Method for producing grain-oriented electromagnetic steel sheet

Abstract

To provide a method for stably producing a grain-oriented electromagnetic steel sheet having low iron loss.SOLUTION: A method for producing a grain-oriented electromagnetic steel sheet comprises: hot rolling a steel slab to produce a hot-rolled sheet; after performing a first cold rolling and a first intermediate annealing without subjecting the hot-rolled sheet to hot band annealing, further performing cold rolling, as performed between the first cold rolling and the first intermediate annealing, twice or more to produce a cold-rolled sheet of final thickness; applying decarburization annealing that also serves as a primary recrystallization annealing to the cold-rolled sheet; and after that, performing a finish annealing to induce a secondary recrystallization. In the method, the rolling reduction ratio of the first cold rolling shall be 20% or more and less than 60%, and the area ratio of the crystal grains with a GAM value of 0.5 or less, observed by EBSD on a cross section perpendicular to the rolling direction of the steel sheet after the first intermediate annealing, shall be 80% or more, thereby, resulting in improved magnetic properties of the grain-oriented electromagnetic steel sheet.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties. [Background technology]

[0002] Grain-oriented electrical steel is a soft magnetic material that is mainly used for the iron cores of transformers and generators. <001> This steel sheet has a crystal structure with a highly aligned orientation (Goss orientation) in the rolling direction of the steel sheet, and has excellent magnetic properties.

[0003] As a technique for increasing the degree of Goss orientation, for example, Patent Document 1 discloses a method in which a cold-rolled sheet is heat-treated at a low temperature during cold rolling and then aged. Patent Document 2 also discloses a method in which the cooling rate during hot-rolled sheet annealing or intermediate annealing before final cold rolling is set to 30°C / s or more, and interpass aging is performed at least twice for 2 minutes or more at a sheet temperature of 150 to 300°C during final cold rolling. Patent Document 3 and other documents also disclose a method in which warm rolling is performed in which the steel sheet temperature is increased during rolling, and dynamic strain aging is used to immediately fix dislocations introduced during rolling with C or N.

[0004] The techniques of Patent Documents 1 to 3 all aim to improve the rolling texture by increasing the steel sheet temperature to an appropriate temperature before, during, or between passes of cold rolling, thereby promoting the diffusion of solute elements carbon (C) and nitrogen (N), pinning dislocations introduced during cold rolling, preventing dislocation movement in subsequent rolling, and promoting shear deformation during rolling.The application of these techniques makes it possible to form many Goss-oriented grains in the primary recrystallized structure, and these Goss-oriented grains grow preferentially during the subsequent secondary recrystallization, thereby increasing the degree of accumulation in the Goss orientation after secondary recrystallization.

[0005] Furthermore, as a technique for further enhancing the effect of the strain aging, Patent Document 4 discloses a method for stably obtaining a steel sheet highly concentrated in the Goss orientation by precipitating fine carbides in the steel in an annealing process immediately before the final cold rolling in the cold rolling process, dividing the subsequent final cold rolling into two parts, a first half and a second half, in which the first half is rolled at a low temperature of 140°C or less with a reduction rate in the range of 30 to 75%, and in the second half, at least two rolling passes are carried out at a high temperature of 150 to 300°C, and the total reduction rate of the first and second half combined is set to 80 to 95%. 2 A method is disclosed in which fine carbides are precipitated in steel by carrying out a heat treatment at 50 to 150°C for 30 seconds to 30 minutes under the above tension.

[0006] The techniques of Patent Documents 1 to 5 all involve the use of {100} α-fiber structure formed during hot rolling. <011> It has the effect of promoting recrystallization of tissue. <011> This structure is known to remain as an unrecrystallized structure even after subsequent cold rolling and primary recrystallization annealing, and inhibits the growth of Goss-oriented grains. <011> It is necessary to promote recrystallization of the tissue.

[0007] Above{100} <011> As a technology focusing on promoting recrystallization of the structure, for example, Patent Document 6 discloses a technology in which a strain rate of 150 -1 This technology allows for the smooth rolling of {100} even in tandem rolling, where the diffusion of C and N during rolling is difficult and the effect of strain aging cannot be fully achieved. <011> It is said that it can promote the recrystallization of tissue. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 50-016610 [Patent Document 2] Japanese Patent Application Publication No. 08-253816 [Patent Document 3] Japanese Patent Application Publication No. 01-215925 [Patent Document 4] Japanese Patent Application Publication No. 09-157745 [Patent Document 5] Japanese Patent Application Publication No. 04-120216 [Patent Document 6] Japanese Patent Application Laid-Open No. 2012-184497 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in recent years, with the increasing demand for energy conservation, there has been an ever-increasing demand for grain-oriented electrical steel sheets with low iron loss, and there has been a strong demand for the development of technology for manufacturing grain-oriented electrical steel sheets with even lower iron loss.

