JPH07118746A - Stable production of grain-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To stably obtain good magnetic properties even if hot rolled sheet annealing is obviated by controlling decarburizing annealing conditions based on the amt. of AlN to be precipitated in a hot rolled steel sheet in which C, Si, Al, N, S or the like are specified, controlling the average grain size of primarily recrystallized grains and executing nitriding treatment. CONSTITUTION:A steel having a compsm. contg. by weight, <=0.075% C, 2.2 to 4.5% Si, 0.01 to 0.06% acid soluble Al, <=0.013% N, S+0.405 Se; <=0.014% or the like is melted. This slab is heated to <1280 deg.C, is subjected to final forced draft cold rolling at >=80% draft and is annealed. At this time, decarburizing annealing conditions are feed-forward-controlled, based on the analysls value of the N content as AlN in the hot rolled sheet. After the completion of the decarburizing annealing, the average grain size of primarily recrystallized grains till the start of the final finish annealing is regulated to 18 to 35mum. Then, nitriding treatment is executed till the start of secondary recrystallization in the final finish annealing after the hot rolling to allow >=0.001% nitrogen to absorb 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 is manufactured by causing secondary recrystallization in the final finishing annealing step to develop a so-called Goss structure having {110} axis on the steel sheet surface and <001> axis in the rolling direction. Has been done. In order to obtain good magnetic properties, it is necessary to highly align <001>, which is the easy magnetization axis, in the rolling direction. Typical manufacturing techniques for such a high magnetic flux density unidirectional magnetic steel sheet are Japanese Patent Publication No. 40-15644 and Japanese Patent Publication No. 51-134698.
There is a method described in Japanese Patent Publication. In the former, MnS and AlN are the main inhibitors, and in the latter, MnS and Mn.
Se, 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.

As for MnS, in the present process, after MnS is completely dissolved at the time of heating the slab before hot rolling,
The method of precipitation during hot rolling is adopted. A temperature of about 1400 ° C. is necessary to completely form a solid solution of 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 has the following disadvantages. 1) A high temperature slab heating furnace exclusively for grain oriented electrical steel is required. 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 a problem, the slab heating temperature should be lowered to the level 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, grain boundary precipitation elements and the like are considered, and known techniques include, for example, 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, an inhibitor is composed mainly of Al and B and nitrogen in addition to S or Se, and secondary annealing 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 low temperature slab heating in the production of grain-oriented electrical steel sheets, great efforts have been made so far. Furthermore, JP-A-59-5652
Japanese Patent Publication No. 2 discloses a technique that 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.

[0009]

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, from the present technical system, it was necessary to reconsider that N was contained in the slab more than necessary.
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 object of the present invention is based on the control of precipitation of AlN in the above process, and by low temperature slab heating,
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.

[0011]

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.
Heating at a temperature of less than, followed by hot rolling, followed by hot-rolled sheet annealing, if necessary, final strong cold rolling with a reduction rate of 80% or more, followed by decarburization annealing and final finish annealing. In the method of producing a unidirectional electrical steel sheet by applying the method, when the N content (weight ratio) as AlN in the hot rolled sheet or the steel sheet after hot rolled sheet annealing is N as AlN, N ^* = N−N as AlN The thermal cycle of decarburization annealing is determined based on the analysis value of, and after the completion of decarburization annealing, the average grain size of primary recrystallized grains until the start of final finishing annealing is set to 18 to 35 μm, and the final finishing annealing after hot rolling is performed. A method for stable production of a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises subjecting a steel sheet to a nitriding treatment for absorbing 0.0010% by weight or more of nitrogen before starting the next recrystallization. (2) In the above item, Sn:
A stable manufacturing method of a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by containing 0.01 to 0.15%.

[0012]

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 studied 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, A in hot rolled sheet
Based on the analysis value of the amount of N as 1N (N as AlN), it was found that the magnetic fluctuation can be drastically reduced by controlling the decarburization annealing condition which is the subsequent process step.

