Heat treatment method of iron-nickel-based high-temperature alloy

Abstract

The invention discloses a heat treatment method of an iron-nickel-based high-temperature alloy, which solves the contradiction between stress relief annealing and performance maintenance through four-step temperature coordinated regulation and control: in the first step, MC type carbide is dissolved through solid solution, segregation is eliminated, and excessive growth of crystal grains is avoided; in the second step, roughening of M23C6 type carbides is inhibited through solid solution, and formation of fine and uniform carbides on grain boundaries is promoted so as to strengthen the grain boundaries; in the third step, the residual stress is reduced through stress relief annealing, and meanwhile grain boundary carbide growth and abnormal grain growth are avoided; and in the fourth step, uniform and stable precipitation of a gamma'phase is promoted through aging, the nanometer size and the high volume fraction are maintained, and coarsening is avoided. Through precise temperature connection, the residual stress is effectively reduced, grain growth, structure nonuniformity or performance degradation caused by traditional annealing are avoided, and finally the application requirement of the superhigh-temperature steam environment at the temperature of 650 DEG C or above is met on the premise that the mechanical property and the corrosion resistance are guaranteed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature alloy heat treatment and relates to a heat treatment method of iron-nickel-based high-temperature alloy. BACKGROUND

[0002] The iron-nickel-based high-temperature alloy is a kind of high-temperature alloy with γ' (Ni3Al) phase strengthening as the main strengthening mode, has good high-temperature strength, fatigue performance and high-temperature oxidation resistance, and can work in a high-temperature environment above 600 DEG C for a long time. Meanwhile, compared with the nickel-based high-temperature alloy and the cobalt-based high-temperature alloy, the iron-nickel-based high-temperature alloy has a significant cost-effective advantage and becomes the material most likely to be applied to the key hot end components of a new generation of supercritical coal-fired units.

[0003] To ensure the high-temperature strength of the iron-nickel-based high-temperature alloy, appropriate amounts of C, B, Ti, Al, Mo and W and the like are added to the material to form carbides and γ' phases in the grain boundary and the grain respectively, so as to realize grain boundary strengthening and grain strengthening. Due to the small size (nanometer level) and high volume fraction (usually not less than 30%) of the precipitated phases and the complex deformation process, the formed component has high residual stress. Under the action of the large residual stress, the component is prone to deformation or size change and is also prone to intergranular corrosion cracking. To reduce the residual stress level of the component, the technical personnel usually adopts stress relief annealing to make the alloy relax the residual stress through internal local plastic deformation or local relaxation process at a certain temperature. Generally speaking, a higher annealing temperature can obtain lower residual stress and higher thermal stability, but easily leads to grain growth and non-uniformity of the structure, reduces the mechanical properties and corrosion resistance of the alloy; while a lower annealing temperature can avoid grain growth and non-uniformity of the structure, but needs a longer annealing time and has high cost. Therefore, how to reduce the residual stress of the alloy while not reducing the mechanical properties and chemical properties of the alloy is a problem to be solved by the engineering and technical personnel. SUMMARY

[0004] In view of the problems in the prior art, the application provides a heat treatment method of iron-nickel-based high-temperature alloy, so as to solve the problem that the stress relief annealing technology in the prior art cannot effectively reduce the residual stress of the iron-nickel-based high-temperature alloy while avoiding the reduction of the mechanical properties and corrosion resistance of the alloy due to improper annealing temperature.

[0005] The application is realized by the following technical scheme: The application provides a heat treatment method of iron-nickel-based high-temperature alloy, which comprises the following steps: S1: performing first solid solution treatment on the iron-nickel-based high-temperature alloy, and the temperature of the first solid solution treatment is controlled in the range of 50-150 DEG C above the MC type carbide precipitation temperature; S2: performing second solution treatment on the iron-nickel based superalloy after the first solution treatment, the temperature of the second solution treatment being controlled within 20-60℃ below the temperature of the second solution treatment; 23 C6 type carbide precipitation temperature below 30-80℃; S3: performing stress relief annealing on the iron-nickel based superalloy after the second solution treatment, the temperature of the stress relief annealing being controlled within 20-60℃ below the temperature of the second solution treatment; S4: performing aging treatment on the iron-nickel based superalloy after the stress relief annealing, the temperature of the aging treatment being controlled within 200-300℃ below the γ' phase precipitation temperature.

