Hot working method of high-Al and Ti difficult-to-deform high-temperature alloy

Abstract

The invention discloses a high-Al and Ti difficult-to-deform high-temperature alloy hot working method, which avoids the melting risk of low-melting-point intermetallic compounds through high-temperature diffusion on one hand, and can realize effective and uniform diffusion of chemical elements on the other hand; on the other hand, through gradual heating number cooling forging, a high-temperature small-deformation forging process is carried out in an as-cast structure interval, and a low-temperature large-deformation process is adopted after the as-cast structure is crushed, so that an ideal uniform and fine recrystallized grain structure is finally realized, and the problems of high possibility of cracking, non-uniform forging structure, coarse grains and the like in a high-temperature alloy forging process are solved; and the high-quality requirement for use of downstream aero-engine components is met.

Description

TECHNICAL FIELD

[0001] The application relates to the alloy processing technical field, in particular to a high-temperature alloy hot processing method for high Al and Ti difficult deformation. BACKGROUND

[0002] With the continuous development of an aero-engine, the service temperature of a turbine disc and blade forging is continuously increased to meet the demand for greater output power and higher thermal efficiency. Meanwhile, in order to meet the material selection demand of an advanced engine with higher temperature resistance, higher high-temperature strength and higher heat corrosion resistance, the development trend of high-temperature alloy materials is that the alloy content is continuously increased, and in particular the Al and Ti contents of the gamma prime phase which plays a major strengthening role in the high-temperature alloy are continuously increased. For example, the alloy Al+Ti content of the current new generation of aero-engine turbine disc materials GH720Li and GH4065A reaches 7.5%, which poses a technical challenge to metallurgical workers.

[0003] In order to pursue large-scale, low-segregation and high-purity high-temperature alloy products, currently high-end high-temperature alloy basically adopts a vacuum induction smelting + vacuum arc remelting double process or a vacuum induction smelting + electroslag remelting + vacuum arc remelting triple process. Then, the ingot type is enlarged, and the mother material for secondary remelting is also increased. If the annealing process is unreasonable, the thermal stress and the organizational stress will cause the internal cracking of the mother material, the vacuum arc remelting smelting process is unstable, and metallurgical defects such as black spots and white spots are generated, and finally the product quality and service life are affected. The alloying degree of this type of material is very high, the sum of Al+Ti content reaches 7.5%, and it is currently the highest grade of deformation high-temperature alloy strengthening phase, so the smelting, forging and other difficulties of the product are very high. Chemical element segregation is easily formed in the smelting process, and intermetallic compounds are easily formed, which are the key to causing metallurgical quality, and cracking, uneven forging structure and coarse grains and other problems are easily generated in the forging process, causing the scrap of the parts. At present, the domestic process is not mature, the production qualified rate of some manufacturers is very low, the production cost is very high, and the delivery rate is very low, which limits the industrial application of high-temperature alloy materials.

[0004] Therefore, it is necessary to provide a high Al and Ti difficult deformation high-temperature alloy hot processing method to solve the defects of the cracking, uneven forging structure and coarse grains and other problems in the high-temperature alloy forging process affecting the qualified rate. SUMMARY

[0005] The application provides a high Al and Ti difficult deformation high-temperature alloy hot processing method, which solves the defects of the cracking, uneven forging structure and coarse grains and other problems in the high-temperature alloy forging process affecting the qualified rate.

[0006] Therefore, the scheme of the application is as follows: The first aspect of the present application is to provide a hot working method of high Al and Ti difficult-to-deform superalloy, comprising the following steps: S1. obtaining or smelting a GH720Li superalloy ingot with qualified composition, dense structure and no inclusions; S2. heating the superalloy ingot to 1100℃, controlling the heating rate, and keeping the temperature for 10-15h every 10℃ in the range of 1100-1170℃, and then keeping the temperature for more than 70h in the range of 1180-1230℃ for high-temperature diffusion; S3. pre-forging the superalloy ingot after high-temperature diffusion at 1100-1170℃ by temperature reduction; S4. keeping the temperature of the pre-forged superalloy ingot at 800-1050℃ for 4-5h; S5. heating the superalloy ingot obtained in step S4 to below 1100℃ for multiple times of upsetting and drawing forging to obtain a superalloy with qualified grain size.

