A process for the swage forming of a body of revolution steel forging

Abstract

The application discloses a kind of rotary body steel forgings'shaped forming process of mould forging, mainly suitable for the flange shaft steel forgings of 500kg or less.The process includes: free forging of steel billet is opened;Configuration split type mould sleeve set;After opening billet, heated and kept;The shaft body region of blank is locally cooled, forming axial gradient temperature field;Put billet into preforming lower die and preform, use the deformation resistance of low temperature shaft body section to constrain metal to flow to flange radial and transition fillet;Preformed piece is transferred to final forging lower pad and is finally forged, pulse magnetic field is applied along the axial direction of forging during final forging;After final forging, cooling is done.The application also discloses a mould forging device for the above process.The application makes the flange root fiber streamline continuous coating, the core organization is dense, the circumferential performance is uniform by the synergistic effect of gradient temperature field and pulse magnetic field, effectively improves the mechanical properties and material utilization of rotary body steel forgings.

Description

Technical Field

[0001] This invention relates to the field of plastic forming technology for steel forgings, and more particularly to a die forging process for rotating steel forgings. Background Technology

[0002] Rotational steel forgings are key components in the transmission systems of equipment such as wind power generation, marine propulsion, and construction machinery. During their service life, they are subjected to alternating bending and torsional loads, placing high demands on their mechanical properties, fatigue life, and dimensional accuracy. Die forging, as a forming method between free forging and die forging, combines flexibility and near-net-shape forming advantages, and is widely used in the production of rotational forgings. Taking flange shaft products as an example, this forging simultaneously includes a flange and a slender shaft, with cross-sectional dimensions changing sharply along the axial direction, making it a type of rotational forging with high forming difficulty. However, existing die forging processes for rotational steel forgings still have the following technical shortcomings: First, metal fiber streamlines are easily cut, limiting the mechanical properties of the product. Fiber streamlines formed during the forging process are a crucial factor affecting the mechanical properties of forgings. Ideally, these streamlines should be continuously distributed along the forging contour and aligned with the direction of force. For rotating forgings like flange shafts with abrupt changes in cross-section, the radial velocity difference between the metal in the transition area between the flange and the shaft is uniformly distributed circumferentially during axial compression. This area is highly susceptible to fiber shearing fracture and folding defects. Chinese patent CN114393167A discloses a forging die and process for a hollow long shaft with a flange, achieving forging of a hollow shaft with a flange through upsetting. While this process reduces subsequent machining steps, it still employs the traditional uniform temperature forging method. The metal flow in the transition area at the flange root lacks active guidance, and the fiber streamlines still face the risk of being cut at the abrupt change in cross-section. Chinese patent CN101293267B discloses a method for upsetting a large flange at the end of a large wind turbine main shaft. The method uses special tooling to achieve flange upsetting, but it mainly solves the problem of upsetting efficiency and does not involve the direction control and optimization of fiber flow lines.

[0003] Secondly, the metal flow in the abrupt cross-section region is difficult to control precisely, resulting in unstable forming quality. Under traditional uniform temperature forging conditions, the plasticity of the billet is uniform throughout, and the metal tends to flow in the direction of least resistance under axial pressure. It is difficult to precisely control its orderly filling into the flange radial direction and transition fillets, leading to forming defects such as folding and incomplete filling. Chinese patent CN112547826B discloses a magnesium alloy forming method with gradient temperature and rate field, which improves the forming performance of magnesium alloy by constructing a gradient temperature field during the forming process. However, this method constructs the gradient temperature field by cooling in successive passes and is applied to magnesium alloy extrusion forming. It does not involve die forging of steel rotating forgings, nor does it solve the problem of fiber continuity in the abrupt cross-section region.