[0010] To manufacture grain-oriented electrical steel sheets with lower iron loss, <011> It is necessary to further promote the recrystallization of the structure. However, in the techniques of Patent Documents 1 to 3, in which the steel sheet is heated during cold rolling, the rise in the steel sheet temperature causes insufficient lubrication during rolling, which leads to a deterioration in the steel sheet shape and a decrease in yield. Therefore, there is a limit to how much the steel sheet temperature can be increased, and a significant improvement in magnetic properties cannot be expected. In addition, the technique of performing carbide precipitation treatment in the annealing process before final cold rolling, as in Patent Documents 4 and 5, is effective in enhancing the effect of strain aging, but it also has a drawback of reducing the {100} <011> This is not desirable in terms of promoting recrystallization of the structure. <011> The structure has the property that strain is difficult to introduce by cold rolling, and dislocations do not accumulate sufficiently. However, strain aging is a technique that uses dislocations in the processed structure as precipitation sites to precipitate carbides or nitrides. <011> This is because it is difficult to precipitate a sufficient amount of carbides and nitrides in the structure. Furthermore, the technology of Patent Document 6 is a technology for reducing the strain rate during cold rolling, which inevitably leads to a slow rolling speed, resulting in a problem of reduced productivity.

[0011] The present invention has been made in consideration of the above-mentioned problems of the prior art, and its object is to improve the {100} <011> The present invention aims to propose a method for stably manufacturing grain-oriented electrical steel sheets with extremely low iron loss by increasing the recrystallization rate of the structure. [Means for solving the problem]

[0012] In order to solve the above problem, the inventors have investigated the {100} <011> We have conducted extensive research into the effects of hot-rolled sheet annealing and subsequent cold rolling on a method for increasing the recrystallization rate of the structure. As a result, we have found that by performing a first cold rolling process with a reduction rate of 20% or more and less than 60% on a hot-rolled steel sheet without hot-rolled sheet annealing, and then performing a first intermediate annealing, the {100} <011> The inventors have found that this can promote recrystallization of the structure, thereby enabling the stable production of grain-oriented electrical steel sheets with low iron loss, which has led to the development of the present invention.

[0013] Based on the above findings, the present invention proposes a method for producing grain-oriented electrical steel sheet, which includes a series of steps of hot-rolling a steel slab to form a hot-rolled sheet, subjecting the hot-rolled sheet to a first cold rolling and a first intermediate annealing without hot-rolled sheet annealing, and then further cold rolling once more or two or more times with intermediate annealing in between to form a cold-rolled sheet of a final thickness, subjecting the cold-rolled sheet to decarburization annealing that also serves as primary recrystallization annealing, and then subjecting the cold-rolled sheet to finish annealing for secondary recrystallization, characterized in that the reduction rate of the first cold rolling is 20% or more and less than 60%, and the area fraction of crystal grains having a GAM value of 0.5 or less when a cross section of the steel sheet after the first intermediate annealing, perpendicular to the rolling direction, is observed by EBSD, is 80% or more.

[0014] The method for producing the grain-oriented electrical steel sheet of the present invention is characterized in that the heating rate between 400°C and 700°C in the heating process of the first intermediate annealing is 5°C / s or more and 100°C / s or less.

[0015] The steel slab used in the method for producing the grain-oriented electrical steel sheet of the present invention is characterized by having a chemical composition containing C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.5 mass%, sol. Al: 0.0100 to 0.0400 mass%, N: 0.0050 to 0.0120 mass%, at least one of S and Se: 0.01 to 0.05 mass% in total, with the balance being Fe and unavoidable impurities.

[0016] The steel slab used in the method for producing the grain-oriented electrical steel sheet of the present invention is characterized by having a chemical composition containing C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.5 mass%, sol. Al: less than 0.0100 mass%, S: less than 0.0100 mass%, Se: less than 0.0100 mass%, and N: less than 0.0050 mass%, with the balance being Fe and unavoidable impurities.

[0017] The steel slab used in the method for producing the grain-oriented electrical steel sheet of the present invention is characterized by containing, in addition to the above-mentioned chemical composition, at least one component selected from the following groups A to C: Note Group A: at least one selected from Sb: 0.005 to 0.500 mass%, Cu: 0.01 to 1.50 mass%, P: 0.005 to 0.500 mass%, Cr: 0.005 to 1.50 mass%, Ni: 0.005 to 1.500 mass%, Sn: 0.005 to 0.500 mass%, Nb: 0.0005 to 0.0200 mass%, Mo: 0.005 to 0.500 mass%, Co: 0.001 to 0.500 mass%, B: 0.00001 to 0.007000 mass%, and Bi: 0.0005 to 0.500 mass% Group B: at least one selected from Ti: 0.0005 to 0.0400 mass%, V: 0.001 to 0.020 mass%, and W: 0.001 to 0.020 mass% C group: at least one selected from Zn: 0.0005 to 0.020 mass%, Zr: 0.001 to 0.020 mass%, Pb: 0.0001 to 0.0100 mass%, As: 0.001 to 0.020 mass%, Ag: 0.001 to 0.050 mass%, Au: 0.001 to 0.050 mass%, Ga: 0.0001 to 0.0050 mass%, Ge: 0.0001 to 0.0050 mass%, Ca: 0.0005 to 0.020 mass%, Mg: 0.0005 to 0.020 mass%, REM: 0.0005 to 0.0200 mass%, and Hf: 0.001 to 0.020 mass% [Effects of the Invention]

[0018] According to the present invention, grain-oriented electrical steel sheets with excellent magnetic properties can be stably produced, which can greatly contribute to reducing energy consumption. DETAILED DESCRIPTION OF THE INVENTION

[0019] First, the experiment that led to the development of the present invention will be described. Steel slabs having a chemical composition containing 0.037 mass% C, 3.4 mass% Si, 0.05 mass% Mn, 0.0085 mass% sol. Al, 0.0042 mass% N, 0.0060 mass% S, and 0.0020 mass% Se, with the balance being Fe and unavoidable impurities, were heated to 1210°C and then hot-rolled to produce hot-rolled sheets of various thicknesses shown in Table 1.

