JP3267261B2 - Method for producing high silicon steel sheet having good surface properties and excellent workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high silicon steel sheet by a siliconizing treatment method.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 62-2270 discloses a method for industrially producing a high silicon steel sheet having a Si content of 4 wt% or more.
No. 78 is known. In this manufacturing method, a thin steel sheet containing less than 4 wt%
₄ is a method of obtaining a high silicon steel sheet by infiltrating Si by reacting at high temperature with Si and diffusing the permeated Si in the thickness direction.
In Japanese Unexamined Patent Application Publication No. 62-227079 and the like, a steel sheet is subjected to continuous siliconizing treatment at a temperature of 1023 ° C. to 1200 ° C. in a non-oxidizing atmosphere containing 5% to 35% by weight of SiCl ₄ to form a coil. High silicon steel sheet is obtained.

[0003] In general, the siliconizing treatment of the steel sheet SiCl ₄ is used as a raw material gas for Si supply, the SiCl ₄
Reacts with the steel sheet according to the following reaction formula, and Si penetrates into the surface layer of the steel sheet. SiCl ₄ + 5Fe → Fe ₃ Si + 2FeCl ₂ The Si that has permeated the steel sheet surface layer in this manner is SiCl ₄
The steel sheet is diffused in the thickness direction by soaking in a non-oxidizing gas atmosphere containing no.

[0004] In order to continuously siliconize a steel sheet by such a process, a continuous siliconizing line as shown in FIG. 5 is used. This continuous siliconizing line is equipped with a heating zone, a siliconizing zone (siliconizing furnace), a diffusion zone and a cooling zone from the entry side. in impregnated with Si by reacting with SiCl _4, then subjected to heat treatment for diffusing Si in the thickness direction in the diffusion soaking zone continuously coiled high silicon by cooling in the cooling zone A steel plate is manufactured.

[0005] When continuously siliconizing treatment steel sheets thus the SiCl ₄ as a raw material gas, silica oxygen component contained in the siliconizing treatment atmosphere (moisture and oxygen) are reacted with SiCl ₄ gas is generated However, there is a problem that the silica adheres to a portion in contact with the steel plate, such as a hearth roll in a furnace, and generates a pressing flaw on the steel plate. In order to solve such a problem, it is desirable to reduce the water content and the oxygen concentration in the siliconizing treatment atmosphere to the utmost, but it takes an extremely long time to reduce the water and oxygen concentrations in the continuous furnace to the utmost. And it is very difficult to achieve.

[0006] In addition, the high silicon steel sheet manufactured by the siliconizing treatment has a problem that the surface and grain boundaries of the steel sheet are oxidized by moisture and oxygen in the siliconizing treatment atmosphere, and the oxidation significantly deteriorates the workability of the steel sheet. There is. Regarding the deterioration of workability due to grain boundary oxidation, when a high silicon steel sheet is held at a high temperature for a long time as in the case of siliconizing treatment, the crystal grains grow and penetrate in the thickness direction. When the boundaries are oxidized, the grain boundary bonding force decreases, and as a result, the workability of the steel sheet deteriorates.

Therefore, in order to avoid such a problem caused by moisture and oxygen contained in the siliconizing atmosphere, it is necessary to add C in advance to the base steel sheet and react this C with oxygen in the atmosphere. (That is, by utilizing the decarburization reaction of the steel sheet), a method of reducing the moisture and oxygen concentrations existing near the steel sheet surface where the siliconizing reaction occurs to a minimum can be considered, and the production of high silicon steel sheet using this method is considered. A method has been proposed in JP-A-8-209325.

In general, when the C content of the manufactured high silicon steel sheet exceeds 0.005 wt%, iron loss deterioration and magnetic aging become problems. The amount of C to be added to the base steel sheet must be determined in consideration of the amount of C sufficient for improving the atmosphere (reduction of moisture and oxygen) and the amount of C remaining after the siliconizing treatment.

[0009]

However, in an industrial continuous furnace, the moisture and oxygen concentrations in the furnace atmosphere are as follows (1) to (3).
It is extremely difficult to obtain a stable and stable atmosphere in which the moisture and oxygen concentrations are constant over time. (1) Moisture and oxygen intrusion due to aging deterioration of the seal at the furnace opening (2) Dissipation of water contained in the refractory inside the furnace due to heat rise (3) Changes in operating conditions (furnace time, furnace time Inside temperature)

Therefore, when the above method is performed,
Although it is inevitable that the decarburization amount of the steel sheet varies due to these factors, changing the C amount of the base steel sheet in accordance with such a change in the decarburization amount in the iron making process requires time. It is impossible at all in terms of cost. For the reasons described above, it is difficult to carry out the method for producing a high silicon steel sheet utilizing the above-described decarburization reaction of a steel sheet on an industrial scale, and therefore, in the related art, silica which impairs the surface properties of the high silicon steel sheet is used. It has been difficult to stably produce a high silicon steel sheet excellent in workability on an industrial scale while preventing generation.

