DESCRPTION
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 suitable for an iron core or the like of an electrical apparatus.
BACKGROUND ART
[0002] A grain-oriented electrical steel sheet is a soft magnetic material, and is used for an iron core or the like of an electrical apparatus such as a transformer. In the grain-oriented electrical steel sheet, Si of about 7 mass% or less is contained. Crystal grains of the grain-oriented electrical steel sheet are highly integrated in the {110}<001> orientation by Miller indices. The orientation of the crystal grains is controlled by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.
[0003] For controlling the secondary recrystallization, it is important to adjust a structure obtained by primary recrystallization before the secondary recrystallization (primary recrystallization grain structure) and to adjust a
fine precipitate called an inhibitor or a grain boundary segregation element. The inhibitor has a function to preferentially grow the crystal grains in the {110}<001> orientation and suppress growth of the other crystal grains, in the primary recrystallization grain structure. [0004] Then, conventionally, there has been proposed a technique aimed at precipitating an inhibitor effectively (Japanese Laid-open Patent Publication No. 62-40315, Japanese Laid-open Patent Publication No. 02-29442). There has also been proposed a technique aimed at improving a magnetic property by controlling a texture in hot rolling (Japanese Laid-open Patent Publication No. 02-274811, Japanese Laid-open Patent Publication No. 02-274812). There has also been proposed a technique on a primary recrystallization grain structure (Japanese Laid-open Patent Publication No. 02-182866, Mat. Sci. Forum 204-206 (1996) p623).
[0005] However, in the conventional techniques, it has been difficult to stably manufacture a grain-oriented electrical steel sheet having a high magnetic flux density industrially.
SUMMARY OF THE INVENTION TECHNICAL PROBLEM
[0006] The present invention has an object to provide a manufacturing method of a grain-oriented
electrical steel sheet capable of stably manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density industrially.
SOLUTION TO PROBLEM
[0007] A manufacturing method of a grain-oriented electrical steel sheet according to a first aspect of the present invention includes: heating a silicon steel material at a predetermined temperature of 1280°C or less, the silicon steel material containing: Si: 0.8 mass% to 7 mass%; acid-soluble Al: 0.01 mass% to 0.065 mass%; N: 0.004 mass% to 0.012 mass%; Mn: 0.05 mass% to 1 mass%; and at least one selected from a group consisting of S and Se: 0.003 mass% to 0.015 mass% in total amount, a C content being 0.085 mass% or less, and a balance being composed of Fe and inevitable impurities; hot rolling the heated silicon steel material to obtain a hot-rolled steel strip; annealing the hot-rolled steel strip to obtain an annealed steel strip; cold rolling the annealed steel strip one time or more to obtain a cold-rolled steel strip; decarburization annealing the cold-rolled steel strip to obtain a decarburization-annealed steel strip in which primary recrystallization is caused; coating an annealing separating agent having MgO as its main component on the decarburization-annealed steel strip; finish annealing the decarburization-annealed steel strip to cause
secondary recrystallization. The method further includes performing a nitriding treatment in which an N content in the decarburization-annealed steel strip is increased during a period of time from the start of the decarburization annealing to the occurrence of the secondary recrystallization in the finish annealing. In a case that S and Se are contained in the silicon steel material, the predetermined temperature is a temperature Tl (°C) or less represented by an equation (1) below, and is a temperature T2 (°C) or less represented by an equation (2) below, and is a temperature T3 (°C) or less represented by an equation (3) below. In a case that Se is not contained in the silicon steel material, the predetermined temperature is the temperature Tl (°C) or less represented by the equation (1) below, and is the temperature T3 (°C) or less represented by the equation (3) below. In a case that S is not contained in the silicon steel material, the predetermined temperature is the temperature T2 (°C) or less represented by the equation (2) below, and is the temperature T3 (°C) or less represented by the equation (3) below. The hot rolling the heated silicon steel material includes: rough rolling the heated silicon steel material at a cumulative reduction of 70% or more with setting an final temperature as 900°C to 1100°C; and finish rolling the heated silicon steel material with setting an final
temperature as 700°C to 950°C. A period of time from
the end of the rough rolling to the start of the
finish rolling is set to 1 second or more.
Tl=14855/(6.82-log([Mn]x[S]))-273 (1)
T2=10733/(4.08-log([Mn]x[Se]))-273 (2)
T3=10062/(2.72-log([Al]x[N]))-273 (3)
Here, [Mn] represents a Mn content (mass%) of the silicon steel material, and [S] represents a S content (mass%) of the silicon steel material, and [Se] represents a Se content (mass%) of the silicon steel material, and [Al] represents an acid-soluble Al content (mass%) of the silicon steel material, and [N] represents the N content (mass%) of the silicon steel material.
[0008] In a manufacturing method of a grain-oriented electrical steel sheet according to a second aspect of the present invention, in the method according to the first aspect, the silicon steel material further contains at least one selected from a group consisting of Cr: 0.3 mass% or less, Cu: 0.4 mass% or less, Ni: 1 mass% or less, P: 0.5 massl or less, Mo: 0.1 mass% or less, Sn: 0.3 mass% or less, Sb: 0.3 mass% or less, B: 0.008 mass% or less, and Bi: 0.01 mass% or less.
[0009] In a manufacturing method of a grain-oriented electrical steel sheet according to a third aspect of the present invention, in the method according to the first or second aspect, when the
amount of N (mass%) precipitated as A1N in the hot-rolled steel strip is represented as NasAlN, the amount of S (mass%) precipitated as MnS in the hot-rolled steel strip is represented as SasMnS, and the amount of Se (mass%) precipitated as MnSe in the hot-rolled steel strip is represented as SeasMnSe, relationships of an expression (4) and an expression (5) below are established.
NasAlN/[N] x 100 ≥60% (4)
(SasMnS + 0. 4 6SeasMnSe) /([S]+0.46[Se])xl00≥40% (5)
ADVANTAGEOUS EFFECTS OF INVENTION
[0010] According to the present invention, it is possible to appropriately precipitate MnS and/or MnSe and A1N in the hot rolling to thereby suppress the precipitation in the decarburization annealing. Consequently, the good inhibitors can be obtained and the good magnetic property can be obtained. Further, these processes can be stably executed industrially.
BRIEF DESCRIPTION OF THE DRAWINGS [0011] Fig. 1 is a flowchart showing a manufacturing method of a grain-oriented electrical steel sheet;
Fig. 2 is a view showing a result of a first experiment; a relationship between the final temperature and the cumulative reduction of the rough
rolling, and the magnetic property obtained after the finish annealing; and
Fig. 3 is a view showing a result of a second experiment; a relationship between the final temperature of the finish rolling and the magnetic property.
