JPH048504B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a high silicon steel plate having an insulating film on its surface.

[Conventional technology]

High-silicon steel sheets are used as electrical steel sheets.
It is known that this type of steel sheet exhibits the best magnetic properties, with the iron loss decreasing as the Si content increases, and at 6.5% Si, the magnetostriction becomes 0 and the maximum magnetic permeability reaches its peak. .

Conventionally, methods for producing high-silicon steel sheets include the rolling method, direct casting method, and silicon extrusion method. Of these, the rolling method can produce Si steel sheets with a Si content of up to about 4%, but Cold working is difficult because the workability deteriorates significantly. In addition, although the direct casting method, so-called strip casting, does not have workability problems like the rolling method, it is still a technology under development and is prone to shape defects, making it particularly difficult to manufacture high-silicon steel sheets. be.

On the other hand, the silicon permeation method produces high-silicon steel sheets by melting low-silicon steel, rolling it into thin sheets, and then infiltrating Si from the surface. A high-silicon steel plate can be obtained without causing any problems.

By the way, electromagnetic steel sheets are usually used in a laminated state, and in this case, each of the laminated steel sheets needs to be insulated. For this reason, electrical steel sheets are coated with an insulating film. Conventionally, this insulating film coating has been performed by applying a liquid coating material, drying it, and baking it.

[Problem that the invention seeks to solve]

However, forming an insulating film by such coating has the following problems.

) Coating film thickness tends to become uneven due to uneven application.

) It is necessary to reheat the steel strip during the drying and baking process.

) If the coating material is inorganic, it is necessary to heat it to approximately 700-800℃ during the drying and baking process, which may cause crystal growth on the steel plate and adversely affect the magnetic properties of the final product. be.

) Because the coated film is thick, when laminating steel plates, the thickness of the laminated material becomes large. (The number of laminated layers per unit thickness is small.) Coating peels off easily.

On the other hand, chemical vapor deposition (hereinafter referred to as
The method of manufacturing high-silicon steel sheets by CVD (CVD) has problems in that the processing takes a long time and the thickness of the deposited Si layer tends to be uneven. This has been one of the obstacles to its application.

The present invention was developed in view of these problems, and it is possible to obtain a uniform Si vapor deposited film in a short time through CVD processing, and also to form a thin and uniform insulating film without the need for baking processing. ,
This makes it possible to form a thin and uniform insulation film with a uniform Si concentration in the direction of the plate surface.
Moreover, it is an object of the present invention to provide a method that can efficiently produce a high-silicon steel plate having a thin and uniform insulating film.

[Means to solve the problem]

For this reason, the present invention uses SiCl ₄ in a mol fraction of 5 to 35
Atmospheric gas is sprayed onto the steel plate from a spray nozzle in a non-oxidizing gas atmosphere containing %
After Si vapor deposition treatment on the steel plate at 1023-1200℃, Si is diffused into the steel plate, then the steel plate surface is irradiated with metal ions of atoms that can form stable oxides, and then O ₂ ⁺ ions are applied to the steel plate. Its basic feature is to form an insulating film on the surface of the steel plate by irradiating it with

In the present invention, after depositing Si on the surface of a steel plate using the CVD method under the conditions described below, a diffusion process is performed to diffuse the Si into the steel plate, and then the high silicon steel plate is insulated using an ion beam irradiation method. Forms a film.

In this insulating film coating process, first,
The surface of the steel sheet is irradiated with metal ions of atoms capable of forming stable oxides such as Mg ⁺ , Si ⁺ , Al ^{+ ,} etc., and the metal is deposited on the surface of the steel sheet. Ion beam irradiation is performed by ionizing atoms, accelerating them in a magnetic field, and causing them to collide with the surface of a steel plate, thereby depositing metal on the surface of the steel plate.

After the above metal ion irradiation, O ₂ ⁺ is added to the steel plate surface.
Ions are irradiated, which oxidizes the previously deposited metal, forming SiO ₂ , MgO,
A very thin (about several hundred μm to several μm) film (oxide film) of Al ₂ O ₃ or the like, which is very dense and has high insulation properties, is formed.

Since this oxide film is formed extremely uniformly and thinly, it also has excellent adhesion to the base material.

Furthermore, since the above-described process for forming an insulating film does not involve drying and baking processes as in the conventional process, it has the advantage that the magnetic properties of the high-silicon steel sheet, which is the base material, are not impaired.

