 0.037%, Si: 3.4%, and Mn: 0.05%, and by mass ppm: S and Se: 31 ppm, N: 50 ppm, and sol.Al: 85 ppm, with the remainder being Fe and unavoidable impurities.

[0020] The hot-rolled sheet was annealed at 1000°C for 60 seconds, then cooled from 800°C to 300°C at a rate of 20°C / s, and finally wound into coils. The annealed hot-rolled sheet was then cold-rolled in one pass using a continuous rolling mill (300mm roll diameter, 5 stands) to produce a cold-rolled sheet with a final thickness of 0.20mm. At this time, the steel sheet (hot-rolled sheet) from the uncoiler was heated to the heating temperatures shown in Table 1 by a heating device located between the uncoiler and the first pass of the rolling mill. After heating, two types of coils were produced: coils where the steel sheet was bitten into the first pass of the rolling mill at the same temperature, and coils where the steel sheet was cooled to room temperature (25°C) before being bitten into the first pass of the rolling mill. Additionally, coils where the steel sheet was not heated and was bitten into the first pass of the rolling mill at room temperature were also produced.

[0021] Then, after performing decarburization annealing on the above-mentioned cold-rolled sheet at a homogenization temperature of 840°C and a homogenization time of 100 seconds, which also serves as a recrystallization annealing, an annealing separating agent with MgO as the main component is coated on the surface of the steel sheet, followed by a second recrystallization annealing.

[0022] The steel plate after the above-mentioned secondary recrystallization annealing is coated with a coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2, and then subjected to planarization annealing at 800℃ for 30 seconds to produce product coils.

[0023] The iron loss of 10 rolls manufactured under the same conditions was measured, and their average value and standard deviation were determined. The iron loss was measured by cutting a sample from the center of the roll length with a total weight of 500g or more and performing an Epstein test. The average value and standard deviation of the iron loss are shown in Table 1.

[0024]

[0025] As shown in Table 1, when the steel sheet is heated to a temperature range of 70°C to 200°C before being introduced into the first pass of the continuous rolling mill for cold rolling, the deviation in iron loss of the coil is small. Furthermore, as shown in Table 1, when the heated steel sheet is cooled before being introduced into the first pass of the continuous rolling mill for cold rolling, the iron loss becomes low.

[0026] The mechanism by which the iron loss was reduced and the iron loss deviation was improved as shown in the above experimental results is still unclear, but the inventors believe the following. The mechanism by which the iron loss deviation is improved is believed to be because: during cold rolling, the steel sheet is heated once from the uncoiler before the first bite, so the time from heat treatment to the first bite is constant among 10 coils, and the time-dependent changes of fine carbides precipitated during heat treatment (heating before bite) are temporarily suppressed.

[0027] Furthermore, the mechanism for achieving low iron loss during the cooling of the steel sheet before the first pass after heating is considered as follows: It is believed that the primary recrystallized Gaussian-oriented grains nucleate from shear bands introduced into the {111}<112> matrix structure, which is one of the stable orientations during rolling. As shown in the above experiments, it is believed that by heating the steel sheet to induce fine carbide precipitation and setting the bite temperature to a low level, the {111}<112> matrix structure is formed through this low-temperature rolling process. Simultaneously, the formation of shear bands is locally promoted by the fine carbides, thereby effectively increasing the number of Gaussian-oriented grains.

[0028] Based on these insights, further research was conducted, leading to the completion of this invention.

[0029] That is, the main idea of ​​this invention is as follows.

[0030] [1] A method for manufacturing an oriented electromagnetic steel sheet includes the following steps: hot rolling a steel billet to produce a hot-rolled sheet; cold rolling once or twice or more with intermediate annealing to produce a cold-rolled sheet with a final sheet thickness; then decarburizing annealing the cold-rolled sheet; and then performing secondary recrystallization annealing.

[0031] The final cold rolling is performed using a continuous rolling mill. This final cold rolling involves heating the hot-rolled plate to a temperature range of 70°C to 200°C, then cooling it to below 60°C, and finally feeding it into the first pass of the continuous rolling mill.

[0032] [2] According to the manufacturing method of the oriented electromagnetic steel sheet described in [1] above, the steel billet has the following composition: C: 0.01-0.10%, Si: 2.0-4.5%, Mn: 0.01-0.5%, Al: 0.01-0.04%, S: 0.01-0.05%, Se: 0.01-0.05% and N: 0.0050-0.012% by mass, with the remainder being Fe and unavoidable impurities.

