JP2535963B2 - Silicon steel sheet having excellent magnetic properties and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a silicon steel sheet having a high density of <100> axes and excellent in magnetic properties in a direction perpendicular to the sheet surface, and a method for producing the same.

[Conventional technology]

Conventionally, silicon steel plates have been used for magnetic cores of electric motors, generators, transformers and the like. The magnetism required for this silicon steel sheet is that there is little magnetic energy loss (iron loss) in an alternating magnetic field and that the magnetic flux density is high in a practical magnetic field. In order to realize these, it is effective to increase the electric resistance and integrate the <100> axis of the bcc lattice, which is the direction of easy magnetization, in the direction of the magnetic field used.

It is a unidirectional silicon steel sheet containing about 3% Si that shows the best magnetic characteristics when the magnetic field used is limited to one direction. As shown in Fig. 2 (a), this is {11
Since the {0} plane is parallel to the plate surface and the <100> axis is integrated in the rolling direction, the magnetic properties are remarkably excellent when a magnetic field is applied in the rolling direction. However, this unidirectional silicon steel sheet is hard to magnetize in a direction other than the rolling direction. Therefore, when a magnetic field acts in various directions within the plate surface, such as in a rotating device such as an electric motor or a generator, no significant effect can be obtained.

What is used when the magnetic field acts in a plurality of directions within the plate surface is a non-oriented silicon steel plate having a texture as shown in FIGS. 2 (b) to (e).

Among non-oriented silicon steel sheets, good magnetic properties are shown in Fig. 2 (b) to (d), where the {100} plane is parallel to the plate surface and the <100> axis is perpendicular to the plate surface. It is a collection of directions. With such a texture, up to two of the three mutually orthogonal <100> axes are parallel to the plate surface. The desired degree of stacking of the two <100> axes parallel to the plate surface depends on the application.

For example, magnetic fields are applied in two directions that are orthogonal to each other within the plate surface.
In the case of an EI type iron core, a texture with {100} <001> and {100} <011> orientations shown in Fig. 2 (b) and (c) is preferable, and the magnetic field can be applied in any direction within the plate surface. In the case of the addition of, use the {100} in-plane non-oriented texture shown in Fig. 2 (d), or Fig. 2 (b) (c)
It can be said that it is preferable to use the {100} <100> and {100} <011> type textures shown in (1) and (2) for punching at different angles in the plate surface and stacking them.

And, such a non-oriented silicon steel sheet having a <100> axis in the direction perpendicular to the plate surface is conventionally prepared by using a solidification structure,
It is manufactured by two methods of high temperature annealing.

Method using solidified structure When solidified with steel, crystals with <100> axis grow in the heat flow direction. When solidified into a plate, the heat flow direction becomes perpendicular to the plate surface that is the cooling surface, and the <100> axis is oriented in this direction. The method using the solidification structure utilizes this orientation, and specifically, there are two methods, that is, the method of ultra-quenching of molten metal and the method of using ingot columnar crystals.

The molten metal super-quenching method is a method in which the molten metal is jetted onto the surface of a cooling roll that rotates at a high speed to directly produce a thin plate having a thickness of 0.05 to 0.5 mm. When a silicon ribbon containing about 6% of Si is manufactured by this method, a columnar grain structure having a long axis in the direction perpendicular to the plate surface or inclined by 20 to 30 ° with respect to the vertical direction is obtained.

The method of using the ingot columnar crystals is to roll the columnar crystal ingot of the [001] fiber structure produced by a special casting method so that the {100} face becomes the rolling face, and anneal at a temperature of 1000 ° C. or higher. 100} <001> A silicon steel sheet with a texture is manufactured.

Method by High Temperature Annealing The following two methods are well known as a method of growing crystal grains having a <100> axis in the direction perpendicular to the plate surface by high temperature annealing.

One is a method of mainly defining an annealing atmosphere, in which a thin silicon steel sheet of 0.15 mm or less is annealed at a temperature of 1000 ° C. or more in a weakly oxidizing atmosphere. According to this annealing, the crystal grains once grow to the size of the plate thickness, and then the crystal grains having the <100> axis in the direction perpendicular to the plate surface preferentially grow using the surface energy as a driving force.

