JP3290446B2 - Method for producing non-oriented electrical steel sheet with excellent magnetic properties and good surface appearance - 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 non-oriented electrical steel sheet having excellent magnetic properties, and more particularly to a method for producing a non-oriented electrical steel sheet having a high magnetic flux density and a good surface appearance. .

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are used as core materials for rotating machines such as various types of motors and stationary devices such as transformers and stabilizers. Therefore, it is necessary to improve the magnetic flux density of the magnetic steel sheet used and to reduce the iron loss. Incidentally, it is known that the magnetism of a non-oriented electrical steel sheet can be improved by enlarging the crystal grains of a steel strip before cold rolling.

[0003] As a method of coarsening the grain size of a steel strip before cold rolling, the inventors have previously disclosed in Japanese Patent Publication No. 57-35628, when hot rolling an electromagnetic steel material, the end temperature of hot rolling was determined by the steel. Above the Ar ₃ transformation temperature determined by the chemical composition of the above, and then heat the hot-rolled steel strip at a temperature below the A ₃ transformation temperature for 30 seconds or more.
A method of annealing for less than 15 minutes was proposed. Further, JP-A-2-1822831 discloses that the hot rolling end temperature is set to the Ar ₃ transformation point temperature or higher, and then the cooling rate after maintaining the hot-rolled steel strip at the A ₃ transformation point temperature or lower for 30 to 15 seconds. A method of controlling has been disclosed.

[0004] However, in these methods, when the annealing time of the hot-rolled steel strip is short, the crystal grains are hardly coarsened in some cases, and as a result, there is a defect that the magnetic properties vary.
Further, on the long-time side, the crystal grains may be excessively large, and as a result, the product may be folded and the surface appearance may be impaired. On the other hand, Japanese Patent Application Laid-Open No. 58-136718 discloses that hot rolling is completed in the γ phase region within a range not exceeding 50 ° C. higher than the Ar ₃ transformation point temperature determined by the same component in the steel as described above. the collected temperature was above 700 ° C. the following a ₃ transformation point, a method to improve the magnetic discloses a ferrite grain size of the hot rolled strip in the No.4 following coarse grains.

Japanese Patent Application Laid-Open No. 54-76422 discloses that the coiling temperature after hot rolling is set at 750 to 1000 ° C., and the grain size is improved to 5 to 6 by self-annealing by the heat possessed by the coil to improve the magnetic properties. A method has been proposed. However, the method of improving the magnetism by setting the winding temperature after hot rolling to 700 ° C or higher and increasing the crystal grains before cold rolling can omit hot-rolled steel strip annealing, but the winding temperature is high. Since the outer winding and the edge of the coil cool faster than the center of the coil, the temperature difference in the coil increases, and eventually, uniform magnetism cannot be obtained over the entire coil and the acidity of the hot rolled steel strip. There are defects such as poor descaling properties due to washing.

[0006] After subjected to rolling reduction from 0.5 to 15% cold rolling the hot rolled strip in JP-B-45-22211, relatively long at a temperature range of ₃ transformation point recrystallization temperature or more A A method is disclosed in which annealing is performed for a long time to increase the crystal grain size of the steel strip before the subsequent cold rolling, thereby improving iron loss. However, the annealing of the hot-rolled steel strip after light cold rolling in this method can be said to be a relatively low temperature and a short period of time at 800 to 850 ° C for 30 minutes to 20 hours (the annealing time in Examples is 10 hours for each). This is a long-time annealing premised on so-called box annealing, which is not only disadvantageous in terms of manufacturing cost, but also has a crystal grain having a grain size of 2.2 and may be excessively large, and has a defect that impairs the surface appearance.

In Japanese Patent Application Laid-Open No. 1-306523, a hot-rolled steel strip is subjected to light-to-cold rolling of 5 to 20%, and then hot-rolled sheet annealing is performed for 850 to 850.
It discloses a method for producing a non-oriented electrical steel sheet having a high magnetic flux density by performing at a temperature of 1000 ° C. for 0.5 to 10 minutes. Although the hot-rolled sheet annealing in this method is performed in a continuous furnace, the annealing time requires a relatively long time of about 2 minutes in the embodiment, and as a result, large equipment is required, which leaves a problem economically.

[0008]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method for lightly cold-rolling a hot-rolled steel strip and a method for subsequently cold-rolling the same in order to moderately coarsen the crystal grains of the raw material before cold rolling. The purpose of the present invention is to propose a method for producing a non-oriented electrical steel sheet having a particularly high magnetic flux density and a good surface appearance by examining the cooling rate of the material C and the annealing together with devising the annealing. Is what you do.

