High-uniformity fine grain forming process for nickel-based superalloy forge piece

Abstract

The invention provides a high-uniformity fine grain forming process for a nickel-based superalloy forge piece. According to the high-uniformity fine grain forming process for the nickel-based superalloy forge piece, pressure maintaining treatment is adopted in the intermittent stage between initial deformation and final forming; in the pressure maintaining treatment at the intermittent stage, crystal grains in the microstructure of the forge piece are effectively refined, the crystal mixing phenomenon is weakened, and the strength, toughness and other mechanical properties of the material are remarkably improved. Meanwhile, the grain structure of the material is optimized, and grain boundaries are increased, so that the stability of the material at high temperature is improved. According to the process, the residual stress in the forge piece can be effectively reduced, the dimensional stability of the material is improved, the stress distribution in the material is more uniform, and deformation or cracking caused by stress concentration is reduced. The high-temperature alloy forge piece obtained through the process has good high-temperature performance such as oxidation resistance, fatigue performance and corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy forging, and particularly to a high-uniformity fine-grain forming process for nickel-based superalloy forgings. Background Art

[0002] Superalloys are known as the "cornerstone of modern advanced engines" due to their excellent high-temperature tolerance and play a crucial role in the aviation field. They are widely used in the core hot-end components of aeroengines, such as turbine disks and turbine blades. With the continuous progress of aeroengine technology, moving towards larger sizes and higher thrust-to-weight ratios, the working temperature of the core hot-end components of aeroengines continues to rise, the loads borne by the components are increasing day by day, and the operating environment is becoming increasingly harsh. This poses unprecedented high standards for the performance of aeroengine components.

[0003] In traditional forging processes, the deformation temperature window of superalloys is relatively narrow, and their recrystallization behavior is difficult to control, making it difficult to control the microstructure of forgings. During hot forming, defects such as ingot cracking and uneven grain coarsening are prone to occur, seriously affecting their mechanical properties. Especially for forgings with complex structures, there are differences in the deformation amounts of different parts, which further exacerbates the non-uniformity of the microstructure, resulting in subsequent heat treatment being difficult to compensate for performance fluctuations. The microstructure and performance differences of different parts are significant, making the forming control of large forgings extremely complex. Coupled with the rapid development of the aviation industry, the demand for nickel-based superalloy forgings is continuously increasing. Therefore, in-depth exploration of the process regulation of nickel-based superalloy forgings is of great significance for improving the manufacturing level of aeroengines in China.

[0004] In view of the above challenges, there is an urgent need to adopt efficient process optimization methods to explore new hot working processes for nickel-based superalloy forgings to guide actual production, achieve precise control of the microstructure of forgings, and thus produce large key components that meet the requirements of modern industry. Summary of the Invention

[0005] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a high-uniformity fine-grain forming process for nickel-based superalloy forgings, which can effectively improve the mixed-grain phenomenon of the superalloy microstructure, achieve uniform refinement of the forging microstructure, and thus achieve the purpose of improving the service performance of the forgings.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The present invention provides a high-uniformity fine-grain forming process for nickel-based superalloy forgings, including the following steps:

[0008] Heat the nickel-based superalloy blank to the forging temperature;

[0009] Place the heated blank in a mold, perform initial deformation, then carry out pressure holding treatment, and subsequently complete the final forming to obtain the target forging.

[0010] Preferably, during the initial deformation process, the deformation amount is 70 - 80% of the total deformation amount, and the downward pressing speed is 15 - 40 mm / s.

[0011] Preferably, during the final forming deformation process, the downward pressing speed is 10 - 30 mm / s;

[0012] The total forging ratio during the initial deformation and the final forming deformation process is 3 - 6.

[0013] Preferably, the pressure for the pressure holding treatment is 10 - 20 MPa, and the pressure holding treatment time is 10 - 300 s.

[0014] Preferably, the forging temperature is 1000 - 1200 °C.

[0015] Preferably, heat the nickel-based superalloy blank to the forging temperature and hold for 5 - 60 min.

