A method for die forging high-strength train binding hooks

Abstract

This invention relates to the field of forging and processing technology for railway ferry components, and discloses a high-strength train binding hook die forging method. This method uses 40Cr steel as the forging billet, employs a three-stage stepped heating process, and utilizes an inert gas atmosphere throughout the heating process to ensure uniform and stable internal metallographic structure of the billet. A continuous die forging process is used to achieve high-precision forming of irregularly shaped components. High-temperature edge trimming is performed using the residual heat of the workpiece after die forging, avoiding defects such as tearing, burrs, and stress concentration caused by cold trimming at room temperature. A slow cooling process in an insulated box is used after forging to effectively suppress cracking and distortion of the forging. The workpiece undergoes normalizing and tempering heat treatment sequentially to obtain excellent comprehensive mechanical properties. This invention solves the problems of poor dimensional accuracy, large fluctuations in mechanical properties, and low finished product qualification rate in traditional processes. The prepared binding hooks exhibit excellent assembly reliability, high production efficiency, and good product quality consistency, making them suitable for stable, large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of forging and processing technology for railway ferry components, specifically to a method for die forging high-strength train binding hooks. Background Technology

[0002] The train lashing hook is the main load-bearing component for securing the train ferry. One end of it fits tightly with the root of the channel steel of the train side beam 1, and the other end is connected to the lashing chain 3 via a pin (e.g., Figure 2 As shown in the figure, the lashing device can securely tighten the train carriages when they experience lateral or longitudinal movement during navigation, and transfer the external force to the deck through the lashing device. Therefore, there are strict requirements for the structural precision, strength, hardness, and contact area of ​​the components.

[0003] Currently, train binding hooks are generally made of 40Cr high-strength alloy steel. The finished products must meet the forging quality standards, with a hardness of HRC33-38 after heat treatment, a safe working load of not less than 100kN, and a minimum breaking load of not less than 200kN. At the same time, because its head needs to be precisely matched with the special shape of the root of the channel steel of the train's side beam, extremely high requirements are also placed on the dimensional accuracy and surface quality of the forging.

[0004] When existing high-strength steel forging processes are applied to this binding hook, the following problems exist: (1) Conventional forging has low billet forming accuracy, especially the poor fit between the hook part irregular structure and the root of the train side beam channel steel. After forging, it needs to be machined, resulting in low production efficiency and high processing cost. (2) Problems such as uneven internal structure and coarse grains are prone to occur during the forging process, which affect the overall strength of the parts and cannot meet the load requirements of train binding; (3) The connection between forging and subsequent heat treatment and finishing processes is not reasonable, resulting in poor dimensional stability of binding hooks, uneven hardness distribution, and some forgings have problems with burrs and flash not being thoroughly treated, which affects the actual assembly and use effect.

[0005] Therefore, there is an urgent need to develop a high-strength train binding hook die forging method to effectively solve the problems of low forming accuracy, unstable mechanical properties, low production efficiency and low finished product qualification rate in the existing technology, so as to comprehensively improve the quality and reliability of train binding hooks and meet the urgent needs of railway ferry transportation safety. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-strength train lashing hook die forging method, which solves the problems of low forming accuracy, unstable mechanical properties, low production efficiency and low finished product qualification rate of the existing process, realizes high-precision and high-strength forming of lashing hooks, optimizes the process flow, improves product quality stability and production efficiency, and meets the usage requirements of train ferry lashing and securing.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a high-strength train binding hook die forging method, wherein the binding hook uses 40Cr steel as the blank, comprising the following steps: S1. The billet is heated in three stages, and inert gas is introduced for protection during the heating process. S2. First, pre-forge the heated billet to initially form the overall outline of the binding hook. Then, while the billet temperature is still within the optimal forging temperature range, perform final forging to form the complete structure of the binding hook in one go. S3. Use the residual heat of die forging to cut the edges at high temperature; S4. After the flash is punched out, the forging is cooled to room temperature in an insulated box, and then the cut edges of the forging are ground. S5. Inspect the appearance, dimensions and internal quality of the polished forgings. S6. Forgings that pass inspection shall be normalized first. S7. After the forging is normalized, it is then machined and drilled. S8. Perform quenching and tempering heat treatment on the forgings after drilling; S9. The product after heat treatment is shot blasted to obtain the finished product, and then the finished product is inspected.

