A heat treatment method for uniformly refining the mixed crystal structure of GH4169 alloy forgings and regulating the content of δ phase

Abstract

The present invention discloses a heat treatment method for uniformly refining the mixed crystal structure and regulating the δ-phase content of GH4169 alloy forgings. The method comprises the following steps: (1) performing δ-phase aging treatment on the GH4169 alloy forging with a mixed crystal structure, controlling the aging temperature at 890-910 °C and the aging time at 9-24 hours; (2) performing three-stage annealing heat treatment on the forging after aging treatment. For the first-stage high-temperature constant-temperature annealing, control the annealing temperature at 990-1000 °C and the annealing time at 3-5 minutes. For the second-stage continuous cooling annealing, control the cooling time at 5-10 minutes and the termination temperature at 980-950 °C. For the third-stage low-temperature constant-temperature annealing, control the temperature at 980-950 °C and the time at 20-30 minutes. The method proposed by the present invention can obtain the required microstructure by adjusting the temperature or time of the third-stage low-temperature constant-temperature annealing in the three-stage annealing heat treatment, thereby synergistically controlling the δ-phase content and refining the grain structure. It can effectively refine the mixed crystal structure uniformly to ASTM11 grade - ASTM12 grade and reduce the δ-phase content to the range of 3% - 6%.

Description

Technical Field

[0001] The present invention relates to a heat treatment method for uniformly refining the mixed crystal structure and regulating the content of δ phase of GH4169 alloy forgings, belonging to the field of forging technology. Background Art

[0002] Among numerous nickel-based superalloy grades, GH4169 superalloy has good high-temperature strength, welding performance, high-temperature stability, as well as good fatigue resistance and corrosion resistance, so it is usually used in the manufacture of key components of aero-engines such as turbine disks. Generally, key components of aero-engines such as turbine disks are formed by die forging. Since the plastic deformation resistance of GH4169 superalloy is large at room temperature and small at high temperature, it is difficult to form these key components by machining at room temperature. Therefore, it usually needs to be heated above the recrystallization temperature for hot die forging. However, due to the high sensitivity of the microstructure of GH4169 alloy to the change of hot working parameters and the narrow processing parameter range, mixed crystal structure is extremely easy to form during hot die forging, thus reducing the performance and service life of parts. Therefore, how to eliminate the mixed crystal structure of GH4169 alloy forgings after die forging is an urgent problem to be solved.

[0003] Due to the existence of meta-dynamic recrystallization and static recrystallization behaviors during the heat treatment process, heat treatment can be used as an effective method to eliminate the mixed crystal structure, and the higher the temperature, the faster the grain growth rate and the δ phase dissolution rate. In addition, when annealing at a high temperature above 980 °C, obvious recrystallization nucleation behavior exists at the phase boundary of the δ phase. At the same time, since the δ phase is non-coherent with the matrix, it can hinder the migration of grain boundaries and has a pinning effect on the growth of recrystallized grains. However, too high a δ phase content is not conducive to the comprehensive performance of GH4169 alloy forgings. Therefore, the new technology mainly takes into account the influence of the δ phase and temperature on recrystallization, uses the first-stage high-temperature isothermal annealing to promote the nucleation of a large number of recrystallized grains and the dissolution of the δ phase, uses the second-stage continuous cooling annealing to quickly cool to the low-temperature stage to avoid excessive grain growth, and at the same time allows the δ phase to continue to dissolve partially, and uses the third-stage low-temperature isothermal annealing to make the large number of recrystallized grains formed in the early stage grow slowly and make the δ phase dissolve further, so as to simultaneously control the δ phase content and refine the grain structure, realize the controllability of eliminating the forging mixed crystal structure, and finally obtain high-performance GH4169 alloy forgings.