[0016] Preferably, heat the nickel-based superalloy blank to the forging temperature at a rate of 5 - 100 °C / min.

[0017] Preferably, place the heated blank in a mold, perform initial deformation, then carry out pressure holding treatment, subsequently complete the final forming, and then cool it by air cooling or slow cooling to obtain the target forging;

[0018] Among them, slow cooling includes: placing the finally formed forging in a ventilated environment for cooling, and the cooling rate is 5 - 15 °C / s.

[0019] Preferably, the volume of the nickel-based superalloy blank is 1.05 - 1.08 times the volume of the target forging.

[0020] The high-uniformity fine-grain forming process of the nickel-based superalloy forging of the present invention has the following beneficial effects compared with the prior art:

[0021] The fine-grained forming process with high uniformity for nickel-based superalloy forgings of the present invention adopts a pressure-holding treatment during the intermittent stage between the initial deformation and the final forming; during the pressure-holding treatment in the intermittent stage, the grains in the microstructure of the forgings are effectively refined, and the phenomenon of mixed grains is weakened. After heat treatment, the mechanical properties such as the strength and toughness of the forging material are significantly improved. Compared with the material without pressure-holding treatment, the hardness is increased by 14.1%, the tensile strength is increased by 8.5%, and the elongation is increased by 15.7%; at the same time, the grain structure of the material is optimized, and the grain boundaries increase, which helps to improve the stability of the material at high temperatures. The above process can effectively reduce the residual stress inside the forgings, improve the dimensional stability of the material, make the stress distribution inside the material more uniform, and reduce the deformation or cracking caused by stress concentration. The superalloy forgings obtained by this process have good high-temperature properties, such as oxidation resistance, fatigue resistance and corrosion resistance. The process of this technical solution has a good theoretical basis, breaks through the traditional process idea of only using plastic deformation to refine the grain structure, obtains forgings with more excellent properties, and has important research value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 Microstructure diagram of the target forging of GH4698 alloy prepared by the process in Example 1;

[0024] Figure 2 Microstructure diagram of the target forging of GH4698 alloy formed once by the process in Comparative Example 1;

[0025] Figure 3 Microstructure diagram of the target forging of GH4698 alloy pre-forged and finally forged by the process in Comparative Example 2;

[0026] Figure 4 Statistical results of the mechanical properties of the target forgings prepared by the methods in Example 1 and Comparative Examples 1-2;

[0027] Figure 5 Microstructure diagram of the target forging of GH4169 alloy prepared by the process in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "upper" is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present invention is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0030] The description order of the following embodiments does not limit the preferred order of the embodiments. Additionally, in the description of the present application, the term "comprising" means "including but not limited to". The various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present invention; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0031] The embodiments of the present application provide a high-uniformity fine-grained forming process for nickel-based superalloy forgings, including the following steps:

[0032] S1. Heat the nickel-based superalloy blank to the forging temperature;

[0033] S2. Place the heated blank in a mold, perform initial deformation, then perform pressure holding treatment, and finally complete the final forming to obtain the target forging.

[0034] The high uniformity fine grain forming process of the nickel-based high temperature alloy forging of the present invention comprises the following steps: feeding the nickel-based high temperature alloy blank into a heating furnace and heating it to a forging temperature; placing the heated blank into a mold, performing initial deformation, and then performing a pressure holding treatment, and then completing the final forming to obtain a target forging; a pressure holding treatment is used in the intermittent stage between the initial deformation and the final forming; during the pressure holding treatment in the intermittent stage, more fine recrystallized grains in the nickel-based high temperature alloy grow and swallow up the deformed grains, which effectively reduces the occurrence of mixed crystals and coarse crystals. In addition, due to the effect of grain boundary migration during grain growth, the deformation storage energy generated inside the material can be effectively released, the residual stress inside the material is reduced, and the dimensional stability of the material is effectively improved.