[0033] [3] According to the manufacturing method of the oriented electromagnetic steel sheet described in [1] above, the steel billet has the following composition: by mass % containing: C: 0.01 to 0.10%, Si: 2.0 to 4.5%, Mn: 0.01 to 0.5%, Al: less than 0.0100%, S: less than 0.0070%, Se: less than 0.0070%, and N: less than 0.0050%, with the remainder being Fe and unavoidable impurities.

[0034] [4] The method for manufacturing the oriented electromagnetic steel sheet according to [2] or [3] above, wherein the steel billet further contains, by mass %, one or more of the following: Sb: 0.005-0.50%, Cu: 0.01-1.50%, P: 0.005-0.50%, Cr: 0.01-1.50%, Ni: 0.005-1.50%, Sn: 0.01-0.50%, Nb: 0.0005-0.0100%, Mo: 0.01-0.50%, B: 0.0010-0.007%, and Bi: 0.0005-0.05%.

[0035] [5] A rolling equipment for manufacturing electromagnetic steel sheets, wherein a heating device and a cooling device are provided on the inlet side of the first stand of a continuous rolling mill for manufacturing electromagnetic steel sheets.

[0036] Here, "final cold rolling" refers to the cold rolling process in which the thickness of the steel sheet becomes the final sheet thickness. Specifically, in one or more cold rolling processes with intermediate annealing, "final cold rolling" refers to the cold rolling process in the single-process method and "second cold rolling" refers to the second cold rolling process in the double-process method.

[0037] According to the present invention, it is possible to stably manufacture oriented electromagnetic steel sheets with excellent magnetic properties using a continuous rolling mill while suppressing iron loss deviation between coils. Attached Figure Description

[0038] Figure 1A This is a partial schematic diagram of the rolling equipment applicable to the present invention.

[0039] Figure 1B This is a partial schematic diagram of the rolling equipment applicable to the present invention. Detailed Implementation

[0040] The present invention will be described in detail below.

[0041] <Steel billet>

[0042] In addition to slabs, blooms and billets can also be used as the steel billet material in the manufacturing method of this invention. For example, steel billets manufactured by known manufacturing methods can be used. Examples of manufacturing methods include steelmaking-continuous casting and billet-segment rolling. In steelmaking, molten steel obtained from converters, electric furnaces, etc., can be refined to the desired composition through secondary refining such as vacuum degassing.

[0043] The composition of the steel billet can be that used in the manufacture of oriented electromagnetic steel sheets, and the components used in oriented electromagnetic steel sheets can be well-known. From the viewpoint of manufacturing oriented electromagnetic steel sheets with excellent magnetic properties, it is preferable to contain C, Si, and Mn. Preferred contents of C, Si, and Mn are as follows. Here, unless otherwise stated, "%" in relation to composition means "mass %".

[0044] C: 0.01~0.10%

[0045] Carbon (C) is an element required to improve the texture of primary recrystallization by precipitating fine carbides. If the C content exceeds 0.10%, it is difficult to reduce it to below 0.0050% to avoid magnetic aging caused by decarburization annealing. On the other hand, if it is less than 0.01%, the amount of fine carbide precipitation is insufficient, and the texture improvement effect is inadequate. Therefore, the C content is preferably 0.01 to 0.10%, and more preferably 0.01 to 0.08%.

[0046] Si: 2.0–4.5%

[0047] Si is an effective element for increasing the electrical resistance of steel and improving iron loss. If the Si content exceeds 4.5%, the workability is significantly reduced, making rolling difficult. On the other hand, if it is less than 2.0%, it is difficult to obtain a sufficient reduction in iron loss. Therefore, the Si content is preferably 2.0 to 4.5%, more preferably 2.5 to 4.5%.

[0048] Mn: 0.01~0.5%

[0049] Mn is an element required to improve hot workability. If the Mn content exceeds 0.5%, the primary recrystallization texture deteriorates, making it difficult to obtain secondary recrystallized grains with a highly integrated Gaussian orientation. On the other hand, if it is less than 0.01%, sufficient hot rolling workability is difficult to obtain. Therefore, the Mn content is preferably 0.01 to 0.5%, more preferably 0.03 to 0.5%.

[0050] In addition to C, Si, and Mn, the composition of the steel billet may also contain Al: 0.01–0.04% and N: 0.0050–0.012% as inhibitors in secondary recrystallization. That is, if the Al and N contents are below the lower limits mentioned above, it may be difficult to obtain the specified inhibitory effect; on the other hand, if they exceed the upper limits mentioned above, the dispersion of the precipitates may become uneven, and it may still be difficult to obtain the specified inhibitory effect.

