High-temperature-resistant austenite heat-resistant casting alloy material and application method thereof

Abstract

The invention discloses a high-temperature-resistant austenite heat-resistant casting alloy material and an application method thereof, and belongs to the technical field of austenite heat-resistant casting 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 content. Wherein the mass percentage contents of the C, Cr, Al and Ti elements meet the condition that the value of f1 obtained by the calculation model 1 meets the condition that f1% is larger than or equal to 2%, and f1% represents the volume percentage content of an M23C6 precipitated phase of the alloy material at the application temperature of 1100 DEG C or above. The alloy material obtained by the invention has remarkable high-temperature creep resistance in an extreme high-temperature environment, has a stable and compact oxidation film and reinforced carbide, and can keep excellent structural stability and high-temperature mechanical properties under a long-term service condition.

Description

Technical Field

[0001] The present invention relates to the technical field of austenitic heat-resistant casting alloy materials, and in particular to a high-temperature resistant austenitic heat-resistant casting alloy material. Background Art

[0002] Austenitic heat-resistant casting alloys are a type of casting alloy with a face-centered cubic (FCC) austenite matrix that can maintain structural stability and mechanical properties at high temperatures. They are suitable for high-temperature components with complex shapes, such as the outlet reformer tubes in iron ore reduction hydrogen production equipment and structural components of high-temperature heat treatment furnaces.

[0003] However, it was found in actual production that the outlet conversion furnace tubes and structural components of the high-temperature heat treatment furnace in the iron ore reduction hydrogen production device need to work for a long time under high-temperature conditions of 1100-1200℃. This temperature is close to the melting point of metal materials at 1400℃, which is an extreme working condition for metal materials. It places extremely high demands on the high-temperature mechanical properties and anti-oxidation corrosion capabilities of the materials.

[0004] Currently, austenitic heat-resistant casting alloys such as ZG45Ni48Cr28W5 (corresponding to G-NiCr28W in the EU EN10027 standard, hereinafter referred to as alloy 28 / 48) are widely used in engineering. They have certain durability in high-temperature environments below 1100℃, but are prone to failure in high-temperature atmospheres above 1100℃. The main failure mechanisms include: (1) the creep rate of the material is significantly accelerated under long-term high-temperature stress, resulting in high-temperature creep deformation, which leads to a decrease in bearing capacity; (2) the surface of the material mainly relies on the Cr2O3 oxide film as a protective layer, but the stability of this oxide film drops sharply above 1100℃, especially in a reducing atmosphere containing water vapor, and it is very easy to decompose or peel off, causing the metal matrix to be directly exposed to high-temperature, reducing atmospheres, resulting in internal and external corrosion reactions, leading to material failure; (3) the strengthening carbides in the material alloy structure will decompose at high temperatures, aggravating the deterioration of the material's mechanical properties and structural stability. Under the combined effect of the above degradation mechanisms, the service life of key components such as furnace tubes is significantly lower than the design expectations. The failure of the material further limits the temperature stability of the device and the further increase of temperature, affecting the process efficiency and production capacity release of the device. Summary of the Invention

[0005] In response to the defects of the prior art, the purpose of the present invention is to provide a high-temperature resistant austenitic heat-resistant casting alloy material, which has significant resistance to high-temperature creep in extreme high-temperature environments above 1100-1200°C, can form a stable and dense oxide film and stable reinforced carbides, and can maintain excellent structural stability and high-temperature mechanical properties under long-term service conditions. It can meet the comprehensive performance requirements of materials under extreme working conditions and significantly improve the high-temperature use safety, reliability and service life of the material.

[0006] The technical solutions of the present invention are as follows: A high-temperature resistant austenitic heat-resistant casting alloy material, comprising the following elements in percentage by mass: 0.1-0.6% of C, greater than 0 and less than 0.5% of Si, greater than 0 and less than 0.3% of Mn, 20-35% of Cr, 1.5-5% of Al, 0.2-1.5% of Nb, greater than 0 and less than 0.5% of Ti, greater than 0 and less than 0.1% of Zr, greater than 0 and less than 0.2% of N, greater than 0 and less than 5% of Mo, greater than 0 and less than 5% of W, 0.01-0.1% of Y, 50-65% of Ni, and the balance of Fe; wherein the mass percentages of C, Cr, Al, and Ti satisfy that the value of f1 obtained by the following calculation model, i.e., model 1, meets f1%≥2%, i.e., f1≥2:

[0007] Wherein, X_C, X_Cr, X_Al, and X_Ti represent the mass percentages of C, Cr, Al, and Ti in the alloy materials, respectively (i.e., values ​​without percentage signs), T represents the absolute temperature of the alloy material's application environment, and a1 to a6 are fitting coefficients with values ​​of a1=2.5695, a2=0.8190, a3=0.5972, a4=-7.2163, a5=-21.0258, and a6=-862.4308, respectively.