[0006] Preferably, the temperature of the first solution treatment is 1060-1120℃.

[0007] Preferably, the holding time of the first solution treatment is 30-90 min, and water cooling is performed to room temperature after the holding time.

[0008] Preferably, the temperature of the second solution treatment is 1000-1040℃.

[0009] Preferably, the holding time of the second solution treatment is 30-60 min, and water cooling is performed to room temperature after the holding time.

[0010] Preferably, the temperature of the stress relief annealing is 940-980℃, the holding time is 2-4 h, and air cooling is performed to room temperature after the holding time.

[0011] Preferably, the temperature of the aging treatment is 650-720℃, the holding time is 8-20 h, and air cooling is performed to room temperature after the holding time.

[0012] Preferably, the iron-nickel based superalloy comprises, by weight percentage: 0.03%≤C≤0.1%, 0

[0013] An iron-nickel based superalloy prepared by the above-mentioned heat treatment method, the residual stress of which is ≤50 MPa, the grain size of which is 2-3.5 grade, the yield strength at 700℃ of which is >600 MPa, and the weight gain after oxidation in 700℃ pure steam for 1000 h of which is ≤1mg / cm 2 .

[0014] The above-mentioned iron-nickel based superalloy is applied in the production of nickel-iron based superalloy plates, rods, tubes and forgings for 650℃ grade supercritical coal-fired units.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a heat treatment method for iron-nickel-based superalloys, systematically solving the problem that existing stress-relief annealing techniques struggle to simultaneously reduce residual stress and maintain performance. The core of this method lies in the coordinated control of temperatures at each step: the first step, solution treatment, is controlled at a temperature 50-150°C above the precipitation temperature of MC-type carbides. This temperature, higher than the precipitation temperature of MC-type carbides, effectively dissolves some MC-type carbides, eliminates elemental segregation, and avoids excessive grain growth, providing a uniform matrix structure for subsequent processing; the second step, solution treatment, is lowered to the M... 23 The precipitation temperature of C6 type carbides is 30~80℃ below the precipitation temperature; this temperature range can suppress M 23 The abundant precipitation of C6-type carbides prevents grain boundary weakening and microstructure inhomogeneity caused by their coarsening, while temperature control promotes M 23 C6 nucleates appropriately at grain boundaries, forming fine, uniformly distributed grain boundary carbides, thus achieving grain boundary strengthening. The third step, stress-relief annealing, further lowers the temperature to 20-60°C below the second step's solution temperature. This temperature effectively reduces residual stress within the component through minute, uniform plastic deformation or relaxation processes, preventing stress-induced deformation or stress corrosion cracking. Furthermore, because the temperature is below M... 23 The precipitation temperature of C6 prevents the growth of existing grain boundary carbides, maintaining the grain boundary strengthening effect while avoiding abnormal grain growth. This reduces stress without sacrificing mechanical properties and corrosion resistance. The fourth step, aging treatment, is controlled at 200-300°C below the γ′ phase precipitation temperature. This temperature promotes uniform nucleation, growth, and stabilization of the γ′ phase, ensuring its nanoscale size and high volume fraction, maintaining high-temperature strength and fatigue performance, while avoiding γ′ phase coarsening caused by over-aging, further guaranteeing alloy performance. Through precise temperature control in these four steps, this invention effectively reduces residual stress while avoiding grain growth, uneven microstructure, or performance degradation caused by improper temperature selection in traditional stress-relief annealing. Ultimately, it meets the requirements for key hot-end components of next-generation supercritical coal-fired power units in ultra-high temperature steam environments above 650°C, while ensuring mechanical and corrosion resistance.

[0016] Furthermore, the temperature of the first solution treatment is 1060~1120℃. This temperature range can effectively dissolve some MC-type carbides, eliminate elemental segregation in the cast or deformed alloy, and avoid excessive grain growth. This provides a uniform and refined matrix structure for subsequent heat treatment steps, optimizes the initial microstructure of the alloy from the source, and lays the foundation for subsequent performance control.

