JP2679928B2 - Manufacturing method of grain-oriented electrical steel sheet with extremely low iron loss - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing 2.5-7.0% S
Since i has a high degree of integration in the (110) [001] orientation of crystal grains and the crystal grain size is finer than ever before,
The present invention provides a method for manufacturing a grain-oriented electrical steel sheet having extremely low iron loss.

[0002]

2. Description of the Related Art Generally, the magnetic properties of a grain-oriented electrical steel sheet are evaluated based on both iron loss properties and excitation properties. Increasing the excitation characteristics is effective in reducing the size of equipment that increases the design magnetic flux density. On the other hand, reducing the iron loss characteristics is effective in that when it is used as an electric device, heat loss is reduced and power consumption can be saved. 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, many studies have been made particularly on this aspect, and various manufacturing techniques have been developed. As a result, there are three typical manufacturing techniques for the typical industrially produced grain-oriented electrical steel sheets.

The first technique is to cause MnS disclosed in JP-B-30-3651 to function as an inhibitor.
There is a manufacturing technology based on the rolling process. This manufacturing method has a relatively good iron loss due to a small particle size of the secondary recrystallization, but has a problem that a high magnetic flux density cannot be obtained. On the other hand, in order to obtain a high magnetic flux density, Japanese Patent Publication No. 40-15644 was disclosed as a second technique. This is a manufacturing technique in which AlN + MnS is made to function as an inhibitor and the rolling reduction in the final cold rolling step is under high pressure exceeding 80%. By this method, the secondary recrystallized grains (1
10) The degree of integration in the [001] direction is high, and B ₈ is 1.87.
A grain-oriented electrical steel sheet having a high magnetic flux density of 0 (T) or more can be obtained. Furthermore, as a third technique, Japanese Patent Publication No. 51-13
A manufacturing technique has been developed in which the MnS or MnSe + Sb disclosed in No. 469 functions as an inhibitor by a double cold rolling process.

However, in the manufacturing method according to the second technique, even if a grain-oriented electrical steel sheet having a high magnetic flux density is obtained, a large secondary recrystallized grain size of the order of 10 mm has been obtained. By the way, generally, iron loss is roughly divided into hysteresis loss and eddy current loss. Physical factors that affect the hysteresis loss include the purity of the material and internal strain in addition to the above-described crystal orientation. In addition, as physical factors that affect the eddy current loss, electrical resistance of the steel sheet (amount of components such as Si), sheet thickness,
There are magnetic domain size (grain size) and tension applied to the steel sheet. In normal grain-oriented electrical steel sheets, the eddy current loss is 3/3 of the total iron loss.
Since it occupies 4 or more, it is more effective to reduce the eddy current loss than the hysteresis loss in reducing the total iron loss.

Therefore, in the manufacturing method according to the second technique, even if a grain-oriented electrical steel sheet having a high magnetic flux density of B ₈ of 1.870 (T) or more is obtained, the secondary recrystallized grain size is 10 mm. Since it is large on the order, the magnetic domain width that affects the eddy current loss is large, and the iron loss is also large accordingly. Therefore, in order to improve iron loss, a method of subjecting a steel sheet disclosed in JP-B-57-2252 to laser treatment, and a method of applying mechanical strain to the steel sheet disclosed in JP-B-58-2569, etc. , Various methods of subdividing magnetic domains have been disclosed.

Further, in order to solve the above problems, there is provided a method for producing a grain-oriented electrical steel sheet having a fine secondary recrystallized grain size to reduce a magnetic domain width and an iron loss lower than conventional ones. What is done is disclosed. For example, in Japanese Patent Laid-Open No. 1-290716, a cold rolled steel sheet is subjected to a super rapid annealing treatment at a heating rate of 100 ° C./sec or more to a temperature of 675 ° C. or more, the strip is decarbonized, and finally subjected to a high temperature annealing treatment. A secondary growth of the strip, whereby the strip has reduced size secondary particles and improved core loss that persists without significant change after stress relief anneal treatment. Has been done. However, although this method can obtain secondary recrystallized grains that are small to some extent, it is intended only for rapid heat treatment, and this production method does not provide a very good iron loss value. found.

[0007]

The present invention provides a method for obtaining a grain-oriented electrical steel sheet having an extremely low iron loss by having a finer secondary recrystallized grain size than that of the above-mentioned method. The feature is in rapid heating and introduction of minute strain during the heating.

[0008]

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. A strip rolled to the final product thickness, containing the balance of Fe and unavoidable impurities, at 80 ° C. /
Rapid heating to a temperature of 700 ° C or higher at a heating rate of 2 seconds or more,
In addition, rapid heating for introducing a minute strain of 0.1% or more of nominal strain during the rapid heating and a process for introducing a minute strain are performed, and the obtained strip is decarburized and annealed, and finally finished annealed. It was found that by doing so, a grain-oriented electrical steel sheet having an extremely low iron loss can be obtained.

