Manufacturing process and mold of high-toughness heavy-load part and manufactured product

Abstract

The invention discloses a manufacturing process of a high-toughness heavy-load part, a mold and a manufactured product, and belongs to the technical field of high-toughness heavy-load part material forming. Near-net forming of the forge piece is achieved through the near-net forming die, the compressive stress state is formed in the forge piece when the forge piece is formed through the surrounding effect of the die, the internal stress of a blank is converted into the compressive stress state from the stress state of complex pull pressure and shear stress, and therefore the evenly-distributed compressive stress is formed; according to the method, as-cast structures such as internal looseness and holes are effectively forged, grain refinement is uniform, the phenomenon of crystal mixing is avoided, and further through grain refinement heat treatment, the forge piece has high strength, toughness and grain size.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength and toughness heavy-load part material forming, and more specifically, relates to a manufacturing process, a mold and a manufactured product of a high-strength and toughness heavy-load part. Background Art

[0002] In recent years, heavy-load components have become indispensable spare parts for industries such as steel, electricity, and transportation. The working conditions of heavy-load components are very harsh. Not only do they have to work under very high loads, they are often accompanied by high temperatures and corrosive media. Once fractures or fatigue cracks occur during service, destructive accidents can easily occur. Therefore, the quality of key parts in heavy-load components directly affects the overall level and operational reliability of the complete set of equipment, and their organization and performance requirements are very strict.

[0003] For large forgings, the changes in the structure during the forging process include both the grain refinement process under the action of dynamic and static recrystallization and metadynamic recrystallization mechanisms, and the coarsening process of grain growth during heating and cooling. This grain refinement and coarsening during hot working is a pair of contradictions in the grain evolution process. How to control the heating system, deformation thermodynamic parameters and cooling system to obtain a fine and uniform grain structure is one of the main goals of forging quality control for heavy-duty parts.

[0004] After searching, patent CN113843383A discloses a composite forging near-net forming method for super-large anvil iron forgings, and the specific steps are: Step 1: select and pre-draw the billet; Step 2: forge jaws for the steel turning machine and the forging manipulator to cooperate in lifting and turning at the nozzle end and the riser end of the billet respectively; Step 3: composite upsetting; Step 4: composite drawing; Step 5: conical surface preforming; Step 6: place the billet in the forming die to complete the forging process of the billet finished product; Step 7: after the forging forming is completed, air cool to post-heat treatment, and adopt the process methods of isothermal annealing, normalizing, and high-temperature tempering to achieve uniform organization and grain refinement.

[0005] Patent CN113059100A discloses a near-net composite forming method for large-scale rings with sudden wall thickness changes, wherein a small-diameter rectangular cross-section ring blank after forging and punching is heated and kept warm, then taken out and put on a hot ring rolling machine for rolling, and rolling is stopped when the outer diameter grows to a target size to obtain a large-diameter rectangular cross-section ring blank, which is then taken out and heated and kept warm; the large-diameter rectangular cross-section ring blank is placed in a forming die for hot forming, and after obtaining a special-section ring blank of a desired shape, it is taken out and heated and kept warm; fine ring rolling near-net forming - the special-section ring blank is placed on a ring rolling machine for fine ring rolling, and the cross-sectional profile of the ring is formed by a special-shaped roller near-net, and rolling is stopped when the outer diameter grows to a target size to obtain a ring with sudden wall thickness changes; the ring with sudden wall thickness changes is quickly placed on a bulging machine, and hot bulging is performed using residual heat to improve dimensional accuracy and roundness and improve residual stress distribution, and pressure is continued after bulging to the target size, and the ring is taken out after cooling to room temperature to obtain the target ring.

[0006] However, the above-mentioned molds only play a forming role. Since heavy-loaded parts are required to be single pieces in small batches, the traditional free forging process only has deformation forces in two vertical directions. As a result, the internal stress of the forgings is complex and changeable during the forming process, and irregular additional tensile stress and shear stress are derived. Various internal cracks are easily formed inside the forgings, and quality problems such as central looseness cannot be improved, segregation cannot be eliminated, internal holes, and gas-formed holes cannot be forged together are easily formed. At the same time, it causes uneven deformation force, inconsistent grain breakage, and the formation of coarse crystals and mixed crystals. The mechanical properties and service life of the products are easily substandard during manufacturing and use. Summary of the invention

[0007] 1. Problem to be solved

[0008] In view of the problem that the existing heavy-duty parts such as slider forks and cross shafts are prone to breakage, cracks and wear, which affects the product life, the first purpose of the present invention is to provide a manufacturing process for high-strength and heavy-duty parts, which uses a die to achieve near-net shape of forgings;

[0009] A second object of the present invention is to provide a die that can achieve near-net-shape forming of forgings;

[0010] The third object of the present invention is to provide a heavy-loaded part made by the above process and mold, which has uniform stress distribution, uniform structure and high strength and toughness.

