A precipitation-strengthened iron-nickel-based superalloy and a method of making the same

Abstract

The application provides a precipitation strengthening type iron-nickel-based high-temperature alloy and a preparation method thereof. According to mass percentage, the precipitation strengthening type iron-nickel-based high-temperature alloy comprises Fe: 24%-36%, Cr: 18%-21%, Co: 0.5%-5.0%, Mo: <=1.0%, W: <=1.0%, Al: 1.7%-2.5%, Ti: 1.9%-2.5%, Nb: <=0.2%, Ta: <=0.1%, Si: <=0.05%, Mn: <=1.0%, C: 0.03%-0.10%, N: <=0.01%, B: 0.002-0.005%, and the balance is Ni; and the following conditions are met: 1.0 <= Ti / Al <= 1.2, Ti+Al >= 3.7%, and W+Mo+Nb <= 1.0%. The high-temperature alloy has excellent high-temperature strength, microstructure stability and corrosion / oxidation resistance, and can meet the application requirements of key components such as superheater and reheater of 700 DEG C grade coal-fired unit.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature metal material processing technology, specifically relating to a precipitation-strengthened iron-nickel-based high-temperature alloy and its preparation method. Background Technology

[0002] In recent years, with the improvement of high-end equipment manufacturing capabilities, the demand for high-performance alloy materials has become increasingly urgent, especially in the fields of energy, chemical industry, and aerospace, where the demand for high-temperature alloy materials has expanded rapidly. High-temperature alloys are hailed as the jewel in the crown of modern industry, and their research and manufacturing capabilities have always been a technological weakness in the field of high-end materials.

[0003] For example, in recent years, coal-fired power units have been seeking technological development paths that achieve high efficiency and low emissions, and high-parameter coal-fired power generation technology is considered the best solution at present. High-temperature alloys are the main candidate materials for key components of next-generation high-parameter coal-fired power units such as superheaters / reheaters; however, the manufacturing of high-temperature alloys has become a major technological bottleneck for improving the parameters of coal-fired power units. Summary of the Invention

[0004] To address the problems of the prior art, this invention provides a precipitation-strengthened iron-nickel-based high-temperature alloy and its preparation method. The high-temperature alloy possesses excellent high-temperature strength, structural stability, and corrosion / oxidation resistance, which can meet the application requirements of key components such as superheaters and reheaters in 700℃-class coal-fired power units.

[0005] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a precipitation-strengthened iron-nickel-based superalloy, comprising, by mass percentage: Fe: 24%-36%, Cr: 18%-21%, Co: 0.5%-5.0%, Mo: ≤1.0%, W: ≤1.0%, Al: 1.7%-2.5%, Ti: 1.9%-2.5%, Nb: ≤0.2%, Ta: ≤0.1%, Si: ≤0.05%, Mn: ≤1.0%, C: 0.03%-0.10%, N: ≤0.01%, B: 0.002-0.005%, with the balance being Ni; and satisfying: 1.0≤Ti / Al≤1.2, Ti+Al≥3.7%, W+Mo+Nb≤1.0%.

[0006] Preferably, the mass content of Cr is not less than 20%, the mass content of C is greater than 0.05%, and the mass content of Fe is not greater than 28%.

[0007] Preferably, the mass content of Cr is less than 20%, and the mass content of Al is greater than 1.9%.

[0008] Preferably, the mass content of Ti element is greater than 2.2%, and the mass content of C element is less than 0.06%.

[0009] Secondly, the present invention provides a method for preparing the precipitation-strengthened iron-nickel-based superalloy, comprising: S1, the elements are batched, smelted, and cast to obtain an alloy ingot; S2, the alloy ingot undergoes homogenization treatment, and then forging is carried out after the homogenization treatment is completed; S3. After forging, the resulting forging is heat-treated and then water-cooled to obtain a precipitation-strengthened iron-nickel-based high-temperature alloy.

[0010] Preferably, in S2, during the heating stage of the homogenization treatment of the alloy ingot, 1-2 heat-holding steps are set, and the heat-holding time meets the following requirements: 1) When the temperature of the insulation step is below 700℃, the insulation time is ≥0.5min / mm*D+60min, where D is the diameter of the alloy ingot; 2) When the temperature of the insulation step is 700℃ or above, the insulation time is ≥0.3min / mm*D+90min, where D is the diameter of the alloy ingot.

[0011] Preferably, the forging temperature range is 850-1180℃, and the forging ratio is not less than 4.

[0012] Preferably, in S3, the heat treatment is a two-stage solution treatment. The first stage solution treatment is performed at 1050-1180℃ for a holding time of ≥0.3min / mm*T+60min, where T is the maximum thickness or diameter of the forging. After completion, the forging is water-cooled to room temperature. The second stage solution treatment is performed at 930-1080℃ for a holding time of not less than 0.5 hours. After completion, the forging is water-cooled to room temperature.

[0013] Furthermore, during the second stage of solution treatment, the heating rate in the 650-950℃ temperature range shall not be less than 200℃ / hour, and no heat preservation step shall be set in this temperature range.