[0008] The functions of the elements in the above austenitic heat-resistant casting alloy material of the present invention include: The element C (carbon) can significantly improve the high-temperature creep resistance of alloy materials through carbide precipitation, and also has an important influence on the fluidity of molten steel; The Al (aluminum) element can form a dense and stable alumina film during the high-temperature alloy casting process, significantly improving the alloy material's resistance to high-temperature oxidation and carburization.

[0009] The inventors unexpectedly discovered that to ensure the integrity of the oxide film, the aluminum content should be controlled above 1.5%. However, if it exceeds 5%, a large number of irregular, large-sized precipitates (mainly in the form of NiAl) are easily formed, which destroys the grain structure and weakens the mechanical properties of the material. Therefore, the aluminum content is preferably within the range of 1.5-4%.

[0010] Cr (chromium) element can form a composite oxide film independently or together with aluminum oxide to improve the oxidation resistance and corrosion resistance of the alloy material. In addition, chromium is also a 23 One of the main components of C6 carbide, it helps to enhance the high temperature strength and creep properties of the alloy.

[0011] Nickel (nickel) stabilizes the austenitic structure (face-centered cubic), improving the alloy's high-temperature toughness and plasticity. It also facilitates carbide precipitation, enhancing the alloy's durability and corrosion resistance. However, in coking environments, nickel is also the primary catalytic substrate, and excessive nickel can accelerate the coking process.

[0012] The inventors unexpectedly discovered that the nickel content is preferably in the range of 50-65%.

[0013] Silicon (Si) acts as a deoxidizer in alloy materials, improving the fluidity of molten steel and enhancing the stability of the oxide film by forming a SiO2 film. However, the stability of the SiO2 film is poor at high temperatures, so the silicon content should be controlled within 0.15%.

[0014] The functions of Mn (manganese) include deoxidation and controlling sulfur content to improve the purity of the alloy material. However, when the content is too high, it is easy to generate spinel with poor thermal stability, which reduces the performance of the alloy.

[0015] The inventors unexpectedly discovered that the manganese content is preferably controlled within a range below 0.15%.

[0016] The rare earth element Y (yttrium) can significantly improve the stability of the oxide film and the high-temperature creep performance of the material, thereby extending the service life.

[0017] Tungsten (W) enhances the alloy's long-term strength and thermal stability through solid solution strengthening at high temperatures (~1100°C). However, excessive W content can lead to the precipitation of Laves and σ phases, affecting plasticity and aluminum diffusion, and ultimately weakening the oxide film's stability.

[0018] The inventors unexpectedly discovered that the best overall performance can be achieved by controlling the tungsten content to be below 2%.

[0019] Mo (molybdenum) element can significantly enhance the long-term performance and stability of alloy materials through solid solution strengthening.

[0020] The inventors unexpectedly discovered that the molybdenum content is preferably controlled within a range below 2%.

[0021] Nb (niobium) element mainly precipitates in the form of MC-type carbides, which can significantly improve the rupture strength and creep resistance.

[0022] The inventors unexpectedly discovered that the niobium content is preferably in the range of 0.5-1.1%.

[0023] Ti (titanium) element can not only improve the creep and crack resistance of alloy materials, but also participate in M 23 The formation of C6 carbides has good thermal stability and helps to inhibit grain coarsening and softening.

[0024] The inventors unexpectedly discovered that the titanium content is preferably in the range of 0.05-0.3%.

[0025] The N (nitrogen) element can improve the high-temperature strength, durability and fatigue resistance of the material by precipitating nitrides, but too high a content will affect plasticity and stability.

[0026] The inventors unexpectedly discovered that the nitrogen content is preferably in the range of 0.02-0.1%.

[0027] Zr (zirconium) element can form stable dispersed ZrC carbide, effectively hindering dislocation movement, improving high temperature hardness and creep resistance, and promoting other strengthening phases (such as M 23 The precipitation of C6) can also combine with impurities such as oxygen and sulfur to reduce the inclusion content and improve the uniformity of the structure and casting performance.

[0028] The inventors unexpectedly discovered that the zirconium content preferably ranges from 0.005 to 0.1%, which can achieve dual optimization of strength and creep performance.

[0029] The inventors unexpectedly discovered that in the high temperature range of 1100-1200°C or above, according to the element composition of the present invention, the γ' phase in the alloy material has been completely dissolved and no longer plays a dominant role in the performance of the alloy material, while the high temperature creep performance of the alloy material is mainly affected by the secondary precipitation phase M 23 The influence of C6 carbide precipitation phase. 23 The C6 precipitate phase is dispersed in the matrix and plays a "pinning" role in the creep process of the material, hindering dislocation slip and climb movement, improving creep resistance, and at the same time, it can stabilize the grain boundary structure between dendrites, which is of great significance to the organizational stability and long-term life of the alloy material. 23 The volume fraction of C6 precipitate phase has an important influence on the performance of alloy materials under high temperature service conditions.