[0004] In summary, there is currently a lack of a process in the existing technology that can effectively control the distribution of fiber streamlines and improve the forming quality of the abrupt change region in the cross-section of rotating steel forgings. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, the present invention aims to provide a die forging process for rotating steel forgings, which solves the technical problems of fiber shear fracture in the transition zone, uneven circumferential properties, and difficulty in eliminating core porosity in rotating steel forgings. This process improves material utilization while significantly enhancing the comprehensive mechanical properties and service reliability of the forgings.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: a die forging process for rotating steel forgings. This includes the following steps: S1 Free Forging: Select the target grade steel billet, perform free forging and drawing deformation, break the cast dendritic structure and eliminate internal porosity defects to obtain a uniform cylindrical billet of revolution. S2 mold tooling preparation: Configure mold tooling, preheat each mold before forging to reduce the temperature drop rate after the billet enters the mold. S3 Billet Heating and Holding: The cylindrical billet obtained in step S1 is sent into the heating furnace, heated to the initial forging temperature according to the forging heating specifications of the corresponding steel grade, and then held to ensure uniform temperature inside and outside the billet, thereby fully improving the plasticity of the material. S4 gradient temperature field construction: After the heat preservation of the blank, the area of ​​the blank corresponding to the finished shaft body is locally cooled so that the temperature of the shaft body section is 50-120℃ lower than the temperature of the flange forming area, forming a gradient temperature field continuously distributed along the axial direction. S5 Pre-forging: The billet after the gradient temperature field is constructed is placed into the pre-forging lower mold cavity for positioning. The mold is closed and forging pressure is applied for pre-forging. The deformation resistance of the low-temperature shaft section is increased to form an internal constraint, which guides the metal to flow in an orderly manner to the flange radial direction and the transition fillet, so that the fiber initially forms a continuous covering shape along the transition fillet. S6 final forging: The pre-forged billet is transferred to the final forging plate for positioning. The die is closed and forging pressure is applied to make the billet metal completely fill the final forging cavity to form a complete flange shaft forging. During the final forging process, a pulsed magnetic field is applied to the forging in the axial direction to simultaneously improve the core density and circumferential structure uniformity. S7 Post-Forging Controlled Cooling and Shaping: The final forged rotary steel forging is removed, cooled to room temperature, and the direction of metal fiber flow and internal metallographic structure of the forging are fixed.

[0007] Furthermore, in step S4, the shaft section is locally cooled by air mist cooling. The cooling area covers all cylindrical sections of the finished shaft corresponding to the blank, and is sprayed evenly 360° along the circumference of the blank to ensure that the circumferential temperature of the shaft section is consistent, which is suitable for the axisymmetric structure of the rotating body.

[0008] Furthermore, in step S4, the temperature of the shaft section is 50-100°C lower than the temperature of the flange forming area.

[0009] Furthermore, in step S6, the magnetic induction intensity of the pulsed magnetic field is 1-3T, the pulse frequency is 5-20Hz, and the pulse rhythm is synchronized with the forging pressing passes.

[0010] Furthermore, in step S6, the final forging process is carried out in 2 to 3 passes to gradually forge the shape.

[0011] Furthermore, in step S1, the total forging ratio of the billet is not less than 3.

[0012] Furthermore, in step S2, the mold preheating temperature is 200℃~400℃.

[0013] Furthermore, in step S7, the cooling method is a combination of air cooling and stack cooling.

[0014] The present invention also provides a forging apparatus for rotary steel forging die for the above-mentioned process, comprising a pre-forging die assembly, a final forging die assembly and a local cooling assembly; The pre-forging die assembly includes a pre-forging upper die and a pre-forging lower die arranged coaxially, and the pre-forging lower die is provided with a forming cavity that matches the shape of the pre-forging billet; The final forging die assembly includes a final forging upper die, a first final forging lower die, a second final forging lower die, and a final forging lower pad, all coaxially and correspondingly arranged. The local cooling component is located on the feeding side of the pre-forging station and is used to perform circumferential and uniform local cooling of the billet shaft section.

[0015] Furthermore, a pulsed magnetic field generator is coaxially provided on the outer side of the final forging die assembly to generate a pulsed magnetic field along the axial direction of the forging during the final forging process.

