A machining method of inconel 718 twelve-corner head bolt

Abstract

The application relates to a machining method of an Inconel 718 twelve-corner head bolt, and belongs to the technical field of bolt machining and manufacturing. The machining method of the Inconel 718 twelve-corner head bolt comprises the following steps: performing aging treatment on a blank after hot upsetting forming of a bolt head to obtain a heat-treated piece; then performing rough turning, fine turning, rod portion grinding on the heat-treated piece, then performing R rolling on a transition arc part between the head and the rod portion, then performing warm rolling thread processing on the rod portion of the bolt blank, and finally performing passivation treatment. The machining method of the Inconel 718 twelve-corner head bolt can improve the strength of the material through heat treatment, thereby avoiding the problem that the internal metal flow line of a bolt workpiece is broken when the bolt workpiece is subjected to fine turning and thread rolling, and the strength, fatigue resistance and vibration resistance of the finished bolt workpiece are ensured.

Description

Technical Field

[0001] This invention relates to a method for processing Inconel 718 twelve-head bolts, belonging to the field of bolt processing and manufacturing technology. Background Technology

[0002] Inconel 718 is currently the most widely used high-temperature alloy in aero-engines, primarily used in the manufacture of various stationary and rotating components in aero-engines, such as discs, rings, casings, shafts, blades, fasteners, and elastic elements. Inconel 718 dodecagonal head bolts are commonly used fasteners in the engine combustion chamber and are representative of high-temperature, high-strength fasteners. The dodecagonal head of the Inconel 718 dodecagonal head bolt has a complex structure with a dodecagonal wrench mechanism, ensuring sufficient force distribution during tightening and preventing the wrench from slipping. Additionally, a flange is located at the bottom of the dodecagonal head to serve as a load-bearing component after installation. The structural diagram of the Inconel 718 dodecagonal head bolt is shown below. Figure 1 As shown in the picture, the actual product is as follows. Figure 2 As shown.

[0003] Since the engine combustion chamber operates at a temperature of 650°C, the Inconel 718 dodecagonal head bolts used in the combustion chamber must be able to operate continuously without failure in an environment ranging from 650°C to 800°C. Therefore, stringent requirements are placed on the various mechanical properties of the Inconel 718 dodecagonal head bolts: high temperature resistance (above 900°C), vibration resistance (unfailing under the enormous vibrations generated by the engine's high-speed rotation), and fatigue resistance (no failure without maintenance at the aircraft's maximum range). Simultaneously, stringent requirements are placed on the raw materials used to manufacture the Inconel 718 dodecagonal head bolts; Inconel 718 material must be selected that has undergone vacuum induction melting followed by vacuum arc furnace remelting.

[0004] Among them, the Inconel 718 high-temperature alloy with a tensile strength Rm ≥ 1517 MPa and a yield strength Rp0.2 ≥ 1379 MPa is the most difficult to process. Due to its high degree of alloying, its hot workability deteriorates, and the hot deformation zone shrinks, thus increasing the difficulty of hot forming. Simultaneously, due to the material's high strength and low plasticity, the tensile strength Rm of Inconel 718 after heat treatment is ≥ 1600 MPa, and its Rockwell hardness is 48–49.5 HRC, further increasing the difficulty of subsequent processing. A schematic diagram of the metal flow lines at the transition arc between the head and shank of the Inconel 718 dodecagonal head bolt is shown below. Figure 3 As shown in the diagram, the metal flow lines of the threaded portion of the Inconel 718 dodecagonal head bolt are as follows: Figure 4As shown. Because the metal flow lines at the junction of the head and shank of the Inconel 718 dodecagonal head bolt cannot be disrupted or cut off, the metal flow lines in the threaded portion must be continuous, with the highest density at the thread root to improve the bolt's fatigue resistance. This places more stringent requirements on the manufacturing and processing of Inconel 718 dodecagonal head bolts. Currently, the processing method for Inconel 718 dodecagonal head bolts includes the following process flow: blanking → conventional turning → centerless grinding → lubrication → hot upsetting → coating removal → sandblasting → heat treatment → sandblasting → CNC turning → deburring → marking → penetrant testing → surface treatment → final inspection → packaging and warehousing. Because the current processing flow for Inconel 718 dodecagonal head bolts includes lubrication before hot upsetting and coating removal after hot upsetting, the process is cumbersome. Furthermore, using CNC turning for threading can disrupt or cut off the metal flow lines in the threaded portion of the Inconel 718 dodecagonal head bolt, resulting in lower fatigue and vibration resistance. Summary of the Invention

[0005] The purpose of this invention is to provide a processing method for Inconel 718 dodecagonal head bolts, which can solve the problem of low fatigue resistance of currently processed Inconel 718 dodecagonal head bolts.

[0006] To achieve the above objectives, the technical solution adopted in the processing method of the Inconel 718 twelve-head bolt of the present invention is as follows:

[0007] A method for processing Inconel 718 twelve-head bolts includes the following steps: hot upsetting the bolt head of the blank and then aging it to obtain a heat-treated part; then rough turning, finish turning, and grinding of the bolt shank; then rolling the transition arc between the head and the shank; then warm thread rolling of the bolt shank; and finally passivation treatment to obtain the Inconel 718 twelve-head bolt; the aging treatment includes a first-stage heat treatment and a second-stage heat treatment performed sequentially, with the temperature of the first-stage heat treatment being 718–720°C and the temperature of the second-stage heat treatment being 612–614°C.

[0008] The processing method for Inconel 718 dodecagonal head bolts of this invention involves hot upsetting the bolt head of the blank followed by heat treatment. This improves the material's strength and avoids the problem of internal metal flow lines breaking during precision turning and thread rolling of the semi-finished bolt workpiece. It ensures a uniform distribution of internal metal flow lines in the semi-finished bolt workpiece, guaranteeing the strength, fatigue resistance, and vibration resistance of the finished bolt. The Inconel 718 dodecagonal head bolts processed by this invention have a tensile strength of up to 1600 MPa, a shear strength of up to 930 MPa, and a fatigue resistance of no less than 65,000 cycles, meeting the requirements for use in the aerospace field.

[0009] Preferably, the first stage of heat treatment lasts for 8 hours.

[0010] Preferably, the second stage of heat treatment lasts for 8 hours.

[0011] Preferably, the cooling rate from the temperature corresponding to the first stage heat treatment to the temperature corresponding to the second stage heat treatment is (56℃±8℃) / h.

