JPH0762437A - Production of grain oriented silicon steel sheet having extremely low iron loss - Google Patents

Abstract

PURPOSE:To provide a good iron loss characteristic by applying an intermediate heating treatment to a strip during finish cold-rolling to a silicon steel having a fixed composition and further, executing rapid heating treatment just before decarburization-annealing. CONSTITUTION:Hot-rolled sheet annealing is executed to the hot-rolled grain oriented silicon steel sheet composed of <=0.10wt.% C, 2.5-7.0% Si and the ordinary inhibitor components and the balance Fe with inevitable impurities. Cold- rollings containing the finish cold-rolling in >=60% the finish rolling reduction ratio at one time or two or more times inserting the intermediate annealing are executed, and after the decarburization-annealing, the last finishing annealing is executed to make the grain oriented silicon steel sheet. In this manufacturing method, the heat treatment held at least at one or more times at >=100 deg.C for >=1mm is given to the steel sheet in the intermediate stage of the finish-rolling and the rapid heating treatment is executed to >=700 deg.C at >=50 deg.C/sec heating speed just before the decarburization-annealing to the strip rolled to the finish thickness. By this method, the silicon steel sheet having extremely low iron loss can be obtd.

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. For example, as disclosed in Japanese Examined Patent Publication No. 54-13846, by imparting a thermal effect of maintaining a steel plate temperature during cold rolling in a temperature range of 50 to 350 ° C. for 1 minute or more, the magnetic properties A very good grain-oriented electrical steel sheet can be obtained. However, although this manufacturing method can reduce iron loss to some extent, the secondary recrystallization macro grain size is still 10 mm.
The order was large, and the eddy current loss, which is a factor affecting iron loss, could not be reduced, and a good iron loss value was not obtained. In order to improve this, the magnetic domain is subdivided by a method of subjecting a steel sheet disclosed in JP-B-57-2252 to a laser treatment, and a method of applying a mechanical strain to the steel sheet in JP-B-58-2569. A variety of methods for implementing the above are disclosed.

Further, in Japanese Patent Application Laid-Open No. 1-290716, a cold rolled steel sheet is subjected to an ultra-rapid annealing treatment at a heating rate of 100 ° C./sec or more to a temperature of 657 ° C. or more,
The strips were decarbonized and subjected to a final high temperature anneal to undergo secondary growth, which improved secondary particles of reduced size and stress relief anneal persisted without significant change. A method characterized by having iron loss is disclosed. However, by simply refining the secondary recrystallized grain size by this manufacturing method, when the insulating film is applied on the forsterite film,
It was difficult to obtain iron loss characteristics comparable to conventional magnetic domain subdivision.

[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-mentioned problems, C: 0.10% or less by weight, Si: 2.5 to 7.0% and usual inhibitor components were obtained. The rest of which is hot-rolled unidirectional electrical steel consisting of Fe and unavoidable impurities and is subjected to hot-rolled sheet annealing, including final cold rolling with a final reduction of 60% or more, and one or two intermediate annealings. In a method for producing a unidirectional electrical steel sheet by performing cold rolling at least once and then performing decarburization annealing after decarburization annealing, in the final cold rolling, at least one or more intermediate plate thickness steps The steel sheet is subjected to a heat treatment of holding it in a temperature range of 100 ° C. or more for 1 minute or more, and the strip rolled to the final plate thickness is heated to 50 ° C./sec or more and 700 ° C. or more immediately before decarburization annealing. Heat treatment to temperature More it was found that the production method of the grain-oriented electrical steel sheet having 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 performing heat treatment at a predetermined temperature in the plate thickness stage during cold rolling, interstitial solid solution elements such as solid solution C are fixed to the dislocations formed by cold rolling, and the deformation mechanism is changed to form a cold rolled texture. By changing the temperature, and immediately before decarburizing and annealing, a heat treatment is performed at a heating rate of 50 ° C./sec or more to a temperature of 700 ° C. or more, so that the (110) <001> orientation is aligned with the rolling direction to form a fine grain of two mm or less. It was found that the next recrystallized grains were 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 a (100) pole figure of fine secondary recrystallized grains having a grain size of 5 mm or less. (A) is a conventional manufacturing method. When decarburizing and annealing a cold-rolled strip, the temperature is raised at a heating rate of 300 ° C./sec, and fine secondary recrystallization is performed when secondary recrystallization is performed. The orientation of the crystal grains, (b), in the example of the present invention, heat treatment was carried out at 230 ° C. for 10 minutes during cold rolling, and after cold rolling to the final product, the temperature was raised by decarburizing annealing at 300 ° C./sec. This is the orientation of fine secondary recrystallized grains when secondary recrystallization is performed at a heating rate. According to the present invention, even fine secondary recrystallized grains are aligned in the rolling direction (110) <00.
1> Direction is obtained. 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. To obtain a proper dispersed state of acid-soluble Al and AlN, 0.01 to 0.04% is desirable. 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 deposit 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, a strip of the final product thickness is obtained by rolling once or twice or more including intermediate annealing. 2 including intermediate annealing
When rolling more than once, the first rolling is a reduction ratio of 5 to 5
For 0%, the intermediate annealing is preferably performed at 950 to 1200 ° C. for 30 seconds to 30 minutes. Next, a final rolling reduction of 60% or more is required in order to obtain a product with a high degree of goss accumulation. The lower limit of 60% is because the necessary Goss nucleus cannot be obtained below this.

