JP2002030340A - Method for producing grain-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a grain-oriented silicon steel sheet excellent in magnetic properties by using AlN, MnSe and MnS compositely as an inhibitor, and controlling slab heating temperature to <=1,350 deg.C. SOLUTION: A silicon steel slab containing C, Si, Mn, Al, N, Se and S by suitable amounts is heated at 1,200 to 1,350 deg.C and is then hot-rolled, the finishing temperature in finish rolling is controlled to the range of 850 to 1,100 deg.C, after the completion of the finish rolling, cooling till coiling is treated so as to satisfy the relation in the following inequality, the steel sheet is coiled at <=700 deg.C, is thereafter subjected to hot rolled sheet annealing, cold rolling, decarburizing annealing and finish annealing and is nitrided in the meanwhile from the decarburizing annealing to the start of secondary recrystallization: in 2<=t<=6, T(t)< FDT-(FDT-700)×t/6.

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 silicon steel sheet, and more particularly to a method for producing a grain-oriented silicon steel sheet having a low iron loss and a high magnetic flux density.

[0002]

2. Description of the Related Art A grain-oriented silicon 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 magnetic flux density and iron loss value. In order to manufacture this unidirectional silicon steel sheet, a generally adopted method is to heat a slab having a thickness of 100 to 300 mm at a temperature of 1200 ° C. or more, then hot-roll the slab, and obtain the obtained hot-rolled sheet. The final thickness is obtained by cold rolling once or twice or more with intermediate annealing, and after decarburizing annealing, an annealing separator is applied, and then finish annealing for the purpose of secondary recrystallization and purification is performed. General. That is, first, the slab is heated at a high temperature to completely dissolve the inhibitor component, and then obtained by hot rolling, furthermore, one or more times of cold rolling and one or more times of annealing. The primary recrystallized grain structure is controlled, and then the primary recrystallized grains are subjected to GOSS orientation ({110} <0
01>) The required magnetic properties are ensured by secondary recrystallization of crystal grains of the orientation.

In order to effectively promote such secondary recrystallization, first, a dispersed phase called an inhibitor for suppressing normal grain growth of primary recrystallized grains is uniformly and appropriately sized in steel. It is important to control the precipitation state so as to disperse the particles and to make the primary recrystallized grain structure have crystal grains of an appropriate size and a uniform distribution over the entire sheet thickness. Representative of such inhibitors are M
nS, MnSe, AlN, VN, Cu ₂ S and CuS
Materials having extremely low solubility in steel, such as sulfides, selenides and nitrides such as e, are used. Also, S
Grain boundary segregation elements such as b, Sn, As, Pb, Ce, Cu and Mo are also used as inhibitors. In any case, in order to obtain a good secondary recrystallization structure, control of the inhibitor from precipitation of the inhibitor in hot rolling to subsequent secondary recrystallization annealing is an important requirement. In order to ensure better magnetic properties, it is obvious that such inhibitor control is extremely important in the production of a grain-oriented electrical steel sheet.

By the way, from the viewpoint of inhibitor control,
As a prior art focusing on the temperature history from finish rolling to winding in a hot rolling process, for example, Japanese Patent Publication No. 38
No. 14009, JP-A-56-33431,
JP-A-59-50118, JP-A-64-7302
JP-A-3-263924, JP-A-2-263924, JP-A-4-
The techniques described in JP-A-323-323, JP-A-2-27481, and JP-A-5-295442 are known.

[0005] Japanese Patent Publication No. 38-14209 discloses a hot rolled steel strip of silicon electric steel having a grain orientation of 790 ° C and 950 ° C.
In order to maintain the carbon as a solid solution by performing a solution treatment at a temperature between ℃ and prevent the generation of intergranular carbide,
From this temperature, it is rapidly quenched to a temperature of 540 ° C. or less, maintained at a temperature of 310 to 480 ° C. at which lens-like precipitates appear in the particles, and quenched. A method for producing a grain-oriented silicon electric steel by alternately performing rolling and annealing is disclosed. However, this technique does not actively add an inhibitor component, and is a technique for mainly controlling the precipitation form of the carbide, and controlling the cooling rate and the holding time in the carbide precipitation temperature range around 700 ° C. Is what you do. Therefore, when this technology was actually applied to the production of a grain-oriented electrical steel sheet containing AlN, MnSe, and MnS, no improvement in characteristics could be expected.

