JP3368409B2 - Manufacturing method of low iron loss unidirectional electrical steel sheet - 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 industrially stably producing a low iron loss grain-oriented electrical steel sheet used for an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are mainly used as iron core materials for transformers and generators, but with the recent demand for energy saving, steel sheets with higher magnetic flux density and less iron loss are available from the market. Is required. Generally, in order to achieve a low iron loss, a method of reducing the eddy current loss by increasing the Si content of the steel sheet as much as possible to increase the specific resistance of the material, and a method of reducing the eddy current loss by reducing the product sheet thickness as much as possible It has been known. Furthermore, in order to achieve low iron loss, it is necessary to highly control the inhibitor, the structure of the steel sheet, and the texture. Control of the inhibitor dispersion morphology, which is one of them, requires that the inhibitor be once solution-treated during high temperature heating of the slab prior to hot rolling, and then hot rolling with an appropriate cooling pattern.

When high temperature heating of the slab for solution treatment of the inhibitor is carried out in a gas combustion type heating furnace, the slab surface is heated, so that the temperature is high at the surface layer of the slab and low at the center of the slab. Therefore, in order to reach the target temperature to the center of the slab, the surface temperature of the slab is considerably higher than that of the center of the slab, and in the gas combustion type heating furnace, the heating rate is 1200 ° C or more and about 1 ° C / minute. Since it is slow, the time to stay in the high temperature region of 1200 ° C. or higher becomes considerably long, and the crystal grain size after heating the slab at high temperature becomes coarse,
This has been a cause of causing secondary recrystallization defects called linear fine grains in the product. As a countermeasure against this, Japanese Patent Publication No.
By using the slab rapid heating method as proposed in Japanese Patent Publication No. 54, it is possible to shorten the slab heating time.

On the other hand, in a method for producing a grain-oriented electrical steel sheet by carrying out one-stage strong cold rolling after annealing a hot rolled sheet, magnetic properties are improved by performing an aging treatment during cold rolling under strong reduction. Has been reported (Japanese Patent Publication No. 54-1384).
No. 6 publication). Further, in a method of manufacturing a grain-oriented electrical steel sheet by performing cold rolling two or more times, an aging treatment is performed at the time of final cold rolling, and a step before the final cold rolling is related to this aging treatment. It has been reported that the magnetic properties are improved by controlling the cooling rate of the intermediate annealing (see Japanese Patent Publication No. 56-3892).
However, these two techniques have not been satisfactory in terms of low iron loss.

Therefore, the inventors of the present invention, in the method of manufacturing the grain-oriented electrical steel sheet by the double cold rolling method, heat the slab at a high temperature of 1200 ° C. or higher to 5 ° C./min or higher, and In the final cold rolling step, it was newly found and proposed that the iron loss characteristics are remarkably improved only when the interpass aging is performed in the temperature range of 150 ° C to 350 ° C (Japanese Patent Application No. 6-110092). . Further, in the single cold rolling method, heating in a high temperature range of 1200 ° C. or higher by slab high temperature heating is 5 ° C./min or higher, and in the cold rolling step, interpass aging is performed in a temperature range of 180 ° C. to 350 ° C. It was newly found and proposed that the iron loss characteristics were significantly improved only when the coating was applied (Japanese Patent Application No. 6-324453).

[0006]

The product obtained by the above-mentioned method is not sufficiently satisfactory in terms of stability when a product having a thin plate is manufactured, and a product having a high iron loss value is generated. In some cases. The present invention suppresses the growth of crystal grains during slab heating, and regulates the cooling rate in final pre-rolling annealing, and the pass aging temperature and pass aging time during cold rolling are within a certain range. It is an object of the present invention to provide a method capable of obtaining a product that is industrially stable and has a low iron loss by controlling the above.

[0007]

