JP2002146508A - Water cooled steel structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water cooled steel structure with deposited protection film having excellent peeling resistance, wear resistance, corrosion resistance and thermal fatigue stress corrosion cracking resistance. SOLUTION: A film of a material containing, by mass, <=15% Cr, <=8% Fe, <=4% Cu, 1 to 3% B, 1.5 to 6% Si, <=2% W and <=1% C, and the balance substantially Ni and having a Charpy impact value of >=170 J/cm2 is deposited on the surface of a structure to have a thickness of 100 to 2,000 μm by a powder spraying method. After that, the region where the film is deposited is held at 1,223 to 1,353K for >=1 sec to deposit a protection film whose surface hardness is controlled to >=20 by HRC scale on the structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-cooled steel structure which is exposed to high-temperature wear and high-temperature corrosion caused by high-temperature exhaust gas and dust, for example, a skirt of a steelmaking plant converter exhaust gas cooling system, a lower hood boiler and the like. The present invention relates to a water-cooled steel structure having improved abrasion and corrosion resistance.

[0002]

2. Description of the Related Art In a converter of a steelmaking plant, as shown in FIG. 4, a skirt 2, a lower hood boiler 3, a boiler 4, A duct 5 is provided. Since these structures are exposed to high-temperature gas during converter blowing, they have a water-cooled structure made of steel. In addition, these structures are subject to significant erosion wear due to high-temperature dust generated from molten steel and various ores input as auxiliary raw materials, corrosive gases such as sulfur, chlorine and fluorine generated from ores, and high-temperature oxidation. High temperature corrosion and thermal stress fatigue due to repeated intermittent blowing. Therefore, if cooling water leaks from the structure due to perforations or cracks in the structure, hot molten steel reacts with water to cause a steam explosion, which may lead to a serious disaster.

[0003] Before such a disaster occurs, it is necessary to stop the facilities (operations) and perform repair work. The following technologies have been proposed to prevent occurrence of disasters.

[0004] Japanese Patent Publication No. 4-80089 proposes a converter OG hood tube for the purpose of improving wear resistance and crack resistance. This is on the surface of the hood tube, C:
0.03 to 0.3%, Si: 0.2 to 1.2%, Mn:
0.3 to 2.6%, Ni: 0.1 to 6.0%, Cr:
8.0-15.0%, Mo: 0.05-4.0%, V:
A metal containing 0.1 to 3.0%, with the balance being Fe, being spray-coated to a coating thickness of 0.5 to 1.5 mm: technology.

Japanese Patent Application Laid-Open No. 7-18320 proposes a cold water skirt for a converter exhaust gas hood having a protective layer formed for the purpose of improving dust erosion resistance. this is,
On the inner surface of the chilled skirt, a protective layer composed of an undercoat layer made of a carbide cermet and a top coat layer made of an oxidation-resistant alloy is formed.

[0006] Japanese Patent Application Laid-Open No. 9-235663 proposes a composite spray-coated member for the purpose of improving corrosion resistance and erosion resistance. This is the surface of the steel-made base material, SiO ₂
And the Al ₂ O ₃ include as an aggregate and applying the slurry as a medium of chromic acid and phosphoric acid - has a porous inorganic film obtained by drying, mainly composed of chromic acid and phosphoric acid on the inorganic film A glassy chromium oxide film obtained by applying or spraying a sealing agent to be described above and then heating and firing it: technology.

[0007] In addition, JI
There is an example in which four types of nickel self-fluxing alloys specified in SH 8303 are applied: technology.

[0008]

However, the above technique has the following problems.

In the technique, since the adhesion mechanism between the base material and the sprayed coating mainly has a mechanical anchoring effect, the bonding properties of the sprayed particles and the adhesion to the base material are not sufficient, and the film is easily peeled off.

[0010] The technology has a high construction cost,
Insufficient erosion resistance.

In the technique, the shape of the object to be constructed is restricted, and the peeling resistance and the wear resistance are not sufficient.

According to the technique, although wear resistance and corrosion resistance are improved, thermal fatigue stress corrosion cracking occurs from the coating surface because the hardness is too high, and this crack propagates to the base material (steel pipe). There is.

[0013] The present invention solves the above-mentioned problems, and provides peel resistance,
An object of the present invention is to provide a water-cooled steel structure formed with a protective film having excellent wear resistance, corrosion resistance, and thermal fatigue resistance and stress corrosion cracking resistance.