[0014] Preferably, in S3, after heat treatment, the surface temperature of the forging before water cooling is not higher than 950°C.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The precipitation-strengthened iron-nickel-based superalloy of the present invention has the following advantages: (1) Intragranular strengthening: To obtain excellent strength performance, this invention adopts precipitation strengthening for alloy design, and combines a large number of experimental verification results to limit the content of Al and Ti, the main forming elements of the strengthening phase, aiming to ensure a high volume fraction of Ni3(Al,Ti) strengthening phase within the service temperature range. In addition, to maximize the strengthening effect within the Al and Ti content range, further limiting requirements are made for the lower limit of the Ti / Al ratio and the lower limit of Ti+Al; in addition, an appropriate amount of Co element is added to reduce the alloy stacking fault energy, improve the creep deformation resistance of the alloy matrix, and improve the high-temperature endurance performance of the alloy.

[0016] (2) Grain boundary strengthening: Grain boundaries are a weakness in the strength performance of high-temperature alloys during high-temperature service. This invention controls the content of C element to regulate the size and distribution of grain boundary carbides, thereby improving the grain boundary strength of the alloy. At the same time, the content of C, Ti and Nb elements is controlled to avoid the formation of large primary carbides or grain boundary network carbides.

[0017] (3) Corrosion / Oxidation Resistance: A high Cr content is key to ensuring the corrosion / oxidation resistance of the alloy, but excessive Cr content will cause the alloy's microstructure and properties to deteriorate. This invention strictly controls the upper limit of Cr content and adopts a synergistic approach of Cr and Al to selectively oxidize and inhibit the formation of Fe-rich corrosion / oxidation products, thereby improving the density and bonding strength of the surface oxide layer and enhancing the alloy's corrosion and oxidation resistance in various environments such as coal ash, flue gas, steam, and air.

[0018] (4) Structure stability: In order to avoid the precipitation of harmful η phase during long-term service, the upper limit of Ti / Al is further limited; the upper limit of the content of ferrite stabilizing elements such as Mo, W and Al is controlled to avoid the growth of harmful phases such as δ-Fe during long-term service; the upper limit of the content of N and Nb elements is controlled to avoid the formation of Z phase, LAVES phase and large-size nitride phase; the Si content is strictly controlled to avoid the formation of G phase during the service of the alloy.

[0019] (5) Machining and weldability: On the basis of ensuring the stability of Ni3 (Al,Ti) strengthening phase growth in the alloy, the Fe content in the alloy is greatly increased to reduce the alloy deformation resistance and improve its hot working performance; the upper limit of Al and Ti content is strictly controlled to avoid the problem of reduced weldability caused by them.

[0020] (6) Composition and structure control: Co element is added and the upper limit of the total content of W+Mo+Nb is strictly controlled to ensure that the alloy matrix obtains a strengthening effect while avoiding segregation and other problems caused by large solid solution strengthening elements, thereby improving the homogenization heat treatment effect of large-size alloy ingots.

[0021] (7) Cost control: Under the premise of ensuring the stability of the alloy structure, the Fe content is increased, and precipitation strengthening elements such as Al and Ti are used as the main elements, while the content of solid solution strengthening elements such as W, Mo, and Ta, as well as precipitation strengthening elements such as Nb and Ta, are limited. Finally, a precipitation-strengthened iron-nickel-based high-temperature alloy with excellent performance is obtained, which has a significant raw material price advantage compared with similar foreign materials (Inconel 617, Inconel 740H, Haynes 282, etc.). The addition of a large amount of Fe and the control of the upper limit of solid solution strengthening element content effectively improve the hot working and forming performance of the alloy, increase the yield of the alloy, and further reduce the price cost of the product.

[0022] In summary, the alloy of this invention possesses excellent high-temperature strength, structural stability, and corrosion / oxidation resistance, meeting the application requirements of key components such as superheaters / reheaters in 700℃-class coal-fired power units. It has already been successfully validated in commercial units and possesses significant market potential. Compared to similar high-temperature alloys, this alloy boasts lower raw material costs, successfully solving the material selection dilemma for key components in 650℃ and above-class coal-fired power units. Furthermore, it shows promising market prospects in multiple fields, including nuclear power, chemical engineering, shipbuilding, and aerospace.

[0023] Furthermore, higher Cr content tends to promote the precipitation of harmful phases such as σ and α-Cr during long-term heat exposure. When the Cr content is high, the lower limit of C content should be increased to stabilize chromium carbide and prevent it from transforming into other phases.

[0024] The present invention relates to a method for preparing precipitation-strengthened iron-nickel-based superalloys. By homogenizing the alloy to improve the uniformity of its composition, and then performing heat treatment after forging to precipitate strengthening phases, a strengthening effect is achieved.

[0025] Furthermore, by using reasonable homogenization treatment parameters, the uniformity of alloy composition is ensured. At the same time, a heat preservation step is set during the heating stage of homogenization treatment to prevent the low-melting-point phase from melting during homogenization treatment.

[0026] Furthermore, by controlling the forging ratio during the alloy forming process, sufficient strain energy is ensured in the alloy, and grain size control is achieved during subsequent heat treatment.

