Process method for improving anti-fatigue performance of hot-corrosion-resistant nickel-based superalloy

Abstract

The invention relates to the technical field of hot-corrosion-resistant high-temperature alloys, in particular to a process method for improving the fatigue resistance of a hot-corrosion-resistant nickel-based high-temperature alloy. The method comprises the following steps: (1) pretreating a master alloy ingot; (2) remelting and refining the pretreated master alloy ingot to obtain an alloy melt; (3) carrying out overtemperature treatment on the alloy melt in the step (2), then cooling to a casting temperature, casting into an alloy casting, and cooling in inert gas; and (4) the alloy casting in the step (3) is subjected to solution treatment and aging treatment. The melt is treated by adopting an overtemperature treatment technology, the heredity of a melt structure is broken, the alloy component uniformity is increased, the dendritic crystal spacing is reduced, the grain size is refined, the structure characteristics of the main strengthening phase gamma'in the alloy are improved by matching with the solid solution and aging heat treatment process, and finally the purpose of improving the anti-fatigue performance of the alloy is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal corrosion resistant high-temperature alloys, and in particular to a process for improving the fatigue resistance of thermal corrosion resistant nickel-based high-temperature alloys. Background Art

[0002] Heat-corrosion-resistant high-temperature alloys are often used to make parts such as turbine blades working in gas turbines. Due to their good comprehensive properties such as high-temperature strength, resistance to oxidation corrosion, creep and high-temperature fatigue, as well as good structural stability, their application in the industrial field is becoming increasingly important and extensive.

[0003] The structure and manufacturing process of heat-corrosion-resistant high-temperature alloy hot-end components are complex, and defects such as pores, cracks, and looseness are prone to occur during the manufacturing process. Furthermore, use in harsh environments such as high temperature, high pressure, oxidation, and corrosion can easily lead to component failure. Fatigue fracture, caused by the cyclic loading of rotating parts, accounts for the vast majority of these failures and is also the most serious form of failure, causing severe damage to gas turbines.

[0004] The refining temperature of the remelted master alloy in a vacuum induction furnace is generally between 1500°C and 1540°C, and the casting temperature is generally controlled between 1410°C and 1460°C. However, as the operating temperature of nickel-based cast superalloys increases, more alloying elements are added. If these highly alloyed cast superalloys are still refined and cast using conventional casting methods, their properties, especially plasticity, will be very low, thus affecting their performance. Superheating the cast superalloy melt can homogenize the melt structure, eliminate TiC and Ni3Al atomic clusters in the melt, and make the dendrite axis and interdendritic composition in the alloy crystal structure more consistent, generally with little effect on the main components. Superheating the cast superalloy melt refines the dendrites; reduces the number of MC carbides and spheroidizes the morphology; and reduces the amount of γ / γ′ eutectics and increases the amount of γ′ phase, which is beneficial for improving mechanical properties.

[0005] Currently, nickel-based high-temperature alloy ingots prepared by traditional methods have problems such as large segregation and uneven composition, resulting in insufficient fatigue performance. Summary of the Invention

[0006] To address the technical issues of high segregation and uneven composition in nickel-based superalloy ingots produced by conventional methods, resulting in insufficient fatigue performance, the present invention provides a process for improving the fatigue resistance of hot-corrosion-resistant nickel-based superalloys. This process primarily utilizes melt overheating technology to break the inherent structure of the alloy melt, thereby increasing the uniformity of the alloy composition, reducing the interdendritic spacing, and refining the grain size, ultimately achieving the goal of improving the alloy's fatigue resistance.

[0007] The technical means adopted in the present invention are as follows:

[0008] A process for improving the fatigue resistance of a hot corrosion-resistant nickel-based high-temperature alloy, using an overheating technique to treat the remelted alloy melt, followed by heat treatment to optimize the alloy structure;

[0009] The steps include:

[0010] (1) Pre-treating the master alloy ingot;

[0011] (2) remelting and refining the pretreated master alloy ingot to obtain an alloy melt;

[0012] (3) subjecting the alloy melt of step (2) to an overheating treatment, cooling it to a casting temperature, casting it into an alloy casting, and cooling it in an inert gas;

[0013] (4) The alloy casting of step (3) is subjected to solution treatment and aging treatment.