Accordingly, an object of the present invention is to prevent the generation of silica due to oxygen contained in the siliconizing atmosphere and to prevent oxidation on the steel sheet surface and grain boundaries, thereby improving both the surface properties and workability. An object of the present invention is to provide a method capable of industrially stably producing an excellent high silicon steel sheet.

[0012]

In order to solve such problems, the method for manufacturing a high silicon steel sheet according to the present invention has the following features. [1] A method for producing a high silicon steel sheet by subjecting a base material steel sheet containing less than 4 wt% of Si to siliconizing treatment in an atmosphere containing SiCl ₄ gas in a siliconizing treatment furnace,
The C content of the base steel sheet is set higher than the target C content of the steel sheet after the siliconizing treatment, and the decarburization reaction of the base steel sheet is caused by the oxygen content contained in the siliconizing treatment atmosphere. In the method of performing the siliconizing treatment of a steel sheet, the S supplied to the siliconizing furnace in accordance with the amount of oxygen contained in the siliconizing atmosphere.
By adjusting the oxygen equivalent in the iCl ₄ containing gas,
Controls the amount of decarburization of the base steel sheet during the siliconizing reaction to achieve the target C
A method for producing a high silicon steel sheet having good surface properties and excellent workability, characterized by obtaining a high silicon steel sheet having a high content.

[2] In the manufacturing method of the above [1], the siloxane is contained in the SiCl ₄ -containing gas supplied to the siliconizing furnace, and the concentration of the siloxane is adjusted.
A method for producing a high silicon steel sheet having good surface properties and excellent workability, characterized by controlling an oxygen equivalent in a Cl ₄ -containing gas. [3] In the method of [1] or [2], the decarburization amount of the base steel sheet during the siliconizing reaction is controlled such that the C content of the high silicon steel sheet after the siliconizing treatment is 30 to 50 ppm. A method for producing a high silicon steel sheet having good surface properties and excellent workability.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention is intended to reduce the Si content to less than 4 wt%.
Steel sheet containing SiCl in a siliconizing furnace
_In producing a high silicon steel sheet by performing a siliconizing treatment in an atmosphere containing _four gases, the C content of the base steel sheet is set to be higher than a target C content of the steel sheet after the siliconizing treatment. This is a method of performing a siliconizing treatment of a base material steel sheet while causing a decarburization reaction of the base material steel sheet by an oxygen content contained in a processing atmosphere.

A method utilizing such a decarburization reaction of the base steel sheet, that is, by adding C in advance to the base steel sheet and reacting this C with oxygen in the atmosphere, the siliconizing reaction can be prevented. When implementing a method of reducing the moisture and oxygen existing near the steel sheet surface that occurs, the amount of C added to the base steel sheet should be an amount that can sufficiently react with the oxygen and moisture existing near the steel sheet surface during the siliconizing treatment. On the other hand, after the siliconizing treatment, it is necessary to reduce the amount to a level that does not adversely affect the magnetic properties, that is, decarburize. On the other hand, as described above, since the water and oxygen concentrations in the furnace atmosphere change with time, it is necessary to control the decarburization reaction corresponding to the change.

In response to such a demand, the present inventors responded to a change in the atmosphere of an ordinary industrial furnace by changing the oxygen equivalent in the SiCl ₄ -containing gas supplied as a raw material into the siliconizing furnace. It has been found that the decarburization reaction can be controlled. That is, even if the oxygen concentration and the water content in the furnace atmosphere change due to the above-described factors, if the oxygen equivalent in the SiCl ₄ -containing gas is significantly changed accordingly, the decarburization reaction of the base steel sheet is performed. Was found to be able to be controlled within a desired range.

