DESCRIPTION
TITLE OF THE INVENTION: MANUFACTURING METHOD OF GRAIN-ORIENTED ELECTRICAL STEEL SHEET
TECHNICAL FIELD
[0001] The present invention relates to a manufacturing method of a grain-oriented electrical steel sheet having a coating film excellent in insulation performance.
BACKGROUND ART
[0002] A grain-oriented electrical steel sheet has been mainly used as an iron core material of a transformer, a generator, or the like. Not only a magnetic property but also surface properties of the steel sheet are important elements related to the quality of the above material, and one of the surface properties is insulation performance of a coating film being a surface coating film and made of colloidal silica and phosphate and so on. The insulation performance of the above coating film is greatly affected by adhesiveness to a glass film having forsterite (Mg2Si04) as its main component and being a base. The above glass film is produced by solid-phase reaction of powder of an annealing separating agent having MgO as its main component and an oxide film based on Si02 on the surface of the
steel sheet during finish annealing. As above, the annealing separating agent not only affects preventing adhesion of the steel sheets, dissolution behavior of an inhibitor such as A1N and controlling secondary recrysta11ization but also has an important function as a raw material of the glass film. [0003] In order to produce the uniform and good glass film, it is necessary to increase activity of the solid-phase reaction to the oxide film on the surface of the steel sheet. Thus, for example, Patent Document 1 proposes that MgO being a main component of an annealing separating agent is made into particles having an average grain size being 2.5 µm or less and having the proportion of particles not passing through a 325 mesh in a particle size distribution being 5% or less.
[0004] When the above annealing separating agent is coated on the steel sheet, it is common that the annealing separating agent dispersed in water, which is in a slurry form, is coated on a decarburization-annealed steel sheet to be dried at 200°C to 300°C. Then, during finish annealing, the annealing separating agent reacts with an oxide film based on Si02 on the surface of the steel sheet, and thereby a glass film is formed during the finish annealing. Thereafter, powder of the redundant annealing separating agent, which is unreacted and left, is removed by light pickling, water cleaning, brushing,
and so on, before the steel sheet has an insulating coating agent to be a raw material of an insulating coating film coated thereon and is baked. [0005] Here, when a holding time when a finish-annealed steel sheet is exposed to the atmosphere after finishing the finish annealing until the powder removing is prolonged, a coarse aggregate having a diameter of several dozen µ m of the annealing separating agent remains on the glass film at the stage of powder removing. When the coarse aggregate remains on the glass film in this manner, even though the insulating coating agent is coated on the glass film in order to produce the coating film having a thickness of 1 µ m to 2 µ m, the coating film has difficulty in adhering to the top of the conductive coarse aggregate to have a sufficient thickness, so that insulation performance failure is caused.
CITATION LIST PATENT LITERATURE [0006]
[Patent Literature 1] Japanese Laid-open Patent Publication No. 06-33138
[Patent Literature 2] Japanese Laid-open Patent Publication No. 07-76376
[Patent Literature 3] Japanese Laid-open Patent Publication No. 10-158744
SUMMARY OF THE INVENTION
TECHNICAL PROBLEM
[0007] In consideration of the previously described
problem, the present invention has an object to
provide a manufacturing method of a grain-oriented
electrical steel sheet having a coating film
excellent in insulation performance.
SOLUTION TO PROBLEM
[0008] In order to solve the above-described
problem, the present invention has characteristics
below.
(1) A manufacturing method of a grain-oriented
electrical steel sheet includes:
decarburization annealing a cold-rolled sheet to obtain a decarburization-annealed steel sheet;
coating an annealing separating agent containing MgO and TiO2 on the decarburization-annealed steel sheet and performing finish annealing to obtain a finish-annealed steel sheet;
performing powder removing on the finish-annealed steel sheet; and
coating and baking an insulating coating agent containing colloidal silica and phosphate on the finish-annealed steel sheet on which the powder removing is performed, in which
a holding time when the finish-annealed steel sheet is exposed to an atmosphere after finishing the
finish annealing until starting the performing the powder removing, and humidity of the atmosphere to which the finish-annealed steel sheet is exposed are controlled to satisfy a condition shown in an expression (1) below.
D ≤ -401og10t + 180 • • • the expression (1) (Here, D denotes the humidity (%) and t denotes the holding time (h).)
