JP4826312B2 - Manufacturing method of bi-directional electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a bi-directional electrical steel sheet, and particularly intends to easily and stably obtain a bi-directional electrical steel sheet having excellent magnetic properties.

In recent years, along with the increasing demand for prevention of global warming and energy saving, high magnetic properties such as low core loss at commercial frequencies and high magnetic flux density at low excitation fields are also applied to grain oriented electrical steel sheets, which are core materials. Characteristics are required.
In order to realize such magnetic characteristics, it is effective to integrate the <001> axis, which is the easy axis of iron, in the direction of the magnetic field used.

  A general grain-oriented electrical steel sheet has a {110} <001> orientation (Goss orientation), that is, a texture in which the {110} plane is parallel to the steel sheet and the <001> axis is focused in the rolling direction. . Thereby, the grain-oriented electrical steel sheet can exhibit extremely high magnetic properties in the rolling direction. For this reason, grain-oriented electrical steel sheets are suitable for applications in which magnetic flux flows only in the rolling direction, such as a wound iron core, and are used as useful magnetic materials.

  However, in a small transformer having a shape like an EI core, about 80% can be designed so that magnetic flux flows in the rolling direction, but about 20% magnetic flux flows in the direction perpendicular to the rolling direction.

  Steel plates with {100} <001> (so-called cube orientation) texture suitable for applications that require excellent magnetic properties not only in one direction but also in the direction perpendicular to it, such as the EI type core, It is called a bi-directional electrical steel sheet. This bi-directional electrical steel sheet is an electrical steel sheet in which the <001> axis is oriented in both the rolling direction in the steel sheet surface and the direction perpendicular to the rolling direction, and exhibits excellent magnetic properties in two orthogonal directions in the steel sheet surface. .

  As a method for producing a bidirectional magnetic steel sheet, a method by cross rolling is known (for example, Patent Document 1 and Patent Document 2). This method is a method in which a silicon steel material is cold-rolled in one direction, further cold-rolled in a direction intersecting with the cold rolling direction, and then subjected to short-time annealing and high-temperature annealing at about 900 to 1300 ° C. It is.

  In addition, recently, as a new method, a manufacturing method using high temperature annealing that causes de-C or de-C and de-Mn (for example, Patent Document 3), and the contents of Si and Mn satisfy a specific relational expression. The steel to be subjected to hot rolling, intermediate annealing requiring rapid heating and cold rolling two or more times, followed by annealing under reduced pressure (Patent Document 4), and further cube orientation However, there is a manufacturing method (Patent Document 5) that obtains {210} to {310} having slightly higher C-direction magnetic properties by rolling and recrystallizing the steel sheet after secondary recrystallization. Proposed.

Japanese Patent Publication No. 35-2657 Japanese Examined Patent Publication No. 38-8213 Japanese Patent Application Laid-Open No. 7-173452 WO98 / 20179 JP 2000-309858 A

At present, it is remarkable for practical application of grain-oriented electrical steel sheets having Goss orientation, and has become a main material for power transformers.
On the other hand, the bi-directional electrical steel sheet has an excellent feature of exhibiting excellent magnetic properties in two directions within the steel sheet surface, but has not yet been put into practical use.
This is because, in order to form a texture that is accumulated in two directions, it is necessary to introduce special equipment, and the manufacturing method itself is extremely difficult.

In addition, the grain-oriented electrical steel sheet that obtains coarse crystals with a diameter of 10 mm or more by utilizing the secondary recrystallization phenomenon has a problem that the shape change such as sagging is large during the punching process in the process of producing the EI type core. .
Therefore, considering the use of bi-directional electrical steel sheets for applications that require punching, such as EI type cores, the cube orientation is not limited to coarse grains that cause problems such as sagging, but rather small grains with only primary recrystallization. It is necessary to obtain.

Since the technique disclosed in Patent Document 5 is not a technique for obtaining a cube orientation in the first place, sufficient magnetic properties cannot be obtained with B _{50 in} the C direction being less than 1.7T.

