Method for improving high-temperature water vapor corrosion resistance of FeCrAl alloy through pre-oxidation

Abstract

The invention discloses a method for improving high-temperature water vapor corrosion resistance of FeCrAl alloy by using pre-oxidation, which comprises the following steps: (1) pretreating the surface of the alloy to make the surface of the alloy smooth and clean; (2) under the mixed atmosphere of oxidizing gas and water vapor, the alloy is heated to be subjected to pre-oxidation treatment, a pre-oxidation layer is obtained, the oxidizing gas comprises oxygen and argon, and the pre-oxidation layer is metastable theta-Al2O3; compared with an alloy material which is not subjected to pre-oxidation treatment, a uniform and compact theta-Al2O3 protective layer is more easily generated after pre-oxidation treatment is carried out in a high-temperature water-oxygen environment, when the pre-oxidized FeCrAl alloy is placed in a subsequent high-temperature water vapor environment, theta-Al2O3 in a metastable state can be gradually converted into alpha-Al2O3 with more stable thermodynamics, and therefore the stability of the FeCrAl alloy is improved. The in-situ phase transformation process is relatively mild, densification of an oxidation film is promoted along with volume shrinkage, and the integrity of the oxidation film is favorably maintained, so that the corrosion weight increment of the alloy is remarkably reduced, and the high-temperature water vapor corrosion resistance is remarkably enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy corrosion protection, in particular to a method for improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by utilizing pre-oxidation. Background Art

[0002] Due to its excellent high-temperature oxidation resistance and mechanical properties, FeCrAl alloys are widely used in fields such as nuclear energy and aerospace. In particular, during nuclear power plant accidents, FeCrAl alloys, as nuclear fuel cladding materials, must maintain structural integrity in high-temperature water vapor environments to prevent the leakage of radioactive materials. Research has shown that high-temperature water vapor environments above 1200°C accelerate the oxidation process of FeCrAl alloys, causing rapid degradation of the alloy. In this environment, the formation and stability of the Al2O3 protective film on the alloy surface plays a decisive role in the material's service performance.

[0003] At present, research on FeCrAl alloys at home and abroad is mainly focused on two directions: composition optimization and surface modification. Composition optimization means that the oxidation resistance of the alloy can be improved by adjusting the content of Cr (20-25wt%) and Al (4-6wt%), but too high a content of alloying elements will significantly reduce the processing performance and mechanical properties of the material. In particular, when the Al content exceeds 6wt%, the plasticity of the alloy drops sharply and the difficulty of manufacturing processing increases significantly. Surface modification technology refers to the treatment of the surface of the alloy material by physical, chemical or mechanical methods to change its surface chemical composition, organizational structure, morphology and other characteristics, thereby improving the specific properties of the material (such as corrosion resistance, wear resistance, oxidation resistance, biocompatibility, etc.) or giving it new functions. Surface modification technologies include chemical vapor deposition, thermal spraying, laser surface treatment, pre-oxidation treatment, etc. Pre-oxidation treatment is to form a stable oxide film on the surface of the material under specific temperature and atmosphere conditions. This oxide film can effectively improve the oxidation resistance and corrosion resistance of the alloy material. Therefore, pre-oxidation treatment can improve its oxidation resistance by pre-forming a dense oxide film on the alloy surface without changing the matrix composition, which can adapt to different engineering application requirements.

[0004] While pre-oxidation treatment of alloy materials can improve their oxidation and corrosion resistance to a certain extent, various factors, such as temperature control, atmosphere conditions, time control, and oxide film composition and structure, must be considered when dealing with alloy materials of varying composition and proportion. Current research focuses on pre-oxidation treatment of FeCrAl alloys to improve their resistance to high-temperature water vapor corrosion. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation, so as to solve the problem that there are too many factors affecting the pre-oxidation treatment of FeCrAl alloy and the high-temperature water vapor corrosion resistance of FeCrAl alloy material is still low.