[0017] Further, the holding time of the first solution treatment is 30-90 min, and after the holding time, water cooling is performed to room temperature. The holding time can ensure that MC carbide is fully dissolved and elements are uniformly diffused, and effectively eliminates composition segregation. After the holding time, water cooling is performed to room temperature, which inhibits the coarsening of precipitated phases through rapid cooling, maintains the uniformity of the structure, avoids unnecessary phase precipitation due to slow cooling, and ensures the purity and uniformity of the matrix structure.

[0018] Further, the temperature of the second solution treatment is 1000-1040℃, which can inhibit the precipitation of M 23 C6 carbide, prevent the grain boundary weakening and structure inhomogeneity caused by the coarsening of the C6 carbide, and promote the M 23 C6 carbide to moderately nucleate at the grain boundary to form fine and uniformly distributed grain boundary carbide, realize grain boundary strengthening, and balance the grain boundary strength and structure uniformity.

[0019] Further, the holding time of the second solution treatment is 30-60 min, and after the holding time, water cooling is performed to room temperature. The holding time can ensure that M 23 C6 carbide is precisely controlled in terms of morphology, size, and volume fraction, avoids insufficient nucleation caused by too short a time or coarsening caused by too long a time, and after the holding time, water cooling is performed to room temperature to quickly fix the structure state, inhibit the abnormal growth of M 23 C6 carbide during cooling, maintain the fine and uniform distribution characteristics of the C6 carbide, strengthen the grain boundary, and optimize the structure uniformity.

[0020] Further, the temperature of the stress relief annealing is 940-980℃, the holding time is 2-4 h, and after the holding time, air cooling is performed to room temperature. The stress relief annealing temperature can effectively prevent the growth of the formed grain boundary carbide, maintain the grain boundary strengthening effect, and avoid abnormal grain growth while reducing residual stress without sacrificing the mechanical properties and corrosion resistance of the alloy. The holding time of 2-4 h combined with air cooling can balance the stress relaxation efficiency and structure stability, and reduce the cost.

[0021] Further, the temperature of the aging treatment is 650-720℃, the holding time is 8-20 h, and after the holding time, air cooling is performed to room temperature. The aging temperature can effectively promote the uniform nucleation, growth, and stabilization of the γ' phase, ensure its nanoscale size and high volume fraction, and maintain the high-temperature strength and fatigue performance of the alloy. The holding time of 8-20 h combined with air cooling can avoid the coarsening of the γ' phase caused by overaging, further ensure the dispersed distribution characteristics of the strengthening phase, and achieve the balance between strength and toughness.

[0022] Further, the iron-nickel-based high-temperature alloy comprises, in percentage by weight: 0.03%≤C≤0.1%, 0 23 C6) formation, strengthening the grain boundary; B (≤0.006%) improves the grain boundary bonding force and inhibits intergranular corrosion; Cr (15-18%) provides corrosion resistance, especially high-temperature oxidation resistance; Mo (0.5-1%), W (≤1%) improves the strength through solid solution strengthening; Al (1-2.2%), Ti (1.5-3%) forms γ' phase to achieve main strengthening; Fe (40-47%) reduces the cost, and the remaining amount of Ni ensures the continuity of the matrix; the synergistic effect of each element supports the formation and performance of the strengthening phase (γ', carbide), finally realizes the balance of residual stress reduction, mechanical properties and corrosion resistance, and meets the application requirements in the super-high-temperature steam environment above 650°C. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0024] Figure 1 The metallographic picture of the iron-nickel-based high-temperature alloy pipe material after heat treatment in Example 1 of the present application; Figure 2 The metallographic picture of the iron-nickel-based high-temperature alloy pipe material after heat treatment in Example 2 of the present application; Figure 3 The metallographic picture of the iron-nickel-based high-temperature alloy pipe material after heat treatment in Example 3 of the present application; Figure 4 The metallographic picture of the iron-nickel-based high-temperature alloy pipe material after heat treatment in Example 4 of the present application; Figure 5 The metallographic picture of the iron-nickel-based high-temperature alloy pipe material after conventional heat treatment in Comparative Example 1; Figure 6 The metallographic picture of the iron-nickel-based high-temperature alloy pipe material after conventional heat treatment in Comparative Example 2. DETAILED DESCRIPTION

[0025] To enable persons skilled in the art to understand the features and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have their usual meanings to those skilled in the art of the present application, and in the event of conflict, the definitions contained herein prevail.

