KR102462477B1 - Cored wire for high temperature corrosion and wear resistance - Google Patents

Abstract

The present invention relates to a melted metal sheathed on a surface of a boiler tube used for a boiler where severe corrosion and abrasion occur at a high temperature. More specifically, the present invention relates to a melted metal, which has an excellent corrosion resistance and abrasion resistance at a high temperature and is able to improve the life of a boiler tube, and a cored wire for welding and spraying with an excellent corrosion resistance and abrasion resistance at a high temperature, which is to generate the melted metal. According to the present invention, the melted metal comprises: 26-29 wt% of Cr; 15-18 wt% of Mo; 1-3 wt% of C; 2-4 wt% of B; and remaining Fe and unavoidably contained impurities. The molten metal has an excellent corrosion resistance and abrasion resistance at a high temperature. According to the present invention, the cored wire for welding and spraying, which is made of an outer cover and a filler filling the inside of the outer cover. The outer cover comprises: 0.12 wt% or lower of C; 16-18 wt% of Cr; and remaining Fe and unavoidable impurities. The outer cover is a stainless steel unit, which contains a content of 56.5-63.5 % of the total weight of the cored wire. The filler contains a content of 36.5-43.5 % of the total weight of the cored wire. The filler comprises: 16-17 wt% of metal chrome powder (containing 9-11 wt% of C); 2.5-3.5 wt% of B4C powder; 16-17 wt% of metal molybdenum powder; 1-3 wt% of ferroboron powder; and 1-3 wt% of metal chrome powder.

Description

Cored wire for welding and thermal spraying with excellent high temperature corrosion resistance and abrasion resistance

The present invention relates to a metal deposited on the surface of a boiler tube used in a boiler that undergoes severe corrosion and wear at high temperatures. It relates to a welding metal and a cored wire for welding and thermal spraying excellent in high temperature corrosion resistance and wear resistance to produce the welding metal.

Recently, in thermal power plants, the use of boilers using a mixture of low-grade coal containing a large amount of sulfur and biomass, a waste resource for urban life, is increasing. In boilers using these low-grade fuels, high-temperature corrosion and high-temperature erosion have increased significantly, leading to premature damage to boiler tubes.

The main causes of these damage are high-temperature corrosion due to sulfurous acid (SO ₂ ) gas generated during low-grade coal combustion and chlorine (Cl) gas generated from biomass combustion, and fly ash generated during the combustion process of these fuels. ), it is known that the boiler tubes are damaged at an early stage due to a complex action of erosion caused by the collisions.

In order to solve this problem, a boride-reinforced modified alloy-based cored wire is introduced in Patent Registration No. 10-0499820. However, although this technology contributes to some degree of improvement in wear resistance, it does not solve the corrosion resistance at high temperature.

Therefore, there is an urgent need to develop an alloy material capable of simultaneously improving corrosion resistance and wear resistance at high temperatures to prevent damage to boiler tubes.

Republic of Korea Patent No. 10-1631233 (registered on June 10, 2016)

S. Mrowec, The problem of Sulfur in High-Temperature Corrosion, Oxid. Met. 1995, 44 (1/2): Documents cited in Fig. 2 W. Kai, D. L. Douglass, and F. Gesmundo, The Corrosion of Fe-Mo Alloys in H2/H2O/H2S Atmosphere, Oxidation of Metals, 1992,37(5/6):p389

The present invention has been devised to solve the above problems, that is, the problem of shortening the lifespan of a boiler tube used in a harsh environment in which high temperature corrosion and high temperature erosion (abrasion) occur in a complex manner. An object of the present invention is to provide a welded metal having excellent high-temperature corrosion and high-temperature erosion performance and a cored wire for welding and thermal spraying for producing the welded metal.

In order to achieve the above object, the present invention

Cr: 26-29% by weight, Mo: 15-18%, C: 1-3%, B: 2-4%, and has a composition consisting of the remaining Fe and inevitably contained impurities, high-temperature corrosion resistance and Provided is a weld metal produced by welding or thermal spraying with a cored wire characterized in that it has excellent wear resistance.

Also, the present invention.

