JPH0465902B2 - - Google Patents

Description

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

[Conventional technology]

Electrical 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 be uneven due to uneven coating.

() 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 iron plate and adversely affect the magnetic properties of the final product. There is.

() Because the coated film is thick, when using laminated iron plates, the thickness of the laminated material becomes large (the number of laminated layers per unit thickness is small).

() The coating peels off easily.

Furthermore, conventionally, a method is known in which a steel plate is enriched with Si (silicon treatment) using a chemical vapor deposition method (CVD method) to obtain a high-silicon steel plate. However, conventional CVD
The CVD method requires a long processing time due to the slow deposition rate of Si, and for this reason, it has been practically difficult to apply the CVD method to a continuous production line for high-silicon steel sheets.

The present invention was made in view of these problems, and is based on the premise that silicon iron plates can be manufactured efficiently in a short period of time through silicon extrusion treatment. The purpose of this invention is to provide a method for efficiently manufacturing iron plates.

[Means to solve the problem]

For this reason, the present invention provides steel plates with 1023
After heating to a temperature of ~1200℃, the steel plate at this temperature
In a non-oxidizing gas atmosphere containing 5 to 35% of SiCl ₄ in terms of mol fraction, silica treatment is carried out by chemical vapor deposition method,
The basic feature is that an element capable of forming a stable oxide is deposited on the obtained silicon iron plate, and then the silicon iron plate is cooled in a weakly oxidizing atmosphere to form an insulating film.

The present invention will be explained in detail below.

In the present invention, first, a steel plate is prepared in a non-oxidized state from 1023 to
After heating to a temperature of 1200℃, the steel plate at this temperature is
In a non-oxidizing gas atmosphere containing 5 to 35% of SiCl ₄ by mole fraction, a silicon steel plate is obtained by carrying out a silicon exfoliation treatment by a chemical vapor deposition method (CVD method). This bleed silicon treatment is
This is usually done by continuous processing of steel plates.

The non-oxidizing gas containing SiCl ₄ means a neutral or reducing gas, and Ar, N ₂ , He, H ₂ , CH ₄ , etc. can be used as a carrier gas for SiCl ₄ . Among these carrier gases, when considering the processability of exhaust gas, _H2 , _CH4 , etc. have the disadvantage of generating HCl and needing to be disposed of, whereas 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 plate surface during CVD treatment is 5Fe+SiCl ₄ →Fe ₃ Si+2FeCl ₂ ↑. Sil atoms are deposited on the steel plate surface to form a Fe ₃ Si layer, Fe2 atoms become FeCl ₂ , and the boiling point of FeCl ₂ is 1023
It is emitted from the steel sheet surface in a gaseous state at temperatures above ℃. Therefore, since the Si atomic weight is 28.086 and the Fe atomic weight is 55.847, the mass of the steel plate decreases,
Along with this, the plate thickness will also decrease. By the way, when a 6.5% Si steel plate is manufactured using CVD treatment using a 3% Si steel plate as a base material, the mass decreases by 8.7% and the plate thickness decreases by approximately
Decrease by 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. The inventors of the present invention have studied the following and found that the following factors are necessary for performing CVD processing quickly.

Optimizing the SiCl ₄ concentration in the atmospheric gas Optimizing the processing temperature Promoting the diffusion of SiCl ₄ to the steel sheet surface and the dissipation of FeCl ₂ from the steel sheet surface Therefore, in the present invention, the Si concentration in the atmospheric gas in the CVD treatment is and specify the processing temperature.

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-limiting, 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 when 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. However, according to experiments conducted by the present inventors, the melting point of Fe 3 Si is 1250°C, even when processed at about 1230°C, which is lower than 1250°C. , the surface of the steel plate partially melts, and the edges of the steel plate melt due to overheating. The reason why the steel sheet melts even below 1250°C is presumed to be because Si is vapor deposited on the surface of the steel sheet at a Si concentration of 14.5% or more equivalent to Fe ₃ Si.
On the other hand, if the processing temperature is below 1200℃, no melting of the steel plate surface will be observed, and overheating of the edges can still be suppressed to about 1220℃ by setting the average temperature at the center of the steel plate to 1200℃. It was experimentally confirmed that this is possible and requires only a small amount of dissolution. 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 strip at a predetermined temperature.It must be carried out in a non-oxidizing atmosphere to avoid oxidizing the steel plate surface, and the higher the temperature Less processing time is required.

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 rises, so as diffusion progresses, the temperature is 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 increasing the solid temperature by converting kinetic energy into thermal energy.

The ion species collided in this 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) For ionization, a gaseous substance is preferable, and FeCl ₂ (boiling point 1023°C) generated during the CV process can be used.

Note that 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 the present invention, the silicon iron plate thus obtained is heated, and an element capable of forming a stable oxide is vapor-deposited on its surface.

As this vapor deposition element, a metal element such as Si, Cr, Mg, etc. is used. As a vapor deposition method, an appropriate method can be used, such as a chemical vapor deposition (hereinafter referred to as CVD) method or a PVD method including an ion beam irradiation method.

In the CVD process, an iron plate is treated in a CVD processing furnace in an atmospheric gas containing a metal halide as a vapor deposition element, whereby a predetermined element (an element that can form a stable oxide) is vapor-deposited on the surface of the iron plate.

In addition, in the ion beam irradiation method, Si, Cr, Mg
Irradiate the iron plate surface with a metal ion beam of elements such as
These elements are vapor-deposited.

