Preparation method of U520 alloy

Abstract

The invention relates to the technical field of high-temperature alloy preparation, and discloses a preparation method of a U520 alloy, which specifically comprises the following steps: carrying out vacuum induction melting on the U520 alloy; carrying out electroslag remelting on the blank subjected to vacuum induction melting; carrying out vacuum consumable remelting treatment on the blank subjected to electroslag remelting; the blank obtained after electroslag remelting is subjected to homogenization treatment; pressing and forging the homogenized blank by a press; and performing air cooling to room temperature, and performing heat treatment to finish forging. According to the method, the problem of forging cracking of the U520 alloy is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature alloy preparation, and in particular to a preparation method of a U520 alloy. Background Art

[0002] For forging, although the purpose of the process is to break up coarse structures and increase the density of the material, there is no unified standard process. Especially for highly alloyed alloys with a total alloy content of more than 40%, the degree of alloying is high, and it is quite difficult to reasonably formulate the forging process. If the alloy contains active metal elements such as aluminum and titanium, it is easy to form a large number of intermetallic compounds, making it even more difficult to reasonably formulate the forging process. The reason is that highly alloyed materials contain a large amount of second phases, which hinder the movement of grain boundaries and dislocations during deformation, hinder recrystallization, cause stress concentration, and lead to cracking.

[0003] For U520 alloy, the γ' phase content exceeds 50%. During deformation, processes such as recrystallization and slip are severely inhibited by the γ' phase, making deformation quite difficult. The most common problem is forging cracking. According to the deformation mechanism of metal materials, the Gleeble thermal simulation experiment was used to calculate the thermal processing diagram of U520 alloy, and the deformation temperature and strain rate were formulated. The Gleeble thermal simulation scheme was implemented using the press forging method, and the forging and preparation of U520 alloy was successfully completed. Summary of the invention

[0004] Purpose of the invention: In view of the problems existing in the prior art, the present invention provides a method for preparing U520 alloy, which effectively solves the forging cracking problem of U520 alloy by controlling the forging temperature and strain rate.

[0005] Technical solution: The present invention provides a method for preparing U520 alloy, comprising the following steps: S1. Vacuum induction melting of U520 alloy; S2. electroslag remelting the billet obtained in S1; S3. The blank obtained in S2 is homogenized; S4. The billet obtained in S3 is pressed and forged by a press: The blank obtained in S3 is taken out, wrapped and put back into the furnace to keep warm; Forging: The blank is forged by a press; the press speed is 5~12mm / s, and the strain rate is ≤0.3s -1 The deformation of a single pressing is 3-8%, and the total deformation of this pressing is 5-15%; the initial forging temperature of the billet is 1160-1180°C; the final forging temperature is 1080-1120°C; the billet is returned to the furnace after forging, and when the temperature of the billet reaches 1180°C, it is kept warm; Repeat the same forging steps as described in step b until the billet reaches the target size; During the forging process, the material is subjected to external forces and undergoes plastic deformation. This deformation causes changes in the microstructure inside the material, including the deformation and movement of grains. When the strain rate is high, the deformation occurs faster, which may lead to large dislocation density and local stress concentration areas inside the material. High-alloyed alloys usually contain many alloying elements, and the addition of these elements will lead to increased grain boundary strength, hindered dislocation activity, and other phenomena, making the material more prone to cracking. At high strain rates, these alloying elements cannot fully diffuse and rearrange, resulting in more significant stress concentration and easier crack formation and expansion. When the strain rate is low, the deformation occurs more slowly, and the dislocation movement and rearrangement of the grains are more orderly. This can reduce the mutual interference between grain boundaries and dislocations and reduce the degree of stress concentration inside the material. In addition, lower strain rates also help alloying elements to diffuse and rearrange more fully, thereby reducing local structural inhomogeneity and improving material uniformity and toughness. Therefore, by reducing the strain rate, the internal stress concentration and dislocation accumulation of high-alloyed alloys during forging can be reduced, thereby reducing the tendency to crack. The invention controls the deformation rate to make the deformation inside the material more uniform and orderly, thereby improving the toughness and crack resistance of the material during the forging process.

[0006] S5. The billet obtained in S4 is cooled to room temperature; S6. Heat treatment to obtain U520 alloy: The specific operation of the heat treatment is: the first time of keeping warm at 1180℃±10℃ for 2h, and air cooling to room temperature; the second time of keeping warm at 1080℃±10℃ for 4h, and air cooling to room temperature; the third time of keeping warm at 845℃±5℃ for 24h, and air cooling to room temperature; the fourth time of keeping warm at 760℃±5℃ for 16h, and air cooling to room temperature.

