JP2948455B2 - Method for stable production of unidirectional electrical steel sheets with excellent magnetic properties - Google Patents

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 and used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is mainly used as an iron core material for transformers and other electric equipment, and is required to have excellent magnetic properties such as excitation properties and iron loss properties. Numerical values representing the excitation characteristics include a normal magnetic field strength of 8
A magnetic flux density B _{8 at} 00 A / m is used. Further, as a numerical value representing the iron loss characteristic, an iron loss W _17/50 per kg when magnetized at a frequency of 50 Hz to 1.7 Tesla (T).
You are using The magnetic flux density is the largest controlling factor of the iron loss characteristics. Generally, the higher the magnetic flux density, the better the iron loss characteristics. In general, when the magnetic flux density is increased, the secondary recrystallized grains become large, and the iron loss characteristics may become poor. In contrast, by controlling the magnetic domain, the iron loss characteristics can be improved regardless of the particle size of the secondary recrystallized grains.

[0003] This grain-oriented electrical steel sheet is manufactured by causing secondary recrystallization in the final finish annealing step to develop a so-called Goss structure having {110} on the steel sheet surface and a <001> axis in the rolling direction. Have been. In order to obtain good magnetic properties, it is necessary that <001>, which is the axis of easy magnetization, be highly aligned in the rolling direction.

[0004] As a typical production technique of such a high magnetic flux density unidirectional magnetic steel sheet, Japanese Patent Publication No. 40-15644 is disclosed.
And JP-B-51-13469. In the former, MnS and AlN are used as main inhibitors, and in the latter, MnS, MnSe, Sb and the like are used. Therefore, it is indispensable in the current technology to appropriately control the size, morphology, and dispersion state of the precipitates functioning as these inhibitors. With regard to MnS, in the current process, MnS is used during slab heating before hot rolling.
Is once dissolved completely 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.

[0005] This is 2 times lower than the slab heating temperature of ordinary steel.
Since the temperature is higher than 00 ° C., this high-temperature slab heat treatment has the following disadvantages. 1) A high-temperature slab heating furnace dedicated to directional magnetic steel is required. 2) The unit energy consumption of the heating furnace is high. 3) The amount of the molten scale increases, and the adverse effect on the operation is large as seen in so-called scraping.

In order to avoid such a problem, the heating temperature of the slab may be reduced to the level of ordinary steel.
This means at the same time that the amount of MnS effective as an inhibitor is reduced or not used at all, which necessarily leads to instability of secondary recrystallization. Therefore, in order to realize low-temperature slab heating, it is necessary to reinforce the inhibitor with a precipitate other than MnS in some form, and to sufficiently suppress normal grain growth during finish annealing.

[0007] In addition to sulfides, nitrides, oxides, and intergranular precipitation elements can be considered as such inhibitors. Known techniques include, for example, the following. In Japanese Patent Publication No. 54-24687, As, Bi, Sn, S
Japanese Patent Application Laid-Open No. 52-24116 discloses a method in which a slab heating temperature is controlled to be in the range of 1050 to 1350 ° C. by containing a grain boundary segregation element such as b in steel. A method is disclosed in which a slab heating temperature is set in a range of 1100 to 1260 ° C. by containing a nitride-forming element such as B, Nb, Ta, V, Cr, and Mo. In Japanese Patent Application Laid-Open No. 57-158322, low-temperature slab heating is performed by lowering the Mn content and the Mn / S ratio to 2.5 or less, and further, the secondary recrystallization is stabilized by adding Cu. To disclose the technology.

[0008] 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,
By adding elements such as Se, Sb, Bi, Pb, Sn, and B, and combining the columnar crystal ratio of the slab and the secondary cold rolling reduction, a low-temperature slab heating of 1100 to 1250 ° C. is realized. Further, in JP-A-59-190324, an inhibitor is constituted mainly of Al, B and nitrogen in addition to S or Se, and this is subjected to pulse annealing at the time of primary recrystallization annealing after cold rolling to perform secondary recrystallization. The technology to stabilize is disclosed.