[0006] To achieve the above object, the first aspect of the present invention provides a method for improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation, comprising the following steps:

[0007] (1) Pre-treat the alloy surface to make it smooth and clean;

[0008] (2) The alloy is heated in a mixed atmosphere of an oxidizing gas and water vapor for pre-oxidation treatment to obtain a pre-oxidation layer, wherein the oxidizing gas includes oxygen and argon, and the pre-oxidation layer is a metastable θ-Al2O3.

[0009] Preferably, in step (1), the alloy surface is smoothed by removing pits on the alloy surface so that the surface roughness of the alloy is less than 0.8; the alloy surface is cleaned by washing with anhydrous acetone or alcohol until the alloy surface is dust-free and oil-free, and then blowing it clean with an air gun or drying it.

[0010] Preferably, in step (2), the volume percentage of oxygen in the oxidizing gas is 3-8%, and the volume percentage of water vapor in the mixed atmosphere is 50-70%.

[0011] More preferably, in step (2), the volume percentage of oxygen in the oxidizing gas is 5%.

[0012] Preferably, in step (2), the flow rate ratio of the oxidizing gas to the water vapor is 0.43-1.

[0013] Preferably, in step (2), the heating temperature is 800-850° C., the pre-oxidation treatment time is 30-60 h, and the thickness of the pre-oxidation layer is 150-200 μm.

[0014] The mechanism by which the pre-oxidation treatment in the present invention can improve the high-temperature water vapor corrosion resistance of FeCrAl alloy is as follows:

[0015] Since FeCrAl alloy is easily corroded by corrosive media in a high-temperature water vapor environment at 1000-1200°C, the present invention pre-oxidizes the alloy in a high-temperature water vapor environment to form a pre-oxidation layer, which serves as a protective oxide layer. The protective oxide layer is mainly θ-Al2O3, so the pre-oxidation layer should be conducive to the formation of a continuous and dense α-Al2O3 protective layer on the alloy in the subsequent high-temperature water vapor environment. According to the alloy oxidation characteristics, the FeCrAl alloy of the present invention is pre-oxidized for 30-60 hours in a mixed atmosphere of 5% O2+Ar and water vapor at 800-850°C, and metastable oxides such as θ-Al2O3 and γ-Al2O3 are mainly formed on the alloy surface. Such relatively mild oxidation conditions are conducive to the formation of a uniform and continuous oxide film, and the oxide film has good metallurgical bonding with the substrate. Moreover, the pre-oxidation layer acts as a diffusion barrier, which can effectively reduce the diffusion rate of water vapor molecules and slow down the diffusion of Al elements in the substrate to the surface, thereby inhibiting further oxidation. If the heating temperature of the pre-oxidation treatment is increased to 900-1100°C, on the one hand, the above temperature is relatively high, closer to the accident condition, and has low safety, and cannot be applied to the early pretreatment process of the material. On the other hand, too high a pre-oxidation temperature may cause the alloy grains to grow rapidly, resulting in a significant decrease in the mechanical properties of the alloy, which will affect the actual service performance.

[0016] In the present invention, the water-oxygen ratio of the mixed atmosphere is controlled by adjusting the flow rate ratio of the oxidizing gas and water vapor during the pre-oxidation process. If the water-oxygen ratio is relatively low, the formation of the surface θ-Al2O3 layer will become difficult, and the protective effect of the surface oxide film formed during the pre-oxidation process will also be weak. This is because the presence of an appropriate amount of water vapor will reduce the formation energy barrier of the surface aluminum oxide, which is more conducive to the formation of a dense oxide film from a thermodynamic point of view.

[0017] The present invention also makes specific restrictions on the thickness of the pre-oxidation layer. When the thickness of the surface pre-oxidation film generated during the pre-oxidation process is less than 150nm, due to the influence of surface undulations and the diffusion rate of oxygen elements, its protective effect will be significantly weakened from a kinetic point of view. Therefore, it is necessary to strictly control the water-oxygen ratio of the pre-oxidation atmosphere and the pre-oxidation time, so that the surface oxide film formed by pre-oxidation can significantly improve the high-temperature oxidation resistance of the alloy. The present invention also makes specific restrictions on the pre-oxidation time. When the pre-oxidation time is excessively extended, since the pre-oxidation temperature is usually relatively mild, the pre-oxidation film formed on the surface of the alloy is sufficient to resist further oxidation. Usually, the oxide film thickness will stabilize at a specific value. Therefore, when the oxide film thickness is basically stable over time, it is not meaningful to continue to extend the pre-oxidation time.