(2) The manufacturing method of the grain-oriented electrical steel sheet according to (1), in which the holding time when the finish-annealed steel sheet is exposed to the atmosphere after finishing the finish annealing until starting the performing the powder removing, the humidity of the atmosphere to which the finish-annealed steel sheet is exposed, and a temperature of the atmosphere are controlled to further satisfy a condition shown in an expression
(2) below.
D ≤ -0.132L + 224 • • • the expression (2) (Here, L = (273 + T) X { (log10t) + 1.2}, D denotes the humidity (%), t denotes the holding time (h), and T denotes the temperature (°C) . )
(3) The manufacturing method of the grain-oriented
electrical steel sheet according to (1), in which a
content of TiO2 contained in the annealing separating
agent is 0.1 parts by mass to 7.5 parts by mass
relative to 100 parts by mass of MgO.
(4) The manufacturing method of the grain-oriented electrical steel sheet according to (1), in which MgO contained in the annealing separating agent is particles having an average grain size measured with a laser diffraction type particle size analyzer being 2.5 µ m or less and having the proportion of particles passing through a 325 mesh in a particle size distribution being 95% or more.
ADVANTAGEOUS EFFECTS OF INVENTION
[0009] According to the present invention, the holding time when the finish-annealed steel sheet is exposed to the atmosphere after finishing the finish annealing until the powder removing and the humidity of the atmosphere during the holding time are properly controlled, and thereby it is possible to provide the grain-oriented electrical steel sheet having a coating film excellent in insulation performance .
BRIEF DESCRIPTION OF DRAWINGS
[0010] Fig. 1 is a conceptual diagram showing a cross section in the vicinity of a surface of a grain-oriented electrical steel sheet in the case when a coating film is normally coated on the grain-oriented electrical steel sheet;
Fig. 2 is a conceptual diagram showing a cross section in the vicinity of a surface of the grain-
oriented electrical steel sheet in the case when a coarse aggregate of an annealing separating agent is adhered on a glass film;
Fig. 3 is a view explaining how insulation performance failure is caused in the case when the grain-oriented electrical steel sheets are stacked;
Fig. 4 is a view showing evaluation of insulation performance of a coating film with regard to a holding time and humidity of an atmosphere in a first example of the present invention; and
Fig. 5 is a view showing evaluation of insulation performance of a coating film with regard to a holding time, and humidity and temperature of an atmosphere in a second example of the present invent ion.
DESCRIPTION OF EMBODIMENTS
[0011] The present invention will be hereinafter
explained.
In manufacturing processes of a grain-oriented electrical steel sheet, powder removing by light pickling, water cleaning, and brushing is performed, before coating and baking of an insulating coating agent. Thus, when a holding time when a finish-annealed steel sheet is exposed to the atmosphere after finishing finish annealing until the powder removing is prolonged, the frequency of occurrence of trouble caused by insulation performance failure of a
coating film is increased. When the above cause was examined, the following facts became clear.
[0012] Fig. 1 is a conceptual diagram showing a cross section in the vicinity of a surface of a grain-oriented electrical steel sheet in the case when a coating film 1 is normally coated on the grain-oriented electrical steel sheet.
When an annealing separating agent dispersed in water and having MgO as its main component, which is in a slurry form, is coated on a steel sheet obtained after decarburization annealing, an oxide film based on SiO2 on the surface of a steel sheet 3 reacts with MgO in the annealing separating agent and a glass film 2 having Mg2Si04 as its main component is formed during finish annealing. When an insulating coating agent having colloidal silica and phosphate as its main component is coated on the glass film 2 and is baked, the insulating coating film 1 is formed on the glass film 2. At this time, for example, the thickness of the coating film 1 is 1 µ m to 2 µ m, and the thickness of the glass film 2 is 2 µ m to 3 µ m.
[0013] Fig. 2 is a conceptual diagram showing a cross section in the vicinity of a surface of the grain-oriented electrical steel sheet in the case when a coarse aggregate 4 of the annealing separating agent is adhered on the glass film 2.