[0008] Optionally, the three-stage stepped heating includes the following steps: S11. Heat from room temperature to 400℃ at a heating rate of 80℃ / h, and hold for 1h. S12. Heat from 400℃ to 850℃ at a heating rate of 100℃ / h, and hold for 1.5h. S13. Heat from 850℃ to 1180℃ at a heating rate of 120℃ / h, and hold for 2 hours.

[0009] Optionally, the pre-forging mold cavity is enlarged by 8%-10% according to the linear dimension of the finished hook outline to reserve machining allowance, and the pre-forging pressure is 800-900MPa.

[0010] Optionally, the final forging temperature is maintained at 850-950℃, and the final forging pressure is 1000-1100MPa.

[0011] Optionally, the temperature of the forging is 700-850℃ when punching the flash, the pressure for punching the flash is 500-600MPa, and the surface roughness Ra of the cut edge of the forging is ≤25μm.

[0012] Optionally, when using the slow cooling method of the insulation box, the thickness of the insulation sand inside the insulation box shall not be less than 100mm.

[0013] Optionally, during the normalizing process, the forging is heated to 860-880℃, held at that temperature for 2 hours, and then air-cooled to room temperature.

[0014] Optionally, the connecting holes can be machined after the forging has been normalized.

[0015] Optionally, during the quenching and tempering heat treatment, the drilled forging is first heated to 840-860℃, held for 1.5 hours, and then oil-cooled to complete the quenching treatment. The quenched forging is then heated to 520-540℃, held for 3 hours, and then air-cooled to room temperature to complete the tempering treatment.

[0016] Optionally, after the tempering heat treatment, the product is shot blasted to make the product surface meet the Sa2.5 requirement, and the finished product inspection includes dimensional accuracy, surface quality, and hardness testing.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention employs a staged die forging process that includes pre-forging and final forging, allowing the metal material to initially flow and form during the pre-forging stage and precisely fill the cavity during the final forging stage. This effectively solves the problem of difficulty in forming complex irregular structures in one step and significantly improves the forming accuracy of the hook mating surface. The pre-forging and final forging are carried out continuously within the optimal forging temperature range, avoiding structural changes and oxidation defects caused by secondary heating, and ensuring the continuity of metal flow and forming quality. High-temperature edge trimming using residual heat from die forging can significantly reduce flash hardness and edge trimming resistance, making the trimmed surface smoother. This effectively avoids microcracks and step defects that are easily generated by room temperature cold trimming, and improves the surface quality and fatigue life of the product. (2) In this invention, the final binding hook fits tightly with the root of the channel steel of the train side beam. It can be directly assembled without additional repair, which effectively avoids the stress concentration problem caused by excessive fitting gap. At the same time, it greatly reduces the subsequent finishing allowance, significantly improves the material utilization rate, and reduces the production cost. (3) In this invention, the three-stage stepped heating process can gradually eliminate the internal stress generated in the billet during rolling and blanking, so that the temperature inside and outside of the billet is evenly distributed, ensuring sufficient austenitization and fine grains, providing a good microstructure for subsequent forging. During the heating process, an inert gas is introduced to form a positive pressure protective atmosphere, which effectively prevents oxidation and decarburization reactions on the surface of the billet, avoiding the problems of reduced surface hardness and performance degradation; (4) In this invention, the slow cooling process of the heat preservation box with controllable rate is adopted, which enables the forging to cool slowly and evenly, effectively avoiding the quenching cracks and deformations that are easily generated by the rapid cooling of 40Cr steel due to its good hardenability, and ensuring the dimensional stability and internal structure uniformity of the forging. (5) In this invention, through the composite heat treatment process of normalizing and tempering, normalizing can further refine the coarse grains generated during forging, uniform structure, and eliminate residual stress; tempering can enable the forging to obtain uniform and stable hardness and good strength and toughness matching, meet the strength and load requirements of train binding hooks, and eliminate safety hazards. (6) In this invention, the process parameters of the whole process are optimized in a coordinated manner, the connection between each process is smooth, the intermediate waiting time and repetitive operation are reduced, and the production efficiency is effectively improved. After the forging is completed, the appearance, size and internal quality of the forging are fully inspected, which can remove defective products with defects in advance and avoid the waste of manpower and material resources caused by defective products flowing into subsequent processes. Moreover, the systematic process optimization greatly improves the consistency of product quality and significantly improves the finished product qualification rate, which can well meet the needs of industrial mass production. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of the high-strength train binding hook die forging method in an embodiment of the present invention; Figure 2 This is a schematic diagram of the existing technology for securing trains with lashing hooks; Figure 3 This is a schematic diagram of the structure of a train lashing hook in the existing technology; Figure 4 This is a blank drawing of the binding hook produced using this method in an embodiment of the present invention; Figure 5 This is a product image of a binding hook manufactured using this method in an embodiment of the present invention; Among them, 1. Train side beam; 2. Binding hook; 21. Connecting hole; 22. Force-bearing surface; 3. Binding chain. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. These drawings are simplified schematic diagrams, which are only used to illustrate the basic structure of the present invention and therefore only show the components relevant to the present invention.