[0018] When a pre-oxidized FeCrAl alloy is placed in a high-temperature steam environment, the metastable aluminum oxide gradually transforms into the more thermodynamically stable α-Al2O3. This in-situ phase transformation is relatively gentle, accompanied by volume shrinkage that promotes densification of the oxide film, which helps maintain its integrity. Furthermore, the composite protective layer formed by the small amount of Cr oxide and Al oxide in the oxide film, combined with the repair effect of the Al reserve in the matrix, can provide continuous protection for the alloy in high-temperature steam environments. In contrast, for alloys without pre-oxidation, the rapid penetration of the corrosive medium into the matrix hinders the formation of a continuous α-Al2O3 layer, resulting in a thicker corrosion layer and a detrimental effect on the alloy's hot corrosion resistance.

[0019] Preferably, in step (1), the alloy is a FeCrAl-based alloy, which comprises the following components in percentage by mass: Cr 10.0-12.0%, Al 4.3-5.5%, Mo 1.8-2.6%, Nb 1.0-1.5%, Si 0.1-0.3%, Ta 0.1-0.2%, Zr 0.1-0.3%, Y 0.05-0.1%, C≤0.008%, N≤0.005%, O≤0.003%, and the balance is iron and unavoidable impurities.

[0020] Preferably, in step (1), the total mass percentage of Cr, Al and Si elements is ≥14.5%, and the total mass percentage of Zr and Y elements is ≥0.25%.

[0021] The present invention has strict limits on the content of each metal element in the FeCrAl-based alloy. The total mass percentage of Cr, Al, and Si elements is ≥14.5% to maintain the good room temperature mechanical strength of the FeCrAl alloy. At the same time, to prevent the FeCrAl alloy from hardening and exacerbating its radiation embrittlement tendency, which may cause brittle fracture of the alloy during reactor operation and processing, the Cr and Al contents should be strictly controlled and reduced while ensuring that the FeCrAl alloy has good resistance to high-temperature steam oxidation. The mass percentage of Cr in the present invention is ≤12.0%. In addition, the total mass percentage of Zr and Y elements is ≥0.25% to synergistically improve the alloy's resistance to high-temperature oxidation.

[0022] Preferably, in step (1), the preparation method of the FeCrAl-based alloy is:

[0023] The various alloying elements are weighed according to mass percentage to form a steel billet, and the steel billet is subjected to multiple hot rolling to obtain a hot-rolled plate. The hot-rolled plate is then subjected to high-temperature solid solution treatment, low-temperature rolling and two annealing treatments in sequence, and then taken out and cooled to room temperature to prepare a FeCrAl-based alloy.

[0024] More preferably, in step (1), the preparation method of the FeCrAl-based alloy is:

[0025] The various alloy elements are weighed according to mass percentage to form a steel billet, and the steel billet is hot forged and then hot rolled, wherein the initial forging temperature is not less than 1000° C. and the final forging temperature is not less than 900° C. After forging, the steel billet is hot rolled at a temperature of 800° C. and a rolling ratio of 40%, followed by high-temperature homogenization annealing and warm rolling. The hot-rolled steel plate is heated to 1150-1250° C., solution-treated for 1.5-3.0 hours, and rolled to a set thickness at 420° C. with a rolling ratio of 65%. After rolling, it is air-cooled, and then straightened by cold rolling and subjected to two annealing passes, wherein the first high-temperature annealing temperature is 1130-1170° C., the annealing time is 15-20 seconds, and then water-cooled; and then a second low-temperature annealing is performed at a temperature of 600-650° C. and the annealing time is 30-60 minutes. The alloy is then taken out and air-cooled to room temperature, which prevents the growth of Laves second-phase particles during processing and heat treatment, and obtains fine second-phase particles densely precipitated on the subgrain boundaries, ensuring the room-temperature and high-temperature strengthening effects of the alloy. At the same time, a large number of subgrain boundaries help the diffusion of elements in the early stage of corrosion oxide film formation, making it easier to form a uniform and dense protective oxide layer on the alloy surface, which helps to improve its corrosion resistance.

