KR960006447B1 - High silicon steel sheet excellent in workability - Google Patents

Abstract

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Description

Electrical steel sheet

1 is a graph showing the relationship between the three-point bending characteristics of the steel sheet according to the present invention and the degree of vacuum in the final heat treatment air.

2 is a graph showing the relationship between the elongation of the steel sheet according to the present invention and the oxygen content in the grain boundaries.

3 is a graph showing the relationship between three-point bending characteristics and grain boundary strength parameters of a steel sheet according to the present invention.

4 is a graph showing the relationship between the three point bending characteristics of the steel sheet according to the present invention and the average diameter of the crystals.

5 is a diagram showing a three-point bending test method for inspecting the workability of the steel sheet.

6 is a graph showing the relationship between the three point bending characteristics of the steel sheet of Example 1 and the oxygen content in the grain boundary.

7 is a graph showing the relationship between the three point bending characteristics of the steel sheet of Example 2 and the oxygen content in the grain boundary.

8 is a graph showing the relationship between many defects in the shearing section of the steel sheet of Example 3 and the oxygen content in the grain boundaries.

9 is a graph showing the relationship between the elongation of the steel sheet of Example 4 and the oxygen content in the grain boundaries.

10 is a graph showing the relationship between the three point bending characteristics of the steel sheet of Example 6 and the oxygen content in the grain boundary

11 is a graph showing the relationship between the three-point bending characteristics of the steel sheet according to the present invention and the sulfur content at the grain boundaries.

12 is a graph showing the relationship between the elongation of the steel sheet according to the present invention and the sulfur content in the grain boundaries.

13 is a graph showing the relationship between the elongation of the steel sheet according to the present invention and the oxygen content and sulfur content in the grain boundaries.

14 is a graph showing the relationship between the three point bending characteristics of the steel sheet according to the present invention and the average diameter of the crystals.

15 is a graph showing the relationship between the three-point bending characteristics of the steel sheet of Example 7 and the sulfur content in the grain boundaries.

16 is a graph showing the relationship between the three-point bending characteristics of the steel sheet of Example 9 and the sulfur content at the grain boundaries.

The present invention relates to high silicon electrical steel sheets used as core materials for transformers and electric motors.

Electrical steel is widely used as core material for electric motors and transformers. Electrical steels generally contain silicon to control texture and improve resistivity. Zinc alloy containing 6.5 wt% of silicon exhibits the softest magnetism because the magnetostriction is close to zero. However, when the silicon content is increased, the brittleness of the steel is increased, and high silicon steel containing 4% by weight or more of silicon cannot be formed into a thin steel sheet by a conventional rolling rolling method. In order to solve this problem, a method of manufacturing a thin high silicon steel sheet has been proposed. One of the methods is metal solidification (rapid solidification) for producing thin high silicon steel sheet directly from melting by casting as disclosed in Japanese Patent Publication No. 60-32705. As another method, a special rolling rolling method disclosed in Japanese Patent Publication No. 3-80846 is applied, and another method is disclosed in Japanese Patent Publication No. 2-60041, which is supplied by rolling rolling.低) There is a siliconizing method for reinforcing silicon in silicon steel sheet. Of these methods, the siliconization method has already been used conventionally.

High silicon steel sheets produced by the above methods need to be punched, sheared and bent before being applied to electric motors and transformers. However, the high silicon steel sheet has a problem of brittleness which causes cracks and chips at punched or sheared corners, and there are many problems that may occur during bending. Therefore, various methods have been proposed for the purpose of improving the processing method of high silicon steel sheet.

In Japanese Patent Publication No. 61-15136, to have a columnar crystal grown vertically on the surface of a thin steel sheet by adjusting the crystal size in the range of 1-100 μm and substantially removing the ordered lattice. A method for obtaining a high silicon steel sheet having excellent workability and magnetism by controlling coysta grains is disclosed.

Japanese Laid-Open Patent Publication No. 62-270723 discloses a method of manufacturing a high silicon steel sheet having high workability by molding steel having a rolled rolled texture into a product shape produced by annealing.

In Japanese Unexamined Patent Publication No. 4-165050, a high silicon grain-oriented steel sheet having high processability by adding Mn and increasing the crystal orientation in order to prevent the adverse effect of sulfur solid solution. How to obtain is public.

Nevertheless, the method disclosed in Japanese Patent Publication No. 61-15136 does not exhibit a target effect when the diameter of the crystal increases to 100 μm or more, and this method does not show a phase of aligned crystals for high silicon steel. It is necessary to adopt a quenching process, such as water quenching, at a high temperature of 900 ° C. or more to substantially remove). After all, this method faces difficulties in practical application.

The method of Japanese Patent Publication No. 62-270723 adopts a steel working having a rolled rolled texture and requires high temperature annealing after processing. Therefore, this method has a disadvantage in that a separate special process must be added to the manufacturing process of the transformer and the electric motor.

