A closed forging method and tooling for improving the properties of high alloy steel forgings

Abstract

The present invention relates to a closed forging method and tooling for improving the properties of high alloy steel forgings, belonging to the technical field of closed forging, and solves the technical problem that the grain size uniformity of each part of the forgings prepared by the existing forging methods is poor and it is difficult to meet the requirements. The above method includes: Step 1, perform cogging forging on the blank; Step 2, after cogging forging, perform the first forging heat treatment and then put it into the furnace for supplementary temperature; Step 3, assemble the closed forging tooling; Step 4, place the blank after supplementary temperature in the closed forging tooling; Step 5, perform closed upsetting treatment on the blank in the closed forging tooling; Step 6, directly produce the finished product after the closed upsetting treatment. Compared with open die forging, the closed forging method provided by the present invention has less blank cooling, good stress state, good surface quality of the blank, and is not easy to appear crack damage.

Description

Technical Field

[0001] The present invention relates to the technical field of closed forging, and particularly to a closed forging method and tooling for improving the properties of high alloy steel forgings. Background Art

[0002] High alloy steel materials such as austenitic stainless steel and nickel-based superalloys have excellent characteristic properties respectively according to different alloy compositions, such as good corrosion resistance, high-temperature properties, creep resistance, etc., and are widely used in the fields of electric power energy, marine engineering and aerospace. Due to the high alloy content of such materials, small forging temperature range, great forging difficulty, easy cracking at high temperature, and because of having a single austenite phase, the grains cannot be refined by heat treatment, and only the grains can be controlled by plastic deformation, resulting in difficult control of grain size.

[0003] Especially for short-axis and cake-shaped forgings with large cross-sections and small tonnages, due to the ingot type limitation, if the finished product is obtained by drawing, the drawing ratio is small, and the forgings cannot meet the conditions of complete dynamic recrystallization; if the finished product is obtained by upsetting, the deformation of each part of the forging is uneven, the stress-strain states vary greatly, and the degree of recrystallization of each part is different, which easily leads to poor uniformity of grain size of each part of the forging, making it difficult for the forging to meet the requirements of ultrasonic flaw detection, grain size and mechanical property indexes in the technical conditions. Summary of the Invention

[0004] In view of the above analysis, the embodiments of the present invention aim to provide a closed forging method and tooling for improving the properties of high alloy steel forgings, so as to solve the problem that the uniformity of grain size of each part of the forgings prepared by the existing forging methods is poor, making it difficult for the forgings to meet the requirements of ultrasonic flaw detection, grain size and mechanical property indexes.

[0005] The object of the present invention is mainly achieved by the following technical solutions:

[0006] On the one hand, the present invention provides a closed forging tooling for improving the properties of high alloy steel forgings, including an upsetting rod, an upsetting outer die and a working platform;

[0007] The upsetting rod is assembled on the die holder of the movable crossbeam of the press, the upsetting outer die is arranged above the working platform, and the upsetting outer die is centered with the upsetting rod for centering marking;

[0008] The billet after cogging forging is placed in the billet accommodation space formed by the working platform, the upsetting outer die and the upsetting rod.

[0009] In a possible design, lubricant is coated on the lower end surface of the upsetting rod and the inner surface of the upsetting outer die.

[0010] On the other hand, the present invention also provides a closed-die forging method for improving the properties of high-alloy steel forgings, which uses the above-mentioned closed-die forging tooling for improving the properties of high-alloy steel forgings; and includes a closed upsetting process.

[0011] The closed upsetting process includes: using an upsetting rod to extrude the billet downward, and the billet fits against the inner side of the closed upsetting outer die under the downward pressure of the upsetting rod. Then, continue to apply a pressure equal to the maximum load of the press and hold the pressure for 2 - 3 minutes. After the pressure holding is completed, demold the billet and perform spray cooling to obtain the upset billet.

[0012] Furthermore, the above-mentioned closed-die forging method for improving the properties of high-alloy steel forgings includes the following steps:

[0013] Step 1: Perform cogging forging on the billet, and the forging ratio is greater than 2.5.

[0014] Step 2: After the cogging forging of the billet, perform the first forging heat treatment. The heating temperature is 1100 - 1150 °C, and the holding time is 1.5 - 2 hours. After holding, take it out of the furnace, perform descaling and wrap it with an asbestos sleeve, and then put it back into the furnace for supplementary heating.