[0014] Furthermore, the master alloy ingot described in step (1) is a hot corrosion-resistant nickel-based high-temperature alloy, and its composition is: C: 0.04~0.09wt%, Cr: 15.4~16.3wt%, Co: 10.0~11.5wt%, W: 4.7~5.9wt%, Mo: 1.6~2.3wt%, Al: 2.8~3.3wt%, Ti: 4.2~5.0wt%, Nb: 0.1~0.3wt%, B: 0.06~0.1wt%, Hf: 0.2~0.4wt%, and Ni balance.

[0015] Furthermore, the pretreatment described in step (1) is: cutting the master alloy ingot into a cylindrical rod with the dimensions of: bottom diameter × height: (20-50) mm × (80-120) mm, then using a grinding wheel to grind the cut master alloy ingot, clean and dry it.

[0016] Furthermore, the remelting and refining process described in step (2) is: placing the pretreated master alloy ingot in a crucible of a vacuum induction melting furnace, turning on the cooling water of the vacuum induction melting furnace, evacuating the vacuum, and setting the temperature and time for remelting and refining to obtain an alloy melt.

[0017] Furthermore, the vacuum degree in step (2) is less than or equal to 1 Pa, the cooling water flow rate is 35-40 L / min, the temperature is 1500-1540° C., and the alloy is remelted to a molten state.

[0018] Furthermore, the overheating treatment in step (3) is as follows: maintaining the molten state of the alloy melt in step (2), heating it to 1600-1800°C, holding it for 10-20 minutes, and then standing it for 10-50 seconds; the pouring temperature is 1480-1500°C, and the cooling rate to the casting temperature is 20-40°C / min.

[0019] Furthermore, the heating rate from the alloy melt to the superheating treatment temperature is 30-60°C / min, and each time the temperature is increased by 30-60°C, it is maintained for at least 10 seconds after reaching the temperature, and then the temperature is continued to be increased until the superheating treatment temperature is reached.

[0020] Furthermore, the solution treatment process described in step (4) is as follows: heating the alloy casting to 1150-1185°C at a heating rate of 10-20°C / min, maintaining this temperature for 2.5-4.5 hours, and then air cooling.

[0021] Furthermore, the aging treatment process described in step (4) is as follows: the alloy casting after solution treatment is heated to 1020-1080°C at a heating rate of 10-15°C / min, kept at this temperature for 3-5 hours, cooled to room temperature in air, then heated to 800-900°C, kept at this temperature for 10-20 hours, and cooled in air.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The present invention provides a process for improving the fatigue resistance of nickel-based high-temperature alloys resistant to thermal corrosion. The composition of the dendrite trunk and the interdendritic components in the crystalline structure of the prepared castings are more consistent, with little effect on the main components, which can further improve the fatigue resistance of nickel-based high-temperature alloys.

[0024] 2. The present invention provides a process for improving the fatigue resistance of nickel-based high-temperature alloys resistant to thermal corrosion. By overheating the melt, the heredity of the melt structure is broken, TiC and Ni3Al atomic groups in the melt are eliminated, and highly homogeneous preparation of the alloy is achieved, thereby achieving the purpose of improving the fatigue resistance of nickel-based high-temperature alloys.

[0025] 3. The method provided by the present invention for improving the fatigue resistance of nickel-based high-temperature alloys through melt superheating and heat treatment processes refines the grains and reduces the size to 1 / 12 to 1 / 2 of that without melt superheating (Comparative Example 1).

[0026] 4. The method provided by the present invention for improving the fatigue resistance of nickel-based high-temperature alloys through melt overheating and heat treatment process reduces the dendrite spacing, and the secondary dendrite spacing of the casting is reduced by 10 to 50% compared with the traditional smelting method (Comparative Example 1).

[0027] In summary, the application of the technical solution of the present invention can improve the problem of insufficient fatigue resistance of the castings caused by large segregation and uneven composition of nickel-based high-temperature alloy ingots prepared by traditional methods.

