JPH11302731A - Production of grain-oriented silicon steel sheet excellent in magnetic characteristic and punching property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel sheet having excellent punching property by suppressing formation of a film without causing deterioration in magnetic characteristics by using a steel ingot of a specified compsn., using an annealing separating agent which essentially consists of Al2 O3 and has a specified range of specific surface area measured by using H2 O as the adsorption seed, and carrying out the finish annealing in an atmosphere at a specified or higher temp. by controlling the nitrogen concn. of the atmosphere to a specified value or smaller. SOLUTION: A steel ingot containing, by wt.%, 0.005 to 0.070 C; 1.5 to 7.0 Si; 0.03 to 2.50 Mn; <=0.01 total of S and Se; 0.005 to 0.017 Al, 0.003 to 0.010 N; and 0.010 to 0.080 Sb is heated at <=1,300 deg.C, hot rolled, and cold rolled once or plural times including intermediate annealing, into a sheet having the finish thickness. Then the sheet is subjected to primary recrystallization annealing. Then an annealing separating agent essentially comprising Al2 O3 and having 80 to 150 m<2> /g specific surface area by BET method using H2 O as the adsorption seed is applied and dried. Then the sheet is subjected to finish annealing at >=800 deg.C while the nitrogen concn. in the atmosphere is controlled to <=1%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented silicon steel sheet used for iron cores of transformers and other electric equipment, and more particularly to a low power magnetic field characteristic better than a high magnetic field characteristic, such as an iron core and an EI core of a small generator. The present invention relates to an advantageous method for producing a grain-oriented electrical steel sheet which is suitable for use in which it is necessary to use.

[0002]

2. Description of the Related Art Oriented silicon steel sheets are manufactured by subjecting a steel slab to hot rolling and cold rolling, followed by primary recrystallization annealing, and then final finishing annealing for secondary recrystallization. It is common. Then, secondary recrystallization occurs during the final finish annealing, and coarse crystal grains having a uniform axis of easy magnetization in the rolling direction are generated.

[0003] Since this finish annealing is performed at a high temperature for a long time, it is general to apply an annealing separator to prevent the steel sheet from burning. As the annealing separator, a material mainly containing MgO is generally used. This MgO reacts with the oxide layer formed on the surface of the steel sheet during annealing, so that a coating mainly composed of forsterite is formed. Further, a phosphate-silica-based inorganic coating is usually formed on the coating in order to improve the iron loss by increasing the tension effect and to secure insulation.

[0004] When grain-oriented electrical steel sheets are used as an EI core or a small iron core material, it is necessary to reduce iron loss in a low magnetic field, and it is effective to reduce the particle size of secondary recrystallized grains. It is. Therefore, the applicant has proposed a method of reducing the amount of Al of the material component, adding Sb, and optimizing the conditions of hot-rolled sheet annealing and decarburizing annealing in Japanese Patent Application No. 8-286720. . By this method, the magnetic properties in a low magnetic field could be remarkably improved.

[0005] On the other hand, the EI core is usually punched into a predetermined shape by a die and laminated to produce. At this time, if the forsterite coating as described above is present, there is a problem that the mold is worn, and various proposals have been made.

For example, Japanese Patent Application Laid-Open No. 7-278669 discloses a method in which MgO is used as an annealing separator and a chlorine compound is added thereto. JP-A-6-17137 discloses a method in which MgO is used as a main component of an annealing separator, and an alkali metal compound is added thereto to increase the nitrogen partial pressure in the finish annealing atmosphere to 30% or more. By these methods, the formation of a forsterite film is suppressed to some extent and a product with good magnetic properties is obtained, but the problem that the film formation cannot be completely suppressed by using MgO as the annealing separator is still solved. Not done. For this reason, it is necessary to provide an extra step of removing the coating by pickling or the like after annealing, resulting in an increase in cost.

