JPH08333631A - Production of grain oriented silicon steel sheet with low iron loss - Google Patents

Abstract

PURPOSE: To industrially and stably produce a grain oriented silicon steel sheet with low iron loss by controlling the temp. rise rate at the time of heating a continuously cast slab of specific composition, the cooling velocity at hot rolled plate annealing, and the aging temp. and time between passes at the time of cold rolling, respectively. CONSTITUTION: A steel, having a composition consisting of, by weight, 0.015-0.100% C, 2.0-4.0% Si, 0.03-0.12% Mn, 0.010-0.065% sol.Al, 0.0040-0.0100% N, 0.005-0.050% S and/or Se, and the balance Fe, is used. A continuously cast slab of this composition is heated and soaked to and at 1320-1450 deg.C and hot-rolled into plate. This steel plate is subjected to hot rolled plate annealing, to preliminary cold rolling, and to cold rolling while process-annealed between cold rolling stages. The resulting steel sheet is subjected to decarburizing and primary recrystallization annealing, final finish annealing, etc. At this time, heating for the slab in a temp. region as high as >=1200 deg.C is carried out at >=5 deg.C/min temp. rise rate, and cooling at hot rolled plate annealing through the temp. region from 700 to 150 deg.C is performed at a rate of >=8 deg.C/sec. The steel sheet is held, at least once between the passes at preliminary cold rolling, at 100-400 deg.C for >=1min.

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 low iron loss unidirectional 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.

In order to control the inhibitor dispersion morphology, which is one of them, it is necessary to temporarily solution the inhibitor during high temperature heating of the slab prior to hot rolling, and then perform hot rolling with an appropriate cooling pattern. . When high-temperature heating of the slab for solution treatment of the inhibitor is performed in a gas combustion type heating furnace, the slab surface is heated, so 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 up to the center of the slab, the surface temperature of the slab is considerably higher than that of the center of the slab, and the temperature rise rate is 1200 ° C in the gas combustion type heating furnace.
As described above, since it is slow at about 1 ° C./minute, the residence time in the high temperature region of 1200 ° C. or higher becomes considerably long. Therefore, the crystal grain size after heating the slab at high temperature becomes coarse, which causes a secondary recrystallization defect called linear fine grain in the product. As a countermeasure against this, if a slab rapid heating method as proposed in Japanese Patent Publication No. 56-18654 is used,
It became possible to shorten the heating time of the slab.

On the other hand, in a method for producing a grain-oriented electrical steel sheet by a double cold rolling method in which final cold rolling with a reduction rate of 40 to 80% is performed, during the first cold rolling and during the second cold rolling. A method of improving the magnetic properties by performing an aging treatment has been disclosed (see Japanese Patent Application Laid-Open No. 58-25425). Further, in a method for producing a unidirectional electrical steel sheet by performing cold rolling two or more times including final cold rolling with a strong reduction having a rolling reduction of more than 80 to 95%, 600 ° C. to 20 ° C. in a cooling process of hot rolled sheet annealing.
Cool between 0 ° C. at 5 ° C./sec or more, and apply the steel plate 50 at least once between multiple passes in the first cold rolling.
A method has been disclosed in which the magnetic properties are improved by holding the temperature range of up to 500 ° C. for 1 minute or more (see Japanese Patent Application Laid-Open No. 62-202024).

[0005]

However, the products obtained by the above-mentioned conventional methods are not satisfactory in terms of low iron loss. The present invention suppresses the growth of crystal grains during slab heating by controlling the temperature rising rate of slab heating in the high temperature region during slab heating, and controls the cooling rate during hot-rolled sheet annealing, during cold rolling. By controlling the aging temperature between passes and the aging time between passes within a certain range, a method for obtaining a product with low iron loss is provided.

