JP2500033B2 - Manufacturing method of 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 iron core materials for rotating machines such as various motors and stationary machines such as transformers and ballasts. In order to do so, it is necessary to improve the magnetic flux density of the electromagnetic steel sheet used and reduce iron loss. By the way, it is known that in order to improve the magnetism of the non-oriented electrical steel sheet, the crystal grains of the steel strip before cold rolling may be coarsened.

As a method for coarsening the crystal grains of a steel strip before cold rolling, the inventors have previously disclosed that when hot rolling an electromagnetic steel material in Japanese Patent Publication No. 57-35628, the end temperature of hot rolling is set to the steel. The Ar ₃ transformation point temperature determined by the chemical composition of the above is not exceeded, and then this hot-rolled steel strip is kept for 30 seconds or more at a temperature below the A ₃ transformation point temperature.
A method of annealing for 15 minutes or less was proposed. Further, in Japanese Patent Laid-Open No. 2-182831, the hot rolling finish temperature is set to an Ar ₃ transformation point temperature or higher, and then the hot rolling steel strip is kept at the A ₃ transformation point temperature or lower for 30 to 15 seconds, and then the cooling rate is set. A method of controlling is disclosed.

However, in these methods, there is a case in which coarsening of crystal grains does not easily occur on the side where the hot-rolled steel strip annealing time is short, and as a result, there is a defect that the magnetic characteristics vary.
In addition, the crystal grains may become excessive on the long time side, and as a result, there is a problem that the product is creased and the surface appearance is impaired. On the other hand, in Japanese Patent Application Laid-Open No. 58-136718, hot rolling is terminated in the γ phase region within a range not exceeding 50 ° C. higher than the Ar ₃ transformation point temperature determined by the composition in the steel as described above, and the winding is performed. A method is disclosed in which the taking temperature is raised from the A ₃ transformation point or lower to 700 ° C. or higher and the ferrite grain size of the hot-rolled steel strip is set to coarse grains of No. 4 or less to improve magnetism.

Further, in Japanese Patent Laid-Open No. 54-76422, the coiling temperature after hot rolling is set to 750 to 1000 ° C., and the magnetism is improved by self-annealing by the heat retained in the coil to recrystallize into grain sizes No. 5 to 6. A method for achieving this has been proposed. However, these methods of improving the magnetism by increasing the coiling temperature after hot rolling to 700 ° C or more and increasing the grain size before cold rolling can omit hot-rolled steel strip annealing, but the coiling temperature is high. Since the outer coil and the edge of the coil cool faster than the center of the coil, the temperature difference inside the coil becomes large, 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 property due to washing.

In Japanese Patent Publication No. 452212/1985, a hot rolled steel strip is cold-rolled at a rolling reduction of 0.5 to 15%, and then relatively long in a temperature range from the recrystallization temperature to the A ₃ transformation point. A method is disclosed in which iron loss is improved by performing annealing for a time to coarsen the crystal grains of the steel strip before the subsequent cold rolling. However, the annealing after light cold rolling of the hot-rolled steel strip by this method is carried out at 800 to 850 ° C for 30 minutes to 20 hours (the annealing time in each example is 10 hours) even though the temperature is relatively low and the time is short. Since it is a long-time annealing premised on so-called box annealing, not only is it disadvantageous in terms of manufacturing cost, but the crystal grains sometimes become excessively large with a grain size of No. 2.2, which is a defect that impairs the surface appearance.

Further, in JP-A-1-306523, hot-rolled steel strip is annealed at 850-
It discloses a method for producing a non-oriented electrical steel sheet having a high magnetic flux density by performing the treatment at a temperature of 1000 ° C. for 0.5 to 10 minutes. Although the hot-rolled sheet annealing of this method is performed in a continuous furnace, the annealing time in the embodiment requires a relatively long time of about 2 minutes, and as a result, large equipment is required, which is economically problematic.

