GRAIN-ORIENTED ELECTRICAL STEEL SHEET AND METHOD FOR PRODUCING SAME

Abstract

A grain-oriented electrical steel sheet having a composition containing, in mass %, C: 0.005% or less, Si: 2.0% to 4.5%, and Mn: 0.5% or less, and also containing Sb and P in respective ranges satisfying 0.01%[% Sb]0.20% and 0.02%[% P]2.0[% Sb], with a balance being Fe and incidental impurities, wherein when the steel sheet is excited to 1.0 T at 50 Hz in a rolling transverse direction, a magnetizing force (TD-H.sub.10) and an iron loss (TD-W.sub.10) are respectively (TD-H.sub.10)200 A/m and (TD-W.sub.10)1.60 W/kg. Thus, a grain-oriented electrical steel sheet having excellent transformer core loss can be obtained industrially stably at low cost.

Claims

1. A grain-oriented electrical steel sheet having a composition containing, in mass %, C: 0.005% or less, Si: 2.0% to 4.5%, and Mn: 0.5% or less, and also containing Sb and P in respective ranges satisfying 0.01%[% Sb]0.20% and 0.02%[% P]2.0[% Sb], with a balance being Fe and incidental impurities, wherein when the steel sheet is excited to 1.0 T at 50 Hz in a rolling transverse direction, a magnetizing force (TD-H.sub.10) and an iron loss (TD-W.sub.10) are respectively (TD-H.sub.10)200 A/m and (TD-W.sub.10)1.60 W/kg.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the composition further contains, in mass %, one or more selected from Ni: 0.005% to 1.50%, Sn: 0.03% to 0.20%, Cu: 0.02% to 0.50%, Cr: 0.02% to 0.50%, Mo: 0.01% to 0.50%, and Nb: 0.002% to 0.01%.

3. A method for producing a grain-oriented electrical steel sheet, comprising: providing a steel slab having a composition containing, in mass %, C: 0.08% or less, Si: 2.0% to 4.5%, and Mn: 0.5% or less, containing each of S, Se, and O: less than 50 ppm, N: less than 60 ppm, and sol.Al: less than 100 ppm, and also containing Sb and P in respective ranges satisfying 0.01%[% Sb]0.20% and 0.02%[% P]2.0[% Sb], with a balance being Fe and incidental impurities; optionally reheating the steel slab; thereafter hot rolling the steel slab to obtain a hot rolled sheet; optionally hot band annealing the hot rolled sheet; thereafter cold rolling the hot rolled sheet either once, or twice or more with intermediate annealing performed therebetween, to obtain a cold rolled sheet having a final sheet thickness; thereafter performing decarburization and primary recrystallization annealing on the cold rolled sheet, to obtain a decarburization and primary recrystallization annealed sheet; thereafter applying an annealing separator mainly composed of MgO to the decarburization and primary recrystallization annealed sheet; thereafter performing secondary recrystallization annealing on the decarburization and primary recrystallization annealed sheet, to obtain a secondary recrystallization annealed sheet; and further performing flattening annealing on the secondary recrystallization annealed sheet, wherein 2.0 mass % to 15.0 mass % magnesium sulfate is contained in the annealing separator, the flattening annealing is performed at a temperature of 830 C. or more in an atmosphere having a H.sub.2 partial pressure of 0.3% or more, and when the steel sheet is excited to 1.0 T at 50 Hz in a rolling transverse direction, a magnetizing force (TD-H.sub.10) and an iron loss (TD-W.sub.10) are respectively (TD-H.sub.10)200 A/m and (TD-W.sub.10)1.60 W/kg.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0083] In the accompanying drawings:

[0084] FIG. 1 is a graph illustrating the relationship between the additive amount of P, the additive amount of Sb, and the magnetic flux density;

[0085] FIG. 2A is a graph illustrating the influence of the flattening annealing temperature on the iron loss (W.sub.17/50) in the rolling direction;

[0086] FIG. 2B is a graph illustrating the influence of the H.sub.2 partial pressure in the annealing atmosphere on the iron loss (W.sub.17/50) in the rolling direction;

[0087] FIG. 3A is a graph illustrating the influence of the flattening annealing temperature on the iron loss degradation (W) upon measuring roll rolling reduction;

[0088] FIG. 3B is a graph illustrating the influence of the H.sub.2 partial pressure in the annealing atmosphere on the iron loss degradation (W) upon measuring roll rolling reduction;

