JP5664287B2 - Method for producing high silicon steel sheet - Google Patents

Description

  The present invention relates to a method for producing a high silicon steel sheet by a siliconization treatment method.

High-silicon steel plates are frequently used for iron cores such as transformers and motors because they have excellent high-frequency magnetic properties such as low iron loss and high magnetic permeability. In particular, it is known that when the Si concentration is 6.5 mass%, the magnetostriction is 0, and the high-frequency magnetic characteristics such as a peak of maximum permeability are exhibited. Conventionally, as a method for producing such a high silicon steel sheet, a so-called siliconization treatment method is known in which Si is permeated and diffused from the steel sheet surface after the low silicon steel is rolled into a thin sheet (for example, Patent Document 1). .
In general, SiCl ₄ is used as a raw material gas for supplying Si in the siliconizing treatment of the steel sheet, and this SiCl ₄ reacts with the steel sheet (SiCl ₄ + 5Fe → Fe ₃ Si + 2FeCl ₂ ) and Si permeates the steel sheet surface layer. Thus Si penetrated into the steel sheet surface layer is diffused in the thickness direction by soaking the steel sheet in a non-oxidizing gas atmosphere containing no SiCl _4.

When continuously siliciding a steel sheet using SiCl ₄ as a raw material gas, the oxygen content (water and oxygen) contained in the silicidation atmosphere reacts with the SiCl ₄ gas to produce silica, and this silica is generated in the furnace. There exists a problem of adhering to the part which contacts steel plates, such as a hearth roll, and generating a pushing rod in a steel plate. In addition, the high silicon steel sheet produced by the siliconization treatment has a problem that the surface and grain boundaries of the steel sheet are oxidized by moisture and oxygen in the atmosphere of the siliconization treatment, and the workability of the steel sheet is significantly deteriorated by this oxidation.
In order to avoid such problems due to moisture and oxygen contained in the siliconizing atmosphere, an appropriate amount of C is added to the raw steel plate in advance, and this C is allowed to react with the oxygen content in the atmosphere (ie, steel plate). By using this decarburization reaction), a method of reducing the moisture and oxygen concentration existing near the steel plate surface where the silicification reaction occurs to the limit is considered, and a method for producing a high silicon steel plate using this method is disclosed in Patent Literature 2 proposed.

JP-A-62-227078 Japanese Patent Application Laid-Open No. 08-209325

  However, when the raw steel plate to which an appropriate amount of C is added as in the method of Patent Document 2, the decarburization reaction of the steel plate does not proceed as expected, and the steel plate after the siliconization treatment (product) C) remains in a high concentration, and this high concentration of C has a problem of adversely affecting the magnetic properties of the steel sheet (product). Specifically, when the C concentration of the steel plate after the siliconization treatment is high, magnetic aging occurs and the iron loss deteriorates with time. In particular, a high silicon steel sheet is used for high frequency applications, so that deterioration of magnetic characteristics over time causes problems such as breakage of high frequency equipment and abnormal temperature rise, which is a serious problem in practice.

The problem of magnetic aging of such a high silicon steel sheet is essentially that the C concentration of the steel sheet (product) after siliconization exceeds a certain level regardless of whether or not the method of Patent Document 2 is performed. There is a risk of it.
Accordingly, an object of the present invention is to provide a production method capable of stably producing a high silicon steel sheet that does not cause deterioration with time of iron loss due to magnetic aging by a siliconization method.

  In order to solve the above-mentioned problems, the present inventors have repeatedly studied the factors that hinder the reaction (decarburization reaction of the steel sheet) between C in the steel sheet and the oxygen content in the atmosphere in the siliconization treatment, and countermeasures thereof. As a result, (i) S (sulfur) in the steel sheet hinders the movement of C during the silicidation treatment and inhibits the decarburization reaction of the steel sheet (that is, C does not escape well from the steel sheet). (Ii) Therefore, by optimizing the relationship between the S concentration and the C concentration of the material steel plate, there is no problem with the C concentration of the steel plate after the siliconization treatment. It has been found that a high silicon steel sheet can be stably produced without causing deterioration with time of iron loss due to magnetic aging.

