Forging method for improving microstructure uniformity of GH4720Li alloy and application thereof

Abstract

The application discloses a forging method for improving the structure uniformity of GH4720Li alloy and belongs to the technical field of high-temperature alloy hot working, which comprises the following steps: firstly, performing multi-cycle axial upsetting and drawing on a cast ingot to preliminarily break the structure; secondly, performing axial upsetting and drawing combined with chamfering to round the blank and promote stress penetration; thirdly, performing multi-fire lengthening to further refine and homogenize the structure; and fourthly, completing the forming of finished rod materials through lengthening and rounding. The application combines different forging forms, homogenizes the internal stress field and recrystallization behavior of the blank, and thus obtains the GH4720Li alloy rod material with uniform structure and stable performance.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy hot working technology, and relates to GH4720Li high-temperature alloy, specifically to a forging method for improving the uniformity of the microstructure of GH4720Li alloy and its application. Background Technology

[0002] GH4720Li alloy is a nickel-based age-hardening superalloy, with the γ′ phase being the main strengthening phase. This alloy exhibits excellent comprehensive properties below 730℃, possessing good resistance to oxidation, hot corrosion, fatigue, and creep.

[0003] However, because the total Al and Ti content in the GH4720Li alloy exceeds 8%, the volume fraction of the reinforcing γ′ phase reaches approximately 40%, resulting in a significant increase in the alloy's deformation resistance during hot working and making plastic deformation difficult. Under these conditions, stress is difficult to effectively transfer to the core of the material, leading to uneven stress field distribution within the billet and uneven recrystallization behavior, thus affecting the forming quality.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a forging method and its application for improving the uniformity of the microstructure of GH4720Li alloy, so as to improve the problem of uniformity of GH4720Li alloy components.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This forging method improves the uniformity of the microstructure of GH4720Li alloy, such as Figure 1 As shown, the specific steps include: Step 1: Heat the GH4720Li alloy ingot, and then perform axial upsetting forging at a temperature higher than the heating temperature to fully break down the original as-cast structure and obtain an octagonal cross-section billet a. Repeat the axial upsetting for 3 to 4 cycles. Step 2: Axially upset and chamfer the billet a to obtain a billet b with a circular cross section. Repeat the axial upset and chamfering process 2 to 4 times. Step 3: Perform four-pass drawing forging on the billet b to obtain a billet c with uniform microstructure; Step 4: Perform a finishing forging process on the billet c to complete the forming of the target bar.

[0007] Further, in step 1, the GH4720Li alloy ingot is held at a temperature range of 980℃ to 1050℃ for 60 min to 180 min, and then heated to 1100℃ to 1130℃ and held for 180 min to 270 min in the furnace. The GH4720Li alloy ingot is then subjected to axial upsetting forging, wherein the elongation deformation of the axial upsetting forging is 15% to 25% and the upsetting deformation is 20% to 40%.

[0008] Further, in step 2, after holding the billet a at a temperature range of 1140℃ to 1160℃ for 120 min to 180 min, the billet a is subjected to axial upsetting forging. The elongation deformation of the axial upsetting forging is 25% to 40%, and the upsetting deformation is 15% to 30%.

[0009] Furthermore, in step 3, the four-stage drawing and forging process specifically includes: First, after holding the billet b at a temperature range of 1140℃ to 1160℃ for 120 min to 180 min, the billet b is subjected to a single-pass anvil drawing, with a deformation of 15% to 30%. Then, after holding the billet obtained by the anvil drawing at a temperature range of 1080℃ to 1120℃ for 120 min to 180 min, the billet is subjected to a three-pass flat anvil drawing, with a deformation of 30% to 50%.

[0010] Furthermore, in step 4, after holding the billet c at a temperature range of 1120℃ to 1140℃ for 90 min to 150 min, the billet c is drawn and rounded once and then cooled, with a deformation of 30% to 50%.

[0011] Furthermore, the GH4720Li alloy ingot mentioned in step 1 is made using a three-stage melting process of "vacuum induction melting + protective atmosphere electroslag melting + vacuum consumable melting".

