Heat treatment method for enhancing flue gas and coal ash corrosion resistance of iron-nickel-based high-temperature alloy and product

Abstract

The invention discloses a heat treatment method for enhancing flue gas and coal ash corrosion resistance of an iron-nickel-based high-temperature alloy and a product, and the heat treatment method comprises the following steps: heating the iron-nickel-based high-temperature alloy to 1100-1160 DEG C, and cooling to room temperature after heat preservation; the alloy obtained through treatment is heated to the solid solution temperature T, cooling is conducted in a controlled cooling mode after heat preservation, and in the process of reducing the solid solution temperature T to (T-500 DEG C)-(T-400 DEG C), the cooling rate is controlled to be 150-350 DEG C / min; in the process of reducing the temperature from (T-500 DEG C) to (T-400 DEG C) to the room temperature, the cooling rate is controlled to be 50-120 DEG C / min; and the alloy obtained through treatment is heated to 680-720 DEG C, and after heat preservation, the alloy is cooled to the room temperature. The invention further discloses the iron-nickel-based high-temperature alloy prepared according to the heat treatment method. On the premise that the structure stability of the iron-nickel-based superalloy is guaranteed, the smoke and coal ash corrosion resistance of the iron-nickel-based superalloy can be improved.

Description

Technical Field

[0001] This invention relates to the field of iron-nickel-based superalloy technology, specifically to a heat treatment method and product for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion. Background Technology

[0002] Superheaters and reheaters, as key components in boilers responsible for recovering energy from coal-fired flue gas, heating steam, and achieving energy conversion, are simultaneously subjected to oxidation from high-temperature steam inside the boiler and flue gas corrosion caused by pulverized coal combustion outside the furnace tubes. For existing 600℃-class boiler superheaters / reheaters, the corrosion rate on the flue gas side can reach as high as 1 mm / a, leading to thinning of the superheater / reheater tube walls and causing tube ruptures and unauthorized maintenance, thus seriously affecting the safety, reliability, and economy of the power plant. Studies have shown that as the temperature further increases, alkali metal oxides in coal ash absorb SO3 from the flue gas, forming low-melting-point molten complex sulfates, which then undergo a dissolution corrosion reaction with the oxide layer on the alloy surface, accelerating the corrosion process and the cracking and peeling of the oxide layer. Based on this, it is predicted that the corrosion rate of heat-resistant steel used in existing superheaters / reheaters will be very rapid in the temperature range of 650℃ to 750℃.

[0003] Iron-nickel-based superalloys use γ′(Ni3Al) as the main strengthening phase and are supplemented with M 23 C6 grain boundary precipitation strengthening exhibits excellent mechanical properties and significant cost-effectiveness advantages, making it the most promising material for key hot channel components in next-generation 650℃ ultra-supercritical coal-fired power units. However, due to its high Fe content, the corrosion resistance of iron-nickel-based superalloys is slightly inferior to that of nickel (cobalt)-based superalloys of the same grade. To address this issue, current technologies mainly employ the following two approaches:

[0004] 1) Increase the content of elements such as Cr and Si in the alloy; 2) Apply a Cr-rich coating to the surface of the alloy.

[0005] However, while increasing the Cr content can effectively improve the resistance to flue gas and coal ash corrosion in iron-nickel-based superalloys, high Cr content promotes the precipitation of harmful phases such as α-Cr, reducing the alloy's microstructure stability and thus impairing its high-temperature creep strength. Furthermore, applying Cr-rich coatings typically requires high temperatures (above 900°C), which poses significant risks to both the workpiece's performance and the environment. Additionally, this method is inefficient, costly, and poorly suited for large pipeline-type workpieces, thus limiting its application. Summary of the Invention

[0006] The purpose of this invention is to address the problems in the prior art by providing a heat treatment method and product for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion. This method improves the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion while ensuring the stability of the alloy's microstructure, making the treated alloy particularly suitable for superheaters / reheaters of high-temperature boilers at 650°C and above.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A heat treatment method for enhancing the resistance of iron-nickel-based superalloys to flue gas ash corrosion includes:

[0009] S1. Heat the iron-nickel-based high-temperature alloy to 1100℃~1160℃, hold it at that temperature, and then cool it to room temperature;

[0010] S2. The alloy obtained in step S1 is heated to the solution temperature T, held at that temperature, and then cooled by controlled cooling. The solution temperature T is 1000℃~1060℃. The controlled cooling includes: during the process of reducing the solution temperature T to (T-500℃)~(T-400℃), the cooling rate is controlled at 150℃ / min~350℃ / min; during the process of reducing the solution temperature T to room temperature, the cooling rate is controlled at 50℃ / min~120℃ / min.