First, the effect of the present invention will be described based on experimental results. FIG. 1 shows the relationship between the N—N as AlN amount and the decarburization annealing temperature in the hot rolled sheet and the magnetic flux density of the product. in this case,
By weight, C: 0.028%, Si: 2.9%, acid-soluble Al: 0.039%, N: 0.0070%, Mn: 0.1.
A slab with a thickness of 250 mm containing 2% and S: 0.006% and the balance Fe and unavoidable impurities is used.
After holding at a temperature of 0 to 1210 ° C. for about 120 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.

The hot-rolled sheet was subjected to strong reduction rolling with a reduction rate of about 85% without annealing the hot-rolled sheet to obtain a final sheet thickness of 0.3.
35mm cold rolled sheet, 810, 820, 830, 84
Six types of decarburization annealing are carried out at temperatures of 0,850 and 860 ° C for 150 seconds respectively, and then at the time of annealing at 750 ° C for 30 seconds, NH ₃ gas is mixed into the annealing atmosphere to absorb nitrogen into the steel sheet. It was born.

The amount of N after this nitriding treatment is 0.0211-
It was 0.0248% by weight, and the average particle size (average value of equivalent circle diameters) of primary recrystallized grains was 21 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 apparent from FIG. 1, the hot rolled sheet N--N
The decarburization annealing temperature at which the magnetic flux density was maximum was different depending on the amount of as AlN. N-N as A in the hot rolled sheet shown in FIG.
The mechanism by which the appropriate decarburization annealing temperature differs depending on the amount of 1N is not necessarily clear, but the present inventors presume as follows.

The present invention has been proposed by the present inventors 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 Japanese Patent Application Laid-Open No. 2-182866, if the crystal structure after decarburization annealing is controlled, good magnetic properties can be obtained, but it is optimum depending on the AlN precipitation state during decarburization annealing. Decarburization annealing conditions (temperature, time)
Are considered to be different.

If the AlN precipitation state can be completely controlled during hot rolling, the decarburizing and annealing conditions can be made constant.
Starting from a slab of about 5 to 20 tons, heating the slab,
When performing hot rolling, it is not easy to make the AlN precipitation state constant in the hot rolled sheet. N-N of the hot rolled sheet of the experiment shown in FIG.
The relationship between as AlN and decarburization annealing temperature and magnetic properties is that there is an appropriate temperature for decarburization annealing to obtain an appropriate crystal structure in decarburization annealing depending on the precipitation state of AlN in the hot rolled sheet. It is considered to indicate.

This also means that N-N as A of hot rolled sheet
It is shown that the proper condition in decarburization annealing can be predicted by the amount of 1N. 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. Since almost 100% of N is precipitated as a nitride in the hot-rolled sheet, the amount of N-N as AlN is mainly the amount of Si ₃ N ₄ , F ₈₁₆ N ₄ or the like that is precipitated after winding after hot rolling. It is understood that it indicates the amount of precipitation.

It is considered that these unstable nitrides decompose during decarburization annealing and reprecipitate as AlN. This AlN
Has a tendency to precipitate finely during the temperature rise of decarburization annealing, with dislocations increased by cold rolling as precipitation nuclei. Therefore, the amount of N-N as AlN in the hot rolled sheet is It is understood that it indirectly represents the amount of AlN.

When the amount of this fine AlN is large, it is necessary to raise the decarburization annealing temperature for obtaining an appropriate primary recrystallization structure. On the contrary, when the amount of this fine AlN is small, the decarburization for obtaining an appropriate primary recrystallization structure is required. It is necessary to lower the charcoal annealing temperature. Thus, it is estimated that the amount of N—N as AlN in the hot rolled sheet can be an important parameter in predicting and controlling the material quality of the 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%, swelling of the steel plate surface called a blister occurs, so 0.013
It was set to 0% 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 a secondary recrystallization defective portion becomes high no matter 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 appropriate range of Sn is 0.01 to 0.
It was set to 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, it is possible to contain 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 was 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 if the time between passes is increased, the amount of AlN precipitation may increase, and the slab heating temperature may be increased or a heat insulating cover may be placed on the steel sheet between passes. If so, the amount of AlN precipitation tends to decrease.

