A high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forging produced by hot rotary forging technology and its production process and application

Abstract

The present invention discloses a high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forging produced by hot rotary forging technology, and its production process and application, belonging to the technical field of metal material processing. The production process comprises the following steps: S01, heating the forging blank to 1200°C to 1250°C, and keeping the temperature for 1 to 2 hours; S02, placing the forging blank on a hot rotary forging machine for rotary forging; S03, performing multiple rotary forgings according to the workpiece size requirements; S04, the last rotary forging; S05, air cooling the workpiece after rotary forging to room temperature. The grain size of the forging of the present invention is not less than grade 6, and the difference in tensile strength between the diameter direction and the perpendicular diameter direction of the forging does not exceed 5%, and the difference in impact energy does not exceed 10%. The forging of the present invention is used in steel thin-walled pipe fittings such as gears, gears with shafts, flanges with shafts, disc-like parts or special-shaped parts with bosses. The workpiece produced by the process of the present invention has significantly refined grains, significantly improved strength and toughness, and significantly reduced anisotropy.

Description

Technical Field

[0001] The present invention relates to a high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forging produced by hot rotary forging technology, a production process and application thereof, and belongs to the technical field of metal material processing. Background Art

[0002] Large-diameter, thin-walled steel forgings, such as large gears, discs, and special-shaped parts with bosses, are typically formed using hot die forging. Due to the large contact area between the workpiece and the die and the long metal flow distance during forging, the final forging temperature is often high and deformation is uneven, which can easily lead to coarse grains and uneven structure in the forgings. Even after improvement through heat treatments such as quenching and tempering, these problems cannot be completely resolved. Furthermore, banded segregation in the raw material typically extends along the diameter after forging, resulting in anisotropic mechanical properties in the radial and transverse directions of the forging. Some large-diameter, thin-walled steel forgings with long axes or rods are even difficult to form using traditional hot die forging.

[0003] Swaging is a forging process that reduces the cross-sectional area by hammering between two or more rotating die blocks. Hot swaging is widely used in the production of high-strength, low-plasticity materials, such as refractory metals like tungsten, molybdenum, and niobium, and their alloys, to reduce the diameter of round bars. Cold swaging is widely used to form extremely thin, curved or cylindrical parts from aluminum or steel sheets, increasing their diameter. Due to limitations in equipment costs and workpiece temperature drop, hot swaging is rarely used in forging processes that require increasing the workpiece diameter. This involves thinning the workpiece by applying forging pressure perpendicular to the workpiece diameter (i.e., in the direction of the wall thickness).

[0004] Therefore, there is an urgent need for a production process that uses hot rotary forging technology to produce high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forgings that require increasing diameter and reducing wall thickness, significantly refining the workpiece grains and improving strength, toughness and uniformity. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a production process for high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forgings produced using hot rotary forging technology. Compared with the traditional hot die forging process, the workpieces produced using the process of the present invention have significantly refined grains, significantly improved strength and toughness, and significantly reduced anisotropy.

[0006] At the same time, the present invention provides a high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forging produced by hot rotary forging technology.

[0007] At the same time, the present invention provides a high-strength, high-toughness, high-homogeneity, large-diameter thin-walled steel forging produced by hot rotary forging technology for use in steel thin-walled pipe fittings such as gears, gears with shafts, flanges with shafts, disc-like parts or special-shaped parts with bosses.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A production process for high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forgings produced using hot rotary forging technology comprises the following steps:

[0010] S01, heat the forging billet to 1200℃~1250℃ and keep it warm for 1~2h;

[0011] S02, the forging blank is placed on a hot rotary forging machine for rotary forging, with the starting forging temperature being not less than 1150°C, the first rotary forging reduction being not less than 30%, the rotary die speed of the hot rotary forging machine being 30-60 rpm, and the rotary die displacement speed being not more than 0.5 times the contact surface diameter of the rotary die and the workpiece per second; and the final forging temperature of the first rotary forging being not less than 1050°C;

[0012] S03, according to the workpiece size requirements, multiple passes of rotary forging are performed. Starting from the second pass of rotary forging, the start forging temperature is not less than 950°C, the reduction is not less than 15%, the rotating die speed is not less than 60 rpm, and the rotating die displacement speed is not greater than 1 times the contact surface diameter of the rotating die and the workpiece / second;

[0013] S04, the starting temperature of the last rotary forging is higher than the A C3 Temperature +50℃ and lower than 950℃, reduction 10-15%, rotating die speed not lower than 90 rpm, rotating die displacement speed not higher than 1.5 times the contact surface diameter of rotating die and workpiece / second, final forging temperature not lower than Ar3 temperature of workpiece composition;

[0014] S05, the workpiece after rotary forging is air-cooled to room temperature, and then quenched and tempered at 500-600°C; or the workpiece after rotary forging is directly placed in a cooling tank for quenching, and the quenched workpiece is tempered at 500-600°C after cooling.