[0020] Example 1, as Figures 1-5As shown, this embodiment provides a high-strength train binding hook die forging method. The binding hook 2 is made of 40Cr high-strength alloy steel conforming to national standards and is specifically used for securing train carriages during train ferry transportation. The entire production process is completed in a standardized forging workshop, and the equipment used is all conventional and general-purpose equipment in the forging industry, requiring no special customization and directly adaptable to existing industrial production lines. The specific implementation steps include: raw material blanking, billet heating, die forging, high-temperature trimming using the residual heat of die forging, grinding after cooling, forging inspection, drilling after normalizing treatment, quenching and tempering heat treatment, and finished product inspection.

[0021] Raw material preparation: First, incoming raw materials undergo inspection. The chemical composition of 40Cr round steel is analyzed using a spectrometer, and its mechanical properties are tested using a tensile testing machine to confirm compliance with the national standard GB / T3077-2015. The surface quality of each round steel bar is inspected, and unqualified raw materials with defects such as surface cracks, inclusions, scabs, and folds are rejected.

[0022] Based on the finished net weight of the binding hook 2 and material losses such as flash and burning during the forging process, a reasonable blanking size is calculated and determined. A CNC saw is used for blanking, with strict control over the sawing feed speed and saw blade rotation speed to ensure a flat end face of the blank, free from beveling, chipping, and burrs. Each blank is weighed after blanking to control the weight error within a predetermined range, ensuring that the metal material can fully fill the mold cavity during subsequent forging, while avoiding material waste.

[0023] The weighed and qualified billets are neatly stacked on a special material rack, and batch labels are made, indicating information such as raw material specifications, furnace number, and feeding date, before they are ready to enter the next process.

[0024] Billet heating: The neatly stacked billets are loaded into the trolley-type heating furnace in batches. A three-stage stepped heating process is used to heat the billets. During the heating process, argon gas is continuously introduced into the furnace for protection, maintaining positive pressure inside the furnace and preventing air from entering and causing the billets to oxidize and decarburize. The heating process is divided into three stages.

[0025] The first stage is the low-temperature preheating stage, in which the billet is slowly heated from room temperature to 400℃ at a controlled heating rate of 80℃ / h, and then held at that temperature for 1 hour. The main purpose of this stage is to gradually eliminate the internal stress generated in the billet during rolling and blanking, and to prevent the billet from developing hot cracks due to rapid heating.

[0026] The second stage is the medium-temperature homogenization stage, where the billet is heated to 850℃ at a rate of 100℃ / h and held at that temperature for 1.5 hours. The main purpose of this stage is to ensure that the internal and external temperatures of the billet are uniform, preparing it for subsequent high-temperature austenitization and preventing uneven deformation due to excessive internal and external temperature differences.

[0027] The third stage is the high-temperature austenitizing stage, in which the billet is heated to 1180℃ at a heating rate of 120℃ / h and held at that temperature for 2 hours. The main purpose of this stage is to fully austenitize the internal structure of the billet, obtain good plastic deformation capacity, and ensure that the metal can flow smoothly and fill the cavity during the forging process.

[0028] After heating is complete, check through the furnace door inspection hole to confirm that the billet has a uniform color and no localized overheating or underheating. It is then ready for forging. After exiting the furnace, the billet should be quickly transferred to the forging station to minimize its time in the air and prevent excessive temperature drop.