[0012] Preferably, the gas used in the protective atmosphere electroslag smelting is helium.

[0013] Furthermore, in the forging process described in step 1, asbestos needs to be wrapped around the surface of the material for each heat. Specifically, asbestos is wrapped around the surface of the material after each heat is held at a certain temperature and before forging.

[0014] Furthermore, in step 4, the target bar has a specification of Φ130mm~Φ250mm.

[0015] Further, the GH4720Li alloy ingot mentioned in step 1 has the following chemical composition by mass percentage: carbon 0.01%~0.02%, cobalt 14.0%~15.5%, chromium 15.5%~16.5%, molybdenum 2.75%~3.25%, aluminum 2.25%~2.75%, titanium 4.75%~5.25%, zirconium 0.025%~0.050%, tungsten 1.00%~1.50%, boron 0.01~0.02%, phosphorus ≤0.015%, sulfur ≤0.001%, silicon ≤0.20%, copper ≤0.01%, manganese ≤0.15%, iron ≤0.50%, oxygen ≤0.002%, nitrogen ≤0.0032%, with the remainder being nickel.

[0016] Furthermore, the present invention also provides the application of GH4720Li alloy bars prepared by some or all of the forging methods described above in the manufacture of key rotating components of aero-engines.

[0017] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: This invention employs axial upsetting, multi-stage drawing, and chamfering / rounding operations to alter the metal flow direction and break down the original coarse structure, thereby achieving a more uniform stress field distribution within the billet and obtaining a more uniform and fine recrystallized grain structure from the surface to the core. Furthermore, since sulfur (S) and copper (Cu) are harmful elements, this invention effectively reduces their tendency to cause grain boundary brittleness by controlling their content within specific ranges. Attached Figure Description

[0018] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A flowchart of a forging method for improving the microstructure uniformity of GH4720Li alloy provided by the present invention; Figure 2 High-magnification microstructure images of the core, R / 4, R / 2, 3R / 4 and edge positions of the GH4720Li high-temperature alloy Φ150mm bar provided in Embodiment 1 of the present invention (wherein) Figure 2 a is a high-magnification tissue image of the heart region. Figure 2 b is a high-magnification tissue image at position R / 4. Figure 2 c is a high-magnification tissue image at position R / 2. Figure 2d is a high-magnification tissue image at position 3R / 4. Figure 2 e is a high-magnification tissue image of the edge position); Figure 3 High-magnification microstructure images of the core, R / 4, R / 2, 3R / 4 and edge positions of the GH4720Li high-temperature alloy Φ130mm bar provided in Embodiment 2 of the present invention (wherein) Figure 3 a is a high-magnification tissue image of the heart region. Figure 3 b is a high-magnification tissue image at position R / 4. Figure 3 c is a high-magnification tissue image at position R / 2. Figure 3 d is a high-magnification tissue image at position 3R / 4. Figure 3 e is a high-magnification tissue image of the edge position); Figure 4 High-magnification microstructure images of the core, R / 4, R / 2, 3R / 4 and edge positions of the GH4720Li high-temperature alloy Φ250mm bar provided in Embodiment 3 of the present invention (wherein) Figure 4 a is a high-magnification tissue image of the heart region. Figure 4 b is a high-magnification tissue image at position R / 4. Figure 4 c is a high-magnification tissue image at position R / 2. Figure 4 d is a high-magnification tissue image at position 3R / 4. Figure 4 e is a high-magnification tissue image of the edge position); Figure 5 High-magnification microstructure images of the core, R / 4, R / 2, 3R / 4 and edge positions of GH4720Li high-temperature alloy bars provided for comparative examples (where...) Figure 5 a is a high-magnification tissue image of the heart region. Figure 5 b is a high-magnification tissue image at position R / 4. Figure 5 c is a high-magnification tissue image at position R / 2. Figure 5 d is a high-magnification tissue image at position 3R / 4. Figure 5 e is a high-magnification tissue image of the edge position. Detailed Implementation

[0021] Exemplary embodiments will now be described in detail. The embodiments described below are not representative of all embodiments consistent with this invention. Rather, they are merely examples consistent with some aspects of the invention as detailed in the appended claims.

