Molding method capable of improving structure performance of large step long shaft type forge piece

Abstract

The invention discloses a forming method capable of improving the structure performance of a large-scale step long shaft type forge piece, and belongs to the technical field of forge piece hot working. The forming method comprises the steps that a blank is subjected to first-time heating treatment, a rod part is forged and lengthened till the section is rectangular, and a first prefabricated body is obtained; heating the first prefabricated body for the second time, and lengthening the rod part of the first prefabricated body to be cylindrical to obtain a second prefabricated body; machining the rod part of the second prefabricated body to obtain a third prefabricated body of which the difference value between the diameter of the rod part and the diameter of the rod part of the target forged piece is 20mm; the head of the third prefabricated body is heated and then placed in a preheated die to be forged and formed, and a primary forged product is obtained; and after the primary forging product is subjected to normalizing treatment, first tempering treatment, quenching treatment and second tempering treatment in sequence, machining is carried out, and the alloy is obtained. And the effect of improving the structure uniformity, integrity and stability of the forge piece can be achieved.

Description

Technical Field

[0001] The present application belongs to the field of hot working technology of forgings, and specifically relates to a forming method capable of improving the microstructure and performance of large-scale stepped long shaft forgings. Background Art

[0002] Large stepped long shaft forgings can reach lengths of 2000mm to 2500mm, with shaft diameters ranging from only φ180mm to φ200mm, but head diameters as high as φ550mm to φ600mm. These forgings are characterized by their long overall length, wide cross-sectional variations, high grain size requirements (uniform grains and a grain size ≥ Grade 4), and sustained high-temperature operation (≥100h). This places higher demands on forging and heat treatment processes to optimize the structural and performance indicators of these forgings.

[0003] The conventional forging method is to first heat the whole piece and then upset the head, and then heat the whole piece and then draw the rod to form it. To ensure coaxiality, a large amount of raw material costs are usually required, and the appearance of the forgings formed by free forging is usually less consistent, which will affect the product's dimensional accuracy, grain size and high-temperature durability index (especially for large forgings with large cross-sectional differences). In other words, this conventional forging method has the following disadvantages: (1) the utilization rate of raw materials is low, the microstructure of the forged product is uneven, and the grain size grade of the product is ≤4; (2) the high-temperature durability of the product is unqualified and cannot meet the requirements of technical indicators. This greatly limits the development of production and application of large-scale stepped long shaft forgings.

[0004] Therefore, a new forging method is urgently needed to improve the structural uniformity, forming consistency and high-temperature long-term stability of forgings. Summary of the Invention

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

[0006] To achieve the above-mentioned purpose, the present application provides a forming method capable of improving the microstructure and properties of a large-scale stepped long shaft forging, wherein the large-scale stepped long shaft forging comprises a rod portion and a head portion arranged in sequence, and comprises the following steps: The blank is subjected to a first heating treatment, and the rod portion is forged and elongated to a rectangular cross section to obtain a first preform; performing a second heating treatment on the first preform, and stretching the stem portion of the first preform into a cylindrical shape to obtain a second preform; Machining the rod portion of the second preform to obtain a third preform having a rod diameter that differs from a target forging rod diameter by 20 mm; The head of the third preform is heated and then placed in a preheated die for forging to obtain a pre-forged product; The as-forged product is subjected to normalizing treatment, first tempering treatment, quenching treatment and second tempering treatment in sequence, and then mechanically processed to obtain the product.

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

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

[0009] Furthermore, the temperature of the second heating treatment is 1000° C. to 1150° C., and the shape of the rod after the second heating treatment is cylindrical.

[0010] Furthermore, the head of the third preform is heated at a temperature of 1000° C. to 1150° C., and the preheated portion of the preheated mold corresponds to the heated portion of the third preform.

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

[0012] Furthermore, the temperature of the normalizing treatment is 990° C. to 1010° C., the holding time is 5 hours, and after the normalizing treatment, the steel is cooled to room temperature by air.

[0013] Furthermore, the temperature of the first tempering treatment is 680° C. to 700° C., the holding time is 10 hours, and after the first tempering treatment, the steel is cooled to room temperature by air; After the first tempering treatment, an inner hole is machined at the axis of the forged product, and the diameter of the inner hole is φ80 mm.

