阅读说明：本技术 受热面具有铝增强型熔覆复合涂层的水冷壁及其制备方法 (Water-cooled wall with aluminum-enhanced cladding composite coating on heating surface and preparation method thereof ) 是由 曲作鹏 田欣利 赵文博 于 2021-08-20 设计创作，主要内容包括：本发明涉及一种用于水冷壁受热面的铝增强型熔覆复合涂层,其为镍基自熔合金表面渗铝复合涂层,具体包括镍基自熔合金涂层和铝涂层,并且在镍基自熔合金涂层的表层均匀渗透有Al形成过渡层。本发明还涉及受热面具有上述铝增强型熔覆复合涂层的水冷壁及其制备方法,该水冷壁包括水冷壁基体和包覆于水冷壁受热面的铝增强型熔覆复合涂层。与原熔焊方法制备的涂层相比,铝增强型熔覆复合涂层孔隙度明显降低,且与水冷壁受热面形成冶金结合,防护性能及服役寿命均明显提高；同时,由于复合涂层的厚度减小约50％,而且涂层中大部分材料为成本低廉的铝粉,所以该复合涂层的运行成本比堆焊要下降30％以上。(The invention relates to an aluminum-enhanced cladding composite coating for a heating surface of a water-cooled wall, which is a nickel-based self-fluxing alloy surface aluminizing composite coating and specifically comprises a nickel-based self-fluxing alloy coating and an aluminum coating, wherein an Al forming transition layer is uniformly permeated on the surface layer of the nickel-based self-fluxing alloy coating. The invention also relates to a water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating and a preparation method thereof. Compared with the coating prepared by the original fusion welding method, the porosity of the aluminum-enhanced cladding composite coating is obviously reduced, and the aluminum-enhanced cladding composite coating forms metallurgical bonding with the heating surface of the water wall, so that the protective performance and the service life are obviously improved; meanwhile, the thickness of the composite coating is reduced by about 50%, and most materials in the coating are aluminum powder with low cost, so that the running cost of the composite coating is reduced by more than 30% compared with that of surfacing.)

1. An aluminum-enhanced cladding composite coating for a heating surface of a water-cooled wall is a nickel-based self-fluxing alloy surface aluminizing composite coating.

2. The composite coating of claim 1, wherein the nickel-based self-fluxing alloy surface aluminized composite coating comprises a nickel-based self-fluxing alloy coating and an aluminum coating, and an Al forming transition layer is uniformly infiltrated on the surface layer of the nickel-based self-fluxing alloy coating.

3. A waterwall having a heated surface with an aluminum-enhanced clad composite coating, comprising a waterwall substrate, and the aluminum-enhanced clad composite coating of claim 1 or 2 coated on the waterwall surface.

4. The waterwall of claim 3, wherein the aluminum-enhanced clad composite coating is metallurgically bonded to the waterwall heating surface.

5. A preparation method of a water cooled wall with an aluminum-enhanced cladding composite coating on a heating surface comprises the following steps:

c, carrying out sand blasting treatment on the heated surface of the water-cooled wall to obtain the water-cooled wall with a roughened heated surface;

d, spraying a nickel-based self-fluxing alloy coating material on the heating surface of the tube bank in a flame spraying mode to obtain a water-cooled wall with the heating surface provided with a nickel-based self-fluxing alloy bottom layer;

e, performing high-frequency induction cladding treatment on the water-cooled wall with the heating surface provided with the nickel-based self-melting alloy bottom layer; obtaining a water-cooled wall with a heating surface provided with a nickel-based self-fluxing alloy high-frequency induction cladding layer;

step F, when the water-cooled wall with the high-frequency induction cladding layer of the nickel-based self-fluxing alloy on the heating surface just comes out of the high-frequency induction coil and the surface of the tube bank is still in a red hot state, spraying an aluminum coating on the surface of the high-frequency induction cladding layer by using electric arcs or flames to obtain the water-cooled wall with the aluminum coating and the high-frequency induction cladding layer on the heating surface;

and G, carrying out cladding treatment on the water-cooled wall with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer to obtain the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating.

6. The method of claim 5, wherein the inter-frequency induction cladding process is performed in G using a dual-coil inter-frequency induction heating apparatus, comprising: and automatically shutting down the high-frequency induction coil, starting the medium-frequency induction coil, simultaneously feeding the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer relative to the coil, and carrying out medium-frequency induction cladding treatment on the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer of the heating surface to obtain the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating.

7. The method as claimed in claim 6, wherein the dual-coil different-frequency induction heating device is composed of a group of high-frequency induction coils and medium-frequency induction coils which are arranged in parallel at intervals, and a coil support which is arranged at the bottom of the coils and used for fixing the coils; preferably, the high-frequency induction coil and the intermediate-frequency coil are insulated from each other; further preferably, the distance between the high-frequency induction coil and the intermediate-frequency coil is 500 mm; still further preferably, the high frequency induced current frequency is >50kHz, the medium frequency induced current frequency is 1-10 kHz; in particular, the tube top surface is at a distance of 5 ± 1mm from the induction coil.