Japanese Unexamined Patent Publication (Kokai) No. 56-33431 discloses a method for controlling a winding temperature in a temperature range of 700 to 1000 ° C., and keeping the coil for 10 minutes to 5 hours after winding at a high temperature of 700 to 1000 ° C. And 700 to 10
A method of rapidly cooling the coil after winding at a high temperature of 00 ° C. is disclosed. This technique is a method of improving the precipitation and dispersion of AlN as an inhibitor. However, non-uniform decarburization proceeds due to self-annealing in the coil shape after winding, and the formation of the cold rolled texture is also unstable. And the variation in product characteristics becomes large. In particular, water cooling or the like in a coil shape causes unevenness in the cooling rate, which causes a variation in product characteristics.

Japanese Unexamined Patent Publication (Kokai) No. 59-50118 discloses that the following (1)
A method of cooling at a cooling rate of 7 to 40 ° C./sec to a temperature range calculated from the formula (2), and then winding and cooling the hot rolled steel strip and leaving the final stand after finishing the following (3)
There is disclosed a method of cooling at a temperature of 7 to 30 ° C./sec below the temperature calculated by the formula, winding, and then water cooling the wound steel strip. (35 × logV + 515) ° C. (1) (445 × logV-570) ° C. (2) (20 × logV + 555) ° C. (3) V: Cooling rate of hot-rolled steel strip from leaving the final finishing stand to winding up (° C./sec) However, this technology is intended for the case where AlN is not used as an inhibitor, and AlN and MnSe, Mn are used.
No effect can be expected for the production of a grain-oriented electrical steel sheet using S in combination.

Japanese Patent Application Laid-Open No. 64-73023 discloses that the average cooling rate and the winding temperature range from 10 ° C./sec. To less than 40 ° C./sec. A method in which the take-up temperature is from 600 ° C. to 750 ° C., and a take-up temperature of 550 to 750 ° C. at an average cooling rate of 40 to 80 ° C./sec
Is disclosed. This technology is also disclosed in
As in the technology disclosed in Japanese Patent No. -50116, MnS and MnSe are used as inhibitors, and there is no mention of a method for producing a grain-oriented electrical steel sheet using AlN. In addition, all of these methods only determine the average cooling rate from the end of finishing to winding up with respect to the cooling rate. That is, there is no mention of the high-temperature residence time immediately after the end of finish rolling, which essentially affects the composite precipitation state of AlN as an inhibitor and MnSe and MnS as in the present invention.

In Japanese Patent Application Laid-Open No. 2-263924, C: 0.02 to 0.100% by mass%, Si: 2.
Containing 5-4.5% as well as the usual inhibitor components,
The remainder is hot-rolled with a silicon steel slab consisting of Fe and unavoidable impurities, and without being subjected to hot-rolled sheet annealing, the reduction rate is kept at 80%.
% Of cold-rolled, decarburized annealing, and final finish annealing to produce a grain-oriented electrical steel sheet, wherein the hot-rolling end temperature is 750 to 1150 ° C, and at least 1 second or more, 700 ° C or more after hot-rolling ends. And the winding temperature is 700
A technique for lowering the temperature to less than ° C. is disclosed. From the viewpoint of cost reduction, this technique promotes recrystallization by maintaining a high temperature after finish rolling, improves the structure, and eliminates hot-rolled sheet annealing. By promoting recrystallization after hot rolling by this technique, the structure is improved, and annealing of the hot rolled sheet can be omitted, but a better inhibitor precipitation state than before has not been obtained. Moreover, this technology omits hot rolled sheet annealing,
There is a problem in that the precipitation control of the inhibitor must be sacrificed.

