JPH093541A - Production of grain oriented silicon steel sheet with extremely high magnetic flux density - Google Patents

Abstract

PURPOSE: To stably obtain a grain oriented silicon steel sheet having extremely high magnetic flux density by using a steel slab having a Bi-added specific composition as a starting material and specifying the flow rate of atmospheric gas at finish annealing. CONSTITUTION: A slab, having a composition consisting of, by weight, 0.03-0.15% C, 2.5-4.0% Si, 0.02-0.30% Mn, 0.005-0.040% S and/or Se, 0.015-0.040% acid soluble Al, 0.0030-0.0150% N, 0.0005-0.05% Bi, and the balance Fe, is heated and hot-rolled. The resulting hot rolled plate is finished to product sheet thickness by being subjected to hot rolled plate annealing and to finish cold rolling, or by being cold-rolled plural times while process-annealed between cold rolling stages, or by being subjected to hot rolled plate annealing and then cold-rolled plural times while process-annealed between cold rolling stages. Then, decarburizing annealing is performed. After the application of a separation agent at annealing, finish annealing is done. In this manufacturing method, the flow rate of atmospheric gas at finish annealing is regulated to a value in the range satisfying (flow rate of atmospheric gas)/(furnace volume steel sheet volume)>=0.5Nm<3> /(h.m<3> ). By this method, the grain oriented silicon steel sheet with extremely high magnetic flux density, having >=1.92T magnetic flux density B8 , can be stably obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultra-high magnetic flux density unidirectional electrical steel sheet having a highly developed {110} <001> orientation integration used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are mainly used as iron core materials for transformers and other electric equipment, and are required to have excellent magnetic characteristics such as excitation characteristics and iron loss characteristics. The value that shows the excitation characteristics is usually 800 A /
Magnetic flux density B in a magnetic field of m (this is shown below as B ₈ )
Is used. Also, as a representative numerical value showing the iron loss characteristic,
W _17/50 (iron loss per unit of 1 kg when magnetized to 1.7 _{T at a} frequency of 50 Hz) is used.

[0003] The magnetic flux density is an important controlling factor of the iron loss characteristics. Generally speaking, the higher the magnetic flux density, the better the iron loss. However, when the magnetic flux density is too high, abnormal eddy current loss is increased due to an increase in secondary recrystallized grains, and iron loss may be deteriorated. On the other hand, iron loss can be improved by controlling the magnetic domains regardless of the secondary recrystallized grains.

[0004] In the finish annealing in the manufacturing process, the grain-oriented electrical steel sheet causes secondary recrystallization to cause {110} on the steel sheet surface.
It is obtained by developing a so-called Goss structure having <001> in the rolling direction. Among them, B ₈ ≧
Those having excellent excitation characteristics of 1.88T are called high magnetic flux density unidirectional magnetic steel sheets.

As a typical method for producing a high magnetic flux density unidirectional electrical steel sheet, there are JP-B-40-15644 and JP-B-51-13469. Goss
MnS and AlN are used in the former, and MnS, MnSe, Sb, etc. are used in the latter as main inhibitors that cause secondary recrystallization of the tissue. Products produced by these manufacturing methods are currently produced worldwide. According to Japanese Examined Patent Publication No. 40-15644, the manufacturing method is characterized in that after the hot-rolled sheet is annealed, the cold-rolling rate is 80-95% once.

By the way, recently, an ultrahigh magnetic flux density unidirectional electrical steel sheet having an extremely excellent excitation characteristic of B ₈ ≧ 1.92T has been reported. As a typical example thereof, Japanese Patent Laid-Open No. 6-88
No. 174 publication is cited. Further, as a typical example of the manufacturing method thereof, there is JP-A-6-88171.
All of them are characterized by containing Bi in the slab, but the others are the same as the manufacturing method described in Japanese Patent Publication No. 40-15644 and there are no major restrictions.