[0004] The name of Patent CN 109252120 B is "A Method for Uniformly Refining the Microstructure of GH4169 Alloy Forgings", and the name of Patent CN111575620 B is "A Method for Obtaining Ultrafine-grained Forgings of GH4169 Alloy". Both of these patents disclose heat treatment processes for refining the forged mixed-grain microstructure. However, the above-disclosed technical solutions still have the following deficiencies: (1) In Patent CN109252120 B, it is proposed to first perform a first annealing on the forged mixed-grain microstructure, then perform an aging treatment, and then perform a constant-temperature annealing in 3 to 6 stages. After annealing for a certain time in each stage, quenching is carried out. Although this process can refine the mixed-grain microstructure to a certain extent, the grain size of the alloy after annealing can only reach ASTM 10 grade and below, and the process is relatively complex; (2) In Patent CN 111575620 B, it is proposed to first perform an aging treatment on the forged mixed-grain microstructure, and then perform a continuous cooling annealing treatment. Although this process can refine the forged mixed-grain microstructure to ASTM 12 grade, the universality of this process is low, and it is difficult to synergistically control the δ-phase content and refine the grain microstructure by adjusting process parameters, which is not conducive to obtaining the desired annealing microstructure with high grain size and low δ-phase content.

[0005] Therefore, there is an urgent need to propose a new annealing method that is economical, efficient, simple to operate, and has good universality to achieve the synergy of δ-phase content control and grain microstructure refinement, so as to regulate and eliminate the mixed-grain microstructure of GH4169 alloy forgings into a microstructure with high grain size and low δ-phase content. Summary of the Invention

[0006] The purpose of the present invention is to provide a heat treatment method for uniformly refining the mixed-grain microstructure of GH4169 alloy forgings and regulating the δ-phase content. This method uses a first-stage high-temperature constant-temperature annealing to promote the nucleation of a large number of recrystallized grains and the dissolution of the δ-phase, uses a second-stage continuous cooling annealing to quickly cool to a low-temperature stage to avoid excessive grain growth, and at the same time allows the δ-phase to continue to dissolve partially. And a third-stage low-temperature constant-temperature annealing is used to slowly grow the large number of recrystallized grains formed in the early stage and further dissolve the δ-phase. And it mainly adjusts the temperature and time of the third-stage low-temperature constant-temperature annealing, so that the elimination of the mixed-grain microstructure is relatively controllable, and then an annealing microstructure with high grain size and low δ-phase content is obtained, solving the problem that the existing heat treatment process has low universality and it is difficult to obtain a high-grain-size microstructure and a low-δ-phase-content microstructure at the same time.

[0007] The solution of the present invention to solve the above problems is:

[0008] Step 1: Perform a δ-phase aging treatment on the GH4169 alloy forging with a mixed-grain microstructure. The process parameters of the aging treatment are: the aging temperature is between 890 and 910 °C, and the aging time is between 9 and 24 hours;

[0009] Step 2: Perform three-stage recrystallization annealing on the aged forgings. The three stages are: the first-stage high-temperature isothermal annealing, the second-stage continuous cooling annealing, and the third-stage low-temperature isothermal annealing. The process parameters for the three-stage recrystallization annealing are as follows: the temperature for the first-stage high-temperature isothermal annealing is between 990 and 1000 °C, and the annealing time is between 3 and 5 minutes; the termination temperature for the second-stage continuous cooling annealing is between 980 and 950 °C, and the cooling time is between 5 and 10 minutes; the annealing temperature for the third-stage low-temperature isothermal annealing is between 980 and 950 °C, and the annealing time is between 20 and 30 minutes.

[0010] The beneficial effects of the present invention are as follows: This method fully considers the effects of the δ phase, heat treatment temperature, and time on dynamic and static recrystallization. Through the first-stage high-temperature isothermal annealing, a large number of recrystallized grains are promoted to nucleate and the δ phase is dissolved. Through the second-stage continuous cooling annealing, rapid cooling to the low-temperature stage is carried out to avoid excessive grain growth, and at the same time, part of the δ phase continues to dissolve. Through the third-stage low-temperature isothermal annealing, the large number of recrystallized grains formed in the early stage grow slowly and the δ phase is further dissolved. Moreover, the control of the δ phase content and the refinement of the grain structure can be coordinated by adjusting the temperature and time of the third-stage low-temperature isothermal annealing, thereby obtaining the required microstructure. For example, when the temperature of the third-stage low-temperature isothermal annealing is set to a relatively low value (such as 950 °C), the annealing time of the third stage can be extended (such as 30 minutes), and finally, the mixed grain structure can be refined to a high degree (ASTM 12 grade), while the residual content of the δ phase in the annealed structure is relatively high (5.69%); when the temperature of the third-stage low-temperature isothermal annealing is set to a relatively high value (such as 980 °C), the annealing time of the third-stage low-temperature isothermal annealing can be shortened (such as 20 minutes), the content of the δ phase can be reduced to a relatively low level (3.28%), and the mixed grain structure can still be uniformly refined (ASTM 11 grade). Description of the Drawings

