JPH11131149A - Continuous processing furnace of steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the carburization of a steel strip in bringing the steel strip during passing through in a furnace into contact with a carbon base refractory, in the continuous treating furnace using carbon base refractory to at least a part of a member in the furnace. SOLUTION: In the continuous treating furnace for executing heat treatment or desiliconize-treatment to the steel strip at high temp. and using the carbon base refractory to at least a part of the structural member in the furnace, a coating layer containing one or two kinds selected from Si3 N4 and SiO2 is formed on the surface of the carbon base refractory stationarily or non- stationarily contacting with the steel strip during passing through in the furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous furnace for continuously heat treating or siliconizing steel strip at a high temperature.

[0002]

2. Description of the Related Art In a continuous heat treatment furnace for heat-treating a steel strip at a high temperature or in a continuous siliconization treatment furnace for producing a high-silicon steel strip by subjecting the steel strip to a high-silicon steel strip, the components in the furnace or the components thereof are used. Partly carbon fiber composite carbon material (so-called C / C composite)
Etc. may be used. This carbon-based refractory has excellent mechanical strength at high temperatures, and exhibits excellent corrosion resistance even in an acidic atmosphere or a corrosive atmosphere. Also,
In particular, in a continuous siliconizing furnace, the atmosphere of the furnace contains a highly corrosive Si compound gas (such as SiCl ₄ ). However, since carbon-based refractories do not react with this Si compound gas, components in the furnace Can be a suitable material.

[0003]

By the way, in the steel strip continuous processing furnace as described above, the steel strip during the passing of the steel strip is partially formed due to abnormal catenary or excessive meandering of the steel strip. May come into contact with When such contact of the steel strip occurs with the carbon-based refractory, the carburization reaction from the carbon-based refractory to the steel strip occurs at a remarkable rate, and the carbon content of the product steel strip increases. Therefore, when the product steel strip is a high silicon steel strip, magnetic properties (iron loss) are significantly deteriorated. Further, when the carbon content of the steel strip is significantly increased by the carburizing reaction, the melting point of the steel strip is lowered, so that troubles such as melting of the steel strip and breakage of the steel strip easily occur in the furnace.

[0004] Also, from the viewpoint of mechanical strength and corrosion resistance in a high-temperature atmosphere, it is preferable that a part or all of the transfer roll in the furnace is also made of a carbon-based refractory such as a carbon fiber composite carbon material. However, due to the problems described above, a carbon-based refractory cannot be used in a roll portion that may be in constant contact with the steel strip or may be irregularly contacted.

Accordingly, an object of the present invention is to provide a continuous processing furnace using a carbon-based refractory for at least a part of the in-furnace components, even if the steel strip in the passing plate contacts the carbon-based refractory. An object of the present invention is to provide a continuous processing furnace capable of effectively preventing carburization.

[0006]

Means for Solving the Problems The present inventor has proposed a method of continuously carburizing a carbon-based refractory based on the idea of coating the surface of the carbon-based refractory as a means for preventing carburization when the steel strip comes into contact with the carbon-based refractory. Study to find coating materials that can stably coat refractories over a long period of time without impairing the strength and corrosion resistance of carbon-based refractories even in a high-temperature and corrosive atmosphere such as in a processing furnace. And, as a result, Si ₃ N ₄ and / or SiO ₂
Was found to be optimal.

The present invention has been made based on such findings, and the features thereof are as follows. (1) A furnace for heat-treating or siliconizing a steel strip at a high temperature, and in a continuous processing furnace in which a carbon-based refractory is used for at least a part of the structural members in the furnace, a steel strip in a threaded sheet is used. The surface of the carbon-based refractory that comes into contact with stationary or non-stationary, S
A steel strip continuous processing furnace, wherein a coating layer containing one or two selected from i ₃ N ₄ and SiO ₂ is formed.

