JPH09157747A - Production of grain oriented silicon steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain, more stably, a high Mn grain oriented silicon steel sheet having superior magnetic properties by using a slab containing an appreciable amount of C and specifying a metallic structure before cold rolling. SOLUTION: A steel plate, which has a composition consisting of, by weight, >0.010-0.030% C, 1.5-4.0% Si, 1.0-5.0% Mn, <=0.01% S, 0.003-0.03% sol.Al, 0.0010-0.010% N, and the balance Fe and satisfying Si(%)-0.5×Mn(%)<=2.0% and in which 10-70% of the whole plate thickness from both surfaces is formed into recrystallized part, is used. This steel plate is cold-rolled once or is cold- rolled twice while process-annealed between the cold rolling stages to the final sheet thickness, and the resultant cold rolled steel sheet is rapidly heated to undergo annealing and then finish-annealed at 825-1050 deg.C. Moreover, in order to form 10-70% of the whole plate thickness from both surfaces into recrystallized part, hot rolling is performed under the condition that the relation between finishing temp. (FT: deg.C) and coiling temp. (CT: deg.C) satisfies an inequality and also 780<=FT<=930 or CT<=600 is satisfied, and further, annealing is clone at 625-950 deg.C after hot rolling.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a transformer, a generator,
The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet widely used as a core material and a magnetic shield material for an electric motor.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are soft magnetic materials that have a crystal orientation of 110 <001> orientation called Goss orientation as their metallographic structure and have excellent excitation characteristics and iron loss characteristics particularly in the rolling direction. The conventional general manufacturing method of this steel sheet is to hot-roll a slab of steel containing about 3% of Si, and directly or after annealing (hot-rolled sheet annealing), perform 2 times with one or intermediate annealing. After cold rolling more than one time to the final thickness, then primary recrystallization and atmospheric gas decarburization in a continuous annealing furnace, apply an annealing separating agent for seizure prevention and wind it into a coil. Finish annealing at ultra high temperature of 1200 ℃. After that, remove the separating agent, flattening annealing,
Surface insulation coating is applied to make the product. The purpose of the finish annealing is to form a texture that is integrated in the Goss orientation by secondary recrystallization, and thereafter to remove the fine precipitates of the inhibitor used for forming the orientation of this secondary recrystallization. This step of removing the precipitate is also called purification annealing and is an essential step for obtaining good magnetic properties together with secondary recrystallization.

Mn is an inhibitor of this secondary recrystallization.
Although sulfide-based precipitates such as S are used, the solubility product of sulfide-based precipitates is small. Therefore, in order to effectively disperse fine precipitates uniformly, the amount of Mn should be suppressed and The heating temperature of the slab during hot rolling should be as high as possible and the sulfide should be dissolved sufficiently. On the other hand, the electrical steel sheet has a high Si content for the purpose of increasing the electrical resistance, but when the Si content is extremely low and the carbon content is extremely low, the γ phase does not appear and the α phase becomes from normal temperature to high temperature. In that case, not only the inhibitor dispersion becomes worse, but since the α-γ transformation does not occur during the hot rolling process, the crystal grains of the hot rolled sheet become coarse together with the high temperature heating of the slab. The hot-rolled sheet with coarse crystal grains causes cracking during cold rolling, ridging in the final product, or deterioration of its magnetic properties. Therefore, a slab containing C to some extent is used so that the γ phase appears so that the inhibitor is dispersed and atomized. However, since this C remarkably deteriorates the magnetic characteristics, it is decarburized in the atmosphere in the annealing process after cold rolling to be extremely low carbon. Furthermore, fine precipitates, which were essential for developing the secondary recrystallized grains in the Goss orientation, are extremely harmful to the magnetic properties of the electrical steel sheet of the final product and must be removed. The atmosphere removes S in the steel from the surface. In this case, in order to decompose the sulfide and diffuse it as solid solution S to the surface and then react with hydrogen, it has to be treated for a long time in an ultrahigh temperature range of 1100 to 1200 ° C.

The grain-oriented electrical steel sheet produced by the above-mentioned manufacturing method is said to be hot-rolled by slab heating at 1300 ° C or higher, continuously decarburized annealed, or finish-annealed at an ultrahigh temperature of 1100 ° C or higher during the manufacturing process. Requires a special process,
This is extremely expensive because it requires dedicated equipment.