[0089] FIG. 4A is a graph illustrating the influence of the flattening annealing temperature on the iron loss (TD-W.sub.10) in the transverse direction;

[0090] FIG. 4B is a graph illustrating the influence of the H.sub.2 partial pressure in the annealing atmosphere on the iron loss (TD-W.sub.10) in the transverse direction;

[0091] FIG. 5A is a graph illustrating the influence of the flattening annealing temperature on the magnetizing force (TD-H.sub.10) in the transverse direction;

[0092] FIG. 5B is a graph illustrating the influence of the H.sub.2 partial pressure in the annealing atmosphere on the magnetizing force (TD-H.sub.10) in the transverse direction;

[0093] FIG. 6 is a graph illustrating the relationship between the iron loss (TD-W.sub.10) in the transverse direction and the iron loss (W.sub.17/50) in the rolling direction; and

[0094] FIG. 7 is a graph illustrating the relationship between the magnetizing force (TD-H.sub.10) in the transverse direction and the iron loss degradation (W) in the rolling direction.

DETAILED DESCRIPTION

[0095] One of the disclosed embodiments is described in detail below.

[0096] The reasons for limiting the chemical composition of a steel slab to the aforementioned range in this embodiment are described first.

C: 0.08% or less

[0097] C is an element useful in improving primary recrystallized texture. If the C content is more than 0.08%, however, the primary recrystallized texture degrades. The C content is therefore limited to 0.08% or less. The C content is desirably in the range of 0.01% to 0.06%, in terms of magnetic property. In the case where the required level of magnetic property is not so high, the C content may be 0.01% or less in order to omit or simplify decarburization in primary recrystallization annealing.

[0098] Moreover, it is essential to reduce the C content to 0.005% or less in the steel sheet after final annealing, in order to prevent magnetic aging.

[0099] Si: 2.0% to 4.5%

[0100] Si is an element useful in improving iron loss by increasing electrical resistance, and so the Si content is 2.0% or more. If the Si content is more than 4.5%, however, cold rolling manufacturability decreases significantly. The upper limit of the Si content is therefore 4.5%. The addition of Si may be omitted depending on the required iron loss level.

[0101] Mn: 0.5% or less

[0102] Mn has an effect of improving hot workability during manufacture.

[0103] If the Mn content is more than 0.5%, however, the primary recrystallized texture deteriorates and leads to lower magnetic property. The Mn content is therefore limited to 0.5% or less. The lower limit of the Mn content is preferably 0.05%.

[0104] S, Se, and O: less than 50 ppm each

[0105] If the content of each of S, Se, and O is 50 ppm or more, secondary recrystallization is difficult. This is because a coarse oxide or MnS or MnSe coarsened due to slab heating makes the primary recrystallized texture non-uniform. The content of each of S, Se, and O is therefore limited to less than 50 ppm.

[0106] N: less than 60 ppm

[0107] Excessive N also makes secondary recrystallization difficult, as with S, Se, and O. Particularly if the N content is 60 ppm or more, secondary recrystallization is unlikely to occur, and the magnetic property degrades. The N content is therefore limited to less than 60 ppm.

[0108] sol.Al: less than 100 ppm

[0109] Excessive Al also makes secondary recrystallization difficult. Particularly if the sol.Al content is 100 ppm or more, secondary recrystallization is unlikely to occur under the low-temperature slab heating condition, and the magnetic property degrades. Al is therefore limited to less than 100 ppm in sol.Al content.

[0110] Sb and P: 0.01%[% Sb]0.20% and 0.02%[% P]2.0[% Sb] respectively

[0111] In this embodiment, it is important to contain Sb and P in combination in these respective ranges. By adding Sb and P in combination in these ranges, the desired sulfurization effect in this embodiment is effectively achieved, and magnetic property degradation due to surface oxidation is suppressed. As a result, favorable magnetic property and base film property can be obtained throughout the coil length. If the Sb content or the P content is less than the aforementioned range, the effect cannot be achieved. If the Sb content or the P content is more than the aforementioned range, not only the magnetic property degrades, but also the formation of the base film is difficult.

[0112] While the essential components have been described above, the following elements may be contained as appropriate as components for improving the magnetic property industrially more stably in this embodiment.

