JP2015086414A - Method for manufacturing oriented electromagnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for providing an oriented electromagnetic steel sheet having less iron loss.SOLUTION: SnOor SnO is contained in a range of 2 to 10 mass% to 100 mass% of MgO in an annealing separation agent and a furnace tension is 11.8 MPa (1.2 kgf/mm) or less during flatness annealing.

Description

  The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet capable of obtaining a grain-oriented electrical steel sheet having a small iron loss.

  The grain-oriented electrical steel sheet is a soft magnetic material used as a core material for transformers and generators, and in order to reduce the iron loss and magnetostriction noise of the grain-oriented electrical steel sheet, it is necessary to secure film tension. From this point of view, it is important to apply tension with a base film mainly composed of forsterite.

  Conventionally, various methods for improving the coating film from the viewpoint of coating appearance and adhesion have been proposed. For example, a method of mixing an additive with the main component MgO of the annealing separator is known.

That is, as a method of mixing an additive with the main component MgO of the annealing separator, Patent Document 1 discloses a method of adding TiO ₂ to MgO, and Patent Document 2 discloses a method of adding an Sr compound to MgO. Patent Document 3 proposes a method of adding TiO ₂ , SnO ₂ and Sr compound to MgO in combination.

Japanese Patent Publication No.51-12451 Japanese Patent Publication No.57-32716 JP-A-9-291313

However, the conventional method focuses on the superiority in terms of ensuring the appearance of the coating and the adhesion of the coating, and the viewpoint of coating tension that is important in order to reduce the iron loss and magnetostriction noise of the grain-oriented electrical steel sheet. The improvement from was not noticed.
Here, during the production process of the grain-oriented electrical steel sheet, the undercoat is formed at the time of final finish annealing, but it is necessary to complete secondary recrystallization at the same time in the final finish annealing.
That is, even if it has the effect of improving the film tension, it may adversely affect secondary recrystallization, and the optimal conditions for both may not be met. In particular, SnO ₂ and SnO, which have a decomposition temperature that overlaps with the secondary recrystallization temperature, are known to have an effect of improving the film tension. Usually, the addition amount is suppressed to 3% or less with respect to MgO.

The present invention advantageously solves the above-mentioned problems. In the annealing separator, SnO ₂ or SnO is contained in an amount of 2 to 10% by mass with respect to MgO, and the undercoat film tension in the rolling direction is 3 MPa or more. It aims at proposing the manufacturing method which can obtain a grain-oriented electrical steel sheet with a low iron loss by ensuring.

That is, the gist configuration of the present invention is as follows.
1. In mass%, C: 0.10% or less, Si: 2.0-4.5%, and Mn: 0.01-0.5%, sol.Al is reduced to 100 mass ppm or less, and S, Se, and N are reduced to 50 mass ppm or less, respectively. After the steel slab composed of Fe and inevitable impurities is subjected to low-temperature slab heating of 1300 ° C or lower, hot-rolled sheet annealing is performed, and then cold rolling is performed to obtain a final sheet thickness. , Continuous primary recrystallization annealing and decarburization annealing, and after applying batch final finishing annealing to form an undercoat by applying an annealing separator mainly composed of MgO, flattening annealing In the method for producing a grain-oriented electrical steel sheet,
In the annealing separator, SnO ₂ and / or SnO is contained in a range of 2 to 10% by mass with respect to MgO: 100% by mass,
A method for producing a grain-oriented electrical steel sheet in which the furnace tension is 11.8 MPa (1.2 kgf / mm ² ) or less during the flattening annealing.

2. 2. The method for producing a grain-oriented electrical steel sheet according to 1 above, wherein the steel slab further contains 0.15% by mass or less of Sn.

3. The steel slab is further mass%,
Ni: 0.005-1.50%,
Sb: 0.005-0.50%,
Cu: 0.01 to 0.50%,
P: 0.005-0.50%,
Cr: 0.01-1.50% and
Mo: 0.01-0.50%
3. The method for producing a grain-oriented electrical steel sheet according to the above 1 or 2, comprising a composition containing at least one selected from the above.

According to the present invention, a large amount of SnO ₂ or SnO having an effect of improving the film tension can be contained in the annealing separator. As a result, a grain-oriented electrical steel sheet with small iron loss can be obtained, and its industrial value is extremely high.