[0035] The present invention aims at the problems of coarse and uneven grains, serious mixed crystal phenomenon and fluctuation of mechanical properties caused by the difficulty in controlling the dynamic recrystallization behavior of nickel-based high-temperature alloys in traditional forging processes, and proposes a hot working method that adjusts the dynamic recrystallization behavior by adding an intermittent stage during the deformation process. The method comprises: sending a nickel-based high-temperature alloy billet into a heating furnace to heat it to a suitable forging temperature, transferring the heated billet to a forging device, and forging the billet according to pre-designed forging process parameters. The forging process first performs an initial deformation on the billet, then stops the deformation and maintains the pressure for a period of time, and then completes the final forging. The thermal insulation treatment releases the stored energy, refines the grains and reduces the mixed crystals, which significantly improves the mechanical properties, high temperature stability and dimensional uniformity of the forging. The process of this technical solution has a good theoretical basis, breaks through the traditional process idea of ​​using plastic deformation to refine the grain structure, solves the technical problem of uneven structure of complex structure forgings, and is suitable for the precision manufacturing of key parts of aircraft engines.

[0036] In some embodiments, during the initial deformation process, the applied pressure is 200-300 MPa, the deformation amount is 70-80% of the total deformation amount, and the pressing speed is 15-40 mm / s.

[0037] In some embodiments, during the final forming deformation process, the applied pressure is 200-300 MPa and the pressing speed is 10-30 mm / s;

[0038] The total forging ratio during the initial deformation and the final forming deformation process is 3 to 6.

[0039] Specifically, the deformation during the initial deformation process is 70-80% of the total deformation, and the deformation during the final forming deformation process is 30-20% of the total deformation, that is, the sum of the deformations during the initial deformation process and the final forming deformation process is the total deformation. During the pressure holding process, the blank does not deform due to the low pressure.

[0040] Specifically, the reasons for controlling the deformation rate and the deformation amount during the initial deformation process in the forging process are to ensure the number of recrystallization nuclei during the deformation process, ensure sufficient post-dynamic recrystallization grain growth during the heat preservation process, and prevent material cracking caused by excessive deformation rate. The forgings obtained by the method of the present invention not only have no defects such as uneven grain coarsening, but also have high forming accuracy. The present invention effectively improves the mechanical properties of nickel-based superalloy forgings.

[0041] Specifically, the definitions of the deformation amount, the downward pressing speed, and the forging ratio are as follows:

[0042] Definition of the deformation amount: It refers to the degree of change in the shape and size of the blank during the forging process. It is usually expressed by the ratio of the size change of the blank in a certain direction to the original size, which is a dimensionless quantity and is generally presented in the form of a percentage; calculation formula: deformation amount = (size of the blank after deformation - original size of the blank) ÷ original size of the blank × 100%. For example, if the original length of the blank is 100 mm and the length becomes 80 mm after forging, the deformation amount in the length direction is (80 - 100) ÷ 100 × 100% = -20%. The negative sign indicates a decrease in size, that is, compressive deformation has occurred;

[0043] Definition of the downward pressing speed: It refers to the speed at which the forging tool (such as a punch, a hammer head, or a die, etc.) moves in the vertical direction when applying pressure to the blank to cause deformation during the forging process. It reflects the speed of blank deformation during the forging process, and the unit is usually meters per second (m / s) or millimeters per second (mm / s);

[0044] Definition of the forging ratio: It is an index to measure the degree of metal deformation during the forging process. It represents the relative change relationship of dimensions such as the cross-sectional area or length of the blank under the condition that the volume remains unchanged before and after forging. The larger the forging ratio, the greater the degree of deformation of the metal during the forging process, the denser its internal structure, and the corresponding improvement in mechanical properties; for the calculation formula of the forging ratio of upsetting: it is calculated based on the change in the cross-sectional area of the blank, that is, forging ratio = cross-sectional area after forging ÷ original cross-sectional area of the blank. For example, if the original cross-sectional area of the blank is 20 mm 2 , and it becomes 100 mm 2 after forging, then the forging ratio is 100 ÷ 20 = 5. For the calculation formula of the forging ratio of stretching: it is calculated based on the change in the cross-sectional area of the blank, that is, forging ratio = original cross-sectional area of the blank ÷ cross-sectional area after forging. For example, if the original cross-sectional area of the blank is 20 mm 2 , and it becomes 4 mm 2 after stretching, then the forging ratio is 20 ÷ 4 = 5.

