JPH07138642A - Production of grain-oriented electrical steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To economically stabilize magnetic properties at a higher order by discriminating the necessity or unnecessity of annealing after hot rolling by low temp. slab heating method from AIN precipitation quantity and, as necessary, adding the annealing of hot rolled sheet. CONSTITUTION:A slab consisting of, by weight, <=0.075% C, 2.2-4.5% Si, 0.010-0.060% acid-soluble Al, <=0.0130% N, <=0.014% S+0.405 Se, 0.045-0.8% Mn and the balance Fe essentially is used. After the slab is heated to <1280 deg.C and hot rolled, the final high draft cold rolling of >=80% draft is executed, next, in a stage where decarburization annealing and final finish annealing are executed, when N content as AlN after hot rolling is taken as NasAlN and, at the time of N-NasAlN >=0.0010% and (NasAlN)/N <=0.75, the annealing of hot rolled sheet at 800-1200 deg.C is applied. After the completion of decarburization annealing, the grain size of primary crystallization until the final finish annealing is started is taken as 18-36mum, nitriding is executed while secondry recrystallization in the final finish annealing is started and nitrogen of >=0.0010% is absorbed into the steel sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which is used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional magnetic steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and are required to have excellent magnetic characteristics such as excitation characteristics and iron loss characteristics. As a numerical value showing the excitation characteristic, the strength of a normal magnetic field is 8
A magnetic flux density B _{8 at} 00 A / m is used. In addition, as a numerical value showing the iron loss characteristic, the iron loss per kg when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz is W _17/50.
Are using. The magnetic flux density is the most dominant factor of the iron loss characteristics, and generally speaking, the higher the magnetic flux density, the better the iron loss characteristics. Generally, when the magnetic flux density is increased, the secondary recrystallized grains become large, which may result in poor iron loss characteristics. On the other hand, by controlling the magnetic domains, the iron loss characteristics can be improved regardless of the grain size of the secondary recrystallized grains.

This unidirectional electrical steel sheet undergoes secondary recrystallization in the final finishing annealing step to develop a so-called Goss structure having {110} on the steel sheet surface and <001> axis in the rolling direction. Being manufactured. In order to obtain good magnetic properties, it is necessary to highly align <001>, which is the easy magnetization axis, in the rolling direction.

A typical technique for producing such a high magnetic flux density unidirectional electrical steel sheet is Japanese Patent Publication No. 40-15644.
There is a method described in JP-B No. 51-13469. In the former, MnS and AlN are used as main inhibitors, and in the latter, MnS, MnSe, Sb, etc. are used. Therefore, in the current technology, it is essential to appropriately control the size, morphology and dispersion state of the precipitates that function as these inhibitors. Speaking of MnS, in the current process, MnS is generated when the slab is heated before hot rolling.
A method is used in which the solid solution is once completely dissolved and then precipitated during hot rolling.

A temperature of about 1400 ° C. is required to completely dissolve the required amount of MnS for secondary recrystallization. This is higher than the slab heating temperature of ordinary steel by 200 ° C or more, and this high-temperature slab heating treatment requires 1) a high-temperature slab heating furnace dedicated to grain-oriented electrical steel. 2) The energy intensity of the heating furnace is high. 3) The amount of molten scale increases, and the adverse effect on operation is large, as seen in so-called shaving.

In order to avoid such problems, the slab heating temperature should be lowered to the same level as that of ordinary steel, but at the same time, the amount of MnS effective as an inhibitor should be reduced or not used at all. Means that the destabilization of the secondary recrystallization is inevitably brought about. Therefore, in order to realize low-temperature slab heating, it is necessary to strengthen the inhibitor in some form with precipitates other than MnS to sufficiently suppress normal grain growth during finish annealing.