[0051] Furthermore, in addition to Al and N, as inhibitory components, it may also contain S: 0.01–0.05% and Se: 0.01–0.05%. The presence of these components allows the formation of sulfides (MnS, Cu₂S, etc.) and selenides (MnSe, Cu₂Se, etc.). Sulfides and selenides can also precipitate in combination. Here, if the S and Se contents are below the aforementioned lower limits, it is difficult to achieve a sufficient inhibitory effect. On the other hand, if they exceed the aforementioned upper limits, the dispersion of the precipitates becomes uneven, and the inhibitory effect still cannot be fully achieved.

[0052] In addition, as a component composition, the Al content can be suppressed to less than 0.0100%, which is suitable for inhibitor-free systems. In this case, the composition can be N: less than 0.0050%, S: less than 0.0070%, and Se: less than 0.0070%.

[0053] Furthermore, in order to improve magnetic properties, in addition to the above-mentioned composition, one or more elements selected from Sb: 0.005–0.50%, Cu: 0.01–1.50%, P: 0.005–0.50%, Cr: 0.01–1.50%, Ni: 0.005–1.50%, Sn: 0.01–0.50%, Nb: 0.0005–0.0100%, Mo: 0.01–0.50%, B: 0.0010–0.007%, and Bi: 0.0005–0.05% may be included. Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi are elements useful for improving magnetic properties. From the viewpoint of not hindering the development of secondary recrystallized grains and fully obtaining the effect of improving magnetic properties, when included, the above-mentioned ranges are preferred.

[0054] It should be noted that the remaining components in the steel billet composition, besides the components mentioned above, are Fe and unavoidable impurities.

[0055] <Manufacturing Process>

[0056] In the manufacturing method of the present invention, steel billets and other steel blanks are hot-rolled to produce hot-rolled plates. The steel billets may be heated before hot rolling. From the viewpoint of ensuring hot rollability, the heating temperature is preferably around 1050°C or higher. There is no particular upper limit to the heating temperature, but temperatures exceeding 1450°C are close to the melting point of steel, making it difficult to maintain the shape of the steel billets and other steel blanks; therefore, temperatures below 1450°C are preferred.

[0057] There are no special restrictions on hot rolling conditions other than those specified; well-known conditions can be applied.

[0058] The obtained hot-rolled sheet can be subjected to hot-rolled annealing. Especially when the subsequent cold rolling is only once, hot-rolled annealing is preferred. In addition, depending on the situation, descaling can also be performed by pickling or other methods after hot-rolled annealing and before cold rolling.

[0059] Then, the hot-rolled sheet (the hot-rolled sheet after annealing) is cold-rolled once to produce a cold-rolled sheet of the final thickness, or it is cold-rolled twice or more with intermediate annealing to produce a cold-rolled sheet of the final thickness. The total reduction rate of the cold rolling is not particularly limited and can be 70% to 95%. The final reduction rate of the cold rolling is not particularly limited and can be 60% to 95%. The final sheet thickness is not particularly limited and can be, for example, 0.1 mm to 1.0 mm.

[0060] The highest temperature in the final annealing before cold rolling, i.e., the annealing of the hot-rolled plate during the first cold rolling and the intermediate annealing during the second or more cold rolling, is preferably 900°C to 1200°C. Furthermore, the average cooling rate in the cooling process of the final annealing before cold rolling, within a temperature range of 800°C to 300°C, is preferably 15°C / s or more. More preferably, it is 20°C / s or more.

[0061] The final cold rolling is performed using a continuous rolling mill. Here, before the steel sheet (hot-rolled sheet) is fed from the uncoiler and introduced into the first pass of the continuous rolling mill, it is heated to a temperature range of 70°C to 200°C, and then cooled to below 60°C. That is, the temperature of the steel sheet introduced into the first pass of the continuous rolling mill is below 60°C. Since the fine carbides precipitated during the above heating may coarsen, the cooling is preferably performed within 30 seconds after heating, more preferably within 15 seconds. It should be noted that rolling other than the final cold rolling, i.e., the first cold rolling in the two-stage process, can be performed using a continuous rolling mill or a reversible rolling mill like Sendzimir.

[0062] If the heating temperature is below 70°C, fine carbides will not be fully precipitated. On the other hand, if the heating temperature exceeds 200°C, the carbon diffusion rate becomes too high, and coarse carbides precipitate, thereby eliminating the effect of improving texture through strain aging and deteriorating the magnetic properties. The preferred heating temperature is 100°C to 170°C.

