JPH0949023A - Production of grain oriented silicon steel sheet excellent in iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize secondary recrystallization by specifying Cu, S + Se, and Sb + Sn, respectively, and to improve iron loss characteristic by reducing the size of grains. SOLUTION: A slab, having a composition consisting of 0.025-0.075% C, 2.5-4.0% Si, 0.02-0.10% P, 0.010-0.050% acid soluble Al, 0.0040-0.0130% N, 0.007-0.020% S and/or Se, 0.05-0.5% Mn, 0.06-0.20% Sn + Sb, 0.03-0.50% Cu, and the balance Fe with inevitable impurities, is heated at <1280 deg.C and hot- rolled and then subjected to hot rolled plate annealing or cold-rolled one or more times while process-annealed between cold rolling stages. After decarburizing annealing, nitriding treatment is performed in the state where a strip is allowed to travel. Then, a separation agent at annealing, composed essentially of MgO, is applied and final finish annealing is performed. By this method, magnetic flux density is increased and the size of secondary recrystallized grains is regulated to about 10mm, and iron loss can be remarkably improved.

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 having excellent magnetic properties, which is 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 characteristic, the magnetic flux density B ₈ at a magnetic field strength of 800 A / m is standardized by JIS and is normally used. As a characteristic value indicating energy loss, the energy loss (iron loss) W _17/50 per 1 kg of steel sheet when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz is also JIS.
Has been standardized in.

[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. Further, in general, when the magnetic flux density becomes high, the secondary recrystallized grains become large, and the 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.

This unidirectional electrical steel sheet has a so-called Goss structure having {110} on the surface of the steel sheet and <001> axis in the rolling direction by causing secondary recrystallization in the final finishing annealing step. 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 technology for producing such a high magnetic flux density unidirectional electrical 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. 40-15644), MnS, MnSe, There is a method using 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 in actual hot rolling, steel ingot (slab)
It is necessary to set the heating temperature of 1350 ° C. or higher.

There are a number of disadvantages and inconveniences in heating at this high temperature. Therefore, 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.
Many inventions have been made as the development of this technology, and a method of performing nitriding in a temperature rising process from decarburization annealing to final finishing annealing for forming an inhibitor (JP-A-62-45285, JP-A-60-179855). ), And further, a method of performing a nitriding treatment using a mixed gas of hydrogen, nitrogen and ammonia under a condition in which the strip is allowed to travel (JP-A-2-775).
25, JP-A-1-82400, and JP-A-3-82400.
180460, JP-A-1-317592)
Was disclosed.

Further, a method of controlling the primary recrystallized grain size at an intermediate stage from the completion of primary recrystallization during decarburization annealing to the completion of secondary recrystallization during final annealing (Japanese Patent Laid-Open No. 29442/1993).
No. 5, JP-A-2-96275, JP-A No. 2-5
No. 9020 and Japanese Patent Application Laid-Open No. 1-82393). Further, regarding the addition of grain boundary segregation type elements such as Sn in unidirectional electrical steel, JP-A-3-211
No. 232, etc.

By the way, recently, recycling of scrap has been promoted in order to save energy for iron products. Especially,
Since the content of Sn, P, and Cu in the scraps of empty cans is large, it is required to manufacture steel having a different composition from the conventional manufacturing method using a blast furnace.

[0009]

Problems to be Solved by the Invention JP-A-58-2341
The technique disclosed in Japanese Patent No. 4 has a heating temperature of a steel ingot (slab) of 13
The present invention relates to the production of a grain-oriented electrical steel sheet produced by completely dissolving an inhibitor component at 50 ° C. or higher. As described above, such high temperature slab heating has a number of disadvantages.

