JP3570331B2 - Method for producing high silicon steel sheet with excellent surface properties - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a high silicon steel sheet by a siliconizing treatment method.
[0002]
[Prior art]
Silicon steel sheets, which are widely used as core materials for electric equipment such as transformers and motors, are usually added with Si for controlling texture and increasing specific resistance. It is known that the soft magnetic properties of this silicon steel sheet improve with the addition amount of Si, and exhibit the highest magnetic permeability especially at around 6.5% by weight. In addition, a silicon steel sheet having a Si content of more than about 4% by weight, which is called a high silicon steel sheet, has a high electric resistance and thus has excellent magnetic properties particularly in a high frequency range.
[0003]
As a method of industrially producing a high silicon steel sheet, a siliconizing treatment method is known. In this production method (for example, a production technique disclosed in Japanese Patent Publication No. 5-49745), a thin steel sheet of 4 wt% or less of Si that can be rolled by an industrial process is reacted with silicon tetrachloride at a high temperature. This is a method of obtaining a high silicon steel sheet by infiltrating Si in the direction of the thickness of the steel sheet and diffusing the infiltrated Si in the thickness direction. For example, Japanese Patent Publication No. 5-49745 discloses that a steel sheet is made of silicon tetrachloride of 5-35 vol% In a non-oxidizing gas atmosphere contained, siliconizing treatment is continuously performed at a temperature of 1023 to 1200 ° C. to obtain a coiled high silicon steel sheet. Normally, in this siliconizing treatment, silicon tetrachloride is used as a raw material gas for supplying Si, and this silicon tetrachloride reacts with the steel sheet by the following siliconizing reaction formula to form an Si-enriched layer on the surface layer of the steel sheet. I do.
SiCl ₄ + 5Fe → Fe ₃ Si + 2FeCl ₂
[0004]
The Si in the Si-enriched layer thus grown on the surface of the steel sheet is diffused in the thickness direction by soaking the steel sheet in a non-oxidizing atmosphere containing no silicon tetrachloride.
[0005]
In the high silicon steel sheet manufactured in this manner, silicon oxide is generated by oxygen and moisture in the atmosphere in which the siliconizing treatment is performed, and the silicon oxide is caused by generation of surface defects and grain boundary oxidation. Deterioration of workability has conventionally been a problem in manufacturing. On the other hand, conventionally, a method of improving by controlling the atmosphere has been adopted.
[0006]
[Problems to be solved by the invention]
However, even if the above measures are taken, production of a high silicon steel sheet having sufficiently excellent surface properties and workability has not been realized.
[0007]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a high silicon steel sheet having excellent surface properties and further excellent workability.
[0008]
[Means for Solving the Problems]
The present inventors have conducted various studies to solve the above-mentioned problems, and have obtained the following findings.
-If an organic compound is present in the Si supply raw material gas during the siliconizing treatment, local carburization is performed on the steel sheet surface during the siliconizing treatment, and the melting point of the steel sheet decreases. As a result, local melting and pores due to melting are generated, and the surface properties are significantly deteriorated. Therefore, in order to prevent melting due to carburization and to improve the surface properties, it is important to reduce the carbon concentration in the supply gas indicating the amount of organic matter present in the raw material gas for Si supply. During the siliconizing treatment, a difference in the Si concentration occurs between the surface layer of the steel sheet (high-concentration Si layer) and the inner layer of the steel sheet. There is a significant difference in the diffusion rate of iron, and as a result, the movement of iron cannot keep up with the movement of Si, and a large number of voids (voids) are generated. The voids (voids) not only deteriorate the magnetic properties (permeability) of the steel sheet, but also adversely affect workability. In order to suppress the generation of voids (voids) generated in the steel sheet, it is effective to suppress the amount of siliconizing once and alternately perform the siliconizing treatment and the diffusion soaking process plural times. Was found.
[0009]
The present invention has been made based on such knowledge, and has the following configuration.
[1] Si: A heat treatment, a siliconizing treatment, a diffusion soaking treatment and a cooling treatment are sequentially performed on a base steel sheet having a content of less than 4% by weight, and the silicon steel sheet is subjected to a siliconizing treatment in a method of producing a high silicon steel sheet. This is a method for producing a high silicon steel sheet having excellent surface properties, wherein the carbon concentration [C] in the supplied gas is 0.2% by weight or less.
