An austenitic steel surface aluminosilicate coating for boilers and a method for its production

Abstract

The application discloses a preparation method of an austenitic steel surface aluminum-silicon coating for a boiler. After sand blasting treatment of a workpiece, metal coating raw material slurry is coated on the surface of the workpiece, and the thickness of the coated slurry layer is 0.1-1.0 mm; then, drying, solidification and sintering are carried out to obtain an aluminum-silicon-rich high-temperature corrosion-resistant coating. In the solid phase component, 50-80% of aluminum powder, 0-10% of silicon powder, 0-20% of aluminum oxide, 0-20% of chromium oxide, 1-5% of ammonium chloride and 1-5% of lanthanum oxide are included according to mass percentage. In the liquid phase component, 10-30% of Al(H2PO4), 5-15% of sodium silicate, 10-20% of an organic binder and 0-30% of a curing agent are included according to mass percentage. The method is suitable for various carbon steels, austenitic steels and high-temperature alloys and the like metal parts, and the prepared metal powder coating has good surface quality, high production efficiency, excellent corrosion resistance and excellent oxidation resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of surface coating, and particularly relates to an austenitic steel surface aluminum-silicon coating for a boiler and a preparation method thereof. BACKGROUND

[0002] The problem of thermal corrosion of the inner surface of a boiler pipeline has been one of the factors restricting thermal power generation, and it is urgent to improve the thermal corrosion performance of the inner surface of the pipeline, especially since the working conditions of thermal power generation are developing towards higher steam temperature and pressure. The methods for improving the corrosion resistance of a workpiece include: the first method is to add specific metal elements to the workpiece during the preparation process of the workpiece, so as to improve the corrosion resistance of the workpiece itself; and the second method is to prepare a corrosion-resistant coating on the surface of the workpiece, so as to isolate oxygen and protect the workpiece.

[0003] The most common anti-corrosion technology at present is alloy surface permeation of corrosion-resistant metal technology, such as permeation of Al, Si and chromium; an Al film is formed on the alloy surface through permeation of Al, and the compactness of aluminum oxide hinders the corrosion of water vapor on the base material; the corrosion resistance of the base material is improved through permeation of Si, and the overall corrosion resistance is improved by combining the two. Due to the surface defect problem of the film coated by metal powder, the corrosion resistance of the coating is limited. Due to the limitation of the coating preparation process, the adhesion of the coating is often poor, resulting in limited service life of the coating.

[0004] Metal surface activation treatment is a method for improving the performance of a metal surface, and is usually used to treat a metal with insufficient surface roughness and containing oxides. Through activation treatment of the metal surface, the physical properties and bonding strength of the metal are improved, and the penetration effect of the subsequent metal coating is improved. In addition to improving the quality of the coating before coating preparation, the corrosion resistance of the coating can also be improved by filling rare earth elements into the coating raw material. Taking lanthanum oxide as an example, the addition of lanthanum oxide can increase the adhesion of the coating, improve the hardness and wear resistance of the coating film, and prolong the service life of the coating. SUMMARY

[0005] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification of the present application in order to avoid obscuring the purpose of this section, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0006] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0007] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a preparation method of an austenitic steel surface aluminum-silicon coating for a boiler.

[0008] To solve the above technical problems, the present application provides the following technical solutions, comprising,

[0009] The mixed metal mixed powder is ball milled, the obtained solid phase component and liquid phase component are mixed uniformly, and are coated on the surface of the workpiece after sand blasting treatment; a slurry layer is formed; and then drying, solidification and sintering are performed to obtain the austenitic steel surface aluminum silicon coating for boilers.

[0010] The solid-liquid ratio of the solid phase component and the liquid phase component is 10:1-5.

[0011] The solid phase component comprises, in mass fraction, 50-80% of aluminum powder, 0-10% of silicon powder, 0-20% of aluminum oxide, 0-20% of chromium oxide, 1-5% of ammonium chloride and 1-5% of lanthanum oxide.