In the cored wire consisting of a shell and a filler filled inside the shell,

The outer shell is a stainless steel strip having a component composition of C: 0.12% or less, Cr: 16-18%, remaining Fe and inevitable impurities by weight%, and has a content of 56.5-63.5% based on the total weight of the cored wire,

The filler has a content of 36.5 to 43.5% based on the total weight of the cored wire, metal chromium powder (containing 9 to 11% C): 16 to 17%, B4C powder: 2.5 to 3.5%, metal molybdenum powder : 16~17%, Ferroboron powder: 1~3%, Metal chromium powder: 1~3% Provides a cored wire for welding and thermal spraying with excellent high temperature corrosion resistance and abrasion resistance performance do.

According to the present invention, it is possible to easily and economically coat the surface of a boiler tube, which is a steel material, with an alloy containing iron (Fe) as a main component and an element that improves high-temperature corrosion and high-temperature erosion characteristics in the field. It is possible to improve the wear resistance properties.

Therefore, due to the present invention, a new countermeasure against premature damage to the boiler tube due to the use of low-grade fuel (coal and bio-blended fuel with high sulfur content) in thermal power plants is recently established, thereby increasing the service life of the boiler tube and increasing the power generation efficiency and power plant. A significant reduction in operating costs can be expected.

Figure 1 Fe-Cr phase diagram showing the σ-phase formation section according to the Cr content.
Figure 2. Sulfidation rate and oxidation rate according to the temperature of various metals
rate) graph
Figure 3. Graph showing the effect of Mo content on sulfidation rate in pure iron
Figure 4. Cross-sectional view of the present invention cored wire
Figure 5. Microscopic tissue photograph of the thermal sprayed layer by arc spraying with the original name of the cored wire
Figure 6. The microscopic tissue photograph of the thermal sprayed layer arc sprayed with a conventional cored wire. The left side is a picture before corrosion, and the right side is a picture after corrosion.
Figure 7. The microscopic tissue photograph of the thermal sprayed layer arc sprayed with the cored wire of the present invention, on the left is a photograph before corrosion, and on the right is a photograph after corrosion.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Deposited metal coated on the surface of the boiler tube of the present invention is Cr: 26-29%, Mo: 15-18%, C: 1-3%, B: 2-4%, remaining Fe and inevitably contained by weight% It has a component composition made of impurities, and is characterized by excellent high temperature corrosion resistance and abrasion resistance performance.

Hereinafter, the reasons for limiting the composition of these components will be described.

1) Chromium (Cr)

Chromium (Cr) in the iron (Fe) matrix generally causes solid solution strengthening in the iron matrix as seen in stainless steel to improve strength, and reacts with oxygen on the surface to form a dense oxide film (Cr ₂ O ₃ ) to form a high temperature Strongly inhibits oxidation and corrosion of internal metals. In addition, some of the added chromium is combined with carbon (C) or boron (B) to form carbides (Cr ₂₃ C ₆ , Cr ₇ C ₃ ) or borides (CrB) with high hardness to increase the hardness of the base material to increase wear resistance. It serves to improve performance.

If the chromium content is less than 26% by weight, the solid solution strengthening effect is insufficient due to the insufficient amount of chromium in the iron matrix, and the formation of a dense oxide film is not formed, so that the oxidation and corrosion resistance properties cannot be sufficiently exhibited, as well as carbides with high hardness and Abrasion resistance performance is deteriorated due to insufficient boride formation. On the other hand, when the chromium content is added to 29% by weight or more, as shown in Fig. 1, a large amount of sigma phase (σ-phase (FeCr), which is highly brittle and highly corrosive, is formed, making the material weak. Therefore, the chromium content is reduced from 26 to It is preferable to add 29% by weight

2) Molybdenum (Mo)

Molybdenum (Mo) increases high-temperature strength by solid solution strengthening with iron (Fe). In particular, molybdenum is highly resistant to corrosion by sulfur. The sulfidation rate of molybdenum and sulfur has strong resistance to sulfur corrosion to a degree similar to the oxidation rate of chromium as shown in FIG. 2 .

On the other hand, the effect of the molybdenum content on the corrosion rate in the iron alloy is as shown in FIG. 3, that the corrosion rate decreases at all temperatures as the molybdenum content increases up to 10 wt%, but 10 From weight % to 40 weight %, the corrosion rate is almost constant even if the molybdenum content is increased. Therefore, it is preferable to add 15 to 18% molybdenum.

