JPH09287025A - Production of grain oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve magnetic properties by specifying cold rolling conditions. SOLUTION: A slab of prescribed composition is heated at <1,280 deg.C, hot- rolled, subjected to hot rolled plate annealing, and then cold-rolled one or more times while process-annealed between cold rolling stages. At the time of cold rolling, the diameter D(mm) of a work roll and the temp. T( deg.C) at which a steel sheet is held for >=1min at least one pass are regulated so that they satisfy 40<=D<=500 and 3/40D+115.5<=T<=3/40D+295.5. By this procedure, the size of Goss grains in the final product is decreased, and iron loss is improved. In succession to the cold rolling, decarburizing annealing is performed and then nitriding treatment is carried out under the condition where a strip is allowed to travel. Then, after the application of a separation agent at annealing, composed essentially of MgO, final finish annealing is done.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet 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 excellent in magnetic characteristics such as excitation characteristics and iron loss characteristics. Required for reduced energy loss. As a characteristic value representing the excitation characteristics, magnetic flux density B ₈ in the strength of 800A / m of the magnetic field standardized by JIS it is normally used. Further, as the characteristic value indicating the energy loss, the energy loss (iron loss) W _17/50 per kg of the steel sheet when magnetized at a frequency of 50 Hz to 1.7 Tesla (T) is also JI.
Standardized by S.

[0003] The magnetic flux density is the largest controlling factor of iron loss. Generally, the higher (larger) the magnetic flux density, the better the iron loss characteristics. In general, as the magnetic flux density increases, the size of the secondary recrystallized grains increases, and iron loss may deteriorate. In this case, as already widely known, by controlling the magnetic domain, the iron loss can be improved irrespective of the grain size of the secondary recrystallization.

[0004] This unidirectional electrical steel sheet has a so-called goss structure in which secondary recrystallization occurs in the final finish annealing step and has {110} on the steel sheet surface and <001> axis in the rolling direction. In order to obtain good magnetic properties, it is necessary that <001>, which is the axis of easy magnetization, be highly aligned in the rolling direction. The manufacturing technology of such high magnetic flux density unidirectional magnetic steel sheet has been developed for a long time, and in Japan, a method using MnS or AlN as a so-called inhibitor (Japanese Patent Laid-Open No. 40-1).
5644), a method using Mns, MnSe, Sb and the like (JP-A-51-13469). In these cases, complete solid solution of the inhibitor at the hot rolled sheet stage is required, and it is necessary to set the heating temperature of the steel ingot (slab) to 1350 ° C. or higher during actual hot rolling.

There are a number of disadvantages and inconveniences in heating at this high temperature. For this reason, attempts have been made to lower the heating temperature of the steel ingot (slab) during hot rolling. JP-A-59-56522 discloses one of them. A number of inventions have been made as a development of this technology, and a method of performing nitridation in the process of increasing the temperature from decarburizing annealing to final finish annealing to form inhibitors (Japanese Patent Application Laid-Open Nos. 62-45285 and 60-179855). ), And a method of performing a nitriding treatment using a mixed gas of hydrogen, nitrogen and ammonia while the strip is running (JP-A-2-77525, JP-A-1-82400, JP-A-3-180).
460, JP-A-1-317592) have been proposed.

A method of controlling the primary recrystallized grain size at an intermediate stage from the completion of the primary recrystallization at the time of decarburizing annealing to the completion of the secondary recrystallization at the time of final finishing annealing (Japanese Patent Laid-Open No. 3-294425).
JP, JP-A-2-96275, JP-A-2-59
020, JP-A-1-82393) have also been proposed. By the way, a transformer is indispensable as a voltage conversion device today, and a large energy loss in the transformer is a serious social and economic problem. Transformers are
Due to the optimal design of the transformer, the manufacturer of electrical steel sheets
We are working hard to save energy by improving the quality of electrical steel sheets. Numerous methods have been devised and implemented to date, in short, to improve the quality of electrical steel sheets. In particular, regarding energy saving, it is to reduce iron loss of the magnetic steel sheet (energy loss consumed as heat when the magnetic steel sheet is excited).