[0028] Based on the above reasons, the present invention can be promoted in the fields of alloy preparation and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The as-cast structure of the alloy prepared in Comparative Example 1;

[0030] Figure 2 The as-cast structure of the alloy prepared in Example 2;

[0031] Figure 3 The grain morphology of the alloy prepared in Comparative Example 1;

[0032] Figure 4 The grain morphology of the alloy prepared in Example 2;

[0033] Figure 5 Comparison of regional segregation coefficients of main elements in the alloys of Comparative Example 1 and Examples 1-3;

[0034] Figure 6 γ′ phase morphology of the alloy prepared in Comparative Example 1;

[0035] Figure 7 This is the γ′ phase morphology of the alloy prepared in Example 2. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of the exemplary embodiments is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] Unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions, and numerical values ​​described in these embodiments do not limit the scope of the present invention. Techniques, methods, and apparatus known to those skilled in the art are not discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, specific parameter values ​​should be interpreted as merely exemplary and not limiting.

[0038] The present invention provides a method for improving the composition uniformity of nickel-based high-temperature alloys by superheating melt treatment and heat treatment, which is described below with examples and comparative examples:

[0039] The embodiment and comparative example all use the same raw materials and vacuum induction melting to prepare the master alloy ingot, and the pretreatment method is as follows:

[0040] ①The raw material is a rod-shaped master alloy ingot with the following composition;

[0041] C: 0.06%; Cr: 15.8%; Co: 10.7%; W: 5.3%; Mo: 2.0%; Al: 3.1%; Ti: 4.6%; Nb: 0.2%; B: 0.08%; Hf: 0.3%; Ni balance.

[0042] ② Cut the rod-shaped alloy into cylinders with a height of 100 mm and a diameter of 50 mm, and use a grinding wheel to polish the cut alloy ingot to remove surface stains and oxide scale;

[0043] ③ Clean the polished alloy ingot: Use deionized water and alcohol in an ultrasonic cleaning machine to clean the polished alloy ingot;

[0044] ④After cleaning, the alloy ingot is naturally air-dried for subsequent remelting;

[0045] The tensile, endurance and fatigue performance tests in the examples and comparative examples were carried out in accordance with national standards GB / T4338-2006, GB / T2039-1997, and GB / T 3075-2008, respectively.

[0046] Example 1

[0047] (1) Remelting and refining:

[0048] ① Clean the inside of the vacuum induction melting furnace: wipe the crucible with acetone or alcohol to ensure that the crucible is clean and free of pollution;

[0049] ② Place the pretreated alloy ingot in the middle of the crucible and close the furnace door;

[0050] ③ Turn on the cooling water and maintain the flow rate at 35-40 liters / minute. Evacuate the smelting chamber of the smelting furnace to a vacuum degree of 0.4 Pa.

[0051] ④ Remelt the alloy ingot in the crucible at a temperature of 1500-1540°C and refine for about 30 minutes to obtain an alloy melt;

[0052] (2) Overheating treatment of alloy melt:

[0053] ① Maintain the molten state of the alloy in the crucible of step (1), let it stand for about 10 minutes, slowly increase the temperature at a rate of 50°C / min, and increase the temperature in steps of 50°C. After reaching the temperature, keep it for at least 10 seconds, and then continue to increase the temperature to 1800°C for overheating treatment. The holding time is 12 minutes to decompose the clusters in the melt and improve the uniformity of the alloy melt;

[0054] ②After the overheating treatment, the melt is allowed to stand for 45 seconds;

[0055] ③ After the vacuum induction melting furnace is cooled to 1480-1500°C at a cooling rate of 30°C / min, the vacuum degree of the melting chamber is maintained to complete the pouring and prepare the alloy casting;

[0056] ④ Cool under inert gas protection and remove the casting.

[0057] (3) Solution treatment;

[0058] The superheated melt-treated castings were placed in a muffle furnace for a matching solution treatment at a heating rate of 10°C / min to 1180°C, where they were held for three hours and then air-cooled. Solution treatment dissolves grain boundary carbides and unevenly precipitated γ' phases of various sizes within the solidified structure, allowing the elements to re-enter the matrix and facilitate the precipitation of specific sized γ' phases during subsequent cooling.

[0059] (4) Aging treatment

[0060] The solution-treated castings were aged at a rate of 10°C / min to 1050°C, held for 4 hours, and then air-cooled. The temperature was then raised to 900°C, held for 20 hours, and air-cooled. Aging the solution-treated alloy castings further precipitates fine γ' phase, optimizes its size and morphology, and improves the alloy's plasticity and strength.

