Method for producing grain-oriented electrical steel sheet

Abstract

When manufacturing a oriented electrical steel sheet by heating a steel slab containing, in mass%, C: 0.020–0.10%, Si: 2.0–4.0%, Mn: 0.005–0.50%, Al: less than 0.010%, and N, S, and Se each less than 0.0050% to a temperature of 1280°C or lower, hot rolling, hot-rolled sheet annealing, two or more cold rollings with one cold rolling or intermediate annealing in between, primary recrystallization annealing combined with decarburization annealing, applying an annealing separating agent to the surface of the steel sheet, finishing annealing, and flattening annealing, in any one or more of the annealing of the hot-rolled sheet annealing and intermediate annealing, from 800°C to 300°C during the cooling process from the maximum reached temperature By rapidly cooling the material at an average cooling rate of 200 ℃ / s or more, a directional electrical steel sheet with excellent magnetic properties is stably obtained.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a oriented electrical steel sheet suitable for use as a core material for transformers, etc. Background Technology

[0002] Grained electrical steel is a soft magnetic material used as a core material for transformers or generators, and is characterized by excellent magnetic properties because it has a crystal structure in which the <001> orientation, which is the easy magnetization axis of iron, is highly aligned in the rolling direction of the steel sheet. The above crystal structure is formed by preferentially recrystallizing and growing the {110} <001> orientation grains, referred to as the so-called Goss orientation, during the finishing annealing process of the manufacturing process of grained electrical steel.

[0003] As a method for inducing the above secondary recrystallization, a technique using a precipitate called an inhibitor is generally used. For example, Patent Document 1 discloses a method using AlN or MnS as an inhibitor, and Patent Document 2 discloses a method using MnS or MnSe as an inhibitor, and these methods have been commercialized industrially.

[0004] However, while the method of using these inhibitors is very useful for stably developing secondary recrystallized grains, in order to finely disperse the inhibitors in the steel, it is necessary to heat the slab to a high temperature of 1300°C or higher and dissolve the inhibitor-forming components once. In addition, since the inhibitor-forming components cause the deterioration of magnetic properties after secondary recrystallization, it is necessary to perform a purification treatment to remove precipitates and inclusions such as inhibitors from the iron under a controlled atmosphere at a high temperature of 1100°C or higher.

[0005] Meanwhile, Patent Document 3 and others disclose a method for inducing secondary recrystallization and developing Goss orientation grains using a material that does not contain inhibitor-forming components. This method is a technique that enables secondary recrystallization of Goss orientation grains without using inhibitors by maximally excluding impurities such as inhibitor components, thereby realizing the dependence of the grain boundary energy of the primary recrystallized grains on the grain boundary orientation difference angle; the effect is called the "texture inhibition effect." Since this method does not require fine dispersion of the inhibitor within the steel, high-temperature slab heating, which was previously essential, becomes unnecessary, thus offering significant advantages in terms of fuel costs and equipment maintenance.

[0006] However, in the method of using a material that does not contain inhibitor-forming components, controlling the texture becomes very important as the inhibitor is not utilized. As for techniques for controlling the texture, for example, Patent Document 4 proposes a method to control carbides precipitated during cooling by accelerating the cooling rate of hot-rolled sheet annealing, and to improve the texture of the primary recrystallized annealed sheet after cold rolling. However, in the examples of this patent document, the cooling rate is up to 70 ℃ / s, and rapid cooling such as 100 ℃ / s or higher is not performed. This is presumed to be because it was thought that a cooling rate of less than 100 ℃ / s was sufficient for controlling carbides, and also because there was no cooling device capable of realizing a cooling rate higher than that.

[0007] However, recently, the development of cooling technology for thin steel sheets has been progressing. For example, Patent Document 5 discloses a rapid cooling quenching device capable of suppressing shape defects occurring in the metal sheet during rapid cooling quenching and suppressing a decrease in the cooling rate of the metal sheet in a continuous annealing facility that performs annealing while continuously passing metal sheets. This rapid cooling quenching device aims to control the microstructure by rapid cooling and obtain a high-strength steel sheet with a desired strength. However, since there is no need to obtain high strength in oriented electrical steel sheets, the above rapid cooling has not been applied. Prior art literature

[0008] Japanese Patent Publication No. Sho 40-015644, Japanese Patent Publication No. Sho 51-013469, Japanese Published Patent Application No. 2000-129356, Japanese Published Patent Application No. 2012-077380, Japanese Published Patent Application No. 2018-066065 The problem to be solved

[0009] Therefore, the objective of the present invention is to propose a method for manufacturing a oriented electrical steel sheet that can stably obtain a oriented electrical steel sheet with excellent magnetic properties while maintaining advantages in terms of manufacturability and manufacturing cost by applying the rapid cooling technology to the manufacture of a oriented electrical steel sheet using a material that does not contain inhibitor-forming components. means of solving the problem

