JPH0465898B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is directed to chemical vapor deposition (hereinafter referred to as CVD).
The present invention relates to a method for manufacturing high-silicon steel strip by a method. [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 et al. However, all of the previously proposed methods require an infiltration treatment time of 30 minutes.
There is a fundamental problem that the process is long (more than 1 minute) and cannot be applied to industrial continuous production. Also, the processing temperature
Since the temperature is extremely high at around 1230°C, the shape of the thin steel sheet after the penetration treatment is extremely poor, and in addition, because the treatment temperature is too high, there is a risk that the edges may melt due to overheating. 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 through a short-time leaching process using the leaching process. The purpose is to provide. [Means for solving the problem] For this reason, the present invention provides steel strips with 1023
After heating to a temperature of ~1200℃, the steel strip at this temperature
In a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction, silicon is continuously treated by chemical vapor deposition, and after the treatment, it is cooled in a non-oxidizing state and is not cooled to room temperature. Its basic feature is that it is wound into a coil in a hot or warm state, and then batch annealed in a vacuum to diffuse Si into the steel strip. The details of the present invention will be explained below. In the present invention, the composition of the steel strip serving as the base material is not particularly limited, but it is preferably determined as follows in order to obtain excellent magnetic properties. In the case of a 3-6.5% Si-Fe alloy, C: 0.01% or less, Si: 0-4%, Mn: 2 or less, and other unavoidable impurities are desirably 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. Note that the thickness of the steel strip is reduced by CVD treatment, and therefore it is necessary to use a steel strip with a thickness that is equal to the thickness of the final product plus the reduced thickness. The present invention provides such steel strips with [silicon treatment by CVD method]...[diffusion treatment by vacuum batch annealing]
A high-silicon steel strip is obtained by applying this process. FIG. 1 shows an example of a thin steel plate manufacturing process according to the method of the present invention, and shows a case where the method is applied to the treatment of a steel strip S. In the figure, 1 is a heating furnace, and 2 is a heating furnace.
CVD processing furnace, 3 is cooling furnace, 4 is coil winding room,
6 is a batch annealing furnace. The steel strip is heated in heating furnace 1 at a CVD treatment temperature of 1023~
After being heated to 1200℃ without oxidation, CVD treatment furnace 2
in a non-oxidizing 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.Ar, He, and _N2 , which do not cause such problems, are Among these, Ar and He are particularly preferred 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,
Along with this, the plate thickness will also decrease. By the way, when a 6.5% Si steel strip is manufactured using CVD treatment using a 3% Si steel strip as a base material, the mass decreases by 8.7% and the plate thickness decreases by approximately
Decrease by 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 subsequent diffusion process. In other words, when the SiCl ₄ concentration exceeds 35%, voids are significantly generated and remain even after the diffusion treatment. Figure 9 shows a cross section of the steel strip immediately after CVD treatment in an atmosphere containing 20% SiCl ₄ , and voids are seen in the deposited layer. Figure 10 shows this steel strip heated to 1200℃.
This shows a cross section after vacuum batch annealing for ×1 hr, and the voids immediately after the CVD treatment have almost completely disappeared. In contrast, Figure 11 shows SiCl ₄ 40%.