It is a figure which shows the relationship between curvature amount and film tension. It is a diagram showing the relationship between SnO ₂ / MgO values and film tension and iron loss. It is a figure which shows the relationship between the furnace tension at the time of planarization annealing, and an iron loss. It is a figure which shows the relationship between the furnace tension at the time of planarization annealing, and a film tension.

Hereinafter, the present invention will be specifically described.
First, the experimental results that led to the present invention will be described. In addition, unless otherwise indicated, the "% and ppm" display regarding a steel plate component and the component of an annealing separator shall mean the mass% and the mass ppm.
The inventors paid attention to the improvement of the undercoat tension in earning the grain-oriented electrical steel sheet with a small iron loss, and have intensively studied the measures for improving the undercoat tension. As a result, we are known to be useful in film formation, an inhibitor such as AlN were often constrained like the amount and decarburization annealing conditions in a manner to be contained in the steel slab, the SnO ₂ I recalled and tried to apply it.

(Experiment 1)
Inhibitor-free component system containing C: 0.025%, Si: 3.3%, Mn: 0.06%, Sb: 0.03%, Al 70ppm, N 40ppm, S, Se and 0 reduced to 20ppm or less The steel slab was heated to 1210 ° C. and hot rolled to a thickness of 2.7 mm. Subsequently, hot-rolled sheet annealing was performed at a temperature of 1065 ° C. for 30 seconds, 1000 to 750 ° C. being cooled at a cooling rate of 20 ° C./second, and 750 to 300 ° C. being rapidly cooled at a cooling rate of 40 ° C./second. After hot-rolled sheet annealing, it was cold-rolled at a maximum temperature of 220 ° C. and finished to a final thickness of 0.29 mm.

Subsequently, continuous decarburization annealing was performed in an atmosphere of dew point: 53 ° C., hydrogen: 55% by volume, nitrogen: 45% by volume, and soaking at 840 ° C. for 100 seconds.
Furthermore, SnO ₂ is added to the annealing separator mainly composed of MgO containing TiO ₂ : 3%, SrSO ₄ : 1.6%, Mg ₂ SO ₄ : 1.2% with respect to MgO: 100%. Then, various experiments were conducted to change the content of SnO ₂ .

After applying the annealing separator, final finish annealing is performed by holding at 1200 ° C for 10 hours in a hydrogen atmosphere, and finally flattening at 835 ° C for 20 seconds in a dry nitrogen and hydrogen mixed atmosphere Annealing was performed to correct the shape. The furnace tension during the flattening annealing was 8.8 MPa (0.91 kgf / mm ² ).
In order to evaluate the base film tension, coating was not performed.

Using the obtained product plate, the magnetic flux density (B ₈ ) and iron loss (W _17/50 ) in the rolling direction were measured. Furthermore, in order to evaluate the film tension, a sample of 280 mm in the rolling direction and 30 mm in the width direction was cut out, the base film on one side was removed by pickling, and from the measured amount of warpage using the following formula (1) The film tension was calculated.
σ ′ = Ed / 2R (1)
Where (1)
E: Young's modulus d: Plate thickness (mm)
R≈L ² / 2a (curvature radius)
a: Warpage (mm)
L: Warpage measurement length σ ′: film tension means
In the above experiment,
Warp measurement length (L) is 250mm,
The value of E was 132 GPa.

FIG. 1 shows the relationship between the amount of warpage in each of the RD direction (rolling direction) and TD direction (direction perpendicular to the rolling direction) and the film tension. It has been confirmed that the magnetic flux density (B ₈ ) of the product plate in Experiment 1 is 1.92 to 1.93 T under all conditions.

FIG. 2 shows the relationship between SnO ₂ content, film tension, and iron loss. When the SnO ₂ content is in the range of 2 to 10% with respect to MgO: 100%, a good iron loss of W _17/50 = 1.00 W / kg or less is obtained, and 3 MPa or more in that range. It can be seen that the coating tension can be secured.

On the other hand, when the appearance of the film was observed, film defects (glitter) occurred when the SnO ₂ content was 12% or more with respect to MgO: 100%. Conventionally, due to the release of oxygen accompanying the decomposition of SnO ₂ , surface oxidation of the inhibitor component was promoted and secondary recrystallization failure occurred. However, in the method using the inhibitor-free component as in the present invention, the film tension is reduced. The optimum addition amount from the viewpoint was 8%, and it was found that the amount could be increased regardless of the occurrence of secondary recrystallization.