Various researches and developments have been made in order to solve the problems of cost and simplification of process conditions. The present inventors previously found that C: 0.01% or less, Si: 0.5-
2.5%, Mn: 1.0 to 2.0%, a grain-oriented electrical steel sheet mainly characterized by lower Si and higher Mn than before, and low temperature finish annealing without the need for decarburization annealing in the intermediate step. Inventing a method of manufacturing the same (Japanese Patent Publication No.
No. 1). This method lowers the hardness of the material by lowering Si to facilitate rolling, and can greatly contribute to the cost reduction of the grain-oriented electrical steel sheet by omitting decarburization annealing and lowering the finish annealing temperature. Further, JP-A-6-96
In Japanese Patent Publication No. 66, this method is improved and Si: 1.
5 to 3.0%, Mn: 1.0 to 3.0%, and Si (%)-
A high-Mn-type grain-oriented electrical steel sheet and a method for manufacturing the same are presented, which are steels in which 0.5 × Mn (%) ≦ 2.0.

The greatest feature of this method for producing a high Mn-type grain-oriented electrical steel sheet is that it uses a nitride-based precipitate (iron and steel: Vol.80 (1994), No. 8, page 659) as an inhibitor. is there. For this reason, Mn can be contained in a large amount, and thus, even if a slab with extremely low carbon is used, the γ phase appears, so that α-γ transformation occurs, and decarburization in the subsequent annealing step becomes unnecessary. ing. In addition, increasing the Mn content also has the effect of increasing the electrical resistance. This nitride-based precipitate has a larger solubility product than the sulfide-based precipitate and is sufficiently solid-solved at a low temperature. Therefore, the slab heating temperature should be the same as that for the production of ordinary hot-rolled steel sheet (1150-
It is possible to reduce the temperature to 1250 ℃). Further, since the fine precipitate used as the inhibitor in the secondary recrystallization has a low solid solution temperature and the diffusion rate of N in steel is much faster than that of S, it can be removed at a low temperature of 1000 ° C or less and in a short time. . As described above, the method for producing a high Mn-type grain-oriented electrical steel sheet is an epoch-making method in that the processing temperature of the process that conventionally required a high temperature can be greatly reduced and no special dedicated equipment is required. is there.

However, it is difficult to say that all the manufacturing conditions are sufficiently established for application of this method for manufacturing a high Mn-type grain-oriented electrical steel sheet in mass production, and many points to be improved remain. Has been done.

[0008]

DISCLOSURE OF THE INVENTION The present invention relates to a method for producing a high Mn-type grain-oriented electrical steel sheet disclosed in the above-mentioned Japanese Patent Laid-Open No. 6-9666, and the level of stability and ultimate performance of the production. Is further improved.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have studied various manufacturing conditions in order to improve the characteristic level of the product and stabilize it in the method of manufacturing a high Mn-type grain-oriented electrical steel sheet. In that case, since decarburization is not performed in the process in the middle, until now, C harmful to the characteristics has been sufficiently decarburized by vacuum treatment of molten steel in the steelmaking stage. However, in the process of studying, C in the slab during steelmaking or at the end of hot rolling is reduced during the manufacturing process even if some remains, and the final product has the same C content level as before. It has become clear that This is because C in the steel reacts with hydrogen and a small amount of water in the atmosphere on the surface of the steel during the annealing during the process, especially by heating in the atmosphere containing hydrogen for a long time at high temperature during finish annealing. It is considered that carbon monoxide and the like were eliminated.

If the target level of decarburization at the steelmaking stage can be increased to some extent, the vacuum processing time of molten steel can be shortened,
In addition, the amount of oxide inclusions in the steel can be reduced. Reduction of oxide inclusions leads to improvement of magnetic properties. Furthermore, there is a possibility of cost reduction by relaxing restrictions on the purity of raw materials used. Therefore, as a result of conducting an investigation to clarify the allowable limit of the amount of C at the stage of the material after the hot rolling, the presence of an appropriate amount of C in the material not only stabilizes the magnetic properties, It turned out to improve. This is because the inclusions are reduced as described above, but rather than that, C which is an interstitial solid solution element in the steel.
By the presence of, the nuclei of crystals that develop next in the Goss orientation are generated more during cold rolling and primary recrystallization, improving the texture of the steel sheet after secondary recrystallization, and as a result, It was estimated that the magnetic properties were improved.