[0014]

According to the present invention, the above object is achieved by the following structures.

[0015] The structure of the first aspect is characterized in that the surface of the structure has a mass.
%, Cr: 15% or less, Fe: 8% or less, Cu: 4% or less,
B: 1 to 3%, Si: 1.5 to 6%, W: 2% or less, C: 1
% Or less, the balance being substantially Ni, and forming a film having a Charpy impact value of 1.70 J / cm ² or more to a thickness of 100 to 2000 μm by powder spraying.
Holding more than one second to a temperature of 223～1353K, a water-cooled steel-made structures to form a protective coating the film surface hardness was H _R C scale 20 or more.

[0016] The structure of the second aspect is characterized in that the surface of the structure has a mass.
%, Cr: 15% or less, Fe: 8% or less, Cu: 4% or less,
B: 1 to 3%, Si: 1.5 to 6%, W: 2% or less, C: 1
% Or less, and the balance substantially consists of Ni, and a Charpy impact value of 1.70 J / cm ² or more is formed by a powder spraying method to form a film having a thickness of 50 to 1000 μm, and then mass%
, Cr: 9 to 25%, Fe: 5% or less, Cu: 4% or less, M
o: 4% or less, B: 1.5 to 5%, Si: 2 to 5%, C:
0.4 to 1.2%, with the balance being substantially Ni
After coating forming one or more layers with a thickness of 0~1000μm by powder spraying method, and held for more than one second film-forming region to a temperature of 1223～1353K, the film surface hardness in H _R C scale 30
It is a water-cooled steel structure on which a protective coating of ~ 65 is formed.

According to the above-mentioned structure, the protective film is densified, the corrosion resistance is improved, and the adhesion between the steel substrate and the film is increased, whereby the peeling resistance is improved. Furthermore, the surface hardness of the film is secured by the precipitation of hard components in the film,
The wear resistance is improved. Further, the occurrence of thermal fatigue stress corrosion cracking can also be prevented.

[0018]

Embodiments of the present invention will be described below. FIG. 4 is a side view showing a converter exhaust gas cooling system. High-temperature exhaust gas discharged from the converter 1 at the time of converter blowing is introduced into the dust collector 6 via the skirt 2, the hood boiler 3, the boiler 4, and the duct 5. The skirt 2, the hood boiler 3, and the boiler 4 are made of a water-cooled steel structure, and have a cross section as shown in FIG. 1 or FIG. FIG. 1 shows a water cooling tube 11 having fins 12 formed on one outer surface (referred to as a finned semicircular tube). FIG. 2 shows a water cooling tube 11 having fins 12 formed on a central outer surface thereof ( Center fin round tube)
It is. The protective film 13 is formed on the gas-passing side wall of such a water-cooled steel structure by the method described below.
Alternatively, protective films 13a, 13b, 13c are formed.

First, the gas-passing side wall surface of the water-cooled steel structure is subjected to a blast treatment to remove scale and dirt on the surface, thereby forming a rough surface from which the sprayed coating does not peel off. Hereinafter,% of each component means mass%. "In the case of the protective film of the first embodiment (corresponding to claim 1)": Cr: 15% or less, Fe: 8
%, Cu: 4% or less, B: 1 to 3%, Si: 1.5 to 6
%, W: 2% or less, C: 1% or less, the balance being substantially made of Ni, and having a Charpy impact value of 1.70 J / cm ² or more by powder spraying to a thickness of 100 to 2000 μm. Form a film.

As the above powder type thermal spraying method, a flame type thermal spraying method using a combustion flame, a supersonic flame thermal spraying method, and a plasma thermal spraying method using electric energy can be applied.

After the formation of the film, the formed film and the vicinity of the substrate surface are maintained at a temperature of 1223 to 1353 K for 1 second or more, and the film is solid-liquid coexistent to fuse the film-forming particles and form a diffusion layer with the substrate. Thus, hard components such as Cr boride and Cr carbide are precipitated in the film.

In this way, the protective film is densified and corrosion resistance is improved, and the adhesion between the steel substrate and the film is increased by alloying at the interface, thereby improving the peeling resistance. Further, the film surface hardness by precipitation of hard component in the coating, H _R C scale becomes 20 or more, the wear resistance is improved.

The heating temperature of 1223 to 1353 K means that the temperature below 1223 K is below the solidus temperature of the material, the reaction between the coating and the substrate becomes a solid diffusion reaction, and the adhesion between the coating and the steel substrate. Insufficient strength. On the other hand, if the temperature exceeds 1353 K, the temperature becomes higher than the liquidus temperature of the material, and the coating fluidizes and flows out of the surface of the structure, making it impossible to form a uniform coating.