In the grain-oriented electrical steel sheet in which insulation performance failure occurs, the
conductive coarse aggregate 4 having a diameter of several dozen micrometers of the annealing separating agent remains on the glass film 2 at the stage of powder removing before flattening annealing is performed. The mechanism of the above phenomenon has not fully figured out, but it has been conceivable that the dried annealing separating agent after the finish annealing absorbs moisture in the atmosphere. Then, it is assumed that the coarse aggregate 4 firmly adheres to the glass film 2 by some chemical/physical reaction as the time goes by, thereby making it difficult to remove the above coarse aggregate 4 by light pickling, water cleaning, brushing, and so on. In the above case, even though the previously described insulating coating is applied, the liquid insulating coating agent to be a raw material of the insulating coating film has difficulty in coating to the top of the coarse aggregate 4 to have a sufficient thickness. Thus, as shown in Fig. 3, when the grain-oriented electrical steel sheets are stacked, the coarse aggregates 4 come into contact with each other and insulation performance failure occurs. Incidentally, the reason why the coarse aggregate 4 of the annealing separating agent and the glass film 2 are conductive is conceivably because an oxide of Ti contained in the annealing separating agent and an oxide of Fe contained in the steel sheet are contained.
[0014] The inventor of the present invention focused attention on the above-described phenomenon and conducted experiments in which the holding time when the finish-annealed steel sheet is exposed to the atmosphere after finishing the finish annealing until the powder removing, the humidity and temperature of the atmosphere are changed. Then, an adhesion state of the coarse aggregate of the annealing separating agent after the powder removing, and electrical resistance between the coating film and the steel sheet base Fe after the insulating coating were examined with a tester.
[0015] As a result, it was found that in the case when a relationship between the holding time when the finish-annealed steel sheet is exposed to the atmosphere after finishing the finish annealing until performing the powder removing, the humidity of the atmosphere, and the temperature of the atmosphere satisfies specific conditions, it is prevented that the coarse aggregate of the annealing separating agent firmly adheres to the glass film to remain, thereby enabling the coating film having the good insulation performance to be formed stably, and the present invention was completed.
[0016] Hereinafter, a manufacturing method of a grain-oriented electrical steel sheet according to an embodiment of the present invention will be explained.
r
[0017] First, casting of a silicon steel material with a predetermined composition for the grain-oriented electrical steel sheet is performed to manufacture a slab. The method of casting is not limited in particular. As long as the components of the silicon steel material are the same as those of an ordinary grain-oriented electrical steel sheet, the effect of the present invention can be obtained, and typical components are preferably such that Si: 2.5 mass% to 4.5 mass%, C: 0.03 mass% to 0.10 mass%, acid-soluble Al: 0.01 mass% to 0.04 mass%, N: 0.003 mass% to 0.015 mass%, Mn: 0.02 mass% to 0.15 mass%, and S: 0.003 mass% to 0.05 mass% are contained and a balance is composed of Fe and inevitable impurities. Limitation reasons of the respective components will be hereinafter explained.
[0018] When a content of Si is increased, electrical resistance increases to improve a core loss property, and thus the lower limit of the content is preferably set to 2.5 mass%. On the other hand, when the content of Si is too much, the silicon steel material easily cracks in cold rolling to thus have difficulty in being processed, so that the upper limit of the content is preferably set to 4.5 mass%. [0019] C is an element effective for controlling a primary recrystallization structure, so that the lower limit of a content of C is preferably set to 0.03 mass%. On the other hand, C adversely affects a
magnetic property, so that decarburization is necessary to be performed before the finish annealing. Thus, the upper limit of the content is preferably set to 0.10 mass% so as not to make the decarburization difficult to be performed industrially.
[0020] Further, components below are components to be used as a precipitate dispersed phase for secondary recrystallization, and appropriate amounts of the components are preferably contained. That is, two types or more of acid-soluble Al: 0.01 mass% to 0.04 mass%, N: 0.003 mass% to 0.015 mass%, Mn: 0.02 mass% to 0.15 mass%, and S: 0.003 mass% to 0.05 mass% are combined appropriately, and thereby secondary recrystal1ization in which the orientation of crystal grains is highly integrated in the {110}<001> orientation can be obtained.
[0021] Besides the above, Sb, Cu, and Sn further strengthen inhibitors, so that at least one type of Sb, Cu, and Sn may also be contained so as to have a content of 1 mass% or less.
[0022] After the slab is manufactured from the silicon steel material with such a composition, the slab is heated. Next, the slab is hot rolled, and thereby a hot-rolled steel sheet is obtained. The thickness of the hot-rolled steel sheet is not limited in particular, and is set to 1.8 mm to 3.5 mm, for example.
[0023] Thereafter, the hot-rolled steel sheet is annealed, and thereby an annealed steel sheet is obtained. The condition of the annealing is not limited in particular, and the annealing is performed, for example, at a temperature of 750°C to 1200°C for 30 seconds to 10 minutes. The magnetic property is improved by the above annealing.