The first one is silicon steel with a small amount of Al added at 0 ° and 90 °.
This is a method of rolling (cross rolling) in the direction of (1) and performing final annealing at a temperature of 1150 ° C. According to this method, {100} 〈001〉
The crystal grains in the orientation are obtained by secondary recrystallization.

However, both methods are very problematic.

[Problems to be solved by the invention]

Among the methods using the solidification structure, in the method using the molten metal quenching method, the <100> axial density in the direction perpendicular to the plate surface is only 3 to 6 times as high as that without orientation, and the plate thickness accuracy is low. The high space factor required for electrical steel sheets cannot be secured.

In the method using the ingot columnar crystals, if the <100> axis is densely integrated in the direction perpendicular to the plate surface, the crystal grain structure becomes extremely large, and the grain size is usually 10 to 100 times the plate thickness. Therefore, although the magnetic characteristics are good in the static magnetic field, the eddy current loss is large in the alternating magnetic field, and a sufficient low iron loss cannot be obtained. Further, since a special casting method is used, it can be said that it is very difficult to carry out on an industrial scale.

Any of the methods using high temperature annealing has the same problem as the method using ingot columnar crystals.

That is, both in the case of annealing in a weakly oxidizing atmosphere and in the case of performing cross rolling, when trying to improve the integration accuracy of the <100> axis in the direction perpendicular to the plate surface, a very large crystal grain structure is formed and in an alternating magnetic field. Of the iron loss is deteriorated.

Furthermore, in the former case of annealing in a weakly oxidizing atmosphere, 0.
There is a restriction that can be applied only to thin plates of 15 mm or less,
The latter method of cross rolling has restrictions that cannot be applied to a long thin plate, and neither can be said to be an industrial method.

The present invention provides a silicon steel sheet having a crystal grain structure capable of solving all of these problems and a method for producing the same.

[Means for solving problems]

The present invention is characterized in that γ →
When α-transformation occurs, a silicon steel sheet with a low iron loss and a high magnetic flux density, in which the <100> axis is densely integrated in the direction perpendicular to the sheet surface, has a highly accurate thickness and limits the thickness, etc. It is based on the finding that it can be easily manufactured on an industrial scale without receiving it.

That is, the final annealing of the conventional silicon steel sheet is usually performed in the temperature range of the α-ferrite single phase. On the other hand, a cold-rolled silicon steel sheet in which an appropriate amount of C is added to expand the temperature range of the austenite phase (γ phase) is used in a temperature range where a single phase is formed when decarburization is completed, for example, in a weak decarburizing atmosphere. When this is annealed, the annealing is performed in the α + γ2 phase region or the γ single phase temperature region since C is sufficiently contained in this annealing.

As a result, the region from the surface to a depth of 5 to 50 μm is decarburized, and only this portion becomes the α single phase. If the α single-phase region is held so that it does not reach the deep part, as shown in Fig. 1 (a), only the crystal grains having the <100> axis in the direction perpendicular to the plate surface are parallel to the plate surface. Grow to.

Thus, the surface layer has an α single-phase texture in which the <100> axis is strongly integrated in the direction perpendicular to the plate surface. It is presumed that this grain growth was driven by surface energy. The α particles in the surface layer at this stage are columnar particles having a size of about 30 to 300 μm in the direction parallel to the plate surface.

Subsequently, for example, when decarburization proceeds in a strong decarburizing atmosphere, the α particles in the surface layer grow toward the α + γ2 phase region or the γ phase region inside, and finally as shown in FIG. 1 (B). As described above, the columnar grains extending inward from both surfaces collide at the central portion of the plate thickness to form a single-phase columnar grain structure.

As described above, if the γ → α transformation occurs during the decarburization process, the {100} texture grown on the surface is passed down to the inside by grain growth, and the entire plate can be easily turned into the {100} texture. . Furthermore, the degree of integration of the <100> axis in the direction perpendicular to the plate surface also improves during the grain growth process. This grain growth mechanism has been clarified by the research conducted by the present inventors.

Further, in such a highly integrated {100} texture, when the columnar crystals have a diameter of several times or less of the plate thickness, the eddy current loss is significantly lower than that of the conventional one, and It was also found that the magnetic flux density was high.