[0029] The die forging process is completed on a hot die forging press. The pre-forging die and the final forging die are installed on two stations of the press, respectively, to achieve continuous operation of pre-forging and final forging.

[0030] First, a pre-forging process is performed. The heated billet is quickly removed from the heating furnace and accurately placed into the lower cavity of the pre-forging die, ensuring that the billet is centered and without deviation. The hot forging press is started, and the billet is pre-forged at a pressure of 800-900 MPa. The cavity of the pre-forging die is enlarged by 8%-10% according to the linear dimensions of the finished outline of the binding hook 2, with a machining allowance. The cavity design adopts a smooth transition to avoid sharp corners and abrupt changes, allowing the metal material to flow initially under relatively small deformation forces, forming the overall outline of the binding hook 2, especially the complex irregular structure of the hook part matching the root of the channel steel of the train side beam 1. After pre-forging is completed, the press slide returns, and the operator uses a special fixture to remove the pre-forged billet from the pre-forging die.

[0031] Next comes the final forging process. The pre-forged billet is immediately and accurately placed into the lower cavity of the final forging die (ensuring the billet temperature is still within the optimal forging temperature range), ensuring accurate billet positioning. The hot forging press is started, and the billet is forged at a pressure of 1000-1100 MPa to ensure that the metal material fully fills all corners of the cavity, forming the complete structure of the binding hook 2 in one go, including all arc transition parts and mating surfaces. During the final forging process, the billet temperature is strictly controlled to ensure that the final forging temperature is maintained within the optimal forging temperature range of 850-950℃. This avoids cracks or incomplete forming in the forging due to excessively low temperature, and also avoids coarse grains due to excessively high temperature. After the final forging is completed, the press slide returns, removing the forged part from the final forging die.

[0032] The forging process utilizes the residual heat of the die forging process to trim the edges. After final forging, the forging has a ring of flash at the parting surface, which needs to be trimmed. After the final forging is naturally cooled to the predetermined temperature range of 700-850℃, it is quickly transferred to a 630T trimming press, where a special trimming die is used to punch away the flash and burrs.

[0033] As described above, utilizing the residual heat from die forging for high-temperature trimming significantly reduces the hardness and trimming resistance of the flash, making the trimming process smoother and the trimmed surface flatter. It also effectively avoids the trimming cracks and step defects that are prone to occur during room temperature cold trimming. The pressure for punching the flash is controlled at 500-600 MPa to ensure that the flash is completely punched away without residue.

[0034] After cooling and grinding, and after punching, the forgings are removed from the trimming die and promptly transferred to the cooling area for slow cooling in an insulated box. A layer of dry quartz sand at least 100mm thick is laid in advance as insulating sand inside a dedicated insulated box. The forgings are placed on the insulating sand, and then the box lid is closed to prevent excessive cooling. Furthermore, to facilitate mass production, products placed in the insulated box can be stacked without spacing restrictions. The covered insulated box provides slow cooling and is easy to operate. Products in the insulated box can be stacked, allowing them to come into contact with each other.

[0035] By controlling the thickness of the insulating sand and the density of the forgings, the forgings are slowly cooled to room temperature. This cooling method effectively avoids quenching cracks and deformation caused by rapid cooling of 40Cr steel, ensuring the dimensional stability and internal uniformity of the forgings. During the cooling process, it is strictly forbidden to spray water or blow air onto the forgings to prevent defects caused by localized rapid cooling. The cooling time is generally no less than 12 hours; the forgings can only be removed from the insulating box after they have completely cooled to room temperature.

[0036] After the forging has completely cooled to room temperature, remove it from the insulation box, clean off the surface of the insulating sand, and then use a hand-held grinder to grind the cut edges and the hook-shaped stress surface 22. Focus on grinding the cut edges and smooth areas as required by the drawing, removing any remaining burrs and cutting marks, ensuring that the surface is free of obvious steps, sharp edges, and burrs, and that the surface roughness meets the requirements. During grinding, carefully control the grinding force and direction to avoid over-grinding that could cause the forging to exceed dimensional tolerances, and also take care to protect the mating surfaces of the forging.

[0037] Grinding of the hook bearing surface 22: A grinding wheel and polishing machine are used to finely grind the bearing surface 22, which mates with the root of the channel steel of the train side beam, to remove surface oxide scale and cutting edge defects, ensuring that the bearing surface 22 is flat and smooth and the contact area meets the design requirements. During the grinding process, care should be taken to protect other surfaces of the forging to avoid scratches.