[0015] Preferably, the diameter of the rotating die of the hot rotary forging machine is not larger than the diameter of the forging blank and not smaller than 1 / 7 of the maximum diameter of the workpiece after rotary forging.

[0016] Preferably, in S01, the forging blank includes a cylindrical blank.

[0017] Further preferably, the cylindrical blank comprises a cylindrical blank with a long axis or a long rod, and the long axis and the long rod are perpendicular to the rotary forging plane of the forging blank.

[0018] Preferably, in S03, if the temperature of the workpiece is lower than 950°C, the workpiece is reheated. The heating and subsequent deformation process should repeat steps S01 to S05.

[0019] Preferably, in S02 to S04, the rotating die should be continuously hot forged along the processing surface in a clockwise or counterclockwise direction; each hot forging process starts from the outer edge of the workpiece, moves toward the center of the circle after completing one circle, and then starts the next circle of hot forging, with the overlap rate of two adjacent circles not less than 10%, until all the positions requiring hot forging are forged; for workpieces with non-circular disk surfaces, a single circle of hot forging is allowed to be disconnected at a position where there is no workpiece.

[0020] Preferably, the forging blank material is medium carbon low alloy steel, the ratio of the height to the diameter of the forging blank material before rotary forging is less than 1, and the thickness of the workpiece after rotary forging is greater than 20 mm.

[0021] Preferably, under the premise of meeting the requirements in S02 to S05, the reduction amounts at different positions during each hot rotary forging process may be inconsistent.

[0022] A high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forging produced using hot rotary forging technology, wherein the grain size of the forging is not less than level 6, the difference in tensile strength between the diameter direction and the perpendicular diameter direction of the forging does not exceed 5%, and the difference in impact energy does not exceed 10%.

[0023] Preferably, the diameter of the large-diameter thin-walled steel forging is 400mm to 1200mm, and the thickness is 20mm to 60mm; the large-diameter thin-walled steel forging with a long shaft or a long rod includes an integrally formed shaft gear or shaft flange, the shaft diameter is less than 1 / 4 of the disk diameter, and the shaft length is tens of centimeters to 1 to 2 meters.

[0024] The invention discloses an application of high-strength, high-toughness, high-homogeneity, large-diameter thin-walled steel forgings produced by hot rotary forging technology in thin-walled steel pipe fittings. The thin-walled steel pipe fittings include gears, gears with shafts, flanges with shafts, disc-like parts or special-shaped parts with bosses.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) Compared with traditional hot die forging, hot rotary forging can ensure sufficient local pressure and short-distance metal flow due to the small contact area between the rotating hard die and the workpiece, thereby improving the plasticity of the material during thermal deformation, and achieving a larger reduction and a lower final forging temperature. It is beneficial to the first rotary forging to break up the raw material dendrites and refine the grains throughout the process, thereby achieving the purpose of improving the grain size and toughness of the workpiece. For workpieces that require quenching and tempering, they can be directly quenched, reducing the energy consumption of reheating the workpiece.

[0027] (2) Compared with traditional hot die forging, the amount of rotary forging reduction at different positions of the workpiece can be adjusted and precisely controlled. This solves the problems of uneven deformation and dead zones in complex-shaped workpieces, improves the uniformity of the entire disc surface structure, and ultimately improves the uniformity of the mechanical properties of the entire disc surface. In addition, precise control can also be performed on workpieces that require local strengthening or toughening.

[0028] (3) Since the hot rotary forging rotates the hard die to guide the metal to rotate locally, the direction of the solidification segregation band can be destroyed. The segregation bands that originally extended along the rolling direction (along the diameter direction after traditional die forging) are completely broken up and randomly distributed, significantly reducing the anisotropy of the workpiece.