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 vapor deposition treatment, the silicon iron plate is placed in a weakly oxidizing atmosphere (e.g., O ₂ concentration 21 vol% or less, preferably
5vol% or less). As a result, the above-mentioned vapor-deposited elements are oxidized, and SiO ₂ , MgO,
A very thin film (oxide film) of Al ₂ O ₃ or the like is formed, which is strict and has high insulation properties.

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

In the present invention, a vapor deposition process for forming an insulating film can be performed using the heating conditions of the silicon extrusion process and the Si diffusion process.

Typical embodiments of the continuous steel plate processing process according to the present invention described above are illustrated below.

(1) A steel plate was heated to 1023 by CVD method in a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction.
Continuous silica treatment at a temperature of ~1200℃, then in a non-oxidizing gas atmosphere without _SiCl4
A diffusion process is performed to diffuse Si into the steel sheet in a predetermined state, and then an element capable of forming a stable oxide is deposited by CVD, followed by cooling in a weakly oxidizing atmosphere to form an insulating film.

(2) A steel plate was heated to 1023 by CVD method in a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction.
By continuously silica treatment at a temperature of ~1200℃ and then irradiating the steel plate with an ion beam.
Si is diffused into the steel sheet, and then an element capable of forming a stable oxide is deposited by CVD, followed by cooling in a weakly oxidizing atmosphere to form an insulating film.

In the above embodiment, by selecting Si as the vapor deposition element for the insulating film, the process itself can be made more efficient and can be operated economically.

In other words, CVD is generally used for the purpose of treating exuded silicon.
During processing, O ₂ and other gases are added to the processing gas introduced into the furnace.
While it is necessary to avoid contamination of gas components such as Cl as much as possible, in CVD treatment for the purpose of forming an insulating film, a rough processing gas containing O ₂ and Cl can be used. Therefore, the processing gas discharged from the CVD processing furnace for silica processing (Si addition processing) still contains a considerable amount of SiCl ₄ gas (O ₂ ,
This exhaust gas can be introduced into a CVD processing furnace for forming an insulating film to perform CVD processing.

In addition, in the above-mentioned CVD treatment for the purpose of Si vapor deposition, in order to increase the CVD treatment speed to the point where continuous treatment of steel plates is possible, the concentration of SiCl ₄ in the atmospheric gas and the treatment temperature must be optimized as described above. In addition to this, it is necessary to
By promoting SiCl ₄ diffusion and FeCl ₂ dissipation from the steel sheet surface, it is possible to further increase the CVD processing speed.

Conventionally, it has been believed that large flow of reactant gas during CVD processing will cause voids to occur in the deposited layer and reduce 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.

Based on these facts, we further investigated the results and found that by blowing atmospheric gas onto the treated material using a blowing nozzle in the CVD treatment zone, or by forcing the atmosphere to circulate using a fan, etc.
Diffusion of SiCl ₄ onto the steel plate surface and reaction products
Significantly accelerates the dissipation of FeCl ₂ from the steel plate surface, achieving a high evaporation rate while suppressing non-uniformity of the evaporated film.
It was found that CVD treatment was possible.

A method in which atmospheric gas is sprayed onto the steel plate surface using a spray nozzle is particularly effective for improving CVD processability. 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 atmospheric gas containing SiCl ₄ is sprayed onto the steel plate surface. Fourth
Figures A and B 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. In general,
A sufficient effect can be obtained with a flow rate of 5 Nm/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 much better Si than the method of simply threading the steel plate in the atmosphere.
It can be seen that an enrichment effect (CVD processability) is 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,
0.2N from the perpendicular direction to the steel plate using a slit nozzle
Atmospheric gas was blown at a flow rate of m/sec. As can be seen from the figure, it took 7 minutes with atmosphere method A to obtain the amount of Si vapor deposited 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.

〔Example〕

Figure 1 shows an example of a thin plate production line in which Si vapor deposition and elemental vapor deposition for forming an insulating film are performed using the CVD method, where 1 is a heating zone and 2 is a heating zone.
A CVD treatment zone, 3 is a diffusion treatment zone, 4 is a CVD treatment zone, and 5 is a cooling 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 Ar: 80% and SiCl: 20% is blown onto the steel strip surface 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 to undergo a diffusion treatment, which results in a 6.5
%Si iron plate is obtained. Next, the iron plate is led to the CVD processing furnace 4, where it is subjected to a silicon etchant treatment at 1200°C in a [SiCl ₄ (5%) + Ar] atmosphere for 1 minute, and then cooled in a cooling furnace 5 in an N ₂ atmosphere containing 5% O ₂ . do.

For example, by such treatment, a stable oxide layer of about 1.0 μm is formed on the surface of a high-silicon iron plate.

〔Effect of the invention〕

According to the present invention described above, a silicon iron plate can be obtained efficiently in a short time by the CVD method, and a uniform and thin insulating film can be formed without baking treatment, and baking is not necessary. Therefore, the magnetic properties of the silicon iron plate are not impaired. Therefore, according to the present invention, a silicon iron plate having a uniform and thin insulating film and having excellent magnetic properties can be efficiently manufactured in a short time.

[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. After heating a steel plate to a temperature of 1023 to 1200°C in a non-oxidizing state, the steel plate at this temperature is subjected to chemical vapor deposition in a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction. The method is characterized in that an element capable of forming a stable oxide is vapor-deposited on the silicon iron plate obtained by silica treatment, and then an insulating film is formed by cooling the silicon iron plate in a weakly oxidizing atmosphere. A method for producing a silicon iron plate having an insulating film on its surface.