As such inhibitors, in addition to sulfides, nitrides, oxides and grain boundary precipitation elements are considered,
Examples of known techniques include the following.
In Japanese Examined Patent Publication No. 54-24685, As, Bi, Sn,
A method of controlling the slab heating temperature in the range of 1050 to 1350 ° C. by containing grain boundary segregation elements such as Sb in steel is disclosed. JP-A-52-24116 discloses Al, Zr, Ti, It discloses a method for controlling the slab heating temperature in the range of 1100 to 1260 ° C. by containing a nitride forming element such as B, Nb, Ta, V, Cr and Mo. Further, in JP-A-57-158322, low-temperature slab heating is performed by lowering the Mn content and setting the Mn / S ratio to 2.5 or less, and further adding Cu to stabilize secondary recrystallization. The technology to do is disclosed.

Techniques have also been disclosed in which improvements are made from the metallographic side in combination with the reinforcement of these inhibitors. That is, in JP-A-57-89433, S, in addition to Mn,
Elements such as Se, Sb, Bi, Pb, Sn, and B are added, and the columnar crystal ratio of the slab and the secondary cold rolling reduction are combined to realize low-temperature slab heating at 1100 to 1250 ° C. Further, in JP-A-59-190324, in addition to S or Se, an inhibitor is mainly composed of Al and B and nitrogen, and a secondary recrystallization is performed by performing pulse annealing at the time of primary recrystallization annealing after cold rolling. The technology to stabilize is released.

As described above, in order to realize the low temperature slab heating in the production of grain-oriented electrical steel sheet, great efforts have been made so far. Furthermore, JP-A-59-56522
In Japanese Patent Laid-Open Publication No. 2008-242242, a technique is disclosed which enables low temperature slab heating by setting Mn to 0.08 to 0.45% and S to 0.007% or less. By this method, the problem of defective linear secondary recrystallization of the product due to coarsening of the slab crystal grains during heating of the high temperature slab was solved.

[0010]

Although the method using low temperature slab heating is originally intended to reduce the manufacturing cost, it cannot be industrialized unless it is a technique that can stably obtain good magnetic characteristics. The present inventors, for industrialization of low-temperature slab heating, control the average grain size of primary recrystallization before final finishing annealing, and after hot rolling, nitriding the steel sheet between the start of secondary recrystallization of final finishing annealing. We have built a technology that is based on The nitride formed by this nitriding treatment is mainly AlN at the start of secondary recrystallization. As an inhibitor that does not easily change at high temperatures, Al
N is selected, and in that sense, the inclusion of Al in the slab is an essential condition.

On the other hand, it is necessary to reconsider that N is contained in the slab more than necessary from the viewpoint of the present technical system.
In other words, if there is an indispensable Al in the slab and a certain amount of N or more, in the process from slab heating to decarburization annealing, Al
N is formed, which affects the grain growth of primary recrystallized grains during decarburization annealing. An object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet which has excellent characteristics without magnetic fluctuation due to low-temperature slab heating, based on AlN precipitation control in the above process.

[0012]

The gist of the present invention is as follows. (1) C: 0.075% or less by weight ratio, Si: 2.2
4.5%, acid-soluble Al: 0.010 to 0.060%,
N: 0.0130% or less, S + 0.405Se: 0.0
A slab containing 14% or less, Mn: 0.05 to 0.8%, and the balance Fe and unavoidable impurities at 1280 ° C.
In the method for producing a unidirectional electrical steel sheet by heating at a temperature of less than 1, hot rolling, final cold rolling with a draft of 80% or more, followed by decarburizing annealing and final finishing annealing. The N amount (weight ratio) as AlN in the plate is N as AlN
And N-N as AlN and (N as AlN) / N
Based on the value of, it is determined whether or not hot-rolled sheet annealing is performed, and after decarburization annealing is completed, the average grain size of primary recrystallized grains until the start of final finishing annealing is set to 18 to 35 μm, and after hot rolling, final finishing is performed. 0.0010% by weight of steel plate before the start of secondary recrystallization of annealing
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which is characterized by performing the nitriding treatment for absorbing nitrogen as described above.