Means for Solving the Problems That is, the present invention is as follows: (1) in% by weight, C: 0.015 to 0.100%, S
i: 2.0 to 4.0%, Mn: 0.03 to 0.12%,
Sol.Al: 0.010 to 0.065%, N: 0.
0040 to 0.0100%, one or two kinds selected from S and Se total: 0.005 to 0.050%,
Furthermore, Sb, Sn, Cu, Mo, Ge, B, Te, A
A continuous casting slab containing 0.003 to 0.3% of each element amount of one or more selected from s and Bi at 1320 ° C.
~ 1450 ℃ soaked and then hot rolled, pre-cold rolled,
0.25 after intermediate annealing and final cold rolling with multiple passes
In a method for producing a grain-oriented electrical steel sheet by decarburization / primary recrystallization annealing and final finishing annealing with a final thickness of 5 mm or less, heating the slab in a high temperature range of 1200 ° C. or higher to 5
° C. / min performs the above heating rate, at least one of said between 700 ° C. to 150 DEG ° C. and cooled at 8 ° C. / sec or more in the cold <br/> retirement process of intermediate annealing and a final cold rolling step Is a method for producing a low iron loss unidirectional electrical steel sheet characterized by holding the steel sheet in a temperature range of 200 ° C. to 350 ° C. for 1 minute or more between the passes of (2) hot rolling A method for producing a low iron loss unidirectional electrical steel sheet according to the above item (1), characterized by performing sheet annealing.
Further, (3) wt%, C: 0.015 to 0.100%, S
i: 2.0 to 4.0%, Mn: 0.03 to 0.12%,
Sol.Al: 0.010 to 0.065%, N: 0.
0040 to 0.0100%, one or two kinds selected from S and Se total: 0.005 to 0.050%,
Furthermore, Sb, Sn, Cu, Mo, Ge, B, Te, A
A continuous casting slab containing 0.003 to 0.3% of each element content of one or more selected from s and Bi at 1320 ° C.
Heat soaked to -1450 ° C, then hot rolled, hot rolled sheet annealed, cold rolled with multiple passes to a final sheet thickness of 0.25 mm or less, decarburization / primary recrystallization annealing, final finishing annealing 700 ° C. a method for producing a grain-oriented electrical steel sheets, performs heating of 1200 ° C. or more high temperature zone of the slab at 5 ° C. / min or more heating rate, in the course of cooling said hot rolled sheet annealing by 150 Between 8 ° C / sec and at least 1 pass between the cold rolling steps.
A method for producing a low iron loss unidirectional electrical steel sheet, which is characterized by holding in a temperature range of 00 ° C to 350 ° C for 1 minute or more, (4) Before heating a slab in a high temperature range of 1200 ° C or more. To
The method for producing a low iron loss unidirectional electrical steel sheet according to any one of (1), (2) or (3) above, wherein hot deformation is applied at a rolling reduction of 50% or less.

The inventors of the present invention investigated a method for stably producing a grain-oriented electrical steel sheet having a low iron loss, and found that slab heating in a high temperature range during slab heating was performed at a heating rate of 5 ° C./min or more. It suppresses the growth of crystal grains during slab heating, and 700 ° C to 150 ° C in the cooling process of hot-rolled sheet annealing.
The solid solution C, N
It has been found that it is very effective to enrich the steel and control the aging temperature between passes and the aging time between passes during the final cold rolling within a certain range.

FIG. 1 shows the relationship between the average cooling rate of intermediate annealing and product characteristics. That is, C: 0.070%, Si: 3.19%, Mn: in the composition range according to the present invention.
0.071%, S: 0.022%, Sol.Al: 0.03
A slab containing 1%, N: 0.0077%, and Sn: 0.11% is set at an ultimate temperature of 1390 ° C. by an electric heating furnace capable of short-time heating, and 1200 ° C. to 1390 ° C. is set to 1
Plate thickness using a slab heated at a heating rate of 0 ° C./min 2.
A hot rolled sheet of 00 mm was produced. Then, it was pre-cold rolled to 1.65 mm. After soaking at 1000 ° C for 2 minutes, an intermediate annealing of cooling 700 ° C to 150 ° C, which is considered to be a precipitation temperature range of C, at various cooling temperatures was performed, and in the final cold rolling step, the intermediate plate thickness was 1.00 mm and 0%. Steel plate 1 at 300 ° C at the step of 0.5mm
Hold for 0 minutes to give a final finished thickness of 0.22 mm. The obtained cold-rolled sheet was decarburized and annealed by a known method, and after applying a bake-separating material, final finishing annealing was performed and a coating liquid was applied to obtain a product.

The magnetic flux density of the product n = 5 thus obtained,
FIG. 1 shows the result of investigation on the relationship between the iron loss and the cooling rate of 700 ° C. to 150 ° C. in the intermediate annealing. As is clear from the figure, stable magnetic properties can be obtained by setting the cooling rate of 700 ° C. to 150 ° C. in the intermediate annealing to 8 ° C./sec or more.

