JP3498978B2 - Manufacturing method of grain-oriented electrical steel sheet with extremely low iron loss - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has an S content of 2.5 to 7.0%.
The present invention provides a method for producing a grain-oriented electrical steel sheet containing i and having a low iron loss.

[0002]

2. Description of the Related Art Generally, the magnetic properties of a grain-oriented electrical steel sheet are evaluated by both the iron loss property and the excitation property. Increasing the excitation characteristics is effective for downsizing equipment that increases the design magnetic flux density. On the other hand, reducing the iron loss characteristics is effective in reducing the loss of heat energy when used as an electric device and saving the power consumption. further,
Aligning the <100> axes of the crystal grains of the product in the rolling direction can improve the magnetization characteristics and lower the iron loss characteristics.
In recent years, much research has been conducted especially in this respect, and various manufacturing techniques have been developed. For example, Japanese Patent Publication No. 40-15644 discloses a method for producing a grain-oriented electrical steel sheet in order to obtain a high magnetic flux density. This is a production in which AlN + MnS is made to function as an inhibitor and the reduction ratio in the final cold rolling step is a strong reduction exceeding 80%. By this method, a grain-oriented electrical steel sheet having a high degree of integration of the (110) <001> orientation of secondary recrystallized grains and a high magnetic flux density of B ₈ of 1.870 T or more can be obtained. However, although this manufacturing method can reduce iron loss to some extent, the grain size of the secondary recrystallization macro is still large on the order of 10 mm, and eddy current loss, which is a factor affecting iron loss, cannot be reduced. No good iron loss value was obtained. In order to improve this, a method of subjecting a steel sheet to laser treatment disclosed in JP-B-57-2252, and JP-B-58-2569.
Japanese Patent Publication discloses various methods for subdividing magnetic domains, such as a method for applying mechanical strain to a steel sheet.

On the other hand, in Japanese Unexamined Patent Publication No. 1-290716, ultra-rapid annealing treatment is applied to a cold rolled steel sheet at a heating rate of 100 ° C./sec or more to a temperature of 657 ° C. or more to decarbonize the strip. A final high temperature anneal to effect secondary growth, whereby the strip has reduced size secondary particles and improved core loss that persists without significant change after stress relief anneal. A featured method is disclosed. But,
It has been difficult to obtain iron loss characteristics comparable to the conventional subdivision of magnetic domains when an insulating film is applied on a forsterite film by simply refining the secondary recrystallized grain size by this manufacturing method.

[0004]

With the above conventional manufacturing method, it is difficult to obtain a grain-oriented electrical steel sheet having a sufficiently low iron loss, and the present invention provides a manufacturing method for solving the problem. Is.

[0005]

In the present invention, as a result of repeated studies to solve the above problems, C: 0.10% or less, Si: 2.5 to 7.0%, Mn: 0 by weight. 0.02 to 0.15%, S: 0.001 to 0.05%, acid-soluble Al: 0.01 to 0.04%, N: 0.003 to 0.02%, Cu, Sn, Sb, Cr , Bi at least 1.0%, the balance is Fe and unavoidable impurities, and the unidirectional electrical steel hot-rolled sheet is subjected to hot-rolled sheet annealing and cold rolling once. In the method of producing a unidirectional electrical steel sheet by performing decarburization annealing and then final finishing annealing, in the cold rolling, the cold rolling reduction is more than 89% and the final sheet thickness is 0.2.
The strip rolled to 7 mm or less is heated to a temperature of more than 700 ° C. at a heating rate of 290 ° C./sec or more immediately before decarburization annealing to obtain secondary recrystallized grains having a grain size of 5 mm or less.
It has been found that a method of manufacturing a grain-oriented electrical steel sheet with a very low iron loss is obtained.

