A high-temperature-resistant austenitic heat-resistant cast alloy material and an application method thereof

Abstract

The application discloses a high-temperature-resistant austenitic heat-resistant cast alloy material and an application method thereof, and belongs to the technical field of austenitic heat-resistant cast alloy materials.The alloy material comprises C, Si, Mn, Cr, Al, Nb, Ti, Zr, N, Mo, W, Y, Ni and Fe elements with specific mass percentage contents; wherein the mass percentage contents of C, Cr, Al and Ti elements satisfy that a value of f1 obtained by a calculation model 1 meets f1% >= 2%, wherein f1% represents the volume percentage content of C6 precipitated phase of the alloy material at an application temperature above 1100 DEG C. 23 The alloy material obtained by the application has significant high-temperature creep resistance in an extremely high-temperature environment, has a stable dense oxide film and strengthened carbide, and can maintain excellent structural stability and high-temperature mechanical properties under long-term service conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of austenitic heat-resistant cast alloy materials, and particularly relates to a high-temperature-resistant austenitic heat-resistant cast alloy material. BACKGROUND

[0002] The austenitic heat-resistant cast alloy is a kind of cast alloy with face-centered cubic (FCC) austenite as a matrix, which can maintain the stability of the microstructure and mechanical properties at high temperatures, and is suitable for high-temperature components of complex shapes, such as outlet converter tubes in iron ore reduction hydrogen production devices, structural components of high-temperature heat treatment furnaces, etc.

[0003] However, it is found in actual production that the outlet converter tubes in the iron ore reduction hydrogen production device, the structural components of the high-temperature heat treatment furnace, etc. need to work at a high temperature of 1100-1200℃ for a long time, which is close to the melting point temperature of 1400℃ of the metal material, and is an extreme working condition for the metal material. Therefore, high requirements are put forward for the high-temperature mechanical properties and oxidation corrosion resistance of the material.

[0004] At present, the austenitic heat-resistant cast alloy grades widely used in engineering, such as ZG45Ni48Cr28W5 (corresponding to G-NiCr28W in the EN10027 standard of the European Union, hereinafter referred to as alloy 28 / 48), have certain durability in a high-temperature environment below 1100℃, but are easily failed in a high-temperature atmosphere above 1100℃. The main failure mechanisms include: (1) the creep rate of the material is significantly accelerated under long-term high-temperature stress, high-temperature creep deformation occurs, and the carrying capacity is reduced; (2) the material surface mainly relies on the Cr2O3 oxidation film as a protective layer, but the stability of the oxidation film is dramatically decreased above 1100℃, especially in the reducing atmosphere containing water vapor, and the oxidation film is easily decomposed or peeled off, so that the metal matrix is directly exposed to the high-temperature and reducing atmosphere, and internal and external corrosion reactions occur, resulting in material failure; (3) the strengthening carbides in the material alloy organization are decomposed at high temperatures, which aggravates the deterioration of the mechanical properties and the stability of the material organization. Under the combined action of the above deterioration mechanisms, the service life of the key components such as the furnace tube is significantly lower than the design expectation. The failure of the material further limits the temperature stability and the further improvement of the temperature of the device, and affects the process efficiency and the release of the production capacity of the device. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a high-temperature-resistant austenitic heat-resistant cast alloy material, which has significant high-temperature creep resistance in an extremely high-temperature environment above 1100-1200 DEG C, can form a stable and dense oxide film and stable strengthening carbide, can maintain excellent structural stability and high-temperature mechanical properties under long-term service conditions, can meet the comprehensive performance requirements of materials under extreme working conditions, and significantly improves the high-temperature use safety, reliability and service life of the material.

[0006] The technical scheme of the present application is as follows:

[0007] A high-temperature-resistant austenitic heat-resistant cast alloy material, comprising the following mass percentage of elements: 0.1-0.6% of C element, greater than 0 and less than 0.5% of Si element, greater than 0 and less than 0.3% of Mn element, 20-35% of Cr element, 1.5-5% of Al element, 0.2-1.5% of Nb element, greater than 0 and less than 0.5 of Ti element, greater than 0 and less than 0.1% of Zr element, greater than 0 and less than 0.2% of N element, greater than 0 and less than 5% of Mo element, greater than 0 and less than 5% of W element, 0.01-0.1% of Y element, 50-65% of Ni element and the balance of Fe; and wherein the mass percentage of C element, Cr element, Al element and Ti element satisfies that the value of f1 obtained by the following calculation model, model 1, meets f1% >= 2, i.e. f1 >= 2:

[0008]

[0009] Wherein, X_C, X_Cr, X_Al and X_Ti respectively represent the numerical value of the mass percentage of C element, Cr element, Al element and Ti element in the alloy material (i.e. the numerical value without percentage), T represents the absolute temperature of the application environment of the alloy material, and a1-a6 are fitting coefficients, and the values are respectively a1=2.5695, a2=0.8190, a3=0.5972, a4=-7.2163, a5=-21.0258 and a6=-862.4308.

[0010] The role of each element in the above austenitic heat-resistant cast alloy material of the present application includes:

[0011] The C (carbon) element can significantly improve the high-temperature creep resistance of the alloy material through carbide precipitation, and also has an important influence on the fluidity of molten steel;

[0012] The Al (aluminum) element can form a dense and stable aluminum oxide film during the high-temperature alloy casting process, which significantly improves the high-temperature oxidation resistance and carburization resistance of the alloy material.