[0029] The main principles of the present invention are as follows:

[0030] The forging blank is heated to 1200℃~1250℃ and kept at this temperature for 1~2h to ensure that the forging blank is softened by heat and stores enough heat. The main purpose of the first rotary forging is to break up defects such as dendrites and loose welds in the as-cast structure. A large reduction should be used for deformation, so the reduction should not be less than 30%. To ensure that the forging blank does not crack during the large reduction rotary forging process, the rotating die speed should be slightly lower, selecting 30-60 rpm. To ensure the deformation penetration effect and deformation uniformity of the entire disk surface, the displacement speed of the rotating die should not exceed 0.5 times the contact surface diameter of the die and the workpiece per second. Due to the large deformation in the first rotary forging, the forging blank needs to have good plasticity and be able to undergo austenite grain recrystallization. Therefore, the final forging temperature of the first rotary forging should not be lower than 1050℃.

[0031] Depending on the dimensional relationship between the forging blank and the final workpiece, the workpiece can be subjected to multiple passes of rotary forging. During the hot deformation process, the temperature of the deformed position will increase significantly. In order to ensure the continuity of the workpiece metal and avoid excessive temperature drop at individual positions due to no deformation, each pass of hot rotary forging is required to continuously cover every position of the workpiece. The specific deformation amount setting for each position can be designed according to the specific shape of the final workpiece. Since the temperature of the workpiece edge drops faster than the center, the hot rotary forging process proceeds from the outer edge to the center of the circle. At the same time, the deformed position will push the outer metal away from the center of the circle. The outer metal will deform and thin first, which can reduce the resistance to metal movement and avoid the formation of defects such as folding.

[0032] To avoid critical deformation and abnormal grain growth, except for the first and final hot forging passes, the reduction during subsequent hot forging passes must be no less than 15%, the rotating die speed must be no less than 60 rpm, and the displacement rate must be no more than 1 times the die-workpiece contact diameter per second. If the workpiece temperature is below 950°C, this hot forging pass should be considered the final pass. If the workpiece is not yet formed, it can be reheated. However, to ensure grain refinement, the heating and subsequent deformation processes should be repeated, steps S01 to S05.

[0033] The last rotary forging is the final process to refine the structure and improve the surface quality of the workpiece. During the last rotary forging, the workpiece should be in the austenite non-recrystallization zone to ensure the refinement effect while not deforming and cracking in the two-phase zone. Therefore, the forging temperature should be higher than the A of the workpiece composition. C3The temperature should be +50°C but lower than 950°C, and the final forging temperature should not be lower than the Ar3 temperature of the workpiece composition. To ensure microstructure refinement, the reduction should be 10-15%. To ensure surface quality and prevent excessive temperature drop in the unswaged portion, the swaging speed should be increased. The rotating die speed should be no less than 90 rpm, and the rotating die displacement speed should be no more than 1.5 times the contact diameter of the die and workpiece per second.

[0034] To avoid uneven deformation and penetration at different distances from the center of the circle during the same forging pass, and to prevent folding at the overlap, the overlap rate of two adjacent turns must be no less than 10%. To ensure a significant grain refinement effect and forging speed, and to avoid excessive temperature drop in the workpiece during a single forging pass, exceeding the required deformation temperature range, the rotating die of the hot forging machine must be no larger than the billet diameter and no less than 1 / 7 of the maximum diameter of the workpiece after forging.

[0035] This invention targets large-diameter, thin-walled steel forgings. Therefore, the billet height-to-diameter ratio before swaging should be less than 1, otherwise forging efficiency will be too low. If the billet height is greater than the diameter, open forging can be performed to reduce the ratio before forging according to the present invention. The workpiece thickness after swaging should be greater than 20 mm to avoid cracking during swaging or excessive deformation during subsequent quenching.

[0036] Conventional forging has a high final forging temperature and coarse austenite grains. After air cooling or quenching and tempering, the microstructure is very coarse and lacks strength and toughness. Therefore, the workpiece needs to be cooled and then normalized or quenched and tempered again. After using the process of the present invention, the microstructure of the workpiece after final forging is significantly refined and the microstructure uniformity is improved. Direct air cooling can meet the performance requirements of non-quenched and tempered steel parts; direct preheating quenching followed by high-temperature tempering at 500-600°C can meet the performance requirements of quenched and tempered steel parts.