As described above, in any of these cases, it is intended to improve the magnetic properties by coarsening the crystal grain size before cold rolling, but there is a limit to the improvement of the magnetic properties in consideration of the surface appearance and the economical efficiency of the equipment. there were. Further, as a method of manufacturing a semi-processed electromagnetic steel sheet, for example, JP-A-1-139721 or JP-A-1-191741 discloses that the final step is 3 to 15%.
The method of giving a skin pass and producing a product is disclosed. However, the skin pass rolling in the semi-processed material is intended to adjust the hardness of the product, and the annealing after processing guarantees the magnetic properties on the assumption of long-term holding such as 750 ° C. × 2 hr. Therefore, even if such a semi-processed material is annealed for a short time on the premise of continuous annealing, it is not possible to stably obtain high magnetic properties.

[0009]

In view of the above problems, the present invention has devised an annealing condition for achieving an appropriate coarsening of crystal grains of a hot-rolled steel strip after light cold rolling. It is an object of the present invention to propose a method for producing a non-oriented electrical steel sheet having a magnetic property, particularly a high magnetic flux density, and a good surface appearance by controlling the diameter.

[0010]

[Means for Solving the Problems] That is, the present invention contains C: 0.02% or less, Si or Si + Al: 4.0% or less, Mn: 1.0% or less, P: 0.2% or less by weight%, and further Depending on the sum of one or two of Sb and Sn,
A slab containing 0.10% or less and the balance being substantially Fe is hot-rolled to form a hot-rolled steel strip, which is further cold-rolled at a rolling reduction of 5 to 15%, and then heated at a heating rate of 3 ° C / sec or more. At a predetermined temperature, hold at that temperature for 5 to 30 seconds, perform short-time annealing to obtain a crystal grain size of 100 to 200 μm, and further cold-roll to obtain the final plate thickness, and then perform final annealing. It is a method for producing a non-oriented electrical steel sheet having excellent magnetic properties and a good surface appearance.

Still further, the present invention provides C: 0.02% by weight.
% Or less, Si or Si + Al: 4.0% or less, Mn: 1.0% or less, P: 0.2% or less, and if necessary Sb and
The sum of any one or two of Sn contains 0.10% or less,
A slab whose balance consists essentially of Fe is hot-rolled to form a hot-rolled steel strip, which is further cold-rolled at a reduction rate of 5 to 15% and then annealed to a grain size of 100 to 200 μm. After cold rolling, annealing is performed with a crystal grain size of 20 μm or less, and further cold rolling of 1 to 15% is performed to obtain a product sheet thickness, and then final annealing is performed. It is a method for producing a non-oriented electrical steel sheet with a good surface appearance, and as annealing to obtain a crystal grain size of 100 to 200 μm, heating to a predetermined temperature at a heating rate of 3 ° C./sec or more,
It is desirable to employ short-time annealing in which the temperature is maintained for 5 to 30 seconds. The crystal grain size and the crystal grain size described below mean the crystal grain size as an average value of the steel sheet.

[0012]

[Operation] First, the background of the present invention will be described based on experimental results. % By weight, C: 0.010%, Si: 0.15%,
Mn: 0.25%, P: 0.08%, Sb: 0.045%, S: 0.004
%, Al: 0.0008%, and the balance made of molten steel consisting essentially of Fe was heated to 1250 ° C and hot rolled into a 2.3 mm thick hot-rolled steel strip by ordinary hot rolling. Subsequently, the hot-rolled steel strip was lightly cold-rolled with a rolling reduction of 0 to 20%,
Hot-rolled steel strip annealing for 10 seconds at a temperature of 00 ° C was performed in a continuous furnace. The heating rate at this time was 5 ° C./sec. The A ₃ transformation point temperature of this material was 915 ° C. Then, after pickling and finishing to 0.50 mm thickness by ordinary cold rolling,
A product was manufactured by continuous annealing that combines decarburization and recrystallization in a humid atmosphere at 800 ° C for 75 seconds. Fig. 1 shows the relationship between the magnetic flux density of these products and the cold rolling ratio when the hot-rolled steel strip is subjected to light cold rolling. From this figure, light cold rolling of hot-rolled steel strip can be achieved by rolling reduction of 5
It is clear that the magnetic flux density B _{50 of the} product which was made 15% and which was subjected to the hot strip annealing at 850 to 915 ° C. (A ₃ transformation temperature) was higher than the ones treated under other conditions. And
The conditions under which this high magnetic flux density B ₅₀ was obtained, that is, the crystals after hot-rolled steel strip annealing at 850 to 915 ° C. for 10 seconds at a rolling reduction of the hot-rolled steel strip of 5 to 15%, were obtained. Grain size 100 to 2
It was in the range of 00 μm, and the product had a good surface appearance with no creases on the surface.

