Forming method for improving structure and performance of large stepped long axis type forgings

Abstract

This application discloses a forming method for improving the microstructure and properties of large stepped long-shaft forgings, belonging to the field of forging hot working technology. The forming method includes: subjecting the billet to a first heat treatment, forging and elongating the rod portion to a rectangular cross-section to obtain a first preform; subjecting the first preform to a second heat treatment, elongating the rod portion of the first preform to a cylindrical shape to obtain a second preform; machining the rod portion of the second preform to obtain a third preform with a rod diameter difference of 20 mm from the target forging rod diameter; heat-treating the head of the third preform, then forging it in a preheated mold to obtain a preliminary forging; subjecting the preliminary forging to normalizing, first tempering, quenching, and second tempering treatments, followed by machining to obtain the final product. This method can improve the microstructure uniformity, integrity, and stability of the forging.

Description

Technical Field

[0001] This application belongs to the field of hot working technology of forgings, and specifically relates to a forming method that can improve the microstructure and properties of large stepped long shaft forgings. Background Technology

[0002] Large stepped long shaft forgings can reach lengths of 2000mm to 2500mm, with a shaft diameter of only φ180mm to φ200mm, but a head diameter as high as φ550mm to φ600mm. Therefore, large stepped long shaft forgings are characterized by their long overall length, large variations in cross-section, high grain size requirements (uniform grains and grain size ≥4), and high-temperature creep resistance (≥100h). This necessitates higher requirements for forging and heat treatment technologies to optimize the microstructure and performance of these forgings.

[0003] Conventional forging methods involve first heating the entire part and then upsetting the head, followed by heating the entire part again and drawing out the elongated rod. To ensure coaxiality, a large amount of raw material costs are usually required, and the shape of forgings formed by free forging is usually inconsistent, which will affect the dimensional accuracy, grain size, and high-temperature creep performance of the product (especially for large forgings with large cross-sectional differences). That is, this conventional forging method has the following disadvantages: (1) low utilization rate of raw materials, uneven microstructure of forged products, and grain size of the product ≤ 4; (2) unqualified high-temperature creep performance of the product, which cannot meet the technical requirements. This greatly restricts the development of production and application of large stepped long shaft forgings.

[0004] Therefore, there is an urgent need for a new forging method to improve the microstructure uniformity, forming consistency and high-temperature durability of forgings. Summary of the Invention

[0005] The purpose of this application is to provide a forming method that can improve the microstructure and properties of large stepped long-shaft forgings, thereby improving the microstructure uniformity, forming consistency, and high-temperature creep stability of the forgings.

[0006] To achieve the above objectives, this application provides a forming method for improving the microstructure and properties of large stepped long shaft forgings, wherein the large stepped long shaft forging includes a rod and a head arranged sequentially, and includes the following steps: The billet is subjected to a first heat treatment, and the rod is forged and stretched to a rectangular cross-section to obtain the first preform. The first preform is subjected to a second heat treatment, and the rod portion of the first preform is stretched into a cylindrical shape to obtain the second preform; The rod portion of the second preform is machined to obtain a third preform with a rod diameter difference of 20 mm from the rod diameter of the target forging. The head of the third preform is heated and then placed in a preheated mold for forging to obtain a preliminary forging. The initial forging is subjected to normalizing, first tempering, quenching and second tempering in sequence, and then machined to obtain the final product.

[0007] Furthermore, the diameter of the rod portion of the large stepped long shaft forging is φ180mm~φ200mm, the diameter of the head of the large stepped long shaft forging is φ550mm~φ600mm, the length of the head of the large stepped long shaft forging is 450mm~500mm, and the total length of the large stepped long shaft forging is 2000mm~2500mm.

[0008] Furthermore, the temperature of the first heat treatment is 1000℃~1150℃, and the deformation of the rod after the first heat treatment is 80%~120%.

[0009] Furthermore, the temperature of the second heat treatment is 1000℃~1150℃, and the rod after the second heat treatment is cylindrical.