In Japanese Patent Laid-Open No. 2-74811, C: 0.021 to 0.075% by mass%, Si:
2.0-4.5%, acid-soluble Al: 0.010-0.0
60%, N: 0.0030 to 0.000130%, S +
0.405Se: 0.014% or less, Mn: 0.05 to
A slab containing 0.8%, the balance consisting of Fe and unavoidable impurities, was heated at a temperature below 1280 ° C.,
Perform hot rolling, then perform hot rolled sheet annealing as necessary,
Then, the steel sheet is subjected to one or more cold rolling steps including intermediate annealing as necessary, including final cold rolling at a reduction ratio of 80% or more, and then subjected to decarburizing annealing and final finishing annealing to produce a unidirectional electrical steel sheet. In the method, the hot rolling end temperature is set at 750 to 1150
A technique is disclosed in which the temperature is maintained at 700 ° C or higher for at least 1 second or more after the completion of hot rolling, and the winding temperature is lower than 700 ° C. This technique is intended to promote recrystallization by maintaining a high temperature after finish rolling in a manufacturing process in which low-temperature slab heating is performed, thereby improving and stabilizing magnetic properties. However, in low-temperature slab heating, A
Although 1N can form a solid solution, a solid solution of MnS and MnSe is not sufficiently achieved. In particular, when applied to hot rolling cooling according to a production method in which a high-temperature slab heating is performed to sufficiently dissolve the inhibitor, it is not possible to stably produce a product having excellent magnetic properties because the precipitation behavior of the inhibitor is different. . That is, in the step of performing the low-temperature slab heating, there is a problem that the control of the inhibitor is not effective, so that a product having excellent magnetic properties cannot be stably manufactured.

Japanese Patent Application Laid-Open No. 5-295442 discloses that after exiting a hot-rolling finishing stand,
When the relationship between the average cooling rate Ta (° C./sec) to 0 ° C. and the Ti content is Ta ≧ 30 ° C./sec and Ti ≦ 0.003% by mass, T
When a ≧ −7 / 3Ti + 100 0.003 <Ti ≦ 0.008% by mass, Ta ≦ −1
１ ／ Ti + 206 Here, the steel sheet after hot rolling with Ta: ° C./sec and Ti: 10 ^-4 mass% is subjected to a final cold rolling reduction of 80%.
The method of cold rolling has been disclosed above. This method is a technique aimed at reducing the influence of Ti as an unavoidable impurity under hot rolling conditions.

Japanese Patent Application Laid-Open No. 8-100126 discloses that the slab heating temperature is specified to be 1280 ° C. or higher using AlN and MnS or MnSe as inhibitors.
The finish rolling temperature of hot rolling, the temperature history up to winding, and the winding temperature are specified.

[0013]

What the above prior arts have in common is that good inhibitor deposition control is not realized. That is, in these conventional techniques, since the precipitation control of the inhibitor was not properly performed, there was a problem that a unidirectional silicon steel sheet excellent in both the magnetic flux density and the iron loss value could not be manufactured.

Accordingly, an object of the present invention is to provide a technique for producing a grain-oriented electrical steel sheet having excellent magnetic properties in the production of a grain-oriented electrical steel sheet using a combination of AlN, MnSe, and MnS as an inhibitor. It is in. Another object of the present invention is to provide AlN and MnSe as inhibitors.
In the production of a grain-oriented electrical steel sheet using MnS in combination, nitriding is performed between decarburization annealing and the start of secondary recrystallization to promote the development of a secondary recrystallization structure that effectively contributes to the improvement of magnetic properties. An object of the present invention is to establish a technology for manufacturing a unidirectional silicon steel sheet having high magnetic flux density and low iron loss.

[0015]

Means for Solving the Problems The inventors of the present invention have studied in detail various factors in the hot rolling process for realizing the above-mentioned object, and have found that the cooling history after the finish rolling in the hot rolling is completed. It has been found that the secondary recrystallization defect rate of the product is reduced, and high magnetic flux density and low iron loss can be realized. The present invention is based on the above findings,
The gist is mass%, C: 0.01 to 0.10%, S
i: 2.0 to 4.5%, Mn: 0.02 to 0.12%,
Al: 0.005 to 0.05%, N: 0.002 to 0.
01%, and Se: 0.003 to 0.05%,
S: A silicon steel slab containing one or two selected from 0.003 to 0.05%, the balance being substantially Fe, is heated at a temperature of 1200 ° C. to 1350 ° C. Rolled, hot-rolled steel sheet is subjected to hot-rolled sheet annealing, and then cold-rolled once or twice or more with intermediate annealing, followed by decarburizing annealing, and secondary recrystallization from decarburizing annealing In producing a unidirectional silicon steel sheet through a step of performing nitriding during the start and finish annealing, the finish rolling end temperature of the hot rolling is set to a range of 850 to 1100 ° C., This is a method for producing a unidirectional silicon steel sheet having excellent magnetic properties, wherein the steel sheet is cooled while satisfying the relationship of the following expression between the temperature and the time from the end of the finish rolling, and is wound at 700 ° C. or less. When 2 ≦ t ≦ 6, T (t) <FDT- (FDT-7
00) × t / 6, where T (t): steel sheet temperature (° C.), FDT: finish rolling finish temperature (° C.), t: time from finish finish of hot rolling (second)