[0026] Theories and mechanisms described and disclosed herein, whether correct or not, should not be considered limiting on the scope of the present application, i.e., the present application can be practiced without regard to any particular theory or mechanism.

[0027] Herein, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, amounts, contents and concentrations, are for the sake of brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have encompassed and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0028] Herein, unless otherwise specified, "comprise", "include", "contain", "have" or similar words encompass the meaning of "consist of" and "consist essentially of", for example, "A comprises a" encompasses the meaning of "A comprises a and other" and "A comprises only a".

[0029] Herein, for the sake of brevity, all possible combinations of the technical features in each embodiment or example are not described. Therefore, as long as the combinations of the technical features do not contradict each other, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope of the present specification.

[0030] The present application provides a heat treatment method of iron-nickel-based superalloy, which can eliminate the residual stress of the iron-nickel-based superalloy while not reducing its mechanical properties and corrosion resistance. Specifically, the method comprises the following steps: S1: performing first solid solution treatment on the iron-nickel-based superalloy, the temperature of the first step of solid solution treatment is controlled in the range of 50-150℃ above the MC-type carbide precipitation temperature; In a preferred embodiment, the temperature of the first solid solution treatment is 1060-1120℃, preferably 1080℃; The holding time of the first solid solution treatment is 30-90 min, preferably 30 min, and after the end, water cooling to room temperature; The iron-nickel-based high-temperature alloy comprises, in percentage by weight: 0.03%≤C≤0.1%, 0<B≤0.006%, 15%≤Cr≤18%, Co≤3%, 0.5%≤Mo≤1%, 0≤W≤1%, Ta≤0.05%, Zr≤0.05%, 1≤Al≤2.2%, 1.5%≤Ti≤3%, 40%≤Fe≤47%, and the balance is Ni; Preferably, C: 0.08%, B: 0.006%, Cr: 15%, Co: 3%, Mo: 0.8%, Al: 1.5%, Ti: 1.8%, Ta: 0.05%, Fe: 40%, and the balance is Ni; S2: performing second solid solution treatment on the iron-nickel-based high-temperature alloy after the first solid solution treatment, the temperature of the second solid solution treatment being controlled within a range of 20-60℃ below the temperature of the second solid solution treatment; 23 30-80℃ below the precipitation temperature of C6-type carbide; In one preferred embodiment, the temperature of the second solid solution treatment is 1000-1040℃, preferably 1000℃; Further, the holding time of the second solid solution treatment is 30-60 min, preferably 30 min, and after the end, water cooling to room temperature is performed; S3: performing stress relief annealing on the iron-nickel-based high-temperature alloy after the second solid solution treatment, the temperature of the stress relief annealing being controlled within a range of 20-60℃ below the temperature of the second solid solution treatment; In one preferred embodiment, the temperature of the stress relief annealing is 940-980℃, preferably 960℃; Further, the holding time of the stress relief annealing is 2-4 h, preferably 2 h, and after the end, air cooling to room temperature is performed; S4: performing aging treatment on the iron-nickel-based high-temperature alloy after the stress relief annealing, the temperature of the aging treatment being controlled within a range of 200-300℃ below the precipitation temperature of γ' phase.

[0031] In one preferred embodiment, the temperature of the aging treatment is 650-720℃, preferably 680℃; The holding time of the aging treatment is 8-20 h, preferably 10 h, and after the end, air cooling to room temperature is performed.

