Fe-BASED ALLOY, AND CORROSIVE WEAR RESISTANT AND WEAR RESISTANT Fe-BASED ALLOY FILM

Abstract

To provide an alloy film having excellent environmental resistance even in an environment where corrosion and wear simultaneously occur at high temperatures; and an alloy from which the alloy film can be formed.SOLUTION: An Fe-based alloy characterized by comprising, in terms of mass%, 10≤Cr≤40, 15≤Ni≤50, 0.03≤C≤0.9, 0.3≤Si≤2, and 1.5≤B≤3.5, the remainder consisting of Fe and unavoidable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an Fe-based alloy and an Fe-based alloy coating, and more particularly to an Fe-based alloy and an Fe-based alloy coating that can form an alloy coating having excellent environmental resistance in high-temperature environments where corrosion and corrosive wear are problematic. [Background technology]

[0002] Inside incinerators that burn waste, biomass, etc., the chlorine contained in the fuel creates a severe high-temperature, corrosive environment. In particular, chlorides contained in the atmosphere concentrate and accumulate on the surfaces of heat exchangers, which are colder than the ambient temperature, causing severe corrosion. Furthermore, in the case of fluidized-bed boilers, in addition to corrosion, wear caused by the fluidized medium can cause severe thinning. Protectors are installed to prevent this thinning. While installing protectors is effective, it also reduces the heat transfer efficiency of heat exchangers. Therefore, surface treatments such as thermal spraying and overlay welding are often used to prevent thinning.

[0003] Common issues with thermal spray coatings include the formation of pores in the coating and poor adhesion to the substrate. High-velocity oxygen fuel (HVOF) thermal spraying, which increases the particle velocity during spraying, can reduce the porosity of coatings compared to plasma spraying. However, it is not possible to completely eliminate pores, and the coating is only physically bonded to the substrate, resulting in weak adhesion. Therefore, self-fluxing alloy spraying, which remelts the coating after spraying to form a metallurgical reaction layer with the substrate and eliminates pores in the spray coating, significantly improving the properties of the sprayed coating. Self-fluxing alloy spraying is known to impart excellent corrosion resistance because the remelting process reduces pores in the coating and prevents the intrusion of corrosive substances. However, the composition of self-fluxing alloy powders that can be used for self-fluxing alloy spraying is limited. Self-fluxing alloys are required to have a melting onset temperature below 1,000°C and a wide temperature range between their liquidus and solidus. If the melting point is too high, not only will it be difficult to melt, but there is also the concern that raising the temperature to the melting point may have a thermal effect on the base material.On the other hand, if the temperature range is too narrow, it will be difficult to control the temperature during the remelting process, making it difficult to produce a high-quality coating.

[0004] The most commonly used self-fluxing alloy powder is SFNi4 (2.14A NiCrCuMoBSi 69 15 3 3A), as specified in JIS H8303:2010. SFNi4 is a Ni-Cr alloy consisting of 12-17 wt% Cr, 4 wt% or less Mo, 3.5-5.0 wt% Si, 5 wt% or less Fe, 0.4-0.9 wt% C, 2.5-4.0 wt% B, 1 wt% or less Co, 4 wt% or less Cu, and the remainder Ni. It possesses corrosion resistance in a wide range of environments and a high hardness of 50-60 HRC, making it an alloy with excellent corrosion and wear resistance. SFNi4 is also easy to process (remelting process), making it widely used. Modified versions of SFNi4 have also been proposed for specific applications.

[0005] For example, proposed is a Ni-based self-fluxing alloy powder that contains 10 wt% to 16.5 wt% Cr, 4.0 wt% or less Mo, 3.0 wt% to 5.0 wt% Si, 15.0 wt% or less Fe, 0.01 wt% to 0.9 wt% C, 2.0 wt% to 4.0 wt% B, 3.0 wt% or less Cu, 50 ppm to 500 ppm O, with the remainder being Ni and unavoidable impurities, and that satisfies a Si / B ratio of 1.2 to 1.7, and that has reduced fluidity during remelting treatment, as well as a part that has a coating formed from this Ni-based self-fluxing alloy powder by a thermal spraying method and has excellent corrosion resistance and / or wear resistance (Patent Document 1).

[0006] Also proposed is a Ni-based self-fluxing alloy powder that contains 12 wt% to 17 wt% Cr, 3 wt% to 8 wt% Mo, 3.5 wt% to 5.0 wt% Si, 5.0 wt% or less Fe, 0.4 wt% to 0.9 wt% C, 2.5 wt% to 4.0 wt% B, 4.0 wt% or less Cu, 200 ppm or less O, and the remainder being Ni and unavoidable impurities, and that satisfies 0 ppm ≧ −20Mo% + 100 (Patent Document 2).

[0007] Furthermore, a Ni-based self-fluxing alloy powder for thermal spraying has been proposed (Patent Document 3), which contains 30.0 wt% to 42.0 wt% Cr, 0.5 wt% to 2.0 wt% Mo, 2.0 wt% to 4.0 wt% Si, 5.0 wt% or less Fe, 2.5 wt% to 4.5 wt% C, 1.5 wt% to 4.0 wt% B, and the remainder being Ni and unavoidable impurities. This Ni-based self-fluxing alloy powder for thermal spraying is produced by atomization, and it is disclosed that chromium carbide with a particle size of 5 μm or less is uniformly precipitated inside the particles, resulting in improved high-temperature erosion resistance.

[0008] Furthermore, a corrosion-resistant and abrasion-resistant heat transfer tube for heat exchange has been proposed, in which a protective coating made of a Ni-based self-fluxing alloy containing 12 wt% to 17 wt% Cr, 4 wt% or less Mo, 3.5 wt% to 5.0 wt% Si, 5.0 wt% or less Fe, 0.4 wt% to 0.9 wt% C, 2.5 wt% to 4.5 wt% B, and 4.0 wt% or less Cu is formed on the outer surface of an iron-based metal tube (Patent Document 4).

[0009] However, conventional Ni-based self-fluxing alloys are not sufficiently resistant to erosion-corrosion (hereinafter sometimes abbreviated as "EC"), which is the simultaneous occurrence of corrosion and wear, and they also have the drawback of being expensive because they contain large amounts of expensive Ni.

[0010] On the other hand, when inexpensive Fe is used as the main component, it is known that the melting point of the alloy rises, making remelting difficult, and there are no Fe-based self-fluxing alloys in the JIS standard, so Fe-based alloys are generally used as overlay welding. Overlay welding has a large heat input during construction, which has a large thermal impact on the base material and can cause deformation.