[0006]

That is, the present invention is as follows.
(1)% 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: 0.00
40 to 0.0100%, one or two kinds selected from S and Se total: 0.005 to 0.050%, and further from Sb, Sn, Cu, Mo, Ge, B, Te, As and Bi One or two or more selected from 0.003 to
A continuous cast slab containing 0.3% and the balance being substantially Fe is heated and soaked at 1320 ° C to 1450 ° C, hot rolled, hot rolled sheet annealed, and pre-cold rolled. In the method for producing a grain-oriented electrical steel sheet by intermediate annealing, final cold rolling, decarburization / primary recrystallization annealing, and final finish annealing, heating the slab in a high temperature range of 1200 ° C or higher to 5 ° C.
At a temperature rising rate of not less than 1 minute / minute, and in the cooling process of hot-rolled sheet annealing, between 700 ° C. and 150 ° C. is cooled at 8 ° C./second or more, and at least once between the passes of multiple passes in the preliminary cold rolling. Is a method for producing a low iron loss unidirectional electrical steel sheet, characterized in that the steel sheet is held in a temperature range of 100 ° C. to 400 ° C. for 1 minute or more, and (2) an intermediate sheet in the final cold rolling step. The method for producing a low iron loss unidirectional electrical steel sheet according to the above item (1), characterized in that the steel sheet is held in a temperature range of 150 ° C. to 350 ° C. for at least 1 minute between at least one pass of the thickness step. And (3) 1 for the slab
Before heating to a high temperature range of 200 ° C. or higher, hot deformation is applied at a reduction rate of 50% or less, (1),
It is a method for producing a low iron loss unidirectional electrical steel sheet according to the item (2).

The present inventor has studied a method for producing a grain-oriented electrical steel sheet having a low iron loss. As a result, the slab heating is performed at a temperature rising rate of 5 ° C./min or more in the high temperature range during slab heating. During the cooling process of hot-rolled sheet annealing while suppressing the growth of crystal grains at the time of
By cooling at ℃ / sec or more, it is possible to enrich solid solution C, N, fine carbides and fine nitrides, and to control the aging temperature between passes and the aging time between passes during cold rolling within a certain range. It was found to be effective.

FIG. 1 shows an example of the result of an experiment conducted by the present inventor. That is, C in the component range according to the present invention:
0.075%, Si: 3.23%, Mn: 0.071
%, S: 0.025%, Sol. Al: 0.030%,
A slab containing N: 0.0080% and Sn: 0.11% is brought to a reaching temperature of 1350 ° C. by an electric atmosphere control type induction heating furnace capable of heating for a short time, and 1200 ° C. to 135 ° C.
Hot-rolled sheets having a plate thickness of 2.30 mm were produced using cast pieces heated to 0 ° C. at various heating rates. And 100 to this
A hot-rolled sheet was annealed at 0 ° C. for 2 minutes and then cooled at 15 ° C./sec. After pickling, preliminary cold rolling was performed to obtain a sheet thickness of 1.45 mm. During the preliminary cold rolling, the plate thickness is 2.00 mm and 1.7.
Aging was performed for 10 minutes at various temperatures at a step of 0 mm. Then, after intermediate annealing of soaking at 1000 ° C. for 2 minutes and rapid cooling, final cold rolling was performed to a final finished thickness of 0.17 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. FIG. 1 shows the results of an examination of the relationship between the iron loss of the product sheet thus obtained, the slab heating rate, and the interpass aging temperature. As is clear from the figure, the slab temperature rising rate is set to 5 ° C./min or more, and 1
It can be seen that good magnetic characteristics can be obtained by performing aging between passes at a temperature of 00 to 400 ° C.

FIG. 2 also shows an example of experimental results. That is, C: 0.070% and Si: in the composition range according to the present invention.
3.20%, Mn: 0.070%, S: 0.022%,
Sol. Al: 0.031%, N: 0.0075%, S
A slab containing n: 0.10% was heated to a final temperature of 1390 ° C. by electric heating capable of heating for a short time, and a slab heated from 1200 ° C. to 1390 ° C. at a heating rate of 10 ° C./min was used. A hot rolled plate having a plate thickness of 2.30 mm was produced. Then, this is annealed at 1000 ° C. for 2 minutes and then annealed at 15 ° C./sec for annealing, hot-rolled after pickling, and cold-rolled at 1.35.
The plate thickness was mm. During the preliminary cold rolling, the plate thickness is 2.0
The steel plate was kept at 250 ° C. for various times at the steps of 0 mm and 1.70 mm. Then, after intermediate annealing of soaking at 1000 ° C. for 2 minutes and rapid cooling, final cold rolling was performed to a final finished thickness of 0.17 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. FIG. 2 shows the results of an examination of the relationship between the magnetic flux density and the iron loss of the product sheet thus obtained and the inter-pass aging temperature. As is clear from the figure, good magnetic characteristics can be obtained when the aging time between passes is 1 minute or more.