In the present invention, a CVD method is used as a method for depositing Si on the surface of a steel plate.

Continuous treatment of steel plates by CVD method uses mol of SiCl ₄
The process is carried out continuously at a temperature of 1023 to 1200° C. in an atmosphere of non-oxidizing gas containing 5 to 35% in fraction.

The non-oxidizing gas containing SiCl ₄ means a neutral or reducing gas, and Ar, N ₂ , He, H ₂ , CH ₄ or the like can be used as a carrier gas for SiCl ₄ . Among these carrier gases, when considering exhaust gas treatment methods, _H2 , _CH4 , etc. have the disadvantage of generating HCl, which requires treatment.Ar, He, and _N2 , which do not cause such problems, are Preferably,
Furthermore, from the viewpoint of preventing nitridation of the material, Ar and He are particularly preferred among these.

The main reaction on the steel sheet surface during CVD treatment is 5Fe+SiCl ₄ →Fe ₃ Si+2FeCl ₂ ↑. Si1 atoms are deposited on the steel plate surface to form a Fe ₃ Si layer, and Fe2 atoms become FeCl ₂ which is diffused from the steel plate surface in a gaseous state at a temperature higher than the boiling point of FeCl ₂ of 1023°C.
Therefore, the Si atomic weight is 28.086 and the Fe atomic weight is 55.847.
Therefore, the mass of the steel plate decreases, and the thickness of the steel plate decreases accordingly. By the way, when a 6.5% Si steel plate is manufactured using CVD treatment using a 3% Si steel plate as the base material, the mass decreases by 8.7% and the plate thickness decreases by approximately 7.1%.

Traditionally, CVD processing takes too long because
This is thought to be due to insufficient consideration being given to the CVD treatment conditions. According to our research, we have found that the following factors are necessary for speedy CVD treatment.

Optimization of SiCl ₄ concentration in atmospheric gas.

Optimization of processing temperature.

Promotion of diffusion of SiCl ₄ to the steel plate surface and dissipation of FeCl ₂ from the steel plate surface.

For this reason, the present invention specifies the Si concentration in the atmospheric gas, the processing temperature, and the method of supplying the atmospheric gas to the steel sheet in the CVD treatment.

First, the concentration of SiCl ₄ in the non-oxidizing gas atmosphere in the CVD process is defined as 5 to 35% in terms of mol fraction,
The steel plate is continuously subjected to CVD treatment in such an atmosphere.

Expect less than 5% _SiCl4 in the atmosphere
Si enrichment effect cannot be obtained, and for example, Si in steel plate
It takes more than 5 minutes to enrich 1.0%, etc.
Processing takes too much time, making it difficult to make it a continuous process.

On the other hand, even if SiCl ₄ is contained in excess of 35%, the reaction at the interface becomes rate-determining, and no further Si enrichment effect can be expected.

Furthermore, in the CVD process, the higher the SiCl ₄ concentration, the more likely large voids called Kirkendahl voids are generated. These voids are hardly seen until the SiCl ₄ concentration is around 15%, but begin to form when it exceeds 15%. However, when the _SiCl4 concentration is below 35%,
Even if voids are generated, they can be almost completely eliminated by the diffusion process that is performed following the CVD process. In other words, when the SiCl ₄ concentration exceeds 35%, voids are significantly generated and remain even after the diffusion treatment.

The CVD treatment temperature is in the range of 1023 to 1200°C.
Since the CVD treatment reaction is a reaction on the steel sheet surface, the treatment temperature is strictly the steel sheet surface temperature.

The boiling point of FeCl ₂ , which is a reaction product from CVD processing, is 1023°C, and below this temperature, FeCl ₂ is not dissipated from the steel plate surface in a gaseous state, but adheres to the steel plate surface in a liquid state and inhibits the vapor deposition reaction. Put it away. According to the results of basic experiments conducted by the present inventors, the enrichment rate of Si per unit time differs markedly at the boiling point of FeCl ₂ , and the deposition rate is low below 1023°C, making it difficult to apply it to a continuous process. Have difficulty. Therefore, the lower limit of the processing temperature is set at 1023°C.