[0010] The inventors repeatedly examined the effect of cooling rates, such as hot-rolled sheet annealing, on the magnetic properties of oriented electrical steel sheets. As a result, they discovered that in a method for manufacturing oriented electrical steel sheets using a material that does not contain inhibitor-forming components, by increasing the cooling rate of hot-rolled sheet annealing or intermediate annealing prior to cold rolling compared to conventional technology—specifically, by increasing the cooling rate from 800°C to 300°C to 200°C / s or higher—the slip system of dislocations during cold rolling changes, and as a result, the primary recrystallization texture is improved, leading to a significant improvement in magnetic properties, and thus they developed the present invention.

[0011] That is, the present invention relates to a method for manufacturing an oriented electrical steel sheet comprising a series of processes including heating a steel slab having a composition comprising C: 0.020 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.004 to 0.50 mass%, and also containing Al: less than 0.010 mass%, N, S, and Se each less than 0.0050 mass%, with the remainder being Fe and unavoidable impurities, to a temperature of 1280°C or lower, hot rolling to form a hot-rolled sheet, performing annealing of the hot-rolled sheet, performing cold rolling two or more times with an intermediate annealing in between to form a cold-rolled sheet of final thickness, performing primary recrystallization annealing combined with decarburization annealing, applying an annealing separating agent to the surface of the steel sheet, performing finish annealing, and performing flattening annealing, wherein the hot-rolled sheet A method for manufacturing a oriented electrical steel sheet is proposed, characterized by rapidly cooling from 800°C to 300°C from the maximum reached temperature at an average cooling rate of 200°C / s or more during one or more of annealing, including annealing and intermediate annealing.

[0012] The method for manufacturing the oriented electrical steel sheet of the present invention is characterized by, following the rapid cooling, cooling from 300°C to 100°C at an average cooling rate in the range of 5 to 40°C / s.

[0013] In addition, the method for manufacturing the oriented electrical steel sheet of the present invention is characterized by having a heating rate of 500 to 700 ℃ at a rate of 500 ℃ / s or higher during the heating process of the primary recrystallization annealing combined with the decarburization annealing.

[0014] In addition, the method for manufacturing the oriented electrical steel sheet of the present invention is characterized in that, in the heating process of the finishing annealing, a preservation treatment is performed by maintaining the material at any temperature between 800 and 950°C for 5 to 200 hours, or by heating the material between 800 and 950°C at an average heating rate of 5°C / hr or less to induce secondary recrystallization, and additionally, the material is heated to a temperature of 1100°C or higher to complete secondary recrystallization, and then maintained at that temperature for 2 hours or more for purification treatment.

[0015] In addition, the steel slab used in the method for manufacturing the oriented electrical steel sheet of the present invention comprises, in addition to the above component composition, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, Ni: 0.01 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, B: 0.0002 to 0.0025 mass%, Nb: 0.0010 to 0.0100 mass%, Sn: 0.010 to 0.400 mass%, Sb: 0.010 to 0.150 mass%, Mo: 0.010 to 0.200 mass%, P: 0.010 to 0.150 mass%, V: 0.0005 to 0.0100 mass%, and Ti: It is characterized by containing one or more types selected from 0.0005 to 0.0100 mass%. Effects of the invention

[0016] According to the present invention, since oriented electrical steel sheets with excellent magnetic properties can be manufactured cheaply and stably while maintaining advantages in terms of manufacturability and manufacturing costs by using a material that does not contain inhibitor-forming components, the industrial effect is significant. Specific details for implementing the invention

[0017] First, I will explain the experiment that served as the impetus for inventing the present invention.

[0018] <Experiment 1>

[0019] A steel having a composition of C: 0.045 mass%, Si: 3.0 mass%, Mn: 0.05 mass%, Al: 0.0050 mass%, N: 0.0030 mass%, and S: 0.0020 mass%, with the remainder being Fe and unavoidable impurities, was melted in a vacuum melting furnace and cast to form a steel ingot. The steel ingot was then heated to a temperature of 1250 ℃ and hot-rolled to form a hot-rolled plate with a thickness of 2.0 mm. Subsequently, the hot-rolled plate was subjected to hot-rolled plate annealing with a maximum reached temperature of 1000 ℃. At that time, the cooling process of the hot-rolled sheet annealing from 1000°C to room temperature was divided into three sections as shown in Table 1: between 1000°C and 800°C, between 800°C and 300°C, and between 300°C and 100°C, and the cooling was performed by varying the average cooling rate of each section. Afterward, the sheet was cold-rolled to be finished as a cold-rolled sheet with a thickness of 0.23 mm, and then a first recrystallization annealing combined with decarburization annealing was performed under a humid atmosphere of 50 vol% H2 - 50 vol% N2 and a dew point of 50°C, with a cracking temperature of 850°C × a cracking time of 100 s. Next, an annealing separator based on MgO was applied to the surface of the steel plate, and secondary recrystallization was induced by heating at a heating rate of 30 ℃ / hr between 800 ℃ and 950 ℃ (without correction), and then secondary recrystallization was completed by heating to 1200 ℃ at a heating rate of 20 ℃ / hr between 950 ℃ and 1050 ℃, followed by a finishing annealing treatment in which the plate was maintained at that temperature for 5 hours under a hydrogen atmosphere.