[0038] Forging inspection includes three parts: visual inspection, dimensional inspection, and internal quality inspection. Detailed records must be kept for all inspections.

[0039] Visual inspection: Each forging is inspected for defects such as cracks, shrinkage cavities, porosity, heavy scale, folds, and overheating using visual inspection and a 5x magnifying glass. Any forging found to have any of the above defects is deemed unqualified and is rejected.

[0040] Dimensional Inspection: Using general measuring tools such as vernier calipers and radius gauges, as well as specialized inspection tools, the outline dimensions, part dimensions, and dimensions of irregularly shaped arc sections of forgings are measured piece by piece to ensure that dimensional deviations are within allowable ranges. For batch-produced forgings, sampling inspection is used to monitor dimensional stability. When inspecting the dimensions of forgings, a deviation of ±1mm for the outline dimensions and ±0.5mm for irregularly shaped arc sections is considered acceptable.

[0041] Internal quality inspection: Ultrasonic flaw detectors are used to inspect the forgings for internal quality defects such as internal cracks, inclusions, and porosity. The flaw detection standards are in accordance with relevant national standards; forgings with defects exceeding the standards are deemed unqualified and rejected.

[0042] Only forgings that pass all three inspections can proceed to the next heat treatment process. Defective products are isolated and disposed of according to the defective product handling procedure and are strictly prohibited from entering subsequent processes.

[0043] After normalizing, drilling is performed. First, the forgings that pass inspection are normalized. The forgings are neatly arranged on the rack of the heat treatment furnace, maintaining appropriate spacing between them to ensure uniform furnace gas flow. The furnace temperature is heated to 860-880℃ and held for 2 hours. After holding, the forgings are removed from the furnace and allowed to cool naturally to room temperature in still air. Normalizing effectively refines the coarse grains generated during forging, homogenizes the microstructure, eliminates residual forging stress, improves the machinability of the forgings, and prepares the microstructure for subsequent quenching treatment.

[0044] Re-machining of connecting hole 21: The connecting hole 21 on the forging is drilled using a CNC drilling machine. During the machining process, the dimensional accuracy, positional accuracy and surface roughness of the hole are strictly controlled.

[0045] Tempering heat treatment: The required hardness and good strength-toughness are obtained through tempering heat treatment. The heat treatment process is carried out in a box-type resistance furnace. The furnace temperature uniformity and holding time are strictly controlled during the heat treatment process.

[0046] During the quenching and tempering heat treatment process, the drilled forgings are first placed back into the heat treatment furnace and heated to 840-860℃, then held for 1.5 hours. After holding, the forgings are quickly removed from the furnace and immersed in quenching oil for rapid cooling to obtain higher hardness. During quenching, care must be taken to control the oil temperature and stirring speed to ensure uniform cooling of the forgings and avoid quenching cracks and deformation.

[0047] The quenched forgings should be tempered promptly, generally within 4 hours. Place the quenched forgings in a tempering furnace and heat to 520-540℃, holding for 3 hours. After holding, remove the forgings from the furnace and allow them to cool naturally to room temperature in air. Tempering eliminates internal stresses generated during quenching, adjusts the hardness and toughness of the forgings, and gives them uniform and stable mechanical properties.

[0048] After heat treatment, the forgings undergo random hardness testing. A Rockwell hardness tester is used to measure the hardness at different locations on the forgings to ensure that the hardness meets design requirements. Forgings that fail to meet hardness standards should be re-heat treated. Furthermore, after tempering, the products must be shot-blasted to achieve a surface hardness of Sa2.5, thus removing rust.

[0049] Finished Product Inspection: A final inspection is conducted on heat-treated forgings to ensure they meet end-use requirements. In addition to visual inspection, dimensional inspection, and hardness testing, the inspection may include a fit test between the hook and the root of the channel steel of the train side beam 1. The binding hook 2 is assembled with a standard train side beam channel steel sample, and a feeler gauge is used to check the fit clearance, ensuring it is uniform, tight, and free from looseness or jamming. Only products that pass all inspection items are considered qualified finished products.