(2) In the preceding paragraph, N-N as A is used for the hot rolled sheet.
1N ≧ 0.0010% and (N as AlN) / N ≦ 0.
In the case of 75, a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by performing hot-rolled sheet annealing at 800 to 1200 ° C. (3) A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which further comprises Sn: 0.01 to 0.15% as a component of the slab in the above (1) and (2).

[0014]

The unidirectional electrical steel sheet targeted by the present invention is
Molten steel obtained by the conventional steelmaking method is cast by a continuous casting method or an ingot casting method, and if necessary, a slab is formed by interposing the agglomeration process, and subsequently hot rolled into a hot rolled sheet. According to the above, the hot-rolled sheet is annealed, then subjected to final cold rolling with a reduction rate of 80% or more, and then sequentially subjected to decarburization annealing and final finishing annealing.

The present inventors have examined in detail the cause of magnetic fluctuation and its solution when a low temperature slab heating material is manufactured by a single cold rolling method in which hot-rolled sheet annealing is omitted. And
As a result, the amount of N as AlN in the hot rolled sheet (N as Al
Based on N), by performing feedback to hot rolling conditions or feedforward such as decarburization annealing conditions,
They found that the magnetic fluctuation could be drastically reduced.

However, the hot rolling process is 5 to 20 TON.
Since it is a process that is manufactured with a slab or strip of a certain degree, if the N amount as AlN in the hot rolled sheet deviates from a proper range, in the subsequent step in the process that does not perform hot rolled sheet annealing, He found that he could not make up for the material deficiency. As a coping measure in this case, it was found that it is very effective to judge whether or not the hot-rolled sheet needs to be annealed based on the amount of N as AlN in the hot-rolled sheet.

First, the effect of the present invention will be described based on experimental results. FIG. 1 shows the relationship between the amount of N—N as AlN in the hot rolled sheet and the magnetic flux density of the product. In this case, the weight ratio is C:
0.026 to 0.048%, Si: 2.6 to 3.2%,
Acid-soluble Al: 0.024 to 0.039%, N: 0.0
002 to 0.0096%, Mn: 0.09 to 0.14
%, S: 0.005 to 0.007% is contained,
A 250 mm-thick slab with the balance being Fe and inevitable impurities was held at a temperature of 1000 to 1250 ° C. for about 120 minutes, followed by rough hot rolling in 7 passes to a thickness of 40 mm, and then 6
Finishing hot rolling was performed with a pass to a thickness of 2.3 mm. At this time, water cooling was performed during rough rolling, the time between rough hot rolling and finish hot rolling was intentionally changed, and the time from the end of hot rolling to the start of water cooling was variously changed.

The hot rolled sheet is (A) not annealed, (B) treated at 1000 ° C. for 3 minutes (soaking) and then rapidly cooled, and then subjected to a strong rolling reduction of about 85%. Rolling was performed to obtain a cold rolled sheet having a final sheet thickness of 0.335 mm. The cold-rolled sheet was subjected to decarburizing annealing at 840 ° C. for 150 seconds, and then, at the time of annealing at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the annealing atmosphere to allow the steel sheet to absorb nitrogen.

The amount of N after this nitriding treatment is 0.0185-
It was 0.0243% by weight, and the average particle size of the primary recrystallized grains (average value of equivalent circle diameter) was 20 to 28 μm.
An annealing separator containing MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed. After that, the magnetic flux density of the product was measured and taken for a hot-rolled sheet with the same composition and the same hot-rolling condition ΔB ₈ = B ₈ (with hot-rolled sheet annealing) -B ₈
The value (without hot-rolled sheet annealing) was determined. In the hot-rolled sheet in this experiment, the amount of N (weight ratio) present as AlN [N as AlN] was determined by chemical analysis, and N-N as A
The amount of IN, (N as AlN) / N was calculated for each sample.