FIG. 2 shows characteristics of a product manufactured by the following steps. That is, C: 0.075%, Si: 3.12%, Mn: in the composition range according to the present invention.
0.080%, S: 0.020%, Sol.Al: 0.02
A slab containing 5%, N: 0.0070%, and Sn: 0.10% is set to a reaching temperature of 1380 ° C by an induction heating furnace capable of heating for a short time, and the temperature from 1200 ° C to 1380 ° C is set to 1
A hot rolled sheet having a sheet thickness of 2.20 mm was produced using a slab heated at a temperature rising rate of 0 ° C./minute or 1 ° C./minute. And
Pre-cold rolled to 1.70 mm. After soaking at 1000 ℃ for 2 minutes,
Intermediate annealing of cooling 700 ° C. to 150 ° C., which is considered to be the precipitation temperature range of C, at an average cooling rate of 1 ° C./second, 8 ° C./second, or 15 ° C./second is performed, and the final cold rolling step involves intermediate plate thickness. The steel sheets were held at various temperatures for 10 minutes at 1.10 mm and 0.55 mm steps to give a final finished thickness of 0.22 mm. The obtained cold-rolled sheet was decarburized and annealed by a known method, and after applying a baking separating material, final finishing annealing was performed and a coating solution was applied to obtain a product.

The relationship between the magnetic flux density, the iron loss, the cooling rate at 700 ° C. to 150 ° C. in the intermediate annealing, and the interpass aging temperature of the product sheet thus obtained is examined and the results are shown in FIG. As is clear from the figure, 700 ° C to 1 in the intermediate annealing
It can be seen that stable magnetic properties can be obtained by setting the cooling rate at 50 ° C. to 8 ° C./sec or more and performing the interpass aging at the temperature of 200 ° C. to 350 ° C. in the final cold rolling step.

As described above, according to the present invention, in the high temperature slab heating, the temperature rising rate of the slab is 5 ° C./min or more, and in the cooling process of the intermediate annealing, the temperature between 700 ° C. and 150 ° C. is cooled at 8 ° C./sec or more. And in the final cold rolling step, 200 ° C to 350 ° C
It was completed based on a completely new finding that stable and good magnetic properties can be obtained by performing aging for 1 minute or more at a temperature of ° C.

The reason why the magnetic characteristics are improved by the present invention is not necessarily clarified, but it is considered as follows. By suppressing the growth of crystal grains during slab heating by increasing the slab heating rate, the structure and precipitates of the hot-rolled sheet can be made uniform after hot rolling, and the grain size of the hot-rolled sheet can be reduced. Become. The texture also has {100} oriented grains decreased and {111} oriented grains increased. When the crystal grain size before cold rolling becomes small, after primary recrystallization,
The number of {110} oriented grains that nucleate from inside the grain decreases, and the number of {111} oriented grains that nucleate near the grain boundary increases. {11
The increase of 1} oriented grains and the decrease of {100} oriented grains bring about stability of secondary recrystallization, while {110}
A low iron loss cannot be stably obtained because the number of oriented grains decreases.

Therefore, in the cooling process of the final pre-rolling annealing, solid solution C and N are enriched and the aging temperature between passes is limited to a narrower range than before, so that the solid solution C and N are subjected to cold rolling. When the deformation mechanism is greatly affected by the action of adhering to the formed defect such as dislocation and the {110} <001> oriented grains are increased, the {110} oriented grains and the {111} oriented grains increase, Grains of {100} orientation are reduced, and a grain-oriented electrical steel sheet having a lower iron loss and more stable than conventional ones can be obtained.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the reasons for limiting the components and processing conditions of the present invention will be described. Si has a lower limit of 2.0
If it is less than%, good iron loss cannot be obtained, and if it exceeds the upper limit of 4.0%, the cold rolling property deteriorates significantly. C is the lower limit 0.015%
If it is less than 2, the secondary recrystallization becomes unstable, and the upper limit is 0.1.
The content of 00% is limited because if C is larger than this, the time required for decarburization becomes long and it is economically disadvantageous.

If the lower limit of Mn is less than 0.03%, hot embrittlement occurs, and if it exceeds the upper limit of 0.12%, the magnetic properties are deteriorated. S and Se are elements necessary for forming MnS and MnSe. If the total of one or two of these is less than the lower limit of 0.005%, the absolute amount of MnS and MnSe is insufficient, and the upper limit is 0.050%. If it exceeds, hot cracking occurs, and purification in final finish annealing becomes difficult.

Sol.Al is an element necessary for forming AlN. If the lower limit is less than 0.010%, the absolute amount of AlN is insufficient, and if the upper limit is more than 0.065%, a suitable dispersed state of AlN is obtained. I can't. N is an element necessary for forming AlN. If the lower limit is less than 0.0040%, the absolute amount of AlN is insufficient, and if it exceeds the upper limit of 0.0100%, a proper dispersed state of AlN cannot be obtained. Sb, Sn, Cu, Mo,
Ge, B, Te, As, and Bi segregate at grain boundaries,
Stabilizes the secondary recrystallization, but the lower limit of each element amount
If it is less than 0.003 %, the segregation amount is insufficient, and the upper limit of 0.3% is due to economic reasons and deterioration of decarburization.