[0010] Furthermore, the head of the third preform is heated at a temperature of 1000℃~1150℃, and the preheated part of the mold corresponds to the part of the third preform that is heated.

[0011] Furthermore, the deformation during the forging process is 40% to 60%.

[0012] Furthermore, the normalizing treatment temperature is 990℃~1010℃, the holding time is 5h, and the normalizing treatment is followed by air cooling to room temperature.

[0013] Furthermore, the temperature of the first tempering treatment is 680℃~700℃, the holding time is 10h, and air cooling is used to cool to room temperature after the first tempering treatment. After the first tempering treatment, an inner hole is machined at the center of the initial forging, with a diameter of φ80mm.

[0014] Furthermore, the quenching temperature is 1000℃~1020℃, the holding time is 5h, and after the quenching, the temperature is cooled to 200℃~300℃ by oil cooling.

[0015] Furthermore, the temperature of the second tempering treatment is 660℃~710℃, the holding time is 7h, and after the second tempering treatment, air cooling is used to cool to room temperature.

[0016] In summary, this application has the following advantages: The forming method described in this application employs multi-stage temperature-controlled forming technology. After elongation of the rod through overall heating, localized heating is used in conjunction with precision upsetting of the head using a die, combined with a gradient heat treatment process. This optimized process not only improves material utilization but also significantly enhances the uniformity of the microstructure and grain size (reaching level 5-6), while simultaneously improving the high-temperature creep resistance of large stepped long-shaft forgings. Furthermore, the modular die design allows for rapid upper die replacement and a universal lower die configuration, enabling the production of forgings of various specifications within the same series. This reduces overall manufacturing costs and unit product energy consumption, resulting in significant technical and economic advantages. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a forming method for improving the microstructure and properties of large stepped long-axis forgings according to an embodiment of this application. Figure 2 This is a dimensioned drawing of the forging model in the embodiment; Figure 3 This is a dimensioned drawing of the target forging prepared in Example 1; Figure 4 This is a schematic diagram of the structure of the billet in Example 1; Figure 5 This is a schematic diagram of the structure of the first prefabricated body in Example 1; Figure 6 This is a schematic diagram of the structure of the second preform in Example 1; Figure 7 This is a schematic diagram of the structure of the third prefabricated body in Example 1; Figure 8 This is a schematic diagram of the structure and assembly of the mold used in Example 1; Figure 9 This is a schematic diagram of the forging product after machining the inner hole in Example 1. Detailed Implementation

[0018] The principles and features of this application are described below with reference to embodiments. The examples are for illustrative purposes only and are not intended to limit the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0019] 1Cr11Ni2W2MoV is a chromium-nickel-tungsten-molybdenum-vanadium martensitic heat-resistant steel with excellent thermomechanical properties and corrosion resistance, making it suitable for important applications in high-temperature and corrosive environments. The chemical composition of 1Cr11Ni2W2MoV includes elements such as carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, molybdenum, nitrogen, tungsten, and vanadium. The rational proportions of these elements ensure the stability and durability of the steel under high-temperature and corrosive conditions. Its physical properties include high density, thermal conductivity, and coefficient of linear expansion, making it suitable for high-temperature environments. Therefore, 1Cr11Ni2W2MoV, with its excellent heat resistance, good mechanical properties, and outstanding corrosion resistance, is widely used in the manufacture of key components in steam turbine blades and aerospace equipment (important parts such as engine blades, discs, and shafts operating below 600℃), making it a crucial material choice for high-temperature environments.

[0020] The forming method described in this application is for large 1Cr11Ni2W2MoV stepped long shaft forgings, which are characterized by large differences in cross-section, long rod length, and high requirements for microstructure and properties. In the production process, there are not only difficulties in forging, but also the requirement that the grain size of the forging microstructure be grade 5 or above, and the high temperature creep performance be ≥100h. This leads to higher requirements for the forging process and heat treatment process of large stepped long shaft forgings in actual production.