The present invention will be described in detail below. The unidirectional electrical steel sheet can be manufactured by sufficiently causing secondary recrystallization during the final annealing in the manufacturing process to obtain a so-called Goss texture. In order to obtain this Goss texture, growth coarsening of primary recrystallized grains is suppressed and they are aligned in the rolling direction (11
0) Only recrystallized grains of <001> orientation are selectively grown in a certain temperature range. In other words, it is necessary to make a base material for secondary recrystallization. For that purpose, fine inclusions such as MnS, AlN, and Cu ₂ S must be uniformly dispersed in the material as an inhibitor (inhibitor) for the growth of primary recrystallized grains. Further, it is necessary to increase the number of (110) plane oriented recrystallized grains as much as possible at the stage of primary recrystallization.

However, according to the conventional manufacturing method, secondary recrystallized grains having a relatively large grain size of several mm or more can have a (110) <001> orientation aligned in the rolling direction. When the grain size is smaller than the following, there is a problem that secondary recrystallization that is largely deviated from the rolling direction occurs. This tendency is unavoidable especially in the case of taking a measure as in Japanese Patent Laid-Open No. 1-290716 to reduce the average secondary recrystallized grain size to reduce the magnetic domain width to obtain a target low iron loss.
10) The ratio of fine secondary recrystallized grains in which the <001> orientation is deviated from the rolling direction increases, and the improvement rate of the iron loss value when a film such as forsterite or an insulating film is applied to the surface of the steel sheet later is improved. There was a problem that it did not grow so much.

Therefore, in order to obtain the (110) <001> orientation aligned in the rolling direction even in the case of secondary recrystallized grains having a small crystal grain size, as a result of repeated studies on improvement of the primary recrystallized structure, cold rolling It was found that the rolling conditions and the conditions immediately before decarburization annealing or at the temperature rising stage have a great influence on the orientation of secondary recrystallized grains having a small grain size. That is, by setting the cold rolling reduction rate to be higher than 89%, the degree of integration of (110) plane-oriented recrystallized grains, which becomes the nucleus of secondary recrystallization, in the rolling direction in the primary recrystallization step is increased, and decarburization is performed. Immediately before annealing, by heating at a heating rate of 290 ° C./sec or more to a temperature of more than 700 ° C., (110) <00
1> It was found that fine secondary recrystallized grains with an orientation of 5 mm or less aligned in the rolling direction can be obtained. As a result, there is a large margin of improvement in the iron loss value when a coating is applied to the surface of the steel sheet later, and it is possible to obtain a low iron loss.

FIG. 1 shows the cold rolling reduction ratio and the product plate thickness of 0.225 mm.
The relationship of the iron loss is shown with the heating rate of decarburization annealing as a parameter. With the rapid heating material, good magnetic properties were obtained with a rolling reduction of more than 89%. FIG. 2 shows a (100) pole figure of fine secondary recrystallized grains having a grain size of 5 mm or less. (A) is the orientation of the fine secondary recrystallized grains when the cold rolling reduction is 80% by the conventional manufacturing method and (b) is the reduction of 90% in the example of the present invention. In each case, the temperature rise during decarburization annealing was performed at a heating rate of 300 ° C./sec. According to the present invention, even the fine secondary recrystallized grains have the (110) <001> orientation aligned in the rolling direction. Thus, by applying film tension by forsterite on the surface of the secondarily recrystallized steel sheet, an insulating film, or the like, there is a large improvement rate of iron loss, and an extremely low iron loss value can be obtained.

[0010]

In the present invention, the reason why the steel composition and manufacturing conditions are limited as described above will be explained in detail. The reasons for limiting the steel composition are as follows. The upper limit of 0.10% for C is limited because if the amount exceeds C, the time required for decarburization becomes long, which is economically disadvantageous. Si has a lower limit of 2.5% in order to improve iron loss, but if it is too much, it is easily cracked during cold rolling and working becomes difficult, so the upper limit is made 7.0%.