FIG. 3 shows an example of the experimental results for examining the relationship between the cooling rate and magnetism. That is, C: 0.069%, Si: 3.23%, Mn: in the composition range according to the present invention.
0.070%, S: 0.028%, Sol. Al: 0.0
A slab containing 30%, N: 0.0074%, and Sn: 0.10% is brought to a reaching temperature of 1400 ° C by electric heating capable of heating for a short time, and the temperature from 1200 ° C to 1400 ° C is set to 1
Plate thickness using a slab heated at a heating rate of 0 ° C./min 2.
A 30 mm hot rolled sheet was prepared. After soaking at 1000 ℃ for 2 minutes,
Hot-rolled sheet annealing was performed at 700 ° C to 150 ° C, which is considered to be the precipitation temperature range of C, at various cooling rates, and after pickling, preliminary cold rolling was performed to a sheet thickness of 1.25 mm. During the preliminary cold rolling, the steel plate was held at 250 ° C. for 5 minutes at the stages of the plate thickness of 2.00 mm and 1.60 mm. After that, after the intermediate annealing of soaking at 1000 ° C. for 2 minutes and the rapid cooling, the final cold rolling is performed to 0.17.
The final finished thickness was 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 iron loss of the product sheet thus obtained and 700 ° C to 1 in hot-rolled sheet annealing
The result of having investigated the relationship with the cooling rate of 50 ° C. is shown in FIG. As is clear from the figure, 700 ° C during hot-rolled sheet annealing
It can be seen that good magnetic properties can be obtained by setting the cooling rate of ˜150 ° C. to 8 ° C./sec or more.

As described above, according to the present invention, the high temperature slab heating is performed at a slab temperature rising rate of 5 ° C./min or more, and in the cooling process of the hot-rolled sheet annealing, the temperature between 700 ° C. and 150 ° C. is 8 ° C./min.
It cools for more than a second, and 100 ℃ -40 in the preliminary cold rolling process.
It was completed on the basis of a completely new finding that magnetic properties are improved by performing aging for 1 minute or more at a temperature of 0 ° C.

The reasons for limiting the conditions of the present invention will be described below. If Si is less than the lower limit of 2%, good iron loss cannot be obtained, and if it exceeds the upper limit of 4%, cold ductility is significantly deteriorated. C
When the lower limit is less than 0.015%, the secondary recrystallization becomes unstable, and the upper limit of 0.100% is limited because the time required for decarburization becomes longer and the economically disadvantageous if the C content exceeds the upper limit. .

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 deteriorate rather. 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, and if the lower limit is less than 0.010%, the absolute amount of AlN is insufficient, and if it exceeds the upper limit of 0.065%, a proper dispersed state of AlN cannot be obtained. 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, T
e, As, and Bi segregate at the grain boundaries to stabilize the secondary recrystallization, but if the lower limit is less than 0.03%, the segregation amount is insufficient, and the upper limit of 0.3% is for economic reasons and decarburization. It is due to deterioration.

The slab heating temperature is 1320 ° C. to 1450.
However, if the temperature is lower than 1320 ° C., the iron loss of the product varies greatly. 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.

When the cooling rate of 700 ° C. to 150 ° C. in the annealing of hot rolled sheet is less than 8 ° C./sec as shown in FIG. 3, the effect of improving the magnetic properties is small. The reason why the temperature range is 700 ° C. to 150 ° C. is that the temperature range is considered to be the precipitation temperature range of C.

As shown in FIGS. 1 and 2, the interpass aging temperature at the time of pre-cold rolling is lower than 100 ° C., the effect of improving the magnetic properties is poor, and even if it exceeds 400 ° C., the effect of improving the magnetic properties is low. Less is. The aging treatment is effective even once,
By repeating rolling and aging treatment alternately, the magnetic properties of the product are further improved. If the aging time between passes is less than 1 minute, the effect of improving the magnetic properties is small.

