JPH06306467A - Production of nonoriented silicon steel sheet extremely excellent in magnetic property - Google Patents

Abstract

PURPOSE:To produce a nonoriented silicon steel sheet having random cube texture and extremely excellent in magnetic properties in the all-around direction. CONSTITUTION:The nonoriented silicon steel sheet is produced by using a cast steel strip prepared by solidifying a molten steel for nonoriented silicon steel sheet, having a composition consisting of, by weight, <=4.0% Si, <=2.0% Al, and the balance Fe with inevitable impurities and satisfying (Si+2Al)>2.5%, by means of an updatedly moving cooling body surface. At this time, cold rolling draft is regulated to 5-<40% and also solidification rate and the {100} plane strength of central layer of cast slab, with respect to random, are regulated to >=10 deg.C/sec and >=2.3, respectively, by which random cube ({100}<0vw>) is developed. By this method, the nonoriented silicon steel sheet extremely excellent in magnetic properties in the all-around direction can be obtained.

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 a very high magnetic flux density and a low iron loss.

[0002]

2. Description of the Related Art In recent years, demands for quality improvement of non-oriented electrical steel sheets as magnetic core materials for rotating machines have become stronger from the viewpoint of energy saving. In order to meet this demand, research and development for improving the magnetic properties of non-oriented electrical steel sheets has been promoted even on the side of the electromagnetic steel sheet manufacturing sakers, and industrially, a number of them have been stipulated in JIS. Non-oriented electrical steel sheets are manufactured. In the manufacturing process of non-oriented electrical steel sheet, in order to obtain a product having a low iron loss value, conventionally, the steel is highly purified in its melting stage, or the Si content in the steel is increased, Means such as sufficient temperature and time have been adopted in finish annealing. However, when these technical means are used, the iron loss value of the product is low, but the magnetic flux density is low.

In order to solve this problem, so-called self-annealing in which hot rolling is carried out at a high temperature for hot rolling, or a method of annealing a hot-rolled sheet has been adopted. Furthermore, recently, it is solidified by a moving and renewing cooling body surface into a cast steel strip, and then,
A method has been developed to obtain a non-oriented electrical steel sheet which is cold-rolled from a corresponding cast steel strip to a predetermined thickness and then finish-annealed.
Even with these methods, when the cold rolling reduction is, for example, 60% or more, which is usually performed, the texture after finish annealing is not only {100} but also {100} as the surface index parallel to the steel plate surface. The 111} plane was also quite strong, and there was a limit to improving the magnetic properties, especially the magnetic flux density.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above problems in the prior art, is extremely excellent as an iron core material for rotating machines, has a low iron loss in all circumferential directions, and has an extremely high magnetic flux density. It is an object to provide a manufacturing method for supplying a non-oriented electrical steel sheet.

[0005]

The feature of the present invention is that, by weight%, Si ≦ 4.0%, Al ≦ 2.0%, and (Si + 2Al)> 2.5%, and the balance: Fe and Molten steel consisting of unavoidable impurities (so-called non-transformed steel) is solidified by the moving and renewing surface of the cooling body to form a cast steel strip,
Then, in the method for producing a non-oriented electrical steel sheet, in which the corresponding cast steel strip is cold-rolled to a predetermined thickness (final sheet thickness) and then finish-annealed, the rolling rate is 5% or more in the cold rolling.
%, And the texture after casting by the surface of the cooling body which is moved and renewed in casting and the solidification rate during casting are simultaneously defined.

The present invention will be described in detail below. The inventors, as a result of intensive studies to solve the technical problem in the present invention, directly obtained casting delay from the molten steel, then,
In the production of cold-rolled and annealed non-oriented electrical steel sheet, it was found that there is a close relationship between the cold rolling ratio and texture of the slab and the magnetism after finish annealing. That is, it was found that the texture of the product after finish annealing strongly depends not only on the cold rolling reduction but also on the texture of the slab and the speed at the time of solidification. Due to these synergistic effects, we have succeeded in obtaining a non-oriented electrical steel sheet having an extremely high magnetic flux density and a good iron loss (low iron loss value).