As described above, great efforts have been made so far to realize the low-temperature slab heating in the production of grain-oriented electrical steel sheets. Further, JP-A-59-5652
No. 2 discloses a technology that enables low-temperature slab heating by reducing Mn to 0.08 to 0.45% and S to 0.007% or less. By this method, the problem of occurrence of defective linear secondary recrystallization of a product due to coarsening of slab crystal grains during heating of a high-temperature slab was solved.

[0010]

The method using the low-temperature slab heating originally aims at reducing the manufacturing cost, but it cannot be industrialized unless it is a technique to obtain good magnetic properties stably as a matter of course. The present inventors, for industrialization of low-temperature slab heating, control of the average grain size of primary recrystallization before final finish annealing, and nitriding treatment of steel sheet after hot rolling and before the start of secondary recrystallization of final finish annealing. Has been built as a pillar. The nitride formed by this nitriding treatment is mainly AlN at the start of the secondary recrystallization. Al as an inhibitor that does not change easily at high temperatures
N is selected, and in that sense, it is an essential condition that Al is contained in the slab.

On the other hand, the fact that the slab contains N more than necessary has room for reconsideration in view of the present technical system.
In other words, if there is essential Al and a certain amount of N in the slab, in the process from slab heating to decarburizing annealing, Al
N is formed and affects the grain growth of primary recrystallized grains during decarburizing annealing. The purpose of the present invention is to examine a control method of AlN precipitation in the above process, and to perform 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 by omitting hot-rolled sheet annealing.

[0012]

The gist of the present invention is as follows. (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 + 0.405Se: 0.0
A slab containing 14% or less, Mn: 0.05 to 0.8%, and the balance being Fe and inevitable impurities is 1280 ° C.
Heating is performed at a temperature less than or equal to, and hot rolling is performed, and then, without subjecting the hot-rolled sheet to annealing, cold rolling is performed at a final high rolling rate of 80% or more, and then decarburizing annealing and final finishing annealing are performed. In the method for producing a conductive magnetic steel sheet, the cumulative draft of the rough hot rolling is set to 60% or more, and the time between the rough hot rolling and the finish hot rolling is 1
Seconds or more, the content (% by weight) of acid-soluble Al and N in the slab and the starting temperature FoT (° C.) of the finish hot rolling are controlled within the range of the following formula (1). Nitriding treatment in which the average grain size of the primary recrystallized grains before the start is 18 to 35 μm, and after hot rolling, the steel sheet is subjected to nitrogen absorption of 0.0010% by weight or more before the secondary recrystallization of the final finish annealing is started. A stable production method of a grain-oriented electrical steel sheet having excellent magnetic properties. 800 ≦ FoT (° C.) ≦ 900 + 9500 × {Al (%) − (27/14) × N (%)} (1) Al: Acid-soluble Al (2) In the preceding paragraph, Sn is further added as a component of the slab. :
A stable production method for a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by containing 0.01 to 0.15%.

[0013]

The grain-oriented electrical steel sheet to which the present invention is directed is:
The molten steel obtained by the conventional steelmaking method is cast by the continuous casting method or the ingot-making method, and if necessary, the slab is sandwiched by the sizing process, and subsequently hot-rolled to form a hot-rolled sheet. It is manufactured by performing final cold rolling in which the rolling reduction becomes 80% or more without annealing the rolled sheet, and then sequentially performing decarburizing annealing and final finishing annealing.

The present inventors have studied in detail the causes of magnetic fluctuations and the solutions to the problem when a low-temperature slab heating material is manufactured by a single cold rolling method omitting hot-rolled sheet annealing. And, as a result, the acid-soluble Al amount of the slab, the finish hot rolling start temperature is controlled according to the N amount, and the cumulative rolling reduction of the rough hot rolling, and the time between the rough hot rolling and the finish hot rolling are controlled, It has been found that the magnetic fluctuation can be drastically reduced.