The present invention has been made on the basis of such findings and has the following gist.
That is, by subjecting the material steel plate to a siliconization treatment, the average Si concentration in the plate thickness direction is 4.0 to 7.0 mass%, and the Si concentration (mass%) of the plate surface layer portion and the Si concentration of the plate thickness center portion In the method for producing a high silicon steel sheet satisfying 2.0 ≦ ΔSi / t ≦ 40.0, in which the deviation ΔSi (mass%) from (mass%) is related to the plate thickness t (mm),
The carbon concentration of the material steel plate is made higher than the target C concentration of the steel plate after the siliconization treatment, and the decarburization reaction of the material steel plate is caused by oxygen contained in the atmosphere of the siliconization treatment. It is a method of manufacturing a high silicon steel sheet with a target C concentration by performing processing,
A steel plate having a C concentration of more than 40 mass ppm and a C concentration [C] (mass ppm) and an S concentration [S] (mass ppm) satisfying any of the following (a) to (c): A method for producing a high silicon steel sheet, characterized in that the C concentration of the high silicon steel sheet after siliconization is 50 mass ppm or less .
(A) [S] ≦ 30, [C] ≦ 110
(B) 30 <[S] <100, [C] ≦ −0.857 [S] +135.71
(C) 100 ≦ [S], [C] ≦ 50

  According to the manufacturing method of the present invention, a high silicon steel plate that does not cause deterioration with time of iron loss due to magnetic aging can be stably manufactured by a siliconization method.

Explanatory drawing showing a continuous siliconization treatment line for steel sheets A graph showing the magnetic properties (degree of deterioration of iron loss with time) of the high-silicon steel plate manufactured in Example 1 in relation to the C concentration and S concentration of the raw steel plate. A graph showing the magnetic characteristics (degree of deterioration of iron loss with time) of the high silicon steel plate manufactured in Example 2 in relation to the C concentration and S concentration of the raw steel plate.

In the present invention, by subjecting the raw steel plate to a siliconization treatment, the average Si concentration in the plate thickness direction is 4.0 to 7.0 mass%, and the Si concentration (mass%) of the plate surface layer portion and the plate thickness center portion A high silicon steel sheet satisfying 2.0 ≦ ΔSi / t ≦ 40.0 is manufactured in relation to the deviation ΔSi (mass%) from the Si concentration (mass%) and the plate thickness t (mm) of the steel sheet. Is the method.
Here, if the average Si concentration in the plate thickness direction of the steel plate to be produced is less than 4.0 mass%, sufficient high-frequency magnetic properties as a high silicon steel plate cannot be obtained, whereas if it exceeds 7.0 mass%, embrittlement occurs. A tendency is recognized, workability falls, and processing, such as a cutting board process, may become difficult.

In order to produce a high silicon steel sheet by continuously siliconizing the steel sheet, it is usually equipped with a heating zone, a siliconized treatment zone, a diffusion soaking zone, and a cooling zone as shown in FIG. A continuous siliconization line is used.
The material steel sheet has a Si concentration of less than 4 mass% (usually about 2.8 to 3.8 mass%), and after this material steel sheet is continuously heated to the treatment temperature in the heating zone, it reacts with SiCl _{4 in the} siliconization treatment zone. Si is infiltrated into the surface layer of the steel sheet, and then a continuous heat treatment for diffusing Si in the thickness direction in the diffusion soaking zone is followed by cooling in the cooling zone to form coiled high silicon. A steel plate is produced. Usually, in the siliconized zone, a processing gas having a SiCl ₄ concentration of about 5 to 35 mol% is supplied, and the steel sheet is processed at a temperature of about 1023 to 1200 ° C. in an atmosphere having a dew point of −30 ° C. or lower and an oxygen concentration of 10 ppm or lower. It is siliconized at temperature. In the diffusion soaking zone, heat treatment is performed at about 700 to 1250 ° C. in a non-oxidizing gas atmosphere containing no SiCl ₄ . The steel sheet immediately after the siliconization treatment has an extreme Si concentration gradient in which the steel sheet surface layer portion has a maximum Si concentration of 14.5 mass%, whereas the center thickness of the steel plate has substantially the same Si concentration as the material steel plate. However, this Si concentration gradient gradually changes in a uniform direction by diffusion heat treatment.

  As described above, in the diffusion soaking zone, Si permeated into the steel sheet surface layer by the siliconization treatment in the siliconization zone is diffused in the thickness direction, but depending on the time of this diffusion heat treatment, the degree of diffusion of Si, That is, the deviation ΔSi (mass%) between the Si concentration (mass%) in the surface portion of the plate and the Si concentration (mass%) in the central portion of the thickness differs. Although it takes a relatively long time to diffuse Si in the surface portion of the steel sheet substantially uniformly in the thickness direction by diffusion heat treatment, the present invention satisfies 2.0 ≦ ΔSi / t ≦ 40.0, which is the object of manufacture. The high silicon steel sheet is a high silicon steel sheet having a relatively short diffusion heat treatment time of about 0.1 to 5.0 minutes and a large Si concentration gradient in the thickness direction. The present invention has been made on the basis of knowledge about such a high silicon steel sheet that satisfies 2.0 ≦ ΔSi / t ≦ 40.0.