Furthermore, it has been found that it is necessary to pay attention to the relationship between the in-furnace tension and the material component in the flattening annealing from the viewpoint of securing the film tension.
The film tension is generated by the difference in the degree of contraction between the film and the base iron when cooled to room temperature after the film is formed at a high temperature, that is, the difference in thermal expansion coefficient. While it is necessary to correct the shape and to apply tension, if the steel sheet is stretched by applying more tension than necessary, the film tension due to the difference in thermal expansion coefficient is diminished. Therefore, in the present invention, from the viewpoint of securing the film tension, it is important that the tension applied to the steel sheet in the furnace during the flattening annealing is 11.8 MPa (1.21 kgf / mm ² ) or less.

Moreover, in order to suppress the elongation of the steel sheet, securing the hot strength of the steel sheet itself is also effective for securing the film tension.
In particular, the addition of Sn has an effect of improving the hot strength, suppressing the elongation of the steel sheet in the flattening annealing, and improving the film tension, so that the addition amount is advantageous. However, when Sn is contained in the steel slab, too much content causes hot embrittlement and has the effect of causing hesitation, so the content in the steel slab is 0.15% or less. It is preferable to do this.

On the other hand, in the case of the steel plate component according to the present invention, the addition of SnO ₂ to the annealing separator is effective as a means for increasing the Sn content in the steel plate. Here, when the SnO ₂ content in the annealing separator is 8% with respect to MnO: 100%, the Sn content in the steel sheet increases by about 0.03%, but the Sn at that time is the film tension. In addition to strengthening, it has almost the same effect as Si in improving specific resistance.
For this reason, the means for adding SnO ₂ in the annealing separator in the form of SnO ₂ is an extremely effective means for reducing iron loss so that the Sn content in the steel sheet is 0.05%, which is less likely to cause hege. it is conceivable that.

Hereinafter, the reasons for defining the other constituent elements of the present invention will be described.
The steel slab in this invention is manufactured by a well-known method, for example, steel making-continuous casting (or ingot-making-bundling rolling). At that time, the component composition of the steel slab is defined as follows.
C is an element useful for improving the primary recrystallization texture by controlling carbides, so it is specified to be 0.10% or less. If the C content is higher than this, it becomes difficult to decarburize until the product plate is obtained, magnetic aging occurs in the product plate, and the magnetic properties are deteriorated.

  Si is an element useful for reducing iron loss by increasing electric resistance, and is added in an amount of 2.0% or more to obtain the effect. On the other hand, if it exceeds 4.5%, troubles such as cracking occur during cold rolling and it becomes difficult to pass the sheet, so the upper limit is specified to 4.5%.

  Mn has an effect of improving workability during hot rolling, so 0.01% or more is added. On the other hand, if it exceeds 0.5%, the primary recrystallized texture deteriorates, and it becomes difficult to obtain secondary recrystallized grains accumulated in the Goth orientation, and the magnetic properties are deteriorated. For this reason, it is specified to be 0.5% or less.

  In the present invention, the inhibitor element Al is reduced to 100 ppm or less, and N, S, and Se are reduced to 50 ppm or less, preferably 30 ppm or less. Also, other nitride-forming elements such as Ti, Nb, B, Ta, and V are each reduced to 50 ppm or less, which is effective in preventing deterioration of iron loss and ensuring good workability. .

  For the purpose of reducing iron loss, Sn may be added to the steel slab, but since it becomes easy to generate scabs due to embrittlement during hot rolling, the Sn content when added to the steel slab is As described above, it is preferably 0.15% or less.

  In the present invention, Ni can be added to improve the hot rolled sheet structure and improve the magnetic properties. Here, if the amount of Ni added is less than 0.005%, the amount of improvement in magnetic properties becomes small. On the other hand, if it exceeds 1.50%, secondary recrystallization becomes unstable and the magnetic properties deteriorate. Is preferably 0.005 to 1.50%.

  Furthermore, in the present invention, for the purpose of improving iron loss characteristics, Sb: O.005 to 0.50%, Cu: 0.01 to 0.50%, P: O.005 to 0.50%, Cr: O.01 to 1.50%, and Mo : One of O.01 to 0.50% can be added alone, or two or more can be added in combination. When the addition amount is less than the lower limit amount, there is no effect of improving the iron loss, while when the upper limit amount is exceeded, the development of secondary recrystallized grains is suppressed.