[0015] Step 3: Before forging, assemble the upsetting rod to the die holder of the movable crossbeam of the press, place the closed upsetting outer die on the working platform and align it with the upsetting rod for scribing, and then perform preheating treatment on the closed upsetting outer die.

[0016] Step 4: After the billet is completed with supplementary heating in the furnace and the closed upsetting outer die is preheated, take the billet and place it at the center of the scribing on the working platform, put the closed upsetting outer die outside the billet, and align it with the scribing.

[0017] Step 5: Perform the above-mentioned closed upsetting process. During the closed upsetting process, the maximum load of the press is 190 MN - 230 MN.

[0018] Step 6: Directly produce finished products after the closed upsetting treatment.

[0019] Furthermore, in Step 3, the preheating temperature of the closed upsetting outer die is 350 - 400 °C.

[0020] Furthermore, in Step 5, the billet is upset to fit against the inner side of the closed upsetting outer die at a deformation rate of 0.01 - 0.1 S -1 .

[0021] Furthermore, in Step 5, before the closed upsetting process, the height-diameter ratio of the billet ≤ 2.5; during the closed upsetting process, the reduction of the billet ≥ 40%.

[0022] Furthermore, in Step 5, the billet is upset to fit against the inner side of the closed upsetting outer die at a deformation rate of 0.05 S -1 .

[0023] Further, in step 5, the heating temperature during the closed-die upsetting process is 1100 - 1130 °C.

[0024] Further, in step 5, the pressure holding time is 2.5 min.

[0025] Further, the high-alloy steel forgings include austenitic stainless steel and nickel-based superalloys. The forging height-to-diameter ratio of the austenitic stainless steel and nickel-based superalloys is less than 1.5, and the diameter is ≥ 800 mm; the shapes of the austenitic stainless steel and nickel-based superalloys are short-axis types or disk types.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0027] (1) The closed-die forging method provided by the present invention for improving the properties of high-alloy steel forgings mainly targets high-alloy steels such as austenitic stainless steel and nickel-based superalloys. On the one hand, by controlling the heating temperature (the heating temperature for the first forging after cogging is 1100 - 1150 °C, and the heating temperature for closed-die upsetting is 1100 - 1130 °C), the growth rate of grains before and after deformation is regulated. On the other hand, at a deformation rate of 0.01 - 0.1 S-1 during closed-die upsetting, with sufficient deformation (forging ratio greater than 2.5), dynamic recrystallization occurs in most areas of the billet and a high level of distortion energy is stored. Finally, the high additional energy provided by the fully enclosed high-load pressure retention in the die promotes the nucleation and growth of static recrystallization, enabling the billet to complete full static recrystallization. By controlling the temperature, deformation amount, deformation rate, and high-load pressure (the maximum load of the press is 190 MN - 230 MN), a dynamic balance is achieved among dynamic recrystallization, static recrystallization, and grain growth within the billet, resulting in grain refinement and improved overall uniformity of the billet.

[0028] (2) The method for obtaining finished products by closed-die upsetting provided by the present invention always deforms inside the outer die of the closed-die forging tooling. Compared with open-die forging, the billet has less temperature drop, better stress state, better surface quality of the billet, and is not prone to crack damage.

[0029] (3) After cogging the billet, the present invention conducts two forging heating operations. The heating temperature for the first forging is 1100 - 1150 °C (for example, 1120 °C, 1140 °C). Controlling the heating temperature for the first forging at 1100 - 1150 °C can prevent the precipitation of harmful phases in the superalloy and avoid poor grain uniformity in various parts of the forging. The second forging heating operation is carried out during the closed-die upsetting process, and the heating temperature for the second forging is 1100 - 1130 °C (for example, 1120 °C, 1125 °C). Controlling the heating temperature for the second forging at 1100 - 1130 °C can ensure the generation of a uniform recrystallized structure inside the billet.

[0030] (4) The closed-die forging tooling of the present invention includes a upsetting rod, a upsetting outer die, and a working platform; the upsetting rod is assembled on the die holder of the movable crossbeam of the press, the upsetting outer die is arranged above the working platform, and the upsetting outer die is centered with the upsetting rod for centering scribing; the billet after cogging forging is placed in the billet accommodating space formed by the working platform, the upsetting outer die, and the upsetting rod. Compared with the prior art, by using the above-mentioned closed-die forging tooling, the present invention can achieve the purpose of improving the performance of high-alloy steel. The present invention uses the closed-die forging tooling to forge billets, reducing the investment in dies, improving production efficiency, and reducing production costs.