DESCRIPTION OF EMBODIMENTS
[0012] The present inventors thought that in a manufacturing method of a grain-oriented electrical steel sheet in which slab heating before hot rolling is performed at a relatively low temperature, which is called low-temperature slab heating, conditions of hot rolling may affect behavior of primary recrystallization, and thus conducted various experiments. Here, an outline of the manufacturing method of the grain-oriented electrical steel sheet will be explained. Fig. 1 is a flowchart showing the manufacturing method of the grain-oriented electrical steel sheet.
[0013] First, as shown in Fig. 1, in step S1, a silicon steel material (slab) having a predetermined composition is heated to a predetermined temperature, and in step S2, the heated silicon steel material is hot rolled. By the hot rolling, a hot-rolled steel strip is obtained. Thereafter, in step S3, the hot-rolled steel strip is annealed to normalize a structure in the hot-rolled steel strip and to adjust
precipitation of an inhibitor. By the annealing, an annealed steel strip is obtained. Subsequently, in step S4, the annealed steel strip is cold rolled. The cold rolling may be performed only one time, or may also be performed a plurality of times with intermediate annealing performed therebetween. By the cold rolling, a cold-rolled steel strip is obtained. Incidentally, in the case of the intermediate annealing being performed, it is also possible to omit the annealing of the hot-rolled steel strip before the cold rolling to perform the annealing (step S3) in the intermediate annealing. That is, the annealing (step S3) may be performed on the hot-rolled steel strip, or may also be performed on a steel strip obtained after being cold rolled one time and before being cold rolled finally. [0014] After the cold rolling, in step S5, the cold-rolled steel strip is decarburization-annealed. In the decarburization annealing, primary recrystallization occurs. Further, by the decarburization annealing, a decarburization-annealed steel strip is obtained. Next, in step S6, an annealing separating agent having MgO (magnesia) as its main component is coated on a surface of the decarburization-annealed steel strip, and finish annealing is performed. In the finish annealing, secondary recrystallization occurs, and a glass film having forsterite as its main component is formed on
the surface of the steel strip, and the steel strip is purified. As a result of the secondary recrystallization, a secondary recrystallization grain structure arranged in the Goss orientation is obtained. By the finish annealing, a finish-annealed steel strip is obtained. Further, during a period of time from the start of the decarburization annealing to the occurrence of the secondary recrystallization in the finish annealing, a nitriding treatment to increase the amount of nitrogen in the steel strip is performed (step S7).
[0015] In this manner, the grain-oriented electrical steel sheet can be obtained. [0016] Further, details will be described later, but as the silicon steel material, there is used one containing Si: 0.8 mass% to 7 mass%, acid-soluble Al: 0.01 mass% to 0.065 mass%, N: 0.004 mass% to 0.012 mass%, and Mn: 0.05 mass% to 1 mass%, and further at least one selected from a group consisting of S and Se: 0.003 mass% to 0.015 mass% in total amount, a C content being 0.085 mass% or less, and a balance being composed of Fe and inevitable impurities. [0017] Then, as a result of the various experiments, the present inventors found that it is important to adjust the conditions of the hot rolling (step S2) to then generate a precipitate in a form effective as an inhibitor in the hot-rolled steel strip. Concretely, the present inventors found that
by the adjustment of the conditions of the slab heating and the hot rolling, MnS and/or MnSe, and A1N are preferentially precipitated not in the decarburization annealing but in the hot rolling, thereby enabling appropriate sized inhibitors to be obtained uniformly, and thus a homogeneous primary recrystallization grain structure are adjusted. Then, the present inventors obtained knowledge capable of stably manufacturing the grain-oriented electrical steel sheet having a good magnetic property, and completed the present invention. [0018] Here, the experiments conducted by the present inventors will be explained. [0019] (First Experiment)
In the first experiment, first, steel containing Si: 3.3 mass%, C: 0.06 mass%, acid-soluble Al: 0.028 mass%, N: 0.007 mass%, Mn: 0.14 mass%, and S: 0.007 mass%, and a balance being composed of Fe and inevitable impurities was melted, and the steel was casted to form silicon steel slabs each having a thickness of 60 mm to 160 mm. Next, the silicon steel slabs were heated at a temperature of 1200°C and were hot rolled. In the hot rolling, rough rolling was performed such that the final temperature becomes 1150°C to 850°C, and thereafter, finish rolling was performed such that the final temperature becomes 870°C. The final temperature of the rough rolling was adjusted during a period of time from the end of the
heating at 1200°C to the start of the rough rolling (rough rolling start time). The final temperature of the finish rolling was adjusted during a period of time from the end of the rough rolling to the start of the finish rolling. The period of time was 3 seconds to 30 seconds. Further, a cumulative reduction of the rough rolling was set to 58% to 84%. Further, thicknesses of steel strips obtained after the rough rolling were set to 25 mm, and thicknesses of steel strips obtained after the finish rolling (hot-rolled steel strips) were set to 2.3 mm. Subsequently, the hot-rolled steel strips were annealed at 1100°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, decarburization annealing was performed for 100 seconds in moist atmosphere gas at 830°C to obtain decarburization-annealed steel strips. Subsequently, the decarburization-annealed steel strips were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.023 mass%. Next, an annealing separating agent having MgO as its main component was coated on the decarburization-annealed steel strips, and the decarburization-annealed steel strips were heated to 1200°C at a speed of 15°C/h so as to perform finish annealing. In this manner, various samples were formed. Note that theoretically, in the steels with the above-described
composition, a sold solution temperature of A1N is 1292°C, and a solid solution temperature of MnS is 1238°C.