In the present invention, a steel plate having a C concentration [C] (mass ppm) and an S concentration [S] (mass ppm) satisfying any of the following (a) to (c) is used as the material steel plate.
(A) [S] ≦ 30, [C] ≦ 110
(B) 30 <[S] <100, [C] ≦ −0.857 [S] +135.71
(C) 100 ≦ [S], [C] ≦ 50
S (sulfur) in the steel sheet inhibits the decarburization reaction of the steel sheet by hindering the movement of C during the siliconizing treatment of the steel sheet, and the degree of inhibiting the decarburization reaction increases as the S concentration in the steel sheet increases. . Here, in the case of a high silicon steel plate satisfying 2.0 ≦ ΔSi / t ≦ 40.0, which is the object of manufacture of the present invention, the C concentration of the steel plate (product) after the siliconization treatment is 50 mass ppm. If exceeded, iron loss may deteriorate due to magnetic aging. As shown in the results of Examples (FIGS. 2 and 3) to be described later, by optimizing the C concentration and S concentration of the material steel plate to a relationship satisfying any of the above (a) to (c), The C concentration of the steel plate (product) after the siliconization treatment is 50 mass ppm or less, and deterioration of iron loss due to magnetic aging can be suppressed. That is, it is possible to manufacture a high silicon steel sheet that does not cause deterioration of iron loss with time due to magnetic aging.
Here, when the C concentration of the raw steel plate exceeds 110 mass ppm, it becomes difficult to set the C concentration of the steel plate to 50 mass ppm or less in a normal silicidation treatment. Therefore, the C concentration of the raw steel plate is 110 mass ppm or less. It is preferable. Moreover, since the method of the present invention utilizes the decarburization reaction of C in the raw steel plate as described above, it is preferable that the C concentration in the raw steel plate is 10 mass ppm or more, more desirably more than 40 mass ppm. .

Preferred conditions for the other components of the material steel plate are as follows.
If the content of Mn is less than 0.01 mass%, there is a risk of causing problems of hot brittleness and cold brittleness due to the solid solution S. On the other hand, if it exceeds 0.5 mass%, the steel sheet is hardened due to solid solution strengthening by Mn. Since there exists a possibility, 0.01-0.5 mass% of content of Mn is preferable.
If the Al content exceeds 1.0 mass%, the cold rollability may be deteriorated, so it is preferable to set the content to 1.0 mass% or less.
N is an element that deteriorates the magnetic properties. However, if it is 0.01 mass%, there is almost no influence. Therefore, N is preferably 0.01 mass% or less.
O is an element that deteriorates workability and magnetic properties, but if it is 0.01 mass% or less, there is almost no substantial influence, so it is preferably 0.01 mass% or less.
Usually, a raw steel plate is a thin steel plate obtained through hot rolling, pickling, and cold rolling, and generally has a thickness of about 0.03 to 0.5 mm from the viewpoint of magnetic properties and work assembly. .

In the production method of the present invention, the C concentration of the raw steel plate is made higher than the target C concentration of the steel plate after the siliconization treatment (high silicon steel plate), and the raw steel plate is removed by the oxygen content contained in the siliconization atmosphere. Although it is not limited to the method of performing the silicidation process of a raw steel plate while causing a carbon reaction, it is particularly useful when using this method. According to this method, it is possible to reduce the moisture and oxygen concentrations existing near the steel plate surface where the silicification reaction occurs, and the oxygen content (moisture and oxygen) reacts with the SiCl ₄ gas to generate silica. In addition, it is possible to prevent the steel sheet surface and grain boundaries from being oxidized by moisture and oxygen, thereby obtaining a high silicon steel sheet having both excellent surface properties and workability.