(2) In the continuous processing furnace of the above (1), a horizontal furnace type continuous siliconizing furnace for siliconizing a steel strip, wherein a steel strip is provided above and below a steel strip pass line in the furnace. A gas nozzle for blowing the processing gas onto the strip surface and a partition plate substantially parallel to a steel strip pass line for flowing the processing gas blown from the gas nozzle along the steel strip surface are provided, and the partition plate is formed of a carbon-based material. What is claimed is: 1. A continuous furnace for continuous treatment of steel strip, comprising a refractory continuous siliconizing furnace, wherein a coating layer is formed on at least an upper surface of a partition plate below a steel strip pass line.

(3) In the continuous processing furnace described in (1) or (2) above, the total content of one or two of Si ₃ N ₄ and SiO ₂ in the coating layer is 30 to 45 wt%. Characteristic continuous strip furnace. (4) In the continuous processing furnace of the above (3), the coating layer is mainly composed of one or two kinds of coating agents selected from Si ₃ N ₄ powder and SiO ₂ powder, and a binder, The ratio of the coating agent in the inside is 30
A continuous treatment furnace for steel strips, which is a coating layer obtained by applying a treatment liquid adjusted to ~ 45 wt% on the surface of a carbon-based refractory and drying it.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A continuous processing furnace to which the present invention is directed is a continuous processing furnace for heat-treating or siliconizing a steel strip at a high temperature. A carbon-based refractory (for example, carbon fiber composite carbon material) having excellent mechanical strength and exhibiting excellent corrosion resistance even in an acidic atmosphere or a corrosive atmosphere (in particular, it does not react with a Si compound gas in the atmosphere in a siliconizing furnace). , Isotropic graphite, etc.). Examples of the in-furnace constituent members include a gas supply nozzle, a transport roll, and a member for controlling a gas flow (for example, a partition plate or a baffle plate). Also, usually
Since carburization of the steel strip by contact with the carbon-based refractory occurs remarkably at 800 ° C. or higher, a furnace for processing the steel strip at a temperature of 800 ° C. or higher may be used as a continuous processing furnace.

According to the present invention, in such a continuous processing furnace, one or two or more selected from Si ₃ N ₄ and SiO ₂ are formed on the surface of a carbon-based refractory which may come into contact with a steel strip in a threaded plate. Form a seed-containing coating layer. Here, the carbon-based refractory to which the steel strip in the passing is likely to come into contact is the carbon-based refractory to which the steel strip that normally passes is constantly in contact, and the carbon-based refractory that is constantly in contact with the passing. Refers to both carbon-based refractories where the steel strip may come into contact (i.e., may come into contact irregularly). For example, the former example includes a transport roll, and the latter example includes a gas supply nozzle and a gas flow control member.

Si ₃ N ₄ and SiO ₂ have excellent heat resistance and corrosion resistance as coating materials, and do not react with Si compound gas or carbon-based refractories in a furnace atmosphere even at high temperatures. Even when exposed to a high-temperature acidic or corrosive atmosphere with the surface of the refractory coated, a stable coating layer can be maintained for a long time, and the strength and corrosion resistance of the carbon-based refractory are not impaired. .

[0013] The coating layer containing Si ₃ N ₄ and / or SiO ₂ is composed of one or two kinds of coating agents selected from Si ₃ N ₄ powder and SiO ₂ powder and a binder (for example, sodium silicate). Can be obtained by applying a treatment liquid obtained by dissolving or dispersing the above in a solvent to the surface of a carbon-based refractory and drying. At this time, it is preferable to apply the treatment liquid uniformly by brushing, spraying or the like so as not to cause thickness unevenness on the surface of the refractory. If the coating layer has uneven thickness, the coating layer will crack or peel off when the furnace temperature rises or falls.