Further, when the content of C is in the above range,
It has been found that the effect of improving the texture of the steel sheet after secondary recrystallization becomes more remarkable by performing the warm rolling. This is because the slip system of the rolling process changes and the working state changes, and during subsequent primary recrystallization of annealing, more nuclei of crystals that develop in the Goss orientation in the above secondary recrystallization are generated. Conceivable.

When the Si content is high and the carbon content is extremely low, when the metallographic structure of the steel plate cross section is observed under an optical microscope, it is observed that the vicinity of the surface of the steel sheet is recrystallized and that the work structure remains inside due to the hot rolling conditions. There are many cases. When the ratio between the recrystallized state portion and the processed structure state portion changes, the magnetic properties of the final product change significantly, and the magnetic properties are further improved at a specific ratio. As a result of applying this effect to a slightly high carbon, it was similarly effective. The term "recrystallized portion or processed texture portion" does not mean that the material is recrystallized or is in a non-recrystallized state in a strict sense, but a portion in which the state of the texture looks like that in an optical microscope observation. Point to.

Therefore, with respect to the carbon content of the raw material and the metallographic structure before cold rolling, the conditions for obtaining particularly excellent magnetic characteristics were studied in detail, and the method of the present invention was completed.

The features of the manufacturing method of the present invention are as follows.

(1) C by weight%: more than 0.01% to 0.030%,
Si: 1.5-4.0%, Mn: 1.0-5.0%, S: 0.01%
Below, sol.Al: 0.003 to 0.03%, N: 0.0010 to 0.010
%, And Si (%)-0.5 x Mn (%) ≤ 2.0, with the balance being Fe and inevitable impurities, and the total thickness from 10 to 70 from both surfaces. % Of the recrystallized steel sheet is cold-rolled once, or cold-rolled twice with intermediate annealing, then rapidly heated and annealed.
Finish annealing in the temperature range of ℃.

(2) When the partially recrystallized steel sheet having the above composition is rolled once or twice with intermediate annealing to obtain the final thickness, at least one rolling is performed at 50 to 250 ° C.
It is warm-rolled in the temperature range, then rapidly heated and annealed, and then finish annealed in the temperature range of 825 to 1050 ° C.

(3) In the manufacturing method of (1) or (2) above, the finishing temperature (FT: ° C) and the coiling temperature (CT: ° C) of the hot rolling process satisfy the following equations and equations. By doing so, the total thickness of 10 to 70
The steel plate with the% as the recrystallized portion is used.

1250- (2/3) × FT ≦ CT ≦ 1300- (2/3) × FT 780 ≦ FT ≦ 930 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (4) In the manufacturing method of (1) or (2) above, the coiling temperature of hot rolling is set to 600 ° C or less, the obtained coil is descaled, annealed in the temperature range of 625 to 950 ° C, and cold rolled. First, make a steel sheet with 10 to 70% of the total thickness from both surfaces as the recrystallized portion.

Here, 10 to 70% of the total plate thickness from both surfaces
The state of the recrystallized part is not necessarily equal from the upper and lower surfaces of the plate, for example, when the recrystallized part is 40% of the total plate thickness, it is not necessary that each of the upper and lower surfaces is 20% from the surface, It is desirable that at least 5% of the total plate thickness is on the side with few recrystallized portions.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the production method of the present invention, the contents of elements other than C and N determined in the steelmaking stage are almost the same as the contents of the final product. There is a big difference between the content of and the final product. The component contents here are for the steel sheet after hot rolling. In the following description, all "%" are% by weight.

(1) C C has an adverse effect on the magnetic properties, so that it is less than 0 in the final product.
It is desirable that the content be 0050% or less. However, at the stage of the raw material steel slab or the raw steel sheet before cold rolling, the C content is more than 0.010% and 0.030% or less. This is because if the content is made 0.010% or less in the steelmaking stage, the amount of oxide inclusions in the steel will increase, and in addition, the degassing treatment time of molten steel for extremely low carbonization will increase, leading to higher costs. Also, the effect of improving the texture due to the presence of the solid solution C is not significant below 0.010%. On the other hand, if it exceeds 0.030%, it will not be possible to achieve extremely low carbon at the stage of finish annealing, and further, by the above-mentioned hot rolling condition management and hot rolled sheet annealing, before cold rolling, the total thickness of 10 to 10 It becomes difficult to make 70% into the recrystallized portion.