3) carbon (C)

Carbon components combine with iron and chromium to form carbides with high hardness (Fe ₃ C, Cr ₂₃ C ₆ , etc.) The higher the carbon content, the higher the amount of carbide, the higher the hardness of the material, but the lower the toughness, the lower the wear resistance. Therefore, it is preferable to maximize the abrasion resistance by limiting the carbon content to 1 to 3% by weight.

4) boron (B)

As a metalloid element like carbon, boron is combined with iron (Fe) and chromium (Cr) to form boride (Fe ₂ B, Cr ₂ B, etc.) having a higher hardness than the carbide, thereby improving wear resistance. improve If the content of these elements is too high, it increases brittleness and decreases wear resistance, so it is limited to 2 to 4% by weight.

When the alloy (welded metal) having such a composition is coated on the surface of the boiler tube, it has excellent corrosion resistance and abrasion resistance at high temperatures, thereby improving the lifespan of the boiler tube.

In addition, the present invention is a cored wire consisting of a shell and a filler filled inside the shell, wherein the shell is C: 0.12% or less by weight, Cr: 16-18%, remaining Fe and unavoidable impurities having a component composition It uses a stainless steel strip and has a content of 56.5 to 63.5% based on the total weight of the cored wire,

The filler is a powder having a diameter of 0.044 to 0.25 mm having a content of 36.5 to 43.5% based on the total weight of the cored wire, and metal chromium powder (containing 9 to 11% C): 16 to 17%, B4C powder: 2.5 to 3.5%, metal molybdenum powder: 16-17%, ferroboron powder: 1-3%, metal chromium powder: characterized in that it consists of a component composition of 1-3%, and the size of the added filler powder is 0.044 It is characterized by limiting it to ~0.25mm.

The reason for limiting the components of the cored wire of the present invention will be described in detail as follows.

The reason for limiting the cored wire to such a composition in the present invention is that the deposited metal coating layer produced when welding or thermal spraying using a cored wire having such a composition is weight% Cr: 26 to 29%, Mo: 15 to 18%, C: 1 to 3%, B: 2 to 4%, the remaining Fe and an alloy of a composition consisting of inevitably contained impurities can be obtained, and in this alloy composition range, the high temperature pursued by the present invention This is because it has excellent properties of corrosion resistance and abrasion resistance.

The reason for using a stainless steel strip (SUS 430) having a component composition of C: 0.12% or less, Cr: 16-18%, the remaining Fe and inevitable impurities as an outer shell is that stainless steel strip (SUS 430) is a cored wire by weight %: C: 0.12% or less This is because it is suitable for filling the filler as a shell of, and it is possible to reduce the amount of these components added to the filler by using the Cr, C, and Fe components contained therein,

The reason why the content of the stainless steel strip (SUS 430) is limited to 56.5 to 63.5% based on the total weight of the cored wire is because it is easy to match the contents of Cr, C, and Fe added to the entire wire within this range.

Of course, a steel plate may be used instead of the stainless steel strip. However, in this case, the amount of the added filler (metal powder) must be used more and more, and the metal powder is an expensive product, which is economically disadvantageous, and it is difficult to use it because it is difficult to calculate an appropriate amount.

The reason for adding 16~17% of high-carbon-containing metal chromium powder (containing 9~11% C) is that Cr and C required for the alloy are simultaneously supplied, and the content of Cr and C required for the deposited metal in this range is reduced. because you can match it.

Metal chromium powder: The reason for adding 1 to 3% is that the added high carbon-containing metal chromium powder (containing 9 to 11% C) lacks the total Cr content, so it is additionally added to satisfy this deficiency.

B4C powder: The reason for adding 2.5~3.5% is that B and C required for the alloy are supplied at the same time, and the content of B and C required for the deposited metal can be matched within this range.

Ferroboron powder: The reason for adding 1-3% is that B and Fe required for the alloy are supplied at the same time, and the content of B and Fe required in the deposited metal can be matched in this range.

Metal molybdenum powder: The reason for adding 16 to 17% is to supply the Mo component required for the alloy (welded metal).

In addition, the reason for limiting the size of the added filler powder to 0.044 to 0.25 mm is that when the size of the filler powder is coarser than 0.25 mm, it cannot be dissolved during arc spraying and is welded. In this case, the size is limited to 0.044~0.25mm because a lot of oxidation loss occurs during arc spraying and deteriorates the material performance of the coating layer.

