JP2005008921A - Protective film of cooler in converter off-gas treatment facility and method of forming the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film-forming method whereby a protective film having no pore is formed on a cooler wall near an off-gas passage, wherein a cooler composes the off-gas passage of a converter off-gas treatment facility, so that chlorine ions or corrosive gas such as hydrogen sulfide contained in the off-gas cannot enter the protective film. <P>SOLUTION: When forming the protective film on the cooler wall near the off-gas passage, wherein the cooler composes the off-gas passage which cools and safely leads the converter off-gas to a dust collector, rust on the cooler wall is removed and the wall is subjected to blast treatment. Then, self-fluxing alloy powder of Ni, Co, etc. is sprayed onto the cooler wall with a high-pressure/ultra-high-speed spraying gun at a spray rate of 780-1,200 m/s to form a film with a thickness of 0.1-1 mm. Then, the film is melted at about 1,040°C and welded onto the cooler wall. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Industrial application fields]
The present invention relates to a cooler that constitutes an exhaust gas passage that cools high-temperature exhaust gas generated from a converter in a steelmaking factory and leads it safely to a dust collector, and the cooler includes a large amount of dust, chlorine ions, and sulfide contained in the exhaust gas. The present invention relates to the formation of a coating film excellent in wear resistance and corrosion resistance for protecting from a corrosive gas such as hydrogen on a cooler, and the durability can be remarkably improved.
[0002]
[Prior art]
The exhaust gas passage in the exhaust gas treatment facility of the converter has a temperature discharged from the converter of about 1,450 ° C. to 1,800 ° C., and dust (iron powder), chlorine ions (Cl ⁻ ), hydrogen sulfide (H ₂ SO ₄ ) has a function of a cooler that cools exhaust gas containing a large amount of corrosive gas and safely guides it to a dust collector.
Corrosive gases such as dust, chlorine ions, and hydrogen sulfide contained in this exhaust gas reduce the thickness of the water pipe by reducing the thickness of the water pipe by, for example, wearing and corroding the iron water pipe that constitutes the cooler. Meat is the cause of damage.
Therefore, in order to protect the water pipe from thinning, it is necessary to form a wear-resistant and corrosion-resistant coating on the surface of the water pipe on the exhaust gas passage side.
Conventionally, to form this coating on the surface of the water tube, as described in Japanese Patent Publication No. 4-80089, C = 0.03 to 0.3%, Si = 0.2% on the surface of the water tube. -1.2%, Mn = 0.3-2.6%, Ni = 0.1-6.0%, Cr = 8.0-15.0%, Mo = 0.05-4.0%, A metal powder composed of V = 0.1 to 3.0% and the remainder of Fe is sprayed by plasma jet spraying or the like to form a protective coating having a thickness of 0.5 to 1.5 mm on the surface of the water tube. .
However, the above prior art can prevent wear due to dust in the exhaust gas with a coating on the surface of the water tube, but the coating is laminated while sequentially spraying metal powder on the surface of the water tube at an injection speed of about 200 m / s to 480 m / s. The sprayed coating density is relatively high at about 88 to 92%, but when the sprayed particles collide with the sprayed particles on the surface of the water tube, the pressing force of the sprayed particles is Therefore, the bubbles formed between the sprayed particles are not crushed and remain as pores. As a result, the porosity is as high as 8 to 12%. For this reason, there is a problem that corrosive gases such as chlorine ions and hydrogen sulfide contained in the exhaust gas enter from the pores and reach the surface of the water tube, where the corrosion of the water tube proceeds.
In addition, since the above-described prior art is merely for thermal spraying of metal powder, the joint between the coating and the water tube is not metallurgically bonded, so that the coating is easy to peel off from the surface of the water tube. is there.
[0003]
An improvement of the above prior art is described in Japanese Patent Application Laid-Open No. 2002-146508. In this case, Cr = 15% or less, Fe = 8% or less, Cu = 4% or less, B = 1 to 3%, Si = 1 on the water pipe surface of the cooler constituting the exhaust gas passage of the converter exhaust gas treatment facility. .5-6%, W = 2% or less, C = 1% or less, the remainder being Ni material metal powder by thermal spraying with a powder type spraying method such as supersonic flame spraying, about 0.1 mm to 2 mm A protective film is formed with a thickness.