[0011] S3. Heat the alloy obtained after step S2 to 680℃~720℃, hold it at that temperature, and then cool it to room temperature.

[0012] As a preferred embodiment, in step S2, the alloy obtained after step S1 is heated to the solution temperature T, and then cooled by controlled cooling. The cooling method is any one or a combination of air cooling, air cooling and water mist cooling.

[0013] As a preferred embodiment, the room temperature is 10℃~30℃.

[0014] As a preferred embodiment, in step S1, where the iron-nickel-based superalloy is heated to 1100°C to 1160°C, the iron-nickel-based superalloy is in a cold-rolled state.

[0015] As a preferred embodiment, during the process of cooling to room temperature after heat preservation in step S1, the heat preservation time is 0.5h to 1h, and the cooling method is water cooling.

[0016] As a preferred embodiment, during the process of cooling to room temperature after heat preservation in step S3, the heat preservation time is 10h to 24h, and the cooling method is air cooling.

[0017] A nickel-based superalloy prepared by the heat treatment method for enhancing the resistance of the nickel-based superalloy to flue gas ash corrosion comprises the following components by weight percentage:

[0018] 0.03% ≤ C ≤ 0.08%, 0 < B ≤ 0.006%, 16% ≤ Cr ≤ 20%, 0 < W ≤ 0.5%, 0 ≤ Si < 0.05%, 1% ≤ Al ≤ 2%, 1.5% ≤ Ti ≤ 2.5%, 28% ≤ Fe ≤ 35%, and the balance is Ni.

[0019] As a preferred solution, a dense and continuous Cr2O3 film can be formed in the simulated boiler flue gas coal ash environment at 700 °C, and the Cr2O3 film does not exfoliate during the 1000h corrosion process.

[0020] As a preferred solution, it is used as the tube wall material for the flue gas passage of superheaters in high-temperature boilers at 650 °C and above.

[0021] As a preferred solution, it is used as the tube wall material for the flue gas passage of reheaters in high-temperature boilers at 650 °C and above.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] Through the heat treatment method proposed by the present invention, the treated iron-nickel-based superalloy can form a dense and continuous Cr2O3 film in the simulated boiler flue gas coal ash environment at 700 °C, and the Cr2O3 film grows stably and does not exfoliate during the 1000h corrosion process, thereby improving its resistance to flue gas coal ash corrosion without promoting the precipitation of α-Cr phase and reducing the stability of the alloy microstructure. The heat treatment method of the present invention first heats the iron-nickel-based superalloy to 1100 °C - 1160 °C, cools it to room temperature and then heats it to the solid solution temperature T, and after holding for a certain time, it is cooled in a controlled manner. By controlling the cooling, the distribution form of Al in the alloy is optimized, the formation of Al-rich oxides in the transient oxide film is inhibited, and a dense and continuous protective Cr2O3 film is formed in the alloy without increasing the Cr content, solving the technical problem of having to rely on increasing the Cr content or applying a Cr-rich coating to improve the resistance of iron-nickel-based superalloys to flue gas coal ash corrosion, and avoiding the possibility of reducing the microstructure stability and high-temperature mechanical properties due to too high Cr content. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and those of ordinary skill in the art can obtain other related drawings without creative efforts based on these drawings.

[0025] Figure 1 The corrosion kinetics curves of each alloy in the embodiments of the present invention in the simulated boiler flue gas coal ash environment at 700 °C;

[0026] Figure 2 Cross-sectional morphology of the alloy obtained in Example 1 of this invention after 1000 hours of corrosion in a simulated boiler flue gas and coal ash environment at 700℃.