Therefore, by monitoring the water content (dew point) and oxygen concentration in the siliconizing treatment atmosphere and adjusting the oxygen equivalent in the SiCl ₄ -containing gas introduced into the siliconizing treatment furnace according to the changes, Regardless of the change in the water content and oxygen concentration in the siliconizing atmosphere, the decarburization amount of the base steel sheet is controlled to a desired level, whereby a high silicon steel sheet having a target C content can be obtained. . On the other hand, the oxygen content existing near the surface of the base steel sheet is consumed by the decarburization reaction of the steel sheet, so that generation of silica and oxidation of the steel sheet due to oxidation of SiCl ₄ are appropriately prevented. Generally, 1023-120
At a siliconizing temperature of 0 ° C., SiCl ₄ is easily oxidized near the surface of the steel sheet, but the decarburization reaction reduces the oxygen content near the surface of the base steel sheet, thereby effectively suppressing the generation of silica. Also, oxidation of the steel sheet surface and grain boundaries is suppressed.

For this reason, in the method of the present invention, the oxygen equivalent in the SiCl ₄ -containing gas supplied into the siliconizing furnace is adjusted according to the amount of oxygen (water content and oxygen concentration) contained in the siliconizing atmosphere. By doing so, the amount of decarburization of the base material steel sheet during the siliconizing reaction is controlled, and a high silicon steel sheet having a target C content is obtained.

Further, SiCl supplied into the siliconizing furnace is
_As a means for controlling the oxygen equivalent in the _4- containing gas, an oxide of SiCl ₄ as a raw material gas is used.
Focusing on siloxanes having similar material properties and l _4,
This siloxane is converted to liquid or gaseous SiCl ₄
Or SiCl ₄ is contained in containing gas, by managing the content level, SiCl ₄ supplied to the siliconizing treatment furnace
The following experiment was conducted under the idea of controlling the oxygen equivalent in the contained gas.

In this experiment, SiCl ₄ -containing gas (source gas + carrier gas) was added by adding siloxane to the SiCl ₄ gas supplied into the test continuous siliconizing furnace.
The oxygen equivalent in the medium was changed, and a base material steel sheet having a different C content was subjected to a siliconizing treatment, and the decarburization amount was measured for each base material steel sheet. The siliconizing conditions (silicide amount, processing temperature, furnace time, etc.) for all base steel sheets are all the same, and the furnace atmosphere is dew point -30.
° C and the oxygen concentration were adjusted to 10 ppm. The result is shown in FIG.

According to FIG. 1, although there is a difference in the level of the decarburization amount due to the difference in the C content of the base steel sheet, the oxygen equivalent (siloxane concentration) in the SiCl ₄ -containing gas is changed in any base steel sheet. It is understood that the decarburization amount of the base steel sheet can be appropriately controlled by changing the value. As described above, in the method of controlling the decarburization amount of the base steel sheet by adding siloxane to the raw material gas (SiCl ₄ ) and adjusting the concentration thereof, the raw material gas supplied to the steel sheet surface is directly oxygenated via the siloxane. Can be directly supplied to the surface of the steel sheet reacting with the raw material gas to react with C in the steel sheet. Therefore, the supplied oxygen can be made to react more efficiently with C in the steel sheet as compared with the method of supplying water or oxygen into the SiCl ₄ -containing gas or the siliconizing atmosphere supplied into the furnace. The charcoal reaction can be controlled directly and easily.

On the other hand, the siloxane added to the SiCl ₄ -containing gas also causes a reaction to generate silica by polymerizing itself. However, by regulating the upper limit of the oxygen equivalent in the SiCl ₄ -containing gas including siloxane, and preferably controlling this to 2.5% or less,
The above reaction can be at a level that does not cause any problem, that is, a level that does not adversely affect the surface properties of the steel sheet even if silica is generated.

As described above, the amount of decarburization of the base steel sheet can be easily controlled by controlling the oxygen equivalent in the SiCl ₄ -containing gas supplied into the siliconizing atmosphere by the siloxane addition amount. Therefore, for example, the C content of the base steel sheet is set higher than a target C content of the steel sheet after the siliconizing treatment by a certain level or more, and the water content and the oxygen concentration in the siliconizing treatment atmosphere are monitored (measured). In response to this, the amount of siloxane added to the SiCl ₄ -containing gas is controlled so that the decarburization amount of the base steel sheet (therefore, the C content of the steel sheet after the siliconizing treatment) becomes a target level. The amount of moisture and oxygen existing near the surface of the base steel sheet during the siliconizing treatment can be reduced as much as possible, and the C content in the steel sheet after the siliconizing treatment can be reduced to a sufficiently low level. Thereby, generation of silica and oxidation of the steel sheet are prevented, and a high silicon steel sheet having good surface properties without press flaws and excellent workability can be stably manufactured.

