JPH01319632A - Production of silicon steel plate - Google Patents

Abstract

PURPOSE:To produce the silicon steel sheet having excellent magnetic characteristics by subjecting a cold rolled silicon steel sheet contg. specific ratios of C and N to weak decarburizing and denitrizing, then further to annealing in the decarburizing and denitrizing atmosphere. CONSTITUTION:The cold rolled silicon steel sheet which contains, by weight %, 0.2-6.5% Si, >=0.005% Nb, >=0.03% C+N or further contains one or >=2 kinds of <=4.0% Mn, <=3.0% Al, and <=1.0% Co is annealed in a vacuum or the weak decarburizing and denitrizing atmosphere of an inert gas, CO, CO2, H2, etc., in the two phase region of alpha-ferrite+austenite or the single phase region of austenite and in the temp. region where the alpha-austenite alone is formed when C and N are removed. The surface layer part is decarburized and denitrized by this annealing, by which the single phase of the alpha-austenite is formed and the two phases of the alpha-ferrite+austenite or the single phase of the alpha-austenite still remains in the inside. The steel sheet is subjected to the strong decarburizing and denitrizing annealing so as to attain <=0.01% C+N in gaseous H2 to integrate the <100> axes at a high rate to the steel sheet surface to form the columnar grain structure of the alpha-ferrite phase. The silicon steel sheet having the excellent magnetic characteristics as the magnetic core of a transformer, etc., is thus obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a silicon steel plate having a 1001-plane texture, in particular consisting of crystal grains grown perpendicular to the plate surface, The present invention relates to a method of manufacturing a silicon steel plate for electromagnetic use in which <100> axes are highly integrated in the vertical direction.

More specifically, the present invention relates to a method of manufacturing a silicon steel sheet with excellent magnetic properties used as a magnetic core for rotating machines, transformers, generators, etc.

(Prior Art) Silicon steel plates have conventionally been used for magnetic cores of rotating machines, transformers, etc. The magnetic properties required of this silicon steel plate include low magnetic energy loss (core loss) in an alternating magnetic field and high magnetic flux density in a practical magnetic field. To achieve this, the electrical resistance must be increased, and bc is the easy magnetization direction.
When using the <100> direction of the c lattice, it is necessary to use steel plates that are integrated in the direction of the magnetic field.

Currently, unidirectional silicon steel sheets containing about 3% Si have <100> axes accumulated in the rolling direction, and exhibit excellent magnetic properties when used with a magnetic field applied in the rolling direction. However, in cases where the magnetic field is applied in various directions within the plate surface, such as in a rotating machine,
This unidirectional silicon steel cannot be used because it is difficult to magnetize in directions other than the rolling direction, and so-called non-oriented silicon steel sheets have been used.

When a magnetic field is applied not only in one direction but in two or more directions within the plate surface, the most suitable texture is one in which <100> axes are accumulated in the direction perpendicular to the plate surface. This is because in this case, two of the three <100> axes orthogonal to each other, that is, the easy magnetization directions, are always within the plate plane.

The desired degree of accumulation of <100> axes within the plate surface varies depending on the application. For example, in the case of an E I-type magnetic core where the magnetic field is applied in two mutually orthogonal directions within the plate surface (
A texture of 1001<001> or (1001<011> orientation is preferable, and in the case of a rotating machine where a magnetic field is applied in all directions within the plate plane, a texture of 1100 + in-plane non-directional set Mi texture is used, or (100) <00
1>, +100+ <011> type textures are preferably punched out at different angles within the plane of the plate and used in a stacked manner.

The method of producing a crystal grain structure having a <1.00> axis in the direction perpendicular to the plate surface that has been known so far is as follows.

(1) Method using solidification structure: When steel is solidified, crystals with a <1.00> axis in the direction of heat flow grow. Therefore, when solidified into a plate shape, the heat flow force IJ L
i It is perpendicular to the plate surface which is the cooling surface, and in this direction < 10
0> A crystal grain structure with oriented axes.