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The prior art described above is disclosed in
Except for those described in Japanese Patent No. 274811, it is assumed that the inhibitor is built by solid solution in the slab (re) heating in hot rolling, but the present invention does not slag the slab heating temperature. Although the inhibitor element is completely dissolved at a temperature of 1350 ° C. or less, the greatest feature is that an insufficient amount of inhibitor strength for secondary recrystallization is nitrided between decarburization annealing and the start of secondary recrystallization.

First, a description will be given of an experiment which has led to the present invention, and a configuration of the present invention. Experiment 1 Steel having the components shown in Table 1 was melted by a vacuum melting method, cast, reheated to 1200 ° C., and rolled to a thickness of 40 mm. A sample having a size of 40 mm × 300 mm × 400 mm in length was taken from this, heated at 1280 ° C. to form a solution of the inhibitor component, and then subjected to hot rolling to a sheet thickness of 2.3 mm.
After finishing at 5 ° C., various coolings as shown in FIG. 1 were performed to 500 ° C., and subsequently, it was kept in a furnace at 500 ° C. for 1 hour to simulate winding by hot rolling, and then air-cooled to room temperature. Primary cold rolling after annealing these hot rolled sheets,
Then, after performing intermediate annealing, it was subjected to secondary cold rolling to obtain 0.23
mm. Thereafter, decarburizing annealing is performed at 850 ° C. for 2 minutes in a wet hydrogen atmosphere to increase N by 120%.
１３０130 ppm, and after applying an annealing separator containing MgO as a main component, 1200
A final finish annealing at 20 ° C. for 20 hours was performed. Table 2 shows the results of an investigation on the magnetic properties of the product thus obtained.

[0018]

[Table 1]

[0019]

[Table 2]

Under the conditions A and B, the secondary recrystallization is good, but does not satisfy the standard value B8 ≧ 1.80T of the grain-oriented electrical steel sheet specified in JIS. Experiment 2 Steel having the components shown in Table 3 was melted by a vacuum melting method, cast, reheated to 1200 ° C., and rolled to a thickness of 40 mm. A sample having a size of 40 mm × 300 mm × 400 mm in length was taken from this, and after heating at 1330 ° C. to form a solution of the inhibitor component, hot rolling at a plate thickness of 2.3 mm was completed at 1025 ° C. 2 was cooled to 600 ° C., and subsequently kept in a furnace at 600 ° C. for 1 hour to simulate winding by hot rolling, and then air-cooled to room temperature. After annealing these hot rolled sheets, 1.5 hours
5 mm was subjected to primary cold rolling and then intermediate annealing, followed by secondary cold rolling to a final thickness of 0.23 mm. Thereafter, decarburizing annealing is performed at 850 ° C. for 2 minutes in a wet hydrogen atmosphere, nitriding is performed at 150 to 160 ppm by increasing nitrogen, and an annealing separator mainly containing MgO is applied. A final finish annealing at 20 ° C. for 20 hours was performed. Table 4 shows the results of investigation on the magnetic properties of the products thus obtained.

[0021]

[Table 3]

[0022]

[Table 4]

Experiment 3 Steel having the components shown in Table 5 was melted by a vacuum melting method, cast, reheated to 1200 ° C., and rolled to a thickness of 40 mm. A sample having a size of 40 mm × 300 mm × 400 mm in length was taken from this, heated at 1400 ° C. to form a solution of the inhibitor component, and hot rolling to 2.3 mm in thickness was completed at 1075 ° C. After cooling variously to 550 ° C. as shown in FIG. 3, the steel sheet was kept in a furnace at 550 ° C. for 1 hour to simulate winding by hot rolling, and then air-cooled to room temperature. These hot-rolled sheets were annealed, then subjected to primary cold rolling, then intermediate annealing, and then subjected to secondary cold rolling to finish to a final thickness of 0.23 mm. Thereafter, decarburizing annealing is performed at 850 ° C. for 2 minutes in a wet hydrogen atmosphere, the material is prepared under conditions not to perform nitriding, and then an annealing separating agent containing MgO as a main component is applied. 12
Final finish annealing was performed at 00 ° C. for 20 hours. Table 6 shows the results of an investigation on the magnetic properties of the product thus obtained.