Further, in the technique disclosed in Japanese Patent Laid-Open No. 3-212232, although the slab heating temperature is low, Sn is less than 0.
When adding about 04%, W _{17/50 of} iron loss is _0.29mm
The limit was 0.96 W / kg. Further, when the added amount of Sn was 0.15%, the secondary recrystallization failure occurred. With respect to the above-mentioned problems, the present invention improves iron loss by adding Sn or Sb and adding Cu together when the slab heating temperature is relatively low. Further, the use of the present invention makes it possible to manufacture a grain-oriented electrical steel sheet having excellent magnetic characteristics by containing Sn and Cu in a larger amount than in the past, which is extremely useful.

[0011]

There are various measures for improving the iron loss of the grain-oriented electrical steel sheet, but in principle, reduction of eddy current loss and hysteresis loss is performed. In the present invention, attention has been paid to optimizing the size of crystal grains, which is one of the influential factors of eddy current loss.

In the technique disclosed in Japanese Patent Laid-Open No. 3-212232, it is stated that the secondary recrystallization becomes unstable when Sn is added in an amount of more than 0.10%. However, in the process of producing a grain-oriented electrical steel sheet at a slab heating temperature similar to that of ordinary steel, nitriding is suppressed and secondary recrystallization tends to be unstable when Sn is added alone, When Cu is added in combination,
It has been found that good secondary recrystallization is possible even if nitriding during the finish annealing process is suppressed.

The reason for this is not clear, but it is considered that CuS compensated the weakening of the inhibitor AlN due to the suppression of nitriding. It was found that a similar phenomenon occurs even if Sn is replaced with Sb.

Further, similar to the technique disclosed in Japanese Patent Laid-Open No. 58-23414, the effects of Sn and Sb which are grain boundary segregation elements are exhibited, and the secondary recrystallization size is reduced. It has been found that this significantly improves iron loss.

The gist of the present invention is as follows. (1) C: 0.025 to 0.075% by weight, Si:
2.5-4.0%, P: 0.02-0.10%, acid-soluble Al: 0.010-0.050%, N: 0.0040
~ 0.0130%, 0.0% of at least one of S and Se
07-0.020%, Mn: 0.05-0.5%, Sn
+ Sb: 0.06 to 0.20%, Cu: 0.03 to 0.
A slab consisting of 50% and the balance Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot-rolled, hot-rolled sheet annealed, intermediate-annealed one or more cold-rolled, decarburized annealed. Iron loss characteristics characterized by performing a nitriding treatment in a mixed gas of hydrogen, nitrogen and ammonia in a state where a post strip is run, and then applying an annealing separation material containing MgO as a main component and performing final finishing annealing. Of excellent grain-oriented electrical steel sheet.

(2) C: 0.025 to 0.07 by weight ratio
5%, Si: 2.5 to 4.0%, P: 0.02 to 0.1
0%, acid-soluble Al: 0.010 to 0.050%, N:
0.0040 to 0.0130%, at least one of S and Se is 0.007 to 0.020%, Mn: 0.05 to
0.5%, Sn + Sb: 0.06 to 0.20%, Cu:
A slab containing 0.03 to 0.50% and the balance of Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot rolling is performed, hot-rolled sheet annealing is not performed, and intermediate anneal is performed at least once. After decarburizing and annealing, nitriding is performed in a mixed gas of hydrogen, nitrogen, and ammonia under conditions where the strip is allowed to run, and then an annealing separator containing MgO as a main component is applied and final finishing annealing is performed. And a method for manufacturing a grain-oriented electrical steel sheet having excellent iron loss characteristics.

(3) Cr: 0.05 as a molten steel component
The method according to (1) or (2), wherein the content is 0.30%.

(4) Further Ni: 0.01 as a molten steel component
0.1% is contained (1),
The method according to (2) or (3).

Next, the reasons for limitation of the present invention will be described. C
When the content is less than 0.025%, the secondary recrystallization becomes unstable, and the magnetic flux density (B ₈ value) of the product becomes low even below 1.80T even when the secondary recrystallization is performed. . On the other hand, when the content of C exceeds 0.075% and becomes too large, the decarburization annealing time becomes long and the productivity is remarkably impaired.