[0007]

However, if Bi is contained in the steel, secondary recrystallization failure that is considered to be caused by this or reduction of {110} <001> orientation integration degree may occur even after secondary recrystallization. It often happens that the exciting characteristic of B ₈ ≧ 1.92T cannot be obtained. An object of the present invention is to avoid such a problem and to stably manufacture a grain-oriented electrical steel sheet having an extremely high magnetic flux density.

[0008]

The features of the present invention are as follows. 1) wt%, C: 0.03 to 0.15%, Si: 2.
5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0.005 to 0.040%, acid-soluble Al: 0.015 to 0.040%, N: 0. 0030 ~
0.0150%, Bi: 0.0005 to 0.05%, balance: Fe and slab consisting of unavoidable impurities are heated as a starting material, then hot rolled, hot rolled sheet annealed, then finish cold rolled, or intermediate annealed. After finishing the product sheet thickness by multiple cold rolling including multiple cold rolling including hot-rolled sheet annealing or intermediate annealing after annealing, decarburization annealing, after applying an annealing separator, finish annealing is performed. In the method for producing a grain-oriented electrical steel sheet, the method for producing an ultra-high magnetic flux density grain-oriented electrical steel sheet having B ₈ ≧ 1.92 T, characterized in that the atmospheric gas flow rate in finish annealing is set in the following range. Atmospheric gas flow rate / (furnace volume-steel plate volume) ≧ 0.5 Nm ³
/ (H ・ m ³ )

2) C: 0.03 to 0.15 by weight%
%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.3%
0%, S and / or Se: 0.005-0.040
%, Acid-soluble Al: 0.015 to 0.040%, N:
0.0030 to 0.0150%, Sn: 0.05 to 0.
50%, Bi: 0.0005 to 0.05%, balance: Fe
And the method for producing an ultrahigh magnetic flux density unidirectional electrical steel sheet according to 1), which uses a slab made of unavoidable impurities as a starting material.

3) C: 0.03 to 0.15 by weight%
%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.3%
0%, S and / or Se: 0.005-0.040
%, Acid-soluble Al: 0.015 to 0.040%, N:
0.0030 to 0.0150%, Sn: 0.05 to 0.
50%, Cu: 0.01 to 0.10%, Bi: 0.00
The method for producing an ultra-high magnetic flux density grain-oriented electrical steel sheet according to 1) above, wherein a slab consisting of 05 to 0.05% and the balance: Fe and inevitable impurities is used as a starting material.

4) C: 0.03 to 0.15 by weight%
%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.3%
0%, S and / or Se: 0.005-0.040
%, Acid-soluble Al: 0.015 to 0.040%, N:
0.0030 to 0.0150%, Sb and / or M
o: 0.0030 to 0.3%, Bi: 0.0005 to
The method for producing an ultrahigh magnetic flux density grain-oriented electrical steel sheet according to 1) above, wherein a slab consisting of 0.05% and the balance of Fe and inevitable impurities is used as a starting material.

The present invention will be described in detail below. First, the component conditions of the present invention will be described. If C is less than 0.03%, crystal grains grow abnormally during slab heating prior to hot rolling, and secondary recrystallization defects called linear fine grains occur in the product, which is not preferable. On the other hand, when the content exceeds 0.15%, decarburization annealing after cold rolling requires a long time for decarburization, which is not economical, and the decarburization is likely to be incomplete, resulting in a magnetic aging called magnetic aging in products. It is not preferable because it causes defects.

Si is an extremely effective element for increasing the electric resistance of steel and reducing the eddy current loss that constitutes a part of iron loss, but if it is less than 2.5%, the eddy current loss of the product cannot be suppressed. . Further, if it exceeds 4.0%, the workability is remarkably deteriorated and cold rolling at room temperature becomes difficult, which is not preferable.

Mn is an important element that forms MnS and / or MnSe called an inhibitor that influences secondary recrystallization. If it is less than 0.02%, the absolute amount of MnS necessary for causing secondary recrystallization is insufficient, which is not preferable. On the other hand, if it exceeds 0.30%, not only is it difficult to form a solid solution during heating of the slab, but also the precipitation size during hot rolling tends to become coarse, and the optimum size distribution as an inhibitor is impaired, which is not preferable.