[0014] Furthermore, the quenching treatment temperature is 1000° C. to 1020° C., the holding time is 5 hours, and after the quenching treatment, the steel is cooled to 200° C. to 300° C. using oil cooling.

[0015] Furthermore, the temperature of the second tempering treatment is 660° C. to 710° C., the holding time is 7 hours, and air cooling to room temperature is adopted after the second tempering treatment.

[0016] In summary, this application has the following advantages: The forming method of this application adopts a multi-stage temperature-controlled forming technology. After the rod is stretched through overall heating, local heating is used, and the die is used to precisely upset the head, combined with a gradient heat treatment process. After process optimization, the material utilization rate is improved, and the microstructure uniformity and grain size are significantly improved (grain size reaches level 5 to 6). At the same time, the high-temperature durability performance of large-scale stepped long shaft forgings is improved. In addition, the modular die design enables rapid replacement of the upper die and universal configuration of the lower die, which can adapt to the production of forgings of various specifications in the same series, thereby reducing the overall manufacturing cost and energy consumption per unit product, and has significant technical and economic advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of a process for improving the microstructure and performance of large-scale stepped long shaft forgings according to an embodiment of the present 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 Schematic diagram of the structure of the blank in Example 1; Figure 5 Schematic diagram of the structure of the first preform in Example 1; Figure 6 Schematic diagram of the structure of the second preform in Example 1; Figure 7 Schematic diagram of the structure of the third preform in Example 1; Figure 8 The structure and assembly diagram of the mold used in Example 1; Figure 9 This is a schematic diagram of the forging product after inner hole processing in Example 1. DETAILED DESCRIPTION

[0018] The principles and features of the present invention are described below in conjunction with the examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Where specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0019] 1Cr11Ni2W2MoV is a chromium-nickel-tungsten-molybdenum-vanadium martensitic heat-resistant steel with excellent thermomechanical and corrosion resistance, making it suitable for critical applications in high-temperature and corrosive environments. Its chemical composition includes carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, molybdenum, nitrogen, tungsten, and vanadium. The optimal proportions of these elements ensure the steel's stability and durability under high-temperature and corrosive conditions. Its physical properties, characterized by high density, thermal conductivity, and linear expansion coefficient, make it suitable for high-temperature environments. Therefore, due to its excellent heat resistance, good mechanical properties, and superior corrosion resistance, 1Cr11Ni2W2MoV is widely used in the manufacture of turbine blades and key components of aviation industry equipment (such as engine blades, disks, and shafts operating below 600°C), making it a key material choice for high-temperature environments.

[0020] The forming method of this application is for large 1Cr11Ni2W2MoV stepped long shaft forgings, which have the characteristics of large cross-sectional variations, high rod length and structural performance requirements. In the production process, there is not only the difficulty of forging, but also the grain size of the forging structure is required to be level 5 or above, and the high-temperature endurance performance is required to be ≥100h. This leads to the actual production process requiring higher requirements on the forging process and heat treatment process of large stepped long shaft forgings.

[0021] The large step long shaft forging referred to in this application includes: a rod portion and a head portion arranged in sequence. Figure 3 and Figure 9 As shown, the connection between the shaft and the head forms a transition zone, dividing the shaft into a buffer section and a long axis section. The diameter gradually decreases from the head toward the shaft to the standard diameter of the shaft. The buffer section includes a first cross-section near the head end and a second cross-section near the long axis end. The diameter of the first cross-section is φ250mm, while the diameter of the second cross-section is the same as the shaft diameter. The buffer section is 200mm long.

[0022] The dimensions of large-scale 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 large-scale stepped long shaft forgings is 2000mm~2500mm.

[0023] Based on this, the present application provides a forming method that can improve the microstructure and performance of large step long shaft forgings, such as Figure 1 As shown, the following steps are included: S1. The blank is subjected to a first heating treatment, and the rod portion is forged and elongated to a rectangular cross section to obtain a first preform.