[0032] The heat treatment process provided by the application first performs first solid solution treatment on the iron-nickel-based high-temperature alloy, the temperature of the first solid solution treatment being controlled within a range of 50-150℃ above the precipitation temperature of MC-type carbide, and through the first solid solution treatment, partial precipitation phase is dissolved, element composition segregation is eliminated, and appropriate grain size is obtained. Then, second solid solution treatment is performed on the iron-nickel-based high-temperature alloy after the first solid solution treatment, the temperature of the second solid solution treatment being controlled within a range of 20-60℃ below the temperature of the second solid solution treatment. 23The MC carbide in the present application is an interstitial compound formed by strong carbide forming elements (such as titanium Ti, niobium Nb, vanadium V, etc.) and carbon (C) in the high-temperature alloy, which has a simple cubic crystal structure (such as TiC, NbC, VC, etc.). 23 The C6 carbide is nucleated at the grain boundaries, and the M 23 The morphology, size and volume fraction of the C6 carbide; the third step of stress relief annealing is controlled within the range of 20-60℃ below the second step of solid solution treatment, so as to minimize the residual stress in the alloy and avoid the growth of the grain boundary carbide; the fourth step of aging treatment is controlled within 200-300℃ below the γ' phase precipitation temperature, so as to promote the γ' phase to nucleate, grow and tend to be stable as much as possible. The present application can reduce the residual stress of the nickel-iron-based high-temperature alloy under the premise of ensuring the mechanical properties and corrosion resistance of the alloy, so that the alloy is particularly suitable for the super-high-temperature steam environment above 650℃, and meets the material requirements of the key hot end components of the new generation of supercritical coal-fired units.

[0033] The MC carbide in the present application is an interstitial compound formed by strong carbide forming elements (such as titanium Ti, niobium Nb, vanadium V, etc.) and carbon (C) in the high-temperature alloy, which has a simple cubic crystal structure (such as TiC, NbC, VC, etc.).

[0034] The MC carbide in the present application is an interstitial compound formed by strong carbide forming elements (such as titanium Ti, niobium Nb, vanadium V, etc.) and carbon (C) in the high-temperature alloy, which has a simple cubic crystal structure (such as TiC, NbC, VC, etc.). 23 The C6 carbide is a common complex metal carbide in the high-temperature alloy, and its chemical formula can be represented as (M,M') 23 C6, wherein M represents a strong carbide forming element (such as chromium Cr, molybdenum Mo, tungsten W, etc.) in the alloy, and M' is another alternative metal element (such as nickel Ni, iron Fe, etc.). This kind of carbide usually has a face-centered cubic crystal structure.

[0035] The γ' phase in the present application is the core strengthening phase in the nickel-iron-based high-temperature alloy, which is essentially an intermetallic compound based on Ni3Al (the chemical formula can be represented as Ni3(Al,Ti)), which has an L12 type face-centered cubic crystal structure (i.e. Ni atoms occupy the vertices of the face-centered cubic lattice, and Al / Ti atoms occupy the positions of the cubic center).

[0036] Meanwhile, the present application also discloses the nickel-iron-based high-temperature alloy after heat treatment prepared by the above method, and the residual stress of the nickel-iron-based high-temperature alloy after heat treatment is not more than 50MPa, the grain size is 2 grade≤grain size≤3.5 grade, the yield strength at 700℃ is higher than 600MPa, and the weight gain after oxidation in 700℃ pure water steam for 1000h is not more than 1 mg / cm 2 .

[0037] The present invention also discloses the application of the above-mentioned heat-treated iron-nickel-based high-temperature alloy in the production of iron-nickel-based high-temperature alloy plates, bars, tubes and forgings for 650℃-class supercritical coal-fired power units.

[0038] The present invention discloses a heat treatment method for iron-nickel-based superalloys, which can eliminate residual stress in iron-nickel-based superalloys without reducing their mechanical properties and corrosion resistance. It can replace the existing heat treatment process for iron-nickel-based superalloys and be embedded into their production process, thus saving costs.

[0039] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0040] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0041] Example 1 The chemical composition, by weight percentage, for producing 100mm diameter iron-nickel-based high-temperature alloy bars is as follows: C: 0.03%, B: 0.003%, Cr: 16%, Mo: 0.6%, W: 0.8%, Al: 2.1%, Ti: 2.5%, Fe: 43%, balance Ni.

[0042] The bar stock was heated to 1060℃ in the furnace, held for 45 minutes, and then water-cooled to room temperature. Then the temperature was raised to 1000℃ in the furnace, held for 30 minutes, and water-cooled to room temperature. Next, the temperature was raised to 940℃ in the furnace, held for 2 hours, and air-cooled to room temperature. Finally, the temperature was raised to 650℃ in the furnace, held for 8 hours, and air-cooled to room temperature.

[0043] The residual stress of the heat-treated bar was measured by the circumferential cutting method, and the residual stress was 16 MPa.