S and / or Se are Mn and M listed above.
It is an important element that forms nS and / or MnSe. If it deviates from the above range, a sufficient inhibitory effect cannot be obtained, so it is necessary to limit the content to 0.005 to 0.040%.

Acid-soluble Al is a main inhibitor constituent element for high magnetic flux density grain-oriented electrical steel sheet, and is 0.0
If it is less than 15%, it is not preferable because the amount is insufficient and the inhibitor strength is insufficient. On the other hand, if it exceeds 0.040%, AlN precipitated as an inhibitor becomes coarse, and as a result, the inhibitor strength is lowered, which is not preferable.

N is an important element which forms AlN with the acid-soluble Al mentioned above. If it deviates from the above range, a sufficient inhibitory effect cannot be obtained, so 0.0030 to 0.0
It must be limited to 150%.

Further, Sn is effective as an element for stably obtaining secondary recrystallization of thin products, and also has an action of reducing secondary recrystallized grains. To get this effect,
It is necessary to add 0.05% or more, and if it exceeds 0.50%, the action is saturated, so from the viewpoint of cost increase, it is limited to 0.50% or less.

Cu is effective as an element for improving the primary coating of Sn-added steel. If it is less than 0.01%, the effect is small, and if it exceeds 0.10%, the magnetic flux density of the product is undesirably reduced.

Sb and / or Mo are effective as elements for stably obtaining secondary recrystallization of thin products.
In order to obtain this effect, it is necessary to add 0.0030% or more. If it exceeds 0.30%, the effect is saturated, so that the content is limited to 0.30% or less from the viewpoint of cost increase.

Bi is an essential element in the slab in the production of the superhigh magnetic flux density grain-oriented electrical steel sheet of B ≧ ₈ ≧ 1.92T according to the present invention. That is, if the magnetic flux density improving effect is less than 0.0005%, the effect is not sufficiently obtained, and if it exceeds 0.05%, not only the magnetic flux density improving effect is saturated, but also at the end of the hot rolled coil. It is not preferable because cracks occur.

Next, the manufacturing process of the present invention will be described.
The molten steel for producing an ultra-high magnetic flux density unidirectional electrical steel sheet having the components adjusted as described above is cast by a usual method. There is no particular limitation on the casting method. Then, it is rolled into a hot rolled coil by ordinary hot rolling.

Subsequently, the product sheet thickness is finished by hot-rolled sheet annealing followed by finish cold-rolling, a plurality of cold-rolled sheets including intermediate annealing, or a plurality of cold-rolled sheets including hot-rolled sheet annealing and intermediate annealing. In the annealing before finish cold rolling, the crystal structure is homogenized and AlN precipitation is controlled.

After cold rolling, continuous decarburization annealing is performed, and an annealing separator containing MgO as a main component is applied, followed by finish annealing. At this time, the atmospheric gas flow rate should be within the range shown below. The present invention is characterized. Atmospheric gas flow rate / (furnace volume-steel plate volume) ≧ 0.5 Nm ³
/ (H · m ³ ) After finish annealing, continuous strain relief annealing / secondary coating application and baking are performed. Further, laser irradiation and magnetic domain subdivision processing such as grooves are performed if necessary.

The reason why the atmospheric gas flow rate during finish annealing is set within the above range will be described below. The present inventors conducted the following experiments by paying attention to the atmospheric gas flow rate during finish annealing in order to stably manufacture an ultra-high magnetic flux density unidirectional electrical steel sheet.

[Experiment 1] C: 0.079%, Si: 3.26%, Mn: 0.08
%, S: 0.025%, acid-soluble Al: 0.025%,
N: 0.0086%, Bi: 0-0.0200% A slab of 0.5 m ³ containing at least MgO
The process was performed up to the application of the annealing separation material containing as a main component. After that, the furnace was inserted into a finishing annealing furnace with a volume of 1 m ³ , and nitrogen: hydrogen =
The flow rate of the atmosphere gas composed of 1: 3 is 0.1 to 10 Nm.
Finish annealing was performed as ³ , and the post-process was further performed, and the B ₈ value of the obtained steel sheet was measured. 1 and Bi content, the atmosphere gas flow rate / - shows the value of (furnace capacity steel volume), the B ₈ value of the resulting steel sheet.