[0020] Samples were taken from the steel sheet after finishing annealing obtained in this way, and the magnetic flux density B8 (magnetic flux density when excited at 800 A / m) was measured using the method described in JIS C2550, and the results are shown in Table 1. From these results, it was found that during the cooling process of hot-rolled sheet annealing, the magnetic flux density is greatly improved by rapidly cooling at an average speed of 200 ℃ / s or more from 800 ℃ to 300 ℃.

[0021]

[0022] In the case where a material that does not contain inhibitor-forming components is used, the mechanism by which magnetic flux density is improved by increasing the average cooling rate from 800 to 300 ℃ to 200 ℃ / s or higher during the cooling process of hot-rolled sheet annealing, as described above, has not yet been fully elucidated, but the inventors believe as follows.

[0023] The temperature range of 800 to 300°C during the cooling process of hot-rolled sheet annealing is a temperature range that significantly affects the precipitation state of carbides, and conventionally, cooling to about 100°C / s has been carried out for the purpose of increasing solid solution C or fine carbides. However, the mechanism for improving magnetic properties in this case is thought to be different from that caused by the increase in solid solution C or fine carbides.

[0024] Steel sheets subjected to hot-rolled annealing are in the pre-decarburization annealing (primary recrystallization annealing) stage and have a high carbon content; consequently, heating during annealing causes a portion of the material to undergo reverse transformation, changing from the α phase to the γ phase. The transformed γ phase and the surrounding α phase have different crystal structures (γ phase is FCC, α phase is BCC) and different coefficients of thermal expansion. Under these conditions, if rapid cooling is performed at a rate of 200 ℃ / s or higher, the γ phase does not transform into the α phase due to supercooling and remains in its original state after shrinking. Consequently, due to the difference in coefficients of thermal expansion, deformation different from the usual occurs at the phase interface between the γ phase and the α phase. As a result, it is believed that magnetic properties were improved as the sliding system of dislocations in the cold rolling of the next process changed, the {411} orientation grains of the steel sheet after the first recrystallization annealing (decarburization annealing) increased, and the texture was improved. In addition, it is thought that deformation occurs at the phase interface even at a cooling rate of 100 ℃ / s or less, but as the cooling rate is slow, the deformation is easily relieved, and it is thought that the above effect was not sufficiently obtained.

[0025] Meanwhile, regarding cooling from 300°C to 100°C following the rapid cooling mentioned above, additional improvement in magnetic properties was confirmed in the range of an average cooling rate of 5 to 40°C / s. This is thought to be due to the fact that by performing slow cooling as described above, the remaining γ phase undergoes martensitic transformation, introducing higher strain and further improving the primary recrystallization texture. Although it is well known that the γ phase undergoes martensitic transformation by rapid cooling, it is thought that when cooling to less than 100°C with rapid cooling of 200°C / s or more, the γ phase is supercooled, making it difficult to even cause martensitic transformation.

[0026] <Experiment 2>

[0027] A steel having a composition of C: 0.060 mass%, Si: 3.2 mass%, Mn: 0.1 mass%, Al: 0.080 mass%, N: 0.0045 mass%, S: 0.0010 mass%, and Se: 0.0030 mass%, with the remainder being Fe and unavoidable impurities, was melted in a vacuum melting furnace and cast to form a steel ingot. The steel ingot was then heated to a temperature of 1200°C and hot-rolled to form a hot-rolled plate with a thickness of 2.5 mm. Subsequently, the hot-rolled plate was subjected to hot-rolled plate annealing with a maximum reached temperature of 1050°C, cold-rolled once to an intermediate plate thickness of 1.5 mm, and intermediate annealing was performed with a maximum reached temperature of 1050°C. At this time, during the cooling process from 1050 ℃ to room temperature in the intermediate annealing, the average cooling rate between 1050 ℃ and 800 ℃ was set to 10 ℃ / s, and the average cooling rate between 300 ℃ and 100 ℃ was set to 30 ℃ / s. Additionally, the average cooling rate between 800 ℃ and 300 ℃ in the above temperature range was varied as shown in Table 2. Afterward, the second cold rolling (final cold rolling) was performed to finish the cold-rolled sheet with a final thickness of 0.20 mm. Then, a first recrystallization annealing combined with decarburization annealing was performed under a humid atmosphere of 50 vol% H2 - 50 vol% N2 and a dew point of 60 ℃, with a cracking temperature of 860 ℃ × a cracking time of 120 s. At this time, the average heating rate between 500 and 700 ℃ during the heating process of the first recrystallization annealing was varied to three levels: 300 ℃ / s, 500 ℃ / s, and 1000 ℃ / s.Next, an annealing separator based on MgO was applied to the surface of the steel sheet after the first recrystallization annealing, and a second recrystallization was induced by heating at a heating rate of 30 ℃ / hr between 800 and 950 ℃ (without correction), and then the second recrystallization was completed by heating to 1200 ℃ at a heating rate of 20 ℃ / hr between 950 and 1050 ℃, and then a final annealing treatment was performed by maintaining the temperature at that temperature for 5 hours under a hydrogen atmosphere.

