JPH03140442A - Silicon steel sheet having excellent magnetic characteristics and its manufacture - Google Patents

Abstract

PURPOSE:To improve the surface properties and magnetic characteristics in the silicon steel sheet by subjecting a cold rolled silicon steel sheet having a multilayer structure in which the compsn. of the surface layer parts and inner layer part is specified to decarburizing, thereafter subjecting the steel sheet to decarburizing annealing and reducing the content of C to specified value or below. CONSTITUTION:The compsn. of both surface layer parts of at least 10mum thickness from the surface of a cold rolled silicon steel sheet having a multilayer structure is formed from, by weight, 0.02 to 1% C, <=3% Si, 0.5 to 5% Mn, <=0.1% P, <=0.05% S, <=0.005% N, <=0.1% Al and the balance Fe with inevitable impurities. The inner layer part is formed from 0.02 to 1% C, 3 to 7% Si, 0.5 to 5% Mn, <=0.1% P, <=0.05% S, <=0.005% N, <=0.1% Al and the balance Fe with inevitable impurities. The silicon steel sheet is decarburized and is thereafter subjected to decarburizing annealing at a temp. in which a ferrite single phase is substantially formed to regulate the content of C in the surface layer parts and inner layer part to <=0.1%. In this way, the silicon steel sheet in which the <100> axis in the crystalline grains is integrated in a direction vertical to the sheet face with high density can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a silicon steel plate with excellent surface properties and excellent magnetic properties in which <100> axes are densely concentrated in the direction perpendicular to the mask, and a method for manufacturing the same.

(Prior Art) Silicon steel sheets are roughly classified into the following two types. One type is non-oriented silicon steel sheet, which is used in the iron cores of motor rotors and stators, the iron cores of general-purpose small transformers, and the ballasts of lighting equipment. It is a material with low crystal orientation. The other type is a material called unidirectional silicon steel plate, which is used in equipment that requires excellent soft magnetic properties, such as large transformers and high-frequency transformers. This is a material with high crystal orientation in which the <100> direction, which is an axis of easy magnetization called the Goss orientation, is concentrated in the longitudinal direction of the steel sheet through texture control (1101<001> texture has been significantly developed).

Incidentally, in recent years, there has been a strong demand for improved magnetic properties of these silicon steel plates, such as lower iron loss and higher magnetic flux density, in order to reduce power loss and downsize devices.

Regarding low iron loss, conventional methods for non-oriented silicon steel sheets include increasing the amount of Si in the steel to increase the specific resistance, and reducing impurity elements in the steel to adjust the grain size to the optimum value. The main methods used are methods such as Of these, S
Although increasing the amount of i is effective in reducing iron loss, increasing the amount of St reduces the Fe content accordingly.
Magnetic flux density decreases. Furthermore, increasing the amount of Si causes many problems in the manufacturing process as described below.

That is, if the amount of Si in steel is increased, ■ low melting point scale (F
The formation of e1SlOa) is promoted, making pickling after hot rolling difficult, ■ reducing toughness and making edge cracks more likely to occur during cold rolling, ■ deteriorating weldability,
In pickling lines and continuous annealing lines, it may lead to breakage of welded joints, or the surface of the steel plate may become inert, reducing the wettability between the insulating film and the steel plate that is finally applied to the surface of the electrical steel plate. For example, if 6.5% Si is contained, the magnetostriction becomes zero and the magnetic permeability becomes high, but the steel becomes extremely brittle and difficult to process into a steel plate by rolling. . For this reason, currently S is easy to roll.
Silicon steel sheets with an i content of 4% or less are often used.