[0061] The microstructure characteristics of the alloy after the process steps of Example 1 are as follows: the average secondary dendrite arm spacing is about 23 μm, and the average grain diameter is about 158 ​​μm. Compared with the alloy of Comparative Example 1 (without melt superheat treatment), the average secondary dendrite arm spacing is reduced by 50%; the average grain diameter is reduced to 1 / 10.

[0062] The mechanical properties of the alloy after the process steps of Example 1 are as follows:

[0063] 900℃ tensile strength R m =712.5MPa; yield strength R p0.2 =469.5MPa; elongation A = 18.3%;

[0064] Persistent lifespan τ 900℃ / 274MPa =241.3 hours;

[0065] At 900℃, when the maximum stress is 420MPa, the stress ratio is R=0.1, and the frequency is 98Hz, the fatigue life N f >1×10 7 times (reaching 1×10 7 times without breaking).

[0066] Example 2

[0067] (1) Remelting and refining:

[0068] ① Clean the inside of the vacuum induction melting furnace: wipe the crucible with acetone or alcohol;

[0069] ② Place the pretreated alloy ingot in the middle of the crucible and close the furnace door;

[0070] ③ Turn on the cooling water and maintain the flow rate at 35-40 liters / minute. Evacuate the smelting chamber of the smelting furnace to a vacuum degree of 0.8 Pa.

[0071] ④ Remelt the alloy ingot in the crucible at 1500-1540°C and refine for about 35 minutes to obtain an alloy melt;

[0072] (2) Overheating treatment of alloy melt:

[0073] ① Maintain the molten state of the alloy in the crucible of step (1), let it stand for about 10 minutes, slowly increase the temperature at a rate of 50°C / min, and increase the temperature in steps of 50°C. After reaching the temperature, keep it for at least 10 seconds, and then continue to increase the temperature to 1720°C for overheating treatment, and keep it at this temperature for 10 minutes;

[0074] ②After the overheating treatment, the melt is allowed to stand for 30 seconds;

[0075] ③ After the vacuum induction melting furnace is cooled to 1480-1500°C at a cooling rate of 35°C / min, the vacuum degree of the melting chamber is maintained to complete the pouring and prepare the alloy casting;

[0076] ④ Cool under inert gas protection and remove the casting.

[0077] (3) Solution treatment;

[0078] The castings treated with super-temperature melt were placed in a muffle furnace for solution treatment at a heating rate of 15°C / min to 1180°C, maintained at this temperature for 3 hours, and then air-cooled.

[0079] (4) Aging treatment

[0080] The castings after solution treatment were subjected to aging treatment, with a heating rate of 10°C / min, raised to 1050°C, kept at this temperature for 4 hours, air-cooled, then heated to 870°C, kept at this temperature for 20 hours, and cooled in air.

[0081] The microstructure characteristics of the alloy after the process steps of Example 1 are as follows: the average secondary dendrite arm spacing is about 32 μm, and the average grain diameter is about 130 μm. Compared with the alloy of Comparative Example 1 (without melt superheat treatment), the average secondary dendrite arm spacing is reduced by 30%; the average grain diameter is reduced to 1 / 12.

[0082] The mechanical properties of the alloy after the process steps of Example 2 are as follows:

[0083] 900℃ tensile strength R m =660.4MPa; yield strength R p0.2 =450.2MPa; elongation A=27.5%;

[0084] Persistent lifespan τ 900℃ / 274MPa =211.5 hours;

[0085] At 900℃, when the maximum stress is 420MPa, the stress ratio is R=0.1, and the frequency is 98Hz, the fatigue life N f =9.86×10 6 .

[0086] Example 3

[0087] (1) Remelting and refining:

[0088] ① Clean the inside of the vacuum induction melting furnace: wipe the crucible with acetone or alcohol;

[0089] ② Place the pretreated alloy ingot in the middle of the crucible and close the furnace door;

[0090] ③ Turn on the cooling water and maintain the flow rate at 35-40 liters / minute. Evacuate the smelting chamber of the smelting furnace to a vacuum degree of 1Pa.