In the method of Japanese Patent Laid-Open No. 4-165050, it is required to use highly grain oriented steel, and it is difficult to obtain high orientation because an adhesive recrystallization using an inhibitor is unstable. In addition, this method has a drawback that cannot be applied to non-oriented silicon steel sheets.

An object of the present invention is to provide an electrical steel sheet having a high workability, in order to achieve this object, the present invention comprises a crystal grain and a Si containing a grain boundary (30 atomic% oxygen content) It provides an electrical steel sheet containing 4-10% by weight.

More preferably, the electrical steel sheet is 0.01 wt% or less of C, 4-10 wt% of Si, 0.5 wt% or less of Mn, 0.01 wt% or less of P, 0.01 wt% or less of S, Sol. It is composed of 0.2 wt% or less of Al, 0.01 wt% or less of N, 0.02 wt% or less of O, equilibrium with Fe and inevitably present impurities.

The present invention also provides an electrical steel sheet containing 4-10% by weight of (Si- + Al), including grain boundaries and grain boundaries containing 30 atomic% or less of oxygen.

More preferably, the electrical steel sheet is 0.01 wt% or less of C, 4-10 wt% of (Si + Al), 0.5 wt% or less of Mn, 0.01 wt% or less of P, 0.01 wt% or less of S, and 0.01 wt% of N. % Or less, O is 0.02% or less by weight, and is composed of impurities inevitably present with equilibrium.

In addition, the present invention provides an electrical steel sheet containing 4 to 10% by weight of Si containing grains and grains having an oxygen content of 30 atomic% or less and a sulfur content of 0.2 atomic% or less.

More preferably, the electrical steel sheet is 0.01 wt% or less of C, 4-10 wt% of Si, 0.5 wt% or less of Mn, 0.01 wt% or less of P, 0.01 wt% or less of S, and 0.2 wt% of Al solution. % Or less, N or 0.01% by weight or less, O or 0.02% by weight or less, and equilibrium with Fe inevitably present.

Furthermore, the present invention provides an electrical steel sheet containing 4-10 wt% of (Si + Al) containing grain boundaries having a grain size and an oxygen content of 30 atomic% or less and a sulfur content of 0.2 atomic% or less.

More preferably, the electrical steel sheet is 0.01 wt% or less of C, 4-10 wt% of (Si + Al), 0.5 wt% or less of Mn, 0.01 wt% or less of P, 0.01 wt% or less of S, and 0.01 wt% of N. Hereafter, O is made up of 0.02% by weight or less, and is composed of impurities inevitably present with the equilibrium Fe.

Since the mother phase of a high silicon steel sheet is inherently brittle, it has been thought that this plate cannot actually improve workability. In the meantime, the inventors have conducted a series of experiments aimed at improving the workability of high silicon steel sheet at various levels of oxygen concentrations and dewpoints in the final heat-treated air, and improving the workability of high silicon steel sheets. It has been found that there is a steel sheet showing a relatively high workability. Figure 1 shows the test results for the workability of the steel sheet. The degree of vacuum is changed during the test to change the oxygen concentration and dew point in the anneal air. The horizontal axis represents the degree of vacuum and the vertical axis represents the amount of bending of the specimen in the three-point bending test as an indicator of machinability (this test is to determine the maximum stroke before rupturing the specimen under the downward pressurization conditions shown in FIG. 5). . Annealing proceeds at 1,200 ° C. for 15 minutes. The test results show that the higher the degree of vacuum the better the processability.

(Preferred Example-1)

Test samples were inspected to clarify the fracture process of high silicon steel sheets and a close relationship between machining performance and fracture surface was found. Specifically, the high silicon steel sheet exhibiting poor workability exhibits many intergranular shapes at the fracture surface, and the steel sheet exhibiting excellent workability exhibits many cleavage at the fracture surfaces. High and low porosity samples were studied using auger electron spectroscopy to determine the oxygen content on the grain boundary surface, where the high process samples showed low oxygen content in the grain boundaries and crystallized in low processability samples. The oxygen content in the grain boundary was high.

Further investigation of the auger spectrum obtained from the test results reveals that there is a relationship between the workability and the oxygen content in the grain boundaries and processability, as well as the carbon content and workability in the grain boundaries. Since the conditions for adjusting the amount of carbon cannot be determined in the above-mentioned test, the change in the amount of carbon in the grain boundary is considered to be a phenomenon associated with the movement of grain boundary oxygen. However, the detailed process is unknown. In addition, it has been found that the change in the annealing temperature makes it easy to adjust the diameter of the crystal and greatly change the processability.

As a result, the present inventors found that the workability of a high silicon steel sheet, which originally considered bad workability, actually has a very high correlation with the grain boundary characteristics, and that a high silicon steel sheet having excellent workability is obtained by adjusting the grain boundaries. Found.

The invention will be elucidated in more detail as the preferred range of each element.

Carbon is a factor that inhibits soft magnetic properties. When the carbon content exceeds 0.01% by weight, the soft magnetic properties deteriorate with time, which is called age degrading. In order to prevent such a defect, it is preferable to make carbon content into 0.01 weight% or less.