As is apparent from FIG. 1, in the hot-rolled sheet, N-N as AlN ≧ 0.0010% and (N as
When AlN) /N≦0.75, the value of B ₈ is improved by 0.03 T or more by performing hot-rolled sheet annealing, and good magnetic properties are obtained. A in the hot-rolled sheet shown in FIG.
Although the mechanism of the relationship between the amount of 1N precipitation and the effect of hot-rolled sheet annealing is not necessarily clear, the present inventors presume as follows.

The present invention was made by the inventors of the present invention as disclosed in JP-A-2-182.
It belongs to a technical system disclosed in Japanese Patent No. 866, which is basically based on making the crystal structure after decarburization annealing appropriate. on the other hand,
N dissolved in the solid solution at the completion of slab heating is a fine nitride (mainly AlN) during hot rolling or during decarburization annealing (especially at temperature rise).
It is believed that It is considered that the size and precipitation amount of this fine nitride fluctuate even with a slight temperature change during decarburization annealing. However, the grain growth suppression effect (Zener factor) by the precipitate is inversely proportional to the size of the precipitate and proportional to its volume fraction. Therefore, even if the amount of solute N at the time of completion of slab heating is reduced too much, the effect of suppressing grain growth of precipitates becomes too small, and as a result, grain growth at the time of decarburization annealing becomes too conspicuous to control the crystal structure Will be difficult.

As described above, it is important to control the precipitation of AlN in the upper step, but it is not easy to control it by adjusting the process conditions such as the composition and hot rolling. In the case of the technique of performing hot-rolled sheet annealing only in an unavoidable situation, a new norm for AlN precipitation control is required. From this viewpoint, the present inventors have obtained the knowledge of FIG. 1 as a result of extensive experiments and analysis. That is, when the amount of N as AlN and the ratio with respect to the amount of N in the hot rolled sheet are within a predetermined range, the magnetic stabilization by the hot rolled sheet annealing is remarkable.

This predetermined range corresponds to the case where AlN precipitation is insufficient in the hot-rolled sheet, and it is possible to stabilize the magnetism by subjecting the hot-rolled sheet annealing to uniform AlN precipitation. It is thought that it will greatly contribute to. In the case of the above-mentioned predetermined range, a product having good magnetism cannot be stably obtained without annealing the hot-rolled plate, so that it can be judged in the state of the hot-rolled plate, and the product has good magnetism. The industrial significance of carrying out actions (hot rolled sheet annealing) is great.

Next, the reasons for limiting the constituent features of the present invention will be described. First, the reasons for limiting the components of the slab and the slab heating temperature will be described in detail. If C is too large, the decarburization annealing time becomes long and it is not economical, so it was made 0.075% by weight (hereinafter simply referred to as%) or less. In terms of magnetic properties, a particularly preferable range is 0.020 to 0.070%. When Si exceeds 4.5%, cracking during cold rolling becomes significant, so the content of Si is set to 4.5% or less. On the other hand, if it is less than 2.2%, the specific resistance of the material is too low, and the low iron loss required for the transformer core material cannot be obtained. Al is AlN or (Al, S, which is necessary for stabilizing the secondary recrystallization.
i) 0.010 as acid-soluble Al for securing N
% Or more is required. If the acid-soluble Al exceeds 0.060%, the AlN of the hot-rolled sheet becomes unsuitable and the secondary recrystallization becomes unstable, so the content was made 0.060% or less.

When N exceeds 0.0130%, blisters on the surface of the steel sheet called blisters occur, so N is set to 0.0130% or less. Even if MnS and MnSe are present in the steel, it is possible to improve the magnetic properties by properly selecting the conditions of the manufacturing process. However, if S and Se are high, secondary recrystallization defective portions called linear fine grains tend to occur, and in order to prevent the generation of this secondary recrystallization defective portion, (S + 0.405Se) ≦ 0.014
Should be%. When S or Se exceeds the above value, the probability of occurrence of a secondary recrystallization defect portion increases even if the manufacturing conditions are changed, which is not preferable. In addition, the time required for purification in the final finish annealing is too long, which is not preferable, and it is meaningless to increase S or Se unnecessarily from this viewpoint.