[0012] Preferably, the aging treatment includes a first-stage heat treatment, a second-stage heat treatment, and a cooling treatment performed sequentially. The cooling treatment is achieved by gas quenching, and the atmosphere used for gas quenching is argon with a pressure of 150-200 MPa.

[0013] Preferably, hot upsetting involves heating the bolt head of the blank to a specified temperature and holding it at that temperature before upsetting. The blank has a diameter of 13.297–13.3 mm, a specified temperature of 880–920°C, a heating time of 3–6 seconds, and a holding time of 3–6 seconds. Alternatively, the blank has a diameter of 15.297–15.3 mm, a specified temperature of 890–920°C, a heating time of 3–6 seconds, and a holding time of 3–6 seconds. Or, the blank has a diameter of 16.597–16.7 mm, a specified temperature of 900–920°C, a heating time of 6–8 seconds, and a holding time of 6–8 seconds.

[0014] Preferably, the warm thread rolling process involves first heating the thread blank, and then performing thread rolling on the heated thread blank; the heating temperature is 180-200℃, and the time is 5-8 seconds.

[0015] Preferably, the passivation treatment method is as follows: the thread rolling parts are subjected to degreasing, hot water washing, room temperature water washing, activation, first flowing water washing, passivation, second flowing water washing, neutralization, third flowing water washing, hot pure water washing and drying in sequence.

[0016] Preferably, the passivation involves placing the bolt workpiece after the first cold water wash in dilute nitric acid and immersing it at room temperature for 30–60 minutes. The dilute nitric acid is prepared by mixing concentrated nitric acid with a density of 1.42 g / mL and water, with a mass concentration of 68% for the concentrated nitric acid and a concentration of 380–390 g / L for the concentrated nitric acid in the dilute nitric acid.

[0017] Preferably, the activation involves immersing the bolted workpiece, after it has been washed with room temperature water, in hydrochloric acid with a concentration of 100–150 g / L for 0.5–2 minutes at room temperature; the water temperature used for the room temperature water wash, the first flowing water wash, and the second flowing water wash is room temperature; and the water temperature used for the hot water wash and the hot pure water wash is 60–80°C. Attached Figure Description

[0018] Figure 1 This is a structural diagram of the Inconel 718 dodecagonal head bolt used in this invention;

[0019] Figure 2 This is a photograph of the Inconel 718 dodecagonal head bolt used in this invention.

[0020] Figure 3 This is a schematic diagram of the metal flow lines at the transition arc between the head and shank of the Inconel 718 dodecagonal head bolt in this invention;

[0021] Figure 4 This is a schematic diagram of the metal flow lines of the threaded portion of the Inconel 718 dodecagonal head bolt in this invention;

[0022] Figure 5 This is a schematic diagram of the structure of the blank processed in Embodiment 1 of the present invention;

[0023] Figure 6 This is a schematic diagram of the structure of the semi-finished bolt workpiece processed in Embodiment 1 of the present invention;

[0024] Figure 7 This is a schematic diagram of the rough-turned part processed in Embodiment 1 of the present invention;

[0025] Figure 8 This is a schematic diagram of the structure of the grinding part processed in Embodiment 1 of the present invention;

[0026] Figure 9 This is a schematic diagram of the structure of the vibration marker processed in Embodiment 1 of the present invention;

[0027] Figure 10 This is a schematic diagram of the structure of the rolled R-machined part processed in Embodiment 1 of the present invention;

[0028] Figure 11 This is a schematic diagram of the structure of the thread rolling part processed in Embodiment 1 of the present invention;

[0029] Figure 12 This is a photograph of the finished bolt workpiece processed in Embodiment 1 of the present invention;

[0030] Figure 13 The image shows the metallographic structure of the Inconel 718 dodecagonal head bolt processed according to Embodiment 1 of the present invention.

[0031] Figure 14 The image shows the metallographic structure of the Inconel 718 dodecagonal head bolt processed in Comparative Example 1 of this invention.

[0032] Figure 15 The image shows the metallographic structure of the Inconel 718 dodecagonal head bolt processed in Comparative Example 2 of this invention.

[0033] Figure 16 This is a picture of the tooth breakage of the thread rolling wheel after rolling in step (8) of Comparative Example 3 of the present invention;

[0034] Figure 17 The image shows defects such as cracks and excessive folding at the thread of the Inconel 718 dodecagonal head bolt processed in Comparative Example 3 of this invention. Detailed Implementation

[0035] The processing method for Inconel 718 dodecagonal head bolts of this invention is a pioneering invention. This method involves sequentially hot-forging, heat treatment, turning, R-rolling, and thread rolling of the blank to obtain the Inconel 718 dodecagonal head bolt. This avoids the problem of internal metal flow lines breaking during precision turning and thread rolling of semi-finished bolt workpieces, ensuring a uniform distribution of internal metal flow lines and guaranteeing the strength, fatigue resistance, and vibration resistance of the finished bolt workpiece.

[0036] The processing flow of the Inconel 718 dodecagonal head bolt of this invention is as follows: blanking → conventional turning → centerless grinding → hot upsetting → sandblasting → heat treatment → sandblasting → conventional turning → CNC turning → conventional turning → deburring → marking → centerless grinding → radius rolling → thread rolling → penetrant testing → surface treatment → final inspection → packaging and warehousing. This invention uses hot upsetting to form the dodecagonal head, thus achieving a smooth transition between the head and shank of the finished bolt. Simultaneously, by controlling the heating temperature, heating time, and holding time during hot upsetting, the grain size of the bolt after hot upsetting fully meets the standard requirements, completely solving the problems of overheating, burning, or poor grain size in the blank after hot upsetting. It also improves the material strength, thereby avoiding the problem of internal metal flow line breakage during precision turning and thread rolling of the semi-finished bolt. This ensures a uniform distribution of internal metal flow lines in the semi-finished bolt, guaranteeing the strength, fatigue resistance, and vibration resistance of the finished bolt.

[0037] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0038] Example 1

[0039] The processing method for the Inconel 718 twelve-head bolt in this embodiment, taking the processing specification of .5-20UNJF-3A Inconel 718 twelve-head bolt as an example, specifically includes the following steps:

[0040] (1) Inconel 718 alloy bars conforming to standard AMS 5962 and smelted by vacuum induction melting followed by vacuum arc furnace remelting were selected as the raw materials for processing Inconel 718 twelve-head bolts. The diameter and length of the Inconel 718 alloy bars were calculated and determined based on the specifications and length of the Inconel 718 twelve-head bolts to be processed. Based on the length of a single Inconel 718 twelve-head bolt, the Inconel 718 alloy bars were cut into single bars using a sawing machine. Then, a three-jaw chuck was used to clamp the single bar onto a conventional hexagonal lathe. Both ends of the single bar were machined to a smooth finish, and chamfers were then machined on both ends. Finally, a CNC centerless grinder was used to grind the outer diameter of the bar to ensure consistent outer diameter dimensions, resulting in the desired shape. Figure 5 The blank shown is suitable for hot upsetting.