[0013] The inventors have surprisingly found that, in order to ensure the integrity of the oxide film, the aluminum content should be controlled to be greater than 1.5%, but if it is greater than 5%, a large number of irregular, large-size precipitates (mainly in the form of NiAl) are easily generated, which destroys the grain structure and weakens the mechanical properties of the material. Therefore, the aluminum content is preferably in the range of 1.5-4%.

[0014] The Cr (chromium) element can form a composite oxide film independently or together with aluminum oxide, thereby improving the oxidation resistance and corrosion resistance of the alloy material. In addition, chromium is also an important element for the formation of M 23 C6 carbide is one of the main elements of the C6 carbide, which helps to enhance the high-temperature strength and creep properties of the alloy.

[0015] The Ni (nickel) element has a stable austenite structure (face-centered cubic), which can improve the high-temperature toughness and plasticity of the alloy material. At the same time, nickel is beneficial to the precipitation of carbides, thereby enhancing the durability and corrosion resistance of the alloy material. However, in the coking environment, nickel is also the main catalytic matrix, and if the nickel content is excessive, the coking process may be accelerated.

[0016] The inventors have surprisingly found that the nickel content is preferably in the range of 50-65%.

[0017] The Si (silicon) element in the alloy material can be used as a deoxidizer to improve the fluidity of the molten steel and improve the stability of the oxide film by generating a SiO2 film. However, the SiO2 film has poor stability at high temperatures, so the silicon content should be controlled to be less than 0.15%.

[0018] The role of the Mn (manganese) element includes deoxidation and control of sulfur content to improve the purity of the alloy material, but if the content is too high, it is easy to generate spinel with poor thermal stability, thereby reducing the performance of the alloy.

[0019] The inventors have surprisingly found that the manganese content is preferably controlled to be less than 0.15%.

[0020] The rare earth element Y (yttrium) can significantly improve the stability of the oxide film and the high-temperature creep properties of the material, thereby prolonging the service life.

[0021] The W (tungsten) element can improve the endurance strength and thermal stability of the alloy material through solid solution strengthening at high temperatures (~1100°C). However, if the content is too high, it may lead to the precipitation of Laves phase and σ phase, affecting the plasticity and diffusion of aluminum, and thereby weakening the stability of the oxide film.

[0022] The inventors have surprisingly found that the tungsten content is preferably controlled to be less than 2% to achieve the best overall performance.

[0023] The Mo (molybdenum) element can significantly enhance the endurance properties and stability of the alloy material through solid solution strengthening.

[0024] The inventors have surprisingly found that the content of molybdenum element is preferably controlled in a range of 2% or less.

[0025] The Nb (niobium) element is mainly precipitated in the form of MC carbide, which can significantly improve the creep strength and creep resistance.

[0026] The inventors have surprisingly found that the content of niobium element is preferably controlled in a range of 0.5-1.1%.

[0027] The Ti (titanium) element can not only improve the creep and crack resistance of the alloy material, but also participate in the formation of M 23 C6 carbide, which has good thermal stability and helps to inhibit grain coarsening and softening.

[0028] The inventors have surprisingly found that the content of titanium element is preferably controlled in a range of 0.05-0.3%.

[0029] The N (nitrogen) element can improve the high-temperature strength, endurance performance and fatigue resistance of the material by precipitating nitrides, but too high content will affect the plasticity and stability.

[0030] The inventors have surprisingly found that the content of nitrogen element is preferably controlled in a range of 0.02-0.1%.

[0031] The Zr (zirconium) element can form stable and dispersed ZrC carbide, effectively hinder dislocation movement, improve high-temperature hardness and creep resistance, and promote the precipitation of other strengthening phases (such as M 23 C6), and can also combine with impurities such as oxygen and sulfur to reduce the content of inclusions, improve the uniformity of the structure and the casting performance.

[0032] The inventors have surprisingly found that the content of zirconium element is preferably controlled in a range of 0.005-0.1%, which can realize the dual optimization of strength and creep performance.

[0033] The inventors have surprisingly found that in the high-temperature range above 1100-1200℃, according to the element composition of the application, the γ' phase in the alloy material has been completely solid-solved, and no longer plays a leading role in the performance of the alloy material, and the high-temperature creep performance of the alloy material is mainly affected by the secondary precipitation phase M 23 C6 type carbide precipitate. The M 23 C6 precipitate is distributed in the form of dispersion in the matrix, plays a "pinning" role in the creep process of the material, hinders dislocation slip and climb movement, and improves the creep resistance, and it can also stabilize the grain boundary structure between dendrites, which is of great significance to the structural stability and endurance life of the alloy material. Therefore, the volume fraction of the M 23 C6 precipitate has an important influence on the performance of the alloy material under high-temperature service conditions.

[0034] The model 1 proposed by the application can quickly and simply obtain the M23 the volume fraction of C6 precipitate phase, further, the inventors unexpectedly found that M 23 When the volume fraction of C6 precipitate phase is greater than or equal to 2%, the high-temperature performance of the alloy material can be effectively improved, and the high-temperature creep resistance can be significantly improved.

[0035] According to some preferred embodiments of the present application, the mass percentage content of C, Cr, Al and Ti in the high-temperature-resistant austenitic heat-resistant cast alloy material satisfies that the value of f1 obtained by model 1 is 2%≤f1%≤10%, that is, f1 is 2-10.