(2) Si Si is an element that greatly affects the magnetic properties, and as the content increases, the electrical resistance of the steel sheet increases and the eddy current loss decreases, resulting in a reduction in iron loss. However, if the content exceeds 4.0%, even if the Mn content is increased, the secondary recrystallization becomes unstable, and the workability is reduced to make cold rolling difficult. On the other hand, if the content is less than 1.5%, the electric resistance of the steel sheet is too small, and the reduction of iron loss becomes insufficient. Therefore, the Si content is in the range of 1.5 to 4.0%.

(3) Mn Mn is an element necessary for causing the γ phase to appear during heating in the hot rolling of a high Si, low carbon steel slab, and therefore for causing the α-γ transformation. The occurrence of transformation promotes homogenization of the structure of the hot-rolled sheet and homogenization of the inhibitor during the hot rolling process, and as a result stabilizes secondary recrystallization with high integration in the Goss orientation during finish annealing. Make progress. Therefore, Mn
On the other hand, the appearance of the γ phase during finish annealing destroys the Goss orientation obtained by secondary recrystallization, and therefore it is not preferable to add too much. Such γ transformation is determined by the balance of the contents of Si, which is a ferrite-forming element, and Mn, which is an austenite-forming element.
The content of n must be adjusted accordingly. In the present invention, Mn is added to Si so that Si (%) − 0.5 × Mn (%) ≦ 2.0. This makes it possible to cause transformation in the hot rolling process and prevent transformation during finish annealing.

In order to satisfy the above formula when the Si content is 4.0%, which is the upper limit of the present invention, 4.0% or more of Mn is required. Further, even for a material having a Si content of less than 2.0%, a Mn content of 1.0% or more is necessary for stabilizing secondary recrystallization. Mn
Is effective in increasing the electric resistance of the steel sheet, and it is necessary to contain 1.0% or more of Mn for the purpose of reducing iron loss. But 5.
Since Mn exceeding 0% deteriorates the cold workability, the upper limit of the content is 5.0%. That is, the Mn content is 1.0 to 5.
It must be 0% and satisfy the above condition.

(4) S S forms Mn S together with Mn and is utilized as an inhibitor in the conventional method for producing grain-oriented electrical steel sheet, so it is essential that the slab is contained in a certain amount or more. However, in the present invention, since nitride is used as the main inhibitor, it is not necessary to add a large amount of S, and in the method of the present invention, the desulfurization effect cannot be expected because the finish annealing is as low as 1050 ° C or less. Furthermore, if a large amount of MnS particles remain in the final product, iron loss will be deteriorated. Therefore, the S content is 0.010% or less in both the product and the steel slab as the raw material, but the smaller the S content, the better, and the more desirable it is.
It is 0.005% or less.

(5) sol.Al (acid-soluble Al) Al is a major inhibitor AlN which plays an important role in the occurrence of secondary recrystallization in the Goss orientation in the present invention.
It is an important element for forming a nitride such as (Al, Si) N or (Al, Si, Mn) N. sol.
When Al is less than 0.003%, the amount of nitride is insufficient and a sufficient inhibitory effect cannot be obtained, and when it exceeds 0.03%, the amount of inhibitor becomes too large and its dispersion state becomes improper and stable secondary recrystallization does not occur. . Therefore, sol.
The Al content is limited to 0.003 to 0.03%.

(6) N N is necessary for forming the above-mentioned inhibitor nitride, and is an important element until the secondary recrystallization is completed.
0.001 at the stage of hot rolled steel sheet of slab or material
If the content is less than 0.1%, the desired inhibitory effect cannot be obtained because the precipitation amount of nitride is too small during the secondary recrystallization, and if the content exceeds 0.010%, the effect is saturated.
A range of 10% is suitable. However, since the presence in the final product deteriorates the magnetic properties, the smaller the content, the better. The N content in the final product is preferably 0.005% or less and is reduced to this desired low value during finish annealing.