The slab heating temperature is 1320 ° C. to 1450.
However, if the temperature is lower than 1320 ° C, the variation in iron loss of the product is large. When it exceeds 1450 ° C, the slab melts. Regarding slab heating in a high temperature range, the temperature rising rate of 1200 ° C or higher is set to 5 ° C / min or higher, but less than 1200 ° C, in order to suppress coarsening of the crystal grain size during heating and to improve the texture and texture. In this case, since the influence on grain growth is small, it is not necessary to specify the heating rate. This is because if the heating rate is less than 5 ° C./minute, the effect of improving the magnetic properties is small.

The cooling rate of 700 ° C. to 150 DEG ° C. in the intermediate annealing, improvement of the magnetic properties is small as less than 8 ° C. / sec, as shown in FIG. The temperature of 700 ° C to 150 ° C is
This is because that temperature range is considered to be the C precipitation temperature range.

The aging temperature between passes during the final cold rolling is shown in FIG.
As shown in (1), when the temperature is lower than 200 ° C., the effect of improving the magnetic properties is poor, and when the temperature exceeds 350 ° C., the effect of improving the magnetic properties is small. Although the aging treatment is effective even once, the rolling and aging treatment are alternately repeated to further improve the magnetic properties of the product. If the aging time between passes is less than 1 minute, the effect of improving the magnetic properties is small.

Applying hot deformation under a pressure of 50% or less before heating the slab in a high temperature range of 1200 ° C. or higher destroys the columnar crystals and is effective in homogenizing the structure of the hot-rolled sheet. Reduce variations. The upper limit of the rolling reduction is set to 50% because the magnetic characteristic value does not change even if the rolling reduction is further increased.

The reason for limiting the product plate thickness to 0.25 mm or less is to obtain a product with low iron loss in response to the recent demand needs. In the two-time cold rolling method, hot rolled sheet annealing is carried out as necessary. It is effective in homogenizing the structure and precipitates of the hot-rolled sheet and reduces the variations in the magnetic properties of the product.

[0024]

【Example】

[Example 1] [C] 0.072%, [Si] 3.21
%, [Mn] 0.088%, [S] 0.025%, [So
l.Al] 0.022%, [N] 0.0089%, [S
n] 0.10%, [Cu] 0.06% containing slab preheating is performed in a gas combustion type heating furnace at a temperature of the slab center of 12
The sample was heated until it reached the temperature range of 00 ° C., and thereafter, the sample Nos. 7 and 8 were subjected to hot deformation at a reduction rate of 25%, and the other samples were not subjected to hot deformation.
Guided to induction heating furnace, and then heated up to 1380 ℃ 1 ℃
/ Min or 10 ° C / min, the slab heated to a high temperature was hot-rolled to obtain a hot-rolled sheet having a thickness of 1.8 mm. Then, after soaking at 1100 ° C for 2 minutes, hot-rolled sheet annealing for cooling the temperature range of 700 ° C to 150 ° C at various cooling rates is performed,
During the cold rolling process, at the stages of 1.2 mm and 0.6 mm in thickness,
Aging was performed at 250 ° C. for 3 minutes between passes to give a final finished thickness of 0.22 mm. The obtained cold-rolled sheet was decarburized and annealed by a known method, coated with a bake-separating material, and then finally finished annealed to apply a coating solution to obtain a product.

The slab temperature rising rate at this time, 7
Shows the cooling rate at 00 ° C to 150 ° C, the presence or absence of slab reduction before high temperature heating of slab, and the average magnetic flux density B ₈ , iron loss W _17/50 , and variation of iron loss of the obtained product n = 10. Shown in 1.
From this, it is understood that the inventive example can stably obtain the low iron loss material as compared with the comparative example.

[0026]

[Table 1]

