JPH06279858A - Production of non-oriented electric steel sheet excellent in magnetic property and surface property - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a method for producing a non-oriented electrical steel sheet having a high magnetic flux density and excellent surface properties [Structure] C: 0.0050 wt% or less, Si: 0.1
~ 1.5 wt%, Mn: 0.2-1.0 wt%, P:
0.20 wt% or less, S: 0.010 wt% or less, A
1: 0.004 wt% or less or 0.100 to 0.5
Steel containing 00 wt%, N: 0.0050 wt% or less, balance Fe and unavoidable impurities is hot-rolled at a predetermined heating temperature and a finishing temperature, and then a predetermined winding defined by the amounts of Si and Al in the steel. After winding at picking temperature and pickling, light reduction rolling is performed twice with the rolling direction reversed, and in this light reduction rolling, the reduction rate per rolling is 0.5 to 3.0%, and twice. The total reduction of the rolling is set to 2.0 to 5.0%, and then hot-rolled sheet annealing, one or two or more cold rolling including intermediate annealing, and finish annealing are sequentially performed under predetermined conditions.

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, particularly high magnetic flux density, and excellent surface properties.

2. Description of the Related Art Non-oriented electrical steel sheets used as iron core materials for motors, transformers, etc. are desired to have low iron loss and high magnetic flux density in order to achieve high efficiency and miniaturization of electrical equipment. Among them, so-called low-to-intermediate grade non-oriented electrical steel sheets are often used in electric devices having a relatively small capacity, and the ratio of the exciting current to the loss is high.
High magnetic flux density is important not only from the viewpoint of miniaturization of equipment but also from the viewpoint of high efficiency.

Generally, in order to increase the magnetic flux density of a non-oriented electrical steel sheet, it is important to optimize the microstructure before cold rolling, specifically, to coarsen the crystal grains. Various are disclosed. For example, JP-A-57-
No. 35628, JP-A-58-204126 and the like disclose a technique for coarsening crystal grains by subjecting a hot-rolled sheet to annealing of the hot-rolled sheet, and also JP-A-54-68717 and JP-A-58-68717. No. 56-98420 discloses a technique of adding a special element such as Sb or Sn and then annealing the hot-rolled sheet to coarsen the crystal grains. Further, JP-A-63-1868.
23, JP-A-1-139721, JP-A-1-306
No. 523, JP-A-1-309921, etc., a hot-rolled sheet is lightly rolled at a reduction rate of 1 to 5% to 12 to 20%, then annealed, and secondary recrystallization by strained grain growth is utilized. A technique for coarsening crystal grains is disclosed.

[0003]

However, these techniques lack the examination of the surface texture of the product, and as will be described below, when the magnetic flux density is sufficiently increased, the surface texture is inevitably deteriorated. Therefore, the commercial value of the product is impaired, and conversely, if it is attempted to prevent the deterioration of the surface quality, a sufficiently high magnetic flux density cannot be obtained, and in the end, both the magnetic flux density and the surface quality cannot be satisfied at the same time. .

That is, among the above-mentioned conventional techniques, the technique for coarsening the crystal grains only by annealing the hot-rolled sheet is intended to utilize the grain boundary energy as the driving force for the secondary recrystallization. Since the driving force is only the grain boundary energy, the driving force itself is small. Therefore, the coarsening of the crystal grains is insufficient in the low temperature annealing, and the margin for improving the magnetic flux density is small. Is required. Furthermore, since the driving force itself is small as described above, only a small number of crystal grains exceeding the critical energy for secondary recrystallization can be obtained even if high temperature annealing is performed,
As a result of the small number of crystal grains eclipsing the surrounding crystal grains and secondary recrystallization proceeds, only an extremely coarse structure is obtained. For this reason, the magnetic flux density is sufficiently improved, but the product has remarkably coarse grains due to the remarkably coarse grains of the hot-rolled sheet.
The surface properties are significantly deteriorated. Also, in the technique of annealing a hot rolled sheet after adding a special element such as Sb or Sn,
The generation of coarse particles as described above cannot be suppressed, and the same problem occurs.

In contrast to these techniques, the technique of annealing a hot-rolled sheet after light reduction rolling uses grain boundary energy as a driving force for secondary recrystallization, and utilizes strain by light rolling which is overwhelmingly larger than this. The secondary recrystallization proceeds mainly due to strained grain growth as a mechanism even if the annealing is performed at a relatively low temperature.
Coarsening of crystal grains is achieved. However, it is still difficult to satisfy both the magnetic flux density and the surface quality by simply defining the reduction ratio of light reduction rolling as in the above-mentioned conventional technique. That is, although the details will be described later, the reduction ratio of the light reduction rolling is about 5% as in most of the conventional techniques.
When the above is relatively high, the strain as the driving force is sufficiently imparted, but at the same time, the number of crystal grains exceeding the critical energy for secondary recrystallization increases, which causes the structure to become coarser. However, the degree is not sufficient, and the margin for improving the magnetic flux density is not always sufficient. On the other hand, when the reduction ratio of the light reduction rolling is as low as about 2% or less, the number of crystal grains exceeding the critical energy for secondary recrystallization is small, and only the hot-rolled sheet annealing described above is performed. Similarly to the above, the structure becomes too coarse, and thus the magnetic flux density is sufficiently improved, but the surface quality is deteriorated. Furthermore, when low temperature annealing is performed,
There may be a part where secondary recrystallization is not completed in the central part of the plate thickness, and in this case, the margin for improving the magnetic flux density becomes small. Further, when the reduction ratio of the light reduction rolling is in the range of approximately 2 to 5%, both the margin for improving the magnetic flux density and the degree of improvement of the surface quality are halfway, and in both cases, high magnetic flux density and good surface quality It is difficult to achieve security at the same time.

As described above, the conventional technique has a problem in that it is impossible to sufficiently improve the magnetic flux density while ensuring good surface properties. The present invention has been made in view of such conventional problems, without impairing the surface properties,
It is an object of the present invention to provide a method for manufacturing a non-oriented electrical steel sheet which can significantly improve the magnetic properties of the non-oriented electrical steel sheet, particularly the magnetic flux density.

