CN104404430A - Iron-based non-crystalline composite coating for protecting heat exchange pipes in flue gas waste heat recovery system of power station boiler and laser re-melting and moulding technology thereof - Google Patents

Abstract

The invention discloses an iron-based amorphous composite coating for heat exchange tube protection in a power plant boiler flue gas waste heat recovery system and its laser remelting forming process, and the components in the iron-based amorphous composite coating and their mass percentages The wt.% is: Fe: 55.1-66.2, Cr: 24.4-34.3, B: 2.4-3.4, Si: 1.5-2.9, Mo: 1.7-3.9, Nb: 1.6-3.8. The molding process includes: preparing iron-based amorphous powder core wire, using supersonic arc spraying method, first preparing an iron-based thermal spray alloy layer on the surface of a steel heat exchange tube; then using Nd-doped yttrium aluminum garnet laser as a heat source Laser remelting is performed on the thermally sprayed coating at the part where low-temperature acid dew point corrosion is likely to occur locally, forming a dense iron-based amorphous composite coating, which is metallurgically bonded to the substrate without cracks and voids. The invention prevents the transfer of low-temperature acid dew point corrosion, thereby significantly improving the service period of the flue gas waste heat recovery system, and reducing the problem of low-temperature acid dew point corrosion, and has great application potential.

Description

Iron-based amorphous composite coating for heat exchange tube protection in power plant boiler flue gas waste heat recovery system and its laser remelting forming process

technical field

The invention belongs to the field of power plant boiler surface protection, and specifically refers to an iron-based amorphous composite coating for heat exchange tube protection in a power plant boiler flue gas waste heat recovery system and a laser remelting forming process thereof.

Background technique

In order to make full use of the waste heat of the flue gas, reduce the temperature of the exhaust gas, and improve the thermal efficiency of the boiler, most power plant boilers are equipped with air preheaters and economizers and other flue gas waste heat recovery systems. However, as the air preheater and low-temperature economizer at the tail of the boiler, it is usually a low-temperature flue gas area containing water vapor and sulfuric acid vapor. The working conditions are relatively harsh, and low-temperature corrosion and ash plugging are prone to occur. There are two reasons: one is the presence of sulfur trioxide in the flue gas; the other is that the metal wall temperature of the heating surface is lower than the acid dew point temperature in the flue gas. When burning fuel with a high sulfur content, most of the sulfur in the fuel turns into sulfur dioxide after combustion, and a small part of it is further oxidized into sulfur trioxide gas under certain conditions.

Sulfur trioxide gas and water vapor can combine to form sulfuric acid vapor, and its condensation dew point temperature is as high as 120°C. The higher the dew point temperature, the greater the acid content of the flue gas, and the more serious the corrosion and ash blocking. When the temperature of the tube wall of the air preheater is lower than the dew point of the generated sulfuric acid, the sulfuric acid will condense on the tube wall and cause low temperature corrosion. Sulfuric acid is like a layer of glue film, one side sticks to the pipe wall and corrodes, and the other side keeps sticking to soot, forming various sulfates, which gradually thicken, which is low-temperature slagging. The air preheater and low-temperature economizer in the low-temperature area of the boiler, once low-temperature corrosion and ash blocking occur, the flue gas channel will be blocked, the resistance of the induced draft will increase, and the boiler will burn under positive pressure. This not only reduces the output of the boiler, but even causes the boiler to be shut down.

As a result of corrosion, the pipes of the air preheater and the low-temperature economizer will be leaked and damaged, resulting in serious air leakage and deterioration of combustion conditions. In severe cases, the heating surface has to be replaced frequently, which not only increases the maintenance workload and material loss, but also affects the normal operation of the boiler. Cold air entering the flue gas side will also reduce the flue gas temperature, and accelerate the speed of low-temperature corrosion and ash blocking, thus affect the safe operation of the boiler.