[0020] Then, a relationship between the final temperature and the cumulative reduction of the rough rolling, and the magnetic property obtained after the finish annealing was examined. A result thereof is shown in Fig. 2. In Fig. 2, the horizontal axis indicates the final temperature of the rough rolling, and the vertical axis indicates the cumulative reduction of the rough rolling. As shown in Fig. 2, in the case that the final temperature of the rough rolling was 900°C to 1100°C and the cumulative reduction of the rough rolling was 70% or more, a magnetic flux density B8 of 1.90 T or more was obtained. It is conceivable that this is because in general, strain in a steel strip triggers precipitation of MnS, so that precipitation is promoted by strain introduced by the strong draft of 70% or more. Further, it is also conceivable that the temperature zone of 900°C to 1100°C is a temperature zone where MnS is preferentially precipitated for a short period of time. Thus, it is conceivable that by the appropriate combination of the temperature zone and the cumulative reduction of the rough rolling, the precipitation of MnS is promoted and thereby the good magnetic property is obtained. Such a tendency is similarly conceivable
also on MnSe. Incidentally, the magnetic flux density B8 is a magnetic flux density generated in the grain-oriented electrical steel sheet when a magnetic field of 800 A/m is applied to the grain-oriented electrical steel sheet. [0021] (Second Experiment)
In the second experiment, first, steel containing Si: 3.3 mass%, C: 0.06 mass%, acid-soluble Al: 0.028 mass%, N: 0.007 mass%, Mn: 0.14 mass%, and S: 0.007 mass%, and a balance being composed of Fe and inevitable impurities was melted, and the steel was casted to form silicon steel slabs each having a thickness of 160 mm. Next, the silicon steel slabs were heated at a temperature of 1200°C and were hot rolled. In the hot rolling, rough rolling was performed such that the final temperature becomes 1000°C, and thereafter, finish rolling was performed such that the final temperature becomes 1000°C to 650°C. The final temperature of the rough rolling was adjusted during a period of time from the end of the heating at 1200°C to the start of the rough rolling (rough rolling start time). The final temperature of the finish rolling was adjusted during a period of time from the end of the rough rolling to the start of the finish rolling. The period of time was 5 seconds to 25 seconds. Further, a cumulative reduction of the rough rolling was set to 84%. Further, thicknesses of steel strips obtained after
the rough rolling were set to 25 mm, and thicknesses of steel strips obtained after the finish rolling (hot-rolled steel strips) were set to 2.3 mm. Subsequently, the hot-rolled steel strips were annealed at 1100°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, decarburization annealing was performed for 100 seconds in moist atmosphere gas at 830°C to obtain decarburization-annealed steel strips. Subsequently, the decarburization-annealed steel strips were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.023 mass%. Next, an annealing separating agent having MgO as its main component was coated on the decarburization-annealed steel strips, and the decarburization-annealed steel strips were heated to 1200°C at a speed of 15°C/h to perform finish annealing. In this manner, various samples were produced. Note that theoretically, in the steels with the above-described composition, a sold solution temperature of A1N is 1292°C, and a solid solution temperature of MnS is 1238°C. [0022] Then, a relationship between the final temperature of the finish rolling and the magnetic property obtained after the finish annealing was examined. A result thereof is shown in Fig. 3. In Fig. 3, the horizontal axis indicates the final temperature of the finish rolling, and the vertical
axis indicates the magnetic flux density B8 after the finish annealing. As shown in Fig. 3, in the case of the final temperature of the finish rolling being 700°C to 950°C, the magnetic flux density B8 of 1.90 T or more was obtained. It is conceivable that this is because the temperature zone of 700°C to 950°C is a temperature zone of a nose of A1N precipitation, and MnS precipitated before the finish rolling triggers precipitation of A1N at the time of finish rolling. Thus, it is conceivable that by the appropriate combination of the conditions of the rough rolling and the conditions of the finish rolling, the precipitation of A1N is promoted, and the good magnetic property is obtained. Such a tendency is similarly conceivable also on MnSe.
[0023] Next, an embodiment of the present invention made on the knowledge will be explained.
[0024] First, limitation reasons of the components of the silicon steel material will be explained.
[0025] The silicon steel material used in this embodiment contains Si: 0.8 mass% to 7 mass%, acid-soluble Al: 0.01 mass% to 0.065 mass%, N: 0.004 mass% to 0.012 mass%, Mn: 0.05 mass% to 1 mass%, and S and Se: 0.003 mass% to 0.015 mass% in total amount, a C content being 0.085 mass% or less, and a balance being composed of Fe and inevitable impurities.
[0026] Si increases electrical resistance to reduce a core loss. However, when a Si content exceeds 7
mass%, the cold rolling becomes quite difficult to be performed, and a crack occurs easily at the time of cold rolling. Thus, the Si content is set to 7 mass% or less, and is preferably 4.5 mass% or less, and is more preferably 4 mass% or less. Further, when the Si content is less than 0.8 mass%, a y transformation is caused at the time of finish annealing to thereby make a crystal orientation of the grain-oriented electrical steel sheet deteriorate. Thus, the Si content is set to 0.8 mass% or more, and is preferably 2 mass% or more, and is more preferably 2.5 mass% or more.
[0027] C is an element effective for controlling the primary recrystallization grain structure, but adversely affects the magnetic property. Thus, in this embodiment, before the finish annealing (step S6), the decarburization annealing is performed (step S5). However, when the C content exceeds 0.085 mass%, a time taken for the decarburization annealing becomes long, and productivity in industrial production is impaired. Thus, the C content is set to 0.085 mass% or less, and is preferably 0.07 mass% or less .
[0028] Acid-soluble Al bonds to N to be precipitated as (Al, Si)N and functions as inhibitors. In a case that a content of acid-soluble Al falls within a range of 0.01 mass% to 0.065 mass%, the secondary recrystallization is stabilized. Thus,
the content of acid-soluble Al is set to not less than 0.01 mass% nor more than 0.065 mass%. Further, the content of acid-soluble Al is preferably 0.02 mass% or more, and is more preferably 0.025 mass% or more. Further, the content of acid-soluble Al is preferably 0.04 mass% or less, and is more preferably 0.03 mass% or less.
[0029] N bonds to Al to function as an inhibitor. When an N content is less than 0.004 mass%, a sufficient amount of the inhibitor cannot be obtained. Thus, the N content is set to 0.004 mass% or more, and is preferably 0.006 mass% or more, and is more preferably 0.007 mass% or more. On the other hand, when the N content exceeds 0.012 mass%, a hole called a blister occurs in the steel strip at the time of cold rolling. Thus, the N content is set to 0.012 mass% or less, and is preferably 0.010 mass% or less, and is more preferably 0.009 mass% or less. [0030] Mn, S and Se produce MnS and MnSe to be a nucleus for which A1N is precipitated. In a case that a Mn content falls within a range of 0.05 mass% to 1 mass%, the secondary recrystallization is stabilized. Thus, the Mn content is set to not less than 0.05 mass% nor more than 1 mass%. Further, the Mn content is preferably 0.08 mass% or more, and is more preferably 0.09 mass% or more. Further, the Mn content is preferably 0.50 mass% or less, and is more preferably 0.2 mass% or less.