When Si content is less than 2.5%, it is difficult to obtain a product with low iron loss, while Si content is 4.5.
If the amount is too much over%, cracks and fractures frequently occur during cold rolling of the material, making stable cold rolling work impossible.

One of the features of the component system of the starting material of the present invention is that S is 0.020% or less, preferably 0.015.
% Or less. Conventionally known technology, for example, Japanese Patent Publication No. 40-15644 or Japanese Patent Publication No. 47-2525.
In the technique disclosed in Japanese Patent Laid-Open No. 0, S was essential as an element for forming MnS, which is one of the precipitates necessary for causing secondary recrystallization.

In the above-mentioned known technology, there is a content range in which S is most effective, and it has been defined as the amount of MnS which can be solid-dissolved in the slab heating step performed prior to hot rolling. However, in Japanese Unexamined Patent Publication (Kokai) No. 3-212132, which uses (Al, Si) N as an inhibitor, MnS is not particularly required, and therefore 0.015 at maximum.
%, Preferably 0.010% or less.

However, in the present invention, since Cu is added and the compound of Cu and S is used as the precipitation nucleus of the inhibitor,
Some S is necessary. When S exceeds 0.020%, a large amount of MnS precipitates, so when the slab heating temperature of the present invention is as low as less than 1280 ° C, secondary recrystallization becomes unstable. Therefore, the upper limit was made 0.020%.

However, it is preferably 0.015% or less. On the other hand, if it is less than 0.007%, Cu-S is not properly precipitated and the magnetic flux density (B ₈ ) is inferior, so the lower limit is 0.007%.
And Se is also the same as S.

It has been reported that P has the effect of improving the primary recrystallization texture. If the P content is low, this effect is small and the steelmaking cost is increased, so the lower limit is 0.02.
%. Regarding the upper limit, if it exceeds 0.10%, P tends to segregate at the grain boundaries to cause brittle fracture, and industrial production becomes difficult. Therefore, the upper limit is set to 0.10%.

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. 0.010 as Al
Add 0.050%.

If the content of Mn is too small, the secondary recrystallization becomes unstable, while if it is too large, it becomes difficult to obtain a product having a high magnetic flux density. Proper content is 0.050
0.5%. Preferably 0.070 to 0.030
%.

If N is less than 0.0010%, the development of secondary recrystallized grains becomes poor. On the other hand, if it exceeds 0.0120%, swelling of the steel sheet called blister occurs.

Sn and Sb are, as is conventionally said,
In the primary recrystallization texture, it has an effect of increasing {110} <001> oriented grains and an effect of uniformly precipitating sulfide. Therefore, in the present invention, Cu-S, M
The effect of controlling the precipitation of sulfides such as n-S is enhanced.

Further, when Sn and Sb are added in a considerably large amount as in the present invention, there is a tendency that oxidation during decarburization annealing is difficult and primary recrystallized grain growth becomes difficult. Therefore, the decarburization annealing temperature has to be increased by about 20 ° C. from the conventional 820 to 840 ° C. This is a direction that facilitates the formation of the primary coating of the grain-oriented electrical steel sheet.

Further, since the secondary recrystallized grain size is reduced by adding Sb and Sn, the iron loss (particularly low magnetic field iron loss) becomes better than that without addition. Since Sb and Sn are adjacent to each other in atomic number, they are defined by Sb + Sn.

If Sb + Sn is less than 0.06%, the secondary recrystallized grains do not become so small. Also, Sb + Sn
When it exceeds 0.20%, nitriding treatment after decarburization annealing becomes difficult, which is not suitable for industrial production. Further, as will be described later, the magnetic flux density decreases, so the upper limit is made 0.20%.

Cu combines with S and precipitates during hot rolling to form (Al, Si) N precipitation nuclei. Therefore, it is considered that the secondary recrystallization inhibitor is ideally dispersed. When Sn is added, the secondary recrystallization becomes unstable, but the grain size becomes small and the iron loss becomes low. However, when Cu is added, the secondary recrystallization is stabilized by the interaction with Sn even if Sn is high. 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%.