[0009]

That is, the present invention relates to a method for producing a non-oriented electrical steel sheet in which a low carbon steel slab is hot-rolled, then cold rolled to a product thickness and then annealed. With C 0.005 to 0.020%, Si or Si
+ Al 1.5% or less, Mn 1.0% or less, P 0.2% or less, and, if necessary, a slab consisting of Sb and Sn containing 0.10% or less in total of one or more of Sb and Sn and substantially consisting of Fe, and Rolled into a hot-rolled steel strip, cold-rolled at a reduction rate of 5 to 15%, and then heated at a heating rate of 3 ° C / sec or more to 850 ° C
Heating to a temperature range below the Ac ₃ transformation temperature, holding at that temperature range for 5-30 seconds, and then cooling between the Ar ₃ to Ar ₁ transformation temperature at a rate of 2-10 ° C./sec, or Excellent magnetic properties of maintaining at or above the Ar ₁ transformation temperature within a range of 50 ° C for 5 to 30 seconds and then cooling from the Ar ₁ transformation temperature to 100 ° C at a rate of 10 ° C / sec or more And a method for producing a non-oriented electrical steel sheet having a good surface appearance, and a method for hot-rolling a low-carbon steel slab, then making the product thickness by cold rolling, and then performing annealing. 0.005 to 0.020% by weight, Si or Si + Al
1.5% or less, Mn 1.0% or less, P 0.2% or less, and if necessary, the sum of one or two of Sb and Sn is 0.1%.
A slab containing 10% or less and substantially consisting of Fe is formed into a hot-rolled steel strip by hot rolling, and further subjected to cold rolling at a rolling reduction of 5 to 15%. ° C to A
₃ Heat to a temperature range lower than the transformation point temperature, and
Hold for 30 seconds and then between Ar ₃ and Ar ₁ transformation temperature
After holding 5-30 seconds to it from within the range of 50 ° C. by Ar ₁ transformation temperature or higher during cooling at a rate of 10 ° C. / sec, from Ar ₁ transformation temperature to 100 ° C. 10 ° C. / sec or more This is a method for producing a non-oriented electrical steel sheet having excellent magnetic properties and a good surface appearance when cooled at a high speed.

[0010]

Next, the operation of the present invention and the circumstances leading to the present invention will be described based on experimental results. In weight%, C 0.0
18%, Si 0.1%, Mn 0.26%, P 0.07%, S 0.004
Slab made from molten steel containing 0.1% Al, 0.0009% Al, and 0.05% Sb, heated to 1250 ° C, at a hot rolling end temperature of 820 ° C.
A 2.3 mm thick hot rolled steel strip was made. Next, a sample is taken from the hot-rolled steel strip, and subjected to a low-temperature cold rolling of 0 to 20% in a laboratory. Then, the hot-rolled steel sheet is annealed at a heating rate of 5 ° C./sec. Hold for 10 seconds at a temperature of ℃,
Subsequent cooling is performed at a rate of 5 ° C./sec from the Ar ₃ (878 ° C.) to Ar ₁ (793 ° C.) transformation point temperature, and then from the Ar ₁ transformation point temperature to 100 ° C. at a rate of 50 ° C./sec. Cool. The A ₃ transformation point temperature of this material was 935 ° C.

Next, the annealed sheet was finished to a thickness of 0.50 mm by cold rolling, and then annealed in a humid atmosphere at 800 ° C. for 75 seconds for both decarburization and recrystallization annealing to produce a product. FIG. 1 shows the relationship between the magnetic flux density of these products and the rolling reduction in light rolling of a hot-rolled sheet. As it is apparent from this figure, a light cold rolling of hot rolled sheet to 5-15%, and 935 ° C. The hot-rolled steel sheet annealing after Keihiya extending from 850 ° C. (A ₃ transformation temperature) was treated with 10 seconds the magnetic flux density B ₅₀ of the product is apparent to be higher than those treated with other conditions. Although the high magnetic flux density was obtained, the crystal grains after annealing of the hot-rolled steel sheet had a grain size of No.4.
-3, and no folds occurred on the surface of the product, and the surface appearance was good.