[0024] Subsequently, the annealed steel sheet is cold rolled, and thereby a cold-rolled steel sheet is obtained. The cold rolling may be performed only one time, or may also be performed a plurality of times with intermediate annealing being performed therebetween. The intermediate annealing is performed, for example, at a temperature of 750°C to 1200°C for 30 seconds to 10 minutes. [0025] Incidentally, when the cold rolling is performed without the intermediate annealing as described above being performed, there is sometimes a case that a uniform property is not easily obtained. Further, when the cold rolling is performed a plurality of times with the intermediate annealing being performed therebetween, a uniform property is easily obtained, but a magnetic flux density is sometimes reduced. Thus, the number of times of the cold rolling and whether or not the intermediate annealing is performed are preferably determined according to the property and cost required for the
grain-oriented electrical steel sheet to be obtained finally.
[0026] Next, in order to remove C contained in the cold-rolled steel sheet to then cause primary recrysta 11ization, the cold-rolled steel sheet is decarburization-annealed, and thereby a
decarburization-annealed steel sheet is obtained. At this time, in order to increase an N content in the steel sheet, nitridation annealing may be performed simultaneously with the decarburization annealing, or nitridation annealing may also be performed after the decarburization annealing.
[0027] In the case of decarburization and nitridation annealing in which the decarburization annealing and the nitridation annealing are performed simultaneously, the decarburization and nitridation annealing is performed in an atmosphere in which gas having nitriding capability such as ammonia is further contained in a moist atmosphere containing hydrogen, nitrogen, and water vapor. In the above atmosphere, the decarburization and the nitridation are performed simultaneously to thereby make a steel sheet structure and a steel sheet composition that are suitable for the secondary recrystal1ization. The decarburization and nitridation annealing in this occasion is performed at a temperature of 800°C to 950°C, for example.
[0028] Further, in the case when the decarburization annealing and the nitridation annealing are performed continuously, the decarburization annealing is first performed in a moist atmosphere containing hydrogen, nitrogen, and water vapor. Thereafter, the nitridation annealing is performed under an atmosphere containing hydrogen, nitrogen, water vapor, and further gas having nitriding capability such as ammonia. At this time, the decarburization annealing is performed at a temperature of 800°C to 950°C, for example, and the nitridation annealing thereafter is performed at a temperature of 700 °C to 850 °C, for example.
[0029] Next, the annealing separating agent having MgO as its main component in a water slurry form is coated on the surface of the decarburization-annealed steel sheet, and the decarburization-annealed steel sheet is wound up in a coil shape. Then, batch-type finish annealing is performed on the coil-shaped decarburization-annealed steel sheet, and thereby a coil-shaped finish-annealed steel sheet is obtained. By the above finish annealing, the secondary recrystal1ization is caused, and further the glass film is formed on the surface of the finish-annealed steel sheet.
[0030] Here, MgO being the main component of the annealing separating agent is preferably particles having an average grain size measured with a laser
diffraction type particle size analyzer being 2.5 µ m or less and having the proportion of particles passing through a 325 mesh in a particle size distribution being 95% or more, for example. When the average grain size exceeds 2.5 µ m, the reaction of forming the glass film during the finish annealing becomes non-uniform, resulting that there is sometimes a case that the good glass film cannot be obtained. Further, when the proportion of particles passing through a 325 mesh is less than 95%, for the similar reason, there is sometimes a case that the uniform and good glass film cannot be obtained. [0031] Further, Ti02 is contained in the annealing separating agent in order to make the reaction of forming the glass film during the finish annealing uniform and good, for example. Then, Ti02 is preferably contained to have a content of 0.1 parts by mass to 7.5 parts by mass relative to 100 parts by mass of MgO. Further, in order to promote the reaction of forming the glass film, one type or two types or more of chemical components of Nb, Sr, B, and so on are preferably contained to have a content of 0.1 parts by mass to 7.5 parts by mass in total. When the content of the chemical component/chemical components is less than 0.1 parts by mass, the effect of which the reaction of forming the glass film improves does not appear, and conversely, when the content exceeds 7.5 parts by mass, there is sometimes
a case that a defect of coating film formation failure, discoloration, or the like is caused by peroxidation reaction. Incidentally, it is assumed that the fact that Ti02 is contained is one reason why the coarse aggregate and the glass film are conduct ive.