In order to control the oxygen equivalent in the SiCl ₄ -containing gas in the method of the present invention, it is simplest to add siloxane to the SiCl ₄ -containing gas and adjust the content as described above. Although it is advantageous in that the decarburization reaction of the steel sheet can be directly and easily controlled, it is possible to control the concentration of SiCl ₄ containing gas supplied into the furnace together with or instead of the addition of such siloxane and the control of its concentration. A method of adding moisture or oxygen to the atmosphere for the siliconizing treatment can also be performed.

Further, SiCl ₄ introduced into a siliconizing furnace is used.
As a method of adding siloxane to a gas, a siloxane liquid is gasified, and this is converted to SiCl ₄ gas or SiCl _4.
Although it can be added to the contained gas (SiCl ₄ gas + carrier gas), unreacted Si discharged from the siliconizing furnace is
Since siloxane is inevitably generated in the step of recovering Cl ₄ , it is most convenient to use this siloxane. That is, in the siliconizing treatment equipment exhaust gas containing unreacted SiCl ₄ discharged from siliconizing treatment furnace is guided to SiCl ₄ recovery facility, where it SiCl ₄ unreacted is condensed recovered as a liquid, the recovery process In SiCl ₄
Reacts with water and oxygen contained in the exhaust gas to inevitably produce siloxane. Therefore, by recycling such recovered SiCl ₄ containing siloxane as at least a part of the source gas, it is possible to supply the SiCl ₄ -containing gas containing siloxane to the siliconizing furnace.

FIG. 2 and FIG. 3 show that SiCl _4
3 shows an example of a source gas recovery / supply system in which the oxygen equivalent in a SiCl ₄ -containing gas is controlled using siloxane generated in the recovery facility. In FIG. 2, reference numeral 1 denotes a silicon-silica treatment furnace, and 2 denotes an SiCl ₄ recovery facility for receiving exhaust gas discharged from the silicon-silica treatment furnace 1 and recovering unreacted SiCl ₄ in the exhaust gas as a liquid. In the recovery step, siloxane is inevitably generated).
₄ A recovery tank for storing a mixed solution of SiCl ₄ recovered in the recovery facility 2 and siloxane generated during the recovery process, 4 is a stock solution tank of SiCl ₄ , 5 is a SiCl ₄ + siloxane solution from the recovery tank 3 And an evaporating tank for receiving a SiCl ₄ stock solution from the stock solution tank 4 and evaporating the stock solution to generate a stock gas.

A liquid supply pipe 6 having a pump 7 is connected between the SiCl ₄ recovery equipment 2 and the recovery tank 3,
A pump 9 and a liquid supply pipe 8 having a flow control valve 10 are connected between the recovery tank 3 and the evaporating tank 5, and a pump 1 is connected between the undiluted liquid tank 4 and the evaporating tank 5.
2 and a liquid supply pipe 11 having a flow control valve 13,
Further, the evaporating tank 5 and the siliconizing furnace 1 are provided with a flow control valve 15.
Are connected by a gas supply pipe 14 having Gas chromatography 16 and 17 for analyzing and measuring the siloxane concentration in the liquid are arranged in the recovery tank 3 and the evaporating tank 5, respectively. Further, the evaporating tank 5 has a heating element 18 immersed in a liquid inside the tank, and a raw material gas is generated by evaporating the raw material liquid by heating by the heating element 18.

According to the equipment shown in FIG. 2, the exhaust gas containing unreacted SiCl ₄ discharged from the silicon
It is led to the Cl ₄ recovery facility 2 where the unreacted SiCl ₄
Is condensed and recovered as a liquid. In this recovery process, SiCl ₄ reacts with moisture and oxygen contained in the exhaust gas to inevitably generate siloxane. Therefore, the recovered SiCl ₄ liquid contains siloxane. The recovered SiCl ₄ + siloxane liquid is sent to the recovery tank 3 for storage through the liquid supply pipe 6, and further sent to the evaporation tank 5 through the liquid supply pipe 8. The SiCl ₄ stock solution in the stock solution tank 4 is also sent to the evaporation tank 5 through the liquid supply pipe 11.

In the recovery tank 3 and the evaporating tank 5, gas chromatography is performed.
According to graphs 16 and 17, SiCl ₄+ In siloxane liquid
The siloxane concentration is monitored from time to time,
Siloxane concentration (that is, required
SiCl₄Liquid supply according to the oxygen concentration in the contained gas).
The opening of the flow control valves 10, 13 of the supply pipes 8, 11 is controlled.
SiCl which is sent to the evaporation tank 5₄+ Siloxane solution, S
iCl₄The amount of stock solution is adjusted.