[0028] Samples were taken from the steel sheet after finishing annealing obtained in this way, and the magnetic flux density B8 (magnetic flux density when excited at 800 A / m) was measured by the method described in JIS C2550, and the results are shown in Table 2. From these results, it was found that the magnetic flux density is greatly improved by rapidly cooling the average rate from 800 ℃ to 300 ℃ at 200 ℃ / s or higher during the cooling process of intermediate annealing, and by increasing the heating rate between 500 ℃ and 700 ℃ at 500 ℃ / s or higher during the heating process of the primary recrystallization annealing after subsequent cold rolling.

[0029]

[0030] As described above, the mechanism by which the magnetic flux density is significantly improved by increasing the average cooling rate from 800°C to 300°C during the cooling process of intermediate annealing to 200°C / s or more, and also increasing the heating rate from 500°C to 700°C during the heating process of primary recrystallization annealing to 500°C / s or more, has not yet been fully elucidated, but the inventors believe as follows.

[0031] As described in <Experiment 1> above, when the average cooling rate from 800 to 300 ℃ during the cooling process of intermediate annealing is increased to 200 ℃ / s or higher, it is thought that a deformation different from the usual occurs at the phase interface between the γ phase and the α phase. It is thought that when cold rolling is performed in such a state, a deformation zone different from the usual occurs. This deformation zone is a deformation zone where {411} orientation grains with a high recrystallization temperature are prone to nucleation. It is thought that by increasing the heating rate during the heating process of the first recrystallization annealing to a very fast rate of 500 ℃ / s or higher, the {411} orientation grains increase further, the texture is improved, and the magnetic properties are greatly enhanced.

[0032] The present invention was developed based on the above-mentioned novel findings.

[0033] Next, the reason for limiting the composition of the steel material (slab) used in the manufacture of the oriented electrical steel sheet of the present invention will be explained.

[0034] C : 0.020 ∼ 0.10 mass%

[0035] If C is less than 0.020 mass%, the microstructure becomes an α single phase during casting or hot rolling, causing the steel to become embrittled, resulting in cracks in the slab or cracks on the edges of the steel plate after hot rolling, which hinders manufacturing. On the other hand, if it exceeds 0.10 mass%, it becomes difficult to reduce it to 0.005 mass% or less, where self-aging does not occur during decarburization annealing. Therefore, C is set within the range of 0.020 to 0.10 mass%. Preferably, it is in the range of 0.025 to 0.050 mass%.

[0036] Si : 2.0 ~ 4.5 mass%

[0037] Si is an element necessary to increase the resistivity of steel and improve iron loss, but if it is less than 2.0 mass%, the above effect is insufficient, while if it exceeds 4.5 mass%, the workability of the steel decreases, making it difficult to manufacture by rolling. Therefore, Si is set in the range of 2.0 to 4.5 mass%. Preferably, it is in the range of 2.5 to 3.8 mass%.

[0038] Mn : 0.004 ∼ 0.50 mass%

[0039] Mn is an element necessary to improve the hot workability of steel, but if it is less than 0.004 mass%, the above effect is insufficient, while if it is added in excess of 0.50 mass%, the magnetic flux density of the product plate decreases. Therefore, Mn is set in the range of 0.004 to 0.50 mass%. Preferably, it is in the range of 0.03 to 0.20 mass%.

[0040] Al: less than 0.010 mass%, N, S, and Se each less than 0.0050 mass%

[0041] In order to manufacture a oriented electrical steel sheet using a steel material that does not contain inhibitor-forming components, the content of the inhibitor-forming components Al, N, S, and Se needs to be reduced as much as possible. Therefore, in the present invention, Al is limited to less than 0.010 mass%, and N, S, and Se are each limited to less than 0.0050 mass%. Preferably, Al is less than 0.007 mass%, N is less than 0.0040 mass%, and S and Se are each less than 0.0030 mass%.