[0007]

In order to achieve the above object, the present inventors have coarsened a structure before cold rolling, that is, a hot-rolled sheet structure to such an extent that a magnetic flux density is sufficiently improved, and the surface of a product. Studies have been repeated on a method capable of suppressing coarse particles.
That is, the present inventors first of all, the surface coarse particles of the product is mainly caused by excessive coarsening of the crystal grains of the surface layer portion of the hot-rolled sheet, and if this is suppressed to an appropriate grain size, the sheet thickness central portion It was thought that the generation of coarse particles on the surface of the product could be suppressed even if the crystal grains of were coarse. Furthermore, if the crystal grains in the central portion of the plate thickness are sufficiently large, it is considered that the magnetic flux density is sufficiently improved even if the crystal grains in the surface layer portion do not become coarse. A method for controlling the surface layer portion to have an appropriate grain diameter while sufficiently coarsening was investigated. As a result, the coiling temperature of the hot-rolled sheet was controlled according to the amounts of Si and Al in the steel, the pre-structure was optimized during coarsening, and the appropriate amount of strain was divided into two by light reduction rolling. Moreover, it was found that the above-mentioned hot-rolled sheet structure can be obtained by applying the material with the rolling direction reversed and then performing hot-rolled sheet annealing under appropriate conditions.

The present invention has been made on the basis of such knowledge, and its characteristic constitution is as follows. (1) C: 0.0050 wt% or less, Si: 0.1
1.5 wt%, Mn: 0.2 to 1.0 wt%, P: 0.
20 wt% or less, S: 0.010 wt% or less, Al:
0.004 wt% or less or 0.100 to 0.500
wt%, N: 0.0050 wt% or less, steel consisting of balance Fe and unavoidable impurities is heated to 1050 to 1250 ° C., and then hot-rolled at a finishing temperature of 750 to 880 ° C. to satisfy the following formula. 37 (Si + Al) + 570 ≦ CT ≦ 41 (Si + A
l) +686 However, CT: coiling temperature (° C) Si: Si content (wt%) Al: Al content (wt%) The hot rolled sheet is pickled, and a rolling reduction of 0.5 to 3.0%. The first light reduction rolling is carried out in the following manner, and then the second light reduction rolling is carried out at the reduction ratio of 0.5 to 3.0% by reversing the rolling direction from the first light reduction rolling. The total reduction ratio of the two light reduction rollings was 2.0 to 5.0%, and then 750 ° C.
To Ac ₁ for 30 minutes to 10 hours or 850
Hot-rolled sheet annealing is performed for 30 seconds to 5 minutes in a temperature range of ℃ to Ac ₁ , and then cold rolling is performed once or twice or more with intermediate annealing, and then in a temperature range of 700 to 900 ° C. Three
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and surface properties, characterized by performing a finish annealing for 0 seconds to 5 minutes.

(2) C: 0.0050 wt% or less, S
i: 0.1 to 1.5 wt%, Mn: 0.2 to 1.0 wt
%, P: 0.20 wt% or less, S: 0.010 wt% or less, Al: 0.004 wt% or less, or 0.100 to
A steel consisting of 0.500 wt%, N: 0.0050 wt% or less, the balance Fe and unavoidable impurities is
After heating to 250 ° C., hot rolling at a finishing temperature of 750 to 880 ° C. and winding at a winding temperature satisfying the following formula, 37 (Si + Al) + 570 ≦ CT ≦ 41 (Si + A
l) +686 However, CT: coiling temperature (° C) Si: Si content (wt%) Al: Al content (wt%) The hot rolled sheet is pickled, and a rolling reduction of 0.5 to 3.0%. The first light reduction rolling is carried out in the following manner, and then the second light reduction rolling is carried out at the reduction ratio of 0.5 to 3.0% by reversing the rolling direction from the first light reduction rolling. The total reduction ratio of the two light reduction rollings was 2.0 to 5.0%, and then 750 ° C.
To Ac ₁ for 30 minutes to 10 hours or 850
Hot-rolled sheet annealing is performed for 30 seconds to 5 minutes in the temperature range of ℃ to Ac ₁ , followed by cold rolling once or twice or more with intermediate annealing, and then in the temperature range of 600 to 850 ° C. Three
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and surface properties, which comprises performing finish annealing for 0 seconds to 5 minutes, performing shearing, punching, and the like, and then performing stress relief annealing.

(3) C: 0.0050 wt% or less, S
i: 0.1 to 1.5 wt%, Mn: 0.2 to 1.0 wt
%, P: 0.20 wt% or less, S: 0.010 wt% or less, Al: 0.004 wt% or less, or 0.100 to
A steel consisting of 0.500 wt%, N: 0.0050 wt% or less, the balance Fe and unavoidable impurities is
After heating to 250 ° C., hot rolling at a finishing temperature of 750 to 880 ° C. and winding at a winding temperature satisfying the following formula, 37 (Si + Al) + 570 ≦ CT ≦ 41 (Si + A
l) +686 However, CT: coiling temperature (° C) Si: Si content (wt%) Al: Al content (wt%) The hot rolled sheet is pickled, and a rolling reduction of 0.5 to 3.0%. The first light reduction rolling is carried out in the following manner, and then the second light reduction rolling is carried out at the reduction ratio of 0.5 to 3.0% by reversing the rolling direction from the first light reduction rolling. The total reduction ratio of the two light reduction rollings was 2.0 to 5.0%, and then 750 ° C.
To Ac ₁ for 30 minutes to 10 hours or 850
Hot-rolled sheet annealing is performed for 30 seconds to 5 minutes in the temperature range of ℃ to Ac ₁ , followed by cold rolling once or twice or more with intermediate annealing, and thereafter in the temperature range of 650 to 800 ° C. Three
Finish annealing is performed for 0 seconds to 5 minutes, and then 1.0 to 12.
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and surface properties, which is characterized by performing temper rolling at a pressure regulation rate of 0%, performing shearing, punching and the like and then performing stress relief annealing.