[0011] A low-carbon, high-silicon, high-chromium, boron-niobium, iron-based corrosion-resistant, wear-resistant alloy has been proposed for use in Fe-based overlay welding. The alloy contains 15-31 wt% Cr, 10 wt% or less Mo, 2.5-4.5 wt% Si, 0.5-2.0 wt% C, 0.5-3.5 wt% B, 10 wt% or less Mn, 7 wt% or less Cu, 16 wt% or less Ni, 8 wt% or less Nb + V, and the remainder is iron and unavoidable impurities. The alloy satisfies a specific formula: low-carbon, high-silicon, high-chromium, boron-niobium alloy. This alloy exhibits improved wear resistance through the precipitation of carbides, while exhibiting corrosion resistance due to the Cr in the base metal. It has excellent wear resistance and corrosion resistance, and its low Ni content means that its material costs are lower than those of Ni-based alloys. However, Patent Document 5 evaluates corrosion resistance in an aqueous solution, and does not provide data on corrosion resistance in a high-temperature environment containing Cl. Therefore, it is unclear what corrosion resistance and wear resistance the material will have in the high-temperature, highly corrosive, and highly abrasive environment to which immersed heat transfer tubes in fluidized bed boilers are exposed.

[0012] In order to provide a metal component having excellent corrosion resistance and wear resistance, a method has been proposed in which a thermal spray coating having excellent corrosion resistance and wear resistance is formed by high-velocity flame or plasma spraying of a high-carbon iron-based alloy powder consisting of 3.0 to 6.0 wt% C, 5.0 to 15.0 wt% Cr, 5.0 to 8.0 wt% V, 2.0 to 6.0 wt% Ni, 0.5 to 3.0 wt% Mo, 1.0 to 4.0 wt% Si, and the balance Fe (Patent Document 6). However, the examples in this publication show that either wear resistance or corrosion resistance is improved compared to a cast material piece, but do not disclose an alloy coating that improves both.

[0013] Also, C: 0.5 to 1.5%, Si: 1.0 to 4.0%, Mn: 0.5 to 2.0%, C A high Cr alloy with excellent resistance to high-temperature erosion and corrosion has been proposed, which contains 35 to 60% Cr, the balance being Co and / or Fe and unavoidable impurities, and has a Cr to C ratio of 35≦Cr / C≦90 (Patent Document 7).

[0014] Patent Document 8 proposes a continuous casting roll that is excellent in corrosion resistance and wear resistance and that is to be installed in continuous casting equipment. The roll surface has a weld overlay that contains, by mass%, 0.07% or less C, 0.2 to 1.5% Si, 3% or less Mn, 13 to 20% Cr, 0.5 to 4% Ti, 0.1 to 0.5% N, the balance being Fe and unavoidable impurities, and that satisfies 1≦Ti / N≦20. Patent Document 8 discloses that chromium is uniformly distributed in the metal matrix and that the roll contains titanium nitride, thereby achieving excellent corrosion resistance, wear resistance, and thermal crack resistance.

[0015] The present applicants have also reported a Ni-based thermal spray alloy powder (Patent Document 9) characterized by containing 15 wt% to 25 wt% Cr, 0 wt% to 5 wt% Mo, 0.5 wt% to less than 2.0 wt% Si, 5 wt% or less Fe, 0.3 wt% to 0.7 wt% C, and 4 wt% to 7 wt% B, with the balance being Ni and unavoidable impurities; a Ni-Fe-based alloy powder characterized by containing 15 mass% to 35 mass% Cr, 10 mass% to 50 mass% Fe, 0 mass% to 5 mass% Mo, 0.3 mass% to 2 mass% Si, 0.3 mass% to 0.9 mass% C, and 4 mass% to 7 mass% B, with the balance being Ni and unavoidable impurities; and a Ni-Fe-based alloy powder characterized by containing 15 mass% to 35 mass% Cr, 10 mass% to 50 mass% Fe, 0 mass% to 5 mass% Mo, 0.3 mass% to 2 mass% Si, 0.3 mass% to 0.9 mass% C, and 4 mass% to 7 mass% B, with the balance being Ni and unavoidable impurities. The following documents have been proposed: a method for producing a corrosion-resistant, wear-resistant alloy coating using an Fe-based alloy powder to produce nodular precipitates with a coverage of 30% or more (Patent Document 10); and a corrosion-resistant, wear-resistant and wear-resistant alloy coating (Patent Document 11), which contains 10% by mass or more and 50% by mass or less of Cr, 0% by mass or more and 70% by mass or less of Ni, 0% by mass or more and 10% by mass or less of Mo, 0% by mass or more and less than 5% by mass of Si, 0.05% by mass or more and 1% by mass or less of C, 0% by mass or more and 10% by mass or less of B, with the remainder being Fe and unavoidable impurities, and which has on its surface a plurality of protrusions with a maximum diameter of 0.1 mm or more and 3 mm or less and a maximum height of 0.1 mm or more and 2 mm or less, spaced at a maximum distance of 0.1 mm or more and 5 mm or less. These Ni-Fe-based alloy coatings contain a matrix containing γNi and Ni3B eutectic and 30 vol% of precipitates containing borides and carbides, and by forming unique irregularities on the surface of the alloy coating, they improve corrosion resistance and wear resistance at high temperatures. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-143372 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-265591 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-161132 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-119781 [Patent Document 5] Patent No. 4310368 [Patent Document 6] Japanese Patent Application Publication No. 10-121221 [Patent Document 7] Japanese Patent Application Publication No. 11-80902 [Patent Document 8] WO2010 / 047137 [Patent Document 9] Japanese Patent Application Laid-Open No. 2018-131645 [Patent Document 10] Japanese Patent Application Publication No. 2019-210499 [Patent Document 11] Patent Publication No. 2021-80524 Summary of the Invention [Problem to be solved by the invention]

[0017] The present invention aims to provide an alloy coating film having excellent environmental resistance even in high-temperature environments where corrosion and wear occur simultaneously, and an alloy capable of forming such an alloy coating film. In particular, the present invention aims to provide an alloy coating film having excellent environmental resistance even in high-temperature, highly wear-resistant, and highly corrosive environments such as immersed heat transfer tubes in internal circulating fluidized bed boilers. The present invention aims to provide an alloy coating that has excellent corrosion and wear resistance at high temperatures for equipment used in the manufacturing of electronic equipment, and an alloy, preferably a thermal spray alloy, that can form such an alloy coating. [Means for solving the problem]

[0018] The present invention provides an alloy coating having excellent environmental resistance even in a high-temperature environment where corrosion and wear occur simultaneously, an alloy capable of forming the alloy coating, a method for producing the alloy coating, a heat transfer tube having the alloy coating, and an incinerator or boiler equipped with the heat transfer tube.