Silicon containing approximately 6.5% makes magnetostriction zero and exhibits the softest magnetism. When Si content is 4 weight% or less, a silicon steel plate does not show a desired magnetism. When the Si content exceeds 10% by weight, the saturation flux density significantly decreases. Therefore, the Si content is specified in the range of 4-10% by weight. Some Si may also be replaced with Al. In that case, the total amount of Si + Al needs to be specified. If the total amount of Si + Al is 4% by weight or less, the magnetism aimed at in the present invention cannot be achieved, and the workability of the steel sheet does not cause any particular problem. When the Si content exceeds 10% by weight 5, the saturation magnetic flux density decreases significantly. As a result, when a part of Si is replaced by Al, the total amount of Si + Al is specified in the range of 4-10% by weight.

Manganese combines with S to form MnS to improve hot workability in the slab stage. However, when the Mn content exceeds 0.5% by weight, the decrease in the saturation magnetic flux density is significant, which is undesirable. Therefore, the Mn content is preferably 0.5% by weight or less.

Since phosphorus is a soft magnetic reducing element, it is desirable to reduce the content as much as possible. Since the P content of 0.01% by weight or less does not adversely affect and is economically preferable, the P content is preferably limited to 0.01% by weight or less. Sulfur is a factor that increases brittleness and reduces soft magnetism during the hot rolling step. As a result, the content should be reduced as much as possible. Since the S content of 0.01% by weight or less does not actually adversely affect and is economically profitable, the S content is preferably 0.01% by weight or less.

Aluminum had the function of cleaning steel by removing oxygen, and had the function of increasing electrical resistance in the magnetic surface. In steels containing 4-10% by weight of Si, magnetic improvement is performed by Si and Al is believed to only perform oxygen removal. Therefore, the Al solution content is preferably limited to 0.2% by weight or less. On the other hand, when a part of Si is replaced with Al, the total amount of Si + Al is specified in the range of 4-10% by weight as described above.

Nitrogen is a factor that reduces soft magnetism and causes magnetic age change, and therefore its content should be reduced as much as possible. The N content of 0.01% by weight or less is preferably 0.01% by weight or less because N content of 0.01% by weight or less does not actually adversely affect and is economically beneficial.

Oxygen is a factor that reduces soft magnetism and its content should be as low as possible. As will be described later, the most important element in the present invention is the oxygen content in the grain boundary, and the oxygen content represents the total oxygen content in both the grain boundary and the inside of the crystal. The present invention provides excellent processability by adjusting the oxygen content in the grain boundaries inevitably present in the steel sheet, which will be described later. When the oxygen content in the steel sheet exceeds 0.02% by weight, oxygen is present at both the inside of the crystal and the grain boundary under all heat treatment conditions, and in that state, it is difficult to reduce the oxygen content in the grain boundary to 30 atomic% or less. In other words, it is possible to selectively adjust the oxygen presence region (inside the crystal or in the grain boundary) only when the oxygen content is 0.02% by weight or less. Therefore, O content is limited to 0.02 weight% or less. On the other hand, the lower limit of the oxygen content is not clearly defined. A simple reduction in the O content does not cause a decrease in the oxygen concentration at the grain boundaries. However, if oxygen is excessively reduced, the production cost is increased. After all, for economic reasons it is not desirable to reduce the oxygen content to less than 0.0005% by weight.

In addition to the above-mentioned elements, steel impurities include Cr, Ni, Cu, Sn and Mo. These elements, contained about 0.03% by weight each, do not affect the effect of the present invention.

The O content in the grain boundaries of the steel of the present invention (the oxygen content fractionated in the grain boundaries in the element) is required to be 30 atomic% or less. This is the most important condition of the present invention. Oxygen content in the grain boundary means oxygen content in the urea divided within the grain boundary. Generally, Auger electroscopy is used to determine the oxygen content. Depending on the spectrometer, the specimens are ruptured in a vacuum chamber kept below 1 x (1/10 ⁹ ) Torr, and the Auger Electron Spectrometer is an intergranular fractured surface that is not contaminated by atmospheric air. Applied to observe. By this method, elemental analysis on the fracture surface of the clean grain boundary is performed.

The following is a common method of determining elements using Auger electron spectroscopy (see Kyoritsu Shuppan, 1989, "Practical Auger Electron Spectrocopy for user"). When urea determination is performed on a material surface, the measured auger electron intensity (this is obtained by the difference in energy and expressed as the peak height) and the auger electrons for each element Relative sensitivity, an indicator of radioactivity, is replaced by

[X] (atomic%) = {(X / x) / [(A / a) + (B / b) + (C / c) +. + (X / x) +... ]} × 100

Wherein A, B, C, and D... Represents the Auger electron strength of each element.