  The present invention advantageously solves the above-mentioned problems, does not require special equipment dedicated to the two-way electrical steel sheet, can be formed by normal primary recrystallization of the cube orientation, and has excellent magnetic properties. It aims at proposing the advantageous manufacturing method of a two-way electrical steel sheet.

Now, the inventors examined a grain-oriented electrical steel sheet that does not have a film such as forsterite as a material for forming a cube orientation.
The Goss orientation single crystal is a specific orientation that accumulates highly again in the Goss orientation, which is the initial orientation, after rolling at a rolling reduction of about 70% and then performing recrystallization annealing. Therefore, an experiment was repeatedly conducted to determine whether the other position could be formed by applying a disturbance.

Hereinafter, the experimental results that led to the present invention will be described.
In a mixed atmosphere of 10% CO-4.2% H ₂ OH ₂ (balance), the grain-oriented electrical steel sheet obtained by ordinary secondary recrystallization method is pickled and the forsterite film is removed. The steel was carburized at 700 ° C for 48 hours to contain 100 ppm of carbon in the steel. For comparison, a material (C content: 10 ppm) annealed at 700 ° C. for 48 hours in an N ₂ atmosphere was also prepared. These materials were soaked at 900 ° C. for 60 s to precipitate carbides, and annealed by cooling the cooling process under three conditions of 10 ° C./s, 30 ° C./s, and 50 ° C./s. In addition, those cooled at 50 ° C./s were subjected to aging treatment at 400 ° C. for 30 s. By these treatments, various carbides were precipitated in the crystals of the material subjected to the carburizing treatment.
This was subjected to rolling at a reduction ratio of 10%, 30%, 50%, 70%, 80%. Rolling was performed at a roll temperature of room temperature, 50 ° C., 100 ° C., 150 ° C., and 200 ° C., and then recrystallization annealing at 650 ° C. for 2 minutes was performed in a wet atmosphere. The amount of C in the steel after annealing was less than 50 ppm.

  All of the obtained recrystallized annealed plates had no sufficiently large grains due to abnormal grain growth, and were sufficiently small crystals having a thickness of 1/2 or less.

  In addition, the texture of each annealed plate is shown as an X-ray positive point Schulz method (100) pole figure, which is analyzed by software (Textool) using the ADC (Arbitrarily Difined Cells) method, and the degree of cube orientation accumulation Was investigated.

Table 1 shows the results of investigating the effects of carburization treatment, carbide precipitation, aging treatment, roll temperature, and rolling reduction on the degree of accumulation in the cube orientation.
Note that the degree of cube orientation accumulation is indicated by the ratio of cube strength to random reinforcement (hereinafter referred to as random intensity ratio). Marked with a circle.

From this experiment, it has been found that obtaining the texture accumulated in the cube orientation is limited to carburizing treatment and rolling at a rolling reduction of 50% or more.
In addition, it has been found that a high degree of accumulation can be obtained particularly when the carbide is coarsened by an aging treatment and when the roll temperature is warm rolling at 100 ° C. or higher.

These are presumed to be due to the following mechanism.
As described above, it is generally known that when the Goth direction is rolled and recrystallized, it is accumulated again in the Goth direction. In fact, materials that were not carburized were accumulated in the Goth direction (Fig. 1; Condition 1 etc.).

  In the experiment described above, when carburizing treatment was performed and the carbide was coarsely precipitated, the accumulation degree of the cube orientation was increased, and it is considered that the carbide was extremely useful as a disturbance factor. That is, it is considered that when rolling, carbides having completely different hardness from the parent phase exist, stress concentrates around the carbides and different crystal rotations occur. In order to realize this, it is estimated that a certain degree of rolling reduction (50% in the above experiment) was indispensable.