Further, in order to produce a grain-oriented electrical steel sheet, it is preferable to add the following component elements as usual inhibitor components. When using MnS as an inhibitor, Mn and S are added. In order to obtain an appropriate dispersed state of MnS, Mn is preferably 0.02 to 0.15%. S is an element necessary for forming MnS, (Mn.Fe) S, and is 0.00 to obtain an appropriate dispersed state.
1 to 0.05% is desirable. Furthermore, when using AlN as an inhibitor, acid-soluble Al and N are added. The acid-soluble Al is preferably 0.01 to 0.04% in order to obtain a proper dispersed state of AlN. N is also preferably 0.003 to 0.02% in order to obtain AlN. Other, C
At least one of u, Sn, Sb, Cr and Bi may be added in an amount of 1.0% or less for the purpose of strengthening the inhibitor.

Next, the above molten steel is subjected to a conventional ingot casting method or continuous casting method and hot rolling to obtain a strip having an intermediate thickness. At this time, the strip casting method can also be applied to the present invention. Further, when a nitride is required as an inhibitor, it is necessary to use 950 to 12 because of precipitation of AlN or the like.
It is desirable to perform intermediate annealing for 30 seconds to 30 minutes at 00 ° C. Next, obtain a final product thickness strips by rolling once. The cold rolling is carried out at a rolling reduction of more than 89% in order to obtain fine secondary recrystallized grains having a (110) <001> orientation of several mm or less with a high degree of integration in the rolling direction. Lower limit 89% more than is,
This is because the Goss nuclei having a (110) <001> orientation with a high degree of integration in the rolling direction cannot be obtained below this.

As the cold rolling method at this time, the final plate thickness is obtained by passing through each plate thickness step by a plurality of passes during the cold rolling, but in order to improve the magnetic properties, at least one or more of them is performed. The steel plate may be subjected to a thermal effect of holding it in a temperature range of 100 ° C. or higher for a time of 1 minute or longer in the middle of the plate thickness step. As described above, the strip rolled to the final product thickness is subjected to heat treatment. First, the strip is rapidly heated to a temperature above 700 ° C. at a heating rate of 290 ° C./sec or higher. At this time, the lower limit of the heating rate of 290 ° C./sec is (110) <00 after the primary recrystallization, which is the nucleus of the secondary recrystallization below this.
1> The number of oriented grains is reduced, and fine secondary recrystallized grains cannot be obtained, so this is limited. Further, the lower limit of more than 700 ° C. is limited because recrystallization does not start below this. It should be noted that this rapid heat treatment is preferably carried out in a reducing atmosphere or a non-oxidizing atmosphere as much as possible because of problems such as film formation.

The rapid heat treatment described above can be carried out before the subsequent decarburization annealing, or can be incorporated into the decarburization annealing step as a heating step of the decarburizing annealing, but the latter method is preferable. Is desirable because there are few steps. After that, decarburization annealing is performed in a wet hydrogen atmosphere. At this time, carbon must be reduced to 0.005% or less so as not to deteriorate the magnetic characteristics of the product. Here, the slab heating temperature in hot rolling is low,
When only AlN is used as an inhibitor, nitriding treatment may be added in an ammonia atmosphere. Further, by applying an annealing separator such as MgO and performing secondary annealing and finishing annealing at 1100 ° C. or higher for purification, a film such as forsterite formed on the surface of the steel sheet with a diameter of 5
Fine secondary recrystallized grains of mm or less are obtained.

On the other hand, a unidirectional electrical steel sheet having extremely low iron loss characteristics can be manufactured by further applying an insulating film on a film such as forsterite.
The above-mentioned magnetic characteristics maintain a low iron loss that does not change even after the subsequent strain relief annealing. In addition, in the obtained product,
Further, in order to improve the iron loss, the unidirectional electrical steel sheet can be subjected to a treatment for subdividing the magnetic domains.