[0031] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the following specification, and some advantages can be made obvious from the specification, or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained from the content specifically pointed out in the embodiments of the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference signs represent the same components.

[0033] Figure 1 is a schematic diagram of the closed-die forging tooling of the present invention;

[0034] Figure 2 is a dynamic recrystallization microstructure diagram provided by the present invention.

[0035] Reference Signs:

[0036] 1 - upsetting rod; 2 - upsetting outer die; 3 - billet; 4 - working platform. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following will specifically describe the preferred embodiments of the present invention with reference to the drawings. The drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0038] As Figure 1 shown, the present invention provides a closed-die forging tooling for improving the performance of high-alloy steel forgings. The closed-die forging tooling includes a upsetting rod 1, a upsetting outer die 2, and a working platform 4; the upsetting rod 1 is assembled on the die holder of the movable crossbeam of the press, the upsetting outer die 2 is arranged above the working platform 4, and the upsetting outer die 2 is centered with the upsetting rod 1 for centering scribing; the billet after cogging forging is placed in the billet 3 accommodating space formed by the working platform 4, the upsetting outer die 2, and the upsetting rod 1.

[0039] Compared with the prior art, the present invention can achieve the purpose of improving the properties of high-alloy steel by using the above-mentioned closed-die forging tooling. The present invention uses the closed-die forging tooling to forge billets, reducing the investment in molds, improving production efficiency, and reducing production costs.

[0040] A lubricant, such as boron nitride lubricant, is coated on the lower end face of the upsetting rod 1 and the inner surface of the upsetting outer die 2.

[0041] Example 1

[0042] This example provides a closed-die forging method for improving the properties of high-alloy steel forgings, including the following steps:

[0043] Step 1: Perform cogging forging on the billet with a large deformation ratio, and the forging ratio is greater than 2.5;

[0044] In the above Step 1, controlling the forging ratio of cogging forging to be greater than 2.5 can effectively break coarse grains and obtain a relatively uniform forging structure.

[0045] Step 2: After the billet is cogged and forged, perform the first forging heat treatment. The temperature of the first forging heat treatment is 1100 - 1150 °C (for example, 1120 °C, 1140 °C), the holding time after heating is 1.5 - 2 h, after holding, take out of the furnace for descaling and wrap with an asbestos sleeve, and then put into the furnace for supplementary heating;

[0046] It should be noted that controlling the first forging heat treatment temperature at 1100 - 1150 °C can prevent the precipitation of harmful phases in the superalloy and avoid poor grain uniformity in each part of the forging.

[0047] Step 3: Before forging, assemble the upsetting rod 1 onto the die holder of the press moving crossbeam, place the upsetting outer die 2 on the working platform 4 and align it with the upsetting rod 1 for scribing, and then preheat the upsetting outer die 2, and the preheating temperature is 350 - 400 °C;

[0048] In the above Step 3, controlling the preheating temperature at 350 - 400 °C (for example, 360 °C, 380 °C) can effectively prevent the rapid temperature drop during the heat transfer process when the billet contacts the upsetting outer die 2, thus affecting the upsetting effect.

[0049] Step 4: After the billet is supplementary heated, use the manipulator to pick up the billet and place it at the scribing center of the working platform 4, put the upsetting outer die 2 outside the billet, and align it with the scribing;

[0050] Step 5: Use the upsetting rod 1 to squeeze the billet downward. Under the downward pressure of the upsetting rod 1, the billet fits against the inner side of the upsetting outer die 2. Continue to apply a pressure equal to the maximum load of the press (the maximum load of the press is 190 MN - 230 MN), and then the holding pressure time is 2 - 3 min. After the holding pressure is completed, demold the billet and perform spray cooling to obtain the upset billet 3;

[0051] It should be noted that before closed die upsetting, the height-diameter ratio of the blank is ≤ 2.5, and during closed die upsetting, the reduction is ≥ 40% (for example, 50%, 60%). Within the deformation rate range of 0.01 - 0.1 s -1 a uniform and fine dynamic recrystallization structure can be obtained by strictly controlling the above upsetting conditions. When the deformation rate is 0.01 s -1 and the reduction is 50%, the grain size structure diagram is as shown in Figure 2 the figure below.