[0026] The second aspect of the present invention provides the use of the FeCrAl alloy prepared by the above method in the preparation of nuclear reactor fuel cladding materials, aircraft engine structural materials, and power plant steam pipe structural materials.

[0027] The present invention pre-oxidizes the surface of an alloy material in a high-temperature steam environment. The key to this pre-oxidation treatment is the formation of a continuous, dense θ-Al2O3 protective film. The pre-oxidation temperature, duration, and atmosphere significantly influence the phase composition, density, and bonding strength of the oxide film. For example, pre-oxidation within the 1000-1100°C temperature range promotes the formation of α-Al2O3, but because this temperature range is closer to accident operating conditions, it is not suitable for early material pretreatment. Low-temperature pre-oxidation, on the other hand, tends to form metastable θ-Al2O3. Furthermore, factors such as water vapor partial pressure and heating rate can also affect the growth kinetics and structural stability of the oxide film. This study of the effects of pre-oxidation on the high-temperature steam oxidation resistance of FeCrAl alloys is of great significance. It not only provides a basis for material selection in the event of severe nuclear power plant accidents, but also provides technical support for applications in other high-temperature service environments. This invention provides a deeper understanding of the formation mechanism, growth kinetics, and structural evolution of the oxide film during the pre-oxidation process, and plays an important role in guiding the development of new surface treatment processes for high-temperature steam oxidation resistance. At the same time, this research also has important practical application value in improving nuclear safety performance and extending the service life of materials. The pre-oxidation treatment method of the present invention has a wide range of applications.

[0028] Therefore, the present invention adopts the above-mentioned method of improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation, which has the following beneficial effects:

[0029] Compared with the unpreoxidized alloy, the preoxidation process conditions in the present invention are relatively mild, with a moderate oxygen partial pressure, which is conducive to the formation of a uniform and continuous protective oxide layer, the main component of which is metastable θ-Al2O3. The specific oxidation time makes the oxide layer have a moderate thickness, which not only ensures continuity but also prevents it from peeling off due to excessive thickness. This mild preoxidation condition is conducive to the formation of a good metallurgical bond between the oxide film and the substrate, reduces the growth stress between the oxide layers, and reduces the risk of interface cracking and peeling. At the same time, when the preoxidation temperature is too high (>1000℃), the subgrain structure formed by rolling and multiple heat treatments during the sample preparation process will grow rapidly, resulting in a significant decrease in the mechanical properties of the sample. Therefore, the temperature range control during the preoxidation process is also extremely critical.

[0030] In the subsequent high-temperature water vapor environment, the metastable alumina gradually transforms into α-Al2O3. This in-situ phase transformation process is relatively gentle and accompanied by volume shrinkage, which is conducive to promoting the densification and integrity of the oxide film. From the perspective of oxidation kinetics, the thickness of the corrosion layer of the alloy after pre-oxidation treatment is significantly reduced, and its corrosion layer thickness is approximately 40% of that of the unpre-oxidized alloy. The alloy's corrosion weight gain rate is also significantly reduced, with a reduction of more than 70%, and its hot corrosion resistance is significantly enhanced.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The oxidation kinetics curves of the alloy materials of Example 1 and Example 3 in a high-temperature water vapor environment at 1000°C and 1200°C;

[0033] Figure 2 This is a cross-sectional view of the pre-oxidation layer obtained by the pre-oxidation treatment in Example 1;

[0034] Figure 3 This is a cross-sectional elemental surface scan distribution diagram of the alloy without pre-oxidation treatment in Example 3 after being subjected to high-temperature water vapor corrosion;

[0035] Figure 4 This is a cross-sectional element line scan image of the alloy without pre-oxidation treatment in Example 3 after being corroded by high-temperature water vapor;

[0036] Figure 5 This is a cross-sectional morphology diagram of the alloy material after pre-oxidation treatment in Example 3 and after high-temperature water vapor corrosion. DETAILED DESCRIPTION

[0037] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the present invention is not limited to this embodiment.