[0030] The present invention can quickly and simply obtain the M of the alloy material at an application temperature above 1100°C through the proposed model 1.23 The volume fraction of C6 precipitated phase, further, combined with the unexpected discovery of M 23 When the volume fraction of the C6 precipitated phase is greater than or equal to 2%, it can effectively improve the high-temperature performance of the alloy material and significantly improve its high-temperature creep resistance.

[0031] According to some preferred embodiments of the present invention, the mass percentages of C, Cr, Al and Ti elements in the high-temperature resistant austenitic heat-resistant casting alloy material satisfy the requirement that the value of f1 obtained by model 1 satisfies 2%≤f1%≤10%, i.e., f1 is 2~10.

[0032] According to some preferred embodiments of the present invention, in the high-temperature resistant austenitic heat-resistant casting alloy material, the mass percentages of the Al element and the N element satisfy the following calculation model, i.e., the value of f2 obtained by Model 2, which satisfies f2%≤0.05%, i.e., f2≤0.05:

[0033] Among them, X_Al and X_N represent the mass percentage of Al and N elements in the alloy material, respectively. b1~b3 are fitting coefficients, and their values ​​are: b1=0.0151, b2=2.6775, b3=-0.1274.

[0034] The inventors unexpectedly discovered that the AlN precipitate phase is a brittle second phase with high hardness. It can improve the strength and creep resistance of the alloy material to a certain extent. However, if its content exceeds a certain threshold, it will precipitate in large quantities at the grain boundaries or within the grains, forming a local stress concentration source, weakening the overall toughness of the alloy material, and adversely affecting the high-temperature toughness and service stability of the alloy material. This is particularly evident in cast heat-resistant alloys. During the high-temperature service process of furnace tubes or related structures using cast heat-resistant alloy materials, the combined action of thermal stress and structural stress will further promote the initiation of microcracks in the AlN precipitate phase-enriched area, resulting in a decrease in material plasticity, increased thermal crack sensitivity, and local strain concentration, ultimately significantly shortening 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 within the conventional heat treatment temperature range. Therefore, once it precipitates in excess, the adverse structural structure it forms is difficult to eliminate through subsequent thermal processing or heat treatment processes. Therefore, its formation tendency should be strictly controlled during alloy composition design and smelting.

[0035] The inventors unexpectedly discovered that in industrial practice, the AlN precipitation phase is significantly affected by process conditions. For casting processes carried out in a non-vacuum environment, such as sand casting, demoulding casting, centrifugal casting, etc., the molten steel flows or tumbles violently in the air, and comes into contact with the air, thereby increasing the nitrogen (N) content. Therefore, the precipitation of AlN is closely related to the content of aluminum (Al) and nitrogen (N) elements in the alloy. The present invention further obtains the volume fraction of the AlN precipitate phase of the heat-resistant casting alloy during the solidification process of the molten steel through Model 2, and limits it to below 0.05% based on the inventors' unexpected discovery.

[0036] The inventors unexpectedly discovered that the AlN precipitated phase within this range can enhance the high-temperature performance of the alloy material without weakening its high-temperature plasticity (when its content exceeds 0.05%, it will have a significant adverse effect on the high-temperature plasticity of the alloy material), which helps to improve the comprehensive reliability of the alloy material under high-temperature and complex working conditions.

[0037] According to some preferred embodiments of the present invention, the high-temperature resistant austenitic heat-resistant casting alloy material further contains impurity elements with a mass percentage of less than 400 ppm, and the impurity elements include S element with a mass percentage of less than 100 ppm and P element with a mass percentage of less than 300 ppm.

[0038] In the above preferred embodiment, P (phosphorus) and S (sulfur) are harmful impurities, which are mainly introduced by raw materials. Controlling their contents below 300 ppm and 100 ppm respectively can ensure the high-temperature service performance of the alloy material.

[0039] Further preferably, the mass percentages of Si, Mn, Y and S in the high-temperature resistant austenitic heat-resistant casting alloy material satisfy the requirement that the value of f3 obtained by the following calculation model, i.e., Model 3, satisfies f3%>0:

[0040] Among them, X_Si, X_Mn, X_Y, and X_S represent the mass percentages of Si, Mn, Y, and S in the alloy materials, respectively. c1 to c5 are fitting coefficients, with values ​​of c1=-0.5055, c2=-0.5401, c3=1.7910, c4=-0.0994, and c5=-0.0367, respectively.