[0011]

The details of the present invention will be described below together with the reasons for limitation. First, the light reduction rolling condition of the hot rolled sheet, which is the most important requirement in the present invention, will be described. FIG. 1 shows a case where light reduction rolling of a hot-rolled sheet is performed once by using a two-stand rolling mill, and one-stand rolling, for steel A described in Table 1 which is a steel type of the present invention. After performing the first rolling using the mill, the rolling direction was reversed and the second rolling was performed, and the magnetic flux density and plate grain size of the product were determined by the reduction ratio (2 In the case of rolling, the total rolling reduction is summarized. Here, the particle size of the plate surface of the product is not the particle size of the microstructure observed by a so-called optical microscope, but the particle size when visually evaluating the size of the coarse particles of the plate surface of the product, which is a problem as the surface texture. Pointing to. Further, the manufacturing conditions other than the light reduction rolling were set within the scope of the present invention as shown below. Further, in the case of the second rolling, when the total rolling reduction is 1.0 to 6.0%, the respective rolling reductions of the first rolling and the second rolling are in the range of 0.5 to 3.0%. there were. Hot rolling: heating temperature 1200 ° C, finishing temperature 800 ° C, winding temperature 640 ° C, finishing thickness 2mm Hot rolled sheet annealing: 890 ° C x 2 minutes Cold rolling: finishing thickness 0.5mm Finishing annealing: 730 ° C x 2 minutes

FIG. 2 shows the results of a test similar to that of FIG. 1 performed on steel F, which is the steel type of the present invention shown in Table 1. Here, the manufacturing conditions other than the light reduction rolling are shown in FIG.
As in the case of the test related to each, it was set within the scope of the present invention,
The condition itself was set to a value different from that in the case of FIG. 1 as shown below. Further, in the case of the second rolling, when the total rolling reduction is 1.0 to 6.0%, the respective rolling reductions of the first rolling and the second rolling are in the range of 0.5 to 3.0%. there were. Hot rolling: heating temperature 1100 ° C., finishing temperature 860 ° C., winding temperature 730 ° C., finishing thickness 2 mm Hot rolled sheet annealing: 880 ° C. × 3 hours Cold rolling: finishing thickness 0.5 mm Finishing annealing: 860 ° C. × 3 minutes

As mentioned above in the description of the prior art, as is clear from FIGS. 1 and 2, the light rolling of the hot-rolled sheet is simply 1
As long as rolling is performed once, it is not possible to achieve both high magnetic flux density and securing excellent surface properties. That is, when the reduction ratio of the light reduction rolling is approximately 5% or more, the driving force for the secondary recrystallization during the subsequent hot-rolled sheet annealing is sufficiently given, and as a result, the critical energy for causing the secondary recrystallization is increased. The number of exceeded crystal grains becomes excessive. For this reason, the degree of coarsening of the structure after annealing the hot rolled sheet is not sufficient, and although the surface quality is not deteriorated by the coarse grains, the magnetic flux density is not sufficiently improved. On the other hand, when the reduction ratio of the light reduction rolling is in the range of about 1 to 2%, the driving force for the secondary recrystallization is small, so that the number of crystal grains exceeding the critical energy for causing the secondary recrystallization is small. Therefore, while the structure after annealing of the hot rolled sheet is sufficiently coarsened and a high magnetic flux density can be obtained, the sheet surface grain size of the product is 4
It becomes 5 mm or more, and the surface quality is remarkably deteriorated by the coarse particles. Further, when the reduction ratio of the light reduction rolling is approximately 1% or less, the driving force becomes too small, and therefore the plate thickness surface layer portion after the hot rolled sheet annealing is occupied by sufficiently coarse secondary recrystallized grains, but this It cannot grow until it covers the entire thickness,
Part of the fine grain where secondary recrystallization cannot be completed remains in the central portion of the plate thickness. For this reason, the surface quality of the product is deteriorated by the coarse particles of the product, and the margin for improving the magnetic flux density is small. Also,
When the reduction rate of the light reduction rolling is approximately 2 to 5%, the plate surface grain size of the product becomes finer as the reduction rate increases, but at the same time, the magnetic flux density also decreases, which is also high. The magnetic flux density and the excellent surface quality cannot be satisfied at the same time.

On the other hand, when the hot-rolled sheet light reduction rolling is performed by two times of rolling with the rolling directions reversed, the total reduction rate is controlled within an appropriate range to obtain a high magnetic flux density and an excellent surface. It can be seen that the properties are secured together. In particular,
By controlling the total rolling reduction of the two rollings to 2.0 to 5.0% for both steel A and steel F having different composition, the magnetic flux density of steel A is 1.81 T or more, and ,
With Steel F, a value of 1.78 T or more was obtained, and the grain size of the plate surface was both 3 mm or less, which was a value that was not problematic in terms of surface texture, and a high magnetic flux density and excellent surface texture were secured. There is. Further, when the total reduction ratio is in the range of 2.0 to 5.0%, when comparing the magnetic flux density with that of the same plate surface grain size that was obtained by performing one light rolling of the hot rolled sheet, the magnetic flux density was The density is generally higher than 0.02T, and from this fact as well, the light reduction rolling of the hot-rolled sheet is performed by two times of rolling with the rolling directions reversed, and the total reduction rate at that time is 2.0 to 5.0. You can understand the effectiveness of controlling to%. For the above reasons, in the present invention, the light rolling of the hot rolled sheet is performed by two rollings with the rolling directions reversed, and the total rolling reduction of the two rollings is 2.0 to.
It is specified as 5.0%. The single rolling referred to here includes rolling performed in one stand or in two or more stands (that is, rolling in one pass or two or more passes).

In the above-mentioned test, the light reduction rolling of the hot rolled sheet is carried out by using a two-stand rolling machine in the case of performing this rolling once, and by carrying out two rollings with the rolling directions reversed. When it is carried out, a one-stand rolling machine is used, and the number of rolling passes is two in both cases. Therefore, the essential difference between the two lies in whether each pass is performed in the same rolling direction or in the opposite direction. Therefore, in the present invention, there is no special significance in performing the light reduction rolling of the hot-rolled sheet in two times, and it is essential meaning that the rolling direction is reversed between the first rolling and the second rolling. There is.