We solved the problems in the manufacturing process due to the increase in the amount of Si.
JP-A-63-114940 proposes an invention that attempts to solve this problem by forming an electromagnetic steel sheet into a multilayer structure and making the alloy composition of the surface layer thinner than that of the inner layer. This invention means that the Si content in the surface layer of a constant thickness is 1
By reducing the Si content to less than wt% and increasing the ductility of the surface layer, we aim to improve the surface, reduce edge cracking, improve weldability, and improve the adhesion of the insulation film, and reduce the Si content in the inner layer to 1 to 7wt.
% to ensure magnetic properties equivalent to conventional ones.

Therefore, the invention described in JP-A-63-114940 does not particularly aim at controlling the texture to further improve the magnetic properties.

In order to increase the magnetic flux density, it is necessary to control the texture. Ideally, a non-oriented silicon steel sheet has a texture in which the <100> orientation, which is the axis of easy magnetization, is distributed non-directionally within the sheet surface, and in order to form such a texture, It is necessary that the <ioo> axes are concentrated in a direction perpendicular to the plate surface. On the other hand, silicon steel plates used in equipment such as El cores have a [100
A texture in which <100> axes exist in two directions within a plane, such as a 1<001> orientation or a (1001<011> orientation), is most suitable.

Conventionally, the following method is known as a method for manufacturing such an electrical steel sheet having a <100> axis in a direction perpendicular to the sheet surface.

(1) Method using solidified structure This method utilizes the 1lool fiber structure of the ingot with a high columnar height, and the columnar high height ingot manufactured by a special casting method is cast so that the +100) plane is parallel to the plate surface. It is cut out, rolled, and annealed at a temperature of 1000°C or higher.

(2) Method using surface energy This is a method in which a thin silicon steel plate with a thickness of 0.15 mm or less is annealed at a temperature of 1000"C or more in a slightly oxidizing atmosphere, and the crystal grains are once reduced to the size of the plate thickness. After growth, crystal grains having <ioo> axes in the direction perpendicular to the plate surface preferentially grow using surface energy as a driving force.

(3) Method using cross rolling Silicon steel to which a small amount of A2 etc. has been added is cross rolled in the 0° and 90' directions, final annealed at 1150°C, (JOOI
This is a method of secondary recrystallization of <001> oriented crystal grains.

(4) Method by cooling from the γ single-phase temperature range This method is
As disclosed in Japanese Patent Application Laid-open No. 53-31515,
A steel plate that essentially does not contain C is heated to the T single-phase region and then slowly cooled, and the T-α transformation at that time results in <
100 > axis is integrated.

However, when trying to increase the degree of integration using methods (1) to (3) above, the result is a very large grain structure, and although the magnetic properties are good, eddy current loss becomes large in an AC electric field, and it is difficult to obtain a sufficiently low iron The disadvantage is that you cannot make a profit. Furthermore, method (1) requires the use of an ingot made by a special casting method, method (2) can only be applied to thin plates with a thickness of 0.15 mm or less, and method (3) Both methods are extremely difficult to put into practical use industrially, as they cannot be applied to long thin plates because of the special rolling called cross rolling. Further, in method (4), although the <100> axis density in the direction perpendicular to the plate surface becomes random, it is only about 3 to 7 times as large, and sufficient magnetic properties cannot be ensured.

(Problems to be Solved by the Invention) An object of the present invention is to provide a silicon steel sheet with a grain structure that can solve all of the above-mentioned problems in the manufacturing process associated with increasing the amount of Si and problems in conventional texture control, and to manufacture the same. The purpose is to provide a method.

(Means for Solving the Problems) Although the method described in the above-mentioned Japanese Patent Application Laid-open No. 114940/1983 can improve the problems in the manufacturing process, it cannot further improve the magnetic properties.
However, the present inventors developed a cold-rolled silicon steel sheet with a multilayer structure containing large amounts of C and Mn, in which the Si content in the surface layer of a certain thickness from the steel sheet surface was lower than that in the inner layer, and the decarburization annealing of the silicon steel sheet progressed. When T→α transformation occurs in the process, a silicon steel plate with a crystal grain structure with low iron loss and high magnetic flux density, in which <100> axes are concentrated in a high density in the direction perpendicular to the plate surface, is formed with a high precision plate thickness. It was confirmed that the method can be easily manufactured on an industrial scale without being subject to such limitations.