[0091] ④ Remelt the alloy ingot in the crucible at a temperature of 1500-1540°C and refine for about 32 minutes to obtain an alloy melt;

[0092] (2) Overheating treatment of alloy melt:

[0093] ① Maintain the molten state of the alloy in the crucible of step (1), let it stand for 10 minutes, slowly increase the temperature at a rate of 50°C / min, and increase the temperature in steps of 50°C. After reaching the temperature, keep it for at least 10 seconds, and then continue to increase the temperature to 1600°C for overheating treatment, and keep it at this temperature for 20 minutes;

[0094] ②After the overheating treatment, the melt is allowed to stand for 20 seconds;

[0095] ③ After the vacuum induction melting furnace is cooled to 1480-1500°C at a cooling rate of 35°C / min, the vacuum degree of the melting chamber is maintained to complete the pouring and prepare the alloy casting;

[0096] ④ Cool under inert gas protection and remove the casting.

[0097] (3) Solution treatment;

[0098] The castings treated with super-temperature melt were placed in a muffle furnace for solution treatment at a heating rate of 15°C / min to 1160°C, where they were kept at this temperature for 4.5 hours and then air-cooled.

[0099] (4) Aging treatment

[0100] The castings after solution treatment were subjected to aging treatment, with a heating rate of 10°C / min, raised to 1070°C, kept at this temperature for 3 hours, air-cooled, then heated to 900°C, kept at this temperature for 15 hours, and cooled in air.

[0101] The microstructure characteristics of the alloy after the process steps of Example 3 are as follows: the average secondary dendrite arm spacing is about 41 μm, and the average grain diameter is about 780 μm. Compared with the alloy of Comparative Example 1 (without melt superheat treatment), the average secondary dendrite arm spacing is reduced by 10%; the average grain diameter is reduced to 1 / 2.

[0102] The mechanical properties of the alloy after the process steps of Example 3 are as follows:

[0103] 900℃ tensile strength R m =670.5MPa; yield strength R p0.2 =455.4MPa; elongation A=25.3%;

[0104] Persistent lifespan τ 900℃ / 274MPa =175.2 hours;

[0105] The fatigue life N under the conditions of 900℃, maximum stress 420MPa, stress ratio R=0.1 and frequency 98Hz f =9.56×10 6 .

[0106] Comparative Example 1

[0107] (1) Remelting and refining:

[0108] ① Clean the inside of the vacuum induction melting furnace: wipe the crucible with acetone or alcohol;

[0109] ② Place the pretreated alloy ingot in the middle of the crucible and close the furnace door;

[0110] ③ Turn on the cooling water, adjust the flow rate to 35-40 liters / minute, and evacuate the smelting chamber of the smelting furnace to a vacuum degree of 0.8 Pa;

[0111] ④ Remelt the alloy ingot in the crucible at a temperature of 1500-1540°C and refine for about 30 minutes to obtain an alloy melt;

[0112] ⑤ After the vacuum induction melting furnace is cooled to 1480-1500°C at a cooling rate of 35°C / min, the vacuum degree of the melting chamber is maintained to complete the pouring and prepare the alloy casting;

[0113] ⑥ Cool under inert gas protection and remove the casting.

[0114] (2) Solution treatment;

[0115] The remelted casting was placed in a muffle furnace for subsequent solution treatment at a heating rate of 15°C / min to 1180°C, maintained at this temperature for 3 hours, and then air-cooled.

[0116] (3) Aging treatment

[0117] The castings after solution treatment were subjected to aging treatment, with a heating rate of 10°C / min, raised to 1050°C, kept at this temperature for 4 hours, air-cooled, then heated to 870°C, kept at this temperature for 20 hours, and cooled in air.

[0118] The microstructure characteristics of the alloy after the process steps of Comparative Example 1 are as follows: the average secondary dendrite arm spacing is about 46 μm; the average grain diameter is about 1.56 mm.

[0119] The mechanical properties of the alloy after the process steps of Comparative Example 1 are as follows:

[0120] 900℃ tensile strength R m =622.3MPa; yield strength R p0.2 =423.5MPa; elongation A=14.2%;

[0121] Persistent lifespan τ 900℃ / 274MPa =166.5 hours;

[0122] At 900℃, when the maximum stress is 420MPa, the stress ratio is R=0.1, and the frequency is 98Hz, the fatigue life N f =4.55×10 6 .