[0041] (2) Place the blank (diameter 13.3mm, upper deviation 0mm, lower deviation -0.03mm) into a hot forging mold, and use a 315-ton press to hot forge the blank. For example, forge a twelve-point bolt head at one end of the blank, and then remove the oxide scale and oxide color by sandblasting to obtain the desired result. Figure 6The semi-finished bolt workpiece is shown. During hot upsetting, a portable transistor induction heating device is first used to heat the twelve-corner area of ​​the bolt head. After the heating temperature and time meet the requirements, the heated blank is immediately placed into the hot upsetting mold for hot upsetting. Using a portable transistor induction heating device to heat the twelve-corner area of ​​the bolt head effectively controls the heating temperature, heating time (heating time refers to the time it takes to heat the surface and core of the workpiece to a specified temperature, which is the heating temperature), and holding time (holding time refers to the time it takes to maintain the specified heating temperature after the workpiece reaches it). This ensures that the grain size of the bolt after hot upsetting is ≤5 and that there is no overheating or burning in the microstructure, completely solving the problems of overheating, burning, and poor grain size of the blank after hot upsetting. In this embodiment, the heating parameters during hot upsetting are shown in Table 1. The cooling time in Table 1 refers to the time interval between the completion of heating the blank and its placement in the hot upsetting mold to begin hot upsetting.

[0042] Table 1 Heating parameters during hot forging

[0043]

[0044]

[0045] Because the Inconel 718 dodecagonal head bolts used in aerospace engines are made of high-temperature resistant Inconel 718 alloy, the dodecagonal head cannot be formed by cold forging. In addition, the bolt has a dodecagonal flange head type. In order to obtain good head shape, size and batch production stability, hot forging is used to forge the dodecagonal head. This not only achieves the purpose of forming the dodecagonal flange head of the bolt, but also ensures the integrity of the metal flow line at the transition arc between the bolt head and the shank, thereby indirectly improving the fatigue resistance of the bolt. This invention employs hot upsetting for the twelve-corner bolt head. Since hot upsetting involves forming the twelve-corner head under heating, it not only solves the problem that cold upsetting cannot be used for high-temperature resistant Inconel 718 alloy materials, but also ensures that the blank diameter is close to the final product's smooth rod diameter. This reduces subsequent machining operations and prevents the metal flow lines at the lower r-shaped section of the head from being cut off due to excessive machining of the support surface and shank during precision turning, thus guaranteeing the integrity of the metal flow lines at the transition arc between the bolt head and shank. In this embodiment, metallographic analysis was used to inspect the metal flow lines from the head to the shank of the semi-finished bolt workpiece. The results show that the metal flow lines from the head to the shank of the semi-finished bolt workpiece obtained in this embodiment are intact, and the metallographic structure shows no signs of overheating or burning.

[0046] (3) The semi-finished bolt workpieces are subjected to aging treatment, followed by sandblasting to remove oxide scale and oxide color, resulting in heat-treated parts. The aging treatment involves placing the semi-finished bolt workpieces in the heating chamber of a horizontal vacuum gas quenching furnace, heating them to 718℃, holding them at this temperature for 8 hours, then cooling them to 612℃ at a rate of (56℃±8℃) / h, holding them at this temperature for 8 hours. Finally, the semi-finished bolt workpieces are transferred to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, with an argon pressure of 150–200 MPa. The vacuum degree of the vacuum gas quenching furnace used for the aging treatment is 1×10⁻⁶. -3 The leakage rate of the vacuum quenching furnace is 20 μmHg / h.

[0047] Since Inconel 718 high-temperature alloy bars are cold-drawn raw material blanks with material specifications AMS5962 and have undergone work hardening through hot upsetting, the product requires heat treatment to achieve its final performance. This involves aging strengthening to reach a precipitation hardening state, thereby obtaining high strength and good plasticity. This invention employs an aging heat treatment process. The purpose of aging treatment is to strengthen the microstructure and strength of the high-temperature alloy to obtain a suitable γ / γ' microstructure, effectively solving the problem of tensile strength testing for semi-finished bolt workpieces.

[0048] In this invention, the heat treatment is performed before rough turning, which can improve the strength of the material and avoid the problem of the internal metal flow lines of the bolt workpiece breaking during the finish turning and thread rolling of the semi-finished bolt workpiece. This can make the internal metal flow lines of the semi-finished bolt workpiece uniformly distributed, and ensure the strength, fatigue resistance and vibration resistance of the finished bolt workpiece.

[0049] (4) Using a three-jaw chuck, the heat-treated part is clamped onto a conventional hexagonal lathe, and its shape is rough-machined to obtain the following result: Figure 7 The rough-machined part shown.

[0050] (5) The rough-turned part is clamped onto a CNC lathe using a three-jaw chuck, and its shape is finished by finishing to obtain a finished part; the thread blank shank of the finished part is ground using a CNC centerless grinder to make the thread blank shank diameter and surface roughness meet the processing requirements before thread rolling, resulting in a finished part. Figure 8 The workpiece shown is a workpiece that has been ground.

[0051] (6) Clamp the ground workpiece on the worktable of the vibration marking machine, and use the vibration marking machine to vibrate and mark the identification mark on the twelve-cornered head end face of the ground workpiece, obtaining the following... Figure 9 The vibration marker shown.

[0052] (7) Place the vibration marker on the roller of a CNC roller mill, and perform roller milling on the transition arc between the head and the rod of the vibration marker to strengthen the bond between the head and the rod, resulting in the following: Figure 10 The illustrated part shows a rolled radius (R) part. In this invention, the transition arc between the head and shank of the vibration marker is rolled, achieving secondary strengthening of this area, improving the bolt's fatigue resistance, and solving the problem of easy breakage at the joint between the bolt head and shank. Using a rolling radius machine and selecting appropriate rolling wheels to roll the transition arc between the head and shank of the semi-finished bolt workpiece can improve the surface finish of the transition arc, enhance the density of the metal flow lines at the transition arc, and effectively improve the fatigue resistance of the Inconel 718 twelve-head bolt.