[0063] If the cooling temperature after heating exceeds 60°C, the formation of the {111}<112> matrix structure becomes insufficient, and the effect of improving texture through heating is lost. It should be noted that no lower limit is specifically set, but if it is below 0°C, the material becomes brittle, which adversely affects manufacturability. Therefore, the steel plate temperature at the time of the first pass is preferably above 0°C.

[0064] In order to form a {111}<112> matrix structure in the first pass of the final cold rolling and to suppress shear deformation during rolling, the work roll roughness of the first pass (first stand) of the continuous rolling mill is preferably low. Specifically, the arithmetic mean roughness Ra of the first pass of the continuous rolling mill is preferably 1.0 μm or less, more preferably 0.5 μm or less.

[0065] The heating method described above is not particularly limited, and examples include air bath, oil bath, sand bath, induction heating, spraying heated lubricating oil onto the steel plate, and heated water. However, since the heating is carried out on the inlet side of the continuous rolling mill, a method that can heat the steel plate in a short time is preferred. It should be noted that the heating temperature refers to the temperature of the steel plate at the outlet side of the heating device.

[0066] The cooling method described above after heating is not particularly limited, and examples include spraying coolant onto the steel plate, cooling rollers, oil baths, etc. However, since cooling is carried out on the inlet side of the continuous rolling mill, cooling needs to be carried out in a short time. As a cooling method, there are methods as described above, but it is preferable to be able to independently control the temperature of the heat removal medium so that the steel plate can be cooled to the desired temperature before the first pass.

[0067] Heat treatments such as aging or warm rolling can be inserted into cold rolling, but it is preferable to divide the final rolling into two parts, a first half and a second half, as described in Patent Document 4 above, with the first half rolled at a low temperature and the second half rolled at a high temperature.

[0068] In the manufacturing method of this invention, a cold-rolled sheet having a final thickness can be subjected to decarburization annealing followed by secondary recrystallization annealing to obtain an oriented electromagnetic steel sheet. An insulating film can be applied after the secondary recrystallization annealing.

[0069] There are no particular limitations on the conditions for decarburization annealing. Decarburization annealing is generally combined with a recrystallization annealing, and it can also be combined with a recrystallization annealing in the manufacturing method of the present invention. In this case, there are no particular limitations on the conditions, and known conditions can be applied. For example, annealing conditions of 800°C for 2 minutes in a warm hydrogen atmosphere can be cited.

[0070] After decarburization annealing, the cold-rolled sheet undergoes a final annealing process for secondary recrystallization (secondary recrystallization annealing). Before the final annealing, an annealing separating agent can be applied to the surface of the steel sheet. There are no particular limitations on the annealing separating agent; any known annealing separating agent can be used. Examples include annealing separating agents with MgO as the main component and, if necessary, TiO2, etc., added; and annealing separating agents with SiO2 and Al2O3 as the main components.

[0071] After secondary recrystallization annealing, it is preferable to coat the steel plate surface with an insulating film and then sinter it. Planarization annealing is then performed as needed to adjust the shape of the steel plate. There is no particular limitation on the type of insulating film. When forming an insulating film that imparts tensile tension on the steel plate surface, it is preferable to use a coating solution containing phosphate-colloidal silica as described in Japanese Patent Application Publication Nos. 50-79442, 48-39338, and 56-75579, and sinter at around 800°C.

[0072] <Rolling equipment for manufacturing electromagnetic steel sheets>

[0073] Furthermore, the rolling equipment for manufacturing electromagnetic steel sheets of the present invention includes a heating device and a cooling device on the inlet side of the first stand of the continuous rolling mill for manufacturing electromagnetic steel sheets. With such equipment, the aforementioned orientation-oriented electromagnetic steel sheets can be manufactured stably.

[0074] Figure 1A This is a partial schematic diagram of the aforementioned rolling equipment. Figure 1A In the illustrated equipment, a heating device 1 and a cooling device 2 are installed from the upstream side at the entrance side of the first pass (first stand) of the rolling mill (rolls) 4. With this configuration, the steel strip 3 (hot-rolled plate) about to be introduced into the rolling mill can be heated by the heating device 1 and then cooled by the cooling device 2. It should be noted that... Figure 1B As shown, a temperature control device 5 that can control the temperature of the heat removal medium in the cooling device 2 can also be installed in the rolling equipment.