The lower limit of Mn is 0.05%. 0.0
If it is less than 5%, the shape (flatness) of the hot-rolled sheet obtained by hot rolling, that is, the side edge portion of the strip becomes wavy, which causes a problem of lowering the product yield. On the other hand, when the Mn content exceeds 0.8%, the magnetic flux density of the product is lowered, which is not preferable, so the upper limit of the Mn content was set to 0.8%. Sn
Is known as a grain boundary segregation element and is an element that suppresses grain growth. On the other hand, Sn is completely in solid solution during heating of the slab, and it is considered that Sn is evenly dissolved in the slab during heating having a temperature difference of several tens of degrees C. which is usually considered. Therefore, it is considered that Sn, which is uniformly distributed in the slab during heating despite the temperature difference, also acts locally in terms of the grain growth suppressing effect during decarburization annealing.

Therefore, it is considered that Sn has the effect of diluting the non-uniformity of grain growth during decarburization annealing due to the non-uniformity of AlN. Therefore, the addition of Sn is effective in further reducing the fluctuation of the magnetic properties of the product. The proper range of Sn is 0.01 to 0.15%
And Below this lower limit, the grain growth suppressing effect is too small, which is not preferable. On the other hand, if the upper limit is exceeded, nitriding of the steel sheet becomes difficult, which causes secondary recrystallization failure, which is not preferable.

In addition, it may be contained a small amount of Sb, Cu, Cr, Ni, B, Ti, Nb, etc., which are known as inhibitor constituent elements. In particular, B, Ti,
Nb and other nitride constituent elements are solid solution N in steel during slab heating.
It may be added positively to reduce the amount. When there are elements having a higher affinity for N than Al, B, Ti, and Nb contained from the total N amount when calculating the amount of N—N as AlN in the hot rolled sheet described later It is preferable to subtract the N amount of the nitride formed in order to improve the accuracy of the control effect in the present invention.

The slab heating temperature is limited to less than 1280 ° C. for the purpose of cost reduction in the same manner as ordinary steel. It is preferably 1200 ° C or lower. The heated slab is subsequently hot rolled to form a hot rolled plate. The hot rolling process is
Usually, after heating a slab having a thickness of 100 to 400 mm, both are rough hot rolling and finish hot rolling which are carried out by a plurality of passes. The method of rough hot rolling is not particularly limited, but Al
In order to promote N precipitation, it is preferable to take measures such as actively performing water cooling.

Regarding the time from rough hot rolling to finish hot rolling,
Although not particularly limited, starting the finish hot rolling over 1 second or more is preferable from the viewpoint of promoting precipitation of AlN.
Subsequent hot rolling for finishing is usually performed by high-speed continuous rolling for 4 to 10 passes. In the rolling distribution of normal hot rolling, the rolling ratio is high in the front stage and lower in the rear stage, and the shape is improved by lowering the rolling ratio. The rolling speed is usually 100 to 3000 m / min, and the time between passes is 0.01 to 100 seconds.

In order to secure the amount of AlN precipitation in the hot-rolled sheet, it is necessary to positively adjust the finish hot-rolling start temperature and finish temperature, and adjust the reduction distribution. It is also an effective means for controlling the amount of AlN precipitation that the work-induced precipitation is caused by positively increasing the rolling reduction in the temperature range (800 to 950 ° C.) where AlN is easily precipitated or in the vicinity thereof.

After the final pass of hot rolling, the steel sheet is usually 0.1-1
After being air-cooled for about 00 seconds, it is water-cooled, wound at a temperature of 300 to 700 ° C., and gradually cooled. The cooling process is not particularly limited, but a method of performing air cooling for 1 second or more after hot rolling and holding the steel sheet in the precipitation temperature range of AlN as long as possible is used for controlling the precipitation amount of AlN. Is preferred.