Amorphous state is a form of matter that people have long been familiar with, and it usually refers to melts, liquids, and non-metallic substances that do not have a crystalline structure. The amorphous state is a structural state different from the crystalline state. The spatial arrangement of its atoms or molecules does not have long-range order, but due to the interrelationship between atoms, it still maintains it in a small area of several atomic distances. Some short-range order features. Amorphous alloys, also known as metallic glasses (Metallic-Glasses), are alloys whose atoms are arranged in a long-range disorder in three-dimensional space in a solid state, and only have short-range order, and maintain this state in a certain temperature range. It is a material with completely different properties of both metal and glass. Due to the unique structural characteristics of amorphous materials, the mechanical, physical and chemical properties of amorphous alloys have many advantages, such as high strength, hardness, wear resistance, corrosion resistance, and excellent soft magnetic properties.

In recent years, with the discovery of bulk amorphous alloy components and the development of preparation technology, people pay more and more attention to various properties of amorphous alloys. The development of laser cladding can be traced back to the 1960s. At that time, many scholars were committed to cladding wear-resistant materials on low-melting point substrates. These materials include: tungsten and its carbides, aluminum, dan, lai, ni, chin and its carbides and alumina, most of which are plasma or flame sprayed. The method, the cladding material is pre-placed on the base material, followed by laser cladding. In 1976, .DS.Gnanamuthu, an American AVCO company, obtained a patent for an automatic wire-feeding laser cladding device.

Due to technical problems, laser cladding experienced a period of relatively slow development from the mid-1970s to the mid-1980s. By the end of the 1980s, laser cladding technology had developed rapidly. In recent years, some research on the use of laser cladding technology to manufacture large-thickness coatings has also gradually emerged. After more than 40 years of development, laser cladding has become a frontier and hot topic in the field of material surface engineering.

Laser cladding is suitable for parts that are prone to wear, impact, erosion, oxidation and corrosion locally, and parts that require special properties (local photosensitive, heat sensitive, superconducting, strong magnetic performance requirements), and the composition of the material is not affected by the usual metallurgical thermodynamics. Conditional restrictions, so the application is quite extensive. Laser cladding not only cladding high-melting-point materials on the surface of low-melting-point substrates to improve the performance of the surface layer of the material, but also endows it with new properties, shortens the production cycle, and reduces manufacturing costs, especially in the limited strategic metal elements contained in the earth. Today's mass consumption, the technology has aroused great attention from western countries.

Contents of the invention

One of the objectives of the present invention is to provide an iron-based amorphous composite coating for heat exchange tube protection in a power plant boiler flue gas waste heat recovery system. The enhanced protection against dew point corrosion prevents the transfer of low-temperature acid dew point corrosion, thereby significantly improving the service period of the flue gas waste heat recovery system and reducing the problem of low-temperature acid dew point corrosion. The application potential is huge.

The above object of the present invention is achieved through the following technical scheme: the iron-based amorphous composite coating for heat exchange tube protection in the power plant boiler flue gas waste heat recovery system is characterized in that: each group of the iron-based amorphous composite coating Components and their mass percentage wt.% are: Fe: 55.1-66.2, Cr: 24.4-34.3, B: 2.4-3.4, Si: 1.5-2.9, Mo: 1.7-3.9, Nb: 1.6-3.8.

In the present invention, as a preferred example, the components in the iron-based amorphous composite coating and their mass percentage wt.% are: Fe: 63.3-65.0, Cr: 26.3-27.0, B: 2.9-3.4 , Si: 1.7-1.8, Mo: 2.0-3.9, Nb: 1.9.

In the present invention, the iron-based amorphous composite coating uses iron (Fe) as a matrix element, which can be dissolved into alloy elements such as chromium (Cr) and molybdenum (Mo) with corrosion resistance. The basic elements of corrosion resistance and pitting resistance in oxidizing corrosive media, with the increase of chromium content, the erosion resistance of the cladding layer can also be enhanced; the role of molybdenum is to increase the passivation ability of the alloy, so that The passivation stability and pitting corrosion resistance of the cladding layer material are greatly improved, and the local corrosion resistance and chloride intergranular corrosion resistance of the cladding layer material are significantly improved.