[0031] Further, in a case that a content of S and
Se falls within a range of 0.003 mass% to 0.015 mass%
in total amount, the secondary recrystallization is
stabilized. Thus, the content of S and Se is set to
not less than 0.003 mass% nor more than 0.015 mass%
in total amount. Further, in terms of preventing
occurrence of a crack in the hot rolling, an
inequation (6) below is preferably satisfied.
Incidentally, only either S or Se may be contained in
the silicon steel material, or both S and Se may also
be contained in the silicon steel material.
[Mn] /( [S] + [Se] )≥ 4 (6)
[0032] Ti forms coarse TiN to affect precipitation amounts of (Al, Si)N functioning as inhibitors. When a Ti content exceeds 0.004 mass%, the good magnetic property is not easily obtained. Thus, the Ti content is preferably 0.004 mass% or less. [0033] Further, one or more selected from a group consisting of Cr, Cu, Ni, P, Mo, Sn, Sb, B, and Bi may also be contained in the silicon steel material in ranges below.
[0034] Cr improves an oxide layer formed at the time of decarburization annealing, and is effective for forming the glass film when the oxide layer and MgO being the main component of the annealing separating agent react at the time of finish annealing. However, when a Cr content exceeds 0.3
mass%, decarburization is remarkably prevented. Thus, the Cr content is set to 0.3 mass% or less. [0035] Cu increases specific resistance to reduce a core loss. However, when a Cu content exceeds 0.4 mass%, the effect is saturated. Further, a surface flaw called "copper scab" is sometimes caused at the time of hot rolling. Thus, the Cu content is set to 0.4 mass% or less.
[0036] Ni increases specific resistance to reduce a core loss. Further, Ni controls a metallic structure of the hot-rolled steel strip to improve the magnetic property. However, when a Ni content exceeds 1 mass%, the secondary recrystallization becomes unstable. Thus, the Ni content is set to 1 mass% or less .
[0037] P increases specific resistance to reduce a core loss. However, when a P content exceeds 0.5 mass%, a fracture occurs easily at the time of cold rolling due to embrittlement. Thus, the P content is set to 0.5 mass% or less.
[0038] Mo improves a surface property at the time of hot rolling. However, when a Mo content exceeds 0.1 mass%, the effect is saturated. Thus, the Mo content is set to 0.1 mass% or less. [0039] Sn and Sb are grain boundary segregation elements. The silicon steel material used in the embodiment contains Al, so that there is sometimes a case that Al is oxidized by moisture released from
the annealing separating agent depending on the condition of the finish annealing. In this case, variations in inhibitor strength occur depending on positions in the grain-oriented electrical steel sheet, and the magnetic property also sometimes varies. However, in a case that the grain boundary segregation elements are contained, the oxidation of Al can be suppressed. That is, Sn and Sb suppress the oxidation of Al to suppress the variations in the magnetic property. On the other hand, when a content of Sn and Sb exceeds 0.3 mass%, the oxide layer is not easily formed at the time of decarburization annealing, and thereby the formation of the glass film when the oxide layer and MgO being the main component of the annealing separating agent react at the time of finish annealing becomes insufficient. Further, the decarburization is remarkably prevented. Thus, the content of each of Sn and Sb is set to 0.3 mass% or less, and the total content is preferably 0.3 mass% or less .
[0040] B bonds to N to be precipitated as BN and functions as an inhibitor. However, when a B content exceeds 0.008 mass%, the cold rolling becomes difficult to be performed. Thus, the B content is set to 0.008 mass% or less.
[0041] Bi stabilizes a precipitate such as a sulfide to strengthen the function as an inhibitor. However, when a Bi content exceeds 0.01 mass%, the
formation of the glass film is adversely affected. Thus, the Bi content is set to 0.01 mass% or less. [0042] Next, each process in the embodiment will be explained.
[0043] The silicon steel material (slab) having the above-described components may be formed in a manner that, for example, steel is melted in a converter, an electric furnace, or the like, and the molten steel is subjected to a vacuum degassing treatment according to need, and next is subjected to continuous casting. Further, the silicon steel material may also be formed in a manner that in place of the continuous casting, an ingot is made to then be bloomed. The thickness of the silicon steel slab is set to, for example, 150 mm to 350 mm, and is preferably set to 220 mm to 280 mm. Further, what is called a thin slab having a thickness of 30 mm to 70 mm may also be formed.
[0044] After the silicon steel slab is formed, the slab heating is performed (step S1), and the hot rolling is performed (step S2). Then, in the embodiment, the conditions of the slab heating and the hot rolling are set so as to make A1N precipitate with MnS and/or MnSe coarsely.
[0045] The temperature of the slab heating (step S1) is set to 1280°C or less in terms of preventing occurrence of slag. Further, in terms of improving
the magnetic property, the temperature of the slab heating is set so as to satisfy conditions below.
(i) The case when S and Se are contained in the silicon steel slab
a temperature Tl (°C) represented by an expression (1) or less, a temperature T2 (°C) represented by an expression (2) or less, and a temperature T3 (°C) represented by an expression (3) or less
(ii) The case when Se is not contained in the silicon steel slab
the temperature Tl (°C) represented by the expression (1) or less, and the temperature T3 (°C) represented by the expression (3) or less
(iii) The case when S is not contained in the silicon steel slab
the temperature T2 (°C) represented by the
expression (2) or less, and the temperature T3 (°C)
represented by the expression (3) or less
Tl=14855/(6.82-log([Mn]x[s]))-273 (1)
T2=10733/(4.08-log([Mn]x[Se]))-273 (2)
T3=10062/(2.72-log([Al]x[N]))-273 (3)
Here, [Mn] represents the Mn content (mass%) of the silicon steel slab, [S] represents the S content (mass%) of the silicon steel slab, [Se] represents the Se content (mass%) of the silicon steel slab, [Al] represents the acid-soluble Al content (mass%)
of the silicon steel slab, and [N] represents the N content (mass%) of the silicon steel slab. [0046] This is because when the slab heating is performed at such temperatures, A1N, MnS, and MnSe are not completely solid-solved at the time of slab heating, and the precipitations of A1N, MnS, and MnSe are promoted during the hot rolling. [0047] In the hot rolling (step S2), the rough rolling is performed such that the final temperature becomes 900°C to 1100°C, and thereafter, the finish rolling is performed such that the final temperature becomes 700°C to 950°C. The final temperature of the rough rolling can be adjusted during a period of time from the end of the slab heating to the start of the rough rolling, for example. Similarly, the final temperature of the finish rolling can be adjusted during a period of time from the end of the rough rolling to the start of the finish rolling, for example. Further, the cumulative reduction of the rough rolling is set to 70% or more. Further, the period of time from the end of the rough rolling to the start of the finish rolling is set to 1 second or more .