By the way, Japanese Patent Laid-Open Nos. 49-34417 and 50-16610 disclose the final cold rolling of grain-oriented electrical steel. The former defines the cold rolling roll diameter, and the latter defines the temperature at which the steel sheet is held. The present invention differs from these methods in the following points. The slab heating temperature is high, there is no nitriding treatment after decarburization annealing, the roll diameter of cold rolling is 300 mmφ or less, and ordinary cold rolling mills are excluded.

As described above, in the conventional technique, there is a limitation in the diameter of the roll, and since the slab is heated at a high temperature, there is an inherent factor of cost increase.

[0009]

SUMMARY OF THE INVENTION The present invention, as described above, is as follows.
In cold rolling of a grain-oriented electrical steel sheet, the constraint of a cold rolling machine is removed and the easiness of hot rolling is secured, and a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties is provided.

[0010]

The present invention is disclosed in JP-A-2-77.
525, 1-82400, 3-180460, 1-31
In the production method of grain-oriented electrical steel sheet proposed in each publication of 7592, a cold rolling mill and cold rolling conditions are shown in order to obtain more favorable magnetic characteristics. In these patents, the grain-oriented electrical steel sheet can be sufficiently manufactured, but further improvement of magnetic characteristics is strongly demanded in order to meet the recent demand for energy saving.

The present invention meets the above-mentioned needs.
The gist is that C: 0.025 to 0.075 by weight.
%, Si: 2.5 to 4.0%, acid-soluble Al: 0.02
0 to 0.040%, N: 0.005 to 0.010%,
0.005 to 0.015 of at least one of S and Se
%, Mn: 0.05 to 0.8%, the balance consisting of Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot rolled, hot rolled sheet annealed, and intermediate annealed. Cold rolling more than one time, decarburization annealing, nitriding treatment in a mixed gas of hydrogen, nitrogen, and ammonia under the condition of running the strip, and then applying an annealing separator containing MgO as the main component for final finishing. In the final cold rolling of the production of the unidirectional electrical steel sheet to be annealed, the steel sheet is held for 1 minute or more in the work roll diameter D (mm) of the cold rolling mill and in at least one of the multiple passes. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which has a relationship with a temperature T (° C.) of 3 / 40D + 115.5 ≦ T ≦ 3 / 40D + 295.5 (40 ≦ D ≦ 500 mm). Steel composition as needed Su, Sb, Cr, or is contained 0.02 to 0.30% of at least one P, or from 0.03 to 0.30% of Cu and / or Ni 0.03 to
This is a method for producing a grain-oriented electrical steel sheet having an excellent magnetic property of containing 0.3%.

It has been found that the use of the method proposed in the present invention significantly improves the primary recrystallization texture after decarburization annealing. That is, the number of Goss oriented grains is increased to {11
1} {411} oriented grains. In the first place, in order to obtain good magnetic properties (secondary recrystallization texture having Goss orientation with good directionality) in the production of unidirectional electrical steel sheet, optimization of primary recrystallization aggregation after decarburization annealing and It is necessary to secure the inhibitor strength.

Conventionally, in order to optimize the primary recrystallization texture in the production of grain-oriented electrical steel sheets, a certain amount of transformation phase was required during the final cold rolling after the hot rolling. For this reason, carbon is included. However, 12
In the slab heating method of less than 80 ° C, the degree of optimization of the primary recrystallization texture is small. This is the corresponding grain boundary theory of Harase et al.
According to Vol. 9, No. 9 (1995) 917-924), the magnetic characteristics are not so good. That is,
When the present invention is not applied, the number of Goss oriented grains is small and the Σ9
There are many {111} {411} oriented grains having an orientation relation, and in the completed secondary recrystallization, the size of the Goss grains is large and the iron loss is poor.