As described above, the light reduction rolling of the hot-rolled sheet is performed by two times of rolling with the rolling directions reversed, and the total reduction rate is 2.0.
By controlling the content to ˜5.0%, a high magnetic flux density and excellent surface texture can be obtained, but this is because the structure is optimized during the subsequent hot-rolled sheet annealing. That is, the hot-rolled sheet light reduction rolling is performed without reversing the rolling direction.
When the rolling is performed once, as described above, the grain size after hot-rolled sheet annealing is unsatisfactory for both the magnetic flux density and the sheet surface grain size in the rolling reduction range of 2.0 to 5.0%. It's nothing but a thing. On the other hand, light reduction rolling is performed by rolling twice with the rolling direction reversed, and the total reduction rate at this time is 2.0 to
When the hot-rolled sheet is annealed with the content set to 5.0%, it is possible to obtain a crystal grain structure in which the surface layer portion of the sheet is fine grains and the central portion of the sheet thickness is sufficiently coarsened. Here, the fact that the structure after annealing the hot rolled sheet becomes fine grains in the surface layer portion of the sheet means that the grain size of the sheet surface of the product can be made small and the generation of coarse surface grains can be suppressed. Further, since the central portion of the plate thickness has a sufficiently coarse structure, a high magnetic flux density is achieved.

In this way, when the hot rolled sheet light reduction rolling is performed by two times rolling with the rolling directions reversed, and the total reduction rate at that time is controlled to 2.0 to 5.0%, The formation of a structure different from the case where one rolling is performed in the same rolling direction without reversing the rolling direction occurs, which is considered to be due to the following reason.

That is, first, strain energy is imparted to the crystal grains of the hot-rolled sheet in the first rolling, but at this time, the strain energy is mainly concentrated on the crystal grains of the surface layer portion because the rolling reduction is small. In addition, the difference in the crystal orientation of each crystal grain in the surface layer, that is, the accumulated amount of strain energy differs depending on the crystal grain due to the difficulty of plastic deformation due to crystal rotation, so the strain energy is the critical driving force for strain grain growth. A distribution of grains that have accumulated above and those that have not accumulated occurs. Then, the second rolling is performed, but if this rolling is performed in the same rolling direction as the first rolling, crystal rotation hardly occurs in the first rolling due to the crystal orientation, and thus strain energy is not accumulated. The few crystal grains are less likely to cause crystal rotation even in the second rolling performed in the same rolling direction as the first rolling, and thus the strain energy storage amount does not increase so much. Therefore, in the second rolling, the number of crystal grains that can newly obtain strain energy exceeding the critical driving force for causing strained grain growth is small. In this case, among the crystal grains in the surface layer, those that have undergone sufficient crystal rotation in the first rolling to be plastically deformed are less likely to generate new plastic deformation in the second rolling due to work hardening, so Most of the strain energy is applied to the crystal grains on the central side of the plate thickness. Thus, when the second rolling is performed in the same direction as the first rolling, the crystal grains that have accumulated strain energy in excess of the critical driving force for strain grain growth, that is, the nuclei of nuclei at the time of secondary recrystallization The distribution does not cause a large difference between the surface layer portion and the central portion of the plate thickness.

On the other hand, when the second rolling is carried out in the opposite direction to the first rolling, the crystal grains which were hard to cause crystal rotation in the first rolling due to the crystal orientation are in the opposite direction. In the second rolling that is performed, crystal rotation is likely to occur, and plastic deformation is easily performed to obtain strain energy that exceeds the critical driving force for strain grain growth. Therefore, the number of secondary recrystallization nuclei formed in the surface layer portion is significantly increased as compared with the case where the second rolling is performed in the same direction as the first rolling. At the same time, most of the strain energy applied in the second rolling is consumed by the plastic deformation of the crystal grains in the surface layer, so that most of the crystal grains in the center part of the plate thickness exceed the critical driving force for strain grain growth. Strain energy cannot be obtained, and many secondary recrystallization nuclei are not introduced. Thus, when the second rolling is performed in the opposite direction to the first rolling, the secondary recrystallization nuclei have a large distribution in the surface layer portion and a small distribution in the plate thickness central portion. Then, when hot-rolled sheet annealing is performed on this, the surface layer portion has a fine grain structure and the plate thickness center portion has a sufficiently coarse grain structure according to the distribution of nuclei of secondary recrystallization. In addition, since the fine grain structure of the surface layer does not erode the coarse grain structure of the central portion of the plate thickness due to such a difference in crystal grain size, this structure formation proceeds relatively stably. it is conceivable that.

By carrying out the light reduction rolling of the hot-rolled sheet by performing the rolling twice in the opposite rolling directions, it is possible to achieve the formation of a structure capable of ensuring a high magnetic flux density and excellent surface texture. However, in that case, it is also important to optimize the total reduction ratio of the two rollings. That is, the total rolling reduction is 2.
If it is less than 0%, the applied strain energy is too small, so that the number of secondary recrystallization nuclei introduced not only in the central part of the plate thickness but also in the surface layer part of the plate thickness is small. The surface layer portion of does not have a sufficiently fine grain structure, the grain size on the plate surface of the product increases, and the surface texture is impaired. On the other hand, the total rolling reduction is 5.0
%, The strain energy applied is too large, and the number of secondary recrystallization nuclei introduced not only in the plate thickness surface layer part but also in the plate thickness center part is large. As a result, after hot-rolled sheet annealing The central part of the plate thickness does not have a sufficiently coarse grain structure, and a high magnetic flux density cannot be obtained.