[0024]

[Table 5]

[0025]

[Table 6]

From the results of the above experiments, when the slab heating temperature is 1350 ° C. or less, the characteristics of the product are not directly related to the average cooling rate from the end of finish rolling to winding, and the temperature history is 2 ≦ t ≦ 6, T (t) <FDT- (FD
T-700) × t / 6, where T (t): steel sheet temperature (° C.), FDT: finish rolling finish temperature (° C.), t: elapsed time from finish rolling finish (second). It has been found that the cooling after the completion of the finish rolling improves the performance. In other words, even if it is partial, when the steel sheet temperature history deviates from the above conditions and shifts to a high temperature range, the occurrence of secondary recrystallization failure increases and the deviation from the GOSS orientation increases, and the magnetic flux density decreases accordingly And high iron loss occurs. Here, the secondary recrystallization defect rate refers to the product sheet after the finish annealing, which has a diameter of 2 m other than the secondary recrystallized grains.
The area ratio occupied by the region composed of fine grains of m or less on the plate surface.

Further, the reason for defining the slab heating temperature is that at a temperature exceeding 1350 ° C., as is well known, the temperature is too high, so that the construction cost of the heating furnace equipment rises and maintenance becomes difficult due to the generation of slag. It is because it occurs. At a lower limit of 1200 ° C., the inhibitor component elements do not sufficiently form a solid solution, which makes it difficult to operate in decarburization annealing. Desirably, it is 1270 ° C to 1315 ° C. In the case where heating is performed at a temperature exceeding 1350 ° C., there is a component range of an inhibitor constituent element that does not require nitridation in a post-process, but the industrial profit is extremely small.

The finishing rolling end temperature (FDT) is set to 850 to
The reason why the temperature is set to 1100 ° C. is that if the temperature is lower than 850 ° C., undesirable non-uniform precipitation of the inhibitor occurs in the finishing rolling stand, and if the temperature is higher than 1100 ° C., it becomes extremely difficult to achieve both passing and cooling. The preferred finish rolling end temperature range is 900 to 1,050. The reason why the winding temperature is set to 700 ° C. or less is that at a high temperature exceeding 700 ° C., non-uniform decarburization due to self-annealing after winding and uneven precipitation of the inhibitor occur, which is a cause of unstable magnetic properties. . The preferred winding temperature range is 50.
0-600 ° C.

The reason why such an effect is obtained depending on the temperature history after finishing hot rolling is already evident in the production of a unidirectional silicon steel sheet employing a method in which an inhibitor component is dissolved during slab heating, and the added inhibitor component is used. This is because the composite precipitation form of AlN, MnSe, and MnS becomes uneven at the coil position. That is, FIG.
As shown schematically, there are two composite precipitate forms, which differ from each other in the temperature range and time range in which they precipitate. After finishing the hot rolling, it is cooled immediately, avoiding the region I, and the inhibitor precipitated in the low temperature region indicated by II has strong and good inhibitory power, whereas the inhibitor precipitated in the high temperature region of I has the inhibitory force. Is weak and unstable. Accordingly, it is basically important to shorten the high-temperature residence time immediately after the completion of the finishing hot rolling in order to obtain a good inhibitor precipitation morphology, as described in JP-A-5-295442.

In the present invention, other than the conditions described above,
The production conditions in the respective steps such as hot rolling, hot rolled sheet annealing, pickling, intermediate annealing, cold rolling, decarburizing annealing, application of an annealing separator, and finish annealing may be performed according to known methods. As the silicon-containing steel which is a material of the present invention, A
Compatible with those in which 1N, MnSe, and MnS are added as inhibitors. The composition of the components is as follows. The contents described here are all mass%.