[0027] Furthermore, in the second step of solution treatment, the temperature is limited to a range of 650-950℃ to prevent the strengthening phase from growing excessively and causing genetic effects on the tissues to be treated later.

[0028] Furthermore, after heat treatment, the surface temperature of the forging before water cooling should not exceed 950℃, thereby avoiding excessive internal stress in the alloy and preventing grain boundary widening caused by excessive internal stress, which is beneficial to improving the alloy performance. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a typical metallographic structure of Example 1 of the present invention; Figure 2 This is the morphology of the intracrystalline precipitate in Example 2 of the present invention; Figure 3 This is the grain boundary carbide morphology of Example 3 of the present invention; Figure 4 The morphology of the precipitated phase after thermal exposure in Example 2 of the present invention; Figure 5 This is the morphology of the precipitated phase after thermal exposure in Comparative Example 1 of the present invention; Figure 6 The grain boundary morphology is shown in Comparative Example 3 of this invention. Detailed Implementation

[0031] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0032] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0033] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or define the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0034] The precipitation-strengthened iron-nickel-based superalloy of the present invention comprises, by mass percentage, Fe: 24%-36%, Cr: 18%-21%, Co: 0.5%-5.0%, Mo: ≤1.0%, W: ≤1.0%, Al: 1.7%-2.5%, Ti: 1.9%-2.5%, Nb: ≤0.2%, Ta: ≤0.1%, Si: ≤0.05%, Mn: ≤1.0%, C: 0.03%-0.10%, N: ≤0.01%, B: 0.002-0.005%, with the balance being Ni; and satisfying the following conditions: 1.0≤Ti / Al≤1.2, Ti+Al≥3.7%, W+Mo+Nb≤1.0%.

[0035] 1.0≤Ti / Al≤1.2 means that the ratio of the mass content of Ti to the mass content of Al is greater than or equal to 1 and less than or equal to 1.2; Ti+Al means that the sum of the mass content of Ti and the mass content of Al is greater than or equal to 3.7%.

[0036] The alloy design objective of this invention is to possess excellent high-temperature strength, corrosion / oxidation resistance, and long-term structural stability, while also considering low cost and good processability. Therefore, the alloy adopts a precipitation-strengthening-oriented design concept (ensuring high Al and Ti content and a reasonable C content), including intragranular Ni3(Al,Ti) strengthening and grain boundary carbide strengthening. Simultaneously, a high Cr content ensures excellent corrosion / oxidation resistance, while strictly controlling the upper limit of Cr content to avoid its promoting effect on the precipitation of harmful phases, which could lead to a deterioration in the long-term stability of the alloy. The ranges of W, Mo, and Nb are strictly controlled to provide solid solution strengthening while avoiding their adverse effects on long-term stability. A suitable amount of Co is added to reduce the alloy's stacking fault energy without significantly increasing the alloy cost, improving the creep resistance of the alloy matrix and enhancing the alloy's high-temperature endurance. At the same time, while ensuring the stability of Ni3(Al,Ti), the iron content is significantly increased to improve the alloy's hot workability. The upper limits of N and Nb content are controlled to avoid the formation of Z-phase, Laves phase, and large-size nitrides.

[0037] Preferably, in the precipitation-strengthened iron-nickel-based superalloy of the present invention, when the mass content of Cr is not less than 20%, the mass content of C is higher than 0.05%, and the mass content of Fe is not higher than 28%. Higher Cr content tends to promote the precipitation of harmful phases such as σ and α-Cr during long-term heat exposure. While taking into account the higher Cr content, the lower limit of C content is increased to stabilize chromium carbide and prevent it from transforming into other phases.

[0038] Preferably, in the precipitation-strengthened iron-nickel-based superalloy of the present invention, when the mass content of Cr is less than 20%, the mass content of Al is greater than 1.9%.

[0039] Preferably, in the precipitation-strengthened iron-nickel-based superalloy of the present invention, when the mass content of Ti element is greater than 2.2%, the mass content of C element is less than 0.06%.

[0040] In some embodiments of the present invention, 1.0≤Ti / Al≤1.2, that is, the ratio of the mass content of Ti element to the mass content of Al element is greater than or equal to 1 and less than or equal to 1.2.

[0041] The method for preparing precipitation-strengthened iron-nickel-based superalloys according to the present invention includes: S1, the elements are batched, smelted, and cast to obtain an alloy ingot; S2, the alloy ingot undergoes homogenization treatment, and then forging is carried out after the homogenization treatment is completed; S3. After forging, the resulting forging is heat-treated and then water-cooled to obtain a precipitation-strengthened iron-nickel-based high-temperature alloy.

[0042] In some embodiments of the present invention, S1 specifically involves: batching the various elements, employing vacuum induction melting, and inspecting the melt composition during melting to ensure that the O element content is below 30 ppm and the N element content is below 150 ppm. After confirming the composition, the alloy is cast using a die casting method, ensuring that the casting temperature is not lower than 1450°C. After casting, stress-relief annealing should be performed at a temperature above 700°C. After completion, the riser is removed and the surface is machined. Stress-relief annealing after casting prevents excessive residual stress from being generated inside the alloy.