On the other hand, Japanese Patent Application Laid-Open No. 4-337030 proposes a method in which Al ₂ O ₃ is used as a main component of an annealing separator, and ammonia nitriding is performed at any stage from decarburizing annealing to finish annealing. . In this proposal, since Al ₂ O ₃ is used as the annealing separator, it is possible to suppress the formation of a film, but there is a problem in that magnetic properties are easily deteriorated due to poor purification.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a novel method for suppressing the formation of a coating film and improving punchability without causing deterioration of magnetic characteristics. An object of the present invention is to propose a method for manufacturing a grain-oriented silicon steel sheet.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted various studies on a method of improving the punching property by suppressing the formation of a coating without reducing the iron loss in a low magnetic field as a directional silicon steel for an EI core. As a result, it has been found that it is extremely effective to adjust the material components and further control the atmosphere of the finish annealing using a specific annealing separator, and have completed the present invention.

[0010] The present invention relates to a method for producing C: 0.005 to 0.070 wt%,
i: 1.5 to 7.0 wt%, Mn: 0.03 to 2.50 wt%, S and Se
To 0.01 wt% or less in total, Al: 0.005 to 0.017 wt%, N:
A steel ingot containing 0.003 to 0.010 wt% and Sb: 0.010 to 0.080 wt% is heated to a temperature of 1300 ° C. or lower, hot-rolled, and then subjected to one or more cold rolling operations including intermediate annealing. After finishing to the final sheet thickness, subjected to primary recrystallization annealing, then apply an annealing separator, after drying and then performing a final finish annealing to produce a grain oriented silicon steel sheet, the annealing separator, the specific surface area by the BET method when using H ₂ O to adsorbed species is used as a main component 80 m ² / g or more 150 meters ² / g or less of Al ₂ O _3, finish annealing, 8
A method for producing a grain-oriented silicon steel sheet having excellent magnetic properties and punching properties, wherein the method is performed by adjusting the nitrogen concentration in an atmosphere of 00 ° C. or more to 1% or less.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, experimental results which led to the present invention will be described. That is, steel A shown in Table 1
A steel slab having the composition of D and E is heated at 1200 ° C for 30 minutes, hot-rolled to a thickness of 2.5 mm, and hot-rolled at 900 ° C for 1 minute, and then tandem milled. It was cold rolled to a thickness of 0.34 mm and finished to a final thickness. Next, decarburizing annealing was performed at 850 ° C. for 2 minutes with the ratio of the hydrogen partial pressure to the water vapor partial pressure of the atmosphere (less than or equal to P (H ₂ O) / P (H ₂ )) set to 0.45. Thereafter, a slurry-like annealing separator was applied to the surface of the steel sheet by a roll coater and dried to perform final finish annealing.

[0012] The annealing separator has a specific surface area of 80 and 80 according to the BET method when H ₂ O is used as an adsorbent as a main agent.
One consisting of 160 m ² / g of Al ₂ O ₃ was applied. Finish annealing was performed up to 800 ° C in an Ar atmosphere.
From 800 ° C to 1100 ° C, a slight amount of nitrogen was added at various concentrations to a dry hydrogen atmosphere. The heating rate at that time is 30 ° C / h
And Subsequently, purify annealing was performed in a hydrogen atmosphere at 1200
Hold annealing was performed at 5 ° C. for 5 hours. The coil after purification annealing is subjected to an insulation coating process that is mainly composed of magnesium phosphate containing 40 wt% of colloidal silica,
The product was baked at 800 ° C.

The steel sheet thus obtained was cut into test pieces of Epstein size, subjected to strain relief annealing at 800 ° C. for 3 hours, and the magnetic flux density B ₈ (T) was measured. It was evaluated by measuring the diameter. Further, an EI core was punched out of each product, and after the strain relief annealing, an EI core was created by stacking, copper wire winding, and the like, and the iron loss was measured. Furthermore, when a punching operation was performed on each coil with a steel die having a die diameter of 15 mmφ, the number of punchings until the return height reached 50 μm was measured. Table 2 shows the evaluation results of these product qualities.