[0042] The steel material (slab) used to manufacture the oriented electrical steel sheet of the present invention consists of the remainder other than the above components being Fe and unavoidable impurities. However, for the purpose of improving magnetic properties, in addition to the above component composition, additionally Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, Ni: 0.01 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, B: 0.0002 to 0.0025 mass%, Nb: 0.0010 to 0.0100 mass%, Sn: 0.010 to 0.400 mass%, Sb: 0.010 to 0.150 mass%, Mo: 0.010 to 0.200 mass%, P: 0.010 to 0.150 mass%, V: 0.0005 to 0.0100 mass%, and Ti: 0.0005 to 0.0100 One or more of the elements selected from mass% may be appropriately contained. Each of the above elements has the effect of improving the magnetic properties of the oriented electrical steel sheet, but if the content is lower than the above lower limit, a sufficient improvement in magnetic properties cannot be obtained. On the other hand, if the content exceeds the above upper limit, the development of secondary recrystallized grains is inhibited, and there is a risk that the magnetic properties may deteriorate.

[0043] Next, a method for manufacturing a oriented electrical steel sheet according to the present invention will be described.

[0044] The oriented electrical steel sheet of the present invention can be manufactured by a method of manufacturing an oriented electrical steel sheet comprising a series of processes in which a steel material (slab) having the compositional composition described above is heated to a predetermined temperature, hot-rolled to form a hot-rolled sheet, annealed the hot-rolled sheet, cold-rolled two or more times with one cold rolling or intermediate annealing in between to form a cold-rolled sheet of final thickness, first recrystallization annealing combined with decarburization annealing is performed, an annealing separator is applied to the surface of the steel sheet, second recrystallized, then finishing annealing for purification treatment, and flattening annealing.

[0045] The above steel material (slab) can be manufactured by melting steel adjusted to the compositional composition described above in a conventional refining process, and then using a conventional continuous casting method or an ingot-deconstruction rolling method. In addition, a thin billet with a thickness of 100 mm or less may be manufactured by a direct casting method.

[0046] Next, the above slab is heated to a predetermined temperature and then subjected to hot rolling to become a hot-rolled plate of a predetermined thickness. Since the present invention uses a steel material that does not contain inhibitor-forming components, high-temperature heating to dissolve the inhibitor is unnecessary, and the heating temperature of the slab is sufficient at 1280°C or lower. Preferably, it is 1250°C or lower. In addition, the lower limit of the heating temperature should be a temperature that ensures workability in hot rolling, and it is preferably 1100°C or higher.

[0047] Next, the hot-rolled sheet obtained by the above hot rolling is subjected to hot-rolled sheet annealing for the purpose of completely recrystallizing the hot-rolled sheet structure. The maximum temperature reached during this hot-rolled sheet annealing is preferably 950°C or higher from the perspective of reliably obtaining the above effect. More preferably, it is 1000°C or higher. On the other hand, if the maximum temperature reached exceeds 1150°C, the crystal grains after hot-rolled sheet annealing become coarse, making it difficult to obtain a primary recrystallized structure of regular grains; therefore, it is limited to 1150°C or lower. More preferably, it is 1100°C or lower. In addition, the time maintained at the maximum temperature reached is preferably in the range of 5 to 300 s from the perspective of sufficiently obtaining the effect of hot-rolled sheet annealing and ensuring productivity.

[0048] Next, the hot-rolled sheet after annealing is acid-cleaned to descale, and then cold-rolled once or twice or more with intermediate annealing in between to form a cold-rolled sheet of the final thickness. Here, when performing two or more cold-rollings, the annealing temperature during intermediate annealing is preferably in the range of 1000 to 1150°C. This is because it is difficult to achieve complete recrystallization below 1000°C, while if the annealing temperature exceeds 1150°C, the crystal grains after annealing become coarsened, making it difficult to obtain a primary recrystallization structure of regular grains. More preferably, it is in the range of 1020 to 1100°C. In addition, the cracking time for intermediate annealing is preferably in the range of 5 to 300 s from the perspective of sufficiently obtaining the annealing effect and ensuring productivity.

[0049] Here, the most important aspect of the present invention is that, in the annealing prior to cold rolling, specifically in one or more of the annealing processes among hot-rolled sheet annealing and intermediate annealing, it is necessary to perform rapid cooling at an average cooling rate of 200 ℃ / s or more during the cooling process from the highest reached temperature (cracking temperature) between 800 and 300 ℃. As previously mentioned, by making the average cooling rate in this temperature range 200 ℃ / s or more, large deformation is introduced into the steel sheet after cooling, and as a result of improving the texture of the steel sheet after the first recrystallization annealing, the magnetic properties of the product sheet can be improved. Preferably, it is 300 ℃ / s or more. To realize this cooling rate industrially, a rapid cooling device that jets water, such as the one described in the aforementioned Patent Document 5, can be preferably used. Furthermore, although the upper limit of the cooling rate is not specifically specified, the upper limit of the cooling rate of the rapid cooling device is approximately 1200 ℃ / s.