[0075] Example

[0076] (Example 1)

[0077] A steel billet with the following composition is heated to 1210°C and then hot-rolled to produce a hot-rolled plate with a thickness of 2.0 mm. The composition contains C: 0.037 wt%, Si: 3.4 wt%, and Mn: 0.05 wt%, and contains 31 wt ppm of S and Se, 50 wt ppm of N, 85 wt ppm of sol.Al, with the remainder being Fe and unavoidable impurities.

[0078] The hot-rolled sheet was annealed at 1000°C for 60 seconds, then cooled from 800°C to 300°C at a rate of 15°C / s, and then wound into a coil. The hot-rolled sheet after annealing was then cold-rolled once using a continuous rolling mill (300mm roll diameter, 5 stands) to produce a cold-rolled sheet with a final thickness of 0.20mm. At this time, the steel sheet (hot-rolled sheet) was heated to 150°C using a heating device located between the uncoiler and the first pass of the rolling mill. After heating, it was cooled to the temperature shown in Table 2 (the first pass induction temperature) and then bit into the first pass of the rolling mill. It should be noted that the work roll roughness (arithmetic mean roughness Ra) for the first pass was 1.5μm in conditions No. 26–34 of Table 2, and 0.9μm in conditions No. 35–37 of Table 2.

[0079] Then, after performing decarburization annealing on the above-mentioned cold-rolled sheet at a homogenization temperature of 840°C and a homogenization time of 100 seconds, which also serves as a recrystallization annealing, an annealing separating agent with MgO as the main component is coated on the surface of the steel sheet, followed by a second recrystallization annealing.

[0080] The steel plate after the above-mentioned secondary recrystallization annealing is coated with a coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2, and then subjected to planarization annealing at 800℃ for 30 seconds to produce product coils.

[0081] For the product rolls, the iron loss of 10 rolls manufactured under the same conditions was measured, and their average value and standard deviation were calculated. The iron loss was measured by cutting a sample from the center of the length of the roll with a total weight of 500g or more and performing an Epstein test. The average value and standard deviation of the iron loss are shown in Table 2.

[0082]

[0083] As shown in Table 2, materials (coiled materials) introduced into the first pass at a temperature below 60°C after heating exhibit low iron loss. Furthermore, it can be seen that materials with low work roll roughness (arithmetic mean roughness Ra) in the first pass exhibit even lower iron loss.

[0084] (Example 2)

[0085] A steel billet with the following composition is heated to 1400°C and then hot-rolled to produce a hot-rolled plate with a thickness of 2.0 mm. The composition contains C: 0.06 wt%, Si: 3.4 wt%, and Mn: 0.06 wt%, N: 90 wt ppm, sol.Al: 250 wt ppm, S and Se: 0.02 wt%, and the remainder is Fe and unavoidable impurities.

[0086] The hot-rolled sheet was subjected to hot-rolled annealing at 1000°C for 60 seconds. Following the hot-rolled annealing, the hot-rolled sheet underwent a first cold rolling process using a continuous rolling mill (300mm roll diameter, 5 stands). This was followed by an intermediate annealing at 1100°C for 80 seconds in an atmosphere of N2: 75 vol% + H2: 25 vol% and a dew point of 46°C. During the subsequent cooling process, the sheet was cooled from 800°C to 300°C at a rate of 20°C / s. Finally, a final cold rolling process was performed using a continuous rolling mill (300mm roll diameter, 5 stands) to produce a cold-rolled sheet with a final thickness of 0.25mm. During the final cold rolling, the steel sheet was heated to the heating temperatures shown in Table 3 via a heating device located between the uncoiler and the first pass of the rolling mill. It was then cooled to the temperature shown in Table 3 (the first pass induction temperature) and then bitten into the first pass of the rolling mill.

[0087] Then, after performing decarburization annealing on the above-mentioned cold-rolled sheet at a homogenization temperature of 840°C and a homogenization time of 100 seconds, which also serves as a recrystallization annealing, an annealing separating agent with MgO as the main component is coated on the surface of the steel sheet, followed by a second recrystallization annealing.

[0088] The steel plate after the above-mentioned secondary recrystallization annealing is coated with a coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2, and then subjected to planarization annealing at 800℃ for 30 seconds to produce product coils.

[0089] For the product rolls, the iron loss of 10 rolls manufactured under the same conditions was measured, and their average value and standard deviation were calculated. The iron loss was measured by cutting a sample from the center of the length of the roll with a total weight of 500g or more and performing an Epstein test. The average value and standard deviation of the iron loss are shown in Table 3.