[0123] Comparative Example 2

[0124] (1) Remelting and refining:

[0125] ① Clean the inside of the vacuum induction melting furnace: wipe the crucible with acetone or alcohol;

[0126] ② Place the pretreated alloy ingot in the middle of the crucible and close the furnace door;

[0127] ③ Turn on the cooling water and maintain the flow rate at 35-40 liters / minute. Evacuate the smelting chamber of the smelting furnace to a vacuum degree of 0.4 Pa.

[0128] ④ Remelt the alloy ingot in the crucible at a temperature of 1500-1540°C and refine for about 30 minutes to obtain an alloy melt;

[0129] (2) Overheating treatment of alloy melt:

[0130] ① Maintain the molten state of the alloy in the crucible of step (1), let it stand for 10 minutes, slowly increase the temperature at a rate of 50°C / min, and increase the temperature in steps of 50°C. After reaching the temperature, keep it for at least 10 seconds, and then continue to increase the temperature to 1800°C for overheating treatment, and keep it at this temperature for 12 minutes;

[0131] ②After the overheating treatment, the melt is allowed to stand for 45 seconds;

[0132] ③ After the vacuum induction melting furnace is cooled to 1480-1500°C at a cooling rate of 30°C / min, the vacuum degree of the melting chamber is maintained to complete the pouring and prepare the alloy casting;

[0133] ④ Cool under inert gas protection and remove the casting.

[0134] The microstructure characteristics of the alloy after the process steps of Comparative Example 2 are as follows: the average secondary dendrite arm spacing is about 22 μm; the average grain diameter is about 157 μm.

[0135] The mechanical properties of the alloy after the process steps of Comparative Example 2 are as follows:

[0136] Persistent lifespan τ 900℃ / 274MPa =98.4 hours;

[0137] At 900℃, when the maximum stress is 420MPa, the stress ratio is R=0.1, and the frequency is 98Hz, the fatigue life N f =2.89×10 6 .

[0138] Examples 1-3 all underwent melt superheating and solution and aging heat treatments, while the alloy in Comparative Example 1 did not undergo melt superheating. This indicates that the fatigue life of the examples is more than doubled compared to Comparative Example 1. For example, comparing the mechanical property test results of Example 2 with those of Comparative Example 1, the fatigue life of Example 2 was approximately doubled, and tensile and endurance performance were also improved. This demonstrates that melt superheating at a specific temperature significantly improves the fatigue performance of the alloy.

[0139] Examples 1-3 all underwent melt superheating and solution and aging heat treatments, while the alloy in Comparative Example 2 did not undergo solution and aging heat treatments. Mechanical property testing results show that the fatigue performance of Example 1 improved by more than three times, and the endurance life increased by more than 1.8 times, compared to Comparative Example 2. This indicates that appropriate solution and aging heat treatments are necessary after melt superheating at a specific temperature.

[0140] Figure 1 This is the as-cast structure of the alloy prepared in Comparative Example 1. Figure 2 The as-cast structure of the alloy prepared in Example 2 shows that the average spacing between secondary dendrite arms in the alloy is reduced by 30%, indicating that the super-temperature melt treatment can refine the dendrite structure.

[0141] Figure 3 and Figure 4 The grain morphologies of the alloys prepared in Comparative Example 1 and Example 2 are shown respectively. By comparison, it can be seen that the average grain size of the alloy prepared in Example 2 is reduced to 1 / 12, indicating that melt overheating treatment can refine the grains.

[0142] Figure 5 Comparison of the regional segregation coefficients of the main elements in the alloys of Comparative Example 1 and Examples 1 to 3. It can be seen that the segregation coefficients of W, Ta, and Cr in the alloys prepared in the examples are reduced, while the segregation coefficients of Co, Al, and Ti remain largely unchanged, indicating that melt superheating improves the uniformity of element distribution in the alloys.

[0143] Figure 6 and Figure 7 The morphologies of the main strengthening phase γ′ phase in the alloys prepared in Comparative Example 1 and Example 2 are compared. It can be seen that after the process steps of Example 2, the size of the γ′ phase is slightly larger than that of Comparative Example 1, and the volume fraction is increased.