[0011] 2. Technical solution

[0012] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0013] A manufacturing process for high-strength and heavy-duty parts, comprising the following steps:

[0014] The forgings are obtained by cutting materials - homogenizing heating - fine and uniform crystal forging - heat treatment after forging.

[0015] The forging is made of high-strength and tough steel, which is alloy structural quenched and tempered steel and carburized steel, satisfying σb≥1000MPa, σs≥900MPa, ψ≥50%; δ5≥10%; Ak(u)≥60J;

[0016] Preferably, σb≥1200MPa; σs≥1000MPa, ψ≥55%; δ5≥10%; Ak(u)≥70J.

[0017] Preferably, the alloy structural quenched and tempered steel is 25Cr2Ni4MoV, 34CrNi3Mo, 33NiCrMoV14-5, and the carburizing steel is 15CrNi4Mo high-strength carburizing steel.

[0018] Furthermore, the homogenization heating process includes the steps of: heating to 550±10°C and keeping warm for 3 hours; heating to 850±10°C and keeping warm for 6 hours; heating to a homogenization heating temperature of 1260-1280°C and keeping warm for 22 hours; furnace cooling, dropping to 1240±10°C, and keeping warm for 7 hours; and forging, ensuring that the internal components and structure of the billet are uniformly dispersed through high-temperature diffusion through homogenization heating.

[0019] Preferably, the homogenization heating process is: heating to 550±10°C and keeping warm for 3 hours; heating to 850±10°C and keeping warm for 6 hours; heating to the homogenization heating temperature of 1270±10°C and keeping warm for 22 hours; furnace cooling, dropping to 1240±10°C, and keeping warm for 7 hours.

[0020] Furthermore, the fine and uniform crystal forging forming step is carried out in a fine and uniform crystal extrusion near-net-shape forming die. The design of the fine and uniform crystal extrusion near-net-shape forming die is simulated by finite element analysis, which simulates the forming process, analyzes the stress distribution state of the formed part, calculates the extrusion pressure, optimizes the die structure, determines the lubrication method based on the simulated friction coefficient, and obtains a billet shape with low deformation resistance and best filling performance.

[0021] The near-net-shape forming die comprises an upper die seat, a lower die seat and a center punch. The upper die seat is arranged above the lower die seat, and the bottom thereof is fitted with the lower die seat. A center punch protruding upward is arranged at the center of the lower die seat, and a space for accommodating the preform is formed between the inner cavity of the upper die seat and the center punch of the lower die seat. The center punch is arranged above the upper die seat and is used to squeeze the preform downward. Preferably, the upper surface of the lower die seat is concave downward, and a center punch is arranged at the center of the lower die seat, so that a leaky disk is formed around the center punch. The bottom of the upper die seat is fitted with the concave part of the lower die seat.

[0022] Preferably, the mold optimization parameters α=2°-3°, β=5°-6°, and the R arc is 45-50mm, wherein α is the draft angle of the inner wall of the upper die seat, β is the draft angle of the center punch of the lower die seat, and R is the ball head radius of the center punch of the lower die seat.

[0023] When forging is performed using the near-net-shape forming die, the preform is placed in the die and pressed down by the center punch so that the preform is nearly net-shaped in the combined die. The near-net-shape forming combined die is conducive to the formation of deformation compressive stress, thereby effectively forging the internal looseness and crack defects of the material, improving the stress distribution during deformation, making the grains refined and uniform, and preventing mixed crystal phenomena.

[0024] The fine-grained forging process combines forming, grains and stress organically, allowing the forging blank to be nearly net-formed under multi-directional compressive stress, so that the forgings can obtain uniform and fine grains.

[0025] The fine uniform crystal forging forming step in the above manufacturing process specifically includes:

[0026] a. First firing: The temperature is 1220℃-900℃, and the riser removal, upsetting and compaction processes are carried out.

[0027] b. Second firing: The temperature is 1250℃-900℃ to forge the prefabricated billet.

[0028] c. The third fire: The temperature is 1150℃-850℃, and the near-net-shape combined die is used to implement the near-net-shape fine uniform crystal forging forming process, which can effectively forge the internal defects of the material and control the grain size.