[0020] Next, each of the hot-rolled sheets of various thicknesses was divided into two, one of which was subjected to hot-rolled sheet annealing at 1000°C for 60 seconds, and the other was not subjected to hot-rolled sheet annealing. Thereafter, each of the two hot-rolled sheets was subjected to a first cold rolling at various reduction rates shown in Table 1 to an intermediate thickness of 1.3 mm, and then subjected to a first intermediate annealing in which the temperature was increased from 400°C to 700°C at a rate of 3°C / s up to 1000°C and held at that temperature for 60 seconds.

[0021] [Table 1]

[0022] At this time, the step surface perpendicular to the rolling direction of the steel sheet after the first intermediate annealing is 390 mm 2 The crystal orientation was measured using EBSD over a steel sheet thickness of 1.3 mm and rolling direction of 300 mm or more, and the GAM value was calculated. This GAM (Grain Average Misorientation) value is an index that represents the degree of strain of each grain within the measurement surface of the steel sheet, and the smaller the GAM value, the smaller the amount of strain within that grain. Therefore, in this experiment, grains with a GAM value of 0.5 or less were determined to be recrystallized grains, and the ratio of the area of ​​grains with a GAM value of 0.5 or less to the total measured area was calculated. The results are also shown in Table 1.

[0023] The steel sheet after the first intermediate annealing was then subjected to a second cold rolling at a rolling reduction of 85% to obtain a cold-rolled sheet with a final thickness of 0.20 mm. Next, the cold-rolled sheet was subjected to decarburization annealing, which also served as primary recrystallization annealing, at a heating rate of 50°C / s between 400°C and 700°C, a soaking temperature of 840°C, and a soaking time of 100 seconds.

[0024] Next, an annealing separator mainly composed of MgO was applied to the surface of the steel sheet after the decarburization annealing, and then the steel sheet was subjected to finish annealing for secondary recrystallization. Next, a coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel sheet after the finish annealing, and the steel sheet was subjected to planarization annealing at 800°C for 30 seconds to obtain a product sheet having an insulating coating.

[0025] From the product plate thus obtained, samples for magnetic properties were cut out so that the total mass was 500 g or more, and an Epstein test was performed to measure the iron loss W 17 / 50 The results are shown in Table 1.

[0026] From Table 1, it can be seen that the steel sheets that were not subjected to hot-rolled sheet annealing and had a reduction ratio of 20% or more but less than 60% in the first cold rolling had a high area ratio of recrystallized grains of 80% or more after the first intermediate annealing, and the iron loss W of the resulting product sheet was 17 / 50It can be seen that the value is low, below 0.85 W / kg.

[0027] By performing the first cold rolling with the appropriate reduction without hot-rolled sheet annealing, the {100} <011> The inventors believe that the mechanism by which the recrystallization rate of the structure increases and the iron loss improves is as follows: <011> For the structure to recrystallize, it is necessary to accumulate a certain amount of strain before the intermediate annealing. However, when hot-rolled sheet annealing is performed, the strain accumulated during hot rolling disappears due to the annealing. Therefore, even if the first cold rolling is performed after hot-rolled sheet annealing, the {100} <011> Since the amount of strain accumulated is not sufficient for the structure to recrystallize, the first intermediate annealing only results in the annihilation of dislocations due to recovery, and no recrystallization occurs. On the other hand, when hot-rolled sheet annealing is not performed, strain accumulates during the first cold rolling in addition to the strain accumulated during hot rolling, so the first intermediate annealing results in the {100} <011> It is believed that the recrystallization rate increases when a sufficient amount of strain accumulates to cause the structure to recrystallize. The present invention was completed based on the above novel findings and further investigations.

[0028] Next, the chemical composition of the steel material (steel slab) used to manufacture the grain-oriented electrical steel sheet of the present invention will be described. C: 0.01 to 0.10 mass% C is an element necessary for improving the texture of hot-rolled steel sheets. Furthermore, if the C content is less than 0.01 mass%, the texture becomes coarse during slab heating, making it difficult for recrystallization to occur in the subsequent annealing process, leading to deterioration of magnetic properties. On the other hand, if the C content exceeds 0.10 mass%, it becomes difficult to reduce the C content to 0.0050 mass% or less, at which magnetic aging is unlikely to occur during decarburization annealing. Therefore, the C content is preferably in the range of 0.01 to 0.10 mass%, and more preferably in the range of 0.01 to 0.08 mass%.

[0029] Si: 2.0 to 4.5 mass% Si is an element that is effective in increasing the resistivity of steel and reducing iron loss. However, if the Si content is less than 2.0 mass%, a sufficient iron loss reduction effect cannot be obtained. On the other hand, if the Si content exceeds 4.5 mass%, workability decreases significantly, making it difficult to manufacture by rolling. Therefore, the Si content is preferably in the range of 2.0 to 4.5 mass%, and more preferably in the range of 2.5 to 4.5 mass%.

