JPH0549747B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a high-silicon steel strip by chemical vapor deposition (hereinafter referred to as CVD) in a continuous line. [Prior Art] High-silicon steel sheets are used as electromagnetic 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. [Problems to be Solved by the Invention] This infiltration method was proposed by Goyumi and Abe, and was studied in detail by Mitani and Onishi, but all of the previously proposed methods require a long infiltration treatment time. The fundamental problem is that it is long, over 30 minutes, and cannot be applied to continuous lines. In addition, the processing temperature is extremely high at around 1230°C, so the shape of the thin steel sheet after penetration treatment is extremely poor.In addition, because the processing temperature is too high, the edges may melt due to overheating. Stable plate threading cannot be expected. In addition, in the silicon extrusion method, Fe on the steel plate surface is
is dissipated in the form of FeCl ₂ etc., which reduces the plate thickness. However, in this type of treatment, the vapor deposition (film thickness) tends to become non-uniform due to non-uniformity in the atmospheric gas concentration distribution, etc., and as a result, there is variation in the way the plate thickness is reduced, and the plate thickness is There is a problem that it tends to become non-uniform in the direction. The present invention has been made in order to improve the drawbacks of the prior art, and provides a method that can stably produce high-quality high-silicon steel strips in a short period of time on a continuous line using the silicon extrusion method. The purpose is to provide. [Means for Solving the Problems] Therefore, the present invention provides a steel strip that is heated to 1023 to 1200°C by chemical vapor deposition in a non-oxidizing gas atmosphere containing 5 to 35% of SiCl ₄ in terms of mol fraction. The steel strip is subjected to a continuous _silicon leaching treatment at a temperature of
Its basic feature is that the steel strip is plastically worked by rolling at 600-200℃. In addition, the present invention provides an insulating film coating after the above-mentioned diffusion treatment, cooling, and plastic working by rolling.
Another basic feature is that it is then subjected to a baking process. The details of the present invention will be explained below. In the present invention, a steel strip as a base material (starting thin steel strip)
The component composition of is not particularly limited, but is preferably determined as follows in order to obtain excellent magnetic properties. For 3-6.5% Si-Fe alloy C: 0.01% or less, Si: 0-4.0%, Mn: 2%
Below, it is desirable that other unavoidable impurities be as low as possible. For Sendust alloy: C: 0.01% or less, Si: 4% or less, Al: 3-8
%, Ni: 4% or less, Mn: 2% or less, Cr, Ti
It is desirable that the content of elements that increase corrosion resistance, such as 5% or less, and other unavoidable impurities be as low as possible. The steel strip is not limited to one obtained by hot rolling-cold rolling, but may be one obtained by direct casting or rapid solidification. As mentioned above, the thickness of the steel strip is reduced by CVD treatment, and therefore, it is necessary to use a steel strip whose thickness is the final product thickness plus the reduced thickness. The present invention obtains a high-silicon steel strip by subjecting such a steel strip to a silicon exfoliation treatment and diffusion treatment using a CVD method. FIG. 1 shows a continuous treatment line for carrying out the method of the present invention, in which 1 is a heating furnace, 2 is a CVD treatment furnace, 3 is a diffusion treatment furnace, and 4 is a cooling furnace. After the steel strip S is heated in a heating furnace 1 to a temperature at or near the CVD treatment temperature, it is led to a CVD treatment furnace 2 and heated in a nonoxidizing gas atmosphere containing _SiCl4.
A silicone treatment is applied using the CVD method. A non-oxidizing gas containing SiCl ₄ means a neutral or reducing gas, and carrier gases for SiCl ₄ include Ar, N ₂ , He,
_H2 , _CH4, etc. can be used. 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 Among these, Ar and He are most preferable from the viewpoint of preventing nitridation of the material. The main reaction on the steel strip surface during CVD treatment is 5Fe+SiCl ₄ →Fe ₃ Si+2FeCl ₂ ↑. Si1 atoms are deposited on the steel strip 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 strip 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 strip decreases, and the thickness of the steel strip decreases accordingly. By the way, Si3% steel strip is used as the base material, and Si6.5% is reduced by CVD treatment.