(7) Metallographic Structure Before Cold or Warm Rolling One of the features of the method of the present invention in the production of a high Mn-type grain-oriented electrical steel sheet is that the metallographic structure of the steel sheet before cold or warm rolling is That is, a specific range from the surface is partially recrystallized. Whether it is hot rolled or the hot rolled sheet is annealed, it suffices that a recrystallized portion exists on the surface and a processed texture portion remains inside in the range of optical microscope observation of the cross section.

When the ratio of the recrystallized portion from both surfaces to the total plate thickness excluding the worked structure portion is less than 10% or more than 70%, the development of the Goss orientation after finish annealing is insufficient and the iron loss Will increase. This is because when the recrystallized portion is less than 10%, there are few Goss-oriented crystal grains near the surface layer after primary recrystallization, and when it is 70% or more, grains other than the Goss orientation develop in the portion away from the surface layer during secondary recrystallization. It was thought to be easier to do. The recrystallized portion from both surfaces does not necessarily have to have a uniform thickness from the upper and lower surfaces, but in order not to reduce the factor of the development of the Goss-oriented crystal grains, the smaller thickness of the total thickness from the surface It is desirable to be 5% or more. .

The ratio of this recrystallized portion is 10 to 70 of the total plate thickness.
A steel sheet having a percentage of 10% can be produced by the method (8) or (9) described below.

(8) Hot rolling conditions Finishing temperature (FT) and winding temperature (C) of hot rolling
T) changes the ratio of the recrystallized portion of the steel sheet after hot rolling. When both FT and CT are at a high temperature, the recrystallized portion extends to the center of the plate thickness, and at both FT and CT at a low temperature, the recrystallized portion of the surface layer is small. In order to put the ratio of the recrystallized portion within the target range, if FT is high, CT
Is low, and CT is higher when FT is low.

Within the steel composition within the scope of the present invention, the relationship between FT (° C) and CT (° C) for obtaining a hot-rolled steel sheet in which 10 to 70% of the total sheet thickness is a recrystallized portion from both surfaces. Is within the range that can be expressed by the following formula. However, even if the relationship between FT and CT satisfies this formula, the range of the recrystallized portion expands to the inside when FT exceeds 930 ° C, and the range of the recrystallized portion becomes insufficient below 780 ° C. The recrystallized part of the ratio cannot be obtained.

That is, the hot rolling conditions for obtaining the hot rolled sheet in which the recrystallized portions from both surfaces are 10 to 70% of the total sheet thickness are: 1250- (2/3) × FT ≦ CT ≦ 1300- (2/3) x FT ... 780 ≤ FT ≤ 930 .....

(9) Hot-rolled sheet annealing In a hot-rolled sheet before cold rolling, the total thickness of 10 to 10
The state where 70% is the recrystallized portion can also be obtained by annealing after hot rolling. In order to obtain a target recrystallized portion in the steel having the composition range defined by the method of the present invention, the CT of hot rolling is set to 600 ° C or lower and the annealing temperature range is set to 625 to 950 ° C. FT is not specified, but 7
80 to 930 ℃ is desirable.

If CT is 600 ° C. or lower, it may be cooled to room temperature, but if it exceeds 600 ° C., the recrystallized portion may become too large during annealing. The annealing method may be either a box annealing method or a continuous annealing method. If the temperature is lower than 625 ° C, the recrystallized portion is insufficiently developed, and if it exceeds 950 ° C, it is excessively developed. In order to obtain the recrystallized part of the target ratio, in the case of box annealing, soaking at 625 to 750 ℃ for 30 min to 20 h is desirable, and in the case of continuous annealing, 750 to 950 ℃ for 10 s to 5 min.
Soaking is desirable. However, the ratio of the recrystallized portion varies depending on the annealing method even at the same annealing temperature. That is, even if the soaking temperature of the annealing is within the regulation range, if the temperature is too high in the box annealing method or too low in the continuous annealing method, it may deviate from the intended recrystallization range.

(10) Cold Rolling and Intermediate Annealing The reduction ratio for cold rolling a raw steel sheet to a required thickness is
It should be 40-90%. This is because if it is less than 40%, a primary recrystallized structure sufficient to promote secondary recrystallization cannot be obtained, and if it exceeds 90%, the development of the Goss orientation is not good. A reduction rate of 60 to 90% is desirable for more stable secondary recrystallization.