[0045] In some embodiments, the pressure holding treatment time is 10 - 300 s, and the pressure holding pressure is controlled at 10 - 20 MPa.

[0046] In some embodiments, the forging temperature is 1000-1200°C.

[0047] In some embodiments, the nickel-based high-temperature alloy blank is heated to a forging temperature and kept at the temperature for 5 to 60 minutes.

[0048] In some embodiments, the nickel-based high-temperature alloy billet is heated to the forging temperature at a rate of 5-100° C. / min.

[0049] In some embodiments, the heated billet is placed in a mold for initial deformation and pressure holding treatment, and then the final forming is completed, and then air cooling or slow cooling is used to prevent defects such as cracks to obtain a target forging. Specifically, air cooling is: after the final forging is taken out of the mold, it is directly placed in the air to cool naturally to room temperature (25°C); slow cooling is: after the final forging is taken out of the mold, it is placed in a forced ventilation (fan) environment for cooling, and the cooling rate is 5 to 15°C / s.

[0050] In some embodiments, the volume of the nickel-based high-temperature alloy billet is 1.05 to 1.08 times the volume of the target forging.

[0051] In some embodiments, a final forging stage completes the remaining deformation, ensuring that the blank fills the die cavity.

[0052] In some embodiments, the dimensions of the forging die are designed to take into account forging tolerances and shrinkage.

[0053] The high uniformity fine grain forming process of the nickel-based high temperature alloy forging of the present invention adopts a pressure holding treatment in the intermittent stage between the initial deformation and the final forming; in the pressure holding treatment in the intermittent stage, more fine recrystallized grains in the nickel-based high temperature alloy grow and swallow up the deformed grains, which effectively reduces the appearance of mixed crystals and coarse crystals. The grains in the microstructure of the forging are effectively refined, the phenomenon of mixed crystals is weakened, and the mechanical properties such as strength and toughness of the material are significantly improved. At the same time, the grain structure of the material is optimized and the grain boundaries are increased, which helps to improve the stability of the material at high temperatures. The above process can effectively reduce the residual stress inside the forging, improve the dimensional stability of the material, make the stress distribution inside the material more uniform, and reduce deformation or cracking caused by stress concentration. The high temperature alloy forging obtained by this process has good high temperature performance, such as oxidation resistance, fatigue performance and corrosion resistance. The process of this technical solution has a good theoretical basis, breaks through the traditional process idea of ​​only using plastic deformation to refine the grain structure, obtains forgings with better performance, and has important research value.

[0054] The high-uniformity fine-grained forming process of nickel-based superalloy forgings of the present application will be further described by specific embodiments below. This part further illustrates the content of the present invention in combination with specific embodiments, but should not be construed as a limitation to the present invention. Unless otherwise specified, the technical means adopted in the embodiments are conventional means well-known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0055] Example 1

[0056] The embodiment of the present application provides a high-uniformity fine-grained forming process for nickel-based superalloy forgings, including the following steps:

[0057] S1. Heat the nickel-based superalloy blank from room temperature (25°C) to the forging temperature of 1100°C at a rate of 10°C / min and hold for 5 min to ensure temperature uniformity; the nickel-based superalloy blank is GH4698 alloy, and the GH4698 alloy includes the following elements by mass fraction: Cr 14.35%, Mo 2.98%, Ti 2.65%, Nb 2.11%, Al 1.69%, Fe 0.11%, C 0.05%, and the balance is Ni; the shape of the blank is selected as a cylinder, and the volume of the blank is 1.05 times the volume of the target forging;

[0058] S2. Place the heated blank in a die forging die, perform initial deformation, then perform pressure holding treatment, and finally complete the final forming. After forging, cool it by air cooling and perform heat treatment to obtain the target forging;