In the first place, a typical measure for improving the iron loss of grain-oriented electrical steel sheets is to sharpen the Goss-oriented grains of the product sheet and reduce the size of the secondary recrystallized grains. According to the present invention, this ideal grain-oriented electrical steel sheet can be obtained. The reason for this is that if the temperature at the time of cold rolling and the roll diameter of the cold rolling mill are within the range of the present invention, the texture (primary texture) after decarburization annealing is Goss (｛1).
10} <001>) can be increased and {111} <211> (strictly speaking, {7}
78} <447>) and {411} <148> can be reduced. This increased Go during the primary recrystallization
Since the ss grains (nuclei) undergo secondary recrystallization growth, the size of the Goss grains in the final product is reduced and the iron loss is improved. Further, when the present invention is used, the degree of integration of Goss in the primary recrystallization is also improved, and the degree of integration of the Goss orientation in the product plate is also improved, so that the iron loss is remarkably improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, in the present invention, the work roll diameter of the cold rolling mill, the steel
Plate temperature and magnetic flux density B ₈The relationship of 0.23mm material is shown as an example.
(Fig. 1), and also work rolls for cold rolling mills.
Diameter, temperature of steel plate and iron loss W_17/50Relationship of 0.23mm material
An example is shown (Fig. 2). 1 and 2 show C: 0.050
~ 0.060%, Si: 3.15 ~ 3.30%, acid soluble
Property Al: 0.026 to 0.029%, N: 0.0075
~ 0.0085%, S: 0.0070 to 0.0080
%, Mn: 0.08 to 0.11%, Cr: 0.08 to
0.12%, Sn: 0.04 to 0.07%
After heating the slab at 1150 ° C, hot-roll it in the usual way,
Wind up at 530-580 ℃, then 1120 ℃ for 2 minutes
After annealing the hot rolled sheet between
Rolling the steel sheet once and holding the steel sheet at each temperature in between,
Post decarburization annealing, strip nitriding, MgO as the main component
The annealing separator was applied and after secondary recrystallization annealing. Then flat
Smooth annealing and apply a tension insulating coating consisting mainly of phosphate
It is the result of measuring the magnetic properties after the test. In this way
Good magnetic flux density is obtained in the bright range.

Next, the reason for limiting the roll diameter will be described. If the maximum value exceeds 500 mm, rolling of a thin material such as a grain-oriented electrical steel sheet becomes impossible due to the "kiss phenomenon" of the roll. The effect of the present invention can be ensured even if the minimum value is 40 mm, but it has not been put to practical use in actual mass production. The smaller the roll diameter, the lower the temperature at which the steel sheet temperature is to be maintained is because the deformed form of the steel sheet is pulled out from the compression and the primary recrystallization texture after decarburization annealing is Gos.
This is because s-oriented grains increase.

If the steel sheet holding temperature is kept above this temperature, recovery occurs during cold rolling, the primary recrystallization texture is not good, and the magnetic properties are poor. On the other hand, even if the temperature is lower than the lower limit temperature, the secondary recrystallization is good but the magnetic properties are not excellent. The work roll diameter (D: mm) and the steel sheet holding temperature (T: ° C) must satisfy the following formula. Assuming that 40 ≦ D ≦ 500 mm, 3 / 40D + 115.5 ≦ T ≦ 3 / 40D + 295.5.

A particularly desirable range is 40≤D≤180 mm
In 3 / 40D + 165.5 ≦ T (° C.) ≦ 3 / 40D + 23
5.5. FIG. 2 shows the iron loss (W _17/50 : W / kg) of FIG. Thus, good iron loss is obtained within the scope of the present invention. Also, when the roll diameter is 40 ≦ D ≦ 180 mm, 3 / 40D + 165.5 ≦ T (° C.) ≦ 3 / 40D + 23
5.5 Particularly good iron loss is obtained, and this range is particularly desirable.

Next, the reasons for limiting the component composition of the electromagnetic steel slab used as the starting material in the present invention are as follows.
C was set to 0.025 to 0.075%. 0.025%
If it is less than 0.27 mm, secondary recrystallization is not stable especially with a thin material of 0.27 mm or less. On the other hand, if it exceeds 0.075%, the productivity in the decarburization step is remarkably impaired, deviating from the object of the present invention.

If the Si content is less than 2.5%, good iron loss cannot be obtained. On the other hand, if it exceeds 4.0%, it becomes difficult to perform steel sheet processing such as cold rolling at room temperature due to brittleness. S and Se are 0.015% or less, desirably 0.013% or less. One-way electromagnetic produced by manufacturing a hot-rolled sheet at a slab heating temperature of 1280 ° C. or lower, and then making an inhibitor after the decarburization annealing step such as strip nitriding after hot-rolled sheet annealing and cold rolling. This is because in the steel sheet, a large amount of S and Se hinders the grain growth of the primary recrystallized grains and is harmful. If it is less than 0.005%, due to unavoidable fluctuation factors in operation in hot rolling (temperature history difference on and between skids, fluctuation of hot rolling temperature due to acceleration of rolling speed, etc.),
Since the variation in the grain growth of the primary recrystallized grains is likely to occur, the product cannot be manufactured industrially stably.

