JP2679927B2 - 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 sheet. The first technology is Japanese Examined Japanese Patent Publication 30-3651.
There is a manufacturing technique disclosed in the above-mentioned publication in which MnS functions as an inhibitor by a two-time cold 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, 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. Furthermore, as a third technology, Japanese Patent Publication Sho 5
MnS or MnSe, disclosed in 1-143469.
A manufacturing technique has been developed in which + Sb functions as an inhibitor by a double cold rolling process.

In general, iron loss is roughly classified 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, the degree of integration of the (110) [001] orientation of the secondary crystal grains is high, and B ₈ has a high magnetic flux density of 1.870 (T) or more. Even if the grain-oriented electrical steel sheet was obtained, the secondary recrystallized grain size was as large as 10 mm, so that the magnetic domain width that affected the eddy current loss was large. In order to improve this, a method of subjecting a steel sheet disclosed in JP-B-57-2252 to a laser treatment, and a method of applying mechanical strain to the steel sheet disclosed in JP-B-58-2569, etc. Various methods have been disclosed for subdividing.

[0006] Therefore, it is disclosed that a method for producing a grain-oriented electrical steel sheet having a finer secondary recrystallized grain size and having a lower iron loss than the conventional one is provided. 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 it is true that secondary recrystallized grains that are small to some extent can be obtained, this method is intended to treat only rapid heating, and it has been found that a very good iron loss value cannot be obtained.

[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 that it is rapidly heated and then immediately followed by cooling.

[0008]

SUMMARY OF THE INVENTION The present invention provides a C:
A strip rolled from a molten steel containing 0.10% or less, Si: 2.5 to 7.0% and a usual inhibitor component, with the balance Fe and unavoidable impurities as a starting material to a final product thickness, 800 80 to above ℃
After heating at a heating rate of ℃ / sec or more and reaching the maximum temperature, 0.
Within 1 second, a cooling treatment at a cooling rate of 50 ° C./second or more to a temperature range of less than 800 ° C. is performed, and the obtained strip is subjected to decarburization annealing and final finishing annealing to obtain an extremely low iron loss. It has been found that a unidirectional electrical steel sheet can be obtained. Furthermore, the method of rapid heating and cooling of the strip is such that it is rapidly heated by energizing between the rolls, and cooling is performed by the roll on the heated side, so that a grain-oriented electrical steel sheet with extremely low iron loss is obtained. I found that I could be.

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 can be obtained. Furthermore, the mechanism achieved in the manufacturing method of the above patent includes two changes, a change in the primary recrystallization composition before the final decarbonization annealing step and a change in the primary recrystallization structure before the high temperature annealing treatment step. However, it has been found that the control of the primary recrystallized structure is insufficient only by this production method.

Therefore, as a result of various studies on the cause of obtaining finer secondary recrystallized grains, the temperature range of 800 ° C. or higher was examined.
After heating at a heating rate of ℃ / sec or more and reaching the maximum temperature, 0.
Cooling to a temperature range of less than 800 ° C at a cooling rate of 50 ° C / sec or more by a roll heated on the side within 1 second prevents precipitates from coarsening in the high temperature range, making it optimal for 100 angstrom order It has been found that a large precipitation size can be maintained, which makes it possible to obtain a small secondary recrystallized grain size, which is unprecedented, and to obtain a grain-oriented electrical steel sheet having extremely low iron loss.

[0012]

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-mentioned molten steel is subjected to a usual ingot casting method or a continuous casting method, and hot-rolled 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 required. The lower limit of 50% is limited because the required Goss nucleus cannot be obtained below this range.

The strip thus rolled to the final product thickness is subjected to a heat treatment in a temperature range of 800 ° C. or higher at a heating rate of 80 ° C./sec or higher. If the lower limit of the heating rate at this time is 80 ° C./second, the (110) <001> oriented grains after the primary recrystallization, which is the nucleus of the secondary recrystallization, are reduced below this, and the fine secondary recrystallized grains are I can't get it, so I limited it. Further, the lower limit of 800 ° C. is limited because recrystallization does not start below this temperature. Furthermore, in order to prevent coarsening of fine precipitates in the heated ultimate temperature range, 0.1
Within a second, it is cooled to a temperature range of less than 800 ° C. at a cooling rate of 50 ° C./second or more. The upper limit value of 0.1 second of the soaking time after reaching the maximum temperature is limited because the precipitates become coarser if the soaking time is longer than this. If the upper limit of the cooling temperature range is less than 800 ° C,
If it exceeds the limit, it will be greatly deviated from the precipitation nose, so it was limited.

FIG. 1 shows that a strip having a thickness of 0.22 mm was heated to 825 ° C. at a heating rate of 180 ° C./sec and then heated to 650 ° C.
The relationship between the cooling rate up to and the iron loss characteristics of the obtained product is shown. A good iron loss value is obtained when cooling is performed at a cooling rate of 50 ° C./sec or more. Note that it is desirable to carry out the above treatment in a reducing atmosphere as much as possible in view of problems after the film formation.

Further, as one of the above rapid heating and cooling treatments, there is a method of energizing between rolls. FIG. 2 shows a schematic diagram of one embodiment of the present invention. Two pairs of upper and lower rolls sandwiching the strip are provided, and the strip S between the rolls R1 and R2 is energized, so that the strip S is moved to 8
By heating to a temperature range of 00 ° C or higher at a heating rate of 80 ° C / sec or higher, and further cooling at point P by the roll R2 on the heated side, heating is performed within 0.1 seconds after reaching the maximum temperature. By the roll on the raised side, cooling is performed at a cooling rate of 50 ° C./sec or more to a temperature range of less than 800 ° C.