[0043] In some embodiments of the present invention, in step S2, the alloy ingot is homogenized at a temperature above 1150°C for a holding time of not less than 45 hours.

[0044] In a further preferred embodiment, during the heating stage of the homogenization treatment of the alloy ingot, 1-2 heat-holding steps are set, and the heat-holding time meets the following requirements: 1) When the temperature of the insulation step is below 700℃, the insulation time is ≥0.5min / mm*D+60min, where D is the diameter of the alloy ingot; 2) When the temperature of the insulation step is 700℃ or above, the insulation time is ≥0.3min / mm*D+90min, where D is the diameter of the alloy ingot.

[0045] By setting reasonable homogenization treatment parameters, the uniformity of alloy composition can be ensured. At the same time, a heat preservation step is set during the heating stage of homogenization treatment to prevent the low melting point phase from melting during homogenization treatment.

[0046] In some embodiments of the present invention, the forging temperature range is 850-1180℃, and the forging ratio is not less than 4.

[0047] After forging, the tube blank can be prepared by hot extrusion forming. The extrusion temperature should not be lower than 1100℃ and the extrusion ratio should not be less than 5. After extrusion, the alloy tube can be prepared by cold rolling / drawing with a rolling ratio of not less than 1.5.

[0048] By controlling the forging ratio, extrusion ratio, and rolling ratio during the alloy forming process, sufficient strain energy is ensured in the alloy, and grain size is controlled during subsequent heat treatment.

[0049] In some embodiments of the present invention, in S3, the heat treatment is a two-stage solution treatment. The first stage solution treatment is performed at 1050-1180℃ for a holding time ≥0.3min / mm*T+60min, where T is the maximum thickness or diameter of the forging. After completion, the forging is water-cooled to room temperature. The second stage solution treatment is performed at 930-1080℃ for a holding time of not less than 0.5 hours. After completion, the forging is water-cooled to room temperature.

[0050] In the second stage of solution treatment, the temperature rise is rapidly passed through the range of 650-950℃, with a heating rate of no less than 200℃ / hour, and no heat preservation steps are set within this temperature range. The second stage of solution treatment is limited to a temperature range of 650-950℃ to avoid excessive growth of the strengthening phase and its genetic effects on the tissues to be treated subsequently.

[0051] If alloy pipes are made after forging, and the bending angle exceeds 15°, a second-stage solution treatment should be performed after bending.

[0052] In some embodiments of the present invention, in step S3, after heat treatment, the surface temperature of the forging before water cooling does not exceed 950°C. This setting can avoid excessive internal stress in the alloy, prevent grain boundary widening caused by excessive internal stress, and is beneficial to improving the alloy performance.

[0053] Example 1 The alloy in this embodiment has the following composition: Fe: 30%, Cr: 19%, Co: 3.0%, Mo: 0.3%, W: 0.5%, Al: 2.0%, Ti: 2.1%, Nb: 0.2%, Ta: 0.1%, Si: 0.02%, Mn: 1.0%, C: 0.05%, N: 0.002%, B: 0.003%, with the balance being Ni.

[0054] The alloy of this embodiment is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1520°C after being poured from the furnace. Before casting, the composition of the alloy was tested: O: 20ppm, N: 80ppm. After demolding, the ingot was stress-relief annealed at 850°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0055] The alloy ingot is heated in the furnace, with holding steps at 550℃ and 900℃ for 2 hours and 3 hours respectively. After heating to 1150℃, it is held for 50 hours, then further heated to 1195℃ and held for 24 hours. After completion, it is removed from the furnace for forging. The initial forging temperature of the alloy is 1150℃, the final forging temperature is 980℃, the forging ratio is 8, and it is cooled to room temperature after the final forging.

[0056] After the alloy forging is completed, the tube blank is prepared by hot extrusion at a temperature of 1170℃ and an extrusion ratio of 5.5. After completion, the tube is cold rolled at a rolling ratio of 1.5 to obtain the alloy tube.

[0057] The alloy tube undergoes a two-stage heat treatment. Before the first stage heat treatment, the temperature is raised in the furnace and a holding step is set at 700℃ for 2 hours. Then, the temperature is raised to 1120℃ for solution treatment and held for 2 hours before water cooling. The second stage heat treatment is then carried out. After the alloy tube is loaded into the furnace at 600℃, the temperature is raised to 1020℃ at a rate of 250℃ / h and held for 0.5 hours before being taken out of the furnace for cooling. After the tube wall temperature reaches 790℃, it is then immersed in water for cooling.

[0058] Example 2 The alloy in this embodiment has the following composition: Fe: 24%, Cr: 18%, Co: 0.5%, Mo: 0.2%, W: 0.3%, Al: 1.95%, Ti: 2.2%, Si: 0.03%, Mn: 1.0%, C: 0.055%, N: 0.003%, B: 0.004%, with the balance being Ni.