As the cold rolling method at this time, in order to improve the magnetic properties, the final sheet thickness is obtained by passing through each sheet thickness step by a plurality of passes during the cold rolling. In the plate thickness stage, the steel plate is given a thermal effect of holding it in a temperature range of 100 ° C. or higher for a time of 1 minute or longer. When the lower limit of the temperature is 100 ° C. and the lower limit of the soaking time is 1 minute, the solid solution C and the like are not fixed to the dislocations below this and the subsequent primary recrystallization texture is changed, and (110) <001> is aligned in the rolling direction. Since fine secondary recrystallization is hard to develop sufficiently, it was limited.

As described above, the strip rolled to the final product thickness is heat-treated. First, the strip is rapidly heated to a temperature of 700 ° C. or higher at a heating rate of 50 ° C./sec or higher. At this time, the lower limit of the heating rate of 50 ° C./sec is (110) <00 after the primary recrystallization, which becomes 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. The lower limit of 700 ° C. is limited because recrystallization does not start below this temperature. 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 performed before the decarburization annealing to be performed next, or can be incorporated into the decarburization annealing step as a heating step of the decarburization annealing, but the latter is a process. It is desirable because it reduces the number. 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 of hot rolling is low,
When only N 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, fine secondary recrystallized grains with a film such as forsterite formed on the surface of the steel sheet are obtained. .

On the other hand, a unidirectional electrical steel sheet having extremely low iron loss characteristics is manufactured by further applying an insulating coating on the coating of forsterite or the like.
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.

[0017]

【Example】

(Example 1) A hot rolled sheet containing the chemical components shown in Table 1 and hot rolled to a thickness of 2.3 mm was annealed at 1100 ° C for 1 minute. Then, during rolling, the steel sheet was annealed at a temperature of 200 ° C. for 2 minutes and rolled, and rolled at a normal temperature of 30 ° C. by two kinds of cold rolling methods to a final sheet thickness of 0.27 mm. . Further, when the obtained strip is decarburized and annealed, it is heated at 10 ° C./sec, 85 ° C./sec, 300 ° C./sec.
After heating for 3 seconds, decarburization annealing was performed in wet hydrogen, MgO powder was applied, and then high temperature annealing was performed at 1200 ° 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. 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.

[0018]

[Table 1]

[0019]

[Table 2]

(Example 2) Molten steel containing the chemical composition shown in Table 3 was cast, heated to a slab, and then hot-rolled to 2.3 mm.
The hot-rolled steel sheet of was obtained. This was annealed at 1100 ° C. for 5 minutes, further pickled, then annealed at a steel plate temperature of 250 ° C. for 5 minutes during rolling, and cold-rolled to a thickness of 0.22 mm. The rolled steel sheet was heated to 845 ° C at a heating rate of 290 ° C / sec with two pairs of direct-current heating rolls. After that, decarburization annealing was performed in wet hydrogen at the same uniform temperature of 845 ° C. Next, after applying MgO powder, high temperature annealing was performed at 1200 ° 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, W _17/50 = 0.7
A grain-oriented electrical steel sheet having a low iron loss of 6 w / kg was obtained.

[0021]

[Table 3]

(Example 3) A molten steel containing the composition shown in Table 3 was cast, heated to a slab, and then hot-rolled to 2.3 mm.
The hot-rolled steel sheet of was obtained. This was annealed at 1000 ° C. for 4 minutes and rolled to 1.60 mm. This is annealed at 1120 ° C. for 5 minutes, further pickled, and then 250 during cold rolling.
The steel sheet was annealed at a steel sheet temperature of 6 ° C. for 6 minutes, cold-rolled,
22mm thick. The rolled steel sheet was heated to 840 ° C. at a heating rate of 300 ° C./sec with two pairs of direct passage heating rolls. After that, decarburization annealing was performed in the same uniform temperature of 840 ° C. and wet hydrogen. Next, after applying MgO powder, 1200
High temperature annealing was performed in a hydrogen gas atmosphere at 10 ° C. for 10 hours.
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 = 1.93T, W
_{A grain} -oriented electrical steel sheet having a low iron loss of _17/50 = 0.75 w / kg was obtained.

[0023]

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]

1 (a) and 1 (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 the front page (72) Inventor Haruo Fukasawa 1 Fuji-machi, Hirohata-ku, Himeji City Nippon Steel Corporation Hirohata Works

Claims (2)

[Claims] 1. C: 0.10% or less by weight, Si: 2.
5 to 7.0% as well as the usual inhibitor components,
The balance is a hot-rolled unidirectional electrical steel sheet consisting of Fe and unavoidable impurities that is subjected to hot-rolled sheet annealing, and one-time or intermediate annealing including final cold rolling with a final reduction of 60% or more.
In a method for producing a unidirectional electrical steel sheet by performing cold rolling at least once and then performing decarburization annealing after decarburization annealing, in the final cold rolling, at least one or more intermediate plate thickness steps 1 on steel plate in the temperature range of 100 ℃ or more
It is characterized in that a heat treatment for holding for a time of not less than a minute is given, and that a strip rolled to a final plate thickness is heated to a temperature of 700 ° C. or more at a heating rate of 50 ° C./sec or more immediately before decarburization annealing. A method for producing a grain-oriented electrical steel sheet having low iron loss. 2. The method according to claim 1, wherein the rapid heat treatment is performed as a heating step of decarburization annealing.