By the way, although the magnetic flux density B ₅₀ did not improve so much, the crystal grains after hot-rolled steel strip annealing had a grain size of less than 100 μm. Subjected to 5-15% of the light cold-rolled to a hot rolled strip, as described above, subsequent 850 to 915 ° C. In the hot rolled strip annealing (A ₃ transformation temperature), relatively high temperatures and short time of 10 seconds The reason that the magnetic flux density is improved in the treatment of is that the crystal grains grow into coarse grains by the hot-rolled steel strip annealing, and as a result, the texture of the product can be improved. Further, the reason why the crystal grains become coarse during annealing of the hot rolled steel strip is that the strain necessary for coarsening (abnormal growth) is applied to the hot rolled steel strip by light cold rolling.

Furthermore, another experimental result will be shown. weight%
, C: 0.010%, Si: 0.15%, Mn: 0.25%, P: 0.08
%, Sb: 0.045%, S: 0.004%, Al: 0.0008%, and the balance is a slab made of molten steel consisting essentially of Fe at 1250 ° C.
Then, the hot-rolled steel strip having a thickness of 2.3 mm was formed by ordinary hot rolling. Subsequently, after performing a light cold rolling with a reduction rate of 10%, short-time annealing was performed at a temperature of 915 ° C. for 10 seconds in a continuous furnace. The heating rate at this time was changed in the range of 1 to 5 ° C./sec. Crystal grain after hot-rolled steel strip annealing was observed and grain size was 200μ
FIG. 2 shows the relationship between the heating rate and the ratio (area ratio) of grains coarser than m. If the number of coarse particles is large, the product plate is likely to be wrinkled. Although the state of occurrence of folding wrinkles in the product plate is also shown, it is clear from the figure that increasing the heating rate to reduce the proportion of coarse particles is advantageous for improving the surface properties.

Next, the conditions of cold rolling / annealing subsequent to annealing of the hot rolled steel sheet will be described. A hot-rolled steel sheet having the same composition as the above-mentioned hot-rolled steel sheet is used, lightly cold-rolled by 10%, and then annealed at a temperature of 900 ° C. for 10 seconds during annealing of the hot-rolled steel sheet. The crystal grain size at this time was 120 μm. The annealed plate is cold rolled to a thickness of 0.50 to 0.65 mm. Then, it is annealed at 600 to 750 ℃ to make the crystal grain size 10 to 30 μm, lightly cold rolled to 0 to 20% to finish the thickness to 0.50 mm, and then 800 ℃ in a wet atmosphere.
The product was annealed also for decarburization for 60 seconds to obtain a product.

FIG. 3 shows the relationship between the magnetic flux density of these products, the crystal grain size after cold rolling annealing, and the reduction ratio of light cold rolling. As can be seen, during cold rolling / annealing after hot-rolled steel sheet annealing, B ₅₀ of a product having a grain size of 20 μm or less after cold-rolling annealing and a reduction ratio of 1 to 15% in light cold rolling is another condition. It is clear that it is higher than that of The product surface with high magnetic flux density was good without unfolding.