[0014]

[Table 1]

[0015]

[Table 2]

From Table 2, it can be seen that the magnetic properties and punching properties are significantly improved by using the material component A and reducing the N ₂ partial pressure in the finish annealing atmosphere.
On the other hand, in the case of the material D containing Se, although the magnetic flux density is high, the reduction of iron loss is insufficient, and in the case of the material E to which Sb is not added, the sub-scale generated during the decarburization annealing remains and has no metallic luster. The surface appearance was obtained, and the punching property was also deteriorated. On the other hand, as for the annealing separator, when H ₂ O was used as the adsorbate,
When Al ₂ O ₃ having a specific surface area of 160 m ² / g by the BET method was used as a main component, both the magnetic properties and the punching property were deteriorated. Although it is not clear why the product quality has changed, the inventors think as follows.

Normally, when Al ₂ O ₃ is used as an annealing separator, the steel sheet does not purify. However, in the case of the material A which does not contain S and Se as in the case of the material A of the present invention, the load of the purification is small. It is considered that even if the agent was Al ₂ O ₃ , it was purified.

In the case of a material that does not contain Sb, such as the material C, a sub-scale mainly composed of SiO ₂ is formed deep into the steel sheet during the decarburizing annealing.
While O ₂ will remain without floating to the surface, the addition of Sb, subscale during decarburization annealing is generated only at the outermost surface, removal of the coating at the time of finish annealing is facilitated. further,
Since Sb is segregated on the steel sheet surface, a small amount of oxygen in the atmosphere enters the steel sheet during finish annealing and reacts with Al and Si in the steel.
Al ₂ O ₃ and SiO ₂ also function to inhibit the new generation, and also prevent poor purification.

Similarly, Al ₂ O ₃ which is a main component of the annealing separator
The specific surface area by the BET method when H ₂ O is used as the adsorbed species corresponds to the amount of moisture remaining after drying the Al ₂ O ₃ slurry and the amount brought into the finish annealing,
Since the air permeability of the atmosphere when the coil is tightly wound is affected, by appropriately controlling the specific surface area, moisture can escape from the steel sheet surface and oxygen can be prevented from entering the steel.

For the above reasons, S and Se of the raw material components are reduced, Sb is added, and the ratio of Al ₂ O ₃ as an annealing separator by the BET method when H ₂ O is used as an adsorbent is used. By controlling the surface area, a steel sheet having excellent magnetic properties and excellent punching properties can be obtained.

However, even with such a material, good characteristics cannot be obtained if the nitrogen partial pressure of the atmosphere during the finish annealing is high. This is because the nitrogen in the atmosphere penetrates into the steel, resulting in insufficient purification, and the infiltration of the nitrogen into the steel prevents the subscale SiO _{2 from} floating on the steel sheet surface. It is considered to be.

Next, the reasons for limiting the constituent elements of the present invention will be described. First, the range of the component composition of the material of the present invention is as follows. C: 0.005 to 0.070 wt% If C exceeds 0.070 wt%, the amount of γ transformation becomes excessive, the distribution of Al during hot rolling becomes uneven, and the amount of AlN precipitated during the temperature rise process of hot-rolled sheet annealing is increased. The distribution is also non-uniform, resulting in poor magnetism. On the other hand, if the content is less than 0.005 wt%, the effect of improving the structure cannot be obtained and the secondary recrystallization becomes unstable, which also causes the deterioration of the magnetic properties. Therefore, it is limited to the range of 0.005 to 0.070 wt%.

Si: 1.5 to 7.0 wt% Si is an essential component for increasing electric resistance and reducing iron loss. For this purpose, it is necessary to contain 1.5 wt% or more, but 7.0 wt% If it exceeds the limit, the workability will deteriorate and the production and processing of the product will be extremely difficult.
To the range.

Mn: 0.03 to 2.50 wt% Mn is also a component necessary for increasing electric resistance and improving hot workability at the time of production. For that, 0.
It is necessary to contain more than 03wt%, but if it exceeds 2.50wt%, it induces γ transformation and the magnetic properties deteriorate, so
It was limited to the range of 0.03 to 2.50 wt%.

S and Se in a total of 0.01 wt% or less As described above, S and Se are used for purifying even if an annealing separator mainly containing Al ₂ O ₃ is used. , To a total of 0.01 wt% or less.