[0029] Furthermore, the post-forging heat treatment adopts a double normalizing-supercooling heat treatment+high temperature tempering and hydrogen expansion method.

[0030] Its process such as Figure 7 As shown, the specific steps include:

[0031] a. Primary normalizing: After the materials are prepared at 550°C and the forgings are assembled, they are heated to the austenitizing temperature 1 at a heating rate of ≤60°C / h, which is 890-910°C, preferably 890°C, 900°C, 910°C, and kept at this temperature for 10 hours;

[0032] b. Secondary normalizing: heating at a heating rate of ≤60℃ / h to austenitizing temperature 2, which is 860-880℃, preferably 860℃, 870℃, 880℃, keeping warm for 10h, then cooling to 250℃ by air blowing after taking out of the furnace;

[0033] c. Supercooling heat treatment: After coming out of the furnace, the forgings are pulled out with the trolley, and cooled to a surface temperature of 250°C by blowing with an industrial fan. Then the forgings and the trolley are pushed into the furnace and kept warm for 7 hours at a supercooling temperature of 280-320°C.

[0034] d. Tempering and hydrogen expansion: Heat to 650℃, temper and expand hydrogen, keep warm for 56h, then furnace cool to 400℃ at ≤40℃ / h, then furnace cool to 250℃ at ≤30℃ / h before taking out of the furnace.

[0035] The finished product obtained after forging undergoes sampling - sample processing - tensile test and Charpy impact test - test report - technical analysis to obtain heavy-load parts that meet the requirements.

[0036] It is worth noting that in the above manufacturing process, the near-net-shape forming die is designed according to the material properties of the high-strength and toughness steel grade, the forging process plan is formulated, the initial forging temperature and post-forging cooling method, the size of the forging after forming and the post-forging heat treatment process are determined.

[0037] Among them, preferably, Cr-Ni-Mo high-strength and tough steel is selected, and the high-strength and tough steel has strong tissue inheritance characteristics. In order to avoid the generation of tissue inheritance, it is extremely important to formulate a suitable forging process, such as forging temperature and forging deformation process, etc. Reasonable forging process and post-forging heat treatment can also refine the grains of these steels, improve the morphology of internal inclusions, and reduce component segregation, so as to achieve the purpose of improving the density of the material and the uniformity of mechanical properties.

[0038] The present invention provides a fine uniform crystal forging forming process method for high-strength and tough heavy-load parts, adopts a specially designed die to achieve near-net-shape forming of the forging, and utilizes the surrounding effect of the die to form a compressive stress state inside the forging during forming, so that the internal stress of the blank is transformed from a complex tensile stress state and a shear stress state to an extrusion stress state, thereby forming a uniformly distributed compressive stress, effectively forging the internal loose, porous and other cast structures, and at the same time, due to the uniform stress, the grains are uniformly refined and no mixed crystal phenomenon occurs.

[0039] Since the working conditions of heavy-duty parts are relatively severe, in addition to high temperature and high pressure, they are often accompanied by alternating loads or impact loads. Therefore, the selection of steel for heavy-duty parts often does not emphasize the higher the strength, the better. At the same time, the toughness and plasticity of the material should be taken into account. The mechanical performance index requirements are as follows: σb ≥ 1200MPa; σs ≥ 1000MPa, ψ ≥ 55%; δ5 ≥ 10%; Ak (u) ≥ 70J. Usually, in the process of selecting steel for heavy-duty parts, not only the chemical composition of the steel should be considered, but also the smelting process should be considered to reduce the number of non-metallic inclusions as much as possible, improve the purity of the steel, rationalize the forging process, obtain a fine-grained structure, a uniform forging blank, and avoid temper brittleness of the material as much as possible through appropriate heat treatment process, so that it has good strength and toughness.

[0040] The result is that in the final heavy-loaded parts, the overall austenite grain size reaches above level 8, and the grain size difference is no more than level 2; the ultrasonic and magnetic particle inspection pass rate reaches 100%; the weight of forgings of high-strength and tough heavy-loaded parts is saved by 20%-30%, the machining hours are reduced by 45%, and the gross to net weight ratio is effectively improved.

[0041] The fine uniform crystal forging process and die of the present application are suitable for heavy-loaded parts such as heavy-load flange forks, welding forks, slider-type fork heads, slider-type flat heads, cross shafts, etc.