[0007] U520 alloy is a precipitation hardening alloy, and its strength mainly comes from the precipitation strengthening phase precipitated during the heat treatment process. The first 1180℃ high temperature insulation treatment is to make the alloy elements dissolve back into the matrix as much as possible, eliminate the larger second phase in the matrix, and make the alloy elements evenly distributed in the matrix. The following three insulation treatments at a lower temperature are to allow the dissolved alloy elements to form compounds again, precipitate, and make the precipitate phase as evenly distributed and small as possible. In this way, the evenly distributed fine precipitate phase can greatly improve the mechanical properties of the alloy.

[0008] Further, in S4, the insulation time in step b is t=H / 100*60min; Wherein, H is the maximum size of the blank, in mm.

[0009] Furthermore, in S1, the specific steps of the vacuum induction melting are as follows: In terms of mass percentage, first add C0.04~0.05%, Cr18~20%, Co11~13%, W0.9~1.2, Mo5.5~6.5%, and after they are completely melted, add Al1.9~2.2%, Ti2.9~3.2%, B0.04~0.08%, Mg0.01~0.1%, Zr0.01~0.05%, and Ni balance, fill with argon, vacuum to 1000~3000Pa, and finally add RE0.5~2.0%, and keep warm for 10~30min; wherein, the melting temperature of the vacuum induction melting is 1280~1350℃, and the vacuum degree is 0.01~0.1Pa.

[0010] Elements that are not easy to burn are added first, then elements that are easy to burn are added, and finally rare earth elements with very active properties are added. The purpose is to protect the active elements from being burned and allow them to play their due role.

[0011] Preferably, before adding RE, argon is blown into the bottom of the molten alloy for 10 to 20 minutes.

[0012] By blowing argon from the bottom, impurities in the metal melt are deoxidized, desulfurized, and decarbonized, thereby improving the purity and quality of the metal. In addition, Re is a rare earth element, which is very active and easily burned, and the yield is very low. Blowing argon from the bottom before adding Re can protect Re from being consumed by impurities in the melt and improve the utilization rate of Re.

[0013] Furthermore, in S2, the specific conditions of the electroslag remelting are: the slag layer thickness is 0.5~1D, and the filling ratio is 0.5~0.7; wherein D is the diameter of the consumable electrode, and the filling ratio is the ratio of the cross-sectional area of ​​the consumable electrode to that of the crystallizer.

[0014] Furthermore, in S3, the specific steps of the homogenization process are as follows: The blank obtained in S2 is heated from room temperature to 850°C at a rate of 100-300°C / h and kept at this temperature for 7-8 hours; Then, the blank is heated from 850°C to 1050°C at a rate of 50-200°C / h and kept at this temperature for 28-30 hours; Then, the blank is heated from 1050°C to 1180°C at a rate of 30-100°C / h and kept at this temperature for 18-20 hours.

[0015] The overall purpose of homogenization treatment is to eliminate uneven casting structure, obtain uniform homogenized structure, and prepare for forging. The specific principles are as follows: 1. Temperature control: During the heat treatment process, the temperature and heating time of the heating equipment are controlled so that the metal workpiece gradually reaches the required treatment temperature. This can prevent thermal stress and uneven structure caused by excessive temperature gradient.

[0016] 2. Time control: Temperature homogenization treatment usually takes a certain amount of time to ensure that the temperature inside the metal reaches a uniform state. Therefore, the heating time needs to be gradually increased during the heating process to ensure that the temperature inside the entire workpiece can reach the required treatment temperature.

[0017] 3. Temperature balance: Once the metal workpiece reaches the required processing temperature, it needs to be maintained for a certain period of time so that the temperature inside the metal can be evenly distributed and reach a stable state. This helps the recrystallization and phase transformation of the metal's internal structure, thereby achieving uniform organization and performance.

[0018] Preferably, after S5, a rolling process is further included: the specific steps of the rolling process are as follows: (1) Heating to a temperature of 1160-1180°C and keeping warm; the keeping warm time t=H / 100*60min, t is time, H is the maximum size of the blank; (2) Rolling: strain rate controlled at 0.2~0.5s -1 , the starting rolling temperature is 1150~1170℃, and the final rolling temperature is 1050~1060℃; (3) Annealing; the annealing temperature is 1160~1180℃, and the annealing time is 20~60min; (4) Roll again and repeat steps (2) and (3) until the target size is reached.

[0019] Beneficial effects: Compared with the prior art, the specific beneficial effects of the present invention are as follows: (1) Solved the forging cracking problem of U520 alloy. By controlling the temperature, strain rate, deformation and other parameters during forging, the forging of high-alloyed U520 alloy was achieved, effectively preventing the forging cracking problem.