The alloy contains a large number of small-size radius atoms such as silicon (Si) and boron (B), which increases the disorder of the complex multi-element iron-based alloy system, which is conducive to improving the formation ability of the microstructure, thereby improving the compactness of the coating. In addition, the addition of the rare earth element niobium (Nb) can refine the grains and strengthen the grains, and can also improve the corrosion resistance of the alloy.

The second object of the present invention is to provide a laser remelting molding process for iron-based amorphous composite coatings for heat exchange tube protection in power plant boiler flue gas waste heat recovery systems. The molding process is simple to operate, has low requirements on construction conditions, and can be formed Iron-based amorphous composite coating. The formed iron-based amorphous composite coating can significantly enhance the local corrosion resistance and chloride intergranular corrosion resistance of boiler heat exchange tubes.

The above object of the present invention is achieved by the following technical solution: laser remelting forming process of iron-based amorphous composite coating for heat exchange tube protection in power plant boiler flue gas waste heat recovery system, characterized in that the process includes the following steps:

(1) Prepare iron-based amorphous powder core wire, each component in the iron-based amorphous powder core wire and the mass percentage wt.% they occupy are: Fe: 55.1-66.2, Cr: 24.4-34.3, B : 2.4-3.4, Si: 1.5-2.9, Mo: 1.7-3.9, Nb: 1.6-3.8, the outer diameter of iron-based amorphous powder core wire is 1.6-2mm;

(2) The surface of the heat exchange tube in the power plant boiler flue gas waste heat recovery system is first sandblasted and derusted until the fresh metal substrate is exposed, and then the iron-based amorphous powder core wire obtained in step (1) is used as the base material , Supersonic arc spraying is carried out on fresh metal substrates, and the spraying thickness is 0.4-0.8mm;

(3) After spraying, for the parts of the heat exchange tube that are prone to acid dew point corrosion, laser remelting is performed with a 400-800W neodymium-doped yttrium aluminum garnet laser as the heat source to form an iron-based amorphous composite coating. The thickness of the iron-based amorphous composite coating is 0.3-0.5mm, and the Vickers hardness is greater than 600HV. The metallurgical bond between the iron-based amorphous composite coating and the metal matrix of the heat exchange tube avoids the acid dew point of the heat exchange tube Corroded parts may have internal voids and cracks to enhance the local corrosion resistance and chloride intergranular corrosion resistance of boiler heat exchange tubes.

In the present invention, as a preferred example, in the step (1), the components in the iron-based amorphous powder core wire and their mass percentage wt.% are: Fe: 63.3-65.0, Cr: 26.3 -27.0, B: 2.9-3.4, Si: 1.7-1.8, Mo: 2.0-3.9, Nb: 1.9.

In the present invention, in the step (1), the iron-based amorphous powder core wire is rolled using the existing powder core wire rolling technology.

In the present invention, the sand material for sandblasting in the sandblasting treatment in the step (2) is white corundum or quartz sand.

In the present invention, the parts where acid dew point corrosion of the heat exchange tube is prone to acid dew point corrosion in the step (3) are the low-temperature inlet section and the elbow section of the heat exchange tube.

In the iron-based amorphous composite coating of the present invention, elements are diffused between the substrate and the coating and are in good metallurgical combination. The laser remelted coating has a completely dense fine-grained structure, and there are few structural defects such as cracks, pores, and inclusions in the coating, so the coating part has strong corrosion resistance and high hardness.

The iron-based amorphous composite coating of the present invention, the flue gas waste heat recovery system performs local low-temperature acid dew point corrosion resistance strengthening protection through laser remelting iron-based amorphous composite coating, prevents the transfer of low-temperature acid dew point corrosion, thereby significantly improving The service period of the flue gas waste heat recovery system can be improved, and the problem of low-temperature acid dew point corrosion can be alleviated. The application potential is huge.