The present invention has been made on the basis of such findings, and has a plate thickness of 0.05 to which C ≦ 0.01 wt% and 0.2 ≦ Si ≦ 6.5 wt% is contained.
A 5 mm cold-rolled silicon steel sheet, consisting of columnar crystal grains that grew inward from the surface in the vertical direction to the plate surface, and the average diameter of the columnar crystal grains in the parallel direction to the plate surface was 1 mm or less. A silicon steel sheet with excellent magnetic properties, in which the axial density of the <100> axis is 8 times or more that of the non-oriented crystal orientation.

0.02 ≦ C ≦ 1wt%, 0.2 ≦ Si ≦ 6.5wt% including the plate thickness 0.0
When decarburizing and annealing a 5 to 5 mm cold rolled silicon steel sheet to C ≦ 0.01 wt%, first in the α + γ range or γ in a weak decarburizing atmosphere.
It is characterized in that the surface layer part is transformed into γ → α by heating to the zone, and then it is heated to the α + γ zone or the γ zone in a strong decarburizing atmosphere to transform the inside into γ → α. It is composed of columnar crystal grains that grow toward, and the axial density of the <100> axis in the direction perpendicular to the plate surface has no crystal orientation.
The gist is a method of manufacturing a silicon steel sheet having a magnetic property which is more than double the magnetic characteristics.

[Operation] Hereinafter, the present invention will be described in detail in the order of component composition, plate thickness, crystal structure, <100> axial density in the direction perpendicular to the plate surface, strip manufacturing method, final annealing, and surface coating to clarify the operation.

Ingredient composition C: In order to control the texture utilizing the γ → α transformation that accompanies decarburization in the final annealing, 0.02 was used in the stage before the final annealing.
%, Preferably 0.05% or more. In order to suppress the decarburization time, the upper limit is 1%, preferably 0.5% or less, more preferably 0.3% or less. In the stage after the final annealing, the content is set to 0.01% or less, preferably 0.005% or less, more preferably 0.003% or less so as not to deteriorate the magnetic properties.

Si: Addition of 0.2% or more, preferably 1% or more is necessary to secure magnetic properties and mechanical properties. The upper limit is 6.5%, preferably 5 to suppress embrittlement and decrease in magnetic flux density.
%, And more preferably 4%.

Mn: It is not an essential element, but it is desirable to add it in order to increase the electrical resistance and reduce the eddy current loss, and to expand the γ phase temperature range and facilitate the texture control using the γ → α transformation. When it is added, 0.5% or more is preferable, and 0.8% or more is more preferable, but in any case, the maximum amount is that which substantially forms an α-ferrite single phase at 850 ° C. or less after decarburization is completed. This is because when a large amount of Mn is added, the temperature at which the α-ferrite single phase is substantially reduced after decarburization is completed, and the annealing temperature must be extremely lowered. If the Si content is high, a large amount of Mn can be added, but the magnetic flux density is lowered, so the content should not exceed 5%. Here, being substantially an α-ferrite single phase means that a slight amount of a second phase such as MnS or AlN may be present.

The components other than C, Si and Mn that can be added without impairing the present invention are as follows.

Al ≦ 3% W, V, Cr, Co, Ni, Mo ≦ 1% Cu ≦ 0.5% Nb ≦ 0.5% N ≦ 0.05% S ≦ 0.5% Sb, Se, As ≦ 0.05% B ≦ 0.005% P ≦ 0.5% Plate Thickness In the present invention, it is not necessary to set an upper limit on the plate thickness in terms of crystal structure. However, if the plate thickness is thick, it takes a long time to decarburize to the inside and the eddy current loss increases, so the thickness is 5 mm or less, preferably 1 mm or less, more preferably 0.5 mm or less. The lower limit is 0.05 mm in order to have a fully accumulated {100} texture, preferably 0.1 mm or more, more preferably
It is 0.15 mm or more.

The crystal structure is basically a structure in which columnar grains extending inward from the surface of the plate collide near the center of the plate thickness, but even if the columnar grain structure penetrates in the plate thickness direction by further promoting grain growth. Good. However, in order to obtain a low iron loss, the average diameter of the columnar crystal grains in the direction parallel to the plate surface is 1 mm or less, preferably 0.5 mm or less, and more preferably 0.35 mm or less.

<100> -axis density in the direction perpendicular to the plate surface
0> axis is integrated with high density. In order to secure sufficient magnetic properties, this degree of integration is 8 times or more, and preferably 15 times to 20 times or more, as compared with the case where there is no crystal orientation orientation (random).