[0019] Conventional SFNi4, which has a relatively low melting point and excellent workability, forms a matrix phase containing γNi and Ni3B eutectic and an alloy film containing 20 vol% of boride and carbide precipitates to improve corrosion resistance and wear resistance. The Ni-Fe-based alloy disclosed in the prior applications (Patent Documents 10 and 11) of the present applicants forms a matrix phase containing γNi and Ni3B eutectic and an alloy film containing 30 vol% of boride and carbide precipitates, and forms unique irregularities on the surface of the alloy film to improve corrosion resistance and wear resistance at high temperatures. As a result of intensive research, the inventors of the present invention have found that the Ni3B eutectic is inferior in corrosion resistance and wear resistance at high temperatures, that boride precipitates are superior to carbide precipitates in corrosion resistance and wear resistance at high temperatures, that by suppressing the oxidation of Cr, which is easily oxidized, the intrusion of Cl into the matrix phase of the alloy film can be prevented and the corrosion resistance can be improved, that by forming an oxide film mainly composed of Fe near the surface of the alloy film, the high-temperature wear resistance and corrosion resistance can be improved, that by controlling the Ni content in the matrix phase of the alloy film, the peeling suppression effect can be exerted, and that by controlling the Cr concentration in the precipitates, the hardness of the alloy film can be improved. Based on these findings, the present invention has been completed. Hereinafter, specific embodiments of the present invention will be described.

[0020] [1] An Fe-based alloy characterized in that, in mass%, 10 ≦ Cr ≦ 40, 15 ≦ Ni ≦ 50, 0.03 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, and the balance is Fe and unavoidable impurities. [2] An Fe-based alloy characterized in that, in mass%, 10 ≦ Cr ≦ 30, 15 ≦ Ni ≦ 40, 0.1 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, and the balance is Fe and unavoidable impurities. [3] The Fe-based alloy according to [1] or [2], characterized in that it contains 10 mass% or more of Fe. [4] The Fe-based alloy according to [1] or [2], characterized in that it contains 30 mass% or more of Fe. [5] In mass%, 50 ≦ Fe ≦ 65, 0 < Cr ≦ 16, 20 ≦ Ni ≦ 35, 0 ≦ B ≦ 0.5, 0 < C ≦ 0.5, 0.5 ≦ Si ≦ 2, and the balance is a matrix phase composed of unavoidable impurities, and In mass percentage, 30 ≦ Fe ≦ 55, 30 ≦ Cr ≦ 60, 0 ≦ Ni ≦ 4, 6 ≦ B ≦ 10, 0 ≦ C ≦ 0.1, 0 ≦ Si ≦ 0.1, and the balance consists of inevitable impurities, and it contains boride precipitates. The boride precipitates are present in the matrix phase at a ratio of 20 vol% or more and 40 vol% or less of the entire alloy, and the Fe-based alloy according to [1] or [2] is characterized by this. [6] In mass percentage, 50 ≦ Fe ≦ 65, 0 < Cr ≦ 16, 20 ≦ Ni ≦ 35, 0 ≦ B ≦ 0.5, 0 < C ≦ 0.5, 0.5 ≦ Si ≦ 2, the balance consists of inevitable impurities, and it contains a matrix phase that does not contain Ni3B. In mass percentage, 30 ≦ Fe ≦ 55, 30 ≦ Cr ≦ 60, 0 ≦ Ni ≦ 4, 6 ≦ B ≦ 10, 0 ≦ C ≦ 0.1, 0 ≦ Si ≦ 0.1, and the balance consists of inevitable impurities, and it contains boride precipitates. The boride precipitates are present in the matrix phase at a ratio of 20 vol% or more and 40 vol% or less of the entire alloy, and the Fe-based alloy according to [1] or [2] is characterized by this. [7] In mass percentage, 10 ≦ Cr ≦ 40, 15 ≦ Ni ≦ 50, 0.03 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, and the balance consists of Fe and inevitable impurities, and an alloy film is characterized by this. [8] In mass percentage, 10 ≦ Cr ≦ 30, 15 ≦ Ni ≦ 40, 0.1 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, and the balance consists of Fe and inevitable impurities, and an alloy film is characterized by this. [9] In mass percentage, 50 ≦ Fe ≦ 65, 0 < Cr ≦ 16, 20 ≦ Ni ≦ 35, 0 ≦ B ≦ 0.5, 0 < C ≦ 0.5, 0.5 ≦ Si ≦ 2, and the balance consists of inevitable impurities, and it contains a matrix phase. In mass percentage, 30 ≦ Fe ≦ 55, 30 ≦ Cr ≦ 60, 0 ≦ Ni ≦ 4, 6 ≦ B ≦ 10, 0 ≦ C ≦ 0.1, 0 ≦ Si ≦ 0.1, and the balance consists of inevitable impurities, and it contains boride precipitates. The boride precipitates are present in the matrix phase at a ratio of 20 vol% or more and 40 vol% or less of the alloy film, and the alloy film according to [7] or [8] is characterized by this.

[10] A heat transfer tube equipped with any one of the alloy films of the following (1) to (6). (1) An alloy coating characterized in that, by mass%, 10 ≦ Cr ≦ 40, 15 ≦ Ni ≦ 50, 0.03 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, and the balance consists of Fe and unavoidable impurities. (2) An alloy coating characterized in that, by mass%, 10 ≦ Cr ≦ 30, 15 ≦ Ni ≦ 40, 0.1 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, and the balance consists of Fe and unavoidable impurities. (3) By mass%, 10 ≦ Cr ≦ 40, 15 ≦ Ni ≦ 50, 0.03 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, the balance consists of Fe and unavoidable impurities, by mass%, a matrix phase consisting of 50 ≦ Fe ≦ 65, 0 < Cr ≦ 16, 20 ≦ Ni ≦ 35, 0 ≦ B ≦ 0.5, 0 < C ≦ 0.5, 0.5 ≦ Si ≦ 2, and the balance consisting of unavoidable impurities, and by mass%, a boride precipitate consisting of 30 ≦ Fe ≦ 55, 30 ≦ Cr ≦ 60, 0 ≦ Ni ≦ 4, 6 ≦ B ≦ 10, 0 ≦ C ≦ 0.1, 0 ≦ Si ≦ 0.1, and the balance consisting of unavoidable impurities, and the alloy coating is characterized in that the boride precipitate is present in the matrix phase at a ratio of 20 vol% or more and 40 vol% or less of the entire alloy coating. An alloy coating characterized in that the boride precipitate is present in the matrix phase at a ratio of 20 vol% or more and 40 vol% or less of the entire alloy coating. (4) By mass%, 10 ≦ Cr ≦ 30, 15 ≦ Ni ≦ 40, 0.1 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, the balance consists of Fe and unavoidable impurities, by mass%, a matrix phase consisting of 50 ≦ Fe ≦ 65, 0 < Cr ≦ 16, 20 ≦ Ni ≦ 35, 0 ≦ B ≦ 0.5, 0 < C ≦ 0.5, 0.5 ≦ Si ≦ 2, and the balance consisting of unavoidable impurities, and by mass%, a boride precipitate consisting of 30 ≦ Fe ≦ 55, 30 ≦ Cr ≦ 60, 0 ≦ Ni ≦ 4, 6 ≦ B ≦ 10, 0 ≦ C ≦ 0.1, 0 ≦ Si ≦ 0.1, and the balance consisting of unavoidable impurities, and An alloy coating characterized in that the boride precipitate is present in the matrix phase at a ratio of 20 vol% or more and 40 vol% or less of the entire alloy coating. (5) By mass%, 10 ≦ Cr ≦ 40, 15 ≦ Ni ≦ 50, 0.03 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, the balance consists of Fe and unavoidable impurities, In mass percentage: 50 ≤ Fe ≤ 65, 0 < Cr ≤ 16, 20 ≤ Ni ≤ 35, 0 ≤ B ≤ 0.5, 0 ≤ C ≤ 0.5, 0.5 ≤ Si ≤ 2, the balance being inevitable impurities, a matrix phase that does not contain Ni3B, and In mass percentage: 30 ≤ Fe ≤ 55, 30 ≤ Cr ≤ 60, 0 ≤ Ni ≤ 4, 6 ≤ B ≤ 10, 0 ≤ C ≤ 0.1, 0 ≤ Si ≤ 0.1, the balance being inevitable impurities, and boride precipitates, The alloy film is characterized in that the boride precipitates are present in the alloy film at a ratio of 20 vol% or more and 40 vol% or less of the entire alloy film. (6) In mass percentage: 10 ≤ Cr ≤ 30, 15 ≤ Ni ≤ 40, 0.1 ≤ C ≤ 0.9, 0.3 ≤ Si ≤ 2, 1.5 ≤ B ≤ 3.5, the balance being Fe and inevitable impurities, In mass percentage: 50 ≤ Fe ≤ 65, 0 < Cr ≤ 16, 20 ≤ Ni ≤ 35, 0 ≤ B ≤ 0.5, 0 ≤ C ≤ 0.5, 0.5 ≤ Si ≤ 2, the balance being inevitable impurities, a matrix phase that does not contain Ni3B, and In mass percentage: 30 ≤ Fe ≤ 55, 30 ≤ Cr ≤ 60, 0 ≤ Ni ≤ 4, 6 ≤ B ≤ 10, 0 ≤ C ≤ 0.1, 0 ≤ Si ≤ 0.1, the balance being inevitable impurities, and boride precipitates, The alloy film is characterized in that the boride precipitates are present in the alloy film at a ratio of 20 vol% or more and 40 vol% or less of the entire alloy film. An incinerator having the heat transfer tube according to