[0016] (III) Beneficial Effects The purpose of this invention is to provide a die forging process for rotating steel forgings, which has the following beneficial effects: To address the inherent challenge of fiber shear fracture in the stepped transition zone of rotating steel forgings, this invention improves fiber continuity by actively constructing an axial gradient temperature field. The principle lies in the fact that the high-temperature deformation resistance of metallic materials increases significantly with decreasing temperature. By locally cooling the shaft section of the billet, the deformation resistance of the shaft section is made higher than that of the flange forming zone, forming a natural rigid constraint boundary within the billet. During axial compression, this constraint boundary inhibits excessive metal elongation along the shaft direction, forcing the metal to flow and fill the flange radial and transition fillet areas in an orderly manner, fundamentally eliminating shear eddies caused by velocity differences at abrupt changes in cross-section. Relying on the axisymmetric structure of the rotating part, localized cooling can be applied uniformly circumferentially, ensuring consistent constraint effects across the 360° transition zone. This increases the fiber integrity in the transition zone from 65%-75% in conventional processes to over 98%, and improves the room-temperature impact performance of the forging by more than 18% compared to ordinary step-by-step die forging. This significantly outperforms the effects achievable through conventional die optimization and pass adjustments, overcoming the common technical bias in the field that forging billets must maintain uniform temperature.

[0017] To address the issues of insufficient core deformation and poor circumferential property uniformity in small-to-medium-sized forgings of revolution, this invention introduces a pulsed magnetic field-assisted final forging process. Based on the magnetoplastic effect, it achieves simultaneous control of core densification and circumferential microstructure homogenization. The principle is that the pulsed magnetic field reduces the resistance to dislocation movement within the metal through the interaction of dislocations and magnetic domains, thereby reducing the deformation resistance of the core metal and promoting plastic flow to fill internal micro-porosity. Simultaneously, the orientation effect of the magnetic field guides the grains to align uniformly along the circumference, weakening microstructure anisotropy. Utilizing the axisymmetric structure of the forging, the axially applied pulsed magnetic field achieves a 360° uniform effect with no blind spots. This reduces the circumferential mechanical property deviation of the forging from 8% to 10% in conventional processes to less than 2%, while completely eliminating core micro-porosity defects. This effect cannot be achieved through conventional forging methods involving purely mechanical deformation.

[0018] Gradient temperature field control, pulsed magnetic field assistance, and step-by-step forming process form a multi-level synergistic mechanism, achieving an integrated improvement in both the external shape accuracy and internal performance of forgings. The gradient temperature field completes the directional flow of metal and preliminary fiber coating during the pre-forging stage, avoiding secondary fiber damage caused by large deformation in the final forging stage, and providing a good rheological basis for precision forming in the final forging. The step-by-step forming process provides independent windows for temperature field control and magnetic field action, avoiding mutual interference between different process parameters. The pulsed magnetic field complements the surface constraint effect formed by the gradient temperature field in the final forging stage. The low-temperature surface region ensures the stability of the forging's external dimensions, while the core region undergoes sufficient deformation and densification under the influence of the magnetic field. Together, they achieve a synergistic effect of maintaining external shape accuracy and significantly improving internal performance. The combination of these three elements provides comprehensive control from macroscopic metal flow and mesoscopic fiber distribution to microscopic microstructure homogenization, resulting in a comprehensive performance improvement far exceeding the sum of the effects of each technique acting alone.