[0050] The addition of a fitting inspection between the hook and the root of the channel steel of the train side beam during finished product inspection ensures product quality from the perspective of final use, guaranteeing that every finished product meets assembly and usage requirements. All qualified finished products undergo rust prevention treatment and packaging according to regulations, and are labeled with product model, batch number, production date, and other information before being stored in the warehouse.

[0051] The equipment used in this invention, such as the bogie-type heating furnace, hot forging press, trimming press, and CNC drilling machine, are all conventional and commonly used equipment in the forging industry. They require no special customization and can be directly adapted to existing industrial production lines, resulting in low modification costs. All process steps and parameters are clearly defined and standardized, making operation simple. Workers can master the techniques after short-term training, facilitating quality control and standardized management during production. Furthermore, the binding hook 2 forged in this invention can be directly used with existing train side beams 1 and binding devices without requiring any additional accessories on the train. Assembly is convenient, and the external force transmission effect is excellent.

[0052] Example 2: This example uses the 3.1kg grade 40Cr high-strength train binding hook 2 for railway ferries as the production object. The equipment used is all conventional general-purpose equipment in the forging industry and does not require special customization.

[0053] Raw material preparation and cutting: φ50mm×6000mm 40Cr hot-rolled round steel conforming to GB / T3077-2015 standard is used as the billet. Based on the finished net weight of 3.1kg for binding hook 2, and considering the forging flash loss and burning loss, the weight of a single billet is calculated to be 3.63kg, corresponding to a cutting length of 235mm. A GZK4232 CNC metal band saw is used for cutting.

[0054] Three-stage stepped heating and inert gas protection: An RT3-180-12 trolley-type heating furnace is used, with 120 billets loaded per batch. Argon gas is continuously introduced during the heating process, and the pressure inside the furnace is controlled at 50-80Pa positive pressure to prevent oxidation and decarburization of the billets.

[0055] Low-temperature preheating stage: Heat from room temperature to 400℃ at a rate of 80℃ / h, hold for 1 hour, and gradually eliminate the internal stress generated during billet rolling and blanking; Medium-temperature homogenization stage: Heat to 850℃ at a rate of 100℃ / h, hold for 1.5h, and use an infrared thermometer to detect multiple points to ensure that the temperature difference between the inside and outside of the billet is ≤20℃; High-temperature austenitizing stage: The temperature is increased to 1180℃ at a rate of 120℃ / h and held for 2 hours to fully austenitize the internal structure of the billet.

[0056] After heating, confirm that the billet is uniformly bright yellow and there is no local overheating or underheating. Use a special high-temperature resistant fixture to quickly transfer it to the forging station to ensure that the initial pre-forging temperature is ≥1150℃.

[0057] Continuous forging in stages: The forging process is completed on the MP-1600 hot forging press, equipped with a dual-station die mounting platform, to realize continuous operation of pre-forging and final forging.

[0058] Die preparation: The pre-forging die cavity is enlarged by 9% according to the linear dimension of the finished product outline of the binding hook 2, with a machining allowance. All corners are smoothly transitioned with R5-R8mm. Before forging, the die is preheated to 250-300℃ and coated with graphite-based release agent.

[0059] Pre-forging process: The heated and qualified billet is accurately placed into the center of the lower mold cavity of the pre-forging die, and pre-forged in one step with a unit pressure of 850MPa to initially form the overall outline of the binding hook 2. After pre-forging is completed, a pneumatic clamp is used to quickly transfer the pre-forged billet to the final forging station.

[0060] Final forging process: Final forging is performed at a unit pressure of 1050MPa, with a holding time of 0.5 seconds, to ensure that the metal material fully fills the cavity. The final forging temperature is monitored in real time to ensure that it remains stable within the optimal forging temperature range of 880-920℃. One piece out of every 50 pieces produced is randomly selected for appearance inspection to ensure that there are no defects such as cracks, folds, or missing material, and that the flash thickness is uniformly 1.5-2mm.

[0061] High-temperature trimming using residual heat: After final forging, the forging is naturally cooled to 750℃ and immediately transferred to a J31-630T closed-type single-point trimming press. A combined trimming die (0.3mm gap between punch and die) is used for flash trimming, with a trimming pressure of 550MPa. High-temperature trimming using residual heat from die forging results in flash hardness of only HB180-200, and the trimmed edge is smooth and flat, without tearing, steps, or microcracks.