[0032] Thereafter, the powder removing is performed by light pickling, water cleaning, brushing, and so on, and the steel sheet has the insulating coating agent having, for example, phosphate and colloidal silica as its main component coated thereon and is baked, and thereby a product of the grain-oriented electrical steel sheet with the insulating coating film adhering thereto is obtained.
[0033] Here, when the finish annealing is finished, the coil-shaped finish-annealed steel sheet is allowed to stand until the powder removing is performed. As the holding time when the finish-annealed steel sheet is exposed to the atmosphere after finishing the finish annealing until the powder removing is shorter, it is possible to prevent the coarse aggregate of the annealing separating agent from adhering to the finish-annealed steel sheet firmly. As the humidity in the atmosphere is higher in particular, the above coarse aggregate adheres to the finish-annealed steel sheet to remain easily. Thus, keeping the humidity of the atmosphere low makes it possible to prevent that the above coarse
aggregate adheres to the finish-annealed steel sheet to remain even though the holding time is prolonged. [0034] As above, the proper range of the relationship between the humidity of the atmosphere and the holding time is expressed by an expression (1) below.
D ≤ -401og10t + 180 • • • the expression (1) Here, D denotes the humidity (%) and t denotes the holding t ime (h) .
[0035] Further, as the temperature of the atmosphere in which the above-described coil-shaped finish-annealed steel sheet is held is higher, the coarse aggregate adheres to the finish-annealed steel sheet to remain easily. Thus, it is preferable that the humidity of the atmosphere is properly controlled according to the holding time of the coil-shaped finish-annealed steel sheet and the temperature of the atmosphere. This makes it possible to prevent that the coarse aggregate further adheres to the finish-annealed steel sheet to remain. [0036] As above, the relationship between the temperature of the atmosphere, the humidity of the atmosphere, and the holding time preferably falls within a range further expressed by an expression (2) below.
D ≤ -0.132L + 224 • • • the expression (2) Here, L = (273 + T) X {(log10t) + 1.2}, D denotes the humidity (%), t denotes the holding time (h), and T
denotes the temperature (°C) in the atmosphere. Incidentally, the humidity D (%) and the temperature T (°C) in the atmosphere are the mean value of the total humidity and the mean value of the total temperature, for example.
EXAMPLE
[0037] Hereinafter, experiments based on the knowledge as above will be explained. Conditions employed in examples are condition examples employed for confirming the applicability and effects of the present invention. Thus, the present invention is not limited to these examples, and can employ various conditions as long as the object of the present invention is achieved without departing from the principles of the present invention. [0038] (Example 1)
Silicon steel materials each containing Si: 3.25 mass%, C: 0.055 mass%, acid-soluble Al: 0.026 mass%, N: 0.005 mass%, Mn: 0.04 mass%, and S: 0.01 mass%, and a balance being composed of Fe and inevitable impurities were cold rolled one time to each set a sheet thickness to 0.23 mm, and were decarburization-annealed. Thereafter, an annealing separating agent containing Ti02: 5.0 parts by mass relative to MgO: 100 parts by mass was put into water to be made into a slurry form, and the annealing separating agent equivalent to 6 g/m2 was coated on one surface of each
of decarburization-annealed steel sheets. Thereafter, the surface temperature of the steel sheets was controlled at 250°C to dry the annealing separating agent.
[0039] Next, finishing annealing was performed, and a holding time when finish-annealed steel sheets were exposed to the atmosphere until powder removing and humidity of the atmosphere were controlled as shown in Table 1 below. Thereafter, powder of the redundant annealing separating agent adhering to the surface of each of the finish-annealed steel sheets was removed by light pickling, water cleaning, and brushing, and an insulating coating agent having colloidal silica and phosphate as its main component was coated on the finish-annealed steel sheets. Then, at 8 5 0 °C, baking for 30 seconds and flattening annealing were performed, and grain-oriented electrical steel sheets were obtained. Coating film properties of the above grain-oriented electrical steel sheets are shown in Table 1 below. [0040]
[Table 1]
[Time (Logarithm) to Humidity]
(Table Removed)
[0041] Fig. 4 shows evaluation of insulation performance of a coating film with regard to the holding time and the humidity of the atmosphere. The insulation performance of each of the coating films, as shown in Fig. 2, was evaluated by electrical
resistance between the top of the coating film 1 and the steel sheet 3 with a tester (for example, VS100 Industrial Tester manufactured by Sanwa Electric Instrument Co., Ltd.).