Al: 0.005 to 0.017 wt% In addition to the above-mentioned elements, the steel must contain an inhibitor component for inducing secondary recrystallization. Therefore, Al is contained as an inhibitor component in an amount of 0.005 to 0.017 wt%. Content within the range. Here, if the Al content is less than 0.005 wt%, the amount of AlN precipitated during the heating process in hot-rolled sheet annealing is insufficient, and if it exceeds 0.017 wt%, the slab at around 1200 ° C is used. It becomes difficult to form a solid solution of AlN at low temperature heating, and the solid solution temperature of AlN rises, so that AlN precipitates in hot rolling, and it becomes impossible to finely precipitate AlN in a heating process of hot-rolled sheet annealing. Good iron loss characteristics in a low magnetic field cannot be obtained. Therefore, Al was contained in the range of 0.005 to 0.017 wt%. In addition, when slab heating is performed at a high temperature of about 1400 ° C. to eliminate the above deficiencies, the crystal grain size of the product becomes coarse, iron loss in a high magnetic field is reduced, and iron loss in a low magnetic field is reduced. As a result, the iron loss of the actual machine deteriorates.

N: 0.003 to 0.010 wt% Since N is a component constituting AlN, it must be contained in an amount of 0.0030 wt% or more. However, if the content exceeds 0.010 wt%, it is gasified in the steel and causes defects such as swelling.

Sb: 0.01 to 0.08 wt% If the content of Sb is less than 0.01 wt%, the formation of the sub-scale proceeds excessively during the decarburizing annealing, and the sub-scale remains after the finish annealing, so that the punching property deteriorates. In addition, Al ₂ O ₃ and SiO ₂ are newly generated during the finish annealing, resulting in poor dullness and degraded magnetic properties. Conversely, if more than 0.08 wt%, Sb
Secondary recrystallization becomes unstable due to excessive progress of grain boundary segregation.

Further, Sb, B, Ti, Nb, Cu, Sn, Cr, Ge, Mo, V, and the like can be further added as an inhibitor-forming component. The preferred amount is Sb: 0.003 to
0.080 wt%, B: 0.0001-0.0020 wt%, Ti: 0.0005-0.
0020 wt%, Nb: 0.0010-0.010 wt%, and Cu, Sn, C
0.001 wt% or more in total of one or two of r, Ge, Mo, V
0.3 wt% or less. Each of these inhibitors can be used alone or in combination.

Next, the reasons for limiting the manufacturing conditions will be described. First, slab heating is performed at a temperature of 1300 ° C. or less. Because, when slab heating is performed at a temperature exceeding 1300 ° C,
Since fine grains of 1 mm or less in the product crystal grains decrease and coarse grains increase, iron loss in a low magnetic field deteriorates. By the way,
In recent years, a method has been proposed in which hot rolling is performed directly after continuous casting without slab heating, but this method is suitable for the method of the present invention since the slab temperature does not increase.

Next, cold rolling is performed once or a plurality of times including intermediate annealing to obtain a final thickness. Incidentally, if necessary, the hot-rolled sheet can be annealed before cold rolling.
At this time, the cold rolling may be tandem rolling or sendzimer rolling, but tandem rolling is desirable from the viewpoint of productivity. After that, primary recrystallization annealing is performed, and after applying an annealing separating agent, final finish annealing is performed.

Here, Al ₂ O ₃ is used as a main component of the annealing separating agent. MgO is not suitable because it forms a forsterite film. In particular, in the main agent Al ₂ O ₃ , H ₂ O
The specific surface area by BET method when using is 80 m ² / g or more 1
Use a powder of 50 m ² / g or less. This is to adjust the air permeability of the steel sheet surface and the amount of water brought in. As disclosed in Japanese Patent Publication No. 58-44152, Sr,
It is also possible to add compounds of Ba and Ca or other compounds.

