JPH0580122B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a high permeability magnetic thin steel sheet free of internal defects, and particularly aims to obtain a product free of internal defects. [Prior art] Fe-Si alloy and Fe-Si-Al alloy include Fe-Si alloy and Fe-Si-Al alloy.
Materials with extremely high magnetic permeability, such as 6.5wt%Si alloy and Fe-9.6wt%Si-5.4wt%Al alloy (Sendust),
Some exhibit excellent soft magnetic properties. In particular, since Sendust was invented by Dr. Masumoto and Dr. Yamamoto in 1973, it has been applied to many electronic devices such as dust cores and magnetic heads. In particular, regarding magnetic heads, as the density of magnetic recording media increases, the coercive force of recording media is increasing, and Sendust, which has a higher saturation magnetization, is a more suitable material for recording than the conventionally used ferrite head. Attention has been paid. Additionally, Fe-6.5wt%Si alloy has a high saturation magnetic flux density, so it is being considered for use in transformer cores and other electrical and electronic devices. When these high-Si alloys with excellent soft magnetic properties are actually applied to electronic parts, etc., the biggest problem is that these alloys exhibit brittleness and cannot be processed into thin pieces by rolling. For this reason, in the case of Sendust, thin pieces for magnetic heads are produced by slicing the material after casting, which is an extremely inefficient process in the head manufacturing process. Furthermore, sendust is prone to cracks and pinholes during casting and solidification, and it is essential to remove these defects, which requires a process. In order to solve the above-mentioned manufacturing process problems, various methods have been tried as described below. Hot rolling and deformation Improving workability with additive elements Melt quenching method Post-rolling component adjustment method The hot rolling and deforming methods are as follows:
This is possible by maintaining an extremely low strain rate at temperatures above 1000°C, but achieving this condition industrially is extremely difficult. Attempts have been made to improve workability by adding elements, but although the workability is slightly improved by the addition of elements, it still shows brittleness, and processing into thin sheets remains difficult, and these additive elements also reduce magnetic properties. The disadvantage is that it gets worse. The melt quenching method aims to directly cast molten metal into a thin plate shape, and is an extremely effective method for materials that exhibit brittleness such as this, in that a thin plate can be obtained without rolling. . The post-rolling composition adjustment method involves melting low-Si and low-Al steel, rolling it into a thin plate, enriching it with Si or Al by permeation from the surface, and finally producing a high-Si steel thin plate. be. This method was proposed by Gokyumi and Abe, and was studied in detail by Mitani, Onishi et al. However, the infiltration methods that have been proposed so far have the drawback that the infiltration treatment time is extremely long, exceeding 30 minutes, and the temperature is extremely high, around 1230°C, resulting in extremely poor shape of the thin steel sheet after the infiltration treatment. It was hot. Furthermore, the most fatal phenomenon in producing high magnetic permeability materials is that with conventional methods, large voids called Kirkendall voids are generated as a result of penetration, and a considerable amount remains even after sintering, resulting in a decrease in magnetic permeability. is significantly reduced. It is no exaggeration to say that the reason why the method of manufacturing high-Si thin steel sheets by Si infiltration method has not yet become a reality is that it is difficult to eliminate voids. To prevent the formation of voids,
As shown in No. 26263, there is a technique that utilizes the base material in a semi-molten state. In this technology, the key points are adjusting the amount of C and setting the corresponding processing temperature in order to create a semi-molten state, but when the amount of C is 0 to 0.15 wt%, the base material becomes a semi-molten state. If Si infiltration treatment is performed in the temperature range where C: 0 wt% is 1250 °C and C: 0.15 wt% is 1200 °C, it will remain in a semi-molten state even if voids occur during the treatment. Therefore, the voids are fused together, and as a result, Si infiltration treatment is performed in a state where void formation is suppressed. However, if Si infiltration treatment is performed in such a temperature range, the change in dimensions and deterioration of the shape of the object to be treated will increase, leading to other problems. Therefore, it has been desired to develop a new Si infiltration treatment that can suppress the generation of voids in the solid phase region with lower temperatures. On the other hand, in Japanese Patent Publication No. 53-42019, the amount of SiCl ₄ in the processing atmosphere is lowered (it is said to contain 25% of its saturated vapor pressure, but this is about 2.5Vol% when converted to volume percentage), and vice versa. A large amount of H ₂ gas (30Vol%) is mixed with the mixture, and the reaction temperature is increased to 1075℃.
At the stage where the base material is brought into contact with the above treatment atmosphere at a low temperature of ~1100℃, SiCl ₄ + 2H ₂ → Si + 4HCl changes.
There is a technique in which a SiCl ₄ reduction reaction progresses to deposit pure Si on the base material (Si chemical vapor phase plating). Although the purpose of this is to improve corrosion resistance, from an industrial perspective, it is inefficient because it requires chemical vapor phase plating of pure Si on the surface of the base material and then separate penetration and diffusion treatments. Rather, the Si-enriched layer that forms on the surface of the base material when it comes into contact with the processing atmosphere is such a pure Si layer.