When producing steel strips, the mass decreases by 8.7% and the plate thickness decreases by about 7.1%. The reason why CVD processing takes too long in conventional methods is thought to be because sufficient consideration has not been given to the CVD processing conditions.
The inventors of the present invention have studied the following and found that the following factors are necessary for performing CVD processing quickly. Optimization of SiCl ₄ concentration in atmospheric gas. Optimization of processing temperature. Promotion of diffusion of SiCl ₄ to the steel strip surface and dissipation of FeCl ₂ from the steel strip surface. For this reason, the present invention specifies the Si concentration in the atmospheric gas and the processing temperature in the CVD processing. 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 strip is continuously subjected to CVD treatment in such an atmosphere. Expect less than 5% _SiCl4 in the atmosphere
For example, the Si enrichment effect cannot be obtained, and
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. Figure 13 shows an atmosphere of 20% Sicl ₄ .
This shows a cross-section of the steel strip immediately after CVD treatment, and voids can be seen in the deposited layer. Figure 14 shows a cross section of this steel strip after being subjected to diffusion treatment at 1200°C for 20 minutes, and the voids immediately after the CVD treatment have almost completely disappeared. In contrast, Fig. 15 shows SiCl ₄ 40
This shows a cross section of a steel strip that has been subjected to CVD treatment at 10% and then diffusion treatment, and it can be seen that voids remain in layers. The CVD treatment temperature is in the range of 1023 to 1200°C.
Since the CVD treatment reaction is a reaction on the steel strip surface, the treatment temperature is strictly the steel strip surface temperature. The boiling point of FeCl ₂ , a reaction product from CVD treatment, is 1023℃, and below this temperature FeCl ₂ does not dissipate from the steel strip surface in a gaseous state, but adheres to the steel strip surface in a liquid state and inhibits the vapor deposition reaction. Resulting in. 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 Fig. 4, but according to experiments by the inventors, even when processed at about 1230°C, which is lower than 1250°C, The steel strip surface is partially melted,
Additionally, the edge of the steel strip melts due to overheating.
The reason why the steel strip melts even below 1250℃ is because
On the surface of the steel strip, 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 strip, and overheating of the edges will be reduced to around 1220℃ by setting the average temperature at the center of the steel strip to 1200℃. It was experimentally confirmed that it is possible to suppress the amount of dissolution, 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 strip S subjected to CVD treatment as described above is
Subsequently, the material is introduced into a diffusion furnace 3 and subjected to a diffusion treatment in a non-oxidizing gas atmosphere containing no SiCl ₄ . That is,
Immediately after CVD treatment, the Si concentration is high near the surface of the steel strip, while the central portion remains at the base metal Si concentration, which must be soaked and diffused to achieve a uniform Si concentration. This diffusion treatment must be performed in a non-oxidizing atmosphere in order not to oxidize the surface of the steel strip, and the higher the temperature, the shorter the treatment time. This diffusion treatment may be performed at a constant temperature, but
As can be seen from the Fe-Si phase diagram in Figure 4, as the diffusion progresses, the Si concentration in the surface layer of the steel strip decreases and its melting point increases, so as the diffusion progresses, the Si concentration gradually increases to the extent that the steel strip does not melt. Diffusion can be promoted by heating (for example, heating 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 account. After such a diffusion treatment, the steel strip S is cooled in a cooling furnace 4 and then rolled up. In the present invention, during this cooling, plastic working by rolling is performed in a warm state. FIG. 3 shows a specific structural example of a cooling furnace for this purpose. An intermediate chamber 8 is provided in the middle of the cooling furnace 4, and a skin pass mill 9 is disposed in this intermediate chamber 8. According to such equipment, the diffusion furnace 3
The steel strip S exiting the cooling furnace 4 is cooled to a warm state in the front cooling chamber 41, then rolled in a skin pass mill 9 in the intermediate chamber 8, and rolled up as it is in the warm state without final cooling. Alternatively, it may be subsequently cooled to room temperature in the rear cooling chamber 42 and then rolled up. As mentioned above, in the CVD process, Fe on the steel strip surface is dissipated in the form of FeCl ₂ due to the vapor deposition reaction, and the thickness of the steel strip decreases. This tends to cause non-uniform Si vapor deposition, which causes variations in the thickness of the steel strip S in the width direction and longitudinal direction after the CVD treatment and diffusion treatment. Therefore, in the present invention, the steel strip S in a warm state is rolled (skin pass rolling or normal rolling) to make the plate thickness uniform.