[0019] The process of this invention possesses excellent production adaptability and economic efficiency. The entire process can be implemented using existing forging equipment, requiring only the addition of localized cooling and magnetic field auxiliary components, without the need for large-scale equipment modifications. The mold cavity constraint enables near-net-shape forming, significantly reducing machining allowances and improving material utilization by more than 15% compared to traditional free forging processes. Simultaneously, the hardenability of the forgings remains consistent with traditional forging processes, allowing direct compatibility with existing heat treatment process specifications without additional adjustments to the production flow. This significantly reduces the overall cost of small- and medium-batch production and has broad industrial application prospects. Attached Figure Description

[0020] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This image shows the S1 free forging blank in the die forging process of a rotating steel forging according to the present invention. Figure 2 The image shows the S5 pre-forging process in the die forging forming process of a rotating steel forging according to the present invention. Figure 3 This image shows the final forging process (S6) of a dime forging process for a rotating steel forging according to the present invention. Figure 4 This is a picture showing the completed process of the die forging of a rotating steel forging according to the present invention.

[0021] In the figure: A-bulk, 11-pre-forging upper die, 12-pre-forging lower die, 13-pad block, 21-final forging upper die, 22-first final forging lower die, 23-second final forging lower die, 24-final forging lower pad plate. Detailed Implementation

[0022] The following will refer to the appendix in the examples of this invention. Figures 1-4 The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 This embodiment provides a die forging process for flange shaft steel forgings weighing up to 500 kg. The forging material is 42CrMo steel, the finished flange shaft has a total mass of about 380 kg, a flange end diameter of 320 mm, a shaft body diameter of 180 mm, and a total length of 1200 mm.

[0024] S1 Free Forging Billet like Figure 1 As shown, a 300mm diameter 42CrMo steel continuously cast round billet with a blank weight of 450kg was selected. The billet was heated to 1200℃±20℃, held for 3 hours, and then removed and elongated on a 5t free forging hammer. The total forging ratio of the billet was 3.5. After repeated upsetting and elongation, a cylindrical billet of revolution with a diameter of 250mm and a length of 572mm was obtained.

[0025] During the billet opening process, the final forging temperature is controlled to be no less than 850℃, and the deformation amount per forging is controlled between 20% and 30% to ensure that the as-cast structure is fully broken and the internal porosity defects are effectively eliminated.

[0026] S2 mold tooling preparation The mold tooling is configured, and all mold materials are selected from 5CrNiMo hot work mold steel. Before forging, each mold is preheated to 300℃±20℃ in the mold heating furnace and held for 2 hours.

[0027] S3 billet heating and heat preservation The cylindrical billet obtained in step S1 is fed into a bogie-type resistance heating furnace and heated to 1200℃ (the initial forging temperature of 42CrMo steel). It is held at this temperature for 2.5 hours to ensure that the temperature inside and outside the billet is uniform and the temperature difference does not exceed ±10℃.

[0028] S4 gradient temperature field construction After being kept at room temperature, the billet is removed from the heating furnace, and a localized cooling method is used to cool the area corresponding to the shaft body of the billet. The annular nozzles of the aerosol cooling device are evenly arranged circumferentially around the outer perimeter of the billet shaft body section, spraying a mixture of compressed air and atomized water. The atomized water flow rate is controlled at 0.5–1.0 L / min, and the compressed air pressure is 0.4–0.6 MPa. The cooling area covers the entire cylindrical section of the finished shaft body corresponding to the billet (i.e., the area from approximately 200 mm from the flange end face to the other end face), and the cooling time is 40–60 seconds.

[0029] After cooling, an infrared thermometer was used to detect the surface temperature of the billet. The temperature of the shaft section dropped to 1080-1100℃, while the temperature of the flange forming area remained at 1180-1200℃. The temperature of the shaft section was 80-100℃ lower than that of the flange forming area. A clear gradient temperature field was formed along the axial direction of the billet, smoothly transitioning from the high-temperature area at the flange end to the low-temperature area at the shaft end.

[0030] S5 Pre-forged Directional Controlled Flow Forming like Figure 2 As shown, the billet, after the gradient temperature field is constructed, is rapidly placed into the pre-forging lower mold cavity within 30 seconds for positioning, ensuring that the billet axis coincides with the mold cavity axis. After mold closing, forging pressure is applied on a 5t free forging hammer for pre-forging.