[0021] The large stepped long-axis forgings referred to in this application include: a rod and a head arranged sequentially. For example... Figure 3 and Figure 9 As shown, the connection between the rod and the head forms a transition area, dividing the rod into a buffer section and a long axis section. The diameter gradually decreases from the head towards the rod to the standard diameter of the rod. The buffer section includes a first cross-section and a second cross-section. The first cross-section is located near the head end, and the second cross-section is located near the long axis section end. The diameter of the first cross-section is φ250mm, and the diameter of the second cross-section is the same as the diameter of the rod. The length of the buffer section is 200mm.

[0022] The dimensions of large stepped long shaft forgings include: the diameter of the rod is φ180mm~φ200mm, the diameter of the head is φ550mm~φ600mm, the length of the head is 450mm~500mm, and the total length of the large stepped long shaft forging is 2000mm~2500mm.

[0023] Based on this, this application provides a forming method that can improve the microstructure and properties of large stepped long-axis forgings, such as... Figure 1 As shown, it includes the following steps: S1. The billet is subjected to a first heat treatment, and the rod is forged and stretched to a rectangular cross-section to obtain the first preform.

[0024] In a specific implementation, the temperature of the first heat treatment is 1000℃~1150℃, and the deformation of the rod after the first heat treatment is 80%~120%.

[0025] In this application, high-temperature heating imparts good plasticity and low deformation resistance to the billet. Elongation treatment causes deformation under triaxial compressive stress, allowing internal defects such as porosity and shrinkage to fuse together. This promotes homogenization of the metal's internal structure and grain refinement, thereby increasing the material's density. Simultaneously, the elongation process extends metal flow lines along the axial direction of the rod, forming a fibrous structure, significantly improving the axial mechanical properties of the forging, especially its strength and toughness. Furthermore, during elongation, inclusions and bubbles within the material are thoroughly broken down and dispersed, further enhancing the internal quality and density of the forging. The rod L is initially stretched into a rectangular cross-section (which can be adjusted to a rectangle or square cross-section according to actual needs), and can be easily transformed into other shapes, such as circular or elliptical cross-sections, laying a solid foundation for subsequent forming processes.

[0026] S2. The first preform is subjected to a second heating treatment to elongate the rod part of the first preform into a cylindrical shape, thereby obtaining the second preform.

[0027] In a specific embodiment, the temperature of the second heat treatment is 1000℃~1150℃, and the rod after the second heat treatment is cylindrical.

[0028] In this application, to more precisely control the cross-sectional shape and dimensions of the forging, the rectangular cross-section is further forged into a cylindrical shape, thereby making it closer to the design requirements of the final product, reducing subsequent machining, improving material utilization, and enhancing the dimensional accuracy and surface quality of the forging. The cylindrical cross-section allows the metal streamlines to be distributed concentrically, which is beneficial for improving the mechanical properties of the forging in all directions, especially radial and circumferential properties, giving the forging superior overall mechanical properties. Reheating (i.e., the second heat treatment) can eliminate residual stress generated in the previous process, making the microstructure more stable and preventing deformation or cracking during subsequent processing and use. Simultaneously, due to the continuous deformation of the first preform at high temperature, the original grains are elongated and a large number of dislocations are generated. These dislocations are rearranged after deformation at high temperature to form new dislocation-free grains. This process refines the recrystallized grains, further improving the strength and toughness of the material.

[0029] Straightening during forging ensures the straightness of the cylinder, eliminates bending deformation generated during forging, and guarantees the geometric accuracy of the forging. Therefore, in one preferred embodiment, to ensure the straightness of the cylinder, this application also performs a straightening operation on the second preform to guarantee the quality of subsequent processing. This not only improves the appearance quality of the forging but, more importantly, ensures the positioning accuracy of subsequent machining, reduces machining errors, and increases the product yield.

[0030] S3. The rod of the second preform is machined to obtain a third preform with a rod diameter difference of 20mm from the rod diameter of the target forging.