[0053] (8) A CNC warm thread rolling machine of model MC-40FI(V) is used to perform warm thread rolling on the shank blank of the R-shaped workpiece, and external threads are rolled on the shank blank to obtain the following result: Figure 11 The thread-rolled part shown is an example of a process where the threaded part is first aged and then warm-rolled. Warm rolling strengthens the threaded portion of the Inconel 718 twelve-head bolt by applying rolling pressure. The Inconel 718 high-temperature alloy requires a tensile strength Rm ≥ 1517 MPa and a yield strength Rp0.2 ≥ 1379 MPa. It has high hardness (Rockwell hardness reaches 43–48 HRC), poor plasticity, and severe work hardening. To avoid defects such as cracks and folds at the threaded part during the rolling process, warm rolling is used in this embodiment. Heating reduces the material's strength, alleviates work hardening, enhances material fluidity, and facilitates thread forming, effectively solving problems such as tooth breakage on the rolling wheel and poor thread quality that occur during cold rolling. In the warm rolling process, the threaded part is first heated, and then the heated part is rolled. During warm rolling, the heating temperature, heating time, and threaded part diameter are key factors for process control and need to be determined through process testing. In this embodiment, the diameter of the screw blank and the parameters for warm rolling are shown in Table 2.

[0054] Table 2. Thread blank diameter and temperature rolling parameters during thread rolling.

[0055]

[0056]

[0057] (9) In accordance with the requirements of the standard ASTM E1417 "Standard Practice for Penetrant Testing", fluorescent penetrant testing (i.e., Class I) and water washing testing (i.e., Method A) are selected, and 100% fluorescent testing is performed on the thread rolling parts with a sensitivity of Level 3. Defective thread rolling parts are picked out and scrapped.

[0058] (10) Passivation treatment is applied to the thread-rolled parts that pass the fluorescent flaw detection to form a dense passivation film on the surface of the finished bolt workpiece, thereby improving the corrosion resistance of the finished bolt workpiece and obtaining the following results: Figure 12 The finished bolt workpiece shown is subjected to the following passivation treatment: the thread-rolled workpiece is subjected to degreasing, hot water washing, room temperature water washing, activation, first running water washing, passivation, second running water washing, neutralization, third running water washing, hot pure water washing, and drying in sequence. The activation process involves immersing the bolted workpieces, after rinsing with room temperature water, in a 100g / L hydrochloric acid solution for 2 minutes at room temperature. During activation, the parts should be manually turned 3-5 times, taking care to control the force applied to prevent damage. The passivation process involves immersing the bolted workpieces, after the first cold water rinse, in dilute nitric acid (prepared by mixing concentrated nitric acid with a density of 1.42g / mL and water, with a mass concentration of 68% and a dosage of 380g / L) at room temperature for 30 minutes. During passivation, the parts should be manually turned 3-5 times to ensure that the surface of the workpiece is in contact with the passivation solution. Taking care to control the force applied to prevent damage. The room temperature water rinse, the first flowing water rinse, and the second flowing water rinse are all at room temperature. The hot water rinse and the hot pure water rinse are at a temperature of 60℃.

[0059] (11) Based on the number of finished bolt workpieces obtained from passivation treatment, a certain number of bolts are randomly selected according to the standard and relevant technical conditions. The mechanical properties of tensile strength, shear strength, fatigue and Rockwell hardness are tested on tensile, fatigue and hardness testing machines. After the test is qualified, a mechanical property test qualification report is issued. Finally, the finished bolt workpieces are packaged and put into storage.

[0060] Example 2

[0061] The processing method for the Inconel 718 twelve-head bolt in this embodiment, taking the processing of an Inconel 718 twelve-head bolt with specification .5625-18UNJF-3A as an example, specifically includes the following steps:

[0062] (1) Inconel 718 alloy bars conforming to standard AMS 5962 and smelted by vacuum induction melting followed by vacuum arc furnace remelting are selected as the raw materials for processing Inconel 718 twelve-head bolts. The diameter and length of the Inconel 718 alloy bars are calculated and determined based on the specifications and length of the Inconel 718 twelve-head bolts to be processed. According to the length of a single Inconel 718 twelve-head bolt, the Inconel 718 alloy bars are cut into single bars using a sawing machine. Then, the single bars are clamped on a conventional hexagonal lathe using a three-jaw chuck. The two ends of the single bars are machined to a smooth finish. Then, chamfers are machined on the two ends. Finally, the outer diameter of the bars is ground using a CNC centerless grinder to ensure consistent outer diameter dimensions, resulting in a blank suitable for hot upsetting.

[0063] (2) The blank (diameter 15.3mm, upper deviation 0mm, lower deviation -0.03mm) is placed in the hot upsetting mold and hot upsetting is performed on the blank using a 315-ton press. A twelve-corner bolt head is upset at one end of the blank. Then, the oxide scale and oxide color are removed by sandblasting to obtain a semi-finished bolt workpiece. During hot upsetting, a handheld transistor induction heating device is first used to heat the area where the twelve-corner bolt head is upset. After the heating temperature and time meet the requirements, the heated blank is immediately placed into the hot upsetting mold for hot upsetting. The heating parameters during hot upsetting are shown in Table 3. The cooling time in Table 3 refers to the time interval between the completion of the blank heating and the start of hot upsetting in the hot upsetting mold.

[0064] Table 3 Heating parameters during hot forging

[0065]

[0066] (3) The semi-finished bolt workpieces are subjected to aging treatment, followed by sandblasting to remove oxide scale and oxide color, resulting in heat-treated parts. The aging treatment involves placing the semi-finished bolt workpieces in the heating chamber of a horizontal vacuum gas quenching furnace, heating them to 718℃, holding them at this temperature for 8 hours, then cooling them to 612℃ at a rate of (56℃±8℃) / h, holding them at this temperature for 8 hours. Finally, the semi-finished bolt workpieces are transferred to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, with an argon pressure of 150–200 MPa. The vacuum degree of the vacuum gas quenching furnace used for the aging treatment is 1×10⁻⁶. -3 The leakage rate of the vacuum quenching furnace is 20 μmHg / h.

[0067] (4) Use a three-jaw chuck to clamp the heat-treated part onto a regular hexagonal lathe and perform rough turning on the shape of the heat-treated part to obtain a rough-turned part.

