Method for manufacturing grain-oriented electrical steel sheet

Abstract

The present invention provides an oriented electromagnetic steel sheet having excellent uniformity of magnetic properties in the sheet width direction, which is manufactured without increasing manufacturing cost. The relationship between the ignition loss of the annealing release agent after drying: IGLOSS (mass %), the storage time T (hr) of the cold-rolled steel sheet, and the carbon dioxide concentration A (mass ppm) in the storage environment of the cold-rolled steel sheet satisfies the following formula (1). A x IGLOSS ≤ -1500 x Ln(T) + 9000 … (1).

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of an oriented electromagnetic steel sheet. BACKGROUND

[0002] Manufacturing of an oriented electromagnetic steel sheet is generally performed by the following processes: hot rolling, annealing and cold rolling of a steel billet adjusted to a prescribed composition, and then, after performing primary recrystallization annealing and decarburization annealing, performing final annealing. In the above processes, in the final annealing process, heat treatment at a high temperature of 1000°C or higher is required. Therefore, in the final annealing process, in order to prevent sintering of the coil, an annealing release agent mainly composed of a powder of magnesium oxide (hereinafter, also referred to as MgO) is generally applied to the surface of the cold-rolled steel sheet.

[0003] The MgO has an effect of forming a forsterite coating film by reacting with an oxide layer (hereinafter, also referred to as SiO2 oxide layer) mainly composed of silicon dioxide (SiO2) in the final annealing. Here, the SiO2 oxide layer is generated on the surface of the cold-rolled steel sheet in the decarburization annealing performed before the final annealing. In addition, the MgO has an effect of purifying the steel sheet by removing precipitates (for example, a part of AlN, MnS, MnSe, Si3N4, TiN, TiC, etc.) called inhibitors that control the grain growth of iron after the final annealing.

[0004] However, carbon in the steel is an element necessary for improving the primary recrystallization texture, for example. However, when a large amount of carbon remains in the final product, sometimes, with the passage of time, it is precipitated in the form of carbide inside the steel sheet. And, this carbide causes a problem of deteriorating magnetic properties, a so-called magnetic aging problem.

[0005] As a technique for solving such a problem, for example, Patent Literature 1 discloses "A manufacturing method of an oriented silicon steel sheet with less deterioration of iron loss accompanying stress relief annealing, characterized by, after performing cold rolling one time or two or more times with interposing intermediate annealing on a hot-rolled sheet for oriented silicon steel, performing decarburization annealing, then applying an annealing release agent mainly composed of MgO containing a Ti compound, and then performing final product annealing, setting the total carbon content in the steel of the steel sheet on which the annealing release agent is applied before the final product annealing and in the annealing release agent to 0.0015 wt% or less".

[0006] In addition, Patent Literature 2 discloses: "A manufacturing method of an oriented electromagnetic steel sheet coil, characterized by including a series of processes of: hot-rolling a silicon steel billet containing 1.0 to 5.0 mass% of Si, then, after performing cold rolling one time or two or more times including annealing treatment to a final sheet thickness, performing primary recrystallization annealing, then, after applying an annealing release agent to the surface of the steel sheet, performing final product annealing,

[0007] As the main agent of the annealing separation agent, a titanium oxide compound having the following composition is used in an amount of 1 to 10 parts by mass with respect to 100 parts by mass of magnesium oxide, which is contained in an amount of at least 50% and is contained as a trace content.

[0008] (M + a, M 2+ b, M 3+ c) TixOy

[0009] wherein 0≤a≤4, 0≤b≤2, 0≤c≤2

[0010] 1≤x≤4, 2≤y≤9

[0011] M + : any one selected from the group consisting of Li, Na, K

[0012] M 2+ : any one selected from the group consisting of Mg, Ca, Sr, Ba, Cr, Co, Mn, Zn, Fe

[0013] M 3+ : any one selected from the group consisting of Fe, Al, Cr, Mn

[0014] Prior Art Documents

[0015] Patent Documents

[0016] Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2-93021

[0017] Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2007-169755 SUMMARY

[0018] However, in the technology of Patent Document 1, there is a problem that the carbon content in the steel in the vicinity of the plate width end portion (hereinafter, also referred to as the coil edge portion) of the steel sheet in the form of a coil obtained after the final annealing is not sufficiently reduced, and the magnetic aging of the coil edge portion is not sufficiently improved.

[0019] In addition, in the technology of Patent Document 2, since the Ti composite oxide having the above-described special composition is required to be used, there is a problem that the manufacturing cost is increased.