[0050] Next, an important aspect of the present invention is that it is preferable to perform the cooling from 300°C to 100°C following the rapid cooling between 800°C and 300°C at an average cooling rate in the range of 5 to 40°C / s. Accordingly, the amount of deformation within the steel sheet after annealing is further increased, and magnetic properties can be further improved. More preferably, the range is 20 to 40°C / s.

[0051] The steel sheet (cold-rolled sheet) after cold rolling with the above-mentioned final thickness is subsequently subjected to a primary recrystallization annealing combined with decarburization annealing. From the perspective of ensuring decarburization, it is preferable to perform this primary recrystallization annealing in the range of a cracking temperature of 800 to 900 ℃ × a cracking time of 50 to 300 s. Also, from the perspective of ensuring decarburization, it is preferable to use a humid atmosphere for this annealing. Furthermore, through this decarburization annealing, the carbon content in the steel sheet is reduced to 0.0050 mass% or less. Additionally, during the heating process of this primary recrystallization annealing, the recrystallization temperature range of 500 to 700 ℃ is heated at a rate of 500 ℃ / s or higher, thereby further improving the texture and enhancing magnetic properties. Preferably, the rate is 600 ℃ / s or higher.

[0052] Next, regarding the steel sheet of the first recrystallization annealing above, if a forsterite film is to be formed by finishing annealing, an annealing separator mainly composed of MgO is applied to the surface of the steel sheet, and then a second recrystallization is induced, followed by a purification treatment and finishing annealing. On the other hand, if stamping workability is prioritized and a forsterite film is not to be formed, an annealing separator is not applied, or an annealing separator mainly composed of silica or alumina is applied to the surface of the steel sheet, and then the finishing annealing above is performed.

[0053] Here, the above-mentioned finishing annealing is preferably performed by maintaining the temperature between 800 and 950°C for 5 to 200 hours during the heating process, or by heating between 800 and 950°C at an average heating rate of 5°C / hr or less to induce secondary recrystallization, and then continuing, or by lowering the temperature to 700°C or lower, reheating, and heating to a temperature of 1100°C or higher at an average heating rate of 5 to 35°C / hr in the temperature range between 950 and 1050°C to complete secondary recrystallization, and then additionally performing a purification treatment by maintaining the temperature for 2 hours or more. Through this purification treatment, Al, N, S, and Se in the steel sheet are reduced to unavoidable impurity levels.

[0054] The preferred correction treatment time between 800 and 950°C is 50 to 150 hr, and the preferred average heating rate between 800 and 950°C is 1 to 3°C / hr. In addition, the preferred temperature for the acclimatization treatment is 1200 to 1250°C, and the preferred holding time is 2 to 10 hr. Furthermore, it is preferable that the atmosphere for the acclimatization treatment of the finishing annealing be an H2 atmosphere.

[0055] After the above-mentioned finishing annealing, it is effective to perform water washing, brushing, acid washing, etc., to remove unreacted annealing separator, and then perform flattening annealing for shape correction to reduce iron loss. In addition, when using laminated steel sheets, it is desirable to form an insulating film on the surface of the steel sheet during the flattening annealing process or any of the processes before or after it to improve iron loss. Furthermore, to further reduce iron loss, it is desirable to use a tension-imparting film in the above-mentioned insulating film. In addition, at that time, methods such as forming a tension-imparting film by interposing a binder, or depositing an inorganic material on the surface layer of the steel sheet using physical vapor deposition or chemical vapor deposition to form a tension-imparting film may be adopted. In addition, to further reduce iron loss, it is desirable to perform magnetic domain subdivision treatment by irradiating the surface of the product plate with a laser beam or plasma beam to induce thermal or impact deformation, or by forming grooves on the surface of the steel plate.

[0056] Example 1

[0057] A steel slab having the composition shown in Table 3, with the remainder being Fe and unavoidable impurities, was manufactured by a continuous casting method, reheated to a temperature of 1280 ℃, and then hot-rolled to a hot-rolled plate with a thickness of 2.2 mm. The hot-rolled plate was subjected to hot-rolled plate annealing at 1050 ℃ × 20 s. At that time, the average cooling rate during the cooling process of the hot-rolled plate annealing was varied between 800 and 300 ℃ and between 300 and 100 ℃ as shown in Table 4. Afterward, the sheet was cold-rolled once to obtain a cold-rolled sheet with a final thickness of 0.23 mm, and then a first recrystallization annealing combined with decarburization annealing was performed at 830 ℃ × 150 s under a humid atmosphere of 60 vol% H2 - 40 vol% N2 with a dew point of 55 ℃. At this time, the average heating rate between 500 and 700 ℃ during the heating process was set to 200 ℃ / s.