The gist of the present invention is the following (i) and (11).

(i) The chemical composition in both surface layers (both 10μ thick) is C≦0.01wt%, Si53wt% from the steel sheet surface.
%, 0.5wt≦Mn≦5wt%, P≦0.1wt%,
s<o, oswt%, N≦0.005wt%, A2≦
0.1wt%, the balance consists of Fe and unavoidable impurities, and the chemical composition in the inner layer is C≦0.01wt%, 3wt%
<Si≦7wt%, 0.5wt≦Mn≦5wt%, P≦
0.1wt%, S≦0.05wt%, N≦0.005w
t%, AIl≦0.1wt%, the balance being Fe and unavoidable impurities. Magnetic properties characterized by the <ioo> axis of the crystal grains being concentrated in the direction perpendicular to the sheet surface (ii) The chemical composition in both surface layers at least 10μ thick from the steel sheet surface is 0.02wt%≦C≦ lwt%,
S+63wt%, 0.5wt≦Mn≦511L%, P≦
Q. 1 wt%, S≦0.05 t%, N≦0.005 t%, A2≦Q. 1wt%, the balance is Fe and unavoidable impurities, and the chemical composition in the inner layer is 0.02wt%≦
C≦lwt%, 3wt%<Si57wt%, 0.5wt
≦Mn≦5wt%, P≦Q. 1wt%, S≦0, 05w
t%, N≦0.005wt%, A2≦0.1wt%, the balance being Fe and unavoidable impurities. A method for producing a silicon steel sheet with excellent magnetic properties, comprising decarburizing and annealing until the C content in the inner layer becomes 0.01 wt% or less.

(effect) The present invention will be explained in detail below.

The silicon steel sheet of the first invention of the present application, that is, the silicon steel sheet consisting of an inner layer part and a surface layer part whose alloy composition is more dilute than the inner layer part, and in which the crystal grains have <ioo> axes accumulated in the direction perpendicular to the mask, has a multilayer structure. It is obtained by decarburizing and annealing a co-rolled silicon steel plate according to the second invention of the present application to control the texture.

The cold rolled silicon steel plate can be manufactured as follows.

(l) Cast a steel ingot that will become the inner layer, immerse it in molten metal, and cast the shell that will become the surface layer to produce a steel ingot in which the alloy composition of the inner layer is thinner than that of the besiel part. A method in which the ingot is hot-rolled directly or after soaking, then scale is removed, and then cold-rolled two or more times with one or intermediate annealing in between.

(2) Cast a shell layer, pour the molten metal that will become the inner layer into it, produce a steel ingot with a dilute alloy composition in the inner layer compared to the shell layer, and process this steel ingot in the same manner as above. how to.

(3) Cast a steel ingot that will become the surface layer and an inner layer, and after processing these separately into steel plates by hot rolling, descaling them, stacking them in 3 layers and cold rolling, Method of making a clad steel plate.

In the present invention, the reason why the thickness of the surface layer and the chemical composition of the surface layer and inner layer of the silicon F4 temporary and cold rolled silicon steel sheets of these final products are limited as described above is as follows.

(a) Thickness of the surface layer The surface layer is provided to facilitate cold rolling of high-Si steel, which is difficult to roll. In order to facilitate cold rolling, the Si content in the surface layer should be 3 wt% or less, and the thickness should be at least 10 microns per side. Even if the Si content in the surface layer is 3wt% or less, the thickness is 1
If it is thinner than 0 μm, cold rolling becomes difficult and edge cracks are likely to occur during rolling. It is desirable to determine the thickness of this surface layer based on the cold rollability and the final required magnetic properties.0 It is advantageous to make the surface layer thicker in order to ensure cold rollability, but if it is too thick, The inner layer becomes thinner,
Since there may be cases where the necessary magnetic properties cannot be obtained, a desirable upper limit is about 273 with respect to the total plate thickness.