[0022] This invention provides a forging method for improving the microstructure uniformity of GH4720Li alloy, the preparation method comprising: Step 1: Hold the GH4720Li alloy ingot at a temperature range of 980℃~1050℃ for 60min~180min, then raise the temperature to 1100℃~1130℃ and hold for 180min~270min. Then, perform axial upsetting forging on the GH4720Li alloy ingot. The elongation deformation is 15%~25%, and the upsetting deformation is 20%~40%, to obtain an octagonal cross-section billet a. Repeat the axial upsetting forging for 3-4 cycles. Step 2: After holding the billet a at a temperature range of 1140℃~1160℃ for 120min~180min, the billet a is subjected to axial upsetting forging with a drawing deformation of 25%~40% and a upsetting deformation of 15%~30%. The billet b with a circular cross section is obtained by chamfering. The axial upsetting and chamfering are repeated for 2-4 cycles. Step 3: After holding the billet b at a temperature range of 1140℃ to 1160℃ for 120 min to 180 min, the billet b is subjected to a single-pass anvil drawing, with a deformation of 15% to 30%; then, after holding the anvil-drawn billet at a temperature range of 1080℃ to 1120℃ for 120 min to 180 min, the billet is subjected to a third-pass flat anvil drawing, with a deformation of 30% to 50%, thereby obtaining a billet c with a uniform structure; Step 4: After holding the billet c at a temperature range of 1120℃~1140℃ for 90min~150min, the billet c is drawn and rounded once and then air-cooled, with a deformation of 30%~50%, thus completing the forming of the target bar.

[0023] The bars prepared by this invention are mainly used in key rotating components of aero engines with service temperatures not exceeding 730 ℃, such as turbine disks and turbine blades.

[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example 1 This embodiment provides a forging method for improving the uniformity of the microstructure of GH4720Li alloy, specifically including the following steps: Step 1: Hold the GH4720Li alloy ingot at 980℃ for 120 min, then heat it to 1100℃ and hold it for 180 min. Then, perform axial upsetting forging on the GH4720Li alloy ingot. The elongation deformation is 20% and the upsetting deformation is 25%, resulting in an octagonal cross-section billet a. Repeat the axial upsetting process for three cycles. Step 2: After holding the billet a at 1140℃ for 120 minutes, the billet a is subjected to axial upsetting forging with a drawing deformation of 25% and a backing deformation of 25%. The billet b with a circular cross section is obtained by chamfering. The axial upsetting and chamfering are repeated for two cycles. Step 3: After holding the billet b at 1140℃ for 120 minutes, the billet b is drawn once with an anvil, and the deformation is 20%; then, after holding the drawn billet at 1120℃ for 150 minutes, the billet is drawn three times with an anvil, and the deformation is 33%, thereby obtaining a billet c with uniform structure. Step 4: After holding the billet c at 1120℃ for 90 minutes, the billet c is drawn and rounded once and then air-cooled. The deformation is 35%, and the target bar with a specification of Φ150mm is formed.

[0026] Example 2 This embodiment provides a forging method for improving the uniformity of the microstructure of GH4720Li alloy, specifically including the following steps: Step 1: Hold the GH4720Li alloy ingot at 1050℃ for 90 min, then heat it to 1130℃ and hold it for 240 min. Then, perform axial upsetting forging on the GH4720Li alloy ingot. The elongation deformation is 15% and the upsetting deformation is 25%, resulting in an octagonal cross-section billet a. Repeat the axial upsetting process for four cycles. Step 2: After holding the billet a at 1160℃ for 150 minutes, the billet a is subjected to axial upsetting forging with a drawing deformation of 25% and a backing deformation of 25%. The billet b with a circular cross section is obtained by chamfering. The axial upsetting and chamfering are repeated for two cycles. Step 3: After holding the billet b at 1160℃ for 180 min, the billet is drawn once with an anvil and the deformation is 25%; then, after holding the drawn billet at 1080℃ for 180 min, the billet is drawn at least three times and the deformation is 40%, thereby obtaining a billet c with a uniform structure. Step 4: After holding the billet c at 1140℃ for 120 minutes, the billet c is drawn and rounded once and then air-cooled. The deformation is 35%, and the target bar with a specification of Φ130mm is formed.