[0041] The inventors unexpectedly discovered that in high-temperature oxidizing environments, the integrity of the oxide film on the material's surface directly determines its high-temperature service life. If the oxide film is loose or unstable, it can easily lead to internal and external oxidation, which, in synergistically with high-temperature creep, accelerates material failure. This is particularly critical at operating temperatures above 1100-1200°C. Under varying atmospheric conditions (such as oxygen and water vapor partial pressures), depending on the elemental composition of the present invention, various oxidation products may form on the alloy surface, such as spinel FeMn2O4, SiO2, Cr2O3, and Al2O3. Among them, FeMn2O4 is unstable in reducing or low-oxygen environments and may decompose into FeO and MnO, resulting in structural instability, cracking or localized shedding of the oxide film, destroying the overall protectiveness; SiO2 is formed by the Si element below the inner layer of Cr2O3 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 temperatures to form silicates, weakening the structural integrity of the oxide film; Cr2O3 is one of the main protective oxides, but at high temperatures above 1000°C, especially when further exposed to water vapor, Cr2O3 is unstable and prone to decomposition; in contrast, Al2O3 has extremely high thermal stability and low oxygen diffusivity, making it the highest-quality protective oxide film.

[0042] The inventors unexpectedly discovered that when an alloy material contains appropriate amounts of Al and Cr, the oxide film is primarily composed of a composite oxide of α-Al2O3 and Cr2O3, with Al2O3 located in the outermost layer of the oxide film and Cr2O3 beneath it. The alloy material's high-temperature corrosion resistance primarily depends on Al2O3. When sufficient Al is present in the alloy matrix, new Al2O3 is continuously produced through diffusion within the matrix, improving the material's high-temperature corrosion resistance. Furthermore, the inventors unexpectedly discovered that the stability of the Al2O3 film is also related to the S and Y elements in the alloy material. Adding a trace amount of Y helps stabilize the Al2O3 film structure and enhances its adhesion, while an excess of S tends to form weak connections at grain boundaries, reducing the film's integrity.

[0043] 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, avoid the interference of FeMn2O4 and SiO2, and reasonably control the content of Y and S elements.

[0044] The present invention quantitatively evaluates the effect of alloying elements on oxide film stability through Model 3 (obtained according to the relative deviation normalization method). When f3 > 0, it indicates that the oxide film on the surface of the alloy material is stable and suitable for long-term service in a high-temperature oxidizing environment. When f3 < 0, it indicates that the oxide film on the surface of the alloy material is unstable and may peel off or fail to provide protection, making it unsuitable for use in harsh high-temperature operating conditions.

[0045] According to some preferred embodiments of the present invention, the mass percentage range of elements in the high-temperature resistant austenitic heat-resistant casting alloy material is: 0.4~0.5% C element, 0.005~0.2% Si element, 0.005~0.1% Mn element, 25~29% Cr element, 1.5~4% Al element, 0.5~1.1% Nb element, 0.1~0.3% Ti element, 0.005~0.01% Zr element, 0.03~0.04% N element, 0.01~0.1% Mo element, 0.01~0.05% W element, 0.01~0.03% Y element, 55~65% Ni element and the balance Fe.

[0046] The present invention further provides the use of the above-mentioned high-temperature resistant austenitic heat-resistant casting alloy material in heat-resistant structures above 1100°C.

[0047] The heat-resistant structure may be a load-bearing pipe, structural component or device used in high temperature (above 1100°C) working conditions, more specifically, a reduction furnace tube in an iron ore reduction hydrogen production device, a structural component of a high-temperature heat treatment furnace, etc.

[0048] Preferably, the high temperature working condition is a working condition of 1100-1250°C.

[0049] Preferably, the heat-resistant structure is also used in a strong oxidizing and corrosive atmosphere.

[0050] According to some preferred embodiments of the present invention, the application includes: forming the high-temperature resistant austenitic heat-resistant casting alloy material into the heat-resistant structure and performing a pre-oxidation treatment.

[0051] The inventors unexpectedly discovered that, in addition to the preferred alloying element compositions proposed in this invention, pre-oxidation treatment can further enhance the density, continuity, and adhesion of the oxide film on the alloy surface, improving the stability and service life of the oxide film under high-temperature service conditions above 1100-1200°C. The mechanism of action is as follows: The oxidation resistance of the alloy material is largely dependent on the composition, crystal structure, microdensity, and adhesion quality of the first oxide film formed on its surface. However, during the initial oxidation stage before actual service, the formation path of the oxide layer is controlled by the combined effect of the alloy material composition and the external oxygen partial pressure.

[0052] 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 lower oxygen partial pressure environment (which can be achieved by regulating the O2 / inert atmosphere ratio) can adjust the starting order of oxidation of alloy elements, promote the preferential oxidation of aluminum, and form a stable and dense α-Al2O3 oxide film on the surface of the alloy material, thereby avoiding the formation of non-protective oxides of elements such as Fe and Mn, and reducing the formation of interface defects or multiphase regions between the film / substrate.