[0031] During pre-forging, the deformation resistance of the low-temperature shaft section (1080–1100℃) is significantly higher than that of the flange forming zone (1180–1200℃), which is equivalent to forming a rigid constraint mandrel inside the billet. Under axial pressure, the metal preferentially flows towards the flange radial and transition fillet areas with lower resistance, rather than excessively extending along the shaft direction. The pre-forging is performed three times, with the billet rotated 90° after each strike to ensure uniform circumferential deformation. After pre-forging, the flange end diameter of the billet reaches 280mm, and the overall length is approximately 980mm. The transition fillet at the flange root is fully filled with metal without any folding defects.

[0032] S6 Final Forging Precision Forming like Figure 3 As shown, the pre-forged billet is transferred to the final forging pad within 60 seconds for positioning, ensuring that the flange end face is tightly fitted with the bottom surface of the lower pad cavity. After mold closing, forging pressure is applied for final forging. The final forging process is carried out in 3 passes, with the reduction amount controlled at 5-10 mm per pass.

[0033] During the final forging process, a pulsed magnetic field is applied along the axial direction of the forging. The coil of the pulsed magnetic field generator is arranged around the periphery of the final forging die, with a magnetic induction intensity of 2.0T and a pulse frequency of 10Hz. The pulse rhythm is synchronized with the forging pressing passes—the magnetic field pulse is activated at the beginning of each pressing pass and paused when pressing is completed. The direction of the magnetic field is along the axial direction of the forging and is consistent with the direction of metal flow.

[0034] Under the assistance of a pulsed magnetic field, the deformation resistance of the core metal decreases and the flow compensation capability is enhanced; at the same time, the grain orientation effect of the magnetic field promotes the homogenization of the circumferential grain arrangement. After the final forging, the flange end diameter reaches 320mm, the shaft diameter is 180mm, and the total length is 1200mm. The metal fibers at the transition fillet at the flange root are continuously distributed along the outline of the forging without any cutting or folding.

[0035] S7 post-forging controlled cooling and shaping The final forged flange shaft is removed and first allowed to cool naturally in air to 500–600°C. Then, it is transferred to an insulated cooling pit for controlled cooling at a rate of 20–30°C / h until it reaches room temperature. During this controlled cooling process, the flow direction of the metal fibers and the internal structure of the forging are stabilized.

[0036] Example 2 The difference between this embodiment and Embodiment 1 is that the temperature difference of the gradient temperature field in step S4 is different.

[0037] In this embodiment, air mist cooling is used to locally cool the shaft section, with a cooling time of 30-40 seconds. After cooling, the shaft section temperature drops to 1120-1140℃, while the flange forming zone temperature remains at 1190-1200℃. The shaft section temperature is 50-70℃ lower than the flange forming zone temperature.

[0038] The remaining steps and parameters are the same as in Example 1. This example is suitable for production scenarios where fiber continuity requirements are slightly lower but molding efficiency requirements are higher. The smaller temperature difference results in slightly lower metal flow resistance during pre-forging, and the number of impacts can be reduced to 2.

[0039] Example 3 The difference between this embodiment and Embodiment 1 is that the parameters of the pulse magnetic field in step S6 are different.

[0040] In this embodiment, the magnetic induction intensity of the pulsed magnetic field is 1.0T, the pulse frequency is 5Hz, and the pulse rhythm is synchronized with the forging pressing passes. The final forging process is carried out in two passes to gradually forge the shape.

[0041] The remaining steps and parameters are the same as in Example 1. This example is suitable for production conditions where the magnetic field generation capability of the equipment is limited. The lower magnetic field strength can still promote core flow compensation and grain homogenization to a certain extent, but the effect is slightly lower than that in Example 1.

[0042] Example 4 The difference between this embodiment and Embodiment 1 lies in the different way the gradient temperature field is constructed in step S4.