[0038] Example 1

[0039] A method for improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation comprises the following steps:

[0040] (1) The chemical composition of the FeCrAl-based alloy in this embodiment is shown in Table 1.

[0041] Table 1 Chemical composition of alloys (by mass percentage)

[0042]

[0043] (2) The components were weighed according to the mass percentage of each metal element in Table 1, and steel billets were made. The steel billets were hot forged and then hot rolled, wherein the initial forging temperature was 1000℃, the final forging temperature was 900℃, the hot rolling temperature was 800℃, and the rolling ratio was 40%. Subsequently, high-temperature homogenization annealing and low-temperature rolling were performed. The hot-rolled plate was heated to 1200℃, solution-treated for 2.0h, and rolled at 420℃ with a rolling ratio of 65%. Finally, a rolled plate with a thickness of 3mm was formed. After rolling, it was air-cooled and then straightened by cold rolling. Two annealings were performed. The first high-temperature annealing temperature was 1150℃, the annealing time was 18s, and then water-cooled. After that, the second low-temperature annealing was performed. The low-temperature annealing temperature was 625℃, the annealing time was 40min, and then it was taken out and air-cooled to room temperature to obtain a FeCrAl-based alloy.

[0044] (3) The FeCrAl-based alloy in step (2) is pretreated, specifically, the FeCrAl-based alloy is processed into a 15mm*10mm*3mm hot corrosion test specimen using a wire cutting machine and a grinder. At this time, the pits on the alloy surface have been removed, and the surface roughness is less than 0.8. Then, the hot corrosion test specimen is polished with 320#, 2000# and 7000# sandpaper, and ultrasonically cleaned with alcohol or anhydrous acetone for 5 minutes to remove dust and oil on the alloy surface. After drying, the pretreated alloy is obtained;

[0045] (4) heating the alloy for pre-oxidation treatment in a mixed atmosphere of oxidizing gas and water vapor at a temperature of 800° C. for 60 h to obtain a pre-oxidation layer, which is a metastable θ-Al2O3;

[0046] The oxidizing gas includes oxygen and argon, the volume percentage of oxygen in the oxidizing gas is 5%, the volume percentage of water vapor in the mixed atmosphere is 70%, and the flow rate ratio of the oxidizing gas to the water vapor is 0.43.

[0047] (5) High-temperature water vapor oxidation experiments were carried out on the alloy materials after pre-oxidation treatment and the FeCrAl-based alloys without pre-oxidation treatment.

[0048] Example 2

[0049] The difference between this embodiment and embodiment 1 is that the heating temperature is 850°C, the pre-oxidation treatment time is 30 hours, the volume percentage of water vapor in the mixed atmosphere is 60%, the flow rate ratio of the oxidizing gas and water vapor is 0.67, and the other steps are the same as those in embodiment 1.

[0050] Example 3

[0051] The difference between this embodiment and embodiment 1 is that the volume percentage of water vapor in the mixed atmosphere is 50%, the flow rate ratio of the oxidizing gas and water vapor is 1, and the other steps are the same as those in embodiment 1.

[0052] Example 4

[0053] The difference between this embodiment and embodiment 1 is that the heating temperature is 850°C, the pre-oxidation treatment time is 30 hours, the volume percentage of water vapor in the mixed atmosphere is 60%, the flow rate ratio of the oxidizing gas and water vapor is 0.67, and the other steps are the same as those in embodiment 1.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that the heating temperature is 600° C., and the other steps are the same as those in Example 1.

[0056] Comparative Example 2

[0057] The difference between this comparative example and Example 1 is that the pre-oxidation treatment time is 200 h.