[0027] Example 3 This embodiment provides a forging method for improving the uniformity of the microstructure of GH4720Li alloy, specifically including the following steps: Step 1: Hold the GH4720Li alloy ingot at 1020℃ for 60 min, then heat it to 1120℃ and hold it for 270 min. Then, perform axial upsetting forging on the GH4720Li alloy ingot. The elongation deformation is 15% and the upsetting deformation is 40%, resulting in an octagonal cross-section billet a. Repeat the axial upsetting process for three cycles. Step 2: After holding the billet a at 1150℃ for 180 minutes, the billet a is subjected to axial upsetting forging with a drawing deformation of 40% and a upsetting deformation of 25%. The billet b with a circular cross section is obtained by chamfering. The axial upsetting and chamfering are repeated for four cycles. Step 3: Hold the billet b at 1150℃ for 150 min, then draw the billet once with an anvil, with a deformation of 30%; then hold the drawn billet at 1100℃ for 120 min, and then draw the billet three times with an deformation of 47%, thereby obtaining a billet c with a uniform structure. Step 4: After holding the billet c at 1130℃ for 150 minutes, the billet c is drawn and rounded once and then air-cooled. The deformation is 50%, and the target bar with a specification of Φ250mm is formed.

[0028] Comparative Example This comparative example provides a forging method for GH4720Li alloy, which is existing technology, and specifically includes the following steps: Step 1: Hold the GH4720Li alloy ingot at 1160℃ for 270 min, and perform axial upsetting forging on the GH4720Li alloy ingot. The elongation deformation is 25% and the upsetting deformation is 30%, to obtain the octagonal cross-section billet a. Repeat the axial upsetting forging for four cycles. Step 2: After holding the billet a at 1130℃ for 180 minutes, the billet a is subjected to axial upsetting forging with a drawing deformation of 25% and a backing deformation of 25%. The billet b with a circular cross section is obtained by chamfering. The axial upsetting and chamfering are repeated for four cycles. Step 3: Hold billet b at 1100℃ for 120 minutes, then draw the billet four times, with a deformation of 40%. Step 4: After holding the billet c at 1080℃ for 120 minutes, the billet c is drawn and rounded once and then air-cooled. The deformation is 45%, and the target bar with a specification of Φ150mm is formed.

[0029] Based on the bars obtained in Example 1 and the comparative example, samples were taken from the microstructure of the core, R / 4, R / 2, 3R / 4 and edge of the forged bars. The grain size grade was evaluated and analyzed according to GB / T6394-2017 "Method for Determination of Average Grain Size of Metals", as shown in Table 1. To further verify the effectiveness of the technical solution of the present invention, the inventors analyzed the high-magnification microstructure of the core, R / 4, R / 2, 3R / 4 and edge positions of the bars obtained in Example 1 and the comparative example, such as... Figure 2 As shown, it is a high-magnification microstructure image of the core, R / 4, R / 2, 3R / 4 and edge positions of the bar obtained in Embodiment 1 of the present invention, as follows. Figure 3 As shown, it is a high-magnification microstructure diagram of the core, R / 4, R / 2, 3R / 4 and edge positions of the bar obtained in the comparative example.

[0030] In summary, as shown in Table 1, the forging method for improving the uniformity of the microstructure of GH4720Li alloy provided by this invention, compared with conventional forging methods, produces GH4720Li alloy bars with a more concentrated grain size, mainly at the 8-10 level. Figure 2 , 3 and 4 and Figure 5 The comparison shows that the bar material prepared using the present invention has a more uniform grain structure from the surface to the core. Improving the uniformity of the structure can enhance the strength, plasticity, and durability of the material. Therefore, the bar material forged by the forging method of the present invention has better strength, plasticity, and durability, and its performance meets the requirements of standard (AETM42A).