[0059] The alloy of this embodiment is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1530°C after being poured from the furnace. Before casting, the composition of the alloy was tested to be 15 ppm O and 100 ppm N. After demolding, the ingot was stress-relief annealed at 880°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0060] The alloy ingot is heated in the furnace, with holding steps at 500℃ and 950℃ for 3 hours each. After reaching 1150℃, it is held for 50 hours, then further heated to 1195℃ and held for 24 hours. After this, it is removed from the furnace and forged. The initial forging temperature is 1160℃, the final forging temperature is 950℃, the forging ratio is 10, and after final forging, it is cooled to room temperature.

[0061] After the alloy forging is completed, the tube blank is prepared by hot extrusion at a temperature of 1200℃ and an extrusion ratio of 6. After completion, the tube is cold rolled at a rolling ratio of 2 to obtain the alloy tube.

[0062] The alloy tube undergoes a two-stage heat treatment. Before the first stage heat treatment, the temperature is raised in the furnace and a holding step is set at 750°C for 1 hour. Then, the temperature is raised to 1100°C for solution treatment and held for 2 hours before water cooling. The second stage heat treatment is then carried out. After loading the furnace, the alloy tube is heated to 1000°C at a rate of 300°C / h and held for 1 hour before being taken out of the furnace for cooling. After the tube wall temperature reaches 820°C, it is placed in water for cooling.

[0063] Example 3 The alloy in this embodiment has the following composition: Fe: 26%, Cr: 19%, Co: 2.0%, Mo: 0.25%, W: 0.3%, Al: 2.0%, Ti: 2.1%, Nb: 0.2%, Si: 0.01%, Mn: 0.8%, C: 0.045%, N: 0.001%, B: 0.003%, with the balance being Ni.

[0064] The alloy of this embodiment is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1490°C. Before casting, the composition of the alloy was tested: O: 25ppm, N: 120ppm. After demolding, the ingot was stress-relief annealed at 800°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0065] The alloy ingot is heated in the furnace, with holding steps set at 550℃ and 950℃ during the heating process, for 3 hours and 2 hours respectively. The temperature is then raised to 1200℃ and held for 48 hours before being removed from the furnace for forging. The initial forging temperature of the alloy is 1150℃, the final forging temperature is 900℃, the forging ratio is 8, and the ingot is cooled to room temperature after the final forging.

[0066] After the alloy forging is completed, the tube blank is prepared by hot extrusion at a temperature of 1170℃ and an extrusion ratio of 5. After completion, the tube is cold rolled at a rolling ratio of 2.1 to obtain the alloy tube.

[0067] The alloy tube undergoes a two-stage heat treatment. Before the first stage heat treatment, the temperature is raised to 1110℃ in the furnace for solution treatment, held for 2.5 hours, and then water-cooled. The second stage heat treatment is then carried out. After loading the furnace, the alloy tube is heated to 1020℃ at a rate of 250℃ / h, held for 0.5 hours, and then cooled after being taken out of the furnace. After the tube wall temperature reaches 810℃, it is then water-cooled.

[0068] Example 4 The alloy in this embodiment has the following composition: Fe: 28%, Cr: 21%, Co: 5.0%, Mo: 0.5%, W: 0.15%, Al: 1.7%, Ti: 2.0%, Nb: 0.1%, Si: 0.015%, Mn: 0.5%, C: 0.06%, N: 0.001%, B: 0.002%, with the balance being Ni.

[0069] The alloy of this embodiment is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1530°C after being poured from the furnace. Before casting, the composition of the alloy was tested: O: 15ppm, N: 75ppm. After demolding, the ingot was stress-relief annealed at 880°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0070] The alloy ingot is heated in the furnace, with holding steps at 500℃ and 950℃ for 3 hours each. After reaching 1150℃, it is held for 50 hours, then further heated to 1195℃ and held for 24 hours. After this, it is removed from the furnace and forged. The initial forging temperature is 1160℃, the final forging temperature is 950℃, the forging ratio is 10, and after final forging, it is cooled to room temperature.

[0071] After the alloy forging is completed, the tube blank is prepared by hot extrusion at a temperature of 1200℃ and an extrusion ratio of 6. After completion, the tube is cold rolled at a rolling ratio of 2 to obtain the alloy tube.

[0072] The alloy tube undergoes a two-stage heat treatment. Before the first stage heat treatment, the temperature is raised in the furnace and a holding step is set at 750℃ for 1 hour. Then, the temperature is raised to 1100℃ for solution treatment and held for 2 hours before water cooling. The second stage heat treatment is then carried out. After loading the furnace, the alloy tube is heated to 1000℃ at a rate of 300℃ / h and held for 1 hour before being taken out of the furnace for cooling. After the tube wall temperature reaches 920℃, it is placed in water for cooling.

[0073] After the alloy tube is heat-treated, it is cold-bent and formed at a bending angle of 30°. After the tube is bent, the temperature is increased to 1020°C at 300°C / h, held for 0.5 hours, and then cooled. After the tube wall temperature reaches 900°C, it is cooled in water.

[0074] Example 5 The alloy in this embodiment has the following composition: Fe: 25%, Cr: 20%, Co: 1.5%, Mo: 0.3%, W: 0.45%, Al: 2.1%, Ti: 2.3%, Nb: 0.15%, Ta: 0.01%, Si: 0.01%, Mn: 1.0%, C: 0.055%, N: 0.001%, B: 0.005%, with the balance being Ni.

