Method for improving notch sensitivity of gh2909 alloy forgings and gh2909 alloy forgings

Abstract

The application discloses a method for improving notch sensitivity of a GH2909 alloy forge piece and the GH2909 alloy forge piece, and comprises the following steps: S1, selecting a rod-shaped blank to be heated for the first time and kept warm; S2, heating the rod-shaped blank in S1 for the second time and keeping warm; S3, placing the rod-shaped blank in S2, which reaches the keeping-warm time, into a forging equipment to be forged into a shape; S4, rapidly cooling the forge piece obtained in S3; S5, performing surface defect treatment on the cooled forge piece; and S6, performing aging heat treatment on the forge piece after the surface defect treatment. The GH2909 forge piece produced by the method has no persistent notch sensitivity problem, and a forge piece with qualified structure and mechanical properties can be obtained.

Description

Methods to improve notch sensitivity of GH2909 alloy forgings and GH2909 alloy forgings Technical Field

[0001] This invention relates to the field of aero-engine technology, and in particular, to a method for improving notch sensitivity of GH2909 alloy forgings. Furthermore, this invention also relates to a GH2909 alloy forging obtained by the above-described method for improving notch sensitivity of GH2909 alloy forgings. Background Technology

[0002] GH2909 alloy is an age-hardening, low-expansion high-temperature alloy with Fe-Ni-Co matrix. It has an almost constant elastic modulus, low coefficient of expansion and good comprehensive properties below 650℃. It is an ideal material for aerospace engines and is mainly used to manufacture important structural components such as heat shield rings, outer casings and casings of aero engines.

[0003] The main precipitated phases of GH2909 alloy are γ' phase, ε phase, Laves phase, and MC phase. The Laves phase is a Nb-rich phase, and Nb is also the main component of the γ' strengthening phase, which is one of the factors affecting the creep rupture properties of alloy forgings. When the Laves phase precipitates in large quantities at grain boundaries, it consumes a large amount of Nb, forming γ'-depleted regions on both sides of the grain boundaries. Although this reduces the strength of the grain boundaries, it facilitates plastic deformation, especially at the notch, where the stress peak is alleviated, and the stress redistributes and tends to flatten, thereby weakening or eliminating the notch sensitivity of the alloy. Another factor affecting the creep rupture properties of alloy forgings is the ε phase. When the ε phase precipitates within the grains, it can improve the creep rupture properties of the alloy, while precipitation at grain boundaries can improve the alloy's resistance to stress-accelerated grain boundary oxidation embrittlement, which is beneficial for eliminating the notch sensitivity of the alloy.

[0004] A certain aero-engine turbine casing, produced using low-temperature forging and standard heat treatment, exhibits unstable microstructure and properties, particularly a high degree of creep rupture sensitivity. Meanwhile, forgings made from GH2909 alloy have consistently suffered from substandard creep rupture properties. Therefore, it is necessary to improve existing forging methods to enhance the content and distribution of granular Laves and ε phases in the microstructure of GH2909 alloy forgings. Summary of the Invention

[0005] This invention provides a method for improving the notch sensitivity of GH2909 alloy forgings and GH2909 alloy forgings, in order to solve the technical problems of notch sensitivity and unsatisfactory creep performance of GH2909 alloy forgings.

[0006] According to one aspect of the present invention, a method for improving notch sensitivity of GH2909 alloy forgings is provided, comprising the following steps:

[0007] S1: Select a rod-shaped billet for the first heating and holding to dissolve the laves phase in the alloy;

[0008] S2: The bar-shaped billet of S1 is heated a second time and held at that temperature to facilitate forging.

[0009] S3: The bar billet that has reached the holding time in S2 is placed in a forging equipment and forged into shape so that the alloy grains break during the forging deformation process, and a uniform and fine grain structure is obtained.

[0010] S4: Rapidly cool the forging obtained in S3 to cause the granular Laves phase to precipitate along the grain boundaries;

[0011] S5: Surface defect treatment is performed on the cooled forgings;

[0012] S6: After surface defect treatment, the forging is subjected to aging heat treatment to allow the ε phase to be fully precipitated at the grain boundaries.

[0013] Furthermore, in S1, the temperature of the first heating is 1060±10℃, the holding time is determined according to the effective thickness, and the holding coefficient is 1.0~2.0min / mm.