[0031] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0032] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A forging method for improving the uniformity of the microstructure of GH4720Li alloy, characterized in that, The forging method includes the following steps: Step 1: Heat the GH4720Li alloy ingot, and then perform axial upsetting forging at a temperature higher than the heating temperature to fully break down the original as-cast structure and obtain an octagonal cross-section billet a. Repeat the axial upsetting for 3 to 4 cycles. Step 2: Axially upset and forged the billet a, and obtain a billet b with a circular cross section by chamfering. Repeat the axial upset and chamfering process for 2 to 4 cycles. Step 3: Perform four-pass drawing forging on the billet b to obtain a billet c with uniform microstructure; Step 4: Perform a finishing forging process on the billet c to complete the forming of the target bar.

2. The forging method for improving the microstructure uniformity of GH4720Li alloy according to claim 1, characterized in that, In step 1, the GH4720Li alloy ingot is held at a temperature range of 980℃ to 1050℃ for 60 min to 180 min, and then heated to 1100℃ to 1130℃ and held for 180 min to 270 min. The GH4720Li alloy ingot is then subjected to axial upsetting forging. The elongation deformation of the axial upsetting forging is 15% to 25%, and the upsetting deformation is 20% to 40%.

3. The forging method for improving the microstructure uniformity of GH4720Li alloy according to claim 1, characterized in that, In step 2, after holding the billet a at a temperature range of 1140℃ to 1160℃ for 120 min to 180 min, the billet a is subjected to axial upsetting forging. The elongation deformation of the axial upsetting forging is 25% to 40%, and the upsetting deformation is 15% to 30%.

4. The forging method for improving the microstructure uniformity of GH4720Li alloy according to claim 1, characterized in that, Step 3, the four-stage drawing and forging process specifically includes: First, after holding the billet b at a temperature range of 1140℃ to 1160℃ for 120 min to 180 min, the billet b is subjected to a single-pass anvil drawing, with a deformation of 15% to 30%. Then, the billet obtained by the above-mentioned anvil drawing is kept at a temperature range of 1080℃~1120℃ for 120min~180min, and then the billet is drawn three times with a flat anvil, with a deformation of 30%~50%.

5. A forging method for improving the microstructure uniformity of GH4720Li alloy according to claim 1, characterized in that, In step 4, after holding the billet c at a temperature range of 1120℃ to 1140℃ for 90 min to 150 min, the billet c is drawn and rounded once and then air-cooled, with a deformation of 30% to 50%.

6. The forging method for improving the microstructure uniformity of GH4720Li alloy according to claim 1, characterized in that, The GH4720Li alloy ingot mentioned in step 1 is made by a three-stage melting process of "vacuum induction melting + protective atmosphere electroslag melting + vacuum consumable melting".

7. The forging method for improving the microstructure uniformity of GH4720Li alloy according to claim 1, characterized in that, In the forging process described in step 1, asbestos needs to be coated on the surface of the material for each forging.

8. A forging method for improving the microstructure uniformity of GH4720Li alloy according to claim 1, characterized in that, In step 4, the target bar has a specification of Φ130mm~Φ250mm.

9. A forging method for improving the uniformity of microstructure of GH4720Li alloy according to claim 1, characterized in that, The GH4720Li alloy ingot mentioned in step 1 has the following chemical composition by mass percentage: carbon 0.01%~0.02%, cobalt 14.0%~15.5%, chromium 15.5%~16.5%, molybdenum 2.75%~3.25%, aluminum 2.25%~2.75%, titanium 4.75%~5.25%, zirconium 0.025%~0.050%, tungsten 1.00%~1.50%, boron 0.01~0.02%, phosphorus ≤0.015%, sulfur ≤0.001%, silicon ≤0.20%, copper ≤0.01%, manganese ≤0.15%, iron ≤0.50%, oxygen ≤0.002%, nitrogen ≤0.0032%, with the remainder being nickel.

10. The application of GH4720Li alloy bars prepared by the forging method according to any one of claims 1 to 9 in the preparation of key rotating components of aero-engines.

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