[0027] Figure 3 Cross-sectional morphology of the alloy obtained in Example 2 of this invention after corrosion in a simulated boiler flue gas and coal ash environment at 700℃ for 1000 hours;

[0028] Figure 4 Cross-sectional morphology of the alloy of Comparative Example 1 after 1000 h of corrosion in a simulated boiler flue gas and coal ash environment at 700℃.

[0029] Figure 5 Cross-sectional morphology of the alloy of Comparative Example 2 after 1000 h of corrosion in a simulated boiler flue gas and coal ash environment at 700℃.

[0030] Figure 6 Cross-sectional morphology of Inconel 740H alloy after 1000 hours of corrosion in a simulated boiler flue gas and coal ash environment at 700℃. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, those skilled in the art can obtain other embodiments without creative effort.

[0032] This invention proposes a heat treatment method to enhance the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion. By controlling the cooling process to optimize the distribution of Al in the alloy, the formation of Al-rich oxides in transient oxides is suppressed, and a dense and continuous protective Cr2O3 film is formed in the iron-nickel-based superalloy. Thus, the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion is improved without increasing the Cr content in the alloy, reducing the stability of the alloy structure, or improving the high-temperature mechanical properties.

[0033] The present invention provides a heat treatment method for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion, comprising the following steps:

[0034] S1. Heat the cold-rolled iron-nickel-based superalloy to 1100℃~1160℃, hold for 0.5h~1h, and then water cool to room temperature;

[0035] S2. The alloy obtained in step S1 is heated to the solution temperature T, held at that temperature, and then cooled by controlled cooling. The solution temperature T is 1000℃~1060℃. The controlled cooling includes: during the process of reducing the solution temperature T to (T-500℃)~(T-400℃), the cooling rate is controlled at 150℃ / min~350℃ / min; during the process of reducing the solution temperature T to room temperature, the cooling rate is controlled at 50℃ / min~120℃ / min.

[0036] S3. Heat the alloy obtained after step S2 to 680℃~720℃, hold for 10h~24h and then air cool to room temperature.

[0037] In one possible implementation, when the alloy obtained in step S1 is heated to the solution temperature T in step S2 and then cooled by controlled cooling after holding at that temperature, the cooling method is any one or a combination of air cooling, air cooling and water mist cooling.

[0038] In one possible implementation, the room temperature in this embodiment of the invention is 10°C to 30°C. In chemical processes, "room temperature" is generally a relative concept and does not have an absolutely fixed value. However, in most cases, room temperature is roughly defined as a temperature range between 20°C and 25°C (or 68°F to 77°F). This range is based on common temperatures in people's daily lives and work environments and is also the reference temperature used in most laboratory and industrial production environments for chemical experiments and process operations. It should be noted that different chemical processes and experimental conditions may have different requirements or definitions for room temperature. For example, in some chemical reactions that require precise temperature control, room temperature may be more precisely defined as 22°C or 23°C, and this temperature needs to be maintained using thermostat equipment. In other cases, room temperature may only be a rough reference temperature, and there may be deviations in actual operation. Furthermore, people's perception of room temperature will vary depending on climate and geographical location. Therefore, in chemical processes, in addition to referring to the conventional definition of room temperature, it is necessary to flexibly adjust and control the temperature according to specific experimental conditions, process requirements, and environmental factors.

[0039] Another embodiment of the present invention provides an iron-nickel-based superalloy prepared by the heat treatment method for enhancing the corrosion resistance of the iron-nickel-based superalloy to flue gas and coal ash, comprising the following components by weight percentage:

[0040] 0.03% ≤ C ≤ 0.08%, 0 < B ≤ 0.006%, 16% ≤ Cr ≤ 20%, 0 < W ≤ 0.5%, 0 ≤ Si < 0.05%, 1% ≤ Al ≤ 2%, 1.5% ≤ Ti ≤ 2.5%, 28% ≤ Fe ≤ 35%, and the balance is Ni.