Magnetic properties are further improved by pre-pass cold aging in pre-cold rolling and pass inter-aging in final cold rolling. The aging temperature between passes during final cold rolling is 1
If the temperature is lower than 50 ° C, the effect of improving the magnetic properties is poor, and if the temperature exceeds 350 ° C, the effect of improving the magnetic properties is low. The aging treatment is effective even once, but the magnetic properties of the product are further improved by repeating rolling and aging treatment alternately. 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 of the slab and is effective in homogenizing the structure of the hot-rolled sheet. Reduce the variation in characteristics. The upper limit of the rolling reduction is 50
The reason why the percentage is set is that the value of the magnetic characteristics does not change even if the rolling reduction is further increased.

[0021]

【Example】

[Example 1] [C] 0.075%, [Si] 3.25
%, [Mn] 0.088%, [S] 0.025%, [S
ol. Al] 0.022%, [N] 0.0080%, [S
n] 0.10%, [Cu] 0.05% containing slab is preheated in a gas combustion type heating furnace until the temperature of the slab center reaches a temperature range of 1200 ° C., and thereafter, Sample Nos. 7 and 8 were subjected to hot deformation at a reduction rate of 25%, and the other samples were introduced into an atmosphere-controlled induction heating furnace without hot deformation and then heated up to 1380 ° C. A slab that was heated at a high temperature under the condition of 1 ° C / min or 12 ° C / min was hot-rolled to obtain a hot-rolled sheet having a thickness of 2.2 mm. After soaking at 1000 ° C for 2 minutes on the hot rolled sheet, 700 ° C to 150 ° C
A hot-rolled sheet was annealed to cool the temperature range of 30 ° C. at an average of 30 ° C./sec. After pickling, preliminary cold rolling was performed to obtain a thickness of 1.50 mm. During the preliminary cold rolling, a pass aging was performed for 3 minutes at various temperatures at a stage of a plate thickness of 1.85 mm. After a while
After intermediate annealing of soaking at 1000 ° C for 2 minutes and rapid cooling, final cold rolling was performed to a final finished thickness of 0.17 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 wave was applied to obtain a product. Slab heating rate at this time,
Interpass aging rolling temperature in pre-cold rolling, presence / absence of billet reduction before high temperature heating, and average magnetic flux density B of obtained product n = 10
₈ and iron loss W _17/50 are shown in Table 1. From this, it is understood that the example of the present invention can obtain a low iron loss material as compared with the comparative example.

[0023]

[Table 1]

[Example 2] [C] 0.074%, [S
i] 3.24%, [Mn] 0.087%, [S] 0.0
14%, [Se] 0.014%, [Sb] 0.025
%, [Mo] 0.03%, [Sol. Al] 0.024
%, [N] 0.0077% in a slab containing an induction-controlled induction furnace with an ultimate temperature of 1370 ° C. and 1200 ° C.
The slab that had been heated at a high temperature of 15 ° C / sec to -1370 ° C was hot-rolled into a hot-rolled sheet having a thickness of 2.3 mm. After soaking at 1000 ° C for 2 minutes on the hot rolled sheet, 700 ° C to 150 ° C
The hot-rolled sheet is annealed at an average temperature of 40 ° C / sec.
Precooled to 45 mm. After that, an intermediate anneal of 1100 ° C. × 2 minutes soaking and then rapid cooling was performed, and the final cold rolling step was performed in a 0.
The final finished plate thickness was 17 mm. During the rolling, the following three types of treatment were performed. Pre-pass cold rolling and final cold rolling were not aged between passes. Plate thickness during pre-cold rolling 2.
Aging was performed for 10 minutes at 300 ° C. at 0 mm and 1.7 mm. No aging was performed during the final cold rolling.
300 ° C when plate thickness is 2.0 mm and 1.7 mm during pre-cold rolling
During the final cold rolling, the interpass aging was performed for 10 minutes at 300 ° C. for 10 minutes when the plate thickness was 0.7 mm.