Furthermore, the rapid heating of the strip and the process of introducing the slight strain have a very low iron loss due to the method of rapidly heating the roll by supplying electricity between the rolls and introducing the slight strain in the roll on the heated side. It is possible to obtain unidirectional electrical steel sheets. Furthermore, they have found that even if the rapid heating and the treatment for introducing a slight strain are carried out as a heating step of decarburization annealing, a grain-oriented electrical steel sheet having an extremely low iron loss can be obtained.

Hereinafter, the present invention will be described in detail. The grain-oriented 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, coarsening of primary recrystallized grains is suppressed, and only recrystallized grains of the (110) <001> orientation are selectively grown in a certain temperature range.
That is, it is necessary to make a base material for secondary recrystallization. For that purpose, fine inclusions in the material serve as inhibitors (inhibitors) for the growth of primary recrystallized grains,
Must be evenly dispersed. Further, it is said that the optimum precipitation size at this time is on the order of 100 Å.

The effect of rapid heating is described in JP-A-1-29.
As described in No. 0716, after the rapid heating, the texture after the primary recrystallization (1
10) The number of <001> oriented grains increases, which serves as a nucleus for secondary recrystallization, and secondary recrystallized grains that are small to some extent are obtained. The mechanism of the ultra-rapid heat treatment in the manufacturing method of the above patent includes two changes, a change in primary recrystallization composition before the final decarbonization annealing step and a change in primary recrystallization structure before the high temperature annealing step, and Stated. However, the present inventors have found out that the control of the primary recrystallization structure, that is, the precipitation control of the inhibitor (inhibitor) for the growth of primary recrystallized grains is not sufficient with this manufacturing method alone.

Therefore, as a result of repeated studies on the control method of the precipitation size in the rapid heating, the optimum precipitation size in the high temperature range was obtained by applying a slight strain of 0.1% or more of the nominal strain in the rapid heating stage. It was found that the precipitates of No.1 were strain-induced precipitation, which made it possible to obtain a finer secondary recrystallized grain size than ever before and to obtain a grain-oriented electrical steel sheet with extremely low iron loss. .

[0013]

Next, the reason why the steel composition and the manufacturing conditions are limited as described above in the present invention will be described in detail. The reasons for limiting the steel components are as follows. The upper limit of 0.10% for C is limited because if it is more than this, the time required for decarburization becomes longer and it is economically disadvantageous. The lower limit of Si is set to 2.5% in order to improve iron loss, but if it is too large, it is likely to break during cold rolling and processing becomes difficult, so the upper limit is set to 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 MnS is used as an inhibitor, Mn and S are added. Mn is desirably 0.02 to 0.15% in order to obtain an appropriate dispersion state of MnS. S is an element necessary for forming MnS and (Mn · Fe) S.
1-0.05% is desirable. Further, when AlN is used as an inhibitor, acid-soluble Al and N are added. In order to obtain an appropriate dispersion 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 a proper dispersion state of AlN. In addition, at least one of Cu, Sn, Sb, Cr and Bi may be added at 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, 950 to 120 is required for precipitation of AlN or the like.
It is desirable to perform intermediate annealing at 0 ° C. for 30 seconds to 30 minutes. Next, a strip of the final product thickness is obtained by rolling once or twice or more including intermediate annealing. The final rolling reduction at this time is 50% in order to obtain a product with a high degree of Goss accumulation.
% Or more is desirable. The lower limit of 50% is that the necessary Goss nucleus cannot be obtained below this.

As described above, the strip rolled to the final product thickness is subjected to rapid heating and a process for introducing a slight strain. First, the strip is rapidly heated to a temperature of 700 ° C. or more at a heating rate of 80 ° C./sec or more. Lower limit of heating rate at this time 80 ℃ /
The second is limited because the (110) <001> oriented grains after the primary recrystallization, which is the nucleus of the secondary recrystallization, is reduced below this, and fine secondary recrystallized grains cannot be obtained. Also, the lower limit 700
The temperature was limited to below 0 ° C because recrystallization did not start. Furthermore, during the rapid heating, a nominal strain of 0.1
Introduce a micro strain of at least%. The period of rapid heating refers to the period from the rapid heating start temperature to the completion temperature.

