Forging method for effectively eliminating edge mixed crystal structure of high-temperature alloy bar difficult to deform

Abstract

The invention discloses a forging method for effectively eliminating a mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar, which mainly comprises the following steps of: firstly, carrying out cogging forging on a cast ingot for 2-4 times in total, enabling the deformation temperature to be 1000-1180 DEG C, and enabling the cogging heating number to adopt a mode of combining upsetting and drawing; alternately obtaining an intermediate billet with tetragonal and octagonal section characteristics; and secondly, the intermediate blank is subjected to forming forging for 3-6 times in total, the deformation temperature ranges from 900 DEG C to 1080 DEG C, and in the deformation process, the mode that a square is drawn from all directions firstly, and then the square is drawn from all directions is adopted. Particularly, the eight-direction drawing-out of the forming heating number mainly adopts a mode of large eight directions, middle square directions and small eight directions, an eight-direction and four-direction repeated alternating type forging deformation thought is designed, a high-strain cross area in the eight-direction deformation process is utilized to eliminate a strain dead area in the four-direction deformation process, the grain size of the high-temperature alloy is refined through the method, and the high-temperature alloy yield is improved. And the strain dead zone in the traditional flat anvil forging process is solved.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature alloy hot processing, in particular to a forging method for effectively eliminating mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar. Background Art

[0002] High-temperature alloys refer to high-temperature metal materials that can work for a long time at a temperature above 760°C. Due to their special use conditions, high-temperature alloys are widely used in key components in the aviation and aerospace fields, such as engine turbine disks, blades, and high-temperature fasteners. For Ni-based high-temperature alloys enhanced by γ' phase, as the volume fraction of the strengthening phase increases, the hot working window of the alloy will gradually narrow, making the deformation resistance during the bar forging process large and prone to cracks. Therefore, a reasonable bar forging process design is particularly important for the processing of such high-temperature alloys.

[0003] Reasonable bar forging process design is an important means to ensure organizational uniformity and grain size control, especially for difficult-to-deform high-temperature alloys such as GH738 and GH4141. During the flat anvil free forging process of the bar, there is a strain "dead zone" in the contact area between the anvil and the bar. At the same time, the temperature difference between the bar and the flat anvil causes a surface chilling effect in the area in contact with the anvil, which produces differences in equivalent strain and temperature distribution on the bar, causing insufficient dynamic recrystallization in the local area at the edge of the bar, and ultimately leading to the appearance of mixed crystal structure at the edge of the finished bar, seriously affecting the organizational uniformity of the bar and the service life of the forging. Summary of the invention

[0004] The object of the present invention is to provide a forging method for effectively eliminating the mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy rod, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a forging method for effectively eliminating the mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar, comprising the following steps:

[0006] S1. Performing blank forging of the ingot, the blank forging is performed for 2-4 times, the deformation temperature is 1000-1180°C, and the blank forging is performed by combining upsetting and drawing to alternately obtain intermediate blanks with square and octagonal cross-section characteristics;

[0007] S2. The intermediate billet is forged for a total of 3-6 fires, with a deformation temperature of 900-1080°C. The deformation method is mainly through the method of large eight-sided → medium four-sided → small eight-sided.

[0008] Preferably, during the forming and forging process of the octagonal intermediate billet, the initial pressing surface of the 3rd, 5th and 7th steps forms an angle of 45° with the initial pressing surface of the previous fire.

[0009] Preferably, the minimum equivalent strain value of the edge of the rod obtained in S2 is 0.244-0.369.

[0010] Preferably, the maximum value of the equivalent strain of the edge of the rod obtained in S2 is 3.91-4.53.

[0011] Preferably, in order to control the temperature drop of the edge of the bar during forging in S2, asbestos needs to be wrapped in each firing during the forging process, and if the asbestos falls off, it needs to be replenished in time.

[0012] Preferably, the deformation amount in S3 is designed to be between 1% and 12%.

[0013] Compared with the prior art, the beneficial effects of the present invention are: an innovative eight-way and four-way alternating forging deformation idea is proposed, and the "high strain cross area" in the eight-way deformation process is utilized to eliminate the "strain dead zone" in the four-way deformation process. This method refines the grain size of the high-temperature alloy and solves the strain dead zone in the traditional flat anvil forging process. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the free forging process of an embodiment of the present invention;

[0015] Figure 2 (a), (b) and (c) are equivalent strain and temperature distribution diagrams after forging of Example 1;

[0016] Figure 2 (d), (e) and (f) are equivalent strain and temperature distribution diagrams after forging of Example 2;

[0017] Figure 3 (a) and (b) are microstructure diagrams of the rod forged in Example 1. Figure 3 (c) and (d) are microstructure diagrams of the rod forged in Example 2;

[0018] Figure 4 These are the microstructure diagrams of the rod before forging (a) and (b), and after forging (c) and (d) in Example 3. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Embodiment 1:

[0021] Taking GH738 alloy as an example, GH738 bars were prepared using the method provided in patent number 202110660412.8, entitled "A forging method for improving the uniformity of the microstructure of a difficult-to-deform high-temperature alloy". Finite element simulation analysis and microstructure verification were carried out on the forging process and after forging of the bars. The diameter of the bar is Φ230 mm. Figure 2 (a) and (b) are the equivalent strain distribution diagrams of the edge and cross section of the rod, respectively, where the red area represents the high strain area, and the rest of the area is the risk area where the GH738 alloy rod is prone to mixed crystals. The minimum equivalent strain value of the edge of the rod obtained by forging in Example 1 is 0.244, and the maximum equivalent strain of the core is 3.91. Figure 2 (c) is the temperature distribution diagram of the GH738 bar after forging. The maximum temperature rise of the core of the bar forged in Example 1 reaches 1110°C. The microstructure of the GH738 bar prepared in Example 1 after sampling, mechanical polishing and chemical etching is shown in FIG. Figure 3 As shown in (a) and (b), there is a significant mixed crystal structure at the edge of the rod, and the overall microstructure uniformity is poor.