[0007] Further, the GH720Li superalloy ingot has the following components in terms of mass percentage: Cr 15.5-16.5%, Al 2.25-2.75%, Ti 4.75-5.25%, Co 14.0-15.5%, Mo 2.75-3.25%, W 1.00-1.50%, B 0.01-0.02%, C 0.01-0.02%, and Ni as the balance.

[0008] Further, in step S1, the smelting is three-step smelting of vacuum induction melting, electroslag remelting, and vacuum arc remelting.

[0009] Further, in step S2, the heating rate is controlled at 20-60℃ / h.

[0010] Further, in step S3, the pre-forging process is: first heating to 1170℃ for first fire forging, then cooling to 1160℃ for second fire forging, and finally cooling to 1140℃ for third fire forging.

[0011] Preferably, the deformation amount of the first fire forging process is ≤35%; and / or, the deformation amount of the second fire forging process is ≤35%, and / or, the deformation amount of the third fire forging process is ≤50%.

[0012] Preferably, the first fire forging and the second fire forging are each independently selected from upsetting or drawing, and the third fire forging is performed by upsetting and drawing.

[0013] Further, in step S5, the forging process is 2-4 times.

[0014] The second aspect of the present application is to provide a high-temperature alloy material, which is obtained by the method of the first aspect. The high-temperature alloy material has obvious plasticity after hot working, and the grain size is 8 or more, preferably 9, and more preferably 10. The mechanical properties of the material meet the application requirements of related components of an aero-engine.

[0015] The third aspect of the present application is to provide the use of the high-temperature alloy material of the second aspect in the preparation of a turbine disc and blade of an aero-engine.

[0016] Compared with the prior art, the present application has the following beneficial effects: The hot working method provided by the present application can avoid the risk of melting of low-melting-point intermetallic compounds, and at the same time, can realize effective and uniform diffusion of chemical elements, by gradually dissolving the eutectic phase organization in the range of 1100-1170 DEG C through temperature gradient holding, and by gradually cooling and forging in each heating cycle, high-temperature small deformation forging process is carried out in the cast state organization interval, and after the cast state organization is broken, low-temperature large deformation process is used, and finally ideal uniform and fine recrystallized grain organization is realized, which solves the problems of cracking, uneven forging organization and coarse grain in the forging process of high-temperature alloy, and meets the high quality requirements of downstream aero-engine components. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The thermodynamic equilibrium phase diagram of the GH720Li high-temperature alloy before hot working according to the present application.

[0018] Figure 2 The grain size diagram of the high-temperature alloy after hot working according to the third embodiment of the present application.

[0019] Figure 3 The cracking situation of the high-temperature alloy after forging according to the first comparative example of the present application.

[0020] Figure 4 The physical diagram of the high-temperature alloy after hot working according to the second comparative example of the present application.

[0021] Figure 5 The grain size diagram of the high-temperature alloy after hot working according to the second comparative example of the present application. DETAILED DESCRIPTION

[0022] The technical solutions of the present application will be described in detail below in combination with preferred embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0023] GH720Li superalloy is an age-strengthened nickel-based alloy, and the chemical composition according to mass fraction is as follows: Cr 15.5-16.5%, Al 2.25-2.75%, Ti 4.75-5.25%, Co 14.0-15.5%, Mo 2.75-3.25%, W 1.00-1.50%, B 0.01-0.02%, C 0.01-0.02%, and Ni is the balance. It is calculated by Thermo-Cale thermodynamic software that the main precipitated phases in the GH720Li superalloy are γ' phase, σ phase, μ phase and carbide (MC, M23C6). The thermodynamic equilibrium phase diagram of the GH720Li superalloy calculated by JMatPro software is shown as 1. Due to the very much γ' strengthening phase precipitated in the GH720Li superalloy, the forging process is prone to cracking, uneven forging structure and coarse grain, etc., causing the scrap of parts.

[0024] In order to obtain good performance and structure, high-purity metallurgical technology must be used to ensure low oxygen, low nitrogen, high purity and accurate control of alloy composition, and at the same time, through ideal hot working process, fine and uniform grain size is obtained, and the number, size and morphology of the strengthening phase after heat treatment are suitable to ensure the requirements of the alloy in high temperature and high strength application state. In order to meet the harsh requirements of the use environment of the aero-engine material, the material needs to meet the characteristics of high alloying, purification, high homogenization and high reliability, so as to meet the high quality requirements of the aero-engine, and through the use of the optimal process route, the material meeting the high performance and high stability requirements of the aero-engine is obtained.