[0012] As a preferred scheme of the preparation method of the austenitic steel surface aluminum silicon coating for boilers, in the ball milling, the ball milling speed is 350-400 r / min, and the ball milling time is 6-24 h.

[0013] As a preferred scheme of the preparation method of the austenitic steel surface aluminum silicon coating for boilers, the liquid phase component comprises, in mass fraction, 10-30% of Al(H2PO4)3, 5-15% of sodium silicate, 10-20% of an organic binder and 0-30% of a curing agent.

[0014] As a preferred scheme of the preparation method of the austenitic steel surface aluminum silicon coating for boilers, the organic binder comprises one or more of polyurethane, nitrocellulose, polyvinyl acetate.

[0015] As a preferred scheme of the preparation method of the austenitic steel surface aluminum silicon coating for boilers, the curing agent comprises one or more of an acid anhydride, resol, amino resin, dicyandiamide and hydrazide.

[0016] As a preferred scheme of the preparation method of the austenitic steel surface aluminum silicon coating for boilers, in the sand blasting, the sand blasting particle diameter is 0.1-1.0 mm, the sand blasting pressure is 0.5-1.0 MPa, and the sand blasting time is 10-30 min.

[0017] As a preferred scheme of the preparation method of the austenitic steel surface aluminum silicon coating for boilers, the thickness of the slurry layer is 0.1-1.0 mm.

[0018] As a preferred scheme of the preparation method of the austenitic steel surface aluminum-silicon coating for boilers, the drying and curing is performed by a sectional gradient curing process, specifically, pre-drying at 75-85 DEG C for 5-30 min, then drying at 140-160 DEG C for 30-60 min, and finally curing at 250-300 DEG C for 30-60 min.

[0019] As a preferred scheme of the preparation method of the austenitic steel surface aluminum-silicon coating for boilers, the sintering is performed at a temperature of 500-650 DEG C for 5-30 min, and the temperature rising rate is 950-1050 DEG C / min.

[0020] The present application aims at overcoming the deficiencies in the prior art, and provides an austenitic steel surface aluminum-silicon coating for boilers.

[0021] The present application has the following advantages:

[0022] (1) The metal powder raw material adopted in the present application is suitable for various metal workpieces whose surfaces need to be strengthened, including carbon steel, austenitic stainless steel and high-temperature alloy workpieces, and has a wide application range and high practicability.

[0023] (2) The coating prepared by the present application adds rare earth elements, effectively improving the coating bonding strength and reducing the porosity.

[0024] (3) The preparation method of the present application does not need to be performed under vacuum conditions, and the preparation process is simple, and the aluminum-silicon layer prepared by the method has high preparation efficiency, small pollution, adjustable thickness, good wear resistance, and especially excellent high-low temperature corrosion resistance and steam oxidation resistance.

[0025] (4) The workpiece treated by the sand blasting process has an increased specific surface area, improves the metal element penetration and the coating adhesion, and further strengthens the surface coating strength and corrosion resistance. The addition of lanthanum oxide increases the coating adhesion, improves the coating film hardness and wear resistance, and prolongs the coating service life. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0027] Figure 1 The process flow chart of the present application.

[0028] Figure 2 The sample coating cross-section diagram prepared by the embodiment 1 of the present application.

[0029] Figure 3 The cross-sectional microstructure of Example 1 without lanthanum oxide. DETAILED DESCRIPTION

[0030] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference made to the embodiments of the present application.

[0031] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details and other implementations can be employed. Therefore, the scope of the present application is defined by the appended claims, not by the following detailed description.

[0032] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. The "in one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent of or selected from other embodiments.

[0033] The raw materials used in the present application are all commercially available unless otherwise specified.

[0034] The steam oxidation resistance of the device is measured by the following method: the device is placed in a 650℃ steam environment for 500h, and the weight gain is measured.