[0030] Mn: 0.01 to 0.5 mass% Mn is an element necessary for improving hot workability. However, if the Mn content is less than 0.01 mass%, the above-mentioned improvement effect cannot be sufficiently obtained. On the other hand, if the Mn content exceeds 0.5 mass%, the primary recrystallization texture deteriorates, making it difficult to obtain secondary recrystallized grains with a high concentration of Goss orientation. Therefore, the Mn content is preferably in the range of 0.01 to 0.5 mass%, and more preferably in the range of 0.03 to 0.5 mass%.

[0031] The above components other than C, Si and Mn differ depending on whether or not an inhibitor is used to induce secondary recrystallization. When an inhibitor is used for secondary recrystallization, if AlN is used as the inhibitor, it is preferable to contain 0.0100 to 0.0400 mass% sol. Al and 0.0050 to 0.0120 mass% N in addition to the above C, Si, and Mn. If the Al content and N content are below the above lower limits, it becomes difficult to achieve the desired inhibitor effect. On the other hand, if the Al content and N content exceed the above upper limits, the dispersion state of the inhibitor precipitates becomes non-uniform, and the desired inhibitor effect cannot be achieved. More preferably, the sol. Al content is in the range of 0.0150 to 0.0350 mass% and the N content is in the range of 0.0060 to 0.0100 mass%.

[0032] Furthermore, in addition to the inhibitor-forming elements Al and N, it is preferable to contain at least one of S and Se in a total amount of 0.01 to 0.05 mass%. These elements form sulfides (MnS, CuS, etc.) or selenides (MnSe, CuSe, etc.) that act as inhibitors, further enhancing the inhibitor effect. S and Se may also be added simultaneously to precipitate a composite of sulfide and selenide. If the S and Se contents are below the respective lower limits, the inhibitor effect cannot be fully achieved. Conversely, if the S and Se contents exceed the respective upper limits, the dispersion of the inhibitor precipitates becomes non-uniform, again making it impossible to fully achieve the desired inhibitor effect. More preferably, the total amount of S and Se is in the range of 0.015 to 0.04 mass%.

[0033] On the other hand, when no inhibitor is used in secondary recrystallization, it is preferable to reduce the components that form inhibitors as much as possible. Specifically, it is preferable to reduce the sol.Al content to less than 0.0100 mass%, N content to less than 0.0050 mass%, S content to less than 0.0100 mass%, and Se content to less than 0.0100 mass%. More preferably, the sol.Al content is 0.0090 mass% or less, N content to 0.045 mass% or less, S content to 0.0080 mass% or less, and Se content to 0.0080 mass% or less.

[0034] In order to further improve the magnetic properties, the steel material used in the present invention may contain, in addition to the above components, at least one component from the following groups A to C. Group A: at least one selected from Sb: 0.005 to 0.500 mass%, Cu: 0.01 to 1.50 mass%, P: 0.005 to 0.500 mass%, Cr: 0.005 to 1.50 mass%, Ni: 0.005 to 1.500 mass%, Sn: 0.005 to 0.500 mass%, Nb: 0.0005 to 0.0200 mass%, Mo: 0.005 to 0.500 mass%, Co: 0.001 to 0.500 mass%, B: 0.00001 to 0.007000 mass%, and Bi: 0.0005 to 0.500 mass% Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, Co, B, and Bi are all elements useful for improving magnetic properties and have the effect of improving magnetic properties without inhibiting the growth of secondary recrystallized grains. However, to ensure the above effects, it is preferable to add them within the above ranges.

[0035] Group B: at least one selected from Ti: 0.0005 to 0.0400 mass%, V: 0.001 to 0.020 mass%, and W: 0.001 to 0.020 mass% Ti, V, and W all form fine carbides and nitrides, which refine the crystal grains after intermediate annealing, thereby improving bending properties and preventing sheet threading problems. However, if the content is less than the lower limit, the above effects are not fully achieved, while if the content exceeds the upper limit, the above effects saturate and raw material costs increase.

[0036] Group C: at least one selected from Zn: 0.0005 to 0.020 mass%, Zr: 0.001 to 0.020 mass%, Pb: 0.0001 to 0.0100 mass%, As: 0.001 to 0.020 mass%, Ag: 0.001 to 0.050 mass%, Au: 0.001 to 0.050 mass%, Ga: 0.0001 to 0.0050 mass%, Ge: 0.0001 to 0.0050 mass%, Ca: 0.0005 to 0.020 mass%, Mg: 0.0005 to 0.020 mass%, REM: 0.0005 to 0.0200 mass%, and Hf: 0.001 to 0.020 mass% Zn, Zr, Pb, As, Ag, Au, Ga, Ge, Ca, Mg, REM, and Hf all concentrate at grain boundaries or form compounds at the grain boundaries, thereby strengthening the grain boundaries and suppressing the occurrence of defects due to grain boundary fracture. However, if the content is less than the lower limit, the above effect is not fully achieved, while if added in excess of the upper limit, the above effect saturates and raw material costs increase, which is not preferable.

[0037] The steel material used in the present invention essentially contains Fe and unavoidable impurities as the remainder, in addition to the above-mentioned components. However, for the purposes of further improving magnetic properties, corrosion resistance, tensile strength, fatigue properties, and other properties, improving castability and threading, and improving productivity through scrap utilization, trace elements such as In, Te, Ce, Os, Re, Ta, Y, La, and Yb may be added in a total amount of 5.0 mass% or less, preferably 2.0 mass% or less, and more preferably 1.0 mass% or less, in place of a portion of the remaining Fe. Furthermore, elements other than those listed above may be included in the steel as impurities, as long as the effects of this embodiment are not impaired.