[0037] As a local forming processing method, the hot rotary forging of the present invention has the advantages of high applied pressure and good deformation penetration, which can significantly refine the grains at the deformation position and improve the strength and toughness of the workpiece. It is also possible to adjust the deformation amount and other processes in real time according to the shape of the workpiece to achieve the purpose of precise control and reduce subsequent processing. It is particularly suitable for the production of large-diameter thin-walled steel forgings that require high strength, toughness and high homogeneity, and at the same time solves the problem of difficulty in forming the disk portion of large-diameter thin-walled steel forgings with long axes or long rods. In addition, local hot rotary forging can also interrupt the banded segregation extending along the diameter with the swirling flow of local metal, avoiding the problem of anisotropy of mechanical properties. The forging machine with hot rotary forging function has been successfully developed and has begun to be used in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the microstructure morphology of the air-cooled plate at a position 2 / 3 from the center of the circle after rotary forging of the workpiece in Example 1 of the present invention;

[0039] Figure 2 This is the microstructure of the longitudinal section of the disc at a position 2 / 3 from the center of the circle after the workpiece of Example 2 of the present invention is quenched and tempered after rotary forging;

[0040] Figure 3 The microstructure of the workpiece of comparative example 1 at the position 2 / 3 from the center of the air-cooled plate after free forging upsetting + two-pass hot die forging;

[0041] Figure 4 This is the microstructure morphology of the longitudinal section of the disk at 2 / 3 of the distance from the center of the circle after the workpiece of comparative example 2 was subjected to free forging upsetting + two-pass hot die forging and then quenching and tempering treatment. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples. The following examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0043] Example 1

[0044] A production process for high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forgings using hot rotary forging technology. The final dimensions require a hot-forged gear blank made of medium-carbon, low-alloy (grade 42CrMo) steel with a diameter of 800 mm and a wall thickness of 50 mm. A raw blank with a diameter of 400 mm and a height of 210 mm is selected and heated to 1220°C for 100 minutes. The rotary die of the rotary forging machine is selected to have a diameter of 300 mm. After removal, the first rotary forging temperature is 1190°C, the reduction is 35%, and the rotary die speed is 60 rpm. The contact surface between the die and the workpiece is approximately 260 mm in diameter, and the rotary die displacement speed is selected to be 100 mm / s. The final forging temperature of the first rotary forging pass is 1080°C. The second and third forging passes were 40mm and 38mm in reduction, respectively. The start forging temperatures were 1080℃ and 990℃, respectively. The rotating die speed was 90 rpm. At this time, the contact surface diameters of the die and the workpiece were approximately 204mm and 197mm, respectively. The rotating die displacement speed was selected to be 160mm / s. The final forging pass had a reduction of approximately 7mm, reaching a final thickness of 50mm, a reduction of approximately 12%. Material A C3 The temperature and Ar3 temperature are approximately 792°C and 780°C respectively. The start forging temperature is 940°C and the final forging temperature is about 830°C. The rotating hard die rotates at a speed of 120 rpm. At this time, the contact surface diameter of the hard die and the workpiece is about 90mm, and the rotating hard die displacement speed is 120mm / s. The 4 hot forgings all start from the outer edge of the workpiece. After completing one circle, they move toward the center of the circle and start the next circle of hot forging. The overlap rate of the two adjacent circles is about 12%. After the final forging, the workpiece is air-cooled to room temperature. The actual grain size of the workpiece at a radius of 2 / 3 from the center of the circle is measured. The results are shown in Table 1. The microstructure morphology of the air-cooled disk of the workpiece after forging is shown in Table 1. Figure 1 .

[0045] Example 2

[0046] The same as Example 1, the only difference is that the workpiece is oil quenched after final forging and tempered at 560℃ after cooling. The tensile strength and impact energy of the workpiece after tempering are measured at a position 2 / 3 of the radius from the center of the circle along the diameter direction and perpendicular to the diameter direction. The results are shown in Table 1. The microstructure of the longitudinal section of the disk part of this example after quenching and tempering treatment at a position 2 / 3 of the radius from the center of the circle is shown in Table 1. Figure 2 .