[0044] like Figure 1 As shown, heat-treated bars were taken and their grain size was determined according to GB / T 6394-2002 "Metallic Materials - Determination of Average Grain Size". The bars have uniform equiaxed grains and a grain size grade of 3.1.

[0045] The average oxidation rate was 6.29 x 10 -3 g / m 2 •h, and the results are shown in Table 1.

[0046] The high-temperature tensile property test was performed at 700℃, and the results are shown in Table 2.

[0047] Example 2 A nickel-based high-temperature alloy rod with a diameter of 300mm was prepared, and the chemical composition was as follows in terms of weight percentage: C: 0.08%, B: 0.006%, Cr: 15%, Co: 3%, Mo: 0.8%, Al: 1.5%, Ti: 1.8%, Ta: 0.05%, Fe: 40%, and the balance being Ni.

[0048] The iron-nickel-based high-temperature alloy rod was heated to 1080℃ in the furnace, held for 30min, and water-cooled to room temperature; then heated to 1000℃ in the furnace, held for 30min, and water-cooled to room temperature; then heated to 960℃ in the furnace, held for 2h, and air-cooled to room temperature; finally heated to 680℃ in the furnace, held for 10h, and air-cooled to room temperature.

[0049] The heat-treated rod was taken and residual stress was determined according to the ring cutting method, and the residual stress was 21MPa.

[0050] As Figure 2 shown, the heat-treated rod was taken and grain size was determined according to GB / T 6394-2002 "Metal Average Grain Size Determination Method", and the rod had uniform equiaxed grains with a grain size level of 2.7.

[0051] The average oxidation rate was 5.47 x 10 -3 g / m 2 •h, and the results are shown in Table 1.

[0052] The high-temperature tensile property test was performed at 700℃, and the results are shown in Table 2.

[0053] Example 3 An iron-nickel-based high-temperature alloy rod with a diameter of 600mm was prepared, and the chemical composition was as follows in terms of weight percentage: C: 0.05%, B: 0.006%, Cr: 18%, Co: 2%, Mo: 0.5%, W: 1.0%, Al: 1.72%, Ti: 2.0%, Fe: 47%, and the balance being Ni.

[0054] The bar is heated to 1100℃ with the furnace, and kept for 45min, and then water-cooled to room temperature; then heated to 1020℃ with the furnace, and kept for 45min, and then water-cooled to room temperature; then heated to 960℃ with the furnace, and kept for 3h, and then air-cooled to room temperature; finally heated to 700℃ with the furnace, and kept for 12h, and then air-cooled to room temperature.

[0055] The residual stress of the bar after heat treatment is measured according to the ring cutting method, and the residual stress is 36MPa.

[0056] As shown in Figure 3 , the grain size of the bar after heat treatment is measured according to GB / T 6394-2002 "Metal Average Grain Size Determination Method", and the bar has uniform equiaxed grains, and the grain size grade is 2.3.

[0057] The oxidation resistance performance is evaluated according to GB / T 13303-1991 "Steel Oxidation Resistance Performance Determination Method", and the average oxidation rate is 8.41x10 -3 g / m 2 h, and the results are shown in Table 1.

[0058] The high temperature tensile property test is carried out at 700℃, and the results are shown in Table 2.

[0059] Example 4 The iron-nickel-based high-temperature alloy bar with a diameter of 1200mm is made, and the chemical composition is, in terms of weight percentage: C: 0.1%, B: 0.003%, Cr: 17%, Mo: 1.0%, W: 0.8%, Al: 1.0%, Ti: 1.5%, Ta: 0.02%, Zr: 0.05%, Fe: 45%, and the balance is Ni.

[0060] The bar is heated to 1120℃ with the furnace, and kept for 90min, and then water-cooled to room temperature; then heated to 1040℃ with the furnace, and kept for 60min, and then air-cooled to room temperature; then heated to 980℃ with the furnace, and kept for 4h, and then water-cooled to room temperature; finally heated to 720℃ with the furnace, and kept for 20h, and then air-cooled to room temperature.

[0061] The residual stress of the bar after heat treatment is measured according to the ring cutting method, and the residual stress is 43MPa.

[0062] As shown in Figure 4 , the grain size of the bar after heat treatment is measured according to GB / T 6394-2002 "Metal Average Grain Size Determination Method", and the bar has uniform equiaxed grains, and the grain size grade is 2.3.