The steel slab containing the above components may be melted and formed into a steel slab by the ingot-making / bundling method or the continuous casting method, or may be a thin cast piece having a thickness of 100 mm or less by the direct casting method.
Such steel slabs or thin cast slabs are heated to 1300 ° C. or lower (low temperature slab heating) and hot-rolled to perform hot-rolled sheet annealing. After performing hot-rolled sheet annealing, rolling (cold rolling or warm rolling) is performed to obtain a cold-rolled sheet. Increasing the temperature of the steel sheet during rolling to 100 to 250 ° C., or performing aging treatment at 100 to 250 ° C. one or more times during cold rolling develops a structure of Goss orientation. Effective above.

Subsequently, continuous decarburization annealing is performed. Continuous decarburization annealing is performed in a wet hydrogen atmosphere at 750 to 900 ° C., and C is reduced to 50 ppm or less, preferably 30 ppm or less.
After decarburization annealing, after applying an annealing separator mainly composed of MgO, batch type final finishing annealing for forming a base film (forsterite film) is performed.
In the present invention, in order to reduce the iron loss, SnO ₂ is contained in the annealing separator in a range of 2 to 10% with respect to MgO: 100% to ensure a film tension of 3 MPa or more. If it is less than 2%, the film tension cannot be secured, and the iron loss is insufficiently reduced. On the other hand, if it exceeds 10%, a film formation failure tends to occur. In the present invention, the same effect can be obtained by using SnO instead of SnO ₂ . In the present invention, MgO as a main component means that MgO is contained in the annealing separator in an amount of 50% by mass or more, and the remainder other than that prescribed in the present invention is usually an annealing separator. Is used as an inevitable impurity.

In the present invention, the temperature at the final finish annealing is preferably set to 1000 ° C. or more for forming the forsterite film.
Further, after the final finish annealing, flattening annealing is performed to correct the shape of the steel sheet. In the case of flattening annealing, if the tension applied to the steel sheet in the furnace is 11.8 MPa (1.2 kgf / mm ² ) or less, it is effective in suppressing the elongation of the steel sheet and ensuring the film tension. In the flattening annealing, the tension applied to the steel sheet in the furnace (in-furnace tension) is set to 11.8 MPa (1.2 kgf / mm ² ) or less. The conditions for the flattening annealing other than the in-furnace tension may follow a conventional method.

Further, adding Sn to the steel slab or adding SnO ₂ or SnO to the annealing separator is effective for suppressing the elongation of the steel sheet and strengthening the coating tension.
After performing the flattening annealing, an insulating coating may be applied to the surface of the steel plate. In particular, in order to reduce the iron loss, it is preferable to perform tension coating in which phosphate and colloidal silica are mixed.

Example 1
Inhibitor-free steel slabs A and C containing 0.024%, Si: 3.3%, Mn: 0.05%, Al 75 ppm, N 41 ppm, S, Se and 0 reduced to 20 ppm or less : Inhibitor-free component system containing 0.024%, Si: 3.3%, Mn: 0.05%, Sn: 0.05%, Al: 70ppm, N: 40ppm, S, Se and 0 reduced to 20ppm or less Steel slabs B were each heated to 1220 ° C. and hot-rolled to a thickness of 2.5 mm. Subsequently, hot-rolled sheet annealing was performed at 1025 ° C. for 30 seconds, 1000 to 750 ° C. at a cooling rate of 20 ° C./second, and 750 to 300 ° C. at a cooling rate of 40 ° C./second. After hot-rolled sheet annealing, it was cold-rolled at a maximum temperature of 200 ° C and finished to a final thickness of 0.26 mm.
Subsequently, continuous decarburization annealing was performed in an atmosphere of dew point: 53 ° C., hydrogen: 55% by volume, and nitrogen: 45% by volume under the conditions of holding at 840 ° C. for 100 seconds.
Furthermore, SnO ₂ was further added to the annealing separator mainly composed of MgO added with TiO ₂ : 3%, SrSO ₄ : 1.6%, Mg ₂ SO ₄ : 1.2% with respect to MgO: 100%, An experiment was conducted in which the SnO ₂ content was 8% with respect to MgO: 100%.
The final finish annealing was performed in a hydrogen atmosphere at 1200 ° C. for 10 hours.
After the final finish annealing, flattening annealing was performed for 30 seconds at 850 ° C. in a dry nitrogen and hydrogen mixed atmosphere to correct the shape. The in-furnace tension in the flattening annealing was changed in the range of 5.9 to 12.7 MPa (0.6 to 1.31 (kgf / mm ² )).
Using the product plate thus obtained, the magnetic flux density (B ₈ ) and iron loss (W _17/50 ) in the rolling direction were measured. Furthermore, in order to evaluate the film tension, a sample of 280 mm in the rolling direction and 30 mm in the width direction was cut out, the base film on one side was removed by pickling, and the film was measured from the measured amount of warpage using the above formula (1). The tension was calculated.
The measurement results of the magnetic flux density of the product ranged from 1.92 to 1.94T.
FIG. 3 shows the relationship between the furnace tension and the iron loss at the time of flattening annealing. Further, FIG. 4 shows the relationship between the furnace tension and the film tension during flattening annealing.