[0047] Comparative Example 1

[0048] The material, final size of the workpiece, raw material size and heating system (i.e., the forging blank is heated to 1220°C and kept warm for 100 minutes) are the same as in Example 1. After heating, free forging upsetting + two-pass hot die forging are adopted. The deformation of a single free forging is about 35%, the final die forging temperature is about 1050°C, and the final forging deformation is about 10%. After the final forging, the workpiece is air-cooled to room temperature, and the actual grain size of the workpiece at a radius of 2 / 3 from the center of the circle is measured. The results are shown in Table 1. The microstructure morphology of the air-cooled disc at a radius of 2 / 3 from the center of the circle after the workpiece is free forging upsetting + two-pass hot die forging is shown in Table 1. Figure 3 .

[0049] Comparative Example 2

[0050] The same as comparative example 1, except that the workpiece is oil quenched after final forging and tempered at 560℃ after cooling. The tensile strength and impact energy of the workpiece after tempering are measured at a radius of 2 / 3 from the center of the circle along the diameter direction and perpendicular to the diameter direction. The results are shown in Table 1. The microstructure of the longitudinal section of the disk part at a radius of 2 / 3 from the center of the circle after the workpiece of this comparative example is shown in Table 1. Figure 4 .

[0051] From the microstructure morphology of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 (see Appendix Figure 1 ~Attachment Figure 4 ) and mechanical properties (Table 1) show that the actual grain size of the gear blank produced by hot forging reaches level 7 (such as Figure 1 As shown), it is much finer than the 4-level air-cooled gear produced by die forging in the control example (as shown Figure 3 As shown). Figure 2 As shown in the figure, the longitudinal section of the gear blank produced by hot rotary forging has almost no band segregation, while Figure 4The longitudinal cross-section of the die-forged gear blank shown shows distinct banded color distribution caused by banded segregation, indicating significant structural anisotropy. The impact energy of the hot-rotary-forged gear blank after quenching and tempering is 2.8 times that of the die-forged quenched and tempered gear in the control example. The difference in tensile strength between the transverse and longitudinal directions is only 1.7%, and the difference in impact energy between the transverse and longitudinal directions is only 6.3%, far less than the die-forged quenched and tempered gear in the control example. Gears produced using hot-rotary-forging exhibit significantly improved toughness and homogeneity.

[0052] Example 3

[0053] A production process for high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forgings produced using hot rotary forging technology. The final size requires a hot forging blank made of medium-carbon low-alloy (grade 40CrNiMo) steel with a central vertical long axis of 600mm in diameter and 25mm in wall thickness. The original billet with a diameter of 400mm and a height of 57mm is selected, in which the central vertical long axis has been forged. The original billet is heated to 1250℃ and kept warm for 60 minutes. The diameter of the rotary die of the selected rotary forging machine is 200mm. After being taken out, the forging temperature of the first rotary forging is 1200℃, the reduction is 50%, about 28mm, and the rotation speed of the rotary die is 30 rpm. The contact surface diameter of the die and the workpiece is about 138mm, and the displacement speed of the rotary die is selected to be 60mm / s. The final forging temperature of the first rotary forging is 1060℃. The reduction in the last rotary forging is about 3.5mm, reaching the final thickness of 25mm, with a reduction of about 12%; Material A C3 The temperature and Ar3 temperature were approximately 774°C and 743°C, respectively. The start forging temperature was 950°C, and the final forging temperature was approximately 800°C. The rotating die rotated at 120 rpm, with the contact surface diameter between the die and the workpiece approximately 52 mm. The rotating die displacement speed was 75 mm / s. Both hot rotary forging passes began at the outer edge of the workpiece, moving toward the center after completing one rotation to begin the next hot rotary forging pass. The overlap ratio between adjacent rotations was approximately 15%. After final forging, the workpiece was air-cooled to room temperature, then heated to 860°C for oil quenching. After cooling thoroughly, it was tempered at 510°C. The actual grain size of the disc at a radius of 2 / 3 from the center after air cooling, as well as the tensile strength and impact energy values ​​of the workpiece disc at a radius of 2 / 3 from the center after quenching and tempering, along the diameter and perpendicular to the diameter, were measured. The results are shown in Table 1. The actual grain size of the disc after air cooling was 7.5, with minimal difference in transverse and longitudinal properties, indicating good toughness and homogeneity of the workpiece.