It was specified that whether or not to perform hot-rolled sheet annealing should be determined based on the values of N-N as AlN and (N as AlN) / N of the steel sheet after hot rolling. This is because it is possible to determine whether or not hot-rolled sheet annealing is necessary in order to stabilize the magnetic characteristics as shown in FIG. 1 by these amounts. Furthermore, if these ranges are N-N as AlN ≧ 0.0010% and (N
as AlN) /N≦0.75, 800-
Since the magnetic characteristics are stabilized when the hot-rolled sheet is annealed at 1200 ° C., these quantities are specified. The upper limit of N-N as AlN is not particularly limited, and is the upper limit of the N amount of 0.0130%.
Is allowed up to. Further, the lower limit of (N as AlN) / N is not particularly limited and can be up to 0. This is because it is possible to sufficiently precipitate AlN during annealing of the hot-rolled sheet, even if AlN is not precipitated at all in the hot-rolled sheet.

The lower limit of the temperature of hot-rolled sheet annealing is 800 ° C. Below this temperature, it is not easy to deposit AlN in a short time. The upper limit of the temperature of hot-rolled sheet annealing is 1
It was set to 200 ° C. This is because if this temperature is exceeded, the solid solution of AlN becomes remarkable and it is meaningless in terms of AlN precipitation, which is the greatest role of the hot-rolled sheet annealing in the present invention. In addition, the heat cycle of hot-rolled sheet annealing was performed at a high temperature (1000-
It is preferable that the temperature is 1200 ° C.) and the latter stage is low temperature (800 to 1000 ° C.) in terms of low temperature and uniform precipitation of the local non-uniformity of fine AlN precipitation due to partial solid solution of AlN.

This hot-rolled sheet is then subjected to hot-rolled sheet annealing as required based on the above-mentioned criteria, and finally cold-rolled at a rolling reduction of 80% or more. The reduction ratio of the final cold rolling is set to 80% or more by setting the reduction ratio within the above range by sharpening the {110} <001> oriented grains in the decarburized plate and the corresponding oriented grains ( This is because an appropriate amount of {111} <112> oriented grains, etc. can be obtained, which is preferable in increasing the magnetic flux density. The steel sheet after such cold rolling is subjected to decarburization annealing, annealing separation agent coating, and final finishing annealing by a usual method to obtain a final product. Here, after the decarburization annealing is completed, the average particle size of the primary recrystallized grains until the start of the final finishing annealing is 18 to 35 μm.
It is necessary to control to m. The reason is that it is easy to obtain a good magnetic flux density in the range of the average particle size, and the change of the magnetic flux density due to the particle size variation is small.

Then, it is defined that the steel sheet is subjected to the nitriding treatment before the secondary recrystallization of the final finish annealing after the hot rolling.
This is because the inhibitor strength required for secondary recrystallization tends to be insufficient in the process that is premised on low temperature slab heating as in the present invention. The nitriding method is not particularly limited, and a method of mixing NH ₃ gas in an annealing atmosphere after decarburization annealing to perform nitriding, a method of using plasma, adding a nitride to an annealing separator and adding a nitride to the final finishing annealing is performed. Any method such as a method of absorbing nitrogen formed by separation of nitrides in the temperature into the steel sheet, a method of increasing the N ₂ partial pressure in the atmosphere of final annealing and nitriding the steel sheet may be used. The nitriding amount is required to be 10 ppm or more in order to stably develop the secondary recrystallization.