[0014] Furthermore, in S2, the temperature of the second heating is 990±10℃, the holding time is determined based on the effective thickness, and the holding coefficient is 0.4~0.6min / mm.

[0015] Furthermore, S3 specifically includes the following steps:

[0016] S31: Preheat the forging equipment and tooling before forging;

[0017] S32: The billet that has reached the holding time of S2 is placed in the preheated forging equipment and forged into shape.

[0018] Furthermore, in step S31, the hammer, anvil, punch, and fixture of the forging equipment are preheated to 150°C to 250°C.

[0019] Furthermore, in S32, the deformation amount of forging is controlled to be 30% to 80%.

[0020] Furthermore, S3 also includes S33: if the forging cannot be fully formed in one firing, repeat S2, S31 and S32.

[0021] Furthermore, in S33, the final forging deformation is ≥30%.

[0022] Furthermore, in step S4, the forging obtained in step S3 is immediately placed in water for cooling.

[0023] Furthermore, in S1, the dimensions of the rod-shaped blank are Φ80×155mm, the temperature of the first heating is 1060±10℃, and the holding time is 160min;

[0024] In step S2, the temperature of the second heating is 990±10℃, and the holding time is 40min~100min;

[0025] In step S3, the bar-shaped billet that has reached the holding time in S2 is subjected to upsetting and punching and expanding deformation in the first heat treatment, with a deformation amount of 80%, to obtain a ring billet with dimensions of Φ162±3×Φ90±3×40±2mm; the ring billet is then reheated in the furnace at a temperature of 990±10℃ for a holding time of 20min~80min, and after reaching the holding time, the ring billet is taken out of the furnace for expanding and forming in the second heat treatment, with a deformation amount of 33%, to obtain a forging with dimensions of Φ236±3×Φ186±3×39±2mm;

[0026] In step S4, the forging is immediately placed in water to cool after being forged;

[0027] In step S6, direct aging heat treatment is performed according to the standard aging heat treatment regime.

[0028] According to another aspect of the present invention, a GH2909 alloy forging is also provided, which is obtained by the above-described method for improving the notch sensitivity of GH2909 alloy forgings.

[0029] The present invention has the following beneficial effects:

[0030] The method for improving the creep notch sensitivity of GH2909 alloy forgings provided by this invention involves controlling the temperature of the first heating in the pre-forging pretreatment to dissolve the Laves phase in the alloy, facilitating its precipitation along grain boundaries during subsequent forging. The second heating controls the forging temperature and deformation amount, causing grain breakage during forging deformation, resulting in a uniform and fine grain structure. Rapid cooling of the forging further promotes the precipitation of granular Laves phase along grain boundaries. Direct aging heat treatment increases intragranular and grain boundary defects, providing favorable thermodynamic and kinetic conditions for the precipitation of the ε phase, accelerating its nucleation, and enabling its full precipitation at grain boundaries, thereby improving creep notch sensitivity. GH2909 alloy forgings produced by this method are free from creep notch sensitivity and possess satisfactory microstructure and mechanical properties.

[0031] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0032] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0033] Figure 1 is a flowchart of a preferred embodiment of the method for improving notch sensitivity of GH2909 alloy forgings according to the present invention;

[0034] Figure 2 is a high-magnification microstructure diagram of the GH2909 alloy forging with qualified creep performance according to a preferred embodiment of the present invention. Most of the granular Laves phase is distributed at the grain boundaries, and a small amount is precipitated in the grains. Detailed Implementation

[0035] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0036] As shown in Figure 1, the method for improving notch sensitivity of GH2909 alloy forgings in this embodiment includes the following steps.

[0037] S1: Select a rod-shaped billet for the first heating and holding to dissolve the laves phase in the alloy;

[0038] S2: The bar-shaped billet of S1 is heated a second time and held at that temperature to facilitate forging.

[0039] S3: The bar billet that has reached the holding time in S2 is placed in a forging equipment and forged into shape so that the alloy grains break during the forging deformation process, and a uniform and fine grain structure is obtained.

[0040] S4: Rapidly cool the forging obtained in S3 to cause the granular Laves phase to precipitate along the grain boundaries;

[0041] S5: Surface defect treatment is performed on the cooled forgings;

[0042] S6: After surface defect treatment, the forging is subjected to aging heat treatment to allow the ε phase to be fully precipitated at the grain boundaries.