[0020] The present application has been developed in order to solve the above-described problems, and has an object to provide a method of manufacturing an oriented electromagnetic steel sheet in which the carbon content of the coil edge portion after the final annealing is stabilized at a low level without causing an increase in the manufacturing cost, and the magnetic aging in the plate width direction of the entire coil (hereinafter, also referred to as "excellent uniformity of the magnetic properties in the plate width direction") is improved.

[0021] In addition, the inventors have conducted intensive research from the viewpoint of production management in order to achieve the above object without increasing manufacturing costs.

[0022] As a result, the inventors have found that in the technique of Patent Literature 1, the carbon content in the steel of the coil edge portion is not sufficiently reduced because the annealing separator applied to the coil edge portion carbonizes and carburization occurs during the period from after the application of the annealing separator and the winding into a coil to the start of the final annealing, i.e., during the standby in the coil yard.

[0023] In addition, based on the above insight, the inventors have further conducted research and found that by satisfying the following relationship of the ignition loss of the dried annealing separator: IGLOSS (mass %), the storage time T (hr) of the cold-rolled steel sheet, and the carbon dioxide concentration A (mass ppm) in the storage environment of the cold-rolled steel sheet, the carbon content of the coil edge portion after the final annealing is stabilized at a low level, thereby improving the magnetic aging in the sheet width direction of the entire coil.

[0024] A x IGLOSS ≤ -1500 x Ln(T) + 9000... (1)

[0025] The present application has been further researched based on the above situation and completed.

[0026] That is, the gist of the present application is as follows.

[0027] 1. A manufacturing method of an oriented electromagnetic steel sheet, characterized by comprising the steps of:

[0028] a step of preparing a cold-rolled steel sheet having a composition of C: 0.0100 mass% or more and Si: 1.0 mass% or more;

[0029] a step of performing decarburization annealing on the cold-rolled steel sheet;

[0030] a step of applying an annealing separator mainly composed of MgO to the surface of the cold-rolled steel sheet and drying the annealing separator;

[0031] a step of storing the cold-rolled steel sheet after winding the cold-rolled steel sheet into a coil shape;

[0032] a step of performing final annealing on the cold-rolled steel sheet,

[0033] the ignition loss of the dried annealing separator: IGLOSS (mass %), the storage time T (hr) of the cold-rolled steel sheet, and the carbon dioxide concentration A (mass ppm) in the storage environment of the cold-rolled steel sheet satisfy the following relationship of Expression (1).

[0034] A x IGLOSS ≤ -1500 x Ln(T) + 9000... (1)

[0035] Effects of Invention

[0036] According to the present application, an oriented electromagnetic steel sheet having excellent uniformity of magnetic properties in the sheet width direction can be produced at low cost. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a schematic view showing a sample collection position for evaluating magnetic aging. DETAILED DESCRIPTION

[0038] The present application will be described based on the following embodiments.

[0039] The manufacturing method of the oriented electromagnetic steel sheet of one embodiment of the present application has the following steps:

[0040] a step of preparing a cold-rolled steel sheet having a composition containing C: 0.0100 mass% or more and Si: 1.0 mass% or more (hereinafter, also referred to as a preparation step);

[0041] a step of performing decarburization annealing on the cold-rolled steel sheet (hereinafter, also referred to as a decarburization annealing step);

[0042] a step of applying an annealing release agent mainly containing MgO to the surface of the cold-rolled steel sheet and drying the annealing release agent (hereinafter, also referred to as an application and drying step);

[0043] a step of winding the cold-rolled steel sheet into a roll shape and storing the cold-rolled steel sheet (hereinafter, also referred to as a storage step);

[0044] a step of performing final annealing on the cold-rolled steel sheet (hereinafter, also referred to as a final annealing step),

[0045] the ignition loss of the annealing release agent after drying (IGLOSS (mass%)), the storage time T (hr) of the cold-rolled steel sheet, and the carbon dioxide concentration A (mass ppm) in the storage environment of the cold-rolled steel sheet satisfy the following relation of formula (1).

[0046] A x IGLOSS ≤ -1500 x Ln(T) + 9000... (1)

[0047] Hereinafter, each step will be described.

[0048] [Preparation Step]

[0049] First, a cold-rolled steel sheet having a composition containing C: 0.0100 mass% or more and Si: 1.0 mass% or more is prepared.

[0050] Here, the preparation method of the cold-rolled steel sheet is not particularly limited. For example, a steel billet having a composition of C: 0.0100 mass% or more and Si: 1.0 mass% or more is subjected to hot-rolling to obtain a hot-rolled steel sheet. The hot-rolled steel sheet is subjected to hot-rolled sheet annealing as necessary, and then cold-rolled once or two or more times with an intermediate annealing interposed to produce a cold-rolled steel sheet. Thus, a cold-rolled steel sheet having the above composition can be prepared.