Ni: 0.005% to 1.50%

[0113] Ni has a function of improving the magnetic property by enhancing the uniformity of the hot rolled sheet texture. To do so, the Ni content is preferably 0.005% or more. If the Ni content is more than 1.50%, secondary recrystallization is difficult, and the magnetic property degrades. Accordingly, the Ni content is desirably in the range of 0.005% to 1.50%.

[0114] Sn: 0.03% to 0.20%

[0115] Sn has a function of suppressing the nitriding or oxidation of the steel sheet during secondary recrystallization annealing and promoting the secondary recrystallization of crystal grains having favorable crystal orientation to effectively improve the magnetic property, in particular the iron loss property. To do so, the Sn content is preferably 0.03% or more. If the Sn content is more than 0.20%, cold rolling manufacturability decreases. Accordingly, the Sn content is desirably in the range of 0.03% to 0.20%.

[0116] Cu: 0.02% to 0.50%

[0117] Cu is a useful element that suppresses the nitriding or oxidation of the steel sheet during secondary recrystallization annealing and promotes the secondary recrystallization of crystal grains having favorable crystal orientation to effectively improve the magnetic property. To do so, the Cu content is preferably 0.02% or more. If the Cu content is more than 0.50%, cold rolling manufacturability decreases. Accordingly, the Cu content is desirably in the range of 0.02% to 0.50%.

[0118] Cr: 0.02% to 0.50%

[0119] Cr has a function of stabilizing the formation of the forsterite base film. To do so, the Cr content is preferably 0.02% or more. If the Cr content is more than 0.50%, secondary recrystallization is difficult, and the magnetic property degrades. Accordingly, the Cr content is desirably in the range of 0.02% to 0.50%.

[0120] Mo: 0.01% to 0.50%

[0121] Mo has a function of suppressing high-temperature oxidation and reducing surface defects called scab. To do so, the Mo content is preferably 0.01% or more. If the Mo content is more than 0.50%, cold rolling manufacturability decreases. Accordingly, the Mo content is desirably in the range of 0.01% to 0.50%.

[0122] Nb: 0.002% to 0.01%

[0123] Nb is a useful element that inhibits the growth of primary recrystallized grains and promotes the secondary recrystallization of crystal grains having favorable crystal orientation to improve the magnetic property. To do so, the Nb content is desirably 0.002% or more. If the Nb content is more than 0.01%, Nb remains in the steel substrate and degrades the iron loss. Accordingly, the Nb content is desirably in the range of 0.002% to 0.01%.

[0124] The following describes a production method in this embodiment.

[0125] A steel slab adjusted to the aforementioned chemical composition range is, after or without being reheated, hot rolled. In the case of reheating the slab, the reheating temperature is desirably about 1000 C. or more and 1300 C. or less. Slab heating exceeding 1300 C. is meaningless in this embodiment in which the slab contains no inhibitor, and not only causes an increase in cost but also significantly degrades the magnetic property due to the growth of giant crystal grains. If the reheating temperature is less than 1000 C., the rolling load increases, making the rolling difficult.

[0126] Following this, the hot rolled sheet is optionally hot band annealed. The hot rolled sheet is then cold rolled once, or twice or more with intermediate annealing therebetween, to obtain a final cold rolled sheet. The cold rolling may be performed at normal temperature. Alternatively, the cold rolling may be warm rolling with the steel sheet temperature being higher than normal temperature, e.g. about 250 C.

[0127] The final cold rolled sheet is then subjected to decarburization/primary recrystallization annealing. A first objective of the decarburization/primary recrystallization annealing is to cause the primary recrystallization of the cold rolled sheet having rolled microstructure to adjust it to an optimal primary recrystallized texture for secondary recrystallization. For this objective, the annealing temperature in the primary recrystallization annealing is desirably about 800 C. or more and less than about 950 C. The annealing atmosphere is desirably a wet hydrogen nitrogen atmosphere or a wet hydrogen argon atmosphere.

[0128] A second objective is decarburization. If more than 0.005% carbon is contained in the product sheet, the iron loss degrades. The carbon content is therefore desirably reduced to 0.005% or less.

[0129] A third objective is to form a subscale made up of an internal oxidation layer of SiO.sub.2 which is the raw material of the base film mainly composed of forsterite. If the upstream-stage temperature of decarburization annealing is less than 800 C., oxidation reaction and decarburization reaction do not progress sufficiently, and necessary oxidation and decarburization cannot be completed.