As described above, the magnetic flux density is improved by controlling the crystal grain size after the cold rolling annealing subsequent to the hot-rolled steel sheet annealing and the cold rolling reduction rate thereafter. This is the effect of improving the texture through selection. Next, the reason why the light cold rolling of the hot rolled steel sheet is limited to the rolling reduction of 5 to 15% in the present invention will be described. When the hot-rolled steel sheet annealing following the light cold-rolling of the hot-rolled steel sheet is performed at a relatively high temperature for a short time holding treatment or at a low temperature for a long time treatment, distortion is insufficient if the rolling reduction is less than 5%, and the hot rolled steel sheet The grain size does not reach 100 μm and the magnetic flux density cannot be improved due to insufficient grain coarsening during annealing. When the rolling reduction exceeds 15%, the same as in ordinary cold rolling, and the grain size becomes 1 after annealing of hot-rolled steel sheet.
This is because it will not be 00 μm.

Further, in the present invention, it is preferable that the heating rate is 3 ° C./sec or more in the hot strip annealing. This is because if the heating rate is less than 3 ° C./sec, some grain growth occurs during heating, and uniform and appropriate grain growth does not occur when held at a relatively high temperature for a short time, and mixed grains tend to form. A more preferable heating rate is 5 ° C./sec or more. Next, the reason for limiting the crystal grain size of the hot rolled steel strip to 100 to 200 μm after cold rolling under light reduction and annealing is explained.

If the particle size exceeds 200 μm, the surface appearance of the product sheet is impaired, so in this case the particle size was set to 200 μm as the upper limit.
In order to improve the magnetic properties, the lower limit is 100 μm.
It is necessary to The annealing conditions in this case are 5 to 30 at a relatively high temperature of 850 ° C. or higher and A ₃ transformation point or less when using a continuous annealing furnace which is advantageous in terms of manufacturing cost and quality stability.
A short time treatment of seconds is preferred. In this case, if the temperature is lower than 850 ° C., grain growth becomes insufficient, and the magnetic flux density cannot be sufficiently improved.

Further, the annealing temperature of the hot-rolled steel strip is from 850 ° C to
In the case of the A ₃ transformation point, if the time is less than 5 seconds, the coarsening of the crystal grains is insufficient and the grain size does not reach 100 μm, so the improvement in the magnetic flux density is small. Further, if the holding time exceeds 30 seconds, the crystal grains become too coarse and the grain size becomes larger than 200 μm. As a result, although the magnetic flux density is improved, creases are generated on the product surface and the surface appearance is impaired. There is a problem that this tatami wrinkle causes a decrease in space factor.

Further, as described above, the crystal grain size is 100 to 2
After being annealed to 00 μm, it was further cold-rolled and then annealed to a grain size of 20 μm or less.
It is also one of the present inventions to carry out final annealing after cold rolling at -15% to give a product sheet thickness. In this case, there is no particular problem in the annealing in which the crystal grain size becomes 100 to 200 μm in either the continuous annealing furnace or the batch furnace, and the heating temperature is 850
There is no particular problem even if the crystal grain can be coarsened to 100 to 200 μm by prolonging the annealing time even under the condition of not more than ° C.

Further, the light reduction cold rolling performed after the annealing for adjusting the grain size requires a reduction rate of 1% or more in order to improve the texture described above. However, if it exceeds 15%, recrystallization often occurs as in the case of normal cold rolling, so improvement in texture that leads to improvement in magnetic properties cannot be expected. Next, the reasons for limiting the raw material components in the present invention will be described.

If C exceeds 0.02%, not only is it harmful to magnetism, but also decarburization is unsatisfactory during final annealing, which is disadvantageous for non-aging, so C was made 0.02% or less. Si or Si + Al has a high specific resistance, and if the amount is increased, the iron loss decreases and the saturation magnetic flux density decreases. Therefore, iron loss
This amount is adjusted according to the magnetic flux density requirement. But,
If the amount of Si + Al exceeds 4.0%, the cold rolling property is significantly impaired, so the upper limit is 4%.