[0059] Among them, during the initial deformation process, the applied pressure is 250 MPa, the deformation amount is 80% of the total deformation amount, and the downward pressing speed is 30 mm / s;

[0060] During the final forming deformation process, the applied pressure is 250 MPa, and the downward pressing speed is 20 mm / s; the deformation amount during the final forming deformation process is 20% of the total deformation amount;

[0061] The total forging ratio during the deformation process is 5;

[0062] The pressure holding treatment time is 30 s, and the pressure holding pressure is 10 MPa;

[0063] The heat treatment is specifically: heat the forging after air cooling at 1120°C for 8 h, air cool to room temperature, then heat to 1000°C and hold for 4 h, air cool to room temperature, then heat up to 775°C and hold for 16 h, and then air cool to room temperature again.

[0064] Comparative Example 1

[0065] This comparative example provides a high-uniformity fine-grained forming process for nickel-based superalloy forgings, including the following steps:

[0066] S1. Heat the nickel-based superalloy billet from room temperature (25 °C) to the forging temperature of 1100 °C at a rate of 10 °C / min and hold for 5 min to ensure uniform temperature. The nickel-based superalloy billet is GH4698 alloy, and GH4698 alloy contains the following elements by mass fraction: Cr 14.35%, Mo 2.98%, Ti 2.65%, Nb 2.11%, Al 1.69%, Fe 0.11%, C 0.05%, and the balance is Ni. The shape of the billet is selected as a cylinder, and the volume of the billet is 1.05 times the volume of the target forging.

[0067] S2. Place the heated billet in a die forging die and perform a one-step forming operation. Design the shape of the billet according to the shape of the forging, and during the forging process, strictly control the forging ratio and the degree of deformation. Specifically, during the forming (i.e., deformation) process, apply a pressure of 250 MPa, a downward pressing speed of 30 mm / s, and a forging ratio of 5. After deformation, cool it by air cooling to prevent defects such as cracks. After deformation and cooling, perform heat treatment to finally obtain the target forging. The heat treatment is specifically as follows: Hold the air-cooled forging at a temperature of 1120 °C for 8 h, air-cool to room temperature, then heat it to 1000 °C and hold for 4 h, air-cool to room temperature, then heat it to 775 °C and hold for 16 h, and then air-cool to room temperature again.

[0068] Comparative Example 2

[0069] This comparative example provides a high-uniformity fine-grained forming process for nickel-based superalloy forgings, including the following steps:

[0070] S1. Heat the nickel-based superalloy billet from room temperature (25 °C) to the forging temperature of 1100 °C at a rate of 10 °C / min and hold for 5 min to ensure uniform temperature. The nickel-based superalloy billet is GH4698 alloy, and GH4698 alloy contains the following elements by mass fraction: Cr 14.35%, Mo 2.98%, Ti 2.65%, Nb 2.11%, Al 1.69%, Fe 0.11%, C 0.05%, and the balance is Ni. The shape of the billet is selected as a cylinder, and the volume of the billet is 1.05 times the volume of the target forging.

[0071] S2. Place the heated blank in the pre-forging die and perform pre-forging operation. At this time, the main purpose is to preliminarily form the blank to be close to the final shape of the forging. During the pre-forging process, strictly control the forging ratio and the degree of deformation. The pre-forging deformation amount is controlled at 80% of the total deformation amount, the applied pressure is 250 MPa, and the downward pressing speed is 30 mm / s. After pre-forging is completed, cool it in the air to prevent defects such as cracks. Next, reheat the pre-forged blank to the final forging temperature of 1200 °C, slightly higher than the pre-forging temperature, and the holding time is 5 min. Then, put the heated blank into the final forging die and perform the final forging operation. During the final forging operation, the applied pressure is 250 MPa, the downward pressing speed is 20 mm / s, the final forging operation deformation amount is 20% of the total deformation amount, and the total forging ratio during the deformation process is 5. After the final forging is completed, cool it in the air to prevent defects such as cracks. After deformation and cooling, perform heat treatment to finally obtain the target forging. The specific heat treatment is as follows: Hold the air-cooled forging at a temperature of 1120 °C for 8 h, air-cool to room temperature, then heat it to 1000 °C and hold for 4 h, air-cool to room temperature, then raise the temperature to 775 °C and hold for 16 h, and then air-cool to room temperature again.