[0042] 3. Beneficial effects

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The method of the present invention utilizes a die to achieve near-net-shape forgings, and utilizes the enveloping effect of the die to form a compressive stress state inside the forgings during forming, thereby transforming the internal stress of the blank from a complex tensile stress state and a shear stress state into a compressive stress state, thereby forming a uniformly distributed compressive stress, effectively forging the internal loose, porous and other cast structures, and at the same time, due to the uniform stress, the grains are uniformly refined, and no mixed crystal phenomenon occurs;

[0045] (2) The present invention optimizes the parameters of the near-net-shape forming mold, and the design of the mold is optimized according to the shape of the heavy-loaded parts, so as to obtain a blank shape with low deformation resistance and best filling performance. The near-net-shape forming mold is suitable for heavy-loaded parts such as heavy-loaded flange forks, welding forks, slider-type fork heads, slider-type flat heads, cross shafts, etc.;

[0046] (3) The heavy-loaded parts made using the process and mold of the present invention have uniform stress distribution, uniform structure, and high strength and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but it should be understood that these drawings are designed only for explanation purposes and are not intended to limit the scope of the present invention. In addition, unless otherwise specified, these drawings are intended only to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.

[0048] Figure 1 A finished product model of a specific embodiment of the present invention;

[0049] Figure 2 This is the homogenization heating process curve before forging of the present invention;

[0050] Figure 3 It is a blank making diagram before die forging of the present invention;

[0051] Figure 4This is a stress distribution diagram of a forging formed by a die with initial parameters (α=5°, β=10°, R=55 mm) in Example 1 of the present invention;

[0052] Figure 5 The stress distribution diagram of the forging formed by the die with optimized parameters (α=2.5°, β=5.8°, R=45mm) in Example 1 of the present invention;

[0053] Figure 6 A schematic diagram of a near-net-shape die structure optimized for the present invention;

[0054] Figure 7 This is the post-forging heat treatment process curve of the present invention. DETAILED DESCRIPTION

[0055] The following detailed description of exemplary embodiments of the present invention refers to the accompanying drawings, which form a part of the description, and in which exemplary embodiments of the present invention that can be implemented are shown as examples. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention, it should be understood that other embodiments can be implemented and various changes can be made to the present invention without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but is only for the purpose of illustrating and not limiting the description of the characteristics and features of the present invention, so as to propose the best mode for performing the present invention and to enable those skilled in the art to implement the present invention. Therefore, the scope of the present invention is limited only by the appended claims.

[0056] It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention. As used herein, the terms "parallel" and "perpendicular" are not limited to their strict geometric definitions, but include tolerances for reasonable and inconsistent machining or human errors.

[0057] The steel type of the present application is high-strength and tough alloy structural quenched and tempered steel and carburized steel. During the preparation process, a steel ingot containing the steel type components is used as a raw material for cutting and forging. The components and contents thereof are shown in Table 1.

[0058] Table 1 Steel grades and chemical composition (wt%)

[0059]

[0060]

[0061] Note: N≤70ppm, H≤1.5ppm, O≤40ppm, Ca≤15ppm. Harmful element content (%): Sb≤0.01, Bi≤0.01, Sn≤0.015, As≤0.015, Pb≤0.01, total content ≤0.05.

[0062] The steel grades in Table 1 have adjusted the Ni, Cr, Mo elements that are beneficial to improving strength and toughness, as well as the V and Mn elements that are beneficial to refining grains and improving impact toughness, and controlled the contents of H, O, N and the five harmful elements to meet the requirements of mechanical properties and high strength and toughness.

[0063] The finite element analysis software may be any software available on the market that can implement finite element analysis.

[0064] Example 1

[0065] A near-net-shape forming die for fine uniform crystal extrusion of heavy-duty parts is designed and manufactured. The forming process is simulated through numerical simulation using finite element analysis software, the stress distribution state of the formed part is analyzed, the extrusion pressure is calculated, the die structure is optimized, and the lubrication method is determined based on the simulated friction coefficient.

[0066] The near-net-shape forming die includes an upper die seat, a lower die seat and a center punch. The upper surface of the lower die seat is concave downward, and a center punch that bulges upward is provided in the center of the lower die seat, so that a leaky disk is formed around the center punch. The bottom of the upper die seat fits in the concave part of the lower die seat, and a space for accommodating the preform is formed between the inner cavity of the upper die seat and the convex part of the lower die seat. The center punch is provided above the upper die seat and is used to squeeze the preform downward. The preform is placed in the die, and the preform is pressed downward by the center punch so that the preform is nearly net-shaped in the combined die. The designed near-net-shape forming die is as follows: Figure 6 shown.