[0051] Note that the conditions of the hot-rolling, the hot-rolled sheet annealing, the intermediate annealing, and the cold-rolling are not particularly limited and can be performed according to conventional methods.

[0052] In addition, the cold-rolled steel sheet prepared has the following reasons for the limitation of the composition.

[0053] C: 0.0100 mass% or more

[0054] C is a component useful for generating grains having a Goss orientation. To effectively exert such an effect, the C content is set to 0.0100 mass% or more. On the other hand, when C is too much, even if decarburization annealing is performed, decarburization failure sometimes occurs. Therefore, the C content is preferably 0.1000 mass% or less.

[0055] Si: 1.0 mass% or more

[0056] Si is an element that increases the electrical resistance to reduce the iron loss. In addition, Si is also an element that stabilizes the BCC structure of iron to enable high-temperature heat treatment. Therefore, the Si content is set to 1.0 mass% or more. The Si content is preferably 2.0 mass% or more. On the other hand, if Si is too much, there is a case where cold-rolling becomes difficult. Therefore, the Si content is preferably 5.0 mass% or less.

[0057] In addition, in the composition of the cold-rolled steel sheet prepared, in addition to the above elements, any of the following elements can be arbitrarily contained in mass%:

[0058] (a) Mn: 0.01 to 1.0%,

[0059] (b) sol. Al: 0.003 to 0.050%,

[0060] (c) N: 0.001 to 0.020% and

[0061] (d) at least one selected from S: 0.001 to 0.05% and Se: 0.001 to 0.05%, alone or in combination with (a) to (d).

[0062] Mn is effective in improving the hot shortness of the steel. In addition, Mn forms precipitates such as MnS, MnSe, etc. with S and Se, and functions as an inhibitor. From the viewpoint of sufficiently obtaining this effect, the Mn content is preferably 0.01 mass% or more. On the other hand, if Mn is too much, the precipitates such as MnSe, etc. become coarse. Thus, the effect as an inhibitor is sometimes lost. Therefore, the Mn content is preferably 1.0 mass% or less.

[0063] sol.Al is a useful component that forms AlN in the steel and functions as an inhibitor as a dispersed second phase. If Al is too little, the amount of AlN precipitates is sometimes insufficient. On the other hand, if Al is too much, AlN is coarsely precipitated, and the effect as an inhibitor is sometimes lost. Therefore, the sol.Al content is preferably 0.003 to 0.050 mass%.

[0064] N is a component for forming AlN, like Al. If N is too little, the precipitation of AlN becomes insufficient. On the other hand, if N is too much, bulging, etc. occurs at the time of slab heating. Therefore, the N content is preferably 0.001 to 0.020 mass%.

[0065] Both S and Se are useful components that function as an inhibitor. That is, S and Se form compounds such as MnSe, MnS, Cu 2－x Se, Cu 2－x S, etc. with Mn, Cu. Moreover, these compounds function as an inhibitor as a dispersed second phase in the steel. If S and Se are too little, the effect of their addition is sometimes insufficient. On the other hand, if S and Se are too much, solid solution at the time of slab heating becomes incomplete. In addition, defects on the surface of the product are sometimes caused. Therefore, the S and Se contents are respectively preferably 0.001 to 0.05 mass%.

[0066] In addition, in the composition of the prepared cold-rolled steel sheet, in addition to the above-described elements, the following are arbitrarily contained in mass%:

[0067] at least one selected from Cu: 0.01 to 0.2%, Ni: 0.01 to 0.5%, Cr: 0.01 to 0.5%, Sb: 0.01 to 0.1%, Sn: 0.01 to 0.5%, Mo: 0.01 to 0.5%, and Bi: 0.001 to 0.1%.

[0068] Cu, Ni, Cr, Sb, Sn, Mo, and Bi are all elements that have the effect as an auxiliary inhibitor, and contribute to the improvement of magnetic properties. If any of the elements is less than the above-described content, the effect is difficult to obtain. On the other hand, if the above-described content is exceeded, defects in the appearance of the coating, and secondary recrystallization defects are sometimes easily caused. Therefore, the contents of these elements are preferably within the above-described ranges.

[0069] In addition, in the composition of the prepared cold-rolled steel sheet, in addition to the above-mentioned elements, there are also contained, as needed, in mass %:

[0070] at least one element selected from the group consisting of B: 0.001 to 0.01 %, Ge: 0.001 to 0.1 %, As: 0.005 to 0.1 %, P: 0.005 to 0.1 %, Te: 0.005 to 0.1 %, Nb: 0.005 to 0.1 %, Ti: 0.005 to 0.1 %, and V: 0.005 to 0.1 %.