As is clear from the figure, the Bi content is 5 p
When it is less than pm, even if the atmospheric gas flow rate / (furnace volume-steel plate volume) <0.5 Nm ³ / (h · m ³ ), the magnetic flux density is 0.5 Nm ³ / (h · m ³ ) or more No difference is seen with that. However, when the Bi content is 5 ppm or more, the atmospheric gas flow rate / (internal furnace volume-steel plate volume) <0.5
In the case of Nm ³ / (h · m ³ ), B ₈ <1.92T
On the other hand, in the case of 0.5 Nm ³ / (h · m ³ ) or more, B ₈ ≧ 1.92T.

This is due to the removal of Bi generated during finish annealing.
The behavior has a great influence on the atmosphere gas flow during the finish annealing, and this also affects the grain growth before the initiation of secondary recrystallization and the decomposition of the inhibitor, {110} <0.
01> It is considered that this is causing a low degree of orientation integration and secondary recrystallization failure.

The finish annealing is generally performed in a coil shape. Therefore, it can be easily imagined that the contact state with the atmospheric gas is greatly different between the inner and outer peripheral portions and the upper and lower portions of the coil. It is considered that this difference in the contact state causes a difference in the Bi removal behavior in each part of the coil. It is considered that when Bi stays in the base iron or the surface oxide layer more than necessary, it suppresses the crystal grain growth before the initiation of secondary recrystallization. It is considered that this causes the initiation of secondary recrystallization on the lower temperature side and secondary recrystallization of crystal grains other than the {110} <001> orientation, resulting in a product with a low degree of integration.

It is also considered that the excessive residence of Bi in the base iron or in the surface oxide layer delays the decomposition of the inhibitor, which raises the secondary recrystallization onset temperature. This is considered to cause secondary recrystallization failure because normal grain growth is likely to occur in crystal grains other than the {110} <001> orientation.

From the results of Experiment 1 above, it is possible to set the atmospheric gas flow rate during finish annealing within the following range: {11
It has been found that it is extremely important for the production of an ultrahigh magnetic flux density grain-oriented electrical steel sheet having a very high degree of 0} <001> orientation integration. Atmospheric gas flow rate / (furnace volume-steel plate volume) ≧ 0.5 Nm ³
/ (H · m ³ ) The upper limit value of the atmospheric gas flow rate / (furnace internal volume-steel plate volume) is not particularly limited, but is 20 Nm ³ / (h · m ³ ) or less from the viewpoint of cost. Is desirable. The atmosphere gas is preferably a mixed gas of nitrogen and hydrogen, but the mixing ratio thereof is not particularly limited.

Based on such an idea, the most preferable range is shown in FIG. The content of Bi is 0.
001 to 0.01%, atmosphere gas flow rate / (furnace volume-steel plate volume) is 1.0 or more and 20 or less (Nm ³ / (h · m ³ ))
It is.

Controlling the gas flow rate during finish annealing in the manufacture of high magnetic flux density grain-oriented electrical steel sheets has been previously described. For example, Japanese Patent Laid-Open No. 12581/1991
No. 5 publication is mentioned. This is because when the gas flow rate during finish annealing is set to 2 cc / min · kg or more, the purification of S, Se, and N in the base iron and forsterite is significantly improved, and the magnetic flux density and iron loss characteristics are improved. I am trying.

On the other hand, the present invention considers that the behavior of Bi in the base steel during finish annealing has a great influence on the secondary recrystallization behavior, and the behavior is controlled by the gas flow rate during finish annealing. Which is completely different from the prior art.