[0062] Slow cooling and grinding in an insulated box: After punching, the forgings are transferred to a special insulated box with dimensions of 5m × 3m × 1.5m, and the box is lined with 150mm thick dry quartz sand. After the forgings are placed, the lid of the insulated box is closed, and then the forgings are cooled to room temperature.

[0063] After the forging has cooled, use an M1040 hand-held grinder to grind the cut edges, and use a 120-grit grinding wheel to rough grind away any residual burrs to ensure a smooth surface.

[0064] Comprehensive quality inspection of forgings: All ground forgings must pass the following three inspections before proceeding to the next process: Visual inspection: Each piece is inspected visually and with a 5x magnifying glass to remove forgings with defects such as cracks, shrinkage cavities, porosity, double scale, folds, and overheating. Dimensional inspection: Use calipers, angle gauges, radius gauges and other inspection tools to inspect the dimensions. The overall outline dimension deviation should be ≤ ±0.8mm, the deviation of the irregular arc part of the hook should be ≤ ±0.4mm, and the straightness of the rod should be ≤ 0.3mm / m. Internal quality inspection: Use a CTS-22 ultrasonic flaw detector to perform flaw detection according to GB / T6402-2008 standard Class II, and reject forgings with internal defects exceeding the standard.

[0065] Normalizing treatment and machining of connecting hole 21: Normalizing was performed using an RX3-120-9 box-type resistance furnace. The forgings were neatly arranged on the rack (100mm spacing), heated to 870℃, held for 2 hours, and then removed from the furnace and allowed to cool naturally to room temperature in still air. After normalizing, the hardness of the forgings was HB200-230, and the residual stress was ≤80MPa.

[0066] The φ20mm connecting hole 21 at the tail of the binding hook 2 is machined using a ZK5140 CNC drilling machine: drill with a φ20mm high-speed steel drill bit (rotation speed 800r / min, feed rate 0.15mm / r), and finally use a special chamfering cutter to chamfer the hole opening with R0.5mm.

[0067] The quenching and tempering heat treatment and surface treatment were carried out in the RX3-120-8 quenching furnace and the RX3-120-6 tempering furnace. Quenching treatment: After drilling, the forging is heated to 850℃ and held at that temperature for 1.5 hours. Then, it is quickly immersed in No. 20 machine oil for cooling. The oil temperature is controlled at 40-60℃, and the stirring speed in the oil bath is 0.5m / s. The hardness of the forging after quenching is HRC45-50. Tempering treatment: After quenching, the forgings are transferred to a tempering furnace within 4 hours, heated to 530°C, held for 3 hours, and then air-cooled to room temperature.

[0068] One piece out of every 20 pieces was randomly selected for hardness testing. Three points were measured at the hook, rod, and tail of the forging, and the hardness value was stable at HRC33-36, which meets the design requirements.

[0069] The surface treatment is carried out using a Q326 shot blasting machine with 0.8mm diameter cast steel shot, blasting time of 15 minutes, and shot blasting intensity of 0.3A, so that the rust removal grade of the product surface reaches Sa2.5 level.

[0070] Final inspection and warehousing of finished products: Appearance and dimensional re-inspection: Confirm that there is no damage caused during transportation and handling, and that key dimensions meet the requirements; Hardness retest: Hardness is tested on each piece to ensure uniformity and stability; Fit test: Use standard No. 14 train side beam channel steel sample for assembly. Use a 0.02mm feeler gauge to check the fit clearance. The clearance should be ≤0.2mm, the fit should be tight, and there should be no looseness or jamming. Sampling mechanical property test: Three finished products were randomly selected from each batch for tensile test and breaking load test. The results showed that the tensile strength was ≥1020MPa, the yield strength was ≥820MPa, the elongation was ≥14%, the impact energy (Akv) was ≥52J, and the minimum breaking load was ≥220kN.

[0071] After passing inspection, the finished products are coated with anti-rust primer, individually packaged with vapor phase anti-rust paper, placed in standard cartons, and labeled with the product model, specifications, quantity, furnace number, production date, and inspector code before being stored in the warehouse.

[0072] This invention, through synergistic optimization of various process steps, significantly improves the finished product qualification rate, shortens the production cycle, and extends fatigue life compared to traditional forging processes. The produced binding hook 2 fits tightly to the root of the channel steel of the train side beam 1, allowing for direct assembly without additional repairs. It has been successfully applied to multiple railway ferry lines, demonstrating stable and reliable performance.