[0071] Thereby, the restraining force is further enhanced, and a higher magnetic flux density can be stably obtained.

[0072] In the composition of the prepared cold-rolled steel sheet, the remainder other than the above-mentioned elements is Fe and inevitable impurities. Note that, in the case where the content of the above-mentioned optional added element is lower than the lower limit, the optional added element is contained as an inevitable impurity.

[0073] In addition, the sheet thickness of the prepared cold-rolled steel sheet is not particularly limited, and is preferably set to 0.14 to 0.50 mm. In addition, the sheet width (width in the direction perpendicular to the rolling) of the prepared cold-rolled steel sheet is not particularly limited, and is preferably set to 900 to 1500 mm. Note that, the preferable range of the sheet thickness and the sheet width of the cold-rolled steel sheet wound in a roll shape is the same.

[0074] [Decarburization annealing step]

[0075] Next, decarburization annealing is performed on the cold-rolled steel sheet prepared in the above-mentioned preparation step. The conditions of the decarburization annealing are not particularly limited, and can be performed according to a conventional method. For example, from the viewpoint of reliably decarburizing and forming a SiO2 oxide layer, the atmosphere in the decarburization annealing is preferably set to a wet hydrogen atmosphere. Note that, the SiO2 oxide layer reacts with MgO in the annealing separator at the final annealing as described above, and forms a forsterite coating.

[0076] Here, the wet hydrogen atmosphere refers to an atmosphere in which the hydrogen concentration is 50 vol% or more, and the dew point is 40°C to 65°C. In addition, the decarburization annealing temperature is preferably 800°C to 900°C. By setting the hydrogen concentration in the wet hydrogen atmosphere to 50 vol% or more, the decarburization rate and the oxidation rate can be stably controlled. In addition, when the decarburization annealing temperature is too low or the dew point is too low, decarburization failure sometimes occurs. On the other hand, when the decarburization annealing temperature is too high or the dew point is too high, an internal oxide layer is excessively formed, and product failure sometimes occurs. Note that, in the wet hydrogen atmosphere, the remainder other than hydrogen is not particularly limited, and for example, a neutral gas such as nitrogen, argon, or the like can be cited. In particular, the remainder other than hydrogen in the wet hydrogen atmosphere is preferably nitrogen (that is, as the wet hydrogen atmosphere, a mixed atmosphere of hydrogen and nitrogen is used).

[0077] In addition, the decarburization annealing is usually performed as a primary recrystallization annealing, but the decarburization annealing and the primary recrystallization annealing can be performed separately. Note that the conditions other than the above are not particularly limited and can be performed according to a conventional method. For example, the annealing time is preferably set to 30 to 180 seconds.

[0078] [coating and drying step]

[0079] Next, the annealing release agent mainly containing MgO is coated on the surface of the cold-rolled steel sheet that has undergone the decarburization annealing step, and the annealing release agent is dried.

[0080] For example, the annealing release agent mainly containing MgO is made into a slurry and coated on the surface of the cold-rolled steel sheet using a roll coater or the like. At this time, the slurry temperature is preferably controlled within a certain range (±5°). Note that if the slurry temperature is controlled at a temperature deviating too much from the normal temperature, energy is wasted, and thus the central value of the control of the slurry temperature is preferably 5°C to 30°C. Then, the cold-rolled steel sheet on which the annealing release agent mainly containing MgO is coated is dried using an infrared heating furnace, a hot air furnace, or the like, and excess moisture in the annealing release agent is removed. The final sheet temperature (hereinafter, also referred to as a drying temperature) is preferably 350°C or higher. Thereby, magnesium hydroxide (Mg(OH)2) generated by the hydration reaction is returned to MgO. In addition, at this time, the reactivity of the generated MgO is very high, and thus the forsterite coating film formed at the final annealing is also in a good state.

[0081] Here, the main component of MgO means that the MgO content of the annealing release agent is 50% by mass or more. If the MgO content is less than 50% by mass, the amount of the forsterite coating film is insufficient. The MgO content of the annealing release agent is preferably 60% by mass or more, and more preferably 80% by mass or more.

[0082] Note that the remaining portion other than MgO of the annealing release agent contains, for example, TiO2, sulfides, sulfates, oxides, and hydroxides of alkaline earth metals, and the like.