[0035] Example 1

[0036] The present embodiment provides a preparation method of an austenitic steel surface aluminum-silicon coating for a boiler, referring to Figure 1 , specifically:

[0037] 1) Cleaning the surface of the pipe

[0038] The surface of the pipe is cleaned with alcohol / acetone to remove oil stains, dust, etc. The treated workpiece is then sandblasted, with a sandblasting particle diameter of 0.3mm, a sandblasting pressure of 0.1MPa, and a sandblasting time of 20min.

[0039] 2) Pipe surface slurry coating

[0040] The slurry is coated to an appropriate thickness at one time, and cannot be coated in multiple layers; the thickness of the slurry layer is 1.0mm.

[0041] The preparation method of the metal powder coating raw material is as follows: According to the mass percentage of the solid phase component, weigh 60% aluminum powder, 5% silicon powder, 15% alumina, 10% chromium oxide, 5% ammonium chloride, and 5% lanthanum oxide respectively. The mixed metal powder is then ball-milled at 350 r / min for 8 hours to obtain the final solid phase component. According to the mass percentage of the liquid phase component, weigh 15% Al(H2PO4)3, 10% sodium silicate, 12% organic binder (polyvinyl acetate), and 20% curing agent (melamine-formaldehyde resin), and mix them with deionized water as the solvent to obtain the liquid phase component. The solid and liquid phase components are then mixed at a solid-liquid (g:ml) ratio of 10:2 to obtain the final metal powder coating raw material.

[0042] 3) Drying and curing

[0043] The metal pipes were pre-dried at 60℃ for 5 minutes, then dried at 100℃ for 55 minutes, and finally cured at 250℃ for 30 minutes.

[0044] 4) Rapid sintering

[0045] The pipeline was subjected to rapid sintering diffusion chromium infiltration by rapid heating, followed by air cooling to room temperature; the heating rate was set to 1000℃ / min, the holding temperature was 500℃, the holding time was 30min, and the coating thickness was 32μm.

[0046] Figure 2 The figure shows a cross-sectional view of the sample coating obtained in Example 1 of the present invention. As can be seen from the figure, the thickness of the infiltrated layer is 30-40 μm. The infiltrated layer is relatively dense, especially the outermost layer, and it is well bonded to the substrate, indicating that the coating prepared by this method is good.

[0047] Example 2

[0048] The difference between this embodiment and Embodiment 1 is that the binder is changed to nitrocellulose, while the rest of the preparation process is the same as in Embodiment 1, and an aluminum-silicon co-permeation coating is obtained.

[0049] Example 3

[0050] The difference between this embodiment and Embodiment 1 is that the adhesive is changed to polyurethane, while the rest of the preparation process is the same as in Embodiment 1, resulting in an aluminum-silicon co-permeation coating.

[0051] The coatings prepared in the above embodiments were subjected to performance tests, and the results compared with those of Example 1 are shown in Table 1.

[0052] Table 1

[0053] Example 1 Example 2 Example 3 Coating effective coverage area (%) 98 75 80 Porosity (%) 0.01 0.02 0.01 Hardness (HV) 632 436 479 650°C in steam for 500 h Weight gain (mg / cm 2 )]]> 0.0363 0.0719 0.0527

[0054] From the above table, it can be seen that adjusting the binder has a significant effect on the performance of the coating, which is due to the different adhesion effects of different binders in the preparation method of the coating. According to the results in the above table, the best technical effect can be obtained when the binder in the present application is polyvinyl acetate.

[0055] Example 4

[0056] The difference between this example and Example 1 is that the curing agent is adjusted to be m-phenylenediamine, and the rest of the preparation process is the same as that of Example 1, and an aluminum-silicon co-permeation coating is prepared.

[0057] Example 5

[0058] The difference between this example and Example 1 is that the curing agent is adjusted to be ethylenediamine, and the rest of the preparation process is the same as that of Example 1, and an aluminum-silicon co-permeation coating is prepared.