Incidentally, although the magnetic flux density did not improve so much, the crystal grains after annealing of the hot-rolled steel sheet had a grain size of less than No. 4. As described above, hot-rolled steel strip is lightly cold-rolled by 5 to 10%,
At 850 ℃ ~ A ₃ transformation point temperature in a subsequent hot-rolled steel sheet annealing
The reason why the magnetic flux density is improved by controlling the cooling rate at a relatively high temperature for a short time of 10 seconds is described later together with the fact that the crystal grains are coarsened by annealing the hot-rolled steel sheet. This is because the texture was improved due to an increase in the amount of solute C by cooling control in hot-rolled steel sheet annealing. It is to be noted that coarsening of crystal grains during annealing of a hot-rolled steel sheet is coarsening (abnormal grain growth).
Required by light cold rolling.

Next, the cooling rate in the hot-rolled steel sheet annealing performed after lightly cold-rolling the hot-rolled steel sheet will be described. After using a hot-rolled steel sheet of the same composition as the above-mentioned hot-rolled steel sheet and applying 10% light cold rolling,
The temperature is raised at a heating rate of 7 ° C / sec in the hot-rolled steel sheet annealing,
After holding at a temperature of 10 ° C for 10 seconds, Ar ₃
From the Ar ₁ transformation temperature to the cooling rate of 2 to 15 ° C / sec.
Or Ar ₁ transformation point temperature + 20 ℃, Ar ₁ + 50 ℃, Ar ₁ +70
℃ After holding for 15 seconds at each temperature, 1 from Ar ₁ transformation temperature
A process was performed in which the cooling rate was changed in the range from 2 ° C./sec to water cooling up to 00 ° C.

Next, the product was finished to a thickness of 0.50 mm by cold rolling, and subsequently subjected to annealing at 800 ° C. for 15 seconds in a humid atmosphere for both decarburization and recrystallization to obtain a product. FIG. 2 shows the relationship between the magnetic flux density of these products and the cooling conditions during hot-rolled steel sheet annealing. As can be seen, the cooling rate from the Ar ₃ transformation point to the Ar ₁ transformation point during the cooling process in hot-rolled steel sheet annealing is set to 2 to 10 ° C / sec or maintained at a temperature of the Ar ₁ transformation point + 50 ° C. ,
In addition, it is clear that the product cooled from the Ar ₁ transformation point temperature to 100 ° C. at a cooling rate of 10 ° C./sec or more has a B ₅₀ higher than that obtained under other conditions. The product surfaces with these high magnetic flux densities were good without folding.

As described above, the reason why the magnetic flux density is improved by controlling the cooling rate during annealing of a hot-rolled steel sheet is due to the improvement of the texture by increasing the amount of solid solution C as described above. Next, in the present invention, the cold rolling of the hot-rolled steel sheet is limited to the rolling reduction of 5 to 15% because the annealing of the hot-rolled steel sheet subsequent to the light cold rolling of the hot-rolled steel sheet is performed at a relatively high temperature and at a high temperature as in the present invention. In the case of high-speed and short-time holding treatment, if the rolling reduction is less than 5%, the strain is insufficient, and the coarsening of the crystal grains during annealing of a hot-rolled steel sheet is insufficient. .4 and the magnetic flux density cannot be improved. On the other hand, if the rolling reduction exceeds 15%, it becomes the same as ordinary cold rolling, and the size of crystal grains does not become grain size No. 4 after annealing of a hot-rolled steel sheet.

On the other hand, the reason why the heating rate is set to 3 ° C./sec or more in the annealing of hot-rolled steel sheet is that if the heating rate is less than 3 ° C./sec, partial grain growth occurs during heating, and as in the present invention, 850 ° C. ° C ~
Although a short time held at a relatively high temperature of A ₃ transformation point because there is uniform and moderate grain growth becomes mixed grain does not occur, the preferred heating rate is 5 ° C. / sec or more. Also with limited annealing temperature of hot-rolled sheet annealing 850 ° C. ~ A ₃ transformation point, at a relatively high temperature in a continuous annealing furnace which is advantageous in production cost and stable quality surface in the present invention, 5 to 30 seconds This is because short-time processing is premised, and if the temperature is lower than 850 ° C., the grain growth is insufficient, and the magnetic flux density cannot be sufficiently improved. Even if the annealing temperature is lower than the recrystallization temperature to 850 ° C, it is possible to make the crystal grains coarser by increasing the annealing time, but it is disadvantageous in terms of manufacturing cost, so 850 ° C
Less than was excluded. Further, the upper limit of the hot-rolled sheet annealing temperature A ₃
The transformation point temperature was determined to be above this temperature when the α phase → γ phase,
This is because the transformation from the γ phase to the α phase causes the crystal grains to be fine, and the magnetic flux density cannot be improved.