The coating sprayed on the surface of the water tube is kept at a temperature of 850 ° C. to 1,080 ° C. for 1 second or longer to be in a solid-liquid coexistence state, and hard components such as Cr boride and Cr carbide are deposited in the coating. It is intended to improve the corrosion resistance by densifying the inside of the film, and by heating, the interface between the water tube and the film is alloyed to increase the adhesion, thereby improving the peel resistance. .
However, in this prior art, since the spraying speed is 630 m / s to 780 m / s, when the sprayed particles collide with the particles sprayed on the surface of the water tube, the pressing force due to the collision causes the bubbles between the particles. The bubbles between the particles due to thermal spraying remain as pores in the coating (see the partial micrograph of the coating in Fig. 4), and corrosive gas enters from these pores to corrode the water tube. As a result, the protective film does not necessarily have sufficient peel resistance.
As described above, in the prior art, the cause of peeling of the protective film still remains, such as corrosive gas entering from the pores formed in the protective film and corroding the cooler. The protective function for preventing thinning cannot be maintained for a long time.
[0004]
[Patent Document] Japanese Patent Application Laid-Open No. 4-80089 [Patent Document] Japanese Patent Application Laid-Open No. 2002-146508
[Problems to be solved]
The present invention relates to the formation of a protective coating on the wall of the cooler that constitutes the exhaust gas passage in the converter exhaust gas treatment facility, particularly for corrosive gases such as chlorine ions and hydrogen sulfide contained in the exhaust gas. An object of the present invention is to devise a film forming method for forming a protective film having no pores on the wall surface of the cooler so as not to enter the protective film.
[0006]
[Measures taken to solve the problem]
[Solution 1]
Means for solving the above-mentioned problem of the present invention is to form a protective coating on the wall on the exhaust gas passage side of the cooler that constitutes the exhaust gas passage that cools the converter exhaust gas and safely leads it to the dust collector. This is due to (a) to (c).
(A) removing the rust on the wall surface of the cooler and applying a surface treatment to roughen the wall surface;
(B) A self-fluxing alloy powder such as Ni-base or Co-base is sprayed onto the cooler wall surface at a spraying speed of 780 m / s to 1200 m / s with a high-pressure / ultra-high-speed spray gun to form a coating of 0.03 mm to 1 mm Forming,
(C) Melting the film at a temperature of about 1,040 ° C. and welding it to the wall surface of the cooler.
[0007]
[Action]
JIS standard Ni-based or Co-based self-fluxing alloy powder is ultra-high speed of 780m / s to 1200m / s on the wall of the cooler that constitutes the exhaust gas passage that cools the converter exhaust gas and safely leads it to the dust collector The film is sprayed at a spraying speed of about 0.03 mm to 1 mm, and this film is heated at a temperature of about 1,040 ° C. to remelt and form a film. The particles of the molten alloy powder collide with particles sprayed on the wall surface with a strong pressing force, and all the bubbles formed between the particles are crushed to form a coating without pores. Furthermore, the hardness of the coating becomes very high and the wear rate of the coating becomes slow.
Further, the heat treatment of the protective coating causes an interface between the coating and the surface of the water pipe made of iron constituting the cooler to cause metallurgical bonding, thereby increasing the tight bonding force and improving the peelability.
If the spraying speed is less than 780 m / s, the thermal spray coating hardness of the wall surface is low and the density is low, so it is necessary to be 780 m / s or more. On the other hand, the upper limit of the spraying speed is a speed at which spraying is possible and a film having a thickness of 0.03 mm to 1 mm can be formed, and technically, it can be up to 1200 m / s.
Further, if the thickness of the coating is less than 0.03 mm, the thermal spray coating is not formed, and if it exceeds 1 mm greatly, cracking tends to occur in the thermal spray coating.