The reason why the heating time is 1 second or longer is that if the heating time is less than 1 second, the desired film performance cannot be exhibited. Examples of the heating method include a method using a gas burner, a method using high-frequency induction heating, and a method using a gas furnace or an electric furnace whose atmosphere has been adjusted. However, when the size and shape are limited, in order to prevent or minimize the deformation (strain) generated in the structure when heating,
It is necessary to use an appropriate restraining jig.

Among the components of the material, B and Si have the effect of lowering the melting point of the alloy and the role of a solvent during melting, and have the effect of removing oxides in the coating. S
When i: less than 1.5%, the effect is small, and when B: more than 3%, when Si: more than 6%, excessive boride or intermetallic compound is generated, thereby lowering the Charpy impact value.

Regarding the film thickness, as shown in Table 1, when the film thickness is less than 100 μm, heat treatment causes dilution of the Fe component from the base material and diffusion of C into the base material (carburization).
The hardness of the film is reduced and the wear resistance is significantly reduced. On the other hand, when the thickness exceeds 2000 μm, the adhesion of the film becomes low due to the internal stress generated in the film, and the film is easily cracked. Further, when the film is heated, it is difficult to form an alloy layer with the substrate, resulting in deterioration of the film quality, and it is not advisable to increase the film thickness more than necessary from the viewpoint of cost. The Charpy impact value shown in Table 1 is obtained by melting a sprayed material having the chemical components shown in the table, casting the material, and applying JIS Z 22
A No. 3 test piece specified in 02 was prepared and measured using a Charpy impact tester.

[0027]

[Table 1]

"In the case of the protective film of the second embodiment (corresponding to claim 2)"
%, Fe: 8% or less, Cu: 4% or less, B: 1 to 3%, S
i: 1.5 to 6%, W: 2% or less, C: 1% or less, balance substantially consisting of Ni, Charpy impact value of 1.70 J / cm
Film thickness: 50 to 10 of ^two or more materials by powder spraying
After forming with a film of 00 μm, Cr: 9-25%, F
e: 5% or less, Cu: 4% or less, Mo: 4% or less, B: 1.5
-5%, Si: 2-5%, C: 0.4-1.2%, the remainder substantially consisting of Ni, forming one or more layers with a thickness of 50-1000 μm by powder spraying. I do.

For the above-mentioned reasons, it is desirable that the total thickness of each layer is 100 to 2000 μm.

As for the layer structure, practically two or three layers are sufficient.
If abrasion resistance is required, it is necessary to increase the surface hardness of the outermost layer.
9-25% of Cr, 0.4-1.2% of C, 1.5-5 of B
% And Si in a range of 2 to 5%, Fe is 5% or less,
Cu to 4% or less, Mo to 4% or less, 1223-1353
And more than one second to a temperature of K, to 30 to 65 the surface hardness of the protective coating in H _R C scale.

The description of the powder spraying method, the heating temperature, the heating holding time, and the like are the same as those in the first embodiment (corresponding to claim 1), and will not be repeated.

The water-cooled steel structure is preferably provided with a protective coating according to the invention before the complete assembly is completed, generally in the form of components consisting of 3 to 15 tubes. Form a protective film. In addition,
If an appropriate deformation-preventing restraining jig is used and gas burner heating is performed, a protective film can be formed after the entire assembly.

[0033]

Next, comparative examples and examples of the present invention will be described. "Comparative Example 1" The water-cooled steel base material of the lower hood boiler without the protective film was reduced in pipe thickness by up to 2 mm after about 8 months of use, and measures such as welding repair were implemented. "Comparative Example 2" Self-fluxing alloy (JIS H 8303) SFNi 4 kinds 50
The water-cooled steel base material of the lower hood boiler formed with a film having a thickness of 0 to 1000 μm caused cracks in the film after about 8 months of use and required repair. "Example 1 of the present invention" 14.02% Cr, 3.86% Fe, 0.05% Cu, 2.41% B,
3.65% Si, 0.03% W, 0.69% C, balance being substantially Ni, the material of the Charpy impact value 1.75J / cm ² 300~70
After forming a film by a powder spraying method to a thickness of 0 μm,
Hold at a temperature of 1353 K for about 5 seconds to reduce the film surface hardness to H _R C
What was set to 42-47 was attached to the converter exhaust gas cooling system, and was used for about 8 months.

