JPH07138643A - Production of grain-oriented electrical steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To stabilize magnetic properties at a higher order by controlling the hot rolling conditions of subsequent slabs based on AlN precipitation quantity of a hot rolled sheet of a low temp. heated slab. CONSTITUTION:The slab contg. 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, 0.05-0.8% Mn and the balance Fe is used. This slab is heated to <=1280 deg.C, hot rolled and, after the final cold rolling at >=80% draft is executed without annealing the hot rolled sheet, decarburization annealing and the final finish rolling are executed. In such a case, N content as AIN of the hot rolled sheet is taken as NasAlN, N'=N-NasAlN of a first hot rolled sheet is compared with a proper value that is preliminarily determined and the hot rolling conditions of the subsequent slabs are determined. After the completion of decarburization annealing, the grain size of a primary crystallization until the final finish annealing is started is taken as 18-35mum, nitriding is executed during the secondary recrystallization of the final finish annealing and nitrogen of 0.010% 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 1 kg when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz is W _17/15.
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 exclusively for grain-oriented electrical steel, and 2) a high energy consumption rate of the heating furnace. 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, sulfides, nitrides, oxides, grain boundary precipitation elements, and the like are considered, and known techniques include, for example, the following. In Japanese Patent Publication No. 54-24685, As, Bi, Sn, S
A method of controlling the slab heating temperature in the range of 1050 to 1350 ° C. by including grain boundary segregating elements such as b in the 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
Since N is selected, it is essential that Al is contained in the slab in that sense.

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. The purpose of the present invention is to study the AlN precipitation control strategy in the above process,
Another object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet having excellent properties without magnetic fluctuation even if hot-rolled sheet annealing is omitted.

[0012]

The gist of the present invention is as follows. (1) C: 0.075% or less, Si: 2.2 by weight ratio
~ 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.
Heating at a temperature of less than 1 hour, hot rolling, followed by final hot rolling with a reduction of 80% or more without hot-rolled sheet annealing, followed by decarburization annealing and final finishing annealing in one direction In a method for producing a heat-resistant electrical steel sheet, the method comprising:
When the N content (weight ratio) is N as AlN, N ^*
= N-N as AlN is used to determine the conditions of hot rolling performed after the hot rolling, and the average value of primary recrystallized grains after the completion of decarburizing annealing is 18 to 35 μm
The unidirectional electromagnetic wave having excellent magnetic properties, characterized in that the steel sheet is subjected to a nitriding treatment for absorbing 0.0010% by weight or more of nitrogen before the secondary recrystallization of the final finish annealing after hot rolling. Steel plate manufacturing method. (2) In the above paragraph, Sn:
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by containing 0.01 to 0.15%.

[0013]

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 making method, and if necessary, the slab is separated by a slab, and then hot-rolled into a hot-rolled sheet. Without being annealed, the rolled sheet is subjected to final cold rolling with a reduction rate of 80% or more, followed by decarburization annealing and final finishing annealing in this order.

The present inventors have examined in detail the cause of magnetic fluctuation and its solution in the case of producing a low temperature slab heating material by the single cold rolling method without hot-rolled sheet annealing. And
As a result, the amount of N as AlN in the hot rolled sheet (N as Al
Based on the analysis value of N), it was found that the magnetic fluctuation can be drastically reduced by controlling the hot rolling conditions after the hot rolling.

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 (A)
C: 0.029%, Si: 2.8%, acid-soluble Al: 0.
035%, N: 0.0050%, Mn: 0.13%,
S: 0.007%, (B) C: 0.035%, Si:
3.10%, acid soluble Al: 0.037%, N: 0.0
25% containing 075%, Mn: 0.14%, S: 0.006%, and the balance Fe and inevitable impurities.
A 0 mm thick slab of two components was made. And 1
After holding at a temperature of 050 to 1250 ° C. for about 90 minutes, rough rolling was performed in 7 passes to a thickness of 40 mm, and finish hot rolling was performed in 6 passes 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.

Without hot-rolling sheet annealing, the hot-rolled sheet was subjected to strong reduction rolling of about 85% to obtain a cold-rolled sheet having a final thickness of 0.335 mm, N ₂ : 25%, H ₂ : 75%, D. P. =
Decarburization annealing was performed at 830 ° C. for 150 seconds in a 62 ° C. atmosphere, and then NH ₃ gas was mixed into the annealing atmosphere during annealing at 750 ° C. for 30 seconds to cause nitrogen absorption in the steel sheet.

