A method of forging a nickel-based superalloy bar to refine the microstructure of the bar

Abstract

This invention provides a forging method for refining the microstructure of forged nickel-based superalloy bars, specifically including the following steps: 1) Selecting a forged nickel-based superalloy ingot with an Al+Ti content of 4.2%–4.8%, and using a flat anvil on a high-speed forging mill to prepare an intermediate billet, with asbestos encasing during the forging process; 2) Drawing the intermediate billet on a high-speed forging mill using upper and lower V-shaped anvils to forge the forged nickel-based superalloy bar, with asbestos encasing during the forging process; 3) After forging, air-cooling the material for ≥2 hours, followed by air cooling to room temperature. This invention aims to solve the problem of coarse grain size in the core of the bar prepared using the flat anvil forging method throughout the process, and the large grain size difference between the core and edge, resulting in poor microstructure uniformity and consistency. Using this method, the core grain size of the bar can be refined, and the grain size difference between the core and edge can be reduced, thereby producing fine-grained, difficult-to-deform nickel-based superalloy forged bars with high microstructure uniformity.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal processing technology, specifically relating to a forging method for refining the microstructure of difficult-to-deform nickel-based high-temperature alloy bars. Background Technology

[0002] Difficult-to-deform nickel-based superalloys are nickel-based wrought superalloys that are precipitation-strengthened with γ′ phase as the main strengthening phase. These alloys have a service temperature of 760℃~870℃. In addition, they have excellent oxidation and corrosion resistance and high high-temperature strength, so they are widely used in aviation, aerospace, petroleum, chemical and power generation fields. They are particularly suitable for manufacturing parts such as turbine disks, working blades, high-temperature fasteners, rocket launchers, shafts, and turbine casings.

[0003] It is well known in the industry that the grain size and microstructure uniformity of nickel-based superalloys have a significant impact on their performance. As grain inhomogeneity increases, the alloy's creep rupture life decreases significantly. Furthermore, difficult-to-deform nickel-based superalloys have a narrow deformation temperature range, and their microstructure is extremely sensitive to deformation amount and temperature, easily leading to incomplete dynamic recrystallization and mixed grain formation, thus affecting the alloy's performance. Traditionally, difficult-to-deform nickel-based superalloy bars are forged entirely on flat anvils. Due to their large critical deformation for complete recrystallization and poor forging penetration, flat anvil forging typically employs large deformation (≥40%) and large single-hammer reduction in the forming heat stages. This results in severe forging temperature rise in the core, especially when the bar size is large. The heat in the core cannot be dissipated quickly enough, and the core microstructure remains at high temperatures for an extended period after complete recrystallization, leading to severe grain coarsening in the core and exacerbating the significant grain size difference between the core and edges. This inhomogeneous microstructure can also be inherited during subsequent heat treatment processes. Therefore, to ensure the uniformity of the microstructure and properties of subsequent forgings, it is most important to ensure that the microstructure of the forged bar is as fine and uniform as possible.

[0004] In view of this, the inventors propose a forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars to overcome the shortcomings of the prior art. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars. This forging method can refine the core grain size of the difficult-to-deform nickel-based superalloy bars to grade 4.5 or finer, while reducing the grain size difference between the core and the edge to within grade 2, thereby ensuring the uniformity of the microstructure and properties of the forgings prepared from the bars.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars, the forging method comprising the following steps;

[0008] Step 1: Select a difficult-to-deform nickel-based high-temperature alloy ingot with an Al+Ti content of 4.2% to 4.8%, and perform upsetting and drawing on a high-speed forging machine using a flat anvil for 5 to 7 passes. Each forging process is wrapped with heat-insulating asbestos to obtain an intermediate billet.

[0009] Step 2: The intermediate billet obtained in Step 1 is drawn in 3 passes and 1 heat on a high-speed forging machine using upper and lower V-shaped anvils to complete the forming and forging of the difficult-to-deform nickel-based high-temperature alloy bar.

[0010] Step 3: After air cooling the difficult-to-deform nickel-based high-temperature alloy bar formed and forged in Step 2 for at least 2 hours, air cool it to room temperature.