[0054] Example 4

[0055] A production process for high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forgings using hot rotary forging technology. A raw billet with a diameter of 400 mm and a height of 180 mm, whose central vertical axis has already been forged, is selected. The raw billet is heated to 1200°C and held for 120 minutes. The rotary die of the rotary forging machine has a diameter of 300 mm. After removal, the first rotary forging temperature is 1180°C, with a 50% reduction (approximately 90 mm) and a rotary die speed of 30 rpm. The contact surface between the die and the workpiece has a diameter of approximately 275 mm, and the rotary die displacement speed is selected to be 100 mm / s. The final forging temperature of the first rotary forging pass is 1090°C. The second and third forging passes were 45mm and 21.5mm in reduction, respectively. The start forging temperatures were 1090℃ and 995℃, respectively. The rotating die speed was 90 rpm. At this time, the contact surface diameters of the die and the workpiece were approximately 214mm and 154mm, respectively. The rotating die displacement speed was selected to be 130mm / s. The final forging pass had a reduction of approximately 3.5mm, reaching a final thickness of 20mm, with a reduction of approximately 15%. Material A C3 The temperature and Ar3 temperature are approximately 774°C and 743°C respectively. The start forging temperature is 970°C and the final forging temperature is about 770°C. The rotating hard die rotates at a speed of 150 rpm. At this time, the contact surface diameter of the hard die and the workpiece is about 64mm, and the rotating hard die displacement speed is 85mm / s. The four hot forgings all start from the outer edge of the workpiece. After completing one circle, they move toward the center of the circle and start the next circle of hot forging. The overlap rate of the two adjacent circles is about 15%. After the final forging, the workpiece is air-cooled to room temperature, and then the whole is heated to 860°C for oil quenching. After cooling thoroughly, it is tempered at 500°C. A hot forged and tempered part with a final diameter of 1200mm and a wall thickness of 20mm is obtained, which is a medium-carbon low-alloy (grade 40CrNiMo) steel disc with a central vertical long axis.

[0056] Example 5

[0057] A production process for high-strength, high-toughness, high-homogeneity, large-diameter, thin-walled steel forgings using hot rotary forging technology. The final dimensions are 400mm diameter and 60mm wall thickness for hot-forged gear blanks made of medium-carbon, low-alloy (grade 42CrMo) steel. A starting blank with a diameter of 250mm and a height of 155mm is heated to 1240°C and held for 80 minutes. The rotary die of the rotary forging machine has a diameter of 200mm. After removal, the first forging pass begins at a temperature of 1220°C, with a reduction of 40% and a rotary die speed of 60 rpm. The contact surface between the die and the workpiece is approximately 185mm in diameter, and the rotary die displacement speed is 80mm / s. The final forging temperature of the first forging pass is 1100°C. The second forging pass is performed with a reduction of 26mm, a starting temperature of 1090°C, and a rotary die rotation speed of 90 rpm. The contact surface diameter between the die and the workpiece is approximately 134mm, and the rotary die displacement speed is 100mm / s. The final forging pass reduces the workpiece by approximately 7mm, achieving a final thickness of 60mm, a reduction of approximately 10%. The starting forging temperature is 960°C, and the final forging temperature is approximately 850°C. The die rotates at 120 rpm, with the contact surface diameter between the die and the workpiece approximately 74mm. The die moves at a speed of 100mm / s. All three hot forging passes begin at the outer edge of the workpiece, moving toward the center after each pass to begin the next. The overlap between successive passes is approximately 18%. After final forging, the workpiece is oil quenched and, after cooling, tempered at 600°C.

[0058] Table 1 Actual grain size of air-cooled workpieces and tensile strength and impact energy of quenched and tempered workpieces

[0059]

[0060] Note: Longitudinal refers to sampling along the diameter direction, and horizontal refers to sampling perpendicular to the diameter direction.

[0061] The actual grain size is determined using the ferrite mesh method in accordance with the national standard GB / T 6394-2017 "Method for determination of average grain size of metals".

[0062] The tensile strength refers to the national standard GB / T 228.1-2021 "Tensile test of metallic materials Part 1: Room temperature test method".

[0063] The impact energy refers to the national standard GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0064] Difference percentage = (longitudinal value - transverse value) / longitudinal value × 100%.

[0065] It should be understood that in order to streamline the present disclosure and aid understanding of one or more of the various inventive aspects, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in less than all of the features of the previously disclosed embodiments. Accordingly, the claims that follow the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of the invention.