It would be very desirable from an industrial perspective if it were to be Fe _{3 Si instead of Fe 3} Si. [Summary of the Invention] The present invention has been made to improve the above-mentioned drawbacks of the prior art, and has developed a manufacturing method that can suppress the generation of voids to an extremely low level by improving the post-rolling composition adjustment method. This is what we are trying to provide. As a result of a detailed study of Si infiltration conditions in a temperature range that provides a solid phase region without dimensional change or shape deterioration of the base material, the present inventors found that no voids remain after Si infiltration treatment or diffusion homogenization treatment. I found the conditions.
Moreover, as a result of adjusting the amount of Si to a desired level through this Si infiltration treatment, it was possible to obtain a high-Si thin plate with extremely high magnetic permeability. That is, as a result of repeated tests and research by the present inventors,
Regarding the rate of penetration of Si from the external atmosphere, if the atmosphere does not contain highly reactive gases such as H ₂ gas, the partial pressure of the Si compound is an extremely important factor; They found that the higher the pressure, the faster the rate of Si penetration, but on the other hand, the higher the partial pressure, the greater the amount of voids. Figure 1 shows the results when processing Fe-5.4%Al steel in a SiCl ₄ atmosphere and changing the amount of SiCl ₄ in the introduced gas to 10 vol%, 16 vol%, and 55 vol% to change the SiCl ₄ partial pressure. Shows weight change. Weight change is Si
This is a parameter that expresses the degree of penetration of Si, and the larger the weight change, the more Si has penetrated. This phenomenon is caused by FeCl ₂ leaving the system as 5Fe+
It is thought that this is due to the reaction of SiCl ₄ →Fe ₃ Si + 2FeCl ₂ . From FIG. 1, it is clear that the higher the Si partial pressure, the faster the Si permeation rate. However, the amount of voids tends to increase as the Si partial pressure increases in the solid phase region where dimensional changes and shape deterioration of the base material are small. Figure 2 shows Si
It shows the relationship between the amount of SiCl ₄ and the amount of voids after infiltration treatment and diffusion homogenization treatment, and clearly shows that the amount of voids increases as the Si partial pressure increases. Although the reason for this is not clear, it is thought to be as follows. In other words, if the amount of SiCl ₄ in the introduced gas (atmosphere that does not contain reactive gases such as H ₂ ) is reduced, the amount of Si penetrating from the outside per unit time and unit surface area will decrease, but this will occur through the Kirkendall interface. This indicates that the amount of Si atoms penetrating into the interior is also reduced, and the occurrence of vacancies, or Kirkendall voids, is also reduced. Under such circumstances,
This phenomenon occurs because the sample is thermally active, unlike the phenomenon that occurs when the sample is in a semi-molten state, which promotes the fusion of voids.
Because the diffusion of Fe and Si atoms progresses in parallel with the permeation phenomenon of Si, the Kirkendall voids are absorbed and annihilated by internal dislocations, etc., before they aggregate and become stable voids. It becomes easier. Therefore, by slowing down the penetration speed of Si, the remaining voids can be suppressed. The present inventors further investigated the Si partial pressure and the magnetic properties of the obtained product, and as a result, as shown in FIG. 3, they found that the smaller the amount of SiCl ₄ , the lower the coercive force. The present invention is based on the knowledge obtained through these experimental studies, and by controlling the Si partial pressure in the Si infiltration treatment atmosphere, it is possible to obtain a product with no voids and excellent magnetic properties. be. That is, in the present invention, C produced by a normal process:
When placing a thin steel plate of 0.01wt% or less in an atmosphere containing SiCl ₄ and infiltrating the thin steel plate with Si, the amount of SiCl ₄ in the atmosphere should be 6 Vol% or more and 25 Vol% or less, and the Si permeation temperature should be more than 1100°C and less than 1200°C. The basic feature is that Si infiltration treatment is performed according to the following reaction formula under conditions of a treatment time of 30 minutes or less, and then a diffusion treatment is performed in an inert atmosphere. 5Fe＋SiCl ₄ →Fe ₃ Si＋2FeCl _2The reason for these limitations will be explained. First, regarding the amount of C in the base material, if it is contained in excess of 0.01 wt%, the magnetic properties (particularly magnetic permeability) will be significantly lowered. Therefore, the upper limit was set at 0.01wt%. Next, regarding the amount of SiCl ₄ in the atmosphere during Si infiltration treatment, as is clear from Figure 2, the amount of SiCl ₄
Void hardly occurs below 25Vol%. Moreover, from FIG. 3, the decrease in coercive force is saturated when the amount of SiCl ₄ is 25 Vol% or less. From these two viewpoints, in the present invention, the amount of SiCl ₄ in the Si infiltration treatment atmosphere is limited to 25 Vol% or less. On the other hand, in Figure 1, 80%, 85%, 90%, 95%
As is clear from FIG. 7 (log-logarithmic scale), which shows the relationship between the amount of _SiCl4 in the introduced gas (Vol%) and the Si infiltration treatment time when the weight of In order to reduce the time to 30 minutes or less, the amount of SiCl ₄ in the introduced gas must be 6 Vol% or more. In addition, when the penetration temperature is below 1100℃, Si penetration is extremely slow, and when it exceeds 1200℃, a Si penetration layer is formed.