Next, the appropriate reduction ratio in each rolling when the hot-rolled sheet light reduction rolling is divided into two rollings will be described. FIGS. 3 and 4 show steel A and steel F, which are the steel types of the present invention shown in Table 1, in light rolling of a hot rolled sheet by two rollings in which the rolling direction is reversed using a one-stand rolling mill. The magnetic flux density of the product and the grain size of the plate surface in the case where the rolling is performed are arranged and shown in relation to the respective reduction ratios of the first and second rollings. Here, the manufacturing conditions other than the light reduction rolling of the hot rolled sheet are steel A
2 was the same as the test conditions of FIG. 1 described above, and Steel F was the same as the test conditions of FIG.

According to FIGS. 3 and 4, the first time and the second time
The total rolling reduction of the second rolling is within the range of the present invention of 2.0 to
Even if it is 5.0%, if the reduction ratios of the first rolling and the second rolling are not within the range of 0.5 to 3.0%, respectively,
It can be seen that a high magnetic flux density and excellent surface properties cannot be secured at the same time. This is because if the rolling reduction of one rolling is less than 0.5%, the strain energy applied is too small, so that any of the crystal grains in the surface layer has a strain energy exceeding the critical driving force for strain grain growth. Is not accumulated and nuclei for secondary recrystallization are not formed. On the other hand, when the rolling reduction of one rolling exceeds 3.0%, the strain energy applied is too large and the strain energy accumulated in the central portion of the sheet thickness increases, and the crystal grains in the central portion of the sheet thickness increase. This is because, as a result, the one exceeding the critical driving force for strained grain growth, that is, the number of secondary recrystallization nuclei rapidly increases, and as a result, the central portion of the sheet thickness after hot-rolled sheet annealing does not become sufficiently coarse. For this reason, in the present invention, the reduction rate per rolling in the hot rolled sheet light reduction rolling is defined as 0.5 to 3.0%.

Next, the appropriate range of the coiling temperature during hot rolling will be described. This requirement is also important for optimizing the structure after hot-rolled sheet annealing and obtaining a high magnetic flux density and excellent surface properties. is there. FIG. 5 shows steel A, which is the steel type of the present invention described in Table 1.
For steel and steel F, the effects of the winding temperature on the magnetic flux density and grain size of the sheet were investigated by varying the winding temperature during hot rolling, and the results are summarized and shown. The manufacturing conditions other than the winding temperature were within the scope of the present invention as shown below.

Steel A: Hot rolling: Heating temperature 1200 ° C., finishing temperature 800 ° C., finishing thickness 2 mm Hot rolled sheet light reduction rolling: reduction of 1.2% of first rolling Second rolling (reverse of first rolling) Direction) 1.6% 1st and 2nd total reduction 2.8% Hot rolled sheet annealing: 890 ° C x 2 minutes Cold rolling: Finished thickness 0.5mm Finish annealing: 730 ° C x 2 minutes Steel F; hot rolling: heating temperature 1100 ° C., finishing temperature 860 ° C., finishing thickness 2 mm Hot rolled sheet light reduction rolling: reduction of the first rolling 2.6% Reduction of the second rolling (direction opposite to the first rolling) Rate 1.2% First and second total reduction rate 3.8% Hot rolled sheet annealing: 880 ° C x 3 hours Cold rolling: Finished thickness 0.5 mm Finishing annealing: 860 ° C x 3 minutes

From the results of FIG. 5, in order to obtain a high magnetic flux density and excellent surface properties at the same time, the winding temperature has an upper limit and a lower limit, and it is necessary to control the winding temperature within the range between the upper limit and the lower limit. I know that there is. That is, when the coiling temperature is lower than the lower limit temperature, the plate surface grain size of Steel A is about 1
In the case of mm and steel F, the problem of surface quality is 1 mm or less, but the magnetic flux density is lowered. On the other hand, when the winding temperature exceeds the upper limit temperature, the magnetic flux density of Steel A is 1.8.
Although there is no problem with 2T or more and with Steel F of 1.78T or more, the grain size of the plate surface is 4 mm or more, and the surface quality is deteriorated. From the point of view of structure formation after hot-rolled sheet annealing, this is
When the coiling temperature is below the lower limit, the structure in the central part of the plate thickness does not become sufficiently coarse, and the magnetic flux density decreases, and conversely, when the coiling temperature exceeds the upper limit, the structure of the plate thickness surface layer part is sufficiently fine-grained. It cannot be said that the grain size of the plate surface of the final product increased and the surface quality deteriorated.

Here, the reason why the structure formation after hot-rolled sheet annealing is defective when the coiling temperature is not within the proper range is not always clear, but when the coiling temperature is below the lower limit, the steel is In both A and Steel F, a region where recrystallization is not completed is observed in the center part of the thickness of the hot rolled sheet before light reduction rolling, and this is considered to be one of the causes. That is, since recrystallization is not completed in this region, even if strain is applied by hot rolling of the hot rolled sheet, strain grain growth does not occur during subsequent hot rolled sheet annealing, and so-called nucleation-primary growth It is considered that the grain size does not reach the grain size obtained by strained grain growth because coarsening of crystal grains occurs due to the recrystallization-grain growth process. Considering the case where the coiling temperature exceeds the upper limit, it is considered that the secondary recrystallization nuclei are mainly formed at the grain boundaries during light reduction rolling of the hot rolled sheet. When the crystal grain of the plate thickness surface layer portion after hot rolling grows to exceed the proper grain diameter by exceeding the upper limit temperature, the decrease in the nucleation site of the secondary recrystallization due to the decrease in the grain boundary area becomes remarkable, As a result, it is considered that the surface layer portion of the sheet thickness does not become finely grained to such an extent that the surface quality does not occur during annealing of the hot rolled sheet.

As described above, regarding the coiling temperature during hot rolling as well, if the structure after annealing of the hot rolled sheet is optimized to obtain a high magnetic flux density and excellent surface properties, this is controlled within an appropriate range. However, it is considered that the upper and lower limits of this appropriate range may be influenced by the steel composition or process conditions, as is clear from the results shown in FIG. Therefore, in order to confirm this, various changes were made to the steel composition and process conditions within the scope of the present invention, and the same arrangement as in the test of FIG. 5 was tried. As a result, the winding temperature in each case has an upper limit and a lower limit, and if it deviates from this, the structure of the hot-rolled sheet is deficient due to the structure of the hot-rolled sheet as described above, It has been clarified that a high magnetic flux density and excellent surface properties cannot be obtained at the same time, and that the upper and lower limit temperatures of the coiling temperature change depending on the amounts of Si and Al among steel components regardless of process conditions. became.