[0024] In a specific embodiment, the temperature of the first heat treatment is 1000° C. to 1150° C., and the deformation of the rod after the first heat treatment is 80% to 120%.

[0025] In the present application, the blank is made to have good plasticity and low deformation resistance by high-temperature heating, and the material is subjected to a drawing treatment so that the material is deformed under a three-dimensional compressive stress state, so that internal defects such as internal pores and shrinkage are welded, which is beneficial to the homogenization of the internal structure of the metal and the refinement of the grains, thereby improving the density of the material. At the same time, the drawing treatment causes the metal streamlines to extend axially along the rod to form a fibrous structure, thereby significantly improving the axial mechanical properties of the forging, especially the strength and toughness. In addition, during the drawing process, defects such as inclusions and bubbles inside the material are fully broken and dispersed, which is beneficial to improving 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 rectangular or square cross-section according to actual needs), which can be easily converted into other shapes, such as a circular or elliptical cross-section, laying a good foundation for subsequent forming processes.

[0026] S2. The first preform is subjected to a second heating treatment, and the rod portion of the first preform is elongated into a cylindrical shape to obtain a second preform.

[0027] In a specific embodiment, the temperature of the second heat treatment is 1000° C. to 1150° C., and the shape of 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 more closely matching the design requirements of the final product. This reduces subsequent machining, improves material utilization, and enhances the dimensional accuracy and surface quality of the forging. The cylindrical cross-section allows for concentric distribution of metal streamlines. This streamline distribution improves the mechanical properties of the forging in all directions, particularly the radial and circumferential directions, resulting in superior overall mechanical properties. Reheating (i.e., a second heat treatment) eliminates residual stresses generated in the previous process, further stabilizing the microstructure and preventing deformation or cracking during subsequent processing and use. Furthermore, 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 material's strength and toughness.

[0029] Straightening during the forging process ensures the straightness of the cylinder, eliminates bending deformation during the forging process, and ensures the geometric accuracy of the forging. Therefore, in one preferred embodiment, to ensure the straightness of the cylinder, the present application also performs a straightening operation on the second preform to ensure 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 processing errors, and improves the product qualification rate.

[0030] S3. Machining the rod portion of the second preform to obtain a third preform having a rod diameter that differs from the rod diameter of the target forging by 20 mm.

[0031] During the heat treatment process, forgings inevitably deform due to factors such as microstructural transformation and thermal stress. Therefore, this application opts for a 20mm machining allowance to provide ample room for compensation for heat treatment deformation, ensuring that the forgings can still achieve the desired finished dimensions through subsequent finishing (such as grinding and turning) after heat treatment, guaranteeing the dimensional accuracy of the final product. This not only eliminates minor defects and decarburized layers that may exist on the forged surface, achieving higher surface roughness requirements, but also eliminates surface oxidation, decarburization, or contamination that may occur during heat treatment, thereby ensuring the surface quality and internal performance of the forgings.

[0032] S4. The head of the third preform is heat-treated and then placed in a preheated die for forging to obtain a primary forged product.

[0033] In a specific embodiment, the head of the third preform is heated at the same temperature and time as the second heat treatment, and the preheated portion of the preheated mold corresponds to the heat-treated portion of the third preform. The deformation during the forging process is 40% to 60%.

[0034] The present application uses local heating to heat only the head at a high temperature, while keeping the rod at room temperature. This can accurately control the plastic deformation area to be concentrated on the head, avoid unnecessary deformation of the rod, and thus achieve refined forming of the forging, ensuring the dimensional accuracy and surface quality of the forging. At the same time, since the deformation is mainly concentrated in the head, the rod material does not participate in the severe plastic deformation. This solution uses local heating, and local deformation avoids the problems of grain coarsening and high-temperature long-term performance degradation of the rod caused by overall heating but no deformation of the rod in the traditional solution. At the same time, there is no oxide scale on the rod caused by heating, which improves material utilization, reduces material waste, and reduces production costs.