Compared with prior art, the present invention has following remarkable effect:

1. Use the same iron-based amorphous powder core wire base material for arc thermal spraying and laser remelting construction to realize the combined protection of the iron-based amorphous composite thermal spraying layer and laser remelting layer on the economizer system; thermal spraying It is suitable for high-efficiency and rapid construction. The laser remelting layer is suitable for the low-temperature acid dew point corrosion parts such as the low-temperature inlet section of the flue gas waste heat recovery system. Through laser remelting treatment, internal cracks and voids can be eliminated, residual stress can be reduced, and corrosion protection Strengthen severe areas.

2. The laser remelted iron-based amorphous composite coating has the characteristics of low processing cost and excellent wear resistance and corrosion resistance. It is suitable for local strengthening and protection of the flue gas waste heat recovery system of power plants.

3. The laser remelted iron-based amorphous composite coating is a composite structure of amorphous and nanocrystalline, the volume fraction of amorphous phase is 30%-50%, and the Vickers hardness is greater than 600HV; nanocrystalline particles are evenly distributed in the amorphous In the substrate, compared with the pure amorphous thermal spray coating that requires a higher cooling rate, the cost performance of the laser remelted amorphous composite coating is outstanding.

4. The YAG laser remelted iron-based amorphous composite coating of the present invention can greatly increase the service life of the flue gas waste heat recovery system, reduce the maintenance cost of corroded parts of the power plant and the consumption of raw materials, and open up new opportunities for energy saving and consumption reduction in the power generation industry. A new way, the YAG laser here refers to the neodymium-doped yttrium aluminum garnet laser.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is the metallographic photograph of the iron-based amorphous composite coating that the embodiment of the present invention one obtains;

Fig. 2 is the X-ray diffractogram of the iron-based amorphous composite coating that the embodiment of the present invention one obtains, among the figure, abscissa: is diffraction angle 2θ, is the angle that diffraction spectrometer scans, and the unit is degree (°); Coordinates: the intensity of the diffraction peak, unit: atomic unit (a.u.);

Fig. 3 is the scanning electron micrograph of the iron-based amorphous composite coating obtained in Example 1 of the present invention, and the lines in the figure are the scanning lines taken by line scanning;

Fig. 4 is the energy spectrum analysis curve EDS of the iron-based amorphous composite coating that the embodiment of the present invention obtains, and among the figure, the abscissa is the distance from the scanning starting point, and the unit is micron (μm), and the ordinate is the element relative to the standard The content of is a dimensionless unit;

Fig. 5 is the hardness graph of the iron-based amorphous composite coating obtained in Example 1 of the present invention. Among the figures, the abscissa: represents the distance from the substrate and the contact surface of the coating, and the unit is micron (μm); the ordinate: is Microhardness, unit: Vickers hardness (HV).

Detailed ways

Embodiment one

This embodiment discloses an iron-based amorphous composite coating for heat exchange tube protection in a power plant boiler flue gas waste heat recovery system. The components in the iron-based amorphous composite coating and their mass percentage wt.% are: Fe: 63.3, Cr: 26.3, B: 2.9, Si: 1.7, Mo: 3.9, Nb: 1.9.

The laser remelting process of the iron-based amorphous composite coating for heat exchange tube protection in the above-mentioned utility boiler flue gas waste heat recovery system includes the following steps:

(1) The iron-based amorphous powder core wire is prepared by the existing powder core wire rolling technology, and the mass percentage wt.% of each component in the iron-based amorphous powder core wire is: Fe: 63.3, Cr : 26.3, B: 2.9, Si: 1.7, Mo: 3.9, Nb: 1.9, the outer diameter of the iron-based amorphous powder core wire is 1.6mm;

(2) The surface of the heat exchange tube in the flue gas waste heat recovery system of the power station boiler is first sandblasted and derusted until the fresh metal substrate is exposed. The rust on the surface of the heat exchange tubes increases the surface roughness of the heat exchange tubes and promotes the close combination of the coating and the metal base material. Then, the iron-based amorphous powder core wire obtained in step (1) is used as the base material, and the fresh metal base material Supersonic arc spraying is carried out on the material, the spraying distance is 300 mm, the moving speed of the spray gun is 5 cm/s, and the spraying thickness is 0.4 mm;