[0075] The alloy of this embodiment is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1520°C after being poured from the furnace. Before casting, the composition of the alloy was tested: O: 25ppm, N: 90ppm. After demolding, the ingot was stress-relief annealed at 850°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0076] The alloy ingot was heated in the furnace, with holding steps at 550℃ and 900℃ for 2 hours and 3 hours respectively. After reaching 1150℃, it was held for 50 hours, then further heated to 1195℃ and held for 24 hours. After completion, it was removed from the furnace for forging. The initial forging temperature was 1160℃, the final forging temperature was 920℃, the forging ratio was 8, and it was cooled to room temperature after the final forging.

[0077] After the alloy forging is completed, the tube blank is prepared by hot extrusion at a temperature of 1170℃ and an extrusion ratio of 5.5. After completion, the tube is cold rolled at a rolling ratio of 1.5 to obtain the alloy tube.

[0078] The alloy tube undergoes a two-stage heat treatment. Before the first stage heat treatment, the temperature is raised in the furnace and a holding step is set at 700℃ for 2 hours. Then, the temperature is raised to 1120℃ for solution treatment and held for 2 hours before water cooling. The second stage heat treatment is then carried out. After the alloy tube is loaded into the furnace at 600℃, the temperature is raised to 1020℃ at a rate of 250℃ / h and held for 0.5 hours before being taken out of the furnace for cooling. After the tube wall temperature reaches 840℃, it is then immersed in water for cooling.

[0079] After the alloy tube is heat-treated, it is cold-bent to a bending angle of 10°. After bending, the surface is pickled, ground, and packaged for storage.

[0080] Example 6 The alloy in this embodiment has the following composition: Fe: 27%, Cr: 19.5%, Co: 2.5%, Mo: 0.2%, W: 0.5%, Al: 2.0%, Ti: 2.2%, Nb: 0.2%, Si: 0.02%, Mn: 0.7%, C: 0.04%, N: 0.001%, B: 0.003%, with the balance being Ni.

[0081] The alloy of this embodiment is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1520°C after being poured from the furnace. Before casting, the composition of the alloy was tested to be 15 ppm O and 110 ppm N. After demolding, the ingot was subjected to stress-relief annealing at 780°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0082] The alloy ingot was heated in the furnace, with holding steps at 550℃ and 930℃ for 3 hours and 2 hours respectively. After reaching 1170℃, it was held for 50 hours, then further heated to 1210℃ and held for 48 hours to complete the forging process. The initial forging temperature was 1150℃, the final forging temperature was 930℃, the forging ratio was 8, and the ingot was cooled to room temperature after the final forging.

[0083] Alloy forgings undergo a two-stage heat treatment. In the first stage, the furnace temperature is raised before the first stage heat treatment, and a holding step is set at 700℃ for 2 hours. Then, the temperature is raised to 1120℃ for solution treatment, held for 2 hours, and then water-cooled. In the second stage heat treatment, the alloy is loaded into the furnace at 400℃ and heated to 1020℃ at a rate of 350℃ / h. After holding for 1.5 hours, the alloy is removed from the furnace and cooled. After the wall temperature reaches 820℃, it is water-cooled.

[0084] Example 7 The alloy in this embodiment has the following composition: Fe: 25%, Cr: 18.8%, Co: 3.0%, Mo: 0.5%, W: 0.3%, Al: 2.1%, Ti: 2.4%, Nb: 0.12%, Ta: 0.1%, Si: 0.05%, Mn: 0.8%, C: 0.03%, N: 0.002%, B: 0.002%, with the balance being Ni.

[0085] The alloy of this embodiment is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1520°C after being poured from the furnace. Before casting, the composition of the alloy was tested: O: 25ppm, N: 100ppm. After demolding, the ingot was stress-relief annealed at 750°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0086] The alloy ingot was heated in the furnace, with holding steps at 580℃ and 920℃ for 3 hours and 2 hours respectively. After reaching 1160℃, it was held for 50 hours, then further heated to 1190℃ and held for 36 hours. After completion, it was removed from the furnace for forging. The initial forging temperature was 1120℃, the final forging temperature was 870℃, the forging ratio was 9, and it was cooled to room temperature after the final forging.

[0087] Alloy forgings undergo a two-stage heat treatment. In the first stage, the furnace temperature is raised before the first stage heat treatment, and a holding step is set at 800℃ for 1.5 hours. Then, the temperature is raised to 1110℃ for solution treatment, held for 1.5 hours, and then water-cooled. In the second stage heat treatment, the alloy is loaded into the furnace at 500℃ and heated to 1020℃ at a rate of 350℃ / h. After holding for 1 hour, the alloy is removed from the furnace and cooled. After the wall temperature reaches 780℃, it is water-cooled.

[0088] Comparative Example 1 The alloy in this comparative example has the following composition: Fe: 28%, Cr: 21%, Co: 0.5%, Mo: 0.3%, W: 0.5%, Al: 2.0%, Ti: 2.1%, Nb: 0.2%, Si: 0.05%, Mn: 1.0%, C: 0.045%, N: 0.0015%, B: 0.002%, with the balance being Ni.