[0072] Example 2

[0073] The embodiment of the present application provides a high-uniformity fine-grained forming process for nickel-based superalloy forgings, including the following steps:

[0074] S1. Heat the nickel-based superalloy blank from room temperature (25 °C) to the forging temperature of 1050 °C at a rate of 10 °C / min and hold for 5 min to ensure uniform temperature. The nickel-based superalloy blank is GH4169 alloy, and the GH4169 alloy includes the following elements by mass fraction: Fe 18.35%, Cr 19.96%, Nb 5.23%, Mo 3.01%, Ti 1.00%, Al 0.59%, C 0.03%, and the balance is Ni. The shape of the blank is selected as a cylinder, and the volume of the blank is 1.05 times the volume of the target forging.

[0075] S2. Place the heated blank in the die forging die, perform initial deformation, then perform pressure holding treatment, and then complete the final forming. After the forging is completed, cool it in the air and perform heat treatment to obtain the target forging.

[0076] Among them, during the initial deformation process, the applied pressure is 200 MPa, the deformation amount is 80% of the total deformation amount, and the downward pressing speed is 30 mm / s.

[0077] During the final forming deformation process, the applied pressure is 200 MPa, the downward pressing speed is 20 mm / s; the deformation amount during the final forming deformation process is 20% of the total deformation amount.

[0078] The total forging ratio during the deformation process is 5;

[0079] The pressure holding time is 30 s and the pressure holding pressure is 10 MPa.

[0080] The heat treatment is specifically as follows: The forging after air cooling is held at a temperature of 950 °C for 1 h. After air cooling to room temperature, it is reheated to 720 °C and held for 8 h, then cooled to 620 °C and held for 8 h, and then air cooled to room temperature again.

[0081] Performance characterization

[0082] The target forgings are prepared according to the methods in Examples 1-2 and Comparative Examples 1-2 above; a cylindrical specimen is selected from the target forging, and after cutting along the central axis, metallographic observation is carried out.

[0083] Figure 1 It is the microstructure diagram of the GH4698 alloy of the target forging prepared according to the process in Example 1, and uniform grains can be seen.

[0084] Figure 2 It is the microstructure diagram of the GH4698 alloy of the forging formed in one step according to the process in Comparative Example 1, and the appearance of mixed crystal phenomenon can be observed.

[0085] Figure 3 It is the microstructure diagram of the GH4698 alloy of the forging formed by pre-forging and final forging according to the process in Comparative Example 2, and it is observed that the grains are coarser. Comparing Figure 1 、 Figure 2 、 Figure 3 It can be known that the average grain size in Example 1 is 24.1 μm, and the average grain sizes in Comparative Example 1 and Comparative Example 2 are 34.2 μm and 47.3 μm respectively. In Example 1, the structure is relatively uniform and there is no obvious mixed crystal phenomenon. While in Comparative Example 1, obvious mixed crystal phenomenon appears. In Comparative Example 2, although the grains are relatively uniform, the grains are significantly coarsened. The long heating time promotes the process of grain growth, the grain boundaries are straight and the grains present uniform equiaxed grains. The grain size of the target forging prepared in Example 1 is controlled above grade 7 and the grade difference is within 2 grades. While the grain size of the target forging prepared in Comparative Example 1 is controlled above grade 6, but the grade difference is within 3 grades. The grain size of the target forging prepared in Comparative Example 2 can only be controlled above grade 5, and the grade difference can be controlled within 2 grades. Therefore, the post-dynamic recrystallization behavior during the deformation interval can promote grain refinement, which shows that the process of the present invention can improve the uniformity of the material microstructure and refine the grains.