[0036] According to some preferred embodiments of the present application, the mass percentage content of Al and N in the high-temperature-resistant austenitic heat-resistant cast alloy material satisfies that the value of f2 obtained by the following calculation model, model 2, is f2%≤0.05%, that is, f2≤0.05:

[0037]

[0038] Wherein, X_Al and X_N respectively represent the numerical value of the mass percentage content of Al and N in the alloy material, and b1-b3 are fitting coefficients, and the values are respectively b1=0.0151, b2=2.6775, and b3=-0.1274.

[0039] The inventors unexpectedly found that the AlN precipitate phase is a high-hardness brittle second phase, which can improve the strength and creep resistance of the alloy material to a certain extent, but if its content exceeds a certain threshold, it will precipitate in large quantities at the grain boundary or in the grain, forming a stress concentration source locally, weakening the overall toughness of the alloy material, and adversely affecting the high-temperature toughness and service stability of the alloy material. The performance of the cast heat-resistant alloy is particularly significant. During the high-temperature service of the furnace tube or related components using the cast heat-resistant alloy material, the combined action of thermal stress and organizational stress will further promote the initiation of micro-cracks in the AlN precipitate phase-rich region, leading to a decrease in material plasticity, an increase in thermal crack sensitivity, a local strain concentration, and ultimately a significant reduction in the service life of the furnace tube or related components. In addition, the AlN precipitate phase has high thermal stability and is difficult to redissolve in the conventional heat treatment temperature range, so once it is excessively precipitated, the adverse organizational structure formed by it is difficult to eliminate through subsequent heat processing or heat treatment processes, and therefore, its formation tendency should be strictly controlled during alloy composition design and smelting.

[0040] The inventors have unexpectedly found that in industrial practice, the AlN precipitates are significantly affected by the process conditions, and for casting processes performed in non-vacuum environments such as sand casting, shakeout casting, centrifugal casting, etc., the molten steel is in contact with air due to the flow or violent tumbling of the molten steel in air, thereby causing the nitrogen (N) content to increase, and thus the precipitation of AlN is closely related to the content of aluminum (Al) and nitrogen (N) elements in the alloy. The present application further obtains the volume fraction of the AlN precipitates in the molten steel during the solidification process of the heat-resistant casting alloy through model 2, and limits it to less than 0.05% according to the unexpected discovery of the inventors.

[0041] The inventors have unexpectedly found that the AlN precipitates in this range can enhance the high-temperature performance of the alloy material, while not weakening its high-temperature plasticity (when the content range exceeds 0.05%, it will have a more obvious adverse effect on the high-temperature plasticity of the alloy material), which helps to improve the comprehensive reliability of the alloy material under complex high-temperature working conditions.

[0042] According to some preferred embodiments of the present application, the high-temperature-resistant austenitic heat-resistant casting alloy material further contains impurity elements with a mass percentage of less than 400ppm, including S elements less than 100ppm and P elements less than 300ppm.

[0043] In the above preferred embodiments, P (phosphorus) and S (sulfur) elements are harmful impurities, mainly brought in by raw materials, and by controlling them to be less than 300ppm and 100ppm respectively, the high-temperature service performance of the alloy material can be guaranteed.

[0044] Further preferably, the mass percentage of Si, Mn, Y and S elements in the high-temperature-resistant austenitic heat-resistant casting alloy material satisfies that the value of f3 obtained by the following calculation model, i.e. model 3, meets f3%>0:

[0045]

[0046] Wherein, X_Si, X_Mn, X_Y and X_S represent the numerical values of the mass percentage of Si, Mn, Y and S elements in the alloy material, and c1-c5 are fitting coefficients, and the values are respectively: c1=-0.5055, c2=-0.5401, c3=1.7910, c4=-0.0994, and c5=-0.0367.

[0047] The inventors have unexpectedly found that in a high-temperature oxidation environment, the integrity of the surface oxide film of the material directly determines its high-temperature service life. If the oxide film is not dense or stable, internal and external oxidation is easily triggered, which accelerates the failure of the material in cooperation with high-temperature creep, especially in a working condition above 1100-1200℃. Under different atmosphere conditions (such as oxygen partial pressure and water vapor partial pressure), according to the element composition of the present application, a plurality of oxidation products may be generated on the surface of the alloy material, such as spinel FeMn2O4, SiO2, Cr2O3 and Al2O3, etc. Among them, FeMn2O4 is unstable in a reducing or low-oxygen environment and may decompose into FeO and MnO, thereby causing the oxide film structure to be unstable, cracked or partially detached, and the overall protection to be damaged; SiO2 is formed below the inner layer of Cr2O3 by Si elements, and is relatively dense, but if low-melting-point oxides such as FeO and MnO appear in the alloy material, SiO2 will react with them at high temperature to generate silicates, thereby weakening the structural integrity of the oxide film; Cr2O3 is one of the main protective oxides, but it is unstable and prone to decomposition at a high temperature above 1000℃, especially when further exposed to water vapor; in comparison, Al2O3 has extremely high thermal stability and low oxygen diffusion rate, and is the best protective oxide film.