During this time, peeling, abrasion,
Exposure of the substrate due to corrosion and thermal fatigue stress corrosion cracking did not occur. "Example 2 of the present invention" 10.38% Cr, 2.2% Fe, 0.08% Cu, 1.55% B,
2.91% Si, 0.02% W, the balance is substantially made of Ni, and a material having a Charpy impact value of 2.00 J / cm ² is formed to a thickness of 300 to 500 μm by a powder spraying method.
2.46% Fe, 0.06% Cu, 2.23% B, 3.64% Si, 0.03% W,
A material consisting of 50% C and the balance of Ni is formed into a film having a thickness of 300 to 500 μm by a powder spraying method.
3.2% Fe, 2.02% Cu, 2.5% Mo, 3.54% B, 4.68% Si, 0.8
9% C, the balance being substantially Ni is 300 to 500
After forming a film by powder spraying to a thickness of μm,
Hold at a temperature of 353K for about 10 seconds to reduce the film surface hardness to H _R C
What was set to 51-58 was attached to the converter exhaust gas cooling equipment, and was used for about 8 months.

During this time, peeling, abrasion,
Exposure of the substrate due to corrosion and thermal fatigue stress corrosion cracking did not occur.

The above description has been given of the example in which the protective film of the present invention is applied to the converter exhaust gas cooling equipment. However, if the protective film of the present invention is applied to another water-cooled steel structure used in a similar environment. The same effect as described above can be obtained.

[0037]

The water-cooled steel structure according to the present invention has
In a high-temperature corrosive atmosphere containing a base metal, it has excellent corrosion resistance and abrasion resistance, hardly causes thermal fatigue stress corrosion cracking, and has a protective film excellent in exfoliation resistance. This reduces equipment downtime,
Alternatively, the operation rate of the factory can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semicircular tube with fins on which a protective film according to the present invention is formed.

FIG. 2 is a sectional view of a center fin circular tube on which a protective film according to the present invention is formed.

FIG. 3 is a perspective view of a lower hood boiler on which a protective film according to the present invention is formed.

FIG. 4 is a side view showing a converter exhaust gas cooling system.

[Description of Signs] 1 Converter 2 Skirt 3 Lower hood boiler 4 Boiler 5 Duct 6 Dust collector 11 Water cooling tube 12 Fin 13, 13a, 13b, 13c Protective coating

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toru Mukai 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Kyosuke Shirasaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (72) Inventor Takayoshi Izu Naga 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. No. 16 Fujiki Kosan Co., Ltd. (72) Inventor Tomio Morita 4-16 Honjo 4-chome, Hachimanishi-ku, Kitakyushu-shi, Fukuoka F-term in Fujiki Kosan Co., Ltd. 4K002 BA09 4K031 AA04 AB04 AB08 AB09 BA01 CB08 CB22 CB24 CB26 CB28 DA01 DA04 FA01 4K056 AA02 BA06 CA02 DC03

Claims (2)

[Claims] 1. The surface of a structure has a mass% of Cr: 15% or less, Fe: 8% or less, Cu: 4% or less, B: 1 to 3%, Si:
1.5 to 6%, W: 2% or less, C: 1% or less, balance substantially consisting of Ni, powder having a Charpy impact value of 1.70 J / cm ² or more to a thickness of 100 to 2000 μm After film formation by the thermal spraying method, the film formation area is
The temperature was held for more than one second, water-cooled steel-made structures, characterized in that the film surface hardness to form a protective film was H _R C scale 20 or more. 2. The surface of the structure has a mass% of Cr: 15% or less, Fe: 8% or less, Cu: 4% or less, B: 1 to 3%, Si:
1.5 to 6%, W: 2% or less, C: 1% or less, balance substantially composed of Ni, and a film having a Charpy impact value of 1.70 J / cm ² or more by a powder spraying method. : 50-1000
After forming a film of μm, Cr: 9 to 25 is further added by mass%.
%, Fe: 5% or less, Cu: 4% or less, Mo: 4% or less, B:
1.5-5%, Si: 2-5%, C: 0.4-1.2%,
After forming at least one layer of a material substantially consisting of Ni with a thickness of 50 to 1000 μm by powder spraying, the remaining part is made of a material substantially composed of Ni.
Water-cooled steel-made structures, characterized in that the formation of the protective coating the outermost layer of the film surface hardness was 30 to 65 in H _R C scale.