This is a cross section of a steel strip that was subjected to CVD treatment and then vacuum batch annealing, 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 Figure 2. However, according to experiments conducted by the inventors, even when treated 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°C is presumed to be because Si is deposited on the surface of the steel strip 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 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
Si diffusion heat treatment is performed by vacuum batch annealing. When the steel material is a steel strip as in this example, it is necessary to wind it into a coil after CVD treatment, but the surface layer of the steel strip immediately after CVD treatment (before diffusion heat treatment) contains more than 10 wt% of Si, and it is When rolled up, cracks occur in the steel strip, making it nearly impossible to wind it up at room temperature. Therefore, the steel strip S is cooled from the CVD treatment temperature to a predetermined temperature in a non-oxidizing state (including a reducing atmosphere) in a cooling furnace 3, and then wound into a coil in a hot or warm state. The lower limit of this winding temperature varies depending on the C thickness of the steel strip S, the amount of Si vapor deposited, etc., but for example, when the Si concentration in the surface layer of the steel strip is 14 to 15 wt%, it is usually necessary to wind it at 600° C. or higher. Note that there is no problem even if the film is cooled to room temperature after winding. The wound coil 7 is charged into a batch annealing furnace 6 and batch annealed in a vacuum state. Through this heat treatment, the Si deposited on the surface layer of the steel strip is diffused into the interior of the steel strip, resulting in a high-silicon steel strip having a substantially uniform Si concentration. In the present invention, by performing such diffusion heat treatment by batch annealing, sufficient diffusion and soaking can be performed, thereby making it possible to obtain an electromagnetic material with a uniform Si concentration. In addition, in the present invention, this batch annealing is performed under a vacuum condition, which allows crystal grains to grow larger than in normal atmosphere annealing, making it possible to obtain a steel material with excellent magnetic properties. High-silicon steel sheets are extremely susceptible to corrosion (rust) in the atmosphere, and this rust inhibits the growth of crystal grains during heat treatment, which in turn deteriorates the magnetic properties of the steel sheet. This corrosion includes atmospheric oxidation and moisture-induced rust (due to OH groups), with the latter corrosion being caused by dew condensation to be a major problem. In the present invention, the diffusion treatment is performed by batch annealing to ensure uniform diffusion of Si into the steel sheet. Because I have no choice but to leave it alone,
The occurrence of rust as described above becomes a major problem. The melting point of rust is 1000 to 1200°C, but since annealing in an atmosphere such as N ₂ is performed under normal pressure, the degree of scattering and purification of rust due to evaporation is extremely small. Furthermore, although oxygen is removed by annealing in a reducing atmosphere,
A rough and rough skin condition remains. Therefore, in such atmosphere annealing, since a liquid layer or residue of rust exists on the surface of the steel sheet, almost no growth of crystal grains can be expected as shown in the comparative material of Example 2, which will be described later. On the other hand, in the method of the present invention, in which Si diffusion treatment is performed by vacuum annealing, the evaporation of molten rust is promoted by the reduced pressure effect in vacuum, so the rust eventually scatters. The surface of the steel sheet is purified, and therefore the growth of crystal grains is significantly promoted. In addition, in the present invention, by performing the Si diffusion treatment by vacuum annealing, voids, which are a problem when manufacturing high-silicon steel sheets by silicon extrusion treatment, are completely eliminated,
Excellent magnetic properties of the steel plate can be ensured.
In other words, if impurities containing oxygen atoms are present in the surface layer of the steel sheet during the Si diffusion process, the oxygen atoms have the effect of fixing the Kirkendahl voids that occur with the diffusion of Si.
Even after the diffusion of the steel is completed, voids remain and deteriorate the magnetic properties of the steel sheet. In this regard, according to the present invention, since Si is diffused in a vacuum, impurities in the surface layer are removed as described above, and as a result, voids are prevented from remaining. This makes it possible to produce a high-silicon steel sheet with excellent magnetic properties. 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 concentration 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 is possible to further increase the CVD processing speed. Previously, it was believed that if the reactive gas was allowed to flow too much during CVD processing, voids would occur in the deposited layer, and the sluggishness of the deposited layer would also decrease.Therefore, the idea was 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 3 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. . Fourth
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 ratio increases in proportion to the increase in the flow velocity of the gas colliding with 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. Generally, 5N
A sufficient effect can be obtained at a flow rate of m/sec or less. It should be noted 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 methods including pretreatment can be used. 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, the cooling method in the cooling furnace 4 is not particularly limited, and various cooling methods such as gas jet cooling, mist cooling, radiation cooling, etc. can be employed singly 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%. [Examples] Γ Example 1 Using a small CVD processing furnace, the influence of SiCl ₄ concentration and CVD processing temperature on CVD processing performance was investigated.
The results are shown in FIGS. 5 and 6. 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 strip surface at a flow rate of 0.5 m/s as shown in Figure 3. This shows the case of 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 strip 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 strip (base metal Si amount + vapor deposited Si amount) for atmosphere method A and nozzle spraying method B using a similar CVD processing furnace.Si: 3%,
A steel strip with a thickness of 0.5 mm was treated with SiCl ₄ concentration of 21% and a treatment temperature of 1150.