The energy location for measuring auger electron strength is defined for each element. For example, Fe uses the peak at the highest energy side of the three LMM transitions, O uses the KLL transition, C uses the KLL transition, and S uses the LVV transition. Relative sensitivity is already known for the transition of each element and these values are described in the literature cited above. Depending on the Phai unit, this value is 0.220 for Fe, 0.140 for C, 0.400 for O, and 0.75 for S. In this way, Auger electron beams have been widely used to determine the amount of each element. As described above, the inventors used this method to determine grain boundaries on each material of good workability and poor workability, performed elemental analysis at grain boundaries, and the O content in the grain boundaries was very much related to the ease of processing. Found a close relationship.

As an example, FIG. 2 shows the relationship between the amount of oxygen and the elongation at grain boundaries determined by Auger electron spectroscopy using a high silicon steel sheet composed of the chemical composition shown in Table 1 and having a plate of 0.1 mm thickness. According to FIG. 2, the steel sheet shows that the smaller the amount of oxygen in the grain boundary, the better the elongation. The showing of more than 3% elongation in the test steel causes plastic deformation. In addition, when the ruptured surface is observed by scanning electron microscopy, it can be seen that the steel sheet having excellent elongation shows cleavage failure rather than grain boundary fracture, and the steel sheet with low elongation shows grain boundary fracture. It can be seen that there is a tendency towards. It has conventionally been accepted that high silicon steel sheets of this type do not cause plastic deformation. However, it has been found that plastic deformation occurs when the amount of oxygen in the grain boundary is 30 atom% or less. In conclusion, the present invention limits the amount of oxygen to 30 atomic% or less. It can be seen from FIG. 2 that better processability is provided when the amount of oxygen in the grain boundary is 15 atomic% or less.

Table 1. (wt%)]

In addition to the oxygen content effects in the grain boundaries described above, it has been found that carbon in grain boundaries clearly plays an important role in processability, as described above. Specifically, even when the oxygen content range in the grain boundary is 30 atom% or less, the elongation is further increased when the amount of carbon in the grain boundary (the amount of carbon in the elements fractionated in the grain boundary) is 0.5 atom% or more. Improved and processability improved. Although the process is not yet known in detail, the carbon in the grain boundary is thought to exert a pressing action on the grain boundary crack.

Therefore, in order to obtain good workability of the high silicon steel sheet, the oxygen limitation in the grain boundary needs to be cooperated by the carbon action in the grain boundary. In order to confirm this effect, the inventors prepared a grain boundary intensity parameter represented by the following equation from oxygen and carbon in the grain boundary and corresponded to the actual three point bending test results.

Grain boundary strength parameter = [C (284)] / [O (531)]

In this equation, C (284) and O (531) represent the signal strength determined by differentiating the energy and auger spectrum, and the numbers in parentheses indicate the energy at which the peaks of C and O are represented, respectively.

3 shows the relationship between grain boundary strength parameters and three points bending characteristid. According to this figure, the workability shown according to the three point bending characteristic is very closely related to the grain boundary strength parameter described above. In this respect, when the amount of bending in the three-point bending test is 5 mm or more, it is judged that the workability is improved compared with the materials of the prior art, and thus the numerical value (C grain boundary strength parameter) of (C / Fe) / (O / Fe) When) is 0.5 or more, workability is improved. In the three-point bend test, it is estimated that the workability is greatly improved when the bending amount is 10 mm or more. Therefore, the grain boundary strength parameter is preferably limited to 1.0 or more.

Considering the C content in the grain boundary, when the O content in the grain boundary exceeds 30 atomic%, there is no effect of improving workability, and when the O content in the grain boundary is less than 30 atomic%, the C in the grain boundary If the content is 0.5 atomic% or more, the grain boundary strength increases, and workability is improved. As a result, the C content in the grain boundary is preferably limited to 0.5 atomic percent or more. For further improved workability, the C content in the grain boundary is preferably limited to 0.8 atomic percent or more.

In addition to these developments on the effects of oxygen and carbon in grain boundaries, it has been found that the diameter of the crystals affects the workability and that the workability improves when the average diameter of the crystals appearing from the steel sheet surface is 2,0 mm or less. . The reason for this effect is that when the O and C contents in the grain boundaries are limited to strengthen the grain boundaries, the strength within the crystals decreases relatively to facilitate cracking across the crystals, so that the excess crystal diameter makes the workability It is assumed to reduce. In the high silicon steel sheet (thickness: 0.1 mm) having the chemical composition listed in Table 1, the surface of the plate was tested by the high silicon steel sheet with O content in the grain boundary of about 5 atomic% and C content in the grain boundary of about 1 atomic%. The relationship between the average crystal diameter shown in Fig. 3 and the three point bending characteristics under various crystal diameters is discussed. This result is shown in FIG. 4, according to this drawing, the workability is improved by specifying an average crystal diameter of 2.0 mm or less.

The high silicon steel sheet adopted in the above experiment has a very good grain growth to form granulated crystals by heat treatment and tends to form a bamboo structure in which grains pass in the thickness direction of the plate. Nevertheless, as described above, the crystal diameter of the steel sheet is preferably 2.0 mm or less from the viewpoint of workability, and the steel sheet needs to be adjusted to a controlled heat treatment condition so as not to produce excessive granulated crystals. When the grains of the high silicon steel sheet formed a bamboo structure, the inventors found that the grain growth stopped at a diameter approximately 3-4 times the thickness of the steel sheet. As a result, in order to maintain the diameter of the crystal at 2.0 mm or less, the plate thickness is preferably selected to be 0.5 m or less. In this case, it is not necessary to consider the heat treatment conditions.