[0041] The iron-nickel-based superalloy prepared in the embodiment of the present invention can form a dense and continuous Cr2O3 film in the simulated boiler flue gas coal ash environment at 700 °C, and the Cr2O3 film grows stably without spalling during the 1000-hour corrosion process. This characteristic is of great significance for improving the service life of the alloy in high-temperature and corrosive environments. The Cr2O3 film has excellent oxidation resistance and can effectively prevent oxygen from further reacting with the alloy matrix, thereby protecting the alloy from further oxidation. The dense and continuous Cr2O3 film means that there are no obvious pores or cracks inside the film layer, which can more effectively block the penetration of corrosive media. At the same time, the continuous film layer also enhances its mechanical strength, making it less likely to spall. During the 1000-hour corrosion process, the Cr2O3 film can grow stably without spalling, which shows the excellent corrosion resistance of the alloy in high-temperature and corrosive environments. The stability of the film is mainly due to its dense structure and good bonding force with the alloy matrix. Since the alloy can maintain stable performance for a long time in high-temperature and corrosive environments, it can significantly improve the service life of key components such as boiler superheaters and reheaters, and reduce the downtime maintenance and replacement costs caused by corrosion. The stable Cr2O3 film can prevent the alloy matrix from being further eroded, thereby avoiding equipment failure or safety accidents caused by corrosion. The iron-nickel-based superalloy prepared in the embodiment of the present invention is not only suitable for 600 °C boilers, but can also perform well in boilers at higher temperatures (such as 700 °C), providing a new material choice for the development of high-temperature boiler technology.

[0042] The iron-nickel-based superalloy prepared by the heat treatment method according to the embodiments of the present invention is particularly suitable as the flue gas passage wall material for superheaters or reheaters of high-temperature boilers of 650℃ and above. For superheaters or reheaters of high-temperature boilers of 650℃ and above, the working environment is extremely harsh, requiring materials not only to withstand thermal stress at high temperatures but also to possess good oxidation and corrosion resistance to ensure long-term stable operation. The superheater is a key component in the boiler that heats saturated steam into superheated steam, and its tube wall material must withstand the scouring and corrosion of high-temperature, high-pressure steam. The reheater is used to reheat the steam discharged from the high-pressure cylinder of the turbine to increase the steam temperature and pressure, thereby improving the unit's thermal efficiency. Its working environment is equally harsh, and the requirements for materials are also very high. The iron-nickel-based superalloy treated according to the heat treatment method of the present invention is one of the ideal materials that meets these requirements. It not only meets the performance requirements under extreme working environments such as high temperature, high pressure, and corrosion but also has good processing performance and long-term stability, providing a strong guarantee for the safe and efficient operation of high-temperature boilers.

[0043] The corrosion problem faced by superheaters and reheaters in existing 600℃ boilers is a complex and severe challenge. High-temperature steam inside the boiler reacts with the superheater / reheater tube wall material, causing gradual thinning of the tube wall. This oxidation reaction is particularly pronounced at high temperatures, which accelerate the oxidation rate. Furthermore, the exterior of the boiler tubes is corroded by flue gas from pulverized coal combustion, with major corrosive agents including SO3 and alkali metal oxides. As the temperature rises further, these corrosive substances become more active, forming low-melting-point molten complex sulfates that dissolve and corrode the oxide layer on the alloy surface, accelerating the corrosion process and the cracking and peeling of the oxide layer. Simultaneously, the diffusion rate of elements in the alloy also increases, further accelerating the corrosion reaction. The composition, microstructure, and surface condition of the superheater / reheater tube wall material all affect its corrosion resistance. Current corrosion prevention measures include: 1. Controlling tube wall temperature: Strictly controlling the tube wall temperature of the heated surfaces to prevent and mitigate corrosion. 1. Controlling the wall temperature of the heating surface by limiting steam parameters; 2. Low-oxygen combustion technology; 3. Furnace outlet temperature control: Selecting and controlling a suitable furnace outlet temperature to avoid excessively high flue gas temperature at the furnace outlet; 4. Regular soot blowing: Regularly blowing soot onto the boiler heating surfaces to remove ash layers containing alkali metal oxides and complex sulfates, preventing high-temperature corrosion. However, it should be noted that when high-temperature corrosion already exists, excessive soot blowing may accelerate the corrosion process by blowing off the ash layer; 5. Rational combustion organization: Improving the aerodynamic field inside the furnace to prevent thermal deviations caused by slagging on water-cooled walls and furnace center tilting, reducing fouling and slagging on superheaters and reheaters; 6. Selecting corrosion-resistant materials; 7. Protective coatings: Applying protective coatings, such as plasma-sprayed chromium carbide (or tungsten carbide) or surface borosilicate treatment, to vulnerable components to improve their corrosion resistance. However, these existing measures have some drawbacks in terms of reliability and cost, and their effects are not ideal.