[0031] During heat treatment, forgings inevitably undergo some deformation due to factors such as microstructure transformation and thermal stress. Therefore, this application selects a 20mm machining allowance to provide sufficient compensation space for heat treatment deformation, ensuring that the forgings can still achieve the expected finished dimensions through subsequent finishing processes (such as grinding and turning) after heat treatment, thus guaranteeing the dimensional accuracy of the final product. This not only eliminates potential minor defects and decarburized layers on the forging surface, achieving higher surface roughness requirements, but also avoids surface oxidation, decarburization, or contamination that may occur during heat treatment by removing the surface layer, ensuring the surface quality and internal properties of the forgings.

[0032] S4. Heat the head of the third preform, then place it in a preheated mold to forge and shape it, thus obtaining the initial forging.

[0033] In this specific embodiment, the head of the third preform is heated at the same temperature and for the same duration as the second heating treatment. The preheated portion of the mold corresponds to the portion of the third preform that is being heated. The deformation during the forging process is 40% to 60%.

[0034] This application utilizes localized heating, applying high-temperature heating only to the head while maintaining the rod at room temperature. This allows for precise control of the plastic deformation zone, concentrating it at the head and preventing unnecessary deformation in the rod. This results in refined forming of the forging, ensuring dimensional accuracy and surface quality. Simultaneously, because deformation is primarily concentrated at the head, the rod material does not participate in intense plastic deformation. This localized heating and deformation approach avoids the grain coarsening and high-temperature durability degradation problems associated with traditional methods that involve overall heating without rod deformation. Furthermore, the absence of oxide scale generated during heating improves material utilization, reduces waste, and lowers production costs.

[0035] This application utilizes localized heating forging to induce dynamic recrystallization of the head metal at high temperatures. This process refines the grains, homogenizes the microstructure, and eliminates anisotropy in the fibrous structure, significantly improving the high-temperature creep resistance of the forging and ensuring it meets design requirements. Simultaneously, due to the third heat treatment, the rod portion does not undergo high-temperature heating and severe deformation, thus preserving its original microstructure and properties. This avoids problems such as coarse microstructure and decreased high-temperature creep resistance that can occur with overall heating and localized non-deformation.

[0036] In this application, such as Figure 8 By employing a combined mold, the height L3 of the upper mold and the cavity size can be adjusted to produce forgings of the same type with a rod diameter smaller than ΦC, a rod length greater than L4, and a head size that varies with the upper mold cavity. This improves the versatility and economy of the mold. Compared to a single mold, this combined mold not only allows for upper mold replacement to produce different forgings but also extends the life of the lower mold and directly eliminates the preheating cost of the lower mold. Furthermore, in step S5, only the head needs to be heated. Therefore, in the use of the combined mold, only the upper mold needs to be preheated, which reduces the manufacturing cost and preheating energy consumption of the mold.

[0037] S5. The initial forging is subjected to normalizing, first tempering, quenching and second tempering in sequence, and then machined to obtain the final product.

[0038] In this application, normalizing and first tempering processes refine grain size, eliminate stress, and improve machinability, while quenching and second tempering processes enhance strength and plasticity, adjust mechanical properties, and stabilize the microstructure. Strict control of temperature and time ranges is crucial for ensuring effective heat treatment. Excessively high or low temperatures, or excessively long or short holding times, can lead to deterioration of material properties or failure to meet design requirements. Therefore, strictly adhering to process parameters is an important prerequisite for ensuring the stable quality and performance of forgings in this application.

[0039] In a specific embodiment, the normalizing temperature is 990℃~1010℃, the holding time is 5 hours, and air cooling to room temperature is performed after normalizing. The normalizing treatment in this application heats the material to above the austenitizing temperature, causing a phase transformation and forming a fine pearlite structure during air cooling, thereby refining the grain size. The normalizing treatment in this application can eliminate residual stress generated during forging, improve the uniformity of the material's microstructure, and improve the strength and plasticity of the material by refining the microstructure, providing a good microstructure basis for subsequent quenching and second tempering treatments.