[0068] (5) The rough-turned part is clamped on the CNC lathe using a three-jaw chuck, and the shape of the rough-turned part is precision turned to obtain the precision-turned part; the screw rod of the precision-turned part is ground using a CNC centerless grinder to make the screw rod diameter and screw rod roughness meet the processing requirements before thread rolling, and the ground part is obtained.

[0069] (6) The grinding workpiece is clamped on the worktable of the vibration marking machine, and the vibration marking machine is used to mark the identification mark on the twelve-cornered head end face of the grinding workpiece to obtain the vibration marking part.

[0070] (7) Place the vibration marker on the roller of the CNC roller and perform roller rolling on the transition arc between the head and the rod of the vibration marker to strengthen the bonding strength between the head and the rod, and obtain the roller-rolled part.

[0071] (8) A CNC warm thread rolling machine (model MC-40FI(V)) is used to perform warm thread rolling on the shank of the threaded part, rolling external threads into the shank to obtain the threaded part. During the warm thread rolling process, the shank is first heated, and then the heated shank is thread rolled. In the warm thread rolling process, the heating temperature, heating time, and shank diameter are key factors for manufacturing process control and need to be determined through process experiments. In this embodiment, the shank diameter and warm thread rolling parameters are shown in Table 4.

[0072] Table 4. Thread blank diameter and temperature rolling parameters during thread rolling.

[0073]

[0074] (9) In accordance with the requirements of the standard ASTM E1417 "Standard Practice for Penetrant Testing", fluorescent penetrant testing (i.e., Class I) and water washing testing (i.e., Method A) are selected, and 100% fluorescent testing is performed on the thread rolling parts with a sensitivity of Level 3. Defective thread rolling parts are picked out and scrapped.

[0075] (10) Passivation treatment is performed on the threaded parts that pass the fluorescent flaw detection to form a dense passivation film on the surface of the finished bolt workpiece, thereby improving the corrosion resistance of the finished bolt workpiece and obtaining the finished bolt workpiece. The passivation treatment method is as follows: the threaded parts are subjected to degreasing, hot water washing, room temperature water washing, activation, first flowing water washing, passivation, second flowing water washing, neutralization, third flowing water washing, hot pure water washing and drying in sequence. The activation process involves immersing the bolted workpieces, after washing with room temperature water, in a 120g / L hydrochloric acid solution for 1 minute at room temperature. During activation, the parts should be manually turned 3-5 times, taking care to control the force applied to prevent damage. The passivation process involves immersing the bolted workpieces, after the first cold water rinse, in dilute nitric acid (prepared by mixing concentrated nitric acid with a density of 1.42g / mL and water, with a mass concentration of 68% and a dosage of 385g / L) at room temperature for 45 minutes. During passivation, the parts should be manually turned 3-5 times to ensure that the surface of the workpiece is in contact with the passivation solution. Taking care to control the force applied to prevent damage. The room temperature water rinse, the first flowing water rinse, and the second flowing water rinse are all at room temperature. The hot water rinse and the hot pure water rinse are at 70℃.

[0076] (11) Based on the number of finished bolt workpieces obtained from passivation treatment, a certain number of bolts are randomly selected according to the standard and relevant technical conditions. The mechanical properties of tensile strength, shear strength, fatigue resistance and hardness are tested on tensile, fatigue and hardness testing machines. After the test is qualified, a mechanical property test qualification report is issued. Finally, the finished bolt workpieces are packaged and put into storage.

[0077] Example 3

[0078] The processing method for the Inconel 718 twelve-head bolt in this embodiment, taking the processing of an Inconel 718 twelve-head bolt with a specification of .625-18UNJF-3A as an example, specifically includes the following steps:

[0079] (1) Inconel 718 alloy bars conforming to standard AMS 5962 and smelted by vacuum induction melting followed by vacuum arc furnace remelting are selected as the raw materials for processing Inconel 718 twelve-head bolts. The diameter and length of the Inconel 718 alloy bars are calculated and determined based on the specifications and length of the Inconel 718 twelve-head bolts to be processed. According to the length of a single Inconel 718 twelve-head bolt, the Inconel 718 alloy bars are cut into single bars using a sawing machine. Then, the single bars are clamped on a conventional hexagonal lathe using a three-jaw chuck. The two ends of the single bars are machined to a smooth finish. Then, chamfers are machined on the two ends. Finally, the outer diameter of the bars is ground using a CNC centerless grinder to ensure consistent outer diameter dimensions, resulting in a blank suitable for hot upsetting.

[0080] (2) The blank (diameter 16.7mm, upper deviation 0mm, lower deviation -0.03mm) is placed in the hot upsetting mold and hot upsetting is performed on the blank using a 315-ton press. A twelve-corner bolt head is upset at one end of the blank. Then, the oxide scale and oxide color are removed by sandblasting to obtain a semi-finished bolt workpiece. During hot upsetting, a handheld transistor induction heating device is used to heat the area where the twelve-corner bolt head is upset. The heating parameters during hot upsetting are shown in Table 5.

[0081] Table 5 Heating parameters during hot forging

[0082]

[0083] (3) The semi-finished bolt workpieces are subjected to aging treatment, followed by sandblasting to remove oxide scale and oxide color, resulting in heat-treated parts. The aging treatment involves placing the semi-finished bolt workpieces in the heating chamber of a horizontal vacuum gas quenching furnace, heating them to 718℃, holding them at this temperature for 8 hours, then cooling them to 612℃ at a rate of (56℃±8℃) / h, holding them at this temperature for 8 hours. Finally, the semi-finished bolt workpieces are transferred to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, with an argon pressure of 150–200 MPa. The vacuum degree of the vacuum gas quenching furnace used for the aging treatment is 1×10⁻⁶. -3 The leakage rate of the vacuum quenching furnace is 20 μmHg / h.

[0084] (4) Use a three-jaw chuck to clamp the heat-treated part onto a regular hexagonal lathe and perform rough turning on the shape of the heat-treated part to obtain a rough-turned part.

[0085] (5) The rough-turned part is clamped on the CNC lathe using a three-jaw chuck, and the shape of the rough-turned part is precision turned to obtain the precision-turned part; the screw rod of the precision-turned part is ground using a CNC centerless grinder to make the screw rod diameter and screw rod roughness meet the processing requirements before thread rolling, and the ground part is obtained.

[0086] (6) The grinding workpiece is clamped on the worktable of the vibration marking machine, and the vibration marking machine is used to mark the identification mark on the twelve-cornered head end face of the grinding workpiece to obtain the vibration marking part.