(3) After spraying, the parts of the heat exchange tube that are prone to acid dew point corrosion are remelted with a Nd-doped yttrium aluminum garnet laser with a power of 400 as the heat source to form a dense iron-based amorphous composite coating. The parts where the heat exchange tube is prone to acid dew point corrosion are the low-temperature inlet section and the elbow section of the heat exchange tube. The thickness of the formed iron-based amorphous composite coating is 0.3mm, and the Vickers hardness is 620HV, greater than 600HV. There is a metallurgical bond between the amorphous composite coating and the metal matrix of the heat exchange tube. The interior of the iron-based amorphous composite coating is a composite structure of amorphous phase and nanophase. The volume fraction of amorphous phase is 30%. The crystal particles are distributed in the amorphous matrix, so as to avoid the occurrence of internal voids and cracks in the parts of the heat exchange tube that are prone to acid dew point corrosion, so as to enhance the local corrosion resistance and chloride intergranular corrosion resistance of the boiler heat exchange tube. performance.

Laser remelting is a very complex dynamic melting process, involving heat conduction, convection, energy transfer and other issues, and is an important method for surface modification of materials. It first sprays the alloy material to be remelted such as powder, wire or rod on the surface of the substrate by thermal spraying. This part is also called the pretreatment process, and then scans the coating surface with a laser beam. The coating surface absorbs The laser energy increases the temperature, and at the same time transfers the surface heat to the interior through heat conduction, melting the coating or part of the substrate. After the laser beam leaves, the molten metal solidifies rapidly, thereby forming a metallurgically bonded alloy zone on the surface of the substrate. The thermal spray coating has improved the surface hardness, corrosion resistance and oxidation resistance of the substrate to a certain extent, but since the thermal spray coating and the substrate are mainly mechanically bonded, and the laser remelting after thermal spraying can form a denser High-performance alloy layer, and when a certain laser energy density is reached, the combination of the coating and the substrate is a metallurgical combination, which greatly improves its bonding strength and meets the needs of actual production.

As a modification of this embodiment, quartz sand may also be used as the sand material for sand blasting in the sand blasting treatment in the above step (2).

The heat exchange tubes in the power plant boiler flue gas waste heat recovery system mentioned in this embodiment refer to the heat exchange tubes of heat exchangers such as economizers and heat exchangers in power plant boiler flue gas waste heat utilization for waste heat recovery and utilization.

The metallographic photograph of the interface region of the laser remelted iron-based amorphous composite coating obtained in this example is shown in Figure 1. The bright area is the iron-based amorphous composite coating after remelting, and the dark area is the carbon steel substrate. , it can be seen that the organizational structure is dense, without large voids and cracks. Figure 2 is the X-ray diffraction pattern of the laser remelted iron-based amorphous composite coating, showing obvious amorphous diffusion peaks and iron-rich nanocrystalline broadening peaks. Figure 3 and Figure 4 are the scanning electron microscope images and EDS energy spectrum analysis of the cross-section of the laser remelted iron-based amorphous composite coating, and there is obvious element diffusion near the interface. Fig. 5 is a hardness curve diagram of the cross-section of the laser remelted iron-based amorphous composite coating, and the average hardness of the coating near the surface area is as high as 600HV or more.

Embodiment two

This embodiment discloses an iron-based amorphous composite coating for heat exchange tube protection in a power plant boiler flue gas waste heat recovery system. The components in the iron-based amorphous composite coating and their mass percentage wt.% are: Fe: 63.9, Cr: 27.0, B: 3.4, Si: 1.8, Mo: 2.0, Nb: 1.9.