[0058] Next, an annealing separator based on MgO was applied to the surface of the steel sheet after the first recrystallization annealing, and a second recrystallization was induced by heating at a heating rate of 30 ℃ / hr between 800 ℃ and 950 ℃ (without correction), and then the second recrystallization was completed by heating to 1200 ℃ at a heating rate of 20 ℃ / hr between 950 ℃ and 1050 ℃, and then a finishing annealing treatment was performed by maintaining the temperature at that temperature for 10 hours under a hydrogen atmosphere.

[0059] Test specimens were taken from the steel plate after finishing annealing obtained in this way, and the magnetic flux density B8 (magnetic flux density when energized at 800 A / m) was measured by the method described in JIS C2550, and the results are shown in Table 4. From Table 4, it can be seen that steel plates using a steel material having a composition suitable for the present invention and rapidly cooling the hot-rolled plate annealing under conditions suitable for the present invention all have excellent magnetic flux densities, and in particular, the faster the cooling rate of the hot-rolled plate annealing between 800 and 300°C, the better the magnetic flux density.

[0060]

[0061]

[0062] Example 2

[0063] A steel slab containing C: 0.049 mass%, Si: 3.5 mass%, Mn: 0.069 mass%, sol. Al: 0.0070 mass%, N: 0.0035 mass%, and S: 0.0010 mass%, with the remainder being Fe and unavoidable impurities, was manufactured by a continuous casting method, reheated to a temperature of 1230 ℃, and then hot-rolled to a hot-rolled plate with a thickness of 2.0 mm, and the hot-rolled plate was subjected to hot-rolled plate annealing at 950 ℃ × 20 s. After that, the plate was cold-rolled once to an intermediate thickness of 1.3 mm, and after intermediate annealing at 1060 ℃ × 60 s, it was cold-rolled a second time to a cold-rolled plate with a final thickness of 0.20 mm. At that time, the average cooling rate between 800 and 300 ℃ and between 300 and 100 ℃ during the cooling process of hot-rolled plate annealing and intermediate annealing was varied as shown in Table 5. Subsequently, primary recrystallization annealing combined with decarburization annealing was performed on the cold-rolled plate at 850 ℃ × 60 s under a humid atmosphere of 55 vol% H2 - 45 vol% N2 with a dew point of 60 ℃. At this time, the average heating rate between 500 and 700 ℃ during the heating process was set to 400 ℃ / s.

[0064] Next, an annealing separator based on MgO was applied to the surface of the steel sheet after the first recrystallization annealing, and a second recrystallization was induced by heating at a heating rate of 25 ℃ / hr between 800 ℃ and 950 ℃ (without correction), and then the second recrystallization was completed by heating to 1225 ℃ at a heating rate of 20 ℃ / hr between 950 ℃ and 1050 ℃, and then a finishing annealing treatment was performed by maintaining the temperature at that temperature for 10 hours under a hydrogen atmosphere.

[0065] Test specimens were taken from the steel plate after finishing annealing obtained in this way, and the magnetic flux density B8 (magnetic flux density when excited at 800 A / m) was measured by the method described in JIS C2550, and the results are shown in Table 5. From Table 5, it can be seen that steel plates in which hot-rolled plate annealing and / or intermediate annealing were performed under conditions suitable for the present invention using a steel material having a composition suitable for the present invention all have excellent magnetic flux density.

[0066]

[0067] Example 3

[0068] In the same manner as in Example 2, a steel slab containing C: 0.049 mass%, Si: 3.5 mass%, Mn: 0.069 mass%, sol. Al: 0.0070 mass%, N: 0.0035 mass%, and S: 0.0010 mass%, with the remainder being Fe and unavoidable impurities, was manufactured by a continuous casting method, reheated to a temperature of 1280 ℃, and then hot-rolled to a hot-rolled plate with a thickness of 2.5 mm, and hot-rolled plate annealing was performed on the hot-rolled plate at 1000 ℃ × 60 s. At that time, the average cooling rate during the cooling process of the hot-rolled plate annealing between 800 and 300 ℃ and between 300 and 100 ℃ was varied as shown in Table 6. After that, the intermediate plate thickness was set to 1.8 mm by the first cold rolling, and after performing intermediate annealing at 1080 ℃ × 60 s, the second cold rolling was performed to produce a cold-rolled plate with a final plate thickness of 0.23 mm. At that time, the average cooling rate between 800 and 100 ℃ during the cooling process of the intermediate annealing was set to 40 ℃ / s.