[0040] The normalizing temperature should not exceed 1010℃, as excessively high temperatures will lead to coarse grains, thereby reducing the strength and toughness of the material; nor should it be lower than 990℃, otherwise the microstructure transformation will be incomplete, failing to achieve the effect of refining the grains. The normalizing treatment requires a holding time of 5 hours to avoid insufficient microstructure uniformity and incomplete stress relief due to insufficient holding time.

[0041] In this specific embodiment, the temperature of the first tempering treatment is 680℃~700℃, and the holding time is 10 hours. After the first tempering treatment, air cooling to room temperature is used. After the first tempering treatment, an inner hole with a diameter of φ80mm is machined on the shaft of the initial forging. Since the material hardness is high after normalizing, this application uses tempering treatment to reduce the material hardness and improve the material toughness. At the same time, tempering treatment can also make the microstructure more stable, reduce the risk of deformation during subsequent processing and use, and further eliminate the stress that may remain during normalizing. The temperature of the first tempering treatment should not be too high, otherwise it will cause the material hardness to decrease too much, thereby affecting the strength of the material. If the temperature is too low, it may be impossible to effectively reduce the material hardness or improve the material toughness.

[0042] In this specific implementation, the quenching temperature is 1000℃~1020℃, the holding time is 5 hours, and after quenching, the material is cooled to 200℃~300℃ using oil cooling. The rapid cooling (oil cooling) during quenching allows the material to form a martensitic structure, significantly improving its hardness. Furthermore, the rapid cooling after high-temperature heating refines the grain size of the forging, thereby improving the overall mechanical properties of the material. If the quenching temperature is too high, it may lead to coarse austenite grains, resulting in coarse martensite and reducing the material's toughness. If the quenching temperature is too low, it may result in insufficient austenitization, failing to obtain a uniform martensitic structure and affecting the material's hardness. Insufficient holding time during quenching leads to uneven microstructure transformation, affecting the stability of the material's properties; excessive holding time increases energy consumption and may also cause grain growth, which is detrimental to subsequent production and use.

[0043] In this specific embodiment, the temperature of the second tempering treatment is 660℃~710℃, the holding time is 7 hours, and air cooling to room temperature is used after the second tempering treatment. The material after quenching has high hardness. This application uses a second tempering treatment to adjust the hardness and toughness, achieving the comprehensive mechanical properties required by the design. Furthermore, the stress generated during quenching may cause deformation or cracking of the forging. The second tempering treatment can also eliminate stress and stabilize the microstructure, thereby reducing dimensional changes during subsequent use. If the temperature of the second tempering treatment is too high (>710℃), it may cause an excessive decrease in the hardness of the forging, further affecting the wear resistance and strength of the material; if the temperature of the second tempering treatment is too low (<660℃), it cannot effectively eliminate quenching stress, resulting in insufficient improvement in toughness. Too short a holding time for the second tempering treatment will lead to insufficient stress elimination and microstructure stabilization, while too long a holding time will increase energy consumption and may affect production efficiency. Therefore, strict control of the temperature and time range is crucial to ensuring the heat treatment effect.

[0044] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0045] Example A forming method for improving the microstructure and properties of large stepped long-shaft forgings, the large stepped long-shaft forgings being named 1Cr11Ni2W2MoV long-shaft forgings, includes the following steps: (1) Determine the dimensions of the raw materials according to the design requirements of the forging model.

[0046] The billet needs to be cut to a suitable length (L) according to the design requirements of the forging mold, such as Figure 4 Lleft + Lright = L, and the diameter of the billet (ΦM) must meet the requirements of subsequent forging. The dimensions of the forging model are as follows: Figure 2 The dimensions of the target forging are as follows: Figure 3 .