(b) Chemical composition C: C expands the γ phase region, resulting in (α+T)→α transformation or T→α
In order to control the texture by transformation, at least 0.02 wt%, preferably, at a stage before the final annealing described below.
It is necessary to contain 0.05 wt% or more. The upper limit is 11% or less, preferably 0.3w to suppress decarburization time.
t% or less. In addition, after decarburization annealing (final annealing),
In order not to deteriorate the magnetic properties, the content is set to 0.01 wt% or less, preferably 0.003 wt% or less.

Si: As mentioned above, the content of Si in the outer layer is 3 wt% or less in order to suppress cracking during cold rolling. In the inner layer part, the amount is set to exceed 3 wt% for the effect of improving magnetic properties. Furthermore, up to about 6.5wt% Si can be expected to have effects such as reducing brush strain, improving magnetic permeability, and lowering the number of iron members;
%, the magnetic permeability decreases significantly and the advantages in terms of alloy design decrease, so the upper limit is set at 7 wt %.

Mn: To increase electrical resistance and reduce eddy current 7wt.
It is added to expand the γ phase region and facilitate texture control through (α10γ)→α transformation or T→α transformation. If the content is small, these effects cannot be obtained, so the lower limit is 0.
The content shall be 5 wt% or more. On the other hand, if added in a large amount, the transformation temperature will drop excessively and the magnetic flux density will also drop, so the upper limit is preferably 5 wt%.

In order to obtain crystal grains in which <100> axes are accumulated in the direction perpendicular to the plate surface, it is necessary to perform annealing at a temperature at which α single phase is formed after decarburization in the latter stage of final annealing. If a large amount of Mn is added, the temperature at which the α-single phase becomes substantially after decarburization is completed will be lowered, and the annealing temperature must be extremely low. It is desirable to add so that the transformation temperature from the α phase to the (α+γ) phase is 800'C or higher.

The amount of Mn1l that can actually be added is related to the content of Si and Al, which are α-range expanding elements, but when containing 2 wt% of Si, it is approximately 3.5 wt% or less, and when containing 3 wt% of Si, it is approximately 54 wt%. % or less.

Like Si, P is an α-stabilizing element and increases the resistivity, so it is an effective element for improving the AC magnetic properties. However, it is also an element that segregates at ferrite grain boundaries and makes steel brittle.

Particularly in steels containing more than 1.0 wt% of Si, the embrittlement effect of P becomes significant, so the content is set to 0.1 wt% or less.

S: Since S is a harmful element to magnetic properties, it is desirable to reduce it as much as possible. If it is 0.05 wt% or less, the adverse effects caused by S are relatively small.

N: Like C, N is an element that participates in magnetic aging, so it is desirable to have as little as possible. Its content is 0.005
If it is less than wt%, its contribution to magnetic aging is small.

82: Al contributes to the improvement of AC magnetic properties through the same effect as Si, but when added in a large amount compared to Si, alumina inclusions are formed significantly during the steelmaking stage, reducing the cleanliness of the material. , the content is 0. ]wt% or less.

(C) T100I texture This is the process by which a cold-rolled silicon steel sheet with the above chemical composition, which has a higher C content than the final product, is heated to a temperature at which it becomes substantially a single phase of ferrite after decarburization, so that the C content in the surface layer and the inner layer increases. Reduce the amount to 0.
It can be obtained by decarburization annealing until it becomes 0.01 wt% or less.

Final annealing of conventional silicon steel sheets is usually carried out in the α single phase temperature range. On the other hand, if a cold-rolled silicon steel sheet with an appropriate amount of C added to expand the temperature range of the T phase is annealed in a weakly decarburizing atmosphere such as vacuum in a temperature range where the α single phase is formed when decarburization is completed. Since a sufficient amount of C is contained in this annealing process, annealing is performed in the α+12 phase region or T single phase temperature region.