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 in order to obtain a particularly high magnetic flux density. Then Sb and Sn
If the content of one or two of the above exceeds 0.10%, the magnetic properties are rather deteriorated. Therefore, the content is limited to 0.10% or less even when either one alone or in combination. Mn is added as a deoxidizer or for controlling the hot embrittlement due to S, but if it exceeds 1.0%, the cost increases, so Mn is 1.
0% or less.

P may be added in order to increase hardness and punchability, but if it exceeds 0.20%, it becomes brittle, so it must be 0.20% or less. Next, examples of the present invention will be described. Note that Examples 1 to 5 correspond to the invention of claim 1, and Examples 6 to 9 correspond to the invention of claim 2, respectively.

[0026]

EXAMPLES Example 1 Molten steel melted in a converter and vacuum degassed is continuously cast,
Made slabs from 1 to 9. Their chemical composition is C:
0.006%, Si: 0.35%, Mn: 0.25%, P: 0.08%, Al:
The balance was 0.0009% and the balance was substantially Fe. The slabs were hot rolled into ordinary hot rolled steel strips with a thickness of 2.3 mm. The A ₃ transformation point of the hot rolled steel strip was 955 ° C.

Subsequently, the hot-rolled steel strip was lightly and cold-rolled, and then hot-rolled steel strip was annealed. Table 1 shows the cold rolling ratio and the annealing conditions. Then, the product was finished by one cold rolling to a thickness of 0.50 mm, and subsequently subjected to decarburization / recrystallization annealing at 850 ° C. for 75 seconds. Table 2 shows the results of measuring the magnetism of these products and the stress after strain relief annealing at 750 ° C for 2 hours with an Epstein test piece.
From these, if the reduction ratio of the light and cold rolling of the hot rolled steel strip and the annealing conditions of the hot rolled steel strip are set in an appropriate range as in the conformity example of the present invention,
The crystal grains after the hot-rolled steel strip annealing are appropriately coarsened, and as a result,
It is clear that the texture of the product can be improved and that the magnetic flux density B ₅₀ is particularly high and the surface appearance is good.

[0028]

[Table 1]

[0029]

[Table 2]

Example 2 As in Example 1, C: 0.007%, Si: 1.0%, Mn: 0.
30%, P: 0.018%, Al: 0.30%, the balance is substantially
I made a slab of Fe from 10 to 15. Then, a hot-rolled steel strip having a thickness of 2.0 mm was formed by ordinary hot rolling. The A ₃ transformation point of these hot-rolled steel strips was 1050 ° C.

Subsequently, the hot-rolled steel strip was lightly and cold-rolled, and then hot-rolled steel strip was annealed. Table 3 shows those conditions. Next, after one cold rolling to finish the thickness to 0.50mm,
The product was decarburized and recrystallized at 75 ° C for 75 seconds. Table 4 shows the results of measuring the magnetism of these products and the stress after strain relief annealing at 750 ° C for 2 hours with an Epstein test piece. From these, it is apparent that the conforming example of the present invention has an especially excellent magnetic flux density and a good surface appearance as compared with the comparative example.

[0032]

[Table 3]

[0033]

[Table 4]

Example 3 Molten steel melted in a converter and subjected to vacuum degassing was continuously cast,
Made 16 to 22 slabs. Their chemical composition is C: 0.0
05%, Si: 0.33%, Mn: 0.25%, P: 0.07%, Al: 0.00
The balance was 08% and Sb: 0.050%, and the balance was essentially Fe. The slabs were hot rolled into ordinary hot rolled steel strips with a thickness of 2.3 mm. The A ₃ transformation point temperature of the hot rolled steel strip was 950 ° C.

Subsequently, after lightly and cold rolling the hot-rolled steel strip,
Hot-rolled steel strip annealing was performed in a continuous furnace. Table 5 shows the cold rolling rate and the annealing conditions. Next, it was finished by cold rolling once to a thickness of 0.50 mm and then subjected to decarburization and recrystallization annealing at 810 ° C for 60 seconds to obtain a product. Table 6 shows the results obtained by measuring the magnetism of these products and the stress after annealing for 2 hours at 750 ° C with an Ebstein sample. From these, if the reduction ratio of the hot-rolled steel strip and the subsequent hot-rolled steel strip annealing conditions are set in an appropriate range as in the conformity example of the present invention, magnetic flux density is particularly high, and a magnetic steel sheet having a good surface appearance can be obtained. It is clear.