The proportion of the coating agent (Si ₃ N ₄ and / or SiO ₂ ) in the coating layer is 30 to 4
It is preferable to adjust to a range of 5 wt%. If the content of the coating agent is less than 30 wt%, the effect of using Si ₃ N ₄ or SiO ₂ as the coating agent cannot be sufficiently obtained, and the effect of suppressing carburization for a long time by the coating layer cannot be obtained. On the other hand, if the content of the coating agent exceeds 45 wt%, the adhesion of the coating layer is poor,
Peeling of the coating layer occurs.

FIG. 1 shows Si ₃ N ₄ as a coating agent,
The relationship between the content of Si ₃ N _{4 in} the coating layer and the adhesion of the coating layer is shown for the coating layer using sodium silicate as a binder. In the test shown in the figure, the carbon-based refractory having the coating layer formed thereon was continuously used in a nitrogen atmosphere at 1200 ° C.
It is an examination of the coating layer peeling area ratio after the lapse of time. According to this, if the content of the coating agent in the coating layer is 45 wt% or less, the coating layer hardly peels off.

It is preferable to use a non-aqueous binder as the binder in order to prevent the burning of the carbon-based refractory. Examples of the non-aqueous binder include sodium silicate and phenol-based binders, and sodium silicate is particularly preferred because it is relatively easily available and inexpensive.

Further, even if the content of the coating agent is within the above range and the coating thickness is uniform,
If the thickness of the coating layer exceeds 1.0 mm, the coating layer may be cracked or peeled when the temperature in the furnace is raised or lowered.
It is preferably set to 0 mm or less. Further, if the thickness of the coating layer is less than 0.5 mm, it is difficult to form the coating layer uniformly, so the thickness of the coating layer is 0.5
mm or more is preferable. Comparing Si ₃ N ₄ and SiO ₂ , S
Since i ₃ N ₄ is more excellent in heat resistance, in the case of a continuous processing furnace having a particularly high temperature atmosphere (around 1200 ° C.), such as a siliconizing furnace, a coating layer containing Si ₃ N ₄ is used. Preferably, it is formed.

By forming a coating layer as described above on the surface of a carbon-based refractory (for example, a transport roll, a gas supply nozzle, a gas flow controlling member or a part thereof), which is a component in the furnace, Even if the steel strip comes into contact with the refractory, carburization to the steel strip is appropriately prevented, and a stable carburizing suppression effect can be obtained for a long period without impairing the strength and corrosion resistance of the carbon-based refractory.

[0019]

2 to 4 show a part of a horizontal furnace type continuous siliconizing furnace for producing a high silicon steel strip by performing a siliconizing treatment on a low silicon steel strip. In the figure, 1 is a furnace body of a siliconizing furnace, 2 is a transport roll arranged at appropriate intervals in the furnace length direction to transport a steel strip S horizontally in the furnace, 3
Are gas nozzles (slit nozzles) arranged at appropriate intervals above and below the steel strip pass line in the furnace length direction, and the processing gas is blown onto the steel strip surface from the slits 30 of each gas nozzle 3.

Reference numeral 4 denotes a partition plate provided above and below the steel strip pass line between the gas nozzles adjacent in the furnace length direction and substantially parallel to the steel strip pass line. In the siliconizing treatment, it is necessary to cause a uniform siliconizing reaction on the steel strip surface.
When i is added, the lattice constant decreases and shrinks, and if an excessive siliconizing reaction occurs locally on the steel strip surface, the shrinkage at that portion increases and the steel strip buckles. For this reason, a partition plate 4 as shown in the figure is provided, and the processing gas blown from the gas nozzle to the steel strip surface is introduced between the partition plate 4 and the steel strip S so that the processing gas flows along the steel strip S. Thus, a uniform siliconizing reaction is caused on the steel strip surface. In FIG. 3, the partition plate 4 above the steel strip pass line is omitted.