[0043] In this embodiment, a water-cooled copper pipe contact cooling method is used to locally cool the shaft section. The water-cooled copper pipe with built-in circulating cooling water is placed in close contact with the surface of the blank shaft section, and the cooling time is 50 to 70 seconds. After cooling, the temperature of the shaft section drops to 1060 to 1090°C, while the temperature of the flange forming area is maintained at 1180 to 1200°C. The temperature of the shaft section is 90 to 110°C lower than that of the flange forming area.

[0044] The remaining steps and parameters are the same as in Example 1. Water-cooled copper tube contact cooling has higher cooling efficiency and is suitable for production scenarios with large temperature difference requirements, but care should be taken to avoid local overcooling that could lead to cracking.

[0045] Comparative Example 1 This comparative example uses a traditional uniform temperature forging process. The difference from Example 1 is that the gradient temperature field construction in step S4 is not performed.

[0046] The specific steps are as follows: The billet after heat preservation is taken directly from the heating furnace when the overall temperature is 1200℃±10℃. Without any local cooling treatment, it is directly placed into the pre-forging lower mold cavity for pre-forging. The remaining steps are the same as in Example 1. No pulsed magnetic field is applied during the final forging process.

[0047] Because the billet has a uniform temperature and consistent deformation resistance in all parts, the metal cannot form an effective flow constraint under axial pressure during pre-forging. The metal not only flows radially towards the flange but also extends excessively along the shaft direction. The metal filling at the transition fillet at the flange root is insufficient, resulting in obvious folding defects.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that no pulsed magnetic field is applied in step S6.

[0049] The specific steps are as follows: Steps S1 to S5 are exactly the same as in Example 1. In step S6, no pulsed magnetic field is applied during the final forging precision forming. The final forging is completed only by conventional forging pressure. The remaining parameters are the same as in Example 1.

[0050] Due to the lack of the auxiliary effect of the pulsed magnetic field, the core metal has a high resistance to deformation during the final forging process, the core flow and feeding are insufficient, and the micro-porosity defects cannot be completely eliminated; at the same time, the circumferential grain arrangement lacks the homogenizing effect of the magnetic field, and the circumferential performance deviation of the forging is about 6% to 8%.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that the gradient temperature field construction in step S4 is not performed, but a pulsed magnetic field is applied in step S6.

[0052] The specific steps are as follows: After the billet is heated to 1200℃±10℃, it is directly pre-forged. During the final forging process, a pulsed magnetic field is applied with a magnetic induction intensity of 2.0T and a frequency of 10Hz. The other parameters are the same as in Example 1.

[0053] Due to the lack of flow direction constraint from the gradient temperature field, the metal flow is disordered during the pre-forging stage, and the fibers in the transition zone at the flange root have already undergone a certain degree of shearing and folding. Although the pulsed magnetic field in the final forging stage can improve the core density and circumferential uniformity to some extent, it cannot repair the fiber streamline defects that have already occurred.

[0054] Comparative Example 4 The difference between this comparative example and Example 1 is that the temperature difference in the gradient temperature field in step S4 is too large.

[0055] In this embodiment, the shaft section is cooled for a long time using air mist cooling, which takes 90 to 120 seconds. After cooling, the shaft section temperature drops to 1030 to 1050°C, while the flange forming area temperature is maintained at 1180 to 1200°C. The shaft section temperature is 130 to 150°C lower than the flange forming area temperature.

[0056] Due to the excessively low temperature of the shaft section, approaching the final forging temperature of 850℃ for 42CrMo steel, the plasticity of the shaft section decreased significantly, while the deformation resistance increased sharply. During the pre-forging process, the shaft section not only served a restraining function but also exhibited a tendency for localized cracking, resulting in microcracks on the surface of the forging. After final forging, ultrasonic testing revealed multiple crack defects in the shaft section, rendering the product unusable.

[0057] Comparative Example 5 The difference between this comparative example and Example 1 is that the magnetic induction intensity of the pulsed magnetic field in step S6 is too large.