[0037]

【Example】

Example 1 By weight%, Si: 2.95%, C: 0.031%, acid-soluble Al: 0.030%, N: 0.0061%, Mn:
A 250 mm thick slab containing 0.13% and S: 0.006% was held at 1200 ° C. for 90 minutes, and then 40 times in 7 passes.
After roughly hot rolling to a thickness of mm, finishing hot rolling was performed in 6 passes to obtain a hot rolled sheet having a thickness of 2.3 mm. N as A of this hot rolled sheet
1N was analyzed to analyze N-N as AlN and (N as Al
N) / N is calculated to be 0.0031% and 0.4, respectively.
It was 9. In this case, it was predicted from FIG. 1 that the magnetic flux density was improved by 0.03 T or more by performing the hot-rolled sheet annealing.

Therefore, the hot rolled sheet was (1) annealed at 1100 ° C. for 30 seconds and then at 900 ° C. for 30 seconds and then rapidly cooled. And for comparison, (2)
The hot rolled sheet was annealed under the condition that it was not annealed. After about 8
Cold rolling at a rolling reduction of 5% to form a 0.335 mm thick cold rolled sheet, and decarburization annealing (25% N ₂
+ 75% H ₂ , dew point 62 ° C), and then 770
Annealing is performed for 30 seconds at ℃, and NH _{3 is} added in the annealing atmosphere.
Gas was mixed and the steel sheet was made to absorb nitrogen. The N content of the steel sheet after nitriding was 0.0218 to 0.0229%, and the average grain size of the primary recrystallized grains of the steel sheet was 21 to 25 μm. Then, an annealing separator having MgO as a main component was applied to this steel sheet, and final finish annealing was performed by a known method. Table 1 shows the experimental conditions and the results of magnetic properties.

[0039]

[Table 1]

Example 2 By weight%, Si: 2.92%, C: 0.030%, acid-soluble Al: 0.036%, N: 0.0064%, Mn:
A 250 mm thick slab containing 0.12% and S: 0.005% was held at 1080 ° C for 90 minutes, and then 4 times in 7 passes.
Rough hot rolling was performed to a thickness of 0 mm, and then finish hot rolling was performed in 6 passes to obtain a hot rolled sheet having a thickness of 2.3 mm. N as A of this hot rolled sheet
1N was analyzed to analyze N-N as AlN and (N as Al
N) / N is calculated to be 0.0006% and 0.9, respectively.
It was 1. In this case, it was predicted from FIG. 1 that the improvement of the magnetic flux density due to the hot-rolled sheet annealing was less than 0.03T.

Therefore, this hot-rolled sheet was pickled without annealing the hot-rolled sheet, cold-rolled at a rolling reduction of about 88%, and then 0.28.
A cold rolled sheet having a thickness of 5 mm was used. Then, decarburization annealing (25% N ₂ + 75% H ₂ , holding at 840 ° C. for 150 seconds, dew point 62
° C.) alms, thereafter, subjected to annealing for holding 30 seconds at 750 ° C., was allowed to absorb nitrogen steel is mixed NH ₃ gas into the annealing atmosphere. The N content of the steel sheet after nitriding is 0.0235.
%, And the average grain size of the primary recrystallized grains of the steel sheet is 24 μm.
Met. Then, an annealing separator having MgO as a main component was applied to this steel sheet, and final finish annealing was performed by a known method. The result of this magnetic property was B ₈ (T) = 1.91T.