[0038] Next, a method for producing the grain-oriented electrical steel sheet of the present invention will be described. <Steel material> The steel material (steel slab) used in the manufacturing method of the present invention can be one manufactured by a known method for manufacturing a material for grain-oriented electrical steel sheet. For example, the manufacturing method may involve subjecting molten steel obtained in a converter, electric furnace, or the like to secondary refining, such as vacuum degassing, to adjust the chemical composition suitable for the present invention, and then forming the steel material into a steel material by a known method, such as continuous casting or ingot casting-blooming rolling.

[0039] <Hot rolling> Next, the steel slab obtained as described above is hot-rolled to form a hot-rolled sheet. The steel slab is preferably heated to a predetermined temperature before hot-rolling. The heating temperature of the slab is preferably about 1050°C or higher from the viewpoint of ensuring hot-rollability. There is no particular upper limit to the heating temperature, but if it exceeds 1450°C, it is close to the melting point of the steel, making it difficult to maintain the shape of the slab and increasing scale loss, so it is preferable to set it to 1450°C or lower. Other hot-rolling conditions are not particularly limited and may be the same as known conditions for rolling grain-oriented electrical steel sheets.

[0040] Next, the steel sheet after the hot rolling (hot-rolled sheet) is subjected to the first cold rolling without being subjected to hot-rolled sheet annealing. <011> The structure recovers and partially recrystallizes, and then the first intermediate annealing is performed without sufficient strain accumulation. <011> If the temperature is too low, a high recrystallization rate of the structure cannot be obtained. The hot-rolled sheet may be descaled by pickling or the like before the first cold rolling.

[0041] In the present invention, it is important that the reduction ratio of the first cold rolling be 20% or more and less than 60%. If the reduction ratio is less than 20%, sufficient strain cannot be accumulated in the hot-rolled sheet, so the {100} <011> On the other hand, if the rolling reduction is 60% or more, the {100} <011> Although it can increase the recrystallization rate of the structure, <011> The recrystallization of structures other than the above is also excessively promoted, resulting in deterioration of the primary recrystallization texture, which in turn leads to deterioration of the magnetic properties.

[0042] In the first intermediate annealing following the first cold rolling, the heating rate during the heating process between 400°C and 700°C is preferably set to 5°C / s or more and 100°C / s or less. By setting the heating rate at 5°C / s or more, the recovery of the rolled texture during heating is suppressed, and the material is heated to a high temperature in a state of high strain, resulting in the {100} <011> In addition, increasing the heating rate in the first intermediate annealing step can promote the recrystallization of the structure. <011> Since the recrystallization of the structure is not excessively promoted, the effect on the primary recrystallization texture is small, and a synergistic effect with the recrystallization promotion effect of cold rolling without hot-rolled sheet annealing can be expected. <011> The recrystallization promoting effect of the structure becomes saturated, and the manufacturing cost for increasing the heating rate increases. The annealing temperature of the first intermediate annealing may be in the range of 800°C or higher and 1200°C or lower. Other conditions may be in accordance with conventional methods and are not particularly limited.

[0043] By performing the first intermediate annealing while satisfying the above conditions, the area ratio of recrystallized crystal grains having a GAM value of 0.5 or less when measured by EBSD over a cross section perpendicular to the rolling direction of the steel sheet after intermediate annealing over an area (total sheet thickness × 300 mm or more) can be more stably set to 80% or more. The area ratio of the recrystallized crystal grains is preferably 85% or more, and more preferably 90% or more.

[0044] The cold rolling after the first intermediate annealing may be performed in one cold rolling to produce a cold-rolled sheet of the final thickness, or may be performed in two or more cold rolling steps with intermediate annealing in between to produce a cold-rolled sheet of the final thickness, and is not particularly limited.

[0045] If the rolling to the final thickness in the cold rolling process is defined as "final cold rolling," then the reduction ratio of the final cold rolling is preferably in the range of 70% to 95%. If the reduction ratio of the final cold rolling is less than 70%, sufficient strain cannot be imparted and accumulated in the unrecrystallized portion remaining after the intermediate annealing immediately before the final cold rolling, resulting in deterioration of the primary recrystallization texture. On the other hand, a reduction ratio of more than 95% is not preferred because work hardening increases the rolling load, making rolling difficult.

[0046] The final thickness (product thickness) of the grain-oriented electrical steel sheet of the present invention is not particularly limited, but is preferably in the range of 0.1 mm to 1.0 mm.

[0047] Next, the cold-rolled sheet having the final thickness is subjected to decarburization annealing, which also serves as primary recrystallization annealing. The conditions for this decarburization annealing may be according to commonly known conditions and are not particularly limited, but for example, conditions of 750 to 900°C x 30 to 600 seconds in a warm hydrogen atmosphere are preferred. This decarburization annealing reduces the C content in the steel sheet to 0.0050 mass% or less, which makes it less likely to cause magnetic aging.