On the other hand, the reason why the upper limit is specified as 1200°C is as follows. The melting point of Fe ₃ Si is 1250°C, as is clear from the Fe-Si phase diagram shown in Figure 2, but according to experiments by the inventors, even when treated at about 1230°C, which is lower than 1250°C, The steel plate surface is partially melted,
Additionally, the edge of the steel plate melts due to overheating.
The reason why steel plates melt even below 1250℃ is because
On the surface of the steel sheet, the Si concentration is 14.5% or more, which is equivalent to Fe ₃ Si.
It is presumed that this is due to the fact that it is vapor-deposited. On the other hand, if the processing temperature is below 1200℃, no melting will be observed on the surface of the steel plate, and overheating of the edges will be prevented by setting the average temperature at the center of the steel plate to 1200℃.
It was experimentally confirmed that it is possible to maintain the temperature at around 1220°C, and only a small amount of dissolution is required. For the above reasons, the CVD treatment temperature is specified as 1023°C to 1200°C.

The steel plate on which Si has been vapor-deposited as described above is subsequently subjected to a Si diffusion treatment. In other words, immediately after Si vapor deposition, the Si concentration is high near the surface of the steel plate, and the Si concentration in the center remains the same as the base metal.
It is necessary to carry out a diffusion treatment to obtain a uniform Si concentration or a predetermined concentration distribution.

Methods for diffusing Si into the steel strip include a soaking diffusion method and an ion beam irradiation diffusion method.

The soaking diffusion method diffuses Si by holding the steel plate at a predetermined temperature.It must be carried out in a non-oxidizing atmosphere to prevent the surface of the steel plate from being oxidized, and the higher the temperature, the more difficult the process will be. It takes less time.

This diffusion treatment may be performed at a constant temperature, but
As can be seen from the Fe-Si phase diagram in Figure 2, as diffusion progresses, the Si concentration in the surface layer of the steel sheet decreases and its melting point increases, so as diffusion progresses, the temperature should be gradually raised to an extent that does not melt the steel sheet. Diffusion can be promoted by increasing the temperature (for example, by increasing the temperature in multiple steps). For example, in the case of 6.5% Si steel, it is possible to raise the temperature to 1400°C even if overheating of the edges is taken into consideration.

In addition, in the latter ion beam irradiation method, ions with high kinetic energy collide with the solid surface, resulting in the spatter phenomenon (the effect of hitting the solid surface at high speed) and the accelerated diffusion effect, as well as the effect of ion collisions. Si is diffused by the effect of increasing solid temperature by converting kinetic energy into thermal energy.

The ion species collided in such a diffusion process include inert gas ions such as Ar ⁺ and He ⁺ ;
Fe ⁺ ions etc. can be used. Among these, inert gas ions can be said to be suitable when the surface reaction of the steel sheet is an issue. However, when these ions are used, Ar, He, etc. remain in the surface layer of the steel sheet. On the other hand, the following advantages can be obtained by using Fe ⁺ ions.

(a) Since it is the same element as the base material, there will be no problems due to residuals.

(b) The mass of the ions is large, and the collision effect is large.

(c) Fe in the steel strip is consumed in the CVD process, but this consumption can be compensated for, albeit slightly.

(d) FeCl ₂ (boiling point 1023℃) is preferably gaseous and is generated during the CVD process for ionization.
can be used.

The above diffusion treatment may be performed until Si is uniformly diffused into the steel sheet, but in some cases, the treatment may be performed while the surface layer Si concentration is higher than the Si concentration at the center of the steel sheet in the thickness direction. It is also possible to obtain a steel plate with non-uniform Si concentration in the thickness direction.

In CVD processing for Si vapor deposition, CVD
In order to increase the processing speed to the point where continuous processing of steel plates is possible, as mentioned above, the
It is necessary to optimize the SiCl ₄ concentration and treatment temperature, but in addition to this, SiCl ₄ diffusion to the steel plate surface and
By promoting the diffusion of FeCl ₂ from the surface of the steel sheet, it becomes possible to further increase the CVD processing speed and obtain a Si vapor deposited film with a uniform thickness.