[0035] This application uses localized heating during forging to dynamically recrystallize the metal in the head at high temperatures, which refines the grains, homogenizes the structure, and eliminates anisotropy in the fiber structure, significantly improving the high-temperature durability of the forging and ensuring that it meets design requirements. Furthermore, due to the third heating treatment, the rod portion does not experience high-temperature heating and severe deformation, preserving its original structural properties. This avoids the problems of overall heating and localized non-deformation that could lead to coarsening of the non-deformed rod portion and decreased high-temperature durability.

[0036] In this application, if Figure 8 By using a combination mold, it is possible to adjust the height L3 of the upper mold and the size of the cavity to produce the same type of forgings with a rod diameter less than ΦC, a rod length greater than L4, and a head size that changes with the upper mold cavity, thereby improving the versatility and economy of the mold. Compared with the integral mold, the combination mold can not only replace the upper mold to produce different forgings, but also extend the life of the lower mold and directly reduce the preheating cost of the lower mold. At the same time, in step S5, only the head needs to be heated. Therefore, during the use of the combination mold, the present application only preheats the upper mold, which can reduce the manufacturing cost and preheating energy consumption of the mold.

[0037] S5. The initially forged product is subjected to normalizing treatment, first tempering treatment, quenching treatment and second tempering treatment in sequence, and then mechanically processed to obtain a product.

[0038] In this application, normalizing and first tempering treatments refine grain size, eliminate stress, and improve processability. Quenching and second tempering treatments enhance strength and plasticity, adjust mechanical properties, and stabilize the structure. 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 decreased material properties or failure to meet design requirements. Therefore, strict adherence to process parameters is a crucial prerequisite for ensuring forging quality and stable performance in this application.

[0039] In a specific embodiment, the temperature of the normalizing treatment is 990°C to 1010°C, the holding time is 5 hours, and air cooling is used to cool to room temperature after the normalizing treatment. The normalizing treatment of the present application causes the material to undergo a phase transformation by heating it to above the austenitizing temperature, and forms a fine pearlite structure during the air cooling process, thereby refining the grains. The normalizing treatment of the present application can eliminate the residual stress generated during the forging process and improve the structural uniformity of the material; and by refining the structure, the strength and plasticity of the material are improved, providing a good structural foundation for subsequent quenching and second tempering treatments.

[0040] The normalizing temperature must not exceed 1010°C, as excessively high temperatures will result in coarsening of the grains, reducing the material's strength and toughness. It must also not be lower than 990°C, as this will result in incomplete microstructural transformation and failure to achieve grain refinement. Normalizing treatment requires a 5-hour hold to avoid insufficient microstructural uniformity and incomplete stress relief due to insufficient hold time.

[0041] In a specific embodiment, the temperature of the first tempering treatment is 680°C~700°C, 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, the inner hole is processed at the axis of the initial forging, and the aperture of the inner hole is φ80mm. Since the hardness of the material after normalizing treatment is relatively high, this application uses tempering treatment to reduce the hardness of the material and improve the toughness of the material. At the same time, tempering treatment can also make the organization more stable, reduce the risk of deformation during subsequent processing and use, and further eliminate the stress that may remain during the normalizing process. The temperature of the first tempering treatment should not be too high, otherwise it will cause the hardness of the material to drop too much, thereby affecting the strength of the material. If the temperature is too low, it may result in the inability to effectively reduce the hardness of the material or improve the toughness of the material.

[0042] In a specific embodiment, the quenching temperature is 1000°C–1020°C, the holding time is 5 hours, and the material is cooled to 200°C–300°C using oil cooling after quenching. The rapid cooling (oil cooling) during quenching allows the material to form a martensitic structure, significantly increasing 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. Excessively high quenching temperatures may lead to coarsening of the austenite grains, resulting in coarse martensite and reduced toughness. Excessively low quenching temperatures may result in incomplete austenitization, preventing a uniform martensitic structure and affecting the material's hardness. Furthermore, insufficient holding time during quenching can lead to uneven microstructural transformation, compromising the stability of the material's properties. Excessively long holding times during quenching can increase energy consumption and potentially cause grain growth, hindering subsequent production and use.