When the magnetic properties are further improved or a thinner magnetic steel sheet is required, cold rolling is performed twice with intermediate annealing to obtain the required sheet thickness. Although the rolling reduction of the first cold rolling is not specified, it is preferably 40 to 90%. If it is less than 40%, abnormal grain growth may occur during intermediate annealing, and if it exceeds 90%, it becomes difficult to achieve it in the case of high Si. The desirable range of intermediate annealing temperature is 600 to 950 ° C. This is because if the temperature is less than 600 ° C, sufficient strain relief cannot be achieved, and if the temperature exceeds 950 ° C, the crystal grains become coarse and the secondary recrystallization during finish annealing becomes insufficient. The annealing method may be a box annealing method or a continuous annealing method.

The desirable range of the reduction ratio of the second cold rolling is 50 to 80%. If it exceeds or falls below this range, the magnetic properties of the final product will deteriorate.

(11) Warm rolling When the content of C exceeds 0.010%, the magnetic properties of the final product are improved by warming the temperature of the plate during the cold rolling. The temperature shall be 50-250 ℃. 50
When the temperature is lower than 250 ° C, the effect is small, and when the temperature exceeds 250 ° C, problems such as deterioration of plate thickness accuracy, deterioration of flatness, deterioration of surface quality and the like occur.

In the case of two rollings sandwiching the intermediate annealing, either rolling may be warm rolling, but it is sufficiently effective that only one rolling is warm rolling. The coil may be warmed by charging it in a furnace before rolling, heating it, heating it by high-frequency or electric current during rolling, blowing hot air, or the like.

(12) Primary Recrystallization Annealing In order to stably generate secondary recrystallization and develop the Goss orientation in the finish annealing described later, it is necessary to perform primary recrystallization by rapid heating annealing. The continuous annealing method is used. Desirable conditions are a heating rate of about 5 to 20 ° C./s, an annealing temperature of about 700 to 1000 ° C., and a soaking time of about 5 to 300 s.

(13) Finish Annealing The finish annealing after the primary recrystallization annealing is performed in the temperature range of 825 to 1050 ° C., but the annealing in the first half for the purpose of developing the Goss orientation by the secondary recrystallization and subsequent precipitates Includes late annealing for removal or purification.

In order to sufficiently develop the secondary recrystallized grains in the Goss orientation, it is desirable to anneal in a hydrogen atmosphere containing nitrogen. The reason is to prevent the nitride, which is an inhibitor, from decreasing due to denitrification and to make the progress of the secondary recrystallization unstable, and more positively, to prevent the nitride from becoming an inhibitor due to nitrogen absorption from the annealing atmosphere. This is for increasing the amount of precipitates and more effectively performing secondary recrystallization with a high degree of integration in the Goss orientation. For this purpose, the nitrogen content in the annealing atmosphere is desirably 10% or more.

However, the upper limit of the amount of nitrogen in the atmosphere is 100
Considering the progress of nitrification, it is better that 1% or more of hydrogen is present.

The temperature at which the secondary recrystallization is performed is 8
A range of 25-925 ° C is desirable. If the temperature is lower than 825 ° C., the inhibitory effect on the grain growth of the inhibitor is too strong to cause secondary recrystallization,
This is because in the temperature range exceeding 925 ° C., the inhibitor effect is weak, so that secondary recrystallized grains having a low degree of Goss orientation accumulation are generated, or primary recrystallized grains are coarsened by ordinary grain growth. The retention time in the range of 825 to 925 ° C is at least
7h is required, but holding for more than 100h is economically disadvantageous because there is no further grain growth. For these reasons, in the process aiming at the development of secondary recrystallized grains in the first half of finish annealing, at a temperature of 825 to 925 ° C in a nitrogen-containing atmosphere,
It is desirable to hold for 7 to 100 hours.

The nitride used as an inhibitor is harmful in terms of magnetic properties and must be removed after the secondary recrystallization is completed. For this purpose, annealing in a hydrogen atmosphere is effective, and at the same time, C harmful to magnetic properties is also removed. For the purpose of this purification, it takes a long time at a temperature lower than 850 ° C., so it is desirable to anneal at 850 ° C. or higher. However, 10
When the temperature exceeds 50 ° C, the γ phase appears and the Goss orientation α
In addition to destroying the grain structure, the removal rate of C and N is reduced. The holding time of this purification annealing is at least
7 h is required, but holding for more than 100 h is not necessary because removal is saturated. Therefore, in the latter half of the finish annealing, a purification annealing is performed in a hydrogen atmosphere in a temperature range from 925 ° C. to 1050 ° C., preferably for 7 to 100 hours.