[0086] The grain size of the above-mentioned target forgings is smaller as the level increases; the grain size of level 7 is a medium to fine grain size with good comprehensive mechanical properties, such as strength and toughness. This grain size enables the internal structure of the forging to bear stress more evenly when it is under load, reducing the performance unevenness caused by excessively large or small grains; the difference is within 2 levels: the difference refers to the degree of difference in grain size in different parts of the same forging. The difference within 2 levels means that the grain size variation range of each part of the forging is small and the grain size is relatively uniform.

[0087] Figure 4 The statistical results of mechanical properties of target forgings prepared by the methods in the above-mentioned Example 1 and Comparative Examples 1-2 are given.

[0088] from Figure 4 It can be seen that the hardness, tensile strength and elongation of the target forging prepared in Example 1 are 357HV, 1220MPa and 31% respectively; the hardness, tensile strength and elongation of the target forging prepared in Comparative Example 1 are 313HV, 1124MPa and 26.8% respectively; the hardness, tensile strength and elongation of the target forging prepared in Comparative Example 2 are 307HV, 1130MPa and 33% respectively. Compared with Comparative Example 1, the hardness, tensile strength and elongation of the target forging prepared in Example 1 are improved; and compared with Comparative Example 2, the hardness and tensile strength of the target forging prepared in Example 1 are significantly improved while ensuring that the elongation is not significantly reduced and meets the requirements of the forging. This shows that the process of the present invention can improve the mechanical properties of high-temperature alloy forgings.

[0089] Figure 5 The microstructure diagram of the GH4169 alloy of the target forging prepared according to the process in Example 2 has an average grain size of 19.8 μm, and uniform grains can be seen.

[0090] The grain size of the target forging prepared in Example 2 is controlled to be above level 8, and the level difference is within level 2, which meets the requirements of GH4169 alloy forgings. The hardness, tensile strength and elongation of the forging are 431HV, 1312MPa and 18.1% respectively, which also meet the requirements of GH4169 alloy forgings.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high uniformity fine grain forming process for nickel-based high temperature alloy forgings, characterized in that: The following steps are involved: heating a nickel-based high-temperature alloy billet to a forging temperature; The heated billet is placed in a die for initial deformation, followed by pressure holding treatment, and then final forming to obtain the target forging.

2. The high uniformity fine grain forming process for nickel-based high temperature alloy forgings according to claim 1, characterized in that: During the initial deformation process, the deformation amount is 70-80% of the total deformation amount, and the pressing speed is 15-40 mm / s.

3. The high uniformity fine grain forming process for nickel-based high temperature alloy forgings according to claim 1, characterized in that: During the final forming deformation process, the pressing speed is 10 to 30 mm / s; The total forging ratio during the initial deformation and the final forming deformation process is 3 to 6.

4. The high uniformity fine grain forming process for nickel-based high temperature alloy forgings according to claim 1, characterized in that: The pressure of the pressure holding treatment is 10 to 20 MPa, and the pressure holding treatment time is 10 to 300 s.

5. The high uniformity fine grain forming process for nickel-based high temperature alloy forgings according to claim 1, characterized in that: The forging temperature is 1000-1200°C.

6. The high uniformity fine grain forming process for nickel-based high temperature alloy forgings according to claim 1, characterized in that: Heat the nickel-based high-temperature alloy billet to the forging temperature and keep it at this temperature for 5 to 60 minutes.

7. The high uniformity fine grain forming process for nickel-based high temperature alloy forgings according to claim 1, characterized in that: The nickel-based high-temperature alloy billet is heated to a forging temperature at a rate of 5 to 100° C. / min.

8. The high uniformity fine grain forming process for nickel-based high temperature alloy forgings according to claim 1, characterized in that: The heated blank is placed in a die for initial deformation, followed by pressure holding treatment, and then final forming, followed by air cooling or slow cooling to obtain the target forging; The slow cooling includes placing the final forging in a ventilated environment for cooling at a cooling rate of 5 to 15°C / s.

9. The high uniformity fine grain forming process for nickel-based high temperature alloy forgings according to claim 1, characterized in that: The volume of the nickel-based high-temperature alloy blank is 1.05 to 1.08 times the volume of the target forging.

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