[0043] In a specific embodiment, the second tempering treatment is performed at a temperature of 660°C to 710°C, with a holding time of 7 hours. After the second tempering treatment, the material is air-cooled to room temperature. The material has a high hardness after quenching. This application further applies a second tempering treatment to adjust the hardness and toughness to achieve the comprehensive mechanical properties required by the design. Furthermore, the stress generated during the quenching process may cause deformation or cracking of the forging. The second tempering treatment can also relieve stress and stabilize the microstructure, thereby reducing dimensional changes during subsequent use. If the second tempering temperature is too high (>710°C), the hardness of the forging may drop too much, further affecting the wear resistance and strength of the material. If the second tempering temperature is too low (<660°C), the quenching stress cannot be effectively eliminated, resulting in insufficient improvement in toughness. If the holding time of the second tempering treatment is too short, stress relief and microstructure stabilization will be inadequate. However, if the holding time is too long, energy consumption will increase and production efficiency may be affected. Therefore, strict control of the temperature and time range is key to ensuring the effectiveness of the heat treatment.

[0044] The above technical solutions of the present application are described in detail below with reference to specific embodiments.

[0045] Example A forming method for improving the microstructure and properties of large-scale stepped long shaft forgings, wherein the large-scale stepped long shaft forgings are 1Cr11Ni2W2MoV long shaft forgings, comprises the following steps: (1) Determine the size of the raw material according to the design requirements of the forging model.

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

[0047] Assume that the head of the forging model has a diameter of ΦA and a length of L1; the diameter of the shank is ΦB, and the total length of the shank is L2. By adding allowance to the dimensions of the forging model, the target forging dimensions are obtained. The target forging head has a diameter of ΦA' and a length of L1'; the diameter of the shank is ΦB', and the total length of the shank is L2'. These parameters satisfy the following relationship: ΦA'=ΦA+machining allowance, L1'=L1+machining allowance, ΦB'=ΦB+machining allowance, L2'=L2+machining allowance.

[0048] Cutting size: 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 blank is placed in a high-temperature heating field, the temperature is set to 1150 ° C, and the portion on the right of L in the blank is stretched into a square cross-section by forging, and the deformation is controlled to be 80%~120%, and the first preform (such as Figure 5 ).

[0050] (3) The first preform is heated to 1150°C again, and the right portion of L that has been deformed into a square is further forged to make it cylindrical, and then straightened to obtain the second preform (such as Figure 6 ).

[0051] (4) After the primary 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 20 mm larger than the diameter of the target forging (ΦB), and the third preform (such as Figure 7 ).

[0052] (5) The head of the third preform is placed in a high-temperature heating field for heating at 1150°C, and the rod is placed at room temperature. The heated third preform is then placed in a combination die and forged on a 300MN die forging hydraulic press, with the deformation controlled at 40% to 60%, to obtain a pre-forged product.

[0053] Among them, such as Figure 8 As shown, the combined die is assembled from a preheated upper die and an unpreheated lower die. The preheating temperature is 300°C and the preheating time is 15 hours. The interior of the upper die must be coated with water-based graphite lubricant, and then the head of the heated third preform is transferred into the upper die within no more than 40 seconds. 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 less than 850°C.

[0054] (6) The formed forged product is heat treated to obtain the target forging (such as Figure 3 shown), including: 1) Normalizing treatment: temperature is 1000℃, holding time is 5h, and air cooling is used to cool to room temperature after normalizing treatment; 2) First tempering treatment: temperature is 700℃, holding time is 10h, and air cooling is used to cool to room temperature after the first tempering treatment; 3) Use the machine to process the inner hole at the axis, 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, cooling oil is used to cool to 300℃; 5) Second tempering treatment: temperature is 700℃, holding time is 7h, and air cooling to room temperature is adopted after the second tempering treatment.

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

[0057] Four parallel tests were conducted to perform physical and chemical tests on forging products obtained by conventional forging and by the forging method of the embodiment of the present application. The results are shown in Tables 1 and 2.

[0058] Table 1 Physical and chemical test results of conventional forgings

[0059] Table 2 Physical and chemical test results of forgings formed in Example

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

[0061] Room temperature tensile properties: In terms of room temperature tensile properties, the forgings formed by the embodiment, such as σb, σ0.2, δ4%, ψ% and Aku, are better than or equivalent to those of the conventional forgings.