The amount of N after this nitriding treatment is 0.0181-
It was 0.0247% by weight, and the average particle size of primary recrystallized grains (average value of equivalent circle diameter) was 20 to 27 μm.
An annealing separator having MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed. In the hot rolled sheet in this experiment, the amount of N existing as AlN (= N as AlN) (weight ratio) was determined by chemical analysis, and N-
N as AlN was calculated to find the relationship with the magnetic flux density of the product.

As is clear from FIG. 1, the hot rolled sheet N--N
There is a correlation between the amount of as AlN and the magnetic flux density of the product.
The optimum value of -N as AlN varied depending on the components.
The mechanism of the effect of controlling the AlN precipitation amount in the hot rolled sheet shown in FIG. 1 is not necessarily clear, but 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,
In the case of low temperature slab heating as in the present invention, A during slab heating
Complete solution of 1N is not guaranteed. The AlN precipitation state during decarburization annealing affects the grain growth behavior of the primary recrystallized grains. As disclosed in JP-A-2-182866, if the crystal structure after decarburization annealing is controlled, good magnetic properties can be obtained. Therefore, the decarburization annealing temperature can be extremely lowered. If the temperature is increased, or the decarburization annealing time is extremely shortened or lengthened, decarburization becomes insufficient, or the oxide state of the surface layer such as FeO or SiO ₂ becomes inadequate and the product coating It causes a defect.

Therefore, since the temperature and time of decarburization annealing are naturally controlled, there is a desirable range for the precipitation state of AlN during decarburization annealing. The decarburization annealing conditions (annealing atmosphere, dew point, temperature, time) of the experiment shown in FIG. 1 are in a good condition range in terms of decarburizing property and product coating. Under this condition, it is shown that there is an appropriate range in the precipitation amount of AlN of the hot-rolled sheet, which means that the appropriate precipitation state of AlN during decarburization annealing can be changed to N-N as AlN of the hot-rolled sheet. It indicates that the amount can be indirectly checked.

Grain Growth Suppression Effect (Zener)
Factor) is inversely proportional to the size of the precipitate and proportional to its volume fraction. Almost 100% of N is precipitated as a nitride in the hot-rolled sheet, so the amount of N-N as AlN is mainly the amount of precipitation of Si ₃ N ₄ , Fe ₁₆ N _4, etc. that is precipitated after winding after hot rolling. Is understood to indicate. These unstable nitrides are
It is considered that it decomposes during decarburization annealing and reprecipitates as AlN. This AlN has dislocations increased by cold rolling as precipitation nuclei, and tends to be finely precipitated during the temperature rise during decarburization annealing. Therefore, the amount of N—N as AlN in the hot rolled sheet is It is understood that it indirectly represents the amount of fine AlN.

If the amount of this fine AlN is too large, grain growth during decarburization annealing is excessively suppressed, and the optimum decarburization annealing temperature becomes too high, which may even exceed the heating capacity of the decarburization annealing furnace. . Alternatively, if the amount of the fine AlN is too small, grain growth during decarburization annealing becomes too easy, and the optimum decarburization annealing temperature becomes too low, which may cause decarburization failure or surface oxide layer formation failure. Thus, N-N as A in hot rolled sheet
It is estimated that the 1N amount can be an important parameter in predicting and controlling the material quality of an intermediate product.

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 necessary for stabilizing the secondary recrystallization.
Alternatively, in order to secure (Al, Si) N, acid-soluble A
0.01% or more is required as l. Acid soluble Al
Is more than 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. Regarding N, if it exceeds 0.0130%, blisters on the surface of the steel sheet called blister occur, so 0.01
It was set to 30% 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, S and Se
If the value is high, secondary recrystallization defects called linear fine grains tend to occur. To prevent the generation of secondary recrystallization defects, (S + 0.405Se) ≦ 0.014% should be satisfied. Is.

If S or Se exceeds the above value, the probability of occurrence of secondary recrystallization defects becomes high regardless of how 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%.
If it is less than 0.05%, 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,
If 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, when heating the slab S
It is considered that n is completely in solid solution, and is uniformly dissolved even in the slab at the time of 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 nonuniformity of grain growth during decarburization annealing due to the nonuniformity 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.
%. 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 to this, it may be contained a small amount of Sb, Cu, Cr, Ni, B, Ti, Nb, etc. which are known as inhibitor constituent elements. Especially B, T
Nitride constituent elements such as i and Nb may be positively added in order to reduce the amount of solid solution N in the steel during slab heating. 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 control the precipitation amount of N, it is possible to take measures to actively perform water cooling, or to take a measure to lengthen the time between passes. On the contrary, in order to prevent the precipitation amount from being excessively increased, it is possible to take measures such as increasing the slab heating temperature or covering the steel sheet with a heat insulating cover between passes.