FIG. 1 shows the relationship between the strain introduced into the strip and the product iron loss characteristics obtained when the strip having a thickness of 0.22 mm is rapidly heated to 825 ° C. at a heating rate of 180 ° C./sec. A good iron loss value is obtained at 0.1% or more of the nominal strain. As a result, the lower limit of the nominal strain is 0.1%
Limited to. In addition, it is desirable to carry out the above rapid heating and minute strain introduction treatment in a reducing atmosphere or a non-oxidizing atmosphere as much as possible in view of problems such as film formation.

Further, the rapid heating and the process for introducing a slight strain can be performed by a method of energizing between rolls.
FIG. 2 shows a schematic diagram of one embodiment of the treatment method according to the present invention. Two pairs of upper and lower rolls sandwiching the strip are provided,
By energizing the strip S between the rolls R1 and R2, the strip S is rapidly heated to a temperature of 700 ° C. or more at a heating rate of 80 ° C./sec or more, and further heated by the roll R2 on the heated side to a rapid heating completion temperature. Nominal strain of 0.1 at point P
Introduce a micro strain of more than%. At this time, it is conceivable that the temperature of the strip may slightly drop due to heat removal from the roll.

From the problems of film formation and the like, it is desirable to carry out the above treatment in the apparatus box B in a reducing atmosphere as much as possible. It is also possible to improve the shape of the heated strip by introducing this slight strain. The rapid heating and the process for introducing the slight strain may be performed before the decarburization annealing to be performed next, or may be incorporated in the decarburization annealing step as a heating step of the decarburization annealing.

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 properties of the product. Here, when the slab heating temperature in hot rolling is low and only AlN is used as an inhibitor, nitriding treatment may be added in an ammonia atmosphere. Further, an annealing separator such as MgO is applied, and 1100 is used for secondary recrystallization and purification.
By performing finish annealing at a temperature of ℃ or more, a grain-oriented electrical steel sheet having extremely low iron loss characteristics can be manufactured. In order to further improve the iron loss of the obtained product, it is possible to subject the above-mentioned grain-oriented electrical steel sheet to a treatment for subdividing magnetic domains.

[0021]

【Example】

Example 1 A strip containing the chemical components shown in Table 1 and finally cold rolled to a thickness of 0.22 mm was heated under various conditions by a direct current heating device having a set of heating electrodes. At the same time, the tension was changed between the heating electrodes to introduce various strains. Table 2 shows the heating rate, the ultimate temperature, and the introduced strain at that time. After the above processing, it was cooled to room temperature in a reducing atmosphere.

Next, 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. Table 2 shows the secondary recrystallized grain size and magnetic properties of the obtained products. The magnetic property of the product is 0.1%
By introducing the above-mentioned minute strain, a finer secondary recrystallized grain size than before and a grain-oriented electrical steel sheet having extremely low iron loss have been obtained.

[0023]

[Table 1]

[0024]

[Table 2]

Example 2 Including the chemical components shown in Table 1,
The strip finally cold rolled to a thickness of 0.27 mm was heated to 840 ° C. at a heating rate of 250 ° C./sec by a direct current heating device. At the same time, tension is applied between the heating electrodes to 0.25
% Strain was introduced. The strip was subsequently decarburized annealed in wet hydrogen at a uniform temperature of 840 ° C.

After this, MgO powder was applied and then 1200
High temperature annealing was performed in a hydrogen gas atmosphere at 10 ° C. for 10 hours.
The average secondary recrystallized grain size of the product thus obtained was 3.
It was 2 mm. The magnetic characteristics are B ₈ = 1.94T,
A _grain -oriented electrical steel sheet having an extremely low iron loss of W _17/50 = 0.89 (W / kg) was obtained.

(Example 3) Molten steel containing the chemical components shown in Table 3 was cast, heated to a slab, and then hot-rolled to 2.3 mm.
Was obtained. This was annealed at 1100 ° C. for 5 minutes, further pickled, and then cold rolled to a thickness of 0.27 mm. The rolled steel sheet was heated to 835 ° C. at a temperature rising rate of 280 ° C./sec by the direct current heating roll shown in FIG. 2, and 0.15% strain was introduced immediately after reaching the heating by the exit roll. After the above processing, it was cooled to room temperature in a reducing atmosphere.

Next, 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. The product thus obtained had an average secondary recrystallized grain size of 3.2 mm. In addition, the magnetic properties of the _grain -oriented electrical steel sheet were B ₈ = 1.93T and W _17/50 = 0.88 (W / kg), which had extremely low iron loss.

[0029]

[Table 3]

(Example 4) Molten steel containing the chemical composition shown in Table 4 was cast, heated to a slab, and then hot-rolled to 2.3 mm.
Was obtained. This was annealed at 1100 ° C. for 5 minutes, further pickled, and then cold rolled to a thickness of 0.22 mm. The rolled steel plate is directly heated by an electric heating roll. 2
It was heated to 845 ° C. at a heating rate of 90 ° C./second, and then 0.13% strain was introduced by the exit roll. Although the strip heated at this time showed a temperature drop of about 160 ° C due to the heat removal from the outlet roll, it was immediately heated to a uniform temperature of 845 ° C at a heating rate of 20 ° C / sec, and the strip was heated in wet hydrogen. Decarburized and annealed.