Cr is added to secure the amount of oxygen after decarburization annealing necessary for forming a forsterite film.
If it is less than 0.05%, as in the present invention (Sn + Sb)
When added, the amount of oxygen becomes extremely small. Also 0.3
If it exceeds 0%, the amount of oxygen increases extremely, and good forsterite is not formed. Also, the magnetic flux density decreases.

If Ni is less than 0.01%, secondary recrystallization becomes unstable. Even if the content exceeds 0.10%
Although it is effective as shown in Japanese Patent Publication No. 10, it is expensive. Therefore, the upper limit is 0.10%. 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 test results will be described. Cu: 0.07
%, S: 0.012%, C: 0.050 to 0.055
%, Si: 3.20 to 3.30%, Al: 0.026 to
0.030%, Cr: 0.09 to 0.20%, Ni:
0.03-0.08%, P: 0.04-0.07%, M
n: 0.09 to 0.11%, N: 0.0075 to 0.0
Based on 085%, Sn + Sb = 0.04,0.
Molten steel changed to 10, 0.15, 0.20, 0.25% is made into a slab by a normal method, heated at 1100 to 1150 ° C, and hot-rolled by a normal method to obtain a temperature between 500 to 600 ° C. I wound it up. The finish thickness of the hot-rolled sheet at this time is 2.
It was 6 mm.

After that, hot-rolled sheet annealing was performed at 1120 ° C. for 2 minutes, pickling, warm rolling at 180 to 220 ° C. for at least two passes, and cold rolling to 0.285 mm. Then 82
N ₂ : 25%, H at each temperature of 0 ° C, 830 ° C, and 840 ° C
₂ : Annealed at a dew point of 65 ° C. for 150 seconds in an atmosphere gas of 75% to perform decarburization primary recrystallization and oxide film formation.

After that, nitriding was performed in a strip state, and the nitrogen content thereafter was set to 200 to 210 ppm. Then MgO
An annealing separator having as a main component was applied. In the subsequent finish annealing, it was heated to 1200 ° C at a temperature rising rate of 15 ° C / hour.

At this time, the atmosphere gas is H ₂ : 75%, N
It was ₂ : 25%. Then, at 1200 ℃ for 20 hours, H
₂ : 100% pure annealing was performed.

After cooling, shape correction and phosphate-in a continuous line
A colloidal silica-based tension coating was applied. After this, a sample for so-called Epstein was cut out and 850
Magnetic properties were measured by carrying out strain relief annealing at ℃ × 2 hours.

The magnetic properties, B _8, W _13/50, a W _17/50. Figure 1 B ₈ and W _17/50, Fig. 2 shows the relationship of B ₈ and W _13/50. In this way Sn + Sb = 0.04%
Therefore, even if B ₈ is high, the secondary recrystallization is considerably large (for example, the visual diameter is 20 to 50 mm), and the iron loss is not so good.

However, if the amount of addition of Sn + Sb is increased, the secondary recrystallized grains become smaller and the iron loss is improved. But S
If the amount of n + Sb increases too much (0.25%), the magnetic flux density decreases. In this case a low magnetic field iron loss (W _13/50) is not so much deterioration, high magnetic field core loss (W _17/50) has deteriorated.

[0043]

【Example】

Example 1 A steel ingot having the following components was manufactured by a usual method and 1100-1
After heating the slab at 150 ° C., it was finished to a hot-rolled sheet thickness of 2.3 mm that does not show normal hot rolling. After that, hot-rolled sheet annealing was performed at 1120 ° C. for 2 minutes, and after pickling, warm rolling was performed at 180 to 220 ° C. for a minimum of two passes and then cold rolling to 0.220 mm.
Then, decarburization primary recrystallization annealing was performed at 830 ° C. in an atmosphere gas of N ₂ : 25% and H ₂ : 75% at a dew point of 62 ° C. for 100 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%.

Thereafter, the temperature is set to 1200 ° C. for 20 hours, and H ₂ : 10
A 0% purification annealing was performed. Thereafter, application of a commonly used tension coating and smoothing treatment were performed. Table 1 shows the results.