[0130] After the decarburization/primary recrystallization annealing, an annealing separator mainly composed of magnesia (MgO) is applied to the surface of the steel sheet. Here, magnesium sulfate is added to the annealing separator mainly composed of MgO, in order to improve the magnetic property by the sulfurization treatment of increasing the amount of S in the steel substrate after the primary recrystallization annealing and before the completion of secondary recrystallization.

[0131] If the additive amount of magnesium sulfate is less than 2.0%, the magnetic property improving effect is insufficient. If the additive amount of magnesium sulfate is more than 15.0%, the grain growth is suppressed excessively, and the magnetic property improving effect is insufficient and also the formation of the base film is adversely affected.

[0132] The expression mainly composed of magnesia in this embodiment means that 50% or more magnesia is contained in the annealing separator. Sub-components such as Na.sub.2S.sub.2O.sub.3 and TiO.sub.2 may be added to the annealing separator in small amounts, according to conventional methods.

[0133] After this, secondary recrystallization annealing is performed. During the secondary recrystallization annealing, magnesium sulfate decomposes and exerts the sulfurization effect, thus realizing crystal texture highly aligned with the Goss orientation. Favorable magnetic property can be obtained in this way.

[0134] The secondary recrystallization annealing is effectively performed by diffusing S into the steel substrate with a heating rate of 30 C./H or less, as disclosed in JP 4321120 B. The annealing atmosphere may be any of N.sub.2, Ar, and mixed gas thereof. Here, H.sub.2 is not used as atmosphere gas until the completion of secondary recrystallization. This is because S in the annealing separator goes out of the system as H.sub.2S (gas), causing lower sulfurization effect especially in the coil edges.

[0135] After the secondary recrystallization annealing, an insulating coating is further applied to the surface of the steel sheet and baked. The type of the insulating coating is not particularly limited, and may be any conventionally well-known insulating coating. For example, a method of applying an application liquid containing phosphate-chromate-colloidal silica described in JP S50-79442 A and JP S48-39338 A to the steel sheet and baking it to also perform flattening annealing is preferable.

[0136] Flattening annealing is then performed. This flattening annealing is important in this embodiment.

[0137] The flattening annealing temperature needs to be 830 C. or more. If the flattening annealing temperature is less than 830 C., strain for shape adjustment remains, which decreases the iron loss in the TD direction and simultaneously degrades the iron loss in the RD direction. The iron loss in the TD direction for preventing degradation in the iron loss in the RD direction in the product sheet is 1.60 W/kg or more.

[0138] Moreover, 0.30% or more hydrogen needs to be introduced into the flattening annealing atmosphere. If the hydrogen partial pressure in the atmosphere is less than 0.30%, the coating film tension decreases, and the magnetizing force in the TD direction decreases. This results in higher degradation of transformer core loss due to the application of strain associated with processing into a transformer. To reduce the iron loss degradation caused by the application of strain associated with processing into a transformer and improve the transformer core loss, the magnetizing force when exciting the product sheet to 1.0 T in the TD direction needs to be 200 A/m or more.

EXAMPLES

Example 1

[0139] A continuously cast slab having a composition containing C: 0.03%, Si: 3.5%, Mn: 0.08%, sol.Al: 75 ppm, N: 45 ppm, S: 30 ppm, Se: 1 ppm, O: 9 ppm, P: 0.06%, and Sb: 0.10% with the balance being Fe and incidental impurities was reheated to 1230 C., and then hot rolled to obtain a hot rolled sheet of 2.5 mm in sheet thickness. The hot rolled sheet was then hot band annealed at 1050 C. for 10 s, and subsequently cold rolled at 200 C. to a sheet thickness of 0.27 mm. The cold rolled sheet was then subjected to primary recrystallization annealing also serving as decarburization at 850 C. for 120 s in an atmosphere of H.sub.2: 55%, N.sub.2: 45%, and dew point: 55 C., with the heating rate from 500 C. to 700 C. being 20 C./s. The C content after this annealing was 30 ppm.

[0140] A sample was collected from the obtained primary recrystallization annealed sheet, and an annealing separator having MgO as a main ingredient and containing magnesium sulfate in the proportion shown in Table 2 was applied at 12.5 g/m.sup.2 to the sheet surface and dried. The sample was then subjected to secondary recrystallization annealing under the condition of heating to 800 C. at a heating rate of 15 C./h, heating from 800 C. to 850 C. at a heating rate of 2.0 C./h, retaining at 850 C. for 50 h, and then heating to 1160 C. at a heating rate of 5.0 C./h and soaking for 5 h. As the atmosphere gas, N.sub.2 gas was used up to 850 C., and H.sub.2 gas was used at 850 C. or more.