8. The method according to claim 5, wherein the high-frequency induction cladding treatment is performed in G using a single-coil high-frequency induction heating apparatus, which comprises: and (3) making the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer perform reverse feeding motion relative to the coil, and performing high-frequency induction cladding treatment on the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer to obtain the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating.

9. The method according to claim 8, wherein the frequency of the current induced at high frequency in the single coil high frequency induction heating apparatus is >50kHz and the distance from the tube top surface to the induction coil is 5 ± 1 mm.

10. The method of any one of claims 5-9, wherein the nickel-based self-fluxing alloy bottom layer has a thickness of 0.5 ± 0.02 mm; and/or the thickness of the aluminum coating is (0.5-0.7) ± 0.02 mm.

Technical Field

The invention belongs to the technical field of alloy materials, and relates to a water-cooled wall with an aluminum-reinforced cladding composite coating on a heating surface and a preparation method thereof.

Background

With the accelerated implementation of the national strategy for developing new energy, the domestic waste incineration power generation industry develops rapidly in recent years. For a long time, the bottleneck problem restricting the technical development of waste incineration power generation is that the high-temperature corrosion of four pipes of a boiler is serious, and the phenomenon of pipe explosion is frequent. The corrosion resistance of the inconel625 alloy is improved by adopting a method for surfacing the inconel625 alloy on a heated surface of a pipe, and the inconel625 alloy has the biggest problems of high dilution rate, low efficiency, high cost and the like because the thickness of the surfacing layer is not less than 2mm for reducing the dilution rate.

In 2018, Jiangsu Kehuan company adopts a composite method of flame spraying nickel-based self-fluxing alloy and high-frequency induction remelting (also called fusion welding) to prepare coatings on heating surfaces such as water-cooled walls, superheaters and the like, and has a good application effect in a high-temperature corrosion environment of boilers for years. Not only the performance and service life of the coating are not lower than those of surfacing, but also the preparation efficiency and cost are better than those of surfacing, so the development potential is very good. The structure of the water wall tube bank is shown in figure 1, the remelting process of the water wall tube bank is shown in figure 2, the external structure of the remelting coil is formed by fixedly connecting a plurality of copper tubes with closed rectangular sections, wherein the four sides connected side by side are all planes. During remelting, the coil is fixed, and the tube row is pulled by a lower transmission chain (not shown in the figure) to move forwards in a feeding way.

So far, most of the waste incineration boilers in China are medium-temperature and medium-pressure boilers, and the application effect of surfacing welding and induction fusion welding is good, but for high-parameter boilers which are gradually increased and have strong development tendency, the long-acting protection capability of the high-parameter boilers faces new challenges due to the further increase of parameters such as temperature and pressure. Therefore, the development of a new technology with better protection performance and longer service life becomes a task to be solved urgently before people.

Disclosure of Invention

One of the purposes of the invention is to provide an aluminum-enhanced cladding composite coating for a heating surface of a water-cooled wall, aiming at the defects in the prior art, wherein the aluminum-enhanced cladding composite coating is a nickel-based self-fluxing alloy surface aluminizing composite coating.

The invention also aims to provide the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface, and the coating enables the protection performance of the tube bank to be more excellent and the service life to be longer.

The invention also aims to provide a preparation method of the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface, and the method for preparing the water-cooled wall has low cost and high efficiency.

Therefore, the invention provides an aluminum-enhanced cladding composite coating for a water-cooled wall heating surface, which is a nickel-based self-fluxing alloy surface aluminizing composite coating.

According to the invention, the aluminized composite coating on the surface of the nickel-based self-fluxing alloy comprises the nickel-based self-fluxing alloy coating and an aluminum coating, and an Al forming transition layer is uniformly permeated on the surface layer of the nickel-based self-fluxing alloy coating.

The invention provides a water-cooled wall with an aluminum-enhanced cladding composite coating on a heating surface, which comprises a water-cooled wall substrate and the aluminum-enhanced cladding composite coating coated on the surface of the water-cooled wall according to the first aspect of the invention.

According to the invention, the aluminum-enhanced cladding composite coating and the heating surface of the water wall are metallurgically bonded.

The third aspect of the invention provides a preparation method of a water-cooled wall with an aluminum-enhanced cladding composite coating on a heating surface, which comprises the following steps:

c, carrying out sand blasting treatment on the heated surface of the water-cooled wall to obtain the water-cooled wall with a roughened heated surface;

d, spraying a nickel-based self-fluxing alloy coating material on the heating surface of the tube bank in a flame spraying mode to obtain a water-cooled wall with the heating surface provided with a nickel-based self-fluxing alloy bottom layer;

e, performing high-frequency induction cladding treatment on the water-cooled wall with the heating surface provided with the nickel-based self-melting alloy bottom layer; obtaining a water-cooled wall with a heating surface provided with a nickel-based self-fluxing alloy high-frequency induction cladding layer;

step F, when the water-cooled wall with the high-frequency induction cladding layer of the nickel-based self-fluxing alloy on the heating surface just comes out of the high-frequency induction coil and the surface of the tube bank is still in a red hot state, spraying an aluminum coating on the surface of the high-frequency induction cladding layer by using electric arcs or flames to obtain the water-cooled wall with the aluminum coating and the high-frequency induction cladding layer on the heating surface;

and G, carrying out cladding treatment on the water-cooled wall with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer to obtain the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating.