[0011] This invention selects nickel-based superalloy ingots with Al+Ti content of 4.2% to 4.8% as the corresponding range for medium-difficult-to-deform superalloys. Alloys with content lower than this range are easier to forge and can obtain a good microstructure without using this method; however, alloys with content higher than this range are too difficult to forge and cannot obtain a sufficiently uniform fine-grained microstructure using this method.

[0012] Furthermore, in step one, the heating temperature for each heating cycle is set to 1080–1160°C, and the deformation amount is set to 15%–35%.

[0013] Furthermore, the heating temperature in step two is set to 1040–1080°C.

[0014] Furthermore, the specific implementation process of the three passes in step two is as follows:

[0015] The deformation amount for the first and second passes is set to 15% to 25%, with one step every two revolutions. The rotation angle for each revolution is set to 45°, the feed rate is set to 90 to 110 mm, and the press pressing speed is set to 50 to 70 mm / s.

[0016] The deformation amount for the third pass is set to 2% to 8%, with one revolution per step, each rotation angle set to 30°, the feed rate set to 30 to 50 mm, and the press pressing speed set to 90 to 110 mm / s.

[0017] Furthermore, during the forming and forging process in step 2, the outer side is wrapped with insulating asbestos.

[0018] Furthermore, the difficult-to-deform nickel-based superalloy ingot selected in step 1 has an Al+Ti content of 4.35-4.7%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention discloses a forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars. Compared to existing technologies that use flat anvil forging throughout the entire process, this invention employs double V-anvil forging in the forming stage. The main deformation is carried out in two passes of 15% to 25%. By setting reasonable rotation angles, feed rates, and press reduction rates, sufficient total deformation is ensured, resulting in a fully recrystallized microstructure. Furthermore, the use of V-anvil forging significantly reduces the difference in equivalent deformation between the core and edges. Simultaneously, controlling the single hammer reduction (reduction in the height direction of the material in a single pass) within a suitable range avoids excessive temperature rise in the core, improving circumferential uniformity of deformation. In addition, rapid air cooling after the final forming forging accelerates heat dissipation from the core, reducing the high-temperature residence time of the core microstructure after deformation. In summary, this forging method avoids the mixed crystal phenomenon caused by incomplete crystallization, resulting in a reasonably refined core microstructure in the final forged bar, with a good microstructure exhibiting a small difference in grain size between the core and edges. Attached Figure Description

[0021] 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.

[0022] 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.

[0023] Figure 1 This is a flowchart of a forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars according to the present invention;

[0024] Figure 2 This is a microstructure of the core of the difficult-to-deform nickel-based superalloy bar prepared in Example 1 of this invention;

[0025] Figure 3 This is a microstructure image of the edge of the difficult-to-deform nickel-based superalloy bar prepared in Example 1 of this invention;

[0026] Figure 4 This is a microstructure of the core of a difficult-to-deform nickel-based superalloy bar prepared entirely by flat anvil forging using traditional techniques.

[0027] Figure 5 This is a microstructure image of the edge of a difficult-to-deform nickel-based superalloy bar produced entirely by flat anvil forging using traditional techniques. Detailed Implementation

[0028] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses consistent with some aspects of the invention as detailed in the appended claims.

[0029] 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.

[0030] Example 1

[0031] Please see Figure 1 As shown, this embodiment provides a forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars, which specifically includes the following steps;

[0032] 1) Select a difficult-to-deform nickel-based superalloy ingot with an Al+Ti content of 4.35%, heat it for 15 hours, and then forge it. Perform five upsetting and drawing operations on a high-speed forging mill using a 650mm wide flat anvil. The first three upsettings are performed at 1150℃, with each upsetting and drawing operation controlling the deformation to 15-25%, utilizing high-temperature upsetting and drawing to fully break down the as-cast microstructure. The fourth and fifth upsettings are performed at 1080℃, with each upsetting and drawing operation controlling the deformation to 20-30%, utilizing medium-temperature upsetting to further break down the microstructure and refine the grains. Complete the preparation of the intermediate billet. Asbestos is wrapped during each forging operation. After the first four upsettings, the hot material is returned to the furnace, and after the fifth upsetting, it is air-cooled.