For these reasons, the preferred thickness of the steel sheet is 0,5 mm or less.

The effect of the present invention is obtained irrespective of the grain orientation distribution in the silicon steel sheet. Therefore, the present invention is not limited to the oriented silicon steel sheet or the non-oriented silicon steel sheet. Ordinary electrical steel sheet is coated with an insulating film, the present invention is independent of the presence or absence of the coating film.

The present invention is not limited to the method for producing a thin plate, and the present invention can be applied to a high silicon steel sheet produced by a special rolling rolling method, the above-mentioned siliconization method and other titration methods.

(Example)

(Example 1)

Steels with the compositions listed in Table 1 are melted, hot rolled and warm rolled into plates with a thickness of 0,1 mm. The plate is heat treated (final annealed) at 1200 ° C. for 15 minutes under various reducing pressures in the range of 5 Torr-1 × (1/10) ⁵ Torr. The ambient temperature in the laboratory is 27 ° C and the humidity is 80%. The specimen obtained here was tested by the three point bending device shown in FIG. 5 to determine the maximum pressing stroke before rupture. The remaining specimens were placed in an Auger electron spectrometer to rupture at a vacuum pressure of 8 x (1/10) ¹⁰ Torr. The fracture surface of each specimen is observed and the composition within the grain boundaries is analyzed. Analysis of the composition showed that the C content in the grain boundaries of all specimens was 0.5 atomic% or less. The average diameter of the crystals in all specimens is approximately 0.19 nm. Figure 6 shows the effect of O content in grain boundaries at constant bending in the three point bending test. The figure shows that decreasing the O content in the grain boundary clearly increases the bending amount, which means that the lower the O content in the grain boundary, the better the workability.

(Example 2)

For steel with the same composition as in Example 1, work treatment is carried out under various atmospheric conditions. The specimen thus prepared is subjected to a three point bending test. Samples for auger electron spectroscopy are supplied to the rest of the three-point bend test specimen. These samples rupture under vacuum conditions in an Auger electron spectrometer to determine the O and C composition within the grain boundaries.

The relationship between O content and C content and three-point bending characteristics in grain boundaries was studied. For specimens with an O content in the grain boundary of 30 atomic percent or more, there is no relationship between the O content, the C content and the bend amount in the grain boundary. However, for specimens with O content below 30 atomic percent, there is a clear relationship between them. 7 shows the relationship between the three-point bending characteristics and the C content in the grain boundary for specimens (average diameter 0.19 mm of crystal) having an O content of about 10 atomic percent in the grain boundary. According to this figure, the steel containing C to some extent in the grain boundary clearly improves the workability.

(Example 3)

The specimens tested in Examples 1 and 2 were shear tested using a shear tester with a clearance of 3 μm. The shear plane was observed with an optical microscope (× 200) to count the number of defects such as cracks per 10 cm of shear length. The results are shown in FIG. 8 with respect to O content in grain boundaries. This figure shows the same trend as the results of the three point bending test, which clearly shows the effect of limiting the oxygen content in the grain boundary.

(Example 4)

The steel with the composition reported in Table 2 is melted, hot rolled and warm rolled to form a 0.35 mm thick plate. The plate was heat-treated for 15 minutes at 1,200 ° C in a nitrogen atmosphere with various dew point ranges from 0-70 ° C to prepare several steel specimens with different oxygen content in the grain boundaries. These specimens are tested with a tensile tester (tensometer using JIS 5 class specimen). The O content in the grain boundaries of each specimen was determined according to the method used in Example 1 and the relationship between the elongation measured in the tensile tester and the O content in the grain boundaries was studied. For all specimens, the C content in the grain boundary is in the range of 0.2-0.8 atomic percent and the average diameter of the crystal is in the range of 1-1.4 mm. This result is shown in FIG. This figure shows that the steel sheet having a low O content in grain boundaries shows a larger elongation.

Table 2. (wt%)]

(Example 5)

Steels with the compositions reported in Table 3 are melted, hot rolled and warm rolled to obtain plates of various thicknesses. These plates were pressurized to 1 × (1/10) ⁴ Torr pressure and subjected to final annealing at various annealing temperatures in the range of 800-1,300 ° C. for 15 minutes to produce specimens with various plate thicknesses and average diameters of crystals. The remaining specimens were placed on auger electron spectrometer to determine O content and C content in grain boundaries. Auger electron spectroscopy shows that the O content in the grain boundaries of all specimens is in the range of 5 ± 2 atomic% and the C content in the grain boundaries is 0.8-2 atomic%. Table 4 shows the average diameter of the crystals and the three-point bend test results for each specimen. This table shows that the larger the average crystal diameter, the overall decrease in bending characteristics. In particular, when the average diameter of the crystal exceeds 2.0 mm, the bending property is greatly reduced. For specimens with a thickness exceeding 0.5 mm, the bending characteristics are deteriorated even when the average crystal diameter is 2.0 mm or less.