The siliconizing reaction is required to have symmetry on both sides of the steel strip. This is because, for the same reason as described above, the silicon carbide reaction on both sides of the steel strip is asymmetric because the silicon carbide reaction on both sides of the steel strip is asymmetric. This is because a warp toward the side with a large number) is caused. A place where the contact state between the processing gas and the steel strip surface is clearly asymmetric on both sides of the steel strip S to be passed is a place where the transport roll 2 is installed. That is, at the place where the transport roll 2 is installed, the transport roll 2 which is an obstacle to the processing gas flow exists on the lower side of the steel strip, whereas such an obstacle is located on the upper side of the steel strip. Therefore, the contact state between the processing gas on both sides of the steel strip and the steel strip surface at the location of the transport roll 2 becomes apparently asymmetric, thereby causing a difference in the amount of silicon carbide on both sides of the steel strip. easy.

For this reason, in the embodiment shown in FIGS. 2 to 4, the processing gas flow is blocked at a position substantially opposed to the transport roll 2 across the steel strip pass line (that is, almost immediately above the transport roll 2). A shield 5 is provided along the furnace width direction,
The shield 5 allows the transport roll 2 on the lower side of the steel strip.
On the steel strip upper surface side, thereby producing a reaction length between the steel strip S and the processing gas on both sides of the steel strip (the processing gas is applied to the steel strip in the longitudinal direction of the steel strip). Along the length of the steel strip) to make the siliconizing reaction uniform on both sides of the steel strip.

The shield 5 has the same effect as the transport roll 2 on the processing gas flow.
It is necessary to arrange the steel strip S on the upper surface side only by providing a small gap between the steel strip S. The board cannot be made substantially. That is, when the steel strip is first passed through the continuous siliconizing furnace, the end of the steel strip coil is directly or rope-connected to a threading bar having a thickness sufficient to maintain rigidity between the transport rolls 2. It is customary to carry out the initial threading by passing the threading bar through the furnace and causing the steel strip coil to follow it. Therefore, in the case where the shield is fixedly installed just above the transport roll 2 as described above, the passing bar hits the shield and the initial passing becomes impossible.

Therefore, in this embodiment, this shield 5 is
Through the upper part, the structure is held so as to be swingable or rotatable in the furnace length direction, and a passing bar moving in the furnace at the time of initial passing abuts against the shield 5 and is swung so as to push it upward. Or, it is rotated so that it can pass through the shield. As this holding structure, for example, a mounting hole is provided in the upper part of the shield 5, a support shaft fixed to the furnace body side is inserted into the mounting hole, and the shield 5 is swingably or rotatably held on the support shaft. Such a structure can be adopted. After passing through the passing bar, the shield 5 rotates or swings by its own weight and returns to the original position.

In this embodiment, the shield 5 is constituted by a plurality of divided parts 50 arranged in parallel along the furnace width direction. Each of the divided portions 50 includes a ring-shaped portion a and a bar-shaped portion b below the ring-shaped portion a, and a mounting hole 6 is formed in the ring-shaped portion a. In a state where these divided parts 50 are arranged in parallel along the furnace width direction, the support shaft 7 fixed to the furnace body side is inserted into each of the mounting holes 6 to swing or rotate the support shaft 7 in the furnace length direction. It is held freely.

As described above, the shield 5 is divided into a plurality of divided parts 50.
When the passing bar passes through the shield 5 at the time of initial passing, only the shielding portion of the width of the passing bar, not the entire shield, is pushed up by the passing bar. As a result, the shielding member 5 can be pushed with a smaller lifting force than in the case where the shielding member 5 has an integral structure.
Can be pushed up, and the shield 5 can be prevented from being damaged accordingly. Further, even if a part of the shield 5 is damaged due to a collision of the passing bar or the like, the divided portion 5
There is also an advantage that it is sufficient to replace only 0.