[11]

[10] . A boiler having the heat transfer tube according to

[12]

[10] .

[13] In mass percentage: 10 ≤ Cr ≤ 40, 15 ≤ Ni ≤ 50, 0.03 ≤ C ≤ 0.9, 0.3 ≤ Si ≤ 2, 1.5 ≤ B ≤ 3.5, the balance being Fe and inevitable impurities, In mass percentage: 50 ≤ Fe ≤ 65, 0 < Cr ≤ 16, 20 ≤ Ni ≤ 35, 0 ≤ B ≤ 0.5, 0 ≤ C ≤ 0.5, 0.5 ≤ Si ≤ 2, the balance being inevitable impurities, a matrix phase, and In mass percentage: 30 ≤ Fe ≤ 55, 30 ≤ Cr ≤ 60, 0 ≤ Ni ≤ 4, 6 ≤ B ≤ 10, 0 ≤ C ≤ 0.1, 0 ≤ Si ≤ 0.1, the balance being inevitable impurities, and boride precipitates, the boride precipitates are present in the matrix at a ratio of 20 vol% to 40 vol% of the entire alloy by thermal spraying powder of an Fe-based alloy to form a thermal spray coating; the thermal spray coating is subjected to a remelting treatment by high-frequency induction heating at a temperature between the liquidus temperature and solidus temperature of the parent phase of the Fe-based alloy; A method for producing an alloy film, comprising forming an alloy film. [Effects of the Invention]

[0021] The Fe-based alloy of the present invention can form an alloy coating that enables the extension of the life of heat transfer tubes, etc., without significantly impairing the heat transfer efficiency of the heat exchanger, as in the case of a protector, even in severely corrosive and abrasive environments at high temperatures where chlorides are present, such as in waste and biomass incinerators and boilers. As a result, it is possible to provide incinerators and boilers that have improved equipment operating rates by extending the life of components without reducing the heat exchange efficiency of the heat transfer tubes. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram illustrating an apparatus used in a corrosion resistance and abrasion resistance test. [Figure 2] Cross-sectional microstructure observation photographs of six alloys. [Figure 3] EPMA map analysis of Ni. [Figure 4] EPMA map analysis photograph of Fe-35Ni alloy. [Figure 5] EPMA map analysis photograph of Fe-65Ni alloy. [Figure 6] EPMA map analysis photograph of Ni-25Cr alloy. [Figure 7] EPMA map analysis photograph of Fe-25Cr alloy. [Figure 8] Graph showing EC test results of Ni-xFe-5Cr alloy. [Figure 9] Graph showing EC test results for pure Ni and Ni-92Ni3B alloy. [Figure 10]SEM images of the surfaces of (a) pure Ni and (b) Ni-92Ni3B alloy after EC testing. [Figure 11] Graph showing EC test results for boride-based precipitates and carbide-based precipitates [Figure 12] 1 is a graph showing the results of a high-temperature EC test of an alloy with a high Cr concentration in the parent phase. [Figure 13] 1 is a graph showing the results of a high-temperature EC test of an alloy with a low Cr concentration in the matrix. [Figure 14] 1 is a graph showing the volume ratio of precipitates in an alloy coating and the results of an EC test. [Figure 15] Graph showing EC test results of various alloys according to the examples. [Figure 16] Microstructure observation photograph of Fe-20Ni-20Cr-2.6B-1Si-0.5C (wt.%). [Figure 17] Microstructure observation photograph of Fe-20Ni-15Cr-2.6B-1Si-0.5C (wt.%). [Figure 18] Microstructure observation photograph of Fe-20Ni-25Cr-2.6B-1Si-0.5C (wt.%). [Figure 19] Microstructure observation photograph of Fe-25Ni-20Cr-2.6B-1Si-0.5C (wt.%). [Figure 20] Photographs showing the thermal spraying and remelting treatments performed using Fe-15Cr-20Ni-2.6B-1Si-0.5C (wt.%) alloy powder. [Figure 21] Microscope observation photographs of alloy coatings at various remelting temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0023] First, various test conditions described in this specification will be explained.

[0024] [Corrosion and abrasion resistance test (hereinafter sometimes abbreviated as "EC test")] Test specimens with a thickness of 1 mm were cut from the arc-melted alloy. Both surfaces were polished with SiC abrasive paper, and finally polished with #1200 abrasive paper before use. As shown in Figure 1, the test specimen (sample) was fixed to the tip of a sample holder and inserted into a quartz tube containing sand containing 0.5 wt% KCl-50 mol% NaCl salt. The sand heated to 700°C was induced to flow by blowing 400°C compressed air into the bottom of the device at 25 L / min, and collided with the sand at a 45° impact angle. Cooling water was circulated inside the sample holder to create an atmosphere and temperature gradient similar to that of a real machine, maintaining the sample surface temperature at 330–350°C. During the test, salt was continuously supplied to the sand by vaporizing a NaCl-40KCl-20 mol% CaCl2 mixed salt solution installed at the bottom of the device. Sand was replenished and salt replaced every 50 hours, and the test was continued for up to 250 hours. The mass change before and after the test was measured, and the amount of corrosion wear (mg / cm 2 ) was calculated.