[0069] Next, a first recrystallization annealing combined with decarburization annealing was performed on the above cold-rolled plate under a humid atmosphere of 55 vol% H2-45 vol% N2 with a dew point of 58 ℃ at a rate of 850 ℃ × 100 s. At this time, the average heating rate between 500 and 700 ℃ during the heating process was varied as described in Table 6. Subsequently, an annealing separating agent mainly composed of MgO was applied to the surface of the steel plate after the first recrystallization annealing, and after completing the second recrystallization, a finishing annealing treatment was performed by maintaining the temperature at 1225 ℃ for 10 hours under a hydrogen atmosphere. At that time, the heating conditions until the completion of the secondary recrystallization of the finishing annealing (heating conditions until secondary recrystallization occurs between 800 and 950 ℃, whether or not the temperature was lowered to 680 ℃ thereafter, and the average heating rate between 950 and 1050 ℃) were changed as shown in Table 6.

[0070] Test specimens were taken from the steel plate after finishing annealing obtained in this way, and the magnetic flux density B8 (magnetic flux density when excited at 800 A / m) was measured by the method described in JIS C2550, and the results are shown in Table 6. From Table 6, it can be seen that the magnetic flux density of the product plate is further improved by performing a correction treatment of 5 hours or more between 800 and 950°C during the finishing annealing heating process, or by raising the temperature between 800 and 950°C at a rate of 5°C / s or less, regardless of whether the subsequent temperature is lowered to 680°C. In addition, it can be seen that the magnetic flux density is further improved by increasing the average heating rate between 500 and 700°C during the first recrystallization annealing heating process to 500°C / s or more.

[0071]

Claims

Claim 1 A method for manufacturing a oriented electrical steel sheet comprising a series of processes including heating a steel slab having a composition of C: 0.020 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.004 to 0.50 mass%, and also containing less than 0.010 mass%, N, S, and Se each less than 0.0050 mass%, with the remainder being Fe and unavoidable impurities, to a temperature of 1280°C or lower, hot rolling to form a hot-rolled sheet, performing annealing of the hot-rolled sheet, performing cold rolling or two or more times with intermediate annealing in between to form a cold-rolled sheet of the final thickness, performing primary recrystallization annealing combined with decarburization annealing, applying an annealing separating agent to the surface of the steel sheet, performing finish annealing, and performing flattening annealing, wherein the hot-rolled sheet A method for manufacturing a oriented electrical steel sheet, characterized in that, in one or more annealing processes among annealing and intermediate annealing, the cooling process from 800 ℃ to 300 ℃ from the maximum reached temperature is rapidly cooled at an average cooling rate of 200 ℃ / s or more, and following the rapid cooling, the cooling from 300 ℃ to 100 ℃ is cooled at an average cooling rate in the range of 5 to 40 ℃ / s. Claim 2 A method for manufacturing a oriented electrical steel sheet according to claim 1, characterized in that the heating rate between 500 and 700 ℃ during the heating process of the primary recrystallization annealing combined with the decarburization annealing is 500 ℃ / s or higher. Claim 3 A method for manufacturing a oriented electrical steel sheet according to claim 1 or 2, characterized in that, in the heating process of the finishing annealing, a preservation treatment is performed by maintaining at any temperature between 800 and 950°C for 5 to 200 hours, or by inducing secondary recrystallization by heating between 800 and 950°C at an average heating rate of 5°C / hr or less, then heating to a temperature of 1100°C or higher to complete secondary recrystallization, and then maintaining at that temperature for 2 hours or more for purification treatment. Claim 4 In claim 1 or 2, the steel slab comprises, in addition to the above compositional components, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, Ni: 0.01 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, B: 0.0002 to 0.0025 mass%, Nb: 0.0010 to 0.0100 mass%, Sn: 0.010 to 0.400 mass%, Sb: 0.010 to 0.150 mass%, Mo: 0.010 to 0.200 mass%, P: 0.010 to 0.150 mass%, V: 0.0005 to 0.0100 mass%, and Ti: 0.0005 A method for manufacturing a oriented electrical steel sheet characterized by containing one or more types selected from ~ 0.0100 mass%. Claim 5 In claim 3, the steel slab, in addition to the above compositional components, further comprises: Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, Ni: 0.01 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, B: 0.0002 to 0.0025 mass%, Nb: 0.0010 to 0.0100 mass%, Sn: 0.010 to 0.400 mass%, Sb: 0.010 to 0.150 mass%, Mo: 0.010 to 0.200 mass%, P: 0.010 to 0.150 mass%, V: 0.0005 to 0.0100 mass%, and Ti: 0.0005 to A method for manufacturing a oriented electrical steel sheet characterized by containing one or more types selected from 0.0100 mass%.

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