[0025] Therefore, the present application provides the following hot working method: 1. In order to obtain the GH720Li superalloy ingot with qualified chemical composition, dense structure, no inclusion and other macrosegregation defects, a Φ508mm alloy ingot is smelted by a vacuum induction melting (VIM)→ electroslag remelting (ESR)→ vacuum arc remelting (VAR) three-link smelting process, according to the chemical composition characteristics of the alloy, the main precipitated phases of the alloy are γ' phase, σ phase, μ phase and carbide (MC, M23C6) and γ / γ' eutectic phase; 2. The alloy ingot utilizes an innovative high-temperature diffusion process. First, the alloy ingot is heated to 1100℃, and then the heating rate is controlled at 20-60℃ / h for slow heating. Within the range of 1100~1170℃, the temperature is held for 10~15h for every 10℃ increase, and the eutectic phase gradually dissolves. When the temperature reaches a certain temperature in the range of 1180~1230℃, it is held for ≥70h for high-temperature diffusion. The melting point of the eutectic phase varies from 1100~1160℃ depending on the composition. This process avoids the risk of melting of low-melting-point intermetallic compounds and at the same time enables the effective and uniform diffusion of chemical elements, resulting in an alloy ingot with a basically consistent chemical composition. 3. After the high-temperature diffusion process, the alloy ingot is heated to 1100~1170℃ and subjected to sequential cooling forging. A high-temperature, small-deformation forging process is performed within the as-cast microstructure range. After the as-cast microstructure is broken down, a low-temperature, large-deformation process is used. A slow cooling process, holding at 800~1050℃ for 4~5 hours, precipitates a large number of γ′ phase particles. Forging is then performed below 1100℃, ultimately achieving an ideal, uniform, and fine recrystallized grain structure. The specific steps are as follows: 3.1 Pre-forging First heat: Heating to the upper limit of 1170℃, at which temperature the alloy γ′ phase is completely dissolved in the matrix, the alloy has low resistance to hot working deformation, and upsetting forging is carried out with a deformation of less than 35% to ensure that the columnar crystal structure is basically broken. Second heat: The temperature drops to 1160℃. At this temperature, the alloy γ′ phase is completely dissolved in the matrix. The alloy has low resistance to hot working deformation. It is then drawn up, with the deformation amount within 35%, to ensure that the columnar crystal structure is basically broken. The forging deformation methods of the first heat and the second heat are different. Upsetting and drawing up are performed respectively. Third heat treatment: The temperature drops to 1140℃. At this temperature, the γ′ phase of the alloy is completely dissolved in the matrix. The alloy has low resistance to hot working deformation. Upsetting and drawing deformation are carried out with a deformation amount of less than 50% to ensure a more uniform crystal structure.

[0026] 3.2 Slow Cooling Process

[0027] After the forging process is completed, a slow cooling process is performed, maintaining the temperature in the range of 800–1050℃. 4~5h At this temperature, a large amount of γ' phase precipitates, and the γ' phase particles are uniformly distributed.

[0028] 3.3 Fine-grained forging

[0029] After a slow cooling process, the ingot is heated to below 1100℃ to prevent the γ' phase from dissolving. After 2-4 upsetting and drawing processes, the γ' phase particles grow continuously at this temperature, which improves the forging plasticity. At the same time, the γ' phase particles are used to hinder grain growth, resulting in a fine grain structure with a grain size of 8 to 10.

[0030] In the following examples, the Φ508mm alloy ingots are all made by VIM+ESR+VAR triple process, with qualified chemical composition, compact structure and no macrosegregation defects such as inclusions.

[0031] Example 1

[0032] Chemical composition of the alloy ingot:

[0033] The above alloy ingot is subjected to hot working, with the following steps: 1) High temperature diffusion: the alloy ingot is first heated to 1100℃, and then heated at a rate of 50℃ / h, with 15h of heat preservation for every 10℃ increase in the range of 1100~1170℃, and then heated to 1180℃ at a rate of 50℃ / h, with 75h of heat preservation.

[0034] 2) Pre-forging: First fire: heated at an upper limit of 1170℃, with 35% deformation for upsetting; Second fire: the temperature is reduced to 1160℃, with 35% deformation for elongation; Third fire: the temperature is reduced to 1140℃, with 50% deformation for upsetting and elongation.