[Example 2] [C] 0.073%, [S]
i] 3.22%, [Mn] 0.070%, [Se] 0.
014%, [S] 0.014%, [Sol.Al] 0.02
4%, [N] 0.0077%, [Sb] 0.025%,
A slab containing 0.03% of [Mo] is heated to an induction temperature of 1370 ° C. in an induction heating furnace, and the temperature is 1200 ° C. to 1370 ° C.
The slab that was heated at a high temperature of 2 ° C./sec was hot-rolled to obtain a hot-rolled sheet having a thickness of 2.3 mm. Sample Nos. 1 and 2 were annealed at 100 ° C. for 2 minutes, and Sample Nos. 3 and 4 were not even annealed. In the subsequent pre-cold rolling, the plate thickness was set to 1.6 mm, and then intermediate annealing was carried out at 1000 ° C. for 2 minutes soaking, and then the cooling rate of 700 ° C. to 150 ° C. was 0.2 ° C./sec and 30 ° C./sec. Cooled at 2 levels. During the final cold rolling process, aging was performed at a temperature of 1.1 mm and 0.6 mm at a temperature of 300 ° C for 10 minutes at a stage of 0.17.
The final finished thickness was mm. The obtained cold rolled sheet was decarburized and annealed by a known method to apply a bake separating material, and then final finish annealing was performed to apply a coating solution to obtain a product. Table 2 shows the average magnetic flux density B ₈ , iron loss W _17/50 , and variation of iron loss of the obtained product n = 10. From this, it is understood that the inventive example can stably obtain the low iron loss material as compared with the comparative example.

[0028]

[Table 2]

[0029]

As described above, according to the present invention, a grain-oriented electrical steel sheet having a low iron loss can be manufactured industrially stably, and its industrial effect is very large.

[Brief description of drawings]

FIG. 1 is a relationship diagram of an average cooling rate of 700 ° C. to 150 ° C. in intermediate annealing, magnetic flux density B _{8 of} a product, and iron loss W _17/50 .

FIG. 2 Slab temperature rising rate during high temperature heating of slab, aging time between passes during final cold rolling, and 700 ° C. during intermediate annealing
150 ° C cooling rate, product magnetic flux density B ₈ , iron loss W _17/5
It is a relationship diagram of ₀ .

Continuation of front page (56) Reference JP-A-1-201425 (JP, A) JP-A-63-259024 (JP, A) JP-A-3-115529 (JP, A) JP-B-56-3892 (JP , B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 8/12 C22C 38/00 303 C22C 38/06 C22C 38/60 H01F 1/16

Claims (4)

(57) [Claims] 1. By weight%, C: 0.015 to 0.100%, Si: 2.0 to 4.0%, Mn: 0.03 to 0.12%, Sol.Al: 0.010 to 0.065%, N: 0.0040 to 0.0100%, one or two kinds selected from S and Se in total:
0.005 to 0.050%, and further Sb, Sn, Cu, Mo, Ge, B, Te, A
A continuous casting slab containing 0.003 to 0.3% of each element amount of one or more selected from s and Bi at 1320 ° C.
~ 1450 ℃ soaked and then hot rolled, pre-cold rolled,
0.25 after intermediate annealing and final cold rolling with multiple passes
In a method for producing a grain-oriented electrical steel sheet by decarburization / primary recrystallization annealing and final finishing annealing with a final thickness of 5 mm or less, heating the slab in a high temperature range of 1200 ° C. or higher to 5
° C. / min performs the above heating rate, at least one of said between 700 ° C. to 150 DEG ° C. and cooled at 8 ° C. / sec or more in the cold <br/> retirement process of intermediate annealing and a final cold rolling step The steel sheet is held in a temperature range of 200 ° C. to 350 ° C. for 1 minute or more between the passes of 1. 2. The method for producing a low iron loss unidirectional electrical steel sheet according to claim 1, wherein the hot rolled sheet is annealed. 3. By weight%, C: 0.015 to 0.100%, Si: 2.0 to 4.0%, Mn: 0.03 to 0.12%, Sol.Al: 0.010 to 0.065%, N: 0.0040 to 0.0100%, one or two kinds selected from S and Se in total:
0.005 to 0.050%, and further Sb, Sn, Cu, Mo, Ge, B, Te, A
A continuous casting slab containing 0.003 to 0.3% of each element amount of one or more selected from s and Bi at 1320 ° C.
Heat soaked to -1450 ° C, then hot rolled, hot rolled sheet annealed, cold rolled with multiple passes to a final sheet thickness of 0.25 mm or less, decarburization, primary recrystallization annealing, final finishing annealing 700 ° C. a method for producing a grain-oriented electrical steel sheets, performs heating of 1200 ° C. or more high temperature zone of the slab at 5 ° C. / min or more heating rate, in the course of cooling said hot rolled sheet annealing by 150 Between 8 ° C / sec and at least 1 pass between the cold rolling steps.
A method for producing a low iron loss grain-oriented electrical steel sheet, which is characterized by holding in a temperature range of 00 ° C to 350 ° C for 1 minute or more. 4. The low deformation according to claim 1, wherein hot deformation is applied at a reduction rate of 50% or less before heating the slab in a high temperature range of 1200 ° C. or higher. Method for manufacturing iron loss grain-oriented electrical steel sheet.