[0048] The inventors have unexpectedly found that when the alloy material contains appropriate amounts of Al and Cr elements, the oxide film is mainly a composite oxide of α-Al2O3 and Cr2O3, wherein Al2O3 is located in the outermost layer of the oxide film and Cr2O3 is below it, and the high-temperature corrosion resistance of the alloy material mainly depends on Al2O3. When there is sufficient Al element in the matrix of the alloy material, new Al2O3 can be continuously produced through diffusion in the matrix to improve the high-temperature corrosion resistance of the material. On the other hand, the inventors have unexpectedly found that the stability of the Al2O3 film is also related to the S and Y elements in the alloy material, and the addition of a small amount of Y element helps to stabilize the Al2O3 film structure and enhance the adhesion of the film, while an excessive amount of S element tends to form a weak connection at the grain boundary, thereby reducing the integrity of the film.

[0049] Therefore, in order to improve the thermal stability of the oxide film of the alloy material above 1100-1200℃, it is necessary to reasonably control the content of Mn and Si elements to avoid the interference of FeMn2O4 and SiO2, and to reasonably control the content of Y and S elements.

[0050] The present application quantitatively evaluates the influence of alloy elements on the stability of the oxide film by model 3 (obtained according to the relative deviation normalization method). When f3>0, it indicates that the surface oxide film of the alloy material is stable and is suitable for long-term service in a high-temperature oxidation environment; when f3<0, it indicates that the surface oxide film of the alloy material is unstable and may appear peeling, protection failure, etc., and cannot be applied to severe high-temperature working conditions.

[0051] According to some preferred embodiments of the present application, the high-temperature-resistant austenitic heat-resistant cast alloy material contains the following elements in the following ranges: 0.4-0.5% of C, 0.005-0.2% of Si, 0.005-0.1% of Mn, 25-29% of Cr, 1.5-4% of Al, 0.5-1.1% of Nb, 0.1-0.3% of Ti, 0.005-0.01% of Zr, 0.03-0.04% of N, 0.01-0.1% of Mo, 0.01-0.05% of W, 0.01-0.03% of Y, 55-65% of Ni, and the balance of Fe.

[0052] The present application further provides an application of the above-mentioned high-temperature-resistant austenitic heat-resistant cast alloy material to a heat-resistant structure at a temperature above 1100℃.

[0053] The heat-resistant structure can be a load-bearing pipe, a structural component, or a device, etc. that is used in a high-temperature (above 1100℃) working condition, and more specifically, a reduction furnace pipe in a hydrogen production device by iron ore reduction, a structural component of a high-temperature heat treatment furnace, etc.

[0054] Preferably, the high-temperature working condition is a working condition at a temperature of 1100-1250℃.

[0055] Preferably, the heat-resistant structure is also used in a strong oxidizing and corrosive atmosphere.

[0056] According to some preferred embodiments of the present application, the application includes forming the high-temperature-resistant austenitic heat-resistant cast alloy material into the heat-resistant structure and performing a pre-oxidation treatment.

[0057] The inventors have unexpectedly found that, in addition to the preferred scheme for the alloy element composition proposed in the present application, a pre-oxidation treatment can further enhance the compactness, continuity, and adhesion of the surface oxide film of the alloy material, and improve the stability of the oxide film and the service life of the material under high-temperature service conditions at a temperature above 1100-1200℃. The mechanism of action includes that the oxidation resistance of the alloy material is largely dependent on the composition, crystal structure, micro-compactness, and adhesion quality between the first layer of the surface oxide film and the substrate. However, in the initial oxidation stage before actual service, the formation path of the oxide layer is controlled by the combined action of the composition of the alloy material and the external oxygen partial pressure.

[0058] Regarding the pre-oxidation treatment conditions, the inventors unexpectedly discovered that when the oxygen partial pressure is high, oxides such as Fe2O3 and Cr2O3 are preferentially generated, which may inhibit the selective oxidation of Al and reduce the stability of the oxide film. Therefore, pre-oxidation in a low oxygen partial pressure environment (which can be achieved by adjusting the O2 / inert atmosphere ratio) can adjust the oxidation initiation order of alloying elements, promote the preferential oxidation of aluminum, and generate a stable and dense α-Al2O3 oxide film on the surface of the alloy material. This avoids the formation of non-protective oxides by elements such as Fe and Mn, and reduces the generation of interfacial defects or multiphase regions between the film and the substrate.

[0059] Meanwhile, the inventors unexpectedly discovered that the synergistic effect of a slower heating rate and a preferred oxygen partial pressure can promote the formation of microcrystalline or subcrystalline α-Al2O3 films with more uniform structure. Their density and adhesion are significantly better than those of coarse-grained films formed by rapid oxidation. They not only have excellent barrier effects on oxygen diffusion, but also improve the thermal stress coordination between the film and the substrate, effectively avoiding the peeling, cracking or failure of the oxide film during thermal cycling.

[0060] Therefore, more preferably, the pre-oxidation treatment includes: heating from room temperature to 850-950°C at a heating rate of 45-55°C / h in a mixed atmosphere, and then holding at that temperature for 12-36h, wherein the mixed atmosphere includes water vapor with a volume percentage of less than 10% and an inert atmosphere with a volume percentage of more than 90%.

[0061] After completing the above pre-oxidation treatment, the furnace tube can be directly heated to the service temperature according to the specific application scenario without any other treatment steps.

[0062] In addition, when alloy materials experience large temperature fluctuations, such as a sudden drop in temperature due to equipment shutdown, the oxide film on its surface may develop microcracks, holes, or peel off, affecting its protective function. Therefore, a pre-oxidation treatment can be carried out again before the furnace tube is put back into use to repair and rebuild the surface protective film structure and ensure stable and reliable material performance.