[0010]
[2] The method for producing a high-silicon steel sheet having excellent surface properties according to the above [1], wherein the siliconizing treatment and the diffusion soaking heat treatment are alternately performed a plurality of times.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the details of the present invention will be described together with the reasons for limitation.
The method for producing a high silicon steel sheet according to the present invention comprises, as a base steel sheet, a steel sheet having an Si content of less than 4% by weight, which is easy to manufacture by rolling, and subjecting this base steel sheet to heat treatment, siliconizing treatment, diffusion soaking treatment, A high silicon steel sheet is manufactured by sequentially performing a cooling process.
[0012]
In the following, an embodiment will be described. First, steel having less than 4% by weight of Si is hot-rolled and cold-rolled to obtain a thin plate (base material steel plate). The base steel sheet is heated to or near the siliconizing temperature in a non-oxidizing gas atmosphere, and then continuously at a temperature of 1023 to 1200 ° C. in a non-oxidizing gas atmosphere containing 5 to 35 vol% of silicon tetrachloride. The base steel sheet is subjected to siliconizing treatment.
[0013]
Next, the siliconized steel sheet is subjected to diffusion soaking in a non-oxidizing gas atmosphere containing no silicon tetrachloride to diffuse the Si-enriched layer formed on the sheet surface in the sheet thickness direction. After cooling to room temperature to 300 ° C., winding is performed to obtain a high silicon steel sheet.
[0014]
The obtained high silicon steel sheet is annealed, and a coating for insulation is applied as necessary. Examples of the type of the insulating film include an organic type containing oxygen or an oxide, an organic-inorganic mixed type, and an inorganic type.
Also, if necessary, a varnish is impregnated for the purpose of molding the insulation and core shape.
[0015]
It is preferable that the content of Si in the high silicon steel sheet manufactured in this way is 4 to 7% by weight. If Si is less than 4% by weight, iron loss is large, while if it exceeds 7% by weight, it becomes brittle.
[0016]
In the present invention, in such a method for producing a high silicon steel sheet, the carbon concentration [C] in the supply gas during the siliconizing treatment is set to 0.2% by weight or less. Here, as a source of the organic compound (carbon) mixed into the raw material gas for Si supply, volatilization of lubricating oil (grease) installed in each sliding equipment of the furnace and the gas processing system, and prevention of steel to be processed. Rust, volatilization of oil brought into the furnace by rolling oil, and the like. Further, as a method of reducing this, it is conceivable to reduce the area of each seal portion, strengthen cleaning of a steel plate, or the like.
[0017]
As a result of examining the relationship between the carbon concentration in the supply gas and the frequency of occurrence of the melting trace of the steel sheet (measured as a hole having a depth of 5 μm or more as a melting trace), if the carbon concentration in the supply gas is 0.2% by weight or less, It was found that the occurrence of melting traces was suppressed to 1.0 particles / m ² or less, and the surface properties did not deteriorate. Further, it was found that if the carbon concentration in the supply gas was 20 ppm or less, the occurrence of traces of melting could be suppressed to zero. From the above, the carbon concentration [C] in the supply gas is set to 0.2% by weight or less, preferably 20 ppm or less.
[0018]
Further, in the present invention, in addition to the above conditions, it is desirable to alternately perform the siliconizing treatment and the soaking diffusion treatment plural times. By alternately performing the siliconizing treatment and the soaking process, each time, the generation of voids generated in the steel sheet can be suppressed, and the internal defects are eliminated by suppressing the generation of voids. In addition, the workability is improved, and the effect of improving the magnetic properties, particularly, the magnetic permeability is obtained.
[0019]
Here, it does not matter whether the object of the present invention is a oriented silicon steel sheet or a non-oriented silicon steel sheet. Also, a film for the purpose of insulation is usually formed on the surface of the electromagnetic steel sheet or varnish is impregnated, but the effect of the present invention is not affected by the type of such a film or varnish.