Further, S for the upper and lower limits of this winding temperature
When the influence of the i amount and the Al amount is formulated, the lower limit temperature is (CT) _L = 37 (Si + Al) +570 (CT) _L : Lower limit of winding temperature (° C.) Si: Si content (wt%) ) Al: Al content (wt%) is obtained, while the upper limit temperature is (CT) _U = 41 (Si + Al) +686 (CT) _U : Upper limit of coiling temperature (° C) Si: Si Content (wt%) Al: The relationship of Al content (wt%) was obtained. Therefore, in the present invention, the coiling temperature during hot rolling is set to 37 (Si + Al) + 570 ≦ CT ≦ 41 (Si + A
l) +686 However, it is necessary to control so as to satisfy the relationship of CT: coiling temperature (° C.) Si: Si content (wt%) Al: Al content (wt%).

The hot-rolled sheet is subjected to hot-rolled sheet annealing after light reduction rolling, and this hot-rolled sheet annealing condition also optimizes the structure formation during the hot-rolled sheet annealing to obtain a high magnetic flux density and excellent surface texture. It is important for getting. In the present invention, hot-rolled sheet annealing may be performed by so-called batch annealing or continuous annealing, but in the case of batch annealing, it is necessary to perform annealing for 30 minutes to 10 hours in the temperature range of 750 to Ac _1. , 850 for continuous annealing
It is necessary to anneal for 30 seconds to 5 minutes in the temperature range of to Ac ₁ . If the annealing temperature is lower than each of the above lower limit temperatures, the secondary recrystallization due to strained grain growth is not completed, and especially the coarsening of the structure in the central portion of the plate thickness becomes insufficient, and the magnetic flux density deteriorates. on the other hand,
If the annealing temperature exceeds each of the above upper limit temperatures, γ / α transformation occurs, the texture deteriorates, and the magnetic flux density decreases. With respect to the annealing time as well, if the lower limit of each of the above is exceeded, the secondary recrystallization is not completed and the magnetic flux density decreases. Further, with respect to the upper limit of the annealing time, in the present invention, the coarsening of the structure during hot-rolled sheet annealing is caused by secondary recrystallization due to strain grain growth. Even if annealing is performed, the degree of coarsening due to this is small, which rather increases the energy cost, which is not desirable. In addition, if annealing is performed for a long time exceeding the above respective upper limits, an internal oxide layer or a nitride layer will be generated, and the magnetic characteristics will deteriorate.

As described above, in the present invention, the coiling temperature during hot rolling is optimized according to the amounts of Si and Al in the steel components, and then light rolling is performed twice under a predetermined rolling reduction. By performing hot-rolled sheet annealing under predetermined conditions, the structure after hot-rolled sheet annealing is optimized, and high-order magnetic flux density and excellent surface properties can be obtained. Of course, it is also important to optimize other process conditions, that is, process factors such as steel composition and finish annealing conditions. Therefore, these will be described below. First, the reasons for limiting the steel components will be described.

C: An element that deteriorates magnetic properties and causes magnetic aging.
It is necessary to set it to 0050 wt% or less. Si: An element that improves iron loss by increasing the specific resistance, but in order to obtain this effect sufficiently, addition of 0.1 wt% or more is necessary. On the other hand, S exceeding 1.5 wt%
The addition of i significantly lowers the magnetic flux density, so the upper limit is made 1.5 wt%. Mn: In order to improve hot ductility, it is necessary to add 0.2 wt% or more. However, if it exceeds 1.0 wt%, not only the effect is saturated, but also the decrease in magnetic flux density becomes large, so the upper limit is 1.0 wt. %.

P: An element that improves punchability by increasing hardness, and may be added up to 0.20 wt% if necessary, but if the addition amount exceeds 0.20 wt%, the effect is saturated. However, since the magnetic flux density is remarkably reduced, the addition amount must be 0.20 wt% or less. S: MnS is an element that deteriorates magnetic properties by forming Mn, and in order to avoid this, the upper limit of the amount of S is 0.0.
It is necessary to set it to 10 wt%.

Al: When a small amount of Al is contained,
Fine AlN is formed, which impairs magnetic properties. Therefore,
In order to avoid the formation of this fine AlN, the amount of Al needs to be 0.004 wt% or less. On the other hand, when Al is contained in an amount of 0.100 wt% or more, the amount of Al formed is sufficiently large so that the magnetic characteristics are not deteriorated and rather the iron resistance is reduced by increasing the specific resistance. However, if the addition amount exceeds 0.500 wt%, the magnetic flux density will be significantly reduced. Therefore, when Al is positively added, the upper limit is set to 0.500 wt%. Therefore, Al is 0.004 wt% or less or 0.100 to
0.500 wt%. N: It is an element that deteriorates magnetic properties, and its upper limit is 0.0050 wt% in order to avoid this. Other elements: For the purpose of additionally improving magnetic properties,
Sb, Sn, B, Cu, Se, Ge, Co, Zr, C
It is possible to add an appropriate amount of one or more of a, REM and the like.

Next, process conditions such as finish annealing will be described. Hot rolling: When the heating temperature exceeds 1250 ° C., the yield is significantly decreased due to the generation of scale, and the magnetic properties are significantly decreased by the increase of internal oxidation and grain boundary oxidation. Therefore, the upper limit of the heating temperature is 1250. ℃. on the other hand,
When the heating temperature is lower than 1050 ° C., the rolling temperature is generally lowered, so that the rolling load is increased. Therefore, the lower limit of the heating temperature is 1050 ° C. Regarding the finishing temperature, if it exceeds 880 ° C., the amount of reduction in the α region becomes too small, and the development of favorable texture at the hot rolled sheet stage becomes insufficient, resulting in deterioration of magnetic properties. Therefore, the upper limit of finishing temperature is 880 ° C.
And Further, when the finishing temperature is lower than 750 ° C, the rolling load increases remarkably, so the lower limit of the finishing temperature is set to 750 ° C.