[0033] 2) The intermediate billet obtained in step 1) is drawn in one pass on a high-speed forging mill using upper and lower V-shaped anvils. The heating temperature is 1050℃, and after heating for 8 hours, it is taken out of the furnace for forging. A total of 3 forging passes are performed. The deformation amount of the first pass is 18%, with two rotations and one step, and each rotation angle is 45° and the feed amount is 110mm. After the first pass, the material is emptied and returned to the starting forging position for unidirectional drawing forging. The deformation amount of the second pass is 15%, with two rotations and one step, and each rotation angle is 45° and the feed amount is 100mm. The press is set to a pressing speed of 60mm / s. After the second pass, the material is emptied and returned to the starting forging position for unidirectional drawing forging. The deformation amount of the third pass is 5%, with one rotation and one step, and each rotation angle is 30° and the feed amount is 40mm. The press is set to a pressing speed of 100mm / s. That is, the difficult-to-deform nickel-based high-temperature alloy bar is forged by one fire and three passes of double V-anvil forging, and the outer side is wrapped with heat-insulating asbestos during the forming forging process, and finally forged to the finished size of Φ250mm.

[0034] 3) After the difficult-to-deform nickel-based superalloy bar formed and forged in step 2) is air-cooled for ≥2 hours, it is then air-cooled to room temperature. Utilizing timely air cooling after forging reduces the time the core structure remains in the high-temperature zone after forging, preventing the fine-grained core structure from coarsening during the slow air cooling process.

[0035] Figures 2-3 The images show the core and edge microstructure of a difficult-to-deform nickel-based superalloy bar prepared by the microstructure refinement forging method of this invention. Figures 4-5 Microstructure images of the core and edge of a difficult-to-deform nickel-based superalloy bar prepared entirely by flat anvil forging, serving as a comparative example. As can be seen from the accompanying figures, compared to the microstructure of the bar prepared entirely by flat anvil forging, the microstructure of the core of this invention, after employing a forging method that refines the microstructure, is refined from grade 3 to grade 4.5, while the difference in microstructure grade between the core and edge is reduced from grade 4 to grade 2.

[0036] Example 2

[0037] This embodiment provides a forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars, which specifically includes the following steps;

[0038] 1) Select a difficult-to-deform nickel-based superalloy ingot with an Al+Ti content of 4.5%, heat it for 17 hours, and then forge it. Perform six upsetting and drawing operations on a high-speed forging mill using a 650mm wide flat anvil. The first three upsettings are performed at 1160℃, with deformation controlled between 18% and 23% per operation, utilizing high-temperature upsetting and drawing to fully break down the as-cast microstructure. The fourth to sixth upsettings are performed at 1090℃, with deformation controlled between 25% and 30% per operation, utilizing medium-temperature upsetting to further break down the microstructure and refine the grains. Complete the preparation of the intermediate billet. Asbestos is wrapped during each forging operation. After the first five upsettings, the hot material is returned to the furnace, and after the sixth upsetting, it is air-cooled.

[0039] 2) The intermediate billet obtained in step 1) is drawn in one pass on a high-speed forging mill using upper and lower V-shaped anvils. The heating temperature is 1060℃, and after heating for 9 hours, it is taken out of the furnace for forging. A total of 3 forging passes are performed. The deformation amount of the first pass is 20%, with two rotations and one step, and each rotation angle is 45° and the feed amount is 100mm. After the first pass, the material is emptied and returned to the starting forging position for unidirectional drawing forging. The deformation amount of the second pass is 17%, with two rotations and one step, and each rotation angle is 45° and the feed amount is 90mm. The press is set to a pressing speed of 60mm / s. After the second pass, the material is emptied and returned to the starting forging position for unidirectional drawing forging. The deformation amount of the third pass is 4%, with one rotation and one step, and each rotation angle is 30° and the feed amount is 40mm. The press is set to a pressing speed of 110mm / s. That is, the difficult-to-deform nickel-based high-temperature alloy bar is forged by one fire and three passes of double V-anvil forging, and the outer side is wrapped with heat-insulating asbestos during the forming forging process, and finally forged to the finished product size Φ310mm.

[0040] 3) After the difficult-to-deform nickel-based superalloy bar formed and forged in step 2) is air-cooled for ≥2 hours, it is then air-cooled to room temperature. Utilizing timely air cooling after forging reduces the time the core structure remains in the high-temperature zone after forging, preventing the fine-grained core structure from coarsening during the slow air cooling process.