In the evaporating tank 5, the raw material liquid is evaporated by heating with the heating element 18, and SiCl ₄ gas (raw gas) containing siloxane is generated. In the evaporating tank 5, the amount of evaporation of the raw material liquid by heating the heating element 18 is controlled according to the amount of raw material gas supplied. The raw material gas is supplied to the siliconizing furnace 1 through the gas supply pipe 14 while the flow rate is adjusted by the flow control valve 15.

The carrier gas is mixed with the raw material gas supplied to the siliconizing furnace 1 through the gas supply pipe 14 on the downstream side of the flow control valve 15. The mixed gas (processing gas) is heated by a suitable heating means (for example, a heater installed in a gas nozzle) at a stage before being introduced into the siliconizing furnace 1, and then introduced into the siliconizing furnace 1. Is done.
In addition, the oxygen and moisture contents in the siliconizing furnace 1 are constantly measured by a continuous measuring device, and samples are periodically taken from the steel sheet after the siliconizing treatment to measure the decarburization amount of the steel sheet. Based on the data, the siloxane concentration in the SiCl ₄ + siloxane solution in the evaporation tank 5 is determined, and the liquid supply pipes 8 and 11 are set as described above so that the siloxane concentration measured by the gas chromatography 17 becomes the value. The amounts of the SiCl ₄ + siloxane solution and the undiluted SiCl ₄ solution supplied to the evaporation tank 5 are adjusted by adjusting the opening degrees of the flow control valves 10 and 13.

FIG. 3 shows another example of the equipment, in which the silicidation furnace 1 receives the exhaust gas discharged from the silicification furnace 1 and recovers the unreacted SiCl ₄ in the exhaust gas as a liquid. ₄ recovery equipment 2, a recovery tank 3 for storing a mixture of SiCl ₄ recovered by the SiCl ₄ recovery equipment 2 and siloxane generated during the recovery step, SiCl
₄ is similar to the equipment shown in FIG. 2 except that an evaporating tank 5 a for receiving the SiCl ₄ undiluted solution from the undiluted liquid tank 4 and a SiC
An evaporating tank 5b for receiving the l ₄ + siloxane liquid is separately provided, and is supplied to the siliconizing furnace 1 while adjusting the ratio of each source gas generated in the evaporating tanks 5a and 5b. .

A liquid supply pipe 6 having a pump 7 is connected between the SiCl ₄ recovery equipment 2 and the recovery tank 3,
A liquid supply pipe 8 having a pump 9 is connected between the recovery tank 3 and the evaporation tank 5b, and a liquid supply pipe 11 having a pump 12 is provided between the stock solution tank 4 and the evaporation tank 5a. Has been contacted. Further, the evaporating tank 5
a, 5b and the siliconizing furnace 1 are connected by a gas supply pipe 14, which is connected to a flow control valve 15;
a and 15b, each of which is composed of branch pipes 14a and 14b attached to each of the evaporation tanks 5a and 5b, and a main pipe 14c where these pipes merge.

A gas chromatography 19 for analyzing and measuring the siloxane concentration in the liquid is disposed in the evaporating tank 5b. Each of the evaporation tanks 5a and 5b has heating elements 18a and 18b immersed in the liquid inside the tanks, and generates a source gas by evaporating the source liquid by heating by the heating elements 18a and 18b.

According to the equipment shown in FIG. 3, similarly to the equipment shown in FIG.
SiCl ₄ is condensed recovered as a liquid in the SiCl ₄ recovery facility 2 from exhaust gas containing Cl _4. Then, the SiCl ₄ + siloxane liquid containing siloxane generated in the recovery process is sent to the recovery tank 3 for storage through the liquid supply pipe 6, and further sent to the evaporation tank 5 b through the liquid supply pipe 8. Further, the SiCl ₄ stock solution in the stock solution tank 4
1 to the evaporating tank 5a.

In the evaporation tanks 5a and 5b, the heating elements 18a and 18
b, the raw material liquid is evaporated by heating in the evaporating tank 5a.
In this case, SiCl ₄ gas is generated, and in the evaporation tank 5b, SiCl ₄ gas containing siloxane is generated. These evaporation tanks 5
a, 5b, the heating elements 18a,
The amount of evaporation of the raw material liquid by heating at 18b is controlled. The raw material gas generated in each of the evaporation tanks 5a and 5b is supplied to the flow control valve 15
The gas is supplied to the siliconizing furnace 1 through the gas supply pipe 14 while the flow rate is adjusted by a and 15b.