[0022] Embodiment 2:

[0023] The bar forging method provided by the present invention is used to prepare a GH738 bar with a diameter of Φ230 mm, comprising the following steps:

[0024] (1) Rapid forging and blank forging of GH738 ingots are performed, with 2-4 fires in total, and the deformation temperature is 1000-1180°C. The blank forging is performed by combining upsetting and drawing to obtain an intermediate blank with octagonal cross-section characteristics;

[0025] (2) The GH738 with the characteristics of the eight-sided intermediate billet is forged for a total of 3-6 fires, with a deformation temperature of 900-1080°C. The deformation method is mainly through the large eight-sided → medium four-sided → small eight-sided method. After the material chamfering is completed, the hot material is returned to the furnace;

[0026] (3) The finished product forging of GH738 bars is carried out with a total of 1 fire rounding, and the deformation is designed to be between 1% and 12%. After the process is completed, the bars are air-cooled to room temperature.

[0027] Among them, during the forming and forging process of the eight-sided intermediate billet, the initial pressing surface of the 3rd, 5th and 7th steps is at an angle of 45° with the initial pressing surface of the previous fire.

[0028] Using the same initial forging temperature and boundary conditions as in Example 1, a finite element simulation analysis was performed on the bar forging process and after forging. The results are as follows: Figure 2As shown in (d) and (e), the minimum value of the equivalent strain at the edge of the bar obtained by forging in Example 2 increased from 0.244 to 0.369, and the maximum value of the equivalent strain increased from 3.91 to 4.53. The overall strain dead zone of the edge of the bar was significantly improved, which solved the problem of incomplete recrystallization caused by insufficient equivalent strain and temperature drop at the edge of the bar during flat anvil forging.

[0029] Figure 2 (f) is the temperature distribution diagram of the GH738 bar after forging. The maximum temperature rise of the core of the bar forged in Example 2 reaches 1100°C, which is 10°C lower than that in Example 1, which is beneficial to inhibit the excessive growth of the core structure and obtain a fine and uniform structure. The microstructure of the GH738 bar prepared in Example 2 after sampling, mechanical polishing, and chemical etching is shown in FIG. Figure 3 As shown in (c) and (d), the grain sizes in different parts of the rod are small and uniform.

[0030] Example 3

[0031] The structure of a batch of GH738 bars is as follows Figure 4 As shown in (a) and (b), the diameter of the rod is Φ230mm, and there are obvious coarse grains and mixed crystal structures on the edge of the rod. The batch of rods was heated to 1080℃, kept warm for 90 minutes, and then upset to a diameter of Φ300mm using a fast forging machine, with an upsetting deformation of about 41%. Then, the rod was rotated 90° clockwise along the axial direction to be stretched and deformed along the axial direction of the rod, with a stretching deformation of about 41%. The deformation method was the same as that in Example 1, through the method of large octagonal → medium octagonal → small octagonal, and the material was air-cooled to room temperature after chamfering. Figure 4 (c) and (d) are the microstructures of the rod after forging. After the forging process of the present invention is used to treat the coarse crystals and mixed crystals in the original rod, the mixed crystals have disappeared and the grains are fine and uniform.

[0032] In summary, the present invention innovatively proposes an idea of ​​alternating eight-sided and four-sided forging deformation, and utilizes the "high strain cross area" in the eight-sided deformation process to eliminate the "strain dead zone" in the four-sided deformation process. By matching the deformation mode, deformation amount, deformation rate and other factors, the edge mixed crystal problem caused by the local strain dead zone in the flat anvil free forging deformation of high-temperature alloys is effectively improved. This method does not require increasing the number of forging fires, is simple and reduces the probability of mixed crystals, and effectively improves the uniformity of the organization.

[0033] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A forging method for effectively eliminating the mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar, characterized in that: The following steps are involved: S1. Performing blank forging of the ingot, the blank forging is performed for 2-4 times, the deformation temperature is 1000-1180°C, and the blank forging is performed by combining upsetting and drawing to alternately obtain intermediate blanks with square and octagonal cross-section characteristics; S2. The intermediate billet is forged for 3-6 times in total, with a deformation temperature of 900-1080°C. The deformation method is mainly through large square → medium square → small square. After the chamfering of the material is completed, the hot material is returned to the furnace; S3, the intermediate billet bar is forged into finished product, with a total of 1 rounding process. After the process is completed, the bar is air-cooled to room temperature.

2. A forging method for effectively eliminating the mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar according to claim 1, characterized in that: During the forming and forging process of the intermediate blank of the octagonal shape, the initial pressing surface of the third, fifth and seventh steps forms an angle of 45° with the initial pressing surface of the previous fire.

3. A forging method for effectively eliminating the mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar according to claim 1, characterized in that: The minimum equivalent strain value of the edge of the rod in S3 is 0.244-0.

369.

4. A forging method for effectively eliminating the mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar according to claim 1, characterized in that: The maximum value of the equivalent strain at the edge of the rod in S3 is 3.91-4.

53.

5. A forging method for effectively eliminating the mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar according to claim 1, characterized in that: In the above S2, in order to control the edge temperature drop during the forging process of the bar, asbestos needs to be wrapped in each firing during the forging process, and if the asbestos falls off, it needs to be replenished in time.

6. A forging method for effectively eliminating the mixed crystal structure at the edge of a difficult-to-deform high-temperature alloy bar according to claim 1, characterized in that: The deformation amount in S3 is designed to be between 1% and 12%.

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