[0035] 3) Slow cooling process

[0036] After the above forging, the slow cooling process is carried out, with 3h of heat preservation at 1000℃.

[0037] 4) Fine grain forging

[0038] After the slow cooling process, the ingot is heated to 1100℃, and then forged by 2 times of upsetting and elongation process to obtain the target size of alloy rod.

[0039] Example 2

[0040] Chemical composition of the alloy ingot:

[0041] The above alloy ingot is subjected to hot working, with the following steps: 1) High temperature diffusion: the alloy ingot is first heated to 1100℃, with a controlled heating rate of 40℃ / h, with 12h of heat preservation for every 10℃ increase in the range of 1100℃~1170℃, so that the eutectic structure gradually dissolves, and then heated to 1200℃ at a controlled rate of 40℃ / h, with 72h of high temperature diffusion at 1200℃.

[0042] 2) Pre-forging: First fire: heated at an upper limit of 1170℃, with 30% deformation for upsetting; Second fire: temperature is reduced to 1160 °C, elongation deformation is carried out, and deformation amount is 30%; Third fire: temperature is reduced to 1140 °C, upsetting and elongation deformation are carried out, and deformation amount is 50%.

[0043] 3) Slow cooling process

[0044] After the above forging is completed, the slow cooling process is carried out, and the temperature is maintained at 850 °C for 5 h.

[0045] 4) Fine grain forging

[0046] After the slow cooling process, the ingot is heated to 1000 °C, and is forged through 4 times of upsetting and elongation process to obtain an alloy rod of target size.

[0047] Example 3

[0048] Chemical composition of the alloy ingot:

[0049] The above alloy ingot is subjected to hot working, and the steps are as follows: 1) High temperature diffusion: the alloy ingot is first heated to 1100 °C, the heating rate is controlled to be 60 °C / h, the eutectic phase structure is gradually dissolved by maintaining the temperature at 1100 °C~1170 °C for 10 h for every 10 °C increase, then the heating rate is controlled to be 50 °C / h to increase the temperature to 1230 °C, and high temperature diffusion is carried out at 1230 °C for 70 h.

[0050] 2) Pre-forging: First fire: heating at an upper limit of 1170 °C, upsetting deformation is carried out, and deformation amount is 32%; Second fire: temperature is reduced to 1160 °C, elongation deformation is carried out, and deformation amount is 30%; Third fire: temperature is reduced to 1140 °C, upsetting and elongation deformation are carried out, and deformation amount is 55%.

[0051] 3) Slow cooling process

[0052] After the above forging is completed, the slow cooling process is carried out, and the temperature is maintained at 850 °C~1050 °C for 4 h~5 h.

[0053] 4) Fine grain forging

[0054] After the slow cooling process, the ingot is heated to 1050 °C, and is forged through 3 times of upsetting and elongation process to obtain an alloy rod of target size.

[0055] Comparative Example 1

[0056] The alloy ingot in Example 1 is subjected to hot working treatment, and the details are as follows: 1) High temperature diffusion: using traditional process 1160℃ 25h, then 1190℃ 70h; 2) Forging: using 60MN fast forging machine to forge; Production situation: surface cracking is serious when forging 2 times, and it cannot continue to forge.

[0057] Comparative Example 2

[0058] The alloy ingot in Example 1 was taken for heat treatment, and the specific process was as follows: 1) High temperature diffusion: same as Example 1; 2) Forging: heating at 1160℃-1170℃, and forging by 3 times of upsetting + 4 times of elongation.

[0059] Comparative Example 3

[0060] The alloy ingot in Example 1 was taken for heat treatment, and the difference between the treatment method and Example 1 was that the high temperature diffusion process in step 1) was as follows: the alloy ingot was first heated to 1100℃, heated at a rate of 50℃ / h, and then kept at 1150-1170℃ for 25h, and then the temperature was raised to 1230℃ and kept for 70h of high temperature diffusion. It did not go through the process of keeping at 1100℃-1170℃ for 10-15h respectively for every 10℃ increase. The other steps were the same as Example 1. Cracking occurred during forging, and the forging could not continue.

[0061] Comparative Example 4

[0062] The alloy ingot in Example 1 was taken for heat treatment, and the difference between the treatment method and Example 1 was that it did not go through the slow cooling process in step 3). The other steps were the same as Example 1.