First, the effects of the present invention will be described based on experimental results. FIG. 1 shows Al (%)-(27 /
14) The relationship between the amount of × N (%) (where Al: acid-soluble Al), the finish hot rolling start temperature FoT (° C.), and the variation of the magnetic flux density of the product. In this case, C: 0.024-0.
035%, Si: 2.5 to 3.2%, acid-soluble Al:
0.026 to 0.040%, N: 0.0050 to 0.0
078%, S: 0.005 to 0.007%, Mn: 0.
A 250 mm thick slab containing 10 to 0.14%, the balance being Fe and unavoidable impurities was prepared.

Then, the temperature of about 1050 to 1250 ° C.
After holding for 0 minutes, rough hot rolling was performed in 7 passes to obtain a thickness of 40 mm, and then finishing hot rolling was performed in 6 passes to obtain a 2.3 mm thick hot rolled sheet. In this hot rolling, water cooling is performed between passes in rough hot rolling, the time between passes is changed, the time between rough hot rolling and finish hot rolling is positively changed, and the finish hot rolling start temperature is changed. Taken extensively.

The hot-rolled sheet is subjected to strong rolling at a rolling reduction of about 85% without subjecting the hot-rolled sheet to annealing to obtain a final sheet thickness of 0.3%.
35 mm cold rolled sheet, 810 ° C, 820 ° C, 83
Four conditions of decarburizing annealing at 150 ° C. and 150 ° C. for 150 seconds, and then annealing at 750 ° C. for 30 seconds, mixing NH ₃ gas into the annealing atmosphere to absorb nitrogen into the steel sheet. I was born.

The amount of N after the nitriding treatment is 0.0194 to
0.0247% by weight, and the average particle size of primary recrystallized grains (average value of equivalent circle diameters) 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. Thereafter, the magnetic flux density of the product was measured, and the difference ΔB ₈ between the highest value and the lowest value of B ₈ under the four conditions of decarburization annealing obtained for the hot-rolled sheet having the same components and the same hot-rolling conditions was determined. .

As is apparent from FIG. 1, 800 ≦ Fot
(° C) ≦ 900 + 9500 × ΔAl (%) − (27/1
4) In the range of × N (%)｝, ΔB ₈ ≦ 0.02T, and stable magnetic characteristics are obtained. The mechanism of the effect of controlling the finish hot rolling start temperature in accordance with the amounts of the acid-soluble Al and N in the slab shown in FIG. 1 is not necessarily clear, but the present inventors presume as follows. I have.

The present invention relates to a method disclosed by the present inventors in JP-A-2-182.
It belongs to a technical system disclosed in Japanese Patent Publication No. 866 which is based on making the crystal structure after decarburization annealing appropriate. on the other hand,
N dissolved in the slab at the time of completion of slab heating is fine nitride (mainly AlN) during hot rolling or during decarburizing annealing (especially during heating).
It is thought that it becomes. It is considered that the size and the amount of precipitation of this fine nitride fluctuate even with a slight temperature change during decarburization annealing.

However, the grain growth suppressing effect (Zener factor) of the precipitate is inversely proportional to the size of the precipitate.
It is proportional to its volume fraction. Therefore, even if the amount of solute N at the time of completion of slab heating is excessively reduced, the effect of suppressing grain growth of precipitates becomes too small, and as a result, the grain growth during decarburization annealing becomes too remarkable, and the control of the crystal structure Becomes difficult.

800 ≦ FoT (° C.) ≦ 90 in FIG.
0 + 9500 × ｛Al (%) − (27/14) × N
(%)｝ Depends on the amount of acid-soluble Al and N in the slab,
This means that the hot rolling start temperature is set. here,
The larger the ratio of Al (%)-(27/14) × N (%), the smaller the amount of solute N at the start of hot-rolling for finishing. Means that the tolerance is wide. The lower limit of FoT is understood from the viewpoint of recrystallization during hot rolling rather than from the viewpoint of precipitation of AlN. That is, when the finish hot rolling is performed at a temperature of less than 800 ° C., it is considered that hot rolling recrystallization hardly occurs, and as a result, the magnetic properties become unstable.