Next, after applying MgO powder, high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. The average secondary recrystallized grain size of the product thus obtained is 3.6 mm.
Met. The magnetic characteristics are B ₈ = 1.94T, W
_{A grain} -oriented electrical steel sheet having an extremely low iron loss of _17/50 = 0.81 (W / kg) was obtained.

[0032]

[Table 4]

(Example 5) Molten steel containing the composition shown in Table 5 was cast, heated to a slab, and hot-rolled to 2.3 mm.
Was obtained. This was annealed at 1100 ° C. for 5 minutes, further pickled, and then cold rolled to a thickness of 0.22 mm. The rolled steel sheet was heated to 851 ° C. at a heating rate of 250 ° C./sec with two pairs of direct-current heating rolls, and a strain of 0.12% was introduced by the exit side roll. Although the strip heated at this time showed a temperature drop of about 150 ° C due to heat removal from the outlet roll, it was immediately heated to a uniform temperature of 850 ° C at a heating rate of 20 ° C / sec, and the strip was heated in wet hydrogen. Decarburized and annealed.

Further, the same steel sheet was heated by induction heating to 746 ° C. at a heating rate of 250 ° C./sec, no distortion was introduced as it was, and further heated to 850 ° C. at 15 ° C./sec and decarburized and annealed in wet hydrogen. . Next, after applying MgO powder, 1
High temperature annealing was performed at 200 ° C. for 10 hours in a hydrogen gas atmosphere. Table 6 shows the magnetic properties of the obtained products. The magnetism of the product was satisfactory with the current-carrying roll method.

[0035]

[Table 5]

[0036]

[Table 6]

(Example 6) Molten steel containing the composition shown in Table 7 was cast, heated to a slab, and then hot-rolled to 2.3 mm.
Was obtained. Next, it was annealed at 1100 ° C. for 5 minutes, further pickled, and then cold rolled to a thickness of 0.22 mm. The rolled steel plate is directly heated by an electric heating roll 29
It was heated to 846 ° C. at a heating rate of 0 ° C./second, and 0.21% strain was introduced by the exit roll. Note that the strip heated at this time showed a temperature drop of about 80 ° C due to the removal of heat from the outlet roll, but it was immediately heated to a uniform temperature of 850 ° C at a heating rate of 20 ° C / sec. Decarburized and annealed.

Next, a nitriding treatment is carried out in an ammonia atmosphere, MgO powder is applied, and then the temperature is set to 1200 ° C. for 10 hours.
High temperature annealing was performed in a hydrogen gas atmosphere. The product thus obtained had an average secondary recrystallized grain size of 3.6 mm.
The magnetic characteristics are B ₈ = 1.91T, W _17/50 = 0.
A grain-oriented electrical steel sheet having an extremely low iron loss of 83 (W / kg) was obtained.

[0039]

[Table 7]

[0040]

EFFECTS OF THE INVENTION According to the present invention, a unidirectional electrical steel sheet having secondary recrystallization smaller than ever, high magnetic flux density, and extremely low iron loss characteristics is manufactured by rapid heating and a process for introducing a slight strain. Therefore, the industrial contribution is extremely large.

[Brief description of the drawings]

FIG. 1 is a chart showing the relationship between strain introduced during rapid heating and iron loss characteristics.

FIG. 2 is a schematic view of an embodiment of an electric roll heating method according to the present invention.

Claims (3)

(57) [Claims] 1. C: 0.10% or less by weight, Si: 2.
5 to 7.0% as well as the usual inhibitor components,
A strip rolled to the final product thickness, the balance consisting of Fe and inevitable impurities, is rapidly heated to a temperature of 700 ° C. or more at a heating rate of 80 ° C./sec or more, and a nominal strain of 0 is obtained during the rapid heating. . One-way electromagnetic wave with extremely low iron loss, characterized by performing rapid heating that introduces a minute strain of 1% or more and minute strain introduction treatment, decarburizing annealing the resulting strip, and performing final finishing annealing. Steel plate manufacturing method. 2. The rapid heating and microstrain introduction treatment of the strip is characterized in that the strip is rapidly heated by energizing between the rolls, and the microstrain is introduced by the roll on the side where the strip is heated. The method described in 1. 3. The method according to claim 1, wherein the rapid heating and the treatment for introducing a slight strain are performed as a heating step of decarburization annealing.