[0052] In the above step 5, the heating temperature of the blank for the closed die upsetting pass should comprehensively consider the equipment capacity, the temperature conditions for the occurrence of dynamic and static recrystallization of the material, and the growth trend of the material grain size with temperature. Since most high alloys are austenitic stainless steels, it is difficult to refine the grains by heat treatment. In the present invention, the grains are refined by dynamic recrystallization. The second forging pass temperature (closed forging temperature) takes into account the "heat increase" effect of closed die upsetting. The upper limit of the heating temperature for the second forging pass is 20 - 30 °C lower than the upper limit temperature of the heating temperature for the first forging pass; for example, the heating temperature for the closed die upsetting pass of the present invention is 1100 - 1130 °C (for example, 1120 °C, 1125 °C).

[0053] In the above step 5, when the upsetting rod 1 presses down the blank until it can no longer be pressed down, at this time, the applied pressure is equal to the pressure of the maximum load of the press, and the pressure is maintained for 2 - 3 min. The internal grain size uniformity of the blank is improved by the combined effects of the dynamic recrystallization generated by the large deformation of upsetting and the strengthening and promoting effects of the high additional energy during the full-closed pressure maintenance in the upsetting outer die 2 on the static recrystallization of the blank.

[0054] Step 6: Directly produce finished products after closed die upsetting treatment.

[0055] The closed forging method for improving the properties of high alloy steel provided in this embodiment is applicable to the control of grain size uniformity and the improvement of surface quality of high alloy steel forgings including austenitic stainless steels and nickel-based superalloys, etc.; among them, the forging height-diameter ratio of austenitic stainless steels and nickel-based superalloys is less than 1.5, and the diameter ≥ 800 mm; the shapes of austenitic stainless steels and nickel-based superalloys are short-axis types or disc types.

[0056] The above forging method requires placing the blank in the lower die for closed die upsetting, and maintaining the pressure after the blank fits against the upsetting outer die 2 and can no longer be pressed down. The internal grain size uniformity of the blank is improved by the combined effects of the dynamic recrystallization generated by the large deformation of upsetting and the strengthening and promoting effects of the high additional energy during the full-closed pressure maintenance in the die on the static recrystallization of the blank, and further improves the various performance indexes of the blank (such as the anisotropy of the blank and the uniformity of the internal quality).

[0057] The closed-die forging method provided by the present invention is particularly suitable for controlling the grain size uniformity and improving the surface quality of materials such as short-axis and cake-shaped austenitic stainless steels and nickel-based superalloys with large cross-sections, small tonnages, and a height-to-diameter ratio of less than 1.5.

[0058] In the prior art, for short-axis and cake-shaped forgings with large cross-sections and small tonnages, due to the limitation of the ingot type, if the forging method of drawing out the finished product is adopted, the drawing ratio is small, and the forging cannot meet the conditions of complete dynamic recrystallization; if the forging method of upsetting out the finished product is adopted, the deformation of each part of the forging is uneven, the stress-strain states vary greatly, and the degree of recrystallization in each part is different, which easily leads to poor grain size uniformity of each part of the forging, making it difficult for the forging to meet the requirements of ultrasonic flaw detection, grain size, and mechanical property indicators in the technical conditions.

[0059] On the one hand, the present invention controls the growth rate of grains before and after deformation by selecting a reasonable heating temperature (the heating temperature of the first forging heat is 1100 - 1150 °C, and the heating temperature of the forging heat during the closed-die upsetting process is 1100 - 1130 °C). On the other hand, through sufficient deformation and a large deformation rate, dynamic recrystallization occurs in most areas of the billet and a high distortion energy is stored. Finally, the high additional energy maintained by the high load pressure in the fully enclosed die promotes the nucleation and growth of static recrystallization, enabling the billet to complete full static recrystallization. With the reasonable combination of the four parameters of temperature, deformation, deformation rate, and high load pressure maintenance, dynamic balance is achieved among dynamic recrystallization, static recrystallization, and grain growth inside the billet, and the average grain size can reach above grade 4, realizing grain refinement inside the billet and improving its overall uniformity.

[0060] The forging method provided by the present invention for improving the properties of high-alloy steel forgings adopts the method of closed-die upsetting to produce the finished product. This method ensures that the billet is always deformed inside the outer die of the closed-die forging tooling, and has the following three advantages compared with free forging: First, the present invention has near-net shape forming, regular shape, and no cracks; second, the stress state of the billet provided by the present invention is triaxial compressive stress, with a large hydrostatic pressure and good compactness; finally, the average strain of the entire interface of the billet forged by the present invention is uniform, dynamic recrystallization is sufficient, and the average grain size is uniformly fine.