[0053] At the same time, the inventors unexpectedly discovered that the synergistic effect of a slower heating rate and a preferred oxygen partial pressure can promote the formation of a more uniformly structured microcrystalline or subcrystalline α-Al2O3 film, whose density and adhesion are significantly better than the coarse-grained film formed by rapid oxidation. It not only has an excellent barrier effect on oxygen diffusion, but also can improve the thermal stress coordination between the film and the substrate, effectively avoiding peeling, cracking or failure of the oxide film during thermal cycling.

[0054] 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 keeping warm 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%.

[0055] 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.

[0056] In addition, when the alloy material experiences large temperature fluctuations, such as a sudden drop in temperature due to equipment shutdown, microcracks, holes or peeling may appear on its surface oxide film, affecting its protective function. Therefore, before the furnace tube is put back into use, pre-oxidation treatment can be implemented again to repair and rebuild the surface protective film structure to ensure stable and reliable material performance.

[0057] The inert atmosphere includes argon and / or nitrogen.

[0058] The high-temperature resistant austenitic heat-resistant casting alloy material obtained by the present invention has significant high-temperature creep resistance in extreme high-temperature environments above 1100-1200°C, can form a stable and dense oxide film and stable reinforced carbides, and can maintain excellent structural stability and high-temperature mechanical properties under long-term service conditions. It can meet the comprehensive performance requirements of materials under extreme working conditions and significantly improve the high-temperature use safety, reliability and service life of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1M is obtained by simulation with JMatPro software and calculation with formula 1 for samples 1, 2, 3, 4, 8, 9, 10 and 11 in the embodiment. 23 Comparison of volume fraction of C6 precipitate phase.

[0060] Figure 2 This is a comparison chart of the volume fraction of AlN precipitated phase obtained by JMatPro software simulation and formula 2 for samples 1, 2, 3, 4, 10 and 11 in the embodiment.

[0061] Figure 3 These are the SEM and energy spectrum images of sample 3 in the embodiment.

[0062] Figure 4 1 and 2 are SEM and energy spectrum images of sample 10 in the embodiment.

[0063] Figure 5 1 is a stress-LMP curve diagram of samples 1, 2, 3, 4, 8, 9, 10, 11, and 12 obtained in the examples.

[0064] Figure 6 Graph showing weight gain of samples 1, 2, 4, 5, 6, 7, 12, 13, 14 and 15 obtained in the examples. DETAILED DESCRIPTION

[0065] The technical solutions of the present invention will be further described below in conjunction with the embodiments and drawings of the present invention. The embodiments described below are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0066] The furnace tube samples described in the following examples were obtained by centrifugal casting under the same process conditions. The furnace tubes had an outer diameter of 110 mm, an inner diameter of 90 mm, and a wall thickness of 10 mm.

[0067] The f1 value, f2 value, and f3 value described in the following embodiments are the values ​​of functions f1, f2, and f3 obtained according to the following calculation models (hereinafter referred to as Formulas 1, 2, and 3, respectively):

[0068] Wherein, X_C, X_Cr, X_Al, and X_Ti represent the mass percentages of carbon, chromium, aluminum, and titanium in the alloy material, respectively (i.e., values ​​without percentage signs), T represents the absolute temperature (unit: K) of the material application environment (set to 1100°C in this embodiment), and a1-a6 are fitting coefficients, with values ​​of a1=2.5695, a2=0.8190, a3=0.5972, a4=-7.2163, a5=-21.0258, and a6=-862.4308, respectively.

[0069]

[0070] Where X_Al and X_N represent the mass percentages of aluminum and nitrogen in the alloy material, respectively (i.e., values ​​without percentage signs), and b1 to b3 are fitting coefficients with values ​​of b1=0.0151, b2=2.6775, and b3=-0.1274, respectively.

[0071]

[0072] Where X_Si, X_Mn, X_Y, and X_S represent the mass percentages of silicon, manganese, yttrium, and sulfur in the alloy, respectively (i.e., values ​​without percentage signs). c1–c5 are fitting coefficients, with values ​​of c1=-0.5055, c2=-0.5401, c3=1.7910, c4=-0.0994, and c5=-0.0367, respectively.

[0073] The JMatPro software described in the following examples is a commercial software that simulates the phase transformation behavior of alloys with different compositions at a given temperature based on the CALPHAD method, combining a thermodynamic database with a diffusion kinetics model, and outputs the volume fraction of the corresponding precipitated phase. (Although this software has high accuracy, its complex model structure, numerous parameters involved, and insufficient coverage of some nickel-based casting alloy systems in the current database have certain limitations in its application in actual factory production, material screening, and quality control. Formulas 1-3 constructed in the present invention are empirical prediction models based on the content of major alloying elements and temperature parameters. They are simpler in form, more convenient for rapid estimation and parameter optimization, and are particularly suitable for initial screening and rapid decision-making of heat-resistant alloy materials in research and development and engineering applications.)