Table 3. (wt%)]

TABLE 4

(Example 6)

A silicon steel sheet (0.3 mm thick) having the chemical composition listed in Table 5 was prepared. This plate was subjected to siliconization diffusion treatment to produce 6.5% silicon steel sheet. Siliconization was carried out using heterogeneous mixed gas as carrier gas. That is, one was mixed with high purity nitrogen gas (dew point: -70 ° C) and the other was mixed with normal nitrogen gas (dew point: -30 ° C). The specimens obtained were subjected to three-point bend testing and the remaining specimens were analyzed by Auger electron spectroscopy to determine the O content in the grain boundaries. All specimens showed that the C content in the grain boundary was in the range of 0.2-1.2 atomic percent and the average diameter of the crystal was about 0.89 mm. This result is summarized in FIG. This figure shows that limiting the O content in the grain boundaries is effective in improving the workability even for high silicon steel sheets obtained by the Si diffusion-infiltration process.

[Table 5. (wt%)]

(Preferred Example-2)

The present inventors observed the grain boundaries in detail as a detailed study and found other factors related to workability besides the O content in the grain boundaries. Specifically, the present inventors used samples having a constant O content in the grain boundaries to investigate the effects of various elements fractionated in the grain boundaries on machinability, and the effect of sulfur on the machinability separately from the oxygen effect. We found that we have FIG. 11 shows the relationship between the three point bending characteristic (test piece pressurized stroke in the three point bending tester described above) and the S content detected at the grain boundaries using an Auger electron spectrometer. The specimens used here were heat treated in an N ₂ atmosphere containing 6.49% by weight of Si, 0.005% by weight of Mn, 0.0015% by weight of S and 0.0022% by weight of O, 0.35 mm thick, and 0.1 volume% of H ₂ S. It became. The specimens showed almost the same total amount of S within the range of analytical error after heat treatment. The O content in the grain boundaries determined by Auger electron spectrometer ranged from 3-5 atomic percent for all tested specimens. According to FIG. 11, the workability is closely related to the S content in the grain boundary, which indicates that S in the grain boundary decreases the workability. The details of the close relationship between S content and machinability in grain boundaries have not been elucidated, but the fact that grain boundaries do not contain elements such as Mn to form sulfur is probably S in the form of a solid solution. Imply that it exists within the grain boundary.

Control of the crystal size is easily controlled by changing the annealing temperature. However, the tests described above show that the change in annealing temperature greatly increases the workability.

As described above, the present inventors have found that the workability of a high silicon steel sheet, which was originally considered to be low in workability, has a very close correlation with the grain boundary characteristics, and can adjust such properties to provide a high silicon steel sheet having excellent workability.

As an example, a high silicon steel sheet having a thickness of 0.1 mm and having the composition reported in Table 6 and having almost the same oxygen content in the grain boundaries determined by the Auger electron spectrometer is measured in the grain boundaries measured by the Auger electron spectrometer. It was adopted to determine the relationship between S content and elongation. This result is shown in FIG. This figure shows that specimens with less S content in grain boundaries exhibit high elongation. During the test, specimens with an elongation of 3% or more undergo plastic deformation. Scanning of the fracture surface by scanning electron microscopy shows that the specimens with higher elongation provide more cleavage fracture rather than the grain boundary, and that the steel sheet with the lower elongation is oriented toward the grain boundary. It turned out. It is known that plastic deformation of this type of high silicon steel sheet does not occur conventionally. However, it was found that plastic deformation occurs when the S content in the grain boundary is 0.2 atom% or less. As a result, the present invention specifies the S content to 0.2 atomic% or less.

Table 5

As described above, the present invention needs to specify not only the S content in the grain boundary but also the O content in the grain boundary (O content in elements fractionated in the grain boundary) to 30 atomic percent or less. Do. In other words, the effect of reducing the S content in the grain boundary is required only when the oxygen content in the grain boundary is sufficiently low. For this purpose, the oxygen content in the grain boundary needs to be reduced to 30 atomic% or less. Figure 13 shows the relationship between the three-point bending characteristic (pressurization stroke of the specimen in the three-point bending characteristic tester described above) and the S content in the grain boundary. The specimen used herein has a composition of 6.66 wt% Si, 0.001 wt% S, 0.001 wt% Al solution and 0.0025 wt% O, and has a thickness of 0.35 mm, and includes different O contents in the grain boundaries. . This figure shows the correlation between the S content in the grain boundary and the three-point bending characteristics when the O content in the grain boundary is 0.3 atomic% or less, and the S in the grain boundary when the O content in the grain boundary is 30 atomic% or more. It is shown that even if the content is less than 0.2 atomic%, the three point bending characteristic hardly changes. Therefore, the present invention limits the O content in the grain boundary to 30 atomic% or less, most preferably 15 atomic% or less.