[0083] Note that the conditions other than the above are not particularly limited and can be performed according to a conventional method. For example, the unit area weight of the annealing release agent is preferably set to 2.5 to 10 g / m2per one side of the steel sheet after drying. 2 In addition, the drying time is preferably set to 1 to 5 minutes.

[0084] [storage step]

[0085] Next, the cold-rolled steel sheet that has undergone the coating and drying step is wound into a roll shape, and the cold-rolled steel sheet is stored. Note that the storage of the cold-rolled steel sheet is usually performed at a coil yard.

[0086] Further, in the manufacturing method of the grain-oriented magnetic steel sheet according to an embodiment of the present application, it is extremely important in the storage process that the relationship between the ignition loss (IGLOSS (% by mass)) of the dried annealing separator, the storage time T (hr) of the cold-rolled steel sheet, and the carbon dioxide concentration A (ppm by mass) in the storage environment of the cold-rolled steel sheet satisfies the following formula (1).

[0087] A x IGLOSS ≤ -1500 x Ln(T) + 9000... (1)

[0088] Note that Ln in the formula means a natural logarithm.

[0089] That is, in order to reduce the carbon concentration in the final product of the grain-oriented magnetic steel sheet, particularly to less than 40 ppm by mass, it is important to preferably:

[0090] (1) sufficiently remove carbon from the steel sheet in the decarburization annealing;

[0091] (2) reduce the carbon concentration in the annealing separator, and

[0092] (3) suppress carbonation caused by CO2 in the atmosphere during the coil storage.

[0093] The conditions of the storage process are closely related to (3) the suppression of carbonation during the coil storage.

[0094] That is, as the mechanism of the carbonation during the coil storage of (3), as shown in the following reaction formula, it is considered that basic magnesium carbonate is generated by carbonation of magnesium hydroxide (Mg(OH)2).

[0095] (m + 1)Mg(OH)2+ mCO2→ mMgCO3· Mg(OH)2· mH2O... (2)

[0096] In the above reaction formula, m is an integer of 3 to 5.

[0097] Note that in the above Patent Document 2, it is described that since the operation state of the final annealing device is unstable, it is difficult to control the storage time in the coil storage which corresponds to the reaction time of the chemical reaction of the above reaction formula. In addition, it is described that controlling the CO2 concentration and humidity in the atmosphere would cost a huge amount, and thus is impractical.

[0098] However, Mg(OH)2on the left side of the above formula (2) is generated by a series of processes in which an annealing separator mainly composed of MgO is applied to the surface of the steel sheet in the form of a water slurry and dried. Further, it is considered that the content of Mg(OH)2in the dried annealing separator can be measured as the ignition loss (IGLOSS) prescribed in JIS K 0067: 1992.

[0099] Here, in JIS K 0067:1992, the ignition temperature is prescribed as 650°C ± 50°C. However, when the ignition temperature is set to 650°C ± 50°C to measure the ignition loss of the annealing separator after drying, it is known that the ignition loss includes a loss of MgCO3 in addition to a loss of Mg(OH)2.

[0100] Therefore, the inventors and others further repeated research, and as a result, obtained the following insights.

[0101] • In order to accurately measure the loss of Mg(OH)2, it is necessary to set the ignition temperature to 500°C ± 10°C and the soaking time to 30 minutes to measure the ignition loss of the annealing separator after drying.

[0102] • By causing the ignition loss of the annealing separator after drying measured under such conditions: IGLOSS (mass %), the storage time T (hr) of the cold-rolled steel sheet, and the carbon dioxide concentration A (mass ppm) in the storage environment of the above cold-rolled steel sheet to satisfy the following formula (1), it is possible to suppress carbonation of the annealing separator applied to the edge portion of the coil, and further suppress carburization to the edge portion of the coil. As a result, it is possible to manufacture an oriented electromagnetic steel sheet in which the uniformity of magnetic properties in the sheet width direction is excellent.

[0103] Here, the ignition loss of the annealing separator after drying: IGLOSS (mass %) is measured as follows.

[0104] That is, 2 g of the annealing separator after drying is sampled in powder form from the surface of the cold-rolled steel sheet that has undergone the above application and drying process. The sampled annealing separator after drying is used as a test sample, and the loss (decrease in mass when the test sample is ignited) is measured by a method according to JIS K 0067:1992 under conditions of an ignition temperature of 500°C and a soaking time of 30 minutes. Furthermore, the measured loss is expressed as a mass percentage, and is used as the ignition loss of the annealing separator after drying: IGLOSS (mass %).

[0105] In addition, the storage time T (hr) of the cold-rolled steel sheet is set to the time from the end time of winding of the cold-rolled steel sheet to the start time of the final annealing.