First, the {100} plane strength parallel to the surface of the slab in the slab thickness center layer will be described with respect to randomness (hereinafter referred to as {100} plane strength). As shown in FIG. 1, {10
When a slab having a {0} surface strength of 2.3 times or more is cold-rolled at a cold rolling rate of 5 to 40% and annealed, B ₅₀ is remarkably good all around.
Is obtained. In addition, B ₅₀ ≧ 1.70 T was defined as a good range. As a method for increasing the {100} plane strength to be 2.3 times or more, it is necessary to significantly develop columnar crystals, and a method of solidifying by a moving and renewing cooling body surface to form a cast steel strip is extremely suitable.

Further, the solidification rate of the central layer of the cast slab is defined by the intervals of dendrites when the actual solidification rate is evaluated, but the central layer corrodes the dendrites more clearly than the surface layer. Because it is more observable, it is more practical. The non-oriented electrical steel sheet has a solidification rate of 10
If the temperature is less than ℃ / sec, the columnar crystals are not completely developed {10
Since 0} strength is weak, it is set to 10 ° C./sec or more.

As a method of setting the {100} strength of the central layer of the cast slab to 2.3 or more and the solidification rate of the central layer of the slab to 10 ° C./sec or more, for example, ΔT (molten metal) Increase the degree of superheat)
Increasing the casting temperature) It is conceivable to obtain the desired texture at the time of solidification by improving the efficiency of heat removal at the solidification part, and further to freeze the desired texture at room temperature by rapid cooling immediately after solidification. Specifically, the temperature at the time of molten metal casting is raised. Then, ・ Use a material with high thermal conductivity for the surface of the cooling body to be moved and updated. -Forced cooling of the cooling body to be moved and updated with water etc. -The surface of the cooling body to be moved and updated should be shaped to have a high heat removal rate. -Use an inert gas with high thermal conductivity as the atmosphere gas for casting. -There is a method to increase the heat removal rate by suppressing the liquid surface on the surface of the cooling body that dynamically moves and updates. Then, there are strong water cooling and strong gas cooling immediately after solidification.

Attention should be paid here. In order to increase the {100} strength of the central layer of the cast slab to 2.3 or more,
The coagulation rate does not necessarily have to be 10 ° C./second or more. That is, in addition to the above method, it is possible to change the composition, and it is possible to add an element that hinders the movement of grain boundaries. For example, by adding Cr, Ti, W, etc., fine so-called inhibitors (CrC, WC,
By forming TiN, TiC, etc.), a fairly strong {100} strength can be obtained even if the solidification rate is slow. However, adding such a so-called inhibitor {10
To secure 0} strength deteriorates the magnetic properties (especially iron loss) after the final annealing. Therefore, in the non-oriented electrical steel sheet,
Not suitable. Therefore, also in the present invention, even if the solidification rate is the same, if the components are different, the {100} strength will be slightly different.

Next, the component system will be explained. In order to improve the mechanical properties of the product, magnetic properties, rust resistance, etc., or for other purposes, Mn, P, B, Ni, Cr, S.
The effect of the present invention is not impaired even if b, Sn, and Cu are contained in one kind or two or more kinds.

If C is 0.012% or less, the object of the present invention can be achieved. The non-oriented electrical steel sheet is mainly used in rotating machines, and from the viewpoint of stable magnetic characteristics, it is required that magnetic property deterioration (magnetic aging) does not occur during use of the non-oriented electrical steel sheet. . In the present invention, the solidification rate is high and the cooling rate after solidification is necessarily high, so that C
May form a solid solution in steel and cause magnetic aging during use in electrical equipment, so it should be 0.0030% or less at the product stage, but C during casting is 0.012%. If it is below, decarburization in the subsequent step is relatively easy, so
012% or less. Also, if C is added in a larger amount,
The cast structure can have the same effect as when the solidification rate is fast (development of columnar crystals: extremely develops the cube texture), and it is theoretically possible to decarburize this harmful C in the subsequent process. Is. However, excessive decarburization is not productive. Also, the conditions during finish annealing are high temperature and long time,
There is a possibility of so-called columnar grain growth, in which the decarburization phenomenon is positively used to form a random cube texture, but it is not suitable for industrial production.