[0063] Test Example

[0064] 1. Grain inspection

[0065] The grain size of the alloy rods obtained in the above examples and comparative examples was inspected, and it was found that Examples 1-3 could all reach the grain size standard of 9-10 levels, meeting the requirement of 7 levels or less on the surface of an aero-engine. The grain size chart observed under a metallographic microscope of Example 3 is shown in Figure 2 , the edge grain size reaches 10 levels (right), and the core grain size reaches 9 levels (left).

[0066] Comparative Example 1 occurred surface cracking using traditional process, as shown in Figure 3 , and it could not continue to produce because it could not continue to forge. As shown in Figures 4-5 , Comparative Example 2 had coarse grains after forging (Figure 5 In the figure, the left is the core grain, the right is the edge grain, more than about 30% of the grain size is 4-5 grade, which does not meet the requirement of the surface of the aero-engine being finer than 7 grade. The comparative example 3 also leads to cracking during forging and cannot continue to produce without the process of holding at 1100℃~1170℃ respectively for every 10℃ increase; the alloy bar obtained in the comparative example 4 has 30% of the grains under the microscope being coarser than 7 grade.

[0067] 2. Mechanical property test

[0068] The alloy bars obtained in the above examples 1-3 are respectively tested to detect the indexes shown in Table 1, and the test standards are as follows: ASTM E8 / E8M tensile test of metal materials, ASTM E21 high temperature tensile test of metal materials.

[0069] The results are as follows: Table 1:

[0070] It is obvious from the test results that the alloy bar obtained by the hot working method provided by the present application can meet the mechanical property requirement of the aero-engine material.

[0071] Although the embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method of hot working a high Al, Ti, difficult to deform, superalloy characterized by the steps of The application relates to a high-temperature alloy material and a preparation method thereof. S1. obtaining or smelting a GH720Li high-temperature alloy ingot with qualified components, compact structure and no inclusions; S2. heating the high-temperature alloy ingot to 1100 DEG C, controlling the heating speed, and keeping the temperature at 1100-1170 DEG C for 10-15 h every time the temperature is increased by 10 DEG C, then keeping the temperature at 1180-1230 DEG C for more than 70 h to perform high-temperature diffusion; S3. pre-forging the high-temperature alloy ingot after high-temperature diffusion at 1100-1170 DEG C in each fire; S4. keeping the high-temperature alloy ingot after pre-forging at 800-1050 DEG C for 4-5 h; S5. heating the high-temperature alloy ingot obtained in step S4 to below 1100 DEG C to perform multi-fire upsetting and drawing forging to obtain a high-temperature alloy with qualified grain size.

2. The method of claim 1, wherein, The high-temperature alloy ingot is composed of the following components in percentage by mass: Cr 15.5-16.5%, Al 2.25-2.75%, Ti 4.75-5.25%, Co 14.0-15.5%, Mo 2.75-3.25%, W 1.00-1.50%, B 0.01-0.02%, C 0.01-0.02%, and Ni as the balance.

3. The method of claim 1, wherein, In step S1, the smelting is three combined smelting of vacuum induction melting, electroslag remelting and vacuum arc remelting.

4. The method of claim 1, wherein, In step S2, the heating speed is controlled at 20-60 DEG C / h.

5. The method of claim 1, wherein, In step S3, the pre-forging process is: first heating to 1170 DEG C to perform first fire forging, then cooling to 1160 DEG C to perform second fire forging, and finally cooling to 1140 DEG C to perform third fire forging.

6. The method of claim 5, wherein, The deformation amount of the first fire forging process is less than or equal to 35%; and / or, the deformation amount of the second fire forging process is less than or equal to 35%, and / or, the deformation amount of the third fire forging process is less than or equal to 50%.

7. The method of claim 5, wherein, The first fire forging and the second fire forging are respectively selected to be upsetting or drawing, and the third fire forging is selected to be upsetting and drawing.

8. The method of claim 1, wherein, In step S5, the forging process is 2-4 fires.

9. A high temperature alloy material, characterized by, The high-temperature alloy material is prepared by the method in any one of claims 1-8, and the grain size of the high-temperature alloy material is more than 8.

10. The application of the high-temperature alloy material in claim 9 in the preparation of turbine discs and blades of an aero-engine.

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