[0044] The products prepared according to the embodiments of the present invention are compared with those of the comparative examples to demonstrate the effectiveness of the embodiments of the present invention.

[0045] Example 1

[0046] The cold-rolled iron-nickel-based high-temperature alloy tube was heated to 1160℃ in the furnace, held at that temperature for 0.5h, and then water-cooled to room temperature.

[0047] The aforementioned alloy tube was heated to 1060°C in the furnace and held for 0.5 hours. Then, it was cooled to 660°C at a cooling rate of 350°C / min using water mist spray cooling, and then cooled to room temperature from 660°C at a cooling rate of 120°C / min.

[0048] Finally, the alloy tube from the previous step is heated to 680℃ in the furnace, held at that temperature for 24 hours, and then air-cooled to room temperature.

[0049] Example 2

[0050] The cold-rolled iron-nickel-based high-temperature alloy tube with the same deformation as in Example 1 was heated to 1100°C in the furnace, held for 1 hour, and then water-cooled to room temperature.

[0051] The aforementioned alloy tube was heated to 1000°C in the furnace and held for 1 hour. Then, it was cooled to 500°C at a cooling rate of 150°C / min using compressed air, and then cooled to room temperature at a cooling rate of 50°C / min.

[0052] Finally, the alloy tube from the previous step is heated to 720°C in the furnace, held at that temperature for 10 hours, and then air-cooled to room temperature.

[0053] Example 3

[0054] The iron-nickel-based high-temperature alloy tube with the same deformation amount as in Example 1 was heated to 1130°C in the furnace, held at that temperature for 0.75 hours, and then water-cooled to room temperature.

[0055] The aforementioned alloy tube was heated to 1020°C in the furnace and held at that temperature for 0.75 hours. Then, it was cooled to 580°C by air cooling at a rate of 260°C / min, and then cooled to room temperature from 580°C at a rate of 100°C / min.

[0056] Finally, the alloy tube obtained in the previous step is heated to 700℃ in the furnace, held at that temperature for 12 hours, and then air-cooled to room temperature.

[0057] Comparative Example 1

[0058] The cold-rolled iron-nickel-based high-temperature alloy tube with the same composition and deformation as in Example 1 was heated to 1160°C in the furnace, held for 0.5 hours, and then water-cooled to room temperature.

[0059] The aforementioned alloy tube was heated to 1060°C in the furnace, held at that temperature for 0.5 hours, and then water-cooled to room temperature.

[0060] Finally, the alloy tube from the previous step is heated to 680℃ in the furnace, held at that temperature for 24 hours, and then air-cooled to room temperature.

[0061] Comparative Example 2

[0062] The cold-rolled iron-nickel-based high-temperature alloy tube with the same composition and deformation as in Example 3 was heated to 1130°C in the furnace, held for 0.75 h, and then water-cooled to room temperature.

[0063] The aforementioned alloy tube was heated to 1020°C in the furnace, held at that temperature for 0.75 hours, and then water-cooled to room temperature.

[0064] Finally, the alloy tube obtained in the previous step is heated to 700℃ in the furnace, held at that temperature for 12 hours, and then air-cooled to room temperature.

[0065] The mass changes of the alloys obtained in Examples 1 and 2, as well as the alloys in Comparative Examples 1 and 2, were measured when they were corroded in a simulated boiler flue gas and coal ash environment at 700°C.