Next, the reasons for limiting the constituent elements 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 excessively large, the decarburizing annealing time becomes long and it is not economical. Therefore, the content of C is set to 0.075% by weight (hereinafter simply referred to as%) or less. A particularly preferable range in terms of magnetic properties is 0.020 to 0.070%. If the content of Si exceeds 4.5%, cracking at the time of cold rolling becomes remarkable, so the content is set to 4.5% or less. If it is less than 2.2%, the specific resistance of the material is too low, and a low iron loss required as a transformer core material cannot be obtained.

Al is AlN necessary for stabilizing secondary recrystallization.
Alternatively, to secure (Al, Si) N, acid-soluble A
l must be 0.010% or more. Acid soluble Al
Exceeds 0.060%, the AlN of the hot-rolled sheet becomes inappropriate and secondary recrystallization becomes unstable. When N exceeds 0.0130%, blisters on the surface of the steel plate called blisters are generated.
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, when S or Se is high, a secondary recrystallization defective portion called linear fine grain tends to occur. To prevent the occurrence of the secondary recrystallization defective portion, (S + 0.405Se) ≦ 0.014 Should be%. If S or Se exceeds the upper limit, the probability of occurrence of a secondary recrystallization defective portion increases, 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. From such a viewpoint, it is meaningless to increase S or Se unnecessarily.

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 corrugated, 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. Therefore, the upper limit of the Mn content is set to 0.8%.

Sn is an element which is known as a grain boundary segregation element and suppresses grain growth. On the other hand, Sn at the time of slab heating is considered to be completely solid-dissolved, and even in a slab at the time of heating having a temperature difference of several tens of degrees which is normally considered, a solid solution is considered. Therefore, it is considered that Sn which is uniformly distributed in the slab at the time of heating despite the temperature difference also acts on the grain growth suppressing effect at the time of decarburizing annealing uniformly in place. For this reason, it is considered that Sn has the effect of diluting the spatial nonuniformity of the grain growth during the decarburizing annealing caused by the spatial nonuniformity of the AlN. Therefore, the addition of Sn is effective in further reducing the variation in the magnetic properties of the product. The proper range of Sn is 0.01 to 0.15.
%. Below this lower limit, the effect of suppressing grain growth is undesirably too small. On the other hand, if it exceeds the upper limit, nitriding of the steel sheet becomes difficult, which causes secondary recrystallization failure, which is not preferable.

In addition, trace amounts of Sb, Cu, Cr, Ni, B, Ti, Nb, etc., which are known as inhibitor constituent elements, may be contained. In particular, B, Ti,
The nitride constituent elements such as Nb are dissolved N in the steel during slab heating.
It may be added positively to reduce the amount. In the case where there is an element having a higher affinity for N than Al, when calculating a formula for defining the hot rolling start temperature to be described later, it is formed for B, Ti, and Nb contained from the total N amount. Subtracting the N content of the nitride is preferable in increasing 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 reducing costs to the same level as ordinary steel. Preferably 1200 ° C
It is as follows.

The heated slab is subsequently hot-rolled into a hot-rolled sheet. The hot rolling process generally comprises a rough hot rolling and a finishing hot rolling, which are performed in a plurality of passes after heating a slab having a thickness of 100 to 400 mm. The cumulative rolling reduction of this rough rolling is 60
% Or more. In the case of the AlN precipitation control technique as in the present invention, it is necessary to introduce many dislocations as precipitation nuclei of AlN. If the cumulative rolling reduction is less than 60%, the introduction of the dislocations is insufficient, so it is specified as 60% or more. The upper limit of the cumulative rolling reduction is not particularly limited.
It is allowable up to about 9.9%.

The inter-pass time between the rough hot rolling and the finish hot rolling was specified to be 1 second or more. This is to cause the precipitation of AlN between the passes, and less than 1 second has little effect. The upper limit of the inter-pass time is not particularly limited, but taking an inter-pass time of 1 hour or more is not preferable in terms of productivity.