In the structure of the above continuous siliconizing furnace, the partition plate 4 is made of a carbon-based refractory such as a carbon fiber composite carbon material or isotropic graphite from the viewpoint of strength and corrosion resistance. I have. Then, with respect to the partition plate 4 made of the carbon-based refractory, at least the upper surface x of the partition plate 4 below the steel strip pass line has Si ₃ N ₄ and / or SiO 2.
Form a coating layer containing ₂ . This is because when a catenary abnormality occurs in the steel strip S passing through the siliconizing furnace,
This is because the steel strip portion between the transport rolls 2 is loosened and comes into contact with the upper surface x of the partition plate 4 below the steel strip pass line, causing carburization of the steel strip S from the carbon-based refractory partition plate 4.

It is preferable that the shield 5 is also made of the above-mentioned carbon-based refractory from the viewpoint of strength and corrosion resistance, and when the shield 5 is made of a carbon-based refractory as described above. It is preferable to form a coating layer containing Si ₃ N ₄ and / or SiO ₂ on at least the lower end surface y of the shield 5 (the lower end surface of the bar-shaped portion b). As described above, since the lower end of the shield 5 has only a slight gap between the lower end of the shield 5 and the steel strip S, the steel strip S comes into contact with the steel strip when a shape defect occurs. This is because, when such contact of the steel strip S occurs, carburization of the steel strip S from the carbon-based refractory shield 5 occurs.

[0029]

As described above, according to the continuous steel strip treating furnace of the present invention, even if the steel strip comes into contact with a carbon-based refractory constituting a furnace internal member or a part thereof, the steel strip is carburized. Can be effectively prevented, and the melting and breaking of the steel strip due to carburization and the deterioration of the magnetic properties of the high silicon steel strip can be appropriately prevented.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the content of Si ₃ N _{4 in} a coating layer and the adhesion of the coating layer.

FIG. 2 is a sectional view of a furnace showing one embodiment of the present invention.

FIG. 3 is a perspective view showing the inside of the furnace of the embodiment shown in FIG. 1;

FIG. 4 is an exploded perspective view showing the shield used in FIG. 1 and its components.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Furnace body, 2 ... Conveyance roll, 3 ... Gas nozzle, 4 ... Partition plate, 5 ... Shield, 6 ... Mounting hole, 7 ... Support shaft, 30 ... Slit, 50 ... Dividing part, a ... Ring-shaped part, b: bar-shaped part, x: upper surface, y: lower end surface

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuhisa Okada, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Nippon Kokan Co., Ltd. (72) Toru Miwa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Honko Co., Ltd.

Claims (4)

[Claims] 1. A furnace for heat-treating or siliconizing a steel strip at a high temperature, wherein a carbon-based refractory is used for at least a part of the structural members in the furnace. A steel characterized in that a coating layer containing one or two selected from Si ₃ N ₄ and SiO ₂ is formed on the surface of a carbon-based refractory with which a band constantly or irregularly contacts. Ozone continuous processing furnace. 2. A horizontal furnace type continuous siliconizing furnace for siliconizing a steel strip, comprising gas nozzles for blowing a processing gas onto a steel strip surface above and below a steel strip pass line in the furnace. A partition plate substantially parallel to a steel strip pass line for flowing the processing gas blown from the gas nozzle along the steel strip surface is provided, and in a continuous siliconizing furnace in which the partition plate is made of a carbon-based refractory. 2. The steel strip continuous processing furnace according to claim 1, wherein a coating layer is formed on at least the upper surface of the partition plate below the steel strip pass line. 3. Si ₃ N ₄ and Si in a coating layer
The total content of one or two types of O ₂ is 30 to 45 wt%
The steel strip continuous processing furnace according to claim 1 or 2, wherein: 4. The coating layer comprises, as main components, one or two coating agents selected from Si ₃ N ₄ powder and SiO ₂ powder and a binder, and the ratio of the coating agent in the solid content is 30%. 4. A coating layer obtained by applying a treatment liquid adjusted to .about.45 wt% on the surface of a carbon-based refractory and drying it.
A continuous furnace for treating steel strip according to claim 1.