According to some embodiments of the present invention, the inter-frequency induction cladding process using the dual-coil inter-frequency induction heating apparatus in G includes: and automatically shutting down the high-frequency induction coil, starting the medium-frequency induction coil, simultaneously feeding the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer relative to the coil, and carrying out medium-frequency induction cladding treatment on the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer of the heating surface to obtain the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating.

In some embodiments of the present invention, the dual-coil different-frequency induction heating device is composed of a group of high-frequency induction coils and a group of medium-frequency induction coils which are arranged in parallel at intervals, and a coil support which is arranged at the bottom of the coil and used for fixing the coil; preferably, the high-frequency induction coil and the intermediate-frequency coil are insulated from each other; further preferably, the distance between the high-frequency induction coil and the intermediate-frequency coil is 500 mm; still further preferably, the high frequency induced current frequency is >50kHz, the medium frequency induced current frequency is 1-10 kHz; in particular, the tube top surface is at a distance of 5 ± 1mm from the induction coil.

According to further embodiments of the present invention, the high-frequency induction cladding process using the single-coil high-frequency induction heating apparatus in G includes: and (3) making the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer perform reverse feeding motion relative to the coil, and performing high-frequency induction cladding treatment on the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer to obtain the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating.

In some embodiments of the invention, the frequency of the current induced at high frequency in the single coil high frequency induction heating apparatus is >50kHz, and the distance from the tube top surface to the induction coil is 5 ± 1 mm.

In the invention, the thickness of the nickel-based self-fluxing alloy bottom layer is 0.5 +/-0.02 mm; and/or the thickness of the aluminum coating is (0.5-0.7) ± 0.02 mm.

The aluminum-enhanced cladding composite coating for the heating surface of the water-cooled wall, provided by the invention, is a nickel-based self-fluxing alloy surface aluminizing composite coating, and comprises a nickel-based self-fluxing alloy coating and an aluminum coating, wherein Al is uniformly permeated on the surface layer of the nickel-based self-fluxing alloy coating to form a transition layer. The invention further provides the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating and a preparation method thereof, wherein the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating comprises a water-cooled wall matrix and the aluminum-enhanced cladding composite coating coated on the surface of the water-cooled wall, the bonding surface of the nickel-based self-fluxing alloy coating and the heating surface of the water-cooled wall is diffusion-type metallurgical bonding, and the bonding surface of the nickel-based self-fluxing alloy coating and the aluminum coating is micro-metallurgical bonding.

The tissue structure of the aluminized layer formed by the high-frequency/medium-frequency induction heating aluminizing process adopted in the process of preparing the water-cooled wall with the aluminum-enhanced cladding composite coating on the heated surface is different from that of other aluminizing processes, because the austenite grains of the surface layer (aluminum coating) are not grown in time by the induction rapid heating, the grains are refined, and the diffusion speed of aluminum atoms is obviously increased, the surface embrittlement zone is not generally generated.

Compared with the coating prepared by the original induction fusion welding method, the porosity of the nickel-based self-fluxing alloy coating is obviously reduced, the metallurgical bonding is formed between the aluminum-enhanced cladding composite coating and the heating surface of the water-cooled wall, and the protective performance and the service life ratio are both obviously improved; meanwhile, the thickness of the composite coating is reduced by about 50%, and most materials in the coating are aluminum powder with low cost, so that the running cost of the composite coating is reduced by more than 30% compared with that of surfacing.

The heat conductivity coefficient of the aluminum coating is very close to that of the substrate although the surface is provided with a ceramic film (Al)₂O₃Cermet membrane) reduces the coefficient of thermal conductivity, but does not substantially affect the heat transfer of the pipe because the thickness of the membrane layer is only a few to tens of microns.

Drawings

The invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a water wall structure.

Fig. 2 is a schematic diagram of a high-frequency induction cladding treatment process performed on a water-cooled wall in the prior art.

FIG. 3 is a schematic diagram of the tube bank remelting-aluminizing reciprocating stroke process.

FIG. 4 is a schematic view of a tube bank remelting-aluminizing single-pass process.

The reference numerals in fig. 1 to 4 have the following meanings; 1 water wall (tube bank); 10 heating surface of water wall (tube row); 12 a substrate; 13 fins; 14 outer tube wall of the base; 15 inner tube wall of matrix; 21 coating the curved surface of the pipe; 22 tube root and fin coating; 30 high-frequency induction remelting coils (rectangular copper pipes); 40 medium frequency induction aluminizing coil (rectangular copper pipe); 50 spraying aluminum (the aluminum spraying operation is performed in the place); 60 coil support; 70 driving chain rollers; 80 high frequency induction remelting coil (rectangular copper tube, common with aluminizing in fig. 3).

Detailed Description

In order that the invention may be readily understood, a more particular description thereof will be rendered by reference to the appended drawings. However, before the invention is described in detail, it is to be understood that this invention is not limited to particular embodiments described. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, the preferred methods and materials are now described.