[0025] [Corrosion test] The test specimens were polished using abrasive paper and finally polished with a diamond abrasive with a 3μm grit size, and then subjected to an embedment test in sand containing 1 wt.% mixed salt (NaCl-40KCl-20mol%CaCl2). The embedment test involves placing the mixed salt in a crucible, burying the test specimen to a certain depth, and corroding it at high temperatures without allowing the mixed salt to flow (JIS Z2293 2004). The test temperature was 480°C, and the test time was up to 49 hours, allowing observation of the oxide film formed only by corrosion without wear. Cross-sectional structure observation was performed using a SEM, and map analysis was performed using an EPMA.

[0026] Next, the Fe-based alloy of the present invention will be described. (1)Fe-based alloy The Fe-based alloy of the present invention is suitable as a thermal spray alloy for forming an alloy coating with improved corrosion resistance and wear resistance at high temperatures, and is characterized by the following mass %: 10≦Cr≦40, 15≦Ni≦50, 0.03≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, with the balance being Fe and inevitable impurities. The content of each element is explained below.

[0027] [Fe] The Fe-based alloy of the present invention is primarily composed of Fe. It is known that Fe generally has inferior corrosion resistance compared to Ni, and that its high-temperature chloride corrosion resistance is particularly inferior to Ni. Fe alone significantly reduces corrosion resistance in high chlorine partial pressure environments, and its melting point rises, reducing workability. However, it has been discovered that an Fe-based oxide film has excellent corrosion and wear resistance at high temperatures, and that when the chlorine partial pressure is low, the inclusion of Fe improves corrosion resistance and significantly increases corrosion and wear resistance.

[0028] Corrosion tests were conducted on Fe only, Ni only, Fe-35Ni, Fe-65Ni, Fe-25Cr, and Ni-25Cr (all alloys are expressed in wt%), and cross-sectional structure observations and EPMA map analyses were performed.

[0029] The cross-sectional structure observation results of the six alloys are shown in Figure 2 (2000x magnification). When only Fe was used, corrosion was observed throughout the entire specimen, when only Ni was used, corrosion was observed only on the surface, when Fe-35Ni alloy corrosion was less than that of either Fe or Ni, with slight corrosion observed in the surface layer, and when Fe-65Ni alloy corrosion was more inhibited than that of Fe-35Ni alloy.

[0030] An EPMA map analysis photograph of Ni is shown in Figure 3. When Ni is used alone, a nickel oxide layer is formed on the surface of the nickel layer, and it can be seen that Cl is concentrated between the nickel oxide layer and the nickel layer.

[0031] Figure 4 shows an EPMA map analysis photograph of the Fe-35Ni alloy, and Figure 5 shows an EPMA map analysis photograph of the Fe-65Ni alloy. Figures 4 and 5 show that in the Fe-Ni alloy, a nickel layer is stacked on top of an iron layer, and iron oxide is formed between the iron and nickel layers and on the surface of the nickel layer. Comparing Figures 4 and 5, no Cl penetration is observed in the Fe-65Ni (Figure 5), while slight Cl penetration is observed in the iron oxide and nickel layers in the Fe-35Ni (Figure 4). However, compared to Ni (Figure 3), the degree of Cl concentration is low, and it can be said that in the Fe-Ni alloy, the iron oxide layer that forms on the surface prevents Cl penetration.

[0032] For reference, EPMA map analysis photographs of the Ni-25Cr alloy are shown in Figure 6, and EPMA map analysis photographs of the Fe-25Cr alloy are shown in Figure 7. No Cl enrichment was observed in Figures 6 and 7. In the Ni-25Cr alloy (Figure 6), Ni and Cr coexist throughout, and an oxide layer of Ni and Cr was observed on the surface. In the Fe-25Cr alloy (Figure 7), Fe and Cr coexist throughout, and iron oxide and chromium oxide were observed on the surface. The surface defects in Figures 6 and 7 are due to polishing during the preparation of the specimen for observation. Figures 2 to 7 indicate that the use of an Fe-based alloy results in the formation of an iron oxide layer on the surface, improving corrosion resistance and wear resistance compared to conventionally known corrosion-resistant alloys. Furthermore, Figures 2 to 7 indicate that the alloys containing Fe and Ni have no defects in the surface oxide layer, indicating a spalling-inhibiting effect.

[0033] Figure 8 shows the results of an EC test conducted up to 100 hours with the Fe content (x) of a Ni-xFe-5Cr (expressed in wt%) alloy varied by mass: 5%, 10%, 30%, 60% by mass, and 80% by weight. Sand was added and salt was replaced after 50 hours. Figure 8 shows that the greater the Fe content, the less metal loss there is. Ni-Fe-Cr alloys with an Fe content of 10% by mass, or preferably 30% by mass or more, exhibit significantly reduced metal loss and are therefore superior in corrosion and wear resistance. Therefore, it is desirable for the Fe content of a Ni-Fe-Cr alloy to be 10% by mass or more, and preferably 30% by mass or more.

[0034] [Ni] The Fe-based alloy of the present invention contains 15% by mass or more and 50% by mass or less, preferably 40% by mass or less, and more preferably 20% by mass or more and 25% by mass or less of Ni. Ni is known to have excellent corrosion resistance, particularly excellent high-temperature chloride corrosion properties, and it is generally believed that the higher the Ni content, the better the material properties. However, because Ni is expensive, it is desirable to reduce the amount added from a cost perspective.

[0035] Figure 9 shows the results of EC tests conducted for up to 50 hours using pure Ni and Ni-92Ni3B (vol%) alloys, and Figure 10 shows SEM photographs of the alloy surfaces after the EC test. Figure 9(a) shows the comparison of corrosion wear amounts of the alloys, and Figure 9(b) shows the comparison of metal loss amounts. From Figure 9, it can be seen that the Ni alloy containing Ni3B had a larger metal loss amount and thickness reduction. In Figure 10(b), the large, shining white dots are thought to be borate glass formed by the reaction of B2O3 (boric acid), which is the oxidation of B, with silica sand and sodium oxide. Because borate glass has a low melting point of around 450°C, it is thought to have become semi-sintered during the EC test, volatilized or mobilized, making it more susceptible to metal loss. Figures 9 and 10 show that Ni3B reduces corrosion and wear resistance. Therefore, it is desirable to set the content so that the balance between Ni and B can be controlled so as to prevent the formation of Ni3B eutectic as much as possible.

[0036] [Cr] The Fe-based alloy of the present invention contains 10% by mass or more and 40% by mass or less, preferably 30% by mass or less, and more preferably 15% by mass or more and 25% by mass or less of Cr. Cr is an essential element for maintaining corrosion resistance at high temperatures, but excessive Cr content increases the melting point, leading to poor coating application. As will be described later, it has been confirmed that Cr forms precipitates (Cr borides and Cr carbides) with B and C, increasing the hardness of the alloy and improving its wear resistance. Therefore, it is desirable to control the content so that the balance of Cr, B, and C can be controlled so that precipitates containing Cr borides and Cr carbides can be formed.