(1-1) Recently, the molten metal is blown out onto the surface of a cooling roll that rotates at high speed, which is called the molten metal super-quenching method, and the molten metal is 0.05 to 0.5 m thick.
A method for directly manufacturing deer thin plates with a thickness of m is being researched.

When a silicon steel ribbon containing about 6% of 31 is produced by this method, it has a columnar grain structure with its long axis perpendicular to the plate surface or inclined at 20 to 30 degrees therefrom. However, the <100> axis density in the direction perpendicular to the sheet surface is at most 3 to 6 times that of the non-oriented one, and the density of <1.0 (1>) axes is insufficient.In addition, this manufacturing method has poor sheet thickness accuracy. Unfortunately, the high space factor required for electrical steel sheets cannot be secured.

(1-2) Ingo No. 1 - In the method for producing (100) <001> textured silicon steel using the (100) fiber structure of columnar crystals, a columnar crystal ingot manufactured by a special casting method is ) is rolled so that the surface becomes the rolled surface, and annealed at a temperature of 1000° C. or higher.

(2) High-temperature annealing method: (2-1) For thin silicon steel sheets with a thickness of 0.15 mm or less,
When annealed at a temperature of 1000°C or higher in a slightly oxidizing atmosphere, the crystal grains grow to a size comparable to the thickness of the plate, and then the crystal grains with <100> axes perpendicular to the plate surface drive surface energy. Prioritize growth as a strength.

(2-2) When silicon steel to which a certain amount of Al or the like is added is cross-rolled (a rolling method in which cold rolling is performed twice in the 0' and 90° directions) and the final annealing is performed at a temperature of 1150°C (100° )
Since crystal grains with <001> orientation undergo secondary recrystallization, this is utilized to increase their degree of integration.

(Problem H to be solved by the invention) As described above, several proposals have already been made in the prior art, but considering the characteristics required today, (1)
In method -1), the degree of integration of the <100> axis is low and the plate thickness accuracy and space factor are poor.

On the other hand, the structures obtained by methods (1-2>, (2-1), and (2-2) become very large grain structures when trying to increase the degree of integration, resulting in crystals that are 10 to 100 times the thickness of the normal plate. Therefore, even if the magnetization characteristics in a static magnetic field are good, the eddy current loss is large in an alternating magnetic field, and the loss is not sufficiently low.

In addition, (1-2) uses an ingot made by a special casting method, and (2-1) can only be applied to thin plates of 0.15 mm or less (2-2) can only be applied to long A plates by cross rolling. This method uses an inapplicable rolling method and is extremely difficult to put into practical use industrially.

In addition, Si:
A high-silicon iron alloy super-quenched ribbon containing 2.0-8.0% by weight and C: 0.016-1.000% by weight is 600-13% by weight.
A method for manufacturing an in-plane non-oriented electromagnetic iron sheet is disclosed, which is characterized by decarburizing annealing at 00°C. This is a method for promoting grain growth, and there is no mention of crystal orientation control.

(Means for Solving the Problems) As a result of repeated research to solve the above problems, the present inventors have found that cold-rolled silicon steel sheets containing C and N are weakly decarburized and decarburized. During nitride annealing, when transforming from austenite phase to α-ferrite phase, <
The present invention was completed by discovering that the 100> axis is strongly oriented and that if this crystal is shifted by strong decarburization and denitrification annealing, it grows toward the center of the plate thickness.

The gist of the present invention is that Si: 0.2-6.5%, N:≧
A cold rolled steel strip containing 0.005 wt% and C+N: 20.03 wt% is decarburized at a temperature at which it becomes a single austenite phase or a two-phase state of austenite I phase and α-ferrite phase.・After denitrification, each time annealing is performed at a temperature at which α-ferrite becomes a single phase and in a decarburizing/denitrifying atmosphere until C+N: 50.01 wt%. This is a method for producing a silicon steel plate characterized by highly integrating .00> axes.

In addition to the above components, the cold rolled steel strip further includes Mn=
54wt%, 8Q: 53wt% and co=
One or more of these may be contained in an amount of 51 wt%.