The finishing hot rolling start temperature FoT (° C.) is set to 800 ≦
FoT (° C.) ≦ 900 + 9500 × ΔAl (%) − (2
7/14) × N (%)}. This is because, as shown in FIG. 1, it is necessary to keep this range in order to stabilize the magnetic characteristics. There is no particular limitation on the method for setting the finish hot rolling start temperature in the above range. Method of adjusting slab heating temperature, adjustment of inter-pass time of rough hot rolling, adjustment of inter-pass time of rough hot rolling and finishing hot rolling, control of cooling between rough hot rolling and its pass, rough hot rolling and finishing hot rolling , Or temperature control by water cooling or the like.

The subsequent finishing hot rolling is usually performed by high-speed continuous rolling of 4 to 10 passes. Normally, the rolling reduction of the finish hot rolling is such that the rolling reduction is higher in the former stage and the rolling reduction is lower in the latter stage so that the shape is good. Rolling speed is usually 100-300
0m / min and the time between passes is 0.01-10
0 seconds.

Although the present invention does not limit the conditions for finishing hot rolling, in order to perform AlN precipitation, in addition to controlling the starting temperature of finishing hot rolling, which is one of the features of the present invention, the finishing hot rolling is also performed. Adjusting the end temperature or adjusting the rolling reduction should be aggressive. In the temperature range (800 to 950 ° C.) where AlN is likely to be precipitated (800 to 950 ° C.) or in the vicinity thereof, the rolling reduction is positively increased to cause the work-induced precipitation.
This is an effective means for controlling the amount of precipitation.

After the final pass of hot rolling, the steel sheet is usually 0.1 to 1
After air cooling for about 00 seconds, it is water cooled, wound up 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 at least one second after hot rolling and maintaining the steel sheet in the AlN precipitation temperature range for as long as possible is used for controlling the amount of AlN precipitation. Is preferred.

Next, the hot-rolled sheet is subjected to final cold rolling at a rolling reduction of 80% or more without performing hot-rolled sheet annealing. The reason why the rolling reduction of the final cold rolling is set to 80% or more is that the sharpening {110} <0 in the decarburized plate is achieved by setting the rolling reduction within the above range.
This is because an appropriate amount of <01> orientation grains and corresponding orientation grains (e.g., {111} <112> orientation grains) easily susceptible to silkworm can be obtained, which is preferable in increasing the magnetic flux density. The steel sheet after such cold rolling is subjected to decarburizing annealing, application of an annealing separating agent, and final finish annealing by a usual method, and becomes a final product. Here, it is necessary to control the average grain size of the primary recrystallized grains from 18 to 35 μm after the completion of the decarburization annealing until the start of the final finish annealing. The reason is that a good magnetic flux density is easily obtained in the range of the average particle diameter, and the change of the magnetic flux density with respect to the fluctuation of the particle diameter is small.

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

[0037]

【Example】

Example 1 By weight%, Si: 3.05%, C: 0.036%, acid-soluble Al: 0.032%, N: 0.0060%, Mn:
For a 250 mm thick slab containing 0.14%, S: 0.006%, Z (° C.) = 900 + 9500 × ｛Al
(%) − (27/14) × N (%)} was calculated to be 1,094. From FIG. 1, it could be predicted that it is necessary to set the finish hot rolling start temperature to 800 to 1094 ° C. in order to obtain good magnetic properties. So, slab (1)
1100 ° C. and, for comparison, (2) after holding at each temperature of 1250 ° C. for 90 minutes, rough hot rolling to 40 mm thickness by 7 passes (cumulative rolling reduction: 84%), and then finishing hot rolling Until the start, after air cooling for 15 seconds, finish hot rolling in 6 passes,
A hot-rolled sheet having a thickness of 2.3 mm was obtained. The finish hot rolling start temperature at this time is (1) 1002 ° C. with respect to each slab heating temperature.
(2) It was 1142 ° C.