Term of

The term "waterwall" as used herein is also referred to as a "waterwall," "waterwall tubes," or "waterwall tube banks" (referred to simply as tube banks). The steel pipes are usually vertically laid on the inner wall surface of the boiler wall, and are mainly used for absorbing heat emitted by flame and high-temperature flue gas in the boiler.

The term "aluminized composite coating on the surface of the nickel-based self-fluxing alloy" used in the present invention refers to a composite coating formed by aluminum infiltrated into the nickel-based self-fluxing alloy coating from the surface thereof.

The term "inner surface" as used herein refers to the surface of the tube for a waterwall or the surface of the tube for a nickel-based self-fluxing alloy coating or aluminum coating that faces the axis.

The term "outer surface" as used herein refers to the surface of the tube for a waterwall or the surface of the nickel-based self-fluxing alloy coating or aluminum coating that faces away from the axis.

The terms "tube arc segment" and "tube curved surface" are used interchangeably herein and refer to the arc segment of the tube that forms the waterwall.

The term "tube top surface" as used in the present invention refers to a local surface near the highest point (radial end perpendicular to the horizontal position) of the tubes constituting the water wall.

The terms "remelting" and "cladding" are used interchangeably herein.

The term "metallurgical bond" as used herein refers to a bond formed by interdiffusion of interfacial atoms between two metals.

The term "diffusion type metallurgical bonding" in the invention is a metallurgical bonding formed by mutual alloy diffusion between the sprayed nickel-based self-fluxing alloy bottom layer and the interface of a substrate through high-frequency cladding.

The term "micro metallurgical bonding" in the present invention is a metallurgical bonding formed by high frequency/medium frequency cladding such that aluminum in an aluminum coating layer uniformly penetrates into a surface layer of a high frequency clad nickel-based self-fluxing alloy layer.

The terms "about," "substantially," and "primarily," when used in conjunction with a range of elements, concentrations, temperatures, or other physical or chemical properties or characteristics, as described herein, cover variations that may exist in the upper and/or lower limits of the range for the property or characteristic, including variations due to, for example, rounding, measurement, or other statistical variations. As used herein, numerical values associated with amounts, weights, and the like, are defined as all values for each particular value plus or minus 1%. For example, the term "about 10%" should be understood as "9% to 11%".

II, embodiments

The aluminizing of the metal surface is a traditional surface strengthening method and is an effective way for improving the corrosion resistance of the metal material. Aluminum alloy is usually sprayed on the surface of a metal component in the industry, a steel matrix is protected due to the protection effect of a sacrificial anode formed by the negative potential of aluminum and steel, and the method belongs to a main method with remarkable corrosion prevention effect and low cost. However, aluminum has a low melting point, and is theoretically not suitable for use in a high-temperature environment. However, in practice, aluminum is very easy to produce an alumina film on the surface at high temperature, that is, if the aluminum coating is applied in the high temperature environment of boiler waste incineration, the aluminum is very easy to react with oxygen in the air to form compact Al₂O₃And (5) oxidizing the film. Although the film thickness is only in the order of microns, the ceramic film has an effect of being "ten times" compared with the metal coating for high temperature corrosion prevention. The film has high density and is tightly combined with the coating, and on the other hand, the film has strong regeneration capability and can be quickly regenerated at high temperature even if the film falls off, thereby playing the role of effectively protecting the coating. And the thickness of the ceramic film is only in micron order, and the influence on heat conduction is basically avoided.

However, the inventor researches and discovers that if only one layer of aluminum is sprayed on the surface of the original remelted layer, the coating is loose, and the mechanical combination between the coating and the substrate is easy to fall off. The present inventors have further investigated and found that this problem can be solved by a process of aluminizing which produces a diffusion transition layer between the aluminum coating and the nickel-based self-fluxing alloy coating, thus achieving a micro-metallurgical bond between the two coatings and reducing the porosity.

Specifically, the aluminum-enhanced cladding composite coating for preventing corrosion of the heating surface of the water-cooled wall is a nickel-based self-fluxing alloy surface aluminizing composite coating, the nickel-based self-fluxing alloy surface aluminizing composite coating comprises a nickel-based self-fluxing alloy coating and an aluminum coating coated on the outer surface of the nickel-based self-fluxing alloy coating, and Al is uniformly permeated in the surface layer part, close to the bonding interface with the aluminum coating, of the nickel-based self-fluxing alloy coating, so that a transition layer is formed; preferably, the composite aluminized coating on the surface of the nickel-based self-fluxing alloy consists of a nickel-based self-fluxing alloy coating and an aluminum coating coated on the outer surface of the nickel-based self-fluxing alloy coating, and Al is uniformly permeated on the surface layer of the nickel-based self-fluxing alloy coating to form a transition layer, so that micro-metallurgical bonding between the two coatings is realized, and the bonding strength of the nickel-based self-fluxing alloy coating and the aluminum coating is enhanced; the thickness of the transition layer is about 8-10 μm.