  Further, even when the roll temperature was high and the material subjected to so-called warm rolling had a high degree of cube orientation accumulation, this effect was obtained without the presence of coarse carbides. Therefore, in this case, in addition to the effect of stress concentration due to carbide, the effect of formation of the Cottrell atmosphere due to solute carbon overlaps, resulting in different crystal rotation, and the same effect as in the case of coarse carbide can be obtained. It is thought that.

Further, FIG. 1 shows the texture of the annealed plates obtained under conditions 1, 10 and 16 in Table 1 (positive point Schulz method (100) pole figure by X-ray).
As shown in the figure, when the conventional method was followed (condition 1), only the Goss orientation as in the prior art was obtained, whereas when carburizing was performed (condition 10), further carburizing treatment was performed. In addition, when aging treatment and warm rolling were performed (condition 16), a high random strength ratio could be obtained.
The present invention is based on the above findings.

That is, the gist of the present invention is as follows.
( 1 ) By mass%, C: 0.005% or more and 0.030% or less and Si: 2.0% or more and 4.5% or less, and a grain-oriented electrical steel sheet after secondary recrystallization having no forsterite film is 100 to 400 ° C. Two directions characterized by annealing in the temperature range of, then rolling at a reduction rate of 50% or more, then performing recrystallization annealing, and making the crystal grain size after recrystallization less than 1/2 of the final plate thickness Method for producing an electrical steel sheet.

( 2 ) By mass%, C: 0.005% or more and 0.030% or less and Si: 2.0% or more and 4.5% or less, and a grain-oriented electrical steel sheet after secondary recrystallization that does not have a forsterite film has a roll temperature of 100 After rolling at a reduction rate of 50% or more using a work roll set at ℃ or higher, recrystallization annealing was performed, and the crystal grain size after recrystallization was reduced to 1/2 or less of the final thickness. A method for producing grain-oriented electrical steel sheets.

According to the present invention, an electrical steel sheet having a cube orientation with a relatively small crystal, not a coarse crystal using abnormal grain growth, can be manufactured without using special equipment.
That is, according to the present invention, a bi-directional electrical steel sheet having good magnetic properties in two directions can be produced industrially stably.

Hereinafter, the present invention will be specifically described. Unless otherwise specified, “%” in relation to ingredients means mass%.
The present invention uses a grain-oriented electrical steel sheet having no forsterite coating as a material. In addition, as long as it is highly integrated in the Goss direction, it is not necessarily limited to the grain-oriented electrical steel sheet, but the material that can be obtained most easily is the grain-oriented electrical steel sheet, and an alternative to this Is considered not to currently exist.

  With regard to the grain-oriented electrical steel sheet as such a material, the forsterite film may be removed by pickling the grain-oriented electrical steel sheet existing in the market, or may be removed by mechanical polishing. . Also, in the manufacturing process of grain-oriented electrical steel sheets, it is possible to use a material that does not form a forsterite film on the surface by using alumina as an annealing separator or using a powder of chloride added to magnesia. Well, not particularly limited.

  Among the components of the grain-oriented electrical steel sheet, C is the most important element in the present invention in order to form carbides in the crystal and to serve as a disturbance factor during rolling and recrystallization. However, if the content is less than 0.005%, the amount of carbide formed is not sufficient. On the other hand, if it exceeds 0.030%, the structure of a ferrite single phase is not formed, and the secondary recrystallization structure is destroyed. Therefore, the amount of C in the material is limited to the range of 0.005% to 0.030%. More preferably, it is 0.008 to 0.025% of range.

  Normally, C does not remain in the grain-oriented electrical steel sheet after secondary recrystallization, which is a raw material, and therefore it is necessary to make the C concentration at least 0.005% by performing a carburizing process or the like. The carburizing method is not particularly limited, but a carburizing annealing with CO gas or a method of annealing after attaching graphite to the steel sheet surface can be considered.

  Si is a useful element that improves iron loss by increasing electrical resistance, and because the final use of electrical steel sheets requires good magnetic properties, it does not contain at least 2.0% Si As a result, the iron loss characteristics are not sufficient. Nevertheless, rolling becomes extremely difficult when the Si content exceeds 4.5%. Therefore, the amount of Si in the material was limited to Si: 2.0% to 4.5%.