Since Fe ₃ Si will melt, the temperature should be above 1100°C and below 1200°C. However, in order to suppress voids,
It is advantageous to set the temperature as high as possible (in the present invention, C is specified to be 0.01wt% or less, so 1200℃
Even in the case of , the base material is in a solid state). Furthermore, regarding the infiltration treatment time, when trying to increase the weight change of the substrate (when using a large Si infiltration degree), the amount of SiCl ₄ in the introduced gas should be
The lower it is set within the range of 25 Vol%, the longer the processing time will take, and if it exceeds 30 minutes, it is unfavorable from the viewpoint of production yield. Therefore, in the present invention, the upper limit of the infiltration treatment time is set to 30 minutes. After a predetermined amount of Si permeates through the process under the above conditions, the components are made uniform through a diffusion process, but this diffusion process can be continued without cooling the substrate by switching the atmosphere to an inert gas. Alternatively, the substrate may be cooled to around a constant room temperature and the diffusion treatment may be performed again. The types of high magnetic permeability thin sheets that can be produced by the method of the present invention include 3 to 6.5 wt% Si-Fe alloy and sendust alloy, but the starting thin steel sheet used for Si infiltration has the following components: It is preferable to define it as follows. For 3-6.5wt% Si-Fe alloy: C0.01wt% or less, Si0-4.0%wt%, Mn2wt%
Below, it is desirable that other unavoidable impurities be as low as possible. For Sendust alloy: C0.01wt% or less, Si4wt% or less, Al3~8wt
%, Ni 4wt% or less, Mn 2wt% or less, elements that increase corrosion resistance such as Cr and Ti 5wt% or less, and other unavoidable impurities as low as possible. [Example] A thin plate having a thickness of 0.40 mm was produced by hot and cold rolling an alloy having the chemical components shown below, and this was used as a substrate.

[Table] This substrate was subjected to Si infiltration treatment using the apparatus shown in FIG. In FIG. 4, 1 is a round bottom flask filled with SiCl ₄ , 2 is a constant temperature water bath, 3 is a furnace, and X is a sample.

[Table] _{SiCl 4} in the introduced gas is
The temperature was changed by controlling the temperature. In addition, the penetration treatment conditions were such that Si was 9.6wt%.
The conditions have been adjusted to ensure that it penetrates even further. Furnace 3 used for Si infiltration treatment has a silicon carbide heating element, and the furnace core tube is made of ceramic with an inner diameter of 40 mm.
Ar is used as a carrier gas for SiCl ₄ and its flow rate is 0.5/min. Chemical analysis of the samples subjected to Si infiltration treatment revealed that the target amount of Si (9.6wt%) was achieved in both cases.
It was found that it contains Figures 5 and 6 show the results after Si infiltration treatment and at 1200℃.
The cross-sectional microstructure photographs of samples A to D after diffusion homogenization treatment in an inert atmosphere for 1 hour are shown. in the introduced gas
As the amount of SiCl ₄ increases, the generation of voids becomes more pronounced both after Si infiltration treatment and after diffusion homogenization treatment. Looking at the structure after the diffusion homogenization treatment, sample D has large and numerous residual voids, whereas sample A
-C, almost no voids are observed.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between Si infiltration treatment time and weight change, Figure 2 is a graph showing the relationship between _SiCl4 amount and void amount, and Figure 3 is a graph showing the relationship between _SiCl4 amount and coercive force. Graph, Figure 4 is a schematic diagram of the apparatus for carrying out the example, Figures 5 and 6 are micrographs showing the cross-sectional structure of the metal, and Figure 7 shows the Si infiltration treatment time and the amount of SiCl ₄ in the introduced gas. It is a graph showing a relationship.

Claims (1)

[Claims] 1. A thin steel plate with a carbon content of 0.01wt% or less manufactured by a normal process is placed in an atmosphere containing _SiCl4 , and the thin steel plate is
When infiltrating Si, the _amount of SiCl4 in the atmosphere is 6 Vol% or more and 25 Vol% or less,
High magnetic permeability with no internal defects characterized by performing Si infiltration treatment according to the following reaction formula at a Si infiltration temperature of over 1100℃ and below 1200℃ and treatment time within 30 minutes, followed by diffusion treatment in an inert atmosphere. A method for producing magnetic thin steel sheets. 5Fe＋SiCl ₄ →Fe ₃ Si＋2FeCl ₂