(effect) The present invention will be explained in more detail as follows.

A cold-rolled silicon steel whose austenite phase region has been expanded with C and N is first in the α-ferrite-thaustenite two composition or austenite phase temperature range, and when C and N are removed, it becomes an α-ferrite l-single phase. So, generally 85
In a vacuum at a temperature range of 0 to 1000℃ or at a dew point of -20
Annealing is performed in a weakly decarburizing/denitrifying, weakly oxidizing or non-oxidizing atmosphere such as an inert gas, CO1CO2, and hydrogen gas atmosphere at a temperature below 0.9°C. By this annealing, a portion of 5 to 50 μm from the surface is decarburized and denitrified, resulting in a single α-ferrite phase. The interior is still α-ferrite + Austenite I two-phase or α-ferrite single phase.

In such a weakly decarburizing and denitrifying atmosphere, the surface portion is easily decarburized, but it takes a very long time to decarburize and denitrify up to 100 μm from the surface. The α-ferrite grains on the surface grow only slowly inward, and grow two-dimensionally in the in-plane direction of the plate. At this time, grains with <100> axes perpendicular to the plate surface preferentially grow, and the α-ferrite single phase region on the surface has a structure in which the <100> axis is strongly oriented in the direction perpendicular to the plate surface. becomes.

The diameter of these surface α-ferrite grains is at most 30 to 300μ.
m, but the degree of integration is very high.

Subsequently, strong decarburization and denitrification occur, for example, when the dew point is +30°
When annealing in C hydrogen at a temperature of 600°C or higher and at a temperature at which α-ferrite becomes a single phase after decarburization and denitrification, the surface α-ferrite grains shift toward the internal α-ferrite + austenite dual phase or austenite I composition. Eventually, the columnar grains grown inward from both surfaces collide at the center of the plate thickness, resulting in a columnar grain structure of the α-ferrite phase.

In this way, the aggregated MJ weave generated on the surface by utilizing α-ferrite → austenite transformation is continued to the inside.

In the present invention, various limitations are made regarding the steel composition, heat treatment conditions, and structure, and the reasons for the limitations are as follows. Note that "%" is "4%" unless otherwise specified.

Silicon: 0.2% or more in order to increase magnetic permeability and electrical resistance, reduce iron loss, and increase mechanical strength. On the other hand, if too much is added, the magnetic flux density will decrease,
In addition, it becomes brittle, so the content should be 6.5% or less. Preferably 0
．． 6% or more, 5% or less, more preferably 0.8% or more,
It is 4% or less.

Expanding the C,N niostenite region and austenite
C, to control texture by α-ferrite transformation;
The total amount of one or two types of N is 0.005% or more, and C]-N is 0.03% or more. It is necessary to remove C to 0.005% or less, preferably 0.003% or less, and N to 0.01% or less, preferably 0.005% or less by final annealing. Since denitrification annealing takes a long time, the total amount is preferably 1% or less.

Preferably 0.04 wt% or more and 0.5 wt% or less,
More preferably, it is 0.06 wt% or more and 0.3 wt% or less. In addition, it is difficult to add N to silicon steel in an amount of 0.1% or more, and especially when Al is included,
Since C is fixed as lN and does not easily dissolve into steel at temperatures below 1000°C, it is preferable to use C instead of N.

It is preferable to add Mn to facilitate texture control through niostenite-α-ferrite transformation. However, Mn is an element that expands the austenite region, and if it is added in too large a quantity, the transformation temperature will drop excessively. In the latter stage of final annealing, it is necessary to anneal at a temperature at which α-ferrite becomes a single phase after decarburization and denitrification.In order not to lower this annealing temperature too much, α-ferrite changes to austenite after decarburization and denitrification. A small amount is added so that the transformation temperature of is 850°C or higher. Furthermore, for a silicon steel plate, if too much is added, the magnetic flux density will decrease, so it is preferably 4% or less. The specific amount of Mn that can be added depends on the amount of Si and Al, which are α-ferrite I and range-expanding elements, but when 1% of 31 is contained, it is approximately 2.2% Mn or less, and 2% of Si is contained. In this case, the Mn content is approximately 3.5% or less.