Manufacturing method of strip Any manufacturing method may be used as long as cold rolling is performed at a rolling reduction of 10% or more, preferably 30% or more, and more preferably 50% or more. Usually, it is a process of continuous casting-hot working-cold rolling. In this case, it is possible to prevent the annealing from being performed once or plural times during processing. In addition to the continuous casting method, for example, a method of cold rolling after a diameter or hot working of a thin slab diameter-solidified to a plate thickness of 50 mm or less or an ultra-thin plate by a melt quenching method may be used. Here, cold rolling refers to rolling at 500 ° C. or lower at which recrystallization does not occur.

Final annealing After completion of decarburization, decarburization annealing is performed in a temperature range where an α-ferrite single phase is formed. As a result, the part that has not been decarburized is annealed at the temperature of the α + γ2 phase region or the γ single-phase region, and while the decarburization proceeds, γ → α inward from the surface layer.
A transformation occurs and a substantially α single-phase columnar grain structure in which the <100> axis is strongly integrated in the direction perpendicular to the plate surface is obtained. In particular,
In order to increase the annealing efficiency, it is preferable to perform the following annealing.

First, in a weakly decarburizing atmosphere, for example, in a vacuum of 10 ^-1 Torr or less, or H ₂ , He, Ne, Nr, Kr, Xe, Rn, N _{2 having a} dew point of 0 ° C. or less.
In one or more atmospheres, and is annealed at a temperature of 850 ° C. or higher to form an α single-phase region in a region having a depth of 5 to 50 μm from the plate surface. The annealing time is preferably about 1 to 48 hours.

Then, a strong decarburizing atmosphere, for example, H _{2 with a} dew point of 0 ° C. or more
Inert gas or CO, CO _{2 in} H ₂ with medium or dew point 0 ℃ or more
In a gas containing 650 to 900 ° C. to grow the α single phase region formed in the surface layer portion of the plate toward the inside of the plate. The annealing time is preferably about 5 minutes to 20 hours.

The step of strong decarburization may be performed in a temperature range where a mixed phase of α phase and cementite is added when C is added.

Surface coating It is preferable to form an insulating film on the surface, but this step may be performed after the final annealing or after annealing in a weak decarburizing atmosphere. In the latter case, the surface coating is followed by annealing in a strong decarburizing atmosphere.

[Example 1] A vacuum-melted ingot of 9 kinds of compositions shown in Table 1 by A to I was hot forged into a plate having a thickness of 10 mm, and each plate was hot-rolled to a thickness of 3 mm, and then to a thickness of 1.0 mm. Cold rolled. After that, each plate was subjected to a final deanneal of 870 to 1150 ° C in vacuum for 30 minutes to 24 hours as a weak decarburizing anneal, followed by 850 ° C for 5 minutes in an Ar gas flow containing 20% of H ₂ at a dew point of + 40 ° C. Strong decarburization annealing was performed for up to 5 hours.

The C content after the final annealing was 0.003% or less for all the samples, and the structure was a single phase.

Then, from the surface of each sample after the final annealing,
X-ray diffraction measurement was performed at the position of 5, and the <100> axis density in the direction perpendicular to the plate surface was obtained from the {200} plane reflection intensity by a multiple of the non-oriented one, and from the SEM observation of the cross-sectional structure,
The average grain size of the crystal grains in the direction parallel to the plate surface was obtained. The results are shown in Table 2 together with the final annealing conditions.

The ingot of the composition B has a C content of less than 0.02%, and a manufacturing method using the same does not fall within the scope of the present invention. Other compositions A, C ~
All of the ingots I satisfy the manufacturing method of the present invention, and the final annealing conditions also satisfy the manufacturing method of the present invention.

The results of investigations on the compositions A and C to I indicate that all silicon steel sheets have a columnar grain structure of α phase grown in the direction perpendicular to the plate surface,
Moreover, the <100> axis is strongly integrated in the direction perpendicular to the plate surface, which shows the effectiveness of the present invention.