[0059] The performance of the coating prepared in the above examples is tested, and the comparison results with Example 1 are shown in Table 2.

[0060] Table 2

[0061]

[0062]

[0063] From the above table, it can be seen that adjusting the curing agent has a significant effect on the performance of the coating, which is due to the large difference in the effect of different curing agents during the curing process, which directly affects the deepening effect of the effective components during the sintering process. According to the results in the above table, the best technical effect can be obtained when the curing agent in the present application is melamine formaldehyde resin.

[0064] Example 6

[0065] The difference between this example and Example 1 is that the aluminum dihydrogen phosphate in the solvent is adjusted to be sodium dihydrogen phosphate, and the rest of the preparation process is the same as that of Example 1, and an aluminum-silicon co-permeation coating is prepared.

[0066] Example 7

[0067] The difference between this example and Example 1 is that the aluminum dihydrogen phosphate in the solvent is adjusted to be potassium dihydrogen phosphate, and the rest of the preparation process is the same as that of Example 1, and an aluminum-silicon co-permeation coating is prepared.

[0068] The performance of the coating prepared in the above examples is tested, and the comparison results with Example 1 are shown in Table 3.

[0069] Table 3

[0070] Example 1 Example 6 Example 7 Coating aluminium content (%) 25 10 10 650°C in steam for 500 h Weight gain (mg / cm 2 )]]> 0.0363 0.7851 0.7742

[0071] As can be seen from the above table, adjusting the composition of the liquid phase solvent has a significant effect on the performance of the coating. This is because aluminum phosphate brings aluminum source, and P2O5 is released during sintering, forming ceramic bonding, and not generating low-melting substances at high temperature, which also plays a role in high-temperature bonding of the coating. According to the results in the above table, the best technical effect can be obtained when aluminum phosphate is used as the liquid phase solvent in the present application.

[0072] Example 8

[0073] The difference between this example and Example 1 is that the content of lanthanum oxide is adjusted to 2.5%, and the rest of the preparation process is the same as Example 1, and an aluminum-silicon co-permeation coating is prepared.

[0074] Example 9

[0075] The difference between this example and Example 1 is that the content of lanthanum oxide is adjusted to 6%, and the rest of the preparation process is the same as Example 1, and an aluminum-silicon co-permeation coating is prepared.

[0076] Example 10

[0077] The difference between this example and Example 1 is that lanthanum oxide is replaced by cerium oxide, and the rest of the preparation process is the same as Example 1, and an aluminum-silicon co-permeation coating is prepared.

[0078] Example 11

[0079] The difference between this example and Example 1 is that lanthanum oxide is replaced by yttrium oxide, and the rest of the preparation process is the same as Example 1, and an aluminum-silicon co-permeation coating is prepared.

[0080] The performance of the coatings prepared in the above examples was tested, and the comparison results with Example 1 are shown in Table 4.

[0081] Table 4

[0082]

[0083] As can be seen from the above table, the addition of rare earth elements has a significant effect on the performance of the coating. Rare earth elements can change the microstructure and performance of the coating. By affecting the microstructure and texture development of the coating, the performance can be improved. The amount and type of rare earth elements added may have adverse effects on the coating. This may be due to the reaction of rare earth elements with other elements in the coating, forming compounds or phases that are not conducive to the performance of the coating, or the addition of rare earth elements changes the microstructure of the coating, resulting in a decrease in performance. For example, rare earth elements may cause excessive growth or precipitation of certain phases in the coating, affecting the uniformity and density of the coating, and thus affecting the protective performance and wear resistance of the coating. In summary, the best technical effect can be obtained by using 5% lanthanum oxide in the present application.

[0084] Comparative Example 1

[0085] The present comparative example differs from example 1 in that lanthanum oxide is not added, and the rest of the preparation process is the same as example 1, and an aluminizing and silicizing coating is prepared.