[0037] [B] The Fe-based alloy of the present invention contains 1.5% by mass or more and 3.5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or more and 3% by mass or less of B. B is an essential element for workability (remeltability) and also improves hardness by precipitating as Cr borides. However, if the B content is too high, the amount of Cr consumed as borides increases, reducing the corrosion resistance of the matrix and making it too hard and brittle. Therefore, it is desirable to control the B content so that the balance between Cr and B is appropriate for the matrix and precipitates. As mentioned above, it has been confirmed that the presence of NiB eutectic in the matrix deteriorates corrosion resistance and wear resistance. Therefore, it is preferable to prevent the formation of NiB eutectic in the matrix, and it is desirable to control the B content so that the balance between Ni and B in the matrix is regulated. Furthermore, as described below, it is preferable to limit the amount of precipitates to 20% by volume or more and 40% by volume or less. To form such precipitates, the B content in the Fe-based alloy is preferably 1.5% by volume or more and 3.5% by mass or less.

[0038] [C] The Fe-based alloy of the present invention contains 0.03% by mass or more and 0.9% by mass or less of C, preferably 0.1% by mass or more and 0.9% by mass or less. C forms hard Cr carbides and improves hardness. However, if the C content is too high, too much Cr in the matrix is consumed as carbides, resulting in a deterioration in corrosion resistance. Therefore, it is desirable to set the content so that the balance between Cr and C can be properly regulated in the matrix and precipitates. As will be described later, it has been confirmed that borides improve corrosion resistance and wear resistance more than carbides in precipitates. Therefore, it is desirable to set the content so that the balance between C and B can be properly regulated, which promotes the formation of borides and suppresses the formation of carbides.

[0039] The results of an EC test conducted on alloys prepared so that the ratios of carbide and boride precipitates were as shown in Table 1 are shown in Figure 11.

[0040] [Table 1]

[0041] As shown in Fig. 11, when comparing the amount of weight loss, the carbide-based alloy has slightly more than the boride-based alloy, and it can be confirmed that Cr boride is more excellent in corrosion resistance and wear resistance than Cr carbide.

[0042] [Si] The Fe-based alloy of the present invention contains Si in an amount of 0.3% by mass or more and 2% by mass or less, preferably 1.5% by mass or less, more preferably 0.5% by mass or more and 1.5% by mass or less. Si is an element that improves oxidation resistance and contributes to the improvement of corrosion resistance. However, if it is too much, the corrosion and wear resistance will decrease, and in an environment containing a small amount of chlorine, the corrosion resistance will decrease. Also, if it is too little, the workability (remelting treatment) will be inferior, and it cannot be remelted sufficiently to form a sufficiently dense film.

[0043] The Fe-based alloy of the present invention further comprises, in mass%, a matrix phase consisting of 50 ≦ Fe ≦ 65, 0 ≦ Cr ≦ 16, 20 ≦ Ni ≦ 35, 0 ≦ B ≦ 0.5, 0 < C ≦ 0.5, 0.5 ≦ Si ≦ 2, and the balance being inevitable impurities, and a boride precipitate consisting of 30 ≦ Fe ≦ 55, 30 ≦ Cr ≦ 60, 0 ≦ Ni ≦ 4, 6 ≦ B ≦ 10, 0 ≦ C ≦ 0.1, 0 ≦ Si ≦ 0.1, and the balance being inevitable impurities, and the boride precipitate is preferably present in the matrix phase at a ratio of 20 vol% or more and 40 vol% or less.

[0044] [Matrix phase] The matrix phase of the Fe-based alloy consists of 50 ≦ Fe ≦ 65, 0 ≦ Cr ≦ 16, 20 ≦ Ni ≦ 35, 0 ≦ B ≦ 0.5, 0 < C ≦ 0.5, 0.5 ≦ Si ≦ 2, and the balance being inevitable impurities, in mass%.

[0045] [Fe] The matrix phase of the Fe-based alloy of the present invention contains Fe in an amount of 50% by mass or more and 65% by mass or less, preferably 55% by mass or more and 65% by mass or less. An oxide film of Fe, which is excellent in corrosion resistance and wear resistance at high temperatures, is formed in a region close to the surface of the matrix phase of the alloy.

[0046] [Cr] The matrix of the Fe-based alloy of the present invention contains 0 to 16% by mass, preferably 5 to 16% by mass, of Cr. Cr exists as precipitates in the form of Cr borides and Cr carbides rather than in the matrix of the alloy, thereby improving corrosion resistance and wear resistance.

[0047] EC tests were conducted on two alloys with high and low Cr concentrations in the matrix, with the compositions shown in Table 2, with the B content varied from 0 mass%, approximately 2 mass%, and approximately 5 mass%, respectively. The results are shown in Figures 12 and 13. During the EC test, the amount of mass change was measured while the sand was replaced every 50 hours. The composition of the precipitates and matrix was analyzed by observing multiple locations with an EPMA and calculating the average value.

[0048] [Table 2]

[0049] Table 2 also shows the amount of metal loss after 150 hours of EC testing. Therefore, when the matrix does not contain B, the alloy with a higher matrix Cr concentration has less metal loss, but when the matrix contains approximately the same amount of B, the alloy with a lower matrix Cr concentration has less metal loss.

[0050] [B] The matrix of the Fe-based alloy of the present invention contains 0% to 0.5% by mass, preferably 0.1% to 0.4% by mass, of B. The presence of NiB eutectic in the matrix of the Fe-based alloy deteriorates corrosion resistance and wear resistance, while the presence of Cr boride in the precipitates improves corrosion resistance and wear resistance. Therefore, it is preferable that the amount of B present in the matrix is small.

[0051] [Ni] The matrix of the Fe-based alloy of the present invention contains Ni in an amount of 20% by mass to 35% by mass, preferably 25% by mass to 35% by mass. As described above, Ni has the effect of suppressing spalling, and it has been confirmed that the presence of NiB eutectic in the matrix deteriorates corrosion resistance and wear resistance. Therefore, it is preferable that Ni is present in the matrix as Ni rather than as NiB eutectic.

[0052] [C] As mentioned above, since the corrosion resistance and wear resistance are improved when the amount of Cr carbide in the precipitates is small, it is preferable that C is present in the matrix rather than precipitated. The matrix of the Fe-based alloy of the present invention contains more than 0 mass% and 0.5 mass% or less of C, preferably 0.05 mass% or more and 0.5 mass% or less.

[0053] [Si] Si is present almost entirely in the matrix. The matrix of the Fe-based alloy of the present invention contains 0.5 to 2 mass % of Si, preferably 0.5 to 1.5 mass %.

[0054] [Precipitate] The Fe-based alloy of the present invention has precipitates dispersed in the matrix, and the precipitates preferably account for 20 vol % to 40 vol %, and more preferably 25 vol % to 35 vol %, of the alloy.