[0047] Assume the diameter of the head of the forging model is ΦA, and its length is L1; the diameter of the rod is ΦB, and the total length of the rod is L2. The dimensions of the target forging are obtained by allowing for allowances in the dimensions of the forging model. The diameter of the head of the target forging is ΦA', and its length is L1'; the diameter of the rod is ΦB', and the total length of the rod is L2'. The above parameters satisfy the following relationship: ΦA' = ΦA + machining allowance, L1' = L1 + machining allowance, ΦB' = ΦB + machining allowance, L2' = L2 + machining allowance.

[0048] The blanking dimensions are: ΦM×L; ΦM=SQRT(ΦA'×ΦA'×L1' / (1.8~2.0)L1'); L=1.05×[(ΦA'×ΦA'×L1' / ΦM / ΦM)+(ΦB'×ΦB'×L2' / ΦM / ΦM)].

[0049] (2) The billet is placed in a high-temperature heating field, and the temperature is set to 1150℃. The L-shaped part of the billet is stretched into a square cross-section by forging, and the deformation is controlled to be 80%~120% to obtain the first preform (e.g. Figure 5 ).

[0050] (3) The first preform is reheated to 1150°C, and the L-shaped right part, which has already been deformed into a square, is further forged to make it cylindrical. Then it is straightened to obtain the second preform (e.g. Figure 6 ).

[0051] (4) After the initial forging is completed to obtain the second preform, in order to allow the rod to smoothly enter the special mold for the next forging, the rod of the second preform is machined until the diameter of the rod is 20mm larger than the diameter (ΦB) of the target forging, thus obtaining the third preform (e.g. Figure 7 ).

[0052] (5) The head of the third preform is placed in a high-temperature heating field and heated to 1150°C, while the rod is kept at room temperature. Then the heated third preform is placed in the combined mold and forged on a 300MN die forging hydraulic press, with the deformation controlled at 40%~60%, to obtain the initial forging.

[0053] Among them, such as Figure 8 As shown, the combined mold is assembled from a preheated upper mold and a non-preheated lower mold. The preheating temperature is 300℃, and the preheating time is 15 hours. A water-based graphite lubricant must be applied to the inside of the upper mold. Then, within no more than 40 seconds, the head of the heated third preform is transferred into the upper mold. The forging process includes: ① the idle stage, from 630mm to 330mm from the zero point, at a speed of 110mm / s; ② the first pressing stage, from 330mm to 50mm from the zero point, at a speed of 10mm / s; ③ the second pressing stage, from 50mm to 5mm from the zero point, at a speed of 3mm / s; the final forging temperature is not lower than 850℃.

[0054] (6) The formed preliminary forging is heat-treated to obtain the target forging (e.g. Figure 3 (as shown), including: 1) Normalizing treatment: The temperature is 1000℃ and the holding time is 5h. After normalizing treatment, air cooling is used to cool to room temperature. 2) First tempering treatment: The temperature is 700℃ and the holding time is 10h. After the first tempering treatment, air cooling is used to cool to room temperature. 3) Machining the inner hole on the shaft using a machine, such as... Figure 9 The inner hole is a through hole with a diameter of φ80mm.

[0055] 4) Quenching: The temperature is 1000℃, the holding time is 5h, and after quenching, the temperature is cooled to 300℃ with cooling oil. 5) Second tempering treatment: The temperature is 700℃ and the holding time is 7h. After the second tempering treatment, air cooling is used to bring the temperature down to room temperature.

[0056] (7) Machining: Through operations such as turning, milling, and drilling, the target forging is made to meet the precise dimensions and surface finish standards specified in the drawings, while ensuring that all key parts meet the design requirements. The final forging product, such as... Figure 9 As shown.

[0057] Four parallel tests were set up to conduct physical and chemical tests on the forging products obtained by conventional forging and the forming method of the present application. The results are shown in Table 1 and Table 2.

[0058] Table 1. Physical and chemical test results of forgings formed by conventional forging.

[0059] Table 2. Physicochemical test results of the forgings formed in the examples.

[0060] In Tables 1 and 2, σb represents tensile strength, σ0.2 represents yield strength, δ4% represents elongation, ψ% represents reduction of area, and Aku represents impact energy. The testing standards comply with the national military standards GJB 2294-95 and GJB 2294A-2014.