[0041] Example 3

[0042] This embodiment provides a forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars, which specifically includes the following steps;

[0043] 1) Select a difficult-to-deform nickel-based superalloy ingot with an Al+Ti content of 4.7%, heat it for 18 hours, and then forge it. Perform seven upsetting and drawing operations on a high-speed forging mill using a 650mm wide flat anvil. Upsetting and drawing operations for operations 1-3 are performed at 1160℃, with deformation controlled between 18% and 23% per operation, utilizing high-temperature upsetting and drawing to fully break down the as-cast microstructure. Upsetting operations 4-7 are performed at 1100℃, with deformation controlled between 25% and 33% per operation, utilizing medium-temperature upsetting to further break down the microstructure and refine the grains. Complete the preparation of the intermediate billet. Asbestos is wrapped during each forging operation. The hot material is returned to the furnace after operations 1-6, and air-cooled after the seventh operation.

[0044] 2) The intermediate billet obtained in step 1) is drawn in one pass on a high-speed forging mill using upper and lower V-shaped anvils. The heating temperature is 1070℃, and after heating for 10 hours, it is taken out of the furnace for forging. A total of 3 forging passes are performed. The deformation amount of the first pass is 23%, with two rotations and one step, and each rotation angle is 45° and the feed amount is 90mm. After the first pass, the material is emptied and returned to the starting forging position for unidirectional drawing forging. The deformation amount of the second pass is 20%, with two rotations and one step, and each rotation angle is 45° and the feed amount is 90mm. The press is set to a pressing speed of 60mm / s. After the second pass, the material is emptied and returned to the starting forging position for unidirectional drawing forging. The deformation amount of the third pass is 4%, with one rotation and one step, and each rotation angle is 30° and the feed amount is 40mm. The press is set to a pressing speed of 110mm / s. That is, the difficult-to-deform nickel-based high-temperature alloy bar is forged by one fire and three passes of double V-anvil forging, and the outer side is wrapped with heat-insulating asbestos during the forming forging process, and finally forged to the finished product size Φ350mm.

[0045] 3) After the difficult-to-deform nickel-based superalloy bar formed and forged in step 2) is air-cooled for ≥2 hours, it is then air-cooled to room temperature. Utilizing timely air cooling after forging reduces the time the core structure remains in the high-temperature zone after forging, preventing the fine-grained core structure from coarsening during the slow air cooling process.

[0046] 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.

[0047] 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 refining the microstructure of difficult-to-deform nickel-based superalloy bars, characterized in that, The forging method includes the following steps; Step 1: Select a difficult-to-deform nickel-based superalloy ingot with an Al+Ti content of 4.2%–4.8%, and perform upsetting and drawing on a high-speed forging machine using a flat anvil for 5–7 passes. Each forging pass is wrapped with insulating asbestos to obtain an intermediate billet. The heating temperature for each pass is set to 1080–1160℃, and the deformation is set to 15%–35%. Step 2: The intermediate billet obtained in Step 1 is drawn in one heat and three passes on a high-speed forging mill using upper and lower V-shaped anvils to complete the forming and forging of the difficult-to-deform nickel-based superalloy bar; wherein the heating temperature is set to 1040-1080℃; the specific implementation process of the three passes is as follows: The deformation amount for the first and second passes is set to 15% to 25%, with one step every two revolutions. The rotation angle for each revolution is set to 45°, the feed rate is set to 90 to 110 mm, and the press pressing speed is set to 50 to 70 mm / s. The deformation amount for the third pass is set to 2% to 8%, with one revolution per step, each rotation angle set to 30°, the feed rate set to 30 to 50 mm, and the press pressing speed set to 90 to 110 mm / s. Step 3: After air cooling the difficult-to-deform nickel-based high-temperature alloy bar formed and forged in Step 2 for at least 2 hours, air cool it to room temperature.

2. The forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars according to claim 1, characterized in that, In step 2, the outer side is wrapped with insulating asbestos during the forming and forging process.

3. The forging method for refining the microstructure of difficult-to-deform nickel-based superalloy bars according to claim 1, characterized in that, The difficult-to-deform nickel-based superalloy ingot selected in step 1 has an Al+Ti content of 4.35-4.7%.

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