[0086] Figure 3 The coating cross-section microstructure of the present comparative example without lanthanum oxide is shown in Figure 2, and the coating cross-section microstructure of example 1 is shown in Figure 1. Figure 2 As can be seen from the comparison, there are more pores in the aluminizing layer, and the bonding effect of the coating is also greatly different from the coating obtained in example 1.

[0087] In summary, the coating prepared by the present application adds rare earth elements, improves the bonding strength of the coating, and effectively reduces the porosity. It is suitable for various types of metal workpieces that need to be strengthened, including carbon steel, austenitic stainless steel, and high-temperature alloy workpieces, and has a wide application range and strong practicality. The preparation method of the present application does not need to be carried out under vacuum conditions, and the preparation process is simple. The sintering and diffusion chromizing is carried out by rapid heating, which helps the coating to form uniform and good adhesion characteristics. At the same time, the aluminizing and silicizing layer with lanthanum oxide has high preparation efficiency, small pollution, adjustable thickness, good wear resistance, excellent high and low temperature corrosion resistance and steam oxidation resistance.

[0088] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and they should be included in the scope of the claims of the present application.

Claims

1. A method for preparing an aluminum-silicon coating on the surface of austenitic steel for boilers, characterized in that: include, The mixed metal powder is ball-milled to obtain a uniformly mixed solid and liquid components, which are then coated onto the surface of the sandblasted workpiece to form a slurry layer. The slurry layer is then dried, cured, and sintered to obtain an aluminum-silicon coating on the surface of austenitic steel for boilers. The solid-liquid ratio of the solid phase component and the liquid phase component is 10:1~5; The solid phase component comprises, by mass fraction, 50-80% aluminum powder, 0-10% silicon powder, 0-20% alumina, 0-20% chromium oxide, 1-5% ammonium chloride, and 1-5% lanthanum oxide. The liquid phase component comprises, by mass fraction, 10-30% Al(H2PO4)3, 5-15% sodium silicate, 10-20% organic binder, and 0-30% curing agent.

2. The method for preparing an aluminum-silicon coating on the surface of austenitic steel for boilers as described in claim 1, characterized in that: The ball milling process involves a rotation speed of 350-400 r / min and a milling time of 6-24 h.

3. The method for preparing an aluminum-silicon coating on the surface of austenitic steel for boilers as described in claim 1, characterized in that: The organic binder includes one or more of polyurethane, nitrocellulose, and polyvinyl acetate.

4. The method for preparing an aluminum-silicon coating on the surface of austenitic steel for boilers as described in claim 1, characterized in that: The curing agent includes one or more of acid anhydride, methyl phenolic resin, amino resin, dicyandiamide, and hydrazide.

5. The method for preparing an aluminum-silicon coating on the surface of austenitic steel for boilers as described in claim 1, characterized in that: The sandblasting process involves sandblasting particles with a diameter of 0.1 to 1.0 mm, sandblasting pressure of 0.5 to 1.0 MPa, and sandblasting time of 10 to 30 minutes.

6. The method for preparing an aluminum-silicon coating on the surface of austenitic steel for boilers as described in claim 1, characterized in that: The thickness of the slurry layer is 0.1 to 1.0 mm.

7. The method for preparing an aluminum-silicon coating on the surface of austenitic steel for boilers as described in claim 1, characterized in that: The drying and curing process adopts a segmented gradient curing process, specifically: pre-drying at 75-85 ℃ for 5-30 min, then drying at 140-160 ℃ for 30-60 min, and finally curing at 250-300 ℃ for 30-60 min.

8. The method for preparing an aluminum-silicon coating on the surface of austenitic steel for boilers as described in claim 1, characterized in that: The sintering temperature is 500~650℃, the time is 5~30min, and the heating rate is 950~1050℃ / min.

9. The aluminosilicate steel surface coating for boilers prepared by any one of the preparation methods described in claims 1 to 8.

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