[0106] Here, the end time of winding of the cold-rolled steel sheet refers to the time when a continuous steel sheet is wound, and then the steel sheet is cut to separate the steel sheet in the form of a coil. In addition, the start time of the final annealing refers to the time when the coil is placed on a coil support in the final annealing furnace.

[0107] Furthermore, the carbon dioxide concentration A (mass ppm) in the storage environment of the cold-rolled steel sheet is measured as follows.

[0108] That is, the carbon dioxide concentration in the atmosphere at 0 minutes in Coordinated Universal Time (UTC) is measured when the cold-rolled steel sheet is stored. Also, the arithmetic mean of the carbon dioxide concentration in the atmosphere at 0 minutes in Coordinated Universal Time (UTC) measured in the storage of the cold-rolled steel sheet is taken as the carbon dioxide concentration A in the storage environment of the cold-rolled steel sheet.

[0109] Note that, in order to satisfy the above formula (1), for example, in the case where it is known in advance that T becomes longer due to maintenance of the equipment or the like, it is effective to lower IGLOSS by making the drying temperature of the annealing separator 400°C or higher, or increasing the drying time. Also, in this case, since the amount of return of the temporarily generated magnesium hydroxide (Mg(OH)2) to magnesium oxide (MgO) increases, the appearance of the forsterite coating after the final annealing becomes uniform, and thus is preferable.

[0110] Also, in the case where T becomes longer than planned due to equipment failure or the like, it is necessary to lower the carbon dioxide concentration in the storage environment of the cold-rolled steel sheet. As such a method, for example, a method of performing nitrogen purging by covering the coil with a plastic cover and supplying liquid nitrogen into the cover can be given.

[0111] Note that, there is no particular limitation as long as the above formula (1) is satisfied, and generally, it is preferable that IGLOSS be 1.5 to 5.0 mass%, the storage time T of the cold-rolled steel sheet be 4 to 240 hr, and the carbon dioxide concentration A in the storage environment of the cold-rolled steel sheet be 200 to 800 mass ppm.

[0112] The conditions other than the above are not particularly limited, and can be performed according to a conventional method.

[0113] [Final annealing step]

[0114] Next, the cold-rolled steel sheet that has undergone the above storage step is subjected to final annealing. The conditions for the final annealing are not particularly limited, and can be performed according to a conventional method. For example, the annealing temperature is preferably set to 1100 to 1250°C, and the annealing time is preferably set to 5 to 20 hours.

[0115] Also, after the final annealing step, planarization annealing can be performed as necessary. The conditions for the planarization annealing are not particularly limited, and can be performed according to a conventional method.

[0116] Example

[0117] Example 1

[0118] A steel billet having a composition in mass% of C: 0.0400%, Si: 3.25%, Mn: 0.08%, S: 0.002%, sol. Al: 0.015%, N: 0.006%, Cu: 0.05%, and Sb: 0.01%, with the balance being Fe and inevitable impurities, was heated under conditions of a slab heating temperature of 1150°C and a holding time of 20 minutes. Subsequently, the steel billet was hot-rolled to obtain a hot-rolled steel sheet having a sheet thickness of 2.4 mm. Subsequently, the obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing under conditions of an annealing temperature of 1000°C and an annealing time of 60 seconds (1 minute). Subsequently, the hot-rolled steel sheet was cold-rolled to prepare a cold-rolled steel sheet having a sheet thickness (final sheet thickness) of 0.27 mm. Note that the composition of the prepared cold-rolled steel sheet was the same as the composition of the above-mentioned steel billet.

[0119] The prepared cold-rolled steel sheet was subjected to decarburization annealing serving also as primary recrystallization annealing under conditions of an annealing temperature of 820°C and an annealing time of 60 seconds in a wet hydrogen atmosphere of hydrogen: 50 vol% - nitrogen: 50 vol% and a dew point of 50°C. Note that the average temperature increase rate from room temperature to 820°C was set to 100°C / s. In addition, the carbon content of the matrix iron portion of the cold-rolled steel sheet after decarburization annealing was 5 mass ppm.

[0120] Subsequently, an annealing separator mainly composed of MgO, specifically, an annealing separator prepared by mixing 5 mass parts of TiO2with respect to 100 mass parts of MgO was made into a water slurry and subjected to hydration treatment at 15°C x 2.0 hours. Subsequently, the annealing separator was applied to the cold-rolled steel sheet after decarburization annealing so that the weight per unit area of one side of the steel sheet after drying was 6.5 g / m2. 2 Subsequently, the annealing separator was dried at a drying temperature of 350°C and a drying time of 1 minute.