As a result, a region from the surface to a depth of 5 to 50 μm is decarburized, and only this portion becomes α single phase. If this α single phase region is maintained so as not to reach deep parts, only crystal grains having <100> axes in the direction perpendicular to the plate surface will grow in the direction parallel to the plate surface.

In this way, the surface layer has a single α-phase aggregate Mi structure with <100> axes strongly integrated in the direction perpendicular to the plate surface.

At this stage, the number of α grains in the surface layer is 30 to 300 in the direction parallel to the plate surface.
The crystal grains have a size of approximately μm.

Subsequently, when decarburization is allowed to proceed in a strongly decarburizing atmosphere such as I-12 with a dew point of °C or higher, the α grains in the surface layer become α+12 inside.
It grows toward the phase region or T-phase region, and finally becomes an α single-phase columnar crystal MX weave in which columnar high schools extending inward from both surfaces collide at the center of the plate thickness.

The present invention will be further explained below with reference to Examples.

(Example 1) An ingot having the chemical composition shown in Table 1 obtained by a conventional method was hot forged into a steel billet having a thickness of 50 mm.

For steel type A with Nα1, the temperature is 3.2 after heating to 1200°C.
Rolled into thick steel plate. At this point, many cracks had started, but after removing the flaws, we tried pickling and cold rolling.
Cracks were severe and subsequent rolling was interrupted.

Steel types B-H with Nα2 to Nα8 were hot-rolled and cold-rolled into steel plates with a thickness of 1.5 mm (steel plates for surface layer materials). Similarly, the steel types (b) to (h) were hot rolled into W4 plates (steel plates for inner layer material) with a thickness of 20II1 m. Next, after removing these surface scales, the steel plate for the inner layer material was wrapped with the N plate for the outer layer material, and assembled by welding. 12 of these
After heating to 50''C, it was hot rolled to a thickness of 3.5111 m, and after removing scale, it was cold rolled to a thickness of 0.7 mm.

At this point, cracking was severe in the case of Nα6, and further investigation was discontinued. For Nα2 to Nα5 and Nα7 to NαB, which were made into sound rad steel plates by rolling, the thickness of one side of the surface layer and the inner layer was observed by microscopic Mi weave observation and found to be 25 μm and 0.65 mm, respectively.

Small pieces were collected from these and annealed for the first time at 950°C.
The test was carried out in a vacuum of 10-' Torr for 7 hours. This is weak decarburization annealing. After this first annealing, the vertical cross section was examined by microscopic structure observation, and it was found that i・1α7 was an equiaxed grain as a whole, but for Nos. 2 to 5, the surface layer was decarburized by about 100 μm, and that part was decarburized. were columnar grains.

Furthermore, a second annealing was carried out at 850°C for 2 hours in a hydrogen atmosphere with a dew point of 20°C. After decarburization, microscopic structure observation of the longitudinal section was performed in the same manner, and it was found that Nα2,
In both cases of Nα7, the crystal grains penetrated through the plate thickness, but in case of Nα8, cementite was still present and decarburization had not been completed, so annealing was performed twice under the same conditions. As a result, for ;4oB, the crystallinity η penetrated through the plate thickness, but the grain size was very large, 500 μm.

No. 2 to No. 5 and No. thus obtained
, For electromagnetic steel sheets of 7 to Nα8, X in the direction perpendicular to the sheet surface
Line diffraction integrated intensity (axial density), <100> axial density in the rolling direction (R, [+,), magnetic flux density, and iron loss were measured. The results are shown in Table 1 together with the amount of C after final annealing.

(Hereinafter, blank space) As is clear from Table 1, all of the examples of the present invention, Nα2 to Nα5, have a <100> axis density in the direction perpendicular to the plate surface that is 30 to 40 times higher, and furthermore, the magnetic properties in the rolling direction are also good.