There are disclosed many methods of nitriding a steel sheet from decarburizing annealing to finish annealing. However, this method is extremely harmful from the viewpoint of magnetic properties in a low magnetic field, and nitriding is performed as little as possible. Need to be

In the final annealing, the partial pressure of nitrogen in an atmosphere of 800 ° C. or more is set to 1% or less. If the nitrogen partial pressure exceeds 1%, the steel sheet is nitrided and the magnetic properties deteriorate.
It should be noted that the temperature pattern may follow the general rules for silicon steel sheets. Thereafter, an insulating coat is applied and flattening annealing is performed to finish the product. The insulating coating may be a known tension coat, but it is also possible to apply an organic resin-based coating to further improve the punching property. By such a processing step, a directional silicon steel having excellent magnetic properties and punching workability can be obtained.

[0035]

EXAMPLE 1 Molten steel having the component compositions of A to M shown in Table 1 above was formed into a slab by continuous casting while being subjected to electromagnetic stirring, heated to 1180 ° C., and then subjected to rough 5 passes to form a 45 mm thick sheet. Bar and finish exit temperature: 2.2mm by 7-pass finish hot rolling at 950 ° C
Rolled to thickness. Then, the obtained hot rolled coil was 900
℃, 1 minute hot rolled sheet annealing, 0.34mm in tandem rolling mill
Until cold-rolled. After that, decarburization annealing was performed at 850 ° C for 2 minutes, and BE when H ₂ O was used as an adsorbent as an annealing separator
After applying Al ₂ O ₃ having a specific surface area of 120 m ² / g according to the T method, finish annealing was performed. Finish annealing from 800 ℃ to 1200 ℃
The temperature was raised at a rate of 30 ° C./h, followed by holding annealing at 1200 ° C. for 5 hours. When the temperature is raised, an Ar atmosphere up to 800 ° C and a hydrogen atmosphere (nitrogen concentration: 0 to 800 ° C to 1200 ° C) are used.
%). After the finish annealing, magnesium bichromate containing a vinyl acetate resin was applied, baked and heat flattened to obtain a product.

A specimen of Epstein size was cut out from the steel sheet thus obtained, subjected to strain relief annealing at 800 ° C. for 3 hours, and then subjected to a bending peel test and to a magnetic flux density B
₈ (T) was measured. Also, punching EI cores from each product,
After strain relief annealing, EI is obtained by stacking, winding copper wire, etc.
A core was prepared and its iron loss was measured. Furthermore, when each coil was punched with a steel die having a die diameter of 15 mmφ, the number of punches until the return height reached 50 μm was measured. As shown in Table 3, the grain-oriented electrical steel sheet obtained by the method of the present invention has good iron loss and excellent punching properties.

[0037]

[Table 3]

Example 2 Molten steel having the H component composition shown in Table 1 above was subjected to electromagnetic stirring.
Slab by continuous casting while framing, heated to 1180 ° C
After that, make a 45 mm thick sheet bar with 5 coarse passes and finish exit temperature
Degree: 2.2mm thick by 7 pass finishing hot rolling at 950 ℃
Rolled up. Then, the obtained hot rolled coil was 900
℃, 1 minute hot rolled sheet annealing, 0.34mm in tandem rolling mill
Until cold-rolled. Then, decarburization annealing at 850 ° C for 2 minutes
To the adsorbed species as an annealing separator_TwoBE with O
120m specific surface area by T method^Two/ g Al _TwoO_ThreeOr apply
Then, finish annealing was performed. Finish annealing from 800 ° C to 1200 ° C
At 30 ° C / h, then keep at 1200 ° C for 5 hours
Annealing was performed. When the temperature rises, up to 800 ° C in an Ar atmosphere
From 800 ° C to 1100 ° C in a hydrogen atmosphere
Atmosphere of various degrees and a hydrogen atmosphere at 1100 ° C or more
I went in the atmosphere. After this finish annealing, it contains vinyl acetate resin.
Apply and bake magnesium dichromate coating
The product was subjected to heat flattening.