It is preferable to add #Al because it increases magnetic permeability and electrical resistance and decreases iron loss.

However, since excessive addition causes embrittlement and facilitates surface oxidation and internal oxidation during final annealing, it is preferably 3% or less. More preferably it is 1% or less, and still more preferably 0.8% or less.

Co+ may be added to increase the magnetic flux density, but 1
If it exceeds %, it has no effect.

Other elements and amounts that do not reduce the effect even if added as desired are as follows.

Ni52%, Mo51%, Cr51%, Cu51%, S
≦0.5%, P≦0.5%, 8S≦0.0
5%, Se≦0.05%, sb≦0.1%, B≦0.0
1%, TaS2.1%, 750.05%, TiS2.0
5%.

Saida 1st day sashigata: There is no particular problem as long as it is cold rolled.

Here, cold rolling refers to rolling at a temperature of 500° C. or lower where recrystallization does not occur. During cold rolling, preferably 2
A rolling ratio of 0% or more, more preferably 50% or more is good.

Further, rolling may be performed multiple times with intermediate annealing interposed therebetween. There is no limit to the board thickness depending on the quality of the wood, but from a practical standpoint, it is preferably 0.05 mm or more to improve the degree of integration, and 2 mm or less because decarburization and denitrification require a long time.

It is preferable to carry out the process at a temperature of 600°C or higher in order to carry out four-fold recrystallization.

During this annealing, in order to obtain a structure with strongly oriented <100> axes in the direction perpendicular to the plate surface, first (1) before decarburization and denitrification, a two-phase mixed state of α-ferrite phase and austenite phase or austenite phase is formed. It is carried out in a single phase state and at a temperature at which α-ferrite I becomes a single phase when substantially decarburized and denitrified. The atmosphere at this time is 5 to 70 μm from the plate surface.
Decarburization and denitrification are carried out in a region with a depth of about m, and α-ferrite I
・It is preferable to have a weakly decarburizing, weakly denitrifying, or both atmosphere that becomes a single phase and makes it difficult for decarburization and denitrification to proceed further into the interior.

If the austenite phase is slowly transformed into the α-ferrite phase through such slow decarburization and denitrification, and the α-ferrite grains are grown in a direction parallel to the plate surface,
α-ferrite grains with <100> axes in the direction perpendicular to the plate surface are selectively generated and grown. (2) In order to shorten the time for the α-ferrite grains on the surface to grow into the interior, in an atmosphere where strong decarburization and denitrification occur, the α-ferrite grains are heated again at a temperature at which the α-ferrite phase becomes a single phase after decarburization and denitrification. Preferably, it is annealed. This is the second stage annealing. The atmosphere at this time is a strongly decarburizing atmosphere, a strong denitrifying atmosphere, or both, in which decarburization and denitrification proceed to the inside.

The first and second stage annealing described above may be performed continuously, or an insulating coating may be applied after the first stage annealing, and then the second stage annealing may be performed.

Atmosphere 11P According to a preferred embodiment, one of the following is selected as the atmosphere for the first stage annealing.

(],) 1. Vacuum up to Torr: In order to selectively generate and grow α grains with a <100> axis perpendicular to the plate surface, a vacuum, especially a vacuum below 1 Torr, is preferable and can be achieved industrially. A vacuum as low as possible may be used.

(2) An atmosphere consisting of one or more of inert gas, C01CO8 and 11□ gas at a temperature of less than -20°C and more than -70°C at point n is used.

Since the rate of decarburization and denitrification is high and a highly integrated texture is not formed due to surface oxidation, the above gas has a dew point of less than -20°C, and the dew point may be as low as industrially achievable.

On the other hand, in order to increase the rate of decarburization and denitrification, the annealing atmosphere in the second stage is an atmosphere consisting of an inert gas with a dew point of Q'C or higher and one or more gases. It is preferable to use However, C as long as it is not carburized.
It may contain O and CO□ gases.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Steel having the composition shown in Table 1 was vacuum melted to produce an ingot, which was then hot rolled to a thickness of 3 mm, and then cold rolled to a thickness of 0.5 mm. This thin plate was subjected to first-stage and second-stage annealing under the annealing conditions shown in Table 2.