[0063] The inert atmosphere includes gases such as argon and / or nitrogen.

[0064] The high-temperature resistant austenitic heat-resistant casting alloy material obtained by this invention has significant resistance to high-temperature creep in extreme high-temperature environments above 1100-1200℃. It can form a stable and dense oxide film and stable reinforced carbides. Under long-term service conditions, it can maintain excellent structural stability and high-temperature mechanical properties, meet the comprehensive performance requirements of materials under extreme working conditions, and significantly improve the safety, reliability and service life of materials at high temperatures. Attached Figure Description

[0065] Figure 1The M values ​​obtained from JMatPro software simulation and Equation 1 for samples 1, 2, 3, 4, 8, 9, 10, and 11 in the examples are... 23 Comparison of volume fractions of C6 precipitates.

[0066] Figure 2 This is a comparison chart of the volume fraction of AlN precipitates obtained from JMatPro software simulation and Equation 2 for samples 1, 2, 3, 4, 10 and 11 in the examples.

[0067] Figure 3 The image shown is the SEM and energy dispersive spectroscopy image of sample 3 in the example.

[0068] Figure 4 The images shown are SEM and energy dispersive spectroscopy images of sample 10 in the examples.

[0069] Figure 5 The stress-LMP curves for samples 1, 2, 3, 4, 8, 9, 10, 11, and 12 obtained in the examples are shown.

[0070] Figure 6 The weight gain curves of samples 1, 2, 4, 5, 6, 7, 12, 13, 14, and 15 obtained in the examples are shown. Detailed Implementation

[0071] The technical solutions of the present invention will be further described below with reference to the embodiments and accompanying drawings. The embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0072] The furnace tube samples described in the following examples were obtained by centrifugal casting under the same process conditions. The outer diameter of the furnace tube is 110 mm, the inner diameter is 90 mm, and the wall thickness is 10 mm.

[0073] The values ​​of f1, f2, and f3 mentioned in the following examples are the numerical values ​​of functions f1, f2, and f3 obtained according to the following calculation models (hereinafter referred to as Formulas 1, 2, and 3, respectively):

[0074]

[0075] Wherein, X_C, X_Cr, X_Al, X_Ti represent the numerical values of the mass percentage of carbon, chromium, aluminum and titanium elements in the alloy material (i.e. the numerical values without percentage), T represents the absolute temperature (unit: K) of the material application environment (set to 1100℃ in the embodiment), a1~a6 are fitting coefficients, and the values are a1=2.5695, a2=0.8190, a3=0.5972, a4=-7.2163, a5=-21.0258, and a6=-862.4308.

[0076]

[0077] Wherein, X_Al, X_N represent the numerical values of the mass percentage of aluminum and nitrogen elements in the alloy material (i.e. the numerical values without percentage), b1~b3 are fitting coefficients, and the values are b1=0.0151, b2=2.6775, and b3=-0.1274.

[0078]

[0079] Wherein, X_Si, X_Mn, X_Y, X_S represent the numerical values of the mass percentage of silicon, manganese, yttrium and sulfur elements in the alloy material (i.e. the numerical values without percentage), c1~c5 are fitting coefficients, and the values are c1=-0.5055, c2=-0.5401, c3=1.7910, c4=-0.0994, and c5=-0.0367.

[0080] The JMatPro software described in the following embodiments is a commercial software based on the CALPHAD method, combining a thermodynamic database and a diffusion dynamics model, simulating the phase transition behavior of alloys with different compositions at a given temperature, and outputting the volume fraction of the corresponding precipitated phase (although the software has high precision, due to its complex model structure, a large number of parameters involved, and the current database covering insufficient part of the nickel-based casting alloy system, there are certain limitations in the application in actual factory production, material selection and quality control, while the formulas 1-3 constructed in the present application are empirical prediction models based on the content of main alloy elements and temperature parameters, which are more simple in form and more convenient for rapid estimation and parameter optimization, especially suitable for the initial selection and rapid decision-making of heat-resistant alloy materials in research and engineering application).

[0081] Embodiments 1-4

[0082] Four kinds of austenitic heat-resistant casting alloy materials are provided, i.e. sample 1-4, the component content and corresponding f1, f2, f3 values of which are shown in Table 1 as follows:

[0083] Table 1 Component content and f1-f3 values of sample 1-4

[0084]

[0085] Comparative Examples 1-3

[0086] Comparative Examples 1-3 provide three samples of furnace tubes made from austenitic heat-resistant cast alloy materials, i.e., samples 5-7, the component contents and corresponding f1, f2, f3 values of which are shown in Table 2 below:

[0087] Table 2 Component contents of samples 5-7 and their f1-f3 values

[0088]

[0089] Comparative Examples 4-5

[0090] Comparative Examples 4-5 provide two samples of furnace tubes made from austenitic heat-resistant cast alloy materials, i.e., samples 8-9, the component contents and corresponding f1, f2, f3 values of which are shown in Table 3 below:

[0091] Table 3 Component contents of samples 8-9 and their f1-f3 values

[0092]

[0093] Comparative Examples 6-7

[0094] Comparative Examples 6-7 provide two samples of furnace tubes made from austenitic heat-resistant cast alloy materials, i.e., samples 10-11, the component contents and corresponding f1, f2, f3 values of which are shown in Table 4 below:

[0095] Table 4 Component contents of samples 10-11 and their f1-f3 values

[0096]