[0011] Figure 1 Preparation process curve of GH4169 forgings;

[0012] Figure 2 Deformed structure of GH4169 billet after forging;

[0013] Figure 3 Heat treatment process route of GH4169 forgings in Example 1;

[0014] Figure 4 Microstructure of GH4169 forgings after heat treatment in Example 1;

[0015] Figure 5 Heat treatment process route of GH4169 forgings in Example 2;

[0016] Figure 6The microstructure of the GH4169 forging after heat treatment in Example 2. Detailed implementation mode

[0017] The present invention will be described in detail below with reference to the accompanying drawings and specific implementation cases.

[0018] The present invention is a heat treatment method for uniformly refining the mixed crystal structure of GH4169 alloy forgings and regulating the content of δ phase. In all the following examples, the billets of the forgings are sourced from typical industrial GH4169 alloy forging billets, and the forging process route of the forgings is as Figure 1 shown, and the initial structure of the forgings is as Figure 2 shown.

[0019] Example 1

[0020] Step 1: Perform δ phase aging treatment on the GH4169 alloy forging, with the aging temperature being 900 ± 5 °C and the aging time being 12 hours;

[0021] Step 2: Perform three-stage annealing heat treatment on the forging obtained in Step 1. The process of the three-stage annealing heat treatment is as follows: the temperature of the first-stage high-temperature constant-temperature annealing is controlled at 1000 ± 5 °C, and the annealing time is 3 minutes; the termination temperature of the second-stage continuous cooling annealing is controlled at 950 ± 5 °C, and the cooling time is 5 minutes; the temperature of the third-stage low-temperature constant-temperature annealing is controlled at 950 ± 5 °C, and the time is 30 minutes.

[0022] The process route of implementing Steps 1 and 2 on the GH4169 forging is as Figure 3 shown, and the structure after heat treatment is as Figure 4 shown.

[0023] Perform EBSD and SEM observations on the grain structure of the GH4169 forging before and after heat treatment, and the results are respectively as Figure 2 、 Figure 4 shown. From Figure 2It can be seen that the forging structure contains many large deformed grains and many fine recrystallized grains, presenting a mixed-grain structure state, which will greatly reduce the performance of the forgings. After three-stage annealing, the oblong deformed grains in the structure are significantly reduced, the mixed-grain structure is almost eliminated, and the structure is significantly refined and homogenized. After statistics, the grain size after heat treatment is 4.92 μm (the grain size reaches ASTM grade 12), and the δ-phase content is reduced to 5.69%. Compared with Patent CN 111575620 B, the grain structure of the alloy is further refined. The above experiments show that in the three-stage annealing process, by utilizing the effects of the δ-phase, heat treatment temperature, and time on sub-dynamic and static recrystallization, the coordination of δ-phase content control and grain structure refinement can be achieved, thereby homogenizing and refining the mixed-grain structure. Compared with other annealing methods, the three-stage annealing process takes into account the promotion of nucleation at high temperatures and the inhibition of the growth of recrystallized grains at low temperatures. At the same time, the high-temperature stage and the low-temperature stage are quantified with heat treatment parameters, and the required annealing structure can be obtained by adjusting the temperature / time of the low-temperature isothermal annealing in the third stage. The elimination of the mixed-grain structure is relatively controllable, with the advantages of simple operation, high error tolerance, low cost, easy implementation, and can greatly reduce the requirements for the forging process.