[0036]

[Table 5]

[0037]

[Table 6]

Example 4 As in Example 3, C: 0.008%, Si: 1.1%, Mn: 0.
28%, P: 0.018%, Al: 0.31%, Sn: 0.055%, the balance is 23 to 28 slabs from molten steel consisting essentially of Fe, C: 0.007%, Si: 1.1%, Mn: 0.30% , P: 0.019
%, Al: 0.30%, Sb: 0.03%, Sn: 0.03%, and the balance is made of molten steel consisting of substantially 29% to 31% slab. And The A ₃ transformation point of the hot rolled steel strips of 23 to 28 is 1045 ° C and the A ₃ transformation point of the hot rolled steel strips of 29 to 31 is A ₃
The transformation point was 1055 ° C.

Subsequently, the hot-rolled steel strip was lightly and cold-rolled, and then hot-rolled steel strip was annealed in a continuous furnace. Table 7 shows these light cold rolling and hot strip annealing conditions. Next, in one cold rolling, 0.
After finishing to a thickness of 50 mm, the product was decarburized and recrystallized at 830 ° C for 75 s to obtain a product. Those products and 750 ℃,
Table 8 shows the results of measuring the magnetism after stress relief annealing of 2 Hr with an Epstein test piece.

From these, it is apparent that the conforming example of the present invention has a particularly excellent magnetic flux density and a good surface appearance as compared with the comparative example.

[0041]

[Table 7]

[0042]

[Table 8]

Example 5 C: 0.002%, Si: 3.26%, Mn: 0.14%, P: 0.02%,
Al: A molten steel containing 0.61% and the balance consisting essentially of Fe 32 to 32
37 slabs, C: 0.003%, Si: 3.31%, Mn: 0.
A slab of 38-41 from molten steel consisting of 15%, P: 0.02%, Al: 0.59%, Sb: 0.06% and the balance consisting essentially of Fe, C: 0.002%, Si: 3.33%, Mn: 0.16% , P: 0.02%,
A slab of 42 to 45 was made from molten steel consisting of Al: 0.62%, Sb: 0.03%, Sn: 0.04% and the balance consisting essentially of Fe, and a hot rolled steel strip with a thickness of 2.0 mm was formed by normal hot rolling. . These 32-45 hot-rolled steel strips were untransformed steels.

Subsequently, the hot-rolled steel strip was lightly and cold-rolled and then hot-rolled steel strip was annealed in a continuous furnace. Table 9 shows these light cold rolling and hot strip annealing conditions. Next, in one cold rolling, 0.
After finishing to a thickness of 50 mm, recrystallization annealing was performed at 1000 ° C for 30 seconds to obtain a product. Table 10 shows the results of measuring the magnetism of these products and the stress after strain relief annealing at 750 ° C x 2 hr using Epstein test pieces. From these, it is apparent that the conforming example of the present invention has a lower iron loss and a better surface appearance as the magnetic flux density improves, as compared with the comparative example.

[0045]

[Table 9]

[0046]

[Table 10]

Example 6 Molten steel produced in a converter and vacuum degassed is continuously cast,
Slavic. This C: 0.007%, Si: 0.15%, Mn: 0.
25%, P: 0.03%, Al: 0.0008% including the balance
The slab of Fe was hot rolled into a hot rolled steel sheet of 2.0 mm. A ₃ transformation point of the steel plate was 920 ° C..