[0067] Finite element analysis software is used to perform numerical simulation to optimize the relevant parameters of the forming die. The specific optimization steps include:

[0068] S1. Construct the models of the blank, upper die base, lower die base and center punch respectively, which are:

[0069] a. Construct the blank model: the initial parameters of the blank are 250mm×150mm; the blank grid is divided into 8000, the blank boundary conditions are that the upper surface is in contact with the center punch, the inner side is tangent to the arc of the lower die seat, and the outer side is in contact with the inner cavity of the upper die. The material is 25Cr2Ni4MoV, and the initial temperature is 1180℃;

[0070] b. Construct the center punch model: the initial parameters of the center punch are R55mm; no meshing is required, the boundary condition of the center punch is in contact with the upper surface of the blank, the material is H13 die steel, the initial temperature is 300℃, and the pressing speed is 10mm / s;

[0071] c. Construct the upper die base model: the upper die base is made of rigid material, and the initial parameter of the upper die base is the outer diameter (inner hole )×290mm; draft angle α=5°, the boundary condition of the upper die base is that the lower surface is in contact with the lower die base, the material is H13 die steel, and the initial temperature is 300℃;

[0072] d. Construct the lower die base model: the lower die base is made of rigid material, and the initial parameter of the lower die base is the outer diameter (inner hole mm), center punch R55 mm×120 mm, draft angle β=10°; the boundary condition of the lower die base is that the upper surface contacts the upper die base, the arc of the center punch is tangent to the blank, the material is H13 die steel, and the initial temperature is 300℃;

[0073] S2, adjusting the positions of the blank, the upper die seat, the lower die seat and the center punch, so that the blank is arranged in the cavity of the upper die seat and the lower die seat, the center punch is located above the blank, and the positions of the four satisfy vertical symmetry;

[0074] S3, the initial contact mode is point contact; the lubrication method is hot forging, and the friction coefficient is 0.7;

[0075] S4. Get the simulation results, including the stress distribution state of the formed part, such as Figure 4 As shown in the figure, when α=5°, β=10°, and the R arc is 55m, the stress of the blank at the contact point with the inner wall of the upper die seat is small, and the problem of infilling is prone to occur, and the deformation force is large, and the deformation stress distribution is uneven;

[0076] The uniformity of stress distribution is improved by adjusting and optimizing the draft angle α of the inner wall of the upper die seat, the draft angle β of the center punch of the lower die seat, and the punch radius R.

[0077] The optimal parameters of the die are α = 2.5°, β = 5.8°, and the R arc is 45 mm, where α is the draft angle of the inner wall of the upper die seat, β is the draft angle of the center punch of the lower die seat, and R is the ball head radius of the center punch of the lower die seat. When the die structure is the above parameters, the internal tissue stress of the forging is a uniform compressive stress state such as Figure 5 shown.

[0078] It should be noted that the mold of the present application is generally used as a mold for forming the blank in the prior art, and its fillability is generally considered. It is surprisingly found that by changing the design of the above parameters, not only the fillability of the blank can be improved, but more importantly, it is conducive to the formation of deformation compressive stress, thereby effectively forging the internal looseness and crack defects of the material, obtaining a uniform deformation stress distribution, making the grains refined uniform, and preventing mixed crystal phenomenon.

[0079] The obtained near-net-shape forming die subjects the formed forging to uniform superimposed compressive stress, improves the grain and structure, and reduces the gross-to-net weight ratio; the forging has a structure with high strength and toughness, long life, and a shape close to the finished product.

[0080] Example 2

[0081] A manufacturing process for high-strength and heavy-duty parts, the finished product is a flange fork, the shape of which is shown in Figure 1 , the preset forging shape is shown in Figure 3 , which includes the following process routes:

[0082] Cutting - homogenization heating - fine uniform crystal forging - double normalizing after forging + supercooling heat treatment + tempering + hydrogen expansion treatment - rough machining - quenching - tempering - sampling - sample processing - tensile test and Charpy impact test - test report - technical analysis.

[0083] Specifically, the forging process includes the following steps:

[0084] a. Homogenization heating process such as Figure 2 As shown, the steps include: heating to 550±10℃ according to power; heating to 850±10℃ at a rate of 60℃ / h, keeping warm for 6h; heating to 1270±10℃ according to power, keeping warm for 22h; furnace cooling, dropping to 1240±10℃, keeping warm for 7h; and forging. Ensure that the internal components and structure of the steel ingot are uniformly dispersed through high-temperature diffusion.

[0085] b. First firing: The temperature is 1220℃-900℃, and the riser removal, upsetting and compaction processes are carried out.