[0058] Comparative Example 3

[0059] The difference between this comparative example and Example 1 is that the volume percentage of water vapor in the mixed atmosphere is 10%, and the flow rate ratio of the oxidizing gas and water vapor is 9.

[0060] Comparative Example 4

[0061] The difference between this comparative example and Example 1 is that the pre-oxidized FeCrAl-based alloy is replaced with a commercial Zr-4 alloy, wherein the composition ratio of the commercial Zr-4 alloy is Fe 0.21%, Cr 0.12%, Al 0.0033%, Si 0.009%, C ≤ 0.008%, N ≤ 0.018%, O 0.13%, and the rest is Zr element and other impurities that meet the standards of commercial Zr-4 alloy.

[0062] Comparative Example 5

[0063] The difference between this comparative example and Example 1 is that the content of Cr in the FeCrAl-based alloy is changed, and no pre-oxidation treatment process is performed. Specifically, the low-Cr and high-strength and toughness alloy prepared in Example 4 of Chinese patent CN117187705B is used. The composition ratio of the above alloy is Cr 12.8%, Al 4.3%, Mo2.0%, Nb 1.0%, Si 0.15%, V 0.15%, Hf0.15%, Ga 0.1%, Ni 0.15%, La 0.05%, C≤0.008%, N≤0.005%, O≤0.003%, and the balance is iron. The impurity content meets the current standards for commercial industrial pure iron and ferritic stainless steel. The two-pass annealing process is 1100°C-30s-550°C-120min.

[0064] Test example

[0065] High-temperature steam oxidation experiments were conducted on the FeCrAl alloys prepared in Examples 1 to 4 and the alloys in Comparative Examples 1 to 5 using a TGA device. The specific test process is as follows:

[0066] The FeCrAl-based alloy that had not been pre-oxidized and the alloy materials obtained in Example 1, Example 2, Comparative Example 4 and Comparative Example 5 were subjected to high-temperature water vapor corrosion tests at 1000°C on a TGA device. The alloy materials obtained in Example 3, Example 4, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were subjected to high-temperature water vapor corrosion tests at 1200°C on a TGA device. The parameters of the high-temperature water vapor corrosion tests were: liquid water supply flow rate of 100 μL / min, corrosion time of 2 h, and argon carrier gas flow rate of 50 mL / min.

[0067] The heat corrosion resistance of Examples 1 to 4 and Comparative Examples 1 to 5 was determined by sampling and weighing at intervals and performing an in-situ high-temperature water vapor corrosion test. The test results are shown in Tables 2 and Figures 1 to 5 .

[0068] Table 2 Comparison of high temperature water vapor corrosion parabolic constants of Examples 1 to 4 and Comparative Examples 1 to 4

[0069]

[0070] Figure 1The following are the oxidation kinetic curves of the materials of Examples 1 and 3 in high-temperature water vapor environments at 1000°C and 1200°C. As can be seen from the figure, whether the high-temperature steam oxidation experiment is carried out at 1000°C or 1200°C, the high-temperature water vapor corrosion parabolic constant of the pre-oxidized FeCrAl alloy is significantly lower than that of the non-pre-oxidized group. This phenomenon is more significant at a higher water-oxygen corrosion temperature (1200°C), with a reduction of up to 70%. This may be due to the easier phase transformation from the metastable θ-Al2O3 phase to the α-Al2O3 phase at high temperatures, resulting in a stronger protective effect.

[0071] Figure 2 The cross-sectional view of the pre-oxidized layer obtained by pre-oxidation under the conditions of 800℃-60h and 5% O2+Ar and water vapor mixed atmosphere flow rate ratio of 0.43 in Example 1 of the present invention can be seen from the figure. Its main structure is metastable θ-Al2O3 with a thickness of about 150-200nm. Figure 3 A comparative analysis of the morphology of the α-Al2O3 phase in the θ-Al2O3 phase shows that the grain size of the θ-Al2O3 phase is smaller and presents a distinct columnar morphology, which also provides a basis for the densification of the protective oxide film caused by the subsequent phase transformation.