Regarding the time from rough hot rolling to finish hot rolling,
Although not particularly limited, if the time between passes is long, A
The precipitation amount of 1N tends to increase, and the precipitation of AlN is suppressed by covering the steel plate with the heat insulating cover to reduce the temperature decrease. Subsequent hot rolling for finishing is usually performed by high-speed continuous rolling for 4 to 10 passes. In the rolling distribution of the normal finish hot rolling, the rolling ratio is high in the front stage and is lowered toward the rear stage, and the shape is improved.

The rolling speed is usually 100 to 3000 m / min.
And the time between passes is 0.01 to 100 seconds. This finish hot rolling was applied to the precipitation temperature range of AlN (80
Performing at 0 to 1000 ° C. tends to increase the precipitation amount of AlN. After the final pass of hot rolling, the steel sheet is usually 0.
Air-cooled for about 1 to 100 seconds, then water-cooled, 300 to 70
It is wound at a temperature of 0 ° C. and gradually cooled. The cooling process is not particularly limited, but if the time from hot rolling to water cooling is extended, the precipitation amount of AlN tends to increase.

N ^* = on hot-rolled sheet or sheet after hot-rolled sheet annealing
It was stipulated that the thermal cycle of decarburization annealing should be determined based on the analysis value of N-N as AlN. Explaining an example of a process in which hot-rolled sheet annealing is not performed, as shown in FIG.
^{This is because the} decarburization annealing thermal cycle for obtaining good magnetic properties differs depending on the analysis value of ^* = N-N as AlN. In the case of FIG. 1, the decarburization annealing temperature is controlled, but the decarburization annealing time may be controlled, and both the temperature and the time may be used as control parameters.

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, N ^* = N-N as A in the hot rolled sheet
When the analysis value of 1N is measured, and if this value is larger than the appropriate value, a heat cycle that facilitates grain growth during high temperature or long time decarburization annealing may be used, and conversely, N ^* in the hot rolled sheet may be used ^. =
When the analysis value of N—N as AlN is smaller than the appropriate value, a thermal cycle in which grain growth is difficult during decarburization annealing such as low temperature or short time may be used. 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.

On the other hand, in the case of the hot-rolled sheet annealing process, N ^* = N-N as AlN in the hot-rolled sheet is the same as above.
It is also possible to determine the thermal cycle of decarburization annealing based on the analysis value of. Further, in order to further improve the control accuracy, the thermal cycle of decarburization annealing can be determined based on the analysis value of N ^* = NN-AlN in the steel sheet after hot-rolled sheet annealing. For the purpose of controlling the crystal structure, transformation phase, AlN precipitation, etc.,
When performing hot-rolled sheet annealing, it is performed at 800 to 1200 ° C. The cycle of hot-rolled sheet annealing is not particularly limited, but is 800 to adjust the precipitation amount of AlN.
It is also preferable to hold at 1000 ° C. for a relatively long time.

This hot-rolled sheet is then annealed, if necessary, and then 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 because the reduction ratio is set within the above range so that the decarburizing plate has a sharp {1
This is because it is possible to obtain an appropriate amount of 10} <001> oriented grains and the corresponding oriented grains ({111} <112> oriented grains and the like) that are easily eroded by silkworms, which is preferable in increasing the magnetic flux density. The cold rolled steel sheet is subjected to decarburization annealing according to the amount of N ^* = N-N as AlN of the hot rolled sheet or the steel sheet after the hot rolled sheet annealing, and then subjected to the annealing separator application and final finishing annealing. It is applied to make the final product. Here, after the decarburization annealing is completed, the average grain size of the primary recrystallized grains until the start of the final finish annealing is 18 to 35.
It is necessary to control to μm. The reason is that it is easy to obtain a good magnetic flux density in this 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.