The photographs of the cross-sectional structures shown in FIGS. 1 (a) and (b) are about 0.5 mm thick samples produced by hot forging-hot rolling-cold rolling of steel having the composition shown by F in Table 1. belongs to. (A) The stage after this sample was subjected to weak decarburizing annealing at 950 ° C for 9 hours in vacuum, and (b) after this annealing, in a 40% H ₂ + Ar stream with a dew point of + 40 ° C. These are the images taken at × 100 and × 50, respectively, after the stage of strong decarburizing annealing at 850 ° C for 30 minutes.

[Example 2] A steel having a composition shown by I in Table 1 was manufactured in a vacuum and cast, and an ingot was hot cast into a plate having a thickness of 10 mm.
After hot rolling to m thickness, cold rolling to 1mm thickness, 850
After intermediate annealing at 5 ° C. for 5 minutes, cold rolling was performed to a thickness of 0.1 to 0.8 mm. Each of the obtained plates was annealed at 970 ° C for 24 hours in an Ar gas atmosphere with a dew point of -50 ° C as the final annealing, and then dew point of + 20 ° C.
750 ° C. In 0% H ₂ -Ar gas flow, and annealed for 30 minutes.

Then, the <100> axial density in the plate surface vertical direction and the average diameter of the columnar grains in the plate surface parallel direction of each sample after the final annealing were obtained by the same method as in Example 1, while the inner diameter of each sample was 50 mm,
A ring-shaped test piece having an outer diameter of 60 mm was punched out, and a primary coil and a secondary coil were wound around each ring-shaped test piece for 100 turns to measure magnetic characteristics. Measurements of magnetic properties were performed on the magnetic flux density when subjected to an external magnetic field of 5000A / m (B _50), the iron loss when magnetized to 1.5T in alternating magnetic field 50H _z and (W _15/50) . For comparison, the same investigation was conducted on a 0.35 mm thick commercial high-grade non-oriented silicon steel sheet (JIS S-9).
The results are shown in Table 3.

In all of the 0.1 to 0.8 mm thick silicon steel sheets, the <100> axis is strongly integrated in the direction perpendicular to the sheet surface, and the magnetic flux density is higher and the iron loss is lower than the commercially available high grade non-oriented silicon steel sheet. This indicates that the present invention is not only effective in improving the magnetic properties of silicon steel sheets, but its effectiveness is not affected by the sheet thickness.

〔The invention's effect〕

As is apparent from the above description, the present invention provides a non-oriented silicon steel sheet with excellent magnetic properties, and also enables the production of a bi-directional silicon steel sheet with excellent magnetic properties by combining a rolling ratio, intermediate annealing, etc. To do. In addition, no special technique is required for the material surface and the rolling surface, so that it is easy to implement and the implementation cost is low. Further, since the normal cold rolling method can be adopted, the plate thickness accuracy is high and the stacking rate in the state where the steel plates are laminated is also improved. Furthermore, it is not affected by the plate thickness. Therefore, it can be said that the invention has a great industrial effect, which is extremely suitable for implementation on an industrial scale.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a photograph of a sectional structure of a silicon steel sheet according to the present invention, and FIG. 2 is a schematic view showing crystal orientations of various silicon steel sheets.

Claims (2)

(57) [Claims] 1. A cold-rolled silicon steel sheet containing C ≦ 0.01 wt% and 0.2 ≦ Si ≦ 6.5 wt% and having a plate thickness of 0.05 to 5 mm, and columnar crystal grains grown inward from the surface in the direction perpendicular to the plate surface. Consists of
A silicon steel sheet with excellent magnetic properties, in which the average diameter of the columnar crystal grains in the direction parallel to the plate surface is 1 mm or less, and the axial density of the <100> axis in the direction perpendicular to the plate surface is 8 times or more that of those without crystal orientation. 2. A cold rolled silicon steel sheet having a thickness of 0.05 to 5 mm containing 0.02 ≦ C ≦ 1 wt% and 0.2 ≦ Si ≦ 6.5 wt% is C ≦ 0.01 wt%.
When decarburizing and annealing up to α + in a weak decarburizing atmosphere
Vertical direction of plate surface characterized by heating to γ or γ region to transform the surface layer to γ → α, and then heating to α + γ region or γ region in strong decarburizing atmosphere to transform γ → α inside Consists of columnar grains grown from the surface to the inside,
A method for producing a silicon steel sheet having excellent magnetic properties, wherein the axial density of the <100> axis in the direction perpendicular to the plate surface is 8 times or more that of the one without crystal orientation.