The carrier gas is mixed with the raw material gas supplied to the siliconizing furnace 1 through the gas supply pipe 14 on the downstream side of the flow control valve 15. The mixed gas (processing gas) is heated by a suitable heating means (for example, a heater installed in a gas nozzle) at a stage before being introduced into the siliconizing furnace 1, and then introduced into the siliconizing furnace 1. Is done.
In addition, the oxygen and moisture contents in the siliconizing furnace 1 are constantly measured by a continuous measuring device, and samples are periodically collected from the steel sheet after the siliconizing treatment to measure the decarburization amount. SiCl ₄ to be supplied to the siliconizing furnace 1 based on
The oxygen equivalent in the contained gas is determined, and the flow control valve 15 is adjusted so that the oxygen equivalent in the SiCl ₄ -containing gas becomes the value.
The raw material gas from the evaporation tank 5a and the evaporation tank 5
The flow ratio of the source gas from b is adjusted. Evaporation tank 5b
In, the siloxane concentration in the SiCl ₄ + siloxane solution is constantly measured by the gas chromatography 19, and this is data for determining the flow rate ratio of the source gas.

In the method of the present invention, the C content of the base steel sheet is made higher than the target C content of the steel sheet after the siliconizing treatment in accordance with the required decarburization amount. It is preferable to control the amount of decarburization of the base steel sheet during the siliconizing reaction so that the C content of the high silicon steel sheet after the treatment is 20 to 50 ppm.
If the C content of the high silicon steel sheet after the siliconizing treatment exceeds 50 ppm, the iron loss characteristics of the product steel sheet are significantly deteriorated, which is not preferable. On the other hand, when the C content is less than 20 ppm, the effect of suppressing the generation of silica on the surface layer of the steel sheet due to the excess of oxygen and moisture in the siliconizing atmosphere is lost, thus deteriorating the surface properties of the steel sheet and reducing the grain boundaries of the steel sheet. Deterioration of workability due to oxidation occurs.

In the production of high-silicon steel sheets by the siliconizing treatment method, which is the object of the present invention, SiCl
₄ concentration is supplied approximately 5～35Mol% about SiCl ₄ containing gas (SiCl ₄ + carrier gas) gas, steel introduced into the siliconizing treatment furnace is siliconizing treatment at a processing temperature of about from 1,023 to 1,200 ° C. Then, it is introduced into a diffusion soaking furnace and soaked at a treatment temperature of 1230 ° C. or less. Further, the silicon content of the manufactured high silicon steel sheet is arbitrary, but generally, a high silicon steel sheet having Si: 5 to 10 wt% is manufactured.

[0040]

[Example 1] As an example of the present invention, in a siliconizing treatment facility having a source gas recovery / supply system as shown in FIG. Content: 3 wt%, C content: 50 ppm, sheet thickness 0.3 mm
Was subjected to continuous siliconizing treatment to produce a 6.5% Si steel sheet. In a siliconizing furnace, 12 in an N ₂ + SiCl ₄ atmosphere.
A siliconizing treatment of 00 ° C. × 5 minutes is performed, and then, in a N ₂ atmosphere of a diffusion soaking furnace, a diffusion soaking treatment for diffusing Si added to the surface of the steel sheet in the thickness direction by the siliconizing reaction is performed at 1200 ° C. X 15 minutes.

As a comparative example, the siliconizing treatment furnace used was a siliconizing treatment facility having a raw material gas recovery / supply system as shown in FIG. The base material steel plate was subjected to continuous siliconizing treatment to produce a 6.5% Si steel plate. Here, in the source gas recovery / supply system shown in FIG.
SiCl ₄ was condensed and recovered as a liquid from the exhaust gas containing unreacted SiCl ₄ discharged from the siliconizing furnace 1 in a SiCl ₄ recovery facility 2, and a SiCl ₄ liquid containing siloxane generated in the recovery process was provided with a pump 24. Liquid supply pipe 2
3 to a collection tank 20 for storage,
The liquid is sent from the recovery tank 20 to the undiluted liquid tank 21 through a liquid supply pipe 25 provided with a pump 26 and a flow control valve 27. SiCl containing siloxane in this stock solution tank 21
_{The four} liquids are supplied from the tank 21 to the pump 29 and the flow control valve 30.
Is sent to the evaporation tank 22 through a liquid supply pipe 28 provided with
In the evaporating tank 22, SiCl ₄ gas (source gas) containing siloxane is generated by evaporating the source liquid by heating with the heating element 31. The source gas is silicified through a gas supply pipe 32 provided with a flow control valve 33. It is supplied to the processing furnace 1.