[0066] The mass change of an alloy during corrosion in a simulated boiler flue gas and coal ash environment at 700℃ is an important indicator for evaluating its corrosion resistance under extreme conditions. This mass change typically reflects the interaction between the alloy and various corrosive components in the flue gas and coal ash (such as sulfur and alkali metals), as well as the growth and detachment of the oxide film or corrosion products formed on the alloy surface. Specifically, the mass change can be characterized by the following aspects:

[0067] 1. Corrosion rate

[0068] An increase in mass usually indicates the formation of corrosion products (such as oxides and sulfides) on the alloy surface. The formation rate of these products is directly related to the corrosion rate of the alloy. The faster the mass increase, the higher the corrosion rate of the alloy in that environment, and the worse its corrosion resistance. Conversely, a slow or almost constant mass increase indicates that the alloy has good corrosion resistance. If there are significant fluctuations in the mass change, it indicates that the corrosion products on the alloy surface are unstable and may have dissolved or peeled off.

[0069] 2. The protective properties of oxide films

[0070] During corrosion, an oxide film forms on the alloy. The density, stability, and adhesion of this film to the substrate directly affect the alloy's corrosion resistance. If the oxide film effectively blocks further erosion by corrosive media, the alloy's quality will change relatively slowly. Conversely, if the oxide film is loose and porous, easily peels off, or is not firmly bonded to the substrate, the alloy will suffer more severe corrosion, and the quality change will be more pronounced.

[0071] 3. Differences in corrosion resistance among alloys

[0072] The difference in mass change of different alloys under the same corrosive environment can reflect the difference in their corrosion resistance. For example, some alloys may have better corrosion resistance due to the presence of higher levels of elements such as chromium and aluminum, and their mass increase during corrosion is smaller; while other alloys may have a larger mass increase under the same conditions due to their composition or microstructure, exhibiting poorer corrosion resistance.

[0073] By measuring the mass change of the alloy during the corrosion process and combining it with other characterization methods (such as scanning electron microscopy and energy dispersive spectroscopy), the corrosion mechanism of the alloy can be further revealed. For example, the increase in mass is accompanied by the formation of specific corrosion products, which can help infer the main type of corrosion of the alloy in this environment (such as oxidation corrosion, sulfide corrosion, etc.); while the trend and pattern of mass change can reflect the dynamic characteristics of the alloy corrosion process.

[0074] The mass change data of the alloy in a simulated boiler flue gas and coal ash environment at 700℃ is of great reference value for evaluating its application potential in high-temperature and high-pressure equipment such as ultra-supercritical boilers.

[0075] In summary, the mass change of the alloy during corrosion in a simulated boiler flue gas and coal ash environment at 700℃ is an important basis for evaluating its corrosion resistance, revealing the corrosion mechanism, and guiding practical applications.

[0076] The corrosion performance of the iron-nickel-based superalloys and Inconel 740H alloy prepared in the examples and comparative examples was determined in a simulated boiler flue gas and coal ash environment. In experiments simulating this environment, alloy samples are typically placed in an environment containing coal ash and synthetic flue gas to simulate the corrosion conditions in an actual boiler. Coal ash mainly consists of Al2O3, SiO2, Fe2O3, Na2SO4, K2SO4, etc., while flue gas contains gases such as N2, CO2, O2, and SO2. The experimental temperature is usually set at 700℃-750℃, which is the typical operating temperature range for ultra-supercritical boilers. Because Inconel 740H alloy exhibits excellent corrosion performance in the simulated boiler flue gas and coal ash environment, it has become an important candidate material for superheater / reheater tubes and thick-walled pipes in ultra-supercritical power plant boilers with steam parameters of 700℃-750℃. This alloy not only has excellent corrosion resistance and high-temperature strength, but also good processing, welding and manufacturing properties, which can meet the high requirements of modern power plant boilers for material performance. Therefore, the embodiments of this invention take Inconel 740H alloy as the reference.

[0077] In this embodiment of the invention, the flue gas composition (vol.%) was: 0.3% SO2 + 81.2% N2 + 10% CO2 + 3.5% O2 + 5% H2O, and the coal ash composition (wt.%) was: 6% Fe2O3 + 2% Na2SO4 + 2% K2SO4 + 29% CaSO4 + 39% SiO2 + 22% Al2O3. The test temperature was 700℃, and the test duration was 1000h. To ensure the accuracy of the experimental data, three parallel samples were tested for each embodiment (comparative example), and the average corrosion rate within 1000h is shown in Table 1.