Al combines with N to form AlN,
In the present invention, since it is essential to form (Al, Si) N by nitriding the steel after the post-process, ie, after the completion of the primary recrystallization, a certain amount of free Al is required. Therefore, sol. 0.020 or more as Al
Add 0.040%. If the content of Mn is too small, secondary recrystallization becomes unstable, while if it is too large, it becomes difficult to obtain a product having a high magnetic flux density. The appropriate content is 0.
05 to 0.8%. Preferably, 0.070-0.0.
3%.

If N is less than 0.005%, the development of secondary recrystallized grains becomes poor. On the other hand, when it exceeds 0.010%, swelling of steel plate called blister occurs. It has been reported that P improves the primary recrystallization texture. At a low P, this effect is small and the cost of steelmaking increases, so the lower limit is made 0.02%. With respect to the upper limit, if it exceeds 0.30%, P segregates at the grain boundary and brittle fracture is likely to occur, and industrial production becomes difficult. Therefore, the upper limit is set to 0.30%.

Sn and Sb are, as has been conventionally said,
The primary recrystallization texture has the effect of increasing the {110} <001> orientation grains and has the effect of uniformly depositing sulfides. Therefore, in the present invention, Cu-S, M
The effect of controlling the precipitation of sulfides such as n-S is enhanced. Furthermore, when Sn and Sb are added in a large amount, there is a tendency that oxidation during decarburization annealing is hardly performed and primary recrystallized grains grow hardly. For this reason, the decarburization annealing temperature is set to the conventional 820-84.
There is no choice but to raise it by 20 ° C from 0 ° C. This is a direction that facilitates the formation of the primary coating of the grain-oriented electrical steel sheet. In addition, since the secondary recrystallized grain size is reduced by adding Sb and Sn, iron loss (particularly, low magnetic field iron loss) is improved as compared with no addition. On the other hand, when Sb or Sn is less than 0.02%, the secondary recrystallized grains do not become too small. On the other hand, when Sb or Sn exceeds 0.30%, nitriding treatment after decarburizing annealing becomes difficult, which is not suitable for industrial production.

[0024] Cr is added to secure the amount of oxygen after decarburization annealing necessary for forming a farsterite film.
If it is less than 0.02%, the amount of oxygen becomes extremely small. On the other hand, if it exceeds 0.30%, the amount of oxygen increases extremely, and good forsterite is not formed. Also, the magnetic flux density decreases. If Cu is less than 0.03%, the effect is small. On the other hand, if it exceeds 0.5%, Cu-S precipitates are coarsened and the effect is reduced. Further, during hot rolling, the frequency of occurrence of so-called "Cu hegging" defects sharply increases. Preferably, it is 0.05 to 0.10%.

If Ni is less than 0.03%, the effect is small, and if it exceeds 0.3%, it is effective as shown in Japanese Patent Laid-Open No. 5-306410, but it becomes expensive. Therefore, the upper limit is 0.30%. The addition of Cr and Ni further improves the effect of the present invention, and may be added in amounts that are commensurate with cost. Next, the necessity of annealing the hot rolled sheet will be described. Magnetic properties are not stable unless hot-rolled sheet annealing is performed. The reason for this is that if hot-rolled sheet annealing is not performed, the Goss orientation is small in terms of primary recrystallization texture, and according to the corresponding grain boundary theory, the grain size of the final product tends to be large and iron loss tends to be poor. An effective means for securing the amount of Goss-oriented grains in the primary recrystallization texture, reducing the grain size of the final product, and improving iron loss is to perform hot-rolled sheet annealing.

[0026]

【Example】

 <Example 1> A steel ingot having the components shown in Table 1 was produced by a usual method.
After heating the slab at 1100-1150 ° C, normal hot rolling
The hot-rolled sheet thickness was finished to 2.3 mm. Then 1120 ° C x 2
Hot-rolled sheet is annealed for 180 min.
Low 2 pass warm rolling and 0.22mm cold rolling
Was. Thereafter, at 820 ° C. to 840 ° C., N_Two: 25%,
H _Two: Dew point depending on C content in 75% atmospheric gas
Decarburization primary recrystallization annealing is performed at 62 ° C for 70 seconds to 90 seconds.
Was.