[0048] The reason why the final temperature of the rough rolling is set to 900°C to 1100°C and the cumulative reduction of the rough rolling is set to 70% or more is that the result of the first experiment was considered. That is, it is
conceivable that in the case that these conditions are satisfied, by the appropriate combination of the final temperature and the cumulative reduction of the rough rolling, the precipitations/precipitation of MnS and/or MnSe are/is promoted, and the good magnetic property is obtained. Incidentally, the upper limit of the cumulative reduction of the rough rolling is not limited in particular. However, if the cumulative reduction is increased, an installation load is increased, so that the cumulative reduction is preferably set to about 95% or less.
[0049] The reason why the period of time from the end of the rough rolling to the start of the finish rolling is set to 1 second or more is to precipitate MnS and/or MnSe sufficiently. If the period of time is less than 1 second, MnS and/or MnSe are/is not precipitated sufficiently, and in the subsequent decarburization annealing, MnS and/or MnSe are/is likely to be precipitated non-uniformly. Incidentally, the upper limit of the period of time is not limited in particular. However, setting the period of time to over 30 minutes is not preferable in terms of productivity.
[0050] The reason why the final temperature of the finish rolling is set to 700°C to 950°C is that the result of the second experiment was considered. That is, it is conceivable that in the case that the
condition is satisfied, by the appropriate combination of the conditions of the rough rolling and the conditions of the finish rolling, the precipitation of A1N is promoted, and the good magnetic property is obtained.
[0051] Incidentally, a mechanism in which the good magnetic property is obtained in the case that these conditions are satisfied is not clarified, but is conceivable as follows.
[0052] MnS, MnSe, and A1N to be precipitated in the hot rolling are each provided with a sufficient size as an inhibitor, and are easily precipitated uniformly. Further, in general, Mn, S, Se, acid-soluble Al, and N that are not precipitated as MnS, MnSe, or A1N but are left in the hot rolling can be precipitated as MnS, MnSe, or A1N in the decarburization annealing. Here, a precipitate to be precipitated in the decarburization annealing is small in size as compared with those to be precipitated in the hot rolling, and is further precipitated non-uniformly in many cases. Thus, if large amount of MnS, MnSe, or A1N is precipitated in the decarburization annealing, an average grain diameter in the primary recrystallization is likely to become small, and large variations are likely to occur in grain size distribution. The primary recrystallization grain structure is an important control factor for the secondary recrystallization,
so that in a case that the average grain diameter in the primary recrystallization is small, the magnetic property deteriorates, and in a case that large variations exist in the grain size distribution, the secondary recrystallization becomes unstable. [0053] Thus, as long as large amounts of MnS, and/or MnSe, and A1N are preferentially precipitated in the hot rolling, MnS, MnSe, or A1N is not easily precipitated in the decarburization annealing, and the good primary recrystallization grain structure is obtained, so that the good magnetic property can be obtained stably. Then, in terms of MnS, and/or MnSe, and A1N to be precipitated in the hot rolling, relationships of inequations (4) and (5) below are preferably established.
NASALN/ [N] × 100 ≥ 60% (4)
(SasMns + 0.4 6SeasMnSe) /([S]+0.46[Se])×100 ≥ 40% (5)
Here, NasAlN represents the amount of N (mass%) precipitated as A1N in the hot-rolled steel strip, [N] represents the amount of N (mass%) contained in the hot-rolled steel strip, SasMnS represents the amount of S (mass%) precipitated as MnS in the hot-rolled steel strip, [S] represents the amount of S (mass%) contained in the hot-rolled steel strip, SeasMnSe represents the amount of Se (mass%) precipitated as MnSe in the hot-rolled steel strip, and [Se] represents the amount of Se (mass%) contained in the hot-rolled steel strip.
Incidentally, the amounts of N, S, and Se contained in the hot-rolled steel strip are equal to those of N, S, and Se contained in the silicon steel slab. [0054] In the case that the relationships of the inequations (4) and (5) are established, it can be said that especially the good precipitates are generated in the hot rolling, and thus especially the good magnetic property can be obtained. The left-hand side of the inequation (4) indicates the ratio of N precipitated as A1N to N contained in the hot-rolled steel strip, and it is more preferably 70% or more, and still more preferably 80% or more. Further, the left-hand side of the inequation (5) indicates the sum of the ratio of S precipitated as MnS to S contained in the hot-rolled steel strip and the ratio of Se precipitated as MnSe to Se contained in the hot-rolled steel strip, and it is more preferably 50% or more, and still more preferably 60% or more.
[0055] After the hot rolling (step S2), the hot-rolled steel strip is annealed (step S3). Next, the cold rolling is performed (step S4). As described above, the cold rolling may be performed only one time, or may also be performed a plurality of times with the intermediate annealing performed therebetween. In the cold rolling, the final cold rolling rate is preferably set to 80% or more. This
is because to develop a good primary recrystallization texture.
[0056] Thereafter, the decarburization annealing is performed (step S5). As a result, C contained in the steel strip is removed. The decarburization annealing is performed in a moist atmosphere, for example. Further, the decarburization annealing is preferably performed at a time such that, for example, the crystal grain diameter obtained by the primary recrystallization in the temperature zone of 770°C to 950°C becomes 15 urn or more. This is because to obtain the good magnetic property. Subsequently, coating of the annealing separating agent and the finish annealing are performed (step S6). As a result, the crystal grains oriented in the {110}<001> orientation preferentially grow by the secondary recrystallization.
[0057] Further, during a period of time from the start of the decarburization annealing to the occurrence of the secondary recrystallization in the finish annealing, the nitriding treatment is performed (step S7). This is to form inhibitors of (Al, Si)N. The nitriding treatment may be performed during the decarburization annealing (step S5), or may also be performed during the finish annealing (step S6). In the case that the nitriding treatment is performed during the decarburization annealing, the annealing may be performed in an atmosphere
containing gas having nitriding capability such as ammonia, for example. Further, the nitriding treatment may be performed during a heating zone or a soaking zone in a continuous annealing furnace, or the nitriding treatment may also be performed at a stage after the soaking zone. In the case that the nitriding treatment is performed during the finish annealing, a powder having nitriding capability such as MnN, for example, may be added to the annealing separating agent.
[0058] In order to perform the secondary recrystallization more stably, it is desirable that the degree of nitriding in the nitriding treatment (step S7) is adjusted and the compositions of (Al, Si)N in the steel strip obtained after the nitriding treatment are adjusted. For example, according to the acid-soluble Al content, the B content, and a content of Ti existing inevitably, the degree of nitriding is preferably controlled so as to satisfy an inequation (7) below, and the degree of nitriding is more preferably controlled so as to satisfy an inequation (8) below.