This study investigated the case of CVD treatment at ℃. In the nozzle spraying method, atmospheric gas was sprayed from a perpendicular direction onto the steel strip at a flow rate of 0.2 Nm/sec using a slit nozzle. As can be seen from the figure,
While atmospheric method A takes 7 minutes to obtain a Si vapor deposition amount equivalent to 6.5% Si steel, nozzle spraying method B takes
I was able to process it in 1.5 minutes. Figure 8 shows the relationship between the collision gas flow velocity and the Si enrichment ratio of the steel strip (same as Figures 5 and 6) in the nozzle blowing method. The Si enrichment ratio of steel strip is increasing. ΓExample 2 By the continuous process shown in Figure 1, the plate thickness was 0.35mm.
The 3% Si steel was heated to 1150°C, then subjected to CVD treatment at a SiCl ₄ concentration of 20% in the atmospheric gas for 2 minutes, and after cooling, it was rolled up at 800°C, and then slowly cooled in a non-oxidizing state. After that, heat it in a vacuum furnace at 1200℃ x 1.
After soaking and holding for a period of time, 6.5% Si steel was produced. As a comparative material, CVD treatment was performed under the same conditions, and then 1200℃ x 1 in an atmosphere of N ₂ + H ₂ (H ₂ 25%).
A 6.5% Si steel was produced by batch annealing for several hours.
The table below shows the grain size and core loss value of the present invention material and comparative material, and it can be seen that a high silicon steel material having excellent magnetic properties is obtained by the method of the present invention.

[Table] [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 1200℃, problems such as poor shape of the steel strip and edge melting do not occur. In particular, high-silicon steel strips have the problem of being extremely susceptible to rust when left in the atmosphere, but in the present invention, the Si diffusion treatment is performed by vacuum annealing, which prevents rust due to the reduced pressure effect in a vacuum. Since it can promote evaporation, it can effectively scatter the rust that inevitably occurs when left in the atmosphere after silica treatment and purify the steel plate surface, which can significantly promote the growth of crystal grains. be able to. In addition, Si
Impurities including oxygen atoms in the surface layer are removed by vacuum annealing, which completely eliminates the voids that are a problem when manufacturing high-silicon steel sheets, resulting in excellent steel sheets. Magnetic properties can be ensured. From the above, by using the Si diffusion infiltration treatment method, it is possible to efficiently produce a high-silicon steel strip with excellent magnetic properties without increasing the length of the line.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the treatment process of the method of the present invention. FIG. 2 is a phase diagram of the Fe-Si system. Third
Figures A and B in Figure 4 are based on the nozzle spray method.
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. FIG. 7 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. 8 shows the relationship between the flow velocity of atmospheric gas colliding with the steel strip and the Si enrichment ratio of the steel strip in CVD treatment using the nozzle spraying method. Figures 9 to 11 are enlarged microscopic photographs showing the metal structures of cross sections of steel strips of the present invention material and comparative material;
The figure shows the structure immediately after CVD treatment in an atmosphere of 20% SiCl ₄ , Figure 10 shows the structure after diffusion heat treatment of the steel strip, and Figure 11 shows the structure after CVD treatment in 40% SiCl ₄ and then diffusion treatment. It shows the later organization. In the figure, 1 is a heating furnace, 2 is a CVD processing furnace,
3 is a cooling furnace, 5 is a batch annealing furnace, and S is a steel strip.

Claims (1)

[Claims] 1. After heating the steel strip to a temperature of 1023 to 1200 °C in a non-oxidizing state, the steel strip at this temperature is heated to a chemical vapor phase in a non-oxidizing gas atmosphere containing 5 to 35% SiCl ₄ by mole fraction. Continuously treated with silicon by vapor deposition method, after treatment,
It is characterized by being cooled in a non-oxidizing state, wound into a coil in a hot or warm state before being cooled to room temperature, and then batch annealed in a vacuum state to diffuse Si into the steel strip. Method for manufacturing high silicon steel strip.