[0058] In this comparative example, the magnetic induction intensity of the pulsed magnetic field is 6.0T, and the pulse frequency is 10Hz. Due to the excessively high magnetic field strength, the magnetic field generating device is bulky and cannot be effectively integrated into the forging production line. Simultaneously, the strong magnetic field exerts significant magnetic attraction and electromagnetic interference on the steel structure of the forging equipment, affecting the normal operation and striking accuracy of the forging press. After final forging, the dimensional deviation of the forgings exceeds the tolerance range, resulting in defective products.

[0059] Comparison of test results Sampling and testing were conducted on the flange shaft forgings prepared in Examples 1-4 and Comparative Examples 1-5. Samples were cut from the transition zone at the flange root (50 mm from the flange end face) and the shaft section, respectively. Mechanical property tests were performed according to GB / T228.1—2021 "Metallic materials, tensile testing—Part 1: Test at room temperature" and GB / T229—2020 "Metallic materials, Charpy pendulum impact test method". Sampling was performed according to GB / T2975—2018 "Sampling location and sample preparation for mechanical property testing of steel and steel products". Simultaneously, hot acid etching tests were performed on the longitudinal sections of the forgings according to GB / T226—2015 "Acid etching test for low magnification structure and defects of steel" to observe the morphology of fiber flow lines.

[0060] Table 1 Comparison of process conditions between each embodiment and the comparative example Table 2. Mechanical property test results of each embodiment and comparative example. Table 3 Comparison of circumferential performance deviation and yield of each embodiment and comparative example Analysis of experimental results: Comparative Example 1, using traditional isothermal forging, showed significant folding and cutting of fiber streamlines at the flange root, with a tensile strength of 1127 MPa and an impact absorption energy of 89.8 J. In Example 1, after constructing a temperature gradient of 80–100 °C, the increased deformation resistance of the low-temperature shaft section created internal rigid constraints, forcing the metal to flow radially and orderly towards the flange. The fiber streamlines continuously covered the flange along the transition fillet, increasing the tensile strength to 1210 MPa and the impact absorption energy to 112.5 J, representing increases of approximately 7.4% and 25.3% respectively compared to Comparative Example 1. This demonstrates that the gradient temperature field actively guided the metal flow path. Comparative Example 2, using only a gradient temperature field, showed an increase of approximately 4.7% in tensile strength. Comparative Example 3, using only a pulsed magnetic field, only showed an increase of approximately 2.0%, and the fiber cutting defect remained, indicating that the gradient temperature field plays a decisive role in solving the fiber continuity problem.

[0061] Under the premise of using a gradient temperature field, Example 1, which applied a pulsed magnetic field, completely eliminated the micro-porosity defects in the core compared to Comparative Example 2, which did not apply a pulsed magnetic field. The circumferential tensile strength deviation decreased from 7.2% to 1.8%, and the impact absorption energy increased from 100.5 J to 112.5 J. The mechanism is that the magnetic field promotes the dislocation movement in the core to improve the flow compensation ability, while using the grain orientation effect to homogenize the circumferential structure, thereby effectively solving the problem of insufficient core deformation in small and medium-sized rotating bodies.

[0062] Using a gradient temperature field alone increases tensile strength by approximately 4.7%, while using a pulsed magnetic field alone increases it by approximately 2.0%, with a theoretical cumulative increase of approximately 6.7%. However, when used synergistically, the actual increase reaches 7.4%, exceeding the target by approximately 9.2%. The physical mechanism of this synergistic effect lies in the fact that the low-temperature, hard constraint on the surface and the high-temperature, easily deformable state of the core created by the gradient temperature field provide an ideal window for the pulsed magnetic field to function. The magnetic field's promoting effect on dislocation motion is more significant in the high-temperature core, while the surface constraint function is unaffected by the magnetic field. The two elements complement each other, with the external shape constrained by the temperature field and the core flow-promoting effect driven by the magnetic field. The performance improvement exceeds the reasonable expectations of those skilled in the art based on the effect of a single method.