In addition to the above-described C and Si, the element forming elements such as Mn and Sb, Sn, Ni, Cu, Cr, and P remaining in ordinary grain-oriented electrical steel sheets remain in the steel. .
About content of these components, as shown below, it is preferable to set it as a general amount conventionally.
Mn: 0.01 to 0.5%, Sb: 0.2% or less, Sn: 0.2% or less, Ni: 0.5% or less, Cu: 0.5% or less, Cr: 0.5% or less, P: 0.3% or less.

  Carbides are deposited on the grain-oriented electrical steel sheet containing C within the above range. In particular, annealing for precipitation control is not necessary, but the coarser the carbide, the greater the effect. Therefore, it is effective to coarsen the carbide by performing an aging treatment at about 100 to 400 ° C. If the temperature is lower than 100 ° C, the movement speed of the carbon is slow. On the other hand, if the temperature exceeds 400 ° C, the movement speed of the carbon is too high and precipitates at the grain boundary, which is a more preferential precipitation site. And cannot be precipitated as a carbide.

  In the next step, the secondary recrystallized grains in which carbides are precipitated in the grains are rolled. At this time, the rolling reduction needs to be 50% or more. This is because when the rolling reduction is 50% or less, the stress concentration around the carbide is not sufficient, and only normal crystal rotation occurs, so that the cube orientation cannot be generated.

Next, recrystallization annealing is performed. The annealing temperature at this time is preferably about 650 to 950 ° C. This recrystallization annealing also serves as decarburization annealing, and it is preferable to reduce C to less than 0.005% after annealing.
That is, in this recrystallization annealing, the resulting crystal structure is strongly accumulated in {100} <001> by causing recrystallization and subsequent normal grain growth. And an electromagnetic steel sheet exhibiting good magnetic properties. Here, excessive recrystallization annealing causes abnormal grain growth and deteriorates the texture. Therefore, recrystallization annealing is performed under the condition that a recrystallized structure having a crystal grain size of at least 1/2 or less of the plate thickness is obtained. There is a need to do.

Since the steel sheet after rolling does not have an insulating coating, various insulating coatings may be applied before recrystallization annealing, and may be combined with baking by recrystallization annealing, or in a separate process after recrystallization annealing. An insulating coating may be applied.
The type of insulating film is not particularly limited as long as it has an insulating effect. That is, any conventionally known insulating coating is suitable. For example, a coating generally containing phosphate-chromic acid-colloidal silica disclosed in JP-A-50-79442 and JP-A-48-39338 is generally used for grain-oriented electrical steel sheets. The solution may be applied to a steel sheet and baked at about 800 ° C., or disclosed in Japanese Patent Publication No. Sho 55-1348 used for non-oriented electrical steel sheets, and a water solution having phosphoric acid, chromic acid, boric acid, and thio bond. Any conventionally known insulating film can be used, such as a method of applying a treatment liquid in which an organic compound and alum are mixed.

  Further, the shape of the steel sheet can be adjusted by flattening annealing, and in this case, it can be performed as flattening annealing that also serves as baking of the insulating film.

Example 1
Si: subjected to pickling oriented electrical steel sheet after secondary recrystallization containing 3.3%, relative to the material to remove the forsterite film, CO, varying the density balance of H ₂ O at 5 conditions, the balance Was carburized at 700 ° C. for 48 hours in a mixed atmosphere composed of H ₂ to contain 10 ppm, 30 ppm, 50 ppm, 60 ppm, 100 ppm, and 105 ppm of C in the steel. Next, an aging treatment was performed at 200 ° C. for 30 s to control carbide precipitation, and carbide was precipitated in the crystal. Thereafter, rolling was performed at a reduction ratio of 10%, 50%, and 80%, so that the final thickness was 0.20 mm. In this rolling, the roll temperature was room temperature. The recrystallization annealing was performed in a humid atmosphere at 800 ° C. for 1 min. The C content in the steel sheet after recrystallization annealing was less than 50 ppm, and the crystal grain size was less than 1/2 of the final thickness.