[N] ≥14/27 [Al]+14/11[B]+14/48 [Ti] (7)
[N] ≥2/3 [Al]+14/11 [B]+14/48 [Ti] (8)
Here, [N] represents the N content (mass%) of the steel strip obtained after the nitriding treatment, [Al] represents the acid-soluble Al content (mass%) of the steel strip obtained after the nitriding
treatment, [B] represents the B content (mass%) of the steel strip obtained after the nitriding treatment, and [Ti] represents the Ti content (mass%) of the steel strip obtained after the nitriding treatment.
[0059] The method of the finish annealing (step S6) is also not limited in particular. For example, the temperature is increased to 1200°C in atmosphere gas containing hydrogen and nitrogen, and the atmosphere gas is switched to hydrogen atmosphere gas at 1200°C, and the precipitates are purified.
[0060] According to this embodiment as above, the grain-oriented electrical steel sheet excellent in the magnetic property can be manufactured stably.
EXAMPLE
[0061]
In Example 1, the effect of the Mn content was confirmed in a component base containing Mn and S.
[0062] First, slabs containing, in mass%, Si: 3.2%, C: 0.06%, acid-soluble Al: 0.028%, N: 0.008%, and S: 0.007%, and further Mn having an amount shown in Table 1 (0.05% to 0.20%), and a balance being composed of Fe and inevitable impurities were formed. Thicknesses of the slabs were each set to 160 mm. Next, the slabs were heated at a temperature of 1200°C and were hot-rolled. In the hot rolling, the slabs were rough rolled until the thicknesses each became
4 0 mm, and thereafter were finish rolled to obtain hot-rolled steel strips each having a thickness of 2.3 mm. The final temperature of the rough rolling was set to 950°C, and the final temperature of the finish rolling was set to 890°C. Subsequently, the hot-rolled steel strips were annealed at 1100°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, the cold-rolled steel strips were decarburization-annealed for 100 seconds at a temperature of 830°C in moist atmosphere gas, and subsequently were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.021 mass%. Next, an annealing separating agent having MgO as its main component was coated on the steel strips, and then finish annealing was performed. In the finish annealing, the steel strips were heated to 1200°C at a speed of 15°C/h. [0063] Then, the magnetic flux density B8 was measured as the magnetic property obtained after the finish annealing. A result of the measurement is shown in Table 1. Further, the amounts of the precipitates (NasAlN and SasMnS) in the hot-rolled steel strips were also measured after the hot rolling. A result of the measurement is also shown in Table 1. Further, in Table 1, the value of the left-hand side in the inequation (4) (NasAlN/ [N] × 100) and the value of
the left-hand side in the inequation (5) ( SasMns/ [S ] × 100 ) are also shown. [0064] [Table 1]
(Table Removed)
[0065]
In Example 2, the effect of the Mn content was confirmed in a component base containing Mn and Se. [0066] First, slabs containing, in massl, Si: 3.3%, C: 0.06%, acid-soluble Al: 0.028%, N: 0.008%, and Se: 0.007%, and further Mn having an amount shown in Table 2 (0.04% to 0.20%), and a balance being composed of Fe and inevitable impurities were formed. Thicknesses of the slabs were each set to 160 mm. Next, the slabs were heated at a temperature of 1140°C and were hot-rolled. In the hot rolling, the slabs were rough rolled until the thicknesses each became 3 0 mm, and thereafter were finish rolled to obtain hot-rolled steel strips each having a thickness of 2.3 mm. The final temperature of the rough rolling was set to 930°C, and the final temperature of the finish rolling was set to 870°C. Subsequently, the hot-rolled steel strips were annealed at 1120°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, the cold-rolled steel strips were decarburization-annealed for 100 seconds at a temperature of 830°C in moist atmosphere gas, and subsequently were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.022 mass%. Next, an annealing separating agent having MgO as its main component was coated on the steel strips, and then finish annealing was
performed. In the finish annealing, the steel strips were heated to 1200°C at a speed of 15°C/h. [0067] Then, the magnetic flux density B8 was measured as the magnetic property obtained after the finish annealing. A result of the measurement is shown in Table 2. Further, the amounts of the precipitates (NasAlN and SeasMnSe) in the hot-rolled steel strips were also measured after the hot rolling. A result of the measurement is also shown in Table 2. Further, in Table 2, the value of the left-hand side in the inequation (4) (NasAlN/[N] × 100) and the value of the left-hand side in the inequation (5) (SeasMnSe/[Se] × 100) are also shown. [0068] [Table 2]
(Table Removed)
[0069]
In Example 3, the effect of the Mn content was confirmed in a component base containing Mn, S, and Se.
[0070] First, slabs containing, in mass%, Si: 3.3%, C: 0.06%, acid-soluble Al: 0.027%, N: 0.007%, S: 0.006%, and Se: 0.004%, and further Mn having an amount shown in Table 3 (0.05% to 0.20%), and a balance being composed of Fe and inevitable impurities were formed. Thicknesses of the slabs were each set to 160 mm. Next, the slabs were heated at a temperature of 1180°C and were hot-rolled. In the hot rolling, the slabs were rough rolled until the thicknesses each became 40 mm, and thereafter were finish rolled to obtain hot-rolled steel strips each having a thickness of 2.3 mm. The final temperature of the rough rolling was set to 940°C, and the final temperature of the finish rolling was set to 880°C. Subsequently, the hot-rolled steel strips were annealed at 1100°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, the cold-rolled steel strips were decarburization-annealed for 100 seconds at a temperature of 830°C in moist atmosphere gas, and subsequently were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.023 mass%. Next, an annealing separating agent having MgO as its main component was
coated on the steel strips, and then finish annealing was performed. In the finish annealing, the steel strips were heated to 1200°C at a speed of 15°C/h. [0071] Then, the magnetic flux density B8 was measured as the magnetic property obtained after the finish annealing. A result of the measurement is shown in Table 3. Further, the amounts of the precipitates (NasAlN, SasMns, and SeasMnSe) in the hot-rolled steel strips were also measured after the hot rolling. A result of the measurement is also shown in Table 3. Further, in Table 3, the value of the left-hand side in the inequation (4) ( NasAlN/[N] × 100) and the value of the left-hand side in the inequation (5) ( (SasMnS + 0. 46SeasMnSe) / ( [S]+0. 46 [Se] ) × 100) are also shown. [0072] [Table 3]
(Table Removed)
[0073] < Example 4>
In Example 4, the effect of the temperature of the slab heating was confirmed in a component base containing Mn and S.