[0144] It can be seen that through the process steps in the embodiment, the grain size is refined, the γ′ phase characteristics are optimized and adjusted, and the element segregation is improved, which is also the main factor for improving the mechanical properties of the alloy.

[0145] The method of the present invention utilizes a melt superheating process followed by solution and aging heat treatment. This process combines the melt superheating process's ability to reduce clustering heritability in nickel-based superalloys with grain refinement and reduced secondary dendrite arm spacing. Furthermore, the solution and aging processes adjust the characteristics of the γ′ phase, the primary strengthening phase in the alloy, enhancing the uniformity of element distribution in the nickel-based superalloy. The resulting ingot's secondary dendrite spacing is reduced by at least 10% compared to a control, and the grain size is reduced by at least half.

[0146] The present invention has been described in detail according to various embodiments and comparative examples. Modifications to the technical solutions described in the aforementioned embodiments, or equivalent replacements of some or all of the technical features therein, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for improving the fatigue resistance of a hot corrosion resistant nickel-based high-temperature alloy, characterized by: The alloy melt after remelting and refining is treated by overheating technology, and then the alloy structure is optimized by heat treatment; The steps include: (1) Pretreatment of the master alloy ingot; (2) remelting and refining the pretreated master alloy ingot to obtain an alloy melt; (3) subjecting the alloy melt of step (2) to an overheating treatment, cooling it to a casting temperature, casting it into an alloy casting, and cooling it in an inert gas; (4) The alloy casting of step (3) is subjected to solution treatment and aging treatment.

2. The process according to claim 1, wherein: The master alloy ingot described in step (1) is a hot corrosion-resistant nickel-based high-temperature alloy, and its composition is: C: 0.04-0.09wt%, Cr: 15.4-16.3wt%, Co: 10.0-11.5wt%, W: 4.7-5.9wt%, Mo: 1.6-2.3wt%, Al: 2.8-3.3wt%, Ti: 4.2-5.0wt%, Nb: 0.1-0.3wt%, B: 0.06-0.1wt%, Hf: 0.2-0.4wt%, and Ni balance.

3. The process according to claim 1, characterized in that: The pretreatment described in step (1) is as follows: cutting the master alloy ingot into a cylindrical rod with the following dimensions: bottom diameter × height: (20-50) mm × (80-120) mm, then grinding the cut master alloy ingot using a grinding wheel machine, and cleaning and drying.

4. The process according to claim 1, characterized in that: The remelting and refining process described in step (2) is as follows: placing the pretreated master alloy ingot in a crucible of a vacuum induction melting furnace, turning on the cooling water of the vacuum induction melting furnace, evacuating the furnace, and setting the temperature and time for remelting and refining to obtain an alloy melt.

5. The process according to claim 4, characterized in that: The vacuum degree of the vacuum pumping is less than or equal to 1 Pa, the cooling water flow rate is 35-40 L / min, the temperature is 1500-1540° C., and the alloy is remelted to a molten state.

6. The process according to claim 1, characterized in that: The overheating treatment described in step (3) is as follows: maintaining the molten state of the alloy melt in step (2), heating it to 1600-1800°C, holding it for 10-20 minutes, and then standing it for 10-50 seconds; the pouring temperature is 1480-1500°C, and the cooling rate to the casting temperature is 20-40°C / min.

7. The process according to claim 6, characterized in that: The heating rate from the alloy melt to the superheating treatment temperature is 30-60°C / min. Every time the temperature is increased by 30-60°C, it is kept for at least 10 seconds after reaching the temperature, and then the temperature is continued to be increased until the superheating treatment temperature is reached.

8. The process according to claim 1, characterized in that: The solution treatment process described in step (4) is as follows: heating the alloy casting to 1150-1185°C at a heating rate of 10-20°C / min, maintaining this temperature for 2.5-4.5 hours, and then air cooling.

9. The process according to claim 1, characterized in that: The aging treatment process described in step (4) is as follows: the alloy casting after solution treatment is heated to 1020-1080°C at a heating rate of 10-15°C / min, kept at this temperature for 3-5 hours, cooled to room temperature in air, then heated to 800-900°C, kept at this temperature for 10-20 hours, and cooled in air.

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