Further, the heating temperature “about 1,040 ° C.” for heating and remelting is optimal from 940 ° C. to 1,220 ° C. When the temperature is lower than 940 ° C., the sprayed coating becomes unmelted, and 1,220 ° C. Beyond, the bonding of the melt film becomes poor.
[0008]
Embodiment
Next, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a side view conceptually showing a converter exhaust gas treatment facility installed in a steelmaking factory.
This converter exhaust gas treatment facility treats high-temperature exhaust gas at a temperature of about 1,450 ° C. to 1,800 ° C. generated during blowing of the converter 1.
In this exhaust gas, dust having a small particle size of about 30 μm and dust having a large particle size of 100 μm or more are mixed, and the exhaust gas contains corrosive gases such as chlorine ions and hydrogen sulfide. For this reason, the water pipe 10 of the cooler provided as the exhaust gas passage of the exhaust gas treatment facility is very troublesome to handle, such as being worn by dust or corroded by corrosive gas.
The cooler 9 of this exhaust gas treatment facility is composed of a skirt 3, a lower hood 4, an upper hood 5, and a radiating section 6 provided with a cooler function above the furnace port 2 of the converter 1. It consists of an iron water pipe. The cooler 9 serving as the exhaust gas passage is provided with a primary dust collector 7 and a secondary dust collector 8 behind the radiating section 6, and the exhaust gas cooled by the dust collectors 7 and 8 is provided in the exhaust gas passage. The dust contained is collected.
By the way, in the above exhaust gas treatment equipment, molten steel, slag, etc. are blown up together with the exhaust gas from the converter 1, so that the skirt 3 and the hoods 4 and 5 are in particular a membrane structure so that they are difficult to adhere. It is. The dust having a large particle size of 100 μm or more contained in the dust is separated from the flow of the exhaust gas around the upper hood 5 and slides down the wall surface of the hood portions 4 and 5 of the membrane structure toward the converter. . For this reason, the hoods 4, 5 and the like are severely worn.
In addition, the iron water tube surface is worn by dust contained in the exhaust gas and corroded by chlorine ions and hydrogen sulfide, so a coating is formed on the surface of the iron water tube to protect it from wear and corrosion. By extending the service life, replacement with a new product and repair work are greatly reduced.
[0009]
Next, a film forming work procedure for forming a film on the wall surface of the cooler of the present invention will be described with reference to FIG.
The protective coating is formed by spraying a sprayed powder of a self-fluxing alloy onto the wall surface of the cooler 9 on the exhaust gas passage side using a high-pressure / ultra-high-speed spray gun to form a coating having a predetermined thickness, and the coating is heated and melted. It is a metallurgical combination.
The above-mentioned sprayed powder is made of a self-fluxing alloy of JIS standard Ni-base alloy or Co-base alloy, and its components are Ni-base alloy Cr = 0-20%, B = 1-4.5%, Si = 1.5-5%, C = 0-1.1%, Co = 1% or less, Mo = 4% or less, Cu = 4% or less, Fe = 5% or less, the balance being Ni, Co-based alloy Ni = 0-30%, Cr = 16-24%, B = 1.5-3%, Si = 1.5-4.5%, C = 1.5% or less, Mo = 7% or less, W = 0-15%, Fe = 5% or less, and the balance is Co.
In spraying the sprayed powder of the self-fluxing alloy onto the wall surface of the cooler 9, that is, the surface of the iron water pipe 10 and the fin 11 constituting the cooler 9, first, the water pipe 10 and fins on the converter exhaust gas passage side The surface of No. 11 is blasted to remove the rust, roughen the wall surface and increase the surface area.
Next, the surface of the water tube 10 and the fin 11 subjected to the base treatment is sprayed with a high-pressure / ultra-high-speed spray gun in a semi-molten state at a spray speed of 780 m / s or more in a thickness of 0.03 mm to 1 mm. The coating 12 is formed by continuously spraying until a predetermined target value is reached. In this case, although the said injection speed changes with individual implementation conditions and implementation conditions, 780 m / s-900 m / s are practical from the relationship between cost and efficiency. However, technically it is possible up to 1200 m / s.