It is not always necessary to clearly distinguish the secondary recrystallization process and the purification annealing process as described above. In the temperature range of 825 to 1050 ° C., an atmosphere containing nitrogen at a relatively low temperature in the initial stage of annealing, From the middle stage to the latter stage, an atmosphere in which the amount of nitrogen is reduced and the amount of hydrogen is increased at a higher temperature may be used, and the total time of finish annealing may be up to 200 hours.

The application of the annealing separating agent for preventing the seizure during the annealing before the finish annealing is the same as the usual method for producing a grain-oriented electrical steel sheet. As a process after the finish annealing, as in the case of a normal grain-oriented electrical steel sheet, after removing the annealing separator, an insulating coating may be applied or a flattening annealing may be performed.

[0049]

【Example】

[Example 1] A slab having a steel composition shown in Table 1 was heated at a temperature of 1253.
℃, finishing temperature (FT) 870 ℃, and winding temperature (C
T) Hot rolling was performed at 700 ° C. to obtain a plate thickness of 2.3 mm. At this stage, when observing the optical microscope structure of the cross section of each steel sheet, it was confirmed that the recrystallized portions from both surfaces of each steel sheet were about 20% of the total plate thickness, that is, about 10% on each side. . After pickling these and cold rolling to 0.35 mm thickness,
Continuous annealing was performed at 80 ° C. for 30 s soaking, and then an annealing separator was applied to finish annealing. For finish annealing, secondary recrystallization was performed by soaking at 875 ° C for 24 hours in an atmosphere of 25% nitrogen and the balance of hydrogen, and then an atmosphere of 100% hydrogen was used.
It was soaked at 50 ° C for 30 hours. After the flattening and annealing, a test piece was cut out from each steel sheet in parallel with the rolling direction by the method specified in JIS, and the magnetic properties were measured using an Epstein frame.

[0050]

[Table 1]

The measurement results of the magnetic properties are also shown in Table 1. The magnetic properties of the test Nos. 1 and 9-12 are compared with the magnetic properties of the products of the extremely low C slab having a C content of less than 0.01%, and are determined by the present invention. Test Nos. 2, 5 and 8 with slabs containing some C in the range have excellent magnetic flux density and iron loss. Here, in the test number 3, C is too high, and decarburization cannot be sufficiently performed in the annealing process. In Test Nos. 4 and 6, the Al content was out of the range defined by the present invention, and in Test No. 7 since Si and Mn exceeded the regulation range defined by the formula, it is considered that the γ phase appeared during finish annealing. The development of Goss orientation was insufficient.

Example 2 Using the B steel shown in Table 1, the slab heating temperature was set to 1250 ° C., FT and CT were changed, and hot rolling was performed. Then, depending on the steel sheet, the hot rolled sheet was further annealed. Table 2 shows these conditions. The optical microscope structure of the cross section of each of the steel sheets before cold rolling was observed, and the results of examining the ratio of the recrystallized portion are also shown in Table 2. Next, these steel plates were cold-rolled to obtain the final plate thickness. In addition, some steels were further subjected to intermediate annealing and secondary cold rolling. The manufacturing process conditions are also shown in Table 2.

[0053]

[Table 2]

After cold rolling, continuous annealing was performed at 890 ° C. for 30 seconds soaking, and then an annealing separator was applied and finish annealing was performed. The finish annealing conditions are 875 ° C and 24 hours in an atmosphere of 25% nitrogen and the balance hydrogen.
After soaking, the atmosphere was changed to 100% hydrogen and 950 ℃ for 24 hours.
And soaking. After flattening and annealing, a test piece was cut out from each steel sheet, and magnetic properties were measured using an Epstein frame. The measurement results of these magnetic properties are also shown in Table 2.

In Test Nos. 15 and 20, the recrystallized portion ratio of the steel sheet before cold rolling is out of the range defined by the present invention.
In comparison with them, in the case of all other test numbers, magnetic flux density and iron loss both show excellent values, and the ratio of the recrystallized portion of the steel sheet before cold rolling deviates from the range determined by the method of the present invention. It is clear that this results in poor magnetic properties.