[0055] Figure 14 shows the relationship between the precipitate percentage and the amount of metal loss after 150 hours of EC testing for each Fe-based alloy with the composition shown in Table 2. As shown in Table 2 and Figure 14, if the precipitate percentage is less than 20 vol% or more than 40 vol%, the amount of metal loss increases and corrosion cannot be sufficiently suppressed. Furthermore, alloys with a large amount of precipitates are very brittle and difficult to work with.

[0056] The precipitates contain, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, with the remainder being Cr borides consisting of unavoidable impurities. The precipitates are primarily Cr borides, but a small amount of unavoidably formed Cr carbides may also be present. As mentioned above, it has been confirmed that Cr borides improve corrosion resistance and wear resistance more than Cr carbides.

[0057] [Fe] The Cr boride precipitate contains 30 mass % or more and 55 mass % or less of Fe, preferably 35 mass % or more and 55 mass % or less.

[0058] [Cr] The Cr boride precipitate contains 30% by mass or more and 60% by mass or less, preferably 35% by mass or more and 60% by mass or less of Cr. Cr can exist as a carbide or a boride, but in the present invention, In the present invention, it is preferable that Cr exists as a Cr boride in order to improve corrosion resistance and wear resistance.

[0059] [Ni] The Cr boride precipitate contains Ni in an amount of 0% by mass or more and 4% by mass or less, and preferably 1% by mass or more and 3.5% by mass or less.

[0060] [B] To improve corrosion resistance and wear resistance, B is preferably present in the precipitate as Cr boride rather than in the matrix. The Cr boride precipitate contains B in an amount of 6 to 10 mass%, preferably 6.5 to 9.5 mass%.

[0061] [C] C is preferably present in the matrix rather than in the precipitates as Cr carbides. The precipitates may contain 0% to 0.1% by mass, preferably 0% to 0.05% by mass, of C. The lower the C content in the precipitates, the better.

[0062] [Si] It is preferable that Si is not precipitated but exists in the matrix. The precipitate contains Si in an amount of 0 mass % or more and 0.1 mass % or less, preferably 0 mass % or more and 0.05 mass % or less.

[0063] The Fe-based alloy of the present invention can be used to form an alloy coating on a substrate that has excellent corrosion resistance and wear resistance at high temperatures. The alloy coating of the present invention will be described below.

[0064] (2) Alloy coating The alloy coating of the present invention is characterized in that, in mass%, 10 ≦ Cr ≦ 40, 15 ≦ Ni ≦ 50, 0.03 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, and the balance is Fe and inevitable impurities. The details of each element are as described above for Fe-based alloys.

[0065] Also, the alloy coating of the present invention is characterized in that, in mass%, 10 ≦ Cr ≦ 30, 15 ≦ Ni ≦ 40, 0.1 ≦ C ≦ 0.9, 0.3 ≦ Si ≦ 2, 1.5 ≦ B ≦ 3.5, and the balance is Fe and inevitable impurities. The details of each element are as described above for Fe-based alloys.

[0066] Furthermore, the alloy coating of the present invention includes a matrix phase consisting of, in mass%, 50 ≦ Fe ≦ 65, 0 < Cr ≦ 16, 20 ≦ Ni ≦ 35, 0 ≦ B ≦ 0.5, 0 < C ≦ 0.5, 0.5 ≦ Si ≦ 2, and the balance being inevitable impurities, and a boride precipitate consisting of, in mass%, 30 ≦ Fe ≦ 55, 30 ≦ Cr ≦ 60, 0 ≦ Ni ≦ 4, 6 ≦ B ≦ 10, 0 ≦ C ≦ 0.1, 0 ≦ Si ≦ 0.1, and the balance being inevitable impurities, It is preferable that the precipitate is present in the matrix phase at a ratio of 20 vol% or more and 40 vol% or less of the alloy coating. The details of each element, the matrix phase, and the precipitate are as described above for Fe-based alloys.

[0067] Also, on the surface of the alloy coating of the present invention, nodular precipitates of the corrosion and wear resistant alloy coating of Patent Document 10 and specific-shaped irregularities of the corrosion and wear resistant alloy coating of Patent Document 11 are not formed.

[0068] The alloy coating of the present invention can be formed by performing spraying using the Fe-based alloy powder of the present invention and then performing remelting treatment by high-frequency induction heating. The remelting treatment temperature is preferably a temperature between the liquidus temperature and the solidus temperature of the matrix phase of the Fe-based alloy. For example, the remelting treatment temperature is preferably 1100 °C or higher and 1250 °C or lower, more preferably 1150 °C or higher and 1200 °C or lower. Having a composition of Fe-20Ni-15Cr-2.6B-1Si-0.5C When using an Fe-based alloy powder, the remelting temperature is preferably set to 1160°C or higher and 1180°C or lower.

[0069] The Fe-based alloy of the present invention can be used to form an alloy coating on a substrate, thereby improving corrosion resistance and wear resistance in high-temperature corrosive environments. Therefore, the present invention also provides a heat transfer tube having the alloy coating of the present invention, as well as a heat exchanger, an incinerator, and a boiler having the heat transfer tube. [Example]

[0070] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0071] The compositions of the alloys having the four compositions shown in Table 3 and a comparative example, a Ni-30Fe-20Cr-5.5B-1Si-0.5C thermal spray material, were analyzed using an EPMA. The EC test described above was then carried out for 100 hours, and the structure after the EC test was observed using an SEM. The EC test results are shown in Figure 15, and photographs of the structure before the EC test are shown in Figures 16 to 19. For reference, Figure 15 also shows the EC test results for the Ni-30Fe-20Cr-5.5B-1Si-0.5C arc spray material.

[0072] As shown in FIG. 15, it can be confirmed that the Fe-based alloy of the present invention has a reduced amount of metal loss compared to the conventional alloy (thermal spray material), and is excellent in corrosion resistance and wear resistance.

[0073] 16 to 19, the precipitate ratio was approximately 30 vol%, achieving the target ratio. Although there was some variation in the structure because the alloy was produced using arc melting, composition analysis using EPMA confirmed that the precipitates were borides.

[0074] [Table 3]

[0075] The precipitate content was confirmed for alloys having the four compositions shown in Table 4. In Examples 1 and 2, which are Fe-based alloys of the present invention, the precipitate content was in the range of 20 vol% to 40 vol%, but in Comparative Examples 1 and 2, which had a B content exceeding 3.5 wt%, the precipitate content exceeded 40 vol%.

[0076] [Table 4]

[0077] An alloy coating was formed by thermal spraying using an alloy powder of Fe-15Cr-20Ni-2.6B-1Si-0.5C (wt.%) and then remelting using high-frequency induction heating. The remelting temperature was varied in 20°C increments from 1120°C to 1200°C, as shown in Figure 20. Microscope photographs of the cross sections of the alloy coating after remelting at each temperature are shown in Figure 21.