Further, the thickness of the coating 12 may be appropriately selected to a value suitable for a specific purpose in each case.
Further, the coating 12 is heated to a temperature of about 1,040 ° C. by a burner to be melted by heating, and is metallurgically bonded to the water tube 10 and the fin 11. The coating temperature in this case is appropriately adjusted while visually confirming the melting state of the coating.
By this film forming method, the protective film has a high hardness with a film density of 98% or more.
Furthermore, since the pressing force when the sprayed particles collide with the sprayed powder previously sprayed on the surfaces of the water tube 10 and the fin 11 is strong, most of the bubbles formed between the particles are crushed and almost no pores remain. (See FIG. 3).
Further, since the coating 12, the water tube 10, and the fin 11 are reheated and melted at a temperature of about 1,040 ° C., the bonds between the particles existing in the coating, the surface of the water tube 10, the fin 11, and the coating 12 is metallurgically bonded, the coating 12 is densified and the hardness is increased, and the tight bonding force is greatly increased due to alloying of the interface between the coating 12 and the surface of the water tube 10 and the fin 11, thereby preventing peeling. Is significantly improved.
The durability of the coating film is superior to that of the protective film according to the prior art.
[0010]
【effect】
The present invention relates to a cooler constituting an exhaust gas passage of a converter exhaust gas treatment facility, after removing the rust and scale from the wall on the exhaust gas passage side of the cooler and roughening the wall surface, A coating is formed by spraying a self-fluxing alloy powder material such as Ni-base or Co-base at an ultra-high speed, and this coating is reheated at a temperature of about 1,040 ° C. together with a cooler to melt the coating and form a protective coating. This cooler wall surface is dense and high in hardness, is free from wear due to dust, etc., and can form a protective film without pores, corrosive gas of chlorine ions and hydrogen sulfide. Does not penetrate into the coating, resulting in a significant reduction in cooler corrosion. Also, the coating does not peel from the water pipe because the coating diffuses to the cooler wall surface and is completely metallurgically bonded. Accordingly, since the surface of the water pipe is not exposed to the exhaust gas passage side, the wear resistance and the corrosion resistance are extremely high.
[Brief description of the drawings]
FIG. 1 is a conceptual side view of a converter exhaust gas treatment facility.
FIG. 2 is an AA enlarged sectional view of FIG. 1;
3A is a micrograph of a partial plane of a coating formed on the wall surface of the cooler of the present invention, and FIG. 3B is a micrograph of its cross section.
4A is a micrograph of a partial plane of a coating formed on a cooler wall surface by a conventional powder spraying method, and FIG. 4B is a micrograph of its cross section.
FIG. 5 is a flowchart of a film forming operation procedure.
[Explanation of symbols]
1: Converter 2: Furnace port 3: Skirt 4: Lower hood 5: Upper hood 6: Radiation section 7: Primary dust collector 8: Secondary dust collector 9: Cooler 10: Water pipe 11: Fin 12: Coating

Claims (3)

In the method of forming a coating on the wall on the exhaust gas passage side of the cooler constituting the exhaust gas passage of the converter exhaust gas treatment facility,
Remove the rust on the wall of the cooler and perform blasting,
A self-fluxing alloy powder such as Ni-base or Co-base is sprayed on the cooler wall surface at a spraying speed of 780 m / s to 1200 m / s with a high-pressure / ultra-high-speed spray gun to form a film of 0.03 mm to 1 mm. ,
A method for forming a protective coating for a cooler in a converter exhaust gas treatment facility, wherein the coating is melted at a temperature of about 1,040 ° C. and welded to a wall surface of the cooler. A protective coating for a cooler in a converter exhaust gas treatment facility, which is formed by spraying Ni-based or Co-based self-fluxing alloy powder at an ultra-high speed of 780 m / s to 1200 m / s, and having a thickness of 0.03 mm to 1 mm Protective coating. The protective coating according to claim 2, wherein the coating is melted at a temperature of about 1,040 ° C and welded to the wall surface of the cooler, and the coating has a high hardness of 98% or more.

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