[0074] Examples 1-4 Four furnace tube samples made of austenitic heat-resistant casting alloy materials, namely samples 1-4, are provided. The component contents and corresponding f1, f2, and f3 values ​​are shown in Table 1 below: Table 1 Component contents and f1-f3 values ​​of samples 1-4

[0075] Comparative Examples 1-3 Comparative Examples 1-3 provide furnace tube samples made of three austenitic heat-resistant casting alloy materials, namely samples 5-7, whose component contents and corresponding f1, f2, and f3 values ​​are shown in Table 2 below: Table 2 Component contents and f1-f3 values ​​of samples 5-7

[0076] Comparative Examples 4-5 Comparative Examples 4-5 provide furnace tube samples made of two austenitic heat-resistant casting alloy materials, namely samples 8-9, whose component contents and corresponding f1, f2, and f3 values ​​are shown in Table 3 below: Table 3 Component contents and f1-f3 values ​​of samples 8-9

[0077] Comparative Examples 6-7 Comparative Examples 6-7 provide furnace tube samples 10-11 made of two austenitic heat-resistant casting alloy materials, and their component contents and corresponding f1, f2, and f3 values ​​are shown in Table 4 below: Table 4 Component contents and f1-f3 values ​​of samples 10-11

[0078] Comparative Example 8 Comparative Example 8 provides a furnace tube sample, Sample 12, made of an austenitic heat-resistant casting alloy material ZG45Ni48Cr28W5 (Alloy 28 / 48), which is widely used in the prior art. The component contents and corresponding f1, f2, and f3 values ​​are shown in Table 5 below: Table 5 Component contents and f1-f3 values ​​of sample 12

[0079] Comparative Examples 9-11 Comparative Examples 9-11 provide furnace tube samples 13-15 made of three austenitic heat-resistant casting alloy materials, and their component contents and corresponding f1, f2, and f3 values ​​are shown in Table 6 below: Table 6 Component contents and f1-f3 values ​​of samples 13-15

[0080] Sample analysis: Under the steady-state condition of 1100℃ (1373.15K), the above samples 1, 2, 3, 4, 8, 9, 10 and 11 were selected and the M content in the alloy was calculated using JMatPro software simulation and formula 1. 23 The volume fraction of C6 carbide precipitation phase 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 drawings).

[0081] By attaching Figure 1 It can be seen that the simulation data obtained by JmatPro software is consistent with the M calculated by formula 1. 23 The volume fraction distribution range of C6 carbide precipitation phase is roughly the same, both between 0-8%, covering a wide range of material composition and tissue response range; 23 When the volume fraction of C6 carbide precipitation phase ≥2% is taken as the effective range for strengthening effect, the calculation results of formula 1 are consistent with the prediction trend of JMatPro software.

[0082] Under the steady-state condition of the complete solidification temperature of molten steel (about 1350℃, 1623.15K), the above samples 1, 2, 3, 4, 10 and 11 were selected and the volume fraction of AlN precipitate phase in the alloy was calculated using JMatPro software simulation and formula 2. The results are shown in the attached figure. Figure 2 shown.

[0083] By attaching Figure 2 It can be seen that the volume fraction distribution range of the AlN precipitate phase obtained by the simulation data obtained by the JmatPro software is roughly the same as that calculated by Formula 2. This indicates that when the volume fraction of the AlN precipitate phase is ≤0.05% as the effective interval for strengthening, the calculation results of Formula 2 are consistent with the prediction trend of the JMatPro software.

[0084] In order to evaluate the prediction reliability of formulas 1 and 2 under actual conditions, representative samples 3 and 10 were selected and subjected to high-temperature heat treatment at 1100℃ for 2000 hours, followed by water quenching to retain their microstructures in the high-temperature stable state. The carbide precipitation was observed by scanning electron microscopy and energy spectrum analysis. Sample 3 was mainly used to observe M 23 The volume percentage of the C6 precipitated phase was divided by ImageJ software. The results are shown in the attached figure. Figure 3 Sample 10 was mainly used to observe the volume percentage of AlN precipitated phase. Because its precipitated content was much lower than 1%, it was difficult to analyze it using ImageJ software. Therefore, it was magnified by electron microscope. The presence of AlN phase was found and confirmed by magnifying the image. The results are shown in the attached figure. Figure 4 As shown in the figure (where Selected Area 1 indicates the area selected for the energy spectrum test, and EDS spot 1 indicates the test point selected for the energy spectrum test).