[0024] Example 2

[0025] Step 1: Perform δ-phase aging treatment on the GH4169 alloy forging, with the aging temperature at 900 ± 5 °C and the aging time at 12 hours;

[0026] Step 2: Perform three-stage annealing heat treatment on the forging obtained in Step 1. The process of the three-stage annealing heat treatment is as follows: The temperature of the first-stage high-temperature isothermal annealing is controlled at 1000 ± 5 °C, and the annealing time is 3 minutes; The termination temperature of the second-stage continuous cooling annealing is controlled at 980 ± 5 °C, and the cooling time is 5 minutes; The temperature of the third-stage low-temperature isothermal annealing is controlled at 980 ± 5 °C, and the time is 20 minutes.

[0027] The process route of implementing Steps 1 and 2 on the GH4169 alloy forging is as Figure 5 shown, and the structure after heat treatment is as Figure 6 shown.

[0028] EBSD and SEM observations were carried out on the grain structure of the GH4169 forging before and after recrystallization heat treatment, and the results are respectively as Figure 2 、 Figure 6 shown. From Figure 6It can be seen that most of the deformed large grains in the structure after three-stage annealing heat treatment have been consumed and eliminated by recrystallized grains, and the degree of uniform refinement of the structure has increased significantly. After statistics, the grain size after heat treatment is 7.02 μm (the grain size reaches ASTM grade 11), and at the same time, the δ-phase content is reduced to 3.28%. Compared with Patent CN 109252120 B, while the δ-phase content is greatly reduced, the grain structure is refined to above ASTM grade 10. The above experiments show that in the process of three-stage annealing, by utilizing the influence of the δ-phase, heat treatment temperature and time on sub-dynamic and static recrystallization, the coordination of δ-phase content control and grain structure refinement can be achieved, thereby uniformly refining the mixed grain structure, and through comparison Figure 4 and Figure 6 it can be found that when the temperature and time of the third-stage annealing are appropriately selected, a structure with a higher grain size and a lower δ-phase content can be obtained. Compared with other annealing methods, the three-stage annealing process takes into account the promotion of nucleation at high temperature and the inhibition of the growth of recrystallized grains at low temperature, and quantifies the heat treatment parameters in the high-temperature stage and the low-temperature stage respectively, so that the coordination of grain structure refinement and δ-phase content control can be achieved, and it can obtain the required annealing structure by adjusting the temperature / time of the third-stage low-temperature isothermal annealing. The elimination of the mixed grain group is relatively controllable, and it has the advantages of simple operation, high error tolerance, low cost, easy implementation, and can greatly reduce the requirements for the forging process.

[0029] The embodiments of the present invention have been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above specific embodiments. The above specific embodiments are only exemplary and not restrictive. Any invention creation that does not exceed the claims of the present invention is within the protection scope of the present invention.

Claims

1. A heat treatment method for uniformly refining the mixed crystal structure of GH4169 alloy forgings and regulating the content of δ phase, characterized in that This method can regulate the content of δ phase while uniformly refining the mixed crystal structure of GH4169 alloy forgings through the combined process of δ phase aging treatment and three-stage recrystallization annealing treatment. This method includes the following steps: Step 1: Perform δ phase aging treatment on the GH4169 alloy forging with a mixed crystal structure; Step 2: Perform three-stage recrystallization annealing treatment on the forging after aging treatment. The three stages are: the first-stage high-temperature isothermal annealing, the second-stage continuous cooling annealing, and the third-stage low-temperature isothermal annealing; The process parameters of the aging treatment in Step 1 are: the aging temperature is between 890 and 910 °C, and the aging time is between 9 and 24 hours; The process parameters of the three-stage recrystallization annealing treatment in Step 2 are: the temperature of the first-stage high-temperature isothermal annealing is between 990 and 1000 °C, and the annealing time is between 3 and 5 minutes; the termination temperature of the second-stage continuous cooling annealing is between 950 and 980 °C, and the cooling time is between 5 and 10 minutes; the annealing temperature of the third-stage low-temperature isothermal annealing is between 950 and 980 °C, and the annealing time is between 20 and 30 minutes.

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