C is an element useful for not only making the composition uniform and fine during hot rolling and cold rolling, but also for developing the Goss orientation, and it is necessary to contain at least 0.01%. However, if the content exceeds 0.10%, decarburization becomes difficult, and the Goss orientation is rather disturbed. Therefore, the upper limit is set to 0.10%. Preferably it is in the range of 0.03 to 0.08%.

Si increases the specific resistance of the steel sheet and contributes to the reduction of iron loss. When the Si content is less than 2.0%, the effect of reducing iron loss is not sufficient, and in the finish annealing at a high temperature performed for purification and secondary recrystallization, randomization of crystal orientation due to α-γ transformation occurs. Sufficient magnetic properties cannot be obtained. On the other hand, if it exceeds 4.5%, the cold rollability is impaired, and the production becomes difficult. Therefore, the Si content is 2.0-4.
5%. Preferably, it is in the range of 3.0 to 3.5%.

Mn is an effective element for preventing cracking during hot rolling due to hot embrittlement, and its effect is 0.02%.
% Cannot be obtained. On the other hand, if added in excess of 0.12%, the magnetic properties deteriorate. Therefore, the Mn content is
0.02 to 0.12%. Preferably 0.03 to
It is in the range of 0.09%. Al is an element that forms AlN and acts as an inhibitor. Al content is
If the content is less than 0.005%, the suppression power is not sufficiently secured, while if the content exceeds 0.05%, the effect is impaired.
0.005 to 0.05%. Preferably 0.02-
It is in the range of 0.035%.

N is an element that forms AlN and acts as an inhibitor. If the N content is less than 0.002%, the suppression force is not sufficiently secured, while if it exceeds 0.10%, a defect of a steel sheet called a blister (two sheets)
Therefore, the content is made 0.002 to 0.01%. Preferably it is in the range of 0.003 to 0.007%. Se is
It is a powerful element that forms MnSe and acts as an inhibitor. If the Se content is less than 0.003%, the suppression power is not sufficiently secured, while if it exceeds 0.05%, the effect is impaired. Therefore, the content is set to 0.003 to 0.05% in either case of single addition or combination addition with S. In addition, it is preferably in the range of 0.01 to 0.02%.

S is a powerful element that forms MnS and acts as an inhibitor. S content is 0.003
%, The suppression power is not sufficiently secured.
If it exceeds 5%, its effect will be impaired.
Or 0.003 or more in any case of addition with Se
0.05%. Incidentally, preferably 0.01 to 0.0
It is in the range of 2%.

In the present invention, in addition to S, Se and Al described above as inhibitor components, Cu, S
Since n, Sb, Mo, Te, Bi, and the like also have an advantageous effect, they can be contained together with the above components.
The preferable addition ranges of these components are Cu, Sn:
0.01-0.15%, Sb, Mo, Te, Bi: 0.
005 to 0.1%. Each of these inhibitor components can be used alone or in combination.

The reason for performing the nitriding treatment between the start of the secondary recrystallization after the decarburizing annealing is as follows. If the slab heating temperature is extremely high (1350 ° C. or higher), industrial difficulty is involved and is outside the scope of the present invention. In order to make this temperature lower than the ultra-high temperature so that the inhibitor is completely dissolved in the hot-rolling heating furnace, it is necessary to further reduce the content of the inhibitor constituent element. This is because when the content of such an inhibitor constituent element is reduced, the inhibitor strength for secondary recrystallization cannot be maintained unless nitriding is performed.

The nitriding method can be carried out in a mixed gas of hydrogen, nitrogen, and ammonia under a known strip running condition, or it can be used as a nitriding agent containing MgO as a main component at the time of finish annealing. It is also possible to mix substances (CrN, MnN, etc.). This nitriding increase is 0.00
1 to 0.03%. The optimum value can be determined by the steel composition and the slab heating temperature.