Based on the above, the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface comprises a water-cooled wall matrix and the aluminum-enhanced cladding composite coating coated on the surface of the water-cooled wall, wherein the aluminum-enhanced cladding composite coating is metallurgically bonded with the heating surface of the water-cooled wall; specifically, in the aluminum-enhanced cladding composite coating, the inner surface of the nickel-based self-fluxing alloy coating and the heating surface of the water-cooled wall are in diffusion type metallurgical bonding, so that the coating can be well prevented from falling off; and Al in the aluminum coating uniformly permeates into the surface layer of the nickel-based self-fluxing alloy coating through the bonding interface of the aluminum coating and the nickel-based self-fluxing alloy coating (or the outer surface of the nickel-based self-fluxing alloy coating) to form a transition layer, so that micro-metallurgical bonding is formed between the nickel-based self-fluxing alloy coating and the aluminum coating, and the bonding strength of the nickel-based self-fluxing alloy coating and the aluminum coating is enhanced.

The aluminum-reinforced cladding composite coating is characterized in that:

(1) the thickness of the aluminum coating is about 0.5mm, the aluminum coating is coated on the outer surface of the nickel-based self-fluxing alloy coating and forms a composite coating with the nickel-based self-fluxing alloy coating;

(2) the inner surface of the nickel-based self-fluxing alloy coating and the heating surface of the water wall form diffusion type metallurgical bonding, so that the coating can be well prevented from falling off; al in the aluminum coating uniformly permeates into the surface layer of the nickel-based self-fluxing alloy coating through the bonding interface of the aluminum coating and the nickel-based self-fluxing alloy coating (or the outer surface of the nickel-based self-fluxing alloy coating) to form a transition layer, so that micro-metallurgical bonding is formed between the nickel-based self-fluxing alloy coating and the aluminum coating, and the bonding strength of the nickel-based self-fluxing alloy coating and the aluminum coating is enhanced; the thickness of the transition layer is about 8-10 μm;

(3) because the using environment is a waste incineration boiler, the environment temperature is generally above 400 ℃, when in use, the surface of the aluminum coating on the outermost layer of the aluminum enhanced cladding composite coating is on>Is rapidly oxidized at a high temperature of 400 ℃ to form Al₂O₃The thickness of the metal ceramic membrane is less than 10 mu m and is about several micrometers, so that the metal ceramic membrane has a good protective effect on a water-cooled wall;

(4) even Al on the outer surface of the aluminum coating during use₂O₃The cermet film is abraded or eroded away with the aluminum coating on the outer surface>Can be rapidly oxidized under the high-temperature environment of 400 ℃ to form Al₂O₃The metal ceramic membrane has a good protective effect on the water-cooled wall; in this respect, Al corresponds to the outer surface of the aluminum coating₂O₃The cermet membrane is regenerable during use.

The preparation method of the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface can be understood as a method for preparing the aluminum-enhanced cladding composite coating on the heating surface of the water-cooled wall, and can also be understood as a method for improving the corrosion resistance of the water-cooled wall through the aluminum-enhanced cladding composite coating. In some specific embodiments of the present invention, the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface of the present invention is prepared by the following specific method:

the first step is as follows: carrying out sand blasting treatment on the heated surface (including the curved surface, the root and the fins) of the water-cooled wall to obtain the water-cooled wall with a roughened heated surface;

the second step is that: overlaying nickel-based self-fluxing alloy powder on the heating surface of the water-cooled wall tube bank by adopting a flame spraying system, wherein the thickness of the nickel-based self-fluxing alloy powder is about 0.5mm, and the water-cooled wall with the heating surface provided with a nickel-based self-fluxing alloy bottom layer is obtained;

the third step: the coating is subjected to high-frequency induction remelting, and only the nickel-based self-fluxing alloy is heated to a melting point (1050 ℃) and then recrystallized due to the heating skin effect of the high-frequency induction coil, so that the influence of the temperature on the matrix is small. After remelting, diffusion type metallurgical bonding can be realized between the induction welding layer and the 20G substrate, and the porosity of the spraying layer (the high-frequency induction cladding layer of the nickel-based self-fluxing alloy) is lower than 1.5 percent, so that the water-cooled wall with the high-frequency induction cladding layer of the nickel-based self-fluxing alloy on the heating surface is obtained;

the fourth step: when a water-cooled wall (tube bank) with a high-frequency induction cladding layer of nickel-based self-fluxing alloy on a heating surface is remelted and then just comes out of an induction coil, and the surface of the tube bank is still in a red hot state, an aluminum coating with the thickness of about 0.5mm is sprayed on the surface of the high-frequency induction cladding layer by electric arc or flame; in the spraying area, namely within 500mm of the tube row coming out of the induction coil, the temperature is reduced to about 650-; under the combined action of remelting high temperature and spraying, the stacking effect of the obtained high-energy aluminum powder particles on a softer matrix in a red hot state is utilized to improve the bonding strength between layers; thereby obtaining a water cooled wall with an aluminum coating and a high-frequency induction cladding layer on a heating surface;

the fifth step: and after the aluminum spraying coating (aluminum spraying for short) is finished, cladding treatment is carried out on the water cooled wall with the heating surface provided with the aluminum coating and the nickel-based self-melting alloy high-frequency induction cladding layer, so that the water cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating is obtained.

Preferably, the specific preparation method of the water-cooled wall with the aluminum-reinforced cladding composite coating on the heating surface further comprises a sixth step of detecting the quality of the coating on the surface of the tube bank and repairing local defects.