[0141] A treatment liquid containing phosphate-chromate-colloidal silica at a mass ratio of 3:1:3 was applied to the surface of the secondary recrystallization annealed sheet obtained under the aforementioned condition, and subsequently flattening annealing was performed under the condition shown in Table 2.

[0142] The magnetic property of the obtained product sheet was then examined. The magnetic property was evaluated based on the magnetic flux density B.sub.8 when exciting the sheet at 800 A/m in the rolling direction and the iron loss W.sub.17/50 when exciting the sheet to 1.7 T at 50 Hz in an alternating magnetic field in the rolling direction, the magnetizing force (TD-H.sub.10) and iron loss (TD-W.sub.10) when exciting the sheet to 1.0 T at 50 Hz in the transverse direction, and the strain sensitivity.

[0143] The strain sensitivity was evaluated based on the change (W) in iron loss W.sub.17/50 value when passing the sheet while pressing it by measuring rolls, which were made up of steel rolls of 100 mm in diameter and 50 mm in width, with a rolling reduction force of 1.5 MPa (15 kgf/cm).

[0144] Table 2 shows the obtained results. Magnetic flux density B.sub.8 of 1.94 T or more, iron loss W.sub.17/50 of 0.82 W/kg or less, and W of 0.005 W/kg or less are regarded as excellent properties.

TABLE-US-00002 TABLE 2 Flattening annealing condition Additive amount of Soaking H.sub.2 partial pressure in Magnetic property of product sheet magnesium sulfate temperature atmosphere B.sub.8 W.sub.17/50 TD-H.sub.10 TD-W.sub.10 W No. (%) ( C.) (%) (T) (W/kg) (A/m) (W/kg) (W/kg) Remarks 1 2.5 850 3.0 1.943 0.812 271 1.903 0.005 Example 2 5.0 850 3.0 1.955 0.784 280 1.993 0.004 Example 3 10.0 850 3.0 1.960 0.775 290 2.011 0.003 Example 4 10.0 880 3.0 1.957 0.763 272 2.028 0.004 Example 5 0 850 3.0 1.911 0.880 188 1.774 0.023 Comparative Example 6 20.0 850 3.0 1.868 1.050 292 2.044 0.003 Comparative Example 7 5.0 800 3.0 1.953 0.883 280 1.503 0.004 Comparative Example 8 5.0 850 0 1.956 0.788 180 1.983 0.028 Comparative Example

[0145] As is clear from Table 2, by using the material containing P and Sb in combination, applying the annealing separator mainly composed of MgO and containing 2.0% or more magnesium sulfate, and performing secondary recrystallization annealing according to the disclosure, favorable magnetic flux density was obtained. Moreover, by setting the flattening annealing temperature to 830 C. or more, the iron loss in the TD direction was 1.60 W/kg or more, resulting in favorable iron loss in the rolling direction. Further, by introducing 0.30% or more a hydrogen atmosphere into the flattening annealing atmosphere, the magnetizing force when exciting the sheet to 1.0 T in the transverse direction was ensured to be 200 A/m or more, as a result of which the iron loss degradation caused by the application of strain associated with processing into a transformer was reduced.

Example 2

[0146] A continuously cast slab composed of various components shown in Table 3 was reheated to 1230 C., and then hot rolled to obtain a hot rolled sheet of 2.2 mm in sheet thickness. The hot rolled sheet was then hot band annealed at 1050 C. for 10 s, and subsequently cold rolled at 200 C. to a sheet thickness of 0.23 mm. The cold rolled sheet was then subjected to decarburization annealing at 850 C. for 120 s in an atmosphere of H.sub.2: 55%, N.sub.2: 45%, and dew point: 55 C., with the heating rate from 500 C. to 700 C. being 20 C./s. The C content after the decarburization annealing was 30 ppm.

[0147] A sample was collected from the decarburization annealed sheet, and an annealing separator having MgO as a main ingredient and containing magnesium sulfate in the proportion shown in Table 4 was applied at 12.5 g/m.sup.2 to the sheet surface and dried. The sample was then subjected to secondary recrystallization annealing under the condition of heating to 800 C. at a heating rate of 15 C./h, heating from 800 C. to 850 C. at a heating rate of 2.0 C./h, retaining at 850 C. for 50 h, and then heating to 1160 C. at a heating rate of 5.0 C./h and soaking for 5 h. As the atmosphere gas, N.sub.2 gas was used up to 850 C., and H.sub.2 gas was used at 850 C. or more.