A test piece of Epstein size was cut out from the steel sheet thus obtained, and subjected to a strain relief annealing at 780 ° C. for 3 hours.
₈ (T) was measured. Also, punching EI cores from each product,
After strain relief annealing, EI is obtained by stacking, winding copper wire, etc.
A core was prepared and its iron loss was measured. Furthermore, when each coil was punched with a steel die having a die diameter of 15 mmφ, the number of punches until the return height reached 50 μm was measured. As shown in Table 4, by setting the nitrogen concentration in the finish annealing atmosphere to 1% or less, a product having good iron loss and excellent punching property can be obtained.

[0040]

[Table 4]

Example 3 Molten steel having the H composition shown in Table 1 above was formed into a slab by continuous casting while being subjected to electromagnetic stirring, heated to 1180 ° C., and formed into a 45 mm-thick sheet bar with five coarse passes. Finishing Outlet Temperature: Rolled to 2.2 mm thickness at 950 ° C. by 7 passes of finishing hot rolling. Then, the obtained hot rolled coil was 900
℃, 1 minute hot rolled sheet annealing, 0.34mm in tandem rolling mill
Until cold-rolled. After that, decarburization annealing was performed at 850 ° C for 2 minutes, and BE when H ₂ O was used as an adsorbent as an annealing separator
After applying Al ₂ O ₃ having a specific surface area of 70 to 160 m ² / g according to the T method, finish annealing was performed. Finish annealing from 800 ℃ to 1200
The temperature was raised to 30 ° C at 30 ° C / h, followed by holding annealing at 1200 ° C for 5 hours. When the temperature is raised, an Ar atmosphere up to 800 ° C and a hydrogen atmosphere from 800 ° C to 1200 ° C (nitrogen concentration:
0%). After this finish annealing, apply a magnesium dichromate coating containing vinyl acetate resin,
The product was baked and subjected to heat flattening.

A test piece of Epstein size was cut out from the steel sheet thus obtained, and subjected to a strain relief annealing at 700 ° C. for 3 hours.
₈ (T) was measured. Also, punching EI cores from each product,
After strain relief annealing, EI is obtained by stacking, winding copper wire, etc.
A core was prepared and its iron loss was measured. Furthermore, when each coil was punched with a steel die having a die diameter of 15 mmφ, the number of punches until the return height reached 50 μm was measured. The results are as shown in Table 5, by a specific surface area by the BET method when using H ₂ O adsorption species used Al ₂ O ₃ of 80 to 150 m ² / g as particularly annealing separator, iron A product having good loss and excellent punching properties can be obtained.

[0043]

[Table 5]

[0044]

According to the present invention, it is possible to manufacture a grain-oriented silicon steel sheet having excellent magnetic properties and punching properties, which greatly contributes to improving the quality of an electromagnetic steel sheet.

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C23C 22/00 C23C 22/00 A H01F 1/16 H01F 1/16 B (72) Inventor Atsuto Honda 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture (No address) Inside the Mizushima Steel Works of Kawasaki Steel Co., Ltd. (72) Inventor Tetsuo Toge 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture (No address) Inside the Mizushima Steel Works of Kawasaki Steel Corporation

Claims (1)

[Claims] (1) C: 0.005 to 0.070 wt%, Si: 1.5 to 7.0
wt%, Mn: 0.03 to 2.50 wt%, S and Se in total of 0.01 wt% or less, Al: 0.005 to 0.017 wt%, N: 0.003 to 0.010 wt%, and Sb: 0.010 to 0.080 wt% After heating to a temperature of 1300 ° C. or less, hot rolling is performed, and then cold rolling is performed once or a plurality of times including intermediate annealing to finish the final sheet thickness, and then, primary recrystallization annealing is performed, and then annealing is performed. In producing a grain-oriented silicon steel sheet by a series of steps of applying a separating agent, drying and then performing final finish annealing, the annealing separating agent includes:
When H ₂ O is used as an adsorbent, the specific surface area by the BET method is 80.
with which the m ² / g or more 150 meters ² / g or less of Al ₂ O ₃ as a main component, finish annealing, characterized in that, by adjusting the nitrogen concentration in the atmosphere above 800 ° C. to less than 1% A method for producing a grain-oriented silicon steel sheet having excellent magnetic properties and punching properties.