[0046]

[Table 1]

Example 2 A steel ingot having the following components was produced by a usual method, and
After heating the slab at 1130 ° C, normal hot rolling was performed to finish the hot rolled sheet thickness to 2.6 mm. Then, pickling was performed without performing hot-rolled sheet annealing, and cold rolling was performed to 0.335 mm.

After that, it is degreased by alkali cleaning to obtain 83
N ₂ : 25 at any of 5,840 and 845 ° C.
%, H ₂ : 150% at 75% dew point in ambient gas
Second decarburization primary recrystallization annealing was performed. After that, strip nitriding treatment was performed so that the total nitrogen content was 225 to 235 ppm, and an annealing separation material containing MgO as a main component was applied and finish annealing was performed.

In this finish annealing, the temperature was raised at 10 to 20 ° C./hour, and the atmosphere was N ₂ : 30% and H ₂ : 70%.
After that, a purification treatment was performed at 1200 ° C. for 35 hours. After cooling, a phosphoric acid-based tension coating, which is usually used, was applied and a smoothing treatment was performed. The results are shown in Table 2.

[0050]

[Table 2]

[0051]

EFFECT OF THE INVENTION According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having a high Sn content, which is manufactured at a slab heating temperature similar to that of ordinary steel and has good magnetic characteristics.

[Brief description of drawings]

FIG. 1 is a chart showing a relationship between B ₈ and W _17/50 of a material of the present invention.

FIG. 2 is a _table showing the relationship between B ₈ and W _13/50 of the material of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hisawa Kitakawa No. 1 Tobahata-cho, Tobata-ku, Kitakyushu City, Nippon Steel Co., Ltd., Yawata Works (72) Inventor Katsuro Kuroki, Nakahara 46, Tobata-ku, Kitakyushu 59 Nittetsu Plant Design Co., Ltd.

Claims (4)

[Claims] 1. C: 0.025 to 0.075%, Si: 2.5 to 4.0%, P: 0.02 to 0.10%, and acid-soluble Al: 0.010 to 0 by weight. 0.050%, N: 0.0040 to 0.0130%, 0.007 to 0.020 at least one of S and Se
%, Mn: 0.05 to 0.5%, Sn + Sb: 0.06 to 0.20%, Cu: 0.03 to 0.50%, and a balance of 1280 slabs composed of Fe and inevitable impurities.
Heating at a temperature below ℃, hot rolling, hot-rolled sheet annealing, cold rolling at least once with intermediate annealing sandwiched between hydrogen, nitrogen, and ammonia under conditions that allow strips to run after decarburization annealing. Nitriding is performed in a mixed gas, then Mg
A method for manufacturing a grain-oriented electrical steel sheet having excellent iron loss characteristics, which comprises applying an annealing separator containing O as a main component and performing final finishing annealing. 2. C: 0.025 to 0.075%, Si: 2.5 to 4.0%, P: 0.02 to 0.10%, and acid-soluble Al: 0.010 to 0 by weight. 0.050%, N: 0.0040 to 0.0130%, 0.007 to 0.020 at least one of S and Se
%, Mn: 0.05 to 0.5%, Sn + Sb: 0.06 to 0.20%, Cu: 0.03 to 0.50%, and a balance of 1280 slabs composed of Fe and inevitable impurities.
Heating at a temperature of less than ℃, hot-rolling, hot-rolled sheet annealing is not performed, one or more cold-rolling with intermediate annealing is performed, hydrogen, nitrogen under the condition of running the strip after decarburization annealing,
Nitriding is performed in a mixed gas of ammonia, then M
A method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics, which comprises applying an annealing separator containing gO as a main component and performing final finishing annealing. 3. As a molten steel component, Cr: 0.05-
The method according to claim 1 or 2, wherein the content is 0.30%. 4. Ni: 0.01 to 0.01 as a molten steel component
The content of 0.10% is contained.
Or the method of 3.