[0061] Example 2

[0062] This embodiment provides a forging method for improving the properties of high-alloy steel forgings such as short-axis austenitic stainless steels and nickel-based superalloys with a height-to-diameter ratio of less than 1.5.

[0063] For a certain nickel-based high-alloy short-axis forging, the large diameter of the forging finished product is 900 mm, and the forging weighs 6 tons. After the ingot is subjected to large-deformation cogging forging, closed-die upsetting forging is carried out.

[0064] The above-mentioned closed-die forging method for improving the properties of high-alloy steel forgings includes the following steps:

[0065] Step 1: Perform cogging forging on the blank with a large deformation amount, and the forging ratio is 2.5;

[0066] Step 2: After the blank is cogging forged, perform the first forging heat treatment. The heating temperature is 1100 °C, the holding time is 1.5, after holding and taking out of the furnace for descaling, wrap it with an asbestos sleeve, and then put it into the furnace for supplementary heating;

[0067] Step 3: Before forging, assemble the upsetting rod 1 onto the die holder of the moving crossbeam of the press, place the upsetting outer die 2 on the working platform 4 and align it with the upsetting rod 1 for alignment marking, and then preheat the upsetting outer die 2, and the preheating temperature is 400 °C;

[0068] Step 4: After the blank is supplemented with heat, use the manipulator to pick up the material and place it at the center of the marking on the working platform 4, put the upsetting outer die 2 outside the blank, and align it with the marking;

[0069] Step 5: Perform the closed-die upsetting process;

[0070] This closed-die upsetting process includes: using the upsetting rod 1 to extrude the blank downward, the blank fits against the inner side of the upsetting outer die 2 under the downward pressure of the upsetting rod 1. When the upsetting rod 1 presses the blank downward until it can no longer be pressed down, at this time, the applied pressure is equal to the pressure of the maximum load of the press, the maximum load of the press is 200 MN, and then the holding time is 2 min. After the holding is completed, the blank is demolded and sprayed with water for cooling to obtain the upset blank 3.

[0071] Among them, the deformation rate of the blank during the closed-die upsetting process is 0.05 S -1 , the height-diameter ratio of the blank before closed-die upsetting is 2.5, and the reduction amount during closed-die upsetting is 40%;

[0072] Step 6: Directly produce finished products after closed-die upsetting treatment.

[0073] In the prior art, high-alloy steel forgings such as short-axis type, cake-type austenitic stainless steel, and nickel-based superalloy are formed by multiple free upsetting and drawing on a free forging hydraulic press. For the nickel-based alloy forged by this method, the overall grain size uniformity of the forging is poor during subsequent inspection, the grain size grade difference is more than 3, and the ultrasonic inspection sensitivity and inspection results are not easily satisfied with the performance requirements. For the nickel-based alloy forged by the closed-die upsetting forging method of the present invention, the overall grain size of the forging reaches grade 5 during subsequent inspection, and the ultrasonic inspection sensitivity and inspection results are qualified.

[0074] Example 3

[0075] This embodiment provides a forging method for improving the performance of high-alloy steel forgings such as cake-type austenitic stainless steel and nickel-based superalloy with a height-diameter ratio less than 1.5.

[0076] For a nickel-based high-alloy disc forging, the finished forging has a large diameter of 1200 mm and weighs 9 tons. After the ingot is subjected to heavy deformation and cogging forging, closed-die upset forging is carried out.

[0077] The specific forging process is as follows:

[0078] Step 1: Subject the billet to heavy deformation and cogging forging with a forging ratio of 3.5;

[0079] Step 2: After the billet is cogged forged, it is heated in a forging heat treatment. The heating temperature is 1145 °C, and the holding time is 1.7 h. After holding and then discharging from the furnace for descaling, it is wrapped with an asbestos sleeve and then put into the furnace for short-time supplementary heating to 1145 °C;

[0080] Step 3: Before forging, assemble the upsetting rod 1 onto the die holder of the moving crossbeam of the press. Place the upsetting outer die 2 on the working platform 4 and align it with the upsetting rod 1 for centering and scribing. Then preheat the upsetting outer die 2 to a preheating temperature of 390 °C;

[0081] Step 4: After the billet is supplementary heated, use the manipulator to pick up the billet and place it at the scribed center of the working platform 4. Put the upsetting outer die 2 outside the billet and align it with the scribing;