In the example of the present invention, in the raw material gas recovery / supply system shown in FIG. 2, the siloxane concentration in the raw material gas is controlled and controlled in accordance with the water content and the oxygen concentration in the siliconizing treatment furnace. The decarburization amount of the base steel sheet was made substantially uniform. On the other hand, in the comparative example, since the source gas recovery / supply system shown in FIG. 4 was used, the control and management of the siloxane concentration in the source gas were not performed. In both the present invention example and the comparative example, the first day, the seventh day, the 14th day, the 21st day,
Table 1 shows the C content of the product steel sheet, the decarburization amount of the base steel sheet, the surface properties of the product steel sheet (whether or not product pressing flaws are generated) and the workability (critical bending radius) sampled on the 28th day.

According to Table 1, in the comparative example in which the siloxane concentration in the raw material gas was not controlled / managed, the decarburization amount of the steel sheet during the siliconizing treatment changed (increased) with time. After the day, pressing flaws due to silica have occurred. This is because the siloxane concentration in the raw material gas was relatively excessive in order to obtain a proper decarburization reaction, and the water and oxygen in the siliconizing atmosphere were not sufficiently consumed for decarburization of the steel sheet. It is considered that silica was generated by moisture and oxygen in the atmosphere. Similarly, the workability (critical bending radius) deteriorated on and after the 14th day, because the siloxane concentration in the raw material gas became relatively excessive.
Moisture and oxygen in the siliconizing atmosphere are not sufficiently consumed for decarburization of the steel sheet, resulting in grain boundary oxidation of the steel sheet due to moisture and oxygen in the atmosphere, or excessive decarburization of the steel sheet. It is considered that the amount of the product C was extremely reduced (less than 20 ppm).

On the other hand, in the case of the present invention, the siloxane concentration in the raw material gas is controlled and controlled according to the change in the water content and the oxygen concentration in the siliconizing atmosphere, so that during the entire operation period, In addition, moisture and oxygen near the surface of the steel sheet in the siliconizing atmosphere are sufficiently consumed for the decarburization reaction with the steel sheet, and the decarburization amount is appropriately controlled in the range of 23 to 25 ppm. For this reason, a high silicon steel sheet having no pressing flaws due to silica as in the comparative example and having excellent workability (critical bending radius) is stably obtained.

[0045]

[Table 1]

[Example 2] As an example of the present invention, a silicon-containing treatment furnace having a material gas recovery / supply system as shown in FIG. Amount: 3 wt%, C content: 80 ppm, sheet thickness 0.3 m
m was continuously siliconized to produce a 6.5% Si steel sheet. In the siliconizing furnace, 1 in an N ₂ + SiCl ₄ atmosphere.
A siliconizing treatment at 200 ° C. for 5 minutes is performed, and then, in a N ₂ atmosphere of a diffusion soaking furnace, a diffusion soaking treatment for diffusing Si added to the surface of the steel sheet by the siliconizing reaction in the thickness direction is performed at 1200 ° C. X 15 minutes.

Further, as a comparative example, a silicon-silicon treatment furnace using a silicon-silicon treatment facility having a source gas recovery / supply system as shown in FIG. 4 (silicone treatment facility as shown in FIG. 5) was used. The base material steel plate was subjected to continuous siliconizing treatment to produce a 6.5% Si steel plate. In the example of the present invention, in the raw material gas recovery / supply system shown in FIG. 3, the siloxane concentration in the raw material gas is controlled and controlled according to the water content and the oxygen concentration in the siliconizing furnace, and the base material during the siliconizing process is controlled. The decarburization amount of the steel sheet was made almost uniform. On the other hand, in the comparative example, since the source gas recovery / supply system shown in FIG. 4 was used, the control and management of the siloxane concentration in the source gas were not performed.

In both the present invention example and the comparative example, the C content of the product steel sheet sampled on the first day, the seventh day, the 14th day, the 21st day, and the 28th day during the operation period of 28 days, the base steel sheet Table 2 shows the decarburization amount, iron loss value and workability (critical bending radius) of the product steel sheet. According to Table 2, in the comparative example in which the siloxane concentration in the raw material gas was not controlled and controlled, the C content of the product steel sheet was 5 because the decarburization amount was extremely small at the beginning of the operation.
Exceeding 0 ppm, which results in poor workability (critical bending radius) and iron loss.

