JPH07116516B2 - Method for manufacturing high magnetic flux density grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for producing a grain-oriented electrical steel sheet having a {110} <001> orientation as a main orientation and a high magnetic flux density.

(Prior Art) Grain-oriented electrical steel sheet is a soft magnetic material that is widely used mainly in iron core materials and magnetic shield materials for power transformers, generators, electric motors, etc. It is composed of crystal grains with a crystal orientation called (110} <001> orientation), and the <100> axis, which is the easy axis of magnetization, is parallel to the rolling direction. Has iron loss characteristics.

In order to obtain such a crystal structure having a Goss orientation as a main orientation, so-called secondary recrystallization in which primary recrystallized grains selectively grow during finish annealing after cold rolling is used. Therefore, the point of production of the grain-oriented electrical steel sheet is only how stable and accurate secondary recrystallization of Goss orientation is generated during finish annealing. In order to generate this secondary recrystallization, it is necessary to appropriately disperse fine precipitates called inhibitors that suppress the growth of grains other than the Goss orientation. MnS, MnSe, AlN, etc. are known as inhibitors. A method for producing a grain-oriented electrical steel sheet using AlN as a main inhibitor is disclosed in JP-B-46-23820, JP-A-58-100627, and JP-A-62-83421.

However, the method described in JP-B-46-23820 requires costly decarburization annealing before finish annealing for performing secondary recrystallization, and the method described in JP-A-58-100627 is The final annealing for performing the secondary recrystallization is a very special annealing in which a temperature difference of 2 ° C. or more is applied per 1 cm ² parallel to the steel plate surface, which is not suitable for actual mass production. In contrast to these methods, the method described in JP-A-62-83421 does not require decarburization annealing, and finishing annealing is not a special condition, so it is suitable for actual production and has stable magnetic properties. It is possible to manufacture a characteristic electromagnetic steel sheet. However, recently, products having even better magnetization characteristics, that is, higher magnetic flux density have been demanded, and it is difficult to meet the recent required quality even with this method.

(Problems to be Solved by the Invention) An object of the present invention is to produce a grain-oriented electrical steel sheet having a much higher magnetic flux density at low cost and stably without requiring costly decarburization annealing or special annealing. To provide a way to do it.

(Means for solving the problem) As a method capable of inexpensively and stably producing a grain-oriented electrical steel sheet having an excellent magnetic flux density without adopting aggressive decarburization annealing or special annealing in the steps after hot rolling, Japanese Patent Laid-Open No. 62-
There is a manufacturing method described in Japanese Patent No. 83421. This method is used for steels that do not require positive decarburization annealing in the process after hot rolling.
Ultra low carbon steel whose Sol.Al content is adjusted to a specific range is used as the material, and winding is performed at 600 ° C or less, hot-rolled sheet annealing, intermediate annealing in cold rolling and primary annealing at 5 ° C / sec or more. It is performed under the condition that the temperature is maintained in the α range of 700 to 950 ° C. In this method, annealing other than finish annealing is performed at a rapid heating rate of 5 ° C / sec or more to properly disperse AlN and nitrides containing Si and Mn, and to select accurate Goss-oriented grains by secondary recrystallization. Magnetically grown to improve magnetic properties.

However, even if the present inventors do not perform the annealing by such rapid heating, the annealing before cold rolling at least the final plate thickness is gradually heated, and the annealing is soaked at a specific temperature and the final plate is obtained. By properly selecting the reduction ratio of cold rolling to be thick, the dispersion of nitride and the primary recrystallization texture are optimized,
It has been found that a grain-oriented electrical steel sheet having stable secondary recrystallization and a high magnetic flux density can be obtained.

The gist of the present invention resides in the following method for producing a high magnetic flux density grain-oriented electrical steel sheet.

% By weight, C: 0.01% or less, Si: more than 1.0% to 2.5% or less, Mn: 1.0% or less, S: 0.015% or less, Sol.Al: 0.003 to 0.015%, N: 0.0010 to 0.0100%, balance: A hot-rolled sheet consisting of Fe and unavoidable impurities is added at 200 ° C /
After annealing to heat to 750-900 ℃ at a heating rate of h or less and soaking, final cold rolling is performed with a reduction rate of 60-95% to obtain the final plate thickness, and then α of 800 ℃ or more. A method for producing a high magnetic flux density grain-oriented electrical steel sheet, which comprises performing continuous annealing for primary recrystallization in a temperature range and finish annealing for secondary recrystallization in a temperature range of 800 ° C or higher.

(Function) In the present invention, the reason why the chemical composition of the material hot-rolled sheet, the reduction ratio of the final cold rolling and each annealing condition are limited as described above will be described below.