[0063] The oxidation resistance performance is evaluated according to GB / T 13303-1991 "Steel Oxidation Resistance Performance Determination Method", and the average oxidation rate is 6.57x10-3 g / m 2 •h, the results are shown in Table 1.

[0064] High-temperature tensile properties were tested at 700℃, and the results are shown in Table 2.

[0065] Comparative Example 1 Using the same iron-nickel-based high-temperature alloy bars as in Example 1, conventional heat treatment was performed. The bars were heated in the furnace to 1080°C, held for 70 minutes, and then water-cooled to room temperature. Then, the furnace temperature was raised to 1000°C, held for 30 minutes, and water-cooled to room temperature. Finally, the furnace temperature was raised to 680°C, held for 8 hours, and air-cooled to room temperature.

[0066] The residual stress of the heat-treated bar was measured by the circumferential cutting method, and the residual stress was 320 MPa.

[0067] like Figure 5 As shown, a bar that has undergone conventional heat treatment was taken, and its grain size was determined according to GB / T 6394-2002 "Metallic Materials - Determination of Average Grain Size". The bar has uniform equiaxed grains and a grain size of 2.5.

[0068] The oxidation resistance was evaluated according to GB / T 13303-1991 "Determination of Oxidation Resistance of Steel", and the average oxidation rate was 7.54 × 10⁻⁶. -3 g / m 2 •h, the results are shown in Table 1.

[0069] High-temperature tensile properties were tested at 700℃, and the results are shown in Table 2.

[0070] Comparative Example 2 Using the same iron-nickel-based high-temperature alloy bars as in Example 1, a low-temperature long-term aging treatment was performed. The bars were heated to 1100°C in the furnace, held for 45 minutes, and then water-cooled to room temperature. Then, the temperature was raised to 1020°C in the furnace, held for 45 minutes, and water-cooled to room temperature. Finally, the temperature was raised to 680°C in the furnace, held for 20 hours, and air-cooled to room temperature.

[0071] The residual stress of the heat-treated bar was measured by the circumferential cutting method, and the residual stress was 120 MPa.

[0072] like Figure 5 As shown, a bar that has undergone conventional heat treatment was taken, and its grain size was determined according to GB / T 6394-2002 "Metallic Materials - Determination of Average Grain Size". The bar has uniform equiaxed grains and a grain size of 2.5.

[0073] The oxidation resistance was evaluated according to GB / T 13303-1991 "Determination of Oxidation Resistance of Steel", and the average oxidation rate was 7.30 × 10⁻⁶. -3 g / m2 • h, the results are shown in Table 1.

[0074] The average oxidation rate of the heat-treated iron-nickel-based superalloy obtained in Examples 1-4 and Comparative Examples 1-2 is shown in Table 1. As shown in Table 1, the average oxidation rate of the heat-treated iron-nickel-based superalloy obtained in Examples 1-4 is lower than that of Comparative Examples 1 and 2, indicating that the heat treatment process of the present application effectively improves the oxidation resistance of the alloy. This is mainly due to the fact that the method of the present application achieves precise control of grain boundary carbides, reducing the oxidation sensitive points at the grain boundary; the precipitation of γ' phase provides a stable Al source, promoting the formation of complete Cr2O3 oxide film, thereby inhibiting the diffusion of oxygen atoms; at the same time, the synergistic effect of Cr (15-18%) and Al (1-2.2%) in the alloy composition, through the formation of Cr2O3 oxide film, enhances the oxidation resistance.

[0075] In addition, the high-temperature tensile property test results of the heat-treated iron-nickel-based superalloy obtained in Examples 1-4 and Comparative Examples 1-2 at 700℃ are shown in Table 2. As shown in Table 2, the yield strength and tensile strength of Examples 1-4 are higher or close to those of Comparative Examples, while the elongation remains at a reasonable level, reflecting the characteristics of "strength and plasticity balance". The method of the present application, through step-by-step solid solution treatment (dissolution of MC type carbide, control of M 23 C6 type carbide) and aging treatment (γ' phase nanoscale dispersion), through fine-grain strengthening, second-phase strengthening and solid solution strengthening mechanisms, significantly improves the high-temperature strength; in addition, stress relief annealing effectively reduces the residual stress, such as the residual stress of Example 1 being only 16 MPa, avoiding brittle fracture caused by stress concentration; at the same time, uniform equiaxed grains reduce local stress concentration, maintaining appropriate elongation.