For this sample, the state of the crystal grain structure was observed by cross-sectional optical microscopy, and if columnar grains were growing inward from the surface, the depth from the surface of the columnar grain portion was measured, and the C
, N content was analyzed.

The density of the <100> axis is E CP (Elect
The direction of 200 crystal grains was measured for each specimen using the ron Channel Pattern method, and the ratio of the number of crystal grains with <1.00> axes within ±5° from the perpendicular direction to the plate surface to the total was calculated. , the value was divided by the ratio of the case without orientation.

It is clear that the method according to the present invention has a high degree of integration +1
00) Tissue synapse is formed.

Example 2 Steel having the grade shown in Table 1 was melted in vacuum, the ingot was hot rolled to a thickness of 3 mm, and then,
Rolled to a thickness of 1 mm by cold rolling and heated at 850°C.
It was annealed for 3 minutes and then cold rolled again to a thickness of 0.1-0.5 mm. The sheet was annealed at 1000°C in Ar-tLz containing 3% th with a dew point of -35°C and then (A) 20% 112- with a dew point of +25°C.
Annealing was performed under the following heat treatment conditions: 850°C x 15ml in Ar, or (B) 850°C x 24h in ++2 with a dew point of -25°C.

The heat treatment conditions of (A) are (
B) is what happens when this is not done.

A ring-shaped sample with an inner diameter of 50 mm and an outer diameter of 60 mm was punched out from this sample, and a 100 Coun primary coil and a 100 mm
Wrap the secondary coil of the turn around this and the magnetizing force will be 5000.
The magnetic flux density Bso at Δ/m and the iron loss WIS150 when magnetized in an alternating magnetic field of 50 Hz until the magnetic flux density reached 1.5 T were determined. The results are shown in Table 3.

It is considered that the larger the magnetic flux density value is, the smaller the iron loss value is, the weaker the magnetic properties are.

From the results in Table 3, it can be seen that the samples of the present invention all have sloppy magnetic properties compared to the comparative example. Those that underwent strong decarburization and denitrification showed even more distorted magnetic properties.

Table 3 (Effects of the Invention) Thus, according to the method of the present invention: (1) For example, at a relatively low annealing temperature of 850 to 1000°C, the <100> axis can be sufficiently aligned in the direction perpendicular to the plate surface. Can be strongly oriented.

(2+0) It is possible to manufacture silicon steel sheets in a wide range of structures, from a low Si content of 2% to a high Si content of 6.5%.

(3) It is not affected by the plate thickness, and the texture can be sufficiently controlled even with a thickness of several mm.

(4) In the case of texture controlled by secondary recrystallization,
Although the crystal grains are coarse, ranging in size from several millimeters to several millimeters, in the present invention, the grains are fine columnar grains of about 50 to 500 μm, and eddy current loss is further reduced.

As detailed above, the present invention skillfully utilizes the preferential grain growth during the γ-α transformation that occurs with decarburization and denitrification, and the +1001 plane texture is easily formed. Therefore, the magnetic properties have been significantly improved, and this is of great significance.

Claims (2)

[Claims] (1) Si: 0.2 to 6.5 wt%, N: ≧0.005
wt% and C+N:≧0.03wt% at a temperature at which the cold rolled steel strip contains a single austenite phase or a two-phase state of an austenite phase and an α-ferrite phase, after decarburization and denitrification. , C+N:≦0 at a temperature at which α-ferrite becomes substantially single phase and in a decarburizing/denitrifying atmosphere.
．． A method for manufacturing a silicon steel sheet, characterized in that <100> axes are highly integrated on the sheet surface by annealing the steel sheet to 0.01 wt%. (2) The cold rolled steel strip further has Mn≦4wt%, A
The method according to claim 1, characterized in that the method contains one or more of L:≦3wt% and Co:≦1wt%.