[0087] (7) Place the vibration marker on the roller of the CNC roller and perform roller rolling on the transition arc between the head and the rod of the vibration marker to strengthen the bonding strength between the head and the rod, and obtain the roller-rolled part.

[0088] (8) A CNC warm thread rolling machine (model MC-40FI(V)) is used to perform warm thread rolling on the shank of the threaded part, rolling external threads into the shank to obtain the threaded part. During the warm thread rolling process, the shank is first heated, and then the heated shank is thread rolled. In the warm thread rolling process, the heating temperature, heating time, and shank diameter are key factors for process control and need to be determined through process experiments. In this embodiment, the shank diameter and warm thread rolling parameters are shown in Table 6.

[0089] Table 6. Thread blank diameter and temperature rolling parameters during thread rolling.

[0090]

[0091] (9) In accordance with the requirements of the standard ASTM E1417 "Standard Practice for Penetrant Testing", fluorescent penetrant testing (i.e., Class I) and water washing testing (i.e., Method A) are selected, and 100% fluorescent testing is performed on the thread rolling parts with a sensitivity of Level 3. Defective thread rolling parts are picked out and scrapped.

[0092] (10) Passivation treatment is performed on the threaded parts that pass the fluorescent flaw detection to form a dense passivation film on the surface of the finished bolt workpiece, thereby improving the corrosion resistance of the finished bolt workpiece and obtaining the finished bolt workpiece. The passivation treatment method is as follows: the threaded parts are subjected to degreasing, hot water washing, room temperature water washing, activation, first flowing water washing, passivation, second flowing water washing, neutralization, third flowing water washing, hot pure water washing and drying in sequence. The activation process involves immersing the bolted workpieces, after washing with room temperature water, in a 150g / L hydrochloric acid solution for 0.5 minutes at room temperature. During activation, the parts should be manually turned 3-5 times, taking care to control the force applied to prevent damage. The passivation process involves immersing the bolted workpieces, after the first cold water rinse, in dilute nitric acid (prepared by mixing concentrated nitric acid with a density of 1.42g / mL and water, with a mass concentration of 68% and a dosage of 390g / L) at room temperature for 60 minutes. During passivation, the parts should be manually turned 3-5 times to ensure that the surface of the workpiece is in contact with the passivation solution. Taking care to control the force applied to prevent damage. The room temperature water rinse, the first flowing water rinse, and the second flowing water rinse are all at room temperature. The hot water rinse and the hot pure water rinse are at 80℃.

[0093] (11) Based on the number of finished bolt workpieces obtained from passivation treatment, a certain number of bolts are randomly selected according to the standard and relevant technical conditions. The mechanical properties of tensile strength, shear strength, fatigue resistance and hardness are tested on tensile, fatigue and hardness testing machines. After the test is qualified, a mechanical property test qualification report is issued. Finally, the finished bolt workpieces are packaged and put into storage.

[0094] Example 4

[0095] The difference between the processing method of the Inconel 718 dodecagonal head bolt in this embodiment and the processing method of the Inconel 718 dodecagonal head bolt in Embodiment 1 is that the aging treatment in step (3) of the processing method of the Inconel 718 dodecagonal head bolt in this embodiment involves placing the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum quenching furnace, heating it to 720°C, and holding it at this temperature for 8 hours. Then, the temperature is reduced to 614°C at a rate of (56°C ± 8°C) / h, and held at this temperature for 8 hours. Finally, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, and the argon pressure is 150-200 MPa.

[0096] Example 5

[0097] The difference between the processing method of the Inconel 718 dodecagonal head bolt in this embodiment and the processing method of the Inconel 718 dodecagonal head bolt in Embodiment 2 is that the aging treatment in step (3) of the processing method of the Inconel 718 dodecagonal head bolt in this embodiment involves placing the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum quenching furnace, heating it to 720°C, and holding it at this temperature for 8 hours. Then, the temperature is reduced to 614°C at a rate of (56°C ± 8°C) / h, and held at this temperature for 8 hours. Finally, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, and the argon pressure is 150-200 MPa.

[0098] Example 6

[0099] The difference between the processing method of the Inconel 718 dodecagonal head bolt in this embodiment and the processing method of the Inconel 718 dodecagonal head bolt in Embodiment 3 is that the aging treatment in step (3) of the processing method of the Inconel 718 dodecagonal head bolt in this embodiment involves placing the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum quenching furnace, heating it to 720°C, and holding it at this temperature for 8 hours. Then, the temperature is reduced to 614°C at a rate of (56°C ± 8°C) / h, and held at this temperature for 8 hours. Finally, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, and the argon pressure is 150-200 MPa.

[0100] Comparative Example 1

[0101] The processing method of the Inconel 718 dodecagonal head bolt in this comparative example differs from that in Example 1 in that the heat treatment in step (3) of the processing method of the Inconel 718 dodecagonal head bolt in this comparative example includes solution treatment and aging treatment performed sequentially. The solution treatment involves placing the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum quenching furnace, heating it to 1000°C, and holding it at this temperature for 1 hour. Then, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, and the argon pressure is 150–200 MPa. The aging treatment is the same as that in Example 1.

[0102] Comparative Example 2

[0103] The difference between the processing method of the Inconel 718 dodecagonal head bolt in this comparative example and the processing method of the Inconel 718 dodecagonal head bolt in Example 1 is that in step (3) of the processing method of the Inconel 718 dodecagonal head bolt in this comparative example, the aging treatment involves placing the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum quenching furnace, heating it to 725°C, and holding it at this temperature for 8 hours. Then, the temperature is reduced to 612°C at a rate of (56°C ± 8°C) / h, and held at this temperature for 8 hours. Finally, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, and the argon pressure is 150-200 MPa.

[0104] Comparative Example 3

[0105] The difference between the processing method of the Inconel 718 dodecagonal head bolt in this comparative example and the processing method of the Inconel 718 dodecagonal head bolt in Example 1 is that in step (3) of the processing method of the Inconel 718 dodecagonal head bolt in this comparative example, the aging treatment involves placing the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum quenching furnace, heating it to 710°C, and holding it at this temperature for 8 hours. Then, the temperature is reduced to 612°C at a rate of (56°C ± 8°C) / h, and held at this temperature for 8 hours. Finally, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum quenching furnace for gas quenching. The atmosphere in the cooling chamber is argon, and the argon pressure is 150-200 MPa.