[0078] Table 1 Average corrosion rate of the alloy

[0079]

[0080]

[0081] Inconel 740H alloy is a high-performance nickel-based superalloy. Due to its excellent oxidation resistance, corrosion resistance, and high-temperature strength, it is considered a promising candidate for applications in high-temperature components such as superheaters in 700℃ ultra-supercritical coal-fired power plants. The chemical composition of Inconel 740H alloy mainly includes nickel, chromium, molybdenum, tungsten, titanium, and aluminum. The combined effect of these alloying elements gives Inconel 740H alloy its excellent performance under high-temperature conditions. The density of Inconel 740H alloy is approximately 8.0 g / cm³. 3 -8.2g / cm 3 This value is slightly higher than that of ordinary steel, reflecting its higher nickel content and the influence of other alloying elements. The melting point is 1370℃-1425℃, the thermal conductivity at 25℃ is 11.3 W / (m·K), and the specific heat capacity at 20℃ is 0.427 J / (g·K). Inconel 740H alloy exhibits extremely high tensile strength, reaching 850 MPa at room temperature. Its yield strength can reach 550 MPa at room temperature, demonstrating excellent resistance to deformation during high-temperature forming. The elongation is approximately 25%-35%, indicating good plasticity. Under standard heat treatment conditions, the hardness is HRC32-38. The solution treatment temperature for Inconel 740H alloy is generally between 1120℃ and 1160℃, the purpose of which is to dissolve carbides, nitrides, and other precipitated phases in the alloy into the matrix, improving the material's plasticity and toughness. The aging treatment consists of two steps. The first step involves aging at 760℃-800℃ for 8-12 hours followed by air cooling. The second step involves aging at 650℃-700℃ for 16-24 hours. The purpose of the aging treatment is to improve the high-temperature strength and hardness of the Inconel 740H alloy by precipitating strengthening phases (such as the γ' phase). The precipitation temperature of the γ′(Ni3(Al,Ti)) strengthening phase is approximately between 650℃ and 900℃, and this phase transformation process is crucial for improving the high-temperature strength and durability of the alloy.

[0082] Please see Figure 1 To provide a more intuitive analysis, the average corrosion rate of the alloy over 1000 hours was calculated, as shown in Table 1. Clearly, this embodiment of the invention, by controlling cooling, can reduce the corrosion rate of the alloy without increasing the Cr content or changing the content of other alloying elements. Its resistance to flue gas and coal ash corrosion is superior to that of Inconel 740H alloy under the same conditions, and its average corrosion rate over 1000 hours remains positive, indicating that the oxide film still provides protection.

[0083] The tensile strength and elongation of the alloys in the test examples and comparative examples at 700°C are shown in Table 2.

[0084] Table 2. Tensile strength and elongation of the alloy at 700℃

[0085]

[0086] As can be seen from the results shown in Table 2, the heat treatment process of this invention improves the alloy's resistance to flue gas and coal ash corrosion without changing the alloy composition, and at the same time does not weaken the alloy's high-temperature mechanical properties.

[0087] The cross-sectional morphology images of Examples 1 and 2 after corrosion in a simulated boiler flue gas and coal ash environment at 700℃ for 1000 hours are shown below. Figure 2 and Figure 3 As shown, a single, dense, and continuous Cr2O3 film is formed, with a semi-continuous Al2O3 layer between the Cr2O3 film and the substrate. The cross-sectional morphologies of the alloys of Comparative Example 1 and Comparative Example 2 after corrosion in a simulated boiler flue gas and coal ash environment at 700℃ for 1000 hours are shown in the figures below. Figure 4 and Figure 5 As shown: the outer layer is a loose (Fe,Cr)₂O₃ layer that is bulging and cracked, while the inner layer is a relatively dense Cr₂O₃ film. Beneath the Cr₂O₃ film, the substrate contains Cr₂O₃ and Al₂O₃ internal oxidation zones, as well as Cr… x S y The inner vulcanization zone.

[0088] The cross-sectional morphology of Inconel 740H alloy after 1000 hours of corrosion under the same conditions is as follows. Figure 6 As shown:

[0089] The outer layer is a loose (Ni,Fe,Cr)₂O₃ layer that is bulging and cracked, while the inner layer is a relatively dense Cr₂O₃ film, with Cr forming in the underlying matrix. x S y The inner vulcanization zone.