[0072] Figure 3 This is the cross-sectional element surface scanning distribution diagram of Example 3 after being subjected to high-temperature water vapor corrosion at 1200°C for 2h without pre-oxidation. Figure 4 This is a cross-sectional element line scan image of Example 3 after high-temperature water vapor corrosion at 1200°C for 2h without pre-oxidation. It can be seen from the figure that the outer layer is an α-Al2O3 phase in an equiaxed crystal state. It can be seen that the outer oxide film is uniform and dense, which plays a protective role on the FeCrAl matrix.

[0073] Figure 5 This is a cross-sectional morphology of Example 3 after pre-oxidation at 800°C for 60h, a flow rate ratio of 5% O2+Ar to water vapor mixed atmosphere of 1, and then undergoing high-temperature water vapor corrosion at 1200°C for 2h. It can be seen from the figure that its main structure is also a stable α-Al2O3 phase, but the thickness (~1.04μm) is significantly lower than that of Figures 3-4 The thickness of the oxide film in the high-temperature steam oxidation experiment without pre-oxidation is shown in the figure (~4.37μm), which is consistent with the Figure 1 The trend of the kinetic curve in is also consistent. The weight gain rate of the pre-oxidized sample is significantly lower than that of the non-pre-oxidized group, indicating that the pre-oxidized alloy has better resistance to high-temperature water vapor corrosion.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation, characterized in that: The following steps are involved: (1) Pre-treat the alloy surface to make it smooth and clean; (2) The alloy is heated in a mixed atmosphere of oxidizing gas and water vapor for pre-oxidation treatment to obtain a pre-oxidation layer. The oxidizing gas includes oxygen and argon. The pre-oxidation layer is metastable θ-Al2O3.

2. The method of improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation according to claim 1, characterized in that: In step (1), the alloy surface is smoothed by removing the pits on the alloy surface so that the surface roughness of the alloy is less than 0.8; the alloy surface is cleaned by washing with anhydrous acetone or alcohol until the alloy surface is dust-free and oil-free, and then blowing it clean with an air gun or drying it.

3. The method of improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation according to claim 1, characterized in that: In step (2), the volume percentage of oxygen in the oxidizing gas is 3-8%, and the volume percentage of water vapor in the mixed atmosphere is 50-70%.

4. The method of improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation according to claim 1, characterized in that: In step (2), the flow rate ratio of the oxidizing gas to the water vapor is 0.43~1.

5. The method of improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation according to claim 1, characterized in that: In step (2), the heating temperature is 800-850° C., the pre-oxidation treatment time is 30-60 h, and the thickness of the pre-oxidation layer is 150-200 μm.

6. The method of improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation according to claim 1, characterized in that: In step (1), the alloy is a FeCrAl-based alloy, which includes the following components in terms of mass percentage: Cr 10.0-12.0%, Al 4.3-5.5%, Mo 1.8-2.6%, Nb 1.0-1.5%, Si 0.1-0.3%, Ta 0.1-0.2%, Zr 0.1-0.3%, Y 0.05-0.1%, C≤0.008%, N≤0.005%, O≤0.003%, and the balance is iron and unavoidable impurities.

7. The method of improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation according to claim 6, characterized in that: In step (1), the total mass percentage of Cr, Al and Si elements is ≥14.5%, and the total mass percentage of Zr and Y elements is ≥0.25%.

8. The method of improving the high-temperature water vapor corrosion resistance of FeCrAl alloy by pre-oxidation according to claim 7, characterized in that: In step (1), the preparation method of the FeCrAl-based alloy is: The various alloying elements are weighed according to mass percentage to form a steel billet, and the steel billet is subjected to multiple hot rolling to obtain a hot-rolled plate. The hot-rolled plate is then subjected to high-temperature solid solution treatment, low-temperature rolling and two annealing treatments in sequence, and then taken out and cooled to room temperature to prepare a FeCrAl-based alloy.

9. Use of the FeCrAl alloy prepared according to the method according to any one of claims 1 to 8 in the preparation of nuclear reactor fuel cladding materials, aircraft engine structural materials, and power plant steam pipe structural materials.

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