Pickling: The pickling condition itself may be a conventional method, but in order to prevent the strain in the light rolling of the hot rolled sheet from being consumed by the scale layer, the pickling should be performed before the light rolling of the hot rolled sheet. I like to do it. Cold rolling: Cold rolling may be a conventional method, and the number of times of cold rolling may be one cold rolling or two or more cold rolling including intermediate annealing.

Finishing Annealing: In the production of so-called full process materials in which the strain relief annealing is not carried out by the consumer after the finishing annealing, the finishing annealing temperature is in the range of 700 to 900 ° C. This is because the crystal grain size of the product is too small and the iron loss increases when the annealing temperature is lower than 700 ° C. On the other hand, when the annealing temperature is higher than 900 ° C., the development of (111) texture becomes remarkable and the magnetic flux density increases. This is because it deteriorates. Regarding the annealing time, 30
If the annealing time is less than 2 seconds, grain growth is insufficient, the crystal grain size of the product becomes too small, and iron loss increases, so the lower limit of the annealing time is set to 30 seconds. On the other hand, even if annealing is performed for more than 5 minutes, the change in the structure is small and the energy cost is only increased, so the upper limit of the annealing time is set to 5 minutes.

Next, in the production of a semi-processed material which is subjected to processing such as shearing and punching at the consumer without being temper-rolled after finish annealing, and then strain relief annealing, the finish annealing temperature is set. It shall be in the range of 600 to 850 ° C. In this case, since the final microstructure formation for obtaining the predetermined magnetic properties is performed at the time of stress relief annealing at the consumer, it is not necessary to optimize the finish annealing temperature in this sense, but the finish annealing temperature is 600 ℃
If it is below the range, it becomes too hard, which increases the wear of the shearing blade and the punching die. On the other hand, if the finish annealing temperature exceeds 850 ° C., it becomes soft, which causes shearing, sagging during punching, and burrs, which is not preferable. The lower limit of the annealing time is set to 30 seconds in order to prevent the hardness from becoming unnecessarily high. On the other hand, the upper limit is set to 5 minutes because, like the full process material, even if annealing is performed for more than 5 minutes, the microstructure change is small and the energy cost is rather increased.

Further, in the production of a semi-processed material which is temper-rolled after finish annealing and subjected to processing such as shearing and punching at the consumer and then stress relief annealing, the finish annealing temperature is set to 6
The temperature is in the range of 50 to 800 ° C. The purpose of the temper rolling is
It is to improve iron loss by causing grain growth during stress relief annealing by secondary recrystallization due to pressure-controlled strain.To achieve this object, optimization of the crystal grain size before temper rolling is required. It becomes important. Controlling the finish annealing temperature in the range of 650 to 800 ° C. is necessary for optimizing the crystal grain size. That is, since recrystallization is not completed when the finish annealing temperature is lower than 650 ° C., a perfect secondary recrystallization structure cannot be obtained during strain relief annealing even when temper rolling is performed. Further, when the finish annealing temperature exceeds 800 ° C., the crystal grain size becomes excessive,
When temper rolling is performed, the secondary recrystallized structure after strain relief annealing becomes too coarse, and iron loss is improved but magnetic flux density deteriorates. Regarding the annealing time as well, the lower limit is set to 30 seconds in order to completely recrystallize the structure after finish annealing. Also,
The upper limit is set to 5 minutes, because, like the two cases described above, even if annealing is performed for more than 5 minutes, the change in structure is small and the energy cost is increased.

Temper rolling: When temper rolling is performed after finish annealing, this temper rolling is performed to cause secondary recrystallization during strain relief annealing as described above, and the pressure regulating rate is It is necessary to set it in the range of 1.0 to 12.0%. When the pressure regulation rate is less than 1.0%, secondary recrystallization nuclei are not generated. On the other hand, when the pressure regulation rate exceeds 12.0%, not the secondary recrystallization but the primary recrystallization-grain growth occurs at the time of stress relief annealing, and the predetermined recrystallization is caused. The particle size cannot be obtained. In the present invention, as described above, the steel components are optimized for each process condition, but in particular, the coarsening of the structure before cold rolling by the combination of hot-rolled sheet light reduction rolling and hot-rolled sheet annealing is performed. It means that the texture of the product is improved. Therefore, it goes without saying that the magnetic flux density is improved and the iron loss characteristics are also improved.

[0040]

[Examples] Steels A to I described in Table 1 were hot-rolled to a thickness of 2.0 mm, then pickled, and further subjected to light reduction rolling of hot-rolled sheet and annealing of hot-rolled sheet. . Subsequently, after cold rolling once, this was finish annealed to obtain a product having a plate thickness of 0.5 mm. Further, for some of the products, after finish annealing, temper rolling was further carried out to obtain a product having a plate thickness of 0.5 mm. In order to evaluate the degree of coarse particles on the surface of the product thus obtained, the plate surface was lightly etched by nital corrosion, and then the plate surface grain size was visually measured (actually magnified 5 times). did. In addition, a 25 cm Epstein sample was sheared from the product and either unsheared or partially strain relief annealed (750
After applying (° C x 2 hours), magnetic properties (L, C average value)
Was measured. Tables 2 to 4 show the details of the respective production conditions at that time and the presence or absence of temper rolling and strain relief annealing, and Table 5 shows the measurement results of the magnetic properties and plate surface grain size of the product.

As is clear from Table 5, according to the method of the present invention, it is possible to obtain a product having a high magnetic flux density and a small plate surface grain size, that is, an excellent surface property. The iron loss value is also sufficiently low and good. On the other hand, in the comparative method in which the steel composition or the manufacturing conditions deviated from the scope of the present invention, the magnetic flux density was lower by about 0.02 T or the grain size of the plate surface was 4 mm or more as compared with the examples of the present invention. It is impossible to obtain the magnetic flux density and the excellent surface properties at the same time.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

According to the present invention described above, it is possible to easily manufacture a non-oriented electrical steel sheet having both a high magnetic flux density which has not been heretofore available and excellent surface properties.