[0020] (2) Homogenization heat treatment provides forging with a uniformly organized billet. By designing a reasonable homogenization heat treatment process, the alloy elements are evenly distributed, and the formed second phase is evenly distributed and small in size, providing a good microstructural foundation for forging. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a cross-sectional view of a U520 alloy forged by a conventional method; Figure 2 This is a physical picture of the U520 alloy prepared in the present invention. DETAILED DESCRIPTION

[0022] The present invention is described in detail below in conjunction with the embodiments.

[0023] Implementation 1: This embodiment provides a forging method of U520 alloy, and the specific steps are as follows: S1. Vacuum induction melting of U520 alloy: first add C0.04~0.05%, Cr18~20%, Co11~13%, W0.9~1.2, Mo5.5~6.5% by mass percentage, and then add Al1.9~2.2%, Ti2.9~3.2%, B0.04~0.08%, Mg0.01~0.1%, Zr0.01~0.05%, Ni balance after complete melting, fill with argon, vacuum to 1000~3000Pa, and finally add RE0.5~2.0%, keep warm for 10~30min. The melting temperature of vacuum induction melting is 1280~1350℃, and the vacuum is 0.01~0.1Pa.

[0024] Optionally, before adding RE, the melted alloy liquid can be treated with bottom argon blowing for 10-20 minutes; S2. Electroslag remelting the billet obtained in S1: the slag layer thickness is 0.5~1D, and the filling ratio is 0.5~0.7; wherein D is the diameter of the consumable electrode, and the filling ratio is the ratio of the cross-sectional area of ​​the consumable electrode to the crystallizer; S3. The blank obtained in S2 is homogenized: The blank obtained in S2 is heated from room temperature to 850°C at a rate of 100-300°C / h and kept at this temperature for 7-8 hours; Then, the blank is heated from 850°C to 1050°C at a rate of 50-200°C / h and kept at this temperature for 28-30 hours; Then, the blank is heated from 1050°C to 1180°C at a rate of 30-100°C / h and kept at this temperature for 18-20 hours; S4. The billet obtained in S3 is pressed and forged by a press: The blank obtained in S3 is taken out, wrapped and put back into the furnace to keep warm; Forging: The blank is forged by a press; the press speed is 5 mm / s and the strain rate is ≤ 0.3 s -1 The deformation of a single pressing is 3%, and the total deformation of this pressing is 6%; the initial forging temperature of the billet is 1160℃; the final forging temperature is 1080℃; the billet is returned to the furnace after forging, and when the temperature of the billet reaches 1180℃, it is kept warm for a time of t=H / 100*60min; where H is the maximum size of the billet, in mm; Repeat the same forging steps as described in step b until the billet reaches the target size; S5. The billet obtained in S4 is cooled to room temperature; S6. The billet obtained in S5 is subjected to rolling treatment: (1) Heating to a temperature of 1160-1180°C and keeping warm; the keeping warm time t=H / 100*60min, t is time, H is the maximum size of the blank; (2) Rolling: strain rate controlled at 0.2~0.5s -1 , the starting rolling temperature is 1150~1170℃, and the final rolling temperature is 1050~1060℃; (3) Annealing; the annealing temperature is 1160~1180℃, and the annealing time is 20~60min; (4) Rolling again, repeating steps (2) and (3) until the target size is reached; S8. Heat treatment to obtain U520 alloy: the billet obtained in S7 is first kept at 1180℃±10℃ for 2h, and air-cooled to room temperature; secondly kept at 1080℃±10℃ for 4h, and air-cooled to room temperature; thirdly kept at 845℃±5℃ for 24h, and air-cooled to room temperature; fourthly kept at 760℃±5℃ for 16h, and air-cooled to room temperature.

[0025] Implementation 2: This embodiment is substantially the same as Embodiment 1, except that, in this embodiment, step b of S4 is forging: the blank is forged by a press; wherein the press head speed is 8 mm / s, and the strain rate is ≤0.3 s -1 The deformation of a single pressing is 5%, and the total deformation of this pressing is 15%; the initial forging temperature of the billet is 1170℃; the final forging temperature is 1100℃; the billet is returned to the furnace after forging, and when the temperature of the billet reaches 1180℃, it is kept warm for a time of t=H / 100*60min; where H is the maximum size of the billet, in mm.

[0026] Apart from this, this embodiment is completely the same as Embodiment 1 and will not be described in detail here.

[0027] Implementation 3: This embodiment is substantially the same as Embodiment 1, except that, in this embodiment, step b of S4 is forging: the blank is forged by a press; wherein the press head speed is 12 mm / s, and the strain rate is ≤0.3 s -1 The deformation of a single pressing is 8%, and the total deformation of this pressing is 8%; the initial forging temperature of the billet is 1180°C; the final forging temperature is 1120°C; the billet is returned to the furnace after forging, and when the temperature of the billet reaches 1180°C, it is kept warm for a time of t=H / 100*60min; wherein H is the maximum size of the billet, in mm.