Conventionally, it has been believed that large flow of reactive gas during CVD processing causes voids to occur in the deposited layer and reduces the purity of the deposited layer, so the idea has been to keep the gas flow to the minimum necessary. . However, in the research conducted by the present inventors, due to the gas flow being suppressed in this way, the diffusion movement of the reaction gas to the base material interface and the separation of reaction by-products from the interface surface layer do not occur smoothly. It was found that the process required a long time and that the gas flow was suppressed, resulting in a distribution of the reactant gas concentration within the CVD treatment zone, resulting in non-uniformity in the thickness of the deposited film. It goes without saying that such non-uniformity in the thickness of the deposited film leads to non-uniformity in the Si concentration in each part of the steel plate (in the direction of the plate surface) after the diffusion treatment, which is unfavorable in terms of the quality of the steel plate.

Based on these facts, we further investigated and found that by spraying atmospheric gas onto the steel plate using a spray nozzle in the CVD treatment zone,
Diffusion of SiCl ₄ onto the steel plate surface and reaction products
It significantly promotes release of FeCl ₂ from the steel sheet surface, allowing high evaporation rate while suppressing non-uniformity of the evaporated film.
It was found that CVD treatment was possible.

In order to improve CVD processability, a method in which atmospheric gas is sprayed onto the steel plate surface using a spray nozzle is particularly effective, compared to a method in which the atmosphere is forced to circulate using a fin or the like. FIG. 3 shows the implementation status of this nozzle spraying method, in which a spray nozzle 6 is arranged in the CVD treatment zone 2 facing the steel strip S, and an atmospheric gas containing SiCl ₄ is sprayed onto the steel plate surface.
FIGS. 4A and 4B show the spraying conditions by the spray nozzle 6, and the spray can be applied perpendicularly to the steel plate surface as shown in A, or obliquely as shown in B.

Si per unit time by such nozzle spraying
The enrichment ratio increases in proportion to the increase in the flow velocity of gas colliding with the steel plate surface, but even if the flow velocity is increased excessively, the reaction rate at the interface becomes rate-limiting, so no further Si enrichment effect can be expected. Generally, 5N
A sufficient effect can be obtained at a flow rate of m/sec or less.

Figures 5 and 6 show the relationship between CVD processability and
The influence of SiCl ₄ concentration and CVD treatment temperature was investigated.

In the figure, A is the atmosphere method, that is, CVD treatment without nozzle spraying, and B is the nozzle spraying method, that is, spraying atmospheric gas onto the steel plate surface at a flow rate of 0.5 m/s as shown in Figure 3. Shows the case after CVD treatment. Note that the Si enrichment ratio indicates the Si increase due to the CVD treatment with respect to the initial Si concentration of the base material.

According to this, a large Si enrichment effect is obtained when the SiCl ₄ concentration is 5% or more and the CVD treatment temperature is 1023° C. or more. Also, even under the same conditions, the method of spraying atmospheric gas with a spray nozzle produces significantly better Si than the method of simply threading the steel plate in the atmosphere.
It can be seen that an enrichment effect (CVD treatment method) has been obtained.

Figure 7 shows the relationship between the deposition time and the Si concentration _in the steel sheet (base metal Si amount + deposited Si amount) for atmosphere method A and nozzle spraying method B. twenty one
%, and was investigated using CVD treatment at a treatment temperature of 1150°C. In addition, in the nozzle spray method,
perpendicular to the steel plate using a slit nozzle
Atmospheric gas was blown at a flow rate of 0.2 Nm/sec. As can be seen from the figure, it took 7 minutes with atmosphere method A to obtain a Si vapor deposition amount equivalent to 6.5% Si steel, whereas with nozzle spraying method B, it took 1.5 minutes.

Figure 8 shows the relationship between the collision gas flow rate and the Si enrichment ratio of the steel plate (same as Figures 5 and 6) in the nozzle blowing method. The Si enrichment ratio is increasing.

Based on the above-mentioned Si vapor deposition process-diffusion process,
Embodiments of the continuous treatment process for steel plates according to the present invention are illustrated below.

(1) In a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction, atmospheric gas is sprayed onto the steel plate from a spray nozzle, and the steel plate is continuously subjected to Si vapor deposition treatment at a treatment temperature of 1023 to 1200°C. Then _SiCl4
A diffusion process is performed to diffuse Si into the steel sheet in a predetermined state in a non-oxidizing gas atmosphere that does not contain
After cooling, the steel plate is first irradiated with metal ions of atoms capable of forming stable oxides, and then O ₂ ⁺ ions are irradiated to form an insulating film on the steel plate surface.