S is an element that is inevitably mixed in during the melting stage of steel, and it is desirable that S be as low as possible in order to promote the growth of crystal grains in the final annealing and to reduce the pinning effect of magnetic domains in the product plate. . Therefore, it should be 0.008% or less. N, like S, is an element that is inevitably mixed in during the melting stage of steel, and in order to promote crystal grain growth in the final annealing and reduce the pinning effect of magnetic domains in the product plate, N should be as low as possible. desired. If it exceeds 0.006%, swelling (air bubbles: so-called blisters) may occur in the product plate added for the above reason. Therefore, N should be 0.006% or less.

Si is added to increase the specific resistance of the steel sheet and reduce eddy current loss, as is well known in the art. If Si is added in excess of 4.0%, the workability is extremely deteriorated and cold rolling becomes difficult. Al, like Si, is added to increase the specific resistance of the steel sheet and reduce eddy current loss. For this purpose, a maximum of 2.0% Al has been added to non-oriented electrical steel sheets that have not been transformed so far. Although it is possible in principle to increase the addition amount, a maximum of 2.0 is taken into consideration in consideration of cold rollability as in Si.
%. Therefore, in the present invention, the upper limit is defined in consideration of workability, and the lower limit is defined in consideration of the presence or absence of transformation. That is, S
i, Al range by weight%, Si ≦ 4.0%, Al ≦ 2.
0% and (Si + 2Al)> 2.5%. The effect of the present invention in (Si + 2Al) ≦ 2.5% with transformation has not been confirmed yet.

If the content of Mn is less than 0.1%, the workability of the product deteriorates, and Mn is added to render S harmless. However, the addition amount of Mn is 2.
If it exceeds 0%, the magnetic flux density of the product will deteriorate significantly, so M
It must be n ≦ 2.0%. P is added within the range of up to 0.1% in order to improve the punchability of the product. If P ≦ 0.2%, there is no problem from the viewpoint of magnetic properties of the product. B is added to make N harmless. Since the balance with the amount of N is necessary, the maximum content is set to 0.005%. If ultra low nitrogen steel is melted, N
Can be rendered harmless, and in this case, the need for addition is small.

Next, the conditions for the manufacturing process of the present invention will be described. The inventors have found that when a cast steel strip obtained by solidifying by a moving and renewing cooling body surface is rolled at a relatively low cold rolling rate (5 to 40%), the magnetic flux density becomes extremely high. It was Then, it was found that the magnetic properties are synergistically further improved by defining the texture and solidification rate of the slab. The reason for this is not yet clear, but it is estimated as follows. That is, when the {100} strength of the slab center layer is strong, at a cold rolling rate of 5 to 40%,
Since the amount of accumulated strain is small and the cold-rolled strain accumulation position is limited, the rate of nucleation grain growth is small in the strain release during final annealing, and the random cube is sharpened mainly by strain-induced grain boundary movement. . On the other hand, if the {100} strength is weak (the number of equiaxed grains is large), strain accumulation during cold rolling is large and occurs randomly, and the probability is that the frequency of nucleation grain growth increases.

The range of cold rolling reduction will be described. If it is less than 5%, shape correction after casting is not sufficient and magnetism is not good. Although the upper limit is less than 40%, it is preferably 30% or less. When the cold-rolling reduction rate is as high as 40% or more, the texture after cold-rolling is almost the same, and no random cube appears. In the method for producing a non-oriented electrical steel sheet, which is solidified by a cooling body surface moving and updated to FIG. 2 to form a cast steel strip, and then the cast steel strip is cold-rolled to a predetermined thickness and then finish-annealed, The relationship between the cold rolling rate and the magnetic flux density (B ₅₀ (T)) is shown. ○ is {100}
Strength: 2.8, ●: {100} strength: 2.1.
However, the thickness of the final annealed plate is different because it is a test using the same material. Also, in this figure, the cold rolling reduction rate is 2
The first peak appears near 0% and the second peak appears near 70%, and the present invention relates to the first peak. In the present invention, the magnetic flux density B _{50 in the} entire circumferential direction is 1.70T.
The above cases are considered “good”. That is, even if the {100} surface strength is less than 2.3 times the randomness and the solidification rate of the slab thickness center layer is less than 10 ° C./sec, the cold rolling reduction ratio is 5% or more and less than 40%. If so, a magnetic property of 60% or more, which is considerably better than that of the conventional method, can be obtained.