[0085] By attaching Figure 3It can be seen that the microstructure of sample 3 mainly includes MC phase (M is mainly Nb element, that is, forming NbC phase) and M 23 C6 phase (M is mainly Cr element), where M 23 C6 phase is dispersed in the material, and some M 23 The C6 phase is slightly coarse. The grayscale calculation by ImageJ software shows that the M 23 The volume percentage of C6 phase is 4.87%, which is close to the f1 value (5.73%), indicating that the M 23 The C6 phase exists stably for a long time at 1100℃ and is dispersed inside the material, which can optimize the high-temperature creep performance of the material. Its actual observed volume percentage is close to the predicted result of the f1 value.

[0086] By attaching Figure 4 It can be seen that in a very small observation area, the microstructure of sample 10 includes M 23 C6 phase and AlN phase, among which the AlN phase has a microscopic morphology that is significantly different from other precipitated phases, and its edges and corners 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 shows that the AlN phase in sample 10 exists stably for a long time at 1100°C, and its microstructure is prone to stress concentration, thereby reducing the high-temperature creep performance of the material.

[0087] Furthermore, high-temperature creep specimens were taken from Samples 1, 2, 3, 4, 8, 9, 10, 11, and 12 for high-temperature durability testing. These specimens were taken from the mid-thickness region of the furnace tube and machined along the tube axis. The tensile section had an 8mm diameter. The tests covered three different temperature and stress conditions to simulate the material's actual load-bearing behavior under harsh service conditions: 1100°C, 16.5 MPa; 1175°C, 11.5 MPa; and 1150°C, 9 MPa. Under each condition, the specimens were continuously loaded at a constant temperature and stress until fracture, and the time to fracture was recorded (in hours). The Larsen-Miller Parameter (LMP) method was used to uniformly evaluate the high-temperature durability of the materials under different temperature and time conditions.

[0088] The LMP calculation formula used in the evaluation is as follows: LMP value = (test temperature (°C) + 273.15) / 1000 * (20 + Log (break time (hours))).

[0089] The calculated LMP value is used as the horizontal axis and the corresponding test stress value is used as the vertical axis to draw the stress-LMP curve of the sample to evaluate the endurance strength level of the material. According to this method, under the same temperature and stress conditions, the longer the fracture time, the larger the corresponding LMP value, indicating that the material has better high-temperature endurance performance. The test results are shown in the attached Figure 5 shown.

[0090] According to the calculation results and Figure 5 It can be seen that the M of samples 1, 2, 3, and 4 23 The volume percentage of C6 precipitated phase (f1%) is greater than 2%, concentrated between 4-6%, and the volume percentage of AlN precipitated phase (f2%) is less than 0.05%, meeting the requirements of the present invention for f1 and f2 values. Under the condition of stress of 10 MPa, its LMP value is between 33-33.5. 23 The volume percentage of the C6 precipitated phase (f1%) is close to 0, and the volume percentage of the AlN precipitated phase (f2%) is lower than 0.05%, which meets the requirement of the present invention for the f2 value, but does not meet the requirement of the present invention for the f1 value. Under the condition of a stress of 10 MPa, its LMP value is about 32, which is lower than that of samples 1-4, and the endurance performance is average; the M values ​​of samples 10 and 11 are 23 The volume percentage of the C6 precipitated phase (f1%) is greater than 5%, and the volume percentage of the AlN precipitated phase (f2%) is above 2%, which meets the requirement of the present invention for the f1 value, but does not meet the requirement of the present invention for the f2 value. Under the condition of a stress of 10 MPa, the LMP value is approximately 31-31.5, which is lower than that of samples 1-4, and the endurance performance is average.

[0091] It can be seen that the high temperature durability of the material is affected by M 23 The C6 precipitation phase and the AlN precipitation phase have a joint influence. If f1% is too small, the strengthening effect is not obvious. If f2% is too large, the brittle phase of the material will precipitate too much, which will increase the failure risk. Only when f1% ≥ 2% and f2% < 0.05%, the material will show the best creep resistance and high temperature fracture life. Furthermore, high-temperature oxidation specimens were taken from samples 1, 2, 4, 5, 6, 7, 12, 13, 14, and 15 to carry out high-temperature cyclic oxidation tests. The specimens were taken from the furnace tubes and had dimensions of 20 mm × 20 mm × 2 mm. The surface of the specimens was machined to a surface roughness of Ra ≈ 3.2 μm. 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.

[0092] The testing process includes: The high-temperature oxidation sample was subjected to a pre-oxidation treatment, which was as follows: the sample was placed in an atmosphere composed of 10 vol% water vapor and 90 vol% inert gas, heated from room temperature to 900°C at a rate of 50°C / h, kept at that temperature for 24 hours, then cooled to 500°C at a rate of 50°C / h, and then cooled to room temperature to obtain a pre-oxidation sample; Weigh the pre-oxidized sample and record its initial mass; In order to simulate the thermal stress and oxide film response behavior caused by repeated heating-holding-cooling of materials under actual service conditions, high-temperature cyclic oxidation treatment was carried out on the 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 minutes, then cooling to 500℃ at a rate of 50℃ / h, and stopping the furnace to cool to room temperature. After completing 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.