On the other hand, in the case of the present invention, since the siloxane concentration in the raw material gas is controlled and controlled in accordance with the change in the water content and the oxygen concentration in the siliconizing atmosphere, during the entire operation period. In addition, moisture and oxygen near the surface of the steel sheet in the siliconizing treatment atmosphere are sufficiently consumed for the decarburization reaction with the steel sheet, and the decarburization amount is appropriately controlled in the range of 34 to 43 ppm. Therefore, there is no deterioration in workability and iron loss in the early stage of operation as in the comparative example, and a high silicon steel sheet having excellent magnetic properties and workability (critical bending radius) during the entire operation period is stably obtained. .

[0050]

[Table 2]

[0051]

According to the present invention described above, by controlling the oxygen equivalent in the SiCl ₄ -containing gas supplied to the siliconizing furnace, the amount of decarbonization of the base steel sheet during the siliconizing reaction can be appropriately controlled. It is possible to reduce the water and oxygen concentration near the surface of the base steel sheet during the siliconizing treatment as much as possible, thereby properly preventing the generation of silica and the oxidation of the steel sheet surface and grain boundaries, The C content after the siliconizing treatment can be controlled to a desired level, so that a high silicon steel sheet having good magnetic properties and excellent surface properties and workability can be stably manufactured on an industrial scale.

Further, in particular, according to the invention of claim 2 of the present application.
If unreacted SiCl discharged from the siliconizing furnace₄Times
Si using siloxane generated inevitably in the collection process
Cl ₄It controls the oxygen equivalent in the contained gas.
In the source gas recovery and supply system,₄Contained moth
Control of oxygen equivalents in wastewater can be performed very easily
At the same time, the raw material gas supplied to the steel plate surface
To supply oxygen directly into the steel plate
Can efficiently react with C.
The decarburization reaction can be controlled more directly and easily
You.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an oxygen equivalent in a raw material gas supplied to a siliconizing furnace and a decarburization amount of a base steel sheet.

FIG. 2 is an explanatory view showing an example of a raw material gas recovery / supply facility provided for carrying out the method of the present invention.

FIG. 3 is an explanatory view showing another example of a source gas recovery / supply facility provided for carrying out the method of the present invention.

FIG. 4 is an explanatory view showing source gas recovery / supply equipment used in a comparative example of the embodiment.

FIG. 5 is an explanatory view showing a continuous siliconizing treatment facility for a steel sheet.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicitizing furnace, 2 ... SiCl ₄ recovery equipment, 3 ... Recovery tank, 4 ... Undiluted solution tank, 5,5a, 5b ... Evaporation tank, 6
8, 11 ... liquid supply pipe, 7, 9, 12 ... pump, 10, 1
3 ... Flow control valve, 14 ... Gas supply pipe, 14a, 14b ...
Branch pipe, 14c: Main pipe, 15, 15a, 15b: Flow control valve, 16, 17, 19: Gas chromatography, 18,
18a, 18b ... heating element

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichiro Fujita 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-8-209325 (JP, A) JP-A-8 JP-A-209326 (JP, A) JP-A-9-176826 (JP, A) JP-A-9-176825 (JP, A) JP-A-6-212397 (JP, A) JP-A-8-3723 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) C23C 10/08 C21D 1/76

Claims (3)

(57) [Claims] 1. A method for producing a high silicon steel sheet by subjecting a base steel sheet containing less than 4 wt% of Si to siliconizing treatment in an atmosphere containing SiCl ₄ gas in a siliconizing furnace. The C content of the steel sheet is set higher than the target C content of the steel sheet after the siliconizing treatment, and the decarburization reaction of the base steel sheet is caused by the oxygen content in the atmosphere of the siliconizing treatment. In a method of performing a siliconizing treatment of a steel sheet, a siliconizing reaction is performed by adjusting an oxygen equivalent in a SiCl ₄ -containing gas supplied into a siliconizing furnace according to an amount of oxygen contained in a siliconizing treatment atmosphere. A method for producing a high silicon steel sheet having good surface properties and excellent workability, comprising controlling a decarburization amount of a base steel sheet at the time of obtaining a high silicon steel sheet having a target C content. 2. The method according to claim 1, wherein the siloxane is contained in the SiCl ₄ -containing gas supplied to the siliconizing furnace and the concentration of the siloxane is adjusted to control the oxygen equivalent in the SiCl ₄ -containing gas. Item 4. A method for producing a high silicon steel sheet having good surface properties and excellent workability according to item 1. 3. The high silicon steel sheet after the siliconizing treatment has a C content of 3
The high-silicon steel sheet having good surface properties and excellent workability according to claim 1 or 2, wherein the amount of decarburization of the base steel sheet during the siliconizing reaction is controlled so as to be 0 to 50 ppm. Production method.