[0121] Subsequently, the cold-rolled steel sheet was wound into a roll and stored for a certain period of time under the conditions shown in Table 1. Note that the ignition loss (mass%) of the dried annealing separator was measured by the above-mentioned method, and the value was 3.0 mass%. In addition, the carbon dioxide concentration A in the storage environment of the cold-rolled steel sheet was controlled by the above-mentioned method.

[0122] Next, the cold-rolled steel sheet was subjected to final annealing at an annealing temperature of 1200°C and an annealing time of 5 hours. It should be noted that the heating time from 300°C to 800°C was set to 100 hours, and the average heating rate from 800°C to 1200°C was set to 50°C / hr. It should be noted that after final annealing, unreacted annealing separating agent was removed with a brush. Then, the cold-rolled steel sheet was subjected to planarization annealing in a non-oxidizing atmosphere of nitrogen (98 vol%) and the balance hydrogen at an annealing temperature of 800°C and an annealing time of 30 seconds to obtain the oriented electromagnetic steel sheet as the final product.

[0123] Next, the magnetic aging of the obtained oriented electromagnetic steel sheet was evaluated.

[0124] That is, such as Figure 1 As shown, samples with a length of 300 mm × width (in the width direction of the sheet) of 1000 mm were collected from the center of the coil (the center of the sheet width) and the edge of the coil, respectively, at a position 1000 mm inward from the outermost part of the coil of the obtained oriented electromagnetic steel sheet (unrolled). It should be noted that in the sample collected from the center of the coil (the center of the sheet width), the center position in the width direction is the center position of the sheet width of the coil. In addition, in the sample collected from the edge of the coil, the center position in the width direction is located 60 mm from the end of the sheet width of the coil (i.e., the area 10 mm from the end of the sheet width is cut off).

[0125] Next, the iron loss (W) of samples collected from the center of the roll (center of the roll width) and the edge of the roll was measured. 17 / 50 The measurement results are recorded in Table 1. It should be noted that the W values ​​of samples taken from the center (center of the sheet width) and the edge of the roll (before stress-relief annealing) are different. 17 / 50 All values ​​were in the range of 0.88–0.93 W / kg. Furthermore, the B8 values ​​of samples taken from the center (center of the sheet width) and the edge of the roll (before stress-relief annealing) were both in the range of 1.895–1.905 T.

[0126] Next, the samples were stress-relieved annealed in a nitrogen atmosphere at an annealing temperature of 800°C and an annealing time of 3 hours. Then, the iron loss and carbon content of the base metal portion of the stress-relieved samples were measured. Then, for each sample collected from the center of the roll (center of the plate width) and the edge of the roll, the iron loss ratio before and after stress-relief annealing was calculated (=[iron loss measured in the stress-relief annealed sample] / [iron loss measured in the sample before stress-relief annealing]), and the uniformity of the magnetic properties in the plate width direction was evaluated according to the following criteria.

[0127] Pass (excellent): the ratio of iron loss before and after stress relief annealing is 1.05 or less in both samples taken from the central part of the coil (central part of the plate width) and the edge part of the coil

[0128] Fail: the ratio of iron loss before and after stress relief annealing exceeds 1.05 in at least one of the samples taken from the central part of the coil (central part of the plate width) and the edge part of the coil

[0129] The results are collectively shown in Table 1.

[0130]

[0131]

[0132] As shown in Table 1, excellent uniformity of the magnetic properties in the plate width direction was obtained in all of the inventive examples. In addition, in the inventive examples, the carbon content of the base metal in the edge part of the coil was suppressed to 40 mass ppm or less. Furthermore, good coating appearance was obtained in all of the inventive examples.

[0133] On the other hand, in the comparative examples, sufficient uniformity of the magnetic properties in the plate width direction was not obtained.

[0134] Example 2

[0135] A steel billet having, in mass%, C: 0.0100%, Si: 2.00%, Mn: 0.07%, S: 0.015%, Sb: 0.015%, and Cr: 0.03%, with the balance being Fe and unavoidable impurities was heated under conditions of a slab heating temperature of 1350°C and a holding time of 40 minutes. Subsequently, the steel billet was hot-rolled to obtain a hot-rolled steel sheet having a plate thickness of 2.6 mm. Subsequently, the obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing under conditions of an annealing temperature of 900°C and an annealing time of 60 seconds. Subsequently, the hot-rolled steel sheet was subjected to cold-rolling with interposing intermediate annealing under conditions of an annealing temperature of 1050°C and an annealing time of 60 seconds, and a cold-rolled steel sheet having a plate thickness (final plate thickness) of 0.30 mm was prepared. Note that the composition of the prepared cold-rolled steel sheet was the same as the composition of the above-described steel billet.