[0073] In summary, the high-strength train binding hook die forging method proposed in this invention achieves a synergistic effect through the organic combination and interaction of various process steps. Step heating provides uniform and qualified billets for graded die forging, which ensures high-precision forming. High-temperature edge trimming utilizes residual heat from die forging to optimize subsequent processes. Box cooling prevents forging deformation and cracking. Composite heat treatment ultimately endows the forging with excellent mechanical properties, and a dual quality control system ensures product quality throughout the entire process. This synergistic effect enables the technical solution of this invention to achieve optimal comprehensive performance in terms of precision, strength, efficiency, and cost while solving existing technical problems, thus comprehensively improving the quality and reliability of the train binding hook 2.

[0074] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many improvements and modifications under the guidance of the present invention without departing from the spirit and scope of the claims. These improvements and modifications should also be considered within the scope of protection of the present invention.

[0075] In the description of this invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0076] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0077] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

Claims

1. A method for die-forging high-strength train binding hooks, wherein the binding hooks are made of 40Cr steel as the blank, characterized in that... Includes the following steps: S1. The billet is heated in three stages, and inert gas is introduced for protection during the heating process. S2. First, pre-forge the heated billet to initially form the overall outline of the binding hook. Then, while the billet temperature is still within the optimal forging temperature range, perform final forging to form the complete structure of the binding hook in one go. S3. Use the residual heat of die forging to cut the edges at high temperature; S4. After the flash is punched out, the forging is cooled to room temperature in an insulated box, and then the cut edges of the forging are ground. S5. Inspect the appearance, dimensions and internal quality of the polished forgings. S6. Forgings that pass inspection shall be normalized first. S7. After the forging is normalized, it is then machined and drilled. S8. Perform quenching and tempering heat treatment on the forgings after drilling; S9. The product after heat treatment is shot blasted to obtain the finished product, and then the finished product is inspected.

2. The high-strength train binding hook die forging method according to claim 1, characterized in that, The three-stage stepped heating includes the following steps: S11. Heat from room temperature to 400℃ at a heating rate of 80℃ / h, and hold for 1h. S12. Heat from 400℃ to 850℃ at a heating rate of 100℃ / h, and hold for 1.5h. S13. Heat from 850℃ to 1180℃ at a heating rate of 120℃ / h, and hold for 2 hours.

3. The high-strength train binding hook die forging method according to claim 1, characterized in that, The pre-forging mold cavity is enlarged by 8%-10% according to the linear dimension of the finished hook outline to reserve machining allowance, and the pre-forging pressure is 800-900MPa.

4. The high-strength train binding hook die forging method according to claim 3, characterized in that, The final forging temperature is maintained at 850-950℃, and the final forging pressure is 1000-1100MPa.

5. The high-strength train binding hook die forging method according to claim 1, characterized in that, The temperature of the forging is 700-850℃ when the flash is punched, the pressure for punching the flash is 500-600MPa, and the surface roughness Ra of the cut edge of the forging is ≤25μm.

6. The high-strength train binding hook die forging method according to claim 1, characterized in that, When using the slow cooling method of the insulation box, the thickness of the insulation sand inside the insulation box shall not be less than 100mm.

7. The high-strength train binding hook die forging method according to claim 1, characterized in that, During the normalizing process, the forging is heated to 860-880℃, held at that temperature for 2 hours, and then air-cooled to room temperature.

8. The high-strength train binding hook die forging method according to claim 7, characterized in that, The connecting holes are machined after the forging is normalized.

9. The high-strength train binding hook die forging method according to claim 8, characterized in that, During the quenching and tempering heat treatment, the drilled forging is first heated to 840-860℃, held for 1.5 hours, and then oil-cooled to complete the quenching treatment. After the quenching treatment, the forging is heated to 520-540℃, held for 3 hours, and then air-cooled to room temperature to complete the tempering treatment.

10. The high-strength train binding hook die forging method according to claim 9, characterized in that, After the heat treatment, the product is shot blasted to make the surface of the product meet the Sa2.5 requirement, and the finished product inspection includes dimensional accuracy, surface quality and hardness testing.

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