[0074] First, slabs containing, in mass%, Si: 3.2%, C: 0.06%, acid-soluble Al: 0.028%, N: 0.008%, Mn: 0.1%, and S: 0.007%, and a balance being composed of Fe and inevitable impurities were formed. Thicknesses of the slabs were each set to 160 mm. Next, the slabs were each heated at a temperature shown in Table 4 (1100°C to 1300°C) and were hot-rolled. In the hot rolling, the slabs were rough rolled until the thicknesses each became 40 mm, and thereafter were finish rolled to obtain hot-rolled steel strips each having a thickness of 2.3 mm. The final temperature of the rough rolling was set to 920°C to 1070°C, and the final temperature of the finish rolling was set to 870°C to 950°C. Subsequently, the hot-rolled steel strips were annealed at 1100°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, the cold-rolled steel strips were decarburization-annealed for 100 seconds at a temperature of 830°C in moist atmosphere gas, and subsequently were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.021 mass%. Next, an annealing separating agent having MgO as its main component was
coated on the steel strips, and then finish annealing was performed. In the finish annealing, the steel strips were heated to 1200°C at a speed of 15°C/h.
[0075] Then, the magnetic flux density B8 was measured as the magnetic property obtained after the finish annealing. A result of the measurement is shown in Table 4. Further, the amounts of the precipitates (NasAlN and SasMnS) in the hot-rolled steel strips were also measured after the hot rolling. A result of the measurement is also shown in Table 4. Further, in Table 4, the value of the left-hand side in the inequation (4) (NasAlN/[N]× 100) and the value of the left-hand side in the inequation (5)
(SasMnS/ [S ] × 100 ) are also shown.
[0076]
[Table 4]
(Table Removed)
[0077]
In Example 5, the effect of the temperature of the slab heating was confirmed in a component base containing Mn and Se.
[0078] First, slabs containing, in mass%, Si: 3.3%, C: 0.06%, acid-soluble Al: 0.028%, N: 0.008%, Mn: 0.15% and Se: 0.007%, and a balance being composed of Fe and inevitable impurities were formed. Thicknesses of the slabs were each set to 160 mm. Next, the slabs were each heated at a temperature shown in Table 5 (1100°C to 1300°C) and were hot-rolled. In the hot rolling, the slabs were rough rolled until the thicknesses each became 30 mm, and thereafter were finish rolled to obtain hot-rolled steel strips each having a thickness of 2.3 mm. The final temperature of the rough rolling was set to 900°C to 1060°C, and the final temperature of the finish rolling was set to 850°C to 950°C. Subsequently, the hot-rolled steel strips were annealed at 1100°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, the cold-rolled steel strips were decarburization-annealed for 100 seconds at a temperature of 830°C in moist atmosphere gas, and subsequently were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.022 mass%. Next, an annealing separating agent having MgO as its main component was
coated on the steel strips, and then finish annealing was performed. In the finish annealing, the steel strips were heated to 1200°C at a speed of 15°C/h.
[0079] Then, the magnetic flux density B8 was measured as the magnetic property obtained after the finish annealing. A result of the measurement is shown in Table 5. Further, the amounts of the precipitates (NasAlN and SeasMnSe) in the hot-rolled steel strips were also measured after the hot rolling. A result of the measurement is also shown in Table 5. Further, in Table 5, the value of the left-hand side in the inequation (4) (NasAlN/[N] × 100) and the value of the left-hand side in the inequation
(5) ( SeasMnSe/[ Se ] x l 00 ) are also shown.
[0080]
[Table 5]
(Table Removed)
[0081]
In Example 6, the effect of the temperature of the slab heating was confirmed in a component base containing Mn, S, and Se.
[0082] First, slabs containing, in mass%, Si: 3.3%, C: 0.06%, acid-soluble Al: 0.027%, N: 0.007%, Mn: 0.16%, S: 0.006%, and Se: 0.004%, and a balance being composed of Fe and inevitable impurities were formed. Thicknesses of the slabs were each set to 160 mm. Next, the slabs were each heated at a temperature shown in Table 6 (1100°C to 1300°C) and were hot-rolled. In the hot rolling, the slabs were rough rolled until the thicknesses each became 40 mm, and thereafter were finish rolled to obtain hot-rolled steel strips each having a thickness of 2.3 mm. The final temperature of the rough rolling was set to 920°C to 1080°C, and the final temperature of the finish rolling was set to 870°C to 950°C. Subsequently, the hot-rolled steel strips were annealed at 1100°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, the cold-rolled steel strips were decarburization-annealed for 100 seconds at a temperature of 830°C in moist atmosphere gas, and subsequently were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.023 mass%. Next, an annealing separating agent having MgO as its main component was
coated on the steel strips, and then finish annealing was performed. In the finish annealing, the steel strips were heated to 1200°C at a speed of 15°C/h.
[0083] Then, the magnetic flux density B8 was measured as the magnetic property obtained after the finish annealing. A result of the measurement is shown in Table 6. Further, the amounts of the precipitates (NasAlN, SasMnS, and SeasMnSe) in the hot-rolled steel strips were also measured after the hot rolling. A result of the measurement is also shown in Table 6. Further, in Table 6, the value of the left-hand side in the inequation (4) (NasAlN/[N] × 100) and the value of the left-hand side in the inequation
(5) ( (SasMnS + 0. 46SeasMnSe) / ( [S]+0. 46 [Se] ) ×100) are also shown.
[0084]
[Table 6]
(Table Removed)
[0085]
In Example 7, the effect of added components was confirmed.
[0086] First, slabs containing components shown in Table 7 and a balance being composed of Fe and inevitable impurities were formed. Next, the slabs were heated at a temperature of 1100°C and were hot-rolled. In the hot rolling, the slabs were rough rolled until the thicknesses each became 40 mm, and thereafter were finish rolled to obtain hot-rolled steel strips each having a thickness of 2.3 mm. The final temperature of the rough rolling was set to 900°C to 960°C, and the final temperature of the finish rolling was set to 850°C to 920°C. Subsequently, the hot-rolled steel strips were annealed at 1100°C. Next, cold rolling was performed to obtain cold-rolled steel strips each having a thickness of 0.22 mm. Thereafter, the cold-rolled steel strips were decarburization-annealed for 120 seconds at a temperature of 820°C to 850°C in moist atmosphere gas, and subsequently were annealed in an ammonia containing atmosphere to increase nitrogen in the steel strips to 0.020 mass% to 0.025 mass%. Next, an annealing separating agent having MgO as its main component was coated on the steel strips, and then finish annealing was performed. In the finish annealing, the steel strips were heated to 1200°C at a speed of 15°C/h.