[Example]

1) Prototype production

4 is a view schematically showing a cross section of a cored wire for welding and thermal spraying manufactured according to an embodiment of the present invention. In order to manufacture the outer shell 1 and the inner filler 2 as shown in FIG. 4, the constituent materials were prepared as shown in Table 1.

Physical properties of outer shell and filler for manufacturing cored wire of the present invention Raw material name Chemical composition (wt%) division Addition (wt%) Metal Chrome (10%C) C:9~11%, Cr:87~90% Filler (0.25-0.044mm powder) 16-17% B4C C: 21-23%, B: 77-79% Filler (0.25-0.044mm powder) 2.5~3.5% Metal Molybdenum Mo>99% Filler (0.25-0.044mm powder) 16-17% Ferro Boron C<0.5%, B:17-20%, Fe:Bal. Filler (0.25-0.044mm powder) 1-3% Metal Chrome C<0.1%, Cr>99.0% Filler (0.25-0.044mm powder) 1-3% SUS430 C<0.12%, Cr: 16-18%, Fe: Bal. Outer sheath (thickness: 0.3mm steel strip) 56.5~63.5%

As shown in Table 1, the outer shell (1) uses a 0.3mm thick SUS430 stainless steel sheet, and for the filler, the powders indicated in Table 1 are classified with a sieve, and the powder with a size of 0.044∼0.25mm is mixed with a kneader ( After kneading in a mixer) for 24 hours or more, the kneaded filler was filled in a U-shaped outer shell, and the outer shell was drawn to surround the filler to prepare a cored wire in the form of FIG. 4 having an outer diameter of 1.6 mm.

2) Prototype evaluation

The properties of the deposited metal coating layer produced by arc spraying on a carbon steel sheet using the cored wire prepared as above were evaluated. The composition of the coating layer showed the composition of C:2.13wt%, Mo:16.52wt%, Cr:27.05wt%, B:2.72wt%, remaining Fe and other unavoidable impurities as a result of analysis.

The microscopic structure of the coating layer is as shown in FIG. 5, and as shown in the photograph, a dense structure is shown. The hardness value of the coating layer was measured as Hv 1013, 1092, 1120, 1062, 1032 when Vickers microhardness was measured with a load of 0.2Kg, and the average hardness value was Hv1063, indicating a high hardness value.

Meanwhile, the abrasion resistance of the cored wire of the present invention was comparatively evaluated according to ASTM G65 standard, and the volume loss of the coating layer of the present invention was 16.3mm ³ , and the volume loss of the conventional cored wire of our company (registered patent 10-1631233) as a comparison target It was confirmed that the abrasion resistance was increased by 15% to 19.2mm ³ .

The corrosion resistance of the present invention was compared and evaluated with that of our conventional cored wire (Registered Patent No. 10-1631233). The coating layer was polished and immersed in sulfuric acid (95.0-98.0%) at room temperature for 5 minutes, and then the degree of corrosion was evaluated under a microscope. 6 is a micrograph before (left) and after (right) corrosion of the conventional coating layer of our company's cored wire (Registration Patent No. 10-1631233), and it can be seen that the surface after corrosion is severely corroded. 7 is a micrograph before (left) and after (right) corrosion of the cored wire coating layer of the present invention, and it can be seen that almost no corrosion occurs.

1. Integument
2. Filler

Claims (3)

delete In the cored wire consisting of a shell and a filler filled inside the shell,
The outer shell is a stainless steel strip having a component composition of C: 0.12% or less, Cr: 16-18%, remaining Fe and inevitable impurities by weight%, and has a content of 56.5-63.5% based on the total weight of the cored wire,
The filler has a content of 36.5 to 43.5% based on the total weight of the cored wire, metal chromium powder (containing 9 to 11% C): 16 to 17%, B4C powder: 2.5 to 3.5%, metal molybdenum powder : 16~17%, ferroboron powder: 1-3%, metal chromium powder: 1-3% cored wire for welding and thermal spraying with excellent high temperature corrosion resistance and abrasion resistance performance 3. The method of claim 2,
The filler powder is a cored wire for welding and thermal spraying excellent in high temperature corrosion resistance and abrasion resistance, characterized in that it has a size of 0.044 to 0.25 mm.

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