In some embodiments, the nickel-based self-fluxing alloy underlayer has a thickness of 0.5mm plus or minus 0.02 mm.

In other embodiments, the aluminum coating has a thickness of (0.5-0.7) ± 0.02 mm.

The method of the invention is characterized in that: and in a red hot high-temperature area after remelting is finished, spraying aluminum powder on the soft surface of the fusion welding layer, and improving the bonding strength between the surface layer (aluminum coating) and the bottom layer (nickel-based self-fluxing alloy coating) by utilizing the pinning effect.

The aluminum spraying operation in the present invention is not particularly limited as long as the spraying is smooth and uniform, and for example, an aluminum coating may be sprayed by a method conventional in the art.

In the present invention, the nickel-based self-fluxing alloy coating material includes, but is not limited to, a nickel-based self-fluxing alloy base stock comprising 2 wt% to 3 wt% of B and 2.5 wt% to 3.5 wt% of Si; preferably, the nickel-based self-fluxing alloy coating material is a nickel-based self-fluxing alloy base material containing 2 wt% to 3 wt% of B and 2.5 wt% to 3.5 wt% of Si.

It will be appreciated by those skilled in the art that the nickel-based self-fluxing alloy base material of the present invention contains, in addition to the above-mentioned B and Si, other components, such as Ni: 60-70 wt%, Cr: 17 wt% -18 wt%, Mo: 11-13 wt%, Cu: 1.7 wt% -2 wt%, Fe: 3 to 5 weight percent.

In the present invention, there are two options for the operation of the fifth step:

(1) a single-stroke scheme:

and (3) carrying out different-frequency induction cladding treatment by adopting a double-coil different-frequency induction heating device. As shown in fig. 4, the dual-coil different-frequency induction heating apparatus includes a group of high-frequency induction coils 30 and a group of medium-frequency induction coils 40 which are arranged in parallel at intervals, and a coil support 60 which is arranged at the bottom of the coil and used for fixing the coil.

The pilot frequency induction heating device is mainly obtained by a great deal of research, design and modification based on the high frequency induction equipment (see figure 2) which is used for preparing the water wall with the high frequency cladding coating and is originally owned by the company, so that the pilot frequency induction heating device also comprises a transmission chain (see figure 4) for conveying the tube bank and a transmission chain roller 70 which is driven by the transmission chain and is used for conveying the tube bank besides the high frequency induction coil and the medium frequency induction coil which are arranged in parallel at intervals and a coil bracket which is arranged at the bottom of the coil and is used for fixing the coil, and the transmission chain roller 70 is also shown in figures 2 and 4.

In order to prevent the high frequency induction coil 30 and the intermediate frequency induction coil 40 arranged in parallel at intervals from interfering with each other, the high frequency induction coil 30 and the intermediate frequency induction coil 40 are arranged in an insulated manner. The insulation means in the present invention is not particularly limited, and the insulation arrangement may be implemented by a conventional technique in the art.

In the present invention, the high frequency induction coil 30 and the intermediate frequency coil 40 are closely spaced from each other, and are actually arranged in parallel at a certain distance, and the distance between the high frequency induction coil and the intermediate frequency coil is 500 mm.

In the invention, the current frequency induced by the high frequency is more than 50kHz, and the current frequency induced by the medium frequency is 1-10 Khz.

In particular, the tube top surface is at a distance of 5 ± 1mm from the induction coil.

After the high-frequency induction remelting-aluminum spraying stroke is completed, the high-frequency induction coil is automatically closed, the medium-frequency induction coil is started, meanwhile, the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer continuously performs feed motion relative to the coil and enters the medium-frequency induction coil (a second induction coil, also called an aluminizing coil), and medium-frequency induction cladding treatment is performed on the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer on the heating surface, so that the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface is obtained. In the process, the distance between the two coils is about 500mm, the heating of the coils can slightly melt the aluminum surface layer (namely the aluminum coating) and partially permeate the bottom layer (namely the nickel-based self-fluxing alloy high-frequency induction cladding layer), and the surface layer and the bottom layer are mutually fused, so that the bonding strength between the layers (the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer) is further improved. Meanwhile, the heating temperature of the coil is lower than the melting point of the nickel-based self-fluxing alloy, and the high-frequency induction has the skin effect, so that the bottom layer of the nickel-based self-fluxing alloy is not affected basically.

For example, in some examples, the specific method for performing the different-frequency induction cladding treatment by using the dual-coil different-frequency induction heating device in the third to fifth steps is as follows:

in the step E, starting the high-frequency induction coil 30, and simultaneously enabling the tube bank 1 to also perform forward feeding motion relative to the high-frequency induction coil 30, and performing high-frequency remelting on the nickel-based self-melting alloy bottom layer of the heating surface of the water-cooled wall 1 to obtain the water-cooled wall with the heating surface provided with the nickel-based self-melting alloy high-frequency induction cladding layer;

in the step F, when the water-cooled wall with the high-frequency induction cladding layer of the nickel-based self-fluxing alloy on the heating surface just comes out of the high-frequency induction coil 30 and the surface of the tube bank 1 is still in a red hot state, spraying an aluminum coating 50 (within 500mm of the distance between the high-frequency induction coil and the medium-frequency induction coil) on the surface of the high-frequency induction cladding layer of the nickel-based self-fluxing alloy by using electric arc or flame to obtain the water-cooled wall with the aluminum coating and the high-frequency induction cladding layer of the nickel-based self-fluxing alloy on the surface

And G, automatically shutting down the high-frequency induction coil 30, starting the medium-frequency induction coil 40, simultaneously feeding the tube bank with the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer on the heating surface relative to the medium-frequency induction coil 40, and carrying out medium-frequency induction cladding treatment on the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer on the heating surface to obtain the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface.