[0089] The alloy of this comparative example is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1520°C after being poured from the furnace. Before casting, the composition of the alloy was tested to be 30 ppm O and 100 ppm N. After demolding, the ingot was stress-relief annealed at 850°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0090] The alloy ingot is heated in the furnace, with holding steps at 550℃ and 900℃ for 2 hours and 3 hours respectively. After reaching 1150℃, it is held for 50 hours, then further heated to 1195℃ and held for 24 hours. After completion, it is removed from the furnace for forging. The initial forging temperature is 1150℃, the final forging temperature is 980℃, the forging ratio is 8, and it is cooled to room temperature after final forging.

[0091] After alloy forging, hot extrusion is used to prepare tube blanks at an extrusion temperature of 1170℃ and an extrusion ratio of 5.5. After completion, cold rolling is performed on the tubes at a rolling ratio of 1.5.

[0092] The alloy tube undergoes a two-stage heat treatment. Before the first stage heat treatment, the temperature is raised in the furnace and a holding step is set at 700℃ for 2 hours. Then, the temperature is raised to 1120℃ for solution treatment and held for 2 hours before water cooling. The second stage heat treatment is then carried out. After the alloy tube is loaded into the furnace at 600℃, the temperature is raised to 1020℃ at a rate of 250℃ / h and held for 0.5 hours before being taken out of the furnace for cooling. After the tube wall temperature reaches 870℃, it is then immersed in water for cooling.

[0093] Comparative Example 2 The alloy in this comparative example has the following composition: Fe: 30%, Cr: 19%, Mo: 0.6%, W: 1.0%, Al: 1.6%, Ti: 1.8%, Nb: 1.6%, Si: 0.02%, Mn: 0.2%, C: 0.02%, Zr: 0.02%, B: 0.003%, with the balance being Ni; The alloy of this comparative example is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1520°C after being poured from the furnace. Before casting, the composition of the alloy was tested: O: 20ppm, N: 90ppm. After demolding, the ingot was stress-relief annealed at 890°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0094] The alloy ingot is heated in the furnace, with holding steps at 600℃ and 950℃ for 1 hour and 2 hours respectively. After reaching 1150℃, it is held for 50 hours, then further heated to 1195℃ and held for 24 hours. After completion, it is removed from the furnace for forging. The initial forging temperature is 1150℃, the final forging temperature is 980℃, the forging ratio is 8, and it is cooled to room temperature after final forging.

[0095] After alloy forging, hot extrusion is used to prepare tube blanks at an extrusion temperature of 1170℃ and an extrusion ratio of 5.5. After completion, cold rolling is performed on the tubes at a rolling ratio of 1.5.

[0096] The alloy tube undergoes a two-stage heat treatment. Before the first stage heat treatment, the temperature is raised in the furnace and a holding step is set at 700℃ for 2 hours. Then, the temperature is raised to 1120℃ for solution treatment and held for 2 hours before water cooling. The second stage heat treatment is then carried out. After the alloy tube is loaded into the furnace at 600℃, the temperature is raised to 1020℃ at a rate of 250℃ / h and held for 0.5 hours before being taken out of the furnace for cooling. After the tube wall temperature reaches 890℃, it is then immersed in water for cooling.

[0097] Comparative Example 3 The alloy in this comparative example has the following composition: Fe: 30%, Cr: 19%, Co: 3.0%, Mo: 2.0%, W: 2.0%, Al: 2.0%, Ti: 2.1%, Nb: 0.2%, Ta: 0.1%, Si: 0.02%, Mn: 1.0%, C: 0.05%, N: 0.002%, B: 0.003%, with the balance being Ni.

[0098] The alloy of this comparative example is prepared by the following steps: The alloy was melted using vacuum induction melting, and the ingot was cast at a stable temperature of 1520°C after being poured from the furnace. Before casting, the composition of the alloy was tested: O: 20ppm, N: 80ppm. After demolding, the ingot was subjected to stress-relief annealing at 850°C. After completion, the riser was removed, the surface was machined, and then vacuum induction remelting was performed.

[0099] The alloy ingot is heated in the furnace, with holding steps at 550℃ and 900℃ for 2 hours and 3 hours respectively. After reaching 1150℃, it is held for 50 hours, then further heated to 1195℃ and held for 24 hours. After completion, it is removed from the furnace for forging. The initial forging temperature is 1150℃, the final forging temperature is 980℃, the forging ratio is 8, and it is cooled to room temperature after final forging.

[0100] After the alloy forging is completed, the tube blank is prepared by hot extrusion at a temperature of 1170℃ and an extrusion ratio of 5.5. After completion, the tube is cold rolled at a rolling ratio of 1.5 to obtain the alloy tube.