The structure of the electrical steel sheet thus obtained was measured by the positive point Schulz method, and the obtained result was analyzed by ODF (crystallite orientation distribution function) by the ADC method.
Table 2 shows the results obtained by examining the degree of accumulation of the cube orientation of the obtained steel sheet and B ₅₀ (L) and B ₅₀ (C) in the rolling direction (L direction) and the direction perpendicular to the rolling direction (C direction).
The cube orientation accumulation degree was indicated by a random intensity ratio, and when the random intensity ratio was 4 or more, the accumulation degree was judged to be good, and indicated by a circle in the table.

As is clear from the table, all the inventive examples manufactured under the conditions satisfying the requirements of the present invention showed a strong accumulation in the cube orientation.
On the other hand, those that did not satisfy the requirements of the present invention did not show as strong an accumulation in the cube orientation as the present invention, and had a very sharp goth structure ({110 } <001>).

Example 2
Alumina is used as the annealing separator, and Si content: 2.5% grain oriented electrical steel sheet with no forsterite film formed. CO: 5.0%, H ₂ O: 3.7%, balance is H ₂ Carburizing treatment was performed in an atmosphere at 700 ° C. for 48 hours to contain 80 ppm of carbon in the steel. Next, the carbide precipitation state in the crystal was changed depending on whether or not an aging treatment was performed at 250 ° C. for 30 s to control carbide precipitation. Thereafter, rolling was performed at a rolling reduction of 30% and 80%, so that the final thickness was 0.10 mm. This rolling was performed under two conditions of a roll temperature of room temperature and 150 ° C. The recrystallization annealing was performed under conditions of 750 ° C. and 2 minutes, and decarburization annealing was performed in a humid atmosphere at 700 ° C. for 1 minute. The C content in the steel after decarburization annealing was less than 50 ppm, and the crystal grain size was less than 1/2 the final plate thickness.

The structure of the electrical steel sheet thus obtained was measured by the positive electrode Schulz method, and the obtained result was subjected to ODF analysis by the ADC method.
Table 2 shows the results obtained by examining the degree of accumulation of the cube orientation of the obtained steel sheet and B ₅₀ (L) and B ₅₀ (C) in the rolling direction (L direction) and the direction perpendicular to the rolling direction (C direction).
The cube orientation accumulation degree was indicated by a random intensity ratio, and when the random intensity ratio was 4 or more, the accumulation degree was judged to be good, and indicated by a circle in the table.

  As shown in the table, all the steel sheets obtained according to the present invention showed strong accumulation in the cube orientation. In addition, particularly when the precipitation of carbide was promoted and when warm rolling was performed, a further effect was obtained.

FIG. 2 is a (100) pole figure obtained by the positive point Schulz method using X-rays of the texture of the annealed plates obtained under conditions 1, 10 and 16 in Table 1.

Claims (2)

  The grain-oriented electrical steel sheet after secondary recrystallization containing C: 0.005% or more and 0.030% or less and Si: 2.0% or more and 4.5% or less and having no forsterite film in a mass range of 100 to 400 ° C. Bidirectional electrical steel sheet, characterized in that after annealing at 50% or more and rolling at a reduction rate of 50% or more, recrystallization annealing is performed, and the crystal grain size after recrystallization is set to 1/2 or less of the final thickness. Manufacturing method.   A grain-oriented electrical steel sheet after secondary recrystallization containing C: 0.005% or more and 0.030% or less and Si: 2.0% or more and 4.5% or less, and having a forsterite film, at a roll temperature of 100 ° C. or more. The bi-directional electromagnetic is characterized in that after rolling at a reduction rate of 50% or more using a rolled work roll, recrystallization annealing is performed and the crystal grain size after recrystallization is reduced to 1/2 or less of the final plate thickness. Steel plate manufacturing method.