[0066] Although the present invention has been described with respect to a limited number of embodiments, it will be apparent to those skilled in the art, having benefit of the foregoing description, that other embodiments are contemplated within the scope of the invention thus described. Furthermore, it should be noted that the language used in this specification has been selected primarily for readability and didactic purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Consequently, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is intended to be illustrative rather than restrictive of the scope of the invention, which is defined by the appended claims.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A production process for high-strength, high-homogeneity, large-diameter, thin-walled steel forgings produced using hot rotary forging technology, characterized in that: The following steps are involved: S01, heat the forging billet to 1200℃~1250℃ and keep it warm for 1~2h; S02, the forging blank is placed on a hot rotary forging machine for rotary forging, the start forging temperature is not less than 1150°C, the first rotary forging reduction is not less than 30%, the rotary die speed of the hot rotary forging machine is 30-60 rpm, and the rotary die displacement speed is not more than 0.5 times the contact surface diameter of the rotary die and the workpiece / second; the final forging temperature of the first rotary forging is not less than 1050°C; S03, according to the workpiece size requirements, multiple rounds of rotary forging are carried out. Starting from the second round of rotary forging, the start forging temperature is not less than 950°C, the reduction is not less than 15%, the rotating die speed is not less than 60 rpm, and the rotating die displacement speed is not greater than 1 times the contact surface diameter of the rotating die and the workpiece / second; S04, the opening temperature of the last rotary forging is higher than the A of the workpiece composition C3 Temperature +50℃ and lower than 950℃, reduction 10-15%, rotating die speed not lower than 90 rpm, rotating die displacement speed not higher than 1.5 times the contact surface diameter of the rotating die and the workpiece / second, final forging temperature not lower than the Ar3 temperature of the workpiece composition; S05, the workpiece after rotary forging is air-cooled to room temperature, and then quenched and tempered at 500-600°C; or the workpiece after rotary forging is directly placed in a cooling tank for quenching, and the quenched workpiece is tempered at 500-600°C after cooling; In S01, the forging blank includes a cylindrical blank; The cylindrical blank includes a cylindrical blank with a long axis or a long rod, wherein the long axis and the long rod are perpendicular to the rotary forging plane of the forging blank; In S02~S04, the rotating hard die should be hot forged continuously along the processing surface in a clockwise or counterclockwise direction; each hot forging starts from the outer edge of the workpiece, moves toward the center of the circle after completing one circle, and then starts the next circle of hot forging. The overlap rate of two adjacent circles shall not be less than 10%, until all the positions requiring hot forging are forged. For workpieces with non-circular disk surfaces, a single circle of hot forging is allowed to be disconnected at a position where there is no workpiece.

2. The production process according to claim 1, characterized in that: The diameter of the rotating hard die of the hot rotary forging machine shall not be larger than the diameter of the forging blank and shall not be smaller than 1 / 7 of the maximum diameter of the workpiece after rotary forging.

3. The production process according to claim 1, characterized in that: In S03, if the temperature of the workpiece is lower than 950°C, the workpiece is reheated, and the heating and subsequent deformation processes are repeated from S01 to S05.

4. The production process according to claim 1, characterized in that: The forging blank material is medium carbon low alloy steel, the ratio of the height to the diameter of the forging blank material before rotary forging is less than 1, and the thickness of the workpiece after rotary forging is greater than 20 mm.

5. A high-strength, high-homogeneity, large-diameter, thin-walled steel forging produced by hot rotary forging technology according to the production process of any one of claims 1 to 4, characterized in that: The grain size of forgings shall not be less than grade 6, the difference in tensile strength between the diameter direction and the perpendicular diameter direction of the forgings shall not exceed 5%, and the difference in impact energy shall not exceed 10%.

6. The high-strength, high-homogeneity, large-diameter, thin-walled steel forging produced by hot rotary forging technology according to claim 5, characterized in that: The diameter of large-diameter thin-walled steel forgings is 400mm~1200mm, and the thickness is 20mm~60mm; large-diameter thin-walled steel forgings with long shafts or long rods include one-piece shaft gears or shaft flanges, the shaft diameter is less than 1 / 4 of the disc diameter, and the shaft length is tens of centimeters to 1~2 meters.

7. The use of a high-strength, high-homogeneity, large-diameter thin-walled steel forging produced by hot rotary forging technology in a steel thin-walled pipe fitting according to claim 5, characterized in that: Steel thin-walled pipe fittings include gears, gears with shafts, flanges with shafts, disc-like parts or special-shaped parts with bosses.

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