[Example 1]
In the continuous siliconization treatment line as shown in FIG. 1, a raw steel plate having a plate thickness of 0.10 mm and a Si concentration of 3 mass% is continuously siliconized, and the surface Si concentration in the plate thickness direction is 6.5 mass%. A high silicon steel sheet having a deviation ΔSi of 0.5 mass% (ΔSi / t = 5.0) between the Si concentration (mass%) of the surface layer portion of the plate and the Si concentration (mass%) of the central portion of the plate thickness was manufactured. . In addition, C density | concentration (C content) and S density | concentration (S content) in a raw steel plate are the values shown in FIG. 2, and content of other components (Mn, Al, N, O) is described above. It was within the preferable range. In the continuous siliconization treatment line, the siliconization treatment is performed at 1200 ° C. in a N ₂ + SiCl ₄ atmosphere (dew point: −30 ° C. or less, oxygen concentration: 10 ppm or less) in the siliconization treatment zone. Diffusion soaking was performed at 1230 ° C. in an N ₂ atmosphere.

The manufactured high silicon steel sheet was allowed to stand in an atmosphere of 200 ° C. for 100 hours, and the change rate of iron loss with time was measured by measuring the rate of increase in iron loss before and after that, and evaluated according to the following criteria. The iron loss in this example was W10 / 400 (1T, 400 Hz). FIG. 2 shows the results of the test arranged in relation to the C concentration and S concentration of the steel sheet.
○ (Good): Increase rate of iron loss with time is 8% or less △ (Acceptable): Increase rate of iron loss with time is more than 8% and 10% or less × (Poor): Increase rate with time of iron loss is more than 10% The C concentration of the steel sheet after the treatment is 50 mass ppm or less for all the results of “◯”, and 50 mass for all of the results of “△”.
All of the results exceeding “ppm” exceeding 55 ppm by mass were exceeding 55 mass ppm.

[Example 2]
In the continuous siliconization treatment line as shown in FIG. 1, a raw steel plate having a thickness of 0.2 mm and a Si concentration of 3 mass% is continuously siliconized, and the surface Si concentration in the thickness direction is 6.5 mass%. A high silicon steel sheet having a deviation ΔSi of 2.0 mass% (ΔSi / t = 40) between the Si concentration (mass%) of the surface layer portion of the plate and the Si concentration (mass%) of the central portion of the plate thickness was manufactured. In addition, C density | concentration (C content) and S density | concentration (S content) in a raw steel plate are the values shown in FIG. 3, and content of other components (Mn, Al, N, O) is described above. It was within the preferable range. In the continuous siliconization treatment line, the siliconization treatment is carried out at 1200 ° C. in the same N ₂ + SiCl ₄ atmosphere as in Example 1 in the siliconization treatment zone, followed by diffusion at 1200 ° C. in the N ₂ atmosphere in the diffusion soaking zone. Soaking was performed.

The manufactured high silicon steel sheet was allowed to stand in an atmosphere of 200 ° C. for 100 hours, and the change rate of iron loss with time was measured by measuring the rate of increase in iron loss before and after that, and evaluated according to the following criteria. The iron loss in this example was W10 / 400 (1T, 400 Hz). FIG. 3 shows the results of this test arranged in relation to the C concentration and S concentration of the steel sheet.
○ (Good): Increase rate of iron loss with time is 8% or less △ (Acceptable): Increase rate of iron loss with time is more than 8% and 10% or less × (Poor): Increase rate with time of iron loss is more than 10% The C concentration of the steel sheet after the treatment is 50 mass ppm or less for all the results of “◯”, and 50 mass for all of the results of “△”.
All of the results exceeding “ppm” exceeding 55 ppm by mass were exceeding 55 mass ppm.

Claims (1)

By subjecting the material steel plate to a siliconization treatment, the average Si concentration in the plate thickness direction is 4.0 to 7.0 mass%, and the Si concentration (mass%) in the plate surface layer portion and the Si concentration in the plate thickness center portion (mass) %) In relation to the plate thickness t (mm), in a method for producing a high silicon steel sheet satisfying 2.0 ≦ ΔSi / t ≦ 40.0,
The carbon concentration of the material steel plate is made higher than the target C concentration of the steel plate after the siliconization treatment, and the decarburization reaction of the material steel plate is caused by oxygen contained in the atmosphere of the siliconization treatment. It is a method of manufacturing a high silicon steel sheet with a target C concentration by performing processing,
A steel plate having a C concentration of more than 40 mass ppm and a C concentration [C] (mass ppm) and an S concentration [S] (mass ppm) satisfying any of the following (a) to (c): A method for producing a high-silicon steel sheet, characterized by being used and the C concentration of the high-silicon steel sheet after siliconizing treatment being 50 mass ppm or less .
(A) [S] ≦ 30, [C] ≦ 110
(B) 30 <[S] <100, [C] ≦ −0.857 [S] +135.71
(C) 100 ≦ [S], [C] ≦ 50

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