[0082] Step 5: Carry out the closed-die upsetting process;

[0083] This closed-die upsetting process includes: using the upsetting rod 1 to extrude the billet downward. Under the downward pressure of the upsetting rod 1, the billet fits against the inner side of the upsetting outer die 2. When the upsetting rod 1 presses the billet until it can no longer be pressed down, at this time, the applied pressure is equal to the pressure of the maximum load of the press. The maximum load of the press is 230 MN. Then the holding time is 2.5 min. After the holding is completed, the billet is demolded and water-sprayed for cooling to obtain the upset billet 3.

[0084] Among them, the deformation rate of the billet during the closed-die upsetting process is 0.1 S -1 , and the height-diameter ratio of the billet before closed-die upsetting is 2.0, and the reduction in height during closed-die upsetting is 50%.

[0085] Step 6: Directly produce the finished product after closed-die upsetting treatment.

[0086] The nickel-based alloy forged by using the closed-die upset forging method in this embodiment has an overall grain size of grade 6 during subsequent inspection, and the sensitivity and inspection results of ultrasonic inspection are qualified.

[0087] It should be noted that in the prior art, forging of high alloy steel forgings such as short-axis type, cake type austenitic stainless steel, nickel-based superalloy, etc. is carried out by multiple free upsetting and drawing on a free forging hydraulic press. For the nickel-based alloy forged by this method, the overall grain size uniformity of the forging is poor during subsequent inspection, the grain size grade difference is more than 3, and it is not easy to meet the performance requirements for ultrasonic inspection sensitivity and inspection results.

[0088] As described above, the above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A closed forging method for improving the properties of high alloy steel forgings, characterized in that, It includes the following steps: Step 1: Perform cogging forging on the billet, with a forging ratio greater than 2.5; Step 2: After the cogging forging of the billet, conduct the first forging heat treatment. The heating temperature is 1100 - 1150 °C, the holding time is 1.5 - 2 h. After holding, take it out of the furnace, descale and wrap it with an asbestos sleeve, and then put it back into the furnace for supplementary heating; Use a closed-die forging tooling for forging. The closed-die forging tooling includes a upsetting rod, an upsetting outer die, and a working platform; Step 3: Before forging, assemble the upsetting rod onto the die holder of the press moving crossbeam, place the upsetting outer die on the working platform and align it with the upsetting rod for scribing, and then conduct preheating treatment on the upsetting outer die; Step 4: After the billet finishes supplementary heating in the furnace and the upsetting outer die finishes preheating, take the billet and place it at the scribing center of the working platform, put the upsetting outer die over the billet, and align it with the scribing; Step 5: Perform the closed-die upsetting process. Before the closed-die upsetting process, the height-diameter ratio of the blank ≤ 2.5; during the closed-die upsetting process, the reduction of the blank ≥ 40%; the maximum load of the press during the closed-die upsetting process is 190 MN - 230 MN; upset the blank to fit against the inner side of the closed-die upsetting outer die at a deformation rate of 0.01 - 0.1 S -1 ; the forging heating temperature during the closed-die upsetting process is 1100 - 1130 °C; Step 6: Directly produce the finished product after closed-die upsetting treatment to obtain a high-alloy steel forging. The high-alloy steel forging is austenitic stainless steel or nickel-based superalloy, with an internal structure of austenite, and the average grain size can reach above grade 4.

2. The closed-die forging method for improving the properties of high-alloy steel forgings according to claim 1, characterized in that, In the said Step 3, the preheating temperature of the upsetting outer die is 350 - 400 °C.

3. The closed die forging method for improving the properties of high alloy steel forgings according to claim 1, characterized in that, At a deformation rate of 0.05S -1 upset the blank to fit against the inner side of the upsetting outer die.

4. The closed-die forging method for improving the properties of high-alloy steel forgings according to claim 1, characterized in that, In the said Step 5, the holding pressure time is 2.5 min.

5. The closed forging method for improving the properties of high alloy steel forgings according to any one of claims 1 to 4, characterized in that, The said high-alloy steel forging includes austenitic stainless steel and nickel-based superalloy. The forging height-to-diameter ratio of the austenitic stainless steel and nickel-based superalloy is less than 1.5, and the diameter is ≥800 mm; The shape of the austenitic stainless steel and nickel-based superalloy is short-axis type or cake type.

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