[0016]

Examples (Example 1) Including the chemical components shown in Table 1, 3.2 mm, 2.8 mm, 2.
For hot-rolled sheet hot-rolled to a thickness of 0 mm 3 conditions 11
Annealing was performed at 00 ° C for 1 minute. Then, cold rolling was performed to a final plate thickness of 0.27 mm. Further, when the obtained strip is decarburized and annealed, it is heated at 20 ° C./sec.
It is heated to 840 ° C. under three conditions of 85 ° C./sec and 300 ° C./sec, then decarburized and annealed in wet hydrogen at the same uniform temperature of 840 ° C., and after applying MgO powder, 1200 ° C. for 10 hours, High temperature annealing was performed in a hydrogen gas atmosphere. Excess MgO of the obtained steel sheet was removed, and an insulating film was applied on the formed forsterite film. Table 2 shows the magnetic properties of the obtained products. According to the present invention, a grain-oriented electrical steel sheet having excellent iron loss characteristics is obtained.

[0017]

[Table 1]

[0018]

[Table 2]

(Example 2) Molten steel containing the chemical composition shown in Table 3 was cast, and after heating the slab, hot rolling was performed to obtain a 2.4 mm hot rolled steel sheet. This is annealed at 1100 ° C. for 5 minutes and further pickled,
It was cold rolled to a thickness of 0.22 mm. The cold rolling reduction ratio at this time is 90.8%. Rolled steel sheet is heated to 845 ° C at a heating rate of 290 ° C / sec with two pairs of direct current heating rolls.
Heated up. After that, decarburization annealing was performed in wet hydrogen at the same uniform temperature of 845 ° C. Next, after applying MgO powder, 1
High temperature annealing was performed at 200 ° C. for 10 hours in a hydrogen gas atmosphere. Excess MgO of the obtained steel sheet was removed, and an insulating film was applied on the formed forsterite film. The magnetic properties of the product thus obtained are B ₈ = 1.94T,
A _grain -oriented electrical steel sheet having a low iron loss of W _17/50 = 0.76 w / kg was obtained.

[0020]

[Table 3]

[0021]

According to the present invention, it is possible to produce a grain-oriented electrical steel sheet having good iron loss characteristics, and therefore, the industrial contribution is extremely large.

[Brief description of drawings]

FIG. 1 is a chart showing the relationship between cold rolling reduction and iron loss.

2 (a) and 2 (b) are grain sizes of 5 mm obtained by the cold rolling method.
It is a pole figure which shows the change of the following secondary recrystallized grain orientations.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tadao Kiriyama 1 Fuji-machi, Hirohata-ku, Himeji-shi Nippon Steel Corporation Hirohata Works (56) Reference JP-A-4-160114 (JP, A) HEI 2-77524 (JP, A) JP-A-3-72026 (JP, A) JP-A-3-219021 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 8 / 12 C21D 9/46 501 C22C 38/00-38/60 H01F 1/16

Claims (2)

(57) [Claims] 1. By weight, C: 0.10% or less, Si: 2.5 to 7.0%, Mn: 0.02 to 0.15%, S: 0.001 to 0.05%, acid Soluble Al: 0.01 to 0.04%, N: 0.003 to 0.02%, 1.0% or less of at least one of Cu, Sn, Sb, Cr and Bi, and the balance is Fe and unavoidable. Unidirectional electrical steel made of static impurities is annealed to hot rolled annealed steel, cold rolled once, decarburized annealed, and finally finished annealed to produce unidirectional electrical steel. In the method, in the cold rolling, the cold rolling reduction is more than 89% and the final strip thickness is 0.2.
A secondary reconstitution with a grain size of 5 mm or less , characterized in that the strip rolled to 7 mm or less is heat-treated to a temperature of more than 700 ° C. at a heating rate of 290 ° C./sec or more immediately before decarburization annealing.
A method for producing a grain-oriented electrical steel sheet having extremely low iron loss having crystal grains . 2. The method according to claim 1, wherein the rapid heat treatment is performed as a heating step of decarburization annealing.