Example 3 By weight%, Si: 3.11%, C: 0.040%, acid-soluble Al: 0.037%, N: 0.0068%, Mn:
0.13%, S: 0.007%, and (1) S
Two 250 mm thick slabs containing n <0.005% and (2) Sn: 0.07% were held at 1150 ° C. for 90 minutes, then roughly hot rolled to 40 mm thickness in 7 passes, and then ,
Finishing hot rolling was performed in 6 passes to obtain a hot rolled sheet having a thickness of 2.6 mm.
In this hot rolling, forced water cooling is performed during (A) rough hot rolling, and the finish hot rolling start temperature is 90 to 1 from the slab heating temperature.
The hot rolling method in which the temperature is lowered by 00 ° C., (B) by water cooling which is lighter than A, the finish hot rolling start temperature is 30 to 30
Two types of hot rolling, which are hot rolling methods of lowering the temperature by 50 ° C., were performed.
These hot rolled sheets were analyzed for N as AlN, and N-N asA
1N and (N as AlN) / N were calculated, and when it was predicted from FIG. 1 that the improvement of the magnetic flux density by performing hot-rolled sheet annealing was 0.03 T or more, the hot-rolling was performed at 1000 ° C. for 180 seconds. The sheet was annealed, and when the improvement in the magnetic flux density was less than 0.03T, the hot-rolled sheet was not annealed. When the hot-rolled sheet was annealed, it was subjected to a post-process even under the condition that the hot-rolled sheet was not annealed for comparison.

Then, cold rolling is performed at a reduction rate of about 87%,
It was a cold-rolled sheet having a thickness of 0.335 mm. Then, decarburization annealing (25% N ₂ + 75% H ₂ , holding at 840 ° C. for 150 seconds,
Dew point was 62 ° C.), and then annealing was carried out at 750 ° C. for 30 seconds, and NH ₃ gas was mixed into the annealing atmosphere to allow the steel sheet to absorb nitrogen. The N content of the steel sheet after nitriding was 0.
It was 0220 to 0.0243%, and the average grain size of the primary recrystallized grains was 21 to 27 μm. Then, an annealing separator having MgO as a main component was applied to this steel sheet, and final finish annealing was performed by a known method. Table 2 shows the experimental conditions and the results of magnetic properties.

[0044]

[Table 2]

[0045]

According to the present invention, the necessity of annealing the hot-rolled sheet is judged based on the amount of AlN precipitation in the hot-rolled sheet, the average grain size of the primary recrystallized grains is controlled, and after hot rolling, the final finishing is performed. By subjecting the steel sheet to nitriding treatment before the start of secondary recrystallization of annealing, and further by adding Sn, good magnetic characteristics can be stabilized even if low-temperature slab heating is performed and hot-rolled sheet annealing is omitted. Therefore, the industrial effect is great.

[Brief description of drawings]

FIG. 1 is an amount of N—N as AlN in a hot rolled sheet, (N as Al
It is a graph showing the relationship between the amount of N) / N and the margin of improvement of the magnetic flux density by performing hot-rolled sheet annealing.

Claims (3)

[Claims] 1. By weight ratio, C: 0.075% or less, Si: 2.2-4.5%, acid-soluble Al: 0.010-0.060%, N: 0.0130% or less, S + 0. 405 Se: 0.014% or less, Mn: 0.05 to 0.8%, 128 slabs with the balance Fe and unavoidable impurities
In a method of producing a unidirectional electrical steel sheet by heating at a temperature of less than 0 ° C., hot rolling, final hot rolling at a rolling reduction of 80% or more, followed by decarburizing annealing and final finishing annealing, The N content (weight ratio) of AlN in the hot rolled sheet is N as
When AlN, N-N as AlN and (N as Al
Based on the value of N) / N, it is determined whether or not hot-rolled sheet annealing is performed, and after decarburization annealing is completed, the average grain size of primary recrystallized grains until the start of final finishing annealing is set to 18 to 35 μm, and hot rolling is performed. Then, before the secondary recrystallization of the final finish annealing, 0.001
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises performing a nitriding treatment for absorbing 0% by weight or more of nitrogen. 2. A N-based hot rolled sheet is used as a standard for annealing the hot rolled sheet.
N as AlN ≧ 0.0010% and (N as AlN) /
N ≦ 0.75 and the annealing temperature at that time is 800 to 1
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the temperature is 200 ° C. 3. As a slab component, Sn: 0.01-
0.15% is contained, The manufacturing method of the grain-oriented electrical steel sheet excellent in the magnetic characteristic of Claim 1 or 2 characterized by the above-mentioned.