[0043] The method for improving the creep notch sensitivity of GH2909 alloy forgings provided by this invention involves controlling the temperature of the first heating in the pre-forging pretreatment to dissolve the Laves phase in the alloy, facilitating its precipitation along grain boundaries during subsequent forging. The second heating controls the forging temperature and deformation amount, causing grain breakage during forging deformation, resulting in a uniform and fine grain structure. Rapid cooling of the forging further promotes the precipitation of granular Laves phase along grain boundaries. Direct aging heat treatment increases intragranular and grain boundary defects, providing favorable thermodynamic and kinetic conditions for the precipitation of the ε phase, accelerating its nucleation, and enabling its full precipitation at grain boundaries, thereby improving creep notch sensitivity. GH2909 alloy forgings produced by this method are free from creep notch sensitivity and possess satisfactory microstructure and mechanical properties.

[0044] In this embodiment, in step S1, the temperature of the first heating is 1060±10℃, the heat preservation time is determined according to the effective thickness, and the heat preservation coefficient is 1.0~2.0min / mm.

[0045] In this embodiment, in step S2, the temperature of the second heating is 990±10℃, the heat preservation time is determined based on the effective thickness, and the heat preservation coefficient is 0.4~0.6min / mm.

[0046] In this embodiment, step S3 specifically includes the following steps:

[0047] S31: Preheat the forging equipment and tooling before forging;

[0048] S32: The billet that has reached the holding time of S2 is placed in the preheated forging equipment and forged into shape.

[0049] In this embodiment, in step S31, the hammer, anvil, punch, and fixture of the forging equipment are preheated to 150°C to 250°C.

[0050] In this embodiment, in step S32, the deformation amount of forging is controlled to be 30% to 80%. If the deformation amount is lower than the specified amount, the microstructure will be relatively coarse, and the amount of Laves phase distributed along the grain boundaries will be greatly reduced, which will easily lead to notch sensitivity problems.

[0051] In this embodiment, S3 further includes S33: if the forging cannot be fully formed in one firing, repeat S2, S31 and S32.

[0052] In this embodiment, in step S33, the final forging deformation is ≥30%.

[0053] In this embodiment, in step S4, the forging obtained in step S3 is immediately placed in water for cooling.

[0054] Example

[0055] S1. Place the Φ80×155mm rod-shaped billet in an electric furnace for the first heating. The heating temperature is 1060±10℃, the holding coefficient is 2.0min / mm, and the holding time is 160min.

[0056] S2. The rod-shaped billet heated in S1 is placed in another electric furnace for a second heating. The heating temperature is 990±10℃ and the heat preservation coefficient is 0.5min / mm. Therefore, the lower limit of the heat preservation time is 40min. The upper limit of the heat preservation time is the lower limit of the heat preservation time plus 60min. Therefore, the heat preservation time is 40min to 100min.

[0057] S3. The bar billet that has reached the holding time in S2 is subjected to upsetting and punching and expanding deformation for the first heat treatment, with a deformation amount of 80%, to obtain a ring billet with dimensions of Φ162±3×Φ90±3×40±2mm. The ring billet is then reheated in the furnace to a temperature of 990±10℃, with a holding time of 20min~80min. While still hot, the holding time is halved, while ensuring that the upper limit of the holding time minus the lower limit of the holding time is ≥60min. After reaching the holding time, the ring billet is removed from the furnace and subjected to expanding and forming for the second heat treatment, with a deformation amount of 33%, to obtain a forging with dimensions of Φ236±3×Φ186±3×39±2mm.

[0058] S4. Immediately immerse the forged part in water to cool it after forging.

[0059] S5. After cooling, the forgings undergo surface defect treatment.

[0060] S6. Perform direct aging heat treatment according to the standard aging heat treatment regime.

[0061] The GH2909 alloy forging is now complete.