The cold-rolled sheet thus obtained was decarburized and annealed by a known method, and after applying a bake-separating material, final finishing annealing was performed to apply a coating liquid to obtain a product. The obtained product n
Table 2 shows the average magnetic flux density B ₈ and the iron loss W _17/50 of = 10. From this, it can be seen that the inventive example can obtain a lower iron loss material than the comparative example.

[0026]

[Table 2]

[Example 3] [C] 0.074%, [S
i] 3.20%, [Mn] 0.075%, [Se] 0.
023%, [Sol. Al] 0.025%, [N] 0.0
A slab containing 080% and [Sb] 0.025% is set to a temperature of 1370 ° C in an electric heating furnace and 1200 ° C to 13 ° C.
The slab that had been heated to 70 ° C. at a heating rate of 20 ° C./sec at a high temperature was hot-rolled into a hot-rolled sheet having a thickness of 2.3 mm. The hot rolled sheet was annealed at 1000 ° C. for 2 minutes to anneal the hot rolled sheet. The average cooling rate of 700 ° C to 150 ° C in hot-rolled sheet annealing is
There were two levels of 0.2 ° C./sec and 20 ° C./sec. After pickling, it was pre-cold rolled to 1.80 mm. At the stage of the plate thickness during the pre-cold rolling, there are two kinds of treatments: (a) 2.1 mm thickness, 1.95 mm thickness, 250 ° C. × 10 minutes pass aging, and (b) no treatment. did. After that, 1100 ℃ ×
After soaking for 2 minutes, it was subjected to intermediate annealing in which it was rapidly cooled to a final finished thickness of 0.22 mm in the final cold rolling step.

The cold-rolled sheet thus obtained was decarburized and annealed by a known method, and a baking separator was applied, followed by final finish annealing and application of a coating solution to obtain a product. The obtained product n
Table 3 shows the average magnetic flux density B ₈ and the iron loss W _17/50 of = 10. From this, it can be seen that the inventive example can obtain a lower iron loss material than the comparative example.

[0029]

[Table 3]

[0030]

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 diagram showing a relationship between a temperature rising rate in heating a continuously cast slab in a high temperature range of 1200 ° C. or higher, an aging temperature between passes during pre-cold rolling, and an iron loss W _17/50 of a product.

FIG. 2 is a diagram showing a relationship between an aging time between passes during pre-cold rolling, a magnetic flux density B _{8 of} a product, and an iron loss W _17/50 .

FIG. 3 is a diagram showing a relationship between a cooling rate of 700 ° C. to 150 ° C. in a hot rolled sheet annealing, a magnetic flux density B _{8 of} a product, and an iron loss W _17/50 .

Claims (3)

[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:
0.005-0.050%, Sb, Sn, Cu, M
A continuous cast slab containing 0.003 to 0.3% of one or more selected from o, Ge, B, Te, As and Bi, and the balance being substantially Fe composition.
Heat soaked at 0 ° C to 1450 ° C, then hot rolled, hot-rolled sheet annealed, unidirectional by preliminary cold rolling, intermediate annealing, final cold rolling, decarburization / primary recrystallization annealing, and final finishing annealing. Of the above slab in a method for producing a magnetic electrical steel sheet
Heating in a high temperature range of 0 ° C. or higher is performed at a temperature rising rate of 5 ° C./min or higher, and 700 ° C. to 1 ° C. in the cooling process of hot rolled sheet annealing.
The steel sheet is cooled at a rate of 8 ° C./sec or more between 50 ° C., and the steel plate is cooled to 100 times at least once between the passes of the preliminary cold rolling.
A method for producing a low iron loss grain-oriented electrical steel sheet, which is characterized by holding at a temperature range of ℃ to 400 ℃ for 1 minute or more. 2. The steel sheet is heated to 150 ° C. to 350 ° C. during at least one pass of the intermediate thickness step in the final cold rolling process.
The method for producing a low iron loss unidirectional electrical steel sheet according to claim 1, wherein the temperature is maintained for 1 minute or more. 3. A low iron loss unidirectional electromagnetic field according to claim 1, wherein hot deformation is applied at a rolling reduction of 50% or less before heating the slab to a high temperature region of 1200 ° C. or higher. Steel plate manufacturing method.