[0035]

【Example】

Example 1 By weight%, Si: 2.85%, C: 0.029%, acid-soluble Al: 0.034%, N: 0.0064%, Mn:
A 250 mm thick slab containing 0.14% and S: 0.007% was held at 1200 ° C. for 60 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
ln was analyzed and N-N as AlN was calculated to be 0.0
It was 028%. In this case, the appropriate decarburization annealing temperature was predicted to be 845 ° C. from FIG.

The hot rolled sheet was pickled and cold rolled at a reduction rate of about 85% to obtain a cold rolled sheet having a thickness of 0.335 mm. After that,
(1) 845 ℃, and for comparison, (2) 835 ℃ 2
Decarburization annealing (25% N ₂ +
75% H ₂ , dew point 62 ° C), and then 770 ° C
Annealing was performed 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 0.0227 to 0.0239%, and the average grain size of the primary recrystallized grains of the steel sheet was 21 to 23 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.

[0037]

[Table 1]

Example 2 By weight, Si: 3.20%, C: 0.035%, acid-soluble Al: 0.033%, N: 0.0055%, Mn:
A 250 mm-thick slab containing 0.14% and S: 0.005% was held at 1100 ° 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
ln was analyzed and N-N as AlN was calculated to be 0.0
It was 025%. In this case, the appropriate decarburization annealing temperature was predicted to be 835 ° C. from FIG. 1.

This hot-rolled sheet was pickled and cold-rolled at a rolling reduction of about 88% to obtain a 0.285 mm-thick cold-rolled sheet. After that,
(1) 835 ℃, and for comparison, (2) 845 ℃ 2
Decarburization annealing (25% N ₂ +
75% H ₂ , dew point 60 ° C), and then 750 ° C
Annealing was performed 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 0.0228 to 0.0241%, and the average grain size of the primary recrystallized grains of the steel sheet was 22 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.

[0040]

[Table 2]

Example 3 By weight%, Si: 2.79%, C: 0.029%, acid-soluble Al: 0.035%, N: 0.0058%, Mn:
0.13%, S: 0.007%, and
(1) Sn <0.005%, (2) Sn: 0.06%,
(3) Three types of slabs with a thickness of 250 mm containing Sn: 0.11% were held at 1100 ° C. for 60 minutes, then roughly hot rolled to a thickness of 40 mm in 7 passes, and then finish hot rolled in 6 passes. The hot rolled sheet having a thickness of 2.6 mm was obtained. N as of this hot rolled sheet
When AlN was analyzed and N-N as AlN was calculated, (1) 0.0021%, (2) 0.0021%,
(3) It was 0.0022%. In this case, from FIG.
The proper decarburization annealing temperature was predicted to be 830 ° C.

The hot-rolled sheet was pickled and cold-rolled at a reduction rate of about 87% to obtain a cold-rolled sheet having a thickness of 0.335 mm. After that,
(A) 830 ° C., and (B) 845 ° C. 2 for comparison
Decarburization annealing (25% N ₂ +
75% H ₂ , dew point 62 ° C), then 750 ° C
Annealing was performed 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 0.0225 to 0.0238%, and the average grain size of the primary recrystallized grains of the steel sheet was 23 to 26 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.

[0043]

[Table 3]

Example 4 Si: 3.28%, C: 0.049%, acid-soluble Al: 0.030%, N: 0.0074%, Mn: wt%
A 250 mm-thick slab containing 0.10% and S: 0.006% was held at 1150 ° 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. Then, (1) 112
Hold at 0 ° C for 30 seconds, then hold at 900 ° C for 30 seconds and then quench, (2) Hold at 1100 ° C for 3 minutes, then quench. 2
Street hot rolled sheet was annealed. When N as AlN of the steel sheet after this hot-rolled sheet annealing is analyzed and N-N as AlN is calculated, (1) 0.0012% and (2) 0.0028, respectively.
%Met. In this case, from FIG. 1, the appropriate decarburization annealing temperatures were predicted to be (1) 820 ° C. and (2) 850 ° C., respectively.