[0063] Regarding the determination of the temperature difference range, in Example 2, when the temperature difference was reduced to 50–70°C, the fiber streamline coating effect weakened, and the impact absorption energy dropped to 105.2 J. In Comparative Example 4, when the temperature difference was expanded to 130–150°C, the shaft section temperature approached the lower limit of the final forging temperature, and the decrease in plasticity led to surface cracks in the pre-forging, resulting in product scrap. Therefore, the temperature difference was limited to 50–120°C, preferably 80–100°C. Regarding the magnetic field strength, in Example 3, when the magnetic induction intensity was reduced to 1.0T, the micro-porosity in the core could not be completely eliminated. In Comparative Example 5, when it was increased to 6.0T, the strong magnetic field significantly interfered with the forging press, and the impact accuracy decreased, resulting in dimensional deviations. Therefore, the magnetic induction intensity was limited to 1–3T, preferably 1.5–2.5T.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A die forging process for a rotating steel forging, characterized in that, Includes the following steps: S1 Free Forging: Select a steel billet for free forging and drawing to break up the as-cast structure and eliminate internal porosity defects, and obtain a cylindrical billet of revolution. S2 mold tooling preparation: Configure mold tooling and preheat each mold; S3 billet heating and holding: The cylindrical billet obtained in step S1 is sent into the heating furnace, heated to the initial forging temperature and then held. S4 gradient temperature field construction: After the heat preservation, the blank is taken out and the area corresponding to the shaft body is locally cooled so that the temperature of the shaft body section is 50-120℃ lower than the temperature of the flange forming area, forming a gradient temperature field distributed along the axial direction. S5 Pre-forging: The billet after the gradient temperature field is constructed is placed into the pre-forging lower mold cavity for positioning. The mold is closed and forging pressure is applied for pre-forging. The deformation resistance of the low-temperature shaft section is used to guide the metal to flow radially towards the flange and the transition fillet. S6 final forging: The pre-forged billet is transferred to the final forging lower plate for positioning. The die is closed and forging pressure is applied to fill the final forging cavity with billet metal to form a complete flange shaft forging. During the final forging process, a pulsed magnetic field is applied to the forging axially. S7 Post-forging controlled cooling and shaping: The flange shaft forging that has been finally forged is taken out and cooled to room temperature.

2. The die forging process for the rotating steel forging according to claim 1, characterized in that, In step S4, the shaft section is locally cooled using an air mist cooling method, and the cooling area covers all cylindrical sections of the finished shaft corresponding to the blank.

3. The die forging process for the rotating steel forging according to claim 1, characterized in that, In step S4, the temperature of the shaft section is 50-100°C lower than the temperature of the flange forming zone.

4. The die forging process for the rotating steel forging according to claim 1, characterized in that, In step S6, the magnetic induction intensity of the pulsed magnetic field is 1-3T, the pulse frequency is 5-20Hz, and the pulse rhythm is synchronized with the forging pressing passes.

5. The die forging process for the rotating steel forging according to claim 1, characterized in that, In step S6, the final forging process is carried out in 2 to 3 passes to gradually forge the shape.

6. The die forging process for the rotating steel forging according to claim 1, characterized in that, In step S1, the total forging ratio of the billet is not less than 3.

7. The die forging process for the rotating steel forging according to claim 1, characterized in that, In step S2, the mold preheating temperature is 200℃~400℃.

8. The die forging process for the rotating steel forging according to claim 1, characterized in that, In step S7, the cooling method is a combination of air cooling and stack cooling.

9. A forging apparatus for rotary steel forging die for the process described in any one of claims 1 to 8, characterized in that, This includes pre-forging die assemblies, final forging die assemblies, and localized cooling assemblies; The pre-forging die assembly includes a pre-forging upper die (11), a pre-forging lower die (12), and a pad block (13) arranged coaxially. The final forging die assembly includes a final forging upper die (21), a first final forging lower die (22), a second final forging lower die (23), and a final forging lower pad (24) arranged coaxially. The local cooling component is located on the feeding side of the pre-forging station and is used to locally cool the billet shaft section.

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