Shape correction and surface roughness adjustment can also be performed by such rolling. Note that the rolling may be performed not with a light reduction such as skin pass rolling, but with a larger reduction (normal rolling) for the purpose of reducing the plate thickness. The object of the present invention is to manufacture a high-silicon steel strip, and therefore rolling is performed in a warm state where the temperature of the steel strip S is 200 to 600°C. Figure 16 shows Si after diffusion treatment.
This shows the relationship between the rolling temperature and elongation due to rolling of a steel strip with a concentration of 6.5%, and it can be seen that the desired plastic workability cannot be obtained when the steel strip temperature is less than 200°C. Steel strip S is usually rolled at room temperature to 300℃, and generally has a high Si content (for example,
4.0% or less), it is preferable to wind up relatively thick steel strips in a warm manner. Therefore, the steel strip S is cooled from a hot state to the above-mentioned temperature range in the cooling furnace 4, then subjected to plastic working by rolling, and then rolled up in the warm state, or when rolled up at room temperature. , After the above rolling, it is finally cooled down to room temperature in the latter stage of the cooling furnace.
Afterwards, it is rolled up. In the actual production line, a plate thickness gauge and a profile gauge are installed upstream of the mill, and the mill is controlled based on the detection of plate thickness and plate shape by these gauges. In order to increase the CVD processing speed to the point where continuous processing of steel strips is possible, it is necessary to optimize the SiCl ₄ concentration in the atmospheric gas and the processing temperature as described above. By promoting the diffusion of SiCl ₄ into the steel strip and the diffusion of FeCl ₂ from the surface of the steel strip, it becomes 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 furthermore, because the gas flow was suppressed, the concentration of the reactant gas in the CVD processing furnace was distributed, resulting in non-uniformity in the thickness of the deposited film. Based on these facts, we conducted further studies and found that by blowing atmospheric gas onto the treated material using a blowing nozzle in the CVD processing furnace, or by forcing the atmosphere to circulate using a fan, etc.
Diffusion of SiCl ₄ onto the steel strip surface and reaction products
It significantly promotes the dissipation of FeCl ₂ from the surface of the steel strip, achieving a high deposition rate while suppressing the non-uniformity of the deposited film.
It was found that CVD treatment was possible. A method in which atmospheric gas is sprayed onto the steel strip surface using a spray nozzle is particularly effective for improving CVD processability. Figure 5 shows the implementation status of this nozzle spraying method, in which a spray nozzle 5 is placed in the CVD treatment furnace 2 facing the steel strip S, and atmospheric gas containing SiCl ₄ is sprayed onto the surface of the steel strip. . 6th
Figures A and B show the spraying conditions by the spray nozzle 5, and the spray can be applied perpendicularly to the steel strip surface as shown in A, or obliquely as shown in B. Si per unit time by such nozzle spraying
The enrichment rate increases in proportion to the increase in the flow velocity of gas impinging on the steel strip surface, but even if the flow velocity is increased excessively, the reaction rate at the interface becomes rate-determining, 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. Further, in the present invention, after the above-mentioned diffusion treatment, cooling, and plastic working by rolling, the steel strip can be continuously coated with an insulating film, and can be rolled up after the baking treatment. FIG. 2 shows a continuous processing line for this purpose, in which 6 is a coating device and 7 is a baking furnace. 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. A steel strip with a Si content of 4.0% or more is a brittle material at room temperature and hardly undergoes plastic deformation. For this reason, insulating film coating is applied by CVD.
If this is done on a separate line from the processing line, there is a risk that the steel strip will break during unwinding or unwinding of the coil.
Therefore, in the present invention, after plastic working by diffusion treatment, cooling, and rolling, an insulating paint is applied to the steel strip S in a coating device 6, and then a baking treatment is performed in a paint baking furnace 7. As the insulating paint, appropriate inorganic or organic paints can be used. Examples of inorganic paints include magnesium phosphate, chromic anhydride,
Silica sol etc. are used, and as the organic paint, plastic resin etc. are used. The paint is applied to the steel strip S using a roll coater method, spray method, etc.