[0097] Comparative Example 8

[0098] Comparative Example 8 provides a sample of a furnace tube made from an austenitic heat-resistant cast alloy material widely used in the prior art, i.e., ZG45Ni48Cr28W5 (alloy 28 / 48), the component contents and corresponding f1, f2, f3 values of which are shown in Table 5 below:

[0099] Table 5 Component contents of sample 12 and their f1-f3 values

[0100]

[0101] Comparative Examples 9-11

[0102] Comparative Examples 9-11 provide three samples of furnace tubes made from austenitic heat-resistant cast alloy materials, i.e., samples 13-15, the component contents and corresponding f1, f2, f3 values of which are shown in Table 6 below:

[0103] Table 6. Component content and f1-f3 values ​​of samples 13-15

[0104]

[0105] Sample analysis:

[0106] Under steady-state conditions at 1100℃ (1373.15K), samples 1, 2, 3, 4, 8, 9, 10, and 11 were selected. The M content in the alloy was calculated using JMatPro software simulation and Formula 1. 23 The volume fraction of C6 type carbide precipitates is shown in the attached figure. Figure 1 As shown (samples 1, 2, 3, etc. are referred to as 1, 2, 3, etc. in all the attached figures).

[0107] Through append Figure 1 It can be seen that the simulation data obtained by JmatPro software and the M calculated by Formula 1 are consistent. 23 The volume fraction distribution range of C6 type carbide precipitates is roughly the same, all between 0-8%, covering a wide range of material composition and microstructure response; this indicates that M 23 When the volume fraction of C6 type carbide precipitates is ≥2% as the effective range for strengthening effect, the calculation results of Formula 1 are consistent with the prediction trend of JMatPro software.

[0108] Under steady-state conditions at the complete solidification temperature of molten steel (approximately 1350℃, 1623.15K), samples 1, 2, 3, 4, 10, and 11 were selected. The volume fraction of AlN precipitates in the alloys was calculated using JMatPro software simulation and Formula 2. The results are shown in the attached figure. Figure 2 As shown.

[0109] Through append Figure 2 It can be seen that the simulation data obtained by JMatPro software is roughly the same as the volume fraction distribution range of AlN precipitates calculated by Formula 2; indicating that when the volume fraction of AlN precipitates is ≤0.05% as the effective range with enhancing effect, the calculation results of Formula 2 are consistent with the prediction trend of JMatPro software.

[0110] To evaluate the predictive reliability of Formulas 1 and 2 under actual conditions, representative samples 3 and 10 were selected and subjected to 2000 hours of high-temperature heat treatment at 1100℃, followed immediately by water quenching to preserve their microstructure in a high-temperature stable state. The carbide precipitation was observed using scanning electron microscopy and energy dispersive spectroscopy. Sample 3 was primarily used to observe M... 23The precipitation volume percentage of the C6 precipitate was determined using ImageJ software for phase separation, and the results are shown in the attached figure. Figure 3 As shown in the attached figure. Sample 10 was mainly used to observe the precipitation volume percentage of the AlN precipitate. Because its precipitation content was far below 1%, it was difficult to analyze using ImageJ software. Therefore, it was magnified by electron microscopy. The presence of the AlN phase was found and confirmed by magnifying the image. The results are shown in the attached figure. Figure 4 As shown (where Selected Area1 represents the area selected for the energy spectrum test, and EDS spot 1 represents the test point selected for the energy spectrum test).

[0111] Through append Figure 3 It can be seen that the microstructure of sample 3 mainly includes the MC phase (M is mainly composed of Nb element, i.e., forming the NbC phase) and M 23 C6 phase (M is mainly composed of Cr element), where M 23 The C6 phase is dispersed throughout the material, with some M... 23 The C6 phase is slightly coarse. Grayscale calculations performed using ImageJ software show that the M phase in the image is... 23 The volume percentage of the C6 phase was 4.87%, which is close to the f1 value (5.73%), indicating that M in sample 3... 23 The C6 phase exists stably at 1100℃ for a long time and is dispersed throughout the material, which can optimize the high-temperature creep performance of the material. Moreover, the actual observed volume percentage is close to the predicted result of the f1 value.

[0112] Through append Figure 4 It can be seen that within a very small observation area, the microstructure of sample 10 includes M 23 The C6 phase and AlN phase are present. Among them, the AlN phase has a microstructure that is significantly different from the other precipitated phases. Its edges are very sharp. Therefore, stress concentration is likely to occur at the AlN boundary, which seriously affects the high-temperature creep plasticity of the material. Figure 4 This indicates that the AlN phase in sample 10 is stable at 1100℃ for a long time, and its microstructure is prone to stress concentration, thereby reducing the high-temperature creep performance of the material.

[0113] Further, high temperature creep samples were cut from samples 1, 2, 3, 4, 8, 9, 10, 11, and 12 for high temperature stress rupture testing. The samples were taken from the middle thickness region of the furnace tube and were processed along the axial direction of the furnace tube. The diameter of the tensile section was 8 mm. The test covered three different temperature and stress conditions to simulate the actual load behavior of the material in harsh service environments, including 1100°C, 16.5 MPa; 1175°C, 11.5 MPa, and 1150°C, 9 MPa. Under each condition, the sample was continuously loaded at a constant temperature and stress until it fractured, and the fracture time (in hours) was recorded. The high temperature stress rupture performance of the material at different temperatures and times was evaluated uniformly by the Larsen-Miller Parameter (LMP) method.