These hot rolled sheets were pickled and cold rolled at a rolling reduction of about 85% to form a 0.335 mm thick cold rolled sheet.
Decarburizing annealing (25% N ₂ + 75% H ₂ , holding at 150 ° C., 820 ° C., 830 ° C., 840 ° C. for 150 seconds)
(Dew point: 62 ° C.). Thereafter, annealing was performed at 770 ° C. for 30 seconds, and NH ₃ gas was mixed in the annealing atmosphere to absorb nitrogen into the steel sheet. The N content of the steel sheet after nitriding is 0.
0198 to 0.0212%, and the average grain size of the primary recrystallized grains of the steel sheet was 19 to 28 µm.

Next, an annealing separator containing MgO as a main component was applied to the steel sheet, and final finish annealing was performed by a known method. Table 1 shows the experimental conditions and the results of the magnetic characteristics.

[0040]

[Table 1]

Example 2 Si: 2.89%, C: 0.028%, acid-soluble Al: 0.029%, N: 0.0068%, Mn:
For a 250 mm thick slab containing 0.14%, S: 0.007%, Z (° C.) = 900 + 9500 × ΔAl
(%) − (27/14) × N (%)} was calculated to be 1051. From FIG. 1, it could be predicted that it is necessary to set the finish hot rolling start temperature to 800 to 1051 ° C. in order to obtain good magnetic properties. Therefore, (1) After holding the slab at 1150 ° C. for 60 minutes, it was roughly hot-rolled to a thickness of 50 mm in 7 passes (cumulative rolling reduction: 80%), and then air-cooled for 20 seconds until the finish hot rolling was started. Finish hot rolling was performed in 6 passes to obtain a 2.3 mm thick hot rolled sheet. The hot rolling start temperature at this time was 1038 ° C. Also, for comparison,
(2) After holding the slab of the same component at 1150 ° C. for 60 minutes, it was roughly hot-rolled to a thickness of 60 mm in 7 passes (cumulative rolling reduction: 76
%), After that, until the start of the finish hot rolling, cover the steel sheet with the steel sheet for 10 seconds, and heat it with the burner inside the heat keep cover. Then, finish hot rolling in 6 passes, and make a 2.3 mm thick sheet. A hot rolled sheet was used. The hot rolling start temperature at this time was 1107
° C.

These hot-rolled sheets were pickled without being subjected to hot-rolled sheet annealing, and cold-rolled at a rolling reduction of about 85% to obtain 0.335 mm
A thick cold rolled sheet was used. After that, 810 ° C, 820
Decarburization annealing (25% N ₂ + 75% H ₂ , dew point 60 ° C.) for 150 seconds at each of ℃, 830 ° C. and 840 ° C., and then annealing for 30 seconds at 750 ° C. NH ₃ gas was mixed into the atmosphere to absorb nitrogen into the steel sheet. The N content of the steel sheet after nitriding is 0.0215 to
0.0228%, and the average particle size of the primary recrystallized grains of the steel sheet was 21 to 30 μm. Next, Mg was added to this steel sheet.
Apply an annealing separator containing O as a main component, and by a known method,
The final finish annealing was performed. Table 2 shows the experimental conditions and the results of the magnetic properties.

[0043]

[Table 2]

Example 3 In terms of weight%, Si: 3.12%, C: 0.034%, acid-soluble Al: 0.025%, N: 0.0074%, Mn:
0.14%, S: 0.007%,
For two 150 mm thick slabs containing (1) Sn <0.005% and (2) Sn: 0.05%, Z
(° C.) = 900 + 9500 × ΔAl (%) − (27/1
4) × N (%)} was calculated to be 1002. From FIG. 1, the finish hot rolling start temperature is 800 to 1002 ° C.
Can be predicted to be necessary to obtain good magnetic properties. Then, (A) the slab is heated to 1000 ° C for 60
After holding for a minute, the sheet was roughly hot-rolled to a thickness of 50 mm in 7 passes (cumulative rolling reduction: 67%). Thereafter, it was air-cooled for 15 seconds until the start of the finish hot rolling, followed by finish hot rolling in 6 passes. It was a hot-rolled sheet having a thickness of 3 mm.