[0086] b. Second fire: temperature is 1250℃-900℃, according to the blank making drawing ( Figure 3 ) The preformed billet is forged by free forging.

[0087] c. The third fire: The temperature is 1150℃-850℃. The near-net-forming combined die is used to implement the near-net-forming and fine-grained forging forming process to effectively forge the internal defects of the material and control the grain size.

[0088] Furthermore, the post-forging double normalizing + supercooling heat treatment + tempering + hydrogen expansion treatment including hydrogen expansion process is as follows Figure 7 As shown, the specific steps include:

[0089] a. Primary normalizing: After the materials are prepared at 550℃ and the forgings are assembled, heat to 900℃ at a heating rate of ≤60℃ / h and keep warm for 10h;

[0090] b. Supercooling heat treatment: After coming out of the furnace, the forgings are pulled out with the trolley, and cooled to a surface temperature of 250°C by blowing with an industrial fan. Then the forgings and the trolley are pushed into the furnace and kept at a supercooling temperature of 280-320°C for 7 hours;

[0091] c. Secondary normalizing: heat to 870℃ at a rate of ≤60℃ / h, keep warm for 10h, then take out of the furnace and cool to 250℃ by air blowing;

[0092] d. High temperature tempering and hydrogen expansion: Then push it into the furnace, raise the temperature to 650℃ according to the power, temper and expand hydrogen, keep warm for 56h, then cool it to 400℃ at ≤40℃ / h, and then cool it to 250℃ at ≤30℃ / h before taking it out of the furnace.

[0093] After forging, double normalizing + tempering and hydrogen expansion treatment are used for grain refinement heat treatment at two different austenitizing temperatures.

[0094] By adjusting the beneficial elements that are beneficial to grain refinement and impact toughness improvement in terms of composition, reducing the five small harmful elements, and controlling the H, O, and N contents within a certain range, the mechanical performance requirements and grain size standards are met; designing near-net-shape forming molds, and rationally optimizing the draft angles α, β, and R arc of the mold cavity through finite element calculation and numerical simulation analysis, ensuring that the fine and uniform near-net-shape forming of the last fire makes the forgings in a uniform extrusion stress state, thereby effectively improving the stress state of the last fire forgings to be a compressive stress state; grain refinement heat treatment, using different higher austenitizing temperatures and different cooling methods, through two double positive tempering treatments at different austenitizing temperatures, to find the best heat treatment process parameters to obtain a grain size that meets the customer's technical requirements.

[0095] Among them, mechanical properties refer to the ability of metal materials to resist external forces.

[0096] Grain size refers to the scale that indicates the size of the grains of metal materials; it has a great influence on the mechanical properties and processing properties of metals. The smaller the grain, the higher the yield strength, and the better the plasticity and toughness.

[0097] Gross-to-net weight ratio: the ratio of the forging blank weight to the finished product weight.

[0098] Ultrasonic flaw detection: uses the propagation characteristics of ultrasound to detect defects in materials.

[0099] Magnetic particle testing: Utilizes the magnetization characteristics of ferromagnetic materials when subjected to a magnetic field to detect cracks and defects on the surface or near the surface of the material.

[0100] Machining time is the calculation of the final time and piece time of the machining process.

[0101] The mechanical properties of the forgings finally obtained in Example 1 after quenching and tempering meet the following requirements: σb (tensile strength) is 1350 MPa; σs (yield strength) is 1120 MPa, ψ (sectional reduction rate) is 61%; δ5 (elongation at break) is 18%; Ak(u) (impact energy) is 96 J.

[0102] Grain size: Grain size is related to deformation stress state and deformation amount. The overall austenite grain size reaches level 9, and the grain size difference is no more than level 2. Ultrasonic and magnetic particle inspection: The pass rate reaches 100%. Ultrasonic and magnetic particle inspection are related to the purity of the material. Gross-to-net weight ratio: The near-net forming process is related to the gross-to-net ratio. The weight of forgings of high-strength and tough heavy-load parts can save 25% of the material and reduce the machining time by 50%.

[0103] Example 3

[0104] A manufacturing process for a high-strength and tough heavy-duty part, wherein the finished product is a flange fork. The forming process is the same as that of Example 1, except that the steel used in the forging process is alloy structural quenched and tempered steel, which uses 33NiCrMoV14-5 steel.

[0105] The mechanical properties of the forgings after quenching and tempering meet the following requirements: σb is 1310MPa; σs is 1080MPa, ψ is 59%; δ5 is 18%; Ak(u) is 95J.