[Brief description of drawings]

FIG. 1 is a graph showing influences of a method of light reduction rolling of a hot rolled sheet and a reduction rate thereof on a magnetic flux density and a sheet surface grain size of a steel A of an example which is a steel type of the present invention.

FIG. 2 is a graph showing the influence of the method of light reduction rolling of hot-rolled sheet and the reduction rate thereof on the magnetic flux density of the product and the grain size of the sheet for steel F of the example which is a steel type of the present invention.

FIG. 3 shows the influence of the rolling reduction of the first rolling and the rolling reduction of the second rolling of the hot-rolled sheet light reduction rolling on the magnetic flux density of the product and the sheet surface grain size of steel A of the example which is a steel type of the present invention. Graph showing

FIG. 4 shows the influence of the reduction ratio of the first rolling and the reduction ratio of the second rolling of the hot-rolled sheet light reduction rolling on the magnetic flux density of the product and the sheet surface grain size of steel F of the example which is a steel type of the present invention. Graph showing

FIG. 5 is a graph showing the influence of the hot rolling coiling temperature on the magnetic flux density and the grain size of the plate surface of the steels A and F of the examples which are steel types of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoyoshi Okita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (3)

[Claims] 1. C: 0.0050 wt% or less, Si:
0.1-1.5 wt%, Mn: 0.2-1.0 wt%,
P: 0.20 wt% or less, S: 0.010 wt% or less,
Al: 0.004 wt% or less or 0.100 to 0.
500 wt%, N: 0.0050 wt% or less, balance Fe
And steel consisting of unavoidable impurities,
After heating to 0 ° C., hot rolling at a finishing temperature of 750 to 880 ° C. and winding at a winding temperature satisfying the following formula, 37 (Si + Al) + 570 ≦ CT ≦ 41 (Si + A
l) +686 However, CT: coiling temperature (° C) Si: Si content (wt%) Al: Al content (wt%) The hot rolled sheet is pickled, and a rolling reduction of 0.5 to 3.0%. The first light reduction rolling is carried out in the following manner, and then the second light reduction rolling is carried out at the reduction ratio of 0.5 to 3.0% by reversing the rolling direction from the first light reduction rolling. The total reduction ratio of the two light reduction rollings was 2.0 to 5.0%, and then 750 ° C.
To Ac ₁ for 30 minutes to 10 hours or 850
Hot-rolled sheet annealing is performed for 30 seconds to 5 minutes in a temperature range of ℃ to Ac ₁ , and then cold rolling is performed once or twice or more with intermediate annealing, and then in a temperature range of 700 to 900 ° C. Three
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and surface properties, characterized by performing a finish annealing for 0 seconds to 5 minutes. 2. C: 0.0050 wt% or less, Si:
0.1-1.5 wt%, Mn: 0.2-1.0 wt%,
P: 0.20 wt% or less, S: 0.010 wt% or less,
Al: 0.004 wt% or less or 0.100 to 0.
500 wt%, N: 0.0050 wt% or less, balance Fe
And steel consisting of unavoidable impurities,
After heating to 0 ° C., hot rolling at a finishing temperature of 750 to 880 ° C. and winding at a winding temperature satisfying the following formula, 37 (Si + Al) + 570 ≦ CT ≦ 41 (Si + A
l) +686 However, CT: coiling temperature (° C) Si: Si content (wt%) Al: Al content (wt%) The hot rolled sheet is pickled, and a rolling reduction of 0.5 to 3.0%. The first light reduction rolling is carried out in the following manner, and then the second light reduction rolling is carried out at the reduction ratio of 0.5 to 3.0% by reversing the rolling direction from the first light reduction rolling. The total reduction ratio of the two light reduction rollings was 2.0 to 5.0%, and then 750 ° C.
To Ac ₁ for 30 minutes to 10 hours or 850
Hot-rolled sheet annealing is performed for 30 seconds to 5 minutes in the temperature range of ℃ to Ac ₁ , followed by cold rolling once or twice or more with intermediate annealing, and then in the temperature range of 600 to 850 ° C. Three
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and surface properties, which comprises performing finish annealing for 0 seconds to 5 minutes, performing shearing, punching, and the like, and then performing stress relief annealing. 3. C: 0.0050 wt% or less, Si:
0.1-1.5 wt%, Mn: 0.2-1.0 wt%,
P: 0.20 wt% or less, S: 0.010 wt% or less,
Al: 0.004 wt% or less or 0.100 to 0.
500 wt%, N: 0.0050 wt% or less, balance Fe
And steel consisting of unavoidable impurities,
After heating to 0 ° C., hot rolling at a finishing temperature of 750 to 880 ° C. and winding at a winding temperature satisfying the following formula, 37 (Si + Al) + 570 ≦ CT ≦ 41 (Si + A
l) +686 However, CT: coiling temperature (° C) Si: Si content (wt%) Al: Al content (wt%) The hot rolled sheet is pickled, and a rolling reduction of 0.5 to 3.0%. The first light reduction rolling is carried out in the following manner, and then the second light reduction rolling is carried out at the reduction ratio of 0.5 to 3.0% by reversing the rolling direction from the first light reduction rolling. The total reduction ratio of the two light reduction rollings was 2.0 to 5.0%, and then 750 ° C.
To Ac ₁ for 30 minutes to 10 hours or 850
Hot-rolled sheet annealing is performed for 30 seconds to 5 minutes in the temperature range of ℃ to Ac ₁ , followed by cold rolling once or twice or more with intermediate annealing, and thereafter in the temperature range of 650 to 800 ° C. Three
Finish annealing is performed for 0 seconds to 5 minutes, and then 1.0 to 12.
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties and surface properties, which is characterized by performing temper rolling at a pressure regulation rate of 0%, performing shearing, punching and the like and then performing stress relief annealing.