[Example 3] Using the E steel slabs shown in Table 1, hot rolling was performed at a heating temperature of 1200 ° C, FT 820 ° C and CT 500 ° C to obtain a plate thickness of 2.3 mm, and after pickling for 3 hours at 650 ° C. Annealed. Using this steel sheet, warm rolling was performed at the temperature shown in Table 3 to finish it to a thickness of 0.35 mm, and after continuous annealing at 850 ° C for 1 min soaking, 875 ° C in an atmosphere of 25% nitrogen and the balance hydrogen.
After soaking for 24 h at 950 ° C, 24 hours in an atmosphere of 100% hydrogen.
h Soaking finish annealing was performed.

In the case of test number 27, after rolling to 0.9 mm
Intermediate annealing is performed at 900 ° C for 30 s, then rolled
It was 0.35 mm. Rolling temperature in this case is 235 ℃
And

The magnetic measurement results of the obtained steel sheet are also shown in Table 3. By applying warm rolling as compared with ordinary cold rolling,
It can be seen that both iron loss and magnetic flux density are improved.

[0059]

[Table 3]

FIG. 1 shows the relationship between the iron loss of the product steel sheet and the magnetic flux density. Here, the production conditions from the hot rolling to the final annealing are the same as in the case of the present invention for the case where the plate thickness of the product steel sheet as a result of Examples 1 to 3 is 0.35 mm, but the C content of the material steel sheet is the same. Is displayed separately from an example outside the range defined by the present invention. As is clear from this, when the C content of the raw steel sheet is in the range defined by the present invention, the iron loss is lower than that in the case of extremely low C, and further, if warm rolling is applied, the iron content is further improved. It is clear that both loss and magnetic flux density are improved.

[0061]

As is clear from the above description, according to the manufacturing method of the present invention, by using a slab containing a small amount of C in the manufacture of a high Mn-type grain-oriented electrical steel sheet,
It becomes possible to more stably manufacture a steel sheet having more excellent magnetic properties.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between iron loss (W _17/50 ) and magnetic flux density (B ₈ ) of a product steel sheet.

Claims (4)

[Claims] 1. In weight%, C: more than 0.010% to 0.030%,
Si: 1.5-4.0%, Mn: 1.0-5.0%, S: 0.01%
Below, sol.Al: 0.003 to 0.03%, N: 0.0010 to 0.010
%, And Si (%)-0.5 x Mn (%) ≤ 2.0, with the balance being Fe and inevitable impurities, and the total thickness from 10 to 70 from both surfaces. % Of the recrystallized steel sheet is cold-rolled once or cold-rolled twice with intermediate annealing to obtain the final thickness, then rapidly heated and annealed, and then at 825 to 1050 ° C. A method for producing a high Mn-type grain-oriented electrical steel sheet, which comprises performing finish annealing in the temperature range of 1. 2. The total plate thickness of 10 from both surfaces according to claim 1.
When the steel sheet with 70% to 70% recrystallized is rolled once or twice with intermediate annealing to obtain the final thickness, at least one rolling is performed in a temperature range of 50 to 250 ° C. A method for producing a high Mn-type grain-oriented electrical steel sheet, which comprises rolling, followed by rapid heating and annealing, and then finish annealing in a temperature range of 825 to 1050 ° C. 3. Finishing temperature in hot rolling process (FT: ° C.)
And the coiling temperature (CT: ° C.) satisfy the following formulas and formulas to make a steel sheet with 10 to 70% of the total plate thickness from both surfaces before re-rolling. The method for producing a high Mn-type grain-oriented electrical steel sheet according to claim 1 or 2, which is characterized. 1250- (2/3) × FT ≦ CT ≦ 1300- (2/3) × FT ··· 780 ≦ FT ≦ 930 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 4. A coiling temperature of hot rolling is set to 600 ° C. or lower,
After descaling the obtained coil, it is annealed in the temperature range of 625 to 950 ℃, and 10 to 70% of the total thickness from both surfaces before cold rolling.
3. The method for producing a high Mn-based grain-oriented electrical steel sheet according to claim 1 or 2, wherein the steel sheet is a recrystallized portion.