[0106] Grain size: the overall austenite grain size reaches 8.5, and the grain size difference is no more than 2 levels; ultrasonic and magnetic particle inspection: the qualified rate reaches 100%; gross to net weight ratio: the weight of forgings of high-strength and tough heavy-load parts is reduced by 26%, and the machining hours are reduced by 45%.

[0107] Example 4

[0108] A manufacturing process for a high-strength and heavy-duty part, the finished product of which is a flange fork, has the same components as those in Example 1, and the same forming process as those in Example 1, except that:

[0109] Austenitizing temperature 1 is 890°C, austenitizing temperature 2 is 860°C;

[0110] The steps of heat treatment after forging specifically include:

[0111] a. Primary normalizing: After the materials are prepared at 550℃ and the forgings are assembled, heat to the austenitizing temperature 1, 890℃, at a heating rate of ≤60℃ / h and keep warm for 10h;

[0112] b. Secondary normalizing: heat to austenitizing temperature 1, 860℃, at a heating rate of ≤60℃ / h, keep warm for 10h, then take out of the furnace and cool to 250℃ by air blowing;

[0113] c. Supercooling heat treatment: After coming out of the furnace, the forgings are pulled out with the trolley, and the forgings are cooled to a surface temperature of 250°C by blowing with an industrial fan. Then the forgings and the trolley are pushed into the furnace and kept at a supercooling temperature of 280°C for 7 hours.

[0114] d. Tempering and hydrogen expansion: Then push it into the furnace, raise the temperature to 650℃ according to the power, temper and expand the hydrogen, keep it warm for 56h, then cool it to 400℃ at ≤40℃ / h, and then cool it to 250℃ at ≤30℃ / h before taking it out of the furnace.

[0115] The mechanical properties of the final forgings after quenching and tempering meet the following requirements: σb is 1290MPa; σs is 1090MPa, ψ is 58%; δ5 is 19%; Ak(u) is 92J.

[0116] Grain size: Grain size is related to deformation stress state and deformation amount. The overall austenite grain size reaches 8.5, and the grain size difference is no more than 2 levels. Ultrasonic and magnetic particle inspection: The pass rate reaches 100%. Ultrasonic and magnetic particle inspection are related to the purity of the material. Gross-to-net weight ratio: The near-net forming process is related to the gross-to-net ratio. The weight of forgings of high-strength and tough heavy-load parts can save 24% of material and reduce machining hours by 52%.

[0117] Example 5

[0118] A manufacturing process for high-strength and tough heavy-duty parts, wherein the finished products are other heavy-duty parts other than flange forks. The fine uniform crystal forging forming step is performed in a fine uniform crystal extrusion near-net-shape forming die. The design of the fine uniform crystal extrusion near-net-shape forming die is based on the shape of the heavy-duty parts. Through finite element analysis and simulation, the forming process is simulated, the stress distribution state of the formed parts is analyzed, the extrusion pressure is calculated, the die structure is optimized, and the lubrication method is determined according to the simulated friction coefficient to obtain a blank shape with low deformation resistance and the best filling property.

[0119] Comparative Example 1

[0120] A manufacturing process for high-strength and tough heavy-load parts is compared with the original free forging process, and the difference is that the finished product is made by the free forging process.

[0121] Table 2 Comparison of mechanical properties of forgings of Example 1 and Comparative Example 1

[0122]

[0123] Among the forgings produced:

[0124] Grain size comparison: the grain size of the forgings made by the free forging process is ≥6, with mixed crystals; the grain size of the forgings made by the near-net forming process of the present invention is ≥8, with uniform grains and no mixed crystals;

[0125] Comparison of ultrasonic and magnetic particle inspection pass rates: the pass rate of forgings made by free forging process is 99.1%; the pass rate of forgings made by the near-net-shape forming process of the present invention is 99.8%;

[0126] Gross-to-net weight ratio: the gross-to-net weight ratio of the forgings made by the free forging process is 3; the gross-to-net weight ratio of the forgings made by the near-net forming process of the present invention is 2.2;

[0127] Processing time: The near-net-shape forming process of the present invention reduces the machining time by 45%.

[0128] The invention rationalizes the element range of grain refinement, controls harmful elements, controls the contents of O and H within 20ppm and 1.7ppm, and completes composition optimization; performs a near-net forming fine uniform crystal near-net forming process on a workpiece blank through a near-net forming combined die, so that the entire outer surface, inner hole and the inside of the material are in a uniform compressive stress state, which is conducive to fully forging the internal defects generated in the blank making stage and ensures that the flaw detection meets the technical requirements; and then performs a grain refinement heat treatment through austenitization double normal tempering treatment twice, which ensures the refinement of the organization and improves the qualified rate of finished products.