[0106] Comparative Example 4

[0107] The difference between the processing method of the Inconel 718 twelve-head bolt in this comparative example and the processing method of the Inconel 718 twelve-head bolt in Example 1 is that in step (8) of the processing method of the Inconel 718 twelve-head bolt in this comparative example, the temperature of the shank blank is room temperature during the thread rolling process.

[0108] Comparative Example 5

[0109] The difference between the processing method of the Inconel 718 twelve-head bolt in this comparative example and the processing method of the Inconel 718 twelve-head bolt in Example 1 is that step (7) is omitted in the processing method of the Inconel 718 twelve-head bolt in this comparative example, that is, the vibration marker is not rolled R, but the vibration marker is directly rolled.

[0110] Comparative Example 6

[0111] The difference between the processing method of the Inconel 718 twelve-head bolt in this comparative example and the processing method of the Inconel 718 twelve-head bolt in Example 2 is that step (7) is omitted in the processing method of the Inconel 718 twelve-head bolt in this comparative example, that is, the vibration marker is not rolled R, but the vibration marker is directly rolled.

[0112] Comparative Example 7

[0113] The difference between the processing method of the Inconel 718 twelve-head bolt in this comparative example and the processing method of the Inconel 718 twelve-head bolt in Example 3 is that step (7) is omitted in the processing method of the Inconel 718 twelve-head bolt in this comparative example, that is, the vibration marker is not rolled R, but the vibration marker is directly rolled.

[0114] Experimental Example 1

[0115] This experiment tested the metallographic structure and mechanical properties of Inconel 718 dodecagonal head bolts processed in Example 1 and Comparative Examples 1-3. Metallographic images are shown below. Figures 13-15 As shown in Table 7, the mechanical property test results were obtained. Tensile strength and yield strength were tested according to the methods in ASTM E8 / E8M-24, and Rockwell hardness was tested according to the methods in NASM 1312-6. Three samples were used for testing, and the average value of the test results was taken as the final result.

[0116] Table 7. Mechanical property test results of Inconel 718 dodecagonal head bolts processed in Example 1 and Comparative Examples 1-3.

[0117] Dodecagonal head bolts Tensile strength Rm / MPa Yield strength Rp0.2 / MPa Shear strength / MPa Rockwell hardness / HRC Example 1 1676 1603 932 49.5 Comparative Example 1 1632 1571 928 47.5 Comparative Example 2 1626 1570 907 47.7 Comparative Example 3 1615 1552 910 47.0

[0118] The metallographic images of the Inconel 718 dodecagonal head bolts processed in Example 1 and Comparative Examples 1-3 show that the Inconel 718 dodecagonal head bolts processed in Comparative Example 1 have coarsened grain size, lack δ phase at grain boundaries and within grains, and exhibit notch sensitivity, making them suitable for products with high grain size requirements. The Inconel 718 dodecagonal head bolts processed in Comparative Example 2 have fewer δ phases, which improves the material's strength and impact resistance, making them suitable for direct aging heat treatment of cold-drawn raw materials. The Inconel 718 dodecagonal head bolts processed in Example 1 have δ phases at grain boundaries, which helps eliminate notch sensitivity. Furthermore, statistical tests were conducted on the scrap rate (the scrap rate refers to the percentage of bolts with surface cracks or other defects when producing 100 dodecagonal head bolts) of the Inconel 718 dodecagonal head bolts processed in Example 1 and Comparative Examples 1-3 when preparing the same number of Inconel 718 dodecagonal head bolts. The results are shown in Table 8.

[0119] Table 8. Scrap rate and batch quality stability of Inconel 718 dodecagonal head bolts processed in Example 1 and Comparative Examples 1-3.

[0120] Dodecagonal head bolts scrap rate Example 1 5％ Comparative Example 1 15％ Comparative Example 2 9％ Comparative Example 3 13％

[0121] As shown in Tables 7 and 8, the Inconel 718 dodecagonal head bolts processed in Example 1 exhibit the best mechanical properties and the best processing quality stability. Therefore, the heat treatment regime in Example 1 is the optimal heat treatment regime.

[0122] Experiment Example 2

[0123] This experimental example statistically analyzes the service life of the thread rolling wheel in step (8) of the machining method for Inconel 718 twelve-head bolts in Examples 1 and 4, and also statistically analyzes the defects at the threads of the machined Inconel 718 twelve-head bolts. The results show that in step (8) of Comparative Example 4, the thread rolling wheel experiences tooth breakage after rolling several or dozens of products, such as... Figure 16 As shown. Meanwhile, the threads of the Inconel 718 dodecagonal head bolts machined in Comparative Example 4 are prone to defects such as cracks and excessive folding, as shown. Figure 17 As shown.

[0124] Experimental Example 3

[0125] This experiment tested the mechanical properties of Inconel 718 dodecagonal head bolts processed in Examples 1-3 and Comparative Examples 5-7. The results are shown in Table 9. Tensile strength was tested according to the method in standard ASTM E8 / E8M-24, yield strength was tested according to the method in standard ASTM E8 / E8M-24, Rockwell hardness was tested according to the method in standard NASM 1312-6, and fatigue resistance was tested according to the method in standard NASM 1312-11.

[0126] Table 9. Mechanical properties of Inconel 718 dodecagonal head bolts processed in Examples 1-3 and Comparative Examples 5-7

[0127] Dodecagonal head bolts Tensile strength Rm / MPa Yield strength Rp0.2 / MPa Rockwell hardness / HRC Fatigue resistance Example 1 ≥1600 ≥1540 48～49.5 68,000 to 130,000 times Example 2 ≥1600 ≥1540 48～49.5 65,000 to 125,000 times Example 3 ≥1600 ≥1540 48～49.5 65,000 to 115,000 times Comparative Example 5 1542～1595 1500～1530 47.5～48.9 ≤46,000 times Comparative Example 6 1542～1590 1500～1525 47.5～48.9 ≤45,000 times Comparative Example 7 1542～1550 1500～1510 47.5～48.9 ≤43,000 times

[0128] As shown in Table 9, in the methods of Examples 1-3, the transition arc between the bolt head and the shank is rolled (R-rolling), which strengthens this transition arc and significantly improves the fatigue life, meeting the standard requirement of an average of no less than 65,000 cycles. In contrast, in the methods of Comparative Examples 5-7, the transition arc between the bolt head and the shank is not rolled (R-rolling), resulting in a fatigue life of less than 50,000 cycles. Furthermore, as the bolt size increases, the fatigue life decreases and fails to meet the standard requirement of an average of no less than 65,000 cycles.