[0027]

[Table 1]

Then, the total nitrogen content is adjusted to 195 to 210 pp.
m, a strip nitriding treatment was performed, an annealing separator containing MgO as a main component was applied, and finish annealing was performed. In this finish annealing, the temperature is raised at 10 to 20 ° C./hour, and the atmosphere is
N ₂ : 25%, H ₂ : 75%. Then 1200
A purification annealing of H ₂ : 100% was performed at 20 ° C. for 20 hours.
Thereafter, application of a commonly used tension coating and smoothing treatment were performed. The results are shown in Table 2.

[0029]

[Table 2]

Example 2 A steel ingot having the components shown in Table 3 was manufactured by a usual method, the slab was heated at 1100 to 1150 ° C., and then the hot rolled sheet was finished to a thickness of 2.6 mm by ordinary hot rolling. After that, hot-rolled sheet annealing is performed at 1120 ° C for 2 minutes, and after pickling, 180
0.2 at least 220 warm rolling at ~ 220 ℃
Cold rolled to 9,0.26 mm. After that 820 ℃ ~ 84
Decarburization primary recrystallization annealing was performed at 0 ° C. in an atmosphere gas of N ₂ : 25% and H ₂ : 75% at a dew point of 62 ° C. for 150 to 170 seconds.

Then, the total nitrogen content is adjusted to 195 to 210 pp.
m, a strip nitriding treatment was performed, an annealing separator containing MgO as a main component was applied, and finish annealing was performed. In this finish annealing, the temperature is raised at 10 to 20 ° C./hour, and the atmosphere is
N ₂ : 25%, H ₂ : 75%.

[0032]

[Table 3]

Thereafter, the temperature is set to 1200 ° C. for 20 hours, and H ₂ : 10 is set.
A 0% purification annealing was performed. Thereafter, application of a commonly used tension coating and smoothing treatment were performed. The results are shown in Table 4.

[0034]

[Table 4]

[0035]

EFFECTS OF THE INVENTION By applying the present invention, it is possible to manufacture a grain-oriented electrical steel sheet having excellent magnetic properties,
An extremely large amount of energy can be saved.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a 0.23 mm material showing the relationship between the work roll diameter of a cold rolling mill, the temperature of a steel plate, and the magnetic flux density B ₈ .

FIG. 2 is a diagram showing a relationship between a work _roque diameter of a cold rolling mill, a temperature of a steel plate, and an iron loss W _17/50 .

(72) Inventor Norihiro Yamamoto 1-1 Tobata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture Inside Nippon Steel Corporation Hachiman Works (72) Inventor Koji Yamazaki 1-Tobata-cho, Tobata-ku, Kitakyushu, Fukuoka 1- 1 Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor Katsuro Kuroki 59 Nippon Steel Plant Design Co., Ltd., 46 Nakahara, Tobata-ku, Kitakyushu, Fukuoka

Claims (4)

[Claims] 1. By weight ratio, C: 0.025 to 0.075% Si: 2.5 to 4.0%, acid soluble A1: 0.020 to 0.040%, N: 0.005 to 0. 0.010%, 0.005 to 0.015 of at least one of S and Se
%, Mn: 0.05 to 0.8%, 128 slabs with the balance Fe and unavoidable impurities
Heating at a temperature of less than 0 ° C., hot rolling, hot-rolled sheet annealing, cold rolling at least once with intermediate annealing sandwiched between hydrogen, nitrogen, and decarburization annealing, and running strips.
Nitriding is performed in a mixed gas of ammonia, then M
In the final cold rolling of the production of the grain-oriented electrical steel sheet in which the annealing separator having gO as a main component is applied and the final finish annealing is performed, the work roll diameter D (mm) of the cold rolling mill and the number of passes The relationship with the temperature T (° C) at which the steel sheet is held for 1 minute or more in at least one pass of the above is 3 / 40D + 115.5 ≤ T ≤ 3 / 40D + 295.5 (40 ≤ D ≤ 500 mm). A method of manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties. 2. The production of a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, further comprising 0.02 to 0.30% of at least one of Sn, Sb, Cr and P. Method. 3. The method for producing a grain-oriented electrical steel sheet with excellent magnetic properties according to claim 1, further comprising 0.03 to 0.30% of Cu. 4. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, further comprising 0.03 to 0.3% of Ni.