Further, FIG. 3 shows the texture of the product. This is a cold rolling reduction of 20% and {1
00} positive electrode point, when the {100} strength is 3.2 (solidification rate of about 57 ° C./sec). Random cube ({100} <0 which is ideal for non-oriented electrical steel sheets
It can be seen that vw>) is expressed.

[0019]

The embodiments of the present invention will be described below. The molten steel having the components shown in Table 1 (the balance consisting of Fe and unavoidable impurities) is solidified on the surface of the moving and renewed cooling body to directly form 0.56
Steel strips of mm, 0.62 mm, 1.20 mm and 2.0 mm were obtained. In this case, casting was performed by a method of holding the liquid surface on the surface of the cooling body that dynamically moves and renews (using a molten steel contact limiting plate) and an ordinary method (using no molten steel contact limiting plate). After that, it was pickled and cold-rolled to a thickness of 0.50 mm and 0.95 mm. The cold-rolled steel sheet was degreased and annealed at 975 ° C. for 30 seconds in a continuous annealing furnace (decarburization conditions were set as necessary). Then, the magnetic characteristics (average every 22.5 degrees) were measured by the Epstein method, and the results are also shown in Table 1.

[0020]

[Table 1]

Manufacturing of a non-oriented electrical steel sheet in which a cast steel strip is solidified by the moving and renewing surface of the cooling body to form a cast steel strip, and then the cast steel strip is cold-rolled to a predetermined thickness and then finish-annealed. In the method, the rolling ratio is set to 5% or more and less than 40% during cold rolling, and the slab center layer {10
By setting the 0} strength to 2.3 times or more and the solidification rate to 10 ° C./second or more, an extremely excellent non-oriented silicon steel sheet can be obtained.

[0022]

As described above, according to the present invention, it is possible to obtain a non-oriented electrical steel sheet having a low iron loss in all azimuth directions and an extremely high magnetic flux density as the iron core material for a rotating machine.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between {100} strength of a cast slab center layer and magnetic flux density in the entire circumferential direction.

FIG. 2 is a diagram showing a relationship between a cold rolling rate and a magnetic flux density.

FIG. 3 is a {100} positive electrode diagram of the material after finish annealing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Kubota 1-1 Tobahata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture New Nippon Steel Corporation Yawata Works

Claims (2)

[Claims] 1. By weight% Si ≦ 4.0%, Al ≦ 2.0% and (Si + 2Al)> 2.5% balance: Molten steel consisting of Fe and unavoidable impurities is solidified by a moving and renewing cooling body surface. At the very least, cast steel strip,
Then, the corresponding cast steel strip is cold rolled to a predetermined thickness,
In the production of a non-oriented electrical steel sheet that undergoes finish annealing, the thickness of the slab in the case of solidification by the moving and renewing surface of the cooling body to form a cast steel strip is parallel to the surface of the slab {10
0} surface strength relative to random is 2.3 times or more, and the cold rolling reduction is 5% or more and less than 40%, and a method for producing a non-oriented electrical steel sheet having extremely excellent magnetic properties. . 2. Si = 4.0% in weight%, Al ≦ 2.0% and (Si + 2Al)> 2.5% balance: Molten steel consisting of Fe and unavoidable impurities is solidified by the surface of a cooling body which is moved and renewed. At the very least, cast steel strip,
Then, the corresponding cast steel strip is cold rolled to a predetermined thickness,
In the production of non-oriented electrical steel sheets that undergo finish annealing, when the molten steel is solidified by the moving and renewing surface of the cooling body to form a cast steel strip, the solidification rate of the slab thickness central layer is 10 ° C / sec or more, and A method for producing a non-oriented electrical steel sheet having extremely excellent magnetic properties, characterized in that a reduction ratio of hot rolling is 5% or more and less than 40%.