[0136] The prepared cold-rolled steel sheet was subjected to decarburization annealing serving also as primary recrystallization annealing under conditions of an annealing temperature of 840°C and an annealing time of 60 seconds in a wet hydrogen atmosphere of hydrogen: 60 vol% - nitrogen: 40 vol% and a dew point of 55°C. Note that the average temperature increase rate from room temperature to 820°C was set to 700°C / s. In addition, the carbon content of the base iron part of the cold-rolled steel sheet after decarburization annealing was 4 mass ppm.

[0137] Next, the annealing separator mainly composed of MgO, specifically, the annealing separator in which 3 parts by mass of TiO2 is mixed with 100 parts by mass of MgO was made into a water slurry, and subjected to a hydration treatment at the temperature described in Table 2 for 1.0 hour. Next, the annealing separator was applied to the cold-rolled steel sheet after decarburization annealing so that the dry unit area weight per single side of the steel sheet was 6.5 g / m2. 2 Next, the annealing separator was dried under the drying temperature and drying time described in Table 2: 1 minute.

[0138] Next, the cold-rolled steel sheet was wound into a coil, and stored for a certain period of time under the conditions described in Table 2. In addition, the ignition loss (mass %) of the dried annealing separator was measured by the above-described method. The results of the measurement are described in Table 2. In addition, the carbon dioxide concentration A in the storage environment of the cold-rolled steel sheet was controlled by the above-described method.

[0139] Next, the cold-rolled steel sheet was subjected to final annealing under the conditions of an annealing temperature: 1200°C, and an annealing time: 5 hours. Note that the temperature increase time from 300°C to 700°C was set to 100 hours, and the average temperature increase rate from 700°C to 1200°C was set to 20°C / hr. Note that the unreacted annealing separator was removed with a brush after the final annealing. Next, the cold-rolled steel sheet was subjected to flattening annealing under the conditions of an annealing temperature: 820°C, and an annealing time: 30 seconds in a non-oxidizing atmosphere in which the nitrogen: 98 vol%, and the balance is hydrogen, to obtain an oriented electromagnetic steel sheet that became a final product.

[0140] Then, in accordance with the same procedure as in Example 1, samples having a length: 300 x width (sheet width direction): 100 mm were collected from the central portion of the coil (central portion in the sheet width direction) and the edge portion of the coil, and the magnetic aging of the obtained oriented electromagnetic steel sheet was evaluated. The results are described in Table 2. Note that the evaluation criteria were the same as in Example 1. In addition, the W 17 / 50 values of the samples collected from the central portion of the coil (central portion in the sheet width direction) and the edge portion of the coil before the stress relief annealing were all in the range of 1.10 to 1.20 W / kg. In addition, the B8 values of the samples collected from the central portion of the coil (central portion in the sheet width direction) and the edge portion of the coil before the stress relief annealing were all in the range of 1.865 to 1.875 T.

[0141]

[0142] As shown in Table 2, excellent uniformity of the magnetic properties in the sheet width direction was obtained in all of the inventive examples. In addition, in the inventive examples, the carbon content of the base metal in the edge portion of the coil was all suppressed to less than 40 mass ppm. Furthermore, good film appearance was obtained in all of the inventive examples.

[0143] On the other hand, in the comparative example, the uniformity of the magnetic properties in the plate width direction was not sufficient.

Claims

1. A method of manufacturing an oriented electromagnetic steel sheet, comprising the steps of: preparing a cold-rolled steel sheet having a composition comprising C: 0.0100 mass% or more and Si: 1.0 mass% or more; subjecting the cold-rolled steel sheet to decarburization annealing; applying an annealing separator mainly comprising MgO to the surface of the cold-rolled steel sheet and drying the annealing separator; storing the cold-rolled steel sheet after winding the cold-rolled steel sheet into a coil shape; and subjecting the cold-rolled steel sheet to final annealing; wherein a relationship between an ignition loss IGLOSS of the dried annealing separator, a storage time T of the cold-rolled steel sheet, and a carbon dioxide concentration A in a storage environment of the cold-rolled steel sheet satisfies the following formula (1), A x IGLOSS ≤ -1500 x Ln(T) + 9000 (1), wherein the ignition loss IGLOSS of the dried annealing separator is measured at a burning temperature of 500°C ± 10°C and a soaking time of 30 minutes, the unit of IGLOSS is mass%, the unit of T is hr, and the unit of A is mass ppm. ​ ​ ​ ​ ​ ​ ​ wherein ​

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