According to FIG. 3, it can be seen that the core loss during the flattening annealing is set to 11.8 MPa (1.2 kgf / mm ² ) or less, and at the same time, Sn is added to reduce the iron loss. Further, according to FIG. 4, it can be seen that the in-furnace tension during the flattening annealing is set to 11.8 MPa (1.2 kgf / mm ² ) or less, and at the same time, Sn is added to increase the film tension.

(Example 2)
Steel slabs having the components shown in Table 1 were heated to 1230 ° C. and hot-rolled to a finish of 2.4 mm. Hot-rolled sheet annealing was performed under the conditions of holding at 1050 ° C. for 30 seconds, rapidly cooling 1000 to 750 ° C. at 20 ° C./second and 750 to 300 ° C. at 40 ° C./second. After hot-rolled sheet annealing, it was cold-rolled with a maximum temperature of 220 ° C. to a final thickness of 0.26 mm.
Subsequently, continuous decarburization annealing was performed by a method of holding at 850 ° C. for 100 seconds in an atmosphere of dew point: 55 ° C., hydrogen: 55 vol%, and nitrogen: 45 vol%.
Furthermore, SnO is further added to the annealing separator mainly composed of MgO added with TiO ₂ : 3%, SrSO ₄ : 1.6%, Mg ₂ SO ₄ : 1.2% with respect to MgO: 100%. An experiment was conducted in which the SnO content was 5% with respect to MgO: 100%.
The final finish annealing was performed by a method of holding at 1200 ° C. for 10 hours in a hydrogen atmosphere.
After the final finish annealing, flattening annealing was performed for 30 seconds at 850 ° C. in a dry nitrogen and hydrogen mixed atmosphere to correct the shape. The furnace tension during flattening annealing was 6.9 MPa (0.7 kgf / mm ² ).
Using the product plate thus obtained, the magnetic flux density (B ₈ ) and iron loss (W _17/50 ) in the rolling direction were measured.
The results obtained by this evaluation are also shown in Table 1.

According to Table 1, in the steel slab with the inhibitor-free component specified in the present invention, the furnace tension during flattening annealing is 11.8 MPa (1.2 kgf / mm ² ) or less, and at the same time, iron loss is achieved by adding SnO. Can be improved.

Claims (3)

In mass%, C: 0.10% or less, Si: 2.0-4.5%, and Mn: 0.01-0.5%, sol.Al is reduced to 100 mass ppm or less, and S, Se, and N are reduced to 50 mass ppm or less, respectively. After the steel slab composed of Fe and inevitable impurities is subjected to low-temperature slab heating of 1300 ° C or lower, hot-rolled sheet annealing is performed, and then cold rolling is performed to obtain a final sheet thickness. , Continuous primary recrystallization annealing and decarburization annealing, and after applying batch final finishing annealing to form an undercoat by applying an annealing separator mainly composed of MgO, flattening annealing In the method for producing a grain-oriented electrical steel sheet,
In the annealing separator, SnO ₂ and / or SnO is contained in a range of 2 to 10% by mass with respect to MgO: 100% by mass,
A method for producing a grain-oriented electrical steel sheet in which the furnace tension is 11.8 MPa (1.2 kgf / mm ² ) or less during the flattening annealing.   The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the steel slab further contains 0.15 mass% or less of Sn. The steel slab is further mass%,
Ni: 0.005-1.50%,
Sb: 0.005-0.50%,
Cu: 0.01 to 0.50%,
P: 0.005-0.50%,
Cr: 0.01-1.50% and
Mo: 0.01-0.50%
The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, comprising a composition containing at least one selected from the above.

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