[0093] The test results are as attached Figure 6 shown.

[0094] According to the calculation results and Figure 6 It can be seen that the f3 values ​​of samples 1, 2 and 4 are all greater than 0. During high-temperature cyclic oxidation, the change in sample mass is small, the oxide film growth process is stable, and the peeling rate is low, indicating that the oxide film formed has good density and adhesion, can effectively block oxygen diffusion, prevent further oxidation of the substrate, and exhibit excellent high-temperature antioxidant properties.

[0095] The f3 values ​​of samples 5, 6, 7 and 15 are between -2 and 0. During the high-temperature cyclic oxidation process, the sample mass fluctuates greatly. The oxide film begins 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 oxide film are poor and the antioxidant performance is limited.

[0096] Sample 12 (28 / 48 alloy) is a commonly used high-temperature material. Its oxide film is mainly composed of Cr2O3. There is obvious oxide film peeling during the high-temperature cyclic oxidation process, reflecting that the Cr2O3 film is not stable enough in high-temperature environments and it is difficult to meet the requirements for oxide film adhesion and integrity under long-term service conditions.

[0097] The Si and Mn contents in Sample 13 exceeded the requirements of the present invention. Mn and Si formed corresponding oxides, which were unstable and decomposed at high temperatures, affecting the stability of Al2O3 and Cr2O3 and causing oxide scale shedding.

[0098] The S content in sample 14 exceeds the requirements of the present invention, and the Y content is lower than the requirements of the present invention, which affects the adhesion of the Al2O3 film and reduces its stability.

[0099] It can be seen from the above test results that the materials meeting the element composition, content range and f3 value requirements of the present invention can maintain excellent antioxidant properties at high temperatures (1160°C).

[0100] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the technical solutions of the present invention. Any modifications to the technical solutions described in the aforementioned embodiments, or equivalent replacements of technical features made by persons of ordinary skill in the art that fall within the spirit and principles of the present invention, shall be included within the scope of protection of the present invention.

Claims

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

2. The high temperature resistant austenitic heat resistant casting alloy material according to claim 1, characterized in that: These include: 1.5~4% Al element, greater than 0 and less than or equal to 0.15% Si element, greater than 0 and less than or equal to 0.15% Mn element, greater than 0 and less than or equal to 2% W element, greater than 0 and less than or equal to 2% Mo element, 0.5~1.1% Nb element, 0.05~0.3% Ti element, 0.02~0.1% N element and 0.005~0.1% Zr element.

3. The high temperature resistant austenitic heat resistant casting alloy material according to claim 1, characterized in that: The mass percentage contents of C, Cr, Al and Ti elements satisfy the requirement that the value of f1 obtained by model 1 complies with 2%≤f1%≤10%.

4. The high temperature resistant austenitic heat resistant casting alloy material according to claim 1, characterized in that: The mass percentages of Al and N satisfy the following calculation model, i.e., the value of f2 obtained by Model 2, which satisfies f2%≤0.05%. ； Among them, X_Al and X_N represent the mass percentage of Al and N elements in the alloy material, respectively. b1~b3 are fitting coefficients, and their values ​​are: b1=0.0151, b2=2.6775, b3=-0.1274.

5. The high temperature resistant austenitic heat resistant casting alloy material according to claim 1, characterized in that: It also contains impurity elements with a mass percentage content of less than 400 ppm, including less than 100 ppm of S element and less than 300 ppm of P element.

6. The high temperature resistant austenitic heat resistant casting alloy material according to claim 5, characterized in that: The mass percentages of Si, Mn, Y, and S satisfy the following calculation model, i.e., the value of f3 obtained by Model 3, which satisfies f3%>0: ； Among them, X_Si, X_Mn, X_Y, and X_S represent the mass percentages of Si, Mn, Y, and S in the alloy materials, respectively. c1 to c5 are fitting coefficients, with values ​​of c1=-0.5055, c2=-0.5401, c3=1.7910, c4=-0.0994, and c5=-0.0367, respectively.

7. The high temperature resistant austenitic heat resistant casting alloy material according to claim 1, characterized in that: The mass percentage of elements is: 0.4~0.5% C, 0.005~0.2% Si, 0.005~0.1% Mn, 25~29% Cr, 1.5~4% Al, 0.5~1.1% Nb, 0.1~0.3% Ti, 0.005~0.01% Zr, 0.03~0.04% N, 0.01~0.1% Mo, 0.01~0.05% W, 0.01~0.03% Y, 55~65% Ni and the balance Fe.

8. Use of the high-temperature resistant austenitic heat-resistant casting alloy material according to any one of claims 1 to 6 in heat-resistant structures above 1100°C.

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

10. The use according to claim 9, characterized in that 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 keeping the temperature for 12-36 hours, 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%.

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