[0048] The steel sheet subjected to the decarburization annealing is then coated with an annealing separator on its surface and then subjected to finish annealing for secondary recrystallization. The annealing separator may be a known one, and is not particularly limited. Examples include an annealing separator containing MgO as the main component (over 50 mass%) with TiO added as needed, or an annealing separator containing SiO or AlO as the main component. Furthermore, in the finish annealing, after the secondary recrystallization, the temperature may be raised to 1100°C or higher, and a purification treatment may be performed in a hydrogen atmosphere. This purification treatment reduces Al, N, S, Se, and other elements to impurity levels, thereby further improving magnetic properties.

[0049] After the above-mentioned finish annealing, the steel sheet is preferably subjected to planarization annealing to adjust the shape of the steel sheet, or an insulating coating is applied and baked on the surface of the steel sheet, as necessary. The type of insulating coating is not particularly limited, but when an insulating coating that imparts tensile strength to the steel sheet surface is formed, it is preferable to use a coating liquid containing phosphate and colloidal silica, as described in JP-A-50-79442, JP-A-48-39338, JP-A-56-75579, etc., and bake the coating at about 800°C.

[0050] For the purpose of further reducing iron loss, magnetic domain refining treatment may be performed by forming grooves on the surface of the steel sheet after the final cold rolling by etching or the like, by irradiating the surface of the steel sheet coated with the insulating coating with thermal energy such as an electron beam or laser beam to form a thermally distorted region after the finish annealing, or by forming a distorted region on the surface of the steel sheet with a roller or the like. [Example]

[0051] Steel slabs having a chemical composition containing 0.06 mass% C, 3.4 mass% Si, 0.06 mass% Mn, 0.0190 mass% sol. Al, 0.0090 mass% N, 0.02 mass% S, and 0.02 mass% Se, with the balance being Fe and unavoidable impurities, were heated to 1400°C and then hot-rolled to produce hot-rolled sheets of various thicknesses shown in Table 2.

[0052] [Table 2]

[0053] Next, the hot-rolled sheet was divided into two, one of which was subjected to hot-rolled sheet annealing at 1050°C for 60 seconds, and the other was not subjected to hot-rolled sheet annealing but was subjected to a first cold-rolling at various reductions shown in Table 2 to an intermediate sheet thickness of 1.0 mm. Thereafter, the temperature was raised between 400°C and 700°C at a rate of 3°C / s, and the first intermediate annealing was performed by soaking at 1000°C for 60 seconds, after which a second cold-rolling at a reduction of 80% was performed to obtain a cold-rolled sheet with a final sheet thickness of 0.20 mm. At this time, a cross section perpendicular to the rolling direction of the steel sheet after the intermediate annealing was cut to 300 mm. 2 The crystal orientation was measured using EBSD over a specimen (1.0 mm thick x 300 mm) or larger, and the GAM value was calculated. Grains with a GAM value of 0.5 or less were determined to be recrystallized grains, and the proportion of the area occupied by recrystallized grains to the total measured cross-sectional area was calculated. The results are also shown in Table 2.

[0054] Thereafter, the cold-rolled sheet was subjected to decarburization annealing, which also served as primary recrystallization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds.

[0055] Next, an annealing separator mainly composed of MgO was applied to the surface of the steel sheet after the decarburization annealing, dried, and wound into a coil. After that, it was subjected to finish annealing to induce secondary recrystallization, and then a coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel sheet after the finish annealing, and it was subjected to flattening annealing at 800°C for 30 seconds to produce a product sheet coil.

[0056] From the product sheet coil thus obtained, samples for magnetic properties were cut out so that the total mass was 500 g or more, and an Epstein test was performed to measure the iron loss W 17 / 50 The results are shown in Table 2.

[0057] From Table 2, it can be seen that the steel sheets that were not subjected to hot-rolled sheet annealing and had a reduction ratio of 20% or more but less than 60% in the first cold rolling had a high recrystallization rate of 80% or more in the grains of the intermediate annealed sheet, and the {100} <011> The strength is also low at 1.5 or less, and the iron loss W 17 / 50 It can be seen that the iron loss is low, at 0.85 W / kg or less. [Example]

[0058] A steel slab having a chemical composition containing C: 0.06 mass%, Si: 3.4 mass%, Mn: 0.06 mass%, sol. Al: 0.0120 mass%, N: 0.0060 mass%, S: 0.02 mass%, and Se: 0.02 mass%, with the remainder being Fe and unavoidable impurities, was heated to 1400°C and then hot-rolled to form a hot-rolled sheet having a thickness of 2.5 mm.

[0059] Next, the hot-rolled sheet was subjected to a first cold rolling with a reduction ratio of 30% to obtain an intermediate sheet thickness of 1.75 mm. Thereafter, the temperature was increased between 400°C and 700°C at various heating rates shown in Table 3, and intermediate annealing was performed by soaking at 1100°C for 60 seconds, followed by a second cold rolling to obtain a cold-rolled sheet with a final thickness of 0.20 mm. At this time, crystal orientation measurement was performed by EBSD in the same manner as in Example 1, and the recrystallization rate of the steel sheet after intermediate annealing was determined, and the results are also shown in Table 3.

[0060] [Table 3]

[0061] Thereafter, the cold-rolled sheet was subjected to decarburization annealing, which also served as primary recrystallization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds.

[0062] Next, an annealing separator mainly composed of MgO was applied to the surface of the steel sheet after the decarburization annealing, dried, and wound into a coil. After that, it was subjected to finish annealing to induce secondary recrystallization, and then a coating liquid containing phosphate-chromate-colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel sheet after the finish annealing, and it was subjected to flattening annealing at 800°C for 30 seconds to produce a product sheet coil.