[0039]

EXAMPLE A continuously cast silicon steel slab having a chemical composition shown in Table 7 and a balance of substantially Fe and having a thickness of 200 mm and a width of 1000 mm was heated in a normal gas heating furnace, and then heated in an induction heating furnace. After heating at 1270 ° C. to form a solution of the inhibitor component, hot rough rolling, hot finishing rolling at a rolling end temperature of 1050 ° C. to a thickness of 2.3 mm, and controlled cooling at each temperature history shown in FIG. 550 ° C. This hot-rolled sheet is subjected to hot-rolled sheet annealing and pickling, then cold-rolled to an intermediate sheet thickness, and subjected to intermediate annealing, and then to a final sheet thickness (0.2
3 mm). Next, the obtained cold-rolled sheet is subjected to decarburizing annealing at 850 ° C. for 2 minutes in a wet hydrogen atmosphere, and 0.012% as a nitrogen increase in a strip running state.
After nitriding, an annealing separator containing MgO as a main component was applied, and final finish annealing was performed in a hydrogen atmosphere at 1200 ° C. for 20 hours to obtain a product. The magnetic properties of the obtained product were measured. Table 8 shows the results.

[0040]

[Table 7]

[0041]

[Table 8]

Table 8 shows that the method of the present invention exhibits excellent magnetic properties such as high magnetic flux density and low iron loss.
On the other hand, in the comparative examples out of the range of the present invention, it can be seen that the secondary recrystallization is good but the maintenance magnetic properties are inferior.

[0043]

As described above, according to the method of the present invention,
In the production of grain-oriented electrical steel sheets that use a combination of AlN, MnSe, and MnS as inhibitors, and nitridate between decarburization annealing and the start of secondary recrystallization without setting the slab heating temperature to an extremely high temperature exceeding 1350 ° C. In addition, the problems of the conventional method can be solved, and a unidirectional silicon steel sheet having excellent magnetic properties can be manufactured. Further, according to the method of the present invention, in the production of a grain-oriented electrical steel sheet using a combination of AlN, MnSe, and MnS as an inhibitor, the development of a secondary recrystallized structure that effectively contributes to the improvement of magnetic properties is promoted. It is possible to manufacture a unidirectional silicon steel sheet having high magnetic flux density and low iron loss and excellent magnetic properties.

[Brief description of the drawings]

FIG. 1 is a graph showing a cooling history after finish rolling of hot rolling in Experiment 1.

FIG. 2 is a graph showing a cooling history after finishing rolling of hot rolling in Experiment 2.

FIG. 3 is a graph showing a cooling history after finish rolling of hot rolling in Experiment 3.

FIG. 4 is a schematic diagram showing the relationship between complex precipitation of an inhibitor and temperature and time.

FIG. 5 is a graph showing a cooling history after finish rolling of hot rolling in an example.

Continued on the front page (72) Yoshifumi Ohata 1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation Yawata Works (72) Inventor Noriyoshi Fujii Tobita-cho, Tobata-ku, Kitakyushu-shi, Fukuoka 1-1 Nippon Steel Corporation Yawata Works (72) Inventor Norihiro Yamamoto 1-1 Nichihata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation Yawata Works (72) Inventor Katsuro Kuroki F-Term (reference) 4K033 AA02 BA02 CA09 FA01 FA03 FA10 FA12 HA01 HA03 JA04 5E041 AA02 AA19 CA02 HB05 HB07 HB11 NN01 NN17 NN18

Claims (1)

[Claims] 1. A mass% of C: 0.01 to 0.10%,
Si: 2.0-4.5%, Mn: 0.02-0.12
%, Al: 0.005 to 0.05%, N: 0.002 to
0.010%, and Se: 0.003 to 0.05
%, S: 1 selected from 0.003 to 0.05%
A silicon steel slab containing one or two kinds is heated to a temperature of 1200 ° C. or more and 1350 ° C. or less, hot-rolled, and then subjected to hot-rolled sheet annealing, and then is subjected to one or intermediate annealing 2
Cold rolling at least twice, and then decarburizing annealing and finish annealing, and nitriding between the decarburizing annealing and the start of secondary recrystallization to produce a unidirectional silicon steel sheet. A magnetic property wherein the finish rolling end temperature is in the range of 850 to 1100 ° C., and cooling after finishing the finish rolling until winding is performed so as to satisfy the relationship of the following formula, and winding is performed at 700 ° C. or less. A method for producing a unidirectional silicon steel sheet with excellent performance. When 2 ≦ t ≦ 6, T (t) <FDT- (FDT-7
00) × t / 6, where T (t): steel sheet temperature (° C.), FDT: finish rolling end temperature (° C.), t: elapsed time from the end of hot rolling finish rolling (seconds)