[0028] Apart from this, this embodiment is completely the same as Embodiment 1 and will not be described in detail here.

[0029] The properties of the U520 alloy prepared in Embodiment 1 of the present invention were tested, and the results are shown in Table 1: Table 1

[0030] As can be seen from Table 1, the tensile strength and elongation of the U520 alloy prepared in Embodiment 1 of the present invention are improved at 800°C and 20°C. Figure 1-2 As shown, Figure 1 The U520 alloy forged by conventional methods has obvious cracks in the cross section. Figure 2 The U520 alloy prepared by the present invention has no cracking phenomenon, which shows that the present invention effectively prevents the problem of forging cracking.

[0031] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing U520 alloy, characterized in that: The following steps are involved: S1. Vacuum induction melting of U520 alloy; S2. electroslag remelting the billet obtained in S1; S3. The blank obtained in S2 is homogenized; S4. The billet obtained in S3 is pressed and forged by a press: The blank obtained in S3 is taken out, wrapped and put back into the furnace to keep warm; Forging: The blank is forged by a press; the press speed is 5~12mm / s, and the strain rate is ≤0.3s -1 The deformation of a single pressing is 3-8%, and the total deformation of this pressing is 5-15%; the initial forging temperature of the billet is 1160-1180°C; the final forging temperature is 1080-1120°C; the billet is returned to the furnace after forging, and when the temperature of the billet reaches 1180°C, it is kept warm; Repeat the same forging steps as described in step b until the billet reaches the target size; S5. The billet obtained in S4 is cooled to room temperature; S6. Heat treatment to obtain U520 alloy: The specific operation of the heat treatment is: the first time of keeping warm at 1180℃±10℃ for 2h, and air cooling to room temperature; the second time of keeping warm at 1080℃±10℃ for 4h, and air cooling to room temperature; the third time of keeping warm at 845℃±5℃ for 24h, and air cooling to room temperature; the fourth time of keeping warm at 760℃±5℃ for 16h, and air cooling to room temperature.

2. The method for preparing the U520 alloy according to claim 1, characterized in that: In S4, the insulation time in step b is t=H / 100*60min; Wherein, H is the maximum size of the blank, in mm.

3. The method for preparing the U520 alloy according to claim 1, characterized in that: In S1, the specific steps of vacuum induction melting are as follows: In terms of mass percentage, first add C0.04~0.05%, Cr18~20%, Co11~13%, W0.9~1.2, Mo5.5~6.5%, and after they are completely melted, add Al1.9~2.2%, Ti2.9~3.2%, B0.04~0.08%, Mg0.01~0.1%, Zr0.01~0.05%, and Ni balance, fill with argon, vacuum to 1000~3000Pa, and finally add RE0.5~2.0%, and keep warm for 10~30min; wherein, the melting temperature of the vacuum induction melting is 1280~1350℃, and the vacuum degree is 0.01~0.1Pa.

4. The method for preparing the U520 alloy according to claim 3, characterized in that: Before adding RE, argon was blown into the bottom of the molten alloy for 10 to 20 minutes.

5. The method for preparing the U520 alloy according to claim 1, characterized in that: In S2, the specific conditions of the electroslag remelting are: the slag layer thickness is 0.5~1D, and the filling ratio is 0.5~0.7; wherein D is the diameter of the consumable electrode, and the filling ratio is the ratio of the cross-sectional area of ​​the consumable electrode to the crystallizer.

6. The method for preparing the U520 alloy according to claim 1, characterized in that: In S3, the specific steps of the homogenization process are as follows: The blank obtained in S2 is heated from room temperature to 850°C at a rate of 100-300°C / h and kept at this temperature for 7-8 hours; Then, the blank is heated from 850°C to 1050°C at a rate of 50-200°C / h and kept at this temperature for 28-30 hours; Then, the blank is heated from 1050°C to 1180°C at a rate of 30-100°C / h and kept at this temperature for 18-20 hours.

7. The method for preparing the U520 alloy according to claim 1, characterized in that: After S5, rolling treatment is also included: the specific steps of the rolling treatment are as follows: (1) Heating to a temperature of 1160-1180°C and keeping warm; the keeping warm time t=H / 100*60min, t is time, H is the maximum size of the blank; (2) Rolling: strain rate controlled at 0.2~0.5s -1 , the starting rolling temperature is 1150~1170℃, and the final rolling temperature is 1050~1060℃; (3) Annealing; the annealing temperature is 1160~1180℃, and the annealing time is 20~60min; (4) Roll again and repeat steps (2) and (3) until the target size is reached.

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