[0063] From the product sheet coil thus obtained, samples for magnetic properties were cut out so that the total mass was 500 g or more, and an Epstein test was performed to measure the iron loss W 17 / 50 The results are shown in Table 3.

[0064] From Table 3, when the temperature rise rate of the intermediate annealing is set to 5°C / s or more, the recrystallization rate after the first intermediate annealing is 90% or more. 17 / 50 The magnetic flux density is also below 0.80 W / kg, which indicates that the magnetic properties have been further improved. [Example]

[0065] A steel having a composition containing 0.036 mass% C, 3.4 mass% Si, 0.06 mass% Mn, 0.0072 mass% sol.Al, 0.0035 mass% N, 0.0031 mass% S, and 0.0031 mass% Se, with other components selected from Group A as shown in Table 4, and the balance consisting of Fe and unavoidable impurities, was melted and formed into a steel slab. The slab was then heated to 1210°C and hot-rolled to form a hot-rolled sheet having a thickness of 2.5 mm.

[0066] [Table 4]

[0067] Next, the hot-rolled sheet was subjected to a first cold rolling with a reduction ratio of 40% to obtain an intermediate thickness of 1.5 mm, and then intermediate annealing was performed by raising the temperature between 400°C and 700°C at a rate of 3°C / s and soaking at 1100°C for 60 seconds.After that, the hot-rolled sheet was subjected to a second cold rolling to obtain a cold-rolled sheet with a final thickness of 0.20 mm.

[0068] The cold-rolled sheet was then subjected to decarburization annealing, which also served as primary recrystallization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. Next, an annealing separator primarily composed of MgO was applied to the surface of the steel sheet after the decarburization annealing, dried, and wound into a coil. After that, the steel sheet was subjected to finish annealing to induce secondary recrystallization, and then a coating liquid containing phosphate, chromate, and colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel sheet after the finish annealing. The steel sheet was then subjected to flattening annealing at 800°C for 30 seconds to produce a product sheet coil.

[0069] From the product sheet coil thus obtained, samples for magnetic measurement were cut out so that the total mass was 500 g or more, and an Epstein test was performed to measure the iron loss W 17 / 50 The results are shown in Table 4.

[0070] From Table 4, it can be seen that the steel sheets to which at least one element selected from the group A elements Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, and Bi was added in addition to the above-mentioned C, Si, Mn, Al, S, and Se all had a low iron loss W 17 / 50 is lower than 0.80 W / kg, which shows that the iron loss is reduced compared to the material without the additive. [Example]

[0071] A steel having a composition containing 0.036 mass% C, 3.4 mass% Si, 0.06 mass% Mn, 0.0072 mass% sol.Al, 0.0032 mass% N, 0.0031 mass% S, and 0.0031 mass% Se, with other elements selected from Group B and Group C as shown in Table 5, and the balance consisting of Fe and unavoidable impurities, was melted and formed into a steel slab. The slab was then heated to 1210°C and hot-rolled to form a hot-rolled sheet having a thickness of 2.5 mm.

[0072] [Table 5]

[0073] Next, the hot-rolled sheet was subjected to a first cold rolling with a reduction ratio of 40% to obtain an intermediate thickness of 1.5 mm, and then intermediate annealing was performed by raising the temperature between 400°C and 700°C at a rate of 3°C / s and soaking at 1100°C for 60 seconds.After that, the hot-rolled sheet was subjected to a second cold rolling to obtain a cold-rolled sheet with a final thickness of 0.20 mm.

[0074] The cold-rolled sheet was then subjected to decarburization annealing, which also served as primary recrystallization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. Next, an annealing separator primarily composed of MgO was applied to the surface of the steel sheet after the decarburization annealing, dried, and wound into a coil. After that, the steel sheet was subjected to finish annealing to induce secondary recrystallization, and then a coating liquid containing phosphate, chromate, and colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel sheet after the finish annealing. The steel sheet was then subjected to flattening annealing at 800°C for 30 seconds to produce a product sheet coil.

[0075] From the product sheet coil thus obtained, samples for magnetic measurement were cut out so that the total mass was 500 g or more, and an Epstein test was performed to measure the iron loss W 17 / 50 The results are shown in Table 5.

[0076] From Table 5, it can be seen that the steel sheets containing at least one element selected from the group B and group C elements Ti, V, W, Zn, Zr, Pb, As, Ag, Au, Ga, Ge, Ca, Mg, REM, and Hf in addition to the above-mentioned C, Si, Mn, Al, S, and Se all have iron loss values ​​of 0.85 W / kg or less, which is equivalent to that of the non-additive material. <011> It is clear that the magnetic properties are improved by promoting recrystallization of the structure. [Example]

[0077] A steel having a composition containing 0.036 mass% C, 3.4 mass% Si, 0.06 mass% Mn, 0.0065 mass% sol.Al, 0.0028 mass% N, 0.0020 mass% S, and 0.0015 mass% Se, with other components selected from groups A to C as shown in Table 6, and the balance consisting of Fe and unavoidable impurities, was melted and formed into a steel slab. The slab was then heated to 1210°C and hot-rolled to form a hot-rolled sheet having a thickness of 2.5 mm.