Inorganic paints are baked at about 800°C, and organic paints are baked at about 200-300°C. Note that the heating furnace 1 performs non-oxidation heating, and for this reason, a heating method such as electric indirect heating, induction heating, radiant tube indirect heating, direct fire reduction heating, etc., may be used alone or in an appropriate combination. . Note that when using an indirect heating method, a pretreatment such as electric washing is performed prior to heating. For example, the following heating method including pretreatment can be adopted. Pretreatment - [Preheating] - Electric indirect heating (or induction heating) Pretreatment - [Preheating] - Radiant tube heating -
Electric indirect heating (or induction heating) [Preheating] - Direct flame reduction heating - Electric indirect heating (or induction heating) Pretreatment - [Preheating] - Radiant tube indirect heating (ceramic radiant tube method) [Preheating] - Direct flame reduction heating Further, there is no particular limitation on the cooling method used in the cooling furnace 4, and various cooling methods such as gas jet cooling, mist cooling, radiation cooling, etc. can be employed alone or in combination. As mentioned above, the present invention is suitable for manufacturing steel strips with extremely high silicon content, such as 6.5%Si steel strips, but conventionally, when manufacturing by rolling method, there are many deformations. Si with poor yield: 2 to 4
It has the advantage of being able to easily produce steel strips with a high silicon content of about 10%. [Example] ΓExample 1 Using a small CVD processing furnace-diffusion processing furnace, CVD
The effects of SiCl ₄ concentration and CVD treatment temperature on processability were investigated. The results are shown in FIGS. 7 and 8. In the figure, A is the atmosphere method, that is, CVD treatment without nozzle spraying, and B is the nozzle spraying method, that is, as shown in Figure 5, atmospheric gas is sprayed onto the steel strip surface at a flow rate of 0.5 m/S. This shows the case of CVD treatment. Note that the Si enrichment ratio is the difference between the initial Si concentration of the base material after CVD treatment and diffusion treatment.
Shows the increase in Si. 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 strip in the atmosphere.
It can be seen that an enrichment effect (CVD processability) is obtained. Figure 9 shows the relationship between the deposition time and Si concentration in the steel strip (Si concentration after diffusion treatment) for atmosphere method A and nozzle spraying method B using a similar CVD treatment furnace-diffusion treatment furnace.
This study investigated the case where a steel strip with Si: 3% and a plate thickness of 0.5 mm was subjected to CVD treatment at a SiCl ₄ concentration of 21% and a treatment temperature of 1150°C. In addition, in the nozzle spraying method, a slit nozzle is used to spray the steel strip from the perpendicular direction.
Atmospheric gas was blown at a flow rate of 0.2 Nm/sec. As can be seen from the figure, it takes 7 minutes to obtain 6.5% Si steel using the atmosphere method A, while the nozzle spraying method B
I was able to process it in 1.5 minutes. FIG. 10 shows the magnetic properties of the steel strips obtained in this way, and good results were obtained in all cases. Figure 11 shows the relationship between the collision gas flow velocity and the Si enrichment ratio of the steel strip (the ratio after diffusion treatment) in the nozzle blowing method. The enrichment rate is increasing. Γ Example 2 In a process line that incorporates the skin pass mill shown in Figure 3 into the continuous process shown in Figure 1, a steel strip containing 3.5% Si with a thickness of 0.33 mm is used as the base material, and a 25 mpm
With line speed, target plate thickness 0.30mm, width
A 900 mm steel strip containing 6.5% Si was produced. At this time, steel strips were manufactured under the following four conditions. A) CVD treatment is performed in an atmosphere of 80% Ar and 20% SiCl ₄ without skin pass rolling. B) Perform the same CVD treatment as in A and perform skin pass rolling. C) CVD treatment was performed on the steel strip using a nozzle spraying method with a reactive gas of 80% Ar and 20% SiCl ₄ at 0.3 Nm/sec.
The rolling process is carried out by colliding the gas at a gas flow rate of D) CVD treatment was performed in the same manner as in C), and skin pass rolling was performed. Table 1 shows the results of measuring the plate thickness deviation (increase/decrease from the target plate thickness) and surface roughness for the samples in each of these cases, and shows that the plate thickness is accurate and uniform by skin pass rolling. It is clear that it has changed.