[0035]

【Example】

[Example 1] C: 0.078%, Si: 3.23%, M
n: 0.08%, S: 0.025%, acid-soluble Al:
0.025%, N: 0.0084%, Bi: 0.002
A 0.4 m ³ slab containing 6% was heated at 1350 ° C. and immediately hot rolled to give a hot rolled coil of 2.4 mm thickness.

The hot rolled coil was annealed at 1100 ° C., cold rolled once to a thickness of 0.220 mm, and then decarburized and annealed at 850 ° C. Next, after applying an annealing separation material containing MgO as a main component, it was inserted into a finish annealing furnace having a furnace internal volume of 1 m ³ , and the flow rate of an atmosphere gas composed of nitrogen: hydrogen = 1: 1 was adjusted to 0.
Annealed at ² Nm ³ / h and 0.6 Nm ³ / h. afterwards,
A secondary coating was applied.

Atmosphere gas flow rate / (furnace volume-steel plate volume)
The magnetic flux density B ₈ is shown in Table 1.

[0038]

[Table 1]

As is clear from Table 1, the atmospheric gas flow rate / (furnace volume-steel plate volume) was 1.00 Nm ³ / (h.
m ³ ), an extremely excellent magnetic flux density is obtained.

Table 2 shows the _iron loss value W _17/50 after magnetic domain control was performed on the samples shown in Table 1 by laser irradiation.

[0041]

[Table 2]

As is clear from Table 2, the iron loss characteristics after the magnetic domain subdivision treatment are also extremely excellent, and can be said to be industrially very valuable and useful.

[Example 2] C: 0.076%, Si:
3.28%, Mn: 0.08%, S: 0.025%, acid-soluble Al: 0.028%, N: 0.0080%, S
n: 0.12%, Bi: 0.0031% in 0.1%.
A 65 m ³ slab was heated at 1330 ° C. and immediately hot rolled to form a hot rolled coil having a thickness of 2.3 mm. After pickling, it was pre-cold rolled to 1.60 mm and annealed at 1000 ° C. to 0.200 mm.

Next, after applying an annealing separation material containing MgO as a main component, it was inserted into a finishing annealing furnace having a furnace internal volume of 1 m ³ .
Annealing was performed with the flow rate of the atmosphere gas composed of nitrogen: hydrogen = 3: 1 set to 0.1 Nm ³ / h and 20.0 Nm ³ / h. Then, a secondary coating was applied. Atmosphere gas flow rate / - (the furnace capacity steel volume) and the magnetic flux density B ₈ shown in Table 3.

[0045]

[Table 3]

As is clear from Table 3, the atmospheric gas flow rate / (furnace volume-steel plate volume) was 0.57 Nm ³ / (h ·
m ³ ), an extremely excellent magnetic flux density is obtained.

[Example 3] C: 0.078%, Si:
3.30%, Mn: 0.08%, S: 0.025%, acid-soluble Al: 0.033%, N: 0.0084%, S
1 m ³ slab containing Bi: 0.0115% added to molten steel containing n: 0.16% and Cu: 0.060%
Immediately after heating at 350 ° C., hot rolling was performed to obtain a hot rolled coil having a thickness of 2.5 mm. The hot rolled coil is annealed at 1050 ° C and then 98
After twice cold rolling sandwiching an intermediate annealing of 0 ° C to a thickness of 0.220 mm, decarburization annealing was performed at 840 ° C.

Next, after applying an annealing separation material containing MgO as a main component, it was inserted into a finishing annealing furnace having a furnace internal volume of 1.5 m ³ , and the flow rate of an atmosphere gas composed of nitrogen: hydrogen = 1: 3. Was annealed at 0.2 Nm ³ / h and 0.25 Nm ³ / h.
Then, a secondary coating was applied. Atmosphere gas flow rate / - (the furnace capacity steel volume) and the magnetic flux density B ₈ shown in Table 4.

[0049]

[Table 4]

As is clear from Table 4, the atmospheric gas flow rate / (furnace volume-steel plate volume) was 0.5 Nm ³ / (h · m ³ ).
As a result, an extremely excellent magnetic flux density is obtained.