(I) Chemical composition of hot-rolled sheet In a general grain-oriented electrical steel sheet, C is added in an appropriate amount for controlling precipitates and texture in the hot-rolling step and subsequent steps. In this case, since C is detrimental to the magnetic properties, decarburization annealing is used as annealing for performing primary recrystallization to reduce the amount of C. However, in the present invention, in order to reduce the manufacturing cost, active decarburization is not performed in the steel sheet stage, so it is necessary to reduce the C content in the hot rolled sheet stage to the extent that magnetic properties are not adversely affected. is there. When the C content in the steel sheet exceeds 0.01%, adverse effects on magnetic properties such as deterioration of iron loss and deterioration of magnetic aging become significant, so the C content was set to 0.01% or less.

Si When the Si content is increased, the eddy current loss decreases and the iron loss decreases due to the increase in the electrical resistance of the steel sheet. But 1.0%
With the following contents, iron loss did not decrease as targeted, and
%, The secondary recrystallization becomes unstable and the cold rolling property deteriorates, making it difficult to stably manufacture a steel sheet. Therefore, the Si content is more than 1.0% and not more than 2.5%. did.

Mn: Mn is an element effective in increasing the electrical resistance of the steel sheet and reducing the iron loss, similar to Si. However, if the content exceeds 1.0%, the cold rolling property deteriorates, so the Mn content is 1.0%.
The following was set. It should be noted that the lower limit of the Mn content is not specified because even if Mn is not contained, if Si is contained in an amount of more than 1%, the iron loss value may be sufficiently satisfied.

However, when Si is contained by 1.8% or more, it is better to add Mn. In a low C steel such as a hot rolled sheet used in the present invention, if Si is contained in an amount of 1.8% or more and Mn is not included, the α-γ transformation disappears and the structure of the hot rolled sheet becomes coarse,
Secondary recrystallization during finish annealing tends to be unstable, but Mn
Addition of α can make α-γ transformation appear in such a steel sheet, and it is possible to stabilize secondary recrystallization in addition to reducing iron loss.

S In the present invention, AlN or a nitride containing Si and Mn is used as an inhibitor for controlling secondary recrystallization. Therefore, it is not necessary to add a large amount of S as in the conventional grain-oriented electrical steel sheet using MnS as a main inhibitor. Addition of a large amount of S tends to deteriorate iron loss, so the S content is 0.015
% Or less.

Sol.Al: Al is an important element forming AlN which is a major inhibitor. The content of Al is set to 0.003 to 0.015% in terms of Sol.Al content because if it is less than 0.003%, the absolute amount of AlN as an inhibitor is insufficient and a sufficient inhibitory effect cannot be expected, and it exceeds 0.015%. And the amount of the inhibitor becomes too large, the distribution morphology becomes unsuitable, and stable secondary recrystallization hardly occurs.

N: N is an important element that forms a nitride containing AlN or Si and Mn and serves as an inhibitor that suppresses grain growth until secondary recrystallization occurs. However, if the content is less than 0.0010%, the desired inhibitory effect cannot be obtained, and even if the content exceeds 0.0100%, the effect as an inhibitor is saturated. Therefore, the N content is defined as 0.0010 to 0.0100%. It was

(Ii) Manufacturing conditions (a) Annealing before cold rolling to obtain the final plate thickness Annealing before cold rolling to obtain the final plate thickness means that a hot-rolled sheet having the above-mentioned composition is obtained by one cold rolling method. When the thickness is set, the hot rolled sheet annealing is the annealing before cold rolling to obtain the final sheet thickness. on the other hand,
When the final plate thickness is obtained by two or more cold rolling methods sandwiching the intermediate annealing, the intermediate annealing performed before the final cold rolling is the annealing before the cold rolling to obtain the final plate thickness.

Annealing before cold rolling to obtain this final plate thickness, that is, in the case of one cold rolling method, hot-rolled sheet annealing is heated to 750 to 900 ° C at a heating rate of 200 ° C / h or less and soaked. It is important to do it under the conditions. On the other hand, in the case of two or more cold rolling methods sandwiching the intermediate annealing, it is important to perform at least the intermediate annealing before the final cold rolling under the same conditions. If the annealing before cold rolling to obtain the final plate thickness is performed at a heating rate and a soaking temperature outside the above range, a high magnetic flux density cannot be obtained after finish annealing.