This hot-rolled sheet is treated under the cold-rolling annealing conditions shown in Table 11 to obtain a structure having a crystal grain size shown in Table 11. The heating rate for this annealing was 0.02 for batch furnace heating.
° C / sec, otherwise 5 ° C / sec. Further, this was cold rolled under a large pressure to a thickness of 0.50 to 0.60 mm and then annealed at 600 to 800 ° C. Table 11 also shows the crystal grain size at that time. In addition, Table 11
Finished to a product thickness of 0.50 mm at the cold rolling reduction as shown in, and subjected to decarburization annealing at 800 ° C for 75 s to obtain a product.

Table 11 also shows the results and surface properties of these products measured with Epstein test pieces. In addition, as a comparative example, a case where a product is obtained by annealing after the second cold rolling is also included. It is apparent that the examples of the present invention are superior to the comparative examples in both the magnetic flux density and the surface properties.

[0050]

[Table 11]

Example 7 Molten steel produced in a converter and vacuum degassed is continuously cast,
Slavic. This C: 0.006%, Si: 0.18%, Mn: 0.
A slab containing 25%, P: 0.003%, Al: 0.0011%, and Sb: 0.06%, and the balance being substantially Fe was formed into a hot rolled steel sheet of 2.0 mm by ordinary hot rolling. The A ₃ transformation point of this steel sheet is
It was 925 ° C.

This hot-rolled sheet is treated under the cold-rolling annealing conditions shown in Table 12 to obtain a structure having a crystal grain size shown in Table 12. The heating rate during this annealing is 7 ° C / sec.
Furthermore, after cold rolling this to a thickness of 0.50 to 0.60 mm, 600 to 800 ° C
Annealed. Table 12 also shows the crystal grain size at that time. Further, at a cold rolling reduction ratio as shown in Table 12, a product thickness of 0.50 mm was finished and decarburization annealing was performed at 800 ° C for 75 s to obtain a product.

Table 12 shows the results and surface properties of these products measured with Epstein test pieces. In addition, as a comparative example, a case where a product is obtained by annealing after the second cold rolling is also included. It is apparent that the examples of the present invention are superior to the comparative examples in both the magnetic flux density and the surface properties.

[0054]

[Table 12]

Example 8 Molten steel melted in a melting furnace and vacuum degassed is continuously cast,
Slavic. This C: 0.008%, Si: 0.35%, Mn: 0.
35%, P: 0.05%, Al: 0.0012%, Sb: 0.05%, Sn: 0.
A slab containing 03% and the balance being essentially Fe was subjected to ordinary hot rolling to obtain a 2.0 mm hot rolled steel sheet. A ₃ transformation point of the steel plate was 940 ° C..

This hot-rolled sheet is treated under the cold-rolling annealing conditions shown in Table 13 to obtain a structure having a crystal grain size shown in Table 13. The heating rate for this annealing was 0.02 for batch furnace heating.
° C / sec, otherwise 5 ° C / sec. Further, this was cold rolled to a thickness of 0.50 to 0.60 mm and then annealed at 600 to 800 ° C.
The crystal grain size at that time is also shown in Table 13. Furthermore, at the cold rolling reduction rate as shown in Table 13, finish to a product thickness of 0.50 mm,
The product was decarburized and annealed at 800 ° C for 75s to obtain a product.

Table 13 also shows the results and surface properties of these products measured with Ebstein test pieces. In addition, as a comparative example, a case where a product is obtained by annealing after the second cold rolling is also included. It is apparent that the examples of the present invention are superior to the comparative examples in the magnetic flux density and surface properties.

[0058]

[Table 13]

Example 9 Molten steel produced in a converter and vacuum degassed is continuously cast,
Slavic. Slabs 97-101 have C: 0.002%, S
i: 3.31%, Mn: 0.16%, P: 0.02%, Al: 0.64%, and the balance consists essentially of Fe. The slabs of 102-106 are
C: 0.003%, Si: 3.25%, Mn: 0.15%, P: 0.02%,
Al: 0.62%, Sb: 0.05%, and the balance substantially Fe.