[0101] The alloy tube undergoes a two-stage heat treatment. Before the first stage heat treatment, the temperature is raised in the furnace and a holding step is set at 700℃ for 2 hours. Then, the temperature is raised to 1120℃ for solution treatment and held for 2 hours before water cooling. The second stage heat treatment is then carried out. After the alloy tube is loaded into the furnace at 600℃, the temperature is raised to 1020℃ at a rate of 250℃ / h and held for 0.5 hours before being taken out of the furnace and water cooled to room temperature.

[0102] Figure 3 The image shows the grain boundary carbide morphology of the alloy in Example 3 of this invention. It can be seen that the grain boundary carbide is uniform in size and distribution, which can improve the grain boundary strength of the alloy.

[0103] By comparison Figure 2 and Figure 4 It was found that the alloy microstructure obtained in Example 2 was an austenitic matrix, with Ni3Al reinforcing phases of tens of nanometers in diameter dispersed within the grains after heat treatment. Discontinuous carbide precipitation occurred at the grain boundaries, and after heat exposure, the Ni3Al reinforcing phases within the grains coarsened and grew. Figure 5 As shown, when the Cr content in the alloy is too high (Comparative Example 1) and the C content is relatively low, the supersaturated solid solution of Cr will precipitate in the form of α-Cr during the heat exposure process, which will have an adverse effect on the alloy properties.

[0104] The higher Al and Ti content helps ensure the alloy has better high-temperature creep strength performance. Compared with the fracture time of 936 hours of the alloy in Comparative Example 2 at 750℃ / 200MPa, the fracture time of Example 1 under the same test conditions reached 1791 hours, and the high-temperature creep strength performance of the alloy was significantly improved.

[0105] Furthermore, controlling the immersion temperature after the final heat treatment of the alloy helps prevent excessive internal stress. For example... Figure 1 and Figure 6 As shown, compared with Example 1, after the solution treatment of Comparative Example 3, it was directly immersed in water and cooled to room temperature. The internal stress of the alloy was high, and grain boundary widening phenomenon occurred, which had an adverse effect on the alloy performance.

[0106] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A precipitation-strengthened iron-nickel-based superalloy, characterized in that, The composition, by mass percentage, includes Fe: 24%-36%, Cr: 18%-21%, Co: 0.5%-5.0%, Mo: ≤1.0%, W: ≤1.0%, Al: 1.7%-2.5%, Ti: 1.9%-2.5%, Nb: ≤0.2%, Ta: ≤0.1%, Si: ≤0.05%, Mn: ≤1.0%, C: 0.03%-0.10%, N: ≤0.01%, B: 0.002-0.005%, with the balance being Ni; and satisfies the following conditions: 1.0≤Ti / Al≤1.2, Ti+Al≥3.7%, W+Mo+Nb≤1.0%. When the mass content of Cr is not less than 20%, the mass content of C is greater than 0.05%, and the mass content of Fe is not greater than 28%; When the mass content of Cr is less than 20%, the mass content of Al is greater than 1.9%.

2. The precipitation-strengthened iron-nickel-based superalloy according to claim 1, characterized in that, The mass content of Ti is greater than 2.2%, and the mass content of C is less than 0.06%.

3. The method for preparing the precipitation-strengthened iron-nickel-based superalloy according to any one of claims 1-2, characterized in that, include: S1, the elements are batched, smelted, and cast to obtain an alloy ingot; S2, the alloy ingot undergoes homogenization treatment, and then forging is carried out after the homogenization treatment is completed; S3. After forging, the resulting forging is heat-treated and then water-cooled to obtain a precipitation-strengthened iron-nickel-based high-temperature alloy.

4. The method for preparing precipitation-strengthened iron-nickel-based superalloys according to claim 3, characterized in that, In S2, during the heating stage of homogenization treatment, the alloy ingot is provided with 1-2 holding steps, and the holding time meets the following requirements: 1) When the temperature of the insulation step is below 700℃, the insulation time should be ≥0.5min / mm. D+60min, where D is the diameter of the alloy ingot; 2) When the temperature of the insulation step is 700℃ or above, the insulation time should be ≥0.3 min / mm. D+90min, where D is the diameter of the alloy ingot.

5. The method for preparing precipitation-strengthened iron-nickel-based superalloys according to claim 3, characterized in that, The forging temperature range is 850-1180℃, and the forging ratio is not less than 4.

6. The method for preparing precipitation-strengthened iron-nickel-based superalloys according to claim 3, characterized in that, In S3, the heat treatment is a two-stage solution treatment. The first stage of solution treatment involves holding at 1050-1180℃ for a time ≥0.3 min / mm. T+60min, where T is the maximum thickness or diameter of the forging. After completion, the forging is cooled to room temperature by water. The second stage of solution treatment is carried out at 930-1080℃ for a holding time of not less than 0.5 hours. After completion, the forging is cooled to room temperature by water.

7. The method for preparing precipitation-strengthened iron-nickel-based superalloys according to claim 6, characterized in that, During the second stage of solution treatment, the heating rate in the 650-950℃ temperature range shall not be less than 200℃ / hour, and no heat preservation step shall be set in this temperature range.

8. The method for preparing precipitation-strengthened iron-nickel-based superalloys according to claim 3, characterized in that, In S3, after heat treatment, the surface temperature of the forging before water cooling should not exceed 950℃.

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