On the other hand, the comparative example Ma7 has a weak <100> axis density and a strong <111> axis density, so its magnetic properties are extremely poor, and k8 has a <100> axis density. >Although the shaft density is strong, the iron loss is extremely large. This is considered to be because the particle size is very coarse, so the eddy current fitM and abnormal eddy current loss become large. In addition, when the difference in the set & 11 weave between the surface layer and the inner layer of these steel plates was investigated, it was confirmed that there was no significant difference.

(Example 2) Plate thickness 311I with the same chemical composition as steel type C used in Example 1
IO hot-rolled steel plates (steel plates for surface materials) were produced, and after removing scale, they were welded and assembled into a box shape with an internal volume of 40 mm, a height of 40 mm, and a height of 250 vw, with one side open.

Next, a molten metal having the same chemical composition as the steel type (C) used in Example 1 was poured inside to produce a cladding material. After casting, 5011IB was cut off from the upper end, heated to 1200'C, hot rolled to a thickness of 3.21mm, and after removing scale, it was rolled to a thickness of 0.5mm.
8■ Cold rolled to the point of ugliness. This cold-rolled steel sheet was annealed under the same conditions as in Example 1 to control the texture. Table 2 shows the results of investigating the magnetic properties.

It can be seen that even those obtained by the casting method have excellent magnetic properties.

In addition, a steel ingot of steel type (C) for the inner layer material is made, immersed in molten metal of steel type C for the outer layer material, and pulled out after a solidified shell of a predetermined thickness has grown, and this steel ingot is treated in the same manner as above. A final product was prepared by the method described above, and its characteristics were evaluated, and results comparable to those of the examples of the present invention shown in Tables 1 and 2 were obtained.

(Effects of the Invention) As is clear from the examples, according to the method of the present invention, it is possible to improve the rollability of high-Si non-oriented silicon steel sheets, which could not be easily rolled up to now, and to achieve even better magnetic properties. It is possible to add characteristics.

Claims (2)

[Claims] (1) The chemical composition of both surface layers at least 10 μm thick from the steel plate surface is C≦0.01wt%, Si≦3wt%.
%, 0.5wt≦Mn≦5wt%, P≦0.1wt%,
S≦0.05wt%, N≦0.005wt%, Al≦0
．． 1wt%, the balance is Fe and unavoidable impurities, and the chemical composition in the inner layer is C≦0.01wt%, 3wt%<
Si≦7wt%, 0.5wt≦Mn≦5wt%, P≦0
．． 1wt%, S≦0.05wt%, N≦0.005wt
%, Al≦0.1wt%, the balance being Fe and unavoidable impurities, the silicon steel sheet has crystal grains that grow from the surface to the inside in a direction perpendicular to the sheet surface, A silicon steel sheet with excellent magnetic properties, characterized in that <100> axes of grains are concentrated in a direction perpendicular to the sheet surface. (2) The chemical composition of both surface layers with a thickness of at least 10 μm from the steel sheet surface is 0.02wt%≦C≦1wt%, S
i≦3wt%, 0.5wt≦Mn≦5wt%, P≦0.
1wt%, S≦0.05wt%, N≦0.005wt%
, Al≦0.1wt%, the balance consists of Fe and unavoidable impurities, and the chemical composition in the inner layer is 0.02wt%≦C≦
1wt%, 3wt%<Si≦7wt%, 0.5wt≦M
n≦5wt%, P≦0.1wt%, S≦0.05wt%
, N≦0.005wt%, Al≦0.1wt%, balance F
A cold-rolled silicon steel sheet with a multilayer structure consisting of E and inevitable impurities is decarburized and annealed at a temperature at which it becomes substantially a single phase of ferrite after decarburization until the C content in the surface layer and inner layer becomes 0.01 wt% or less. A method for producing a silicon steel sheet with excellent magnetic properties.