(2) In a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction, atmospheric gas is sprayed onto the steel plate from a spray nozzle, and the steel plate is continuously subjected to Si vapor deposition treatment at a treatment temperature of 1023 to 1200°C, and then , Si is diffused into the steel plate by irradiating the steel plate with an ion beam, then metal ions of atoms that can form stable oxides are irradiated on the steel plate surface, and then
An insulating film is formed on the surface of the steel plate by irradiating O ₂ ⁺ ions.

The object of the present invention is not limited to steel strips, but can also be applied to processed materials such as cut plates and pressed products, and when the object is such, the steel material is conveyed through each processing band by a conveyor device etc. will be done.

〔Example〕

Figure 1 shows an example of a thin plate manufacturing line in which CVD processing and soaking diffusion are used for Si vapor deposition processing and diffusion processing, where 1 is a heating zone, 2 is a CVD treatment zone,
3 is a diffusion treatment zone, 4 is a cooling zone, 5a is a first ion beam irradiation zone (Al ⁺ implantation zone), and 5b is a second ion beam irradiation zone (O ₂ ⁺ implantation zone).

An example of a manufacturing process using such a line will be described. First, the steel strip S is heated in a heating zone 1 to 1150° C. without oxidation, and then guided to a CVD treatment zone 2.
Here, a reactive gas containing 80% Ar and 20% SiCl ₄ is blown onto the surface of the steel strip from a nozzle at a flow rate of 0.3 Nm/S to perform a silicon-etching treatment. Next, the steel strip is led to a diffusion treatment zone 3, where it is soaked and held at 1200° C. in a non-oxidizing atmosphere, and is subjected to a diffusion treatment. Next, it is cooled to room temperature or winding temperature in the cooling zone 4, and subsequently, in the first ion beam irradiation zone 5a,
Ionized Al ⁺ is irradiated onto the steel strip surface at approximately 150 keV, and then in the second ion beam irradiation zone 5b, O ₂ ⁺
Ions are irradiated with similar acceleration energy, thereby forming a stable insulating film of aluminum oxide (for example, about 300 nm thick) on the surface of the steel strip.

〔Effect of the invention〕

According to the present invention described above, since a uniform Si vapor deposition film can be obtained in the CVD treatment, it is possible to obtain a high-silicon steel sheet with a uniform Si concentration in each part of the steel sheet (in the direction of the sheet surface), and it is also possible to perform the baking treatment. A thin and uniform insulating film can be formed without any problems, and since no baking treatment is required, a high-quality magnetic steel sheet can be obtained without damaging the magnetic properties of the high-silicon steel sheet. Moreover, the present invention
According to the CVD treatment conditions, the treatment can be carried out in a short time, and the insulation film forming process can be carried out efficiently in a short time because drying and baking processes are not necessary. From the above, according to the manufacturing method of the present invention, a high-silicon steel sheet with a uniform Si concentration in the sheet surface direction, a thin and uniform insulation film, and excellent magnetic properties can be manufactured with high industrial productivity. It has the effect of being able to

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a continuous processing line for implementing the present invention. FIG. 2 is a phase diagram of the Fe-Si system. 3 and 4A and 4B show the CVD treatment situation using the nozzle spraying method. FIG. 3 is an overall explanatory diagram, and FIGS. 4A and 4B are explanatory diagrams showing the nozzle spraying method, respectively. FIG. 5 shows the relationship between the SiCl ₄ concentration in the gas and the Si enrichment ratio in the steel strip in the CVD treatment, and FIG. 6 shows the relationship between the CVD treatment temperature and the Si enrichment ratio in the steel strip. Figure 7 is
The relationship between the Si vapor deposition time and the Si concentration in the steel strip is shown by comparing the atmospheric method and the nozzle spray method.
Figure 8 shows the results of CVD treatment using the nozzle spraying method.
Collision gas flow velocity of atmospheric gas against steel strip and steel strip Si
This shows the relationship with the enrichment ratio.

Claims (1)

[Claims] 1 In a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction, atmospheric gas is sprayed onto the steel plate from a spray nozzle, and the steel plate is subjected to Si vapor deposition treatment at a treatment temperature of 1023 to 1200°C, and then Si is deposited inside the steel plate. After that, the steel plate surface is irradiated with metal ions of atoms that can form stable oxides, and then O ₂ ⁺
A method for manufacturing a high-silicon steel sheet having an insulating film, the method comprising forming an insulating film on the surface of the steel sheet by irradiating ions.