Fig. 1 shows C: 0.003%, Si: 1.2%, Mn: 0.16%, S: 0.00
5.Sol.Al: 0.007%, N: 0.0051%, steel slab consisting of balance Fe and unavoidable impurities is hot-rolled to 2.3mm thickness, and then heating rate is changed to 850 ℃, and at this temperature 1
Annealed for time soaking, then 0.3 mm with 87% rolling reduction
After cold-rolling to thickness, 87 to perform primary recrystallization
A test piece was taken from a steel sheet that had been continuously annealed at 5 ° C for 30 seconds and finish annealed for secondary recrystallization, and was magnetized with a magnetic force of B ₈ (800 A / m) in the rolling direction. Is the result of examining the magnetic flux density). The final annealing is 2 at 870 ℃.
After soaking for 4 hours, soaking is further performed at 925 ° C for 24 hours, and the annealing atmosphere is 875 ° C at 75% N ₂ and 25% H until soaking for 24 hours.
A mixed gas of ₂ and then 100% H ₂ gas were used.

As is apparent from FIG. 1, when the heating rate of the annealing before cold rolling is 200 ° C./h or less, it is understood that an extremely high magnetic flux density can be obtained.

Fig. 2 shows hot-rolled sheet with the same composition at a heating rate of 30 ° C / h.
Tested from steel sheets that have been heated to a temperature of 0 to 1000 ° C, soaked and annealed at each temperature for 1 hour, then cold-rolled, continuously annealed for primary recrystallization and finish annealed for secondary recrystallization The results are obtained by collecting pieces and examining the magnetic flux density B ₈ in the rolling direction. The conditions of cold rolling, continuous annealing and finish annealing were the same as above.

From FIG. 2, it can be seen that an extremely high magnetic flux density can be obtained when the soaking temperature is 750 to 900 ° C. From these results, the annealing performed before cold rolling to obtain the final plate thickness is
The temperature was 200 ℃ / h or less and the soaking temperature was 750-900 ℃. The reason why a high magnetic flux density can be obtained under such conditions is that the dispersed state of nitride such as AlN, which becomes an inhibitor, is optimized, and that secondary re-growth such that accurate Goss-oriented grains selectively grow by finish annealing is performed. It is considered that crystals are generated.

It should be noted that the annealing before cold rolling to obtain the final plate thickness is preferably performed in a box annealing furnace rather than a continuous annealing furnace because the heating rate is slow. When the final plate thickness is obtained by cold rolling two or more times with the intermediate annealing sandwiched between them, the annealing performed before the intermediate annealing before the final cold rolling does not need to specify the conditions. If at least the final intermediate annealing before cold rolling is performed under the above conditions, the annealing before that may be normal conditions.

(B) Cold Rolling What is important in cold rolling is that when cold rolling is performed once to the final sheet thickness, the cold rolling is performed at a reduction rate of 60 to 95%. When processing to the final thickness by two or more cold rolling processes with intermediate annealing, the cold rolling before the final cold rolling may be performed at any reduction rate, but the final cold rolling is 60%.
It is necessary to carry out the reduction rate of ~ 95%. If the final cold rolling reduction falls outside the range of 60 to 95%, good magnetic properties cannot be obtained. The reason for this is that the appropriate primary recrystallized texture cannot be obtained by the annealing of the primary recrystallization performed in the next continuous annealing, and this hinders the formation of an accurate Goss-oriented texture in the secondary recrystallization in the final annealing. It is thought to be because of this.

(C) Primary Recrystallization Annealing The primary recrystallization annealing is performed after cold rolling for finishing to the final plate thickness and before finish annealing for performing secondary recrystallization. This annealing is important for adjusting the dispersion state and primary recrystallization texture of the nitride such as AlN and for producing the desired secondary recrystallization in the final annealing. For this purpose, it is preferable to perform it in the α region of 800 ° C. or higher. If the annealing temperature is lower than 800 ° C, proper primary recrystallization texture cannot be obtained. Further, even if it is annealed at a high temperature such that a γ phase is generated, a proper AlN dispersion state and a good primary recrystallization texture cannot be obtained.

In the α region above 800 ° C, it is desirable to raise the temperature at a heating rate of 5 ° C / sec or more. Therefore, continuous annealing is suitable for this primary recrystallization annealing. When heated rapidly in this way, nitrides such as AlN that act as inhibitors are finely dispersed and precipitated,
Accurate Goss-oriented grains grow by secondary recrystallization.

(D) Finish annealing The finish annealing requires a temperature at which secondary recrystallization is sufficiently generated, and it is necessary to set the temperature to an α range of 800 ° C or higher. Further, in the present invention, since a nitride such as AlN is used as an inhibitor, if denitrification occurs before secondary recrystallization occurs, the amount of nitride precipitation is reduced, and the inhibitor effect is weakened. Recrystallization may not occur. Therefore,
It is desirable to perform finish annealing in an atmosphere containing N ₂ until secondary recrystallization is completed.