The slabs of 107 to 111 have C: 0.002% and Si:
3.28%, Mn: 0.17%, P: 0.02%, Al: 0.58%, Sb: 0.
It contains 03% and Sn: 0.04%, and the balance consists essentially of Fe. The above slab was hot rolled into a hot rolled steel sheet of 2.0 mm. These steel sheets have not been transformed. The hot-rolled sheet is treated under the cold-rolling annealing conditions shown in Table 14 to obtain a structure having a crystal grain size shown in Table 14. The heating rate during this annealing is 7 ° C./sec. Further, this was cold rolled to 0.50 to 0.60 mm and annealed at 600 to 800 ° C. The crystal grain size at that time is also shown
Shown in 14. Furthermore, the cold rolling reduction ratio as shown in Table 14 is 0.
Finished to a product thickness of 50 mm and subjected to recrystallization annealing at 1000 ° C for 30 s to obtain a product. Table 14 also shows the results and surface properties of these products measured by Epstein test pieces.

[0061]

[Table 14]

[0062]

As described above, the light-rolled steel strip is appropriately lightly cold-rolled, and the hot-rolled steel strip is annealed to obtain proper crystal grains, or further, annealing after cold-rolling is combined with light reduction. As a result, a non-oriented electrical steel sheet having a particularly high magnetic flux density and a good surface appearance can be manufactured stably at low cost.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a magnetic flux density B ₅₀ and a cold rolling rate of a hot rolled steel strip.

FIG. 2 is a graph showing a relationship between a heating rate and a ratio of coarse grains after hot-rolled sheet annealing.

FIG. 3 is a graph showing the relationship between the cold rolling rate before final annealing, the crystal grain size before that, and the magnetic flux density of the product.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Obara 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Hideo Kobayashi 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. Corporate Technology Research Headquarters (72) Inventor Kazumi Morita 1-chome Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (no address) Kawasaki Steel Co., Ltd. Mizushima Works (72) Inventor Yoshiaki Iida 1-chome Mizushima-kawasaki-dori, Kurashiki-shi Okayama ( No address) Kawasaki Steel Works Mizushima Works

Claims (4)

(57) [Claims] 1. By weight%, C: 0.02% or less, Si or
A slab containing Si + Al: 4.0% or less, Mn: 1.0% or less, P: 0.2% or less, and the balance being substantially Fe, is hot-rolled into a hot-rolled steel strip, which is cold-rolled at a reduction rate of 5 to 15%. After rolling, it is heated to a predetermined temperature at a heating rate of 3 ° C / sec or more and kept at that temperature for 5 to 30 seconds.
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and a good surface appearance, which comprises performing a short-term annealing of 00 μm, further cold rolling to a final thickness, and then performing a final annealing. 2. C: 0.02% or less by weight%, Si or
A slab containing Si + Al: 4.0% or less, Mn: 1.0% or less, P: 0.2% or less, and the balance being substantially Fe, is hot-rolled into a hot-rolled steel strip, which is cold-rolled at a reduction rate of 5 to 15%. After rolling, annealing is performed so that the crystal grain size is 100 to 200 μm, further cold rolling is performed, then annealing is performed to reduce the crystal grain size to 20 μm or less, and further cold rolling of 1 to 15% is performed. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and a good surface appearance, which is characterized by subjecting a sheet thickness to final annealing. 3. Annealing with a crystal grain size of 100 to 200 μm is performed by heating to a predetermined temperature at a heating rate of 3 ° C./sec or more,
The method for producing a non-oriented electrical steel sheet having excellent magnetic properties and good surface appearance according to claim 2, characterized in that the annealing is performed for a short period of time at which the temperature is maintained for 5 to 30 seconds. 4. The slab composition, in% by weight, C: 0.02% or less, Si or Si + Al: 4.0% or less, Mn: 1.0% or less,
P: 0.2% or less, the sum of any one or two of Sb and Sn is 0.10% or less, and the balance consists essentially of Fe, The magnetic material according to claim 1, 2 or 3. A method for producing a non-oriented electrical steel sheet with excellent characteristics and good surface appearance.