Regarding the time from rough hot rolling to finish hot rolling,
Although not particularly limited, if it is better to promote the precipitation of AlN, it is possible to take measures such as extending the time between passes, and conversely, if it is necessary to suppress the precipitation of AlN. For this, measures such as covering the steel plate with a heat retaining cover to reduce the temperature decrease are allowed. 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 the present invention, the finishing hot rolling conditions are not limited, but in order to secure the AlN precipitation amount in the hot rolled sheet,
Water is actively cooled between the passes, and the precipitation temperature range of AlN (80
It is also permitted to perform hot rolling for finishing at 0 to 1000 ° C., or conversely, to increase the rolling speed and raise the end temperature of finishing hot rolling in order to prevent excessive precipitation of AlN.

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 or the like for 1 second or more after hot rolling and keeping the steel sheet in the AlN precipitation temperature range as long as possible is not used for controlling the AlN precipitation amount. forgiven.

It was stipulated that the conditions of hot rolling performed after the hot rolling should be determined based on the analysis value of N ^* = NN-AlN in the hot rolled sheet. This is because there is a strong correlation between N ^* and magnetic characteristics as shown in FIG. Further, when hot rolling is performed in a factory, there are some fluctuation factors such as the temperature of the slab heating furnace, rough hot rolling, and cooling during finish hot rolling. Therefore, the analysis value of N ^* = N-N as AlN is measured with the hot rolled sheet, and if this value is larger than the appropriate value, the subsequent hot rolling conditions may be changed so that AlN is easily precipitated. If N ^* is smaller than the appropriate value, the subsequent hot rolling conditions may be changed so that AlN is hard to precipitate.

The method of determining the appropriate value of N ^* is not particularly limited, and a method of determining based on the result of the preceding experiment can be used. Further, the measures to control the subsequent hot rolling conditions are not particularly limited, slab heating temperature, rough hot rolling conditions, time between passes of rough hot rolling and finish hot rolling, air cooling time after finish hot rolling, Any of the cooling conditions such as hot rolling may be changed. The details of the change and the relationship between the change and the precipitation of AlN are as described in the section for explaining the hot rolling conditions of the present invention.

This hot-rolled sheet is then subjected to final cold rolling with a rolling reduction of 80% or more without performing hot-rolled sheet annealing. The reduction ratio of the final cold rolling is set to 80% or more because the reduction ratio in the above range makes the sharp decarburized plate {110} <0.
01> oriented grains and the corresponding oriented grains ({1
11} <112> oriented grains, etc.)
This is because it is preferable for increasing the magnetic flux density. The steel sheet after such cold rolling is decarburized and annealed by an ordinary method, an annealing separator is applied,
The final product is annealed to obtain the final product. Here, it is necessary to control the average grain size of the primary recrystallized grains to 18 to 35 μm after the completion of decarburization annealing and before the start of final finish annealing. 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.

[0036]

【Example】

Example 1 By weight%, Si: 3.05%, C: 0.030%, acid-soluble Al: 0.037%, N: 0.0080%, Mn:
A 250 mm-thick slab containing 0.14% and S: 0.006% was held at 1150 ° C for 1 hour, 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
ln was analyzed and N-N as AlN was calculated to be 0.0
It was 034%. In this case, it was expected that the magnetic properties would be poor. Therefore, when hot rolling the slab of the same component next time, (A) during rough hot rolling, forced water cooling was performed to set the finish hot rolling start temperature to the slab heating temperature. Hot rolling was performed by lowering the temperature by 70 to 80 ° C. For comparison, hot rolling under the same conditions as the hot rolling of (B) was also performed. In the case of the hot rolling condition of (A),
The N as AlN of the hot-rolled sheet was analyzed, and the N-N as AlN was calculated to be 0.0025%.

These two kinds of hot rolled sheets were pickled and cold rolled at a reduction rate of about 85% to obtain cold rolled sheets having a thickness of 0.335 mm. Then, decarburization annealing (25% at 150 ° C for 150 seconds)
N ₂ + 75% H ₂ , dew point 60 ° C.), and then 7
Annealing is carried out at 50 ° C for 30 seconds, and N
The steel plate was made to absorb nitrogen by mixing H ₃ gas. The N content of the steel sheet after nitriding is 0.0215 to 0.0232%,
The average grain size of the primary recrystallized grains of the steel sheet was 21 to 24 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.