[0090]

[0091] As shown in Table 3, even when using billets with a large amount of added inhibitors and performing cold rolling with intermediate annealing, the iron loss is good and the deviation is small.

[0092] (Example 3)

[0093] The steel with the following composition is melted, made into a billet, heated to 1210°C, and then hot-rolled to produce a hot-rolled plate with a thickness of 2.0 mm. The composition contains C: 0.036 wt%, Si: 3.4 wt%, and Mn: 0.06 wt%, N: 50 wt ppm, sol.Al: 72 wt ppm, S: 31 wt ppm, and Se: 31 wt ppm each. Other components include Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi as shown in Table 4, with the remainder being Fe and unavoidable impurities.

[0094] The hot-rolled sheet is annealed at 1000°C for 60 seconds, then cooled from 800°C to 300°C at a rate of 50°C / s, and then wound into a coil. The hot-rolled sheet after annealing is then cold-rolled once using a continuous rolling mill (300mm roll diameter, 5 stands) to produce a cold-rolled sheet with a final thickness of 0.30mm. At this point, the steel sheet (hot-rolled sheet) is heated to 150°C using a heating device located between the uncoiler and the first pass of the rolling mill. After heating, it is cooled to 25°C and then bitten into the first pass of the rolling mill.

[0095] Then, after performing decarburization annealing on the above-mentioned cold-rolled sheet at a homogenization temperature of 840°C and a homogenization time of 100 seconds, which also serves as a recrystallization annealing, an annealing separating agent with MgO as the main component is coated on the surface of the steel sheet, followed by a second recrystallization annealing.

[0096] The steel plate after the above-mentioned secondary recrystallization annealing is coated with a coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2, and then subjected to planarization annealing at 800℃ for 30 seconds to produce product coils.

[0097] For the product rolls, the iron loss of 10 rolls manufactured under the same conditions was measured, and their average value and standard deviation were calculated. The iron loss was measured by cutting a sample from the center of the length of the roll with a total weight of 500g or more and performing an Epstein test. The average value and standard deviation of the iron loss are shown in Table 4.

[0098]

[0099] As shown in Table 4, the iron loss of steel plates with one or more of Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi is below 0.84 W / kg. In particular, the iron loss is reduced and the characteristic deviation in the length direction of the coil is also small.

[0100] Symbol Explanation

[0101] 1. Heating device

[0102] 2. Cooling device

[0103] 3 steel strip

[0104] 4. Rolling rolls (rolling mill stand)

[0105] 5. Temperature control device

Claims

1. A method for manufacturing an oriented electromagnetic steel sheet, comprising the following steps: hot rolling a steel billet to produce a hot-rolled sheet; performing one cold rolling or two or more cold rollings with intermediate annealing to produce a cold-rolled sheet with a final sheet thickness; then performing decarburization annealing on the cold-rolled sheet; and finally performing secondary recrystallization annealing. The final cold rolling is performed using a continuous rolling mill. This final cold rolling involves heating the hot-rolled plate to a temperature range of 70°C to 200°C, and then cooling it to below 60°C within 30 seconds after heating by a cooling method selected from spraying coolant onto the steel plate, cooling rollers, and an oil bath. The plate is then introduced into the first pass of the continuous rolling mill.

2. The method of producing an oriented electromagnetic steel sheet according to claim 1, wherein The steel billet has the following composition: by mass % C: 0.01-0.10%, Si: 2.0-4.5%, Mn: 0.01-0.5%, Al: 0.01-0.04%, S: 0.01-0.05%, Se: 0.01-0.05%, and N: 0.0050-0.012%, with the remainder being Fe and unavoidable impurities.

3. The method of producing an oriented electromagnetic steel sheet according to claim 1, wherein The steel billet has the following composition: by mass % C: 0.01-0.10%, Si: 2.0-4.5%, Mn: 0.01-0.5%, Al: less than 0.0100%, S: less than 0.0070%, Se: less than 0.0070%, and N: less than 0.0050%, with the remainder being Fe and unavoidable impurities.

4. The method of producing an oriented electromagnetic steel sheet according to claim 2 or 3, wherein The steel billet further contains, by mass%, one or more of the following: Sb: 0.005–0.50%, Cu: 0.01–1.50%, P: 0.005–0.50%, Cr: 0.01–1.50%, Ni: 0.005–1.50%, Sn: 0.01–0.50%, Nb: 0.0005–0.0100%, Mo: 0.01–0.50%, B: 0.0010–0.007%, and Bi: 0.0005–0.05%.

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