In addition to the effect of S content and O content in grain boundaries, it has been found that the crystal diameter affects the workability. It has been found that when the average crystal diameter seen from the steel sheet surface is 2.0 mm or less, workability is further improved. The cause of this effect is thought to be that the strength in the crystal is relatively reduced in response to the increase in grain boundary strength due to the S effect in the crystal threshold, which increases the cracks across the crystal and excessive crystal diameter reduces the workability. High-silicon steel with the composition listed in Table 1 contains high silicon containing about 5 atomic% O in the grain boundary, about 1 atomic% C in the grain boundary and about 0.05 atomic% S in the grain boundary The steel plates were tested to determine the relationship between the average crystal diameters seen from the steel surface and the three point bending characteristics under various crystal diameters. This decision is shown in FIG. According to this figure, workability is improved by limiting the crystal mean diameter to 2.0 mm or less.

The high silicon steel sheets used in the above experiments have very good grain growth to form granulated crystals, and tend to form bamboo structures in which the grains penetrate in the thickness direction of the plate. Nevertheless, as mentioned above, the crystal diameter of the steel is preferably 2.0 mm or less in terms of workability, and the steel needs to be adjusted to select heat treatment conditions so as not to form excessive granulated crystals. When the grain structure of the high silicon steel sheet formed a bamboo structure, the inventors found that the grain growth actually stopped at a diameter of about 3-4 times the thickness of the steel sheet. Finally, in order to maintain a crystal diameter of 2.0 mm or less, the plate thickness is preferably selected to 0.5 mm or less. In this case, it is not necessary to consider the heat treatment conditions. For this reason, the preferable thickness of steel is good to be 0.5 mm or less.

The effect of the present invention is obtained regardless of the crystal directional distribution in the silicon steel sheet. Therefore, this invention is not limited to either a oriented silicon steel plate or a non-oriented silicon steel plate. Usually electrical steel sheet is coated by an insulating film, the present invention is irrespective of the presence or absence of the coating film.

The present invention is not limited to the method of providing a thin plate, and the present invention can be applied to a high silicon steel sheet produced by a special rolling rolling method.

(Example 7)

High silicon steel sheets (thickness: 0.1 mm) with the compositions listed in Table 7 are heat-treated (final annealed) at 1,200 ° C for 15 minutes at different pressures in the range of 5 Torr-1 x (1/10 ₅ ) Torr. . The ambient temperature in the laboratory is 27 ° C and the humidity is 80%. The specimens thus obtained were tested by a three point bending device to determine the highest pressure stroke before rupture. The residue of each specimen was placed in an Auger electron spectrometer to break at a vacuum of 8 x (1/10) Torr. The fracture surface of each specimen was examined and the composition within the grain boundary was analyzed. Based on the compositional analysis by Auger electron spectrometer, specimens with O content in the grain boundary of 3-5 atomic%, C content in the grain boundary of about 0.3 atomic% and crystal mean diameter of about 0.2 mm were selected. The effect of S content on grain boundaries with the amount of bending in the three-point bending test was determined. Figure 15 shows this result. This figure shows that the bending amount is markedly increased when the S content in the grain boundary decreases, which shows that the lower the S content in the grain boundary, the better the workability.

[Table 7. (Atom%)]

(Example 8)

High-silicon steel sheets with different thicknesses with the compositions listed in Table 8 were pressurized to a pressure of 1 × (1/10 ⁴ ) Torr and finally annealed for 15 minutes at various annealing temperatures in the range 800-1,300 ° C. to each other. Specimens were prepared with different plate thicknesses and with different crystal mean diameters. The specimens thus obtained are tested by a three point bending device. Residues of each specimen were placed in an Auger electron spectrometer to determine O content, C content and S content in grain boundaries. Auger electron spectroscopy shows that all of these specimens ranged from 8 ± 2 atomic% in the grain boundary and 0.8 to 2 atomic% in the grain boundary. Table 4 shows the average crystal diameter and three-point bending test results for each specimen. This table shows that when the crystal mean diameter is larger than 2.0 mm, the bending property is significantly reduced. For specimens with a thickness of more than 0.5 mm, bending characteristics are inferior even if the average crystal diameter is 2.0 mm or less.

Table 8. (wt%)]

(Example 9)

A high silicon steel sheet (thickness: 0.3 mm) having the composition recorded in Table 9 was prepared. The plates were siliconized-diffused (Si volcanic and infiltrated) at 1,200 ° C. Siliconization was carried out using a heterogeneous mixed gas as a carrier gas: one is SiCl ₄ mixed with a high purity nitrogen gas (dew point: -70 ° C) and the other is a normal nitrogen gas (dew point: -30 ° C). ) And SiC1 ₄ . The specimens obtained were subjected to a three-point bend test and the remaining specimens were analyzed by Auger electron spectrometer to determine O content, C content and S content in grain boundaries. Among the tested specimens, the O content in the grain boundary was about 10 atomic%, the C content in the grain boundary was about 0.7 atomic% and the crystal mean diameter was about 0.80 mm, so that the S content and three points in the grain boundary were selected. The relationship between the amount of bending in the bending test was determined. This result is summarized in FIG. This figure shows that limiting the S content in the grain boundaries is effective in improving the workability for high silicon steel sheets obtained by the Si diffusion-infiltration method.