From the problems of film formation and the like, the above-mentioned treatment is preferably carried out 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 distortion.

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 may be performed in an ammonia atmosphere. Furthermore, by applying an annealing separator such as MgO and performing secondary annealing and finishing annealing at 1100 ° C. or higher for purification, a unidirectional electrical steel sheet having extremely low iron loss characteristics is 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.

[0020]

【Example】

(Example 1) A molten steel containing the component composition shown in Table 1 was cast,
After slab heating, hot rolling was performed to obtain a 2.3 mm hot-rolled steel sheet. 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 sheet was heated under various conditions by a direct current heating device having a set of heating electrodes. Further, the steel sheet immediately after heating was subjected to various soaking times and cooling conditions. Table 2 shows the heating rate and the ultimate temperature at that time, and the cooling conditions after heating.

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 product. The magnetic properties of the product are 80
Heating to a temperature range of 0 ° C or more at a heating rate of 80 ° C / sec or more
And, within 0.1 seconds after reaching the maximum temperature, by applying cooling to the temperature range below 800 ° C. at a cooling rate of more than 50 ° C. / sec, the secondary recrystallized grain size fine is obtained than the conventional , A grain-oriented electrical steel sheet having an extremely low iron loss has been obtained.

[0022]

[Table 1]

[0023]

[Table 2]

(Example 2) A molten steel containing the composition shown in Table 3 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 sheet was heated under various conditions by the direct current roll heating device shown in FIG. Immediately after heating, the exit roll was preheated and the passage speed was controlled, so that various soaking times and cooling conditions were applied. Table 4 shows the heating rate and the ultimate temperature at that time, and the cooling conditions for the outlet roll.

Next, decarburization annealing is performed in wet hydrogen, nitriding treatment is performed in an ammonia atmosphere, and MgO powder is applied.
High temperature annealing was performed in a hydrogen gas atmosphere at 1200 ° C. for 10 hours. Table 4 shows the secondary recrystallized grain size of the obtained product,
It shows magnetic properties. The magnetic characteristics of the product are 800 when energized.
Heating to a temperature range of ℃ or more at a heating rate of 80 ℃ / second or more,
Secondary recrystallization finer than conventional by performing cooling to a temperature range of less than 800 ° C. at a cooling rate of 50 ° C./sec or more by a roll on the side heated within 0.1 seconds after reaching the maximum temperature. Grain-sized, grain-oriented electrical steel sheets having extremely low iron loss have been obtained.

[0026]

[Table 3]

[0027]

[Table 4]

(Example 3) A 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 0.27 mm. The rolled steel plate is directly heated by an electric heating roll. 2
It is heated up to 825 ° C at a heating rate of 50 ° C / sec, and 0.01 seconds after reaching the maximum on the exit side roll, and then reached 680 ° C to 23000
Cooled at a cooling rate of ° C / sec.

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 3.5 mm. In addition, the magnetic properties of the _grain -oriented electrical steel sheet were B ₈ = 1.94T and W _17/50 = 0.89 (W / kg), which had extremely low iron loss. Further, the obtained steel sheet was subdivided into magnetic domains by laser treatment, and the magnetic properties were B ₈ = 1.92T and W _17/50 = 0.8.
A grain-oriented electrical steel sheet having an extremely low iron loss of 1 (W / kg) was obtained.

[0030]

[Table 5]

(Example 4) Molten steel containing the chemical composition shown in Table 6 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 sheet is heated to 851 ° C. at a heating rate of 250 ° C./sec by two pairs of direct current heating rolls, and 0.01 sec after reaching the maximum on the exit roll, and then to 790 ° C. 24
It cooled at the cooling rate of 500 degreeC / sec. Next, decarburization annealing was performed in wet hydrogen.

The same steel sheet was heated to 746 ° C. at a heating rate of 250 ° C./second by induction heating, was not cooled as it was, and was further heated to 850 ° C. at 15 ° C./second for decarburization annealing in wet hydrogen. After applying MgO powder to the above two types of decarburized annealed plates, high-temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. Table 7 shows the magnetic properties of the obtained products. The magnetism of the product was satisfactory with the current-carrying roll method.

[0033]

[Table 6]

[0034]

[Table 7]

[0035]

According to the present invention, by the rapid heating method and the rapid cooling method, a unidirectional electrical steel sheet having a secondary recrystallized grain size smaller than ever before, a high magnetic flux density and an extremely low iron loss characteristic can be obtained. Since it can be manufactured, its industrial contribution is extremely large.

[Brief description of the drawings]

FIG. 1 is a chart showing a relationship between a cooling rate of an exit roll and an iron loss value.

FIG. 2 is a schematic view of an example of an electric 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,
Remainder as a starting material molten steel consisting of Fe and unavoidable impurities, the strips rolled to the final product thickness, 8
Heating to a temperature range of 00 ℃ or more at a heating rate of 80 ℃ / sec or more, and cooling to a temperature range of less than 800 ℃ at a cooling rate of 50 ℃ / sec or more within 0.1 seconds after reaching the maximum temperature. A method for producing a grain-oriented electrical steel sheet having an extremely low iron loss, which is characterized by subjecting the obtained strip to decarburization annealing and final finishing annealing. 2. The rapid heating and cooling treatment of the strip is performed by conducting current between the rolls, and the cooling treatment is performed by the roll on the side where the strip is heated. Method. 3. The method according to claim 1, wherein the grain-oriented electrical steel sheet is subjected to a treatment for subdividing a magnetic domain.