(2) A double-stroke scheme:

and carrying out high-frequency induction cladding treatment by adopting a single-coil high-frequency induction heating device. The single-coil high-frequency induction heating apparatus is shown in fig. 3, and includes a high-frequency induction coil [ a coil (rectangular copper tube) shared by high-frequency induction remelting and aluminizing ]80 and a coil holder 60 disposed at the bottom of the coil for fixing the coil.

The high-frequency induction coil 80 in the single-coil high-frequency induction heating apparatus is the same as or different from, preferably the same as, the high-frequency induction coil 30 in the double-coil different-frequency induction heating apparatus.

The single-coil high-frequency induction heating apparatus of the present invention is a high-frequency induction device (see fig. 2) originally owned by the present company for preparing a water wall having a high-frequency cladding coating, and includes a driving chain (see fig. 2) for transporting a tube bank, and a driving chain roller 70 for transporting the tube bank, which is driven by the driving chain, in addition to the above-mentioned high-frequency induction coil, and a coil support provided at the bottom of the coil for fixing the coil, as shown in fig. 2 and 3.

In some embodiments of the invention, the frequency of the current induced at high frequency in the single coil high frequency induction heating apparatus is >50kHz, and the distance from the tube top surface to the induction coil is 5 ± 1 mm.

After the remelting-aluminum spraying process is completed, the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer moves in a reverse feeding mode relative to the coil, the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer is subjected to high-frequency induction cladding treatment, and an aluminizing process is completed through the remelting-aluminizing shared coil 80, so that the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating is obtained. Under the working condition, the parameters of the induction coil are unchanged, and the optimal aluminizing effect is obtained by adjusting the feeding speed of the return stroke of the tube bank. The scheme can save one induction coil and reduce equipment investment.

The scheme is characterized in that: the remelting and aluminizing process uses a coil, and two processes of remelting and aluminizing are completed through two reciprocating strokes. Namely, the new technology is organically embedded into the original technology, so that the protection performance is obviously improved while the equipment investment is reduced.

For example, in some examples, the specific method of performing the high-frequency induction cladding treatment using the single-coil high-frequency induction heating apparatus in the third to fifth steps is as follows:

thirdly, starting the high-frequency induction coil 80, simultaneously, enabling the tube bank 1 to start to feed forwards relative to the coil 80, and carrying out high-frequency induction remelting on the nickel-based self-melting alloy bottom layer of the heating surface of the water-cooled wall to obtain the water-cooled wall with the heating surface provided with the nickel-based self-melting alloy high-frequency induction melting layer;

fourthly, when the water-cooled wall with the high-frequency induction cladding layer of the nickel-based self-fluxing alloy on the heating surface just comes out of the induction coil 80 and the surface of the tube bank 1 is still in a red hot state, spraying an aluminum coating 50 (within a region of 500mm from the induction coil) on the surface of the high-frequency induction cladding layer of the nickel-based self-fluxing alloy by using electric arcs or flames to obtain the water-cooled wall with the aluminum coating and the high-frequency induction cladding layer of the nickel-based self-fluxing alloy on the heating surface;

fifthly, the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer moves in a reverse feeding mode relative to the coil 80, and the tube bank with the heating surface provided with the aluminum coating and the nickel-based self-fluxing alloy high-frequency induction cladding layer is subjected to high-frequency induction cladding treatment, so that the water-cooled wall with the heating surface provided with the aluminum-enhanced cladding composite coating is obtained.

According to the method of the invention, the speed of the feed movement is 1-3.5 mm/sec in the third to fifth steps.

The invention aims to creat a method which has comprehensive performance superior to that of the traditional surfacing welding method and the existing induction fusion welding method so as to meet the high-temperature corrosion protection requirement of a high-parameter boiler. Although the aluminizing technology is a traditional surface strengthening technology and direct aluminizing on the surface of a thermal power boiler pipe has been reported abroad, the aluminizing technology is still pioneered when being used on a heating surface of a waste boiler pipe and a composite coating is prepared on the surface of the coating.

The invention has the following advantages:

(1) compared with the coating with the thickness of about 0.5mm prepared by the original induction fusion welding method, the total thickness of the composite coating exceeds 1mm (the thickness of the self-fluxing alloy remelting coating is 0.5mm, and the thickness of the aluminum coating is 0.5mm), so the protection life is obviously prolonged compared with the original method. Compared with the traditional surfacing (the thickness of the traditional surfacing layer is at least more than 2 mm), the thickness of the composite coating is reduced by about 50% under the condition that the protective performance is not reduced, and most materials in the coating are aluminum powder with low cost, so the running cost of the composite coating is reduced by more than 30% compared with that of surfacing, and the cost is improved by less than 20% compared with that of the original surfacing coating.