The reason why the annealing time of the hot-rolled steel sheet is limited to 5 to 30 seconds, which has not been conventionally performed in this method, is that the annealing temperature of the hot-rolled steel strip is 850 at a heating rate of 3 ° C./sec.
℃ For to A ₃ transformation point, a small increase in the magnetic flux density for not reaching the particle size No.4 insufficient grain coarsening is less than 5 seconds. On the other hand, if the holding time exceeds 30 seconds, the crystal grains become excessively coarse and become larger than the particle size No. 2. As a result, although the magnetic flux density is improved, folds occur on the product surface and the surface appearance is impaired. This tatami wrinkle has the problem of lowering the space factor. Therefore, the holding time of the hot-rolled steel sheet annealing is 5 to control the crystal grains after annealing of the hot-rolled steel sheet so that the magnetic flux density can be improved and the surface appearance of the product is not impaired. Limited to 30 seconds.

Next, in the cooling process of the hot-rolled steel sheet annealing, A
Slowly cooling from the r ₃ transformation point temperature to the Ar ₁ transformation point temperature or maintaining the temperature over the Ar ₁ transformation point temperature within the range of 50 ° C. for 5 to 30 seconds increases the solid solution amount of C and continues This is because the amount of solid solution C is finally increased by rapidly cooling the temperature from the Ar ₁ transformation point temperature to 100 ° C. at 10 ° C./sec or more to improve the texture by solid solution C.

Next, the reasons for limiting the chemical components in the present invention will be described. In the present invention, from the viewpoint of effectively utilizing solid solution C in addition to coarsening of crystal grains before cold rolling, the effect is reduced if the C content is less than 0.005%, and even if C exceeds 0.02%. Since the amount of solid solution C does not increase and the decarburization is poor during the final annealing, which is disadvantageous for non-aging, C is 0.005%.
To 0.020%.

Si or Si + Al has a high specific resistance,
Increasing the amount reduces iron loss, but lowers the saturation magnetic flux density, making it difficult to obtain a high magnetic flux density.
Alternatively, the content of Si + Al is set to 1.5% or less. Since the magnetic flux density of Sb and Sn is improved by improving the texture, it is desirable to add Sb and Sn as needed to obtain a particularly high magnetic flux density. In that case, the total of one or two of Sb and Sn is 0.10
%, The magnetic properties are rather deteriorated, so that the content is limited to 0.10% or less even when used alone or in combination.

Mn is added as a deoxidizing agent or for controlling hot brittleness due to S. However, if it exceeds 1.0%, the cost increases, so Mn is set to 1.0% or less. P may be added in order to increase the hardness and improve the punching property, but if it is more than 0.20%, it becomes brittle, so it needs to be 0.20% or less.

[0022]

EXAMPLE 1 Molten steel produced in a converter and vacuum degassed was continuously cast.
Slab. C 0.007%, Si 0.35%, Mn 0.25%,
A slab containing 0.03% of P and 0.0008% of Al and substantially the remainder of Fe was formed into a 2.0 mm hot-rolled steel sheet by ordinary hot rolling. The Ac ₃ transformation point of these hot-rolled steel sheets was 950 ° C, the Ar ₃ transformation point was 870 ° C, and the Ar ₁ transformation point was 805 ° C.

Next, a 10% light rolling was performed, and the following hot rolled steel sheet was annealed.

[0024]

[Table 1]

Then, after a single cold rolling to finish to a thickness of 0.50 mm, the product was subjected to decarburization and recrystallization annealing at 800 ° C. for 75 seconds to obtain a product. As a result of measurement using Epstein test pieces of these products, both the magnetic flux density and the surface shape were good.

[0026]

[Table 2]

Example 2 Molten steel melted in a converter and vacuum degassed was continuously cast.
1 to 9 slabs were made. Their chemical components are C
0.015%, Si 0.35%, Mn 0.25%, P 0.02%, Al 0.
It contained 0008% and 0.10% of Sn, and the balance was substantially Fe.
The slabs were hot rolled into 2.3 mm hot rolled steel strips. Note A ₃ transformation temperature of the hot rolled strip was 947 ° C.. The Ar ₃ and Ar ₁ transformation temperatures were 877, respectively.
° C and 809 ° C. Subsequently, the hot-rolled steel strip was lightly and cold-rolled and then annealed. Table 3 shows the conditions. Then, after finishing to 0.50mm thickness by one cold rolling, 800
The product was subjected to decarburization and recrystallization annealing at 75 ° C. for 75 seconds to obtain a product. Table 3 also shows the results of measuring the magnetism of the products and the strain after annealing at 750 ° C. for 2 hours using Epstein test pieces. From these, if the conditions of light cold rolling of a hot-rolled steel strip and annealing conditions of the hot-rolled steel strip are set to appropriate ranges as in the applicable example of the present invention, coarsening of crystal grains after annealing of the hot-rolled steel strip and formation of solid solution C effective use makes it improve the texture, the comparative example, particularly high magnetic flux density B _50, and it is evident that those good surface appearance is obtained.