[Table] ΓExample 3 The continuous process shown in Fig. 1 resulted in a plate thickness of 0.35 mm and a plate width of 0.35 mm.
Using a 900 mm steel strip containing 3.5% Si as a base material, a steel strip containing 6.5% Si was manufactured at a line speed of 25 mpm.
In addition, in the CVD processing furnace, the spray nozzle method
An atmospheric gas with a SiCl ₄ concentration of 20 mol % using Ar as a carrier gas was blown onto the steel plate at a gas flow rate of 0.3 Nm/sec. Figure 12 shows the thermal cycle in this case. In this example, the temperature was 1200℃ to 1320℃ during the diffusion process.
A two-stage heating process was carried out. This results in W _10/50 :
We were able to produce high-quality 6.5% Si steel strip with an extremely low core loss of 0.55W/Kg. [Effects of the Invention] According to the present invention described above, CVD treatment can be performed in a short time on a continuous line, and
Since CVD treatment is performed at temperatures below ℃, there are no problems such as poor shape of the steel strip or melting of edges, and it is possible to obtain steel sheets with uniform thickness, which can lead to longer lines. High-quality high-silicon steel sheets can be efficiently manufactured without any problems.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams showing continuous processing lines for carrying out the method of the present invention, respectively. FIG. 3 is an explanatory diagram showing a specific example of the configuration of the cooling furnace shown in FIGS. 1 and 2. FIG. FIG. 4 is a phase diagram of the Fe-Si system. 5 and 6A and 6B show the CVD treatment situation using the nozzle spraying method. FIG. 5 is an overall explanatory diagram, and FIGS. 6A and 6B are explanatory diagrams showing the nozzle spraying method, respectively. Figure 7 is
The relationship between the SiCl ₄ concentration in the gas and the steel strip Si enrichment ratio in CVD treatment, Figure 8 shows the relationship between the CVD treatment temperature and the steel strip Si enrichment rate.
This shows the relationship with the enrichment ratio. FIG. 9 shows a comparison of the relationship between the Si vapor deposition time and the Si concentration in the steel strip in the present invention using the atmosphere method and the nozzle spraying method. FIG. 10 shows a comparison of the magnetic properties of steel strips obtained by the method of the present invention, those obtained by the atmosphere method and those obtained by the nozzle blowing method. FIG. 11 shows the relationship between the flow velocity of the atmospheric gas colliding with the steel strip and the Si enrichment ratio of the steel strip in the CVD treatment using the nozzle spraying method.
FIG. 12 shows a thermal cycle in an embodiment of the present invention. Figures 13 to 15 _are microscopically enlarged photographs showing the metal structures of cross-sections of steel strips of the present invention material and comparative material. The figure shows the structure of the steel strip after diffusion heat treatment, and Figure 15 shows the structure of the steel strip after diffusion heat treatment.
The structure is shown after CVD treatment with SiCl ₄ :40% and subsequent diffusion treatment. FIG. 16 shows the relationship between the rolling temperature of the steel strip after the diffusion treatment and the elongation due to rolling. In the figure, 1 is a heating furnace, 2 is a CVD processing furnace,
3 is a diffusion treatment furnace, 4 is a cooling furnace, 6 is a coating device, 7 is a baking furnace, 9 is a skin pass mill, and S is a steel strip.

Claims (1)

[Claims] 1. A steel strip is processed by chemical vapor deposition in a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction.
Continuous silicon exfoliation treatment at a temperature of 1023-1200℃, then Si in a non-oxidizing gas atmosphere without _SiCl4
During the subsequent cooling process, the steel strip is heated to a temperature of 600 to 200
A method for producing a high-silicon steel strip on a continuous line, characterized by plastic working by rolling at °C. 2 A steel strip is processed by chemical phase deposition in a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction.
Continuous silicon exfoliation treatment at a temperature of 1023-1200℃, then Si in a non-oxidizing gas atmosphere without _SiCl4
During the subsequent cooling process, the steel strip is heated to a temperature of 600 to 200
1. A method for producing a high-silicon steel strip in a continuous line, characterized by plastic working by rolling at ℃, followed by insulation coating and baking treatment.