[0020]
【Example】
(Example 1)
In a continuous siliconizing treatment facility having a heating zone 1, a siliconizing zone 2, a soaking zone 3 and a cooling zone 4 as shown in FIG. Treatment, siliconizing treatment, diffusion soaking treatment, and cooling treatment were performed to produce a high silicon steel sheet containing 6.5% by weight of Si. At this time, by changing the mixing ratio of the organic compound, the carbon concentration in the supplied gas is changed from 0 to 1% by weight to perform the siliconizing treatment, and the generation of a melting mark (a hole depth of 5 μm or more) on the steel sheet surface after the treatment is generated. The frequency was measured. 2 and 3 show the relationship between the carbon concentration in the supply gas and the frequency of occurrence of the trace of melting. In FIG. 2 and FIG. 3, the frequency of occurrence of the melting trace was determined by measuring the number of melting trace occurrences that can be visually confirmed by an inspector between fixed coil lengths.
[0021]
From FIG. 2, it can be seen that, when the carbon concentration in the supplied gas is 0.2% by weight or less, the frequency of occurrence of melting traces is 1.0 / m ² or less, which is reduced to a level without a problem, and the surface properties are good. I understand.
[0022]
Further, it can be seen from FIG. 3 that if the carbon concentration in the supply gas is 20 ppm or less, the occurrence of melting traces can be completely eliminated, and the surface properties are more favorable.
[0023]
(Example 2)
In a continuous siliconizing treatment facility including a heating zone 1, a siliconizing zone 2, a soaking zone 3, and a cooling zone 4 in order from the entry side shown in FIG. A siliconizing treatment, a diffusion soaking heat treatment and a cooling treatment were performed to produce a high silicon steel sheet with 6.5% by weight of Si. At this time, the silicon concentration treatment was performed with the carbon concentration in the supplied gas being 20 ppm or less, and the siliconizing treatment and the diffusion soaking heat treatment were alternately performed a plurality of times, and the void generation rate and the maximum permeability of the high silicon steel sheet obtained in each case. The magnetic susceptibility was measured. FIG. 4 shows the measured void generation rate and maximum magnetic permeability. In FIG. 4, the number of times of passing means the number of times of performing the siliconizing treatment and the diffusion soaking heat treatment. Further, the processing speed was adjusted so that the total diffusion processing time was the same irrespective of the number of passes. The number of voids was determined by measuring the number of voids generated per 1 mm of the sheet width.
[0024]
FIG. 4 shows that as the number of passes increases, the void generation rate decreases and the maximum magnetic permeability increases, and a high silicon steel sheet having good surface properties and no internal defects is obtained.
[0025]
【The invention's effect】
According to the present invention, a high silicon steel sheet having excellent surface properties can be obtained. Further, by alternately performing the siliconizing treatment and the diffusion soaking process a plurality of times, a high silicon steel sheet having excellent surface properties and free from internal defects, particularly excellent in magnetic properties, particularly magnetic permeability, can be obtained. The high silicon steel sheet obtained according to the present invention is excellent in surface properties or workability, and thus is suitable as a core material for electric equipment such as transformers and motors.
[Brief description of the drawings]
FIG. 1 is a diagram showing a continuous Si siliconizing treatment line.
FIG. 2 is a diagram showing a relationship between a carbon concentration in a supply gas and a frequency of occurrence of a melting trace.
FIG. 3 is a second diagram showing the relationship between the carbon concentration in the supplied gas and the frequency of occurrence of the trace of melting.
FIG. 4 is a diagram showing the relationship between the number of repetitions of siliconizing treatment and diffusion soaking treatment, void generation rate, and maximum magnetic permeability.
[Explanation of symbols]
1 heating zone 2 silicification zone 3 mean tropical zone 4 cooling zone

Claims (2)

Si: Heat treatment, siliconizing treatment, diffusion soaking treatment, and cooling treatment are sequentially performed on a base steel sheet having a content of less than 4% by weight, and in a method of producing a high silicon steel sheet, in a supply gas for siliconizing treatment. A method for producing a high silicon steel sheet having excellent surface properties, wherein the carbon concentration [C] is 0.2% by weight or less. 2. The method according to claim 1, wherein the siliconizing treatment and the diffusion soaking treatment are alternately performed a plurality of times.

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