[0062] Regarding high-temperature endurance performance: Forgings formed in the example forged products lasted for 101 hours without fracture in a high-temperature endurance test at 450°C and 540 MPa, meeting the standard requirement of ≥100 hours. Conventional forgings exhibited unstable high-temperature endurance performance under the same conditions, with duration fluctuating significantly, and some samples failed to meet the standard requirement.

[0063] Regarding grain size: The grain size of the forgings formed by the embodiment is 5.5 at the head and 5 at the shank, meeting the standard requirement of ≥4, with finer grain size and more uniform structure. The grain size of the forgings formed by conventional forging is 3 at the head and 3.5-4 at the shank, which does not meet the standard requirement of ≥4, and has larger grain size and uneven structure.

[0064] In summary, the forgings forged using the examples of this application outperform conventional forgings in terms of mechanical properties, high-temperature durability, and structural uniformity, better meeting technical standards and possessing higher reliability and service life. This demonstrates that the forging process of the examples has significant advantages in optimizing material properties, not only improving raw material utilization but also resulting in uniform structural forgings with a grain size of 5 to 5.5, meeting the standard requirement of high-temperature durability of ≥100 hours.

[0065] Although the specific embodiments of the present application have been described in detail, this should not be construed as limiting the scope of protection of the present application. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of the present application.

Claims

1. A forming method for improving the microstructure and performance of large-scale step long shaft forgings, characterized in that: The large stepped long shaft forging includes a rod portion and a head portion arranged in sequence, and includes the following steps: The blank is subjected to a first heating treatment, and the rod portion is forged and elongated to a rectangular cross section to obtain a first preform; performing a second heating treatment on the first preform, and stretching the stem portion of the first preform into a cylindrical shape to obtain a second preform; Machining the rod portion of the second preform to obtain a third preform having a rod diameter that differs from a target forging rod diameter by 20 mm; The head of the third preform is heated and then placed in a preheated die for forging to obtain a pre-forged product; The as-forged product is subjected to normalizing treatment, first tempering treatment, quenching treatment and second tempering treatment in sequence, and then mechanically processed to obtain the product.

2. The molding method according to claim 1, characterized in that The rod diameter of the large-scale stepped long shaft forging is φ180mm~φ200mm, the head diameter of the large-scale stepped long shaft forging is φ550mm~φ600mm, the head length of the large-scale stepped long shaft forging is 450mm~500mm, and the total length of the large-scale stepped long shaft forging is 2000mm~2500mm.

3. The molding method according to claim 1, characterized in that The temperature of the first heating treatment is 1000° C. to 1150° C., and the deformation of the rod after the first heating treatment is 80% to 120%.

4. The molding method according to claim 1, characterized in that The temperature of the second heating treatment is 1000° C. to 1150° C., and the shape of the rod after the second heating treatment is cylindrical.

5. The molding method according to claim 1, characterized in that The head of the third preform is heated at a temperature of 1000° C. to 1150° C., and the preheated portion of the preheated mold corresponds to the heated portion of the third preform.

6. The molding method according to claim 1, characterized in that The deformation amount during the forging process is 40% to 60%.

7. The molding method according to claim 1, characterized in that: The temperature of the normalizing treatment is 990° C. to 1010° C., the holding time is 5 hours, and the normalizing treatment is followed by air cooling to room temperature.

8. The molding method according to claim 1, characterized in that: The temperature of the first tempering treatment is 680° C. to 700° C., the holding time is 10 hours, and after the first tempering treatment, the material is cooled to room temperature by air; After the first tempering treatment, an inner hole is machined at the axis of the initially forged product, and the diameter of the inner hole is φ80 mm.

9. The molding method according to claim 1, characterized in that: The temperature of the quenching treatment is 1000° C. to 1020° C., the holding time is 5 hours, and after the quenching treatment, the steel is cooled to 200° C. to 300° C. using oil.

10. The molding method according to claim 1, characterized in that: The temperature of the second tempering treatment is 660° C. to 710° C., the holding time is 7 hours, and air cooling is adopted to room temperature after the second tempering treatment.

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