The laser remelting process of the iron-based amorphous composite coating for heat exchange tube protection in the above-mentioned utility boiler flue gas waste heat recovery system includes the following steps:

(1) The iron-based amorphous powder core wire is prepared by the existing powder core wire rolling technology, and the mass percentage wt.% of each component in the iron-based amorphous powder core wire is: Fe: 63.9, Cr : 27.0, B: 3.4, Si: 1.8, Mo: 2.0, Nb: 1.9, the outer diameter of the iron-based amorphous powder core wire is 1.8mm;

(2) The surface of the heat exchange tube in the flue gas waste heat recovery system of the power station boiler is first sandblasted and derusted until the fresh metal substrate is exposed. The rust on the surface of the heat exchange tubes increases the surface roughness of the heat exchange tubes and promotes the close combination of the coating and the metal base material. Then, the iron-based amorphous powder core wire obtained in step (1) is used as the base material, and the fresh metal base material Supersonic arc spraying is carried out on the material, the spraying distance is 300mm, the moving speed of the spray gun is 6cm/s, and the spraying thickness is 0.6mm;

(3) After spraying, the parts of the heat exchange tubes that are prone to acid dew point corrosion are remelted with a Nd-doped yttrium aluminum garnet laser with a power of 400-800W as the heat source to form a dense iron-based amorphous composite coating. layer, the parts where the heat exchange tube is prone to acid dew point corrosion are the low-temperature inlet section and the elbow section of the heat exchange tube. The thickness of the formed iron-based amorphous composite coating is 0.3-0.5mm, and the Vickers hardness is 630HV, which is greater than 600HV, there is a metallurgical bond between the iron-based amorphous composite coating and the metal matrix of the heat exchange tube. The interior of the iron-based amorphous composite coating is a composite structure of amorphous phase and nanophase, and the volume fraction of the amorphous phase is 40%, nanocrystalline particles are distributed in the amorphous matrix, so as to avoid the occurrence of internal voids and cracks in the parts of the heat exchange tube that are prone to acid dew point corrosion, so as to enhance the local corrosion resistance and chloride resistance of the boiler heat exchange tube performance of intergranular corrosion.

Embodiment Three

This embodiment discloses an iron-based amorphous composite coating for heat exchange tube protection in a power plant boiler flue gas waste heat recovery system. The components in the iron-based amorphous composite coating and their mass percentage wt.% are: Fe: 65.0, Cr: 26.5, B: 2.9, Si: 1.7, Mo: 2.0, Nb: 1.9.

The laser remelting process of the iron-based amorphous composite coating for heat exchange tube protection in the above-mentioned utility boiler flue gas waste heat recovery system includes the following steps:

(1) The iron-based amorphous powder core wire is prepared by adopting the existing powder core wire rolling technology, and the mass percentage wt.% of each component in the iron-based amorphous powder core wire is: Fe: Fe: 65.0 , Cr: 26.5, B: 2.9, Si: 1.7, Mo: 2.0, Nb: 1.9, the outer diameter of the iron-based amorphous powder core wire is 2mm;

(2) The surface of the heat exchange tube in the flue gas waste heat recovery system of the power station boiler is first sandblasted and derusted until the fresh metal substrate is exposed. The rust on the surface of the heat exchange tubes increases the surface roughness of the heat exchange tubes and promotes the close combination of the coating and the metal base material. Then, the iron-based amorphous powder core wire obtained in step (1) is used as the base material, and the fresh metal base material Supersonic arc spraying is carried out on the material, the spraying distance is 300mm, the moving speed of the spray gun is 8cm/s, and the spraying thickness is 0.8mm;

(3) After spraying, the parts of the heat exchange tubes that are prone to acid dew point corrosion are remelted with a Nd-doped yttrium aluminum garnet laser with a power of 400-800W as the heat source to form a dense iron-based amorphous composite coating. layer, the parts where the heat exchange tube is prone to acid dew point corrosion are the low temperature inlet section and the elbow section of the heat exchange tube, the thickness of the formed iron-based amorphous composite coating is 0.5mm, and the Vickers hardness is 650 HV, greater than 600HV , the metallurgical bond between the iron-based amorphous composite coating and the metal matrix of the heat exchange tube, the interior of the iron-based amorphous composite coating is a composite structure of amorphous phase and nanophase, and the volume fraction of the amorphous phase is 50 %, nanocrystalline particles are distributed in the amorphous matrix, so as to avoid the occurrence of internal voids and cracks in the parts of the heat exchange tube that are prone to acid dew point corrosion, so as to enhance the localized corrosion resistance of the boiler heat exchange tube and the resistance to chloride crystals. corrosion performance.