[0076] Table 1 Average oxidation rate of heat-treated iron-nickel-based superalloy in pure steam at 700℃

[0077] Table 2 High-temperature mechanical properties of heat-treated iron-nickel-based superalloy rods at 700℃

[0078] The heat treatment method in the present application can eliminate the residual stress of the iron-nickel-based superalloy, while basically not reducing the mechanical properties and corrosion resistance of the iron-nickel-based superalloy, and the heat-treated iron-nickel-based superalloy is suitable for producing iron-nickel-based superalloy plates, rods, pipes and forgings for 650℃ grade supercritical coal-fired generating unit.

[0079] Finally, it should be noted that the above examples are merely intended to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A heat treatment method for iron-nickel-based superalloys, characterized in that, It includes the following steps: S1: Conduct the first solution treatment on the iron-nickel-based superalloy, and control the temperature of the first solution treatment within the range of 50 - 150 °C above the precipitation temperature of MC-type carbides; S2: A second solution treatment is performed on the iron-nickel-based superalloy after the first solution treatment. The temperature of the second solution treatment is controlled at M. 23 The temperature range of C6 type carbide precipitation is 30~80℃ below the precipitation temperature; S3: Conduct stress relief annealing on the iron-nickel-based superalloy after the second solution treatment, and control the temperature of the stress relief annealing within the range of 20 - 60 °C below the temperature of the second solution treatment; S4: Conduct aging treatment on the iron-nickel-based superalloy after stress relief annealing, and control the temperature of the aging treatment within the range of 200 - 300 °C below the precipitation temperature of γ'-phase.

2. The heat treatment method for an iron-nickel-based superalloy according to claim 1, characterized in that, The temperature of the first solution treatment is 1060 - 1120 °C.

3. The heat treatment method for an iron-nickel-based superalloy according to claim 1, characterized in that, The holding time of the first solution treatment is 30 - 90 min, and after completion, it is water-cooled to room temperature.

4. The heat treatment method for an iron-nickel-based superalloy according to claim 1, characterized in that, The temperature of the second solution treatment is 1000 - 1040 °C.

5. The heat treatment method for an iron-nickel-based superalloy according to claim 1, characterized in that, The holding time of the second solution treatment is 30 - 60 min, and after completion, it is water-cooled to room temperature.

6. The heat treatment method for an iron-nickel-based superalloy according to claim 1, characterized in that, The temperature of the stress relief annealing is 940 - 980 °C, the holding time is 2 - 4 h, and after completion, it is air-cooled to room temperature.

7. The heat treatment method for an iron-nickel-based superalloy according to claim 1, characterized in that, The temperature of the aging treatment is 650 - 720 °C, the holding time is 8 - 20 h, and after completion, it is air-cooled to room temperature.

8. The heat treatment method for an iron-nickel-based superalloy according to claim 1, characterized in that, The iron-nickel-based superalloy, by weight percentage, includes: 0.03% ≤ C ≤ 0.1%, 0 < B ≤ 0.006%, 15% ≤ Cr ≤ 18%, Co ≤ 3%, 0.5% ≤ Mo ≤ 1%, 0 ≤ W ≤ 1%, Ta ≤ 0.05%, Zr ≤ 0.05%, 1 ≤ Al ≤ 2.2%, 1.5% ≤ Ti ≤ 3%, 40% ≤ Fe ≤ 47%, and the balance is Ni.

9. A nickel-based superalloy, characterized in that, The iron-nickel-based superalloy obtained by the heat treatment method according to any one of claims 1 to 8 has a residual stress ≤ 50 MPa, a grain size of grade 2 ≤ 3.5, a yield strength at 700℃ > 600 MPa, and a weight gain ≤ 1 mg / cm³ after oxidation in pure water vapor at 700℃ for 1000 h. 2 .

10. The iron-nickel-based superalloy as described in claim 9, characterized in that, Application in the production of iron-nickel-based superalloy plates, bars, tubes and forgings for 650 °C class supercritical coal-fired power unit.

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