[0114] The LMP calculation formula used for evaluation is as follows:

[0115] LMP value = (test temperature (°C) + 273.15) / 1000 * (20 + Log(fracture time (hours))).

[0116] The calculated LMP value was taken as the abscissa, and the corresponding test stress value was taken as the ordinate to draw the stress-LMP curve of the sample, which was used to evaluate the stress rupture strength level of the material. According to this method, under the same temperature and stress conditions, the longer the fracture time, the greater the corresponding LMP value, indicating that the high temperature stress rupture performance of the material is superior. The test results are shown in Table 2. Figure 5

[0117] According to the calculation results and the attached Figure 5 It can be seen that the M 23 The volume percentage content (f1%) of the C6 precipitated phase of samples 1, 2, 3, and 4 was greater than 2%, and the volume percentage content (f2%) of the AlN precipitated phase was less than 0.05%, meeting the requirements of the present application for f1 and f2. Under a stress of 10 MPa, the LMP value was between 33 and 33.5. The M 23 The volume percentage content (f1%) of the C6 precipitated phase of samples 8 and 9 was close to 0, and the volume percentage content (f2%) of the AlN precipitated phase was less than 0.05%, meeting the requirement of the present application for f2 but not meeting the requirement of the present application for f1. Under a stress of 10 MPa, the LMP value was about 32, which was lower than that of samples 1-4, and the stress rupture performance was general. The M 23 ​The volume percentage of C6 precipitate (f1%) is greater than 5%, and the volume percentage of AlN precipitate (f2%) is greater than 2%, which meets the requirements of this invention for the f1 value, but does not meet the requirements of this invention for the f2 value. Under a stress of 10 MPa, its LMP value is about 31-31.5, which is lower than that of samples 1-4, and its creep performance is generally poor.

[0118] It can be seen that the high-temperature durability of the material is affected by M 23 The combined effect of C6 and AlN precipitates shows that if f1% is too small, the strengthening effect is not obvious; if f2% is too large, too much brittle phase precipitates, which exacerbates the failure risk. Only when f1% ≥ 2% and f2% < 0.05% does the material exhibit optimal creep resistance and high-temperature fracture life.

[0119] Furthermore, high-temperature oxidation samples were taken from samples 1, 2, 4, 5, 6, 7, 12, 13, 14, and 15 to conduct high-temperature cyclic oxidation tests. The samples were taken from the furnace tube and had a size of 20mm × 20mm × 2mm. The surface of the samples was machined to a surface roughness Ra≈3.2μm. The test surface was perpendicular to the radial direction of the furnace tube to simulate the oxidation behavior of the outer surface of the furnace tube in actual service.

[0120] The testing process includes:

[0121] The pre-oxidation treatment of the high-temperature oxidation sample is as follows: the sample is placed in an atmosphere composed of 10 vol% water vapor and 90 vol% inert gas, heated from room temperature to 900℃ at a rate of 50℃ / h and held at that temperature for 24 hours, and then cooled to 500℃ at a rate of 50℃ / h. The furnace is then stopped and cooled to room temperature to obtain the pre-oxidized sample.

[0122] Weigh the pre-oxidized sample and record its initial mass;

[0123] To simulate the thermal stress and oxide film response behavior caused by repeated heating-holding-cooling under actual service conditions, high-temperature cyclic oxidation treatment was carried out on pre-oxidized samples. The pre-oxidized samples were placed in an air atmosphere for 100 thermal cycles. Each thermal cycle included: heating from room temperature to 1160℃ at a rate of 50℃ / h, holding at 1160℃ for 30 min, cooling to 500℃ at a rate of 50℃ / h, and then cooling to room temperature. After every 10 thermal cycles, the samples were taken out and weighed, and the mass change was recorded to evaluate the growth behavior or peeling degree of the oxide film.

[0124] The test results are attached. Figure 6 As shown.

[0125] Based on the calculation results and appendix Figure 6It can be seen that the f3 values of samples 1, 2 and 4 are all greater than 0, the change range of sample mass is small in high-temperature cyclic oxidation, the oxidation film growth process is stable, and the peeling rate is low, which indicates that the oxidation film formed has good compactness and adhesion, can effectively block the diffusion of oxygen, prevent further oxidation of the matrix, and exhibits excellent high-temperature oxidation resistance.

[0126] The f3 values of samples 5, 6, 7 and 15 are between -2 and 0, the sample mass fluctuates greatly in the high-temperature cyclic oxidation process, the oxidation film starts to peel off after about 10-20 cycles, resulting in a decrease in the total mass of the material, indicating that the stability and adhesion of the oxidation film are poor, and the oxidation resistance is limited.

[0127] Sample 12 (28 / 48 alloy) is a commonly used high-temperature material, and its oxidation film is mainly composed of Cr2O3. In the high-temperature cyclic oxidation process, there is a significant peeling phenomenon of the oxidation film, which reflects the insufficient stability of the Cr2O3 film in a high-temperature environment, and it is difficult to meet the requirements for the adhesion and integrity of the oxidation film under long-term service conditions.

[0128] In sample 13, the contents of Si and Mn elements exceed the requirements of the present application, and the oxides corresponding to Mn and Si elements are unstable and decompose at high temperatures, affecting the stability of AL2O3 and Cr2O3, resulting in peeling of the oxidation scale.