[0129] Experiment Example 4

[0130] This experiment evaluates the passivation effects of different nitric acid treatments. Three commercially available nitric acid grades were selected, numbered 1, 2, and 3. Nitric acid grade 1 had a density of 1.38 g / mL, analytical purity, and a mass concentration of 68%; nitric acid grade 2 had a density of 1.42 g / mL, analytical purity, and a mass concentration of 68%; and nitric acid grade 3 had a density of 1.40 g / mL, chemical purity, and a mass concentration of 68%. The three grades of nitric acid were then mixed with water to obtain a diluted solution with a mass fraction of 380 g / mL. The passivated thread-rolled parts that passed fluorescent flaw detection were then passivated according to the methods described in Examples 1, 2, or 3. The passivated bolts were then subjected to a salt spray resistance test according to GJB715.1. The time at which corrosion began to appear on the bolts was recorded during the experiment. The test results are shown in Table 10.

[0131] Table 10. Salt spray test results of threaded parts treated with different nitric acid.

[0132]

[0133]

[0134] Experimental Example 5

[0135] This experiment statistically analyzes the scrap rate (scrap rate refers to the percentage of bolts with surface cracks or other defects when producing 100 twelve-head bolts) of the processing methods of each embodiment and comparative example. The results are shown in Table 11.

[0136] Table 11 Scrapping rates of processing methods in each embodiment and comparative example

[0137] Processing methods scrap rate Example 1 5％ Example 2 5％ Example 3 7％ Example 4 6％ Example 5 5％ Example 6 6％ Comparative Example 1 15％ Comparative Example 2 9％ Comparative Example 3 85％ Comparative Example 4 35％ Comparative Example 5 36％ Comparative Example 6 39％

[0138] In summary, by controlling the key processes described above, the processing method of this invention effectively solves the problems of unqualified tensile strength and failure to meet standard requirements in fatigue tests for Inconel 718 dodecagonal head bolts. It also effectively addresses issues such as manufacturing difficulty, high scrap rate, long production and delivery cycle, poor batch quality stability, and failure to meet standard mechanical performance requirements for Inconel 718 dodecagonal head bolts. The processing method for Inconel 718 dodecagonal head bolts of this invention can be performed by general operators, resulting in extremely high processing efficiency. It boasts advantages such as efficient production process and simple operation, ensuring both dimensional accuracy and geometric tolerances for Inconel 718 dodecagonal head bolts, while also guaranteeing that mechanical performance meets standard requirements. Furthermore, the finished bolts processed by this invention exhibit high dimensional accuracy, geometric tolerances, and mechanical performance that meet standard design requirements. Measurement is convenient; calipers, micrometers, and projectors can be used to measure the dimensions and geometric tolerances of Inconel 718 dodecagonal head bolts.

Claims

1. A method for processing Inconel 718 twelve-head bolts, characterized in that, Includes the following steps: After hot upsetting the bolt head of the blank, an aging treatment is performed to obtain a heat-treated part. Then, the heat-treated part is rough-turned, finish-turned, and the bolt shank is ground. Next, the transition arc between the head and the shank is rolled, followed by warm thread rolling of the bolt shank. Finally, a passivation treatment is performed to obtain an Inconel 718 twelve-head bolt. The aging treatment includes a first-stage heat treatment and a second-stage heat treatment performed sequentially. The temperature of the first-stage heat treatment is 718~720℃, and the temperature of the second-stage heat treatment is 612~614℃. Hot upsetting involves heating the bolt head of the blank to a specified temperature and holding it at that temperature before upsetting. The specified temperature is 880~920℃.

2. The processing method for the Inconel 718 dodecagonal head bolt as described in claim 1, characterized in that, The first stage of heat treatment lasts for 8 hours.

3. The processing method for the Inconel 718 dodecagonal head bolt as described in claim 1, characterized in that, The second stage of heat treatment lasts for 8 hours.

4. The processing method for the Inconel 718 dodecagonal head bolt as described in claim 1, characterized in that, The cooling rate from the temperature corresponding to the first stage of heat treatment to the temperature corresponding to the second stage of heat treatment is (56±8)℃ / h.

5. The processing method of the Inconel 718 dodecagonal head bolt as described in any one of claims 1-4, characterized in that, After the second stage of heat treatment, a cooling process is carried out. The cooling process is achieved by gas quenching, and the atmosphere used for gas quenching is argon with a pressure of 150-200 MPa.

6. The method for processing the Inconel 718 dodecagonal head bolt as described in any one of claims 1-4, characterized in that, The billet has a diameter of 13.297~13.3mm, a specified temperature of 880~920℃, a heating time of 3~6s to the specified temperature, and a holding time of 3~6s; or the billet has a diameter of 15.297~15.3mm, a specified temperature of 890~920℃, a heating time of 3~6s to the specified temperature, and a holding time of 3~6s; or the billet has a diameter of 16.597~16.7mm, a specified temperature of 900~920℃, a heating time of 6~8s to the specified temperature, and a holding time of 6~8s.

7. The method for processing the Inconel 718 dodecagonal head bolt as described in any one of claims 1-4, characterized in that, Warm thread rolling involves first heating the shank of the thread blank, and then performing thread rolling on the heated shank; the heating temperature is 180-200℃, and the time is 5-8 seconds.

8. The method for processing the Inconel 718 dodecagonal head bolt as described in any one of claims 1-4, characterized in that, The passivation process is as follows: the thread rolling parts are subjected to degreasing, hot water washing, room temperature water washing, activation, first running water washing, passivation, second running water washing, neutralization, third running water washing, hot pure water washing, and drying in sequence.

9. The processing method of the Inconel 718 twelve-head bolt as described in claim 8, characterized in that, The passivation process involves placing the bolt workpiece, after the first rinse with flowing water, into dilute nitric acid and immersing it at room temperature for 30-60 minutes. The dilute nitric acid is prepared by mixing concentrated nitric acid with a density of 1.42 g / mL and water, and the amount of concentrated nitric acid used is 380-390 g / L.

10. The processing method of the Inconel 718 dodecagonal head bolt as described in claim 8, characterized in that, The activation process involves immersing the bolted workpiece, which has been washed with room temperature water, in hydrochloric acid with a concentration of 100-150 g / L for 0.5-2 minutes at room temperature; the first and second running water washes are performed at room temperature; and the hot water washes and hot pure water washes are performed at a temperature of 60-80°C.

Images