[0148] A treatment liquid containing phosphate-chromate-colloidal silica at a mass ratio of 3:1:3 was applied to the surface of the secondary recrystallization annealed sheet obtained under the aforementioned condition, and subsequently flattening annealing was performed under the condition shown in Table 4.

[0149] The magnetic property of the obtained product sheet was then examined. The method of evaluating the magnetic property is the same as that in Example 1.

[0150] Table 4 shows the obtained results.

TABLE-US-00003 TABLE 3 Chemical composition (mass %) No. C Si Mn Sb P S Se O Al N Others Remarks 1 0.03 3.3 0.07 0.052 0.055 0.001 0.001 0.001 0.003 0.003 Conforming steel 2 0.04 3.2 0.08 0.066 0.075 0.002 0.001 0.001 0.004 0.002 Ni: 0.30 Conforming steel 3 0.02 3.2 0.08 0.036 0.055 0.002 0.001 0.001 0.004 0.002 Sn: 0.10 Conforming steel 4 0.03 3.4 0.11 0.044 0.045 0.001 0.001 0.001 0.005 0.003 Cu: 0.10 Conforming steel 5 0.04 3.3 0.06 0.078 0.077 0.002 0.001 0.001 0.006 0.001 Cr: 0.08 Conforming steel 6 0.03 3.1 0.07 0.055 0.058 0.001 0.001 0.001 0.004 0.003 Mo: 0.1 Conforming steel 7 0.02 3.2 0.08 0.060 0.050 0.002 0.001 0.001 0.004 0.002 Nb: 0.004 Conforming steel 8 0.03 3.5 0.05 0.001 0.001 0.002 0.001 0.001 0.007 0.003 Comparative steel 9 0.04 3.3 0.06 0.001 0.050 0.002 0.001 0.001 0.006 0.001 Comparative steel 10 0.04 3.3 0.06 0.053 0.001 0.002 0.001 0.001 0.006 0.001 Comparative steel 11 0.04 3.3 0.07 0.064 0.041 0.001 0.024 0.001 0.003 0.003 Comparative steel 12 0.03 3.4 0.06 0.045 0.068 0.021 0.001 0.011 0.003 0.003 Comparative steel 13 0.02 3.2 0.07 0.035 0.050 0.001 0.001 0.001 0.023 0.003 Comparative steel 14 0.03 3.3 0.09 0.045 0.049 0.002 0.001 0.001 0.003 0.008 Comparative steel

TABLE-US-00004 TABLE 4 Additive amount of Magnetic property of product sheet magnesium sulfate B.sub.8 W.sub.17/50 TD-H.sub.10 TD-W.sub.10 W No. (%) (T) (W/kg) (A/m) (W/kg) (W/kg) Remarks 1 3 1.949 0.81 282 2.003 0.004 Example 2 10 1.960 0.80 278 1.922 0.005 Example 3 5 1.950 0.77 285 2.022 0.003 Example 4 5 1.954 0.78 288 2.101 0.002 Example 5 3 1.950 0.79 286 2.076 0.003 Example 6 3 1.950 0.78 278 1.983 0.005 Example 7 10 1.960 0.78 281 2.000 0.004 Example 8 0 1.909 0.90 220 1.703 0.008 Comparative Example 9 0 1.951 0.89 188 1.783 0.030 Comparative Example 10 0 1.905 0.93 238 1.803 0.010 Comparative Example 11 0 1.830 1.45 160 1.432 0.045 Comparative Example 12 0 1.802 1.77 145 1.382 0.059 Comparative Example 13 0 1.804 1.72 138 1.432 0.055 Comparative Example 14 0 1.811 1.62 165 1.543 0.044 Comparative Example

[0151] As is clear from Table 4, by using the material containing appropriate amounts of P and Sb in combination, applying the annealing separator having MgO as a main ingredient and containing 2.0% or more magnesium sulfate, performing secondary recrystallization annealing, and further applying an appropriate flattening annealing condition according to the disclosure, not only favorable magnetic flux density was obtained, but also iron loss degradation caused by the application of strain associated with processing into a transformer was reduced.