[0042] As shown in Table 1 and Fig. 4, the electrical resistance was °° on the insulating coating film. Further, in such a case of a coarse aggregate existing, the coating film was not coated on the coarse aggregate and the electrical resistance was zero. As a result of the above experiment, in the case when the holding time when the finish-annealed steel sheet was exposed to the atmosphere after finishing the finish annealing until the powder removing and the humidity of the atmosphere satisfied the condition of the previously described expression (1), the coarse aggregate was hardly observed after the finish-annealed steel sheet had the insulating coating agent coated thereon and was baked, and the insulation performance was good. [0043] (Example 2)
Grain-oriented electrical steel sheets were obtained by processes similar to those of Example 1 except that a holding time when finish-annealed steel sheets were exposed to the atmosphere after finishing finish annealing until powder removing, and humidity and temperature of the atmosphere were controlled as shown in Table 2 below. Coating film properties of
the grain-oriented electrical steel sheets are shown
in Table 2 below.
[0044]
[Table 2]
[L VALUE TO HUMIDITY & TEMPERATURE]
(Table Removed)
(*) L = (273 + T) × i(log10t) + 1.2}
[0045] Fig. 5 shows evaluation of insulation performance of a coating film with regard to the holding time and the humidity and temperature of the atmosphere. In Fig. 5, a value L is a value defined by the previously described expression (2). Incidentally, the insulation performance of each of the coating films was evaluated by a method similar to that of Example 1.
[0046] As shown in Table 2 and Fig. 5, the electrical resistance was ∞ on the insulating coating film. Further, in such a case of a coarse aggregate existing, the coating film was not coated on the coarse aggregate and the electrical resistance was zero. As a result of the above experiment, in the case when the holding time when the finish-annealed steel sheet was exposed to the atmosphere after finishing the finish annealing until the powder removing, and the humidity and temperature of the atmosphere satisfied the condition of the previously described expression (2), the coarse aggregate was
hardly observed after the finish-annealed steel sheet had the insulating coating agent coated thereon and was baked, and the insulation performance was good.
It should be noted that the above embodiments merely illustrate concrete examples of implementing the present invention, and the technical scope of the present invention is not to be construed in a restrictive manner by these embodiments. That is, the present invention may be implemented in various forms without departing from the technical principles or main features thereof.
INDUSTRIAL APPLICABILITY
[0047] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet having a coating film excellent in insulation performance, and the grain-oriented electrical steel sheet can be used as an iron core material of a transformer, a generator, or the like.

CLAIMS
1. A manufacturing method of a grain-oriented electrical steel sheet, comprising:
decarburization annealing a cold-rolled sheet to obtain a decarburization-annealed steel sheet;
coating an annealing separating agent containing MgO and TiO2 on the decarburization-annealed steel sheet and performing finish annealing to obtain a finish-annealed steel sheet;
performing powder removing on the finish-annealed steel sheet; and
coating and baking an insulating coating agent containing colloidal silica and phosphate on the finish-annealed steel sheet on which said powder removing is performed, wherein
a holding time when the finish-annealed steel sheet is exposed to an atmosphere after finishing said finish annealing until starting said performing the powder removing, and humidity of the atmosphere to which the finish-annealed steel sheet is exposed are controlled to satisfy a condition shown in an expression (1) below.
D ≤ -401og10t + 180 • • • the expression (1) (Here, D denotes the humidity (%) and t denotes the holding time (h).)
2. The manufacturing method of the grain-
oriented electrical steel sheet according to claim 1,
wherein
the holding time when the finish-annealed steel sheet is exposed to the atmosphere after finishing said finish annealing until starting said performing the powder removing, the humidity of the atmosphere to which the finish-annealed steel sheet is exposed, and a temperature of the atmosphere are controlled to further satisfy a condition shown in an expression
( 2) below.
D ≤ -0.132L + 224 • • • the expression (2)
(Here, L = (273 + T) X {(log10t) + 1.2}, D denotes the humidity (%), t denotes the holding time (h), and T denotes the temperature (°C) .)
3. The manufacturing method of the grain-
oriented electrical steel sheet according to claim 1,
wherein
a content of Ti02 contained in the annealing separating agent is 0.1 parts by mass to 7.5 parts by mass relative to 100 parts by mass of MgO.
4. The manufacturing method of the grain-
oriented electrical steel sheet according to claim 1,
wherein
MgO contained in the annealing separating agent is particles having an average grain size measured with a laser diffraction type particle size analyzer being 2.5 µ m or less and having the proportion of
particles passing through a 325 mesh in a particle size distribution being 95% or more.