Annealing before cold rolling with the final plate thickness above, the holding time in primary recrystallization annealing and finish annealing does not have to be particularly limited, but the effect of each annealing is not sufficiently obtained when it is short, and the production is long. Therefore, it is desirable that the annealing before cold rolling to obtain the final plate thickness is 30 minutes to 10 hours, the primary recrystallization annealing is 5 seconds to 10 minutes, and the final annealing is 10 to 60 hours.

The invention is further described by the examples.

(Example 1) A steel slab having the composition shown in Table 1 was hot-rolled to a thickness of 2.3 mm, pickled, and then heated to 850 ° C at an average heating rate of 25 ° C / h and soaked for 4 hours. The box was annealed. Then 0.3 mm
After cold rolling to thickness, 88 in order to carry out primary recrystallization.
Continuous annealing was performed at 0 ° C. for 30 seconds soaking, and finish annealing was performed in order to apply an annealing separator and perform secondary recrystallization.
Finish annealing is soaked at 875 ℃ for 24 hours, then at 925 ℃.
After soaking for 24 hours, the annealing atmosphere is a mixed gas of 75% N ₂ and 25% H ₂ until soaking at 875 ° C for 24 hours, then 10
Performed at 0% H ₂ . Note that the latter half of the finish annealing, that is, the annealing for 24 hours at 925 ° C., is intended for purification annealing for removing nitrides and the like.

After finish annealing, cut out test pieces from each steel plate,
The magnetic properties were investigated. The results are also shown in Table 1.

In Table 1, steel types A to E have almost the same composition except Sol.Al. In this case, the steel type A and the steel type E in which the amount of Sol.Al is lower than the range specified in the present invention have remarkably poor magnetic properties. Steel types F to I have almost the same composition except sulfur (S), but steel type I having a high sulfur content is inferior in magnetic properties, and steel type J has a low silicon (Si) content, Other than that, the steel loss is inferior to the steel type C having almost the same composition, and the steel type K having a high carbon (C) content is inferior to the steel type G having almost the same composition except carbon. On the other hand, all of the examples of the present invention show good magnetic characteristics.

(Example 2) A steel slab having the same composition as the steel type C in Example 1 was set to 2.3 m.
After hot rolling to m thickness, after pickling, hot rolled sheet annealing followed by one cold rolling, or two cold rolling steps with intermediate annealing without hot rolled sheet annealing to obtain final sheet thickness. (However, in Test No. 5, pickling was performed after annealing the hot rolled sheet). Then, after performing continuous annealing for performing primary recrystallization, finish annealing was performed for applying an annealing separator and performing secondary recrystallization. The finish annealing was soaked at 875 ° C. for 24 hours and then at 925 ° C. for 24 hours, and the atmosphere was the same as in Example 1.

Table 2 shows the conditions of hot-rolled sheet annealing, intermediate annealing, cold rolling and continuous annealing, and the results of examining the magnetic properties.

In all of the examples of the present invention, good magnetic properties were obtained, whereas test number 1 in which the annealing temperature before final cold rolling was lower than the range specified in the present invention, test number 4 was too high, and final cold rolling. Test No. 5 in which the heating rate of the previous annealing was too fast, Test No. 6 in which the soaking temperature of continuous annealing for primary recrystallization was too low
And, the test number 8 in which the reduction ratio of the final cold rolling is too low is inferior in the magnetic properties.

(Effects of the Invention) As described above, according to the manufacturing method of the present invention, costly decarburization annealing and special annealing conditions are not required, and a high magnetic flux density grain-oriented electrical steel sheet can be manufactured inexpensively and stably. It can be manufactured.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the heating rate and the magnetic flux density of the annealing before cold rolling, which is the final thickness, and FIG. 2 is the soaking temperature of the annealing before cold rolling, which is the final thickness. It is a graph which shows the relationship with magnetic flux density.

Claims (1)

[Claims] 1. By weight%, C: 0.01% or less, Si: more than 1.0% to 2.5% or less, Mn: 1.0% or less, S: 0.015% or less, Sol.Al: 0.003 to 0.015%, N: 0.0010 to 0.0100%, balance: Fe and unavoidable impurities on hot-rolled sheet, 200 ℃ /
After annealing to 750 to 900 ℃ at a heating rate of less than h and soaking, final cold rolling is performed at a reduction rate of 60 to 95% to obtain the final plate thickness, and then 800 ° C or higher α A method for producing a high magnetic flux density grain-oriented electrical steel sheet, which comprises performing continuous annealing for primary recrystallization in a temperature range and finish annealing for secondary recrystallization in a temperature range of 800 ° C or higher.