[0062] For GH2909 alloy, the granular laves distributed at grain boundaries have a suppressive effect on creep notch sensitivity. When the granular laves phase generated during the alloy's hot deformation is dispersed within the grains with few grain boundaries, creep notch sensitivity occurs. However, when the laves phase is granular or blocky and discontinuously distributed at the grain boundaries, creep notch sensitivity is weakened or even eliminated. The purpose of the first heating pretreatment is to dissolve a large amount or even all of the laves phase in the alloy, so that it can re-precipitate as granules at the grain boundaries during the subsequent hot deformation process (i.e., low-temperature forging deformation). The subsequent aging process promotes the precipitation of the ε phase along the grain boundaries, resulting in a more ideal microstructure distribution, thereby improving the notch sensitivity problem of the part.

[0063] Figure 2 shows a high-magnification microstructure photograph of the GH2909 alloy forging in this embodiment. As can be seen from Figure 2, there are fewer Laves phases in the grains. The Laves phases are mainly granular and discontinuously distributed at the grain boundaries, which is an ideal microstructure for forgings without notch sensitivity issues.

[0064] The mechanical property data of the GH2909 alloy forging in this embodiment are shown in Table 1.

[0065] Table 1 Mechanical property data of forgings

[0066]

[0067] As shown in Table 1, the tensile strength and yield strength are approximately 100 MPa higher than the standard requirements, and the creep rupture life is significantly higher than the standard requirement, reaching over 100 hours. The forgings obtained using the above technical solution have satisfactory microstructure and mechanical properties, and no creep rupture notch sensitivity issues occur.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving notch sensitivity in GH2909 alloy forgings, characterized in that, The process includes the following steps: S1: Select a rod-shaped billet and heat it for the first time and hold it at that temperature to dissolve the ε phase in the alloy. The temperature of the first heating is 1060±10℃, and the holding time is determined based on the effective thickness. The holding coefficient is 1.0~2.0min / mm. S2: Heat the rod-shaped billet from S1 for the second time and hold it at that temperature to facilitate forging. The temperature of the second heating is 990±10℃, and the holding time is determined based on the effective thickness. The holding coefficient is 0.4~0.6min / mm. S3: Place the rod-shaped billet that has reached the holding time in S2 into a forging machine and forge it to form a uniform and fine grain structure by causing grain breakage during the forging deformation process. S4: Immediately immerse the forging obtained in S3 in water to cool it, so that the granular ε phase precipitates along the grain boundaries. S5: Perform surface defect treatment on the cooled forging. S6: Perform aging heat treatment on the forging after surface defect treatment, so that the ε phase precipitates fully at the grain boundaries.

2. The method for improving notch sensitivity of GH2909 alloy forgings according to claim 1, characterized in that, The S3 specifically The process includes the following steps: S31: Preheating the forging equipment and tooling before forging; S32: Forging the billet that has reached the holding time in S2 into the preheated forging equipment.

3. The method for improving notch sensitivity of GH2909 alloy forgings according to claim 2, characterized in that, In step S31, the hammer, anvil, punch, and fixture of the forging equipment are preheated to 150°C to 250°C.

4. The method for improving notch sensitivity of GH2909 alloy forgings according to claim 2, characterized in that, In S32, the deformation amount of forging is 30% to 80%.

5. The method for improving notch sensitivity of GH2909 alloy forgings according to claim 2, characterized in that, S3 also includes S33: If the forging cannot be fully formed in one firing, repeat S2, S31 and S32.

6. The method for improving notch sensitivity of GH2909 alloy forgings according to claim 5, characterized in that, In S33, the final forging deformation is ≥30%.

7. The method for improving notch sensitivity of GH2909 alloy forgings according to claim 1, characterized in that, In step S1, the size of the bar billet is Φ80×155mm, and the holding time for the first heating is 160min; in step S2, the holding time for the second heating is 40min~100min; in step S3, the bar billet that has reached the holding time in step S2 is subjected to upsetting and punching and expanding deformation for the first heat, with a deformation amount of 80%, to obtain a ring billet with a size of Φ162±3×Φ90±3×40±2mm; the ring billet is returned to the furnace and heated to a temperature of 990±10℃, with a holding time of 20min~80min, and after reaching the holding time, the ring billet is taken out of the furnace and subjected to expanding and forming for the second heat, with a deformation amount of 33%, to obtain a forging with a size of Φ236±3×Φ186±3×39±2mm; in step S6, direct aging heat treatment is performed according to the standard aging heat treatment regime.

8. A GH2909 alloy forging, characterized in that, It is prepared by any one of the methods for improving notch sensitivity of GH2909 alloy forgings according to claims 1 to 7.

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