[0090] Among the three, the Cr2O3 film on the surface of Embodiments 1 and 2 of the present invention is the thinnest and densest, and no sulfides are formed in the substrate below it. This is because an Al2O3 layer with a slower growth rate and higher stability is formed, which effectively hinders the inward diffusion of anions and the outward diffusion of cations, inhibits the formation of Ni-rich or Fe-rich oxides, and at the same time reduces the growth rate of the Cr2O3 film, thus improving the alloy's resistance to flue gas ash corrosion.

[0091] This invention provides a heat treatment method to enhance the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion. After heating the alloy to the solution temperature, cooling is performed by controlled cooling, which optimizes the distribution of Al in the alloy and inhibits the formation of Al-rich oxides in the transient oxide film. This promotes the formation of a dense and continuous protective Cr2O3 film in the alloy without increasing the Cr content. This solves the technical problem that it is necessary to increase the Cr content or apply a Cr-rich coating to improve the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion, and avoids the defects of reduced microstructure stability and high-temperature mechanical properties caused by excessive Cr content.

[0092] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A heat treatment method for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion, characterized in that, Comprising: S1. Heat the iron-nickel-based superalloy to 1100°C to 1160°C, hold for a certain time and then cool to room temperature; S2. Heat the alloy obtained after step S1 to the solution temperature T, hold for a certain time and then cool down in a controlled cooling manner; the solution temperature T is 1000°C to 1060°C; the controlled cooling manner includes: during the process of reducing from the solution temperature T to (T - 500°C) to (T - 400°C), control the cooling rate at 150°C / min to 350°C / min; during the process of reducing from (T - 500°C) to (T - 400°C) to room temperature, control the cooling rate at 50°C / min to 120°C / min; S3. Heat the alloy obtained after step S2 to 680°C to 720°C, hold for a certain time and then cool to room temperature.

2. The heat treatment method for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion according to claim 1, characterized in that, When step S2 heats the alloy obtained after step S1 to the solution temperature T, holds for a certain time and then cools down in a controlled cooling manner, the cooling method adopts any one or a combination of air cooling, air cooling and water mist cooling.

3. The heat treatment method for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion according to claim 1, characterized in that, The room temperature is 10°C to 30°C.

4. The heat treatment method for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion according to claim 1, characterized in that, In step S1, when heating the iron-nickel-based superalloy to 1100°C to 1160°C, the iron-nickel-based superalloy is in cold-rolled state.

5. The heat treatment method for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion according to claim 1, characterized in that, During the process of cooling to room temperature after holding in step S1, the holding time is 0.5h to 1h, and the cooling method is water cooling.

6. The heat treatment method for enhancing the resistance of iron-nickel-based superalloys to flue gas and coal ash corrosion according to claim 1, characterized in that, During the process of cooling to room temperature after holding in step S3, the holding time is 10h to 24h, and the cooling method is air cooling.

7. A nickel-based superalloy prepared by the heat treatment method for enhancing the resistance of nickel-based superalloys to flue gas ash corrosion as described in any one of claims 1 to 7, characterized in that, By weight percentage, it includes the following components: 0.03% ≤ C ≤ 0.08%, 0 < B ≤ 0.006%, 16% ≤ Cr ≤ 20%, 0 < W ≤ 0.5%, 0 ≤ Si < 0.05%, 1% ≤ Al ≤ 2%, 1.5% ≤ Ti ≤ 2.5%, 28% ≤ Fe ≤ 35%, and the balance is Ni.

8. The iron-nickel-based superalloy according to claim 7, characterized in that, It can form a dense and continuous Cr2O3 film in the simulated boiler flue gas coal ash environment at 700°C, and the Cr2O3 film does not spall during the 1000h corrosion process.

9. The iron-nickel-based superalloy according to claim 7, characterized in that, As the wall material of the flue gas passage of a high-temperature boiler superheater at 650°C and above.

10. The iron-nickel-based superalloy according to claim 7, characterized in that, As the wall material of the flue gas passage of a high-temperature boiler reheater at 650°C and above.

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