[0028]

[Table 3]

Example 3 As in Example 2, C 0.007%, Si 1.0%, Mn 0.25
%, P 0.02%, Al 0.25%, Sb 0.03%, Sn 0.06%
And a 2.0 mm thick hot-rolled steel strip was produced by ordinary hot rolling of a slab substantially containing Fe. The A ₃ transformation point, Ar ₃ and Ar ₁ transformation temperature of these hot rolled steel strips are 1
010 ° C, 940 ° C and 880 ° C. After performing cold-rolling on these hot-rolled steel strips, hot-rolled steel strip annealing was performed. Table 4 shows these conditions. Then, it was finished to a thickness of 0.50 mm by one cold rolling, and subsequently decarburized and recrystallized at 880 ° C. for 90 seconds to obtain a product. Table 4 also shows the magnetism of this product. From these, it is clear that the conforming example of the present invention has a particularly high magnetic flux density and a good appearance of the product surface as compared with the comparative example.

[0030]

[Table 4]

[0031]

As described above, after an appropriate light and cold rolling is performed on a hot-rolled steel strip, the hot-rolled steel strip is kept at a high temperature for a short time by rapid heating in the hot-rolled steel strip annealing, and by controlling the cooling rate. The texture can be improved by making the crystal grains of the band coarser and utilizing solid solution C. As a result, a non-oriented electrical steel sheet having a particularly high magnetic flux density and a good surface appearance can be manufactured.

[Brief description of the drawings]

1 is a diagram showing the relationship between the light cold rolling rate of hot rolled strip and product magnetic flux density B _50.

2 is a diagram showing a relationship between cooling conditions and product magnetic flux density B ₅₀ in the hot rolled strip annealing.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-136718 (JP, A) JP-A-2-1822831 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 8/12 C22C 38/00 303 C22C 38/06

Claims (3)

(57) [Claims] 1. A method for producing a non-oriented electrical steel sheet, in which a low-carbon steel slab is hot-rolled, then cold-rolled to a product thickness, and then annealed, wherein C is 0.005 to 0.020% by weight.
%, Si or Si + Al 1.5% or less, Mn 1.0% or less, P
A slab containing 0.2% or less and substantially consisting of Fe is formed into a hot-rolled steel strip by hot rolling, and further subjected to cold rolling at a reduction rate of 5 to 15%. ° C ~
A ₃ Heat to a temperature range below the transformation point temperature,
Hold for ~ 30 seconds, then switch between the Ar ₃ to Ar ₁ transformation temperature
Cool at a rate of 1010 ° C./sec, or maintain the temperature above the Ar ₁ transformation temperature and within a range of 50 ° C. for 5 to 30 seconds, and then reduce the temperature from the Ar ₁ transformation temperature to 100 ° C. by 10 ° C. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and excellent surface appearance, characterized by cooling at a rate of at least ° C / sec. 2. A method for producing a non-oriented electrical steel sheet in which a low-carbon steel slab is hot-rolled, then cold-rolled to a product thickness and then annealed, wherein C is 0.005 to 0.020% by weight.
%, Si or Si + Al 1.5% or less, Mn 1.0% or less, P
A slab containing 0.2% or less and substantially consisting of Fe is formed into a hot-rolled steel strip by hot rolling, and further subjected to cold rolling at a reduction rate of 5 to 15%. ° C ~
A ₃ Heat to a temperature range below the transformation point temperature,
Hold for ~ 30 seconds, then switch between the Ar ₃ to Ar ₁ transformation temperature
While cooling at a rate of up to 10 ° C / sec, maintain the temperature above the Ar ₁ transformation point within a range of 50 ° C for 5 to 30 seconds, and then increase the temperature from the Ar ₁ transformation point temperature to 100 ° C by 10 ° C / sec or more. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and excellent surface appearance, characterized by cooling at a constant speed. 3. The composition of a low-carbon steel slab in weight%,
0.005 to 0.020%, Si or Al 1.5% or less, Mn 1.0%
Below, P 0.2% or less, any one of Sb and Sn or 2
The method for producing a non-oriented electrical steel sheet having excellent magnetic properties and a good surface appearance according to claim 1 or 2, wherein the total of the seeds is 0.10% or less, and the balance is substantially composed of Fe.