(2) The heat conductivity coefficient of the aluminum alloy is very close to that of the matrix, and although the surface of the aluminum alloy is provided with a ceramic film to reduce the heat conductivity coefficient, the thickness of the film is only a few to dozens of micrometers, so that the heat transfer of the pipeline is not affected basically.

(3) The organization structure of the high-frequency induction heating aluminized layer is different from that of other aluminizing processes, and a surface brittleness area cannot be generated generally. This is because the rapid induction heating causes austenite grains of the surface layer to grow short of time, which leads to grain refinement and a significant increase in the diffusion rate of aluminum atoms.

III, detection method

According to the invention, the porosity of the pilot frequency induction cladding coating (the nickel-based self-fluxing alloy high-frequency induction cladding coating and the nickel-based self-fluxing alloy medium-frequency induction cladding coating) on the heating surface of the water wall is monitored according to GB/T l7721-1999 (metal covering layer porosity test).

The bonding strength between the cladding layer metal and the base body surface metal (for example, the bonding strength between the nickel-based self-fluxing alloy high-frequency induction cladding coating and the nickel-based self-fluxing alloy medium-frequency induction cladding coating and the outer surface of the water wall) is measured by adopting a pulling test method: preparing a cladding test plate, and processing the cladding test plate into a T-shaped pulling test piece; grinding, polishing and corroding the surface of the cladding layer combined with the substrate to form a small-size section; putting the T-shaped pulling test piece into a pulling clamp, and mounting the T-shaped pulling test piece and the T-shaped pulling test piece on an mts-50KN metal tensile testing machine (Jinan Mei Te Si test technology Co., Ltd.); and carrying out a pulling test at a certain loading speed after clamping and fixing, gradually increasing the acting force until the T-shaped pulling test piece is broken along the joint surface of the cladding layer and the base metal, wherein the highest strength value obtained by the test is the joint strength of the cladding layer and the surface of the base metal, and the unit is MPa.

The corrosion resistance of the water wall or the coating thereof in the invention is directly detected by utilizing the actual consumption rate in production.

IV, examples

In order that the present invention may be more readily understood, the following detailed description will proceed with reference being made to examples, which are intended to be illustrative only and are not intended to limit the scope of the invention. The starting materials or components used in the present invention can be obtained commercially or by conventional methods unless otherwise specified.

Example 1:

preparing the water-cooled wall with the aluminum-enhanced cladding composite coating according to the operations and conditions in the first step to the fifth step, which are specifically as follows:

(1) and carrying out sand blasting and coarsening treatment on the surface of the water wall tube bank by using an automatic sand blasting machine.

(2) The flame spraying nickel base self-fluxing alloy bottom layer is about 0.5mm thick.

(3) And carrying out high-frequency induction remelting on the sprayed layer, wherein the distance from the top surface of the tube to the induction coil is 5 +/-1 mm.

(4) And a special tool is adopted to strictly control the deformation of the tube bank in the remelting process.

(5) When the water wall tube bank just comes out of the induction coil and the surface of the tube bank is still in a red hot state, an aluminum coating with the thickness of 0.5-0.7mm is sprayed on the surface of the remelted layer by electric arc or flame within the area of 500mm of the tube bank coming out of the induction coil.

(6) Two schemes are adopted:

1) after the remelting-aluminizing stroke is finished, the tube bank is reversely fed, and an aluminizing process is finished through the remelting-aluminizing shared coil 80 (see figure 3), wherein the feeding speed is determined according to an aluminizing effect test within the range of 1-3.5 mm/s.

2) The tube row then enters a second induction coil 40 for aluminizing (see fig. 4), the two coils being spaced apart (between 30 and 40) by about 500 mm. The coil has a lower power than the remelting coil and is heated to about 950 ℃ so that the aluminum coating is slightly melted and partially penetrates into the bottom layer, and the surface layer and the bottom layer are fused with each other.

(7) And detecting the quality of the coating on the surface of the tube bank, and repairing the local defects.

According to GB/T l7721-1999 (metal covering porosity test), the porosity of the water wall with the aluminum enhanced cladding composite coating on the heating surface in the embodiment is monitored, and the detection shows that the internal porosity of the different frequency induction cladding coating is very small (< 1.5%) and can be ignored basically.

The bonding strength of the aluminum-enhanced cladding composite coating and the outer surface of the water wall is over 100MPa by adopting a pulling test method for measurement.

The actual consumption rate in production is directly used for detecting the corrosion resistance of the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface in the embodiment, and compared with the corrosion resistance of a 20G water-cooled wall tube bank with an original coating, the result shows that the water-cooled wall with the aluminum-enhanced cladding composite coating on the heating surface in the embodiment has good corrosion resistance, the service life of the water-cooled wall can reach more than 6 years at least under the conditions of medium temperature and medium pressure (450 ℃, 4MPa), and the service life of the water-cooled wall is improved by at least 5 years compared with the 20G water-cooled wall tube bank with the original coating.

It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather the invention extends to all other methods and applications having the same functionality.