[0038]

[Table 1]

Example 2 By weight%, Si: 3.25%, C: 0.045%, acid-soluble Al: 0.034%, N: 0.0061%, Mn:
A 250 mm-thick slab containing 0.13% and S: 0.005% was held at 1150 ° C. for 1 hour and then 3 passes 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
ln was analyzed and N-N as AlN was calculated to be 0.0
It was 032%. In this case, it was expected that the magnetic properties would be poor, so (A) when heating the slab of the same component next, the slab heating temperature was set to 1080 ° C., and the other conditions were the same as before. went. Also, for comparison,
(B) Hot rolling was also performed under the same conditions as the above hot rolling. Also in the case of the hot rolling condition of (A), N as AlN of the hot rolled sheet is analyzed, and N
The calculated —N as AlN was 0.0024%.

The two types of hot rolled sheets were pickled and cold rolled at a rolling reduction of about 88% to obtain cold rolled sheets having a thickness of 0.285 mm. Then, decarburization annealing (at 25%
N ₂ + 75% H ₂ , dew point 60 ° C.), and then 7
Annealing is carried out at 50 ° C for 30 seconds, and N
The steel plate was made to absorb nitrogen by mixing H ₃ gas. The N content of the steel sheet after nitriding is 0.0208 to 0.0229%,
The average grain size of the primary recrystallized grains of the steel sheet was 21 to 24 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.

[0041]

[Table 2]

Example 3 By weight%, Si: 2.86%, C: 0.029%, acid-soluble Al: 0.032%, N: 0.0050%, Mn:
0.13%, S: 0.006%, and (1)
Two 250 mm-thick slabs containing Sn <0.005%, (2) Sn: 0.06% were held at 1180 ° C. for 1 hour, and then roughly hot-rolled to 40 mm-thickness in 7 passes. Finishing hot rolling was performed in 6 passes to obtain a hot rolled plate having a thickness of 2.8 mm. This hot rolled sheet was analyzed for N as AlN, and N-N as A
When 1N is calculated, (1) 0.0028%,
(2) It was 0.0030%.

In this case, since it was expected that the magnetic characteristics would be poor, when the slab of the same composition was hot-rolled next,
(A) After the rough hot rolling, air cooling was performed for 60 seconds, and a hot rolling method of lowering the finish hot rolling start temperature by 65 to 75 ° C. from the slab heating temperature was performed. For comparison, hot rolling under the same conditions as the hot rolling of (B) was also performed. In the case of the hot rolling condition of (A),
When N as AlN of the hot rolled sheet was analyzed and N-N as AlN was calculated, (1) 0.0017%, (2) 0.0
It was 020%.

These two kinds of hot rolled sheets were pickled and cold rolled at a rolling reduction of about 88% to obtain cold rolled sheets having a thickness of 0.335 mm. Then, decarburization annealing (at 25%
N ₂ + 75% H ₂ , dew point 60 ° C.), and then 7
Annealing is carried out at 50 ° C for 30 seconds, and N
The steel plate was made to absorb nitrogen by mixing H ₃ gas. The N content of the steel sheet after nitriding is 0.0223 to 0.0232%,
The average grain size of the primary recrystallized grains of the steel sheet was 22 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 3 shows the experimental conditions and the results of magnetic properties.

[0045]

[Table 3]

[0046]

INDUSTRIAL APPLICABILITY In the present invention, the hot rolling conditions are feedback-controlled based on the AlN precipitation amount of the hot rolled sheet, the average grain size of the primary recrystallized grains is controlled, and after the hot rolling, the secondary finish annealing is performed. The steel sheet is nitrided before the start of recrystallization, and further, S
By adding n, it is possible to stably obtain good magnetic characteristics even if the low temperature slab heating is performed and the hot-rolled sheet annealing is omitted, so that the industrial effect is great.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of N—N as AlN in a hot rolled sheet and the magnetic flux density of a product.

Claims (2)

[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 being Fe and unavoidable impurities
It is heated at a temperature lower than 0 ° C, hot-rolled, and subsequently subjected to final strong cold-rolling with a rolling reduction of 80% or more without performing hot-rolled sheet annealing, followed by decarburization annealing and final finishing annealing. In a method for producing a grain-oriented electrical steel sheet, Al in a hot rolled sheet is used.
When the amount of N as N (weight ratio) is N as AlN, N
^* = N-N as AlN Based on the analysis value, determine the conditions of hot rolling to be performed after the hot rolling, and determine the average grain size of the primary recrystallized grains after the completion of decarburizing annealing until the start of final finishing annealing. 18-35
unidirectionality with excellent magnetic properties, characterized in that the steel sheet is subjected to a nitriding treatment to absorb 0.0010% by weight or more of nitrogen before the secondary recrystallization of the final finish annealing after hot rolling. Manufacturing method of electrical steel sheet. 2. 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 characterized by the above-mentioned.