[0087] Then, the magnetic flux density B8 was measured as the magnetic property obtained after the finish annealing. A result of the measurement is shown in Table 7. [0088] [Table 7]
(Table Removed)
[0089]
In Example 8, the effect of the nitriding treatment was confirmed.
[0090] In Example 8, three types of samples (samples No. 8A, No. 8B, and No. 8C) were used. In forming the sample No. 8A, the cold-rolled steel strip of a sample No. 1C in Example 1 was decarburization annealed for 100 seconds at a temperature of 830°C in moist atmosphere gas, an annealing separating agent having MgO as its main component was coated on the steel strip, and then finish annealing was performed. That is, the nitriding treatment (annealing in an ammonia containing atmosphere) was omitted. In forming the sample No. 8B, the cold-rolled steel strip of the sample No. 1C was decarburization annealed at a temperature of 830°C in moist atmosphere gas, and subsequently was annealed in an ammonia containing atmosphere to increase nitrogen in the steel strip to 0.022 mass%. Next, an annealing separating agent having MgO as its main component coated was on the steel strip, and then finish annealing was performed. In forming the sample No. 8C, the cold-rolled steel strip in the sample No. 1C was decarburization annealed at a temperature of 860°C in moist atmosphere gas containing ammonia to increase nitrogen in the steel strip to 0.022 mass%. That is, the nitriding treatment was performed in parallel with the
decarburization annealing. Next, an annealing separating agent having MgO as its main component was coated on the steel strip, and then finish annealed was performed. All the samples were heated to 1200°C at a speed of 15°C/h in the finish annealing. [0091] Then, the magnetic flux density B8 was measured as the magnetic property obtained after the finish annealing. A result of the measurement is shown in Table 8. With reference to Table 8, as for the sample No. 8B, which was subjected to the nitriding treatment after the decarburization annealing, and the sample No. 8C, which was subjected to the nitriding treatment in parallel with the decarburization annealing, the high magnetic flux density B8 was obtained, but as for the sample No. 8A, which was not subjected to the nitriding treatment, the magnetic flux density B8 was low. [0092] [Table 8]
(Table Removed)
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
[0093] The present invention can be utilized in, for example, an industry of manufacturing electrical steel sheets and an industry in which electrical steel sheets are used.

CLAIMS
1. A manufacturing method of a grain-oriented electrical steel sheet, comprising:
heating a silicon steel material at a predetermined temperature of 1280°C or less, the silicon steel material containing: Si: 0.8 mass% to 7 mass%;
acid-soluble Al: 0.01 mass% to 0.065 mass%; N: 0.004 mass% to 0.012 mass%; Mn: 0.05 mass% to 1 mass%; and at least one selected from a group consisting of S and Se: 0.003 mass% to 0.015 mass% in total amount,
a C content being 0.085 mass% or less, and a balance being composed of Fe and inevitable impurities;
hot rolling the heated silicon steel material to obtain a hot-rolled steel strip;
annealing the hot-rolled steel strip to obtain an annealed steel strip;
cold rolling the annealed steel strip one time or more to obtain a cold-rolled steel strip;
decarburization annealing the cold-rolled steel strip to obtain a decarburization-annealed steel strip in which primary recrystallization is caused;
coating an annealing separating agent having MgO as its main component on the decarburization-annealed steel strip; and
finish annealing the decarburization-annealed steel strip to cause secondary recrystallization,
wherein
the method further comprises performing a nitriding treatment in which an N content in the decarburization-annealed steel strip is increased during a period of time from the start of said decarburization annealing to the occurrence of the secondary recrystallization in said finish annealing,
in a case that S and Se are contained in the silicon steel material, the predetermined temperature is a temperature Tl (°C) or less represented by an equation (1) below, is a temperature T2 (°C) or less represented by an equation (2) below, and is a temperature T3 (°C) or less represented by an equation (3) below,
in a case that Se is not contained in the silicon steel material, the predetermined temperature is the temperature Tl (°C) or less represented by the equation (1) below, and is the temperature T3 (°C) or less represented by the equation (3) below,
in a case that S is not contained in the silicon steel material, the predetermined temperature is the temperature T2 (°C) or less represented by the
equation (2) below, and is the temperature T3 (°C) or less represented by the equation (3) below,
said hot rolling the heated silicon steel material comprises:
rough rolling the heated silicon steel material at a cumulative reduction of 70% or more with setting an final temperature as 900°C to 1100°C; and
finish rolling the heated silicon steel material with setting an final temperature as 700°C to 950°C, and
a period of time from the end of the rough rolling to the start of the finish rolling is set to 1 second or more.
Tl=14855/(6.82-log([Mn]x[s]))-273 (1)
T2=10733/(4.08-log([Mn]x[Se]))-273 (2)
T3=10062/(2.72-log([Al]x[N]))-273 (3)
Here, [Mn] represents a Mn content (mass%) of the
silicon steel material, and [S] represents a S content (mass%) of the silicon steel material, and [Se] represents a Se content (mass%) of the silicon steel material, and [Al] represents an acid-soluble Al content (mass%) of the silicon steel material, and [N] represents the N content (mass%) of the silicon steel material.
2. The manufacturing method of the grain-oriented electrical steel sheet according to claim 1, wherein the silicon steel material further contains
at least one selected from a group consisting of Cr: 0.3 mass% or less, Cu: 0.4 mass% or less, Ni: 1 mass% or less, P: 0.5 mass% or less, Mo: 0.1 mass% or less, Sn: 0.3 mass% or less, Sb: 0.3 mass% or less, B: 0.008 mass% or less, and Bi: 0.01 mass% or less.
3. The manufacturing method of the grain-
oriented electrical st.eel sheet according to claim 1
or 2, wherein, when the amount of N (mass%)
precipitated as A1N in the hot-rolled steel strip is
represented as NaSAlN the amount of S (mass%)
precipitated as MnS in the hot-rolled steel strip is
represented as SasMnS, and the amount of Se (mass%)
precipitated as MnSe in the hot-rolled steel strip is
represented as SeasMnSe, relationships of an inequation
(4) and an inequation (5) below are established.
NASAIN/ [N] x l00≥60% (4)
(SasMnS + 0. 4 6SeasMnSe) /([S]+0.46[Se])x100≥40% (5)