[0078] At remelting temperatures of 1120°C and 1140°C, the alloy powder was not completely melted, and some of the sprayed powder particles remained. At remelting temperatures of 1160°C and 1180°C, the sprayed powder particles were completely melted. At a remelting temperature of 1200°C, the surface became wavy, and a uniform alloy coating could not be formed. Therefore, when using an Fe-15Cr-20Ni-2.6B-1Si-0.5C (wt.%) alloy powder, the remelting temperature should be higher than 1140°C and lower than 1200°C, preferably 1150°C or higher and 1190°C or lower, and more preferably 1160°C or higher and 1180°C or lower.

[0079] The remelting temperature must be a temperature at which the sprayed alloy powder can be completely remelted to form a uniform surface, and is preferably a temperature between the solidus temperature and liquidus temperature of the matrix of the alloy powder.

Claims

1. An Fe-based alloy comprising, in mass%, 10≦Cr≦40, 15≦Ni≦50, 0.03≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, and the balance being Fe and inevitable impurities.

2. An Fe-based alloy comprising, in mass%, 10≦Cr≦30, 15≦Ni≦40, 0.1≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, and the balance being Fe and inevitable impurities.

3. 3. The Fe-based alloy according to claim 1, wherein the Fe-based alloy contains 10 mass % or more of Fe.

4. 3. The Fe-based alloy according to claim 1, wherein the Fe-based alloy contains 30 mass % or more of Fe.

5. a mother phase consisting of, in mass%, 50≦Fe≦65, 0<Cr≦16, 20≦Ni≦35, 0≦B≦0.5, 0<C≦0.5, 0.5≦Si≦2, and the remainder being unavoidable impurities; boride precipitates consisting of, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, and the balance being unavoidable impurities; 3. The Fe-based alloy according to claim 1, wherein the boride precipitates are present in the matrix at a ratio of 20 vol % to 40 vol % of the entire alloy.

6. In mass%, 50≦Fe≦65, 0<Cr≦16, 20≦Ni≦35, 0≦B≦0.5, 0<C≦0.5, 0.5≦Si≦2, and the balance being inevitable impurities, ３ a mother phase not containing B; boride precipitates consisting of, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, and the balance being unavoidable impurities; 3. The Fe-based alloy according to claim 1, wherein the boride precipitates are present in the matrix at a ratio of 20 vol % to 40 vol % of the entire alloy.

7. An alloy coating comprising, in mass%, 10≦Cr≦40, 15≦Ni≦50, 0.03≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, and the balance being Fe and inevitable impurities.

8. An alloy coating comprising, in mass%, 10≦Cr≦30, 15≦Ni≦40, 0.1≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, and the balance being Fe and inevitable impurities.

9. a mother phase consisting of, in mass%, 50≦Fe≦65, 0<Cr≦16, 20≦Ni≦35, 0≦B≦0.5, 0<C≦0.5, 0.5≦Si≦2, and the remainder being unavoidable impurities; boride precipitates consisting of, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, and the balance being unavoidable impurities; 9. The alloy coating according to claim 7, wherein the boride precipitates are present in the matrix at a ratio of 20 vol % to 40 vol % of the alloy coating.

10. A heat transfer tube having an alloy coating according to any one of (1) to (6) below: (1) The alloy is characterized by the following components in mass %: 10≦Cr≦40, 15≦Ni≦50, 0.03≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, and the balance being Fe and inevitable impurities. alloy coating, (2) An alloy coating characterized by, in mass%, 10≦Cr≦30, 15≦Ni≦40, 0.1≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, and the balance being Fe and unavoidable impurities. (3) In mass%, 10≦Cr≦40, 15≦Ni≦50, 0.03≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, with the balance being Fe and inevitable impurities; a mother phase consisting of, in mass%, 50≦Fe≦65, 0<Cr≦16, 20≦Ni≦35, 0≦B≦0.5, 0<C≦0.5, 0.5≦Si≦2, and the remainder being unavoidable impurities; boride precipitates consisting of, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, and the balance being unavoidable impurities; an alloy coating, characterized in that the boride precipitates are present in the parent phase at a ratio of 20 vol % to 40 vol % of the entire alloy coating; (4) In mass%, 10≦Cr≦30, 15≦Ni≦40, 0.1≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, with the balance being Fe and inevitable impurities; a mother phase consisting of, in mass%, 50≦Fe≦65, 0<Cr≦16, 20≦Ni≦35, 0≦B≦0.5, 0<C≦0.5, 0.5≦Si≦2, and the remainder being unavoidable impurities; boride precipitates consisting of, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, and the balance being unavoidable impurities; an alloy coating, characterized in that the boride precipitates are present in the parent phase at a ratio of 20 vol % to 40 vol % of the entire alloy coating; (5) In mass%, 10≦Cr≦40, 15≦Ni≦50, 0.03≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, with the balance being Fe and inevitable impurities; In mass%, 50≦Fe≦65, 0<Cr≦16, 20≦Ni≦35, 0≦B≦0.5, 0<C≦0.5, 0.5≦Si≦2, and the balance being inevitable impurities, ３ a mother phase not containing B; boride precipitates consisting of, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, and the balance being unavoidable impurities; an alloy coating, characterized in that the boride precipitates are present in the alloy coating at a ratio of 20 vol % to 40 vol % of the entire alloy coating; (6) In mass%, 10≦Cr≦30, 15≦Ni≦40, 0.1≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, with the balance being Fe and inevitable impurities; In mass%, 50≦Fe≦65, 0<Cr≦16, 20≦Ni≦35, 0≦B≦0.5, 0<C≦0.5, 0.5≦Si≦2, and the balance being inevitable impurities, ３ a mother phase not containing B; boride precipitates consisting of, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, and the balance being unavoidable impurities; The alloy coating is characterized in that the boride precipitates are present in the alloy coating at a ratio of 20 vol % to 40 vol % of the entire alloy coating.

11. An incinerator comprising the heat transfer tube according to claim 10.

12. A boiler comprising the heat transfer tube according to claim 10.

13. In mass%, 10≦Cr≦40, 15≦Ni≦50, 0.03≦C≦0.9, 0.3≦Si≦2, 1.5≦B≦3.5, and the balance being Fe and inevitable impurities, In mass%, 50≦Fe≦65, 0<Cr≦16, 20≦Ni≦35, 0≦B≦0.5, a mother phase consisting of 0<C≦0.5, 0.5≦Si≦2, and the remainder being unavoidable impurities; boride precipitates consisting of, in mass%, 30≦Fe≦55, 30≦Cr≦60, 0≦Ni≦4, 6≦B≦10, 0≦C≦0.1, 0≦Si≦0.1, and the balance being unavoidable impurities; the boride precipitates are present in the matrix at a ratio of 20 vol % to 40 vol % of the entire alloy, and a thermal spray coating is formed by thermal spraying powder of the Fe-based alloy; the thermal spray coating is subjected to a remelting treatment by high-frequency induction heating at a temperature between the liquidus temperature and solidus temperature of the parent phase of the Fe-based alloy; A method for producing an alloy film, comprising forming an alloy film.

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