The annealed steel sheet was cold-rolled at a reduction rate of about 88% to obtain a cold-rolled sheet having a thickness of 0.285 mm. Then, decarburization annealing (25% N ₂ + 75%) for 150 seconds at two temperatures (A) 820 ° C. and (B) 850 ° C.
H _2, dew point 60 ° C.) alms, thereafter, 30 at 750 ° C.
Annealing was performed for 2 seconds, and NH ₃ gas was mixed into the annealing atmosphere to cause the steel sheet to absorb nitrogen. The N content of the steel sheet after nitriding was 0.0205 to 0.0223%, and the average grain size of 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 4 shows the experimental conditions and the results of magnetic properties.

[0046]

[Table 4]

[0047]

INDUSTRIAL APPLICABILITY In the present invention, decarburization annealing conditions are feed-forward controlled based on the amount of AlN precipitation of the hot-rolled sheet or the steel sheet after the hot-rolled sheet annealing, and the average grain size of primary recrystallized grains is controlled, After hot rolling, by nitriding the steel sheet before the start of secondary recrystallization of final finish annealing, and further by adding Sn, it is still good even if low temperature slab heating and hot strip annealing are omitted. Since stable magnetic characteristics can be obtained,
Its industrial effect is great.

[Brief description of drawings]

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

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[Procedure amendment]

[Submission date] January 17, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

This unidirectional electrical steel sheet is manufactured by causing secondary recrystallization in the final finishing annealing step to develop a so-called Goss structure having {110} axis on the steel sheet surface and <001> axis in the rolling direction. Has been done. In order to obtain good magnetic properties, it is necessary to highly align <001>, which is the easy magnetization axis, in the rolling direction. Typical methods for producing such a high magnetic flux density unidirectional electrical steel sheet are the methods described in JP-B- 40-15644 and JP-B- 51-13469 . In the former, MnS and AlN are the main inhibitors, and in the latter, MnS and MnS.
e, Sb, etc. are used. Therefore, in the present technology, the size of precipitates that function as these inhibitors,
Proper control of morphology and dispersion is essential.

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[Document name to be amended] Statement

[Correction target item name] 0019

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This also means that N-N as A of hot rolled sheet
It is shown that the proper condition in decarburization annealing can be predicted by the amount of 1N. 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. Since almost 100% of N is precipitated as a nitride in the hot-rolled sheet, the amount of N—N as AlN is mainly the amount of Si ₃ N ₄ , Fe ₁₆ N ₄ or the like precipitated after winding after hot rolling. It is understood that it indicates the amount of precipitation.

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[Document name to be amended] Statement

[Name of item to be corrected] 0027

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The slab heating temperature was 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 if the time between passes is increased, the amount of AlN precipitation tends to increase, the slab heating temperature is increased, and a heat insulating cover is placed on the steel sheet between passes. If so, the amount of AlN precipitation tends to decrease.

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[Figure 1]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // C22C 38/00 303 U 38/60

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 Fe and unavoidable impurities
It is heated at a temperature of less than 0 ° C., hot-rolled, and subsequently, if necessary, hot-rolled sheet annealing is performed, final cold rolling with a reduction ratio of 80% or more, followed by decarburization annealing and final finish annealing. In the method for producing a unidirectional electrical steel sheet by applying the above, when the N amount (weight ratio) as AlN in the hot rolled sheet or the steel sheet after hot rolled sheet annealing is N as AlN, N ^* = N−N as The thermal cycle of decarburization annealing is determined based on the analysis value of AlN, and after decarburization annealing is completed, the average particle size of primary recrystallized grains until the start of final finishing annealing is set to 18 to 35 μm, and after hot rolling, the final finishing annealing is performed. A stable manufacturing method of a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises subjecting a steel sheet to a nitriding treatment for absorbing 0.0010% by weight or more of nitrogen before starting secondary recrystallization. 2. Sn: 0.01 to as a slab component
The method for stable production of a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein 0.15% is contained.