[0129] In sample 14, the content of S element exceeds the requirements of the present application, and the content of Y element is lower than the requirements of the present application, which affects the adhesion of the Al2O3 film and reduces its stability.

[0130] From the above test results, it can be seen that the material meeting the requirements of element composition, content range and f3 value of the present application can maintain excellent oxidation resistance at high temperature (1160℃).

[0131] It should be noted that the above only describes the preferred embodiments of the present application, which should not limit the protection scope of the technical solutions of the present application. Any modifications made by those skilled in the art to the technical solutions described in the foregoing embodiments, equivalent replacements of technical features, etc. should be included in the protection scope of the present application.

Claims

1. A high temperature resistant austenitic heat resistant cast alloy material, characterized in that, It comprises the following mass percentage of elements: 0.1-0.6% of C element, greater than 0 and less than 0.5% of Si element, greater than 0 and less than 0.3% of Mn element, 20-35% of Cr element, 1.5-5% of Al element, 0.2-1.5% of Nb element, greater than 0 and less than 0.5 of Ti element, greater than 0 and less than 0.1% of Zr element, greater than 0 and less than 0.2% of N element, greater than 0 and less than 5% of Mo element, greater than 0 and less than 5% of W element, 0.01-0.1% of Y element, 50-65% of Ni element and the balance of Fe; and wherein the mass percentage of C element, Cr element, Al element and Ti element satisfies that the value of f1 obtained by the following calculation model, i.e. Model 1, is f1%≥2%: ； Wherein, X_C, X_Cr, X_Al, X_Ti represent the numerical value of the mass percentage of C element, Cr element, Al element and Ti element in the alloy material respectively, T represents the absolute temperature of the application environment of the alloy material, a1-a6 are fitting coefficients, and the values are a1=2.5695, a2=0.8190, a3=0.5972, a4=-7.2163, a5=-21.0258, a6=-862.4308.

2. The high-chromium, high-temperature, austenitic, cast heat-resistant alloy material of claim 1, wherein, It comprises the following mass percentage of elements: 0.1-0.6% of C element, greater than 0 and less than 0.5% of Si element, greater than 0 and less than 0.3% of Mn element, 20-35% of Cr element, 1.5-5% of Al element, 0.2-1.5% of Nb element, greater than 0 and less than 0.5 of Ti element, greater than 0 and less than 0.1% of Zr element, greater than 0 and less than 0.2% of N element, greater than 0 and less than 5% of Mo element, greater than 0 and less than 5% of W element, 0.01-0.1% of Y element, 50-65% of Ni element and the balance of Fe; and wherein the mass percentage of C element, Cr element, Al element and Ti element satisfies that the value of f1 obtained by the following calculation model, i.e. Model 1, is f1%≥2%:

3. The high-chromium, high-temperature, austenitic, cast heat-resistant alloy material of claim 1, wherein, Wherein, X_C, X_Cr, X_Al, X_Ti represent the numerical value of the mass percentage of C element, Cr element, Al element and Ti element in the alloy material respectively, T represents the absolute temperature of the application environment of the alloy material, a1-a6 are fitting coefficients, and the values are a1=2.5695, a2=0.8190, a3=0.5972, a4=-7.2163, a5=-21.0258, a6=-862.4308.

4. The refractory austenitic heat resistant cast alloy material of claim 1, wherein, It further contains impurity elements with a mass percentage of less than 400ppm, and the impurity elements include S element with a mass percentage of less than 100ppm and P element with a mass percentage of less than 300ppm. ； Wherein the mass percentage of Si element, Mn element, Y element and S element satisfies that the value of f3 obtained by the following calculation model, i.e. Model 3, is f3%>0:

5. The refractory austenitic heat resistant cast alloy material of claim 1, wherein, Wherein, X_Si, X_Mn, X_Y, X_S represent the numerical value of the mass percentage of Si element, Mn element, Y element and S element in the alloy material respectively, c1-c5 are fitting coefficients, and the values are c1=-0.5055, c2=-0.5401, c3=1.7910, c4=-0.0994, c5=-0.0367.

6. The high-chromium, high-temperature, austenitic, cast heat-resistant alloy material of claim 5, wherein, ​ ； ​ 7. The refractory austenitic heat resistant cast alloy material of claim 1, wherein, The mass percentage of the elements is: 0.4-0.5% of C element, 0.005-0.2% of Si element, 0.005-0.1% of Mn element, 25-29% of Cr element, 1.5-4% of Al element, 0.5-1.1% of Nb element, 0.1-0.3% of Ti element, 0.005-0.01% of Zr element, 0.03-0.04% of N element, 0.01-0.1% of Mo element, 0.01-0.05% of W element, 0.01-0.03% of Y element, 55-65% of Ni element and the balance of Fe.

8. Use of the high-temperature-resistant austenitic heat-resistant cast alloy material according to any one of claims 1-6 in a heat-resistant structure at 1100℃ or above.

9. Use according to claim 8, comprising: The high-temperature-resistant austenitic heat-resistant cast alloy material is formed into the heat-resistant structure and subjected to a pre-oxidation treatment.

10. Use according to claim 9, characterized in that, The pre-oxidation treatment comprises: heating from room temperature to 850-950℃ at a heating rate of 45-55℃ / h in a mixed atmosphere, and then holding for 12-36h, wherein the mixed atmosphere comprises water vapor with a volume percentage of less than 10% and an inert atmosphere with a volume percentage of more than 90%.

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