[0129] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0130] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A manufacturing process for high-strength and tough heavy-duty parts, comprising the steps of: material cutting - homogenization heating - fine uniform crystal forging - post-forging heat treatment to obtain forgings, characterized in that: The fine uniform crystal forging step is performed in a near net shape die so that the stress distribution on the forging surface is uniform; The near-net-shape forming die comprises an upper die seat, a lower die seat and a center punch. The upper die seat is arranged above the lower die seat, and the bottom is fitted with the lower die seat. An upwardly protruding center punch is provided in the center of the lower die seat, and a space for accommodating the preform is formed between the inner cavity of the upper die seat and the center punch of the lower die seat. The center punch is arranged above the upper die seat and is used to extrude the preform downward.

2. The manufacturing process according to claim 1, characterized in that: The heavy-loaded part is a flange fork, and the parameters of the near-net-shape forming mold satisfy α=2°-3°, β=5°-6°, and the R arc is 45-50mm, wherein α is the draft angle of the inner wall of the upper die seat, β is the draft angle of the center punch of the lower die seat, and R is the ball head radius of the center punch of the lower die seat.

3. The manufacturing process according to claim 1, characterized in that: The homogenization heating process comprises the following steps: heating to 550±10°C and keeping the temperature for 3 hours; heating to 850±10°C and keeping the temperature for 6 hours; heating to a homogenization heating temperature of 1260-1280°C and keeping the temperature for 22 hours; furnace cooling, dropping to 1240±10°C and keeping the temperature for 7 hours; and forging.

4. The manufacturing process according to claim 1, characterized in that: The fine uniform crystal forging forming step comprises: a. First firing: The temperature is 1220℃-900℃, and the riser removal, upsetting and compaction processes are carried out; b. Second fire: the temperature is 1250℃-900℃, forging the prefabricated blank; c. The third fire: the temperature is 1150℃-850℃, and the near-net-shape forming mold is used to implement uniform fine-grained near-net-shape forming.

5. The manufacturing process according to claim 1, characterized in that: The post-forging heat treatment adopts a double normalizing-supercooling heat treatment+high temperature tempering and hydrogen expansion method, which specifically includes the following steps: a. Primary normalizing: After the materials are prepared at 550℃ and the forgings are assembled, heat to 890-910℃ at a heating rate of ≤60℃ / h and keep warm for 10h; b. Secondary normalizing: heat to 860-880℃ at a heating rate of ≤60℃ / h and keep warm for 10h; c. Supercooling heat treatment: After leaving the furnace, the forgings are air-cooled to a surface temperature of 250°C, and then pushed into the furnace and kept at a supercooling temperature of 280-320°C for 7 hours; d. Tempering and hydrogen expansion: Heat to 650℃ according to power, temper and expand hydrogen, keep warm for 56h, then furnace cool to 400℃ at ≤40℃ / h, then furnace cool to 250℃ at ≤30℃ / h before taking out of the furnace.

6. A die for near net-forming of forgings, characterized in that: It includes an upper die seat, a lower die seat and a center punch. The upper die seat is arranged above the lower die seat, and the bottom is in contact with the lower die seat. A center punch protruding upward is provided in the center of the lower die seat, and a space for accommodating the prefabricated blank is formed between the inner cavity of the upper die seat and the center punch of the lower die seat. The center punch is arranged above the upper die seat and is used to extrude the prefabricated blank downward.

7. The mold according to claim 6, characterized in that: The mold parameters satisfy α=2°-3°, β=5°-6°, and the R arc is 45-50mm, wherein α is the draft angle of the inner wall of the upper mold base, β is the draft angle of the center punch of the lower mold base, and R is the ball head radius of the center punch of the lower mold base.

8. A heavy-duty part manufactured by the manufacturing process according to any one of claims 1 to 5, characterized in that: Mechanical indicators of heavy-loaded parts: σb ≥ 1200MPa; σs ≥ 1000MPa, ψ ≥ 55%; δ5 ≥ 10%; Ak (u) ≥ 70J.

9. The heavy-duty component according to claim 8, characterized in that: The austenite grain size of the heavy-duty parts as a whole reaches above grade 8, and the grain size difference is no more than grade 2; the ultrasonic and magnetic particle flaw detection pass rate reaches 100%.

Images