The above-mentioned embodiments of the present invention do not limit the protection scope of the present invention. Under the ideological premise, other modifications, replacements or changes made to the above structure of the present invention in various forms fall within the protection scope of the present invention.

Claims (7)

1. Iron-based amorphous composite coating for heat exchange tube protection in power plant boiler flue gas waste heat recovery system, characterized in that: each component in the iron-based amorphous composite coating and its mass percentage wt.% For: Fe: 55.1-66.2, Cr: 24.4-34.3, B: 2.4-3.4, Si: 1.5-2.9, Mo: 1.7-3.9, Nb: 1.6-3.8. 2. The iron-based amorphous composite coating for heat exchange tube protection in the power plant boiler flue gas waste heat recovery system according to claim 1, characterized in that: each component in the iron-based amorphous composite coating and its components The mass percentage wt.% is: Fe: 63.3-65.0, Cr: 26.3-27.0, B: 2.9-3.4, Si: 1.7-1.8, Mo: 2.0-3.9, Nb: 1.9. 3. Laser remelting forming process of iron-based amorphous composite coating for heat exchange tube protection in power plant boiler flue gas waste heat recovery system, characterized in that the process includes the following steps: (1) Prepare iron-based amorphous powder core wire, each component in the iron-based amorphous powder core wire and the mass percentage wt.% they occupy are: Fe: 55.1-66.2, Cr: 24.4-34.3, B : 2.4-3.4, Si: 1.5-2.9, Mo: 1.7-3.9, Nb: 1.6-3.8, the outer diameter of iron-based amorphous powder core wire is 1.6-2mm; (2) The surface of the heat exchange tube in the power plant boiler flue gas waste heat recovery system is first sandblasted and derusted until the fresh metal substrate is exposed, and then the iron-based amorphous powder core wire obtained in step (1) is used as the base material , Supersonic arc spraying is carried out on fresh metal substrates, and the spraying thickness is 0.4-0.8mm; (3) After spraying, for the parts of the heat exchange tube that are prone to acid dew point corrosion, laser remelting is performed with a 400-800W neodymium-doped yttrium aluminum garnet laser as the heat source to form an iron-based amorphous composite coating. The thickness of the iron-based amorphous composite coating is 0.3-0.5mm, and the Vickers hardness is greater than 600HV. The metallurgical bond between the iron-based amorphous composite coating and the metal matrix of the heat exchange tube avoids the acid dew point of the heat exchange tube Corroded parts may have internal voids and cracks to enhance the local corrosion resistance and chloride intergranular corrosion resistance of boiler heat exchange tubes. 4. The laser remelting molding process of the iron-based amorphous composite coating for heat exchange tube protection in the power plant boiler flue gas waste heat recovery system according to claim 3, characterized in that: the iron-based amorphous powder core wire Each component and its mass percentage wt.% are: Fe: 63.3-65.0, Cr: 26.3-27.0, B: 2.9-3.4, Si: 1.7-1.8, Mo: 2.0-3.9, Nb: 1.9. 5. The laser remelting molding process of the iron-based amorphous composite coating for heat exchange tube protection in the power plant boiler flue gas waste heat recovery system according to claim 3 or 4, characterized in that: the step (1) uses The existing powder core wire rolling technology rolls iron-based amorphous powder core wire. 6. The laser remelting molding process of the iron-based amorphous composite coating for heat exchange tube protection in the power plant boiler flue gas waste heat recovery system according to claim 3 or 4, characterized in that: in the step (2), spray The sand material for sand blasting in sand treatment is white corundum or quartz sand. 7. The laser remelting molding process of the iron-based amorphous composite coating for heat exchange tube protection in the power plant boiler flue gas waste heat recovery system according to claim 3 or 4, characterized in that: in the step (3), the The parts where the heat pipe is prone to acid dew point corrosion are the low temperature inlet section and the elbow section of the heat exchange tube.