[Example 4] C: 0.078%, Si:
3.30%, Mn: 0.08%, Se: 0.025%,
Acid-soluble Al: 0.025%, N: 0.0084%, S
b: 0.022%, Mo: 0.014%, Bi: 0.0
A 0.5 m ³ slab containing 080% was heated at 1330 ° C. and immediately hot rolled to give a hot rolled coil having a thickness of 2.3 mm.
After twice cold rolling with an intermediate anneal at 1000 ° C. sandwiched to a thickness of 0.220 mm, decarburization anneal was performed at 860 ° C.

Next, after applying an annealing separation material containing MgO as a main component, it was inserted into a finishing annealing furnace having a furnace internal volume of 1.0 m ³ , and the flow rate of an atmosphere gas composed of nitrogen: hydrogen = 3: 1. Was annealed at 0.1 Nm ³ / h and 10.0 Nm ³ / h.
Then, a secondary coating was applied. Atmosphere gas flow rate / (furnace capacity - steel volume) and showing a magnetic flux density B ₈ in Table 5.

[0053]

[Table 5]

As is clear from Table 5, the atmospheric gas flow rate / (furnace internal volume-steel plate volume) was 20.0 Nm ³ / (h ·
m ³ ), an extremely excellent magnetic flux density is obtained.

[0055]

As described above, according to the present invention, in the method for producing a grain-oriented electrical steel sheet containing Bi, by adjusting the atmospheric gas flow rate in finish annealing,
The ultrahigh magnetic flux density unidirectional electrical steel sheet is obtained, and the iron loss characteristics after the magnetic domain refinement treatment are also extremely excellent, which is industrially very valuable.

[Brief description of drawings]

FIG. 1 is a table showing the correlation between Bi content, atmospheric gas flow rate / (furnace volume-steel plate volume), and magnetic flux density B ₈ .

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Eiichi Namba 1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo Shin Nippon Steel Co., Ltd. Hirohata Works

Claims (4)

[Claims] 1. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0. 005 to 0.040%, acid-soluble Al: 0.015 to 0.040%, N: 0.0030 to 0.0150%, Bi: 0.0005 to 0.05%, balance: Fe and unavoidable impurities After heating with a slab as a starting material, hot rolling, hot-rolled sheet annealing and finish cold rolling,
Alternatively, after finishing the product sheet thickness by a plurality of cold rolling including intermediate annealing or a plurality of cold rolling including hot rolled sheet annealing and intermediate annealing, decarburization annealing, after applying an annealing separation material, finish annealing is performed. In the method for producing a high magnetic flux density unidirectional electrical steel sheet, the method for producing an ultrahigh magnetic flux density unidirectional electrical steel sheet having B ₈ ≧ 1.92 T, characterized in that the atmospheric gas flow rate in finish annealing is set to the range shown below. . Atmospheric gas flow rate / (furnace volume-steel plate volume) ≧ 0.5 Nm ³
/ (H ・ m ³ ) 2. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0. 005-0.040%, acid-soluble Al: 0.015-0.040%, N: 0.0030-0.0150%, Sn: 0.05-0.50%, Bi: 0.0005-0. 05% Balance: The method for producing an ultrahigh magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein a slab composed of Fe and unavoidable impurities is used as a starting material. 3. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0. 005-0.040%, acid-soluble Al: 0.015-0.040%, N: 0.0030-0.0150%, Sn: 0.05-0.50%, Cu: 0.01-0. 10%, Bi: 0.0005-0.05% The balance: The manufacturing method of the super-high magnetic flux density grain-oriented electrical steel sheet of Claim 1 which used the slab which consists of Fe and inevitable impurities as a starting material. 4. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0. 005-0.040%, acid-soluble Al: 0.015-0.040%, N: 0.0030-0.0150%, Sb and / or Mo: 0.0030-0.3%, Bi: 0. The method for producing an ultra-high magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein a starting material is a slab containing the balance: Fe and unavoidable impurities.