TABLE 9. (wt%)

(Example 10)

0.35 mm thick steel plates with the compositions reported in Table 10 were prepared by rolling rolling and were subjected to various nitrogen atmospheres with dew point in the range of -10- -70 ° C and H ₂ S content in the range of 0-0.1% by volume. The plate was heat treated at 1,200 ° C. for 15 minutes. The specimens thus prepared were tested by a three-point bending device, and the remaining specimens were analyzed by Auger electron spectroscopy to determine the O and S content in the grain boundary, and the specimens in the grain boundary according to the bending amount in the three point bending test. O content and S content effects were determined. The results are well summarized in FIG. This figure shows that the grain boundary O content of 30 atomic% or less imparts a relationship between the grain boundary S content and the bending amount. If the grain boundary O content is 30 atomic% or less, the S content in the grain boundary is 0.2 atomic% or less. Although reduced to, it hardly changes the three-point bending characteristic.

TABLE 10 (wt%)

Claims (20)

Crystal grains and grain boundaries having an oxygen content of 30 atomic% or less include C 0.01% by weight, Si 4-10% by weight, Mn 0.5% by weight or less, P 0.01% by weight or less, and S 0.01% by weight. Hereinafter, an Al steel is 0 2% by weight or less, N is 0.01% by weight or less, O is 0.02% by weight or less, and the electrical steel sheet, characterized in that it is composed of impurities inevitably contained in the equilibrium state and has a thickness of 0.5 mm or less . The electrical steel sheet of claim 1, wherein the oxygen content is in the range of 0.0005-0.02% by weight. The electrical steel sheet according to claim 1, wherein the oxygen content in the grain boundary is 15 atomic% or less. The electrical steel sheet of claim 1, wherein the grain boundaries comprise at least 0.5 atomic percent carbon. The electrical steel sheet of claim 1, wherein the grain boundaries comprise at least 0.8 atomic percent carbon. The electrical steel sheet according to claim 1, wherein the crystal has an average diameter of 2 mm or less. Including grain boundaries with grains and oxygen content of 30 atomic% or less, C is 0.01% by weight or less, (Si + Al) is 4-10% by weight, Mn is 0.5% by weight or less, P is 0.01% by weight or less, and S is 0.01% by weight. An electrical steel sheet comprising at most%, at most 0.01% by weight, at most 0.02% by weight of O, and impurities inevitably contained in equilibrium with Fe, and having a thickness of 0.5 mm or less. The electrical steel sheet according to claim 7, wherein the oxygen content is in the range of 0.0005-0,02% by weight. 8. The electrical steel sheet according to claim 7, wherein the oxygen content in the grain boundary is 15 atomic% or less. 8. The electrical steel sheet of claim 7, wherein the grain boundary comprises at least 0.5 atomic percent carbon. 8. The electrical steel sheet of claim 7, wherein the grain boundary comprises at least 0.8 atomic percent carbon. The electrical steel sheet according to claim 7, wherein the average diameter of the crystals is 2 mm or less. It contains less than 0.01% by weight of C, 4-10% by weight of Si, 0.5% by weight or less of Mn, and 0.01% by weight of P, including grain boundaries with grains and oxygen content of 30 atom% or less and sulfur content of 0.2 atom% or less. Or less than 0.01 wt% of S, 0.2 wt% or less of Al solution, 0.01 wt% or less of N, 0.02 wt% or less of O, and impurities inevitably contained in equilibrium with a thickness of 0.5 mm or less Electrical steel sheet, characterized in that. The electrical steel sheet according to claim 13, wherein the oxygen content is in the range of 0.0005-0.02 wt%. The electrical steel sheet according to claim 13, wherein the oxygen content in the grain boundary is 15 atomic% or less. The electrical steel sheet according to claim 13, wherein the crystals have an average diameter of 2 mm or less. It contains grains and grains with an oxygen content of 30 atomic% or less and a sulfur content of 0.2 atomic% or less, containing 0.01 wt% or less of C, 4-10 wt% of (Si + Al), 0.5 wt% or less of Mn, and P 0.01 It is composed of a weight% or less, S is 0.01% by weight or less, N is 0.01% by weight or less, O is 0.02% by weight or less, and impurities inevitably contained in an equilibrium state and have a thickness of 0.2 mm or less. Electrical steel sheet The electrical steel sheet according to claim 17, wherein the oxygen content is in the range of 0.0005-0.02 wt%. 18. The electrical steel sheet according to claim 17, wherein the oxygen content in the grain boundary is 15 atomic% or less. 18. The electrical steel sheet according to claim 17, wherein the crystal has an average diameter of 2 mm or less.