The hot rolling start temperature at this time was 895 ° C. For comparison, (B) a slab of the same component was kept at 1000 ° C. for 60 minutes, and then roughly hot-rolled to a thickness of 65 mm in seven passes (cumulative rolling reduction: 57%). After air cooling for 15 seconds, finish hot rolling was performed in 6 passes to obtain a 2.3 mm thick hot rolled sheet. The hot rolling start temperature at this time was 923 ° C. Furthermore, for comparison,
(C) After maintaining a slab of the same component at 1000 ° C. for 60 minutes, it is roughly hot-rolled to a thickness of 30 mm in 7 passes (cumulative rolling reduction: 80).
%), And then water-cooled for 25 seconds until the start of hot-rolling, and then hot-rolling in 6 passes to give a 2.3 mm thick hot-rolled sheet. The hot rolling start temperature at this time was 782 ° C.

These hot-rolled sheets were pickled without being subjected to hot-rolling annealing, and were cold-rolled at a rolling reduction of about 88% to obtain 0.285 mm
A thick cold rolled sheet was used. After that, 810 ° C, 820
Decarburizing annealing (25% N ₂ + 75% H ₂ , dew point 64 ° C.) for 150 seconds at each of ℃, 830 ° C., and 840 ° C., and then annealing for 30 seconds at 750 ° C. NH ₃ gas was mixed into the atmosphere to absorb nitrogen into the steel sheet. The N content of the steel sheet after nitriding is 0.0221 to
0.0239%, and the average particle size of the primary recrystallized grains of the steel sheet was 19 to 30 μm. Next, Mg was added to this steel sheet.
Apply an annealing separator containing O as a main component, and by a known method,
The final finish annealing was performed. Table 3 shows the experimental conditions and the results of the magnetic characteristics.

[0047]

[Table 3]

[0048]

According to the present invention, the acid-soluble Al is controlled by controlling the cumulative draft of the rough hot rolling and the time between the rough hot rolling and the finish hot rolling.
Control the finishing hot rolling start temperature based on the amount of N and the amount of N, control the average grain size of the primary recrystallized grains, and after hot rolling, subject the steel sheet to nitriding before the start of the secondary recrystallization of the final finish annealing. Alms, and
By adding Sn, good magnetic properties can be stably obtained even with low-temperature slab heating and omission of hot-rolled sheet annealing, so that the industrial effect is great.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a chart showing a relationship among an acid-soluble Al amount, an N amount, a finish hot rolling start temperature, and a change in magnetic flux density.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C21D 8/12 C22C 38/00 303 C22C 38/06 H01F 1/16

Claims (2)

(57) [Claims] 1. C: 0.075% or less by weight, Si: 2.2 to 4.5%, acid-soluble Al: 0.010 to 0.060%, N: 0.0130% or less, S + 0. 405Se: 0.014% or less, Mn: 0.05 to 0.8%, balance of slab consisting of Fe and unavoidable impurities is 128
Heating is performed at a temperature of less than 0 ° C., hot rolling is performed, followed by final high-pressure cold rolling at a rolling reduction of 80% or more without performing hot-rolled sheet annealing, followed by decarburizing annealing and final finishing annealing. In the method for producing a grain-oriented electrical steel sheet, the cumulative draft of rough hot rolling is set to 60% or more, the time between rough hot rolling and finish hot rolling is set to 1 second or more, and the content of acid-soluble Al and N in the slab. (% By weight), and the starting temperature FoT (° C.) of the finish hot rolling is as follows (1)
After the decarburization annealing is completed, the average particle size of the primary recrystallized grains until the start of the final finish annealing is set to 18 to 35 μm.
Unidirectional electrical steel sheet with excellent magnetic properties, characterized in that the steel sheet is subjected to a nitriding treatment for absorbing at least 0.0010% by weight of nitrogen after hot rolling and before the start of secondary recrystallization in final finish annealing. Stable production method. 800 ≦ FoT (° C.) ≦ 900 + 9500 × {Al (%) − (27/14) × N (%)} (1) where Al: acid-soluble Al 2. The slab component further contains Sn: 0.0
2. The method for stably producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the content is 1 to 0.15%.