[0078] [Table 6-1]

[0079] [Table 6-2]

[0080] Next, the hot-rolled sheet was subjected to a first cold rolling with a reduction ratio of 40% to obtain an intermediate thickness of 1.5 mm, and then intermediate annealing was performed by raising the temperature between 400°C and 700°C at a rate of 3°C / s and soaking at 1100°C for 60 seconds.After that, the hot-rolled sheet was subjected to a second cold rolling to obtain a cold-rolled sheet with a final thickness of 0.20 mm.

[0081] The cold-rolled sheet was then heated at a rate of 20°C / s between 400°C and 700°C, and subjected to decarburization annealing, which also served as primary recrystallization annealing, with a soaking temperature of 840°C and a soaking time of 100 seconds. Next, an annealing separator primarily composed of MgO was applied to the surface of the steel sheet after the decarburization annealing, dried, and wound into a coil. After that, the steel sheet was subjected to finish annealing to induce secondary recrystallization, and then a coating liquid containing phosphate, chromate, and colloidal silica in a mass ratio of 3:1:2 was applied to the surface of the steel sheet after the finish annealing. The steel sheet was then subjected to flattening annealing at 800°C for 30 seconds to produce a product sheet coil.

[0082] From the product sheet coil thus obtained, samples for magnetic measurement were cut out so that the total mass was 500 g or more, and an Epstein test was performed to measure the iron loss W 17 / 50 The results are shown in Table 6.

[0083] From Table 6, it can be seen that in addition to the above-mentioned C, Si, Mn, Al, S and Se, steel sheets to which at least one element selected from the elements of groups A to C, namely Sb, Cu, P, Cr, Ni, Sn, Nb, Mo, B, Bi, Ti, V, W, Zn, Zr, Pb, As, Ag, Au, Ga, Ge, Ca, Mg, REM and Hf, is added have a low iron loss W 17 / 50 is lower than 0.80 W / kg, and the {100} <011> It is clear that the magnetic properties are improved by promoting recrystallization of the structure, and the iron loss is reduced by the added elements.

Claims

1. A method for producing a grain-oriented electrical steel sheet, comprising a series of steps of hot-rolling a steel slab to form a hot-rolled sheet, subjecting the hot-rolled sheet to a first cold rolling and a first intermediate annealing without hot-rolled sheet annealing, and then further cold-rolling the hot-rolled sheet to a final thickness by either a single cold rolling or two or more cold rolling steps sandwiching intermediate annealing therebetween, subjecting the cold-rolled sheet to decarburization annealing which also serves as primary recrystallization annealing, and then subjecting the cold-rolled sheet to finish annealing for secondary recrystallization, The reduction ratio of the first cold rolling is 20% or more and less than 60%, a method for producing a grain-oriented electrical steel sheet, characterized in that the area ratio of crystal grains having a GAM value of 0.5 or less when a cross section perpendicular to the rolling direction of the steel sheet after the first intermediate annealing is observed by EBSD is 80% or more.

2. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the heating rate between 400°C and 700°C in the heating process of the first intermediate annealing is 5°C / s or more and 100°C / s or less.

3. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that the steel slab contains 0.01 to 0.10 mass% of C, 2.0 to 4.5 mass% of Si, 0.01 to 0.5 mass% of Mn, 0.0100 to 0.0400 mass% of sol.Al, 0.0050 to 0.0120 mass% of N, 0.01 to 0.05 mass% in total of at least one of S and Se, and the balance being Fe and unavoidable impurities.

4. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that the steel slab contains C: 0.01 to 0.10 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.01 to 0.5 mass%, sol. Al: less than 0.0100 mass%, S: less than 0.0100 mass%, Se: less than 0.0100 mass%, and N: less than 0.0050 mass%, with the balance being Fe and unavoidable impurities.

5. The method for producing a grain-oriented electrical steel sheet according to claim 3 or 4, wherein the steel slab further contains, in addition to the above-mentioned chemical composition, at least one component selected from the following groups A to C: Note Group A: At least one selected from Sb: 0.005 to 0.500 mass%, Cu: 0.01 to 1.50 mass%, P: 0.005 to 0.500 mass%, Cr: 0.005 to 1.50 mass%, Ni: 0.005 to 1.500 mass%, Sn: 0.005 to 0.500 mass%, Nb: 0.0005 to 0.0200 mass%, Mo: 0.005 to 0.500 mass%, Co: 0.001 to 0.500 mass%, B: 0.00001 to 0.007000 mass%, and Bi: 0.0005 to 0.500 mass% Group B: at least one selected from Ti: 0.0005 to 0.0400 mass%, V: 0.001 to 0.020 mass%, and W: 0.001 to 0.020 mass% ・Group C; Zn: 0.0005 to 0.020 mass%, Zr: 0.001 to 0.020 mass%, Pb: 0.0001 to 0.0100 mass%, A s: 0.001 to 0.020 mass%, Ag: 0.001 to 0.050 mass%, Au: 0.001 to 0.050 mass%, Ga: 0.0001 at least one selected from the group consisting of: Cr: 0.0001 to 0.0050 mass%, Ge: 0.0001 to 0.0050 mass%, Ca: 0.0005 to 0.020 mass%, Mg: 0.0005 to 0.020 mass%, REM: 0.0005 to 0.0200 mass%, and Hf: 0.001 to 0.020 mass%

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