[0061] Regarding room temperature tensile properties: In terms of room temperature tensile properties, the forgings formed in the examples are superior to or equivalent to those of conventionally forged forgings, including σb, σ0.2, δ4%, ψ%, and Aku.

[0062] Regarding high-temperature creep rupture performance: In the example forgings, the high-temperature creep rupture test at 450℃ and 540MPa lasted for 101 hours without fracture, meeting the standard requirement of ≥100 hours. Conventionally forged forgings exhibited unstable high-temperature creep rupture performance under the same conditions, with significant fluctuations in duration, and some samples did not meet the standard requirements.

[0063] Regarding grain size: The forgings produced by the example have a grain size of grade 5.5 at the head and grade 5 at the shank, meeting the standard requirement of ≥ grade 4, and exhibiting finer grain size and more uniform microstructure. The forgings produced by conventional forging have a grain size of grade 3 at the head and grade 3.5-4 at the shank, failing to meet the standard requirement of ≥ grade 4, and exhibiting larger grain size and less uniform microstructure.

[0064] In summary, the forgings produced by the embodiments of this application are superior to conventionally forged forgings in terms of mechanical properties, high-temperature creep resistance, and microstructure uniformity. They better meet technical standard requirements and exhibit higher reliability and service life. This demonstrates that the forging process of the embodiments has significant advantages in optimizing material properties, not only improving raw material utilization but also resulting in forgings with uniform microstructure and a grain size level of 5 to 5.5, while also meeting the standard requirement of ≥100 hours of high-temperature creep resistance.

[0065] While specific embodiments of this application have been described in detail, this should not be construed as limiting the scope of protection of this application. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this application.

Claims

1. A forming method for improving the microstructure and properties of large stepped long-axis forgings, characterized in that, The large stepped long shaft forging includes a rod and a head arranged sequentially, and includes the following steps: The billet is subjected to a first heat treatment, and the rod is forged and stretched to a rectangular cross-section to obtain a first preform. The temperature of the first heat treatment is 1000℃~1150℃, and the deformation of the rod after the first heat treatment is 80%~120%. The first preform is subjected to a second heat treatment to elongate the rod portion of the first preform into a cylindrical shape to obtain the second preform. The temperature of the second heat treatment is 1000℃~1150℃. The rod portion of the second preform is machined to obtain a third preform with a rod diameter difference of 20 mm from the rod diameter of the target forging. The head of the third preform is heated and then forged in a preheated mold to obtain a preliminary forging. The heating temperature for the head of the third preform is 1000℃~1150℃. The preheated part of the preheated mold corresponds to the part of the third preform that is heated. The deformation during the forging process is 40%~60%. The initial forging is subjected to normalizing, first tempering, quenching and second tempering in sequence, and then machined to obtain the product. The rod diameter of the large stepped long shaft forging is φ180mm~φ200mm, the head diameter of the large stepped long shaft forging is φ550mm~φ600mm, the head length of the large stepped long shaft forging is 450mm~500mm, and the total length of the large stepped long shaft forging is 2000mm~2500mm.

2. The molding method according to claim 1, characterized in that, The normalizing treatment temperature is 990℃~1010℃, the holding time is 5h, and the normalizing treatment is followed by air cooling to room temperature.

3. The molding method according to claim 1, characterized in that, The temperature of the first tempering treatment is 680℃~700℃, the holding time is 10h, and the temperature is cooled to room temperature by air after the first tempering treatment. After the first tempering treatment, an inner hole is machined at the center of the initial forging, with a diameter of φ80mm.

4. The molding method according to claim 1, characterized in that, The quenching treatment is performed at a temperature of 1000℃~1020℃ for 5 hours, and then cooled to 200℃~300℃ with oil after the quenching treatment.

5. The molding method according to claim 1, characterized in that, The second tempering treatment is performed at a temperature of 660℃~710℃ for 7 hours, followed by air cooling to room temperature.

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